Solar molten salt furnace refractory brick resistant to cold and heat shock and preparation method

Abstract

The invention discloses a solar molten salt furnace refractory brick capable of resisting thermal shock and a preparation method of the solar molten salt furnace refractory brick capable of resisting thermal shock and the preparation method of the solar molten salt furnace refractory brick. 3 to 5 percent of alpha-Al2O3 micro powder; 8 to 12% of kaolinite; 7-9% of high alumina bauxite; 4-6% of modified fluorite tailing ceramsite; 1-3% of a binding agent; 2.5-3% of refractory mortar; 5-10% of a regenerated bamboo fiber skeleton; mullite: the balance; the combined action of the modified fluorite tailing ceramsite and the regenerated bamboo fiber skeleton effectively improves the cold and heat shock resistance and high temperature molten salt erosion resistance of the brick body, and optimizes the performance of the brick body.

Description

Technical Field

[0001] This invention relates to the field of refractory brick preparation technology, specifically to a refractory brick for a solar molten salt furnace that is resistant to rapid temperature changes and its preparation method. Background Technology

[0002] Solar-powered molten salt furnace refractory bricks are standardized refractory materials specifically designed for the high-temperature working environment of molten salt furnaces. Their main function is to serve as internal lining material for the furnace body, withstanding the dual thermal and chemical erosion under the high-temperature heat transfer medium of molten salt (such as nitrate / sulfate mixtures) (working temperature 250-580℃) and the high temperature of the combustion chamber (locally up to 1350℃). At the same time, they must possess long-term stability and thermal insulation performance. Resistance to thermal shock refers to the material's ability to resist cracking, spalling, or structural damage when the temperature changes rapidly. It is the core indicator for measuring the thermal shock stability of materials and directly determines the durability and safety of refractory materials under drastic temperature fluctuations.

[0003] Frequent start-ups and shutdowns or abnormal molten salt circulation during the operation of molten salt furnaces can lead to sudden changes in local temperature. Bricks with insufficient resistance to thermal shock are prone to micro-cracks due to thermal stress, which accelerates molten salt penetration and causes structural collapse. The interface between refractory bricks and insulation layers is prone to delamination due to the difference in thermal expansion coefficients. Good thermal shock stability can reduce interlayer thermal stress, avoid the risk of furnace shell overheating caused by insulation failure, and maintain the integrity of the insulation layer.

[0004] However, existing refractory bricks have limited resistance to thermal shock and molten salt erosion. Therefore, this application provides a refractory brick for solar molten salt furnaces that is resistant to thermal shock and a method for its preparation. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a refractory brick for a solar molten salt furnace that is resistant to rapid temperature changes and a method for its preparation.

[0006] The technical solution of this invention is: a refractory brick for solar molten salt furnaces resistant to rapid temperature changes, comprising, by weight percentage: sillimanite: 10-15%; α-Al2O3 micro powder: 3-5%; kaolinite: 8-12%; high-alumina bauxite: 7-9%; modified fluorite tailings ceramsite: 4-6%; binder: 1-3%; refractory mortar: 2.5-3%; recycled bamboo fiber skeleton: 5-10%; mullite: balance; The mullite comprises 60-70% coarse particles of 1-3 mm and 30-40% fine powder of ≤45 μm; the sillimanite has a particle size of 0.5-1.2 mm; the α-Al2O3 micro powder has a particle size of 320-360 mesh; the kaolinite has a particle size of ≤10 μm; the high-alumina bauxite has a particle size of 0.8-2 mm; the modified fluorite tailings ceramsite has a particle size of 1-2 mm; the recycled bamboo fiber skeleton is composed of a modified bamboo fiber skeleton and silicon carbide slurry; the refractory mortar is a siliceous refractory mortar or a high-temperature resistant inorganic mortar.

[0007] Furthermore, the preparation method of the modified fluorite tailings ceramsite is as follows: Fluorite tailings ceramsite was impregnated in a 28-30% hydrochloric acid solution at a solid-liquid ratio of 1g:4-6ml for 1.5-2 hours, then filtered and vacuum dried at 55-65℃ and -0.08MPa, followed by heat treatment at 400-500℃ for 15-20 minutes to obtain pretreated ceramsite. The pretreated ceramsite was then impregnated in a 15-20% composite solution of polysiloxane containing borate ester bonds at a solid-liquid ratio of 1g:5-10ml, at a temperature of 80-90℃ for 1-2 hours, and then heat-treated at 800-900℃ for 30-40 minutes to obtain modified fluorite tailings ceramsite. Note: Grafting modification can introduce borate ester bonds into the side chains of polysiloxanes to form a dynamic covalent network structure. When the modified composite system is heated at 250-400℃, the dynamic breaking and recombination of borate ester bonds can be triggered, giving the material a self-healing function.

[0008] Furthermore, the composite solution is obtained by impregnating a polysiloxane alkyl material in a trimethyl borate solvent and then subjecting it to heat treatment; the heat treatment temperature is 120-150℃ and the heat treatment time is 30-35 min. Note: The above temperature can meet the grafting rate requirements while avoiding degradation of the siloxane backbone.

[0009] Furthermore, the method for preparing the regenerated bamboo fiber skeleton is as follows: bamboo fibers with a length of 5-15 mm and a diameter of 0.1-0.3 mm are selected and carbonized under nitrogen protection at 750-800℃ for 2-2.5 h to obtain carbonized bamboo fibers; the pH is adjusted to 3-4, and the carbonized bamboo fibers are impregnated with silica sol with a concentration of 20-25 wt% for 25-35 min to obtain modified bamboo fibers with a nano-SiO2 coating layer; A three-dimensional woven skeleton is achieved by using modified bamboo fiber as the X and Y axis skeleton and filling the Z axis interlayer pores with silicon carbide slurry. The surface porosity is 20%, the middle layer porosity is 45%, and the bottom layer porosity is 30%. Pre-fire at 1000-1100℃ for 0.5-1h to obtain a shaped bamboo fiber skeleton. Then, spray a 15-18% polyvinyl alcohol solution into the interlayer pores for curing. The spray thickness is 0.05-0.08mm, and the nozzle pressure is 0.2-0.3MPa. After spraying, place the shaped bamboo fiber skeleton under gamma rays for irradiation. The irradiation dose is 15-20kGy, the irradiation rate is 0.3-0.5kGy / h, and the irradiation time is 1-5min. After irradiation, anneal at 600-650℃ for 1-1.5h under nitrogen protection. Explanation: The dense surface layer resists molten salt penetration, while its low porosity provides high density to resist external thermal shock and slow down the rate of temperature change transmission; the intermediate buffer layer absorbs energy and dampens vibrations, and its high porosity can also absorb thermal stress through pore collapse, reducing the probability of crack initiation; the bottom support layer maintains structural strength, and its medium porosity balances thermal conductivity and stress buffering, preventing interlayer delamination; nitrogen-protected annealing eliminates residual free radicals from irradiation and stabilizes the cross-linked network structure; the thermal expansion coefficient of silicon carbide particles is close to that of the modified bamboo fiber carbon skeleton, which can reduce the accumulation of interfacial thermal stress caused by temperature changes and avoid interlayer cracking; at the same time, after filling the Z-axis pores, the SiC particles form a three-dimensional support network, dispersing the local stress generated by thermal cycles and significantly improving thermal shock resistance; The high thermal conductivity of SiC promotes rapid heat diffusion along the Z-axis, reduces internal stress caused by temperature gradient, and inhibits crack propagation; gamma-ray irradiation induces the formation of BO-Si dynamic covalent bonds between polyvinyl alcohol and nano-SiO2 coating layer, which can be reversibly fractured and recombined at high temperatures of 250-400℃, realizing the self-repair of microcracks.

[0010] Furthermore, the silicon carbide slurry filling method is vacuum impregnation: the skeleton is placed in an impregnation tank, vacuumed to -0.098MPa, then silicon carbide slurry is injected for impregnation for 5 minutes, after restoring normal pressure, the pressure is increased to 0.3MPa and maintained for 10 minutes; vacuum is then evacuated again to -0.095MPa and maintained for 15 minutes, then vibration with an amplitude of 45-55μm and a frequency of 90-100Hz is applied along the Z direction. After impregnation, the skeleton is placed in an environment with a humidity of 80-90% and a temperature of 30-40℃ for 12 hours, and gradient sintering is performed to obtain a three-dimensional woven skeleton. The silicon carbide slurry, by mass percentage, includes: 8-10% deionized water, 25-30% silica sol, 1-2% ammonium polyacrylate, and the balance silicon carbide particles; the silicon carbide particles include 60-70% coarse particles of 1-3mm and 30-40% fine powder of ≤100μm. After mixing the deionized water, silica sol, ammonium polyacrylate, and silicon carbide particles, the mixture is vacuum stirred at -0.08MPa until the slurry viscosity reaches 3000-4000cP. Explanation: The X / Y direction bamboo fiber skeleton and the Z direction silicon carbide slurry filler form a three-dimensional interlocking structure, avoiding the delamination problem of traditional laminated materials and improving the interfacial bonding strength; in addition, the Z direction silicon carbide filler layer forms a high thermal conductivity channel, which accelerates the heat conduction along the thickness direction and inhibits stress concentration caused by local overheating, thereby effectively improving the brick's resistance to rapid thermal changes.

[0011] Further, the gradient sintering is as follows: heating to 200-400℃ at a heating rate of 2-5℃ / min and holding for 1-1.5h; then heating to 800-1000℃ at a heating rate of 8-10℃ / min and holding for 1.5-2h; finally heating to 1300-1400℃ at a heating rate of 3-7℃ / min under a nitrogen atmosphere and holding for 2.5-3h. Explanation: The first stage can effectively remove residual moisture and organic dispersants; the second stage can convert silica sol into amorphous SiO2; and the third stage can trigger the solid-phase reaction between SiC and SiO2 to generate 3Al2O3·2SiO2 mullite-reinforced phase. The three-dimensional porous network of mullite aerogel combined with the high thermal conductivity of silicon carbide framework enables rapid heat diffusion and suppression of local overheating.

[0012] Furthermore, the binder is an aluminum dihydrogen phosphate solution; Explanation: The aluminum phosphate ceramic phase formed by aluminum dihydrogen phosphate solution has a thermal expansion coefficient that is more compatible with mullite, which can reduce interfacial thermal stress concentration; the thermal expansion coefficient of the silica sol bonding layer is low and differs greatly from that of the high-alumina matrix, making it prone to stress gradients during thermal shock; the nanoscale aluminum phosphate particles generated by the phosphate binder at high temperatures can refine the grains, block the crack propagation path, and improve flexural strength; furthermore, the aluminum phosphate ceramic phase can form an AlPO4 protective layer in a high-temperature molten salt erosion environment, slowing down the molten salt penetration rate; while conventional binder silica sol systems lack such a protective mechanism, and molten salt can easily penetrate along microcracks, leading to structural damage.

[0013] The above-mentioned refractory brick for solar molten salt furnace resistant to rapid thermal changes and its preparation method include the following steps: S1. Raw material preparation Raw material A is obtained by mixing mullite, sillimanite, and refractory mortar; raw material B is obtained by mixing high-alumina bauxite and α-Al2O3 micro powder; raw material C is obtained by mixing kaolinite, binder, and modified fluorite tailings ceramsite. S2, Blank preparation First, take 1 / 4 to 1 / 3 of the raw material A and press it to obtain the bottom blank. Make holes on the left and right sides of the bottom blank, and make the spacing and diameter of each hole equal. Then fill each hole with 1 / 4 to 1 / 3 of the raw material B at a grouting pressure of 0.15 to 0.25 MPa. Then, take 1 / 4 to 1 / 3 of the raw material C and press it to obtain a medium blank. Make a second hole on the top surface of the medium blank, and fill each hole with a recycled bamboo fiber skeleton. Then fill the gaps with the remaining raw material C at a grouting pressure of 0.45-0.55MPa. Finally, the remaining raw material B is pressed to obtain the top billet. Holes are made on the left and right sides of the top billet three times. The remaining raw material A is then filled into each hole with a grouting pressure of 0.95-1.05MPa. The bottom billet, middle billet, and top billet are pressed to form the billet body. The pressing temperature is 150-200℃, and the time is 20-30min; the primary, secondary, and tertiary hole diameters are all Φ3-5mm, with a spacing of 8-10mm; the secondary holes are staggered with a position offset of 30-60° from the primary holes, with a spacing of 6-8mm; and the tertiary holes are staggered with a position offset of 120-150° from the secondary holes, with a spacing of 3-4mm. S3, sintering The green body is placed in a drying tunnel kiln for drying and baking at a temperature of 100-140℃ for 10-12 hours. After drying, it is kept at 600-800℃ for 3.5-4.5 hours, then sintered at 1550-1600℃ for 2-4 hours. Finally, it is cooled to 750-850℃ at a rate of 3-5℃ / min to obtain a solar molten salt furnace refractory brick resistant to rapid thermal changes.

[0014] Explanation: Raw material A forms the main framework structure, and the thermal shock resistance is improved by toughening with mullite whiskers and improving the thermal conductivity of silicon carbide. Raw material B provides a high-alumina matrix, which enhances high-temperature stability and adjusts the matching of thermal expansion coefficients. Raw material C improves molding performance and enhances the resistance to molten salt penetration by sealing pores with putty. Low-temperature drying removes free water and initially solidifies the binder; then, organic matter is decomposed at 600-800℃, causing bamboo fiber to carbonize and form a carbon fiber skeleton; finally, high-temperature sintering allows CaF2 and SiO2 in fluorite tailings to react and form a gunmetal phase, achieving a balance between strength and thermal shock resistance in high-alumina refractory bricks. Primary pores ensure the strength of the matrix skeleton and buffer macroscopic thermal expansion; secondary pores balance the critical ratio between crack deflection effect and densification requirements, blocking crack propagation paths; tertiary pores, through high-density micropores, inhibit microcrack initiation, reduce local stress gradients, and optimize the performance of refractory bricks for solar molten salt furnaces.

[0015] The beneficial effects of this invention are: (1) The present invention utilizes the dense surface area of ​​the recycled bamboo fiber skeleton to resist molten salt penetration, resist external thermal shock, and slow down the rate of temperature change transmission; the middle buffer layer absorbs energy and dampens shock, absorbs thermal stress, and reduces the probability of crack initiation; the bottom support layer maintains structural strength, and at the same time, after filling the Z-direction pores with silicon carbide slurry, the SiC particles form a three-dimensional support network, promote the rapid diffusion of heat along the Z-direction, disperse the local stress generated by the hot and cold cycle, significantly improve the thermal shock resistance, and improve the resistance of the refractory bricks of the solar molten salt furnace to rapid hot and cold changes.

[0016] (2) This invention utilizes modified fluorite tailings ceramsite through graft modification, which can utilize the borosilicate glass layer generated by the high-temperature decomposition of polysiloxane composite solution. This layer can preferentially react with nitrates / sulfates in a molten salt environment to generate stable borate compounds, thereby slowing down the direct erosion of the matrix by molten salt and reducing the dissolution rate to 0.08 mm / h. Its molten salt penetration inhibition rate is >75%. At the same time, borate ester bonds are introduced into the side chain of polysiloxane to form a dynamic covalent network structure. When the modified composite system is heated at 250-400℃, it can trigger the dynamic breakage and recombination of borate ester bonds, giving the material a self-healing function.

[0017] (3) The present invention optimizes the opening layout by using a specific method in the blanking process. By gradually decreasing the hole diameter and adjusting the opening angle, the first, second and third openings are arranged in an alternating manner. The first layer of openings can form a macroscopic thermal expansion buffer layer. The second layer of openings is offset by 30-60° and distributed in an alternating manner to cooperate with the recycled bamboo fiber skeleton. The carbonized fiber forms a heat conduction transition layer to weaken the impact of sudden temperature change. The third opening forms a high-density surface protective layer to inhibit crack initiation. The three-dimensional network formed after the carbonization of recycled bamboo fiber can hinder the crack propagation path and reduce the crack propagation length by more than 60% during thermal shock cycles. Attached Figure Description

[0018] Figure 1 This is a comparison diagram of the thermal shock stability and flexural strength of the refractory bricks obtained in Examples 1-11 and Comparative Examples 1-3 of the present invention; Figure 2 This is a comparison chart of the molten salt erosion rates of refractory bricks obtained in Examples 1-11 and Comparative Examples 1-3 of the present invention; Figure 3 This is a comparison diagram of the thermal shock stability and flexural strength of the refractory bricks obtained in Embodiments 1, 12-17 and Comparative Examples 4-5 of the present invention; Figure 4 This is a comparison chart of the molten salt erosion rates of refractory bricks obtained in Examples 1, 12-17 and Comparative Examples 4-5 of the present invention; Figure 5This is a comparison diagram of the thermal shock stability and flexural strength of refractory bricks obtained in Embodiment 1, Embodiments 18-30 and Comparative Examples 7-8 of the present invention; Figure 6 This is a comparison chart of the molten salt erosion rates of refractory bricks obtained in Embodiment 1, Embodiments 18-30 and Comparative Examples 7-8 of the present invention; Figure 7 This is a schematic diagram showing the positional relationship of the first, second, and third openings in Embodiment 1 of the present invention. Detailed Implementation

[0019] The present invention will now be described in more detail with reference to specific embodiments, so as to better demonstrate the advantages of the present invention.

[0020] Example 1: A solar molten salt furnace refractory brick resistant to rapid temperature changes, comprising, by weight percentage: sillimanite: 13%; α-Al2O3 micro powder: 4%; kaolinite: 10%; high-alumina bauxite: 8%; modified fluorite tailings ceramsite: 5%; binder: 2%; refractory mortar: 2.8%; recycled bamboo fiber skeleton: 7%; mullite: balance; the binder is a 50% aluminum dihydrogen phosphate solution. Mullite comprises 65% coarse particles of 1-3 mm and 35% fine powder of 45 μm; sillimanite has a particle size of 0.5-1.2 mm; α-Al2O3 micro powder has a particle size of 320-360 mesh; kaolinite has a particle size of 10 μm; high-alumina bauxite has a particle size of 0.8-2 mm; modified fluorite tailings ceramsite has a particle size of 1-2 mm; the recycled bamboo fiber skeleton consists of a modified bamboo fiber skeleton and silicon carbide slurry; the refractory mortar is commercially available ZS-1071 type high-temperature resistant inorganic mortar; The preparation method of modified fluorite tailings ceramsite is as follows: Fluorite tailings ceramsite was impregnated in a 29% hydrochloric acid solution at a solid-liquid ratio of 1g:5ml for 1.8h, filtered, and then vacuum dried at 60℃ and -0.08MPa. Finally, it was kept at 450℃ for 18min to obtain pretreated ceramsite. Pretreated ceramsite was impregnated in a composite solution of 18% (w / w) of borate ester-bonded polysiloxane at a solid-liquid ratio of 1g:7ml. The temperature was adjusted to 85℃, the impregnation time was 1.5h, and the solution was kept at 850℃ for 35min to obtain modified fluorite tailings ceramsite. The composite solution was obtained by impregnating polysiloxane material in trimethyl borate solvent and then heat-treating it. The heat treatment temperature was 135℃ and the heat treatment time was 33min. A method for preparing a refractory brick for a solar molten salt furnace resistant to rapid thermal changes includes the following steps: S1. Raw material preparation Raw material A is obtained by mixing mullite, sillimanite, and refractory mortar; raw material B is obtained by mixing high-alumina bauxite and α-Al2O3 micro powder; raw material C is obtained by mixing kaolinite, binder, and modified fluorite tailings ceramsite. S2, Blank preparation First, take 7 / 24 of raw material A and press it to obtain a blank. Make holes on the left and right sides of the blank, and make the spacing and diameter of each hole equal. Then fill each hole with 7 / 24 of raw material B at a grouting pressure of 0.2MPa. Then, 7 / 4 of the raw material C is pressed to obtain a medium blank. The top surface of the medium blank is then opened a second time, and the recycled bamboo fiber skeleton is filled into each opening. Then, the remaining raw material C is filled into the gaps with a grouting pressure of 0.5MPa. Finally, the remaining raw material B is pressed to obtain the top billet. Holes are made on the left and right sides of the top billet three times. The remaining raw material A is then filled into each hole with a grouting pressure of 1 MPa. The bottom billet, middle billet, and top billet are pressed to form the billet body. The pressing temperature is 175℃ and the time is 25 minutes. The primary, secondary, and tertiary apertures are all Φ4mm, with a spacing of 9mm. The secondary apertures are staggered at a 45° offset from the primary apertures, with a spacing of 7mm. The tertiary apertures are staggered at a 135° offset from the secondary apertures, with a spacing of 3.5mm. S3, sintering The green body is placed in a drying tunnel kiln for drying and baking at a temperature of 120℃ for 11 hours. After drying, it is kept at 600-800℃ for 3.5-4.5 hours, then sintered at 1580℃ for 3 hours. Finally, it is cooled to 800℃ at a rate of 4℃ / min to obtain refractory bricks for solar molten salt furnaces that are resistant to rapid temperature changes.

[0021] Example 2: Unlike Example 1, a solar molten salt furnace refractory brick resistant to rapid temperature changes comprises, by weight percentage: sillimanite: 10%; α-Al2O3 micro powder: 3%; kaolinite: 8%; high-alumina bauxite: 7%; modified fluorite tailings ceramsite: 4%; binder: 1%; refractory mortar: 2.5%; recycled bamboo fiber skeleton: 5%; mullite: balance.

[0022] Example 3: Unlike Example 1, a solar molten salt furnace refractory brick resistant to rapid temperature changes comprises, by weight percentage: sillimanite: 15%; α-Al2O3 micro powder: 5%; kaolinite: 12%; high-alumina bauxite: 9%; modified fluorite tailings ceramsite: 6%; binder: 3%; refractory mortar: 3%; recycled bamboo fiber skeleton: 10%; mullite: balance.

[0023] Example 4: Unlike Example 1, the mullite comprises 60% coarse particles of 1-3 mm and 40% fine powder of 45 μm; the sillimanite has a particle size of 0.5-1.2 mm; the α-Al2O3 micro powder has a particle size of 320-360 mesh; the kaolinite has a particle size of 10 μm; the high-alumina bauxite has a particle size of 0.8-2 mm; and the modified fluorite tailings ceramsite has a particle size of 1-2 mm.

[0024] Example 5: Unlike Example 1, the mullite comprises 70% coarse particles of 1-3 mm and 30% fine powder of 45 μm; the sillimanite has a particle size of 0.5-1.2 mm; the α-Al2O3 micro powder has a particle size of 320-360 mesh; the kaolinite has a particle size of 10 μm; the high-alumina bauxite has a particle size of 0.8-2 mm; and the modified fluorite tailings ceramsite has a particle size of 1-2 mm.

[0025] Example 6: Unlike Example 1, fluorite tailings ceramsite was impregnated in a 28% hydrochloric acid solution at a solid-liquid ratio of 1g:4ml for 1.5h, filtered, and then vacuum dried at 55℃ and -0.08MPa, followed by heat treatment at 400℃ for 15min to obtain pretreated ceramsite.

[0026] Example 7: Unlike Example 1, fluorite tailings ceramsite was impregnated in a 30% hydrochloric acid solution at a solid-liquid ratio of 1g:6ml for 2 hours, filtered, and then vacuum dried at 65℃ and -0.08MPa. Finally, it was kept at 500℃ for 20 minutes to obtain pretreated ceramsite.

[0027] Example 8: Unlike Example 1, the pretreated ceramsite was impregnated in a composite solution of 15% by mass of a polysiloxane containing borate ester bonds at a solid-liquid ratio of 1g:5ml. The temperature was adjusted to 80℃, the impregnation time was 1h, and the solution was kept at 800℃ for 30min to obtain modified fluorite tailings ceramsite.

[0028] Example 9: Unlike Example 1, the pretreated ceramsite was impregnated in a composite solution of 20% by mass of a polysiloxane containing borate ester bonds at a solid-liquid ratio of 1g:10ml. The temperature was adjusted to 90℃, the impregnation time was 2h, and the solution was kept at 900℃ for 40min to obtain modified fluorite tailings ceramsite.

[0029] Example 10: Unlike Example 1, the heat treatment temperature was 120°C and the heat treatment time was 30 min.

[0030] Example 11: Unlike Example 1, the heat treatment temperature was 150°C and the heat treatment time was 35 min.

[0031] Example 12: Unlike Example 1, S2, blank preparation First, take 1 / 3 of the raw material A and press it to obtain the bottom blank. Make holes on the left and right sides of the bottom blank, and make the spacing and diameter of each hole equal. Then fill each hole with 1 / 3 of the raw material B at a grouting pressure of 0.15MPa. Then, take 1 / 3 of the raw material C and press it to obtain a medium blank. Make a second hole on the top surface of the medium blank, and fill each hole with a recycled bamboo fiber skeleton. Then fill the gaps with the remaining raw material C at a grouting pressure of 0.45MPa. Finally, the remaining raw material B is pressed to obtain the top billet. Holes are made on the left and right sides of the top billet three times. The remaining raw material A is then filled into each hole with a grouting pressure of 0.95 MPa. The bottom billet, middle billet, and top billet are pressed at 150℃ for 20 minutes to obtain the billet body.

[0032] Example 13: Unlike Example 1, S2, blank preparation First, take 1 / 4 of the raw material A and press it to obtain the bottom blank. Make holes on the left and right sides of the bottom blank, and make the spacing and diameter of each hole equal. Then fill each hole with 1 / 4 of the raw material B at a grouting pressure of 0.25MPa. Then, take 1 / 4 of the raw material C and press it to obtain a medium blank. Make a second hole on the top surface of the medium blank, fill each hole with a recycled bamboo fiber skeleton, and then fill the gaps with the remaining raw material C at a grouting pressure of 0.55MPa. Finally, the remaining raw material B is pressed to obtain the top billet. Holes are made on the left and right sides of the top billet three times. The remaining raw material A is then filled into each hole with a grouting pressure of 1.05 MPa. The bottom billet, middle billet, and top billet are pressed at 200℃ for 30 minutes to obtain the billet body.

[0033] Example 14: Unlike Example 1, the primary, secondary, and tertiary apertures are all Φ3mm with a spacing of 8mm. The secondary apertures are staggered with a spacing of 6mm and offset by 30° from the primary apertures. The tertiary apertures are staggered with a spacing of 3mm and offset by 150° from the secondary apertures.

[0034] Example 15: Unlike Example 1, the primary, secondary, and tertiary apertures are all Φ5mm with a spacing of 10mm. The secondary apertures are staggered with a spacing of 8mm and offset by 60° from the primary apertures. The tertiary apertures are staggered with a spacing of 4mm and offset by 120° from the secondary apertures.

[0035] Example 16: Unlike Example 1, the green body was placed in a drying tunnel kiln for drying and baking at 100°C for 10 hours. After drying, it was kept at 600°C for 3.5 hours, then sintered at 1550°C for 2 hours, and finally cooled to 750°C at a rate of 3°C / min. This yielded a solar molten salt furnace refractory brick resistant to rapid thermal changes.

[0036] Example 17: Unlike Example 1, the green body was placed in a drying tunnel kiln for drying and baking at a temperature of 140°C for 12 hours. After drying, it was kept at 800°C for 4.5 hours, then sintered at 1600°C for 4 hours, and finally cooled to 850°C at a rate of 5°C / min to obtain a solar molten salt furnace refractory brick resistant to thermal shock.

[0037] Example 18: Unlike Example 1, the method for preparing the regenerated bamboo fiber skeleton is as follows: bamboo fibers with a length of 10 mm and a diameter of 0.2 mm are selected and carbonized under nitrogen protection at 775℃ for 2.2 h to obtain carbonized bamboo fibers; the pH is adjusted to 3.5, and the carbonized bamboo fibers are impregnated with silica sol with a concentration of 23 wt% for 30 min to obtain modified bamboo fibers with a nano-SiO2 coating layer; A three-dimensional woven skeleton is achieved by using modified bamboo fiber as the X and Y axis skeleton and filling the Z axis interlayer pores with silicon carbide slurry. The surface porosity is 20%, the middle layer porosity is 45%, and the bottom layer porosity is 30%. The three-dimensional woven skeleton was pre-fired at 1050℃ for 0.8h to obtain a shaped bamboo fiber skeleton. Then, a 17% polyvinyl alcohol solution was sprayed into the interlayer pores for curing. The spray thickness was 0.06mm and the nozzle pressure was 0.25MPa. After spraying, the shaped bamboo fiber skeleton was irradiated under gamma rays with an irradiation dose of 18kGy, an irradiation rate of 0.4kGy / h, and an irradiation time of 3min. After irradiation, it was annealed at 625℃ for 1.3h under nitrogen protection. The silicon carbide slurry, by weight percentage, comprises: 9% deionized water, 28% silica sol, 1.5% ammonium polyacrylate, and the balance silicon carbide particles; the silicon carbide particles comprise 65% coarse particles of 2 mm and 35% fine powder of 100 μm. After mixing the deionized water, silica sol, ammonium polyacrylate, and silicon carbide particles, the mixture is vacuum stirred at -0.08 MPa until the slurry viscosity reaches 3500 cP. The silicon carbide slurry filling method is vacuum impregnation: the skeleton is placed in the impregnation tank, the vacuum is drawn to -0.098MPa, and then silicon carbide slurry is injected for impregnation for 5 minutes. After restoring normal pressure, the pressure is increased to 0.3MPa and maintained for 10 minutes. The vacuum is drawn again to -0.095MPa and maintained for 15 minutes. Then, vibration with an amplitude of 50μm and a frequency of 95Hz is applied along the Z direction. After impregnation, the skeleton is placed in an environment with 85% humidity and 35℃ for 12 hours. Gradient sintering is then performed to obtain the three-dimensional woven skeleton. The gradient sintering process is as follows: the temperature is increased to 300℃ at a heating rate of 4℃ / min and held for 1.3h; then increased to 900℃ at a heating rate of 9℃ / min and held for 1.8h; finally, the temperature is increased to 1350℃ at a heating rate of 5℃ / min under a nitrogen atmosphere and held for 2.8h.

[0038] Example 19: Unlike Example 18, the method for preparing the regenerated bamboo fiber skeleton is as follows: bamboo fibers with a length of 5 mm and a diameter of 0.1 mm are selected and carbonized under nitrogen protection at 750℃ for 2 h to obtain carbonized bamboo fibers; the pH is adjusted to 3, and the carbonized bamboo fibers are impregnated with silica sol with a concentration of 20 wt% for 25 min to obtain modified bamboo fibers with a nano-SiO2 coating layer.

[0039] Example 20: Unlike Example 18, the method for preparing the regenerated bamboo fiber skeleton is as follows: bamboo fibers with a length of 15 mm and a diameter of 0.3 mm are selected and carbonized under nitrogen protection at 800℃ for 2.5 h to obtain carbonized bamboo fibers; pH is adjusted to 4, and the carbonized bamboo fibers are impregnated with silica sol with a concentration of 25 wt% for 35 min to obtain modified bamboo fibers with a nano-SiO2 coating layer.

[0040] Example 21: Unlike Example 18, the three-dimensional woven skeleton was pre-fired at 1000℃ for 0.5h to obtain a shaped bamboo fiber skeleton. Then, a 15% polyvinyl alcohol solution was sprayed into the interlayer pores for curing. The spray thickness was 0.05mm, and the nozzle pressure was 0.2MPa. After spraying, the shaped bamboo fiber skeleton was irradiated under gamma rays with an irradiation dose of 15kGy, an irradiation rate of 0.3kGy / h, and an irradiation time of 1min. After irradiation, it was annealed at 600℃ for 1h under nitrogen protection.

[0041] Example 22: Unlike Example 18, the three-dimensional woven skeleton was pre-fired at 1100℃ for 1 hour to obtain a shaped bamboo fiber skeleton. Then, a 18% polyvinyl alcohol solution was sprayed into the interlayer pores for curing. The spray thickness was 0.08 mm, and the nozzle pressure was 0.3 MPa. After spraying, the shaped bamboo fiber skeleton was irradiated under gamma rays with an irradiation dose of 20 kGy, an irradiation rate of 0.5 kGy / h, and an irradiation time of 1-5 min. After irradiation, the skeleton was annealed at 650℃ for 1.5 hours under nitrogen protection.

[0042] Example 23: Unlike Example 18, the silicon carbide slurry, by weight percentage, comprises: 8% deionized water, 25% silica sol, 1% ammonium polyacrylate, and the balance being silicon carbide particles.

[0043] Example 24: Unlike Example 18, the silicon carbide slurry, by mass percentage, comprises: 10% deionized water, 30% silica sol, 2% ammonium polyacrylate, and the balance being silicon carbide particles.

[0044] Example 25: Unlike Example 18, the silicon carbide particles consist of 70% coarse particles of 1 mm and 30% fine powder of 100 μm. After mixing deionized water, silica sol, ammonium polyacrylate and silicon carbide particles, the mixture is stirred under vacuum at -0.08 MPa until the slurry viscosity reaches 3000 cP.

[0045] Example 26: Unlike Example 18, the silicon carbide particles include 70% coarse particles of 3 mm and 30% fine powder of 00 μm. After mixing deionized water, silica sol, ammonium polyacrylate and silicon carbide particles, the mixture is stirred under vacuum at -0.08 MPa until the slurry viscosity reaches 4000 cP.

[0046] Example 27: Unlike Example 18, the silicon carbide slurry filling method is vacuum impregnation: the skeleton is placed in the impregnation tank, the vacuum is drawn to -0.098MPa, and then silicon carbide slurry is injected for impregnation for 5 minutes. After restoring normal pressure, the pressure is increased to 0.3MPa and maintained for 10 minutes. The vacuum is drawn again to -0.095MPa and maintained for 15 minutes. Then, vibration with an amplitude of 45μm and a frequency of 90Hz is applied along the Z direction. After impregnation, the skeleton is placed in an environment with 80% humidity and 30℃ for 12 hours. Gradient sintering is then performed to obtain the three-dimensional braided skeleton.

[0047] Example 28: Unlike Example 18, the silicon carbide slurry filling method is vacuum impregnation: the skeleton is placed in the impregnation tank, the vacuum is drawn to -0.098MPa, and then silicon carbide slurry is injected for impregnation for 5 minutes. After restoring normal pressure, the pressure is increased to 0.3MPa and maintained for 10 minutes. The vacuum is drawn again to -0.095MPa and maintained for 15 minutes. Then, vibration with an amplitude of 55μm and a frequency of 100Hz is applied along the Z direction. After impregnation, the skeleton is placed in an environment with 90% humidity and 40℃ for 12 hours. Gradient sintering is then performed to obtain the three-dimensional woven skeleton.

[0048] Example 29: Unlike Example 18, the gradient sintering was performed as follows: the temperature was increased to 200°C at a heating rate of 2°C / min and held for 1 hour; then the temperature was increased to 800°C at a heating rate of 8°C / min and held for 1.5 hours; finally, the temperature was increased to 1300°C at a heating rate of 3°C / min under a nitrogen atmosphere and held for 2.5 hours.

[0049] Example 30: Unlike Example 18, the gradient sintering was performed as follows: the temperature was increased to 400°C at a heating rate of 5°C / min and held for 1.5 hours; then the temperature was increased to 1000°C at a heating rate of 10°C / min and held for 2 hours; finally, the temperature was increased to 1400°C at a heating rate of 7°C / min under a nitrogen atmosphere and held for 3 hours.

[0050] Experimental Example: The physicochemical properties of the refractory bricks prepared in Examples 1-30 and Control Examples 1-30 were measured respectively, and the results are as follows: 1. Investigate the influence of the composition of refractory bricks in solar-powered molten salt furnaces on the properties of the bricks. Comparative Example 1: Unlike Example 1, the refractory bricks do not contain sillimanite.

[0051] Comparative Example 2: Unlike Example 1, the refractory bricks do not contain modified fluorite tailings ceramsite.

[0052] Comparative Example 3: Unlike Example 1, the composite solution does not contain borate ester bonds.

[0053] Conclusion: Comparison of Examples 1-7 and Comparative Examples 1-2 shows that the absence of sillimanite in the refractory brick composition and the absence of modified fluorite tailings ceramsite in the refractory brick will weaken the physical and chemical properties of the brick. This is because the SiO2 on the surface of mullite generated by the decomposition of sillimanite has high activity and easily reacts with alkaline molten salts (such as KNO3) to form K2SiO3 with a high melting point. The dissolution rate of the brick without sillimanite in molten salt at 580℃ increased from 0.08mm / h to 0.25mm / h, and the erosion depth increased significantly. During the high-temperature sintering process, sillimanite is partially converted into mullite, and its needle-like crystal structure can form an interlocking reinforcement network. After the removal of sillimanite, the strength decreases significantly due to the combination of coarse and fine mullite particles alone. The difference in the coefficient of thermal expansion of the sillimanite-mullite composite system can inhibit the propagation of interfacial cracks. After its removal, the difference in the coefficient of thermal expansion of the system increases. Modified fluorite tailings ceramsite, acting as a reinforcing skeleton, improves flexural strength through its mechanical interlocking with the matrix. After removal, the room-temperature flexural strength drops to 40 MPa due to the lack of a rigid supporting phase within the matrix. Simultaneously, the gradient porosity of the modified ceramsite absorbs thermal stress, leading to a decrease in the retention rate of flexural strength during thermal shock cycles after removal. Finally, the borosilicate layer on the surface of the modified ceramsite inhibits molten salt penetration, increasing the molten salt dissolution rate from 0.08 mm / h to 0.22 mm / h after removal. As can be seen from the comparison of Examples 1, 8-11 and Comparative Example 3, the polysiloxane composite layer formed by borate ester bonds can generate a borosilicate glass phase at high temperature, which enhances the interfacial bonding strength between the modified ceramsite and the matrix. The borate ester complex can passivate the active sites on the surface of the ceramsite, inhibit the reaction of molten salt and Al2O3 to generate low-melting-point compounds, and because the borate ester bonds have the properties of dynamic fracture and recombination, they can endow the material with self-healing function and optimize the physical and chemical properties of the brick.

[0054] 2. Investigate the influence of brick-making methods on brick properties. Comparative Example 4: Unlike Example 1, the raw materials were directly mixed and used to form a blank.

[0055] Comparative Example 5: Unlike Example 1, the grouting pressure for the first, second, and third openings was 0.25 MPa.

[0056] Conclusion: Comparison of Examples 1, 12-17, and Comparative Examples 4-5 shows that the billet preparation method provided in this application can effectively improve the performance of refractory bricks. This is because primary pores ensure the strength of the matrix skeleton and buffer macroscopic thermal expansion; secondary pores balance the critical ratio between crack deflection effect and densification requirements, blocking crack propagation paths; tertiary pores inhibit microcrack initiation through high-density micropores, reduce local stress gradients, and optimize the performance of refractory bricks for solar molten salt furnaces; the layout method of this application can extend the stress situation of the brick body, thereby optimizing the thermal shock cycle stability and molten salt erosion resistance of the brick body; the offset arrangement of tertiary pores requires molten salt to penetrate along a "Z" shaped path, reducing the effective penetration rate; and the filling of open pores under different grouting pressures can significantly enhance the thermal shock resistance and erosion resistance of refractory bricks by controlling the porosity and pore type (open / closed pore ratio).

[0057] 3. Investigate the influence of the preparation method of recycled bamboo fiber skeleton on the properties of bricks. Comparative Example 6: Unlike Example 18, no gamma-ray irradiation was performed.

[0058] Comparative Example 7: Unlike Example 18, the silicon carbide slurry does not contain ammonium polyacrylate.

[0059] Conclusion: Comparison of Examples 1 and 18-30 shows that the recycled bamboo fiber skeleton prepared by the method provided in this application, when applied in the brick preparation process, can utilize silicon carbide slurry to fill the Z-direction pores, enabling SiC particles to form a three-dimensional support network, promoting rapid heat diffusion along the Z-direction, dispersing local stress generated by thermal cycles, significantly improving thermal shock resistance, improving the resistance to thermal shock in solar molten salt furnace refractory bricks, and significantly enhancing the brick's resistance to thermal shock and molten salt erosion. Considering all factors, Example 18 is the optimal solution. Gamma ray irradiation can cause polyvinyl alcohol to form a cross-linked network, strengthening the interlayer bonding force. Without irradiation, PVA curing is insufficient, porosity increases, and the flexural strength retention rate after 30 thermal shocks decreases from 90% to 72%. Furthermore, without irradiation, the closed-cell rate decreases, the molten salt penetration rate increases from 0.04 mm / h to 0.08 mm / h, and the amount of erosion products generated increases. The absence of ammonium polyacrylate in silicon carbide slurry also leads to an increase in apparent porosity and pore connectivity, with the molten salt penetration rate increasing from 0.04 mm / h to 0.07 mm / h. Furthermore, as a dispersant, ammonium polyacrylate can optimize the distribution of silicon carbide particles and reduce agglomeration. The absence of ammonium polyacrylate results in an imbalance between coarse and fine particles, a decrease in slurry fluidity, and a reduction in flexural strength.

Claims

1. A solar molten salt furnace refractory brick resistant to cold thermal shock, characterized in that, By weight percentage, comprising: sillimanite: 10-15%; α-Al2O3 micro powder: 3-5%; kaolinite: 8-12%; bauxite: 7-9%; modified fluorite tailings ceramsite: 4-6%; binder: 1-3%; refractory mortar: 2.5-3%; regenerated bamboo fiber skeleton: 5-10%; mullite: the balance; The mullite includes 60-70% of 1-3mm coarse particles and 30-40% of ≤45μm fine powder; the particle size of the sillimanite is 0.5-1.2mm; the particle size of the α-Al2O3 micro powder is 320-360 mesh; the particle size of the kaolinite is ≤10μm; the particle size of the bauxite is 0.8-2mm; the particle size of the modified fluorite tailings ceramsite is 1-2mm; the regenerated bamboo fiber skeleton is composed of modified bamboo fiber skeleton and silicon carbide slurry; the refractory mortar is siliceous refractory mortar or high-temperature resistant inorganic mortar.

2. A solar molten salt furnace firebrick resistant to cold thermal shock according to claim 1, wherein, The preparation method of the modified fluorite tailings ceramsite is: The fluorite tailings ceramsite is immersed in a hydrochloric acid solution with a mass fraction of 28-30% according to a solid-liquid ratio of 1g:4-6ml, filtered after immersion for 1.5-2h, vacuum dried at 55-65℃ and-0.08MPa, and then heat treated at 400-500℃ for 15-20min to obtain pretreated ceramsite; The pretreated ceramsite is immersed in a composite solution of borate ester bond-containing polysiloxane with a mass fraction of 15-20% according to a solid-liquid ratio of 1g:5-10ml, the temperature is adjusted to 80-90℃, the immersion time is 1-2h, and the heat treatment is carried out at 800-900℃ for 30-40min to obtain modified fluorite tailings ceramsite.

3. A solar molten salt furnace firebrick resistant to cold thermal shock according to claim 1, wherein The composite solution is obtained by immersing a polysiloxane base in a trimethyl borate solvent and then heat treating; the heat treatment temperature is 120-150℃ and the heat treatment time is 30-35min.

4. A solar molten salt furnace firebrick resistant to cold thermal shock as claimed in claim 1, wherein, The preparation method of the regenerated bamboo fiber skeleton is: selecting bamboo fibers with a length of 5-15mm and a diameter of 0.1-0.3mm, carbonizing the bamboo fibers under nitrogen protection at 750-800℃ for 2-2.5h to obtain carbonized bamboo fibers, adjusting the pH to 3-4, and immersing the carbonized bamboo fibers in a silica sol with a concentration of 20-25wt% for 25-35min to obtain modified bamboo fibers with a nano-SiO2 coating layer; The modified bamboo fibers are used as X and Y direction skeletons, and the silicon carbide slurry is used to fill the Z direction interlayer pores to realize three-dimensional weaving skeleton, wherein the surface layer porosity is 20%, the middle layer porosity is 45%, and the bottom layer porosity is 30%; The formed bamboo fiber skeleton is obtained by pre-sintering at 1000-1100℃ for 0.5-1h, then spraying a polyvinyl alcohol solution with a concentration of 15-18% into the interlayer pores for solidification, the spraying thickness is 0.05-0.08mm, the nozzle pressure is 0.2-0.3MPa, after the spraying is completed, the formed bamboo fiber skeleton is placed under γ-ray irradiation, the irradiation dose is 15-20kGy, the irradiation rate is 0.3-0.5kGy / h, and the irradiation time is 1-5min, and after the irradiation is completed, the formed bamboo fiber skeleton is annealed at 600-650℃ for 1-1.5h under nitrogen protection.

5. A solar molten salt furnace firebrick resistant to cold thermal shock according to claim 4, wherein The silicon carbide slurry filling method is vacuum impregnation: the skeleton is placed in an impregnation tank, vacuum is drawn to -0.098 MPa, then silicon carbide slurry is injected for impregnation for 5 min, after the normal pressure is restored, the pressure is increased to 0.3 MPa and maintained for 10 min; vacuum is drawn again to -0.095 MPa and pressure is maintained for 15 min, then vibration with an amplitude of 45-55 μm and a frequency of 90-100 Hz is applied along the Z direction, after impregnation, the skeleton is placed in an environment with a humidity of 80-90% and a temperature of 30-40 ℃ for 12 h, and gradient sintering is performed to obtain the three-dimensional woven skeleton.

6. A solar molten salt furnace firebrick resistant to cold thermal shock according to claim 5, wherein The silicon carbide slurry comprises, in percentage by mass: 8-10% of deionized water, 25-30% of silica sol, 1-2% of ammonium polyacrylate, and the balance of silicon carbide particles; the silicon carbide particles comprise 60-70% of 1-3 mm coarse particles and 30-40% of ≤100 μm fine powder; the deionized water, the silica sol, the ammonium polyacrylate, and the silicon carbide particles are mixed, and vacuum stirring is performed at -0.08 MPa until the viscosity of the slurry reaches 3000-4000 cP.

7. A solar molten salt furnace firebrick resistant to cold thermal shock according to claim 5, wherein The gradient sintering is performed as follows: the temperature is increased to 200-400 ℃ at a rate of 2-5 ℃ / min, and the temperature is maintained for 1-1.5 h; then the temperature is increased to 800-1000 ℃ at a rate of 8-10 ℃ / min, and the temperature is maintained for 1.5-2 h; finally, the temperature is increased to 1300-1400 ℃ at a rate of 3-7 ℃ / min in a nitrogen atmosphere, and the temperature is maintained for 2.5-3 h.

8. The method of claim 1, wherein the solar molten salt reactor firebrick is prepared by the steps of: mixing the first and second materials to form a mixture; and sintering the mixture to form the solar molten salt reactor firebrick. The binding agent is an aluminum dihydrogen phosphate solution.

9. A method of making a solar molten salt furnace firebrick resistant to cold shock according to any one of claims 1 to 8, wherein, The method comprises the following steps: S1, raw material preparation Mullite, sillimanite, and refractory mortar are mixed to obtain raw material A; high alumina bauxite and α-Al2O3 micro powder are mixed to obtain raw material B; kaolinite, a binding agent, and modified fluorite tailings ceramsite are mixed to obtain raw material C; S2, green body preparation First, 1 / 4-1 / 3 of raw material A is pressed to obtain a bottom green body, the left and right sides of the bottom green body are once perforated, and the interval and aperture of each perforation are equal; then 1 / 4-1 / 3 of raw material B is filled into each perforation at a grouting pressure of 0.15-0.25 MPa; Then, 1 / 4-1 / 3 of raw material C is pressed to obtain a middle green body, the top surface of the middle green body is twice perforated, and the remaining raw material C is filled into each perforation at a grouting pressure of 0.45-0.55 MPa; Finally, the remaining raw material B is pressed to obtain a top green body, the left and right sides of the top green body are thrice perforated, and the remaining raw material A is filled into each perforation at a grouting pressure of 0.95-1.05 MPa; the bottom green body, the middle green body, and the top green body are pressed to obtain a green body; The pressing temperature is 150-200 ℃, and the pressing time is 20-30 min; the aperture of the once perforation, the twice perforation, and the thrice perforation is Φ3-5 mm, the interval is 8-10 mm, the twice perforation is staggered and distributed at an interval of 6-8 mm and with a position offset of 30-60° relative to the once perforation, and the thrice perforation is staggered and distributed at an interval of 3-4 mm and with a position offset of 120-150° relative to the twice perforation; S3, sintering The green body is dried and baked in a drying tunnel kiln at a temperature of 100-140 DEG C for 10-12 h, and then kept at 600-800 DEG C for 3.5-4.5 h, and then high-temperature sintered at 1550-1600 DEG C for 2-4 h, and finally cooled at a rate of 3-5 DEG C / min to 750-850 DEG C, to obtain the solar molten salt furnace refractory brick resistant to cold and hot sudden change.

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