FERRIMAGNETIC SPINELS IN HYDROTHERMAL AND THERMAL-TREATMENT OF MNXFE2-2X(OH)(6-4X)

Products of hydrothermal treatment of the initial amorphous system Mnx Fe2-2x(OH)(6-4x) for 0 less than or equal to x less than or equal to 1 in 0.1 x intervals, and products of their further thermal treatment, were examined by chemical analysis, X-ray, IR, and DTA techniques supp orted by magnetic measurements. After hydrothermal growth for low x, h ematite and goethite phases occurred. Although the goethite phase was still identifiable at x=0.6, formation of a solid solution with the is ostructural groutite was not found. The ferrimagnetic spinel phase, wh ich resists heating up to 400 degrees C, was present at 0.5 less than or equal to x less than or equal to 0.9. At higher temperatures, it tr ansformed into the rhombohedral hematite type phase or into the cubic bixbyite phase. At T greater than or equal to 900 degrees C, a ferrima gnetic spinel structure reappeared up to x=0.8. For x=0.9, the low- an d high-temperature forms of the hausmannite phase occurred, for x=1 pa ssing from one form into another through Mn5O8 and partritgeite. For a primary mixture Mn0.5Fe(OH)(4), corresponding to the manganese ferrit e structure, the lattice parameter of which passes from 8.43 Angstrom through 8.33 Angstrom to 8.50 Angstrom, the probable crystallochemical formula was suggested.