Refractory precast block for tunnel kiln car table and preparation method thereof

Abstract

This invention relates to the field of refractory materials technology, specifically to a refractory precast block for tunnel kiln car platforms and its preparation method, aiming to achieve a synergistic improvement in alkali corrosion resistance and thermal shock resistance under conditions of rich alkali steam and frequent thermal shock coupling. The formulation uses white fused alumina, fused magnesium aluminate spinel, α-alumina, plate alumina, and calcined kaolin as aggregates and matrix, and introduces zirconium phosphate grafted with dimolecular weight methoxy polyethylene glycol silane as a hierarchical template and interfacial coupling unit. Through a low-temperature curing-medium-temperature calcination-infiltration-high-temperature firing process, a tetra-interpenetrating network of calcium hexaaluminate / mullite / magnesium aluminate spinel / aluminum phosphate and a controlled composite pore structure are constructed within the material. This refractory precast block exhibits both high bulk density and low true porosity, with a refractoriness of approximately 1790℃. After 10 cycles of alkali steam-thermal shock, it demonstrates excellent strength retention, controlled dimensional and mass changes, and significantly extends the service life of the kiln car platform.

Description

Technical Field

[0001] This invention relates to the field of refractory materials technology, and in particular to a refractory precast block for the kiln car platform of a tunnel kiln and its preparation method. Background Technology

[0002] As a core thermal equipment in the production of industrial ceramics, building materials, and chemical products, the service performance of the refractory material on the kiln car platform directly affects production efficiency and product quality. In actual operation, the kiln car platform bears the fired products and undergoes a high-temperature firing process of 1200-1500°C, while also facing complex service environment challenges.

[0003] Traditional kiln car platform refractory materials mainly use high-alumina bricks, mullite bricks, or corundum-mullite materials. Although they possess a certain degree of refractoriness and mechanical strength, they exhibit significant shortcomings under the harsh conditions of modern industrial production. Firstly, during the firing process, alkaline oxides (such as K2O and Na2O) in the fired products volatilize at high temperatures, creating an alkaline vapor environment. These alkaline vapors react chemically with the refractory materials, generating low-melting-point alkaline silicates or aluminates, leading to a loose material structure, reduced strength, and in severe cases, deformation or even cracking of the platform.

[0004] Secondly, the kiln car undergoes complex temperature cycles during its operation within the tunnel kiln: it enters the preheating zone from ambient temperature, gradually heats up to the highest temperature of the firing zone, and then cools down to the exit temperature via the cooling zone. This repeated thermal expansion and contraction generates enormous thermal stress, especially in the rapid cooling section where the temperature gradient can reach hundreds of degrees, making it highly susceptible to thermal shock damage. Traditional materials, due to their simple microstructure, struggle to effectively disperse and release thermal stress, leading to the initiation of microcracks that gradually expand and connect, eventually forming through-cracks.

[0005] Even more serious is the fact that alkaline corrosion and thermal shock damage often reinforce each other, creating a vicious cycle. Alkaline vapor preferentially penetrates along the microcracks generated by thermal shock, accelerating the penetration of chemical corrosion; while the low-melting-point phases generated by alkaline corrosion are more prone to cracking under thermal shock, further expanding the damage area. This coupling effect causes traditional materials to experience a sharp deterioration in performance in the early stages of service.

[0006] In existing technologies, increasing the corundum content or introducing alkali oxides is commonly used to improve alkali resistance. However, these measures often come at the cost of sacrificing thermal shock resistance. While a high corundum content improves chemical stability, its high coefficient of thermal expansion and low thermal conductivity significantly increase thermal shock sensitivity. Adding alkali oxides, although it can form a low-melting-point phase to enhance bonding, reduces refractoriness, and the repeated melting and solidification of these phases under temperature fluctuations exacerbates structural instability.

[0007] To improve thermal shock resistance, existing technologies mainly focus on controlling particle size distribution, introducing fiber toughening, or adjusting matrix composition. However, these methods have limited effectiveness in alkaline environments. Fiber-toughened materials are prone to interfacial reactions under alkaline vapor, leading to a decrease in toughening effect. While multi-graded particles improve the packing structure, the large pores between coarse particles provide channels for alkaline vapor to permeate.

[0008] Therefore, developing refractory materials for kiln car platforms that simultaneously possess excellent resistance to alkali corrosion and thermal shock has become a pressing technical challenge in the field of refractory materials. The key lies in balancing density and stress release capability in material design, preventing the deep penetration of alkali media while maintaining sufficient toughness to withstand thermal shock damage, thus achieving synergistic optimization of both performance requirements. Summary of the Invention

[0009] In view of this, the purpose of this invention is to propose a refractory precast block for tunnel kiln car platform and its preparation method, so as to solve the contradiction between alkali corrosion resistance and thermal shock resistance of tunnel kiln car platform under alkaline environment and frequent thermal shock.

[0010] To achieve the above objectives, this invention provides a refractory precast block for a tunnel kiln car platform, which, by weight, is obtained from the following raw materials through mixing, compaction, low-temperature curing, medium-temperature calcination, impregnation, and high-temperature calcination: 4600-5000 parts of white fused alumina powder, 1100-1300 parts of fused magnesium aluminum spinel powder, 100-140 parts of plate-shaped alumina, 1300-1500 parts of α-alumina powder, and calcined kaolin powder. The following components are present: 650-750 parts of powder, 180-220 parts of lightly calcined magnesium oxide powder, 180-220 parts of precipitated calcium carbonate powder, 90-110 parts of nano-grade magnesium aluminum spinel powder, 45-55 parts of anhydrous aluminum fluoride powder, 120-180 parts of chopped alumina fibers, 110-130 parts of double-grafted zirconium phosphate powder, 1800-2200 parts of 50wt% aluminum dihydrogen phosphate aqueous solution, and 450-600 parts of deionized water.

[0011] Preferably, the low-temperature curing is performed by holding at 105°C for 100-140 min, at 110°C for 200-280 min, and at 340-360°C for 210-270 min.

[0012] Preferably, the medium-temperature calcination involves heating at 4-6°C / min to 930-980°C and holding at that temperature for 100-140 minutes.

[0013] Preferably, the high-temperature calcination is performed by heating at a rate of 2.5-3.5°C / min to 1410-1440°C and holding at that temperature for 160-200 min.

[0014] Preferably, the impregnation uses a 50wt% aluminum dihydrogen phosphate aqueous solution, and the amount used is half the weight of the aluminum dihydrogen phosphate aqueous solution in the raw material.

[0015] Preferably, the white molten alumina powder is a mixture of white molten alumina powders with particle sizes D50 of 1.2 mm and 0.6 mm in a weight ratio of 27-29:19-21.

[0016] Preferably, the particle size D50 of the molten magnesium aluminum spinel powder is 1.5 mm, the particle size D50 of the α-alumina powder is 2.1 μm, the particle size D50 of the calcined kaolin powder is 3.8 μm, the particle size D50 of the lightly calcined magnesium oxide powder is 8.2 μm, the particle size D50 of the precipitated calcium carbonate powder is 3.5 μm, and the particle size D50 of the anhydrous aluminum fluoride powder is 4.1 μm.

[0017] Preferably, the plate-shaped alumina has an average sheet thickness of 1.2 μm, an average sheet diameter of 25.4 μm, a particle size D50 of 220 nm for the nano-sized magnesium aluminum spinel powder, and an average diameter of 3.5 μm and an average length of 5.2 mm for the chopped alumina fibers.

[0018] Preferably, the double-grafted zirconium phosphate powder is obtained by grafting α-zirconium phosphate powder with methoxy polyethylene glycol silane.

[0019] Preferably, the weight ratio of the α-zirconium phosphate powder to the methoxy polyethylene glycol silane is 150:16-24; the methoxy polyethylene glycol silane is a mixture of methoxy polyethylene glycol silanes with a weight average molecular weight of 2000 and 20000 in a weight ratio of 1:1.

[0020] Furthermore, the present invention also provides a method for preparing refractory precast blocks for tunnel kiln car platforms, comprising the following steps: (1) Add white molten alumina powder, molten magnesium aluminum spinel powder and plate alumina to a mixer and dry mix at 60 rpm for 10 min. Then add α-alumina powder, calcined kaolin powder, lightly calcined magnesium oxide powder, precipitated calcium carbonate powder, nano-sized magnesium aluminum spinel powder, anhydrous aluminum fluoride powder, short-cut alumina fibers and double-grafted zirconium phosphate powder and dry mix at 120 rpm for 20 min. Then add a portion of 50 wt% aluminum dihydrogen phosphate aqueous solution and deionized water and continue stirring for 15 min to obtain a mixed slurry. (2) The mixed slurry is poured into a steel mold, vibrated at 50 Hz for 5 min, then cured at low temperature, and demolded to obtain a demolded blank; (3) The demolded blank is calcined at a medium temperature to obtain a calcined blank; (4) The calcined green body is immersed in an aqueous solution of aluminum dihydrogen phosphate with a remaining concentration of 50wt% at -0.08±0.01MPa, sonicated for 8-12min, then impregnated at normal pressure for 25-40min, drained and dried at 210-230°C for 150-210min to obtain the impregnated green body. (5) The impregnated blank is calcined at high temperature to obtain refractory precast blocks for the kiln car platform of the tunnel kiln.

[0021] This invention achieves a synergistic improvement in the corrosion resistance and thermal shock resistance of refractory precast blocks for tunnel kiln car platforms in alkaline environments by organically combining key technical features such as dimolecular weight methoxy polyethylene glycol silane grafted zirconium phosphate, multi-level particle gradation design, and vacuum infiltration secondary densification.

[0022] The introduction of two molecular weight grafted zirconium phosphates creates a unique hierarchical template structure. Low molecular weight polyethylene glycol silane segments form submicroporous channels during burn-off, providing a buffer space for stress release; the macromolecular network formed by high molecular weight segments leaves larger pores after thermal decomposition, facilitating the deep distribution of subsequent penetrants. The synergistic effect of the two molecular weight segments enables precise control of the pore structure, ensuring both material compactness and maintaining necessary stress release channels.

[0023] The multi-level particle size distribution design constructs a multi-layered, interpenetrating load-bearing network through the bimodal distribution of white molten alumina, the directional arrangement of plate-like alumina, and the three-dimensional toughening effect of chopped fibers. Large particles provide skeletal support, medium and fine particles fill the voids to improve density, and the preferred orientation of the plate-like alumina during the forming process forms a layered barrier structure that effectively blocks the diffusion path of alkali vapors. The bridging effect of the chopped alumina fibers enhances the interparticle bonding and improves crack propagation resistance.

[0024] The core innovation of this invention is the vacuum infiltration secondary densification process. By eliminating internal gases through negative pressure vacuuming, the aluminum dihydrogen phosphate solution penetrates deeply into the interconnected pores within the material under the drive of capillary force and pressure difference. During high-temperature sintering, the infiltrated aluminum dihydrogen phosphate undergoes a dehydration and condensation reaction, forming a dense aluminum phosphate ceramic phase, achieving in-situ sealing of the pores. Simultaneously, double-grafted zirconium phosphate undergoes a localized reaction at the pore ends, forming a gradient-transition interface bond, avoiding the interfacial stress concentration caused by the difference in thermal expansion coefficients between the penetrant and the matrix in traditional impregnation.

[0025] The formation of a four-phase interpenetrating network structure is key to optimizing material properties. During high-temperature sintering, calcium hexaaluminate plates and mullite whiskers grow synergistically, magnesium aluminum spinel particles provide chemical stability, and the aluminum phosphate phase constructs a continuous framework. The four phases form an interpenetrating network in three-dimensional space. This network structure not only ensures structural stability at high temperatures but also improves thermal shock resistance through energy dissipation mechanisms at the phase interfaces.

[0026] The controlled pore structure design achieves a balance between permeation resistance and stress release. Through the template effect of double-grafted zirconium phosphate and the synergistic effect of permeation-curing, a composite pore structure with closed pores as the main component and controlled open pores is formed inside the material. The closed pores prevent the deep penetration of alkaline vapors, while the remaining controlled open pores provide space for the release of thermal stress, avoiding sudden fracture caused by stress concentration.

[0027] Through the synergistic effect of the above features, the refractory precast blocks prepared by this invention significantly improve the structural stability and service life under the coupled effects of alkaline environment and thermal shock while maintaining high refractoriness, providing an effective solution for the technological upgrading of tunnel kiln car platform materials. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0029] Figure 1 The X-ray diffraction patterns are those of the refractory precast blocks prepared in Examples 1-3 of this invention. Figure 2 X-ray diffraction patterns of the refractory precast blocks prepared in Example 2 and Comparative Examples 1-7 of this invention; Figure 3 The infrared spectra of α-zirconium phosphate powder and double-grafted zirconium phosphate powder in Example 2 of the present invention are shown. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0031] In a highly alkaline environment, it is difficult to simultaneously achieve both alkali corrosion resistance and thermal shock resistance for kiln car platforms. Example 1: (1) 150g of α-zirconium phosphate powder (Sigma-Aldrich, catalog number 464236, average particle size 5μm) was added to 750mL of deionized water and sonicated for 25min. Then, 8g of methoxy polyethylene glycol silane with a weight average molecular weight of 2000 (MilliporeSigma, mPEG2K-Silane) and 8g of methoxy polyethylene glycol silane with a weight average molecular weight of 20000 (MilliporeSigma, mPEG20K-Silane) were added. The mixture was stirred at 58°C for 100min. The pH was adjusted to 4 with acetic acid and stirred for another 75min. After filtration and washing with water until neutral, the mixture was dried at 75°C for 5h to obtain double-grafted zirconium phosphate powder. (2) Add 2700g of white molten alumina powder (D50=1.2mm), 1900g of white molten alumina powder (D50=0.6mm), 1100g of molten magnesium aluminum spinel powder (D50=1.5mm) and 100g of plate-shaped alumina (average plate thickness 1.2μm, average plate diameter 25.4μm) to a planetary high-intensity mixer, dry mix at 60rpm for 10min, and then add 1300g of α-alumina powder (D50=2.1μm), 650g calcined kaolin powder (D50=3.8μm), 180g lightly calcined magnesium oxide powder (D50=8.2μm), 180g precipitated calcium carbonate powder (D50=3.5μm), 90g nano-sized magnesium aluminum spinel powder (D50=220nm), 45g anhydrous aluminum fluoride powder (D50=4.1μm), 120g short-cut alumina fibers (average diameter 3.5μm, average length 5.2mm) and 110g double-grafted zirconium phosphate powder were dry-mixed at 120rpm for 20min, then 900g of 50wt% aluminum dihydrogen phosphate aqueous solution and 600g of deionized water were added, and stirring was continued for 15min to obtain a mixed slurry. (3) The mixed slurry was loaded into the inner wall of a 300×300×40mm steel mold and sprayed with boron nitride release agent. It was compacted on an electromagnetic vibration table at 50Hz for 5 minutes, then kept at 105°C for 100 minutes, 110°C for 200 minutes, and 340°C for 210 minutes. The mold was then demolded to obtain the demolded blank. (4) Heat the demolded blank to 930°C in air at a rate of 4°C / min and hold for 100 min to obtain the calcined blank; (5) Place the calcined green body into a vacuum permeation tank, and after evacuating the vacuum at -0.07MPa for 25 minutes, add 900g of 50wt% aluminum dihydrogen phosphate aqueous solution into the tank, sonicate for 8 minutes, release the vacuum, permeate under normal pressure for 25 minutes, drain the liquid and dry it at 210°C for 150 minutes to obtain the impregnated green body. (6) The impregnated green body is heated to 1410°C in air atmosphere at 2.5°C / min, held for 160min, and cooled to room temperature with the furnace to obtain refractory precast blocks for tunnel kiln car platform.

[0032] Example 2: (1) 150g of α-zirconium phosphate powder (Sigma-Aldrich, catalog number 464236, average particle size 5μm) was added to 800mL of deionized water and sonicated for 30min. Then, 10g of methoxy polyethylene glycol silane with a weight average molecular weight of 2000 (MilliporeSigma, mPEG2K-Silane) and 10g of methoxy polyethylene glycol silane with a weight average molecular weight of 20000 (MilliporeSigma, mPEG20K-Silane) were added. The mixture was stirred at 60°C for 120min. The pH was adjusted to 4 with acetic acid and stirred for another 90min. After filtration and washing with water until neutral, the mixture was dried at 80°C for 6h to obtain double-grafted zirconium phosphate powder. (2) Add 2800g of white molten alumina powder (D50=1.2mm), 2000g of white molten alumina powder (D50=0.6mm), 1200g of molten magnesium aluminum spinel powder (D50=1.5mm) and 120g of plate-shaped alumina (average plate thickness 1.2μm, average plate diameter 25.4μm) to a planetary high-intensity mixer, dry mix at 60rpm for 10min, and then add 1400g of α-alumina powder (D50=2.1μm), 700g calcined kaolin powder (D50=3.8μm), 200g lightly calcined magnesium oxide powder (D50=8.2μm), 200g precipitated calcium carbonate powder (D50=3.5μm), 100g nano-sized magnesium aluminum spinel powder (D50=220nm), 50g anhydrous aluminum fluoride powder (D50=4.1μm), 150g short-cut alumina fibers (average diameter 3.5μm, average length 5.2mm) and 120g double-grafted zirconium phosphate powder were dry-mixed at 120rpm for 20min, then 1000g of 50wt% aluminum dihydrogen phosphate aqueous solution and 500g of deionized water were added, and stirring was continued for 15min to obtain a mixed slurry. (3) The mixed slurry was loaded into the inner wall of a 300×300×40mm steel mold, sprayed with boron nitride release agent, vibrated on an electromagnetic vibration table at 50Hz for 5 minutes, then kept at 105°C for 120 minutes, 110°C for 240 minutes, and 350°C for 240 minutes, and then demolded to obtain a demolded blank. (4) Heat the demolded blank to 950°C in air at a rate of 5°C / min and hold for 120 min to obtain the calcined blank; (5) Place the calcined green body into a vacuum permeation tank, evacuate at −0.08MPa for 30 min, add 1000g of 50wt% aluminum dihydrogen phosphate aqueous solution into the tank, sonicate for 10 min, release the vacuum, permeate at normal pressure for 30 min, drain the liquid and dry at 220°C for 180 min to obtain the impregnated green body. (6) The impregnated green body is heated to 1420°C in air at 3°C / min, held for 180min, and cooled to room temperature with the furnace to obtain refractory precast blocks for the kiln car platform of the tunnel kiln.

[0033] Example 3: (1) 150g of α-zirconium phosphate powder (Sigma-Aldrich, catalog number 464236, average particle size 5μm) was added to 850mL of deionized water and sonicated for 35min. Then, 12g of methoxy polyethylene glycol silane with a weight average molecular weight of 2000 (MilliporeSigma, mPEG2K-Silane) and 12g of methoxy polyethylene glycol silane with a weight average molecular weight of 20000 (MilliporeSigma, mPEG20K-Silane) were added. The mixture was stirred at 62°C for 140min. The pH was adjusted to 4 with acetic acid and stirred for another 105min. The mixture was filtered, washed with water until neutral, and dried at 85°C for 7h to obtain double-grafted zirconium phosphate powder. (2) Add 2900g of white molten alumina powder (D50=1.2mm), 2100g of white molten alumina powder (D50=0.6mm), 1300g of molten magnesium aluminum spinel powder (D50=1.5mm) and 140g of plate-shaped alumina (average plate thickness 1.2μm, average plate diameter 25.4μm) to a planetary high-intensity mixer, dry mix at 60rpm for 10min, and then add 1500g of α-alumina powder (D50=2.1μm), 750g calcined kaolin powder (D50=3.8μm), 220g lightly calcined magnesium oxide powder (D50=8.2μm), 220g precipitated calcium carbonate powder (D50=3.5μm), 110g nano-sized magnesium aluminum spinel powder (D50=220nm), 55g anhydrous aluminum fluoride powder (D50=4.1μm), 180g short-cut alumina fibers (average diameter 3.5μm, average length 5.2mm) and 130g double-grafted zirconium phosphate powder were dry-mixed at 120rpm for 20min, then 1100g of 50wt% aluminum dihydrogen phosphate aqueous solution and 450g of deionized water were added, and stirring was continued for 15min to obtain a mixed slurry. (3) The mixed slurry was loaded into the inner wall of a 300×300×40mm steel mold and sprayed with boron nitride release agent. It was compacted on an electromagnetic vibration table at 50Hz for 5 minutes, then kept at 105°C for 140 minutes, 110°C for 280 minutes, and 360°C for 270 minutes. The mold was then demolded to obtain the demolded blank. (4) Heat the demolded blank to 980°C in air at a rate of 6°C / min and hold for 140 min to obtain the calcined blank; (5) Place the calcined green body into a vacuum permeation tank, evacuate at -0.09MPa for 40 minutes, add 1100g of 50wt% aluminum dihydrogen phosphate aqueous solution into the tank, sonicate for 12 minutes, release the vacuum, permeate at normal pressure for 40 minutes, drain the liquid and dry at 230°C for 210 minutes to obtain the impregnated green body. (6) The impregnated green body is heated to 1440°C in air atmosphere at 3.5°C / min, held for 200min, and cooled to room temperature with the furnace to obtain refractory precast blocks for tunnel kiln car platform.

[0034] Comparative Example 1 The difference between Comparative Example 1 and Example 2 is that step (1) does not use α-zirconium phosphate powder grafted with methoxy polyethylene glycol silane, but instead uses an equal weight of unmodified α-zirconium phosphate powder in subsequent steps, while the other conditions are the same as in Example 2.

[0035] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that: in step (5), the vacuum impregnation process of -0.08MPa vacuuming for 30 minutes and atmospheric pressure impregnation for 30 minutes is cancelled, and no aluminum dihydrogen phosphate aqueous solution and double-grafted zirconium phosphate powder are added. The process proceeds directly to step (6) high-temperature firing, and the remaining conditions are the same as in Example 2.

[0036] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that in step (1), only 20g of methoxy polyethylene glycol silane with a weight average molecular weight of 2000 was added, and methoxy polyethylene glycol silane with a weight average molecular weight of 20000 was not added. The other conditions were the same as in Example 2.

[0037] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that in step (1), only 20g of methoxy polyethylene glycol silane with a weight average molecular weight of 20,000 was added, and no methoxy polyethylene glycol silane with a weight average molecular weight of 2,000 was added. The other conditions were the same as in Example 2.

[0038] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that in step (2), only 4800g of white molten alumina (D50=1.2mm) was added, and no white molten alumina (D50=0.6mm) was added. The other conditions were the same as in Example 2.

[0039] Comparative Example 6: The difference between Comparative Example 6 and Example 2 is that the addition of plate-shaped alumina is omitted in step (2), while the other conditions are the same as in Example 2.

[0040] Comparative Example 7: The difference between Comparative Example 7 and Example 2 is that the addition of short-cut alumina fibers is omitted in step (2), while the other conditions are the same as in Example 2.

[0041] Performance testing: X-ray diffraction analysis: X-ray diffraction was performed using an X-ray diffractometer, and the results are as follows: Figure 1 and Figure 2 As shown.

[0042] Infrared spectroscopy analysis: Fourier transform infrared spectrometer was used for testing, and the results are as follows: Figure 3 As shown.

[0043] Bulk density, apparent porosity and true porosity: Bulk density and apparent porosity were determined by the water displacement method, and true porosity was calculated. The results are shown in Table 1.

[0044] Permanent linear change due to heating: The sample was heated at 1500°C for 2 hours in air atmosphere, and the dimensional change rate was measured after cooling to room temperature. The results are shown in Table 1.

[0045] Evaluation of Alkali Vapor-Thermal Shock Alternating Coupling: Referring to the alkaline medium setup and erosion criteria in GB / T 14983-2008 and combined with the water quenching cycle system in GB / T 30873-2014, a three-stage process for one cycle was constructed: using K2CO3:Na2CO3=7:3 (weight ratio) as the alkali source, with the upper surface of the sample 20 mm away from the alkali source, the sample was exposed to alkaline vapor by holding at 1150°C for 120 min in a tubular electric furnace; then, after the furnace temperature dropped to 1100°C, the sample was immersed in 25°C deionized water for quenching for 150 s within 3 s; after removal, the sample was dried at 110°C for 60 min and allowed to stand at room temperature for 30 min before starting the next cycle; a total of 10 cycles were performed, and the rate of change in coupled cycle mass and the retention rate of room temperature flexural strength were compared. The room temperature flexural strength test followed GB / T 3001 / 2017, and the results are shown in Table 1.

[0046] Refractoriness: Referring to GB / T 7322-2017, the cone was prepared according to the standard and heated in a high-temperature furnace to the temperature at which the top of the cone and the base form a specified angle. The refractoriness value was then read, and the results are shown in Table 1.

[0047] Table 1 Performance Test Results

[0048] Data Analysis: As can be seen from the data in Examples 1-3, the refractory precast blocks prepared by this invention exhibit a comprehensive balance between high density and controlled porosity. Irreversible dimensional changes after heat treatment are minimal, and they maintain high strength and limited mass loss even after alkali vapor-thermal shock coupling cycles, while also possessing a higher level of refractoriness. This may be due to the following: the low-temperature curing and medium-temperature calcination stages provide a connected but controllable pathway for subsequent infiltration; the aluminum dihydrophosphate introduced by vacuum infiltration and the double molecular weight grafted zirconium phosphate undergo controlled burn-off and secondary condensation at the pore ends, promoting self-sealing and secondary densification, thereby limiting the deep penetration of the alkali medium and retaining submicropores for the slow release of thermal strain. During the high-temperature stage, mullite whiskers and calcium hexaaluminate plates grow synergistically, forming a continuous, interpenetrating load-bearing and barrier network together with magnesium aluminum spinel and aluminum phosphate framework; the bridging of short-cut alumina fibers with whiskers and plates effectively disperses thermal shock stress and improves fracture resistance. Multi-level particle gradation and plate-shaped alumina improve the forming density and shorten the diffusion path. Combined with penetration-curing to build a continuous skeleton, the opening pores are controlled and the support dimensions are stable, thus better meeting the service requirements of the kiln car platform under frequent loading and unloading and temperature fluctuations.

[0049] Compared to Example 2, Comparative Example 1 did not graft zirconium phosphate with dimethyl methoxy polyethylene glycol silane, resulting in weakened interfacial coupling and hierarchical template. This made it difficult for the pore ends to form a self-sealing reaction, and the secondary polycondensation and densification synergistic effect of the penetrating sol was insufficient. Alkali vapor could penetrate more easily and promote microcrack connection under thermal shock, leading to a systematic decline in strength retention and dimensional stability.

[0050] Compared to Example 2, Comparative Example 2 eliminated vacuum infiltration and functionalized pore sealing, making it difficult to control the proportion and effective radius of interconnected pores. The phosphate skeleton failed to be continuously generated in the deep layer, the alkali vapor flux increased and was accompanied by deposition reaction, and thermal shock accumulated damage advanced rapidly, which in turn led to a simultaneous weakening of densification, strength maintenance and permanent linear stability.

[0051] Compared to Example 2, Comparative Example 3 only uses low molecular weight methoxy polyethylene glycol silane grafting, lacking a cross-scale template of high molecular weight segments. During the burn-off and polycondensation process, it is difficult to construct hierarchical submicropores and pore-end localized reaction zones, the permeation distribution and interfacial bonding tend to be discrete, the barrier continuity decreases, the alkali invasion front is easy to expand, and the thermal shock resistance and dimensional stability are weakened.

[0052] Compared to Example 3, Comparative Example 4 only used high molecular weight methoxy polyethylene glycol silane grafting, which limited the permeation viscosity and pore matching. After burn-off, it is easy to leave coarse pores, interrupting the self-sealing and secondary densification of the pore ends, and the uneven distribution in the deep layer leads to the discontinuity of the barrier; under the coupling of alkali vapor and thermal shock, cracks are more likely to penetrate, and the strength and refractory stability decline in tandem.

[0053] Compared to Example 3, Comparative Example 5 degrades the bimodal gradation into a unimodal coarse gradation, resulting in larger initial packing pores and higher connectivity. Sintering neck development and deep penetration are hindered, and the pore-dominated flow field intensifies the alkali vapor flux. The reaction layer rapidly expands outward and is superimposed with thermal shock cracking, leading to insufficient densification, persistently low strength, and more difficult-to-control permanent linear and quality changes.

[0054] Compared to Example 3, Comparative Example 6 eliminates the plate-like alumina, thus losing the sheet-like support and orientation structure. At high temperatures, it becomes difficult to form a stable plate-like phase network and crack deflection channels, weakening the overlap of the four-way interpenetrating skeleton and reducing the alkaline medium's resistance capacity. Under cyclic thermal shock, energy dissipation is insufficient, resulting in a simultaneous degradation of dimensional stability and strength.

[0055] Compared to Example 3, Comparative Example 7 eliminated the short-cut alumina fibers, breaking the fiber-whisker-plate structure in the triple bridging. Crack bridging and pinning effects were significantly reduced, and the threshold for microcrack initiation and convergence shifted downward. Accumulated damage accelerated in the alkaline vapor-thermal shock coupled cycle, making it difficult to maintain barrier continuity, and strength, quality, and permanent linear stability weakened simultaneously.

[0056] from Figure 1 It can be seen that the spectra of Examples 1-3 show that the peaks of calcium hexaaluminate (2θ≈32.2°, 33.2°, 57.6°), mullite (26.0°, 33.1°), and spinel (36.8°) are sharper and have higher relative intensity, accompanied by obvious AlPO4 (quartz isotope) framework peaks (20.9°, 26.6°), indicating that the reaction sintering can achieve sufficient generation of high-temperature phase, avoiding excessive corundum residue due to insufficient sintering; through vacuum infiltration and the introduction of double-grafted zirconium phosphate, the densification of the intercrystalline space and the construction of a stable framework structure are achieved, and the residual corundum (35.1°, 43.3°, 57.5°) peaks are weak, confirming that the introduction of double-grafted zirconium phosphate reduces corundum residue.

[0057] from Figure 2 It can be seen that, compared with Example 2, the intensity of the same peak position in Comparative Examples 1, 3, and 4 has decreased, while in Comparative Example 2, where vacuum impregnation was cancelled, the AlPO4 related peaks are significantly weakened, the baseline is raised, and the peak shape becomes blunter; Comparative Examples 5 and 6 show that the relative decrease of the calcium hexaaluminate and spinel peaks and the increase of the corundum (35.1°, 43.3°, 57.5°) residual peaks, which confirms the influence of different raw material gradations and structural units on phase composition and crystallinity.

[0058] from Figure 3 It can be seen that unmodified α-zirconium phosphate at ~3410 cm⁻¹ -1 It exhibits broad OH stretching absorption at ~1640 cm⁻¹ -1 For water bending vibration; ~1155, ~1065cm -1 PO stretch and ~990cm -1The P-OH peak is strong, and the Zr-OP backbone is clear at ~560 cm⁻¹. After grafting with dimethyl methoxy polyethylene glycol silane, the peaks at ~2950 / 2880 cm⁻¹ are also significant. -1 (CH) and ~1460cm -1 (CH2 bending) Newly appeared / reinforced, 1108-1035cm -1 The COC and Si-O-(Zr) absorption bands in the region overlap with and are significantly enhanced by the phosphate group bands, while the absorption at ~990 cm⁻¹ is also significantly enhanced. -1 (P-OH) significantly reduced, ~3410 / 1640cm -1 The decrease indicates that -OH is partially consumed and forms Si-O-Zr bonds.

[0059] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A refractory precast block for a tunnel kiln car platform, characterized in that, The following raw materials, by weight, are mixed, compacted, cured at low temperature, calcined at medium temperature, impregnated, and calcined at high temperature to obtain: 4600-5000 parts of white molten alumina powder, 1100-1300 parts of molten magnesium aluminum spinel powder, 100-140 parts of plate-shaped alumina, 1300-1500 parts of α-alumina powder, 650-750 parts of calcined kaolin powder, 180-220 parts of lightly calcined magnesium oxide powder, 180-220 parts of precipitated calcium carbonate powder, 90-110 parts of nano-sized magnesium aluminum spinel powder, 45-55 parts of anhydrous aluminum fluoride powder, 120-180 parts of chopped alumina fibers, 110-130 parts of double-grafted zirconium phosphate powder, 1800-2200 parts of a 50wt% aluminum dihydrogen phosphate aqueous solution, and 450-600 parts of deionized water. The low-temperature curing involves holding at 105°C for 100-140 min, at 110°C for 200-280 min, and at 340-360°C for 210-270 min; the medium-temperature calcination involves heating at 4-6°C / min to 930-980°C and holding for 100-140 min; the high-temperature calcination involves heating at 2.5-3.5°C / min to 1410-1440°C and holding for 160-200 min. The double-grafted zirconium phosphate powder is obtained by grafting α-zirconium phosphate powder with methoxy polyethylene glycol silane; The impregnation uses a 50wt% aluminum dihydrogen phosphate aqueous solution, and the amount used is half the weight of the aluminum dihydrogen phosphate aqueous solution in the raw material. The white molten alumina powder is a mixture of white molten alumina powders with a particle size D50 of 1.2 mm and 0.6 mm in a weight ratio of 27-29:19-21. The particle size D50 of the molten magnesium aluminum spinel powder is 1.5 mm; The methoxy polyethylene glycol silane is a mixture of methoxy polyethylene glycol silanes with a weight average molecular weight of 2000 and 20000 in a weight ratio of 1:

1. The method for preparing the refractory precast blocks for the tunnel kiln car platform includes: (1) Add white molten alumina powder, molten magnesium aluminum spinel powder and plate alumina to a mixer and dry mix at 60 rpm for 10 min. Then add α-alumina powder, calcined kaolin powder, lightly calcined magnesium oxide powder, precipitated calcium carbonate powder, nano-sized magnesium aluminum spinel powder, anhydrous aluminum fluoride powder, short-cut alumina fibers and double-grafted zirconium phosphate powder and dry mix at 120 rpm for 20 min. Then add a portion of 50 wt% aluminum dihydrogen phosphate aqueous solution and deionized water and continue stirring for 15 min to obtain a mixed slurry. (2) The mixed slurry is poured into a steel mold, vibrated at 50 Hz for 5 min, then cured at low temperature, and demolded to obtain a demolded blank; (3) The demolded blank is calcined at a medium temperature to obtain a calcined blank; (4) The calcined green body is immersed in an aqueous solution of aluminum dihydrogen phosphate with a remaining concentration of 50wt% at -0.08±0.01MPa, sonicated for 8-12min, then impregnated at normal pressure for 25-40min, drained and dried at 210-230°C for 150-210min to obtain the impregnated green body. (5) The impregnated blank is calcined at high temperature to obtain refractory precast blocks for the kiln car platform of the tunnel kiln.

2. The refractory precast block for the tunnel kiln car platform according to claim 1, characterized in that, The particle size D50 of the α-alumina powder is 2.1 μm, the particle size D50 of the calcined kaolin powder is 3.8 μm, the particle size D50 of the lightly calcined magnesium oxide powder is 8.2 μm, the particle size D50 of the precipitated calcium carbonate powder is 3.5 μm, and the particle size D50 of the anhydrous aluminum fluoride powder is 4.1 μm.

3. The refractory precast block for the tunnel kiln car platform according to claim 1, characterized in that, The plate-shaped alumina has an average sheet thickness of 1.2 μm and an average sheet diameter of 25.4 μm. The particle size D50 of the nano-sized magnesium aluminum spinel powder is 220 nm. The average diameter of the chopped alumina fibers is 3.5 μm and the average length is 5.2 mm.

4. The refractory precast block for the tunnel kiln car platform according to claim 1, characterized in that, The weight ratio of the α-zirconium phosphate powder to the methoxy polyethylene glycol silane is 150:16-24.

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