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 ceramics comprises particulate zirconia the particles of which are coated with a hydrous oxide of yttrium and a hydrous oxide of manganese, iron, cobalt, nickel, copper or zinc. Preferably the particles also have an inner coating of titania, zirconia, hafnia or alumina.Ceramics prepared from the particulate zirconia of the invention are resistant to degradation by water at temperatures above 100.degree. C.

Abstract: Green bodies suitable for use in manufacturing ceramic articles are provided. The bodies comprise a coherent mass of particles of aluminium oxide free of organic binder and having a fracture stress measured by a biaxial disc flexure test of at least 10 MPa. The particles of aluminium oxide are coated with at least one inorganic oxide or hydrous oxide.The green body can be shaped by drilling, sawing etc. to a desired shape approximating to that of the ceramic article which it is used to produce. Generally such shaping is considerably easier than shaping the finished ceramic article.

Abstract: Green bodies suitable for use in manufacturing ceramic articles are provided. The bodies comprise a coherent mass of particles of titanium dioxide free of organic binder and having a fracture stress measured by a biaxial disc flexure test of at least 5 MPa. The particles of titanium dioxide are coated with at least one inorganic oxide or hydrous oxide.The green body can be shaped by drilling, sawing etc. to a desired shape approximating to that of the ceramic article which it is used to produce. Generally such shaping is considerably easier than shaping the finished ceramic article.

Abstract: A method which comprises the manufacture of black titanium nitride which comprises heating ammonia and titanium halide by means of an electric plasma formed in a stream of non-oxidizing gas generated by the discharge of direct current electricty between a pair of electrodes. The heated gases are introduced through an inlet nozzle into a reactor so constructed and operated as to induce circulation of the gases with a specifically defined recirculation ratio.

Abstract: Zirconia has been used in the manufacture of ceramics for many years. The desirability of stabilizing the crystal form has been recognized and one or more stabilising agents have been used. The present invention produced a stabilized zirconia carrying a coating of at least one hydrous oxide of yttrium, calcium, magnesium, strontium, barium, or cerium. Preferably also a hydrous oxide of zirconium is also present either a s a separate inner layer or mixed with the other hydrous oxide.

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: Zirconia has been used in the manufacture of ceramics for many years. The desirability of stabilizing the crystal form has been recognized and one or more stabilizing agents have been used.The present invention produced a stabilized zirconia carrying a coating of at least one hydrous oxide of yttrium, calcium, magnesium, strontium, barium or cerium. Preferably also a hydrous oxide of zirconium is also present either as a separate inner layer or mixed with the other hydrous oxide.

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.