Self-diffusion of the sodium ion in the monosodium and disodium forms of α- and γ-zirconium phosphate

α- and γ-zirconium phosphate are layered exchangers that differ both in their structures and the packing sequence of the layers. In γ-zirconium phosphate the structure of the layer is more compact and the interlayer distance is greater than in α-zirconium phosphate. These compounds are therefore good models for studying the effect of the distance between the fixed charges and of the interlayer distance on the transport properties of layered exchangers. The self-diffusion processes of 24Na+ in the monosodium and disodium forms of α- and γ-zirconium phosphate were therefore investigated. In the first stages of the processes, the rate seems to be controlled by fast interfacial isotopic exchange reactions, whereas in the last stages the rate is particle diffusion controlled. The self-diffusion constants and hence the activation energies were calculated by using an approximate equation valid for long diffusion times. The activation energies for self-diffusion increase in the order γ-Zr(NaPO4)2 x 5H2O(33 kJ/mole) < α-ZrHNa(PO4)2 x 5H2O(42 kJ/mole) < γ-ZrHNa(PO4)2 x 3H2O(53 kJ/mole) < α-Zr(NaPO4)2 x 3H2O(69 kJ/mole) and the self-diffusion constants, at 25sup(o)C, correspondingly decrease. It seems, therefore, that the activation energies are lower and the self-diffusion rates faster in the compounds that possess a greater interlayer distance and have a shorter distance between the = P-O- fixed chargers lying on the faces of the layers. (orig.)