CN104671795A - A kind of single-phase α-Si3N4 ultrafine powder and its preparation method - Google Patents

Abstract

The invention relates to a single-phase α-Si ₃ N ₄ ultrafine powder and a preparation method thereof. The technical solution is: first mix 5~30wt% elemental silicon powder, 15~45wt% solid nitrogen source and 40~80wt% halide powder to make a mixture; then put the mixture into a tubular electric furnace In a nitrogen atmosphere, the temperature was raised to 1000-1300°C at a rate of 2-10°C/min, and kept at a temperature of 2-6 hours; then the obtained product was repeatedly washed with deionized water until it was washed with AgNO ₃ and Ca(NO ₃ ) ₂ Titrate the solution until no white precipitate appears; finally dry at 110°C for 10-24 hours to obtain single-phase α-Si ₃ N ₄ ultrafine powder. The invention has the characteristics of low reaction temperature, low cost, simple synthesis process, easy process control, high yield and great industrialization prospect; the prepared single-phase α-Si ₃ N ₄ ultrafine powder has a particle size of 100-500nm, No impurity phase, high activity, small particle agglomeration and uniform particle size distribution. <u/>

Description

A kind of single-phase α-Si3N4 ultrafine powder and its preparation method

technical field

The invention belongs to the technical field of Si ₃ N ₄ ultrafine powder. It specifically relates to a single-phase α-Si ₃ N ₄ ultrafine powder and a preparation method thereof.

Background technique

Silicon nitride (Si ₃ N ₄ ) ceramics and their composites, as a functional material with excellent performance, are widely used in various fields such as machinery, electrical/optical devices, and refractory materials. There are mainly two common crystal structures of Si ₃ N ₄ : α phase and β phase, both of which belong to the hexagonal crystal system. The reason for the formation of two different variants is that the [Si-N ₄ ] plane structures are stacked in different ways to form two two-dimensional network crystal forms: the stacking order of α-Si ₃ N ₄ is ABCDAB…, β-Si ₃ N ₄ The stacking sequence is ABABAB.... α-Si ₃ N ₄ is granular and β-Si ₃ N ₄ is long columnar. α-Si ₃ N ₄ is a thermodynamically unstable phase. At 1300-1600°C, the α-Si ₃ N ₄ tetrahedron rotates 180° around the vertical line of the c-axis and transforms into the high-temperature phase β-Si ₃ N ₄ . Compared with β-Si ₃ N ₄ , α-Si ₃ N ₄ is conducive to the development of columnar grains in ceramic materials, and is easier to sinter densification and self-reinforcement. The mechanical strength and fracture toughness of Si ₃ N ₄ ceramic materials will increase with the The increase of α-Si ₃ N ₄ phase content in the raw material increases. At the same time, the volume effect and surface effect of nano or submicron α-Si ₃ N ₄ ultrafine powder can realize low-temperature sintering of silicon nitride ceramic materials and endow the materials with excellent mechanical properties. Therefore, the particle size, α-phase content and impurity content of silicon nitride powder determine its quality and directly affect the quality of ceramic products.

The quality of silicon nitride powder depends on its preparation method. At present, the main methods for preparing Si ₃ N ₄ powder are: silicon powder direct nitriding method, carbothermal reduction method and chemical vapor deposition method.

The direct nitriding method of silicon powder refers to the reaction of pure silicon powder in a reducing atmosphere of N ₂ , N ₂ +H ₂ or NH ₃ to produce silicon nitride micropowder. This method obtains α-Si ₃ at a lower temperature A mixture of N ₄ and β-Si ₃ N ₄ , only β-Si ₃ N ₄ can be obtained at high temperature. For example, the patented technology of "a production method of high-content α-crystalline silicon nitride powder" (CN 102173396 A) uses mechanical activation to pretreat silicon powder raw materials for 8 hours, and α-Si ₃ N ₄ and nano-amorphous Si ₃ N ₄ As a diluent, nitrogen gas is introduced under normal pressure, and the product is directly nitrided at 1350 ° C. The product is then ground by a vertical grinder for 7 to 10 hours to prepare sub-micron and micron-sized silicon nitride powders with an α-phase content of 97.6. However, this preparation method has relatively high requirements on the particle size of the silicon powder, and some silicon powder remains after the reaction, so the process is complicated and the energy consumption is high.

The carbothermal reduction method refers to the nitriding and reduction reaction of SiO ₂ and C powder in N ₂ atmosphere at high temperature to generate Si ₃ N ₄ fine powder. However, the reaction temperature of this method is high, the α phase content is low, the impurity content, especially the carbon content, is high, and the particle size distribution of the powder is uneven; the chemical vapor deposition method uses silicon halides (SiCl ₄ , SiBr _{4 ,} etc.) or Silicon hydrohalides (SiHCl ₃ , SiH ₂ Cl _{2 ,} etc.) undergo a chemical vapor phase reaction directly in a reducing atmosphere of N ₂ , N ₂ +H ₂ or NH ₃ to form silicon nitride. Si ₃ N produced by this method ₄ The powder has high purity, ultra-fine and uniform particles, and high α-phase content, but the reaction process is not easy to control, the raw materials are expensive, and the requirements for production equipment are high.

Therefore, the current preparation technologies for single-phase α-Si ₃ N ₄ ultrafine powders have certain deficiencies. For example, the price of raw materials is high, the process is complicated, difficult to control, high energy consumption or low degree of industrialization; the prepared product has low purity, uneven particle size distribution of powder or low α phase content.

Contents of the invention

The present invention aims to overcome the deficiencies in the prior art and provide a single-phase α-Si ₃ N ₄ superfine powder with low reaction temperature, low cost, simple synthesis process, easy process control, high yield and great industrialization prospect The preparation method of the body; the single-phase α-Si ₃ N ₄ ultrafine powder prepared by the method has high activity, small particle agglomeration, uniform particle size distribution and high purity of the powder.

In order to achieve the above object, the technical solution adopted in the present invention is: firstly mix 5-30wt% elemental silicon powder, 15-45wt% solid nitrogen source and 40-80wt% halide powder to prepare the mixture; The mixture is placed in a tubular electric furnace, raised to 1000-1300°C at a rate of 2-10°C/min under a nitrogen atmosphere, and kept at a temperature of 2-6 hours; then the resulting product is repeatedly washed with deionized water until the Titrate with AgNO ₃ and Ca(NO ₃ ) ₂ solutions until no white precipitate appears; finally dry at 110°C for 10-24 hours to obtain single-phase α-Si ₃ N ₄ ultrafine powder.

The Si content in the elemental silicon powder is ≥95wt%, and the particle size is ≤50 μm.

The solid nitrogen source is industrially pure or analytically pure, and the particle size is ≤200 μm; the solid nitrogen source is at least one of ammonium chloride, urea and melamine.

The halide powder is industrially pure or analytically pure, and the particle size is ≤200 μm; the halide powder is more than one of sodium chloride, potassium fluoride and sodium fluoride.

Due to the adoption of the above technical solution, the present invention has the following positive effects and outstanding features compared with the prior art:

1. The present invention realizes the atomic-scale mixing of the reactants in the molten salt, enhances the fluidity of the reaction components in the liquid phase, and significantly increases the diffusion rate; it can effectively control the reaction process, reduce the reaction temperature and shorten the reaction time;

2. The present invention can more easily control the shape and size of crystal particles through the molten salt method. The particle size of the powder is 100-500nm. The proportion of each component of the synthetic product is accurate, the composition is uniform, and there is no segregation;

3. The present invention is beneficial to the removal of impurities during the reaction process and the subsequent cleaning process, forming high-purity reactants without impurity phases;

4. The raw material source of the present invention is extensive and cheap, and production cost is low, has very big industrialization prospect;

5. The particles of the product prepared by the present invention are uniformly dispersed in the molten salt, avoiding interconnection, making the particles dispersible well, and greatly reducing the occurrence of agglomeration after dissolution and washing.

Therefore, the present invention has the characteristics of low reaction temperature, low cost, simple synthesis process, easy process control, high yield and great industrialization prospect; the prepared single-phase α-Si ₃ N ₄ ultrafine powder has a particle size of 100- 500nm, no impurity phase, high activity, small particle agglomeration and uniform particle size distribution.

Description of drawings

Fig. 1 is the XRD spectrum of a kind of single-phase α-Si ₃ N ₄ powder prepared by the present invention;

Figure 2 is an SEM image of the single-phase α-Si ₃ N ₄ powder shown in Figure 1;

Fig. 3 is an EDS diagram of the position indicated by the arrow in Fig. 2 .

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, which are not intended to limit the protection scope thereof.

In order to avoid repetition, the raw materials involved in this specific embodiment are first described as follows, and are not repeated in the examples:

The Si content in the elemental silicon powder is ≥95wt%, and the particle size is ≤50 μm.

The ammonium chloride, urea and melamine are all industrially pure or analytically pure, and the particle diameters are all ≤200 μm.

The sodium chloride, potassium fluoride and sodium fluoride are all industrial pure or analytical pure, and the particle diameters are all ≤200 μm.

Example 1

A single-phase α-Si ₃ N ₄ ultrafine powder and a preparation method thereof. First mix 10-20wt% elemental silicon powder, 15-30wt% solid nitrogen source and 60-75wt% halide powder to prepare a mixture; The temperature was raised to 1200-1300°C at a rate of 2-5°C/min, and kept for 2-4 hours; then, the obtained product was repeatedly washed with deionized water until it was titrated with AgNO ₃ and Ca(NO ₃ ) ₂ solutions respectively. Until white precipitate appears again; finally dry at 110°C for 10-24 hours to obtain single-phase α-Si ₃ N ₄ ultrafine powder.

In this embodiment: the solid nitrogen source is melamine; the halide powder is a mixture of 70-90 wt% sodium chloride and 10-30 wt% sodium fluoride.

Fig. 1 is an XRD pattern of a single-phase α-Si ₃ N ₄ powder prepared in the example; Fig. 2 is an SEM image of the single-phase α-Si ₃ N ₄ powder shown in Fig. 1; Fig. 3 is a graph of Fig. 2 The EDS map of the location indicated by the middle arrow. It can be seen from Figures 1 to 3 that the single-phase α-Si ₃ N ₄ ultrafine powder prepared in this example has high purity, no particle agglomeration, and a particle size of 100-200 nm.

Example 2

A single-phase α-Si ₃ N ₄ ultrafine powder and a preparation method thereof. First mix 10-20wt% elemental silicon powder, 15-30wt% solid nitrogen source and 60-75wt% halide powder to prepare a mixture; 2-5°C/min heating rate to 1100-1200°C and keep warm for 2-4 hours; then the product obtained was washed repeatedly with deionized water until it was titrated with AgNO ₃ and Ca(NO ₃ ) ₂ solutions respectively. Until white precipitate appears again; finally dry at 110°C for 10-24 hours to obtain single-phase α-Si ₃ N ₄ ultrafine powder.

In this embodiment: the solid nitrogen source is a mixture of 50-70 wt% melamine and 30-50 wt% ammonium chloride; the halide powder is sodium fluoride.

The single-phase α-Si ₃ N ₄ ultrafine powder prepared in this example has high purity, no particle agglomeration, and a particle size of 150-250 nm.

Example 3

A single-phase α-Si ₃ N ₄ ultrafine powder and a preparation method thereof. Firstly mix 5-15wt% elemental silicon powder, 10-25wt% solid nitrogen source and 70-80wt% halide powder to make a mixture; 1000-1100°C at a heating rate of 5-10°C/min, and kept warm for 4-6 hours; then the resulting product was washed repeatedly with deionized water until it was titrated with AgNO ₃ and Ca(NO ₃ ) ₂ solutions respectively. Until white precipitate appears again; finally dry at 110°C for 10-24 hours to obtain single-phase α-Si ₃ N ₄ ultrafine powder.

In this embodiment: the solid nitrogen source is urea; the halide powder is potassium fluoride.

The single-phase α-Si ₃ N ₄ ultrafine powder prepared in this example has high purity, no particle agglomeration, and a particle size of 300-400 nm.

Example 4

A single-phase α-Si ₃ N ₄ ultrafine powder and a preparation method thereof. Firstly mix 5-15wt% elemental silicon powder, 10-25wt% solid nitrogen source and 70-80wt% halide powder to make a mixture; 1100-1200°C at a heating rate of 5-10°C/min, and kept warm for 4-6 hours; then the resulting product was washed repeatedly with deionized water until it was titrated with AgNO ₃ and Ca(NO ₃ ) ₂ solutions respectively. Until white precipitate appears again; finally dry at 110°C for 10-24 hours to obtain single-phase α-Si ₃ N ₄ ultrafine powder.

In this embodiment: the solid nitrogen source is a mixture of 50-70 wt% urea and 30-50 wt% melamine; the halide powder is 50-60 wt% sodium chloride and 40-50 wt% potassium fluoride mixture.

The single-phase α-Si ₃ N ₄ ultrafine powder prepared in this example has high purity, no particle agglomeration, and a particle size of 350-500 nm.

Example 5

A single-phase α-Si ₃ N ₄ ultrafine powder and a preparation method thereof. First mix 15-30wt% elemental silicon powder, 25-45wt% solid nitrogen source and 40-60wt% halide powder to prepare a mixture; 1000-1100°C at a heating rate of 5-10°C/min, and kept warm for 4-6 hours; then the resulting product was washed repeatedly with deionized water until it was titrated with AgNO ₃ and Ca(NO ₃ ) ₂ solutions respectively. Until white precipitate appears again; finally dry at 110°C for 10-24 hours to obtain single-phase α-Si ₃ N ₄ ultrafine powder.

In this embodiment: the solid nitrogen source is ammonium chloride; the halide powder is sodium chloride.

The single-phase α-Si ₃ N ₄ ultrafine powder prepared in this example has high purity, no particle agglomeration, and a particle size of 150-200 nm.

Example 6

A single-phase α-Si ₃ N ₄ ultrafine powder and a preparation method thereof. First mix 15-30wt% elemental silicon powder, 25-45wt% solid nitrogen source and 40-60wt% halide powder to prepare a mixture; The heating rate was raised to 1200-1300°C at a rate of 2-5°C/min, and the temperature was kept for 4-6 hours; then, the obtained product was repeatedly washed with deionized water until it was titrated with AgNO ₃ and Ca(NO ₃ ) ₂ solutions respectively. Until white precipitate appears again; finally dry at 110°C for 10-24 hours to obtain single-phase α-Si ₃ N ₄ ultrafine powder.

In this embodiment: the solid nitrogen source is a mixture of 50-60 wt% melamine, 20-30 wt% ammonium chloride and 20-30 wt% urea; the halide powder is 45-60 wt% sodium chloride , A mixture of 25-35 wt% sodium fluoride and 15-20 wt% potassium fluoride.

The single-phase α-Si ₃ N ₄ ultrafine powder prepared in this example has high purity, no particle agglomeration, and a particle size of 200-300 nm.

Example 7

A single-phase α-Si ₃ N ₄ ultrafine powder and a preparation method thereof. First mix 15-30wt% elemental silicon powder, 25-45wt% solid nitrogen source and 40-60wt% halide powder to prepare a mixture; 2-5°C/min heating rate to 1100-1200°C and keep warm for 2-4 hours; then the product obtained was washed repeatedly with deionized water until it was titrated with AgNO ₃ and Ca(NO ₃ ) ₂ solutions respectively. Until white precipitate appears again; finally dry at 110°C for 10-24 hours to obtain single-phase α-Si ₃ N ₄ ultrafine powder.

In this embodiment: the solid nitrogen source is a mixture of 50-70 wt% ammonium chloride and 30-50 wt% urea; the halide powder is 50-60 wt% sodium fluoride and 40-50 wt% fluorine Potassium mixture.

The single-phase α-Si ₃ N ₄ ultrafine powder prepared in this example has high purity, no particle agglomeration, and a particle size of 250-350 nm.

Compared with the prior art, this specific embodiment has the following positive effects and outstanding features:

1. In this specific embodiment, the atomic scale mixing of the reactants is realized in the molten salt, so that the fluidity of the reaction components in the liquid phase is enhanced, and the diffusion rate is significantly improved; the reaction process can be effectively controlled and the reaction temperature can be reduced;

2. In this specific embodiment, the shape and size of the crystal particles can be more easily controlled by the molten salt method, and the particle size of the powder is 100-500 nm. The proportion of each component of the synthetic product is accurate, the composition is uniform, and there is no segregation;

3. In the reaction process and the subsequent cleaning process of this specific embodiment, it is beneficial to the removal of impurities and forms a high-purity reactant without impurities;

4. The particles of the product prepared in this specific embodiment are evenly dispersed in the molten salt, avoiding interconnection, making the particle dispersibility very good, and greatly reducing the occurrence of agglomeration after dissolution and washing;

5. The source of raw materials in this specific embodiment is wide and cheap, the production cost is low, and it has great prospects for industrialized production.

Therefore, this embodiment has the characteristics of low reaction temperature, low cost, simple synthesis process, easy process control, and high yield; the prepared single-phase α-Si ₃ N ₄ ultrafine powder has a particle size of 100-500 nm, without heterogeneous phase, high activity, small particle agglomeration and uniform particle size distribution.

Claims (1)

1. A preparation method of single-phase α-Si ₃ N ₄ ultrafine powder, which is characterized in that 5~30wt% elemental silicon powder, 15~45wt% solid nitrogen source and 40~80wt% halide Mix the powder evenly to prepare the mixture; put the mixture into a tube electric furnace, raise the temperature to 1000-1300°C at a rate of 2-10°C/min under a nitrogen atmosphere, and keep it warm for 2-6 hours; then the obtained The product was washed repeatedly with deionized water until no white precipitate appeared after titration with AgNO ₃ and Ca(NO ₃ ) ₂ solutions respectively; finally, it was dried at 110°C for 10-24 hours to obtain single-phase α-Si ₃ N ₄ ultrafine powder.