A zirconium-chromium co-doped phosphate-based high-temperature-resistant composite coating, a preparation method and application thereof

Abstract

This invention discloses a zirconium-chromium co-doped phosphate-based high-temperature resistant composite coating, its preparation method, and its application. The coating is generated in situ by coating and high-temperature treatment of a paint composition comprising aluminum dihydrogen phosphate, zirconium hydroxide, and a trivalent chromium source, wherein the mass ratio of Al(H2PO4)3 to Zr(OH)4 is 3:7 to 7:3, and Cr... 3+ The amount is 10% to 30% of the molar amount of Al(H2PO4)3. The coating composition also contains a composite functional filler composed of boron carbide and silicon dioxide. This invention generates a Zr-O-P precursor sol through a liquid-phase pre-reaction in an 85°C water bath, reducing the curing activation energy from approximately 135 kJ / mol to approximately 72 kJ / mol; it achieves staged degassing and densification through the Cr-O-P crosslinking retardation effect; and it generates a (Zr,Cr,Al)P2O7 multi-principal-element solid solution in situ at 900°C, suppressing thermal stress cracking through lattice distortion. The coating containing B4C-SiO2 filler achieves a thermal shock lifetime of 19 cycles under 900°C water quenching thermal shock conditions, with adhesion grade 0 and abrasion resistance of 3.2 L / μm; the 20% Cr-doped coating achieves a thermal shock lifetime of 23 cycles.

Description

Technical Field

[0001] This invention relates to the field of high-temperature resistant inorganic coating materials, specifically to a high-temperature resistant coating material using zirconium-chromium co-doped aluminum dihydrogen phosphate as a binder matrix and boron carbide and silicon dioxide as composite functional fillers, as well as its preparation method and applications. This coating is suitable for thermal protection and thermal shock resistance of ceramic, metal, or carbon / carbon composite matrices at temperatures of 900℃ and above. Background Technology

[0002] With the rapid development of aerospace, advanced thermal equipment, and high-temperature functional components, the service environment of materials is constantly evolving towards higher temperatures, stronger thermal shock, and more complex atmospheres. For hot-end components and their surface protective layers, long-term high-temperature exposure not only causes oxidation, ablation, and corrosion, but also leads to coating cracking, peeling, and interface failure due to thermal expansion mismatch and thermal cycling stress accumulation. Therefore, developing inorganic protective coatings that combine high-temperature resistance, thermal shock resistance, good interfacial bonding, and structural stability has become an important research direction in the field of high-temperature protection.

[0003] Phosphate-based inorganic coatings have become an important research object for high-temperature protective coatings due to their relatively low curing temperature, good compatibility with various oxides and ceramic fillers, and gradual transformation into a stable ceramic phase during heating. Phosphate binders, represented by aluminum dihydrogen phosphate (Al(H2PO4)3), can form an inorganic polymer network with Al-OP as the main chain on the substrate surface through dehydration condensation, providing reliable protection. However, single aluminum phosphate coatings have the following prominent defects during high-temperature (especially above 900℃) service: (1) high brittleness, with severe volume shrinkage during high-temperature phase transformation, which easily produces microcracks or even macroscopic cracks; (2) insufficient thermal expansion matching, with interface stress concentration under rapid cooling and heating conditions, leading to coating peeling; (3) high curing temperature, with the dehydration condensation activation energy of the pure aluminum dihydrogen phosphate system reaching about 135kJ / mol and the main weight loss peak temperature about 240℃. Severe dehydration shrinkage during high-temperature curing easily causes internal stress concentration and coating defects.

[0004] To address the aforementioned issues, existing technologies have reported modifications to aluminum phosphate by introducing other metallic elements. For example, some studies have introduced Zr into the aluminum phosphate system to improve thermal expansion matching and high-temperature interface stability (Liu et al., J. Adv. Ceram., 2024); some studies have disclosed high-temperature resistant coatings based on the aluminum phosphate chromium system (CN101280130A); and other studies have used a combination of B4C and SiO2 fillers for high-temperature self-healing coatings (PMC, 2024; MDPI Crystals, 2026). Furthermore, JMST 35(2019) 2227 reported equimolar (TiZrHf)P2O7 high-entropy pyrophosphate bulk ceramics, exhibiting high thermal stability and low thermal conductivity; however, this technique is a solid-state synthesis route for equimolar high-entropy bulk ceramics and does not involve in-situ coating formation processes.

[0005] However, the existing technologies mentioned above still have room for improvement in the following aspects: (1) how to reduce the curing temperature of the aluminum phosphate system while taking into account the high-temperature structural stability of the coating; (2) how to reduce pore defects during the curing process of the coating to improve the interfacial bonding strength; (3) how to improve the thermal shock cycle life of the coating under extreme thermal shock conditions of 900℃. Summary of the Invention

[0006] I. Technical problems to be solved This invention aims to solve the following technical problems of existing aluminum phosphate-based high-temperature resistant coatings under extreme thermal shock conditions of 900℃: (1) The curing temperature is too high (the main dehydration condensation peak of the pure aluminum dihydrogen phosphate system is about 240℃). During high-temperature curing, the severe dehydration shrinkage leads to internal stress concentration and coating cracking. (2) Insufficient dehydration and venting during the curing process leads to pore defects inside the coating and insufficient interfacial bonding strength; (3) Under the condition of water quenching at 900℃, the coated ceramic skeleton disintegrates due to lattice thermal stress, and its thermal shock resistance life is limited.

[0007] II. Technical Solution The first aspect of this invention provides a multi-principal-component pyrophosphate solid solution high-temperature thermal shock resistant coating material, which is generated in situ from a coating composition comprising the following components through coating and high-temperature treatment: Aluminum dihydrogen phosphate (Al(H2PO4)3), zirconium hydroxide (Zr(OH)4), and trivalent chromium sources were used as precursors for the formation of the pyrophosphate solid solution, wherein the mass ratio of Al(H2PO4)3 to Zr(OH)4 was 3:7 to 7:3, and the doping amount of chromium was determined by Cr. 3+ It accounts for 10% to 30% of the molar amount of Al(H2PO4)3; The coating material, after being treated at a high temperature of 800-1000℃, forms an in-situ (Zr,Cr,Al)P2O7 substitutional multi-principal solid solution crystal phase with a cubic Pa-3 space group structure, wherein Cr 3+ And Al 3+ Replacement part Zr 4+ The entry of a site into the ZrP2O7 lattice causes lattice contraction and microscopic lattice distortion.

[0008] Preferably, the mass ratio of Al(H2PO4)3 to Zr(OH)4 is 5:5.

[0009] Preferably, the doping amount of chromium is Cr 3+ It accounts for 20% of the molar amount of Al(H2PO4)3.

[0010] Preferably, the trivalent chromium source is chromium nitrate nonahydrate (Cr(NO3)3·9H2O).

[0011] Preferably, the coating composition further comprises added phosphoric acid (H3PO4), the amount of added H3PO4 being such that the molar ratio of P to total metal elements (Al+Zr+Cr) in the system remains the same as the molar ratio of P to total metal elements (Al+Zr) in the system without the addition of a trivalent chromium source.

[0012] Preferably, the coating composition further comprises a composite functional filler consisting of boron carbide (B4C) and silicon dioxide (SiO2).

[0013] Preferably, the mass ratio of B4C to SiO2 is 1:2 to 2:1, more preferably 1:1.

[0014] Preferably, the particle size of B4C is in the micrometer range, preferably 0.5-2 μm; and the particle size of SiO2 is in the nanometer range, preferably 200-800 nm.

[0015] Preferably, the total amount of the composite functional filler added is 8-16 wt% of the solid content of the coating, more preferably 12 wt%.

[0016] Preferably, when the mass ratio of B4C to SiO2 is 1:1, the coating undergoes more than 18 thermal shock failure cycles under water quenching thermal shock cycling conditions at 900°C; more preferably, when the Cr doping content is 20% and the mass ratio of B4C to SiO2 is 1:1, it reaches more than 23 cycles.

[0017] A second aspect of the present invention provides a method for preparing the above-mentioned coating material, comprising the following steps: (1) The aqueous solution of Al(H2PO4)3 and Zr(OH)4 were stirred and reacted in a water bath at 80-85℃ for 1-2 hours to obtain Zr-OP precursor sol; (2) Add Cr(NO3)3·9H2O and H3PO4 to the sol obtained in step (1) and continue stirring until it is evenly dissolved to obtain Cr-Zr-Al-P multi-component precursor sol; (3) Optionally, B4C and SiO2 fillers are added to the sol obtained in step (2), and the mixture is dispersed by ball milling to obtain a coating slurry; (4) Apply the coating slurry to the substrate surface; (5) Curing by gradient heating, including surface drying at 80-150℃ for 30-120 minutes, and then heating to 250-350℃ at a heating rate of 1-5℃ / min and holding for 30-60 minutes to obtain a cured coating; (6) A (Zr,Cr,Al)P2O7 multi-principal solid solution coating is generated in situ by high-temperature treatment at 800-1000℃ for 0.5-3 hours.

[0018] A third aspect of the present invention provides the application of the above-mentioned coating material in the protection of substrate surfaces under high-temperature environments, wherein the substrate includes alumina ceramics, metals, or carbon / carbon composite materials.

[0019] III. Beneficial Effects Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) Significantly reduced curing activation energy, achieving low-temperature densification curing: This invention generates Zr-OP precursor sol through liquid-phase pre-reaction of Zr(OH)4 and Al(H2PO4)3 under 85℃ water bath conditions, significantly reducing the apparent activation energy of the system's dehydration condensation from approximately 135.00 kJ / mol in pure aluminum dihydrogen phosphate to approximately 72.00 kJ / mol (Al:Zr=5:5), a reduction of approximately 46.6%; the main weight loss peak temperature shifts significantly forward from approximately 239.9℃ to approximately 123.6℃. This low-temperature curing characteristic fundamentally avoids the internal stress concentration and coating cracking caused by high-temperature drastic dehydration shrinkage.

[0020] (2) Staged exhaust densification achieved by Cr-OP crosslinking retardation effect: This invention introduces Cr by partially replacing Al(H2PO4)3 with Cr(NO3)3·9H2O. 3+ This forms a Cr-OP octahedral coordination network, inducing a crosslinking lag effect—the main dehydration crosslinking peak is delayed to approximately 149.8-157.3℃ when doped with 20% Cr (delayed by approximately 26-34℃ compared to approximately 123.6℃ in the 0% Cr group), providing sufficient time window for degassing and stress relaxation of the gel network, completely eliminating interfacial porosity defects, enabling the coating adhesion to reach grade 0 (GB / T 9286-2021), and room temperature abrasion resistance to reach 2.13 L / μm (GB / T 23988-2009).

[0021] (3) In-situ generation of (Zr,Cr,Al)P2O7 multi-principal element solid solution to achieve lattice distortion resistance to thermal shock: In this invention, under high temperature treatment at 900℃, Cr 3+ And Al 3+ Replacement part Zr 4+ The Cr submerged into the ZrP2O7 lattice, forming an in-situ (Zr,Cr,Al)P2O7 substitutional multi-principal solid solution with a cubic Pa-3 space group structure. Due to the presence of Cr... 3+ And Al 3+ The ionic radii of all of them are smaller than those of Zr. 4+ This substitution caused lattice shrinkage, resulting in a systematic high-angle shift in XRD diffraction peaks. The resulting micro-lattice distortion field effectively suppressed the propagation of thermal stress microcracks, enabling the coating to withstand 23 failure cycles under extreme water-quenched thermal shock conditions at 900℃ without skeletal disintegration. The 20% Cr-doped group achieved a final residual mass of 82.22% at 900℃.

[0022] (4) Synergistic self-healing achieved by micro- and nano-scale B4C and SiO2: When the mass ratio of B4C (micrometer-scale, approximately 1 μm) to SiO2 (nanometer-scale, approximately 500 nm) is 1:1, the micrometer-scale B4C particles act as a rigid framework, while the nano-scale SiO2 fills the gaps in the framework, constructing the densest multi-scale physical and mechanical framework. In an aerobic environment above 600℃, B4C oxidizes to generate a liquid phase of B2O3 (melting point approximately 450℃), which, along with volume expansion, squeezes and closes the microcracks. Simultaneously, B2O3 reacts with nano-scale SiO2 and the phosphate matrix to generate a phosphobosilicate multiphase glass, forming a dense self-healing glaze. Under this synergistic effect, the coating achieves a 900℃ water quenching thermal shock life of 19 cycles, adhesion grade 0, wear resistance of 3.2 L / μm, and impact resistance of 20 cm.

[0023] (5) 20% Cr doping achieves the optimal balance between curing exhaust dynamics and high-temperature solid solution strengthening: Experiments verified the system comparison of 10%, 20%, and 30% Cr doping amounts -- the 10% Cr group underwent 15 thermal shocks, the 20% Cr group underwent 23 thermal shocks, and the 30% Cr group underwent only 8 thermal shocks. 20% Cr doping achieves the synergistic coupling of sufficient exhaust and densification during the curing stage and the construction of a strong solid solution framework during the high-temperature stage. Attached Figure Description

[0024] This application includes the following figures: Figure 1 Thermogravimetric-differential scanning calorimetry (TG-DSC) curves of pure aluminum dihydrogen phosphate system (10:0) and systems with different Al(H2PO4)3:Zr(OH)4 mass ratios (7:3, 5:5, 3:7); Figure 2X-ray diffraction (XRD) patterns of Al(H2PO4)3:Zr(OH)4 systems with different mass ratios (7:3, 5:5, 3:7) after treatment at 100℃, 300℃, 600℃ and 900℃; Figure 3 Thermogravimetric-derivative thermogravimetric (TG-DTG) curves for systems with different Cr doping concentrations (0%, 10%, 20%, 30%). Figure 4 XRD patterns of systems with different Cr doping concentrations (10%, 20%, 30%) after treatment at 300℃, 600℃, and 900℃; Figure 5 Scanning electron microscope (SEM) images of coatings with different B4C:SiO2 mass ratios (2:1, 1:1, 1:2) after curing at 300℃. Figure 6 Macroscopic morphology photographs of coatings with different B4C:SiO2 mass ratios (2:1, 1:1, 1:2) after calcination at 900℃; Figure 7 SEM microscopic comparison images of coatings with different B4C:SiO2 mass ratios (2:1, 1:1, 1:2) before and after thermal shock; Figure 8 Bar chart showing the number of 900℃ water quenching thermal shock resistance cycles for coatings with different B4C:SiO2 mass ratios; Figure 9 SEM images of coatings with different Cr doping amounts (10%, 20%, 30%) cured at 300℃. Figure 10 Macroscopic morphology photographs of coatings with different Cr doping amounts after calcination at 900℃; Figure 11 Microscopic SEM images of coatings with different Cr doping amounts before and after thermal shock at 900℃; Figure 12 A bar chart showing the number of water quenching thermal shock cycles at 900℃ for coatings with different Cr doping levels. Detailed Implementation

[0025] The present invention will now be described in detail with reference to specific embodiments. These embodiments are intended to help those skilled in the art better understand the present invention, but do not constitute any limitation thereof.

[0026] Unless otherwise stated, all raw materials used in the examples are commercially available industrial products.

[0027] Main raw material sources: - Boron carbide (B4C): purity ≥98%, particle size approximately 1μm; - Silicon dioxide (SiO2): purity ≥99%, particle size approximately 500nm; - Zirconium hydroxide (Zr(OH)4): chemically pure; - Aluminum dihydrogen phosphate (Al(H2PO4)3): purity ≥95%; - Chromium nitrate nonahydrate (Cr(NO3)3·9H2O): purity ≥99%; - Phosphoric acid (H3PO4): concentration ≥85wt%; - Deionized water: prepared in the laboratory.

[0028] General preparation process: (1) Preparation of binder precursor: Weigh Al(H2PO4)3 powder and dissolve it in deionized water to prepare an aqueous solution with a mass concentration of about 30wt%, and pour it into a reaction vessel for water bath heating. When the water bath temperature reaches 80-85℃, add Zr(OH)4 powder according to the set ratio, and react fully for 1-2 hours under stirring to obtain Zr-OP precursor sol.

[0029] (2) Cr doping: In the aforementioned sol, Cr(NO3)3·9H2O and the corresponding amount of 85% H3PO4 are added in a set ratio (the amount of H3PO4 added is determined based on the molar amount of Al replaced by Cr, so that the molar ratio of P element to total metal element Al+Zr+Cr in the system is the same as the molar ratio of P element to total metal element Al+Zr in the system when no Cr source is added), and stirring is continued until completely dissolved to obtain Cr-Zr-Al-P multi-component precursor sol.

[0030] (3) Filler dispersion: Add B4C and SiO2 fillers to the sol in a set ratio, and disperse them by ball milling at a speed of 400-600 r / min for 1-2 hours to obtain a uniform coating slurry. Adjust the amount of deionized water to make the solid content of the slurry 50-60 wt%, preferably 55 wt%.

[0031] (4) Coating: The coating slurry is uniformly coated onto the sandblasted substrate surface by air spraying or brushing. The substrate is an alumina ceramic plate (50mm×50mm×0.5mm).

[0032] (5) Gradient temperature curing: Place the coated test plate in an oven at 80-150℃ for surface drying for 30-120 minutes, then heat it to 300℃ at a heating rate of 1℃ / min and keep it at that temperature for 30 minutes. Then cool it naturally to room temperature to obtain the cured coating.

[0033] (6) High temperature treatment (simulated service): Place the cured coating in a muffle furnace and heat it to 900°C at a certain heating rate in air atmosphere and hold it for 2 hours, then cool it with the furnace.

[0034] Performance testing methods: - Adhesion: Refer to GB / T 9286-2021 "Cross-cut test for paints and varnishes"; - Abrasion resistance: Refer to GB / T 23988-2009 "Determination of abrasion resistance of coatings - Falling sand method"; - Impact resistance: Refer to GB / T 1732-2020 "Determination of impact resistance of paint film"; - Thermal shock cycle test: Refer to GB / T 37246-2018 "Test method for thermal shock resistance of fine ceramics", using the water quenching method (900℃ ⇌ 25℃ deionized water), with the appearance of penetrating macroscopic cracks or the cumulative area of ​​peeling on the coating surface exceeding 15% of the effective area as the failure criterion.

[0035] Example In the following examples, Al(H2PO4)3 was used in the form of an aqueous solution with a mass concentration of about 30 wt% (prepared by dissolving Al(H2PO4)3 powder in deionized water), and the solid content of the coating slurry was adjusted to about 55 wt%.

[0036] Example 1 (Al:Zr=5:5, no Cr doping, B4C:SiO2=1:1) Following a standard preparation process, an aqueous solution of Al(H2PO4)3 and Zr(OH)4 were reacted in a 5:5 mass ratio in an 85°C water bath for 1-2 hours to obtain a Zr-OP precursor sol. Filler (B4C particle size approximately 1 μm, SiO2 particle size approximately 500 nm) was added at a solid content of 12 wt% and a B4C to SiO2 mass ratio of 1:1. The mixture was ball-milled at 500 rpm for 1 hour. The sol was sprayed onto an alumina ceramic substrate and surface-dried at 80-150°C. Then, the temperature was increased to 300°C at a rate of 1°C / min and held for 30 minutes for curing. Finally, the curing process was carried out in a muffle furnace at 900°C for 2 hours.

[0037] The coating prepared in this embodiment has a dense and continuous surface with a uniform ceramic luster. It exhibits adhesion grade 0, abrasion resistance of 3.2 L / μm, and impact resistance of 20 cm. It withstands 19 cycles of water quenching at 900℃, representing the optimal thermal shock resistance ratio in a Cr-free doped system.

[0038] Example 2 (Al:Zr=5:5, no Cr doping, B4C:SiO2=2:1) The preparation method is the same as in Example 1, except that the mass ratio of B4C to SiO2 is 2:1.

[0039] The coating prepared in this embodiment has an abrasion resistance of 1.1 L / μm, an impact resistance of 15 cm, and an adhesion grade of 1. It failed after 12 cycles of water quenching at 900℃. Due to the higher B4C content in this formulation, the high-temperature structural density of the coating decreased, resulting in significantly lower thermal shock resistance compared to Example 1.

[0040] Example 3 (Al:Zr=5:5, no Cr doping, B4C:SiO2=1:2) The preparation method is the same as in Example 1, except that the mass ratio of B4C to SiO2 is 1:2.

[0041] The coating prepared in this embodiment has an abrasion resistance of 1.6 L / μm, an impact resistance of 10 cm, and an adhesion grade of 1. It fails after 15 cycles of water quenching at 900℃. Due to the low B4C content at this formulation, the coating's high-temperature self-healing ability is insufficient, and its thermal shock resistance is lower than that of Example 1.

[0042] Example 4 (Al:Zr=5:5, 20% Cr doping, B4C:SiO2=1:1) Following a common preparation process, an aqueous solution of Al(H2PO4)3 and Zr(OH)4 are reacted in a 5:5 mass ratio in a water bath at 85°C for 1-2 hours to obtain a Zr-OP precursor sol. According to Cr... 3+ Add 20% of the molar amount of Al(H2PO4)3 to Cr(NO3)3·9H2O, and simultaneously add 85% H3PO4 to maintain the same molar ratio of P to total metal elements (Al+Zr+Cr) as when no Cr source was added (the amount of H3PO4 compensation is determined by the amount of Cr substitution and needs to be manually added for precise dosage). After stirring until completely dissolved, add filler at a ratio of 12wt% of total filler in solid content and a B4C to SiO2 mass ratio of 1:1, and ball mill at 500 r / min for 1 hour. Spraying, curing, and high-temperature treatment are the same as in Example 1.

[0043] The coating prepared in this embodiment exhibits an adhesion grade of 0, a wear resistance of 2.13 L / μm, and an impact resistance of 15 cm. It fails after 23 cycles of water quenching and thermal shock at 900℃. The 20% Cr doping achieves an optimal balance between curing exhaust dynamics and high-temperature solid solution strengthening.

[0044] Example 5 (Al:Zr=5:5, 10% Cr doping, B4C:SiO2=1:1) The preparation method is the same as in Example 4, except that the amount of Cr(NO3)3·9H2O added is based on Cr 3+ Based on 10% of the molar amount of Al(H2PO4)3, the amount of H3PO4 compensation is adjusted accordingly.

[0045] The coating prepared in this embodiment has an adhesion grade of 1, an abrasion resistance of 1.8 L / μm, and an impact resistance of 20 cm. It fails after 15 cycles of water quenching and thermal shock at 900℃.

[0046] Example 6 (Al:Zr=5:5, 30% Cr doping, B4C:SiO2=1:1) The preparation method is the same as in Example 4, except that the amount of Cr(NO3)3·9H2O added is based on Cr 3+ Assuming that the amount of H3PO4 accounts for 30% of the molar amount of Al(H2PO4)3, the amount of H3PO4 compensation should be adjusted accordingly.

[0047] The coating prepared in this embodiment exhibits an adhesion grade of 1, a wear resistance of 0.75 L / μm, and an impact resistance of 10 cm. It only fails after 8 cycles of water quenching at 900℃. At this doping level, the coating's internal density decreases and its skeleton becomes excessively brittle, resulting in significantly lower thermal shock resistance compared to Example 4.

[0048] Comparative Example Comparative Example 1 (pure aluminum dihydrogen phosphate, without Zr modification) Weigh out Al(H2PO4)3 and dissolve it in deionized water. Do not add Zr(OH)4 or Cr source. Follow the general preparation process for other steps.

[0049] The pure aluminum dihydrogen phosphate system prepared in this comparative example has an apparent activation energy of approximately 135.00 kJ / mol for dehydration condensation and a main weight loss peak temperature of approximately 239.9 °C. Due to the high curing temperature and lack of Zr-OP heterolinking, the coating developed microcracks during curing due to severe dehydration shrinkage. After high-temperature treatment, its mechanical properties and thermal shock resistance were significantly lower than those of the other examples.

[0050] The coating prepared in this comparative example exhibits an adhesion grade of 2, a wear resistance of 0.06 L / μm, and an impact resistance of 5 cm. It also fails after only 3 cycles of water quenching and thermal shock at 900℃.

[0051] Comparative Example 2 (Al:Zr=7:3, no Cr doping) The preparation method is the same as in Example 1, except that Al(H2PO4)3 and Zr(OH)4 are fed in a mass ratio of 7:3 (precise addition by manual supplementation is required).

[0052] The apparent activation energy of the system at this ratio is approximately 95.00 kJ / mol, and the main weight loss peak temperature is approximately 157.3 °C. The performance of the coating under water quenching thermal shock conditions at 900 °C is significantly lower than that of the 5:5 ratio in Example 1.

[0053] The coating prepared in this comparative example exhibits an adhesion grade of 2, a wear resistance of 0.16 L / μm, and an impact resistance of 5 cm. It also fails after only 5 cycles of water quenching and thermal shock at 900℃.

[0054] Comparative Example 3 (Al:Zr=3:7, no Cr doping) The preparation method is the same as in Example 1, except that Al(H2PO4)3 and Zr(OH)4 are fed in a mass ratio of 3:7.

[0055] The apparent activation energy of the system at this ratio is approximately 65.00 kJ / mol, and the main weight loss peak temperature is approximately 112.2 °C. Although the activation energy is the lowest, the excess Zr(OH)4 leads to a decrease in the stability of the inorganic network structure, resulting in a decline in both the mechanical properties and thermal shock resistance of the coating.

[0056] The coating prepared in this comparative example exhibits an adhesion grade of 3, a wear resistance of 0.36 L / μm, and an impact resistance of 5 cm. It also fails after only 6 cycles of water quenching and thermal shock at 900℃.

[0057] Comparative Example 4 (pure binder, Al:Zr=5:5, no filler) The preparation method is the same as in Example 1, except that B4C and SiO2 fillers are not added.

[0058] Thermogravimetric analysis showed that the pure binder matrix had an extremely low mass loss rate below 900°C, demonstrating that the 5:5 aluminum-zirconium ratio has high intrinsic thermal stability. However, due to the lack of toughening and high-temperature self-healing properties of B4C and SiO2 fillers, its thermal shock resistance after water quenching at 900°C is significantly weaker than that of Example 1 containing fillers.

[0059] The coating prepared in this comparative example exhibits an adhesion grade of 2, a wear resistance of 0.56 L / μm, and an impact resistance of 5 cm. It also fails after only 8 cycles of water quenching and thermal shock at 900℃.

[0060] Experimental Results and Data Analysis Table 1. Curing kinetic parameters of Al(H2PO4)3:Zr(OH)4 systems with different mass ratios As shown in Table 1, the introduction of Zr(OH)4 significantly altered the crosslinking reaction pathway of the system. Compared to the pure aluminum dihydrogen phosphate system, the dehydration condensation activation energy of the Zr-modified system was significantly reduced—the activation energy at Al:Zr=5:5 was reduced by approximately 46.6% compared to the pure system, and the main weight loss peak temperature was reduced by approximately 116.3℃. This allowed the coating to achieve dense curing at a lower temperature, effectively alleviating the internal stress caused by the intense dehydration shrinkage at high temperatures.

[0061] Table 2. Performance comparison of pure binder systems (without fillers) with different Al(H2PO4)3:Zr(OH)4 mass ratios As shown in Table 2, in the pure binder (without filler) system, Al:Zr=5:5 has better wear resistance and thermal shock life than other ratios, which is consistent with the data of Comparative Example 4.

[0062] Table 3. Curing kinetic parameters of systems with different Cr doping concentrations As shown in Table 3, Cr3+ The introduction of Cr delayed the main dehydration crosslinking peak from approximately 123.6℃ to approximately 149.8-157.3℃. Note: The 0% Cr doping group in Table 3 is the Al:Zr=5:5 system. The difference in its activation energy (80.44 kJ / mol) compared to the data for the same system in Table 1 (72.00 kJ / mol) is due to normal fluctuations in the Kissinger multi-rate heating fitting of two independent experimental batches (the main weight loss peak temperatures of both are highly consistent at 10℃ / min, both approximately 123.6℃). Both sets of data are valid experimental values. 3+ The formed Cr-OP octahedral coordination network induces a crosslinking hysteresis effect, providing ample time window for degassing and stress relaxation of the gel network. The 20% Cr doped group exhibits a final residual mass of up to 82.22% at 900℃, demonstrating optimal resistance to thermal disintegration.

[0063] Table 4. Performance comparison of coatings with different B4C:SiO2 mass ratios (Al:Zr=5:5, no Cr doping) As shown in Table 4, the B4C:SiO2 ratio of 1:1 exhibits the best performance across all test indicators. This ratio achieves an optimized balance between the fluxing oxide source and the glass network forging. In an aerobic environment at 900℃, the B2O3 liquid phase generated by B4C oxidation (melting point approximately 450℃) exhibits good wettability and reacts with nano-SiO2 and the phosphate matrix to form a phosphobosilicate multiphase glass, resulting in a dense and tough self-healing glaze.

[0064] Table 5. Performance comparison of coatings with different Cr doping amounts (Al:Zr=5:5, B4C:SiO2=1:1) As shown in Table 5, the 20% Cr doping concentration achieved the best overall performance. The 10% Cr group had insufficient solid solution volume fraction, resulting in a thermal shock lifetime of only 15 cycles; the 30% Cr group, due to decreased density and excessively brittle framework, experienced a sharp drop in thermal shock lifetime to 8 cycles. The 20% Cr group (23 cycles) showed an approximately 53% improvement in thermal shock lifetime compared to the 10% group and an approximately 188% improvement compared to the 30% group.

[0065] XRD evidence of (Zr,Cr,Al)P2O7 solid solution In the XRD pattern after treatment at 900℃, as the Cr doping concentration increased from 10% to 30%, the main characteristic diffraction peaks of ZrP2O7 showed a regular shift towards higher angles. According to the Bragg diffraction equation (2d sinθ = nλ), an increase in the diffraction angle θ implies a continuous decrease in the interplanar spacing d. Because Cr... 3+ And Al 3+ The ionic radii of all of them are smaller than those of Zr. 4+The systematic high-angle shift of the diffraction peaks confirmed that Cr and Al replaced some Zr sites in the ZrP2O7 lattice, resulting in the in-situ formation of a (Zr,Cr,Al)P2O7 substitution-type multi-principal solid solution.

[0066] Industrial applicability The zirconium-chromium co-doped phosphate-based high-temperature resistant composite coating provided by this invention has a simple preparation process, readily available raw materials, and a low curing temperature (300℃), making it suitable for industrial production. This coating exhibits excellent thermal shock resistance and structural stability at 900℃, and can be applied to surface thermal protection in aerospace engine hot-end components, industrial kilns, high-temperature ceramic / metal connectors, and other fields, demonstrating clear industrial application prospects.

Claims

1. A high-temperature thermal shock resistant coating material of multi-principal-component pyrophosphate solid solution, characterized in that, It is generated in situ by coating and high-temperature treatment of a coating composition comprising the following components: Aluminum dihydrogen phosphate (Al(H2PO4)3), zirconium hydroxide (Zr(OH)4), and trivalent chromium sources were used as precursors for the formation of the pyrophosphate solid solution, wherein the mass ratio of Al(H2PO4)3 to Zr(OH)4 was 3:7 to 7:3, and the doping amount of chromium was determined by Cr. 3+ It accounts for 10% to 30% of the molar amount of Al(H2PO4)3; The coating material, after being treated at a high temperature of 800-1000℃, forms an in-situ (Zr,Cr,Al)P2O7 substitutional multi-principal solid solution crystal phase with a cubic Pa-3 space group structure, wherein Cr 3+ And Al 3+ Replacement part Zr 4+ The entry of a site into the ZrP2O7 lattice causes lattice contraction and microscopic lattice distortion.

2. The coating material according to claim 1, characterized in that, The mass ratio of Al(H2PO4)3 to Zr(OH)4 is 5:

5.

3. The coating material according to claim 1, characterized in that, The doping amount of chromium is expressed as Cr 3+ It accounts for 20% of the molar amount of Al(H2PO4)3.

4. The coating material according to claim 1, characterized in that, The trivalent chromium source is chromium nitrate nonahydrate (Cr(NO3)3·9H2O).

5. The coating material according to claim 1, characterized in that, The coating composition further comprises added phosphoric acid (H3PO4), the amount of which is such that the molar ratio of P to total metal elements (Al+Zr+Cr) in the system remains the same as that in the system without the addition of a trivalent chromium source.

6. The coating material according to claim 1, characterized in that, The coating composition also includes a composite functional filler consisting of boron carbide (B4C) and silicon dioxide (SiO2).

7. The coating material according to claim 6, characterized in that, The mass ratio of B4C to SiO2 is 1:2 to 2:

1.

8. The coating material according to claim 6, characterized in that, The particle size of B4C is 0.5-2 μm, and the particle size of SiO2 is 200-800 nm.

9. The coating material according to claim 6, characterized in that, The total amount of the composite functional filler added is 8-16 wt% of the solid content of the coating.

10. The coating material according to claim 7, characterized in that, When the mass ratio of B4C to SiO2 is 1:1, the coating can withstand more than 18 thermal shock failure cycles under water quenching thermal shock cycling conditions at 900℃.

11. The coating material according to claims 3 and 7, characterized in that, When the doping amount of chromium is Cr 3+ When the amount of B4C is 20% of the molar amount of Al(H2PO4)3 and the mass ratio of B4C to SiO2 is 1:1, the coating can withstand more than 23 thermal shock failure cycles under water quenching thermal shock cycling conditions at 900℃.

12. A method for preparing the coating material according to any one of claims 1 to 11, characterized in that, Includes the following steps: (1) The aqueous solution of Al(H2PO4)3 and Zr(OH)4 were stirred and reacted in a water bath at 80-85℃ for 1-2 hours to obtain Zr-OP precursor sol; (2) Add Cr(NO3)3·9H2O and H3PO4 to the sol obtained in step (1) and continue stirring until it is evenly dissolved to obtain Cr-Zr-Al-P multi-component precursor sol; (3) Optionally add B4C and SiO2 fillers to the sol obtained in step (2), and disperse by ball milling to obtain a coating slurry; (4) Apply the coating slurry to the substrate surface; (5) Curing by gradient heating, including surface drying at 80-150℃ for 30-120 minutes, and then heating to 250-350℃ at a heating rate of 1-5℃ / min and holding for 30-60 minutes to obtain a cured coating; (6) A (Zr,Cr,Al)P2O7 multi-principal solid solution coating is generated in situ by high-temperature treatment at 800-1000℃ for 0.5-3 hours.

13. The preparation method according to claim 12, characterized in that, The gradient temperature curing step (5) involves heating to 300°C at a rate of 1°C / min and holding for 30 minutes.

14. The preparation method according to claim 12, characterized in that, In step (6), the high-temperature treatment temperature is 900℃ and the treatment time is 2 hours.

15. The preparation method according to claim 12, characterized in that, In step (1), the mass concentration of the Al(H2PO4)3 aqueous solution is 25-35 wt%; in step (3), the ball milling speed is 400-600 r / min and the ball milling time is 1-2 hours; the solid content of the coating slurry is 50-60 wt%.

16. A method for protecting the surface of a substrate, characterized in that, The coating material according to any one of claims 1 to 11 is applied to the surface of a substrate, wherein the substrate comprises alumina ceramic, metal or carbon / carbon composite material.

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