| 摘要 |
Gamma ferric oxide, the minimum axial ratio of the crystals of which is at least 4:1, is produced by dehydration, reduction and oxidation of ferric oxide hydrate formed by the oxidation of metallic iron by oxygen or air in the presence of an aqueous ferrous salt solution in which ferric oxide hydrate nuclei are suspended, the formation of the FeO(OH) being carried out with a formation velocity of 1g. FeO(OH) per litre per hour at an initial FeO(OH) nuclei content of from 5 to 10 g/l., and the reaction being broken off when the amount of FeO(OH) formed amounts at most to six times the amount by weight of nuclei initially employed. The FeO(OH) nuclei are produced by the rapid oxidation of an aqeuous ferrous hydroxide suspension by oxygen or air within a period of at most 10 hours. Ferrous sulphate is the preferred ferrous salt and suitably has a concentration of 3 to 5%. The conversion of the ferric oxide hydrate to g -ferric oxide is effected in known manner preferably by heating at 400 DEG to 440 DEG C. under reducing conditions until the ferrous iron content of the material amounts to 23 to 25% and subsequently oxidising the reduced material at 200 DEG -260 DEG C. It is stated that the g -ferric oxide crystals produced have a length of 0,4 to 0,6m and a breadth of 0,05 to 0,1m and that the g -ferric oxide has a saturation remanence of at least 460 Gauss g-1 cm3 and a copying suppression of more than 60dB. The g -ferric oxide is particularly suitable for the production of laminated magnetic storers for sound, picture and impulse recording. |
