Abstract: An article is provided which has a surface which is contactable in use with water at a temperature of at least 100.degree. C. The surface of the article is protected from attack by the water, because it is formed of a shaped fired ceramic material which is formed from particulate zirconia having a coating on the particles thereof of a hydrous oxide of yttrium and optionally also a hydrous oxide of zirconium, titanium or aluminum. Preferably the particles have a diameter of not more than 0.5 micron and the amount of hydrous oxide of yttrium falls within the range 0.5 to 10 mole percent as Y.sub.2 O.sub.3 on moles of zirconia. Typical articles are internal combustion engines and parts thereof, mills and impact plates therefor, and pump surfaces. Fuel cells are also described.

Abstract: A composition suitable for use in the manufacture of a ceramic material comprises free-flowing substantially non-aggregated particulate zirconia. A substantial proportion of the zirconia is present in the tetragonal crystalline form and the particles of zirconia contain alumina in an amount of from 1 to 10% by weight expressed as Al on ZrO.sub.2. The particles are substantially free of silica.The particles of zirconia can be coated with an oxide or hydrous oxide of a stabilizing agent for zirconia such as an oxide or hydrous oxide of yttrium, calcium, magnesium, barium, strontium or cerium.An oxidation process is described for the manufacture of the tetragonal crystalline zirconia by the oxidation of zirconium halide in the presence of aluminium halide at high temperature in the vapor phase.

Abstract: The stabilization of zirconia when used as a ceramic by various stabilizers has been known but a new and improved stabilized particulate zirconia has now been developed showing the important advantages.The particulate zirconia now developed is coated with a hydrous oxide of titanium and/or of aluminium and with at least one hydrous oxide of yttrium, calcium, magnesium, strontium or cerium.

Abstract: A product suitable as a ceramic comprises substantially nonaggregated alumina particles with 95% by number having an aspect ratio (i.e., the ratio of the longest dimension to the shortest dimension for any single particle) not greater than 1.1 and more than 80% having an aspect ratio not greater than 1.05 and having a geometric mean size of from 0.02 to 0.5 microns. Usually the product contains no more than 3% by weight as aggregates and preferably the product is as small as can conveniently be manufactured.