Method for deep boron removal from silicon carbide powder and silicon carbide feedstock

Abstract

The application discloses a method for deep boron removal of silicon carbide powder and silicon carbide raw material, which comprises the following steps: placing the silicon carbide raw material in a plasma reaction device, inputting a working gas and applying a plasma power source, and performing low-temperature plasma pretreatment to obtain pretreated silicon carbide raw material; wherein the working gas comprises at least one of inert gas and oxygen; mixing the pretreated silicon carbide raw material with deionized water to obtain a suspension, adjusting the pH to 4-8, adding a functionalized adsorption material for adsorption treatment, and performing solid-liquid separation to obtain silicon carbide powder; wherein the functionalized adsorption material comprises an adsorption material containing hydroxyl and / or amine groups. The application combines low-temperature plasma pretreatment with deep boron removal of the functionalized adsorption material, and synergistically achieves the effect of efficient, low-consumption and environmentally-friendly boron removal. The method has the characteristics of low energy consumption, small pollution and easy mass production, and is suitable for the preparation of low-boron silicon carbide powder for semi-insulating silicon carbide crystal growth.

Description

Technical Field

[0001] This application relates to the field of semiconductor material purification technology, specifically to a method for deep boron removal from silicon carbide powder and silicon carbide raw materials. Background Technology

[0002] Silicon carbide (SiC), as a third-generation wide-bandgap semiconductor material, possesses excellent properties such as a large bandgap, high thermal conductivity, and strong breakdown electric field, making it widely used in high-temperature, high-frequency, and high-power electronic devices. Semi-insulating silicon carbide crystals are key substrate materials for fabricating high-frequency microwave devices, and their quality directly affects device performance. Boron (B) is a common impurity in silicon carbide powder; if its content exceeds the standard (usually required to be ≤0.01ppm), it will cause the grown crystals to yellow, severely affecting their semi-insulating properties.

[0003] Existing methods for removing boron from silicon carbide raw materials mainly include high-temperature volatilization, acid leaching, and CVD purification. High-temperature volatilization requires temperatures above 2200℃, resulting in extremely high energy consumption and a tendency for powder sintering. Acid leaching uses concentrated acids (such as HF and aqua regia), causing severe pollution and having limited effectiveness in removing encapsulated boron. CVD purification is a gas-phase synthesis process with complex equipment and high costs, making it difficult to scale up for powder purification.

[0004] Therefore, the method for removing boron from silicon carbide raw materials needs further improvement.

[0005] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention

[0006] In a first aspect of this application, a method for deep boron removal from silicon carbide raw materials is proposed, comprising: placing the silicon carbide raw material in a plasma reaction device, introducing a working gas and applying a plasma power supply to perform low-temperature plasma pretreatment to obtain pretreated silicon carbide raw material; wherein the working gas includes at least one of an inert gas and oxygen; mixing the pretreated silicon carbide raw material with deionized water to obtain a suspension, adjusting the pH to 4-8, adding functionalized adsorbent material for adsorption treatment, and obtaining silicon carbide powder after solid-liquid separation, wherein the boron content in the silicon carbide powder is less than or equal to 0.005 ppm; wherein the functionalized adsorbent material includes adsorbent material containing hydroxyl and / or amine groups. This application combines low-temperature plasma pretreatment with deep boron removal using functionalized adsorption materials. First, the high-energy active particles of low-temperature plasma are used to destroy the oxide layer and impurity inclusions on the surface of silicon carbide raw materials, transforming shallow boron impurities into volatile or soluble forms. Then, functionalized adsorption materials are used to perform deep adsorption treatment on the dispersed silicon carbide raw material solution, selectively removing trace amounts of boron ions. This synergistic approach achieves efficient, low-consumption, and environmentally friendly boron removal, and the method is energy-efficient, low-polluting, and easy to mass-produce.

[0007] In some embodiments, the functionalized adsorbent material includes at least one of porous ceramics loaded with hydroxylated transition metal oxides, boron-removing resins, mesoporous molecular sieves loaded with hydroxylated Al₂O₃, and amino alcohol-modified graphene oxide-carbon nanotube composite aerogels; optionally, the functionalized adsorbent material includes porous ceramics loaded with hydroxylated transition metal oxides. This facilitates the selective adsorption of boron ions.

[0008] In some embodiments, the mass fraction of the hydroxylated transition metal oxide in the porous ceramic loaded with the hydroxylated transition metal oxide is 8%-15%. This prevents the pores of the porous ceramic support from being overly covered, ensuring the penetration of high-energy plasma particles and fully exposing the adsorption sites.

[0009] In some embodiments, the porous ceramic loaded with hydroxylated transition metal oxides includes at least one of porous ceramics loaded with hydroxylated ZrO2, porous ceramics loaded with hydroxylated TiO2, porous ceramics loaded with hydroxylated CeO2, porous ceramics loaded with hydroxylated HfO2, and porous ceramics loaded with hydroxylated Nb2O5; optionally, the porous ceramic loaded with hydroxylated transition metal oxides includes at least one of porous ceramics loaded with hydroxylated ZrO2 and porous ceramics loaded with hydroxylated TiO2. Therefore, the functionalized adsorbent materials are widely available and easy to promote on a large scale.

[0010] In some embodiments, the method for preparing the porous ceramic loaded with hydroxylated transition metal oxides includes: immersing the porous ceramic in a transition metal salt solution, drying it, sintering it, cooling it, and then immersing it in a hydroxylation solution to obtain the porous ceramic loaded with hydroxylated transition metal oxides. Thus, the hydroxyl groups on the surface of the porous ceramic loaded with hydroxylated transition metal oxides can react with B(OH)₄. - Transition metal ions bind to boron ions (B(OH)4) via hydrogen bonds or coordination bonds. - It easily forms stable coordination bonds, thereby achieving selective adsorption of boron ions.

[0011] In some embodiments, the transition metal salt solution includes at least one selected from ZrOCl2 solution, TiCl4 solution, Ce(NO3)3 solution, and HfCl4 solution; and / or, the concentration of the transition metal salt solution is 0.2 mol / L to 1.8 mol / L. Therefore, the raw materials are widely available and the cost is low, and the loading of transition metal oxides in porous ceramics can be controlled by adjusting the concentration of the transition metal salt solution.

[0012] In some embodiments, the sintering treatment is performed at a temperature of 500°C-600°C for 2-3 hours. This yields a highly active transition metal oxide crystal form and improves hydroxylation efficiency.

[0013] In some embodiments, the hydroxylation solution includes at least one of sodium hydroxide solution, hydrogen peroxide solution, and dilute hydrochloric acid solution. This allows the hydroxyl density on the transition metal oxide surface to be adapted to the plasma activation requirements.

[0014] In some embodiments, the mass ratio of the pretreated silicon carbide raw material to the deionized water is (1:5)-(1:20). This allows the water-soluble boron ions (B(OH)₄) in the silicon carbide raw material to be released. - BO3 3- The silicon carbide raw material is fully dissolved and dispersed in the liquid phase, reducing the agglomeration of silicon carbide raw materials that would cause boron ions to be encapsulated, and promoting effective contact between functionalized adsorbent materials and boron ions.

[0015] In some embodiments, the mass ratio of the functionalized adsorbent material to the pretreated silicon carbide raw material is (1:10) to (1:50). This is beneficial for improving the adsorption efficiency of boron ions.

[0016] In some embodiments, the adsorption treatment is performed at a temperature of 20°C to 60°C for a duration of 1 hour to 4 hours. This provides mild adsorption conditions, avoiding sintering or structural damage to the silicon carbide raw material caused by high temperatures.

[0017] In some embodiments, the temperature of the low-temperature plasma pretreatment is 500℃-800℃, and the time is 0.5h-2h. This facilitates the breaking of chemical bonds in the oxide layer (such as SiO2) on the surface of silicon carbide raw materials, disrupts the dense structure encapsulating boron impurities, and exposes shallow boron impurities; at the same time, it promotes the reaction between the low-temperature plasma and the exposed boron impurities (B, B2O3), achieving morphological transformation.

[0018] In some embodiments, the inert gas includes at least one of argon, helium, neon, and an argon-helium mixture; optionally, the inert gas is argon. This facilitates the formation of high-energy active particles, which, through high-energy impact, destroy the surface oxide layer and impurity inclusions, directly exposing the shallow B and B2O3 layers.

[0019] In some embodiments, the working gas includes at least one of argon, oxygen, and an argon-oxygen mixture with a purity greater than or equal to 99.999%; optionally, the volume ratio of argon to oxygen in the argon-oxygen mixture is (1:1) to (5:1). This facilitates the formation of a suitable amount of... O (oxygen free radical) OH (hydroxyl radical) and Ar + (Argon ions), thereby improving boron removal efficiency.

[0020] In some embodiments, the boron-removing resin includes Tulsimer CH-99 resin or HP119 resin. Thus, the hydroxyl and amino groups in the functional groups (such as N-methylglucosamine groups) on the surface of the boron-removing resin can react with B(OH)4. - It forms bidentate or polydentate coordination bonds, and its binding force on boron ions is much stronger than that on other ions in solution (such as Si). 4+ Na + Cl - This enables the selective capture of boron ions.

[0021] In some embodiments, the boron content in the silicon carbide raw material is 0.1 ppm to 1 ppm, and / or the particle size of the silicon carbide raw material is 1 μm to 50 μm. Therefore, the silicon carbide raw material has a certain purity and high powder sintering activity.

[0022] In some embodiments, the method further includes: soaking the boron-adsorbed functionalized adsorbent material in an acid solution, and washing it with deionized water until neutral to obtain the functionalized adsorbent material; optionally, the acid solution includes at least one selected from sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, and citric acid. This allows for the desorption of adsorbed boron ions, thereby regenerating the functionalized adsorbent material.

[0023] In a second aspect of this application, a silicon carbide powder is provided, prepared using the method described in the first aspect of this application, wherein the boron content of the silicon carbide powder is less than or equal to 0.005 ppm. Therefore, the silicon carbide powder has high purity. Attached Figure Description

[0024] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, wherein, Figure 1 This is a process flow diagram of one embodiment of this application; Figure 2 This is a process apparatus diagram of one embodiment of this application.

[0025] Explanation of reference numerals in the attached figures: 1-Powder silo, 2-Screw feeder, 3-Plasma reaction device, 4-Stirring tank, 5-Functionalized adsorbent material, 6-Centrifugal filter, 7-Vacuum dryer. Detailed Implementation

[0026] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0027] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0028] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0029] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0030] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0031] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0032] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0033] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0034] This application combines low-temperature plasma pretreatment with deep boron removal using functionalized adsorption materials. First, the high-energy active particles of low-temperature plasma are used to destroy the oxide layer and impurity inclusions on the surface of silicon carbide raw materials, transforming shallow boron impurities into volatile or soluble forms. Then, functionalized adsorption materials are used to perform deep adsorption treatment on the dispersed silicon carbide raw material solution, selectively removing trace amounts of boron ions. This synergistic approach achieves efficient, low-consumption, and environmentally friendly boron removal, and the method is energy-efficient, low-polluting, and easy to mass-produce.

[0035] In the first aspect of this application, a method for deep boron removal from silicon carbide raw materials is proposed, referring to... Figure 1 The method includes: S1: Place silicon carbide raw material in a plasma reaction device, introduce working gas and apply plasma power to perform low-temperature plasma pretreatment to obtain pretreated silicon carbide raw material; wherein, the working gas includes at least one of inert gas and oxygen.

[0036] In some embodiments, the temperature of the low-temperature plasma pretreatment is 500℃-800℃ (e.g., 500℃, 600℃, 700℃, or 800℃), and the time is 0.5h-2h (e.g., 0.5h, 1h, 1.5h, or 2h). This facilitates breaking the chemical bonds of the oxide layer (e.g., SiO2) on the surface of the silicon carbide raw material, disrupting the dense structure encapsulating boron impurities, and exposing the shallow boron impurities; simultaneously, it promotes the reaction between the low-temperature plasma and the exposed boron impurities (B, B2O3), achieving morphological transformation.

[0037] In some embodiments, the inert gas includes at least one of argon, helium, neon, and an argon-helium mixture; optionally, the inert gas is argon. This facilitates the formation of high-energy active particles, which, through high-energy impact, destroy the surface oxide layer and impurity inclusions, directly exposing the shallow B and B2O3 layers.

[0038] In some embodiments, the working gas includes at least one of argon, oxygen, and an argon-oxygen mixture with a purity greater than or equal to 99.999%; optionally, the volume ratio of argon to oxygen in the argon-oxygen mixture is (1:1) to (5:1), for example, (1:1), (2:1), (3:1), (4:1), or (5:1), etc. This facilitates the formation of a suitable amount of... O (oxygen free radical) OH (hydroxyl radical) and Ar + (Argon ions), thereby improving boron removal efficiency.

[0039] The physicochemical reactions occurring in the O2 atmosphere and the Ar-O2 mixed atmosphere are as follows: The reaction of elemental boron with oxygen free radicals: 4B + 3 O2→2B2O3 (The generated B2O3 has a high vapor pressure at 500℃-800℃ and is easily volatilized into vapor, which is then removed by a vacuum pump). Boron oxide conversion: If B2O3 is present on the surface of silicon carbide raw material, the plasma in... OH can react with it: B₂O₃ + 2g OH + H₂O → 2B(OH)₄ - (The generated B(OH)4) - It is readily soluble in water, laying the foundation for subsequent adsorption treatment to remove boron. Surface oxide layer treatment: O reacts weakly with SiO2 on the surface of silicon carbide raw materials, but high-energy Ar reacts more strongly. + Some SiO2 can be physically stripped away, further breaking down impurity inclusions. The reaction can be simplified to: SiO2 + Ar + →SiO2 (stripping) + Ar (the stripped SiO2 is discharged with the exhaust gas).

[0040] The reaction in an Ar atmosphere is: Ar + It mainly plays a physical role, using high-energy impact to break the chemical bonds and dense structure of impurity inclusions in the oxide layer (such as SiO2) on the surface of silicon carbide raw materials, thus directly exposing shallow boron impurities (B, B2O3). Although no direct chemical transformation occurs, it creates conditions for the dissolution or volatilization of B2O3 if a trace amount of O2 is introduced or during subsequent water washing.

[0041] The principle of plasma generation and action during low-temperature plasma pretreatment is as follows: After introducing high-purity (≥99.999%) Ar, O2, or a mixed gas, an radio frequency or microwave power supply (500W-2000W) provides energy to ionize the gas molecules, forming plasma containing... O (oxygen free radical) OH (hydroxyl radical), Ar + Low-temperature plasmas such as argon ions. These high-energy active particles (typically with energies of several to tens of electron volts) have extremely strong chemical activity and kinetic energy, and can directly impact the surface of silicon carbide raw materials, producing physical and chemical reactions.

[0042] As an example, the specific steps of low-temperature plasma pretreatment include: placing the silicon carbide raw material in the reaction chamber of the plasma reactor, closing the reaction chamber and evacuating it to 10Pa-100Pa, introducing a working gas (Ar, O2 or a mixture thereof with a purity ≥99.999%), and controlling the gas flow rate to 100sccm-500sccm. Turning on the plasma power supply and adjusting the power to 500W-2000W, heating to 500℃-800℃ at a rate of 5℃ / min-10℃ / min, and holding at this temperature for 0.5 hours-2 hours. After treatment, turning off the power supply, allowing it to cool naturally to room temperature, and then removing the pretreated silicon carbide raw material.

[0043] This application utilizes the aforementioned low-temperature plasma pretreatment to efficiently destroy the oxide layer (SiO2) and boron impurity inclusions on the surface of silicon carbide raw materials, effectively solving the problem of difficult-to-remove encapsulated impurities and opening a "channel" for subsequent boron impurity treatment; simultaneously, it can convert shallow boron impurities (B, B2O3) into easily volatile (B2O3 vapor) or easily soluble in water (B(OH)4) -To achieve pre-boron removal, a portion of the volatile B2O3 is first removed using a vacuum pump, reducing the processing load for subsequent adsorption treatment. The surface roughness of the treated silicon carbide raw material increases slightly, and a small amount of hydrophilic groups remain (such as...). (OH) can improve the dispersibility in deionized water and ensure sufficient contact between the functionalized adsorbent material and boron ions.

[0044] S2: The pretreated silicon carbide raw material is mixed with deionized water to obtain a suspension. The pH is adjusted to 4-8, and functionalized adsorbent material is added for adsorption treatment. After solid-liquid separation, silicon carbide powder is obtained. The boron content in the silicon carbide powder is less than or equal to 0.005 ppm. The functionalized adsorbent material includes adsorbent material containing hydroxyl and / or amine groups.

[0045] In some embodiments, the reagents used to adjust the pH include 0.1 mol / L to 1 mol / L HCl solution or NaOH solution. When the pH is in the range of 4-8, boron mainly exists as B(OH)4. - (Mainly present at pH > 7) and H3BO3 (Mainly present at pH < 7, can partially dissociate into B(OH)4) - Both of these forms readily combine with the active groups of functionalized adsorbent materials. Furthermore, the hydroxyl groups (-OH) on the porous ceramic surface loaded with hydroxylated transition metal oxides exhibit suitable ionization at pH 4-8, and the negatively charged -OH... - Can be combined with B(OH)4 - Boron ions are bound by hydrogen bonds or coordination bonds; at this pH, the functional groups (such as amine groups and hydroxyl groups) of boron-removing resins (such as Tulsimer CH-99) are in an activated state, and their selective adsorption capacity for boron ions is the strongest.

[0046] In some embodiments, the functionalized adsorbent material includes at least one of porous ceramics loaded with hydroxylated transition metal oxides, boron-removing resins, mesoporous molecular sieves loaded with hydroxylated Al₂O₃, and amino alcohol-modified graphene oxide-carbon nanotube composite aerogels; optionally, the functionalized adsorbent material includes porous ceramics loaded with hydroxylated transition metal oxides. This facilitates the selective adsorption of boron ions.

[0047] In some embodiments, the mass fraction of the hydroxylated transition metal oxide in the porous ceramic loaded with the hydroxylated transition metal oxide is 8%-15%, for example, it can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%. It is understood that the adsorption treatment is closely related to the low-temperature plasma pretreatment. The 8%-15% mass fraction limit is a customized parameter design for the low-temperature plasma synergistic mechanism. Its core function is to ensure the penetration of high-energy plasma particles and the activation of adsorption sites, ultimately achieving a synergistic boron removal effect of "plasma-activated boron + adsorption site-captured boron".

[0048] In some embodiments, the porous ceramic loaded with hydroxylated transition metal oxides includes at least one of porous ceramics loaded with hydroxylated ZrO2, porous ceramics loaded with hydroxylated TiO2, porous ceramics loaded with hydroxylated CeO2, porous ceramics loaded with hydroxylated HfO2, and porous ceramics loaded with hydroxylated Nb2O5; optionally, the porous ceramic loaded with hydroxylated transition metal oxides includes at least one of porous ceramics loaded with hydroxylated ZrO2 and porous ceramics loaded with hydroxylated TiO2. Therefore, the functionalized adsorbent materials are widely available and easy to promote on a large scale.

[0049] During the adsorption process, functionalized adsorbent materials achieve selective adsorption of boron ions through coordination bonds: (1) Taking porous ceramics loaded with hydroxylated ZrO2 as an example, Zr 4+ It is a hard acid, containing boron ions (B(OH)4). - Zr is a hard base, and according to the "hard acid-base theory," the two readily form a stable coordinate bond, i.e., Zr 4+ + 4B(OH)4 - →[Zr(B(OH)4)4] (adsorbed state); (2) Boron removal resin: The hydroxyl and amino groups in the functional groups (such as N-methylglucosamine groups) on the surface of the resin can react with B(OH)4 - It forms bidentate or polydentate coordination bonds, and its binding force on boron ions is much stronger than that on other ions in solution (such as Si). 4+ Na + Cl - This enables selective capture.

[0050] The physicochemical reactions that occur during the adsorption process are as follows: (1) Adsorption reaction of porous ceramics loaded with hydroxylated ZrO2: ZrO2 (surface) -OH + B(OH)4 - ZrO2 (surface) - OB(OH)3 + H2O (the reaction is reversible and can proceed in reverse under acidic conditions, providing a basis for the regeneration of subsequent functionalized adsorption materials). (2) Adsorption reaction of boron removal resin (such as Tulsimer CH-99): The N-methylglucosamine group on the resin surface (represented by R-NH-CH2-(CHOH)4-CH2OH) reacts with (OH)4 - reaction: R-NH-CH2-(CHOH)4-CH2OH+B(OH)4 - R-NH-CH2-(CHOH)4-CH2O-B(OH)3+OH - (To form a stable five- or six-membered ring coordination structure, ensuring that boron ions are firmly adsorbed). (3) pH adjustment auxiliary reaction: If HCl is used to adjust the pH, OH- will be generated. - + H + =H₂O (neutralizes residual alkaline groups on the surface of silicon carbide raw materials and controls the pH of the suspension); if NaOH is used for adjustment, H₂O will be generated. + + OH - =H2O (neutralizes acidic groups, preventing excessive acidity from causing B(OH)4) - (It is converted into H3BO3, thus reducing adsorption efficiency).

[0051] In some embodiments, the method for preparing the porous ceramic loaded with hydroxylated transition metal oxides includes: immersing the porous ceramic in a transition metal salt solution, drying it, sintering it, cooling it, and then immersing it in a hydroxylation solution to obtain the porous ceramic loaded with hydroxylated transition metal oxides. Thus, the hydroxyl groups on the surface of the porous ceramic loaded with hydroxylated transition metal oxides can react with B(OH)₄. - Transition metal ions bind to boron ions (B(OH)4) via hydrogen bonds or coordination bonds. - It easily forms stable coordination bonds, thereby achieving selective adsorption of boron ions.

[0052] In some embodiments, the transition metal salt solution includes at least one selected from ZrOCl2 solution, TiCl4 solution, Ce(NO3)3 solution, and HfCl4 solution; and / or, the concentration of the transition metal salt solution is 0.2 mol / L-1.8 mol / L, for example, 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, or 1.8 mol / L. Therefore, the raw materials are widely available and the cost is low, and the loading of transition metal oxides in porous ceramics can be controlled by adjusting the concentration of the transition metal salt solution.

[0053] In some embodiments, the sintering treatment is performed at a temperature of 500°C-600°C (e.g., 500°C, 520°C, 540°C, 560°C, 580°C, or 600°C) for 2 hours to 3 hours (e.g., 2 hours, 2.5 hours, or 3 hours). This allows for the acquisition of highly active transition metal oxide crystal forms and improves hydroxylation efficiency.

[0054] In some embodiments, the hydroxylation solution includes at least one of sodium hydroxide solution, hydrogen peroxide solution, and dilute hydrochloric acid solution. The specific choice depends on the type of transition metal oxide being loaded: for example, a 0.1 mol / L-0.3 mol / L sodium hydroxide solution is used when loading ZrO2 or TiO2, a 5%-10% hydrogen peroxide solution is used when loading CeO2, and a 0.05 mol / L dilute hydrochloric acid solution is used when loading Nb2O5. This allows the hydroxyl density on the transition metal oxide surface to be adapted to the plasma activation requirements.

[0055] As an example, the preparation method of porous ceramics loaded with hydroxylated ZrO2 includes: immersing a porous ceramic support in a 0.5 mol / L-1.5 mol / L ZrOCl2 solution, sonicating for 30 min-60 min, removing it and drying it at 100℃-120℃ for 2 h-4 h, then sintering it at 500℃-600℃ for 2 h-3 h, cooling it and soaking it in a 0.1 mol / L-0.5 mol / L NaOH solution for 1 h-2 h, washing it with deionized water until neutral, to obtain porous ceramics with hydroxylated ZrO2 loaded on the surface.

[0056] In some embodiments, the mass ratio of the pretreated silicon carbide raw material to the deionized water is (1:5)-(1:20), for example, it can be 1:5, 1:8, 1:10, 1:13, 1:15, 1:18, or 1:20. This allows the water-soluble boron ions (B(OH)4) in the silicon carbide raw material to be released. - BO3 3- The silicon carbide raw material is fully dissolved and dispersed in the liquid phase, reducing the agglomeration of silicon carbide raw materials that would cause boron ions to be encapsulated, and promoting effective contact between functionalized adsorbent materials and boron ions.

[0057] In some embodiments, the mass ratio of the functionalized adsorbent material to the pretreated silicon carbide raw material is (1:10)-(1:50), for example, it can be 1:10, 1:20, 1:30, 1:40 or 1:50. This is beneficial to improving the adsorption efficiency of boron ions.

[0058] In some embodiments, the adsorption treatment is performed at a temperature of 20°C-60°C (e.g., 20°C, 30°C, 40°C, 50°C, or 60°C) for a time of 1 hour-4 hours (e.g., 1 hour, 2 hours, 3 hours, or 4 hours). This provides mild adsorption conditions, avoiding the sintering or structural damage of the silicon carbide raw material caused by high temperatures.

[0059] In some embodiments, the boron-removing resin includes Tulsimer CH-99 resin or HP119 resin. Thus, the hydroxyl and amino groups in the functional groups (such as N-methylglucosamine groups) on the surface of the boron-removing resin can react with B(OH)4. - It forms bidentate or polydentate coordination bonds, and its binding force on boron ions is much stronger than that on other ions in solution (such as Si). 4+ Na + Cl - This enables the selective capture of boron ions.

[0060] As an example, the specific steps of the adsorption treatment include: dispersing the silicon carbide raw material treated in step S1 in deionized water, stirring to form a suspension with a solid-liquid ratio of 1:5-1:20, and adjusting the pH to 4-8 with 0.1mol / L-1mol / L HCl or NaOH solution. Adding functionalized adsorbent material at a mass ratio of 1:10-1:50 to the silicon carbide raw material, and stirring at 20℃-60℃ for 1-4 hours for adsorption. During adsorption, the active groups (such as hydroxyl groups) on the surface of the functionalized adsorbent material react with boron ions (BO3+) in the solution. 3- B(OH)4 - Stable coordination bonds are formed to achieve selective adsorption. After adsorption, the silicon carbide powder and functionalized adsorbent are separated by centrifugation or filtration. The silicon carbide powder is then vacuum dried at 80℃-120℃ for 4-6 hours to obtain low-boron silicon carbide powder.

[0061] This application utilizes functionalized adsorption materials to precisely capture trace amounts of boron ions in silicon carbide raw material suspensions (reducing the concentration from 0.03ppm-0.04ppm after low-temperature plasma pretreatment to below 0.005ppm), achieving precise boron removal and meeting the stringent boron content requirements (≤0.01ppm) for semi-insulating silicon carbide crystal growth. The functionalized adsorption materials adsorb only boron ions and do not react with other harmless ions in the silicon carbide raw material or solution (such as Si). 4+ This reaction reduces the introduction of new impurities and improves the purity of the powder.

[0062] In some embodiments, the method further includes step S3, regeneration of the functionalized adsorbent material: soaking the boron-adsorbed functionalized adsorbent material in an acid solution, washing with deionized water until neutral, to obtain the functionalized adsorbent material; optionally, the acid solution includes at least one of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, and citric acid. Specifically, nitric acid is preferred for amine-based adsorbents (to avoid strong oxidizing agents damaging the amine groups), and hydrochloric acid is preferred for transition metal oxide adsorbents (due to its high desorption efficiency). This allows the adsorbed boron ions to desorb, achieving regeneration of the functionalized adsorbent material.

[0063] In some embodiments, the concentration of the acid solution is 0.1 mol / L to 1.5 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L or 1.5 mol / L, etc.

[0064] In some embodiments, the soaking time is 2h-4h, for example, 2h, 3h or 4h.

[0065] In some embodiments, the desorbed functionalized adsorbent material can be reused in the adsorption process of step S2, with a regeneration count of ≥50 times.

[0066] The principle of regenerating functionalized adsorbent materials is "strong acid desorption": during the adsorption process, the coordination bonds formed between the functionalized adsorbent materials and boron ions are activated by high concentrations of H+. + Fractures can occur under certain conditions, H + As the concentration increases, it binds to active groups (such as -OH and amine groups) on the surface of functionalized adsorbent materials, while simultaneously competing with boron ions for coordination sites, causing boron ions to desorb from the surface of the functionalized adsorbent material and re-enter the solution (forming H3BO3); in addition, H2SO4 provides SO42-. 2- It does not react with the adsorbent, nor does it form a precipitate with boron ions. It can be completely removed by subsequent water washing, thus avoiding the occupation of the active sites of the functionalized adsorbent material.

[0067] The physicochemical reactions that occur during the desorption process of functionalized adsorbent materials are as follows: (1) Desorption of porous ceramics loaded with hydroxylated transition metal oxides: Taking porous ceramics loaded with hydroxylated ZrO2 as an example, ZrO2(surface)-OB(OH)3+H2SO4→ZrO2(surface)-OH+H3BO3+HSO4 (H) + (Breaking the Zr-OB coordination bond generates water-soluble H3BO3, which is removed with the eluent). (2) Desorption of boron removal resin: R-NH-CH2-(CHOH)4-CH2O-B(OH)3+H2SO4→R-NH-CH2-(CHOH)4-CH2OH+H3BO3+HSO4 - (H) + (The resin breaks the -OB coordination bond, the resin restores its active groups, and boron ions enter the solution as H3BO3). (3) Water washing and neutralization reaction: After desorption, the functionalized adsorbent material is washed with deionized water until neutral, mainly to remove residual H+. + and SO4 2- The reaction is H + + OH - = H2O (trace amounts of OH in water) - With H + Neutralization), SO4 2- + 2H + + 2OH - =H₂SO₄ + 2OH⁻ - (final SO4) 2- (After being discharged with the washing solution, the surface of the functionalized adsorbent material returns to a neutral and active state).

[0068] In some embodiments, refer to Figure 2 The method for deep boron removal from silicon carbide raw materials includes: placing the silicon carbide raw material in the powder silo 1, and feeding the silicon carbide raw material into the plasma reaction chamber 3 through the screw feeder 2 for low-temperature plasma pretreatment. The pretreated suspension enters the stirring tank 4, where functionalized adsorbent material 5 is added for adsorption treatment. After adsorption treatment, the material is filtered using a centrifugal filter 6, and finally dried using a vacuum dryer 7 to obtain silicon carbide powder.

[0069] This application achieves a regeneration rate of ≥50 times for functionalized adsorbent materials through desorption treatment, significantly reducing their consumption and lowering consumable costs in industrial production. Compared to single-use adsorbents, the cost can be reduced by more than 80%. Simultaneously, it reduces the amount of saturated functionalized adsorbent materials becoming hazardous solid waste, thus reducing solid waste emissions and meeting green and environmentally friendly production requirements. Furthermore, the regenerated functionalized adsorbent materials retain an adsorption efficiency of over 90% of their initial value, allowing for stable and repeated use in deep boron removal steps. This ensures consistent boron removal performance in batch production, reduces performance fluctuations of the functionalized adsorbent materials, and improves the quality stability of silicon carbide powder.

[0070] In a second aspect of this application, a silicon carbide powder is provided, prepared using the method described in the first aspect of this application. The boron content in the silicon carbide powder is less than or equal to 0.005 ppm, for example, it can be 0.001 ppm, 0.002 ppm, 0.003 ppm, 0.004 ppm, or 0.005 ppm, etc. Therefore, the silicon carbide powder has high purity.

[0071] The method for deep boron removal from silicon carbide raw materials described in this application has at least the following beneficial effects: (1) High boron removal efficiency: This application achieves the synergistic effect of "coarse removal + fine removal" through a combination process of "low-temperature plasma pretreatment + functionalized adsorption material adsorption treatment". Low-temperature plasma pretreatment breaks down surface inclusions and releases shallow boron; functionalized adsorption materials deeply capture trace amounts of boron, with a total boron removal rate of over 99%, which can reduce the boron content of silicon carbide raw materials from 0.1ppm-1ppm to below 0.005ppm, meeting the requirements for the growth of semi-insulating silicon carbide crystals; (2) Green and environmentally friendly: The temperature of low-temperature plasma treatment is only 500℃-800℃, and the energy consumption is reduced by more than 70% compared with the traditional high-temperature volatilization method. The working gas is non-toxic. The adsorption treatment process adopts a neutral water system to replace concentrated acid leaching, reducing wastewater discharge by 90%. The functional adsorption material can be recycled, which is conducive to reducing solid waste pollution.

[0072] (3) Easy to mass produce: The plasma reaction device can be designed as a continuous fluidized bed (with a processing capacity of up to 100 kg / h), and the adsorption treatment adopts a stirred tank or a fixed bed reactor, which can be connected to the existing powder production line; the process parameters are stable and controllable, and are suitable for large-scale industrial production.

[0073] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0074] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0075] Example 1 Step 1: Take 1 kg of SiC raw material with an initial boron content of 0.5 ppm and a particle size of 20 μm, place it in a radio frequency plasma reactor, evacuate to 50 Pa, and introduce a mixed gas of Ar and O2 (volume ratio 3:1) at a flow rate of 300 sccm. The power is 1000 W, the temperature is increased to 600℃ at 8℃ / min, held at that temperature for 1 hour, and after cooling, the boron content is measured to be 0.03 ppm.

[0076] Step 2: Disperse the pretreated SiC raw material in 10 L of deionized water, adjust the pH to 6 with 0.5 mol / L HCl, add 100 g of porous ceramic loaded with hydroxylated ZrO2 (the mass fraction of hydroxylated ZrO2 in the porous ceramic loaded with hydroxylated ZrO2 is 10%, prepared according to the aforementioned method), and stir at 40℃ for 2 hours for adsorption. After filtration and drying, the boron content was measured to be 0.004 ppm, and the boron removal rate was 99.2%.

[0077] Regeneration performance: After being regenerated 50 times with 1 mol / L H2SO4, the above-mentioned functionalized adsorbent material still retains more than 90% of its initial adsorption efficiency.

[0078] Conclusion: Radio frequency plasma treatment breaks down the surface coating of SiC raw materials, converting shallow boron into a readily soluble form (such as B(OH)4). - Hydroxylated ZrO2 selectively adsorbs trace amounts of boron ions through coordination bonds, and the two work together to achieve deep boron removal; during the regeneration of the functionalized adsorbent material, H2SO4 breaks the coordination bonds and restores the active sites, so that after 50 regenerations, the adsorption efficiency still remains above 90% of the initial value.

[0079] The energy consumption of Example 1 was measured to be 3 × 10⁻⁶. 3 kWh / ton, wastewater COD value is 516mg / L.

[0080] Example 2 Step 1: Take 2 kg of SiC raw material with an initial boron content of 1 ppm and a particle size of 5 μm, and treat it with microwave plasma (pure O2, flow rate of 200 sccm, power of 1500 W, heat treatment at 700℃ for 1.5 hours). After treatment, the boron content is 0.04 ppm.

[0081] Step 2: Disperse the pretreated SiC raw material in 20 L of water, adjust the pH to 7, add 400g of TulsimerCH-99 resin, and adsorb at 50℃ for 3 hours. The final boron content is 0.003 ppm, and the boron removal rate is 99.7%.

[0082] Conclusion: Microwave plasma has more concentrated energy, and the pure O2 atmosphere enhances the conversion of boron to B2O3 (easily soluble / volatile); the functional groups of Tulsimer CH-99 resin (such as N-methylglucosamine) have a stronger coordination ability for boron ions, resulting in more thorough adsorption.

[0083] Example 3 The difference from Example 1 is as follows: Step 2: Replace the porous ceramic loaded with hydroxylated ZrO2 with a mesoporous molecular sieve loaded with hydroxylated Al2O3.

[0084] Conclusion: The use of mesoporous molecular sieves loaded with hydroxylated Al2O3 for adsorption treatment in Example 3 has low energy consumption and low COD value of wastewater, and has cost and environmental advantages for industrial application, making it suitable for large-scale boron removal from SiC raw materials.

[0085] The energy consumption of Example 3 was measured to be 4 × 10⁻⁶. 3 kWh / ton, wastewater COD value is 534mg / L.

[0086] Example 4 The difference from Example 1 is as follows: Step 2: Replace the porous ceramic loaded with hydroxylated ZrO2 with amino alcohol modified graphene oxide-carbon nanotube composite aerogel.

[0087] Conclusion: In Example 4, the adsorption treatment using amino alcohol-modified graphene oxide-carbon nanotube composite aerogel showed the best boron removal effect (99.8% boron removal rate). The high specific surface area and porosity provide sufficient adsorption sites, and the hydroxyl and amino groups of the amino alcohol can synergistically complex boron. At the same time, low-temperature plasma pretreatment can further activate its surface active sites and enhance the synergistic boron removal efficiency.

[0088] The energy consumption of Example 4 was measured to be 2.1 × 10⁻⁶. 3 kWh / ton, wastewater COD value is 468mg / L.

[0089] Comparative Example 1 The single plasma method, performing only step 1 of Example 1 without adsorption treatment, resulted in a final boron content of 0.03 ppm and a boron removal rate of 94% (which does not meet the requirement of ≤0.01 ppm).

[0090] Conclusion: Plasma treatment alone cannot remove deep lattice boron and cannot capture dissolved trace boron ions, thus failing to achieve deep boron removal.

[0091] Comparative Example 2 The single adsorption method, without low-temperature plasma pretreatment, directly treats SiC raw material with an initial boron content of 0.5 ppm according to step 2 of Example 1, resulting in a final boron content of 0.05 ppm and a boron removal rate of 90% (the surface oxide layer hinders adsorption).

[0092] Conclusion: Without plasma pretreatment, the oxide layer and impurity inclusions on the surface of SiC raw materials hinder the contact between functionalized adsorbent materials and boron, making it impossible to effectively capture encapsulated boron and resulting in low adsorption efficiency.

[0093] Comparative Example 3 The traditional high-temperature volatilization method treats SiC raw material with an initial boron content of 0.5 ppm at 2300℃ in an Ar atmosphere for 4 hours, resulting in a final boron content of 0.02 ppm and a boron removal rate of 96%. However, the energy consumption reaches 1.2 × 10⁻⁶. 4 kWh / ton (4 times that of Example 1), and 30% of the SiC raw material was sintered.

[0094] Conclusion: Although high temperature can volatilize some boron, it cannot remove trace amounts of residual boron; the high temperature of 2300℃ leads to the sintering of SiC raw materials, and the energy consumption of the high temperature process increases dramatically.

[0095] Comparative Example 4 The traditional acid leaching method uses a mixture of 10% HF and 20% HNO3 to leach SiC raw material with an initial boron content of 0.5 ppm (80°C, 2 hours), resulting in a final boron content of 0.08 ppm, a boron removal rate of 84%, and a wastewater COD value of 6200 mg / L (12 times that of Example 1).

[0096] Conclusion: Concentrated acid has difficulty penetrating encapsulated boron impurities, resulting in incomplete boron removal; acid leaching generates a large amount of fluorine- and nitrogen-containing wastewater, causing serious pollution, and the acid solution easily corrodes the surface of SiC raw materials.

[0097] The specific data for the above embodiments and comparative examples are shown in Table 1.

[0098] Table 1

[0099] Examples 1-4 employ a combined process of "low-temperature plasma pretreatment + deep boron removal using functionalized adsorption materials," achieving boron removal rates of 99.2%, 99.7%, 99.0%, and 99.8%, respectively. The final boron content in each example is significantly lower than industry requirements, with low energy consumption and minimal pollution. Comparative Example 1 suffers from problems such as low boron removal rate, substandard final boron content, high energy consumption, and severe pollution due to the limitations of the surface coating layer in the single adsorption method. Comparative Example 3 suffers from high energy consumption and inability to remove trace amounts of boron using the traditional high-temperature volatilization method. Comparative Example 4 suffers from incomplete boron removal and significant pollution due to the traditional acid leaching method. All these examples exhibit problems such as low boron removal rate, substandard final boron content, high energy consumption, and severe pollution. In summary, the combined boron removal method of this application is significantly superior to single or traditional processes in terms of boron removal efficiency, energy consumption control, and environmental friendliness.

[0100] This application solves the problems of high energy consumption, high pollution, and incomplete boron removal of traditional methods by combining "low-temperature plasma pretreatment + functional adsorption". The boron removal rate is >99%, and the boron content can be stably reduced to below 0.005ppm. It is also green and environmentally friendly, easy to mass-produce, and suitable for the industrial preparation of low-boron powder for semi-insulating SiC crystal growth.

[0101] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for deep boron removal from silicon carbide raw materials, characterized in that, include: Silicon carbide raw material is placed in a plasma reaction device, a working gas is introduced and a plasma power supply is applied to perform low-temperature plasma pretreatment to obtain pretreated silicon carbide raw material; wherein, the working gas includes at least one of an inert gas and oxygen; The pretreated silicon carbide raw material is mixed with deionized water to obtain a suspension. The pH is adjusted to 4-8, and functionalized adsorbent material is added for adsorption treatment. After solid-liquid separation, silicon carbide powder is obtained. The boron content in the silicon carbide powder is less than or equal to 0.005 ppm. The functionalized adsorbent material includes adsorbent materials containing hydroxyl and / or amine groups.

2. The method according to claim 1, characterized in that, The functionalized adsorption material includes at least one of the following: porous ceramics loaded with hydroxylated transition metal oxides, boron-free resins, mesoporous molecular sieves loaded with hydroxylated Al2O3, and amino alcohol-modified graphene oxide-carbon nanotube composite aerogels. Optionally, the functionalized adsorbent material comprises a porous ceramic loaded with hydroxylated transition metal oxides.

3. The method according to claim 2, characterized in that, The mass fraction of the hydroxylated transition metal oxide in the porous ceramic loaded with hydroxylated transition metal oxide is 8%-15%.

4. The method according to claim 2, characterized in that, The porous ceramics loaded with hydroxylated transition metal oxides include at least one of the following: porous ceramics loaded with hydroxylated ZrO2, porous ceramics loaded with hydroxylated TiO2, porous ceramics loaded with hydroxylated CeO2, porous ceramics loaded with hydroxylated HfO2, and porous ceramics loaded with hydroxylated Nb2O5. Optionally, the porous ceramic loaded with hydroxylated transition metal oxides includes at least one of porous ceramic loaded with hydroxylated ZrO2 and porous ceramic loaded with hydroxylated TiO2.

5. The method according to claim 4, characterized in that, The method for preparing the porous ceramic loaded with hydroxylated transition metal oxides includes: immersing the porous ceramic in a transition metal salt solution, drying it and then sintering it, cooling it and then immersing it in a hydroxylation solution to obtain the porous ceramic loaded with hydroxylated transition metal oxides.

6. The method according to claim 5, characterized in that, The transition metal salt solution includes at least one of ZrOCl2 solution, TiCl4 solution, Ce(NO3)3 solution, and HfCl4 solution; and / or, The concentration of the transition metal salt solution is 0.2 mol / L to 1.8 mol / L; and / or, The sintering treatment is performed at a temperature of 500℃-600℃ for 2-3 hours; and / or, The hydroxylation solution includes at least one of sodium hydroxide solution, hydrogen peroxide solution, and dilute hydrochloric acid solution.

7. The method according to claim 1, characterized in that, The mass ratio of the pretreated silicon carbide raw material to the deionized water is (1:5)-(1:20); and / or, The mass ratio of the functionalized adsorbent material to the pretreated silicon carbide raw material is (1:10)-(1:50); and / or, The adsorption treatment is performed at a temperature of 20℃-60℃ for 1h-4h.

8. The method according to claim 1, characterized in that, The low-temperature plasma pretreatment is performed at a temperature of 500℃-800℃ for a time of 0.5h-2h.

9. The method according to claim 1, characterized in that, The inert gas includes at least one of argon, helium, neon, and argon-helium mixture. Optionally, the inert gas is argon.

10. The method according to claim 9, characterized in that, The working gas includes at least one of argon, oxygen, and argon-oxygen mixture with a purity greater than or equal to 99.999%. Optionally, the volume ratio of argon to oxygen in the argon-oxygen mixture is (1:1) to (5:1).

11. The method according to claim 2, characterized in that, The boron-removing resin includes Tulsimer CH-99 resin or HP119 resin.

12. The method according to claim 1, characterized in that, The boron content in the silicon carbide raw material is 0.1ppm-1ppm, and / or the particle size of the silicon carbide raw material is 1μm-50μm.

13. The method according to claim 1, characterized in that, Also includes: The functionalized adsorbent material containing boron is soaked in an acid solution and washed with deionized water until neutral to obtain the functionalized adsorbent material. Optionally, the acid solution includes at least one of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, and citric acid.

14. A silicon carbide powder, characterized in that, The silicon carbide powder is prepared by the method according to any one of claims 1-13, wherein the boron content in the silicon carbide powder is less than or equal to 0.005 ppm.

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