CN105837223A - Method for synthesizing aluminum nitride power - Google Patents

Abstract

The invention relates to a method for synthesizing aluminum nitride powder, comprising the following steps: preparing a bulk porous precursor uniformly distributed with an aluminum source and a carbon source, the bulk porous precursor has through holes on the surface and at least partly connected with The connected pore structure formed by the internal through holes connected by the surface through holes; and the obtained blocky porous precursor is subjected to a carbothermal reduction reaction in a nitrogen atmosphere and then carbon is removed to obtain an aluminum nitride powder. The preparation process of the invention is simple, without harsh operating conditions, and the synthesized aluminum nitride powder has controllable particle size and shape, less metal impurities and high sintering activity, and can be used for preparing aluminum nitride ceramics with high thermal conductivity.

Description

A method for synthesizing aluminum nitride powder

technical field

The invention belongs to a ceramic powder preparation process and relates to a synthesis method of aluminum nitride powder.

Background technique

Among ceramic materials, aluminum nitride (AlN) has excellent characteristics such as high theoretical thermal conductivity, small thermal expansion coefficient, high volume resistivity, excellent microwave dielectric properties and good chemical stability, and is considered to be a high-density, high-power and It is an ideal material for high-speed integrated circuit substrate and packaging, and has broad application prospects in aerospace, communication, microelectronics and other fields.

Among ceramic materials, aluminum nitride (AlN) has excellent characteristics such as high theoretical thermal conductivity, small thermal expansion coefficient, high volume resistivity, excellent microwave dielectric properties and good chemical stability, and is considered to be a high-density, high-power and It is an ideal material for high-speed integrated circuit substrates and packaging, and has broad application prospects in the fields of national defense, aerospace, communications, and microelectronics.

Since 1877, the synthesis of aluminum nitride powder has a history of more than 100 years, but it was not until the middle and late 1970s that dense aluminum nitride ceramics were prepared, and its thermal conductivity is far from the theoretical thermal conductivity. It is far away, and the initial product quality is not stable, and the process repeatability is poor, which limits its application in substrates and packaging materials. One of the main reasons for this phenomenon is that the quality of artificially synthesized aluminum nitride powder is not high, the content of metal impurities and oxygen impurities is high, and the sinterability is poor. It is difficult to obtain dense aluminum nitride ceramics, which makes the thermal conductivity of the final product far away. lower than the theoretical value.

As one of the traditional methods for preparing aluminum nitride powder, the carbothermal reduction method has many advantages: (1) wide source of raw materials, low cost, suitable for large-scale production; (2) insensitive to process conditions and good stability; ( 3) The obtained aluminum nitride powder has high purity and narrow particle size distribution, the shape of the product can be controlled by the shape of the raw material, and the powder is easy to form and sinter; and so on. However, the traditional carbothermal reduction process using carbon black as a carbon source has problems such as uneven mixing of raw materials, low loading, incomplete reaction, and high reaction temperature.

In recent years, researchers at home and abroad have done a lot of exploration on improving the carbothermal reduction process. For example, CN 101973534 A discloses a method for preparing aluminum nitride ceramic powder. In this method, aluminum nitrate or aluminum chloride or aluminum sulfate is used as an aluminum source, carbon black is a carbon source, urea, ammonium nitrate, and nitric acid are additives, and the heating reaction Finally, a precursor is obtained, and the precursor is decarburized after a carbothermal reduction reaction to obtain an aluminum nitride powder. For example, CN 104402452 A discloses a method for preparing aluminum nitride ceramic powder. This method utilizes the hydrolysis reaction of high-purity aluminum to obtain an alumina precursor, sucrose as a carbon source, and uses a gel solid-phase method combined with carbon thermal reduction of nitrogen. Through the chemical process, through the control of the purity of aluminum source and carbon source and the decarbonization process of non-air oxidation atmosphere, the ultra-high purity and high sintering activity aluminum nitride powder with a purity of up to 99.99% can be obtained. Another example is CN 102686511 A which discloses a manufacturing method of spherical aluminum nitride powder, which needs to first form spherical granules by granulating alumina powder or alumina hydrate powder as a starting material, and then granulate the spherical granules The material is supplied to the reduction nitriding process, and nitrogen gas permeates into the inside of the granulated material through the gap formed between the particles to perform reduction nitriding. However, these improved methods still have the problem of incomplete solid-gas reaction. For example, the alumina and carbon black used as raw materials for the above-mentioned carbothermal reduction reaction are still piled up in the reactor in powder form, and the nitrogen gas fed into the reactor is difficult to enter the pile. The inside of the powder, resulting in uneven reaction on the upper and lower surfaces of the powder accumulation, so that a large amount of powder cannot be reacted at one time.

Contents of the invention

In view of the above problems, the object of the present invention is to provide a novel method for preparing AlN powder. This method is simple to operate and low in cost, and can solve the problems of low raw material loading, insufficient solid-gas contact and uneven reaction in the traditional carbothermal reduction process, and is suitable for industrial production.

The present invention here provides a method for synthesizing aluminum nitride powder, comprising the following steps: preparing a block-like porous precursor uniformly distributed with aluminum source and carbon source, the block-like porous precursor having through holes on the surface and at least A connected pore structure formed by internal through holes partially communicating with the surface through holes; and performing a carbothermal reduction reaction on the obtained blocky porous precursor in a nitrogen atmosphere and then removing carbon to obtain an aluminum nitride powder.

The present inventors prepared the aluminum source and the carbon source into a bulky porous precursor with a connected pore structure, and then carried out carbothermal reduction and nitriding in a nitrogen atmosphere. With this, on the one hand, nitrogen can smoothly enter the interior of the precursor through the interconnected pore structure, which can increase the contact area of the solid-gas reaction, greatly shorten the reaction time, and significantly improve the reaction efficiency and the uniformity of the powder. On the other hand, a bulky porous precursor is formed, and multiple precursors can be stacked in the reaction furnace to react simultaneously without the problem of uneven reaction on the upper and lower surfaces of the powder stack. In addition, the preparation process of the present invention is simple, without harsh operating conditions, and the synthesized aluminum nitride powder has controllable particle size and shape, less metal impurities, and high sintering activity, and can be used to prepare aluminum nitride ceramics with high thermal conductivity.

Preferably, the pore size of the bulk porous precursor is 1-500 μm. The precursor of the present invention has a wide range of pore size, and can form a multi-level pore structure formed by small pores and macropores.

Preferably, the aluminum source may be at least one of alumina, gibbsite (such as α-gibbsite), boehmite, and gibbsite in crystalline form.

Preferably, the carbon source can be at least one of carbon black, activated carbon, sucrose, glucose, starch, and citric acid.

Preferably, the mass ratio of the aluminum source to the carbon source may be 1:(0.4-5).

Preferably, multiple blocks of the bulk porous precursor are stacked in a reaction furnace while blowing nitrogen gas to perform carbothermal reduction reaction.

Preferably, the preparation method of the porous precursor comprises the following steps:

Fully mix the aluminum source and the carbon source to obtain a raw material mixture;

Uniformly mixing the raw material mixture with the dispersion medium and the additives used to form the gel to obtain a dispersed and stable slurry, the slurry has a solid content of 20-50 wt%, and the content of the additives is 0.3-5.0%; and

After adding a surfactant to the slurry, perform mechanical foaming, inject the mold into a mold for in-situ gel solidification, and dry to obtain a porous precursor, and the mass ratio of the slurry to the surfactant is 1:(0.001～0.10 ).

The present invention prepares a porous precursor through a gel foaming process, and the formed interconnected pores are evenly distributed on the surface and inside of the precursor, and are connected in a three-dimensional network, and the obtained precursor has a certain strength and is suitable for stacking. In addition, the process is simple and controllable, without harsh operating conditions and equipment requirements, and is suitable for industrial production.

Preferably, the aluminum source and the carbon source can be mixed by mechanical dry mixing, such as ball milling. The present invention directly mixes the aluminum source and the carbon source through mechanized dry mixing, so that the introduction of impurities can be strictly prevented during the raw material mixing process, so that the particle size and shape of the finally obtained aluminum nitride powder can be controlled, and the metal impurities Low content, high sintering activity.

Preferably, the slurry is a water-based coagulation system, preferably a polyacrylamide gel system, a polyamine-epoxy resin gel system, or a water-soluble butene-based polymer gel system, wherein the water-soluble cis-butene The butene polymer is preferably any type or combination of poly[(isobutylene-alt-maleic acid, ammonium salt)-co-(isobutylene-alt-maleic anhydride)]. By selecting these water-based gel injection systems, gels can be formed without adding other additives, further reducing the introduction of impurities.

Preferably, the mass ratio of the slurry to the surfactant is 1:(0.001-0.10). Surfactants can stabilize the structure of the pores formed by agitation foaming.

Preferably, the flow rate of nitrogen during the carbothermal reduction reaction may be 1-20 L/min.

Preferably, the reaction temperature of the carbothermal reduction reaction may be 1400°C-1700°C, and the reaction time may be 1-5 hours.

Preferably, the carbon removal temperature may be 500° C. to 750° C., and the carbon removal time may be 1 to 5 hours.

The present invention also provides an aluminum nitride powder synthesized according to the above synthesis method. The purity of the aluminum nitride powder is above 97%.

The aluminum nitride powder provided by the invention has low impurity content and good sintering activity, and is expected to be prepared into dense alumina ceramics.

Description of drawings

Fig. 1 is the scanning electron microscope microanalysis diagram of the precursor that embodiment 1 prepares;

Fig. 2 is the aluminum nitride powder scanning electron microscope microanalysis diagram of embodiment 1 synthetic product sampling;

Fig. 3 is the aluminum nitride powder X-ray diffraction figure of embodiment 1 synthetic product sampling;

Fig. 4 is the scanning electron microscope microanalysis figure of the precursor that embodiment 2 prepares;

Fig. 5 is the aluminum nitride powder scanning electron microscope microanalysis diagram of embodiment 2 synthetic product sampling;

Fig. 6 is the aluminum nitride powder X-ray diffraction figure of embodiment 2 synthetic product sampling;

Figure 7 is a scanning electron microscope microanalysis diagram of the precursor prepared in Example 3;

Fig. 8 is the scanning electron microscope microanalysis figure of the aluminum nitride powder body sampling of the synthetic product of embodiment 3;

Fig. 9 is the aluminum nitride powder X-ray diffractogram of embodiment 3 synthetic product sampling;

Figure 10 is a scanning electron microscope microanalysis diagram of the precursor prepared in Example 4;

Fig. 11 is the scanning electron microscope microanalysis diagram of the aluminum nitride powder of embodiment 4 synthetic product sampling;

Fig. 12 is the aluminum nitride powder X-ray diffraction figure of embodiment 4 synthetic product sampling;

Fig. 13 is a sampling X-ray diffraction pattern of the powder product obtained in Comparative Example 1;

Fig. 14 is the physical figure of the precursor prepared by the method of the present invention;

Figure 15 is a physical diagram of multiple precursor stacks.

detailed description

The present invention will be further described below in conjunction with the drawings and the following embodiments. It should be understood that the drawings and the following embodiments are only used to illustrate the present invention rather than limit the present invention.

In the present invention, the aluminum source and the carbon source are first made into a block-shaped porous precursor with a through-hole structure, and then placed in a nitrogen atmosphere for carbothermal reduction reaction; the powder obtained after the reaction is decarbonized to obtain high-quality nitrogen Aluminum powder.

As the aluminum source, it can be alumina and/or alumina hydrate, specifically, including but not limited to alumina in various crystal forms (including α, γ, θ, η, δ, К, Х), trihydrate Gibbsite (for example α-gibbsite), boehmite, hexagonal gibbsite or a mixture of any of these substances.

As a carbon source, simple carbon and organic carbon precursors that can be cracked into simple carbon at high temperatures can be used. Specifically, for example, simple carbon includes but not limited to carbon black, activated carbon, and organic carbon that can be cracked into simple carbon at high temperatures. Precursors include, but are not limited to, sucrose, glucose, starch, citric acid.

In the bulk porous precursor, the mass ratio of the aluminum source to the carbon source may be 1:(0.4-5), preferably 1:(0.4-3). The mass ratio of the aluminum source to the carbon source is above 1:0.4, which can make the aluminum source react fully and completely; when the mass ratio of the aluminum source to the carbon source is below 1:5, there will not be too much surplus carbon source, which will cause waste and increase The question of carbon removal costs.

The bulk porous precursor should be understood as having a certain strength so as to facilitate handling, transfer, stacking and the like. The block shape is not limited to a block shape, and its outer surface is not required to form an absolutely flat surface.

The pore structure of the bulk porous precursor is preferably a connected hole, that is, at least have a surface through hole (open hole) communicating with the outside, and an internal through hole communicating with the surface through hole, so that the solid-gas contact can be more fully and uniform. The porosity of the porous precursor may be 50-85%, preferably 60-80%. If the porosity is less than 50%, the solid-gas contact may be insufficient; if the porosity is greater than 85%, the space utilization rate of the reaction furnace chamber will be low and the production efficiency will be low. In addition, the pore size of the porous precursor may be 1-800 μm, preferably 200-500 μm. The precursor of the present invention has a wide range of pore size, and can form a multi-level pore structure formed by small pores and macropores.

The bulk porous precursor used in the present invention can be prepared by gel foaming process. For example, a porous precursor is obtained by foaming a slurry (gel system) in which an aluminum source, a carbon source, and an additive for gel formation are uniformly dispersed, and then solidifying the gel. Hereinafter, this gel foaming process will be described as an example.

Firstly, the raw material mixing pretreatment is carried out: the aluminum source and the carbon source are thoroughly mixed evenly to obtain a raw material mixture. The aluminum source can be alumina and/or alumina hydrate as mentioned above, so that the introduction of impurities can be strictly prevented. The aluminum source can be purchased commercially or self-made, for example, can be obtained by alkoxide method, Bayer method, ammonium alum pyrolysis method, ammonium dawsonite (ammoniumdawsonite) pyrolysis method. The median particle diameter of the aluminum source used as a raw material may be 10-3500 nm, and the BET specific surface area may be 1-1000 m ² /g. The carbon source used as a raw material may have a median particle diameter of 5 to 50 nm, and a BET specific surface area of 50 to 1000 m ² /g. The ratio of the aluminum source and the carbon source can be aluminum source: carbon source = 1: (0.4-5) by weight. The mixing method of aluminum source and carbon source is preferably mechanized dry mixing, which can strictly prevent the introduction of impurities. Mechanized dry mixing can be any one of three-dimensional motion mixer, rolling ball mill, and planetary ball mill. Wear-resistant lining and ball milling medium are used in the mixing process. The lining material includes, but is not limited to, any one of nylon, polyurethane, alumina ceramics, and aluminum nitride ceramics. The ball milling medium includes, but is not limited to, any one of alumina balls, aluminum nitride balls, nylon balls, and nylon-coated steel balls. Material: ball weight ratio = 1: (1.5 ~ 3), ball milling time 0.5 ~ 5 hours, to make it fully mixed evenly, the mixed raw materials are taken out and sieved through a 40-mesh sieve.

Next, prepare the slurry: uniformly mix the raw material mixture with the dispersion medium and additives for forming a gel to obtain a stable dispersion slurry. The dispersion medium includes but not limited to water, ethanol, acetone, etc., preferably deionized water (that is, forms a water-based coagulation system). Additives used to form gels include, but are not limited to, five-component systems (polyacrylamide gel systems), three-component systems (polyamine-epoxy resin gel systems) and one-component systems (water-soluble maleic polymer gel systems). glue system), etc. And the water-soluble maleic polymer is poly[(isobutene-alt-maleic acid, ammonium salt)-co-(isobutene-alt-maleic anhydride)] in any model or any combination of models. The mass ratio of the raw material mixture, the dispersion medium and the additive may be 1:(0.5-5):(0.003-0.05). The mixing method of the three can be wet ball milling. Wear-resistant lining and ball milling medium can be selected. The lining material includes, but is not limited to, any one of nylon, polyurethane, alumina ceramics, and aluminum nitride ceramics. The ball milling medium includes, but is not limited to, any one of alumina balls, aluminum nitride balls, nylon balls, and nylon-coated steel balls. Material:ball weight ratio=1:(1.5～3), ball milling time 1～3 hours, obtain dispersed and stable slurry, the solid content of the formed slurry is 20～50wt%, the content of additive is 0.3～5.0wt%.

A surfactant is added to the prepared slurry, and the weight ratio may be slurry:surfactant=1:(0.001-0.10), preferably 1:(0.01-0.05). As surfactants, including but not limited to anionic surfactants (such as stearic acid, sodium dodecylbenzenesulfonate), cationic surfactants (such as quaternary ammonium compounds), zwitterionic surfactants (such as lecithin, amino acid type, betaine) and nonionic surfactants (such as fatty acid glycerides, fatty acid sorbitan, polysorbate). The slurry is subjected to mechanical foaming (for example stirring foaming), and the stirring time may be 0.5-5 minutes. Then inject the slurry into the mold for in-situ gel solidification (for example, stand at 15-60°C for 2-5 hours), and dry (for example, dry at 20-60°C for 2-7 days) to obtain blocky porous Precursor. Wherein, forming molds include but not limited to plastic molds, glass molds, rubber molds, metal or wood assembly molds.

See Figure 1 and Figure 14, which show the physical photos and cross-sectional photos of the bulk porous precursor prepared by the above method, from which it can be seen that the bulk porous precursor has surface pores and internal interconnected pores, and is a three-dimensional network distribution channel structure . Referring to Fig. 15 again, a plurality of precursors can be stacked, and the bulk porous precursor prepared by the present invention has a certain strength.

The preparation method of the porous precursor is described above by taking the gel foaming process as an example, but it should be understood that the porous precursor involved in the present invention can be obtained by other porous ceramic preparation processes. These processes are, for example, described below.

(1) Adding pore-forming agent method

Add flammable or volatile pore-forming agents (such as paraffin, starch, sucrose, etc.) in the slurry preparation process (for example, referring to the slurry preparation in the above-mentioned gel foaming process), after the slurry is solidified, the pore-forming agents can be Burn out at low temperature or volatilize directly, leaving a large number of pores on the surface and inside of the precursor. The shape and size of the pores of the porous precursor can be regulated by controlling the shape, size and addition amount of the pore-forming agent particles.

(2) Organic foam impregnation method

Immerse the organic foam into a dispersed stable slurry (for example, with reference to the slurry preparation in the above-mentioned gel foaming process), and repeatedly extrude, so that the ceramic powder adheres to the cell walls or ribs of the organic foam, thereby The foam structure is replicated, and the organic foam is burned off after drying to obtain a porous precursor. The structure and size of the pores of the porous precursor can be regulated by controlling the pore structure and pore size of the organic foam.

(3) Sol-gel method

First hydrolyze metal aluminum or aluminum alkoxide to obtain a sol, then add an organic carbon source (such as sucrose, glucose, starch, citric acid, etc.) to adjust the pH value, and form a gel with an amorphous network structure through condensation and condensation reactions. Finally, the gel is dried and heat-treated, and the organic matter is decomposed to obtain a porous precursor.

(4) freeze-drying method

Using the freezing effect of water-based slurry (for example, referring to the slurry preparation in the above-mentioned gel foaming process), while controlling the ice growth direction, and sublimating the ice by drying under reduced pressure, a porous precursor with a complex pore structure can be obtained.

The bulk porous precursors were stacked under a nitrogen atmosphere for carbothermal reduction to generate AlN. The reaction temperature may be 1400°C-1700°C, and the reaction time may be 1-5 hours, preferably 1-4 hours. The flow rate of nitrogen can be 1-20 L/min. After carbon removal, aluminum nitride powder can be obtained. The carbon removal temperature may be 500°C-750°C, and the carbon removal time may be 1-5 hours. The particle size of the obtained aluminum nitride powder is 0.1-2 μm, the shape is spherical, ellipsoidal, hexagonal or other irregular polyhedral, and the purity is above 97%.

The present invention mainly has the following advantages:

(1) The prepared precursor has a three-dimensional network-like distribution of pores, which can increase the contact area of the solid-gas reaction, greatly shorten the reaction time, and significantly improve the reaction efficiency and the uniformity of the powder;

(2) The present invention forms a bulk precursor, and multiple precursors can be stacked in a reaction furnace to react simultaneously, with a high loading capacity and suitable for large-scale production;

(3) Wide source of raw materials, low price, convenient transportation and storage, simple and controllable preparation process, no harsh operating conditions and equipment requirements, suitable for industrial production;

(4) The present invention can strictly prevent the introduction of impurities in the process of raw material selection and mixing, and the particle size and shape of the finally obtained aluminum nitride powder can be controlled by selecting the particle size and shape of the raw materials, and the metal impurity content is low , high sintering activity, can be used to prepare aluminum nitride ceramics with high thermal conductivity.

Examples are given below to describe the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention, and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the above contents of the present invention all belong to the present invention scope of protection. The specific process parameters and the like in the following examples are only examples of suitable ranges, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values exemplified below.

Test methods for structure and performance

(particle size)

The particle size test method of aluminum source, carbon source and aluminum nitride powder is laser method.

(specific surface area)

Calculated according to the Brunauer–Emmett–Teller (BET) method.

(Porosity)

The calculation method of the porosity of the porous precursor is as follows: the sample is processed into a regular shape, the length, width, and height are measured, and the volume V is calculated, and then the mass m is obtained by weighing, and the apparent density is:

ρ'=m/V

Then the total porosity of the precursor is:

P=1-ρ'/D _th

where D _th is the theoretical density of the material.

(pore size)

The pore size test method of the porous precursor is as follows: the pore size of the porous precursor can be determined by direct observation of the cross-section, that is, the pore size of the precursor is directly observed through a scanning electron microscope.

(Purity of aluminum nitride powder)

The purity of the aluminum nitride powder was determined by inductively coupled plasma atomic emission spectrometry (ICP).

Example 1:

(1) Use γ-Al ₂ O ₃ (median particle size 20nm, BET 126m ² /g) as the aluminum source, carbon black (median particle size 10nm, BET 320m ² /g) as the carbon source, and alumina by weight : carbon black=7:3 to carry out mechanical dry mixing, select nylon lining, use alumina balls as the ball milling medium, material: ball weight ratio=1:1.5, ball milling time 0.5 hours, make it fully mix evenly, after the mixed raw materials are taken out Sieve through a 40-mesh sieve;

(2) Using a one-component gel system, raw materials by weight: deionized water: water-soluble butene-based polymer = 1:4:0.01, weighed raw materials, deionized water and polymer and mixed by wet ball milling, Nylon lining is selected, alumina balls are used as the ball milling medium, the material:ball weight ratio is 1:1.5, and the ball milling time is 1 hour to obtain a slurry with good dispersibility and stability;

(3) Slurry by weight ratio: Surfactant=1:0.005 Add surfactant triethanolamine lauryl sulfate to the slurry, inject it into the metal mold after mechanical foaming for 2 minutes, the in-situ gel is solidified, and After drying at 20°C for 3 days, the obtained precursor has a porosity of 80%, and the pore size varies from tens to hundreds of microns. The picture of the precursor is shown in Figure 1. It can be seen that the precursor The pore structure is dominated by through holes, the pore diameters vary greatly, and the precursor is isotropic;

(4) Carbothermal reduction reaction was carried out on the precursor under a nitrogen atmosphere, the reaction temperature was 1600°C, the nitrogen flow rate was 10L/min, and the reaction time was 4 hours; the powder obtained after the reaction was decarbonized, the carbon removal temperature was 650°C, and the carbon removal temperature was 650°C. After 3 hours, the aluminum nitride powder was obtained, and its scanning electron microscope microanalysis diagram is shown in Figure 2. It can be seen that the powder has good uniformity, and its X-ray diffraction diagram is shown in Figure 3. It can be seen that the Under the conditions, the aluminum oxide has been completely converted into aluminum nitride, the reaction has been completed, the median particle diameter D ₅₀ is 530nm, and the purity is 97%.

Example 2:

(1) Use α-Al ₂ O ₃ (median particle size 450nm, BET 6.4m ² /g) as aluminum source, carbon black (median particle size 10nm, BET 320m ² /g) as carbon source, and oxidize by weight Aluminum: carbon black = 3:2 for mechanical dry mixing, choose nylon lining, use alumina balls as the ball milling medium, material: ball weight ratio = 1:2, ball milling time 1 hour, make it fully mixed evenly, take out the mixed raw materials Then pass through a 40-mesh sieve;

(2) Use a one-component gel system. According to the weight ratio of raw materials: deionized water: water-soluble butene-based polymer = 1:5:0.04, weigh raw materials, deionized water and polymer and mix through wet ball milling, with alumina balls as the ball milling medium, the material : The ball weight ratio=1:2, the ball milling time is 2 hours, and the slurry with good dispersion and stability is obtained;

(3) Slurry by weight ratio: Surfactant=1:0.01 Add surfactant triethanolamine lauryl sulfate to the slurry, inject it into the metal mold after mechanical foaming for 3 minutes, the in-situ gel is solidified, and Dry at 20°C for 3 days to obtain a precursor with a porosity of 75%. As shown in Figure 4, the pore size of the precursor varies from tens to hundreds of microns, and the precursor is isotropic;

(4) Carbothermal reduction reaction was carried out on the precursor in a nitrogen atmosphere, the reaction temperature was 1650°C, the nitrogen flow rate was 8L/min, and the reaction time was 4 hours; the powder obtained after the reaction was decarbonized, the carbon removal temperature was 650°C, and the carbon removal temperature was 650°C. After 3 hours, the aluminum nitride powder was obtained, and its scanning electron microscope microscopic analysis diagram is shown in Figure 5. It can be seen that the powder has good uniformity, and its X-ray diffraction diagram is shown in Figure 6. It can be seen that the Under the conditions, the aluminum oxide has been completely converted into aluminum nitride, the reaction has been completed, the median particle diameter D ₅₀ is 695nm, and the purity is 97%.

Example 3:

(1) Select boehmite (median particle size 540nm, BET 5.3m ² /g) as the aluminum source, sucrose as the carbon source, carry out mechanical dry mixing according to the weight ratio of alumina: carbon black = 1:5, and use nylon inner Lining, with alumina balls as the ball milling medium, material: ball weight ratio = 1:2, ball milling time 1 hour, make it fully mixed evenly, after the mixed raw materials are taken out, pass through a 40-mesh sieve;

(2) Adopt ternary gel system. According to the weight ratio of raw materials: deionized water: polyamine-epoxy resin = 1:2:0.02, weigh the raw materials, deionized water and polymer and mix them by wet ball milling, with alumina balls as the ball milling medium, material: ball Weight ratio = 1:2, ball milling time 2 hours, to obtain a slurry with good dispersibility and stability;

(3) Slurry by weight ratio: Surfactant=1:0.001 Add surfactant triethanolamine lauryl sulfate to the slurry, inject it into the metal mold after mechanical foaming for 1 minute, the in-situ gel is solidified, and Dry at 20°C for 3 days to obtain a precursor with a porosity of 50%. As shown in Figure 7, the pore size of the precursor varies from tens to hundreds of microns, and the precursor is isotropic;

(4) Carbothermal reduction reaction was carried out on the precursor under a nitrogen atmosphere, the reaction temperature was 1400°C, the nitrogen flow rate was 1L/min, and the reaction time was 2 hours; the powder obtained after the reaction was decarbonized, the carbon removal temperature was 650°C, and the carbon removal temperature was 650°C. After 3 hours, the aluminum nitride powder was obtained, and its scanning electron microscope microscopic analysis diagram is shown in Figure 8. It can be seen that the powder has good uniformity, and its X-ray diffraction diagram is shown in Figure 9. It can be seen that the Under the conditions, the alumina has been completely converted into aluminum nitride, and the reaction has been completed. Its median particle diameter _D50 is 763nm, and its purity is 97%.

Example 4

(1) Use gibbsite (median particle size 521nm, BET 6.1m ² /g) as aluminum source, activated carbon (median particle size 10nm, BET 332m ² /g) as carbon source, alumina by weight ratio: Carbon black = 1:5 for mechanical dry mixing, choose nylon lining, use alumina balls as the ball milling medium, material: ball weight ratio = 1:3, ball milling time 2 hours, make it fully mixed evenly, after the mixed raw materials are taken out, pass through Sieve through a 40-mesh sieve;

(2) A five-component gel system is used. According to the weight ratio of raw materials: deionized water: polyacrylamide = 1:5:0.03, weigh the raw materials, deionized water and polymer and mix them by wet ball milling, using alumina balls as the ball milling medium, material: ball weight ratio = 1:1.5, the ball milling time is 3 hours, and the slurry with good dispersion and stability is obtained;

(3) Slurry by weight ratio: surfactant = 1:0.1 Add surfactant fatty acid glyceride to the slurry, inject it into the metal mold after mechanical foaming for 5 minutes, in situ gel solidification, and under 20 ℃ Dry for 3 days to obtain a precursor with a porosity of 85%. As shown in Figure 10, the pore size of the precursor is different, ranging from tens to hundreds of microns, and the precursor is anisotropic;

(4) Carbothermal reduction reaction was carried out on the precursor under a nitrogen atmosphere, the reaction temperature was 1700°C, the nitrogen flow rate was 20L/min, and the reaction time was 2 hours; the powder obtained after the reaction was decarbonized, the carbon removal temperature was 500°C, and the carbon removal temperature was 500°C. After 5 hours, the aluminum nitride powder was obtained, and its scanning electron microscope microscopic analysis diagram is shown in Figure 11. It can be seen that the powder has good uniformity, and its X-ray diffraction diagram is shown in Figure 12. It can be seen that the Under the conditions, the alumina has been completely converted into aluminum nitride, and the reaction has been completed. Its median particle diameter _D50 is 754nm, and its purity is 97%.

Comparative example 1

(1) with embodiment 1;

(2) with embodiment 1;

(3) Inject the slurry into a metal mold, in-situ gel solidify, and dry at 20°C for 3 days to obtain a precursor;

(4) Grinding the precursor by ball milling to obtain a precursor powder, and performing a carbothermal reduction reaction on the precursor powder under a nitrogen atmosphere at a reaction temperature of 1600° C., a nitrogen flow rate of 10 L/min, and a reaction time of 4 hours; The powder is decarbonized, the carbon removal temperature is 650°C, and the carbon removal time is 3 hours, and the aluminum nitride powder is obtained, as shown in Figure 13. XRD analysis of the aluminum nitride powder shows that there are alumina diffraction peaks in the obtained product, Promptly under this condition raw material has not yet reacted completely, and utilizes the method for embodiment 1, XRD has not detected impurity peak, shows that raw material reacts completely, and this shows that the present invention is practical for improving the carbothermal reduction method to prepare aluminum nitride powder feasible.

Claims (10)

1. the synthetic method of an aluminium nitride powder, it is characterised in that comprise the following steps:

Preparation is evenly distributed with the block porous presoma of aluminum source and carbon source, and described block porous presoma has the intercommunicating pore structure formed by surface through hole and at least part of interior bone with described surface through hole UNICOM；And

The block porous presoma of gained is carried out under nitrogen atmosphere de-carbon after carbothermic reduction reaction, i.e. obtains aluminium nitride powder.

Synthetic method the most according to claim 1, it is characterised in that the porosity of described block porous presoma is 50～85%, and pore-size is 1～800 m.

Synthetic method the most according to claim 1 and 2, it is characterised in that source of aluminium is at least one in the aluminium oxide of crystal habit, gibbsite, boehmite and hexagonal water aluminum stone；Described carbon source is at least one in white carbon black, activated carbon, sucrose, glucose, starch and citric acid；Aluminum source is 1:(0.4～5 with the mass ratio of carbon source).

Synthetic method the most according to any one of claim 1 to 3, it is characterised in that porous presoma heap block described in polylith is overlayed logical nitrogen in reacting furnace and carries out carbothermic reduction reaction simultaneously.

Synthetic method the most according to any one of claim 1 to 4, it is characterised in that the preparation method of described block porous presoma comprises the steps:

Aluminum source and carbon source are sufficiently mixed uniformly, obtain raw mixture；

Raw mixture and disperse medium and being used for being formed the additive of gel mix homogeneously and obtain the slurry of stably dispersing, described slurry solid content is 20～50wt%, and the content of additive is 0.3～5.0%；And

Carrying out mechanical foaming after adding surfactant in the slurry, inject mould and carry out situ-gel solidification, be dried, obtain porous presoma, described slurry is 1:(0.001～0.10 with the mass ratio of described surfactant).

Synthetic method the most according to claim 5, it is characterized in that, described slurry is that water base note coagulates system, optimization polypropylene acrylamide gel system, polyamine-epoxy resin gel rubber system or water solublity maleic base polymer gel rubber system, wherein any one model in water solublity maleic base polymer the most poly-[(isobutene .-alt-maleic acid, ammonium salt)-co-(isobutene .-alt-maleic anhydride)] or the combination of disposable type.

7. according to the synthetic method described in claim 5 or 6, it is characterised in that obtain described slurry, wherein, material: ball weight ratio=1:1.5～3, Ball-milling Time is 1～3 hour by wet ball grinding hybrid mode.

Synthetic method the most according to any one of claim 1 to 7, it is characterised in that during carbothermic reduction reaction, nitrogen flow rate is 1～20L/ minute.

Synthetic method the most according to any one of claim 1 to 8, it is characterised in that the reaction temperature of carbothermic reduction reaction is 1400 DEG C～1700 DEG C, and the response time is 1～5 hour；De-carbon temperature is 500 DEG C～750 DEG C, and the de-carbon time is 1～5 hour.

10. the aluminium nitride powder of the synthetic method synthesis according to any one of a claim 1 to 9, it is characterised in that the purity of described aluminium nitride powder is more than 97%.