The i.r. spectra of some hydrated and dehydrated calcium aluminate hydrates of the type Ca2Al(OH)6+X-·yH2O with X- = Cl-, Br-, J-, ClO3-, NO3-, ClO4- (y = 2) and X- = BrO3-, JO3- (2 <y <4), were recorded between 3800 and 200 cm-1. With increasing interaction of the interlayer water with the anions X-, the absorption bands in the region 3600-3200 cm-1 due to the interlayer water are found at smaller wave numbers. From the i.r. spectra of partially deuterated calcium aluminate hydrates it is found that, at least at room temperature, the water molecules are symmetrically bound to their surroundings. Thus, both OH groups are directed towards the anion X-. From the shift of the uncoupled stretching vibration, ¿OH or ¿OD, due to isotopically dilute HOD molecules, the hydrogen bond enthalpies were estimated; the hydrogen bond enthalpies vary from 1.8 kcal (X- = ClO4-) to 5.5 kcal (X- = JO3-). With increasing hydrogen bond enthalpy, the enthalpies of dehydration of the calcium aluminate hydrates increase.
|Journal||Spectrochimica Acta. Part A : Molecular Spectroscopy|
|Publication status||Published - 1976|