Characterization of condensed phase species produced during the thermal treatment of metal chlorides on a graphite platform using surface analysis techniques

The identification and distribution of condensed phase species produced on a graphite platform at temperatures between 200 and 2000 °C was studied using data obtained by scanning electron microscopy (SEM), energy dispersive (ED) X-ray spectrometry and Raman microanalysis. The first general conclusion is that there is no unique path in the thermal transformation of the metal chlorides tested, even for a particular metal chloride. Sodium, potassium and calcium chlorides showed similar vaporization characteristics, evolving mainly as monochlorides, while magnesium, beryllium and aluminium mainly vaporized as free atoms, following transformation caused by hydrolysis. The replacement of chlorine atoms by oxygen occurred at lower temperatures for beryllium and aluminium chlorides than for magnesium chloride. There were some particular areas on the platform surface where other mechanisms, such as hydrolysis of calcium chloride and dissociation of sodium chloride in the condensed phase, seemed occasionally to occur to a minor extent.