A high-purity, low-thermal-conductivity and low-density carbon fiber / carbon composite thermal field material and its preparation method

Abstract

The present invention provides a high-purity, low-thermal-conductivity, low-density carbon fiber / carbon composite thermal field material and a preparation method thereof. The preparation method of the present invention not only has high production efficiency, low energy consumption, low pollution, and a simple and rapid preparation process, but also the finally prepared low-density carbon fiber / carbon composite thermal field material has superior properties such as uniform distribution of fiber materials, low density, high temperature resistance, low thermal conductivity, high purity, and low electrical conductivity. The density of the composite thermal field material is ≤0.2±0.01 g / cm³; the content of impurity elements is ≤17 ppm; the electrical conductivity is ≤5.7 S / cm. And its thermal conductivity at 1500 °C is ≤0.46 W / (m·K); the power at 2300 °C in a 6-inch silicon carbide crystal growth furnace is ≤14.8 kW.

Description

Technical Field

[0001] The present invention relates to the technical field of high-purity, low-thermal-conductivity, low-density carbon fiber / carbon composite thermal field materials for the semiconductor industry, and particularly relates to a high-purity, low-thermal-conductivity, low-density carbon fiber / carbon composite thermal field material and a preparation method thereof. Background Art

[0002] Low-density carbon fiber / carbon composites (with a density less than 0.5 g / cm³) are widely used in high-temperature thermal field insulation materials due to their excellent high-temperature resistance (1500 - 3000 °C in vacuum or protective gas) and low thermal conductivity (thermal conductivity less than 0.5 W / (mK)). These applications include single-crystal silicon, polycrystalline silicon, silicon carbide crystal growth, silicon carbide epitaxial growth, sapphire crystal growth, optical fiber preform making and drawing, and high-temperature heat treatment of metals. Such materials are usually prepared from carbon fibers (such as PAN-based, viscose-based, pitch-based) and resins (such as phenolic resin, pitch) through processes such as impregnation, curing, carbonization, graphitization, and purification.

[0003] Currently, low-density carbon fiber / carbon composites are mainly divided into two categories: low-density long carbon fiber / carbon composites (carbon fiber length in the centimeter level) and low-density short carbon fiber / carbon composites (carbon fiber length in the millimeter level).

[0004] Classification and Characteristics of the Existing Technology

[0005] Low-density long carbon fiber / carbon composites:

[0006] The carbon fibers are mainly distributed in the X-Y plane, with fewer Z-direction fibers, forming an anisotropic structure and presenting a three-dimensional layered network structure.

[0007] Preparation process: Liquid-phase impregnation and curing molding are carried out with a carbon fiber felt (made of long carbon fibers, white fibers or pre-oxidized fibers) and phenolic resin, followed by high-temperature carbonization and graphitization.

[0008] Advantages: It has good heat insulation performance and is suitable for resistance furnace heating furnaces.

[0009] Disadvantages: Due to the relatively long carbon fibers, it is easy to form a continuous conductive network, resulting in relatively high conductivity and prone to inductive self-heating in an electromagnetic induction furnace. Therefore, it is not suitable for electromagnetic induction furnaces.

[0010] Low-density short carbon fiber / carbon composites:

[0011] Short carbon fibers (such as 3 - 5 mm in length) are used in combination with resins and prepared through processes such as impregnation, curing, carbonization, and graphitization.

[0012] Due to the relatively low anisotropy of short carbon fibers, which are closer to an isotropic structure, they have a relatively high thermal conductivity but low electrical conductivity and are not prone to electromagnetic induction heating. Therefore, they are more suitable for use in electromagnetic induction heating furnaces.

[0013] Electromagnetic induction furnaces have a faster heating rate compared to resistance heating furnaces and are more likely to reach high temperatures above 2000°C. Therefore, many current semiconductor crystal growth furnaces and epitaxial growth furnaces use low-density short carbon fiber / carbon composites as thermal field insulation materials.

[0014] Problems in the existing technology

[0015] Although low-density short carbon fiber / carbon composites have certain application advantages in electromagnetic induction furnaces, there are still the following problems in their preparation process and practical applications:

[0016] Material dispersion uniformity problem:

[0017] Existing preparation methods mostly use liquid-phase impregnation - molding and curing processes. Due to poor interfacial bonding, the resin cannot uniformly coat the carbon fibers, resulting in uneven impregnation. During the curing process, the resin may slide to the bottom due to gravity or accumulate on the outside due to the higher temperature of the external mold while there is less resin inside, resulting in uneven density from top to bottom and inside to outside. This non-uniformity leads to inconsistent mechanical strength and thermal conductivity of the finally prepared composite material, causing problems in practical applications.

[0018] Efficiency, energy, and environmental protection problems:

[0019] A large amount of solvent is used in the liquid-phase impregnation process, which not only increases the environmental protection burden but also results in high energy consumption during the solvent removal process. The addition and removal of the solvent prolong the process time and reduce production efficiency.

[0020] Thermal conductivity evaluation problem:

[0021] Short carbon fiber / carbon composites are usually used in high-temperature environments above 1000°C or even 2000°C, but there are currently few actual use evaluation methods for such materials, making it difficult to accurately measure their actual use effectiveness.

[0022] In summary, the existing low-density short carbon fiber / carbon composites have problems such as uneven material dispersion, inconsistent performance, low production efficiency, high energy consumption, serious environmental pollution, and lack of performance test and evaluation methods. Therefore, material structure design, preparation methods, and evaluation methods urgently need to be improved and innovated. Summary of the invention

[0023] The object of the present invention is to provide a preparation method of a high-purity, low-thermal-conductivity, low-density carbon fiber / carbon composite thermal field material with high production efficiency, low energy consumption, low pollution, and a simple and rapid preparation process.

[0024] Another object is to provide a high-purity, low-thermal-conductivity, low-density carbon fiber / carbon composite thermal field material with uniform fiber material distribution, low density, high temperature resistance, low thermal conductivity, high purity, and low electrical conductivity.

[0025] The technical solution of the present invention:

[0026] A high-purity, low-thermal-conductivity, low-density carbon fiber / carbon composite thermal field material, which has the following characteristics:

[0027] Density: ≤0.2±0.01 g / cm³;

[0028] Content of impurity elements: ≤17 ppm;

[0029] Electrical conductivity: ≤5.7 S / cm.

[0030] In addition, the material has the following characteristics:

[0031] Thermal conductivity at 1500 °C: ≤0.46 W / (m·K);

[0032] Power at 2300 °C in a 6-inch silicon carbide crystal growth furnace: ≤14.8 kW.

[0033] The present invention also discloses a preparation method of a high-purity, low-thermal-conductivity, low-density carbon fiber / carbon composite thermal field material, and the preparation method includes the following steps:

[0034] Step 1: Dispersing the powdered resin material and the chopped carbon fiber by high-speed shear dry method;

[0035] Step 2: Forming by rotational pressing and heating for curing;

[0036] Step 3: After fixing with carbon fiber cloth and high-density perforated carbon fiber / carbon composite material plates, performing high-temperature carbonization and graphitization;

[0037] Step 4: Chemically purifying the material at high temperature using a mixed powder of chlorinated polyvinyl chloride and polytetrafluoroethylene.

[0038] Preferably, the mass ratio of the chopped carbon fiber to the powdered resin is 100:(10 - 50).

[0039] Preferably, in step 2, the heating and curing regime is 100 °C / 1h - 150 °C / 2h - 200 °C / 2h, and the heating rate is 100 - 200 °C / h.

[0040] Preferably, in step 3, the temperature for high-temperature carbonization and graphitization is 2000°C - 3000°C, and the heating rate is 100 - 200°C / h; the curing rotation rate is 1 - 5 revolutions per minute.

[0041] Preferably, in step 4, the purification materials are chlorinated polyvinyl chloride powder and polytetrafluoroethylene powder, and their mass ratio is (100 - 300):100, and the dosage is 10 - 50 times the mass of the impurities.

[0042] Preferably, in step 4, the transmission rate of the purification materials is 10 g / min - 50 g / min; the purification temperature is 2000°C - 2600°C.

[0043] Preferably, the powdery resin is solid phenolic resin powder or solid asphalt powder, the powder size is 10 - 50 μm, the solid content > 97%, the fluidity is 20 - 30 mm, the polymerization rate is 50 - 90 s (at 150°C), and the residual carbon content is 50 - 60%.

[0044] Preferably, the carbon fiber cloth is of T300 grade, and the gram weight > 200 g / m 2 , and the thickness of the high-density carbon fiber / carbon composite material plate ≥ 10 mm, the tensile strength > 100 MPa, and the flexural strength > 100 MPa.

[0045] The high-purity, low-thermal-conductivity and low-density carbon fiber / carbon composite thermal field material prepared by the present invention has the following characteristics:

[0046] 1. Uniform fiber distribution and low density: the density ≤ 0.16 ± 0.01 g / cm³;

[0047] 2. High temperature resistance: suitable for the growth of silicon carbide crystals at 2300°C.

[0048] 3. High purity: the impurity content is less than ≤ 1.2 ppm.

[0049] 4. Low thermal conductivity: the thermal conductivity ≤ 0.20 W / (m·K).

[0050] 5. Low conductivity: the conductivity ≤ 4.0 S / cm, avoiding the phenomenon of electromagnetic self-heating.

[0051] 6. Environmentally friendly: no solvent is used and there is no pollution.

[0052] 7. High efficiency and low energy consumption: the preparation process is fast and energy-saving.

[0053] Application advantages

[0054] 1. Excellent heat preservation performance: in the silicon carbide crystal growth furnace, the power ≤ 14 kW at 2300°C, showing good heat preservation performance.

[0055] 2. High heating stability: The power is stable at high temperatures, suitable for the thermal field applications of third-generation semiconductor materials.

[0056] 3. Simple and efficient process: The preparation process does not require solvents, shortening the process time and reducing energy consumption. Description of the Drawings

[0057] Figure 1 This is an example of the microscopic morphology of the high-purity, low-thermal-conductivity, low-density carbon fiber / carbon material prepared in Example 1 of the present invention. Among them, Figure 1 Figure a1 in Figure 1 and Figure a2 in Figure 1 are the X-Y plane diagrams of the carbon fiber / carbon composite thermal field material magnified 200 times and 500 times respectively; Figure 1 Figure b1 in

[0058] Figure 2 and Figure b2 in 3 are the X-Z plane diagrams of the carbon fiber / carbon composite thermal field material magnified 200 times and 500 times respectively. Detailed Description of the Invention

[0059] Example 1

[0060] Objective: To prepare a high-purity, low-thermal-conductivity, low-density carbon fiber / carbon composite thermal field material with a density of 0.16 g / cm³.

[0061] Preparation Steps

[0062] S1. High-speed shearing dry dispersion of chopped carbon fibers

[0063] Use chopped viscose-based carbon fibers (length 3 mm), add them to a high-speed shearing disperser, with the rotation speed of the shearing tool being 3000 revolutions per minute, and stir for 5 minutes.

[0064] Add powdered phenolic resin (the mass ratio of carbon fiber to resin is 3:1), and continue to stir for 5 minutes to form a fluffy and dispersed chopped carbon fiber / phenolic resin system.

[0065] S2. Rotational pressing and curing

[0066] Press the dispersion system into a metal mold under a pressure of 100 tons. After locking the mold, place it on the rotating bracket of the heating oven and cure it by rotating at a speed of 3 revolutions per minute.

[0067] Curing regime: 100°C / 1h → 150°C / 2h → 200°C / 2h, with a heating rate of 150°C / h.

[0068] S3, High-temperature carbonization and graphitization

[0069] Wrap it with a layer of T300 carbon fiber cloth (grammage 200 g / m²), and then fix it with a high-density perforated carbon fiber / carbon composite material plate (tensile strength 160 MPa, flexural strength 120 MPa, thickness 10 mm).

[0070] Carry out carbonization and graphitization in a high-temperature furnace, process conditions: 350°C / 1h → 800°C / 1h → 1300°C / 1h → 1800°C / 1h → 2400°C / 1h → 2600°C / 1h.

[0071] 4. High-temperature chemical purification

[0072] Use a mixed powder of chlorinated polyvinyl chloride and polytetrafluoroethylene (mass ratio 100:100), the dosage of the purification powder is 50 times the impurity content, and the feeding speed is 50 g / min.

[0073] Chlorinated polyvinyl chloride: chlorine content 60%, particle size 40 microns; polytetrafluoroethylene: particle size 10 microns.

[0074] Purification temperature 2200°C.

[0075] Results:

[0076] Density: 0.16 ± 0.01 g / cm³

[0077] Impurity content: 1.2 ppm

[0078] Conductivity: 4.0 S / cm

[0079] Thermal conductivity at 1500°C: 0.40 W / (m·K)

[0080] Power at 2300°C: 14 kW

[0081] Service temperature: >2300°C

[0082] Example 2

[0083] Objective: Adjust the purification process to prepare a material with a density of 0.18 g / cm³.

[0084] Adjustment content

[0085] Step S4: The dosage of the purification powder is 30 times the impurity content, and the feeding speed is 30 g / min.

[0086] Results:

[0087] Density: 0.18 ± 0.01 g / cm³

[0088] Impurity content: 8 ppm

[0089] Conductivity: 4.8 S / cm

[0090] Thermal conductivity at 1500 °C: 0.45 W / (m·K)

[0091] Power at 2300 °C: 14.3 kW

[0092] Service temperature: >2300 °C

[0093] Example 3

[0094] Objective: Further adjust the purification process to prepare a material with a density of 0.20 g / cm³.

[0095] Adjustment content

[0096] Step S4: The amount of purified powder is 10 times the impurity content, and the feeding rate is 10 g / min.

[0097] Results:

[0098] Density: 0.20 ± 0.01 g / cm³

[0099] Impurity content: 17 ppm

[0100] Conductivity: 5.7 S / cm

[0101] Thermal conductivity at 1500 °C: 0.46 W / (m·K)

[0102] Power at 2300 °C: 14.8 kW

[0103] Service temperature: >2300 °C

[0104] Comparative example 1

[0105] Adjustment content:

[0106] Step S1: Impregnate with liquid phenolic resin.

[0107] Step S2: Do not perform rotational curing.

[0108] Problems:

[0109] Wet forming results in high drying energy consumption and increased time consumption.

[0110] Production efficiency is reduced, and there is liquid pollution.

[0111] Serious bleeding phenomenon, large density deviation, and unqualified products.

[0112] Comparative example 2

[0113] Adjustment content:

[0114] Step S3: Without using carbon fiber cloth and perforated carbon fiber / carbon composite plates for fixation, directly place it on the high-temperature furnace support.

[0115] Problem:

[0116] The product cracks and is scrapped during the carbonization and graphitization processes.

[0117] Comparative Example 3

[0118] Adjustment content:

[0119] Do not perform the high-temperature chemical purification in Step S4.

[0120] Problem:

[0121] The impurity content is high (300 ppm), and it cannot be applied to the semiconductor field.

[0122] Summary 1.

[0123] Examples 1 - 3:

[0124] By optimizing the dosage of purified powder and the feeding speed, high-purity, low-thermal-conductivity, low-density carbon fiber / carbon composite thermal field materials with different densities were successfully prepared.

[0125] The material has excellent performance and is suitable for high-temperature thermal field applications.

[0126] 2. Comparative Examples:

[0127] Liquid-phase impregnation and non-rotating curing lead to problems such as increased energy consumption, pollution, bleeding, and large density deviation.

[0128] Not using a fixing structure or not performing purification will cause the product to crack or the impurity content to be too high, unable to meet the application requirements.

[0129] The present invention solves the problems of uneven dispersion, high energy consumption, and large pollution in the prior art by optimizing the preparation process, and significantly improves the material performance and application scope.

[0130] Test results.

[0131] .

Claims

1. A preparation method of a high-purity, low-thermal-conductivity and low-density carbon fiber / carbon composite thermal field material, characterized in that, The preparation method includes the following steps: Step 1: Dispersing the powdered resin material and the chopped carbon fibers by high-speed shear dry method; Step 2: Forming by rotational pressing and heating for curing; Step 3: After fixing with carbon fiber cloth and high-density perforated carbon fiber / carbon composite material plates, performing high-temperature carbonization and graphitization; Step 4: Using a mixed powder of chlorinated polyvinyl chloride and polytetrafluoroethylene to chemically purify the material at high temperature; In Step 4, the purification materials are chlorinated polyvinyl chloride powder and polytetrafluoroethylene powder, and their mass ratio is (100 - 300):100, and the dosage is 10 - 50 times the mass of the impurities; The high-purity low-thermal-conductivity low-density carbon fiber / carbon composite thermal field material has the following characteristics: Density: ≤0.2 ± 0.01 g / cm³; Impurity element content: ≤17 ppm; Electrical conductivity: ≤5.7 S / cm; In Step 4, the transfer rate of the purification materials: 10 g / min - 50 g / min; Purification temperature: 2000°C - 2600°C.

2. The high-purity, low-thermal-conductivity, low-density carbon fiber / carbon composite thermal field material according to claim 1, characterized in that, This material has the following characteristics: Thermal conductivity at 1500°C: ≤0.46 W / (m·K); Power at 2300°C in a 6-inch silicon carbide crystal growth furnace: ≤14.8 kW.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the chopped carbon fibers to the powdered resin is 100:(10 - 50).

4. The preparation method according to claim 1, wherein In Step 2, the heating and curing regime is 100 °C / 1h - 150 °C / 2h - 200 °C / 2h, and the heating rate is 100 - 200 °C / h; The curing rotation rate: 1 - 5 revolutions per minute.

5. The preparation method according to claim 1, characterized in that, In Step 3, the temperature of high-temperature carbonization and graphitization is 2000°C - 3000°C, and the heating rate is 100 - 200°C / h.

6. The preparation method according to claim 1, characterized in that, The powdered resin is solid phenolic resin powder or solid pitch powder, with a powder size of 10 - 50 μm, a solid content > 97%, a fluidity of 20 - 30 mm, a polymerization rate of 50 - 90 s at 150°C, and a residual carbon content of 50 - 60%.

7. The preparation method according to claim 1, characterized in that, The carbon fiber cloth is of T300 grade, with a gram weight > 200 g / m2, the thickness of the high-density carbon fiber / carbon composite material plate ≥ 10 mm, a tensile strength > 100 MPa, and a flexural strength > 100 MPa.

Images