Preparation method of silicon carbide nanowire with amorphous twin crystal structure

Abstract

The invention relates to the field of materials, and mainly relates to a preparation method of a silicon carbide nanowire with an amorphous twin structure. The composite nanowire is prepared by taking biphenyl as a carbon source, tetraethyl silicate as a silicon source and iron nitrate nonahydrate as a doping agent through carbon thermal reduction reaction and high-temperature calcination, and the length, the diameter and the thickness of an amorphous layer of the composite nanowire can be adjusted by adjusting the calcination time and the calcination temperature. The preparation method is convenient to operate and can be mastered and learned by common workers, the preparation principle is simple and easy to understand, controllable preparation of the twin crystal ceramic nanowires is achieved, a universal amorphous silicon dioxide coating strategy is developed, and in view of excellent properties of a silicon carbide material in the aspects of mechanics, thermotics and the like, the preparation method has good application prospects. The method has a great application prospect in the fields of aerospace and engineering.

Description

Technical Field

[0001] The invention belongs to the field of materials and relates to the preparation of biphenyl-tetraethyl silicate gel, and in particular to the preparation of silicon carbide-silicon oxide nanowires with a twin amorphous system obtained by calcining the gel. Background Art

[0002] As an important semiconductor and ceramic material, silicon carbide has been extensively studied for its exceptional thermal conductivity, chemical stability, and mechanical properties. Silicon carbide has been widely used in advanced applications. Due to its lightweight, high-strength, and high-temperature resistance, it is currently used in critical components such as aircraft combustion chambers, tail nozzles, and rocket fairings. Due to its antioxidant and neutron radiation resistance, silicon carbide is also the preferred material for nuclear reactor cores and is widely used in military armor and other applications. In recent years, a variety of linear silicon carbide nanostructures have been prepared, including nanosprings, nanorods, bamboo-like nanowires, and beaded nanochains. These diverse morphologies are often associated with various types of stacking faults, and twinning is another type of low-energy stacking fault.

[0003] When two crystals (or two parts of a crystal) form a mirror-symmetrical orientation along a common crystal plane (i.e., a specific orientation), these two crystals are called twins. Twins can be categorized as growth twins and mechanical twins. Growth twins are twins that form during crystal growth or mineral formation. Growth twins are also called annealing twins. Mechanical twins are twins formed by uniform shear deformation of a single crystal. When slip is not readily available, twins become another major form of plastic deformation. Mechanical twins are also called deformation twins. Current research on twins primarily focuses on mechanical twins in metals. Research on growth twins in ceramics is relatively limited, and there is no research on the controlled preparation of twinned ceramics. While the formation mechanism of growth twins remains unexplained, current preparation methods indicate that twin nucleation typically occurs at two- or three-phase interfaces, typically at solid-liquid or solid-liquid-gas interfaces. After being doped with other substances, the surface energy of different interfaces of the original material nucleation will change, causing it to not grow in one direction, thus forming twins.

[0004] Through years of evolution, organisms in nature often possess nearly perfect structures and functions. Therefore, they have long served as models for our learning. Many twinned ceramics exist in nature, such as periodic twins found in conch shells. Because the presence of twin boundaries induces crack propagation, this twinned lamellar structure imparts exceptional mechanical properties. The high density of twins at the tips of wild boar tusks also imparts high strength and toughness.

[0005] Since the middle of the last century, amorphous alloys (also known as metallic glasses) have gradually come into the researchers' field of vision. Through a large number of studies, it has been found that amorphous alloys have different chemical and physical properties from traditional crystalline materials. The most impressive thing is that bulk amorphous alloys have extremely high mechanical strength. The reason is that amorphous alloys do not have defects such as dislocations and grain boundaries in traditional crystalline materials. The interior of the material is almost in an ideal state, so some of its mechanical properties are close to theoretical values. For example, the fracture strength of cobalt-based bulk amorphous alloys can reach 6.0GPa, which is the highest value reported for bulk metal materials to date. Many researchers at home and abroad have proved that by amorphizing the alloy, the mechanical properties of the material can be improved.

[0006] Inspired by twins and amorphous alloys in nature, introducing controllable growth twins into silicon carbide nanowires and then introducing amorphous materials to construct a twin-amorphous composite system is an effective way to prepare new high-strength silicon carbide materials. Summary of the Invention

[0007] The present invention aims to address the difficulty in controlling the preparation of existing twinned ceramic materials. Using inexpensive metal salts, biphenyl, and tetraethyl silicate as raw materials, a sol-gel method is used to obtain carbon silicon iron gel. This gel is then calcined at high temperature under argon protection, achieving the preparation of a one-dimensional ceramic nanostructured with a twinned amorphous composite system. The method comprises the following steps:

[0008] The first step is to prepare 15 mL of a biphenyl-acetone mixed solution (biphenyl mass is 5-15 g, acetone is analytical grade), to which 10-20 mL of analytical grade tetraethyl silicate is added dropwise. During the addition, the solution is kept in a state of vigorous stirring. After the addition is completed, stir for 30 minutes to ensure that the biphenyl, acetone and tetraethyl silicate are completely mixed and the solution is transparent and colorless;

[0009] In the second step, add 1-2g of analytically pure Fe(NO3)3·9H2O to the colorless solution obtained in the first step, adding small amounts and multiple times to ensure that no precipitation occurs. After complete addition, the solution turns orange-yellow. Continue stirring for 2 hours to ensure that the Fe(NO3)3·9H2O is completely dissolved.

[0010] In the third step, 1-5 mL of anhydrous acetic acid is added dropwise to the homogenized orange-yellow solution obtained in the second step to lower the pH of the solution and promote the hydrolysis of the tetraethyl silicate. During the addition, the color of the solution gradually changes from orange-yellow to brown-red. After the addition, the solution is stirred for 24 hours to ensure complete hydrolysis of the tetraethyl silicate.

[0011] Step 4: Prepare 1-5 mL of a urotropine aqueous solution (the mass of urotropine is 1-3 g), stir thoroughly and then quickly add it to the brown-red solution obtained in step 3, and continue stirring until the solution is completely gelled;

[0012] Step 5: Place the gel prepared in step 4 in a vacuum oven and dry it for 12-24 hours at a temperature of 80-150°C to ensure that the acetone is completely removed and the biphenyl is not decomposed;

[0013] Step 6: Weigh 1g of the dried gel, add 100-300mg of carbon powder, and then crush and ball-mill to ensure that the precursor gel and carbon powder are evenly dispersed. The ball-milled sample is then calcined at high temperature under argon atmosphere.

[0014] In the seventh step, the calcined sample is subjected to ultrasonic centrifugation to remove impurities, and the supernatant is retained and dried to obtain silicon carbide silicon dioxide nanowires with an amorphous twin composite system.

[0015] In the present invention, unless otherwise stated, the preparation conditions (such as temperature, humidity, instruments, materials, processes, methods, etc.) are common in the art or can be easily obtained by ordinary technicians according to conventional techniques in the art.

[0016] In the present invention, unless otherwise stated, the dissolution or reaction temperature is room temperature (15-35 degrees Celsius) and normal pressure.

[0017] In the present invention, the chemicals are all analytically pure.

[0018] Furthermore, the silicon carbide silicon dioxide nanowires with an amorphous twin composite system prepared by the present invention have a length range of 5-15 μm and a diameter range of 100-300 nm. The specific length and diameter are determined by the reaction conditions and are adjustable.

[0019] Furthermore, the amorphous silicon oxide thickness of the silicon carbide-silicon dioxide nanowires with an amorphous twin composite system prepared by the present invention is in the range of 2-5 nm, and the specific length and diameter thereof are determined by the reaction conditions and are adjustable.

[0020] Furthermore, in the sixth step, the preferred calcination temperature is 1200-1550° C. and the calcination time is 4-7 h to obtain silicon carbide-silicon dioxide nanowires of an amorphous twin composite system.

[0021] Advantages of the present invention:

[0022] 1. The present invention provides a simple and low-cost method for preparing twinned silicon carbide nanowires. Specifically, biphenyl is used as a carbon source, tetraethyl silicate is used as a silicon source, and ferric nitrate nonahydrate is used as a dopant. The principle of carbothermal reaction is utilized to prepare periodic twinned nanowires. The controllable preparation of grown twinned ceramic nanowires is successfully achieved. The preparation method is simple and has good prospects for industrial preparation.

[0023] 2. This invention creatively constructs a twinned amorphous composite system. By pyrolysis of tetraethyl silicate, a layer of amorphous silicon dioxide is successfully coated on the twinned silicon carbide nanowires. The amorphous layer is uniform, approximately 3-5 nm thick, and exhibits excellent morphology. This method is easy to operate and simple in principle, and can be extended to the preparation of other ceramic nanowires, thereby constructing other crystalline amorphous composite systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a scanning electron microscope (SEM) photograph of silicon carbide-silicon dioxide nanowires with an amorphous twin composite system obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] The present invention will be further described in detail below in conjunction with the accompanying drawings and examples. The solvents, medicines and instruments used below that are not specifically described are all considered to be available in common laboratories or the market. In addition, the examples in this embodiment are only for the reader to understand the specific contents of the present invention rather than the entire content, and do not limit the scope of protection of the present invention in any way. In addition, without departing from the scope of the present invention, optimization or regulation that those skilled in the art can expect are all included in the present invention.

[0026] Example 1

[0027] Preparation method of silicon carbide silicon dioxide nanowires with amorphous twin composite system

[0028] The first step is to prepare 15 mL of a biphenyl-acetone mixed solution (biphenyl mass is 5-15 g, acetone is analytical grade), to which 10-20 mL of analytical grade tetraethyl silicate is added dropwise. During the addition, the solution is kept in a state of vigorous stirring. After the addition is completed, stir for 30 minutes to ensure that the biphenyl, acetone and tetraethyl silicate are completely mixed and the solution is transparent and colorless;

[0029] In the second step, add 1-2g of analytically pure Fe(NO3)3·9H2O to the colorless solution obtained in the first step, adding small amounts and multiple times to ensure that no precipitation occurs. After complete addition, the solution turns orange-yellow. Continue stirring for 2 hours to ensure that the Fe(NO3)3·9H2O is completely dissolved.

[0030] Step 3: Add 1-5 mL of anhydrous acetic acid dropwise to the stirred orange-yellow solution obtained in step 2 to lower the pH of the solution and promote the hydrolysis of tetraethyl silicate. During the addition, the color of the solution gradually changes from orange-yellow to brown-red. After the addition, stir the solution for 24 hours to ensure complete hydrolysis of tetraethyl silicate.

[0031] Step 4: Prepare 1-5 mL of a urotropine aqueous solution (the mass of urotropine is 1-3 g), stir thoroughly and then quickly add it to the brown-red solution obtained in step 3, and continue stirring until the solution is completely gelled;

[0032] Step 5: Place the gel prepared in step 4 in a vacuum oven and dry it for 12-24 hours at a temperature of 80-150°C to ensure that the acetone is completely removed and the biphenyl is not decomposed;

[0033] Step 6: Weigh 1g of the dried gel, add 100-300mg of carbon powder, and then crush and ball-mill to ensure that the precursor gel and carbon powder are evenly dispersed. The ball-milled sample is then calcined at high temperature under argon atmosphere.

[0034] In the seventh step, the calcined sample is subjected to ultrasonic centrifugation to remove impurities, and the supernatant is retained and dried to obtain silicon carbide silicon dioxide nanowires with an amorphous twin composite system.

[0035] In the eighth step, the morphology is characterized using a scanning electron microscope and a high-resolution transmission electron microscope. The twin nanowire lattice stripes are characterized by electron diffraction by rotating the belt axis, and the morphology and size of the amorphous silicon dioxide layer are determined.

[0036] Example 2

[0037] Preparation method of silicon carbide nanowires coated with amorphous silicon oxide

[0038] The first step is to prepare 15 mL of a biphenyl-acetone mixed solution (biphenyl mass is 5-15 g, acetone is analytical grade), to which 10-20 mL of analytical grade tetraethyl silicate is added dropwise. During the addition, the solution is kept in a state of vigorous stirring. After the addition is completed, stir for 30 minutes to ensure that the biphenyl, acetone and tetraethyl silicate are completely mixed and the solution is transparent and colorless;

[0039] In the second step, prepare 1-5 mL of oxalic acid solution (0.05-0.15 g of anhydrous oxalic acid), stir well, and add dropwise to the stirred, colorless solution obtained in the first step to lower the pH of the solution, thereby promoting the hydrolysis of tetraethyl silicate. During the addition, the solution gradually changes from clear to translucent. After the addition, stir the solution for 24 hours to ensure complete hydrolysis of tetraethyl silicate.

[0040] The third step is to prepare 1-5 mL of a urotropine aqueous solution (the mass of urotropine is 1-3 g), stir it thoroughly and then quickly add it to the solution obtained in the second step, and then continue stirring until the solution is completely gelled;

[0041] The fourth step is to place the gel prepared in the third step into a vacuum oven and dry it for 12-24 hours at a temperature of 80-150°C to ensure that the acetone is completely removed and the biphenyl is not decomposed;

[0042] In the fifth step, 1 g of the dried gel was weighed and crushed by ball milling to ensure uniform dispersion of the precursor gel. The ball-milled sample was then placed in a zirconia crucible, a graphite cover was placed on top, and the sample was calcined at high temperature under argon atmosphere to deposit silicon carbide nanowires on the graphite crucible cover through a gas phase reaction.

[0043] In the sixth step, the deposited nanowires on the graphite crucible cover are scraped off, ultrasonically vibrated, and dried to obtain silicon carbide nanowires coated with amorphous silicon oxide.

[0044] In the seventh step, the morphology is characterized using a scanning electron microscope and a high-resolution transmission electron microscope. The twin nanowire lattice stripes are characterized by electron diffraction by rotating the belt axis, and the morphology and size of the amorphous silicon dioxide layer are determined.

[0045] Example 3

[0046] Preparation method of twinned silicon carbide nanowires

[0047] The first step is to prepare 15 mL of a biphenyl-acetone mixed solution (biphenyl mass is 5-15 g, acetone is analytical grade), to which 10-20 mL of analytical grade tetraethyl silicate is added dropwise. During the addition, the solution is kept in a state of vigorous stirring. After the addition is completed, stir for 30 minutes to ensure that the biphenyl, acetone and tetraethyl silicate are completely mixed and the solution is transparent and colorless;

[0048] In the second step, add 1-2g of analytically pure Fe(NO3)3·9H2O to the colorless solution obtained in the first step, adding small amounts and multiple times to ensure that no precipitation occurs. After complete addition, the solution turns orange-yellow. Continue stirring for 2 hours to ensure that the Fe(NO3)3·9H2O is completely dissolved.

[0049] Step 3: Prepare 1-5 mL of oxalic acid solution (0.05-0.15 g of anhydrous oxalic acid), stir well, and then add dropwise to the stirred solution obtained in step 2 to lower the pH of the solution and promote the hydrolysis of tetraethyl silicate. After the addition, stir the solution for 24 hours to ensure complete hydrolysis of tetraethyl silicate.

[0050] Step 4: Prepare 1-5 mL of a urotropine aqueous solution (the mass of urotropine is 1-3 g), stir thoroughly and then quickly add it to the solution obtained in step 3, and continue stirring until the solution is completely gelled;

[0051] Step 5: Place the gel prepared in step 4 in a vacuum oven and dry it for 12-24 hours at a temperature of 80-150°C to ensure that the acetone is completely removed and the biphenyl is not decomposed;

[0052] Step 5: Weigh 1g of the dried gel, add 100-300mg of carbon powder and crush it with ball mill to ensure that the precursor gel is evenly dispersed. Then, the ball-milled sample is calcined at high temperature under argon atmosphere.

[0053] In the sixth step, the prepared product is washed with hydrofluoric acid to remove impurities, and then the precipitate is collected by centrifugation and dried to obtain twinned silicon carbide nanowires.

Claims

1. A method for preparing silicon carbide nanowires having an amorphous twin structure, characterized by The following steps: The first step is to prepare 15 mL of a biphenyl-acetone mixed solution (biphenyl mass is 5-15 g, acetone is analytical grade), to which 10-20 mL of analytical grade tetraethyl silicate is added dropwise. During the addition, the solution is kept in a state of vigorous stirring. After the addition is completed, stir for 30 minutes to ensure that the biphenyl, acetone and tetraethyl silicate are completely mixed and the solution is transparent and colorless; In the second step, add 1-2g of analytically pure Fe(NO3)3·9H2O to the colorless solution obtained in the first step, adding small amounts and multiple times to ensure that no precipitation occurs. After complete addition, the solution turns orange-yellow. Continue stirring for 2 hours to ensure that the Fe(NO3)3·9H2O is completely dissolved. Step 3: Add 1-5 mL of anhydrous acetic acid dropwise to the stirred orange-yellow solution obtained in step 2 to lower the pH of the solution and promote the hydrolysis of tetraethyl silicate. During the addition, the color of the solution gradually changes from orange-yellow to brown-red. After the addition, stir the solution for 24 hours to ensure complete hydrolysis of tetraethyl silicate. Step 4: Prepare 1-5 mL of a urotropine aqueous solution (the mass of urotropine is 1-3 g), stir thoroughly and then quickly add it to the brown-red solution obtained in step 3, and continue stirring until the solution is completely gelled; Step 5: Place the gel prepared in step 4 in a vacuum oven and dry it for 12-24 hours at a temperature of 80-150°C to ensure that the acetone is completely removed and the biphenyl is not decomposed; Step 6: Weigh 1g of the dried gel, add 100-300mg of carbon powder, and then crush and ball-mill to ensure that the precursor gel and carbon powder are evenly dispersed. The ball-milled sample is then calcined at high temperature under argon atmosphere. In the seventh step, the calcined sample is subjected to ultrasonic centrifugation to remove impurities, and the supernatant is retained and dried to obtain silicon carbide silicon dioxide nanowires with an amorphous twin composite system.

2. The method for preparing silicon carbide-silicon oxide nanowires having an amorphous twin system according to claim 1, wherein: The nanowires exhibit good linear morphology, with a length ranging from 5 to 15 μm and a diameter ranging from 100 to 300 nm. The calcination temperature is preferably 1300-1550° C., and the calcination time is preferably 4-7 hours.

3. The method for preparing silicon carbide-silicon oxide nanowires having an amorphous twin system according to claim 1, wherein: The coating of the amorphous layer is very uniform, and its thickness ranges from 3 to 5 nm. The thickness of the amorphous layer can be controlled by calcination temperature and calcination time.

4. Application of any one of claims 1 to 3 in the fields of engineering and materials.

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