Thermal and Mechanochemical Initiated Phase Transformations in Silver Carboxylates

Abstract

Small-angle X-ray scattering, electron and optical microscopy, and thermal analytical investigation of the structure and morphology changes in silver laurate, myristate, palmitate, and stearate show that these fatty acid silver salts undergo an irreversible Martensitic phase change in the 110 – 120°C temperature range. This phase change is characterized by the formation of a more symmetrical phase, compared to the initial crystalline silver carboxylate. The formation of the high temperature phase proceeds according to a Martensitic transition mechanism, which is a diffusionless transformation by a large number of atoms in a cooperative movement. An ordered orientation is observed that separates Martensitic layers in the matrix of the initial crystal-line silver carboxylate. Along with this first phase transition, a micro-twin structure on the basal plane of the crystal is formed. Increasing the temperature above 120°C leads to a decrease in the distance between silver layers in the high temperature phase structure, which is a result of the disordering of the carbon chains of the molecule.