Removal of Cast Surface of Titanium by Chemical Treatment

Objectives: The detrimental hardened surface layer of cast titanium is routinely removed by the sandblasting and chemical treatment. The present study investigated the effect of the surface treatment exposure time on the amounts removed from the cast surface. Methods: Eighty castings (5mmx10mmx10mm) of commercially pure titanium (CP3, ASTM grade 3; T-ALLOY H, GC Corp., Japan) were made using two different types of investment material; a magnesia-based investment (Selevest CB, Selec, Japan) and a phosphate-bonded investment (T-INVEST, GC Corp.). Two surfaces (10mmx10mm) of each specimen were sandblasted with 50 µm Al₂O₃ particles for 30 seconds. After sandblasting, the specimens (n=5) were chemically treated with a HNO₃/HF solution (Chemipolish, Shofu, Japan) at room temperature for 1, 2, 3, 4, 5, 10 or 15 minutes. The reduction of the thickness at 20 randomly chosen sites after the sandblasting and also chemical treatment was determined using a micrometer. The data were analyzed by ANOVA/Tukey's test (a=0.05). Results: The amounts [mean (SD):µm] removed are as follows (means with identical letters in same investment are not significantly different) (p>0.05):

After the sandblasting, the amounts removed from specimens made with T-INVEST were significantly larger than those made with Selevest CB (p<0.05). After chemical treatment, the amounts removed increased with the time, and the total amounts removed in the Selevest CB specimens were significantly larger when the treatment exceeded 3-min (p<0.05). Conclusion: The amounts removed by two cleaning processes depended on the investment materials used. Cleaning procedures of the castings should be adjusted based on the investment used. Partially supported by NIH-NIDCR grant DE011787.