CN114790107A - A method for preparing SiO2-Si3N4 composite ceramics at low temperature by using polysilicon cutting waste - Google Patents

Abstract

The invention belongs to the technical field of metallurgical resource recycling, and discloses a method for preparing SiO by using polycrystalline silicon cutting waste at low temperature ₂ ‑Si ₃ N ₄ A method for compounding ceramics. Processing the polycrystalline silicon cutting waste to the standard of laboratory use, mixing the polycrystalline silicon cutting waste with a diluent, uniformly ball-milling, and controlling a nitriding reaction by reasonably selecting a nitriding atmosphere to obtain a nitriding product; crushing and grinding the nitriding product, and adding SiO ₂ C, sintering aid, ball milling and mixing, and cold isostatic pressing to prepare a sample before ammoniation; through reasonable selection of ammoniation atmosphere and control of ammoniation reaction, SiO is obtained ₂ ‑Si ₃ N ₄ Composite ceramics. The invention has the advantages that the by-product generation is avoided by controlling the powder composition and ammoniation conditions, and SiO is utilized ₂ The volume effect is effectively reduced by the carbothermic reduction reaction of the C and the C, and finally the SiO with uniform components and good performance is obtained ₂ ‑Si ₃ N ₄ The composite ceramic realizes the resource utilization of the photovoltaic industrial chain waste and the economic development of the ceramic industrial chain.

Description

A method for preparing SiO2-Si3N4 composite ceramics at low temperature by using polysilicon cutting waste

technical field

The invention belongs to the technical field of metallurgical resource recycling, and relates to a method for preparing SiO ₂ -Si ₃ N ₄ composite ceramics at low temperature by using polysilicon cutting waste.

Background technique

Polysilicon cutting waste is one of the silicon-based solid waste products brought about by the rapid development of the photovoltaic industry, with an annual output of about 200 kilotons. Recycling elemental silicon products from waste has the problems of difficulty, high cost and high impurity content, which makes a large amount of waste accumulate, which not only occupies a lot of land resources, but also causes resource waste and environmental pollution to a certain extent.

Compared with the recycling of elemental silicon products from polysilicon cutting waste, the waste is directly converted into high value-added resources such as silicon-based ceramics, eliminating the necessary steps of purifying silicon powder, which not only simplifies the process flow, but also reduces the raw material cost of ceramics. And it promotes the production of higher value-added products. Si ₃ N ₄ ceramics is one of the representatives of its high value-added products. Its high strength and corrosion resistance make it widely used in machinery and manufacturing, but it is limited by high dielectric constant and dielectric loss. Development in the aerospace industry is limited. The emergence of SiO ₂ -Si ₃ N ₄ composite ceramics solves this problem. It not only has the high strength and corrosion resistance of Si ₃ N ₄ , but also has the low dielectric constant and dielectric loss of SiO ₂ . High-quality materials for the preparation of aerospace antenna windows, etc. However, in the process of preparing SiO ₂ -Si ₃ N ₄ composite ceramics, if it is simply to mix and sinter silicon powder, silicon dioxide, etc., due to the influence of oxygen content, particle roughness and other factors, the resulting product will inevitably produce By-products such as silicon oxynitride have a great influence on the dielectric properties and mechanical properties of ceramic products, and are difficult to apply in practice. Therefore, how to reasonably avoid the formation of by-products such as silicon oxynitride is the premise for the preparation of excellent SiO ₂ -Si ₃ N ₄ composite ceramics.

Since silicon oxynitride has the characteristics of high temperature decomposition, the current technology usually adopts increasing the sintering temperature and simultaneously increasing the holding time in the high temperature range, so as to eliminate by-products, that is, by-products are generated first, and then by-products are decomposed. However, these control technologies are usually based on high temperature, long aging and high loss, and the actual economic benefits brought are not high. If you want to reduce high temperature sintering and reduce energy consumption, the conventional control method is to add a certain proportion of sintering aids to form a multi-component eutectic in the system with the sintering process, which can reduce the sintering temperature to a certain extent. But at the same time, the formation of part of the multicomponent eutectic will also bring up to 30% or even more volume effect, so that the actual benefit of this control method is not high. Therefore, it is necessary to develop new methods to prepare composite ceramics at low temperature.

SUMMARY OF THE INVENTION

Si and SiO ₂ mixed powder is difficult to generate SiO ₂ -Si ₃ N ₄ composite ceramics in the traditional ceramic preparation process, and it is easy to generate by-products such as silicon oxynitride. Aiming at the problem that by-products are easily generated, the purpose of the present invention is to provide a method for preparing SiO ₂ -Si ₃ N ₄ composite ceramics at low temperature by using polysilicon cutting waste, which can effectively avoid nitrogen oxidation by controlling the powder composition and ammoniation conditions The generation of by-products such as silicon can effectively reduce the volume effect by the carbothermic reduction reaction of SiO ₂ and C, and finally obtain SiO ₂ -Si ₃ N ₄ composite ceramics with uniform composition and good performance, thus realizing the elimination of waste in the photovoltaic industry chain. Resource utilization and economic development of the ceramic industry chain.

The invention provides an idea of preparing composite ceramics by nitriding and ammoniating sintering ceramics from polysilicon cutting wastes, so as to realize the method for preparing _{SiO2 - Si3N4} composite ceramics from polysilicon cutting wastes at low temperature, comprising the following steps :

(1) Purification of polysilicon cutting waste:

The polysilicon cutting waste is dried, pulverized, washed with impurities, dried again, ground and sieved to obtain powder, which is the purified polysilicon cutting waste, wherein the Si purity is 2N;

(2) Nitriding treatment of polysilicon cutting waste

A diluent is added to the purified polysilicon cutting waste obtained in step (1), and after ball milling and mixing, atmosphere nitriding is performed, and a nitriding product is obtained after nitriding reaction;

The diluent is α-Si ₃ N ₄ or β-Si ₃ N ₄ , and the added amount does not exceed 20% of the mass of the purified polysilicon cutting waste.

In the nitriding reaction, the nitriding gas is one of nitrogen gas or nitrogen-hydrogen mixed gas, wherein, in the nitrogen-hydrogen mixed gas, the volume ratio of nitrogen and hydrogen is between 75:25-95:5.

In the nitriding reaction, the nitriding equipment adopts a temperature-controlled atmosphere tube furnace to ensure that the temperature in the furnace is raised to 1200-1450°C at a rate of 1-5°C/min, and then the temperature is kept constant for 0.5-2.5h. The temperature rise system is favorable for the nitridation reaction to proceed.

The use of nitriding atmosphere and diluent can promote the nitriding reaction.

(3) Ammonia firing of SiO ₂ -Si ₃ N ₄ composite ceramics

Grinding the nitrided product in step (2) to below 300 mesh with a mortar, adding a certain proportion of SiO ₂ , C and sintering aids, ball milling until the material is mixed, drying the material, and cold isostatic pressing to obtain ammoniated previous sample. After the ammoniated gas is introduced into the atmosphere tube furnace equipment, the temperature is raised to 1100-1450°C at a rate of 1-5°C/min, then kept at a constant temperature for 1-3 hours, and then cooled to room temperature at a rate of 1-5°C/min. The SiO ₂ -Si ₃ N ₄ composite ceramic was obtained. The heat treatment system can promote the carbothermic reduction reaction, which is beneficial to reduce the volume effect brought by the multi-glass phase eutectic, thereby improving the performance of the ceramic sintered body.

The sintering aid is one or more of MgO, Al ₂ O ₃ , and Y ₂ O ₃ , and the sintering aid can reduce the sintering temperature in the ammoniation process; adding SiO ₂ and C to carry out a carbothermal reduction reaction can reduce ammonia volume effect brought about by the process.

The added amounts of SiO ₂ , C and sintering aids do not exceed 100%, 20%, and 20% of the quality of the nitrided product, respectively.

The ammoniated gas is one of ammonia gas, nitrogen-ammonia mixed gas, hydrogen-ammonia mixed gas and nitrogen-hydrogen-ammonium mixed gas, wherein, when the mixed gas is used, the volume ratio of ammonia gas is controlled to be more than 50%.

The beneficial effects of the present invention are:

(1) The main body of the added raw material is polysilicon cutting waste. The cost of ceramic raw materials is low, and at the same time, it solves the environmental pollution caused by waste stacking, and promotes the formation of an industrial chain of high value-added products.

(2) The nitriding atmosphere used in the nitriding process is a gas in nitrogen and nitrogen-hydrogen mixture. Hydrogen can break the natural oxide film on the silicon surface and effectively promote the nitriding reaction.

(3) The diluent added in the nitriding process is α-Si ₃ N ₄ or β-Si ₃ N ₄ , and the total amount is controlled so as not to exceed 20% of the total weight of the purified polysilicon cutting waste. The addition of the diluent can act as a reaction seed to promote the progress of the nitridation reaction.

(4) The sintering aids added in the ammoniation process are one or more of MgO, Al ₂ O ₃ and Y ₂ O ₃ , and the total amount is controlled not to exceed 20% of the total weight of the nitrided product. The addition of sintering aids can generate a multi-glass phase eutectic, which can effectively reduce the sintering temperature of the ceramic sintered body.

(5) SiO ₂ and C are added in the ammoniation process, and the total amount is controlled so as not to exceed 100% and 20% of the total weight of the nitrided product. The overall reaction formula of the carbothermic reduction reaction is: 3SiO ₂ +6C+4NH ₃ →Si ₃ N ₄ +6CO+6H ₂ , which can effectively reduce the volume effect of the eutectic formed by the sintering aid during the sintering process. Reduce the linear shrinkage of ceramics, thereby improving the mechanical properties of ceramics.

(6) The ammoniated atmosphere used in the ammoniation process is one of ammonia, nitrogen-ammonia mixture, hydrogen-ammonia mixture and nitrogen-hydrogen-ammonia mixture. When the mixed gas is used, the ammonia gas accounts for more than 50% of the total gas, and the ammoniated gas can effectively reduce the sintering temperature of the ceramic sintered body and reduce the generation of by-products.

Description of drawings

FIG. 1 is a process flow diagram of a method for preparing SiO ₂ -Si ₃ N ₄ composite ceramics at low temperature by using polysilicon cutting waste provided by the present invention.

Figure 2 Example XRD results.

Detailed ways

The content and effects of the present invention will be further described below in conjunction with specific embodiments and data.

Example 1:

Take the polysilicon cutting waste in the wire cutting stage of a solar panel company. The components mainly include Si, SiO ₂ and a small amount of metal oxide impurities. The purity of Si after purification treatment is above 99%, and diluent α-Si ₃ N ₄ is added to it. , the addition amount is 20% of the mass of the purified polysilicon cutting waste; the nitrogen-hydrogen (95:5) mixture is selected as the nitriding atmosphere; MgO and Y ₂ O ₃ are added as sintering aids, and the addition amount is 7% of the total mass ; Select nitrogen-ammonia (4:6) gas mixture as ammoniation atmosphere.

In order to further verify the content and effect of the present invention, the following specific process steps are included during implementation:

(1) Put the purified polysilicon cutting waste and diluent into a ball mill jar at the same time, mix them evenly, and place them in an alumina crucible. In a nitriding atmosphere, the temperature is raised to 1400 ° C and kept for 2 hours, and then cooled to room temperature with the furnace to obtain nitrogen. chemical product;

(2) After crushing and grinding the nitrided product in step (1), add sintering aids, SiO ₂ , and C, and after ball milling and mixing again, cold isostatic pressing is formed and placed in a graphite crucible. Example 1 Sample before ammoniation The ingredients are shown in Table 1;

Table 1 Example 1 Sample composition before ammoniation

(3) The temperature is raised to 1350° C. in an ammoniated atmosphere and kept for 2.5 hours, and then cooled to room temperature with the furnace to obtain SiO ₂ -Si ₃ N ₄ composite ceramics. The properties of the obtained composite ceramics were tested.

Example 2:

Take the polysilicon cutting waste from the wire cutting stage of a solar panel company. The components mainly include Si, SiO ₂ and a small amount of metal oxide impurities. The purity of Si after purification treatment is above 99%, and the diluent β-Si ₃ N ₄ is added to it. , the addition amount is 10% of the mass of the purified polysilicon cutting waste; nitrogen-hydrogen (9:1) mixture is selected as the nitriding atmosphere; MgO is added as a sintering aid, and the addition amount is 8% of the total mass; nitrogen-hydrogen ammonia is selected (30:10:60) mixed gas was used as ammoniation atmosphere.

In order to further verify the content and effect of the present invention, the following specific process steps are included during implementation:

(1) Put the purified polysilicon cutting waste and diluent into a ball mill jar at the same time, mix them evenly, and place them in an alumina crucible. In a nitriding atmosphere, the temperature is raised to 1300 ° C and kept for 2 hours, and then cooled to room temperature with the furnace to obtain nitrogen. chemical product;

(2) After crushing and grinding the nitrided product of step (1), add sintering aids, SiO ₂ , C, and after ball milling and mixing again, cold isostatic pressing molding and placing in a graphite crucible, Example 2 before ammoniation The sample composition is shown in Table 2;

Table 2 Example 2 Sample composition before ammoniation

(3) The temperature is raised to 1300° C. in an ammoniated atmosphere and kept for 1.5 hours, and then cooled to room temperature with the furnace to obtain SiO ₂ -Si ₃ N ₄ composite ceramics. The properties of the obtained composite ceramics were tested.

Example 3:

Take the polysilicon cutting waste in the wire cutting stage of a solar panel company. The components mainly include Si, SiO ₂ and a small amount of metal oxide impurities. The purity of Si after purification treatment is above 99%, and diluent α-Si ₃ N ₄ is added to it. , the addition amount is 10% of the mass of the purified polysilicon cutting waste; high-purity nitrogen is selected as the nitriding atmosphere; MgO and Al ₂ O ₃ are added as sintering aids, and the addition amount is 8% of the total mass; ammonia gas is selected as the ammonia atmosphere.

In order to further verify the content and effect of the present invention, the following specific process steps are included during implementation:

(1) Put the purified polysilicon cutting waste and diluent into a ball mill jar at the same time, mix them evenly, and place them in an alumina crucible. In a nitriding atmosphere, the temperature is raised to 1400 ° C and kept for 2 hours, and then cooled to room temperature with the furnace to obtain nitrogen. chemical product;

(2) After crushing and grinding the nitrided product in step (1), adding sintering aids, SiO ₂ , C, and ball-milling and mixing again, cold isostatic pressing and placing in a graphite crucible. Example 3 Before ammoniation The sample composition is shown in Table 3;

Table 3 Example 3 Sample composition before ammoniation

(3) The temperature is raised to 1400° C. and kept for 2 hours in an ammoniated atmosphere, and then cooled to room temperature with the furnace to obtain SiO ₂ -Si ₃ N ₄ composite ceramics. The properties of the obtained composite ceramics were tested.

Example 4:

Take the polysilicon cutting waste from the wire cutting stage of a solar panel company. The components mainly include Si, SiO ₂ and a small amount of metal oxide impurities. The purity of Si after purification treatment is above 99%, and the diluent β-Si ₃ N ₄ is added to it. , the addition amount is 10% of the mass of the purified polysilicon cutting waste; high-purity nitrogen is selected as the nitriding atmosphere; Al ₂ O ₃ and Y ₂ O ₃ are added as sintering aids, and the addition amount is 6% of the total mass; hydrogen is selected Ammonia (5:95) gas mixture was used as the ammoniation atmosphere.

In order to further verify the content and effect of the present invention, the following specific process steps are included during implementation:

(1) The polysilicon cutting waste and the diluent after grinding and cleaning are loaded into the ball mill jar at the same time to ensure that the waste and the diluent are mixed evenly and then placed in an alumina crucible. Under the nitriding atmosphere, the temperature is raised to 1450 ℃ And kept for 2h, cooled to room temperature with the furnace to obtain the nitrided product;

(2) After crushing and grinding the nitrided product of step (1), add sintering aids, SiO ₂ , C, and after ball milling and mixing again, cold isostatic pressing molding and placing in a graphite crucible, Example 4 before ammoniation The sample composition is shown in Table 4;

Table 4 Example 4 Sample composition before ammoniation

(3) The temperature is raised to 1350° C. and kept for 2 hours in an ammoniated atmosphere, and then cooled to room temperature with the furnace to obtain SiO ₂ -Si ₃ N ₄ composite ceramics. The properties of the obtained composite ceramics were tested.

The composite ceramics in Examples 1, 2, 3, and 4 were scanned and analyzed by X-ray diffraction (XRD), and the results are shown in FIG. 2 .

The composite ceramics in Examples 1, 2, 3, and 4 were tested for performance, and the results are shown in Table 5.

Table 5 Performance test results of composite ceramics

Example 1 Example 2 Example 3 Example 4 Relative permittivity 4.8 4.0 4.2 5.1 Linear shrinkage (%) 5.3% 2.62% 4.5% 1.3%

The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the present invention can be implemented without departing from the principle and spirit of the present invention. Various changes, modifications, substitutions and alterations may be made to these embodiments, the scope of the invention being defined by the appended claims and their equivalents.

Claims (10)

1. a method of utilizing polysilicon cutting waste to prepare SiO ₂ -Si ₃ N ₄ composite ceramics at low temperature, is characterized in that, comprises the following steps: (1) purifying the polysilicon cutting waste to obtain purified polysilicon cutting waste, wherein the Si purity is 2N; (2) Nitriding treatment of polysilicon cutting waste: A diluent is added to the purified polysilicon cutting waste obtained in step (1), and after ball milling and mixing, atmosphere nitriding is carried out, and a nitriding product is obtained after nitriding reaction; (3) Ammonia firing of SiO ₂ -Si ₃ N ₄ composite ceramics Grinding the nitrided product in step (2) with a mortar, adding a certain proportion of SiO ₂ , C and sintering aid, ball milling until the material is mixed, drying the material, and cold isostatic pressing to obtain the sample before ammoniation; After the ammoniated gas is introduced into the atmosphere tube furnace equipment, the temperature is programmed to reach the temperature _of the _ammoniated reaction, and the reaction is kept constant for a period of time _. 2. method as claimed in claim 1 is characterized in that, in step (1), the purification treatment process of polysilicon cutting waste is: polysilicon cutting waste is dried, pulverized, washed with impurities, dried again, ground, sieved The process of obtaining powder. 3. The method of claim 1, wherein in step (2), the diluent is α-Si ₃ N ₄ or β-Si ₃ N ₄ , and the addition amount does not exceed the purified polysilicon cutting waste 20% of the mass. 4. The method of claim 1, wherein, in step (2), in the nitriding reaction, the nitriding gas is one of nitrogen gas or a nitrogen-hydrogen mixture, wherein, in the nitrogen-hydrogen mixture , the volume ratio of nitrogen and hydrogen is between 75:25-95:5. 5. The method according to claim 1, wherein, in step (2), in the nitriding reaction, the nitriding equipment adopts a temperature-controlled atmosphere tube furnace to ensure that the temperature in the furnace is 1-5 °C The temperature is raised to 1200-1450°C at the speed of /min, and then the temperature is kept constant for 0.5-2.5h. 6 . The method of claim 1 , wherein, in step (3), the nitrided product is ground to below 300 mesh with a mortar. 7 . 7 . The method of claim 1 , wherein, in step (3), the sintering aid is one or more of MgO, Al ₂ O ₃ and Y ₂ O ₃ . 8 . The method of claim 1 , wherein in step (3), the addition amounts of the SiO ₂ , C and sintering aids do not exceed 100%, 20%, and 20% of the quality of the nitrided product, respectively. 9 . . 9. method as claimed in claim 1, is characterized in that, in step (3), described ammoniated gas is a kind of in ammonia, nitrogen-ammonia mixture, hydrogen-ammonia mixture and nitrogen-hydrogen-ammonia mixture , among which, when using mixed gas, the volume ratio of ammonia gas is controlled to be more than 50%. 10. method as claimed in claim 1 is characterized in that, in step (3), the temperature of ammoniation reaction is 1100-1450 ℃, and constant temperature keeps 1-3h; °C/min.

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