Diffuse reflectance FT-IR spectroscopic study of interactions of α-Al2O3/molten NaNO3 coexisting systems

Abstract

The diffuse reflectance spectra of the α-Al₂O₃/molten NaNO₃ coexisting systems have been measured in order to investigate the interactions of nitrate ions with aluminium oxide. α-Al₂O₃ with various specific surface areas (3.00, 10.0, 17.8 and 32.8 m² g⁻¹) has been used as the solid phase. The liquid content ranged from 10 to 30% of the volume fraction of sodium nitrate. The effect of the solid phase on the nitrate ion absorption bands is discussed in the region of higher wavenumbers ranging from 3000 to 1700 cm⁻¹. For the system containing particles with a lower melt content, the combination band ν₃ + ν₄ decreases with increasing specific surface area of alumina. This decrease in the band position shows that the nitrate ion structure is influenced by the presence of the solid phase. The variation of fitted band components with the specific surface area corroborates the tendency of the band maxima. It is suggested that both D_3h and C_2v symmetry types of nitrate ion co-exist in such hetero-phase systems. The temperature effect on the spectra of the mixtures is described above the NaNO₃ melting point. Spectral measurements have been performed at temperatures up to 723 K. Analysis was carried out above the melting point of sodium nitrate.