Cation Transport during Ion Exchange on Acid Phosphates of Multivalent Metals
The kinetics of an exchange of a proton for alkali metal cations in such layered acid phosphates of multivalent elements as HxY(PO4)2 · nH2O (Y = Ti, Zr, x = 2; or Y = Ta, x = 1), where cations are rather mobile, is studied by a potentiostatic-titration method. The kinetics of the ion exchange in the phosphates is controlled by a two-dimensional cation diffusion through the layer of the forming exchange product. Coefficients of the cation diffusion in the exchange products and basic mechanisms of the defect formation in the phosphates are determined. The nonequilibrium phases with a large substitution degree, which form on the sample surface during the first stage of an exchange, substantially affect the process kinetics.