Method for forming industrial silicon melt stepped solidification reinforced Si8Al6Fe4Ca

Abstract

The invention relates to a method for forming Si8Al6Fe4Ca through stepped solidification reinforcement of industrial silicon melt, and belongs to the technical field of high-value utilization of industrial silicon. Aiming at the practical problems of uncontrollable solidification speed, incomplete conversion of intermetallic compounds, randomization of precipitation of the intermetallic compounds, low selectivity and primary conversion rate of dimethyldichlorosilane when the industrial silicon is used as a raw material to synthesize an organic silicon monomer in an industrial silicon melt casting air cooling process, the invention provides a preparation method of the organosilicone monomer. According to the method disclosed by the invention, the silicon melt subjected to oxidation refining is cast into a casting mold with controllable cooling, and stepped variable-rate condensation is realized through parameter optimization in a solidification process, so that the content of harmful FeSi2 / CaSi2 phases formed in industrial silicon products is reduced, and full conversion of the harmful phases to Si8Al6Fe4Ca, Si2Al2Ca and Si2Al3Fe is promoted. The method has the advantages of full utilization and energy conservation, low capital construction investment, simple process flow, high operability, no environmental pollution and the like.

Description

Technical Field

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

[0002] Industrial silicon is the basic raw material for silicon-based alloys, organosilicon and silicon-based photovoltaic cells. Among them, industrial silicon raw materials for organosilicon need to have low content of FeSi2 / CaSi2 and high Si8Al6Fe4Ca phase. However, the solidification parameters of the industrial silicon melt casting process are uncontrollable, resulting in random precipitation of intermetallic compounds and reducing the synthesis efficiency of organosilicon monomers. For this reason, organosilicon companies usually purchase expensive industrial silicon with low impurity content to avoid the negative impact of precipitation of undesirable intermetallic compounds.

[0003] The selectivity and activity of the organosilicon monomer synthesis process are key parameters for evaluating the quality of the synthesis reaction. In the process of synthesizing (CH3)2SiCl2 from industrial silicon, selectivity refers to the yield of (CH3)2SiCl2 in the synthesized organosilicon monomer, while activity refers to the powder conversion efficiency of industrial silicon. Improving these two production indicators is an effective way to improve the production efficiency and reduce production costs in the organosilicon monomer synthesis process. Relevant literature and production experience show that industrial silicon is an important cost component and influencing factor in the organosilicon monomer synthesis process. Intermetallic compounds in the solidification process of industrial silicon can be divided into two categories according to the requirements for solidification rate. One is that the FeSi2, CaSi2, and TiFeSi2 phases that do not involve the conversion of intermetallic compounds are not affected by the solidification rate. The second is that the Si2Al3Fe, Si2Al2Ca, and Si8Al6Fe4Ca phases involved in the precipitation of intermetallic compounds require sufficient conversion time. Intermetallic compounds in industrial silicon have an important influence on the selectivity and activity of monomer synthesis. Among them, Si2Al2Ca has a significant effect on improving activity but is not conducive to improving selectivity. Si8Al6Fe4Ca is the only phase that can improve selectivity. Si2Al3Fe has no effect on selectivity and activity. The remaining intermetallic compounds are harmful phases for the synthesis of dimethyldichlorosilane from industrial silicon. Therefore, the composition of intermetallic compounds can be regulated by step solidification process, the precipitation of Si8Al6Fe4Ca can be promoted, and the content of CaSi2 and FeSi2 can be reduced, so as to achieve a balance between selectivity and activity, which is helpful to improve the efficiency of organosilicon monomer synthesis and achieve the goal of "reducing costs and increasing efficiency" for related production enterprises. Summary of the invention

[0004] Aiming at the practical problems of uncontrollable solidification speed, uneven segregation, incomplete transformation of intermetallic compounds, random precipitation of intermetallic compounds in the casting air cooling process of industrial silicon melt, low selectivity and primary conversion rate of dimethyldichlorosilane when synthesizing organic silicon monomer with industrial silicon as raw material, the present invention proposes a method for step-solidification strengthening Si8Al6Fe4Ca formation of industrial silicon melt, casting the silicon melt completed by oxidation refining into a mold with controllable cooling, and realizing step-variable rate condensation through solidification process parameters to reduce the content of harmful FeSi2 / CaSi2 phases formed in industrial silicon products, and promote the full transformation of harmful phases to Si8Al6Fe4Ca, Si2Al2Ca and Si2Al3Fe. The present invention has the advantages of no special requirements on the impurity content of silicon melt, full utilization and energy saving, low infrastructure investment, simple process flow, high operability, and no pollution to the environment.

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

[0006] (1) Casting the industrial silicon melt that has been oxidatively refined outside the furnace into a mold with controllable temperature reduction;

[0007] (2) controlling the cooling rate of the industrial silicon melt from 1650-1500°C to 1100-950°C at 15-30°C / min to ensure that FeSi2 and CaSi2 are fully precipitated;

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

[0009] In a method for forming Si8Al6Fe4Ca by step-solidification strengthening of industrial silicon melt, the conversion reactions of Si2Al2Ca, Si8Al6Fe4Ca and Si2Al3Fe are respectively:

[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 the organosilicon monomer in step (3) is 0.50-0.80wt.%.

[0014] The beneficial effects of the present invention are:

[0015] (1) The present invention aims at the practical problems of uncontrollable solidification speed, incomplete transformation of intermetallic compounds, random precipitation of intermetallic compounds, etc. in the casting and air cooling process of industrial silicon melt, and proposes a method for strengthening the formation of Si8Al6Fe4Ca by step solidification of industrial silicon melt. The method is based on the industrial silicon melt that has been refined outside the furnace and the end of heat preservation, and is successively cast into a mold with controllable temperature reduction, cooled by staged temperature control, and air-cooled and solidified to finally achieve the purpose of controlling the intermetallic compounds. After crushing and powdering, an industrial silicon product for organic silicon is obtained, which has the advantages of high product added value, strong raw material applicability, simple modification of existing equipment, high production efficiency, and suitability for industrial production;

[0016] (2) The present invention adopts furnace insulation to make the melt composition uniform, temperature-controlled casting and molding, and at the same time controls the cooling rate, crushing and powder making, etc., to prepare industrial silicon for the synthesis of organic silicon monomers under the condition of simple modification of existing equipment, improve the efficiency of industrial silicon in synthesizing dimethyldichlorosilane, and improve the economic efficiency of enterprises in preparing organic silicon, which is conducive to providing added value of industrial silicon products and production benefits of organic silicon enterprises;

[0017] (3) The industrial silicon prepared by the present invention can improve the production efficiency of dimethyldichlorosilane monomers during the synthesis of organic silicon monomers. At the same time, there are no special requirements for the impurity content of industrial silicon products. It has a positive effect on alleviating the tight supply of industrial silicon materials with low impurity content, achieving "cost reduction and efficiency improvement" for related enterprises, and improving resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0019] Figure 2 The phase content of the industrial silicon ingot with the same solidification rate during the whole solidification process of the comparative example (15°C / min);

[0020] Figure 3 The phase content in the industrial silicon ingot with step solidification control in Example 1. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below in conjunction with specific implementation modes, but the protection scope of the present invention is not limited to the described contents.

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

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

[0024] (1) Casting the industrial silicon melt (typically Si4210, temperature 1550°C) that has been oxidatively refined outside the furnace into a mold with controllable cooling;

[0025] (2) Cooling the industrial silicon melt from 1550°C to 1000°C at a cooling rate of 15°C / min to ensure that FeSi2 and CaSi2 are fully precipitated;

[0026] (3) the industrial silicon melt is cooled to 800°C at a cooling rate of 5°C / min to ensure that Si2Al2Ca, Si8Al6Fe4Ca and Si2Al3Fe are fully converted, and then naturally condensed to room temperature to obtain a silicon ingot, which is crushed and pulverized to obtain industrial silicon powder for synthesizing organic silicon monomers;

[0027] The phase content of the industrial silicon ingot with the same solidification rate during the whole solidification process is shown in Table 1. Figure 2 ,from Figure 2 It can be seen that when the industrial silicon melt solidified at a rate of 15°C / min throughout the whole process, 0.44wt.% of Si8Al6Fe4Ca was precipitated;

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

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

[0030] (1) Casting the industrial silicon melt (typically Si4210, temperature 1650°C) that has been oxidatively refined outside the furnace into a mold with controllable cooling;

[0031] (2) cooling the industrial silicon melt from 1650°C to 950°C at a cooling rate of 20°C / min to ensure that FeSi2 and CaSi2 are fully precipitated;

[0032] (3) the industrial silicon melt is further cooled to 860°C at a cooling rate of 5°C / min to ensure that Si2Al2Ca, Si8Al6Fe4Ca and Si2Al3Fe are fully converted, and then naturally condensed to room temperature to obtain a silicon ingot, which is crushed and pulverized to obtain industrial silicon powder for synthesizing organic silicon monomers;

[0033] The Si8Al6Fe4Ca content in the industrial silicon powder used for the synthesis of the silicone monomer in this embodiment is 0.72wt.%, which is 2.25 times higher than the Si8Al6Fe4Ca content (0.32wt.%) when solidified at an average rate of 20°C / min. At the same time, the time required for step solidification is only 77.30% of that at an average solidification rate of 20°C / min, thereby improving the solidification efficiency of the industrial silicon melt.

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

[0035] (1) Casting the industrial silicon melt (typically Si4210, temperature 1550°C) that has been oxidatively refined outside the furnace into a mold with controllable cooling;

[0036] (2) cooling the industrial silicon melt from 1550°C to 1100°C at a cooling rate of 20°C / min to ensure that FeSi2 and CaSi2 are fully precipitated;

[0037] (3) the industrial silicon melt is further cooled to 800°C at a cooling rate of 10°C / min to ensure that Si2Al2Ca, Si8Al6Fe4Ca and Si2Al3Fe are fully converted, and then naturally condensed to room temperature to obtain a silicon ingot, which is crushed and pulverized to obtain industrial silicon powder for synthesizing organic silicon monomers;

[0038] The Si8Al6Fe4Ca content in the industrial silicon powder used for the synthesis of the silicone monomer in this embodiment is 0.70wt.%, which is 2.19 times higher than the Si8Al6Fe4Ca content (0.32wt.%) when solidified at an average rate of 20°C / min. At the same time, the time required for step solidification is only 64.42% of that at an average solidification rate of 20°C / min, thereby improving the solidification efficiency of the industrial silicon melt.

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

[0040] (1) Casting the industrial silicon melt (typically Si4210, temperature 1550°C) that has been oxidatively refined outside the furnace into a mold with controllable cooling;

[0041] (2) cooling the industrial silicon melt from 1550°C to 1000°C at a cooling rate of 25°C / min to ensure that FeSi2 and CaSi2 are fully precipitated;

[0042] (3) the industrial silicon melt is further cooled to 780°C at a cooling rate of 8°C / min to ensure that Si2Al2Ca, Si8Al6Fe4Ca and Si2Al3Fe are fully converted, and then naturally condensed to room temperature to obtain a silicon ingot, which is crushed and pulverized to obtain industrial silicon powder for synthesizing organic silicon monomers;

[0043] The Si8Al6Fe4Ca content in the industrial silicon powder used for the synthesis of the silicone monomer in this embodiment is 0.63wt.%, which is 1.97 times higher than the Si8Al6Fe4Ca content (0.32wt.%) when solidified at an average rate of 20°C / min. At the same time, the time required for step solidification is only 55.83% of that at an average solidification rate of 20°C / min, thereby improving the solidification efficiency of the industrial silicon melt.

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

[0045] (1) Casting the industrial silicon melt (typically Si4210, temperature 1550°C) that has been oxidatively refined outside the furnace into a mold with controllable cooling;

[0046] (2) cooling the industrial silicon melt from 1500°C to 1000°C at a cooling rate of 30°C / min to ensure that FeSi2 and CaSi2 are fully precipitated;

[0047] (3) the industrial silicon melt is further cooled to 800°C at a cooling rate of 8°C / min to ensure that Si2Al2Ca, Si8Al6Fe4Ca and Si2Al3Fe are fully converted, and then naturally condensed to room temperature to obtain a silicon ingot, which is crushed and pulverized to obtain industrial silicon powder for synthesizing organic silicon monomers;

[0048] The Si8Al6Fe4Ca content in the industrial silicon powder used for the synthesis of the silicone monomer in this embodiment is 0.75wt.%, which is 2.34 times higher than the Si8Al6Fe4Ca content (0.32wt.%) when solidified at an average rate of 20°C / min. At the same time, the time required for step solidification is only 55.15% of that at an average solidification rate of 20°C / min, thereby improving the solidification efficiency of the industrial silicon melt.

[0049] The specific implementation modes of the present invention are described in detail above, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A method for forming Si8Al6Fe4Ca by step-solidification strengthening of industrial silicon melt, characterized in that: The specific steps are as follows: (1) Casting the industrial silicon melt that has been oxidatively refined outside the furnace into a mold with controllable temperature reduction; (2) controlling the cooling rate of the industrial silicon melt from 1650-1500°C to 1100-950°C at 15-30°C / min to ensure that FeSi2 and CaSi2 are fully precipitated; (3) The industrial silicon melt is cooled to 860-700°C at a cooling rate of 5-10°C / min to ensure that Si2Al2Ca, Si8Al6Fe4Ca and Si2Al3Fe are fully converted, and then naturally condensed to room temperature to obtain a silicon ingot. The silicon ingot is crushed and pulverized to obtain industrial silicon powder for synthesizing organic silicon monomers.

2. The method for forming Si8Al6Fe4Ca by step-solidification strengthening of industrial silicon melt according to claim 1, characterized in that: The content of Si8Al6Fe4Ca in the industrial silicon powder used for synthesizing the organosilicon monomer in step (3) is 0.50-0.80wt.%.

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