Method for preparing large-grain silicon carbide coating on surface of large-size graphite basal disc

Abstract

The invention relates to preparation of crystals, in particular to a method for preparing a large-grain silicon carbide coating on the surface of a large-size graphite basal disc, which comprises the following steps: uniformly smearing a release agent on the surface of the graphite basal disc, uniformly mixing silicon carbide seed crystal powder and magnetostrictive material particles, and uniformly paving; the preparation method comprises the following steps: putting silicon carbide powder into a crucible of a vacuum furnace, heating under negative pressure, extruding melt from the bottom of the crucible, and putting extrudate on a graphite base plate when the temperature is 1300 DEG C; putting the graphite base plate into a sine wave electromagnetic field, keeping applying pressure to silicon carbide on the graphite base plate, and slowly reducing the temperature to normal temperature; magnetostriction material particles can be regularly stretched in a sine wave electromagnetic field, in the early stage of silicon carbide crystallization, crystals can be fused with small crystal grains under micro vibration, seed crystals with large crystal grain sizes appear, the silicon carbide crystals can grow upwards from the surface of the base disc and become larger, and the silicon carbide coating with large crystal grains on the surface is prepared.

Description

Technical Field

[0001] The invention relates to the preparation of crystals, in particular to a method for preparing a large-grain silicon carbide coating on the surface of a large-size graphite substrate. Background Art

[0002] The preparation of high-quality silicon crystals has extremely high requirements for equipment. The method of growing silicon crystals on silicon carbide coatings is a method for preparing high-quality silicon crystals. Silicon carbide coatings can conduct heat quickly, which is conducive to the rapid and stable growth of crystals. However, after repeated annealing and heat conduction, the silicon carbide coating will crack due to stress accumulation. Frequent replacement of silicon carbide substrates will affect the stability of silicon crystal performance and excessive production costs. In practice, it is found that the larger the grain size of silicon carbide crystals, the better the thermal conductivity of silicon carbide, and the cracking rate is low after multiple annealing. Therefore, large-grain silicon carbide coatings are the key to preparing high-quality silicon crystals with stable performance indicators. Summary of the invention

[0003] Aiming at the problem that the existing method of preparing silicon crystals with silicon carbide coatings is prone to cracking after annealing, resulting in a low number of uses, the present invention provides a method for preparing a large-grain silicon carbide coating on the surface of a large-size graphite substrate, the method comprising the following steps:

[0004] 1. Apply the release agent evenly on the surface of the graphite substrate, mix the silicon carbide seed powder and magnetostrictive material particles evenly, and then spread them evenly;

[0005] 2. Put the silicon carbide powder into the crucible of the vacuum furnace, heat it to 2800-3000℃ under negative pressure to melt the silicon carbide powder, apply pressure to the crucible to extrude the melt from the bottom of the crucible, and when the temperature drops to 1300℃, place the extrudate on the graphite substrate of step 1 and apply pressure to make it consistent with the shape of the graphite substrate;

[0006] 3. Place the graphite substrate in a sinusoidal electromagnetic field, keep the pressure on the silicon carbide on the graphite substrate, and slowly reduce the temperature to room temperature, so as to obtain a large-grain silicon carbide coating on the surface of the large-sized graphite substrate.

[0007] In the above method, for the convenience of uniform paving, the particle size of silicon carbide seed powder and magnetostrictive material particles is the same, both of which are 300-1000 mesh. The magnetostrictive amount of the magnetostrictive material is 600-1200ppm, and is selected from one of terbium dysprosium iron alloy, terbium iron alloy or nickel cobalt alloy.

[0008] The present invention applies a sinusoidal electromagnetic field to magnetostrictive material particles during the silicon carbide crystallization process. The magnetostrictive material particles will expand and contract regularly in the sinusoidal electromagnetic field, causing micro-vibration to the surrounding materials. In the early stage of silicon carbide crystallization, small crystal grains will fuse under the micro-vibration of the magnetostrictive material particles, thereby producing crystal seeds with larger grain sizes. On the basis of the larger crystal seeds, the silicon carbide crystals will grow larger from the surface of the base plate upwards, and a silicon carbide coating with large crystal grains on the surface is prepared. The present invention directly performs silicon carbide crystallization on the surface of a large-sized graphite base plate, and can be used to prepare silicon crystals after disordered subsequent processing after crystallization. The process steps are simple. The method of the present invention is suitable for preparing a large-grain silicon carbide coating on a large-sized graphite base plate with a diameter of 3 to 15 cm in the silicon carbide coating area. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a physical picture of the large-grain silicon carbide coating obtained in Example 1.

[0010] Figure 2 This is a 500-fold magnified image of the surface of the large-grain silicon carbide coating obtained in Example 1.

[0011] Figure 3 for Figure 2 SEM image at point A in the middle.

[0012] Figure 4 for Figure 2 SEM image at point B in the middle.

[0013] Figure 5 for Figure 2 SEM image of the cross section at point A.

[0014] Figure 6 for Figure 2 SEM image of the cross section at point B.

[0015] Figure 7 for Figure 2 SEM image of the cross section at point C.

[0016] Figure 8 This is a 500-fold magnified image of the large-grained silicon carbide coating obtained in Example 1 after being used 50 times. DETAILED DESCRIPTION

[0017] The present invention is described below in conjunction with embodiments. The embodiments are only used to explain the present invention and are not used to limit the scope of the present invention.

[0018] Example 1

[0019] A method for preparing a large-grain silicon carbide coating on a large-size graphite substrate surface comprises the following steps:

[0020] 1. Evenly apply a release agent on the surface of a graphite substrate with a diameter of 10 cm, mix the silicon carbide seed powder with a particle size of 1000 mesh and the terbium dysprosium iron magnetostrictive material particles with a magnetostriction of 1200 ppm in a weight ratio of 1:1, and evenly spread them on the surface of a large-sized graphite substrate with a thickness of 0.3 mm;

[0021] 2. Put the silicon carbide powder into the crucible of the vacuum furnace, heat it to 3000°C at 10Pa to melt the silicon carbide powder, apply pressure to the crucible, open the discharge port at the bottom of the crucible, extrude the melt from the bottom of the crucible, detect the temperature of the extrudate, and when the temperature drops to 1300°C, slowly transfer the extrudate to the graphite substrate in step 1, and apply pressure to make it consistent with the shape of the graphite substrate;

[0022] 3. Place the graphite substrate in a sinusoidal electromagnetic field, keep the pressure on the silicon carbide on the graphite substrate at 50MPa, and slowly cool it down to room temperature at 10℃ / min to obtain a batch of large-grained silicon carbide coatings. The obtained large-grained silicon carbide coatings are shown in the figure below. Figure 1 As shown, the surface crystal structure after 500 times magnification is as follows Figure 2 shown. Figure 3 and Figure 4 They are Figure 2 From the SEM images at points A and B in the figure, it can be seen that the size of the large grains on the surface of the large-grained silicon carbide coating obtained in Example 1 is between 1 and 3 microns, and the grain surface is round and tightly packed. Figure 5 to Figure 7 They are Figure 2 The SEM images of the cross sections at points A, B and C in the middle show that there is an obvious interface between the large-grained silicon carbide coating obtained in Example 1 and the underlying silicon carbide seeds and the mixture of terbium, dysprosium and iron. The interface between the two is tightly bonded. The large-grained silicon carbide coating has a uniform thickness, an average thickness of 90 microns, a fluctuation of 2 microns, and a high flatness.

[0023] The present invention prepares a large-grained silicon carbide coating on the surface of a large-size graphite substrate to prepare high-quality silicon crystals. After the silicon crystals stably grow to a required height on the clean and flat silicon carbide coating, they are demolded. After the demolded silicon carbide coating is cleaned, it can be used for the next silicon crystal preparation. During each silicon crystal preparation process, the silicon carbide coating will be worn after being heated at high temperature and then cooled, and its service life is usually 10 to 30 times. Figure 8 This is a 500-fold magnified image of the large-grained silicon carbide coating obtained in Example 1 after being used 50 times. It can be seen that after being used 50 times, the surface of the coating has obvious wear and tear, and the large grains have also split, but the overall large-grain morphology is still regular.

[0024] Example 2

[0025] A method for preparing a large-grain silicon carbide coating on a large-size graphite substrate surface comprises the following steps:

[0026] 1. Evenly apply a release agent on the surface of a graphite substrate with a diameter of 15 cm, mix the silicon carbide seed powder with a particle size of 500 mesh and the terbium iron magnetostrictive material particles with a magnetostrictive amount of 600 ppm in a weight ratio of 1:2, and evenly spread them on the surface of the large-sized graphite substrate with a thickness of 0.5 mm;

[0027] 2. Put the silicon carbide powder into the crucible of the vacuum furnace, heat it to 2800°C at 10Pa to melt the silicon carbide powder, apply pressure to the crucible, open the discharge port at the bottom of the crucible, extrude the melt from the bottom of the crucible, detect the temperature of the extrudate, and when the temperature drops to 1300°C, slowly transfer the extrudate to the graphite substrate in step 1, and apply pressure to make it consistent with the shape of the graphite substrate;

[0028] 3. Place the graphite substrate in a sinusoidal electromagnetic field, keep the pressure on the silicon carbide on the graphite substrate at 10MPa, and slowly cool it down to room temperature at 15℃ / min, so as to obtain a large-grained silicon carbide coating on the surface of the large-sized graphite substrate.

[0029] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a large-grained silicon carbide coating on a large-size graphite substrate surface, characterized in that: The following steps are involved:

1. Apply the release agent evenly on the surface of the graphite substrate, mix the silicon carbide seed powder and magnetostrictive material particles evenly, and then spread them evenly; 2. Put the silicon carbide powder into the crucible of the vacuum furnace, heat it to 2800-3000℃ under negative pressure to melt the silicon carbide powder, apply pressure to the crucible to extrude the melt from the bottom of the crucible, and when the temperature drops to 1300℃, place the extrudate on the graphite substrate of step 1 and apply pressure to make it consistent with the shape of the graphite substrate; 3. Place the graphite substrate in a sinusoidal electromagnetic field, keep the pressure on the silicon carbide on the graphite substrate, and slowly reduce the temperature to room temperature, so as to obtain a large-grain silicon carbide coating on the surface of the large-sized graphite substrate.

2. The preparation method according to claim 1, characterized in that: The diameter of the large-size graphite base disc is 3 to 15 cm.

3. The preparation method according to claim 1, characterized in that: The silicon carbide seed powder and magnetostrictive material particles are the same, with a size of 300-1000 meshes.

4. The preparation method according to claim 1, characterized in that: The magnetostrictive material has a magnetostriction of 600-1200 ppm and is selected from terbium-dysprosium-iron alloy, terbium-iron alloy or nickel-cobalt alloy.

5. The preparation method according to claim 1, characterized in that: In step 3, the pressure applied to silicon carbide is 10 to 50 MPa.

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