JP4354259B2 - Slag separation method in silicon refining - Google Patents

Description

  The present invention relates to a silicon refining method using slag used in a process for producing high-purity silicon for solar cells.

  Conventionally, various silicon refining methods using slag have been proposed. Among these, (Patent Document 1) and (Patent Document 2) can be cited as proposals that specify the separation of slag and silicon. However, these only describe separation as part of the slag refining process, and do not describe specific methods.

  Further, (Patent Document 3) proposes a container in a method for oxidizing or volatilizing silicon, and as shown in FIG. 1, a method for bringing silicon 3 out from a hole 2 provided in the bottom of the container 1 is proposed. is suggesting. However, this proposal is a method of pouring out silicon, not a method of removing slag outside the container while leaving the silicon remaining.

Therefore, in the refining of silicon by slag, there is no conventional proposal for a method of removing slag outside the crucible while leaving the refined silicon in the vessel.
JP 2003-12317 A JP-A-8-73209 JP-A-11-189407

  In the slag refining of silicon, as shown in FIG. 2, the impurities (boron, phosphorus) 4 in the silicon 3 are mainly transferred to the slag 5, and the silicon 3 is highly purified. In this refining process, the ability to remove the impurities 4 in the slag 5 decreases after a certain period of time. Therefore, as shown in FIG. 3, there is a need to remove the slag 6 with reduced removal ability outside the container 1 and add a new slag 7, but there has been no efficient slag removal method so far.

  Therefore, an object of the present invention is to provide a method for efficiently removing slag in refining silicon using slag.

The present invention has been made to solve the above problems,
(1) Silicon characterized in that the slag is removed by tilting the container containing silicon and slag to less than 90 ° during or after the refining of silicon and tilting the slag with a jig. Slag separation method in refining,
(2) The slag in silicon refining as described in (1), wherein the jig has a shape with a plate attached to the tip of the rod, the width of the plate is 1/3 or less of the inner diameter of the container or one side, and the height is 10 mm to 100 mm. Separation method,
(3) The slag separation method in silicon refining according to (1) or (2), wherein the jig is made of carbon.
(4) The method for separating slag in silicon refining according to (1), wherein the viscosity of the slag is 0.1 poise or more and 5 poise or less,
(5) The slag separation method in silicon refining according to (4), wherein the slag component is adjusted immediately before the slag is scraped, and the viscosity is controlled.
It is.

  By using the slag separation method in the silicon refining of the present invention, it is possible to efficiently take out only the slag and enhance the refining effect when silicon is refined by slag.

The method of the present invention is used for silicon refining with slag. As shown in FIG. 2, the slag refining is a process in which molten silicon 3 and slag 5 are placed in a container 1 and impurities (boron, phosphorus) 4 in silicon are transferred to slag. The slag 5 is composed mainly of an alkaline or alkaline earth oxide such as Na ₂ O or CaO, and the slag 5 may float on the silicon 4 or sink depending on the composition. Divided. The present invention is a method that is used only when floating.

  As shown in FIG. 4, in the method of the present invention, the container 1 containing the slag 5 and the silicon 3 is inclined, and the jig 8 is used to scrape out the slag 5 and remove the slag 5. At this time, the angle 14 of the inner surface 12 on the side for scraping the slag of the container is not 90 ° or more with respect to the direction of gravity 13. This is because silicon flows out when the angle is 90 ° or more.

  As shown in FIG. 5, the jig 8 has a shape in which a plate 10 is attached to the tip portion of the rod 9, and the slag is scraped out by inserting the plate into the slag and pulling it out. When the width of the plate is larger than 1/3 of the inner diameter or one side of the container or when the height exceeds 100 mm, the plate frequently comes into contact with the inner wall of the container, and workability is significantly reduced. Further, when the height is smaller than 10 mm or the width of the plate is smaller than 30 mm, the amount of slag to be scraped out by one drawing is small, and the efficiency of slag removal is poor. In addition, when the thickness of the plate is less than 3 mm, the plate is often cracked or broken, which hinders the work. Therefore, it is desirable that the width of the plate is 30 mm or more at the inner diameter of the container or 1/3 or less of one side, the height is 10 mm or more and 100 mm or less, and the thickness is 3 mm or more and 30 mm or less.

  The properties required for the jig material include no thermal shock cracking, no contamination, and little reaction with the slag. From these viewpoints, carbon is the optimum material for the jig.

  Also, when removing the slag, there is an optimum viscosity of the slag. As shown in FIG. 6A, when the viscosity is large, only the silicon 3 tends to flow out when the container 1 is tilted. Further, when scraping out, the silicon 3 may be rolled out. On the contrary, if the viscosity is small, as shown in FIG. 6B, fine slag 11 is mixed in the silicon 3 and these become impurities. For these reasons, it is desirable that the viscosity of the slag is not less than 0.1 poise and not more than 5 poise.

  Furthermore, controlling the slag viscosity immediately before slag removal is very effective in removing slag. In slags composed mainly of alkaline and alkaline earth oxides and silicon dioxide, the viscosity can be increased by adding acidic oxides such as silicon dioxide. When a basic oxide is added, the viscosity can be lowered. If these operations are performed immediately before slag removal and the slag viscosity is set to 0.1 poise to 5 poise, better slag removal can be achieved.

  By using the above slag removal method, it is possible to efficiently remove only the slag.

  Hereinafter, the present invention will be described in detail by way of examples.

(Example 1)
30 kg of Si was dissolved in a 250 mm diameter container, and refining was performed using the same amount of slag in which sodium oxide and silicon dioxide had a molar ratio of 1: 1. After refining, separation of silicon and slag was attempted. As a separation method, a method of gradually tilting the container so that only the slag flows out of the container (comparative method) and a method of standing still with the container tilted and scraping out the slag using a jig (method of the present invention) is there. The inclination angle of the container was gradually inclined from 50 ° to 70 ° in the comparative method. On the other hand, the method of the present invention was carried out at 65 °. At this time, by adding SiO ₂ or Na ₂ O to the slag, the slag viscosity was adjusted in five ways of 0.05 poise, 0.1 poise, 1 poise, 5 poise, and 10 poise. The jig used for scraping is made of carbon, and the plate attached to the tip has a thickness of 5 mm and a width and height of 80 mm.

  Table 1 shows the results of separation of slag from silicon under the above conditions. In the comparative method, when the slag viscosity was 0.05 poise, 0.1 poise, and 1 poise, the slag flowed out in a finely mixed state with silicon. On the other hand, when the slag viscosity was 5 poise and 10 poise, slag did not flow out and only silicon flowed out. In any case, only the slag could not be taken out of the container by the comparison method.

  On the other hand, in the method of the present invention, the slag could be taken out from the container. However, almost all of the slag was removed when the slag viscosity was 0.1 poise, 1 poise, 5 poise, 10 poise, and when 0.05 poise, a part of the slag remained mixed and remained in the silicon. On the other hand, in the case of 0.05 poise and 10 poise, part of silicon was mixed into the slag and discharged.

  From the above, compared with the comparative method, the method of the present invention is very advantageous for taking out only the slag. Furthermore, among the methods of the present invention, the slag viscosity is particularly 0.1 poise, 1 poise, 5 poise. It was found that almost the entire amount of slag could be taken out without pouring silicon.

(Example 2)
30 kg of Si was dissolved in a 250 mm diameter container and refined using the same amount of slag having a molar ratio of 1: 1 of sodium oxide and silicon dioxide. After refining, separation of silicon and slag was attempted. As a separation method, the container was kept stationary while being tilted, and a method of scraping slag using a jig (the method of the present invention) was carried out. At this time, the angle of the container was 65 °, and the slag viscosity was adjusted to 1 poise by adding SiO ₂ or Na ₂ O to the slag. A carbon jig was used for scraping. Regarding the size of the jig, the thickness of the plate at the tip was 5 mm, and the width and height were 80 mm × 80 mm, 110 mm × 80 mm, 9 mm × 80 mm, and 80 mm × 100 mm.

  As shown in Table 2, the results of the separation of slag from silicon under the above conditions are as follows. As shown in Table 2, when the tip plate size is 110 mm x 80 mm, 80 mm x 100 mm, the jig frequently contacts the wall of the container. However, the amount of silicon that can be taken out has decreased. In addition, since the 9 mm × 80 mm jig has a small amount of slag to be squeezed at a time, the working time becomes longer. The 80 mm × 80 mm jig has a short working time and can squeeze out almost the entire amount of silicon.

  From the above, it has been found that the slag can be extracted most efficiently when the size is 80 mm × 80 mm even in the separation method of the present invention.

The figure explaining an example of the conventional method. Drawing explaining a method for refining silicon using slag. Drawing explaining the necessity of slag replacement in silicon refining with slag. The drawing which shows the outline | summary of this invention method. Drawing which shows the jig | tool used by the method of this invention. The figure which shows the influence of slag viscosity by the method of this invention, However, (a) When a viscosity exceeds 5 poise, (b) When a viscosity is less than 0.1 poise.

Explanation of symbols

1 container,
2 holes,
3 Silicon,
4 Impurities (boron, phosphorus),
5 Slag,
6 Slag with reduced removal capacity,
7 New slag,
8 jigs,
9 sticks,
10 boards,
11 Fine slag,
12 The inner surface of the slag side,
13 Gravity direction,
14 angles.

Claims (5)

  Slag in silicon refining characterized in that slag is removed by tilting a container containing silicon and slag to less than 90 ° and / or scraping out slag with a jig during or after refining silicon Separation method.   2. The slag separation method in silicon refining according to claim 1, wherein the jig has a shape with a plate attached to the tip of the rod, the width of the plate is 1/3 or less of the inner diameter of the container or one side, and the height is 10 mm or more and 100 mm or less.   The slag separation method in silicon refining according to claim 1 or 2, wherein a material of the jig is carbon.   The method for separating slag in silicon refining according to claim 1, wherein the viscosity of the slag is 0.1 poise or more and 5 poise or less.   The method for separating slag in silicon refining according to claim 4, wherein the viscosity is controlled by adjusting a slag component immediately before the slag is discharged.

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