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Bennema’s theory of crystal growth from a solution was modified and used in explaining fractionations of tritiated water in the crystal-growth processes of several inorganic hydrated salts from concentrated aqueous solutions. It was suggested that some water molecules in the aqueous solutions were free to become growth units which are not necessarily activated for entering the crystal surface. The dilution of tritiated water in the crystal was observed; this was explained in a satisfactory way in terms of the surface-diffusion model originally proposed by Burton, Cabrera, and Frank. On the contrary, the volume diffusion model was inadequate for interpreting the fractionation of tritium.

The temperature dependence of the fractionation of tritiated water (HTO) was examined during the crystal growth of alum from its tritiated aqueous solution. When the ratios of the mole fractions of HTO in the water of crystallization to that of the mother liquid, S, at various temperatures are compared, the following order is established:S19.90≈S29.50>S36.52>S41.95>S47.43>S53.70≈S69.50,where the suffixes represent the crystallization temperatures, and where S19.90=0.975 and S69.50=0.949. The concept of the hydration of ions developed recently was applied to the problem of the crystal growth from the solution. Two kinetic parameters, such as the relaxation time of the aluminum ion for entering the surface, τc, and that of the hydrated aluminum ion, Al(OH2)63+, for the exchange of the water with bulk water, τe, were taken into account to explain the fractionation. A surface-diffusion mechanism was suggested as essential in the crystal growth of alum from the solution. The activation free energy for the crys...

A considerable dilution of tritiated water in the water of crystallization was observed in the crystal-growth process of KCr(SO4)2·12H2O from a slightly supersaturated aqueous solution. This was explained in terms of an ionic process in aqueous solution and a surface-diffusion mechanism of crystal growth. It was also found that the tritium content in the hexahydrate was appreciably smaller than that in the liberated water during the course of reaction; KCr(SO4)2·12H2\xrightarrow[in vacuo]40°CKCr(SO4)2·6H2O+6H2O. It seems that the step wise dehydration supports the dehydration mechanism proposed by Garner.

Ammonium chloride tetrachlorozincate, (NH4)3Cl[ZnCl4], decomposes to ZnCl2 in two stages through an intermediate phase (NH4)2[ZnCl4]. In the first stage, 1 mol of NH4Cl is lost by one-dimensional diffusion mechanisms with the activation energy of 138 kJ mol−1, and in the second stage the release of two moles of NH4Cl is controlled by a random nucleation reaction with the activation energy of 126 kJ mol−1, corresponding to the bondbreaking. Anhydrous alkali metal tetrachlorozincate complexes, M2[ZnCl4](M=Na, K, Rb, Cs), are obtained by solid reactions with alkali chlorides when (NH4)3Cl[ZnCl4] decomposes. A dry chemical method using (NH4)3Cl[ZnCl4] as a starting material is proposed for the preparation of the anhydrous chlorozincate complexes, which have thus far been difficult to synthesize.

The fractionation of the tritiated water (HTO) was examined during the crystallization of hydrates, such as (COOH)2·2H2O, (COOK)2·H2O, Cu(HCOO)2·4H2O, and Sr(HCOO)2·2H2O. The dilution of HTO in the organic salts was found to be comparable to that in inorganic salts observed previously. The fractionation of HTO was explained on the basis of an ionic process in an aqueous solution, and the crystal growth mechanism, in a way similar to that described in a previous paper. On the contrary, a considerable dilution was observed for oxalic acid dihydrate. The proton effect on the fractionation in both the ionic and dehydration processes was also discussed.

The fractionation of tritiated water (HTO) was examined during the crystallization of sodium sulfate decahydrate, Na2SO4·10H2O, from a slightly supersaturated solution which contained a trace amount of tritium. No appreciable fractionation of HTO was found to occur in the crystallization under both stirred and unstirred conditions. The factors which may influence the degree of the fractionation were generally considered in connection with the studies by deuterated water. It was suggested that virtually all of the water of crystallization in sodium sulfate decahydrate should come from free water in its aqueous solution, and should integrate into the crystal in accordance with the volume-diffusion model. This model was supported also by the energetical consideration of the sodium ion in the crystallization.

The tritium fractionation in the crystallization of NH4Al(SO4)2·12H2O from a solution was found to be larger than those in NaAl(SO4)2·12H2O and KAl(SO4)2·12H2O. This fact was discussed in terms of the proton exchange between NH4+ and H2O.