A silicon nitride coating for a fused quartz crucible with high bonding strength and a preparation method thereof

Abstract

The present invention discloses a silicon nitride coating for a quartz crucible with high bonding strength and a preparation method thereof, which solves the problems of insufficient coating bonding strength and complex process in the prior art. The method comprises the following steps: preparing slurry A by grinding and vacuum degassing a mixture of graphite powder, silica powder and ethanol; preparing slurry B by grinding and vacuum degassing a mixture of single crystal silicon powder, silicon nitride powder and ethanol; spraying the slurry A onto the surface of an unfired quartz crucible and drying; performing high-temperature calcination in a nitrogen atmosphere to generate a silicon nitride bonding layer through a carbothermal reduction reaction; spraying the slurry B onto the surface of the bonding layer and drying; performing high-temperature sintering in an inert atmosphere to generate a silicon nitride epitaxial layer. The dense bonding layer generated by the carbothermal reduction reaction in the present invention significantly improves the bonding strength between the coating and the quartz crucible, effectively reduces the high-temperature deformation rate, and prolongs the service life of the crucible.

Description

Technical Field

[0001] The present invention relates to the technical field of coating preparation, and particularly relates to a silicon nitride coating for a quartz crucible with high bonding strength and a preparation method thereof. Background Art

[0002] Monocrystalline silicon is the main raw material for producing large-scale integrated circuits and solar cells. During the pulling process, a quartz crucible is required as a container for silicon material. However, due to the easy crystallization of quartz at high temperatures, deformation occurs during the production process, resulting in the failure of crystal pulling, and even serious production accidents such as silicon leakage, which seriously affects the product yield and production capacity, and greatly increases the production cost. Therefore, how to improve the mechanical strength of the quartz crucible, reduce the deformation of the quartz crucible during high-temperature crystal pulling, and thus extend its service life is particularly important for improving the crystal pulling quality and reducing the crystal pulling cost. To solve the above problems, the prior art mainly improves its performance by preparing a coating on the surface of the quartz crucible.

[0003] In the prior art, the silicon nitride coating for the quartz crucible is generally prepared by directly coating silicon nitride slurry or silicon nitride slurry mixed with a binder on the surface of the quartz crucible, and then obtaining the silicon nitride coating by means of high-temperature sintering, such as patents CN201210375860.4 and CN201010271031.2. Although this method has a simple process, the coating prepared by this method is prone to peeling due to insufficient bonding strength between the coating and the quartz crucible. Relatively, the silicon nitride coating with a multi-layer structure shows better mechanical properties and bonding strength. In patent CN201811589756.9, barium acetate, modified sodium silicate, silicon carbide, and silicon nitride are mixed to form an inner coating. However, since the modified sodium silicate needs to be processed in a high-pressure reaction kettle, this method has a high cost. Patent CN202311250827.3 adopts a more complex three-layer structure, in which an organic additive is introduced into the intermediate layer to improve the performance, but the process is complex and the preparation time is long. Patent CN202310507145.X prepares a silicon carbide inner coating and a silicon nitride outer coating on the four sides and the bottom surface of the quartz crucible through a thermal reaction. However, the formation process of silicon carbide is not easy to control. If the conversion is insufficient, carbon impurities will remain, which will affect the crystal pulling quality.

[0004] The above technologies are either limited by insufficient coating bonding strength, or have problems such as complex processes, high costs, and impurity residues, and it is difficult to meet the requirements of industrial production. Therefore, there is an urgent need to develop a preparation method for a silicon nitride coating with a simple process, controllable cost, and high bonding strength to improve the high-temperature stability and service life of the quartz crucible, and at the same time avoid the influence of impurity introduction on the crystal pulling quality. Summary of the Invention

[0005] The object of the present invention is to provide a silicon nitride coating for a quartz crucible with high bonding strength and a preparation method thereof, so as to solve the technical problems of insufficient bonding strength of the existing coating and complex process.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] In the first aspect, the present invention provides a silicon nitride coating for a quartz crucible with high bonding strength and a preparation method thereof, which specifically includes the following steps:

[0008] S1. Prepare spraying slurry A and slurry B: Mix graphite powder, silica powder and ethanol, grind them in a ball mill and perform vacuum degassing to make slurry A; Mix monocrystalline silicon powder, silicon nitride powder and ethanol, grind them in a ball mill and perform vacuum degassing to make slurry B;

[0009] S2. Spray slurry A: Spray the prepared slurry A onto the surface of the unburned quartz crucible to form precursor A, and the spraying thickness is 10-50 μm;

[0010] S3. First firing: First dry precursor A at a temperature of 80-100 °C for 1-2 h to remove ethanol, and then perform high-temperature calcination in a nitrogen atmosphere to generate a dense silicon nitride bonding layer through carbothermal reduction reaction;

[0011] S4. Spray slurry B: Spray the prepared slurry B onto the surface of the silicon nitride bonding layer to form precursor B, and the spraying thickness is 100-250 μm;

[0012] S5. Second firing: Dry precursor B at a temperature of 100-150 °C for 2 h to remove ethanol, and then perform high-temperature sintering in a nitrogen atmosphere to generate a silicon nitride epitaxial layer.

[0013] Further, in step S1, the particle size of the graphite powder is 0.01-3 μm, and the particle size of the silica powder is 0.01-3 μm.

[0014] Further, the weight ratio of the graphite powder, silica powder and ethanol is 1-1.5:5-10:20-35.

[0015] Further, in step S1, the particle size of the monocrystalline silicon powder is 0.01-3 μm, and the particle size of the silicon nitride powder is 1-5 μm.

[0016] Further, the weight ratio of the monocrystalline silicon powder, silicon nitride powder and ethanol is 5-10:30-48:50-70.

[0017] Further, in step S1, the ball mill is a planetary ball mill. During the grinding process, the planetary ball mill rotates forward at 400 rpm for 20 min, rotates backward at 450 rpm for 15 min, stops rotating at 300 rpm for 3 min, rotates forward at 500 rpm for 20 min, rotates backward at 400 rpm for 20 min, and rotates forward at 420 rpm for 20 min.

[0018] Further, in step S3, the temperature of the high-temperature calcination is 1300 °C to 1500 °C, and the calcination time is 3 to 6 h.

[0019] Further, in step S5, the temperature of the high-temperature sintering is 1200 °C to 1500 °C, and the sintering time is 3 to 6 h.

[0020] In a second aspect, the present invention provides a silicon nitride coating for a fused quartz crucible with high bonding strength, which is prepared by the above method.

[0021] Based on the above technical solutions, the embodiments of the present invention can at least produce the following technical effects:

[0022] The present invention provides a silicon nitride coating for a fused quartz crucible with high bonding strength and a preparation method thereof. By spraying the bonding layer and the epitaxial layer step by step and optimizing the carbothermal reduction reaction process, the comprehensive performance of the coating is significantly improved. The preparation method of the silicon nitride coating composed of the bonding layer and the epitaxial layer is simple and has low production cost. The bonding layer formed by the carbothermal reduction reaction has a dense structure and good thermal stability. Its high bonding strength benefits from the strong chemical bonding between the dense silicon nitride bonding layer and the fused quartz crucible substrate, effectively reducing the risk of coating peeling off, and can effectively improve the bonding strength between the fused quartz crucible and the silicon nitride coating; the double-layer structure provides stable mechanical support, greatly reducing the deformation of the fused quartz crucible during the high-temperature crystal pulling process and extending the service life; the coating defects are reduced by the vacuum degassing and precise grinding processes, avoiding the negative impact of impurity residues on the crystal pulling quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0024] Figure 1 It is a process flow chart for preparing the silicon nitride coating of the fused quartz crucible of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions conflicts with each other or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention. Embodiment 1:

[0026] S1. Prepare spraying slurry A and slurry B: After mixing graphite powder with a particle size of 2 μm, silicon dioxide powder with a particle size of 2 μm, and ethanol in a weight ratio of 1:8:25, grind them in a ball mill and perform vacuum degassing to obtain slurry A;

[0027] After mixing monocrystalline silicon powder with a particle size of 2 μm, silicon nitride powder with a particle size of 3 μm, and ethanol in a weight ratio of 8:40:60, grind them in a ball mill and perform vacuum degassing to obtain slurry B; reduce the gas content in the slurry and reduce the oxidation phenomenon of the slurry;

[0028] During the grinding process, the planetary ball mill runs forward at 400 rpm for 20 min, runs in reverse at 450 rpm for 15 min, stops at 300 rpm for 3 min, runs forward at 500 rpm for 20 min, runs in reverse at 400 rpm for 20 min, and runs forward at 420 rpm for 20 min;

[0029] S2. Spray slurry A: Spray the prepared slurry A onto the surface of the unburned quartz crucible to form precursor A, and the spraying thickness is 30 μm;

[0030] S3. First firing: First, place the quartz crucible in an oven and dry precursor A at a temperature of 90 °C for 1 h to remove ethanol, avoiding the rapid evaporation of ethanol during high-temperature calcination, which may cause the coating to bubble; then place the quartz crucible in a muffle furnace and perform high-temperature calcination in a nitrogen atmosphere. The temperature of the high-temperature calcination is 1400 °C, and the time is 4 h. A dense silicon nitride bonding layer is formed through a carbothermal reduction reaction;

[0031] S4. Spray slurry B: Spray the prepared slurry B onto the surface of the silicon nitride bonding layer to form precursor B, and the spraying thickness is 150 μm;

[0032] S5. Second firing: Place the quartz crucible in an oven and dry the precursor B at 120 °C for 2 h to remove ethanol, avoiding bubbling of the coating caused by rapid evaporation of ethanol during high-temperature calcination. Then place the quartz crucible in a muffle furnace and perform high-temperature sintering in a nitrogen atmosphere to generate a silicon nitride epitaxial layer. The temperature of the high-temperature sintering is 1400 °C and the time is 5 h. Example 2:

[0033] S1. Prepare spraying slurry A and slurry B: Mix graphite powder with a particle size of 0.01 μm, silica powder with a particle size of 3 μm, and ethanol in a weight ratio of 1:5:20, grind in a ball mill, and perform vacuum degassing to make slurry A;

[0034] Mix monocrystalline silicon powder with a particle size of 0.01 μm, silicon nitride powder with a particle size of 5 μm, and ethanol in a weight ratio of 5:30:50, grind in a ball mill, and perform vacuum degassing to make slurry B; Reduce the gas content in the slurry to reduce the oxidation phenomenon of the slurry;

[0035] During the grinding process, the planetary ball mill runs forward at 400 rpm for 20 min, runs backward at 450 rpm for 15 min, stops at 300 rpm for 3 min, runs forward at 500 rpm for 20 min, runs backward at 400 rpm for 20 min, and runs forward at 420 rpm for 20 min;

[0036] S2. Spray slurry A: Spray the prepared slurry A onto the surface of the un-fired quartz crucible to form precursor A, and the spraying thickness is 10 μm;

[0037] S3. First firing: First place the quartz crucible in an oven and dry the precursor A at 80 °C for 2 h to remove ethanol, avoiding bubbling of the coating caused by rapid evaporation of ethanol during high-temperature calcination. Then place the quartz crucible in a muffle furnace and perform high-temperature calcination in a nitrogen atmosphere. The temperature of the high-temperature calcination is 1300 °C and the time is 6 h. A dense silicon nitride bonding layer is formed through carbothermal reduction reaction;

[0038] S4. Spray slurry B: Spray the prepared slurry B onto the surface of the silicon nitride bonding layer to form precursor B, and the spraying thickness is 100 μm;

[0039] S5. Second firing: Place the quartz crucible in an oven and dry the precursor B at 100 °C for 2 h to remove ethanol, avoiding bubbling of the coating caused by rapid evaporation of ethanol during high-temperature calcination. Then place the quartz crucible in a muffle furnace and perform high-temperature sintering in a nitrogen atmosphere to generate a silicon nitride epitaxial layer. The temperature of the high-temperature sintering is 1200 °C and the time is 6 h. Example 3:

[0040] S1. Prepare spraying slurry A and slurry B: Mix graphite powder with a particle size of 3 μm, silica powder with a particle size of 0.01 μm, and ethanol in a weight ratio of 1.5:10:35, then grind them in a ball mill and degas under vacuum to make slurry A;

[0041] Mix single crystal silicon powder with a particle size of 3 μm, silicon nitride powder with a particle size of 1 μm, and ethanol in a weight ratio of 10:48:70, then grind them in a ball mill and degas under vacuum to make slurry B; Reduce the gas content in the slurry to reduce the oxidation phenomenon of the slurry;

[0042] During the grinding process, the planetary ball mill runs forward at 400 rpm for 20 min, runs backward at 450 rpm for 15 min, stops at 300 rpm for 3 min, runs forward at 500 rpm for 20 min, runs backward at 400 rpm for 20 min, and runs forward at 420 rpm for 20 min;

[0043] S2. Spray slurry A: Spray the prepared slurry A onto the surface of the unburned quartz crucible to form precursor A, and the spraying thickness is 50 μm;

[0044] S3. First firing: First, place the quartz crucible in an oven and dry precursor A at a temperature of 100 °C for 1 h to remove ethanol, avoiding the rapid evaporation of ethanol during high-temperature calcination, which may cause the coating to bubble; Then place the quartz crucible in a muffle furnace and perform high-temperature calcination in a nitrogen atmosphere. The temperature of the high-temperature calcination is 1500 °C, and the time is 3 h. A dense silicon nitride bonding layer is formed through carbothermal reduction reaction;

[0045] S4. Spray slurry B: Spray the prepared slurry B onto the surface of the silicon nitride bonding layer to form precursor B, and the spraying thickness is 250 μm;

[0046] S5. Second firing: Place the quartz crucible in an oven and dry precursor B at a temperature of 150 °C for 2 h to remove ethanol, avoiding the rapid evaporation of ethanol during high-temperature calcination, which may cause the coating to bubble; Then place the quartz crucible in a muffle furnace and perform high-temperature sintering in a nitrogen atmosphere to generate a silicon nitride epitaxial layer. The temperature of the high-temperature sintering is 1500 °C, and the time is 3 h.

[0047] Comparative Example 1 (Using a single coating to verify the necessity of the layered structure for the bonding strength)

[0048] S1. Prepare slurry: Mix single crystal silicon powder with a particle size of 2 μm, silicon nitride powder with a particle size of 3 μm, and ethanol in a weight ratio of 8:40:60, then grind them in a ball mill and degas under vacuum to make slurry; Reduce the gas content in the slurry to reduce the oxidation phenomenon of the slurry;

[0049] During the grinding process, the planetary ball mill runs forward at 400 rpm for 20 min, runs backward at 450 rpm for 15 min, stops at 300 rpm for 3 min, runs forward at 500 rpm for 20 min, runs backward at 400 rpm for 20 min, and runs forward at 420 rpm for 20 min;

[0050] S2. Spraying the slurry: Spray the prepared slurry onto the surface of the silicon nitride bonding layer to form a precursor, with a spraying thickness of 150 μm;

[0051] S3. Firing: Place the quartz crucible in an oven and dry the precursor at 120 °C for 2 h to remove ethanol, avoiding the rapid evaporation of ethanol during high-temperature calcination, which may cause the coating to bubble; then place the quartz crucible in a muffle furnace and perform high-temperature sintering in a nitrogen atmosphere to generate a silicon nitride epitaxial layer. The temperature of the high-temperature sintering is 1400 °C and the time is 5 h.

[0052] Comparative Example 2 (The first firing is carried out at a low temperature to verify the temperature dependence of the reaction)

[0053] S1. Preparing spraying slurry A and slurry B: Mix graphite powder with a particle size of 2 μm, silicon dioxide powder with a particle size of 2 μm, and ethanol in a weight ratio of 1:8:25, then grind and degas under vacuum in a ball mill to make slurry A;

[0054] Mix monocrystalline silicon powder with a particle size of 2 μm, silicon nitride powder with a particle size of 3 μm, and ethanol in a weight ratio of 8:40:60, then grind and degas under vacuum in a ball mill to make slurry B; reduce the gas content in the slurry to reduce the oxidation phenomenon of the slurry;

[0055] During the grinding process, the planetary ball mill runs forward at 400 rpm for 20 min, runs backward at 450 rpm for 15 min, stops at 300 rpm for 3 min, runs forward at 500 rpm for 20 min, runs backward at 400 rpm for 20 min, and runs forward at 420 rpm for 20 min;

[0056] S2. Spraying slurry A: Spray the prepared slurry A onto the surface of the unfired quartz crucible to form precursor A, with a spraying thickness of 30 μm;

[0057] S3. The first firing: First, place the quartz crucible in an oven and dry precursor A at 90 °C for 1 h to remove ethanol, avoiding the rapid evaporation of ethanol during high-temperature calcination, which may cause the coating to bubble; then place the quartz crucible in a muffle furnace and perform high-temperature calcination in a nitrogen atmosphere. The temperature of the high-temperature calcination is 1100 °C and the time is 4 h. A dense silicon nitride bonding layer is formed through carbothermal reduction reaction;

[0058] S4. Spraying Slurry B: Spray the prepared Slurry B onto the surface of the silicon nitride bonding layer to form Precursor B, with a spraying thickness of 150 μm;

[0059] S5. Second Firing: Place the quartz crucible in an oven and dry Precursor B at a temperature of 120 °C for 2 h to remove ethanol, avoiding the formation of coating bubbles caused by the rapid evaporation of ethanol during high-temperature calcination; then place the quartz crucible in a muffle furnace and perform high-temperature sintering in a nitrogen atmosphere to generate a silicon nitride epitaxial layer. The temperature of the high-temperature sintering is 1400 °C and the time is 5 h.

[0060] Comparative Example 3 (omitting vacuum degassing)

[0061] S1. Preparing Spraying Slurry A and Slurry B: Mix graphite powder with a particle size of 2 μm, silica powder with a particle size of 2 μm, and ethanol in a weight ratio of 1:8:25 to form Slurry A;

[0062] Mix monocrystalline silicon powder with a particle size of 2 μm, silicon nitride powder with a particle size of 3 μm, and ethanol in a weight ratio of 8:40:60 to form Slurry B; reduce the gas content in the slurry and minimize the oxidation of the slurry;

[0063] During the grinding process, the planetary ball mill runs forward at 400 rpm for 20 min, runs backward at 450 rpm for 15 min, stops at 300 rpm for 3 min, runs forward at 500 rpm for 20 min, runs backward at 400 rpm for 20 min, and runs forward at 420 rpm for 20 min;

[0064] S2. Spraying Slurry A: Spray the prepared Slurry A onto the surface of the unfired quartz crucible to form Precursor A, with a spraying thickness of 30 μm;

[0065] S3. First Firing: First, place the quartz crucible in an oven and dry Precursor A at a temperature of 90 °C for 1 h to remove ethanol, avoiding the formation of coating bubbles caused by the rapid evaporation of ethanol during high-temperature calcination; then place the quartz crucible in a muffle furnace and perform high-temperature calcination in a nitrogen atmosphere. The temperature of the high-temperature calcination is 1400 °C and the time is 4 h, and a dense silicon nitride bonding layer is formed through carbothermal reduction reaction;

[0066] S4. Spraying Slurry B: Spray the prepared Slurry B onto the surface of the silicon nitride bonding layer to form Precursor B, with a spraying thickness of 150 μm;

[0067] S5, Second firing: Place the quartz crucible in an oven and dry the precursor B at 120°C for 2 h to remove ethanol, avoiding the formation of coating bubbles caused by the rapid evaporation of ethanol during high-temperature calcination. Then place the quartz crucible in a muffle furnace and perform high-temperature sintering in a nitrogen atmosphere to generate a silicon nitride epitaxial layer. The temperature of the high-temperature sintering is 1400°C and the time is 5 h.

[0068] Experiment: Take the coated quartz crucibles prepared in Examples 1-3 and Comparative Examples 1-3 for testing. The test results are shown in the following table:

[0069]

[0070] Conclusion: From Comparative Example 1, it can be seen that the bonding strength of the single coating is significantly reduced, and the high-temperature deformation rate is as high as 5.2%. It is proved that the dense structure formed by the carbothermal reduction reaction in the bonding layer is the key to improving the performance. From Comparative Example 2, it can be seen that the incomplete carbothermal reduction reaction caused by low-temperature firing results in a decrease in the bonding strength to 58.7 MPa, but it is better than the single coating, indicating that the temperature needs to be strictly controlled above 1300°C. From Comparative Example 3, it can be seen that the porosity of the non-degassed coating is as high as 6.7%, and the bonding strength is reduced to 63.4 MPa, indicating that degassing can effectively reduce bubble defects and improve the coating uniformity.

[0071] The above shows and describes 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 by the above embodiments. The above embodiments and the descriptions in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a quartz crucible silicon nitride coating with high bonding strength, characterized in that: The specific steps include: S1. Preparation of spray slurry A and slurry B: Graphite powder, silicon dioxide powder and ethanol are mixed, ground in a ball mill and vacuum degassed to prepare slurry A; single crystal silicon powder, silicon nitride powder and ethanol are mixed, ground in a ball mill and vacuum degassed to prepare slurry B; S2, spraying slurry A: spraying the prepared slurry A onto the surface of an unfired quartz crucible to form a precursor A, with a spraying thickness of 10 to 50 μm; S3, first firing: first drying the precursor A at a temperature of 80-100°C for 1-2h to remove ethanol, and then calcining it at high temperature in a nitrogen atmosphere to form a dense silicon nitride bonding layer through a carbon thermal reduction reaction; S4, spraying slurry B: spraying the prepared slurry B onto the surface of the silicon nitride bonding layer to form a precursor B, with a spraying thickness of 100 to 250 μm; S5. Second firing: Dry the precursor B at 100-150° C. for 2 h to remove ethanol, and then perform high-temperature sintering in a nitrogen atmosphere to form a silicon nitride epitaxial layer.

2. The method for preparing a quartz crucible silicon nitride coating with high bonding strength according to claim 1, characterized in that: In step S1, the graphite powder has a particle size of 0.01 to 3 μm, and the silicon dioxide powder has a particle size of 0.01 to 3 μm.

3. The method for preparing a quartz crucible silicon nitride coating with high bonding strength according to claim 2, characterized in that: The weight ratio of the graphite powder, the silicon dioxide powder and the ethanol is 1-1.5:5-10:20-35.

4. The method for preparing a quartz crucible silicon nitride coating with high bonding strength according to claim 1, characterized in that: In step S1, the particle size of the single crystal silicon powder is 0.01 to 3 μm, and the particle size of the silicon nitride powder is 1 to 5 μm.

5. The method for preparing a quartz crucible silicon nitride coating with high bonding strength according to claim 4, characterized in that: The weight ratio of the single crystal silicon powder, silicon nitride powder and ethanol is 5-10:30-48:50-70.

6. The method for preparing a quartz crucible silicon nitride coating with high bonding strength according to claim 1, characterized in that: In step S1, the ball mill is a planetary ball mill. During the grinding process, the planetary ball mill runs forward at 400 rpm for 20 min, reverses at 450 rpm for 15 min, stops at 300 rpm for 3 min, runs forward at 500 rpm for 20 min, reverses at 400 rpm for 20 min, and runs forward at 420 rpm for 20 min.

7. The method for preparing a quartz crucible silicon nitride coating with high bonding strength according to claim 1, characterized in that: In step S3, the high temperature calcination temperature is 1300° C. to 1500° C., and the calcination time is 3 to 6 hours.

8. The method for preparing a quartz crucible silicon nitride coating with high bonding strength according to claim 1, characterized in that: In step S5, the high temperature sintering temperature is 1200° C. to 1500° C., and the sintering time is 3 to 6 hours.

9. A silicon nitride coating for a quartz crucible prepared according to the method of any one of claims 1 to 8.

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