Stainless steel spring passivator, preparation method and formation method of stainless steel spring passive film

Abstract

The invention relates to a stainless steel spring passivator, a preparation method and a stainless steel spring passivation film forming method, the stainless steel spring passivator at least comprises the following components: 0.5-2.9 wt% of grape seed polyphenol extract, 0.1-0.8 wt% of nano cellulose crystal, 0.05-0.3 wt% of polyether modified siloxane, 0.5-2.5 wt% of molybdate, 2-5 wt% of organic carboxylate, and the balance of deionized water, the grape seed polyphenol extract is used for replacing heavy metal salt, a catechol structure in the grape seed polyphenol extract and Fe < 3 + > / Cr < 3 + > in the stainless steel spring can form a stable chelate, the antioxidant and self-repairing functions are achieved, and the defects that a traditional passivator is too large in ecological toxicity and poor in environmental protection property are overcome; nano cellulose crystals are introduced as a three-dimensional net-shaped framework, the mechanical strength of a passive film of the stainless steel spring is improved on the whole, and furthermore, polyether modified siloxane is adopted, so that the surface tension of a solution can be reduced to 1t; and full infiltration of spring gaps is achieved, and the passivation effect of the stainless steel spring is improved on the whole.

Description

Technical Field

[0001] The present application relates to the technical field of metal surface treatment, and particularly relates to a passivating agent for stainless steel springs, a preparation method thereof, and a method for forming a passivation film on a stainless steel spring. Background Art

[0002] In currently processed products based on stainless steel as the substrate, the cleanliness of most stainless steel spring surfaces is insufficient, and their surfaces contain some metal contaminants, including impurities embedded in stainless steel, such as copper, zinc, cadmium, lead, low-melting metals, and free iron, etc. The contamination of these metals easily leads to the corrosion and damage of stainless steel. To solve this problem, passivation can be adopted to eliminate the germination sources of various corrosions, and at the same time, the chromium and nickel contained on the stainless steel surface can be enriched and stabilized.

[0003] Among them, the geometric structure of the stainless steel spring is complex, and the passivating agent requires better permeability and coverage, which is poor for the commonly used acidic passivating agents. Summary of the Invention

[0004] In view of this, the present application can provide a passivating agent for stainless steel springs, a preparation method thereof, and a method for forming a passivation film on a stainless steel spring. The passivating agent for stainless steel springs can adopt bio-dolphin extracts to form a biological composite passivation system, which improves the environmental friendliness of the passivating agent as a whole. A passivating agent for stainless steel springs at least includes the following components (by weight percentage): grape seed polyphenol extract 0.5 - 2.9 wt%, nanocrystalline cellulose 0.1 - 0.8 wt%, polyether-modified silicone 0.05 - 0.3 wt%, molybdate 0.5 - 2.5 wt%, and organic carboxylate 2 - 5 wt%, and the balance is deionized water.

[0005] In one embodiment, the grape seed polyphenol extract is prepared by supercritical CO2 extraction method, the content of proanthocyanidins is ≥ 95%, and the average degree of polymerization is 3 - 5.

[0006] In one embodiment, the nanocrystalline cellulose is in a needle-like structure with a diameter of 10 - 30 nm and a length of 150 - 300 nm, and the surface of the nanocrystalline cellulose is oxidized and modified by 2,2,6,6-tetramethylpiperidine-1-oxyl radical, and the carboxyl content is ≥ 1.2 mmol / g.

[0007] In one embodiment, the polyether-modified silicone is trisiloxane ethoxylate, the molecular structural formula of the polyether-modified silicone is Si(CH3)2 - O - [Si(CH3)(C2H4O)6 - O]2 - Si(CH3)3, and at 25 °C in a 1 g / L aqueous solution, the dynamic surface tension of the polyether-modified silicone is ≤ 25 mN / m.

[0008] In addition, a preparation method of the above passivating agent is also provided, including the following steps:

[0009] Step S110: Heat deionized water to 45 - 55°C, and sequentially add organic carboxylate and molybdate, then stir until completely dissolved.

[0010] Step S120: Under the condition of ultrasonic power of 200 - 400 W, add grape seed polyphenol extract, nanocrystalline cellulose and polyether modified silicone in three intervals in sequence, and the interval time for each segment is 5 min.

[0011] Step S130: Age for 12 - 24 h under nitrogen protection to obtain a homogeneous and transparent solution.

[0012] In one embodiment, in step 120, the ultrasonic frequency is 28 - 32 kHz, and the solution temperature during the addition is controlled at 50 ± 2°C, 45 ± 2°C and 40 ± 2°C respectively in sequence.

[0013] In addition, a method for forming a passivation film on a stainless - steel spring is also provided. Using the above passivation agent, this forming method includes:

[0014] Real - time monitor the electrochemical impedance spectrum of the working electrode through a three - electrode system, and trigger the pulse oxidation process when the phase angle θ≥70°. The working electrode is the stainless - steel spring to be processed.

[0015] Apply a square - wave voltage with an amplitude of 0.5 - 1.2 V and a frequency of 5 - 20 Hz, and the pulse duty cycle of the square - wave voltage is 30 - 50%.

[0016] Dynamically adjust the pulse parameters during the passivation film growth stage to make the Cr / Fe atomic ratio of the film layer 4.8 - 5.2.

[0017] In one embodiment, the pulse oxidation process is divided into three stages:

[0018] The first stage (0 - 10 min): The frequency is 5 Hz and the voltage is 0.8 V.

[0019] The second stage (10 - 20 min): The frequency is 15 Hz and the voltage is 1.0 V.

[0020] The third stage (20 - 30 min): The frequency is 20 Hz and the voltage is 0.5 V.

[0021] In one embodiment, the method for forming a passivation film on a stainless - steel spring further includes a pretreatment process:

[0022] Immerse the stainless - steel spring in an activation solution containing 1 - 1.5 wt% citric acid and 0.3 - 0.8 wt% thiourea, and process at 40 - 50°C for 8 - 12 min.

[0023] After the above treatment is completed, ultrasonic cleaning is performed for 5 minutes at a frequency of 40 kHz, and the amplitude is controlled within 30 - 50 μm.

[0024] In addition, a gradient infiltration film-forming device is also provided, which is specifically used to implement the above-mentioned method for forming a passivation film on a stainless steel spring. The gradient infiltration film-forming device includes:

[0025] A multi-stage series ultrasonic reactor, including three-stage ultrasonic reactors connected in series in sequence: a first-stage reactor, a second-stage reactor, and a third-stage reactor. The first-stage reactor is used to complete the pretreatment, the second-stage reactor is used to promote the penetration of the passivating agent components and uniform film formation, and the third-stage reactor is used for the post-cleaning process;

[0026] A microwave-assisted curing module, connected downstream of the ultrasonic reactor. The microwave-assisted curing module is used to perform non-contact curing of the passivation film through microwave radiation, so that the passivation film forms a cross-linked network structure;

[0027] An in-situ electrochemical impedance spectroscopy monitoring system, which is used to execute steps S210 to S230.

[0028] The above-mentioned passivating agent for stainless steel springs at least includes the following components: grape seed polyphenol extract 0.5 - 2.9 wt%, nanocrystalline cellulose 0.1 - 0.8 wt%, polyether-modified siloxane 0.05 - 0.3 wt%, molybdate 0.5 - 2.5 wt%, and organic carboxylate 2 - 5 wt%. The balance is deionized water. By using grape seed polyphenol extract to replace heavy metal salts, the catechol structure in the grape seed polyphenol extract can form stable chelates with Fe 3 + / Cr 3 + in the stainless steel spring, with both antioxidant and self-repair functions, solving the disadvantages of excessive ecological toxicity and weak environmental friendliness of traditional passivating agents. In addition, introducing nanocrystalline cellulose as a three-dimensional network skeleton improves the mechanical strength of the passivation film of the stainless steel spring as a whole. Further, by using polyether-modified siloxane, the surface tension of the solution can be reduced to <25 mN / m, realizing full wetting of the spring gap and improving the passivation effect of the stainless steel spring as a whole. Further, molybdate undergoes a redox reaction with the surface of the stainless steel spring (metals such as Fe, Cr, Ni, etc.) to generate a dense molybdenum oxide (MoO3) composite film, filling the microscopic defects on the stainless steel surface and significantly enhancing the corrosion resistance. Compared with traditional chromate passivation, the molybdate passivation film is more environmentally friendly (without the toxicity of hexavalent chromium), and the salt spray resistance performance can reach the same level (for example: salt spray test ≥ 500 hours without rust). When the passivation film is locally damaged, molybdate can migrate to the damaged area and repair the film layer through a repassivation reaction (MoO4 2- →MoO3), extending the protection life. Further, organic carboxylate complexes free metal ions (Fe3+ ) It inhibits the precipitation of the passivating solution, and at the same time adjusts the pH to an appropriate range together with molybdate, optimizes the film-forming conditions, and molybdate improves the uniformity of the passivating film together with grape seed polyphenol extract. Description of the Drawings

[0029] Figure 1 It is a schematic flow chart of a preparation method of a passivating agent applied to a stainless steel spring provided in an embodiment of the present application;

[0030] Figure 2 It is a schematic flow chart of a method for forming a passivating film on a stainless steel spring provided in an embodiment of the present application;

[0031] Figure 3 It is a schematic flow chart of a method for forming a passivating film on a stainless steel spring provided in another embodiment of the present application;

[0032] Figure 4 It is a schematic block diagram of the structure of a gradient penetration film-forming device provided in an embodiment of the present application.

[0033] The realization, functional features and advantages of the purpose of the present application will be further described with reference to the embodiments and the accompanying drawings. Detailed Embodiments

[0034] The embodiments of the present application will be described in detail below. The examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present application, and should not be construed as a limitation of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0035] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present application: Therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and single values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc. and single numbers within that range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range, and will not be repeated.

[0036] This application can provide a passivating agent for stainless steel springs, which at least includes the following components (by weight percentage): grape seed polyphenol extract 0.5 - 2.9 wt%, nanocrystalline cellulose 0.1 - 0.8 wt%, polyether modified silicone 0.05 - 0.3 wt%, molybdate 0.5 - 2.5 wt%, and organic carboxylate 2 - 5 wt%, with the balance being deionized water.

[0037] In the above passivating agent for stainless steel springs, by using grape seed polyphenol extract to replace heavy metal salts, the catechol structure in the grape seed polyphenol extract can form stable chelates with Fe 3 + / Cr 3 + in the stainless steel spring, having both antioxidant and self - repair functions, solving the disadvantages of excessive ecological toxicity and weak environmental protection of traditional passivating agents. In addition, introducing nanocrystalline cellulose as a three - dimensional network skeleton can overall improve the mechanical strength of the passivation film of the stainless steel spring. Further, by using polyether modified silicone, the surface tension of the solution can be reduced to <25 mN / m, achieving full wetting of the spring gap, and overall improving the passivation effect of the stainless steel spring; further, molybdate undergoes redox reaction with the surface of the stainless steel spring (metals such as Fe, Cr, Ni, etc.) to generate a dense molybdenum oxide (MoO3) composite film, filling the microscopic defects on the stainless steel surface, significantly enhancing the corrosion resistance. Compared with traditional chromate passivation, the molybdate passivation film is more environmentally friendly (without the toxicity of hexavalent chromium), and the salt spray resistance performance can reach the same level (for example: no rust in salt spray test ≥500 hours). When the passivation film is locally damaged, molybdate can migrate to the damaged area and repair the film layer through re - passivation reaction (MoO4 2- →MoO3), extending the protection life; further, organic carboxylate inhibits the precipitation of the passivating solution by complexing free metal ions (Fe 3+ ), and at the same time jointly regulates the pH to a suitable range with molybdate, optimizing the film - forming conditions. Molybdate also improves the uniformity of the passivation film jointly with grape seed polyphenol extract.

[0038] Referring to Table 1, the following are 8 examples (Examples 1 to 8) and 4 comparative examples (Comparative Examples 1 to 4) to verify the influence of different formulations on the performance of the passivation film, and compare the experimental results (refer to Table 2), as shown in the table:

[0039]

[0040] Table 1

[0041]

[0042] Table 2

[0043] Among them, the test items and standards in Table 2 are as follows:

[0044] Passivation film thickness: measured by laser confocal microscope (unit: μm);

[0045] Salt spray test: according to ASTM B117 standard, record the time without rust (hours);

[0046] Film-substrate adhesion: tested by scratch method (unit: MPa);

[0047] Surface roughness (Ra): measured by atomic force microscope (AFM) (unit: nm);

[0048] Composition of passivation film: analyze the Cr / Fe atomic ratio by X-ray photoelectron spectroscopy (XPS)

[0049] According to the above data results, within the component ratio range of Claim 1 (grape seed polyphenol extract 0.5 - 2.9 wt%, nanocrystalline cellulose 0.1 - 0.8 wt%, polyether-modified silicone 0.05 - 0.3 wt%, molybdate 0.5 - 2.5 wt%, and organic carboxylate 2 - 5 wt%, with the balance being deionized water), the performance of the passivation film is significantly better than that of the comparative example. Salt spray test ≥ 800h, adhesion ≥ 28MPa, Cr / Fe atomic ratio ≥ 4.5. When each component takes the upper limit (grape seed polyphenol 3%, nanocrystalline cellulose 0.8%, polyether silicone 0.3%, molybdate 2.5%, organic carboxylate 5%), the salt spray life reaches 1500h, Cr / Fe = 5.2, and the performance is optimal.

[0050] Obviously, Comparative Example 1 (without grape seed polyphenol): poor antioxidant property, Cr / Fe = 3.0, salt spray life only 300h; Comparative Example 2 (without nanocrystalline cellulose): the film layer is loose (Ra = 2.0nm), adhesion drops to 18Mpa; Comparative Example 3 (without polyether-modified silicone): poor wettability of the passivation solution, uneven film thickness (deviation ±0.4μm); Comparative Example 4 (without molybdate): the passivation film has no self-healing ability, salt spray life 200h.

[0051] The above data shows that grape seed polyphenol (antioxidant) and molybdate (corrosion inhibitor) synergistically improve corrosion resistance; nanocrystalline cellulose (reinforcement) and polyether-modified silicone (wetting) jointly optimize the film layer uniformity. When the component ratio exceeds the scope of the above technical solution (such as Comparative Examples 1 to 4), the performance significantly decreases.

[0052] In one embodiment, the grape seed polyphenol extract is prepared by supercritical CO2 extraction method, the proanthocyanidin content ≥ 95%, and the average degree of polymerization is 3 - 5.

[0053] In this embodiment, anthocyanin is the core active ingredient of grape seed extract, and its antioxidant ability far exceeds that of vitamin C and vitamin E. Experiments show that the antioxidant effect of proanthocyanidins is 20 times that of vitamin C and 50 times that of vitamin E. The supercritical CO2 extraction technology can selectively extract high-purity proanthocyanidins by optimizing parameters (such as temperature 55 - 65°C, pressure 35 MPa, entrainer ethanol), while avoiding the destruction of heat-sensitive components by high temperature and ensuring their biological activity. This method has no organic solvent residue and meets the environmental protection requirements of modern natural product extraction; when the proanthocyanidin content ≥ 95%, the free radical scavenging efficiency of the extract is significantly improved. Proanthocyanidins with an average degree of polymerization of 3 - 5 belong to oligomers (OPCs), which have a small molecular weight and high water solubility. The high-purity (≥ 95%) and low-degree-of-polymerization (3 - 5) grape seed polyphenol extract prepared by the supercritical CO2 extraction method not only has strong antioxidant activity, but also realizes the efficient retention of active ingredients and the optimization of bioavailability through process innovation.

[0054] In one embodiment, the nanocrystalline cellulose is a needle-like structure with a diameter of 10 - 30 nm and a length of 150 - 300 nm, and the surface of the nanocrystalline cellulose is oxidized and modified by 2,2,6,6-tetramethylpiperidine-1-oxyl free radical, and the carboxyl group content ≥ 1.2 mmol / g.

[0055] In this embodiment, the needle-like structure (diameter 10 - 30 nm, length 150 - 300 nm) of nanocrystalline cellulose (hereinafter referred to as CNC) gives it a high aspect ratio (5 - 10). This structure can form a three-dimensional network in the composite material and enhance the mechanical properties of the matrix material through mechanical interlocking and hydrogen bonding. For example, adding such CNC to a polymer matrix can increase the elastic modulus to more than 20 GPa and the tensile strength by 50% - 200%. The crystalline region of CNC is complete (crystallinity ≥ 80%), and its tensile strength 2 (~7.7 GPa) is comparable to that of Kevlar fiber, but the density is lower (about 1.6 g / cm 3 ), making it an ideal reinforcement for lightweight and high-strength composite materials.

[0056] In this embodiment, nanocrystalline cellulose is introduced as a three-dimensional network skeleton. By further defining the structural parameters and surface chemical properties of the nanocrystalline cellulose, the mechanical properties of the material are comprehensively improved, and the mechanical strength of the passivation film of the stainless steel spring is further improved as a whole.

[0057] In one embodiment, the polyether-modified silicone is trisiloxane ethoxylate, and the molecular structural formula of the polyether-modified silicone is: Si(CH3)2-O-[Si(CH3)(C2H4O)6-O]2-Si(CH3)3. When the concentration is 1 g / L in aqueous solution and the temperature is 25°C, the dynamic surface tension of the polyether-modified silicone ≤ 25 mN / m.

[0058] In this embodiment, in the molecular structure of trisiloxane ethoxylate, the trisiloxane skeleton is a symmetric siloxane main chain (Si-O-Si), which can endow the molecule with high flexibility and thermal stability (decomposition temperature > 200 °C). The hydrophobic siloxane main chain in the molecule adsorbs on the metal surface, and the hydrophilic ethoxy chain segments extend outward to form an oriented monolayer, reducing the interfacial energy. On the one hand, it has high wettability, which can rapidly reduce the surface tension of the passivating solution and promote the penetration of the passivator into the micropores on the stainless steel surface; on the other hand, its molecules are anchored at the metal / passivating solution interface, inhibiting the defects of the passivation film and improving the interfacial stability.

[0059] In this embodiment, the (C2H4O)6 branch of ethoxy group has a moderate chain length (6 units), which not only ensures water solubility (HLB value ≈ 12) but also avoids the steric hindrance caused by too long chain segments affecting the adsorption efficiency. Its hydrophilic polyether chain segments are grafted onto the siloxane main chain through ether bonds (-O-), forming an amphiphilic structure (hydrophilic-hydrophobic balance). On the one hand, it has a balanced hydrophilicity and hydrophobicity, avoiding the stratification of the passivating solution and achieving optimized water solubility; on the other hand, it forms a hydrogen bond network with polar components such as grape seed polyphenols and molybdates, enhancing the stability of the passivating solution and achieving the effect of synergistic compatibility of the passivator.

[0060] In this embodiment, when in a 1 g / L aqueous solution at a temperature of 25 °C, the dynamic surface tension of the polyether-modified siloxane ≤ 25 mN / m. A low dynamic surface tension indicates that the molecules quickly migrate to the interface and rapidly form an adsorption layer, and can efficiently wet even on high surface energy metals or contaminated surfaces. On the one hand, it can reduce the contact angle of the passivating solution on the metal surface (such as from 70° of stainless steel to < 10°), realizing uniform film formation and achieving the technical effect of improving the uniformity of the passivation film; on the other hand, it can still rapidly spread on the greasy surface, adapting to complex working conditions.

[0061] The dynamic surface tension of traditional siloxane surfactants (such as polydimethylsiloxane) is usually > 30 mN / m, and their compatibility with polar components (such as molybdates) in the passivator is poor. In this embodiment, through precise molecular structure design (trisiloxane ethoxylate) and the limitation of dynamic surface tension parameters, the wettability, film formation uniformity and anti-pollution ability of the passivating solution are significantly improved, realizing the synergistic optimization of ultra-low dynamic tension and the stability of the passivating solution. That is to say, overall, the passivation efficiency is improved, the corrosion resistance of the passivation film layer is enhanced, and at the same time, the requirements of environmental protection processes (low VOC) are met.

[0062] In addition, as Figure 1 shown, a preparation method of the above-mentioned passivator is also provided, including the following steps:

[0063] Step S110: Heat deionized water to 45 - 55°C, and sequentially add organic carboxylate and molybdate, then stir until completely dissolved.

[0064] In this embodiment, the temperature is set to 45 - 55°C. On the one hand, it improves the dissolution efficiency, that is, the solubility of organic carboxylate (such as sodium citrate) and molybdate (such as sodium molybdate) increases significantly under the condition of temperature rise (for example: the dissolution rate of sodium molybdate at 50°C is 3 times faster than at room temperature), avoiding the influence of undissolved particles on the uniformity of the passivation solution; on the other hand, the temperature < 55°C can prevent the premature degradation of the subsequently added grape seed polyphenols (thermal decomposition temperature is about 60°C), providing protection for heat-sensitive components.

[0065] In this embodiment, molybdate (with high pH sensitivity) is preferentially dissolved, and then organic carboxylate is introduced to adjust the pH to 3.5 - 4.5, preventing the local supersaturation precipitation of molybdate under acidic conditions and avoiding the formation of precipitation.

[0066] In one embodiment, reversing the feeding order (adding carboxylate first) will cause the dissolution time of molybdate to extend by 50% (with other process conditions unchanged), and the solution turbidity increases to 20 NTU (the normal process turbidity ≤ 5 NTU).

[0067] Step S120: Under the condition of ultrasonic power of 200 - 400 W, add grape seed polyphenol extract, nanocrystalline cellulose, and polyether-modified silicone in three intervals in sequence, with an interval time of 5 min for each section.

[0068] In this embodiment, the ultrasonic power is selected as 200 - 400 W. The ultrasonic cavitation effect destroys the CNC aggregates, making them disperse in the form of single needle-like crystals (average particle size ≤ 100 nm), enhancing their mechanical strengthening effect in the passivation solution; in addition, under ultrasonic assistance, polyether-modified silicone forms nanoscale micelles (particle size 10 - 50 nm), and the dynamic surface tension is further reduced to ≤ 20 mN / m (compared with the mechanical stirring process which is 30 mN / m), enabling the emulsification of polyether-modified silicone.

[0069] Furthermore, in this embodiment, grape seed polyphenols (active ingredients), CNC (reinforcing phase), and polyether-modified silicone (wetting agent) are added step by step to ensure that each component is adsorbed on the interface of the passivation solution in sequence, reducing the intermolecular steric hindrance and avoiding competitive adsorption of components.

[0070] In one embodiment, when adding materials synchronously, the uneven dispersion of CNC and polyether-modified silicone due to competitive adsorption results in a turbidity > 15 NTU, while after segmented feeding (with other process conditions unchanged), the turbidity ≤ 5 NTU.

[0071] Step S130: Age for 12 - 24 h under nitrogen protection to obtain a homogeneous and transparent solution.

[0072] In this embodiment, nitrogen isolates oxygen. On the one hand, it prevents the oxidation and discoloration of grape seed polyphenols (containing phenolic hydroxyl groups) (for example, when not protected, the chromaticity ΔE of the solution is >5 after 24 hours, and ΔE < 1 after nitrogen protection), and can provide antioxidant protection. On the other hand, the aging time of 12 - 24 hours enables the molybdate and organic carboxylate to be fully complexed to form a stable [MoO4·organic acid] complex, enhancing the self-repair ability of the passivation film and allowing all components to be fully complexed.

[0073] In this embodiment, aging for 12 - 24 hours under nitrogen protection improves the stability of the passivation solution.

[0074] In this embodiment, CNC and polyether-modified silicone micelles are evenly distributed through Brownian motion during static settlement, avoiding stratification, achieving the effect of suppressing the sedimentation of nanoparticles, and making the colloidal system homogeneous.

[0075] In one embodiment, the stratification time of the un-aged solution is <72 hours, and there is no precipitation after aging for >6 months.

[0076] The above preparation method can be further adapted to an industrial-grade reaction kettle (such as a continuous flow ultrasonic device) under the conditions of ultrasonic power and time parameters to achieve ton-level production. The passivation agent prepared by this process has a uniform film formation (film thickness deviation ≤ ±5%), salt spray resistance ≥ 1000 hours, and storage stability ≥ 12 months.

[0077] To further clarify the technical effects of the above preparation method, experimental designs and parameter comparisons were carried out respectively. As shown in Table 3, the experimental groups are divided into three types: the preparation method of this application, the conventional stirring process, and the process without nitrogen protection.

[0078] Table

[0079]

[0080] Table 3

[0081] Among them, the turbidity comparison is as follows in Table 4:

[0082]

[0083] Table 4

[0084] Obviously, due to ultrasonic segmented feeding (destroying the aggregation of nanocellulose crystals) and stepwise dissolution (avoiding competitive adsorption) in the preparation method of this application, the initial turbidity is significantly lower than that of the conventional process (reduced by more than 90%). Nitrogen protection inhibits oxidation and precipitation, and the turbidity only increases by 60% after 24 hours. However, due to uneven dispersion by mechanical stirring in the conventional process, the turbidity increases sharply.

[0085] Among them, the stability of the passivation solution was further verified. As shown in Table 5, obviously, under nitrogen protection, the retention rate of grape seed polyphenols (antioxidant components) > 95%. In the air-exposed group, due to the oxidative degradation of phenolic hydroxyl groups, the activity loss was 15-25%. Ultrasonic dispersion enabled the polyether-modified silicone to form stable micelles (particle size 10-50 nm), inhibiting precipitation and stratification, while the conventional stirring process stratified rapidly due to uneven dispersion.

[0086]

[0087] Table 5

[0088] Among them, a further comparison of the passivation effect (salt spray test) was carried out, as shown in Table 6 below. Obviously, in the preparation method of the present application, the passivation film was uniform and dense (SEM showed a porosity < 1%), and the salt spray resistance reached 1000 h without rust, which was better than 200-300 h of the conventional process. The [MoO4·organic acid] composite passivation film formed under nitrogen protection had strong self-healing ability, and the pitting potential was increased to +0.75 V, and the anti-Cl - erosion ability was significantly improved.

[0089]

[0090] Table 6

[0091] Among them, a further comparison of the microstructure of the passivation film was carried out, as shown in Table 7 below. Obviously, the passivation film formed by the preparation method of the present application was rich in Cr (the proportion of Cr2O3 > 60%), and the surface roughness was extremely low (Ra ≤ 1 nm), inhibiting the penetration of corrosive media. Due to the uneven dispersion of components in the conventional process, the Cr content of the passivation film was low, and active regions of FeOOH were easily formed, accelerating local corrosion.

[0092]

[0093] Table 7

[0094] In summary, in terms of turbidity control (≤ 5 NTU), passivation solution stability (> 6 months without stratification), and passivation film performance (salt spray ≥ 1000 h), the above preparation method is significantly better than the conventional process. Its core advantages are as follows:

[0095] 1) Ultrasonic stepwise feeding: achieving uniform dispersion of nanocrystalline cellulose and polyether-modified silicone, reducing turbidity;

[0096] 2) Aging under nitrogen protection: inhibiting the oxidation of active components and promoting the stable formation of [molybdate-organic acid] complexes;

[0097] 3) Stepwise temperature control: optimizing the dissolution efficiency and protecting heat-sensitive components, improving the uniformity of the passivation film.

[0098] In one embodiment, the ultrasonic frequency in step 120 is 28 - 32 kHz, and the solution temperatures during addition are sequentially controlled at 50 ± 2°C, 45 ± 2°C, and 40 ± 2°C respectively.

[0099] In this embodiment, the ultrasonic frequency is set to 28 - 32 kHz. The 28 - 32 kHz ultrasonic waves generate dense micron-sized cavitation bubbles (with diameters of 10 - 50 μm) in the solution. The local high temperature (>5000 K) and high pressure (>100 MPa) generated by the rupture of these bubbles can break up the aggregates of nanocrystalline cellulose (CNC), enabling it to be uniformly distributed in the passivation solution in a monodisperse needle-like structure (aspect ratio >10). Compared with the strong impact force of low-frequency (20 kHz) (which is likely to damage the CNC structure) or the weak penetrability of high-frequency (>50 kHz) (resulting in uneven dispersion), 28 - 32 kHz, while ensuring the integrity of CNC (fracture rate <5%), enables the dispersed particle size of CNC to be ≤100 nm (measured by a laser particle size analyzer, achieving an optimized energy distribution effect and overall balance between the cavitation effect and dispersion efficiency).

[0100] Furthermore, the mechanical - thermal energy conversion efficiency of the 28 - 32 kHz ultrasound is moderate (solution temperature rise ≤5°C / min), avoiding thermal decomposition of grape seed polyphenols (thermal decomposition temperature 60°C) or polyether-modified siloxanes (thermal decomposition temperature 150°C) caused by local overheating, inhibiting the degradation of heat-sensitive components, and achieving thermal effect control.

[0101] In addition, the solution temperatures during addition are sequentially controlled at 50 ± 2°C, 45 ± 2°C, and 40 ± 2°C respectively. The gradient cooling promotes the synergistic effect of the components, and their respective technical effects are shown in Table 8 below.

[0102]

[0103] Table 8

[0104] In addition, the gradient cooling can also optimize the performance of the passivation film on the stainless steel spring. The gradient cooling arranges the passivating agent components in an orderly manner, with the porosity of the passivation film <1% (SEM analysis), no rusting in the salt spray test for ≥1000 hours, and enhanced film layer compactness; temperature control reduces thermal stress, and the bonding force between the passivation film and the stainless steel substrate ≥30 MPa (tested by the scratch method), which is 50% higher than that of the constant temperature process (20 MPa), improving the film layer bonding force.

[0105] In addition, during the high dissolution stage at 50°C, the cavitation effect of the 28 - 32 kHz ultrasonic waves accelerates the complexation reaction between molybdate and organic carboxylate, and the particle size of the complex ≤50 nm (tested by dynamic light scattering); during the low-temperature stable stage at 40°C, ultrasonic assistance inhibits the sedimentation rate of CNC (sedimentation amount <0.1% / h, compared with >1% / h without ultrasound), and the energy - temperature matching enhances the dispersion stability.

[0106] In addition, the collaborative design of staged temperature reduction and ultrasonic parameters reduces the total energy consumption by 30% (compared with the constant temperature process at 50°C), and is applicable to continuous production (for example, the batch processing time of the reaction kettle is shortened to 2 hours).

[0107] As shown in Table 9 below, the experimental verification data of gradient temperature reduction control are as follows. Obviously, the collaborative design of ultrasonic frequency (28 - 32 kHz) and staged temperature control (50°C → 45°C → 40°C) significantly improves the component dispersion, active retention rate of the passivator, and the performance of the passive film. Its technical effects are reflected in industrial production as reduced energy consumption, enhanced process stability, and extended product life.

[0108]

[0109] Table 9

[0110] In addition, as Figure 2 shown, a method for forming a passivation film on a stainless - steel spring is also provided. Using the above - mentioned passivator, the forming method includes:

[0111] Step S210, real - time monitoring of the electrochemical impedance spectrum of the working electrode through a three - electrode system, and triggering the pulse oxidation process when the phase angle θ ≥ 70°. The working electrode is the stainless - steel spring to be processed.

[0112] In this step, the phase angle θ reflects the capacitance characteristics of the passivation film. θ ≥ 70° indicates that a high - impedance insulating layer has been formed on the passivation film (the film layer is dense, and the porosity < 1%). At this time, triggering the pulse oxidation can accurately match the film layer growth stage, avoiding defects caused by premature oxidation (when θ < 70°, the film layer is loose and the Cr enrichment is insufficient) or over - late oxidation (when θ > 85°, the film layer is too thick and prone to cracking).

[0113] Step S220, applying a square - wave voltage with an amplitude of 0.5 - 1.2 V and a frequency of 5 - 20 Hz, and the pulse duty cycle of the square - wave voltage is 30 - 50%.

[0114] In this step, when it is lower than 0.5 V, the oxidation driving force is insufficient (the oxidation efficiency of Cr 3 + to Cr 6 + is low), and when it is higher than 1.2 V, an oxygen evolution side reaction occurs (the generation of O2 destroys the film layer); high frequency (20 Hz) and short pulses (duty cycle 30%) promote the selective oxidation of Cr (inhibiting Fe dissolution).

[0115] In one embodiment, when the voltage is 1.0 V, the oxidation current efficiency of Cr reaches 85%, and the Fe dissolution rate < 5%.

[0116] Step S230, dynamically adjusting the pulse parameters during the growth stage of the passivation film to make the Cr / Fe atomic ratio of the film layer 4.8 - 5.2.

[0117] In this step, during the pulsed oxidation stage, the periodic start and stop of the square-wave voltage causes Cr 3 + to be preferentially oxidized to Cr2O3 (instead of Fe2O3), and the oxidation competition kinetics of Cr / Fe is controlled by adjusting the duty cycle; when the monitored Cr / Fe atomic ratio < 4.8, the pulse frequency is increased (to 20 Hz) to enhance Cr oxidation; when Cr / Fe > 5.2, the frequency is decreased (to 5 Hz) to inhibit over-oxidation; the passivation film with a Cr2O3 content ≥ 60% has self-healing ability (Cr 3 + migrates to fill the defects), and the Cl - - corrosion resistance is increased by 3 times; XPS analysis shows that when Cr / Fe = 5.0, the ratio of Cr2O3 / Cr(OH)3 in the passivation film reaches 3:1 (the optimal corrosion-resistant structure).

[0118] In one embodiment, when Cr / Fe = 5.0, the Cr2O3 content in the passivation film ≥ 60%, forming a continuous Cr-rich layer (XPS depth analysis), the Fe2O3 content ≤ 10%, inhibiting the active dissolution area (the potentiodynamic polarization curve shows that the passive current density ≤ 1×10 -6 A / cm 2 ), and Cr 3 + migrates to the film layer defects during the pulse interval, and the repair efficiency > 90% (the SEM observation shows that the micropore closing time < 10 s).

[0119] In this embodiment, real-time EIS monitoring and dynamic adjustment of pulse parameters form a closed loop, realizing precise control of the composition, structure and performance of the passivation film, filling the gap of traditional processes relying on empirical parameters; pulsed oxidation (duty cycle 30 - 50%) saves 40% energy compared with the potentiostatic process, reduces the passivation solution consumption by 20%, and the real-time feedback system reduces the unqualified rate of the film layer from 15% to < 2%, which can dynamically adjust and reduce energy consumption and scrap rate as a whole.

[0120] In this embodiment, the passivation film is analyzed by XPS and shows that the Cr / Fe ratio reaches 4.8 - 5.2, and the outer layer is enriched with polyphenol-Cr complex (binding energy 577.3 eV), and the inner layer is dense Cr2O3 (binding energy 576.8 eV). The passivation process parameters are adjusted by in-situ monitoring of electrochemical impedance spectroscopy (EIS): when the phase angle > 70°, pulsed oxidation is started (voltage 0.5 - 1.2 V, frequency 5 - 20 Hz), inducing the formation of a gradient film layer structure. The surface layer is rich in Cr (Cr / Fe = 5.2) to block the corrosion medium, and the transition layer (Cr / Fe = 4.8) improves the film-substrate adhesion, solves the brittleness problem of the high-Cr film, and at the same time reduces the Cr 6 + additive dosage by 50% (depending on in-situ generation of Cr2O3 by pulsed oxidation), reducing the wastewater treatment cost.

[0121] In this embodiment, through the intelligent process of real-time monitoring and pulse regulation, the coordinated optimization of the composition (Cr / Fe atomic ratio), structure (gradient design), and performance (corrosion resistance, adhesion) of the passivation film is achieved, and the technical effect is significantly better than that of traditional methods. The core innovation lies in: (1) Precise control: EIS threshold triggering and dynamic parameter adjustment; (2) Performance breakthrough: Salt spray life ≥ 1200h, film-substrate adhesion ≥ 35MPa; Industrial value; (3) Energy saving and consumption reduction: Suitable for the harsh scenarios of high-end stainless steel springs.

[0122] In one embodiment, the pulse oxidation process is divided into three stages:

[0123] The first stage (0 - 10 min): The frequency is 5 Hz and the voltage is 0.8 V;

[0124] The second stage (10 - 20 min): The frequency is 15 Hz and the voltage is 1.0 V;

[0125] The third stage (20 - 30 min): The frequency is 20 Hz and the voltage is 0.5 V.

[0126] In this embodiment, the first stage (0 - 10 min) is the substrate activation and passivation film nucleation stage. The frequency is 5 Hz and the voltage is 0.8 V. The low frequency promotes ion migration, and the medium voltage drives the selective oxidation of Cr to form a dense substrate. The low frequency (5 Hz) extends the single pulse action time (200 ms), promotes the migration of Cr 3 + to the interface, and forms continuous Cr2O3 crystal nuclei (particle size 10 - 20 nm). The 0.8 V voltage avoids excessive dissolution of Fe (Fe dissolution rate < 5%), and the initial Cr / Fe atomic ratio reaches 3.5 - 4.0 (XPS surface analysis). The second stage is the Cr enrichment and film layer thickening stage: The high frequency accelerates the oxidation of Cr 3 + → Cr 6 +. The high voltage enhances the oxidation driving force and increases the Cr / Fe atomic ratio, achieving the technical effect of Cr enrichment and film layer thickening. The high frequency (15 Hz) shortens the pulse interval (66 ms), accelerates the Cr oxidation kinetics, and the Cr / Fe atomic ratio increases to 4.8 - 5.0. The 1.0 V high voltage drives the generation of Cr 6 +, forming an amorphous / nanocrystalline composite structure (TEM shows that the grain size is 5 - 10 nm), and the film resistance increases to 1×10 5 Ω·cm 2 .

[0127] The third stage is the surface densification and defect repair stage: high frequency refines grains, low pressure inhibits the oxygen evolution side reaction, closes micropores, enables surface densification and defect repair, high frequency (20 Hz) induces grain boundary migration, refines surface grains to 2 - 5 nm, porosity drops to <1%, 0.5 V low pressure inhibits the oxygen evolution reaction (oxygen generation amount decreases by 80%), avoids the accumulation of internal stress in the film layer, and the bonding force is increased to ≥40 MPa.

[0128] In the above pulse oxidation process, the gradient film layer structure composed of a base layer, an intermediate layer and a surface layer is formed with advantages. Base layer (50 - 80 nm): Cr / Fe = 3.8 - 4.0, high toughness amorphous structure, buffering stress; Intermediate layer (150 - 200 nm): Cr / Fe = 5.0, high Cr2O3 content (≥60%), blocking corrosive media; Surface layer (20 - 30 nm): Cr / Fe = 5.2, ultrafine grain dense structure, resistant to Cl - penetration.

[0129] In addition, the staged parameters reduce the total energy consumption by 35% (compared with the constant voltage 1.2 V process), the passivation time is shortened to 30 min (the traditional process requires 60 min), the parameters of each stage are programmable, adaptable to different materials (such as 304, 316L stainless steel), and the fluctuation of the Cr / Fe atomic ratio is <±0.1.

[0130] To sum up, the formation method in this embodiment realizes the precise regulation of the composition, structure and performance of the passivation film through the gradient design of three-stage pulse parameters. Its technical effects are reflected as follows: stepped film formation: gradient growth of substrate activation → Cr enrichment → surface densification; excellent performance: salt spray life ≥1500 h, bonding force ≥40 MPa, far exceeding the traditional process; industrial value: energy-saving and efficient, adaptable to high-end equipment manufacturing, solving the industry pain points of high Cr film being brittle and high Fe dissolution rate.

[0131] In one embodiment, as Figure 3 shown, the formation method of the stainless steel spring passivation film further includes a pretreatment process:

[0132] Step S240, immerse the stainless steel spring in an activation solution containing 1 - 1.5 wt% citric acid and 0.3 - 0.8 wt% thiourea, and process at 40 - 50 °C for 8 - 12 min.

[0133] In this step, citric acid has a dual role: on the one hand, citric acid (pH≈2.0) dissolves the Fe / Cr oxides (such as Fe2O3, Cr2O3) on the surface of stainless steel, exposes the fresh metal substrate, improves the adhesion of the passivation film (bonding force increases by 50%), achieving the effect of removing the oxide layer on the surface; on the other hand, citric acid forms a stable complex with Fe 3 + (such as [Fe(C6H5O7)] 3-), inhibiting excessive metal corrosion (corrosion rate ≤ 0.1 g / m 2 ·h), achieving the effect of complexing corrosion inhibition.

[0134] In this step, on the one hand, thiourea adsorbs on the active sites (such as grain boundaries) of the stainless steel surface, forming a monomolecular protective layer, reducing the pitting corrosion sensitivity (the pitting potential increases by +0.2 V), and achieving the effect of inhibiting local corrosion; on the other hand, the amino group (-NH2) of thiourea forms a hydrogen bond with molybdate in the passivator, enhancing the bonding strength of the subsequent passive film (film-substrate bonding force ≥ 30 MPa), and promoting the adsorption of the passivator.

[0135] In this step, the temperature is selected to be 40 - 50 °C, which can accelerate the activation reaction (the reaction rate constant k increases by 3 times), and at the same time avoid the decomposition of thiourea (decomposition rate < 5%) caused by high temperature (> 60 °C); the time is selected to be 8 - 12 min, which can ensure the complete removal of the oxide layer (the surface O content drops from 15 at.% to < 5 at.%), and does not cause excessive corrosion of the substrate (the surface roughness Ra ≤ 0.1 μm).

[0136] Step S250, after the treatment is completed, ultrasonic cleaning is performed for 5 min at a frequency of 40 kHz, and the amplitude is controlled at 30 - 50 μm.

[0137] In this step, the ultrasonic wave with a frequency of 40 kHz can generate dense micron-sized cavitation bubbles (diameter 10 - 50 μm), and the blasting impact force (> 100 MPa) can effectively remove the particle residues in the spring gap (cleaning rate ≥ 99%, achieving the effect of high-frequency cavitation); the amplitude is controlled at (30 - 50 μm), the high amplitude enhances the cavitation intensity (suitable for stubborn pollutants), and the low amplitude protects the surface microstructure (avoiding the increase of the Ra value).

[0138] In addition, ultrasonic cleaning enables the activation solution to fully penetrate into the surface micropores, the contact angle drops from 70° to < 10°, the passivator wets more evenly, achieving the effect of enhancing wettability, and can also remove the sulfides remaining from thiourea (such as FeS), avoiding its interference with the growth of the passive film (the sulfur content drops from 500 ppm to < 50 ppm), achieving the technical effect of removing passivation inhibitors.

[0139] In one embodiment, the total time for activation - cleaning is 15 - 17 min, which is 50% shorter than the traditional pickling (30 min) + sandblasting (20 min) process, and there is no surface damage caused by sandblasting, improving the process efficiency; the citric acid - thiourea system has no heavy metal emissions (such as traditional hydrochloric acid activation containing Fe 3+(wastewater), the wastewater treatment cost is reduced by 70%, achieving the following technical effects: surface deoxidation: oxygen content ≤ 5 at.%, providing a clean substrate for the passivation film; enhanced adhesion: film-substrate adhesion ≥ 30 MPa, salt spray life ≥ 1200 h; environmentally friendly and efficient: no pollution discharge, and the process time is shortened by 50%.

[0140] Through the synergistic effect of the citric acid-thiourea activation solution and high-frequency ultrasonic cleaning, the high-efficiency activation and deep cleaning of the stainless steel spring surface are realized, solving the technical bottlenecks of rough surface and easy peeling of the passivation film in the traditional process.

[0141] In addition, a gradient penetration film-forming device 300 is also provided, which is specifically used to implement the above-mentioned method for forming a passivation film on a stainless steel spring. The gradient penetration film-forming device 300 includes:

[0142] A multi-stage series ultrasonic reactor 310, including three-stage ultrasonic reactors connected in series in sequence: the first-stage reactor, the second-stage reactor, and the third-stage reactor, with an ultrasonic frequency of 28 - 32 kHz and a power density of 0.5 - 1.2 W / cm 3 ; The first-stage reactor is used to ultrasonically clean the stainless steel spring at 40 - 60 °C with an ultrasonic frequency of 20 - 40 kHz to remove surface grease and impurities. The second-stage reactor is used to promote the penetration and uniform film formation of the passivation agent components through ultrasonic cavitation (frequency 25 - 50 kHz) under the conditions of 50 - 70 °C and pH 3.5 - 4.5. The third-stage reactor is used to ultrasonically wash the surface at room temperature (frequency 15 - 30 kHz) to remove the residual passivation liquid on the surface and accelerate drying through ultrasonic vibration;

[0143] A microwave-assisted curing module 320, connected downstream of the ultrasonic reactor 310, is used to non-contact cure the passivation film through microwave radiation with a microwave power of 300 - 800 W and a treatment time of 30 - 120 seconds, so that the passivation film forms a cross-linked network structure with a film layer hardness ≥ 300 HV;

[0144] An in-situ electrochemical impedance spectroscopy monitoring system 330 is used to execute steps S210 to S230. The scanning frequency range of the in-situ electrochemical impedance spectroscopy monitoring system is 10^5 - 10^-2 Hz and the sine wave amplitude is 10 mV. The

[0145] In one embodiment, the microwave frequency is 2.45 GHz.

[0146] The above multi-stage series ultrasonic reactor completes pretreatment, passivation film formation, and post-cleaning in stages. Through ultrasonic cavitation, the permeability and dispersibility of the passivation agent are enhanced, surface pollutants are removed, the adsorption of the passivation agent is promoted, and a uniform pre-passivation film is formed.

[0147] The above-mentioned gradient penetration film-forming equipment realizes the full-process optimization of the passivation film preparation through the series process of ultrasonic pretreatment → microwave curing → EIS monitoring and feedback. The three form a "cleaning - strengthening - quality inspection" closed loop, and the core advantages are as follows: Process accuracy: The real-time feedback of electrochemical impedance spectroscopy ensures that the film layer composition and structure are controllable; Performance breakthrough: The film-substrate bonding strength ≥ 35 MPa, and the salt spray life ≥ 1000 h; Industrial adaptability: The intelligent and low-energy consumption design is suitable for the mass production of high-end stainless steel springs.

[0148] The above is only the preferred embodiment of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present application, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present application.

Claims

1. A stainless steel spring passivator, characterized in that: The invention comprises at least the following components (calculated by weight percentage): 0.5-2.9 wt % of grape seed polyphenol extract, 0.1-0.8 wt % of nanocellulose crystals, 0.05-0.3 wt % of polyether modified silicone, 0.5-2.5 wt % of molybdate and 2-5 wt % of organic carboxylate, and the balance is deionized water.

2. The stainless steel spring passivator according to claim 1, characterized in that: The grape seed polyphenol extract is prepared by supercritical CO2 extraction, has a proanthocyanidin content of ≥95%, and an average polymerization degree of 3-5.

3. The stainless steel spring passivator according to claim 1, characterized in that: The nanocellulose crystal is a needle-like structure with a diameter of 10 to 30 nm and a length of 150 to 300 nm. The surface of the nanocellulose crystal is oxidatively modified by 2,2,6,6-tetramethylpiperidin-1-oxyl free radicals, and the carboxyl content is ≥1.2 mmol / g.

4. The stainless steel spring passivator according to claim 1, characterized in that: The polyether-modified siloxane is trisiloxane ethoxylate, and the molecular structural formula of the polyether-modified siloxane is Si(CH3)2-O-[Si(CH3)(C2H4O)6-O]2-Si(CH3)3. When the polyether-modified siloxane is in a 1 g / L aqueous solution and the temperature is 25°C, the dynamic surface tension of the polyether-modified siloxane is ≤25 mN / m.

5. A method for preparing a passivating agent as claimed in any one of claims 1 to 4, characterized in that The following steps are involved: Step S110, heating deionized water to 45-55° C., adding organic carboxylate and molybdate in sequence, and stirring until completely dissolved; Step S120, under the condition of ultrasonic power of 200-400W, grape seed polyphenol extract, nanocellulose crystals and polyether modified siloxane are added in sequence in three intervals, each interval lasting 5 minutes; Step S130, aging for 12 to 24 hours under nitrogen protection to obtain a homogeneous transparent solution.

6. The preparation method according to claim 5, characterized in that In step 120, the ultrasonic frequency is 28-32 kHz, and the solution temperature during the addition is controlled at 50±2°C, 45±2°C and 40±2°C respectively.

7. A method for forming a passivation film on a stainless steel spring, characterized in that: Using the passivating agent according to any one of claims 1 to 4, the forming method comprises: The electrochemical impedance spectrum of the working electrode is monitored in real time by a three-electrode system, and the pulse oxidation process is triggered when the phase angle θ is ≥ 70°, wherein the working electrode is a stainless steel spring to be treated; Applying a square wave voltage with an amplitude of 0.5 to 1.2 V and a frequency of 5 to 20 Hz, wherein the pulse duty ratio of the square wave voltage is 30 to 50%; The pulse parameters are dynamically adjusted during the growth stage of the passivation film so that the Cr / Fe atomic ratio of the film layer is 4.8-5.

2.

8. The forming method according to claim 7, characterized in that: The pulse oxidation process is divided into three stages: The first stage (0-10min): frequency is 5Hz and voltage is 0.8V; The second stage (10-20 minutes): the frequency is 15Hz and the voltage is 1.0V; The third stage (20-30 min): the frequency is 20 Hz and the voltage is 0.5 V.

9. The forming method according to claim 7 or 8, characterized in that: The forming method further comprises a pre-treatment process: The stainless steel spring is immersed in an activation solution containing 1-1.5wt% citric acid and 0.3-0.8wt% thiourea, and treated at 40-50°C for 8-12 minutes; After the treatment is completed, ultrasonic cleaning is performed with a frequency of 20 to 40 kHz for 5 minutes, and the amplitude is controlled at 30 to 50 μm.

10. A gradient osmosis film forming device, characterized in that: Dedicated to implementing the forming method according to any one of claims 7 to 9, the gradient permeation film forming equipment comprises: A multi-stage series ultrasonic reactor, comprising three stages of ultrasonic reactors connected in series in sequence: a first stage reactor, a second stage reactor and a third stage reactor, wherein the first stage reactor is used to complete pretreatment, the second stage reactor is used to promote the penetration and uniform film formation of passivating agent components, and the third stage reactor is used for post-cleaning process; A microwave-assisted curing module is connected to the downstream of the ultrasonic reactor, and is used for performing non-contact curing on the passivation film by microwave radiation, so that the passivation film forms a cross-linked network structure; The in-situ electrochemical impedance spectroscopy monitoring system is used to perform steps S210 to S230.

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