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

Abstract

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.