A plating process for a heavy-duty anticorrosive coating on a metal substrate surface

Abstract

The present application relates to the plating technology field of metal material, disclose a kind of plating process of metal substrate surface heavy anticorrosive coating, comprising: to metal substrate is implemented hydroxylation activation treatment, and is coated with the anticorrosive coating including siloxane modified graphene, polyurethane prepolymer and high-boiling organic solvent;Utilize normal temperature stationary induction active siloxane functional group and metal hydroxyl functional site occur polycondensation reaction, and in situ covalently anchored single-layer graphene directional template is constructed in metal interface;Through gradient temperature curing drive solvent unidirectional migration and the normal mechanical shear force generated by polyurethane volume limited shrinkage, guide non-anchor graphene sheet layer to arrange parallel to substrate with the directional template as benchmark, the present application constructs continuous maze shielding structure in coating interior by the synergistic effect of chemical anchoring and physical calendering, inhibit corrosion medium penetration, enhance interface bonding force and stability.

Description

Technical Field

[0001] This invention belongs to the field of metal coating technology, and particularly relates to a coating process for a heavy-duty anti-corrosion layer on the surface of a metal substrate. Background Technology

[0002] The current coating process for heavy-duty anti-corrosion coatings on metal substrates is a core barrier to ensure the long-term operation of marine engineering and nuclear power equipment. In the field of heavy-duty anti-corrosion technology, the mainstream approach is to use modified polyurethane and other organic resins combined with graphene two-dimensional nanofillers to construct a physical shielding layer. This utilizes the layered structure of the filler to extend the penetration path of corrosive media, thereby improving the metal substrate's resistance to salt spray and ultraviolet radiation. However, within the 60-year service life required for coastal nuclear power plants, this coating process, which relies on physical mixing, faces limitations at the physical mechanism level. Due to the large initial thickness of the heavy-duty anti-corrosion coating, thermal convection and surface tension gradient evolution occur inside the liquid film during solvent evaporation and resin curing. As the metal substrate acts as a heat conductor, the underlying solvent close to the metal interface is preferentially heated, and the resulting upward thermal convection drives the graphene sheets to detach from the preset interface coordinates.

[0003] This micro-rheological behavior leads to a random distribution of graphene sheets within the coating, making it difficult to form a continuous labyrinthine shielding structure and creating penetration channels at the metal interface. Attempts to compensate for the loss of shielding performance by simply increasing the coating thickness or the amount of graphene added are logically limited. Increased thickness causes internal stress accumulation, leading to brittle fracture and peeling of the coating under temperature fluctuations; increasing the amount of graphene causes filler agglomeration, disrupting the wetting balance of the plating solution. These linear improvement approaches cannot resolve the fundamental conflict between the perturbation of thick film formation kinetics and the stability of the interface arrangement. Besides macroscopic parameter limitations, existing technologies also have shortcomings in terms of film formation kinetic control mechanisms. For example, [the following is mentioned in publication number CN1]. Chinese invention patent application 15340800A discloses a graphene / silica ceramic resin heavy-duty anti-corrosion coating and its preparation method. It grafts cyclodextrin onto the surface of graphene oxide and loads corrosion inhibitors. It utilizes the chemical bonding or π-π stacking effect between the filler and the resin matrix to improve static dispersibility. The existing solution ignores the micro-rheological behavior of the non-equilibrium film formation process of the thick film coating: during the heating and curing stage, the thermal gradient between the metal substrate and the coating evolves. The bottom solvent is preferentially heated to generate upward thermal convection and form a fluid drag force. It lacks an interface anchoring base and a follow-up orientation driving mechanism. The pre-dispersed graphene sheets are easy to detach from the preset coordinates and undergo pose flipping, making it difficult to form a continuous parallel labyrinth shielding structure inside the coating and form micro-permeation channels at the metal interface.

[0004] Therefore, how to utilize the volume collapse stress during the curing process of the coating layer and the chemical anchoring effect of the interface molecules to achieve the pose locking of graphene at the metal interface and the orderly rolled arrangement inside the coating is the technical problem to be solved by this invention. Summary of the Invention

[0005] To address the problems mentioned in the background art, the technical solution of the present invention is as follows: A coating process for a heavy-duty anti-corrosion layer on the surface of a metal substrate, comprising the following steps:

[0006] Step 101: Sandblasting is performed on the surface of the metal substrate to achieve a roughness of Sa2.5. Hydroxylation activation treatment is performed using an alkaline solution with a mass fraction of 5% to 15% or an anhydrous ethanol with a volume fraction of more than 95% to form chemically active metal hydroxyl functional sites on the surface of the metal substrate.

[0007] Step 102: Coating the surface of the metal substrate with an anti-corrosion coating, the anti-corrosion coating including siloxane-modified graphene, polyurethane prepolymer and high-boiling-point organic solvent with a boiling point of 150°C to 260°C, the surface of the siloxane-modified graphene being grafted with active siloxane functional groups.

[0008] Step 103: Place the coated metal substrate in an environment with a temperature of 15°C to 30°C and let it stand for 30 min to 60 min. Utilize the condensation reaction between the active siloxane functional groups and the metal hydroxyl functional sites to construct an in-situ covalently anchored monolayer graphene oriented template at the metal interface.

[0009] Step 104: Segmented heating and curing of the metal substrate, controlling the heating rate to be 2℃ / min to 5℃ / min. Utilizing the kinetic energy brought by the unidirectional migration and volatilization of the high-boiling-point organic solvent from the inside of the coating to the surface, and the normal mechanical shear force formed by the volume-limited shrinkage of the polyurethane prepolymer in the direction perpendicular to the metal substrate during the curing process, the non-anchored graphene sheets are driven to rotate in the direction parallel to the metal substrate with the single-layer graphene orientation template as the alignment reference, forming a dense heavy-duty anti-corrosion layer with a labyrinth shielding structure on the surface of the metal substrate.

[0010] Preferably, the siloxane-modified graphene is prepared by condensation reaction of graphene oxide with a siloxane coupling agent selected from triethoxysilane, trimethoxysilane, aminopropyltriethoxysilane, or glycidyl etheroxypropyltrimethoxysilane; the mass fraction of the siloxane-modified graphene in the anticorrosive coating is 1.5% to 5.5%; the mass fraction of the high-boiling-point organic solvent in the anticorrosive coating is 20% to 35%, and the high-boiling-point organic solvent is selected from ethylene glycol monobutyl ether, diethylene glycol dimethyl ether, cyclohexanone, or thallium; the polyurethane prepolymer is prepared by reacting polyether polyol with a number average molecular weight of 1000 to 3000 with diphenylmethane diisocyanate under the action of a catalyst.

[0011] Preferably, step 101 further includes the following steps: step 1011, using compressed air to drive abrasives to impact the surface of the metal substrate to remove oxide scale, so that the surface of the metal substrate reveals its metallic color; step 1012, using anhydrous ethanol to continuously wipe the surface of the metal substrate 2 to 3 times to remove microscopic residual grease and generate metal hydroxyl functional sites on the exposed metal surface through air oxidation.

[0012] Preferably, the grafting rate of active siloxane functional groups grafted onto the surface of siloxane-modified graphene is 10% to 22%, and the grafting rate is determined by thermogravimetric analysis under a nitrogen atmosphere to measure the mass loss value of siloxane-modified graphene when heated from 150°C to 800°C.

[0013] Preferably, step 103 is carried out in a closed environment with the relative humidity controlled within the range of 40% to 60%, using the moisture in the environment to initiate partial hydrolysis of the active siloxane functional groups to promote heterogeneous polycondensation with the metal hydroxyl functional sites.

[0014] Preferably, the segmented temperature-curing step 104 includes the following steps: Step 1041, initial temperature-raising stage, raising the temperature from room temperature to 80°C to 100°C and holding it for 20 min to 40 min, so that the high-boiling-point organic solvent evaporates at a uniform rate; Step 1042, high-temperature curing stage, raising the temperature to 150°C to 180°C and holding it for 60 min to 120 min, so that the polyurethane prepolymer forms a three-dimensional cross-linked network.

[0015] Preferably, the preparation process of the anti-corrosion coating includes the following steps: dispersing siloxane-modified graphene in a high-boiling-point organic solvent and subjecting it to ultrasonic treatment, controlling the ultrasonic frequency to 20kHz to 40kHz, adding polyurethane prepolymer and subjecting it to shear dispersion at a speed of 1000rpm to 2500rpm for 30min.

[0016] Preferably, in step 104, the normal mechanical shear force generated by the volume-constrained shrinkage is stronger than the surface tension scouring force generated by the thermal volatilization of the high-boiling-point organic solvent, so as to maintain the covalent bonding state between the monolayer graphene oriented template and the surface of the metal substrate.

[0017] Preferably, the final thickness of the dense heavy-duty anti-corrosion layer is 100 μm to 300 μm, and the low-frequency electrochemical impedance modulus of the dense heavy-duty anti-corrosion layer in a 3.5% (w / w) NaCl solution is not less than [value missing] after immersion for 1000 h. .

[0018] Compared with existing technologies, the coating process for a heavy-duty anti-corrosion layer on the surface of a metal substrate in this invention has the following advantages:

[0019] 1. In the coating of heavy-duty anti-corrosion layers on the surface of metal substrates, the boiling point differences of different components in the mixed solvent system induce gradient evaporation of the solvent. Combined with the flash drying sequence, this drives the wet film layer to undergo volume collapse along a uniaxial direction perpendicular to the substrate. The normal mechanical shear force generated by this collapse drives the graphene sheets to overcome fluid resistance and force them to align parallel to the substrate direction. Compared with methods that rely on external physical field regulation, this mechanism utilizes the energy evolution during the coating's own film formation process to achieve microstructure regularization, eliminating the risk of orientation failure caused by differences in environmental wind speed and workpiece heat capacity, and ensuring that the thick film coating forms a continuous labyrinth shielding effect under complex working conditions.

[0020] 2. The exposed virgin metal hydroxyl groups on the surface of the metal substrate undergo a condensation reaction with the siloxane groups grafted onto the graphene edges within a static window at room temperature, constructing a covalently anchored monolayer graphene template at the metal interface. This template provides a horizontal reference for the deposition of the upper graphene layer during the subsequent volume collapse process. The chemical bonding effect counteracts the upward drag force generated by solvent evaporation, inhibiting the bottom graphene from flipping or detaching during the heating and curing stage due to thermal convection, avoiding the formation of micropores or galvanic corrosion induction points at the interface, and improving the interfacial stability and anti-permeation ability between the coating and the substrate.

[0021] 3. The process uses room-temperature static bonding to lock the interface base, combined with the mechanical calendering effect generated by the volume-limited shrinkage during the high-temperature stage, to enable the graphene sheets to build a highly oriented physical barrier within the polyurethane matrix. At the same time, the delayed retention of high-boiling-point solvents ensures that the polyurethane segments trigger in-situ crosslinking after the graphene is arranged in place. This non-linear synergistic effect of chemical anchoring and physical calendering allows the coating to extend the penetration path of corrosive media without increasing the amount of material used, reducing the electrochemical reaction rate on the metal surface, and meeting the engineering requirements for long-term protection of metal components in extreme environments such as nuclear power plants. Attached Figure Description

[0022] Figure 1 This is a flow chart of the directional coating process for the heavy-duty anti-corrosion layer of this invention;

[0023] Figure 2 This is a diagram illustrating the synergistic reaction and film-forming mechanism of the anti-corrosion coating of this invention. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0025] A coating process for a heavy-duty anti-corrosion layer on a metal substrate surface includes the following steps:

[0026] Step 101: Sandblasting is performed on the surface of the metal substrate to achieve a roughness of Sa2.5. Hydroxylation activation treatment is performed using an alkaline solution with a mass fraction of 5% to 15% or an anhydrous ethanol with a volume fraction of more than 95% to form chemically active metal hydroxyl functional sites on the surface of the metal substrate.

[0027] Step 102: Coating the surface of the metal substrate with an anti-corrosion coating, the anti-corrosion coating including siloxane-modified graphene, polyurethane prepolymer and high-boiling-point organic solvent with a boiling point of 150°C to 260°C, the surface of the siloxane-modified graphene being grafted with active siloxane functional groups.

[0028] Step 103: Place the coated metal substrate in an environment with a temperature of 15°C to 30°C and let it stand for 30 min to 60 min. Utilize the condensation reaction between the active siloxane functional groups and the metal hydroxyl functional sites to construct an in-situ covalently anchored monolayer graphene oriented template at the metal interface.

[0029] Step 104: Segmented heating and curing of the metal substrate, controlling the heating rate to be 2℃ / min to 5℃ / min. Utilizing the kinetic energy brought by the unidirectional migration and volatilization of the high-boiling-point organic solvent from the inside of the coating to the surface, and the normal mechanical shear force formed by the volume-limited shrinkage of the polyurethane prepolymer in the direction perpendicular to the metal substrate during the curing process, the non-anchored graphene sheets are driven to rotate in the direction parallel to the metal substrate with the single-layer graphene orientation template as the alignment reference, forming a dense heavy-duty anti-corrosion layer with a labyrinth shielding structure on the surface of the metal substrate.

[0030] Preferably, the siloxane-modified graphene is prepared by condensation reaction of graphene oxide with a siloxane coupling agent selected from triethoxysilane, trimethoxysilane, aminopropyltriethoxysilane, or glycidyl etheroxypropyltrimethoxysilane; the mass fraction of the siloxane-modified graphene in the anticorrosive coating is 1.5% to 5.5%; the mass fraction of the high-boiling-point organic solvent in the anticorrosive coating is 20% to 35%, and the high-boiling-point organic solvent is selected from ethylene glycol monobutyl ether, diethylene glycol dimethyl ether, cyclohexanone, or thallium; the polyurethane prepolymer is prepared by reacting polyether polyol with a number average molecular weight of 1000 to 3000 with diphenylmethane diisocyanate under the action of a catalyst.

[0031] Preferably, step 101 further includes the following steps: step 1011, using compressed air to drive abrasives to impact the surface of the metal substrate to remove oxide scale, so that the surface of the metal substrate reveals its metallic color; step 1012, using anhydrous ethanol to continuously wipe the surface of the metal substrate 2 to 3 times to remove microscopic residual grease and generate metal hydroxyl functional sites on the exposed metal surface through air oxidation.

[0032] Preferably, the grafting rate of active siloxane functional groups grafted onto the surface of siloxane-modified graphene is 10% to 22%, and the grafting rate is determined by thermogravimetric analysis under a nitrogen atmosphere to measure the mass loss value of siloxane-modified graphene when heated from 150°C to 800°C.

[0033] Preferably, step 103 is carried out in a closed environment with the relative humidity controlled within the range of 40% to 60%, using the moisture in the environment to initiate partial hydrolysis of the active siloxane functional groups to promote heterogeneous polycondensation with the metal hydroxyl functional sites.

[0034] Preferably, in step 104, the orientation degree of the graphene sheets within the dense, heavy-duty anti-corrosion layer... The following logical relationship must be satisfied: ,in, ΔV represents the degree of orientation; ΔV represents the volume shrinkage of the coating during the segmented heating and curing process. θ represents the initial volume of the coating after coating is completed; θ is the initial tilt angle of the non-anchored graphene sheet relative to the surface of the metal substrate.

[0035] Preferably, the segmented temperature-curing step 104 includes the following steps: Step 1041, initial temperature-raising stage, raising the temperature from room temperature to 80°C to 100°C and holding it for 20 min to 40 min, so that the high-boiling-point organic solvent evaporates at a uniform rate; Step 1042, high-temperature curing stage, raising the temperature to 150°C to 180°C and holding it for 60 min to 120 min, so that the polyurethane prepolymer forms a three-dimensional cross-linked network.

[0036] Preferably, the preparation process of the anti-corrosion coating includes the following steps: dispersing siloxane-modified graphene in a high-boiling-point organic solvent and subjecting it to ultrasonic treatment, controlling the ultrasonic frequency to 20kHz to 40kHz, adding polyurethane prepolymer and subjecting it to shear dispersion at a speed of 1000rpm to 2500rpm for 30min.

[0037] Preferably, in step 104, the normal mechanical shear force generated by the volume-constrained shrinkage is stronger than the surface tension scouring force generated by the thermal volatilization of the high-boiling-point organic solvent, so as to maintain the covalent bonding state between the monolayer graphene oriented template and the surface of the metal substrate.

[0038] Preferably, the final thickness of the dense heavy-duty anti-corrosion layer is 100 μm to 300 μm, and the low-frequency electrochemical impedance modulus of the dense heavy-duty anti-corrosion layer in a 3.5% (w / w) NaCl solution is not less than [value missing] after immersion for 1000 h. .

[0039] Example 1: In the industrial scenario of heavy-duty anti-corrosion coating of metal components in coastal nuclear power plants, the surface of the metal substrate is in a high-humidity, high-heat, and salt spray ion environment. In the heating and curing stage of traditional thick film coatings, the metal substrate acts as a heat conductor, causing the bottom solvent close to the metal interface to be preferentially heated and boiled. The upward thermal convection generates mechanical shear force, which is greater than the physical adhesion of the substrate surface. This causes the two-dimensional nanomaterials at the bottom of the liquid film to detach from the metal lattice, forming orientation misalignments and voids inside the coating, providing lateral propagation and vertical penetration channels for corrosive media. To address the technical contradiction of thick film formation dynamics disturbance damaging interfacial adhesion, this coating process addresses the issue of metal substrate... The surface of the material is sandblasted to achieve a roughness of Sa2.5. The metal substrate surface is then wiped two to three times continuously with anhydrous ethanol (volume fraction not less than 95%) to remove residual grease. Chemically active metal hydroxyl functional sites are generated on the exposed metal surface through air oxidation. After completing the interfacial polarity preconstruction, an anti-corrosion coating is applied to the metal substrate surface. The anti-corrosion coating contains siloxane-modified graphene with surface-grafted active siloxane functional groups, a polyurethane prepolymer prepared by reacting polyether polyols with diphenylmethane diisocyanate under a catalyst (number average molecular weight of 1000 to 3000), and a boiling point of 1... High-boiling-point organic solvents with temperatures ranging from 50°C to 260°C are used for coating. After coating, the metal substrate is placed in a closed environment with a temperature of 15°C to 30°C and a relative humidity controlled within the range of 40% to 60% for 30 to 60 minutes. Within this static window at room temperature, there is no volume shrinkage or thermal convection within the fluid. The ambient moisture induces partial hydrolysis of the active siloxane functional groups, promoting heterogeneous condensation between the active siloxane functional groups and the metal hydroxyl functional sites. This constructs an in-situ covalently anchored monolayer graphene oriented template at the metal interface. Specifically, the physicochemical mechanism of this monolayer self-confined growth lies in the following: after the coating contacts the metal substrate, the underlying layer... Siloxane-modified graphene preferentially occupies limited hydroxyl sites on the metal surface through free siloxane groups. Once the first layer completes condensation bonding, the graphene layer spreads out in a large planar shape. Its hydrophobic carbon skeleton plane, lacking active reactive groups, forms a steric barrier to the upper fluid. The unreacted siloxane-modified graphene in the upper layer cannot penetrate the first carbon skeleton to contact the metal hydroxyl groups. Furthermore, it is difficult for adjacent graphene sheets to spontaneously form covalent crosslinks under the static window at room temperature. Thus, under the dual constraints of kinetics and thermodynamics, the occurrence of multilayer anchoring is blocked, ensuring that a single-layer covalent bond with uniform thickness is formed only at the metal-coating interface.

[0040] The static pre-anchoring mechanism transforms the van der Waals force-based physical adhesion interface into a rigid geometric base resisting thermal convection erosion. After confirming the anchoring of the bottom template, the metal substrate is cured by segmented heating, with the heating rate controlled at 2°C / min to 5°C / min. High-boiling-point organic solvents migrate unidirectionally from the inside of the coating to the surface, generating kinetic energy. During the curing process, the polyurethane prepolymer undergoes volume-constrained shrinkage along the direction perpendicular to the metal substrate, forming normal mechanical shear force. The aforementioned kinetic energy and normal mechanical shear force jointly drive the non-anchored graphene sheets to rotate in a direction parallel to the metal substrate, using the single-layer graphene orientation template as the alignment reference. This cross-scale energy transfer mechanism, from macroscopic volume collapse to microscopic sheet pose control, is achieved through a high-viscosity polymer melt as a stress transfer medium. During the uniaxial collapse of the coating, the incompletely cross-linked polyurethane polymer chains are compressed in the vertical direction and forced to expand and flow viscously in a two-dimensional plane parallel to the substrate, suspending within this high-viscosity fluid. Graphene sheets, with their enormous aspect ratio, are extremely sensitive to the microscopic velocity gradients of the surrounding flow field. The lateral creep of polymer chain segments generates viscous drag couples in opposite directions on the upper and lower surfaces of the graphene sheets. This micro-hydrodynamic torque overcomes the disturbances of the random Brownian motion of the nanosheets, allowing them to conform to the flow field of the surrounding polymer chain segments in a rigid planar posture. Ultimately, they are forced by the flow field to be rolled into a low-resistance energy state parallel to the substrate. The mechanical rolling effect induced by uniaxial collapse eliminates the interference of external wind speed and heat capacity differences on the filler arrangement. Through the synergistic effect of room-temperature static chemical anchoring to lock the interface base and high-temperature dynamic physical rolling to force the filler arrangement, the non-anchored graphene sheets complete a high degree of orientation rearrangement within the polyurethane matrix. The increased temperature triggers in-situ crosslinking of polyurethane chain segments, curing a dense heavy-duty anti-corrosion layer with a thickness of 100μm to 300μm on the surface of the metal substrate. The dense heavy-duty anti-corrosion layer has a labyrinth shielding structure. The formula for calculating the orientation degree of the graphene sheets within the dense heavy-duty anti-corrosion layer is as follows: ,in, ΔV represents the orientation degree of the graphene sheets, and ΔV represents the volume shrinkage of the coating during the segmented heating and curing process. Let θ be the initial volume of the coating after coating, and θ be the initial tilt angle of the non-anchored graphene sheet relative to the metal substrate surface. This formula characterizes the direct driving relationship between volume shrinkage and structural regularization. The underlying geometric derivation of this formula is based on the affine deformation theory within an incompressible fluid framework. Under the boundary condition of constant substrate contact area, the linear strain in the vertical direction of the coating is equivalent to the macroscopic volume shrinkage rate. The rigid rotation of graphene sheets under viscous damping is abstracted as the geometric projection of a spatial vector. When a micro-element with an initial tilt angle θ is compressed proportionally in the longitudinal direction along with the macro-fluid domain, the cosine function of its normal vector deflection forms a linear analytical solution with the fluid volume shrinkage rate. Based on the same data empirical logic, the various engineering experience constants extracted from this process control architecture, such as the underlying mapping relationship in the aforementioned formula and the time compensation coefficient k used to correct the substrate activation state in subsequent batch processing, are not custom values ​​lacking physical mapping. Instead, they are deterministic system constants pre-defined by collecting at least 50 sets of physical template data such as polarization resistance bias and activation time increment under the standard operating condition matrix and using the least squares method for polynomial regression fitting. Finally, a continuous and directional physical shielding barrier is established on the surface of the metal substrate, so that the low-frequency electrochemical impedance modulus of the dense heavy-duty anti-corrosion layer after immersion in a 3.5% NaCl solution for 1000 hours is greater than or equal to the value of the same. .

[0041] Example 2: This example provides a test process for verifying corrosion resistance. The test utilizes a programmable temperature and humidity alternating test chamber and an electrochemical workstation to construct a verification platform. The programmable temperature and humidity alternating test chamber has a temperature control accuracy of 0.1℃ and relative humidity fluctuations are controlled within 2%. The electrochemical workstation's AC impedance testing frequency range covers 0.01Hz to 100kHz. During the test, a continuous low-frequency vibration with a frequency of 50.0Hz and an amplitude of 0.2g is applied to the metal substrate using a mechanical exciter to introduce mechanical fatigue disturbances under real industrial conditions. A segmented temperature rise solidification process is also included. The heating rate needs to balance the contradiction between the evaporation flux of high-boiling-point organic solvents and the viscosity increase of the system caused by the thermal crosslinking of polyurethane prepolymers. When the solvent evaporation rate deviates from the viscosity growth curve of the system, too fast evaporation causes the bubbles inside the coating to be trapped, while too slow evaporation causes the filler to agglomerate again before the resin cures. According to this constraint, the heating rate is inversely proportional to the initial dynamic viscosity of the coating system and directly proportional to the boiling point of the solvent. Based on this calculation logic, for the diethylene glycol dimethyl ether solvent system with a boiling point of 205.0℃, 3.5℃ / min was calculated and determined as the constant heating rate for the experimental group.

[0042] Based on the above platform, experimental groups and multiple control groups with different process parameters were set up. The experimental group adopted a process of standing at room temperature for 45.0 min and then curing at a temperature increase of 3.5℃ / min. The first control group omits the room temperature standing step and directly heats and cures. The second control group retains the room temperature standing step but uses a heating rate of 15.0℃ / min during the curing stage. The third to sixth control groups use heating rates of 1.5℃ / min, 2.0℃ / min, 5.0℃ / min and 6.5℃ / min respectively to verify the parameter boundaries. After curing, each group was continuously immersed in a 3.5% NaCl solution for 1000.0 h. The low-frequency electrochemical impedance modulus at 0.01 Hz was extracted as a quantitative indicator of the shielding performance of the dense heavy-duty anti-corrosion layer. The final tilt angle of the non-anchored graphene sheet relative to the surface of the metal substrate was extracted by cross-sectional scanning electron microscopy to calculate the degree of orientation.

[0043] The test data reflects the nonlinear influence of process parameters on microstructure and macroscopic properties. In the experimental group, the initial volume of the coating... for And the volume shrinkage ΔV is The initial tilt angle θ is 45.0 degrees, according to the formula The degree of orientation was calculated. The value is 0.91, corresponding to a low-frequency electrochemical impedance spectroscopy modulus of 0.91. The first control group experienced template failure due to the lack of static covalent anchoring, resulting in a decrease in impedance modulus under mechanical vibration disturbance. The second control group experienced a calendering effect due to solvent boiling caused by excessively rapid heating, which disrupted the normal mechanical shear force and affected the orientation degree. The impedance dropped to 0.35 and the impedance magnitude was The third control group, using a temperature of 1.5℃ / min, experienced graphene agglomeration and sedimentation due to the slow viscosity increase, resulting in an impedance modulus of [value missing]. The impedance modulus of the fourth control group, using a temperature of 2.0℃ / min, was [value missing]. The impedance modulus of the fifth control group, using a temperature of 5.0℃ / min, was [value missing]. Using the sixth control group at 6.5℃ / min, the nonlinear vaporization expansion of the solvent was triggered, leading to local structural collapse of the coating and a decrease in the impedance modulus. The data distribution confirms that the range of 2.0℃ / min to 5.0℃ / min is the working window for resisting thermodynamic disturbances and maintaining a high degree of orientation of the filler. The above test results verify the direct effect of room temperature static chemical anchoring and high temperature dynamic physical calendering mechanism on the regularization of the internal structure of the coating. Within the limited process parameter range, the system drives the internal filler to form an orientation parallel to the metal substrate through controlled volume-limited shrinkage and unidirectional solvent migration. This structure resists interfacial delamination caused by mechanical disturbances and thermal convection, enabling the formed dense heavy-duty anti-corrosion layer to maintain a level of no less than 100°C under corrosive environments. The impedance magnitude.

[0044] Example 3: In the industrial scenario of preparing anti-corrosion coatings for heavy-duty anti-corrosion layers on metal substrates, structural differences and activity deviations in the underlying raw materials cause nanofiller agglomeration and quenching of active functional groups in the coating system, reducing the covalent anchoring bonding force at the metal interface. When preparing siloxane-modified graphene, a 2.0% (w / w) graphene oxide ethanol dispersion is placed in a reaction vessel, and aminopropyltriethoxysilane is added. The mass ratio of aminopropyltriethoxysilane to graphene oxide is set to 1:5. The temperature inside the reaction vessel is controlled at 80°C, the mechanical stirring speed is set to 500 rpm, and the reaction time is maintained for 12.0 h. The ethoxy groups of aminopropyltriethoxysilane hydrolyze and condense with the hydroxyl groups on the surface of graphene oxide to generate siloxane-modified graphene with active siloxane functional groups grafted onto its surface.

[0045] The siloxane-modified graphene was filtered and dried to obtain a solid powder. In the synthesis of polyurethane prepolymer, a polyether polyol with a number average molecular weight of 2000 and diphenylmethane diisocyanate were added to a synthesis reactor at a molar ratio of isocyanate to hydroxyl groups of 1.2:1. Dibutyltin dilaurate (0.1% by mass of the total materials) was added as a catalyst. Under nitrogen protection, the reaction temperature in the synthesis reactor was controlled at 75℃, and the reaction was carried out at a constant temperature for 3.0 h to prepare a polyurethane prepolymer with a free isocyanate mass fraction of 3.5% to 4.5%. When compounding anti-corrosion coatings, 3.0 parts by mass of the siloxane-modified graphene were added... Graphene, 67.0 parts by weight of polyurethane prepolymer, and 30.0 parts by weight of diethylene glycol dimethyl ether were fed into a high-speed disperser. The high-speed disperser was set to 2000 rpm at 25°C and continuously dispersed for 45.0 min. This compounding step maintained the spatial dispersion of active siloxane functional groups and the polymerization activity of polyurethane segments in the system. The resulting anti-corrosion coating was applied to the surface of a metal substrate. The dispersed active siloxane functional groups participated in the metal interface polycondensation, and the in-situ crosslinking of polyurethane and the orientation arrangement of graphene sheets were completed during gradient heating, resulting in a dense and heavy-duty anti-corrosion layer.

[0046] Example 4: In the heavy-duty anti-corrosion coating industrial scenario of metal component production change deployment, the difference in substrate heat capacity and the fluctuation of ambient temperature and humidity cause the interfacial polycondensation reaction process under preset fixed parameters to deviate. In order to determine the process parameters suitable for the current batch of metal components, a reference sample of the same specifications as the metal component to be coated is selected. The anti-corrosion coating is applied to the surface of the reference sample and placed in the actual workshop environment for static treatment. During this process, an infrared spectrometer is turned on to collect the attenuation signal of the absorption peak of the interfacial active siloxane functional group. When the difference in transmittance of the absorption peak in adjacent measurement cycles is less than the preset steady-state threshold, the duration from coating to that moment is recorded. Based on this, the duration is added to a 5-minute time margin to determine the standard static treatment time of this batch of metal components. The above measurement steps establish the time boundary of the heterogeneous polycondensation reaction of the active siloxane functional group by quantitatively monitoring the infrared signal.

[0047] After determining the standard settling time, the actual temperature rise slope is collected using a thermocouple on the bottom surface of a reference sample. Simultaneously, a laser displacement sensor monitors the volume shrinkage ΔV of the anti-corrosion coating. The controller obtains the deviation data between the actual temperature rise slope and the reference temperature rise slope, and adjusts the output power of the heating unit in reverse based on the deviation data. When the laser displacement sensor determines that the volume shrinkage rate of the anti-corrosion coating and the solvent evaporation rate form a monotonically positive correlation, the controller locks the current power output curve and sets it as the heating control parameter for batch coating. This adjustment step compensates for the solvent evaporation lag caused by the difference in heat capacity of different metal substrates. After the above pre-parameter calibration, The dense, heavy-duty anti-corrosion layer, after coating and curing, exhibits a continuous, parallel, oriented arrangement of graphene. In the aforementioned closed-loop control architecture, the system uses a micro-range, high-precision weighing module integrated at the bottom of the reference sample test bench to collect the total mass of the system, including the substrate and the uncured coating, in real time at a microsecond-level sampling frequency. The processing logic inside the controller differentiates the mass difference between adjacent sampling cycles with respect to time. After deducting the extremely small amount of polyurethane crosslinking byproduct mass at the algorithm level, the real-time evaporation rate of the high-boiling-point organic solvent is directly obtained through physical calculation. This hardware measurement link provides reliable data support for the dynamic and collaborative optimization of heating power without extrapolation.

[0048] Example 5: In the industrial scenario of heavy-duty anti-corrosion coating of heterogeneous metal components in multiple batches, the physical fluctuations in the initial oxide layer thickness and surface free energy of the metal substrate cause a shift in the density of hydroxyl functional sites generated by alkaline solution of fixed mass concentration, resulting in local dispersion of the covalent anchoring strength of surface siloxanes. The system establishes an offline calibration and online compensation relationship in the pre-coating stage of batch coating, selects metal substrate samples with different initial oxidation states, and uses a portable contact angle meter to obtain the initial water contact angle of each sample. The samples are immersed in alkaline solutions with different mass concentration gradients, and the polarization resistance data during the immersion process is extracted. When the measured value of polarization resistance in three consecutive sampling cycles is less than the set benchmark value, it indicates that the surface oxide scale has been removed and the hydroxylation reaction is saturated. The mass concentration of alkaline solution and the immersion time at the corresponding time are recorded. A 3D mapping data table is constructed based on the initial water contact angle of the sample, the determined mass concentration of alkaline solution, and the immersion time.

[0049] During the production line deployment phase, visual sensors acquire the initial water contact angle of the metal components to be processed. The controller queries the 3D mapping data table to retrieve the corresponding basic immersion time and target mass concentration. If the mass concentration of the bath solution decreases, causing the polarization resistance monitored in real time to deviate from the set reference value, the controller will adjust the settings according to the formula. Determine the compensation soaking time, among which, To compensate for the soaking time, The base soaking time is output as a 3D mapping data table. For real-time monitoring of polarization resistance, To set a baseline value, k is the time compensation coefficient. The system extends the residence time of the metal component in the bath according to the determined compensation immersion time, compensates for the physical fluctuations in activation quality caused by the difference in the initial state of the substrate, and outputs a metal substrate surface with uniform hydroxyl density, maintaining the constant density of covalently anchored nodes of the subsequent anti-corrosion coating on the metal substrate surface.

[0050] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit of this application and the scope of protection of this invention, and all of these forms are within the protection scope of this application.

Claims

1. A coating process for a heavy-duty anti-corrosion layer on the surface of a metal substrate, characterized in that, Includes the following steps: Step 101: Sandblasting is performed on the surface of the metal substrate to achieve a roughness of Sa2.

5. Hydroxylation activation treatment is performed using an alkaline solution with a mass fraction of 5% to 15% or an anhydrous ethanol with a volume fraction of more than 95% to form chemically active metal hydroxyl functional sites on the surface of the metal substrate. Step 102: Coating the surface of the metal substrate with an anti-corrosion coating, the anti-corrosion coating including siloxane-modified graphene, polyurethane prepolymer and high-boiling-point organic solvent with a boiling point of 150°C to 260°C, the surface of the siloxane-modified graphene being grafted with active siloxane functional groups. Step 103: Place the coated metal substrate in an environment with a temperature of 15°C to 30°C and let it stand for 30 min to 60 min. Utilize the condensation reaction between the active siloxane functional groups and the metal hydroxyl functional sites to construct an in-situ covalently anchored monolayer graphene oriented template at the metal interface. Step 104: Segmented heating and curing of the metal substrate, controlling the heating rate to be 2℃ / min to 5℃ / min. Utilizing the kinetic energy brought by the unidirectional migration and volatilization of the high-boiling-point organic solvent from the inside of the coating to the surface, and the normal mechanical shear force formed by the volume-limited shrinkage of the polyurethane prepolymer in the direction perpendicular to the metal substrate during the curing process, the non-anchored graphene sheets are driven to rotate in the direction parallel to the metal substrate with the single-layer graphene orientation template as the alignment reference, forming a dense heavy-duty anti-corrosion layer with a labyrinth shielding structure on the surface of the metal substrate.

2. The coating process for a heavy-duty anti-corrosion layer on a metal substrate surface according to claim 1, characterized in that, Siloxane-modified graphene is prepared by condensation reaction of graphene oxide with a siloxane coupling agent selected from triethoxysilane, trimethoxysilane, aminopropyltriethoxysilane, or glycidyl etheroxypropyltrimethoxysilane; the mass fraction of siloxane-modified graphene in the anticorrosive coating is 1.5% to 5.5%; the mass fraction of high-boiling-point organic solvent in the anticorrosive coating is 20% to 35%, and the high-boiling-point organic solvent is selected from ethylene glycol monobutyl ether, diethylene glycol dimethyl ether, cyclohexanone, or thallium; the polyurethane prepolymer is prepared by reacting polyether polyol with a number average molecular weight of 1000 to 3000 with diphenylmethane diisocyanate under the action of a catalyst.

3. The coating process for a heavy-duty anti-corrosion layer on a metal substrate surface according to claim 1, characterized in that, Step 101 further includes the following steps: Step 1011, using compressed air to drive abrasives to impact the surface of the metal substrate to remove oxide scale, so that the surface of the metal substrate reveals its metallic color; Step 1012, using anhydrous ethanol to continuously wipe the surface of the metal substrate 2 to 3 times to remove microscopic residual grease and generate metal hydroxyl functional sites on the exposed metal surface through air oxidation.

4. The coating process for a heavy-duty anti-corrosion layer on a metal substrate surface according to claim 1, characterized in that, The grafting rate of active siloxane functional groups grafted onto the surface of siloxane-modified graphene ranged from 10% to 22%. The grafting rate was determined by thermogravimetric analysis under a nitrogen atmosphere, measuring the mass loss of siloxane-modified graphene when heated from 150°C to 800°C.

5. The coating process for a heavy-duty anti-corrosion layer on a metal substrate surface according to claim 1, characterized in that, Step 103 is carried out in a closed environment with the relative humidity controlled within the range of 40% to 60%. The moisture in the environment is used to initiate partial hydrolysis of the active siloxane functional groups to promote heterogeneous polycondensation with the metal hydroxyl functional sites.

6. The coating process for a heavy-duty anti-corrosion layer on a metal substrate surface according to claim 1, characterized in that, Step 104, the segmented temperature rise curing, includes the following steps: Step 1041, the initial temperature rise stage, the temperature is raised from room temperature to 80℃ to 100℃ and held for 20min to 40min, so that the high-boiling-point organic solvent evaporates at a uniform rate; Step 1042, the high-temperature curing stage, the temperature is raised to 150℃ to 180℃ and held for 60min to 120min, so that the polyurethane prepolymer forms a three-dimensional cross-linked network.

7. The coating process for a heavy-duty anti-corrosion layer on a metal substrate surface according to claim 1, characterized in that, The preparation process of the anti-corrosion coating includes the following steps: dispersing siloxane-modified graphene in a high-boiling-point organic solvent and subjecting it to ultrasonic treatment, controlling the ultrasonic frequency to 20kHz to 40kHz, adding polyurethane prepolymer and subjecting it to shear dispersion at a speed of 1000rpm to 2500rpm for 30min.

8. The coating process for a heavy-duty anti-corrosion layer on a metal substrate surface according to claim 1, characterized in that, In step 104, the normal mechanical shear force generated by the volume-constrained shrinkage is stronger than the surface tension scouring force generated by the thermal volatilization of the high-boiling-point organic solvent, so as to maintain the covalent bonding state between the monolayer graphene oriented template and the surface of the metal substrate.

9. The coating process for a heavy-duty anti-corrosion layer on a metal substrate surface according to claim 1, characterized in that, The final thickness of the dense, heavy-duty anti-corrosion layer is 100 μm to 300 μm. The low-frequency electrochemical impedance spectroscopy modulus of the dense, heavy-duty anti-corrosion layer in a 3.5% (w / w) NaCl solution is not lower than [value missing] after immersion for 1000 h. .

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