Preparation of Lightweight Porcelain Body by Mixing Shirasu-Balloon

Lightweight porcelain has been developed by forming closed pores in the porcelain body through the use of hollow micro-spheres made from volcanic ash. These micro-spheres are called Shirasu-balloon. A green for lightweight porcelain was prepared by mixing the Shirasu-balloon with the green by hand. Experimental specimens were obtained by pressing the green, and drying and firing it at temperatures from 1160 to 1400°C for 2h in air. Bulk density, liner shrinkage, and flexural strength were measured, and the morphology and structure of the Shirasu-balloon in the porcelain bodies were observed using SEM. When the Shirasu-balloon was mixed with green of less than 10 mass%, the bulk density was reduced from 2.38 to 1.77 (×103kg·m-3) along the ideal value. The Shirasu-balloon was deformed and was shrunk over 13% by the addition of the Shirasu-balloon at more than 20mass%. The density reduction did not progress ideally beyond this point and approached the saturation value. When the mixing ratio was less than 10 mass%, the reduction of the flexural strength of the lightweight porcelain was slightly suppressed. This might be explained by the residual stress formed in the porcelain body.