Ceramics

S2 TEP

Ceramics

Course-3 M.K. Bahan Konstruksi dan Biosistem Yusuf Wibisono, STP., MSc.

What are ceramics? S2 TEP

The term “ceramic” comes from the Greek word keramikos, which means “burnt stuff,” indicating that desirable properties of these materials are normally achieved through a high-temperature heat treatment process called firing.

From “traditional ceramics” like porcelain, bricks, tiles, glass; to “advanced ceramics” such as semiconductor, electronic devices etc.

Even Semester 2009/2010

Yusuf Wibisono, MSc (吳穎書)

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Crystal Structures S2 TEP

Solid materials may be classified according to the regularity with which atoms or ions are arranged with respect to one another.

A crystalline material is one in which the atoms are situated in a repeating or periodic array over large atomic distances. All metals, many ceramic materials, and certain polymers form crystalline structures under normal solidification conditions.



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Crystal structures and properties S2 TEP



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Assembled atoms S2 TEP



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Energy bonding S2 TEP



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Atomic packing S2 TEP



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Unit cell S2 TEP

The atomic order in crystalline solids indicates that small groups of atoms form a repetitive pattern.

Thus, in describing crystal structures, it is often convenient to subdivide the structure into small repeat entities called unit cells. Unit cells for most crystal structures are parallelepipeds or prisms having three sets of parallel faces.



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An aggregate of many atoms S2 TEP

Unit cell



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The concept of crystal as building block S2 TEP



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Summary concepts S2 TEP



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Diffraction of single crystal S2 TEP



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Kaolinite crystals as ceramic crystal S2 TEP



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Ceramics crystal bonding S2 TEP



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Ceramic bonding 1: Electrically charged ions

The ceramic crystal structures may be thought of as being composed of electrically charged ions instead of atoms. The metallic ions, or cations, are positively charged, because they have given up their valence electrons to the nonmetallic ions, or anions, which are negatively charged.



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Increases with difference in electronegativity


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Stable structure S2 TEP



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Coordination geometry of ceramic crystal S2 TEP

The coordination number (i.e., number of anion nearest neighbors for a cation) is related to the cation–anion radius ratio. For a specific coordination number, there is a critical or minimum rC/rA ratio for which this cation–anion contact is established; this ratio may be determined from pure geometrical considerations. Even Semester 2009/2010


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Coordination numbers and geometries S2 TEP

Zincblende (ZnS)



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Coordination numbers and geometries S2 TEP

Sodium chloride (NaCl)



Cesium chloride (CsCl) 21

Question: S2 TEP



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Ceramic bonding 2: Covalent bonding Silicate ceramics

Silicates are materials composed primarily of silicon and oxygen, the two most abundant elements in the earth’s crust; consequently, the bulk of soils, rocks, clays, and sand come under the silicate classification.

Rather than characterizing the crystal structures of these materials in terms of unit cells, it is more convenient to use various arrangements of an tetrahedron:

Covalent bonding



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Silica S2 TEP



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Silicon dioxide S2 TEP



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Carbon: Diamond S2 TEP

Carbon is an element that exists in various polymorphic forms, as well as in the amorphous state.

This group of materials does not really fall within any one of the traditional metal, ceramic, polymer classification schemes.

However: graphite, one of the polymorphic forms, is sometimes classified as a ceramic, and, in addition, the crystal structure of diamond, another polymorph, is similar to that of zinc blende.



A unit cell for the diamond cubic crystal structure.

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Carbon: Graphite and Fullerenes S2 TEP

Graphite: covalent + van der Walls bonding



Fullerenes (C60)

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New carbon: Carbon Nanotubes S2 TEP

SWNT Even Semester 2009/2010

DWNT Yusuf Wibisono, MSc (吳穎書)

MWNT 28

New carbon: Carbon Nanotubes S2 TEP



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Classification of ceramics S2 TEP

Based on application



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Group 1: Glasses S2 TEP

high thermal treatment crystalline Typical application: containers, lenses, and fiberglass Typical composition: CaO, Na2O, K2O, and Al2O3 non-crystalline Even Semester 2009/2010


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Common commercial glass S2 TEP



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Glass-ceramics: Properties S2 TEP

relatively high mechanical strengths; low coefficients of thermal expansion (to avoid thermal shock); relatively high temperature capabilities; good dielectric properties (for electronic packaging applications); and good biological compatibility; some glass–ceramics may be made optically transparent; others are opaque.



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Glass-ceramics: Applications S2 TEP

The most common uses for these materials are as ovenware, tableware, oven windows, and rangetops— primarily because of their strength and excellent resistance to thermal shock.

They also serve as electrical insulators and as substrates for printed circuit boards, and are used for architectural cladding, and for heat exchangers and regenerators.



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Group 2: Clay S2 TEP

high-temperature firing porcelain, pottery, tableware, china, and plumbing fixtures (sanitary ware) building bricks, tiles, and sewer pipes Even Semester 2009/2010


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Clay: Advantages S2 TEP

This inexpensive ingredient, found naturally in great abundance, often is used as mined without any upgrading of quality.

Ease with which clay products may be formed; when mixed in the proper proportions, clay and water form a plastic mass that is very amenable to shaping. The formed piece is dried to remove some of the moisture, after which it is fired at an elevated temperature to improve its mechanical strength.



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Group 3: Refractories S2 TEP

• the capacity to withstand high temperatures without melting or decomposing, • the capacity to remain unreactive and inert when exposed to severe environments, • the ability to provide thermal insulation. Even Semester 2009/2010

bricks, furnace linings for metal refining, glass manufacturing, metallurgical heat treatment, and power generation.


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Common ceramic refractory S2 TEP



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Refractory: Fireclay S2 TEP

Ingredients: high-purity fireclays, alumina and silica mixtures usually containing between 25 and 45 wt% alumina.

Fireclay bricks are used principally in furnace construction, to confine hot atmospheres, and to thermally insulate structural members from excessive temperatures.



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Refractory: Silica S2 TEP

The prime ingredient for silica refractories, sometimes termed acid refractories, is silica.

These materials, well known for their high-temperature load-bearing capacity, are commonly used in the arched roofs of steel- and glass-making furnaces; for these applications, temperatures as high as 1650oC (3000oF) may be realized. Under these conditions some small portion of the brick will actually exist as a liquid.



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Refractory: Basic S2 TEP

The refractories that are rich in periclase, or magnesia (MgO), are termed basic; they may also contain calcium, chromium, and iron compounds. The presence of silica is deleterious to their hightemperature performance. Basic refractories are especially resistant to attack by slags containing high concentrations of MgO and CaO, and find extensive use in some steel-making open hearth furnaces.



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Refractory: Special S2 TEP

Relatively high-purity oxide materials, many of which may be produced with very little porosity.

Included in this group are alumina, silica, magnesia, beryllia (BeO), zirconia (ZrO2), and mullite (3Al2O3–2SiO2).

Silicon carbide (SiC) has been used for electrical resistance heating elements, as a crucible material, and in internal furnace components.



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Group 4: Abrasives S2 TEP

•used to wear, grind, or cut away other material, which necessarily is softer. •bonded to grinding wheels, as coated abrasives, and as loose grains.


•diamonds, both natural and synthetic •silicon carbide, •tungsten carbide (WC), •aluminum oxide (or corundum), and •silica sand.


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Group 5: Cements S2 TEP

The characteristic feature of these materials is that when mixed with water, they form a paste that subsequently sets and hardens.



•cement, •portland cement, •gypsum, •plaster of paris, •lime.

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Group 5: Advanced ceramics S2 TEP

Utilized in optical fiber communications systems, in microelectromechanical systems (MEMS), as ball bearings, and in applications that exploit the piezoelectric behavior of a number of ceramic materials. Even Semester 2009/2010


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Advanced ceramic: Semiconductor S2 TEP



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Semiconductor S2 TEP



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Fabrication of ceramics S2 TEP



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Press and Blow Technique S2 TEP

Glass-bottle



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Continuous drawing technique S2 TEP

Glass-sheet



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Slip casting technique S2 TEP

Clay molding using plaster of paris mold: a. Solid slip casting b. Drain slip casting



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Powder pressing technique S2 TEP



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Tape casting technique S2 TEP



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