Porous tantalum carbide and preparation method thereof

Abstract

The invention discloses porous tantalum carbide and a preparation method thereof.The preparation method comprises the steps that a tantalum source, a carbon-based binder and a pore forming agent are mixed, and a mixture is obtained; transferring the mixture into a mold, and carrying out first calcining treatment to obtain a porous structure framework; the porous structure framework is sequentially subjected to second calcination treatment and annealing treatment, and the porous tantalum carbide is obtained. Therefore, when the porous tantalum carbide is applied to growth of silicon carbide crystals, inclusions in the silicon carbide crystals can be effectively reduced, so that the crystal quality is effectively improved.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, and more particularly, to porous tantalum carbide and a method for preparing the same. Background Art

[0002] The growth of silicon carbide crystals is generally completed in a graphite container, and the crystal growth temperature is generally between 2100°C and 2400°C. Under high-temperature conditions, the silicon carbide powder gasifies to form silicon carbide gas, which is transported to the surface of the seed crystal under the driving of the temperature gradient and cools and deposits to form silicon carbide crystals. Among them, the silicon carbide gas contains components such as Si2C, SiC2, and Si. Silicon in the components will corrode the graphite container under high-temperature conditions, causing carbon particles to precipitate on the surface of the graphite container, which are transported to the crystal surface with the gas flow and enter the silicon carbide crystal to form inclusions. The inclusions will cause vacancies in the stacking arrangement of silicon and carbon atoms in silicon carbide, and then generate defects, resulting in defects in the crystal and affecting the crystal quality. Therefore, it is necessary to develop a device to filter carbon particles to improve the quality of silicon carbide crystals.

[0003] It should be noted that the above statements are only used to provide background technical information related to this application, and do not necessarily constitute prior art. Summary of the Invention

[0004] In the first aspect of this application, a method for preparing porous tantalum carbide is proposed, including:

[0005] Mixing a tantalum source, a carbon-based binder, and a pore-forming agent to obtain a mixture;

[0006] Transferring the mixture to a mold for a first calcination treatment to obtain a porous structure framework;

[0007] Subjecting the porous structure framework to a second calcination treatment and an annealing treatment in sequence to obtain the porous tantalum carbide.

[0008] This application prepares porous tantalum carbide by the above method. This method is simple and efficient, and is easy to realize industrial production. The porous tantalum carbide prepared by this method has a high porosity and relatively uniform pore size, thus ensuring the smoothness, stability, and uniformity of the gas flow during the growth process of silicon carbide crystals, reducing the impact on the growth efficiency and quality of the crystals; at the same time, the porous tantalum carbide has a high purity, and applying it to the growth of silicon carbide crystals is beneficial to reducing the introduction of metal or non-metal impurities, thereby improving the quality of silicon carbide crystals.

[0009] In addition, the above method for preparing porous tantalum carbide according to this application may further have the following additional technical features:

[0010] In some embodiments of this application, the tantalum source includes tantalum powder, and the D of the tantalum powder 50The particle size is 50 μm to 1000 μm; in some other embodiments of the present application, the D of the tantalum powder 50 The particle size is 100 μm to 500 μm; in some specific examples of the present application, the D of the tantalum powder 50 The particle size is 100 μm to 300 μm. Thus, it is beneficial for tantalum and carbon to fully react and the formed structure is more stable, making the obtained porous tantalum carbide have a suitable porosity.

[0011] In some embodiments of the present application, the purity of the tantalum powder is ≥99.9999%. Thus, it is beneficial to reduce impurities in the porous tantalum carbide and reduce the influence of impurities on the growth of silicon carbide crystals.

[0012] In some embodiments of the present application, the carbon content of the carbon-based binder is ≥80%. Thus, the carbon-based binder has a suitable viscosity, which is beneficial to improving the mixing uniformity.

[0013] In some embodiments of the present application, the carbon-based binder includes at least one of asphalt, graphite glue, and chitosan. Thus, the carbon-based binder has a suitable viscosity, and further makes the mixing more uniform.

[0014] In some embodiments of the present application, the viscosity of the carbon-based binder is 2000 mPa·s to 6000 mPa·s; in some other embodiments of the present application, the viscosity of the carbon-based binder is 3000 mPa·s to 5000 mPa·s; in some specific examples of the present application, the viscosity of the carbon-based binder is 3500 mPa·s to 4500 mPa·s. Thus, it is beneficial to improve the mixing uniformity.

[0015] In some embodiments of the present application, the pore-forming agent includes at least one of NH4HCO3, NH4Cl, and basic magnesium carbonate. Thus, it is beneficial for the porous tantalum carbide to have a porous structure.

[0016] In some embodiments of the present application, the D of the pore-forming agent 50 The particle size is 5 μm to 500 μm; in some other embodiments of the present application, the D of the pore-forming agent 50 The particle size is 10 μm to 300 μm; in some specific examples of the present application, the D of the pore-forming agent 50 The particle size is 20 μm to 100 μm. Thus, it is beneficial to improve the pore-forming effect and obtain more uniform pores.

[0017] In some embodiments of the present application, the molar mass ratio of the tantalum source to the carbon-based binder is 1:1.25. Thus, a sufficient carbon source can be provided to make the tantalum source fully react.

[0018] In some embodiments of the present application, based on the mass of the mixture, the mass fraction of the pore-forming agent is 5% to 50%; in some other embodiments of the present application, based on the mass of the mixture, the mass fraction of the pore-forming agent is 10% to 40%; in some specific examples of the present application, based on the mass of the mixture, the mass fraction of the pore-forming agent is 20% to 30%. Thus, it is beneficial to improve the pore-forming effect.

[0019] In some embodiments of the present application, the stirring speed during mixing is 20 rpm to 1000 rpm; in some other embodiments of the present application, the stirring speed during mixing is 20 rpm to 40 rpm; in some embodiments of the present application, the mixing time is 2 h to 10 h; in some other embodiments of the present application, the mixing time is 3 h to 8 h; in some specific examples of the present application, the mixing time is 4 h to 6 h. Thus, it is beneficial to make the mixing more uniform.

[0020] In some embodiments of the present application, the shape of the mold includes but is not limited to cylindrical, square or conical. In some other embodiments of the present application, the shape of the mold can also be other special-shaped structures. Thus, porous tantalum carbide with different morphological structures can be prepared according to requirements.

[0021] In some embodiments of the present application, the material of the mold includes graphite, and the surface of the mold is coated with a tantalum carbide coating. Thus, it is beneficial to prevent the mold from reacting and sticking to the mixture during the preparation process and facilitate the removal from the mold.

[0022] In some embodiments of the present application, the temperature of the first calcination treatment is 1000 °C to 1200 °C, and the time of the first calcination treatment is 3 h to 5 h. Thus, it is beneficial to remove impurities in the mixture and preliminarily carbonize the carbon-based binder.

[0023] In some embodiments of the present application, the temperature of the second calcination treatment is 2300 °C to 2500 °C; in some other embodiments of the present application, the temperature of the second calcination treatment is 2350 °C to 2450 °C. Thus, it can ensure a high enough temperature for sufficient reaction of tantalum and carbon, and an appropriate temperature helps the carbon saturation in tantalum carbide to be more suitable, which is beneficial to reducing the stress of porous tantalum carbide.

[0024] In some embodiments of the present application, the time of the second calcination treatment is 20 h to 60 h; in some other embodiments of the present application, the time of the second calcination treatment is 25 h to 50 h; in some specific examples of the present application, the time of the second calcination treatment is 30 h to 40 h. Thus, it can ensure a high enough temperature for sufficient reaction of tantalum and carbon, and an appropriate temperature helps the carbon saturation in tantalum carbide to be more suitable, which is beneficial to reducing the stress of porous tantalum carbide.

[0025] In some embodiments of the present application, the second calcination process needs to be filled with inert gas to keep the synthesis pressure at 10 mbar to 30 mbar, thereby improving the quality of porous tantalum carbide.

[0026] In some embodiments of the present application, the annealing treatment includes: increasing the pressure to 500 mbar within 8 hours to 20 hours to reduce the temperature to 1800°C to 2000°C, then cooling to 1000°C to 1200°C within 3 hours to 6 hours, and finally cooling to room temperature. In this way, the excess stress in the porous tantalum carbide can be released, defects can be reduced, the risk of deformation or even cracking of the porous tantalum carbide structural parts due to excessive stress can be reduced, and its structural performance can be improved.

[0027] In the second aspect of the present application, the present application provides a porous tantalum carbide, which is prepared by the method of the first aspect of the present application. Therefore, the porous tantalum carbide has a high porosity and purity, and its application to the growth of silicon carbide crystals is conducive to filtering carbon particles, reducing inclusions in silicon carbide crystals, and thus improving the quality of silicon carbide crystals.

[0028] In some embodiments of the present application, the porosity of the porous tantalum carbide is 65% to 80%, which is conducive to better filtering carbon particles and thus improving the quality of silicon carbide crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0030] Figure 1 The adsorption-desorption isotherm of the porous tantalum carbide of Example 1 of the present application;

[0031] Figure 2 is the pore size distribution curve of the porous tantalum carbide of Example 1 of the present application;

[0032] Figure 3 Detection of silicon carbide wafer inclusions, (a) detection of silicon carbide wafer A inclusions, (b) detection of silicon carbide wafer B inclusions;

[0033] Figure 4 This is a flow chart of preparing porous tantalum carbide according to one embodiment of the present application;

[0034] Figure 5 This is a diagram of the pore-forming mechanism of the pore-forming agent of this application;

[0035] Figure 6 This is a schematic diagram of a large number of pores generated after the template is removed in this application;

[0036] Figure 7It is a structural diagram of a conventional crystal growth thermal field (a) and a structural diagram of a crystal growth thermal field with the porous tantalum carbide of the present application installed (b).

[0037] Explanation of reference numerals: 1 - powder material, 2 - porous tantalum carbide, 3 - seed crystal, 4 - crucible. Detailed implementation manners

[0038] The embodiments of the present application are described in detail below. Examples of the embodiments are shown in the drawings, but there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to prevent the following descriptions from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0039] Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as commonly understood by those skilled in the technical field to which the present application belongs; the terms used in the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application; unless otherwise specified, the numerical values of the various parameters mentioned in the present application can be measured by various commonly used measurement methods in the art (for example, they can be tested according to the methods given in the embodiments of the present application).

[0040] The terms "comprising" and "having" and any variations thereof in the description and claims of the present application are open expressions, that is, including the content specified in the present application, but not excluding other aspects.

[0041] In the description of the present application, all the numbers disclosed herein are approximate values, whether or not the words "about" or "approximately" are used. There may be a difference of less than 10% or a reasonable difference considered by those skilled in the art for each numerical value, such as a difference of 1%, 2%, 3%, 4% or 5%.

[0042] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, 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, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In this application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where both a and b are real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] In the description of this application, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. The "first feature" and "second feature" may include one or more of such features.

[0044] In the description of this application, "A and / or B" may include the case of A alone, the case of B alone, and any one of the cases of A and B, where A and B are only for illustration and may be any technical features connected by "and / or" in this application.

[0045] In this application, the written order of the steps does not mean a strict execution order and does not constitute any limitation on the implementation process. The specific execution order of each step should be determined by its function and possible internal logic. If there is no special instruction, all steps of this application can be carried out sequentially or randomly, and preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out sequentially, or may also include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or may also include steps (a), (c), and (b), or may also include steps (c), (a), and (b), etc.

[0046] In the first aspect of the present application, a method for preparing porous tantalum carbide is proposed. Referring to Figure 4 , the method includes:

[0047] S1: Mix a tantalum source, a carbon-based binder, and a pore-forming agent to obtain a mixture.

[0048] In this step, a certain amount of the tantalum source, the carbon-based binder, and the pore-forming agent can be placed in a container and mixed in proportion. After mixing and stirring for a period of time, a mixture is obtained. The mixing method is not specifically limited and can be flexibly selected according to needs.

[0049] In some embodiments of the present application, the tantalum source includes tantalum powder, and the D 50 particle size of the tantalum powder is 50 μm to 1000 μm, for example, it can be 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, or 1000 μm, etc.; in some other embodiments of the present application, the D 50 particle size of the tantalum powder is 100 μm to 500 μm; in some specific examples of the present application, the D 50 particle size of the tantalum powder is 100 μm to 300 μm. When the D 50 particle size of the tantalum powder is within the above range, it is beneficial for tantalum and carbon to fully react and the formed structure is more stable, so that the prepared porous tantalum carbide has a suitable porosity.

[0050] In the present application, the D 50 particle size refers to the particle size corresponding to when the cumulative particle size distribution percentage of the particle group reaches 50%, and can be measured by a laser particle size analyzer.

[0051] In some embodiments of the present application, the purity of the tantalum powder is ≥99.9999%, for example, it can be 99.9999%, 99.99992%, 99.99994%, 99.99996%, or 99.99998%, etc. Thus, it is beneficial to reduce the influence of impurities on the growth of silicon carbide crystals.

[0052] In some embodiments of the present application, the carbon content of the carbon-based binder is ≥80%, for example, it can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, or 88%, etc. It can be understood that generally, a polymer material with adhesiveness and a relatively high carbon content is selected as the carbon-based binder. Thus, the carbon-based binder has a suitable viscosity, which is beneficial to improving the mixing uniformity.

[0053] In some embodiments of the present application, the carbon-based binder includes at least one of asphalt, graphite glue, and chitosan. Thus, the carbon-based binder has a suitable viscosity, which makes the mixing more uniform.

[0054] In some embodiments of the present application, the viscosity of the carbon-based binder is 2000 mPa·s to 6000 mPa·s, and can be, for example, 2000 mPa·s, 2500 mPa·s, 3000 mPa·s, 3500 mPa·s, 4000 mPa·s, 4500 mPa·s, 5000 mPa·s, 55000 mPa·s or 6000 mPa·s, etc.; in some other embodiments of the present application, the viscosity of the carbon-based binder is 3000 mPa·s to 5000 mPa·s; in some specific examples of the present application, the viscosity of the carbon-based binder is 3500 mPa·s to 4500 mPa·s. Thereby, it is beneficial to improve the mixing uniformity.

[0055] In some embodiments of the present application, the pore-forming agent includes at least one of NH4HCO3, NH4Cl, and basic magnesium carbonate (xMgCO3·yMg(OH)2·zH2O). Thereby, it is beneficial to make the porous tantalum carbide have a porous structure. Among them, the pore-forming mechanism of the pore-forming agent is as Figure 5 shown. The gas generated after the pore-forming agent decomposes at high temperature is released in the mixture, generating a large number of pores, and the generated template will be evenly embedded in the mixture. After the template is removed by washing, a pore structure is generated (as Figure 6 shown).

[0056] In some embodiments of the present application, the D 50 particle size of the pore-forming agent is 5 μm to 500 μm, and can be, for example, 5 μm, 10 μm, 20 μm, 50 μm, 100 μm, 200 μm, 300 μm, 400 μm or 500 μm, etc.; in some other embodiments of the present application, the D 50 particle size of the pore-forming agent is 10 μm to 300 μm; in some specific examples of the present application, the D 50 particle size of the pore-forming agent is 20 μm to 100 μm. The more uniform the particle size of the pore-forming agent, the more uniform the pores formed; the D 50 particle size of the pore-forming agent is required to be moderate, which is beneficial to generate micron-sized pores, obtain more uniform pores, and thus improve the pore-forming effect.

[0057] In some embodiments of the present application, the molar mass ratio of the tantalum source to the carbon-based binder is 1:1.25. Thereby, a sufficient carbon source can be provided to enable the tantalum source to react fully.

[0058] In some embodiments of the present application, based on the mass of the mixture, the mass fraction of the pore-forming agent is 5% to 50%, and for example, it can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%, etc.; in some other embodiments of the present application, based on the mass of the mixture, the mass fraction of the pore-forming agent is 10% to 40%; in some specific examples of the present application, based on the mass of the mixture, the mass fraction of the pore-forming agent is 20% to 30%. Thus, it is beneficial to improve the pore-forming effect and does not affect the reaction between tantalum and carbon.

[0059] In some embodiments of the present application, the stirring speed during mixing is 20 rpm to 1000 rpm, and for example, it can be 20 rpm, 50 rpm, 100 rpm, 200 rpm, 300 rpm, 500 rpm, 800 rpm or 1000 rpm, etc.; in some other embodiments of the present application, the stirring speed during mixing is 20 rpm to 40 rpm; in some embodiments of the present application, the mixing time is 2 h to 10 h, and for example, it can be 2 h, 4 h, 6 h, 8 h or 10 h, etc.; in some other embodiments of the present application, the mixing time is 3 h to 8 h; in some specific examples of the present application, the mixing time is 4 h to 6 h. Within the above stirring speed and mixing time, it is beneficial to make the mixing more uniform.

[0060] S2: Transfer the mixture to a mold for the first calcination treatment to obtain a porous structure framework.

[0061] In this step, the mixture can be transferred to the mold and left standing for a period of time. The purpose of standing is to eliminate the large air bubbles in the mixture. After the standing is completed, the mold is transferred to a high-temperature furnace for the first calcination treatment. Further, before the first calcination treatment, an inert gas can be filled for purging, and the purging time is 2 h.

[0062] In some embodiments of the present application, the shape of the mold includes cylindrical, square or conical. In some other embodiments of the present application, the shape of the mold can also be other special-shaped structures. It can be understood that the mold can be designed according to the matching of the thermal field. Thus, porous tantalum carbide with different morphological structures can be prepared according to requirements.

[0063] In some embodiments of the present application, the material of the mold includes graphite, and the surface of the mold is coated with a tantalum carbide coating. Thus, it is beneficial to prevent the mold from reacting and sticking to the mixture during the preparation process and facilitate the removal from the mold.

[0064] In some embodiments of the present application, the temperature of the first calcination treatment is 1000°C to 1200°C, for example, it can be 1000°C, 1050°C, 1100°C, 1150°C or 1200°C, etc.; the time of the first calcination treatment is 3h to 5h, for example, it can be 3h, 4h or 5h, etc. Thus, it is beneficial to remove impurities in the mixture and preliminarily carbonize the carbon-based binder. During this process, the pore-forming agent decomposes to generate gas under high-temperature conditions. During the release of the gas, a large number of pores will be generated in the mixture, and this process enables the mixture to preliminarily have a porous structural framework.

[0065] S3: Subject the porous structural framework to a second calcination treatment and an annealing treatment in sequence to obtain the porous tantalum carbide.

[0066] In some embodiments of the present application, the temperature of the second calcination treatment is 2300°C to 2500°C, for example, it can be 2300°C, 2350°C, 2400°C, 2450°C or 2500°C, etc.; in some other embodiments of the present application, the temperature of the second calcination treatment is 2350°C to 2450°C. Thus, it can ensure a sufficiently high temperature for the full reaction of tantalum and carbon, and an appropriate temperature helps the carbon saturation in tantalum carbide to be relatively appropriate, which is beneficial to reducing the stress of the porous tantalum carbide.

[0067] In some embodiments of the present application, the time of the second calcination treatment is 20h to 60h, for example, it can be 20h, 30h, 40h, 50h or 60h, etc.; in some other embodiments of the present application, the time of the second calcination treatment is 25h to 50h; in some specific examples of the present application, the time of the second calcination treatment is 30h to 40h. Thus, it can ensure a sufficiently high temperature for the full reaction of tantalum and carbon, and an appropriate temperature helps the carbon saturation in tantalum carbide to be relatively appropriate, which is beneficial to reducing the stress of the porous tantalum carbide.

[0068] In some embodiments of the present application, the second calcination treatment needs to be filled with an inert gas to keep the synthesis pressure at 10 mbar to 30 mbar (such as 10 mbar, 20 mbar or 30 mbar, etc.). Thus, it is beneficial to improve the quality of the porous tantalum carbide.

[0069] In some embodiments of the present application, the annealing treatment includes: increasing the pressure to 500 mbar within 8h to 20h to lower the temperature to 1800°C to 2000°C, then decreasing the temperature to 1000°C to 1200°C within 3h to 6h, and finally cooling to room temperature. Thus, the excess stress in the porous tantalum carbide can be released, the defects can be reduced, the risk of deformation or even cracking of the porous tantalum carbide structural parts due to excessive stress can be reduced, and its structural performance can be improved.

[0070] In some embodiments of the present application, after the second calcination treatment, the porous tantalum carbide is taken out of the mold, and different cleaning processes are selected according to different pore-forming agents, mainly pickling, alkali washing and water washing; after removing some residues, pores are further formed in the vacancies, and finally porous tantalum carbide is obtained.

[0071] As an example, when the pore-forming agent is NH4HCO3, the decomposition equation of NH4HCO3 is: NH4HCO3 = NH3↑ + CO2↑ + H2O↑, and some residues can be removed by pickling.

[0072] When the pore-forming agent is NH4Cl, the decomposition equation of NH4Cl is: NH4Cl = NH3↑ + HCl↑, 1 mol of NH4Cl decomposes to produce 1 mol of NH3 and 1 mol of HCl, and the generated gas is released in the mixture, generating a large number of pores, and some residues can be removed by water washing.

[0073] When the pore-forming agent is basic magnesium carbonate, the decomposition equation of basic magnesium carbonate is: xMgCO3·yMg(OH)2·zH2O → (x + y)MgO + xCO2↑ + (y + z)H2O↑, and the gas generated by the decomposition of basic magnesium carbonate is released in the mixture, generating a large number of pores. The generated MgO serves as a pore-forming template and will be evenly embedded in the mixture. Dilute hydrochloric acid can be selected for cleaning. HCl in dilute hydrochloric acid will react with MgO, and the reaction equation is: MgO + 2HCl = MgCl2 + H2O, and the generated MgCl2 and H2O are removed with deionized water.

[0074] The porous tantalum carbide prepared by the method of the present application has at least the following beneficial effects:

[0075] (1) Applying the porous tantalum carbide of the present application to the growth of silicon carbide crystals can effectively reduce the inclusions in the silicon carbide crystals, thereby effectively improving the quality of the silicon carbide crystals;

[0076] (2) The porous tantalum carbide prepared by this method has a high porosity and relatively uniform pore size, thus ensuring the smoothness, stability and uniformity of the gas flow during the growth of silicon carbide crystals, and reducing the impact on the growth efficiency and quality of silicon carbide crystals;

[0077] (3) The porous tantalum carbide prepared by the present application has a high purity, avoiding the introduction of metal or non-metal impurities and affecting the quality of silicon carbide crystals.

[0078] In the second aspect of the present application, the present application proposes a porous tantalum carbide, which is prepared by the method in the first aspect of the present application. Thus, the porous tantalum carbide has a high porosity and purity, and applying it to the growth of silicon carbide crystals is beneficial to filtering carbon particles, reducing the inclusions in the silicon carbide crystals, and thus improving the quality of the silicon carbide crystals.

[0079] In some embodiments of the present application, the porosity of the porous tantalum carbide is 65% - 80%, for example, it can be 65%, 70%, 75% or 80%, etc. Thus, it is beneficial to better filter carbon particles, and then improve the quality of silicon carbide crystals.

[0080] The solution of the present application will be described below through specific embodiments. It should be noted that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those without specific techniques or conditions noted in the embodiments, they shall be carried out according to the techniques or conditions described in the literature in this field or according to the product specifications. For reagents or instruments without the manufacturer noted, they are all conventional products that can be obtained through commercial purchase.

[0081] Example 1

[0082] (1) The D 50 particle size of the selected tantalum powder is 200 μm, and the purity is 99.9999%; the selected carbon-based binder is graphite glue, which is a mixture of graphite powder and phenolic resin, and the viscosity of the graphite glue is selected as 4500 mPa·s; the selected pore-forming agent is basic magnesium carbonate (xMg2CO3·yMg(OH)2·H2O), and the D 50 particle size of the basic magnesium carbonate is 50 μm;

[0083] (2) The tantalum powder and graphite glue are mixed after being converted into a mass ratio according to a molar ratio of 1:1.25; the selected mixing method is stirring, and bubbles are avoided from being introduced into the mixture during the stirring process; basic magnesium carbonate is slowly added during the stirring process, and the addition amount of basic magnesium carbonate is 25% of the total mass of the mixture. The stirring speed is 30 rpm, and the stirring time is 5 h to fully mix the raw materials;

[0084] (3) After mixing, the mixture is transferred to a mold and left to stand for 2 h;

[0085] (4) After standing, the mold is transferred to a heat field and placed in a high-temperature furnace for calcination. First, gas purging is carried out, and the selected purging gas is argon, and the purging time is 2 h; after purging, it is heated to 1200 °C in 8 h and kept warm for 4 h to preliminarily carbonize the mixture; the gas generated by the decomposition of basic magnesium carbonate is released in the mixture, generating a large number of pores; the generated MgO serves as a pore-forming template and will be evenly embedded in the mixture, and this process makes the mixture initially have a porous structure framework. Then it is heated to 2350 °C and maintained for 35 h, and the synthesis pressure during this process is kept at 10 mbar to make tantalum and carbon fully react; annealing stage: the pressure is increased to 500 mbar in 15 h to lower the temperature to 1950 °C, then the temperature is lowered to 1200 °C in 4 h, and finally it is cooled to room temperature in 24 h;

[0086] (5) After the calcination is completed, the porous tantalum carbide device is taken out of the mold and washed with dilute hydrochloric acid. The generated MgCl2 and H2O are removed with deionized water.

[0087] Example 2

[0088] The preparation method is the same as that of Example 1, and the differences are as follows:

[0089] (1) The D of the tantalum powder selected 50 The particle size is 50 μm; the carbon-based binder selected is asphalt, and the viscosity of the asphalt is selected to be 2000 mPa·s; the pore-forming agent selected is NH4Cl, and the D of NH4Cl 50 The particle size is 5 μm;

[0090] (2) The addition amount of NH4Cl is 5% of the total mass of the mixture. The stirring speed is 20 rpm, and the stirring time is 10 h;

[0091] (4) After the purge is completed, the temperature is raised to 1100 °C in 8 h and held for 3 h to preliminarily carbonize the mixture; NH4Cl decomposes to produce NH3 and HCl, and the generated gas is released in the mixture, generating a large number of pores; then the temperature is raised to 2300 °C and maintained for 60 h, and the synthesis pressure during this process is maintained at 15 mbar to allow the tantalum and carbon to react fully; annealing stage: the pressure is raised to 500 mbar in 8 h to lower the temperature to 1800 °C, then the temperature is lowered to 1000 °C in 3 h, and finally cooled to room temperature in 24 h;

[0092] (5) After the calcination is completed, the porous tantalum carbide device is taken out of the mold and washed with deionized water. The deionized water can dissolve the residual amine compounds and chlorides in the mixture and form pores.

[0093] Example 3

[0094] The preparation method is the same as that of Example 1, and the differences are as follows:

[0095] (1) The D of the tantalum powder selected 50 The particle size is 1000 μm; the carbon-based binder selected is chitosan, and the viscosity of the chitosan is selected to be 6000 mPa·s; the pore-forming agent selected is NH4HCO3, and the D of NH4HCO3 50 The particle size is 500 μm;

[0096] (2) The addition amount of NH4HCO3 is 50% of the total mass of the mixture. The stirring speed is 1000 rpm, and the stirring time is 2 h;

[0097] (4) After the purging is completed, the temperature is raised to 1000 °C in 8 h and held for 5 h to preliminarily carbonize the mixture; NH4HCO3 decomposes to produce NH3 and CO2, and the generated gases are released in the mixture, generating a large number of pores; then the temperature is raised to 2500 °C and maintained for 20 h, and the synthesis pressure during this process is maintained at 30 mbar to allow tantalum and carbon to fully react; Annealing stage: The pressure is raised to 500 mbar in 20 h to lower the temperature to 2000 °C, then the temperature is lowered to 1200 °C in 6 h, and finally cooled to room temperature in 24 h;

[0098] (5) After the calcination is completed, the porous tantalum carbide device is taken out of the mold and washed with dilute hydrochloric acid.

[0099] Testing method and results:

[0100] (1) The pore structure of the porous tantalum carbide in Example 1 was characterized by adsorption-desorption technology. The adsorption-desorption isotherm is as Figure 1 shown, and the pore size distribution curve is as Figure 2 shown. The porosity is 75.6%, and the porosity is relatively high; and the pore size is distributed between 175 nm and 325 nm, belonging to micron-sized pores.

[0101] (2) A silicon carbide crystal A was prepared by a conventional crystal growth process. The conventional crystal growth thermal field structure is as Figure 7 (a) shown. By slicing, grinding, polishing, and cleaning, the inclusion situation of the silicon carbide wafer A was detected under a halogen lamp, and it was found that there were strip-shaped and flocculent inclusions (as Figure 3 (a) shown); The porous tantalum carbide prepared in Example 1 was placed on the surface of the silicon carbide powder, and a silicon carbide crystal B was prepared by a conventional crystal growth process. The crystal growth thermal field structure with the porous tantalum carbide of this application installed is as Figure 7 (b) shown. By slicing, grinding, polishing, and cleaning, the inclusion situation of the silicon carbide wafer B was detected under a halogen lamp, and it was found that no inclusions appeared (as Figure 3 (b) shown).

[0102] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same constitution and the same function and effect as the technical idea within the technical solution scope of this application are all included in the technical scope of this application. In addition, within the scope not departing from the gist of this application, various modifications that those skilled in the art can think of to the embodiments, and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of this application.

Claims

1. A method for preparing porous tantalum carbide, characterized in that, Comprising: Mixing a tantalum source, a carbon-based binder, and a pore-forming agent to obtain a mixture; Transferring the mixture into a mold for a first calcination treatment to obtain a porous structure framework; Subjecting the porous structure framework to a second calcination treatment and an annealing treatment in sequence to obtain the porous tantalum carbide.

2. The method according to claim 1, characterized in that The tantalum source includes tantalum powder, and the D 50 particle size of the tantalum powder is 50 μm to 1000 μm, preferably 100 μm to 500 μm, and more preferably 100 μm to 300 μm.

3. The method according to claim 2, characterized in that, The purity of the tantalum powder is ≥99.9999%.

4. The method according to claim 1, wherein The carbon content of the carbon-based binder is ≥80%; and / or The carbon-based binder includes at least one of pitch, graphite glue, and chitosan; and / or The viscosity of the carbon-based binder is 2000 mPa·s to 6000 mPa·s, preferably 3000 mPa·s to 5000 mPa·s, more preferably 3500 mPa·s to 4500 mPa·s.

5. The method according to claim 1, wherein The pore-forming agent includes at least one of NH4HCO3, NH4Cl, and basic magnesium carbonate; and / or The D of the pore former 50 has a particle size of 5 μm to 500 μm, preferably 10 μm to 300 μm, more preferably 20 μm to 100 μm.

6. The method according to claim 1, wherein The molar mass ratio of the tantalum source to the carbon-based binder is 1:1.

25.

7. The method according to claim 1, wherein Based on the mass of the mixture, the mass fraction of the pore-forming agent is 5% to 50%, preferably 10% to 40%, more preferably 20% to 30%.

8. The method according to claim 1, wherein The stirring speed during the mixing is 20 rpm to 1000 rpm, preferably 20 rpm to 40 rpm; the mixing time is 2 h to 10 h, preferably 3 h to 8 h, more preferably 4 h to 6 h.

9. The method according to claim 1, wherein The shape of the mold includes but is not limited to at least one of a cylindrical shape, a square shape, a conical shape, and other special-shaped structures; and / or The material of the mold includes graphite, and the surface of the mold is coated with a tantalum carbide coating.

10. The method according to claim 1, characterized in that, The temperature of the first calcination treatment is 1000°C to 1200°C, and the time of the first calcination treatment is 3 h to 5 h.

11. The method according to claim 10, wherein The temperature of the second calcination treatment is 2300°C to 2500°C, preferably 2350°C to 2450°C; The time of the second calcination treatment is 20 h to 60 h, preferably 25 h to 50 h, more preferably 30 h to 40 h; The second calcination treatment requires filling with an inert gas to keep the synthesis pressure at 10 mbar to 30 mbar.

12. The method according to claim 1, wherein The annealing treatment includes: raising the pressure to 500 mbar in 8 h to 20 h to lower the temperature to 1800°C to 2000°C, then lowering the temperature to 1000°C to 1200°C in 3 h to 6 h, and finally cooling to room temperature.

13. A porous tantalum carbide, characterized in that, It is prepared by the method according to any one of claims 1 to 12.

14. The porous tantalum carbide according to claim 13, wherein, The porosity of the porous tantalum carbide is 65% to 80%.

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