Phase Change And Morphology Evolution Patterns In Hydrogen Reduction Of Molybdenum Oxide From Medium-scale Tests

Molybdenum has been widely used in metallurgical, electronic, mechanical, aerospace and other industry fields due to its good physical properties. Despite many scholars had researched on the process and kinetics mechanism of molybdenum preparation through two-stage reduction by hydrogen, which were all mini-scale tests distinct greatly from actual production. Based on the actual production conditions in factory, the processing parameters of hydrogen reduction of molybdenum oxide, their phase change and morphology evolution were researched in detail by the medium-scale tests.The transformation laws of reduction rate in the course of the two-stage reduction process was researched by changing the reduction temperature, hydrogen flow, size of the molybdenum boat, reduction time and material thickness respectively. The process and products were investigated by employing X- diffraction(XRD) and scanning electron microscopy(SEM). The main results are as follows.(1) Reduction rate was increased as the reduction temperature raised. However, over-rising temperature would cause stage-one reduction to be easily over-reductive and agglomerative, and stage-two reduction to be easily over-burnt. The best reduction temperature of two stages was 540℃ and 920℃.(2) Reduction rate raised with the increase of hydrogen flow. When the hydrogen was excessed, reduction rate changed a little while reduction temperature became the main factor of the two stages reduction. The best hydrogen flow of two stages were all 1.0m3/h.(3) When other conditions were fixed and material thickness less than or equal to half molybdenum boat height, the higher the height of molybdenum boat wall relative to material thickness was, the lower reduction rate was. Therefore, it’s advisable to choose the molybdenum boat whose height is equivalent to that of material layer.(4) When the height of molybdenum boat and material thickness were same, the reduction rate decreased with the increase of the thickness of material under the same reduction condition. Material thickness had an effect on products phase of first stage reduction. When MoO3 being reducted for 60 min, the upper-layer products were MoO2 while the inner layer products were mainly M4O11 as the contact of middle and lower layer material with hydrogen was impeded. After the reduction for 70 minz Mo appared in upper-layer products and middle-and-lower-layer products were well-reducted MoO2.(5) It was a continuous reduction process that MoO3 transformed into MoO2 in which Mo4O11 was the intermediate phase. MoO3â†'Mo4O11 and Mo4O11â†'MoO2 happened simultaneously, however the reaction rate of the former reaction was higher. There was no intermediate phase in the process of MoO2â†'Mo.In addition, microstructure evolution during MoO2â†'Mo was in accordance with the split model.