A method for manufacturing a quartz crucible

Abstract

The application discloses a preparation method of a quartz crucible and relates to the technical field of quartz crucibles. According to the preparation method, the quartz crucible is prepared into a prefabricated piece first, and then a transparent layer is coated through gas refining, so that the interface mixing of high-purity inner sand and low-purity middle sand or outer sand is avoided, the interface is clearer, and the amount of the inner sand is reduced. Since the glassy high-purity quartz sand is softened and then melted, when the synthesized glassy high-purity quartz sand is used as the inner sand, the preparation method of the quartz crucible avoids the coating of the inner sand on the middle sand, and the bubbles in the transparent layer of the quartz crucible are reduced, so that the adverse influence of the existence of the bubbles on the use effect and service life of the quartz crucible is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of quartz crucible, in particular to a preparation method of quartz crucible. BACKGROUND

[0002] The quartz crucible belongs to a sub-product in quartz products, and has the properties of cleanliness, homogeneity and high temperature resistance. In terms of physical thermal properties, the deformation point of the quartz crucible is about 1100℃, the softening point is 1730℃, the maximum continuous use temperature is 1100℃, and the maximum short-time use temperature is 1450℃. At present, the quartz crucible is widely used in the production process of refining crystalline silicon in the fields of solar energy and semiconductors, and is a consumable in the production process of crystalline silicon.

[0003] The early quartz crucible is a fully transparent structure. Such a transparent structure is easy to cause uneven heat transfer conditions, increase the difficulty of crystal bar growth, and has a large demand for high-quality high-purity quartz sand, and the cost is high. Therefore, the preparation method of such a quartz crucible has been basically eliminated.

[0004] At present, the quartz crucible is generally produced by an electric arc method. The principle is that high-purity quartz powder with different purities is loaded into a rotating forming mold with an arbitrary tilting angle in steps, and is formed by centrifugal force (the conventional ratio is that the inner layer sand: the middle layer sand: the outer layer sand is composed of 3:4:3), the device with the formed crucible shape is moved to the electrode rod, then the electrode is powered on to start the arc, and the vacuum system is started at the same time, so that the quartz is quickly melted into a crucible-shaped molten quartz, and after cooling, the quartz crucible is taken out, and the melting of a quartz crucible is completed.

[0005] The quartz crucible prepared by the electric arc method is translucent, has an inner and outer layer structure, the outer layer is a high-bubble-density area, which is called a bubble composite layer (corresponding to the low-purity outer layer sand and / or middle layer sand). The bubble composite layer is uniformly heated and has good heat preservation effect; the inner layer is a 3-5mm low-bubble-density area, which is called a transparent layer (prepared by using high-purity inner layer sand). During the use of the crucible, the inner surface in contact with the silicon liquid is continuously dissolved into the silicon liquid, and the micro-bubbles in the transparent layer continuously grow, the bubbles near the innermost surface (1-2mm part closest to the inner surface in the transparent layer) break, and the silicon liquid releases quartz micro-particles and micro-bubbles. These impurities in the form of micro-particles and micro-bubbles flow through the entire silicon melt along with the silicon liquid, directly affecting the crystallization of silicon (whole bar rate, crystallization rate, heating time, direct processing cost, etc.) and the quality of single-crystal silicon (punching sheet, black chip, etc.). Therefore, how to reduce the gas-liquid inclusions in the high-purity natural quartz sand in the transparent layer becomes the key to improving the quality of the quartz crucible, but the gas-liquid inclusions in the natural quartz sand cannot be completely removed by the prior art.

[0006] In order to solve the problem that the gas-liquid inclusions in natural quartz sand cannot be completely removed, technical personnel prepared glassy high-purity quartz sand by a synthetic method. However, when the glassy high-purity quartz sand is used to replace part of the natural quartz sand as the inner layer sand, it is found that because the glassy high-purity quartz sand is amorphous and has a low softening temperature, the gas-liquid inclusions in the natural quartz sand (crystalline) cannot be removed, resulting in an increase in the number and size of bubbles in the quartz crucible, which limits the application of the glassy high-purity quartz sand in the quartz crucible.

[0007] On the other hand, because the high-purity inner layer sand is mixed with the low-purity middle layer sand or outer layer sand at the interface during the mold forming process, the amount of the high-purity inner layer sand is relatively large, resulting in an increase in cost. SUMMARY

[0008] The technical problem to be solved by the present application is to provide a preparation method of a quartz crucible, which not only has a small amount of inner layer sand, but also has few bubbles in the transparent layer when the glassy synthetic quartz sand is used as the inner layer sand.

[0009] The technical problem to be solved by the present application is solved by the following technical solutions:

[0010] The present application provides a preparation method of a quartz crucible, comprising the following steps:

[0011] S1, pouring the outer layer sand into a rotating mold, and forming the crucible outer layer by melt forming with a forming rod;

[0012] S2, pouring the middle layer sand into the rotating mold in which the crucible outer layer has been formed, and forming the crucible middle layer by melt forming with the forming rod;

[0013] S3, placing the rotating mold in which the crucible outer layer and the crucible middle layer have been formed in a melting area, and using the vacuum arc method to melt and demold to obtain a quartz crucible preform;

[0014] S4, adding the inner layer sand to the quartz crucible preform, and using the gas refining melt method to rotate the quartz crucible preform, so that the molten inner layer sand is coated on the inner surface of the quartz crucible preform to form a transparent layer, thereby obtaining a quartz crucible.

[0015] Further, the outer layer sand is at least one of natural quartz sand and synthetic quartz sand with a purity greater than 99.9%. Preferably, the outer layer sand is natural quartz sand with a purity greater than 99.9%. The price of natural quartz sand is relatively low.

[0016] Further, the middle layer sand is at least one of natural quartz sand and synthetic quartz sand with a purity greater than 99.99%. Preferably, the middle layer sand is natural quartz sand with a purity greater than 99.99%. The outer layer sand and the middle layer sand are preferably natural quartz sand, which can reduce the preparation cost of the quartz crucible.

[0017] Further, the inner layer sand is at least one of natural quartz sand and synthetic quartz sand with purity greater than 99.998%. Preferably, the inner layer sand is synthetic quartz sand with purity greater than 99.998%. The synthetic quartz sand has high purity and no gas-liquid inclusions, and the prepared transparent layer of the crucible has few bubbles.

[0018] Further, the synthetic quartz sand comprises at least one of glassy high-purity quartz sand and crystalline high-purity quartz sand. Preferably, the synthetic quartz sand is glassy high-purity quartz sand. Compared with the crystalline state, the glassy state has low melting point, is easy to melt in the preparation of the crucible, and is easy to process.

[0019] Further, the particle size of the outer layer sand, the middle layer sand and the inner layer sand ranges from 50 to 140 mesh. Appropriate particle size or different particle sizes can be selected according to needs.

[0020] Further, the vacuum pressure of the melting in step S3 can reach the limit pressure value of -0.099 MPa.

[0021] Further, the gas used in the gas refining melting method in step S4 is hydrogen and oxygen.

[0022] Further, in order to prevent the quartz crucible preform from cracking during the gas refining coating process, the quartz crucible preform is preheated before the inner layer sand is added in step S4, and the preheating temperature is 500-900°C.

[0023] Further, the flame of the gas refining melting in step S4 should follow the melting of the inner layer sand to ensure that the inner layer sand is uniformly coated on the inner surface of the quartz crucible preform without damaging the quartz crucible preform. On the other hand, the gas refining melting method increases the content of hydroxyl groups in the quartz sand, reduces the viscosity of the quartz, and is beneficial to improve the flowability and facilitate coating. These two technical effects are difficult to achieve by the electric arc method.

[0024] The application also provides a preparation method of glassy high-purity quartz sand, comprising the following steps:

[0025] (1) preparing a slurry by adding water to nanoscale amorphous silicon dioxide, and spray drying the slurry to obtain nanoscale silicon dioxide agglomerates;

[0026] (2) mechanically and statically pressing the nanoscale silicon dioxide agglomerates prepared in step (1) to obtain blocky silicon dioxide;

[0027] (3) crushing, calcining and cooling the blocky silicon dioxide prepared in step (2) to obtain glassy high-purity quartz sand.

[0028] Further, the average particle size of the nanoscale amorphous silicon dioxide is 5-100 nm. Amorphous silicon dioxide is a non-crystalline silicon dioxide, and the nanoscale amorphous silicon dioxide is used as a raw material to prepare the glassy high-purity quartz sand. The high-purity quartz sand in nature is crystalline, and the high-purity quartz sand prepared by the present application is glassy, which belongs to amorphous and has a relatively low processing temperature.

[0029] Further, the solid content of the slurry is 5-50%. In the present application, if the solid content is lower than the range, the fine particles of the powder obtained by spray drying are more, and the flowability is poor; if the solid content is higher than the range, the viscosity of the slurry is large, and the nozzle is easily blocked.

[0030] Further, the inlet air temperature of the spray drying is 280-350℃, and the outlet air temperature is 80-120℃. In the present application, the nanoscale amorphous silicon dioxide is converted into nanosilica agglomerates by spray drying.

[0031] Further, the average particle size of the nanosilica agglomerates is 100-500 μm. If the particle size is too large, the uniformity is poor; if the particle size is too small, it is not easy to prepare. Of course, the particle size of the nanosilica agglomerates is also affected by the particle size of the raw material nanoscale amorphous silicon dioxide.

[0032] Further, the pressure of the mechanical static pressure is 150-250 MPa, and the time is 10-40 min. Since the nanosilica powder is very fluffy, if the pressure is directly applied to the powder, the powder will expand and become loose again when the pressure is removed, so it is necessary to first add water to prepare a slurry, and then to prepare large particles by spray drying. In the present application, the mechanical static pressure is used to overcome the repulsive force between the nanosilica particles, so that the distance between the nanosilica particles is closer, thereby reducing the porosity of the product after sintering.

[0033] Further, the average particle size of the blocky silicon dioxide after mechanical crushing is 50-400 μm.

[0034] Further, the calcination temperature is 1000-1600℃, and the time is 3-8 h. The crushed blocky silicon dioxide is densified by calcination, and if the calcination temperature is too high or the calcination time is too long, crystallization will occur, and the energy consumption is high; if the calcination temperature is too low or the calcination time is too short, the blocky silicon dioxide cannot be completely melted, and the product has a porous structure. Preferably, the calcination temperature is 1100-1200℃, and the time is 5-6 h.

[0035] The present application has the following advantages:

[0036] 1. The quartz crucible is prepared first and then gas refining and coating transparent layer, which avoids the interface mixing of high purity inner layer sand and low purity middle layer sand or outer layer sand, makes the interface more clear, and reduces the amount of inner layer sand.

[0037] 2. Since the glassy high-purity quartz sand is softened and then melted, when the synthetic glassy high-purity quartz sand is used as the inner layer sand, the preparation method of the quartz crucible avoids the coating of the inner layer sand on the middle layer sand, reduces the bubbles in the transparent layer of the quartz crucible, and thus solves the adverse effects of the existence of bubbles on the use effect and service life of the quartz crucible. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 It is a structure schematic diagram of the quartz crucible after gas refining and melting in Example 2.

[0039] Figure 2 It is a structure schematic diagram of each layer of the quartz crucible before arc melting in Comparative Example 1.

[0040] Figure 3 It is a structure schematic diagram of each layer of the quartz sand after arc melting. Figure 2

[0041] Figure 4 It is a cross-sectional view of the quartz crucible obtained in Example 1.

[0042] Figure 5 It is a cross-sectional view of the quartz crucible obtained in Comparative Example 2. DETAILED DESCRIPTION

[0043] In order to make the technical means, creative features, purposes and effects realized by the present application easy to understand, the present application is further described below in combination with specific examples and drawings.

[0044] The middle layer sand is quartz sand of PQSF type purchased from Jiangsu Pacific Quartz Co., Ltd.

[0045] The outer layer sand is quartz sand of PQSX1 type purchased from Jiangsu Pacific Quartz Co., Ltd.

[0046] Example 1

[0047] Preparation of the quartz crucible:

[0048] S1, pour the outer layer sand (80-130 mesh) into the rotating mold, the mold is placed at an angle of 45-56°, the rotating speed is 65-70 rpm, and the molding rod is used for fusion molding.

[0049] S2, pour the middle layer sand (60-120 mesh) into the rotating mold in which the outer layer of the crucible has been molded, the mold is placed at an angle of 45-56°, the rotating speed is 65-70 rpm, and the molding rod is used for fusion molding. ​

[0050] S3, the rotary mold in which the outer layer and the middle layer of the crucible have been shaped is placed in the melting area, and vacuum arc melting is used for 10 min, the vacuum pressure value is -0.099 MPa, the arc power is 10 kW, and natural cooling is performed, demolding is performed, and a quartz crucible preform is obtained.

[0051] S4, the quartz crucible preform is preheated to 500 DEG C, and then the inner layer sand (50-100 mesh, natural quartz sand, USA Unimin Company, model ITOA-6) is added to the quartz crucible preform, and hydrogen / oxygen gas refining melting is performed.

[0052] S5, the quartz crucible preform is rotated, so that the molten inner layer sand is coated on the inner surface of the quartz crucible preform to form a transparent layer, and a quartz crucible is obtained.

[0053] The mass ratio of the outer layer sand, the middle layer sand, and the inner layer sand is 3:4:3.

[0054] Example 2

[0055] The preparation method of the quartz crucible in Example 2 is the same as that in Example 1, except that the inner layer sand is glassy high-purity quartz sand.

[0056] Preparation of the glassy high-purity quartz sand: amorphous silicon dioxide with a D50 particle size of 25 nm is added to water to prepare a slurry with a solid content of 20%; the slurry is spray dried to obtain nanosilica agglomerates with a D50 particle size of 300 pm; the nanosilica agglomerates are subjected to mechanical static pressure (pressure of 250 MPa, time of 0.5 h) to obtain bulk silicon dioxide; the bulk silicon dioxide is mechanically broken into particles of 40-85 mesh, and is calcined at 1200 DEG C for 5 h, and is naturally cooled to obtain glassy high-purity quartz sand of 50-100 mesh.

[0057] As shown in FIG. 2, the quartz crucible obtained in Example 2 has a transparent layer and a bubble layer from inside to outside, and does not form a transition layer. Figure 1

[0058] Example 3

[0059] The preparation method of the quartz crucible in Example 3 is the same as that in Example 1, except that the inner layer sand is crystalline high-purity quartz sand synthesized according to Example 5 in the reference patent CN202310980924.1.

[0060] Amorphous silicon dioxide (particle size 5 nm, specific surface area 200 m 2 / g) 3 kg, dried at 100 DEG C for 2 h, 30 g of a coupling agent (CH3O)3Si(CH2) 10 ​CH3 was mixed with 100 g of ethanol to obtain a modified liquid, the modified liquid was mixed with the dried amorphous silica uniformly, dried (100°C, 2 h), calcined at 1170°C for 10 h, naturally cooled, and scattered by air flow to obtain high-purity cristobalite with an average particle size of 180 μm (about 80 mesh).

[0061] Comparative Example 1

[0062] The preparation method of the quartz crucible in Comparative Example 1 was the same as that in Example 1, except that the air refining melting was not performed, and the outer layer sand, the middle layer sand and the inner layer sand were sequentially poured into the rotating mold, and then fused by the molding rod, and then fused by the vacuum arc method.

[0063] As shown in Figure 2 , a mixed layer was formed between the inner layer sand and the middle layer sand before the arc melting, and the mixed layer contained the inner layer sand and the middle layer sand.

[0064] As shown in Figure 3 , the quartz crucible obtained after the arc melting was sequentially composed of a transparent layer, a transition layer and a bubble layer from the inside to the outside.

[0065] Comparative Example 2

[0066] The preparation method of the quartz crucible and the glassy high-purity quartz sand in Comparative Example 2 was the same as that in Example 1, except that the mechanical static pressure was not performed on the nano-silica agglomerates when the glassy high-purity quartz sand was prepared.

[0067] Preparation of the glassy high-purity quartz sand: amorphous silica with a D50 particle size of 25 nm was added to water to prepare a slurry with a solid content of 20%; the slurry was spray dried to obtain nano-silica agglomerates with a D50 particle size of 300 μm; the nano-silica agglomerates were calcined at 1200°C for 5 h, and then naturally cooled to obtain glassy high-purity quartz sand (opaque) with a particle size of 50-100 mesh.

[0068] Comparative Example 3

[0069] The preparation method of the quartz crucible and the glassy high-purity quartz sand in Comparative Example 3 was the same as that in Example 1, except that the pressure of the mechanical static pressure was too small when the glassy high-purity quartz sand was prepared.

[0070] Preparation of glassy high-purity quartz sand: amorphous silicon dioxide with a D50 particle size of 25 nm was added to water to prepare a slurry with a solid content of 20%; the slurry was spray dried to obtain nanosilica agglomerates with a D50 particle size of 300 μm; the nanosilica agglomerates were subjected to mechanical static pressing (pressure of 5 MPa, time of 1 h) to obtain bulk silicon dioxide; the bulk silicon dioxide was mechanically broken into particles of 40-85 mesh, calcined at 1200°C for 5 h, and naturally cooled to obtain glassy high-purity quartz sand (opaque) of 50-100 mesh.

[0071] Comparative Example 4

[0072] The preparation method of the quartz crucible and the glassy high-purity quartz sand in Comparative Example 4 is the same as in Example 1, except that the calcination temperature is too low when preparing the glassy high-purity quartz sand.

[0073] Preparation of glassy high-purity quartz sand: amorphous silicon dioxide with a D50 particle size of 25 nm was added to water to prepare a slurry with a solid content of 20%; the slurry was spray dried to obtain nanosilica agglomerates with a D50 particle size of 300 μm; the nanosilica agglomerates were subjected to mechanical static pressing (pressure of 5 MPa, time of 1 h) to obtain bulk silicon dioxide; the bulk silicon dioxide was mechanically broken into particles of 40-85 mesh, calcined at 1200°C for 5 h, and naturally cooled to obtain glassy high-purity quartz sand (opaque) of 50-100 mesh.

[0074] The quartz crucibles prepared in the above examples and comparative examples were subjected to determination of the thickness of the transparent layer and the number of bubbles in accordance with JC-T 1048-2007 "Quartz Crucible for Single Crystal Silicon Growth"; the content of hydroxyl groups in the transparent layer was tested by infrared spectroscopy, and the results are shown in Table 1.

[0075] Table 1

[0076]

[0077] As can be seen from Table 1, the quartz crucibles prepared in Example 2 and Example 3 using synthetic glassy high-purity quartz sand and high-purity tridymite as the inner layer sand, respectively, and using the arc + gas refining melting method do not have bubbles in the transparent layer.

[0078] The quartz crucible of Example 1 uses high-purity natural quartz sand as the inner layer sand, but because it contains gas-liquid inclusions, it contains a certain amount of bubbles in the transparent layer (as shown in Table 1). Figure 4

[0079] The quartz crucible of Comparative Example 1 is prepared by the conventional arc melting method after the outer layer sand, the middle layer sand, and the inner layer sand are all formed, and because the interface between the middle layer sand and the inner layer sand is mixed, a transition layer is formed, resulting in a reduced thickness of the transparent layer.​

[0080] Examples 1-3 involve first melting the outer and middle layers of sand using an electric arc method, and then melting the inner layer of sand using gas refining. The middle and inner layers of sand do not mix at the interface, resulting in a clear interface. Under the condition of the same amount of inner layer sand, the thickness of the transparent layer of the quartz crucible is large.

[0081] Comparative Examples 2-5, prepared under the corresponding process conditions, produced glassy high-purity quartz sand with numerous pores, resulting in opaque glassy high-purity quartz sand. When used as an inner layer sand, a transparent layer could not be obtained (e.g., Figure 5 (As shown).

[0082] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a quartz crucible, characterized in that, Includes the following steps: S1. Pour the outer layer of sand into a rotating mold and use a forming rod to melt and shape it to form the outer layer of the crucible; S2. Pour the middle layer sand into the rotating mold that has completed the outer layer of the crucible, and use the molding rod to melt and shape it to form the middle layer of the crucible; S3. Place the rotating mold with the outer and middle layers of the crucible already formed in the melting area, melt it using the vacuum arc method, demold it, and obtain the quartz crucible preform. S4. Add inner layer sand to the quartz crucible preform, use gas refining melting method, rotate the quartz crucible preform, so that the molten inner layer sand is coated on the inner surface of the quartz crucible preform to form a transparent layer, and obtain the quartz crucible. The outer layer sand is at least one of natural quartz sand and synthetic quartz sand with a purity greater than 99.9%; The intermediate layer sand is at least one of natural quartz sand and synthetic quartz sand with a purity greater than 99.99%; The inner layer sand is high-purity glassy quartz sand with a purity greater than 99.998%; The preparation method of the glassy high-purity quartz sand includes the following steps: (1) Nanoscale amorphous silica was mixed with water to form a slurry, and the slurry was spray-dried to obtain nanoscale silica agglomerates; (2) The nano-silica agglomerates prepared in step (1) are subjected to mechanical static pressing to obtain bulk silica; (3) The blocky silica prepared in step (2) is crushed, calcined and cooled to obtain glassy high-purity quartz sand.

2. The method for preparing the quartz crucible according to claim 1, characterized in that: The outer layer sand is natural quartz sand with a purity greater than 99.9%.

3. The method for preparing the quartz crucible according to claim 1, characterized in that: The intermediate layer sand is natural quartz sand with a purity greater than 99.99%.

4. The method for preparing the quartz crucible according to claim 1, characterized in that: The particle size range of the outer, middle, and inner sand layers is 50-140 mesh.

5. The method for preparing the quartz crucible according to claim 1, characterized in that: The vacuum pressure for melting in step S3 reaches the limit pressure value of -0.099 MPa.

6. The method for preparing the quartz crucible according to claim 1, characterized in that: The gases used in the gas refining and melting method described in step S4 are hydrogen and oxygen.

7. The method for preparing the quartz crucible according to claim 1, characterized in that: In step S4, the quartz crucible preform is preheated before adding the inner layer of sand, and the preheating temperature is 500~900℃.

8. The method for preparing the quartz crucible according to claim 1, characterized in that: In step S4, the flame of gas refining moves along with the molten inner layer sand.

9. The method for preparing the quartz crucible according to claim 1, characterized in that: The average particle size of the nanoscale amorphous silica is 5~100 nm.

10. The method for preparing the quartz crucible according to claim 1, characterized in that: The solid content of the slurry is 5-50%.

11. The method for preparing the quartz crucible according to claim 1, characterized in that: The inlet air temperature of the spray dryer is 280~350℃, and the outlet air temperature is 80~120℃.

12. The method for preparing the quartz crucible according to claim 1, characterized in that: The average particle size of the nano-silica agglomerates is 100~500 μm.

13. The method for preparing the quartz crucible according to claim 1, characterized in that: The mechanical static pressure is 150~250 MPa, and the time is 10~40 min.

14. The method for preparing the quartz crucible according to claim 1, characterized in that: The average particle size of the blocky silica after mechanical crushing is 50~400 μm.

15. The method for preparing the quartz crucible according to claim 1, characterized in that: The calcination temperature is 1000~1600℃, and the time is 3~8 h.

16. The method for preparing the quartz crucible according to claim 15, characterized in that: The calcination temperature is 1100~1200℃, and the time is 5~6 h.

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