Ultralow-impurity nitride powder and preparation method thereof

Abstract

The invention provides ultralow impurity nitride powder and a preparation method thereof, and relates to the technical field of ceramic materials. The preparation method comprises the following steps: respectively carrying out purification pretreatment on a raw material and a carbon source, and mixing the two pretreated products to obtain a pretreated substance, the raw material being selected from Al2O3 or SiO2. And heating the pretreated material to 600-900 DEG C, and introducing a mixed gas containing N2 and HCl to perform in-situ impurity removal so as to obtain a purified material. And in a nitrogen atmosphere, pre-nitriding the purified material, and then carrying out nitridation reaction for 2-6 hours to obtain a nitridation product. And carrying out post-treatment on the nitridation product to obtain the ultralow-impurity nitride powder. Impurity introduction is blocked from the source through raw material purification pretreatment, impurities are removed through in-situ chlorination volatilization in the reaction process, gas phase impurities are dynamically removed, reaction post-treatment is carried out, product deep purification is carried out, impurities are removed to the maximum extent, and dependence on a high-cost reactor is not needed.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials technology, and in particular to an ultra-low impurity nitride powder and its preparation method. Background Technology

[0002] Nitrides (such as aluminum nitride AlN and silicon nitride Si3N4) have wide applications in electronics, aerospace, machinery, and optoelectronics due to their excellent thermal conductivity, high temperature resistance, and corrosion resistance. However, traditional nitride preparation methods often face the problem of high impurity content. For example, the presence of impurities such as iron (Fe), silicon (Si), and calcium (Ca) can negatively affect the performance of the final product. Iron impurities significantly affect the electrical and thermal properties of AlN and Si3N4, while silicon and calcium impurities affect their mechanical properties and stability. Currently, although some methods exist to reduce the content of these impurities, precisely controlling the impurity content, especially the content of iron, silicon, and calcium impurities, remains a technical challenge in the carbothermic reduction method for nitride preparation.

[0003] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides an ultra-low impurity nitride powder and its preparation method.

[0005] According to a first aspect of the present invention, a method for preparing ultra-low impurity nitride powder is provided, comprising: S1, the raw material and carbon source are purified and pretreated separately, and the two pretreated products are mixed to obtain the pretreated product, wherein the raw material is selected from Al2O3 or SiO2; S2, the pretreated material is heated to 600~900℃, a mixed gas containing N2 and HCl is introduced, and the temperature is maintained for 25~60 minutes to remove impurities in situ and obtain purified material; S3, under a nitrogen atmosphere, the purified material is pre-nitrided and then nitrided at 1500~1800℃ for 2~6h to obtain the nitrided product; S4, the nitrided product is post-processed to obtain ultra-low impurity nitrided powder, wherein the post-processing steps include ethanol vapor treatment and / or microwave-induced dechlorination treatment.

[0006] In an exemplary embodiment of the present invention, in step S2, the pretreated material is loaded into a graphite crucible, placed in a tube furnace, evacuated to 40~100Pa, heated to 700~900℃, and a mixed gas of N2 and HCl with a volume fraction of 1~3% is introduced. After holding at this temperature for 20~40 minutes, the material is cooled down and removed to obtain the purified material.

[0007] In an exemplary embodiment of the present invention, in step S3, the prenitriding conditions are a temperature of 700~900°C and a time of 1~3h.

[0008] In an exemplary embodiment of the present invention, CO and CO2 gases in a volume ratio of 1:2 to 3 are introduced during the nitriding reaction.

[0009] In an exemplary embodiment of the present invention, the step of ethanol vapor treatment includes: passing the nitrided product through a mixture of ethanol and an inert gas at a temperature of 500-700°C, wherein the volume fraction of ethanol is 55-65%, and reacting for 0.5-1.5 hours.

[0010] In an exemplary embodiment of the present invention, the step of microwave-induced dechlorination treatment includes: placing the nitrided product in a microwave reactor, introducing a mixture of NH3 and an inert gas, and reacting for 15 to 30 minutes, wherein the volume fraction of NH3 is 8 to 12%, and the microwave power is 5 to 10 W / g.

[0011] In an exemplary embodiment of the present invention, step S1, the step of purifying and pretreating the raw material Al2O3, includes: immersing the raw material Al2O3 in a mixed solution of oxalic acid and hydrofluoric acid for gradient leaching to separate the pretreated Al2O3; wherein, the mixed solution of oxalic acid and hydrofluoric acid is prepared by adding a hydrofluoric acid solution with a volume fraction of 1.5-3% to an oxalic acid solution with a concentration of 0.4-0.6 mol / L, wherein the mass fraction of the hydrofluoric acid solution is 40%; the gradient leaching conditions are leaching at 75-85°C for 1-3 hours, then cooling to 55-65°C and leaching for 3-5 hours, wherein the liquid-to-solid ratio of the mixed solution to the raw material Al2O3 is 4-7 mL:1 g.

[0012] In an exemplary embodiment of the present invention, step S1, the step of purifying and pretreating the raw material SiO2, includes: placing the raw material SiO2 in a complex solution of citric acid and ammonia, stirring at 65-75°C for 2-4 hours, and then centrifuging to obtain pretreated SiO2. The liquid-to-solid ratio of the raw material SiO2 is 5-10 mL:1 g.

[0013] In an exemplary embodiment of the present invention, the step of purifying and pretreating the carbon source includes: placing the carbon source in concentrated sulfuric acid (98 wt%), heating to 160-200°C, reacting for 2-4 hours, cooling and removing the product, and washing it with deionized water to obtain an activated product. The activated product is then placed in a 3-8% (w / w) EDTA solution, stirred at 55-65°C for 1-3 hours, and centrifuged to obtain the pretreated carbon source.

[0014] According to a second aspect of the present invention, an ultra-low impurity nitride powder is provided, which is prepared according to the preparation method described in any one of the above claims.

[0015] The beneficial effects of the ultra-low impurity nitride powder and its preparation method in this invention are: The ultra-low impurity nitride powder provided in this invention firstly employs specific purification pretreatment methods tailored to the characteristics of different raw materials, reducing impurities to extremely low levels and preventing impurity introduction at the source. Secondly, during the reaction process, impurities are removed through in-situ chlorination volatilization, generating gaseous FeCl3 and CaCl2 to dynamically remove gaseous impurities. Furthermore, the coupling process of chlorination volatilization and pre-nitriding effectively improves the impurity removal rate. During the nitriding reaction, the carbon balance is adjusted by introducing CO-CO2, effectively reducing carbon residue. After the nitriding reaction, deep purification of the product is achieved through ethanol vapor etching and microwave-induced dechlorination, maximizing impurity removal without relying on high-cost reactors.

[0016] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a SEM image of the ALN powder obtained in Example 4 of the present invention.

[0019] Figure 2 This is a SEM image of the Si3N4 powder obtained in Example 5 of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions in the embodiments of this disclosure will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] This invention provides a method for preparing ultra-low impurity nitride powder, comprising: S1, the raw material and carbon source are purified and pretreated separately, and the two pretreated products are mixed to obtain the pretreated product, wherein the raw material is selected from Al2O3 or SiO2; S2, the pretreated material is heated to 600~900℃, a mixed gas containing N2 and HCl is introduced, and the temperature is maintained for 25~60 minutes to remove impurities in situ and obtain purified material; S3, under a nitrogen atmosphere, the purified material is pre-nitrided and then nitrided at 1500~1800℃ for 2~6h to obtain the nitrided product; S4, the nitrided product is post-processed to obtain ultra-low impurity nitrided powder, wherein the post-processing steps include ethanol vapor treatment and / or microwave-induced dechlorination treatment.

[0022] Specifically, in step S1, the raw materials and carbon source are first purified and pretreated to prevent the introduction of impurities at the source. The raw materials (Al2O3 / SiO2, carbon source) contain Fe / Ca impurities, typically at a concentration greater than 50 ppm (mg / kg). This invention employs specific purification and pretreatment processes for different raw materials, effectively reducing impurities in the raw materials.

[0023] In one embodiment, step S1, the purification and pretreatment of the raw material Al2O3, includes: immersing the raw material Al2O3 in a mixed solution of oxalic acid and hydrofluoric acid for gradient leaching, and separating the pretreated Al2O3. Specifically, the mixed solution of oxalic acid and hydrofluoric acid is prepared by adding a hydrofluoric acid solution with a volume fraction of 1.5% to 3% to an oxalic acid solution with a concentration of 0.4 to 0.6 mol / L, wherein the mass fraction of the hydrofluoric acid solution is 40%.

[0024] Furthermore, in the purification pretreatment step of the raw material Al2O3, the gradient leaching conditions are as follows: leaching is performed at 75-85℃ for 1-3 hours using a water bath or oil bath, followed by cooling to 55-65℃ and leaching for 3-5 hours. The liquid-to-solid ratio of the mixed solution to the raw material Al2O3 is 4-7 mL:1 g. This treatment ensures that Fe ≤ 3 ppm and Ca ≤ 5 ppm in the raw material Al2O3.

[0025] In one embodiment, step S1, the purification pretreatment of the raw material SiO2, includes: placing the raw material SiO2 in a complexing solution of citric acid and ammonia, stirring for 2-4 hours at 65-75°C using a water bath or oil bath, and then centrifuging to obtain the pretreated SiO2. The complexing solution of citric acid and ammonia is prepared as follows: a citric acid solution with a mass fraction of 8-12% is prepared, and then slowly added to ammonia solution with a mass fraction of 20-28%, adjusting the pH to 4.3-4.8 to obtain the complexing solution. Further, the liquid-to-solid ratio of the complexing solution to the raw material SiO2 is 5-10 mL:1 g. By utilizing the complexing effect of citric acid to remove impurities from SiO2, metallic impurities such as Fe and Ca can be effectively removed, resulting in Fe ≤ 4 ppm and Ca ≤ 6 ppm in the raw material SiO2. This method is gentle and causes minimal damage to the SiO2 matrix.

[0026] In one embodiment, in step S1, the carbon source can be, for example, petroleum coke. The purification and pretreatment steps for the carbon source include: placing the carbon source in concentrated sulfuric acid, heating to 160-200°C, reacting for 2-4 hours, cooling and removing the reactant, and washing to obtain the activated product; placing the activated product in a 3-8% (w / w) EDTA solution (ethylenediaminetetraacetic acid solution), stirring at 55-65°C for 1-3 hours, and centrifuging to obtain the pretreated carbon source. Through the above treatment, by oxidative activation with concentrated sulfuric acid followed by complexation with EDTA, the Fe content of the carbon source can be reduced to ≤2 ppm.

[0027] After purifying and pretreating the raw materials, the process proceeds to step S2, where the pretreated material undergoes in-situ impurity treatment. Specifically, the pretreated material is placed in a graphite crucible, placed in a tube furnace, evacuated to 40-100 Pa, heated to 700-900℃, and a mixed gas of N2 and HCl (1-3% by volume) is introduced. After holding at this temperature for 20-40 minutes, the material is cooled and removed to obtain the purified material. In this step, by introducing the N2-HCl mixed gas, impurities such as Fe and Ca react with HCl to form volatilizable FeCl3 and CaCl3, which are then removed. This achieves in-situ chlorination and volatilization of impurities, dynamically removing gaseous impurities, thus effectively further removing impurities during the nitriding process without the need for high-cost reactors with BN (boron nitride) liners.

[0028] After in-situ impurity removal, the process proceeds to step S3, the nitriding reaction section. Specifically, in step S3, the pre-nitriding conditions are a temperature of 700~900℃ and a time of 1~3h. Through pre-nitriding treatment, a dense nitrided layer is formed.

[0029] Furthermore, in step S3, during the nitriding reaction, CO and CO2 gases with a volume ratio of 1:2~3 are introduced. The gas flow rate can be, for example, 0.2 L / min. By introducing a specific ratio of CO and CO2 mixed gas, carbon balance control in the carbothermic reduction process can be achieved, improving the nitriding effect, avoiding the generation of free carbon, and eliminating the need for acid washing with 5wt% HF after nitriding.

[0030] Furthermore, to further improve the purity of the product, the obtained nitrided product undergoes post-processing. In one embodiment, the post-processing step includes: first performing ethanol vapor treatment, and then performing microwave-induced dechlorination treatment.

[0031] Specifically, in step S4, the ethanol vapor treatment step includes: passing a mixture of ethanol and an inert gas (e.g., Ar) into the nitrided product at 500-700°C for 0.5-1.5 hours. The volume fraction of ethanol in the mixture is 55-65%. Through ethanol vapor etching, ethanol decomposes at high temperature to generate H2, CO reducing gas, and a carbon source. The iron oxide impurities are reduced and react with CO to generate iron carbonyl, which volatilizes at temperatures above 100°C to further remove Fe impurities from the product. See the reaction process below: FeO + H₂ → Fe + H₂O↑ Fe₂O₃ + 3H₂ → 2Fe + 3H₂O↑ FeO + CO → Fe + CO2↑ 2FeO + C → 2Fe + CO2↑ Metallic iron reacts with CO to form iron carbonyl, which is then carried away from the system by an inert gas. Fe + 5CO → Fe(CO)₅↑ The overall reaction equation is as follows: Specifically, in step S4, the microwave-induced dechlorination process includes: placing the nitrided product in a microwave reactor, introducing a mixture of NH3 and an inert gas (e.g., Ar), and reacting for 15-30 minutes. The volume fraction of NH3 in the mixture is 8-12%, and the microwave power is 5-10 W / g. Microwave-induced dechlorination effectively removes chlorine, as shown in the following reaction process: Microwave energy causes NH3 molecules to dissociate into highly reactive free radicals: NH3→NH2·+ H· NH3→NH·+ H2 H• (atomic hydrogen) and NH2• (amino radical) have strong reducing properties. Chlorine impurities in the product (present as metal chlorides such as FeCl3 or organochlorines) are reduced and removed, as shown in the following reaction equation: Atomic hydrogen reduction dechlorination: FeCl3 + 3H· → Fe + 3HCl↑ R-Cl + 2H· → RH + HCl↑ (R represents an organic group) amino radical substitution dechlorination: FeCl3+3NH2·→Fe(NH2)3+3Cl· Cl· + H· → HCl↑ The overall reaction equation (taking FeCl3 as an example) is as follows: 2FeCl3 + 6H· → 2Fe + 6HCl↑ FeCl3+3NH2·→FeN+ NH3↑+3HCl↑ This invention also provides an ultra-low impurity nitride powder, which is prepared according to the above-described preparation method.

[0032] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0033] Example 1 This embodiment provides a pretreated Al2O3 powder, obtained by the following steps: Prepare a 0.5 mol / L oxalic acid solution, then add a 2% (40 wt%) HF solution to obtain solution A. Prepare industrial-grade Al₂O₃ powder (Fe, Ca ≥ 50 ppm) and add it to solution A at a liquid-to-solid ratio of 5:1 to obtain solution B. Place solution B in an oil bath and heat to 80°C for leaching for 2 hours, then cool to 60°C and leach for another 4 hours. Filter to obtain the solid, wash, and dry to obtain pretreated Al₂O₃.

[0034] According to inductively coupled plasma atomic emission spectrometry, the pretreated Al2O3 obtained in this embodiment contains Fe ≤ 3 ppm and Ca ≤ 5 ppm.

[0035] Example 2 This embodiment provides a pretreated SiO2 powder, obtained according to the following steps: Prepare a 10wt% citric acid solution and a 25wt% ammonia solution. Slowly add the citric acid solution dropwise to the ammonia solution to adjust the pH to approximately 4.5, obtaining solution a. Add SiO2 powder (Fe, Ca ≥ 50ppm) to solution a at a liquid-to-solid ratio of 8:1, obtaining solution b. Place solution b in an oil bath and heat to 70℃, stirring for 3 hours. Then centrifuge to obtain a solid. Wash and dry the solid to obtain pretreated SiO2.

[0036] According to inductively coupled plasma atomic emission spectrometry, the pretreated SiO2 obtained in this embodiment contains Fe ≤ 4 ppm and Ca ≤ 6 ppm.

[0037] Example 3 This embodiment provides a pretreated petroleum coke, obtained by the following steps: Concentrated sulfuric acid (98 wt%) was placed in a high-pressure reactor (PTFE-lined), and petroleum coke was added at a liquid-to-solid ratio of 10:1. The mixture was heated to 180°C and reacted for 3 hours. After cooling, the product was removed, centrifuged, and washed with deionized water until neutral to obtain product a. Product a was then placed in a 5 wt% EDTA solution at a liquid-to-solid ratio of 5:1. The mixture was heated in an oil bath to 60°C and stirred for 2 hours. After centrifugation, the product was washed and dried to obtain pretreated petroleum coke.

[0038] According to inductively coupled plasma atomic emission spectrometry, the pretreated petroleum coke obtained in this embodiment contains ≤2ppm of Fe.

[0039] Example 4 This embodiment provides an ultra-low impurity nitride AlN powder, which is obtained by the following steps: (1) Take 30 g of pretreated Al2O3 (Example 1) and 15 g of petroleum coke (Example 3), mix them, put them into an ordinary graphite crucible, and place them in a tube furnace. Evacuate to 50 Pa, heat to 800 °C, and introduce N2 and HCl gas with a volume ratio of 98:2 at a gas flow rate of 0.5 L / min. After holding at this temperature for 30 min, cool down and take out the product to obtain product I.

[0040] (2) Product I was placed in a common graphite crucible and placed in a tube furnace. N2 was introduced and the temperature was raised to 800℃ for pre-nitriding for 2 hours. Then the temperature was raised to 1600℃ and the reaction was carried out for 4 hours. During the reaction, a mixture of CO and CO2 with a volume ratio of 1:3 was introduced at a gas flow rate of 0.2 L / min. After the reaction was completed, the product was cooled and removed to obtain product II.

[0041] (3) Heat anhydrous ethanol to about 40°C to produce ethanol vapor. Place product II in a tube furnace, heat to 600°C, and introduce ethanol vapor and Ar gas in a volume ratio of 6:4. React for 1 hour to obtain product III.

[0042] (4) Place product III in a microwave reactor and adjust the microwave power to 8 W / g. Introduce NH3 and Ar gas in a volume ratio of 1:9 and react for 20 min to obtain ultra-low impurity nitride AlN powder.

[0043] like Figure 1The image shows an SEM image of the AlN obtained in this embodiment. As can be seen from the image, the obtained AlN has a dense microstructure and a uniform particle size distribution.

[0044] Example 5 This embodiment provides an ultra-low impurity nitride Si3N4 powder, which is obtained according to the following steps: (1) Take 20 g of pretreated SiO2 (Example 2) and 10 g of petroleum coke (Example 3), mix them, put them into an ordinary graphite crucible, and place them in a tube furnace. Evacuate to 50 Pa, heat to 800 °C, and introduce N2 and HCl gas with a volume ratio of 98:2 at a gas flow rate of 0.5 L / min. After holding at this temperature for 30 min, cool down and take out the product to obtain product I.

[0045] (2) Product I was placed in a common graphite crucible and placed in a tube furnace. N2 was introduced and the temperature was raised to 800℃ for pre-nitriding for 2 hours. Then the temperature was raised to 1600℃ and the reaction was carried out for 4 hours. During the reaction, a mixture of CO and CO2 with a volume ratio of 1:3 was introduced at a gas flow rate of 0.2 L / min. After the reaction was completed, the product was cooled and removed to obtain product II.

[0046] (3) Heat anhydrous ethanol to about 40°C to produce ethanol vapor. Place product II in a tube furnace, heat to 600°C, and introduce ethanol vapor and Ar gas in a volume ratio of 6:4. React for 1 hour to obtain product III.

[0047] (4) Place product III in a microwave reactor and adjust the microwave power to 8 W / g. Introduce NH3 and Ar gas in a volume ratio of 1:9 and react for 20 min to obtain ultra-low impurity nitride Si3N4.

[0048] like Figure 2 The image shows an SEM image of the Si3N4 obtained in this embodiment. As can be seen from the image, the obtained Si3N4 has a dense microstructure and a uniform particle size distribution.

[0049] Example 6 This embodiment provides an ultra-low impurity nitride AlN powder, which differs from Example 4 in that: In step (2), product I was placed in a common graphite crucible, placed in a tube furnace, and N2 was introduced. The temperature was raised to 800°C and pre-nitrided for 2 hours. Then the temperature was raised to 1600°C and the reaction was carried out for 4 hours. After the reaction was completed, the product was cooled and removed to obtain product II.

[0050] Comparative Example 1 This comparative example provides a nitride AlN powder, which is obtained according to the following steps: (1) Take 30 g of industrial grade Al2O3 powder (Fe, Ca≥50ppm) and 15 g of petroleum coke, mix them, put them into an ordinary graphite crucible, and place them in a tube furnace. Introduce N2, heat to 1600℃, react for 4 h, and obtain product I.

[0051] (2) Product I was placed in an air atmosphere and decarburized at 650°C for 3 h to obtain AlN powder.

[0052] Comparative Example 2 This comparative example provides a Si3N4 nitride powder, which is obtained according to the following steps: (1) Take 20g of SiO2 powder (Fe, Ca≥50ppm) and 10g of petroleum coke, mix them, put them into an ordinary graphite crucible, and place them in a tube furnace. Introduce N2, heat to 1600℃, react for 4h, and obtain product I.

[0053] (2) Product I was placed in an air atmosphere and decarburized at 650°C for 3 h to obtain Si3N4 powder.

[0054] Comparative Example 3 This comparative example provides a nitride AlN powder, which differs from Example 4 in that: In step (2), product I was placed in a common graphite crucible, placed in a tube furnace, and N2 was introduced. The temperature was raised to 1600℃ and the reaction was carried out for 4 hours. After the reaction was completed, the product was cooled and removed to obtain product II.

[0055] Comparative Example 4 This comparative example provides a nitride AlN powder, which is prepared according to the following steps: (1) Product II was obtained according to steps (1) and (2) in Example 4.

[0056] (2) Grind and sieve product II (200 mesh), place it in a polytetrafluoroethylene (PTFE) container, add 5wt% HF solution, and the solid-liquid ratio is 1g:15mL. Heat in a water bath to 60℃, stir magnetically for 3 hours, let stand and cool to room temperature, and pour off the supernatant (HF-containing waste liquid needs to be collected separately and neutralized with excess lime milk). Wash the precipitate repeatedly with deionized water by centrifugation (≥5 times) until the pH of the supernatant is approximately 7. Finally, wash once with anhydrous ethanol and dry in a vacuum drying oven at 80~100℃ for 12 hours to obtain AlN powder.

[0057] Test case The products obtained in Examples 3-6 and Comparative Examples 1-4 were subjected to impurity (Fe, Ca, Cl) analysis by inductively coupled plasma mass spectrometry (ICP-MS). - The free carbon content was determined using a LECO carbon-sulfur analyzer. The results are shown in Table 1.

[0058] Table 1 project Fe content, ppm Ca content, ppm Cl- residue, ppm Free carbon, ppm Example 4 8 15 19 240 Example 5 10 18 21 850 Example 6 18 14 18 250 Comparative Example 1 20 40 28 300 Comparative Example 2 30 45 33 1120 Comparative Example 3 18 20 18 310 Comparative Example 4 12 17 21 330 As can be seen from Table 1, the Fe and Ca impurities in the nitride powder obtained in the embodiments of the present invention are all at extremely low levels, and the content of free carbon is low, which has good market application prospects.

[0059] The above description does not cover all embodiments. The detailed description of embodiments in this disclosure is not intended to limit the scope of the claimed disclosure, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in this disclosure without inventive effort are within the scope of protection of this disclosure.

Claims

1. A method for preparing ultra-low impurity nitride powder, characterized in that, include: S1, the raw material and carbon source are purified and pretreated separately, and the two pretreated products are mixed to obtain the pretreated product, wherein the raw material is selected from Al2O3 or SiO2; S2, the pretreated material is heated to 600~900℃, a mixed gas containing N2 and HCl is introduced, and the temperature is maintained for 25~60 minutes to remove impurities in situ and obtain purified material; S3, under a nitrogen atmosphere, the purified material is pre-nitrided and then nitrided at 1500~1800℃ for 2~6h to obtain the nitrided product; S4, the nitrided product is post-processed to obtain ultra-low impurity nitrided powder, wherein the post-processing steps include ethanol vapor treatment and / or microwave-induced dechlorination treatment.

2. The method for preparing ultra-low impurity nitride powder according to claim 1, characterized in that, In step S2, the pretreated material is placed in a graphite crucible, placed in a tube furnace, evacuated to 40~100Pa, heated to 700~900℃, and a mixed gas of N2 and HCl with a volume fraction of 1~3% is introduced. After holding at this temperature for 20~40 minutes, the material is cooled and removed to obtain the purified material.

3. The method for preparing ultra-low impurity nitride powder according to claim 1, characterized in that, In step S3, the pre-nitriding conditions are a temperature of 700~900℃ and a time of 1~3h.

4. The method for preparing ultra-low impurity nitride powder according to claim 3, characterized in that, During the nitriding reaction, CO and CO2 gases with a volume ratio of 1:2~3 are introduced.

5. The method for preparing ultra-low impurity nitride powder according to claim 1, characterized in that, The ethanol vapor treatment step includes: passing a mixture of ethanol and inert gas into the nitrided product at 500~700°C, wherein the volume fraction of ethanol is 55~65%, and reacting for 0.5~1.5 hours.

6. The method for preparing ultra-low impurity nitride powder according to claim 1, characterized in that, The microwave-induced dechlorination process includes: placing the nitrided product in a microwave reactor, introducing a mixture of NH3 and inert gas, and reacting for 15-30 minutes, wherein the volume fraction of NH3 is 8-12%, and the microwave power is 5-10 W / g.

7. The method for preparing ultra-low impurity nitride powder according to claim 1, characterized in that, In step S1, the purification and pretreatment of the raw material Al2O3 includes: immersing the raw material Al2O3 in a mixed solution of oxalic acid and hydrofluoric acid for gradient leaching to separate the pretreated Al2O3; wherein, the mixed solution of oxalic acid and hydrofluoric acid is prepared by adding a hydrofluoric acid solution with a volume fraction of 1.5-3% to an oxalic acid solution with a concentration of 0.4-0.6 mol / L, wherein the mass fraction of the hydrofluoric acid solution is 40%; the gradient leaching conditions are leaching at 75-85℃ for 1-3 hours, then cooling to 55-65℃ and leaching for 3-5 hours, wherein the liquid-solid ratio of the mixed solution to the raw material Al2O3 is 4-7 mL:1 g.

8. The method for preparing ultra-low impurity nitride powder according to claim 1, characterized in that, In step S1, the purification and pretreatment of the raw material SiO2 includes: placing the raw material SiO2 in a complex solution of citric acid and ammonia, stirring at 65-75°C for 2-4 hours, and then centrifuging to obtain the pretreated SiO2; wherein the liquid-to-solid ratio of the raw material SiO2 is 5-10 mL: 1 g.

9. The method for preparing ultra-low impurity nitride powder according to claim 1, characterized in that, The steps for purifying and pretreating the carbon source include: placing the carbon source in concentrated sulfuric acid, heating it to 160-200℃, reacting for 2-4 hours, cooling it down and removing it, and washing it to obtain the activated product; placing the activated product in a 3-8% EDTA solution, stirring it at 55-65℃ for 1-3 hours, and centrifuging it to obtain the pretreated carbon source.

10. A nitride powder with ultra-low impurities, characterized in that, Prepared by the preparation method according to any one of claims 1 to 9.

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