A method for strengthening the formation of Si8Al6Fe4Ca by step solidification of industrial silicon melt

Abstract

This invention relates to a method for strengthening the formation of Si8Al6Fe4Ca from industrial silicon melt through stepped solidification, belonging to the technical field of high-value utilization of industrial silicon. Addressing the practical problems of uncontrollable solidification rate, incomplete intermetallic compound transformation, and random precipitation of intermetallic compounds in the air-cooling casting process of industrial silicon melt, as well as low selectivity and primary conversion rate of dimethyldichlorosilane when synthesizing organosilicon monomers using industrial silicon as raw material, this invention casts the oxidized and refined silicon melt into a mold with controllable cooling. Through optimization of solidification process parameters, stepped variable-rate solidification is achieved to reduce the content of harmful FeSi2 / CaSi2 phases in industrial silicon products and promote the full conversion of harmful phases to Si8Al6Fe4Ca, Si2Al2Ca, and Si2Al3Fe. This invention has the advantages of fully utilizing and saving energy, low infrastructure investment, simple process flow, high operability, and no environmental pollution.

Description

Technical Field

[0001] This invention relates to a method for strengthening the formation of Si8Al6Fe4Ca by step solidification of industrial silicon melt, belonging to the technical field of high-value utilization of industrial silicon. Background Technology

[0002] Industrial silicon is the fundamental raw material for silicon-based alloys, organosilicon, and silicon-based photovoltaic cells. Specifically, industrial silicon raw materials for organosilicon require low content of FeSi2 / CaSi2 and high Si8Al6Fe4Ca phase. However, the solidification parameters of the industrial silicon melt casting process are uncontrollable, leading to random precipitation of intermetallic compounds and reducing the synthesis efficiency of organosilicon monomers. Therefore, organosilicon companies typically purchase expensive industrial silicon with low impurity content to avoid the negative impact of undesirable intermetallic compound precipitation.

[0003] The selectivity and activity of organosilicon monomer synthesis processes are key parameters for evaluating the quality of the synthesis reaction. In the synthesis of (CH3)2SiCl2 from industrial silicon, selectivity refers to the yield of (CH3)2SiCl2 in the synthesized organosilicon monomers, while activity refers to the powder conversion efficiency of industrial silicon. Improving these two production indicators is an effective way to increase the production efficiency and reduce the production cost of organosilicon monomer synthesis processes. Relevant literature and production experience show that industrial silicon is an important cost component and influencing factor in the organosilicon monomer synthesis process. During the solidification process in industrial silicon, intermetallic compounds can be divided into two categories according to their solidification rate requirements. The first category includes FeSi2, CaSi2, and TiFeSi2 phases, which do not involve intermetallic compound conversion and are unaffected by the solidification rate. The second category includes Si2Al3Fe, Si2Al2Ca, and Si8Al6Fe4Ca phases, which involve the precipitation of intermetallic compounds and require sufficient conversion time. Intermetallic compounds in industrial silicon significantly influence the selectivity and activity of monomer synthesis. Si₂Al₂Ca significantly improves activity but hinders selectivity. Si₈Al₆Fe₄Ca is the only phase that improves selectivity, while Si₂Al₃Fe has no effect on either selectivity or activity. Other intermetallic compounds are detrimental to the synthesis of dimethyldichlorosilane from industrial silicon. Therefore, a stepped solidification process can be used to control the composition of intermetallic compounds, promoting the precipitation of Si₈Al₆Fe₄Ca and reducing the content of CaSi₂ and FeSi₂, achieving a balance between selectivity and activity. This helps improve the efficiency of organosilicon monomer synthesis, achieving the goal of "cost reduction and efficiency improvement" for relevant production enterprises. Summary of the Invention

[0004] To address the practical problems of uncontrollable solidification rate, uneven segregation, incomplete transformation of intermetallic compounds, and random precipitation of intermetallic compounds in the air-cooling process of industrial silicon melt casting, resulting in low selectivity and primary conversion rate of dimethyldichlorosilane when synthesizing organosilicon monomers using industrial silicon as raw material, this invention proposes a method for strengthening the formation of Si8Al6Fe4Ca from industrial silicon melt through stepped solidification. The method involves casting the oxidized and refined silicon melt into a mold with controllable cooling, and achieving stepped variable-rate solidification by controlling solidification process parameters. This reduces the content of harmful FeSi2 / CaSi2 phases in the industrial silicon product and promotes the complete transformation of harmful phases into Si8Al6Fe4Ca, Si2Al2Ca, and Si2Al3Fe. This invention offers advantages such as no special requirements on the impurity content of the silicon melt, full utilization and energy saving, low infrastructure investment, simple process flow, high operability, and no environmental pollution.

[0005] A method for strengthening the formation of Si8Al6Fe4Ca by step solidification of industrial silicon melt, the specific steps of which are as follows:

[0006] (1) The industrial silicon melt that has been refined by oxidation outside the furnace is poured into a mold with controllable cooling.

[0007] (2) The industrial silicon melt is cooled from 1650-1500℃ to 1100-950℃ at a cooling rate of 15-30℃ / min to ensure that FeSi2 and CaSi2 are fully extracted.

[0008] (3) The industrial silicon melt is cooled to 860-700℃ at a cooling rate of 5-10℃ / min to ensure the full conversion of Si2Al2Ca, Si8Al6Fe4Ca and Si2Al3Fe.

[0009] In a method for strengthening the formation of Si8Al6Fe4Ca using industrial silicon melt through stepped solidification, the conversion reactions of Si2Al2Ca, Si8Al6Fe4Ca, and Si2Al3Fe are as follows:

[0010] CaSi2+2Al→Si2Al2Ca;

[0011] 4FeSi2+Si2Al2Ca+4Al→Si8Al6Fe4Ca+2Si;

[0012] FeSi2+3Al→Si2Al3Fe;

[0013] Preferably, the Si8Al6Fe4Ca content in the industrial silicon powder used for synthesizing organosilicon monomers in step (3) is 0.50–0.80 wt.%.

[0014] The beneficial effects of this invention are:

[0015] (1) This invention addresses the practical problems of uncontrollable solidification rate, incomplete transformation of intermetallic compounds, and random precipitation of intermetallic compounds in the air-cooling process of industrial silicon melt casting. It proposes a method for step solidification strengthening of Si8Al6Fe4Ca formation in industrial silicon melt. Based on the industrial silicon melt after ladle refining and heat preservation, it is successively cast into a mold with controllable cooling, cooled in stages with controlled temperature, and solidified in air-cooled form. Finally, the purpose of controlling intermetallic compounds is achieved. After crushing and powdering, industrial silicon products for organosilicon are obtained. It has the advantages of high added value, strong raw material applicability, only simple modification of existing equipment, high production efficiency, and suitability for industrial production.

[0016] (2) This invention uses furnace heat preservation to make the melt composition uniform, temperature control casting and molding while controlling the cooling rate, crushing and powdering, etc., to prepare industrial silicon for organosilicon monomer synthesis under the condition of simple modification of existing equipment, improve the efficiency of industrial silicon synthesis of dimethyldichlorosilane, improve the economic efficiency of enterprises in preparing organosilicon, and help to provide added value of industrial silicon products and production benefits of organosilicon enterprises.

[0017] (3) The industrial silicon prepared by this invention can improve the production efficiency of dimethyldichlorosilane monomer during the synthesis of organosilicon monomers. At the same time, there are no special requirements for the impurity content of industrial silicon products. It plays a positive role in alleviating the tight supply of low impurity content industrial silicon materials, realizing the "cost reduction and efficiency improvement" of relevant enterprises, and improving resource utilization. Attached Figure Description

[0018] Figure 1 Typical morphology of intermetallic compounds in industrial silicon melt: (a) 20℃·min -1 (b) 5℃·min -1 (c) Step solidification control in Example 1; (d) Step solidification control in Example 2;

[0019] Figure 2 The phase content of industrial silicon ingots with a consistent solidification rate throughout the solidification process (15℃ / min) was used as a comparative example.

[0020] Figure 3 The phase content in industrial silicon ingots under step solidification control in Example 1. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0022] Comparative example: Industrial silicon melt (typical Si4210, temperature 1550℃) refined by furnace oxidation was cast into a mold with controllable cooling. The industrial silicon melt was cooled from 1550℃ to room temperature at cooling rates of 20℃ / min, 15℃ / min, and 5℃ / min, respectively, to obtain silicon ingots. The silicon ingots were crushed and powdered to obtain industrial silicon powder (20℃ / min), industrial silicon powder (15℃ / min), and industrial silicon powder (5℃ / min).

[0023] Example 1: A method for strengthening the formation of Si8Al6Fe4Ca by step solidification of industrial silicon melt, the specific steps of which are as follows:

[0024] (1) The industrial silicon melt (typical Si4210, temperature 1550℃) that has been refined by oxidation outside the furnace is poured into a mold with controllable cooling.

[0025] (2) The industrial silicon melt was cooled from 1550°C to 1000°C at a cooling rate of 15°C / min to ensure that FeSi2 and CaSi2 were fully extracted;

[0026] (3) The industrial silicon melt is cooled down to 800°C at a cooling rate of 5°C / min to ensure that Si2Al2Ca, Si8Al6Fe4Ca and Si2Al3Fe are fully converted. Then it is naturally cooled to room temperature to obtain silicon ingots. The silicon ingots are crushed and powdered to obtain industrial silicon powder for the synthesis of organosilicon monomers.

[0027] The phase content of industrial silicon ingots with a consistent solidification rate throughout the solidification process (15℃ / min) in the comparative example is shown below. Figure 2 ,from Figure 2 It can be seen that when the industrial silicon melt solidifies at a rate of 15℃ / min throughout the entire process, 0.44wt.% of Si8Al6Fe4Ca is precipitated.

[0028] The phase content of the industrial silicon ingot with stepped solidification control in this embodiment is shown in the figure. Figure 3 ,from Figure 3 It can be seen that the step solidification precipitated 0.73 wt.% Si8Al6Fe4Ca content; the Si8Al6Fe4Ca content of step solidification was increased by 1.66 times compared with the uniform solidification at 15℃ / min, and the time required for step solidification was only 75.91% of that of uniform solidification at 15℃ / min, which improved the solidification efficiency of industrial silicon melt.

[0029] Example 2: A method for strengthening the formation of Si8Al6Fe4Ca by step solidification of industrial silicon melt, the specific steps are as follows:

[0030] (1) The industrial silicon melt (typical Si4210, temperature 1650℃) that has been refined by oxidation outside the furnace is poured into a mold with controllable cooling.

[0031] (2) The industrial silicon melt was cooled from 1650℃ to 950℃ at a cooling rate of 20℃ / min to ensure that FeSi2 and CaSi2 were fully extracted.

[0032] (3) The industrial silicon melt is cooled down to 860℃ at a cooling rate of 5℃ / min to ensure that Si2Al2Ca, Si8Al6Fe4Ca and Si2Al3Fe are fully converted. Then it is naturally cooled to room temperature to obtain silicon ingots. The silicon ingots are crushed and powdered to obtain industrial silicon powder for the synthesis of organosilicon monomers.

[0033] In this embodiment, the Si8Al6Fe4Ca content in the industrial silicon powder used for synthesizing organosilicon monomers is 0.72 wt.%, which is 2.25 times higher than the Si8Al6Fe4Ca content (0.32 wt.%) when solidifying at a uniform rate of 20℃ / min. At the same time, the time required for stepped solidification is only 77.30% of that for uniform solidification at 20℃ / min, thus improving the solidification efficiency of industrial silicon melt.

[0034] Example 3: A method for strengthening the formation of Si8Al6Fe4Ca by step solidification of industrial silicon melt, the specific steps of which are as follows:

[0035] (1) The industrial silicon melt (typical Si4210, temperature 1550℃) that has been refined by oxidation outside the furnace is poured into a mold with controllable cooling.

[0036] (2) The industrial silicon melt was cooled from 1550℃ to 1100℃ at a cooling rate of 20℃ / min to ensure that FeSi2 and CaSi2 were fully extracted.

[0037] (3) The industrial silicon melt is cooled down to 800℃ at a cooling rate of 10℃ / min to ensure that Si2Al2Ca, Si8Al6Fe4Ca and Si2Al3Fe are fully converted. Then it is naturally cooled to room temperature to obtain silicon ingots. The silicon ingots are crushed and powdered to obtain industrial silicon powder for the synthesis of organosilicon monomers.

[0038] In this embodiment, the Si8Al6Fe4Ca content in the industrial silicon powder used for synthesizing organosilicon monomers is 0.70 wt.%, which is 2.19 times higher than the Si8Al6Fe4Ca content (0.32 wt.%) when solidifying at a uniform rate of 20℃ / min. At the same time, the time required for stepped solidification is only 64.42% of that for uniform solidification at 20℃ / min, thus improving the solidification efficiency of industrial silicon melt.

[0039] Example 4: A method for strengthening the formation of Si8Al6Fe4Ca by step solidification of industrial silicon melt, the specific steps of which are as follows:

[0040] (1) The industrial silicon melt (typical Si4210, temperature 1550℃) that has been refined by oxidation outside the furnace is poured into a mold with controllable cooling.

[0041] (2) The industrial silicon melt was cooled from 1550℃ to 1000℃ at a cooling rate of 25℃ / min to ensure that FeSi2 and CaSi2 were fully extracted.

[0042] (3) The industrial silicon melt is cooled to 780°C at a cooling rate of 8°C / min to ensure that Si2Al2Ca, Si8Al6Fe4Ca and Si2Al3Fe are fully converted. Then it is naturally cooled to room temperature to obtain silicon ingots. The silicon ingots are crushed and powdered to obtain industrial silicon powder for the synthesis of organosilicon monomers.

[0043] In this embodiment, the Si8Al6Fe4Ca content in the industrial silicon powder used for synthesizing organosilicon monomers is 0.63 wt.%, which is 1.97 times higher than the Si8Al6Fe4Ca content (0.32 wt.%) when solidifying at a uniform rate of 20℃ / min. At the same time, the time required for stepped solidification is only 55.83% of that for uniform solidification at 20℃ / min, thus improving the solidification efficiency of industrial silicon melt.

[0044] Example 5: A method for strengthening the formation of Si8Al6Fe4Ca by step solidification of industrial silicon melt, the specific steps of which are as follows:

[0045] (1) The industrial silicon melt (typical Si4210, temperature 1550℃) that has been refined by oxidation outside the furnace is poured into a mold with controllable cooling.

[0046] (2) The industrial silicon melt was cooled from 1500℃ to 1000℃ at a cooling rate of 30℃ / min to ensure that FeSi2 and CaSi2 were fully extracted.

[0047] (3) The industrial silicon melt is cooled to 800℃ at a cooling rate of 8℃ / min to ensure that Si2Al2Ca, Si8Al6Fe4Ca and Si2Al3Fe are fully converted. Then it is naturally cooled to room temperature to obtain silicon ingots. The silicon ingots are crushed and powdered to obtain industrial silicon powder for the synthesis of organosilicon monomers.

[0048] In this embodiment, the Si8Al6Fe4Ca content in the industrial silicon powder used for synthesizing organosilicon monomers is 0.75 wt.%, which is 2.34 times higher than the Si8Al6Fe4Ca content (0.32 wt.%) when solidifying at a uniform rate of 20℃ / min. At the same time, the time required for stepped solidification is only 55.15% of that for uniform solidification at 20℃ / min, thus improving the solidification efficiency of industrial silicon melt.

[0049] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method of industrial silicon melt step solidification enhanced Si8Al6Fe4Ca formation, characterized by, The specific steps are as follows: (1) pouring the industrial silicon melt refined by the secondary refining process into a controllable cooling mold; (2) controlling the cooling rate of the industrial silicon melt at 15-30 ℃ / min to ensure the analysis of FeSi2 and CaSi2, and to cool the industrial silicon melt from 1650-1500 ℃ to 1100-950 ℃; (3) controlling the cooling rate of the industrial silicon melt at 5-10 ℃ / min to ensure the sufficient conversion of Si2Al2Ca, Si8Al6Fe4Ca and Si2Al3Fe, and then naturally condensing to room temperature to obtain a silicon ingot, which is crushed to obtain the industrial silicon powder for synthesizing organosilicon monomers.

2. The method of claim 1 of industrial silicon melt step solidification enhanced Si8Al6Fe4Ca formation, characterized by: The content of Si8Al6Fe4Ca in the industrial silicon powder for synthesizing organosilicon monomers in step (3) is 0.50-0.80 wt.%.

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