Silicon carbide ceramic heat exchange tube and preparation method thereof

Abstract

The application discloses a silicon carbide ceramic heat exchange pipe and a preparation method thereof, and belongs to the technical field of silicon carbide ceramics. The preparation method of the silicon carbide ceramic heat exchange pipe comprises the following steps: dispersing a modifier in anhydrous ethanol, adding silicon carbide fine powder to react, and obtaining modified silicon carbide fine powder; stirring and uniformly mixing phenolic resin, modified benzoxazine and anhydrous ethanol, adding carbon black, fly ash, modified silicon carbide fine powder and silicon carbide coarse powder in sequence, stirring and uniformly mixing, performing aging, refining, extrusion molding and drying, and obtaining a silicon carbide green body; and placing the silicon carbide green body into a high-temperature furnace for heat treatment, so that the silicon carbide ceramic heat exchange pipe is obtained. The silicon carbide ceramic heat exchange pipe prepared by the application has excellent density, bending strength and fracture toughness.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide ceramic technology, specifically to a silicon carbide ceramic heat exchange tube and its preparation method. Background Technology

[0002] Ceramic heat exchangers can recover and utilize waste heat, improving energy efficiency, reducing energy consumption, and decreasing pollution emissions. They have broad application prospects in chemical, metallurgical, petroleum, and power industries. Silicon carbide ceramics possess advantages such as high thermal conductivity, high temperature resistance, corrosion resistance, wear resistance, and good chemical stability, making them an ideal choice for heat exchanger materials under extreme conditions such as high-temperature environments, strong acid and alkali corrosion, and severe wear. However, the shortcomings of silicon carbide ceramic materials (such as poor flexural strength and fracture toughness) are one of the important factors restricting the preparation and widespread application of high-performance silicon carbide ceramic heat exchange tubes. Due to the extremely strong covalent bonds and extremely low diffusion coefficient of silicon carbide, it is very difficult to completely densify silicon carbide ceramics, affecting their mechanical properties. Furthermore, the shrinkage stress generated during the crosslinking of phenolic resin can easily lead to deformation and cracking of the ceramic preform, affecting product performance.

[0003] Chinese invention patent CN114560702A discloses a pressureless sintering extrusion process for silicon carbide ceramics. The silicon carbide ceramics are composed of silicon carbide, titanium diboride, carbon black, boron carbide, polyethylene glycol, corn starch, sodium carboxymethyl cellulose, epoxy resin, ethanolamine, modifier and stabilizer, phytic acid, emulsified fatty acids, and deionized water. The process includes mixing, refining, aging, extrusion molding, high-frequency electromagnetic vibration treatment, drying, and sintering. This process has low equipment investment, low energy consumption, low cost, and simple process. The products prepared have high thermal conductivity, corrosion resistance, wear resistance, and high temperature resistance, but their mechanical properties are still insufficient. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a silicon carbide ceramic heat exchange tube and its preparation method.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing a silicon carbide ceramic heat exchange tube includes the following steps:

[0007] (1) Disperse the modifier in anhydrous ethanol, add silicon carbide fine powder and react to obtain modified silicon carbide fine powder;

[0008] (2) Phenolic resin, modified benzoxazine and anhydrous ethanol are stirred and mixed, and carbon black, fly ash, modified silicon carbide fine powder and silicon carbide coarse powder are added in sequence and stirred and mixed. After aging, kneading, extrusion molding and drying, silicon carbide blank is obtained.

[0009] (3) The silicon carbide blank is placed in a high-temperature furnace for heat treatment to obtain silicon carbide ceramic heat exchange tubes.

[0010] The modifier is prepared by the following method:

[0011] S1: Diphenylsilanediol reacts with 3-aminopropylmethyldimethoxysilane to form a linear polysiloxane; the reaction equation is shown below.

[0012] .

[0013] S2: A linear polysiloxane reacts with γ-chloropropyltrimethoxysilane to generate a modifier; the reaction equation is shown below:

[0014] .

[0015] In step S1, the molar ratio of diphenylsilanediol to 3-aminopropylmethyldimethoxysilane is (0.9-1):1; in step S2, the mass ratio of linear polysiloxane to γ-chloropropyltrimethoxysilane is 2:(0.8-1).

[0016] The modified benzoxazine was prepared by the following method:

[0017] N1: The amino-terminated polyether reacts with 3-chloro-1,2-propanediol to form a dipropanediol-modified polyether; the reaction equation is shown below:

[0018] .

[0019] N2: Dipropanediol-modified polyether reacts with 4-aminophenylboronic acid to generate borate ester-modified polyether; the reaction equation is shown below:

[0020] .

[0021] N3: Boronate-modified polyether reacts with phenol in the presence of paraformaldehyde to generate modified benzoxazine. The reaction equation is shown below:

[0022] .

[0023] In step N1, the molar ratio of the terminal amino polyether to 3-chloro-1,2-propanediol is 1:2.05.

[0024] In step N2, the molar ratio of the dipropanediol modified polyether to 4-aminophenylboronic acid is 1:2.1.

[0025] In step N3, the molar ratio of the borate ester modified polyether to phenol is 1:2.1.

[0026] In steps (1) to (2), the weight parts of each component added are as follows: 25-35 parts of silicon carbide fine powder, 50-60 parts of silicon carbide coarse powder, 10-12 parts of carbon black, 4-5 parts of fly ash, 0.5-0.8 parts of modifier, 8-10 parts of phenolic resin, and 4-6 parts of modified benzoxazine.

[0027] In step (1), the mass ratio of the modifier to anhydrous ethanol is 1:200.

[0028] In step (3), the heat treatment process is to keep the temperature at 900-1100℃ for 1-2 hours and at 1600-1700℃ for 2-3 hours.

[0029] A silicon carbide ceramic heat exchange tube is prepared by the above method.

[0030] Due to the adoption of the above technical solutions, the beneficial effects of the present invention include:

[0031] The silicon carbide ceramic heat exchange tube prepared by this invention has excellent density, flexural strength, and fracture toughness. The modifier added to the components reduces interfacial defects by forming covalent bonds, improves the dispersibility of silicon carbide fine powder, and enhances the density and mechanical properties of silicon carbide ceramics; the modified benzoxazine added to the components reduces shrinkage stress and internal defect density, thereby improving the flexural strength and fracture toughness of the ceramic. Detailed Implementation

[0032] The following description, in conjunction with specific embodiments, provides further details, but the present invention is not limited to these embodiments.

[0033] Example 1: Preparation of the modifier:

[0034] S1: 0.09 mol diphenylsilanediol, 0.1 mol 3-aminopropylmethyldimethoxysilane and 0.08 g Ba(OH)2 were added to a reaction vessel, stirred and mixed, and the mixture was heated to 75 °C under nitrogen protection and reacted for 7 h. After cooling to room temperature, 300 ml tetrahydrofuran was added and stirred to dissolve. The mixture was filtered, and the filtrate was distilled under reduced pressure at 45 °C for 3 h to obtain a pale yellow transparent viscous linear polysiloxane (amino content of 0.28 mol / 100 g).

[0035] S2: Add 200 ml of anhydrous toluene, 20 g of linear polysiloxane, 10 g of γ-chloropropyltrimethoxysilane, 0.06 mol of potassium carbonate, and 5 mmol of potassium iodide to a reaction vessel. Under nitrogen protection, heat to 70 °C and react for 24 h. Cool to room temperature, filter to remove insoluble matter, and distill under reduced pressure at 70 °C for 3 h to obtain the modifier.

[0036] Example 2: Preparation of the modifier:

[0037] S1: 0.095 mol diphenylsilanediol, 0.1 mol 3-aminopropylmethyldimethoxysilane and 0.08 g Ba(OH)2 were added to a reaction vessel, stirred and mixed, and the mixture was heated to 80 °C under nitrogen protection and reacted for 6 h. After cooling to room temperature, 300 ml tetrahydrofuran was added and stirred to dissolve. The mixture was filtered, and the filtrate was distilled under reduced pressure at 45 °C for 3 h to obtain a pale yellow transparent viscous linear polysiloxane (amino content of 0.27 mol / 100 g).

[0038] S2: Add 200 ml of anhydrous toluene, 20 g of linear polysiloxane, 9 g of γ-chloropropyltrimethoxysilane, 0.06 mol of potassium carbonate, and 5 mmol of potassium iodide to a reaction vessel. Under nitrogen protection, heat to 75 °C and react for 22 h. Cool to room temperature, filter to remove insoluble matter, and distill under reduced pressure at 70 °C for 3 h to obtain the modifier.

[0039] Example 3: Preparation of the modifier:

[0040] S1: Add 0.1 mol diphenylsilanediol, 0.1 mol 3-aminopropylmethyldimethoxysilane and 0.08 g Ba(OH)2 to a reaction vessel, stir and mix well, heat to 85℃ under nitrogen protection, react for 5 h, cool to room temperature, add 300 ml tetrahydrofuran and stir to dissolve, filter, and distill the filtrate at 45℃ under reduced pressure for 3 h to obtain a pale yellow transparent viscous linear polysiloxane (amino content is 0.26 mol / 100 g).

[0041] S2: Add 200 ml of anhydrous toluene, 20 g of linear polysiloxane, 8 g of γ-chloropropyltrimethoxysilane, 0.06 mol of potassium carbonate, and 5 mmol of potassium iodide to a reaction vessel. Under nitrogen protection, heat to 80 °C and react for 20 h. Cool to room temperature, filter to remove insoluble matter, and distill under reduced pressure at 70 °C for 3 h to obtain the modifier.

[0042] Example 4: Preparation of modified benzoxazine:

[0043] N1: Add 400 ml of isopropanol and 0.1 mol of amino-terminated polyether (model ZED-601, number average molecular weight 600) to a reaction vessel, stir and mix well, then add 0.205 mol of 3-chloro-1,2-propanediol dropwise over 30 min. Heat to 60℃ and react for 8 h (the pH is controlled to 10 using 10 wt% NaOH solution during this period). Cool to room temperature, adjust the pH to 7 using 1 M hydrochloric acid solution, and distill under reduced pressure at 60℃ for 3 h. Add 350 ml of acetone, stir and heat to 50℃, cool to room temperature, filter to remove solids, and distill the filtrate under reduced pressure at 40℃ for 2 h. Add 200 ml of n-hexane, stir to precipitate, filter, and dry under vacuum at 50℃ for 12 h to obtain dipropanediol modified polyether (number average molecular weight 743).

[0044] N2: Add 500 ml of tetrahydrofuran and 0.1 mol of dipropanediol modified polyether to a reaction vessel, stir and mix well. At room temperature, add 0.21 mol of 4-aminophenylboronic acid in batches (10 batches, 15 min apart). Stir at 60 °C for 20 h, distill under reduced pressure at 45 °C for 2 h, add 300 ml of n-hexane and stir to precipitate, filter, and dry under vacuum at 60 °C for 12 h to obtain borate ester modified polyether (with a number average molecular weight of 945).

[0045] N3: Add 600 ml toluene and 15 g paraformaldehyde to a reaction vessel and stir for 30 min. Then add 0.1 mol borate-modified polyether and 0.21 mol phenol in sequence. Under nitrogen protection, heat to reflux and react for 20 h. Cool to 60 °C and distill under reduced pressure for 3 h. Add 350 ml of a mixed solution of ethyl acetate and n-hexane (volume ratio 2:1), stir and heat to dissolve. Keep warm for 30 min, cool to 0 °C and stand for 2 h to precipitate. Filter and dry under vacuum at 50 °C for 12 h to obtain the modified benzoxazine monomer.

[0046] Example 5: Preparation of silicon carbide ceramic heat exchange tubes:

[0047] (1) Weigh the following by weight: 250g of fine silicon carbide powder, 500g of coarse silicon carbide powder, 100g of carbon black, 40g of fly ash, 5g of modifier (prepared in Example 1), 80g of phenolic resin, and 40g of modified benzoxazine (prepared in Example 4).

[0048] (2) Disperse the modifier in 1000g of 98wt% ethanol aqueous solution and stir to mix well. Add silicon carbide fine powder and heat to reflux. React for 7h, cool to room temperature, filter, wash with 800ml of anhydrous ethanol, and vacuum dry at 80℃ for 6h to obtain modified silicon carbide fine powder.

[0049] (3) Add phenolic resin, modified benzoxazine and 150g of anhydrous ethanol to a mixer and stir at 200r / min for 30min until they are evenly mixed. Then add carbon black, fly ash, modified silicon carbide fine powder and silicon carbide coarse powder in sequence and stir at 500r / min for 30min. After the mixture is sealed and aged for 24h at 15℃ and 60% humidity, it is placed in a vacuum plow and kneaded at 25℃ and 0.09MPa for 30min to obtain plow material. The plow material is extruded and molded at 1MPa and 0.09MPa vacuum. It is then dried at 150℃ for 24h to obtain silicon carbide preform.

[0050] (4) Place the silicon carbide blank in a high-temperature furnace. Under nitrogen protection, heat the blank to 150°C at a heating rate of 2°C / min and hold for 12 hours. Turn on the vacuum pump and control the vacuum in the high-temperature furnace to 80Pa. Heat the blank to 900°C at a heating rate of 2°C / min and hold for 2 hours. Heat the blank to 1600°C at a heating rate of 2°C / min. Turn off the vacuum pump, introduce nitrogen, and hold for 3 hours. Allow the blank to cool naturally to room temperature to obtain the silicon carbide ceramic heat exchange tube.

[0051] Example 6: Preparation of silicon carbide ceramic heat exchange tubes:

[0052] (1) Weigh out the following by weight: 300g of fine silicon carbide powder, 560g of coarse silicon carbide powder, 110g of carbon black, 45g of fly ash, 7g of modifier (prepared in Example 2), 90g of phenolic resin, and 50g of modified benzoxazine (prepared in Example 4).

[0053] (2) Disperse the modifier in 1400g of 98wt% ethanol aqueous solution and stir well. Add silicon carbide fine powder and heat to reflux. React for 8h, cool to room temperature, filter, wash with 800ml of anhydrous ethanol, and vacuum dry at 80℃ for 6h to obtain modified silicon carbide fine powder.

[0054] (3) Add phenolic resin, modified benzoxazine and 180g of anhydrous ethanol to a mixer and stir at 200r / min for 30min until they are evenly mixed. Then add carbon black, fly ash, modified silicon carbide fine powder and silicon carbide coarse powder in sequence and stir at 500r / min for 30min. After sealing and aging the mixture at 15℃ and 60% humidity for 24h, put it into a vacuum ply mill and mix at 25℃ and 0.09MPa vacuum for 30min to obtain ply material. Extrude the ply material into shape at 1MPa and 0.09MPa vacuum and dry at 160℃ for 24h to obtain silicon carbide preform.

[0055] (4) Place the silicon carbide blank into a high-temperature furnace, turn on the vacuum pump, control the vacuum degree in the high-temperature furnace to 80 Pa, raise the temperature to 1000℃ at a heating rate of 2℃ / min and hold for 1.5h, raise the temperature to 1650℃ at a heating rate of 2℃ / min, turn off the vacuum pump, introduce nitrogen gas, hold for 2.5h, and cool naturally to room temperature to obtain the silicon carbide ceramic heat exchange tube.

[0056] Example 7: Preparation of silicon carbide ceramic heat exchange tubes:

[0057] (1) Weigh out the following by weight: 350g of fine silicon carbide powder, 600g of coarse silicon carbide powder, 120g of carbon black, 50g of fly ash, 8g of modifier (prepared in Example 3), 100g of phenolic resin, and 60g of modified benzoxazine (prepared in Example 4).

[0058] (2) Disperse the modifier in 1600g of 98wt% ethanol aqueous solution and stir to mix well. Add silicon carbide fine powder and heat to reflux. React for 9h, cool to room temperature, filter, wash with 800ml of anhydrous ethanol, and vacuum dry at 80℃ for 6h to obtain modified silicon carbide fine powder.

[0059] (3) Add phenolic resin, modified benzoxazine and 200g of anhydrous ethanol to a mixer and stir at 200r / min for 30min until they are evenly mixed. Then add carbon black, fly ash, modified silicon carbide fine powder and silicon carbide coarse powder in sequence and stir at 500r / min for 30min. After sealing and aging the mixture at 15℃ and 60% humidity for 24h, put it into a vacuum ply mill and mix at 25℃ and 0.09MPa vacuum for 30min to obtain ply material. Extrude the ply material into shape at 1MPa and 0.09MPa vacuum and dry at 180℃ for 24h to obtain silicon carbide preform.

[0060] (4) Place the silicon carbide blank into a high-temperature furnace. Under nitrogen protection, heat it to 1100℃ at a heating rate of 2℃ / min and hold it for 1 hour. Turn on the vacuum pump and control the vacuum degree in the high-temperature furnace to 80Pa. Heat it to 1700℃ at a heating rate of 2℃ / min. Turn off the vacuum pump, introduce nitrogen, hold it for 2 hours, and let it cool naturally to room temperature to obtain the silicon carbide ceramic heat exchange tube.

[0061] Comparative Example 1

[0062] The preparation method of silicon carbide ceramic heat exchange tube is basically the same as that of Example 6, except that the modifier added to the component (prepared in Example 2) is replaced with an equal weight of linear polysiloxane (prepared in step S1 of Example 2).

[0063] Comparative Example 2

[0064] The preparation method of the silicon carbide ceramic heat exchange tube is basically the same as that in Example 6, except that the modifier added to the components (prepared in Example 2) is replaced with an equal weight of the modifier prepared by the following method:

[0065] The preparation method of the modifier is basically the same as that in Example 2, except that 3-aminopropylmethyldimethoxysilane in step S1 is replaced with an equimolar amount of 3-aminopropyltrimethoxysilane.

[0066] Comparative Example 3

[0067] The preparation method of the silicon carbide ceramic heat exchange tube is basically the same as that in Example 6, except that the modifier added to the components (prepared in Example 2) is replaced with an equal weight of the modifier prepared by the following method:

[0068] 200 ml of anhydrous toluene, 20 g of amino-terminated silicone oil (amine content 2 mmol / g), 8 g of γ-chloropropyltrimethoxysilane, 0.06 mol of potassium carbonate, and 5 mmol of potassium iodide were added to a reaction vessel. Under nitrogen protection, the mixture was heated to 80 °C and reacted for 22 h. After cooling to room temperature, the insoluble matter was removed by filtration, and the mixture was distilled under reduced pressure at 70 °C for 3 h to obtain the modifier.

[0069] Comparative Example 4

[0070] The preparation method of the silicon carbide ceramic heat exchange tube is basically the same as that in Example 6, except that the modified benzoxazine (prepared in Example 4) added to the components is replaced with an equal weight of the modified benzoxazine prepared by the following method:

[0071] The preparation method of modified benzoxazine is basically the same as that in Example 4, except that the terminal amino polyether (model ZED-601, number average molecular weight 600) in step N1 is replaced with an equimolar amount of terminal amino polyether (model ZD-1200, number average molecular weight 2000).

[0072] Comparative Example 5

[0073] The preparation method of the silicon carbide ceramic heat exchange tube is basically the same as that in Example 6, except that the modified benzoxazine (prepared in Example 4) added to the components is replaced with an equal weight of the modified benzoxazine prepared by the following method:

[0074] The preparation method of modified benzoxazine is basically the same as that in Example 4, except that the terminal amino polyether (model ZED-601, number average molecular weight 600) in step N1 is replaced with an equimolar amount of terminal amino polyether (model ZD-123, number average molecular weight 230).

[0075] Comparative Example 6

[0076] The preparation method of the silicon carbide ceramic heat exchange tube is basically the same as that in Example 6, except that the modified benzoxazine (prepared in Example 4) added to the components is replaced with an equal weight of the modified benzoxazine prepared by the following method:

[0077] 600 ml of toluene and 15 g of paraformaldehyde were added to a reaction vessel and stirred for 30 min. Then, 0.1 mol of amino-terminated polyether (model ZED-601, number average molecular weight 600) and 0.22 mol of phenol were added sequentially. Under nitrogen protection, the mixture was heated to reflux and reacted for 20 h. The mixture was then cooled to 60 °C and distilled under reduced pressure for 3 h. 350 ml of a mixed solution of ethyl acetate and n-hexane (volume ratio 2:1) was added and stirred until dissolved. The mixture was kept at this temperature for 30 min and then cooled to 0 °C and allowed to stand for 2 h to precipitate. The precipitate was filtered and dried under vacuum at 50 °C for 12 h to obtain the modified benzoxazine monomer.

[0078] The amino-terminated polyethers ZED-601, ZD-123, and ZD-1200 used in this application are from Zibo Zhengda Polyurethane Co., Ltd.; the silicon carbide fine powder, model F1200, with an average particle size of 4μm, is from Weifang Kaihua Silicon Carbide Micro Powder Co., Ltd.; the silicon carbide coarse powder, with a particle size distribution of 10-50mm, is from Anyang Huatuo Metallurgy Co., Ltd.; and the carbon black, model N660, with a particle size distribution of 50-60nm, is from Shandong Zhongxiang New Materials Co., Ltd. Limited Company; the fly ash contains 56.1wt% SiO2, 26.6wt% Al2O3, 3.2wt% Fe2O3, 4.4wt% Na2O, 1.2wt% CaO, and 2.8wt% MgO, and is produced by Zhengzhou Jinyuan Fly Ash Co., Ltd.; the phenolic resin is model PF-214, produced by Shandong Chenghui New Materials Co., Ltd.; the amino-terminated silicone oil is model Cheersil 8110, produced by Suzhou Qitian New Materials Co., Ltd.

[0079] The apparent density, flexural strength and fracture toughness of the silicon carbide ceramic heat exchange tubes prepared in Examples 5-7 and Comparative Examples 1-6 were tested, and the results are shown in Table 1.

[0080] The sample preparation method was the same as that in the examples and comparative examples, except that a silicon carbide preform of 3 mm × 4 mm × 40 mm was obtained by changing the die of the extrusion nozzle and the cutting distance, while the other steps remained unchanged.

[0081] The apparent density test was conducted according to GB / T 25995-2010 standard, in which the immersion of the sample was carried out by the boiling method in 6.2.1.

[0082] The bending strength test was conducted in accordance with the GB / T 6569-2006 standard. A CMT-5105 microcomputer-controlled electronic universal testing machine was used to perform the three-point bending test on the specimen, with a span of 30 mm and a loading rate of 0.5 mm / min.

[0083] Fracture toughness testing was conducted according to GB / T 23806-2009 standard. The specimen was tested using the four-point bending method, with a lower span of 30 mm and an upper span of 10 mm.

[0084] Table 1 Performance Test Data

[0085]

[0086] As can be seen from Examples 5, 6 and 7 in Table 1, the silicon carbide ceramic heat exchange tube prepared by the present invention has excellent apparent density, bending strength and fracture toughness.

[0087] The silicon carbide ceramic heat exchanger tube prepared by this invention exhibits high density, flexural strength, and fracture toughness. The modifier added to the composition contains a linear polysiloxane structure and methoxysilane. The methoxysilane is converted to silanol groups in an aqueous ethanol solution, which then undergo a condensation reaction with the -Si-OH groups on the surface of the silicon carbide fine powder, grafting onto the powder surface and reducing interfacial defects and porosity, thereby improving the density and strength of the green body. The linear polysiloxane structure prevents the agglomeration of silicon carbide fine powder particles through steric hindrance. In contrast, the polysiloxane in the modifier used in Comparative Example 2 has a network structure with poor structural regularity, leading to a decrease in the mechanical properties of the ceramic after calcination.

[0088] The modified benzoxazine prepared in this invention contains a benzoxazine structure, polyether segments, and dynamic borate ester bonds. The benzoxazine structure undergoes a curing reaction with the ortho-position of phenolic hydroxyl groups in phenolic resin under heating conditions. The flexible polyether segments can absorb the shrinkage strain generated during the curing process through segmental movement, reducing the internal defect density and thus improving the mechanical properties of the final ceramic. The dynamic reversibility of the borate ester bonds allows them to preferentially break and recombine in stress concentration areas, thereby redistributing stress, avoiding excessive stress concentration, reducing the initiation of microcracks during curing, and releasing boron atoms as a sintering aid during high-temperature sintering, which is beneficial for densification. Boron atoms replace carbon sites in the silicon carbide lattice, inducing lattice distortion, hindering dislocation movement, and improving the flexural strength and fracture toughness of silicon carbide ceramics. The benzoxazine structure, polyether segments, and dynamic borate ester bonds in the modified benzoxazine work synergistically to improve the density, flexural strength, and fracture toughness of silicon carbide ceramics. In Comparative Example 4, the modified benzoxazine had longer polyether segments, resulting in lower crosslinking density and accelerated cracking during calcination, leading to a decrease in density. In Comparative Example 5, the modified benzoxazine had shorter polyether segments, resulting in reduced flexibility and an inability to effectively alleviate curing shrinkage stress, which in turn led to a decrease in the mechanical properties of the ceramic.

[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. However, any modifications, alterations, and variations made by those skilled in the art without departing from the scope of the present invention based on the disclosed technical content are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a silicon carbide ceramic heat exchanger tube, characterized in that, Includes the following steps: (1) Disperse the modifier in anhydrous ethanol, add silicon carbide fine powder and react to obtain modified silicon carbide fine powder; (2) Phenolic resin, modified benzoxazine and anhydrous ethanol are stirred and mixed, and carbon black, fly ash, modified silicon carbide fine powder and silicon carbide coarse powder are added in sequence and stirred and mixed. After aging, kneading, extrusion molding and drying, silicon carbide blank is obtained. (3) The silicon carbide blank is placed in a high-temperature furnace for heat treatment to obtain silicon carbide ceramic heat exchange tubes. The modifier is prepared by the following method: S1: Diphenylsilanediol reacts with 3-aminopropylmethyldimethoxysilane to form a linear polysiloxane. S2: A modifier is generated by reacting linear polysiloxane with γ-chloropropyltrimethoxysilane; In step S1, the molar ratio of diphenylsilanediol to 3-aminopropylmethyldimethoxysilane is (0.9-1):1; in step S2, the mass ratio of linear polysiloxane to γ-chloropropyltrimethoxysilane is 2:(0.8-1). The modified benzoxazine was prepared by the following method: N1: The amino-terminated polyether reacts with 3-chloro-1,2-propanediol to form a dipropanediol-modified polyether. N2: Dipropanediol-modified polyether reacts with 4-aminophenylboronic acid to generate borate ester-modified polyether. N3: Boronate-modified polyether reacts with phenol under the action of paraformaldehyde to generate modified benzoxazine; The structural formula of the modified benzoxazine is as follows: ； In step N1, the molar ratio of the terminal amino polyether to 3-chloro-1,2-propanediol is 1:2.05; in step N2, the molar ratio of the dipropanediol modified polyether to 4-aminophenylboronic acid is 1:2.1; in step N3, the molar ratio of the borate ester modified polyether to phenol is 1:2.

1.

2. The method for preparing a silicon carbide ceramic heat exchanger tube according to claim 1, characterized in that, In steps (1) to (2), the weight parts of each component added are as follows: 25-35 parts of silicon carbide fine powder, 50-60 parts of silicon carbide coarse powder, 10-12 parts of carbon black, 4-5 parts of fly ash, 0.5-0.8 parts of modifier, 8-10 parts of phenolic resin, and 4-6 parts of modified benzoxazine.

3. The method for preparing a silicon carbide ceramic heat exchanger tube according to claim 1, characterized in that, In step (1), the mass ratio of the modifier to anhydrous ethanol is 1:

200.

4. The method for preparing a silicon carbide ceramic heat exchanger tube according to claim 1, characterized in that, In step (3), the heat treatment process is to keep the temperature at 900-1100℃ for 1-2 hours and at 1600-1700℃ for 2-3 hours.

5. A silicon carbide ceramic heat exchange tube, characterized in that, It is prepared by the method according to any one of claims 1 to 4.

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