High-temperature protective coating and preparation method thereof

Abstract

The invention relates to the technical field of high-temperature protective coatings, and aims to solve the problem that the existing high-temperature coating generates a large number of pores after an organic film forming matter is decomposed, so that the structure is degraded and the protection performance is reduced. The invention discloses a high-temperature protective coating and a preparation method thereof, the coating composition comprises an organic film-forming resin low-softening-point inorganic glass powder and a high-temperature-resistant inorganic aggregate capable of generating phase change under stress induction, and through a sequential coupling mechanism, the organic resin is decomposed at high temperature to generate a pore network, so that the high-temperature-resistant performance of the coating is improved. According to the method, the destructive process of organic matter decomposition is converted into a constructive link of coating self-densification, the bionic self-healing capacity of the finally formed inorganic layer for resisting thermal shock microcracks is improved, and the thermal shock resistance of the inorganic layer is improved. The core problem that a traditional high-temperature coating loses efficacy due to structural deterioration and brittle fracture is solved, and the long-term service reliability under severe working conditions is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a high-temperature protective coating and a preparation method thereof, and belongs to the technical field of high-temperature protective coatings. BACKGROUND

[0002] The current commonly used technical method is to bond high-temperature-resistant inorganic ceramic fillers such as alumina and silicon dioxide together by using an organic film-forming material such as silicone resin, and to coat the fillers on the surface of a device substrate to form a protective layer. This method effectively solves the basic problems of coating storage, construction and film adhesion in normal temperature environment, and thus becomes the current mainstream technical choice.

[0003] However, when this coating is applied to industrial kilns or cracking furnaces and other real working conditions that undergo repeated temperature cycles, an inherent limitation in the design principle will be revealed, that is, the organic film-forming resin as a temporary scaffold at low temperature will vaporize and escape after reaching its decomposition temperature. Although this process is predictable, its direct consequence is that a large number of randomly distributed pores are left in the coating, which not only provides a channel for the subsequent invasion of corrosive atmosphere, but more importantly, the weak interface between these pores and inorganic filler particles will become the source of micro-cracks under the action of repeated thermal expansion and cold contraction stress, ultimately leading to the premature peeling of the coating layer by layer.

[0004] To alleviate this problem, the skilled person in the art attempts to develop more high-temperature-resistant organic resins or increase the packing density of inorganic fillers to delay the failure of the coating, but these improvements do not touch the core of the problem. Because as long as there is decomposition and mass loss of organic matter, the generation of pores is inevitable. Simply increasing the thickness of the coating or the density of the filler will only exacerbate the thermal stress inside the coating, and fall into the dilemma of thicker and easier to crack. This phenomenon reveals a deeper technical contradiction. Specifically, the existing technology mainly has the following deficiencies: 1. During the transition from the organic composite film to the inorganic layer, there is a lack of an internal mechanism to maintain the structural continuity and density of the coating; 2. The pores generated by the decomposition of organic resins only exist as an unavoidable defect in the existing technology, and their negative effects cannot be effectively managed or utilized; 3. The existing improvement ideas are all aimed at resisting or delaying the decomposition of organic matter, but fail to transform this inevitable physical and chemical process into an opportunity to reconstruct the coating structure and improve the final protective performance. Therefore, how to design a coating composition that can self-repair the internal pores generated by mass loss after the decomposition of the organic film-forming material at high temperature and form a dense and complete inorganic composite protective layer in situ has become a technical problem to be solved by the present application. SUMMARY

[0005] The present application provides a high-temperature protective coating and a preparation method thereof, which mainly aims to solve the problem of structural degradation and decline of protective performance caused by a large number of pores generated after the decomposition of an organic film-forming material in the existing high-temperature coating.

[0006] To achieve the above-mentioned purpose, the present application provides a high-temperature protective coating, which comprises:

[0007] an organic film-forming resin that will decompose at a decomposition temperature ;

[0008] a low-softening-point inorganic glass powder with a softening point temperature ;

[0009] a high-temperature-resistant inorganic aggregate with a melting point higher than the decomposition temperature , and the high-temperature-resistant inorganic aggregate is at least partially ceramic particles capable of undergoing a martensitic phase transition under stress induction; wherein the temperature relationship of each component in the composition is set to satisfy the decomposition temperature lower than the softening point temperature ; when the temperature rises, when the temperature reaches the decomposition temperature , the organic film-forming resin decomposes to form a three-dimensional 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 generate a liquid phase.

[0010] Preferably, the content of the organic film-forming resin is ten to thirty parts by weight based on one hundred parts by weight of the total weight of the composition; the content of the low-softening-point inorganic glass powder is fifteen to forty parts by weight; and the content of the high-temperature-resistant inorganic aggregate is forty to seventy parts by weight.

[0011] Preferably, the composition further comprises a reactive thickening agent with the same chemical composition as the high-temperature-resistant inorganic aggregate, and the average particle size of the reactive thickening agent is nanoscale, and the reactive thickening agent generates a higher viscosity phase by in-situ chemical reaction with the liquid phase under the condition that the temperature is higher than the softening point temperature , thereby inhibiting the flow of the liquid phase.

[0012] Preferably, the decomposition temperature of the organic film-forming resin is four hundred to six hundred degrees Celsius; and the softening point temperature of the low-softening-point inorganic glass powder is six hundred and fifty to eight hundred and fifty degrees Celsius.

[0013] Preferably, the composition further comprises zinc powder; the zinc powder forms a galvanic cell with the substrate as an anode to provide cathodic protection in a normal temperature and humid environment; and when the temperature reaches the decomposition temperature of the organic film-forming resin during the temperature rising process, the gasified zinc reacts with the existing oxides on the surface of the substrate as a reducing agent.

[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 present application has the following advantages:

[0023] 1、The coating composition of the present application establishes a time sequence coupling relationship between organic matter decomposition and inorganic phase melting flow. In 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 for the subsequent melting liquid phase of low-softening-point glass powder. The liquid phase wets and welds all high-temperature-resistant inorganic aggregates in the channel, so that the coating is self-remodeled from a loose particle accumulation body into a dense glass-ceramic composite structure. The whole process converts the normal heating process step of the equipment into a necessary link for the coating to complete the final densification molding. Therefore, the structural degradation problem caused by the decomposition of organic matter in the traditional coating is changed into a prerequisite process for the coating to achieve the final structural integrity in the present application.

[0024] 2、The present application introduces ceramic particles that can undergo crystal phase transformation under stress as at least part of the high-temperature-resistant inorganic aggregate, so that the finally formed dense inorganic protective layer obtains a damage response mechanism; when the coating initiates microcracks under thermal shock, the stress field concentrated at the crack tip will trigger the volume expansion of the surrounding ceramic particles, forming a compressive stress field in situ in the crack area. The compressive stress field plays a clamping role on the continuous expansion of the crack and dissipates part of the tensile stress that causes the crack. This way does not prevent the generation of microcracks, but changes the crack propagation behavior in the material, making the failure process of the coating evolve from unpredictable brittle fracture to a more moderate performance degradation process, thereby improving its use reliability under repeated temperature fluctuation conditions.

[0025] 3、The present application further comprises zinc powder in the coating composition, so that the same component assumes two protective roles based on different physical and chemical principles in different life cycle stages of the coating; in the normal temperature and humid environment during equipment shutdown or storage, the zinc powder provides sacrificial anode protection for the substrate through electrochemical mechanism, and when the equipment is heated to the temperature range where the organic resin decomposes, the vaporized zinc reacts with the existing oxides on the substrate surface as a reducing agent, completing the chemical purification and activation of the bonding interface before the glass phase is about to melt and bond with the substrate. The combination of the two effects extends the protective function of the coating from the high-temperature working interval to the whole cycle in the non-working state, and changes the bonding mode of the coating and the substrate from physical coverage to interface welding based on in-situ chemical reaction. BRIEF DESCRIPTION OF DRAWINGS

[0026] Fig. 1 Flow chart of in-situ densification and damage response mechanism of the coating of the present application;

[0027] Fig. 2The influence of the reactive thickening agent of the present application on the sag resistance and melt viscosity of the coating is shown in the following graph;

[0028] Fig. 3 The microstructure evolution and toughening mechanism of the coating of the present application during temperature rise are shown in the following schematic diagram. DETAILED DESCRIPTION

[0029] To make the technical solutions and advantages of the present application clearer, the present application will be described in further detail below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0030] The present application provides a high-temperature protective coating and a preparation method thereof. By time sequence coupling of the physical and chemical behaviors of different components in the thermal process, the coating is reshaped in situ from an organic-inorganic composite state to a pure inorganic dense protective layer. The composition system comprises an organic film-forming resin serving as a low-temperature temporary binder, a high-temperature-resistant inorganic aggregate serving as a final structural framework, and a low-softening-point inorganic glass powder serving as a high-temperature healing medium. The three components work together in a preset temperature rise program to use the pores generated by the decomposition of the organic resin as channels to guide the capillary filling and melting welding of the molten glass phase, thereby forming a dense glass-ceramic composite protective layer on the surface of the substrate which is tightly combined with the substrate. In the high-temperature equipment, especially in the industrial furnace inner wall protection application which undergoes repeated start-stop temperature cycle, a technical problem is that the internal organic binder of the conventional coating will decompose and escape after being subjected to the first high temperature, leaving a loose porous structure accumulated by inorganic fillers, which is prone to cracking and peeling under the action of subsequent thermal stress. To address this challenge, the role of the organic film-forming resin in the composition of the present application is set to provide basic film-forming property and adhesion during construction and room temperature curing stage, and to uniformly fix all inorganic components on the surface of the substrate. The decomposition of the organic film-forming resin at high temperature is regarded as a preset programmed step. Specifically, methylphenyl silicone resin is selected as the organic film-forming resin, and the main decomposition temperature interval of the resin is determined by thermogravimetric analysis to be 400-600℃. When the coating is heated to this temperature interval, the resin pyrolyzes and gasifies and escapes, and the corresponding mass loss forms a three-dimensionally connected pore network in the coating, which provides a spatial channel for the subsequent structural remodeling. In this way, the decomposition process of the organic film-forming resin is transformed from a link that leads to structural degradation to a prelude function 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 application has an organic film-forming resin content of 10-30 parts by weight, a low-softening-point inorganic glass powder content of 15-40 parts by weight, and a high-temperature-resistant inorganic aggregate content of 40-70 parts by weight, based on 100 parts by weight of the total composition. The ratio range is determined based on the following: when the content of the organic film-forming resin is less than 10 parts by weight, the slurry stability before application and the initial film-forming property after application of the coating are insufficient, and it is difficult to form a uniform coating; when the content is more than 30 parts by weight, the mass loss caused by the decomposition of the organic matter at high temperatures is too large, the total pore volume formed exceeds the filling capacity of the subsequent glass liquid phase, and a high porosity is left in the final coating; when the content of the low-softening-point inorganic glass powder is less than 15 parts by weight, the generated molten liquid phase is not enough to completely fill the pores and coat the aggregate, and a continuous and dense matrix phase cannot be formed; and when the content is more than 40 parts by weight, the glass phase accounts for too high a proportion in the final coating, which reduces the maximum use temperature and wear resistance of the coating. Correspondingly, the high-temperature-resistant inorganic aggregate, as the main structure, has a content matched with other components, so as to achieve the required mechanical properties and high-temperature resistance of the final composite protective layer under the premise of being fully wetted and bonded.

[0033] In some applications requiring the coating to be applied to vertical surfaces or having higher temperature safety window requirements, in order to inhibit the sagging phenomenon of the glass phase due to the decrease in viscosity under working conditions far exceeding its softening point , the composition can further comprise a reactive thickening agent; the thickening agent is selected from ultra-fine powders having the same chemical composition as the high-temperature-resistant inorganic aggregate but an average particle size in the nanometer range, for example, when the aggregate is alumina, the thickening agent is nano-alumina; the mechanism of action is that, near the normal working temperature , the nano-powder is dispersed in the glass liquid phase as a filler; when the temperature rises, the nano-powder will react with the molten borosilicate glass liquid phase due to its specific surface area and reactivity, generating an aluminoborosilicate phase with a higher melting point in situ, this reaction consumes the low-viscosity liquid phase and generates a new phase with high viscosity, resulting in a jump in the viscosity of the entire melt, thereby physically inhibiting its macroscopic flowability, and the coating obtains the self-adaptive ability to resist over-temperature sagging.

[0034] In order to solve the corrosion problem of the substrate in a normal temperature and humid environment including storage and shutdown maintenance before the coating is glass-formed at high temperature, the composition can further comprise zinc powder; this component plays a dual role in the life cycle of the coating: in a normal temperature and humid environment, the zinc powder, as a more active metal than the steel substrate, provides electrochemical cathodic protection for the substrate through the sacrificial anode mechanism, preventing the occurrence of bottom rust; and during the heating of the equipment, when the temperature enters the decomposition temperature range of the organic resin When the temperature reaches the softening point of the glass powder, the zinc vapor, which has been melted and started to vaporize, will react with the trace amount of oxides that might exist on the surface of the substrate as a reducing agent, and will chemically clean and activate the bonding interface before the glass phase melts and bonds with the substrate. This design extends the protective function of the coating from the high-temperature working state to the non-working state, and changes the bonding mechanism of the coating with the substrate from physical covering to chemical bonding.

[0035] In addition, to ensure the time sequence relationship can be stably realized in an industrial environment with fluctuating chemical atmosphere, and a chemical atmosphere buffer can also be included in the composition; the buffer is selected from transition metal oxides that can undergo reversible redox reactions within the working temperature range, such as iron trioxide; the mechanism is that when the external reducing atmosphere, penetrates into the coating, it will preferentially react with and reduce it, thereby consuming the reducing gas and protecting the softening point of the glass powder from being lowered; and when the external oxidizing atmosphere, penetrates in, the reduced will be quickly re-oxidized to , thereby consuming oxygen and protecting the decomposition temperature of the organic resin from being lowered; through this reversible change in valence, the buffer dynamically maintains the stability of the microenvironment inside the coating, ensuring the reliable triggering of the core time sequence mechanism.

[0036] To convert the invisible vitrification process inside the coating into a signal that can be externally observed for quality control, a thermochemical process indicator can also be included in the composition; the indicator is selected from transition metal oxides that appear in a first color in solid state, and can make the glass appear in a second irreversible color after completely dissolving in the molten glass phase, such as cobalt oxide; the solid cobalt oxide powder is black, and the entire coating appears dark gray before vitrification is completed; when the temperature reaches , the glass phase melts and flows and completes the filling of the pores and the welding of the aggregate, the black cobalt oxide particles will simultaneously dissolve in the glass liquid phase, dyeing the glass with a characteristic cobalt blue color; therefore, after the equipment cools down, whether the in-situ vitrification process inside the coating has been completed in all areas can be judged by visually checking whether the coating has uniformly turned into cobalt blue.

[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 low-softening-point inorganic glass powder particles, which were originally solid, begin to soften and transform into a high-viscosity molten liquid phase. This liquid phase, driven by capillary force, flows along the pore network formed by the decomposition of the silicone resin in the previous step to fill and wet. This process melts and welds all the independent high-temperature-resistant inorganic aggregate particles and part of the partially stabilized zirconia particles into a whole, forming a continuous, dense, and pore-free glass-ceramic composite phase. The decomposition of the organic silicone resin, which leads to structural degradation in conventional technology, and the pore structure it produces, and the molten flow behavior of the low-softening-point glass powder form a synergistic relationship in terms of timing. The former creates a path for repair and densification for the latter, thereby resolving the contradiction between the removal of organic matter and the maintenance of structural integrity.

[0040] During the startup of the cracking furnace to operating temperature and subsequent temperature reduction and reheating cycles, the coating is subjected to thermal shock, and microcracks may occur in the coating due to the mismatch in thermal expansion coefficients between the glass phase and the inorganic aggregate particles. When the tip of a microcrack expands under stress to the vicinity of a partially stabilized zirconia particle, the stress field concentrated at the crack tip triggers a martensitic phase transition from the tetragonal phase to the monoclinic phase in the particle. The volume expansion accompanying the phase transition applies a compressive stress field at the crack tip, which constrains the continued opening of the crack and absorbs part of the fracture energy. The high-temperature-resistant inorganic aggregate not only exists as a structural framework, but the partially stabilized zirconia it contains is an internal defense mechanism that is activated when damage occurs. This mechanism enables the final dense inorganic layer to have damage tolerance and meets the technical requirements for density and toughness. After several complete temperature rise and fall cycles, the inorganic composite protective layer formed on the surface of the region coated with the coating of the present application remains intact, dense, and free of cracks or peeling, and forms a firm bond with the substrate. In contrast, the region protected by the conventional silicone high-temperature-resistant coating without partially stabilized zirconia and low-softening-point glass powder shows extensive pulverization and layered peeling.

[0041] Example 2: To objectively verify the self-densification and heat shock resistance of the coating composition of the present application at high temperature, a set of comparative tests was established in this example. Two groups of samples were used, one control group without low-softening-point inorganic glass powder and partially stabilized zirconia, and one sample group of the present application containing all the core components as described in the detailed description. The test substrate was a 100 mm x 100 mm x 5 mm Q235 carbon steel plate that had been sandblasted. The coating was applied to the surface of the substrate by air spraying, and the dry film thickness was controlled at 150 ± 10 μm. The test was carried out in a programmable high-temperature muffle furnace. To simulate the actual temperature rise and heat shock conditions of industrial equipment, the heat treatment program was set as follows: the temperature was raised from room temperature to 550°C at a rate of 10°C / min, and the sample was kept at this temperature for 1 h to completely decompose the organic film-forming resin; then, the temperature was raised to 750°C (Ts interval) at a rate of 10°C / min, and the sample was kept at this temperature for 2 h to complete the melting, flowing and welding process of the glass phase; after the heat preservation was completed, the sample was cooled to room temperature in the furnace to complete the initial sintering; then, the heat shock cycle test was carried out, each cycle including heating the sample from room temperature to 800°C at a rate of 20°C / min, keeping it at this temperature for 30 min, then taking it out and placing it at room temperature for forced air cooling, a total of 20 cycles.

[0042] After the initial sintering is completed and cooled to room temperature, the performance of the coating of the two groups of samples is characterized; the open porosity of the coating is measured by mercury injection method, the porosity of the coating of the control group is measured as 21.3%, while the porosity of the coating of the sample group of the application is only 3.8%; the data difference is due to the fact that the pore network left after the decomposition of the organic resin in the control group is permanently retained, forming a high porosity structure, while in the sample group of the application, the pore network formed by the decomposition of the resin is filled and healed by the subsequent liquid phase of the low softening point inorganic glass powder; after completing 20 times of thermal shock cycle test, the coating state of the two groups of samples is evaluated again; under the alternating action of high frequency thermal stress, the stress concentration occurs at the structural defects existing in the coating of the control group sample due to the high porosity, leading to the expansion and finally the penetration of microcracks, causing macroscopic cracking and peeling; on the contrary, the coating of the sample group of the application, firstly, the initial low porosity structure reduces the source of cracks; secondly, when the thermal shock stress locally induces microcracks, the stress-induced martensitic phase transition occurs in the part of the stable zirconia particles in front of the crack tip and is accompanied by volume expansion, forming a compressive stress field at the crack tip, which inhibits the further expansion of the crack, so that the coating as a whole shows tolerance to thermal shock damage; the test results show that compared with the coating composition not containing low softening point inorganic glass powder and partially stabilized zirconia, the coating composition of the application can form a dense inorganic protective layer with low porosity in situ after experiencing initial high temperature, and the protective layer shows higher structural stability and anti-cracking and peeling ability under repeated thermal shock conditions; this performance confirms the effectiveness of the time sequence coupling mechanism of organic matter decomposition and inorganic phase melting and the stress-induced phase transition toughening mechanism.

[0043] In the application of the coating composition of the application in the first firing of a newly built hot blast stove, the coating composition further contains ferrous oxide as a chemical atmosphere buffer and cobalt oxide as a thermochemical process indicator; in the early stage of the firing, there is a local oxygen-rich atmosphere in the stove due to insufficient combustion, which can accelerate the oxidative decomposition of the organic film-forming resin, and has the risk of causing premature failure, while the ferrous oxide contained in the coating composition plays a buffering role in the decomposition rate of the resin by consuming the infiltrated oxygen, thereby maintaining the stability of the time sequence relationship; As the firing temperature continues to rise and reaches the interval, the operator can directly monitor the color change of the coating from the initial dark gray to the characteristic cobalt blue through the observation hole in the stove wall, and use it as an intuitive basis for judging whether the temperature in each region of the stove reaches the glass sintering temperature uniformly, when the entire stove lining presents a uniform cobalt blue color, it is confirmed that the self-healing in-situ glass sintering process of the entire coating has been completed, thereby providing quality assurance for the subsequent formal production.

[0044] Example 3: This example combines Figs. 1 to 3 A description of a high-temperature protective coating and its preparation method is provided, such as... Fig. 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 Fig. 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 Fig. 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%, No further reduction, but its melt viscosity at 750°C then appears a sharp rise, hampering its ability to effectively fill the pores; through this calibration procedure, the amount of reactive thickener added is correlated with its sag resistance at over-temperature and flow performance at normal softening temperature; test data show that, under this particular condition, there is a working window for the addition amount of nano-sized alumina powder that takes into account both sag resistance and pore filling flow performance; for this application, its addition amount is determined to be in the range of 1.5% to 2.5% of the total mass of inorganic components, within which range the coating composition after being subjected to over-temperature heating in the vertical plane forms a protective layer with uniform thickness, and its initial densification process is not affected.

[0049] Example 5: When applying the coating composition of the present application to a heat treatment furnace with a specific chemical atmosphere, to ensure that the performance fluctuations of the raw materials used do not affect To stably achieve this core timing relationship, the present embodiment establishes a set of standardized raw material adaptability verification procedures applied before field deployment; the working condition that this procedure aims to address is that the user receives a new batch of 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 program heating rate of 15°C / min.

[0050] The specific steps of this verification procedure are as follows: first, according to the specific embodiment, take a small amount of the new batch of low softening point inorganic glass powder and standard batches of organic film-forming resin and high-temperature resistant inorganic aggregate, and prepare a test coating composition sample; then, place the sample in a simultaneous thermal analyzer, which can simultaneously perform thermogravimetric analysis and differential scanning calorimetric analysis; to simulate the field working condition, set the heating rate of the simultaneous thermal analyzer to 15°C / min, and pass a nitrogen gas mixture with a carbon monoxide concentration of 1% identical to the atmosphere in the field furnace into the test cavity; run the temperature rising program under this condition, the TGA curve will record the mass loss of the sample due to the decomposition of the organic film-forming resin, and the temperature corresponding to the fastest weight loss rate is recorded as the actual decomposition temperature ; at the same time, the DSC curve will record the endothermic peak of the sample due to the glass transition and softening of the low softening point inorganic glass powder, and the initial temperature of the endothermic peak is recorded as the actual softening point temperature under this condition; by comparing the values of and , the adaptability of the new batch of raw materials can be determined, if is higher than and maintains a temperature window of no less than 50°C, it indicates that the batch of raw materials is suitable for this specific working condition, and the verification is passed.

[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.

2. A high temperature protective coating according to claim 1, characterised in that, The content of the organic film-forming resin is 10-30 parts by weight, 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, based on 100 parts by weight of the total weight of the composition.

3. The high temperature protective coating of claim 1, wherein, The composition further comprises a reactive thickener having the same chemical composition as the refractory inorganic aggregate, the average particle size of the reactive thickener being 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 form a higher viscosity phase.

4. The high temperature protective coating of claim 1, wherein, 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.

5. 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 vaporized zinc chemically reacts with the existing oxides on the surface of the substrate as a reducing agent.

6. A high temperature protective coating according to claim 1, wherein The composition further comprises a chemical atmosphere buffer, which is a transition metal oxide capable of undergoing reversible oxidation-reduction reactions to change its valence state according to the external environmental 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 thermo-chemical process indicator, which is a transition metal oxide that exhibits a first color in a solid state and, after the completion of the molten welding process, completely dissolves in the formed glass phase, causing the glass phase to exhibit a second irreversible color different from the first color.

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

8. 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 a borosilicate glass powder; and the ceramic particles capable of undergoing a martensitic phase transition under stress induction are partially stabilized zirconia.

9. The high temperature protective coating of claim 1, wherein, After the composition is cooled and solidified, the dense inorganic composite protective layer formed has the following structural characteristics: the high-temperature-resistant inorganic aggregate is uniformly distributed in the continuous glass phase matrix formed by the low-softening-point inorganic glass powder; and the porosity of the coating layer measured by the mercury intrusion method is less than 5%.

10. A process for the preparation of a high temperature protective coating according to any one of claims 1 to 9, characterized in that The method 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 interval, and keeping the temperature, so that the organic film-forming resin is completely decomposed, thereby forming a three-dimensionally connected pore network inside the coating; then, continuing to heat to the softening point temperature interval, and keeping 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.

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