The Thermal Stabilization and Sintering of Gold Smoke Deposits

Gold smokes made by evaporation in an inert gas atmosphere are initially in a thermodynamically unstable state. A theory based on diffusion of vacant sites to the surface of the crystallites has been developed to describe the process by which the deposit approaches equilibrium. Measurement at different temperatures of the change of resistance associated with the loss of vacant sites gives a value of 23.5 kcal./g atom for the activation energy of this process. When heated above 100°C the deposits sinter rapidly and undergo pronounced changes in optical properties. However, a gold smoke deposit can be stabilized, by heat treatment at 70°C, so that sintering proceeds at an appreciably slower rate.