JP2019048750A - Method of correcting quartz glass crucible - Google Patents

Abstract

To properly reshape, without any increase in cost, a quartz crucible which has become oblate around an axis as a result of use for single-crystal lifting.SOLUTION: The present invention relates to a method of correcting a quartz glass crucible C having become oblate around a crucible axis, the method including the steps of: measuring a first diameter of an opening part C4 of the quartz glass crucible and a second diameter orthogonal thereto; mounting the quartz glass crucible on a base 10 with the opening part of the quartz glass crucible laid laterally such that a diameter larger between the first diameter and second diameter is in a perpendicular direction; maintaining a predetermined range on a lower side of the quartz glass crucible, having the opening part laid laterally, with mold members 2, 3 and 4; and heating the quartz glass crucible to cause the quartz glass crucible to deform by gravitation, and bringing the predetermined range of the crucible into contact with the mold members.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method of repairing a quartz glass crucible, for example, to a method of modifying a quartz glass crucible which can be repaired without discarding a used deformed quartz glass crucible.

  The CZ method is widely used for the growth of silicon single crystals. In this method, a seed crystal is brought into contact with the surface of a silicon melt contained in a quartz glass crucible, and while rotating the crucible, the seed crystal is pulled upward while rotating in the opposite direction, thereby making the seed crystal A single crystal is formed at the lower end.

  By the way, in the initial stage of silicon single crystal growth, the operation must be stopped when a defect such as the single crystal having dislocation occurs. In the case of shutdown, it is possible to recover the silicon single crystal during growth, but the quartz glass crucible used is slightly off-centered around the axis, and conventionally it is to be reused as it is Because it can not be

  To solve such problems, Patent Document 1 discloses a method of regenerating a quartz glass crucible using a core having an outer diameter slightly smaller than the inner diameter of the crucible and a rotary mold for adjusting the outer peripheral surface of the quartz glass crucible. ing. In this regeneration method, as shown in FIG. 8 (a), the quartz glass crucible C is turned downward, the core 51 is covered, and the quartz glass crucible C is changed by its own weight in a heating furnace (not shown). The first step in which the inner and outer diameters of the quartz glass crucible C are slightly reduced along the core 51 by heating to a temperature as described above, and as shown in FIG. And the second step of rotating the quartz glass crucible C while heating it to a temperature at which the quartz glass crucible C is deformed and pressing the quartz glass crucible C against the inner peripheral surface of the mold to deform it by centrifugal force. .

JP 2004-323338 A

However, in the method for molding a quartz glass crucible (reproduction method) disclosed in Patent Document 1, not only the mold but also a mechanism for rotating the mold is required, so there is a problem that the cost is increased.
Further, according to the experience of the inventors of the present invention, even if the entire outer peripheral surface of the crucible is pressed with a mold to adjust the shape, a difference in cooling rate occurs between the side and the bottom of the quartz glass crucible. There is a problem that stress concentrates on the part and distortion occurs.

  As a result of intensive studies by the inventors of the present invention for these problems, in order to adjust the shape of the quartz glass crucible, the entire quartz glass crucible is not covered with a mold, but a part of the quartz glass crucible is molded It came to find that the shape could be adjusted without distortion by covering with.

  The present invention has been made under the above-mentioned circumstances, and for example, it is possible to control the shape of a quartz glass crucible which is eccentrically rotated around an axis by using it for pulling a single crystal, etc. while suppressing the cost and without distortion. It is an object of the present invention to provide a method of correcting a quartz glass crucible that can be made.

  A method of correcting a quartz glass crucible according to the present invention made to achieve the above object is a method of correcting a quartz glass crucible having a circularly-circular shape around a crucible axis, the first diameter at the opening of the quartz glass crucible And a step of measuring a second diameter perpendicular thereto, and in a state in which the opening of the quartz glass crucible is in a lateral direction, the larger diameter of the first diameter and the second diameter is in the vertical direction Placing the quartz glass crucible on the base so as to become the above, holding a predetermined range under the quartz glass crucible whose opening is made horizontal, with a mold member, and the quartz glass crucible Heating the quartz glass crucible and deforming the quartz glass crucible by its own weight to bring a predetermined range of the crucible into close contact with the mold member.

In the step of heating the quartz glass crucible and deforming the quartz glass crucible by its own weight to bring the predetermined range of the crucible into close contact with the mold member, the viscosity of the quartz glass crucible on the base is 10 ^14.5. -10 ^13.2 It is desirable to heat the said quartz glass crucible until it becomes poise.
Further, after the step of heating the quartz glass crucible and deforming the quartz glass crucible by its own weight to bring a predetermined range of the crucible into close contact with the mold member, the difference between the first diameter and the second diameter It is desirable to carry out the step of stopping heating and cooling the quartz glass crucible when the value of.
Alternatively, in the step of heating the quartz glass crucible and deforming the quartz glass crucible by its own weight to bring a predetermined range of the crucible into close contact with the mold member, along the vertical direction at the opening of the quartz glass crucible A rod member may be arranged to indicate the length of the target diameter, and heating may be stopped and cooled to the height of the tip of the rod at the timing when the height of the opening deforms.

Further, in the step of holding a predetermined range on the lower side of the quartz glass crucible in which the opening is horizontal, with the mold member, the predetermined range on the lower side of the quartz glass crucible in which the opening is horizontal is the mold Preferably, the member is supported from the crucible opening to the crucible bottom corner.
Furthermore, in the step of holding the lower predetermined range of the quartz glass crucible in which the opening is horizontal, by the mold member, the lower predetermined range of the quartz glass crucible in which the opening is horizontal is the above It is desirable that 50% to 80% of the inner diameter of the crucible in the lateral width direction be supported by the mold member.

According to such a method, in the quartz glass crucible having a circular shape, the opening is placed sideways so that the maximum diameter of the circular portion is in the vertical direction, and heating is performed to a predetermined temperature (1000 ° C. to 1300 ° C.) Thus, the crucible can be made viscous and deformed by its own weight to correct the eccentricity of the quartz glass crucible.
In addition, at that time, a part of the quartz glass crucible, specifically, the lower half of the quartz glass crucible with the opening facing side is supported by the mold member, so that the quartz glass crucible has a shape intended for the purpose. It becomes easy to deform, and it is possible to correct the shape of the deviated circle with high accuracy.

  According to the present invention, for example, it is possible to adjust the shape without distortion with respect to a quartz glass crucible which is eccentrically rotated around an axis by being used for single crystal pulling or the like.

FIG. 1 is a perspective view of a jig (mold member) used in the method of correcting a quartz glass crucible according to the present invention. FIG. 2 is a front view showing a state in which the quartz glass crucible is held by the jig shown in FIG. FIG. 3 is a side view showing a state in which the quartz glass crucible is held by the jig shown in FIG. FIG. 4 is a plan view showing a state in which the quartz glass crucible is held by the jig shown in FIG. FIG. 5 is a flow chart showing a flow of a method of correcting a quartz glass crucible using the jig shown in FIG. FIG. 6 is a schematic view showing a state transition in the method of correcting a quartz glass crucible using the jig shown in FIG. FIG. 7 is a schematic view showing a modification of the method for repairing a quartz glass crucible according to the present invention. FIG. 8 is a cross-sectional view for explaining a conventional method of regenerating a quartz glass crucible.

  Hereinafter, an embodiment of a method for correcting a quartz glass crucible according to the present invention will be described based on the drawings. FIG. 1 is a perspective view of a jig (mold member) used in the method of correcting a quartz glass crucible according to the present invention. 2 is a front view showing a state in which the quartz glass crucible is held by the jig, FIG. 3 is a side view showing a state in which the quartz glass crucible is held by the jig, and FIG. 4 is a quartz glass crucible by the jig It is a top view which shows the state which hold | maintained.

  The quartz glass crucible C to be corrected in the present invention is formed to have, for example, a diameter (aperture) of 810 mm, and a bottom portion C1 having a predetermined curvature (large R portion) as shown in FIGS. It has a bottom corner (small R portion inflection point) C2 formed around it and having a predetermined curvature, and a straight body portion C3 extending upward from the bottom corner C2. The upper end of the straight body portion C3 is an opening C4.

  A jig 1 shown in FIG. 1 includes a base 10, a pair of body holding members 2 and 3 disposed on the base 10, and the pair of body holding members 2 on the base 10 shown in FIG. , 3 and a bottom holding member 4 arranged at the rear. The jigs 1 are all formed of silicon carbide (SiC) which is more excellent in heat resistance and deformation resistance than quartz glass.

  The pair of barrel holding members 2 and 3 are arranged at a predetermined position to support the quartz glass crucible C by moving in the horizontal direction (direction parallel to the upper surface of the base 10) or from the predetermined position It is possible to get rid of it. When arranged at the predetermined position to be supported, as shown in FIGS. 2 to 4, the lower half of the straight body portion C3 of the straight body portion C3 of the quartz glass crucible C in a state in which the opening C4 is turned sideways Is configured.

That is, the body holding members 2 and 3 have the concave surfaces 2a and 3a corresponding to the outer peripheral surface of the straight body C3 of the quartz glass crucible C, and the concave surfaces 2a and 3a are the direct surfaces of the quartz glass crucible C. It is supported in a state of being in contact with the body portion C3.
Further, since the concave curved surfaces 2a and 3a are formed to have a target curvature, when the straight body portion C3 of the quartz glass crucible C having a circular deviation is supported, a gap is generated ( When the quartz glass crucible C is deformed by heat treatment to be described later, the straight body portion C3 and the concave curved surfaces 2a and 3a are in close contact with each other, and the gap disappears.
The height H1 of the concave curved surfaces 2a and 3a is determined so that the concave surface 2a and 3a can be supported to the height of the radial half of the straight body portion C3 of the quartz glass crucible C with the opening C4 sideways oriented. . Specifically, the diameter of the quartz glass crucible C is preferably 24 inches (about 610 mm) or more and 36 inches (about 910 mm) or less, and the dimension H1 is half the diameter of the crucible diameter. The size of the dimension H1 is about 305 mm or more and about 455 mm or less.
Further, the dimension L1 in the crucible axial direction of the curved surfaces 2a and 3a is defined as the length supported from the crucible opening end (opening C4) to the small R inflection point (bottom corner C2) in the straight barrel C3. It is done.

The bottom portion holding member 4 is movable in the horizontal direction, and is disposed at a predetermined position on the base 10, whereby the bottom portion C1 of the quartz glass crucible C in a state in which the opening C4 is turned sideways. It is configured to support the lower half.
That is, the bottom holding member 4 has a concave surface 4a corresponding to the bottom surface C1 outer surface (curved surface) of the quartz glass crucible C, and the support is performed in a state where the concave surface 4a is in contact with the bottom C1 of the quartz glass crucible C It is supposed to be
In addition, since the concave surface 4a is formed to have a target curvature, a gap is generated when supporting the bottom portion C1 of the quartz glass crucible C having a circular shape (a heat treatment described later) As a result, the bottom portion C1 and the concave surface 4a are in close contact with each other by the deformation of the quartz glass crucible C, and the gap disappears).
Incidentally, as shown in FIG. 3, the dimension H2 in the height direction of the concave surface 4a is determined so that the concave surface 4a can be supported to the height in the radial direction half of the bottom portion C1 of the quartz glass crucible C in which the opening C4 is oriented horizontally. ing. Specifically, the diameter of the quartz glass crucible C is preferably 24 inches (about 610 mm) to 36 inches (about 910 mm), and the dimension H2 is half the diameter of the crucible diameter. The size of the dimension H2 is about 305 mm or more and about 455 mm or less.
Further, as shown in FIG. 4, the dimension L2 in the width direction of the concave surface 4a is determined so as to support a region of 50% to 80% of the inner diameter of the crucible.
This is because when the dimension L2 in the width direction is less than 50% of the inner diameter of the crucible, the bottom C1 may be deformed excessively, which is not preferable. When the dimension L2 is more than 80%, the bottom is not easily deformed and not preferable. It is.

Then, the correction method of the quartz glass crucible using such a jig | tool 1 is demonstrated using the schematic diagram which shows the flow of FIG. 5, and the state transition of FIG.
First, measure the maximum diameter y (first or second diameter) and the minimum diameter x (first or second diameter) orthogonal to the maximum diameter y at the opening C4 of the quartz glass crucible C which is deviated circularly around the crucible axis. It lengthens (step S1 of FIG. 5). Specifically, the outer surface of the crucible is exposed by the outer diameter measuring device (a device for measuring the shape of the crucible without placing the crucible) or an outer diameter measuring jig (contact type with a caliper or the like) (from the opening) Measure at a position of 10 mm in the bottom direction, and define the maximum / minimum of the measured value as the maximum diameter y / the minimum diameter x.

Next, on the base 10, as shown in FIG. 6A, the opening C4 of the quartz glass crucible C is turned to the side as shown in FIG. The straight barrel portion C3 of the quartz glass crucible C is disposed so as to be located between 3 (Step S2 in FIG. 5). The pair of body holding members 2 and 3 are in a state in which the concave surfaces 2a and 3a are opposed to each other, and the concave surfaces 2a and 3a are in a state of facing the outer peripheral surface of the straight body C3 of the crucible.
At this time, as shown in FIG. 2, the quartz glass crucible C is disposed such that the maximum diameter y in the crucible opening C4 which is offset is in the vertical direction (the minimum diameter x of the crucible opening C4 is disposed in the horizontal direction) To do).

Further, as shown in FIG. 6B, the pair of body holding members 2 and 3 are moved in directions approaching each other, and the respective concave curved surfaces 2a and 3a are brought into contact with the straight body C3 of the quartz glass crucible C and supported. Yes (there is a gap at this point).
As a result, the lower half in the radial direction of the straight barrel C3 of the quartz glass crucible C whose opening C4 is turned sideways is held by the trunk holding members 2 and 3 (step S3 in FIG. 5).

Further, as shown in FIG. 6C, the bottom holding member 4 is moved closer to the bottom C2 of the quartz glass crucible C on the base 10, and the concave curved surface 4a is brought into contact with the bottom C2 of the quartz glass crucible C Yes (there is a gap at this point).
As a result, the lower half in the radial direction of the bottom C1 of the quartz glass crucible C whose opening C4 is oriented horizontally is held by the bottom holding member 4 (step S4 in FIG. 5).

When the quartz glass crucible C is held by the jig 1, as shown in FIG. 6D, the quartz glass crucible C is accommodated in the heat treatment furnace 20 together with the base 10 and heat treatment is performed by the heater 21 at 1000 ° C. to 1300 ° C. (Step S5 in FIG. 5).
When the quartz glass crucible C is heated to this temperature, its viscosity becomes 10 ^14.5 poise to ^10.13 poise, and as shown in the figure, the quartz glass crucible C whose opening C 4 is horizontally oriented has its height direction by its own weight It is deformed so that the width is low. That is, the opening diameter y (maximum diameter) in FIG. 2 becomes shorter, and the opening diameter x (minimum diameter) becomes longer (in step S6 in FIG. 5).
Here, the lower half of the quartz glass crucible C in which the opening C4 is oriented horizontally is deformed until it adheres to the concave curved surfaces 2a, 3a, 4a of the body holding members 2, 3 and the bottom holding member 4, The half deforms to the same shape to balance with the lower half.

When the lower half of the quartz glass crucible C whose opening C4 is oriented horizontally is in close contact with the concave surface 2a, 3a, 4a of the body holding members 2, 3 and the bottom holding member 4, heating is continued as follows: Since the upper half of the crucible is deformed too much, it is necessary to stop the heating at a predetermined timing.
As the timing to stop the deformation (heating) of the quartz glass crucible C, it is assumed that the diameter y = x of the opening by length measurement or visual observation, and the quartz glass crucible C is cooled at this time to stop the deformation. The circle is removed (step S7 in FIG. 5). Specifically, if the opening diameter y (maximum diameter)-the opening diameter x (minimum diameter) becomes 0.4 mm or less by this processing, it can be used as a modified quartz glass crucible C.

As described above, according to the embodiment of the present invention, in the quartz glass crucible C having a circular shape, the opening C4 is oriented sideways so that the maximum diameter of the circular portion is in the vertical direction, By heating to a temperature of 1000 ° C. to 1300 ° C.), the viscosity of the crucible can be imparted and the crucible can be deformed by its own weight, and the eccentric circle of the quartz glass crucible C can be corrected.
Further, at that time, a part of the quartz glass crucible C, specifically, the lower half of the quartz glass crucible C with the opening C4 sideways is supported by the jigs 2, 3 and 4 as mold members. As a result, the quartz glass crucible C can be easily deformed into a target shape, and the shape of the eccentric circle can be corrected with high accuracy.

In the above embodiment, when the edge portion of the quartz glass crucible C is deformed by its own weight, the measurement criteria for when the maximum diameter y = x is obtained by performing non-contact length measurement or visually Any method can be adopted.
Alternatively, as shown in the front view of FIG. 7 (a) and the side view of FIG. 7 (b), a rod member 15 showing the length of the target diameter is disposed along the maximum diameter y. Heating may be stopped and cooling may be performed at timing when the height of the opening C4 is deformed to the height. The material of the rod member 15 is preferably silicon carbide (SiC).

Moreover, in the said embodiment, although the quartz glass crucible C was arrange | positioned so that the largest diameter y in the crucible opening part C4 which carried out the deviation circle might become a perpendicular direction, in this invention, it is limited to the form is not.
For example, the first diameter and the second diameter perpendicular to the first diameter are measured at the opening of the quartz glass crucible, and the first diameter and the second diameter are measured in a state where the opening of the quartz glass crucible is oriented horizontally. The quartz glass crucible may be placed on the base so that the larger diameter in the vertical direction is in the vertical direction.

  Then, the correction method of the quartz glass crucible which concerns on this invention is further demonstrated based on an Example. In the present example, the method for correcting a quartz glass crucible shown in the above embodiment was carried out on a quartz glass crucible (diameter about 812 mm) after single crystal pulling use, and the effect was verified.

(Experiment 1)
In Examples 1 to 3, the degree of eccentricity is determined for each of the quartz glass crucible before use for pulling a single crystal, the quartz glass crucible after use, and the quartz glass crucible subjected to the correction method of the present invention after use. Thus, the effects of the present invention were verified.
In order to determine the degree of deviation, the predetermined position at the opening is 0 °, the diameter at 0 ° -180 ° and the diameter at 90 ° -270 ° orthogonal thereto are determined, and the difference is the degree of deviation (mm) And
Table 1 shows the conditions of Examples 1 to 3 and the results of the degree of deviation. In Table 1, “before use” indicates “a silica glass crucible before use for pulling a single crystal”, “before treatment” indicates a “a silica glass crucible after use for pulling a single crystal”, and “after a treatment” "A quartz glass crucible which has been subjected to the correction method of the present invention after being used for single crystal pulling".

  As shown in Table 1, by applying the correction method of the present invention to the quartz glass crucible before treatment, it was confirmed that the degree of eccentricity was improved to the same extent as before use.

(Experiment 2)
In Examples 4 to 8, the eccentricity with respect to viscosity is changed for the quartz glass crucible before use for pulling a single crystal, the quartz glass crucible after use, and the quartz glass crucible for which the correction method of the present invention is implemented after use. By asking for, the effect of the present invention was verified.
The silica glass crucibles with different viscosities of Example 4 to Example 8 were used to determine the degree of deviation before use, before treatment, and after treatment. The definitions before use, before treatment and after treatment are the same as in Experiment 1. Further, the degree of deviation was determined by the same method as in Experiment 1.
Table 2 shows the conditions of Example 4 to Example 8 and the results of the degree of deviation.

As shown in the results of Table 2, in Example 4 and Example 8, the degree of deviation after treatment increases as 0.6, and the appropriate range of viscosity is 10 ^14.5 poise to 10 ^13.2 poise. It confirmed that it was.

(Experiment 3)
In Examples 9 to 12, a quartz glass crucible before use for pulling a single crystal, a quartz glass crucible after use, and a quartz glass crucible subjected to the correction method of the present invention after use are treated silica glass crucibles. The effect of the present invention was verified by pulling a single crystal using.
Using the large (> 0.4 mm) quartz glass crucible of Example 9 to Example 12, the degree of eccentricity before use, before treatment, and after treatment was determined. Then, the single crystal was pulled using the treated quartz glass crucible, and the grown single crystal was evaluated. The definitions before use, before treatment and after treatment are the same as in Experiment 1. Further, the degree of deviation was determined by the same method as in Experiment 1.
Table 3 shows the conditions of Examples 9 to 12 and the results of the degree of deviation.

  From the results shown in Table 3, it was confirmed that single crystals can be pulled well even if the treated silica glass crucible is used if the degree of deviation after treatment is 0.4 or less.

(Experiment 4)
In Examples 13 to 18, the quartz glass crucible before being used for pulling a single crystal, the quartz glass crucible after being used, and the correction method of the present invention after being used are implemented on the condition of the aperture size of the quartz glass crucible. The degree of eccentricity was determined for each of the quartz glass crucibles, and the size of the crucible diameter at which the effects of the present invention could be obtained was verified.
The silica glass crucibles having different diameters from Example 13 to Example 18 were used to determine the degree of eccentricity before use, before treatment, and after treatment. The upper end position for supporting the lower side of the crucible in a state in which the crucible opening was in the horizontal direction was half the height of the diameter of the crucible. The definitions before use, before treatment and after treatment are the same as in Experiment 1. Further, the degree of deviation was determined by the same method as in Experiment 1.
Table 4 shows the conditions of Example 13 to Example 18 and the results of the degree of deviation.

As shown in Table 4, in the case of a 22-inch quartz glass crucible, the degree of deviation after treatment was poor, and in the second evaluation, the side wall thickness was thin, and breakage occurred when the crucible was taken out from the pulling apparatus. In the case of a crucible of 24 inches or more, good results were obtained for the degree of deviation after treatment. Therefore, it was confirmed that the crucible diameter at which the effect of the present invention can be obtained is at least 24 inches (about 610 mm) to 36 inches (910 mm).
Moreover, it confirmed that the upper end position at the time of supporting a crucible lower side in the state which made the crucible opening part side was about 305 mm-about 455 mm of the half according to a crucible caliber by this result.

  From the experimental results of the above examples, according to the method for correcting a quartz glass crucible according to the present invention, the strain is suppressed while the cost is reduced with respect to the quartz glass crucible which is eccentrically rotated around the axis by using for pulling single crystals. It was confirmed that the shape could be adjusted without.

1 Jig (mold member)
Reference Signs List 2 body holding member 3 body holding member 4 bottom holding member 10 base C quartz glass crucible C1 bottom C2 bottom corner C3 straight body C4 opening

Claims (6)

It is a correction method of a quartz glass crucible which is eccentrically rotated around the crucible axis, and
Measuring a first diameter and an orthogonal second diameter at the opening of the quartz glass crucible;
The quartz glass crucible is placed on the base so that the larger diameter of the first diameter and the second diameter is in the vertical direction, with the opening of the quartz glass crucible being in the horizontal direction. Step and
Holding a predetermined range on the lower side of the quartz glass crucible whose opening is turned sideways by a mold member;
Heating the quartz glass crucible and deforming the quartz glass crucible by its own weight to bring a predetermined range of the crucible into close contact with the mold member;
A method of repairing a quartz glass crucible characterized in that the method comprises: Heating the quartz glass crucible and deforming the quartz glass crucible by its own weight to bring a predetermined range of the crucible into close contact with the mold member;
The method for repairing a quartz glass crucible according to claim 1, wherein the quartz glass crucible is heated until the viscosity of the quartz glass crucible on the base is in the range of 10 ^14.5 poise to 10 ^13.2 poise. . After the step of heating the quartz glass crucible and deforming the quartz glass crucible by its own weight to bring a predetermined range of the crucible into close contact with the mold member,
3. The method according to claim 1, wherein the step of stopping heating and cooling the quartz glass crucible is performed when the difference between the first diameter and the second diameter is 0.4 mm or less. How to fix a quartz glass crucible. Heating the quartz glass crucible and deforming the quartz glass crucible by its own weight to bring a predetermined range of the crucible into close contact with the mold member;
A rod member indicating the length of the target diameter is disposed along the vertical direction at the opening of the quartz glass crucible, and heating is performed at the timing when the height of the opening is deformed to the height of the tip thereof. The method for correcting a quartz glass crucible according to claim 1 or 2, characterized by stopping and cooling. In the step of holding a predetermined range under the quartz glass crucible whose opening is turned sideways with a mold member,
The predetermined range under the quartz glass crucible where the opening is turned to the side is supported from the crucible opening to the crucible bottom corner by the mold member. How to fix the quartz glass crucible described in. In the step of holding a predetermined range under the quartz glass crucible whose opening is turned sideways with a mold member,
The predetermined range on the lower side of the quartz glass crucible in which the opening portion is oriented in the lateral direction is supported by 50% to 80% of the crucible inner diameter in the lateral width direction by the mold member. How to fix a quartz glass crucible.

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