Alumina ceramic comprising a siliceous binder and at least one of zirconia and hafnia

Claim 1

A ceramic composed of from 1 to 15 percent of glass and 99 and 85 percent of a mixture of particulate Al 2 O 3 and at least one other particulate material selected from the group consisting of ZrO 2 , HfO 2 , ZrO 2 --HfO 2 solid solutions and Y 2 O 3 , the particulates all being finer than 15 microns in ultimate particle size, ZrO 2 , HfO 2 and Y 2 O 3 constituting from 15 to 25 percent based upon the weight of ZrO 2 , HfO 2 , Y 2 O 3 and Al 2 O 3 in the ceramic, Y 2 O 3 constituting up to 12 percent based upon the weight of the ZrO 2 , HfO 2 and Y 2 O 3 , and said glass constituting a vitreous phase bonding the mixture of particulates into a dense, gas impervious structure, and being a calcium magnesium silicate glass containing from 45 to 80 percent of SiO 2 , from 8 to 55 percent of CaO and MgO, and not more than 15 percent of Al 2 O 3 .

Claim 9

A method for producing a ceramic, said method comprising pressing a batch into a desired shape, firing the shape to a temperature from about 1350° to about 1650° to mature the ceramic, cooling the ceramic, and refiring the ceramic to a temperature of at least about 870° but not so high that the ceramic is subject to microcracking upon standing under ambient temperatures, said batch being one which, after firing of the shape to about 1350° to about 1650° to maturity, produces a ceramic composed of from 1 to 15 percent of glass and 99 to 85 percent of a mixture of particulate Al 2 O 3 and at least one other particulate material selected from the group consisting of ZrO 2 , HfO 2 , ZrO 2 --HfO 2 solid solutions and Y 2 O 3 , the particulates all being finer than 15 microns in ultimate particle size, ZrO 2 , HfO 2 and Y 2 O 3 constituting from 15 to 25 percent based upon the weight of ZrO 2 , HfO 2 , Y 2 O 3 and Al 2 O 3 in the ceramic, Y 2 O 3 constituting up to 12 percent based upon the weight of the ZrO 2 , HfO 2 and Y 2 O 3 , and said glass being a calcium magnesium silicate glass containing from 45 to 80 percent of SiO 2 , from 8 to 55 percent of CaO and MgO, and not more than 15 percent of Al 2 O 3 .

Claim 10

A method for producing a ceramic, said method comprising pressing a batch into a desired shape, firing the shape to a temperature from about 1350° to about 1650° to mature the ceramic, cooling the ceramic, and refiring the ceramic to a temperature of at least about 870° but not so high that the ceramic is subject to microcracking upon standing under ambient temperatures, said batch being one which, after firing of the shape to about 1350° to about 1650° to maturity, produces a ceramic composed of from 1 to 15 percent of glass and 99 to 85 percent of a mixture of particulate Al 2 O 3 and at least one other particulate material selected from the group consisting of ZrO 2 , HfO 2 , ZrO 2 --HfO 2 solid solutions and Y 2 O 3 , the particulates all being finer than 15 microns in ultimate particle size, ZrO 2 , HfO 2 and Y 2 O 3 constituting from 15 to 25 percent based upon the weight of ZrO 2 , HfO 2 , Y 2 O 3 and Al 2 O 3 in the ceramic, Y 2 O 3 constituting up to 12 percent based upon the weight of the ZrO 2 , HfO 2 and Y 2 O 3 , and said glass being a calcium magnesium silicate glass containing from 45 to 80 percent of SiO 2 , from 8 to 55 percent of CaO and MgO, and not more than 15 percent of Al 2 O 3 .