FUNDAMENTALS OF GLASS-TO-METAL BONDING. VIII. WETTABILITY OF IRON BY MOLTEN SODIUM DISILICATE. Technical Progress Report No. 8

An experimental unit was developed to allow the application of the glass specimen onto the metal surface at elevated temperatures under controlled atmospheric conditions at low pressures. The contact angle of sodium disilicate glass on platinum served as a check on the atmosphere. Sodium disilicate glass on Armco iron has a contact angle of 55 plus or minus 2 deg at 900 to 1000 deg C in vacuum and poor adherence: on magnetite, 2 plus or minus 1 deg excellent adherence. Behavior on oxidized iron was affected by the ability of the glass to rapidly dissolve large quantities of the oxide. Glass when dropped onto a lightly oxidized surface spread toward lower angles and retracted to the 55 deg angle upon solution of the oxide; adherence, in this case, correspondingly ranged from good to poor. When the glass dissolved a sufficient amount of iron oxide to cause crystallization of fayalite, the contact angle was in the range of 15 to 55 deg , the best adherence was obtained, and etching of the metal at the interface occurred. Vaporization of iron in vacuum at 1000 deg C did not seem to be retarded by thin oxide films. Presence of zirconium foilmore » in the evacuated system tended to reduce grain growth of the iron. (auth)« less