MAGNET CORE OF LI-ZN-MN FERRITE

Abstract: In order to obtain a soft magnetic ferrite which is suitable in particular for use as an annular core in deflection yokes for T.V. and which excels by a high electric resistance and low power losses, Bi₂O₃ and V₂O₅ are added to an Li-Zn-Mn ferrite of the composition: (Li 0.5 Fe 0.5 ) 1-Z Zn z Mn y II Mn x III Fe 2-x+δ O₄+ 3 / 2δ+ε with 0.45 ≦ z ≦0.62 0.01 ≦ x+y ≦ 0.25 -0.35 ≦ δ ≦ +0.05 -0.5 x ≦ ε The quantities of Bi₂O₃ and V₂O₅ are from 0.1 to 1% by weight, but together are never more than 1.2% by weight.

Description: "Magnet core of Li-Zn-Mn ferrite". The invention relates to a magnet core of oxidic, ferromag- netic material from a spinel ferrite having a cubic crystal structure. Magnet cores of the above-mentioned type can be used inter alia as annular magnet cores of deflection devices for television receivers and as cores of transformers and coils in modern power-supply apparatus. In both types of application the power losses occurring in the ferrite material are decisive to a high extent for the applicability thereof. This obtains still greater force since there is a tendency towards operating deflection coils in television deflection devices at higher and higher frequencies. Normally, Mn-Zn ferrite is used as a tore material in the frequency range below 1 MHz. However, this has the disadvantage of an insufficiently high electric resistance, which makes it necessary, especially when coils are wound around the cores, to provide the cores with an electrically insulating layer. In the frequency range above 1 MHz, Ni-Zn ferrite with which a resitivity of the order of 105 A cm can be reached is normally used. The cost-price of Ni-Zn ferrite, however, is very high. It is the object of the invention to provide a substitute ferrite system which couples a comparatively low cost-price with a sufficiently high electric resistance and low Watt (power) losses. The invention provides such a ferrite system. This is characterized by the following composition: (Li0.5Fe0.5)1-zZnzMnyIIMnxIIIFe2-x+#04+3/2#+# with 0.45 # z # 0.62 0.1 # x+y # 0.20 -0.35 / & +0.05 -0.5xz to which has been added as a sintering agent. p% by weight of Bi2O3 + q% by weight of V205 wherein 0.1#p#1.0 0.1#q#1.0 p + q # 1.2 In addition to a cost-saving of approximately 30% which the use of this ferrite system based on Li-Zn Mn ferrite provides in a magnet cores, it has proved possible with a correct control of the Fecontent, to realise a resistivity in the order of 10 Q an (the highest resistance values are realised with a Fe-deficiency for which it holds that -0.15###-0.05). The Zn-content is decisive for the magnetic permeability. If the 7,n-content becomes lower than 0.45, the magnetic permeability drops below 300, is undesired. For most applications in the present range, Zncontents of at least 0.50 which give rise to magnetic permeabilities of at least 350, are desired. Preferably, z > 0.55, as a result of which magnetic permeabilities exceeding 500 can be realised. The upper limit in the Zn-content is determined by the Curie tenperature which is permissible. The presence of a small but specific quantity of Mn in combination with a specific quantity (preferably 0.4 to 0.8% by weight) of Bi203 + V205 as a sintering agent proves to be essential for low losses. Since at higher sintering temperatures or in a less oxidising medium Mn can become entirely bivalent, in the formlrla -0.5x. #. It has surprising- ly been found that minimal power losses are realised when a combination of Bi203 and V205 is used as a sintering agent. When V205 alone is used as a sintering agent, the electric losses prove to be reduced. When Bi2O3 alone is used as a sintering agent, the power losses prove to be considerably higher. In a certain case even more than 100% higher. The overall power loss P of a magnet core is composed of the hysteresis loss Ph and the eddy current loss Pe : P = Pe +Ph. The overall power loss can be defined as P = VL I cos e, wherein VL is the voltage between the ends of a coil which is provided on the core, I is the current through the coil and # is the phase angle between V and I. If # = 90 , the loss is zero. The material of the core then is free from losses. When the material is not free from losses, the loss can be measured by measuring the product of V and I during one cycle. Example Starting material for the manufacture of magnet cores according to the invention were weighed in the following quantities 367.5 g of Fe203 9.5 g of Mn 003 106.3 g of Zn O 16.7 g of Li2 C03 and ground in a ball mill containing 1 litre of water for 6 hours, the ball mill having a capacity of 2 litres. The powder-water mixture was then kept at a temperature of 110 C for 16 hours in order to dry it. The resulting material was crushed and the prefired in a chamberkiln at 700 C for 2 hours. 3.0 g of Bi2O3 and 1 g of V2O5 were added and the mixture was ground in a ball mill with 1 litre of water for 6 hours, the capacity of the ball mill being 1 litre. The resulting mixture was then dried at 1100C for 16 hours and crushed. It was then granulated by means of a binder. Rings were compressed from the granulate having an outside diameter of 14 nan, an inside diameter of 9 trm and a height of 4 imi (pressure 0.5 tons/cm2). The properties of the sintered rings which has a composition which satisfied the formula: 0.205 Zn0.59 Mn0.035 Fe2 07 03.85 + 0.6 wt.% Bi203 + +0.2 wt.% V2O5 were: specific density d = 4.92 g/cm magnetic permeability /U = 760 specific electric resistance # = 1.5 x 106#m Curie temperature Tc = 166 C. The power losses of the annular cores provided with a winding were measured at four different frequencies (16, 64, 128 and 256 kHz), the driving of the coils being such that the induction B was 100 mT. The temperature of the cores was kept at 25 C. Result: EMI3.1 <tb> Frequency <SEP> Power <SEP> Losses <tb> <SEP> 16 <SEP> kHz <SEP> 86 <SEP> mW/cm <SEP> (87) <tb> <SEP> 64 <SEP> kHz <SEP> 405 <SEP> mW/cm <SEP> (422) <tb> <SEP> 128 <SEP> kHz <SEP> 993 <SEP> mW/cm <SEP> (1184) <tb> <SEP> 256 <SEP> kHz <SEP> 2390 <SEP> mW/cm <SEP> (3043) <tb> After the measured values are stated in brackets the value of the losses which were measured at cores which were provided with a winding and which (not counting the fact that they comprised no V205) were quite identical. The influence of the addition of V205 to the Bi2O3 sintering agent is significant. A second series of rings was manufactured having the same composition as in the preceding example. The process steps were identical to those of the example, except for the fact that sintering was carried out in oxygen at a (peak) temperature of 12250C. The properties of this series of rings were compared with those of rings manufactured under the same conditions and comprising 0.6% by weight of Bi2O3; 0.2% by weight of V205 and no addition at all, respectively, instead of 0.6% by weight of Bi2O3 + 0.2% by weight of V205. The result is summarized in the Table below. Table EMI4.1 <tb> Addition <SEP> (wt.%) <SEP> 0.6 <SEP> Bi2O3 <SEP> + <SEP> 0.2 <SEP> V2O5 <SEP> 0.6 <SEP> Bi2O3 <SEP> 0.2 <SEP> V2O5 <SEP> <tb> <SEP> 850 <SEP> 725 <SEP> 760 <SEP> 500 <tb> <SEP> d <SEP> (g/cm ) <SEP> 91 <SEP> 4.87 <SEP> 4.85 <SEP> 4.74 <tb> l(106#m) <SEP> <SEP> 6.0 <SEP> 14 <SEP> 1.10-4 <SEP> 4.2 <tb> Tc <SEP> ( C) <SEP> 185 <SEP> 196 <SEP> 190 <SEP> 204 <tb> Pw(mW/cm ) <SEP> at <SEP> 16 <SEP> kHz <SEP> 86 <SEP> 100 <SEP> 84 <SEP> 120 <tb> <SEP> 64 <SEP> kHz <SEP> 432 <SEP> 527 <SEP> 450 <SEP> 660 <tb> <SEP> 128 <SEP> kHz <SEP> 1010 <SEP> 1260 <SEP> 1060 <SEP> 1480 <tb> In the Table power losses are indicated by P . The effect of w the investion becomes more prominal herefrom.

Claims: 1. A magnet core of oxidic, ferromagnetic material consisting of a spinel ferrite having a cubic crystal structure, characterized in that the ferrite has the following composition: (Li0.5Fe0.5)1-z Znz MnyII MnxIII Fe2-x+#@4+3/#+# 2 with 0.45#z#0.62 0.01#x+y#0.20 -0.35###+0.05 -0.5 x to which has been added as a sintering agent. p% by weight of Bi2O3 + q% by weight of V2O5 wherein 0.1 < p 41.0 0.1#g#1.0 p+q#1.2 2. A magnet core as claimed in Claim 1, characterized in that 0.4#p+q#0.8. 3. A magnet core as claimed in Claim 1, characterized in that -0.15###-0.05.

Inventors: ESVELDT, CORNELIS JACOBUS INT. OCTROOIBUREAU B.V., HENKET, BERNARDUS HUBERTUS INT. OCTROOIBUREAU B.V., KOPPENS, LEONARDUS JOSEPHUS INT. OCTROOIBUREAU B.V
Applicants: N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1984
Main classification: C04B35
IPC codes: C04B35