Process for producing zirconia yttria grinding media used for grinding magnetic coating powder

Claim 2

A process for producing zirconia grinding media used for grinding a magnetic coating powder having an improved packing density comprising: (a) preparing primary particle powder of zironium oxide, said primary particle having monoclinic crystal structure and tetragonal crystal structure which includes about 3.6 to 8.0 percent by weight of yttrium oxide as dispersed solid solution, said primary particle powder having the mean grain size of less than 0.5 micron, (b) compacting said primary particle powder at a pressure of more than 500 kg/square centimeter into a green compact, and (c) sintering said green compact in the air or an inert gas atmosphere at a temperature of about 1400° C. to 1800° C. to obtain thereby a sintered body having a mean grain size of up to about 2 microns and a relative theoretical density of at least 98 percent.

Claim 3

A process for producing zirconia grinding media used for grinding a magnetic coating powder having an improved packing density comprising: (a) preparing primary particle powder of zirconium oxide, said primary particle having monoclinic crystal structure and tetragonal crystal structure which includes about 3.6 to 8.0 percent by weight of yttrium oxide as dispersed solid solution, said primary particle powder having the mean grain size of less than 0.5 micron, (b) compacting said primary particle powder at a pressure of more than 500 kg/square centimeter into a green compact, (c) presintering said green compact in the air or in an inert gas atmosphere at a temperature of about 1200° C. to 1650° C. produce a presintered body having a relative theoretical density of about 95 percent to 98 percent, and (d) subjecting said presintered body to a hot isostatic pressing in an inert gas atmosphere at a pressure of more than 500 kg/square centimeter and a temperature of about 1200° C. to 1550° C. to obtain thereby a sintered body having a mean grain size of up to about 2 microns and a relative theoretical density of at least 99 percent.

Claim 4

A process for producing zirconia grinding media used for grinding a magnetic coating powder having an improved packing density comprising: (a) preparing primary particle powder of zirconium oxide, said primary particle having monoclinic crystal structure and tetragonal crystal structure which includes about 3.6 to 8.0 percent by weight of yttrium oxide as dispersed solid solution, said primary particle powder having the mean grain size of less than 0.5 micron, (b) compacting said primary particle powder at a pressure of more than 500 kg/square centimeter into a green compact, (c) presintering said green compact in the air or in an inert gas atmosphere at a temperature of about 1200° C. to 1650° C. produce a presintered body having a relative theoretical density of about 95 percent to 98 percent, and (d) subjecting said presintered body to a hot isostatic pressing in an inert gas atmosphere at a pressure of more than 500 kg/square centimeter and a temperature of about 1200° C. to 1550° C. to obtain thereby a sintered body having a mean grain size of up to about 2 microns and a relative theoretical density of at least 99 percent.