阅读说明：本技术 一种氮化硅粉体的制备方法 (Preparation method of silicon nitride powder ) 是由 张晶 孙峰 张伟儒 董廷霞 徐学敏 姜自飞 段伟斌 王春河 王梅 于 2020-07-14 设计创作，主要内容包括：本发明涉及先进陶瓷粉体制备技术领域,尤其涉及一种氮化硅粉体的制备方法。本发明利用硅和氮化硅热膨胀系数的差异,在真空或惰性气氛中以3℃/min以上的升温速率迅速升温50℃以上然后降温,使硅粉表面的氮化硅层破碎,从而提高氮化反应速率,缩短氮化周期；本发明整个制备过程只有在1350℃以下才会通入氮气或氮氢混合气,硅粉氮化反应才会发生,可以防止β氮化硅生成,因此更有利于α-Si<Sub>3</Sub>N<Sub>4</Sub>的生成,得到的α-Si<Sub>3</Sub>N<Sub>4</Sub>含量在93％以上；本发明前一次反应生成的氮化硅层破碎后可以充当下一次反应的稀释剂,因此不需要额外加入氮化硅作为稀释剂,从而提高了氮化硅粉体的净产率,降低了生产成本。(The invention relates to the technical field of advanced ceramic powder preparation, in particular to a preparation method of silicon nitride powder. The method utilizes the difference of the thermal expansion coefficients of silicon and silicon nitride, rapidly heats up to more than 50 ℃ at a heating rate of more than 3 ℃/min in vacuum or inert atmosphere, and then cools down to break the silicon nitride layer on the surface of the silicon powder, thereby improving the nitridation reaction rate and shortening the nitridation period; the whole preparation process of the invention only leads in nitrogen or nitrogen-hydrogen mixed gas below 1350 ℃, the silicon powder nitridation reaction can occur, which can prevent beta silicon nitride from generating, thus being more beneficial to alpha-Si 3 N 4 Formation of the resulting alpha-Si 3 N 4 The content is more than 93 percent; the silicon nitride layer generated in the previous reaction can be used as a diluent for the next reaction after being crushed, so that the silicon nitride does not need to be additionally added to be used as a diluentReleasing the agent, thereby improving the net yield of the silicon nitride powder and reducing the production cost.)

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

(1) putting silicon powder into a hearth, heating the hearth to T1 under a vacuum-pumping condition, stopping vacuum-pumping when the temperature reaches T1, continuously introducing nitrogen or a nitrogen-hydrogen mixed gas into the hearth, and simultaneously heating the temperature of a system in the hearth from T1 to T2 to perform a first nitridation reaction; the temperature of the T1 is 600-900 ℃, and the temperature of the T2 is 1100-1350 ℃;

(2) after the first nitridation reaction is finished, vacuumizing the obtained reaction system or filling inert gas to replace nitrogen or nitrogen-hydrogen mixed gas in the reaction system, heating the temperature of the system from T2 to T3, then cooling the temperature from T3 to T4, and after the temperature reaches T4, continuously filling nitrogen or nitrogen-hydrogen mixed gas into the system to perform a second nitridation reaction; the temperature difference between the T3 and the T2 is more than 50 ℃, and the heating rate from T2 to T3 is more than 3 ℃/min; the temperature difference between the T4 and the T3 is more than 50 ℃, and the T4 is 1100-1350 ℃;

(3) and (3) repeating the step (2) for 1-3 times after the second nitridation reaction is completed, so as to obtain the silicon nitride powder.

2. The preparation method according to claim 1, wherein the silicon powder has a median particle size of 1-74 μm and a purity of more than 99%.

3. The method according to claim 1, wherein before performing step (1), the method further comprises drying the silicon powder; the drying is carried out in vacuum, inert atmosphere or nitrogen, the drying temperature is 60-300 ℃, and the drying time is 1-12 h.

4. The preparation method according to claim 1, wherein the time of each nitriding reaction is independently 1-10 h.

5. The method according to claim 1, wherein the volume fraction of hydrogen in the nitrogen-hydrogen mixture gas is 20% or less.

6. The preparation method according to claim 1, wherein the temperature rise rate from T1 to T2 is 20-120 ℃/h.

7. The method according to claim 1, wherein the pressure in the furnace during each nitriding reaction is 102 to 110 kPa.

8. The preparation method according to claim 1, wherein the temperature is maintained for 0-2 hours after the temperature is raised to T3.

9. The method of claim 1, wherein the cooling time from T3 to T4 is 10-60 min.

Technical Field

The invention relates to the technical field of advanced ceramic powder preparation, in particular to a preparation method of silicon nitride powder.

Background

The silicon nitride ceramic has the characteristics of small specific gravity, good thermal shock resistance, low creep, chemical erosion resistance, wear resistance, excellent mechanical property and the like, and is widely applied to various fields of national defense, energy, aerospace, machinery, automobiles, petrifaction, metallurgy, electronics and the like, for example, the silicon nitride ceramic is used as a part of an automobile engine, a ceramic bearing ball, a cutting tool and the like. The sintering modes of the silicon nitride ceramics comprise conventional modes such as pressureless sintering, air pressure sintering, hot pressing sintering, hot isostatic pressing sintering, reaction sintering and the like and special sintering modes such as plasma sintering, microwave sintering and the like. Except for reactive sintering, other sintering modes all need silicon nitride powder as a raw material. The properties (such as purity, granularity, alpha phase content and the like) of the silicon nitride powder have very important influence on the sintering, structure, performance and function of the silicon nitride ceramic.

The preparation method of the silicon nitride powder mainly comprises a direct silicon powder nitriding method and SiO₂Carbothermal reduction nitridation, self-propagating high-temperature synthesis, thermal decomposition, and the like.

SiO₂SiC and Si are easily generated in the reaction process of the carbothermic reduction nitridation method₂N₂O, and the product is often accompanied by incomplete reaction of SiO₂Or residual C, which makes the purity of the product difficult to be ensured and can not meet the performance requirement of high-quality silicon nitride powder, so that the industrial production is not realized at present.

Reaction of self-propagating high temperature synthesisThe temperature is not easy to control, and the reaction temperature is usually too high to cause more beta-Si₃N₄And (4) generating. At present, although the self-propagating method has already realized the industrialized production, the synthesized silicon nitride powder has low sintering activity and is not suitable for being used as the raw material of high-performance silicon nitride ceramics.

The thermal decomposition method has the advantages of high reaction speed, high purity of the prepared powder, uniform and fine particle size, higher requirement on production equipment and more rigorous reaction conditions, so the preparation cost is higher. Currently, only the Japanese Utility department (UBE) uses the method to industrially produce silicon nitride powder.

Compared with the method, the process of the direct silicon powder nitriding method is relatively simple, convenient to operate and more suitable for industrial production, but the traditional direct silicon powder nitriding process has a long nitriding period, generally requires 5-6 days to complete the whole nitriding process, and causes low production efficiency. In addition, in order to prevent the silicon powder from micro-sintering due to overhigh local temperature in the nitriding process, 10-50% of silicon nitride powder is required to be added as a diluent, and the preparation cost of the silicon nitride powder is increased to a certain extent.

Disclosure of Invention

The invention aims to provide a preparation method of silicon nitride powder, which has the advantages of short nitridation period, high production efficiency, low cost and high net yield.

In order to achieve the above object, the present invention provides the following technical solutions:

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

(1) putting silicon powder into a hearth, heating the hearth to T1 under a vacuum-pumping condition, stopping vacuum-pumping when the temperature reaches T1, continuously introducing nitrogen or a nitrogen-hydrogen mixed gas into the hearth, and simultaneously heating the temperature of a system in the hearth from T1 to T2 to perform a first nitridation reaction; the temperature of the T1 is 600-900 ℃, and the temperature of the T2 is 1100-1350 ℃;

(2) after the first nitridation reaction is finished, vacuumizing the obtained reaction system or filling inert gas to replace nitrogen or nitrogen-hydrogen mixed gas in the reaction system, heating the temperature of the system from T2 to T3, then cooling the temperature from T3 to T4, and after the temperature reaches T4, continuously filling nitrogen or nitrogen-hydrogen mixed gas into the system to perform a second nitridation reaction; the temperature difference between the T3 and the T2 is more than 50 ℃, and the heating rate from T2 to T3 is more than 3 ℃/min; the temperature difference between the T4 and the T3 is more than 50 ℃, and the T4 is 1100-1350 ℃;

(3) and (3) repeating the step (2) for 1-3 times after the second nitridation reaction is completed, so as to obtain the silicon nitride powder.

Preferably, the median particle size of the silicon powder is 1-74 micrometers, and the purity is more than 99%.

Preferably, before the step (1), drying the silicon powder; the drying is carried out in vacuum, inert atmosphere or nitrogen, the drying temperature is 60-300 ℃, and the drying time is 1-12 h.

Preferably, the time of each nitridation reaction is independently 1-10 h.

Preferably, the volume fraction of hydrogen in the nitrogen-hydrogen mixed gas is below 20%.

Preferably, the temperature rising rate from T1 to T2 is 20-120 ℃/h.

Preferably, the pressure in the furnace during each nitriding reaction is 102-110 kPa.

Preferably, after the temperature is raised to T3, the temperature is kept for 0-2 h.

Preferably, the cooling time from T3 to T4 is 10-60 min.

The invention provides a preparation method of silicon nitride powder, which comprises the following steps: (1) putting silicon powder into a hearth, heating the hearth to T1 under a vacuum-pumping condition, stopping vacuum-pumping when the temperature reaches T1, continuously introducing nitrogen or a nitrogen-hydrogen mixed gas into the hearth, and simultaneously heating the temperature of a system in the hearth from T1 to T2 to perform a first nitridation reaction; the temperature of the T1 is 600-900 ℃, and the temperature of the T2 is 1100-1350 ℃; (2) after the first nitridation reaction is finished, vacuumizing the obtained reaction system or filling inert gas to replace nitrogen or nitrogen-hydrogen mixed gas in the reaction system, heating the temperature of the system from T2 to T3, then cooling the temperature from T3 to T4, and after the temperature reaches T4, continuously filling nitrogen or nitrogen-hydrogen mixed gas into the system to perform a second nitridation reaction; the temperature difference between the T3 and the T2 is more than 50 ℃, and the heating rate from T2 to T3 is more than 5 ℃/min; the temperature difference between the T4 and the T3 is more than 50 ℃, and the T4 is 1100-1350 ℃; (3) and (3) repeating the step (2) for 1-3 times after the second nitridation reaction is completed, so as to obtain the silicon nitride powder.

The conventional direct silicon powder nitriding process has a long nitriding period because silicon nitride generated when silicon powder and nitrogen start to react is coated outside unreacted silicon to form a silicon nitride layer, so that the nitrogen and the silicon are prevented from further contacting, and the nitriding reaction rate is slowed down. Compared with the traditional process, the invention has the beneficial effects that:

(1) after the first nitridation reaction is carried out, a silicon nitride layer is formed on the surface of the silicon, the temperature of the silicon and the silicon nitride layer is rapidly raised to be higher than 50 ℃ at the temperature raising rate of higher than 3 ℃/min in vacuum or inert atmosphere by utilizing the difference of the thermal expansion coefficients of the silicon and the silicon nitride, and then the temperature is lowered, so that the silicon nitride layer on the surface of the silicon powder is crushed, the nitridation reaction rate is improved, and the nitridation period is shortened;

(2) the nitrogen or the nitrogen-hydrogen mixed gas is introduced only below 1350 ℃ in the whole preparation process, the silicon powder nitridation reaction can occur, and the generation of beta silicon nitride can be prevented, so that the preparation method is more favorable for alpha-Si₃N₄Formation of the resulting alpha-Si₃N₄The content is more than 93 percent;

(3) the silicon nitride layer generated in the previous reaction can be used as a diluent for the next reaction after being crushed, so that silicon nitride does not need to be additionally added as the diluent, the net yield of silicon nitride powder is improved, and the production cost is reduced.

Drawings

FIG. 1 is an XRD pattern of the product of example 1;

FIG. 2 is an XRD pattern of the product prepared in example 2;

figure 3 is an XRD pattern of the product prepared in example 3.

Detailed Description

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

(1) putting silicon powder into a hearth, heating the hearth to T1 under a vacuum-pumping condition, stopping vacuum-pumping when the temperature reaches T1, continuously introducing nitrogen or a nitrogen-hydrogen mixed gas into the hearth, and simultaneously heating the temperature of a system in the hearth from T1 to T2 to perform a first nitridation reaction; the temperature of the T1 is 600-900 ℃, and the temperature of the T2 is 1100-1350 ℃;

(2) after the first nitridation reaction is finished, vacuumizing the obtained reaction system or filling inert gas to replace nitrogen or nitrogen-hydrogen mixed gas in the reaction system, heating the temperature of the system from T2 to T3, then cooling the temperature from T3 to T4, and after the temperature reaches T4, continuously filling nitrogen or nitrogen-hydrogen mixed gas into the system to perform a second nitridation reaction; the temperature difference between the T3 and the T2 is more than 50 ℃, and the heating rate from T2 to T3 is more than 5 ℃/min; the temperature difference between the T4 and the T3 is more than 50 ℃, and the T4 is 1100-1350 ℃;

(3) and (3) repeating the step (2) for 1-3 times after the second nitridation reaction is completed, so as to obtain the silicon nitride powder.

According to the invention, silicon powder is placed in a hearth, the hearth is heated to T1 under the vacuum-pumping condition, the vacuum-pumping is stopped when the temperature reaches T1, nitrogen or nitrogen-hydrogen mixed gas is continuously introduced into the hearth, and the temperature of a system in the hearth is simultaneously heated from T1 to T2 to carry out a first nitridation reaction.

In the invention, the median particle size of the silicon powder is preferably 1-74 micrometers, more preferably 2-50 micrometers, and most preferably 5-10 micrometers; the purity of the silicon powder is preferably greater than 99%, more preferably greater than 99.9%.

According to the invention, the silicon powder is preferably dried firstly, and then the silicon powder is placed in the hearth for subsequent steps. In the present invention, the drying is preferably performed in vacuum, an inert atmosphere, or nitrogen to prevent oxidation of the silicon powder; the drying temperature is preferably 60-300 ℃, more preferably 100-250 ℃, and most preferably 150-200 ℃; the drying time is preferably 1-12 h, more preferably 3-10 h, and most preferably 5-8 h.

According to the invention, dried silicon powder is preferably loaded into a reaction sintering silicon nitride material boat, and then the material boat is placed into a hearth for subsequent steps. In the present invention, the silicon nitride powder is preferably prepared in a vacuum atmosphere furnace.

The temperature is preferably raised from room temperature to T1, wherein the temperature of the T1 is 600-900 ℃, and the temperature of the T1 is preferably 650-800 ℃. The heating time required for heating from room temperature to T1 is preferably 1-5 h, and more preferably 2-4 h.

When the temperature reaches T1, the vacuum pumping is stopped. In the present invention, the degree of vacuum after the evacuation is stopped is preferably 0.01Pa or less.

After the vacuumizing is stopped, the nitrogen or the nitrogen-hydrogen mixed gas is continuously introduced into the hearth, and the temperature of a system in the hearth is increased from T1 to T2 to perform a first nitridation reaction. In the present invention, the nitrogen gas or the nitrogen-hydrogen mixture gas (i.e., the mixture gas of nitrogen gas and hydrogen gas) is used as a raw material for the silicon nitride reaction. When the nitrogen-hydrogen mixed gas is adopted, the volume fraction of hydrogen in the nitrogen-hydrogen mixed gas is preferably less than 20%, and more preferably 5-15%. Because the surface of the silicon powder usually contains a layer of silicon dioxide film, the nitrogen-hydrogen mixed gas is adopted, and the hydrogen in the nitrogen-hydrogen mixed gas can react with the silicon dioxide, so that the oxygen content in the target product silicon nitride is reduced.

In the present invention, the T2 is 1100 to 1350 ℃, and more preferably 1100 to 1200 ℃. The heating rate from T1 to T2 is preferably 20-120 ℃/h, more preferably 40-100 ℃/h, and most preferably 50-80 ℃/h. In the present invention, T2 is the temperature of the first nitridation reaction, and in the present invention, the time of the first nitridation reaction is preferably 1 to 10 hours (i.e., the holding time at T2), more preferably 2 to 8 hours, and most preferably 3 to 5 hours. In the first nitridation reaction process, the pressure in the furnace is preferably 102-110 kPa. In the first nitridation reaction process, silicon powder is contacted with nitrogen or a nitrogen-hydrogen mixed gas to carry out nitridation reaction, and a layer of silicon nitride is formed on the surface of the silicon powder.

After the first nitridation reaction is finished, the obtained reaction system is vacuumized or filled with inert gas to replace nitrogen or nitrogen-hydrogen mixed gas in the reaction system, the temperature of the system is increased from T2 to T3, then the temperature is decreased from T3 to T4, and after the temperature reaches T4, the nitrogen or nitrogen-hydrogen mixed gas is continuously introduced into the system to carry out a second nitridation reaction.

In the present invention, the temperature difference between T3 and T2 is 50 ℃ or more, preferably 100 ℃ or more, more preferably 100 ℃. In the present invention, the temperature increase rate from T2 to T3 is 5 ℃/min or more, preferably 10 ℃/min or more. After the temperature is raised to T3, the temperature is preferably kept for 0-2 h, and more preferably 0.5-1.5 h. Because the temperature transfer needs a certain time, the invention utilizes the heat preservation to ensure that the temperature of the materials in the furnace reaches the set temperature.

When the temperature of the system reaches T3, the temperature of the invention is reduced from T3 to T4, and after the temperature reaches T4, nitrogen or a nitrogen-hydrogen mixed gas is continuously introduced into the system to carry out a second nitration reaction. In the present invention, the nitrogen-hydrogen mixture gas is the same as the nitrogen-hydrogen mixture gas in the above steps, and the details are not repeated herein. In the present invention, the temperature difference between T4 and T3 is 50 ℃ or more, preferably 100 ℃ or more, and more preferably 100 ℃, and T4 satisfies the condition that T4 is 1100 to 1350 ℃. In the invention, the T4 is preferably 1150-1250 ℃. The T4 is the temperature of the second nitridation reaction. In the invention, the cooling time from T3 to T4 is preferably 10-60 min, and more preferably 20-50 min. In the present invention, the time of the second nitration reaction is preferably 1 to 10 hours (i.e., the holding time at T4), more preferably 2 to 8 hours, and most preferably 3 to 5 hours. In the second nitridation reaction process, the pressure in the furnace is preferably 102-110 kPa.

The method utilizes the difference of the thermal expansion coefficients of silicon and silicon nitride, rapidly heats up to more than 50 ℃ at a heating rate of more than 3 ℃/min in vacuum or inert atmosphere, and then cools down to break the silicon nitride layer on the surface of the silicon powder, thereby improving the nitridation reaction rate and shortening the nitridation period; meanwhile, the silicon nitride layer generated in the previous reaction can be used as a diluent for the next reaction after being crushed, so that silicon nitride does not need to be additionally added as the diluent, the net yield of silicon nitride powder is improved, and the production cost is reduced.

After the second nitridation reaction is completed, the process from the completion of the first nitridation reaction to the second nitridation reaction is repeated for 1 to 3 times (i.e., the nitridation reaction is performed for 3 to 5 times in total), and preferably repeated for 2 times (i.e., the nitridation reaction is performed for 4 times in total) to obtain the silicon nitride powder.

The specific parameters in the repeating process refer to the parameters from the completion of the first nitridation reaction to the performance of the second nitridation reaction, and are not described in detail herein.

After the final nitridation reaction is completed, the invention preferably performs processing treatments such as crushing and/or grinding on the product of the final nitridation reaction to obtain the silicon nitride powder. The invention has no special requirements on the grain diameter of the silicon nitride powder, and the technical personnel in the field can regulate and control the grain diameter according to the actual requirements.

The whole preparation process of the invention can only lead in nitrogen or nitrogen-hydrogen mixed gas below 1350 ℃, and silicon powder nitridation reaction can only occur, thereby being more beneficial to alpha-Si₃N₄Formation of the resulting alpha-Si₃N₄The content is more than 93 percent.

The following will explain the preparation method of silicon nitride powder provided by the present invention in detail with reference to the examples, but they should not be construed as limiting the scope of the present invention.