JP2016074592A - Mn-Zn-BASED FERRITE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Mn-Zn-based ferrite capable of achieving high magnetic permeability property with initial permeability at 10 kHz and room temperature of 10000 or more by burning at relatively low temperature and for a short time and large cost down.SOLUTION: There is provided a Mn-Zn-based ferrite containing FeO:52 to 54 mol%, ZnO:20 to 23 mol% and MnO:23 to 28 mol%, and further SiO:0.005 mass% or less and CaO:0.030 mass% or less with the Al content of the FeOin a range of 0.040 to 0.10 mass%.SELECTED DRAWING: None

Description

  The present invention relates to a Mn—Zn-based ferrite suitable as a transformer core used for transmission and amplification of digital signals in communication equipment, acoustic equipment, and the like.

  Mn—Zn-based oxide magnetic materials So-called Mn—Zn-based ferrites are widely used as magnetic core materials for coils and transformers of various communication devices and power supplies. In particular, recently, with the downsizing and thinning of electronic equipment, Mn-Zn ferrites are also required to have a particularly small core, and in response to this, magnetic characteristics that are superior to those of the past, that is, high magnetic permeability. It is desirable to have.

In order to improve the above-mentioned magnetic properties in Mn-Zn ferrite, it is important to add a trace compound that segregates at the ferrite grain boundaries and changes the properties of the material in various ways. Various attempts have been made to improve the magnetic properties by adding such trace components.
For example, Patent Document 1 proposes that an appropriate amount of Bi ₂ O ₃ is added to Mn—Zn-based ferrite, and a characteristic with an initial permeability μi = 9500 at 10 kHz is obtained. Here, the initial permeability μi is expressed as a ratio to the vacuum permeability μo.
However, the technique according to this proposal has an initial magnetic permeability limited to about 10,000 at most, and in order to realize an initial magnetic permeability of 10,000 or more necessary for downsizing of the core, which is increasing in practical use. Not enough improvement has been made.

On the other hand, in Patent Document 2, Patent Document 3 and Patent Document 4, Mn—Zn ferrite having an initial permeability of 10,000 or more can be obtained by using aluminum oxide (Al ₂ O ₃ ) as a trace additive. It has been shown.
Patent Document 2 discloses an Mn—Zn-based ferrite in which μi> 12000 is achieved by adding Al ₂ O ₃ : 0.005 to 0.05 mass% and firing at 1350 ° C. for 5 hours. However, it is specialized in magnetic head materials and requires a long time of 5 hours for holding at a high temperature of 1350 ° C. or higher, which causes an increase in cost and a decrease in productivity.

In addition, in Patent Document 3, Al ₂ O ₃ : 0.005 to 0.05 mass% is added, and Mn—Zn ferrite in which μi> 18000 is achieved by firing at 1330 to 1370 ° C. for 4 hours. However, it requires a long firing time of 4 hours for holding at a high temperature of 1330 ° C. or higher, which also raises a problem of cost increase.
Furthermore, Patent Document 4 shows an Mn—Zn ferrite in which μi> 15000 is achieved by adding Al ₂ O ₃ : 0.005 to 0.03 mass% and firing at 1370 ° C. for 3 hours. Has been.

Japanese Examined Patent Publication No. 62-53446 JP-A-51-53299 Japanese Patent Laid-Open No. 2-129063 JP 10-335130 A

  However, even the technique described in Patent Document 4 requires high-temperature firing at 1370 ° C. or higher, and there are problems in productivity, such as rapid deterioration of the firing furnace refractory.

  An object of the present invention is to advantageously solve the above problems by reviewing and improving the above-described conventional technology, and in particular, has a high magnetic permeability characteristic in which the initial permeability at 10 kHz and room temperature is 10,000 or more. An object of the present invention is to propose a Mn—Zn-based ferrite that can be achieved by firing at a relatively low temperature and in a short time, and that can greatly reduce the cost.

We, for the realization of the object was studied conditions which may produce a Mn-Zn ferrite having a high initial permeability in MnO-ZnO-Fe ₂ O ₃ ternary ferrite.
That is, paying attention to the raw iron oxide obtained by roasting the iron chloride solution, we have intensively studied what kind of raw iron oxide the impurity content can be used to increase the initial permeability in the final core. As a result, we obtained new knowledge that limiting the amount of Al (aluminum) in the raw iron oxide within a certain range is extremely effective in achieving the intended purpose.

That is, the gist configuration of the present invention is as follows.
_{(1) Fe 2 O 3:} 52~54mol%,
ZnO: 20-23 mol% and MnO: 23-28 mol%
Further contain SiO _2: 0.005 mass% or less and CaO: containing less 0.030 mass%,
The Mn—Zn based ferrite characterized in that the Fe ₂ O ₃ has an Al content of 0.040 to 0.10 mass%.

(2) The Mn—Zn ferrite as described in (1) above, wherein the initial permeability at 10 kHz is 10,000 or more.

  According to the present invention, an Mn—Zn ferrite having an initial permeability of 10,000 or more can be produced by a firing process at a relatively low temperature for a short time. Therefore, a transformer used for transmission and amplification of digital signals such as communication equipment. Materials useful as a core can be provided at low cost.

Hereinafter, the Mn—Zn ferrite targeted by the present invention will be described in detail. First, the basic component composition of Mn—Zn-based ferrite will be described in order from the reason for limiting it to the above range.
· Fe ₂ O _3: 52~54mol%
The magnetostriction constant of Mn—Zn-based ferrite varies greatly depending on the content of Fe ₂ O _3. If this magnetostriction constant is zero, the magnetic permeability increases greatly. The content of Fe ₂ O ₃ at which the magnetostriction constant becomes zero is around 52.5 mol%, and in order to realize a high initial permeability, it is necessary to control the Fe ₂ O ₃ content as close to 52.5 mol% as possible. There is. If the amount is too small, the saturation magnetic flux density also decreases. Therefore, in order to achieve a high initial permeability while maintaining a high value, the content of Fe ₂ O ₃ needs to be 52 mol% or more. On the other hand, if the content of Fe ₂ O ₃ is too large, the magnetic anisotropy constant increases, loss increases, and magnetic permeability decreases, so the upper limit is made 54 mol%.

ZnO: 20-25 mol%
When the content of ZnO is too small, the saturation magnetic flux density decreases, but if the composition with Fe ₂ O ₃ is adjusted to an appropriate range, the magnetic anisotropy constant at room temperature is maintained while maintaining a high saturation magnetic flux density. As a result, the initial permeability increases. Here, when the content of ZnO is small, the initial permeability is reduced, but in order to maintain the initial permeability of 10,000 or more, the content of ZnO needs to be 20 mol% or more. On the other hand, if the ZnO content is too large, the magnetic anisotropy constant at room temperature increases, and not only the saturation magnetic flux density decreases but also the Curie temperature decreases, which is disadvantageous. Therefore, in order to maintain the initial permeability of 10,000 or more, the upper limit of the ZnO content is 25 mol%.

MnO: 23 to 28 mol%
When the content of MnO is less than 23 mol%, the magnetic anisotropy constant at room temperature increases with a negative value due to the balance of Fe ₂ O ₃ and ZnO. On the other hand, if the content of MnO exceeds 28 mol%, the magnetic anisotropy constant increases with a positive value, so that it is difficult to maintain an initial permeability of 10,000 or more.

As described above, it is of course the most important to determine the basic composition of Fe ₂ O ₃ , ZnO, and MnO, but this alone realizes a large initial permeability as described above by firing at a low temperature for a short time. Has its limits. Therefore, the inventors further studied. As a result, it has been newly found out that the above problem can be solved by regulating the amount of Al in particular among impurities in the raw iron oxide recovered by baking the iron chloride solution.
Here, the effects of various impurities including Al ₂ O ₃ in the Mn—Zn ferrite are described, for example, on page 47 of the document “Ferrite” (Hiraga et al., Maruzen, 1986). This is a reference to the result of adding and firing as an additional component later to a ferrite material produced using the above raw material, and does not consider the trace components originally contained in the raw material. Therefore, it has not been described at all how the aluminum element in the raw iron oxide originally contained has any influence on the initial permeability of ferrite.

On the other hand, in order to realize both the coarsening of the crystal grains and the uniform particle size distribution, which are indispensable for increasing the initial permeability, the inventors have changed the content of Al in the raw iron oxide to 0.040-0. It was found that it should be limited to the range of .10 mass%.
Here, the mechanism of the effect of Al in the raw iron oxide on the properties of the final sintered body has not been clarified yet, but Al is contained from the iron oxide stage in the production process of Mn-Zn ferrite. In the process involving chemical reaction such as calcining process and firing process after mixing raw materials, it may affect the crystal growth and crystal structure and affect the properties of the final sintered body, especially the initial permeability. .
In other words, compared to the conventional mixing of raw materials and mixing as an additive in the form of Al oxide in the pulverization step after calcination, the influence on the formation of the crystal structure in the mixing of raw materials to the firing step becomes significant. It is considered that a suitable crystal structure can be obtained even by firing at a low temperature for a short time and high initial permeability can be realized.

  Based on the above new findings, further studies were made on the proper Al content in iron oxide, which was expected by setting the Al content in the raw iron oxide in the range of 0.040 to 0.10 mass%. It has been found that characteristics can be obtained. That is, when the Al content is less than 0.040 mass%, the effect on crystal growth is small, and high-temperature and long-time firing is required as in the conventional case. On the other hand, when the Al content exceeds 0.10 mass%, the crystal growth is reversed. The effect becomes too great, abnormal grain growth occurs, and the initial permeability deteriorates.

  In addition, as the iron oxide with limited amount of Al, the iron chloride aqueous solution is roasted to recover the iron oxide having an Al content of 0.040 to 0.10 mass% from the iron chloride aqueous solution. If it can be obtained, it will not specifically limit. However, iron oxide produced by roasting a high-purity iron chloride aqueous solution obtained by refining the pickling waste liquid (waste hydrochloric acid) discharged in the steel pickling process is particularly preferable. The amount of Al in the iron oxide after the roasting step can be controlled by adjusting the amount of Al chloride used as an agglomerating / precipitating agent for impurities in the purification step.

More specifically, the pickling waste liquid contains impurities such as unconsumed hydrochloric acid, silica and phosphorus in addition to the main component ferrous chloride (FeCl ₂ ). Therefore, it is necessary to remove silica and phosphorus as much as possible from this pickling waste liquid. Therefore, an amount of Al chloride determined by the target impurity removal rate is mixed as an aggregating / sedimenting agent to separate and remove impurities. At that time, the Al content in the iron oxide raw material is adjusted to the expected range by adjusting the amount of Al chloride mixed according to the amount of Al remaining in the iron oxide raw material. Thereafter, when the waste liquid is spray roasted with a roaster, hydrochloric acid is recovered while iron oxide is by-produced. Finally, if impurities such as Ca, Mg and Cl contained in the iron oxide are removed by washing as necessary, iron oxide containing high purity and predetermined Al can be obtained.

In the Mn—Zn ferrite of the present invention, the following components can be further added.
・ SiO ₂ : 0.005 mass% or less ・ CaO: 0.030 mass% or less SiO ₂ is an additive component useful for increasing the initial permeability by increasing the sinterability and increasing the resistance of the grain boundary phase to reduce the loss. It is. For that purpose, it is preferable to add at least 0.0005 mass%. However, when SiO ₂ is too large, the influence of the impurity which reduces initial permeability prevents the domain wall motion increases. Therefore, when adding SiO ₂ , the upper limit is made 0.005 mass%.

CaO has an effect of increasing the initial permeability by increasing the resistance of the grain boundary together with SiO ₂ to reduce the loss. For that purpose, it is preferable to add at least 0.005 mass%. However, if the addition amount is too large as in SiO ₂ , the influence as an impurity that impedes domain wall movement and lowers the initial magnetic permeability increases. Therefore, when adding CaO, the upper limit is made 0.030 mass%.

  Next, the Mn—Zn-based ferrite of the present invention is usually calcined by mixing the powder raw materials so as to have the predetermined final composition described above. That is, in the calcining step, the zinc oxide and the manganese compound are mixed with the iron oxide recovered in the roasting step and calcined. As conditions for calcination, it is preferable to hold in the air in the range of 850 to 1000 ° C. for 1 to 3 hours.

The calcined product obtained in this calcining step is pulverized to a predetermined particle size and then formed into a predetermined shape. Here, the predetermined particle diameter is an average particle diameter of about 1 to 1.5 μm, and the shape is generally a toroidal shape with an outer diameter of about 3 mm to about 50 mm.
As molding conditions, it is common to use a molding pressure in the range of 1 to ² ton / mm ² depending on the shape.
The ferrite calcined powder is mixed with the above-mentioned additional components (SiO ₂ : 0.005 mass% or less and CaO: 0.030 mass% or less), pulverized, and granulated and compression molded.

  Next, the molded product obtained in the molding step is fired at a maximum holding temperature of 1300 to 1330 ° C. and a holding time of 1 to 2 hours. Here, the maximum holding temperature is 1300 to 1330 ° C. in order to complete the crystal structure of MnZn ferrite and realize a uniform crystal structure, and the holding time is the holding time at the maximum holding temperature. is there. The reason why the holding time is set to 1 to 2 hours is that the crystal structure of Mn—Zn ferrite is similarly completed to achieve a uniform crystal structure, and productivity can be improved by short-time firing. The holding time is the time from when the temperature reaches the maximum temperature until the temperature is maintained and before cooling starts.

In the present invention, it is preferable that the maximum holding temperature during firing is maintained at 1300 ° C. or higher, and the rate of temperature increase from 500 ° C. to the maximum holding temperature is 600 ° C./h or higher. Here, if the heating rate during firing is less than 600 ° C./h, it is difficult to achieve a high sintered density by short-time firing, and the initial permeability may be reduced. Therefore, it is preferable that the rate of temperature increase during firing in the production of Mn—Zn-based ferrite is 600 ° C./h or more.
Subsequently, it is heated to a temperature of 1300 ° C. or higher at the above-described rate of temperature rise in the atmosphere or nitrogen, or a mixed gas thereof, and baked while maintaining the temperature at 1300 to 1330 ° C. When the maximum holding temperature at the time of firing is less than 1300 ° C., the density of the sintered body becomes low and it becomes difficult to obtain a high initial magnetic permeability. In addition, although holding time changes with compositions of a ferrite, normally about 3 to 8 hours are required in order to implement | achieve high magnetic permeability. However, in the case of the present invention, since the sinterability is promoted by the effect of Al contained in the raw iron oxide, it is sufficient to hold for a short time of 1 to 2 hours.

Next, this invention is demonstrated based on an Example.
First, when recovering high-purity iron oxide by roasting the iron chloride solution after purifying the pickling waste liquid (waste hydrochloric acid), the amount of Al chloride used for coprecipitation and removal of impurities should be adjusted. Thereby producing iron oxides containing various amounts of Al. The amount of Al in iron oxide was measured by fluorescent X-ray analysis. Next, the raw materials were mixed under the composition of Fe ₂ O ₃ and ZnO having various compositions shown in Table 1 and the balance being MnO, and then calcined at 930 ° C. for 3 hours. To this calcined product, various amounts of SiO ₂ and CaO as additives listed in Table 1 were added, pulverized with a ball mill for 12 hours, and molded into a ring shape having an outer diameter of 36 mm, an inner diameter of 24 mm, and a height of 12 mm. Firing was carried out at 1320 ° C. for 1.5 hours in a nitrogen and air mixed gas with controlled oxygen partial pressure (3 to 5%). At this time, the rate of temperature increase from 500 ° C. to 1330 ° C. was set to 650 ° C./h.

The ring sample thus obtained was subjected to 10 windings, and the initial permeability was measured at a frequency of 10 kHz at room temperature.
The measurement results are also shown in Table 1.
In the same table, Invention Example No. 1-12 and Comparative Example No. 1 in which any requirement of the present invention is out of range for comparison. 1-10 are shown.
Further, as shown in Table 2, as Comparative Examples 11 to 14, in addition to the above-mentioned additive components, the calcined product produced in the same manner as described above except that high-purity iron oxide (Al: 0.001 mass%) was used. The Mn—Zn-based ferrite that was pulverized, shaped and fired in the same manner as described above by adding Al ₂ O ₃ was also evaluated.
The results are also shown in Table 2.

As can be seen from Table 1, in all of the inventive examples, the initial magnetic permeability was as high as 10,000 or more by limiting the amount of Al in the raw iron oxide to a range of 0.040 to 0.10 mass%.
On the other hand, all the comparative examples had an initial permeability of less than 10,000. In particular, Comparative Examples 11 to 14 shown in Table 2 are examples in which an Al oxide is added to the above calcined product and the Al amount in the final product is made the same as that of the inventive example, but all have an initial permeability of 10,000. Was less than.

Claims (2)

Fe ₂ O _3: 52~54mol%,
ZnO: 20-23 mol% and MnO: 23-28 mol%
Further contain SiO _2: 0.005 mass% or less and CaO: containing less 0.030 mass%,
The Mn—Zn based ferrite characterized in that the Fe ₂ O ₃ has an Al content of 0.040 to 0.10 mass%.   2. The Mn—Zn ferrite according to claim 1, wherein an initial permeability at 10 kHz is 10,000 or more.