Mullite-type Na0.67Al6O9.33 and a discussion of iota-alumina
Mullite-type Na0.67Al6O9.33 and a discussion of iota-alumina
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DOI：
10.1016/j.jeurceramsoc.2020.03.038
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发表时间：
2020-09-01
影响因子：
5.7
通讯作者：
Fischer, Reinhard X.
中科院分区：
文献类型：
--
作者：
Lenz, Stephan;Schneider, Hartmut;Fischer, Reinhard X.
在过去的六十年里，几位作者表示，他们已经合成了iota-氧化铝（iota-Al2O3），它是莫来石组成系列Al-2[Al2+2xSi2-2x]O10-x（x = 1）的假设端元。iota-氧化铝被认为是一种不含二氧化硅的铝酸盐，具有类似莫来石的X射线衍射图样。然而，尚未提供有关其晶体结构的详细信息。因此，我们重现了 iota-Al2O3 的典型溶胶-凝胶合成，并通过 X 射线粉末衍射 (XRPD)、EDS 分析和热处理对所得材料进行了研究。我们的粉末衍射图符合所有已发表的 iota-氧化铝 XRPD 数据，但 Rietveld 和 EDS 分析表明，假定的 iota-Al2O3 实际上是钠铝酸盐莫来石 (Na0.67Al6O9.33)，其伪四方晶系：a = 7.6778(4) 埃，b = 7.6767(3) 埃，并且c = 2.9163(1) 埃。因此，我们假设文献中大多数被称为 iota-氧化铝的相实际上是钠铝酸盐莫来石。因此，莫来石型结构的iota-Al2O3是否存在仍然存在争议。
Within the last sixty years, several authors stated that they have synthesized iota-alumina (iota-Al2O3), the hypothetical endmember of the mullite compositional series Al-2[Al2+2xSi2-2x]O10-x with x = 1. Iota-alumina is supposed to be a silica-free aluminate having a mullite-like X-ray diffraction pattern. However, no detailed information about its crystal structure has been provided. Therefore, we reproduced a typical sol-gel synthesis of iota-Al2O3 and investigated the obtained material by X-ray powder diffraction (XRPD), EDS analysis, and thermal treatment. Our powder-diffraction diagrams conform to all published XRPD data of iota-alumina, but Rietveld and EDS analyses revealed that the putative iota-Al2O3 actually is a Na-aluminate mullite (Na0.67Al6O9.33) with its pseudo-tetragonal metric: a = 7.6778(4) angstrom, b = 7.6767(3) angstrom, and c = 2.9163(1) angstrom. For this reason, we assume that most of the phases designated as iota-alumina in the literature are in fact Na-aluminate mullites. Thus, the existence of iota-Al2O3 with mullite-type structure is still a matter of debate.