HVEM STUDIES OF THE SINTERING OF MGO NANOCRYSTALS PREPARED BY MG(OH)2 DECOMPOSITION

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 with a roughly equal volume of pores. This structure was characterized by selected-area and optical-diffraction techniqucs 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 measurc of coarsening during in-situ heating in the temperature range 350-900-degrees-C. Consistent results were obtained from electron diffraction, optical diffraction and Foufier transforms of digitized images. These measurements were complementary to direct imaging by HREM or conventional imaging techniques.