Development of Compressive Surface Stresses in Slip-Cast Fused Silica

摘要

Compressive surface stresses have been used for many years to strengthen glassy ceramics. An attempt was made to develop compressive surface stresses in slip-cast fused silica to increase its load-carrying capabilities. The method used to accomplish this was based on the development of stresses in a silica composite by causing the center portion of a cylindrical specimen to contract more than the exterior shell. This was accomplished by preparing specimens with two fused silica slips having different particle sizes, or different devitrification rates. The different particle sizes provided a differential sintering shrinkage, while variations in devitrification rates led to different cristobalite contents and resulted in a differential contraction as the specimens were cooled through the cristobalite inversion temperature. Modulus of rupture tests were used to evaluate these specimens and values obtained for several groups of composites had increased mean strengths and/or decreased standard deviations. Although the strength increases were not as high as predicted, the standard deviations were significantly lower (40-80) for the composites compared with single phase specimens (600-1200). Strength variability is often related to surface flaws, and the reduction in variability suggests that the effect of surface flaws on the composite specimens has been significantly reduced, as a result of the development of compressive prestress. (Author)