Abstract: A relatively dense composite refractory material which has reasonable strength and good thermal shock resistance comprises an alumina matrix material within which are dispersed particles of polycrystalline zirconia comprises from 1.0 to 40 percent by volume of the composite material. Each particle of zirconia is an agglomerate of microcrystals which are strongly bonded together. Due to the agglomerates of the bonding together of the microcrystals at their grain boundaries. The microcrystals contain no matrix material within their agglomerates, and exhibit strong thermal expansion anisotropy. They have a size such that cracks do not form spontaneously within the agglomerates during cooling from about 1600.degree. C. to room temperature. Typically the agglomerates have a mean diameter of from 10 to 15 micrometers, while the average diameter of the microcrystals in an agglomerate is from 1 to 2 micrometers.

Abstract: Magnesia partially stabilized zirconia materials, having a cubic phase zirconia content in the range 70 to 25 percent (by volume) and a metal oxide additive which forms an insoluble zirconate, and a microstructure in the form of grains of stabilized cubic phase zirconia containing precipitates of tetragonal phase zirconia, are produced for use at low (less than 400.degree. C.) intermediate (between 400.degree. C. and 700.degree. C.), high (700.degree. C. to 1000.degree. C.) or very high (greater than 1000.degree. C.) temperatures. The higher the temperature of use of the ceramic material, the more the tetragonal precipitates need to be transformed into monoclinic phase zirconia. The extent to which the tetragonal precipitates are transformed is controlled by the way in which a fired, pressed mixture of the ceramic components is cooled from about 1400.degree. C. to about 1000.degree. C. An "ageing" of the ceramic material may be effected by an isothermal hold, preferably at 1350.degree. C. and then at 1100.

Abstract: A refractory material consists of a zircon matrix with zirconia particles dispersed in it. The zirconia particles comprise from 5 to 30 percent (by weight) of the material. A method of making this material involves milling zircon sand particles and zirconia particles until they have a respective predetermined particle size distribution, adding a fugitive binder, moulding a green ware, firing the green ware at a temperature in the range from 1400.degree. C. to 1800.degree. C., and furnace cooling the fired ware. Preferably the ware is held at the firing temperature for one hour.

Abstract: A magnesia partially stabilized zirconia ceramic material possessing from about 2.8 to about 4.0 wt percent magnesia, and made from a zirconia powder containing no more than about 0.03 percent silica is described. The ceramic material has a microstructure, produced as a consequence of the method by which the material is made, which provides both high strength and good thermal shock resistance properties. This microstructure comprises grains of cubic stabilized zirconia within which are formed, during cooling from the firing temperature, precipitates of tetragonal zirconia. These precipitates are elliptical in shape, with a long axis of about 1500 Angstrom units. Additionally, some of the tetragonal zironcia precipitates are made to transform into a non-twinned microcrystalline monoclinic form of zirconia by reducing the temperature of the material to below 800.degree. C., then subsequently holding the material at a temperature in the range from 1000.degree. C. to about 1400.degree. C.