H₂O and the dehydroxylation of phyllosilicates: An infrared spectroscopic study

As shown by in situ infrared spectroscopy and analysis of quenched samples, phyllosilicates (muscovite, sericite, pyrophyllite, and talc) under dehydroxylation conditions lack the characteristic bands near 1600 cm ^-1 (bending) and 5200 cm^-1 (combination) of H ₂O, and they contain virtually no H₂O but an abundance of OH. This observation appears to be at variance with the formal description of dehydroxylation in bulk samples as 2(OH) → H₂O + O, whereas it is suggested that hydrogen diffuses in the form of (OH)^- or/and H⁺ in dehydroxylation. The upper limit of H₂O in the dehydroxlated bulk is likely to be at the parts per million level in phyllosilicates that contain structural OH ions equivalent to 4-5 wt% H ₂O. The observations suggest that H₂O molecules are probably formed near the surface of the sample.