Patent GB-862821-A (GB)
Title: Improvements in or relating to methods of manufacturing bodies of ferromagnetic materials
IPC: C04B35/26
Filed: 1958-05-09
Abstract: 862,821. Magnetic compositions. PHILIPS ELECTRICAL INDUSTRIES Ltd. May 9, 1958 [May 13, 1957], No. 14916/58. Class 38 (2). Bodies of ferrite materials with an improved orientation of the particles are made from mixtures of metal oxides and/or oxide-yielding compounds and/or compounds of two or more oxides, including at least one ferromagnetic material having directional properties but which is different from the final product, and are prepared by sintering the mixture in a magnetic field while the particles are still movable among themselves. During sintering the directionable component reacts with the other components to provide material having the desired orientational alignment. The directionable component is preferably mostly monocrystals. The magnetic field is homogeneous to avoid de-mixing, and may be stationary or rotational and may vary in intensity. Directionable components exhibiting a preferred direction of magnetization are BaFe 12 O 19'  Ba 3 Mg 2 Fe 24 O 41 , BaNi 2  Fe 16 O 27  and CoFe 2 O 4 , and directionable components exhibiting a preferred plane of magnetization are Ba 3 CO 2 Fe 24 O 41 , Ba 2 Zn 2 Fe 12 O 22  and BaCo 2 Fe 16 O 27 . The product materials comprise constituents 8-21 mol. % AO 5-21 mol. % MeO and 58-83 mol. % Fe 2 O 3 , where A may be one or more of the metals Ba, Sr, Pb, Ca and Me the metals Fe, Mn, Co, Ni, Zn, Mg, Cu or the complex Li<SP>1</SP> + Fe<SP>111</SP>/2. Included therein are (a) AMe 2 Fe 16 O 27 , where A is from Ba, Sr, Pb and not more than <SP>2</SP>/ 5  part Ca and Me is from Fe, Mn, Co, Ni, Mg or the complex above; (b) A 3 Me 2 Fe 24 O 41'  where A is from Ba, not more than 1/3 Sr, not more than <SP>1</SP>/ 5  Pb and/or not more than <SP>1</SP>/ 10  Ca, and Me is from Fe, Mn, Co, Ni, Zn, Mg, Cu or the complex above ; (c) A 2 Me 2 Fe 12 O 22  wherein A represents Ba, not more than ¢ Sr, not more than  Pb and not more than  Ca and Me represents Fe, Mn, Co, Ni, Zn, Mg and Cu; (d) A 4 Me 2 Fe 36 O 60 , wherein A represents Ba, not more than <SP>1</SP>/ 3  Sr, not more than <SP>1</SP>/ 5  Pb and not more than <SP>1</SP>/ 10  part Ca and Me represents Fe, Co, Ni, Mg and not more than <SP>3</SP>/ 10  Mn or Cu; (e) A 2 Me 2 Fe 28 O 46 , wherein A represents Ba Sr Pb and not more than <SP>2</SP>/ 5  Ca and wherein Me represents Fe Mn Co Ni Zn Mg or the complex. Titanium ferrites are also possible. In one method the mixture is ground in alcohol for 8 hours, suspended in acetone, and moulded into a block at a pressure of 1000 kg/cm.<SP>2</SP> in a field of 7500 oersted. The block is heated to 500 C. within 16 hours, 500 to 1250 C. within 5 hours, and heated at 1250 in O 2  for 16 hours. In variations of this method the time for heating at 1250 may be 3 hours, the time for heating to 500 may be 1¢ hours, and the field may be 8000 oersted. In other methods a double moulding is performed, the first at 300 kg. in a rotating field (1 c/s. at 50 c/s.) of 3800 oersted, this being followed by moulding at 1000 kg/cm.<SP>2</SP>. In another example the heating times may be up to 1000 C. within ¢ hour, 1000 C. for 1 hour, 1000-1300 C. within  hour and finally 1300 C. for 2 hours. The improved orientation may be demonstrated by X-ray diffraction.