SINTERING OF PSEUDO-BOEHMITE AND GAMMA-AL2O3
SINTERING OF PSEUDO-BOEHMITE AND GAMMA-AL2O3
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DOI：
10.1007/bf01130139
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发表时间：
1991-11-01
影响因子：
4.5
通讯作者：
GEUS, JW
中科院分区：
文献类型：
--
作者：
TIJBURG, IIM;DEBRUIN, H;GEUS, JW
研究了拟薄水铝石、拟薄水铝石脱水产生的针状γ-Al_2O_3和γ-Al_2O_3 EX明矾的烧结。用X射线衍射仪、选区电子衍射仪和BET比表面积测量等手段对烧结过程进行了研究。与α-Al_2O_3的固相反应导致比表面积急剧下降，降至10m2g-1以下。针状拟薄水铝石和γ-Al_2O_3载体呈现中间状态，针状颗粒呈棒状，比表面积约为300~100m2g-1。确定了生成α-Al_2O_3的反应是通过形核和生长机制进行的，因此烧结是通过形核和生长机制进行的。限速步骤是α-Al_2O_3的形核。因此，基本氧化铝颗粒之间的接触控制着烧结过程。拟薄水铝石的针状基元粒子与所研究的伽马-Al_2O_3之间的接触导致样品在1050℃下保持145小时后，与α-Al_2O_3的反应几乎完全。明矾的分解产生了非常小的颗粒，它们之间的接触可以忽略不计。因此，表现出更高的热稳定性。氧化铝用水处理，干燥后形成干凝胶，在干凝胶中，基本粒子之间的接触更加紧密。因此，在1050摄氏度的处理会导致表面积急剧下降。
Sintering of pseudo-boehmite, acicular gamma-Al2O3 produced by dehydration of pseudo-boehmite, and gamma-Al2O3 ex alum was investigated. The sintering process was studied by X-ray diffraction, transmission electron microscopy with selected area electron diffraction and BET surface area measurements. The solid state reaction to alpha-Al2O3 causes a steep drop of the surface area to less than 10m2g-1. The acicular pseudo-boehmite and gamma-Al2O3 supports exhibit an intermediate state where the acicular particles assume a rod-like shape and the surface area falls from about 300 to 100 m2g-1. It was established that reaction to alpha-Al2O3 and, hence, sintering proceeds via a nucleation and growth mechanism. The rate-limiting step is nucleation of alpha-Al2O3. Consequently, the contacts between the elementary alumina particles dominate the sinter process. The contact between the acicular elementary particles of pseudo-boehmite and gamma-Al2O3 studied leads to the reaction to alpha-Al2O3 to be almost complete after keeping samples for 145 h at 1050-degrees-C. Decomposition of alum produces very small particles showing negligible mutual contacts. Consequently an elevated thermal stability is exhibited. Treatment of the alumina ex alum with water and drying results in a xerogel in which contact between elementary particles is much more intimate. Accordingly, treatment at 1050-degrees-C causes a sharp drop in surface area.