CN101812730B - Preparation method of ultralong monocrystal beta-SiC nanowire metal-free catalyst - Google Patents

Abstract

The invention provides a preparation method of an ultralong monocrystal beta-SiC nanowire metal-free catalyst, comprising the following steps of: carrying out heat preservation for 1-6h by adopting a chemical vapor deposition method by taking a carbonaceous gas as a carbon source, a mixture of silicon monoxide or monox and silicon as a silicon source and Ar or N2 as a carrier gas in a vacuum tube type furnace or a chemical vapor deposition furnace under the conditions that the temperature is 1350-1600 DEG C, the flow of the gas of the carbon source is 10-80sccm, the flow of the carrier gas is 20-80sccm and the air pressure is 1.1-1.5atm, and depositing and growing on a porcelain boat, a corundum sheet or a silicon wafer to obtain a monocrystal beta-SiC nanowire, the length of which reaches the centimetre grade. The invention synthesizes the monocrystal beta-SiC nanowire completely without adding a metal catalyst and without a growing template by adopting a simple pollution-free process which is simple and easy to operate and control and low in cost, and the synthetized monocrystal beta-SiC nanowire has the characteristics of small diameter, even distribution, length reaching the centimetre grade, high yield and the like and is beneficial to industrial production.

Description

Preparation method of ultralong single crystal β-SiC nanowire metal-free catalyst

technical field

The invention belongs to the field of preparation of single-crystal β-SiC nanowires, and relates to a method for preparing ultra-long single-crystal β-SiC nanowires without a metal catalyst.

technical background

Silicon carbide nanowires have excellent mechanical, optical, electrical, semiconductor properties, field emission, physical and chemical stability, high temperature stability and other properties, and are ideal materials for preparing nano-optoelectronic devices such as blue light-emitting diodes, laser diodes and high-power transistors. At the same time, it is also an ideal reinforcement phase material for composite materials such as metal matrix, ceramic matrix and polymer, so it has attracted more and more attention from researchers and enterprises.

Large-scale and large-area preparation of ultra-long silicon carbide nanowires is the primary problem for realizing its industrial production and practical application. In 2009, gong-yi Li of National University of Defense Technology reported the use of CVD method to prepare centimeter-scale β-SiC nanowires with a mixture of ferrocene, L-Ps and activated carbon as the starting material. (Large Areas of Centimeters-Long SiC Nanowires Synthesized by Pyrolysis of a Polymer Precursor by a CVD Route (CVD pyrolysis of polymer precursors to prepare a few centimeters long SiC nanowires in a large area). J.Phys.Chem.C 2009, 113, 17655- 17660), the above preparation method uses metal catalysts to grow silicon carbide nanowires through a gas-liquid-solid growth mechanism, and the product contains more impurities such as metal catalysts, which will pollute the silicon carbide nanowires and affect the properties of the silicon carbide nanowires. The research on the structure and performance of the characteristic brings difficulties and raises the technical requirements for the subsequent processing and practical application.

The document "Y.Yao, S.T.Lee, F.H.Li, Direct synthesis of 2H-SiC nanowhiskers (direct synthesis of 2H-SiC nanowires), Chemical Physics Letters 2003, 381, 628-633" discloses a method based on methane and SiO A method for preparing 2H-SiC nano-whiskers under a reaction pressure condition of 300 Torr. Literature "J.Z.Guo, Y.Zuo, Z.J.Li, W.D.Gao, J.L.Zhang, Preparation of SiC nanowires with fins by chemical vapor deposition (chemical vapor deposition method to prepare SiC nanowires with fins), Physica E, 2007, 39, 262- 266" discloses a method for preparing β-SiC nanowires using a mixture of methane, silicon oxide and silicon as the starting material under a reaction pressure of 200 Torr. However, the output of the above preparation methods is low, and the prepared silicon carbide nanowires have a small aspect ratio and uneven diameter distribution, making it difficult to realize industrial production and practical application. In recent years, research on silicon carbide nanowires has achieved certain results, however, there are still many deficiencies. If the temperature is too high; the process is complex, multi-step synthesis is required; the output is low, the length-diameter ratio is small, and it is difficult to produce on a large scale; some inevitably generate a large number of silicon carbide particles, which are difficult to separate. In particular, many methods Metal catalysts need to be added, and the presence of metal catalysts greatly affects the performance of silicon carbide nanomaterials.

Contents of the invention

The technical problem to be solved by the present invention is that in order to overcome the shortcomings of most of the existing technologies that require the use of metal catalysts and templates, the aspect ratio is small, and the output is small, and it is difficult to realize its industrial production, the present invention proposes an ultra-long single crystal carbonization A method for preparing a metal-free catalyst for silicon nanowires. This method does not require the addition of metal catalysts and growth templates. The process is simple, easy to operate and control, low in cost, non-polluting, small in diameter, uniform in distribution, centimeter in length, and large-scale growth possible Single crystal β-SiC nanowires.

Technical solution of the present invention is as follows:

A method for preparing an ultra-long single crystal β-SiC nanowire metal-free catalyst, characterized in that, in a vacuum tube furnace or a chemical vapor deposition furnace, a carbon-containing gas is used as a carbon source, and silicon monoxide, a mixture of silicon and silicon oxide As the silicon source, Ar or _N2 as the carrier gas, at a temperature of 1350-1600 ° C, a carbon source gas flow rate of 10-80 sccm, a carrier gas flow rate of 20-80 sccm, and heat preservation for several hours under superatmospheric pressure conditions, on the substrate Single crystal β-SiC nanowires with lengths up to centimeters were obtained by deposition and growth.

The heating process is as follows: heat up to 300°C at a speed of 5-10°C/min, keep warm for 10 minutes, then raise the temperature to 1350-1600°C at a speed of 5-10°C/min, and keep warm for 1-6h; the cooling process is divided into two In the second stage, first cool down to 1200°C at a rate of 10-15°C/min, keep warm for 1 hour, then cool down to 600°C at a rate of 6-8°C/min, and then turn off the power and naturally cool to room temperature.

The mixing ratio of silicon and silicon oxide mixture is 1:1-1:3.

The heat preservation time is 1-6h.

The total reaction pressure is 1.1-1.5 atm.

The substrate is porcelain boat, corundum sheet or silicon sheet.

Among these parameters, the total reaction pressure, temperature, carbonaceous gas flow rate and the setting of the second holding temperature are the key parameters. The growth of silicon carbide nanowires in the present invention is based on a gas-solid growth mechanism. The specific reaction growth process is carried out according to the following reaction equation, wherein only the reactions (2), (3) and (4) need to be carried out when SiO is used as the silicon source:

Si _(solid) + SiO _2(solid) = 2SiO _(gas) (1)

CH4 _(gas) ＝C _(gas) + _2H2(gas) (2)

SiO _(gas) +2C _(gas) = SiC _(solid) +CO _(gas) (3)

SiO _(gas) +3CO _(gas) = SiC _(solid) +CO _{2 (gas)} (4)

Since the temperature of reaction (1) or SiO gasification is above 1250°C, the lower limit of the reaction temperature is 1250°C. At the same time, when the reaction temperature does not exceed 1400°C, reaction (4) cannot proceed, and the growth of silicon carbide nanowires can only be achieved by Reaction (3) is carried out, so that the growth rate of silicon carbide nanowires is reduced, the yield is reduced, and the length is shorter. In addition, the existing technologies are all carried out under the condition of no more than one atmospheric pressure. Creating such an environment is mainly controlled by a vacuum pump or directly flows through the furnace through the carrier gas so that the pressure inside and outside the furnace is at one atmospheric pressure, so that a large amount of SiO , C, CO and CO ₂ gases are lost with the discharge of the carrier gas. In this way, it is more difficult to achieve supersaturation conditions under the conditions of lower temperature and reaction pressure not exceeding one atmospheric pressure, so the yield of silicon carbide nanowires grown is low, and the length is relatively short, the longest being in the range of millimeters. Studies have shown that when the pressure of CO gas in the furnace reaches supersaturation, reaction (4) can proceed (YHGao, Y.Bando, K.Kurashima, T.Sato, J.Mater.Sci.37, 2023(2002) ; J. Wei, KZLi, HJLi, QGFu, L. Zhang, Mater. Chem. Phys. 95, 140 (2006)). Therefore, in order to solve this problem, we adopt appropriately higher temperature and total reaction pressure to realize. Wherein, increasing the reaction pressure is achieved by reducing the exhaust volume. On the one hand, the loss of SiO gas can be reduced, and on the other hand, C and CO can be fully reacted as follows: C _(gas) + CO _{2 (gas)} = 2CO _{(gas )} , so that the SiO and CO gases can quickly reach a supersaturated state even at a lower temperature, so that the reaction (4) can proceed smoothly, which has not been considered in the prior art. However, considering the cost and safety of the experiment, when the temperature is too low, the reaction time will be prolonged, and when the temperature and air pressure are too high, it may exceed the safe use range of the equipment or require the equipment to have higher performance, thereby greatly increasing the technical cost (domestic The normal operating conditions of conventional CVD deposition equipment are that the temperature is lower than 1800°C and the total pressure does not exceed 0.5MPa). Therefore, the ranges we choose for the two key parameters of the total reaction pressure and temperature are: the total reaction pressure is between 1.1-1.5atm Between, the temperature is between 1350-1600°C. On the other hand, if the carbon-containing gas flow exceeds 80 sccm, the carbon source will be in excess at a temperature of 1350-1600° C. and a total reaction pressure of 1.1-1.5 atm, so the remaining carbon will be deposited on the surface of the SiC nanowire and become pollutants, so we choose the carbon-containing gas flow rate between 10-80sccm. In the present invention, we set the second heat preservation at 1200°C, the purpose of which is to have enough time for other types of silicon carbide nanowires (such as 2H-SiC, etc.) to convert into β-SiC nanowires and remove the reaction process In addition, in order to avoid the disproportionation and decomposition reaction of SiO gas during the heat preservation process (SiO(g)→Si(g)+SiO ₂ (g), the decomposition temperature is greater than 1250 ℃), the substances produced by the SiO 2 (g) will contaminate the SiC nano Wire. For this reason, we use a faster cooling rate to cool down to 1200 ° C to solve the problem.

Beneficial effect:

The beneficial effects of the present invention are: (1). The synthesis process is simple and controllable, without adding metal catalysts, without growth templates, and avoiding the pollution of metal catalysts to the product; (2). Since the growth process is a gaseous carbon source and The gaseous silicon source reacts, the reaction is sufficient, and the product is separated from the raw material such as the silicon source, so the synthesized single crystal β-SiC nanowire is not polluted by the solid silicon source, and the temperature control curve is set at 1200 °C. The second holding time (as shown in Figure 1) is beneficial for other types of silicon carbide nanowires (such as 2H-SiC, etc.) to have enough time to convert into β-SiC nanowires, while avoiding the disproportionation and decomposition reactions of SiO (SiO (g)→Si(g)+SiO ₂ (g)) produces substances that contaminate the silicon carbide nanowires, thereby ensuring that the purity of the single crystal β-SiC nanowires reaches more than 95%. It can be seen from Figure 2 and Figure 3 that the product is very clean and there are no other substances present. EDS (FIG. 4), XRD (FIG. 5), Raman (FIG. 6) and FTIR (FIG. 7) analyzes also demonstrated the absence of metal catalysts and unreacted raw materials in the product. And the SiC nanowires prepared by the prior art are generally polluted by metal catalysts and unreacted raw materials, and its purity is generally lower than 90%; (3). Another outstanding feature is that it can be obtained by increasing the initial silicon The amount of source material, appropriately increasing the reaction temperature and extending the holding time can effectively control the length and yield of single crystal β-SiC nanowires. Because increasing the amount of silicon source material can provide enough silicon source gas for a long time, appropriately increasing the reaction temperature can make reactions (3) and (4) easier to carry out, thereby improving the conversion rate of silicon carbide nanowires, increasing the yield, and extending the time The reaction (3) and (4) can be carried out for a longer time, so that the silicon carbide nanowires can continue to grow, thus ensuring the synthesis of large-scale centimeter-scale single crystal β-SiC nanowires. These advantages make the method capable of large-scale industrial production.

Description of drawings

Fig. 1 is the program control temperature curve of setting;

Figure 2 is a low-magnification and high-magnification SEM image of a single crystal β-SiC nanowire;

Figure 3 is the low-magnification and high-magnification TEM, HRTEM and SAED images of single crystal β-SiC nanowires;

Fig. 4 is the EDS figure of single crystal β-SiC nanowire;

Fig. 5 is the XRD pattern of single crystal β-SiC nanowire;

Fig. 6 is the Ramam spectrogram of single crystal β-SiC nanowire;

Fig. 7 is an FTIR spectrum of a single crystal β-SiC nanowire.

Detailed ways

The present invention is realized by adopting the following scheme: adopting chemical vapor deposition method, taking vacuum tube furnace as experimental equipment, using carbon-containing gas as carbon source, silicon monoxide or a mixture of silicon oxide and silicon as silicon source, and inert gas as carrier Gas, according to the temperature curve set by the program to raise and lower the temperature (as shown in Figure 1), when the temperature is 1350-1600 ℃, the carbon source gas flow is 10-80sccm, the carrier gas flow is 20-80sccm, and the furnace pressure is 11- Under the condition of 1.5atm, heat preservation for 1-6 hours, large-scale deposition and growth of single crystal β-SiC nanowires with a length of centimeters on substrates such as porcelain boats, corundum sheets, and silicon sheets.

After the above preparation process, take out the substrate such as the porcelain boat from the tube furnace, and you can see a large layer of light blue or light green products covering the surface of the substrate, the length of which can reach several centimeters. SEM, TEM, HRTEM, SEAD, EDS, X-ray diffraction, Raman, FTIR and other analyzes showed that a single crystal β-SiC nanowire was prepared (as shown in Figure 2-7). When the flow rate of the carbon source gas is lower than 40 sccm, the surface of the nanowire is smooth and the diameter is uniform, with an average diameter of about 40-50 nm. With the increase of reaction temperature, the deposition area, yield and length of silicon carbide nanowires increased, and the diameter of nanowires also slightly increased. At the same time, when the carbon source gas flow rate increases to 80 sccm, a layer of carbon with a rough surface is attached to the surface of the silicon carbide nanowire, and the purity decreases. However, after the product is burned in the air, a pure light blue silicon carbide nanowire can be obtained. The length can also reach centimeter level.

The present invention will be described in further detail below in conjunction with figure and specific implementation process:

Example 1. Divide 4.0g of SiO into three parts and load it into a porcelain boat, place it in the center of a horizontal vacuum tube-type high-temperature furnace, use a mechanical pump to vacuumize the tube-type furnace to -0.1Mpa, and then pass it through a mass flow meter to clean it. Filling with high-purity argon (99.999%) to 1 atm and cleaning for 20 minutes, control the flow at 80 sccm, after the flow is stable, start to heat up to 1400°C according to the temperature curve shown in Figure 1, and fill with 20 sccm of high-purity CH ₄ , adjust the air pressure in the furnace cavity to 1.1-1.5atm, keep warm for 3 hours, then cool down to 1200°C according to the temperature curve set by the program, keep warm for 1 hour, then drop to 600°C according to the temperature curve, turn off the power, and cool down to room temperature naturally. Single crystal β-SiC nanowires with an average size of 40-50nm and a length of centimeters were deposited on the surface of the boat and the surface of the corundum tube.

Example 2. Divide 4.0g of SiO into three parts and pack into a porcelain boat, place it in the center of a horizontal vacuum tube-type high-temperature furnace, use a mechanical pump to vacuumize the tube-type furnace to -0.1Mpa, and then pass it through a mass flow meter to clean it. The method is filled with high-purity argon (99.999%) to 1 atm and cleaned for 20 minutes, the flow rate is controlled at 80 sccm, and after the flow rate is stable, the temperature is raised to 1400 ° C according to the temperature curve shown in Figure 1, and 40 sccm of high-purity CH _is charged. , adjust the air pressure in the furnace cavity to 1.1-1.5atm, keep warm for 3 hours, then cool down to 1200°C according to the temperature curve set by the program, keep warm for 1 hour, then drop to 600°C according to the temperature curve, turn off the power, and cool down to room temperature naturally. Single crystal β-SiC nanowires with an average size of 40-50nm and a length of centimeters were deposited on the surface of the boat and the surface of the corundum tube.

Embodiment 3. Divide 4.0g SiO into three parts and pack into a porcelain boat, place it in the center of a horizontal vacuum tube-type high-temperature furnace, use a mechanical pump to vacuumize the tube-type furnace to -0.1Mpa, and then pass it through a mass flow meter to clean it. Filling with high-purity argon (99.999%) to 1 atm and cleaning for 20 minutes, control the flow at 80 sccm, after the flow is stable, start to heat up to 1400°C according to the temperature curve shown in Figure 1, and fill with 80 sccm of high-purity CH ₄ , adjust the air pressure in the furnace cavity to 1.1-1.5atm, keep warm for 3 hours, then cool down to 1200°C according to the temperature curve set by the program, keep warm for 1 hour, then drop to 600°C according to the temperature curve, turn off the power, and cool down to room temperature naturally. A large number of black and light blue products were deposited on the surface of the boat and the surface of the corundum tube. After burning the long black products on the surface in the air, a light blue product was obtained. The average size of the product was 50-70nm, and the length was up to centimeters. single crystal β-SiC nanowires.

Embodiment 4. 4.0g SiO is divided into two parts, 2.0gSi and 3.0gSiO The mixture is divided into _two parts and packed into a porcelain boat, after placing the center of the horizontal vacuum tube type high temperature furnace, the tube furnace is evacuated to - 0.1Mpa, then fill high-purity argon gas (99.999%) to 1 atm by mass flow meter and clean it for 20 minutes, then control the flow rate at 20 sccm, and start to heat up according to the temperature curve shown in Figure 1 after the flow rate is stable. 1500°C, filled with 40sccm high-purity CH ₄ , adjusted the pressure in the furnace chamber to 1.1-1.5atm, kept it for 3 hours, then lowered the temperature to 1200°C according to the temperature curve set by the program, kept it for 1 hour, and then lowered it to 600 according to the temperature curve ℃, turn off the power, and naturally cool down to room temperature, a large number of single crystal β-SiC nanowires with an average size of 40-50nm and a length of centimeters were deposited on the surface of the porcelain boat and in the corundum tube.

Embodiment 5. 2.0gSi and 3.0gSiO _The mixture is divided into two parts and loaded into a porcelain boat, and after being placed in the center of a horizontal vacuum tube type high-temperature furnace, a mechanical pump is used to vacuum the tube type furnace to -0.1Mpa, and then through a mass flow rate Fill the meter with high-purity argon gas (99.999%) to 1 atm in a cleaning manner and after cleaning for 20 minutes, control the flow rate at 80 sccm. For high-purity CH ₄ , adjust the pressure in the furnace chamber to 1.1-1.5atm, keep warm for 3 hours, then cool down to 1200°C according to the temperature curve set by the program, keep warm for 1 hour, then drop to 600°C according to the temperature curve, turn off the power, and cool down naturally At room temperature, there is no β-SiC nanowire deposition on the surface of the porcelain boat and the surface of the corundum tube.

Embodiment 6. 2.0gSi and 3.0gSiO _The mixture is divided into two parts and loaded into a porcelain boat, and after being placed in the center of a horizontal vacuum tube-type high-temperature furnace, a mechanical pump is used to evacuate the tube-type furnace to -0.1Mpa, and then pass a mass flow rate Fill the meter with high-purity argon (99.999%) to 1 atm and clean it for 20 minutes, then control the flow rate at 80 sccm. For high-purity CH ₄ , adjust the pressure in the furnace chamber to 1.1-1.5atm, keep warm for 3 hours, then cool down to 1200°C according to the temperature curve set by the program, keep warm for 1 hour, then drop to 600°C according to the temperature curve, turn off the power, and cool down naturally At room temperature, a small amount of single crystal β-SiC nanowires with an average size of 40-50nm and a length of millimeters were deposited on the surface of the porcelain boat and the surface of the corundum tube.

Example 7. 2.0gSi and 3.0gSiO _The mixture is divided into two parts and loaded into a porcelain boat, and after being placed in the center of a horizontal vacuum tube type high temperature furnace, a mechanical pump is used to evacuate the tube type furnace to -0.1Mpa, and then pass the mass flow Fill the meter with high-purity argon gas (99.999%) to 1 atm in a cleaning manner and after cleaning for 20 minutes, control the flow rate at 80 sccm. For high-purity CH ₄ , adjust the pressure in the furnace chamber to 1.1-1.5atm, keep it warm for 1 hour, then lower the temperature to 1200°C according to the temperature curve set by the program, keep it warm for 1 hour, then drop it to 600°C according to the temperature curve, turn off the power, and cool down naturally At room temperature, a large number of single crystal β-SiC nanowires with an average size of 40-50nm and a length of centimeters were deposited on the surface of the porcelain boat and the surface of the corundum tube.

Example 8. 2.0gSi and 3.0gSiO _The mixture is divided into two parts and loaded into a porcelain boat, and after being placed in the center of a horizontal vacuum tube type high-temperature furnace, a mechanical pump is used to vacuum the tube type furnace to -0.1Mpa, and then through a mass flow rate Fill the meter with high-purity argon gas (99.999%) to 1 atm by cleaning and clean it for 20 minutes. For high-purity C ₂ H ₂ , adjust the pressure in the furnace chamber to 1.1-1.5atm, keep warm for 6 hours, then cool down to 1200°C according to the temperature curve set by the program, keep warm for 1 hour, then drop to 600°C according to the temperature curve, turn off the power, Naturally cooled to room temperature, a large number of single crystal β-SiC nanowires with an average size of 40-50nm and a length of centimeters were deposited on the surface of the porcelain boat and the surface of the corundum tube.

Embodiment 9. 4.0g SiO is divided into two parts, 2.0gSi and 3.0gSiO The mixture is divided into _two parts and packed into a porcelain boat, after placing the center of the horizontal vacuum tube type high-temperature furnace, the tube furnace is evacuated to - 0.1Mpa, then fill high-purity nitrogen gas (99.999%) to 1 atm by mass flow meter and clean it for 20 minutes, then control the flow at 40 sccm, and start to heat up to 1500 according to the temperature curve shown in Figure 1 after the flow is stable ℃, fill in 40sccm high-purity CH ₄ , adjust the pressure in the furnace chamber to 1.1-1.5atm, keep warm for 3 hours, then cool down to 1200℃ according to the temperature curve set by the program, keep warm for 1 hour, and then drop to 600℃ according to the temperature curve , turn off the power, and naturally cool down to room temperature. The surface of the porcelain boat and the surface of the corundum tube deposited single crystal β-SiC nanowires with an average size of 50-60nm and a length of centimeters.

Example 10. 2.0gSi and 3.0gSiO The mixture is divided into _two parts and loaded into a porcelain boat. After placing it in the center of a horizontal vacuum tube-type high-temperature furnace, a mechanical pump is used to evacuate the tube-type furnace to -0.1Mpa, and then through a mass flow rate Fill the meter with high-purity argon gas (99.999%) to 1 atm by cleaning and clean it for 20 minutes. For high-purity CH ₄ , adjust the pressure in the furnace chamber to 1.1-1.5atm, keep warm for 3 hours, then cool down to 1200°C according to the temperature curve set by the program, keep warm for 1 hour, then drop to 600°C according to the temperature curve, turn off the power, and cool down naturally At room temperature, a large number of single crystal β-SiC nanowires with an average size of 40-50nm and a length of centimeters were deposited on the surface of the porcelain boat and the surface of the corundum tube.

Example 11. Divide 2.0g of SiO into two parts and put it into a porcelain boat, place _it in the center of a horizontal vacuum tube type high-temperature furnace, use a mechanical pump to vacuum the tube type furnace to -0.1Mpa, and then pass it through a mass flow meter to clean Fill in high-purity argon (99.999%) to 1 atm and clean for 20 minutes, then control the flow rate at 80 sccm. After the flow rate is stable, start to heat up to 1400°C according to the temperature curve shown in Figure 1, and fill in 40 sccm of high-purity CH _4. Adjust the air pressure in the furnace chamber to 1.1-1.5atm, keep warm for 3 hours, then cool down to 1200°C according to the temperature curve set by the program, keep warm for 1 hour, then drop to 600°C according to the temperature curve, turn off the power, and cool down to room temperature naturally. A small amount of single crystal β-SiC nanowires with thicker diameters and millimeter-scale lengths were deposited on the surface of the porcelain boat and the surface of the corundum tube.

Embodiment 12. 4.0g SiO is divided into two parts, 2.0gSi and 3.0gSiO The mixture is divided into two parts and loaded into a porcelain boat, and after being placed in the center of a horizontal vacuum tube type high temperature furnace, a mechanical pump is used to evacuate the tube type furnace to -0.1 Mpa, then fill in high-purity argon (99.999%) to 1 atm by mass flow meter and clean it for 20 minutes, then control the flow at 20 sccm, and start to heat up to 1600 according to the temperature curve shown in Figure 1 after the flow is stable ℃, fill in 40sccm high-purity CH ₄ , adjust the pressure in the furnace chamber to 1.1-1.5atm, keep warm for 3 hours, then cool down to 1200℃ according to the temperature curve set by the program, keep warm for 1 hour, and then drop to 600℃ according to the temperature curve , turn off the power, and naturally cool down to room temperature. A large number of single crystal β-SiC nanowires with an average size of 60-80nm and a length of centimeters are deposited on the surface of the porcelain boat and in the corundum tube.

Claims (7)

1. the preparation method of a ultralong monocrystal beta-SiC nanowire metal-free catalyzer is characterized in that, in vacuum tube furnace or chemical vapor deposition stove, take carbonaceous gas as carbon source, the mixture of silicon monoxide or silicon and silicon oxide is the silicon source, Ar or N ₂Being carrier gas, is that 1350-1600 ℃, carbon-source gas flow are that 10-80sccm, carrier gas flux are 20-80sccm, are incubated a few hours under condition of super atmospheric pressure in temperature, and deposition growing obtains the single-crystal silicon carbide nanowires that length reaches centimetre-sized on substrate.

2. the preparation method of ultralong monocrystal beta-SiC nanowire metal-free catalyzer according to claim 1 is characterized in that, described carbonaceous gas is methane, acetylene or ethene.

3. the preparation method of ultralong monocrystal beta-SiC nanowire metal-free catalyzer according to claim 1, it is characterized in that, temperature-rise period is: adopt the speed of 5-10 ℃/min to be warmed up to 300 ℃, be incubated 10 minutes, speed with 5-10 ℃/min is warmed up to 1350-1600 ℃ again, is incubated 1-6h again; Temperature-fall period was divided into for two stages, and the speed with 10-15 ℃/min cools to 1200 ℃ first, insulation 1h, and the speed with 6-8 ℃/min cools to 600 ℃ again, and then powered-down naturally cools to room temperature.

4. the preparation method of ultralong monocrystal beta-SiC nanowire metal-free catalyzer according to claim 1 is characterized in that, the mixing quality ratio of silicon and silicon oxide is 1:1-1:3.

5. the preparation method of ultralong monocrystal beta-SiC nanowire metal-free catalyzer according to claim 1 is characterized in that, described soaking time is 1-6h.

6. the preparation method of ultralong monocrystal beta-SiC nanowire metal-free catalyzer according to claim 1 is characterized in that, described super-atmospheric pressure is 1.1-1.5atm.

7. the preparation method of each described ultralong monocrystal beta-SiC nanowire metal-free catalyzer is characterized in that according to claim 1～6, and substrate is porcelain boat, corundum sheet or silicon chip.

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