CN104465004B - Method for manufacturing high-saturation-flux-density soft magnetic composite material according to alkaline bluing technique - Google Patents

Abstract

The invention discloses a method for manufacturing a high-saturation-flux-density soft magnetic composite material according to the alkaline bluing technique. The method for manufacturing the high-saturation-flux-density soft magnetic composite material according to the alkaline bluing technique comprises the steps that the surface of magnetic powder is oxidized according to the alkaline bluing technique, so that a layer of uniform Fe3O4 insulating layer is generated, and then the novel soft magnetic composite material is manufactured through bonding, press-forming and heat treatment. The method for manufacturing the high-saturation-flux-density soft magnetic composite material according to the alkaline bluing technique has the advantages that Fe3O4 prepared according to the alkaline bluing technique grows on the surface of the magnetic powder in an in-situ mode, in this way, the degree of binding of the insulating cladding layer and the magnetic powder is high, and uniform and compact cladding is achieved; due to the fact that Fe3O4 has high specific resistance, the insulating effect is good; on the other hand, the ferromagnetic Fe3O4 is taken as the insulating cladding layer, in this way, magnetic attenuation caused when non-magnetic materials are taken as cladding agents in the prior art is avoided, and higher magnetic conductivity and higher magnetic flux density can be achieved; according to the alkaline bluing technique, operation is easy, cost is low, and industrial production can be achieved easily.

Description

Method for preparing soft magnetic composite material with high saturation magnetic flux density by alkaline baking bluing process

technical field

The invention relates to the field of magnetic materials, in particular to a method for preparing a soft magnetic composite material with high saturation magnetic flux density by an alkaline roasting process.

Background technique

Soft magnetic composite material is a kind of soft magnetic material manufactured by powder metallurgy process. Its special magnetic properties make it incomparable to other materials in many applications. So far, this material has become an important part of soft magnetic materials. The production of soft magnetic composite materials has a long history, but the real industrialization began in the 1980s. With the rapid development and wide application of inverter technology, along with the demand for EMC, soft magnetic composite materials have been widely used ; Entering the 21st century, with the high frequency and high power density of the inverter circuit and the higher requirements of EMC, coupled with the further deepening of people's understanding of soft magnetic composite materials, the industrialization of soft magnetic composite materials has developed rapidly More than any other soft magnetic material.

The iron powder core can not be saturated under high magnetization field, and has good DC superposition stability. Moreover, its production process is simple, and its price is the lowest among all kinds of metal soft magnetic powder cores. Generally, iron powder cores can be preferred if the requirements of use can be met. At present, among all kinds of metal soft magnetic powder cores, it is the most widely used and the most used one.

The traditional preparation process of soft magnetic composite materials is to passivate with phosphoric acid to form iron phosphide, then add binder, press molding, and anneal or not anneal at a lower temperature to obtain soft magnetic powder core. Because the iron phosphide will decompose at a higher temperature, resulting in a decrease in insulation performance, so the annealing temperature is lower, so that the internal stress generated during pressing cannot be completely eliminated, which is not conducive to reducing the hysteresis loss. Therefore, in recent years, There have been different methods of preparing magnetic powder cores coated with oxides. For example, Mitsubishi Corporation has invented an evaporation method to coat a layer of MgO insulating layer on the surface of iron powder. In addition, in recent years, there has also been the use of sol There are reports on the preparation of oxide-coated magnetic powder cores by the gel method. The magnetic powder cores prepared by the above methods can be annealed at a higher temperature, so it is beneficial to eliminate the internal stress of compression molding, but the insulating layers prepared by these methods are non-conductive. The magnetic phase, therefore, will cause magnetic dilution, resulting in a decrease in the saturation magnetic induction of the magnetic powder core.

Contents of the invention

The object of the present invention is to provide a method for preparing soft magnetic composite materials with high saturation magnetic flux density by alkaline baking blueing process in view of the above phenomenon. Oxidize the surface of the magnetic powder to form a uniform insulating layer of Fe ₃ O ₄ through the alkaline baking blueing process. Since Fe ₃ O ₄ is a ferrimagnetic alloy, it can effectively reduce the magnetic dilution of the alloy and is beneficial to improve the alloy’s magnetic properties. Permeability and saturation flux density. At the same time, the insulation coating of the alkaline blueing process is an in-situ reaction process, so the prepared Fe ₃ O ₄ is produced by direct reaction with the Fe on the surface of the magnetic powder, so it has a higher degree of binding and is easy to form a dense layer. Insulation protective layer.

A method for preparing a soft magnetic composite material with high saturation magnetic flux density by an alkaline roasting process is as follows:

1) Insulation coating of magnetic powder: Dissolve NaOH, NaNO ₃ , and NaNO ₂ in H ₂ O to prepare an alkaline bluing solution, and control the concentrations of NaOH, NaNO ₃ , and NaNO ₂ to 0.4~0.7 g/ml, 0.06 ~0.15 g/ml, 0.02~0.05 g/ml, heat the prepared alkaline bluish liquid to boil, add magnetic powder, and ensure that the concentration of magnetic powder is less than 0.75 g/ml, continue heating and keep boiling for 5~35 min, so that The surface of the magnetic powder is coated with an insulating layer, then filtered and dried to obtain soft magnetic alloy powder;

2) Add binder: pour 0.5% - 2% binder of magnetic powder into the coated soft magnetic alloy powder, heat and stir until the mixture is dry and evenly mixed;

3) Compression molding: add the alloy powder mixed uniformly above to the magnetic powder with 0.25% zinc stearate and 0.25% barium stearate as lubricants, and press it into a magnetic core under a pressure of 400-2000 MPa;

4) Heat treatment: heat treatment at 400-700 ^o C for 0.5-2 h under the protection of inert gas to eliminate the internal stress generated by pressing and obtain a soft magnetic composite material.

The binder is one or more of silicone resin, melamine resin, phenolic resin, epoxy resin, silicone resin, low-melting glass powder, and _SiO2 .

The magnetic powder is iron powder or iron silicon powder.

The soft magnetic composite material prepared by this method will not cause too much loss to the saturation magnetic flux density of the soft magnetic composite material because the layer of Fe ₃ O ₄ coated on the surface of the magnetic powder is a ferrimagnetic material, and the soft magnetic composite material can be further improved. The saturation magnetic flux density of the composite material. In addition, compared with evaporation, sol-gel method and other methods, the alkaline baking blueing process has simple process and low preparation cost, which is more conducive to realizing large-scale industrial production.

Description of drawings

Figure 1 shows the hysteresis loops of iron powder cores prepared by alkaline blueing process and traditional phosphoric acid passivation process.

detailed description

In the soft magnetic composite material of the present invention, a layer of Fe ₃ O ₄ is formed on the surface of iron powder as an insulating layer by subjecting the magnetic powder to alkaline bluing treatment, then adding a binder, pressing and forming, and then annealing to form the soft magnetic composite material.

The steps of the soft magnetic composite material preparation method are as follows:

1) Insulation coating of magnetic powder: Dissolve NaOH, NaNO ₃ , and NaNO ₂ in H ₂ O to prepare an alkaline bluing solution, and control the concentrations of NaOH, NaNO ₃ , and NaNO ₂ to 0.4~0.7 g/ml, 0.06 ~0.15 g/ml, 0.02~0.05 g/ml, heat the prepared alkaline bluish liquid to boil, add magnetic powder, and ensure that the concentration of magnetic powder is less than 0.75 g/ml, continue heating and keep boiling for 5~35 min, so that The surface of the magnetic powder is coated with an insulating layer, then filtered and dried to obtain soft magnetic alloy powder;

2) Add binder: pour 0.5% - 2% binder of magnetic powder into the coated soft magnetic alloy powder, heat and stir until the mixture is dry and evenly mixed;

3) Compression molding: add the alloy powder mixed uniformly above to the magnetic powder with 0.25% zinc stearate and 0.25% barium stearate as lubricants, and press it into a magnetic core under a pressure of 400-2000 MPa;

4) Heat treatment: heat treatment at 400-700 ^o C for 0.5-2 h under the protection of inert gas to eliminate the internal stress generated by pressing and obtain a soft magnetic composite material.

The present invention is described in further detail below in conjunction with example:

Example 1:

Dissolve 50 g NaOH, 10 g NaNO ₃ and 3 g NaNO ₂ in 100 ml H ₂ O, stir evenly, heat to boiling, then add 60 g Fe powder, continue heating to keep the solution boiling for 10 min, then filter, use Wash with absolute ethanol three times repeatedly, and stir at 80 ^o C until the obtained iron powder is dry.

Add the obtained iron powder into 2wt% silicone resin and 10wt% ethylene glycol solution, stir at 80 ^o C until the powder is dry, then add 0.25wt% zinc stearate and 0.25wt% barium stearate , pressed into a dense ring under the condition of 800 MPa, and annealed the ring sample at 450 ^o C for 1 h to make a soft magnetic composite material.

After testing, the saturation magnetic flux density of the soft magnetic alloy is 1.6 T, and the magnetic permeability is 83. Figure 1 shows the hysteresis loops of iron powder cores prepared by alkaline blueing process and traditional phosphoric acid passivation process. It can be seen from Figure 1 that the iron powder core prepared by the alkaline baking blueing process has higher saturation magnetic flux density and magnetic permeability.

Example 2:

Dissolve 40 g NaOH, 6 g NaNO ₃ and 5 g NaNO ₂ in 100 ml H ₂ O, stir evenly, heat to boiling, then add 75 g Fe powder, continue heating to keep the solution boiling for 5 min, then filter, use Water and ethanol were washed repeatedly for 3 times, and stirred at 80 ^o C until the obtained iron powder was dry.

Add the obtained iron powder into 0.5wt% epoxy resin and 10wt% acetone solution, stir at 80 ^o C until the powder is dry, then add 0.25wt% zinc stearate and 0.25wt% barium stearate , pressed into a dense ring under the condition of 400 MPa, and annealed the ring sample at 400 ^o C for 2 h to make a soft magnetic composite material.

After testing, the saturation magnetic flux density of the soft magnetic alloy is 1.5 T, and the magnetic permeability is 78.

Example 3:

Dissolve 70 g NaOH, 15 g NaNO ₃ and 2 g NaNO ₂ in 100 ml H ₂ O, stir evenly, heat to boiling, then add 50 g iron silicon powder, continue heating to keep the solution boiling for 35 min, then filter , washed three times with absolute ethanol, and stirred at 80 ^o C until the obtained iron powder was dry.

Add the obtained iron powder into 1wt% phenolic resin, 1wt% SiO ₂ and 10wt% acetone solution, stir at 80 ^o C until the powder is dry, then add 0.25wt% zinc stearate and 0.25wt% hard Barium fatty acid was pressed into a dense ring under the condition of 2000 MPa, and the ring sample was annealed at 700 ^o C for 0.5 h to make a soft magnetic composite material.

After testing, the saturation magnetic flux density of the soft magnetic alloy is 1.6 T, and the magnetic permeability is 95.

Claims (3)

1. a kind of alkalescence technique of giving a protective coating to metal objects prepares the method for high saturation magnetic flux density soft-magnetic composite material it is characterised in that its step As follows:

1) insulating wrapped of magnetic powder: take naoh, nano₃、nano₂It is dissolved in h₂Be configured to alkalescence in o to give a protective coating to metal objects liquid, control naoh, nano₃、nano₂Concentration be respectively 0.4 ~ 0.7 g/ml, 0.06 ~ 0.15 g/ml, 0.02 ~ 0.05 g/ml, by the alkali preparing Property give a protective coating to metal objects liquid heated and boiled, add magnetic powder, and ensure that the concentration of magnetic powder is less than 0.75 g/ml, continues heating and keeps boil condition 5 ~ 35 min, so that magnetic powder Surface coating one layer insulating, then filter, and are dried, obtain soft-magnetic alloy powder；

2) add binding agent: the binding agent of magnetic powder mass percent 0.5% -2% is poured into the soft-magnetic alloy powder having coated In, heat and be stirred well to mixture drying, mix homogeneously；

3) compressing: by after above-mentioned mix homogeneously alloy powder add magnetic powder mass percent 0.25% zinc stearate, 0.25% barium stearate, as lubricant, depresses to magnetic core in the pressure of 400 ~ 2000 mpa；

4) heat treatment: 400 ~ 700 under the protection of noble gases^oHeat treatment 0.5 ~ 2 h at a temperature of c, to eliminate compacting The internal stress producing, obtains soft-magnetic composite material.

2. method according to claim 1 is it is characterised in that described binding agent is silicones, melmac, phenol Urea formaldehyde, epoxy resin, silicone resin, glass powder with low melting point, sio₂One or more of.

3. method according to claim 1 is it is characterised in that described magnetic powder is iron powder or ferrum silica flour.