2166.     ---------------.  [MAMPEL, K. L.]  [Time Versus Amount of Reaction Formulas for Heterogeneous Reactions at the Phase Boundaries of Solids.  II.  Time Versus Amount of Reaction Formulas for a Powder Consisting of Spherical Particles.]  Ztschr. physik. Chem., vol. 187, A, 1940, pp. 235-249; Chem. Abs., vol. 35, 1941, p. 7809.

        Mathematical and theoretical.  Spherical particles of uniform size are assumed.  For large radius the equation has the form kt/r=1-¹√1-x, in which the symbols have their usual meaning.  For small radius the equation is x=1-c₁e^-4k₁^r2t.  The intermediate case is approximated by either of these equations.  This intermediate type is characterized by a reaction velocity greater than that of either of the other 2 cases.  For all 3 cases there is an induction period during which the reaction follows a 4^th-power time law; this period is short for the first 2 cases and long for the intermediate case.  The experimental testing of the results is complicated by the tendency of particles to become smaller during the course of the reaction.