Research On Influencing Factors Of The Grain Size Of MoSi₂Prepared By Self-propagating High-temperature Synthesis

MoSi2heating element can be used various atmosphere, which is particularly suitable for the oxidation atmosphere, and its maximum temperature has reached1850℃. MoSi2heating element widely is used for glass, ceramics, electronic and electrical, semiconductor materials and other industrial fields as well as laboratory equipment. As the self-propagating high-temperature synthesis (SHS) has the advantages of energy-saving, simple process, easy to operate and fast response. Raw material is prepared by self-propagating high-temperature synthesis. In order to better control of the particle size and morphology of combustion product, it is necessary to research the processing parameters, such as raw materials, atmosphere, body molding pressure, preheating temperature and addition, In this work, the morphology and particle size of the raw materials, body molding pressure and addition were investigated.The molding pressure mainly affects the relative density of the green body, the greater body molding pressure, the greater the relative density. With increasing the pelletizing pressure, the size and shape of MoSi2grain change obviously. The grain of MoSi2is spherical, the contacts between grains is loose under the lower molding pressure, while the grains are irregular in shape and grow larger under the higher molding pressure. The molding pressure had no influence on the phase composition.Raw materials, Mo and Si powders, were ground respectively. The milled Mo powder exhibited flake agglomerates due to its fracture-welding process. Nevertheless, fine particles appeared in the milled Si powder, because of its brittle fracture process.The morphology of Mo powder has no effect on phase composition of the products.But with increasing milling time, the grain size of the synthesized product was gradually increased, and the contour of the crystal grains becomes gradually clear. However, the particle size of Si powder had a significant influence on phase composition of products. As grinding time increases, the impurity phase Mo5Si3obviously appeared.The fracture strength and toughness of MoSi2material is insufficient, so it is difficult to install the heating element. In this work, two parts are included:1.The Mo powder Si powder and Al2O3powder were mixed, then studied the morphology of synthesized product.2.The Mo powder and Al2O3powder were co-milled for5h, then prepared MoSi2by SHS. The result show that with the increase of content of Al2O3, the particle size of grains become smaller. After Mo powder and Al2O3powder were co-milled, the size of the flake Mo becomes small, the thickness of the flake Mo increases. At the same time, the surface of the flake Mo is not smooth. In addition, some cracks appeared in the surface of the flake Mo. The purity of the combustion product was improved, which was synthesized by co-milled Mo powder and Al2O3powder.