Synthetic quartz glass powder and silica glass powder, quartz glass product and method for producing same

Abstract

The present invention is a synthetic quartz glass powder, wherein the synthetic quartz glass powder contains an internal OH group therein, the synthetic quartz glass powder has a particle size distribution in which the weight of synthetic quartz glass powder having a particle diameter of more than 150 μm and 355 μm or less is 40% or more among the entire synthetic quartz glass powder, and among the synthetic quartz glass powder, the average internal OH group concentration Da of synthetic quartz glass powder a having a particle diameter of 250 μm or less and the average internal OH group concentration Db of synthetic quartz glass powder b having a particle diameter of more than 250 μm and 425 μm or less satisfy the relationship of formula (1) or formula (2). As a result, a synthetic quartz glass powder capable of suppressing the generation of bubbles at the time of melting during the production of a quartz glass product is provided.　Formula (1): (Da-Db) / Da≤40% when Da ≥ Db Formula (2): (Db-Da) / Db≤40% when Da ≤ Db

Description

Synthetic quartz glass powder and silica glass powder, as well as quartz glass products and their manufacturing methods

[0001] The present invention relates to synthetic quartz glass powder and silica glass powder, as well as to quartz glass products and methods for producing the same.

[0002] Quartz glass products used in fields such as optical communications and semiconductors require high purity. A known method for producing such quartz glass products is to obtain the desired product by melting synthetic quartz glass powder produced by the sol-gel method or glass gob crushing method. When producing quartz glass products, bubbles (gas bubbles) generated during melting can be problematic. One source of bubbles is the presence of internal OH (silanol) groups contained in the synthetic quartz glass powder.

[0003] The sol-gel method, one of the methods for producing synthetic quartz glass powder, involves hydrolyzing a metal alkoxide to obtain silica gel, drying the resulting silica gel, and then calcining it to obtain synthetic quartz glass powder for use in, for example, a crucible for pulling silicon single crystals. However, this sol-gel method has the problem that the OH (silanol) groups present during hydrolysis and gelation remain as residual internal OH groups in the particles even after calcination, resulting in a high internal OH group content. Therefore, methods such as those described in Patent Document 1, in which calcination is performed in an atmosphere with a low water vapor partial pressure, are known to reduce the internal OH group concentration.

[0004] However, as described in Patent Document 2, it is known that when silica gel powder is actually placed in a container and fired, the internal OH group concentration of the resulting synthetic quartz glass powder varies greatly depending on the position in the container during firing. Specifically, this method results in a variation of approximately 30 ppm, ranging from 50 to 80 ppm. To prevent this, a heat-resistant structure with good thermal conductivity is inserted into the silica gel powder in a heat-resistant container and fired, thereby suppressing the variation in the internal OH group concentration due to position.

[0005] As other methods, Patent Document 3 describes a method in which silica gel powder filled in a heat-resistant container is fired while introducing dehumidified gas with a dew point of -30°C or lower into the inside of the container, and Patent Document 4 describes a method in which, when firing silica gel powder to produce synthetic quartz glass powder, the silica gel powder is fired and then the resulting synthetic quartz glass powder is mixed until the measured value variation in the internal OH group concentration is within ±5%, thereby reducing the variation in the internal OH group concentration within the container. However, even when the variation within the container is reduced by these methods, bubbles still occur during melting when producing quartz glass products.

[0006] JP 2-289416 JP 8-175821 JP 8-26741 JP 10-182140 JP 2-199037

[0007] As described above, when manufacturing quartz glass products, there has been a problem of bubbles being generated during melting.

[0008] The present invention has been made in consideration of the above problems, and aims to provide synthetic quartz glass powder and silica glass powder that can suppress the generation of bubbles during melting in the production of quartz glass products.

[0009] The present invention has been made to solve the above-mentioned problems and provides a synthetic quartz glass powder which contains internal OH groups within the synthetic quartz glass powder, has a particle size distribution in which synthetic quartz glass powder with a particle size of more than 150 μm and up to 355 μm accounts for 40% or more by weight of the total synthetic quartz glass powder, and is characterized in that the average internal OH group concentration Da of synthetic quartz glass powder a with a particle size of 250 μm or less and the average internal OH group concentration Db of synthetic quartz glass powder b with a particle size of more than 250 μm and up to 425 μm satisfy the relationship of the following formula (1) or (2): If Da≧Db, then (Da−Db) / Da≦40%...formula (1) If Da≦Db, then (Db−Da) / Db≦40%...formula (2)

[0010] Such synthetic quartz glass powder has an internal OH group concentration within the above range between particle sizes, which makes it possible to suppress the occurrence of uneven melting due to differences in internal OH group concentration during melting in the production of quartz glass products, and as a result, to suppress the occurrence of bubbles (air bubbles) in the quartz glass products.

[0011] In this case, it is preferable that the weight of the synthetic quartz glass powder having a particle size of more than 425 μm is 10% or less of the total weight of the synthetic quartz glass powder.

[0012] In this way, by reducing the proportion of synthetic quartz glass powder with a relatively large particle size of over 425 μm, melting can be made easier.

[0013] The present invention also provides a quartz glass product obtained by using any of the above synthetic quartz glass powders as a raw material.

[0014] Such quartz glass products are manufactured using synthetic quartz glass powder in which the internal OH group concentration between particle sizes falls within the above range, and therefore the generation of bubbles can be suppressed.

[0015] The present invention also provides a method for producing a quartz glass product, characterized in that the quartz glass product is produced using any of the synthetic quartz glass powders described above as a raw material.

[0016] When a quartz glass product is manufactured using this manufacturing method, it is produced using synthetic quartz glass powder whose internal OH group concentration between particle sizes falls within the above range, so that the generation of bubbles within the quartz glass product can be suppressed.

[0017] The present invention has been made to solve the above-mentioned problems and provides a silica glass powder which contains internal OH groups inside, has a particle size distribution in which silica glass powder having a particle size of more than 150 μm and not more than 355 μm accounts for 40% or more by weight of the total silica glass powder, and is characterized in that an average internal OH group concentration Da of silica glass powder a having a particle size of not more than 250 μm and an average internal OH group concentration Db of silica glass powder b having a particle size of more than 250 μm and not more than 425 μm satisfy the relationship of the following formula (1) or (2): When Da≧Db, (Da−Db) / Da≦40%...formula (1) When Da≦Db, (Db−Da) / Db≦40%...formula (2)

[0018] Such silica glass powder has an internal OH group concentration between the particle sizes falling within the above range. This makes it possible to suppress uneven melting due to differences in the internal OH group concentration during melting in the production of silica glass products, and as a result, to suppress the generation of bubbles (gas bubbles) in the silica glass products. In the description of the present invention, the term "silica glass" has the same meaning as the term "quartz glass" and is a synonym. Furthermore, "silica glass" is a concept that includes "synthetic quartz glass" and is not limited to silica glass (quartz glass) produced by synthetic methods.

[0019] The synthetic quartz glass powder and silica glass powder of the present invention have an internal OH group concentration within a specific range between specific particle sizes, which makes it possible to suppress the occurrence of uneven melting due to differences in the internal OH group concentration during melting in the production of quartz glass products (silica glass products), and as a result, to suppress the occurrence of bubbles in the quartz glass products (silica glass products).

[0020] As mentioned above, conventionally, when manufacturing quartz glass products (silica glass products), there has been a problem of bubbles being generated during melting. In order to overcome this problem, the present inventors have conducted extensive research and found that by keeping the difference in internal OH group concentration between particle sizes within a specific range, it is possible to suppress uneven melting due to differences in internal OH group concentration and to inhibit the generation of bubbles, which led to the present invention.

[0021] The present invention will be described in more detail below. The present invention relates to a synthetic quartz glass powder containing internal OH groups therein, having a particle size distribution in which synthetic quartz glass powder having a particle size of more than 150 μm and not more than 355 μm accounts for 40% or more by weight of the total synthetic quartz glass powder, and wherein the average internal OH group concentration Da of synthetic quartz glass powder a having a particle size of not more than 250 μm and the average internal OH group concentration Db of synthetic quartz glass powder b having a particle size of more than 250 μm and not more than 425 μm satisfy the relationship of the following formula (1) or (2): When Da≧Db, (Da−Db) / Da≦40%...formula (1) When Da≦Db, (Db−Da) / Db≦40%...formula (2)

[0022] The present invention also provides a silica glass powder containing internal OH groups, having a particle size distribution in which silica glass powder having a particle size of more than 150 μm and not more than 355 μm accounts for 40% or more by weight of the entire silica glass powder, and wherein an average internal OH group concentration Da of silica glass powder a having a particle size of not more than 250 μm and an average internal OH group concentration Db of silica glass powder b having a particle size of more than 250 μm and not more than 425 μm satisfy the relationship of the following formula (1) or (2): When Da≧Db, (Da−Db) / Da≦40%...formula (1) When Da≦Db, (Db−Da) / Db≦40%...formula (2)

[0023] The following description will focus on the synthetic silica glass powder of the present invention, but all of the following can be applied to the description of the silica glass powder of the present invention. That is, "synthetic silica glass" can be read as "silica glass," "synthetic silica glass powder" can be read as "silica glass powder," and "quartz glass product" can be read as "silica glass product."

[0024] According to the inventors' research, when thermal dehydration is performed to reduce the OH group concentration, regardless of the manufacturing method of synthetic quartz glass powder, such as the sol-gel method or glass gob crushing method, powders with smaller particle sizes tend to be more easily dehydrated due to their larger specific surface area. In other words, the smaller the particle size, the lower the internal OH group concentration tends to be. For example, in Patent Document 5, silica gel is crushed, calcined, and classified, and then each classified powder is subjected to oxyhydrogen fusion to obtain bubble-free quartz glass ingots with controlled internal OH group concentrations. However, the document only covers the internal OH group concentration of the resulting ingot, and makes no mention of the relationship between the difference in internal OH group concentration between specific particle sizes in the powder state and bubbles.

[0025] In contrast, in the case of powder obtained only by crushing glass lumps, the internal OH group concentration increases depending on the atmosphere during crushing, and conversely, the smaller the particle size, the higher the internal OH group concentration tends to be. In this case, too, as in the case described above, if the difference in internal OH group concentration between particle sizes becomes large, it will cause bubbles.

[0026] In the present invention, by keeping the difference in internal OH group concentration between particle sizes within a specific range, melting unevenness due to differences in internal OH group concentration can be suppressed and bubble formation can be suppressed. More specifically, synthetic quartz glass powder is classified into synthetic quartz glass powder a (small particles) with a relatively small particle size of 250 μm or less and synthetic quartz glass powder b (large particles) with a relatively large particle size of more than 250 μm and 425 μm or less, and the average internal OH group concentration Da of synthetic quartz glass powder a and the average internal OH group concentration Db of synthetic quartz glass powder b are compared and defined. The above formulas (1) and (2) stipulate that (Da - Db) / Da or (Db - Da) / Db be 40% or less. If the difference in these internal OH group concentrations exceeds 40%, bubble formation in the quartz glass product cannot be suppressed. Furthermore, the difference in these internal OH group concentrations is preferably 35% or less, and more preferably 30% or less. In addition, when Da = Db, both (Da - Db) / Da in formula (1) and (Db - Da) / Db in formula (2) are 0%, and both formulas (1) and (2) are satisfied. This case is also within the scope of the present invention.

[0027] The synthetic quartz glass powder of the present invention has a particle size distribution in which the weight ratio of synthetic quartz glass powder having a particle size of more than 150 μm and not more than 355 μm is 40% or more. Synthetic quartz glass powder having such a particle size distribution is suitable for use in melting to manufacture quartz glass products.

[0028] Furthermore, the synthetic silica glass powder of the present invention is premised on the inclusion of internal OH groups within the powder, and the concentration of these internal OH groups is preferably 200 ppm or less, and more preferably 150 ppm or less, for all particle sizes. When the internal OH group concentration is 200 ppm or less, the generation of bubbles can be more effectively suppressed. Note that ppm in the description of the present invention refers to ppm by weight.

[0029] Furthermore, in the synthetic quartz glass powder of the present invention, it is preferable that the weight of synthetic quartz glass powder having a particle size of more than 425 μm is 10% or less of the total synthetic quartz glass powder. By reducing the proportion of synthetic quartz glass powder with a relatively large particle size of more than 425 μm, melting can be made easier.

[0030] In defining the particle size distribution of the synthetic quartz glass powder of the present invention, the particle size distribution can be determined, for example, using a metal sieve. More specifically, it can be determined by classifying the powder using metal sieves with openings of 425, 355, and 150 μm in accordance with JIS Z-8801 and measuring the weight of the powder remaining on the sieve. A particle size of more than 150 μm refers to the powder remaining on the sieve when vibrated for 10 minutes using a sieve with openings of 150 μm, and a particle size of 355 μm or less refers to the powder that passes through a sieve with openings of 355 μm when vibrated for 10 minutes.

[0031] The internal OH group concentration of the synthetic quartz glass powder can be measured using infrared spectroscopy (IR). Specifically, an FT-IR (Nicolet iS10, manufactured by Thermo Fisher Scientific) is fitted with a diffuse reflectance accessory, UpDRIFT, and the internal OH group concentration of the powder can be measured by the diffuse reflectance method. In this case, an aluminum plate can be used for background measurement.

[0032] The synthetic quartz glass powder of the present invention may be produced by any method as long as it satisfies the above requirements. However, methods such as the sol-gel method, which obtain synthetic quartz glass powder via a porous dry gel containing a large amount of OH groups, are not suitable because they require an extremely low concentration of OH groups.

[0033] Furthermore, the average internal OH group concentration in synthetic quartz glass powder varies depending on the particle size, depending on the manufacturing conditions. For example, when thermally dehydrated, the smaller the particle size of synthetic quartz glass powder (the larger the specific surface area), the easier it is for OH groups to escape. On the other hand, when pulverized under high humidity or in water, the opposite phenomenon occurs. That is, the smaller the particle size of synthetic quartz glass powder (the larger the specific surface area), the easier it is for OH groups to enter. Based on these findings, the manufacturing method of the synthetic quartz glass powder of the present invention can be, for example, as follows. This method adjusts the internal OH group concentration ratio between particle sizes of the synthetic quartz glass powder by pulverizing synthetic quartz glass chunks, classifying and washing the pulverized product, and combining this with a step of reducing internal OH groups by oxygen treatment or the like.

[0034] That is, the method for producing synthetic quartz glass powder of the present invention can be a method comprising the following steps: (Step 1) Prepare raw synthetic quartz glass masses. (Step 2) Crush the prepared synthetic quartz glass masses to obtain raw synthetic quartz glass powder. (Step 3) Classify the raw synthetic quartz glass powder. (Step 4) Acid-wash the classified raw synthetic quartz glass powder. (Step 5) Reduce the average internal OH group concentration of the raw synthetic quartz glass powder that has undergone acid washing. Of these, Step 2 has the effect of increasing the internal OH group concentration of the synthetic quartz glass powder, and Step 4 may also have the effect of increasing the internal OH group concentration of the synthetic quartz glass powder. Meanwhile, Step 5 reduces the internal OH group concentration of the synthetic quartz glass powder.

[0035] As described above, in the steps of increasing the internal OH group concentration of the synthetic quartz glass powder (specifically, steps 2 and 4), the smaller the particle size, the higher the internal OH group concentration. This is because the smaller the particle size, the larger the specific surface area. On the other hand, in the step of decreasing the internal OH group concentration of the synthetic quartz glass powder (specifically, step 5), the smaller the particle size, the lower the OH group concentration. This is also because the smaller the particle size, the larger the specific surface area. By utilizing the difference in the increase / decrease in internal OH group concentration due to particle size distribution in each of these steps, the difference in internal OH group concentration between particle sizes is reduced. Those skilled in the art can achieve the satisfaction of formula (1) or formula (2) that the synthetic quartz glass powder of the present invention must satisfy by adjusting the conditions of each step.

[0036] In step 1, synthetic quartz glass gobs are prepared as raw materials. The synthetic quartz glass gobs are preferably prepared by a soot method using a soot body. For example, the OVD (Outside Vapor Deposition) method is preferred. In a typical OVD method, silicon tetrachloride or the like, which is the raw material for quartz glass, is first introduced into an oxyhydrogen flame in a burner, and the quartz glass particles (such as silicon dioxide) synthesized by a hydrolysis reaction are attached to a rotating starting material. The soot grown from this is then heated and sintered to become transparent, resulting in a synthetic quartz glass gob.

[0037] The method of pulverization in step 2 is not particularly limited, but it can be carried out by pulverizing with a hammer in an atmospheric atmosphere. By pulverizing the synthetic quartz glass lump in an atmospheric atmosphere, the surface of the pulverized synthetic quartz glass powder comes into contact with moisture in the air, and the internal OH group concentration of the synthetic quartz glass powder increases.

[0038] The classification method in step 3 is not particularly limited, and known methods such as a method using a metal sieve can be used. Classification only slightly changes the internal OH group concentration of the synthetic quartz glass powder. This is because the classification process causes a reaction, but the effect of changing the internal OH group concentration is very small.

[0039] Step 4, acid washing, is a step in which the crushed and classified synthetic quartz glass powder is washed with acid, and known methods can be used. For example, washing can be performed using hydrochloric acid or hydrofluoric acid (hydrofluoric acid). This step may increase the internal OH group concentration of the synthetic quartz glass powder. In particular, when hydrofluoric acid is used, etching tends to increase the internal OH group concentration.

[0040] Step 5, the process of reducing the average internal OH group concentration of the synthetic quartz glass powder, can be referred to as a dehydroxylation step or a dehydroxylation step. For example, this can be done by heating at a high temperature in a dry atmosphere (an atmosphere that is substantially moisture-free) (thermal dehydration). The dry atmosphere can be a dry oxygen-containing gas, particularly a commercially available 100% oxygen gas or dry air. Heating can be performed at, for example, 800°C or higher. This reduces the internal OH group concentration of the synthetic quartz glass powder. This step can be referred to as a dehydroxylation step or a dehydroxylation step.

[0041] Furthermore, even if the synthetic quartz glass powder of the present invention is produced by a manufacturing method other than the above-mentioned manufacturing method, it can be obtained by selecting one that satisfies the specified range of internal OH group concentration between particle sizes in the synthetic quartz glass powder of the present invention.

[0042] The synthetic quartz glass powder of the present invention as described above has an internal OH group concentration within a specific range between specific particle sizes, so that when melted to produce quartz glass products, uneven melting due to differences in internal OH group concentration can be suppressed, and as a result, the generation of bubbles in the quartz glass products can be suppressed.

[0043] Furthermore, in the method for manufacturing a quartz glass product of the present invention, the above-mentioned synthetic quartz glass powder of the present invention can be used as a raw material to manufacture a quartz glass product. In this way, a quartz glass product obtained by using the above-mentioned synthetic quartz glass powder of the present invention as a raw material can be manufactured.

[0044] Such quartz glass products are manufactured using synthetic quartz glass powder in which the internal OH group concentration between particle sizes falls within the above range, and therefore the generation of bubbles can be suppressed.

[0045] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0046] Example 1: 50 kg of synthetic quartz glass lump with an average internal OH group concentration of 120.8 ppm was prepared by the OVD method. The synthetic quartz glass lump was crushed with an Fe-based hammer in an air atmosphere and classified using 150 μm and 425 μm metal sieves. It was then acid-washed with 33% hydrochloric acid for 16.5 hours and then with 19% hydrofluoric acid for 10 minutes. It was then heated in a tubular furnace at 1100°C with a dry oxygen-containing gas flowing through it and rotating at a throughput of 5 kg / hr, yielding synthetic quartz glass powder.

[0047] Next, the particle size distribution and internal OH group concentration of the synthetic quartz glass powder produced in Example 1 were evaluated as follows.

[0048] (Particle size distribution) The powder was classified using metal sieves with mesh sizes of 425, 355, and 150 μm in accordance with JIS Z-8801. Next, the weight of the powder remaining on the sieve was measured, and the weight ratios of particles greater than 150 μm and less than 355 μm and particles greater than 425 μm relative to the total weight were determined. "More than 150 μm" refers to particles remaining on the sieve when vibrated for 10 minutes using a sieve with a mesh size of 150 μm, and "355 μm or less" refers to particles that passed through a sieve with a mesh size of 355 μm when vibrated for 10 minutes.

[0049] (Measurement of Average Internal OH Group Concentration of Synthetic Quartz Glass Powder) Synthetic quartz glass powder was classified using metal sieves with mesh sizes of 425 and 250 μm in accordance with JIS Z-8801 to obtain synthetic quartz glass powder a of 250 μm or less and synthetic quartz glass powder b of more than 250 μm and 425 μm or less. Next, the average internal OH group concentration of each synthetic quartz glass powder a and b was measured using IR. Specifically, a diffuse reflectance accessory UpDRIFT was attached to an FT-IR (Nicolet iS10: manufactured by Thermo Fisher Scientific Inc.) and the internal OH group concentration of the synthetic quartz glass powder was measured by the diffuse reflectance method (measurement of internal OH group concentration of powder). An aluminum plate was used for background measurement. The internal OH group concentration of the powder was calculated from the obtained spectrum after Kubelka-Munk transformation using the following method. First, the 3673 cm peak attributable to internal OH groups was measured. －１ and virtually no absorption at 4100 cm －１ From the difference, the peak height 1 was calculated as 2651 cm derived from the silica skeleton. －１ and virtually no absorption at 4100 cm －１ Peak height 2 was calculated from the difference between the peak height 1 and the peak height 2. Next, peak height 1 was divided by peak height 2 to calculate the sample peak height ratio m (peak height 1 / peak height 2). Finally, the sample peak height ratio m was substituted into a relational expression obtained from the relationship between the internal OH group concentration and the peak height ratio of a plurality of standard samples with known internal OH group concentrations, which were obtained by the same analytical procedure, to calculate the internal OH group concentration.

[0050] The particle size distribution of the synthetic quartz glass powder obtained in Example 1 was measured, and the weight of particles greater than 150 μm and less than 355 μm accounted for 65.4% of the total synthetic quartz glass powder, and the weight of particles greater than 425 μm accounted for 3.1%.

[0051] The internal OH group concentration measurements of the synthetic quartz glass powder obtained in Example 1 were carried out three times for each of the synthetic quartz glass powders a and b. The results for the synthetic quartz glass powder a were 84.9 ppm, 82.1 ppm, and 84.6 ppm. The average of the three measurements was calculated to be 83.9 ppm, which was designated as the average internal OH group concentration Da for the synthetic quartz glass powder a. The results for the synthetic quartz glass powder b were 96.1 ppm, 98.9 ppm, and 96.2 ppm. The average of the three measurements was calculated to be 97.1 ppm, which was designated as the average internal OH group concentration Db for the synthetic quartz glass powder b. In this case, since Da≦Db, formula (2) was applied, and (Db−Da) / Db was 13.6% ("Calculation result 2" in the table).

[0052] (Bubble Density) Next, a quartz glass crucible was manufactured using the synthetic quartz glass powder of Example 1, and the number of bubbles exposed on the inner surface of the quartz glass crucible was measured. Specifically, a crucible was manufactured by arc melting using natural quartz powder as the raw material powder for the outer layer and the synthetic quartz glass powder of Example 1 as the raw material powder for the inner layer. Next, based on the evaluation method of JP 2013-14518 A, the bubble density of the crucible composite layer after VBT (vacuum firing test) was measured. For each sample, a vacuum of 2 × 10 －２ The sample was heated to a pressure of 1000 Pa or less and held at 1650°C for 2 hours and 10 minutes to generate bubbles. After that, the density of bubbles exposed on the surface of each sample was visually confirmed. As a result, the number of bubbles exposed on the inner surface was 0.03 / cm. ２ It was.

[0053] The average internal OH group concentration and the number of bubbles exposed on the inner surface of the synthetic quartz glass powder are shown in Table 1. The measurements performed in Example 1 were also performed in the subsequent Examples and Comparative Examples, and the average internal OH group concentration and the number of bubbles exposed on the inner surface are shown in Tables 1 and 2.

[0054] Example 2: 50 kg of synthetic quartz glass lump with an average internal OH group concentration of 124.8 ppm was prepared by the OVD method. The synthetic quartz glass lump was crushed in an air atmosphere with an Fe-based hammer and classified using 150 μm and 425 μm metal sieves. It was then acid-washed with 33% hydrochloric acid for 16.5 hours and then with 19% hydrofluoric acid for 10 minutes. Subsequently, the lump was heated at a throughput rate of 9 kg / hr while rotating in a tubular furnace at 1100 °C while flowing dry oxygen-containing gas, yielding synthetic quartz glass powder. Measurement of the particle size distribution of the obtained powder revealed that the weight of the powder was greater than 150 μm and less than 355 μm, and the weight of the powder greater than 425 μm was 5.0%.

[0055] Example 3: 50 kg of synthetic quartz glass lump with an average internal OH group concentration of 96.8 ppm was prepared by the OVD method. The synthetic quartz glass lump was crushed in an air atmosphere with an Fe-based hammer and classified using 150 μm and 425 μm metal sieves. It was then acid-washed with 33% hydrochloric acid for 16.5 hours and then with 19% hydrofluoric acid for 10 minutes. Subsequently, dry oxygen-containing gas was passed through a tubular furnace at 1250 °C, and the mixture was heated at a throughput of 9 kg / hr while rotating, yielding synthetic quartz glass powder. The particle size distribution of the resulting powder was measured, and it was found that the weight of the powder was greater than 150 μm and less than 355 μm, and the weight of the powder greater than 425 μm was 62.7%, and 4.9%, respectively.

[0056] Example 4 The acid-washed powder obtained in Example 3 was heated in a tubular furnace at 1250° C. while rotating it in a flow of dry oxygen-containing gas at a throughput of 5 kg / hr to obtain a synthetic quartz glass powder.

[0057] Example 5: 50 kg of synthetic quartz glass lump with an average internal OH group concentration of 85.3 ppm was prepared by the OVD method. The synthetic quartz glass lump was crushed with an Fe-based hammer in an air atmosphere and classified using 150 μm and 425 μm metal sieves. It was then acid-washed with 33% hydrochloric acid for 16.5 hours and then with 19% hydrofluoric acid for 10 minutes. Subsequently, dry oxygen-containing gas was passed through a tubular furnace at 800 °C, and the mixture was heated at a throughput of 5 kg / hr while rotating, yielding synthetic quartz glass powder. The particle size distribution of the resulting powder was measured, and it was found that the weight of the powder was greater than 150 μm and less than 355 μm, and the weight of the powder greater than 425 μm was 73.0%, and 3.8%, respectively.

[0058] Comparative Example 1 The acid-washed powder obtained in Example 3 was heated in a tubular furnace at 1250° C. while rotating it in a flow of dry oxygen-containing gas at a throughput of 3 kg / hr to obtain a synthetic quartz glass powder.

[0059] (Comparative Example 2) Synthetic quartz glass powder a having a particle size of 250 μm or less obtained in Example 2 and synthetic quartz glass powder b having a particle size of more than 250 μm and 425 μm or less obtained in Example 3 were mixed in a 1:1 ratio by weight to obtain a synthetic quartz glass powder.

[0060] The number of bubbles exposed on the inner surface is 1.5 / cm ２ One of the criteria is that the number of particles is 1.0 or less per cm ２ It is more preferable that the number of bubbles exposed on the inner surface is less than 1.5. As can be seen from Tables 1 and 2, when Calculation Result 1 satisfies Formula (1) or Calculation Result 2 satisfies Formula (2) (Examples 1 to 5), the number of bubbles exposed on the inner surface of the quartz glass crucible was sufficiently small, and good results were obtained. In particular, in Examples 1 to 3 and 5, where the difference in internal OH group concentration was 35% or less, the number of bubbles exposed on the inner surface was particularly small, and good results were obtained. On the other hand, in the comparative example, the number of bubbles exposed on the inner surface was 1.5 / cm. ２ This exceeded the standard and was not a good result.

[0061] The present invention is not limited to the above-described embodiments, which are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that provides similar effects is included within the technical scope of the present invention.

Claims

1. A synthetic quartz glass powder containing internal OH groups within the synthetic quartz glass powder, having a particle size distribution in which synthetic quartz glass powder having a particle size of more than 150 μm and no greater than 355 μm accounts for 40% or more by weight of the total synthetic quartz glass powder, and wherein the average internal OH group concentration Da of synthetic quartz glass powder a having a particle size of no greater than 250 μm and the average internal OH group concentration Db of synthetic quartz glass powder b having a particle size of more than 250 μm and no greater than 425 μm satisfy the relationship of the following formula (1) or (2): When Da≧Db, (Da−Db) / Da≦40%...formula (1) When Da≦Db, (Db−Da) / Db≦40%...formula (2) 2. The synthetic quartz glass powder according to claim 1, characterized in that the weight of the synthetic quartz glass powder having a particle size of more than 425 μm accounts for 10% or less of the total weight of the synthetic quartz glass powder.

3. A quartz glass product obtained by using the synthetic quartz glass powder according to claim 1 or 2 as a raw material.

4. A method for producing a quartz glass product, comprising using the synthetic quartz glass powder according to claim 1 or 2 as a raw material to produce the quartz glass product.

5. Silica glass powder, wherein the silica glass powder contains internal OH groups, and has a particle size distribution in which silica glass powder having a particle size of more than 150 μm and not more than 355 μm accounts for 40% or more by weight of the total silica glass powder, and wherein an average internal OH group concentration Da of silica glass powder a having a particle size of not more than 250 μm and an average internal OH group concentration Db of silica glass powder b having a particle size of more than 250 μm and not more than 425 μm satisfy the relationship of the following formula (1) or (2): When Da≧Db, (Da−Db) / Da≦40% ...formula (1) When Da≦Db, (Db−Da) / Db≦40% ...formula (2)

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