JP2017036203A - Opaque quartz glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optically highly-homogeneous opaque quartz glass excellent in shading property of infrared light.SOLUTION: There is provided opaque quartz glass produced by using powder in which a number density of silica aggregate is 100/cmor lower.SELECTED DRAWING: None

Description

  The present invention relates to an opaque quartz glass that is excellent in infrared light shielding properties and optically highly homogeneous.

  Opaque quartz glass is used for applications that require heat barrier properties. The heat shielding property is related to the infrared light shielding property, and the opaque quartz glass having a higher light shielding property is superior in the heat shielding property.

  Conventionally, as a method for producing opaque quartz glass, a method in which a foaming agent such as silicon nitride is added to crystalline silica or amorphous silica and melted (for example, see Patent Documents 1 to 3) is known. However, in the opaque quartz glass manufactured by such a manufacturing method, the foaming agent is vaporized to form pores, so that the average diameter of the pores is large, and those having strength that can be used practically have low pore content density. There is a problem that the light shielding property of infrared light is lowered.

  On the other hand, a method in which a molded body of amorphous silica powder is heated at a temperature equal to or lower than its melting temperature without adding a foaming agent, the heat treatment is interrupted before being fully densified, and partially sintered (for example, Patent Document 4) has also been proposed. In the opaque quartz glass manufactured by such a manufacturing method, it is possible to reduce the average diameter of the pores. However, if sintering is performed until the pores become closed pores, the density of the pores decreases, and the infrared light does There is a problem that the light-shielding property is lowered, and there is a problem that the average diameter of the pores is too small and the light-shielding property of long-wavelength infrared light is lowered. Further, according to this method, there is a problem that a density distribution is easily generated in the sintered body of the opaque quartz glass due to the temperature distribution in the electric furnace, and it is difficult to obtain a homogeneous opaque quartz glass having a large size.

  Moreover, although the method (for example, refer patent document 5) of heat-firing a quartz glass porous body under high-pressure conditions is proposed, in the opaque quartz glass manufactured by such a manufacturing method, wavelength 200-5000 nm is proposed. The light transmittance is 0.5 to 2.0%, and there is a problem that the light blocking property of infrared light on the long wavelength side is lowered. Moreover, since this method performs high-pressure baking, a special apparatus is required, and it cannot be said that it is a simple method.

JP-A-4-65328 JP-A-5-254882 JP 7-61827 A JP-A-7-267724 WO2008 / 069194

  An object of the present invention is to provide an opaque quartz glass which is excellent in infrared light shielding properties and optically highly homogeneous.

  As a result of intensive studies, the present inventors mixed amorphous silica powder and pore former powder (hereinafter sometimes simply referred to as pore former) so as to reduce amorphous silica aggregates, After forming the mixed powder, it was found that an opaque quartz glass with uniform pores can be obtained by sintering at a predetermined temperature, and the present invention has been completed. Note that the amorphous silica aggregate is an overview of the entire mixed powder because the pore-forming agent is not uniformly dispersed in the amorphous silica powder when the mixing of the amorphous silica powder and the pore-forming agent powder is insufficient. In this case, it indicates that the amorphous silica exists locally in a certain size. Further, here, the obtained opaque quartz glass has uniform pores, that is, when the entire glass is looked down, the pore density is locally low and the portion where the silica density is high is extremely small. Therefore, it has been found that the opaque quartz glass has high optical homogeneity.

  Hereinafter, the present invention will be described in more detail.

  The opaque quartz glass of the present invention has uniform pores, that is, when the entire glass is looked down, the pore density is locally low, and the portion where the silica density is high is extremely small. Therefore, the opaque quartz glass of the present invention has high optical homogeneity. In particular, the opaque quartz glass of the present invention has a very small portion that locally transmits infrared light, and can be suitably used as a member of a heating device. Optically high homogeneity can be shown by parameters obtained by an image processing method described later.

The present invention is a histogram obtained by image processing, binarized by setting a threshold value so as to be separated into a portion through which visible light is transmitted and a portion other than that, and an area of 0.04 mm ² or more of the portion exceeding the threshold value The present invention relates to an opaque quartz glass characterized in that m / R is 50 or less, where m is the number of portions (hereinafter referred to as “white spots”) and the area of the entire image is Rcm ² . Here, the white spots in the opaque quartz glass indicate a portion of a certain size through which visible light is transmitted.

  In the present invention, the image subjected to image processing can be exemplified by an image obtained by observing opaque quartz glass using a general optical microscope, and the observation magnification is preferably x50. An image to be subjected to image processing can be analyzed with sufficient accuracy if an observation image of 50 times the optical microscope is used and at least a range of 1/4 or more is selected as a target.

  The optical microscope is preferably connected to a personal computer in which image processing software is installed. Thus, it is possible to perform image processing on a personal computer immediately after taking an observation image.

  The image processing may be performed by at least one of commercially available software and free software, and free software such as ImageJ 1.46 can be exemplified. See the description of the examples for the specific procedure. It is sufficient that the image processing software can convert (binarize) the image to black and white with a specific threshold as a reference, and select all or part of the image, and within that range, the vertical axis represents the number of pixels, It is preferable if it is possible to draw a histogram with the horizontal axis as the luminance value. An example of a histogram is shown in FIG.

  In the present application, if the histogram obtained by the image processing described above is optically completely homogeneous in the target range of the observation image of the opaque quartz glass, it can be assumed that the histogram draws a normal distribution. If there is a part having a luminance that is so large that it deviates from the normal distribution, the image is binarized between the part and the other part, and after black and white display, a part having a large luminance exists continuously, and A portion having a size exceeding the area can be defined as a white portion, and the number thereof can be determined as m described above.

  It is sufficient to determine the threshold as follows. That is, in the histogram actually obtained as shown in FIG. 2, when the luminance indicating the maximum number of pixels is a and the lower luminance among the luminances indicating the minimum number of pixels is b, Assume a normal distribution with a range of 2 × (ab). In such a case, the normal distribution has a luminance ranging from b to a + a−b (that is, 2a−b). The luminance 2a-b is used as a threshold value, and the image is binarized. By processing this binarized image, it is possible to specify a white spot. Specifically, after binarization, a portion having a predetermined area or more among the portions having luminance of 2a-b or more is set as a white-out portion.

  The opaque quartz glass of the present application preferably has a transmittance of 1% or less at a wavelength of 1.5 μm to 5 μm when the sample thickness is 1 mm. Thereby, it can be suitably used for a member of a heating device or the like.

  The opaque quartz glass of the present application preferably has a transmittance of 0.5% or less at a wavelength of 3 μm to 5 μm when the sample thickness is 1 mm. Thereby, it can be suitably used for a member of a heating device or the like.

  Next, the manufacturing method of the opaque quartz glass of this invention is demonstrated.

The method for producing opaque quartz glass of the present invention uses a mixed powder of an amorphous silica powder and a pore former powder as a raw material, and a histogram obtained by image processing from the mixed powder has the largest number of pixels for each luminance value. The luminance value is set as a threshold value and binarized. Among the portions exceeding the threshold value, n is the number of portions having an area of 0.04 mm ² or more, and the entire image area is Scm ² , and n / S is 100 or less. It is characterized by being.

  In the production method of the present invention, the image of the mixed powder subjected to image processing can be exemplified by an image obtained by observing opaque quartz glass using a general optical microscope, and the observation magnification is preferably × 50. . The optical microscope may be a reflection microscope. For example, a method in which a mixed powder of amorphous silica powder and pore former is sandwiched between quartz glass plates so that the thickness of the powder layer is about 0.5 to 1.5 mm from both sides, and an image is taken with a reflection microscope. Can be illustrated.

  The optical microscope is preferably connected to a personal computer in which image processing software is installed. Thus, it is possible to perform image processing on a personal computer immediately after taking an observation image.

  The image processing of the mixed powder may be performed in the same manner as in the case of the opaque quartz glass except that the threshold is set to the luminance indicating the maximum number of pixels.

  Hereinafter, the method for producing the opaque quartz glass of the present invention will be described in detail for each step. As can be said for all processes, it is necessary to sufficiently select the equipment to be used so that impurity contamination does not occur during the process.

(1) Selection of raw material powder First, the amorphous silica powder used by this invention is selected. The method for producing the amorphous silica powder is not particularly limited. For example, amorphous silica powder produced by hydrolysis of silicon alkoxide or amorphous silica produced by hydrolyzing silicon tetrachloride with an oxyhydrogen flame or the like. Powder or the like can be used. Moreover, the powder which crushed quartz glass can also be used.

  The average particle size of the amorphous silica powder used in the present invention is preferably 20 μm or less. If the particle size is too large, sintering requires a high temperature and a long time, which is not preferable. Amorphous silica powder produced by various production methods can be adjusted to the above particle size by pulverization and classification with a jet mill, ball mill, bead mill or the like.

  Next, the pore former powder used in the present invention is selected. The particle size of the pore-forming agent of the present invention is closely related to the average pore size of the opaque quartz glass, and it is necessary to use a pore-forming agent having a particle size equal to or larger than the desired average pore size. The reason for using a pore-forming agent having a particle diameter equal to or larger than the pore diameter is that the pores may be smaller than the original size in the sintering stage after the pore-forming agent disappears. When a spherical powder of graphite or amorphous carbon is used as the pore forming agent, in order to obtain an opaque quartz glass having an average pore diameter of 5 to 20 μm, the particle size of the pore forming agent is preferably 5 to 40 μm, and 9 to 30 μm. It is more preferable that

  The type of the pore-forming agent of the present invention is not particularly limited as long as it is thermally decomposed at a temperature lower than the sintering temperature of amorphous silica and vaporizes and disappears. Graphite powder, amorphous carbon powder, phenol resin powder, Acrylic resin powder, polystyrene powder, or the like can be used. Among these, graphite powder or amorphous carbon powder is preferable in that the gas component generated during pyrolysis is harmless and odorless.

  The purity of the amorphous silica powder and pore former powder used in the present invention is desirably 99.9% or more. When quartz glass contains an impurity element such as an alkali metal element, alkaline earth element, or transition metal element at a high concentration, cristobalite is generated in the quartz glass at a temperature of about 1300 ° C. or higher. Cristobalite undergoes a phase transition from a high temperature type to a low temperature type at a temperature of 230 to 300 ° C. and causes volume shrinkage. When the amount of cristobalite contained in the opaque quartz glass is more than 2%, cracks tend to occur in the fired body due to this volume shrinkage. In particular, when the fired body is large, this tendency is remarkable in, for example, opaque quartz glass having a diameter of 140 mm or more. When the purity of the amorphous silica powder and the pore-forming agent powder is low, a purification treatment may be performed. The purification method is not particularly limited, and chemical treatment, dry gas purification, evaporation of impurities by high-temperature baking, and the like can be performed. It should be noted that even when the amount of metal impurities contained in the opaque quartz glass is small, a large amount of cristobalite may be generated depending on the moisture content, furnace atmosphere, furnace material purity, firing time, etc. Keep it.

  The shape of the pore-forming agent of the present invention is preferably spherical in that it can be homogeneously mixed with the amorphous silica powder and the pressure can be favorably transmitted when the powder is molded by pressing. The aspect ratio representing the ratio of the major axis to the minor axis of the particles is preferably 3.0 or less.

(2) Mixing of raw material powder Next, the selected amorphous silica powder and pore former powder are mixed. The addition amount of the pore-forming agent powder needs to be mixed so that the volume ratio is 0.04 or more with respect to the amorphous silica powder, but the preferred range varies depending on the type of pore-forming agent and the average particle diameter, If the pore former powder is a graphite powder or an amorphous carbon powder having an average particle diameter of 5 to 40 μm, the volume ratio with respect to the amorphous silica powder is preferably 0.04 to 0.35. If the amount of the pore-forming agent powder is small, the amount of pores contained in the opaque quartz glass is small, and the light shielding property of infrared light is lowered, which is not preferable. On the other hand, if the addition amount is too large, the density of the opaque quartz glass becomes too low, which is not preferable.

The mixing method of the amorphous silica powder and the pore former powder is not particularly limited as long as the number density per unit area of the amorphous silica aggregate in the mixed powder is 100 pieces / cm ² or less. A rocking mixer, a cross mixer, a pot mill, a ball mill, a sieve, etc. can be used. In particular, in the mixing of the present invention, it is preferable to use a method of mixing through a sieve because a powder that can easily reduce the number density per unit area of the amorphous silica aggregate can be obtained.

(3) Molding of mixed powder Next, the mixed powder is molded. As a molding method, a dry press such as a casting method, a cold isostatic press (CIP) method, a mold press method, or the like can be used. In particular, it is preferable to use the CIP method for molding according to the present invention because a molded body can be easily obtained with few steps. Further, a method for producing a disk-shaped, cylindrical, or ring-shaped molded body using the CIP method is not particularly limited, but a molding method using a plastically deformable mold such as foamed polystyrene (for example, Japanese Patent Application Laid-Open No. Hei 4). -107797) and a method using a mold form (for example, see Japanese Patent Application Laid-Open No. 2006-241595) using a bottom plate made of a material having less compression deformation than the upper punch.

(4) Sintering of molded body Next, the molded body molded by the above method is heated at a predetermined temperature to eliminate the pore-forming agent contained in the molded body. Although the heating temperature varies depending on the type of pore forming agent, for example, when graphite powder or amorphous carbon is used as the pore forming agent, the heating temperature is 700 ° C. to 1000 ° C.

Heating for disappearance of the pore forming agent is performed for an arbitrary time depending on the type of pore forming agent, the amount of the pore forming agent added, the size of the molded body, and the heating temperature. For example, graphite powder or amorphous carbon is used as the pore forming agent. When the addition amount is 0.1 to 0.2 in volume ratio with the amorphous silica powder, the volume of the molded body is 2 × 10 ³ cm ³ , and the heating temperature is 800 ° C., the heating time is 24 hours to 100 hours. To do.

  Next, the molded body from which the pore forming agent has disappeared is fired at a predetermined temperature until the pores contained in the sintered body become closed pores. The firing temperature is preferably 1350 to 1500 ° C. When the firing temperature is lower than 1350 ° C., it is not preferable because firing for a long time is required before the pores become closed pores. When the firing temperature exceeds 1500 ° C., the amount of cristobalite contained in the fired body increases, and cracks may occur in the fired body due to volume shrinkage accompanying the phase transition from the high temperature type to the low temperature type of cristobalite.

  The firing time is carried out for an arbitrary time depending on the addition amount of the pore-forming agent and the firing temperature. For example, the addition amount is 0.1 to 0.2 by volume ratio with the amorphous silica powder, and the firing temperature is 1350 to 1500. In the case of ° C., the firing time is 1 to 20 hours. If the firing time is short, sintering does not proceed sufficiently and the pores become open pores, which is not preferable. In addition, if the firing time is too long, the sintering proceeds too much and pores become smaller, so that the light shielding property of infrared light is reduced, and the amount of cristobalite contained in the fired body is increased. Due to the volume shrinkage accompanying the transition, cracks may occur in the fired body, which is not preferable.

  Heating for disappearance of the pore forming agent is performed in an atmosphere in which the pore forming agent disappears. For example, when graphite powder or amorphous carbon is used as the pore forming agent, it is performed in an atmosphere in which oxygen is present.

  There is no particular limitation on the atmosphere for firing for closed pore formation, and it can be performed in an air atmosphere, a nitrogen atmosphere, or a vacuum atmosphere.

  Thus, the opaque quartz glass manufacturing method of the present application includes a mixing step of mixing raw material powders to reduce silica agglomerates so as to have the aforementioned characteristics, and a forming step of forming the mixed powder obtained in the mixing step. It is preferable to have a firing step of sintering the molded body obtained in the molding step.

  Since the opaque quartz glass of the present invention is excellent in heat shielding performance, it is a member for a heat treatment device, a member for a semiconductor manufacturing device, a member for an FPD manufacturing device, a member for a solar cell manufacturing device, a member for an LED manufacturing device, and a MEMS manufacturing device. It can utilize for a member, an optical member, etc. Specific examples include constituent materials such as flanges, heat insulating fins, furnace core tubes, soaking tubes, chemical solution refining cylinders, and other constituent materials such as silicon melting crucibles.

  The member as described above may be used alone by the opaque quartz glass, or may be used by providing a transparent quartz glass layer on a part or the whole of the opaque quartz glass surface. The transparent quartz glass layer provides perfect sealing even when opaque quartz glass is used for applications that require sealing properties, and the pores contained in the opaque quartz glass are exposed on the sealing surface and packing is used. It is given considering that it is difficult. In addition, in the cleaning process that is performed as needed while using opaque quartz glass in various applications, the pores exposed on the outermost surface are scraped, and part of the surface of the opaque quartz glass falls off, causing the generation of particles. It may become. For the purpose of preventing this, a transparent quartz glass layer is provided.

  The method of applying the transparent quartz glass layer to the opaque quartz glass is not particularly limited. The method of melting the surface of the opaque glass with an oxyhydrogen flame to form the transparent quartz glass, and the opaque quartz glass and the transparent quartz glass to the oxyhydrogen flame. Heating and bonding with an electric furnace, an amorphous silica powder that becomes opaque quartz glass, a mixed powder of a pore-forming agent, and an amorphous silica powder that becomes transparent quartz glass. There is a method of forming and firing in accordance with the position of the above.

  The opaque quartz glass of the present invention is optically homogeneous and therefore has little variation in heat shielding performance. Particularly, various furnace core tubes, jigs, and containers such as bell jars used in the semiconductor manufacturing field, such as silicon It can be used as a constituent material for a furnace core tube for wafer processing, its flange, a heat insulating fin, a chemical purification tube, a silicon melting crucible and the like.

It is an example of the histogram of the luminance-the number of pixels obtained by carrying out image processing of the observation image of opaque quartz glass. It is a schematic diagram of the threshold value determination performed when image processing the observation image of opaque quartz glass. It is the image which image | photographed the mixed powder of Example 1 with the reflection type microscope. 2 is an image obtained by binarization based on the image of FIG. 1. This is an image obtained by performing up to “Invert” based on the image of FIG. This is an image obtained from “Analyze particles” based on the image of FIG. It is the image which image | photographed the mixed powder of the comparative example 1 with the reflection type microscope. 6 is an image obtained by binarization based on the image of FIG. It is the image performed to "Invert" based on the image of FIG. It is the image performed to "Analyze particles" based on the image of FIG. It is the image which image | photographed the opaque quartz glass of Example 1 with the stereomicroscope. This is an image obtained by binarizing based on the image of FIG. 9 and performing up to “Invert”. FIG. 10 is an image that has been processed up to “Analyze particles” based on the image of FIG. 9. It is the image which image | photographed the opaque quartz glass of the comparative example 1 with the stereomicroscope. This is an image obtained by binarizing based on the image of FIG. 12 and performing up to “Invert”. 13 is an image obtained up to “Analyze particles” based on the image of FIG.

  Hereinafter, the present invention will be described in detail according to specific examples, but the present invention is not limited thereto. The physical properties of silica powder and opaque quartz glass were measured according to the following procedure.

(Average particle size)
As the average particle diameter of the amorphous silica powder, the value of the median diameter (D50) measured using a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, trade name “SALD-7100”) was used.

(Number density of amorphous silica aggregates)
The number density per unit area of the amorphous silica aggregate in the mixed powder was measured by the following method. First, a mixed powder of amorphous silica powder and pore former was sandwiched between quartz glass plates from both sides, and a scaled image was taken with a reflection microscope (manufactured by Keyence Corporation, DIGITAL MICROSCOPE VHX-900). The thickness of the powder layer sandwiched between quartz glass was about 1 mm. Next, the image processing software (ImageJ 1.46) was used, and the image processing of the image image | photographed in the following procedures was performed. Launched ImageJ and opened a file for image processing. “Image” → “Type” → “8-bit” was executed. Subsequently, “Image” → “Adjust” → “Threshold” was executed.

Since the window of the histogram opens, the luminance value having the largest number of pixels for each luminance value is set as a threshold value, and then “Apply” is executed to binarize. After putting a straight line so as to overlap the scale part of the image, execute “Analyze” → “Set Scale”, input the scale value in “Know distance”, enter the unit of scale in “Unit of length”, “OK” was performed and the length per pixel was set. An arbitrary range of the image was specified so as to remove the scale, “Image” → “Crop” was executed, and the image was cut out. “Process” → “Binary” → “Skeletonize” was executed, and the pixels were repeatedly removed from the edge of the target in the monochrome image until the skeleton became a single pixel. “Process” → “Binary” → “Dilate” was executed, and each adjacent pixel was replaced with the maximum value (dark value) of the adjacent 3 × 3 pixels. “Dilate” was performed twice. “Edit” → “Invert” was executed, and black and white were reversed. “Analyze” → “Analyze particles” was executed. 0.04-Infinity was entered in “Size (mm ^ 2)”. “Show” was changed to “Outlines”, “Display results” and “Summerize” were checked, and “OK” was executed. The number “n” of the portions (amorphous silica aggregates) having an area of 0.04 cm ² or more was displayed as “Count”. Also, the total value of the areas having an area of 0.04 cm ² or more as “Total Area” and the area of the area having an area of 0.04 cm ² or more with respect to the entire image area as “% Area” Since the ratio occupied by the total value is displayed, the area Scm ² of the entire image was obtained from these values. The number density per unit area of the amorphous silica aggregate was determined from n and S by the following formula.
Number density per unit area of amorphous silica aggregate = n / S

(Number density of white spots)
The number density per unit area of white spots in the opaque quartz glass was measured by the following method. A non-transparent quartz glass was cut with a diamond blade to prepare a sample having a length of 20 mm, a width of 20 mm, and a thickness of 3 mm, and transmitted light was applied from the back of the sample, and a scale was placed with a stereomicroscope (SMZ745T manufactured by Nikon Corporation). An image was taken. Next, the image processing software (ImageJ 1.46) was used and the image processing image | photographed in the following procedures was performed. Launched ImageJ and opened a file for image processing. After putting a straight line so as to overlap the scale part of the image, execute “Analyze” → “Set Scale”, input the scale value in “Know distance”, enter the unit of scale in “Unit of length”, “OK” was performed and the length per pixel was set. An arbitrary range of the image is designated by a rectangle so as to remove the scale, and “Image” → “Crop” is executed to cut out the image. “Image” → “Type” → “8-bit” was executed. “Image” → “Adjust” → “Threshold” was executed. Since the window of the histogram opens, the threshold is set so that it is divided into the transparent part and the other part, and binarized. For the threshold value, the luminance value having the largest number of pixels for each luminance value is a, the minimum luminance value is b, and 2a-b is adopted as the threshold value. “Edit” → “Invert” was executed.

“Analyze” → “Analyze particles” was executed. 0.04-Infinity was entered in “Size (mm ^ 2)”. “Show” was changed to “Outlines”, “Display results” and “Summerize” were checked, and “OK” was executed. As “Count”, the number m of the portions (open areas) having an area of 0.04 cm ² or more is displayed. Also, the total value of the areas having an area of 0.04 cm ² or more as “Total Area” and the area of the area having an area of 0.04 cm ² or more with respect to the entire image area as “% Area” Since the ratio occupied by the total value is displayed, the area Rcm ² of the entire image was obtained from these values. From m and R, the number density per unit area of white spots was determined by the following equation.
Number density per unit area of white spots = m / R

(Infrared transmittance)
The infrared spectrum of the opaque quartz glass was measured using an FTIR apparatus (manufactured by Shimadzu Corporation, trade name “IR Prestige-21”). The measurement sample was processed by surface grinding to a thickness of 1 mm.

Example 1
As the silica raw material powder, an amorphous silica powder having a chemical purity of 99.9 wt% or more (trade name “MKC silica PS100” manufactured by Nippon Kasei Co., Ltd.) is used until the average particle diameter (median diameter D50) becomes 4 μm. What was pulverized with a jet mill was used. As the pore former powder, spherical graphite powder having an average particle diameter of 18 μm (manufactured by Nippon Carbon Co., Ltd., trade name “Nika Beads”) was used.

  Amorphous silica powder and graphite powder were put in a bag so that the volume ratio was 0.1, shaken for 3 minutes, and then passed through a sieve having an opening of 184 μm once to obtain a mixed powder. The mixed powder was observed at an observation magnification of × 50, and image processing was performed by designating a range of 90% or more excluding the reflected scale portion in image processing. 3, 4, 5 and 6 show images in the course of image processing of the mixed powder of Example 1, and FIGS. 11, 12 and 13 show images in the course of image processing of the opaque quartz glass of Example 1. FIG.

  The mixed powder was filled in a foam polystyrene mold, the entire foam polystyrene mold was sealed under reduced pressure in a polystyrene bag, and cold isostatic pressing (CIP) molding was performed under the conditions of a pressure of 280 MPa and a holding time of 1 minute.

  A cylindrical molded body having a diameter of 173 mm and a thickness of 44 mm after CIP molding is heated from room temperature to 650 in a furnace floor raising and lowering resistance heating electric furnace (manufactured by Hiroki Co., Ltd., model “HPF-7020”) in an air atmosphere. Up to 100 ° C / hour, 50 ° C / hour from 650 ° C to 800 ° C, held at 800 ° C for 36 hours, heated from 800 ° C to maximum firing temperature of 1425 ° C at 50 ° C / hour, maximum firing temperature of 1425 ° C And baked for 4 hours. The temperature was lowered to 50 ° C. at 100 ° C./hour and then cooled in the furnace to obtain opaque quartz glass. Table 1 shows the number density of the silica aggregates of the used mixed powder and the number density of white spots in the opaque quartz glass.

Example 2
A mixed powder was obtained in the same manner as in Example 1 except that the number of times of passing through the sieve was changed to 2. Using the obtained mixed powder, a molded body was produced in the same manner as in Example 1, and the molded body was fired under the same conditions as in Example 1 to obtain an opaque quartz glass. Table 1 shows the number density of the silica aggregates of the used mixed powder and the number density of white spots in the opaque quartz glass.

Example 3
A mixed powder was obtained in the same manner as in Example 1 except that the number of times of passing through the sieve was changed to 3. Using the obtained mixed powder, a molded body was produced in the same manner as in Example 1, and the molded body was fired under the same conditions as in Example 1 to obtain an opaque quartz glass. Table 1 shows the number density of the silica aggregates of the used mixed powder and the number density of white spots in the opaque quartz glass.
Example 4
A mixed powder was obtained in the same manner as in Example 1 except that the powder mixing was changed to a method of mixing for 3 hours in a pot mill. Using the obtained mixed powder, a molded body was produced in the same manner as in Example 1, and the molded body was fired under the same conditions as in Example 1 to obtain an opaque quartz glass. The number density of silica aggregates in the mixed powder used was 0 / cm ² , and the number density of white spots in the obtained opaque quartz glass was 0 / cm ² . When the sample thickness of the obtained opaque quartz glass is 1 mm, the linear transmittance at a wavelength of 1.5 μm to 5 μm is 1% or less, the transmittance at a wavelength of 2 μm is 0.82%, and the transmittance at a wavelength of 4 μm is 0.8. It was 46%.

Comparative Example 1
A mixed powder was obtained in the same manner as in Example 1 except that the number of times of passing through the sieve was 0. Using the obtained mixed powder, a molded body was produced in the same manner as in Example 1, and the molded body was fired under the same conditions as in Example 1 to obtain an opaque quartz glass. Table 1 shows the number density of the silica aggregates of the used mixed powder and the number density of white spots in the opaque quartz glass.

  7, 8, 9 and 10 show images in the course of image processing of the mixed powder of Comparative Example 1, and FIGS. 14, 15 and 16 show images in the course of image processing of the opaque quartz glass of Comparative Example 1, respectively.

  It is an opaque quartz glass having a high heat shielding effect, and can be suitably used for a member for a semiconductor manufacturing apparatus.

Claims (5)

In the histogram obtained by image processing, a threshold value is set so as to be separated into a transparent part and other parts, and binarized, and the number of parts having an area of 0.04 mm ² or more among the parts exceeding the threshold value is represented by m. An opaque quartz glass, wherein the area of the entire image is Rcm ² and m / R is 50 or less. 2. The opaque quartz glass according to claim 1, wherein the transmittance at a wavelength of 1.5 μm to 5 μm at a sample thickness of 1 mm is 1% or less. A method for producing opaque quartz glass using a mixed powder of amorphous silica powder and pore former powder, wherein the mixed powder is a histogram obtained by image processing, and has the largest number of pixels for each luminance value The value is set as a threshold value and binarized. Among the portions exceeding the threshold value, the number of portions having an area of 0.04 mm ² or more is n, the area of the entire image is Scm ² , and n / S is 100 or less. An opaque quartz glass manufacturing method characterized by the above.   4. The method for producing opaque quartz glass according to claim 3, wherein the pore-forming agent powder has an average particle diameter of 5 to 40 [mu] m.   The method for producing opaque quartz glass according to claim 3 or 4, wherein the pore-forming agent is graphite powder.

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