DE2735440C3 - Manganese zinc ferrite - Google Patents

Description

For the function of filter coils, in addition to the quality, the temperature coefficient of the initial permeability of the core, hereinafter referred to as TK for the initial permeability, is the most important property of the inductive component. The temperature coefficient of the inductance, which in the filter must be opposite to that of the capacitance, determines the frequency deviation in the often unavoidable temperature fluctuations according to the relationship: where L [deep] 0 and C [deep] 0 denote the inductance or capacitance at 0 ° C, with small alpha [low] L the temperature coefficient of the inductance and with small alpha [low] C the temperature coefficient of the capacitance.

Only in the event that small alpha [low] L (small theta) = -small alpha [low] C (small theta), the filter frequency can be approximately constant, ie the value small omega [low] small theta roughly equals small omega [low] 0, whereby with a small omega [low] 0 the frequency at the set temperature with the values L [low] 0 and C [low] 0 is. In addition, ferrite materials are also of interest for filters with a temperature coefficient that fluctuates only slightly around zero, e.g. for resonant circuits with mica capacitors for wide temperature ranges, e.g. in portable devices, in which small alpha [low] L is approximately equal to small alpha [low] C is approximately equal to 0.

The µ [deep] i (small theta) curve of manganese-zinc ferrites and thus also the associated losses of medium and high permeability ferrites depend on the temperature curve of the saturation magnetization and the temperature curve of various energy parameters caused by the crystal anisotropy energy, the magnetostriction etc. can be determined. By choosing suitable compositions and sintering conditions, these dependencies can be controlled in such a way that so-called secondary permeability maxima or kinks occur in the µ [deep] i (small theta) curve in individual temperature ranges. This makes it possible to achieve small, approximately constant temperature coefficients in certain temperature ranges above these singularities.

For example, with the help of the Fe [high] 2+ component in the ferrite lattice, the crystal anisotropy energy can be influenced, whereby a certain Fe [high] 2+ amount is required to lower the crystal anisotropy energy to zero at a certain temperature. The lower this temperature should be - only above this zero crossing - the temperature coefficient is sufficiently small, easily controllable and the losses, especially the hysteresis losses, are low - the more Fe [high] 2+ ions must be present in the ferrite lattice.

The Fe [high] 2+ ion content in the ferrite lattice can be controlled in two ways, namely

1. About the total iron content, because part of the iron ions, which exceeds the weighted in 50 mol% Fe [deep] 2O [deep] 3, becomes bivalent during ferrite formation for reasons of charge neutrality - formally FeOFe [deep ] 2O [deep] 3 - and

2. As can be inferred from German patents 13 00 860, 12 23 734 and 16 71 035, about the incorporation of tetravalent ions such as Sn and Ti ions, which make two - initially trivalent - iron ions divalent in each case to a tetravalent metal ion, by formally Ti [high] 4 + Fe [low] 2 [high] 2 + O [low] 4 or Sn [high] 4 + Fe [low] 2 [high] 2 + O [low] 4.

In addition to Fe [high] 2+ ions, the crystal anisotropy can also be strongly influenced by cobalt ions and thus the temperature coefficient of the initial permeability can be controlled.

Each of these methods of controlling the TC, namely the use of a stoichiometric iron content, the substitution of some of the main components by tin and / or titanium or the addition of cobalt has already been used to control the TC of manganese-zinc ferrites, with the different procedures can sometimes produce similar results.

The present invention is based on the object of creating a Sn- and Ti-substituted, highly or medium-permeable, low-loss and Ca-containing manganese-zinc ferrite with a wide temperature coefficient of the initial permeability and thus a ferrite which enables the components to be reduced in size and in addition to narrowing the wide range of types required up to now.

Surprisingly, it has been found that a suitable combination of those listed above known substitutions and additions brings results that are even better than those previously known, that in particular a very small addition of cobalt in a manganese-zinc-ferrite already optimized by tin and titanium allows an expansion of the application temperature range.

To solve the problem, the invention provides a ferrite with about 0.03 to 0.4 wt .-% CaO of the following composition of its starting components:

49 to 55 mol% Fe [deep] 2O [deep] 3

of which 0.2 to 5 mol% (SnO [deep] 2 + TiO [deep] 2)

Remainder MnO and ZnO

which additionally contains very small amounts of CoO, in particular only 0.02 to 0.5% by weight of CoO, the CoO amount being in accordance with the target Fe [high] 2+ content, controlled by the proportion of Sn, Ti and super stoichiometric iron, is chosen so that the desired TK of the initial permeability is established.

An advantageous process for producing a ferrite of the above type provides that the following composition of starting components:

49 to 55 mol% Fe [deep] 2O [deep] 3

of which 0.2 to 5 mol% (SnO [deep] 2 + TiO [deep] 2)

Remainder MnO and ZnO

additionally 0.02 to 0.5% by weight of CoO

mixed, if necessary thermally pretreated, with the addition of about 0.05 to 0.4% by weight CaCO [deep] 3, ground, pressed into cores, in pure inert gas, in particular N [deep] 2 at sintering temperature, in particular 1100 to 1300 ° C, sintered at this temperature in O [deep] 2 -containing N [deep] 2 atmosphere and cooled in N [deep] 2 atmosphere with decreasing O [deep] 2 partial pressure.

The possible control of the TC of the initial permeability according to the invention by appropriate addition of CoO can be seen, for example, from FIGS. 1 and 2, with FIG. 1 showing a basic composition of

52.95 mol% Fe [deep] 2O [deep] 3

32.60 mole percent MnO

13.55 mole percent ZnO

0.50 mol% SnO [deep] 2

0.40 mol% TiO [deep] 2

and in Fig. 2 for a basic composition of

52.43 mol% Fe [deep] 2O [deep] 3

32.62 mole percent MnO

13.55 mole percent ZnO

0.50 mol% SnO [deep] 2

0.90 mol% TiO [deep] 2

the temperature dependence of the initial permeability µ [deep] i on the CoO content is shown. For each +0.01% by weight CoO or 0.016 mol% CoO, the secondary permeability maximum or the µ [deep] i-shoulder is around -7 ° C or around -7 to -10 ° C moved. The same shift of the secondary permeability maximum from -7 to -10 ° C by Fe [high] 2+ ions requires about ten times as many Fe [high] 2+ ions as Co ions. It is thus possible to work with extremely low iron values and still get a kink in the µ [deep] i (small theta) curve at a very low temperature. The advantage that can be achieved in this way is, inter alia, that the symptoms of disaccommodation that occur with a high iron content are avoided. An additional advantage of the TC control of the µ [deep] i with the help of Co ions is that you can work not only with low iron contents but also with low zinc contents, ie at high Curie temperatures, without the µ [deep] i (small theta) curve sags between the high and low temperature maximum. A possible cause for this is a tertiary permeability maximum generated by the Co ions (see FIG. 3 Ferrite A), this ferrite being deliberately sintered in such a way that the maximum, which is here at approx. + 90 ° C., is clearly expressed . Normally, however, the sintering will be chosen so that the ferrite has the µ [deep] i (small theta) curve drawn in broken lines in FIG. 3, with the small alpha [deep] L then being constant over a wide range. An example of this is the ferrite B. Small alpha / µ [deep] i is 0.4 x 10 [high] -6K [high] -1 so small that the effective permeability µ [deep] i can be doubled, if the same capacitor is used in the filter as before when using substances with small alpha / µ [deep] i = 0.8 x 10 [high] -6K [high] -1. The smoothing of the µ [deep] i (small theta) curve was achieved in the present case by shifting the maxima marked I, II and III, namely the Hopkinson or primary maximum, secondary maximum and third maximum closer together, so that there is no more ripple in the µ [deep] i (small theta) curve.

The invention is explained below with the aid of examples, which show in particular the advantageous manner in which Co ions can be used in extremely low doses to control the TK (Sn + Ti) -substituted manganese-zinc-ferrites and how, at the same time, very low loss values and a small inconsistency can be achieved.

Embodiment 1

A mixture with the following composition of its starting components:

51.5 mol% Fe [deep] 2O [deep] 3

31.0 mole percent MnO

16.5 mole percent ZnO

0.5 mol% SnO [deep] 2

0.5 mol% TiO [deep] 2

additionally 0.2% by weight CoO

was mixed in distilled water in vibrating mills for 2 to 4 hours, thermally pretreated for one hour at 850 ° C. and then with the addition of a CaCo [deep] 3 amount, which leads to about 0.06% by weight of CaO in the end product, for 2 hours wet milled. The toroidal cores pressed from the dried mixture with 1 kBar were heated in pure N [deep] 2 gas and sintered at 1250 to 1300 ° C. in 2 to 4 vol% O [deep] 2 -containing N [deep] 2 atmosphere and cooled in an N [deep] 2 atmosphere with decreasing O [deep] 2 partial pressure, with only </ = 20 ppm O at 1100 ° C and 0.8% by volume of O [deep] 2 and below 900 ° C [deep] 2 are present.

The temperature dependence of the initial permeability μ [deep] i on the temperature is shown for this ferrite in FIG. 3 (see ferrite B). This highly permeable ferrite has a Curie temperature of 175 ° C and, in a wide temperature range, the smallest loss coefficients and a strictly constant positive TC.

The technical data of this ferrite are:

µ [deep] i = 3500

tan small delta / µ [low] i = 1.5 x 110 [high] -6 at 100 kHz

= 0.8 x 10 [high] -6 at 20 kHz

= 0.5 x 10 [high] -6 at 5 kHz small Eta [low] B = 0.25 x 10 [high] -6 / mT at 100 kHz

= 0.15 x 10 [high] -6 / mT at 20 kHz

D / µ [low] i = 2 x 10 [high] -6, 2 h 20 h,

measured at 60 ° C.

The related temperature coefficient small alpha / µ [low] i is constant between -40 and + 80 ° C and only positive and is (0.4 +/- 0.05) x 10 [high] -6K [high] -1. It can also be set to (0.7 +/- 0.1) x 10 [high] -6K [high] -1 for the same temperature range through stronger oxidation during cooling.

A material of the same composition, but without the addition of CoO according to the invention, has otherwise analogous electrical properties

small alpha / µ [low] i = 0.2 x 10 [high] -6K [high] -1 from 20 to 60 ° C

and

small alpha / µ [low] i = (1.5 to 2.5) x 10 [high] -6K [high] -1 from 20 to -40 ° C,

thus a strong kink in the µ [deep] i (small theta) curve.

Embodiment 2

A ferrite with the following composition of its starting components:

50.55 mol% Fe [deep] 2O [deep] 3

32.25 mole percent MnO

14.75 mole percent ZnO

0.61 mol% SnO [deep] 2

1.84 mol% TiO [deep] 2

an additional 0.05% by weight of CoO was pretreated in the manner explained in Example 1 and 0.1% by weight of CaCO [deep] 3 was added. The compacts produced from this were then heated to 1150 to 1200 ° C. in pure N [deep] 2 gas, sintered at this temperature in an N [deep] 2 atmosphere containing 1 to 2% O [deep] 2 and sintered in N [ deep] 2 atmosphere with decreasing O [deep] 2 content, such that 180 ppm O [deep] 2 were still present at 1000 ° C and 10 ppm O [deep] 2 were still present at 900 ° C. The medium-permeable ferrite obtained in this way had the following technical data:

µ [deep] i = 1600

tan small delta / µ [low] i = 1.1 x 10 [high] -6 at 100 kHz

= 6.7 x 10 [high] -6 at 500 kHz

small eta [deep] B = 0.2 x 10 [high] -6 / mT (100 kHz)

D / µ [low] i = 3 x 10 [high] -6 measured at 60 ° C,

between 2 h and 8 pm

small alpha / µ [low] i = (0.45 +/- 0.05) x 10 [high] -6K [high] -1

from -20 to + 80 ° C.

A similarly composed substance without the proportion of Co according to the invention has the following temperature coefficients with otherwise the same properties:

small alpha / µ [low] i = 0.6 x 10 [high] -6K [high] -1 from 20 to 80 ° C

small alpha / µ [low] i = (1.5 2.5) x 10 [high] -6K [high] -1

from 20 to -40 ° C.

Embodiment 3

A low-permeability material with the following sample composition:

51.4 mol% Fe [deep] 2O [deep] 3

33.1 mole percent MnO

14.1 mole percent ZnO

0.5 mol% SnO [deep] 2

0.9 mol% TiO [deep] 2

additionally 0.15% by weight of CoO

and 0.1 wt% CaCo [deep] 3

was treated essentially in the manner set out in Example 1. The 1 to 2 hour sintering took place at 1150 ° C. in an N [deep] 2 atmosphere containing 1% O [deep] 2. The cooling was carried out in an N [deep] 2 atmosphere with a steadily decreasing O [deep] 2 content to <20 ppm at 900 ° C.

The ferrite manufactured in this way is characterized by the following properties:

µ [deep] i = 1200

tan small delta / µ [low] i = 1.5 x 10 [high] -6 (100 kHz)

= 5.0 x 10 [high] -6 (500 kHz)

= 15 x 10 [high] -6 (800 kHz)

small eta [deep] B = 0.4 x 10 [high] -6 / mT (100 kHz)

D / µ [low] i <5 x 10 [high] -6, at 60 ° C,

between 2 and 8 pm

small alpha / µ [low] i = (0.75 +/- 0.05) x 10 [high] -6K [high] -1

from -40 to + 80 ° C

Without the addition of Co according to the invention, there is a strong kink in the μ [deep] i (small theta) curve with otherwise similar properties at room temperature, with

small alpha / µ [low] i = 0.2 x 10 [high] -6K [high] -1 from 20 to 60 ° C

small alpha / µ [low] i = (1.5 2) x 10 [high] -6K [high] -1 from 20 to -40 ° C.

Embodiment 4

In table 1 it is shown on the basis of the substances small beta 1 to small beta 5, how the kink or the maximum in the µ [deep] i (small theta) with a given composition due to increasing McoO amounts (see Fig. 2) -Curve is shifted towards lower temperatures, while at the same time extremely low loss coefficients occur in the low temperature range (and at temperatures above the temperature of the maximum). This gives you materials that can be used together with TK-O capacitors, for example. The substances small beta 1 to small beta 4 are most favorable in practice. These are medium-permeable substances that can be used very well up to frequencies of a few 100 kHz. Small beta 0 shows the properties of a substance without the additive according to the invention. The compacts are produced as in Example 1. The cores were sintered at 1190 ° C. in a 2.2% O [deep] 2 -containing N [deep] 2 atmosphere. The cores were cooled in an N [deep] 2 atmosphere with steadily decreasing O [deep] 2 partial pressure.

Embodiment 5

In Table 2 substances are compiled which also have a temperature coefficient fluctuating around zero, with a permeability of about 2000 N [deep] 2 atmosphere containing% O [deep] 2, cooled in N [deep] 2 with decreasing O [deep] 2 content.

Table 1:

Medium-permeable materials with extremely low losses at low and normal temperatures and a temperature coefficient fluctuating around +/- zero over a wide temperature range

Table 2:

Highly permeable materials with low loss coefficients in a wide temperature range and a temperature coefficient fluctuating around +/- zero in a wide temperature range

Claims (2)

1. Sn-Ti-substituted, high or medium permeability, low-loss and calcium-containing manganese-zinc ferrite with a constant and positive temperature coefficient of initial permeability over a wide temperature range, in particular between -60 ° C and + 100 ° C, or temperature coefficient that fluctuates only slightly around zero , characterized in that a ferrite mixed with approximately 0.03 to 0.4% by weight of CaO has the following composition of its starting components: 49 to 55 mol% Fe [deep] 2O [deep] 3 of that 0.2 to 5 mol% (SnO [deep] 2 + TiO [deep] 2) Remainder MnO and ZnO additionally contains very small amounts of CoO, in particular only 0.02 to 0.5% by weight of CoO, the amount of CoO being in accordance with the target Fe [high] 2+ content, controlled by the proportion of Sn, Ti and overstoichiometric iron, is chosen so that the desired TK of the initial permeability µ [deep] i is established. 2. A method for producing a manganese-zinc ferrite according to claim 1, characterized in that the following composition of starting components: 49.55 mol% Fe [deep] 2O [deep] 3 0.2 to 5 mol% SnO [deep] 2 and / or TiO [deep] 2 Remainder MnO and ZnO additionally 0.02 to 0.5% by weight of CoO mixed, in particular thermally pretreated, with the addition of about 0.05 to 0.4% by weight CaCO [deep] 3, ground, pressed into cores, in pure inert gas, in particular N [deep] 2, at sintering temperature, in particular 1100 to 1300 ° C, sintered at this temperature in O [deep] 2 -containing N [deep] 2 atmosphere and cooled in N [deep] 2 atmosphere with decreasing O [deep] 2 partial pressure.