Wetting, Interfacial Interactions, and Vacuum Metallization of SnO₂ Ceramics by Liquid Metals and Alloys

The wetting behavior of SnO₂-ceramic substrates with metallic melts, such as Au, Ag, Cu, Sn, Ga, Pb, Ni, Al, Ge, Ag-Cu, Ag-Ge, Ag-Si, Cu-Si, Cu-Ni, Cu-Ge, Cu-Sn, Ag-Ti, Sn-Ti, Ag-Cu-Ti, and Cu-Sn-Ti in vacuum, was investigated. Wetting experiments at high temperatures (1270-1370 K) were carried out using sessile drop method with two types of SnO₂ ceramics: low-density pure SnO₂, and high-density SnO₂ with 1 wt.% Fe₂O₃. Molten copper and its alloys with high Cu-concentration, such as Cu-Ag, Cu-Sn, and Cu-Ni, wet the ceramics, because SnO₂ decomposes during heating in vacuum, resulting in formation of oxygen, which dissolves in the melt and acts as an adhesion-active additive. The dependence of the contact angle on the composition of the melt for various binary alloys (Ag-Cu, Ag-Si, Ag-Sn, Cu-Ni, Cu-Sn, and Cu-Si) was investigated. The results showed that the Cu-Ni system is the most promising filler for metallization and vacuum brazing of SnO₂ ceramics. A method of vacuum metallization, using Cu-Ni filler, resulting in strong adhesion of coatings, which are uniformly deposited on the SnO₂ ceramic surface, is proposed.