阅读说明：本技术 一种高纯α相氮化硅纤维毡的制备方法 (Preparation method of high-purity alpha-phase silicon nitride fibrofelt ) 是由 王志江 戴丁 于 2020-12-29 设计创作，主要内容包括：一种高纯α相氮化硅纤维毡的制备方法,它涉及一种高纯α相氮化硅的制备方法。本发明要解决现有高纯氮化硅原料粉体匮乏且成本较高的问题。制备方法：一、制备碳纤维毡前驱体；二、烧结反应；三、除碳处理。本发明用于高纯α相氮化硅纤维毡的制备。(A preparation method of a high-purity alpha-phase silicon nitride fibrofelt relates to a preparation method of high-purity alpha-phase silicon nitride. The invention aims to solve the problems of shortage of high-purity silicon nitride raw material powder and high cost. The preparation method comprises the following steps: firstly, preparing a carbon fiber felt precursor; secondly, sintering reaction; and thirdly, carbon removal treatment. The method is used for preparing the high-purity alpha-phase silicon nitride fiber felt.)

1. A preparation method of a high-purity alpha-phase silicon nitride fibrofelt is characterized by comprising the following steps:

firstly, preparing a carbon fiber felt precursor:

soaking the carbon fiber felt in 5-20% nitrate catalyst solution for 2-48 h, and drying in a drying oven to obtain a carbon fiber felt precursor;

secondly, sintering reaction:

laying reaction silicon source powder at the bottom of a graphite crucible to obtain a reaction silicon source layer, then covering a carbon fiber felt precursor on the surface of the reaction silicon source layer, putting the graphite crucible containing reactants into a tubular furnace, introducing nitrogen as reaction gas at the flow rate of 0.05-2L/min, carrying out sintering reaction for 0.5-24 h at the reaction temperature of 1200-1800 ℃, and naturally cooling to room temperature after the reaction is finished to obtain a felt after the reaction;

the mass ratio of the carbon fiber felt in the first step to the reaction silicon source in the second step is 1 (1-10);

thirdly, carbon removal treatment:

and placing the felt after reaction in a muffle furnace, performing decarbonization treatment for 0.5 to 10 hours at the temperature of between 200 and 1000 ℃, and naturally cooling to room temperature to obtain the high-purity alpha-phase silicon nitride fiber felt.

2. The method of claim 1, wherein the nitrate catalyst solution in step one is ferric nitrate solution, cobalt nitrate solution or cupric nitrate solution.

3. The method for preparing a high purity alpha-phase silicon nitride fiber felt according to claim 1, wherein the drying in the oven in the first step is carried out for 2 to 12 hours at a drying temperature of 40 to 180 ℃.

4. The method of claim 1, wherein the reactive silicon source powder in step two is SiO₂Powder or Si/SiO₂And mixing the powders.

5. The method of claim 4, wherein the Si/SiO is selected from the group consisting of₂The mixed powder is prepared by the following steps: under the conditions that the power is 1 Hz-20 Hz and the rotating speed is 60 r/min-100 r/min, Si powder and SiO powder are mixed by a ball mill₂Mixing the powder for 1-10 h, wherein the Si powder and the SiO powder₂The molar ratio of the powder is 1 (0.1-2).

6. The method of claim 5, wherein the purity of the Si powder is 95.0-99.99%, and the particle size of the Si powder is 50-1000 mesh.

7. The method for preparing a high purity α -phase silicon nitride fiber mat according to claim 1, wherein the carbon fiber mat in the first step has a thickness of 3mm to 10mm and a density of 500g/m²～1000g/m²。

8. The preparation method of the high-purity alpha-phase silicon nitride fiber felt according to claim 1, characterized in that in the step one, the carbon fiber felt is immersed in a nitrate catalyst solution with the mass percent of 5% for 24 h-48 h, and then dried in an oven to obtain a carbon fiber felt precursor.

9. The method for preparing the high-purity alpha-phase silicon nitride fibrofelt according to claim 1, wherein nitrogen is introduced as reaction gas at a flow rate of 1L/min to 2L/min, and the sintering reaction is carried out for 0.5h to 24h at a reaction temperature of 1200 ℃ to 1800 ℃.

10. The method for preparing the high-purity alpha-phase silicon nitride fibrofelt according to claim 1, characterized in that the decarbonization treatment is carried out for 5 to 10 hours at the temperature of 800 to 1000 ℃ in the third step.

Technical Field

The invention relates to a preparation method of high-purity alpha-phase silicon nitride.

Background

Silicon nitride is a high-temperature structural ceramic material with excellent comprehensive performance, and is often used as a high-temperature working part of a heat engine, a cutting tool and the like because the silicon nitride has high strength, high hardness and high temperature resistance, and still has ultrahigh strength at 1400 ℃ which is far higher than other ceramic materials. Meanwhile, the silicon nitride has good chemical stability, ideal high thermal conductivity, good insulativity and high-temperature dielectric property, and can be used as a substrate of an integrated circuit and an antenna housing material of an airplane and a missile.

Silicon nitride is covalently bonded, the sintering difficulty is high, the requirement on raw material powder for preparing high-performance silicon nitride ceramic is high, the symmetry of the silicon nitride ceramic is reduced due to the arrangement mode of alpha phase atoms, the internal strain is large, the free energy is high, the silicon nitride ceramic is a low-temperature stable phase, the thermal stability of beta phase is high, alpha phase crystal grains are firstly dissolved in a liquid phase when the temperature reaches above 1450 ℃, the alpha phase crystal grains are precipitated out when the temperature is reduced, the crystal form conversion from the alpha phase to the beta phase is generated, and the reaction driving force can be increased. Therefore, the high-purity alpha-phase submicron-grade silicon nitride powder and even nano powder are ideal raw material powder. In recent years, the demand for silicon nitride powder, especially high-purity silicon nitride powder, is increasing, but the high production cost thereof restricts the application of silicon nitride ceramic materials.

The existing methods for preparing silicon nitride include silicon powder direct nitriding method, carbothermic method, self-propagating high-temperature synthesis method, sol-gel method, thermal decomposition method and the like. Compared with other methods, the carbothermic method has the advantages of low raw material price, simple process, small particle size of the obtained powder and alpha-Si₃N₄High content, faster reaction speed than direct nitriding method, mass production, but the defect is that SiC and Si may appear₂N₂O and the like.

Disclosure of Invention

The invention provides a preparation method of a high-purity alpha-phase silicon nitride fibrofelt, aiming at solving the problems of shortage of high-purity silicon nitride raw material powder and high cost.

A preparation method of a high-purity alpha-phase silicon nitride fibrofelt is completed according to the following steps:

firstly, preparing a carbon fiber felt precursor:

soaking the carbon fiber felt in 5-20% nitrate catalyst solution for 2-48 h, and drying in a drying oven to obtain a carbon fiber felt precursor;

secondly, sintering reaction:

laying reaction silicon source powder at the bottom of a graphite crucible to obtain a reaction silicon source layer, then covering a carbon fiber felt precursor on the surface of the reaction silicon source layer, putting the graphite crucible containing reactants into a tubular furnace, introducing nitrogen as reaction gas at the flow rate of 0.05-2L/min, carrying out sintering reaction for 0.5-24 h at the reaction temperature of 1200-1800 ℃, and naturally cooling to room temperature after the reaction is finished to obtain a felt after the reaction;

the mass ratio of the carbon fiber felt in the first step to the reaction silicon source in the second step is 1 (1-10);

thirdly, carbon removal treatment:

and placing the felt after reaction in a muffle furnace, performing decarbonization treatment for 0.5 to 10 hours at the temperature of between 200 and 1000 ℃, and naturally cooling to room temperature to obtain the high-purity alpha-phase silicon nitride fiber felt.

The invention has the beneficial effects that:

1. the high-purity alpha-phase silicon nitride fiber felt material prepared by the invention adopts the raw materials of carbon fiber felt, reaction silicon source powder and nitrate catalyst solution, and the high-purity alpha-phase silicon nitride fiber felt is obtained through the carbothermic reduction reaction without SiC and Si₂N₂Impurities such as O, alpha-Si₃N₄The content can reach more than 93 percent. The method has the advantages of low preparation cost, easily obtained raw materials and simple process, and the silicon nitride powder can be obtained by grinding, thereby providing possibility for batch production of the silicon nitride powder and solving the problems of shortage and high cost of the existing high-purity silicon nitride raw material powder.

2. The carbon fiber felt prepared by the method has low price, and simultaneously, the macro morphology of the carbon fiber felt enables the contact mode of the carbon fiber felt and a reaction silicon source to be a surface contact type, so that the contact area of a reaction intermediate and reaction gas is increased, the reaction is completely carried out, the obtained product has high purity, high alpha phase content and uniform morphology, and the carbon fiber felt is high-quality raw material powder for preparing high-performance silicon nitride ceramics; meanwhile, the composite material has the performances of light weight, high temperature resistance, stable chemical property and the like, has the dielectric constant of 2-4 and the dielectric loss of 0.01-0.1, and can also be used as a wave-transmitting material, a refractory material and the like.

The invention is used for a preparation method of a high-purity alpha-phase silicon nitride fibrofelt.

Drawings

FIG. 1 is an XRD pattern of a high purity alpha phase silicon nitride fiber mat prepared in example one, 1 is a high purity alpha phase silicon nitride fiber mat prepared in example one, 2 is alpha-Si₃N₄Standard card PDF # 70-3756;

FIG. 2 is an SEM image of a carbon fiber mat according to step one of the example;

FIG. 3 is an SEM image of a high purity alpha-phase silicon nitride fiber mat made according to example one;

FIG. 4 is a graph of the dielectric constant of a high purity alpha phase silicon nitride fiber mat made in accordance with one example;

FIG. 5 is a graph of dielectric loss for a high purity alpha phase silicon nitride fiber mat made in accordance with one example;

FIG. 6 is an XRD pattern of the high purity alpha phase silicon nitride fiber mat prepared in example two, 1 being the high purity alpha phase silicon nitride fiber mat prepared in example two, 2 being alpha-Si₃N₄PDF # 41-0360;

FIG. 7 is an SEM image of a high purity alpha-phase silicon nitride fiber mat made according to example two;

FIG. 8 is an XRD pattern of the high purity alpha phase silicon nitride fiber mat prepared in example three, 1 being the high purity alpha phase silicon nitride fiber mat prepared in example three, 2 being alpha-Si₃N₄PDF # 76-1410;

fig. 9 is an SEM image of the high purity alpha phase silicon nitride fiber mat prepared in example three.

Detailed Description

The first embodiment is as follows: the embodiment of the invention relates to a preparation method of a high-purity alpha-phase silicon nitride fibrofelt, which is completed according to the following steps:

firstly, preparing a carbon fiber felt precursor:

soaking the carbon fiber felt in 5-20% nitrate catalyst solution for 2-48 h, and drying in a drying oven to obtain a carbon fiber felt precursor;

secondly, sintering reaction:

laying reaction silicon source powder at the bottom of a graphite crucible to obtain a reaction silicon source layer, then covering a carbon fiber felt precursor on the surface of the reaction silicon source layer, putting the graphite crucible containing reactants into a tubular furnace, introducing nitrogen as reaction gas at the flow rate of 0.05-2L/min, carrying out sintering reaction for 0.5-24 h at the reaction temperature of 1200-1800 ℃, and naturally cooling to room temperature after the reaction is finished to obtain a felt after the reaction;

the mass ratio of the carbon fiber felt in the first step to the reaction silicon source in the second step is 1 (1-10);

thirdly, carbon removal treatment:

and placing the felt after reaction in a muffle furnace, performing decarbonization treatment for 0.5 to 10 hours at the temperature of between 200 and 1000 ℃, and naturally cooling to room temperature to obtain the high-purity alpha-phase silicon nitride fiber felt.

The principle is as follows: in the reaction process of the embodiment, when the reaction silicon source is Si/SiO₂When the powder is mixed, the following chemical reactions occur in the system:

SiO₂(s)+Si(s)＝2SiO(g) (1)

SiO₂(s)+C(s)＝SiO(g)+CO(g) (2)

SiO(g)+3CO(g)＝SiC(s)+2CO₂(g) (3)

3SiO(g)+3CO(s)+2N₂(g)＝Si₃N₄(s)+3CO₂(g) (4)

CO₂(g)+C(s)＝2CO(g) (5)

the carbon source used in the embodiment is the carbon fiber felt, and the carbon fiber felt has the macroscopic morphology of the carbon fiber felt and can form surface contact with the reaction silicon source, so that reaction intermediates SiO, CO and N are added₂The contact (2) is favorable for forming silicon nitride and inhibiting the generation of silicon carbide. Meanwhile, metal salt is used as a catalyst, and a metal element and Si form a liquid phase alloy at high temperature, so that the contact area of nitrogen and silicon powder is increased, and the reaction efficiency is improved.

The beneficial effects of the embodiment are as follows:

1. the raw materials of the high-purity alpha-phase silicon nitride fiber felt material prepared by the embodiment are carbon fiber felt, reaction silicon source powder and nitrate catalyst solution, and the high-purity alpha-phase silicon nitride fiber felt is obtained through carbothermic reduction reaction and is free of SiC and Si₂N₂Impurities such as O, alpha-Si₃N₄The content can reach more than 93 percent. The method has the advantages of low preparation cost, easily obtained raw materials and simple process, and the silicon nitride powder can be obtained by grinding, thereby providing possibility for batch production of the silicon nitride powder and solving the problems of shortage and high cost of the existing high-purity silicon nitride raw material powder.

2. The carbon fiber felt prepared by the embodiment has low price, and simultaneously, the macro morphology of the carbon fiber felt enables the contact mode of the carbon fiber felt and a reaction silicon source to be a surface contact type, so that the contact area of a reaction intermediate and reaction gas is increased, the reaction is completely carried out, the obtained product has high purity, high alpha phase content and uniform morphology, and the carbon fiber felt is high-quality raw material powder for preparing high-performance silicon nitride ceramics; meanwhile, the composite material has the performances of light weight, high temperature resistance, stable chemical property and the like, has the dielectric constant of 2-4 and the dielectric loss of 0.01-0.1, and can also be used as a wave-transmitting material, a refractory material and the like.

The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: the nitrate catalyst solution in the first step is ferric nitrate solution, cobalt nitrate solution or copper nitrate solution. The rest is the same as the first embodiment.

The third concrete implementation mode: this embodiment is different from the first or second embodiment in that: the drying in the oven in the step one is drying for 2 to 12 hours under the condition that the drying temperature is 40 to 180 ℃. The other is the same as in the first or second embodiment.

The fourth concrete implementation mode: the difference between this embodiment mode and one of the first to third embodiment modes is: the reaction silicon source powder in the step two is SiO₂Powder or Si/SiO₂And mixing the powders. The others are the same as the first to third embodiments.

SiO according to the present embodiment₂The purity of the powder was analytical grade.

The fifth concrete implementation mode: the difference between this embodiment and one of the first to fourth embodiments is: the Si/SiO₂The mixed powder is prepared by the following steps: under the conditions that the power is 1 Hz-20 Hz and the rotating speed is 60 r/min-100 r/min, Si powder and SiO powder are mixed by a ball mill₂Mixing the powder for 1-10 h, wherein the Si powder and the SiO powder₂The molar ratio of the powder is 1 (0.1-2). The rest is the same as the first to fourth embodiments.

The sixth specific implementation mode: the difference between this embodiment and one of the first to fifth embodiments is: the purity of the Si powder is 95.0-99.99%, and the granularity of the Si powder is 50-1000 meshes. The rest is the same as the first to fifth embodiments.

The seventh embodiment: the difference between this embodiment and one of the first to sixth embodiments is: the carbon fiber felt in the step oneHas a thickness of 3mm to 10mm and a density of 500g/m²～1000g/m². The others are the same as the first to sixth embodiments.

The specific implementation mode is eight: the present embodiment differs from one of the first to seventh embodiments in that: in the first step, the carbon fiber felt is soaked in a nitrate catalyst solution with the mass percent of 5% for 24-48 h, and then dried in a drying oven to obtain the carbon fiber felt precursor. The rest is the same as the first to seventh embodiments.

The specific implementation method nine: the present embodiment differs from the first to eighth embodiments in that: and in the second step, nitrogen is introduced at the flow rate of 1L/min-2L/min as reaction gas, and sintering reaction is carried out for 0.5 h-24 h at the reaction temperature of 1200-1800 ℃. The other points are the same as those in the first to eighth embodiments.

The detailed implementation mode is ten: the present embodiment differs from one of the first to ninth embodiments in that: in the third step, under the condition of the temperature of 800-1000 ℃, the decarbonization treatment is carried out for 5-10 h. The other points are the same as those in the first to ninth embodiments.

The following examples were used to demonstrate the beneficial effects of the present invention:

the first embodiment is as follows:

a preparation method of a high-purity alpha-phase silicon nitride fibrofelt is completed according to the following steps:

firstly, preparing a carbon fiber felt precursor:

soaking 2g of the carbon fiber felt in 2% nitrate catalyst solution for 12 hours, and then drying in an oven to obtain a carbon fiber felt precursor;

secondly, sintering reaction:

laying 14.7g of reaction silicon source powder at the bottom of a graphite crucible to obtain a reaction silicon source layer, then covering a carbon fiber felt precursor on the surface of the reaction silicon source layer, putting the graphite crucible containing reactants into a tubular furnace, introducing nitrogen as reaction gas at the flow rate of 0.1L/min, carrying out sintering reaction for 3 hours at the reaction temperature of 1500 ℃, and naturally cooling to room temperature after the reaction is finished to obtain a felt after the reaction;

thirdly, carbon removal treatment:

and placing the felt after reaction in a muffle furnace, performing decarbonization treatment for 3 hours at the temperature of 700 ℃, and naturally cooling to room temperature to obtain the high-purity alpha-phase silicon nitride fiber felt.

The nitrate catalyst solution in the first step is ferric nitrate solution.

The drying in the oven in the step one is specifically drying for 8 hours at a drying temperature of 80 ℃.

The reaction silicon source powder in the second step is Si/SiO₂And mixing the powders.

The Si/SiO₂The mixed powder is prepared by the following steps: under the conditions of power of 1Hz and rotating speed of 60r/min, Si powder and SiO powder are mixed by a ball mill₂Mixing the powder for 10h, wherein the Si and the SiO are₂In a 1:1 molar ratio.

The purity of the Si powder is 99.9%, and the granularity of the Si powder is 200 meshes.

The thickness of the carbon fiber felt in the step one is 5mm, and the density is 700g/m²。

FIG. 1 is an XRD pattern of a high purity alpha phase silicon nitride fiber mat prepared in example one, 1 is a high purity alpha phase silicon nitride fiber mat prepared in example one, 2 is alpha-Si₃N₄Standard card PDF # 70-3756; by comparing with the standard card, the peak in XRD and the alpha-Si of the standard card PDF #70-3756 can be known₃N₄The coincidence proves that the main phase of the silicon nitride fiber felt prepared by the embodiment is alpha-Si₃N₄Is free of SiC and Si₂N₂O, and the like, and alpha-Si₃N₄The occupancy ratio is about 95%.

FIG. 2 is an SEM image of a carbon fiber mat according to step one of the example; FIG. 3 is an SEM image of a high purity alpha-phase silicon nitride fiber mat made according to example one; by comparison, the microscopic morphology of the silicon nitride fiber felt prepared in the embodiment substantially maintains the original morphology of the carbon fiber felt, which means that silicon nitride is generated in situ on the carbon fiber felt and the morphology is uniform.

FIG. 4 is a graph of the dielectric constant of a high purity alpha phase silicon nitride fiber mat made in accordance with one example; FIG. 5 is a graph of dielectric loss for a high purity alpha phase silicon nitride fiber mat made in accordance with one example; as can be seen from the figure, the high-purity alpha-phase silicon nitride fiber felt has the dielectric constant of 3.1 and the dielectric loss of 0.03 at the frequency of 10GHz, and has good wave-transmitting performance.

Example two: the difference between the present embodiment and the first embodiment is: and sintering reaction for 2 hours in the second step. The rest is the same as the first embodiment.

FIG. 6 is an XRD pattern of the high purity alpha phase silicon nitride fiber mat prepared in example two, 1 being the high purity alpha phase silicon nitride fiber mat prepared in example two, 2 being alpha-Si₃N₄PDF # 41-0360; by comparing with the standard card, the peak in XRD and the alpha-Si of the standard card PDF #41-0360 can be known₃N₄The coincidence proves that the main phase of the silicon nitride fiber felt prepared by the embodiment is alpha-Si₃N₄Is free of SiC and Si₂N₂O, and the like, and alpha-Si₃N₄The occupancy is about 93%.

FIG. 7 is an SEM image of a high purity alpha-phase silicon nitride fiber mat made according to example two; as can be seen from the figure, the microscopic morphology of the silicon nitride fiber felt prepared by the embodiment basically maintains the original morphology of the carbon fiber felt, and shows that the silicon nitride is generated in situ on the carbon fiber felt.

Example three: the difference between the present embodiment and the first embodiment is: and in the second step, sintering reaction is carried out for 3 hours at the reaction temperature of 1550 ℃. The rest is the same as the first embodiment.

FIG. 8 is an XRD pattern of the high purity alpha phase silicon nitride fiber mat prepared in example three, 1 being the high purity alpha phase silicon nitride fiber mat prepared in example three, 2 being alpha-Si₃N₄PDF # 76-1410; by comparing with the standard card, the peak in XRD and the alpha-Si of the standard card PDF #76-1410 can be known₃N₄The coincidence proves that the main phase of the silicon nitride fiber felt prepared by the embodiment is alpha-Si₃N₄Is free of SiC and Si₂N₂O, and the like, and alpha-Si₃N₄The occupancy ratio is about 95%.

FIG. 9 is an SEM image of a high purity alpha-phase silicon nitride fiber mat made in example III; the microscopic morphology of the silicon nitride fiber felt prepared in this example substantially maintained the original morphology of the carbon fiber felt, which means that silicon nitride was generated in situ on the carbon fiber felt.