Studies on the Dental Casting II. Ethyl Silicate Investiment for High Fusion Metals

Investiments of silicic acid gel bonded with either quartz or alundum were examined for the dental casting of Co-Cr alloy. Silicic acid is made by hydrolysis of ethyl silicate in the presence of hydrochloric acid and then gelatinized with magnesia mixed in the sand. Test specimens made of various fineness of quartz mixture bonded with silicic acid was fired. at 900°C for 30 minutes and cooled to room temperature to strengthen it against compression. The ratio of 60-100# sand to 200-250# sand : -60: 37 mixture was the hardest. The investiment bonded with concentrated silicic acid was hard. Thermal expansions of quartzsilicic acid investiments and alundum-silicic acid investiment were estimated +1.2-1.3 at, 600-900°C and +0.45% at 800-900°C respectively.