Speciation and diffusion profiles of H2O in water-poor beryl: comparison with cordierite

摘要: This paper reports on water speciation and diffusion in synthetic beryl samples treated CO2-rich atmosphere, at 700 MPa 800 °C, respectively. The study has been conducted by means of polarized FTIR (Fourier transform infrared) integrated with FPA (focal plane array) imaging. As expected, the infrared spectra show presence CO2 but also minor H2O interpreted as resulting from moisture present starting materials used for experiments. FPA-FTIR images that diffuses into matrix along structural channels oriented parallel to [001]. Spectra collected profiles c-axis subtle changes a function distance crystal edge; these can be correlated progressive change coordination environment channel, response varying H2O/alkali ratio. In particular, data when 2H2O > Na+ apfu (atoms per formula unit), assume both type I II orientation; latter case, each Na cation coordinates two H2O[II] molecules (doubly coordinated H2O). If < apfu, then are singly cation. same feature is observed commented structurally related cordierite. Diffusion coefficients activation energies have determined types molecules.