FORMATION MECHANISM OF ALUMINUM HYDROXIDE POLYMORPHS
FORMATION MECHANISM OF ALUMINUM HYDROXIDE POLYMORPHS
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DOI：
10.1346/ccmn.1993.0410509
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发表时间：
1993-10-01
影响因子：
2.2
通讯作者：
HUANG, PM
中科院分区：
文献类型：
--
作者：
VIOLANTE, A;HUANG, PM
对Al(OH)(3)晶型的形成机理进行了大量的研究。Al沉淀产物的性质对Al(OH)(3)晶型形成的影响尚不清楚。对初始pH为8.2、柠檬酸/铝摩尔比为0.01、时效3小时至60天的铝沉淀进行了X射线衍射、红外、热分析和电子显微镜观察，结果表明，从最初形成的非晶态物质向拟薄水铝石的转变是通过形成具有不同有序度和颗粒大小的中间物质而发生的，这些中间物质显然具有广泛的溶解度。将铝沉淀产物悬浮液的pH值提高到10.0，在3h、3、11、31、60d或更长时间后，结晶产物分别为水铝石、钠闪石和水铝石、钠闪石和拟薄水铝石、拟薄水铝石和三水铝石以及拟薄水铝石。这项工作表明，随着起始Al析出物性质的改变，它们的溶解速度明显改变，从而形成各种Al(OH)(3)晶型。因此，这些数据证实了这样一种假设，即Al(OH)(3)晶型的形成机制由其形核速度决定，而形核速度又受最初形成的非晶态或无序Al-氧化物的溶解速度的影响。
Substantial studies have been carried out to investigate the mechanism of the formation of Al(OH)(3) polymorphs. The influence of the nature of Al precipitation products on the formation of Al(OH)(3) polymorphs still remains obscure. In this study, X-ray diffraction, infrared and thermal analyses, and electron microscopic observations of the Al precipitates formed at the initial pH 8.2 and at a citric acid/Al molar ratio of 0.01 and aged for 3 hr to 60 days revealed that the transformation from the initially formed noncrystalline materials to pseudoboehmite occurred through the formation of intermediate materials with various degrees of ordering and sizes of particles that apparently had a wide range of solubility. By increasing the pH of the suspension of precipitation products of Al to 10.0 after 3 hr and 3, 11, 31, and 60 days or longer, the crystalline precipitation products were bayerite, nordstrandite and bayerite, nordstrandite and pseudoboehmite, pseudoboehmite and gibbsite, and pseudoboehmite, respectively. This work shows evidence that, as the nature of the starting Al precipitates changed, the rate of their dissolution apparently changed, and various Al(OH)(3) polymorphs consequently formed. Therefore, the data substantiate the hypothesis that the mechanism of the formation of an Al(OH)(3) polymorph is determined by the rate of its nucleation, which is, in turn, influenced by the rate of dissolution of the noncrystalline or poorly ordered Al-oxides initially formed.