JP5299042B2 - Silicon cutting powder oxidation inhibiting method and silicon cutting powder oxidation inhibiting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicon oxidation suppression method substituted for a pH control method using a pH sensor suppressing oxidation of a silicon cutting powder in a coolant liquid and enhancing solid/liquid separation property of the silicon cutting powder and the coolant liquid, and to particularly provide a silicon oxidation suppression method with sufficient responsiveness for a long period of time capable of accurately suppressing oxidation. <P>SOLUTION: In the oxidation suppression method of the silicon cutting powder in the coolant liquid, a silicon coagulation bulk is cut while applying the coolant liquid, and the coolant liquid containing the generated silicon cutting powder is transferred to a coolant liquid tank. On an upper part of the coolant liquid tank, a concentration of hydrogen generated from a water surface is measured and an acidic agent is added to the coolant liquid according to the hydrogen concentration value to suppress oxidation of the silicon cutting powder. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention is to provide a solid-liquid separation of silicon cutting powder and coolant water efficiently in coolant water containing silicon cutting powder generated when a silicon coagulum is cut using a blade or the like while applying coolant water. The present invention relates to a method for suppressing oxidation of silicon cutting powder and an apparatus for suppressing oxidation of silicon cutting powder.

  In the production of polycrystalline silicon and single crystal silicon for solar cells, for the purpose of improving the purity of silicon, after putting molten silicon into a container, by lowering the temperature by cooling etc. from one direction, a temperature gradient is added, Unidirectional solidification is performed in which solidification is gradually solidified from one direction (for example, the lower part), and impurities (iron, aluminum, etc.) in silicon are moved and concentrated in the other direction (for example, the upper part).

  The silicon coagulum having impurities concentrated at the end (for example, the upper end) can be removed by cutting the end and the high-purity silicon coagulum can be recovered as the remainder. During this cutting, silicon cutting powder is generated.

  For example, as shown in FIG. 1, the silicon coagulated mass 1 is cut using a blade 2 or the like while the blade 2 is cooled. In order to cool the blade 2, cooling water (also referred to as coolant water) 5 is used, and pure water is often used. As a result, silicon cutting powder is generated in a state mixed with coolant water. After the coolant water is temporarily stored in the coolant water tank 3, it is again applied to the blade 2 as the cooling water 5 by the pump 4, and is normally used repeatedly.

  The coolant water in the coolant tank 3 is discarded when the concentration of the silicon cutting powder exceeds a certain value. In order to discard, it is usually discarded after filtering and separating the silicon cutting powder and the liquid part. However, as will be described later, a part of the silicate ions in the coolant water becomes a gel or a colloid so as to cover the filtration surface, and there is a problem that filtration is difficult because filtration resistance is increased.

  That is, the main component of this silicon cutting powder is metallic silicon, which contains a large amount of fine powder on the order of μm, and the specific surface area of this silicon cutting powder is very large and active. Therefore, a part of the silicon cutting powder reacts with a hydroxyl group in the coolant water to generate hydrogen and becomes silicate ions, and the stronger the alkalinity, the more this silicate ion amount increases. A part of this silicate ion further reacts with water and is oxidized to silicon dioxide (silica) to form a gel or colloid, which deteriorates the solid-liquid separation property when separating silicon cutting powder from coolant water. There was a problem.

  In addition, when the generated silicate ions further react with water and are oxidized to silicon dioxide (silica), the silicon cutting powder is recovered from raw material mainly because it contains metallic silicon immediately after cutting. However, there is also a problem that effective utilization is difficult because it is oxidized to silica.

  On the other hand, since the oxidation of the silicon cutting powder is affected by the pH, the pH is predetermined by the acid agent 6 while measuring the pH of the wastewater by the pH sensor 13 with respect to the wastewater discharged from the grinding / polishing apparatus. There has been proposed a method for suppressing the oxidation of silicon cutting powder by controlling within the range (for example, see Patent Document 1).

  In order to improve the solid-liquid separation property, it is necessary to control the pH of the coolant water to the acidic side. However, if the pH is lowered too much, the problem of equipment corrosion occurs. Therefore, the pH is preferably controlled to 4 or more.

  However, since silicon cutting powder contains fine cutting powder containing fine powder of the order of μm, the generated hydrogen adheres to the silicon cutting powder, and the phenomenon that the fine silicon cutting powder floats occurs, resulting in the glass of the pH sensor. When the surfaced silicon cutting powder adheres to the electrode surface, the responsiveness and measurement accuracy of the pH sensor are lowered, and pH control becomes difficult. Moreover, it is difficult to completely remove the adhered fine silicon cutting powder by cleaning with water, and even if maintenance is performed by cleaning the electrode part, the responsiveness and measurement accuracy are not recovered so much and stable for a long time. There was also a problem that it was difficult to control.

JP 2002-192465 A

  In view of the above problems, the present invention provides a method for suppressing silicon oxidation that replaces a pH control method using a pH sensor, which suppresses oxidation of silicon cutting powder in coolant water and improves solid-liquid separation of silicon cutting powder and coolant water. The purpose is to provide. In particular, an object of the present invention is to provide a method for suppressing silicon oxidation, which has good responsiveness over a long period of time and can accurately suppress oxidation.

The features of the present invention are as follows.
(1) Cutting the silicon solidified lump while applying the coolant water, transferring the coolant water containing the generated silicon cutting powder to the coolant water tank, and placing the cylinder so that one side of the cylinder is immersed in the coolant surface in the coolant water tank. It is installed, the concentration of hydrogen generated from the water surface inside the cylinder is measured, and an acid agent is added to the coolant water according to the hydrogen concentration value to suppress oxidation of the silicon cutting powder. A method for suppressing oxidation of silicon cutting powder in coolant water.
(2) The method for inhibiting oxidation of silicon cutting powder in coolant water according to claim 1, wherein the acidic agent is added so that the measured hydrogen concentration is a predetermined value or less .
(3 ) The silicon cutting powder in the coolant water according to (1) or (2) , wherein the coolant water in the coolant water tank is circulated and used as coolant water for cutting the silicon solidified lump. Of oxidation inhibition.
( 4 ) The method further comprises extracting a part or all of the coolant water containing silicon cutting powder from the coolant water tank, setting the pH of the extracted coolant water to 4 or less, and stopping the oxidation of silicon. The method for suppressing oxidation of silicon cutting powder in coolant water according to any one of (1) to ( 3 ).
(5) the oxidation control method of a silicon cuttings according to any one of the circulation, characterized in that cooling prior to use coolant water to use (1) to (4).
( 6 ) An oxidation suppression apparatus for silicon cutting powder used in the method for suppressing oxidation of silicon cutting powder according to (3 ), wherein a coolant tank and coolant water containing silicon cutting powder are transferred to the coolant tank. According to piping, a cylinder installed so that one side is immersed in the coolant surface in the coolant tank, a hydrogen concentration sensor installed inside the cylinder, and a hydrogen concentration value measured by the hydrogen concentration sensor An apparatus for suppressing oxidation of silicon cutting powder in coolant water, comprising an acid agent storage tank capable of adjusting the amount of acid agent charged.

  According to the present invention, it is possible to stably suppress the oxidation of silicon cutting powder in the coolant water generated when cutting the silicon solidified lump with a blade or the like, and improve the solid-liquid separation between the silicon cutting powder and the coolant water. It becomes.

It is the figure which showed the example of the equipment structure which cut | disconnects a silicon solidified lump using a blade. In addition, FIG. FIG. 6 is a diagram illustrating Example 3. It is the figure which showed the influence of pH with respect to the amount of hydrogen generation in 50 degreeC (molar amount of hydrogen generated per 1 hr from 1 kg of silicon cutting powder). It is the figure which calculated the relationship between total amount of hydrogen generation and SiO2 / (SiO2 + Me-Si). It is the figure which showed the influence of the water temperature with respect to the amount of hydrogen generation in pH7.2 (molar amount of hydrogen generated per hour from 1 kg of silicon cutting powder). It is the figure which showed the responsiveness of the hydrogen concentration in the case where it does not install with the case where a cylinder is installed as a spreading | diffusion suppression measure of generated gas. As an example of the generated gas diffusion suppression measure, it is a diagram in the case where a cylinder with a hydrogen concentration sensor is installed on the upper part of the coolant tank covered with a lid. It is the figure explaining that coolant water containing silicon cutting powder was moved to the water tank for stationary, made pH4 or less, and oxidization of silicon was controlled early. It is a figure explaining the comparative example 1. FIG. It is the figure which showed the example of the apparatus of this invention. It is also a diagram illustrating a reference example . FIG. 6 is a diagram illustrating Example 2. FIG. 6 is a diagram illustrating Example 4.

  In this invention, in order to circulate and use coolant water, it can apply, for example under the installation structure as shown in FIG. The reason for circulating the coolant water is to reduce wastewater treatment costs.

  First, the apparatus configuration of the present invention will be described with reference to FIG.

  There is a blade 2 for cutting the silicon coagulated lump 1, and coolant water 5 is fed to the blade by a pump 4 via a coolant water transfer pipe 26 and cooled. The cooling water 5 applied to the blade 2 returns to the coolant water tank via the coolant water transfer pipe 26. In the upper part of the coolant water tank, a cylinder 8 (both ends open), which will be described later, is installed with the lower end of the cylinder immersed in the water surface of the coolant water tank 3. A hydrogen gas concentration sensor 9 is provided in the cylinder 8, and hydrogen generated in the coolant water measures the hydrogen concentration when rising in the cylinder. When the hydrogen concentration exceeds a certain value, the acid agent 6 in the acid agent storage tank 27 is introduced into the coolant water tank 3 by the pump 7. Further, the temperature of the coolant water in the coolant water tank 3 is measured by the thermometer 10, and when it reaches a certain value, it is cooled by the cooling device 11.

  Next, the influence of the pH of the coolant water on the hydrogen generation amount will be described.

  100 ml of coolant water containing 10% silicon cutting powder was sampled, stirred in an Erlenmeyer flask and adjusted to a constant 50 ° C., and the pH was changed with dilute sulfuric acid or sodium hydroxide solution to investigate the effect. . The resulting hydrogen generation amount is shown in FIG. 3 (effect of coolant water pH on hydrogen generation amount). The more hydrogen is generated, the more hydrogen is generated. However, when the pH is 7 or less, the hydrogen generation is decreased. When the pH is 6 or less, almost no hydrogen is generated, and when the pH is 4.3 or less, the hydrogen generation is zero. In the hydrogen generation region exceeding pH 4.3, as shown in the following (formula 1), silicon reacts with a hydroxyl group to generate hydrogen, and as shown in (formula 2), silicate ions are in a gel or colloidal silica. Thus, the solid-liquid separability of the silicon cutting powder and the coolant water which have not reacted in accordance with the progression of (Equation 1) is deteriorated. Particularly in the high pH region (alkali side), it can be said that the amount of gel-like or colloidal silica generated from silicate ions increases, and as a result, the solid-liquid separation property is remarkably deteriorated. Therefore, by setting the pH of the coolant water to 7 or less, preferably 6 or less, the oxidation of silicon can be suppressed, and the solid-liquid separability of silicon cutting powder and coolant water can be improved.

Si (silicon) + 3OH ^- (hydroxyl) → SiO ₃ ^2- (silicate ions) + 3 / 2H ₂ ↑ (Equation 1)
SiO ₃ ^2- ＋ (X + 1) H ₂ O
_{→ SiO 2 · XH 2 O ↓} ( gel or colloidal silica) + 2OH ^- (Equation 2)
Next, the generation amount of hydrogen and the generation amount of gel or colloidal silica with poor solid-liquid separation will be described.

Based on (Formula 1) and (Equation 2), for hydrogen generation amount in the presence of a metal silicon 1g, the degree of oxidation of silicon (= resulting SiO ₂ mass / (resulting SiO ₂ mass + remaining FIG. 4 shows the relationship with the mass of metal silicon.

  It can be seen that as the metal silicon is oxidized, more hydrogen is generated. That is, by observing the amount of hydrogen generated and adjusting the reaction system so as to reduce the amount of generated hydrogen, the oxidation of metal silicon can be suppressed, and the generation of gel or colloidal silica that is difficult to filter can be reduced. I understand.

  Next, the influence of the coolant temperature on the amount of hydrogen generated will be described.

  100 ml of coolant water containing 10% silicon cutting powder is sampled, stirred in an Erlenmeyer flask, adjusted to a constant pH 7.2 with dilute sulfuric acid or sodium hydroxide solution, and the water temperature is adjusted to 5 to 70 ° C. The effect was investigated by fluctuating between. The amount of hydrogen generated at that time is shown in FIG.

  It can be seen that the higher the water temperature, the greater the amount of hydrogen generated, and the lower the water temperature, the smaller the amount of hydrogen generated. Therefore, by lowering the coolant temperature, hydrogen generation is suppressed as shown in (Formula 1) and generation of silicate ions is suppressed, so that the gel-like or colloidal silica of (Formula 2) Generation | occurrence | production can be suppressed and it can be said that the solid-liquid separability of silicon cutting powder and coolant water can be improved. In particular, when the temperature exceeds 40 ° C., the amount of hydrogen generated increases rapidly, so the water temperature is preferably adjusted to 40 ° C. or lower, and more preferably adjusted to 30 ° C. or lower. The water temperature can be adjusted by, for example, arranging a cooling water pipe in the coolant tank.

  3 and 5, it can be seen that the oxidation of the silicon cutting powder can be suppressed by adjusting the pH and the water temperature low so that the amount of hydrogen generated is reduced.

  However, in adjusting the water temperature, a slight amount of hydrogen is generated even when the water temperature is lowered to 5 ° C. Since the oxidation of silicon is an exothermic reaction, it always generates heat even at a water temperature of 5 ° C. Further, when the silicon solidified lump is cut, heat is generated due to friction with the blade. In addition, since the cutting operation is usually performed in a room temperature room, coolant water is applied to the blade and the silicon coagulated mass, so that it is difficult to completely insulate. Furthermore, the equipment cost increases for cooling to room temperature or lower. For these reasons, there is a limit to lowering the water temperature. On the other hand, it is easy to keep the pH low by adding an acid agent. Therefore, in the present invention, the pH adjustment is more preferable than the water temperature adjustment for the adjustment of coolant water containing silicon cutting powder for suppressing silicon oxidation and hydrogen generation.

  Moreover, the oxidation amount of the silicon cutting powder is also related to the contact time (oxidation time) with the coolant water in addition to the pH and water temperature factors related to the oxidation rate. That is, in order to suppress the oxidation of the silicon cutting powder, it is also one means to stop the oxidation reaction itself by separating it early from the coolant water.

  That is, in the present invention, (A) in order to suppress the oxidation rate, (a-1) the amount of hydrogen generation (concentration) is monitored, and an acid agent is added so that the amount of generation (concentration) decreases. (A-2) Further, a means for lowering the water temperature may be added, and (B) In order to suppress the oxidation time, silicon cutting powder is used. After the occurrence, means for separating the coolant water and the cutting powder from the coolant tank at an early stage may be added.

  In the means of (a-1), by adding an acidic agent so as to reduce the measured hydrogen concentration, the pH of the coolant water is lowered and the oxidation of the silicon cutting powder is suppressed. Since the generated hydrogen concentration is lower, the relationship between the silicon cutting powder oxidation suppression degree and the hydrogen concentration is investigated in advance, and a predetermined hydrogen concentration is set according to the required oxidation suppression degree. It is preferable to add the acid agent so that the hydrogen concentration is lower than the hydrogen concentration.

  However, it is not preferable that the set value of the hydrogen concentration is zero or a value lower than the detection lower limit of the hydrogen concentration sensor. That means that the hydrogen concentration is zero or below the detection limit means that the pH may be too low. As will be described in detail later, if the pH of the coolant water is too low, the steel materials constituting the apparatus will be This is because there is a high possibility of corrosion. Therefore, it is preferable to set the hydrogen concentration with the upper limit being a predetermined value or less and the lower limit being over the detection limit. The relationship between pH and steel corrosion will be described below.

  Cutting machines, polishing machines, water tanks, etc. are mainly manufactured from ordinary steel. If the wetted part that contacts the coolant water is lined with an acid-resistant material such as stainless steel or FRP lining, the problem of corrosion will not be a problem, but the coolant water attached to the cutting blade or polishing disk that is the rotating part will not be a problem. In consideration of scattering, it is necessary to adopt stainless materials or to coat with acid-resistant materials for all members in the region where the splashes are scattered, which increases the equipment cost.

In ordinary steel, the iron surface is covered with a hydroxide film in the pH range of 4 to 9, and corrosion is determined by repolarization by oxygen passing through the film regardless of the pH of the water. Generally, when the pH is 4 or less, the hydroxide film dissolves away to generate hydrogen, and severe corrosion occurs. In areas where harmful chlorides and the like are dissolved in the film, it varies somewhat, but water containing Cl ^- and HCO ^3- increases corrosion and tends to generate rust bumps. In other words, without lowering the pH of the coolant water to 4 below, and, as an acidic agent, Cl ^- it is preferable to select those which do not contain and HCO ^3-. Examples of preferable acid agents include sulfuric acid, nitric acid, hydrofluoric acid, formic acid, and acetic acid.

  Next, a method for measuring the hydrogen concentration in the present invention will be described based on the apparatus example of FIG.

  Hydrogen generated when the silicon cutting powder is oxidized is detected by a hydrogen concentration sensor 9 installed in the upper part of the coolant water tank 3. In the hydrogen concentration control using the hydrogen concentration sensor 9, the sensor portion does not come into contact with the liquid, so that problems such as coating do not occur unlike the pH sensor, and the oxidation state of the silicon cutting powder can be grasped. However, since the upper part of the coolant tank 3 is diluted with the air in the surrounding area, the hydrogen concentration becomes low and unstable, so that the silicon cutting powder oxidation state can be obtained simply by managing the hydrogen concentration with the hydrogen concentration sensor 9. Can be grasped, but it is difficult to grasp accurately and responsively. In addition, by installing the hydrogen concentration sensor 9 in the vicinity of the coolant surface, dilution of hydrogen by air can be suppressed to some extent. However, since the water surface position in the coolant water tank 3 slightly fluctuates, Must be grounded with sufficient margin, and there is a limit.

  Therefore, as shown in FIG. 2, it is preferable that one end of a cylinder (also referred to as a hydrogen measurement cylinder) 8 with both ends of the cylinder open in the upper part of the coolant tank is immersed in water. Dilution from the horizontal direction by surrounding air can be suppressed by the cylinder, and hydrogen is not diluted, but hydrogen is lighter than air, so it rises in the cylinder and is released from the upper part of the cylinder. Since there is no dilution from the horizontal direction with air, the hydrogen concentration in the cylinder increases and stabilizes. By installing a hydrogen concentration sensor in the cylinder, the oxidation status of silicon cutting powder is accurately and responsive. I can grasp it well.

  FIG. 6 shows the responsiveness of the hydrogen concentration when the cylinder is installed and when the cylinder is not installed, and shows the change in the hydrogen concentration from when the hydrogen concentration in the cylinder is zero. The distance from the water surface to the hydrogen concentration sensor is 13 cm in both cases, the inner diameter of the cylinder is 5 cm, and the length is 1 m. It can be seen that when the cylinder is installed, dilution by air from the surrounding area is reduced, the responsiveness of the hydrogen concentration is increased, the hydrogen concentration is increased, and the measurement sensitivity is improved.

  When the cylinder is not installed, the value of hydrogen concentration is low, and in 120 to 180 seconds, due to dilution with surrounding air, hydrogen is generated, but near the detection limit (0.1%). Value. In other words, by installing the hydrogen concentration sensor and the diffusion preventing cylinder, it is considered that the responsiveness can be improved without the hydrogen concentration sensor coming into contact with the coolant water.

  Since the optimum hydrogen concentration setting differs in each case depending on the size of the cylinder, the installation environment, etc., the control range of the hydrogen concentration is preferably set by obtaining the relationship as shown in FIG. preferable. The lower the hydrogen concentration, the more the oxidation is suppressed. However, when the hydrogen concentration is 0%, the pH of the coolant water is 4.3 or less, and in some cases, the pH may be 4 or less. Since there is a concern about equipment corrosion, it is preferable to set the lower limit to the extent that the hydrogen concentration is slightly detected in order to prevent this.

  For example, when the distance from the water surface to the hydrogen concentration sensor is 13 cm, the inner diameter of the cylinder is 5 cm, and the length is 1 m, the hydrogen concentration is 0.5% or less, preferably 0.3% or less. By adding the agent, the oxidation of the silicon cutting powder is greatly suppressed. The lower limit can be set, for example, by 0.1% or by preventing the measured hydrogen concentration from being below the detection limit.

  Moreover, by suppressing dilution by surrounding air, the amount of generated hydrogen maintains a relationship proportional to the hydrogen concentration, and by measuring the hydrogen concentration, oxidation of silicon cutting powder can be suppressed.

  From the standpoint of preventing equipment corrosion, the acid agent can be diluted and used so that the pH does not become 4 or less even when a large amount of the acid agent is added to the coolant water. However, if the acid agent is diluted too much, when a large amount of hydrogen is generated, it takes time to reduce the hydrogen concentration. Therefore, it is necessary to dilute appropriately in consideration of the balance between prevention of equipment corrosion and hydrogen concentration reduction. It is preferable to do.

  The control mechanism for adding the acid agent so that the measured hydrogen concentration becomes a predetermined value or less is not particularly limited. For example, a flow control valve is installed in the middle of the pipe from the acid agent storage tank to the coolant tank, What is necessary is just to perform PID control etc. by the signal from a densitometer.

  In FIG. 2, in order to eliminate dilution by air from the horizontal direction in the coolant tank, the cylinder is installed. However, as shown in FIG. 7, the coolant tank is entirely covered with a lid or the like, and the cylinder is placed above the lid. The hydrogen concentration can be measured with high accuracy and responsiveness by installing and measuring the hydrogen concentration in the cylinder. In this case, the hydrogen concentration in the cylinder will be even higher and stable, and the responsiveness of the hydrogen concentration will increase, but the equipment cost will increase. You should consider.

  The coolant water containing silicon cutting powder whose pH is adjusted by hydrogen concentration management and whose oxidation is suppressed is partially or completely taken out from the coolant water tank after being operated for a predetermined time or a predetermined number of days, and is solid-liquid separated. In the coolant water, almost no gel or colloidal silica is present or only a small amount is present, so that solid-liquid separation can be easily performed and the separation time can be shortened. As a solid-liquid separation method, filtration, sedimentation separation, centrifugation, etc. may be performed alone or in combination. The separated coolant water can be returned to the coolant tank for reuse. Further, the separated silicon cutting powder can be reused as a silicon raw material, but is good as a silicon raw material because of its low oxidation rate.

  However, even if the method of the present invention is performed, if the pH of the coolant water eventually exceeds 4.3, hydrogen is always generated in a small amount, so that the oxidation of the silicon cutting powder is suppressed. Although it is, it will be in the progressing state. Therefore, in order to further suppress the oxidation of the silicon cutting powder, it is preferable to shorten the oxidation time of the silicon cutting powder by separating the generated silicon cutting powder from the coolant water at an early stage.

  Then, next, shortening of the oxidation time of the silicon cutting powder by solid-liquid separation is described.

  By the above-described hydrogen concentration control and water temperature control, the oxidation rate of the silicon cutting powder is suppressed. Suppressing the oxidation rate of silicon cutting powder means that the amount of generated hydrogen is reduced, the ratio of floating silicon cutting powder is decreased, the ratio of precipitated silicon cutting powder is increased, and expensive equipment such as filtration is required. Separation can be achieved by precipitation without use.

  An example thereof will be described with reference to FIG. By moving part or all of the coolant water in the coolant water tank used for a certain period of time to the stationary water tank 14 while containing silicon cutting powder, the acid agent 16 is added and stirred therein, and the pH is adjusted to 4 or less. Stops the oxidation of silicon and completely suppresses the generation of hydrogen. Then, it is left still for about several hours to several days, and solid-liquid separation is performed. The supernatant is recovered in the supernatant recovery water tank 17 and can be reused as the acid agent 16 or the acid agent 6 described in FIG. The excess supernatant is neutralized with an alkaline agent such as sodium hydroxide solution and discarded. The silicon grinding powder precipitated in the stationary water tank 14 can be recovered while maintaining a high metal silicon content.

(Comparative Example 1) No pH sensor control + No hydrogen concentration control + No water temperature control (Conventional normal operation method)
This will be described with reference to FIG. The silicon solidified mass 1 was cut with the blade 2 while the coolant water 5 was being applied. After the coolant water 5 was applied to the blade 2, the coolant water 5 was discharged to the subsequent coolant water tank 3, and the coolant water 5 was repeatedly applied to the blade to cool the blade 2. The coolant water 5 used was 300L. Since the coolant 5 was not subjected to pH control or water temperature control, it varied within a pH range of 7 to 8, and the water temperature varied within a range of 40 to 60 ° C. Since the silicon cutting powder was mixed into the coolant water 5, the slurry concentration gradually increased, and was used continuously for 2 days until the slurry concentration reached 100 g / L, and then discharged. Hydrogen was always generated from the coolant water 5 containing silicon cutting powder.

1 L of discharged coolant water was collected and suction filtered using filter paper 5A. The filtration pressure was 0.05 MPa. The filtration area was 78.5 cm ² . The time required for the filtration was about 3900 minutes, and it took a long time for the filtration. This is because most of the silicon is oxidized to gel or colloidal silica gel (analytically measured as SiO ₂ ). The obtained residue was Me-Si: 9.8% and SiO ₂ : 89.2%.

(Comparative example 2) With pH sensor control + Without hydrogen concentration control + Without water temperature control It demonstrates based on FIG. The silicon solidified mass 1 was cut with the blade 2 while the coolant water 5 was being applied. After the coolant water 5 was applied to the blade 2, the coolant water 5 was discharged to the subsequent coolant water tank 3, and the coolant water 5 was repeatedly applied to the blade 2 to cool the blade 2. The coolant water 5 used was 300L. The coolant water 5 was a glass electrode 18 for pH measurement, (1 + 20) sulfuric acid was used, the pH was controlled at 6, and the water temperature was not controlled. Although it was controlled at pH 6 at the beginning, the surface of the glass electrode of the pH meter 18 was gradually covered with deposits (fine silicon cutting powder), and the fluctuation of the pH gradually increased, and the pH ranged from 2 to 8. It showed a pH of 4 or less, which is a corrosion area of steel, and there was concern about corrosion of the steel part. The water temperature varied in the range of 40-60 ° C. Since the silicon cutting powder was mixed into the coolant water 5, the slurry concentration gradually increased, and was used continuously for 2 days until the slurry concentration reached 100 g / L, and then discharged. Hydrogen was always generated from the coolant water 5 containing silicon cutting powder.

1 L of discharged coolant water was collected and suction filtered using filter paper 5A. The filtration pressure was 0.05 MPa. The filtration area was 78.5 cm ² . The time required for the filtration was about 3500 minutes. The residue obtained, Me-Si: 20.1%, SiO 2: 78.5%.

  Similarly, when the coolant water is replaced with new water and the process is repeated three times, deposits further adhere to the surface of the glass electrode portion of the pH meter. The vicinity of 5 is indicated, and the coolant water always indicates pH 4 or less which is a corrosive pH region.

( Reference example ) With hydrogen concentration control + Without water temperature control Description will be made based on FIG. The silicon solidified mass 1 was cut with the blade 2 while the coolant water 5 was being applied. After the coolant water 5 was applied to the blade 2, the coolant water 5 was discharged to the subsequent coolant water tank 3, and the coolant water 5 was repeatedly applied to the blade 2 to cool the blade 2. The coolant water 5 used was 300L. In the upper part of the coolant tank 3, a hydrogen concentration sensor 9 was installed 15 cm above the water surface, and the hydrogen concentration was measured in advance to determine the set value of the hydrogen concentration.
Therefore, when the hydrogen concentration increases to 0.3%, the acid agent 6 ((1 + 20) sulfuric acid solution) is dropped into the coolant water tank 3, and when the hydrogen concentration reaches 0.1%, the dropping is stopped and the hydrogen concentration is reduced to 0.3. Control was made to be less than%. The above-mentioned cylinder for measuring hydrogen is not used. The water temperature was not controlled. As a result, the pH of the coolant 5 was measured batchwise so that the electrode of the pH meter was not adhered and solidified by fine silicon, and varied from pH 5 to 6.5, but the average value of pH was pH 5.5. The water temperature varied in the range of 40-60 ° C. Since the silicon cutting powder was mixed into the coolant water 5, the slurry concentration gradually increased, and was used continuously for 2 days until the slurry concentration reached 100 g / L, and then discharged. From the coolant water 5 containing silicon cutting powder, hydrogen was always generated, although it was slight.

1 L of discharged coolant water was collected and suction filtered using filter paper 5A. The filtration pressure was 0.05 MPa. The filtration area was 78.5 cm ² . The time required for filtration was about 200 minutes. The obtained residue was Me-Si: 95.0% and SiO ₂ : 4.0%. Compared with Comparative Example 1 and Comparative Example 2, the amount of gel or colloidal silica (SiO ₂ component) generated was suppressed, so that the filtration time could be greatly shortened.

(Embodiment 2) Hydrogen concentration control using cylinder + no water temperature control will be described with reference to FIG. The silicon solidified mass 1 was cut with the blade 2 while the coolant water 5 was being applied. After the coolant water 5 was applied to the blade 2, the coolant water 5 was discharged to the subsequent coolant water tank 3, and the coolant water 5 was repeatedly applied to the blade 2 to cool the blade 2. The coolant water 5 used was 300L. In the upper part of the coolant tank 3, the above-mentioned hydrogen measuring cylinder 8 (inner diameter 5 cm, length 1 m) is placed on the water surface so that the lower end is immersed in water (approximately 5 cm). The sensor 9 was installed 15 cm above the water surface, and the hydrogen concentration was continuously measured while preventing dilution of hydrogen generated from the water surface from the horizontal direction. The hydrogen concentration was measured in advance, and the set value of the hydrogen concentration was determined. Therefore, when the hydrogen concentration increases to 0.3%, the acid agent 6 ((1 + 20) sulfuric acid solution) is dropped into the coolant water tank 3, and when the hydrogen concentration reaches 0.1%, the dropping is stopped and the hydrogen concentration is reduced to 0.3. Control was made to be less than%. The water temperature was not controlled. As a result, the pH of the coolant 5 varied from pH 4.8 to 6, but the average pH was pH 5.3. The water temperature varied in the range of 40-60 ° C. Since the silicon cutting powder was mixed into the coolant water 5, the slurry concentration gradually increased, and was used continuously for 2 days until the slurry concentration reached 100 g / L, and then discharged. From the coolant water 5 containing silicon cutting powder, hydrogen was slightly generated but always generated.

1 L of discharged coolant water was collected and suction filtered using filter paper 5A. The filtration pressure was 0.05 MPa. The filtration area was 78.5 cm ² . The time required for the filtration was about 120 minutes. The obtained residue was Me-Si: 97.0% and SiO ₂ : 2.5%. Compared with the reference example , the filtration time could be further shortened by further suppressing the generation amount of gel-like or colloidal silica (SiO ₂ component).

(Embodiment 3) Hydrogen concentration control using cylinder + water temperature 30 ° C. control There will be described based on FIG. The silicon solidified mass 1 was cut with the blade 2 while the coolant water 5 was being applied. After the coolant water 5 was applied to the blade 2, the coolant water 5 was discharged to the subsequent coolant water tank 3, and the coolant water 5 was repeatedly applied to the blade 2 to cool the blade 2. The coolant water 5 used was 300L. In the upper part of the coolant tank 3, the above-mentioned hydrogen measuring cylinder 8 (inner diameter 5 cm, length 1 m) is placed on the water surface so that the lower end is immersed in water (approximately 5 cm). The sensor 9 was installed 15 cm above the water surface, and the hydrogen concentration was continuously measured while preventing dilution of hydrogen generated from the water surface from the horizontal direction. The hydrogen concentration was measured in advance, and the set value of the hydrogen concentration was determined. Therefore, when the hydrogen concentration increases to 0.3%, the acid agent 6 ((1 + 20) sulfuric acid solution) is dropped into the coolant water tank 3, and when the hydrogen concentration reaches 0.1%, the dropping is stopped and the hydrogen concentration is reduced to 0.3. Control was made to be less than%. Moreover, about the water temperature, the cooling pipe 11 was installed in the coolant water tank 3, and the water temperature in the coolant water tank 3 was controlled to 30 degrees C or less by flowing cooling water in it. As a result, the pH of the coolant 5 varied from pH 4.7 to 6.0, but the average pH was pH 5.2. The water temperature varied in the range of 25-30 ° C. Since the silicon cutting powder was mixed into the coolant water 5, the slurry concentration gradually increased, and was used continuously for 2 days until the slurry concentration reached 100 g / L, and then discharged. From the coolant water 5 containing silicon cutting powder, hydrogen was slightly generated but always generated.

1 L of discharged coolant water was collected and suction filtered using filter paper 5A. The filtration pressure was 0.05 MPa. The filtration area was 78.5 cm ² . The time required for filtration was about 60 minutes. The obtained residue was Me-Si: 98.6% and SiO ₂ : 1.0%. Although the pH was almost the same as in Example 2, the water concentration was often below the detection limit (0.1%) because the water temperature was controlled to 30 ° C. or lower. By further reducing the amount of gel or colloidal silica (SiO ₂ component) generated, the filtration time could be further shortened.

(Example 4) When silicon cutting powder was immediately separated The same control as in Example 2 was performed using the apparatus of FIG. The silicon solidified mass 1 was cut with the blade 2 while the coolant water 5 was being applied. After the coolant water 5 is applied to the blade 2, the coolant water 5 is put into the coolant water tank 5 and filtered by the filtration device 20 installed in the coolant water tank 5, and the filtrate is put into the coolant water temporary storage tank 25. The blade 2 was repeatedly applied as coolant water 5 to cool the blade 2. On the other hand, the silicon cutting powder 23 separated by the filtering device 20 was transferred to the silicon cutting powder storage tank 22 together with a part of coolant water by a pump 21 that operates intermittently. An aqueous solution adjusted to pH 2 with dilute sulfuric acid was previously introduced into the silicon cutting powder storage tank 22 to completely stop the oxidation reaction of the silicon cutting powder. The coolant water used was 300L. In the upper part of the coolant tank 3, the above-mentioned hydrogen measuring tube (inner diameter 5 cm, length 1 m) is placed on the water surface so that the lower end is immersed in water (about 5 cm). Was placed 15 cm above the water surface, and the hydrogen concentration was continuously measured while preventing dilution of hydrogen generated from the water surface in the horizontal direction. The hydrogen concentration was measured in advance, and the set value of the hydrogen concentration was determined. Therefore, when the hydrogen concentration increases to 0.3%, the acid agent 6 ((1 + 20) sulfuric acid solution) is dropped into the coolant water tank 3, and when the hydrogen concentration reaches 0.1%, the dropping is stopped and the hydrogen concentration is reduced to 0.3. Control was made to be less than%. Moreover, about the water temperature, the cooling pipe 11 was installed in the coolant water tank 3, and the water temperature in the coolant water tank 3 was controlled to 30 degrees C or less by flowing cooling water in it. The coolant water was used continuously for 2 days and then discharged. As a result, the pH of the coolant water varied from pH 4.7 to 5.8, but the average value of pH was pH 5.1. The water temperature varied in the range of 25-30 ° C. A small amount of hydrogen was always generated from the coolant water containing silicon cutting powder.

1 L of discharged coolant water (slurry concentration: 5 g / L) was collected and suction filtered using a filter paper 5A. The filtration pressure was 0.05 MPa. The filtration area was 78.5 cm ² . The time required for filtration was about 1 minute. The obtained residue was Me-Si: 99.5% and SiO ₂ : 0.2%. Compared with Example 3, the Me-Si ratio was higher by immediately adding silicon cutting powder into water adjusted to pH 2.

(Example 5) In Example 3, the entire amount of coolant water is discharged every 0.5 days and adjusted to pH 3. In the same manner as in Example 3, the pH and temperature of the coolant water are controlled, and the coolant water is used continuously. did. In Example 5, it used continuously for 0.5 days, and after that, the coolant water whole quantity (300L) was discharged | emitted to the stationary water tank 14 shown in FIG. Although the pH of the coolant water in 0.5 days fluctuated from 4.6 to 6.0, the average value of the pH was 5.3. The water temperature varied in the range of 25-30 ° C. The slurry concentration of the discharged coolant was 20 to 25 g / L. The discharged coolant water was adjusted to pH 3 by adding an acid agent 16 ((1 + 20) sulfuric acid solution) and allowed to stand for 1 day. Most of the silicon cutting powder settled, and the supernatant became almost transparent. The supernatant was transferred to another supernatant recovery water tank and used as an acid agent when the next coolant water was used. The silicon cutting powder deposited in the lower part of the stationary water tank was Me-Si: 98.8% and SiO ₂ : 0.8%.

(Example 6) In Example 3, half of the coolant water is discharged every 0.5 days and adjusted to pH 3. In the same manner as in Example 3, the pH and temperature of the coolant water are controlled, and the coolant water is used continuously. did. In Example 6, it was used continuously for 0.5 days, and then the coolant water containing the silicon cutting powder was used, and half of the coolant water (150 L) every 0.5 days (150 L) was for stationary use as shown in FIG. It discharged to the water tank 14. Although the pH of the coolant water in 0.5 days fluctuated from 4.5 to 5.8, the average value of the pH was 5.2. The water temperature varied in the range of 25-30 ° C. The slurry concentration of the discharged coolant was 20 to 25 g / L. The discharged coolant water was adjusted to pH 3 by adding an acid agent 16 ((1 + 20) sulfuric acid solution) and allowed to stand for 1 day. Most of the silicon cutting powder settled, and the supernatant became almost transparent. The supernatant was transferred to another supernatant recovery water tank and used as an acid agent when the next coolant water was used. The silicon cutting powder deposited in the lower part of the stationary water tank was Me-Si: 98.5% and SiO ₂ : 1.0%.

The silicon cutting powders collected in Examples 2 to 6 have a high metal silicon content of 90% or more, and can be said to be good silicon raw materials.

DESCRIPTION OF SYMBOLS 1 Silicon coagulum 2 Blade 3 Coolant water tank 4 Pump 5 Coolant water 6 Acidic agent 7 Pump 8 Tube 9 Hydrogen concentration sensor 10 Thermometer 11 Cooling device 12 Replenishing water 13 Lid 14 Standing water tank 15 Pump 16 Acidic agent 17 Supernatant water recovery Tank 18 pH meter 20 Filtration device 21 Pump 22 Silicon cutting powder storage tank 23 Silicon cutting powder 24 Pump 25 Coolant water temporary storage tank 26 Coolant water transfer pipe 27 Acid agent storage tank

Claims (6)

Cutting the silicon solidified lump while applying the coolant water, transferring the coolant water containing the generated silicon cutting powder to the coolant water tank, and setting the cylinder so that one side of the cylinder is immersed in the coolant surface in the coolant water tank, A coolant characterized in that the concentration of hydrogen generated from the water surface inside the cylinder is measured, and an acid agent is added to the coolant water in accordance with the hydrogen concentration value to suppress oxidation of the silicon cutting powder. Method for suppressing oxidation of silicon cutting powder in water.   The method for suppressing oxidation of silicon cutting powder in coolant water according to claim 1, wherein the acid agent is added so that the measured hydrogen concentration is a predetermined value or less.   The method for inhibiting oxidation of silicon cutting powder in coolant water according to claim 1 or 2, wherein the coolant water in the coolant water tank is circulated and used as coolant water for cutting the silicon coagulum.   2. The method according to claim 1, further comprising: extracting a part or all of the coolant water containing silicon cutting powder from the coolant water tank, setting the pH of the extracted coolant water to 4 or less, and stopping the oxidation of silicon. The method for suppressing oxidation of silicon cutting powder in coolant water according to any one of -3.   The method for suppressing oxidation of silicon cutting powder according to any one of claims 1 to 4, wherein the coolant water to be circulated is cooled before use.   An apparatus for suppressing oxidation of silicon cutting powder, which is installed so that one side is immersed in a coolant water tank, a pipe for transferring coolant water containing silicon cutting powder to the coolant water tank, and a coolant surface in the coolant water tank. A cylinder, a hydrogen concentration sensor installed inside the cylinder, and an acid agent storage tank capable of adjusting an input amount of the acid agent according to a hydrogen concentration value measured by the hydrogen concentration sensor An oxidation inhibitor for silicon cutting powder in coolant water.

Images