Closed, heated reaction chamber design for dynamic high-temperature x-ray-diffraction analyses of gas/solid displacement reactions

A closed, x-ray transparent chamber for containing a hot reactive gas (generated from an internal condensed source) has been designed and evaluated for use in dynamic x-ray-diffraction analysis of a gas/solid displacement reaction. The chamber consisted of a square-bottom base and lid machined from dense pyrolytic graphite. The base contained a flat pedestal, upon which SiO2 microshells (the reactant oxide) were placed, raised above adjacent cavities holding Mg flakes (the condensed precursor to the reactive gas). Upon heating to 650 °C, the Mg evaporated and reacted with the SiO2 inside the sealed chamber. By passing incident and diffracted x rays through the vertical side walls of the chamber and by blocking undesired graphite-diffracted x rays with platinum, the Mg(g)∕SiO2(s) displacement reaction could be tracked with time. This is the first use of dynamic high-temperature x-ray diffraction analysis to monitor the progress of a displacement reaction involving a reactant gas that was generated and confined within a closed reaction chamber.