Factors for maintenance of a high surface area of silica-coated α-alumina after heating >1573 K
Factors for maintenance of a high surface area of silica-coated α-alumina after heating >1573 K
复制标题
加热 >1573 K 后保持二氧化硅涂层 α-氧化铝高表面积的因素
DOI：
10.1039/jm9930300861
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发表时间：
1993
影响因子：
--
通讯作者：
Toshiaki Mori
中科院分区：
文献类型：
--
作者：
T. Horiuchi;T. Sugiyama;Toshiaki Mori
为了在 > 1573 K 加热后保持高表面积，多孔氧化铝（TM-100 和 ALO-4）上涂有一层薄薄的二氧化硅。在没有涂层的情况下，两种氧化铝在 1473 K 时都完全转变为 α 相。用 5.2 wt.% 二氧化硅涂覆 TM-100 不会导致 1573 K 时 θ 相发生变化，而对于 2.7 wt.% 二氧化硅则几乎完全转变为 α-氧化铝。对于 3.6 wt.% 的二氧化硅，θ 相和 α 相在 1573 K 下共存。由于相变不完全，TM-100 的表面积很高，即对于 5.2 wt.% 和 3.6 wt.% 的涂层二氧化硅，TM-100 的表面积分别为 46 和 37 m2 g–1。在 1673 K 下加热后，所有二氧化硅涂层的 TM-100 均转化为 α-氧化铝，并且还形成莫来石，涂层二氧化硅含量为 3.6 和 5.2 wt.%。含有 2.7 wt.% 涂层二氧化硅的 α-Phase TM-100 的表面积为 17 m2 g–1。然而，大量的涂层二氧化硅并没有导致高表面积的维持，这可能是由于莫来石的形成。电子显微照片显示，由于具有高表面积，二氧化硅涂层显着抑制了晶体生长。尽管对于 ALO-4 也观察到二氧化硅涂层的类似效果，但这些效果不太明显。在1573 K下加热ALO-4时，即使大量涂覆二氧化硅，相变也几乎完成，并且表面积低于TM-100。起始 TM-100 的高分散特性可以解释所观察到的二氧化硅涂覆的 α-氧化铝的高表面积。 TM-100 和 ALO-4 之间二氧化硅涂层效果的差异也可能归因于它们分散特性的差异。
In order to maintain a high surface area after heating at > 1573 K, porous aluminas (TM-100 and ALO-4) were coated with a thin layer of silica. Without coating, both the aluminas were transformed completely to the α-phase at 1473 K. Coating TM-100 with 5.2 wt.% silica caused no change in the θ-phase at 1573 K, while almost complete transformation to α-alumina occurred for 2.7 wt.% silica. For 3.6 wt.% silica, both the θ- and α-phases coexisted at 1573 K. As a result of the incomplete phase transformation, the surface area of TM-100 was high, i.e. 46 and 37 m2 g–1 for 5.2 and 3.6 wt.% coating silica, respectively. After they had been heated at 1673 K, all silica-coated TM-100s were transformed to α-alumina and mullite was also formed for 3.6 and 5.2 wt.% coating silica. α-Phase TM-100 with 2.7 wt.% coating silica exhibited a surface area of 17 m2 g–1. However, a large amount of coating silica did not lead to the maintenance of a high surface area, probably owing to the formation of mullite. Electron micrographs revealed that, in accordance with a high surface area, silica coating markedly suppressed the crystal growth. Although similar effects of silica coating were also observed for ALO-4, these effects were less pronounced. On heating ALO-4 at 1573 K, the phase transformation was almost completed even for the large amount of coating silica, and surface area was lower than that of TM-100. The highly dispersive character of the starting TM-100 may explain the observed high surface area of the silica-coated α-alumina. The difference in the effect of silica coating between TM-100 and ALO-4 may also be ascribed to the difference in their dispersive characteristics.