Recycling technology of waste slurry from wire cutting of silicon carbide single crystal

Abstract

The present invention discloses a recycling process for waste mortar from wire cutting of silicon carbide single crystals, and belongs to the technical field of recycling mortar for cutting of silicon carbide wafers. The present invention uses a simple high-speed centrifugation method to separate the oil solvent and the solid part in the waste mortar, and first recovers the clarified oil solvent. Then, a low-cost and environmentally friendly surfactant aqueous solution is used to clean the oil remaining on the solid surface, and at the same time, the agglomerated silicon carbide particles and the silicon carbide particles adsorbed on the diamond surface are dispersed, and then an inorganic acid aqueous solution is used to remove metal impurities such as iron in the solid, and a green chelating agent aqueous solution is used to secondary clean the residual metal ions. Finally, diamond powder is separated under low speed and short time conditions according to the difference in particle size between diamond and silicon carbide. Different from the organic solvent cleaning method that is mostly used, the present invention uses an aqueous solution for cleaning, which has the advantages of being environmentally friendly, simple to operate, and low cost.

Description

Technical Field

[0001] The invention belongs to the technical field of recycling silicon carbide wafer cutting mortar, and specifically relates to a recycling process for silicon carbide single crystal wire cutting waste mortar. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] As the third generation semiconductor material, the biggest advantage of silicon carbide over the previous two generations of semiconductor materials is its wider bandgap, showing advantages such as high saturation drift velocity, high thermal conductivity, high breakdown electric field and high radiation resistance. It can be widely used as a substrate material for devices and plays an important role in new energy vehicles, photovoltaics, smart grids, etc. As the global industry's demand for silicon carbide increases, how to reduce the preparation cost of silicon carbide is a key problem in the promotion of silicon carbide industrialization.

[0004] The Mohs hardness of silicon carbide crystal is as high as 9.2, second only to the Mohs hardness of diamond of 10. At present, the diamond slurry wire cutting method is mainly used in the market to process silicon carbide single crystals. The diamond slurry wire cutting method relies on an oily cutting fluid made by mixing oil solvents with diamond powder. During cutting, the diamond powder is evenly distributed on the cutting line with the movement of the oily cutting fluid, and the silicon carbide single crystal is cut by rolling-indentation between the free diamond abrasive particles in the cutting fluid and the workpiece. As the cutting process progresses, a large amount of debris is gradually mixed into the oily cutting fluid. The introduction of debris, water, and chemical changes in the cutting fluid will cause the cutting fluid to fail. When the cutting fluid cannot be effectively cut, it needs to be disposed of. The treatment process is cumbersome and complicated, the cost is high, and the pollution to the environment cannot be ignored. Therefore, the recycling of oily cutting fluid is of great significance.

[0005] Diamond powder is evenly and stably dispersed in the oily cutting fluid. Due to the effect of surface tension, diamond powder cannot be separated by conventional solid-liquid separation, solid-solid separation and other means. Directly discarding the cutting fluid will cause waste of diamond powder and increase the production cost of silicon carbide. In order to effectively recover the diamond particles in the cutting fluid, it is necessary to remove the oily solvent, silicon carbide microparticles lost in the cutting process, and metal impurities mixed in by cutting line wear. Patent CN 116160569 A discloses a method for recovering abrasive particles and basic solvents in multi-wire cutting slurry for silicon carbide wafers. The oily solvent is separated by centrifugation, and then the residual oil and metal contaminants on the surface of the solid part of the slurry are removed by organic solvents such as N-methylpyrrolidone, isopropyl alcohol, Dow CA-2500 dispersant solution, and SC-1 solution. It uses various organic solvents to remove the silicon carbide particles lost in the cutting process and the metal impurities introduced by the cutting wire wear. The recovery process is cumbersome, and the emission and treatment of organic solvents will greatly increase the recovery cost, which is contrary to the original intention of reducing the cost of silicon carbide single crystal processing. Summary of the invention

[0006] In order to solve the deficiencies of the prior art, the purpose of the present invention is to provide a process for recycling waste slurry from wire cutting of silicon carbide single crystals. The process provided by the present invention is simple and low in cost, and the obtained diamond powder has a clean surface and high purity.

[0007] In order to achieve the above object, the technical solution of the present invention is:

[0008] The first aspect of the present invention provides a process for recycling waste mortar from wire sawing of silicon carbide single crystals, comprising the following steps:

[0009] Step 1: Centrifuge the waste slurry from wire cutting of silicon carbide single crystal to obtain oil solvent and solid A;

[0010] Step 2: mixing a surfactant aqueous solution with solid A, ultrasonicating, and performing solid-liquid separation to obtain solid B; wherein the surfactant is selected from one or more of α-sulfo fatty acid methyl ester, alkyl sugar polyglycoside, glucose amide, alcohol ether carboxylate, monoalkyl phosphate, or alkyl glucose amide;

[0011] Step 3: Add an inorganic acid aqueous solution to solid B, perform ultrasonication, and perform solid-liquid separation to obtain solid C;

[0012] Step 4: adding a chelating agent aqueous solution to solid C, performing ultrasonication, and performing solid-liquid separation to obtain solid D;

[0013] Step 5: Disperse solid D in water and recover diamond powder by centrifugation.

[0014] In some embodiments of the present invention, in step 1, the centrifugal force of the centrifugal reaction is 5000-20000 g, and the centrifugal time is 30-60 min.

[0015] In some embodiments of the present invention, in step 2, the concentration of the surfactant aqueous solution is 5-10%, mass percentage; the mass ratio of the surfactant aqueous solution to the solid A is 1:0.1-0.5.

[0016] In some embodiments of the present invention, in step 2, the ultrasound is performed for a time of 1-2 hours.

[0017] In some embodiments of the present invention, in step 3, the concentration of the inorganic acid aqueous solution is 1-5%, mass percentage; the mass ratio of the inorganic acid aqueous solution to the solid B is 1:0.2-1.

[0018] In some embodiments of the present invention, the inorganic acid includes hydrochloric acid, sulfuric acid or nitric acid.

[0019] In some embodiments of the present invention, in step 3, the ultrasound is performed for a time of 1-2 hours.

[0020] In some embodiments of the present invention, in step 4, the concentration of the chelating agent aqueous solution is 1-5%, by mass; and the mass ratio of the chelating agent aqueous solution to the solid C is 1:0.5-1.

[0021] Preferably, the chelating agent is selected from tetrasodium glutamate diacetate and trisodium N,N-dicarboxymethylalanine.

[0022] In some embodiments of the present invention, in step 4, the ultrasound is performed for a time of 1-2 hours.

[0023] In some embodiments of the present invention, in step 5, the centrifugal force of the centrifugal reaction is 3000-5000 g, and the centrifugal time is 1-5 min.

[0024] The beneficial effects of the present invention are:

[0025] Because the role of surfactants in cleaning oil stains is significant. The present invention achieves the simultaneous removal of residual oil and silicon carbide microparticles lost in the cutting process by optimizing the types of surfactants. The surfactants used in the present invention can significantly increase the solubility of residual oil in water by the distribution of micelles and the change of interfacial tension. This property is used to clean oil stains, and the originally hydrophobic oily substances are solubilized in water through the formed micelles to achieve the purpose of oil removal. At the same time, the surfactants used in the present invention can significantly reduce the interfacial tension between solid and liquid, thereby increasing the adsorption and compatibility between solid and liquid, and forming an interfacial film around the solid silicon carbide particles in the form of a hydration layer or a charged layer, thereby preventing the aggregation of solid silicon carbide particles and playing the role of dispersing solid silicon carbide particles (deagglomeration).

[0026] The present invention recovers the oil solvent in the waste slurry by centrifuging it at high speed and for a long time, and obtains a mixed solid containing diamond powder for subsequent treatment. The residual oil on the surface of the mixed solid is cleaned with a green surfactant aqueous solution, which is low in cost, environmentally friendly, and safer than cleaning the oil with an organic solvent. At the same time, the surfactant can also be used as a dispersant to disperse the agglomerated silicon carbide particles and the silicon carbide particles adsorbed on the surface of the diamond, and further achieve the removal of residual oil and silicon carbide microparticles lost during the cutting process. Subsequently, a low-concentration inorganic acid aqueous solution is used to remove metal impurities such as iron in the solid, and then a green chelating agent aqueous solution is used to perform a secondary cleaning of the metal ions. Finally, by using the difference in the particle size of diamond and silicon carbide, the diamond powder with a larger particle size and heavier weight is separated from the dispersion by centrifuging the aqueous dispersion of the mixed solid at a low speed and for a short time, so as to obtain diamond powder with a higher purity. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0028] Figure 1 It is an oil solvent separated from waste mortar by high-speed and long-term centrifugation;

[0029] Figure 2 The solid A part of the waste slurry separated by high-speed and long-term centrifugation;

[0030] Figure 3 is a scanning electron microscope (SEM) image of solid E (diamond) recovered in Example 1;

[0031] Figure 4 is a SEM image of the diamond recovered in Comparative Example 1. DETAILED DESCRIPTION

[0032] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] The present invention provides a recycling process for waste mortar from wire sawing of silicon carbide single crystals, comprising the following steps:

[0034] Step 1: Centrifuge the waste slurry from wire cutting of silicon carbide single crystal to obtain oil solvent and solid A;

[0035] Step 2: mixing a surfactant aqueous solution with solid A, ultrasonicating, and performing solid-liquid separation to obtain solid B; wherein the surfactant is selected from one or more of α-sulfo fatty acid methyl ester (MEC), alkyl polyglycoside (APG), glucamide (APA), alcohol ether carboxylate (AEC), monoalkyl phosphate (MAP), and alkyl glucamide (MECA);

[0036] Step 3: Add an inorganic acid aqueous solution to solid B, perform ultrasonication, and perform solid-liquid separation to obtain solid C;

[0037] Step 4: adding a chelating agent aqueous solution to solid C, performing ultrasonication, and performing solid-liquid separation to obtain solid D;

[0038] Step 5: Disperse solid D in water and recover diamond powder by centrifugation.

[0039] In the prior art, organic solvent mixtures are used to clean the oil on the surface of solids or carcinogens (methyl iodide solution) are used to separate silicon carbide and diamond mixtures. This process is not only costly, but also harmful to the environment and operators. In the present invention, high-speed and long-term centrifugation is used to first recover the oil solvent in the waste mortar, and then a low-cost and environmentally friendly surfactant aqueous solution is used to further remove the oil remaining on the solid surface and disperse the agglomerated particles. A low-concentration inorganic acid aqueous solution is used to remove metal impurities such as iron in the solid, and a chelating agent aqueous solution is used to perform a secondary cleaning of the remaining metal ions. Finally, the difference in the particle size of diamond and silicon carbide is used to separate high-purity diamond powder from the aqueous dispersion of the mixed solid through low-speed and short-time centrifugation. Different from the organic solvent cleaning methods that are mostly used, the present invention has the advantages of being environmentally friendly, simple to operate, and low cost.

[0040] The present invention has no particular limitation on the sources of all raw materials, and any raw materials available on the market can be used.

[0041] In some examples of this implementation mode, in step 1, the centrifugal force of the centrifugation is preferably 5000-20000 g, and the centrifugal time is preferably 30-60 min. From these parameters, it can be seen that the waste mortar is centrifuged at high speed and for a long time in step 1. The high-speed and long-term centrifugation can completely recover the oil solvent in the waste mortar, reduce the residual amount of the oil solvent, and reduce the influence of the oil solvent on the removal process of other substances.

[0042] In some examples of this embodiment, in step 2, the concentration of the surfactant aqueous solution is preferably 5-10%, mass percentage; the mass ratio of the surfactant aqueous solution to the solid A is 1:0.1-0.5, and the appropriate mass ratio can be selected according to the weight of the obtained solid A, that is, when the mass of solid A is large, the amount of the surfactant aqueous solution is also increased accordingly. In order not to introduce new metal impurities and reduce damage to the environment, the present invention adopts green environmentally friendly surfactants. The concentration of the surfactant needs to be greater than its own critical micelle concentration (CMC), therefore, the surfactant concentration in the present invention is determined to be 5-10%.

[0043] In the present invention, the surfactant plays two roles: when the concentration is higher than CMC, the surfactant generates micelles and other aggregates with hydrophilic periphery and hydrophobic inner cavity in water, and the oil stains can be solubilized in the hydrophobic inner cavity and dissolved in water, thereby achieving the purpose of removing the oil stains on the solid surface. At the same time, the surfactant forms an interfacial film around the solid silicon carbide particles in the form of a hydration layer or a charged layer, preventing the aggregation between the solid silicon carbide particles, thereby playing the role of dispersing the solid silicon carbide particles (i.e., deagglomeration).

[0044] In some examples of this embodiment, in step 2, the ultrasonication is preferably performed for 1-2 hours. The ultrasonication time should not be too short, otherwise it will lead to incomplete cleaning.

[0045] In some examples of this implementation mode, in step 3, the concentration of the inorganic acid aqueous solution is preferably 1-5%, by mass percentage; the mass ratio of the inorganic acid aqueous solution to the solid B is 1:0.2-1, and the appropriate mass ratio can be selected according to the weight of the obtained solid B, that is, when the mass of solid B is large, the amount of the inorganic acid aqueous solution is also increased accordingly. To ensure the cleaning effect, the concentration of the inorganic acid should not be too low. To save costs, the concentration of the inorganic acid should not be too high. Balancing the cleaning effect and cost, it is finally determined that the concentration of the inorganic acid in the present invention is 1-5%.

[0046] In some examples of this embodiment, the inorganic acid includes but is not limited to hydrochloric acid, sulfuric acid or nitric acid.

[0047] In some examples of this embodiment, in step 3, the ultrasonication is preferably performed for 1-2 hours. The ultrasonication time should not be too short, otherwise it will lead to incomplete cleaning.

[0048] In some examples of this embodiment, in step 4, the concentration of the chelating agent aqueous solution is preferably 1-5%, mass percentage; the mass ratio of the chelating agent aqueous solution to the solid C is 1:0.5-1, and the appropriate mass ratio can be selected according to the weight of the obtained solid C, that is, when the mass of the solid C is large, the amount of the chelating agent aqueous solution is also increased accordingly. The chelating agent used in the present invention is a green and environmentally friendly chelating agent, selected from one of tetrasodium glutamate diacetate (GLDA) and trisodium N,N-dicarboxymethyl alanine (MGDA). To ensure the effect of cleaning metal ions, the concentration of the chelating agent should not be too low. To save costs, the concentration of the chelating agent should not be too high. Balancing the cleaning effect and cost, it is finally determined that the concentration of the chelating agent in the present invention is 1-5%.

[0049] In some examples of this embodiment, in step 4, the ultrasonication is preferably performed for 1-2 hours. The ultrasonication time should not be too short, otherwise it will lead to incomplete cleaning.

[0050] In some examples of this embodiment, in step 5, the centrifugal force is preferably 3000-5000g, and the centrifugal time is preferably 1-5min. It can be seen from this parameter that the solid D is centrifuged at a low speed and for a short time in step 5. The present invention utilizes the difference in particle size between diamond and silicon carbide, and separates the diamond powder with a larger particle size and heavier weight from the dispersion by centrifuging the aqueous dispersion of the mixed solid at a low speed and for a short time, thereby obtaining diamond powder with a higher purity. Low centrifugal force and short centrifugal time can make the separated diamond have a higher purity. Increasing the centrifugal force or extending the centrifugal time will cause part of the silicon carbide to be centrifuged off, affecting the purity of the diamond.

[0051] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0052] Example 1

[0053] A recycling process for waste mortar from wire sawing of silicon carbide single crystals comprises the following steps:

[0054] Step 1: Centrifuge the waste mortar at a centrifugal force of 5000g for 30 minutes to recover the oil solvent and solid A.

[0055] Step 2: Solid A is mixed with a 3% by mass MEC aqueous solution and ultrasonically mixed for 1 hour, the mass ratio of the 3% by mass MEC aqueous solution to solid A is 1:0.1-0.5, and the liquid portion is removed after standing to obtain solid B.

[0056] Step 3: Solid B is mixed with a 2% by mass aqueous solution of hydrochloric acid and subjected to ultrasonic treatment for 1 hour, wherein the mass ratio of the 2% by mass aqueous solution of hydrochloric acid to solid B is 1:0.2-1. After standing, the liquid portion is removed to obtain solid C.

[0057] Step 4: Solid C is mixed with a 2% by mass MGDA aqueous solution and ultrasonically mixed for 1 hour, wherein the mass ratio of the 2% by mass MGDA aqueous solution to solid C is 1:0.5-1. After standing, the solution is removed to obtain solid D.

[0058] Step 5: Disperse solid D evenly in water and centrifuge at 1000 g for 2 min to obtain diamond powder with a recovery efficiency of 90%.

[0059] Example 2

[0060] A recycling process for waste mortar from wire sawing of silicon carbide single crystals comprises the following steps:

[0061] Step 1: Centrifuge the waste slurry at a centrifugal force of 10,000 g for 30 minutes to recover the oil solvent and solid A.

[0062] Step 2: Mix solid A with 3% by mass APA aqueous solution and ultrasonicate for 1 hour, the mass ratio of 3% by mass APA aqueous solution to solid A is 1:0.1-0.5, and remove the liquid part after standing to obtain solid B.

[0063] Step 3: Solid B is mixed with a 2% by mass aqueous solution of hydrochloric acid and subjected to ultrasonic treatment for 1 hour, wherein the mass ratio of the 2% by mass aqueous solution of hydrochloric acid to solid B is 1:0.2-1. After standing, the liquid portion is removed to obtain solid C.

[0064] Step 4: Solid C is mixed with a 2% by mass GLDA aqueous solution and ultrasonically treated for 1 hour, wherein the mass ratio of the 2% by mass GLDA aqueous solution to solid C is 1:0.5-1. After standing, the solution is removed to obtain solid D.

[0065] Step 5: Disperse solid D evenly in water and centrifuge at 1000 g for 2 min to obtain diamond powder with a recovery efficiency of 88%.

[0066] Example 3

[0067] A recycling process for waste mortar from wire sawing of silicon carbide single crystals comprises the following steps:

[0068] Step 1: Centrifuge the waste slurry at a centrifugal force of 15000g for 30 minutes to recover the oil solvent and solid A.

[0069] Step 2: Solid A is mixed with a 5% by mass MEC aqueous solution and ultrasonically mixed for 1 hour, wherein the mass ratio of the 5% by mass MEC aqueous solution to solid A is 1:0.1-0.5. After standing, the liquid portion is removed to obtain solid B.

[0070] Step 3: Solid B is mixed with a 3% by mass aqueous sulfuric acid solution and ultrasonically mixed for 1 hour, wherein the mass ratio of the 3% by mass aqueous sulfuric acid solution to solid B is 1:0.2-1. After standing, the liquid portion is removed to obtain solid C.

[0071] Step 4: Solid C is mixed with a 2% by mass MGDA aqueous solution and ultrasonically mixed for 1 hour, wherein the mass ratio of the 2% by mass MGDA aqueous solution to solid C is 1:0.5-1. After standing, the solution is removed to obtain solid D.

[0072] Step 5: Disperse solid D evenly in water and centrifuge at 1000 g for 3 min to obtain diamond powder with a recovery efficiency of 93%.

[0073] Comparative Example 1

[0074] A recycling process for waste mortar from wire sawing of silicon carbide single crystals comprises the following steps:

[0075] Step 1: Centrifuge the waste mortar at a centrifugal force of 5000g for 30 minutes to recover the oil solvent and solid A.

[0076] Step 2: Solid A is mixed with a 2% by mass aqueous solution of hydrochloric acid and subjected to ultrasonic treatment for 1 hour, wherein the mass ratio of the 2% by mass aqueous solution of hydrochloric acid to solid B is 1:0.2-1. After standing, the liquid portion is removed to obtain solid B.

[0077] Step 3: Solid B is mixed with a 2% by mass MGDA aqueous solution and ultrasonically mixed for 1 hour, the mass ratio of the 2% by mass MGDA aqueous solution to solid C is 1:0.5-1, and after standing, the solution portion is removed to obtain solid C.

[0078] Step 5: Solid C was evenly dispersed in water and centrifuged at 1000 g for 2 min to obtain diamond powder, which could not be effectively separated.

[0079] Figure 3 This is a SEM image of the solid E (diamond) recovered in Example 1. It can be seen that the surface of the recovered solid E (diamond) is very clean, that is, the recovered diamond is of high purity. Figure 4 This is a SEM image of the diamonds recovered in Comparative Example 1. It can be seen that the surface of the diamonds recovered in this comparative example carries a large amount of impurities, that is, its purity is relatively low. Figure 3 and Figure 4By comparison, it can be seen that using surfactant to clean the residual oil on the solid surface and separate the agglomerated particles is important for recovering diamond powder with clean surface from waste slurry.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A process for recycling waste slurry from wire cutting of silicon carbide single crystal, characterized in that: The steps include: Step 1: Centrifuge the waste slurry from wire cutting of silicon carbide single crystal to obtain oil solvent and solid A; Step 2: mixing a surfactant aqueous solution with solid A, ultrasonicating, and performing solid-liquid separation to obtain solid B; wherein the surfactant is selected from one or more of α-sulfo fatty acid methyl ester, alkyl sugar polyglycoside, glucose amide, alcohol ether carboxylate, monoalkyl phosphate, or alkyl glucose amide; Step 3: Add an inorganic acid aqueous solution to solid B, perform ultrasonication, and perform solid-liquid separation to obtain solid C; Step 4: adding a chelating agent aqueous solution to solid C, performing ultrasonication, and performing solid-liquid separation to obtain solid D; Step 5: Disperse solid D in water and recover by centrifugation to obtain diamond powder; The surfactant aqueous solution is used to further remove the oil remaining on the solid surface and disperse the agglomerated particles; In step 3, the concentration of the inorganic acid aqueous solution is 1-5%, mass percentage; In step 4, the concentration of the chelating agent aqueous solution is 1-5%, mass percentage; the mass ratio of the chelating agent aqueous solution to the solid C is 1:0.5-1; The chelating agent is selected from tetrasodium glutamate diacetate and trisodium N, N-dicarboxymethyl alanine; In step 5, the centrifugal force is 3000-5000 g, and the centrifugal time is 1-5 min.

2. The recycling process of silicon carbide single crystal wire sawing waste mortar according to claim 1, characterized in that: In step 1, the centrifugal force is 5000-20000 g, and the centrifugal time is 30-60 min.

3. The recycling process of silicon carbide single crystal wire sawing waste slurry according to claim 1, characterized in that: In step 2, the concentration of the surfactant aqueous solution is 5-10%, mass percentage; the mass ratio of the surfactant aqueous solution to the solid A is 1:0.1-0.

5.

4. The recycling process of silicon carbide single crystal wire sawing waste mortar according to claim 1, characterized in that: In step 2, the ultrasonication time is 1-2 h.

5. The recycling process of silicon carbide single crystal wire sawing waste mortar according to claim 1, characterized in that: In step 3, the mass ratio of the inorganic acid aqueous solution to the solid B is 1:0.2-1.

6. The recycling process of silicon carbide single crystal wire sawing waste slurry according to claim 1, characterized in that: The inorganic acid includes hydrochloric acid, sulfuric acid or nitric acid.

7. The recycling process of silicon carbide single crystal wire sawing waste slurry according to claim 1, characterized in that: In step 3, the ultrasonication time is 1-2 h.

8. The recycling process of silicon carbide single crystal wire sawing waste slurry according to claim 1, characterized in that: In step 4, the ultrasonication time is 1-2 h.

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