Mechanism of Calcination of Ammonium Molybdate with Lanthanum by Centrifugal Drying Method
Ammonium molybdate with lanthanum was prepared by centrifugal drying,which was calcined to molybdenum trioxide with lanthanum.The thermal decomposition of ammonium molybdate with lanthanum in air was analyzed by XRD and TG-MS,and the morphology and physicochemical properties of molybdenum trioxide with lanthanum were studied at different calcination temperatures.The result shows that the structure of molybdenum trioxide with lanthanum is amorphous and microspheres exist with hollow space inside.There are three stages in the process of the thermal decomposition of ammonium molybdate with lanthanum.Firstly,the centrifugal drying powder changes from amorphous to crystalline state due to heat-treatment from room temperature to 196.5 ℃.Secondly,the residual ammonia ion in ammonium molybdate is decomposed from 196.5 ℃ to 337.8 ℃,and metastable molybdenum trioxide is formed.Finally,metastable h-MoO3 turns into α-MoO3 from 337.8 to 410.1 ℃.Molybdenum trioxide with lanthanum prepared at different calcined temperatures inherits the morphology of centrifugal drying powder with the increase in temperature,the surface of powder is coarser,the breakage of powder is more serious,and the internal small particles of powder change from irregular bonded state to relatively regular flake.The change of calcined temperature has little effect on the contents of the impurity elements in molybdenum trioxide with lanthanum,but with the increase in calcined temperature,the apparent density and particle size reduce slightly.
ammonium paramolybdate with lanthanumcalcinationcentrifugal drying
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