High temperature protective coating and method of making same

Abstract

The present application relates to the technical field of high-temperature protective coating, and aims to solve the problem that the existing high-temperature coating has a decreased protective performance due to structural degradation caused by a large number of pores generated after decomposition of an organic film-forming material. A high-temperature protective coating and a preparation method thereof are disclosed. The coating composition comprises an organic film-forming resin, low-softening-point inorganic glass powder, and high-temperature-resistant inorganic aggregate capable of phase transition under stress induction. Through a time-coupling mechanism, the pore network generated by high-temperature decomposition of the organic resin is used as a capillary channel for guiding the subsequent molten glass liquid phase to fill and weld in situ, thereby forming a dense inorganic protective layer. The present application converts the destructive process of organic decomposition into a constructive link of self-densification of the coating, and improves the biomimetic self-healing ability of the inorganic layer formed finally against thermal shock microcracks, solves the core problem of failure of traditional high-temperature coatings due to structural degradation and brittle fracture, and improves the long-term service reliability under severe working conditions.

Description

Technical Field

[0001] This invention relates to a high-temperature protective coating and its preparation method, belonging to the technical field of high-temperature protective coatings. Background Technology

[0002] The currently prevalent technical approach is to use organic film-forming materials such as silicone resins to bond high-temperature resistant inorganic ceramic fillers such as alumina and silica together, and then coat them onto the surface of the equipment substrate to form a protective layer. This method effectively solves the basic problems of coating storage, application, and film adhesion at room temperature, and has therefore become the mainstream technical choice.

[0003] However, when this coating is applied to real-world conditions such as industrial kilns or pyrolysis furnaces that undergo repeated heating and cooling cycles, an inherent limitation in its design principle becomes apparent. The organic film-forming resin, which acts as temporary scaffolding at low temperatures, will vaporize and escape after reaching its decomposition temperature. While this process is expected, its direct consequence is that it leaves a large number of randomly distributed pores inside the coating. This not only provides a channel for the subsequent intrusion of corrosive atmospheres, but more importantly, the weak interfaces between these pores and inorganic filler particles become the source of microcracks under repeated thermal expansion and contraction stress, ultimately leading to premature peeling of the coating layer by layer.

[0004] To alleviate this problem, those skilled in the art have attempted to delay coating failure by developing more heat-resistant organic resins or increasing the packing density of inorganic fillers. However, these improvements have not addressed the core issue. As long as there is decomposition and mass loss of organic matter, the formation of pores is inevitable. Simply increasing the coating thickness or filler density will exacerbate the internal thermal stress of the coating, leading to a vicious cycle where thicker coatings are more prone to cracking. This phenomenon reveals a deeper technical contradiction. Specifically, existing technologies have the following shortcomings: 1. During the transformation from an organic composite film to an inorganic layer, the coating lacks an intrinsic mechanism to maintain its structural continuity and density; 2. The pores generated by the decomposition of organic resins are treated merely as an unavoidable defect in existing technologies, and their negative effects cannot be effectively managed or utilized; 3. Existing improvement approaches focus on combating or delaying the decomposition of organic matter, failing to transform this inevitable physicochemical process into an opportunity to reconstruct the coating structure and improve ultimate protective performance. Therefore, the technical problem to be solved by this invention is how to design a coating composition that can self-repair the internal pores caused by mass loss after the organic film-forming material decomposes at high temperature, and form a dense and complete inorganic composite protective layer in situ. Summary of the Invention

[0005] This invention provides a high-temperature protective coating and its preparation method. Its main purpose is to solve the problem that existing high-temperature coatings suffer from structural degradation and decreased protective performance due to the generation of a large number of pores after the decomposition of organic film-forming materials.

[0006] To achieve the above objectives, the present invention provides a high-temperature protective coating comprising:

[0007] At the decomposition temperature Organic film-forming resins that decompose under certain conditions;

[0008] A low softening point inorganic glass powder, the softening point temperature of which is ;

[0009] A high-temperature resistant inorganic aggregate, wherein the melting point of the high-temperature resistant inorganic aggregate is higher than its decomposition temperature. Furthermore, the high-temperature resistant inorganic aggregate is at least partially composed of ceramic particles capable of undergoing martensitic phase transformation under stress-induced conditions; wherein the temperature relationship of the components in the composition is set to satisfy the decomposition temperature. Below the softening point temperature During heating, when the temperature reaches the decomposition temperature... At this point, the organic film-forming resin decomposes to form a three-dimensional interconnected porous network within the coating; as the temperature continues to rise to the softening point temperature... At that time, inorganic glass powder with a low softening point melts to produce a liquid phase.

[0010] Preferably, based on 100 parts by weight of the total composition, the content of the organic film-forming resin is 10 to 30 parts by weight; the content of the low softening point inorganic glass powder is 15 to 40 parts by weight; and the content of the high-temperature resistant inorganic aggregate is 40 to 70 parts by weight.

[0011] Preferably, the composition further comprises a reactive thickener with the same chemical composition as the high-temperature resistant inorganic aggregate, the reactive thickener having an average particle size in the nanometer range, and operating at temperatures above its softening point. Under certain conditions, it undergoes an in-situ chemical reaction with the liquid phase to generate a phase with higher viscosity, thereby inhibiting the flow of the liquid phase.

[0012] Preferably, the decomposition temperature of the organic film-forming resin The softening point temperature is between 400 and 600 degrees Celsius; the softening point temperature of low-softening-point inorganic glass powder. The temperature ranges from 650 to 850 degrees Celsius.

[0013] Preferably, the composition further comprises zinc powder; the zinc powder, under normal temperature and humid conditions, acts as an anode to form a galvanic cell with the substrate to provide cathodic protection; and during the heating process, when the temperature reaches the decomposition temperature of the organic film-forming resin... When the temperature reaches a certain range, the vaporized zinc acts as a reducing agent and reacts chemically with the existing oxides on the substrate surface.

[0014] Preferably, the composition further comprises a chemical atmosphere buffer, which is a transition metal oxide capable of undergoing a reversible redox reaction to change its valence state according to the external ambient atmosphere within the temperature range in which the coating operates; when an external reducing atmosphere penetrates, the buffer is reduced to consume the reducing atmosphere; when an external oxidizing atmosphere penetrates, the reduced buffer is reoxidized to consume the oxidizing atmosphere. The composition further comprises a thermochemical process indicator, which is a transition metal oxide that exhibits a first color in its solid state, and after the fusion welding process is completed, it completely dissolves in the formed glass phase, causing the glass phase to exhibit a second irreversible color different from the first color.

[0015] Preferably, the average particle size of the high-temperature resistant inorganic aggregate is greater than the average particle size of the low-softening-point inorganic glass powder.

[0016] Preferably, the organic film-forming resin is an organosilicon resin; the low softening point inorganic glass powder is borosilicate glass powder; and the ceramic particles capable of undergoing martensitic phase transformation under stress are partially stabilized zirconium oxide.

[0017] Preferably, after the composition is cooled and cured, the resulting dense inorganic composite protective layer has the following structural characteristics: high-temperature resistant inorganic aggregate is uniformly distributed as a dispersed phase in a continuous glass phase matrix formed by low softening point inorganic glass powder; and the coating porosity measured by mercury intrusion porosimetry is less than 5%.

[0018] A method for preparing a high-temperature protective coating, the method comprising the following steps:

[0019] Step a: The organic film-forming resin, high-temperature resistant inorganic aggregate, low softening point inorganic glass powder and reactive thickener are uniformly mixed to obtain a coating composition slurry.

[0020] Step b: Apply the coating composition slurry to the substrate surface;

[0021] Step c involves heat-treating the substrate coated with the paint composition slurry. Specifically, this heat treatment involves first heating the substrate to its decomposition temperature. The temperature is maintained within the specified range to allow the organic film-forming resin to completely decompose, thereby forming a three-dimensional interconnected porous network within the coating; then, the temperature is further increased to the softening point temperature. The temperature range is maintained to allow the low softening point inorganic glass powder to melt and generate a liquid phase. This liquid phase then flows capillarily along the pore network formed by the decomposition of the resin to fill the pore network, thereby melting and welding the high-temperature resistant inorganic aggregate into a single unit. Finally, the substrate is cooled to obtain a dense inorganic composite protective layer.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. The coating composition of the present invention establishes a temporal coupling relationship between the decomposition of organic matter and the melting and flow of inorganic phase. During the heating process, the pore network formed by the decomposition of organic film-forming resin does not exist passively as a structural defect, but provides a pre-set capillary channel throughout the system for the subsequent molten liquid phase of low softening point glass powder. The liquid phase wets and welds all the high-temperature resistant inorganic aggregates in this channel, so that the coating is transformed from a loose particle accumulation into a dense glass-ceramic composite structure. The entire process transforms the normal heating process of the equipment into a necessary step for the coating to complete the final densification. Thus, the structural deterioration problem that is inevitable due to the decomposition of organic matter in traditional coatings is transformed into a preliminary process for the coating to achieve the final structural integrity in the present invention.

[0024] 2. This invention introduces ceramic particles that can undergo phase transformation under stress as at least part of the high-temperature resistant inorganic aggregate, thereby enabling the final dense inorganic protective layer to acquire a damage response mechanism. When the coating develops microcracks under thermal shock, the stress field concentrated at the crack tip triggers the volume expansion of the surrounding ceramic particles, forming a compressive stress field in situ in the crack area. This compressive stress field acts as a clamp to the continued propagation of the crack and dissipates some of the tensile stress that caused the crack. This method does not prevent the generation of microcracks, but rather changes the propagation behavior of cracks within the material, causing the failure process of the coating to evolve from unpredictable brittle fracture to a more gradual performance degradation process, thereby improving its reliability under repeated temperature fluctuations.

[0025] 3. The present invention further includes zinc powder in the coating composition, so that the same additive component plays two protective roles in different life stages of the coating based on different physicochemical principles. In the normal temperature and humidity environment when the equipment is shut down or stored, the zinc powder provides sacrificial anode protection for the substrate through an electrochemical mechanism. When the equipment is heated to the temperature range of organic resin decomposition, the vaporized zinc acts as a reducing agent and reacts with the existing oxides on the substrate surface. Before the glass phase melts and bonds with the substrate, it completes the chemical purification and activation of the bonding interface. The combination of these two effects extends the protective function of the coating from the high temperature working range to the entire life cycle of the non-working state. At the same time, it changes the bonding method between the coating and the substrate from physical coverage to interface fusion based on in-situ chemical reaction. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating the in-situ densification and damage response mechanism of the coating of this invention.

[0027] Figure 2This is a graph showing the effect of the reactive thickener of the present invention on the coating's anti-sagging properties and melt viscosity;

[0028] Figure 3 This is a schematic diagram illustrating the microstructure evolution and toughening mechanism of the coating of the present invention during the heating process. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be described in further detail 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.

[0030] This invention provides a high-temperature protective coating and its preparation method. By sequentially coupling the physicochemical behaviors of different components during the thermal process, it achieves in-situ reshaping of the coating from an organic-inorganic composite state to a pure inorganic dense protective layer. The composition system includes an organic film-forming resin as a low-temperature temporary binder, a high-temperature resistant inorganic aggregate as the final structural skeleton, and a low-softening-point inorganic glass powder as a high-temperature healing medium. These three components work synergistically in a preset heating program, using the pores generated by the decomposition of the organic resin as channels to guide the molten glass phase for capillary filling and fusion welding, thereby forming a dense glass-ceramic composite protective layer on the substrate surface that is tightly bonded to the substrate. This is particularly useful in high-temperature equipment. In industrial furnace wall protection applications that undergo repeated start-stop temperature cycles, a technical problem arises: after the initial high-temperature exposure, conventional coatings often exhibit decomposition and release of their organic binders, leaving behind a loose, porous structure composed of inorganic fillers. This structure is prone to cracking and peeling under subsequent thermal stress. To address this challenge, the organic film-forming resin in the composition of this invention is designed to provide fundamental film-forming properties and adhesion during application and room-temperature curing, uniformly fixing all inorganic components to the substrate surface. Its decomposition at high temperatures is considered a pre-programmed step. Specifically, methylphenyl silicone resin is selected as the organic film-forming resin, and its main decomposition temperature range is determined through thermogravimetric analysis. The temperature range is 400℃ to 600℃. When the coating is heated to this temperature range, the resin undergoes pyrolysis and vaporization, and its mass loss correspondingly forms a three-dimensional interconnected pore network inside the coating. This pore network provides a spatial channel for subsequent structural remodeling. In this way, the decomposition process of the organic film-forming resin is transformed from a link that leads to structural deterioration into a pre-functional link that triggers structural densification.

[0031] In existing technologies, the formation of the aforementioned porous network can compromise structural integrity. This invention further incorporates low-softening-point inorganic glass powder to utilize this network structure. Therefore, the system employs a specific borosilicate glass powder as a structural repair agent. Its mechanism of action is that, when the temperature is below its softening point, it exists as an inorganic filler, while when the temperature rises to its softening point... Upon reaching this point, it transforms into a fluid, molten liquid phase; to achieve seamless integration with the resin decomposition process, the softening temperature of the glass powder... By adjusting its oxide composition and The proportions were calibrated, and their values ​​were determined using a hot-stage microscope. Within the range of 650℃ to 850℃, this setting ensures Higher than ,Right now < As the equipment continues to heat up and crosses... During this process, the softened glass phase, driven by surface tension and capillary effect, flows along the pore network formed by resin decomposition in the previous step, filling all pores and wetting and welding all the high-temperature resistant inorganic aggregate particles. This design utilizes high temperature to drive the coating's self-repair and densification, ultimately forming an inorganic composite protective layer with a porosity of less than 5%. To ensure the structural reliability of the final inorganic protective layer under thermal shock conditions and to address the risk of microcrack propagation as a brittle material, the high-temperature resistant inorganic aggregate in the composition of this invention at least partially employs ceramic particles capable of undergoing martensitic phase transformation under stress-induced conditions; specifically, it employs yttrium oxide-partially stabilized... As part of the aggregate, the physical mechanism of zirconia particles lies in the fact that when microcracks initiate within the coating due to thermal stress mismatch, stress concentration occurs at the crack tip. This stress field triggers a phase transformation in the zirconia particles in front of them, from a metastable tetragonal phase to a stable monoclinic phase, accompanied by a 3-5% volume expansion. This in-situ volume expansion creates a compressive stress field at the crack tip, which acts as a clamp to the continued crack propagation and enhances the fracture toughness of the material by absorbing and dissipating the energy of crack propagation. Through this mechanism, the failure mode of the coating changes from brittle fracture to gradual performance degradation, thereby extending its service life.

[0032] The coating composition of the present invention, based on 100 parts by weight of the total composition, contains 10 to 30 parts by weight of organic film-forming resin, 15 to 40 parts by weight of low softening point inorganic glass powder, and 40 to 70 parts by weight of high-temperature resistant inorganic aggregate. This range of proportions is determined because when the content of organic film-forming resin is less than 10 parts by weight, the stability of the slurry before application and the initial film-forming properties after application are insufficient, making it difficult to form a uniform coating. Conversely, when the content is greater than 30 parts by weight, the mass loss caused by the decomposition of organic matter at high temperatures is too large, resulting in an excessively large total pore volume. The filling capacity of the subsequent glass liquid phase is exceeded, resulting in a high porosity in the final coating. When the content of low softening point inorganic glass powder is less than 15 parts by weight, the generated molten liquid phase is insufficient to completely fill the pores and coat the aggregate, and cannot form a continuous and dense matrix phase. When it is more than 40 parts by weight, the proportion of glass phase in the final coating is too high, which will reduce the maximum service temperature and wear resistance of the coating. Accordingly, the high-temperature resistant inorganic aggregate, as the main structural component, has its content matched with other components to achieve the mechanical properties and high-temperature resistance required by the final composite protective layer under the premise of being fully wetted and bonded.

[0033] In some applications where coatings need to be applied to vertical surfaces or where there are higher temperature safety requirements, it is necessary to suppress the glass phase at temperatures far above its softening point. To address the sagging phenomenon caused by viscosity decrease under certain operating conditions, the composition may further include a reactive thickener. This thickener is selected from ultrafine powders with the same chemical composition as the high-temperature resistant inorganic aggregate but with an average particle size in the nanometer range. For example, when the aggregate is alumina, the thickener is nano-alumina. Its mechanism of action is that, at normal operating temperature... Nearby, nanoparticles are dispersed as fillers in the glass liquid phase. When the temperature rises, the nanoparticles, due to their specific surface area and reactivity, will undergo an interfacial reaction with the molten borosilicate glass liquid phase, generating an aluminoborosilicate phase with a higher melting point in situ. This reaction consumes the low-viscosity liquid phase and generates a new high-viscosity phase, causing a jump in the viscosity of the entire melt, thereby physically inhibiting its macroscopic flowability and enabling the coating to have an adaptive ability to resist overheating and sagging.

[0034] To address the corrosion issue of the substrate under ambient temperature and humidity conditions, including storage and downtime maintenance, before the coating undergoes high-temperature vitrification, the composition may further include zinc powder. This component plays a dual role throughout the coating's lifecycle. Under ambient temperature and humidity conditions, zinc powder, being a more reactive metal than steel, provides electrochemical cathodic protection to the substrate through a sacrificial anode mechanism, preventing underlying corrosion. During equipment heating, when the temperature enters the decomposition temperature range of the organic resin... At that time, the zinc vapor that has melted and begun to vaporize acts as a reducing agent and will undergo an in-situ chemical reaction with the trace oxides that may exist on the substrate surface. Before the glass phase melts and bonds with the substrate, the bonding interface is chemically purified and surface activated. This design extends the protective function of the coating from the high-temperature working state to the non-working state and changes its bonding mechanism with the substrate from physical coverage to chemical bonding.

[0035] In addition, to ensure < The time-series relationship can be stably achieved in industrial environments with fluctuating chemical atmospheres. The composition may also contain a chemical atmosphere buffer; this buffer is selected from transition metal oxides capable of reversible redox reactions within the operating temperature range, such as ferric oxide; its mechanism is that when an external reducing atmosphere, When penetrating the coating, it will preferentially interact with... The reaction reduces the glass powder, thereby consuming the reducing gas and protecting the softening point of the glass powder. It is not reduced; however, in an external oxidizing atmosphere, During infiltration, the already reduced It will then be rapidly re-oxidized into This consumes oxygen and protects the decomposition temperature of organic resins. It is not reduced; through this reversible valence change, the buffer dynamically maintains the stability of the microenvironment inside the coating, ensuring the reliable triggering of the core timing mechanism.

[0036] To convert the invisible vitrification process within the coating into an externally observable signal for quality control, the composition may also include a thermochemical process indicator. This indicator is typically a transition metal oxide, such as cobalt oxide, that exhibits a first color in its solid state but imparts a second, irreversible color to the glass upon complete dissolution in the molten glass phase. Solid cobalt oxide powder is black, and the coating appears dark gray overall before vitrification is complete. When the temperature reaches… When the glass phase melts and flows, completing the filling of pores and welding of aggregates, the black cobalt oxide particles simultaneously dissolve in the glass liquid phase, dyeing the glass with a characteristic cobalt blue color. Therefore, after the equipment cools down, by visually inspecting whether the coating has uniformly turned into cobalt blue, it can be determined whether the in-situ vitrification process inside has been completed in all areas.

[0037] The method for preparing the protective layer formed by the above-mentioned high-temperature protective coating includes the following steps: organic film-forming resin, high-temperature resistant inorganic aggregate, low-softening-point inorganic glass powder, and other additives such as reactive thickeners added as needed are uniformly mixed in a solvent, such as xylene or butyl acetate, using a high-speed disperser or ball mill to obtain a coating composition slurry with suitable solid content and viscosity; the slurry is applied to the surface of a substrate that has undergone degreasing and rust removal pretreatment by spraying, brushing, or dipping, and cured into a film at room temperature or low temperature; finally, the substrate coated with the coating is subjected to heat treatment, which can be completed using the initial heating process of the equipment, specifically, the substrate is first heated to... Within the specified temperature range, maintain the temperature to allow the organic film-forming resin to completely decompose and form a porous network, and then continue to raise the temperature to... The temperature range is maintained, allowing the low-softening-point inorganic glass powder to melt and complete the filling of pores and welding of aggregates. Finally, it is cooled with the furnace, resulting in a dense inorganic composite protective layer on the surface of the substrate.

[0038] Example 1: In an application of internal wall protection for a large ethylene cracking furnace, after a shutdown and maintenance, the furnace needs to be restarted and heated to an operating temperature above 800°C. During the maintenance, the furnace environment is humid. To prevent corrosion of the newly installed carbon steel structural components, a high-temperature protective coating is applied to their surfaces. This coating acts as a physical protective film formed by inorganic fillers bonded with silicone resin. The zinc powder within this coating provides electrochemical corrosion protection to the substrate through a sacrificial anode mechanism during this humid, ambient temperature stage, preventing underlying corrosion at the interface between the coating and the substrate. When the cracking furnace starts its heating process, the furnace temperature gradually rises from room temperature, reaching and entering a temperature range of 400°C to 600°C. During this temperature range, the silicone resin in the coating undergoes pyrolysis and vaporization, forming a three-dimensional interconnected porous network in situ within the coating. Macroscopically, the coating transforms into a loose structure composed of high-temperature resistant inorganic aggregates, low-softening-point inorganic glass powder particles, and some stable zirconium oxide particles. Its adhesion to the substrate is at its lowest point at this stage. Conventional techniques fail at this stage due to the loss of structural integrity, while this process of the present invention provides capillary channels for subsequent structural reshaping. Simultaneously, within this temperature range, the vaporized zinc undergoes a reduction reaction with trace oxides that may exist on the substrate surface, chemically purifying the interface that will soon combine with the molten glass.

[0039] As the heating process continues, the furnace temperature rises further and exceeds 650°C. After the interval, the originally solid low-softening-point inorganic glass powder particles begin to soften and transform into a high-viscosity molten liquid phase. Driven by capillary forces, this liquid phase flows, fills, and wets along the pore network formed by the decomposition of organosilicon resin in the previous step. This process melts and welds all the independent high-temperature resistant inorganic aggregate particles and some stable zirconia particles into a whole, forming a continuous, dense, and non-porous glass-ceramic composite phase. The pore structure generated by the decomposition of organosilicon resin, which leads to structural degradation in conventional technologies, and the molten flow behavior of the low-softening-point glass powder constitute a temporal synergistic relationship. The former creates a path for the latter to repair and densify, thereby resolving the contradiction between organic matter removal and structural integrity maintenance.

[0040] During the pyrolysis furnace's operation at operating temperature and subsequent cooling and reheating cycles, the coating undergoes thermal shock. Due to the mismatch in thermal expansion coefficients between the glass phase and the inorganic aggregate particles, microcracks initiate within the coating. When the tip of a microcrack extends to the vicinity of some stable zirconia particles under stress, the stress field concentrated at the crack tip triggers a martensitic phase transformation from tetragonal to monoclinic phase in the particle. The accompanying volume expansion of the phase transformation applies a compressive stress field in situ at the crack tip. This compressive stress field acts as a clamp to prevent further crack propagation and absorbs some of the fracture energy. High-temperature resistant inorganic aggregates here serve not only as... The structural framework exists, and the partially stabilized zirconium oxide it contains is an internal defense mechanism activated when damage occurs. This mechanism enables the final dense inorganic layer to have damage tolerance, meeting the technical requirements of density and toughness. After several complete heating and cooling cycles, the furnace wall was inspected. The inorganic composite protective layer formed on the surface of the area coated with the coating of this invention remained intact, dense, without cracks or peeling, and formed a strong bond with the substrate. In contrast, the area protected by the conventional high-temperature resistant silicone coating that does not contain partially stabilized zirconium oxide and low softening point glass powder showed large-area powdering and layered peeling.

[0041] Example 2: To objectively verify the self-densification ability of the coating composition of the present invention at high temperatures and its resistance to thermal shock, a set of comparative tests was established in this example. Two groups of samples were used: a control group containing no low softening point inorganic glass powder and some stabilized zirconium oxide, and the sample group of the present invention containing all the core components as described in the specific embodiments. The test substrate was a 100mm x 100mm x 5mm Q235 carbon steel plate that had undergone sandblasting. The coating was applied to the substrate surface by air spraying, and the dry film thickness was controlled at 150±10μm. The test was conducted in a programmable high-temperature muffle furnace to simulate the actual heating and thermal shock conditions of industrial equipment. The heat treatment procedure for the experiment was set as follows: the temperature was increased from room temperature to 550°C at a rate of 10°C / min, and held at this temperature for 1 hour to allow the organic film-forming resin to decompose completely; then, the temperature was increased to 750°C (Ts range) at a rate of 10°C / min, and held at this temperature for 2 hours to allow the glass phase to complete the melting, flow and welding process; after the holding period, the sample was cooled to room temperature with the furnace to complete the initial sintering; then, a thermal shock cycle test was performed, each cycle including heating the sample from room temperature to 800°C at a rate of 20°C / min, holding at this temperature for 30 minutes, then removing it and placing it in room temperature for forced air cooling, for a total of 20 cycles.

[0042] After initial sintering and cooling to room temperature, the coatings of both groups of samples were characterized. The open-circuit porosimetry method was used to measure the porosity of the coatings. The porosity of the control group coating was measured to be 21.3%, while the porosity of the coating of the present invention was only 3.8%. This difference is attributed to the fact that in the control group, the pore network left after the decomposition of the organic resin was permanently retained, forming a high-porosity structure. In contrast, in the present invention, the pore network formed by resin decomposition was filled and healed by the subsequently molten low-softening-point inorganic glass powder liquid phase. After completing 20 thermal shock cycles, the coating condition of both groups of samples was evaluated again. Under the high-frequency alternating thermal stress, stress concentration occurred at the structural defects in the control group coating due to its high porosity, leading to the propagation and eventual penetration of microcracks, resulting in macroscopic cracking and peeling. In contrast, the present invention… The coating of the invention exhibits two key advantages: first, the initial low porosity structure reduces the initiation sites of cracks; second, when thermal shock stress locally induces microcracks, some stabilized zirconia particles in front of the crack tip undergo stress-induced martensitic transformation accompanied by volume expansion, forming a compressive stress field at the crack tip. This compressive stress field inhibits further crack propagation, enabling the coating as a whole to exhibit tolerance to thermal shock damage. Experimental results show that, compared with coating compositions that do not contain low-softening-point inorganic glass powder and partially stabilized zirconia, the coating composition of the present invention can form a dense inorganic protective layer with low porosity in situ after initial high temperature exposure. Furthermore, this protective layer exhibits higher structural stability and resistance to cracking and spalling under repeated thermal shock conditions. This performance confirms the effectiveness of the temporal coupling mechanism between organic decomposition and inorganic phase melting, as well as the stress-induced phase transformation toughening mechanism.

[0043] In the application of the coating composition of the present invention to the initial ignition and baking of a large, newly built hot blast stove, the coating composition further includes ferric oxide as a chemical atmosphere buffer and cobalt oxide as a thermochemical process indicator. During the initial baking process, a localized oxygen-rich atmosphere exists within the stove due to incomplete combustion. This oxygen-rich atmosphere accelerates the oxidative decomposition of the organic film-forming resin, potentially leading to… The risk of premature decomposition is mitigated by the ferric oxide in the coating composition, which buffers the rate of resin decomposition by consuming the infiltrated oxygen, thereby maintaining the... < The stability of the time sequence relationship; as the oven temperature continues to rise and reaches... In the furnace section, operators can directly monitor the process of the coating color changing from the initial dark gray to the characteristic cobalt blue through the observation holes in the furnace wall. This serves as an intuitive basis for judging whether the temperature in each area of ​​the furnace is uniform and has reached the glass transition sintering temperature. When the entire furnace wall lining is observed to be uniformly cobalt blue, it is confirmed that the self-healing in-situ glass transition process of the entire coating has been completed, thus providing quality assurance for subsequent formal production.

[0044] Example 3: This example combines Figures 1 to 3 A description of a high-temperature protective coating and its preparation method is provided, such as... Figure 1 As shown, the flow chart on the left illustrates the in-situ densification process of the coating, i.e., after the coating composition is applied, it is heated to the decomposition temperature. and softening point temperature The process involves two stages, culminating in the formation of a dense inorganic composite protective layer with a porosity of less than 5% through fusion welding and cooling. The flow chart on the right demonstrates the damage response mechanism of this protective layer. When factors such as thermal shock cause damage and microcracks to initiate inside the coating, the stress concentration at the crack tip activates the stress-induced phase transformation toughening mechanism. Some stable zirconia particles undergo martensitic phase transformation accompanied by volume expansion, forming a compressive stress field in situ at the crack tip. The effect of this is to restrain the propagation of microcracks and dissipate the crack propagation energy to improve the fracture toughness of the coating, thereby restoring the structure to stability.

[0045] like Figure 2 As shown, nano-sized alumina nanoparticles are used as reactive thickeners. The effect of the amount of additive on the high-temperature performance of the coating, where the horizontal axis represents nanometers. The amount added %, the left vertical axis represents the difference in sag thickness. (μm), the right vertical axis represents the relative value of melt viscosity at 750℃. As can be seen from the curve in the figure, with nanometer... With increasing addition amount, the coating thickness difference increases. The solid line decreases significantly, while the dashed line representing the melt viscosity at 750°C increases accordingly. This figure reveals that by adjusting the content of reactive thickener, the sagging phenomenon of the coating under ultra-high temperature conditions can be effectively suppressed, while maintaining its viscosity within a reasonable range at normal operating temperature.

[0046] like Figure 3 As shown, at the initial state at room temperature, the coating is a uniform organic-inorganic composite layer; when heated to the decomposition temperature... In the 400-600℃ range, the resin decomposition stage begins, with the organic resin decomposing and vaporizing, forming a three-dimensional interconnected porous network in situ within the coating; as the temperature continues to rise to the softening point... In the 650-850℃ range, the glass melting and filling stage begins. Low-softening-point inorganic glass powder melts to generate a liquid phase, which then flows capillarily along the aforementioned pore network, melting and welding the high-temperature resistant inorganic aggregate into a single unit. The key timing conditions for this process are... < After cooling, a dense inorganic composite protective layer is obtained on the substrate surface. When subjected to thermal shock stress, the partially stabilized zirconium oxide inside this protective layer... Particles can generate compressive stress through stress-induced phase transformation, thereby suppressing the propagation of microcracks.

[0047] Example 4: In applications requiring the application of high-temperature protective coatings to the walls of large vertical heating furnaces, the furnace walls may experience localized temperature overshoot due to burner status fluctuations. The surface temperature can, for a short period, far exceed the softening point of the low-softening-point inorganic glass powder. This operating condition places a technical requirement on the coating composition: the molten glass phase needs to be within... The material needs to have sufficient fluidity to fill the pores while maintaining sufficient viscosity at a higher overshoot temperature to resist sagging caused by gravity and avoid a thin-on-top, thick-on-bottom defect in the cured protective layer. To determine the appropriate amount of reactive thickener to meet these requirements, this embodiment establishes an engineering calibration procedure. Based on the sample formulation of this invention, five additional samples were prepared. The amount of nano-sized alumina powder added as the reactive thickener, calculated as a percentage of the total mass of the inorganic components (i.e., low-softening-point inorganic glass powder and high-temperature resistant inorganic aggregate), was 0%, 1%, 2%, 3%, and 4%, respectively. The experimental process included high-temperature sagging tests on the six samples. Specifically, the six coatings were applied to vertically suspended Q235 steel plates of the same size. After drying, a coating thickness of 150 μm was formed. Then, all steel plates were placed in a high-temperature furnace and heated to 950°C at a rate of 10°C / min. This temperature was the preset overshoot temperature and higher than the specified temperature. , and hold at this temperature for 1 hour.

[0048] After the constant temperature period, all steel plates were cooled to room temperature. A coating thickness gauge was then used to measure the coating thickness at three locations on each steel plate: the upper edge, the middle, and the lower edge. The difference between the thickness at the lower edge and the upper edge was calculated. This difference is used to quantify the degree of coating sagging; simultaneously, to evaluate the effect of reactive thickeners on the normal densification process, six additional samples were tested at 750℃. High-temperature viscosity tests were conducted within the specified range; the results showed that when the amount of nano-alumina added was 0%, the coating sagged at 950℃. Exceeding 100μm; when the addition amount is 1%, The particle size decreased to 30 μm; when the addition amount was 2%, Further reduction to 8 μm indicates that the coating thickness remains uniform under these conditions; however, when the addition amount increases to 3% and 4%, While there was no further reduction, its melt viscosity at 750°C increased significantly, hindering its ability to effectively fill pores. This calibration procedure correlated the amount of reactive thickener added with its anti-sagging properties at overshoot temperature and its flow properties at normal softening temperature. Experimental data showed that, under these specific conditions, the amount of nano-sized alumina powder added provides a working window that balances anti-sagging properties and pore-filling flowability. For this application, the addition amount was determined to be between 1.5% and 2.5% of the total inorganic component mass. Within this range, the coating composition, after being subjected to overheating on a vertical surface, formed a uniform protective layer thickness, and its initial densification process remained unaffected.

[0049] Example 5: When applying the coating composition of the present invention to a heat treatment furnace with a specific chemical atmosphere, to ensure that the performance fluctuations of the raw materials used do not affect the process... < To ensure the stable realization of this core timing relationship, this embodiment establishes a standardized raw material compatibility verification procedure for application before field deployment. The procedure is designed to address the following working condition: the user receives a batch of new low softening point inorganic glass powder and plans to apply it to a continuous heat treatment furnace with a reducing atmosphere, i.e., a carbon monoxide volume fraction of 1%, and the furnace has a programmed heating rate of 15°C / min.

[0050] The specific steps of the verification procedure are as follows: First, according to the proportions in the specific implementation method, a small amount of a new batch of low softening point inorganic glass powder and a standard batch of organic film-forming resin and high-temperature resistant inorganic aggregate are taken to prepare a test coating composition sample; then, the sample is placed in a simultaneous thermal analyzer, which can perform thermogravimetric analysis and differential scanning calorimetry simultaneously; to simulate the field conditions, the heating rate of the simultaneous thermal analyzer is set to 15℃ / min, and a nitrogen mixture with a carbon monoxide concentration of 1% is introduced into its test chamber, which is the same as the atmosphere in the furnace at the field; under these conditions, the heating program is run, and the TGA curve will record the mass loss of the sample due to the decomposition of the organic film-forming resin. The temperature corresponding to the point of fastest weight loss is recorded as the actual decomposition temperature under this specific condition. Simultaneously, the DSC curve will record the endothermic peak generated by the glass transition and softening of the sample due to the low softening point inorganic glass powder. The onset temperature of this endothermic peak is recorded as the actual softening point temperature under this operating condition. By comparison and The value can determine the compatibility of the new batch of raw materials. Higher than If a temperature window of no less than 50°C is maintained, it indicates that the batch of raw materials is suitable for this specific working condition, and the verification is successful.

[0051] Example 6: To minimize the porosity of the final inorganic composite protective layer, the initial packing porosity of its precursor, the inorganic dry-mixed powder, must be minimized. This objective is equivalent to maximizing the tap density of the powder. This embodiment establishes a set of methods for finding maximizable... An offline optimization procedure for the particle size distribution between high-temperature resistant inorganic aggregates and low-softening-point inorganic glass powder; the specific steps of this procedure are as follows: first, select the average particle size... Alumina with a fixed particle size of 40 μm was used as a high-temperature resistant inorganic aggregate, and five groups of average particle sizes were prepared. Low-softening-point inorganic glass powders with diameters of 2μm, 5μm, 8μm, 10μm, and 15μm were selected. Five groups of dry-mixed powder samples were then prepared according to a fixed mass ratio of 60 parts by weight of aggregate to 40 parts by weight of glass powder. Each dry-mixed sample was accurately weighed and placed in a standard graduated cylinder. A powder tap density meter was used to vibrate the sample at a uniform frequency and amplitude until the powder volume no longer decreased, and the final packing volume was recorded. Based on sample quality With the final stacked volume Calculate the tap density of the powder under each mix ratio. ,in .

[0052] Test data show that the tapped density As an objective function, its value varies with the particle size ratio. The change exhibits a peak; when the particle size ratio of aggregate to glass powder... The measured tap density when the ratio is smaller (2.7) or larger (20) is... Both are relatively low; while when the particle size ratio When the measured tap density is in the range of 4 to 8, The maximum value is achieved because when the glass powder particles are too large, they cannot effectively fill the gaps between the aggregate particles, while when they are too small, they are prone to agglomeration or adhesion to the aggregate surface, thus failing to achieve the optimal filling effect. Through this procedure, it was determined that in the material system used in this invention, the preferred average particle size ratio of high-temperature resistant inorganic aggregate to low-softening-point inorganic glass powder is 4 to 8 in order to obtain the lowest initial packing porosity. The coatings prepared using powder within this particle size ratio range, after heat treatment, have an inorganic composite protective layer whose porosity, measured by mercury intrusion porosimetry, is consistently below 5%.

[0053] Example 7: To further verify the feasibility of the technical solution of the present invention, this example provides two specific coating composition formulations and correlates the performance of the protective layer prepared by them with the aforementioned test results.

[0054] Table 1: Formulation table of high temperature protective coating composition (unit: parts by weight).

[0055]

[0056] According to the preparation method described above, the components of Formula 1 and Formula 2 in Table 1 were mixed evenly to obtain a coating composition slurry. The slurry was applied to the surface of a sandblasted Q235 carbon steel plate, and the dry film thickness was controlled at 150±10μm. The coating sample prepared using Formula 1 was sintered according to the heat treatment procedure described in Example 2 (heating to 550℃ and holding for 1 hour, then heating to 750℃ and holding for 2 hours). After sintering and cooling, the open porosity of the coating was measured by mercury intrusion porosimetry. The porosity value was 3.8%, which was consistent with the test results of the sample group of the present invention. Subsequently, the sample was subjected to 20 thermal shock cycles. After the test, the coating surface was visually inspected, and no macroscopic cracks or peeling were observed, indicating that it has thermal shock resistance.

[0057] The coating sample prepared using Formula 2 was subjected to a high-temperature sag test according to the method described in Example 4. It was vertically suspended at an overshoot temperature of 950°C and held at that temperature for 1 hour. After cooling, the thickness difference between the lower and upper edges of the coating was measured. The difference The thickness of the coating is 8μm, indicating that the coating thickness remains basically uniform and exhibits resistance to high-temperature sagging. In addition, the coating sample of Formula 2 was cured at room temperature but not sintered at high temperature. The sample was subjected to neutral salt spray test according to GB / T Resin 10125 standard. After 500 hours, no rust spread was observed in the scratched area, which proves that the zinc powder provides effective cathodic protection for the substrate in a normal temperature and humid environment.

[0058] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A high temperature protective coating characterized in that, It comprises: at the decomposition temperature organic film-forming resin which decomposes at the decomposition temperature A low-softening point inorganic glass powder having a softening point temperature of ; A high-temperature-resistant inorganic aggregate, the melting point of the high-temperature-resistant inorganic aggregate is higher than the decomposition temperature , and the high-temperature-resistant inorganic aggregate is at least partially ceramic particles capable of undergoing a martensitic phase transformation under stress induction; wherein the temperature relationship of the components in the composition is set to satisfy the decomposition temperature is lower than the softening point temperature ; when the temperature reaches the decomposition temperature during temperature rise, the organic film-forming resin decomposes to form a three-dimensionally interconnected pore network inside the coating; when the temperature continues to rise to the softening point temperature , the low-softening-point inorganic glass powder melts to produce a liquid phase; And, the composition further comprises a reactive thickener having the same chemical composition as the refractory inorganic aggregate, the reactive thickener having a mean particle size in the nanometer range and chemically reacting in situ with the liquid phase at temperatures above the softening point temperature of the refractory inorganic aggregate to produce a higher viscosity phase ; The composition further comprises a chemical atmosphere buffer, which is a transition metal oxide capable of reversible redox reaction to change its valence state according to the external environment atmosphere within the temperature range of the coating operation; when the external reducing atmosphere penetrates, the buffer is reduced to consume the reducing atmosphere; when the external oxidizing atmosphere penetrates, the reduced buffer is re-oxidized to consume the oxidizing atmosphere, and the composition further comprises a thermal chemical process indicator, which is a transition metal oxide that presents a first color in solid state and presents a second irreversible color different from the first color after the completion of the fusion welding process due to complete dissolution in the formed glass phase. After the composition is cooled and solidified, the dense inorganic composite protective layer formed has the following structural characteristics: high-temperature-resistant inorganic aggregates are uniformly distributed in the continuous glass phase matrix formed by low-softening-point inorganic glass powder; the porosity of the coating measured by mercury injection method is less than 5%; The content of the organic film-forming resin is 10-30 parts by weight based on 100 parts by weight of the total weight of the composition; the content of the low-softening-point inorganic glass powder is 15-40 parts by weight; and the content of the high-temperature-resistant inorganic aggregate is 40-70 parts by weight. The high-temperature protective coating is prepared by the following preparation method, which comprises the following steps: Step a: uniformly mixing the organic film-forming resin, the high-temperature-resistant inorganic aggregate, the low-softening-point inorganic glass powder, and the reactive thickening agent to obtain a coating composition slurry; Step b: applying the coating composition slurry to the surface of the substrate; Step c, heating treatment of the substrate applied with the coating composition slurry, specifically: first, heating the substrate to the decomposition temperature of the organic film-forming resin, and holding the temperature, so that the organic film-forming resin is completely decomposed, thereby forming a three-dimensionally connected pore network in the coating; then, continuing to heat to the temperature range of the softening point of the low softening point inorganic glass powder, and holding the temperature, so that the low softening point inorganic glass powder is melted to produce a liquid phase, and the liquid phase capillary flows along the aforementioned pore network formed by the resin decomposition to fill the pore network, thereby melting and welding the high-temperature-resistant inorganic aggregates into one body; finally, cooling the substrate to obtain a dense inorganic composite protective layer.

2. A high temperature protective coating according to claim 1, characterized in that Decomposition temperature of organic film-forming resin is four hundred degrees Celsius to six hundred degrees Celsius; Softening point temperature of low softening point inorganic glass powder is six hundred fifty degrees Celsius to eight hundred fifty degrees Celsius.

3. The high temperature protective coating of claim 1, wherein, The composition further comprises metallic zinc powder; the metallic zinc powder forms a galvanic cell with the substrate as an anode to provide cathodic protection in a normal temperature and humid environment; and in the process of temperature rise, when the temperature reaches the interval of the decomposition temperature of the organic film-forming resin , the gaseous zinc chemically reacts with the existing oxides on the surface of the substrate as a reducing agent.

4. The high temperature protective coating of claim 1, wherein, The average particle size of the high-temperature-resistant inorganic aggregate is larger than the average particle size of the low-softening-point inorganic glass powder.

5. The high temperature protective coating of claim 1, wherein, The organic film-forming resin is a silicone resin; the low-softening-point inorganic glass powder is borosilicate glass powder; and the ceramic particles capable of undergoing martensitic phase transformation under stress induction are partially stabilized zirconia.

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