JPH0686300B2 - Soot-like silica body and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a soot-like silica body that is a precursor of synthetic quartz glass and a method for producing the same, and particularly soot-like silica fine particles on a rotating heat-resistant substrate. TECHNICAL FIELD The present invention relates to a soot-like silica body formed by depositing and a method for producing the same.

“Prior Art” Soot-like silica particles have been conventionally deposited by depositing fine particles of soot-like silica produced by an oxidation / hydrolysis reaction of a silica-forming gas phase raw material such as silicon tetrachloride in a flame (hereinafter referred to as “soot-like silica body”). A soot body) and then sintering the soot body in a predetermined atmosphere to obtain a transparent molten glass body.
A method for producing so-called vapor phase synthetic quartz glass is known.

The soot body that is a precursor of such synthetic quartz glass is manufactured by supplying a silicon compound such as silicon tetrachloride and oxygen and hydrogen to a concentric annular oxyhydrogen flame burner, and oxidizing and hydrolyzing the silicon compound in an oxyhydrogen flame. By decomposing soot-like silica fine particles, which are successively deposited on a rotating heat-resistant substrate such as quartz glass, carbon, silicon carbide, alumina, etc., soot of a predetermined diameter and a predetermined length is obtained. The way to get a body is common.

And such a manufacturing method is such that while the heat-resistant substrate is sequentially moved in the axial direction with respect to the burner or burners arranged in a row along the heat-resistant substrate axis, the soot-like silica fine particles are conically formed on the substrate. A technique for producing a soot body by laminating (JP-A-56-104740, JP-A-58-9835, etc., hereinafter referred to as the first prior art), and also a deposition rate of soot-like silica fine particles on a heat-resistant substrate. In order to improve the above, a burner row in which a large number of burners are arranged in a row over the entire length of the soot-like silica fine particle deposition site of the heat resistant substrate is used, or a slit opening is provided along the soot body axial direction. A technique in which a ribbon-shaped burner is used to uniformly deposit soot-shaped silica fine particles in the axial direction on a heat-resistant substrate rotated by the burner (row) (Japanese Patent Laid-Open No. 53-70449, hereinafter referred to as second conventional technique). .), But these manufacturing techniques Since is a process for producing a soot body to either batchwise, in order to enhance the productivity of the quartz glass becomes large is essential condition of the soot body.

"Problems to be solved by the invention" However, the production method is a batch method, in other words, each time the deposition of a predetermined amount of soot-like silica fine particles on each heat-resistant substrate is completed, the flame from the burner is extinguished, Once cooled to a predetermined temperature or less and then transferred to the sintering / melting step of the next step, the soot body is porous and has a significantly smaller heat capacity than the transparent glass body. As the flame is extinguished, the surface of the soot body is rapidly cooled.
At that time, the larger the size of the soot body, especially the larger the diameter, the larger the temperature difference between the cooled surface and the inside, and the shrinkage of the cooled surface causes tensile stress on the surface of the soot body, causing cracking. become.

Further, since the soot body is formed by simply depositing soot-like silica fine particles to form a porous form, its mechanical strength is extremely fragile and easily cracks when tensile stress is generated due to the temperature change in the radial direction. Will result in. Therefore, it has been considered extremely difficult to obtain a soot body having a large diameter by the thermal shock by the conventional manufacturing method.

Further, in the soot body manufactured by the above-mentioned conventional technique, particularly the first conventional technique, the deposition density at the inner portion in contact with the heat-resistant substrate is likely to be the lowest, so that the heat-resistant substrate and the soot body are heat-treated. Since the expansion rate is different, the problem that cracks are most likely to occur in the inner part is also derived.

In order to solve such a defect, a method of increasing the deposition density in the radial direction of the deposition site of the soot body over the entire region can be considered, but if such a manufacturing method is adopted, it is contrary to the above. The presence of internal stress becomes too large, and local deformation and cracks occur, which still cannot solve the above problems.

In view of the above-mentioned drawbacks of the prior art, the present invention provides a soot body and a method for manufacturing the soot body that can be easily made large and have a large diameter without causing cracks or the like on the surface or the inner portion of the soot body. With the goal.

"Means for Solving Problems" First, the present inventors examined various causes of cracking, which is the biggest obstacle in obtaining a large soot body as described above, and the progress leading to the solution is described. It will be explained step by step.

First, during the manufacturing process of the soot body, since the soot body supported on the heat-resistant substrate is located in the oxyhydrogen flame in which soot-like silica fine particles are generated, the soot body naturally deposits during the silica fine particle deposition. It is maintained at a high temperature.

However, after the soot-like silica fine particles are deposited, the outer surface of the soot body is cooled rapidly as the oxyhydrogen flame burner flame extinguishes, but the soot body has a thermal conductivity due to the presence of the porous void layer. Is low and the cooling of the surface is not immediately transmitted to the inside, so the inside of the soot body is still in a state of being kept warm.

Therefore, shrinkage starts on the cooled outer surface, but does not start inside the heat-retaining state, and tensile stress is unavoidably generated on the outer surface which is about to shrink due to the difference in shrinkage ratio between the two.

And this phenomenon is as the temperature difference between the outer surface and the inside is larger,
That is, the larger the diameter of the soot body becomes, the more remarkable it becomes, and the mechanical strength of the soot body is extremely brittle as described above, so that the tensile stress causes the outer surface to crack. Become.

Further, the deposition density is lowest on the inner surface of the soot body, that is, the inner portion in contact with the heat-resistant substrate, and gaps are formed by cooling due to the difference in coefficient of thermal expansion from the heat-resistant substrate. Then, as described above, since the mechanical strength is extremely brittle, a tensile stress due to the contraction of the soot body or a slight impact due to the rotational movement of the soot body causes cracking.

Since the soot body is formed into a porous form by depositing soot-like silica fine particles, the conditions governing the thermal state during deposition are changed, in other words, the soot-like silica fine particles are provided at the time of deposition. It is possible to easily adjust and change the deposition density distribution in the radial direction of the soot body by changing the thermal energy per unit time.

That is, the soot-like silica fine particles produced in the oxyhydrogen flame are softened and deformed when they are subjected to sufficient heat energy, and the surface thereof becomes viscous, and the viscous soot-like silica fine particles tend to be fused to each other. The bonding area between the soot-like silica fine particles increases dramatically. As a result, the deposition density of the soot body increases and the binding force between the soot-like silica particles increases, so that the mechanical strength of the soot body increases.

Therefore, during the step of depositing soot-like silica particles, by providing sufficient heat energy to a desired site, the degree of bonding between the soot-like silica particles at that site increases, which leads to an increase in the deposition density and mechanical strength.

Therefore, it is possible to obtain a soot body having mechanical strength capable of withstanding the tensile stress by increasing the deposition density of the inner and outer surfaces of the soot body where tensile stress is generated by cooling, that is, the inner portion and outer surface in contact with the heat resistant substrate, It is possible to completely prevent the occurrence of cracks.

Therefore, the gist of the first aspect of the present invention is that a hollow tube is used for the heat-resistant substrate, and the deposition density distribution of the silica fine particles in the radial direction of the silica body is set in the radial direction from the inner portion in contact with the heat-resistant substrate. It is set to gradually decrease and reach a minimum in the intermediate region, and then increase again as it progresses to the outer surface region, in other words, the deposition density on the inner and outer surface sides of the soot body is set to be larger than that in the intermediate region. In addition, the outer diameter of the silica body is 300 m or more.

In this case, since the inner portion is a portion that is in direct contact with the heat resistant substrate and the tensile stress generated by the difference in the heat shrinkage ratio with the substrate is the largest, the deposition density of the inner portion is
The effect of the present invention can be achieved more smoothly by setting the deposition density higher than the deposition density on the outer surface portion.

On the other hand, the second invention provides a method for smoothly producing the soot body described in the first invention, and the gist of the method is the thermal energy per unit time applied during the deposition of the silica fine particles. Along the radial direction, specifically, the thermal energy is gradually reduced in the radial direction from the inner portion in contact with the heat-resistant substrate, reaches a minimum in the intermediate region, and then increases again as it goes to the outer surface portion. That is, the silica fine particles are sequentially deposited on the heat resistant substrate while changing the above.

In this case, in order to change the thermal energy, the rotation speed of the heat-resistant substrate is adjusted, and the combustible gas (hydrogen gas or the like) or / and the combustion-supporting gas (oxygen gas or the like) supplied to the burner for producing silica fine particles is used. The thermal energy can be easily changed and adjusted by adjusting the gas flow rate, adjusting the distance between the burner and the silica fine particle deposition surface, or using any one or a combination of other adjusting means. I can do things.

In the second aspect of the present invention as well, it is preferable to make the deposition density in the axial direction of the same laminated portion (inner portion, intermediate region, outer surface) of the soot body as uniform as possible. The ribbon-shaped burner or burner row extending to
A flame for producing silica fine particles is formed over almost the entire length of the silica fine particle deposition site so that the silica fine particles can be uniformly laminated in the axial direction of the heat resistant substrate, and in particular, the flame and the heat resistant substrate penetrate through the axis line. The effect can be achieved more smoothly by depositing silica fine particles while relatively reciprocating along the direction.

[Embodiment] Hereinafter, a preferred embodiment of the present invention will be exemplarily described in detail with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the components described in this embodiment are not intended to limit the scope of the present invention only thereto, but merely illustrative examples. Nothing more than.

2 (A), (B) and (C) are schematic views showing an apparatus for producing a soot body according to an embodiment of the present invention, and FIG. 1 is a sectional view of the soot body produced by such a production apparatus.

In FIG. 2, reference numeral 1 denotes a burner row formed by vertically arranging a large number of oxyhydrogen flame burners 1a on the burner base 11 in a single row. The flame openings of each burner 1a are parallel to the heat-resistant substrate 2 axis. The burner array 1 is positioned on the horizontal line, and the burner row 1 has the entire length, that is, the burner 1a ... Arrangement intervals and the number of the burner rows 1 are appropriately selected according to the length of the soot body 3 deposited on the heat resistant substrate 2. .

As is well known, the oxyhydrogen flame burner 1a used for the burner array 1 burns hydrogen and oxygen to form a flame 4, and in the flame 4, a silica-forming gas phase raw material such as silicon tetrachloride is oxygen. It is sent together with a carrier gas such as, and causes a hydrolysis reaction in the flame 4 to generate soot-like silica fine particles 3a.

On the other hand, the heat-resistant substrate 2 is made of alumina or another heat-resistant material in the shape of a hollow cylinder, and the peripheral surface of the heat-resistant substrate 2 is positioned in the flame 4 formed by the burners 1a. The burner array 1 is arranged so as to extend in the horizontal direction in parallel with the burner array 1, and is made rotatable about the axis of the heat-resistant substrate 2 by a driving means described later as shown in FIG. 2 (A), for example. The soot-like silica fine particles generated in the flame 4 are stacked and deposited on the peripheral surface of the heat-resistant substrate 2 at a uniform deposition density in the length direction by the reciprocating motion with a constant amplitude in the length direction. I can do things.

The reciprocating motion of the heat-resistant substrate 2 eliminates the defects in the shape of the inner and outer surfaces of the deposited layer caused by the interference of the oxyhydrogen flame 4 between the burners 1a ... And makes the density of the soot body 3 uniform in the longitudinal direction. The amplitude is
It is recommended to set the distance to be the same as the distance between adjacent burners 1a.

Further, the reciprocating motion of the heat-resistant substrate 2 may be that the burner row 1 and the heat-resistant substrate 2 move relatively in parallel, so that, for example, the burner row 1 side may be reciprocated, or the burner may be reciprocated. Both the row 1 and the heat resistant substrate 2 may be reciprocated with different amplitudes.

In order to smoothly achieve the present invention, it is necessary to have an adjusting means capable of sequentially adjusting the amount of thermal energy (flame 4) applied per unit time in the silica fine particle deposition step in the radial direction according to the amount of deposition. .

As such heat energy adjusting means, for example, the second
As shown in Fig. (A), each of the burners 1a ... And the hydrogen supply source
61 or / and a supply pipe 63 connecting the oxygen supply sources 62 with flow rate adjusting valves 64, 65, and hydrogen sources or / and oxygen supplies to the burners 1a ... by the control valves 64, 65. The amount may be adjusted, and as shown in FIG. 2 (B), the burner base 11 holding each of the burners 1a ... Can be moved only in the direction orthogonal to the axial direction of the heat resistant substrate 2. The slider 70 is attached to the slider 70 so that the distance between the opening of the flame 4 of the burner 1a and the soot silica particle deposition surface on the soot body 3 side can be separated and contacted according to the amount of soot silica particle deposition. May be.

Further, as shown in FIG. 2 (C), the transmission 52 is applied to the drive means 51 for applying the rotational force to the heat resistant substrate 2 (for example, when a DC motor is used as the drive means 51, the voltage regulator is changed to the speed change gear). (Which can be used as the machine 52), and by adjusting the transmission 52, the number of rotations of the heat-resistant substrate 2 can be adjusted according to the amount of the soot-like silica particles deposited. It is possible to adjust the amount of heat energy per unit time by means, which makes it possible to easily manufacture the soot body 3 having a predetermined deposition density distribution in the radial direction.

As means for reciprocating the heat-resistant base body 2, for example, the rotational force of the driving means 51 is transmitted to the cam means 54 which can swing axially within a predetermined range through the reduction gear 53, and the cam means is heat-resistant. By connecting to the heat-resistant substrate 2, the heat-resistant substrate 2 can be easily reciprocated.

Therefore, the soot body 3 manufactured by such a manufacturing apparatus is
For example, as shown in FIG. 1 and FIG. 3, the deposition density of the inner portion 31 in contact with the heat-resistant substrate 2 is maximized, and gradually decreases outward from the inner portion 31 in the radial direction, and the intermediate region 32 thereof is gradually reduced.
It is easy to set the deposition density so as to increase again as it goes to the outer surface part 33, and this makes it possible to cool the burner 1a ... It is possible to obtain the soot body 3 having a mechanical strength capable of withstanding the tensile stress generated as a result.

Further, in the present embodiment, the soot body 3 exists because the burner row 1, that is, the flame 4 that produces soot-like silica fine particles exists over the entire area of the soot body 3 deposition site of the heat resistant substrate 2 in the axial direction. The soot-shaped silica fine particles can be uniformly deposited in the length direction of the.

Next, a confirmation experiment based on such an example will be described in detail.

Example 1 First, using a manufacturing apparatus shown in FIG. 2 (C), a rod-shaped sintered body containing alumina as a main component and having a diameter of 80 mm and a length of 2000 mm was used as the heat-resistant substrate 2, and the heat-resistant substrate 2 was used. And oxyhydrogen flame 4 burner
1mm with oxyhydrogen flame burner 1a ...
Twelve pieces of the heat resistant substrate 2 were arranged linearly in the longitudinal direction at intervals of 00 mm. Oxygen hydrogen flame burner 1a ... with oxygen 0.2Nm ³ / h as carrier gas, gaseous silicon tetrachloride 1500g / h, oxygen 0.4Nm ³ / h
Hydrogen and hydrogen were supplied at 1.8 Nm ³ / h, respectively, and soot-like silica fine particles generated from the oxyhydrogen flame 4 were deposited on the heat resistant substrate 2. At this time, the heat-resistant substrate 2 is rotated at 65 rpm, and the burner 1a ... 100 mm at a speed of 320 mm / min in the arrangement direction.
Reciprocate with the amplitude of. As a result, the soot-like silica fine particles are uniformly laminated in the length direction of the heat resistant substrate 2, and the soot body becomes thicker with the lapse of time.

Then, during the soot-like silica fine particle deposition step, first, the rotation speed of the heat-resistant substrate 2 is set to 65 rpm, and the rotation speed is reduced by the transmission 52 at a rate of 0.47 rpm / min for 15 minutes to reduce the deposition density. A high layer 31 was formed. After 15 minutes, at 58 rpm, the rotation speed was maintained for 440 minutes. As a result, the thickness of the soot body increases with the deposition of soot-like silica fine particles even when the rotation speed of the heat-resistant substrate 2 is constant, and the peripheral speed thereof increases, so that the deposition density gradually decreases.

After that, at a rate of 0.165 rpm / min, the rotation speed was reduced for 170 minutes to increase the deposition density again, and at 28 rpm,
The rotation speed was reduced at a rate of 0.025 rpm / min for 40 minutes to form the second high-density layer 33, and the soot-like silica fine particle deposition was completed.

As a result, it is possible to obtain a silica body having a density distribution as shown in Fig. 5, and to manufacture a soot body with a large outer diameter of 300 mm without cracking due to thermal shock even after burner 1a ... extinguishing fire. Was completed.

[Example 2] Next, when depositing soot-like silica fine particles under the same conditions as in the above example using the manufacturing apparatus shown in Fig. 2 (A), first, the rotation speed of the heat resistant substrate 2 was 65 rpm / min. Fixed to
Oxyhydrogen flame burner 1a ...
The amount of oxygen and the amount of hydrogen supplied to were adjusted.

First, oxygen was added for 15 minutes to deposit soot-like silica particles.
0.5 nm ³ / h, 2.0 Nm hydrogen ³ / h respectively supplied to the first high density layer 31
Was formed. After 120 minutes, oxygen was added to 0.45 Nm ³ /
h, hydrogen respectively reduced to 1.9 nm ³ / h, was further after 200 minutes, oxygen respectively decreased 0.4 Nm ³ / h, hydrogen 1.8 Nm ³ / h, in, decreasing the deposition density. After 120 minutes, to increase the deposition density again, gradually increase the oxygen content and hydrogen content, and after 170 minutes, add oxygen respectively.
0.6 nm ³ / h, and increased hydrogen 2.7 Nm ³ / h, to complete the additional 40 minutes the formed sooty silica particles depositing a second high-density layer 33 by continuing to deposit in this state.

As a result, it was possible to manufacture a large-diameter soot body having an outer diameter of 300 mm and a deposition density distribution similar to that of the soot body obtained in the above example.

Next, when a synthetic quartz glass was manufactured by sintering and melting the soot body manufactured based on the confirmation experiments 1 and 2, the amount of bubbles trapped on the surface side of the glass body was significantly reduced as compared with the conventional case. Moreover, the planar shape of the inner surface side could be formed to be almost smooth.

"Effects of the Invention" As described above, it is possible to easily increase the size and diameter of the soot body 3 without causing cracks or the like on the surface or the inner side of the soot body, and to obtain its practical value. It is extremely large.

[Brief description of drawings]

2 (A), (B) and (C) are schematic views showing an apparatus for producing a soot body according to an embodiment of the present invention, and FIG. 1 is a sectional view of the soot body produced by such a production apparatus. FIG. 3 is a distribution diagram showing the deposition density of the soot body shown in FIG.

Claims (3)

[Claims] 1. A soot-like silica body formed by depositing silica fine particles on an axially rotating heat-resistant substrate, wherein a hollow tubular body is used as the heat-resistant substrate, and silica in the radial direction of the silica body is used. The deposition density distribution of the fine particles is set so as to gradually decrease in the radial direction from the inner portion in contact with the heat-resistant substrate, reach the minimum in the intermediate region, and then increase again as it progresses to the outer surface portion. Soot-like silica body characterized by having an outer diameter of 300 mm or more 2. A method for producing a soot-like silica body by sequentially depositing silica fine particles produced by hydrolysis or oxidation in a flame on a rotating heat-resistant substrate, wherein the heat-resistant substrate has an axial direction. A ribbon-shaped burner or a row of burners arranged in parallel with the base forms a flame for forming silica fine particles over substantially the entire length of the silica fine particle deposition site, and the flame and the heat-resistant base line are aligned with each other. While gradually reciprocating along the direction, the thermal energy per unit time applied during the silica fine particle deposition is gradually reduced in the radial direction from the inner portion in contact with the heat resistant substrate, and reaches the minimum in the intermediate region, Then, a method for producing a soot-like silica body, characterized in that silica particles are successively deposited on a heat-resistant substrate while changing so that the number increases again as it goes to the outer surface site. 3. A plurality of burners are arranged in a row along the axial direction of the heat resistant base in parallel with the base, and the burner row and the base are arranged to have an interval substantially equal to the arrangement interval of the burners. While relatively reciprocating with the amount of amplitude, the thermal energy applied per unit time during the silica fine particle deposition is gradually reduced in the radial direction from the inner part in contact with the heat resistant substrate and reaches the minimum in the intermediate region. 3. A method for producing a soot-like silica body according to claim 2, characterized in that silica particles are successively deposited on the heat-resistant substrate while changing so as to increase again toward the outer surface site.