Study On The Preparation Processing Of Magnesium Oxide Whiskers

Whiskers are filamentary crystals with high aspect ratio, which are remarkable for their small dimensions, surface perfection and high strength that approach the theoretical tensile strength of the perfect crystals. Therefore, whiskers belong to attractive materials for fiber reinforcement of ceramic composites, which possess high temperature and stress applications. Magnesium oxide (MgO) whiskers are important reinforce composite materials with a high-melting point (2850℃). MgO whiskers with well-controlled dimensions attract special attention due to their unique capability.MgO whiskers were synthesized from soluble magnesium salt and sodium carbonate by a precursor decomposition route at mild conditions. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are employed to analyze the composition and morphology of the precursor and final products. The formation process of MgO whiskers such as the detailed reaction condition was investigated.The current results show that MgO whiskers with the aspect ratios between 10 and 50 have been synthesized by precursor decomposition route. By controlling the detailed reaction conditions, whiskers with different aspect ratios were obtained. According to XRD and SEM measurements, the precursors were magnesium carbonate hydrate, which was denoted as MgCO3·3H2O. MgO whiskers have been obtained by calcining the precursor whisker in muffle oven at appropriate conditions. The results indicate that the morphology of precursor had an important effect on the morphology of MgO whiskers.The shape evolution of the precursor whiskers was investigated by the analysis of SEM observations. When the precipitation begins, numerous small crystallites were initially formed from the mixture solution. With prolonging reaction time, the morphology of the synthesized samples varies from particles to whiskers. Finally, all particles were changed into whiskers with a uniform diameter distribution.The optimized reaction conditions for the preparing of MgO whiskers were determined as follows: the reaction between magnesium chloride and sodium carbonate with Mg²⁺ CO₃^2-=1:1, the raw material concentration was 1 M, the calcination temperature was 600 ℃, and the calcination time was 3 hours.