X-ray diffraction analyses of 3D MgO-based replicas of diatom microshells synthesized by a low-temperature gas/solid displacement reaction

Abstract

The nanostructural features of the gas-phase displacement reaction 2Mg(g)+SiO₂→2MgO(s)+{Si}, where SiO₂ is in the form of diatom shells were studied via X-ray diffraction and Fourier methods. Diatomaceous powder heated to 700 °C in a sealed graphite cell in the presence of Mg vapor formed MgO via a displacement reaction. Warren-Averbach analysis performed on samples reacted for different times showed an initial sharp MgO grain size distribution which broadened with time. New MgO crystallization was shown to occur until about 60 min, whereafter only MgO grain growth occurred. Median MgO crystallite size increased from 7.5 to 24.9 nm during this period, whereas microstrain decreased dramatically past 60 min annealing time.