WETTABILITY OF SILICON-CARBIDE BY LIQUID SILVER AND BINARY SILVER SILICON ALLOY

The wetting behaviour of monocrystalline silicon carbide by liquid silver and a binary silver-silicon alloy has been investigated between their melting points and 1430-degrees-C using the sessile drop method in argon and with a very low oxygen partial pressure. Under the experimental conditions, the experimental results show that the wetting behaviour of the Ag/SiC system exhibits two different characteristics depending on temperature: (a) At temperatures below 1130-degrees-C, the contact angle does not change significantly with temperature. The intrinsic contact angle value of the Ag/SiC system was evaluated to be equal to 128-degrees. (b) At temperatures above 1130-degrees=C, the contact angle suddenly decreases to about 60-degrees and then very rapidly increases to 110-degrees. During further increase in temperature the spreading-contracting behaviour of the silver drop on the silicon carbide substrate continues repeatedly and the contact angle values oscillate between 60-degrees and 110-degrees. This behaviour was attributed to the repeated dissolution of silicon carbide in liquid silver. An addition of 10 at% silicon to silver enables the dissolution of silicon carbide in liquid silver to be suppressed, and no spreading-contracting phenomenon was observed for the silver-10 at% silicon alloy on the silicon carbide. It has been shown, on the other hand, that silicon is an active element and preferentially adsorbs at the Ag/SiC interface. Consequently, the addition of a small quantity of this element to a silver matrix induces a rapid decrease in the contact angle of the Ag/SiC system.