Structural Change of Ionic Species in the α-Al 2O 3 Powder/CoCl 2 Aqueous Solution System

Visible (VIS) absorption spectra were measured for the dispersion system consisting of α-Al 2O 3 powder and CoCl 2 aqueous solution. The VIS spectra of the paste differed from that of the bulk solution. The absorption bands of the Co(II) octahedral complex were shifted and broadened, whereas the intensity of the Co(II) tetrahedral complex ([CoCl 4 2-) at ca. 15,000 cm -1 increased with the solid content and the specific surface area of α-Al 2O 3 powder. The intensity ratio of the absorption bands of the tetrahedral complex to the octahedral complex, R 4/6 , correlated with the apparent average thickness of the impregnating liquid layer. The relationship between the VIS spectra and electrical conductivity was also examined. The activation energies for the electrical conductivity, Δ E a, and R 4/6 were correlated linearly. It is concluded that variation of the VIS spectra of the paste sample was caused by the structural change of the dissolved ionic species in the liquid layer which is ca. 20-30 nm thick near the solid surface.