Kinetics of chlorination of Co and Co-10 At. Pct Pt alloy by reaction with HCI gas

The reaction of alloys with HCI gas is generally more complicated than that of pure metals, and is, typically, a dealloying process. In this work the rates of a model dealloying process, Co(Co-Pt) + 2HC1 → CoCl2(g) + H2 were measured in the temperature range 973 to 1273 K. The only reaction product for the HC1/H2 gas mixtures used in the experiments was gaseous CoCl2. Weight loss during the reaction was continuously monitored with a recording balance. Experimental variables included gas composition, gas flow rate, and temperature for Co-10 at. pct Pt and for pure Co samples. The rate of the reaction was constant with time and very nearly as high for the alloy as for the pure metal, in spite of the fact that Pt was inert for the conditions. A surface instability occurred for the alloy yielding an open porous structure of ever increasing surface area. Transport of CoCl2(g) in the gas boundary layer was important for determining the rate of the chlorination reaction for both the alloy and pure metal.