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Phase formation and crystal-chemical characterization of low- and high-alumina mullite-type compounds

低铝和高铝莫来石型化合物的相形成和晶体化学表征

基本信息

批准号：
283003582
负责人：
Professor Dr. Reinhard X. Fischer
金额：
--
依托单位：
Fachbereich 05: Geowissenschaften
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2016
资助国家：
德国
起止时间：
2015-12-31 至 2019-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/283003582?language=en
关键词：
Phase formation crystal chemical characterization

项目摘要

It is the aim of this project to understand the complete structural evolution of the phases in the alumino-silicate system of mullite-type compounds with the endmembers sillimanite (Al2O3 . SiO2, x=0) and jota-alumina (Al2O3, x=1) in the compositional series Al4+2xSi2-2xO10-x. While sillimanite and synthetic mullite with its most abundant phases 2:1-mullite (2Al2O3 . SiO2, x=0.4) and 3:2-mullite (3Al2O3 . 2SiO2, x=0.25) have been studied extensively within the last decades, there is essentially no information on the crystal structures of these compounds at the low (x < 0.2) and high-alumina (x > 0.8) side of the series. Minerals (usually containing some Fe) are known to exist in the low-alumina range, but there are no crystal-structure investigations available. The existence or nonexistence of jota-alumina is still a matter of debate. In hypothetical models derived from DFT calculations a highly disordered structure was proposed (Aryal et al., Phys. Rev. B84, 2011, 174123) with AlO6 and AlO5 polyhedra forming the polyhedral chain crosslinked by di-, tri-, and tetraclusters of AlO4 tetrahedra. Instead, we suggest that it could consist of AlO6 octahedra and of AlO4 forming tetrahedral tetraclusters only. However, experimental proof is still missing. We propose to study a series of natural mullites already available and to be collected in the Eifel area as members of the low-alumina compounds. Since we have shown just recently (Fischer et al., Amer. Mineral. 2015, in press) that a mineral exists which has structural features from both sillimanite (Si/Al ordering) and mullite (O vacancies) it will be especially interesting to characterize these Eifel minerals structurally and microchemically. It is also planned to synthesize these intermediate low-alumina phases by annealing sillimanite at high temperatures and pressures in a piston cylinder apparatus. High-alumina compounds including jota-alumina will be synthesized in a microwave system following known routes. It will be the first time that crystal-structure investigations are performed on these compounds. Since mullite-type materials are most important ceramic constituents it will be extremely important to extend our knowledge on these compounds towards the hitherto unknown crystal structures of the low- (x<0.2) and high- (x>0.8) alumina mullites and mullite-type phases.

这是本项目的目的，以了解完整的结构演变的阶段，在铝硅酸盐系统的莫来石型化合物与端员硅线石（Al 2 O3。SiO2，x=0）和氧化铝（Al 2 O3，x=1）组成系列Al 4 + 2xSi 2 - 2xO 10-x。而硅线石和合成莫来石以其最丰富的相2：1-莫来石（2Al 2 O3. SiO2，x=0.4）和3：2-莫来石（3Al 2 O3. 2SiO 2，x=0.25）的晶体结构进行了广泛的研究，但基本上没有关于这些化合物在该系列的低（x < 0.2）和高氧化铝（x > 0.8）侧的晶体结构的信息。已知矿物（通常含有一些Fe）存在于低氧化铝范围内，但没有可用的晶体结构研究。氧化铝的存在与否仍然是一个有争议的问题。在从DFT计算导出的假设模型中，提出了高度无序的结构（Aryal等人，Phys.Rev.B84，2011，174123），其中AlO 6和AlO 5多面体形成通过AlO 4四面体的二簇、三簇和四簇交联的多面体链。相反，我们认为，它可以由AlO 6八面体和AlO 4形成四面体四簇。然而，实验证据仍然缺失。我们建议研究一系列的天然莫来石已经可用，并收集在艾菲尔地区的低铝化合物的成员。由于我们最近已经表明（Fischer等人，Amer.Mineral.2015，出版中），存在一种矿物，其具有来自硅线石（Si/Al有序）和莫来石（O空位）的结构特征，在结构和微观化学上表征这些Eifel矿物将是特别有趣的。还计划通过在活塞缸装置中在高温和高压下退火硅线石来合成这些中间低氧化铝相。高氧化铝化合物，包括氧化铝将在微波系统中按照已知的路线合成。这将是首次对这些化合物进行晶体结构研究。由于莫来石型材料是最重要的陶瓷成分，因此将我们对这些化合物的知识扩展到迄今未知的低（x<0.2）和高（x>0.8）氧化铝莫来石和莫来石型相的晶体结构将是极其重要的。