Processing defects and their relevance to strength in alumina ceramics made by slip casting

Al2O3 made by slip casting inherently contained the elongated and the spherical shaped defects. The pores of elongated shape were formed through the liquid flow during the casting process, since they were found in all slip cast specimens and not found in the spontaneously dried specimen where no rigorous flow of water happened. The formation of these defects was insensitive to the slurry properties. The origin of spherical pores was likely due to the entrapped air bubbles during de-airing procedure. Their removal by de-airing was easy for a dispersed slurry having a low viscosity, but difficult for a flocculated slurry of high viscosity. The Weibullʹs plots for the flexural strengths are essentially the same in the region of high strengths. Specimens made from the flocculated slurry contain a higher concentration of the spherical pores, and some of the resultant specimens have low strength. The lower strength of those ceramics has been ascribed to more detrimental defects, i.e. the spherical ones.