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Article

Enhancement of the Corrosion and Wear Resistance of an Epoxy Coating Using a Combination of Mullite Powder and PVB

1
School of Civil Engineering and Architecture, Wuyi University, Wuyishan 354300, China
2
China Testing and Certification International Group Co., Ltd. Room, Chaoyang District, Beijing 100024, China
3
Qingyuan County Experimental Forest Farm, Lishui 323800, China
*
Authors to whom correspondence should be addressed.
These authors contributed equally to this work.
Coatings 2025, 15(1), 41; https://doi.org/10.3390/coatings15010041
Submission received: 27 November 2024 / Revised: 30 December 2024 / Accepted: 31 December 2024 / Published: 3 January 2025
(This article belongs to the Section Corrosion, Wear and Erosion)

Abstract

:
Currently, with the gradual development of corrosion-resistant materials, coatings often exhibit ultra-high hydrophobic properties while possessing corrosion resistance, complicating the preparation of corrosion-resistant coatings. To explore a novel coating that combines high corrosion resistance with simplified preparation methods, mullite/kaolin powder was stirred using ball milling, and polyvinyl butyral was added to serve as a binder, thereby preparing a hydrophilic and highly corrosion-resistant coating. The coating was characterized using SEM, IR, XRD, and other testing methods. The results revealed that the components of the coating are connected through physical crosslinking, avoiding chemical reactions. Regarding the coating’s performance, electrochemical and salt spray tests were conducted to characterize the prepared coating. According to electrochemical impedance spectroscopy tests, after immersion for 7 days, the electrochemical impedance spectroscopy impedance value of the A4C6EP coating reached 1.13 × 108 Ω·cm2, several times higher than that of other coatings, demonstrating its superior corrosion resistance. After a salt spray test for 2000 h, the coating surface showed neither bubbles, further validating the excellent corrosion resistance of the A4C6EP coating. The A4C6EP coating underwent an abrasion test using sandpaper and, after 100 cycles, the contact angle decreased by only 2.3°, with only slight scratches appearing on the surface, indicating very high mechanical abrasion resistance. This research demonstrates the successful preparation of a hydrophilic coating with excellent corrosion resistance and ultra-high mechanical abrasion resistance through a simple method, providing new insights for the development of hydrophilic corrosion-resistant coatings and reducing the cost of such coatings.

1. Introduction

Corrosion is defined as the degradation of substances due to chemical interactions with the surrounding environment, which has a significant impact on the use and value of vehicles, consumer electronics, aircraft, and industrial sites, such as power generation and transmission, pharmaceutical manufacturing, desalinated water, petrochemical product processing, etc. [1,2]. After the corrosion of pipes and equipment made of metal materials, the damage to equipment and structure will gradually increase, which will bring about various problems, such as discharge, leakage and environmental pollution of raw materials and products, especially the corrosion and damage of metal structures belonging to ships and aircraft [3,4,5]. Metal corrosion is an ongoing problem that is often difficult to eliminate, and prevention is more practical and accessible than complete elimination [6].
Epoxy coating (EP) has been widely recognized by a wide range of researchers due to its advantages in aviation, aerospace, automotive, renewables, and other related fields, due to its good anti-corrosion properties, chemical stability, low curing shrinkage, excellent adhesion and mechanical processing properties [7,8]. Unfortunately, the higher crosslinking density can also be a “disadvantage” of epoxy thermoset plastics, which can lead to reduced fracture toughness, loss of flexibility and difficulties in processing material recovery, so it is difficult to apply this EP in the field of composites and coatings requiring high flame retardancy and corrosion resistance [9]. Ma et al. added hydrophobic particles and graphite nanosheets to the epoxy resin, giving the epoxy coating super hydrophobic properties and high corrosion resistance [10]. Lv et al. added polytetrafluoroethylene and kaolin to the epoxy coating and, adjusting the size of different MoS2 under the action of the modifier, the coating had excellent corrosion resistance [11]. However, whether graphite nanosheets or MoS2, dispersion in the coating is often irregular, so they cannot accurately fix all the defects of epoxy coating.
As the most stable mineral in the Al2O3-SiO2 system [12,13], mullite has been widely used in ceramic coatings [14], refractory materials, and other applications due to its high-temperature resistance [15], corrosion resistance [16], low coefficient of thermal expansion [17], excellent thermal shock resistance and other advantages [18]. Xie et al. applied a poly-pyrrole-modified Alo-Mullite coating on aluminum alloy by chemical oxidation polymerization, which enabled poly-pyrrole nanoparticles to gradually grow and combine on the surface of the mullite coating, finally forming a dense and uniform poly-pyrrole layer, which protected the composite coating from severe salt spray erosion [19]. This improves the corrosion resistance of the poly-pyrrole coating. However, the most important factor is the growth form of poly-pyrrole nanoparticles, which does not reflect the influence of mullite particles on corrosion resistance. Polyvinyl butyl (PVB), as a viscous composite particle, is mainly used as a bonding aid before sintering ceramics and is rarely used in coatings. By adjusting the content of alumina and aluminum nitride, Zhang et al. added PVB and found that a plastic-like coating was formed, which had excellent corrosion resistance and specific self-cleaning ability, providing a new idea for hydrophilic self-cleaning super-anticorrosive coating [20]. However, the central role of PVB is in forming a plastic-like surface in contact with water in the air during curing, and it does not show an adhesive effect.
This study aims to simplify the preparation method of corrosion-resistant coatings by developing a novel hydrophilic coating with exceptional corrosion resistance. The coating was prepared by ball milling a mixture of mullite, kaolin, and PVB, with controlled addition of mullite content into an epoxy coating. The corrosion resistance of the coating was verified through electrochemical and salt spray tests, while its mechanical abrasion resistance was assessed through sandpaper friction tests. The results indicate that the A4C6EP coating exhibits superior corrosion resistance and exceptionally high mechanical abrasion resistance.

2. Experimental Section

2.1. Materials

Mullite powder (5 µm, 99.5%); Kaolin superfine powder(5 µm, 92%) and PVB powder were manufactured by McLean Co., Ltd. (Shanghai, China) (EP (E-44) and Polyamide curing agent (PA) manufactured by McLean Co., Ltd. Absolute ethyl alcohol (AR) was manufactured by Tianjin Fuyu Fine Chemical Co., Ltd. (Tianjin, China) and Q235 steel plate (5 cm W × 20 cm L × 5 mm T) from Shenzhen Dinglong Metal Materials Co., Ltd. (Shenzhen, China).

2.2. Preparation of Composite Coatings

First, the Q235 steel plate was pretreated. The steel plate was polished with 100 mesh sandpaper to remove the oxide film and rust of the steel plate, and then the steel plate was polished with 1200 mesh sandpaper. After 30min of ultrasound, clean with anhydrous ethanol for 3 times and put in the oven to dry.
Using ball milling, mullite powder and kaolin powder (with a weight ratio of 2:8), 1 g of PVB powder, and 0.4 g of castor oil were uniformly mixed in an ethanol solution. After adding EP and PA (in a weight ratio of 1:1), continuous stirring was carried out to obtain a mixed emulsion. This emulsion was then evenly applied onto a pretreated Q235 steel plate using a coating machine and allowed to cure at room temperature to obtain the A2C8EP coating. The preparation process of A3C7EP coating is the same as that for A2C8EP coating. The addition of mullite powder was changed to an amount of 3 g, and the addition of kaolin powder to 7 g. By analogy, four AxCyEP coatings (x is the mullite content, y is the kaolin content) were prepared.

2.3. Surface Characterization

The coating’s contact angle was measured using the water drop method for ~4 μL. Each sample was measured five times using a static contact angle tester and a contact angle meter (SPCAX1, Beijing Haco test instrument Co., LTD., Beijing, China). Each sample was measured five times and these measurements were averaged [21]. Field emission scanning electron microscopy (SEM, ZEISS GeminiSEM 300, Hitachi, Tokyo, Japan) and a roughness tester (Mitutoyo SJ-210, Tokyo, Japan) were used to observe the surface morphology of the films [22]. Fourier infrared spectroscopy (FTIR, Fisher Scientific Nicolet iS20, Shimadzu, Kyoto, Japan) and X-ray diffractometer (XRD, Rigaku SmartLab SE, Woburn, MA, USA) was used to observe the composition of the coating and composition.

2.4. Electrochemical Measurement and Salt Spray Test

A salt spray test and electrochemical analysis of the coating were carried out. The coating’s corrosion resistance was assessed in this way. The electrochemical tests were conducted on the DH7000 workstation [23], utilizing a saturated calomel reference electrode and a platinum auxiliary electrode [24]. The corrosion potential was measured with a step size of 1 s, and the electrode’s working surface area was 4 square centimeters. The electrochemical impedance spectroscopy (EIS) was conducted at frequencies ranging from 10 mHz to 10 kHz, with an amplitude of 10 mV. Prior to testing, all samples were submerged in a 3.5% NaCl solution to induce various impedance states. All samples were immersed in NaCl solution because it was necessary to build an open circuit, so the samples had a stable impedance arc when measuring EIS. The corrosion resistance of the coating is judged by the size of the impedance arc diameter. The larger the impedance diameter, the better the corrosion resistance of the coating. The Tafel polarization test was performed at a constant scan rate of 1 mV/s, yielding the corrosion potential (Ecorr) and corrosion current (Icorr).
For the salt spray test (SSCT), a 3.5% NaCl solution was used in a salt spray chamber. The chamber’s pressure was maintained below 100 kPa, and the temperature was held at 30 °C ± 1 °C. The corrosion resistance of the sample was assessed by the presence of corrosion and air bubbles on the sample surface after a specific time of exposure to salt spray [25,26].

2.5. Evaluation of Mechanical Durability

According to ISO 7784-3:222, a linear wear test was used to reflect the change in coating properties through the change in contact angle, and the coating can be considered to have excellent wear resistance within 5° of the change in contact angle and no significant surface wear [20]. In the wear resistance test, the covered glass substrate was contacted with 1000 mesh sandpaper and, under the action of 500 g weights, the horizontal push of 2 cm is a cycle [10], and the contact angle was measured every five cycles for the first 50 times, and every ten cycles for the last 50 times [27]. The variation trend in the contact angle and the surface state of the film along with the friction cycle were observed.

3. Results and Discussion

3.1. Characterization of Samples and Coatings

3.1.1. Morphology Characterization of Samples and Coatings

To investigate the effect of mullite content on coatings, SEM analysis was conducted on various coatings, with the results presented in Figure 1. By comparing Figure 1a–d, it is evident that, as mullite content rises and kaolin content falls, the coating’s density increases. This enhancement in density prolongs the path that corrosive agents like H2O and O2 must travel along to penetrate the coating, thereby boosting its corrosion resistance. However, once the mullite/kaolin ratio reaches a specific threshold, cracks form on the surface of the A5C5EP coating (see Figure S1). These cracks facilitate the ingress of corrosive agents, like H2O and O2, into the coating, reaching the metal surface and causing corrosion. Consequently, the cracks shorten the corrosion path and degrade the coating’s corrosion resistance. The experiments reveal that the A4C6EP coating exhibits the highest density and optimal corrosion protection. As mullite content increases, it fills pores and cracks in the epoxy resin coating, facilitated by PVB glue, leading to a progressive reduction in coating roughness (Figure 1i–l). This results in an increase in the coating’s contact angle, peaking at 74.05°. Notably, the A4C6EP coating has a contact angle of 68.47°, classifying it as a hydrophilic coating.

3.1.2. Structural Characterization of Samples and Coatings

The FTIR and XRD findings are illustrated in Figure 2. In the coating depicted in Figure 2a, the distinctive vibration peak of the C-O bond, originally at 1059 cm−1 in pure epoxy resin, shifts to a higher wavenumber. Similarly, the specific vibration peak of the C-H bond at 883 cm−1 and the Si-O bond at 1170 cm−1 also exhibit shifts to the right compared to pure epoxy resin. The unique vibration peaks of the Al-O bond at 684 cm−1 and Zr-O bond at 548 cm−1 align with the infrared spectra of mullite/kaolin, while the vibration peaks of C-N at 1121 cm−1 correspond to PVB. This evidence suggests that mullite is physically filled into the pores and cracks of the epoxy coating through PVB bonding.
To further confirm this physical filling of mullite into the epoxy coating via PVB bonding, XRD tests were performed on each sample and the coating. The results, shown in Figure 2b, indicate a significant weakening of the characteristic peak associated with epoxy resin in the coating. Additionally, the characteristic peaks of mullite and PVB are observed, confirming that the mullite powder’s size has been reduced after ball milling. With the assistance of PVB, the powder adheres to the pores and cracks of the coating, rendering the characteristic peaks of the epoxy resin less prominent.

3.1.3. Electrochemical Test

To assess the impact of the mullite content on the coating’s corrosion resistance, the coating was immersed in 3.5 wt% NaCl solution for durations of 7, 14, and 30 days, followed by an EIS test [28]. The EIS results are shown in Figure 3, and detailed data are presented in Table S1. We have tested three coatings, A4.5C5.5EP, A5C5EP and A6C4EP, and the electrochemical results are shown in Figure S2. We found that the impedance diameter of A4.5C5.5EP coating is close to that of A5C5EP coating, which is much larger than A6C4EP coating, so A5C5EP coating is used in the text for comparison. Following a 7-day immersion in 3.5 wt% NaCl (Figure 3a), the impedance diameter of the A4C6EP coating reaches 6.74 × 107 Ω·cm2, which is 6 times that of A2C8EP coating and more significant than that of A5C5EP and A3C7EP, proving that A4C6EP has the best corrosion resistance. When the soaking time reaches 14 days (Figure 3b), the EIS semi-circle diameter of A4C6EP coating remains the largest, and the impedance value is the largest, 5.02 × 107 Ω·cm2, which is consistent with the rule of soaking for 3 days. When the soaking time reaches 30 days, the impedance value of the A4C6EP coating is reduced to 4.52 × 107 Ω·cm2, but this is still higher than other coatings. This proves that A4C6EP has the highest corrosion resistance.
To delve deeper into the coating’s corrosion resistance, its electrochemical behavior was meticulously examined and analyzed, and the Bode test was used for analysis [29]. Figure 4 presents the Bode plots of the coating after soaking in 3.5 wt% sodium chloride solution for 7, 14, and 30 days. In the low-frequency range, the modulus value of the coating initially rises and then declines. Notably, the A4C6EP coating exhibits the highest modulus value, approximately 107.8 Ω·cm2, indicating its superior corrosion resistance compared to the A2C8EP, A3C7EP, and A5C5EP coatings. Figure 3b reveals that, although the |Z| value of the A4C6EP coating in the low-frequency region decreases slightly, it remains the largest among the four coatings, aligning with the EIS findings. As can be seen from Figure 3c, the values of A2C8EP, A3C7EP and A5C5EP coatings all decrease in the low frequency region |Z|. However, the A4C6EP coating maintains the highest |Z| value, consistent with Nyquist plot results. These findings collectively confirm that the A4C6EP coating possesses the best corrosion resistance properties.
To investigate the effect of mullite on the corrosion resistance of epoxy resin coatings [19,30], four coatings were immersed in a 3.5% NaCl solution for durations of 7, 14, and 30 days, and Tafel polarization curves were obtained, as depicted in Figure 5, providing insights into the Ecorr and Icorr value. Typically, a lower Ecorr and a smaller Icorr indicate corrosion resistance of the coating. Detailed data are presented in Supplementary Table S2.
Figure 5a reveals that, compared to the other three coatings, the cathode and anode polarization curves of the A4C6EP coating shift towards the lower right corner of the coordinate system. This suggests that the cathode and anode polarization of the A4C6EP coating are the most suppressed, resulting in a more stable electrode surface with potential changes. As indicated in Supplementary Table S2, on the 7th day of immersion, the A4C6EP coating exhibited an increased corrosion potential of −502.31 mV and a decreased corrosion current density of 5.40 × 10−7 A·cm2, both lower than those of the other coatings, thereby demonstrating its excellent corrosion resistance.
Similarly, Figure 5b shows that the A4C6EP coating has the highest Ecorr (−513.98 mV) and the lowest Icorr (5.56 × 10−7 A·cm2) compared to the other three coatings after 14 days of immersion. In Figure 5c, after 30 days of immersion, the A4C6EP coating had an Ecorr of −527.79 mV and an Icorr of 7.99 × 10−7 A·cm2. The cathode and anode polarization curves of the A4C6EP coating continued to shift towards the lower right corner, aligning with the trend observed after 3 and 7 days of immersion, further confirming the excellent corrosion resistance of the A4C6EP coating.
The impedance radius of the prepared A4C6EP coating was compared with that in other literature, and the results are shown in Table 1. The impedance diameter of the hydrophilic coating prepared by us after soaking in salt water for 7 days is greater than that of most epoxy coatings, and even greater than that of some hydrophobic epoxy numerical coatings with graphite added. The optimal value of the hydrophobic coating with graphite added is also close, which proves the excellent corrosion resistance of the hydrophilic epoxy coating prepared.

3.1.4. Salt Spray Test

To directly observe the coating’s corrosion resistance, four kinds of coating scraped on the Q235 steel plate were placed in a 3.5wt% neutral salt spray test chamber to observe the surface phenomenon. After 2000 h in the neutral salt spray test chamber, the images are shown in Figure 6.
After 2000 h in neutral salt spray, large bubbles appear on the surface of the A2C8EP coating (Figure 6a), and the coating showed weak corrosion resistance. Sligh but larger bubbles appear on the surface of the A3C7EP coating (Figure 6b), and the corrosion resistance of the A3C7EP coating is increased compared with that of the A2C8EP coating. Slight tiny bubbles appear on the surface of A5C5EP coating (Figure 6d). Compared with A3C7EP coating, the number and size of bubbles are reduced, and the corrosion resistance is further increased. There are no bubbles on the surface of the A4C6EP coating (Figure 6c). Compared with the A3C7EP coating, the bubbles disappear, which proves that the A4C6EP coating has the most robust corrosion resistance.

3.2. Mechanical Durability Test

In order to fully evaluate the wear resistance of A4C6EP coating, a series of detailed experimental procedures were carried out [31,32,33,34]. First, the coated surface was placed on 1000-mesh sandpaper, an industry-standard method to simulate everyday wear and tear. Then, 500 g was applied to the surface of the coating, and the sandpaper was moved ~3 cm per cycle in the direction shown in Figure 7a to ensure sufficient friction on the surface of the coating per cycle. During the initial phase of the experiment, changes in the contact angle were measured every five friction cycles for evaluation.
All samples were tested for wear resistance, and the change in contact angle is shown in Table S3. The contact angle of the other three coatings is reduced by more than 5° after 100 friction cycles, and the A4C6EP coating is only reduced by 2.3°, showing excellent wear resistance. At the beginning, after five cycles of friction, the contact angle shows a significant decrease, of about 1.5°. When the number of cycles of friction reaches 20 times, the contact angle has a linear rise, which may be because the protective effect of the coating itself creates a short rise in the contact angle. After 100 cycles of friction, the contact angle presents a gentle downward trend, although there is a rebound phenomenon in the middle, but the rebound is gentle, which should be the case after the coating adapts to the friction. After 100 cycles of friction, the contact angle only decreased by 2.33°, and there was no obvious trace on the surface of the coating, which proved the excellent friction resistance of the coating.

3.3. Corrosion Resistance Mechanism of Coating

Figure 8 illustrates the reaction mechanisms of both the hydrophilic corrosion-resistant coating and the pure EP coating. Specifically, Figure 8a depicts the mechanism of the pure EP coating. Water and oxygen molecules from the air penetrate the coating through pores, defects, and cracks in the epoxy resin, making contact with the Q235 steel substrate, which leads to the formation of large bubbles on the steel plate. When mullite and PVB are incorporated (Figure 8b), the finely ball-milled mullite particles fill the pores and cracks of the epoxy resin coating under the adhesive action of PVB. This filling action prevents corrosive particles, such as water and oxygen molecules, from entering the coating and reaching the substrate, thereby prolonging the time before the substrate comes into contact with these corrosive particles and enhancing the coating’s corrosion resistance. Furthermore, due to the adhesive properties of PVB, the mullite particles are securely fixed within the coating, providing a stable structure. After undergoing 100 cycles of friction using 1000-grit sandpaper and a 500 g weight, the contact angle decreases by only 2.333°, demonstrating the coating’s exceptional mechanical wear resistance.

4. Conclusions

We have demonstrated a cost-effective method of applying a robust hydrophilic coating to a steel substrate by scraping a suspension of EP, mullite, and PVB. Mullite particles are filled into the pores of epoxy resin coating under PVB adhesion, obtaining excellent corrosion and wear resistance. According to the electrochemical impedance test, the EIS impedance value obtained by the electrochemical impedance test reached 1.13 × 108 Ω·cm2 at the initial immersion stage. After 60 days of immersion, the electrochemical impedance value of the coating dropped to 5.70 × 107 Ω·cm2. The surface of the coating still has a high impedance value, little change, and stable corrosion resistance. In addition, after the 2000 h salt spray test, the coating has good adhesion, with no bubbling phenomenon on the coating, showing the best anti-corrosion performance. Under 1000-mesh sandpaper 500-g weight pressure, the 100 cyclic contact angles only decreased by 2.3°, showing very high mechanical wear resistance. This provides a new idea for developing hydrophilic anti-corrosion coating and reduces the cost of anti-corrosion coating.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/coatings15010041/s1, Figure S1: SEM image of A5C5EP; Figure S2: After soaking tests in 3.5 wt% NaCl solution for 7 d, the Nyquist plots of A5C5EP, A4.5C5.5EP, and A6C4EP, respectively; Table S1: EIS data of Ethanol-type epoxy resin coating regulated by mullite powder; Table S2: Tafel data of Ethanol-type epoxy resin coating regulated by mullite powder; Table S3: Hydrophobic Angle wear resistance variation diagram.

Author Contributions

Conceptualization, K.L. and Y.Z.; methodology, H.M. and Z.G.; investigation, Z.H. and Y.W.; writing—original draft preparation. All authors have read and agreed to the published version of the manuscript.

Funding

The authors acknowledge that this work has been supported by Nanping City resource chemical industry science and technology innovation joint funding project no. N2021Z003, Fujian Provincial transportation technology project no. LS202304, Wuyi University to introduce talents research start-up funding project no. YJ202309, Innovative training program for college students no. S202210397076 and 202310397026, Fujian Province first-class undergraduate specialty construction no. SJZY2020004, and Fujian Province first-class curriculum construction no. SJYLKC202106.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data are contained within this article and Supplementary Materials.

Acknowledgments

The authors acknowledge that this work has been supported by Young Elite Scientists Sponsorship Program by CAST (No. 2022QNRC001), the National Natural Science Foundation of China, under Grant No. 52102119.

Conflicts of Interest

Authors Huachao Ma and Kuilin Lv were employed by the company China Testing & Certification International Group Co, Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Figure 1. SEM images of various dioxides: A2C8EP coating (a); A3C7EP coating (b); A4C6EP coating (c); A5C5EP coating (d); A2C8EP coating enlarged drawing (e); A3C7EP coating enlarged drawing (f); A4C6EP coating enlarged drawing (g); A5C5EP coating enlarged drawing (h); A2C8EP coating roughness (i), A3C7EP coating roughness (j), A4C6EP coating roughness (k) and A5C5EP coating roughness (l).
Figure 1. SEM images of various dioxides: A2C8EP coating (a); A3C7EP coating (b); A4C6EP coating (c); A5C5EP coating (d); A2C8EP coating enlarged drawing (e); A3C7EP coating enlarged drawing (f); A4C6EP coating enlarged drawing (g); A5C5EP coating enlarged drawing (h); A2C8EP coating roughness (i), A3C7EP coating roughness (j), A4C6EP coating roughness (k) and A5C5EP coating roughness (l).
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Figure 2. FTIR image of A4C6EP and samples (a), XRD image of A4C6EP and samples (b).
Figure 2. FTIR image of A4C6EP and samples (a), XRD image of A4C6EP and samples (b).
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Figure 3. After soaking tests in 3.5 wt% NaCl solution for 7 d (a), 14 d (b) and 30 d (c), the Nyquist plots of A2C8EP, A3C7EP, A4C6EP and A5C5EP, respectively.
Figure 3. After soaking tests in 3.5 wt% NaCl solution for 7 d (a), 14 d (b) and 30 d (c), the Nyquist plots of A2C8EP, A3C7EP, A4C6EP and A5C5EP, respectively.
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Figure 4. After soaking tests in 3.5 wt% NaCl solution for 7 d (a), 14 d (b) and 30 d (c), the Bode plots of A2C8EP, A3C7EP, A4C6EP and A5C5EP, respectively.
Figure 4. After soaking tests in 3.5 wt% NaCl solution for 7 d (a), 14 d (b) and 30 d (c), the Bode plots of A2C8EP, A3C7EP, A4C6EP and A5C5EP, respectively.
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Figure 5. After soaking tests in 3.5 wt% NaCl solution for 7 d (a), 14 d (b) and 30 d (c), the Tafel plots of A2C8EP, A3C7EP, A4C6EP and A5C5EP, respectively.
Figure 5. After soaking tests in 3.5 wt% NaCl solution for 7 d (a), 14 d (b) and 30 d (c), the Tafel plots of A2C8EP, A3C7EP, A4C6EP and A5C5EP, respectively.
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Figure 6. Digital photographs of A2C8EP (a), A3C7EP (b), A4C6EP (c) and A5C5EP (d) after immersion for 2000 h by neutral salt spray test.
Figure 6. Digital photographs of A2C8EP (a), A3C7EP (b), A4C6EP (c) and A5C5EP (d) after immersion for 2000 h by neutral salt spray test.
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Figure 7. Wear resistance of A4C6EP coating. (a) Friction test of sandpaper on the surface of coating; (b) The influence of the number of cycles of friction on the contact angle.
Figure 7. Wear resistance of A4C6EP coating. (a) Friction test of sandpaper on the surface of coating; (b) The influence of the number of cycles of friction on the contact angle.
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Figure 8. Processing image of EP (a) and A4C6EP (b).
Figure 8. Processing image of EP (a) and A4C6EP (b).
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Table 1. Anticorrosion properties of mullite/kaolin reinforced WEP.
Table 1. Anticorrosion properties of mullite/kaolin reinforced WEP.
SamplesImmersion Duration in 3.5% NaCl (Days)Coating
Thickness (μm)
Rc
(Ω cm2)
CPEc (F)Reference
A4C6EP725 ± 26.74 × 1077.78 × 10−11This Work
EG1500SO0.1SN0.9EP30 (min)25 ± 0.54.65 × 1067.54 × 10−810
AO0.3AN0.7EP725 ± 12.42 × 1077.22 × 10−1120
EG5000/C1P0.2EP725 ± 22.58 × 1083.94 × 10−1127
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MDPI and ACS Style

Zhao, Y.; Ma, H.; Gao, Z.; Huang, Z.; Wu, Y.; Lv, K. Enhancement of the Corrosion and Wear Resistance of an Epoxy Coating Using a Combination of Mullite Powder and PVB. Coatings 2025, 15, 41. https://doi.org/10.3390/coatings15010041

AMA Style

Zhao Y, Ma H, Gao Z, Huang Z, Wu Y, Lv K. Enhancement of the Corrosion and Wear Resistance of an Epoxy Coating Using a Combination of Mullite Powder and PVB. Coatings. 2025; 15(1):41. https://doi.org/10.3390/coatings15010041

Chicago/Turabian Style

Zhao, Yan, Huachao Ma, Zhenglu Gao, Ziyan Huang, Yuanyuan Wu, and Kuilin Lv. 2025. "Enhancement of the Corrosion and Wear Resistance of an Epoxy Coating Using a Combination of Mullite Powder and PVB" Coatings 15, no. 1: 41. https://doi.org/10.3390/coatings15010041

APA Style

Zhao, Y., Ma, H., Gao, Z., Huang, Z., Wu, Y., & Lv, K. (2025). Enhancement of the Corrosion and Wear Resistance of an Epoxy Coating Using a Combination of Mullite Powder and PVB. Coatings, 15(1), 41. https://doi.org/10.3390/coatings15010041

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