阅读说明：本技术 一种超细铁氧体粉末的制备方法 (Preparation method of superfine ferrite powder ) 是由 陈新彬 于 2019-08-19 设计创作，主要内容包括：本发明涉及超细粉料制备领域,公开了一种超细铁氧体粉末的制备方法,步骤为：(1)将铁氧体原材料在950~1050℃下预烧后得到高温预烧料；(2)将高温预烧料直接投入冷却介质中,冷却后得到粗粉碎浆料；(3)将粗粉碎浆料与辅料一起进行二次研磨,得到铁氧体浆料；(4)铁氧体浆料经喷雾干燥后即得超细铁氧体粉末。本发明将高温预烧料直接投入冷却介质中,一方面可以使高温预烧料实现快速冷却,避免有效的磁性成分被过度氧化；另一方面实现了对高温预烧料的粗粉碎,使得高温预烧料的快速冷却和粗粉粹可以同时进行,节约了降温时间和粗研磨步骤,不但可以提高铁氧体粉末的各项性能,还提高了生产效率。(The invention relates to the field of superfine powder preparation, and discloses a preparation method of superfine ferrite powder, which comprises the following steps: (1) pre-burning a ferrite raw material at 950-1050 ℃ to obtain a high-temperature pre-burnt material; (2) directly putting the high-temperature pre-sintered material into a cooling medium, and cooling to obtain coarse crushing slurry; (3) carrying out secondary grinding on the coarsely crushed slurry and auxiliary materials to obtain ferrite slurry; (4) and spray drying the ferrite slurry to obtain the superfine ferrite powder. According to the invention, the high-temperature pre-sintering material is directly added into the cooling medium, so that on one hand, the high-temperature pre-sintering material can be rapidly cooled, and the effective magnetic components are prevented from being excessively oxidized; on the other hand, the coarse crushing of the high-temperature pre-sintered material is realized, so that the rapid cooling and the coarse crushing of the high-temperature pre-sintered material can be simultaneously carried out, the cooling time and the coarse grinding step are saved, the performances of the ferrite powder can be improved, and the production efficiency is also improved.)

1. A preparation method of superfine ferrite powder is characterized by comprising the following steps:

(1) pre-burning a ferrite raw material at 950-1050 ℃ to obtain a high-temperature pre-burnt material;

(2) directly putting the high-temperature pre-sintered material into a cooling medium, and cooling to obtain coarse crushing slurry;

(3) carrying out secondary grinding on the coarsely crushed slurry and auxiliary materials to obtain ferrite slurry;

(4) and spray drying the ferrite slurry to obtain the superfine ferrite powder.

2. The method for preparing an ultra-fine ferrite powder as claimed in claim 1, wherein the pre-sintering time in step (1) is 2 to 4 hours.

3. The method for preparing an ultrafine ferrite powder according to claim 1, wherein the cooling medium in step (2) is lime water or deionized water having a mass concentration of 0.02 to 0.10%.

4. The method for preparing an ultra-fine ferrite powder as claimed in claim 1 or 3, wherein the mass ratio of the high-temperature pre-sintered material to the cooling medium in step (2) is 1: (0.6-1.0).

5. The method for preparing an ultra fine ferrite powder as claimed in claim 1 or 3, wherein the cooling time in step (2) is less than 10 s.

6. The method for preparing ultrafine ferrite powder according to claim 1, wherein the secondary grinding in step (3) is performed by wet ball milling or sand milling, and the mass ratio of material balls is 1: (5-7).

7. The method for preparing an ultrafine ferrite powder according to claim 3, wherein the cooling medium is lime water, and the auxiliary material in step (3) is SiO in a ferrite slurry at a concentration of 0 to 0.005wt%₂And 0.02 to 0.05wt% Nb₂O₅And/or 0.02 to 0.05wt% ZrO₂。

8. The method for preparing an ultra-fine ferrite powder as claimed in claim 3, wherein the cooling medium is deionized water, and the auxiliary material in step (3) is SiO in the ferrite slurry at a concentration of 0-0.005 wt%₂0.03 to 0.08wt% of CaCO₃And 0.02 to 0.05wt% Nb₂O₅And/or 0.02 to 0.05wt% ZrO₂。

9. The method for preparing an ultra fine ferrite powder as claimed in claim 1, 5 or 6, wherein the secondary grinding time in step (3) is 60 to 90 min.

Technical Field

The invention relates to the field of superfine powder preparation, in particular to a preparation method of superfine ferrite powder.

Background

Ferrite generally refers to a complex oxide of the iron group and one or more other suitable metal elements. The conductivity is a semiconductor, but it is used as a magnetic medium in applications. Ferrites can be largely classified into seven classes according to their lattice types: spinel type, garnet type, magnetoplumbite type, perovskite type, ilmenite type, sodium chloride type, rutile type. According to its characteristics and application, it can be divided into five categories of soft magnet, permanent magnet, absolute magnet, moment magnet and piezomagnet. Because of abundant raw materials, low manufacturing cost, stable performance and the like, the material is widely applied to various fields of magnetic recording, microwave absorption, magnetic separation, magnetic sealing, electronic elements and the like, and is an indispensable basic functional material in industrial production.

The ferrite molding blank is generally prepared by pressing, molding and sintering ferrite powder, so that the particle size, the surface activity and the like of the ferrite powder have great influence on the performance of the sintered ferrite molding blank. In the prior art, when ferrite powder is prepared, ferrite powder is pre-sintered at a certain temperature for a period of time and then slowly cooled along with a furnace, the pre-sintered material and an additive (or an auxiliary material) are directly put into a ball mill (or a sand mill) to be ground to prepare slurry, and then the slurry is dried to obtain the ferrite powder. For example, a "production process of soft magnetic manganese zinc ferrite powder" disclosed in chinese patent literature, whose publication number CN100418921C, comprises the following process steps: wet grinding the raw materials, spraying for granulation, presintering, carrying out vibration ball milling on the presintered materials, carrying out secondary wet grinding, and carrying out secondary spray granulation. According to the invention, the raw materials are subjected to wet grinding before pre-sintering, and vibration ball milling, secondary wet grinding and secondary spray granulation are adopted after pre-sintering, so that on one hand, the full completion of a solid phase reaction in the pre-sintering is facilitated, the initial permeability of the product is improved, the power loss is reduced, and meanwhile, the dust pollution of a working place and the energy consumption of the product are reduced.

However, by adopting the method in the prior art, the pre-sintered material is slowly cooled along with the furnace and is directly subjected to ball milling, the particle size and the surface activity of the prepared ferrite powder are still to be improved, and the ferrite blank obtained by sintering after press forming is easy to generate the problems of insufficient blank magnetic force, sintering adhesion, sintering cracking and the like, so that the increasingly high requirements of the market can not be met.

Disclosure of Invention

The invention provides a preparation method of ultrafine ferrite powder, aiming at overcoming the problems that in the prior art, a pre-sintered material is slowly cooled along with a furnace and directly subjected to ball milling, the particle size and the surface activity of the prepared ferrite powder are still to be improved, and a ferrite blank obtained by sintering after press forming is easy to generate blank magnetic force deficiency, sintering adhesion and sintering cracking.

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of ultrafine ferrite powder comprises the following steps:

(1) pre-burning a ferrite raw material at 950-1050 ℃ to obtain a high-temperature pre-burnt material;

(2) directly putting the high-temperature pre-sintered material into a cooling medium, and cooling to obtain coarse crushing slurry;

(3) carrying out secondary grinding on the coarsely crushed slurry and auxiliary materials to obtain ferrite slurry;

(4) and spray drying the ferrite slurry to obtain the superfine ferrite powder.

Taking manganese-zinc ferrite as an example, the ferrite raw material Fe₂O₃、Mn₃O₄And ZnO are metal oxides without magnetism, and the ferrite raw material can perform solid-phase reaction at the high temperature of 950-1050 ℃ through the pre-sintering in the step (1) to generate manganese zinc ferrite (MnZn) Fe₂O₄And manganese ferrite MnFe₂O₄And the like, so that the obtained high-temperature pre-sintering material has magnetism.

If the high-temperature pre-sintering material is slowly cooled in air, a series of reactions with oxygen can occur at different temperatures:

1050℃：

MnFe₂O₄+1/4O₂→Fe₂O₃+1/2Mn₂O₃

1000℃：

3MnFe₂O₄+1/2O₂→β-Mn₃O₄·3Fe₂O₃

950℃：

2(β-Mn₃O₄)+1/2O₂→3(α-Mn₂O₃)

the reaction proceeds rapidly because of the higher temperature of the high temperature pre-sinter. When the temperature is continuously reduced to 950-600 ℃, the MnFe₂O₄Will be further oxidized and simultaneously has a face-centered cubic structure of gamma-Fe₂O₃α -Fe with body-centered cubic structure can be precipitated by exsolution₂O₃：

4MnFe₂O₄+O₂→2Mn₂O₃·4Fe₂O₃

(α-Mn₂O₃)·(γ-Fe₂O₃)→α-Mn₂O₃+α-Fe₂O₃

Continuously reducing the temperature to 600-500 ℃, and MnFe₂O₄Will be almost totally oxidized to Mn₂O₃And Mn₃O₄The remaining Mn²⁺Continuously react with oxygen to generate Mn³⁺：

2Mn₃O₄+Fe₂O₃+1/2O₂→3(α-Mn₂O₃)+Fe₂O₃

Thus, MnFe₂O₄Mn in (1)²⁺The magnetic property of the pre-sintering material is greatly reduced. And, when MnFe is contained in the powder₂O₄When the content is too small and the magnetization degree is too low, the shrinkage of the size of the magnetic core is small, and because the gap between the magnetic core blanks is small, the adjacent magnetic cores are touched together due to insufficient shrinkage, and the surfaces of the ferrite blanks are stuck together to generate sintering adhesion after melting. The finally prepared ferrite has magnetism which can not meet the use requirement and low yield. Meanwhile, if the pre-sintering material is not sufficiently oxidized, the blank is re-oxidized in the final sintering process of the ferrite, so that a thermal expansion effect is generated, a sintering cracking phenomenon is generated, and the product is cracked. Therefore, the high-temperature pre-sintering material is cooled under proper cooling conditions, the oxidation degree of the high-temperature pre-sintering material is reasonably controlled, and the magnetic performance and the good quality of the ferrite are improvedThe rate has an important role.

In order to avoid the phenomena of magnetic reduction, sintering adhesion or sintering cracking which can occur when the high-temperature pre-sintering material is slowly cooled, the high-temperature pre-sintering material obtained in the step (1) is directly put into a cooling medium through the step (2), on one hand, the cooling medium can isolate the contact between the high-temperature pre-sintering material and air, and the temperature difference between the cooling medium and the high-temperature pre-sintering material is large, so that the high-temperature pre-sintering material can be rapidly cooled, and the phenomenon that the effective magnetic components of the high-temperature pre-sintering material are excessively oxidized under the conditions of high temperature and oxygen existence, the magnetic property is greatly reduced, and the shrinkage rate is reduced is effectively. On the other hand, when the high-temperature pre-sintered material is put into the cooling medium, the high-temperature pre-sintered material is cracked due to uneven shrinkage of each part in the rapid cooling process, so that the coarse crushing of the high-temperature pre-sintered material is realized, the rapid cooling and the coarse crushing of the high-temperature pre-sintered material can be simultaneously carried out, the cooling time and the coarse grinding step are saved, various performances of the ferrite powder can be improved, and the production efficiency is also improved.

The coarse grinding slurry obtained after the rapid cooling and the coarse grinding is subjected to secondary grinding in the step (3) to further reduce the particle size, and the ferrite slurry obtained after the secondary grinding has narrow particle size distribution and small particle size

Large specific surface area, and the like, and can greatly improve and improve the electromagnetic property of the finally prepared ferrite.

Preferably, the pre-sintering time in the step (1) is 2-4 h. The pre-sintering is the most important step in the ferrite preparation process, and a series of physical and chemical reactions occur in the ferrite raw material in the pre-sintering process.

Taking manganese-zinc ferrite as an example, Mn is added when the reaction temperature is 500-600 ℃ in the pre-sintering process²⁺Can be oxidized to form Mn³⁺At 400-700 deg.C, part of Fe₂O₃α -Fe of body-centered cubic structure₂O₃Gamma-Fe converted into face-centered cubic structure₂O₃：

2Mn²⁺+1/2O₂→2Mn³⁺+O^2-

2Mn₃O₄+1/2O₂→3Mn₂O₃

α-Fe₂O₃→γ-Fe₂O₃

When the temperature continues to rise to 750 ℃, ZnO starts to react with Fe₂O₃React to generate zinc ferrite ZnFe₂O₄Meanwhile, at the temperature of 750-850 ℃, a part of Mn₂O₃Continuously carrying out a solid solution-decomposition process with ZnO:

ZnO+Fe₂O₃→ZnFe₂O₄

when the temperature is further increased to 850 ℃, the following reaction starts to occur:

3Mn₂O₃→2Mn₃O₄+1/2O₂

Mn₃O₄+Fe₂O₃→MnFe₂O₄+Mn₂O₃

in the production of manganese ferrite MnFe₂O₄While producing Mn₂O₃Continued conversion to new Mn₃O₄Thereby continuously generating new MnFe₂O₄。

ZnFe₂O₄Starting with MnFe at 950 ℃₂O₄Generating MnZnFe₂O₄。

MnFe₂O₄+ZnFe₂O₄→2MnZnFe₂O₄

As the temperature continues to rise, the amount of material participating in the reaction increases.

Therefore, the pre-sintering time has a large influence on the generation ratio of ferrite crystals, and thus has a significant influence on the performance of the final ferrite product. The pre-sintering time is insufficient, the reaction cannot be fully carried out, the magnetic performance of the product is influenced, and sintering adhesion is easy to occur; the long pre-sintering time can cause sintering cracking easily in the subsequent sintering process. By adopting the pre-sintering time in the invention, the magnetic performance of the product can be ensured, and the occurrence of sintering adhesion and sintering cracking can be effectively avoided.

Preferably, the cooling medium in the step (2) is 0.02-0.10 wt% of lime water or deionized water. Lime water is used as a cooling medium, so that the cooling speed can be increased, and the ferrite powder is dried to obtain Ca (OH)₂Will decompose to CaO and be uniformly dispersed in the powder. When the ferrite powder is used for preparing ferrite, CaO and SiO are mixed during high-temperature sintering of the ferrite powder₂The reactants are uniformly distributed on the grain boundary, so that the resistivity of the ferrite can be greatly improved, the eddy current loss is reduced, and the performance of the prepared ferrite is improved.

Preferably, the mass ratio of the high-temperature pre-sintering material to the cooling medium in the step (2) is 1: (0.6-1.0). By adopting the proportion, the high-temperature pre-sintered material can be rapidly cooled, and the proportion of CaO generated after drying is moderate, so that the performance of the product is not affected.

Preferably, the cooling time in step (2) is less than 10 s. In the cooling time range, the high-temperature pre-sintering material can be fully cooled, and the oxidation proportion of effective components in the high-temperature pre-sintering material can be ensured, so that sintering adhesion and sintering cracking cannot occur in the subsequent sintering process.

Preferably, the secondary grinding in the step (3) adopts wet ball milling or sand milling, and the mass ratio of the material balls is 1: (5-7). The wet ball milling or sanding is carried out by adopting the material ball ratio, so that the slurry subjected to secondary grinding has narrow particle size distribution, small particle size and large specific surface area, and the electromagnetic property of the ferrite can be greatly improved.

Preferably, the cooling medium is lime water, and the auxiliary material in the step (3) is SiO with the concentration of 0-0.005 wt% in the ferrite slurry₂And 0.02 to 0.05wt% Nb₂O₅And/or 0.02 to 0.05wt% ZrO₂。

Preferably, the cooling medium is deionized water, and the auxiliary material in the step (3) is SiO with the concentration of 0-0.005 wt% in the ferrite slurry₂0.03 to 0.08wt% of CaCO₃And 0.02 to 0.05wt% Nb₂O₅And/or 0.02 to 0.05wt% ZrO₂。

When the cooling medium is lime water, drying ferrite powder to obtain Ca (OH)₂Decomposed into CaO and uniformly dispersed in the powder, and SiO is added in the mass range of the present invention₂When used as an auxiliary material, SiO₂The reaction product of the CaO and the ferrite is mainly enriched in the grain boundary, so that the resistance of the grain boundary is improved, and the eddy current loss of the ferrite is reduced. But if SiO₂Excessive SiO addition₂Will react with Fe₂O₃Reaction to form Fe₂(SiO₃)₃The melting point is 1150 ℃, and the ferrite becomes a crystal boundary liquid phase in the sintering process of the ferrite, so that abnormal grain growth is caused.

When the cooling medium is distilled water, CaCO is added as adjuvant₃And SiO₂，CaCO₃Also decomposed into CaO and SiO₂The reaction improves the grain boundary resistance and reduces the eddy current loss of the ferrite.

Meanwhile, the invention also adds a certain mass of Nb into the auxiliary materials₂O₅And/or ZrO₂，Nb₂O₅And ZrO₂The method can refine grains, promote the grains to be uniform and compact, improve the initial permeability and the resistivity of the ferrite and reduce the power loss of the material. On the other hand, if the amount of addition is outside the range of the present invention, the number of pores in the grain boundary increases, the ferrite density and resistivity decrease, and the power consumption increases.

Preferably, the secondary grinding time in the step (3) is 60-90 min. The proper grinding time can ensure that the granularity of the ground slurry meets the requirement.

Therefore, the invention has the following beneficial effects:

(1) the high-temperature pre-sintering material is directly added into the cooling medium, so that on one hand, the high-temperature pre-sintering material can be rapidly cooled, and the situation that the effective magnetic components of the high-temperature pre-sintering material are excessively oxidized at high temperature in the presence of oxygen, so that the magnetic property is greatly reduced and the shrinkage rate is reduced is effectively avoided. On the other hand, when the high-temperature pre-sintered material is put into a cooling medium, the high-temperature pre-sintered material is cracked due to uneven shrinkage of each part in the rapid cooling process, so that the coarse crushing of the high-temperature pre-sintered material is realized, the rapid cooling and the coarse crushing of the high-temperature pre-sintered material can be simultaneously carried out, the cooling time and the coarse grinding step are saved, the performances of the ferrite powder can be improved, and the production efficiency is also improved;

(2) the coarsely crushed slurry after being rapidly cooled and coarsely crushed is subjected to secondary grinding, so that the particle size of ferrite powder can be further reduced, the specific surface area is increased, and the magnetic performance of a product is further improved;

(3) during secondary grinding, a proper amount of auxiliary materials are added, so that the grain boundary resistance is improved, and the eddy current loss of ferrite is reduced; the method has the advantages of refining grains, promoting the uniformity and compactness of the grains, improving the initial permeability and the resistivity of the ferrite and reducing the power loss of the material.

Detailed Description

The invention is further described with reference to specific embodiments.