Magnetic and optical studies of chromium oxides. Part 1.—Calcination of chromium trioxide supported on alumina

Abstract

Magnetic and optical studies were made on chromium trioxide supported at various concentrations on a porous alumina, the impregnated samples having been calcined at different temperatures over the range 50-1150° C. The measurements of magnetic susceptibility and electron paramagnetic resonance spectra were carried out at controlled temperatures from –196 to 300°C. Optical reflectance spectra were obtained at room temperature on selected samples. The results suggest that clustering of the chromium oxide occurs, even at the lowest concentration studied (1.8 wt % Cr); heat treatment in air, or reaction with hydrogen, leads to the formation of Cr³⁺ ions, which are coupled by strong exchange interactions. Both processes of reduction occur more readily as the concentration of chromium oxide is increased.