CN111115634B - Method for preparing SiC fibers by using silicon wafer cutting waste - Google Patents

Abstract

The invention provides a method for preparing SiC fibers by using silicon chip waste, which comprises the steps of firstly removing organic matters in the silicon chip waste through alcohol washing and water washing, then mixing with commercially available quartz powder, generating gas-phase SiO in a high-temperature reactor, and introducing CH ₄ Reacting to generate SiC fibers; followed by high temperature, H ₂ Roasting in the atmosphere to remove the surplus free carbon in the fiber; and cooling and collecting the high-quality SiC fibers with low carbon content. The raw materials used by the invention are diamond wire cutting silicon chip waste materials in the photovoltaic industry, have wide sources and low price, and do not contain toxic and harmful substances; the preparation method of the high-quality SiC fiber is provided while solving the problem of recycling of the diamond wire-cutting silicon wafer waste, and the recycling of solid waste resources is developed towards the direction of green, high efficiency and high yield.

Description

A method for preparing SiC fibers from silicon wafer cutting waste

technical field

The invention relates to the technical field of semiconductor material preparation, in particular to a method for preparing SiC fiber material, especially a method for preparing SiC fiber by using silicon chip cutting waste.

Background technique

When preparing crystalline silicon solar cells, multi-wire cutting technology must be used to cut polycrystalline silicon ingots or monocrystalline silicon rods into silicon wafers. Since the diameter of the cutting line is very close to the thickness of the silicon wafer, at least 40% of the crystalline silicon is cut into silicon powder and enters the cutting fluid, and is basically in a state of idle or low-value utilization. The waste produced by the diamond wire cutting technology, which is currently the mainstream in the industry, is mainly composed of Si, a small amount of C and metal impurities. In recent years, researchers at home and abroad have carried out research on the recovery of high-purity silicon from waste, but the recovery process is complicated, and the purity of the recovered silicon powder cannot meet the requirements for the production of photovoltaic grade silicon ingots. For example, the patent application with publication number CN102642835A "From King Kong A method for recovering silicon material from the waste generated by wire cutting crystal silicon". The use of crystalline silicon cutting waste to prepare SiC powder or refractory materials has problems such as low added value. For example, the patent application with the publication number CN107651690B "A method for preparing high-quality silicon carbide from diamond wire cutting waste", and the journal paper "Using solar energy Preparation of Si ₃ N ₄ -SiC composites from high-grade polysilicon cutting waste. Refractories, 2017,51(5):390-393.”. Therefore, finding a high value-added utilization method for crystalline silicon cutting waste has become an urgent problem to be solved in the photovoltaic industry.

SiC fiber is a kind of ceramic fiber with carbon and silicon as the main components, which can be divided into two types: whisker and continuous fiber. SiC fiber has good high temperature performance, high strength, high modulus and chemical stability, the tensile strength can reach 2.5-3.5GPa, the elastic modulus is 200GPa, it has good chemical corrosion resistance, and the coefficient of linear expansion is about It is 3.1×10- ⁶ K- ¹ , resistant to radiation, good in absorbing waves, and has semiconductor properties. It is mainly used to strengthen metal and ceramics and make high temperature resistant metal or ceramic matrix composites. Because of its good performance, it has been applied in cutting-edge technology fields, such as aerospace, rocket engines, nuclear fusion furnaces, etc. In addition, with the development of preparation technology, the application of SiC fiber has gradually expanded to civilian industries such as advanced sports equipment and automobile exhaust gas dust collection.

SiC fiber preparation methods include chemical vapor deposition (such as the patent application CN201810086069.9 "a silicon carbide nanowire airgel and its preparation method"), precursor conversion method (Tang Ming, Yu Zhaoju, Lan Lin, et al. Study on the preparation of silicon carbide fibers by blending solid/liquid polycarbosilane. Functional Materials, 2012,43(16):2267-2272.); Superfine powder extrusion spinning method (Qiu Haipeng, Chen Mingwei, Xie Weijie. SiC /SiC CMC research and application. Aviation Manufacturing Technology, 2015(4):94-97.) and activated carbon fiber conversion method (K.Okada, H.Kato, K.Nakajima, Preparation of Silicon Carbide Fiber from Activated Carbon Fiber and Gaseous SiliconMonoxide .Journal of the American Ceramic Society, 1994, Vol.77(6), pp.1691-1693) and other methods. These methods have the disadvantages of complex preparation process, high cost, and being unfavorable for industrialized production. In addition, in order to further increase the use temperature of silicon carbide fibers, the free carbon content in the fibers needs to be further reduced to below 2%.

Contents of the invention

Aiming at the deficiencies in the prior art, the invention provides a method for preparing SiC fibers by using silicon chip cutting waste. The free carbon content in the prepared SiC fiber is low, the source of raw materials is wide, the cost is low, and no toxic and harmful substances are contained. The invention provides a novel preparation method of high-quality SiC fiber while solving the recycling problem of diamond wire cutting silicon chip waste, and develops solid waste resources towards a green, efficient, and high-yield direction.

A method for preparing SiC fibers by utilizing silicon wafer waste, comprising the steps of:

(1) Cleaning of silicon wafer cutting waste, removing organic matter in silicon wafer waste, filtering and drying to obtain clean waste silicon powder;

(2) Preparation of SiO precursor: Mix waste silicon powder and quartz powder evenly at a mass ratio of 1:2, as a SiO precursor;

(3) SiC fiber preparation: put the SiO precursor in an alumina crucible, put it into an alumina reactor, and pass a mixed gas of Ar, H ₂ , and CH ₄ into the alumina reactor under normal pressure, and the alumina The reactor is slowly inserted into a high-temperature furnace preheated to 1550-1650°C, and reacts in the high-temperature furnace for 60-120 minutes; the silicon powder and quartz powder in the crucible react to form gaseous SiO, and then react with CH ₄ in the mixed gas to form SiC fibers ;

(4) Removal of excess free carbon in SiC fibers: switch the reaction gas to pure H ₂ , keep the temperature in the high-temperature furnace at 1550-1650°C, the excess free carbon in SiC fibers reacts with H ₂ to generate CH ₄ , and removes the excess free carbon in SiC fibers. After 10 to 30 minutes of reaction, the gas is stopped, and the alumina reactor is slowly taken out of the high-temperature furnace; after sufficient cooling, the alumina crucible is taken out from the alumina reactor to obtain low-carbon SiC fibers.

Further, in the step (1), the mass percentage of silicon contained in the silicon wafer cutting waste is Si≥97%.

Further, the particle size of the fine quartz powder in the step (2) is 50-500 μm.

Further, in the step (3), the content of CH ₄ in the mixed gas of Ar, H ₂ and CH ₄ is 2 vol%, the content of H ₂ is 68 vol%, and the content of Ar is 30 vol%.

Further, the SiC fiber with low carbon content obtained in the step (4) has a diameter of 0.3-0.6 μm, a length of 50-200 μm, and a free carbon content of less than 1.5%.

Further, in the step (1), the silicon wafer cutting waste is rinsed with ethanol and deionized water.

The invention first removes the organic matter in the silicon wafer waste by alcohol washing and water washing, and mixes it with quartz powder; the mixed powder reacts in a high-temperature reactor to form gas-phase SiO; and reacts with introduced CH ₄ to form SiC fiber. Subsequent calcination in _H2 atmosphere at high temperature can effectively remove excess free carbon in the fiber, and high-quality SiC fiber with low carbon content can be collected after cooling. The SiC fiber prepared by the invention has a diameter of 0.3-0.6 μm, a length of 50-200 μm, and a free carbon content of less than 1.5%. The obtained SiC fiber has a low carbon content, improves the high temperature resistance of the fiber, and has excellent performance.

The invention utilizes silicon chip waste materials cut by diamond wires in the photovoltaic industry to prepare SiC fibers, and the raw materials have wide source, low price and no poisonous and harmful substances. It provides a high-quality SiC fiber preparation method while solving the recycling problem of diamond wire-cut silicon wafer waste, which solves the problems caused by the recycling of diamond wire-cut silicon wafer waste in the prior art, and can be used in silicon powder waste. Recycling and other fields are widely promoted; the recycling of solid waste resources is developed in the direction of green, efficient and high-yield.

Description of drawings

Figure 1 is a schematic structural view of the alumina reactor used in the preparation method of the present invention.

FIG. 2 is an XRD diffraction pattern of SiC fibers prepared in Example 1.

FIG. 3 is a SEM picture of SiC fibers prepared in Example 1.

FIG. 4 is a TEM picture of SiC fibers prepared in Example 1.

Explanation of reference signs:

1-crucible, 2-alumina inner tube, 3-support rod, 4-SiO precursor, 5-aluminum alloy flange, 6-intake pipe, 7-gas outlet, 8-alumina outer tube.

Detailed ways

The specific embodiments of the present invention will be described in further detail below in conjunction with the accompanying drawings, so as to make the technical solutions claimed in the present invention clearer and more complete. The specific embodiments are a part of the embodiments of the present invention, but not all of them, and the protection scope of the present invention is not limited to the content.

The method for preparing SiC fibers from silicon chip cutting waste according to the present invention first removes organic matter in the silicon chip waste by alcohol washing and water washing, and then mixes it with commercially available quartz powder with a particle size of 50-500 μm as a SiO precursor. The SiO precursor generates gas-phase SiO in the high-temperature reactor, and reacts with the incoming CH ₄ to form SiC fibers; the chemical reaction formula involved in this process is:

Si(s)+SiO2(s)=2SiO(g)

SiO(g)+2CH ₄ (g)=SiC(s)+CO(g)+4H ₂ (g)

CH ₄ (g)=C(s)+2H ₂ (g)

Subsequent roasting at high temperature and _H2 atmosphere removes excess free carbon in the fiber; the chemical reaction formula involved in this process is:

C(s)+2H ₂ (g)=CH ₄ (g)

Finally, cooling collected high-quality SiC fibers with low carbon content.

Example 1

(1) Take 25g of diamond wire cut silicon wafer waste, rinse it with ethanol for 10 minutes, filter it with suction, and rinse it twice with deionized water. Clean waste silicon powder was obtained after suction filtration and drying, and its elemental composition is shown in Table 1.

Table 1. Elemental composition of diamond wire sawed silicon wafer scrap

element Si C o Ca Ni K Na Mg Al Fe Content (wt%) 97.30 1.14 1.35 0.0703 0.0524 0.0085 0.0318 0.0306 0.0087 0.0054

(2) Weigh 3 grams of waste silicon powder cleaned in step (1), weigh 6 grams of commercially available quartz powder with a particle size of 50-500 μm, and mix them uniformly to obtain a SiO precursor.

(3) Pour the SiO precursor 4 of step (2) into the alumina crucible 1, place the crucible 1 in the alumina inner tube, and place it on the support rod 3 at the bottom of the alumina inner tube 2 with openings at both ends , then insert the alumina inner tube 3 into the alumina outer tube 8 with an open end, and seal the alumina outer tube 8 with the aluminum alloy flange 5, as shown in Figure 1, the aluminum alloy flange 5 is provided with an alumina The air outlet 7 communicated with the inside of the outer tube 8 . The upper end opening of the alumina inner tube is inserted into the inlet pipe 6, and a mixed gas of Ar, H ₂ and CH ₄ is passed into the alumina reactor under normal pressure, wherein Ar 30vol%, H ₂ 68vol%, CH ₄ 2vol% , the gas flow rate is set to 2L/min. Slowly insert the alumina reactor into a high-temperature furnace preheated to 1600°C, and keep the reaction for 90 minutes.

(4) After 90 minutes, the reaction gas was switched to pure H ₂ , and the temperature of the high-temperature furnace was kept at 1600° C. for 20 minutes. Next, the gas flow is stopped, and the alumina reactor is slowly lifted out of the high-temperature furnace. After sufficient cooling, the alumina crucible was taken out from the alumina reactor to obtain SiC fibers in the crucible.

The XRD pattern of the obtained SiC fiber is shown in Fig. 2, which indicates that the crystal form of the prepared SiC fiber is β-SiC. According to the SEM images and TEM images shown in Figure 3 and Figure 4, the prepared SiC fiber has a length of 50-200 μm and a diameter of 0.3-0.6 μm. The average free carbon content of the SiC fiber is 1.37% tested by an infrared carbon-sulfur analyzer (the temperature is set at 940° C.). The invention reduces the free carbon content in the SiC fiber to less than 1.5%, and improves the high temperature resistance performance.

Example 2

The procedure is the same as that in Example 1, except that the temperature of the high-temperature furnace is set to 1550° C., kept in an Ar, H ₂ , and CH ₄ mixed gas atmosphere for 120 minutes, and kept in a pure H ₂ atmosphere for 30 minutes. The prepared SiC fiber has a length of 15-80 μm, a diameter of 0.3-0.5 μm, and an average free carbon content of 1.23%.

Example 3

The procedure is the same as that in Example 1, except that the temperature of the high-temperature furnace is set to 1650° C., kept in an Ar, H ₂ , and CH ₄ mixed gas atmosphere for 60 minutes, and kept in a pure H ₂ atmosphere for 10 minutes. The prepared SiC fiber has a length of 20-100 μm, a diameter of 0.3-0.5 μm, and an average free carbon content of 1.41%.

The described embodiment is a preferred implementation of the present invention, but the present invention is not limited to the above-mentioned implementation, without departing from the essence of the present invention, any obvious improvement, replacement or modification that those skilled in the art can make Modifications all belong to the protection scope of the present invention.

Claims (5)

1. A method for preparing SiC fibers by using silicon chip waste is characterized by comprising the following steps:

(1) Cleaning silicon wafer cutting waste, removing organic matters in the silicon wafer cutting waste, filtering and drying to obtain clean waste silicon powder;

(2) Preparing an SiO precursor: uniformly mixing waste silicon powder and quartz powder according to the mass ratio of 1;

(3) Preparing SiC fibers: placing the SiO precursor into an alumina crucible, loading the alumina crucible into an alumina reactor, and introducing Ar and H into the alumina reactor at normal pressure ₂ 、CH ₄ Mixing the gas, slowly inserting the alumina reactor into a high-temperature furnace preheated to 1550-1650 ℃, and reacting for 60-120 min in the high-temperature furnace; the silicon powder in the crucible reacts with the quartz powder to generate gaseous SiO, and the gaseous SiO is mixed with CH in the mixed gas ₄ Reacting to generate SiC fibers;

(4) Removing the surplus free carbon in the SiC fiber: switching the reaction gas to pure H ₂ Keeping the temperature in a high temperature furnace at 1550-1650 ℃, and obtaining the surplus free carbon and H in the SiC fiber ₂ Reaction ofGenerating CH ₄ Removing the surplus free carbon in the SiC fiber, stopping introducing gas after reacting for 10-30 min, and slowly lifting the alumina reactor out of the high-temperature furnace; and after fully cooling, taking out the alumina crucible from the alumina reactor to obtain the low-carbon SiC fiber, wherein the diameter of the low-carbon SiC fiber is 0.3-0.6 mu m, the length of the low-carbon SiC fiber is 50-200 mu m, and the content of free carbon is less than 1.5%.

2. The method of claim 1, wherein: the mass percentage of silicon contained in the silicon wafer cutting waste in the step (1) is that Si is more than or equal to 97%.

3. The method of claim 1, wherein: the particle size of the fine quartz powder in the step (2) is 50-500 μm.

4. The method of claim 1, wherein: ar and H in the step (3) ₂ 、CH ₄ CH in the mixed gas ₄ Content of (2 vol%), H ₂ The content of (3) was 68vol%, and the content of Ar was 30vol%.

5. The method of claim 1, wherein: and (2) rinsing the silicon wafer cutting waste by using ethanol and deionized water in the step (1).

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