A model for solid‐solid or solid‐gas reactions between spherical particles and a fine powder or gas has been developed. The oxidation of uniformly sized nickel spheres has been shown to fit this model to 100% reaction. Previously reported models are inadequate because they do not meet the boundary conditions set down and because the volume of the product was assumed to equal that of one of the reactants. The inadequacy of earlier experimental results has been explained by the failure to experimentally meet the boundary conditions imposed.

Kinetic Model for Solid‐State Reactions

Experimental determination of high-temperature elemental losses from biomass slag

Chapter 3 - Kinetic Background to Thermal Analysis and Calorimetry

Interstitial and vacancy migration in Cu3Au and copper

Quantitative X-ray diffraction methods were used to define the kinetics of spinel formation. Diffusion controlled reaction rate constants were calculated on the basis of the reaction models of Jander, Dunwald-Wagner, Valensi, Zhuravlev et al., Ginstling-Brounshte'n, and Kroger-Ziegler. The model proposed by Valensi is valid for describing solid-solid reaction rates in the later stages of the reaction. Inert markers indicated that diffusion of zinc ions through the spinel layer is the rate controlling mechanism. The activation energy for the process is 54,200 cal/mole. In the early stages of the reaction there is a second-order phase boundary kinetic process with an activation energy of 28,700 cal/ mole. The rate of chemical combination at the zinc-oxide-spinel phase boundary is believed to be rate controlling.

Kinetics and Mechanism of the Reaction Between Zinc Oxide and Aluminum Oxide

Diffusion equations derived from Fick's law are discussed and applied to experimental data in the literature on the diffusion of oxygen in copper and on reaction rates for chemical reactions in the solid phase. Previous limitations on the applicability of the formulae are removed by the use of a simple graphical method so that the theory can be applied to data to which it was previously inapplicable. It is pointed out that the exact solution to Fick's law obtained is equivalent to the parabolic law in the early stages of the diffusion process. The activation energy for the diffusion of oxygen in copper is found to be 50.5 kcal. per g‐atom.

R. T. Ellickson

Papers

Determination of Diffusion Coefficients