platinum metals review - Johnson Matthey Technology Review

E-ISSN 1471–0676

PLATINUM METALS REVIEW A Quarterly Survey of Research on the Platinum Metals and of Developments in their Application in Industry www.platinummetalsreview.com

VOL. 50 JULY 2006 NO. 3

Contents Electro-Spun, Semiconducting, Oriented Fibres of Supramolecular Quasi-Linear Platinum Compounds

112

By Margherita Fontana, Walter Caseri and Paul Smith

Crystallographic Properties of Platinum

118

By J. W. Arblaster

Launch of the Low Carbon and Fuel Cell Knowledge Transfer Network

119

By M. Hugh

The Minting of Platinum Roubles: Part IV

120

By Thilo Rehren

Centenary of the Discovery of Platinum in the Bushveld Complex

130

By R. Grant Cawthorn

Phoscorite-Carbonatite Pipe Complexes

134

By Juarez Fontana

“Platinum 2006”

143

Thermophysical Properties of Palladium

144

By Claus Cagran and Gernot Pottlacher

Abstracts

150

New Patents

154

Final Analysis: Mercury as a Catalyst Poison

156

By J. K. Dunleavy

Communications should be addressed to: The Editor, Barry W. Copping, Platinum Metals Review, [email protected]; Johnson Matthey Public Limited Company, Orchard Road, Royston, Hertfordshire SG8 5HE

DOI: 10.1595/147106706X128412

Electro-Spun, Semiconducting, Oriented Fibres of Supramolecular Quasi-Linear Platinum Compounds OPTICAL AND ELECTRICAL PROPERTIES OF MAGNUS’ GREEN SALT DERIVATIVES By Margherita Fontana, Walter Caseri* and Paul Smith Department of Materials, ETH Zürich, CH-8093 Zürich, Switzerland; *E-mail: [email protected]

The semiconducting Magnus’salt derivatives [Pt(NH2eh)4][PtCl4] and [Pt(NH2dmoc)4][PtCl4], with eh = (R)-2-ethylhexyl and dmoc = (S)-3,7-dimethyloctyl, are compounds that exhibit a supramolecular structure comprising a backbone of linear arrays of platinum atoms. These compounds behave essentially like ordinary polymers. In this work they were processed into fibres by electrospinning from organic solvents such as toluene. X-ray diffraction patterns indicated that the platinum arrays in the fibres were oriented parallel to the axis of the fibres. Accordingly, the fibres show anisotropic optical and electrical properties. The electrical conductivities observed along the fibre axis were 2 × 10–5 S cm–1 for [Pt(NH2dmoc)4][PtCl4] and 7 × 10–7 S cm–1 for [Pt(NH2eh)4][PtCl4]. These exceeded the values for the respective bulk compounds by 2–3 orders of magnitude, in agreement with comparable observations in oriented semiconducting organic polymers.

In their solid state, some metal complexes assume quasi-one-dimensional structures comprising linear arrays of metal atoms (mostly present as cations) (1–3). The anisotropic nature of such materials renders them attractive for their optical and electrical properties (1–3). Among these compounds, the most widely investigated have been Magnus’ green salt (4, 5), [Pt(NH3)4][PtCl4], and its derivatives of the type [Pt(L1)4][Pt(L2)4] (3, 6–8),

where L1 denotes a neutral ligand and L2 denotes an anionic ligand or a corresponding part of a multidentate ligand, respectively. These species comprise a supramolecular arrangement of the planar [Pt(L1)4]2+and [Pt(L2)4]2– units which are stacked alternately (Figure 1). Notably, the alignment of the platinum atoms in these compounds is a consequence of the electrostatic forces between the alternately charged coordination units (7, 9). Fig. 1 Chemical structure of Magnus’ green salt and some of its derivatives (eh = (R)-2-ethylhexyl; dmoc = (S)-3,7-dimethyloctyl)

Platinum Metals Rev., 2006, 50, (3), 112–117

112

These electrostatic forces, as well as crystal packing effects, determine the interplatinum distances that typically amount to 3.1–4.0 Å (7, 10–12). In compounds with Pt–Pt distances shorter than ca. 3.5 Å, the orbitals of adjacent platinum atoms overlap significantly. As a consequence these compounds become semiconductive. Processing of compounds derived from Magnus’ salt has hitherto been cumbersome, if not impossible, because these complexes are largely insoluble and do not melt prior to decomposition. Only recently have solution-processible Magnus’ salt derivatives of the type [Pt(NH2R)4][PtCl4], with R being an alkyl group, been synthesised (7, 9, 13, 14). The side groups R not only favour solubility in organic solvents, but also influence the interplatinum distances, and therefore dictate the physical properties of the corresponding bulk materials. For example, the complex with R = octyl, having a relatively large Pt–Pt distance (ca. 3.6 Å), was found to be an electrical insulator, whereas those with R = (R)-2-ethylhexyl (eh) and R = (S)-3,7dimethyloctyl (dmoc), by contrast, were semiconductors as a consequence of their relatively short Pt–Pt spacings (< 3.3 Å). Importantly, the soluble [Pt(NH2R)4][PtCl4] derivatives could be processed like common polymers (14–16), enabling, for instance, the manufacture of fibres by standard technologies. In the present work, we have explored the use of a process known as electrospinning to produce filaments of selected Magnus’ salt derivatives.

reported the preparation of fibres by electrospinning of the insulating complex [Pt(NH2R)4][PtCl4] with R = octyl (14). The production of these fibres was supported by the particular phase behaviour of these Magnus’ salt derivatives. These compounds formed thermoreversible gels even at low concentrations of the Pt-complex, which strongly facilitated the spinning process. However, the resulting fibres are of only modest interest due to their insulating nature. Hence, in the following, emphasis is placed on the preparation and characterisation of fibres of semiconducting [Pt(NH2R)4][PtCl4] compounds with R = dmoc and eh. This treatment significantly expands on a previous brief sketch on R = dmoc filaments (16). Electrospinning of fibres of previously synthesised [Pt(NH2R)4][PtCl4] (R = eh or dmoc) was performed from solutions of the compound in toluene, using a simple laboratory setup (Figure 2). In principle, it is possible to make very long fibres with this method by using a rotating metal cylinder instead of a metal plate as the negative electrode. Process parameters for the experiment (including optimal conditions) are given in Table I.

Conducting Fibres of Magnus’ Salt Derivatives Electrospinning (17–20) is a relatively old process (dating from the late 1910s), which has provoked renewed interest for the preparation of polymer fibres in recent years. In this technique, fibres are produced from polymer solutions under the action of electrostatic forces. Upon charging a polymer solution, the electric forces at the liquid surface can overcome the surface tension, resulting in a jet of electrically charged solution that is ejected towards an oppositely charged collector. If the solvent concomitantly evaporates, then polymer fibres accumulate at the collector. We have already

Platinum Metals Rev., 2006, 50, (3)

Fig. 2 Schematic illustration of the simple laboratory setup for the creation of filaments by electrospinning

Uniform fibres of [Pt(NH2dmoc)4][PtCl4] were produced, with lengths of 1–5 mm and diameters ranging from 0.1 μm to 2 μm. The large difference between the lengths of fibres obtained for the two compounds is attributed to the shorter Pt chain length of the [Pt(NH2dmoc)4][PtCl4] compound in toluene solution, compared with that for [Pt(NH2eh)4][PtCl4] (9, 13). Fibres of

113

Table I

Process Parameters for Electrospinning of [Pt(NH2R)4][PtCl4] Fibres Parameter

Range

Optimal processing

Solution temperature, ºC

Room temperature to 70

Room temperature

Compound concentration, % w/w

30–50 (R = dmoc) 15–35 (R = eh)

45 (R = dmoc) 30 (R = eh)

Applied voltage, kV

1–20

10 (R = dmoc) 7–10* (R = eh)

Distance between tip of glass vessel and ground plate, cm

3–15

12

Angle of inclination between glass vessel and ground plate, º

0–45

30

* For R = eh, long, thin fibres were obtained when the voltage was gradually increased from 7 to 10 kV during processing

[Pt(NH2eh)4][PtCl4] with a diameter of about 1 μm could be formed into a loop of 20 mm cross-section (Figure 3). This implies that the fibres possessed a considerable flexibility and resistance to bending stresses. These particular fibres broke

Fig. 3 Optical micrograph of a [Pt(NH2eh)4][PtCl4] fibre taken between crossed polarisers. The double arrows indicate the configuration of the polarisers. The intensity minima of the fibre parts oriented parallel to one of the polarisers and the intensity maxima of the fibre parts oriented at a 45º angle to the polarisers indicate that the platinum compound is oriented within the filament


as the loop was further tightened. Unfortunately, the [Pt(NH2dmoc)4][PtCl4] fibres were too short to carry out this experiment on them. Both types of fibres displayed notable birefringence in the polarising optical microscope. For fibres observed between crossed polarisers, light was transmitted at maximum intensity at an angle of 45º between the polarisers and the axis of the fibres. The transmitted light intensity was drastically reduced when the fibre’s axis was parallel or perpendicular to one of the polarisers, indicating that the quasi-one-dimensional structures were indeed oriented within the filaments along the filament axis. Molecular orientation of the Pt-structures within [Pt(NH2eh)4][PtCl4] fibres was confirmed by strong equatorial arcs in wide-angle X-ray diffraction pattern from a bundle of fibres (Figure 4). The average orientation angle derived from the half-width at half-maximum intensity of the major equatorial reflections (21) was found to be ~ 13º. This value indicates a low degree of orientation of the Pt-fibres as compared with that of, for instance, liquid crystalline polymer fibres such as aramids, high-performance polyethylene and poly(hexyl isocyanate) (PHIC) (21). Nevertheless, the orientation of the Pt-fibres is still significant considering that the organisation of the Pt-structures within the fibres is governed by electrostatic forces. A tilt compensator (MgCl2 crystal) revealed a positive sign for the birefringence of

114

Fig. 4 Wide-angle X-ray diffraction pattern of a bundle of oriented [Pt(NH2eh)4][PtCl4] fibres. The double arrow indicates the direction of the fibres

[Pt(NH2dmoc)4][PtCl4] and [Pt(NH2eh)4][PtCl4], demonstrating that the refractive index was greater in the direction of the fibre’s axis than perpendicular to it. Interestingly, at higher magnifications, alternating bright and dark parallel bands appeared when [Pt(NH2eh)4][PtCl4] fibres were examined between crossed polarisers (Figure 5). These bands were separated by 10–15 μm and were perpendicular to the fibre’s axis. These rather striking features strongly resemble those found in aramid fibres, for which their occurrence has been explained by a pleated sheet structure (22). For reasons as yet unknown to us, such bands were not observed in [Pt(NH2dmoc)4][PtCl4] fibres. Scanning electron microscopic studies revealed that the surfaces of the [Pt(NH2dmoc)4][PtCl4] and [Pt(NH2eh)4][PtCl4] fibres were relatively smooth (Figure 6). The bulk electrical conductivity along the axis of [Pt(NH2dmoc)4][PtCl4] fibres amounted to 2 × 10–5 S cm–1, and for [Pt(NH2eh)4][PtCl4] to 7 × 10–7 S cm–1. These values exceeded those for the respective bulk compounds by approximately 2 or 3 orders of magnitude (1.6 × 10–7 S cm–1 and 7 × 10–10 S cm–1, respectively). Similar enhancements with orientation have also been observed for (semi-)conducting organic polymers (23). This is


Fig. 5 Optical micrograph of a [Pt(NH2eh)4][PtCl4] fibre between crossed polarisers displaying bands which are indicative of a pleated sheet structure. The double arrows indicate the configuration of the polarisers

consistent with the assertion that the platinum chain structures in the filaments are oriented preferentially, with the quasi-one-dimensional axis parallel to the fibre’s axis, since the platinum arrays are the principal conduction path. Finally, in order to explore whether metallic platinum fibres could be produced by degradation of the solution-spun Pt-compounds, a number of fibres were subjected to plasma etching under an oxygen atmosphere for 20 min and 1 h periods, conducted in a plasma chamber. Interestingly, the

Fig. 6 SEM image of [Pt(NH2eh)4][PtCl4] fibres produced by electrostatic spinning from solution in toluene

115

macroscopic shape of the fibres was preserved and the samples could still be handled after this plasma treatment. SEM analysis of the morphology of [Pt(NH2eh)4][PtCl4] fibre surfaces after 20 min plasma treatment revealed a surface structure of a characteristic length of 100–200 nm (Figure 7(a)). Upon exposure of 1 h, the structure coarsened and appeared to increase in density (Figure 7(b)). This series of samples showed a weight loss of 25–30%

after 20 min plasma treatment and of ca. 50% after 1 h. After 5 h plasma treatment the fibres had broken into several parts and could not be handled further. Considering that the initial platinum content of [Pt(NH2eh)4][PtCl4] is 37.2% w/w, it was unfortunate that plasma exposure for 1 h did not yield pure elemental platinum, which would have enabled the fabrication of platinum fibres by simple processing of a precursor. Consistently, the plasma-treated fibres did not exhibit electrical conductivities in the metallic range.

Conclusions Like common organic polymers, the quasi-onedimensional platinum compounds [Pt(NH2eh)4][PtCl4] and [Pt(NH2dmoc)4][PtCl4] can be processed to fibres by electrospinning from solution. The thickness and length of the resulting thin crystalline fibres depend on various process parameters such as solution concentration of the platinum compounds, applied voltage, and the distance between the polymer solution and the collector. The longest fibres (up to 30 cm) were obtained with [Pt(NH2eh)4][PtCl4]. The fibres were rather flexible and allowed the formation of loops. X-ray diffraction patterns indicated that the linear supramolecularly arranged coordination units were oriented along the axis of the fibres, which, accordingly, showed highly anisotropic optical properties. The fibres showed electric conductivities in the semiconductor range. Gratifyingly, the conductivities along the axis of the fibres exceeded the values for the non-oriented bulk materials by 2–3 orders of magnitude. Given that films of [Pt(NH2dmoc)4][PtCl4] with oriented fibres are capable of functioning as the active semiconducting layer in, for example, FETs, Magnus’ salt derivatives might possibly pave the way for mass-produced “plastic electronics” (16). Other potential applications include environmentally stable semiconducting fibres (8, 16).

Acknowledgements

Fig. 7 SEM image of a [Pt(NH2eh)4][PtCl4] fibre after (a) 20 min and (b) 1 h etching with an oxygen plasma


The authors are grateful to A. P. H. J. Schenning (Technical University Eindhoven, The Netherlands) for supplying the dmoc and to M. Müller (ETH Zürich) for the SEM studies.

116

References 1 K. Carneiro, in “Electronic Properties of Inorganic Quasi-One-Dimensional Compounds”, Part II (Experimental), ed. P. Monceau, D. Reidel Publishing Co., Dordrecht, 1985, p. 1 2 S. Kagoshima, H. Nagasawa and T. Sambongi, “One-Dimensional Conductors”, Springer, Heidelberg, 1988 3 L. V. Interrante, ‘Electrical Property Studies of Planar Metal Complex Systems’, in “Inorganic Compounds with Unusual Properties”, ed. R. B. King, Advances in Chemistry Series, No. 150, American Chemical Society, Washington, DC, 1976, p. 1 4 G. Magnus, Pogg. Ann., 1828, 14, 239 5 G. Magnus, Ann. Chim. Phys. Sér. 2, 1829, 40, 110 6 J. S. Miller and A. J. Epstein, Prog. Inorg. Chem., 1976, 20, 1 7 J. Bremi, V. Gramlich, W. Caseri and P. Smith, Inorg. Chim. Acta, 2001, 322, (1–2), 23 8 W. Caseri, Platinum Metals Rev., 2004, 48, (3), 91 9 M. Fontana, H. Chanzy, W. R. Caseri, P. Smith, A. P. H. J. Schenning, E. W. Meijer and F. Gröhn, Chem. Mater., 2002, 14, (4), 1730 10 L. V. Interrante and R. P. Messmer, Inorg. Chem., 1971, 10, (6), 1174 11 J. R. Miller, J. Chem. Soc., 1965, 713 12 M. L. Rodgers and D. S. Martin, Polyhedron, 1987, 6, (2), 225

13 J. Bremi, W. Caseri and P. Smith, J. Mater. Chem., 2001, 11, (10), 2593 14 J. Bremi, D. Brovelli, W. Caseri, G. Hähner, P. Smith and T. Tervoort, Chem. Mater., 1999, 11, (4), 977 15 M. G. Debije, M. P. de Haas, T. J. Savenije, J. M. Warman, M. Fontana, N. Stutzmann, W. R. Caseri and P. Smith, Adv. Mater., 2003, 15, (11), 896 16 W. R. Caseri, H. D. Chanzy, K. Feldman, M. Fontana, P. Smith, T. A. Tervoort, J. G. P. Goossens, E. W. Meijer, A. P. H. J. Schenning, I. P. Dolbnya, M. G. Debije, M. P. De Haas, J. M. Warman, A. M. Van De Craats, R. H. Friend, H. Sirringhaus and N. Stutzmann, Adv. Mater., 2003, 15, (2), 125 17 A. Formhals, US Patent 1,975,504; 1934 18 J. Zeleny, Phys. Rev., 1917, 10, (1), 1 19 J. Doshi and D. H. Reneker, J. Electrostat., 1995, 35, (2–3), 151 20 R. Dersch, T. Liu, A. K. Schaper, A. Greiner and J. H. Wendorff, J. Polym. Sci. A: Polym. Chem., 2003, 41, (4), 545 21 A. R. Postema, K. Liou, F. Wudl and P. Smith, Macromolecules, 1990, 23, (6), 1842 22 H. H. Yang, “Kevlar Aramid Fiber”, Wiley, Chichester, 1993 23 K. Kaeriyama, in “Handbook of Organic Conductive Molecules and Polymers”, ed. H. S. Nalwa, Wiley, Chichester, 1997, Vol. 2, p. 271

The Authors Margherita Fontana is presently working at Ciba Speciality Chemicals in Basel as a Laboratory Head. She is leading projects in the development of colour materials for E-paper display applications based on electrophoretic particles as well as electrochromic materials. She is also involved in the characterisation of semiconducting materials and related devices.


Walter Caseri has been active as a Senior Scientist in the Institut für Polymere at the ETH Zürich, Switzerland, since 1996. He is involved in research and teaching. His interests are in polymers containing both organic and inorganic components (polymeric structures with inorganic backbones, nanocomposites and polymers at inorganic interfaces).

Paul Smith has been Professor of Polymer Technology at the ETH Zürich since 1995. His interests lie in the development of advanced polymer materials, polymer phase behaviour, mechanical properties of polymer systems, electrically and optically active polymers, and polymer/metal systems.

117

DOI: 10.1595/147106706X129088

Crystallographic Properties of Platinum NEW METHODOLOGY AND ERRATUM By J. W. Arblaster Coleshill Laboratories, Gorsey Lane, Coleshill, West Midlands B46 1JU, U.K.; E-mail: [email protected]

Equations are given to represent the lattice parameter thermal expansion of platinum from 293.15 K to the melting point at 2041.3 K. This treatment is intended to supersede a combination of dilatometric equations with corrections for thermal vacancy effects.

In the review of the crystallographic properties of platinum by the present author (1), the hightemperature data were represented by expressions derived from precision dilatometric thermal expansion measurements (Equations (i) and (ii)). Above 1000 K temperature, not only did length change measurements derived from lattice parameter measurements fail to agree with one another, they also showed marked scatter around the dilatometric results. The length change measurements were therefore unsuitable for calculating the lattice parameter thermal expansion. This problem was addressed by correcting the dilatometric data for thermal vacancy effects (Equations (iii) and (iv)), based on the consistent set of thermal vacancy parameters given in Table I and explained in the original review (1). On reflection, this procedure is cumbersome

Table I

Thermal Vacancy Parameters for Platinum Parameter

Symbol Value

Thermal vacancy concentration at melting point

cv

7 × 10–4

Enthalpy of monovacancy formation Hvf Entropy of monovacancy formation

f

Sv

1.51 eV 1.32k

Note: k is the Boltzmann constant, given at the time of publication of Reference (1) as 8.617385 × 10–5 eV K–1

and might be considered unsatisfactory. It has therefore been replaced here by Equations (v) and (vi) which are based on a combination of Equations (i) and (iii), and which represent the lattice parameter thermal expansion from 293.15 K to the melting point at 2041.3 K. Equation (v) agrees with a combination of Equations (i) and (iii)

High Temperature Dilatometric Thermal Expansion (293.15–2041.3 K) α* = 7.08788 × 10–6 + 1.04970 × 10–8 T – 2.00846 × 10–11 T2 + 2.28200 × 10–14 T3 – 1.18453 × 10–17 T4 + 2.37348 × 10–21 T5 K–1

(i)

δL/L293.15 K = 7.08788 × 10–6 T + 5.24850 × 10–9 T2 – 6.69487 × 10–12 T3 + 5.70500 × 10–15 T4 – 2.36906 × 10–18 T5 + 3.95580 × 10–22 T6 – 2.39745 × 10–3

(ii)

Thermal Vacancy Corrections (1300–2041.3 K) α*(lattice) = α*(dilatometric) – (5841/T ) e(1.32 – 17523/T) K–1

(iii)

δa/a293.15 K = δL/L293.15 K – (1/3) e(1.32 – 17532/T)

(iv)

2

Note: In Equation (x) of Ref. (1), to which Equation (iv) corresponds, the second δ was incorrectly given as d.

High Temperature Lattice Parameter Thermal Expansion (293.15–2041.3 K) α* = 7.03139 × 10–6 + 1.08937 × 10–8 T – 2.10071 × 10–11 T2 + 2.36623 × 10–14 T3 – 1.20728 × 10–17 T4 + 2.34219 × 10–21 T5 K–1

(v)

δa/a293.15 K = 7.03139 × 10 T + 5.44686 × 10 T – 7.00236 × 10 T + 5.91557 × 10–15 T4 – 2.41456 × 10–18 T5 + 3.90366 × 10–22 T6 – 2.39164 × 10–3

(vi)

–6


–9

2

–12

3

118

to within 4 × 10–9 K–1 and to within ± 2 × 10–9 K–1 overall, well within the accuracy of Equation (i) of ± 2 × 10–8 K–1. In Equations (i), (iii) and (v), α* is the thermal expansion coefficient relative to 293.15 K.

equation on page 19 of (1) (at the top of the righthand column) was incorrectly given. It should have read: n

α = Cp( A + BT + Σ Cj T – j ) j=1

Erratum In the review (1), equations were given representing a precision relationship between thermal expansion and specific heat. However, the third

Reference 1

J. W. Arblaster, Platinum Metals Rev., 1997, 41, (1), 12

Launch of the Low Carbon and Fuel Cell Knowledge Transfer Network On the 25th May, 2006, Fuel Cell Today (www.fuelcelltoday.com), along with its partners CENEX (the U.K.’s newly formed Centre of Excellence for Low Carbon and Fuel Cell Technologies), Fuel Cells UK and Foresight Vehicle, announced the launch of the Low Carbon and Fuel Cell Knowledge Transfer Network (LCFC-KTN). This new development, designed to enhance the U.K.’s competitive position in emerging clean energy technologies, was instigated by the Department of Trade and Industry. The Network was launched simultaneously in Yokohama, Japan, at the Japan Society of Automotive Engineers congress. Fuel Cell Today and the other KTN partners have combined their specialist knowledge to cover broad aspects of sustainable transportation (www.low-carbon-ktn.org.uk) and the full complement of commercial opportunities for fuel cells, from portable battery replacement through to power generation and transport applications. A principal aim is to accelerate the development and deployment of fuel cells in the U.K. The KTN will provide a range of services to the U.K. low carbon and fuel cell community including a dedicated website, Business to Business facilities, networking opportunities, online conferencing, briefing notes, and expert opinions on technology and policy. The launch

of the KTN is timely. As the commercial phase of fuel cell development gets underway, the U.K. fuel cell community now has a real opportunity to influence domestic and even worldwide markets. The advent of the Low Carbon and Fuel Cell Technology KTN is evidence that the U.K. Government is reshaping its approach to boosting U.K. fuel cell industry capabilities and competitiveness in line with broader international industry trends. Currently, the U.K. does not sit with the United States, Japan, Canada and Germany in the first tier of international fuel cell development, but it has an undeniable depth of expertise which bodes well for the future. The U.K. also has some of the most innovative companies in the business. With effort, and continued Government support, the U.K. might yet take a place at the top table. The Fuel Cell KTN website can be viewed at: www.fuelcellktn.com. For further information on this KTN and the services which it offers, contact: [email protected]. M. HUGH Mike Hugh is the Moderator of the Fuel Cell Technology Knowledge Transfer Network website. He is interested in fuel cell paths to market and the corresponding policy process. He is on the staff of Fuel Cell Today, and his Ph.D. thesis focused on drivers and barriers for stationary fuel cell markets in the U.K.

DOI: 10.1595/147106706X129853


119

DOI: 10.1595/147106706X128890

The Minting of Platinum Roubles PART IV: PLATINUM ROUBLES AS AN ARCHIVE FOR THE HISTORY OF PLATINUM PRODUCTION By Thilo Rehren Institute of Archaeology, University College London, London WC1H 0PY; E-mail: [email protected]

This paper augments a series of articles on Russian roubles in this Journal (1–3) with a summary of recent research into the manufacturing history and materials characterisation of these coins. The results are not only significant for the identification of genuine roubles issued between 1828 and 1845, ‘Novodel’issues produced in the late 19th century, and outright forgeries of the 20th century, but offer a fascinating insight into the difficulties encountered at the time in the large-scale refining and processing of platinum metal. A range of instrumental methods have been used to elucidate the magnetic properties, chemical composition and low density of genuine roubles, and to reveal their complex internal structure. The resulting new insights into the historical practice of platinum metallurgy are unbiased by concerns about industrial espionage, state secrets, and professional rivalry.

The first half of the 19th century was a crucial period in the discovery and metallurgical study of platinum and its allied metals, iridium, osmium, palladium, rhodium and ruthenium. Only platinum was known in 1800, but all six were known by 1844 (4–7). The subsequent development of their refining and production processes is not well known, probably due to commercial secrecy. Contemporary ‘best practice’ reports, for instance by Sobolevsky’s Russian Royal Mint in St. Petersburg (8), are therefore not necessarily comprehensive or reliable in their technical detail. When significant deposits of platinum were discovered in the Ural mountains, the Russian authorities, and in particular the then Minister of Finance, Count Egor F. Kankrin wanted to use it for coinage along with gold and silver denominations. The value ratio between the three metals was set at 15.6:5.2:1 for gold, platinum and silver, Fig. 1 3 rouble piece, dated 1831, struck by the Royal Mint in St. Petersburg under the supervision of General Sobolevsky (diameter 23 mm)


respectively. Large-scale platinum ore processing began following the decision in April 1828 to issue platinum roubles. This was done at the Royal Mint in St. Petersburg, supervised by General Sobolevsky. A technically successful process used about 20 tonnes of platinum ore from 1828 to 1845, striking more than 1.3 million 3 rouble pieces (Figure 1), almost 15 thousand 6 rouble pieces and 3474 12 rouble pieces, with a total platinum weight of 485,505 troy ounces (approximately 15.1 tonnes) (Reference (4), page 247). The monetary side, however, was less successful. In 1845 the Russian government demonetised the entire platinum coinage, which was sold to various European platinum refineries for reworking. There was something of an ‘afterlife’ for the Russian platinum roubles when the Russian Royal Mint produced fresh coins (‘Novodels’) for collectors in the late 19th century. Officially struck, using the original dies, these are numismatically identical to the original series. It may be difficult to distinguish authentic early to mid-19th century coins from the ‘Novodels’ by established numismatic criteria, particularly since the latter are typically in mint condition, and more likely to be found in major reference collections. A written provenance is often missing, so a scientific protocol is required to distinguish ‘Novodel’ issues from monetary

120

coins. A further complication is the existence of 20th century forgeries, allegedly produced in the Lebanon, and perhaps also elsewhere. Recent literature (1–3, 9) has drawn attention to a valuable body of technical information. It is the aim of this paper to give an up-to-date, first-hand account of key results from the ongoing research of the author’s group into these coins, and to outline the potential of early coins and medals for providing direct and precise information regarding the development of platinum metallurgy over more than a century.

Early 19th Century Platinum Refining The early metallurgy of platinum was considerably hampered by its chemically and thermally refractory nature, and by the presence in the ore of other, not easily separable elements (typically about 25% in total of varying amounts of the other platinum group elements, plus iron and copper). Most proposed refining methods relied on dissolving the ore in aqua regia (mixed concentrated hydrochloric and nitric acids), followed by selective precipitation of platinum as ammonium hexachloroplatinate. Careful washing was needed to remove as much of any coprecipitated iridium and iron salts as possible without excessive loss of platinum. The dried precipitate was brought to red heat, driving off the ammonia and chlorine, and yielding a metallic platinum sponge. The sponge was then ground, forged and hammered, with repeated annealing cycles. The result was a solid metal which was forged into bars and sheets. The density of the metal sponge increased progressively during hammering to a maximum of around 21 g cm–3, close to that of pure platinum at 21.45 g cm–3. Over twenty years, Wollaston perfected the refining and working of platinum at a laboratory scale to economic success (6). The Royal Mint in St. Petersburg, on the other hand, pioneered industrial use of the early powder metallurgy, reportedly with several refining variants along the way (4, 7, 9, 10). The relative merits and efficacy of the variants in terms of finished metal quality cannot be judged from these publications alone.


Investigation of Russian Platinum Coins Bachmann and Renner’s (11) were the first analytical results, based on scanning electron microscopy and X-ray fluorescence analysis on an 1829 3 rouble piece. There was a significant degree of porosity at the surface, as expected for material produced by powder metallurgy, and with 0.5 wt.% iron and about 0.1 wt.% each of palladium, rhodium and chromium present. The density of the material was 20.7 g cm–3. The authors record a visible improvement of the surface quality of the coins over the production period. There has been no metallographic study, or discussion of the range and origins of impurities, until recently. The present study used a series of 3 rouble coins from 1828 to 1842. It was prompted by the observation of a magnetic moment and substandard density for most of them. Only the 1828 coin was in mint condition; the other eight showed clear signs of wear and circulation. A Russian Olympic commemorative platinum coin struck in 1977 was included to represent more recent metallurgical standards. Analysis was largely non-sampling and non-destructive. Only one of the coins was sampled for metallographic study. Full analytical details and results have been published elsewhere (9, 12–14 and literature cited therein). This paper summarises the results and addresses the coins’ potential significance for the history of platinum metallurgy.

Material Characterisation The 3 rouble coins are inscribed with their nominal weight of 2 zolotnik (zol.) 41 dolya (dol.), or 10.35 g, pure Ural platinum; the measured weights vary from 10.35 g for the 1828 issue to less than 10.1 g for the 1837 coin (Table I). Density values were scattered in the range 20.0 to 20.7 g cm–3; the 1828 issue had a density of 21.3 g cm–3. This agrees with contemporary values from the early 19th century literature of about 20 to 21 g cm–3, while placing the 1828 issue close to the theoretical value for pure platinum. Three of the coins showed a considerable response to an ordinary hand-held magnet; a fourth could be lifted bodily; the other three showed no perceptible response,

121

Table I

Physical Properties of Seven 3 Rouble Platinum Coins Weight, g

Density, g cm–3

*Magnetic value

Theoretical Fe content (XRD), wt.%

Impurities (XRF), wt.%

1828** 1832 1835 1836 1837 1838

10.351 10.281 10.165 10.251 10.076 10.279

21.32 20.25 20.15 20.42 20.03 20.12

0 35 8 22 21 13

0 2.5 0.4 1.9 1.2 0.4

0.7 3.5 1.8 3.5 4.1 4.1

1842

10.311

20.69

17

1.2

3.1

Year

Density determined by immersion in water. *Magnetic value is the dimensionless reading from the Förster deflectometer calibrated to zero on the 1828 issue. Weight per cent impurities are taken from Table II. **‘Novodel’ issue

among them the 1828 coin. It became evident that the uncirculated coin dated 1828 was probably a late-19th century ‘Novodel’ issue. This was used thereafter as an internal standard for technically pure platinum; its chemical characteristics are given below, together with those of the 1977 commemorative issue. Where coins showed a magnetic moment, this was quantified using a Förster deflectometer. The instrument was calibrated on the 1828 coin rather than on a sheet of pure platinum, so that the geometry of the reference piece would be identical to that of the samples. The six other coins gave values between 8 and 35 units – results of little significance in themselves, but clearly not random in the light of other observations (Table I). From an initial qualitative chemical analysis by scanning electron microscopy with microanalysis by energy-dispersive X-ray spectroscopy (SEMEDS), the only readily detectable impurities (chlorine and calcium among others) were probably surface contaminants. Of likely primary contaminants from the ore, only iron was detected. However, due to the extremely dense matrix, the detection limits for this and other elements were rather high, precluding reliable quantification and interpretation of the results. The peaks for other elements such as gold and iridium were too close to the dominant platinum peaks to be properly resolved at low concentrations. Two series of Xray fluorescence (XRF) analyses were performed,


both measuring approximately two thirds of the coins’ surfaces. Iridium, gold and iron were detected in most coins, followed by minor signals for copper, nickel and occasionally zinc. The second series of analyses by energy-dispersive spectroscopy identified iron and iridium as the main contaminants, both at around 1% by weight, followed by copper and gold in the range 0.1–1%. Rhodium, palladium and nickel were typically present at around 0.1% or less. Elements such as titanium, zinc and tin rarely exceeded a few hundred parts per million (Table II). The results for the obverse and reverse of each coin are typically very similar, but several coins showed much higher readings for some elements on one side only – for instance, copper and gold at around 1% each on the reverse of the 1838 issue. This was consistent with macroscopically visible gold specks on the coin’s surface. One of these particles proved to be a high-copper gold alloy with a low silver content, unlike natural gold nuggets which have a rather lower copper content and a higher silver content. The 1844 3 rouble piece analysed by Lupton (2) gave a similar result. The 1837 coin studied here shows abnormally high levels of nickel, silver and tin on its reverse, together with an elevated copper level. Both the magnetic and chemical analyses indicated a significant presence of iron in these coins, but did not distinguish between mechanically incorporated iron-rich particles (either oxide or

122

Table II

XRF Analyses of 3 Rouble Platinum Coins Coin

Ti

Mn

Fe

1829

110

< 20

12,300

100

< 20

12,500

1831 1832 1835 1836 1837

Ni

Cu

Rh

Pd

Ag

Sn

60

2800

1100

1350

680

10

80

3000

1150

1270

900

Os > Rh > Ru Phalaborwa: Pt > Pd > Ru > Ir > Os All the rock samples were graded for particle size distribution by wet screening, followed by

139

Table II

PGE Crust and Mantle Abundance Compared with PGE Concentration in Combined Rock Types from PCP Complexes Material

Platinum, ppt*

Paladium, ppt

Rhodium, ppt

Osmium, ppt

Iridium, ppt

Ruthenium, ppt

400

400

60

50

50

100

Upper mantle (peridotite)‡ Average abundance 6500

5700

n.a.

3500

3500

5800

Crustal average† PGE abundance

Catalão PCP

300,000 up to 2,860,000

300,000 up to 810,000

140,000 up to 600,000

120,000 up to 200,000

n.a.

120,000 up to 200,000

Ipanema PCP

300,000 up to 3,200,000

200,000 up to 1,330,000

400,000 up to 540,000

400,000

n.a.

150,000 up to 490,000

150,000 up to 580,000

260,000

n.a.

300,000 up to 3,280,000

1,100,000 up to 13,500,000

120,000 up to 160,000

Ore concentration, g t–1

0.15 up to 3.20

0.26 up to 1.33

0.14 up to 0.60

0.12 up to 3.28

1.10 up to 13.50

0.12 up to 0.49

Concentration rate: PCP composition/ mantle abundance

89 up to 492 times

45 up to 233 times

n.a.

57 up to 937 times

315 up to 3857 times

27 up to 85 times

Phalaborwa PCP

* ppt = parts per trillion

†Crustal average, Ref. (29) Wedepohl (1995)

chemical and mineralogical analyses as well as magnetic separation studies. The research, which is still in progress, will be followed by systematic chemical and mineralogical studies. At present, total rock geochemical analysis, including major and minor trace elements, including the rare earths, is being determined by AAS and/or ICP spectroscopy. The rock samples will be surveyed for process mineralogy studies, and thin-polished samples will be prepared for optical and scanning electron microscopy analyses. Mineralogical analyses will be performed by X-ray diffraction, optical mineralogy and scanning electron microscopy with energy dispersive X-ray spectrometer (SEM-EDS). Gravitational concentration and heavy minerals extraction for a sensitive mineralogical (microprobe) study will also be undertaken. The author is aware that the following mineralogical study will be much more difficult and time


‡Upper Mantle, Ref. (28) Morgan et al.

consuming, and is of higher risk. The Brazilian laboratory expertise and technical apparatus may not be sufficient. So it is further intended to ask for the collaboration of Russian mineralogists, especially those linked with St. Petersburg University or with NATI Research JSC, St. Petersburg. The main aim will be to identify the PGE mineralogical phases and to establish their relationship with associated silicate and oxide minerals, looking for a probable genetic connection between the PGE concentration process and the evolution of the phoscorite-carbonatite complexes. The laboratory procedures will be performed at the University of São Paulo, and other international academic and commercial research facilities.

Discussion and Conclusions The PGEs, rhenium and gold comprise the socalled highly siderophile elements (HSE), the abundances of which in the upper mantle are often

140

in the parts per trillion (ppt) range, and, which in the undepleted primitive upper mantle, are in approximately chondritic proportions (28, 29). Phoscorite-carbonatite pipes (PCP) are generated in a geodynamic environment which provides appropriate structural control to enable the vertical migration of dense iron-rich melts, over thousands of metres, and, equally important, their concentration into relatively small core zones. There is a limited understanding of the role of the magma mixing, assimilation, crustal metasomatism and other subsolidus processes in the origin and evolution of PCP complexes. However, the role of metasomatism, including late-stage alteration is also important in the ultimate understanding of the PGE enrichment processes. PGE mineralisation has a close spatial and probably genetic relationship with the multistage magmatic and post-magmatic evolution of PCP complexes. The PGE enriched zones, in the core zones of PCP complexes, represent the final product of a series of superimposed events like the progressive PGE fractionation during the evolution of mantle magma and the recurrence of magmatic pulse events. The parental sulfur-poor/oxygen-rich melt system tends to result in a PGE ore mineralogy assemblage similar to those from classical ultramafic platiniferous pipes. These pipes are commercially very attractive because of the low capital cost of establishing ore dressing facilities, that is, the bulk of the PGEs could be recovered by conventional gravity and magnetic separation technologies. The PGE concentrations in Catalão, Ipanema and Phalaborwa provide solid evidence of the PGE potential of PCP complexes, particularly in regare to their ore concentration level. The PGE occurrence in Ipanema shows the need to pay attention to the detection of Fe-Cr and PGE-rich vein-type varieties of spinels. The wide development of such Fe-spinel veins is indicative of a low erosion level at the PCP complex cupola, and consequently, a better PGE potential (22). The theoretical and factual data encourage the assumption that PCP intrusions are a very promising target for PGE mineralisation. It is proposed


that the platiniferous pipe conceptual model should be extended to take into account PCP complexes as a promising new member. For systematic mineral exploration, the PGE exploration strategy for PCP complexes must be directed mainly to a selective structural and geochemistry survey, instead of to conventional saturation rock sampling geochemistry.

Acknowledgements Foskor Limited, Jan H. van der Merwe and the mining staff from Fosfertil SA, Tapira and Catalão are gratefully thanked for permission, technical assistance, hospitality and discussions during field work and sampling at the Phalaborwa, Tapira and Catalão mines, respectively. This study has been partly supported by the São Paulo Research and Development Agency (FAPESP – Grant 03/09481-0) and hosted by the LCT – Technological Characterization Laboratory, Polytechnic School of the University of São Paulo (USP, Mining and Petroleum Engineering Department).

References 1 R. N. Scoon and A. A. Mitchel, ‘Discordant ironrich ultramafic pegmatites in the Bushveld Complex and their relationship to iron-rich intercumulus and residual liquids’, J. Petrol., 1994, 35, 881 2 M. J. Viljoen and M. J. Scoon, ‘The distribution and the main geologic features of discordant bodies on iron-rich Ultramafic pegmatite in the Bushveld Complex’, Econ. Geol., 1985, 90, 1109 3 M. J. Viljoen and L. W. Shürman, ‘Platinum-Group Metals’, in “The Mineral Resources of South Africa”, 6th Edn., eds. M. C. G. Wilson and C. R. Anhaueusser, Council for Geoscience, Handbook 16, Pretoria, 1998, pp. 532–630 4 H. P. Taylor, ‘The Zoned Ultramafic Complexes of Southeastern Alaska’, in “Ultramafic and Related Rocks”, ed. P. J. Wyllie, John Wiley and Sons, Inc., New York, 1967, pp. 97–121 5 P. Laznika, ‘Zoned Mafic-Ultramafic Complexes in Phanerozoic Orogenic Belts (Alaska or Ural Types)’, in “Empirical Metallogeny”, Elsevier, Amsterdam, 1985, Vol. 1, Pt. A, pp. 243–250 6 A. J. Teluk, ‘Platinum Metallogenesis, Ural-Alaskan Type Complexes’, Fifield Platinum Project, NSW, Australia, Geodyne Pty Ltd., Technical Report, 2001, see http://www.rimfire.com.au/PDF/Geodyne%20rep ort%20complete%20with%20figs.pdf 7 V. I. Smirnov, 1977, ‘Deposits of Platinum Metals, Late Magmatic Deposits’, in “Ore Deposits

141

8

9 10

11

12 13

14

15 16

17

18

of USSR”, ed. V. I. Smirnov, Pitman, London, pp. 112–121 ‘Platinum group minerals and associated chromespinels of the Alaskan-type Nizhny Tagil Massif, middle Urals’, in “Mineral Deposits: Processes to Processing”, eds. C. J. Stanley et al., Balkema, Rotterdam, 1999, pp. 787–790 E. F. Stumpfl and J. C. Rucklidge, ‘The platiniferous dunite pipes of the Eastern Bushveld’, Econ. Geol., 1982, 77, 1419 “Phoscorites and Carbonatites from Mantle to Mine: the Key Example of the Kola Alkaline Province”, eds. F. Wall and A. N. Zaitev, The Mineralogical Society of Great Britain and Ireland, London, 2004, 498 pp A. G. Bulakh et al., ‘Overview of carbonatitephoscorite complexes of the Kola Alkaline Province in the context of a Scandinavian North Atlantic Alkaline Province’, in “Phoscorites and Carbonatites from Mantle to Mine: the Key Example of the Kola Alkaline Province”, eds. F. Wall and A. N. Zaitev, The Mineralogical Society of Great Britain and Ireland, London, 2004, pp. 1–36 “Igneous rocks. A Classification and Glossary of Terms”, 2nd Edn., ed. R. W. Le Maitre, Cambridge Univ. Press, Cambridge, U.K., 2002, 236 pp N. I. Krasnova et al., ‘Introduction to phoscorites: occurrence, composition, nomenclature and petrogenesis’, in “Phoscorites and Carbonatites from Mantle to Mine: the Key Example of the Kola Alkaline Province”, eds. F. Wall and A. N. Zaitev, The Mineralogical Society of Great Britain and Ireland, London, 2004, pp. 45–74 N. I. Krasnova et al., ‘Kovdor – classic phoscorites and carbonatites’, in “Phoscorites and Carbonatites from Mantle to Mine: the Key Example of the Kola Alkaline Province”, eds. F. Wall and A. N. Zaitev, The Mineralogical Society of Great Britain and Ireland, London, 2004, pp. 100–132 M. E. Wallace and D. H. Green, ‘An experimental determination of primary carbonatite magma composition’, Nature, 1988, 335, (6188), 343 P. J. Willie and W. J. Lee, ‘Model system controls on conditions for formation of manesiocarbonatite and calciocarbonatite magmas from the mantle’, J. Petrology, 1988, 39, (11/12), 1885 M. J. Lee et al., ‘Carbonatites and phoscorites from the Sokli complex, Finland’, in “Phoscorites and Carbonatites from Mantle to Mine: the Key Example of the Kola Alkaline Province”, eds. F. Wall and A. N. Zaitev, The Mineralogical Society of Great Britain and Ireland, London, 2004, pp. 133–162 N. M. Vielreicher, D. I. Groves and R. M.

19

20

21

22

23

24

25

26 27

28

29

Vielreicher, ‘The Phalaborwa (Palabora) deposit and its potential connection to iron-oxide copper-gold deposits of Olympic Dam Type’, in “Hydrothermal Iron-Oxide Copper-Gold and Related Deposits. A Global Perspective”, ed. T. M. Porter, PGC Publishing, Adelaide, Australia, 2000, Vol. 1, pp. 321–329 Palabora Mining Corp. Ltd., ‘The geology and economic deposits of copper, iron and vermiculite in the Palabora igneous complex: a brief review’, Econ. Geol., 1976, 71, 177 J. F. Brod, ‘Petrology and Geochemistry of the Tapira Alkaline Complex, Minas Gerais State, Brazil’, Ph.D. Thesis, Dept. of Geological Sciences, University of Durham, U.K., 1999 J. F. Brod et al., ‘The kamafugite-carbonatite association in the Alto Paranaíba Igneous Province (APIP) Southeastern Brazil’, Rev. Bras. Geoc., 2000, 30, (3), 408 K. N. Malitch, ‘Assessment of the platinum potential of clinopyroxenite-dunite massifs’, Trans. Russ. Acad. Sci., Earth Sci. Sect., V, 1994, 347A, (3), 400 A. A. Efimov et al., ‘Platiniferous dunites in the Urals and the Aldan Shield, Russia: structural, mineralogical and geochemical evidence for a similar origin’, Abstracts 9th Int. Platinum Symposium, Billings, Montana, U.S.A., 2002 M. G. C. Wilson, ‘Copper’, in “The Mineral Resources of South Africa”, 6th Edn., eds. M. C. G. Wilson and C. R. Anhaueusser, Council for Geoscience, Handbook 16, Pretoria, 1998, pp. 209–225 N. S. Rudaschevsky et al., ‘A review and comparison of PGE, noble-metal and sulphide mineralization in phoscorites and carbonatites from Kovdor and Phalaborwa’, in “Phoscorites and Carbonatites from Mantle to Mine: the Key Example of the Kola Alkaline Province”, eds. F. Wall and A. N. Zaitev, The Mineralogical Society of Great Britain and Ireland, London, 2004, pp. 375–405 H. H. G. J. Ulbrich and C. B. Gomes, ‘Alkaline rocks from continental Brazil’, Earth Sci. Rev., 1981, 17, 135 C. S. Rodrigues et al., “Complexos Carbonatiticos do Brasil: Geologia”, Companhia Brasileira de Mineracao e Metalurgia, Sao Paulo, Brasil, 1984, 44 pp J. W. Morgan et al., ‘Sideophile elements in Earth’s upper mantle and lunar breccias: data synthesis suggests manifestations of some late influx’, Meteorit. Planet. Sci., 2001, 36, 1257 K. H. Wedepohl, ‘The composition of the continental crust’, Geochim. Cosmochim. Acta, 1995, 59, (7), 1217

The Author Dr Juarez Fontana is professor and a mineral exploration expert at the University of São Paulo, Brazil. He is interested in both academic (geological models) and commercial projects, connected with PGE mineralisation and metallogenic processes, especially those related to the alkalic phoscoritecarbonatite intrusive complexes.


142

DOI: 10.1595/147106706X123930

Platinum 2006 Johnson Matthey’s annual surveys of supply and demand of the platinum group metals continue with “Platinum 2006”, published in May 2006 and reporting on the calendar year 2005. Johnson Matthey records a world demand for platinum of 6.7 million oz in 2005, an annual rise of 160,000 oz (2 per cent). Purchases by the autocatalyst sector again grew strongly, with demand increasing by 330,000 oz to a new high of 3.82 million oz. Europe accounted for most of this growth, attributable to continued tightening of emissions rules and greater use of catalysed soot filters in light-duty diesel vehicle applications. Purchases of platinum for jewellery manufacture fell by 200,000 oz (9 per cent) to 1.96 million oz. A strong platinum price prompted stock reductions across the trade, and encouraged the recycling of old jewellery. Chinese jewellery demand for platinum fell to its lowest for seven years. Demand in Japan and North America also contracted. Industrial demand for platinum climbed by 9 per cent to 1.675 million oz in 2005, cited as an all-time high. In the electrical sector there was further growth in the production of data storage disks using a platinum alloy layer. Continuing expansion of liquid crystal display glass manufacturing in Asia drove demand for platinum in glass applications to a record level. Consumption of platinum for making catalysts for petroleum refining and chemical manufacture also increased. World supplies of platinum increased by 2 per cent in 2005, rising to 6.63 million oz, primarily due to greater output from South Africa, which increased by 2 per cent to 5.11 million oz. This increase was less than anticipated, since efforts to expand output were hampered by a number of operational problems. Supplies from North America and Russia fell slightly.

Platinum Metals Rev., 2006, 50, (3), 143

Demand for palladium increased by 7 per cent to 7.04 million oz in 2005, due almost entirely to substantially greater use of the metal in jewellery. Palladium purchases for jewellery manufacture, driven by rapid market development in China, rose by 54 per cent to 1.43 million oz. Autocatalyst demand for palladium increased marginally to 3.81 million oz. Although automotive manufacturers made greater use of palladium catalyst systems than in 2004, average loadings of palladium on catalysts continued to decline. Palladium supplies fell by 2 per cent to 8.39 million oz; growth in South African output did not offset lower production in North America and a drop in sales of Russian metal. Purchases of rhodium expanded by 11 per cent to 812,000 oz in 2005, equalling the previous high recorded in 2000. Use of the metal in autocatalyst, glass and chemical applications increased. A special feature, ‘Other Applications for Platinum’, highlights a wide range of further uses of platinum. These vary from mediumscale automotive and medical applications to many small end uses such as stationary source pollution control, gas safety sensors and cathodic protection. Each of the latter uses requires just a few thousand ounces. In the automotive sector, spark plugs and oxygen sensors account for a combined platinum consumption of more than 130,000 oz in 2005. Biomedical uses of platinum (with an estimated consumption of a little over 100,000 oz in 2005) range from anticancer drugs to devices associated with innovative treatments for heart and brain disease. “Platinum 2006”, Johnson Matthey PLC, Precious Metals Marketing, Orchard Road, Royston, Hertfordshire SG8 5HE, U.K.; Email: [email protected]; website: http://www.platinum.matthey.com/.

143

DOI: 10.1595/147106706X129079

Thermophysical Properties of Palladium DETERMINATIONS (INCLUDING SPECTRAL EMISSIVITY AT 684.5 nm) AT THE MELTING TRANSITION AND IN THE LIQUID STATE By Claus Cagran and Gernot Pottlacher Institut für Experimentalphysik, Technische Universität Graz, Petersgasse 16, A-8010 Graz, Austria; E-mail: [email protected]

The results from fast-pulse heating experiments (of duration 60 μs) performed on pure palladium are presented. Thermophysical properties derived include specific enthalpy, enthalpy of fusion, electrical resistivity, isobaric heat capacity, thermal conductivity and thermal diffusivity, over a range of temperatures from the melting transition up to some hundred degrees higher in the liquid state. Additionally, normal spectral emissivity at wavelength 684.5 nm is presented,

Introduction The Subsecond Thermophysics Group at Graz University of Technology has been working to determine the thermophysical properties of liquid metals for about 25 years. The work remains relevant and of current interest for scientific applications as well as for the metalworking industry. Accurate data for the melting transition and the liquid state are often sparse, but are essential inputs to computer simulations, for instance those of solidification or die-casting. Palladium is used in dentistry, jewellery, watchmaking, spark plugs, the production of electrical contacts, and metallising ceramics (1). Finely divided palladium makes a good catalyst, used to accelerate hydrogenation and dehydrogenation reactions, and for petroleum cracking. The palladium-hydrogen electrode is used in electrochemical studies. Palladium has recently attracted much interest as a potential replacement for higherpriced platinum in catalytic converters for controlling emissions from diesel vehicles. The present experiments on palladium form part of a systematic investigation of the thermophysical properties of the platinum group metals. Measurements on rhodium are scheduled in the present programme; osmium and ruthenium are not available in wire shape. Platinum and iridium have already been investigated (2–4), and show a slight increase of normal spectral emissivity at wavelength 684.5 nm in the liquid phase, similar to


the trend in emissivity values for palladium reported in the present work.

Experimental and Data Reduction Procedures Using a pulse-heating apparatus (Figure 1), the thermophysical properties of conducting materials are accessible from the solid state up to the end of the stable liquid phase. For the present investigations, palladium samples in the form of wire (0.5 mm diameter, 60 mm length, purity 99.9%, purchased from Alfa Aesar, Stock 10279, lot F28J28) were incorporated in a capacitor-driven discharge circuit and resistively pulse-heated. The following parameters were determined directly: • • • • •

electric current voltage drop surface radiance thermal expansion normal spectral emissivity.

From these, the following thermophysical properties were derived: • • • • • • •

sample temperature enthalpy of fusion isobaric heat capacity electrical resistivity at initial geometry electrical resistivity under thermal expansion thermal conductivity thermal diffusivity.

The accessible range of measurement extends

144

Fig. 1 Sketch of pulse-heating circuit

from room temperature up to superheated liquid states. Experimental details are described extensively elsewhere (2, 5). To enable accurate and unambiguous temperature determination over such a large range, pyrometric detection based on Planck’s law of black-body radiation (6) was used. Normal spectral emissivity data were determined by an ellipsometric method (division of amplitude polarimeter; μs-DOAP) (7, 8) to avoid uncertainties arising from the unknown emissivity and its behaviour

Results

In Figure 2, the normal spectral emissivity, ε, of palladium at wavelength 684.5 nm is plotted against radiance temperature, Trad, and compared with literature results. The melting temperature of palladium, Tm, is 1828 K (9), whereas the radiance temperature at melting is 1680 K for wavelength 650 nm. At the latter temperature, the value of the emissivity is 0.36. An average of seven measure-

0.50 0,50 Normal spectral spectral emissivity, 684.5 nm nm normal emissivityε,atat684.5

Fig. 2 Normal spectral emissivity for palladium at wavelength 684.5 nm versus radiance temperature at 650 nm for palladium

over the temperature range of the measurement.

Key:

• Average of seven measure-

0.48 0,48

ments from this work

—— Value from least squares fit

0.46 0,46

V

Ref. (10)

0.44 0,44 0.42 0,42 0.40 0,40 0.38 0,38 0.36 0,36 0.34 0,34 1200

1400

1600

1800

2000

2200

2400

2600

2800

3000

3200

radiancetemperature, temperature at, 650 nm, KK Radiance Trad at 650 nm,


145

ments in the liquid phase produced the following linear fit for normal spectral emissivity in the radiance temperature range 1680 K < Trad < 3200 K: ε = 0.3063 + 3.2258 × 10–5Trad

(i)

At the end of the solid phase, emissivity values were around 0.49 (following surface preparation with abrasive paper of grade 1200 or 4000). As the surface smooths during liquefaction, a strong decrease can be observed; the emissivity is 0.360 at the end of melting. An emissivity of 0.3602 for liquid palladium at the melting temperature is reported (10); this was interpolated for wavelength 684.5 nm. A slight increase of normal spectral emissivity is observed up to 3200 K; this is similar to the behaviour reported for platinum (11). Figure 3 is a plot of specific enthalpy, H, versus temperature, T. Since this work focuses mainly on melting and the beginning of the liquid phase, temperature dependences are shown in all plots from around 1500 K upwards. For the solid and liquid phases in the temperature ranges: 1550 K < T < 1828 K and 1828 K < T < 2900 K respectively, averages of seven pulseheating measurements give: Hs(T) = –95.8103 + 0.2854T

(iia)

Hl(T) = –55.5552 + 0.3507T

(iib)

–1

where H is in kJ kg and T in K. The slope of

Equation (iib) gives a constant value of the isobaric heat capacity, cp, of (351 ± 36) J kg–1 K–1; Arblaster (11) recommends for the liquid a value of 387 J kg–1 K–1. (Our conversion from the molar value uses an atomic weight of 106.42 (11)). At melting, which is indicated in Figure 3 by a vertical broken line, the specific enthalpy changes from Hs = 425.9 kJ kg–1 to Hl = 585.5 kJ kg–1 (the subscripts s and l denoting solid and liquid respectively.) These results yield ΔH = (159.6 ± 16) kJ kg–1 for the enthalpy of fusion. Arblaster (11) recommends specific enthalpy values of 442.3 kJ kg–1 for the onset of melting and 593.4 kJ kg–1 for the end of melting, yielding ΔH = (151.1 ± 6.9) kJ kg–1 for the enthalpy of fusion. Dinsdale (12) reports a value of ΔH = 157.3 kJ kg–1for the enthalpy of fusion. Seydel et al. (13, 14) report specific enthalpy values of 445 kJ kg–1 for the onset of melting and 609 kJ kg–1 for the end of melting, giving ΔH = 164 kJ kg–1 for the enthalpy of fusion. Figure 4 shows electrical resistivity, ρ, as a function of temperature, T. At the onset of melting, indicated by a vertical broken line, a resistivity value of 0.461 μΩ m is obtained for the initial geometry (i.e. with no correction for thermal expansion). The corresponding value at the end of melting is 0.724 μΩ m. Thus an increase Δρ = 0.263 μΩ m is observed at melting. The linear fit to the present values for the liqFig. 3 Specific enthalpy versus temperature for palladium

1000

specific enthalpy,H,kJ·kg Specific enthalpy, kJ kg–1

-1

900 800 700 Key:

600

O

Average of seven measurements from this work

—— Linear least squares fit to mean values of measured data

500

3 Recommended values from Ref. (11) ---

400

Melting temperature (1828 K)

300 1600

1800

2000 2200 2400 Temperature, T, K

2600

2800

temperature, K


146

Fig. 4 Electrical resistivity versus temperature for palladium

0,90 0.90 0,85 0.85

0,75 0.75 0,70 0.70 0,65 0.65

Key: —— Average of seven measurements from this work, without correction for volume expansion, and least squares fit

0,60 0.60 0.55 0,55

X

0.50 0,50

---

Electrical ρ, μΩ m electricalresistivity, resistivity, μΩ·m

0,80 0.80

0.45 0,45

W

0.40 0,40 0.35 0,35

1600

1800

Calculated with volume data from Ref. (13), with correction for volume expansion Melting temperature Recommended values from Ref. (18)

2000

2200

2400

2600

2800

temperature, Temperature, T,KK

uid in the temperature range 1828 < T < 2900 K is: ρ = 0.7777 – 2.9226 × 10–5T

(iii)

where ρ is in μΩm and T in K. For electrical resistivity that is compensated for thermal expansion, ρv, Seydel and Kitzel’s (13) thermal expansivity values for palladium were adopted. Several other authors also report density values for palladium (15–17). The change in diameter (and hence cross-section) of the sample with heating results in a shift to higher resistivity values. At the onset of melting, a volume-adjusted resistivity of 0.495 μΩm was obtained, and at the end of melting 0.844 μΩm. Thus an increase Δρ = 0.349 μΩ m at melting is observed. Matula (18) recommends a resistivity at the onset of melting of 0.46 μΩm and for the end of melting 0.83 μΩm, giving an increase Δρ = 0.37 μΩm at melting. The polynomial fit to the present volumeadjusted values for liquid palladium in the temperature range 1828 K < T < 2900 K is: ρv = 0.8372 + 3.5413 × 10–6T

(iv)

where ρv is in μΩm and T in K. The present resistivity values, compensated for thermal expansion, agree excellently with Matula’s recommendations (18) for the liquid phase, and well for the solid.


Figure 5 is a plot of thermal conductivity, λ, against temperature, T. To estimate thermal conductivity via the Wiedeman–Franz law (6), Seydel and Kitzel’s density data (13) were again used to correct electrical resistivity for actual thermal expansion. For liquid palladium in the temperature range 1828 K < T < 2900 K: λ = 0.8131 + 0.0286T

(v)

where λ is in W m K and T in K. At the onset of melting a thermal conductivity value of 85.3 W m–1 K–1 was obtained, and at the end of melting, for the beginning of the liquid phase, 54 W m–1 K–1. Zinovyev (19) reports a value of 86 W m–1 K–1 at 1600 K. Vlasov et al. (20) as cited by Mills et al. (21) report thermal conductivity values for the end of the solid phase and the beginning of the liquid phase of 99 and 87 W m–1 K–1, respectively. Thermal diffusivity, a, can be estimated from thermal conductivity (2). Thermal diffusivity is not plotted against temperature here; this gives no additional relevant information since λ and cp are used for the calculation. The corresponding fit for liquid palladium in the temperature range 1828 K < T < 2900 K yields: –1

–1

a = –1.7636 × 10–6 + 8.9500 × 10–9T

(vi)

where a is in m2 s–1 and T in K. At the onset of

147

Fig. 5 Thermal conductivity of palladium versus temperature

110 Key: • Average of seven measurements from this work U Values for melting transition from Ref. (20) as reported in Ref. (21) V Value from Ref. (19)

-1 –1 -1–1 Thermal ,Wm thermal conductivity, conductivity,λW·m ·KK

100

90

80

70

60

50 1400

1600

1800

2000

2200

2400

2600

2800

3000

Temperature, temperature,T,K K

melting a value for a of 2.75 × 10–5 m2 s–1 was obtained, and at the end of melting, for the beginning of the liquid phase, a was 1.46 × 10–5 m2 s–1.

Discussion Thermophysical data for liquid palladium are quite sparse in the literature. Seydel and Kitzel (13) report only enthalpy dependences and no temperature dependences, since they did not perform the latter measurements. The values found here for the normal spectral emissivity ε for liquid palladium at wavelength 684.5 nm at the end of melting give an excellent match to that reported by McClure et al. (10). The enthalpy of fusion obtained here compares very satisfactorily with the results reported by Arblaster (11), Dinsdale (12) and Seydel et al. (13, 14), within the range of uncertainty of the present work. Further, selected values from (22), considered the best of their time, must be considered outdated for comparison purposes. The temperature-dependent resistivity values reported here agree well with the recommended values of Matula (18), within the present experimental uncertainty. Only a comparison of the present thermal conductivity values at the onset and end of melting with corresponding data from Vlasov et al. (20) as reported by Mills et al. (21) shows a significant discrepancy, but Zinovyev’s data (19) for the end of the solid phase appear to confirm the thermal conductivity values obtained


in the present work.

Uncertainties Within the terms of (23), the uncertainties reported here are expanded relative uncertainties with a coverage factor of k = 2. The uncertainties given in Table I have been derived for the thermophysical properties calculated here.

Conclusion For liquid palladium, a set of thermophysical data is reported here: enthalpy, isobaric heat capacity, electrical resistivity, thermal conductivity and thermal diffusivity as a function of temperature. Since temperature measurement is combined with simultaneous emissivity measurements, there is no ambiguity in the present temperature-dependent data.

Acknowledgement This research was supported by the Austrian Fonds zur Förderung der Wissenschaftlichen Forschung (FWF), Grant No. P15055.

References 1 “Platinum 2006”, Johnson Matthey PLC, Royston, Hertfordshire, U.K. , 2006, pp. 32–39 2 B. Wilthan, C. Cagran, C. Brunner and G. Pottlacher, Thermochim. Acta, 2004, 415, (1–2), 47 3 B. Wilthan, C. Cagran and G. Pottlacher, Int. J. Thermophys., 2004, 25, (5), 1519

148

Table I

Uncertainties in Thermophysical Properties Determined for Liquid Palladium Thermophysical parameter

Symbol

Uncertainty, %

Temperature

T

4

Normal spectral emissivity

ε

6

Enthalpy

H

4

Enthalpy of fusion

ΔH

10

Specific heat capacity at constant pressure

cp

8

Electrical resistivity with initial geometry

ρ

4

Expansion-corrected electrical resistivity

ρV

6

Thermal conductivity

λ

12

4 C. Cagran and G. Pottlacher, submitted to Int. J. Thermophys. 5 R. Gallob, H. Jäger and G. Pottlacher, Int. J. Thermophys., 1986, 7, (1), 139 6 M. Boivineau and G. Pottlacher, Int. J. Mater. Product Technol., 2006, 26, (3/4), 217 7 A. Seifter, F. Sachsenhofer and G. Pottlacher, Int. J. Thermophys., 2002, 23, (5), 1267 8 C. Cagran, B. Wilthan and G. Pottlacher, Int. J. Thermophys., 2004, 25, (5), 1551 9 R. E. Bedford, G. Bonnier, H. Maas and F. Pavese, Metrologia, 1996, 33, (2), 133 10 J. L. McClure, A. Cezairliyan and E. Kaschnitz, Int. J. Thermophys., 1999, 20, (4), 1149 11 J. W. Arblaster, Calphad, 1995, 19, (3), 365 12 A. T. Dinsdale, Calphad, 1991, 15, (4), 317 13 U. Seydel and W. Kitzel, J. Phys. F: Metal Phys., 1979, 9, (9), L153 14 U. Seydel, H. Bauhof, W. Fucke and H. Wadle, High Temp.–High Press., 1979, 11, (6), 635 15 P. S. Martsenyuk and Yu. V. Ivanschenko, Ukr. Khim. Zhur (SU), 1974, 40, 431 16 L. D. Lucas, C. R. Acad. Sci. (Fr.), 1961, 253, 2526

17 T. Iida and R. I. L. Guthrie, “The Physical Properties of Liquid Metals”, Oxford University Press, Oxford, 1988, p. 71 18 R. A. Matula, J. Phys. Chem. Ref. Data, 1979, 8, (4), 1147 19 V. E. Zinovyev, “Metals at High Temperatures – Standard Handbook of Properties”, Hemisphere Publishing Corporation, New York, 1990 20 B. V. Vlasov, S. G. Taluts, V. E. Zinov’ev, N. A. Korenovskii and V. P. Polykova, Phys. Met. Metall., 1992, 74, (4), 371 21 K. C. Mills, B. J. Monaghan and B. J. Keene, ‘Thermal Conductivities of Liquid Metals – Part 1: Pure Metals’, NPL Report CMMT(A), Teddington, U.K., 1997, p. 53 22 R. Hultgren, P. D. Desai, D. T. Hawkins, M. Gleiser, K. K. Kelley and D. D. Wagman, “Selected Values of the Thermodynamic Properties of the Elements”, American Society for Metals, Metals Park, OH, 1990 23 GUM, “Expression of the Uncertainty of Measurement in Calibration”, EA-4/02, European Co-operation for Accreditation, 1999, http://www.europeanaccreditation.org/n1/doc/EA-4-02.pdf

The Authors Claus Cagran studied physics at Graz University of Technology, Austria, from which he received his master’s (Dipl.-Ing.) and doctoral (Dr. Techn.) degrees. He currently works for the Optical Technology Division at NIST, Gaithersburg, MD, dealing with optical reflectance and emittance measurements of metals, ceramics, and surface coatings.


Gernot Pottlacher studied physics at the Technical University of Graz, Austria, and holds its Dipl.-Ing. and Dr. Techn. degrees. He is a professor at the Institute for Experimental Physics. His main fields of activity are the thermophysical properties of pulseheated liquid metals and alloys, as well as didactic courses in physics for teachers in training.

149

DOI: 10.1595/147106706X129097

ABSTRACTS of current literature on the platinum metals and their alloys Synthesis and Structure of NbPdSi PROPERTIES Study of an Internally-Oxidized Pd0.97Ce0.03 Alloy V. M. AZAMBUJA, D. S. DOS SANTOS, L. PONTONNIER, M. MORALES and D. FRUCHART, Scr. Mater., 2006, 54, (10),

1779–1783

Cold-worked foils of Pd0.97Ce0.03 underwent an internal oxidisation heat treatment at 1073 K for 72 h. TEM showed the precipitation of needle-shaped CeO2 (1) with a cubic lattice parameter of 5.4 Å. (1) exhibited preferential growth directions relative to the Pd matrix which correspond to the diagonal of the Pd cube. (1) were ~ 20–40 nm wide and 1–2 μm long, in coherence with the Pd matrix. X-ray Photoelectron Spectroscopy and Magnetism of Mn–Pd Alloys M. COLDEA, M. NEUMANN, S. G. CHIUZBAIAN, V. POP, L. G. PASCUT, O. ISNARD, A. F. TAKÁCS and R. PACURARIU, J. Alloys

Compd., 2006, 417, (1–2), 7–12

MnxPd1–x alloys and compounds (1) were prepared by Ar arc melting. The samples were melted repeatedly (four times) in the same atmosphere to ensure homogeneity. The electronic structures of (1) were studied using XPS. Both valence band and core level spectra were analysed. The magnetic properties of (1) are strongly correlated with their crystallographic properties and can be explained considering only the near-neighbour antiferromagnetic interactions between both Mn and Pd atoms and Mn–Mn pairs. Dramatic Evolution of Magnetic Properties Induced by Electronic Change in Ce(Pd1–x Agx)2Al3 P. SUN, Q. LU, T. IKENO, T. KUWAI, T. MIZUSHIMA and Y. ISIKAWA, J. Phys.: Condens. Matter, 2006, 18, (24), 5715–5723

Measurements of lattice parameters (a, c), magnetic susceptibility χ(T) and magnetisation M(H), specific heat C(T), and electrical resistivity ρ(T) were made for Ce(Pd1–xAgx)2Al3. It was found that with increasing x the system varies from antiferromagnetism to ferromagnetism at x ~ 0.05, then back at x ~ 0.45. The magnetic evolution resembles that of Ce(Pd1–xCux )2Al3.

CHEMICAL COMPOUNDS Protonation of Platinum(II) Dialkyl Complexes Containing Ligands with Proximate H-Bonding Substituents G. J. P. BRITOVSEK, R. A. TAYLOR, G. J. SUNLEY, D. J. LAW and A. J. P. WHITE, Organometallics, 2006, 25, (8), 2074–2079

Pt(II) dimethyl complexes [Pt(L)Me2], L = unsymmetrically substituted bipyridine, were prepared. Reactions in MeCN with 1 equiv. of a strong acid gave [Pt(L)Me(CH3CN)]+. The selectivity of the protonation reactions is reported to be governed by steric effects rather than H-bonding effects.


M. VALLDOR and R. PÖTTGEN, Z. Naturforsch., 2006, 61b, (3),

339–341

NbPdSi (1) was prepared by melting the elements in an arc furnace. Well-shaped single crystals of (1) were obtained by annealing in an induction furnace. The Pd and Si atoms were shown by powder and single crystal XRD analysis to build up a 3D [PdSi] network where each Pd atom has a strongly distorted tetrahedral Si coordination at Pd–Si of 242–250 pm. The Nb atoms fill channels left in the [PdSi] network.

N-Heterocyclic Carbenes: Synthesis, Structures, and Electronic Ligand Properties W. A. HERRMANN, J. SCHÜTZ, G. D. FREY and E. HERDTWECK,

Organometallics, 2006, 25, (10), 2437–2448

Rh(COD)X(NHC) complexes were synthesised. The relative σ-donor/π-acceptor quality of various NHC ligands was classified by means of IR spectroscopy at the corresponding Rh(CO)2I(NHC). Single crystal XRD studies of Rh pyrazolin- and tetrazolinylidene complexes are reported. Different azolium salts were applied to obtain Rh and Ir complexes with two and four carbene ligands. Bis[iridium(I)] Complex of Inverted N-Confused Porphyrin M. TOGANOH, J. KONAGAWA and H. FURUTA,

Inorg. Chem.,

2006, 45, (10), 3852–3854

When a N-confused tetraphenylporphyrin was treated with 2.0 equiv. of IrCl(CO)2( p-toluidine) and 10 equiv. of NaOAc in toluene/THF = 20/1 (v/v) at 100ºC for 3.5 h, a novel bis[iridium(I)] complex (1), wherein the confused pyrrole ring took an inverted conformation, was obtained in 17% yield. The reactions were significantly accelerated by THF. (1) can be handled in air without special care. No decomposition was observed by heating in 1,2-Cl2C6H4. No demetallation occurred on CF3COOH addition. Fullerene Polypyridine Ligands: Synthesis, Ruthenium Complexes, and Electrochemical and Photophysical Properties Z. ZHOU, G. H. SAROVA, S. ZHANG, Z. OU, F. T. TAT, K. M. KADISH, L. ECHEGOYEN, D. M. GULDI, D. I. SCHUSTER and S. R. WILSON, Chem. Eur. J., 2006, 12, (16), 4241–4248

Fullerene coordination ligands (1) with a single bpy or tpy unit were synthesised. Coordination of (1) to Ru(II) gave linear rod-like donor-acceptor systems. Steady-state fluorescence of [Ru(bpy)2(bpy-C60)]2+ showed a rapid solvent-dependent, intramolecular quenching of the Ru(II) MLCT excited state. Electrochemical studies on [Ru(bpy)2(bpy-C60)]2+ and [Ru(tpy)(tpy-C60)]2+ indicated electronic coupling between the Ru centre and the fullerene core.

150

ELECTROCHEMISTRY

Photophysical Properties of the Photosensitizer [Ru(bpy)2(5-CNphen)]2+ and Intramolecular Quenching by Complexation of Cu(II)

Chemical and Electrochemical Synthesis of Polyaniline/Platinum Composites J. M. KINYANJUI, N. R. WIJERATNE, J. HANKS and D. W. HATCHETT, Electrochim. Acta, 2006, 51, (14), 2825–2835

M. G. MELLACE, F. FAGALDE, N. E. KATZ, H. R. HESTER and R. SCHMEHL, J. Photochem. Photobiol. A: Chem., 2006, 181, (1),

28–32

The direct chemical synthesis of Pt-polyaniline (1) composites was achieved by the oxidation of aniline by PtCl62–. The Pt particles were ~ 1 μm in diameter. Electrochemical synthesis of (1) was initiated by the uptake and reduction of PtCl62– into an a priori electrochemically deposited polyaniline film. This method produced a uniform dispersion of Pt particles with diameters of 200 nm–1 μm.

The lifetime of the 3MLCT emitting state of [Ru(bpy)2(5-CNphen)]2+ has been determined in MeCN by flash photolysis and time correlated single photon counting techniques. The value obtained, τ = 2.2 μs, suggests its potential use as a photosensitiser in molecular devices. Static and dynamic quenching of the complex luminescence by Cu2+ ions was seen.

Electrocatalytic Activity for Hydrogen Evolution of Polypyrrole Films Modified with Noble Metal Particles

ELECTRODEPOSITION AND SURFACE COATINGS

M. TRUEBA, S. P. TRASATTI and S. TRASATTI, Mater. Chem. Phys.,

2006, 98, (1), 165–171

Polypyrrole (Ppy) films with Pt, Ru and Ir particles were electrosynthesised on the surface of austenitic stainless steel by: (a) electrodeposition of a polymer film from a solution already containing an anionic metal complex, followed by potentiodynamic or galvanostatic reduction; or (b) presynthesised Ppy films modified by galvanostatic electrodeposition of the metals from solutions of their metal complexes. The electrocatalytic activity of the modified electrodes for the H2 evolution reaction was tested in H2SO4 (0.05 M) by potentiodynamic techniques (0.5 mV s–1).

PHOTOCONVERSION Platinum–Acetylide Polymer Based Solar Cells: Involvement of the Triplet State for Energy Conversion F. GUO, Y.-G. KIM, J. R. REYNOLDS and K. S. SCHANZE,

Chem.

Commun., 2006, (17), 1887–1889

Blends of a blue-violet absorbing Pt-acetylide polymer (1) with 1-(3-(methoxycarbonyl)propyl)-1phenyl[6.6]C61 (PCBM), can be used as the active material in a photovoltaic device. (1) acts as the chromophore and electron donor blended with PCBM as an electron acceptor. Photoinduced charge separation in the blends is believed to occur via the triplet excited state of the organometallic polymer. Structurally Integrated Organic Light Emitting Device-Based Sensors for Gas Phase and Dissolved Oxygen R. SHINAR, Z. ZHOU, B. CHOUDHURY and J. SHINA, Anal. Chim.

Acta, 2006, 568, (1–2), 190–199

The O2-sensitive dyes Pt- or Pd-octaethylporphyrin (1), were embedded in polystyrene, or dissolved in solution. Their performance was compared to that of Ru(dpp)32+. A green OLED, based on Alq3, was used to excite (1). The O2 level was monitored in the gas phase and in H2O, EtOH and toluene by measuring changes in the PL lifetime τ of (1).


Adhesion and Bonding of Pt/Ni and Pt/Co Overlayers: Density Functional Calculations G. F. CABEZA, N. J. CASTELLANI and P. LÉGARÉ, J. Phys. Chem.

Solids, 2006, 67, (4), 690–697

The electronic and energetic properties of Pt/Ni and Pt/Co surfaces are examined using the fullpotential linearised augmented plane wave method. The results of the shifts in the d-band centers when one metal (Pt) is pseudomorfically deposited on another with smaller lattice constant (Ni, Co) are presented, together with those corresponding to the surface and adhesion energies. The results for pure Ni, Co and Pt surfaces are given to compare with data in the literature. Self-Assembled Palladium Nanowires by Electroless Deposition and J. A. SZPUNAR, Nanotechnology, 2006, 17, (9), 2161–2166

Z. SHI, S. WU

The self-assembly production of Pd nanowires (1) has been carried out by electroless deposition on a porous stainless steel template. Various arrays of selfassembled (1) in the form of single wire, parallel and curved wires, intersections and network structures are obtainable. (1) can be built in a self-assembled manner by the assembly of nanoparticles generated in the initial stages of the deposition without any external field except the chemical reaction. Selective Growth of IrO2 Nanorods Using Metalorganic Chemical Vapor Deposition G. WANG, D.-S. TSAI, Y.-S. HUANG, A. KOROTCOV, W.-C. YEH and D. SUSANTI, J. Mater. Chem., 2006, 16, (8), 780–786

Area-selective growth of IrO2 nanorods (1) was achieved via MOCVD using (MeCp)Ir(COD) on a sapphire (012) or (100) substrate which consisted of patterned SiO2 as the nongrowth surface. Orientation of (1) was controlled by the in-plane epitaxial relation between the IrO2 crystal and sapphire, along with the IrO2 growth habit in the [001] direction. The photolithography method gave better resolution in preserving rod orientation of (1) at the growth and nongrowth boundary zone.

151

APPARATUS AND TECHNIQUE High-Purity COx-Free H2 Generation from NH3 via the Ultra Permeable and Highly Selective Pd Membranes J. ZHANG, H. XU and W. LI, J. Membrane Sci., 2006, 277, (1–2),

85–93

A compact H2 generation system combining NH3 decomposition with separation by a series of Pd membranes (3 μm) has been developed to provide high-purity, COx-free H2 for fuel cell applications. Removal of H2 product in a Pd membrane reactor was shown to promote NH3 conversion over a Nibased catalyst. However, ex situ integration, in which an NH3 cracker was followed by a Pd membrane purifier, was deemed more suitable for practical uses due to its high productivity of pure H2. Nanocomposite of Pd-Polyaniline as a Selective Methanol Sensor and P. P. Actuators B: Chem., 2006, 114, (1), 263–267

A. A. ATHAWALE, S. V. BHAGWAT

KATRE,

Sens.

A Pd-polyaniline nanocomposite (1) was synthesised by oxidative polymerisation of an aniline solution containing Pd nanoparticles. (1) was highly selective and sensitive to MeOH vapours. The selectivity of (1) was further investigated by exposing it to MeOH-EtOH and MeOH-isopropanol. Here (1) exhibited a response identical to that for pure MeOH, except for the response time. Hydrogen Permeation Characteristics of Thin Pd Membrane Prepared by Microfabrication Technology Y. ZHANG, J. GWAK, Y. MURAKOSHI, T. IKEHARA, R. MAEDA and C. NISHIMURA, J. Membrane Sci., 2006, 277, (1–2),

203–209

A Pd membrane (1), ~ 2.5 μm thick, on Si wafer was successfully prepared using microfabrication technology. H2 permeability of (1) was investigated within 473–673 K, and found to be ~ 50–65% that of a 0.70 mm thick Pd membrane. Grain growth was found in (1) after permeation, and the presence of CO2 reduced H2 permeability significantly.

HETEROGENEOUS CATALYSIS Effect of Pt Precursors on Catalytic Activity of Pt/TiO2 (Rutile) for Water Gas Shift Reaction at Low-Temperature H. IIDA, K. KONDO and A. IGARASHI,

Catal. Commun., 2006,

7, (4), 240–244

Pt/TiO2 (rutile) catalysts for the low temperatureWGSR were prepared from various Pt precursors. The catalytic activity decreases for the precursors used: H2PtCl6·6H2O, Pt(C5H7O2)2 > [Pt(NH3)4]Cl2 > [Pt(NH3)4](NO3)2 > cis-[Pt(NO2)2(NH3)2]. There was a linear relationship between catalytic activity and Pt dispersion. The TOF for the LT-WGSR was almost constant regardless of Pt dispersion.


Enhancement of Naphthalene Hydrogenation over PtPd/SiO2-Al2O3 Catalyst Modified by Gold B. PAWELEC, V. LA PAROLA, S. THOMAS and J. L. G. FIERRO, J. Mol. Catal. A: Chem., 2006, 253, (1–2), 30–43

The effect of the support (amorphous silica-alumina (ASA) and C multiwall nanotubes (MWNTs)) on the activity of PtPd catalysts in naphthalene hydrogenation is described. Also, the effect of Au incorporation on PtPd/ASA was studied. AuPtPd/ASA showed the highest naphthalene conversion and lowest deactivation. The less acidic PtPd/C MWNTs did not show S-resistance. The contribution of the acid sites of the support to S-resistance and their deactivation by coke are discussed. Improved CO Oxidation in the Presence and Absence of Hydrogen over Cluster-Derived PtFe/SiO2 Catalysts A. SIANI, B. CAPTAIN, O. S. ALEXEEV, E. STAFYLA, A. B. HUNGRIA, P. A. MIDGLEY, J. M. THOMAS, R. D. ADAMS and M. D. AMIRIDIS,

Langmuir, 2006, 22, (11), 5160–5167

Pt5Fe2/SiO2 and PtFe2/SiO2 samples (1), prepared from organometallic cluster precursors decarbonylated in H2 at 350ºC, were found to be highly active for the oxidation of CO in the presence or absence of H2. Pt-Fe nanoparticles were formed with sizes of 1–2 nm. A higher degree of dispersion and more homogeneous mixing of the metals were observed in (1) as compared to a conventionally impregnation prepared PtFe/SiO2 (2). (1) were also more active than Pt/SiO2 or (2) for the oxidation of CO in air. Hydrogenation of Sunflower Oil on Pd Catalysts in Supercritical Conditions: Effect of the Particle Size C. M. PIQUERAS, M. B. FERNÁNDEZ, G. M. TONETTO, S. BOTTINI and D. E. DAMIANI, Catal. Commun., 2006, 7, (6), 344–347

Sunflower oil hydrogenation was carried out using supercritical propane and Pd/γ-Al2O3. The selectivity to cis-isomers and the production of saturated fatty acids was favoured by a small Pd particle size (< 2 nm). There was no significant variation in the reaction rate nor in the TOF. Despite the fact that during the reaction a phase separation occurred, propane was in supercritical state in both phases. Effects of Natural Water Ions and Humic Acid on Catalytic Nitrate Reduction Kinetics Using an Alumina Supported Pd-Cu Catalyst B. P. CHAPLIN, E. ROUNDY, K. A. GUY, J. R. SHAPLEY and C. J. WERTH, Environ. Sci. Technol., 2006, 40, (9), 3075–3081

The NO3– reduction rate of a H2O sample using PdCu/γ-Al2O3 was 2.4 × 10–01 l/min g cat. The addition of SO42–, SO32–, HS–, Cl–, HCO3–, OH– and humic acid decreased the NO3– reduction rate. Preferential adsorption of Cl– inhibited NO3– reduction to a greater extent than NO2– reduction. Dissolved constituents in groundwater decreased the NO3– reduction rate. Removal of dissolved organic matter using activated C increased the NO3– reduction rate.

152

HOMOGENEOUS CATALYSIS

FUEL CELLS

Recovery and Reuse of Ionic Liquids and Palladium Catalyst for Suzuki Reactions Using Organic Solvent Nanofiltration

Thermal Stability in Air of Pt/C Catalysts and PEM Fuel Cell Catalyst Layers O. A. BATURINA, S. R. AUBUCHON

H. WONG, C. J. PINK, F. C. FERREIRA and A. G. LIVINGSTON,

Green Chem., 2006, 8, (4), 373–379

Organic solvent nanofiltration was used for separating ionic liquids (1) and the catalyst Pd2(dba)3-CHCl3 from Suzuki cross-couplings. The reactions were carried out in 50:50 wt.% ethyl acetate and (1). The post reaction mixture was diluted further with ethyl acetate and then separated by nanofiltration. The product was recovered in the nanofiltration permeate, while (1) and Pd catalyst were retained by the membrane. Unexpected Roles of Molecular Sieves in Palladium-Catalyzed Aerobic Alcohol Oxidation B. A. STEINHOFF, A. E. KING and S. S. STAHL,

High Performance PtRuIr Catalysts Supported on Carbon Nanotubes for the Anodic Oxidation of Methanol J. Am.

Chem. Soc., 2006, 128, (11), 3504–3505

J. Org. Chem.,

The effect of molecular sieves (MS3A) on Pd(OAc)2/pyridine (1) and Pd(OAc)2/DMSO (2) was investigated by performing kinetic studies of alcohol oxidation. MS3A enhanced the rate of (1)-catalysed oxidation of alcohols. This was attributed to the ability of MS3A to serve as a Brønsted base. In contrast, no rate enhancement was observed with (2). Both (1) and (2) exhibit improved catalyst stability in the presence of MS3A, resulting in higher catalytic TONs. The MS3A provided a heterogeneous surface that hinders bulk aggregation of Pd metal.

PtRuIr/C MWNTs system (1) was prepared using an organic colloid synthesis method. (1) has a very high real surface area and is highly active toward the oxidation of MeOH. The Ir component acts as a promoter. The splitting of the Pt(111) XRD feature into four peaks and the shift to larger d spacing reflect the high dispersion of the metallic components.

ELECTRICAL AND ELECTRONIC ENGINEERING Interface Effect on Ferroelectricity at the Nanoscale C.-G. DUAN, R. F. SABIRIANOV, W.-N. MEI, S. S. JASWAL and E. Y. TSYMBAL, Nano Lett., 2006, 6, (3), 483–487

Unsymmetric-1,3-Disubstituted Imidazolium Salt for Palladium-Catalyzed Suzuki-Miyaura CrossCoupling Reactions of Aryl Bromides H.-W. YU, J.-C. SHI, H. ZHANG, P.-Y. YANG, X.-P. WANG and Z.L. JIN, J. Mol. Catal. A: Chem., 2006, 250, (1–2), 15–19

Unsymmetric 1,3-disubstituted-imidazolium salts (1) derived from ferrocene were prepared, and their preliminary activities as precursors of N-heterocyclic carbene ligands for Pd-catalysed cross-coupling of aryl bromides with phenylboronic acid were studied. A combination of Pd(OAc)2 and (1) was an excellent catalyst system for the Suzuki-Miyaura cross-coupling of aryl bromides with phenylboronic acid in the presence of Cs2CO3. Rh(0) Nanoparticles as Catalyst Precursors for the Solventless Hydroformylation of Olefins J.

Mol. Catal. A: Chem., 2006, 252, (1–2), 212–218

The hydroformylation of 1-alkenes can be performed in solventless conditions, using ligand-modified or unmodified Rh(0) nanoparticles (1) prepared in imidazolium ionic liquids as catalyst precursors. Aldehydes were generated when 5.0 nm (1) are used. With smaller nanoparticles, chemoselectivity is decreased; large sized nanoparticles (15 nm) produce only small amounts of aldehydes, similarly to a classical heterogeneous Rh/C catalyst precursor.


The thermal stability of Pt/Vulcan XC 72 and a 46 wt.% Pt/Vulcan XC 72/Nafion layer was studied. Low temperature (100–200ºC) C combustion occured in the presence of Pt. In PEMFC catalyst layers, the thermal decomposition temperature of Nafion is lowered by ~ 100ºC to 300ºC in the presence of Pt/C.

S. LIAO, K.-A. HOLMES, H. TSAPRAILIS and V. I. BIRSS,

2006, 71, (5), 1861–1868

A. J. BRUSS, M. A. GELESKY, G. MACHADO and J. DUPONT,

and K. J. WYNNE, Chem.

Mater., 2006, 18, (6), 1498–1504

A first-principles study of ultrathin KNbO3 ferroelectric films (1) placed between two metal electrodes, either Pt or SrRuO3, was carried out. The strength of bonding and intrinsic dipole moments at the interfaces was shown to control the ferroelectricity. The polarisation profile was inhomogeneous across the film thickness. The critical thickness for the net polarisation of (1) was predicted to be ~ 1 nm for Pt and 1.8 nm for SrRuO3 electrodes. Calculations and Measurements of Contact Resistance of Semi-Transparent Ni/Pd Contacts to p-GaN K. H. A. BOGART and J. CROFTON, J. Electron. Mater., 2006, 35,

(4), 605–612

Calculations of specific contact resistance (1) as a function of doping and barrier height were performed for p-GaN. (1) were measured for oxidised Ni/Au, Pd, and oxidised Ni/Pd ohmic contact metal schemes to p-GaN. The Ni/Pd contact had the lowest (1). Some Ni had diffused away from the GaN surface to the contact surface, with the bulk of the Pd located in between two areas of Ni. Both Ni and Pd interdiffused with the GaN at the semiconductor surface. The majority of the O was as NiO. Predominantly NiO and PdO species were formed, with higher Ni and Pd oxides at the contact surface.

153

DOI: 10.1595/147106706X124669

NEW PATENTS METALS AND ALLOYS

Graphitic Nanotubes in Luminescence Assays

HITACHI LTD

U.S. Patent 7,052,861

MESO SCALE TECHNOL. LLC

Nickel-Based Superalloy British Appl. 2,418,207

A nickel-based superalloy (1) includes (in wt.%): 3–7 Cr, 3–15 Co, 4.5–8 W, 3.3–6 Re, 4–8 Ta, 0.8–2 Ti, 4.5–6.5 Al, 0.1–6 Ru, 0.01–0.2 Hf, < 0.5 Mo, ≤ 0.06 C, ≤ 0.01 B, ≤ 0.01 Zr, ≤ 0.005 O, ≤ 0.005 N, and optionally a rare earth element at 0.1–100 ppm, with the balance Ni. Single crystal turbine blades can be made from (1). (1) has excellent mechanical strength and resistance to corrosion and oxidation.

Electrochemiluminescent complexes of Ru, Os or Re, in particular of Ru (1), are attached to C nanotube supports together with an enzyme cofactor (2), and are used in luminescence assays. The analyte of interest can be detected by bringing the sample into contact with the assay composition, causing oxidation or reduction of (2) and electrochemiluminescence of (1). The latter can be correlated to the presence or amount of analyte.

ELECTRODEPOSITION AND SURFACE COATINGS

HETEROGENEOUS CATALYSIS

Pd-Containing Coating

An exhaust gas catalyst system contains multiple layers of catalysts on solid support. The first layer contains a noble metal active component including Rh, and optionally Pt, with a barely soluble Ba compound. The second layer contains another noble metal which may include Pt or Pd. The system is structured so that the two layers come into contact with the exhaust gas sequentially.

ELTECH SYST. CORP

World Appl. 2006/028,443

An electrocatalytic coating (1) of mixed metal oxide, preferably containing Pt group metal oxides, and an electrode using (1) are used for the electrolysis of a halogen-containing solution. (1) includes a topcoating layer of oxides of Pd, Rh or Co. The Pd oxide component reduces the operating potential of the electrode and removes the necessity of a ‘break-in’ period to reach the lowest electrode potential. Low-Pressure Deposition of Ru and Re Layers TOKYO ELECTRON LTD

U.S. Appl. 2006/068,588

A low pressure method for depositing Ru and Re layers at high deposition rates, with low particulate contamination and good step coverage is described. A Ru- or Re-carbonyl precursor is processed with a carrier gas in a process chamber at a pressure of < 20 mTorr. The metal is deposited onto a surface by thermal chemical vapour deposition. Ru Film-Forming Ink JAPAN SCI. TECHNOL. AG

Japanese Appl. 2005-336,263

An ink can be used to form films of metallic Ru or Ru oxide on a resin film substrate such as polyimides. The ink contains a compound obtained by preheating a β-diketone, β-ketoester or β-diester complex of Ru in an alcohol solution. This ink can be applied to a surface and heated to give the films.

APPARATUS AND TECHNIQUE Membrane for Diffusion Limited Gas Sensors GENERAL ELECTRIC

British Appl. 2,417,561

A micro fuel cell sensor for measuring selected gases in fluid streams is claimed. The sensing element has identical first and second gas diffusing electrodes, made from at least one of Pt/C, Au, Pd, Pd-Pt, Ru, Ir, Os, Rh or Ta. The electrodes are separated from gas-containing media by gas-permeable membranes. A spacer having an acidic electrolyte is placed between the electrodes, facilitating electrochemical oxidation and reduction of gases at the electrodes.


Multiple Layer Exhaust Gas Catalyst European Appl. 1,640,575

CATALER CORP

Manufacture of Noble Metal Alloy Catalysts U.S. Appl. 2006/094,597

UMICORE AG CO KG

Supported noble metal catalysts (1) are manufactured with a high degree of alloying and small crystallite size, < 3 nm, using polyol solvents in a two step process. The first component is a transition metal such as Co, Cr, Ru, preferably Ru; the second is a noble metal such as Pt, Au, Ag, Pd, Rh, Os, Ir or a mixture. (1) can be used as electrocatalysts in fuel cells or as gas-phase catalysts for CO oxidation or exhaust gas purification. Low-Emissions Diesel Fuel U.S. Patent 7,063,729

CLEAN DIESEL TECHNOL. INC

A low-emissions diesel fuel is composed of aviation kerosene, detergent, lubricity additive and a bimetallic, fuel-soluble Pt and Ce fuel-borne catalyst. Retarding engine timing can further reduce NOx and the use of a diesel particulate filter and/or diesel oxidation catalyst can further reduce CO, unburned hydrocarbons and particulates. Exhaust Gas Cleaning Catalyst TOYOTA CENTRAL RES. DEV. LAB. INC


An exhaust gas cleaning catalyst exhibits high NOx removal activity even after exposure to a high-temperature atmosphere, and is prevented from being poisoned by sulfur. There are two catalysts, prepared with a porous oxide powder carrier and a NOx occlusion material, the first carrying Pt and the second containing θ-alumina and carrying Rh. The catalysts intermingle but remain separated by their carriers.

154

HOMOGENEOUS CATALYSIS Ring-Closing Metathesis Process BOEHRINGER ING. INT. GmbH

U.S. Appl. 2006/063,915

A process is described for preparing compounds (1) which are active for the treatment of hepatitis C viral (HCV) infections, or are intermediates for the preparation of active compounds. (1) are formed by cyclising diene compounds (2) in a suitable organic solvent, in the presence of a Ru catalyst (3). The process is performed in a gas such as CO2 or a gas mixture at supercritical or near-supercritical conditions, with (3) at ~ 25–50 mol% relative to (2). Process for Oxidation of Alkanes U.S. Appl. 2006/142,620

CSIR

A Pd complex (1) catalysed process for the oxidation of linear alkanes is claimed which employs molecular O2 as the oxidant, to produce secondary alcohols and ketones in high selectivity. (1) may include monodentate, bidentate or polydentate ligands up to a maximum Pd coordination number of 4. The process may be carried out under a continuous feed of pure or diluted O2 or in air, in the presence or absence of a solvent, and does not require the use of a co-catalyst. Acetic Acid Production Methods U.S. Patent 7,053,241

CELANESE INT. CORP

A method for production of acetic acid by carbonylation of MeOH involves a Rh-based catalyst system, with at least one catalyst stabiliser (1) selected from Ru- or Sn-salts or a mixture. Precipitation of Rh during recovery of acetic acid is minimised by (1), even in low H2O content reaction mixtures and in the presence of an iodide salt copromoter at > ~ 3 wt.% of the reaction mixture. (1) may be present at molar concentrations of metal to Rh from ~ 0.1:1–20:1. Curable Silicone Releasing Agent Composition SHIN-ETSU CHEM. CO LTD


The composition of a curable silicone film with small peel resistance at low-speed/high-speed peeling, with slipperiness and good resistance to air exposure is described. The film includes: (A) a diorganopolysiloxane containing 0.5–5 mol% alkenyl groups bonded to Si; (B) a diorganopolysiloxane with alkenyl groups bonded to Si at the terminals of the molecular chain; (C) an organohydrogenpolysiloxane; and (D) a catalytic amount of Pt-based catalyst.

FUEL CELLS

Carbon-Supported Alloy Nanoparticle Catalysts RES. FOUND. STATE UNIV. NEW YORK

U.S. Patent 7,053,021

C-supported core-shell PtVFe nanoparticle electrocatalysts (1) are formed from a reaction solution (2) including precursors containing metals or salts of Pt, V and Fe plus an organic compound. The process produces nanoparticles of controlled size within the range 1.0–10.0 nm, the size being determined by the composition of (2). (1) are particularly useful for O2 reduction reactions (ORR), exhibiting ORR catalytic activities in the range ~ 2–4 times that of a standard Pt/C catalyst. Reduced Cost Catalyst for Fuel Cell NISSAN MOTOR CO LTD


Manufacturing costs for a fuel cell catalyst containing Pt plus Ir oxide (1) are reduced using the described method. First an Ir complex is formed from a mixture of Ir chloride solution and a hydroxide of an alkali metal or alkaline earth metal. This complex is deposited onto a C support, then baked to high temperature to form (1), without burning the support. Finally Pt is added to the catalyst support which contains (1).

ELECTRICAL AND ELECTRONIC ENGINEERING Self-Aligned Silicide Contact IBM CORP

U.S. Appl. 2006/051,961

A self-aligned Ni alloy silicide contact is described. A conductive Ni-Pt alloy is first deposited onto a Sicontaining semiconductor structure. An O2 diffusion barrier is deposited to prevent metal oxidation, then an annealing step causes formation of a Ni-Si, Pt-Si contact in regions in contact with Si. Finally a selective etching step removes unreacted Ni-Pt from regions not in contact with Si. Iridium Oxide Nanowires SHARP LAB. INC

U.S. Appl. 2006/086,314

Ir oxide nanowires (1) are grown from an Ir-containing precursor, using a MOCVD process from the surfaces of a growth promotion film which has noncontinuous surfaces. (1) have a diameter in the range of 100–1000 Å, a length in the range of 1000 Å–2 μm and an aspect ratio (length:width) of > 50:1. (1) include single-crystal cores covered with an amorphous layer of < 10 Å thickness. Magnetic Recording Media

Carbon Nanotube Pastes and Methods of Use

SEAGATE TECHNOL. LLC

O. MATARREDONA et

A magnetic recording disc includes a disc substrate of glass, quartz, Si, SiO2, ceramic or AlMg, with an etched locking pattern of multiple pits, completely filled with chemically synthesised nanoparticles (1) of a single magnetic species. (1) may consist of Fe-Pt, Co-Pt, Fe-Pd or Mn-Al, and have a grain size of 3–10 nm. (1) exhibit short-range order characteristics, forming self organised magnetic arrays.

al.

U.S. Appl. 2006/039,848

Dispersible pastes consisting of C single-walled nanotubes (SWNTs) in H2O or an organic solvent are prepared. These pastes can be impregnated with noble metal precursors including compounds of Pt. The SWNT-Pt composites can have small Pt clusters distributed evenly over the surface and can be used as catalysts or as electrodes for fuel cells.


U.S. Patent 7,041,394

155

DOI: 10.1595/147106706X128403

FINAL ANALYSIS

Mercury as a Catalyst Poison The effects of permanent poisons on platinum group metal (pgm) catalysts are irreversible (1). The poisons are so strongly absorbed that they cannot be adequately removed, even with aggressive remedial actions such as steaming or thermal regeneration. Typical examples of permanent poisons encountered when processing hydrocarbon feedstocks would be contaminant metals such as nickel, copper, vanadium and, in particular, ‘heavy metals’ such as lead, arsenic and mercury (Hg). All these metals have a significant deactivating effect on precious metal catalysts, but the ‘heavy metals’ have a particularly dramatic impact. This is so even at very low concentrations, either present in the feedstock or accumulated on the catalyst. The metals content of crude oils may vary from a few ppm to several thousand ppm, depending upon the geographical and geological origin of the crude. The primary refining process involves distilling and fractionating the crude into separate hydrocarbon ‘cuts’. Distillation tends to concentrate any metallic components in the oil residue. However, some organometallic compounds are volatilised at distillation temperatures; they therefore distribute in some of the higher-boiling distillate fractions which are then processed further for refinery and petrochemical applications. Mercury is an increasingly common contaminant, detected in natural gas deposits, coal deposits and in some crude oils from a variety of geographical regions such as South East Asia, parts of the Middle East and South America. Hg may be present in a range of chemical forms, including elemental, ionic and organic, and as suspended solids, in concentrations ranging from a few parts per billion (ppb) to several thousand ppb. Catalysts consisting of palladium supported on alumina are widely used for the selective hydrogenation of acetylenes in petrochemical processing (2). These catalysts are adversely affected by heavy metals that accumulate on the surface, and effectively alloy with the precious metal through dπ-dπ

Platinum Metals Rev., 2006, 50, (3), 156

bonding. The result is to effectively remove active centres from the desired reaction scheme. Catalyst poisoning reduces yields and shortens catalyst life. It is therefore essential to reduce inlet Hg concentrations to < 5 ppb to achieve an economically acceptable service life. Hg poisoning, if left unchecked, may require an unplanned and premature catalyst change-out, with all its associated costs, including downtime. Unfortunately, it is not easy to detect and measure Hg at these very low concentrations as the metal is lost on sample lines and container walls. Exacting analytical methods and sampling techniques are necessary if the results are to be reliable and consistent. Neutron activation analysis and cold vapour atomic fluorescence spectroscopy have both proven successful for determining Hg concentrations. The effects of poisons cannot be avoided completely, but they can be mitigated by a carefully designed upstream purification system to protect the pgm catalysts. Although the Hg compounds are not the most reactive, several products have been developed to remove Hg from both gaseous and liquid hydrocarbon streams. Elemental Hg and inorganic Hg species can be very effectively removed (to levels of less than 1 ppb) through surface adsorption on non-regenerable metal sulfide pellets in fixed-bed reactors at ambient temperature. Hg has a high affinity for sulfur, and the metal sulfide reacts chemically with the Hg impurity to form a stable mercuric sulfide. Several approved disposal and treatment options are available for the Hg-laden spent J. K. DUNLEAVY absorbent.

References 1 2

D. E. Grove, Platinum Metals Rev., 2003, 47, (1), 44 ‘Selective hydrogenation of acetylenes and dienes’, Johnson Matthey Catalysts, http://www.jmcatalysts.com/pct/marketshome.asp?marketid=10&id= 374

The Author Dr John Dunleavy is Business Director – Refinery, Oil & Gas Section, Johnson Matthey PCT, PO Box 1, Belasis Avenue, Billingham TS23 1LB, U.K. He has over 20 years’ experience in the catalyst industry.

156