Transparent spinel article and tape cast methods for making

Abstract

A transparent, tape casted, spinel article, as defined herein. Also disclosed is a method of method of making the tape casted, transparent spinel, and laminates of the tape casted, transparent spinel, as defined herein.

1 .- 6 . (canceled) 
     
     
         7 . A method of making a tape casted, transparent spinel, comprising:
 attrition milling, for from 10 min to 10 hrs to form a slurry, a batch mixture comprising a spinel powder having a mean particle size of from 75 to 500 nanometers, a binder, a dispersant, a plasticizer, a defoaming agent, and an aqueous solvent;   degasing the resulting isolated slurry under vacuum;   tape casting the degased slurry to a wet thickness of from 20 to 2,000 micrometers;   controlled drying using an under-bed heater and heated flowing air at from 20 to 100° C. of the tape casted slurry to form a green tape having a dry thickness of from 5 to 1,000 micrometers; and   firing the green tape for a sufficient time and temperature to provide a sintered transparent spinel.   
     
     
         8 . The method of  claim 7  further comprising laminating the green tape into a plurality of green tape layers and then forming to provide a laminated transparent spinel. 
     
     
         9 . The method of  claim 7  wherein the spinel powder has a purity of from 99.5% to 99.9 wt %, and the spinel powder has a low sulfur content of from 0.01 wt % to 0.001 wt %. 
     
     
         10 . The method of  claim 7  wherein the spinel powder, prior to introduction into the slurry, has a BET surface area of from 2 to 30 m 2 /g, and the microstructure of the green tape is homogeneous. 
     
     
         11 . The method of  claim 7  wherein the spinel powder has a ceramic solids loading in the slurry of from 5 to 60 vol %, and the green tape has a ceramic solids loading of from 35 and 85 vol %. 
     
     
         12 . The method of  claim 7  wherein firing the green tape comprises:
 sintering the green tape and accomplishing binder burn out at 1500 to 1600° C. for 2 to 8 hrs to obtain a sintered transparent spinel; 
 hot isostatic pressing the sintered transparent spinel at 1500 to 1600° C. for 4 to 12 hr, and a pressure of from 5 to 60 kpsi to reduce residual porosity in the spinel, wherein the total porosity of the sintered transparent spinel after hot isostatic pressing is less than about 500 ppm; and 
 oxygen hot isostatic pressing of the HIP sintered transparent spinel at 1000 to 1200° C. for 2 to 8 hrs, and a pressure of from 0.2 to 30 kpsi, to reduce objectionable color centers in the resulting oxygen, hot isostatic pressed, sintered transparent spinel. 
 
     
     
         13 . The method of  claim 7  wherein firing is accomplished free of a sintering aid. 
     
     
         14 . The method of  claim 7  wherein the aqueous solvent is deionized water, and the binder, dispersant, plasticizer, defoaming agent, and aqueous solvent have a pH from 9 to 12. 
     
     
         15 . The method of  claim 7  wherein at least one step of the method is accomplished in a particulate controlled environment. 
     
     
         16 . The method of  claim 7  wherein the green tape has a porosity of from about 0.01 to about 25 vol %. 
     
     
         17 . The method of  claim 7  further comprising shape forming the green tape into a desired shape. 
     
     
         18 . The method of  claim 7  further comprising filtering the degased slurry to remove contaminants. 
     
     
         19 . The method of  claim 7  further comprising surface finishing the sintered transparent spinel to a desired thickness and surface texture. 
     
     
         20 . The method of  claim 8  wherein the sintered tape or the sintered tape laminate is insensitive to slight variations in either the amount of the binder in the tape cast slurry or the amount of the porosity, if the green tape ceramic solids loading is greater than 45 volume percent.