Ted B. Flanagan

Kinetics of dehydration of single crystals of copper formate tetrahydrate

Reproducible kinetic data for the dehydration of individual single crystals of copper formate tetrahydrate have been obtained from –45° to +25°C in vacuo. Although structural studies suggest the presence of two differently coordinated types of water molecule, all of the water molecules behave identically with respect to their kinetics of dehydration. The reactant/product interface penetrates into the crystal at a constant rate in only the two dimensions parallel to the planes (001) which contain the copper and formate ions. A two-dimensional contracting envelope equation describes the α(fraction dehydration) against time curves. The energy of activation, 11.2 ± 0.2 kcal/mol H2O, for penetration of the interface is less than the overall heat of dissociation, 12.5 kcal/mol H2O. The kinetics of dehydration are unaffected by an antiferroelectric transition at –37.7°C. The inhibition of the dehydration process by water vapour has been examined and discussed quantitatively.

Electrochemical exchange currents of palladium and palladium alloy electrodes as a function of their hydrogen contents

Electrochemical exchange currents i0 have been measured on palladium/hydrogen and on gold (18.8 %)/palladium/hydrogen electrodes as a function of their hydrogen contents. The values of i0 are markedly dependent upon the hydrogen content of the electrodes. Results are interpreted in terms of the expected dependence of i0 upon the equilibrium hydrogen pressure corresponding to the hydrogen content of the electrodes.

Kinetics of rehydration of crystalline anhydrides. Manganous formate

The anhydride resulting from the dehydration of manganous formate dihydrate is crystalline and its skeletal structure is distinct from the dihydrate. Under the proper conditions of temperature and water vapour pressure the freshly dehydrated anhydride rehydrates readily and completely to the dihydrate. Rehydration against time curves have been obtained for anhydrides prepared from the dihydrate which was in the form of individual single crystals, crystalline powder, ground powder and reactor-irradiated powder. The pressure, time and temperature dependences of the rehydration process have been determined. The extent of rehydration is described by a square-root dependence on time. This suggests that the rehydration is diffusion-controlled. The rate of rehydration increases markedly with pressure. Below a supersaturation ratio of approximately 10, rehydration does not occur; rather there is an appreciable sorption. The rate of sorption is diffusion-controlled with an energy of activation for diffusion of 12.0 kcal /mol. Isotherms have been determined for the sorbed water.

Activation energy for the dehydration of nickel oxalate dihydrate

Extrapolation of rate data for the dehydration of nickel oxalate dihydrate to conditions of zero mass of sample yields data uninhibited by water vapour and an energy of activation of 31·0 kcal mol–1 which is significantly greater than existing values.