Partially stabilized zirconia ceramics

Claim 1

A ceramic material consisting essentially of magnesia partially stabilised zirconia having a magnesia content in the range from about 2.8 to about 4.0 wt percent, characterised in that zirconia powder from which the material has been made contains no more than about 0.03 wt percent silica and the material has a micro-structure comprising grains of cubic stabilised zirconia, each grain containing (a) discrete precipitates of tetragonal zirconia, each precipitate having an elliptical shape with the mean length in the long dimension being about 1500 Angstrom units, and (b) discrete precipitates of microcrystalline monoclinic zirconia, produced by controlled thermal transformation of a proportion of the precipitates of tetragonal zirconia.

Claim 6

A method of making a magnesia partially stabilised zirconia ceramic material comprising the steps of: (a) mixing and wet-milling magnesium oxide powder and zirconium dioxide powder containing no more than 0.03 percent by weight silica, or materials capable of producing, on firing, magnesium oxide and zirconium oxide with no more than 0.03 wt percent silica, in proportions such that the effective magnesium oxide content comprises from about 2.8 to about 4.0 wt percent of the mixture and the mean particle size is about 0.7 micrometer; (b) calcining the powders in the temperature range from about 800° C. to about 1450° C. for about 24 hours; (c) wet-milling the calcined mixture until the mean particle size is about 0.7 micrometer; (d) moulding the wet-milled mixture into a desired shape; (e) firing the moulded mixture at a temperature in the range from about 1550° C. to about 1800° C.; (f) cooling the sintered material from the firing temperature to a nucleating temperature in the range between 800° C. and room temperature, the rate of cooling being controlled so that a tetragonal zirconia precipitate phase forms in the sintered material and coarsens to an elliptical precipitate having a major axis about 1500 Angstrom units long; (g) heating the material immediately after nucleation to an ageing/transformation temperature in the range from 1000° C. to about 1400° C.; (h) holding the material at the ageing/transformation temperature for a time sufficient for from 20 to 30 percent of the tetragonal zirconia precipitate to transform into monoclinic zirconia material; and (i) furnace cooling the material to room temperature.

Claim 7

A method of making a magnesia partially stabilised zirconia ceramic material comprising the steps of: (a) mixing and wet-milling magnesium oxide powder and zirconium dioxide powder containing no more than 0.03 percent by weight silica, or materials capable of producing, on firing, magnesium oxide and zirconium oxide with no more than 0.03 wt percent silica, in proportions such that the effective magnesium oxide content comprises from about 2.8 to about 4.0 wt percent of the mixture and the mean particle size is about 0.7 micrometer; (b) calcining the powders in the temperature range from about 800° C. to about 1450° C. for about 24 hours; (c) wet-milling the calcined mixture until the mean particle size is about 0.7 micrometer; (d) moulding the wet-milled mixture into a desired shape; (e) firing the moulded mixture at a temperature in the range from about 1550° C. to about 1800° C.; (f) cooling the sintered material from the firing temperature to a nucleating temperature in the range between 800° C. and room temperature, the rate of cooling being controlled so that a tetragonal zirconia precipitate phase forms in the sintered material and coarsens to an elliptical precipitate having a major axis about 1500 Angstrom units long; (g) heating the material immediately after nucleation to an ageing/transformation temperature in the range from 1000° C. to about 1400° C.; (h) holding the material at the ageing/transformation temperature for a time sufficient for from 20 to 30 percent of the tetragonal zirconia precipitate to transform into monoclinic zirconia material; and (i) furnace cooling the material to room temperature.

Claim 8

A method of making a magnesia partially stabilised zirconia ceramic material comprises the steps of (a) mixing and wet-milling magnesium oxide powder and zirconium dioxide powder containing no more than 0.03 percent by weight silica, or materials capable of producing, on firing, magnesium oxide and zirconium oxide with no more than 0.03 wt percent silica, in proportions such that the effective magnesium oxide content comprises from about 2.8 to about 4.0 wt percent of the mixture and the mean particle size is about 0.7 micrometer; (b) moulding the mixture into a desired shape; (c) firing the moulded mixture at a temperature in the range from about 1550° C. to about 1800° C.; (d) cooling the sintered material from the firing temperature to a nucleating temperature in the range between 800° C. and room temperature, the rate of cooling being controlled so that a tetragonal zirconia precipitate phase forms in the sintered material and coarsens to an elliptical precipitate having a major axis about 1500 Angstrom units long; (e) heating the material immediately after nucleation to an ageing/transformation temperature in the range from 1000° C. to about 1400° C.; (f) holding the material at the ageing/transformation temperature for a time sufficient for from 2 to 30 percent of the tetragonal zirconia precipitate to transform into monoclinic zirconia material; and (g) furnace cooling the material to room temperature.

Claim 9

A method of making a magnesia partially stabilised zirconia ceramic material comprises the steps of (a) mixing and wet-milling magnesium oxide powder and zirconium dioxide powder containing no more than 0.03 percent by weight silica, or materials capable of producing, on firing, magnesium oxide and zirconium oxide with no more than 0.03 wt percent silica, in proportions such that the effective magnesium oxide content comprises from about 2.8 to about 4.0 wt percent of the mixture and the mean particle size is about 0.7 micrometer; (b) moulding the mixture into a desired shape; (c) firing the moulded mixture at a temperature in the range from about 1550° C. to about 1800° C.; (d) cooling the sintered material from the firing temperature to a nucleating temperature in the range between 800° C. and room temperature, the rate of cooling being controlled so that a tetragonal zirconia precipitate phase forms in the sintered material and coarsens to an elliptical precipitate having a major axis about 1500 Angstrom units long; (e) heating the material immediately after nucleation to an ageing/transformation temperature in the range from 1000° C. to about 1400° C.; (f) holding the material at the ageing/transformation temperature for a time sufficient for from 2 to 30 percent of the tetragonal zirconia precipitate to transform into monoclinic zirconia material; and (g) furnace cooling the material to room temperature.