Specialty Refractory Products

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. 

Chromium oxide-corundum bricks (mixed crystals of AI2O3 with 5 to 10% Cr203) exhibit very good resistance to alkaline slags. They are utilized in parts of blast furnaces (Fig. 5.5-4) and demand for them is expected to increase in the future. 

Pure chromium oxide bricks with 95% Cr203 are manufactured from synthetic Cr203 and are utilized in the refractory linings of tank furnaces for the production of E-glass fibers. 

Zirconia bricks are the most important specialty refractory products 

Importance of chromium oxide-corundum bricks is steadily increasing 

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Refractories may be preformed, ie, shaped, or formed and installed on-site, ie, specialties. Iimovations in placement and vessel constmction has led to a greater emphasis on specialty refractory products. Castables, gunning mixes, and plastic and ramming mixes are used either for repair or for complete new constmction of what is known as monolithic linings. The tendency to use monolithics instead of constmctions using shaped products has been steadily increasing. As of the mid-1990s, monolithic installations are as common as conventional shaped product constmction. 

Specialty Refractories. Bulk refractory products include gunning, ramming, or plastic mixes, granular materials, and hydrauhc setting castables and mortars. These products are generally made from the same raw materials as their brick counterparts. 

Finally, in the 1990s, Pfizer under a new CEO initiated major divestitures. In 1990, it sold off its citric acid business to Archer-Daniels-Midland. Then, in 1992, there followed the spinning off of its other specialty chemicals and refractory products, followed quickly by the sale of the Coty cosmetic and fragrance divisions for 440 million and the overseas portion of its Plax mouthwash business (purchased in 1988) to Colgate-Palmolive for 105 million, and its Shirley heart-valve unit to a subsidiary of Italy s Fiat. ... 

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). 

Continuously operating tunnel kilns heated with gas, oil or electricity, in which the articles travel through a well-defined temperature-time profile, are currently almost exclusively used for the manufacture of the mass-produced articles of the brick, refractory and crockery porcelain industries. Such kilns are 20 to 150 m long and have transit times between 1 and >72 h. Muffle kilns, which operate discontinuously, are still important for small production runs and specialty products. 

ASTM C 71-93 Standard terminology relating to refractories. Annual Book of ASTM Standards, Section 15 General Products, Chemical Specialties, and End Use Products, Volume 15.01 Refractories, Carbon and Graphite Products, Activated Carbon, Advanced Ceramics. Philadelphia ASTM, 1995 15-18. 

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