CN110357631B - Method and equipment for preparing silicon carbide component by microwave treatment-based chemical vapor conversion process - Google Patents
Method and equipment for preparing silicon carbide component by microwave treatment-based chemical vapor conversion process Download PDFInfo
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Abstract
The invention relates to a method for preparing a silicon carbide part, in particular to a method and equipment for preparing a silicon carbide part by a microwave treatment-based chemical vapor phase conversion process. Firstly, drying and exhausting the component through a microwave converter to remove water vapor and other residual volatile substances in a graphite pore structure; then silane gas is introduced, a microwave power supply is started, chemical reaction is triggered through microwave heating, the graphite-silicon carbide component is manufactured, the microwave power is set to be 500W-3000W, the temperature is reduced to the room temperature after the microwave power supply is started, the component is moved out of a microwave treatment furnace, and the process is completed. The method can avoid introducing silicon residue impurities, has high conversion speed, high efficiency, low energy consumption, good uniformity and high safety, and can effectively avoid forming connectivity holes in the graphite-silicon carbide product.
Description
Technical Field
The invention relates to a method for preparing a silicon carbide part, in particular to a method and equipment for preparing a silicon carbide part by a microwave treatment-based chemical vapor phase conversion process.
Background
Silicon carbide (chemical molecular formula: SiC) ceramic is one of modern engineering ceramics, has hardness second to diamond, has outstanding physicochemical properties of small thermal expansion coefficient, high thermal conductivity, good chemical stability, high wear resistance, good mechanical property and oxidation resistance at high temperature and the like, and becomes structural ceramic with the greatest development prospect. Meanwhile, the silicon carbide also has the advantages of low neutron activity, good irradiation damage resistance, high-temperature structural stability and the like, and becomes one of important structural materials in a new generation of nuclear fission and future nuclear fusion reactors.
Modern industries including military, aerospace, radar communication, petroleum, automotive industries, etc. are increasingly demanding high temperature, high power operation and radiation resistant electronic components, and research on wide bandgap semiconductor materials represented by silicon carbide (SiC) and components thereof is attracting attention. Silicon carbide is a third generation semiconductor that appears after the traditional semiconductors of silicon and gallium arsenide, and has the following advantages compared to silicon materials:
1. the forbidden bandwidth is 3 times of that of silicon;
2. the thermal conductivity is high and is 3 times of that of silicon;
3. the breakdown field strength is high and is 10 times of that of silicon;
4. the saturated electron drift rate is high and is 2.5 times of that of silicon;
5. the working temperature is high, 400 ℃ and 600 ℃;
6. the bonding energy is high;
7. high physical strength, and hardness second only to diamond in nature.
Since the first discovery that e.g. acheson1891 made electric melting of diamond, silicon carbide materials have excellent properties and can be widely used in the industrial fields of aerospace, automobiles, machinery, electronics, chemical industry and the like. Currently, silicon carbide is produced mainly by the Acheson process, and annual production is over a million tons. The Qingganning province and the inner Mongolia province in the upper reaches of the yellow river in China have abundant water, fire and electricity resources and high-quality raw materials, silicon carbide manufacturers are numerous, and the silicon carbide industry is one of the prop industries in the region. The annual output of silicon carbide in China is about 38 million tons, which accounts for 40 percent of the annual output in the world, is a great country for using and exporting silicon carbide, and researches in the fields of silicon carbide micro powder, silicon carbide whiskers, silicon carbide composite materials and the like are also active. Silicon carbide can be said to have penetrated into every corner of human life as a versatile engineering material.
At present, the silicon carbide powder prepared by the Acheson method is dominant in yield and scale and is widely applied to various industrial fields. Has the advantages of cheap raw materials, mature method and easy realization of industrial production. The defect is that the powder quality is not high: the specific surface area is low (1-15 m)2The content of oxide is high (1 wt%), the content of metal impurities is high (1400-2800ppm), and additional subsequent treatment processes such as crushing, acid washing and the like are needed to remove the impurities, so that the product purity is improved.
Other silicon carbide preparation techniques, such as hot-pressing sintering and high-temperature isostatic pressing sintering of silicon carbide, can prepare silicon carbide ceramics with higher density, including silicon carbide whiskers and silicon carbide fiber silicon carbide whiskers. However, the silicon carbide preparation technology is difficult to manufacture products with complex shapes, high mechanical strength and good air tightness. Silicon carbide ceramic parts have high brittleness and low fracture toughness, and require additional filler materials such as fibers, whiskers, and particles to improve toughness and strength of the silicon carbide ceramic, for reasons including:
1. according to the published data of the american graphite over-the-counter (POCO), it is shown that silicon carbide parts hot-formed under extremely high temperature and pressure conditions can theoretically reach a density of 97%, and still cannot meet the airtightness requirements of high-end industries such as the semiconductor industry for the parts.
2. Side effects of high temperature sintering agents. Silicon carbide is a strong covalent compound and has low atomic diffusion capability, so that it is difficult to sinter dense at high temperatures. In order to promote sintering and reduce sintering temperature, high-temperature sintering aids are usually required to be added, such as Al-B-C-B4A solid-phase sintering aid system based on C, and Al2O3-Y2O3，AlN-Re2O3(wherein Re2O3Is usually Y2O3、Er2O3、Yb2O3、Sc2O3、Lu2O3Oxides of equal rare earth elements) as a main component. The use of sintering aids can result in reduced mechanical strength and deteriorated thermal properties at high temperatures
3. Residue resulting from incomplete reaction of the raw materials. The reactive sintering of silicon carbide is a blank body which is composed of alpha-silicon carbide and graphite powder according to a certain proportion, and the blank body is heated to react with liquid Si or gas phase Si to generate beta-silicon carbide. The method has low sintering temperature (1400 ℃ C. and 1600 ℃ C.), is suitable for preparing products with complex structures, but 8-20% of free silicon remains in blanks, which limits the high-temperature mechanical property and chemical stability of the silicon carbide and limits the application of the silicon carbide in strong acid and strong alkali.
Therefore, silicon carbide parts currently used in high-precision industries such as the aerospace industry and the semiconductor industry are converted into silicon carbide parts by graphite parts. For example, a precision structure silicon carbide-graphite component used in the semiconductor industry at present is a novel composite material consisting of silicon carbide and graphite, not only retains the excellent performance of isostatic pressure graphite, but also has the advantages of oxidation resistance, wear resistance and corrosion resistance of silicon carbide, can work in a liquid or gaseous corrosive medium for a long time, and is an ideal structural material. Due to a series of excellent characteristics, the material is an important structural material in various high and new technologies and the advanced technology field of national defense in the world. In recent years, the research of isostatic pressing silicon carbide-graphite materials has been increased in English, American, Japanese, Russian and Germany, a new series of products are gradually formed, the application fields of the products are widened, and the products are more applied to the fields of machinery, chemical engineering, metallurgy, aerospace, electronics, bioengineering and the like. Three leading sheep companies, including eastern Japanese carbon (Toyotanso), SiGeri Germany carbon (SGL carbon) and PoCO, have market share of over 60%.
The method for preparing the silicon carbide-graphite composite material under the condition of large-scale production mainly comprises a molten silicon liquid phase impregnation Method (MSI), a chemical vapor phase conversion method (CVC), a chemical vapor deposition method (CVI), a precursor conversion method (PIP) and the like. Among them, the chemical vapor phase conversion method is widely used in the semiconductor and aviation industries with the advantages of high quality and cost-effectiveness.
The principle of the chemical vapor phase conversion method is that Silane (SiH) is reacted at high temperature4) The silicon carbide is generated by the reaction of the silicon carbide and the base body after the silicon carbide is contacted with the base body after the silicon carbide is permeated into the blank body through the pores in the isostatic pressing graphite. At a high temperature of 1650 ℃, the container has a high silane vapor pressure, and when gaseous silicon atoms meet activated carbon atoms activated by the high temperature, the silicon vapor condenses into silicon droplets on the surface of graphite atoms and reacts with the graphite to form SiC crystals.
According to classical gas phase nucleation theory, the formation of new phases during gas phase nucleation is related to the degree of excess of the gas. The larger the supersaturation degree of the gas, the higher the nucleation rate of the crystals. At high temperature, the silicon atoms form crystal nuclei with activated carbon atoms and further grow into SiC crystals. Secondly, the pore structure of the graphite is a curved pore passage communicated with each other. The air in the graphite pores is removed by a vacuum negative pressure method. Then introducing silane to perform graphite conversion. Silane gas enters the graphite body along the graphite pore canal and is condensed into silicon liquid drops, atoms are transferred by means of surface diffusion, liquid silicon penetrates through the silicon carbide layer through the diffusion effect and permeates into the graphite part, and the liquid silicon reacts with the graphite part after contacting the graphite part to continuously generate silicon carbide.
The chemical vapor conversion method can obtain high-quality silicon carbide parts, the structural complexity, the mechanical strength, the air tightness and the thermodynamic performance of the silicon carbide parts are superior to those of the molten silicon liquid phase impregnation Method (MSI) which is mainstream in industry, and the product performance is close to that of the chemical vapor deposition method but the cost is lower. The chemical gas phase conversion method has the disadvantages of long time consumption, high energy consumption and large optimization space. The following is a process for producing graphite-silicon carbide parts disclosed by the U.S. step-and-rise corporation (POCO):
1. isostatic pressing graphite component preparation process;
1) the bulk carbon material is coarsely ground to carbon powder,
2) screening and grading according to the particle size and the impurity content,
3) mechanically pulverizing the mixture into a powdery material,
4) finely ground to regular sized carbon powder (size grades including 1um,5um,10um and 50um),
5) isostatic pressing carbon powder to form a carbon part;
2. high temperature baking of carbon parts increases part density:
3. graphitizing the carbon component to obtain a pure graphite component;
4. chemical vapor conversion (conversion of graphite parts to graphite-silicon carbide parts):
1) the graphite component is subjected to exhaust treatment in a vacuum drying oven for 0.5 to 8 hours,
2) the graphite part is converted in a silane atmosphere furnace for 144-432 hours (the temperature of the atmosphere furnace is controlled between 1500-2200 ℃;
5. grinding and polishing the surface of the part;
6. cleaning the parts;
7. assembling the connecting parts;
8. detecting a complete product;
9. packaging and transferring to storage.
In the above scheme, step 5 is a chemical vapor conversion, with the objective of converting the skin material of the graphite parts to silicon carbide. The chemical reaction process is carried out in two steps:
the first step is as follows: c(s)+SiO2(s)→SiO(g)+CO(g)
The second step is that: c(s)+SiO(g)→SiC(s)+CO(g)。
The temperature and atmosphere control in the reaction process are critical, and under the current process conditions, a tubular furnace is required to be used for heating to keep the component temperature between 1500-2000 ℃, the silane concentration is 500-10,000 ppm, the silicon carbide conversion rate is 40-200um/hour, and the preparation of the component with the silicon carbide thickness of 7mm takes 7 days (144 hours).
In summary, in the graphite-silicon carbide production flow of the main silicon carbide suppliers, the chemical vapor phase conversion step requires very long time and high energy consumption, and has negative effects on the productivity and product quality of silicon carbide, which are specifically as follows:
1. the fifth step of the standard graphite-silicon carbide production flow is chemical vapor phase conversion, 3 steps are needed for converting graphite into silicon carbide in the current production line, the steps are complicated, and the process time is up to 7 days or more than 144 hours;
2. the conversion temperature of the silicon carbide used at present is about 1200-;
3. the currently used material formula and heating process can cause silicon material residue on the surface of the component, and the silicon material residue needs to be removed through additional polishing, grinding and chemical cleaning processes;
4. the atmosphere heating furnace used in the prior art has high energy consumption and low efficiency, the energy consumption per hour exceeds 25 kilowatts, and each product in the chemical conversion step consumes more than 720 kilowatt hours.
In summary, in the current production process of graphite-silicon carbide parts, the chemical vapor phase conversion process causes silicon residue pollution, and has negative effects on the mechanical strength and the thermal stability of the products. In addition, the longer process results in lower production efficiency and reduced service life of graphite-silicon carbide components.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a method for preparing a silicon carbide part by a microwave treatment-based chemical vapor phase conversion process, which avoids introducing silicon residue impurities, has high conversion speed, high efficiency, low energy consumption, good uniformity and high safety, and can effectively avoid the formation of connected holes in a graphite-silicon carbide product; the invention also provides equipment for realizing the method.
The method for preparing the silicon carbide component by the microwave treatment-based chemical vapor phase conversion process comprises the following steps of firstly, drying and exhausting the component by a microwave conversion furnace to remove water vapor and other residual volatile substances in a graphite pore structure; then silane gas is introduced, a microwave power supply is started, a chemical reaction is triggered through microwave heating, the graphite-silicon carbide component is prepared, the temperature is reduced to the room temperature after the chemical reaction is finished, the component is moved out of a microwave treatment furnace, and the process is finished.
Wherein:
silane gas is introduced to control the concentration of silane atmosphere to be between 600ppm and 5000 ppm.
The chemical reaction is triggered by microwave heating, the microwave power is set between 500W and 3000W, and the reaction temperature is controlled at 1200 ℃ and 3200 ℃. Starting a microwave power supply to perform chemical conversion, wherein the power of the microwave power supply is set to be 500-3000W. According to the invention, silane and the graphite component are subjected to chemical reaction to form a uniform and compact silicon carbide layer on the surface of graphite, the compactness of the graphite component is enhanced by utilizing a silicon carbide conversion process, and gaps at the joint of the graphite component are reduced or eliminated. Silane gas is introduced to control the concentration of silane atmosphere to be 600ppm-5000ppm, if the concentration of silane atmosphere is lower than 600ppm, gaps at the joint of the graphite component cannot be removed 100%, and if the concentration of silane atmosphere is higher than 5000ppm, delamination between the silicon carbide layer and the graphite component is caused, and the service life of the component is shortened. The microwave power in the microwave heating module is set to be 500-3000W, the surface temperature of the graphite component can be controlled to be 1200-3200 ℃, if the surface temperature of the graphite component exceeds 3200 ℃, the melting temperature (3652 ℃) of the material is approached, the graphite component is deformed, and if the surface temperature of the graphite component is lower than 1200 ℃, the graphite component cannot be converted into a silicon carbide material.
As a preferable technical scheme, the method for preparing the silicon carbide part by the chemical vapor phase conversion process based on the microwave treatment comprises the following steps:
(1) placing the isostatic pressing graphite component in a microwave converter, starting a microwave power supply to exhaust, and drying and exhausting;
(2) turning off the microwave power supply, and cooling the graphite component;
(3) introducing nitrogen and exhausting air;
(4) introducing silane, controlling the silane concentration by a flowmeter and the flow to be 1-4L/min, and monitoring the air pressure in the gas conversion chamber to be 1-4 atmospheric pressures by using an air pressure controller;
(5) adjusting the flow rate of silane to 50-650mL/min after the air pressure in the conversion chamber reaches 1-4 atmospheric pressures and the air pressure reaches stability;
(6) starting a microwave power supply to carry out chemical conversion, wherein the microwave power is set to be 500-3000W;
(7) in the temperature rising stage of the gas phase conversion furnace, the surface temperature of the graphite component is monitored by using an infrared temperature sensor, and the surface temperature of the graphite component rises along with the time to reach a stable value of 1600 +/-120 ℃.
(8) In the stable working stage of the gas phase conversion furnace, the microwave power is adjusted to be 500W-1500W, and heating is maintained for 2-10 hours to obtain proper porosity and silicon carbide thickness;
(9) in the cooling stage, the microwave power is sequentially adjusted to 400W, 200W and 100W in three steps, and each step lasts for 10-20 minutes;
(10) turning off the microwave power supply, stopping introducing silane, and introducing nitrogen;
(11) the surface temperature of the graphite component is reduced along with the time, and the nitrogen gas is stopped to be introduced;
(12) and taking out the graphite-silicon carbide part, and finishing the chemical conversion process.
Wherein:
in the step (1), the microwave power is set to be 160W-300W, the temperature is set to be 200 ℃ to 500 ℃, and the drying and exhausting time is 15 minutes to 60 minutes. After the venting is complete, the component contains a concentration of volatile species that is less than one part per million (<1ug/g) of the total weight of the component. If the exhaust effect of the same level is required, the conventional heating furnace needs more than 4 hours.
And (3) cooling the graphite part for 30-60 minutes in the step (2).
And (4) controlling the flow of the introduced nitrogen in the step (3) to be 500L/min-1L/min, and introducing the nitrogen for 25-30 minutes to ensure that the oxygen is completely removed.
The jet time of the gas stream introduced with silane in step (4) lasts for 10-30 minutes, and then the silane concentration reaches a stable value after 5-10 minutes. The higher the air pressure, the better, but the higher the air pressure, the higher the equipment cost, and the higher the air pressure, the potential safety hazard is also brought.
The time for the air pressure to reach the stability in the step (5) is 5 minutes; the concentration value of the silane in the step (5) is determined by controlling the ratio of silane gas and carrier gas, the carrier gas is nitrogen, the volume ratio of the silane to the nitrogen is 1:10-1:1, and the silane/nitrogen with the ratio is introduced to control the concentration of the silane atmosphere to be 600ppm-5000 ppm.
The time for reaching the stable value of 1600 +/-120 ℃ in the step (7) is 120 seconds to 600 seconds. The traditional heating furnace needs to be heated for more than 90 minutes to ensure that the stable value on the graphite component reaches 1600 +/-120 ℃, and the temperature of the graphite component is in gradient distribution (the temperature at the bottom of the component is 50-200 ℃ higher than that at the top).
Heating in the step (8) for 2-10 hours to obtain proper porosity and silicon carbide thickness, if heating for 4 hours, obtaining a silicon carbide part with 19% porosity and 5mm thickness, and if heating for 10 hours, obtaining a silicon carbide part with 11% porosity and 9mm thickness; reference herein to silicon carbide refers to a 100% silicon carbide crystal.
The purpose of step (9) is to ensure the slow and uniform cooling of the component and avoid the generation of structural defects such as cracks, cavities, layering and the like.
Introducing nitrogen in the step (10), controlling the flow to be 500L/min-1L/min, and introducing the nitrogen for 20-30 minutes;
and (3) stopping introducing the nitrogen when the surface temperature of the graphite part in the step (11) is reduced to below 80 ℃ along with time.
After the chemical conversion is finished by adopting the chemical vapor phase conversion process, the graphite component is transferred to the next step of the production line, namely detection and assembly. The general process is as follows: the method comprises the steps of detecting the size of a single silicon carbide part, assembling main silicon carbide parts, assembling connecting parts, assembling a switch door, testing the switch of the door part, integrally assembling the silicon carbide parts, packaging and transferring to storage.
The invention also provides equipment for preparing the silicon carbide component by the microwave treatment-based chemical vapor conversion process, which comprises a microwave treatment furnace body, wherein a microwave heater is arranged in the microwave treatment furnace body, the microwave heater focuses microwaves on the graphite component sample through microwave waveguides, the microwave heater is connected with the microwave treatment furnace body through a support frame, the graphite component sample is placed on a product table, the product table is connected with the microwave treatment furnace body through a support column, the microwave treatment furnace body is provided with an infrared temperature sensor, the side surface of the microwave treatment furnace body is provided with an inlet valve, and the inlet valve is also connected with a gas flowmeter through an air inlet pipe.
Preferably, a rotational bearing is provided inside the support column.
Preferably, two inlet valves are arranged on the side surface of the microwave treatment oven body.
Compared with the prior art, the invention has the following advantages:
(1) the method can effectively catalyze the graphite material of the component to be converted into the silicon carbide material, is suitable for mass production of the silicon carbide component with complex structure, high purity and good mechanical property and thermal property, and avoids using a melting agent, so the purity problem of the silicon carbide component is solved from the source; the production steps are simplified, and the two current processes are replaced by one process.
(2) The invention can prolong the service life of the silicon carbide component, and the service life prolonging time is more than 14%.
(3) The invention has high efficiency, the heat energy is transmitted to the graphite component by the microwave heating way to achieve the effect of catalytic chemical conversion, the conversion speed of the silicon carbide is 38 times of that of the traditional heating furnace, the curing capacity of the graphite component is increased from 2 times per week of each device to 24 times per week of each device, and the capacity of the devices is 12 times of that of the traditional heating furnace.
(4) The invention has low energy consumption, and the power consumption per unit output is only about 1/50 of the traditional heating furnace.
(5) The invention has high safety and solves the problems of arc discharge, local overheating and the like.
(6) The invention has high temperature control precision, safety and reliability, and convenient adjustment of process parameters; the temperature of the graphite component is accurately monitored through the infrared temperature sensor, the surface temperature of the component is accurate, stable and uniform, and the influence on the performance of the component due to overhigh local temperature of the component is avoided.
(7) The invention also has the effect of removing volatile impurities (including moisture and organic residues) from the interior of the component.
(8) The microwave treatment chemical vapor phase conversion process has the advantages of avoiding introducing silicon residue impurities, along with high conversion speed, high efficiency, low energy consumption, good uniformity and high safety, and can effectively avoid the formation of connected holes in graphite-silicon carbide products.
(9) The invention also provides a device for realizing the chemical conversion process of the silicon carbide based on the microwave treatment, which has simple structure, convenient operation and maintenance, basically no maintenance and suitability for industrial mass production; the microwave processing device has the advantages that the complex structure and the air tightness can be realized, the excellent mechanical property of the silicon carbide is kept, the microwave processing device is suitable for the semiconductor industry with high requirements on cleanliness and oxidation resistance, the existing two processes of heating and exhausting and chemical conversion are replaced by one process, and compared with the mainstream technology in the industry, the microwave processing device has the advantages of high conversion speed, good uniformity, high productivity and low energy consumption on graphite parts.
Drawings
FIG. 1 is a photograph of some of the isostatic graphite parts;
FIG. 2 is a silicon carbide part of an epitaxial susceptor for MOCVD prepared by the chemical vapor phase conversion process based on microwave treatment of example 1;
FIG. 3 is a schematic structural view of an apparatus for manufacturing a silicon carbide part by a chemical vapor phase conversion process based on microwave treatment;
in the figure: 1-microwave treatment furnace body, 2-infrared temperature sensor, 3-microwave treatment furnace body, 4-gas flowmeter, 5-inlet valve, 6-microwave waveguide, 7-microwave heater, 8-support frame, 9-product table, 10-support column and 11-graphite component sample.
Detailed Description
The present invention will be further described with reference to the following examples.
Example 1
A method for preparing a silicon carbide part by a chemical vapor phase conversion process based on microwave treatment comprises the following steps:
(1) placing the isostatic pressing graphite component in a microwave conversion furnace, starting a microwave power supply to exhaust, setting the microwave power at 300W, and setting the temperature of the component at 200 ℃ for drying and exhausting for 30 minutes;
(2) turning off the microwave power supply, and cooling the graphite part for 35 minutes;
(3) opening nitrogen gas inlet valve, introducing nitrogen gas, controlling flow at 500mL/min, discharging air, and maintaining for 25 min
(4) Opening a silane air inlet valve, introducing silane, controlling the silane concentration by a flow meter, controlling the flow to be 3L/min, and keeping the air flow injection time for 15 minutes; and monitoring the air pressure in the air conversion chamber to be 1.5 times of atmospheric pressure by using an air pressure controller;
(5) the air pressure in the conversion chamber reaches 1.5 times of atmospheric pressure, and the silane flow is adjusted to 50mL/min after 5 minutes when the air pressure reaches a stable value;
(6) starting a microwave power supply to perform chemical conversion, setting the microwave power to be 1500W, and monitoring the surface temperature of the graphite component by using an infrared temperature sensor;
(7) monitoring the surface temperature of the graphite component by using an infrared temperature sensor, wherein the surface temperature of the graphite component rises along with the time and reaches a stable value of 1600 +/-120 ℃;
(8) in the stable working stage of the gas phase conversion furnace, the microwave power is adjusted to be 500W, and heating is continued for 4 hours to obtain proper porosity and silicon carbide thickness;
(9) in the cooling stage, the microwave power is sequentially adjusted to 400W, 200W and 100W in three steps, and each step lasts for 15 minutes respectively;
(10) closing the microwave power supply, closing the silane air inlet valve, opening the nitrogen air inlet valve, introducing nitrogen, controlling the flow to be 500mL/min, and continuing for 20 minutes;
(11) reducing the surface temperature of the graphite part to be below 80 ℃ along with time, and closing a nitrogen gas inlet valve;
(12) and opening the door of the conversion chamber, taking out the graphite-silicon carbide component, and finishing the chemical conversion process.
Some of the pictures of isostatic pressed graphite parts that can be processed using the method according to the invention are shown in fig. 1.
A product diagram of a silicon carbide part of an epitaxial susceptor for MOCVD prepared by the chemical vapor phase conversion process based on microwave treatment of example 1 is shown in fig. 2.
The utility model provides an equipment of chemical vapor conversion technology preparation carborundum part based on microwave treatment, as shown in figure 3, including microwave treatment furnace body 1, be equipped with microwave heater 7 in the microwave treatment furnace body 1, microwave heater 7 passes through microwave waveguide 6 with the microwave focus on graphite part sample 11, microwave heater 7 passes through support frame 8 and connects microwave treatment furnace body 3, graphite part sample 11 is placed on product platform 9, product platform 9 passes through support column 10 and connects microwave treatment furnace body 3, be equipped with infrared temperature sensor 2 on the microwave treatment furnace body 3, be equipped with (air) intake valve 5 in the side of microwave treatment furnace body 3, air intake valve 5 still passes through intake-tube connection gas flowmeter 4, the inside swivel bearing that sets up of support column 10.
Example 2
A method for preparing a silicon carbide part by a chemical vapor phase conversion process based on microwave treatment comprises the following steps:
(1) placing the isostatic pressing graphite component in a microwave conversion furnace, starting a microwave power supply to exhaust, setting the microwave power at 200W, and setting the temperature of the component at 400 ℃ for drying and exhausting for 40 minutes;
(2) turning off the microwave power supply, and cooling the graphite part for 50 minutes;
(3) opening nitrogen gas inlet valve, introducing nitrogen gas, controlling flow at 800mL/min, discharging air, and maintaining for 25 min
(4) Opening a silane inlet valve, introducing silane, controlling the silane concentration by a flow meter, controlling the flow to be 2L/min, and keeping the air flow injection time for 20 minutes; monitoring the air pressure in the air conversion chamber to be 3 times of atmospheric pressure by using an air pressure controller;
(5) the air pressure in the conversion chamber reaches 3 times of atmospheric pressure, and the silane flow is adjusted to 600mL/min after the air pressure reaches a stable value for 5 minutes;
(6) starting a microwave power supply to perform chemical conversion, setting the microwave power to be 2500W, and monitoring the surface temperature of the graphite component by using an infrared temperature sensor;
(7) monitoring the surface temperature of the graphite component by using an infrared temperature sensor, wherein the surface temperature of the graphite component rises along with the time and reaches a stable value of 1600 +/-120 ℃;
(8) in the stable working stage of the gas phase conversion furnace, the microwave power is adjusted to be 1000W, and heating is continued for 6 hours to obtain proper porosity and silicon carbide thickness;
(9) in the cooling stage, the microwave power is sequentially adjusted to 400W, 200W and 100W in three steps, and each step lasts for 15 minutes respectively;
(10) closing the microwave power supply, closing the silane air inlet valve, opening the nitrogen air inlet valve, introducing nitrogen, controlling the flow to be 800mL/min, and continuing for 20 minutes;
(11) reducing the surface temperature of the graphite part to be below 80 ℃ along with time, and closing a nitrogen gas inlet valve;
(12) and opening the door of the conversion chamber, taking out the graphite-silicon carbide component, and finishing the chemical conversion process.
The equipment for preparing silicon carbide parts using a microwave treatment-based chemical vapor conversion process was the same as in example 1.
Example 3
A method for preparing a silicon carbide part by a chemical vapor phase conversion process based on microwave treatment comprises the following steps:
(1) placing the isostatic pressing graphite component in a microwave conversion furnace, starting a microwave power supply to exhaust, setting the microwave power at 200W, and setting the temperature of the component at 400 ℃ for drying and exhausting for 40 minutes;
(2) turning off the microwave power supply, and cooling the graphite part for 50 minutes;
(3) opening nitrogen gas inlet valve, introducing nitrogen gas, controlling flow at 800mL/min, discharging air, and maintaining for 25 min
(4) Opening a silane inlet valve, introducing silane, controlling the silane concentration by a flow meter, controlling the flow to be 2L/min, and keeping the air flow injection time for 20 minutes; monitoring the air pressure in the air conversion chamber to be 3 times of atmospheric pressure by using an air pressure controller;
(5) the air pressure in the conversion chamber reaches 5 times of the atmospheric pressure, and the silane flow is adjusted to 1200mL/min after the air pressure reaches a stable value for 5 minutes;
(6) starting a microwave power supply to perform chemical conversion, setting the microwave power to be 2500W, and monitoring the surface temperature of the graphite component by using an infrared temperature sensor;
(7) monitoring the surface temperature of the graphite component by using an infrared temperature sensor, wherein the surface temperature of the graphite component rises along with the time and reaches a stable value of 1600 +/-120 ℃;
(8) in the stable working stage of the gas phase conversion furnace, the microwave power is adjusted to be 1000W, and heating is continued for 6 hours to obtain proper porosity and silicon carbide thickness;
(9) in the cooling stage, the microwave power is sequentially adjusted to 400W, 200W and 100W in three steps, and each step lasts for 15 minutes respectively;
(10) closing the microwave power supply, closing the silane air inlet valve, opening the nitrogen air inlet valve, introducing nitrogen, controlling the flow to be 800mL/min, and continuing for 20 minutes;
(11) reducing the surface temperature of the graphite part to be below 80 ℃ along with time, and closing a nitrogen gas inlet valve;
(12) and opening the door of the conversion chamber, taking out the graphite-silicon carbide component, and finishing the chemical conversion process.
The equipment for preparing silicon carbide parts using a microwave treatment-based chemical vapor conversion process was the same as in example 1.
A comparison of the properties of the silicon carbide parts produced by the microwave conversion process of this example with those of commercial products is shown in Table 1.
TABLE 1
Table 1 shows the technical parameters of silicon carbide parts produced by different techniques, including the production of silicon carbide by conventional processes (compression moulding), the production of silicon carbide under vacuum (chemical vapour deposition), and also products from some major silicon carbide suppliers (including hewlett-packard, stephensis, cygri carbon, germany), BK7 borosilicate proportions and aluminium plates as commonly used industrial materials.
Silicon carbide prepared by the traditional powder compression molding method is also the largest product used in the industry. The components of the silicon carbide ceramic material are made of organic coupling agents and inorganic sintering agents, so that the cost is low, but the purity, compactness, heat conductivity and structural uniformity of the silicon carbide of the components are sacrificed, and the silicon carbide products are limited to be widely used in high-value fields such as aerospace and semiconductor industries.
Compared with the silicon carbide prepared by the chemical vapor phase conversion method of America and Germany company, the density, the elastic modulus and the thermal conductivity of the silicon carbide product prepared by the invention all reach or exceed the level of the current industrial product.
The productivity of the silicon carbide prepared by the microwave method conversion method is improved by 120 percent and the production cost is reduced by 40 percent compared with the prior art of American and German companies.
Claims (9)
1. A method for preparing a silicon carbide component by a microwave treatment-based chemical vapor phase conversion process is characterized by comprising the following steps of: firstly, drying and exhausting the graphite component through a microwave converter to remove water vapor and other residual volatile substances in a graphite pore structure; then introducing nitrogen and discharging air; introducing silane gas, starting a microwave power supply to trigger a chemical reaction through microwave heating, controlling the reaction temperature to be 1200-3200 ℃, preparing a graphite-silicon carbide component, stopping introducing silane after the reaction is finished, introducing nitrogen, cooling to room temperature, stopping introducing nitrogen, moving the component out of a microwave treatment furnace, and finishing the process;
wherein silane gas is introduced, the concentration of silane atmosphere is controlled to be 600ppm-5000ppm, the flow is controlled to be 1L/min-4L/min, and a gas pressure controller is utilized to monitor the gas pressure in the gas conversion chamber to be 1-4 atmospheric pressures;
adjusting the flow rate of silane to 50-650mL/min after the air pressure in the conversion chamber reaches 1-4 atmospheric pressures and the air pressure reaches stability; the microwave power supply is then activated.
2. The method for preparing silicon carbide components by a microwave treatment-based chemical vapor conversion process according to claim 1, wherein: the chemical reaction is triggered by microwave heating, and the microwave power is set between 500W and 3000W.
3. A method for preparing silicon carbide components according to the microwave treatment-based chemical vapor conversion process of any of claims 1-2, wherein:
(1) placing the isostatic pressing graphite component in a microwave converter, starting a microwave power supply to exhaust, and drying and exhausting;
(2) turning off the microwave power supply, and cooling the graphite component;
(3) introducing nitrogen and exhausting air;
(4) introducing silane, controlling the silane concentration by a flowmeter and the flow to be 1-4L/min, and monitoring the air pressure in the gas conversion chamber to be 1-4 atmospheric pressures by using an air pressure controller;
(5) adjusting the flow rate of silane to 50-650mL/min after the air pressure in the conversion chamber reaches 1-4 atmospheric pressures and the air pressure reaches stability;
(6) starting a microwave power supply to carry out chemical conversion, wherein the microwave power is set to be 500-3000W;
(7) in the temperature rising stage of the gas phase conversion furnace, monitoring the surface temperature of the graphite component by using an infrared temperature sensor, wherein the surface temperature of the graphite component rises along with time to reach a stable value of 1600 +/-120 ℃;
(8) in the stable working stage of the gas phase conversion furnace, the microwave power is adjusted to be 500W-1500W, and heating is maintained for 2-10 hours to obtain proper porosity and silicon carbide thickness;
(9) in the cooling stage, the microwave power is sequentially adjusted to 400W, 200W and 100W in three steps, and each step lasts for 10-20 minutes;
(10) turning off the microwave power supply, stopping introducing silane, and introducing nitrogen;
(11) the surface temperature of the graphite component is reduced along with the time, and the nitrogen gas is stopped to be introduced;
(12) and taking out the graphite-silicon carbide part, and finishing the chemical conversion process.
4. A method for preparing silicon carbide components according to claim 3, wherein the chemical vapour phase conversion process based on microwave treatment comprises: in the step (1), the microwave power is set to be 160W-300W, the temperature is set to be 200 ℃ to 500 ℃, and the drying and exhausting time is 15 minutes to 60 minutes.
5. A method for preparing silicon carbide components according to claim 3, wherein the chemical vapour phase conversion process based on microwave treatment comprises: and (3) cooling the graphite part for 30-60 minutes in the step (2).
6. A method for preparing silicon carbide components according to claim 3, wherein the chemical vapour phase conversion process based on microwave treatment comprises: and (4) controlling the flow of the introduced nitrogen in the step (3) to be 500L/min-1L/min, and introducing the nitrogen for 25-30 minutes to ensure that the oxygen is completely removed.
7. A method for preparing silicon carbide components according to claim 3, wherein the chemical vapour phase conversion process based on microwave treatment comprises: the jet time of the gas stream introduced with silane in step (4) lasts for 10-30 minutes, and then the silane concentration reaches a stable value after 5-10 minutes.
8. A method for preparing silicon carbide components according to claim 3, wherein the chemical vapour phase conversion process based on microwave treatment comprises: introducing nitrogen in the step (10), controlling the flow to be 500L/min-1L/min, and introducing the nitrogen for 20-30 minutes; and (3) stopping introducing the nitrogen when the surface temperature of the graphite part in the step (11) is reduced to below 80 ℃ along with time.
9. An apparatus for implementing the method of any one of claims 1-8, wherein: including microwave treatment furnace body (1), be equipped with microwave heater (7) in microwave treatment furnace body (1), microwave heater (7) pass through microwave waveguide (6) with microwave focus on graphite part sample (11), microwave heater (7) are through support frame (8) connection microwave treatment furnace body (3), graphite part sample (11) are placed on product platform (9), product platform (9) are through support column (10) connection microwave treatment furnace body (3), be equipped with infrared temperature sensor (2) on microwave treatment furnace body (3), side at microwave treatment furnace body (3) is equipped with (5), air intake valve (5) still pass through intake-tube connection gas flowmeter (4).
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