Atomic absorption: another way for phase transition characterization

Abstract

Phase transitions ocurring in compounds present at ppm levels in powders can be qualitatively and quantitatively observed by atomic absorption spectrometry. Thermodynamic and kinetic aspects of atomic vapour formation during a phase transition are considered. A first generation apparatus for phase transition characterization by atomic absorption spectrometry (PTCAAS) measurements by a fluidized bed technique is presented. As a typical application of this new technique, the determination of ppm amounts of a mixture of mercury(I) and mercury(II) salts in sodium iodide is discussed. The PTCAAS method allows thermal analysis of minor components present in powdered mixtures or as surface layers on solid substrates. By these means one can often obtain data concerning physical state, oxidization state and behaviour during reactions or near equilibrium conditions of low concentration species, for which usual thermal analysis, X ray diffraction or electron microprobe techniques become ineffective. Thus, it could be shown that drying a molar solution of sodium iodide containing less than 10 ppm of sodium iodomercurate results in the formation of solid mercury(I) iodide and correlated destruction of the mercurate complex.