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Article

The Formation of Phytic Acid–Silane Films on Cold-Rolled Steel and Corrosion Resistance

by
Wanjiao Duan
1,
Yunying Fan
1,*,
Baipo Shu
1,
Yichun Liu
1,
Yi Wan
1,
Rongguang Xiao
1,
Jianxin Xu
2,
Shan Qing
2 and
Qingtai Xiao
2
1
Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093, China
2
Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China
*
Author to whom correspondence should be addressed.
Metals 2024, 14(3), 326; https://0-doi-org.brum.beds.ac.uk/10.3390/met14030326
Submission received: 29 January 2024 / Revised: 28 February 2024 / Accepted: 6 March 2024 / Published: 12 March 2024
(This article belongs to the Special Issue Environmentally-Assisted Degradation of Metals and Alloys)
Browse Figures
Versions Notes

Abstract

:
In this work, phytic acid (PA) and 3-mercaptopropyltrimethoxysilane (MPTS) underwent a condensation process to produce a phytic acid–silane (abbreviated PAS) passivation solution. Additionally, it was applied to the surface of cold-rolled steel to create a composite phytic acid–silane film. The functional groups of the passivation solution were analyzed by Fourier transform infrared spectroscopy (FT-IR). The composite film was evaluated using an electrochemical workstation, scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS) and pull-off test. These techniques allowed for the characterization of the film’s micromorphology, oxidation, chemical composition and adhesion strength. The results show that the PAS composite film provides higher protection efficiency compared to cold-rolled steel substrates, low phosphorus passivation films, single phytate passivation films and commercial phosphate films. This composite film also has a higher adhesion strength, which is beneficial for subsequent coating, and a possible corrosion resistance mechanism was proposed as well. The PAS layer successfully prevents the penetration of corrosive media into the cold-rolled steel surface utilizing P–O–Fe bonds, thus improving the corrosion barrier effect of the substrate.

1. Introduction

Steels are extensively used in various industries, including construction, machinery, aerospace, high-speed railway, new energy and so on [1,2,3]. However, the primary challenge in utilizing steels lies in their inherent susceptibility to corrosion [4,5,6]. The common surface treatment technology used for metal corrosion prevention is to prepare a chemically converted film on the metal surface. Traditional pretreatment techniques include chromate passivation [7,8] and inorganic phosphate conversion [9,10,11]. Although these two films exhibit excellent antioxidant and anticorrosive properties, they can cause harm to the environment and human health [12,13,14]. Hence, it is imperative to produce green passivation technology that demonstrates superior efficacy compared to traditional commercial phosphating methods.
Phosphates and phosphonates can be fixed on various surfaces due to their strong chelating ability with metal ions [15]. Phytic acid (PA), a natural medium–strong acid found in grains and seeds [16,17], is composed of hydrophilic phosphoric groups and hydrophobic hydrocarbon groups with potent chelating properties [18,19,20]. The metal surface can adsorb phosphate groups, creating a protective layer of phosphate film that shields the metal matrix. Therefore, PA is a promising candidate for functional material and substrate surface modification. Zhang et al. revealed that PA has good corrosion inhibition properties for all steels under different surface treatments [21]. However, due to PA’s excellent water solubility and feeble intermolecular interactions [22], PA is less ineffective in forming dense coatings directly via the solution immersion process. Therefore, some additives are usually added to the phytic acid solution to assist in the formation of a composite film on the metal surface. Yan et al. prepared a series of phytic acid (PA)–metal composite coatings on iron substrates by directly immersing iron samples in a mixed solution containing PA and metal ions [23]. Zhang et al. [24] deposited PA and polyethyleneimine (PEI) onto polyamide nanofiltration membranes in a layer-by-layer assembly.
3-mercaptopropyltrimethoxysilane (MPTS) as a metal surface rust inhibitor has special effects, commonly used to treat metals such as Cu and Al to improve their corrosion resistance and oxidation resistance [25,26]. However, there are few previously published research results on the use of MPTS as an environmentally friendly steel surface pretreatment material.
This work selects the reaction of PA with MPTS to prepare PA–MPTS (PAS) composite materials. The composition of the PAS material was characterized using Fourier transform infrared spectroscopy (FTIR). The phosphoric acid group in the phytic acid molecule undergoes a dehydration and condensation reaction with the highly reactive silanol formed during the hydrolysis of 3-mercaptopropyltrimethoxysilane [27,28]. The steel surface was treated using a dilute solution of phytic acid and silane hybrid material, leading to the creation of a chemical conversion film composed of phytic acid and silane. The anticorrosion properties of the chemical conversion films prepared were assessed through electrochemical impedance spectroscopy (EIS) and polarization curve methods. The surface morphology of the pretreated layer was investigated by scanning electron microscopy (SEM). The chemical composition of the pretreated layer was analyzed using energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The adhesion performance was evaluated through a pull-off test. The PAS pretreatment layer offers a straightforward and eco-friendly method, poised for widespread adoption in the pretreatment of metal surfaces for corrosion control.

2. Materials and Methods

2.1. Materials and Preparation

Chemical reagents of a high degree of purity, such as 3-mercaptopropyltrimethoxysilane (MPTS, 97%, Macklin) and phytic acid (PA, 90%, Macklin), can be utilized immediately without the necessity for additional purification. NaMoO4(AR), Na3PO4 (AR) and H3BO3 (AR) were purchased from Tianjin Chemical Reagent Co., Ltd (Tianjin, China). Commercial iron phosphating solution (CP) was purchased from Dianke Coating&Plating Co., Ltd. (Kunming, China) Commercial epoxy resin (CEp) was purchased from Haoshun paint Co. Ltd., Zhaoqing, Guangdong, China.
Cold-rolled steel possesses the subsequent chemical composition (expressed in weight percentage): 0.016% Al, 0.02% S, 0.02% P, 0.08% C, 0.3% Mn and the rest is Fe. The substrate was cut into dimensions of 10 mm × 10 mm × 1 mm and 50 mm × 50 mm × 1 mm (pull-off adhesion tester) in size. Each sample was sanded using 800, 1200, and 1500 grit sandpaper. Following this, the specimen surface was cleaned using deionized water.

2.2. Preparation of Passivation Films

In the preparation procedures for the PAS film, several actions are carried out. Firstly, the PAS reagent was prepared by adding 3.2 mL PA and 2 mL MPTS into 100 mL deionized water. A white, clear and transparent solution was obtained by stirring the solution with an electromagnetic stirrer. The cleaned specimens were submerged in the solution and subjected to an assembly process in an ultrasonic cleaner for a duration of four minutes. Subsequently, the sample was allowed to air dry at ambient temperature. The process is depicted in Figure 1. The low phosphorus passivation film Ref. [29] and the PA film comparison groups were established to investigate the performance characteristics of the PAS film. The low phosphorus passivation (LP) solution was mixed with 1 g/L NaMoO4, 2.5 g/L, Na3PO4 and 2 g/L H3BO3. Samples treated with PA (3.2 vol.%) solutions were also prepared for comparison. To show that PAS is environmentally friendly and has commercial value, we added a new set of commercial phosphate solutions to the test.

2.3. Characterization Method

Fourier transform infrared spectroscopy (FT-IR) was utilized to examine the functional groups present within PAS passivation solutions (Bruker, ALPHA II, Karlsruhe, German). Data were recorded between 400 and 4000 cm−1 with a resolution of 4 cm−1. The surface morphology, element species, and chemical composition of the composite films on cold-rolled steel sheets were examined using energy-dispersive X-ray spectroscopy (EDS, Hitachi, Tokyo, Japan) and the Hitachi S3400N scanning electron microscope (SEM, Hitachi, Tokyo, Japan). The chemical composition of the composite films was further determined using an X-ray photoelectron spectrometer (ESCALAB 250Xi, Thermo Scientific, Waltham, MA, USA) equipped with a monochromatic X-ray source. A monochromatic Al Kα radiation source (1486.6 eV) was used, and the energy was calibrated based on the C 1s peak at a binding energy of 284.8 eV. The pull-off adhesion tester (HC-M, Hangzhou, Zhenjiang, China) was used to measure the adhesion strength of coatings with dollies of 20 mm in diameter. Each experimental condition was tested five times and the average value was used to determine the adhesion. The experiments were conducted at room temperature, with each test sample consisting of a minimum of five pairs.

2.4. Electrochemical Testing

Surface film formation was inferred using electrochemical impedance spectroscopy (EIS) testing polarization curves to evaluate the corrosion protection capabilities of cold-rolled steel electrodes that were both unaltered and modified with various passivation films. Polarization measurements and electrochemical impedance spectroscopy (EIS) were carried out using a workstation (CHI660E, Chenhua, Shanghai, China) and a conventional three-electrode system. Each electrode underwent electrochemical tests at ambient temperature using a three-electrode battery. As a conductive solution, 3.5 wt% NaCl solution was employed. A saturated silver chloride electrode was used as the reference electrode and the platinum electrode served as the counter electrode. The working electrode consists of four different samples. Before conducting electrochemical impedance spectroscopy (EIS) and polarization measurements, the samples were immersed in a 3.5 wt% NaCl solution for 1800 s to establish a stable open-circuit potential (EOCP). Impedance spectra were collected across a frequency range of 100 kHz to 0.01 Hz at the EOCP of each working electrode, using perturbation signals with a 10 mV amplitude. The EIS data were analyzed using ZView2 software (ZView2, Scribner, Southern Pines, NC, USA). The potential sweeping rate was set at 0.5 mV/s, and the polarization curve was scanned from −250 mV to +250 mV around the EOCP. All measurements were repeated at least three times to ensure repeatability.

3. Results and Discussion

3.1. Infrared Spectral Characterization of the PAS Passivation Solution

Figure 2 displays the FT-IR spectra of the PAS passivation solution, PA and MPTS. The infrared spectroscopy of the prepared PAS passivation solution exhibited numerous characteristic peaks from phytic acid and MPTS. It was demonstrated that the reaction between silane and phytic acid forms this hybridized substance. The assignments of the peaks are listed in Table 1. The O–H group vibration peaks at 3411 cm−1 exhibit a very broad and strong intensity in the PAS passivation solution’s FT-IR spectra. This peak is related to P–OH and H–OH groups in the aqueous solution. The S–H and Si–C stretching are examined from the peaks at 2071 cm−1 and 1396 cm−1, respectively [27,28,30]. The phosphate group in the PA molecules exhibited P–OH, which was characterized by peaks at 1628 cm−1. The band located in 1180 cm−1 is associated with the P–O–Si stretching [31,32]. The vibrations of terminal groups P–O and PO3 can be observed at 1011 and 1078 cm−1, respectively [33,34]. The peak observed at 635 cm−1 may be associated with the stretching vibration of the P–O bending bands [35,36]. The presence of a significant number of unreacted P–OH groups in the PAS passivation solution is indicated by the peaks observed at 1628 cm−1 in the FT-IR spectra. This allows the preparation of chemical conversion membranes on their surfaces by the reaction of P–OH groups with iron-based metals.

3.2. Anticorrosion Properties

The tests were carried out after 1800 s immersion in a 3.5 wt% NaCl solution. Various films were assessed for their barrier performance using polarization curves [37]. Figure 3 displays the polarization curves of unmodified and passivation layer-modified cold-rolled steel electrodes in a 3.5 wt% NaCl solution. In 3.5 wt% NaCl solution, we observe that the different passivation films can reduce the corrosion current density of cold-rolled steel, but there is a difference in their corrosion resistance. The results clearly demonstrate that the PAS film has a significant influence in reducing the corrosion current density of the substrate when compared to the low phosphorus passivation film, commercial iron phosphorus passivation film and the single phytate passivation film. This significantly improves the efficiency of suppression. Compared to the blank substrate, the corrosion potential of the treated samples shifted in the positive direction, with the shift being most pronounced in the case of the PAS film, where the corrosion inhibition of the substrate was the greatest.
The EIS method was also used to evaluate the corrosion resistance of different pretreatment layers prepared under different conditions [38]. As shown in Figure 4a, the Nyquist plots from the EIS test demonstrate a characteristic irregular semicircular shape commonly observed in the impedance spectra of solid-state electrodes [39]. This morphology is a result of the roughness and imperfections of the electrode surface [5,40]. The low frequency region is where the most significant variations can be observed in the Nyquist plots of different specimens. The illustration showcases a notable augmentation in the radius of the capacitive arc for the cold-rolled steel electrodes that have undergone treatment with a passivation solution, in contrast to the untreated specimens. Among several treatments, the cold-rolled steel electrode treated with the PAS passivation solution has the largest impedance radius, which shows that applying a PAS passivation solution to the electrode efficiently increases its corrosion resistance [5]. Meanwhile, a high impedance modulus of the PAS films in the low-frequency region reflects a high anticorrosion performance [41,42], as shown in the Bode modulus plots in Figure 4c. These results show that the PAS films are able to improve the corrosion resistance of the blank substrate.
EIS data were fitted to corresponding equivalent electrical circuits (EECs), as shown in Figure 4d. The corrosion resistance of the specimens was visually compared in terms of the magnitude of the individual element values. The impedance spectrum of the electrodes can be matched to the equivalent circuit shown in Figure 4d. There are three parameters in the fitted circuit: Rs (representing the solution resistance), Rct (representing charge transfer resistance between the solution and substrate) and Cd (representing the double layer capacitance at the substrate’s surface). To obtain more precise fitting results, the capacitance elements are substituted by constant phase angle elements (CPEs). The CPE1 in the figure represents the double layer capacitance (Cd) model, which assumes that H2O and other ions are adsorbed on the surface [43,44,45]. In Figure 4d, the experimental data illustrated by spheres align closely with the fitting results indicated by the solid line, indicating the suitability and reliability of the chosen equivalent electrical circuits (EECs). Fitting the impedance data yielded values for each of the above components. The impedance parameters obtained from the fitting process are presented in Table 2.
We compare the fitted data presented in Table 2 in our analysis. An increase in the Rct value and a decrease in the Cd value of the cold-rolled steel electrodes modified with each passivation film was seen [46]. Generally, higher values of Rp represent lower electron transfer efficiency between metal and electrolytes. Table 2 shows that the values of the PAS passivation sample are greater than those of the CP sample and the blank sample. It shows that the PAS passivation sample has better corrosion resistance. This film effectively prevents the diffusion of corrosive substances to the carbon steel surface, thereby increasing the resistance at the interface. Out of the five films, the PAS film exhibited the highest corrosion inhibition efficiency, as evidenced by its largest Rct value. Meanwhile, the protection efficiency (PE) of each coating was calculated according to the following formula:
η (%) = (1 − Rct/R′ct) × 100%,
where Rct and R′ct stand for the values of unmodified and passivation film-modified substrates, respectively. The PAS sample had the largest η value (74.29%). This composite film is more efficient in protection. The η of the composite film layer prepared by Wan et al. [47] derived from formula 1 is 40.43%. All the comparative experiments have concluded that this PAS composite film layer can better inhibit the occurrence of matrix corrosion.

3.3. Morphology and Composition

3.3.1. Surface Analysis by SEM–EDS

The surface integrity of a film plays a crucial role in its resistance against oxidation and corrosion. During material application, the propagation of surface microcracks can be accelerated, ultimately leading to their rupture. This rupture compromises the protective function of the film and exacerbates the oxidation and corrosion processes on the surface of the specimen. It is noteworthy that surface defects serve as preferential sites for surface corrosion [48].
Figure 5 shows the scanning electron microscope images of multiple specimens. Upon comparing the four images, a distinct observation is made that the passivated specimens’ surface is covered with a protective film. The specimens’ surface morphology following low phosphorus passivation is displayed in Figure 5b. It displayed that the membrane surface is flat. However, the presence of microcracks on the coating creates channels through which the oxidizing medium can penetrate the substrate’s surface, thereby accelerating the oxidation rate of the substrate. Figure 5c shows the surface morphology of the sample after phytate acid passivation. The film was formed on the substrate surface. However, it does not provide complete coverage and leaves numerous areas uncovered. The corrosion protection performance of such a passivation film layer is definitely poor. As shown in Figure 5d, the surface steel substrate formed a passivation film without very large cracks, which completely covered the substrate and effectively prevented the corrosion caused by the substrate oxide bonding. Meanwhile, the thickness of the film in the SEM cross-sectional image was measured. The average thickness obtained was approximately 12 μm (see Figure 5e). This method allows for a more accurate determination of the presence of a film on the substrate’s surface. The EDS analysis, as shown in Figure 5f, reveals that the main elements present in the PAS film are C, O, Fe, Si, S and P. It indicates that PA and MPTS are involved in the film formation. The presence of the element Fe confirms the substrate is involved in the reaction.

3.3.2. Surface Analysis by XPS

The XPS was used to determine the surface composition of PAS films and explore the formation mechanism. The X-ray photoelectron spectra of the PAS film’s primary element are displayed in Figure 6. The O1s area was matched to two peaks in Figure 6a. The peak at 529.8 eV belongs to iron oxide and the peak for oxygen-containing functional groups in phosphates is located at 531.4 eV [49]. The Si 2p region contains two distinctive chemical states (Figure 6b). The peak at 101.7 eV indicates Si–O–P bonds, whereas the peak at 100.1 eV signifies the presence of C–Si–O bonds [37]. The results indicate that the reactions between substances PA and MPTS occur. As shown in Figure 6c, two pairs of peaks were fitted in the Fe2p region. The first pair of peaks of Fe 2p3 and Fe 2p1 are located at 710.52 eV and 723.76 eV, respectively, which were characteristic peaks of iron oxides, and the other pair of peaks of Fe 2p3 and Fe 2p1 are located at 712.7 eV and 726.1 eV, respectively, which were the peaks of a type of ferric phosphate salt [50,51]. Meanwhile, fitting the P 2p region yielded two different chemical states (Figure 6d), with the peak at 133.0 eV being the P–O–C bond in phytate, while the peak at 134.2 eV corresponded to the P–O–Fe bond [52,53]. The above analysis showed that PA and MPTS formed a PA/MPTS condensate by connecting through Si–O–P bonds. The remaining P–OH bonds of the PA molecule combine with iron ions to form iron phytate, which creates a film on the surface bonded by P–O–Fe bonds.

3.4. The Pull-Off Adhesion Tester

In order to test the effect of different modifications on the subsequent coating effect, a pull-off test was carried out. The pull-off test (Figure 7) clearly shows that PA-only has no beneficial effect on adhesion to epoxy coatings, while the existence of a PAS layer helps to improve the adhesion. The PAS composite layer showed the highest adhesion to commercial epoxy coatings (16.471 MPa), which was higher than that of the unpretreated (7.547 MPa) low phosphorus passivation layers (12.128 MPa) and commercial phosphate conversion layers (12.475 MPa). After the hybridization of PA and MPTS, the adhesion to epoxy coatings is further improved, mainly due to the structures of this composite pretreatment layer.

3.5. Exploring the Formation of the PAS Film

There are two steps in the formation of the PAS film. The production phase of Fe2+ ions is the first, as depicted in Formula (2), from the substrate in solution. The reaction of the substrate and the composite passivation solution is what happens in the second stage. Once the substrate is immersed in the passivation solution, typically, the subsequent reactions take place at the surface of the anode.
Fe → Fe2+ + 2e−
During the preparation of passivation solutions, silanes undergo hydrolysis to form silanol. Subsequently, a condensation reaction takes place between the hydrolyzed silane product and phytic acid. This reaction leads to the formation of a product characterized by a network structure, which is achieved through the amalgamation of Si–O–P bonds. The procedural details of this reaction are depicted in Figure 8.
The PAS passivation solution is an organic acid that contains numerous PA monomers. Similar to PA, this solution exhibits a strong ability to complex with metal ions. When utilized to produce films on the cold-rolled steel substrate, the PA monomer undergoes a reaction with free iron ions in the solution or traps Fe2+ ions near the interface between the substrate and solution. Consequently, a complete film composed of novel organic acid salt is constructed (see Figure 9). The X–ray photoelectron spectra (Figure 6), EDS spectrum (Figure 5f), and SEM images (Figure 5d) of the PAS film illustrate this. A film containing Fe–O–P bonds is adsorbed onto the substrate surface, with the monomers cross-linked by Si–O–P bonds, resulting in a complete film. Comparison with the rest of the experiments shows that the composite film is more complete and has a higher protection efficiency against corrosive penetration into the surface of cold-rolled steel sheets.

4. Conclusions

In this study, the steel surface was treated using a dilute solution of phytic acid and silane hybrid material, leading to the creation of a chemical conversion film composed of phytic acid and silane. The anticorrosion properties of the chemical conversion films prepared were assessed through electrochemical impedance spectroscopy (EIS) and polarization curve methods. The surface morphology of the pretreated layer was investigated by scanning electron microscopy (SEM). The chemical composition of the pretreated layer was analyzed using energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The adhesion performance was evaluated through a pull-off test. A passivation solution was prepared by dehydration and condensation reactions of phytic acid with 3-mercaptopropyltrimethoxysilane. Subsequently, a composite film was generated on the surface of cold-rolled steel utilizing this composite passivation solution. Compared to the bare CRS and other conversion coatings, the PAS film exhibits higher Rct (2968 Ω cm2). All the comparative experiments have concluded that this PAS composite film layer can better inhibit the occurrence of matrix corrosion. From the polarization curve tests, it was seen that the PAS film had a significant impact in reducing the substrate corrosion current density compared to low phosphorus passivation films, commercial iron phosphorus passivation films and single phytate passivation films. This greatly improves the inhibition efficiency. From the scanning electron microscopy results, it can be seen that the pretreated transformed film prepared from the PAS passivation solution is more complete. Phytic acid and MPTS react through the Si–O bonds to create a PAS passivation solution. Furthermore, they produce a film with the substrate by –P–O– bond. The structure formed by PAS in the matrix fills the defects of the phytate passivation film. Corrosive media are successfully prevented from penetrating the composite films. The pull-off test clearly shows that the existence of the PAS layer helps to improve the adhesion. Among the tested coatings, the PAS sample showed the highest adhesion strength. This helps with subsequent painting results. The PAS conversion coating has the potential of becoming an alternative to general phosphate conversion coatings. The PAS passivation solutions possess the distinct advantage of being environmentally friendly and can be widely employed as a pre-corrosion treatment for metal surfaces.

Author Contributions

Conceptualization, Y.F.; Methodology, W.D., Y.W. and R.X.; software, B.S., Y.L. and S.Q.; validation, Y.F., Y.W., R.X. and Q.X.; formal analysis, R.X., J.X. and Q.X.; investigation, W.D., Y.W. and J.X., resources, B.S., Y.L., J.X. and S.Q.; data curation, W.D.; writing—original draft, W.D.; writing—review and editing, Y.F.; visualization, B.S. and S.Q.; supervision, Y.F., Y.L. and Q.X.; project administration, Y.F. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Conflicts of Interest

The authors declare no conflict of interest.

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Metals 14 00326 g001
Figure 1. Preparation flow chart for the PAS film.
Figure 1. Preparation flow chart for the PAS film.
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Figure 2. The FT−IR spectra of PA, MPTS and PAS passivation solution (a), assignments of peaks to each of the pas passivation solutions (b).
Figure 2. The FT−IR spectra of PA, MPTS and PAS passivation solution (a), assignments of peaks to each of the pas passivation solutions (b).
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Figure 3. Polarization curves of untreated and cold−rolled steel electrodes treated with various passivation films.
Figure 3. Polarization curves of untreated and cold−rolled steel electrodes treated with various passivation films.
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Figure 4. EIS plots of the cold−rolled steel electrodes untreated and treated with various passivation films: (a) the Nyquist plot, (b,c) Bode diagram modulus and phase; Electrochemical equivalent circuits for the impedance spectrum (d).
Figure 4. EIS plots of the cold−rolled steel electrodes untreated and treated with various passivation films: (a) the Nyquist plot, (b,c) Bode diagram modulus and phase; Electrochemical equivalent circuits for the impedance spectrum (d).
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Figure 5. SEM images of the substrate’s surface without film (a), with phosphide film (b), mono-phytate film (c), PAS film (d), the cross-section of the substrates with PAS film (e) and EDS plot of surface elements of the PAS film (f).
Figure 5. SEM images of the substrate’s surface without film (a), with phosphide film (b), mono-phytate film (c), PAS film (d), the cross-section of the substrates with PAS film (e) and EDS plot of surface elements of the PAS film (f).
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Figure 6. The X-ray photoelectron spectra of main elements on composite phytic acid–silane film; (a) O 1s, (b) Si 2p, (c) Fe 2p, (d) P 2p.
Figure 6. The X-ray photoelectron spectra of main elements on composite phytic acid–silane film; (a) O 1s, (b) Si 2p, (c) Fe 2p, (d) P 2p.
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Figure 7. Pull-off test results of different samples. 1: blank, 2: LP, 3: PA, 4: CP, 5: PAS.
Figure 7. Pull-off test results of different samples. 1: blank, 2: LP, 3: PA, 4: CP, 5: PAS.
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Figure 8. The procedural details of the PAS passivation solution.
Figure 8. The procedural details of the PAS passivation solution.
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Figure 9. Diagrammatic representation of the composite films’ corrosion prevention mechanism.
Figure 9. Diagrammatic representation of the composite films’ corrosion prevention mechanism.
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Table 1. Assignments of the peaks in FT-IR spectra (PAS passivation solution).
Table 1. Assignments of the peaks in FT-IR spectra (PAS passivation solution).
Frequency (cm−1)AssignmentsFrequency (cm−1)Assignments
3411O–H stretching1180P–O–Si stretching
2071S–H stretching1078 and
1011		P–O (vibrations of terminal groups and PO3 asymmetric stretching)
1628P–OH bending
1396Si–C stretching635P–O bending
Table 2. The impedance parameters obtained from the fitting process.
Table 2. The impedance parameters obtained from the fitting process.
Rs (Ω cm2)Rct (Ω cm2)Cd (μF cm−2)η (%)
blank1.855763.4659
LP5.394116663434.53
PA4.194118762835.69
CP4.666109663930.35
PAS7.235296857274.29
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MDPI and ACS Style

Duan, W.; Fan, Y.; Shu, B.; Liu, Y.; Wan, Y.; Xiao, R.; Xu, J.; Qing, S.; Xiao, Q. The Formation of Phytic Acid–Silane Films on Cold-Rolled Steel and Corrosion Resistance. Metals 2024, 14, 326. https://0-doi-org.brum.beds.ac.uk/10.3390/met14030326

AMA Style

Duan W, Fan Y, Shu B, Liu Y, Wan Y, Xiao R, Xu J, Qing S, Xiao Q. The Formation of Phytic Acid–Silane Films on Cold-Rolled Steel and Corrosion Resistance. Metals. 2024; 14(3):326. https://0-doi-org.brum.beds.ac.uk/10.3390/met14030326

Chicago/Turabian Style

Duan, Wanjiao, Yunying Fan, Baipo Shu, Yichun Liu, Yi Wan, Rongguang Xiao, Jianxin Xu, Shan Qing, and Qingtai Xiao. 2024. "The Formation of Phytic Acid–Silane Films on Cold-Rolled Steel and Corrosion Resistance" Metals 14, no. 3: 326. https://0-doi-org.brum.beds.ac.uk/10.3390/met14030326

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