27Al nuclear magnetic resonance spectroscopy investigation of thermal transformation sequences of alumina hydrates. Part 1.—Gibbsite, γ-Al(OH)3

摘要: High-resolution 27Al magic-angle spinning nuclear magnetic resonance spectroscopy (MAS NMR)(78.15 MHz) spectra are reported for commercial and natural gibbsites materials occurring in the thermal transformation sequences of gibbsite (boehmite; χ, α ρ-aluminas; calcines produced at 400, 700, 900 1000 °C). Separate peaks assignable to aluminiums near-regular six- four-co-ordination oxygen observed which use such sites is believed occur. For ρ-alumina a third peak (at 27 ppm) seen due presence Al five-co-ordination. κ-Alumina may retain approximately hexagonal-close-packed oxygens (with defect structure leading grossly asymmetric contributory line from four-co-ordinate Al) or contain some five-co-ordinate (AlO5) addition AlO6 AlO4 environments (and hence have packing deviating h.c.p.). Distortions/disorders (when present) result broader underlying signals manifest themselves instrumentally most disordered systems as wings extending either side central spectrum.