CN117510236A - Method for preparing silicon carbide coating from methylsilane - Google Patents

Abstract

The application relates to the field of special material manufacturing, in particular to a method for preparing a silicon carbide coating from methylsilane. The methylsilane is used for CVD\CVI deposition of SiC, has moderate decomposition temperature, simple decomposition products, high deposition efficiency, no other byproducts such as hydrogen chloride, safe production, stable equipment operation, no need of frequent shutdown to clean pipelines, vacuum units and deposition chambers, full-automatic system operation, manpower resource saving, low overall production cost and good product quality. The methylsilane is adopted as the precursor of the silicon carbide coating, and the deposition temperature of the precursor is 100-200 ℃ lower than that of the conventional materials such as methyltrichlorosilane, so that a compact SiC polycrystalline film can be formed, the crystal growth and film forming efficiency is high, almost no defect exists, and the precursor is a good CVD\CVI deposition raw material of the SiC coating.

Description

Method for preparing silicon carbide coating from methylsilane

Technical field

The invention relates to the technical field of special material manufacturing, specifically a method for preparing silicon carbide coating using methylsilane.

Background technique

Silicon carbide (SiC) coating is a high-temperature resistant ceramic with a tetragonal crystal structure and a high melting temperature (above 2700°C). Among the many methods for preparing SiC materials, the CVD\CVI process has excellent adaptability to components with complex shapes and internal surfaces, and can achieve close-scale molding of large-sized, thin-walled, complex components, and can be achieved at relatively low temperatures. The coating is prepared at a temperature (700-1200°C) to avoid damage to the material structure caused by high-temperature treatment, and can easily control the composition and fine structure of the coating, which is beneficial to controlling the structure or composition gradient of the coating/substrate interface. , is considered to be the most promising silicon carbide coating preparation method. The silicon carbide crystal prepared by the CVD\CVI process has the characteristics of dense structure, neat lattice arrangement, tight combination with the substrate material, high temperature resistance, abrasion resistance, chemical erosion resistance, and good thermal conductivity.

Using methylsilane as raw material, the following silicon carbide coating can be prepared using CVD\CVI process:

SiC coating for hot-end components of a new generation of high thrust-to-weight ratio aeroengines, such as tail nozzles, combustion chambers, afterburners, turbines, etc.;

SiC coatings for hot-end components of rockets and missiles, such as thrust combustors, flame stabilizers, large exit cones of hydrogen-oxygen engines, blades and floating walls of turbine engines, solid rocket thrust vector nozzles, missile nose cones and other components;

SiC coatings for space station heat-resistant components, space station solar energy collection devices, and lightweight satellite reflectors;

Nuclear reaction high-temperature gas-cooled reactor fuel rod cladding radiation-resistant and oxidation-resistant SiC coating;

Thermal protection SiC coating for near space vehicles;

Stealth absorbing coating on the surface of military weapon systems;

Oxidation-resistant SiC coating for thermal insulation materials in high-temperature industrial furnaces;

SiC coating for fluidized bed and cold/hot hydrogenation reactor components for polycrystalline silicon, SiC coating for carbon/carbon thermal field materials (conductors, crucibles, etc.) for monocrystalline silicon;

SiC coatings for various hot bending molds, ceramic matrix composites, carbon-carbon composites, carbon-ceramic composites, graphite, high-temperature structural parts, corrosion-resistant structural parts, and silicon carbide ceramic matrix composites.

Based on the above reasons, the inventor believes that:

The technology of preparing SiC using CVD or CVI processes has been studied abroad, and the precursor used is mainly methyltrichlorosilane. However, during the application process, this substance will decompose to produce a large amount of hydrogen chloride gas and polysilanes by-products. Not only is the equipment highly corrosive, causing unstable production, poor product quality, and extremely low qualification rates, but polysilanes are also The by-products are extremely easy to spontaneously ignite and pose major safety hazards. At the same time, a large amount of hydrogen needs to be invested to control the C/Si ratio. The process control requirements are high and the risk of explosion is high. These all lead to high equipment investment and maintenance costs. Therefore, regardless of environmental protection, production safety, or sustainable development From the perspective of chemical industry, it is of great significance to develop new environmentally friendly chlorine-free precursors, and methylsilane is undoubtedly one of the best precursors.

Contents of the invention

In view of the problems of equipment corrosion, poor product quality, flammability and explosion caused by the precursors used in the prior art to prepare silicon carbide coatings, for this reason, the method of preparing silicon carbide coatings by methylsilane CVD\CVI disclosed in this application adopts Methylsilane is used as a precursor for the preparation of polycrystalline silicon carbide coatings, using chemical vapor deposition or chemical vapor infiltration processes.

In order to achieve the above objects, the present invention provides the following technical solutions:

The method for preparing a silicon carbide coating from methylsilane includes a process of depositing a silicon carbide coating (thin film) on the surface (or internal pores) of a base material using methylsilane as a precursor through CVD\CVI, and is characterized by: The precursor is methylsilane, the carrier gas is hydrogen, and the diluent gas is argon, which specifically includes the following steps:

S1: CVD\CVI system inert replacement;

S2: heating and vacuuming;

S3: Maintain constant deposition temperature;

S4: Rotating or non-rotating deposition;

S5: CVD\CVI deposition;

S6: Cool down.

Further, hydrogen gas at 0.2-2000L/min is used as the carrier gas, argon gas at 1-8000L/min is used as the diluent gas, and methylsilane at 0.02-5000L/min is fully mixed in the mixing tank and then transported to the CVD\CVI deposition Furnace deposition.

Furthermore, the CVD\CVI deposition furnace maintains a vacuum degree of 0.1 to 5000 Pa through a vacuum unit, and controls a deposition temperature of 600 to 2000°C through resistance or intermediate frequency heating.

Furthermore, the silicon carbide coating deposition thickness can be controlled between 0.5 and 2000um, and the deposition time can be controlled between 0.5 and 500 hours.

Furthermore, the vacuum-suctioned reaction tail gas and unreacted gas are discharged into the tail gas treatment system through pipelines to meet environmental protection and occupational health requirements.

Furthermore, after reaching the deposition time set by the process, the CVD\CVI deposition furnace will maintain a vacuum state of 0.1~8000Pa and automatically enter the cooling stage. In this stage, the pressure of the circulating cooling water is automatically controlled at 100~500KPa through the set program, and the flow rate is At 2 to 200m ³ /h, the temperature is controlled to reach the safe furnace opening temperature of 40 to 80°C, and the cooling time is controlled to 3 to 60 hours.

The above technical solution has the following advantages or beneficial effects:

The method for preparing silicon carbide coating from methylalkylsilane disclosed in this application has dense crystallization of deposited silicon carbide, extremely high binding force and few crystal defects. Because it uses CVD\CVI method, the device is simple, fully automatic controllable, and the equipment runs smoothly. Stable, without corrosive by-products and flammable and explosive by-products, a uniform and high-performance silicon carbide coating can be obtained. Methylsilane is used for CVD\CVI deposition of SiC. It has moderate decomposition temperature, simple decomposition products and high deposition efficiency. , no other by-products such as hydrogen chloride, safe production, stable equipment operation, no need for frequent shutdowns to clean pipelines, vacuum units, and deposition chambers, the system operates fully automatically, saves human resources, has low overall production costs, and has good product quality. Using methylsilane as the silicon carbide coating precursor can form a SiC polycrystalline film with a dense structure at a deposition temperature 100°C to 200°C lower than that of conventional materials such as methyltrichlorosilane. The crystal growth and film formation efficiency is high and almost defect-free. It is a good raw material for SiC coating CVD\CVI deposition.

Description of drawings

Figure 1 is a schematic flow diagram of the process system of the present invention.

Detailed ways

The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate the invention but are not intended to limit the scope of the invention.

In this application, methylsilane is used as the silicon carbide coating precursor. Methylsilane, as a single source substance containing both Si and C elements in the molecule with a Si/C ratio of 1:1, is used for CVD or CVI deposition of silicon carbide. , has the advantages of moderate decomposition temperature, single decomposition product, high deposition efficiency, high safety in use, no spontaneous combustion in the air, and good storage stability. The use of methylsilane precursor can form a stable polycrystalline SiC film at a temperature 100°C to 200°C lower than that of methyltrichlorosilane, with high film-forming efficiency and dense and perfect crystal form. In addition, as a SiC precursor for CVD/CVI, methylsilane is a non-corrosive, single-source silicon-carbon compound with the smallest molecular weight. Due to the high content of SiC components in the precursor molecules, the deposition rate is faster and the deposition temperature is lower. It can be obtained SiC with a close stoichiometric ratio is the optimal solution for growing SiC crystals by CVD\CVI process.

In order to achieve the purpose of the present invention, the process flow of preparing SiC coating using CVD\CVI is as shown in the attached figure. The thickness of silicon carbide coating can be freely adjusted according to the requirements of the finished product.

As shown in the drawings, the process of preparing silicon carbide coating by CVD\CVI using methylsilane as the precursor in this application uses 0.2-2000L/min hydrogen as the carrier gas and 1-8000L/min argon as the diluent gas. , mix thoroughly with 0.02~5000L/min methylsilane in the mixing tank and then transport it to the CVD\CVI deposition furnace. The deposition furnace maintains a vacuum degree of 0.1 to 5000 Pa through a vacuum unit, controls a deposition temperature of 600 to 2000°C through resistance or medium frequency heating, and controls the deposition time to 0.5 to 500 hours according to the silicon carbide coating deposition thickness of 0.5 to 2000um. The suctioned reaction tail gas and unreacted gas are discharged into the tail gas treatment system through pipelines to ensure that environmental protection and occupational health requirements are met. After reaching the deposition time set by the process, the CVD\CVI deposition furnace will maintain a vacuum state of 0.1~8000Pa and automatically enter the cooling stage. In this stage, the pressure of the circulating cooling water is automatically controlled at 100~500KPa through the set program, and the flow rate is between 2~ 200m ³ /h, thereby controlling the temperature to reach the safe furnace opening temperature of 40 to 80°C, and controlling the cooling time to 3 to 60 hours.

The reaction principle of the silicon carbide coating prepared by the CVD\CVI process of this application is as follows:

H ₃ C-SiH ₃ →SiC+3H ₂

The above technical solution has the following advantages or beneficial effects: the method disclosed in this application for preparing a silicon carbide coating using methylalkylsilane makes the deposited silicon carbide crystal dense, with extremely high binding force and few crystal defects. Due to the use of CVD\CVI method, the device is simple, fully automatic controllable, the equipment operates stably, and there are no corrosive by-products and flammable and explosive by-products, and a uniform and high-performance silicon carbide coating can be obtained.

Specific embodiments

The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the accompanying drawings of the present invention. Obviously, the described embodiments are only some of the embodiments of the present application and are intended to explain the inventive concept. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts fall within the scope of protection of the present invention.

Example 1

1) Power on the system, perform various inspections before starting up, vacuum to detect leaks, replace the system with argon gas, and keep the circulating cooling water temperature at 20°C and the pressure at 300KPa.

2) Place the graphite disk to be deposited with silicon carbide coating on the rotating tray of the deposition furnace, and close the deposition furnace.

3) Turn on the vacuum unit and keep the CVD\CVI reactor until the vacuum degree of the vacuum unit is 1000Pa.

4) When the pH of the alkali solution in the exhaust gas treatment system is ≥ 12, the spray tower circulation pump is turned on, and the exhaust gas recovery system is put into normal operation.

5) Turn on the PLC control panel of the CVD furnace system, conduct self-test of the entire system, and set the temperature rise curve as: 0~300℃ 60min; 300~600℃ 60min; 600~900℃ 30min; 900~1100℃ 50min; 1100℃ 20min; 1100℃300min; 1100～80℃600min.

6) Open the measuring scale of the methylsilane storage tank, record the quality of the Class A silane, and open the outlet manual valve. Open the manual valves of the hydrogen and argon storage tanks, and put each automatically controlled mass flow meter into operation.

7) When the CVD furnace temperature reaches 1100°C for 20 minutes; set the argon gas 15L/min (purity 99.9995%) through the CVD furnace system PLC control panel to feed the material to preheat and clean the deposition chamber.

8) When the CVD furnace temperature reaches 1100℃ for 300 minutes, maintain the argon flow rate unchanged, and set Class A silane 0.5L/min (purity 99.99%) and hydrogen 10L/min (purity) through the CVD furnace system PLC control panel is 99.9995%), the CVD deposition furnace tray rotation speed is 2 rpm, and deposition officially begins.

9) Keep the feed amount of each material stable, keep the rotation speed and heating temperature of the CVD reactor tray stable, and coat the graphite disk with CVD deposition using methylsilanesilane.

10) The system operates stably at 1100°C for 300 minutes, and then cools down according to the program.

11) Take the deposited graphite disk for appearance inspection and analysis. The results are as follows:

12) Remove the vacuum pipeline and check the surface deposits: clean and no deposits.

Example 2

1) Power on the system, conduct various inspections before starting, vacuum to detect leaks, replace the system with argon gas, and keep the circulating cooling water temperature at 20°C and the pressure at 350KPa.

2) Suspend the honeycomb graphite paper to be deposited with silicon carbide coating on a special graphite spreader, place it on the rotating tray of the deposition furnace, and close the deposition furnace.

3) Turn on the vacuum unit and keep the CVD\CVI reactor until the vacuum degree of the vacuum unit is 600Pa.

4) When the pH of the alkali solution in the exhaust gas treatment system is ≥ 12, the spray tower circulation pump is turned on, and the exhaust gas recovery system is put into normal operation.

5) Turn on the PLC control panel of the CVD furnace system, perform self-test on the entire system, and set the temperature rise curve as: 0~300℃ 60min; 300~600℃ 60min; 600~900℃ 50min; 900~1050℃ 30min; 1050℃ 30min; 1050℃150min; 1100～80℃780min.

6) Open the measuring scale of the methylsilane storage tank, record the quality of the Class A silane, and open the outlet manual valve. Open the manual valves of the hydrogen and argon storage tanks, and put each automatically controlled mass flow meter into operation.

7) When the CVD furnace temperature reaches 1050°C for 30 minutes; set the argon gas 10L/min (purity 99.9995%) through the CVD furnace system PLC control panel to feed the material to preheat and clean the deposition chamber.

8) When the CVD furnace temperature reaches 1050°C for 150 minutes, maintain the argon flow rate unchanged, and set Class A silane 0.3L/min (purity 99.99%) and hydrogen 8L/min (purity) through the CVD furnace system PLC control panel is 99.9995%), the CVD deposition furnace tray rotation speed is 1 rpm, and deposition officially begins.

9) Keep the feed amount of each material stable, keep the rotation speed and heating temperature of the CVD reactor tray stable, and coat the graphite honeycomb paper with CVI with methylsilane silane.

10) The system runs stably at 1050°C for 150 minutes and cools down according to the program.

11) Take the deposited graphite honeycomb paper for appearance inspection and analysis. The results are as follows:

12) Remove the vacuum pipeline and check the surface deposits: clean and no deposits.

Example 3

1) Power on the system, perform various inspections before starting up, vacuum to detect leaks, replace the system with argon gas, and keep the circulating cooling water temperature at 25°C and the pressure at 380KPa.

2) Support the fiber brake disc to be deposited on a special graphite spreader, place it on the rotating tray of the deposition furnace, and close the deposition furnace.

3) Turn on the vacuum unit and keep the CVD\CVI reactor until the vacuum degree of the vacuum unit is 1500Pa.

4) When the pH of the alkali solution in the exhaust gas treatment system is ≥ 12, the spray tower circulation pump is turned on, and the exhaust gas recovery system is put into normal operation.

5) Turn on the PLC control panel of the CVD furnace system, conduct self-test of the entire system, and set the temperature rise curve as: 0~300℃ 60min; 300~600℃ 40min; 600~900℃ 60min; 900~1150℃ 60min; 1150℃ 30min; 1150℃180min; 1150～80℃640min.

6) Open the measuring scale of the methylsilane storage tank, record the quality of the Class A silane, and open the outlet manual valve. Open the manual valves of the hydrogen and argon storage tanks, and put each automatically controlled mass flow meter into operation.

7) When the CVD furnace temperature reaches 1150°C for 30 minutes; set the argon gas 20L/min (purity 99.9995%) through the CVD furnace system PLC control panel to feed the material to preheat and clean the deposition chamber.

8) When the CVD furnace temperature reaches 1150°C for 180 minutes, maintain the argon flow rate unchanged, and set Class A silane 0.6L/min (purity 99.99%) and hydrogen 12L/min (purity) through the CVD furnace system PLC control panel is 99.9995%), the CVD deposition furnace tray rotation speed is 5 rpm, and deposition officially begins.

9) Keep the feed amount of each material stable, keep the rotation speed and heating temperature of the CVD reactor tray stable, and use methylsilane silane to conduct CVD deposition on the fiber brake disc.

10) The system runs stably at 1150°C for 180 minutes and cools down according to the program.

11) Take the deposited fiber brake disc for appearance inspection and analysis. The results are as follows:

12) Remove the vacuum pipeline and check the surface deposits: clean and no deposits.

Claims (6)

1. A method for preparing a silicon carbide coating using methylsilane, including a process of depositing a silicon carbide coating (thin film) on the surface (or internal pores) of a base material through CVD\CVI using methylsilane as a precursor, which is characterized by: The precursor is methylsilane, the carrier gas is hydrogen, and the diluent gas is argon, which specifically includes the following steps: S1: CVD\CVI system inert replacement; S2: heating and vacuuming; S3: Maintain constant deposition temperature; S4: Rotating or non-rotating deposition; S5: CVD\CVI deposition; S6: Cool down. 2. The method for preparing silicon carbide coating from methylsilane according to claim 1, characterized in that hydrogen gas of 0.2-2000L/min is used as carrier gas, argon gas of 1-8000L/min is used as diluent gas, and 0.02 ~5000L/min methylsilane is fully mixed in the mixing tank and then transported to the CVD\CVI deposition furnace for deposition. 3. The method for preparing silicon carbide coating from methylsilane according to claim 2, characterized in that the CVD\CVI deposition furnace maintains a vacuum degree of 0.1 to 5000 Pa through a vacuum unit and controls 600 to 600 Pa through resistance or medium frequency heating. Deposition temperature of 2000°C. 4. The method for preparing a silicon carbide coating using methylsilane according to claim 3, characterized in that the deposition thickness of the silicon carbide coating can be controlled at 0.5-2000um, and the deposition time can be controlled at 0.5-500 hours. 5. The method for preparing silicon carbide coating from methylsilane according to claim 4, characterized in that the vacuum-suctioned reaction tail gas and unreacted gas are discharged into the tail gas treatment system through pipelines to meet environmental protection and occupational health requirements. 6. The method for preparing silicon carbide coating with methylsilane according to claim 5, characterized in that, after reaching the deposition time set by the process, the CVD\CVI deposition furnace will maintain a vacuum state of 0.1~8000Pa and automatically enter the cooling stage. , this stage automatically controls the pressure of the circulating cooling water at 100~500KPa, the flow rate at 2~ ^200m3 /h, the controlled temperature to reach the safe furnace opening temperature of 40~80℃, and the cooling time at 3~60h through the set program.