Dehydroxylation of muscovite: study of quenched samples

作者：Heller Kallai Lisa^*; Lapides Isaak

来源：Physics and Chemistry of Minerals, 2015, 42(10): 835-845.

DOI：10.1007/s00269-015-0767-4

• Muscovite
• Partial dehydroxylation
• IR spectra
• XRD
• Reaction mechanism

Despite extensive research, many aspects of the changes that occur in muscovite on heating remain unclear. This study concentrated on quenched samples, to supplement data obtained in situ by previous investigators, which seemed to suggest that structural changes precede dehydroxylation. Samples of muscovite were heated to different temperatures at various heating rates and soaking times, rapidly quenched in air and cooled in a dry atmosphere. Infrared spectra (IR) and X-ray diffraction patterns (XRD) were recorded. Aliquots of a single flake, about 20-40 A mu m thick, were used for each set of experiments. Thermal changes in these flakes, heated at 10 A degrees C/min, were almost completely reversed at a parts per thousand currency sign780 A degrees C. Above that temperature, or on more prolonged heating, XRD showed two phases, residual muscovite and dehydroxylated muscovite, with basal spacings ranging between similar to 19.90-19.94 and similar to 20.06-20.14 angstrom, respectively. As dehydroxylation progressed, the basal spacings of all residual muscovites were reduced relative to those of the original samples. The decreases were small, but consistent. The OH stretching bands in IR spectra of the muscovites showed four maxima. After partial dehydroxylation, the frequencies of these maxima remained almost unchanged, but the intensities of the two lower-frequency components were reduced more rapidly than those of the other two. Changes were also observed in the 900- to 600-cm(-1) region of the spectra, reflecting changes in the configuration of the tetrahedral sheets. The structure of the dehydroxylated phase changed with temperature. The trends are general, but the details are sample specific. The decrease in basal spacings of residual muscovite and the corresponding changes in the IR spectra, supported by results obtained in situ by previous investigators, indicate that dehydroxylation proceeds through one or more intermediate phases. This differs from dehydroxylation of other phyllosilicates reported in the literature, which do not form an intermediate phase.

• 出版日期2015-11