HVEM studies of the sintering of MgO nanocrystals prepared by Mg(OH) 2 decomposition

Abstract

Hot-stage high-voltage electron microscopy (HVEM) combined with high-resolution electron microscopy (HREM) has been employed to study the microstructural evolution during in-situ decomposition of thin Mg(OH) 2 flakes and during early-stage sintering of the resultant nanocomposite. The decomposition reaction is known to be pseudomorphic and topotactic, resulting in a regular composite of highly aligned nearly cubic MgO nanocrystals interspersed wit a roughly equal volume of pores. This structure was characterized by selected-area and optical-diffraction techniques as well as by HREM, depending on its microstructural scale. Immediately after decomposition and in the early stages of sintering the fine-scale and regular, nearly periodic nature of the microstructure gave rise to diffuse small-angle diffraction rings that could be used as a measure of coarsening during in-situ heating in the temperature range 350–900†C. Consistent results were obtained from electron diffraction, optical diffraction and Fourier transforms of digitized images. These measurements were complementary to direct imaging by HREM or conventional imaging techniques.