Widely Used Ceramics

The following is a brief summary of applications of some of the more widely used ceramic materials. 

Diamond is the hardest naturally occurring material. Industrial diamonds are used as abrasives for grinding and polishing diamonds. Diamond and diamond-like coatings prepared using chemical vapor deposition processes are used to make abrasion-resistant coatings for many different applications (e.g., cutting tools). They are, of course, also used in jewelry. 

Si02 is probably the most widely used ceramic material. Silica is an essential ingredient in glasses and many glass ceramics. Silica-based materials are used in thermal insulation, refractories, abrasives, fiber-reinforced composites, laboratory glassware, and so on. In the form of long continuous fibers, silica is used to make optical fibers for communication. Powders made using fine particles of silica are used in tires, paints, and many other applications. 

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Knowledge of wetting and bonding in metal/oxide systems is important in many fields of materials engineering because oxides are the most widely used ceramics. Moreover, metal/oxide interfaces play also a key role in metal/metal and metal/non-oxide ceramic couples in which one of the partners is an oxidisable material, such as stainless steel or SiC. Finally, certain oxides lend themselves well to fundamental studies because they can be obtained easily as high-purity and monocrystalline (AI2O3, MgO) or amorphous (SiC>2) solids. 

Silicon dioxide is the most widely used ceramic material in the semiconductor industry, and the majority of Si02 deposits in microelectronic circuits are formed by CVD. Silica layers are used as diffusion sources, intermetallic dielectrics, and dopant and etch barriers in the microelectronics industry. CVD of Si02 is also commonly used in manufacturing energy-efficient glass windows, surface coatings for fiber optics, and micromechanical applications. ... 

It is one of the most widely used ceramic materials because of its unique properties, like high-temperature strength, thermal shock resistance, and low dielectric constant [249]. It is also a good refractory material, due to its high melting... 

Alumina has a high melting point and is a widely used ceramic, but it does have a high expansion coefficient. When deposited via the sol gel method, excessive shrinkage occurs on drying and firing, which has to be counteracted by the addition of AI2O3 [144]. 

The development of ceramic materials for armor since 1970 has been extensive, In addition to alumina and titanium diboride, the most widely used ceramic materials are silicon carbide, boron carbide, and aluminum nitride, as monolithic plates and shapes, which are bonded to a fibrous laminate of fiberglass or Kevlar . A typical impact sequence is shown in Fig. 16.2. On impact, the ceramic plate fractures the projectile core and absorbs a major part of the kinetic energy. The backing material absorbs the residual energy. 

A widely used ceramic material for dielectric applications is alumina. The alumina may be milled and passed through a fine mesh screen (i.e., 400 mesh) to remove large particles. It can also be passed through a magnetic separator to remove all magnetic conductive materials, which would increase the conductivity of the final dielectric product. 

Silicon Carbides. Silicon carbide is a widely used ceramic characterized by high hardness, high strength at elevated temperatures, good thermal shock resistance resulting from its good thermal conductivity, and relatively low thermal expansion. In recent years it... 

One of the most widely used ceramic raw materials is clay. This inexpensive ingredient, found naturally in great abundance, often is used as mined without any upgrading of quality. Another reason for its popularity lies in the 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. TTie formed piece is dried to remove some of the moisture, after which it is fired at an elevated temperature to improve its mechanical strength. 

Uniaxial pressing is the method most widely used to impart shape to ceramic powders (24). Binders, lubricants, and other additives are often incorporated into ceramic powders prior to pressing to provide strength and assist in particle compaction (25). Simple geometries such as rectangular... 

Equally important as tape casting in the fabrication of multilayer ceramics is thick film processing. Thick film technology is widely used in microelectronics for resistor networks, hybrid integrated circuitry, and discrete components, such as capacitors and inductors along with metallization of MLC capacitors and packages as mentioned above. 

Mixing. The most widely used mixing method is wet ball milling, which is a slow process, but it can be left unattended for the whole procedure. A ball mill is a barrel that rotates on its axis and is partially filled with a grinding medium (usually of ceramic material) in the form of spheres, cylinders, or rods. It mixes the raw oxides, eliminates aggregates, and can reduce the particle size. 

Electronic Applications. The PGMs have a number of important and diverse appHcations in the electronics industry (30). The most widely used are palladium and mthenium. Palladium or palladium—silver thick-film pastes are used in multilayer ceramic capacitors and conductor inks for hybrid integrated circuits (qv). In multilayer ceramic capacitors, the termination electrodes are silver or a silver-rich Pd—Ag alloy. The internal electrodes use a palladium-rich Pd—Ag alloy. Palladium salts are increasingly used to plate edge connectors and lead frames of semiconductors (qv), as a cost-effective alternative to gold. In 1994, 45% of total mthenium demand was for use in mthenium oxide resistor pastes (see Electrical connectors). 

Ceramics. In ceramics, talc is widely used in wall tile and hobbyware bodies, in electrical porcelains, and in cordierite formulations. Wall tile and hobbyware ate talc—clay bodies that ate pressed and fast-fired to a high porosity (bisque) and then glazed and tefired to produce the final product. Talc containing tremolite and carbonate is preferred to ensure good porosity. 

Because of their unique combination of physical and chemical properties, manufactured carbons and graphites are widely used in several forms in high temperature processing of metals, ceramics, glass, and fused quartz. A variety of commercial grades is available with properties tailored to best meet the needs of particular appHcations (45). Industrial carbons and graphites are available in a broad range of shapes and sizes. 

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