Specialty Ceramic Products

Alumina fibers for composites with metal and plastics are under development as are structural ceramic products, including engine components. Fine, specialty grades of alumina are also used in toothpaste. 

Zinc phosphate, Zn2(P0 2> forms the basis of a group of dental cements. Chromium and zinc phosphates are utilized in some metal-treating appHcations to provide corrosion protection and improved paint adhesion. Cobalt(II) phosphate octahydrate [10294-50-5] Co2(P0 2 8H20, is a lavender-colored substance used as a pigment in certain paints and ceramics. Copper phosphates exhibit bioactivity and are used as insecticides and fungicides. Zinc, lead, and silver phosphates are utilized in the production of specialty glasses. The phosphate salts of heavy metals such as Pb, Cr, and Cu, are extremely water insoluble. 

Specialty Aluminas. Process control (qv) teclmiques permit production of calcined specialty aluminas ha nng controlled median particle sizes differentiated by about 0.5 ]lm. Tliis broad selection enables closer shrinkage control of high tech ceramic parts. Production of pure 99.99% -AI2O2 powder from alkoxide precursors (see Alkoxides, metal), apparently in spherical form, offers the potential of satisfying the most advanced appUcations for calcined aluminas requiring tolerances of 0.1% shrinkage. 

Calcined alumina markets consume slightly less than 50% of the specialty alumina chemicals production (1—8,20,22—115). Worldwide usage is estimated to be about 50% for refractories (qv), 20% for abrasives, and 25% for ceramics (qv). Calcined aluminas are also used in the manufacture of tabular alumina and calcium aluminate cements (CAC). Quantities are estimated to be over 200,000 and 100,000 t, respectively (7). 

Conversion of fused pentoxide to alloy additives is by far the largest use of vanadium compounds. Air-dried pentoxide, ammonium vanadate, and some fused pentoxide, representing ca 10% of primary vanadium production, are used as such, purified, or converted to other forms for catalytic, chemical, ceramic, or specialty appHcations. The dominant single use of vanadium chemicals is in catalysts (see Catalysis). Much less is consumed in ceramics and electronic gear, which are the other significant uses (see Batteries). Many of the numerous uses reported in the Hterature are speculative, proposed. 

Nickel oxide is used in the ceramic industry for making frit, ferrites, and coloring porcelain. The oxide in sinter form is used in the production of nickel-steel alloys. It supplies oxygen to the melt for removal of carbon as carbon dioxide. Some other important uses of nickel oxide include preparation of many nickel salts, specialty chemicals, and nickel catalysts. It also is used as an electrode in fuel cells. 

Specialty Chemicals Materials Performance Additives Titanium Dioxide Pigments Advanced Ceramics Specialty Compounds Wire Cable Products... 

Another major distinction between ceramics and hydraulic cements is the porosity. Ceramics are made dense unless their application requires some degree of porosity. Hydraulic cements, however, are inherently porous. Porosity is <1 vol% for the best ceramics, but typically 15-20 vol% for cements. Ceramics tolerate very high temperatures, and are corrosion resistant in a wide range of pH, while cements are made for use at ambient temperatures and are affected by high temperature as well as acidic environment. Compared to cements, ceramics are more expensive thus, cement is produced in high volume while ceramics, except few products such as bricks, are specialty products. 

Similar to calcium dihydrogen phosphate, one may use magnesium dihydrogen phosphate (Mg(H2P04)2-H20) as an acid phosphate [5]. Not many commercial applications of this product have been identified and hence its commercial availability has been limited. As a result, though this product can produce excellent ceramics, it can only be used in specialty products such as dental cements. Formation of magnesium phosphate ceramics with this acid phosphate is discussed in Chapter 9 and its use in dental cement in Chapter 18. 

One of the major uses of strontium has been in the production of color cathode ray tubes (CRTs) used in televisions and computer monitors. However, changes in electronics technology and the popularity of flat-panel screens (which use far less or even no strontium) have led to decreased strontium demand for this purpose in the United States and Europe. However, strontium is also used in the manufacture of ceramics and specialty glass. One of its radioactive isotopes is used in industry and medical studies. 

Metallurgical grade silicon is marketed in a coarsely crushed form or as a finely ground powder in different particle sizes. Powders with increased purity due to acid washing, particularly for the removal of metallic impurities, are specialty products. They are utilized, for example, in the manufacture of silicon nitride powder or reaction-bonded silicon nitride ceramic components and are therefore the starting materials for engineering ceramic specialties. 

The industrially most important refractory products are supplemented by specialty products for particular applications. The most important of these is zirconia bricks. They are produced from natural zircon (ZrSi04) with optional addition of quartz or alumina using standard ceramic techniques. They are used in tank furnaces in the glass industry, aluminum melting furnaces and high temperature furnaces. 

The primary use for uranium is in nuclear power reactors and in weapons. Low-enriched metal or ceramic UO2 fuel pellets (enriched in fissile U-235) are produced for commercial power reactors. Smaller quantities of high-enriched fuel are produced for shipboard power reactors and weapons manufacture. Depleted uranium, a by-product of the enrichment process, is used for armor-piercing ammunition for the military, for counter balances and weights, and for radiation shielding. A small amount of uranium is used in specialty chemicals and catalysts. 

Cer-Vit [Owens-Corning]. TM for a glass ceramic having linear expansion coefficient near zero. Used for specialty products, such as telescope mirrors, where minimum distortion is essential. 

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