Patent GB-780975-A (GB)
Title: Manufacture of metal oxides and of ferrites
Inventor: BUCKLEY SIDNEY ERNEST
IPC: C04B35/26
Filed: 1954-03-12
Abstract: Ferric oxide suitable for the production of ferrites is obtained by heating iron powder in a current of steam at 400 DEG  to 650 DEG  C., milling the resultant product in water and calcining the milled product in air at 150 DEG  to 500 DEG  C., preferably between 300 DEG and 500 DEG  C.  Ferrites may be formed by mixing the ferric oxide so obtained with at least one other metallic oxide and pressing the mixture and heat treating it to form a ferrite.  Alternatively the ferrite may be formed by heating a mixture of iron powder and the powder of another metal whose oxide is one constituent of the ferrite in a current of steam at 400-650 DEG  C., milling the product and calcining the milled product in air at 150-1000 DEG  C., and thereafter pressing the mixture into the desired form and heat treating to form the ferrite.  If desired the product after calcining in air may be mixed with the oxide of yet another metal required to constitute the ferrite before pressing and heat treating or alternatively the heating of the iron powder in steam may be effected in the presence of the oxide of a metal which is required in the desired ferrite.  According to examples: (1) carbonyl iron powder was heated in steam at 400 DEG  C. for six hours and the product milled with an equal weight of distilled water, dried out and then calcined at 500 DEG  C. in air for two hours.  The ferric oxide so obtained was mixed with manganese oxide and zinc oxide and further milled in water.  After drying the product was pressed at 35 tons per square inch and heat treated for four hours in a nitrogen atmosphere containing 1 per cent by volume of oxygen at varying temperatures from 1125-1175 DEG  C.  A table sets forth the permeability, the residual loss, the hysteresis loss and the eddy current loss coefficients and also the magnetic properties according to the Jordan expression for core loss; (2) carbonyl iron powder and zinc dust were treated in steam for six hours at 400 DEG  C., the product milled and thereafter calcined at 500 DEG  C. for two hours.  The product was mixed with manganous oxide and after milling and drying was pressed and heat treated as before, to form a ferrite having 48.70 per cent iron, 12.78 per cent manganese, and 9.88 per cent zinc, 1.58 per cent of the iron being ferrous iron, the remainder being ferric; (3) a mixture of iron powder, zinc powder and nickel oxide was heat treated at 600 DEG  C. in steam for three hours and after milling, drying and air calcining at 500 DEG  C. for two hours, the dry powder obtained was pressed into a toroidal ring and heated at 1200 DEG  C. for four hours in oxygen. The resulting ferrite contained 49.9 per cent of ferric oxide, 15.3 per cent of nickel oxide, and 34.8 per cent of zinc oxide. Barium ferrite may be similarly prepared by heating a mixture of iron powder and barium oxide or carbonate; (4) a ferrite was prepared from powdered iron, zinc and nickel in a similar manner; (5) a mixture of iron and manganese and zinc oxide was treated with steam at 400 DEG  C. for six hours to convert 65 per cent of the metals to oxide, after which the product was milled, dried, air calcined at 500 DEG  C. for two hours, and after further milling was pressed and heat treated in a nitrogen atmosphere to form a ferrite. It is desirable in the case of manganese zinc ferrite to stop the air oxidation at a point short of completion and to carry out the first part of the heat treatment after pressing in an atmosphere of air to complete the oxidation, and thereafter heat treating in a nitrogen atmosphere containing a small amount of oxygen as is described in Specification 730,703, [Group XXXV]; (6) a mixture of iron, manganese and zinc powders were steam treated at 450 DEG  C. for three hours and after wet milling and drying, the product was air calcined at 350 DEG  C. for two hours, whereby a powder containing 1.9 per cent of FeO resulted.  The dry powder was pressed at 5 tons per square centimeter into a ring and heated at 1250 DEG  C. in an air current to complete oxidation and thereafter heated at the same temperature in a nitrogen atmosphere containing 1 per cent oxygen and cooled in the same atmosphere.  The final ferrite contained 50.2 per cent Fe2O3, 5.91 per cent FeO, 34.5 per cent MnO and 9.3 per cent ZnO; (7) iron, zinc and manganese powder was steam treated at 450 DEG  C. for three hours and after wet milling and drying the mixture was air calcined at 350 for two hours.  The dry powder was pressed into a toroidal ring which was heated up to a temperature of 1250 DEG  C. in a rapid current of air thereby completing the oxidation to Fe2O3. The ring was maintained at 1250 DEG  C. for two hours in a nitrogen atmosphere containing 1 per cent oxygen and allowed to cool, a portion of the Fe2O3 being converted to FeO during the last part of the sintering; (9) a mixture of iron, manganese and magnesium powders were steam heated at 400 DEG  C. for four hours and after wet milling and drying were air calcined at 400 DEG  C. for two hours. The product was then milled for 24 hours in a steel ball mill with water and dried and pressed into a toroid at 5 tons per square centimeter. The toroid was raised to 1275 DEG  C. in a rapid current of air and maintained at this temperature in a nitrogen atmosphere containing 1 per cent oxygen for two hours and then cooled in pure nitrogen to room temperature during twelve hours. A square loop ferrite suitable for use in digital storage of information, having a Br / Bm (squareness ratio) of 0.9 was obtained.  Specification 683,722, [Group XXXV], also is referred to.