High pressure synthesis of a new aluminium silicate: Al5Si5O17 (OH)

A new aluminium silicate has been produced under hydrous conditions from Al2O3-SiO2 oxide mixes with Si/Al ratios close to unity, at pressures greater than 100 kilobars and at about 1, 000°C. X-ray powder photographs indicated one dominant new phase. From analyses of the electron diffraction Laue zones of minute fragments (∼1μm), a monoclinic structure that fitted the X-ray powder results was identified. This monoclinic structure is described in terms of nine close-packed layers of oxygen with the unit cell containing 72 oxygen atoms. Assuming Si/Al equals 1, the composition of this phase is Al20Si20O72H4. The calculated density of 4.03 g/cc is in good agreement with the value of 4.02 g/cc estimated from the refractive index measurements.