The role of dislocations in the dehydration of nickel sulphate hexahydrate. Part I. Theoretical considerations and stoicheiometry

A critical analysis of previous work on the importance of dislocations in solid-state reactions leads to the conclusion that geometric factors may be more important than energetic factors in governing enhanced reactivity. It is shown, by numerical estimates, that the energy stored at dislocations could, nevertheless, make significant differences to the overall energetics under favourable circumstances. A rough theoretical outline is given of the way in which dislocation energies may modify the free energy terms in two-dimensional nucleation at surfaces and heterogeneous three-dimensional nucleation within the bulk. The stoicheiometry of the thermal dehydration of NiSO4,6H2O, the system to be studied in detail in this series, is established by vacuum microgravimetry, X-ray powder diffraction, and differential enthalpic analysis. Five molecules of water are lost in dehydration at temperatures in the range 30–50°.