NL8402146A - Soft ferromagnetic material - based on lithium zinc manganese ferrite - Google Patents

Abstract

The material has soft ferromagnetic properties and a cubic spinel crystal structure. The general formula is as follows: (LiO.5FeO.5)(1-z-a)Zn(z)Co(a)MnII(y) MnIII(x)Fe(2-x+delta) 0(4+3delta/2+epsilon) with the parameters defined as: z is 0.05 or more but below 0.45; a=0-0.05; x+y=0.01-0.25; delta=0.35 to +0.15; epsilon=0.5x to +0.25a to which has been added p wt.% Bi2O3 and q wt.% V2O5 whereby: p=0-1.2; q=0-1.2; and p+q=0.2-1.2. The material is made by homogenising a powder mixt., pressing into the required magnetic core shapes and sintering at a temp. between 950 and 1100 deg. C.

Description

k ^ HIN.11.089 1 N.V. Philips' Gloeilampenfabrieken, Eindhoven "Magnet core based on lithium-zinc-manganese ferrite"

The invention relates to a magnetic core of an oxidic, ferromagnetic material, consisting of a spinel ferrite with a cubic crystal structure.

Magnetic cores of oxidic, ferromagnetic material, consisting of a spinel ferrite with cubic crystal structure, are widely used in induction coils and in transformers in the fields of telecommunications and industrial and consumer electronics. Depending on the application, the materials in question can be divided into four types: 10 - The first type is a low-loss ferrite resistant for high quality coils used in filters. The magnetic cores are usually round or square pot cores. - - The second type has a high magnetic initial permeability and is intended for low-power broadband and pulse transfarmers.

The magnetic cores are usually toroids, E-cores and different types of pot cores.

- The third type is suitable for high-power applications such as power transformers operating in the frequency range of 10-100 kHz. The range of powers to be processed typically ranges from 10 to 750 W. The magnetic cores are usually U-cores or E-cores.

- The fourth type is intended for use in magnetic cores for high-quality coils that are used in the frequency range of 2-12 MHz. The magnetic cores are usually pot cores, toroids, rods or beads.

Applications not mentioned above are furthermore magnetic cores for antenna rods, interference suppressors and particle accelerators. Memory cores are typically not included.

For use at higher frequencies (in particular higher than 1 MHz), 30 Ni-Zn ferrite has hitherto been used as the magnetic core material due to its high resistance (fi -110 -Cl-cm).

(A material that can be used at frequencies above 1 MHz is of course also suitable for use at frequencies below 1 MHz). In view of the high price of Ni-Zn ferrite, a replacement 8402146 ΕΗΝ.11.089 2 t 4 I ϊ Λ ferrite system with comparable electrical and magnetic properties was sought.

The invention provides such a ferrite system. This is characterized by the following composition 5 «“ ο, Λ, 5> 1 £ ° * ff + 6 with 0.05 ^ z <0.45 0 ^ a <0.05 0.01 <x + y ^ "0 .25 10 -0.35 ^ J £ + 0.15 -0.5x ^ S 0.25a with extra added p wt% + q wt% 15 where 0 <p <1.2 0 ^ q <1 , 0.2 <p + q <1.2

In addition to a cost saving of about 30% that the application of this Li-Zn-Mn ferrite-based ferrite system in magnetic cores 20 provides, an important advantage appears to be that the sintering temperature by the addition of a small amount of ^ ^ 2 ^ 3 V2 ° 57 It is so small that the electrical and magnetic properties are not adversely affected, it can be significantly lower than the sintering temperature of Ni-Zn ferrite, allowing materials of high density to be produced in the present Li-Zn-Mn 25 ferrite system. small grain grain resulting in high mechanical strength. In one case, a breaking strength of five times greater than that of Ni-Zn ferrite with comparable electrical and magnetic properties was measured.

On the one hand, the total amount of added sintering agent must not exceed 1.2% by weight, because in larger quantities the magnetic and electrical properties are adversely affected. The total amount, on the other hand, should not be less than 0.2% by weight, because in smaller amounts the sintering temperature is not lowered sufficiently, as a result of which the material to be sintered can react with the material of the oven, Li can evaporate, and the grains become larger. all at the expense of electrical, magnetic and mechanical properties.

8402146 <i PHN.11.089 3

Another advantage of the lower sintering temperature is that the electrical resistance of the present Li-Zn-Mn ferrites is higher than the electrical resistance of further similar Ni-Zn ferrites.

The presence of a small but specific amount of Mn appears to be essential in caribination with Bi2 and as a sintering agent to obtain a high electrical resistance and low losses comparable to the losses of Ni-Zn ferrite. Depending on the amounts of Zn, Fe, Bi 2 O 3 and V 2 Oj. the amount of Mn should vary from 0.01 to 0.25 formole units.

10

A further part of the Li-Zn-Mn ferrite system described above is that, in particular by varying the Li-Zn ratio, it provides a number of materials that meet various specifications.

With a zinc content z of 0.35 to 0.45 pharmaceutical units, materials with a magnetic permeability of 250 can be realized.

At a zinc content z of 0.25 to 0.35 formula units, materials with magnetic permeabilities of 120 µ can be realized which can be used up to higher frequencies.

At a zinc content z of 0.15 to 0.25 formula units, materials with magnetic permeabilities of 60 can be realized which can be used up to even higher frequencies.

The addition of a maximum of 0.05 formula units Co leads to materials with lower losses and also the temperature factor of the permeability can be controlled with the Co content.

The material in the range that can be used up to the highest frequencies is characterized by a Zn content z of 0.10 to 0.20 formula units. At lower zinc contents, especially below 0.05 formula units, the magnetic permeability becomes too low. The upper limit of the Zn content is determined by the Curie temperature desired.

A number of embodiments of the invention will be further elucidated with reference to the figures.

^ Figure 1 is a graph showing the so-called "iso losses" of a number of Li-Zn-Mn ferrite cores with the same permeability, (^ u = 200) but with different Mi and Zn contents. The losses were measured at 1 MHz.

8 Δ 0? 1-4 'fi * J - * PHN.11.089 4

Figure 2 is the same graph as Figure 1 but measured at 5 MHz.

Figure 3 is the same graph as Figure 1 but measured on cores with a permeability of 250.

Figure 4 is the same graph as Figure 2, but measured on cores with a permeability of 250.

Figure 5 is a graph showing the so-called "iso resistors" of a number of Li-Zn-Mn ferrite cores with the same permeability (^ 1 = 200), but with different Mn and Zn contents.

Figure 6 is the same graph as Figure 5, but measured on cores with a permeability of 250.

Figure 7 is a graph showing the loss factor (-StiL) of a number of Li-Zn-Mn-Co ferrite cores as a function of the Fe content.

Figure 8 is a graph showing the loss factor (of a number of Li-Zn-Mn-Co ferrite cores as a function of the Fe content.

Figure 9 is a graph showing the temperature coefficient of the permeability TF of a number of Li Zn Mn Co ferrite cores 20 with = 60 as a function of the Co content.

Output vocal picture I: ^ 0.30 ^ .4 (^ 0.03 ^ .02 ^ .82 (with 0/46 wt.% Βΐ ,, Ο ^ enQ23 wt.% V20 ^) 25 Preparation: 617/5 kg Fe ^, 26.3 kg Mn ^, 121.5 kg ZnO, 1.87 kg V ^, 3.77 kg Bi2 O3 and 38.1 kg Li ^ CO ^ are weighed and ground with 600 l of water in a ball mill with a capacity of 2000 1. The powder-water mixture is spray dried and the resulting granulate pre-fired in a rotary pipe oven at 850 ° C.

800 kg of the pre-fired granulate is ground with 500 liters of water in a 2000 liter ball mill for 6 hours and then rinsed twice, each with 30 liters of water and 4 liters of a disperser. An amount of binder, for example an emulsion of polymethacrylate in water, is added to the mixture. The concentration of binder 35 is 1 g. fixed binder per 100 g. dry powder. The mixture is then spray dried. Rings (¢) .0 = 9/15 nm) were pressed at a pressure of 1 ton / cm and then sintered in an oven (2 hours at a top temperature of 1025 ° C in air). The properties of the sintered rings are: specific gravity d = 4.75 g / cm, magnetic permeability, u, = 243); magnetic losses (tg ^ = —g / j s- / ijyitiz 56 x 10 and (tgd / yu.) = 260 x 10, temperature coefficient of permeability TF = 17 x 10 ® / ° C between +25 and + 7Ö ° C, specific electrical resistance P = 0.8 x 10¾. M.

Two series of a number of magnetic cores with the composition Liq 2oZno 40Fe2 30-x + y ° 4 +% mst varying Mn and Fe content cp in the manner described above (d (3s other addition of 0.46% by weight and 0.23 wt% V ^ O ^) The cores of the first series all had a permeability, u. 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 had 250 (for this purpose they were sintered at a temperature approximately 150 ° C higher than in embodiment I). The loss factors (* ^ ") of the cores thus produced were measured. In Fig. 1 (measurements at 1 MHz ) and Fig. 2 (measurements at 5 MHz) show the results of the measurements on the cores of the first series as a function of the Mi and Fe contents Points with the same value of the loss factor are connected by lines. the so-called isover-20 groins.y = O indicates the stoichiometric Fe content in both graphs On.

The negative y values represent an excess of Fe and the positive y values represent an excess of Fe. Figures 1 and 2 show that the lowest losses are found in nuclei with a small 2g underside of Fe. Depending on the frequency range, the Mn content of the cores appears to be somewhat lower (at frequencies of 1 MHz) or somewhat higher (at frequencies of 5 MHz) in order to realize minimum values of the loss factor.

In analogous manner, in Fig. 3 (measurements at 1 MHz) and Fig. 4 (measurements at 5 MHz), the results of the loss measurements

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at the centers of the second series.

This also shows that with regard to the losses, a small undersized Fe is optimal. At frequencies of 1 MHz, however, it is precisely found that the Mn content should preferably be low, and at frequencies of 5 MHz, the Mn content should be slightly higher in order to realize minimum values of the loss factor.

Figure 5 shows the results of resistance measurements at the core egg of the first series and Figure 6 the results of resistance measurements 3402146 * * 4 EHN.11.089 6 at the cores of the second series as a function of the Mn and Pe contents. In both cases, the highest resistance values (10¾ m) are found in cores with only a small undersize Fe.

5 Embodiment Example 11 = ^, 33 ^ 0.20 ^ 0.03 ^ 0.04 ^ 2.16 ^, 73 (with 0.4 wt% and 0.2 wt% Bi202)

Preparation: Grinding, spray drying and pre-firing as under I. Then 800 g. pre-fired granulate with 600 ml for 6 hours. 10 water milled in a 1 1. ball mill, then the mixture is evaporated to dryness at 200 ° C and rings are pressed and sintered as under I. To obtain a smaller grain tg that allows lower losses, in this case the s inter temper at 965 ° C.

3

The properties of the sintered rings are: d = 4.53 g / cm, 15 µl = 60 '(tgc * // u) 10 «z = 76 X 10_S«> ^ // "> 40 MHZ = 220 x 10_6 ƒ = 0.2 x 105n m and TF = 20 X 10.

The above properties make the material in question very suitable for use as a magnetic core material in coils operated at higher frequencies. Minimum values of the 20 loss factor can be realized by setting the correct Fe content. This is illustrated with reference to Figures 7 and 8. FIG. 7 shows the losses at 10 MHz of a number of cores with the composition I ^ 3M%, 20Co0.03 ^ (04Fe2.344 + xO44x ^ with varying Fe contents) (each with an addition of 0.4 wt. % V205 and 0.2 wt% Bi ^.) All cores were sintered to have a = 60.

The lowest losses are found in cores with an under Fe of slightly less than 0.2.

Fig. 8 shows the losses measured at 40 MHz. The lowest 30 losses are found in cores with an Fe minimum of about 0.2.

The deviation of the solid diemetric Fe content indicated by the quantity é can be between -0.35 (underfoot Fe) and +0.15 (excess Fe). So -9.35 <cf ^ + 0.15. On the basis of the foregoing, however, there is a preference for an undersized Fe, i.e. -0.35 <é <-0.15

For the most constant temperature coefficient 8402146 HEI. 11.089 7 * * of the permeability, the Co content is important. This is illustrated with reference to Fig. 9. This shows the temperature coefficient TF of a number of cores with the composition LV384.23-aCoa%, 04Fe2.344 + 4 ° 4 + | 4 different 5 Co contents were produced (always adding 0.2 wt% and 0.4 wt%. The cores were sintered at such temperatures that they all had a = 60. Curve a connects points with a constant temperature coefficient in the temperature range of 5-25 ° C and curve b connect points with a constant temperature coefficient in the temperature range of 25-75 ° C. At a Co content a = 0.027 (corresponding to the intersection point p of curves a and b), a temperature coefficient which is constant between 5 and 75 ° C. This applies to ferrite keraen with a given Fe content (Δ = -0.1). In compositions 15 with a larger Fe base (A ζ -Or2) the pint P shifts to the right. the content required to realize a constant TF between 5 and 75 ° C then increases the Co content is about 0.05). Curves a and b may be lower as the undersized Fe increases. The absolute value of TF thus decreases.

It is noted that in an oxidizing environment Co can become 3-valent. In order to obtain a useful material, care must be taken to ensure that the sintering takes place under conditions such that a maximum of half of the Co ions becomes trivalent.

This means that in the formula describing the composition of the ferrite-25 material for magnetic cores according to the invention: (L10,5Fe0,5) 1 -z-aZnzCoaMrixFe2-x + ^ ° 4 + | $ + £ the upper limit of £ equals +0.25 a.

The lower limit of £ is determined by the condition that the Mi can become completely divalent at higher sintering temperatures, or in a less oxidizing environment. To take this into account is 0.5x

It has been established experimentally that materials with optimal combinations of properties can be obtained if the addition of the sintering agent is between 0.3 and 0.7% by weight, while it appears to be most favorable that Bi 2 and V 2 O are both added. - 8 4 0 2 1 4? » ΡΗΝ.11.089 8 5 Λ 9 Ο added. In particular, favorable results were obtained when 0.2 wt.% Bi2 ° 3 and 0.4 V2 ° 5 were added. * Since optimal combinations of properties are not required for all applications, in some cases it can also be used alone or alone. g added to lower the sintering temperature.

10 e 15 20 25 30 35 8 402 146

Claims (8)

1. Magnetic core of oxidic, ferromagnetic material, consisting of a spheroid ferrite with cubic crystal structure, characterized in that the ferrite has the following composition ^ 0.5 ^ 0.51! Vx + <5 Vf - - net 0.05 z <0.45 0 <a ^ 0.05 10 0.01 <xfy ^ 0.25 -0.35 ^ £ <+0.15 -0.5x ^ £. £ + 0.25a with extra added p wt% Bi203 + q wt% V205 15 where 0 · <p <C 1.2 0 <q 1.2 0.2 ^ p + q- ^ 1.2 Magnetic core according to claim 1, characterized in that 0, 3 <p + q <T 0.7. Magnetic core according to claim 1 or 2, characterized in that p> 0 and q> 0. Magnetic core according to claim 1, characterized in that 0.35 2 ^ 0.45. 25 Magnetic core according to claim 1, characterized in that 0.25 <2 <0.35. a y> 0. Magnetic core according to claim 1, characterized in that 0.15 <2 0.25 a> 0. Magnetic core according to claim 1, characterized in that 0.10 ≤ 2 ^ 0.20 a> 0. 35 Method for the production of a magnetic core according to any one of the preceding claims, characterized in that a homogeneous powder mixture is formed, this is pressed into a magnetic core, which is sintered by a thermal treatment at a temperature between 3. o 2 1 4 6 PHN 11.0891050 and 1100 ° C. 5 10 15 20 25 30 35 8 402 146