The kinetics of coarsening in the Al-Al3Ni System

The kinetics of coarsening of the Al-Al₃Ni system during the stage of coarsening during which the microstructure is nearly representative of a random array of dispersed fibers is adequately expressed by conventional kinetics,i.e. Δr ³ ≅t wherer is average fiber radius andt coarsening time. The activation energy for the coarsening process is ∼315 kJ/mol and is composed of two terms: 1) the volume diffusion activation energy for nickel in the aluminum matrix and 2) the heat of solution of nickel in solid aluminum. It is pointed out that the conventional expressions for coarsening kinetics in this system can only be applied over a limited range of coarsening time since the microstructure is not generally representative of microstructures envisaged for coarsening process. Several comments and comparisons regarding the initiation of three-dimensional coarsening in this and other systems are made.     

The vaporization kinetics of Ni3S2

The vaporization of Ni₃S₂ was investigated at high temperatures by a levitation technique. Vaporization was controlled by a mass transfer process within a gas boundary layer around the Ni₃S₂ droplet. The vaporized S₂(g) and Ni(g) recombine within the gas boundary layer, and this recombination along with the condensation of Ni(g) was found to enhance the vaporization rate. A model has been developed to account for the experimentally-obtained mass transfer coefficients. Y. FUKUNAKA, formerly Research Associate, Department of Metallurgy and Materials Science, University of Toronto