Ceramic articles and methods for preparing ceramic articles and for sintering

Claim 1

A method for preparing a net shape ceramic article having a tetragonal crystal structure core and a cubic crystal structure case, said method comprising the steps of compacting a particulate alloy of ZrO 2 and a secondary oxide selected from the group consisting of MgO, CaO, Y 2 O 3 , Sc 2 O 3 , rare earth oxides and combinations thereof, to form a blank, said particulate alloy having a molar ratio of secondary oxide to ZrO 2 of from about 2:98 to about 5:95, a grain size from about 0.1 to about 0.6 micrometers, an agglomerate size of from about 30 to about 60 micrometers, said blank having a density of from about 40 to about 65 percent of the density of said tetragonal crystal structure core of said ceramic article; heating said blank from room temperature to a sintering temperature from about 1400° C. to about 1600° C.; maintaining said blank at said sintering temperature from about 1 hour to about 3 hours; contacting said blank with oxide selected from the group consisting of MgO, CaO, Y 2 O 3 , Sc 2 O 3 , rare earth oxides and combinations thereof during said maintaining step; and cooling said blank from said sintering temperature to room temperature; said heating and cooling steps having temperature ramps of less than 2° C./minute and wherein dimensional shrinkage of said blank during said heating, maintaining and cooling steps is uniform to within 0.001 percent.

Claim 2

A method for preparing a net shape ceramic article having a tetragonal crystal structure core and a cubic crystal structure case, said method comprising the steps of compacting a particulate alloy of ZrO 2 and a secondary oxide selected from the group consisting of MgO, CaO, Y 2 O 3 , Sc 2 O 3 , rare earth oxides and combinations thereof, to form a blank, said particulate alloy having a molar ratio of secondary oxide to ZrO 2 of from about 2:98 to about 5:95, a grain size from about 0.1 to about 0.6 micrometers, an agglomerate size of from about 30 to about 60 micrometers, said blank having a density of from about 40 to about 65 percent of the density of said tetragonal crystal structure core of said ceramic article; heating said blank from room temperature to a sintering temperature from about 1400° C. to about 1600° C.; maintaining said blank at said sintering temperature from about 1 hour to about 3 hours; contacting said blank with oxide selected from the group consisting of MgO, CaO, Y 2 O 3 , Sc 2 O 3 , rare earth oxides and combinations thereof during said maintaining step; and cooling said blank from said sintering temperature to room temperature; said heating and cooling steps having temperature ramps of less than 2° C./minute and wherein dimensional shrinkage of said blank during said heating, maintaining and cooling steps is uniform to within 0.001 percent.

Claim 12

A method for preparing a ceramic article having a tetragonal crystal structure core and a cubic crystal structure case, said method comprising the steps of compacting a particulate alloy of ZrO 2 and a secondary oxide selected from the group consisting of MgO, CaO, Y 2 O 3 , Sc 2 O 3 , rare earth oxides and combinations thereof, to form a blank, said particulate alloy having a molar ratio of secondary oxide to ZrO 2 of from about 2:98 to about 5:95, a grain size from about 0.1 to about 0.6 micrometers, an average grain size of 0.3 micrometers, an agglomerate size of from about 30 to about 60 micrometers, an average agglomerate size of 50 micrometers, and a moisture content of from about 0.2 to 1.0 percent, said blank having a density of from about 40 to about 65 percent of the density of said tetragonal crystal structure core of said ceramic article; heating said blank from room temperature to 300° C. at a rate of 0.3° C./minute, from 300° C. to 400° C. at a rate of 0.1° C./minute, from 400° C. to 600° C. at a rate of 0.4° C./minute, from 600° C. to 1500° C. at a rate of 1.5° C./minute; maintaining said blank at 1500° C. for 2 hours; and contacting said blank with oxide selected from the group consisting of MgO, CaO, Y 2 O 3 , Sc 2 O 3 , rare earth oxides and combinations thereof during said maintaining step; and cooling said blank from 1500° C. to 800° C. at a rate of 2° C./minute, from 800° C. to room temperature at a rate of 1.6° C./minute; wherein dimensional shrinkage of said blank during said heating, maintaining, and cooling steps is uniform to within 0.001 percent.

Claim 13

A method for preparing a ceramic article having a tetragonal crystal structure core and a cubic crystal structure case, said method comprising the steps of compacting a particulate alloy of ZrO 2 and a secondary oxide selected from the group consisting of MgO, CaO, Y 2 O 3 , Sc 2 O 3 , rare earth oxides and combinations thereof, to form a blank, said particulate alloy having a molar ratio of secondary oxide to ZrO 2 of from about 2:98 to about 5:95, a grain size from about 0.1 to about 0.6 micrometers, an average grain size of 0.3 micrometers, an agglomerate size of from about 30 to about 60 micrometers, an average agglomerate size of 50 micrometers, and a moisture content of from about 0.2 to 1.0 percent, said blank having a density of from about 40 to about 65 percent of the density of said tetragonal crystal structure core of said ceramic article; heating said blank from room temperature to 300° C. at a rate of 0.3° C./minute, from 300° C. to 400° C. at a rate of 0.1° C./minute, from 400° C. to 600° C. at a rate of 0.4° C./minute, from 600° C. to 1500° C. at a rate of 1.5° C./minute; maintaining said blank at 1500° C. for 2 hours; and contacting said blank with oxide selected from the group consisting of MgO, CaO, Y 2 O 3 , Sc 2 O 3 , rare earth oxides and combinations thereof during said maintaining step; and cooling said blank from 1500° C. to 800° C. at a rate of 2° C./minute, from 800° C. to room temperature at a rate of 1.6° C./minute; wherein dimensional shrinkage of said blank during said heating, maintaining, and cooling steps is uniform to within 0.001 percent.