Microstructures of magnesium oxychloride

The well-crystallized phases of magnesium oxychloride (MOC) cement have been described as scroll-tubular whiskers and compared to the tobermorite crystals for a long time. However, sporadic evidence of the acicular crystals without enough and consistent detail has befuddled researchers in the microstructural studies of the cement. With the modern technology and powerful computational capability, more detailed and clarified microstructure of the MOC crystalline phases including morphology, crystal habit, grain size, and elemental composition could be revealed. This paper reports the work on microstructural examination of MOC cement providing practical information for further study of the crystal structure of the different reaction phases. The experimental results show that the crystalline phases of MOC cement are in general needle shaped crystals with a granular surface and bundled in different forms. Imprints of bundled needle shaped crystal can also be scrutinized in the massive and dense microstructure of the cement paste with high compressive strength.