A high-temperature-resistant, corrosion-resistant and wear-resistant coating for boilers and a preparation method thereof

Abstract

The present application relates to the technical field of high-temperature protective coating, in particular to a boiler high-temperature-resistant anticorrosive wear-resistant coating and a preparation method thereof, which is composed of A component powder mixture and B component liquid binder, and the mass ratio of A component to B component is 1:0.8 to 1:0.9; according to mass parts, A component includes the following raw materials: 32 to 38 parts of fused mullite powder, 8 to 12 parts of synthetic cordierite powder, 6 to 10 parts of zirconite micro powder, 4 to 8 parts of beta silicon carbide whisker, 11 to 15 parts of alpha alumina micro powder, 9 to 13 parts of borosilicate glass flake, 6 to 9 parts of calcium aluminate cement and 7 to 11 parts of silicon micro powder; the borosilicate glass flake with a softening point of 580 to 620 DEG C is selected, micro-fusion filling pores occur under the typical medium-temperature working condition of the boiler, and the strength collapse problem of the traditional inorganic coating in the range of 200 to 600 DEG C is effectively avoided.

Description

Technical Field

[0001] This invention relates to the field of high-temperature protective coating technology, specifically to a high-temperature resistant, corrosion-resistant, and wear-resistant coating for boilers and its preparation method. Background Technology

[0002] Coal-fired boilers are core thermal equipment in industries such as power, metallurgy, and petrochemicals. The boiler's heating surfaces are subjected to a combined environment of high-temperature flue gas erosion, fly ash wear, and sulfate corrosion. The operating wall temperatures of water-cooled wall tubes and superheater tubes can reach 500 to 900°C, and the flue gas side is also continuously corroded by sulfur- and alkali-containing ash. Statistics show that tube rupture accidents caused by wear and corrosion account for more than 40% of unplanned boiler shutdowns, resulting in significant economic losses and safety hazards.

[0003] Existing high-temperature protective coatings for boilers are mainly divided into two categories: silicone-based and inorganic ceramic-based. Silicone-based coatings use silicone resin as a base material, combined with heat-resistant fillers such as aluminum powder and mica. They have good application performance, but their long-term operating temperature generally does not exceed 600℃. In the high-temperature zone of the boiler, organic components are prone to decomposition and coating powdering. Inorganic ceramic-based coatings use silicates or phosphates as binders, combined with ceramic fillers such as alumina and silicon carbide. They have excellent temperature resistance but have the following shortcomings: First, the coating is brittle, and its coefficient of thermal expansion differs significantly from that of the metal substrate. The thermal cycle during boiler start-up and shutdown can easily lead to cracking and peeling of the coating. Second, there is a low strength trough in the intermediate temperature range during curing, namely between 200 and 600℃, when the binder has not yet been fully ceramicized and the low-temperature curing phase has already begun to decompose, resulting in a loose coating structure that is susceptible to corrosion by flue gas. Third, the anti-corrosion performance depends on the coating density, and the high porosity after curing with a single inorganic binder allows corrosive gases to easily penetrate into the substrate.

[0004] Patent CN100343345C discloses a supercritical boiler anti-wear and anti-corrosion coating, using nano-alumina and titanium carbide as fillers and sodium silicate and epoxy acrylate as binders. The coating can withstand temperatures up to 1250℃, but the organic components decompose at high temperatures, leaving pores and resulting in insufficient long-term service stability. Patent CN117586654A discloses an anti-coking and anti-corrosion coating, using water glass and modified silica sol as binders, combined with fused silica and compounded metal oxides, achieving a temperature resistance of up to 1600℃, but it does not address the strength decay issue in the mid-temperature range. Patent CN101092526A discloses a high-temperature resistant coating using aluminum dihydrogen phosphate and potassium silicate as composite binders, proposing the concept of a dual skeleton of silicates and phosphates. However, its fillers are mainly magnesium oxide and silicon dioxide, primarily used for thermal insulation, and not suitable for the strong erosion, wear-resistant, and anti-corrosion conditions of boiler tubes.

[0005] Therefore, developing a boiler protective coating that can maintain a good ceramic structure at high temperatures, maintain sufficient strength in the medium temperature range to avoid early failure, and at the same time have excellent wear resistance and corrosion resistance is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The primary objective of this invention is to provide a high-temperature resistant, corrosion-resistant, and wear-resistant coating for boilers and its preparation method.

[0007] A further objective of this invention is to provide a boiler high-temperature resistant, corrosion-resistant, and wear-resistant coating, which is composed of a powder mixture of component A and a liquid binder of component B, wherein the mass ratio of component A to component B is 1:0.8 to 1:0.9. By mass, component A comprises the following raw materials: 32 to 38 parts of fused mullite powder, 8 to 12 parts of synthetic cordierite powder, 6 to 10 parts of zircon micro powder, 4 to 8 parts of β-type silicon carbide whiskers, 11 to 15 parts of α-alumina micro powder, 9 to 13 parts of borosilicate glass flakes, 6 to 9 parts of calcium aluminate cement, and 7 to 11 parts of silica micro powder. By mass, component B comprises the following raw materials: Potassium silicate solution 38 to 45 parts, aluminum dihydrogen phosphate solution 22 to 28 parts, silica sol 10 to 16 parts, deionized water 15 to 22 parts, sodium hexametaphosphate 0.4 to 0.8 parts, hydroxypropyl methylcellulose 0.2 to 0.5 parts, silane coupling agent 0.8 to 1.5 parts; The borosilicate glass flakes have a softening point of 580 to 620°C, a thickness of 2 to 4 μm, and a diameter of 20 to 50 μm. The potassium silicate solution has a modulus of 3.2 to 3.4 and a silica mass fraction of 40 to 44%. The aluminum dihydrogen phosphate solution contains 32 to 34% phosphorus pentoxide and 8.0 to 9.0% aluminum oxide by mass.

[0008] Preferably, the fused mullite powder has a particle size d50 of 4 to 6 μm and an aluminum oxide mass fraction of not less than 70%; the synthetic cordierite powder has a particle size d50 of 2 to 4 μm and a chemical composition of 2MgO·2Al2O3·5SiO2.

[0009] Preferably, the zircon micro powder has a particle size d50 of 1.5 to 2.5 μm and a zircon dioxide mass fraction of not less than 65%; the silica micro powder has a particle size d50 of 0.2 to 0.4 μm and a silica mass fraction of not less than 96%.

[0010] Preferably, the diameter of the β-type silicon carbide whisker is 0.3 to 0.8 μm and the aspect ratio is 20 to 40.

[0011] Preferably, the particle size d50 of the α-alumina micro powder is 0.8 to 1.5 μm, and the mass fraction of the α phase is not less than 95%; the mass fraction of aluminum oxide in the calcium aluminate cement is not less than 70%, and the mass fraction of calcium oxide is not more than 28%.

[0012] Preferably, the silica sol has a particle size of 10 to 20 nm, a silica mass fraction of 28 to 32%, and a pH value of 9.0 to 10.0.

[0013] Preferably, the silane coupling agent is γ-glycidoxypropyltrimethoxysilane; and the viscosity of the hydroxypropyl methylcellulose is 3000 to 5000 mPa·s.

[0014] A method for preparing the aforementioned high-temperature resistant, corrosion-resistant, and wear-resistant coating for boilers includes the following steps: Step 1, Preparation of Component A: Weigh out the fused mullite powder, synthetic cordierite powder, zircon micro powder, β-type silicon carbide whiskers, α-alumina micro powder, borosilicate glass flakes, calcium aluminate cement, and silica micro powder according to the formula ratio, and put them into a vertical ribbon mixer. First, mix at a speed of 60 to 80 r / min for 10 to 15 min, then increase the speed to 120 to 150 r / min and continue mixing for 20 to 30 min. During the mixing process, dry air is introduced to control the powder temperature not to exceed 40℃. After mixing, sieve through a 200-mesh standard sieve to obtain the Component A powder mixture. Step 2, Preparation of Component B: First, add sodium hexametaphosphate and hydroxypropyl methylcellulose to deionized water and stir at 400 to 600 r / min for 8 to 12 minutes until completely dissolved. Then, add potassium silicate solution and continue stirring for 5 to 8 minutes. Next, slowly add aluminum dihydrogen phosphate solution over a time of 15 to 20 minutes, maintaining a stirring speed of 600 to 800 r / min and a material temperature not exceeding 50°C. After the addition is complete, add silica sol and silane coupling agent and continue stirring for 10 to 15 minutes to obtain the component B liquid binder. Step 3, finished product preparation: Before use, weigh component A and component B at a mass ratio of 1:0.8 to 1:0.9. First, put component B into a stirring container, and add component A in batches while stirring at a speed of 500 to 700 r / min. After all the components are added, continue stirring for 15 to 20 minutes, and degas under a vacuum of 0.06 to 0.08 MPa for 5 to 8 minutes to obtain the boiler high-temperature resistant, corrosion-resistant, and wear-resistant coating.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses borosilicate glass flakes with a softening point of 580 to 620°C, which undergo micro-melting and fill the pores under typical medium-temperature conditions in boilers, effectively avoiding the strength collapse problem of traditional inorganic coatings in the 200 to 600°C range.

[0016] 2. The high-temperature ceramic transformation of this invention achieves excellent temperature and wear resistance; when the temperature exceeds 900℃, the glass phase reacts in situ with active alumina and silicon micropowder to generate mullite microcrystals, forming a ceramic reinforcing skeleton inside the coating.

[0017] 3. This invention enhances corrosion resistance through a labyrinthine barrier structure; the sheet-like structure of borosilicate glass flakes is stacked in parallel in the coating to form a tortuous labyrinthine penetration path. Combined with the self-healing effect of glass micro-melting, the porosity of the coating is reduced to below 9%, and the resistance to sulfate corrosion is significantly improved.

[0018] 4. The multi-component toughening system of this invention can improve thermal shock stability; the pull-out bridging effect of silicon carbide whiskers, the low thermal expansion characteristics of cordierite, and the high hardness and wear-resistant skeleton effect of zircon (Note: Zircon ZrSiO4 itself does not have phase transformation toughening characteristics, but mainly provides wear-resistant support and microcrack deflection toughening through a high-hardness ceramic phase with a Mohs hardness of 7.5) synergistically improve the toughness and thermal shock resistance of the coating.

[0019] 5. In this invention, potassium silicate provides room temperature strength, calcium aluminate cement provides early and mid-stage hydration strength, and aluminum dihydrogen phosphate participates in the mid-temperature chemical reaction. The three components play a bonding role in different temperature ranges in sequence. Combined with a stepped curing process, this ensures that the coating has stable structural strength at each temperature stage. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Invention Mechanism: The core mechanism of this invention lies in the mid-temperature self-healing effect of borosilicate glass flakes and the high-temperature ceramic transformation pathway.

[0022] Borosilicate glass possesses a low softening temperature and good chemical stability. This invention selects borosilicate glass flakes with a softening point of 580 to 620°C, a temperature range that precisely covers the typical medium-temperature conditions of the flue gas side of a coal-fired boiler. When the coating is within this temperature range, micro-melting occurs at the edges of the glass flakes. The molten glass phase, under capillary force, fills the micron-sized pores and microcracks within the coating, achieving a self-healing effect. Simultaneously, the lamellar structure of the glass flakes themselves forms a labyrinthine barrier path within the coating, significantly extending the penetration distance of corrosive media. The micro-melting of the glass flakes does not destroy their lamellar structure; instead, it makes the bonding between the flakes and surrounding filler particles tighter. Therefore, in the medium-temperature range above 580°C, not only is there no decrease in strength, but the strength is actually increased due to the self-healing effect. In the 200 to 550°C range, the hydration products of calcium aluminate cement (CAH... 10 The calcium aluminum silicate hydrate (CASH phase) is gradually generated by the reaction of silica sol with C2AH8 and other materials. This hydrated product fills the gaps between filler particles, effectively compensating for the strength loss caused by the dehydration and decomposition of the low-temperature binder phase, thereby achieving a stable strength transition across the entire medium-temperature range.

[0023] As the temperature rises further to above 900℃, the increasingly molten glass phase begins to undergo a solid-liquid reaction with the surrounding α-alumina and silica powders. The silica component in the borosilicate glass reacts with α-alumina under the liquid-phase fluxing action of the glass phase to form a mullite crystalline phase, specifically, three molecules of alumina combined with two molecules of silica to form 3Al₂O₃·2SiO₂ type mullite. This reaction grows mullite microcrystals outward from the glass flakes as a substrate, forming whisker-like or columnar mullite precursor structures, constructing a ceramic reinforcing framework within the coating. Meanwhile, cordierite powder and zircon powder, as stable high-temperature resistant aggregates, provide high-temperature strength and wear resistance support for the coating; β-type silicon carbide whiskers toughen the coating through crack deflection, whisker pull-out, and bridging, alleviating thermal stress concentration; in high-temperature environments above 900℃, selective oxidation occurs on the whisker surface to generate a dense SiO2 protective film. This oxide layer has good compatibility with the borosilicate glass phase and can fuse with the glass phase to form a continuous ceramic bonding interface, avoiding performance degradation caused by complete whisker oxidation; calcium aluminate cement provides hydration bond strength in the medium and low temperature stages, and its hydration products react with silica sol in the medium temperature zone to generate a calcium aluminosilicate phase, further enhancing the medium temperature strength. In the binder system, potassium silicate serves as the primary binder, providing room-temperature curing strength and a high-temperature silicon-oxygen network framework. Aluminum dihydrogen phosphate acts as an auxiliary binder, chemically bonding with the surface of the active filler during curing to form a phosphate binder phase. Simultaneously, its acidic groups moderately promote the gelation reaction of potassium silicate. Silica sol, as a nanoscale binding reinforcement phase, fills the gaps between filler particles, improving coating density and interfacial adhesion. During preparation, the dropping rate of aluminum dihydrogen phosphate into the potassium silicate system is controlled to avoid excessive local acid-base reactions leading to uneven gelation. These three components together constitute a potassium silicate-phosphate-silica sol ternary composite binder system, sequentially exerting their effects across different temperature ranges to ensure strength across the entire temperature spectrum. This ternary composite adhesive system forms a stable colloidal dispersion at room temperature. When component B is stored alone, the composite sol formed by aluminum dihydrogen phosphate and potassium silicate is in a kinetically stable state and will not undergo rapid gelation. It can be stored at room temperature in a sealed container for 7 to 10 days (Note: Because the acid-base reaction kinetics of potassium silicate and aluminum dihydrogen phosphate accumulate over time, it is recommended that component B be used within 7 days after preparation to ensure the activity of the curing reaction). When used, after being mixed with component A, the curing reaction proceeds gradually under the catalytic action of the active filler surface.

[0024] The sources and specifications of the raw materials used in the examples are as follows: Fused mullite powder, grade M70, d50 of 5μm, Al2O3 mass fraction of 72%, Zhengzhou Abrasives & Grinding Research Institute Co., Ltd.

[0025] Synthetic cordierite powder, grade COR, d50 3μm, chemical composition 2MgO·2Al2O3·5SiO2, Henan Refractory Materials Research Institute Co., Ltd.

[0026] Zircon micro powder, grade ZIR65, d50 is 2μm, ZrO2 mass fraction is 66%, Guangdong Oriental Zirconium Industry Technology Co., Ltd.

[0027] β-type silicon carbide whiskers, grade β-SiCw-05, with a diameter of 0.3 to 0.8 μm, an aspect ratio of 20 to 40, and a purity of ≥98.5%, were prepared by carbothermal reduction and purchased from Beijing Huawi Ruike Chemical Co., Ltd.

[0028] Alpha alumina micro powder, grade AL-1, d50 is 1μm, α phase mass fraction is 96%, China Aluminum Shandong Branch (Shandong Aluminum Co., Ltd.).

[0029] Type C borosilicate glass flakes, grade REF-050, softening point approximately 590°C, thickness 2 to 4 μm, flake diameter 20 to 50 μm (average particle size approximately 50 μm), NSG original GLASFLAKE® series, purchased from Nippon Sheet Glass Co., Ltd. (NSG Group).

[0030] Calcium aluminate cement, grade CA70, with Al2O3 mass fraction of 71% and CaO mass fraction of 26%, produced by Zhengzhou Dengdian Cement Co., Ltd.

[0031] Silicon micropowder, grade SF96, d50 is 0.3μm, SiO2 mass fraction is 97%, Qinghai Wutong Group Industrial Co., Ltd.

[0032] Potassium silicate solution, modulus 3.3, SiO2 mass fraction 42%, K2O mass fraction 12.7%, Shandong Liaocheng Jin Haiyang Potassium Silicate Co., Ltd.

[0033] Aluminum dihydrogen phosphate solution, with a P2O5 mass fraction of 33%, an Al2O3 mass fraction of 8.5%, and a density of 1.45 g / cm³. 3 Industrial grade, Jiaozuo Zhongzhou Phosphate Chemical Co., Ltd.

[0034] Silica sol, grade JN30, particle size 10 to 20 nm, SiO2 mass fraction 30%, pH value 9.5, Zhejiang Yuda Chemical Co., Ltd.

[0035] Sodium hexametaphosphate, industrial grade, 68% purity, Xingfa Group Co., Ltd.

[0036] Hydroxypropyl methylcellulose, grade HPMC4000, viscosity 4000 mPa·s, Shandong Heda Group Co., Ltd.

[0037] Silane coupling agent KH560, chemical name γ-glycidyl etheroxypropyltrimethoxysilane, purity 98%, Nanjing Shuguang Chemical Group Co., Ltd.

[0038] Example 1: Raw material formula: Component A: 35 parts fused mullite powder, 10 parts synthetic cordierite powder, 8 parts zircon micro powder, 6 parts β-type silicon carbide whiskers, 13 parts α-alumina micro powder, 11 parts borosilicate glass flakes, 7 parts calcium aluminate cement, and 10 parts silica powder. The total amount of all components is 100 parts.

[0039] Component B: 42 parts potassium silicate solution, 25 parts aluminum dihydrogen phosphate solution, 13 parts silica sol, 18 parts deionized water, 0.6 parts sodium hexametaphosphate, 0.3 parts hydroxypropyl methylcellulose, and 1.1 parts silane coupling agent KH560. The total amount of all components is 100 parts.

[0040] The mass ratio of component A to component B is 1:0.85.

[0041] Preparation process: Step 1, Preparation of Component A: Weigh each powder raw material according to the above proportions and put them into a vertical ribbon mixer. Mix at 70 r / min for 12 min, then increase the speed to 130 r / min and continue mixing for 25 min. During the mixing process, dry air is introduced to control the powder temperature at 35℃. After the mixing is completed, the powder is sieved through a 200-mesh standard sieve to obtain the powder mixture of Component A.

[0042] Step 2, Preparation of Component B: First, add sodium hexametaphosphate and hydroxypropyl methylcellulose to deionized water and stir at 500 r / min for 10 min until completely dissolved. Then, add potassium silicate solution and continue stirring for 6 min. Next, slowly add aluminum dihydrogen phosphate solution over 18 min, maintaining a stirring speed of 700 r / min and a material temperature of 45℃ during the addition process. After the addition is complete, add silica sol and silane coupling agent KH560 and continue stirring for 12 min to obtain the liquid binder of Component B.

[0043] Step 3, finished product preparation: Before use, weigh component A and component B at a mass ratio of 1:0.85. First, put component B into the mixing container, and add component A in three batches while stirring at 600 r / min. After all the components are added, continue stirring for 18 min. Degas under a vacuum of 0.07 MPa for 6 min to obtain the finished coating.

[0044] In this embodiment, after the coating has cured at room temperature for 7 days, the coating surface is smooth and flat with no obvious pinholes. After heat treatment at 800℃, the coating is dark gray and has a dense structure.

[0045] Example 2: Raw material formula: Component A: 38 parts fused mullite powder, 8 parts synthetic cordierite powder, 10 parts zircon micro powder, 4 parts β-type silicon carbide whiskers, 15 parts α-alumina micro powder, 9 parts borosilicate glass flakes, 6 parts calcium aluminate cement, and 10 parts silica powder. The total amount of all components is 100 parts.

[0046] Component B: 45 parts potassium silicate solution, 22 parts aluminum dihydrogen phosphate solution, 10 parts silica sol, 20.7 parts deionized water, 0.4 parts sodium hexametaphosphate, 0.4 parts hydroxypropyl methylcellulose, and 1.5 parts silane coupling agent KH560. The total amount of all components is 100 parts.

[0047] The mass ratio of component A to component B is 1:0.82.

[0048] Preparation process: Step 1, Preparation of Component A: Weigh each powder raw material according to the above proportions and put them into a vertical ribbon mixer. Mix at 60 r / min for 15 min, then increase the speed to 150 r / min and continue mixing for 20 min. During the mixing process, dry air is introduced to control the powder temperature at 32℃. After the mixing is completed, the powder is sieved through a 200-mesh standard sieve to obtain the powder mixture of Component A.

[0049] Step 2, Preparation of Component B: First, add sodium hexametaphosphate and hydroxypropyl methylcellulose to deionized water and stir at 400 r / min for 12 min until completely dissolved. Then, add potassium silicate solution and continue stirring for 8 min. Next, slowly add aluminum dihydrogen phosphate solution over 15 min, maintaining a stirring speed of 800 r / min and a material temperature of 42℃ during the addition process. After the addition is complete, add silica sol and silane coupling agent KH560 and continue stirring for 10 min to obtain the liquid binder of Component B.

[0050] Step 3, finished product preparation: Before use, weigh component A and component B at a mass ratio of 1:0.82. First, put component B into the mixing container, and add component A in three batches while stirring at 500 r / min. After all the components are added, continue stirring for 20 min, and degas for 8 min under a vacuum of 0.06 MPa to obtain the finished coating.

[0051] The coating in this embodiment has a higher content of zircon and alumina, and a slightly lower content of mullite and glass flakes. The coating has a higher high-temperature hardness, but its mid-temperature self-healing effect is slightly weaker than that in Example 1.

[0052] Example 3: Raw material formula: Component A: 32 parts fused mullite powder, 12 parts synthetic cordierite powder, 6 parts zircon micro powder, 8 parts β-type silicon carbide whiskers, 11 parts α-alumina micro powder, 13 parts borosilicate glass flakes, 9 parts calcium aluminate cement, and 9 parts silica micro powder. The total amount of all components is 100 parts.

[0053] Component B: 38 parts potassium silicate solution, 28 parts aluminum dihydrogen phosphate solution, 16 parts silica sol, 15.6 parts deionized water, 0.8 parts sodium hexametaphosphate, 0.2 parts hydroxypropyl methylcellulose, and 1.4 parts silane coupling agent KH560. The total amount of all components is 100 parts.

[0054] The mass ratio of component A to component B is 1:0.88.

[0055] Preparation process: Step 1, Preparation of Component A: Weigh each powder raw material according to the above proportions and put them into a vertical ribbon mixer. Mix at 80 r / min for 10 min, then increase the speed to 120 r / min and continue mixing for 30 min. During the mixing process, dry air is introduced to control the powder temperature at 38℃. After the mixing is completed, the powder is sieved through a 200-mesh standard sieve to obtain the powder mixture of Component A.

[0056] Step 2, Preparation of Component B: First, add sodium hexametaphosphate and hydroxypropyl methylcellulose to deionized water and stir at 600 r / min for 8 min until completely dissolved. Then, add potassium silicate solution and continue stirring for 5 min. Next, slowly add aluminum dihydrogen phosphate solution over 20 min, maintaining a stirring speed of 600 r / min and a material temperature of 48℃ during the addition process. After the addition is complete, add silica sol and silane coupling agent KH560 and continue stirring for 15 min to obtain the liquid binder of Component B.

[0057] Step 3, Preparation of finished product: Before use, weigh component A and component B at a mass ratio of 1:0.88. First, put component B into the mixing container, and add component A in three batches while stirring at 700 r / min. After all the components are added, continue stirring for 15 min. Degas under a vacuum of 0.08 MPa for 5 min to obtain the finished coating.

[0058] The coating in this embodiment has a high content of glass flakes and silicon carbide whiskers, resulting in a more significant self-healing effect and toughening effect, as well as better thermal shock resistance.

[0059] Comparative Example 1: Raw material formula: Component A: 46 parts fused mullite powder, 10 parts synthetic cordierite powder, 8 parts zircon micro powder, 6 parts β-type silicon carbide whiskers, 13 parts α-alumina micro powder, 7 parts calcium aluminate cement, and 10 parts silica micro powder. The total amount of all components is 100 parts.

[0060] Component B: 42 parts potassium silicate solution, 25 parts aluminum dihydrogen phosphate solution, 13 parts silica sol, 18 parts deionized water, 0.6 parts sodium hexametaphosphate, 0.3 parts hydroxypropyl methylcellulose, and 1.1 parts silane coupling agent KH560. The total amount of all components is 100 parts.

[0061] The mass ratio of component A to component B is 1:0.85.

[0062] Preparation process: The preparation process is the same as in Example 1, except that component A does not contain borosilicate glass flakes, and the corresponding reduction in mass is made up by fused mullite powder.

[0063] This comparative example is a blank comparative example, which does not contain the core innovative component borosilicate glass flakes, and is used to verify the self-healing effect of glass flakes and their contribution to various properties.

[0064] Comparative Example 2: Raw material formula: Component A: 35 parts fused mullite powder, 10 parts synthetic cordierite powder, 8 parts zircon micro powder, 6 parts β-type silicon carbide whiskers, 13 parts α-alumina micro powder, 11 parts ordinary soda-lime glass flakes, 7 parts calcium aluminate cement, and 10 parts silica powder. The total amount of all components is 100 parts.

[0065] Component B: 42 parts potassium silicate solution, 25 parts aluminum dihydrogen phosphate solution, 13 parts silica sol, 18 parts deionized water, 0.6 parts sodium hexametaphosphate, 0.3 parts hydroxypropyl methylcellulose, and 1.1 parts silane coupling agent KH560. The total amount of all components is 100 parts.

[0066] The mass ratio of component A to component B is 1:0.85.

[0067] Preparation process: The preparation process is the same as in Example 1, except that borosilicate glass flakes are replaced with ordinary soda-lime glass flakes. Ordinary soda-lime glass flakes have a softening point of 720°C, a thickness of 5 to 8 μm, and a diameter of 30 to 60 μm.

[0068] This comparative example uses glass flakes of different materials and softening points to verify the importance of softening point matching.

[0069] Comparative Example 3: Raw material formula: Component A: 35 parts fused mullite powder, 10 parts synthetic cordierite powder, 8 parts zircon micro powder, 6 parts silicon carbide particles, 13 parts α-alumina micro powder, 11 parts borosilicate glass flakes, 7 parts calcium aluminate cement, and 10 parts silica powder. The total amount of all components is 100 parts.

[0070] Component B: 42 parts potassium silicate solution, 25 parts aluminum dihydrogen phosphate solution, 13 parts silica sol, 18 parts deionized water, 0.6 parts sodium hexametaphosphate, 0.3 parts hydroxypropyl methylcellulose, and 1.1 parts silane coupling agent KH560. The total amount of all components is 100 parts.

[0071] The mass ratio of component A to component B is 1:0.85.

[0072] Preparation process: The preparation process is the same as in Example 1, except that β-type silicon carbide whiskers are replaced with silicon carbide particles of equal mass, and the particle size d50 of the silicon carbide particles is 5 μm.

[0073] This comparative example uses granular silicon carbide instead of whisker-shaped silicon carbide to verify the difference in toughening effect between whiskers.

[0074] Comparative Example 4: Raw material formula: Component A: 35 parts fused mullite powder, 10 parts synthetic cordierite powder, 8 parts zircon micro powder, 6 parts β-type silicon carbide whiskers, 13 parts α-alumina micro powder, 11 parts borosilicate glass flakes, and 17 parts silica micro powder. The total amount of all components is 100 parts.

[0075] Component B: 52 parts potassium silicate solution, 15 parts silica sol, 30.5 parts deionized water, 0.6 parts sodium hexametaphosphate, 0.4 parts hydroxypropyl methylcellulose, and 1.5 parts silane coupling agent KH560. The total amount of all components is 100 parts.

[0076] The mass ratio of component A to component B is 1:0.85.

[0077] Preparation process: The preparation process is the same as in Example 1, except that calcium aluminate cement and aluminum dihydrogen phosphate are removed, and the ratio of potassium silicate and silica sol is adjusted accordingly to keep the total binder dosage unchanged.

[0078] This comparative example is a conventional inorganic high-temperature coating formulation based on a single silicate binder system mainly composed of potassium silicate and silica sol, used to compare the overall performance advantages of the ternary composite binder system of the present invention.

[0079] Comparative Example 5: Raw material formula: Component A: 45 parts alumina powder, 15 parts silicon carbide powder, 10 parts zirconium dioxide micro powder, 5 parts bentonite, 5 parts talc powder, and 20 parts silica micro powder. The total amount of all components is 100 parts.

[0080] Component B: 50 parts aluminum dihydrogen phosphate solution, 15 parts potassium silicate solution, 2 parts borax, 32 parts deionized water, and 1 part carboxymethyl cellulose. The total amount of all components is 100 parts.

[0081] The mass ratio of component A to component B is 1:0.9.

[0082] Preparation process: Step 1, Preparation of Component A: Mix all powder raw materials evenly to obtain Component A.

[0083] Step 2, Preparation of Component B: Heat aluminum dihydrogen phosphate solution to 50°C, slowly add potassium silicate solution dropwise, stir evenly, then add borax aqueous solution and carboxymethyl cellulose, and continue stirring to obtain component B.

[0084] Step 3, finished product preparation: Mix component A and component B in the specified proportions and stir until homogeneous to obtain the finished coating.

[0085] This comparative example is a conventional high-temperature resistant coating formulation using aluminum dihydrogen phosphate and potassium silicate as composite binders and alumina and silicon carbide as main fillers.

[0086] Comparative Example 6 Raw material formula: Component A: 35 parts fused mullite powder, 10 parts synthetic cordierite powder, 8 parts zircon micro powder, 6 parts β-type silicon carbide whiskers, 13 parts α-alumina micro powder, 11 parts borosilicate glass flakes, 7 parts calcium aluminate cement, and 10 parts silica powder. The total amount of all components is 100 parts.

[0087] Component B: 42 parts potassium silicate solution, 25 parts aluminum dihydrogen phosphate solution, 13 parts silica sol, 18 parts deionized water, 0.6 parts sodium hexametaphosphate, 0.3 parts hydroxypropyl methylcellulose, and 1.1 parts silane coupling agent KH560. The total amount of all components is 100 parts.

[0088] The mass ratio of component A to component B is 1:0.85.

[0089] Preparation process: Components A and B are mixed together in a single step according to the specified ratio and stirred at high speed for 30 minutes. The finished coating is obtained directly without using stepwise or dripping processes.

[0090] This comparative example is a process control example, using the same raw material component ratio as Example 1, but the preparation process is a conventional one-time mixing method, used to verify the effect of the step-by-step feeding and dripping process of the present invention on the coating performance.

[0091] Comparative Example 7: Raw material formula: Component A: 30 parts alumina micro powder, 15 parts zirconium oxide powder, 10 parts mica powder, 11 parts borosilicate glass flakes, 8 parts silicon carbide powder, and 26 parts silicon micro powder. The total amount of all components is 100 parts.

[0092] Component B: 45 parts sodium silicate solution, 20 parts aluminum phosphate solution, 32 parts deionized water, 1 part dispersant, 0.5 parts defoamer, and 1.5 parts thickener. The total amount of all components is 100 parts.

[0093] The mass ratio of component A to component B is 1:0.9.

[0094] Preparation process: After mixing the various powder raw materials, add them to the liquid material and ball mill for 2 hours to obtain the finished coating.

[0095] This comparative example combines known technologies such as sodium silicate binder, glass flake corrosion protection, and silicon carbide wear resistance.

[0096] Performance testing: The testing method is as follows: 1. Coating Preparation: The coatings of each embodiment and comparative example were sprayed onto the surface of a 20G boiler steel test plate that had been sandblasted. The test plate dimensions were 100mm × 50mm × 5mm, the sandblasting grade was Sa2.5, and the surface roughness Ra was 25 to 35μm. Spraying was performed in two coats, each with a wet film thickness of approximately 0.3mm, with a 2-hour interval between coats. After spraying, the coating was cured at room temperature for 7 days, and then cured according to the following curing regime: the temperature was increased to 150℃ at 2℃ / min and held for 2 hours, then increased to 400℃ at 2℃ / min and held for 1 hour, followed by furnace cooling to room temperature. The total dry film thickness of the coating was 0.4 to 0.5mm.

[0097] 2. Adhesion strength test: The test shall be conducted in accordance with GB / T 5210-2006 "Paints and Varnishes - Pull-off Adhesion Test", using a universal testing machine model WDW-10, with a loading rate of 1 mm / min, and 3 samples in each group are tested and the average value is taken.

[0098] 3. High temperature resistance: The coating sample was placed in a box-type resistance furnace and kept at 800℃, 1000℃ and 1200℃ for 100h respectively. After cooling with the furnace, the appearance of the coating was observed and the residual bonding strength was tested.

[0099] 4. Wear resistance: The test was conducted according to ASTM G65-16(2021) Dry sand / rubber wheel wear test method. The abrasive was 70 mesh quartz sand, the loading force was 130N, the rotation speed was 200r / min, the wear time was 10min, and the wear amount was calculated based on the difference in sample mass before and after the test.

[0100] 5. Thermal shock stability: After holding the sample in an 800℃ resistance furnace for 15 minutes, quickly immerse it in room temperature water. Repeat this cycle 50 times and observe whether the coating shows cracks or peeling. Also test the residual bonding strength.

[0101] 6. Salt spray corrosion resistance: The test shall be conducted in accordance with the provisions of GB / T 10125-2021 "Salt spray test for corrosion test in artificial atmosphere". The salt spray test chamber model is YWX / Q-250. The test medium is 5% NaCl solution, the test temperature is 35℃, and the continuous spraying is carried out for 1000h. The surface condition of the coating shall be observed.

[0102] 7. Medium-temperature strength test: After the coating sample is kept at 600℃ for 50 hours, it is cooled in the furnace and its bonding strength is tested. The strength retention rate is calculated by comparing it with the sample cured at room temperature.

[0103] 8. Porosity test: The porosity of the coating was tested using the mercury intrusion porosimetry method. The instrument model was AutoPore IV 9500, and the test pressure range was 0.1 to 60,000 psia.

[0104] Table 1. Test results of basic coating properties: Test methods: Bond strength was tested according to the pull-out method of GB / T 5210-2006, wear amount was tested according to the dry sand / rubber wheel method of ASTM G65-16(2021), porosity was tested by mercury intrusion porosimetry, and the medium-temperature strength retention rate was the ratio of the bond strength after heat preservation at 600℃ for 50h to the bond strength after curing at room temperature.

[0105] Results Analysis: The bonding strength of Examples 1 to 3 ranged from 15.4 to 17.8 MPa, the wear amount from 35.2 to 42.3 mg, and the porosity from 7.1 to 8.7%, all of which were significantly better than the comparative examples. It should be noted that although Example 2 had the lowest silicon carbide whisker content, its zircon and α-alumina powder contents were the highest among the three examples (10 parts and 15 parts, respectively). Zircon (Mohs hardness 7.5) and α-alumina (Mohs hardness 9) are both high-hardness wear-resistant fillers. The increased content of these materials had a greater effect on improving wear resistance than the decreased whisker content, thus maintaining a high overall wear resistance. This aligns with the principle that the wear resistance of composite materials is determined by the synergistic effect of multiple components. Example 3, with the highest glass flake content, exhibited the most significant mid-temperature self-healing effect, achieving a mid-temperature strength retention rate of 111.8%, meaning that the strength after treatment at 600℃ was actually higher than at room temperature—something traditional inorganic coatings cannot achieve.

[0106] Comparative Example 1, lacking borosilicate glass flakes, exhibited a bonding strength of only 10.3 MPa, a porosity as high as 14.2%, and a mid-temperature strength retention rate of only 81.9%, demonstrating significant mid-temperature strength decay. This proves that the self-healing effect of the glass flakes is the source of the core performance of this invention. Comparative Example 2 used ordinary soda-lime glass flakes. Due to their high softening point, the degree of micro-melting at 600℃ was insufficient, resulting in limited self-healing effects. The mid-temperature strength retention rate was only 91%, still in the decreasing range, proving that softening point matching is a key parameter. Comparative Example 3 replaced silicon carbide whiskers with particulate silicon carbide, resulting in a significant decrease in wear resistance and an increase in wear amount to 62.5 mg, proving that whisker toughening contributes irreplaceably to wear resistance. Comparative Examples 4 and 5, representing existing technologies, showed significantly lower overall performance than the examples. Comparative Example 6, although using the same raw materials, had a simpler preparation process. However, due to uneven reaction between aluminum dihydrogen phosphate and potassium silicate leading to localized gelation, the coating uniformity was poor, and its performance was significantly lower than Example 1. Comparative Example 7 combines known functional components such as glass flakes, silicon carbide, and silicates. Due to the lack of reasonable formulation design and process matching, the performance of each component is at a low level.

[0107] Table 2. High temperature and thermal shock performance test results: Test methods: High-temperature performance testing was conducted in a box-type resistance furnace at a heating rate of 5℃ / min. After reaching the target temperature, the temperature was held for 100 hours, and the furnace was cooled before visual observation. Thermal shock testing was performed using a water-cooling method from 800℃ to room temperature, with 50 cycles followed by observation and testing of residual bond strength.

[0108] Results Analysis: In Examples 1 to 3, the coatings remained intact and crack-free after being held at 1000℃ for 100 hours, and remained intact even after holding at 1200℃, with only a slight gloss on the surface due to the micro-melting of the glass phase. After 50 thermal shock cycles, the coatings showed no cracks or peeling, and the bond strength retention rate reached 81.8% to 87.1%, demonstrating excellent thermal shock stability. Example 3, with its higher content of glass flakes and silicon carbide whiskers, achieved the highest bond strength of 15.2 MPa after thermal shock, proving that the synergistic effect of the toughening system and self-healing mechanism effectively suppressed the generation and propagation of thermal shock cracks.

[0109] After removing the glass flakes in Comparative Example 1, the pores could not heal at high temperatures, leading to thermal stress concentration and rapid crack propagation. Edge spalling occurred after 50 thermal shock cycles. Comparative Example 2, due to the high softening point of the soda-lime glass flakes, exhibited insufficient self-healing at mid-temperatures, and structural weakening due to excessive glass phase flow at high temperatures. Its performance fell between the examples and Comparative Example 1. Comparative Example 3 lacked whisker toughening, resulting in low resistance to thermal shock crack propagation and multiple cracks. Comparative Examples 4 and 5, representing existing technologies, performed poorly in thermal shock tests, both showing significant cracking or spalling. Comparative Example 6, due to its simple process, resulted in uneven component dispersion, leading to decreased thermal shock performance. The formulation in Comparative Example 7 showed the most severe failure under high temperature and thermal shock conditions, demonstrating the irreplaceable nature of the formulation design and preparation process of this invention.

[0110] Table 3. Corrosion resistance test results: Test methods: Salt spray test was performed according to GB / T 10125-2021, using 5% NaCl solution, continuous spraying at 35℃ for 1000h. Acid immersion and alkali immersion tests were performed by immersing the coating in 10% sulfuric acid and 10% sodium hydroxide solutions at room temperature for 30 days, respectively, and observing the surface condition of the coating.

[0111] Results Analysis: Examples 1 to 3 showed no rust spots or blistering after 1000 hours of salt spray treatment, no change after 30 days of acid immersion, and only slight loss of gloss after alkali immersion, demonstrating excellent corrosion resistance. This superior corrosion resistance stems from the combination of the labyrinthine barrier effect and self-healing effect of the glass flakes. On one hand, the flakes extend the penetration path of the corrosive medium; on the other hand, self-healing fills the pores, further reducing permeability. Comparative Example 1, lacking glass flakes, had high porosity, allowing easy penetration of the corrosive medium, resulting in localized blistering and rust spots after salt spray treatment. Comparative Example 2, due to the mismatch in softening points of the glass flakes, exhibited poor self-healing and decreased corrosion resistance. Comparative Example 3, although lacking whiskers, still retained glass flakes, and its corrosion resistance was close to that of the examples, proving that corrosion protection is mainly contributed by the glass flakes. The existing technical formulations of Comparative Examples 4 and 5 showed poor corrosion resistance. Comparative Example 6, due to process issues, had poor coating uniformity and localized defects, resulting in decreased corrosion resistance. The combined coating of Comparative Example 7 had high porosity and the worst corrosion resistance.

[0112] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A high-temperature resistant, corrosion-resistant, and wear-resistant coating for boilers, characterized in that, It consists of a powder mixture of component A and a liquid binder of component B, with the mass ratio of component A to component B being 1:0.8 to 1:0.

9. By mass, component A comprises the following raw materials: 32 to 38 parts of fused mullite powder, 8 to 12 parts of synthetic cordierite powder, 6 to 10 parts of zircon micro powder, 4 to 8 parts of β-type silicon carbide whiskers, 11 to 15 parts of α-alumina micro powder, 9 to 13 parts of borosilicate glass flakes, 6 to 9 parts of calcium aluminate cement, and 7 to 11 parts of silica micro powder. By mass, component B comprises the following raw materials: Potassium silicate solution 38 to 45 parts, aluminum dihydrogen phosphate solution 22 to 28 parts, silica sol 10 to 16 parts, deionized water 15 to 22 parts, sodium hexametaphosphate 0.4 to 0.8 parts, hydroxypropyl methylcellulose 0.2 to 0.5 parts, silane coupling agent 0.8 to 1.5 parts; The borosilicate glass flakes have a softening point of 580 to 620°C, a thickness of 2 to 4 μm, and a diameter of 20 to 50 μm. The potassium silicate solution has a modulus of 3.2 to 3.4 and a silica mass fraction of 40 to 44%. The aluminum dihydrogen phosphate solution contains 32 to 34% phosphorus pentoxide and 8.0 to 9.0% aluminum oxide by mass.

2. The boiler high-temperature resistant, corrosion-resistant, and wear-resistant coating according to claim 1, characterized in that, The fused mullite powder has a particle size d50 of 4 to 6 μm and an aluminum oxide mass fraction of not less than 70%; the synthetic cordierite powder has a particle size d50 of 2 to 4 μm and a chemical composition of 2MgO·2Al2O3·5SiO2.

3. The boiler high-temperature resistant, corrosion-resistant, and wear-resistant coating according to claim 1, characterized in that, The zircon micro powder has a particle size d50 of 1.5 to 2.5 μm and a zircon dioxide mass fraction of not less than 65%; the silica micro powder has a particle size d50 of 0.2 to 0.4 μm and a silica mass fraction of not less than 96%.

4. The boiler high-temperature resistant, corrosion-resistant, and wear-resistant coating according to claim 1, characterized in that, The β-type silicon carbide whiskers have a diameter of 0.3 to 0.8 μm and an aspect ratio of 20 to 40.

5. The boiler high-temperature resistant, corrosion-resistant, and wear-resistant coating according to claim 1, characterized in that, The α-alumina micro powder has a particle size d50 of 0.8 to 1.5 μm and an α-phase mass fraction of not less than 95%; the calcium aluminate cement has an aluminum oxide mass fraction of not less than 70% and a calcium oxide mass fraction of not more than 28%.

6. The boiler high-temperature resistant, corrosion-resistant, and wear-resistant coating according to claim 1, characterized in that, The silica sol has a particle size of 10 to 20 nm, a silica mass fraction of 28 to 32%, and a pH value of 9.0 to 10.

0.

7. The boiler high-temperature resistant, corrosion-resistant, and wear-resistant coating according to claim 1, characterized in that, The silane coupling agent is γ-glycidoxypropyltrimethoxysilane; the viscosity of the hydroxypropyl methylcellulose is 3000 to 5000 mPa·s.

8. A method for preparing a boiler high-temperature resistant, corrosion-resistant, and wear-resistant coating as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1, Preparation of Component A: Weigh out the fused mullite powder, synthetic cordierite powder, zircon micro powder, β-type silicon carbide whiskers, α-alumina micro powder, borosilicate glass flakes, calcium aluminate cement, and silica micro powder according to the formula ratio, and put them into a vertical ribbon mixer. First, mix at a speed of 60 to 80 r / min for 10 to 15 min, then increase the speed to 120 to 150 r / min and continue mixing for 20 to 30 min. During the mixing process, dry air is introduced to control the powder temperature not to exceed 40℃. After mixing, sieve through a 200-mesh standard sieve to obtain the Component A powder mixture. Step 2, Preparation of Component B: First, add sodium hexametaphosphate and hydroxypropyl methylcellulose to deionized water and stir at 400 to 600 r / min for 8 to 12 minutes until completely dissolved. Then, add potassium silicate solution and continue stirring for 5 to 8 minutes. Next, slowly add aluminum dihydrogen phosphate solution over a time of 15 to 20 minutes, maintaining a stirring speed of 600 to 800 r / min and a material temperature not exceeding 50°C. After the addition is complete, add silica sol and silane coupling agent and continue stirring for 10 to 15 minutes to obtain the component B liquid binder. Step 3, finished product preparation: Before use, weigh component A and component B at a mass ratio of 1:0.8 to 1:0.

9. First, put component B into a stirring container, and add component A in batches while stirring at a speed of 500 to 700 r / min. After all the components are added, continue stirring for 15 to 20 minutes, and degas under a vacuum of 0.06 to 0.08 MPa for 5 to 8 minutes to obtain the boiler high-temperature resistant, corrosion-resistant, and wear-resistant coating.

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