A method for preparing isotropic graphite material paste for thorium-based molten salt reactor

Abstract

The application discloses a preparation method of isotropic graphite material paste for a thorium-based molten salt reactor and belongs to the technical field of materials. The method comprises the following steps: S1, raw material selection: the additives comprise modified hyperbranched polyglycerol, bismaleimide-pyridine diamide bridging agent, zinc acetylacetonate and polyethylene glycol diacrylate; S2, dry powder preheating: the aggregate is preheated to 180 DEG C under nitrogen protection, the prepolymer and polyethylene glycol diacrylate are added, and dry mixing is carried out for 15 minutes; S3, first-time kneading: 70% of the total mass of bitumen is added, and kneading is carried out at a temperature of 110-130 DEG C for 30 minutes; S4, second-time kneading: the remaining 30% of the bitumen and the zinc acetylacetonate are added, the temperature is increased to 150-160 DEG C, and kneading is carried out for 40 minutes; and S5, paste cooling, crushing and collecting: the paste is transferred into a cooling and crushing pot, is ground into powder, is selected, and is batched. The application solves the problem of uneven mixing of the aggregate and the binder in the prior art.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of materials and relates to a preparation method of isotropic graphite material paste for a thorium-based molten salt reactor. BACKGROUND

[0002] As a representative of the fourth generation of advanced nuclear energy systems, the thorium-based molten salt reactor has become an important direction for future nuclear energy development due to its inherent safety, high nuclear fuel utilization rate and low radioactive waste production. In the thorium-based molten salt reactor, nuclear graphite, as a neutron moderator and reflector, needs to serve in an extreme environment of high temperature, strong radiation and molten salt corrosion for a long time, and its performance is directly related to the operating efficiency and safety of the reactor. In order to achieve efficient moderation of neutron energy and maintain the stability of the reactor core structure, nuclear graphite needs to have high purity, high thermal conductivity, excellent radiation resistance dimensional stability and isotropy, that is, its physical properties (such as thermal expansion coefficient and elastic modulus) are uniform in any direction, so as to avoid radiation-induced anisotropic stress concentration leading to material cracking failure.

[0003] The preparation of isotropic nuclear graphite is mainly related to the uniformity of its microstructure, and the paste preparation, as the source process of nuclear graphite preparation, directly determines the upper limit of the performance of the final material. In this process, the aggregate (such as isotropic coke powder) and the binder (such as coal tar pitch) are mixed under heating to form a plastic paste, which provides a basis for subsequent isostatic pressing. In the prior art, the preparation of isotropic nuclear graphite paste usually follows a relatively rough process mode: the core process is only to simply mechanically knead the aggregate (such as isotropic coke powder) and the binder (such as coal tar pitch) under heating, which relies on high shear force to forcibly break the macro-agglomeration of the materials, resulting in uneven mixing of the paste. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of isotropic graphite material paste for a thorium-based molten salt reactor, which solves the problem of uneven mixing of aggregate and binder in the paste preparation process.

[0005] The technical scheme adopted by the present application is as follows: a preparation method of isotropic graphite material paste for a thorium-based molten salt reactor, which is used to prepare nuclear graphite paste with D90 in the range of 90-110 μm and mass ratio of volatile matter between 15.5-17.0%, comprising the following steps:

[0006] S1, raw material selection: aggregate, binder and additive, the aggregate adopts isotropic secondary coke, D50 is 9-11 μm, mass ratio of ash content is <0.2%, mass ratio of sulfur content is <0.3%, and true density is 1.98-2.05 g / cm 3 ;

[0007] The binder is asphalt, wherein the mass ratio of ash is <0.05%, the mass ratio of volatile matter is <54%, the mass ratio of coking value is >61%, the mass ratio of softening point is 110-130 DEG C, the mass ratio of quinoline insoluble is 6-9%, and the mass ratio of toluene insoluble is 29-31%;

[0008] The additives include modified hyperbranched polyglycerol, bismaleimide-pyridine diamide bridging agent, zinc acetylacetonate and polyethylene glycol diacrylate;

[0009] S2, dry powder preheating: start the equipment, preheat the aggregate to 180 DEG C under nitrogen protection, add modified prepolymer and polyethylene glycol diacrylate, and dry mix for 15 minutes under normal pressure;

[0010] The prepolymer of the present application immediately undergoes reverse Diels-Alder reaction at 180 DEG C, and is dissociated into monomer components. The modified hyperbranched polyglycerol after dissociation forms hydrogen bond interaction with the oxygen-containing functional groups (carboxyl, phenolic hydroxyl, carbonyl) on the surface of the aggregate through the polyhydroxy structure, realizes chemical anchoring, and the bismaleimide-pyridine diamide bridging agent is adsorbed on the graphitized surface of the aggregate through pi-pi stacking interaction; the spatially uniform reactive sites for subsequent network formation are pre-set, and the risk of agglomeration of the additives is eliminated.

[0011] The polyethylene glycol diacrylate forms hydrogen bond interaction with the aggregate surface through the main chain ether oxygen group, and the flexible long chain spreads on the aggregate interface to form a dynamic lubricating layer. The lubricating layer reduces the van der Waals attraction between particles through steric hindrance effect, reduces the internal friction coefficient of the powder, improves the dispersion uniformity of the aggregate, and creates interface conditions for subsequent asphalt phase infiltration.

[0012] S3, first kneading: add 70% of the total mass of asphalt, and knead for 30 minutes under 0.5 MPa nitrogen pressure and at a temperature of 110-130 DEG C;

[0013] At this stage, the temperature ensures that the asphalt flows and infiltrates fully. After adding 70% of the asphalt, the asphalt phase begins to diffuse and infiltrate the surface of the aggregate under the action of mechanical shear force and temperature in the present application. The modified hyperbranched polyglycerol pre-adsorbed on the surface of the aggregate forms a compatible interface with the asphalt molecules through the lipophilic end group, reduces the wetting contact angle of the asphalt on the surface of the aggregate, and promotes the uniform spreading of the asphalt molecules on the surface of the aggregate. The mechanical shear force destroys the secondary agglomeration structure of the aggregate, and cooperates with the capillary penetration effect of the interface modification layer to make the asphalt phase penetrate into the interstitial space, and initially build the basic structure framework of the aggregate-asphalt composite system.

[0014] S4, second kneading: add the remaining 30% of the asphalt and zinc acetylacetonate, increase the temperature to 150-160 DEG C, maintain the nitrogen pressure at 0.8-1.0 MPa, and knead for 40 minutes;

[0015] The present application is in a "bond-dissociation-rebonding" dynamic equilibrium state under the continuous action of high temperature and high pressure shear field when the temperature rises to 150-160℃. At this time, the network structure has stress relaxation ability. When the local stress exceeds the threshold value, the covalent bond reversibly breaks and re-bonds at a lower energy position, achieving uniform dispersion of stress and adaptive rearrangement of structure, ensuring the isotropy of the paste system from the micro level.

[0016] Zinc acetylacetone is thermally decomposed above 150℃, releasing zinc ions as Lewis acid centers, forming a five-membered ring chelate coordination structure with the catechol groups of the modified hyperbranched polyglycerol, and coordinating with the nitrogen atoms of the pyridine diamide unit in the bismaleimide-pyridine diamide bridging agent; the rigidity of the coordination bond enhances the mechanical strength and high temperature stability of the system.

[0017] The ether oxygen groups of polyethylene glycol diacrylate competitively coordinate with zinc ions, adjusting the coordination bond strength, preventing the network from losing plastic deformation ability due to excessive crosslinking, maintaining the flowability and rearrangement ability of the system under high pressure shear, and ensuring the processability of the paste. Its flexible long chain structure acts as a molecular plasticizer, maintaining the toughness of the network under mechanical action.

[0018] S5, paste cooling, crushing and collection: transfer the paste to a cooling and crushing pot equipped with a pear-shaped cutter head, quickly cool and crush to below 30℃, grind, select and batch.

[0019] Further, the isotropic secondary coke is prepared from pitch coke as raw material, and the surface contains carboxyl, phenolic hydroxyl and carbonyl groups.

[0020] Further, the modified hyperbranched polyglycerol is prepared by the following method:

[0021] A. In a three-necked flask, add glycerol and trimethylolpropane, protect with nitrogen, melt the material uniformly, add potassium hydroxide as catalyst, heat and stir, the system gradually becomes viscous, connect the vacuum system, gradually heat and continue to react under the condition of pressure below 100Pa, after the reaction is completed, dissolve the product in acetone, precipitate with n-hexane, repeat this process three times, vacuum dry to obtain the first compound;

[0022] B. Dissolve furan-2-methanol in anhydrous tetrahydrofuran, cool in ice water bath, add 1,1'-carbonyldiimidazole in batches, control the temperature not to exceed 5℃, continue to react at 0℃ after adding, then react at room temperature, remove the solvent after the reaction is completed, to obtain the activated liquid;

[0023] C. Dissolve 3,4-dihydroxybenzoic acid in anhydrous N,N-dimethylformamide, add imidazole, cool in an ice water bath, dropwise add N,N-dimethylformamide solution containing tert-butyl dimethylsilyl chloride, keep the temperature below 10°C, after the addition, raise the temperature to room temperature, pour into ice water, extract with ethyl acetate, combine the organic phase, wash, dry, concentrate under reduced pressure to obtain solid product; dissolve the above solid product and N-hydroxysuccinimide in anhydrous dichloromethane, cool in an ice water bath, add N,N'-dicyclohexyl carbodiimide, react, filter, concentrate the filtrate, and purify by silica gel column chromatography to obtain activated solid;

[0024] D. Dissolve the first compound in anhydrous N,N-dimethylformamide, add anhydrous potassium carbonate, stir under nitrogen protection, add the activated liquid prepared in step B and the activated solid prepared in step C in sequence, raise the reaction system to 60°C, stir at this temperature for 24 hours, after the reaction is completed, cool to room temperature, filter, concentrate the filtrate to 1 / 3 of the original volume, then dropwise add to ice ethyl ether to precipitate, load the precipitate into a Soxhlet extractor, continuously extract with anhydrous ethanol, and vacuum dry to obtain the second compound;

[0025] E. Dissolve the second compound in anhydrous tetrahydrofuran, stir at room temperature under nitrogen protection, slowly dropwise add 1.0 mol / L tetrabutylammonium fluoride tetrahydrofuran solution, after the addition, continue to react at room temperature, concentrate the reaction liquid to dryness, dissolve the residue in methanol, pass through a strong acid cation exchange resin column, collect the effluent, concentrate, and fractionate by preparative gel permeation chromatography, collect the main fraction with a molecular weight distribution of 1.2, concentrate, and vacuum dry to obtain the modified hyperbranched polyglycerol.

[0026] Further, the bismaleimide-pyridine diamide bridging agent is prepared by the following method:

[0027] B1. In a three-necked flask, add 2,6-pyridinedicarboxylic acid and thionyl chloride, then add N,N-dimethylformamide, heat to reflux and react until the solid is completely dissolved, after the reaction is completed, distill under reduced pressure to obtain a light yellow solid, dissolve the light yellow solid in anhydrous tetrahydrofuran, cool to -5°C in an ice salt bath to obtain solution A; another solution containing ethylenediamine in tetrahydrofuran / water mixed solution is prepared, adjust the pH to 8-9, and cool to 0°C to obtain solution B; slowly dropwise add solution A to solution B under vigorous stirring, control the temperature not to exceed 5°C, keep the pH between 8-9, after the addition, continue to react in an ice bath, filter, wash, and vacuum dry to obtain the third compound;

[0028] B2, in a three-necked flask, 4,4'-diaminobiphenyl was dissolved in anhydrous N-methylpyrrolidone, cooled to 0°C under nitrogen protection, and then added with phosphorus triphenyl and pyridine. The temperature was kept at 0°C, and the third compound was added in batches, with the temperature controlled not to exceed 10°C. After the addition was completed, the temperature was slowly increased to room temperature, and the reaction was continued. The reaction solution was poured into ice water, and the precipitate was collected by filtration, washed, and vacuum dried to obtain the fourth compound;

[0029] B3, in a three-necked flask, the fourth compound was suspended in ethyl acetate and heated to reflux for reaction. The generated water was removed by a water trap during the reaction. After the reaction was completed, it was cooled to room temperature, and the precipitate was collected by filtration, washed with cold ethyl acetate, and vacuum dried. Then it was suspended in a mixture of acetic anhydride and anhydrous sodium acetate. Under nitrogen protection, the reaction was stirred. After the reaction was completed, it was cooled to room temperature, poured into ice water, and the solid was collected by filtration, washed, and purified by silica gel column chromatography. The main component was collected, concentrated, and recrystallized three times with acetonitrile to obtain the bismaleimide-pyridine diamide bridging agent.

[0030] Further, the prepolymer is obtained by polymerization of modified hyperbranched polyglycerol and bismaleimide-pyridine diamide bridging agent, and the specific preparation method is as follows:

[0031] C1, in a three-necked flask, modified hyperbranched polyglycerol and anhydrous N,N-dimethylformamide were added and dissolved under nitrogen protection. The temperature was increased to 60°C and kept constant to obtain solution C. The bismaleimide-pyridine diamide bridging agent was dissolved in anhydrous N,N-dimethylformamide to obtain solution D. Solution D was added dropwise to solution C, and nitrogen was continuously introduced. After the addition was completed, the reaction was continued at 60°C for 4 hours to obtain a mixed solution.

[0032] C2, the mixed solution was cooled to room temperature, and the p-benzenediol polymerization inhibitor was added. The concentrated solution was added dropwise into ice ethyl ether for precipitation. After standing and layering, the supernatant was poured off, and the bottom viscous product was collected. The precipitation operation was repeated three times, and the prepolymer was obtained by vacuum drying.

[0033] The application realizes controllable synchronous dissociation and uniform dispersion by inputting a prepolymer instead of directly inputting monomer forms of modified hyperbranched polyglycerol and bismaleimide-pyridine diamide bridging agent: after the prepolymer is input into the system as a whole, the modified hyperbranched polyglycerol and the bismaleimide-pyridine diamide bridging agent are dissociated at the same spatial position when the reverse Diels-Alder reaction occurs at a high temperature of 180 DEG C. The spatial correlation ensures that the two reaction components are co-located at a molecular level on the aggregate surface. In comparison, if the two monomers are input separately, even if the input ratio is accurately controlled, under the severe mechanical action of high-temperature dry mixing, the two components will have different diffusion rates and adsorption behaviors due to differences in molecular weight, polarity and surface energy, which will directly affect the uniformity and integrity of the dynamic network formed in the second kneading.

[0034] Further, the amount of the modified hyperbranched polyglycerol is 0.3%-0.8% by mass fraction of the aggregate, the amount of the bismaleimide-pyridine diamide bridging agent is 0.1%-0.4%, the amount of zinc acetylacetonate is 0.05%-0.15%, and the amount of polyethylene glycol dipolyacrylate is 0.5%-1.5%.

[0035] Further, the mass ratio of the aggregate to the binder is 78-82:22-18.

[0036] In summary, due to the adoption of the above technical solutions, the application has the following beneficial effects:

[0037] 1. A preparation method of an isotropic graphite material paste for a thorium-based molten salt reactor, which realizes uniform dispersion of two reaction components in the aggregate by preheating dry powder and utilizing the dissociation of modified hyperbranched polyglycerol and bismaleimide-pyridine diamide bridging agent at the same spatial position through reverse Diels-Alder reaction;

[0038] 2. The application realizes uniform dispersion of stress and self-adaptive rearrangement of structure by utilizing the stress relaxation ability of the network structure of the Diels-Alder reaction in the "bonding-dissociation-rebonding" dynamic balance state on the basis structure framework of the preliminary construction of the aggregate-asphalt composite system in the first kneading, ensures the isotropy of the paste system, and enables the aggregate and the binder to continuously optimize the spatial distribution in the kneading process, so as to finally achieve a highly uniform mixing state;

[0039] 3. The present application releases zinc ions by the second kneading acetylacetone zinc thermal decomposition, and forms a five-membered ring chelate coordination structure with the catechol group of the modified hyperbranched polyglycerol, and coordinates with the nitrogen atom of the pyridine diamide unit in the bismaleimide-pyridine diamide bridging agent, thereby enhancing the mechanical strength and high temperature stability of the system; the ether oxygen group of the polyethylene glycol diacrylate competes with zinc ions to coordinate, thereby adjusting the coordination bond strength, preventing the network from losing plastic deformation ability due to excessive crosslinking, maintaining the flowability and rearrangement ability of the system under high pressure shear, and ensuring the processability of the paste. BRIEF DESCRIPTION OF DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced as follows, and it should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor, wherein:

[0041] Figure 1 It is a block diagram of a preparation method of an isotropic graphite material paste for a thorium-based molten salt reactor. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application, that is, the described embodiments are only some embodiments of the present application, but not all embodiments. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0043] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0044] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0045] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0046] Example 1: As Figure 1 As shown in the preferred embodiment of the present invention, a method for preparing an isotropic graphite material paste for thorium-based molten salt reactors is provided. This method is used to prepare a nuclear graphite paste with a D90 in the range of 90-110 μm and a volatile matter mass ratio between 15.5-17.0%, and includes the following steps:

[0047] S1. Raw material selection: Aggregates, binders, and additives. The aggregates used are isotropic secondary coke with a D50 of 9-11 μm, an ash content of <0.2% by mass, a sulfur content of <0.3% by mass, and a true density of 1.98-2.05 g / cm³. 3 ;

[0048] The binder is asphalt, wherein the mass ratio of ash is <0.05%, the mass ratio of volatile matter is <54%, the mass ratio of coking value is >61%, the mass ratio of softening point is 110-130℃, the mass ratio of quinoline insoluble matter is 6-9%, and the mass ratio of toluene insoluble matter is 29-31%.

[0049] Additives include modified hyperbranched polyglycerol, bismaleimide-pyridine diamide bridging agent, zinc acetylacetone, and polyethylene glycol diacrylate;

[0050] S2. Dry powder preheating: Start the equipment and preheat the aggregate to 180°C under nitrogen protection. Add the prepolymer and polyethylene glycol diacrylate and dry mix for 15 minutes under normal pressure.

[0051] S3. First mixing: Add 70% of the total mass of asphalt and mix for 30 minutes under nitrogen pressure of 0.5MPa and temperature of 110-130℃.

[0052] S4, second kneading: adding the remaining 30% of bitumen and zinc acetylacetone, increasing the temperature to 150-160℃, maintaining the nitrogen pressure at 0.8-1.0 MPa, and kneading for 40 minutes;

[0053] S5, paste cooling, crushing and collecting: transferring the paste to a cooling and crushing pot equipped with a pear-shaped cutter head, rapidly cooling and crushing to below 30℃, grinding, selecting and batching.

[0054] The isotropic secondary coke is prepared from bitumen coke as raw material, and the surface contains carboxyl, phenolic hydroxyl and carbonyl.

[0055] The modified hyperbranched polyglycerol is prepared by the following method:

[0056] A, in a 2L three-necked flask equipped with a mechanical stirrer, a thermometer and a nitrogen inlet tube, 460g of glycerol and 67g of trimethylolpropane were added, nitrogen was introduced for protection, stirring and heating to 80℃ to melt the material uniformly, 4.2g of potassium hydroxide was added as catalyst, the temperature was slowly increased to 125℃, and the reaction was stirred at this temperature for 5 hours, the system gradually became viscous, the reaction system was connected to a vacuum system, the temperature was gradually increased to 140℃, and the reaction was continued for 3 hours under the condition of pressure below 100Pa, the reaction endpoint was judged by monitoring the acid value of the system (controlled at <2mgKOH / g), after the reaction was completed, the product was dissolved in 1000mL of acetone and precipitated with 2000mL of n-hexane, this process was repeated three times, and finally dried in a vacuum drying oven at 60℃ for 24 hours, to obtain the first compound;

[0057] B, in a 1L round-bottom flask, 98g of furan-2-methanol was dissolved in 500mL of anhydrous tetrahydrofuran, cooled to 0℃ in an ice-water bath, 162g of 1,1'-carbonyldiimidazole was added in batches, the temperature was controlled not to exceed 5℃, after addition, the reaction was continued at 0℃ for 2 hours, and then slowly increased to room temperature for 4 hours, the disappearance of raw materials was monitored by thin layer chromatography (developing agent: petroleum ether / ethyl acetate=2 / 1) during the reaction, after the reaction was completed, the solvent was removed by rotary evaporator, to obtain the activated liquid;

[0058] C. 154 g of 3,4-dihydroxybenzoic acid was dissolved in 800 mL of anhydrous N,N-dimethylformamide, 136 g of imidazole was added, and the solution was cooled to 0°C in an ice water bath. 200 mL of an N,N-dimethylformamide solution containing 301 g of tert-butyl dimethylsilyl chloride was slowly added dropwise, and the temperature was controlled to be lower than 10°C. After the addition was completed, the solution was allowed to warm to room temperature and reacted for 12 hours. The solution was poured into 2000 mL of ice water, and the organic phase was extracted with ethyl acetate (3 x 500 mL). The combined organic phase was washed with saturated brine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure to obtain a solid product. The solid product was dissolved in 1000 mL of anhydrous dichloromethane together with 115 g of N-hydroxysuccinimide, and the solution was cooled to 0°C in an ice water bath. 206 g of N,N'-dicyclohexylcarbodiimide was added, and the solution was reacted for 2 hours at 0°C and then for 10 hours while being allowed to warm to room temperature. The solution was filtered, and the filtrate was concentrated and purified by silica gel column chromatography (eluent: petroleum ether / ethyl acetate = 4 / 1) to obtain an activated solid;

[0059] D. 200 g of the first compound was dissolved in 1500 mL of anhydrous N,N-dimethylformamide, and 230 g of anhydrous potassium carbonate was added. The solution was stirred under nitrogen, and 255 g of the activated liquid prepared in step B and 247 g of the activated solid prepared in step C were sequentially added. The reaction system was warmed to 60°C, and the solution was stirred at this temperature for 24 hours. After the reaction was completed, the solution was cooled to room temperature, and the solid was removed by filtration. The filtrate was concentrated to 1 / 3 of the original volume, and then slowly added dropwise to 3000 mL of ice ethanol to precipitate. The precipitate was loaded into a Soxhlet extractor, and then continuously extracted with anhydrous ethanol for 48 hours. The extracted product was dried in a vacuum oven at 50°C for 48 hours to obtain a second compound.

[0060] E. 300 g of the second compound was dissolved in 1500 mL of anhydrous tetrahydrofuran, and the solution was stirred at room temperature under nitrogen. A 1.0 mol / L solution of tetrabutylammonium fluoride in tetrahydrofuran was slowly added dropwise, and the temperature was controlled to be lower than 30°C. After the addition was completed, the solution was allowed to react for 12 hours at room temperature. The completion of the deprotection was confirmed by TLC. The solution was concentrated to dryness, and the residue was dissolved in 1000 mL of methanol. The solution was passed through a strong acid cation exchange resin column to remove fluoride ions and other ionic impurities. The eluate was collected, concentrated, and fractionated by preparative gel permeation chromatography (mobile phase: tetrahydrofuran). The main fraction having a molecular weight distribution of 1.2 was collected, concentrated, and dried in a vacuum oven at 60°C for 72 hours to obtain a modified hyperbranched polyglycerol.

[0061] The bismaleimide-pyridine diamide bridging agent was prepared by the following method:

[0062] B1, in a 2L three-necked flask, 167g 2,6-pyridinedicarboxylic acid and 800mL thionyl chloride were added, then 2mL N,N-dimethylformamide was added, heated to reflux for 6 hours until the solid completely dissolved, after the reaction was completed, the excess thionyl chloride was removed by distillation under reduced pressure, to obtain a light yellow solid, the light yellow solid was dissolved in 500mL anhydrous tetrahydrofuran, cooled to -5℃ in an ice-salt bath to obtain solution A; another solution B was prepared by dissolving 120g ethylenediamine in a mixture of tetrahydrofuran / water (1 / 1, 800mL), and adjusting the pH to 8-9 with sodium hydroxide solution, and cooling to 0℃; under vigorous stirring, solution A was slowly added to solution B, the temperature was controlled not to exceed 5℃, and the pH was maintained between 8-9, after the addition was completed, the reaction was continued for 4 hours in an ice bath, filtered, the solid was washed with water, and vacuum dried to obtain the third compound;

[0063] B2, in a 2L three-necked flask, 184g 4,4'-diaminobiphenyl was dissolved in 1200mL anhydrous N-methylpyrrolidone, cooled to 0℃ under nitrogen protection, 310g triphenyl phosphate and 160mL pyridine were added, the temperature was maintained at 0℃, 242g of the third compound was added in batches, the temperature was controlled not to exceed 10℃, after the addition was completed, the reaction system was slowly raised to room temperature, and the reaction was continued for 24 hours, the reaction liquid was poured into 5000mL ice water, the precipitate was collected by filtration, washed with water, and vacuum dried to obtain the fourth compound;

[0064] B3, in a 2L three-necked flask, 430g of the fourth compound was suspended in 1500mL ethyl acetate with 196g maleic anhydride, heated to reflux for 8 hours, and the generated water was removed by a water trap during the reaction, after the reaction was completed, it was cooled to room temperature, the precipitate was collected by filtration, washed with cold ethyl acetate, and then suspended in a mixture of 1000mL acetic anhydride and 82g anhydrous sodium acetate, stirred at 75℃ for 6 hours under nitrogen protection, during which the completion of the reaction was judged by monitoring the appearance of the characteristic absorption of maleimide at 235nm by ultraviolet spectrum, after the reaction was completed, it was cooled to room temperature, poured into ice water, the solid was collected by filtration, washed with water, and purified by silica gel column chromatography (silica gel amount 2kg, eluent: ethyl acetate / petroleum ether = 1 / 2 gradient elution), the main components were collected, concentrated, and then recrystallized with acetonitrile for three times to obtain the bismaleimide-pyridine diamide bridging agent.

[0065] The prepolymer is obtained by polymerization of modified hyperbranched polyglycerol and bismaleimide-pyridine diamide bridging agent, and the specific preparation method is as follows:

[0066] C1, in a 1L three-necked flask equipped with a mechanical stirrer, a thermometer, a nitrogen inlet and outlet, modified hyperbranched polyglycerol and 400mL of anhydrous N,N-dimethylformamide were added, stirred and dissolved under nitrogen protection, heated to 60℃ and kept constant, to obtain solution C; bismaleimide-pyridine diamide bridging agent was dissolved in 100mL of anhydrous N,N-dimethylformamide to obtain solution D, which was slowly added to solution C through a constant pressure dropping funnel, the dropping speed was controlled at 2-3mL / min, the reaction temperature was kept at 60±2℃ during the dropping process, and nitrogen protection was continuously supplied, after the dropping was completed, the reaction was continued at 60℃ for 4 hours to obtain a mixed solution;

[0067] C2, the mixed solution was cooled to room temperature, hydroquinone polymerization inhibitor was added, and the concentrated solution was concentrated to 1 / 3 of the original volume at 50℃ and -0.095MPa using a rotary evaporator, then the concentrated solution was slowly added to 2000mL of vigorously stirred ice ether to precipitate, after standing and separating, the supernatant was decanted, and the bottom viscous product was collected, the precipitation operation was repeated three times to ensure complete removal of unreacted monomers and solvents, and then the product was transferred to a vacuum drying oven and dried at 40℃ and -0.1MPa for 48 hours to obtain a modified prepolymer.

[0068] The amount of the modified hyperbranched polyglycerol was 0.6%, the amount of the bismaleimide-pyridine diamide bridging agent was 0.25%, the amount of zinc acetylacetonate was 0.1%, and the amount of polyethylene glycol diacrylate was 1.0%.

[0069] The mass ratio of the aggregate to the binder was 80:20.

[0070] Example 2: This example was based on example 1, and different from example 1 was that the amount of the modified hyperbranched polyglycerol was 0.3%, the amount of the bismaleimide-pyridine diamide bridging agent was 0.1%, the amount of zinc acetylacetonate was 0.05%, and the amount of polyethylene glycol diacrylate was 0.5%. The rest was the same.

[0071] Example 3: This example was based on example 1, and different from example 1 was that the amount of the modified hyperbranched polyglycerol was 0.8%, the amount of the bismaleimide-pyridine diamide bridging agent was 0.4%, the amount of zinc acetylacetonate was 0.15%, and the amount of polyethylene glycol diacrylate was 1.5%. The rest was the same.

[0072] Example 4: This example was based on example 2, and different from example 2 was that the mass ratio of the aggregate to the binder was 78:22. The rest was the same.

[0073] Example 5: This example is based on Example 2, except that in this example the mass ratio of the aggregate to the binder is 82: 18. The rest is the same as Example 2.

[0074] Comparative Example 1: This comparative example is based on Example 1, except that in this comparative example the modified hyperbranched polyglycerol does not introduce furan groups. The rest is the same as Example 1.

[0075] The modified hyperbranched polyglycerol is prepared by the following method:

[0076] A, in a 2L three-necked flask equipped with a mechanical stirrer, a thermometer and a nitrogen inlet tube, 460g of glycerol and 67g of trimethylolpropane were added, and nitrogen was introduced for protection. The material was stirred and heated to 80°C to melt uniformly, 4.2g of potassium hydroxide was added as catalyst, and the temperature was slowly raised to 125°C. The reaction was stirred at this temperature for 5 hours. The system gradually became viscous. The reaction system was connected to a vacuum system, and the temperature was gradually raised to 140°C. The reaction was continued for 3 hours under the condition of pressure lower than 100Pa. The reaction endpoint was judged by monitoring the acid value (controlled at <2mgKOH / g). After the reaction was completed, the product was dissolved in 1000mL of acetone and precipitated with 2000mL of n-hexane. This process was repeated three times. Finally, it was dried in a vacuum drying oven at 60°C for 24 hours to obtain the first compound;

[0077] B, 154g of 3,4-dihydroxybenzoic acid was dissolved in 800mL of anhydrous N,N-dimethylformamide, 136g of imidazole was added, and the ice water bath was cooled to 0°C. 200mL of N,N-dimethylformamide solution containing 301g of tert-butyl dimethylchlorosilane was slowly added, and the temperature was controlled below 10°C. After the addition was completed, the temperature was raised to room temperature and reacted for 12 hours. It was poured into 2000mL of ice water and extracted with ethyl acetate (3×500mL). The combined organic phase was washed with saturated brine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure to obtain a solid product. The solid product was dissolved in 1000mL of anhydrous dichloromethane with 115g of N-hydroxysuccinimide, cooled to 0°C in an ice water bath, and 206g of N,N'-dicyclohexyl carbodiimide was added. After reacting at 0°C for 2 hours, the temperature was raised to room temperature and the reaction was continued for 10 hours. It was filtered, the filtrate was concentrated, and then purified by silica gel column chromatography (eluent: petroleum ether / ethyl acetate=4 / 1) to obtain the activated solid.

[0078] C. Dissolve 200 g of the first compound in 1500 mL of anhydrous N,N- dimethylformamide, add 230 g of anhydrous potassium carbonate, stir under nitrogen protection, add 247 g of the activated solid prepared in step B, warm the reaction system to 60°C, and stir at this temperature for 24 hours. After the reaction is completed, cool the reaction liquid to room temperature, filter to remove the solid, concentrate the filtrate to 1 / 3 of the original volume, and slowly drop into 3000 mL of ice ethyl ether to precipitate. Put the precipitate into a Soxhlet extractor, continuously extract with anhydrous ethanol for 48 hours, and dry in a vacuum drying oven at 50°C for 48 hours to obtain the second compound;

[0079] D. Dissolve 300 g of the second compound in 1500 mL of anhydrous tetrahydrofuran, stir at room temperature under nitrogen protection, slowly drop 1.0 mol / L of tetrabutylammonium fluoride in tetrahydrofuran solution, control the dropping speed to keep the temperature below 30°C, continue to react at room temperature for 12 hours after the addition is completed, monitor the deprotection completion by TLC, concentrate the reaction liquid to dryness, dissolve the residue in 1000 mL of methanol, remove fluoride ions and other ionic impurities by passing through a strong acid cation exchange resin column, collect the effluent, concentrate, and fractionate by preparative gel permeation chromatography (mobile phase: tetrahydrofuran), collect the main fraction with a molecular weight distribution of 1.2, and concentrate and dry in a vacuum drying oven at 60°C for 72 hours to obtain the modified hyperbranched polyglycerol.

[0080] Comparative Example 2: This comparative example is based on Example 1, except that the modified hyperbranched polyglycerol in this comparative example does not introduce o-dihydroxyphenyl groups. The rest is the same.

[0081] The modified hyperbranched polyglycerol is prepared by the following method:

[0082] A. In a 2L three-necked flask equipped with a mechanical stirrer, a thermometer, and a nitrogen inlet tube, add 460 g of glycerol and 67 g of trimethylolpropane, protect with nitrogen, stir and warm to 80°C to melt the material uniformly, add 4.2 g of potassium hydroxide as a catalyst, slowly warm to 125°C, and stir at this temperature for 5 hours. Gradually warm the system to 140°C under vacuum, and continue to react for 3 hours under a pressure of less than 100 Pa. Determine the reaction endpoint by monitoring the acid value of the system (control at <2 mgKOH / g). After the reaction is completed, dissolve the product in 1000 mL of acetone, precipitate with 2000 mL of n-hexane, repeat this process three times, and finally dry in a vacuum drying oven at 60°C for 24 hours to obtain the first compound;

[0083] B. In a 1 L round bottom flask, 98 g of furan-2-methanol was dissolved in 500 mL of anhydrous tetrahydrofuran, cooled to 0 °C in an ice water bath, 162 g of 1,1'- carbonyldiimidazole was added in batches, the temperature was controlled not to exceed 5 °C, after the addition was completed, the reaction was continued at 0 °C for 2 hours, and then slowly increased to room temperature for 4 hours. During the reaction, the disappearance of the raw material was monitored by thin layer chromatography (developing agent: petroleum ether / ethyl acetate = 2 / 1). After the reaction was completed, the solvent was removed by a rotary evaporator to obtain an activated liquid;

[0084] C. 200 g of the first compound was dissolved in 1500 mL of anhydrous N,N- dimethylformamide, 230 g of anhydrous potassium carbonate was added, stirred under nitrogen protection, 255 g of the activated liquid prepared in step B was added, the reaction system was heated to 60 °C, and stirred at this temperature for 24 hours. After the reaction was completed, the reaction liquid was cooled to room temperature, the solid was removed by filtration, the filtrate was concentrated to 1 / 3 of the original volume, and then slowly added to 3000 mL of ice ethanol to precipitate. The precipitate was loaded into a Soxhlet extractor, continuously extracted with anhydrous ethanol for 48 hours, and then dried in a vacuum drying oven at 50 °C for 48 hours to obtain the second compound;

[0085] D. 300 g of the second compound was dissolved in 1500 mL of anhydrous tetrahydrofuran, stirred at room temperature under nitrogen protection, 1.0 mol / L tetrabutylammonium fluoride tetrahydrofuran solution was slowly added, the dropping speed was controlled to keep the temperature below 30 °C, after the addition was completed, the reaction was continued at room temperature for 12 hours, the deprotection was completed by TLC monitoring, the reaction liquid was concentrated to dryness, the residue was dissolved in 1000 mL of methanol, the fluoride ions and other ionic impurities were removed by passing through a strong acid cation exchange resin column, the effluent was collected, concentrated and fractionated by preparative gel permeation chromatography (mobile phase: tetrahydrofuran), the main fraction with a molecular weight distribution of 1.2 was collected, concentrated and dried in a vacuum drying oven at 60 °C for 72 hours to obtain the modified hyperbranched polyglycerol.

[0086] Comparative Example 3: This comparative example is based on Example 1, except that the bismaleimide-pyridine diamide bridging agent in this comparative example only has a bismaleimide part. The rest is the same.

[0087] The bismaleimide-pyridine diamide bridging agent was prepared by the following method:

[0088] B1, in a 1L three-necked flask equipped with a mechanical stirrer, a thermometer and a reflux condenser, 198g of 4,4'-diaminodiphenylmethane and 500mL of N,N-dimethylformamide were added, stirred to dissolve under nitrogen protection, cooled to 0-5℃, 200mL of N,N-dimethylformamide solution containing 196g of maleic anhydride was added dropwise slowly, the temperature was controlled not to exceed 10℃, after the addition was completed, the reaction was continued at 0-5℃ for 2 hours, then 202g of triethylamine was added, the reaction was carried out at room temperature for 4 hours, poured into 2000mL of ice water, the precipitate was collected by filtration, washed with water until neutral, the wet filter cake was resuspended in a mixture of 500mL of acetic anhydride and 50g of anhydrous sodium acetate, heated to 75-80℃ to reflux for 6 hours, after the reaction was completed, it was cooled to room temperature, poured into 3000mL of ice water, the solid was collected by filtration, recrystallized with ethanol three times to obtain the bismaleimide-pyridine diamide bridging agent.

[0089] Comparative Example 4: This comparative example is based on Example 1, except that in this comparative example, the bismaleimide-pyridine diamide bridging agent only has a pyridine diamide part. The rest is the same as Example 1.

[0090] The bismaleimide-pyridine diamide bridging agent was prepared by the following method:

[0091] B1, in a 1L three-necked flask equipped with a mechanical stirrer, a thermometer and a reflux condenser, 198g of 4,4'-diaminodiphenylmethane and 500mL of N,N-dimethylformamide were added, stirred to dissolve under nitrogen protection, cooled to 0-5℃, 200mL of N,N-dimethylformamide solution containing 196g of maleic anhydride was added dropwise slowly, the temperature was controlled not to exceed 10℃, after the addition was completed, the reaction was continued at 0-5℃ for 2 hours, then 202g of triethylamine was added, the reaction was carried out at room temperature for 4 hours, poured into 2000mL of ice water, the precipitate was collected by filtration, washed with water until neutral, the wet filter cake was resuspended in a mixture of 500mL of acetic anhydride and 50g of anhydrous sodium acetate, heated to 75-80℃ to reflux for 6 hours, after the reaction was completed, it was cooled to room temperature, poured into 3000mL of ice water, the solid was collected by filtration, recrystallized with ethanol three times to obtain the bismaleimide-pyridine diamide bridging agent.

[0092] Comparative Example 5: This comparative example is based on Example 1, except that in this comparative example, the additive does not include modified hyperbranched polyglycerol. The rest is the same as Example 1.

[0093] Comparative Example 6: This comparative example is based on Example 1, except that in this comparative example, the additive does not include the bismaleimide-pyridine diamide bridging agent. The rest is the same as Example 1.

[0094] Comparative Example 7: This comparative example is based on Example 1, except that the additive does not include zinc acetylacetonate in this comparative example. The rest is the same.

[0095] Comparative Example 8: This comparative example is based on Example 1, except that the additive does not include polyethylene glycol diacrylate in this comparative example. The rest is the same.

[0096] Comparative Example 9: This comparative example is based on Example 1, except that the preparation method of the isotropic graphite material paste for a thorium-based molten salt reactor provided in this comparative example does not add a prepolymer, but directly adds a modified hyperbranched polyglycerol and a bismaleimide-pyridine diamide bridging agent, including the following steps:

[0097] S1, raw material selection: aggregate, binder and additive, the aggregate uses isotropic secondary coke, D50 is 9-11 μm, ash content is <0.2%, sulfur content is <0.3%, true density is 1.98-2.05 g / cm 3 ;

[0098] The binder is asphalt, wherein the ash content is <0.05%, the volatile content is <54%, the coking value is >61%, the softening point is 110-130℃, the quinoline insolubles are 6-9%, and the toluene insolubles are 29-31%;

[0099] The additive includes modified hyperbranched polyglycerol, bismaleimide-pyridine diamide bridging agent, zinc acetylacetonate, and polyethylene glycol diacrylate;

[0100] S2, dry powder preheating: start the equipment, preheat the aggregate to 180℃ under nitrogen protection, add modified hyperbranched polyglycerol, bismaleimide-pyridine diamide bridging agent, and polyethylene glycol diacrylate, and dry mix for 15 minutes under normal pressure;

[0101] S3, first kneading: add 70% of the total mass of asphalt, knead for 30 minutes at 0.5 MPa nitrogen pressure and a temperature of 110-130℃;

[0102] S4, second kneading: add the remaining 30% of the asphalt and zinc acetylacetonate, increase the temperature to 150-160℃, maintain the nitrogen pressure at 0.8-1.0 MPa, and knead for 40 minutes;

[0103] S5, paste cooling, crushing and collection: transfer the paste to a cooling and crushing pot equipped with a pear-shaped cutter head, quickly cool and crush to below 30℃, grind the powder, select the powder, and batch. The rest is the same.

[0104] Comparative Example 10: This comparative example is based on Example 1, except that the comparative example provides a preparation method of a paste of isotropic graphite material for a thorium-based molten salt reactor, which only performs one kneading, the kneading temperature is 110-130°C, and includes the following steps:

[0105] S1, raw material selection: aggregate, binder and additive, the aggregate uses isotropic secondary coke, the D50 is 9-11 pm, the ash content is <0.2%, the sulfur content is <0.3%, the true density is 1.98-2.05 g / cm 3 ;

[0106] The binder is pitch, wherein the ash content is <0.05%, the volatile content is <54%, the coking value is >61%, the softening point is 110-130°C, the quinoline insolubles are 6-9%, and the toluene insolubles are 29-31%;

[0107] The additive includes modified hyperbranched polyglycerol, bismaleimide-pyridine diamide bridge coupling agent, zinc acetylacetonate, and polyethylene glycol diacrylate;

[0108] S2, dry powder preheating: start the equipment, preheat the aggregate to 180°C under nitrogen protection, add the prepolymer and polyethylene glycol diacrylate, and dry mix for 15 minutes under normal pressure;

[0109] S3, kneading: add pitch and zinc acetylacetonate, and knead for 70 minutes at a nitrogen pressure of 0.8-1.0 MPa and a temperature of 110-130°C;

[0110] S4, paste cooling, crushing and collection: transfer the paste to a cooling and crushing pot equipped with a pear-shaped cutter head, rapidly cool and crush to below 30°C, grind the powder, select the powder, and batch. The rest is consistent.

[0111] Comparative Example 11: This comparative example is based on Example 1, except that the comparative example provides a preparation method of a paste of isotropic graphite material for a thorium-based molten salt reactor, which only performs one kneading, the kneading temperature is 150-160°C, and includes the following steps:

[0112] S1, raw material selection: aggregate, binder and additive, the aggregate uses isotropic secondary coke, the D50 is 9-11 pm, the ash content is <0.2%, the sulfur content is <0.3%, the true density is 1.98-2.05 g / cm 3 ;

[0113] The binder is pitch, wherein the ash content is <0.05%, the volatile content is <54%, the coking value is >61%, the softening point is 110-130°C, the quinoline insolubles are 6-9%, and the toluene insolubles are 29-31%;

[0114] The additives include modified hyperbranched polyglycerol, bismaleimide-pyridine diamide bridging agent, zinc acetylacetonate, polyethylene glycol diacrylate;

[0115] S2, dry powder preheating: start the equipment, preheat the aggregate to 180°C under nitrogen protection, add the prepolymer and polyethylene glycol diacrylate, and dry mix for 15 minutes under normal pressure;

[0116] S3, kneading: add asphalt and zinc acetylacetonate, and knead for 70 minutes under a nitrogen pressure of 0.8-1.0 MPa and a temperature of 150-160°C;

[0117] S4, paste cooling, crushing and collection: transfer the paste to a cooling and crushing pot equipped with a pear-shaped cutter head, rapidly cool and crush to below 30°C, grind the powder, select the powder, and batch. The rest is consistent.

[0118] Comparative Example 12: This comparative example is based on Example 1, except that in this comparative example, a preparation method of a paste of an isotropic graphite material for a thorium-based molten salt reactor is provided, and no additives are added, including the following steps:

[0119] S1, selection of raw materials: aggregate, binder, the aggregate uses isotropic secondary coke, D50 is 9-11 μm, ash content is <0.2%, sulfur content is <0.3%, and true density is 1.98-2.05 g / cm 3 ;

[0120] The binder is asphalt, wherein the ash content is <0.05%, the volatile content is <54%, the coking value is >61%, the softening point is 110-130°C, the quinoline insolubles are 6-9%, and the toluene insolubles are 29-31%;

[0121] S2, dry powder preheating: start the equipment, preheat the aggregate to 180°C under nitrogen protection, and dry mix for 15 minutes under normal pressure;

[0122] S3, first kneading: add 70% of the total mass of asphalt, and knead for 30 minutes under a nitrogen pressure of 0.5 MPa and a temperature of 110-130°C;

[0123] S4, second kneading: add the remaining 30% of the asphalt, increase the temperature to 150-160°C, maintain the nitrogen pressure at 0.8-1.0 MPa, and knead for 40 minutes;

[0124] S5, paste cooling, crushing and collection: transfer the paste to a cooling and crushing pot equipped with a pear-shaped cutter head, rapidly cool and crush to below 30°C, grind the powder, select the powder, and batch. The rest is consistent.

[0125] Comparative Example 13: This comparative example is based on Example 1, except that in this comparative example, the preparation method of the isotropic graphite material paste for a thorium-based molten salt reactor provided in this comparative example does not add any additives and directly kneads the aggregate and the binder, including the following steps:

[0126] S1, raw material selection: aggregate, binder, the aggregate uses isotropic secondary coke, D50 is 9-11 μm, ash content is <0.2%, sulfur content is <0.3%, true density is 1.98-2.05 g / cm 3 ;

[0127] The binder is pitch, wherein the ash content is <0.05%, the volatile content is <54%, the coking value is >61%, the softening point is 110-130°C, the quinoline insolubles are 6-9%, and the toluene insolubles are 29-31%;

[0128] S2, kneading: add the aggregate and the pitch, raise the temperature to 150-160°C, maintain the nitrogen pressure at 0.8-1.0 MPa, and knead for 70 minutes;

[0129] S3, paste cooling, crushing, and collection: transfer the paste to a cooling and crushing pot equipped with a pear-shaped cutter head, rapidly cool and crush to below 30°C, grind the powder, select the powder, and batch. The rest is the same.

[0130] Test Example 1: The pastes obtained in Examples 1-5 and Comparative Examples 1-13 are subjected to uniformity testing; the results are shown in Table 1.

[0131] The test indicators and methods are as follows:

[0132] 1. Volatile content determination: each group of pastes is systematically sampled according to the grid method, using a 5x4 matrix distribution, a total of 20 sample points, 3-5 g of paste is taken from each sampling point using a special sampler, and immediately sealed for storage; each sample is rapidly crushed to 1-2 mm particles, 1.00 g of sample is accurately weighed into a pre-weighed quartz crucible, the initial weight W1 is recorded, the sample is placed into a preheated heating furnace to 255±2°C, high-purity nitrogen (purity ≥99.999%) is introduced, the flow rate is 50±5 mL / min, and accurate heating is performed for 30 minutes. After cooling and weighing, it is immediately transferred to a desiccator to cool to room temperature, the weight after heating W2 is accurately weighed, the volatile content is calculated: V(%) = (W1-W2) / W1x100%, the average value and standard deviation of 20 samples are calculated.

[0133] 2. Microscopic analysis: Take about 10 g of the paste sample, vacuum impregnate with low viscosity epoxy resin, keep for 30 minutes under 0.1 MPa vacuum degree to ensure full penetration, and then polish with (320, 600, 1200, 2000 mesh) sandpaper in turn, followed by polishing with (3, 1, 0.25 μm) diamond polishing agent, and finally mirror polishing with 0.05 μm silica suspension, observe the SEM image using a field emission scanning electron microscope, randomly select 10 fields of view on each sample, collect one 500x and one 1000x image for each field of view, and score the microscopic uniformity; the scoring criteria are as follows: 9-10 points: extremely uniform aggregate distribution, no visible agglomeration, and complete and continuous asphalt coating; 8-9 points: uniform aggregate distribution, occasional slight agglomeration (<2% area), and good asphalt coating; 7-8 points: relatively uniform aggregate distribution, a small amount of agglomeration (2-5% area), and basically complete asphalt coating; 6-7 points: basically uniform aggregate distribution, obvious agglomeration (5-10% area), and local defects in asphalt coating; 5-6 points: uneven aggregate distribution, more agglomeration (10-15% area), and incomplete asphalt coating; and 1-5 points: severely uneven aggregate distribution, a large amount of agglomeration (>15% area), and very poor asphalt coating.

[0134] 3. Aggregate agglomeration index by image analysis: use Image Pro Plus software to perform threshold segmentation on the image, separate the aggregate phase (light area) from the asphalt phase (dark area), perform binary processing, set the aggregate area as white and the background as black, set the theoretical minimum area Amin of a single aggregate particle, identify and mark all connected regions, calculate the area Ai of each connected region, and the agglomeration index = Σ(Ai) / Σ(Amin x Ni), where Ni is the theoretical particle number.

[0135] Table 1: Paste uniformity detection

[0136]

[0137] According to the data in Table 1, the present application can effectively improve the mixing uniformity of the aggregate and the binder.

[0138] Test Example 2: The pastes obtained in Examples 1-5 and Comparative Examples 1-13 were isostatically pressed (200 MPa, pressure holding for 30 min), and the green bodies with a size of Φ100 x 150 mm were subjected to performance testing: the results are shown in Table 2.

[0139] The test indicators and methods are as follows:

[0140] 1. Density uniformity: 4 layers in axial direction (25mm, 50mm, 75mm, 125mm from end face), 3 points in radial direction (center, 1 / 2 radius, 5mm from edge), total 12 measurement points, mark the measurement position, density measurement by Archimedes method, using deionized water as medium, first measure the weight in air W1, then measure the weight in water W2, calculate the density p = W1 / (W1-W2) x pwater, water temperature control: 23±0.5℃, pwater=0.9975g / cm3, calculate the average density and relative deviation.

[0141] 2. CT pore distribution analysis: microfocus X-ray CT system (Zeiss Xradia 520 Versa) scans the green body sample, scanning conditions: voltage 120 kV, power 10W, resolution 5.0μm / voxel, exposure time 2 seconds / projection, total projection number 1600; the obtained image is reconstructed in three dimensions using the Feldkamp algorithm, beam hardening correction and annular artifact elimination are performed, Otsu automatic threshold method is used to distinguish pores and matrix, all connected pores are identified, volume≥10 voxels, calculate the porosity, pore size distribution and pore sphericity; the reconstructed volume is divided into 64 identical sub-regions (4x4x4), the porosity of each sub-region is calculated, the porosity gradient is calculated, the CT pore distribution rating is performed, the standard is as follows: excellent: uniform pore distribution, no local aggregation, porosity gradient≤15%; good: slight pore aggregation, porosity gradient 16-25%, no obvious defects; medium: obvious pore aggregation, porosity gradient 26-35%, local defects; poor: severe pore aggregation or formation of connected pore channels, porosity gradient>35%.

[0142] Table 2 Green body performance test

[0143]

[0144] According to the data in Table 2, the green body prepared by isostatic pressing of the paste prepared by the present application has a quality significantly higher than that of the green body prepared by directly kneading the aggregate and the binder.

[0145] Test Example 3: After isostatic pressing of the paste obtained in Examples 1-5 and Comparative Examples 1-13 to obtain a green body, heat treatment: carbonization (800℃) + graphitization (2500℃) to obtain a final product, nuclear graphite material, performance test of the nuclear graphite material; the results are shown in Table 3.

[0146] Test index and method are as follows:

[0147] 1. Anisotropy test: 6 axial and radial samples are taken from the product after graphitization, sample size: Φ6.0±0.1mm×25.0±0.2mm, parallelism of both ends ≤0.01mm, perpendicularity ≤0.02mm, surface roughness Ra≤0.8μm, test conditions: instrument: horizontal push rod thermal dilatometer; temperature range: room temperature to 500℃; heating rate: 3℃ / min; protective atmosphere: high-purity helium (purity ≥99.999%), flow rate 50mL / min; calibration standard: sapphire standard sample; the sample is loaded into a quartz sample tube, ensuring good contact, and heated at a rate of 3℃ / min, and the length change is recorded continuously, each sample is tested 3 times, the average value is taken, and the average linear thermal expansion coefficient and anisotropy ratio are calculated;

[0148] 2. Mechanical property test: test the three-point bending strength according to ASTM C1161, sample size: 10×10×80mm, 10 samples per group, surface precision grinding, corner chamfering 0.5mm; test conditions: testing machine: universal material testing machine; loading rate: 0.5mm / min; indenter radius: 5mm; support radius: 2mm; data acquisition frequency: 100Hz; test steps: accurately measure the sample size (accuracy 0.01mm), place the sample in the center, ensure uniform contact with the support, pre-load to 10N, eliminate gap, load at a constant rate until the sample breaks, record the maximum load, and calculate the bending strength;

[0149] 3. Thermal conductivity test: sample size: Φ12.7±0.1mm×2.5±0.1mm, parallelism of both sides ≤0.005mm, surface polished to mirror finish; test conditions: instrument: laser flash method thermal conductivity instrument; temperature range: 25-500℃ (interval 100℃); test environment: high-purity argon protection; data acquisition: test 5 times at each temperature point; test steps: spray a thin layer of graphite on both sides of the sample to improve heat absorption efficiency, heat at the test temperature for 10 minutes, record the sample back temperature rise curve, calculate the thermal diffusivity using the Cowan model, and calculate the thermal conductivity;

[0150] 4. Ash content determination: test conditions: instrument: high-temperature muffle furnace; temperature: 950±20℃; atmosphere: air; crucible: quartz crucible (previously calcined at 950℃ to constant weight); test steps: accurately weigh 5.000±0.001g of graphite sample into the quartz crucible which has been constant weight, calcine at 950℃ for 6 hours until completely ashed, weigh the residue after cooling, and calculate the ash content: Ash (%) = (residue weight / sample weight)×100%.

[0151] Table 3 Properties of nuclear graphite materials

[0152]

[0153] In combination with the data in Table 3, it can be seen that the anisotropy of the core graphite prepared by the paste of the application is closer to 1, which indicates that the isotropic degree of the material is high.

[0154] The above merely provides the preferred embodiment of the application, and is not intended to limit the protection scope of the application. Any modification, equivalent replacement and improvement made by any person skilled in the art within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A method for producing a paste of isotropic graphite material for a thorium-based molten salt reactor, characterized by, The method is used for preparing the core graphite paste with D90 in the range of 90-110 μm and mass ratio of volatile matter in the range of 15.5-17.0%, and comprises the following steps: S1, raw material selection: aggregate, binder and additive, the aggregate adopts isotropic secondary coke, the isotropic secondary coke is prepared by taking pitch coke as raw material, the surface contains carboxyl, phenolic hydroxyl and carbonyl, D50 is 9-11 μm, the mass ratio of ash content is <0.2%, the mass ratio of sulfur content is <0.3%, the true density is 1.98-2.05 g / cm 3 ; The binder is pitch, wherein the mass ratio of ash is <0.05%, the mass ratio of volatile matter is <54%, the mass ratio of coking value is >61%, the mass ratio of softening point is 110-130 ℃, the mass ratio of quinoline insolubles is 6-9%, and the mass ratio of toluene insolubles is 29-31%; The additives include modified hyperbranched polyglycerol, bismaleimide-pyridine diamide bridge agent, zinc acetylacetonate and polyethylene glycol diacrylate; S2, dry powder preheating: start the equipment, preheat the aggregate to 180 ℃ under the protection of nitrogen, add the prepolymer and polyethylene glycol diacrylate, and dry mix for 15 minutes under normal pressure; the prepolymer is obtained by polymerization of modified hyperbranched polyglycerol and bismaleimide-pyridine diamide bridge agent; S3, first-time kneading: add 70% of the total mass of pitch, and knead for 30 minutes under the nitrogen pressure of 0.5 MPa and the temperature of 110-130 ℃; S4, second-time kneading: add the remaining 30% of pitch and zinc acetylacetonate, increase the temperature to 150-160 ℃, maintain the nitrogen pressure at 0.8-1.0 MPa, and knead for 40 minutes; S5, paste cooling, crushing and collecting: transfer the paste to a cooling and crushing pot equipped with a pear-shaped cutter head, rapidly cool and crush to below 30 ℃, grind, select and batch.

2. The method of producing an isotropic graphite material paste for a thorium-based molten salt reactor according to claim 1, characterized by, The modified hyperbranched polyglycerol is prepared by the following method: A, in a three-necked flask, glycerol and trimethylolpropane are added, nitrogen is introduced for protection, the materials are uniformly melted, potassium hydroxide is added for catalysis, and the system is gradually thickened by heating and stirring; a vacuum system is connected, the temperature is gradually increased, and the reaction is continued under the condition that the pressure is lower than 100 Pa; after the reaction is completed, the product is dissolved in acetone, and purified by precipitation with n-hexane; this process is repeated three times, and vacuum drying is performed to obtain a first compound; B, furan-2-methanol is dissolved in anhydrous tetrahydrofuran, an ice-water bath is used for cooling, 1,1'-carbonyldiimidazole is added in batches, the temperature is controlled to be not higher than 5 ℃, after the addition is completed, the reaction is continued at 0 ℃, and then the temperature is increased to room temperature for reaction; after the reaction is completed, the solvent is removed to obtain an activated liquid; C, 3,4-dihydroxybenzoic acid is dissolved in anhydrous N,N-dimethylformamide, imidazole is added, an ice-water bath is used for cooling, and N,N-dimethylformamide solution containing tert-butyl dimethylchlorosilane is added dropwise, the temperature is kept below 10 ℃, after the addition is completed, the temperature is increased to room temperature for reaction, poured into ice water, extracted with ethyl acetate, washed, dried, and concentrated under reduced pressure to obtain a solid product; the solid product is dissolved in anhydrous dichloromethane together with N-hydroxysuccinimide, an ice-water bath is used for cooling, N,N'-dicyclohexyl carbodiimide is added, reacted, filtered, the filtrate is concentrated, and then purified by silica gel column chromatography to obtain an activated solid; D. The first compound is dissolved in anhydrous N,N-dimethylformamide, anhydrous potassium carbonate is added, and stirring is carried out under nitrogen protection. The activated liquid prepared in step B and the activated solid prepared in step C are added in sequence. The reaction system is warmed to 60°C, and stirring is carried out at this temperature for 24 hours. After the reaction is completed, cooling is carried out to room temperature. Filtration is carried out. The filtrate is concentrated to 1 / 3 of the original volume. Then, dropwise addition is carried out into ice ethyl ether for precipitation. The precipitate is loaded into a Soxhlet extractor. Continuous extraction is carried out with anhydrous ethanol. Vacuum drying is carried out. The second compound is obtained. E. The second compound is dissolved in anhydrous tetrahydrofuran. Stirring is carried out at room temperature under nitrogen protection. A 1.0 mol / L tetrabutylammonium fluoride tetrahydrofuran solution is slowly added dropwise. After the addition is completed, continuous reaction is carried out at room temperature. The reaction liquid is concentrated to dryness. The residue is dissolved in methanol. Collection is carried out on a strong acid cation exchange resin column. The effluent is collected. Concentration is carried out. Fractionation is carried out by means of preparative gel permeation chromatography. The main fraction with a molecular weight distribution of 1.2 is collected. Concentration is carried out. Vacuum drying is carried out. The modified hyperbranched polyglycerol is obtained.

3. The method of claim 1, wherein the paste is prepared by mixing the isotropic graphite material with the molten salt at a temperature of 200 to 400°C. The bismaleimide-pyridine diamide bridging agent is prepared by the following method: B1. In a three-necked flask, 2,6-pyridinedicarboxylic acid and sulfur chloride are added. N,N-dimethylformamide is added. Heating reflux reaction is carried out until the solid is completely dissolved. After the reaction is completed, vacuum distillation is carried out. A light yellow solid is obtained. The light yellow solid is dissolved in anhydrous tetrahydrofuran. Ice salt bath cooling is carried out to -5°C. Solution A is obtained. Another solution containing ethylenediamine in a tetrahydrofuran / water mixed solution is prepared. The pH is adjusted to 8-9. Cooling is carried out to 0°C. Solution B is obtained. Under vigorous stirring, solution A is slowly added dropwise into solution B. The temperature is controlled to be not more than 5°C. The pH is maintained between 8-9. After the addition is completed, continuous reaction is carried out under ice bath. Filtration is carried out. Washing is carried out. Vacuum drying is carried out. The third compound is obtained. B2. In a three-necked flask, 4,4'-diaminobiphenyl is dissolved in anhydrous N-methylpyrrolidone. Nitrogen protection is carried out. Cooling is carried out to 0°C. Triphenyl phosphate and pyridine are added. The temperature is maintained at 0°C. The third compound is added in batches. The temperature is controlled to be not more than 10°C. After the addition is completed, slow warming to room temperature is carried out. Continuous reaction is carried out. The reaction liquid is poured into ice water. Filtration is carried out to collect the precipitate. Washing is carried out. Vacuum drying is carried out. The fourth compound is obtained. B3. In a three-necked flask, the fourth compound is suspended in ethyl acetate with maleic anhydride. Heating reflux reaction is carried out. The generated water is removed through a water trap. After the reaction is completed, cooling is carried out to room temperature. Filtration is carried out to collect the precipitate. Washing is carried out with cold ethyl acetate. Vacuum drying is carried out. The precipitate is suspended in a mixed solution of acetic anhydride and anhydrous sodium acetate. Stirring reaction is carried out under nitrogen protection. After the reaction is completed, cooling is carried out to room temperature. Pouring is carried out into ice water. Filtration is carried out to collect the solid. Washing is carried out. Purification is carried out by silica gel column chromatography. The main component is collected. Concentration is carried out. Acetonitrile is used for three times of recrystallization. The bismaleimide-pyridine diamide bridging agent is obtained.

4. The method of claim 1, wherein the paste is prepared by mixing the isotropic graphite material with the molten salt at a temperature of 200 to 400°C. The specific preparation method of the prepolymer is as follows: C1, in a three-necked flask, modified hyperbranched polyglycerol and anhydrous N,N-dimethylformamide were added, stirred and dissolved under nitrogen protection, heated to 60 DEG C and kept constant, to obtain solution C; bismaleimide-pyridine diamide bridging agent was dissolved in anhydrous N,N-dimethylformamide to obtain solution D, solution D was added dropwise to solution C, nitrogen protection was continued, after the dropwise addition was completed, the reaction was continued at 60 DEG C for 4 hours, to obtain a mixed solution; C2, the mixed solution was cooled to room temperature, hydroquinone polymerization inhibitor was added, concentrated to 1 / 3 of the original volume, the concentrated solution was added dropwise into ice ether for precipitation, after standing and layering, the supernatant was poured off, the bottom viscous product was collected, the precipitation operation was repeated three times, and vacuum drying was performed, to obtain a prepolymer.

5. The method of claim 1, wherein the paste is prepared by mixing the isotropic graphite material with the molten salt at a temperature of 200 to 300°C. The modified hyperbranched polyglycerol is used in an amount of 0.3%-0.8% by mass fraction of the aggregate, the bismaleimide-pyridine diamide bridging agent is used in an amount of 0.1%-0.4%, the zinc acetylacetonate is used in an amount of 0.05%-0.15%, and the polyethylene glycol dipolyacrylate is used in an amount of 0.5%-1.5%.

6. The method of claim 1, wherein the paste is prepared by mixing the isotropic graphite material with the molten salt at a temperature of 200 to 300°C. The mass ratio of the aggregate to the binder is 78~82:22~18.

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