TWI888116B - Method of preparing silicon nitride nanomaterial - Google Patents

Abstract

A method of preparing a silicon nitride nanomaterial includes pickling, washing, and drying an agricultural waste containing carbon and silicon dioxide to prepare a biomass raw material. Performing said biomass raw material a low temperature carbon thermal reaction at 600 °C to form a first crude product containing carbon and silicon oxides, then pickling, washing, and drying said first crude product to obtain a carbonized product. Performing said carbonized product a high temperature carbon thermal reaction with an iron - based catalyst in a nitrogen atmosphere at 1300 °C to 1600 °C to form a second crude product comprising silicon nitride nanocrystalline whiskers and silicon nitride nanoparticles. Said iron - based catalyst selected from the group consisting of iron chloride, ferrous chloride, and any combination thereof. And performing an purification treatment by refining said second crude product including separating said silicon nitride nanocrystallines and said silicon nitride nanoparticles in said second crude product from each other with a polar solvent and a non - polar

Description

Preparation method of silicon nitride nanomaterials

The present invention relates to a method for preparing silicon nitride nanomaterials, and in particular to a method for preparing silicon nitride nanomaterials using agricultural waste.

Silicon nitride (Si ₃ N ₄ ) is an advanced ceramic material that has excellent thermomechanical properties, chemical inertness, high temperature resistance, corrosion durability, oxidation resistance, corrosion resistance and high thermal conductivity. Therefore, it is one of the most important engineering ceramics for structural applications.

Silicon nitride has a wide energy gap (5.3eV) and can obtain different electronic or optical properties by doping heterogeneous atoms. Due to its high mechanical strength, thermal stability, chemical stability, high doping concentration, and excellent optoelectronic and mechanical properties, silicon nitride nanomaterials have potential uses in many areas, such as energy conversion and storage in nanobatteries, lasers, chemical sensors and catalysis, light field emission devices, nanocomposites, and enhanced materials. Therefore, silicon nitride is considered to be an important material for future high-temperature microelectronics and optoelectronic devices.

Therefore, the purpose of the present invention is to provide a novel method for preparing silicon nitride nanomaterials.

Therefore, the method for preparing silicon nitride nanomaterials of the present invention comprises the following steps: (1) acid-washing, water-washing and drying agricultural waste containing carbon and silicon dioxide in sequence to prepare biomass raw materials; (2) subjecting the biomass raw materials to low-temperature carbon thermal reaction at 600°C to form a first crude product containing carbon and silicon oxide, and acid-washing, water-washing and drying the first crude product in sequence to obtain a carbonized product containing the carbon and silicon oxide; (3) reacting the carbonized product with an iron-based catalyst in a A high temperature carbon thermal reaction is carried out at 1300°C to 1600°C in a nitrogen atmosphere to form a second crude product containing silicon nitride nano whiskers and silicon nitride nanoparticles, wherein the iron-based catalyst is selected from the group consisting of ferric chloride, ferrous chloride and any combination thereof; and (4). The second crude product is subjected to a purification treatment, wherein the purification treatment includes using a polar solvent and a non-polar solvent to separate the silicon nitride nano whiskers and the silicon nitride nanoparticles in the second crude product.

The effect of the present invention is that: the present invention utilizes the agricultural waste to prepare silicon nitride nanomaterials, and in particular, the iron-based catalyst is used in conjunction with the high-temperature carbon thermal reaction to reduce the generation temperature of the silicon nitride nano whiskers.

Other features and effects of the present invention will be clearly presented in the embodiments with reference to the drawings, wherein: FIG. 1 is the surface morphology of the silicon nitride nano whiskers of Example A of the present invention; FIG. 2 is the surface morphology of the silicon nitride nano whiskers of Example B of the present invention; FIG. 3 is the surface morphology of the silicon nitride nano whiskers of the comparative example A; FIG. 4 is the X-ray diffraction diagram of the silicon nitride nano whiskers of Example A of the present invention; FIG. 5 is the surface morphology of the silicon nitride nano whiskers of the present invention; Figure 6 is an X-ray diffraction diagram of the silicon nitride nano whiskers of Example B of the present invention; Figure 7A and Figure 7B are Raman spectra of the silicon nitride nano whiskers of Example A of the present invention; Figure 8A and Figure 8B are Raman spectra of the silicon nitride nano whiskers of Example B of the present invention; and Figure 9A and Figure 9B are Raman spectra of the silicon nitride nano whiskers of Example A.

The method for preparing the silicon nitride nanomaterial of the present invention comprises the following steps (1) to (4). Steps (1) to (4) are further described in detail below.

[Step (1)]

In step (1), agricultural waste containing carbon and silicon dioxide is acid-washed, water-washed and dried in sequence to produce biomass raw materials.

The agricultural waste includes, but is not limited to, rice.

The pickling is to remove metal impurities and inorganic salts in the agricultural waste with an acidic liquid, such as but not limited to hydrochloric acid with a concentration of 0.5N.

[Step (2)]

In step (2), the biomass raw material is subjected to a low-temperature carbon thermal reaction at 600°C to form a first crude product containing carbon and silicon oxide, and the first crude product is sequentially acid-washed, water-washed and dried to obtain a carbonized product containing the carbon and the silicon oxide.

The time of the low-temperature carbon thermal reaction is, for example but not limited to, 3 hours.

The acid washing is to remove the metal impurities and inorganic salts remaining in the first crude product with an acidic liquid, such as but not limited to hydrochloric acid with a concentration of 0.5N.

[Step (3)]

In step (3), the carbonization product and an iron-based catalyst are subjected to a high-temperature carbon thermal reaction at 1300°C to 1600°C in a nitrogen atmosphere to form a second crude product comprising silicon nitride nanowhiskers, silicon nitride nanoparticles and residual carbon.

The iron-based catalyst is selected from the group consisting of ferric chloride, ferrous chloride and any combination thereof. In some embodiments of the present invention, the amount of the iron-based catalyst is 0.03 grams based on the amount of the carbonized product being 1 gram.

The time range of the high temperature carbon thermal reaction is, for example but not limited to, 4 hours.

The crystal phases of the silicon nitride nano whiskers include α-Si ₃ N ₄ and β-Si ₃ N ₄ , wherein the α-Si ₃ N ₄ is the main crystal phase and the β-Si ₃ N ₄ is the secondary crystal phase.

[Step (4)]

In step (4), the second crude product is subjected to a purification treatment, and the purification treatment includes using a polar solvent and a non-polar solvent to separate the silicon nitride nano whiskers and the silicon nitride nanoparticles in the second crude product from each other; and heating the separated silicon nitride nano whiskers and the silicon nitride nanoparticles at 600°C to remove the residual carbon.

The polar solvent is, for example, but not limited to, water. The non-polar solvent is, for example, but not limited to, xylene.

The present invention will be further described with reference to the following embodiments, but it should be understood that the embodiments are only for illustrative purposes and should not be interpreted as limitations on the implementation of the present invention.

[Embodiment A Group]

(1) The rice straw powder is acid-washed, water-washed and dried in sequence to obtain a biomass raw material. The acid-washing step is to stir and mix the rice straw powder with 0.5N hydrochloric acid at 80°C for 2 hours to remove metal impurities and inorganic salts in the rice straw powder to obtain the acid-washed rice straw powder. The water-washing step is to wash the acid-washed rice straw powder with deionized water until the pH value is neutral.

(2) The biomass raw material is heated at 600°C for 3 hours to perform low-temperature carbonization reduction to form a first crude product containing carbon and silicon oxide, and the first crude product is then acid-washed, water-washed and dried in sequence to obtain a carbonized product containing the carbon and the silicon oxide. Wherein, the acid-washing is to stir and mix the first crude product with 0.5N hydrochloric acid at 80°C for 2 hours to obtain an acid-washed first crude product. The water-washing is to wash the acid-washed first crude product with deionized water until the pH value is neutral.

(3) 1 gram of the carbonized product and 0.03 gram of ferrous chloride are placed in a crucible and heated at 1300°C to 1600°C in a nitrogen atmosphere (nitrogen flow rate is 500 sccm) for high-temperature carbon thermal reaction to generate a second crude product containing silicon nitride nanowhiskers, silicon nitride nanoparticles and residual carbon. Most of the silicon nitride nanowhiskers in the second crude product are attached to the surface of the crucible, and the silicon nitride nanoparticles are coated by the residual carbon.

(4) The second crude product is taken out from the crucible and transferred into a beaker. Deionized water is then added to the beaker and stirred at a speed of 5000 rpm/min using a homogenizer. Xylene is then added to the beaker. Since the xylene and the deionized water are immiscible, they will separate into layers, so that the carbon-coated silicon nitride nanoparticles that are retained are suspended on the liquid surface of the xylene due to their hydrophobicity, while the silicon nitride nanocrystal whiskers settle to the bottom of the beaker. Then, a separatory funnel is used to perform separation filtration to separate the silicon nitride nanocrystal whiskers from the carbon-coated silicon nitride nanoparticles that are retained. Afterwards, the silicon nitride nano whiskers were dried and kept at 600°C for 10 hours to remove the carbon attached due to electrostatic charging, and the silicon nitride nanoparticles coated with the residual carbon were dried and kept at 600°C for 10 hours to remove the coated carbon.

[Embodiment B Group]

The difference between Example B and Example A is that ferric chloride is used instead of ferrous chloride in step (3).

[Comparative Example Group A]

The difference between the control group A and the embodiment group A and the embodiment group B is that the control group A does not use an iron-based catalyst in step (3).

Surface morphology analysis:

The surface morphologies of the silicon nitride nano whiskers obtained in Example A, Example B, and Control Example B were photographed using a field emission scanning electron microscope (brand model: JEOL JSM-6701F). The results are shown in Figures 1 to 3.

X-ray diffraction (XRD) analysis:

The silicon nitride nano whiskers obtained in Example A, Example B and Control Example B were analyzed using an X-ray diffraction instrument (brand model: Bruker D2 phaser). The results are shown in Tables 1 to 3 and Figures 4 to 6.

Raman spectroscopy analysis:

The silicon nitride nanowhiskers obtained in Example A, Example B and Control Example B were analyzed using a Raman spectrometer (brand model: Jobin Yvon/Labram HR, France). The results are shown in Figures 7 to 9.

Yield Analysis:

The following formula is used to calculate the total yield of silicon nitride nanowhiskers and silicon nitride nanoparticles, as well as the proportion of silicon nitride nanowhiskers.

NWs is the weight of silicon nitride nanowhiskers (unit: grams)

NPs is the weight of silicon nitride nanoparticles (unit: grams)

CRs is the weight of carbonization product (unit: gram)

Referring to Table 1 and Table 2, in Example Group A and Example Group B, which are subjected to high-temperature carbon thermal reaction with the addition of an iron-based catalyst, the proportion of silicon nitride nano whiskers obtained at a high-temperature carbon thermal reaction temperature of 1400°C is the highest, and when the temperature of the high-temperature carbon thermal reaction is increased to 1500°C to 1600°C, the proportion of silicon nitride nano whiskers obtained decreases, that is, the proportion of silicon nitride nanoparticles increases relatively. Referring to Table 3, in Control Group A, which is subjected to high-temperature carbon thermal reaction without the addition of an iron-based catalyst, the proportion of silicon nitride nano whiskers increases as the temperature of the high-temperature carbon thermal reaction increases, and the proportion of silicon nitride nano whiskers obtained at a high-temperature carbon thermal reaction temperature of 1600°C is the highest. By contrast, the present invention changes the growth trend of silicon nitride nano whiskers and silicon nitride nanoparticles by adding an iron-based catalyst during high-temperature carbothermal reaction, and can especially obtain more silicon nitride nano whiskers at a lower high-temperature carbothermal reaction temperature (1400°C).

However, the above is only an example of the implementation of the present invention, and it cannot be used to limit the scope of the implementation of the present invention. All simple equivalent changes and modifications made according to the scope of the patent application of the present invention and the content of the patent specification are still within the scope of the patent of the present invention.

Claims (10)

A method for preparing silicon nitride nanomaterials comprises the following steps: (1) acid-washing, water-washing and drying agricultural waste containing carbon and silicon dioxide in sequence to obtain a biomass raw material; (2) subjecting the biomass raw material to a low-temperature carbon thermal reaction at 600°C to form a first crude product containing carbon and silicon oxide, and acid-washing, water-washing and drying the first crude product in sequence to obtain a carbonized product containing the carbon and the silicon oxide; (3) The carbonized product and an iron-based catalyst are subjected to a high-temperature carbon thermal reaction at 1300°C to 1600°C in a nitrogen atmosphere to form a second crude product containing silicon nitride nanowhiskers and silicon nitride nanoparticles, wherein the iron-based catalyst is selected from the group consisting of ferric chloride, ferrous chloride and any combination thereof; and (4) The second crude product is subjected to a purification treatment, wherein the purification treatment includes using a polar solvent and a non-polar solvent to separate the silicon nitride nanowhiskers and the silicon nitride nanoparticles in the second crude product. The method for preparing silicon nitride nanomaterials as described in claim 1, wherein the amount of the iron-based catalyst used is 0.03 grams based on the amount of the carbonized product used being 1 gram. The method for manufacturing silicon nitride nanomaterials as described in claim 1, wherein the crystal phase of the silicon nitride nanowhiskers comprises α-Si ₃ N ₄ . The method for manufacturing silicon nitride nanomaterials as described in claim 3, wherein the crystal phase of the silicon nitride nanowhiskers further includes β-Si ₃ N ₄ . The method for producing silicon nitride nanomaterials as described in claim 1, wherein in the step (4), the polar solvent is water. The method for preparing silicon nitride nanomaterials as described in claim 1, wherein in the step (4), the non-polar solvent is xylene. The method for manufacturing silicon nitride nanomaterials as described in claim 1, wherein the purification process in the step (4) further comprises heating the separated silicon nitride nanowhiskers and the silicon nitride nanoparticles at 600° C. to remove the residual carbon. The method for producing silicon nitride nanomaterials as described in claim 1, wherein in the step (1), the agricultural waste is rice powder. The method for producing silicon nitride nanomaterials as described in claim 1, wherein the pickling in step (1) is to remove metal impurities and inorganic salts in the agricultural waste using an acidic liquid. The method for producing silicon nitride nanomaterials as described in claim 1, wherein the acid washing in the step (2) is to wash the first crude product with an acidic liquid.