Graphite article comprising a ta c / ta 2 c gradient coating and method for producing same

Abstract

The application relates to the technical field of semiconductors, in particular to a graphite piece containing a TaC / Ta2C gradient coating and a preparation method thereof, and at least comprises the following steps: providing slurry suspensions 1, slurry suspensions 2 and suspension slurry 3, coating the slurry suspensions 1 to the surface of a graphite piece, solidifying to form a first pre-coating layer; coating the slurry suspensions 2 to the surface of the first pre-coating layer, drying to form a second pre-coating layer, and solidifying to obtain a preformed piece, sintering the preformed piece to form a double-layer Ta2C buffer layer; coating the suspension slurry 3 to the surface of the double-layer Ta2C buffer layer, solidifying to form a third pre-coating layer, sintering the third pre-coating layer to form a TaC / Ta2C gradient coating, guaranteeing high bonding force of the coating and the graphite, gradually approaching the thermal expansion coefficients between the graphite and the TaC coating layer, and improving the durability and reliability of the material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor, in particular to a graphite piece containing a TaC / Ta2C gradient coating and a preparation method thereof. BACKGROUND

[0002] Tantalum carbide (TaC) has high melting point, high hardness, high thermal conductivity and high chemical stability. Preparing a super-high-temperature, corrosion-resistant and high-purity TaC coating on the surface of a graphite material is expected to significantly prolong the service life of the graphite assembly, inhibit the generation of carbon inclusions and other crystal defects, and thus improve the quality of single crystal growth of indium phosphide (InP), gallium arsenide (GaAs), silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), aluminum nitride (AlN) and the like or reduce the process cost. The main difficulty to be solved for the TaC coating graphite piece is that there is a large difference in physical properties such as thermal expansion coefficient between the TaC coating and the carbon material, the coating prepared has low bonding strength with the graphite substrate, and it is difficult to avoid the generation of cracks, pores and thermal stress, and the coating is easy to peel off in the actual corrosive atmosphere and repeated temperature rising and falling process. The existing technology mainly avoids the problem of low bonding strength of the prepared coating caused by direct contact of TaC with carbon material by alternately depositing a silicon carbide composite layer, a silicon carbide-tantalum carbide composite coating and a tantalum carbide coating multiple times, so it is crucial to provide a TaC coating with high bonding strength on the surface of a graphite piece.

[0003] The TaC coating graphite piece has a huge demand and wide application prospect in the market. At present, the mainstream of manufacturing the TaC coating graphite piece is to rely on a CVD TaC assembly. However, due to the high cost of CVD TaC production equipment and the limited deposition efficiency, it has not completely replaced the traditional SiC coating graphite material. The sintering method can effectively reduce the cost of raw materials and can adapt to graphite pieces with complex shapes, thereby meeting the needs of more different application scenarios. According to the different sintering slurry, a multi-layer buffer layer / TaC layer with gradually close thermal expansion coefficient can be prepared on the surface of the graphite, thereby greatly improving the service life of the TaC coating, reducing the production cost and promoting the alternative update of advanced heat field materials. However, TaC has low plasticity and poor thermal shock resistance, resulting in low bonding strength with the graphite interface, and the configuration of the precursor slurry and the subsequent coating, sintering and other process conditions during the sintering process have a great influence on the quality of the finally prepared graphite piece. SUMMARY

[0004] In order to solve the above problems, the application provides a preparation method of a graphite piece containing a TaC / Ta2C gradient coating, wherein the ratio of TaC and Ta2C is set in the coating design to form a buffer layer with gradient characteristics. The purpose of this layer is to relieve thermal stress caused by temperature changes through gradually transition material properties (such as thermal expansion coefficient, bonding strength, etc.). The TaC / Ta2C gradient buffer layer design effectively solves the bonding strength problem between the TaC coating and the graphite substrate, and reduces the crack and peeling phenomenon caused by the difference in thermal expansion coefficient, providing a more solid foundation for the application of TaC coated graphite pieces and having a wide market prospect.

[0005] In one aspect, the application provides a preparation method of a graphite piece containing a TaC / Ta2C gradient coating, at least comprising the following steps:

[0006] A slurry suspension 1 containing a tantalum source, a dispersant and a binder is provided, the slurry suspension 1 is applied to the surface of the graphite piece, and a first pre-coating layer is formed by solidification;

[0007] A slurry suspension 2 containing tantalum carbide, a sintering agent, a dispersant and a binder is provided, the slurry suspension 2 is applied to the surface of the first pre-coating layer, dried to form a second pre-coating layer, and solidified to obtain a preform, and the preform is sintered to form a double-layer Ta2C buffer layer;

[0008] A slurry suspension 3 containing a tantalum source, a carbon source, a dispersant and a binder is provided, the slurry suspension 3 is applied to the surface of the double-layer Ta2C buffer layer, and a third pre-coating layer is formed by solidification, and the third pre-coating layer is sintered to form a TaC / Ta2C gradient coating.

[0009] As a preferred technical solution, the tantalum source in the slurry suspension 1 includes at least one of Ta2O5, Ta powder, TaOC interionic compound and TaC powder, and preferably is Ta powder.

[0010] Preferably, the particle size of the Ta powder is 20-100 nm, preferably 50-80 nm, and most preferably 60 nm.

[0011] As an example, the particle size of the Ta powder can be 50 nm, 60 nm, 70 nm or 80 nm.

[0012] Preferably, the purity of the Ta powder is ≥99 wt%, and preferably is 99.99 wt%.

[0013] As a preferred technical solution, the sintering agent includes at least one of Fe, Co, Ni, Cr, Al2O3 and acetylacetone, and preferably is nickel (Ni).

[0014] As a preferred technical solution, the purity of the tantalum carbide is 99.99wt%, and the particle size is 100-2000nm, preferably the particle size is 800-1200nm.

[0015] As an example, the particle size of the tantalum carbide can be 800nm, 900nm, 1000nm, 1200nm.

[0016] As a preferred technical solution, the carbon source includes at least one of high-purity carbon powder, carbon black, glucose, graphene, acetylacetone, TaC powder, and preferably acetylacetone.

[0017] As a preferred technical solution, the tantalum source in the suspension slurry 3 is Ta2O5, Ta powder, TaC powder, TaCl 5、 at least one of a tantalum standard solution, TaF5, and preferably TaCl5.

[0018] As a preferred technical solution, the dispersant in the slurry suspension 1, the slurry suspension 2, and the suspension slurry 3 all includes at least one of anhydrous ethanol, deionized water, ethylene glycol, methanol, and isopropyl alcohol, and preferably anhydrous ethanol.

[0019] As a preferred technical solution, the binder in the slurry suspension 1, the slurry suspension 2, and the suspension slurry 3 all includes at least one of polyvinyl butyral, polyvinyl alcohol, polyacrylamide, polyethylene oxide, phenolic resin, and graphite glue, and preferably polyvinyl butyral.

[0020] Preferably, the weight average molecular weight (M W ) of the polyvinyl butyral is 50000-120000, and preferably 70000-90000.

[0021] As an example, the weight average molecular weight (M W ) of the polyvinyl butyral can be 70000, 80000, 90000.

[0022] As a preferred technical solution, the tantalum source in the slurry suspension 1 is added in an amount of 0.5g / mL-1.5g / mL, and preferably 0.7g / mL-1g / mL.

[0023] As an example, the tantalum source in the slurry suspension 1 can be added in an amount of 0.7g / mL, 0.8g / mL, 0.9g / mL, 1g / mL.

[0024] As a preferred technical solution, the binder in the slurry suspension 1 is added in an amount of 2wt%-8wt%, and preferably 3wt%-6wt%.

[0025] As an example, the amount of the binder added in the slurry suspension 1 is 3wt%, 4wt%, 5wt%, 6wt%.

[0026] As a preferred technical solution, the preparation method of the slurry suspension 1 comprises: stirring and mixing the tantalum source with the dispersant and the binder, and then performing ultrasonic treatment after the stirring and mixing until there are no particles, to obtain the slurry suspension. In the ultrasonic treatment, the amplitude horn is 20, the frequency is 15KHz-35KHz, the power is 800W-1200W, and the ultrasonic time is 20min-60min.

[0027] As a preferred technical solution, the mass ratio of the tantalum carbide to the sintering agent in the slurry suspension 2 is (20-50):(1-5), preferably (20-40):(1-3), and most preferably 30:1.

[0028] As an example, the mass ratio of the tantalum carbide to the sintering agent in the slurry suspension 2 can be 20:1, 30:1, 40:1, 20:3, 40:3, or 30:3.

[0029] As a preferred technical solution, the mass ratio of the dispersant to the total mass of the tantalum source and the sintering agent is (3-6):1, and preferably 4:1.

[0030] As an example, the mass ratio of the dispersant to the total mass of the tantalum source and the sintering agent can be 3:1, 4:1, 5:1, or 6:1.

[0031] As a preferred technical solution, the amount of the binder added in the slurry suspension 2 is 0.1wt%-3wt%, preferably 0.5wt%-1.5wt%, and most preferably 1wt%.

[0032] As an example, the amount of the binder added in the slurry suspension 2 can be 0.5wt%, 1wt%, or 1.5wt%.

[0033] As a preferred technical solution, the preparation method of the slurry suspension 2 comprises: mixing the tantalum carbide and the sintering agent, and then adding them into a ball mill tank for ball milling treatment at a speed of 500r / min-1000r / min for 5h-10h; and then stirring and mixing with the dispersant and the binder, and then performing ultrasonic treatment after the stirring and mixing until there are no particles, to obtain the slurry suspension. In the ultrasonic treatment, the amplitude horn is 20, the frequency is 15KHz-35KHz, the power is 800W-1200W, and the ultrasonic time is 20min-60min.

[0034] As a preferred technical solution, the ion concentration of Ta 5+ in the slurry suspension 3 is 0.1-0.5mol / L, and preferably 0.4mol / L.

[0035] As an example, the ion concentration of Ta 5+ in the slurry suspension 3 is 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.4 mol / L.

[0036] As a preferred technical solution, the molar ratio of the tantalum source and the carbon source in the slurry suspension 3 is (0.8-1.2):1, preferably 1:1.

[0037] As an example, the molar ratio of the tantalum source and the carbon source in the slurry suspension 3 can be 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1.

[0038] As a preferred technical solution, the amount of the binder added in the slurry suspension 3 is 0.1wt%-0.8wt%, preferably 0.2wt%-0.6wt%, and most preferably 0.4wt%.

[0039] As an example, the amount of the binder added in the slurry suspension 3 can be 0.2wt%, 0.3wt%, 0.3wt%, 0.5wt%, 0.6wt%.

[0040] As a preferred technical solution, the ratio of the dispersant to the total mass of the tantalum source and the carbon source in the slurry suspension 3 is (15-20):(2-5), preferably 17:3.

[0041] As a preferred technical solution, the slurry suspension 3 is synthesized by a solvothermal method, the solvothermal reaction temperature is 180°C-220°C, and the solvothermal reaction time is 8h-16h.

[0042] As a preferred technical solution, the preparation method of the preform is as follows: the slurry suspension 1 is applied to the surface of the graphite piece, and after natural air drying, it is placed in a vacuum drying oven, and after being kept at 150-250 ℃ for 8h-16h, a first pre-coating layer is formed and solidified; then the slurry suspension 2 is applied to the surface of the first pre-coating layer, and after natural air drying, it is placed in a vacuum drying oven, and after being kept at 150-250 ℃ for 8h-16h, a second pre-coating layer is formed and solidified to obtain a preform.

[0043] As a preferred technical solution, the thickness of the first pre-coating layer is ≤50μm, preferably 20μm-30μm.

[0044] As a preferred technical solution, the thickness of the second pre-coating layer is ≤80μm, preferably 40μm-60μm.

[0045] As a preferred technical solution, the graphite piece is obtained by the following method: polishing the graphite block to be smooth, performing ultrasonic cleaning treatment, sintering the graphite block at ≥ 2300 ℃ for ≥ 3 h to obtain the graphite piece.

[0046] Preferably, the graphite piece is obtained by the following method: cutting high-purity graphite to obtain a graphite block, polishing the surface of the graphite block with 100 mesh, 220 mesh, 400 mesh, and 800 mesh sandpaper in turn, placing the graphite block in alcohol for ultrasonic cleaning treatment, and then placing the graphite block in a graphite induction furnace and sintering at ≥ 2300 ℃ for at least 3 h in an argon atmosphere (slightly positive pressure) to obtain the graphite piece.

[0047] The present application increases the graphitization degree of graphite, improves the purity of graphite, and increases the porosity of graphite through the above treatment.

[0048] As a preferred technical solution, the coating method includes one of vacuum immersion, spraying (ultrasonic spraying), shower coating, and brushing, and is preferably spraying.

[0049] The TaC-coated graphite piece includes: a crucible, a seed crystal holder, and a flow guide ring in a PVT-grown SiC and AlN single crystal furnace; a heater in MOCVD GaN epitaxial layer growth; a wafer carrier, a baffle, an outer floating gas nozzle, a gas guide, a pneumatic conduit, etc. in SiC epitaxy. Due to the different shapes and sizes of the above various graphite pieces, the corresponding vacuum immersion, spraying (ultrasonic spraying), shower coating, and brushing are matched during the coating process to perform slurry suspension coating.

[0050] As a preferred technical solution, the sintering of the preform is specifically: placing the preform into a sintering furnace, sintering at 1600-1800 ℃ in a vacuum environment of 0.1-10 Pa, and holding for 10-30 min.

[0051] As a preferred technical solution, the double-layer Ta2C buffer layer includes a large-grained dense Ta2C bottom layer and a small-grained porous Ta2C surface layer.

[0052] Preferably, the thickness of the large-grained dense Ta2C bottom layer is ≤ 10 μm, and is preferably 5-10 μm.

[0053] Preferably, the thickness of the small-grained porous Ta2C surface layer is ≤ 20 μm, and is preferably 15-20 μm.

[0054] As a preferred technical solution, the thickness of the third pre-coating layer is 80-150 μm, and is preferably 100-150 μm.

[0055] As a preferred technical solution, the preparation method of the TaC / Ta2C gradient coating is specifically: the suspension slurry 3 is applied to the surface of the double-layer Ta2C buffer layer, and after natural air drying, it is placed in a vacuum drying box, and is kept at 150-250 DEG C for 8-16 h to form a third pre-coating and solidify, the third pre-coating is high-temperature sintered, the temperature of high-temperature sintering is 2100-2300 DEG C, the time is 0.5-1 h, the vacuum atmosphere is 0.1-10 Pa, and the TaC / Ta2C gradient coating is formed after natural cooling.

[0056] In order to ensure the service life of the TaC coating under various corrosion conditions, the present application effectively solves the difference in thermal expansion coefficient between the TaC coating and the graphite by preparing a double-layer Ta2C buffer layer. Specifically, the double-layer Ta2C buffer layer provided by the present application includes a large-grained dense Ta2C bottom layer with a thickness of 5-10 μm and a small-grained porous Ta2C surface layer with a thickness of 15-20 μm. Compared with the traditional buffer layer (single dense metal layer and excessively loose porous carbide layer), the binding force with the graphite substrate is high, and the thermal stress generated by the expansion of the TaC crystal can be relieved, the plasticity of the coating interface can be effectively improved, and the impact resistance can be improved.

[0057] Specifically, by optimizing the formula of the slurry suspension 1, the slurry suspension 2 and the suspension slurry 3 of the three elements Ta, O and C, the present application ensures that a large-grained dense Ta2C bottom layer with high bonding strength with the graphite substrate is obtained after sintering; a loose porous small-grained porous Ta2C surface layer; a dense TaC bottom layer without cracks and holes. Especially, the sintering agent in the slurry suspension 2 is controlled to be metal nickel, and the mass ratio of the tantalum carbide and the metal nickel is controlled to be 30:1, so as to ensure that a small-grained porous Ta2C surface layer with a loose porous structure is formed subsequently. Further, by controlling the thickness of the first pre-coating, the second pre-coating and the third pre-coating, the problems of coating cracking and peeling are avoided.

[0058] Further, by optimizing the formula of the suspension slurry 3 of the three elements Ta, O and C and the subsequent sintering process, the present application forms a TaC coating with a certain thickness on the surface of the double-layer Ta2C buffer layer. The TaC coating as the outermost layer has the largest crystal size, no obvious holes and cracks, and presents free orientation growth, which can most effectively resist the corrosion atmosphere and adapt to the repeated temperature rising and falling process.

[0059] The present application also provides a TaC / Ta2C gradient coating, which includes, from top to bottom, a TaC layer, a small-grained porous Ta2C surface layer and a large-grained dense Ta2C bottom layer.

[0060] The TaC / Ta2C gradient coating provided by the application has the advantages of free orientation, no cracks on the surface, high density, and the like, and the prepared optimized and high-quality gradient coating graphite piece can better meet the actual application requirements.

[0061] Advantages

[0062] 1. The application provides a preparation method of a graphite piece containing a TaC / Ta2C gradient coating, which guarantees high bonding force of the coating and the graphite through TaC / Ta2C gradient buffer layer design, and reduces the difference in thermal expansion coefficients of the graphite and TaC.

[0063] 2. The double-layer Ta2C buffer layer provided by the application comprises a large-grain dense Ta2C bottom layer with a thickness of 5-10 microns and a small-grain porous Ta2C surface layer with a thickness of 15-20 microns, and has the advantages of high bonding force with the graphite substrate, and the ability to relieve thermal stress generated by TaC crystal expansion, effectively improve the plasticity of the coating interface, and improve the impact resistance.

[0064] 3. The application optimizes the formula of slurry suspension 1, slurry suspension 2 and slurry suspension 3 of three elements of Ta, O and C, guarantees that a large-grain dense Ta2C bottom layer with high bonding strength with the graphite substrate is obtained after sintering, and guarantees that a porous small-grain porous Ta2C surface layer and a dense TaC bottom layer without cracks and holes are obtained.

[0065] 4. The application controls the sintering agent in the slurry suspension 2 to be metal nickel, and controls the mass ratio of the tantalum carbide and the metal nickel to be 30:1, guarantees that a small-grain porous Ta2C surface layer with a porous structure is formed subsequently, and further cooperates with the control of the thickness of the first pre-coating layer, the second pre-coating layer and the third pre-coating layer to avoid the problems of coating cracking and coating peeling.

[0066] 5. The application optimizes the formula of the slurry suspension 3 of three elements of Ta, O and C and the subsequent sintering process, forms a TaC coating with a certain thickness on the surface of the double-layer Ta2C buffer layer, the TaC coating as the outermost layer has the largest crystal size, no obvious holes and cracks, and presents free orientation growth, and can most effectively resist the corrosive atmosphere and adapt to the repeated temperature rising and falling process. BRIEF DESCRIPTION OF DRAWINGS

[0067] Figure 1 The application provides a TaC / Ta2C gradient coating structure schematic diagram obtained from Example 1, wherein 1 represents a TaC layer, 2 represents a small-grain porous Ta2C surface layer, and 3 represents a large-grain dense Ta2C bottom layer.

[0068] Figure 2SEM characterization of the TaC / Ta2C gradient coating obtained for Example 1, left side of the figure is a cross-section view (x500 magnification), right side is a surface view (x3000 magnification).

[0069] Figure 3 XRD characterization of the TaC layer, small grain porous Ta2C surface layer, large grain dense Ta2C bottom layer in Example 1, left side of the figure is the XRD characterization of the small grain porous Ta2C surface layer (1), large grain dense Ta2C bottom layer (2), right side is the XRD characterization of the TaC layer, wherein 1 is Ta2C, 2 is TaC.

[0070] Figure 4 SEM view of the double layer Ta2C buffer layer in Comparative Example 1 (x30 magnification).

[0071] Figure 5 SEM view of the single layer Ta2C buffer layer in Comparative Examples 2, 3 (without loose porous structure), left side of the figure corresponds to Comparative Example 2 (x897 magnification), right side corresponds to Comparative Example 3 (x1000 magnification).

[0072] Figure 6 SEM characterization of the tantalum-palladium carbide composite coating prepared in Comparative Example 4 (x800 magnification).

[0073] Figure 7 SEM characterization of the single layer Ta2C layer provided in Comparative Example 5, left side of the figure is x500 magnification, right side is x50 magnification.

[0074] Figure 8 SEM characterization of the single layer Ta2C layer provided in Comparative Example 6, left side of the figure is x5000 magnification, right side is x1000 magnification.

[0075] Figure 9 SEM characterization of the single layer Ta2C layer provided in Comparative Example 7, x700 magnification. DETAILED DESCRIPTION

[0076] The application provides a preparation method of a graphite piece containing a TaC / Ta2C gradient coating, wherein the Ta2C gradient layer is used as a buffer layer, and the thicknesses of the Ta2C gradient layers are 5-10 microns and 15-20 microns respectively. The first Ta2C coating layer is tightly combined with the graphite substrate, the crystal grains are large and the combination is dense, the second Ta2C layer has small crystal grains and is a loose porous structure as a whole, and the thermal stress generated by the expansion of the TaC crystal can be relieved. The double-layer Ta2C coating layer is different from the traditional buffer layer (namely, a single dense metal layer and a too loose porous carbide layer), the double-layer buffer layer combines the advantages of the two, the two kinds of Ta2C layers with different crystal sizes and thicknesses not only ensure the high bonding force of the coating and the graphite, but also make the thermal expansion coefficients between the graphite and the TaC coating layer close to each other layer by layer, the design can effectively relieve the thermal stress generated by the expansion of the TaC crystal under high temperature conditions, and the risk of coating cracking and peeling is reduced. The TaC crystal in the outermost layer has the largest size, has no obvious pores and cracks, and presents free orientation growth, can most effectively resist the corrosive atmosphere and adapt to the repeated temperature rising and falling process, and the overall performance and service life of the graphite piece are improved.

[0077] Embodiment 1

[0078] The embodiment 1 of the application provides a preparation method of a graphite piece containing a TaC / Ta2C gradient coating, and comprises the following steps:

[0079] A slurry suspension 1 containing a tantalum source, a dispersant and a binder is provided, the slurry suspension 1 is applied to the surface of the graphite piece, and a first pre-coating layer is formed after solidification;

[0080] A slurry suspension 2 containing tantalum carbide, a sintering agent, a dispersant and a binder is provided, the slurry suspension 2 is applied to the surface of the first pre-coating layer, a second pre-coating layer is formed after drying, and a pre-product is obtained after solidification, the pre-product is sintered to form a double-layer Ta2C buffer layer;

[0081] A slurry suspension 3 (Ta 3.9 O 7.3 C) containing a tantalum source, a carbon source, a dispersant and a binder is provided, the slurry suspension 3 is applied to the surface of the double-layer Ta2C buffer layer, a third pre-coating layer is formed after solidification, and the third pre-coating layer is sintered to form a TaC / Ta2C gradient coating.

[0082] The tantalum source in the slurry suspension 1 is Ta powder, the particle size of the Ta powder is 60 nm, and the purity of the Ta powder is 99.99 wt%, which is provided by Beijing Zhongke Yannuo New Material Technology Co., Ltd.

[0083] The sintering agent is nickel (Ni), which is produced by Jiangxi Guomai Technology Co., Ltd. and has a purity of 99.99 wt% and a particle size of 1000 nm.

[0084] The purity of the tantalum carbide is 99.99wt%, and the particle size is 1000nm, provided by Beijing Yanbang New Material Technology Co., Ltd.

[0085] The carbon source is acetylacetone.

[0086] The tantalum source in the suspension slurry 3 is TaCl5.

[0087] The dispersant in the slurry suspension 1, the slurry suspension 2 and the suspension slurry 3 is anhydrous ethanol.

[0088] The binder in the slurry suspension 1, the slurry suspension 2 and the suspension slurry 3 is polyvinyl butyral.

[0089] The weight average molecular weight (M W ) of the polyvinyl butyral is 70000-90000, provided by Shanghai Maikelin Biochemical Technology Co., Ltd.

[0090] The adding amount of the tantalum source in the slurry suspension 1 is 0.83g / mL.

[0091] The adding amount of the binder in the slurry suspension 1 is 5wt%.

[0092] The preparation method of the slurry suspension 1 comprises: stirring and mixing the tantalum source with the dispersant and the binder, and then putting into an ultrasonic cell crusher for ultrasonic treatment to obtain the slurry suspension, wherein in the ultrasonic treatment: the amplitude bar is 20, the frequency is 19.5KHz, the power is 950W, and the ultrasonic time is 20min.

[0093] The mass ratio of the tantalum carbide to the sintering agent in the slurry suspension 2 is 30:1.

[0094] The ratio of the dispersant to the total mass of the tantalum source and the sintering agent is 4:1.

[0095] The adding amount of the binder in the slurry suspension 2 is 1wt%.

[0096] The preparation method of the slurry suspension 2 comprises: mixing the tantalum carbide and the sintering agent, and then adding into a ball mill tank for ball milling treatment at a rotating speed of 600r / min for 8h; and then stirring and mixing with the dispersant and the binder, and then putting into an ultrasonic cell crusher for ultrasonic treatment to obtain the slurry suspension, wherein in the ultrasonic treatment: the amplitude bar is 20, the frequency is 19.5KHz, the power is 950W, and the ultrasonic time is 20min.

[0097] The ion concentration of Ta 5+ in the slurry suspension 3 is 0.4 mol / L.

[0098] The molar ratio of the tantalum source and the carbon source in the slurry suspension 3 is 1:1.

[0099] The amount of the binder added in the slurry suspension 3 is 0.4wt%.

[0100] The ratio of the dispersant to the total mass of the tantalum source and the carbon source in the slurry suspension 3 is 17:3.

[0101] The slurry suspension 3 is synthesized by a solvothermal method, the solvothermal reaction temperature is 200℃, and the solvothermal reaction time is 12h.

[0102] The preparation method of the preform is as follows: the slurry suspension 1 is applied to the surface of the graphite piece, and after natural air drying, it is placed in a vacuum drying oven, and after being heated at 200℃ for 10h, a first pre-coating layer is formed and solidified; then the slurry suspension 2 is applied to the surface of the first pre-coating layer, and after natural air drying, it is placed in a vacuum drying oven, and after being heated at 200℃ for 10h, a second pre-coating layer is formed and solidified to obtain a preform.

[0103] The thickness of the first pre-coating layer is 25μm.

[0104] The thickness of the second pre-coating layer is 50μm.

[0105] The graphite piece is obtained by the following method: high-purity graphite is cut to obtain a graphite block (10cm*10cm*0.5cm), the surface of the graphite block is polished smooth with 100-mesh, 220-mesh, 400-mesh, and 800-mesh sandpaper in turn, and then the graphite block is placed in alcohol for ultrasonic cleaning treatment, and after being cleaned, the graphite block is placed in a graphite induction furnace and sintered at 2600℃ for 3h in an argon atmosphere (slightly positive pressure), thereby obtaining the graphite piece.

[0106] The application method is spraying.

[0107] The sintering of the preform is as follows: the preform is placed in a sintering furnace, and is heated at 1800℃ in a vacuum environment of 3Pa for 30min.

[0108] The double-layer Ta2C buffer layer includes a large-grained dense Ta2C bottom layer and a small-grained porous Ta2C surface layer.

[0109] The thickness of the large-grained dense Ta2C bottom layer is 10μm.

[0110] The thickness of the small-grained porous Ta2C surface layer is 20μm.

[0111] The thickness of the third pre-coating layer is 120μm.

[0112] The preparation method of the TaC / Ta2C gradient coating is specifically as follows: the suspension slurry 3 is applied to the surface of the double-layer Ta2C buffer layer, and after natural air drying, it is placed in a vacuum drying box, heat preservation is carried out at 200 DEG C for 10 h to form a third pre-coating and solidification, high-temperature sintering is carried out on the third pre-coating, the temperature of high-temperature sintering is 2300 DEG C, the time is 0.5 h, the vacuum atmosphere is 5 Pa, and the TaC / Ta2C gradient coating is formed after natural cooling.

[0113] Referring to Figures 1-3 , the embodiment 1 of the present application further provides a TaC / Ta2C gradient coating, which comprises, from top to bottom, a TaC layer 1, a small-grain porous Ta2C surface layer 2 and a large-grain dense Ta2C bottom layer 3.

[0114] Comparative example 1

[0115] The comparative example 1 of the present application provides a preparation method of a graphite piece containing a TaC / Ta2C gradient coating, and the specific implementation manner is the same as that of the embodiment 1, except that the thickness of the first pre-coating is 150 μm, and the thickness of the second pre-coating is 750 μm. The stress mismatch between the coatings caused by the thicker pre-coating design affects the overall bonding performance. The SEM image of the double-layer Ta2C buffer layer formed is shown in Figure 4 , and it is observed that there are many cracks. The cracks are mainly caused by the fact that the pre-coating with an excessively large thickness cannot effectively relieve thermal stress during coating and sintering, so that the integrity of the coating is affected, and thus the subsequent preparation is not carried out. It can be seen that it is extremely necessary to reasonably set the thickness of the pre-coating to prevent cracking and improve the bonding strength.

[0116] Comparative example 2

[0117] The comparative example 2 of the present application provides a preparation method of a graphite piece containing a TaC / Ta2C gradient coating, and the specific implementation manner is the same as that of the embodiment 1, except that the mass ratio of the tantalum carbide and the sintering agent in the slurry suspension 2 is 30:2. The SEM image of the single-layer Ta2C buffer layer formed is shown in Figure 5 . The change of the ratio causes the single-layer Ta2C buffer layer formed to lack the required loose porous structure, and the coating is crystallized tightly, so that the subsequent preparation is not carried out. The lack of such a structure may affect the thermal stress relieving ability of the coating, and thus cause the coating to be damaged or peeled off in actual application.

[0118] Comparative example 3

[0119] The comparative example 3 of the present application provides a preparation method of a graphite piece containing a TaC / Ta2C gradient coating, and the specific implementation manner is the same as that of the embodiment 1, except that the mass ratio of the tantalum carbide and the sintering agent in the slurry suspension 2 is 30:3. The SEM image of the single-layer Ta2C buffer layer formed is shown inFigure 5 It is observed that the coating crystallizes tightly without forming the expected loose porous structure. Although the dense coating can provide certain bonding strength, the lack of loose porous structure means that the coating may not effectively relieve stress concentration caused by expansion when facing high temperature and thermal stress, and the single-layer dense Ta2C layer may increase the brittleness of the coating, ultimately affecting the service life and performance stability of the coating.

[0120] Comparative Example 4

[0121] The comparative example 4 of the present application is a tantalum-palladium carbide composite coating prepared according to the scheme of example 1 in the patent CN 115637419 A A method for preparing a tantalum-palladium carbide composite coating and its product. In terms of the composition of the buffer layer, the thermal expansion coefficients of Ta and Ta2C are close, and both can play a role in relieving thermal stress. However, the melting point of tantalum metal is much lower than that of Ta2C, and it is easy to soften at a high temperature of 2600℃. Therefore, the thin buffer layer is prone to warping and bending during rapid temperature rise and fall, which can cause a sharp increase in coating stress and lead to coating cracking. In addition, in terms of the morphology of the buffer layer, the SEM image of the tantalum-palladium carbide composite coating is shown in Figure 6 It can be seen that the tantalum layer is combined very tightly, and the thermal expansion coefficient of tantalum is still different from that of graphite, and the buffering effect is worse than that of the porous tantalum layer or Ta2C layer. Therefore, even though the tantalum layer has stronger combination in the microstructure, it cannot effectively cope with the thermal stress under high temperature conditions. Its buffering effect is not as good as that of the porous tantalum layer or Ta2C layer.

[0122] Comparative Example 5

[0123] The comparative example 5 of the present application provides a method for preparing a graphite piece containing a TaC / Ta2C gradient coating, and the specific implementation is the same as that of example 1, except that the tantalum source and carbon source in the slurry suspension 2 are replaced by TaCl5 and carbon powder, and only a single-layer Ta2C layer is prepared. The coating has many cracks, holes and is not uniform, has low density, and cannot completely coat the graphite substrate, so it cannot be used as a good buffer intermediate layer. In the preparation process of the tantalum carbide coating, selecting the appropriate precursor is crucial to ensure the performance of the coating to meet the actual application requirements.

[0124] Comparative Example 6

[0125] The comparative example 6 of the present application provides a method for preparing a graphite piece containing a TaC / Ta2C gradient coating, which has the same specific implementation as the example 1, except that the tantalum source and the carbon source in the slurry suspension 2 are replaced by Ta2O5 and carbon powder, and only a single layer of Ta2C layer is prepared. The number of cracks and holes in the coating is appropriately reduced compared with the comparative example 5, and the TaC grains begin to connect and crystallize, which helps to improve the stability and structural integrity of the coating. However, due to the uneven distribution of pores, the coating has insufficient buffering performance, which cannot effectively reduce the stress caused by the difference in thermal expansion coefficient between materials.

[0126] Comparative example 7

[0127] The comparative example 7 of the present application provides a method for preparing a graphite piece containing a TaC / Ta2C gradient coating, which has the same specific implementation as the example 1, except that the dispersant anhydrous ethanol in the slurry suspension 2 is replaced by deionized water, and only a single layer of Ta2C layer is prepared. During the use of deionized water as a dispersant, the uniform dispersibility of solid powder significantly decreases. Since the surface tension of deionized water is high, solid particles are difficult to disperse sufficiently in its medium, resulting in the agglomeration of powders. This agglomeration not only affects the flowability and formability of the slurry, but also introduces uneven TaC grain size in the finally prepared porous Ta2C layer. This unevenness directly affects the physical and mechanical properties of the coating, making it unable to meet the requirements as a good buffer intermediate layer.

[0128] Performance test

[0129] The present experiment aims to evaluate the effect of different coating structures on the corrosion resistance of graphite components, especially under extreme conditions. We prepared the corresponding coatings on a 100mm diameter graphite disc according to the preparation process in Example 1 (graphite component containing TaC / Ta2C gradient coating), Comparative Example 3 (graphite component containing only dense TaC coating), Comparative Example 6 (graphite component containing only non-dense TaC coating), Comparative Example 7 (graphite component containing only non-dense TaC coating). As shown in the figure, it is placed in a graphite crucible containing 50% by volume of SiC powder, simulating a SiC long crystal atmosphere at 2600°C, which can effectively simulate the corrosion conditions that may be encountered in actual application, ensuring the authenticity and effectiveness of the test. We evaluated the corrosion resistance of TaC coated graphite components prepared in four cases, with a corrosion test time of 6h, an atmosphere of Ar gas (102-103kpa), and a failure condition of one place of graphite substrate exposed and corroded. Comparative Examples 6 and 7 failed to maintain the integrity of the coating in the first corrosion test, which can be considered as failure cases. The main reason for these failures is that their coating structure is not dense, resulting in insufficient protection ability in the corrosion atmosphere. The TaC coatings prepared in Examples 1 and 4 have a certain service life under corrosion conditions. In particular, Example 1 has better thermal shock resistance due to its gradient coating design, which makes its corrosion resistance under extreme conditions significantly better than that of graphite components containing only dense TaC coating (Comparative Example 4). The superiority of this structure lies in the fact that the gradient layer can effectively relieve thermal stress and reduce the risk of coating cracking caused by temperature changes, thereby prolonging the service life of the coating. The results are shown in Table 1.

[0130] Table 1

[0131]

Claims

1. A method for producing a graphite member containing a TaC / Ta2C gradient coating, characterized by, At least comprising the following steps: Providing a slurry suspension 1 containing a tantalum source, a dispersant, and a binder, applying the slurry suspension 1 to the surface of a graphite piece, and solidifying to form a first pre-coating layer; Providing a slurry suspension 2 containing tantalum carbide, a sintering agent, a dispersant, and a binder, applying the slurry suspension 2 to the surface of the first pre-coating layer, drying to form a second pre-coating layer, and solidifying to obtain a preform, sintering the preform to form a double-layer Ta2C buffer layer; the sintering of the preform specifically comprises: placing the preform in a sintering furnace, and sintering at 1600-1800℃ under a vacuum environment of 0.1-10Pa for 10-30min; Providing a slurry suspension 3 containing a tantalum source, a carbon source, a dispersant, and a binder, applying the slurry suspension 3 to the surface of the double-layer Ta2C buffer layer, and solidifying to form a third pre-coating layer, and high-temperature sintering the third pre-coating layer at a temperature of 2100-2300℃ for 0.5-1h to form a TaC / Ta2C gradient coating layer; The mass ratio of the tantalum carbide to the sintering agent in the slurry suspension 2 is (20-50):(1-5). The TaC / Ta2C gradient coating layer comprises, from top to bottom, a TaC layer, a small-grain porous Ta2C surface layer, and a large-grain dense Ta2C bottom layer.

2. The method for preparing a graphite piece with a TaC / Ta2C gradient coating layer according to claim 1, wherein the sintering agent comprises at least one of Fe, Co, Ni, Cr, and Al2O3.

3. The method for preparing a graphite part with a TaC / Ta2C gradient coating according to claim 1, characterized in that, The graphite piece is obtained by polishing a graphite block to be smooth, performing ultrasonic cleaning treatment, and sintering the graphite block at ≥2300℃ for ≥3h.

4. The method for preparing a graphite part with a TaC / Ta2C gradient coating according to claim 1, characterized in that, The thickness of the first pre-coating layer is ≤50μm, and the thickness of the second pre-coating layer is ≤80μm.

5. The method for preparing a graphite part with a TaC / Ta2C gradient coating according to claim 1, characterized in that, The double-layer Ta2C buffer layer comprises a large-grain dense Ta2C bottom layer and a small-grain porous Ta2C surface layer.

6. The method for preparing a graphite part with a TaC / Ta2C gradient coating according to claim 5, characterized in that, The thickness of the large-grain dense Ta2C bottom layer is ≤10μm.

7. The method for preparing a graphite part with a TaC / Ta2C gradient coating according to claim 5, characterized in that, The thickness of the small-grain porous Ta2C surface layer is ≤20μm.

8. The method for preparing a graphite part with a TaC / Ta2C gradient coating according to claim 7, characterized in that, The thickness of the small-grain porous Ta2C surface layer is 15-20μm.

9. The method for preparing a graphite part with a TaC / Ta2C gradient coating according to claim 8, characterized in that, The thickness of the third pre-coating layer is 80-150μm.

10. A TaC / Ta2C gradient coating according to the method of any one of claims 1 to 9, characterized in that From top to bottom, the TaC / Ta2C gradient coating layer comprises a TaC layer, a small-grain porous Ta2C surface layer, and a large-grain dense Ta2C bottom layer.

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