DE1696425B1 - Process for the production of a polycrystalline ferrite body - Google Patents

Description

The invention relates to a method for producing a polycrystalline ferrite body with a specific resistance greater than 10 ² ohm cm, in which a starting mixture of metal oxides and / or carbonates, pre-sintered at a temperature not higher than 950 ° C., in weight ratios corresponding to Composition of the body to be produced according to the formula

Ni ^ CUrCOiFea - ^ - yjiAl, Cr, Mn) _y O_. , 0

is sintered after shaping by pressing in an oxygen atmosphere.

Ferrite bodies which are produced by a known method of this type have a porosity r ₅ of more than 5 percent by volume.

The invention is based on the object of providing ferrite bodies with a porosity of less than 1 percent by volume to accomplish.

Such dense ferrite bodies have a high magnetic coupling factor (a property that is known to be particularly important for use as a magnetomechanical conversion element is) and / or a very low coercive force and / or a high wear resistance compared to mechanical Forces on; the latter are very suitable as magnetic heads for sound recording and reproduction.

It is already known to obtain ferrite bodies which have a density that is only very slightly lower than the theoretical density, which is also called "absolute density" or "X-ray density". Are defined the porosity p, expressed as a percentage of the total volume of the ferrite body, is taken as

35

_{p =}

In which formula d _{s represents} the apparent density, ie the quotient ^ - of the weight w in grams and the external volume ν in cm ³ , and d _{r represents} the "X-ray density ", then magnesium ferrite bodies with a porosity ρ of 0 are already in the specialist literature , 6 percent by volume mentioned. However, these magnesium ferrite bodies contain a high content of divalent iron and consequently have a low specific resistance of less than 10 ² ohm · cm, a fact which considerably limits their application at high frequencies.

The professional world was previously of the opinion that particularly low-pore ceramic bodies only under Using small amounts of so-called modifiers can be produced. These modifiers serve to slow down the grain growth during sintering, but at the same time worsen the electrical and / or magnetic properties of the ferrite bodies. *

The invention overcomes these disadvantages and provides a method of production of the type mentioned in the opening paragraph of ferrite bodies with a porosity less than 1 percent by volume, preferably less than 0.5 percent by volume, in that in the formula

0 ^ a ^ 1
0 < b ^ 1

0 ^ c S 0.2

a + b + c + d = l 0 ^ x ^ 0.08
0 g y ^ 0.25

3.8

is chosen and in which from chemically very pure raw materials with a maximum content of 0.01 percent by weight Starting mixture consisting essentially of no particles larger than sulfate ions 0.5 μ, preferably no particles larger than 0.1 μ are present and the sintering conditions are chosen so that only slow grain growth occurs.

A high magnetic coupling factor occurs particularly in the cases where b = 0 in the above formula; Such ferrite bodies are particularly suitable as magnetomechanical conversion elements. On the other hand, ferrite bodies with compositions in which a < 0.5 and d - 0 in the above formula are high in wear resistance, so that these bodies are mainly used as magnetic heads.

It is well known that ferrite bodies for electromagnetic use are usually produced in the following way: A finely comminuted mixture of metal oxides (if necessary to be replaced by the corresponding metal carbonates or other corresponding metal compounds that are converted into metal oxides when heated strongly) is granulated by means of a binder, into which Pressed desired shape and then sintered at a temperature of over 100O ⁰ C, often even over 1200 C. Usually, before final shaping, the mixture is first presintered by heating it for some time at a temperature lower than the temperature required for the final sintering. Depending on the duration and intensity of the heating during pre-sintering, a more or less large amount of ferrite is already formed from the starting mixture in this phase of the manufacturing process. It has been shown according to the invention that it is important to achieve the purposes set out here to pre-sinter the starting mixture at a temperature not higher than 950 ° C., in any case at a temperature at which only relatively little ferrite formation takes place. The most favorable pre-sintering temperature is of course dependent on the state in which the finely divided starting mixture is. So it does z. B. a big difference, whether it is a compressed mass or a so-called "fluidized bed".

In the context of the invention, it is also important to start from raw materials that are in high Dimensions are chemically pure. "Chemically very pure raw materials" are understood here to mean those raw materials which contain essentially no components that do not form a ferrite body with contribute to a chemical composition in the area of the formula mentioned above. It has shown, that in particular the presence of sulfate ions, even in extremely small quantities, in the raw materials for the production of the present ferrite body is disadvantageous. For obtaining ferrite bodies with a Porosity less than 0.5 percent by volume is therefore allowed

ORIGINAL! NSPECTEO

3 4

Starting mixture not more than 0.01 weight per cent, even densities were achieved that of the

contain sulfate ions. Radiographically determined densities not noticeable

The distribution fineness of the starting mixture differed,

also plays an important role in the context of the invention

Role. Particles larger than 0.5 μ have an unfavorable tip

gen influence. If one wishes to obtain ferrite bodies with a mixture of 18 mol percent porosity less than 0.5 volume percent NiO, 32 mol percent ZnO and 50 mol percent F ₂ O ₃ , the presence of particles must even be assumed. As a basic nickel greater than 0.1 u, the NiO was avoided in the starting mixture as carbonate as possible with less than 0.01 percent by weight. Weighed 10 impurities. The ZnO contains less

In the process of waxing the crystal bodies, 0.01% by weight of impurities must be observed. The Fe ₂ O, during the formation of the ferrite body in the end contains 0.1 percent by weight NiO; Further, it contains less than 0.02 weight percent impurities, pay special attention to the phase of manufacture. It has been shown that growth of the crystal grains that is too rapid during the sulfate ion content is less than 0.01 percent by weight. The Fe, O ₃ preparation consists of moderate formation of intragranular cavities particles with a size of about 0.1 μ. The mixture leads. "Intragranular cavities" are understood to mean cavities that are ground inside the mill for 16 hours with alcohol in a ball. After filtering and drying there are crystal grains, excessive formation of such voids, the mixture was pre-sintered in a crucible for 1 hour to the above-mentioned properties 20 at a temperature of 900 ° C. That the polycrystalline ferrite body is an unfavorable pre-sintered product is made fine and then 16 hours hold. Apparently, in the case of a relatively long, slow grain growth milled with alcohol in a ball mill, the microscopic gas bubbles that are already present in the grain The average particle size of the resulting nern existing microscopic gas bubbles is about 0.4 μ. still find a way out, while in a product that is too fast to grow granules, a quantity of the powder obtained will be surrounded by a dense ferrite layer and enclosed in the granules in a mortar with 12 percent by weight water. * mixed. The moist product is passed through a sieve

The grain growth rate depends closely with 20 meshes per running centimeter rubbed,

with the chemical composition and the reac- 30 and the granular material thus obtained is in one

Activity of the pre-sintered starting mixture to steel die under a pressure of 1 t cm ²

together. To explain, for example, the fact that the blocks are pressed into blocks. One of these blocks will

Essence of copper compounds in the starting point at a rate of 130 C per hour

mixture heated the growth rate of the grains and then heated for 48 hours at a temperature

noticeably increased. Also the type of pre-sintering 35 from 1220 to 1230 C in an oxygen atmosphere

can, as already noted, the reactivity of the sintered.

Material subjected to final sintering noticeably The apparent density of the obtained sintered body

influence. ^{We will therefore always like 3} for a given amount of 5,312. If you take into account.

Composition and reactivity of the starting material that the absolute density of the sintered body is 5,336 g cm ³

mixture the sintering temperature and the sintering time is 40, the porosity ρ is 0.45 percent by volume,

must choose such that the grain growth The sintered body is made of crystals with dimensions

speed remains below certain limits. between 20 and 45 ·>. built up. The special

If the material to be sintered is hard agglomerates, the resistance of the sintered body is fishy contains, it is recommended, the pre-sintered 1.4 · 10 "Ohm · cm, the magnetic initial gear mixture before final sintering in a propeller 45 permeability is 1440 and the coercive force mixing device to deagglomerate. The usual production process for 0.1 Oersted, pressing Example II and granulation preceding sintering is omitted

then. The pre-sintered starting mixture is started from a powder that, like

the final sintering and after any deagglomeration- 50 described in Example I, by pre-sintering, grinding

tion in a propeller mixer isostatically in a ball mill. Filtration and drying are

is compressed under a pressure of at least 0.2 t / m ² . An amount of the powder thus obtained will

mated. Usually this compression takes place under post-treatment in a propeller mixer

a pressure of at least 1 t / cm ² . Under »isosta- and then in a steel die to form a briquette

After compressing the powder, the 55 is pressed here. This briquette is packed in a rubber bag

Applying pressure on all sides to the powder. The rubber bag is evacuated and in

understood, e.g. B. in that a rubber bag in a hydrostatic press vessel under pressure

where the powder is located, immersed in water and compressed ^{by 1 t / cm 2.} The briquette will then come with

a pressure is exerted on the body of water (heated at a rate of 130 ^J C per hour

called "hydrostatic" compression). Pre &> and then for 48 hours at a temperature of

The starting mixture is preferably sintered in an oxygen atmosphere before iso-1230 C. the

static compression in a press die, the apparent density of the sintered body obtained in this way

pressed. is 5.336 g / cm ³ , corresponding to the absolute

The greatest densities of the ferrite bodies became density. Also from a microscopic sub-

achieved in that the sintering and the search for a polished cross-section of the ferrite '

subsequent cooling in a gas atmosphere with body shows that there are essentially no pores

a high oxygen content, e.g. B. are essentially lagging behind. The body is made of crystals

pure oxygen. Built on top of these with dimensions between 40 and 60 μ.

The specific resistance of the body is 1.4 · 10 ⁷ Ohm · cm, the coercive force is 0.065 Oersted and the initial magnetic permeability is 1620.

Example III

A briquette obtained in the manner described in Example II is heated in air to 1000 ° C. over a period of about 16 hours, then heated to a temperature of 1230 ° C. at a rate of 2 (X) C per hour and 24 hours heated in air at this temperature. The apparent density of the obtained sintered body is 5.326 like ³ , which means that the porosity ρ is 0.19 volume percent. The size of the crystals that make up the sintered body. is about 10; x.

IO

The specific resistance of the sintered body is 4 · 10 ^h ohm · cm, the initial magnetic permeability is 1260 and the coercive force is 0.136 oersted.

Example IV

To test the influence of the heating rate, a number of briquettes, which are placed on the im The manner described in Example II are obtained in different ovens at different speeds heated to a temperature of 1230 C and held at this temperature for 3 hours. The heating and sintering take place in an oxygen atmosphere. The table below shows the Influence of the heating rate on the properties of the sintered bodies obtained.

Heating rate, C'hours

Apparent density, like ³

Porosity />, volume percent

Specific resistance, ohm · cm
Initial permeability, u ,,

30th 50 130 260 350 600 5.302 5.314 5.316 5.310 5.230 5.311 0.64 0.41 0.38 0.49 0.30 0.47 6 ⁷ 2 · 10 ⁸ 5 - ΙΟ ⁸ 1 · 10 ⁶ 4 · 10 ⁷ 7 · 10 ⁴ 1320 1150 1380 1460 1200 1500

Example V

It is made from a mixture of 18.367 mole percent NiO. 32.53 mol percent ZnO and 48.98 mol percent Fe ₂ O _{3 were} assumed. The NiO is weighed in as a basic nickel carbonate with less than 0.01 percent by weight impurities. The ZnO contains less than 0.01 weight percent impurities. The Fe ₂ O ₃ contains less than 0.1 weight percent impurities, of which less than 0.01 weight percent is sulfate ions. The particle size of the Fc ₂ O ₃ preparation is between 0.1 and a few microns. The mixture is ground with alcohol in a ball mill for 16 hours, then filtered off, dried and pre-sintered in a crucible at a temperature of 9 (X) C for 1 hour. The pre-sintered product is made fine and then ground in a ball mill with alcohol for 16 hours. After filtering and drying, the milled product is rubbed through a sieve with H) meshes per running centimeter and then thoroughly re-milled in a vibration mill for a further 48 hours. The average particle size of the mill product thus obtained is about 0.4 a.

After filtering and drying, a quantity of the ground product is pressed into a briquette, as described in Example It. The briquette is heated at a rate of 130 C per hour and sintered for 48 hours at a temperature of 1240 C in an oxygen atmosphere. The apparent density of the sintered body thus obtained is 5.291 g cm ³ , which corresponds to a porosity of 0.84 percent by volume. The size of the crystals that make up the sintered body. is on average 15 μ. The specific resistance of the sintered body is 10 ^ ohm · cm, the initial magnetic permeability 1280 and the coercive force 0.0935 Oersted.

Example VI

A mixture of 18 mol percent NiO, 32 mol percent ZnO and 50 mol percent Fe ₂ O is assumed. The NiO is weighed in as a basic nickel carbonate with less than 0.08 percent by weight impurities. The ZnO contains less than 0.01 weight percent impurities. The Fe ₂ O ₃ preparation contains 0.1 percent by weight Cr ₂ O ₃ and 0.4 percent by weight CuO. It also contains less than 0.02 percent by weight of impurities, of which less than 0.01 percent by weight is sulfate ions. The particle size of the Fe ₂ O ₃ preparation is about 0.08 μ. The mixture is ball milled with alcohol for 16 hours.

.15 After filtering and drying, a quantity of the powder obtained is pressed into a briquette, as described in Example II. This briquette is heated at a rate of 2 (X) C per hour and then sintered by heating at 1225 C for 21 hours in an oxygen atmosphere. The apparent density of the sintered body obtained in this way is 5.061 g cm ³ , which corresponds to a porosity ρ of 5.15 percent by volume. The initial magnetic permeability of the sintered body is 1130, the coercive force is 0.19 oersted.

The rest of the powder is pre-sintered in a crucible at a temperature of 9 (X) C for 1 hour. That Presintered product is ground in a ball mill with alcohol for 16 hours. The average Particle size of the mill product obtained is about 0.4 μ. After filtering and drying, a Part of the milled product is pressed into a briquette in the manner described in Example II and then, pre-sintered as described in the previous paragraph. The apparent density of the so obtained Sintered body is 5,320, which corresponds to a porosity of 0.30 percent by volume. The size of the crystals from which the sintered body is built is an average of 30 μ. The specific resistance

<*> of the sintered body is 4.5 x 10 ⁸ ohm cm, and the initial magnetic permeability is 1240. the coercive force is 0.13 oersted.

Example VII

It is made from a mixture of 48.6 mole percent NiO. 1.4 mol percent CoO and 50 mol percent Fe ₂ O ₃ assumed. The NiO is used as a basic nickel carbonate with less than 0.01 percent by weight

impurities weighed in. The CoO is weighed out as cobalt carbonate with less than 0.1 weight percent impurities, _{apart from impurities of about 0.2 weight percent Fe 2} O ₃ and about 0.2 weight percent NiO. The content of impurities in the Fe ₂ O ₃ preparation is less than 0.02 percent by weight, apart from 0.1 percent by weight of NiO. The sulfate ion content in the Fe ₂ O, preparation is less than 0.01 percent by weight. The particle size of the Fe ₂ O ₃ preparation is about 0.1 α. The mixture is ground with alcohol in a ball mill for 16 hours. After filtering and drying, the powder is rubbed through a sieve with 10 meshes per linear centimeter and pre-sintered in a crucible for 1 hour at a temperature of 900 C in oxygen. The pre-sintered product is made fine and then ground in a ball mill with alcohol for 16 hours. The average particle size of the ground product obtained in this way is about 0.4 μ.

After filtering and drying the milled product, a briquette is pressed from the product in the manner described in Example II. The briquette obtained is heated at a rate of 130 ° C. per hour and sintered in oxygen at a temperature of 1240 ° C. for 48 hours. The apparent density of the obtained sintered body is 5.321 g cm ³ . Since the absolute density of the sintered body 5,366gern is ^3, the body has a porosity ρ of 0.84 volume percent. The specific resistance of the sintered body is 10 ⁴ ohm · cm. the coercive force is 2.25 oersteds. Rings with an inside diameter of 20 mm, an outside diameter of 28 mm and a height of 4 mm are drilled from the sintered briquette. The following piezomagnetic coupling factors are measured from these rings:

For strain oscillation k _3i = 0.50,
Door torsional vibration fc ₁₅ = 0.62.

while the measuring temperature is about 33 ° C. in both cases.

Example VIII

A mixture of 39.28 mol percent NiO, 9.82 mol percent CuO, 0.90 mol percent CoO and 50 mol percent Fe ₂ O is assumed. Reference is made to Example VII for the degree of purity of the nickel compound, the cobalt compound and the iron compound. The content of impurities in the CuO preparation is less than 0.03 percent by weight. The mixture is processed in the same way as described in Example VII to give a presintered and ground mass, while a briquette is also formed from this mass in the manner described in Example VII. This briquette is heated at a rate of 200 C per hour and sintered for 48 hours at a temperature of IKX) C in an oxygen atmosphere. ^b0

The apparent density of the sintered body obtained is 5.366 g cm ³ , which means, given a measured absolute density of 5.376 g cm ³ , that the porosity of the body is only 0.19 percent by volume. The specific resistance is 7 · IO ohm · cm. the << 5 coercive force 1.6 oersteds.

Rings with an inside diameter of 20 mm are drilled from the sintered briquette. one

40 outer diameter of 28 mm and a height of 4 mm. A value k = 0.455 at 18 C is measured from these rings for the piezomagnetic coupling factor (expansion oscillation).

Example IX

A mixture of 40 mol percent NiO, 5 mol percent ZnO, 5 mol percent CuO, 2.5 mol percent Mn ₂ O ₃ and 47.5 mol percent Fe ₂ O _{3 is} assumed. The NiO is weighed in as nickel oxide with an impurity content of less than 0.03 percent by weight. The impurity content of the ZnO preparation is less than 0.01 percent by weight. The CuO preparation has an impurity content of less than 0.03 percent by weight. The Mn ₂ O ₃ is weighed in as manganese carbonate with an impurity content of less than 0.04 percent by weight. The FejO ^ preparation consisting of particles with a "size of about 0.1 μ" contains an amount of 0.2 percent by weight NiO. Apart from this, the content of further impurities in the Fe ₂ O preparation is less than 0.05 percent by weight, during particularly the Sulfate ion content is less than 0.01 percent by weight. The mixture is milled with alcohol in a ball mill for 16 hours. After filtering and drying, the mixture is presintered in a crucible for 1 hour at 9 (K) C. The presintered product is made fine and then 16 Milled in a ball mill with alcohol for hours.

The milled product is filtered and dried. In the manner described in Example II, a quantity of the dry ground product is pressed into a briquette. This briquette is heated at a rate of 50 C per hour and sintered in oxygen at a temperature of 1240 C for 48 hours. The apparent density of the sintered body obtained is 5,351 g cm ³ . Since the absolute density of the body is 5.366 g cm ³ , the porosity ρ of the body is 0.28 percent by volume. The body is made up of crystals with an average size of around 75 μ. The resistivity of the body is 3 x 10 7 "ohms cm.

Example X

It is made from a mixture of 24.375 mole percent NiO, 24.375 mole percent ZnO. 1.25 mole percent CoO and 50 mole percent Fe ₂ O ₃ assumed. The NiO is weighed in as nickel oxide with an impurity content of less than 0.03 percent by weight. The ZnO preparation contains less than 0.01 percent by weight of impurities. The CoO is weighed out as cobalt carbonate containing about 0.2 percent by weight Fe ₂ O ₃ and about 0.2 percent by weight NiO, while the remaining impurities are less than 0.1 percent by weight. The Fe ₂ O ₃ preparation with a particle size of about 0.1 μ contains, in addition to about 0.2 percent by weight NiO, less than 0.05 percent by weight of impurities. The sulfate ion content in the Fe ₂ O ₃ preparation is less than 0.01 percent by weight. The mixture is ball milled with alcohol for 16 hours. After filtering and drying, the mixture is presintered at a temperature of 900 ° C. for 1 hour. The pre-sintered product is made fine and then ground in a ball mill with alcohol for 16 hours.

The ground product is filtered and dried, whereupon in the manner described ^{in Example ΐ τ}

909 583166

a briquette is pressed from a quantity of the dry ground product. The briquette is heated at a rate of 180 ° C per hour to a sintering temperature of 1245 ° C. The latter temperature is maintained for 30 minutes. Sintering takes place in an oxygen atmosphere. The sintered body is cooled at a rate of 130 ^° C. per hour. The apparent density of the obtained sintered body is 5.33 g / cm ³ , the absolute density 5.34 g / cm ³ , so that the porosity ρ is about 0.2 percent by volume. The specific resistance of the sintered body is 7 · 10 ⁸ ohm · cm.

Example XI

15th

A mixture of 16.192 mol percent NiO, 34.408 mol percent ZnO and 49.9 mol percent Fe ₂ O _{3 is} assumed. The NiO is weighed out as nickel carbonate with an impurity content of about 0.15 percent by weight. The impurity content of the Zn O preparation is below 0.01 percent by weight. The Fe ₂ O ₃ preparation contains about 0.2 percent by weight Ni O. It also contains less than 0.05 percent by weight of impurities, while the sulfate ion content is less than 0.01 percent by weight. The particle size of the Fe ₂ O ₃ preparation is about 0.1 . The mixture is ground for 16 hours with alcohol in a ball mill. After filtering off and drying, the mixture is presintered for 1 hour at 600 ° C. The presintered product is then ground for 16 hours with alcohol in a ball mill. In this way, a milled product with an average particle size is obtained After filtering and drying the ground product, a briquette is pressed from the product in the manner described in Example IT The briquette is heated to a temperature of 1100 ° C. at a rate of 130 ° C. per hour and 47 ¹ Z are _{held at this temperature for 2} hours. Then the temperature is increased at a rate of 100 ° C. per hour up to 1300 ° C., which temperature is maintained for about 1 hour. The sintering takes place in an oxygen atmosphere Sintering is slowly cooled.

The apparent density of the sintered body obtained is 5,317 g / cm ³ . The absolute density is 5.341 g / cm ³ and the porosity ρ is 0.45 percent by volume. The specific resistance of the sintered body is 8 · 10 ⁸ ohm · cm, the initial magnetic permeability is 2070 and the coercive force is 0.06 oersted.

Claims (6)

Patent claims: 1. A process for the production of a polycrystalline ferrite body with a specific resistance greater than 10 ² ohm ■ cm, in which a ^{starting mixture of metal oxides and / or carbonates pre-sintered at a temperature not higher than 950 0} C in weight ratios corresponding to the composition of the body to be produced according to the formula Ni ₀ Zn ^ Cu ₁ COjFe ,, - ,,.,., (AI, Cr, Mn) ^ O .. is sintered after shaping by pressing in an oxygen atmosphere, characterized in that that to achieve a ferrite body with a porosity less than 1 volume percent, preferably less than 0.5 volume percent, in the formula 0 ύ a ^ 1 0 g b ^ 1 O ^ fg 0.2 0 g d ^ 1 a + b + c + d = I Q ^ x ^ 0.08 0 ^ y ^ 0.25 3.8 I: g 4 is chosen and in which from chemically very pure raw materials with a maximum content of 0.01 weight percent sulfate ion starting mixture consisting essentially of no particles greater than 0.5; z, preferably no particles greater than 0.1 α are present and the sintering conditions be chosen so that only slow grain growth occurs. 2. The method according to claim 1, in particular for the production of a ferrite body for use as a magnetomechanical conversion element, characterized in that b = 0 in the formula. 3. The method according to claim 1, in particular for the production of a ferrite body for use as a magnetic head for sound recording and playback, characterized in that a < 0.5 and d = 0 in the formula. 4. The method according to any one of claims 1 to 3, characterized in that the presintered Starting mixture is deagglomerated in a propeller mixer before final sintering. 5. The method according to any one of claims 1 to 4, characterized in that the pre-sintered starting mixture is compressed isostatically under a pressure of at least 0.2 t / cm ² in a propeller mixer before final sintering and after any deagglomeration. 6. The method according to claim 5, characterized in that the starting mixture before isostatic compression is pre-pressed in a press die.