Method for manufacturing single crystal growth graphite crucible

Abstract

To provide a method for manufacturing a graphite crucible hard to be exhausted even when put at high temperature.SOLUTION: A method for manufacturing a single crystal growth graphite crucible, capable of growing the single crystal on the main surface of a seed crystal substrate by a sublimation recrystallization method comprises: the molding step of molding a raw material including coke mainly constituted of needle coke and binder pitch; the calcination step of calcining the molded molding to obtain a calcined product; the first impregnation calcination step of performing the impregnation and calcination of additional binder pitch once or more to the calcined product to obtain an impregnation calcination product; the graphitization step of heating and graphitizing the impregnation calcination product at 2000°C or more to obtain a graphitization product; and the second impregnation calcination step of performing the impregnation and calcination of additional binder pitch once or more to the graphitization product.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a graphite crucible for single crystal growth. [Background technology]

[0002] A manufacturing method for producing single crystals of SiC or the like by sublimation recrystallization using a graphite crucible is known. When producing single crystals using this manufacturing method, the graphite crucible may be worn out due to being exposed to high temperatures for a long period of time. Patent Document 1 describes forming a carbide coating on the surface of an isotropic graphite base material used in a graphite crucible or the like in order to improve the heat resistance of the isotropic graphite base material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-145022 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 is premised on the use of an isotropic graphite substrate. The raw material for the isotropic graphite substrate is amorphous coke (coke with random crystal orientation, a small aspect ratio, and round chunks). Patent Document 1 does not describe a graphite substrate made from anisotropic coke (needle coke) that is not amorphous coke.

[0005] In addition, graphite crucibles are exposed to high temperatures for long periods of time to grow crystals. An object of the present invention is to provide a method for manufacturing a graphite crucible that is resistant to wear even when exposed to high temperatures when using coke that is mainly composed of needle coke as a raw material. [Means for solving the problem]

[0006] A graphite crucible has large outer and inner surfaces. When a coating is formed on the surface of a graphite crucible, the risk of the coating peeling increases as the coating area increases. Therefore, the inventors considered improving the heat resistance of the graphite crucible itself without relying solely on the coating. As a result of extensive research, the inventors have created the following method for manufacturing a graphite crucible.

[0007] The manufacturing method of the present invention is a manufacturing method of a graphite crucible for growing a single crystal, in which a single crystal is grown on a main surface of a seed crystal substrate by a sublimation recrystallization method, comprising the steps of: a forming step of forming a raw material containing coke mainly composed of needle coke and binder pitch; a firing step of firing the molded product to obtain a fired product; a first impregnation and firing step in which the fired product is impregnated with additional binder pitch and fired one or more times to obtain an impregnated and fired product; a graphitization step of heating the impregnated and fired product to 2000°C or higher to graphitize it, thereby obtaining a graphitized product; a second impregnation and firing step in which the graphitized material is impregnated with additional binder pitch and fired; Equipped with.

[0008] As used herein, "coke primarily composed of needle coke" refers to coke in which needle coke accounts for more than 50 wt% of the total coke. Compared to amorphous coke, "coke primarily composed of needle coke" contains fewer impurities derived from the raw materials, making it easier to prevent the impurities from being mixed into the growing crystals. Furthermore, "coke primarily composed of needle coke" exhibits higher thermal conductivity than amorphous coke. When "coke primarily composed of needle coke" is used in extrusion molding or other molding processes that induce anisotropy, it can have a greater thermal conductivity anisotropy. However, when a graphite crucible is manufactured using "coke primarily composed of needle coke" as a raw material, an abnormal expansion phenomenon of the graphite substrate, known as puffing, can occur during the graphitization process. This abnormal expansion phenomenon, unique to needle coke and unlikely to occur in amorphous coke, can potentially lead to the formation of voids (pores or cracks) within the graphite substrate. Voids generated inside the graphite base material reduce the heat resistance of the graphite crucible, making it more susceptible to wear. However, in the above-described manufacturing method, the second impregnation and firing step is performed after the graphitization step, so the voids can be filled with carbonaceous matter. As a result, the voids are reduced, the specific surface area of ​​the graphite crucible is reduced, and the graphite crucible is less susceptible to wear even when exposed to sublimation gas at high temperatures.

[0009] Performing the impregnation and firing step after the graphitization step means that impurities are again introduced into the graphitized material from which impurities were removed in the graphitization step. The graphitized material of this embodiment is a graphite crucible for single crystal growth. For graphite crucibles for single crystal growth, the purity of the graphite crucible is an important factor affecting the quality of the grown crystal. It has been common technical knowledge among graphite crucible manufacturers to produce graphite crucibles with as few impurities as possible in order to obtain crystals with few impurities. In this context, the present inventors, without being bound by common technical knowledge, have invented a method for producing a graphite crucible for single crystal growth in which an impregnation and firing step, which may add impurities, is performed after the graphitization step.

[0010] After the second impregnation and firing step, a crucible processing step may be performed in which the graphitized material is processed into the shape of a crucible. Even if the second impregnation and firing step causes some adhesion of filler or some consumption or deformation of the material, the desired crucible shape can be processed without being affected by these factors.

[0011] In order to suppress the increase in the amount of impurities in the graphite crucible after the second impregnation and firing step, the binder pitch and carbide powder (e.g., breeze) added in the second impregnation and firing step may be limited. For example, the binder pitch and carbide powder added in the second impregnation and firing step may be limited so that the ash content of the binder pitch and carbide powder added is 0.1% or less. This allows the increase in ash concentration after the second impregnation and firing step to be 0.01% or less, thereby maintaining the graphite crucible at a high purity. A high-purity graphite crucible leads to a reduction in the amount of impurities mixed into the crystals grown in the graphite crucible.

[0012] The number of repetitions of impregnation and firing in the first impregnation and firing step may be set to four or less.

[0013] In the second impregnation and firing step, the impregnation and firing may be repeated.

[0014] The forming step may be an extrusion forming step. A graphite block formed by an extrusion forming step is likely to have a higher proportion of pores than a graphite block formed by CIP forming, and the effect of reducing voids by performing the second impregnation and firing step is more pronounced.

[0015] The process conditions for the second impregnation and firing process may be determined based on the measurement results regarding the voids in the second impregnation and firing process. This allows the graphite crucible to have a desired void density. In general, the smaller the void density, the more preferable it is. Bulk density is an example of a measurement index related to voids. The higher the bulk density, the fewer voids there are, which is preferable. Details of bulk density will be explained in the examples. [Effects of the Invention]

[0016] This makes it possible to provide a method for manufacturing a graphite crucible that is resistant to wear even when exposed to high temperatures. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a flow chart showing main steps of a first embodiment of a method for manufacturing a graphite crucible. [Figure 2] FIG. 2 is a diagram illustrating the aspect ratio of needle coke. [Figure 3] FIG. 1 is a diagram showing an extrusion molding device. [Figure 4A] FIG. 2 is an enlarged view of a cross section of graphite after the graphitization step. [Figure 4B] FIG. 2 is an enlarged view of the cross section of graphite after the second impregnation and firing step. [Figure 5] FIG. 4 is a flow chart showing main steps of a second embodiment of a method for manufacturing a graphite crucible. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, the embodiments of the present invention will be described with reference to the drawings as appropriate. Note that the drawings disclosed in this specification, except for graphs, are schematic illustrations. In other words, the dimensional ratios on the drawings do not necessarily match the actual dimensional ratios, and the dimensional ratios between the drawings do not necessarily match.

[0019] First Embodiment A first embodiment of a method for manufacturing a graphite crucible will be described. FIG. 1 is a flow diagram showing the main steps of the first embodiment. The method for manufacturing a graphite crucible of this embodiment includes a kneaded material obtaining step S11, a molding step S12 for molding the kneaded material into a block body, a first impregnation and firing step S13 for firing the molded block body and impregnating it with binder pitch, a graphitization step S14 for graphitizing the block body after the first impregnation and firing step, a second impregnation and firing step S15 for firing the graphitized block body again and impregnating it with binder pitch, and a crucible processing step S16 for processing the block body after the second impregnation and firing step into the shape of a crucible. Each step will be described in order.

[0020] [Process for obtaining kneaded material] The kneaded material obtaining step S11 is a step of pulverizing prepared coke and kneading the pulverized coke with binder pitch to obtain a kneaded material. More specifically, coke is prepared and pulverized. The pulverized coke is then mixed with a binder called binder pitch (hereinafter, sometimes simply referred to as "pitch") while being heated to prepare a kneaded material. The kneaded material prepared in this manner is obtained.

[0021] Coke called needle coke accounts for more than 50 wt% of the total coke. Needle coke is an anisotropic coke with a shape in which long, needle-like crystal structures are oriented. The amorphous coke described above is a non-anisotropic (or weakly anisotropic) coke with random crystal orientation, a small aspect ratio, and a rounded, lumpy shape. The raw material may contain amorphous coke. As long as the coke contains more than 50 wt% needle coke, the remaining coke may be composed of amorphous coke. As described above, the prepared needle coke is pulverized. In this specification, needle coke and amorphous coke are distinguished by the aspect ratio measured before pulverization. The greater the amount of needle coke contained in the coke, the higher the void density (larger or more numerous voids) of the graphite crucible. In other words, the greater the amount of needle coke contained, the greater the effect of reducing voids by carrying out the second impregnation and calcination step.

[0022] FIG. 2 shows an example of a needle coke. The needle coke 21 has a major axis φL, which is the longest diameter among its outer dimensions, and a minor axis φS, which is an outer diameter perpendicular to the major axis φL. Before the needle coke 21 is pulverized, the aspect ratio of the major axis φL to the minor axis φS (=φL / φS) of the needle coke 21 is 1.1 or more. In this specification, unless otherwise specified, coke with an aspect ratio of 1.1 or more before pulverization is referred to as needle coke. However, the aspect ratio of the needle coke is preferably 1.5 or more, and more preferably 1.7 or more. There is no particular upper limit to the aspect ratio, but for example, the aspect ratio may be 7.0 or less, preferably 6.5 or less, and more preferably 6.0 or less.

[0023] [Molding process] The forming step S12 is a step of forming a block from a kneaded material containing coke and pitch. FIG. 3 shows an example of a forming apparatus. The forming apparatus shown in FIG. 3 is an extrusion molding apparatus. In this embodiment, the block is formed by extruding the kneaded material. The extrusion molding apparatus 30 includes a container 32 that contains the kneaded material 31, a die 33 that squeezes the kneaded material 31, and a pusher 34 that pushes the kneaded material 31 contained in the container 32 toward the die 33. The kneaded material 31 is heated to a temperature at which it is fluid in the container 32 and the die 33, and to a temperature at which its fluidity is significantly lower after it is discharged from the die 33. The heating temperature may be, for example, 60°C or higher and 140°C or lower, and preferably 80°C or higher and 120°C or lower. In the process of squeezing the kneaded material through the die 33, the needle coke 21 contained inside the kneaded material receives resistance, and the needle coke 21 tends to be oriented in a direction parallel to the extrusion direction ED.

[0024] The extrusion molding device 30 extrudes the kneaded material 31 to obtain a cylindrical extrusion-molded material 3. The extrusion-molded material 3 is cut along a direction OD perpendicular to the extrusion direction ED to form a block. The block has a cylindrical shape with the extrusion direction ED as its height direction and the direction OD perpendicular to the extrusion direction ED as its radial direction. Therefore, cylindrical blocks often exhibit a state in which the needle coke 21 is oriented in the height direction. A cylindrical crucible has the advantage that, since the distance from the center is the same, equal force is easily applied in the cross-sectional direction. However, the extrusion-molded material 3 does not necessarily have to be cylindrical; for example, it may be prismatic.

[0025] The size of the block body varies depending on the size of the crucible to be manufactured and the method of cutting the crucible, but the diameter of the block body is preferably 100 mm to 500 mm, more preferably 200 mm to 400 mm, and more preferably 250 mm to 350 mm. The height of the block body is preferably 800 mm to 3000 mm, and more preferably 1500 mm to 2500 mm.

[0026] Although the present embodiment uses the extrusion molding device 30, other molding devices may also be used. For example, a block may be formed by compressing and pressurizing using CIP (Cold Isostatic Press) molding. However, in general manufacturing methods, blocks formed by the extrusion molding process exhibit a high void density, whereas blocks obtained by CIP molding exhibit a relatively low void density. In other words, the void reduction effect of the second impregnation and firing process is greater in graphite crucibles formed by the extrusion molding process than in graphite crucibles formed by the CIP molding process.

[0027] [First impregnation and baking process] The first impregnation and firing step S13 is a step in which the block is placed in a heating furnace and fired to obtain a carbonaceous material. The maximum firing temperature may be, for example, 800°C to 1500°C. The firing time may be, for example, 300 hours or more and 1000 hours or less. First, the block is fired. After firing for a certain period of time, the temperature is lowered and the block is impregnated with pitch.

[0028] After the pitch impregnation, the material is calcined again. That is, (α1) calcination, (α2) pitch impregnation, and (α3) calcination are performed in this order. In this case, the combination of (α2) pitch impregnation and (α3) calcination is performed once, but the combination of (α2) pitch impregnation and (α3) calcination may also be performed twice. That is, the combination of (α1) calcination, (α2) pitch impregnation, (α3) calcination, (α4) pitch impregnation, and (α5) calcination may also be performed in this order. The combination of pitch impregnation and calcination may also be performed three times. That is, the combination of (α1) calcination, (α2) pitch impregnation, (α3) calcination, (α4) pitch impregnation, (α5) calcination, (α6) pitch impregnation, and (α7) calcination may also be performed in this order. Furthermore, the combination of pitch impregnation and calcination may also be repeated four or more times.

[0029] During firing after pitch impregnation, carbide powder other than coke may be packed around the block to efficiently transfer heat and prevent surface oxidation. One example of the packed carbide powder is breeze. breeze is a powder produced by pyrolysis and carbonization of coal pitch, which is a residue of coal carbonization tar. It is a medium for efficient heat transfer and has the effect of preventing oxidation.

[0030] [Graphitization process] In the graphitization step S14, the block body that has been made carbonaceous in the first impregnation and firing step S13 is placed in a heating furnace and graphitized by heating to 2000°C or higher. Pitch and carbide powder contain impurities, but when the block body is exposed to high temperatures in the graphitization step, most of the impurities (substances other than carbon) are removed and the block body is graphitized.

[0031] FIG. 4A shows an enlarged view of the cross section of graphite after the graphitization process. In FIG. 4A, the hatched area 40 is the graphitized area. The unhatched areas (41, 42) are voids. During the graphitization process, the carbonaceous block reaches 1500°C. At this time, the carbonaceous block may undergo abnormal expansion. This phenomenon is called puffing. Puffing causes the block to expand abnormally, and as it shrinks, pores 41 are formed inside the block. When the block with pores 41 further shrinks and the pores 41 are stretched, cracks 42 occur, causing the pores 41 to expand. The direction of the cracks 42 often aligns with the orientation direction of the needle coke 21. As a result, voids (41, 42) containing the pores 41 and cracks 42 are formed after the graphitization process. The voids (41, 42) in the graphitized material increase the specific surface area, and can cause the high-temperature gas to react with the graphite crucible, scraping and wearing away the inner wall of the crucible. In particular, needle coke is more susceptible to voids due to puffing than amorphous coke because it has a larger residual expansion during graphitization.

[0032] When a graphitized material is used as a graphite crucible, if the graphite crucible has many voids (41, 42), the sublimation gas will easily permeate the graphite crucible and leak out of the graphite crucible, which may result in a decrease in the yield of crystal growth or in the crystals adhering to the heating furnace in which the graphite crucible is placed. Furthermore, when the graphite crucible is worn out, inclusions, in which components of the graphite crucible are mixed into the grown crystal, may occur, which may reduce the quality of the grown crystal.

[0033] [Second impregnation and baking process] In order to reduce voids caused by puffing, in this embodiment, a second impregnation and firing step S15 is performed after the graphitization step. In the second impregnation and firing step, the (β1) graphitized block body is again impregnated with pitch, and the (β2) block body is fired. In this embodiment, the (β1) pitch impregnation and (β2) firing are performed only once without being repeated. However, the combination of (β1) pitch impregnation and (β2) firing may be repeated two or three times. The number of times impregnation and firing are repeated in the second impregnation and firing step is preferably less than the number of times in the first impregnation and firing step.

[0034] The maximum temperature reached during firing in the second impregnation and firing step S15 may be, for example, 800° C. to 1500° C. The firing time for one cycle of the second impregnation and firing step may be, for example, 300 hours or more and 1000 hours or less. The firing temperature and firing time in the second impregnation and firing step may be the same as or different from the firing temperature and firing time in the first impregnation and firing step.

[0035] Figure 4B shows an enlarged view of the cross section of graphite after the second impregnation and firing process. The areas that were voids (41, 42) in Figure 4A have been filled with pitch and fired, resulting in the voids being replaced by carbonaceous areas 43. The reduced surface area makes it difficult for the sublimation gas to react with the graphite crucible, preventing the consumption of graphitized material.

[0036] In the second impregnation and firing step S15, carbide powder (such as breeze) other than coke is also packed around the block. As mentioned above, pitch and carbide powder contain impurities. In the first impregnation and firing step S13, most of the impurities contained in the pitch and carbide powder can be removed in the subsequent graphitization step. Therefore, even if the pitch and carbide powder contain a small amount of impurities, this does not pose a significant problem. However, since there is no graphitization step after the second impregnation and firing step S15, it is necessary to pay attention to the amount of impurities contained in the pitch and carbide powder. The pitch and carbide powder used in the second impregnation and firing step S15 may contain impurities other than carbon. Therefore, the amount of pitch and carbide powder added in the second impregnation and firing step is more limited than the amount of pitch and carbide powder added in the first impregnation and firing step.

[0037] It is advisable to limit the amount of pitch and carbide powder added while taking into consideration the amount of impurities contained in the graphitized material in the second impregnation and firing step S15. Regarding the limit on the amount of pitch and carbide powder added in the second impregnation and firing step, for example, the amount of pitch and carbide powder added may be limited so that the ash content of the pitch and carbide powder added is 0.1% or less. This allows the increase in ash concentration after the second impregnation and firing step to be 0.01% or less, and the graphite crucible can be maintained at a high purity. A high-purity graphite crucible leads to a reduction in the amount of impurities mixed into the crystals grown in the graphite crucible.

[0038] By carrying out the second impregnation and calcination step, the number of times the impregnation and calcination steps are repeated in the first impregnation and calcination step may be reduced. Reducing the number of times the impregnation and calcination steps are repeated in the first impregnation and calcination step has the advantage of absorbing the increase in cost and time required for the second impregnation and calcination step.

[0039] After the second impregnation and firing step S15 is performed, the void density, such as bulk density, may be measured, and the process conditions for the second impregnation and firing step S15 may be determined based on the measurement results. The process conditions for the second impregnation and firing step S15 include the temperature, time, and pressure during impregnation, or the number of times impregnation and firing are repeated.

[0040] [Crucible processing process] The crucible processing step S16 is a step in which the block body after the second impregnation and firing step is processed into the shape of a graphite crucible. The graphite crucible has a hollow cylindrical shape as a whole. The graphite crucible is composed of a circular bottom and a cylindrical side wall. The graphite crucible is composed of a container and a lid. The container has a raw material storage section for storing powder that will be the raw material for the crystals inside. The lid includes a circular top plate, a cylindrical side wall, and a seed crystal mounting base arranged inside the top plate. The container and lid are obtained by cutting the graphitized material from the block body, but there are no particular limitations on the cutting method, and the cutting may be performed using a lathe or a milling machine, for example.

[0041] The shapes of the container and lid described above are merely examples. Both the container and the lid may have shapes other than those described above. For example, the lid may have a shape without a sidewall. Furthermore, the bottom surface of the container and the top plate of the lid do not have to be circular. The bottom surface of the container and the top plate of the lid may be, for example, rectangular or hexagonal. The lid may have a shape that fits into the container.

[0042] The thickness of the side walls of the container and the lid is preferably 2 mm to 50 mm, more preferably 5 mm to 30 mm, and even more preferably 10 mm to 20 mm. The thickness of the bottom of the container is preferably 5 mm to 40 mm.

[0043] Second Embodiment A second embodiment of the method for manufacturing a graphite crucible will now be described. FIG. 5 is a flow chart showing the main steps of the second embodiment. The difference from the graphite crucible manufacturing process of the first embodiment is that a crucible processing step S16 is performed after the graphitization step S14 and before the second impregnation and firing step S15. By processing the crucible before the second impregnation and firing step S15, the crucible does not contain hard carbonaceous material, and processing can be performed in a short time with minimal wear on the cutting tool. Other details are the same as those described in the first embodiment.

[0044] The above description has focused on the method for manufacturing a graphite crucible. The present invention is not limited to the above-described manufacturing method, and various improvements and modifications are possible within the scope of the present invention. As described above, this embodiment is a manufacturing method created with the aim of improving the heat resistance of the graphite crucible itself. However, in addition to improving the wear resistance of the graphite crucible itself, a coating that improves wear resistance may be formed on the outer or inner surface of the graphite crucible. [Example]

[0045] <Measurement of bulk density> Two types of graphite substrates were manufactured using different manufacturing methods, and the bulk densities of the manufactured graphite substrates were measured. The two types of graphite substrates are as follows. Note that manufacturing conditions not described below were within the ranges described in the above embodiment, and all samples were manufactured under the same conditions.

[0046] [First sample Sa1] A graphite substrate was manufactured according to the second embodiment of the method for manufacturing a graphite crucible. The main manufacturing conditions are as follows: Step S11 of obtaining kneaded material: Coke containing 90 wt % or more of needle coke was used. Molding step S12: An extrusion molding device was used. First impregnation and firing step S13: After the initial firing, the combination of impregnation and firing was repeated three times. Crucible Processing Step S16: After the graphitization step S14, the graphitized block was cut to obtain pieces with a diameter of 40 mm and a length of 150 mm. Second impregnation and firing step S15: The obtained piece was impregnated and fired once. The piece subjected to the second impregnation and firing step S15 was designated as a first sample Sa1.

[0047] [Second sample Sa2] Step S11 of obtaining kneaded material: Coke containing 90 wt % or more of needle coke was used. Molding step S12: An extrusion molding device was used. First impregnation and firing step S13: After the initial firing, the combination of impregnation and firing was repeated three times. Crucible Processing Step S16: After the graphitization step S14, the graphitized block was cut to obtain a piece (second sample Sa2) having a diameter of 40 mm and a length of 150 mm. That is, the second sample Sa2 was obtained under the same manufacturing conditions as the first sample Sa1, except that the second impregnation and firing step S15 was not performed.

[0048] [measurement] For the first sample Sa1 and the second sample Sa2, bulk density was measured as a property of the produced graphite substrate. Bulk density was determined by measuring the dimensions of the graphite substrate using a vernier caliper to calculate the volume, measuring the weight of the graphite substrate using an electronic balance, and dividing the measured weight by the volume. Since the calculated volume includes voids, the more voids there are, the lower the bulk density. Bulk density measurements were performed in accordance with "JISR7222:2017 Measurement methods for physical properties of graphite materials." The measurement results are shown in Table 1.

[0049] [Table 1]

[0050] As can be seen from Table 1, the bulk density of the first sample Sa1 was 0.04 g greater than the bulk density of the second sample Sa2. This difference in bulk density is presumably due to the fact that the voids were filled with carbonaceous matter by performing the second impregnation and firing step S15.

[0051] <Consumption test> Three types of graphite substrates were manufactured using different manufacturing methods, and wear tests were conducted on the manufactured graphite substrates. The three types of graphite substrates are as follows. Note that manufacturing conditions not described below were within the ranges described in the above embodiment, and all samples were manufactured under the same conditions.

[0052] [First sample Sb1] A graphite substrate was manufactured according to the second embodiment of the method for manufacturing a graphite crucible. The main manufacturing conditions are as follows: Step S11 of obtaining kneaded material: Coke containing 90 wt % or more of needle coke was used. Molding step S12: An extrusion molding device was used. First impregnation and firing step S13: After the initial firing, the combination of impregnation and firing was repeated three times. Crucible Processing Step S16: After the graphitization step S14, the graphitized block was cut to obtain pieces with a diameter of 40 mm and a length of 150 mm. Second impregnation and firing step S15: The obtained pieces were subjected to impregnation and firing once each. The piece that had been subjected to the second impregnation and firing step S15 was cut to obtain two first samples Sb1 each having a diameter of 19 mm and a length of 30 mm.

[0053] [Second sample Sb2] Step S11 of obtaining kneaded material: Coke containing 90 wt % or more of needle coke was used. Molding step S12: An extrusion molding device was used. First impregnation and firing step S13: After the initial firing, the combination of impregnation and firing was repeated three times. Crucible processing step S16: After the graphitization step S14, the graphitized block was cut to obtain a piece having a diameter of 40 mm and a length of 150 mm, and the obtained piece was cut to obtain a second sample Sb2 having a diameter of 19 mm and a length of 30 mm. That is, two second samples Sb2 were obtained under the same manufacturing conditions as the first sample Sb1, except that the second impregnation and firing step S15 was not performed.

[0054] [Third sample Sb3] Step S11 of obtaining kneaded material: Coke containing 5 wt % or less of needle coke (coke containing almost no needle coke) was used. Molding step S12: A CIP molding device was used. First impregnation and firing step S13: After the initial firing, the combination of impregnation and firing was repeated twice. Crucible Processing Step S16: After the graphitization step S14, the graphitized block was cut to obtain two third samples Sb3 each having a diameter of 19 mm and a length of 30 mm.

[0055] [Consumption test] After measuring the mass of each sample (two each of Sb1, Sb2, and Sb3), the first sample Sb1, the second sample Sb2, and the third sample Sb3 were placed in a graphite crucible for single crystal growth containing raw materials. The graphite crucible containing the sample was then heated in a heating furnace under the same conditions as for sublimation recrystallization (2200°C for 240 hours). In other words, each sample was exposed to the same sublimation gas atmosphere as the inner wall of the graphite crucible. After heating and cooling, the mass of each sample was measured again, and the mass loss ratio (average of the two samples) was calculated for the sample after heating compared to the sample before heating. The test results are shown in Table 2.

[0056] [Table 2]

[0057] As can be seen from Table 2, the average mass loss rate of the first sample Sb1 is smaller than the average mass loss rate of the second sample Sb2. This shows that the first sample Sb1, which underwent the second impregnation and firing step, is less susceptible to wear than the second sample Sb2, which did not undergo the second impregnation and firing step, i.e., has higher heat resistance.

[0058] Furthermore, a comparison of the first and second samples Sb1 and Sb2 with the third sample Sb3 reveals that the samples (Sb1 and Sb2) composed mainly of needle coke are less susceptible to wear, i.e., have higher heat resistance, than the sample (Sb3) that contains almost no needle coke. [Explanation of symbols]

[0059] 3: Extrusion molding material 10: Crucible 21: Needle coke 30: Extrusion molding equipment 31:Admixture 32: Container 33: Dice 34: Pusher 40: Graphitized area 41: Pore (part of the cavity) 42: Crack (part of a void) 43: Carbonaceous region S11: Obtaining kneaded material S12: Molding process S13: First impregnation and baking step S14: Graphitization process S15: Second impregnation and baking process S16: Crucible processing process

Claims

1. A method for manufacturing a graphite crucible for growing a single crystal, which grows a single crystal on a main surface of a seed crystal substrate by a sublimation recrystallization method, comprising: a forming step of forming a raw material containing coke mainly composed of needle coke and binder pitch; a firing step of firing the molded product to obtain a fired product; a first impregnation and firing step in which the fired product is impregnated with additional binder pitch and fired one or more times to obtain an impregnated and fired product; a graphitization step of heating the impregnated and fired product to 2000°C or higher to graphitize the product, thereby obtaining a graphitized product; a second impregnation and firing step in which the graphitized material is impregnated with additional binder pitch and fired; A method for manufacturing a graphite crucible for single crystal growth, comprising:

2. The manufacturing method according to claim 1 , further comprising the step of processing the graphitized material into a crucible shape after the second impregnation and firing step.

3. 2. The manufacturing method according to claim 1, wherein the binder pitch and carbide powder added in the second impregnation and firing step are limited so that the ash content of the binder pitch and carbide powder added is 0.1% or less.

4. The method according to any one of claims 1 to 3, wherein the number of repetitions of impregnation and firing in the first impregnation and firing step is set to four or less.

5. The method according to any one of claims 1 to 3, wherein impregnation and firing are repeated in the second impregnation and firing step.

6. The manufacturing method according to any one of claims 1 to 3, wherein the molding step is an extrusion molding step.

7. 4. The manufacturing method according to claim 1, wherein process conditions for the second impregnation and firing step are determined based on measurement results regarding voids in the second impregnation and firing step.

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