The Effect of Mechanical Deformation on Selected Chemical and Physical Properties of Crystalline Solids.

In this investigation it has been shown that microstrains which are produced by many forms of deformation can greatly affect the chemical and physical properties of crystalline solids. It has been shown that these microstrains can affect the electrode potential and corrosion properties of copper wires and powders, the reactivity of lithium fluoride powder with an acid, and the solubility of calcium carbonate in water. They can also produce phase changes as has been shown for lead monoxide with litharge and massicot, calcium carbonate with calcite, aragonite and vaterite, and stainless steel with austenite and martensite. In the case of powders deformed by milling, many of these effects, especially chemical reactivity, were previously thought to be due to small particle sizes, but this investigation has shown that, although this may account for part of the property change, the major cause is a high concentration of microstrains. This work has also demonstrated the importance of the shear stresses, which are produced in the ball mill, on the rate and course of phase transformations. These stresses generate the microstrains which provide the stored energy required to mount the energy barrier to the transformation. These shear stresses can also affect the pressure - temperature phase diagrams such that the region of stability for a particular phase may be contracted or expanded, or a new region may be produced where two phases exist together