离心干燥制备含镧钼酸铵的焙解机制

Mechanism of Calcination of Ammonium Molybdate with Lanthanum by Centrifugal Drying Method

本实验采用离心干燥法,含镧钼酸铵为原料,将其焙解为含镧三氧化钼。通过XRD和TG-MS对含镧钼酸铵在空气中的热分解过程进行了分析,并研究了不同焙解温度制备含镧三氧化钼的形貌及理化性能。结果表明,含镧钼酸铵为非晶态、中空近球形颗粒,在热分解过程中经历了3个阶段:室温至196.5℃,离心干燥粉发生从非晶态到晶态的转变;196.5~337.8℃,铵根离子完全分解,有亚稳态h-MoO_(3)生成;337.8~410.1℃,h-MoO_(3)发生相变生成α-MoO_(3)。含镧三氧化钼“遗传”了离心干燥粉形貌,为近球形,随着焙解温度升高,颗粒表面越粗糙,破碎颗粒增多,内部小颗粒由不规则的粘结颗粒向规则的片状转变。焙解温度对含镧三氧化钼杂质元素含量影响不大,但随着温度升高,含镧三氧化钼的粒度和松装密度稍有减小。

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-MoO_(3) turns intoα-MoO_(3) 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.