CN112239363A

CN112239363A - Silicon nitride magnesium powder and preparation method thereof, ceramic material and heat conducting substrate

Info

Publication number: CN112239363A
Application number: CN202011111308.5A
Authority: CN
Inventors: 曾小锋; 朱福林; 肖亮; 曾庆党; 李勇全
Original assignee: Hengyang Kaixin Special Materials Technology Co ltd
Current assignee: Hengyang Kaixin Special Materials Technology Co ltd
Priority date: 2020-10-16
Filing date: 2020-10-16
Publication date: 2021-01-19
Anticipated expiration: 2040-10-16
Also published as: CN112239363B

Abstract

The invention relates to silicon nitride magnesium powder and a preparation method thereof, a ceramic material and a heat conducting substrate; in the preparation method of the silicon nitride magnesium powder, magnesium silicate and a carbon source are mixed to obtain a mixture; then the mixture is placed in a nitrogen atmosphere for reduction reaction to obtain silicon magnesium nitride powder; wherein the carbon source comprises organic carbon of saccharides and low-carbon alcohol polymer; based on the total mass of the magnesium silicate and the carbon source, the mass percent of the low carbon alcohol polymer is 1 wt% -5 wt%. In the preparation method, the carbon source mainly comprises organic carbon of saccharides and takes a low-carbon alcohol polymer with the mass percent of 1 wt% -5 wt% as an auxiliary material; the low-carbon alcohol polymer with certain high polymerization bonding performance is inserted with a lead in the reduction reaction process, so that the reaction materials are reacted uniformly, and the prepared silicon-magnesium nitride powder has the crystal whisker with a specific length-diameter ratio, regular shape, low oxygen content and high sintering activity.

Description

Silicon nitride magnesium powder and preparation method thereof, ceramic material and heat conducting substrate

Technical Field

The invention relates to the technical field of heat conduction materials, in particular to silicon nitride magnesium powder and a preparation method thereof, a ceramic material and a heat conduction substrate.

Background

With the rapid development of electronic technology, the application of very large scale integrated circuits puts higher requirements on the electronic packaging technology, and a reasonably designed and efficient circuit cooling system is a key ring for realizing the large scale integrated circuits. The substrate material has the functions of supporting, insulating and radiating, and is the most important of the whole electronic packaging system. In order to improve the heat dissipation capability of the substrate, on one hand, the substrate material itself is required to have high thermal conductivity, and on the other hand, the substrate material is required to have excellent strength so as to reduce the thickness of the substrate as much as possible to reduce the thermal resistance. Therefore, the combination of high thermal conductivity and good mechanical properties is the key to solve the heat dissipation problem of the substrate.

The silicon nitride ceramic has high strength, good toughness, corrosion resistance, oxidation resistance, creep resistance and stable high-temperature performance, and is a structural ceramic with excellent performance. The silicon nitride ceramic is used as a substrate material, so that the circuit board can have large flexibility, breaking strength, thermal shock resistance and thermal conductivity. However, the conventional silicon nitride ceramics have not high thermal conductivity, only 20W/m.k to 40W/m.k, and thus are not widely used for the preparation of substrates. In recent years, the skilled artisan has found magnesium silicon nitride (MgSiN)₂) Is a very effective non-oxide sintering aid, can be used for preparing silicon nitride ceramics with high thermal conductivity, and MgSiN₂Has a structure very similar to that of aluminum nitride (AlN), has proper thermal conductivity, relatively good fracture toughness and hardness, good oxidation resistance up to over 920 ℃, and the like. The purity of the silicon magnesium nitride powder is the key to influence the performance and application of the silicon magnesium nitride, and the existence of the impurity oxygen element is the main factor which causes the impurity of the product and restricts the heat conductivity of the product, thereby influencing the heat conductivity of the silicon nitride ceramic prepared when the silicon magnesium nitride powder is used as a sintering aid.

In the prior art, the main synthesis processes of silicon magnesium nitride are self-propagating high-temperature synthesis and a direct nitriding method. Self-propagatingThe high-temperature synthesis method takes magnesium powder and silicon nitride powder as raw materials, or takes magnesium silicide or magnesium silicide and alpha-Si₃N₄The mixture is used as a starting material to prepare the magnesium silicon nitride. Direct nitriding method using silicon powder, alpha-Si₃N₄The magnesium powder and the magnesium nitride powder are used as raw materials and are combusted in the nitrogen atmosphere to synthesize the silicon-magnesium nitride powder. However, the synthesis process of the self-propagating high-temperature synthesis method is difficult to control, reaction products are easy to agglomerate, and the powder quality is low; the direct nitriding method has the disadvantages of intense heat release and more side reactions in the reaction process, so that the prepared silicon-magnesium nitride product has low purity, more impurity content and low sintering activity.

Therefore, there is an urgent need to develop a method for preparing silicon magnesium nitride with less impurities, low oxygen content and high sintering activity.

Disclosure of Invention

Based on the above, the invention provides silicon nitride magnesium powder with less product impurities, low oxygen content and high sintering activity, a preparation method thereof, a ceramic material and a heat-conducting substrate. The silicon nitride magnesium powder prepared by the preparation method has the advantages of low impurity content, low oxygen content, a whisker structure with a certain length-diameter ratio and high sintering activity.

The technical scheme of the invention is as follows.

One aspect of the invention provides a preparation method of silicon nitride magnesium powder, which comprises the following steps:

mixing magnesium silicate and a carbon source to obtain a mixture;

placing the mixture in a nitrogen atmosphere for reduction reaction to obtain silicon magnesium nitride powder;

the carbon source comprises a carbohydrate organic carbon and a polymer of a lower alcohol; based on the total mass of the magnesium silicate and the carbon source, the mass percent of the low-carbon alcohol polymer is 1 wt% -5 wt%.

In some of these embodiments, the carbohydrate organic carbon is selected from at least one of maltose, glucose, riban, fructose, sucrose, lactose, and starch; and/or

The lower alcohol polymer is at least one selected from polyvinyl alcohol, polyethylene glycol and polyvinyl alcohol.

In some embodiments, the mass ratio of the magnesium silicate to the carbon source is 1 (0.5-3).

In some of these embodiments, the temperature control procedure for the reduction reaction is as follows:

firstly, heating to 600-800 ℃ at a heating rate of 4-5 ℃/min; then the temperature is raised to 1200-1500 ℃ at the heating rate of 1-3 ℃/min, and the temperature is kept for 1-25 h.

In some embodiments, the method for preparing magnesium silicon nitride powder further comprises the step of preparing magnesium silicate:

mixing silicate ester, magnesium salt, ammonia and ethanol, and precipitating to obtain precipitate;

and calcining the precipitate to obtain the magnesium silicate.

The invention also provides the silicon nitride magnesium powder prepared by any one of the preparation methods.

The invention also provides the application of the silicon nitride magnesium powder in preparing heat conduction materials.

Further, the present invention provides a ceramic material, the composition of which comprises: silicon nitride powder, sintering aid, nitride whisker and/or carbide whisker, binder and dispersant;

wherein the sintering aid comprises the silicon nitride magnesium powder.

In some embodiments, the silicon nitride powder is 100 parts by mass, the sintering aid is 3-15 parts by mass, the dispersant is 0.3-3 parts by mass, the binder is 1-5 parts by mass, and the nitride whiskers and/or the carbide whiskers are 3-10 parts by mass.

The invention further provides a heat-conducting substrate which is made of the ceramic material.

Advantageous effects

In the preparation method of the silicon magnesium nitride powder, magnesium silicate and a specific carbon source are adopted for reduction reaction, wherein the carbon source mainly comprises saccharide organic carbon and secondarily comprises 1-5 wt% of low-carbon alcohol polymer; the low-carbon alcohol polymer with certain high polymerization bonding performance is inserted with a lead in the reduction reaction process, so that the reaction materials are reacted uniformly, and the prepared silicon-magnesium nitride powder has the crystal whisker with a specific length-diameter ratio, regular shape, low oxygen content and high sintering activity.

In the preparation method of the silicon nitride magnesium powder, the carbohydrate organic carbon and the low carbon alcohol polymer with specific mass form a carbon source, when the mass percentage of the low carbon alcohol polymer is less than 1 wt%, too little low carbon alcohol polymer can cause reduction to cause discontinuous reaction, and the silicon nitride magnesium powder with a whisker structure can not be obtained; when the mass percentage of the low carbon alcohol polymer is more than 5 wt%, the excessive low carbon alcohol polymer can greatly increase the gaps among reduction reactants, so that the reduction reaction is incomplete; when the carbon source is inorganic carbon, the reaction activity of the inorganic carbon powder is far inferior to that of carbon generated by decomposing the organic carbon source, and the purity of the obtained silicon-magnesium nitride powder is low.

Furthermore, the invention provides silicon-magnesium nitride powder, which is prepared by the preparation method, the length of the crystal whisker of the silicon-magnesium nitride powder is 10-50 mu m, the diameter is 0.2-3 mu m, the impurity content is not more than 1.5 wt%, the oxygen content is not more than 2 wt%, the purity is high, and the sintering activity is high. When the silicon nitride magnesium powder is applied to preparing heat conduction materials, the heat conductivity of the heat conduction materials can be improved.

The invention also provides a ceramic material, and the raw materials of the ceramic material comprise silicon nitride powder, a sintering aid, nitride whiskers and/or carbide whiskers, a binder and a dispersing agent; wherein the sintering aid comprises the silicon nitride magnesium powder. The silicon nitride magnesium powder has crystal whisker with certain length-diameter ratio and more excellent sintering activity, and can be used together with nitride crystal whisker and/or carbide crystal whisker to obviously enhance the properties of ceramic material, such as thermal conductivity, bending strength, fracture toughness and the like.

Furthermore, the invention also provides a heat-conducting substrate prepared from the ceramic material, and the heat-conducting substrate has high heat conductivity and good mechanical property.

Drawings

FIG. 1 is an electron micrograph of the magnesium silicon nitride powder of example 1.

Detailed Description

In order that the invention may be more fully understood, a more particular description of the invention will now be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

One embodiment of the present invention provides a method for preparing magnesium silicon nitride powder, which includes the following steps S100 to S200.

Step S100, mixing magnesium silicate and a carbon source to obtain a mixture; the carbon source comprises organic carbon of saccharides and low-carbon alcohol polymer; and the mass percentage of the low carbon alcohol polymer is 1 wt% -5 wt% based on the total mass of the magnesium silicate and the carbon source.

And S200, placing the mixture obtained in the step S100 in a nitrogen atmosphere for reduction reaction to obtain silicon-magnesium nitride powder.

In the preparation method, magnesium silicate and a specific carbon source are adopted for reduction reaction, the carbon source mainly comprises organic carbon of saccharides, 1-5 wt% of low-carbon alcohol polymer is taken as an auxiliary material, and the low-carbon alcohol polymer with certain high polymerization bonding performance is inserted with a lead in the reduction reaction process, so that reaction materials are reacted uniformly, and the prepared silicon nitride magnesium powder has the crystal whisker with a specific length-diameter ratio, regular shape, low oxygen content and high sintering activity.

In the preparation method of the silicon nitride magnesium powder, the carbohydrate organic carbon and the low-carbon alcohol polymer with specific mass form a carbon source, when the mass percentage of the low-carbon alcohol polymer is less than 1 wt%, too little low-carbon alcohol polymer can cause uneven reaction, so that the reduction is discontinuous to cause reaction, and the silicon nitride magnesium powder with a whisker structure cannot be obtained; when the mass percentage of the low carbon alcohol polymer is more than 5 wt%, the excessive low carbon alcohol polymer can greatly increase the gaps among reduction reactants, so that the reduction reaction is incomplete; when the carbon source is inorganic carbon, the reaction activity of the inorganic carbon powder is far inferior to that of carbon generated by decomposing organic matters, and the purity of the obtained silicon-magnesium nitride powder is low.

In some of the embodiments, the mixing step in step S100 is a ball milling method, including the following steps S110 to S120.

Step S110, magnesium silicate and a carbon source are dissolved in a solvent to obtain slurry.

In some of these embodiments, the solvent employed in step S110 is selected from at least one of water, ethanol, and hexane. Further, the ratio of the total mass of magnesium silicate and carbon source to the mass of solvent is 1 (1-2).

And step S120, performing ball milling on the slurry obtained in the step S110, drying and screening to obtain a mixture.

In some embodiments, in step S120, silicon nitride balls or agate balls are used as the ball milling medium, and the ball milling time is 1h to 10 h.

In some embodiments, in step S120, the drying step is vacuum drying, and the temperature of the vacuum drying is 70 ℃ to 95 ℃.

In some embodiments, in step S120, the sieving step uses a sieve with a mesh size of 50-200 meshes.

After ball milling, magnesium silicate and a carbon source in a solvent can be uniformly mixed, and then the mixture is dried and screened to obtain mixed powder so as to ensure subsequent loose-packed material distribution.

In some of the embodiments, in step S100, the organic carbon of the saccharide is selected from at least one of maltose, glucose, a glucan, fructose, sucrose, lactose and starch; and/or

The lower alcohol polymer is selected from at least one of polyvinyl alcohol and polyethylene glycol.

In some of these embodiments, the organic carbon of the saccharide has a purity of greater than 99 wt%.

In some embodiments, in step S100, the mass ratio of the magnesium silicate to the carbon source is 1 (0.3-3). Preferably, the mass ratio of the magnesium silicate to the carbon source is 1 (0.5-3), and further, the mass ratio of the magnesium silicate to the carbon source is 1 (0.5-1).

In some of these embodiments, the magnesium silicate has a purity of greater than 99 weight percent and a particle size of from 0.5 μm to 50 μm.

The magnesium silicate in the present invention includes magnesium silicate (MgSiO) as a compound₃) And complex forms thereof, such as magnesium trisilicate and magnesium hexasilicate, and the like.

In some embodiments, in step S200, the temperature control procedure of the reduction reaction is as follows:

In some embodiments, step S200 further includes, after the reducing step, a step of removing carbon from the reduction product, specifically as follows:

and calcining the reduction product in an oxygen-containing atmosphere.

The carbon removal step can further remove residual impurity carbon in the reduction product, and further improve the purity of the silicon nitride magnesium powder; further, the conditions of calcination are: calcining for 3-10 h at 500-700 ℃.

In some embodiments, the method for preparing magnesium silicon nitride powder further includes a step S300 of preparing magnesium silicate, which specifically includes the following steps S310 to S320.

Step S310, mixing silicate ester, magnesium salt, ammonia and ethanol, and precipitating to obtain a precipitate.

The silicate is hydrolyzed under the action of ammonia to obtain silicic acid, and the silicic acid reacts with magnesium salt to obtain magnesium silicate, and the magnesium silicate is precipitated in ethanol.

In some of these embodiments, the silicate is selected from at least one of methyl orthosilicate and ethyl orthosilicate; further, the silica content of the silicate is greater than 28 wt%.

In some of these embodiments, the magnesium salt is selected from at least one of magnesium nitrate, magnesium sulfate, and magnesium chloride; further, the purity of the magnesium salt is more than 99 wt%, and the particle size range is 0.5-50 μm.

And step S320, calcining the precipitate obtained in the step S310 to obtain magnesium silicate.

The embodiment of the invention also provides the silicon nitride magnesium powder prepared by the preparation method.

The crystal whisker length of the silicon nitride magnesium powder is 20-50 mu m, the diameter is 0.2-1 mu m, the impurity content is less than 1 wt%, the oxygen content is less than 0.5 wt%, the purity is high, and the sintering activity is high.

Further, an embodiment of the present invention provides an application of the magnesium silicon nitride powder in preparing a thermal conductive material.

The crystal whisker of the silicon nitride magnesium powder has the length of 20-50 mu m, the diameter of 0.2-1 mu m, the impurity content of less than 1wt percent, the oxygen content of less than 0.5wt percent, high purity and high sintering activity. When the silicon nitride magnesium powder is used for preparing heat conduction materials, the heat conduction performance of the heat conduction materials can be improved.

In some embodiments, the heat conductive material is a ceramic material, and further, the magnesium silicon nitride powder is used as a sintering aid in preparing the ceramic material.

One embodiment of the present invention provides a ceramic material, which comprises the following raw materials: silicon nitride powder, sintering aid, nitride whisker and/or carbide whisker, binder and dispersant;

wherein the sintering aid comprises the silicon nitride magnesium powder.

The silicon nitride magnesium powder has crystal whisker with certain length-diameter ratio and more excellent sintering activity, and can obviously enhance the properties of the ceramic material, such as heat conductivity, bending strength, fracture toughness and the like by the combined action of the silicon nitride magnesium powder and the nitride crystal whisker and/or the carbide crystal whisker.

In some embodiments, the mass portion of the silicon nitride powder is 100, the mass portion of the sintering aid is 3-15, the mass portion of the dispersant is 0.3-3, the mass portion of the binder is 1-5, and the mass portion of the nitride whisker and/or the carbide whisker is 2-12.

Preferably, the mass portion of the silicon nitride powder is 100, the mass portion of the sintering aid is 3-15, the mass portion of the dispersant is 0.3-3, the mass portion of the binder is 1-5, and the mass portion of the nitride whisker and/or the carbide whisker is 3-10.

In some of these embodiments, the silicon nitride powder has a purity of greater than 99 wt% and a particle size in the range of 0.5 μm to 5 μm.

In some of these embodiments, the nitride whiskers are selected from at least one of aluminum nitride whiskers and silicon nitride whiskers; the carbide whisker is a carbide whisker, and further comprises 0-5 parts by mass of an aluminum nitride whisker, 0-15 parts by mass of a silicon nitride whisker and 0-5 parts by mass of a silicon carbide whisker; the sum of the mass parts of the three components is not more than 10 parts.

The binder may be any type of binder commonly used in the art, and in some embodiments, the binder is selected from at least one of an acrylic system binder and a polyvinyl alcohol system binder.

In some of these embodiments, the binder is polyvinyl butyral.

In some embodiments, the dispersant is one or more of castor oil, tributyl phosphate, fish oil, oleic acid, and Glycerol Trioleate (GTO).

In some of these embodiments, the composition of the ceramic material further comprises other functional additives; furthermore, the mass portion of other functional additives is 0.5 to 3.

In some of these embodiments, the other functional additives are defoamers and/or leveling agents. Specifically, the defoaming agent is tributyl phosphate.

It is understood that other functional additives commonly used in the art may be added according to actual needs.

In some embodiments, the ceramic material is prepared by using a solvent, wherein the solvent is one or more of acetone, butanone, absolute ethyl alcohol, isopropanol, n-butanol and ethyl acetate. Further, the mass portion of the solvent is 50 to 100.

Further, the method for manufacturing the heat conductive substrate includes the following steps S400 to S600.

Step S400, providing the following raw materials: silicon nitride powder, sintering aid, nitride whisker and/or carbide whisker, binder and dispersant; the sintering aid comprises the silicon nitride magnesium powder.

Step S500, preparing the raw material obtained in the step S400 into a green body.

And S600, sintering, molding and cutting the green body obtained in the step S500 to obtain the heat-conducting substrate.

In one embodiment, the step of forming the raw material into a green body in step S500 specifically includes the following steps S510 to S520.

And step S510, mixing the raw material obtained in the step S400 with a solvent, controlling the pH value to be 9-11, and performing ball milling to obtain slurry.

In some of these embodiments, in step S510, the particle size D50 of the slurry is less than 1 μm.

In some embodiments, the ball milling time in step 510 is 12h to 14 h.

In some of the embodiments, the pH controlling agent used to control the pH in step 510 is ammonia.

And step S520, granulating and molding the slurry obtained in the step S510 to obtain a green body.

In some embodiments, the step of forming in step S520 uses slip casting, gel casting, dry pressing or isostatic pressing.

In a specific example, in step S520, the granulating step adopts spray granulation, and the particle size of the powder obtained after granulation is 60 to 80 microns.

In a specific example, in step S520, the step of forming adopts isostatic pressing after dry pressing, and the specific steps are as follows:

and (4) performing dry pressing molding on the slurry obtained in the step (S510) under the pressure of 80-120 MPa, sealing the dry pressed blank body in vacuum by using a vacuum bag, and performing wet isostatic pressing molding under the molding pressure of 120-260 MPa.

It will be appreciated that after the green body is formed, the green body may be subjected to the necessary green body finishing operations as may be required for particular changes.

In some embodiments, in step S600, the step of sintering and shaping the green compact obtained in step S500 specifically includes the following steps:

putting the green body obtained in the step S500 into a hot pressing furnace, heating to 550-1000 ℃ at a heating rate of 5-100 ℃/h, preserving heat, and carrying out degreasing reaction for 2-6 hours; then continuing heating up to 1650-1900 ℃ at the heating rate of 5-200 ℃/h, and preserving heat for hot-pressing sintering, wherein the mixed atmosphere of hydrogen and nitrogen is adopted during hot-pressing sintering; further, the flow ratio of the hydrogen to the nitrogen is 1 (5-10); the pressure of hot-pressing sintering is 50 MPa-200 MPa, and the time is 1-10 hours; finally, the temperature is reduced to 800 ℃ at the cooling speed of 2-5 ℃ per minute, and then the temperature is reduced along with the furnace.

The silicon nitride magnesium powder prepared by the invention has the advantages of less impurities, low oxygen content, whisker structure with certain length-diameter ratio, high sintering activity and capability of obtaining compact silicon nitride ceramics, thereby improving the thermal conductivity of the ceramic material and obtaining the thermal conductive substrate with high thermal conductivity and good mechanical property.

Further, in step S600, the cutting direction of the cutting step is parallel to the hot pressing direction in step S520, so as to obtain the heat conductive substrate.

Specifically, the sintered body was ground to a size of 30mm × 50mm × 25mm, and then cut in a direction parallel to the hot pressing direction, to obtain a heat conductive substrate having a size of 30mm × 50mm × 0.32 mm.

The heat conduction substrate has high heat conductivity and good mechanical property, and can be used as a circuit substrate.

It can be understood that, according to the requirement of the actual circuit, the heat conducting substrates with different sizes can be obtained by cutting, so as to meet the requirements of different sizes and specifications in the circuit substrate.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

The magnesium silicon nitride powder and the preparation method thereof, the ceramic material and the heat conducting substrate according to the present invention are exemplified herein, but the present invention is not limited to the following examples.

Example 1

1) Taking magnesium silicate with the purity of 99 percent and the granularity of 0.5 micron accounting for 50 percent of the total mass of the materials, 47 percent of cane sugar with the purity of 99 percent and 3 percent of polyvinyl alcohol by weight, and then mixing the materials according to the mass ratio of the materials to water of 1:1 adding distilled water, ball-milling and mixing, vacuum drying at 70 ℃, and sieving by a 200-mesh sieve to obtain a mixture.

2) Distributing the mixture obtained in the step 1) in a silicon nitride crucible, placing the silicon nitride crucible in a reaction furnace, vacuumizing, injecting 1MPa nitrogen, heating to 800 ℃ at the heating rate of 5 ℃/min, heating to 1300 ℃ at the heating rate of 3 ℃/min, preserving heat, carrying out reduction reaction for 3h, and calcining for 5h in the air atmosphere of 600 ℃ after the reaction is finished, and carrying out decarbonization treatment to obtain the silicon nitride magnesium powder.

3) Providing the following raw materials: silicon nitride powder, the silicon nitride magnesium powder prepared in the step 2), silicon nitride whiskers, silicon carbide whiskers, a binder polyvinyl butyral, a defoaming agent tributyl phosphate and a solvent absolute ethyl alcohol, adding ammonia water to adjust the pH value of the system to 9, and finally performing ball milling treatment to obtain slurry. The silicon nitride/magnesium nitride/polyvinyl butyral composite material is prepared from 100 parts of silicon nitride powder, 7 parts of silicon nitride/magnesium nitride powder, 5 parts of silicon nitride whisker, 2 parts of silicon carbide whisker, 2 parts of polyvinyl butyral, 1 part of tributyl phosphate and 100 parts of absolute ethyl alcohol. Then, carrying out spray granulation on the slurry to obtain powder particles with the particle size of 80 microns; and performing dry pressing on the powder particles under 120MPa to obtain a blank with the thickness of 37mm multiplied by 61mm multiplied by 30mm, and then performing isostatic pressing forming under vacuum packaging under 180MPa to obtain a green blank.

4) Putting the green body obtained in the step 3) into a hot pressing furnace, heating to 800 ℃ at a heating rate of 30 ℃/h, and carrying out heat preservation and degreasing treatment for 2 hours; and then raising the temperature to 1750 ℃ at a temperature raising speed of 100 ℃/h, preserving the temperature, and carrying out hot-pressing sintering for 5h, wherein a mixed atmosphere of hydrogen and nitrogen is adopted during sintering, the flow ratio of the hydrogen to the nitrogen is 1:5, and the pressure during hot-pressing sintering is 100MPa, so as to obtain the ceramic material.

5) Grinding the ceramic material obtained in the step 4) into the size of 30mm multiplied by 50mm multiplied by 25mm, and then cutting the ceramic material in the direction parallel to the hot pressing direction to obtain the heat conducting substrate with the specification of 30mm multiplied by 50mm multiplied by 0.32 mm.

6) And (3) performance testing:

(1) the purity and the whisker structure of the silicon nitride magnesium powder prepared in the step 2) are tested, and the result shows that: the length of the crystal whisker of the silicon nitride magnesium powder prepared in the step 2) is 25 mu m, the diameter is 0.8 mu m, the impurity content is 0.8 wt%, and the oxygen content is 0.3 wt%. The electron microscope image of the crystal whisker of the silicon nitride magnesium powder is shown as the attached figure 1.

(2) Testing the thermal conductivity, the bending strength and the fracture toughness of the ceramic prepared in the step 4), wherein the thermal conductivity test is in reference to the standard GB/T22588-2008; the bending strength test reference standard GB/T6569-2006; the fracture toughness is referred to the standard GB/T23806-; see table 1 for specific results.

Example 2

1) Taking 50 wt% of magnesium silicate with the purity of 99% and the granularity of 0.5 micron, 49 wt% of cane sugar with the purity of 99% and 1 wt% of polyvinyl alcohol, wherein the mass ratio of the materials to water is 1:1 adding distilled water, ball-milling and mixing, vacuum drying at 70 ℃, and sieving by a 200-mesh sieve to obtain a mixture.

The rest of the procedure was the same as in example 1.

The purity and the whisker structure of the silicon nitride magnesium powder prepared in the example 2 are tested, and the results show that: the length of the crystal whisker of the silicon nitride magnesium powder prepared in the step 2) is 30 mu m, the diameter is 0.5 mu m, the impurity content is 0.8 wt%, and the oxygen content is 0.3 wt%.

Example 3

1) Taking 50 wt% of magnesium silicate with the purity of 99% and the granularity of 0.5 micron, 45 wt% of sucrose with the purity of 99% and 5 wt% of polyvinyl alcohol, wherein the magnesium silicate, the sucrose and the polyvinyl alcohol account for 50 wt% of the total mass of the materials, then adding distilled water according to the mass ratio of the materials to the water of 1:1, carrying out ball milling and mixing, carrying out vacuum drying at 70 ℃, and then carrying out 200-mesh sieve screening to obtain a mixture.

The rest of the procedure was the same as in example 1.

The purity and the whisker structure of the silicon nitride magnesium powder prepared in the example 3 are tested, and the results show that: the length of the crystal whisker of the silicon nitride magnesium powder prepared in the step 2) is 20 mu m, the diameter is 1 mu m, the impurity content is 1 wt%, and the oxygen content is 0.3 wt%.

Example 4

Example 4 is essentially the same as example 1, except that in example 4, step 3) provides the following starting materials: silicon nitride powder, the silicon nitride magnesium powder prepared in the step 2), silicon nitride whiskers, silicon carbide whiskers, a binder polyvinyl butyral, tributyl phosphate and absolute ethyl alcohol, adding ammonia water to adjust the pH value of the system to 9, and finally performing ball milling treatment to obtain slurry. Wherein the raw materials comprise the following components in parts by weight: 100 parts of silicon nitride powder, 15 parts of silicon magnesium nitride powder, 6 parts of silicon nitride whiskers, 3 parts of silicon carbide whiskers, 4 parts of polyvinyl butyral, 3 parts of tributyl phosphate and 100 parts of absolute ethyl alcohol.

The other process steps are the same as in example 1.

Example 5

1) Taking 70 wt% of magnesium silicate with the purity of 99% and the granularity of 0.5 micron, 27 wt% of cane sugar with the purity of 99% and 3 wt% of polyvinyl alcohol, wherein the magnesium silicate, the sucrose and the polyvinyl alcohol account for 70 wt% of the total mass of the materials, and then, according to the mass ratio of the materials to water of 1:1 adding distilled water, ball-milling and mixing, vacuum drying at 70 ℃, and sieving by a 200-mesh sieve to obtain a mixture.

The rest of the procedure was the same as in example 1.

The purity and the whisker structure of the silicon nitride magnesium powder prepared in the example 4 are tested, and the results show that: step 2) the crystal whisker structure of the silicon nitride magnesium powder prepared is not obvious, the length is 10 mu m, the diameter is 3 mu m, the impurity content is 1.5 wt%, and the oxygen content is 2 wt%.

Example 6

Example 6 is essentially the same as example 1, except that in example 6, step 3) provides the following starting materials: silicon nitride powder, the silicon nitride magnesium powder prepared in the step 2), silicon nitride whiskers, silicon carbide whiskers, a binder polyvinyl butyral, a defoaming agent tributyl phosphate and absolute ethyl alcohol, adding ammonia water to adjust the pH value of the system to 9, and finally performing ball milling treatment to obtain slurry. Wherein the raw materials comprise the following components in parts by weight: 100 parts of silicon nitride powder, 7 parts of silicon magnesium nitride powder, 5 parts of silicon nitride whisker powder, 6 parts of silicon carbide whisker, 2 parts of polyvinyl butyral, 1 part of tributyl phosphate and 100 parts of absolute ethyl alcohol.

The other process steps are the same as in example 1.

Comparative example 1

1) Taking 50 wt% of magnesium silicate with the purity of 99% and the particle size of 0.5 micron, 49.5 wt% of sucrose with the purity of 99% and 0.5 wt% of polyvinyl alcohol, and then mixing the materials according to the mass ratio of 1:1 adding distilled water, ball-milling and mixing, vacuum drying at 70 ℃, and sieving by a 200-mesh sieve to obtain a mixture.

The rest of the procedure was the same as in example 1.

The purity and the whisker structure of the prepared silicon nitride magnesium powder are tested, and the result shows that: the crystal whisker structure of the silicon nitride magnesium powder prepared in comparative example 1 was not obvious, the length was 10 μm, the diameter was 5 μm, the impurity content was 2 wt%, and the oxygen content was 2 wt%.

Comparative example 2

1) Taking 50 wt% of magnesium silicate with the purity of 99% and the granularity of 0.5 micron, 44 wt% of cane sugar with the purity of 99% and 6 wt% of polyvinyl alcohol according to the mass ratio of materials to water of 1:1 adding distilled water, ball-milling and mixing, vacuum drying at 70 ℃, and sieving by a 200-mesh sieve to obtain a mixture.

The rest of the procedure was the same as in example 1.

The purity and the whisker structure of the prepared silicon nitride magnesium powder are tested, and the result shows that: the crystal whisker structure of the silicon nitride magnesium powder prepared in comparative example 2 was not obvious, the length was 10 μm, the diameter was 5 μm, the impurity content was 3 wt%, and the oxygen content was 0.3 wt%.

Comparative example 3

Comparative example 3 is substantially the same as example 1 except that sucrose in step 1) of example 1 is replaced with an inorganic carbon powder in step 1) of comparative example 3, and the remaining steps are the same as example 1.

The purity and the whisker structure of the prepared silicon nitride magnesium powder are tested, and the result shows that: comparative example 3 the obtained magnesium silicon nitride powder had no whisker structure, a crystal grain size of about 10 μm, an impurity content of 3 wt%, and an oxygen content of 0.5 wt%.

TABLE 1

	Bending strength (MPa)	Thermal conductivity (W/m.k)	Fracture toughness (MPa. m)^1/2)
				Example 1	920	109	8.7
Example 2	930	88	8.8
				Example 3	880	98	8.5
Example 4	950	95	8.5
				Example 5	750	67	7.0
Example 6	830	70	8.0
				Comparative example 1	770	65	7.2
Comparative example 2	750	63	7.5
				Comparative example 3	650	53	6.5

As can be seen from the test data in Table 1, the ceramic material prepared according to the technical scheme of the application has the thermal conductivity of 109W/m.K, the bending strength of 950MPa and the fracture toughness of 8.8MPa m^1/2。

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above examples only show some embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. The preparation method of the silicon nitride magnesium powder is characterized by comprising the following steps of:

mixing magnesium silicate and a carbon source to obtain a mixture;

2. The method according to claim 1, wherein the organic carbon of the saccharide is at least one selected from the group consisting of maltose, glucose, a glucan, fructose, sucrose, lactose and starch; and/or

3. The preparation method according to claim 1, wherein the mass ratio of the magnesium silicate to the carbon source is 1 (0.5-3).

4. The preparation method according to any one of claims 1 to 3, wherein the temperature control procedure of the reduction reaction is as follows:

5. The method according to any one of claims 1 to 3, wherein the method for preparing the magnesium silicon nitride powder further comprises the step of preparing the magnesium silicate:

and calcining the precipitate to obtain the magnesium silicate.

6. The silicon nitride magnesium powder prepared by the preparation method according to any one of claims 1 to 5.

7. The use of the magnesium silicon nitride powder of claim 6 in the preparation of a thermally conductive material.

8. A ceramic material, characterized in that the composition of the ceramic material comprises: silicon nitride powder, sintering aid, nitride whisker and/or carbide whisker, binder and dispersant;

wherein the sintering aid comprises the magnesium silicon nitride powder according to claim 6.

9. The ceramic material according to claim 8, wherein the silicon nitride powder is 100 parts by mass, the sintering aid is 3 to 15 parts by mass, the dispersant is 0.3 to 3 parts by mass, the binder is 1 to 5 parts by mass, and the nitride whiskers and/or the carbide whiskers are 3 to 10 parts by mass.

10. A heat conductive substrate, wherein the heat conductive substrate is made of the ceramic material according to any one of claims 8 to 9.