Alloy graphite powder applied to reduction furnace preheater and reduction furnace preheater

Abstract

The invention relates to alloy graphite powder applied to a reduction furnace preheater and the reduction furnace preheater, and belongs to the technical field of preheater preparation. The alloy graphite powder comprises the following raw materials: graphite powder, boron nitride and silicon powder, wherein the mass ratio of the graphite powder to the boron nitride to the silicon powder is 1: (0.001%-0.1%): (0.001%-0.1%); the graphite powder, boron nitride and silicon powder are mixed and then heated in a vacuum environment, and alloy graphite powder is obtained after heating is completed. Boron nitride and silicon powder are introduced into graphite powder, alloy graphite powder is formed through high-temperature firing, the obtained alloy graphite powder is subjected to a hot isostatic pressing forming process to obtain the preheater, the service life of the obtained preheater is longer than that of a preheater made of pure graphite, the number of cycles can reach 4-7 in the process of preparing multi-stage silicon in a reduction furnace, and the service life of the preheater is prolonged. The service life of the preheater is prolonged, and the production cost of polycrystalline silicon is greatly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of preheater preparation, and in particular relates to an alloy graphite powder applied to a reduction furnace preheater and a reduction furnace preheater. Background Art

[0002] At present, most polysilicon production enterprises adopt the modified Siemens method to prepare polysilicon. In this process, the vaporized trichlorosilane and hydrogen form a certain molar ratio, and react and deposit on the silicon core at a temperature of 950-1150°C in the reactor to finally obtain the finished polysilicon rod. The silicon core acts as a deposition carrier of the trichlorosilane and hydrogen mixed gas on the one hand, and maintains the temperature of the thermal field in the polysilicon production reduction furnace due to the current passed in on the other hand. The silicon core is a semiconductor material, and its semiconductor characteristic is negative resistance. The resistivity of the silicon core decreases with increasing temperature. Therefore, only when there is enough heat to raise the temperature of the silicon core to above a certain temperature (so that the resistivity of the silicon core drops to a certain value), a high voltage of 10KV is applied to the silicon core to generate about 1KW of electric power to heat the silicon core. As the temperature of the silicon core rises and the resistance of the silicon core decreases significantly, the heating power is further increased, the temperature of the silicon core rises and breaks down, forming a circuit, and then the temperature of the silicon core is controlled by the current to the required temperature of chemical vapor deposition to complete the start-up of the reduction furnace. Therefore, for the electronic grade polysilicon reduction furnace, its preheater needs to provide enough heat atmosphere for the reduction furnace to start the reduction furnace, so as to ensure the subsequent reduction production of polysilicon. At present, in the production of electronic grade polysilicon, the reduction furnace preheater is a graphite preheater, which uses the comprehensive properties of graphite material, such as low resistivity, good thermal shock resistance, good thermal conductivity, good electrical conductivity, good chemical stability, corrosion resistance, and high temperature resistance. After the graphite preheater is powered on, the furnace atmosphere is heated to 450°C, and then the silicon core is broken down by a voltage of 1400V, while reducing the safety hazards of the silicon core during the high voltage breakdown of several thousand volts.

[0003] However, the following problems exist in the use of graphite preheaters: first, the coefficient of thermal expansion (CTE) of graphite itself is much larger than that of silicon, and the CTE value of the raw material of the preheater is too high. The superposition of the differences in the coefficient of thermal expansion (CTE) causes the silicon to crack, peel, and break after the reduction furnace is turned on, which can directly affect the quality of the polysilicon finished product and even cause the reduction furnace to fail to operate normally; secondly, since the graphite preheater is in the high temperature environment of the reduction furnace, its conductivity is easily affected and unstable, resulting in the graphite preheater being unable to meet the waste heat requirements of the silicon core of the reduction furnace after being used for 3-4 batches, resulting in frequent replacement of the graphite preheater; thirdly, the price of high-purity graphite raw materials is relatively high, resulting in excessively high production and manufacturing costs for the preheater; finally, after the existing reduction furnace has been running for 3-4 batches, the preheater cannot meet the requirements for preheating the silicon core due to silicon deposition. Summary of the invention

[0004] In view of the above problems, the present invention provides an alloy graphite powder applied to a reduction furnace preheater and a reduction furnace preheater.

[0005] The first object of the present invention is to provide an alloy graphite powder used in a reduction furnace preheater, comprising the following raw materials: graphite powder, boron nitride and silicon powder.

[0006] Furthermore, the mass ratio of the graphite powder, boron nitride and silicon powder is 1:0.001% to 0.1%:0.001 to 0.1% by mass.

[0007] Furthermore, the alloy graphite powder is prepared by the following steps:

[0008] After graphite powder, boron nitride and silicon powder are mixed, they are heated in a vacuum environment to obtain alloy graphite powder.

[0009] Furthermore, the heating conditions are as follows: the heating temperature is 800-1000° C., the heating time is 10-60 min, the boron content in the alloy graphite powder ranges from 0.001% to 0.05%, the nitrogen content accounts for 0.001% to 0.08%, and the silicon content accounts for 0.001% to 0.06%.

[0010] Preferably, the heating temperature is 800°C, 805°C, 810°C, 815°C, 820°C, 825°C, 830°C, 835°C, 840°C, 845°C, 850°C, 855°C, 860°C, 865°C, 870°C, 875°C, 880°C, 885°C, 890°C, 895°C, 900°C, 905°C, 910°C, 915°C, 920°C, 925°C, 930°C, 935°C, 940°C, 945°C, 950°C, 955°C, 960°C, 965°C, 970°C, 975°C, 980°C, 985°C, 990°C, 995°C or 1000°C.

[0011] Preferably, the heating time is 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min, 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min, 40 min, 41 min, 42 min, 43 min, 44 min, 45 min, 46 min, 47 min, 48 min, 49 min, 50 min, 51 min, 52 min, 53 min, 54 min, 55 min, 56 min, 57 min, 58 min, 59 min or 60 min.

[0012] The second object of the present invention is to provide a method for preparing the alloy graphite powder used in a reduction furnace preheater, comprising:

[0013] After graphite powder, boron nitride and silicon powder are mixed, they are heated in a vacuum environment to obtain alloy graphite powder.

[0014] The third object of the present invention is to provide a reduction furnace preheater made of the above-mentioned alloy graphite powder.

[0015] Furthermore, the reduction furnace preheater is manufactured by the following steps:

[0016] The alloy graphite powder is molded by hot isostatic pressing to obtain a reduction furnace preheater.

[0017] Furthermore, the expansion coefficient of the reduction furnace preheater at room temperature to 1000°C is 3.4×10 -6 / ℃~4.2×10 -6 / ℃.

[0018] Furthermore, the room temperature resistivity of the reduction furnace preheater is 18 μΩm to 19 μΩm, and the 1000° C. resistivity of the reduction furnace preheater is 16.5 μΩm to 18.2 μΩm.

[0019] A fourth object of the present invention is to provide a method for preparing a reduction furnace preheater, comprising:

[0020] The alloy graphite powder is molded by hot isostatic pressing to obtain a reduction furnace preheater.

[0021] Furthermore, the hot isostatic pressing process includes: a temperature of 1000-1200° C., an isotropic high pressure of 100-200 MPa, and maintaining the temperature and pressure for 20 to 40 minutes.

[0022] Beneficial effects of the present invention:

[0023] The present invention discloses an alloy graphite powder used for a reduction furnace preheater and a reduction furnace preheater. Boron nitride and silicon powder are introduced into graphite powder, and alloy graphite powder is formed through high-temperature sintering. The obtained alloy graphite powder is doped with trace elements of boron, nitrogen and silicon. The present invention adjusts the amount of boron nitride and silicon powder (pure silicon powder) added so that the contents of boron, nitrogen and silicon trace elements in the alloy graphene powder are 0.001% to 0.04% boron, 0.001% to 0.06% nitrogen and 0.001% to 0.1% silicon respectively. The present invention utilizes the alloy graphene powder to make a preheater. It is found that the obtained preheater has a longer service life than a preheater made of pure graphite. In the process of preparing multi-grade silicon in the original furnace, the number of cycles can reach 4-7 times, which is longer than the original pure graphite preheater which can be cycled 2-3 times, and greatly reduces the production cost of polysilicon. The reason for the extended life is that the doping of trace elements of boron, nitrogen and silicon does not cause the trend of decreasing mechanical properties of the graphite preheater, but instead has the following positive effects: First, the trace elements of boron, nitrogen and silicon hinder the movement of the graphite lattice at high temperature, reduce the thermal expansion coefficient of graphite, and improve the conductive stability of graphite, inhibiting the change of resistivity; second, the introduction of trace elements of silicon ensures the bonding strength between the subsequent deposited polysilicon and the heater, further reducing the cracking problem of the reduction furnace. The play of these positive effects further realizes the extension of the service life of the alloy graphite powder preheater.

[0024] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and embodiments. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Example 1

[0027] The present invention provides a graphite alloy powder

[0028] Graphite powder, boron nitride and silicon powder are mixed in a mass ratio of 1:0.05%:0.05%, and then the mixed powder is heated in a vacuum environment to obtain alloy graphite powder after heating, wherein the heating temperature is 900° C. and the heating time is 30 minutes.

[0029] Example 2

[0030] The present invention provides a graphite alloy powder

[0031] Graphite powder, boron nitride and silicon powder are mixed in a mass ratio of 1:0.04%:0.03%, and then the mixed powder is heated in a vacuum environment to obtain alloy graphite powder, wherein the heating temperature is 900° C. and the heating time is 30 minutes.

[0032] Example 3

[0033] The present invention provides a graphite alloy powder

[0034] Graphite powder, boron nitride and silicon powder are mixed in a mass ratio of 1:0.07%:0.05%, and then the mixed powder is heated in a vacuum environment to obtain alloy graphite powder, wherein the heating temperature is 900° C. and the heating time is 30 minutes.

[0035] Example 4

[0036] The present invention provides a graphite alloy powder

[0037] Graphite powder, boron nitride and silicon powder are mixed in a mass ratio of 1:0.1%:0.1%, and then the mixed powder is heated in a vacuum environment to obtain alloy graphite powder, wherein the heating temperature is 9000° C. and the heating time is 30 minutes.

[0038] Comparative Example 1

[0039] The comparative example of the present invention provides a graphite powder (the graphite powder in Example 1).

[0040] Example 6

[0041] The embodiment of the present invention provides a reduction furnace preheater

[0042] The alloy graphite powder obtained in Example 1 is molded by hot isostatic pressing to obtain a reduction furnace preheater; wherein the hot isostatic pressing process includes: a temperature of 1000-1100° C., an isotropic high pressure of 100-150 MPa, and maintaining the temperature and pressure for 20 minutes.

[0043] Example 7

[0044] The embodiment of the present invention provides a reduction furnace preheater

[0045] The alloy graphite powder obtained in Example 2 is molded by hot isostatic pressing to obtain a reduction furnace preheater; wherein the hot isostatic pressing process includes: a temperature of 1100-1200°C, an isotropic high pressure of 150-200 MPa, and maintaining the temperature and pressure for 30 minutes.

[0046] Example 8

[0047] The embodiment of the present invention provides a reduction furnace preheater

[0048] The alloy graphite powder obtained in Example 3 is molded by hot isostatic pressing to obtain a reduction furnace preheater; wherein the hot isostatic pressing process includes: a temperature of 1100-1200°C, an isotropic high pressure of 150-200 MPa, and maintaining the temperature and pressure for 40 minutes.

[0049] Example 9

[0050] The embodiment of the present invention provides a reduction furnace preheater

[0051] The alloy graphite powder obtained in Example 4 is molded by hot isostatic pressing to obtain a reduction furnace preheater; wherein the hot isostatic pressing process includes: a temperature of 1000-1100° C., an isotropic high pressure of 100-130 MPa, and maintaining the temperature and pressure for 25 minutes.

[0052] Comparative Example 2

[0053] The comparative example of the present invention provides a reduction furnace preheater

[0054] The graphite powder in comparative example 1 is molded by hot isostatic pressing to obtain a reduction furnace preheater; wherein the hot isostatic pressing process includes: a temperature of 1000-1100° C., an isotropic high pressure of 100-150 MPa, and maintaining the temperature and pressure for 20 minutes.

[0055] The sizes of the reduction furnace preheaters obtained in Examples 6 to 9 and Comparative Example 2 are the sizes of the currently used reduction furnace preheaters. The sizes of the reduction furnace preheaters in other embodiments can also be flexibly adjusted according to actual needs.

[0056] The reduction furnace preheaters obtained in Examples 6 to 9 and Comparative Example 2 were subjected to the following performance tests:

[0057] Expansion coefficient test: Take a 4mm×20mm size test piece to make a test piece for measuring the linear thermal expansion coefficient, use a thermal expansion meter TMA300 to cool down at 50℃ / min, and measure the linear thermal expansion coefficient from 450℃ to 1000℃;

[0058] Resistivity test: Take a 1cm×1cm size and use a high-temperature four-probe dual-electric self-nuclear resistance tester to test the resistivity change at 450℃ and 1000℃, referring to the American ASTM standard;

[0059] Service life test: The sample preheater is subjected to a reduction furnace cycle according to the conditions of polysilicon production, and the number of times the sample preheater cracks is recorded. The service life of the sample preheater is evaluated based on the number of cycles in which the sample preheater cracks.

[0060] The results of the above tests are shown in Table 1.

[0061] Table 1

[0062]

[0063] From the data in Table 1, it can be seen that the expansion coefficient of the preheater obtained in Examples 6-9 is lower than the corresponding performance of the preheater in Comparative Example 2 (pure graphite preheater), indicating that doping nitrogen, boron and silicon in graphite is beneficial to reducing the thermal expansion coefficient of the preheater, thereby reducing the probability of cracking, peeling and breaking of silicon after the reduction furnace is opened due to the difference in expansion coefficient; the difference in resistivity of the preheater obtained in Examples 6-9 at room temperature and 1000°C is lower than the corresponding performance of the preheater in Comparative Example 2, indicating that doping nitrogen, boron and silicon in graphite is beneficial to improving the stability of the resistivity of the preheater, but the service life of the preheater obtained in Example 9 is lower than that of the preheater obtained in Examples 6-8, indicating that when the doping amount of boron, nitrogen and silicon increases, as the doping amount of boron, nitrogen and silicon increases, the defects of the alloy graphite material also increase accordingly, resulting in a decrease in the strength performance of the obtained graphite material, resulting in the accelerated generation of cracks in the obtained preheater during the cyclic heating process, and ultimately resulting in a shortened service life of the obtained preheater.

[0064] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An alloy graphite powder used in a reduction furnace preheater, characterized in that: The invention comprises the following raw materials: graphite powder, boron nitride and silicon powder.

2. The alloy graphite powder used for a reduction furnace preheater according to claim 1, characterized in that: The mass ratio of the graphite powder, boron nitride and silicon powder is 1:0.001%-0.1%:0.001-0.1% by mass.

3. The alloy graphite powder used for a reduction furnace preheater according to claim 1, characterized in that: The method comprises the following steps: After graphite powder, boron nitride and silicon powder are mixed, they are heated in a vacuum environment to obtain alloy graphite powder.

4. The alloy graphite powder used for a reduction furnace preheater according to claim 3, characterized in that: The heating conditions are as follows: the heating temperature is 800-1000° C., the heating time is 10-60 min, the boron content in the alloy graphite powder ranges from 0.001% to 0.04%, the nitrogen content accounts for 0.001% to 0.06%, and the silicon content accounts for 0.001% to 0.1%.

5. The method for preparing alloy graphite powder for use in a reduction furnace preheater according to any one of claims 1 to 4, characterized in that: include: After graphite powder, boron nitride and silicon powder are mixed, they are heated in a vacuum environment to obtain alloy graphite powder.

6. A reduction furnace preheater, characterized in that: Made from the alloy graphite powder described in any one of claims 1 to 4.

7. A reduction furnace preheater according to claim 6, characterized in that: The method comprises the following steps: The alloy graphite powder is molded by hot isostatic pressing to obtain a reduction furnace preheater.

8. A reduction furnace preheater according to claim 6, characterized in that: The expansion coefficient of the reduction furnace preheater at room temperature to 1000°C is 3.4×10 -6 / ℃~4.2×10 -6 / ℃.

9. A reduction furnace preheater according to any one of claims 6 to 8, characterized in that: The room temperature resistivity of the reduction furnace preheater is 18 μΩm to 19 μΩm, and the 1000° C. resistivity of the reduction furnace preheater is 16.5 μΩm to 18.2 μΩm.

10. A method for preparing a reduction furnace preheater according to any one of claims 6 to 9, characterized in that: include: The alloy graphite powder is molded by hot isostatic pressing to obtain a reduction furnace preheater.

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