The thermal reactions of muscovite studied by high-resolution solid-state 29-Si and 27-AI NMR

摘要: Studies of two muscovites different iron contents, using solid-state NMR with magic-angle-spinning (MAS) combined X-ray powder diffraction, thermal analysis and57Fe Mossbauer spectroscopy, suggest that dehydroxylation occurs by a homogeneous rather than an inhomogeneous mechanism, forming dehydroxylate in which the aluminium is predominantly 5-coordinate. On further decomposition at about 1100° C, tetrahedral layer and interlayer K+ form feldspar-like phase similar to leucite (KAISi2O6), remainder spinel, which, contrary previous suggestions, appears contain little silicon. Further heating induces formation mullite (AI6Si2OP13), and, higher-iron sample, corundum (α-Al2O3), addition phase. The presence impurity enhances recrystallization reactions promotes conversion corundum, eventually becomes sole aluminous product high-iron sample. In samples fired higher temperatures, only resonance detectable by27AI NMR, probably because most located either or phases, it broadens octahedral beyond detection.