MECHANISM OF AL-SUBSTITUTION FOR FE-SUBSTITUTION DURING THE ALPHA-(FE, AL)OOH-]GAMMA-(FE, AL)2O3 TRANSFORMATION

The effects of aluminium ions on the crystal structure and magnetic ch aracteristics of the final product and of intermediate phases appearin g during the pseudomozphic transformation of the orthorhombic alpha-fe rric hydroxide oxide in the tetragonal spinel gamma-ferric oxide were studied by X-ray powder diffraction, infrared spectroscopy and magneti c measurements. Solids solutions of the composition alpha-(Fe1-xAlx)1- y/3(OH)1+yO1-y were formed by incorporation of aluminium from the [Al( OH)4]-solution. The ordering of cationic vacancies and the tetragonal superstructure of gamma-(Fe, Al)2O3 were not affected by the substitut ion of aluminium for iron.