β型四钼酸铵的制备及结晶过程

The preparation of ammonium β-tetramolybdate and the crystallization process

研究了用晶种生长法制备 β型四钼酸铵的方法 .其制备分 2步进行 :首先用酸沉法制备四钼酸铵 ;再以酸沉法制得的四钼酸铵为原料 ,氨浸后用晶种法制备 β型四钼酸铵 ,其包含 2个相关过程 (一是晶核的生成过程 ,控制pH值为 1.2 ;二是晶核的长大过程 ,控制pH值为 2～ 3) .对 2种结晶进行差热及热重分析 ,结果表明用酸沉法制得的为α型四钼酸铵 ,用晶种法制得的晶体为 β型四钼酸铵 .用晶种法制得的结晶的晶体形貌与用酸沉法制得结晶的晶体形貌相比 ,颗粒较大且均匀 .对四钼酸铵的结晶过程进行了热力学分析和动力学分析 ,说明结晶反应自发进行的趋势很强 ,速度也较快 .此外 ,初步探讨了四钼酸铵结晶过程机理和晶型的控制 。

The ammonium β tetramolybdate was prepared and the preparing process included two courses: preparing ammonium tetramolybdate by the method of acidified deposition; and preparing ammonium β tetramolybdate by the method of seeded decomposition. The second course included two processes: one was born of crystal seeds(pH=1.2), the other was growth of crystal seeds(pH=2～3). The TGA and DTA proved that the crystal was ammonium α tetramolybdate prepared by the method of acidified deposition and was ammonium β tetramolybdate prepared by the method of seeded decomposition. The thermodynamics and the dynamics of the process were analyzed. The mechanism of crystallization process and the control of the crystalline were discussed simply in this paper.