JP5808076B2 - Tungsten crucible, method for producing the same, and method for producing sapphire single crystal - Google Patents

Description

  The present invention relates to a tungsten crucible, a method for producing the same, and a method for producing a sapphire single crystal, and in particular, a tungsten crucible excellent in high-temperature strength at a corner portion connecting a bottom portion and a side wall portion, a method for producing the same, and such tungsten. The present invention relates to a method for producing a sapphire single crystal using a crucible.

  Conventionally, as a component part of a manufacturing apparatus used at a high temperature such as a metal evaporation container, a metal oxide dissolution container, a crystal production container, etc., a bottomed cylinder with an open top in which a bottom part and a side wall part are connected via a corner part A molybdenum crucible is used.

  Such a molybdenum crucible is manufactured by cutting a forged molybdenum body or drawing a plate made of molybdenum. For example, Japanese Patent Application Laid-Open No. 11-169993 (Patent Document 1) discloses a crucible using a molybdenum forged body. Forging, tungsten crystal grains having a large grain size are formed by pressing or stretching associated with forging. This phenomenon is likely to occur, and this phenomenon becomes remarkable particularly at corners where the amount of processing is large.

In addition, for the method of drawing a plate made of molybdenum, a reduction in the thickness of the side wall is inevitable, and the fiber structure at the corners connecting the bottom and the side wall is likely to be swollen, resulting in large variations in high temperature strength. Occur.
Japanese Patent No. 3917208 (Patent Document 2) discloses a crucible made of a tungsten molybdenum alloy containing 1 to 5% by mass of tungsten. However, since the crystal grain size of molybdenum is as large as 1 mm or more, it cannot be said that the lifetime is sufficient.

Japanese Patent Application Laid-Open No. 11-169993 Japanese Patent No. 3917208

  As described above, conventional molybdenum crucibles are prone to processing strain, and residual strain is likely to occur especially at corners where the amount of processing is large, which accelerates recrystallization of molybdenum crystal grains when used at high temperatures. As a result, the high temperature strength tends to decrease. Furthermore, it is conceivable to secure high-temperature strength by thickening the corners, but it is not always easy to thicken only the corners because a plate material is usually used.

Although various studies have been made to improve the high temperature strength of molybdenum crucibles as described above, molybdenum crucibles that are still excellent in high temperature strength, particularly high temperature strength at the corners connecting the bottom and side walls, Not obtained. In particular, when the usage environment reached a high temperature of 2200 ° C. or higher, the molybdenum crucible was insufficient in durability. One reason for this is that molybdenum has a melting point of 2620 ° C., so that molybdenum melts out when the usage environment becomes high. On the other hand, since tungsten has a high melting point of 3400 ° C., it seems that tungsten is suitable for crucibles used at high temperatures, but conventional tungsten crucibles have insufficient high-temperature strength.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a tungsten crucible that is excellent in high-temperature strength, in particular, high-temperature strength in a corner portion connecting the bottom portion and the side wall portion. Another object of the present invention is to provide a manufacturing method for easily manufacturing such a crucible made of tungsten having excellent high-temperature strength. Furthermore, an object of the present invention is to provide a method for producing a sapphire single crystal using such a tungsten crucible excellent in high temperature strength.

The tungsten crucible of the present invention is a bottomed cylindrical tungsten crucible made of tungsten having a purity of 99.9% or more and having an opening in which a bottom portion and a side wall portion are connected via a corner portion, Tungsten has an average crystal grain size of 20 μm or more and 50 μm or less, and a ratio of the number of tungsten crystal grains having a crystal grain size of 10 μm or more and 80 μm or less of 90% or more. The ratio is 0.8 to 1.2, the relative density is 95% or more, and the corner portion is thicker than the side wall portion.
Further, the tungsten crucible preferably has an opening having an inner diameter of 100 mm or more. The tungsten crucible preferably has a density of 95% or more. Moreover, it is preferable that ratio of the thickness of the said corner | angular part with respect to the said side wall part is 1.2 or more. The tungsten crucible is preferably used as a raw material melt for producing a sapphire single crystal.
The first method for producing a tungsten crucible according to the present invention is a method for producing the tungsten crucible according to the present invention , wherein a tungsten powder having a purity of 99.9% or more is applied at a pressure of 100 MPa or more and 200 MPa or less. A forming step for CIP into a crucible shape, a first sintering step for sintering at 1300 ° C. or higher in a hydrogen atmosphere, and a second sintering for sintering at 2000 ° C. or higher in a reducing or inert atmosphere It has the process, It is characterized by the above-mentioned.
The second tungsten crucible manufacturing method of the present invention is a manufacturing method for manufacturing the tungsten crucible of the present invention , and a forming step of forming tungsten powder having a purity of 99.9% or more into a crucible shape. And a HIP process in which an HIP process is performed at a pressure of 100 MPa or more and 200 MPa or less and 1300 ° C. or more in an inert atmosphere.
The sapphire single crystal production method of the present invention is a sapphire single crystal production method for producing a sapphire single crystal by crystal growth from a raw material melt, and the tungsten of the present invention is used as a crucible for charging the raw material melt. A crucible made of metal is used.
Moreover, it is preferable that the heating temperature of a melt is 2000 degreeC or more.

  According to the present invention, in a tungsten crucible having a bottomed cylindrical shape made of tungsten having a purity of 99.9% or more and having a bottom portion and a side wall portion connected via a corner portion, the average grain size of the tungsten By setting the diameter to 50 μm or less, a tungsten crucible excellent in high-temperature strength, particularly high-temperature strength in the corner portion connecting the bottom portion and the side wall portion can be obtained.

  Further, according to the present invention, in the method of manufacturing a tungsten crucible for manufacturing a bottomed cylindrical tungsten crucible having an open top where the bottom and the side wall are connected via a corner, the first sintering step, By using the first manufacturing method using the second sintering step or the second manufacturing method using HIP sintering, tungsten has excellent high temperature strength, particularly high temperature strength at the corner portion connecting the bottom portion and the side wall portion. The crucible made can be easily manufactured.

  Furthermore, according to the present invention, in the method for producing a sapphire single crystal for producing a sapphire single crystal by crystal growth from a melt of the raw material, by using the tungsten crucible of the present invention as a crucible for charging the melt of the raw material, The operating time of the manufacturing apparatus used for manufacturing the sapphire single crystal can be lengthened, thereby improving the productivity of the sapphire single crystal and reducing the production cost.

Sectional drawing which shows an example of the crucible made from tungsten of this invention. Sectional drawing which shows the modification of the crucible made from tungsten of this invention. Sectional drawing which shows the other modification of the tungsten crucible of this invention. Sectional drawing which shows the other modification of the tungsten crucible of this invention.

Hereinafter, the present invention will be specifically described with reference to the drawings.
FIG. 1 is a sectional view showing an example of a tungsten crucible of the present invention. The tungsten crucible 1 of the present invention is made of tungsten having a purity of 99.9% or more, and has a substantially plate-like bottom 2 and a side wall provided at a predetermined height so as to surround the outer periphery of the bottom 2. 3 and a corner portion 4 connecting the bottom portion 2 and the side wall portion 3, and these are integrally formed so as to form an open bottomed cylindrical shape. The corner portion 4 has a thickness substantially the same as, for example, the bottom portion 2 and the side wall portion 3 and is curved in an arc shape. The side wall portion 3 rises from the corner portion 4 substantially vertically. . Further, the purity should be as high as 99.99% or higher.
That is, it is better that the impurity components other than tungsten are as small as 0.1% by mass or less, and further 0.01% by mass or less. Typical impurity components are 0.01 wt% (100 wtppm) or less of iron, 0.04 wt% (400 wtppm) or less in total of other metal components, 0.01 wt% (100 wtppm) or less of oxygen, and 0. 01 wt% (100 wtppm) or less is preferable. It goes without saying that the smaller the impurity component, the better.

  The shape of the tungsten crucible 1 of the present invention is not particularly limited as long as it has at least a function as a crucible. For example, as shown in FIG. 3, the corner 4 may be bent at a substantially right angle as shown in FIG. 3, for example, and the side wall 3 may be the bottom 2 as shown in FIG. The diameter may be gradually increased from the opening toward the opening.

The tungsten crucible of the present invention has an average crystal grain size of 50 μm or less. By reducing the average particle size, tungsten grains that have grown abnormally can be eliminated, and the high-temperature strength can be increased. When the average crystal grain size exceeds 50 μm, if there are large tungsten crystal grains with grain growth, the structure is distorted, which causes a decrease in high-temperature strength.
Moreover, even if the average crystal grain size is 50 μm or less, it is not preferable that there are too large tungsten crystal grains. Therefore, the proportion of tungsten crystal grains having a crystal grain size of 10 μm or more and 80 μm or less is preferably 90% or more in terms of the number of particles. That is, the ratio of the number of particles having a particle diameter of 10 μm or more and 80 μm or less to the number of particles of the total particle diameter of tungsten crystal grains ((number of particles having a particle diameter of 10 μm or more and 80 μm or less) / (number of particles of all particle diameters) × 100 [ %]) Is 90% or more.

  Thus, by setting the ratio of tungsten crystal grains having a grain size of 10 μm or more and 80 μm or less to 90% or more, in other words, a fine tungsten crystal grain having a grain size of less than 10 μm or an excessively large grain size exceeding 80 μm. By reducing the number of tungsten crystal grains and suppressing a large variation in grain size as a whole, the high temperature strength, in particular, the high temperature strength of the corner portion connecting the bottom portion 2 and the side wall portion 3 can be improved.

  In addition, the tungsten crystal grains having a particle size of 10 μm or more and 80 μm or less included in 90% or more do not necessarily have to be composed of a single particle size selected from 10 μm or more and 80 μm or less. If it is in the range of 10 μm or more and 80 μm or less, it can be composed of tungsten crystal grains having different particle sizes.

  Further, the ratio of the tungsten crystal grains having a grain size of 10 μm or more and 80 μm or less is specifically 2 in the corner portion 4 where a tungsten crystal grain having a large grain size is likely to be generated when manufactured by forging as a conventional example. This is obtained by averaging the proportion of tungsten crystal grains having a particle size of 10 μm or more and 80 μm or less, which is calculated for a total of four measurement locations, that is, a location and any two locations in the side wall portion 3 that are not.

  The average crystal grain size and the ratio of crystal grains of 10 μm or more and 80 μm or less are measured by a line intercept method. First, an enlarged photograph having a size of 500 μm × 500 μm is taken with respect to a cross section as an individual measurement location of the tungsten crucible 1, an arbitrary straight line is drawn on the photograph, and the number of tungsten crystal grains that the straight line crosses is measured. At the same time, the grain size of each tungsten crystal grain traversed by this straight line (the grain diameter at the part traversed by the straight line, ie, the length of the straight line across the tungsten crystal grain) is measured.

And an average value is calculated | required by "the number of tungsten crystal grains on 500 micrometers / straight line 500 micrometers". An average value obtained by performing this operation at three or more arbitrary locations is defined as an average crystal grain size. The average crystal grain size is most preferably obtained by taking an average value at two corners and two side walls as described later.
Further, from the number of tungsten crystal grains measured in a straight line of 500 μm or more and the number of tungsten crystal grains having a grain size of 10 μm or more and 80 μm or less, the particle diameter at each measurement location is 10 μm or more and 80 μm or less by the above formula. The ratio of tungsten crystal grains can be obtained. Further, the average proportion of tungsten crystal grains having a grain size of 10 μm or more and 80 μm or less at each measurement location (2 locations (corner portion 4) +2 locations (side wall portion 3), 4 locations in total)) thus obtained is further averaged. By doing so, the proportion of tungsten crystal grains having a grain size as a final average value of 10 μm or more and 80 μm or less can be obtained.

  Such a tungsten crucible 1 is excellent in high-temperature strength, particularly high-temperature strength at the corners connecting the bottom portion 2 and the side wall portion 3, so that a large-sized one, particularly the inner diameter of the opening portion is 100 mm or more, It can use suitably for what becomes 300 mm or more.

  The average grain size of the tungsten crystal grains is preferably 40 μm or less. Such an average particle diameter tends to be excellent in high temperature strength, in particular, high temperature strength of the corner portion connecting the bottom portion 2 and the side wall portion 3.

  Although the thickness of the side wall part 3 and the corner part 4 may be the same or different, the corner part 4 becomes thicker than the side wall part 3 from the viewpoint of securing the high temperature strength of the corner part 4. For example, the ratio of the thickness of the corner 4 to the side wall 3 (the thickness of the corner 4 / the thickness of the side wall 3) is preferably 1.2 or more. If the thickness ratio is smaller than the above range, the effect of improving the high temperature strength of the corner 4 is not necessarily sufficient, and if it is within the above range, the high temperature strength of the corner 4 may be sufficient. However, if it exceeds this range, the weight of the tungsten crucible 1 may increase unnecessarily, which is not preferable.

  Although the site | part which measures the thickness in the side wall part 3 and the corner | angular part 4 is not necessarily limited, Usually, about the side wall part 3, the height direction of the side wall part 3 as shown, for example by the wavy line 5 of FIG. The corner portion 4 is preferably a substantially intermediate portion, and the corner portion 4 is, for example, a portion connecting the substantially intermediate portions in the radial direction of the inner surface and the outer surface of the curved portion of the corner portion 4 as shown by a wavy line 6 in FIG. Preferably there is.

  Further, the ratio of the average grain size of the tungsten crystal grains in the corner portion 4 to the side wall portion 3 (the average grain size of the tungsten crystal grains in the corner portion 4 / the average grain size of the tungsten crystal grains in the side wall portion 3) is 0.8 or more and 1 .2 or less is preferable. When the ratio of the average particle diameter is out of the above range, in any case, there is a large variation in the average particle diameter between the side wall part 3 and the corner part 4, and the high temperature strength may not be excellent. There is.

  In addition, the average particle diameter of the tungsten crystal grains of the side wall part 3 and the corner part 4 is specifically obtained by further averaging the average particle diameters of the tungsten crystal grains obtained at two arbitrary measurement points. is there. The average grain size of tungsten crystal grains at each measurement location is determined by measuring the number of tungsten crystal grains and the grain diameter of each tungsten crystal grain by the line intercept method as described above. This is obtained by dividing the total diameter by the number of tungsten crystal grains.

  The measurement location of the average grain size of the tungsten crystal grains in the side wall portion 3 and the corner portion 4 is not necessarily limited. For example, the side wall portion 3 has a height of the side wall portion 3 as indicated by a broken line 5 in FIG. It is preferable that it is a substantially middle part in the vertical direction. As for the corner 4, for example, as shown in FIG. 1, when the corner 4 is curved in an arc shape, it is preferably within the range of the arc-curved portion, and for example, as shown in FIG. 3. When the corner 4 is square, it is preferably within a range surrounded by the extended surface 2a of the inner surface of the bottom 2 and the extended surface 3a of the inner surface of the side wall 3 shown in FIG.

The density of the tungsten crucible 1 is preferably 95% or more, more preferably 97% or more and 100% or less. The density is calculated by setting the specific gravity of tungsten to 19.3 g / cm ³ as the theoretical density. Next, an actual measurement value is obtained by the Archimedes method, and a density is obtained by (actual measurement value / theoretical density) × 100%.
By making the density close to the theoretical density of 95% or more, for example, when used for producing a sapphire single crystal, it is possible to prevent the melt of this raw material from oozing out from the tungsten crucible 1.

  Such a tungsten crucible 1 is preferably manufactured by sintering or HIP (hot isostatic pressing) processing of tungsten powder, and particularly preferably not forged. The tungsten crucible 1 of the present invention is preferably not forged, but may be subjected to cutting for adjusting the shape after sintering or HIP treatment, for example.

  Moreover, according to sintering or HIP processing, there are few restrictions on manufacturing like the conventional forging process regarding thickness, and what differs in thickness by the side wall part 3 and the corner | angular part 4 can be manufactured easily. For example, by making the corner 4 thicker than the side wall 3, the corner 4 can be excellent in high-temperature strength.

  Further, when forging is performed, excessive tungsten crystal grains having a grain size exceeding 100 μm are likely to be generated due to stretching due to pressing during processing, and in particular, excessive tungsten in a portion with a large processing amount such as the corner 4. Although crystal grains are generated and the high-temperature strength tends to decrease, the forging process is not performed after the HIP treatment, so that the generation of such excessive tungsten crystal grains is suppressed, and the high-temperature strength, particularly the corner portion 4 is suppressed. It can be made excellent in high temperature strength.

  In addition, when forging is performed, residual distortion is likely to occur in the corners 4, thereby accelerating recrystallization during use at high temperatures and reducing high-temperature strength, but forging after sintering or HIP treatment Therefore, the occurrence of residual strain at the corners 4 can be suppressed, whereby recrystallization can be suppressed and excellent high-temperature strength can be achieved.

Next, a method for manufacturing the tungsten crucible 1 of the present invention will be described. Although the manufacturing method of the tungsten crucible of the present invention is not particularly limited, the following method can be mentioned as a manufacturing method for obtaining efficiently.
The first tungsten crucible manufacturing method of the present invention is a manufacturing method for manufacturing an open bottomed cylindrical tungsten crucible in which a bottom portion and a side wall portion are connected via a corner portion, A molding step of CIPing a tungsten powder having a purity of 99.9% or more into a crucible shape at a pressure of 100 MPa or more, a first sintering step of sintering at 1300 ° C. or higher in a hydrogen atmosphere, and in a reducing atmosphere or inert It has the 2nd sintering process sintered at 2000 degreeC or more in atmosphere, It is characterized by the above-mentioned.

First, the tungsten powder is preferably a high-purity powder having a purity of 99.9% or more, more preferably 99.95% or more. Further, the oxygen content is preferably 0.1 wt% or less.
In the CIP process, a crucible-shaped molded body is produced at a molding pressure of 100 MPa or more. CIP molding (hydrostatic press) is a method in which a mixed powder is packed in a flexible bag such as a rubber bag and molded by applying pressure with water or oil. The molding pressure is 100 MPa or more. When the molding pressure is less than 100 MPa, the density of the molded body becomes insufficient, and it is difficult to obtain a sintered body having a density of 95% or more. The upper limit of the molding pressure is not particularly limited, but is preferably 200 MPa or less.

Next, the 1st sintering process which sinters a molded object at the temperature of 1300 degreeC or more in hydrogen atmosphere is performed. The upper limit of the sintering temperature is preferably lower than the temperature of the second sintering step described later. The sintering time is preferably 8 hours or longer. A large-sized one having an inner diameter of 300 mm or more preferably has a sintering time of 1600 ° C. or more × 10 hours or more.
Next, a second sintering step is performed in which sintering is performed at a temperature of 2000 ° C. or higher in a reducing atmosphere or an inert atmosphere. Examples of the reducing atmosphere include a hydrogen atmosphere and a carbon monoxide atmosphere. The inert atmosphere is preferably argon. The sintering time is preferably 5 hours or more. The upper limit of the sintering temperature in the second sintering step is not particularly limited, but is preferably 2300 ° C. or lower. If the sintering temperature is too high, the burden on the sintering furnace increases. It should be noted that if the sintering time is too long, the average crystal grain size becomes large, so 11 hours or less is preferable.
By performing the first sintering step and, if necessary, the second sintering step in a hydrogen atmosphere (or reducing atmosphere), oxygen in the sintered body that causes a decrease in density can be removed.
After the sintering, it is possible to perform a cutting process for adjusting the shape as necessary.

A second tungsten crucible manufacturing method of the present invention is a manufacturing method for manufacturing a bottomed cylindrical tungsten crucible having an open top, in which a bottom portion and a side wall portion are connected via a corner portion, It comprises a forming step of forming tungsten powder with a purity of 99.9% or more into a crucible shape, and a HIP step of HIP treatment at a pressure of 100 MPa or more and 1300 ° C. or more in an inert atmosphere. .
The molding method is not necessarily limited, and may be performed using, for example, a uniaxial mold press, or after being preformed using, for example, a uniaxial mold press, CIP (cold isostatic pressure using a rubber mold) Press). Moreover, it is preferable that a shaping | molding pressure shall be 50 MPa or more and 200 MPa or less, for example. When the molding pressure is smaller than the above range, for example, even if the HIP treatment is performed, it cannot be sufficiently densified, the high-temperature strength is not sufficient, and the density may not be sufficient. Further, when the molding pressure is larger than the above range, for example, the durability of the molding die may be lowered, which is not preferable.

Next, an HIP process is performed in which an HIP process is performed at a pressure of 100 MPa or higher and 1300 ° C. or higher in an inert atmosphere. The inert atmosphere is preferably an argon atmosphere. The pressure is 100 MPa or more. If it is less than 100 MPa, the density may decrease. The upper limit of the pressure is 200 MPa or less.
Moreover, HIP temperature is 1300 degreeC or more. If it is less than 1300 degreeC, there exists a possibility that a density may fall. The upper limit of the HIP temperature is 2000 ° C. or less. The HIP processing time is preferably 5 hours or more.
After the HIP process, it is possible to perform cutting or the like for adjusting the shape as necessary.

  According to such a manufacturing method, the above-described tungsten crucible 1 having excellent high-temperature strength can be easily manufactured. In addition, about the manufacturing method of the tungsten crucible 1 of this invention, things other than a forging process are not necessarily restrict | limited, For example, the cutting process for adjusting a shape after a HIP process, etc. can also be performed.

HIP treatment is a method in which tungsten powder or a molded body thereof is sealed and deaerated in a metal or glass container that can be coated even at high temperatures, and heated and sintered while isotropically pressurized through an inert atmosphere medium. For example, since the hot press is uniaxially pressed while being isotropic pressed, a more homogeneous and dense sintered body can be obtained by low-temperature sintering.
Further, in the first production method, a method in which the second sintering step is HIP-treated is also effective. For example, after pre-sintering the molded body to a density slightly lower than the theoretical density in advance, The pre-sintered body may be made into a tungsten crucible 1 by HIP treatment. Thus, after pre-sintering in advance, a more homogeneous and dense tungsten crucible 1 can be obtained by HIP treatment.

  In the first production method or the second production method, the average crystal grain size in the finally obtained tungsten crucible 1 is 50 μm or less, and the proportion of tungsten crystal grains of 10 μm or more and 80 μm or less is 90% or more. Preferably, the temperature is appropriately set within the above-described temperature, pressure, and processing time ranges so that the density is 95% or more and the ratio of the average particle diameter of the corners 4 to the side walls 3 is 0.8 or more and 1.2 or less. It is preferable to adjust the pressure and the processing time.

  Moreover, if it is the 1st manufacturing method using CIP processing and the 2nd manufacturing method using HIP processing, a large crucible with an internal diameter of 100 mm or more and also an internal diameter of 300 mm or more can be manufactured. The upper limit of the inner diameter is not particularly limited, but is preferably 600 mm or less. When it exceeds 600 mm, the process of preparing a uniform sintered body at the time of HIP processing becomes complicated.

  The tungsten crucible 1 thus obtained can be suitably used as a component part of a production apparatus used at high temperatures, such as a metal evaporation vessel, a metal oxide dissolution vessel, a crystal production vessel, etc. It can be used for the production of a sapphire single crystal suitably used as a substrate material such as a GaN film-forming substrate.

  In the manufacture of a sapphire single crystal, for example, a raw material is put in a crucible and melted, a seed crystal made of a sapphire single crystal is brought into contact with this melt, and the single crystal is grown by pulling it up while rotating. The tungsten crucible 1 of the present invention is suitably used as a crucible for containing such a raw material melt.

  Specifically, for example, a lifting device having a bottomed cylindrical heating furnace having an open top and a lifting rod arranged so as to be inserted from above the heating furnace is used. A seed crystal is fixed to the lower tip side of the lifting rod. Further, the tungsten crucible 1 is disposed on the inner bottom portion of the heating furnace in such a pulling apparatus.

  In such a pulling apparatus, first, aluminum oxide as a raw material for a sapphire single crystal is put into a tungsten crucible 1 and melted to obtain a melt. Thereafter, seeding is performed by putting a pull-up rod with a seed crystal fixed in a tungsten crucible 1 containing a melt. Thereafter, the pulling rod is pulled up while rotating to obtain a substantially cylindrical single crystal ingot which is a sapphire single crystal. A tungsten crucible shows excellent durability even when the melting temperature is 2000 ° C. or higher, or even 2200 ° C. or higher.

  Hereinafter, the present invention will be specifically described with reference to examples.

(Examples 1-3)
A tungsten powder having a purity of 99.95% or more (average particle size 5 μm, impurity oxygen 0.1 wt%) was used.
Example 1 was CIP treatment (pressure 110 MPa), first heat treatment step (in hydrogen atmosphere, 1350 ° C. × 8 hours), and second heat treatment step (2010 ° C. × 6 hours in argon atmosphere).
Example 2 was CIP treatment (pressure 130 MPa), first heat treatment step (in hydrogen atmosphere, 1460 ° C. × 9 hours), and second heat treatment step (2050 ° C. × 7 hours in argon atmosphere).
Example 3 was CIP treatment (pressure 160 MPa), first heat treatment step (in hydrogen atmosphere, 1660 ° C. × 10 hours), and second heat treatment step (2090 ° C. × 5 hours in argon atmosphere).
The obtained crucible was surface-polished to obtain a tungsten crucible according to Examples 1 to 3.
(Comparative Example 1)
A crucible made of molybdenum was manufactured by forging a plate material made of molybdenum having a purity of 99.90% (average particle diameter of molybdenum crystal grains of 10 μm, impurity oxygen content of 0.05 wt%). The overall shape, corner shape, and thickness (corner portion, side wall portion) of the molybdenum crucible were as shown in Table 1.
(Comparative Example 2)
Using tungsten powder with a purity of 99.95% or more (average particle size 10 μm, impurity oxygen 0.1 wt%), CIP pressure 100 MPa, first heat treatment step in hydrogen atmosphere at 1800 ° C. × 20 hours, second heat treatment step Was manufactured at 2300 ° C. for 15 hours.

  The overall shape, corner shape, and thickness (corner portion, side wall portion) of the tungsten crucible manufactured in each example were as shown in Table 1. That is, the tungsten crucibles of Examples 1 and 3 have corners that are substantially the same thickness as the side walls and curved in an arc shape as shown in FIG. 1, and the side walls 3 rise from the corners 4 substantially vertically. It was supposed to be. In addition, the tungsten crucible of Example 2 has an extremely thick corner as compared with the side wall as shown in FIG.

  Furthermore, the overall shape and the like of each tungsten crucible 1 was adjusted mainly by adjusting the overall shape and the like of the molded body in the molding stage.

  Next, the average crystal grain size of the obtained crucible, the ratio of crystal grains of 10 to 80 μm, the crystal grain size ratio between the side wall and the corner, the amount of impurity oxygen, and the density were determined. In addition, the measurement of each item was measured using the above-mentioned method. The results are shown in Table 2.

In the crucible according to the present example, the average crystal grain size was 50 μm or less, and the proportion of tungsten crystals having 10 to 80 μm was 90% or more. Further, since a hydrogen atmosphere was used in the sintering process, the amount of impurity oxygen was reduced to less than 0.01 wt%.
The density was evaluated using the crucibles according to the examples and comparative examples. For the evaluation of the density, first, after performing a heat treatment step at 2300 ° C. for 1000 hours and 2000 hours with a sapphire melt put in a crucible, the degree of grain growth was measured. Specifically, the same method as the method for measuring the average crystal grain size was performed to determine the average crystal grain size, and the rate of change was determined. The results are shown in Table 3.

  The crucible according to the example showed excellent durability. In contrast, Comparative Example 1 produced by forging a Mo plate material was insufficient in durability. This is because grain growth is accompanied by forging and impurity oxygen is not reduced by a hydrogen reducing atmosphere. Moreover, even if it was made of tungsten as in Comparative Example 2, the one having a large average crystal grain size was deteriorated in durability. This is presumably because grain growth occurs and internal strain occurs.

(Examples 4 to 6)
A tungsten powder having an average particle diameter of 3 μm and an impurity oxygen content of 0.1 wt% was used, and the overall shape and thickness (corner portions and side wall portions) of the tungsten crucible were changed as shown in Table 4.
In Example 4, uniaxial molding was performed at a pressure of 120 MPa, and then HIP treatment (in an argon atmosphere, 120 MPa, 1400 ° C. × 7 hours) was performed. In Example 5, uniaxial molding was performed at 150 MPa, and then HIP treatment (in an argon atmosphere, 180 MPa, 1600 ° C. × 8 hours) was performed. In Example 6, CIP molding at 100 MPa, pre-sintering in a hydrogen atmosphere at 1400 ° C. for 5 hours (first sintering step), and HIP treatment (in an argon atmosphere at 1500 ° C. for 6 hours) were performed. The HIP treatment was performed by enclosing in a stainless capsule.
The same measurements as in Example 1 were performed for Examples 4-7. The results are shown in Tables 4-6.

It turned out that the durability which was excellent also about the crucible which concerns on Examples 4-6 is shown. In addition, since it performed by encapsulating in a capsule when it is HIP processing, Example 4 and 5 in which the reduction | restoration in hydrogen atmosphere is not performed did not perform reduction of the oxygen amount. On the other hand, since Example 6 was sintered in a hydrogen atmosphere in the first sintering step, the amount of oxygen was reduced.
In other words, when it is desired to reduce the amount of impurity oxygen, it is better to perform a sintering step in a hydrogen atmosphere.

1 ... Tungsten crucible 2 ... Bottom 3 ... Side wall 4 ... Corner

Claims (8)

A bottomed cylindrical tungsten crucible having an opening in which a bottom portion and a side wall portion are connected via a corner portion, made of tungsten having a purity of 99.9% or more,
The tungsten has an average crystal grain size of 20 μm or more and 50 μm or less, and a ratio of the number of tungsten crystal grains having a crystal grain size of 10 μm or more and 80 μm or less of 90% or more. A tungsten crucible having a diameter ratio of 0.8 or more and 1.2 or less, a relative density of 95% or more, and a thick corner with respect to the side wall.   2. The tungsten crucible according to claim 1, wherein the tungsten crucible has an inner diameter of 100 mm or more.   The tungsten crucible according to claim 1 or 2, wherein a ratio of a thickness of the corner portion to the side wall portion is 1.2 or more.   The tungsten crucible according to any one of claims 1 to 3, wherein the tungsten crucible is used as a raw material melt for producing a sapphire single crystal. A manufacturing method for manufacturing the tungsten crucible according to claim 1 ,
A molding step of CIPing a tungsten powder having a purity of 99.9% or more into a crucible shape at a pressure of 100 MPa or more and 200 MPa or less;
A first sintering step of sintering at 1300 ° C. or higher in a hydrogen atmosphere;
A second sintering step of sintering at 2000 ° C. or higher in a reducing atmosphere or in an inert atmosphere;
A method for producing a tungsten crucible, comprising: A manufacturing method for manufacturing the tungsten crucible according to claim 1 ,
A molding step of molding a tungsten powder having a purity of 99.9% or more into a crucible shape;
A HIP process in which an HIP process is performed at a pressure of 100 MPa or more and 200 MPa or less and 1300 ° C. or more in an inert atmosphere;
And a method for producing a tungsten crucible. A method for producing a sapphire single crystal comprising producing a sapphire single crystal by crystal growth from a raw material melt,
A method for producing a sapphire single crystal, wherein the crucible made of tungsten according to any one of claims 1 to 4 is used as a crucible for charging the raw material melt.   The method for producing a sapphire single crystal according to claim 7, wherein the heating temperature of the melt is 2000 ° C. or higher.

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