X-Ray Study of Behaviors of Sesquioxides Depositing in a Chromite Grain

It is well known that sesquioxides, Cr2O3, Al2O3 and Fe2O3, are liberated from chromite ore by heat treatment in air. But behaviors of the sesquioxides in ores fired at temperatures below 1000°C have not been studied systematically.In this report, influences of behaviors of the sesquioxides on lattice spacing of the chromite fired below 1300°C and diffusion phenomena of the sesquioxides in the fired chromite grain were examined by X-ray diffraction and fluorescent X-ray analysis. The followings were observed (1) The lattice spacing (440) of the chromite decreased with elevation of heating temperature up to 700°-900°C in air and increased over these temperatures. The diffracted line (440) was most broadened at 700°-900°C. The X-ray pattern of the sesquioxides in α-type appeared over 700°C, and the relative intensity of the diffracted line (014) increased with decrease of its lattice spacing (014) between 700° and 1300°C. (2) By fluorescent X-ray analysis of the chromite grain, ratio of Fe2O3/Cr2O3 on the surface of the grain fired was determined. The ratio increased in the temperature range between 700° and 1100°C, and over this range decreased. So diffusion of the liberated sesguioxides in the spinel phase which presumably consists of a single crystal, was ascertamed.It was concluded that by the liberation of the sesquioxides the chromite phase was made unstable at the heating temperature of 700°-900°C, but was brought into a stable state over 700°-900°C by isolation of two different crystal phases of the sesquioxides and the spinel, with formation of a solid solution of the sesquioxides. The degree of crystallization of the two different phases was raised by heating over 700°-900°C.The author considers that the behaviors, as described above, of the sesquioxide deposited on the surface of the chromite crysta will give a valuable explanation of reactions with the chromite grain.