refractories made from zirconium oxide (zirconium dioxide or zirconia), ZrO2, or zircon, ZrSiO4.
Zirconia (baddeleyite) refractories are made from zirconium oxide by first molding the powder-like substance and then roasting at 1700°–2200°C. The zirconium oxide material used is subjected to prior stabilization by melting or roasting at 1700°–1750°C with the addition of 5–7 percent CaO or other structurally similar oxide. Zirconia refractories have refractoriness above 2000°C and are characterized by high chemical resistance to the action of melts, alkalies, and most acids. They are used as crucibles for melting platinum, palladium, and other metals and quartz glass, in the construction of reactors, and for lining high-temperature furnaces. Lightweight zirconia products, fibers, and granular powders are suitable for high-temperature thermal insulation.
Zircon refractories are made from zircon concentrates or a previously roasted mixture of zircon and clay by pressing and roasting at about 1500°–1550°C. The density of these refractories is 3.0–3.4 g/cm3, the temperature of deformation under a load of 2 kilograms-force/cm2 is 1500°–1570°C, and the refractoriness is 1900°–2000°C. These products are used as ladle nozzles for steel pouring, in furnaces for melting aluminum, in steel-pouring ladles for special steels, and as compounds and coatings.