Environmentally friendly method for removing a platinum layer from an aeronautical blade

Abstract

The application provides an environment-friendly platinum plating removal method for an aero blade, relates to the field of aero blade plating removal treatment technology, and comprises the following steps: cleaning and drying the surface of the aero blade with a platinum plating layer; dissolving an acid solution, an oxidizing agent, a complexing agent and a pH regulator in deionized water, and adjusting the pH value to a weak acid state to prepare a plating removal solution; immersing the pretreated blade in the plating removal solution, and performing plating removal under the conditions of stirring and heating; and taking out the blade after plating removal, and performing cleaning and drying. The method can completely remove the platinum plating layer on the surface of the aero blade, completely avoid the substrate corrosion and toxic gas emission caused by the traditional strong acid method, and realize the high-efficiency, environment-friendly and non-destructive plating removal effect.

Description

Technical Field

[0001] This invention relates to the field of plating removal technology for aircraft blades, and specifically to an environmentally friendly method for removing platinum plating from aircraft blades. Background Technology

[0002] During the repair or remanufacturing of aircraft blades, it is often necessary to completely remove the damaged platinum plating on the surface in order to re-plat them. Currently, the industry commonly uses strong acid solutions, such as aqua regia or high-concentration nitric acid and hydrochloric acid, as the plating stripping solution. Although this method has a certain plating stripping efficiency, it essentially relies on the severe chemical dissolution effect of strong acids on the platinum layer and the substrate.

[0003] However, the existing technology has the following drawbacks: First, strong acid will cause severe corrosion to the blade substrate (usually nickel-based high-temperature alloy), which will easily lead to blade dimensional deviations, increased surface roughness and damage to mechanical properties, seriously affecting its service safety and lifespan; Second, a large amount of toxic and harmful gases such as nitrogen oxides and chlorine will be generated during the process, and the waste liquid contains high concentrations of heavy metal ions and residual acid, which poses a high risk of environmental pollution and is expensive to treat.

[0004] Therefore, there is an urgent need to develop a platinum removal method that can efficiently remove the platinum layer while ensuring the integrity of the substrate and being environmentally friendly. Summary of the Invention

[0005] To address the problems in related technologies, this invention provides an environmentally friendly method for removing platinum coatings from aircraft blades.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: An environmentally friendly method for removing platinum coatings from aircraft blades includes the following steps: Step S1: Clean and dry the surface of the aircraft blade with platinum coating; Step S2: Dissolve the acid solution, oxidant, complexing agent and pH adjuster in deionized water and adjust the pH value to a weakly acidic state to prepare the stripping solution; Step S3: Immerse the pretreated blades in the stripping solution and strip the plating under stirring and heating conditions; Step S4: Remove the deplated blades, clean and dry them.

[0007] Optionally, step S1 specifically includes: Step S1-1: Clean the leaves with anhydrous ethanol using ultrasonic cleaning for 5-10 minutes; Step S1-2: After cleaning, dry at 70-100℃ for 15-30 minutes; Steps S1-3: After drying, weigh the blade and calculate the initial thickness of the platinum coating.

[0008] Optionally, in the components of the stripping solution, the acid solution is selected from at least one of hydrofluoric acid, hydrochloric acid, and sulfuric acid; the oxidant is selected from at least one of hydrogen peroxide, ammonium persulfate, sodium persulfate, and sodium hypochlorite; the complexing agent is selected from at least one of citric acid, ammonium citrate, and aminotrimethylenephosphonic acid; and the pH adjuster is ammonia.

[0009] Optionally, the pH value of the stripping solution is 2.0 to 3.0.

[0010] Optionally, the volume ratio of the oxidant to the acid solution is 1:1 to 3:1.

[0011] Optionally, the concentration of the complexing agent in the stripping solution is 20–50 g / L.

[0012] Optionally, in step S3, the temperature corresponding to the heating conditions is 50℃~80℃.

[0013] Optionally, the processing time for step S3 is 10 to 60 minutes.

[0014] Optionally, step S4 specifically includes: Step S4-1: After removing the leaf, rinse it with deionized water; Step S4-2: Place in deionized water and ultrasonically clean for 10 to 20 minutes; Step S4-3: Rinse 2 to 4 times with room temperature pure water.

[0015] Optionally, the environmentally friendly method for removing platinum coating from aircraft blades further includes step S5 after step S4. Step S5 specifically includes: drying at 70℃ to 100℃ for 15 to 30 minutes, weighing the final mass of the blade, and calculating the amount of platinum coating removed.

[0016] Beneficial effects: 1. Through the above technical solution, firstly, the method of the present invention can establish a complete process flow consisting of "pretreatment—preparation of a stripping solution with specific components and pH range—reaction under heating and stirring—post-treatment." The method of the present invention is fundamentally different from traditional aqua regia or concentrated acid stripping methods. Specifically, the method of the present invention limits the use of a combination of "acid solution, oxidant, complexing agent, and pH adjuster," and explicitly adjusts the pH value to a weakly acidic range. In this way, the chemical mechanism of stripping can be transformed from the traditional "direct dissolution by strong acid" to "removal of platinum through the synergistic effect of oxidation and complexation in a controlled weakly acidic environment." This fundamental path transformation is the basis for all subsequent environmentally friendly (due to avoiding the use of nitric acid, aqua regia, etc.) and substrate protection effects.

[0017] Secondly, since the method of the present invention limits the pH value of the stripping solution to a weakly acidic range, compared with the strong acid or even aqua regia environment (pH<0) commonly used in the prior art, the hydrogen ion concentration in the system is significantly reduced during the stripping process using the method of the present invention. This significantly inhibits the chemical corrosion tendency of hydrogen ions on the high-temperature alloy substrate of aerospace blades from a thermodynamic and kinetic perspective, providing a fundamental guarantee for protecting the dimensional accuracy and mechanical properties of the blade substrate and solving the most fatal problem of "substrate over-corrosion" in traditional methods.

[0018] Third, the method of the present invention involves removing the plating under stirring and heating conditions. Stirring ensures sufficient and uniform contact between the plating solution and the platinum layer on the blade surface, avoiding uneven or residual plating in certain areas due to concentration polarization. Heating provides the necessary activation energy to accelerate the chemical reaction between the oxidant and platinum. This combination of conditions enables the method of the present invention to possess the basic process control elements for achieving uniform and efficient plating removal, helping to overcome the problem of incomplete plating removal that may occur in existing technologies.

[0019] 2. Other beneficial effects or advantages of the present invention will be described in detail in the specific embodiments. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] in: Figure 1 This is a flowchart illustrating the steps of an environmentally friendly method for removing platinum plating from aircraft blades, provided by an exemplary embodiment of the present invention. Figure 2 This is a surface morphology diagram of the corresponding aircraft blade in Example 1; Figure 3 This is a surface morphology diagram of the aircraft blade corresponding to Example 2; Figure 4 This is a surface morphology diagram of the aircraft blade corresponding to Example 3; Figure 5 These are images of the substrate morphology after aqua regia is used to etch the blade substrate in existing related technologies. Figure 6 These are morphological images of the blade substrate after etching using the method of the present invention; wherein, Figure 5 and Figure 6 The corresponding blade substrates are of the same material, weight, and shape, and both have the same corrosion time. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0023] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0024] To facilitate a clearer and more accurate understanding of the technical solutions of this invention by those skilled in the art, the existing related technologies and their technical problems will be described in more detail below.

[0025] After long-term operation in high-temperature and high-pressure environments, the platinum coating applied to the surface of aero-engine turbine blades to improve oxidation resistance may degrade, be damaged, or become uneven in thickness. During blade overhauls or refurbishments, the old platinum layer must be completely and uniformly removed before reliable replating can be performed. Currently, the industry standard stripping process generally uses strong inorganic acid systems, such as aqua regia or concentrated nitric acid-hydrochloric acid mixtures.

[0026] Specifically, the operational examples commonly used in existing technologies are as follows: Maintenance personnel immerse the turbine blades to be treated in a solution of concentrated nitric acid and concentrated hydrochloric acid (i.e., aqua regia) prepared at a volume ratio of approximately 1:3, and chemically dissolve them at room temperature or under slight heating (e.g., 40-60°C). This solution, relying on the high concentration of hydrogen ions and the strong oxidizing properties of nitrate ions, indiscriminately and violently corrodes the platinum layer and the exposed blade substrate until the platinum layer is visually removed.

[0027] The existing technical solution has the following clear and serious technical problems: First, it causes irreversible chemical corrosion damage to the blade substrate. Specifically, components such as nickel and chromium in high-temperature alloys (like the common IN718 alloy) dissolve rapidly in aqua regia, leading to excessive etching of the substrate. For example, in actual rework cases, after using aqua regia to remove plating, the dimensions of critical parts of the blade (such as the blade tip or the edge of the cooling hole) may be reduced by several to tens of micrometers, directly exceeding the tolerance range allowed by the aviation maintenance manual. Such dimensional deviations and surface roughening significantly reduce the fatigue life of the blade, and in severe cases, may even lead to the scrapping of the entire expensive blade.

[0028] Secondly, it poses serious environmental pollution and occupational health hazards. Specifically, the aqua regia stripping process continuously releases large amounts of toxic, brownish-red nitrogen dioxide (NO2) and chlorine (Cl2). For example, even with standard protective masks, operations in poorly ventilated workshops can still damage the respiratory tract of workers due to these irritating gases, posing a risk of acute poisoning. Simultaneously, the generated waste liquid contains high concentrations of platinum, nickel, and chromium ions, as well as unreacted strong acids, classifying it as a highly hazardous chemical. Its subsequent neutralization and heavy metal recovery processes are complex and extremely costly (potentially costing tens of thousands of yuan per ton), placing a heavy environmental compliance burden on enterprises.

[0029] Third, there is a problem of poor process controllability, which can easily lead to uneven plating removal. Specifically, the strong acid reaction is violent and difficult to control precisely. For example, when removing plating from blades with complex shapes or uneven platinum layer thickness, the solution is prone to stagnation in grooves and gaps, causing "over-corrosion," while in protruding areas, hydrogen bubbles may be generated due to excessively rapid reactions, blocking solution contact and ultimately leading to platinum layer residue. These residual platinum layer fragments will seriously affect the adhesion of subsequent new plating layers, becoming a hidden danger of early peeling off of the blade during service.

[0030] Therefore, developing a platinum removal method that can selectively remove platinum layers, maximize the protection of precision high-temperature alloy substrates, and is environmentally friendly has become an urgent and economically valuable technical issue in the field of aviation maintenance.

[0031] In view of this, the present invention provides a novel solution: an environmentally friendly method for stripping platinum coatings from aircraft blades. The technical concept of this invention lies in abandoning the traditional stripping path that relies on indiscriminate chemical corrosion using high-concentration strong acids, and instead constructing a precise stripping system based on the synergistic effect of weak acid oxidation and complexation. Specifically, this invention strictly controls the pH value of the stripping solution within a weak acid range and selects persulfate, hydrogen peroxide, etc., as oxidants. While gently activating the platinum layer, it preferentially oxidizes elemental platinum into an ionic state; then, it uses complexing agents such as citric acid and aminotrimethylenephosphonic acid to perform immediate complexation, forming a stable, soluble complex for removal. This synergistic mechanism of "oxidation-driven + complexation-stabilized" achieves efficient dissolution of the platinum layer while effectively inhibiting the erosion of the high-temperature alloy substrate by hydrogen ions, thus simultaneously solving the two major technical problems inherent in strong acid systems: substrate damage and environmental pollution.

[0032] It is important to note that, in existing technologies, due to platinum's extremely high chemical stability, it is generally believed that only highly corrosive, high-concentration acids such as aqua regia can effectively destroy the robust platinum plating. Weak acid systems are considered insufficient to provide enough driving force to dissolve platinum or have extremely low efficiency, failing to meet industrial maintenance needs. The method of this invention addresses this technological bias, successfully achieving efficient plating removal with a gentle system, thus overcoming this prejudice.

[0033] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0034] In one exemplary embodiment of the present invention, such as Figure 1 As shown, an environmentally friendly method for removing platinum plating from aircraft blades according to the present invention may include the following steps: Step S1: Clean and dry the surface of the aircraft blade with platinum coating; Step S2: Dissolve the acid solution, oxidant, complexing agent and pH adjuster in deionized water and adjust the pH value to a weakly acidic state to prepare the stripping solution; Step S3: Immerse the pretreated blades in the stripping solution and strip the plating under stirring and heating conditions; Step S4: Remove the deplated blades, clean and dry them.

[0035] Through the above technical solution, firstly, the method of the present invention establishes a complete process flow consisting of "pretreatment—preparation of a stripping solution with specific components and pH range—reaction under heating and stirring—post-treatment." The method of the present invention is fundamentally different from traditional aqua regia or concentrated acid stripping methods. Specifically, the method of the present invention limits the use of a combination of "acid solution, oxidant, complexing agent, and pH adjuster," and explicitly adjusts the pH value to a weakly acidic range. In this way, the chemical mechanism of stripping is transformed from the traditional "direct dissolution by strong acid" to "removal of platinum through the synergistic effect of oxidation and complexation in a controlled weakly acidic environment." This fundamental path transformation is the basis for all subsequent environmentally friendly (due to avoiding the use of nitric acid, aqua regia, etc.) and substrate protection effects.

[0036] Secondly, since the method of the present invention limits the pH value of the stripping solution to a weakly acidic range, compared with the strong acid or even aqua regia environment (pH<0) commonly used in the prior art, the hydrogen ion concentration in the system is significantly reduced during the stripping process using the method of the present invention. This significantly inhibits the chemical corrosion tendency of hydrogen ions on the high-temperature alloy substrate of aerospace blades from a thermodynamic and kinetic perspective, providing a fundamental guarantee for protecting the dimensional accuracy and mechanical properties of the blade substrate and solving the most fatal problem of "substrate over-corrosion" in traditional methods.

[0037] Third, the method of the present invention involves removing the plating under stirring and heating conditions. Stirring ensures sufficient and uniform contact between the plating solution and the platinum layer on the blade surface, avoiding uneven or residual plating in certain areas due to concentration polarization. Heating provides the necessary activation energy to accelerate the chemical reaction between the oxidant and platinum. This combination of conditions enables the method of the present invention to possess the basic process control elements for achieving uniform and efficient plating removal, helping to overcome the problem of incomplete plating removal that may occur in existing technologies.

[0038] In one embodiment of the present invention, step S1 may specifically include: Step S1-1: Clean the leaves with anhydrous ethanol using ultrasonic cleaning for 5-10 minutes; Step S1-2: After cleaning, dry at 70-100℃ for 15-30 minutes; Steps S1-3: After drying, weigh the blade and calculate the initial thickness of the platinum coating.

[0039] In this embodiment, steps S1-1 and S1-2 first standardize the pretreatment operation by specifying specific parameters (anhydrous ethanol, ultrasonic cleaning for 5-10 minutes, drying at 70-100°C for 15-30 minutes, etc.). This ensures the consistency of the surface condition (cleanliness, dryness) of each blade before entering the core stripping step. Ultrasonic cleaning effectively removes oil, dust, and loose oxide scale, preventing these contaminants from interfering with the effective contact between the stripping solution and the platinum layer or causing side reactions during the subsequent stripping process. Specific drying temperature and time ensure complete drying of the blade, preventing residual moisture from diluting the stripping solution and thus ensuring the stability of the initial concentration and reactivity of the stripping solution, making the stripping process highly repeatable. More importantly, using anhydrous ethanol for cleaning, compared to cleaning agents that may contain water or other organic solvents, effectively dissolves grease and evaporates completely, leaving no watermarks or other residues that may interfere with the subsequent weakly acidic stripping solution. Combined with a drying temperature range of 70–100°C, this drying temperature can quickly and thoroughly remove ethanol and trace amounts of moisture. At the same time, this temperature is much lower than the heat treatment or aging temperature of high-temperature alloys commonly used in aerospace blades. This can effectively avoid the potential risks of introducing thermal stress or causing adverse changes in the microstructure of the matrix due to improper pretreatment (such as excessively high temperature), thus ensuring the safety of the matrix in the pretreatment stage.

[0040] Secondly, the effects of steps S1 to S3 are not directly applied to the chemical stripping reaction itself, but rather to provide crucial quantitative inputs and a benchmark for process control throughout the entire stripping process. Specifically, by calculating the initial thickness, the approximate time or energy required for subsequent stripping steps can be more scientifically estimated, providing a comparative benchmark for determining the stripping endpoint (e.g., the final weighing described below). This transforms the stripping method from an empirical operation into a controllable process with process monitoring and quantitative assessment capabilities.

[0041] In one embodiment of the present invention, in the components of the stripping solution, the acid solution is selected from at least one of hydrofluoric acid, hydrochloric acid, and sulfuric acid; the oxidant is selected from at least one of hydrogen peroxide, ammonium persulfate, sodium persulfate, and sodium hypochlorite; the complexing agent is selected from at least one of citric acid, ammonium citrate, and aminotrimethylenephosphonic acid; and the pH adjuster is ammonia.

[0042] In this embodiment, firstly, the plating stripping solution of the present invention is a novel system that differs from traditional aqua regia (nitric acid / hydrochloric acid) at the material level. The selected acid solutions (HF, HCl, H2SO4) provide the necessary acidic environment to activate the platinum layer, while avoiding nitric acid, which is a strong oxidizing agent and easily produces toxic gases. The selected oxidants (such as H2O2, persulfate, NaClO) have the ability to oxidize platinum under weakly acidic conditions, and their reduction products are mostly water or sulfate ions, which are environmentally friendly. The selected complexing agents (such as citric acid, ATMP) have a strong complexing ability for platinum ions. Ammonia water, as a regulator, can precisely stabilize the pH value. This specific combination constitutes the chemical basis for achieving selective and environmentally friendly plating stripping.

[0043] Secondly, the plating stripping solution of this invention, through synergistic component analysis, effectively achieves selective platinum stripping and substrate protection. Specifically, the H⁺ environment provided by the acid solution, combined with a specific oxidant, preferentially oxidizes and dissolves platinum; simultaneously, the complexing agent instantly captures the generated platinum ions, forming a stable, soluble complex that removes them from the reaction interface. This accelerates the stripping process and effectively prevents platinum ion redeposition or catalysis of other reactions. Particularly noteworthy is the choice of hydrofluoric acid (HF) in the acid solution. HF effectively dissolves any trace oxide passivation films (such as Cr₂O₃) that may exist on the surface of the high-temperature alloy, exposing a fresh platinum layer to promote the reaction. This effect is controlled and limited within a pH range of 2.0-3.0. This combination creates conditions at the chemical reaction level for selectively attacking the platinum layer while maximizing the protection of the high-temperature alloy substrate.

[0044] Third, compared to traditional technologies that require the use of nitric acid or aqua regia, this implementation method fundamentally eliminates the source of toxic gases such as nitrogen oxides (NO2) (nitric acid). The decomposition or reduction products of the selected oxidants, such as hydrogen peroxide and persulfate, are relatively harmless. Ammonia is used to adjust the pH, making the operation gentle and controllable. Therefore, it effectively reduces the toxicity of the process and the risk of environmental pollution from the source, meeting the requirements of green manufacturing.

[0045] In one embodiment of the present invention, the pH value of the stripping solution is 2.0 to 3.0.

[0046] In this embodiment, firstly, compared to existing technologies where the pH value is typically less than 1 or even negative, such as aqua regia or concentrated acid systems, the pH environment defined in this embodiment reduces the concentration of free H⁺ in the solution by several orders of magnitude. This directly and inevitably leads to a significant and substantial reduction in the thermodynamic driving force and kinetic rate of H⁺-based chemical corrosion (such as hydrogen evolution corrosion), thereby fundamentally avoiding the risks of blade dimensional accuracy loss, surface roughening, and mechanical property degradation caused by strong acid corrosion.

[0047] Secondly, this pH range is not an arbitrary or broad acidic range; rather, it defines a precise interval for the stripping method of this invention, allowing the oxidation-dissolution reaction to proceed effectively while maintaining a mild and controllable reaction. If the pH value is too high (e.g., >3.0), it may lead to insufficient oxidant activity, difficulty in initiating the reaction, or platinum ion hydrolysis; if the pH value is too low (e.g., <2.0), the system will revert to a strong acid corrosion mode, drastically increasing the risk of substrate damage. Therefore, this pH range itself directly brings the dual benefits of reaction controllability and process safety, ensuring that the stripping process can proceed in a predictable and manageable manner, avoiding violent and uncontrollable outgassing or overheating.

[0048] It is important to note that, in this embodiment, the selected pH range fundamentally distinguishes the method of the present invention from all existing stripping techniques that employ strong acids (pH << 1). This difference is not merely numerical, but reflects a completely different technical concept (from corrosion to controlled oxidation) and a qualitative difference in the degree of substrate protection.

[0049] In one embodiment of the present invention, the volume ratio of oxidant to acid solution is 1:1 to 3:1.

[0050] In this embodiment, firstly, this volume ratio ensures that the molar amount of oxidant in the system is sufficient and excessive relative to the H⁺ environment provided by the acid (within the range of 1:1 to 3:1). This provides a sufficient and stable "driving force" (oxidant) for the continuous and rapid oxidation of elemental platinum to platinum ions, thereby ensuring the overall efficiency and completeness of the plating removal reaction and avoiding reaction stagnation or incomplete platinum layer removal due to insufficient oxidant.

[0051] Secondly, the ratio of oxidant to acid solution (1:1 to 3:1) is not merely a simple material ratio; it, along with the previously defined pH value (2.0 to 3.0), precisely sets the "chemical potential" for the stripping reaction. At this specific ratio, the H⁺ concentration provided by the acid solution is sufficient to maintain the system's weak acidity and activate the surface, while avoiding excessive concentrations that could cause severe corrosion to the substrate. Simultaneously, a sufficient amount of oxidant maintains high reactivity at this acidity, preferentially attacking the platinum layer and driving the oxidation-dissolution reaction along the predetermined "platinum → platinum ion" pathway. This ratio range is a key quantitative indicator for achieving an oxidation-dominated rather than acid-corrosion-dominated reaction mechanism.

[0052] Finally, setting the upper limit of the volume ratio to 3:1 ensures oxidation efficiency while avoiding excessive waste of oxidant and controlling the potential side reaction risks (such as rapid decomposition and gas production) or subsequent processing burden caused by excess oxidant. Setting the lower limit to 1:1 ensures the minimum effective supply of oxidant. Therefore, this specific ratio range (1:1 to 3:1) directly achieves an optimized balance between process efficiency, raw material costs, and operational controllability. This makes the method not only technically effective but also economically and safely applicable for industrial use.

[0053] In one embodiment of the present invention, the concentration of the complexing agent in the stripping solution is 20-50 g / L.

[0054] By limiting the concentration of the complexing agent to 20–50 g / L, the necessary and sufficient concentration basis for the real-time and sufficient complexation of platinum ions generated in the oxidation reaction can be provided. This concentration range ensures that a unit volume of stripping solution contains enough complexing agent molecules to combine with the platinum ions continuously generated during the reaction, forming stable water-soluble complexes. This facilitates the effective transfer of platinum ions from the blade reaction interface to the bulk solution, thereby effectively preventing local supersaturation of platinum ions near the surface, redeposition, or the initiation of other side reactions.

[0055] It should be noted that the lower concentration limit of 20 g / L is set to ensure that the kinetic rate of the complexation reaction is sufficient to match the rate of platinum ion formation through oxidation and dissolution. This avoids platinum ion accumulation due to excessively slow complexation, ensuring the stripping reaction proceeds continuously and smoothly in the positive direction. The upper concentration limit of 50 g / L is set to avoid unnecessary excessive addition of the complexing agent while ensuring sufficient complexation capacity. Excessively high concentrations not only waste raw materials but may also adversely affect solution properties or subsequent treatments due to intermolecular interactions or viscosity changes. Therefore, this range achieves a balance between complexation efficiency and process economy.

[0056] More importantly, within the framework of the weakly acidic oxidation-complexation method of this invention, the concentration of the complexing agent (20–50 g / L) can synergistically work with the oxidant and the acidic environment to ensure that the platinum ions "stripped" off by the oxidant can be instantly and stably "captured" and dissolved in the liquid phase, thereby "clearing" the reaction interface and allowing the oxidation reaction to continue acting on the new platinum layer. This "instantaneous formation and complexation" mechanism is the core element for achieving uniform and thorough plating removal and preventing insoluble residues or passivation layer formation, and this concentration range is a key quantitative parameter to ensure the efficient operation of this mechanism.

[0057] In one embodiment of the present invention, in step S3, the temperature corresponding to the heating conditions is 50°C to 80°C.

[0058] By limiting the operating temperature of the plating stripping process to 50–80°C, controllable thermal energy can be input into the reaction system, providing the necessary activation energy for the key oxidation and complexation chemical reactions in the method of this invention, thereby increasing the reaction rate to a level with practical technological value. Within this temperature range, molecular thermal motion intensifies, the effective collision frequency between the oxidant and the platinum layer significantly increases, and the coordination reaction kinetics between platinum ions and the complexing agent are also accelerated. This allows the entire plating stripping process to be completed within a reasonable time scale, overcoming the problems of excessively low reaction rates and excessively long stripping times at room temperature, which may render the process unsuitable for industrial application.

[0059] It should be noted that setting the lower temperature limit to 50°C ensures the reaction system possesses sufficient basic activity to drive an effective stripping process. Setting the upper temperature limit to 80°C prevents a series of adverse consequences that may arise from excessively high temperatures, such as: the violent decomposition of certain oxidants (e.g., hydrogen peroxide) leading to failure, excessively rapid reaction rates that are difficult to control and affect uniformity, excessive evaporation of the solution altering the concentration, and unnecessary thermal stress on the blade substrate or tooling. Therefore, this range directly ensures process controllability and reaction uniformity.

[0060] More importantly, at temperatures between 50 and 80°C, the viscosity of the stripping solution typically decreases moderately, increasing its fluidity. This enhances the mass transfer efficiency of the solution to some extent, allowing fresh stripping solution to be replenished to the reaction interface more effectively. Simultaneously, reaction products (such as platinum complexes) diffuse away more quickly, helping to maintain the concentration gradient at the reaction interface. This ensures the stripping reaction proceeds continuously and stably, and further promotes the synergistic effect of the oxidant, acid solution, and complexing agent within the framework of this invention, thereby improving the overall stripping efficiency and consistency.

[0061] In one embodiment of the present invention, the processing time for step S3 is 10 to 60 minutes.

[0062] Thus, the set lower limit of the processing time (10 minutes) ensures a minimum time window for initiating and completing an effective stripping process, even for thinner platinum layers or under optimal reaction conditions, avoiding incomplete reactions or platinum residue due to excessively short processing times. The set upper limit of the processing time (60 minutes) establishes a clear safety boundary for the process operation, preventing potential risks arising from unrestricted extension of processing time. Although the weakly acidic environment and specific components (as mentioned above) minimize the risk of corrosion to the substrate, excessive extension of any chemical treatment process over time can increase unnecessary mass exchange or extremely minor side reactions that are difficult to completely avoid. The 60-minute upper limit effectively prevents overtreatment due to improper time control, further consolidating the substrate protection effect of the method.

[0063] In one embodiment of the present invention, step S4 may specifically include: Step S4-1: After removing the leaf, rinse it with deionized water; Step S4-2: Place in deionized water and ultrasonically clean for 10 to 20 minutes; Step S4-3: Rinse 2 to 4 times with room temperature pure water.

[0064] This step ensures that the blade surface is chemically neutral, clean, and free of foreign contaminants after the plating is removed. This provides an ideal and consistent surface foundation for subsequent replating, non-destructive testing, or temporary storage. In particular, it avoids the residue of plating solution components (such as trace amounts of acid, oxidants, and complexing agents), which, if not removed, may interfere with the adhesion of subsequent coatings or cause localized corrosion during long-term storage.

[0065] In one embodiment of the present invention, the method of the present invention may further include step S5 after step S4, wherein step S5 may specifically include: drying at 70°C to 100°C for 15 to 30 minutes, weighing the final mass of the blade, and calculating the amount of platinum layer removed.

[0066] In this embodiment, after all processing is complete, final drying and weighing are required to calculate the amount of platinum layer removed. This establishes an objective and quantifiable evaluation endpoint and verification loop for the final effect of the platinum removal method of the present invention. By comparing the initial mass (or initial thickness) recorded in the preceding steps (e.g., steps S1-3), this step can directly and accurately calculate the mass or thickness of the removed platinum. This elevates the effect of the present invention from a qualitative description (e.g., complete removal) to a quantitative evaluation, providing indisputable data for judging whether a single process meets the standards and comparing the process effects under different batches or parameters.

[0067] It should be noted that this implementation method incorporates final drying and quality measurement as essential final steps, thus constructing a complete process data chain from initial measurement to final measurement. This is not only post-implementation verification but also a built-in process quality control mechanism. By analyzing the final removal amount data, the efficiency and uniformity of the stripping process can be confirmed, and feedback can be provided to adjust preceding process parameters (such as stripping time) when necessary.

[0068] The method of the present invention will be further described below with reference to an exemplary embodiment.

[0069] In this exemplary embodiment, the stripping solution includes an acid solution, an oxidant, and a complexing agent, with an overall pH value of 2.0 to 3.0, indicating a weak acidity. The acid solution may be one or more combinations of HF, HCl, and HSO4; the oxidant may include one or more combinations of hydrogen peroxide, ammonium persulfate, sodium persulfate, and sodium hypochlorite; the volume ratio of the oxidant to the acid solution is 1:1 to 3:1; the complexing agent may include one or more combinations of citric acid, ammonium citrate, and aminotrimethylenephosphonic acid; the remainder is a solvent (distilled water or deionized water).

[0070] Specifically, in this exemplary embodiment, the method of the present invention may include the following steps: Step 1: Ultrasonically clean the blade surface with anhydrous ethanol for 5 minutes to remove oil, dust and oxide scale.

[0071] Step 2: Place the blades in a hot air circulating drying oven and dry them at 70℃ to 100℃ for 20 minutes. Record the weight of the platinum layer using a balance and calculate the thickness of the platinum layer. The sample area is 0.2 dm2.

[0072] Step 3: Add the oxidant and acid solution to the deionized water in the specified proportion and stir until completely dissolved; slowly add the oxidant while stirring continuously to prevent violent local oxidation reactions; finally, add the complexing agent and adjust the pH value to 2.0 to 3.0 with ammonia.

[0073] Step 4: Immerse the blade in the platinum stripping solution, ensuring the platinum layer is completely submerged; keep stirring and perform the stripping process at a temperature of 50~80℃, adjusting the time according to the platinum layer thickness.

[0074] Step 5: After the platinum layer is completely removed, quickly remove the blade, rinse it with deionized water, and then ultrasonically clean it for 15 minutes to remove any residual plating solution from the surface; then rinse it three times with room temperature pure water to ensure that there is no residual chemical etching solution.

[0075] Step Six: Place the blades in a hot air circulating drying oven and dry at 70℃ to 100℃ for 20 minutes. Weigh the blades and calculate the platinum layer thickness. The sample area is 0.2 dm². 2 .

[0076] The method of the present invention will be further explained below with reference to three examples.

[0077] Example 1: The components of the plating stripping solution in Example 1 can be found in Table 1 below: Table 1. Components of Example 1 Stripping Solution Example 1 includes the following steps: Step 1: Use anhydrous ethanol to ultrasonically clean the blade surface for 5 minutes; Step 2: Place the blades in a hot air circulating drying oven and dry them at 70℃ to 100℃ for 20 minutes. Record the weight of the platinum layer (0.3689g) using a balance and calculate the platinum layer thickness as 8.60μm. Step 3: Add hydrofluoric acid and sulfuric acid to deionized water in proportion, stir until completely dissolved, slowly add the prepared mixed solution of hydrogen peroxide and ammonium persulfate, and continue stirring to prevent violent local oxidation reaction; finally, add citric acid and adjust the pH value to 2.0 with ammonia water.

[0078] Step 4: Immerse the blade in the plating stripping solution, ensuring the platinum-covered area is completely submerged; keep stirring and perform the stripping process at 80°C for 50 minutes.

[0079] Step 5: Quickly remove the blade, rinse it with deionized water, and then ultrasonically clean it for 15 minutes to remove any residual stripping solution from the surface; then rinse it three times with room temperature pure water to ensure that there is no residual chemical etching solution.

[0080] Step 6: Place the blades in a hot air circulating drying oven and dry at 70℃ to 100℃ for 20 minutes. Record the weight of the platinum layer (0.2261g) using a balance and calculate the platinum layer thickness as 6.20μm.

[0081] The surface morphology diagram of the blade processed by the above steps can be found in [reference]. Figure 2 .

[0082] Example 2: The components of the plating stripping solution in Example 2 can be found in Table 2 below: Table 2. Components of Example 2 Plating Stripping Solution Example 2 includes the following steps: Step 1: Use anhydrous ethanol to ultrasonically clean the blade surface for 5 minutes; Step 2: Place the blades in a hot air circulating drying oven and dry at 70℃ to 100℃ for 20 minutes. Record the weight of the platinum layer (0.4261g) using a balance and calculate the platinum layer thickness as 9.93μm. Step 3: Add HF and HCl to the deionized water in proportion and stir until completely dissolved. Slowly add the prepared sodium hypochlorite and sodium persulfate mixed solution and continue stirring to prevent vigorous local oxidation reaction. Finally, add aminotrimethylenephosphonic acid and adjust the pH value to 3.0 with ammonia water.

[0083] Step 4: Immerse the blade in the plating stripping solution, ensuring the platinum-covered area is completely submerged; keep stirring and perform the stripping process at 60°C for 50 minutes.

[0084] Step 5: Quickly remove the blade, rinse it with deionized water, and then ultrasonically clean it for 15 minutes to remove any residual stripping solution from the surface; then rinse it three times with room temperature pure water to ensure that there is no residual chemical etching solution.

[0085] Step 6: Place the blades in a hot air circulating drying oven and dry at 70℃ to 100℃ for 20 minutes. Record the weight of the platinum layer (0.3542g) using a balance and calculate the platinum layer thickness as 8.26μm.

[0086] The surface morphology diagram of the blade processed by the above steps can be found in [reference]. Figure 3 .

[0087] Example 3: The components of the plating stripping solution in Example 3 can be found in Table 3 below: Table 3. Components of Example 3 Plating Stripping Solution Example 3 includes the following steps: Step 1: Use anhydrous ethanol to ultrasonically clean the blade surface for 5 minutes; Step 2: Place the blades in a hot air circulating drying oven and dry at 70℃ to 100℃ for 20 minutes. Record the weight of the platinum layer (0.3931g) using a balance and calculate the platinum layer thickness as 9.16μm. Step 3: Add HCl to deionized water according to the ratio and stir until completely dissolved. Slowly add the prepared mixed solution of hydrogen peroxide and sodium hypochlorite while stirring continuously to prevent vigorous local oxidation reaction. Finally, add ammonium citrate and adjust the pH value to 2.5 with ammonia water.

[0088] Step 4: Immerse the blade in the plating stripping solution, ensuring the platinum-covered area is completely submerged; keep stirring and perform the stripping process at 70°C for 50 minutes.

[0089] Step 5: Quickly remove the blade, rinse it with deionized water, and then ultrasonically clean it for 15 minutes to remove any residual stripping solution from the surface; then rinse it three times with room temperature pure water to ensure that there is no residual chemical etching solution.

[0090] Step 6: Place the blades in a hot air circulating drying oven and dry at 70℃ to 100℃ for 20 minutes. Record the weight of the platinum layer (0.2892g) using a balance and calculate the platinum layer thickness as 6.74μm.

[0091] The surface morphology diagram of the blade processed by the above steps can be found in [reference]. Figure 4 .

[0092] Through examples one to three above, and Figures 2 to 4 It can be seen that: Using this invention, the rate of the mild chemical reaction system can be easily controlled by temperature, concentration and time to precisely control the platinum layer stripping process, resulting in a smoother surface with higher flatness. It can basically achieve selective stripping of the platinum layer and obtain a uniform and highly reproducible stripping effect.

[0093] The advantages of the method of the present invention compared to existing related technologies will be further explained below with reference to comparative examples (it should be noted that these comparative examples are embodiments in which the method of the present invention and aqua regia were used to corrode blade substrates of the same material, weight, and shape for the same period of time, and the original states of the two blade substrates are similar). Please refer to [link to relevant documentation]. Figure 5 , Figure 5 These are images of the substrate morphology after aqua regia is used to etch the blade substrate in existing related technologies. Figure 6 This is a morphology diagram of the blade substrate after etching using the method of the present invention.

[0094] First, regarding the corrosion rate of the blade substrate, the method of this invention achieves a corrosion rate far lower than that of aqua regia; simultaneously, from... Figure 5It can be seen that the surface morphology of the substrate after etching with aqua regia is not only rough, but also contains large particles. This is a result of the strong corrosiveness of aqua regia (that is, when using aqua regia to strip plating from blades, platinum layer residue and pitting may coexist). Figure 6 As can be seen, by applying the method of the present invention, the surface of the etched substrate is relatively smooth and flat, and the particles are small (that is to say, the method of the present invention can have less impact on the blade substrate and make the surface morphology of the blade after the plating is removed smoother overall).

[0095] In summary, the effects that the method of the present invention can achieve include: First, it enables selective etching of platinum coatings. Specifically, the method of this invention abandons the traditional approach of relying on high-concentration strong acids (such as aqua regia) for indiscriminate etching, and creatively uses oxidants such as hydrogen peroxide, persulfate, and sodium hypochlorite as etching driving forces. It can efficiently and stably oxidize elemental platinum into platinum ions, while simultaneously using complexing agents such as citric acid and aminotrimethylenephosphonic acid (ATMP) for immediate complexation to form stable soluble substances, thereby achieving efficient and selective dissolution of platinum.

[0096] Secondly, it can greatly reduce damage to the substrate. Specifically, the method of this invention uses a unique etching solution system of "weakly acidic control (pH 2.0 to 3.0) + complexing agent synergy" to effectively inhibit the chemical corrosion of the substrate by hydrogen ions. This solves the pain points of traditional strong acid etching, which leads to decreased blade dimensional accuracy and impaired mechanical properties.

[0097] Third, it can significantly reduce the risk of environmental pollution. Specifically, traditional aqua regia or concentrated nitric acid systems continuously produce highly toxic and irritating gases such as nitrogen dioxide and chlorine during operation, which endangers the health of operators and makes waste gas treatment complex. The present invention has weaker acidity, and heavy metal ions are effectively complexed, resulting in a simpler treatment process, lower costs, and compliance with green manufacturing and increasingly stringent environmental regulations.

[0098] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An environmentally friendly method for removing platinum plating from aircraft blades, characterized in that, Includes the following steps: Step S1: Clean and dry the surface of the aircraft blade with platinum coating; Step S2: Dissolve the acid solution, oxidant, complexing agent and pH adjuster in deionized water and adjust the pH value to a weakly acidic state to prepare the stripping solution; Step S3: Immerse the pretreated blades in the stripping solution and strip the plating under stirring and heating conditions; Step S4: Remove the deplated blades, clean and dry them.

2. The environmentally friendly method for removing platinum plating from aircraft blades according to claim 1, characterized in that, Step S1 specifically includes: Step S1-1: Clean the leaves with anhydrous ethanol using ultrasonic cleaning for 5-10 minutes; Step S1-2: After cleaning, dry at 70-100℃ for 15-30 minutes; Steps S1-3: After drying, weigh the blade and calculate the initial thickness of the platinum coating.

3. The environmentally friendly method for removing platinum plating from aircraft blades according to claim 1, characterized in that, In the components of the stripping solution, the acid solution is selected from at least one of hydrofluoric acid, hydrochloric acid, and sulfuric acid; the oxidant is selected from at least one of hydrogen peroxide, ammonium persulfate, sodium persulfate, and sodium hypochlorite; the complexing agent is selected from at least one of citric acid, ammonium citrate, and aminotrimethylenephosphonic acid; and the pH adjuster is ammonia.

4. The environmentally friendly method for removing platinum plating from aircraft blades according to claim 1, characterized in that, The pH value of the stripping solution is 2.0 to 3.

0.

5. The environmentally friendly method for removing platinum plating from aircraft blades according to claim 1, characterized in that, The volume ratio of the oxidant to the acid solution is 1:1 to 3:

1.

6. The environmentally friendly method for removing platinum plating from aircraft blades according to claim 1, characterized in that, The concentration of the complexing agent in the stripping solution is 20–50 g / L.

7. The environmentally friendly method for removing platinum plating from aircraft blades according to claim 1, characterized in that, In step S3, the temperature corresponding to the heating conditions is 50℃~80℃.

8. The environmentally friendly method for removing platinum plating from aircraft blades according to claim 1, characterized in that, The processing time for step S3 is 10 to 60 minutes.

9. The environmentally friendly method for removing platinum plating from aircraft blades according to claim 1, characterized in that, Step S4 specifically includes: Step S4-1: After removing the leaf, rinse it with deionized water; Step S4-2: Place in deionized water and ultrasonically clean for 10 to 20 minutes; Step S4-3: Rinse 2 to 4 times with room temperature pure water.

10. The environmentally friendly method for removing platinum plating from aircraft blades according to claim 1, characterized in that, The environmentally friendly method for removing platinum coating from aircraft blades also includes step S5 after step S4. Step S5 specifically includes: drying at 70℃~100℃ for 15 minutes~30 minutes, weighing the final mass of the blade, and calculating the amount of platinum coating removed.

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