Method for purifying low-purity siC powder and application thereof

Abstract

This invention discloses a method for purifying low-purity SiC powder and its application. The method utilizes rapid thermal shock to purify low-purity SiC powder containing metallic impurities such as Al, Ca, and Mg. Rapid thermal shock technology induces a non-equilibrium reaction state in the system, which allows impurities such as Al, Ca, and Mg to undergo carbothermic reduction reactions at relatively low temperatures, transforming them into gaseous metal compounds that then escape. This efficiently achieves deep removal of impurities, resulting in SiC with a purity of up to 99.9%.

Description

Technical Field

[0001] This invention belongs to the field of chemical synthesis technology, specifically relating to a method for removing impurities and purifying low-purity SiC powder and its application. Background Technology

[0002] The industrial electric arc furnace method is the mainstream process for preparing SiC powder. It synthesizes SiC powder by reacting siliceous raw materials such as quartz sand with carbonaceous raw materials under a high-temperature electric arc. It has significant advantages such as readily available raw materials and a short reaction process, and the preparation cost is more than 40% lower than that of the gas phase method and sol-gel method. However, the purity of the products produced by this process is generally low. The purity of metallurgical grade products is mostly below 80%, and even the purity of refined products can only reach about 90%, which is far from meeting the needs of high-end fields.

[0003] Impurities in low-purity SiC powder mainly include free silicon, free carbon, silicon dioxide, and metals such as Al, Ca, Mg, and Fe, as well as their carbides. Free silicon affects sintering stability, while Al, Ca, Mg, and Fe impurities increase leakage current in semiconductor devices. Impurities such as boron and nitrogen directly alter the electrical properties of the crystal. Due to these impurity limitations, electric arc furnace SiC can only be used in low-end applications such as casting inoculants and ordinary abrasives, failing to meet the demand for high-purity raw materials.

[0004] Existing purification technologies have significant shortcomings: traditional acid-base washing processes require multiple steps, take over 10 hours, and consume large amounts of acid; while high-temperature chlorination can improve purity, it increases energy consumption by more than three times; electromagnetic iron removal can only target ferrous impurities and is ineffective for non-ferromagnetic impurities. Therefore, developing a purification method that can simultaneously remove multiple types of impurities, is simple in process, and has low energy consumption could transform low-cost electric arc furnace SiC into high-value raw materials, significantly expanding its applications in semiconductors, advanced ceramics, and other fields, and possessing significant industrial value. Summary of the Invention

[0005] To address the problems of insufficient purity, complex purification procedures, and long cycles in existing SiC preparation techniques, this application proposes a method for impurity removal and purification of low-purity SiC powder. Based on the characteristics of impurities such as Al, Ca, and Mg contained in low-purity SiC, this invention innovatively proposes a carbothermic reduction method using Joule heating-based high-temperature thermal shock technology to remove Al, Ca, and Mg impurities, resulting in high-value, high-purity SiC. The proposed preparation process is simple, easy to operate, highly reproducible, produces high-purity products, and exhibits high stability, demonstrating excellent application prospects.

[0006] One of the technical solutions of the present invention is to provide a method for removing impurities and purifying low-purity SiC powder: mixing low-purity SiC powder with carbon powder and then subjecting it to Joule thermal shock to obtain purified SiC.

[0007] Furthermore, the molar ratio of SiC to carbon powder in the low-purity SiC powder is 1:1 to 1:20.

[0008] Furthermore, the carbon powder is one or more of coke, graphite, and Ketjen carbon.

[0009] Furthermore, the Joule thermal shock temperature is 1200~2000℃, the holding time is 5~1500s, and the thermal shock heating and cooling rate is 100℃ / s~1000℃ / s.

[0010] Preferably, the thermal shock heating and cooling rate is 100-400℃ / s.

[0011] Furthermore, the Joule thermal shock is performed under inert gas protection.

[0012] Furthermore, the Joule thermal shock method involves spreading a mixture of low-purity SiC powder and carbon powder on a heating substrate, and then energizing the heating substrate.

[0013] The low-purity SiC powder and carbon powder are ground uniformly by ball milling or grinding.

[0014] Furthermore, the heating substrate is an open graphite crucible.

[0015] Furthermore, the mixture of low-purity SiC powder and carbon powder is covered with carbon cloth and carbon felt.

[0016] In some implementation examples, a method for removing impurities from SiC powder includes the following steps: (1) Weigh low-purity SiC and carbon powder, and grind them evenly using a ball mill or grinder; (2) Place the precursor in an open graphite crucible, place the crucible in a high-temperature thermal shock device under an argon atmosphere, and perform a one-step heat treatment at a temperature of 1200~2000℃. After cooling for 5~1500s, a high-purity SiC product with impurities removed is obtained.

[0017] Low-purity SiC contains compounds formed by impurity elements such as Al, Ca, and Mg. By mixing low-purity SiC with carbon powder and using a non-equilibrium reaction system provided by Joule heating via high-temperature thermal shock technology, Al, Ca, and Mg elements can be reduced to their gaseous metallic state and released, thus removing the impurity elements. Simultaneously, amorphous SiO2 can be transformed into high-value, high-purity SiC through a carbothermic reaction. The reaction process is shown below: CaO + C = Ca↑ + CO↑ Al₂O₃ + C = 2Al↑ + 3CO↑ MgO + C = Mg↑ + CO↑ In this invention, the purity of the low-purity SiC used can be 50wt%-95wt%.

[0018] The second technical solution of the present invention is to provide the application of high-purity SiC prepared by the above method in wear-resistant ceramics, new energy materials or semiconductor materials.

[0019] The advantages of this invention are: (1) By using rapid thermal shock technology to make the system form a non-equilibrium reaction state, impurities such as Al, Ca, and Mg can undergo carbothermic reduction reaction at relatively low temperatures, transforming into gaseous metal compounds and overflowing, thereby achieving efficient deep removal of impurities and improving the purity of the product to above 3N.

[0020] (2) The SiC prepared by this invention has high purity and uniform morphology, and can be used in fields such as new energy materials, wear-resistant ceramics and semiconductor materials.

[0021] (3) The preparation method proposed in this invention requires simple equipment, is easy to operate, has controllable conditions, high repeatability, and low preparation cost, making it suitable for large-scale industrial production. Attached Figure Description

[0022] Figure 1 This is a graph showing the temperature variation during the Joule thermal shock technique used in Example 1. Figure 2 The XRD curve of the high-purity SiC obtained in Example 1; Figure 3 SEM image of high-purity SiC obtained in Example 1; Figure 4 EDS image of high-purity SiC obtained in Example 1; Figure 5 The elemental composition table of the high-purity SiC obtained in Example 1 is shown below. Figure 6 EDS images of overflowing impurities collected during the preparation process of Example 1; Figure 7 This is a table showing the elemental content of the overflow impurities collected during the preparation process of Example 1. Detailed Implementation

[0023] The following examples are provided to further illustrate the present invention and are intended to explain the invention, not to limit its scope. Unless otherwise specified, all figures are expressed in parts by weight and weight percentages.

[0024] Unless otherwise specified, the raw materials used in this invention are all conventional commercially available products; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0025] In this invention, the carbon powder used can be in excess and can be removed by high temperature of 800°C after purification.

[0026] The high purity mentioned in this invention refers to a purity of not less than 99%.

[0027] The embodiments of the present invention will be further described below with reference to several examples.

[0028] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0029] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0030] Example 1 (1) Weigh 90wt% SiC and carbon powder in a 1:1 molar ratio of SiC to carbon powder, and mix them evenly in a mortar to obtain the precursor; (2) Weigh 80 mg of the precursor and spread it evenly at the bottom of the cylindrical cavity of the special graphite crucible; (3) Cut carbon cloth and carbon felt of appropriate size, place one layer of carbon cloth and two layers of carbon felt on the top of the powder precursor in a special graphite crucible and press them tightly. (4) The sample was heat-treated using a high-temperature thermal shock apparatus with a heating time of 18 s, a heat treatment temperature of 1800℃, and a holding time of 30 s. After cooling to room temperature, high-purity SiC was obtained. During the high-temperature thermal shock process, the overflow impurities were collected, and their EDS were as follows: Figure 6 As shown.

[0031] The obtained high-purity SiC was characterized. XRD curves showed that the phase was 6H-SiC, and its SEM image is shown below. Figure 3 As shown, this proves that the sample consists of particles ranging from 10 to 80 micrometers.

[0032] Figure 4 and Figure 5 The EDS images and elemental composition table shown demonstrate that SiC has high purity and achieves good impurity removal and purification.

[0033] Example 2 (1) Weigh low-purity SiC and carbon powder at a molar ratio of 1:10 and mix them evenly with a mortar to obtain the precursor; the purity of low-purity SiC is 50wt%.

[0034] (2) Weigh 80 mg of the precursor and spread it evenly at the bottom of the cylindrical cavity of the special graphite crucible; (3) Cut carbon cloth and carbon felt of appropriate size, place one layer of carbon cloth and two layers of carbon felt on the top of the powder precursor in a special graphite crucible and press them tightly. (4) The sample was heat-treated using a high-temperature thermal shock device with a heating time of 15s, a heat treatment temperature of 1800℃, and a holding time of 5s. After cooling to room temperature, high-purity 3C-SiC was obtained.

[0035] (5) Use a muffle furnace to anneal at 800℃ to remove residual carbon powder and obtain high-purity SiC.

[0036] Characterization of its morphology and structure using scanning electron microscopy, transmission electron microscopy, and XRD revealed that high-purity SiC was successfully prepared. The high-purity SiC prepared in this example is composed of nanoparticles.

[0037] Example 3 (1) Weigh low-purity SiC and carbon powder at a molar ratio of 1:20 and mix them evenly with a mortar to obtain the precursor; the purity of low-purity SiC is 70wt%.

[0038] (2) Weigh 80 mg of the precursor and spread it evenly at the bottom of the cylindrical cavity of the special graphite crucible; (3) Cut carbon cloth and carbon felt of appropriate size, place one layer of carbon cloth and two layers of carbon felt on the top of the powder precursor in a special graphite crucible and press them tightly. (4) Use a high-temperature thermal shock device to heat the sample with a heating time of 10s, a heat treatment temperature of 1600℃, and a holding time of 900s, and then cool it to room temperature.

[0039] (5) Use a muffle furnace to anneal at 800℃ to remove residual carbon powder and obtain high-purity SiC.

[0040] Characterization of its morphology and structure using scanning electron microscopy, transmission electron microscopy, and XRD revealed that high-purity 3C-SiC was successfully prepared. The high-purity SiC prepared in this example is composed of nanoparticles.

[0041] Example 4 (1) Weigh low-purity SiC and carbon powder in a molar ratio of 1:2 and mix them evenly in a mortar to obtain a precursor; the purity of low-purity SiC is 90wt%.

[0042] (2) Weigh 80 mg of the precursor and spread it evenly at the bottom of the cylindrical cavity of the special graphite crucible; (3) Cut carbon cloth and carbon felt of appropriate size, place one layer of carbon cloth and two layers of carbon felt on the top of the powder precursor in a special graphite crucible and press them tightly. (4) The sample was heat-treated using a high-temperature thermal shock device with a heating time of 5 s, a heat treatment temperature of 2000℃, and a holding time of 1500s. After cooling to room temperature, high-purity SiC was obtained.

[0043] Characterization of its morphology and structure using scanning electron microscopy, transmission electron microscopy, and XRD revealed that high-purity SiC was successfully prepared. The high-purity SiC prepared in this example is composed of nanoparticles.

[0044] The above embodiments describe in detail the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, shall still fall within the scope of protection of the present invention if they do not exceed the scope covered by the specification.

Claims

1. A method for removing impurities and purifying low-purity SiC powder, characterized in that, Low-purity SiC powder was mixed with carbon powder and then subjected to Joule thermal shock to obtain purified SiC.

2. The method according to claim 1, characterized in that, The molar ratio of SiC to carbon powder in the low-purity SiC powder is 1:1 to 1:

20.

3. The method according to claim 1, characterized in that, The carbon powder is one or more of coke, graphite, and Ketjen carbon.

4. The method according to claim 1, characterized in that, The Joule thermal shock temperature is 1200~2000℃, the holding time is 5~1500s, and the thermal shock heating and cooling rate is 100℃ / s~1000℃ / s.

5. The method according to claim 1, characterized in that, The Joule thermal shock was performed under inert gas protection.

6. The method according to claim 1, characterized in that, The Joule thermal shock method involves spreading a mixture of low-purity SiC powder and carbon powder on a heating substrate, and then energizing the heating substrate.

7. The method according to claim 6, characterized in that, The heating substrate is an open graphite crucible.

8. The method according to claim 6, characterized in that, The mixture of low-purity SiC powder and carbon powder is covered with carbon cloth and carbon felt.

9. A high-purity SiC prepared by the method described in claim 1.

10. An application of the high-purity SiC as described in claim 9 in wear-resistant ceramics, new energy materials, or semiconductor materials.

Images