Preparation method and application of high-purity silicon dioxide powder for photovoltaic Czochralski method crucible

Abstract

The invention belongs to the field of new energy materials, and particularly discloses a preparation method and application of high-purity silicon dioxide powder for a photovoltaic Czochralski method crucible, and the preparation method comprises the following steps: pretreating industrial-grade-purity silicon source powder, heating the treated material in an atmosphere furnace, and introducing oxidizing gas to oxidize the treated material into silicon dioxide coarse powder; and finally, heating by using an atmosphere furnace to remove volatile impurities so as to obtain a finished product. The purity of the prepared high-purity silicon dioxide powder can reach 99.99% or above, the process is simple and convenient, large-scale production is facilitated, and the high-purity silicon dioxide powder has wide prospects in the fields of photovoltaic materials and the like.

Description

Technical Field

[0001] The invention belongs to the field of new energy materials, and specifically relates to a preparation method and application of high-purity silicon dioxide powder for a photovoltaic Czochralski crucible. Technical Background

[0002] The single crystal silicon wafers used in photovoltaic solar cells are made by the Czochralski method. The quartz crucible that holds the molten silicon liquid is the top priority for improving product quality and yield. The purity, hardness, micropore content, etc. of the crucible will significantly affect the quality of the final product. The purity of the inner, middle, and outer layers of the quartz crucible currently used in the industry has reached 4N8, 4N5, and 4N, respectively.

[0003] The high-purity quartz crucible used in the production of photovoltaic single crystal silicon is a type of consumables with an average service life of only 300 to 400 hours. The current demand for high-purity quartz sand is at the level of 100,000 tons. Therefore, in the context of the booming photovoltaic industry, a stable and high-quality supply of high-purity quartz has become a top priority. However, my country's quartz deposits have low odor, small reserves, and great difficulty in purification. They mainly rely on foreign imports, resulting in high costs in the photovoltaic industry. Therefore, it is urgent to develop a stable, reliable method for artificially synthesizing high-purity silicon dioxide that is easy to mass produce. Summary of the invention

[0004] Aiming at the problem that the raw materials of high-purity quartz crucibles are dependent on imports, resulting in high costs, a preparation method and application of high-purity silicon dioxide powder for photovoltaic pulling crucibles are provided.

[0005] The present invention provides a method for preparing high-purity silicon dioxide powder for a photovoltaic Czochralski crucible, comprising the following steps:

[0006] S1: Take industrial grade metallic silicon powder with a purity of 99% to 99.9%, add it into a ball mill, add grinding media and grinding aids, ball mill at a certain speed for a certain period of time, filter the obtained slurry and dry it;

[0007] S2: The material obtained in S1 is placed in an atmosphere furnace for heating, and oxygen and water vapor are introduced into the atmosphere furnace. The atmosphere furnace is heated to the reaction temperature at a certain temperature gradient and kept warm for a period of time;

[0008] S3: the material after the reaction in S2 is mixed evenly with a washing solvent and then placed in a ball mill, a grinding medium and a grinding aid are added, and the ball mill is performed at a certain speed for a certain period of time, and the obtained slurry is filtered, washed and dried, wherein the washing solvent is a mixed acid composed of dilute hydrochloric acid and citric acid;

[0009] S4: The product obtained in S3 is placed in a resistance furnace and heated to a certain temperature and kept warm for a period of time to obtain the final product SiO2.

[0010] Preferably, the grinding media in step S1 and step S3 include one or more ball milling beads selected from the group consisting of zirconium oxide, aluminum oxide, agate, silicon carbide, tungsten carbide, and cemented carbide.

[0011] Preferably, the size and ratio of the ball milling beads in step S1 and step S3 are 6mm:4mm:2mm:1mm=1:2:3:4, and the ball-to-material ratio is 1:5.

[0012] Preferably, the grinding aid in step S1 and step S3 includes one or more of deionized water, methanol, ethanol, isopropanol, n-butanol, and isobutanol.

[0013] Preferably, in step S1 and step S3, the ball milling speed is 50-800 r / min, and the ball milling time is 0.1-24 h.

[0014] Preferably, in step S2, the temperature gradient is 0.1 to 10°C / min, the reaction temperature is 200 to 1200°C, and the insulation time is 0.1 to 12h.

[0015] Preferably, the solvent used for washing after filtration in step S3 is deionized water.

[0016] Preferably, in step S4, the heating temperature is 200-1200° C., and the insulation time is 0.5-6 h.

[0017] The present invention also proposes to apply the high-purity silicon dioxide powder prepared by any of the above methods to a crucible used in preparing single crystal silicon wafers used for photovoltaic solar cells by a Czochralski method.

[0018] Principles and advantages

[0019] The present invention adopts industrial-grade metallic silicon powder (99% to 99.9%) to prepare photovoltaic-grade high-purity silicon dioxide powder, which has low raw material cost, simple process operation, and no toxic and dangerous by-products, and is convenient for environmental protection design and large-scale production.

[0020] Metal silicon powder is a relatively pure silicon single substance made from quartz ore by high-temperature smelting. The equation for the reaction of metal silicon powder with oxygen is Si+O2=SiO2. The chemical reaction rate of this process is mainly controlled by two processes. One is the reaction rate of oxygen with the surface substances of silicon powder particles, and the other is the diffusion rate of oxygen in the oxide layer after the oxide layer is formed on the surface of the particles. Obviously, for larger particles, the latter is the core factor affecting the reaction rate. Therefore, it is necessary to grind the metal silicon powder to a certain particle size, reduce the thickness of the oxide layer, and shorten the diffusion path of oxygen to achieve the purpose of rapid oxidation of silicon powder. At the same time, the introduction of water vapor can catalyze the reaction between silicon and oxygen, accelerate the reaction rate, shorten the production cycle, and reduce energy consumption.

[0021] There are still many similar impurities in the lattice in the oxidized silicon powder, so further ball milling and soaking and washing with mixed acid become a simple means of impurity removal. Various metal impurities, some alkali metal and alkaline earth metal impurities with high solubility can be removed by washing, and some impurities with low solubility but low sublimation point and vaporization point can be removed by secondary heating, and residual washing liquid and surface hydroxyl groups are also removed by heating. The final result is a high-purity silicon dioxide powder with a purity of more than 99.99% that can be used as the middle and inner layer material of quartz crucible. This powder has a small particle size, which can minimize the presence of bubble inclusions during the pressing and molding of the crucible, that is, the arc melting stage, and is more evenly heated and easier to melt. Compared with traditional quartz sand ore, it has obvious advantages.

[0022] Compared with the prior art, the present invention uses industrial metal silicon powder as raw material, which has a wide source, stable price, strong replaceability, and the prepared silicon dioxide has high purity and small particle size, fewer bubble inclusions, and can improve the quality of quartz crucibles. At the same time, the operation is simple, the equipment is simple, the energy consumption is low, the environmental pressure is small, and it is suitable for large-scale production. DETAILED DESCRIPTION

[0023] The following describes the embodiments and comparative examples of the present invention in detail. The embodiments and comparative examples described are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0024] Example 1

[0025] This embodiment discloses a method for preparing high-purity silicon dioxide powder, and the preparation process includes the following main steps:

[0026] S1: Take 100g of industrial-grade purity (about 99.9%) metallic silicon powder and add it to a ball mill, add zirconium oxide ball milling beads and isopropanol grinding aid, the mass ratio of zirconium oxide ball milling beads is 6mm:4mm:2mm:1mm=1:2:3:4, the mass ratio of the ball is 1:5, the mass ratio of the material is 1:1, and the ball mill is carried out at a speed of 400r / min for 6h. The obtained slurry is filtered and dried.

[0027] S2: The material prepared in S1 is placed in an atmosphere furnace for heating, and oxygen and water vapor are introduced into the atmosphere furnace, and the atmosphere furnace is connected to the outside world. The atmosphere furnace is heated to 1100°C at a temperature gradient of 10°C / min and kept at this temperature for 6 hours.

[0028] S3: The material after the reaction in S2 was mixed evenly with 40 ml of 20% wt dilute hydrochloric acid and 10 ml of 0.1 mol / L citric acid solution, and then placed in a clean ball mill. Zirconium oxide ball milling beads and isopropanol grinding aids were added, with the same mass and ratio as S1. The mixture was ball milled at a speed of 400 r / min for 4 hours. The resulting slurry was filtered, washed and dried.

[0029] S4: The product obtained in S3 is placed in a resistance furnace and heated to 800°C for 2 hours to obtain the final product SiO2 (99.99%).

[0030] Comparative Example 1

[0031] The experimental steps of Comparative Example 1 are basically the same as those of Example 1, except that the mass ratio of the balls ground in step S1 is 1:1.

[0032] Comparative Example 2

[0033] The experimental steps of Comparative Example 2 are substantially the same as those of Example 1, except that in step S2, only oxygen is introduced into the atmosphere furnace.

[0034] Comparative Example 3

[0035] The experimental steps of Comparative Example 3 are substantially the same as those of Example 1, except that the washing solvent added in step S3 is only 20%wt dilute hydrochloric acid.

[0036] Comparative Example 4

[0037] The experimental steps of Comparative Example 4 are substantially the same as those of Example 1, except that step S4 is not performed.

[0038] Table 1 Statistics of oxidation rate and impurity content of Examples and Comparative Examples

[0039] Serial number Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Oxidation rate 100％ 93.6％ 84.1％ 100％ 97.2％ Fe 0.0012 0.0014 0.0019 0.0067 0.0041 K 0.0005 0.0003 0.0002 0.0035 0.0011 Na 0.0003 0.0006 0.0007 0.0063 0.0015 Ca 0.00017 0.0021 0.00023 0.0037 0.0028 Mg 0.0004 0.0020 0.0016 0.0008 0.0014 P <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 S <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 Al <0.0001 <0.0001 0.0011 0.0024 0.0046 Zr 0.0032 0.0046 0.0041 0.0038 0.0035 Mn <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 Ti <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 Ni <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 Total content 73ppm 110ppm 119ppm 272ppm 190ppm

[0040] As can be seen from Table 1, Example 1 can completely oxidize metallic silicon and remove impurities thoroughly, with an overall purity of 4N. Comparative Example 1 is not thoroughly ground due to the relatively high ball, the silicon powder particle size is large, and the diffusion range of oxygen is large, so the oxidation is not thorough enough. Comparative Example 2 reflects the key role of water vapor in the oxidation process. Comparative Example 3 shows that reducing acid has a significant effect on the removal of lattice impurities. Comparative Example 4 shows that the final calcination is necessary in removing hydroxyl groups, volatile impurities and final oxidation.

Claims

1. A method for preparing high-purity silicon dioxide powder for photovoltaic pulling crucible, characterized in that: The following steps are involved: S1: Take industrial grade metallic silicon powder with a purity of 99% to 99.9%, add it into a ball mill, add grinding media and grinding aids, ball mill at a certain speed for a certain period of time, filter the obtained slurry and dry it; S2: The material obtained in S1 is placed in an atmosphere furnace for heating, and oxygen and water vapor are introduced into the atmosphere furnace. The atmosphere furnace is heated to the reaction temperature at a certain temperature gradient and kept warm for a period of time; S3: the material after the reaction in S2 is mixed evenly with a washing solvent and then placed in a ball mill, a grinding medium and a grinding aid are added, and the ball mill is performed at a certain speed for a certain period of time, and the obtained slurry is filtered, washed and dried, wherein the washing solvent is a mixed acid composed of dilute hydrochloric acid and citric acid; S4: The product obtained in S3 is placed in a resistance furnace and heated to a certain temperature and kept warm for a period of time to obtain the final product SiO2.

2. The preparation method according to claim 1, characterized in that: The grinding media in step S1 and step S3 include one or more ball milling beads selected from the group consisting of zirconium oxide, aluminum oxide, agate, silicon carbide, tungsten carbide, and cemented carbide.

3. The preparation method according to claim 1, characterized in that: The size and ratio of the ball milling beads in step S1 and step S3 are 6mm:4mm:2mm:1mm=1:2:3:4, and the material-ball ratio is 1:

5.

4. The preparation method according to claim 1, characterized in that: The grinding aids in step S1 and step S3 include one or more of deionized water, methanol, ethanol, isopropanol, n-butanol, and isobutanol.

5. The preparation method according to claim 1, characterized in that: In step S1 and step S3, the ball milling speed is 50-800 r / min, and the ball milling time is 0.1-24 h.

6. The preparation method according to claim 1, characterized in that: In step S2, the temperature gradient is 0.1-10°C / min, the reaction temperature is 200-1200°C, and the insulation time is 0.1-12h.

7. The preparation method according to claim 1, characterized in that: The solvent used for washing after filtering in step S3 is deionized water.

8. The preparation method according to claim 1, characterized in that: In step S4, the heating temperature is 200-1200° C., and the insulation time is 0.5-6 h.

9. A crucible used in preparing single crystal silicon wafers for photovoltaic solar cells by using the high-purity silicon dioxide powder prepared by the method of any one of claims 1 to 8.