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Applied Clay Science 139 (2017) 40–44

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Research paper

Structural and dielectric comparative studies of geopolymers prepared with metakaolin and Tunisian natural clay H. Douiri a,⁎, S. Louati b, S. Baklouti b, M. Arous a, Z. Fakhfakh a a b

Laboratoire des matériaux composites céramiques et polymères, Faculté des sciences de Sfax, Université de Sfax, BP 3018, Sfax, Tunisie Laboratoire de Chimie industrielle, Ecole Nationale d'Ingénieurs de Sfax, Université de Sfax, BP 1173, 3038 Sfax, Tunisie

a r t i c l e

i n f o

Article history: Received 26 September 2016 Received in revised form 20 December 2016 Accepted 15 January 2017 Available online 20 January 2017 Keywords: Metakaolin Natural clay X-ray diffraction Dielectrics Electrical properties

a b s t r a c t Metakaolin and calcined Tunisian natural clay were used as potential aluminosilicate sources to synthesize phosphoric acid - inorganic polymers known as geopolymers. Structural and dielectric properties of these two kinds of clay were studied. X-ray diffraction patterns showed that the main phases presented for both clays were quartz and illite. Besides, these two specimen showed a great similarity in their dielectric properties in a frequency range [102–106] Hz. Nevertheless, a dissimilarity was observed at low frequencies [1−102] Hz as a result of the difference in their mineral compositions. In a second time, a comparative study between two geopolymers made of metakaolin and the calcined natural clay was realized. New crystalline phases, produced during geopolymerization reaction were detected in both geopolymers X-ray diffraction patterns. Dielectric results revealed a difference in their dielectric parameters in the low frequency range. It resulted from a variation in charge distribution into the two geopolymer structures. However, for high frequencies a great similarity was observed for both geopolymers. © 2017 Elsevier B.V. All rights reserved.

1. Introduction In recent years, aluminosilicate geopolymers have received considerable attention because of their excellent physical properties such as high strength, anti-corrosion, resistance to heat, long life (Duxson et al., 2007; Cui et al., 2008) in addition to their good compressive strength (Zhang et al., 2010). Thus, geopolymers are rapidly finding their way into numerous industrial applications such as aviations, refractory ceramics, concrete products and biomaterials (Davidovits, 1991; Jonathan et al., 2008; Derrien et al., 2004; Goung et al., 2012). In order to create aluminosilicate geopolymers, raw materials such as Kaolin clays, metakaolin, fly ash and blast furnace slag are often used. Metakaolin is the most used since its chemical composition is simple, compared to other common precursor materials. Hence, geopolymers can be synthesized by activating metakaolin with strong alkaline solution (Cui et al., 2008; Davidovits, 2008) or phosphoric acid solution (Perera et al., 2008; Liu et al., 2010) at ambient temperature or slightly above. These two kinds of geopolymers have presented different mechanical and dielectric properties (Cui et al., 2011; Liu et al., 2011). In fact, in comparison to the sodium silicate-based geopolymers, phosphoric acid-based geopolymers had superior performance with good mechanical, thermal and low dielectric ⁎ Corresponding author. E-mail address: [email protected] (H. Douiri).

http://dx.doi.org/10.1016/j.clay.2017.01.018 0169-1317/© 2017 Elsevier B.V. All rights reserved.

properties (Liu et al., 2010). They are used as electronic packaging materials and insulated encapsulating materials (Cui et al., 2011). In recent years, there has been increasing interest in studying the use of natural clays in the synthesis of geopolymers because of their low cost and abundance in most countries. For instance, geopolymers made with Tunisian natural clay (Tunisian kaolin) have presented good performance. (Essaidi et al., 2014; Louati et al., 2014; Louati et al., 2016). In previous studies, geopolymers made of calcined Tunisia natural clay (collected from the Tabarka region (Northern Tunisia)) and phosphoric acid have presented good mechanical properties. In fact, this clay was ranked among the purest natural kaolin (Chakchouk et al., 2006). However, dielectric properties of these kinds of materials have never been studied. In our dielectric previous studies released at low frequencies [1 Hz– 1 MHz], we have demonstrated that metakaolin-phosphoric acid based geopolymers were characterized by low dielectric parameters (Douiri et al., 2014, 2016). Some dielectric phenomena were detected such as proton conduction and dipolar polarization at low and high frequency, respectively (Douiri et al., 2014). The aim of the present work is to obtain geopolymers made of the Tunisian natural clay and phosphoric acid presenting dielectric parameters similar to that presented by metakaolin-phosphoric acid based geopolymers. Hence, to compare dielectric properties of geopolymers made of metakaolin and calcined natural clay, a comparative study between the two raw materials should be firstly realized.

H. Douiri et al. / Applied Clay Science 139 (2017) 40–44

41

Raw materials

SiO2

Al2O3

Fe2O3

MgO

Na2O

CaO

K2O

based on an Alpha Analyzer. The measured dielectric permittivity data were collected and evaluated by WinDETA impedance analysis software. The complex dielectric function for the material is expressed as

Kaolin (K) Natural clay (TB)

44.17 62.96

36.55 26.44

1.69 1.89

0.27 0.24

1.83 –

1.81 –

0.73 1.28

ε ðωÞ ¼ ε0 ðωÞ− jε00 ðωÞ

Table 1 Chemical composition of kaolin and natural clay (% of mass).

ð1Þ

The AC conductivity of all samples was calculated from the dielectric losses according to the relation (2):

2. Materials and methods

σ  ¼ jε0 ωε ðωÞ ¼ jε0 ωðε0 −jε00 Þ ¼ ε0 ωε00 þ jε0 ωε0

Well-crystallized Kaolin (K), named codex kaolin, was supplied by the CHEMI-PHARMA society. The natural clay (TB) was Tunisian kaolin collected from the Tabarka region (Northern Tunisia) and operated as an aluminosilicate source. Calcination step for both types of clays consisted on curing them at 700 °C for 5 h in a static bed and then quenching them by air to room temperature (Essaidi et al., 2014). This step ameliorated clay reactivity. Metakaolin based geopolymers were prepared by mixing calcined kaolin (MK), distilled water and phosphoric acid (Douiri et al., 2014; Louati et al., 2014). The solid S- to liquid L ratio S/L was maintained constant and it was equal to 1. After mechanical mixing for several minutes, slurry was vibrated 5 min with ultrasonic waves in a flask to be aqueous and to remove any trapped air before being transferred to cylindrical molds. Because of the exothermic reaction between phosphoric acid and calcined kaolin (MK), the samples were properly sealed to prevent water loss. They were then kept at room temperature for 2 h before curing in a laboratory oven at 60 °C for 24 h. This step will accelerate the polycondensation of samples and is believed to be sufficient to complete geopolymerization. Thereafter, samples were maintained at ambient temperature and pressure for 28 days before demoulding. The same steps were made to prepare geopolymer with calcined natural clay (CTB) and phosphoric acid. The molar ratio Si/P was equal to 1.75 for both types of geopolymer materials. The chemical composition of the clays was determined using X-ray fluorescence (ARL 8400). The mineral phases of different samples were identified by XRD with a BRUKER-AXS-D8-Advance powder diffractometer using CuKα radiation (λ = 0.154 nm) with a scanning rate of 10°/min from10° to 60° (2θ). In dielectric analysis, the sample was placed between two gold parallel plate electrodes. Then, an alternating voltage with amplitude 1 V was applied and a low current was measured. Impedance spectroscopy was carried out on pellets with a diameter of 13 mm and a thickness b1 mm. Measurement were performed in the frequency range from 1 Hz to 1 MHz at room temperature, using a Novocontrol System

ð2Þ

The real part of σ⁎ (ω) is given by: σ 0 ðωÞ ¼ ε0 ωε}ðωÞ

ð3Þ

where ε0 was the dielectric permittivity in vacuum (8.85 × 10−12 F·m−1) and ω was the angular frequency. 3. Results and discussions The chemical compositions of the studied clay samples were presented in Table 1. For kaolin (K) it was clear that besides silica and alumina, it contained an amount of iron, calcium, magnesium and potassium oxides indicating the probable presence of illite. For natural clay (TB), results of chemical analysis showed that this clay is also rich in silica and alumina and contained substantial percentages of iron and potassium oxides. It was noted that the weight percentage of silica was relatively high probably indicating the presence of free silica. It was also noted that the amount of potassium oxide was greater in natural clay (TB) than in kaolin (K). This could be explained by the presence of illite with a higher percentage. The examination of the X-ray patterns of Kaolin (K) before and after calcinations (Fig. 1) indicated the presence of kaolinite and illite minerals associated with quartz into the raw clay (Fig. 1(a)). Result was in accordance with those obtained by fluorescence X. For natural clay (TB), the physico-chemical characterization before and after calcination at 700 °C was already presented by Louati et al. (2014). Indeed, we noticed mainly the presence of kaolinite and illite associated to non-clay minerals such as quartz and anatase (TiO2) as the secondary minerals (Fig. 2(a)). After calcination at 700 °C for 5 h, all diffraction peaks related to kaolinite disappeared for both calcined clays (Fig. 1(b) and Fig. 2(b)). This proves the transformation of kaolinite into metakaolinite. However, the peaks related to quartz and illite persisted after heat treatment.

K

I I

I

5

I Q

I

10

15

I

Q

I

20

(b)

A K K Q K I

K

25

Q

30

35

40

K

45

K K

K+Q

50

55

K

(a) 60

Position[°2Theta] Fig. 1. XRD patterns of (a) raw kaolin and (b) calcined kaolin. K: kaolinite Al2Si2O5(OH)4 (00-001-0527), Q: quartz SiO2 (00-002-0471), I: illite K(Al4Si2O9(OH)3) (01-070-3754) and A: anatase TiO2 (01-071-1167).

42

H. Douiri et al. / Applied Clay Science 139 (2017) 40–44 Q

Q K

I

I

M + I

5

I

I

Q

I

K M M + +K I M A I I I

10

15

20

I

25

30

Q

I

M Q + I K Q K I

35

Q

Q

40

Q

Q

I

KQ

I

45

I

(b)

Q K I AM

K

50

55

(a) 60

Position[°2Theta] Fig. 2. XRD patterns of (a) raw natural clay and (b) calcined natural clay. K: kaolinite Al2Si2O5(OH)4 (00-001-0527), Q: quartz SiO2 (00-002-0471), I: illite K(Al4Si2O9(OH)3) (01-070-3754), M: muscovite (K,Na)(Al,Mg,Fe) 2(Si3.1Al0.9)O10(OH)2 (00-007-0042) and A: anatase TiO2 (01-071-1167).

The XRD analysis of the two geopolymer samples (Fig. 3) showed the presence of quartz and illite which were already presented in calcined clays. These minerals do not contribute to the geopolymerization reaction. Moreover, some new crystalline phases, produced during geopolymerization reaction, appeared in both geopolymers such as monetite (CaHPO4), auguelite (Al2 (PO4)(OH)3) and aluminum phosphate (AlPO4) (Douiri et al., 2014; Louati et al., 2014). In addition, a diffuse halo appeared between 20 and 35° characteristic of an amorphous material related to the formation of a polymeric disordered structure (Louati et al., 2014). This diffuse halo was more important for metakaolin based geopolymer. This could be a sign of the evolution of geopolymerization reaction. Fig. 4 presented variations of the real and imaginary part of dielectric permittivity (ε′, ε″) and conductivity σ′ as a function of frequency for metakaolin (MK) and calcined natural clay (CTB). The measurements were performed at room temperature. We noticed that dielectric

parameters of both metakaolin and calcined natural clay are almost of the same magnitude. However, ε′, ε″ and σ′ decreased for the calcined natural clay at low frequencies. This could be related to the presence of more impurities and defects. Furthermore, the natural clay (TB) has presented a higher percentage of illite in which the distance between the sheets (10A°) is greater than in kaolin (K) (7°A). Thus, through the application of the electric field, part of the moved charges could be trapped at the level of clay-impurities interfaces (Sengwa and Sengwa and Soni, 2005, 2008) and between the sheets. As a result, charge mobility in the material decreased resulting in a decline in the dielectric parameters. At high frequencies (f N 102 Hz), variations of ε″ for natural calcined clay (CTB) revealed a peak probably related to a relaxation phenomenon attributed to the rotational movement of hydroxyl (O\\H) groups fixed on the surfaces of the silica. In fact, it was found that these groups presented dipole moment of the same order of magnitude as that of the water molecules (Spanoudaki et al., 2005). This peak was

Q

I

I

Q M Au A

I I

M

5

10

15

Au Q Au

20

25

Q QI Q A

A Q

M

30

M

35

Q

40

A

Q Au

Q

I

Q

45

50

A

Q

(b)

(a)

55

60

Position[°2Theta] Fig. 3. X-ray patterns of (a) metakaolin based geopolymer and (b) calcined natural clay based geopolymer. Q: quartz SiO2 (00-002-0471), I: illite K(Al4Si2O9(OH)3) (01-070-3754), A: aluminum phosphate AlPO4 (01-072-1161), Au: augelite Al2(PO4)(OH)3 (00-034-015) and M: monetite CaPO3(OH) (00-009-0080).

H. Douiri et al. / Applied Clay Science 139 (2017) 40–44

43

Fig. 4. Real, imaginary part of dielectric permittivity (a, b) and electrical conductivity (c) for metakaolin and calcined natural clay measured at room temperature.

absent for the metakaolin because of the difference of mineral composition for both types of clay. Indeed, the natural clay has a higher percentage of silica (62.96%) compared to kaolin (44.17%). Therefore, the number of hydroxyl groups was higher in the case of natural clay intensifying the relaxation phenomenon. Note that despite the dehydroxylation of natural clay through calcinations, most of the Si\\O\\Si groups were hydroxylated in contact with the atmosphere.

Fig. 5. Real, imaginary part of dielectric permittivity (a, b) and electrical conductivity (c) for both types of geopolymer materials measured at room temperature.

Fig. 5 presents variations of the real and imaginary part of dielectric permittivity (ε′, ε″) and conductivity σ′ as a function of frequency for the two types of the geopolymers at ambient temperature. Results

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H. Douiri et al. / Applied Clay Science 139 (2017) 40–44

showed a great similarity in dielectric behavior for both geopolymers towards high frequencies (f N 102 Hz). Indeed, a peak appeared in ε″ spectra of the two specimen suggesting the presence of relaxing dipoles in the specimen such as water dipoles (Douiri et al., 2014). In fact, water existing in the geopolymers is a polar molecule characterized by a nonstraight H\\O\\H bonding angle. This means that it can be easily polarized by an electric field. However, a difference in dielectric parameters of two geopolymers was observed to lower frequencies. This could be a result of the diversity of charge mobility in the structure of each geopolymer. In fact, the difference in mineral composition of two raw materials led to a difference in geopolymer structures. We noticed that dielectric permittivity and electrical conductivity were less significant for metakaolin based geopolymer. According to XRD patterns, the evolution of geopolymerization reaction was more important for metakaolin based geopolymer. Hence, the decrease in dielectric parameters of geopolymer (MK) could be a result of the reduction in the number of free charges provided by phosphoric acid whose consumption was more important for geopolymerization reaction. Indeed, phosphoric acid is a good proton conductor because of its extensive self-ionization (Douiri et al., 2014). Moreover, conductivity in phosphoric acid based geopolymers is mainly controlled by proton transport through − phosphate ions, i.e. H4PO+ 4 , H2PO4 (Douiri et al., 2014).

4. Conclusion A comparative study of phosphoric acid based geopolymers made of metakaolin and calcined Tunisian natural clay was realized. Mineralogical studies showed that both calcined clays consisted mainly of quartz and illite. Moreover, geopolymers made of the two types of clays combined with phosphoric acid have presented new crystalline phases such as aluminum phosphate and monetite. Dielectric measurements made in a frequency range of [10− 1–106] Hz revealed similar behavior for the two calcined clays and also for their two geopolymers at a frequency range of [102–106] Hz. Hence, phosphoric acid geopolymers made of calcined Tunisian natural clay have presented dielectric properties close to those presented by phosphoric acid geopolymers made of metakaolin. This allows us to develop the abundant natural resources.

References Chakchouk, A., Samet, B., Mnif, T., 2006. Study on the potential use of Tunisian clays as pozzolanic material. Appl. Clay Sci. 33, 79–88. Cui, X.M., Zheng, G.J., Han, Y.C., Su, F., Zhou, J., 2008. A study on electrical conductivity of chemosynthetic Al2O3-2SiO2 geoploymer materials. J. Power Sources 184, 652–656. Cui, X.M., Liu, L.P., He, Y., Chen, J.Y., Zhou, J., 2011. A novel aluminosilicate geopolymer material with low dielectric loss. Mater. Chem. Phys. 130, 1–4. Davidovits, J., 1991. Geopolymers: inorganic polymeric new materials. J. Therm. Anal. 37, 1633–1656. Davidovits, J., 2008. Chemistry and Applications. Institut Géopolymère, Saint-Quentin, France, pp. 41–44. Derrien, A.C., Oudadesse, H., Sangleboeuf, J.C., Briard, P., Lucas-Girot, A., 2004. Thermal behavior of composites aluminosilicate–calcium phosphates. J. Therm. Anal. Calorim. 75, 937–946. Douiri, H., Louati, S., Baklouti, S., Arous, M., Fakhfakh, Z., 2014. Structural, thermal and dielectric properties of phosphoric acid-based geopolymers with different amounts of H3PO4. Mater. Lett. 116, 9–12. Douiri, H., Louati, S., Baklouti, S., Arous, M., Fakhfakh, Z., 2016. Enhanced dielectric performance of metakaolin–H3PO4 geopolymers. Mater. Lett. 164, 299–302. Duxson, P., Ferna'ndez-Jime'nez, A., Provis, J.L., Lukey, G.C., Palomo, A., Van Deventer, J.S.J., 2007. Geopolymer technology: the current state of the art. J. Mater. Sci. 42, 2917–2933. Essaidi, N., Samet, B., Baklouti, S., Rossignol, S., 2014. Feasibility of producing geopolymers from two different Tunisian clays before and after calcination at various temperatures. Appl. Clay Sci. 88–89, 221–227. Goung, F., Fouchal, F., Maillard, P., Rossignol, S., 2012. A geopolymer mortar for wood and earth structures. Constr. Build. Mater. 36, 188–195. Jonathan, B., Matthew, G., Waltraud, K., 2008. Use of geopolymeric cement as a refractory adhesive for metal and ceramic joins. Advance in ceramic coating and ceramic–metal systems. Ceram. Eng. Sci. Proc. 26, 407–413. Liu, L.P., Cui, X.M., Qiu, S.H., Yu, J.L., Zhang, L., 2010. Preparation of phosphoric acid-based porous geopolymers. Appl. Clay Sci. 50, 600–603. Liu, L.P., Cui, X.M., He, Y., Yu, J.L., 2011. Study on the Dielectric Properties of Phosphoric Acid-based Geopolymers. TransTechPublications, Switzerland, pp. 538–541. Louati, S., Hajjaji, W., Baklouti, S., Samet, B., 2014. Structure and properties of new ecomaterial obtained by phosphoric acid attack of natural Tunisian clay. Appl. Clay Sci. 101, 60–67. Louati, S., Baklouti, S., Samet, B., 2016. Acid based geopolymerization kinetics: effect of clay particle size. Appl. Clay Sci. 132–133, 571–578. Perera, D.S., Hanna, J.V., Davis, J., Blackford, M.G., Latella, B.A., Sasaki, Y., Vance, E.R., 2008. Relative strengths of phosphoric acid-reacted and alkali-reacted metakaolin materials. J. Mater. Sci. 43, 6562–6566. Sengwa, R.J., Soni, A., 2005. Low frequency dielectric dispersion and microwave permittivities of Indian granites. Ind. J. Radio Space 34, 341–348. Sengwa, R.J., Soni, A., 2008. Dielectric properties of some minerals of western Rajasthan. Ind. J. Radio Space 37, 57–63. Spanoudaki, A., Albela, B., Bonneviot, L., Peyrard, M., 2005. The dynamics of water in nanoporous silica studied by dielectric spectroscopy. Eur. Phys. J. E. 17, 21–27. Zhang, Y.J., Wang, Y.C., Xu, D.L., Li, S., 2010. Mechanical performance and hydration mechanism. Mater. Sci. Eng. A 527, 6574–6580.