WO2022011830A1 - 一种氮化硅粉体的制备方法 - Google Patents

一种氮化硅粉体的制备方法 Download PDF

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WO2022011830A1
WO2022011830A1 PCT/CN2020/116435 CN2020116435W WO2022011830A1 WO 2022011830 A1 WO2022011830 A1 WO 2022011830A1 CN 2020116435 W CN2020116435 W CN 2020116435W WO 2022011830 A1 WO2022011830 A1 WO 2022011830A1
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temperature
nitrogen
silicon nitride
preparation
powder
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French (fr)
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张晶
孙峰
张伟儒
董廷霞
徐学敏
姜自飞
段伟斌
王春河
王梅
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中材高新氮化物陶瓷有限公司
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Definitions

  • the invention relates to the technical field of advanced ceramic powder preparation, in particular to a preparation method of silicon nitride powder.
  • Silicon nitride ceramics have the characteristics of small specific gravity, good thermal shock resistance, low creep, chemical corrosion resistance, wear resistance and excellent mechanical properties. It has been widely used in the field, such as parts for automobile engines, ceramic bearing balls and cutting tools.
  • the sintering methods of silicon nitride ceramics include conventional methods such as pressureless sintering, gas pressure sintering, hot pressing sintering, hot isostatic pressing sintering, and reaction sintering, as well as special sintering methods such as plasma sintering and microwave sintering. Except for reaction sintering, all other sintering methods require silicon nitride powder as raw material.
  • the properties of silicon nitride powder (such as purity, particle size, ⁇ -phase content, etc.) have a very important impact on the sintering, structure, performance and function of silicon nitride ceramics.
  • the preparation methods of silicon nitride powder mainly include silicon powder direct nitridation method, SiO 2 carbothermal reduction nitridation method, self-propagating high temperature synthesis method and thermal decomposition method.
  • SiC and Si 2 N 2 O are easily generated during the reaction of SiO 2 carbothermic reduction and nitridation, and the product is often accompanied by unreacted SiO 2 or residual C, which makes it difficult to ensure the purity of the product and cannot meet the high requirements.
  • the performance requirements of high-quality silicon nitride powder have not been realized in industrial production at present.
  • the reaction temperature of the self-propagating high-temperature synthesis method is not easy to control, and usually the reaction temperature is too high, resulting in the formation of more ⁇ -Si 3 N 4 .
  • the self-propagating method has achieved industrial production, the synthesized silicon nitride powder has low sintering activity and is not suitable for use as a raw material for high-performance silicon nitride ceramics.
  • the thermal decomposition method has a fast reaction speed, high purity of the prepared powder, and uniform and small particle size, but requires higher production equipment and harsh reaction conditions, so the preparation cost is higher.
  • Ube Ube of Japan uses this method to industrially produce silicon nitride powder.
  • the process of direct nitridation of silicon powder is relatively simple, the operation is convenient, and it is more suitable for industrial production. The entire nitriding process is completed, resulting in lower production efficiency.
  • 10-50% of silicon nitride powder needs to be added as a diluent, which increases the preparation cost of silicon nitride powder to a certain extent.
  • the purpose of the present invention is to provide a preparation method of silicon nitride powder, which has the advantages of short nitriding cycle, high production efficiency, low cost and high net yield.
  • the invention provides a preparation method of silicon nitride powder, comprising the following steps:
  • the obtained reaction system is evacuated or filled with an inert gas to replace nitrogen or nitrogen-hydrogen mixture in the reaction system, the temperature of the system is heated from T2 to T3, and then from T3 Cool down to T4, after reaching T4, continuously feed nitrogen or nitrogen-hydrogen mixture into the system to carry out the second nitridation reaction;
  • the temperature difference between T3 and T2 is above 50 °C, and the temperature rise rate from T2 to T3 is 3 °C/min or more;
  • step (2) is repeated 1 to 3 times to obtain silicon nitride powder.
  • the median particle size of the silicon powder is 1-74 microns, and the purity is greater than 99%.
  • the step (1) before performing the step (1), it also includes drying the silicon powder; the drying is performed in a vacuum, an inert atmosphere or nitrogen, the drying temperature is 60-300°C, and the drying time is 1 ⁇ 12h.
  • the time of each nitridation reaction is independently 1-10 h.
  • the volume fraction of hydrogen in the nitrogen-hydrogen mixture is below 20%.
  • the heating rate from T1 to T2 is 20-120° C./h.
  • the pressure in the furnace is 102-110 kPa during each nitridation reaction.
  • the temperature is kept for 0-2 hours.
  • the cooling time required for cooling from T3 to T4 is 10-60 min.
  • a silicon nitride layer is formed on the surface of the silicon.
  • the present invention utilizes the difference in thermal expansion coefficients of silicon and silicon nitride to rapidly increase the temperature at a rate of over 3°C/min in a vacuum or an inert atmosphere. Raising the temperature above 50°C and then cooling down, the silicon nitride layer on the surface of the silicon powder is broken, thereby increasing the nitriding reaction rate and shortening the nitriding period;
  • Nitrogen gas or nitrogen-hydrogen mixture will be introduced into the whole preparation process only when the temperature is below 1350°C, and the nitridation reaction of silicon powder will take place, which can prevent the formation of ⁇ -silicon nitride, so it is more conducive to the formation of ⁇ -Si 3 N 4 generated, and the content of the obtained ⁇ -Si 3 N 4 is more than 93%;
  • the silicon nitride layer generated in the previous reaction can be used as a diluent for the next reaction after being broken, so there is no need to add silicon nitride as a diluent, thereby improving the net yield of silicon nitride powder and reducing the Cost of production.
  • Fig. 1 is the XRD pattern of the preparation product of embodiment 1;
  • Fig. 2 is the XRD pattern of the preparation product of embodiment 2;
  • FIG. 3 is the XRD pattern of the product prepared in Example 3.
  • the invention provides a preparation method of silicon nitride powder, comprising the following steps:
  • the obtained reaction system is evacuated or filled with an inert gas to replace nitrogen or nitrogen-hydrogen mixture in the reaction system, the temperature of the system is heated from T2 to T3, and then from T3 Cool down to T4, after reaching T4, continuously feed nitrogen or nitrogen-hydrogen mixture into the system to carry out the second nitridation reaction;
  • the temperature difference between T3 and T2 is above 50°C, and the temperature rise rate from T2 to T3 is 5 °C/min or more;
  • step (2) is repeated 1 to 3 times to obtain silicon nitride powder.
  • the silicon powder is placed in the furnace, and the furnace is heated to T1 under the condition of vacuuming. After the temperature reaches T1, the vacuum is stopped, and nitrogen or nitrogen-hydrogen mixture is continuously introduced into the furnace. At the same time, the temperature of the system in the furnace is adjusted The temperature is raised from T1 to T2, and the first nitridation reaction is carried out.
  • the median particle size of the silicon powder is preferably 1-74 microns, more preferably 2-50 microns, and most preferably 5-10 microns; the purity of the silicon powder is preferably greater than 99%, more preferably greater than 99.9%.
  • the silicon powder is preferably dried first, and then the silicon powder is placed in the furnace for subsequent steps.
  • the drying is preferably carried out in a vacuum, an inert atmosphere or nitrogen to prevent oxidation of the silicon powder;
  • the drying temperature is preferably 60-300°C, more preferably 100-250°C, and most preferably 150- 200°C;
  • the drying time is preferably 1-12 hours, more preferably 3-10 hours, and most preferably 5-8 hours.
  • the dried silicon powder is preferably loaded into the reaction sintered silicon nitride material boat, and then the material boat is put into the furnace for subsequent steps.
  • the preparation of the silicon nitride powder is preferably carried out in a vacuum atmosphere furnace.
  • the temperature is preferably raised from room temperature to T1, where T1 is 600-900°C, preferably 650-800°C.
  • the heating time required in the present invention to heat up from room temperature to T1 is preferably 1-5 h, more preferably 2-4 h.
  • the degree of vacuum after the evacuation is stopped is preferably 0.01 Pa or less.
  • the present invention continuously feeds nitrogen or nitrogen-hydrogen mixture into the furnace, and simultaneously increases the temperature of the system in the furnace from T1 to T2 to carry out the first nitridation reaction.
  • the nitrogen gas or the mixed gas of nitrogen and hydrogen ie, the mixed gas of nitrogen and hydrogen
  • the volume fraction of hydrogen in the nitrogen-hydrogen mixture is preferably below 20%, more preferably 5-15%. Since the surface of the silicon powder usually contains a layer of silicon dioxide film, a nitrogen-hydrogen mixture is used, in which the hydrogen can react with the silicon dioxide to reduce the oxygen content in the target product silicon nitride.
  • the T2 1100-1350°C, more preferably 1100-1200°C.
  • the heating rate from T1 to T2 is preferably 20-120°C/h, more preferably 40-100°C/h, and most preferably 50-80°C/h.
  • the T2 is the temperature of the first nitridation reaction.
  • the time of the first nitridation reaction is preferably 1-10 h (that is, the holding time at T2), and more preferably 2 ⁇ 8h, most preferably 3 ⁇ 5h.
  • the pressure in the furnace is preferably 102-110 kPa.
  • the silicon powder is contacted with nitrogen gas or a nitrogen-hydrogen mixture, and a nitridation reaction occurs, and a layer of silicon nitride is formed on the surface of the silicon powder.
  • the present invention evacuates the obtained reaction system or fills it with an inert gas to replace nitrogen or nitrogen-hydrogen mixture in the reaction system, and the temperature of the system is heated from T2 to T3, and then cooled from T3. To T4, after reaching T4, nitrogen gas or nitrogen-hydrogen mixture is continuously introduced into the system to carry out the second nitridation reaction.
  • the temperature difference between T3 and T2 is 50°C or higher, preferably 100°C or higher, more preferably 100°C.
  • the temperature increase rate from T2 to T3 is 5°C/min or more, preferably 10°C/min or more.
  • the present invention preferably maintains the temperature for 0 to 2 hours, and more preferably maintains the temperature for 0.5 to 1.5 hours. Since it takes a certain time to transmit the temperature, the present invention utilizes heat preservation to make the temperature of the material in the furnace reach the set temperature.
  • the temperature of the system reaches T3
  • the temperature of the present invention is further lowered from T3 to T4, and after reaching T4, nitrogen or nitrogen-hydrogen mixture is continuously fed into the system to carry out the second nitridation reaction.
  • the nitrogen-hydrogen mixed gas is the same as the nitrogen-hydrogen mixed gas in the above steps, which will not be repeated here.
  • the T4 is preferably 1150-1250°C.
  • the T4 is the temperature of the second nitridation reaction.
  • the cooling time required for cooling from T3 to T4 is preferably 10-60 min, more preferably 20-50 min.
  • the time of the second nitridation reaction is preferably 1-10 h (ie, the holding time at T4), more preferably 2-8 h, and most preferably 3-5 h.
  • the pressure in the furnace is preferably 102-110 kPa.
  • the invention utilizes the difference in thermal expansion coefficients of silicon and silicon nitride to rapidly increase the temperature by more than 50°C at a heating rate of more than 3°C/min in a vacuum or an inert atmosphere, and then lowers the temperature, so that the silicon nitride layer on the surface of the silicon powder is broken, thereby increasing the nitrogen content.
  • the silicon nitride layer generated by the previous reaction can be used as a diluent for the next reaction after being broken, so there is no need to add silicon nitride as a diluent, thereby improving the silicon nitride powder.
  • the net yield is reduced, and the production cost is reduced.
  • the present invention repeats the above-mentioned process from completing the first nitriding reaction to performing the second nitriding reaction 1 to 3 times (that is, performing the nitridation reaction 3 to 5 times in total), preferably repeating 2 (that is, the nitridation reaction is carried out four times in total) to obtain silicon nitride powder.
  • the product of the last nitridation reaction is preferably subjected to processing such as crushing and/or grinding to obtain silicon nitride powder.
  • the present invention has no special requirements on the particle size of the silicon nitride powder, and those skilled in the art can adjust and control according to actual needs.
  • nitrogen gas or nitrogen-hydrogen mixed gas will be introduced only when the temperature is below 1350°C, and the nitridation reaction of silicon powder will take place, so it is more favorable for the generation of ⁇ -Si 3 N 4 , and the obtained ⁇ -Si 3 N 4 The content is above 93%.
  • a preparation method of silicon nitride powder specifically adopts the following preparation steps:
  • the obtained silicon nitride bulk is subjected to processing such as crushing and grinding to obtain high-performance silicon nitride powder with a content of ⁇ -Si 3 N 4 of 93%.
  • a preparation method of silicon nitride powder specifically adopts the following preparation steps:
  • the nitrogen-hydrogen mixture in the furnace is replaced with argon gas, and then the temperature is rapidly increased to T5 (1350 ° C), and the heating time is 30 min (the heating rate is 3.33 ° C/min), During the period, the argon atmosphere in the furnace was maintained; the temperature reached T5 (1350°C) and then kept for 0.5h, and the argon atmosphere in the furnace was maintained during the period; after the heat preservation, the temperature was lowered to T6 (1300°C), and the cooling time was 10min.
  • the nitrogen-hydrogen mixture in the furnace is replaced by argon gas, and then the temperature is rapidly increased to T7 (1400 ° C), and the heating time is 30 min (the heating rate is 3.33 ° C/min), During the period, the argon atmosphere in the furnace was maintained; the temperature reached T7 (1400°C) and then the temperature was lowered to T8 (1350°C), and the cooling time was 10 minutes, during which the argon atmosphere in the furnace was maintained; after the temperature dropped to T8 (1350°C), the The nitrogen-hydrogen mixture is kept for 10 hours, during which a slight positive pressure (102-110kPa) in the furnace is maintained to carry out the fourth nitridation reaction; after the end of the heat preservation, the complete nitridation of the silicon powder in the furnace can be achieved.
  • the obtained silicon nitride bulk is subjected to processing such as crushing and grinding to obtain high-performance silicon nitride powder with a content of ⁇ -Si 3 N 4 of 94%.
  • a preparation method of silicon nitride powder specifically adopts the following preparation steps:
  • the volume fraction of hydrogen is 15% and continue to heat up to T2 (1200°C) for 2h, during which a slight positive pressure (102-110kPa) is maintained in the furnace; after the temperature reaches T2 (1200°C), the temperature is kept for 8h, and nitrogen is continued to be introduced during this period. Hydrogen mixed gas, maintaining a slight positive pressure in the furnace to carry out the first nitridation reaction;
  • the nitrogen-hydrogen mixture in the furnace is replaced with argon gas, and then the temperature is rapidly increased to T3 (1300 ° C), and the heating time is 30 min (the heating rate is 3.33 ° C/min).
  • Argon atmosphere in the furnace hold the temperature for 1h after the temperature reaches T3 (1300°C), and keep the argon atmosphere in the furnace during the period; cool down to T4 (1250°C) after the heat preservation, and the cooling time is 10min, during which the argon atmosphere in the furnace is maintained. state; after the temperature dropped to T4 (1250°C), a nitrogen-hydrogen mixture was introduced and kept for 8 hours, during which the second nitridation reaction was carried out by maintaining a slight positive pressure in the furnace;
  • Figures 1 to 3 are the XRD patterns of the silicon nitride powders prepared in Examples 1 to 3, respectively. From Figures 1 to 3, it can be seen that the main phase of the silicon nitride prepared by the present invention is ⁇ -Si 3 N 4 . According to XRD The figure can be calculated to obtain the content of ⁇ -Si 3 N 4 , which has been given in the results of the above examples.
  • the period for preparing silicon nitride powder in the present invention is shortened from the traditional 5 to 6 days to 3 days, and no additional silicon nitride is added as a diluent during the preparation process, thereby improving the efficiency of silicon nitride powder.
  • the net yield of powder (above 93%) reduces the production cost.

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Abstract

一种氮化硅粉体的制备方法，其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；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 3N 4的生成，得到的α-Si 3N 4含量在93％以上；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。

Description

一种氮化硅粉体的制备方法
本申请要求于2020年07月14日提交中国专利局、申请号为202010673734.1、发明名称为“一种氮化硅粉体的制备方法”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
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。
背景技术
氮化硅陶瓷具有比重小、抗热震性好、蠕变低、耐化学侵蚀、耐磨和机械性能优良等特点，在国防、能源、航空航天、机械、汽车、石化、冶金及电子等众多领域得到了广泛应用，例如用做汽车发动机的零部件、陶瓷轴承球和切削刀具等。氮化硅陶瓷的烧结方式包括无压烧结、气压烧结、热压烧结、热等静压烧结、反应烧结等常规方式以及等离子烧结、微波烧结等特种烧结方式。除反应烧结以外，其余的烧结方式都需要用到氮化硅粉体作为原料。氮化硅粉体的性能(如纯度、粒度、α相含量等)对氮化硅陶瓷的烧结、结构、性能及功能有着十分重要的影响。
氮化硅粉体的制备方法主要有硅粉直接氮化法、SiO 2碳热还原氮化法、自蔓延高温合成法和热分解法等。
SiO 2碳热还原氮化法反应过程中容易生成SiC和Si 2N 2O，并且产物中往往伴有未反应完全的SiO 2或残留的C，这使得产物的纯度难以得到保证，不能满足高品质氮化硅粉体的性能要求，所以目前没有实现工业化生产。
自蔓延高温合成法的反应温度不易控制，通常反应温度过高而导致较多的β-Si 3N 4生成。目前自蔓延法虽已实现工业化生产，但合成的氮化硅粉体烧结活性低，不适合用作高性能氮化硅陶瓷的原料。
热分解法的反应速度快，制备的粉体纯度高，粒径均匀细小，但对生产设备要求较高，反应条件较为苛刻，因而制备成本较高。目前只有日本宇部(UBE)使用该方法工业化生产氮化硅粉体。
与上述方法相比，硅粉直接氮化法的工艺相对简单，操作方便，更适 合工业化生产，但传统的硅粉直接氮化工艺的氮化周期较长，一般需要5～6天的时间才能完成整个氮化过程，导致生产效率较低。而且氮化过程中为了防止局部温度过高使硅粉发生微烧结，需要加入10～50％的氮化硅粉体作为稀释剂，这些均在一定程度增加了氮化硅粉体的制备成本。
发明内容
本发明的目的在于提供一种氮化硅粉体的制备方法，具有氮化周期短、生产效率高、成本低、净产率高的优点。
为了实现上述发明目的，本发明提供以下技术方案：
本发明提供了一种氮化硅粉体的制备方法，包括以下步骤：
(1)将硅粉置于炉膛内，在抽真空条件下将炉膛升温至T1，待温度达到T1后停止抽真空，向炉膛内持续通入氮气或氮氢混合气，同时将炉膛内体系的温度自T1升温至T2，进行第一氮化反应；所述T1＝600～900℃，所述T2＝1100～1350℃；
(2)完成所述第一氮化反应后，将所得反应体系抽真空或充入惰性气体置换掉反应体系中的氮气或氮氢混合气，将体系的温度从T2升温至T3，再从T3降温至T4，达到T4后，向体系中持续通入氮气或氮氢混合气，进行第二氮化反应；所述T3与T2的温差在50℃以上，从T2升温至T3的升温速率在3℃/min以上；所述T4与T3的温差在50℃以上且所述T4＝1100～1350℃；
(3)完成所述第二氮化反应后，重复进行所述步骤(2)1～3次，得到氮化硅粉体。
优选的，所述硅粉的中位粒径为1～74微米，纯度大于99％。
优选的，进行所述步骤(1)前，还包括将硅粉进行干燥；所述干燥在真空、惰性气氛或氮气中进行，所述干燥的温度为60～300℃，所述干燥的时间为1～12h。
优选的，每次氮化反应的时间独立为1～10h。
优选的，所述氮氢混合气中氢气的体积分数在20％以下。
优选的，所述自T1升温至T2的升温速率为20～120℃/h。
优选的，每次氮化反应过程中炉内压力为102～110kPa。
优选的，升温至所述T3后，保温0～2h。
优选的，从T3降温至T4所需的降温时间为10～60min。
本发明提供了一种氮化硅粉体的制备方法，包括以下步骤：(1)将硅粉置于炉膛内，在抽真空条件下将炉膛升温至T1，待温度达到T1后停止抽真空，向炉膛内持续通入氮气或氮氢混合气，同时将炉膛内体系的温度自T1升温至T2，进行第一氮化反应；所述T1＝600～900℃，所述T2＝1100～1350℃；(2)完成所述第一氮化反应后，将所得反应体系抽真空或充入惰性气体置换掉反应体系中的氮气或氮氢混合气，将体系的温度从T2升温至T3，再从T3降温至T4，达到T4后，向体系中持续通入氮气或氮氢混合气，进行第二氮化反应；所述T3与T2的温差在50℃以上，从T2升温至T3的升温速率在5℃/min以上；所述T4与T3的温差在50℃以上且所述T4＝1100～1350℃；(3)完成所述第二氮化反应后，重复进行所述步骤(2)1～3次，得到氮化硅粉体。
传统的硅粉直接氮化工艺之所以氮化周期长，是因为硅粉和氮气开始反应时生成的氮化硅会包覆在未反应的硅外面形成氮化硅层，阻碍氮气和硅的进一步接触，从而使氮化反应的速率变慢。与传统工艺相比，本发明的有益效果为：
(1)进行第一氮化反应后，在硅的表面形成氮化硅层，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；
(2)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 3N 4的生成，得到的α-Si 3N 4含量在93％以上；
(3)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。
附图说明
图1为实施例1制备产物的XRD图谱；
图2为实施例2制备产物的XRD图谱；
图3为实施例3制备产物的XRD图谱。
具体实施方式
本发明提供了一种氮化硅粉体的制备方法，包括以下步骤：
(1)将硅粉置于炉膛内，在抽真空条件下将炉膛升温至T1，待温度达到T1后停止抽真空，向炉膛内持续通入氮气或氮氢混合气，同时将炉膛内体系的温度自T1升温至T2，进行第一氮化反应；所述T1＝600～900℃，所述T2＝1100～1350℃；
(2)完成所述第一氮化反应后，将所得反应体系抽真空或充入惰性气体置换掉反应体系中的氮气或氮氢混合气，将体系的温度从T2升温至T3，再从T3降温至T4，达到T4后，向体系中持续通入氮气或氮氢混合气，进行第二氮化反应；所述T3与T2的温差在50℃以上，从T2升温至T3的升温速率在5℃/min以上；所述T4与T3的温差在50℃以上且所述T4＝1100～1350℃；
(3)完成所述第二氮化反应后，重复进行所述步骤(2)1～3次，得到氮化硅粉体。
本发明将硅粉置于炉膛内，在抽真空条件下将炉膛升温至T1，待温度达到T1后停止抽真空，向炉膛内持续通入氮气或氮氢混合气，同时将炉膛内体系的温度自T1升温至T2，进行第一氮化反应。
在本发明中，所述硅粉的中位粒径优选为1～74微米，更优选为2～50微米，最优选为5～10微米；所述硅粉的纯度优选大于99％，更优选大于99.9％。
本发明优选先对硅粉进行干燥，然后再将硅粉置于炉膛内进行后续步骤。在本发明中，所述干燥优选在真空、惰性气氛或氮气中进行，以防止硅粉氧化；所述干燥的温度优选为60～300℃，更优选为100～250℃，最优选为150～200℃；所述干燥的时间优选为1～12h，更优选为3～10h，最优选为5～8h。
本发明优选将干燥好的硅粉装入反应烧结氮化硅料舟内，再将料舟放入炉膛内进行后续步骤。在本发明中，所述氮化硅粉体的制备优选在真空 气氛炉内进行。
本发明优选自室温升温至T1，所述T1＝600～900℃，优选为650～800℃。本发明自室温升温至T1所需的升温时间优选为1～5h，更优选为2～4h。
当温度达到T1后停止抽真空。在本发明中，停止抽真空后的真空度优选在0.01Pa以下。
停止抽真空后，本发明向炉膛内持续通入氮气或氮氢混合气，同时将炉膛内体系的温度自T1升温至T2，进行第一氮化反应。在本发明中，所述氮气或氮氢混合气(即氮气与氢气的混合气体)作为氮化硅反应的原料。当采用氮氢混合气时，所述氮氢混合气中氢气的体积分数优选在20％以下，更优选为5～15％。由于硅粉表面通常会含有含有一层二氧化硅薄膜，采用氮氢混合气，其中的氢气可以与二氧化硅反应，减少目标产物氮化硅中的氧含量。
在本发明中，所述T2＝1100～1350℃，更优选为1100～1200℃。所述自T1升温至T2的升温速率优选为20～120℃/h，更优选为40～100℃/h，最优选为50～80℃/h。在本发明中，所述T2即为第一氮化反应的温度，在本发明中，所述第一氮化反应的时间优选为1～10h(也即在T2的保温时间)，更优选为2～8h，最优选为3～5h。本发明所述第一氮化反应过程中，炉内压力优选为102～110kPa。本发明在所述第一氮化反应过程中，硅粉与氮气或氮氢混合气接触，发生氮化反应，在硅粉表面形成一层氮化硅。
完成所述第一氮化反应后，本发明将所得反应体系抽真空或充入惰性气体置换掉反应体系中的氮气或氮氢混合气，将体系的温度从T2升温至T3，再从T3降温至T4，达到T4后，向体系中持续通入氮气或氮氢混合气，进行第二氮化反应。
在本发明中，所述T3与T2的温差在50℃以上，优选在100℃以上，更优选为100℃。在本发明中，从T2升温至T3的升温速率在5℃/min以上，优选在10℃/min以上。升温至T3后，本发明优选保温0～2h，更优选保温0.5～1.5h。由于温度的传递需要一定时间，本发明利用保温使炉内物料温度达到设定温度。
当体系的温度达到T3后，本发明再从T3降温至T4，达到T4后，向体系中持续通入氮气或氮氢混合气，进行第二氮化反应。在本发明中，所述氮氢混合气同上述步骤中的氮氢混合气，这里不再赘述。在本发明中，所述T4与T3的温差在50℃以上，优选在100℃以上，更优选为100℃，且所述T4同时满足T4＝1100～1350℃。在本发明中，所述T4优选为1150～1250℃。所述T4即为第二氮化反应的温度。在本发明中，从T3降温至T4所需的降温时间优选为10～60min，更优选为20～50min。在本发明中，所述第二氮化反应的时间优选为1～10h(也即在T4的保温时间)，更优选为2～8h，最优选为3～5h。本发明所述第二氮化反应过程中，炉内压力优选为102～110kPa。
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；同时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。
完成所述第二氮化反应后，本发明重复上述从完成第一氮化反应到进行第二氮化反应的过程1～3次(即共进行氮化反应3～5次)，优选重复2次(即共进行氮化反应4次)，得到氮化硅粉体。
重复过程中的具体参数，参考从完成第一氮化反应到进行第二氮化反应过程中的参数，这里不再赘述。
当完成最后一次氮化反应后，本发明优选将最后一次氮化反应的产物进行破碎和/或研磨等加工处理，得到氮化硅粉体。本发明对所述氮化硅粉体的粒径没有特殊要求，本领域技术人员可根据实际需求进行调控。
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，因此更有利于α-Si 3N 4的生成，得到的α-Si 3N 4含量在93％以上。
下面结合实施例对本发明提供的氮化硅粉体的制备方法进行详细的说明，但是不能把它们理解为对本发明保护范围的限定。
实施例1
一种氮化硅粉体的制备方法，具体采用以下制备步骤：
(1)将原料硅粉(中位粒径为2微米，纯度为99.9％)在真空中干燥6h，干燥温度设定为80℃；将干燥好的硅粉装入反应烧结氮化硅料舟内，再将料舟放入真空气氛炉内，开始升温；
(2)温度在T1(800℃)以下为抽真空过程，时间为3h；温度达到T1(800℃)后停止抽真空，通入氮氢混合气(氢气的体积分数为5％)继续升温至T2(1150℃)，升温时间为2h，期间保持炉内微正压(102～110kPa)；温度达到T2(1150℃)后保温5h，期间继续通入氮氢混合气，保持炉内微正压(102～110kPa)进行第一氮化反应；
(3)完成所述第一氮化反应后抽真空，然后快速升温至T3(1250℃)，升温时间为20min(升温速率为5℃/min)，期间保持炉内真空状态；当温度达到T3(1250℃)后保温1h，期间保持炉内真空状态；保温结束后降温至T4(1200℃)，降温时间为10min，期间保持炉内真空状态；温度降至T4(1200℃)后通入氮氢混合气，保温10h，期间保持炉内微正压(102～110kPa)进行第二氮化反应；
(4)完成所述第二氮化反应后抽真空，然后快速升温至T5(1300℃)，升温时间为30min(升温速率为3.33℃/min)，期间保持炉内真空状态；温度达到T5(1300℃)后保温0.5h，期间保持炉内真空状态；保温结束后降温至T6(1250℃)，降温时间为10min，期间保持炉内真空状态；温度降至T6(1250℃)后通入氮氢混合气，保温8h，期间保持炉内微正压(102～110kPa)，进行第三氮化反应；
(5)完成所述第三氮化反应后抽真空，然后快速升温至T7(1350℃)，升温时间为30min(升温速率为3.33℃/min)，期间保持炉内真空状态；温度达到T7(1350℃)后保温1h，期间保持炉内真空状态；保温结束后降温至T8(1300℃)，降温时间为10min，期间保持炉内真空状态；温度降至T8(1300℃)后通入氮氢混合气，保温10h，期间保持炉内微正压(102～110kPa)，进行第四氮化反应；保温结束后可以实现炉内硅粉的完全氮化。
将得到的氮化硅块体进行破碎、研磨等加工处理，可以得到α-Si 3N 4含量为93％的高性能氮化硅粉体。
实施例2
一种氮化硅粉体的制备方法，具体采用以下制备步骤：
(1)将原料硅粉(中位粒径为5微米，纯度为99.95％)在氮气保护气氛中干燥12h，干燥温度设定为60℃；将干燥好的硅粉装入反应烧结氮化硅料舟内，再将料舟放入真空气氛炉内，开始升温；
(2)温度在T1(600℃)以下为抽真空过程，时间为2h；温度达到T1(600℃)后停止抽真空，通入氮氢混合气(氢气的体积分数为10％)继续升温至T2(1150℃)，升温时间为3h，期间保持炉内微正压(102～110kPa)；温度达到T2(1150℃)后保温6h，期间继续通入氮氢混合气，保持炉内微正压(102～110kPa)进行第一氮化反应；
(3)完成所述第一氮化反应后通入氩气置换掉炉内的氮氢混合气，然后快速升温至T3(1300℃)，升温时间为40min(升温速率为3.75℃/min)，期间保持炉内氩气气氛状态；当温度达到T3(1300℃)随即降温至T4(1250℃)，降温时间为10min，期间保持炉内氩气气氛状态；温度降至T4(1250℃)后通入氮氢混合气，保温8h，期间保持炉内微正压(102～110kPa)进行第二氮化反应；
(4)完成所述第二氮化反应后通入氩气置换掉炉内的氮氢混合气，然后快速升温至T5(1350℃)，升温时间为30min(升温速率为3.33℃/min)，期间保持炉内氩气气氛状态；温度达到T5(1350℃)后保温0.5h，期间保持炉内氩气气氛状态；保温结束后降温至T6(1300℃)，降温时间为10min，期间保持炉内氩气气氛状态；温度降至T6(1300℃)后通入氮氢混合气，保温8h，期间保持炉内微正压(102～110kPa)，进行第三氮化反应；
(5)完成所述第三氮化反应后通入氩气置换掉炉内的氮氢混合气，然后快速升温至T7(1400℃)，升温时间为30min(升温速率为3.33℃/min)，期间保持炉内氩气气氛状态；温度达到T7(1400℃)随即降温至T8(1350℃)，降温时间为10min，期间保持炉内氩气气氛状态；温度降至T8(1350℃)后通入氮氢混合气，保温10h，期间保持炉内微正压(102～110kPa)，进行第四氮化反应；保温结束后可以实现炉内硅粉的完全氮化。
将得到的氮化硅块体进行破碎、研磨等加工处理，可以得到α-Si 3N 4含量为94％的高性能氮化硅粉体。
实施例3
一种氮化硅粉体的制备方法，具体采用以下制备步骤：
(1)将原料硅粉(中位粒径为10微米，纯度为99.9％)在真空中干燥3h，干燥温度设定为200℃；将干燥好的硅粉装入反应烧结氮化硅料舟内，再将料舟放入真空气氛炉内，开始升温；温度在T1(900℃)以下为抽真空过程，时间为3h；温度T1(900℃)后停止抽真空，通入氮氢混合气(氢气体积分数为15％)继续升温至T2(1200℃)，时间为2h，期间保持炉内微正压(102～110kPa)；温度达到T2(1200℃)后保温8h，期间继续通入氮氢混合气，保持炉内微正压进行第一氮化反应；
(2)完成第一氮化反应后通入氩气置换掉炉内的氮氢混合气，然后快速升温至T3(1300℃)，升温时间为30min(升温速率为3.33℃/min)，期间保持炉内氩气气氛状态；温度达到T3(1300℃)后保温1h，期间保持炉内氩气气氛状态；保温结束后降温至T4(1250℃)，降温时间为10min，期间保持炉内氩气气氛状态；温度降至T4(1250℃)后通入氮氢混合气，保温8h，期间保持炉内微正压进行第二氮化反应；
(3)第二氮化反应结束后通入氩气置换掉炉内的氮氢混合气，然后快速升温至T5(1350℃)，升温时间为30min(升温速率为3.33℃/min)，期间保持炉内氩气气氛状态；温度达到T5(1350℃)后保温0.5h，期间保持炉内氩气气氛状态；保温结束后降温至T6(1300℃)，降温时间为10min，期间保持炉内氩气气氛状态；温度降至T6(1300℃)后通入氮氢混合气，保温10h，期间保持炉内微正压进行第三氮化反应；
(4)第三氮化反应结束后抽真空，然后快速升温至T7(1400℃)，升温时间为30min(升温速率为3.33℃/min)，期间保持炉内真空状态；温度达到T7(1400℃)后保温0.5h，期间保持炉内真空状态；保温结束后降温至T8(1350℃)，降温时间为10min，期间保持炉内真空状态；温度降至T8(1350℃)后通入氮氢混合气，保温10h，期间保持炉内微正压进行第四氮化反应；保温结束后可以实现炉内硅粉的完全氮化。将得到的氮化硅块体进行破碎、研磨等加工处理，可以得到α-Si 3N 4含量为94％的高性能氮化硅粉体。
图1～3分别为实施例1～3制备得到的氮化硅粉体的XRD图，由图1～3可知，本发明制备的氮化硅主要物相为α-Si 3N 4，根据XRD图可计算得到α-Si 3N 4的含量，在上述各实施例的结果中已经给出。
由以上实施例可知，本发明制备氮化硅粉体的周期由传统的5～6天缩短为3天，且在制备过程中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(在93％以上)，降低了生产成本。
以上实施例的说明只是用于帮助理解本发明的方法及其核心思想。应当指出，对于本技术领域的普通技术人员来说，在不脱离本发明原理的前提下，还可以对本发明进行若干改进和修饰，这些改进和修饰也落入本发明权利要求的保护范围内。对这些实施例的多种修改对本领域的专业技术人员来说是显而易见的，本文中所定义的一般原理可以在不脱离本发明的精神或范围的情况下在其它实施例中实现。因此，本发明将不会被限制于本文所示的这些实施例，而是要符合与本文所公开的原理和新颖特点相一致的最宽的范围。

Claims (9)

  1. 一种氮化硅粉体的制备方法，其特征在于，包括以下步骤：
    (1)将硅粉置于炉膛内，在抽真空条件下将炉膛升温至T1，待温度达到T1后停止抽真空，向炉膛内持续通入氮气或氮氢混合气，同时将炉膛内体系的温度自T1升温至T2，进行第一氮化反应；所述T1＝600～900℃，所述T2＝1100～1350℃；
    (2)完成所述第一氮化反应后，将所得反应体系抽真空或充入惰性气体置换掉反应体系中的氮气或氮氢混合气，将体系的温度从T2升温至T3，再从T3降温至T4，达到T4后，向体系中持续通入氮气或氮氢混合气，进行第二氮化反应；所述T3与T2的温差在50℃以上，从T2升温至T3的升温速率在3℃/min以上；所述T4与T3的温差在50℃以上且所述T4＝1100～1350℃；
    (3)完成所述第二氮化反应后，重复进行所述步骤(2)1～3次，得到氮化硅粉体。
  2. 根据权利要求1所述的制备方法，其特征在于，所述硅粉的中位粒径为1～74微米，纯度大于99％。
  3. 根据权利要求1所述的制备方法，其特征在于，进行所述步骤(1)前，还包括将硅粉进行干燥；所述干燥在真空、惰性气氛或氮气中进行，所述干燥的温度为60～300℃，所述干燥的时间为1～12h。
  4. 根据权利要求1所述的制备方法，其特征在于，每次氮化反应的时间独立为1～10h。
  5. 根据权利要求1所述的制备方法，其特征在于，所述氮氢混合气中氢气的体积分数在20％以下。
  6. 根据权利要求1所述的制备方法，其特征在于，所述自T1升温至T2的升温速率为20～120℃/h。
  7. 根据权利要求1所述的制备方法，其特征在于，每次氮化反应过程中炉内压力为102～110kPa。
  8. 根据权利要求1所述的制备方法，其特征在于，升温至所述T3 后，保温0～2h。
  9. 根据权利要求1所述的制备方法，其特征在于，从T3降温至T4所需的降温时间为10～60min。
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