[Application of nitrides to dental casting. 2. Feasibility as coating materials for Co-Cr alloy]

Nitrides used in this experiment are hBN, A1N and Si3N4. We studied feasibility of nitrides as wax pattern coating materials for Co-Cr alloy in an atmosphere of argon. Wax patterns were painted with coating material of nitrides (first investing), then a mixture of phosphate bonded investment and water was used in outer investing (second investing). The temperature of mold was 800 degrees C, and an argon arc vacuum-pressure casting machine was used. We cast the thin specimens in Co-Cr alloy (composition Co: 63 wt%, Cr: 27 wt%, Mo: 5 wt%, Bal.: 5 wt%; melting point: 1,380 degrees C). Surfaces of cast specimens were investigated using the unaided eye, a scanning electron microscope and a surface roughness analyzer. Furthermore, the thick specimens (globular form: phi 6.5 mm) using coating material of hBN were investigated using the unaided eye. Results were summarized as follows; 1. The nitrides controlled remarkably the reaction between cast specimen and investment. 2. The nitrides had the good effect of separation. 3. The cast surface coated the nitrides had less clinging than uncoated one, and this indicated that its cleansability was improved. 4. The nitrides decreased the surface roughness (Rz) of the cast to about 1/3. 5. hBN had the best effect in nitrides. 6. hBN also had the effect in a thick globular specimen.