Square graphite crucible and preparation method thereof

Abstract

The invention relates to the technical field of graphite materials, and provides a square graphite crucible and a preparation method thereof. The square graphite crucible is prepared from, by mass, 65-75 parts of graphitized coke and 25-35 parts of asphalt, and the graphitized coke is silicon resin composite graphitized coke and / or heat treatment graphitized coke. According to the technical scheme, the problem of insufficient strength of the graphite crucible in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of graphite materials, and specifically, to a square graphite crucible and a preparation method thereof. Background Art

[0002] Graphite has excellent properties such as high temperature resistance, electrical conductivity, thermal conductivity, plasticity, and corrosion resistance, and is widely used in industry, mainly for manufacturing electrodes, graphite furnaces, graphite crucibles, pencil leads, etc.

[0003] A graphite crucible, also known as a copper melting ladle or copper melting pot, is mainly formed and fired with graphite. It is a container used to melt metals and turn them from solid to liquid, suitable for small-scale metal casting. According to the use requirements, the surface of the graphite crucible must be smooth, without defects such as cracks and interlayers. At the same time, it should have high mechanical strength, good thermal conductivity, be able to withstand high temperatures, and have good resistance to flux erosion during the high-temperature process to ensure the quality of the melted metal. In addition, the graphite crucible is also required to have good resistance to sudden temperature changes at high heat and not be easily burst and damaged.

[0004] Currently, graphitized coke and asphalt are often used as raw materials to produce graphite crucibles. However, the particle size distribution of graphitized coke is relatively complex, and graphitized coke has many capillary pores and good capillary permeability, which easily leads to uneven mixing of graphitized coke particles and asphalt, and ultimately results in uneven internal structure of the crucible. During subsequent roasting and use, problems such as insufficient local strength are likely to occur, reducing the overall performance and service life of the crucible. Summary of the Invention

[0005] The present invention provides a square graphite crucible and a preparation method thereof, which solve the problem of insufficient strength of graphite crucibles in related technologies.

[0006] The technical solution of the present invention is as follows: A square graphite crucible, the raw materials of which include the following components in parts by mass: 65 - 75 parts of graphitized coke and 25 - 35 parts of asphalt, and the graphitized coke is silicone resin composite graphitized coke and / or heat-treated graphitized coke.

[0007] As a further technical solution, the graphitized coke is composed of silicone resin composite graphitized coke and heat-treated graphitized coke in a mass ratio of 1 - 9:1.

[0008] In the present invention, the graphitized coke can be one or both of silicone resin composite graphitized coke and heat-treated graphitized coke, preferably silicone resin composite graphitized coke and heat-treated graphitized coke. The mass ratio of the silicone resin composite graphitized coke to the heat-treated graphitized coke can be arbitrarily selected. Preferably, the mass ratio of the silicone resin composite graphitized coke to the heat-treated graphitized coke is 1-9:1. For example, it can be 1:1, 1.2:1, 1.5:1, 1.7:1, 2:1, 2.5:1, 3:1, 4:1, 4.5:1, 4.7:1, 5:1, 6.5:1, 7:1, 8:1, 8.5:1, 9:1, etc.

[0009] As a further technical solution, the particle size of the graphitized coke in the silicone resin composite graphitized coke: 0 mm < particle size ≤ 2 mm.

[0010] In the present invention, the particle size of the graphitized coke in the silicone resin composite graphitized coke can be selected from any conventional particle size in the art. Preferably, 0 mm < particle size ≤ 2 mm. The graphitized coke with a smaller particle size can fill the gaps between the coarse grains and form an efficient bonding system with the pitch. Its high specific surface area significantly enhances the physical adsorption with the pitch and forms a uniform coating layer during the kneading process, improving the forming density of the green body. In addition, the graphitized coke with a smaller particle size helps to inhibit the abnormal growth of grains during the graphitization process and optimize the crystal orientation of the final product, thus ensuring the oxidation resistance and service life of the crucible.

[0011] In the present invention, the raw materials of the silicone resin composite graphitized coke include silane, initiator, and graphitized coke with a mass ratio of 20-30:4.5-6:90. For example, the mass ratio can be 20:4.5:90, 20:5:90, 20:5.5:90, 20:6:90, 25:4.5:90, 25:5:90, 25:5.5:90, 25:6:90, 30:4.5:90, 30:4.7:90, 30:5:90, 30:6:90, etc. Preferably, it is 20:4.5:90.

[0012] In the present invention, the silane can be any one or more conventional silanes in the art, preferably 3-(methacryloyloxy)propyltrimethoxysilane, and the initiator can be any one or more conventional initiators in the art, preferably 2,2-azobisisobutyronitrile.

[0013] As a further technical solution, the preparation method of the silicone resin composite graphitized coke includes the following steps: After mixing the graphitized coke and water, heat it to 80-85 °C while stirring, add silane and initiator and continue mixing. After the reaction ends, cool, filter, wash, and dry to obtain the silicone resin composite graphitized coke.

[0014] As a further technical solution, the stirring is carried out under a nitrogen atmosphere.

[0015] As a further technical solution, the washing is specifically: methanol washing.

[0016] In the present invention, a chemical grafting modification technology is adopted to prepare a silicone resin composite graphitized coke, realizing the interfacial functionalization of the graphitized coke material. First, the graphitized coke and water are mixed and stirred under nitrogen protection to form a stable water suspension system. After heating to 80 - 85 °C, silane and an initiator are added for an in-situ grafting reaction. During the reaction, the silane molecules hydrolyze to generate reactive silanol groups, which form Si - O - C covalent bonds with the hydroxyl groups on the surface of the graphitized coke through a condensation reaction. At the same time, the initiator decomposes to generate free radicals to initiate the polymerization of the silicone resin prepolymer, forming a silicone resin grafting layer on the surface of the graphitized coke. After the reaction is completed, the product is separated by filtration, washed with methanol to remove unreacted monomers and by-products, and finally dried to obtain the silicone resin composite graphitized coke.

[0017] As a further technical solution, the particle size of the graphitized coke in the heat-treated graphitized coke: 2 mm < particle size ≤ 8 mm.

[0018] In the present invention, the particle size of the graphitized coke in the heat-treated graphitized coke can be selected from any conventional particle size in the art. Preferably, 2 mm < particle size ≤ 8 mm. The graphitized coke with a larger particle size can be used as the core skeleton material. By forming a multi-level particle support structure, it can significantly improve the mechanical strength and thermal shock resistance of the crucible. Its moderate particle size can not only ensure the formation of a stable pore network during the molding process of the green body but also enhance the structural integrity. In addition, the high thermal conductivity of the graphitized coke in this particle size range can ensure the rapid conduction of heat inside the crucible, effectively alleviating the problem of thermal stress concentration caused by high temperature gradients and reducing the risk of cracking during use.

[0019] In addition, in the present invention, the particle size of the graphitized coke in the silicone resin composite graphitized coke is defined as 0 mm < particle size ≤ 2 mm, and the particle size of the graphitized coke in the heat-treated graphitized coke is 2 mm < particle size ≤ 8 mm, further improving the strength of the graphite crucible. The reason is that: the graphitized coke with a larger particle size acts as the core skeleton and plays a supporting role. After heat treatment, it can increase the oxygen-containing groups, improve the surface activity, enhance the interaction between the graphitized coke and pitch, and between the graphitized coke and the graphitized coke, and improve the overall density during the molding process; the graphitized coke with a smaller particle size plays a filling role. It has a large specific surface area and high surface energy and is prone to agglomeration. After being compounded with the silicone resin, the agglomeration phenomenon can be eliminated, and it can be evenly dispersed in the system, thereby improving the strength of the graphite crucible.

[0020] As a further technical solution, the heat-treated graphitized coke is graphitized coke heat-treated in an environment containing oxygen molecules.

[0021] As a further technical solution, the preparation method of the heat-treated graphitized coke comprises the following steps: heat-treating graphitized coke in a mixed gas at 450-550 °C for 3-5 h to obtain heat-treated graphitized coke; the mixed gas is composed of oxygen and carbon dioxide.

[0022] As a further technical solution, the molar fraction of oxygen in the mixed gas is 50%, and the molar fraction of carbon dioxide is 50%.

[0023] In the present invention, a controlled atmosphere heat treatment technology is adopted to prepare heat-treated graphitized coke, which enhances the surface activity of the graphitized coke material. First, graphitized coke is heat-treated in a mixed gas of oxygen and carbon dioxide at 450-550 °C for 3-5 h. During the process, oxygen and carbon dioxide act synergistically to form oxygen-containing functional groups on the surface of the graphitized coke. At the same time, the presence of carbon dioxide can inhibit over-oxidation and maintain the structural integrity of the material.

[0024] The present invention also provides a preparation method of a square graphite crucible. To prepare the square graphite crucible, the following steps are included: kneading graphitized coke and pitch, forming, and roasting at 950-1200 °C for 25-30 days to obtain a square graphite crucible.

[0025] As a further technical solution, the temperature of the kneading is 135-155 °C, for example, it can be 135 °C, 140 °C, 145 °C, 148 °C, 150 °C, 152 °C, 155 °C, etc., and preferably 150 °C.

[0026] As a further technical solution, during the forming, the pressure is 10-15 MPa, for example, it can be 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa, 15 MPa, etc., and preferably 10 MPa and 15 MPa.

[0027] During the preparation of the square graphite crucible in the present invention, graphitized coke with different particle sizes can be premixed first. When premixing, the coarse-grained material is added first and then the fine-grained material. Because the particles are small and have good fluidity, they are easy to enter the gaps between large particles, so it is easy to mix evenly.

[0028] The kneading time in the present invention can be any conventional time in the field of preparing graphite crucibles, preferably 50-100 min, and more preferably 70 min. If the kneading time is too short, there will be uneven kneading, the phenomenon of dry material clamps, insufficient penetration of pitch into dry material, poor plasticity of the paste, resulting in poor product quality; if the kneading time is too long, the improvement of the kneading uniformity is very little. On the contrary, due to the long kneading time, large particle aggregates will be damaged, the particle size composition of the raw materials will be destroyed, the bulk density will be reduced, the volume density of the product will be low, the porosity will be high, and the strength will be reduced. In addition, when the kneading time is long, the degree of oxidation and condensation of pitch deepens, light fractions escape, and the plasticity of the paste becomes poor.

[0029] The working principle and beneficial effects of the present invention are as follows: 1. A square graphite crucible is provided in the present invention, and its raw materials include graphitized coke and pitch. By optimizing the dosages of the two, the strength of the product is ensured. When the dosage of pitch is small, the paste will become dry, and a complete pitch film cannot be formed on the surface of the graphitized coke, and the particles cannot be well bonded, resulting in poor plasticity of the paste. As the dosage of pitch increases, the fluidity of the paste becomes better, the uniformity is enhanced, and the plasticity becomes better. However, when the dosage of pitch is too much, the roasting rejection rate will increase, the porosity of the roasted product will increase, and deformation is likely to occur. Therefore, by controlling the dosages of graphitized coke and pitch within the ranges of 65 - 75 parts and 25 - 35 parts respectively, the quality of the product can be ensured.

[0030] 2. The graphitized coke in the present invention is silicone resin composite graphitized coke and / or heat-treated graphitized coke. After the graphitized coke is compounded with silicone resin, the interfacial compatibility between the graphitized coke and the pitch can be enhanced. The oxygen-containing functional groups in the heat-treated graphitized coke increase, increasing the affinity between the graphitized coke and the pitch, achieving the effect of improving the strength of the graphite crucible. Specific embodiments

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of the present invention.

[0032] In the following examples and comparative examples: The external dimensions of the square graphite crucible are: 520mm×580mm×1200mm; The pitch is medium-temperature coal pitch, meeting the requirements of No. 1 medium-temperature pitch in GB / T 2290 - 2012; The large-particle-size graphitized coke has a particle size of 2mm < particle size ≤ 8mm; The small-particle-size graphitized coke has a particle size of 0mm < particle size ≤ 2mm.

[0033] Example 1 S1. Treat 90 parts of large-particle-size graphitized coke in a mixed gas (the molar fraction of oxygen is 50% and the molar fraction of carbon dioxide is 50%) at 550°C for 3 hours to obtain heat-treated large-particle-size graphitized coke; S2. Treat 90 parts of small-particle-size graphitized coke in a mixed gas (the molar fraction of oxygen is 50% and the molar fraction of carbon dioxide is 50%) at 550°C for 3 hours to obtain heat-treated small-particle-size graphitized coke; S3. Mix 75 parts of graphitized coke (composed of heat-treated small-sized graphitized coke and heat-treated large-sized graphitized coke with a mass ratio of 9:1) and 25 parts of pitch at 150 °C for 70 min, then form them under 15 MPa and calcine at 1100 °C for 30 days to obtain a square graphite crucible.

[0034] Example 2 S1. Treat 90 parts of large-sized graphitized coke in a mixed gas (mole fraction of oxygen is 50%, mole fraction of carbon dioxide is 50%) at 450 °C for 5 h to obtain heat-treated large-sized graphitized coke; S2. Treat 90 parts of small-sized graphitized coke in a mixed gas (mole fraction of oxygen is 50%, mole fraction of carbon dioxide is 50%) at 450 °C for 5 h to obtain heat-treated small-sized graphitized coke; S3. Mix 65 parts of heat-treated graphitized coke (composed of heat-treated small-sized graphitized coke and heat-treated large-sized graphitized coke with a mass ratio of 9:1) and 35 parts of pitch at 150 °C for 70 min, then form them under 10 MPa and calcine at 950 °C for 30 days to obtain a square graphite crucible.

[0035] Example 3 S1. Mix 90 parts of small-sized graphitized coke with 3000 parts of water, under nitrogen protection, stir and heat up to 80 °C, add 20 parts of 3-(methacryloyloxy)propyltrimethoxysilane and 4.5 parts of 2,2-azobisisobutyronitrile, continue stirring for 4 h, cool to room temperature, filter, wash with methanol, and dry under reduced pressure to obtain silicone resin composite small-sized graphitized coke; S2. Mix 90 parts of large-sized graphitized coke with 3000 parts of water, under nitrogen protection, stir and heat up to 80 °C, add 20 parts of 3-(methacryloyloxy)propyltrimethoxysilane and 4.5 parts of 2,2-azobisisobutyronitrile, continue stirring for 4 h, cool to room temperature, filter, wash with methanol, and dry under reduced pressure to obtain silicone resin composite large-sized graphitized coke; S3. Mix 75 parts of silicone resin composite graphitized coke (composed of silicone resin composite small-sized graphitized coke and silicone resin composite large-sized graphitized coke with a mass ratio of 9:1) and 25 parts of pitch at 150 °C for 70 min, then form them under 15 MPa and calcine at 1100 °C for 30 days to obtain a square graphite crucible.

[0036] Example 4 S1. Treat 90 parts of small-sized graphitized coke in a mixed gas (mole fraction of oxygen is 50%, mole fraction of carbon dioxide is 50%) at 550 °C for 3 h to obtain heat-treated graphitized coke; S2. Mix 90 parts of large - particle - size graphitized coke with 3000 parts of water. Under nitrogen protection, while stirring, heat up to 80°C, add 20 parts of 3 - (methacryloyloxy) propyltrimethoxysilane and 4.5 parts of 2,2 - azobisisobutyronitrile, continue stirring for 4 h, cool to room temperature, filter, wash with methanol, and dry under reduced pressure to obtain silicone - resin - composite graphitized coke; S3. Knead 75 parts of the mixed graphitized coke (composed of heat - treated graphitized coke and silicone - resin - composite graphitized coke with a mass ratio of 9:1) and 25 parts of pitch at 150°C for 70 min, then mold at 15 MPa and bake at 1100°C for 30 days to obtain a square graphite crucible.

[0037] Example 5 S1. Treat 90 parts of large - particle - size graphitized coke in a mixed gas (mole fraction of oxygen is 50% and mole fraction of carbon dioxide is 50%) at 550°C for 3 h to obtain heat - treated graphitized coke; S2. Mix 90 parts of small - particle - size graphitized coke with 3000 parts of water. Under nitrogen protection, while stirring, heat up to 80°C, add 20 parts of 3 - (methacryloyloxy) propyltrimethoxysilane and 4.5 parts of 2,2 - azobisisobutyronitrile, continue stirring for 4 h, cool to room temperature, filter, wash with methanol, and dry under reduced pressure to obtain silicone - resin - composite graphitized coke; S3. Knead 75 parts of the mixed graphitized coke (composed of silicone - resin - composite graphitized coke and heat - treated graphitized coke with a mass ratio of 9:1) and 25 parts of pitch at 150°C for 70 min, then mold at 15 MPa and bake at 1100°C for 30 days to obtain a square graphite crucible.

[0038] Comparative Example 1 Knead 75 parts of the mixed graphitized coke (composed of small - particle - size graphitized coke and large - particle - size graphitized coke with a mass ratio of 9:1) and 25 parts of pitch at 150°C for 70 min, then mold at 15 MPa and bake at 1100°C for 30 days to obtain a square graphite crucible.

[0039] Prepare test specimens according to the preparation processes of Examples 1 - 5 and Comparative Example 1 respectively. The size of the test specimens is a cube of 20 mm×20 mm×20 mm. Test the normal - temperature compressive strength according to Method 2 in GB / T 5072 - 2023, and conduct the test on the number of high - and low - temperature resistance times of the square graphite crucibles obtained in Examples 1 - 5 and Comparative Example 1 in the temperature range of 0 - 1500°C. Record the test results in Table 1.

[0040] Table 1 Test results of normal - temperature compressive strength and number of high - and low - temperature resistance times

[0041] As can be seen from Table 1, the normal temperature compressive strength is above 79.1 MPa, and the number of high and low temperature resistance times within the range of 0~1500℃ is >40 times, indicating that when the graphitized coke is silicon resin composite graphitized coke and / or heat-treated graphitized coke, the strength of the graphite crucible is improved, and it has good high and low temperature resistance performance.

[0042] In addition, the bulk density of the graphite crucibles obtained in Examples 1~5 measured by the method in GB / T 2997-2015 is ≥1.70 g / cm 3 、the apparent porosity is ≤29%, meeting the usage requirements in GB / T 26279-2010.

[0043] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A square graphite crucible, characterized in that, The raw materials include the following components in parts by mass: 65 - 75 parts of graphitized coke and 25 - 35 parts of pitch, and the graphitized coke is silicone resin composite graphitized coke and / or heat-treated graphitized coke.

2. The square graphite crucible according to claim 1, characterized in that, The graphitized coke consists of silicone resin composite graphitized coke and heat-treated graphitized coke with a mass ratio of 1 - 9:

1.

3. A square graphite crucible according to claim 2, characterized in that, The particle size of the graphitized coke in the silicone resin composite graphitized coke: 0 mm < particle size ≤ 2 mm.

4. A square graphite crucible according to claim 3, wherein The raw materials of the silicone resin composite graphitized coke include silane, initiator and graphitized coke with a mass ratio of 20 - 30:4.5 - 6:

90.

5. The square graphite crucible according to claim 4, wherein The preparation method of the silicone resin composite graphitized coke includes the following steps: After mixing graphitized coke and water, heat it to 80 - 85 °C while stirring, add silane and initiator and continue mixing. After the reaction ends, cool, filter, wash, and dry to obtain the silicone resin composite graphitized coke.

6. The square graphite crucible according to claim 2, characterized in that, The particle size of the graphitized coke in the heat-treated graphitized coke: 2 mm < particle size ≤ 8 mm.

7. A square graphite crucible according to claim 6, characterized in that, The heat-treated graphitized coke is graphitized coke heat-treated in an environment containing oxygen molecules.

8. A square graphite crucible according to claim 7, characterized in that, The preparation method of the heat-treated graphitized coke includes the following steps: Heat the graphitized coke in a mixed gas at 450 - 550 °C for 3 - 5 h to obtain the heat-treated graphitized coke; the mixed gas consists of oxygen and carbon dioxide.

9. A method for preparing a square graphite crucible, which is used to prepare the square graphite crucible according to any one of claims 1 to 8, characterized in that, Including the following steps: After kneading graphitized coke and pitch, form it, and bake at 950 - 1200 °C for 25 - 30 days to obtain a square graphite crucible.

10. The preparation method of a square graphite crucible according to claim 9, characterized in that, The temperature of the kneading is 135 - 155 °C; during the forming, the pressure is 10 - 15 MPa.

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