机械活化氢氧化镁-勃姆石(或三水铝石)混合物合成镁铝尖晶石

Synthesis of MgAl_2O_4 spinel from mechanically activated mixtures of magnesium hydroxide-boehmite or-aluminum tri-hydroxide

以氢氧化镁、勃姆石和三水铝石为原料,按MgO与Al2O3的摩尔比为1∶1配制成氢氧化镁-勃姆石混合物和氢氧化镁-三水铝石混合物,在滚动式球磨机中加无水乙醇湿磨混合,经干燥、研碎、过筛后,采用振动球磨机进行0-40 h的高能球磨,使混合物达到不同程度的机械活化,然后在400-1 100℃的空气气氛中热处理5 h。通过对高能球磨前后物料以及热处理前后物料的XRD分析,研究了高能球磨对物料的晶体形态及其尖晶石开始生成温度和尖晶石完全生成温度的影响,并简要讨论了机械活化促进尖晶石生成的机理。结果表明：1）机械活化使得起始物料组分由晶体形态向无定形态转化,减小了物料的颗粒尺寸和晶粒尺寸,提高了起始物料组分在亚微米级的混合均匀性;2）未经机械活化的物料在1 000℃煅烧5 h后没有完全生成尖晶石,而经过5 h机械活化的物料在同样的煅烧条件下形成了纯相尖晶石,即机械活化降低了尖晶石的完全生成温度,同时也降低了尖晶石的开始生成温度;3）氢氧化镁-勃姆石混合物比氢氧化镁-三水铝石混合物更有利于尖晶石的生成,可能归因于无定形三水铝石在研磨过程中转变成无定形勃姆石要消耗一定的机械能量。

Magnesium hydroxide, boehmite and amorphous aluminum tri-hydroxide were used as the starting materials. Two mixtures of magnesium hydroxide -boehmite and magnesium hydroxide -amorphous aluminum tri-hydroxide with MgO/Al2O3 molar ratio of 1 ： 1 were mixed in alcohol with a rolling/rotational ball mill. After drying,crushing and screening,the mixtures were ground with a high-energy ball mill for 1 -40 h to make the mixtures be mechanically activated to different degrees. Then the mixtures were fired in air for 5 h at temperatures between 400 and 1 000 ℃. The influence of high-energy milling on crystalline change of the starting materials, and inception and complete temperatures of spinel formation was investigated using XRD. The mechanisms of mechanical activation for enhancing formation of spinel were briefly discussed. The results indicate that： 1 ）Mechanical activation transformed the starting crystalline components into amorphous state,reduced the particle size and crystalline size, and enhanced the mixing homogeneity of the starting materials at sub-micro level;2）Pure spinel was obtained from the mixture with mechanical activation after firing at 1 000 ℃ for 5 h,while pure spinel was not formed from the mixture without mechanical activation after firing at the same condition, showing that mechanical activation decreased the complete temperature of spinel formation. The inception temperature of spinel formation was also decreased by mechanical activation ;3）Spinel was preferably formed from the mixture of magnesium hydroxide and boehmite than from the one of magnesium hydroxide and amorphous aluminum tri-hydroxide possibly because a certain amount of mechanical energy was consumed during transformation of amorphous aluminum tri-hy- droxide into amorphous boehmite.