JPH043089B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic core of an oxide ferromagnetic material made of a spinel-structured ferrite having a cubic crystal structure, and a method for manufacturing the same. Oxide ferromagnetic cores consisting of spinel-structured ferrites with a cubic crystal structure are used in large numbers in induction coils in the fields of telecommunications and industrial and consumer electronics, and in transformers. Depending on the application, the material in question can be divided into four types. - The first type is a low loss ferrite for high quality coils used in filters. The magnetic core is usually a circular or rectangular pot-shaped core. - The second type has high initial permeability and is intended for low power broadband and pulse transformers. The magnetic cores are usually annular, E-cores and pot-shaped cores of various shapes. - The third form is for high power applications, e.g. 10-100K
Suitable for power transformers operating in the Hz frequency range. Processing power typically ranges from 10 to 750W
It is. The magnetic core is usually a U-core or an E-core. - The fourth type is intended for use in high quality coil cores used in the frequency range from 2 to 12 MHz. The magnetic core is usually a pot-shaped core, a ring, a rod or a bead. Other uses include antenna rods, noise inverters, and magnetic cores for particle accelerators. Memory cores are typically not included. For applications at high frequencies (particularly above 1 MHz), Ni-Zn ferrite has hitherto been used as a magnetic core material due to its high resistance (ρ=10 ⁵ Ω·cm). (Materials that can be used at frequencies above 1MHz are of course also suitable for applications at frequencies below 1MHz.) Due to the high cost of Ni-Zn ferrite, alternative ferrite systems with comparable electrical and magnetic properties were discovered. Efforts were made to do so. The present invention provides such a ferrite system. This has the following composition (Li _0.5 Fe _0.5 ) _1-za Zn _z Co _a Mn〓 _y Mn〓 _X Fe _2-x+ 〓O ₄ +
3/2δ+ε, and the values of z, a, x+y, δ, and ε are each in the range of 0.05z<0.45 0a0.05 0.01x+y0.25 −0.35δ+0.15 −0.5xε+0.25a, and the composition p wt% as sintering agent
It is characterized in that Bi ₂ O ₃ and q% by weight of V ₂ O ₅ are added, and the values of p, q and p+q are in the range of 0p1.2 0q1.2 0.2p+q1.2, respectively. In addition to the cost savings of approximately 80% resulting from the use of this ferrite system in magnetic cores based on Li-Zn-Mn ferrite, an important advantage is that the sintering temperature can be lowered by _lowering the _sintering temperature by reducing _the With the addition of _O5 , Ni−
The sintering temperature can be much lower than that of Zn ferrite, and since the amount added is extremely small, it does not adversely affect the electrical and magnetic properties. As a result, this Li-Zn-Mn ferrite system has a high density This makes it possible to produce materials that bond together in small particles, thereby resulting in greater mechanical stiffness. In some cases,
Ni-Zn with comparable electrical and magnetic properties
A fracture strength five times greater than that of ferrite was measured. The total amount of sintering agent added should, on the one hand, not exceed 1.2% by weight, since using larger amounts would have a negative effect on the magnetic and electrical properties. On the other hand, the total amount is 0.2
The reason for this is that if an amount smaller than this is used, the sintering temperature will not drop sufficiently, resulting in a reaction between the material to be sintered and the furnace material. , Li evaporation occurs and the particles become larger, all at the expense of electrical, magnetic and mechanical properties. Another advantage of lowering the sintering temperature is that this Li−Zn−
The electrical resistance of Mn ferrite is higher than that of otherwise comparable Ni--Zn ferrite. The presence of a small but certain amount of Mn, in combination with Bi ₂ O ₃ and V ₂ O ₅ as sintering agents, results in high electrical resistance and low losses comparable to those of Ni-Zn ferrite. We confirmed that it is essential to obtain the following. Depending on the amount of Zn, Fe, _Bi2O3 and _V2O5 , the amount of Mn must be varied within the range _of formula units from 0.01 to _0.25 . Furthermore, an advantage of the Li--Zn--Mn ferrite system is that, in particular by varying the Li--Zn ratio, it offers a large number of materials meeting different specifications. With a zinc content z in the range from 0.35 to 0.45 formula units, a material with a magnetic permeability of 250 can be obtained. With a zinc content z in the range of formula units from 0.25 to 0.35, a material with a magnetic permeability of 120 is obtained, which can be used up to higher frequencies. With a zinc content z in the range of 0.15 to 0.25 formula units, a material with a magnetic permeability of 60 can be obtained, which is useful up to even higher frequencies.
By adding at most 0.05 formula units of Co, a material with even lower loss can be obtained, and the temperature coefficient of permeability can also be reduced.
It can be controlled by Co content. This series of materials, which can be used up to the highest frequencies, is characterized by a zinc content z in the range from 0.10 to 0.20 formula units. This results in lower zinc content, especially
Below 0.05 formula units, the magnetic permeability becomes too low. The upper limit of Zn content is determined by the desired Curie temperature. A number of examples of the invention will now be explained in more detail with reference to the drawings. Example 1 Li _0.30 Zn _0.40 Mn _0.08 Fe _2.02 O _3.82 (with 0.46 wt% Bi ₂ O ₃ and 0.23 wt % V ₂ O ₅ ) Preparation: 617.5 Kg Fe ₂ O ₃ , 26.3 Kg Mn ₃ O ₄ ,
121.5Kg of ZnO, 1.87Kg of V ₂ O ₅ , 3.77Kg of Bi ₂ O ₃ and 38.1Kg of Li ₂ CO ₃ were weighed and ground together with 600 liters of water in a ball mill with a capacity of 2000 liters for 4 hours. did. The powder-water mixture was spray dried and the resulting granulate was precalcined at 850° C. in a rotary tube furnace. 800 Kg of precalcined granulate was ground with 500 liters of water for 6 hours in a ball mill with a capacity of 2000 liters, then each time
Rinsed twice with 30 liters of water and 4 parts dispersant. Some binder, such as an aqueous emulsion of polymethacrylate, was added to the mixture. The concentration of binder was 1 g solid binder per 100 g dry powder. The mixture was then spray dried. Compress the ring (φ _i /φ _p =9/15 mm) with a pressure of 1 t/cm ² ,
It was then sintered in a furnace: 2 hours in air at a peak temperature of 1025°. The characteristics of the sintered ring are as follows. Specific density d = 4.75
g/cm ³ , magnetic permeability μ=243; magnetic loss (t _g δ/μ) _1M
Hz=56×10 ^-6 and (t _g δ/μ) _5M Hz=260×10 ^-6 ,
Temperature coefficient of magnetic permeability TF=17×10 ^-6 /℃ (+25~+
70℃), resistivity ρ=0.8×10 ⁶ Ωm. Two series of a number of magnetic cores with the composition Li _0.30 Zn _0.40 Mn _x Fe _2.30-x+y O ₄ +3/2y were prepared in the above manner with varying Mn and Zn- contents (therefore 0.46% by weight Bi ₂ O ₃
and 0.23% by weight _{of V2O5} ).
All the cores of the series have a magnetic permeability μ _i of 200 (for this purpose they were sintered at a temperature about 50 °C lower than in Example 1), and the cores of the second series all (for this _purpose they were sintered at a temperature approximately 150° C. higher than in Example 1). The loss coefficient t _g δ/μ of the thus manufactured magnetic core was measured. The measurement results for the first series of magnetic cores are shown in Figure 1 (measurement at 1MHz) and Figure 2.
Recorded in the figure (measured at 5MHz) as a function of Mn and Fe content. Points with equivalent loss coefficients are connected with lines. They exhibit a so-called equal loss. y = 0 in both graphs is stoichiometric Fe
- Indicates the content. Negative y- values indicate Fe deficiency, positive y- values
Indicates an excess of Fe. It can be seen from FIGS. 1 and 2 that the lowest losses are seen in the slightly Fe deficient core. Depending on the frequency range, the Mn content of the core must be slightly lower (at a frequency of 1 MHz) or slightly higher (at a frequency of 5 MHz) to obtain the minimum value of the loss factor. I confirmed it. In a similar manner, Figures 3 (measurements at 1 MHz) and 4 (measurements at 5 MHz) show the results of loss measurements in the second series of magnetic cores. This also shows that a slight deficiency of Fe is optimal in terms of loss. However, it was found that to obtain a minimum value of the loss factor, at a frequency of 1 MHz, the Mn- content should preferably be low, and at a frequency of 5 MHz, it should be slightly higher. . FIG. 5 shows the measured resistance of the first series of magnetic cores, and FIG. 6 shows the measured resistance of the second series of magnetic cores as a function of Mn and Fe content. In both cases, the highest resistance value (10 ⁷ Ωm) is Fe
This is seen in magnetic cores with a slight lack of. Example 2 Li _0.38 Zn _0.20 Co _0.03 Mn _0.04 Fe _2.16 O _3.73 (with 0.4 wt% V ₂ O ₅ and 0.2 wt % Bi ₂ O ₃ ) Preparation: As in example 1, first ground and spray dried. , precalcined and then 800 g of the precalcined granulate was ground in a 2 liter ball mill with 600 ml of water for 6 hours. Then add the mixture to 200
It was evaporated to dryness at 0.degree. C. and compacted into rings, which were sintered as in Example 1. The sintering temperature in this case was 965° C. in order to obtain small particles allowing for low losses. The properties of the sintered ring were as follows: d = 4.53 g/cm ³ , μ _i =60, (t _g δ/μ) _10M Hz =
76×10 ^-6 and (t _g δ/μ) _40M Hz=220×10 ^-6 , ρ=
0.2×10 ⁶ Ωm and TF=20×10 ⁻⁶ . The above properties make the material in question eminently suitable for use as core material in coils operated at higher frequencies. The minimum value of the loss factor is obtained by adjusting the correct Fe content. This becomes clear from FIGS. 7 and 8. Figure 7 shows the changes in Fe content (always 0.4
wt% V ₂ O ₅ and 0.2 wt % Bi ₂ O ₃ )
Produced composition Li _0.384 Zn _0.20 CO _0.032 Mn _0.04 Fe _2.344+x
Figure 3 shows the loss at 10 MHz for multiple magnetic cores with O ₄ +2/3x. All cores were sintered to have μ _i =60. The lowest value is found in cores with a deficiency of Fe, slightly less than 0.2. Figure 8 shows the loss measured at 40MHz. The lowest losses are found in cores with a Fe deficiency of about 0.2. The deviation from the stoichiometric Fe content, indicated by the amount δ, can be between -0.35 (Fe deficiency) and +0.15 (Fe excess). Therefore, the value of δ is −0.35
δ+0.15. However, based on the above, Fe deficiency is preferred. That is, −0.35δ−0.05 The Co content is important for the temperature coefficient of magnetic permeability to be as constant as possible. This is shown in FIG. This figure shows varying Co content (always 0.2
₍ adding wt% _{Bi2O3 and} 0.4wt% _V2O5 )
Produced composition Li _0.384 Zn _0.23-a Co _a Mn _0.04 Fe _2.344 +Δ _O
Figure 3 shows the temperature coefficient TF of a number of magnetic cores, with 4+3/2Δ. The magnetic cores were sintered at a temperature such that they all had μ _i =60. Curve a connects points with a constant temperature coefficient in the temperature range of 5 to 25 °C, and curve b
Connect points with a constant temperature coefficient in the temperature range of 25 to 75 °C. At a Co content a = 0.027 (corresponding to the point of intersection p between curves a and b ), a constant temperature coefficient is obtained between 5 and 75°C. This is compatible with a ferrite core with a given Fe content (Δ=-0.1). In compositions with larger Fe deficits (Δ-0.2), point P moves to the right. Therefore,
The Co content required to obtain a constant TF between 5 and 75°C increases. (The maximum required Co content is approximately 0.05
It is. ) When the Fe deficiency becomes large, curves a and b occupy lower positions. Therefore, the absolute value of TF becomes even smaller. The fact that Co can become trivalent in an oxidizing medium means that
It is noteworthy. To obtain useful materials, one should ensure that sintering is carried out in an environment where at most half of the Co ions are trivalent. This means that the formula describing the composition of the ferrite material for the magnetic core of this invention: (Li _0.5 Fe _0.5 ) _1-za Zn _z Co _a Mn〓 _y Mn〓 _X Fe _2-x+ 〓O ₄ +
3/2 δ+ε means that the upper limit of ε is equal to +0.25 a . The lower limit of ε is determined by the condition that Mn can become completely divalent at higher temperatures or in less oxidizing media. To explain this, ε0.5x. It has been experimentally verified that when the addition of sintering agent is 0.3-0.7% by weight, a material with an optimal combination of properties can be obtained, while adding both Bi ₂ O ₃ and V ₂ O ₅ was found to be the most advantageous. Particularly advantageous results were obtained when adding 0.2% by weight Bi ₂ O ₃ and 0.4% by weight V ₂ O ₅ .
However, since the optimal combination of properties is not required for all applications, in some cases Bi ₂ O ₃ alone or
V ₂ O ₅ alone can be added to lower the sintering temperature.

[Brief explanation of drawings]

Figure 1 has the same magnetic permeability (μ=200), but
A large number of Li−Zn− with different Mn and Zn contents
Loss of Mn ferrite core measured at 1MHz.
This is a graph showing so-called "equal loss," and Figure 2 is the same graph as Figure 1, but with loss measurement.
This is a graph taken at 5MHz. Figure 3 is the same graph as Figure 1, but the loss is measured in a core with a magnetic permeability of 250. Figure 4 is the same graph as Figure 2. is a graph in which the loss was measured for a core with a magnetic permeability of 250, and Fig.
6 is a graph showing the so-called “isoresistivity” of a number of LiZnMn ferrite cores with Zn content;
This figure is the same graph as Figure 5, but the measurement was performed using a core with a magnetic permeability of 250.
The figure is a graph showing the loss coefficient (t _g δ/μ) _10M Hz of a large number of LiZnMnCo-ferrite cores as a function of Fe content, and _FIG . /μ) _{40 MHz} as a function of Fe content, and Figure 9 is a graph of the temperature coefficient of permeability TF as a function of Co content for a number of LiZnMnCo ferrite cores with μ _i =60. .

Claims (1)

[Claims] 1. In a magnetic core of an oxide ferromagnetic material made of spinel structure ferrite having a cubic structure, the ferrite has the following composition: (Li _0.5 Fe _0.5 ) _1-za Zn _z Co _a Mn _y 〓Mn _x 〓Fe _2-x+ 〓O ₄ +
3/2δ+ε, and the values of z, a, x+y, δ, and ε are each in the range of 0.05z<0.45 0a0.05 0.01x+y0.25 −0.35δ+0.15 −0.5xε+0.25a, and the composition p wt% as sintering agent
Lithium-zinc- containing Bi ₂ O ₃ and q% by weight of V ₂ O ₅ and characterized in that the values of p, q and p+q are in the range of 0p1.2 0q1.2 0.2p+q1.2, respectively.
Magnetic core based on manganese ferrite. 2. The magnetic core according to claim 1, wherein the value of p+q is in the range of 0.3p+q0.7. 3 The values of p and q are p>0 and q>0, respectively.
A magnetic core according to claim 1 or 2 falling within the scope of claim 1 or 2. 4. The magnetic core according to claim 1, wherein the value of z is in the range of 0.35z0.45. 5. The magnetic core according to claim 1, wherein the values of z and a are in the ranges of 0.25z0.35 and a>0, respectively. 6. The magnetic core according to claim 1, wherein the values of z and a are in the ranges of 0.15z0.25 and a>0, respectively. 7. The magnetic core according to claim 1, wherein the values of z and a are in the ranges of 0.10z0.20 and a>0, respectively. 8 In the magnetic core of an oxide ferromagnetic material consisting of spinel structure ferrite having a cubic crystal structure, the ferrite has the following composition (Li _0.5 Fe _0.5 ) _1-za Zn _z Co _a Mn _y 〓Mn〓 _X Fe _2-x+ 〓 O ₄ +
3/2δ+ε, and the values of z, a, x+y, δ, and ε are each in the range of 0.05z<0.45 0a0.05 0.01x+y0.25 −0.35δ+0.15 −0.5xε+0.25a, and the composition p wt% as sintering agent
A magnetic core based on lithium-zinc-manganese ferrite with Bi ₂ O ₃ and q% by weight of V ₂ O ₅ and with values of p, q and p+q in the range 0p1.2 0q1.2 0.2p+q1.2 respectively. In manufacturing, a homogeneous powder mixture is formed and compressed to form a magnetic core, with 950~
A method for producing a magnetic core based on lithium-zinc-manganese ferrite, characterized in that it is sintered by heat treatment at a temperature in the range of 1100°C.