High thermal conductivity SiC / GNPs composite ceramic heat exchange tube and its preparation method

Abstract

This invention involves preparing spherical silicon carbide powder through physical shaping, mixing it with graphene dispersion and organic additive solution to obtain SiC / GNPs slurry, aging and kneading the slurry to obtain dense SiC / GNPs slurry, then extruding it using a vacuum screw extruder, followed by drying and pressureless sintering to obtain a high thermal conductivity SiC / GNPs composite ceramic heat exchange tube. Experiments show that the thermal conductivity of the high thermal conductivity SiC / GNPs composite ceramic heat exchange tube obtained by this invention is 207 W / (m·K)-347 W / (m·K), which is far higher than that of silicon carbide ceramic materials obtained by traditional processes. This solves the technical problem that the low thermal conductivity of silicon carbide materials cannot meet the needs of enterprises.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic materials technology, and in particular to a high thermal conductivity SiC / GNPs composite ceramic heat exchange tube and its preparation method. Background Technology

[0002] The heat transfer efficiency of a heat exchanger is closely related to the materials used. There are four main types of matrix materials for heat exchangers: metallic materials, organic polymer materials, ceramic materials, and carbon materials. Considering that heat exchangers are primarily used in chemical, oil refining, machinery, and power industries, and the heat exchange environments are often characterized by high pressure, high temperature, and highly corrosive acid and alkali media, ceramic heat exchangers have a clear advantage. Compared to other ceramic materials, silicon carbide ceramics possess high strength, high hardness, a low coefficient of thermal expansion, and excellent resistance to thermal shock, oxidation, and corrosion, making them the best material for heat exchangers. Currently, ceramic heat exchanger materials include alumina, silicon nitride, mullite, cordierite, and silicon carbide ceramics, with silicon carbide ceramic heat exchangers exhibiting the highest thermal conductivity and the widest range of applications.

[0003] In the prior art, Chinese invention patent CN104926312A discloses a high thermal conductivity pressureless sintered silicon carbide ceramic material and its preparation method. It is composed of the following raw materials in the following mass percentages: silicon carbide 75-95 wt.%, graphene 0.5-10 wt.%, surfactant 1-3 wt.%, dispersant 0.5-2.5 wt.%, binder 2-10 wt.%, and boron carbide 0.5-3.5 wt.%. This invention uses a specific ratio of silicon carbide, graphene, and boron carbide to press into a green body, and then performs pressureless sintering under vacuum conditions to obtain SiC ceramic material. According to its specification, the material prepared by the above method has a thermal conductivity of 147.32 W / (m·K)-169.53 W / (m·K), which is relatively low. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a high thermal conductivity SiC / GNPs composite ceramic heat exchange tube and its preparation method, solving the technical problem that the low thermal conductivity of silicon carbide materials cannot meet the needs of enterprises.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0006] A method for preparing a high thermal conductivity SiC / GNPs composite ceramic heat exchange tube includes the following process steps:

[0007] S1. Preparation of spherical silicon carbide powder;

[0008] S2. Mix graphene, dispersant, and deionized water, and then stir, sonicate, and vibrate to obtain a graphene dispersion;

[0009] S3. Mix the binder, plasticizer, lubricant and deionized water to obtain an organic additive solution;

[0010] S4. The spherical silicon carbide powder and the graphene dispersion are poured into a mixer and mixed. Then the organic additive solution is added to obtain SiC / GNPs slurry.

[0011] S5. Seal the SiC / GNPs clay and maintain the predetermined temperature and humidity for aging;

[0012] S6. The aged SiC / GNPs clay is loaded into a vacuum plow and plowed several times. After further aging, dense SiC / GNPs clay is obtained.

[0013] S7. The dense SiC / GNPs clay is extruded by a vacuum screw to obtain a raw tube;

[0014] S8. The green tube is dried and pressureless sintered to obtain a high thermal conductivity SiC / GNPs composite ceramic heat exchange tube.

[0015] Preferably, in step S2, the dispersant is a mixture of polyvinylpyrrolidone and tetramethylammonium hydroxide in a mass ratio of 1:1.

[0016] Preferably, in step S3, the plasticizer is a mixture of polyethylene glycol and glycerin in a mass ratio of 2:1.

[0017] Preferably, in step S3, the lubricant is a mixture of stearic acid and oleic acid in a mass ratio of 1:1.

[0018] Preferably, in step S3, the adhesive is hydroxymethyl cellulose.

[0019] Preferably, in step S4, the mass ratio of the spherical silicon carbide powder to the graphene is 100:(2-6).

[0020] Preferably, in step 5, the predetermined temperature for aging is 20°C-30°C, and the humidity is 40%-60%.

[0021] Preferably, in step S6, the number of kneading cycles is 10-20 times.

[0022] Preferably, in step S1, obtaining spherical silicon carbide powder includes the following steps:

[0023] A1. Mix polyacrylic acid with deionized water, then add SiC and B4C, stir, and obtain silicon carbide slurry;

[0024] A2. PVA and n-butanol are added to the silicon carbide slurry, and then ground to obtain a silicon carbide organic slurry;

[0025] A3. The silicon carbide organic slurry is granulated by water-based spray granulation to obtain silicon carbide powder pellets;

[0026] A4. Vacuum sinter the silicon carbide powder spheres to obtain spherical silicon carbide powder.

[0027] A high thermal conductivity SiC / GNPs composite ceramic heat exchange tube is prepared by the above-described method for preparing a high thermal conductivity SiC / GNPs composite ceramic heat exchange tube.

[0028] The technical solution adopted in this application can achieve the following beneficial effects:

[0029] This invention involves preparing spherical silicon carbide powder through physical shaping, mixing it with graphene dispersion and organic additive solution to obtain SiC / GNPs slurry, aging and kneading the slurry to obtain dense SiC / GNPs slurry, then extruding it using a vacuum screw extruder, followed by drying and pressureless sintering to obtain a high thermal conductivity SiC / GNPs composite ceramic heat exchange tube. Experiments show that the thermal conductivity of the high thermal conductivity SiC / GNPs composite ceramic heat exchange tube obtained by this invention is 207 W / (m·K)-347 W / (m·K), which is far higher than that of silicon carbide ceramic materials obtained by traditional processes. This solves the technical problem that the low thermal conductivity of silicon carbide materials cannot meet the needs of enterprises. Detailed Implementation

[0030] To facilitate understanding of this application, a more comprehensive description will be provided below with reference to relevant experimental examples. Preferred embodiments of this application are shown in the experimental examples. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to enable a more thorough and comprehensive understanding of the disclosure of this application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0032] A method for preparing a high thermal conductivity SiC / GNPs composite ceramic heat exchange tube, comprising the following materials in the indicated proportions: 100 parts SiC (silicon carbide), 2-5 parts graphene, 0.2-0.4 parts polyacrylic acid, 0.5-0.6 parts B4C (boron carbide), 3-5 parts PVA (polyvinyl alcohol), 0.3-0.5 parts n-butanol, 0.5-0.6 parts dispersant, 5-8 parts binder, 1-3 parts plasticizer, and 1-3 parts lubricant.

[0033] In a specific embodiment, the dispersion is a mixture of polyvinylpyrrolidone and tetramethylammonium hydroxide in a mass ratio of 1:1.

[0034] In a specific embodiment, the plasticizer is a mixture of polyethylene glycol and glycerin in a mass ratio of 2:1.

[0035] In a specific embodiment, the lubricant is a mixture of stearic acid and oleic acid in a mass ratio of 1:1.

[0036] In a specific embodiment, the adhesive is hydroxymethyl cellulose.

[0037] In one embodiment, polyacrylic acid ammonium is mixed with deionized water and stirred for 30 min. Then, SiC and B4C are added. The SiC particle size is D50≤0.8μm and the purity of the SiC is ≥99.5%. The B4C particle size is D50≤1μm and the purity of the B4C is ≥85%. The mixture is stirred at room temperature for 1 h-2 h to obtain silicon carbide slurry.

[0038] PVA and n-butanol are added to silicon carbide slurry, and the mixture is ground for 12-15 hours at a speed of 15-20 rad / min to obtain silicon carbide organic slurry.

[0039] Silicon carbide organic slurry was granulated into powder particles with a particle size of 15μm-30μm by water-based spray granulation. The spray granulation parameters were set as follows: inlet temperature 210℃-240℃, outlet temperature 90℃-110℃, and atomizing disc rotation speed 25HZ-30HZ.

[0040] Silicon carbide powder pellets are placed in a vacuum sintering furnace at a temperature of 600℃-800℃ for 30-50 minutes to obtain spherical silicon carbide powder with a particle size of 5µm-10µm.

[0041] In one embodiment, graphene, dispersant, and deionized water are stirred for 30-60 minutes, then placed in an ultrasonic instrument for heating and vibration. The heating temperature is 40-50°C, and the vibration time is 1-2 hours. Then, stirring is continued for 30-40 minutes to obtain a graphene dispersion.

[0042] Mix the binder, plasticizer, lubricant and deionized water, and stir thoroughly for 30-60 minutes to obtain an organic additive solution.

[0043] The spherical silicon carbide powder and the graphene dispersion are poured into a roller mixer and mixed at a speed of 30 rad / min-40 rad / min for 100 min-120 min. The organic additive solution is added to the mixer in small amounts several times, and the mixing continues for 60 min-100 min to obtain SiC / GNPs slurry.

[0044] In one embodiment, the SiC / GNPs clay is sealed and placed in an environment with a temperature of 20℃-30℃ and a humidity of 40%-60% for aging for 12h-24h. Then, it is repeatedly squeezed and kneaded 10-30 times through a vacuum kneading machine with a vacuum degree of 0.05MPa-0.1MPa and a pressure of 40MPa-60MPa. The kneaded SiC / GNPs clay is then sealed again and aged for 20h-30h to obtain dense SiC / GNPs clay.

[0045] In one embodiment, the dense SiC / GNPs clay is extruded into a preform tube using a vacuum screw extruder. The preform tube is 1.5m long, 5cm in diameter, and 1cm thick.

[0046] In one embodiment, the raw tube is dried using a microwave drying process, firstly by low-temperature drying at 50℃-70℃ for 40min-60min, and then by high-temperature drying at 80℃-100℃ for 100min-120min.

[0047] The dried green tube is placed in a pressureless sintering furnace and sintered at a temperature of 2000℃-2100℃ for 1-2 hours to obtain a high thermal conductivity SiC / GNPs composite ceramic heat exchange tube.

[0048] It should be noted that adding organic additives such as binders, plasticizers, and lubricants to silicon carbide slurry is to ensure that the refined SiC / GNPs slurry has plasticity and fluidity. The amount of organic additive solution added at one time should not be too much, but should be added in small amounts multiple times so that graphene can be evenly coated on the surface of spherical silicon carbide particles through the organic additives, and the liquid phase components can be evenly distributed in the slurry.

[0049] In this invention, aging refers to sealing the clay material, maintaining a predetermined temperature and humidity, and letting it sit for a certain period of time, much like letting dough rest after kneading. Refining the clay refers to repeatedly pounding and pressing it in a specific environment; in this invention, this is done under vacuum conditions. Experimental Example 1 explores the effects of temperature and the number of refining cycles on thermal conductivity during the aging and refining processes.

[0050] Prepare the materials according to the following proportions: 100 parts SiC (silicon carbide), 2 parts graphene, 0.2 parts polyacrylic acid, 0.5 parts B4C (boron carbide), 3 parts PVA (polyvinyl alcohol), 0.3 parts n-butanol, 0.5 parts dispersant, 5 parts binder, 1 part plasticizer, and 1 part lubricant.

[0051] Polyacrylic acid amine is mixed with deionized water and stirred for 30 min. Then SiC and B4C are added. The SiC particle size is D50≤0.8μm and the purity of SiC is ≥99.5%. The B4C particle size is D50≤1μm and the purity of B4C is ≥85%. The mixture is stirred at room temperature for 1.5 h to obtain silicon carbide slurry.

[0052] PVA and n-butanol were added to the silicon carbide slurry, and the mixture was ground for 13 hours at a speed of 18 rad / min to obtain the silicon carbide organic slurry.

[0053] Silicon carbide organic slurry was granulated into powder particles with a particle size of 15μm-30μm by water-based spray granulation. The spray granulation parameters were set as follows: inlet temperature 220℃, outlet temperature 100℃, and atomizing disc rotation speed 30Hz.

[0054] Silicon carbide powder pellets are placed in a vacuum sintering furnace at 700℃ for 40 minutes to obtain spherical silicon carbide powder with a particle size of 5µm-10µm.

[0055] Graphene, dispersant, and deionized water were stirred for 50 minutes, then placed in an ultrasonic instrument for heating and vibration. The heating temperature was 40°C and the vibration time was 1 hour. Then, stirring was continued for 30 minutes to obtain a graphene dispersion.

[0056] Mix the binder, plasticizer, lubricant and deionized water and stir thoroughly for 40 minutes to obtain an organic additive solution.

[0057] The spherical silicon carbide powder and the graphene dispersion were poured into a roller mixer and mixed at a speed of 30 rad / min for 110 min. The organic additive solution was added to the mixer in small amounts several times, and the mixing was continued for 80 min to obtain SiC / GNPs slurry.

[0058] The SiC / GNPs clay was sealed and aged and kneaded according to the relevant parameters shown in Table 1. The kneading process was vacuum kneading with a vacuum degree of 0.1 MPa and a pressure of 60 MPa to obtain dense SiC / GNPs clay.

[0059] The dense SiC / GNPs clay is extruded into a blank tube by a vacuum screw extruder. The blank tube is 1.5m long, 5cm in diameter, and 1cm thick.

[0060] The raw tube is dried using a microwave drying process. First, it is dried at a low temperature of 60°C for 50 minutes, and then dried at a high temperature of 100°C for 110 minutes.

[0061] The dried green tube was placed in a pressureless sintering furnace and sintered at 2100℃ for 1 hour to obtain a high thermal conductivity SiC / GNPs composite ceramic heat exchange tube.

[0062] Further investigation was conducted into the effects of temperature, aging time, and number of kneading cycles on thermal conductivity during the aging and kneading processes. The parameter variations are shown in Table 1.

[0063] Table 1. Thermal conductivity of high thermal conductivity SiC / GNPs composite ceramic heat exchange tubes at different temperatures

[0064]

[0065] Table 1 shows that the thermal conductivity of the SiC / GNPs composite ceramic heat exchange tubes was not significantly different when the first aging temperature was 20℃, 25℃, 30℃, and 35℃. Data shows that the optimal temperature was 25℃, with a thermal conductivity of 198 W / m·K. Further experiments were conducted at 25℃, adjusting the first aging time to 12h, 18h, 24h, and 36h. Data showed that longer aging times resulted in better thermal conductivity, but the increase was relatively small at 18h, 24h, and 36h. Based on these experiments, a first aging time of 18h was preferred. When the number of kneading cycles was changed to 15, 20, 30, and 40, the thermal conductivity continuously increased. Considering the company's time and cost expenditures, this patent recommends a kneading cycle of 20 times.

[0066] Experiment Example 2 explores the effect of different material ratios on thermal conductivity.

[0067] For experiments A1-A15, the experimental methods described above remain unchanged. The material proportions are shown in Table 2, and the test performance is shown in Table 3.

[0068] Table 2. Material proportions for experiments A1-A15

[0069]

[0070] Table 3 Comparison of performance parameters for experiments A1-A15

[0071]

[0072] Tables 2 and 3 show that after continuously adjusting the material ratios in experiments A1-A15, different parameters were obtained, with the optimal parameters found in experiment A14. In experiment A2, slightly adjusting the amount of polyacrylic acid to 0.4 parts increased the thermal conductivity. Experiments A3 and A4 show that increasing the amount of B4C to 0.6 and 0.8 parts respectively, based on experiment A2, resulted in a decrease in thermal conductivity when the amount of B4C was 0.8 parts, indicating that the optimal amount of B4C is 0.6 parts. Experiments A5 and A6, based on experiment A3, changed the amount of PVA to 4 and 5 parts respectively, resulting in increased experimental parameters. In experiment A6, increasing the amount of n-butanol to 5 parts did not change the thermal conductivity. In experiment A6, further increasing the amount of graphene to 5 and 6 parts showed that when the amount of graphene increased to 6 parts, the thermal conductivity decreased. The coefficient decreased instead of increasing, indicating that the optimal amount of graphene added was 5 parts. Based on experiment A8, increasing the dispersant to 0.8 parts increased the thermal conductivity. Experiment A11 further adjusted the amounts of dispersant and binder, and the measured thermal conductivity increased. That is, while keeping other conditions unchanged in experiment A11, increasing the plasticizer from 1 part to 2-3 parts proved that increasing the plasticizer to 2 parts was optimal. Keeping other conditions unchanged in experiment A12, increasing the lubricant to 2-3 parts showed that when the lubricant was increased to 2 parts, the thermal conductivity of the high thermal conductivity SiC / GNPs composite ceramic heat exchange tube was optimal at 347 W / (m·K).

[0073] It should be noted that, firstly, the most significant feature of this experiment is the improvement in process. Physical shaping was used to obtain spherical silicon carbide powder, resulting in silicon carbide powder with extremely high sphericity and a particle size of 5-10 μm. Spherical silicon carbide particles not only possess high sintering activity and high dispersibility but also facilitate tight bonding with graphene. Furthermore, the slurry made from spherical silicon carbide particles exhibits higher plasticity. A secondary spray granulation method further improves the morphology and sphericity of the silicon carbide particles, ensuring uniform coating of the silicon carbide spheres with graphene sheets and enhancing the grain bonding between silicon carbide and graphene. Secondly, in the process… The aging and refining of the clay facilitates the next step of vacuum screw extrusion molding, which is also an important step in the SiC / GNPs composite ceramic heat exchange tube process. Thirdly, in the existing technology, the thermal conductivity of the material is only 147.32 W / (m·K)-169.53 W / (m·K). The thermal conductivity of the SiC / GNPs composite ceramic heat exchange tube obtained by this invention is 207 W / (m·K). After multiple experiments and adjustments to the material composition, the thermal conductivity of the SiC / GNPs composite ceramic heat exchange tube was finally 347 W / (m·K), which is a significant improvement over the existing technology.

[0074] The above-described embodiments merely illustrate the device deployment method of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent application. It should be noted that for those skilled in the art, several adjustments and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing a high thermal conductivity SiC / GNPs composite ceramic heat exchange tube, characterized in that, The process includes the following steps: S1. Preparation of spherical silicon carbide powder; S2. Mix graphene, dispersant, and deionized water, and then stir, sonicate, and vibrate to obtain a graphene dispersion; S3. Mix the binder, plasticizer, lubricant and deionized water to obtain an organic additive solution; S4. The spherical silicon carbide powder and the graphene dispersion are poured into a mixer and mixed. Then the organic additive solution is added to obtain SiC / GNPs slurry. S5. The SiC / GNPs clay is sealed and placed in an environment with a temperature of 25℃ and a humidity of 50% for 18 hours of aging. Then, it is repeatedly squeezed and kneaded 20 times by a vacuum kneading machine with a vacuum degree of 0.1MPa and a pressure of 60MPa. The kneaded SiC / GNPs clay is then sealed and aged for 20 hours to obtain dense SiC / GNPs clay. S6. The dense SiC / GNPs clay is extruded by a vacuum screw to obtain a raw tube; S7. The green tube is dried and pressureless sintered to obtain a high thermal conductivity SiC / GNPs composite ceramic heat exchange tube; The materials are prepared according to the following proportions: 100 parts SiC, 5 parts graphene, 0.4 parts polyacrylic acid, 0.6 parts B4C, 5 parts PVA, 0.5 parts n-butanol, 0.6 parts dispersant, 8 parts binder, 2 parts plasticizer, and 2 parts lubricant.

2. The method for preparing the high thermal conductivity SiC / GNPs composite ceramic heat exchange tube according to claim 1, characterized in that, In step S2, the dispersant is a mixture of polyvinylpyrrolidone and tetramethylammonium hydroxide in a mass ratio of 1:

1.

3. The method for preparing the high thermal conductivity SiC / GNPs composite ceramic heat exchange tube according to claim 1, characterized in that, In step S3, the plasticizer is a mixture of polyethylene glycol and glycerin in a mass ratio of 2:

1.

4. The method for preparing the high thermal conductivity SiC / GNPs composite ceramic heat exchange tube according to claim 1, characterized in that, In step S3, the lubricant is a mixture of stearic acid and oleic acid in a mass ratio of 1:

1.

5. The method for preparing the high thermal conductivity SiC / GNPs composite ceramic heat exchange tube according to claim 1, characterized in that, In step S3, the adhesive is hydroxymethyl cellulose.

6. The method for preparing the high thermal conductivity SiC / GNPs composite ceramic heat exchange tube according to claim 1, characterized in that, In step S4, the mass ratio of the spherical silicon carbide powder to the graphene is 100:(2-6).

7. The method for preparing the high thermal conductivity SiC / GNPs composite ceramic heat exchange tube according to claim 1, characterized in that, In step S1, the preparation of spherical silicon carbide powder includes the following steps: A1. Mix polyacrylic acid with deionized water, then add SiC and B4C, stir, and obtain silicon carbide slurry; A2. PVA and n-butanol are added to the silicon carbide slurry, and then ground to obtain a silicon carbide organic slurry; A3. The silicon carbide organic slurry is granulated by water-based spray granulation to obtain silicon carbide powder pellets; A4. Vacuum sinter the silicon carbide powder spheres to obtain spherical silicon carbide powder.

8. A high thermal conductivity SiC / GNPs composite ceramic heat exchange tube, characterized in that, It is prepared by the method of any one of claims 1-7 for the preparation of high thermal conductivity SiC / GNPs composite ceramic heat exchange tube.

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