Diffuse reflectance FT-IR spectroscopic study of interactions of alpha-Al2O3/molten alkali nitrate coexisting systems

The diffuse reflectance spectra of alpha-Al(2)O(3)/molten MNO(3) (M=K(+), Li(+)) coexisting systems have been measured for the investigation of the physicochemical properties of molten nitrate at the interface of aluminum oxide. In the region of overtone and combination modes from 3000 to 1700 cm(-1), the absorption band nu(3)+nu(4) decreases with increasing specific surface area of alpha-Al(2)O(3) powder for the potassium mixtures. Gaussian resolution of nu(3)+nu(4) also exhibits changes in band positions of components with the variation in the alumina specific surface area and the nitrate melt content. The second-order derivative of the spectra in the region from 1700 to 950 cm(-1) shows a set of peaks at 1645, 1554-1516, and 1452 cm(-1) characteristic of a coordinated nitrate ion. The peak at 1337 cm(-1) suggests a possible formation of nitrite species. The maxima of nu(3)+nu(4), nu(1)+nu(2), and nu(1)+nu(4) shift toward lower frequencies with increasing temperature above the nitrate melting point. This information shows that the intramolecular bonds of NO(3)(-) are affected. These perturbations are attributed to the effect of the solid phase interacting with the liquid phase. The interaction between solid and liquid phases affects the geometry of the ionic species and, therefore, influences the electrical properties of nitrate ions.