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Article

Study on the Corrosion Resistance and Application of Nano-Y2O3/Al2O3-Modified Anchor Rod Coatings Based on Electrodeposition Method

by
Xiujuan Feng
1,2,3,* and
Falong Qiu
1
1
School of Mines, China University of Mining and Technology, Xuzhou 221116, China
2
National Key Laboratory of Deep Coal Safety Mining and Environmental Protection, Anhui University of Science and Technology, Huainan 232001, China
3
School of Carbon Neutrality Science and Engineering, Anhui University of Science & Technology, Hefei 231131, China
*
Author to whom correspondence should be addressed.
Electrochem 2025, 6(2), 14; https://doi.org/10.3390/electrochem6020014
Submission received: 24 February 2025 / Revised: 10 April 2025 / Accepted: 11 April 2025 / Published: 17 April 2025
(This article belongs to the Special Issue Feature Papers in Electrochemistry)
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Abstract

:
In the past ten years, many coal mines have encountered the problem of a premature failure of anchor rod materials. Through field investigation and laboratory research, it was found that the premature failure of these bolt materials is mostly caused by mine water corrosion. In this paper, a Zn-Y2O3-Al2O3 composite coating was prepared by an electrodeposition method for the corrosion protection of underground anchors. Through the single-factor experiment method, the co-deposition process of Zn2+ nano-Y2O3 and nano-Al2O3 particles was studied. Microhardness was used as the index to determine the optimum preparation process for the composite coatings. Combined with FSEM and XRD tests, the results showed that the synergistic effect of nano-Y2O3 and nano-Al2O3 particles made the coating grain refined and reduced the coating defects. The hardness of the coating increased from 98.7 Hv to 347.9 Hv, and the hardness and wear resistance of the coating were improved. The hydrophobicity of the Zn-Y2O3-Al2O3 composite coating was improved, and its static contact angle was 93.28°. The corrosion resistance of the composite coating was studied through electrochemical impedance spectroscopy, the Tafel curve, corrosion morphology, and weight loss. Under the synergistic effect of nano-Y2O3 and nano-Al2O3 particles, the self-corrosion current density decreased from 4.21 × 10−4 A/cm2 to 1.06 × 10−5 A/cm2, which confirmed that the Zn-Y2O3-Al2O3 composite coating had better corrosion resistance and durability. After soaking in mine water for 63 days, the Zn-Y2O3-Al2O3 composite coating had no obvious shedding on the surface and was well preserved. The practical application results show that it has excellent corrosion resistance and durability. The Zn-Y2O3-Al2O3 nano-composite coating material has significant potential advantages in the field of corrosion resistance of underground anchor rods.

1. Introduction

In the process of coal mining, the durability and safety of anchor rods are threatened by corrosion. As a key part of the underground operation, the stability and safety of roadways are very important to production [1,2,3,4]. Anchorage technology is considered to be a safe and efficient support method in deep resource mining. However, in the past ten years, many coal mines have encountered the problem of early damage to bolt materials. Field investigations and laboratory research have found that corrosion is the main reason for the early failure of anchor rod materials. In the complex environment under a mine, anchor rod material is affected by factors such as mine water, a high temperature, the mine atmosphere, and surrounding rock clay for a long time [5,6,7]. Especially in deep mines, the corrosion problem is more serious, which significantly increases the risk of material failure, and then increases the safety hazards of major disasters such as roadway surrounding rock instability, rib spalling, and rock bursts [8,9,10,11]. Therefore, it is particularly important to study the corrosion environment and anti-corrosion technology of mine anchor rod materials.
Many domestic scholars have carried out extensive research on the corrosion characteristics of anchor rods and found that temperature, pH value, oxygen content, corrosion ions, etc., are the main factors causing anchor rod corrosion [12,13,14,15,16]. At present, isolation and insulation technology are widely used as anti-corrosion measures for anchor rods at home and abroad. Common isolation methods include anchor rod coating resin, galvanized treatment, injection bag protection, and casing isolation. According to the type of anti-corrosion measures taken, these methods can be divided into different levels of protection strategies such as single-layer anti-corrosion, double-layer anti-corrosion, and multi-layer anti-corrosion [17,18,19].
As an efficient material surface treatment technology, the main anti-corrosion mechanism of coating protection is to isolate the bolt from the corrosive environment of the coal mine, which is an important means to prevent metal corrosion [20,21]. Pure Zn coating has the advantages of corrosion resistance, a reasonable price, and easy production. For decades, zinc coating has been used for the protection of underground anchors. The common preparation methods of zinc coating mainly include electrodeposition or hot-dip plating [22,23]. Compared with the hot-dip method, the Zn coating obtained through the electrodeposition method is thinner, and the surface finish is higher. The electrodeposition method can prepare a non-porous Zn coating by adjusting the electrodeposition parameters, thereby obtaining higher corrosion resistance and improved mechanical properties [24,25]. However, in harsh environments, pure Zn coatings have the disadvantages of easy shedding, corrosion resistance, and low hardness. Therefore, to improve the performance of zinc coating, it is necessary to modify it.
Composite coatings have gradually attracted widespread attention in the industry due to their excellent wear resistance, hardness, and corrosion resistance [26,27]. Nano-Al2O3 and nano-Y2O3 have the characteristics of high hardness, good wear resistance, good corrosion resistance, and high-temperature stability. They are often used in ceramic materials, refractory materials, coating materials, and other fields [28,29,30]. Kallappa et al. [31] prepared Zn-CeO2-doped ZnO composite coatings on the surface of low carbon steel by electrodeposition. The experimental results show that CeO2-doped ZnO nanoparticles significantly improve the corrosion resistance of zinc coatings. Malatji et al. [32] composited nano-Al2O3/Cr2O3 into a zinc-rich plating layer, in the preparation of Zn-Al2O3-Cr2O3 ternary composite plating. The results showed that the addition of nanoparticles refined the shape of the coating and changed the crystal orientation of the coating. The wear resistance and thermal stability of nano-composite coatings have been improved. For Zn-5g/L Al2O3-5g/L Cr2O3, the microhardness of the composite coating reached 275 Hv. Kanyane et al. [33] used electrodeposition technology to plate thin films with different concentrations of yttrium oxide on the surface of mild steel. Compared with the received sample, the microhardness of the coating was significantly increased, and the microhardness of Zn-Ni-10CeO2-5Y2O3 exceeded 100 HV. Many studies have found that the microhardness and corrosion resistance of Zn-based nano-composite coatings are relatively weak in the existing studies, and their application in complex underground corrosion environments requires further enhancement of the hardness and corrosion resistance of the coatings.
In this paper, the nano-composite coating is applied to the protection of the anchor rod, which has low hardness and a short protection time. At present, the method for preparing composite coatings by incorporating nanometer Y2O3 and Al2O3 particles into Zn matrix has not been published. The application of nano-composite coating to the protection of anchor rod in mines is also less studied. The nano-composite coating was prepared by electrodeposition, and the optimal preparation process was obtained. The differences in mechanical properties and corrosion resistance between nano-composite coatings and traditional zinc coatings are compared and analyzed.

2. Materials and Methods

2.1. Preparation

In this experiment, the coating was prepared by DC electrodeposition. The Q235 steel plate (10 × 10 × 1 mm3) was used as the cathode, and the Zn plate (15 × 20 × 1 mm3) with a purity of 99.99% was used as the anode. The composition and electrodeposition parameters of the electrolyte are shown in Table 1. The reagents used in the experiment were all analytically pure. Nanometer Y2O3 particles (average diameter 30 nm) and nanometer α-Al2O3 particles (average diameter 50 nm) were provided by Aladdin Reagent Co., Ltd. (Shanghai, China).
Figure 1 is a schematic diagram of the experimental device. Before the experiment, the Q235 steel sheet matrix needs to be pretreated. Firstly, the steel sheet was polished step by step with 400 mesh, 800 mesh, 1200 mesh, 1600 mesh, 2000 mesh, and 2500 mesh SiC sandpaper to remove the impurities and oxide layer on the surface of the steel sheet. This was then polished with W2.5 polishing paste to obtain a smooth and flat steel sheet. The polished steel sheet was placed in a NaOH/Na2CO3 solution for alkaline oil treatment and then activated in a 10% HNO3 solution for 30 s to increase its surface activity. The activated steel sheet was taken out, rinsed with deionized water, dried, and placed in a sealed bag for later use. An electronic balance was used to accurately weigh the required amount of drugs. After dissolving with deionized water, the volume was adjusted to the required amount by a volumetric flask. Finally, the pH was adjusted by an HCl/NaOH (1 mol/L) solution. When preparing the composite coating, due to the agglomeration of nanoparticles, the nanoparticles needed to be placed in the configured electrolyte in advance and stirred at a speed of 800 rpm for 18 h to ensure that the nanoparticles were uniformly dispersed into the electrolyte before the electrodeposition experiment. After the experiment, the sample was taken out in time, washed with deionized water, and finally dried and sealed.

2.2. Characterization

The surface and cross-section morphology of the coating were analyzed and observed by the Quatto S-type field emission scanning electron microscope of the Czech FEI Company (Hillsboro, OR, USA). The composition and content of each element on the surface and cross-section of the coating were analyzed by the supporting EDS energy spectrometer. The surface morphology of the coating after wear and corrosion was observed by the MSD460 polarizing microscope (Murdizer (Dongguan) Technology Co., Ltd., Dongguan, China). The coating was tested by the D8 Advance X-ray diffractometer of German Bruce AXS Co., Ltd. (Karlsruhe, Germany), and the test data were analyzed and processed by MDI jade. The measurement parameters of the instrument are Cu target (Kα radiation), the scanning range is 10–90°, and the scanning speed is 5°/min.

2.3. Corrosion Resistance Test

2.3.1. Electrochemical Test

The polarization curve and AC impedance curve of the coating were tested by the Admiral electrochemical workstation. The three-electrode system was used in the experiment, the coated sample was used as the working electrode, the Ag/AgCl electrode was used as the reference electrode, and a platinum electrode with an area of 1 cm2 was used as the counter electrode. The test environment was room temperature, and the test was carried out in a 3.5 wt. %NaCl solution. The scanning range of the voltage was −1.5~1.5 V and the scanning rate was 10 mv/s when the polarization curve was measured. The test results were analyzed and processed by the Tafel extrapolation method, and the corrosion potential (Ecoor) and self-corrosion current density (Icoor) were obtained. When measuring the AC impedance curve, the scanning frequency range was 0.1~100,000 Hz, and the AC impedance data obtained by the ZSimDemo 3.30d software test were fitted.

2.3.2. Immersion Accelerated Corrosion Experiment

The corrosion resistance of the coating in actual mine water was studied by the static immersion weight loss method. Before the experiment, electronic balance was used to accurately measure the initial quality of the experimental samples, and then the experimental samples were placed in the mine water solution. The experiment lasted 9 weeks, and samples were taken every other week. After cleaning and drying, the weight was measured, and the difference between the experimental samples after each sampling and the initial quality before the experiment was calculated to obtain the weight loss or weight gain of the experimental samples. The surface morphology was photographed and recorded every 2 weeks.

2.4. Microhardness Test

The hardness of the coatings was tested by the VH1102 microhardness tester (ITW Test & Measurement (Shanghai) Co., Ltd., Shanghai, China). The test environment was room temperature, the loading load was 50 g, and the loading time was 15 s. Five different regions were selected for each coating sample for testing, and the test was repeated five times. After removing the maximum and minimum values, the remaining three sets of data were used. The average value is the microhardness value of the coating sample.

2.5. Contact Angle Text

The static contact angle of the coating was measured by the JY-PHB contact angle tester (Changzhou Sanfeng Instrument Co., Ltd., Changzhou, China). The experiment was carried out at room temperature, and the contact angle was tested on the surface of the coating with 3 μL of deionized water droplets. Five different regions were selected for each coating sample, and the test was repeated five times. The average value was calculated as the static contact angle of the coating sample.

2.6. Friction Performance Test

The wear resistance of the coatings was tested by the Bruker (CETR) UMT-2 friction and wear tester (Bruker Corporation, Hillsboro, OR, USA). The test environment was room temperature, the GCr15 steel ball with a diameter of 4 mm was used, the friction load was 5 N, the friction rate was 5 mm/s, the friction stroke was 2 mm, and the friction time was 15 min.

3. Results and Discussion

3.1. Preparation of Coating

In the underground environment of coal mines, anchor bolts are exposed to high humidity, as well as acidic or alkaline corrosive media for a long time, which is prone to corrosion, resulting in decreased strength and material failures. The use of a high hardness coating to protect the bolt can effectively resist the mechanical wear and impact of hard objects such as underground rock and coal, prevent the coating from being damaged, and ensuring its integrity. At the same time, it can better block the penetration of a corrosive medium, prolong the service life of an anchor rod, and ensure the safety and stability of an underground support system.
Figure 2a shows the effect of current density on the hardness of a pure Zn coating. It can be seen from the figure that with the increase in current density, the hardness of the Zn coating increases. When the current density is 3 A/dm2, the hardness reaches a maximum of 98.7 Hv and then decreases with the increase in current density. This is because when the current density is too small, the nucleation rate of Zn on the cathode surface decreases, increasing the grain size, and thereby reducing the hardness of the coating. When the current density is too large, more bubbles are observed on the cathode surface, which leads to holes and cracks in the coating, and the uniformity of the coating surface decreases, thereby reducing the hardness of the coating.
Figure 2b shows the effect of the nano-Y2O3 addition on the hardness of the Zn-Y2O3 composite coating. It can be seen from the figure analysis that nano-Y2O3 can significantly improve the hardness of the coating. The hardness of the coating increases with the increase in nano-Y2O3 concentration. When the concentration of nano-Y2O3 is 5 g/L, the hardness of the coating reaches a maximum of 202.4 Hv, which is 103.7 Hv higher than that of the pure Zn coating (98.7 Hv), and then decreases with the increase in nano-Y2O3 concentration. This is due to the nano-Y2O3 addition being uniformly dispersed into the coating by the composite electrodeposition method, and the nature of its high hardness gives the coating. By reducing the ‘tip discharge’ effect of the coating, it plays a role in dispersion strengthening, destroys the continuous growth of the coating, and then refines the grains, making the coating surface more dense and improving the hardness of the coating. When the concentration of nano-Y2O3 added is too large, the nanoparticles are prone to agglomeration, so that the nano-Y2O3 particles cannot be better co-deposited with the metal Zn, thereby reducing the hardness of the coating.
Figure 2c shows the effect of current density on the hardness of the Zn-Y2O3 composite coating. It can be seen from the figure analysis that current density is an important factor affecting the hardness of the coating. The hardness of the coating increases with the increase in the current density. When the current density is 4 A/dm2, the hardness of the coating reaches a maximum of 230.2 Hv, and then decreases with the increase in the current density. The magnitude of the current density determines the strength of the electric field force, which in turn affects the speed of the Zn2+ transported to the cathode surface and the reduction rate of Zn2+. When the current density is small, the Zn2+ in the electrolyte cannot be transported to the cathode surface in time, and the reduction rate of Zn2+ decreases, thereby reducing its deposition rate. Even if there are a large number of active sites formed by the nano-Y2O3 particles on the cathode surface, the nano-Y2O3 particles cannot be coated in time, so some nano-Y2O3 particles return to the electrolyte. The content of the nano-Y2O3 co-deposited with metal Zn in the coating is less, resulting in a decrease in the hardness of the coating.
Figure 2d shows the effect of stirring speed on the hardness of the Zn-Y2O3 composite coating. It can be seen from the figure that the hardness of the coating increases with the increase in the stirring speed. When the stirring speed is 300 rpm, the hardness of the coating decreases with the increase in the stirring speed. The stirring speed determines the dispersion effect of the nanoparticles in the electrolyte during the deposition process. When the stirring speed is 300 rpm, the maximum hardness value of the coating is 230.2 Hv. This is because the nano-Y2O3 particles are uniformly dispersed in the electrolyte at this speed, and the agglomeration phenomenon is effectively improved. Then, the nano-Y2O3 particles are uniformly dispersed in the composite coating to improve the hardness of the coating. In addition, a suitable stirring speed can effectively remove the hydrogen generated during the deposition process, and avoid the results of coating holes and unevenness caused by hydrogen generation.
According to the analysis results of Figure 2b–d, the optimum process conditions for the Zn-Y2O3 composite coating were determined as follows: a nano-Y2O3 concentration of 5 g/L, a current density of 4 A/dm2, and a stirring speed of 300 rpm.
Figure 2e shows the effect of the nano-Al2O3 addition on the hardness of the Zn-Y2O3-Al2O3 composite coating. It can be seen from the figure that the hardness of the coating increases with the increase in nano-Al2O3 concentration, and then decreases with the increase in nano-Al2O3 concentration. When the concentration of nano-Al2O3 is 5 g/L, the hardness of the coating reaches a maximum of 288.8 Hv, which is 190.7 Hv higher than that of the pure Zn coating (98.7 Hv) and 58.6 Hv higher than that of the Zn-Y2O3 composite coating (230.2 Hv). This is due to the uniform dispersion of nano-Al2O3 and nano-Y2O3 particles into the coating by composite electrodeposition, and their high hardnesses give the coating. When the concentration of nano-Al2O3 added is too large, the nanoparticles are prone to agglomeration, so that the nano-Al2O3 and nano-Y2O3 particles cannot better co-deposit with metal Zn, thereby reducing the hardness of the coating.
Figure 2f shows the effect of current density on the hardness of the Zn-Y2O3-Al2O3 composite coating. It can be seen from the figure analysis that when the current density is 4 A/dm2, the hardness of the composite coating reaches the maximum. When the current density is too large, the deposition rate of metal Zn2+ is much larger than that of nano-Al2O3 and nano-Y2O3 particles due to the strong electric field force. The content of the nano-Al2O3 and nano-Y2O3 particles in the coating is less, resulting in a decrease in hardness. At the same time, the rapid reduction of Zn2+ leads to an increase in the number of atoms deposited on the cathode surface and an increase in the thickness of the coating, which may increase the stress of the coating, resulting in a cracking of the coating and a decrease in the hardness of the coating.
Figure 2g shows the effect of stirring speed on the hardness of the Zn-Y2O3-Al2O3 composite coating. It can be seen from the figure analysis that the hardness of the coating increases with the increase in the stirring speed. When the stirring speed is 400 rpm, the maximum hardness of the coating is 347.9 Hv, and then the hardness of the coating decreases with the increase in the stirring speed. When the stirring speed is low, the dispersion effect of the nano-Al2O3 and nano-Y2O3 particles in the electrolyte is poor, and these particles may even be partially deposited at the bottom. The nano-Al2O3 and nano-Y2O3 particles cannot be transported to the cathode surface, resulting in a decrease in the number of active sites formed and the number of nano-Al2O3 and nano-Y2O3 particles co-deposited with metal Zn, reducing the hardness of the coating. Under the condition of a high stirring speed, the collision between nanoparticles will increase, which will lead to the agglomeration of nanoparticles, so that they cannot better co-deposit with metal Zn, thus reducing the hardness of the coating.
According to the analysis results of Figure 2e–g, the optimum process conditions for the Zn-Y2O3-Al2O3 composite coating were determined as follows: the concentration of nano-Al2O3 was 5 g/L, the current density was 4 A/dm2, and the stirring speed was 400 rpm.

3.2. X-Ray Diffraction (XRD)

Figure 3 shows the X-ray diffraction patterns of the Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings under the optimum preparation conditions. It can be seen from the figure analysis that the characteristic diffraction peaks of the Fe matrix did not appear on the three curves, indicating that the three coatings completely coated the matrix. It can be seen that there are five main diffraction peaks in the diffraction pattern of the Zn coating [34], which correspond to the diffraction peaks of crystal plane (002) at 2θ = 36.36°, crystal plane (101) at 2θ = 43.29°, crystal plane (102) at 2θ = 54.38°, crystal plane (110) at 2θ = 70.12°, and crystal plane (112) at 2θ = 82.14°. The X-ray diffraction patterns of the Zn-Y2O3 and Zn-Y2O3-Al2O3 composite coatings showed the above five characteristic peaks, but the diffraction peak intensity changed significantly, especially the two diffraction peaks of crystal plane (002) and crystal plane (101). With the addition of nanoparticles, the diffraction peak intensity of crystal plane (002) was significantly reduced, while the diffraction peak of crystal plane (101) was significantly enhanced, indicating that the addition of nanoparticles leads to a change in the preferential growth orientation so that the coating changes from crystal plane (002) to crystal plane (101). The XRD Rietveld refinement results for the Zn-Y₂O₃ and Zn-Y₂O₃-Al2O3 composite coatings are shown in Figure 3b,c. The results reveal that nanosized Y₂O₃ and Al2O3 particles exist in the composite coatings. However, due to their low content, the corresponding diffraction peaks are not prominent in the XRD patterns. It can be seen from the strong diffraction peak of crystal plane (101) that the diffraction peak of the composite coating is wider. This is due to the addition of nanoparticles, and the dispersion strengthening effect leads to a denser coating and grain refinement [35].

3.3. Surface Morphology of Composite Coatings

Figure 4a–c shows the SEM images of the Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings, respectively. It can be seen from the figure analysis that the pure Zn coating sample exhibits a flaky crystal structure, and the Zn-Y2O3 and Zn-Y2O3-Al2O3 composite coatings also exhibit the same structure. The pure zinc coating exhibits coarse grains and defects (micropores, uneven) on the surface. When the coating is exposed to harsh environments, these defects may become a weak link in the decline of coating quality. However, compared with the pure Zn coating, the Zn-Y2O3, and Zn-Y2O3-Al2O3 composite coatings have denser microstructures and smaller grain sizes. The microstructure refinement of the composite coating is attributed to the uniform dispersion and encapsulation of nanoparticles in the Zn matrix. The incorporation of nanoparticles in the metal matrix promotes an increase in the number of nucleation sites and hinders crystal growth, resulting in small-sized grains [36,37]. The refinement of grain size and a dense microstructure are important reasons for improving the hardness and corrosion resistance of a coating [38].
Figure 5 shows the enlarged FSEM and EDS spectra of the Zn-Y2O3 and Zn-Y2O3-Al2O3 composite coatings. It can be seen from the figure analysis that when nano-Y2O3 and nano-Al2O3 particles are mixed at the same time, the dispersion effect of the nanoparticles in the matrix metal is better, and the agglomeration of nanoparticles is effectively improved. There are peaks for the Zn, Y, and O elements in the EDS energy spectrum of the Zn-Y2O3 composite coating, indicating that the nano-Y2O3 particles were successfully co-deposited with the Zn matrix. At the same time, there are peaks for the Zn, Y, Al, and O elements in the EDS energy spectrum of the Zn-Y2O3-Al2O3 composite coating, indicating that nano-Y2O3 and nano-Al2O3 particles were successfully co-deposited with the Zn matrix.

3.4. Wear Resistance Test

Improving the wear resistance of the coating helps it to resist mechanical wear and the impact of hard objects such as underground rocks and coal blocks, preventing coating damage, ensuring its integrity, and prolonging the service life of the coating. Figure 6 shows the friction coefficients of the Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings. It can be seen from the figure analysis that the friction coefficients of the Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings increase rapidly within 100 s and then tend to be stable. The friction coefficient of the Zn coating tends to be stable at about 0.81, the friction coefficient of the Zn-Y2O3 composite coating tends to be stable at about 0.70, and the friction coefficient of the Zn-Y2O3-Al2O3 composite coating tends to be stable at about 0.58. It can be seen that the addition of nano-Al2O3 and nano-Y2O3 particles improves the wear resistance of the coating. The average friction coefficient of the Zn-Y2O3-Al2O3 composite coating, prepared by adding the second reinforcing phase of nano-Al2O3, is 17.12% and 13.6% lower than that of the Zn coating and the Zn-Y2O3 composite coating, respectively, and its wear resistance is more excellent. This is due to the high hardness of the nano-Al2O3 and nano-Y2O3 particles. At the same time, the nano-Al2O3 and nano-Y2O3 particles are uniformly dispersed in the coating, which makes the coating more dense and the cracks are reduced, thereby enhancing the wear resistance of the coating.

3.5. Contact Angle Text

The corrosion of an anchor rod is mostly caused by the erosion of mine water, so increasing the hydrophobicity of the anchor rod surface can reduce the contact time and area between an anchor rod and a corrosive medium so as to improve its service life. Figure 7 shows the static contact angles of the Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings. It can be seen from the figure analysis that the incorporation of nano-Y2O3 and nano-Al2O3 particles will lead to a difference in the hydrophobic properties of the coating [39]. The static contact angle of the pure Zn coating is 52.9°, the static contact angle of the Zn-Y2O3 composite coating is 80.13°, and the static contact angle of the Zn-Y2O3-Al2O3 composite coating is 93.38°. The composite coating prepared by adding nano-Y2O3 and nano-Al2O3 particles has the best hydrophobic performance, which is consistent with its corrosion resistance test results. The surface of the composite coating can trap a large amount of air inside the material, which makes it more difficult for the coating surface to contact with the corrosive medium, thereby prolonging the contact time. When the coating is immersed in the corrosive medium, these trapped gases form a protective gas film between the corrosive medium and the metal surface, which enhances the corrosion resistance of the coating in a corrosive environment [40].

3.6. Electrochemical Test

As a barrier to protect the anchor rod, the corrosion resistance of the coating itself is very important. When the corrosive medium breaks through the coating barrier, it will affect the anchor rod. The corrosion behavior of the Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings was studied by polarization curves. Figure 8a shows the polarization curves of the Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings in a 3.5 wt% NaCl solution. The self-corrosion current (Icoor) and corrosion voltage (Ecoor) fitted by the Tafel extrapolation method are shown in Figure 8b. In general, the higher the self-corrosion potential of the coating, the lower the self-corrosion current density, indicating that a lower corrosion tendency of the coating [41]. It can be seen from Figure 8b that the corrosion potential of the composite coating is higher than that of the pure zinc coating, indicating that the addition of nano-Y2O3 and nano-Al2O3 particles can effectively improve the corrosion resistance of the zinc coating. When nano-Y2O3 and nano-Al2O3 particles are simultaneously incorporated, the corrosion potential of the composite coating is the largest (−1.045 V). At the same time, the self-corrosion current density of the Zn-Y2O3-Al2O3 nano-composite coating (Icoor = 1.06 × 10−5 A/cm2) was significantly lower than that of the other coatings. From the perspective of corrosion kinetics, the corrosion rate of the Zn-Y2O3-Al2O3 composite coating is slower than that of the pure zinc coating.
The AC impedance test is an important method to characterize the corrosion resistance of a coating [42]. In the AC impedance diagram, the curve is a semi-circular arc in the high-frequency region. The larger the arc radius, the greater the impedance value of the coating and the better the corrosion resistance [43]. The curve deviates from the traditional semi-circular arc trajectory in the middle- and low-frequency regions. This phenomenon is called the dispersion effect. To further analyze the AC impedance diagram, the equivalent circuit model shown in Figure 9b is used to simulate the interface between the coating and the solution. In the equivalent circuit, Rs represents the resistance of the electrolyte, which is the resistance of the current from the working electrode to the reference electrode path, CPE is the constant phase angle element, Rct is the charge transfer resistance, and Wo represents the Warburg impedance. Among them, the charge transfer resistance is an important parameter to evaluate the corrosion resistance of the coating. The larger the charge transfer resistance, the better the corrosion resistance of the coating [44].
An AC impedance test of the Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings prepared under the optimal preparation conditions was carried out, and their corrosion resistance in a 3.5 wt% NaCl solution was further tested. Figure 8a is the Nyquist diagram of the different composite coatings obtained by the EIS test. From the diagram analysis, it can be seen that the arc radius of the Zn-Y2O3-Al2O3 composite coating in the high-frequency region is significantly larger than that of the Zn and Zn-Y2O3 coatings. This shows that the corrosion resistance of the composite coating is the best under the synergistic effect of nano-Y2O3 and nano-Al2O3 particles. The fitting results of the equivalent circuit are shown in Table 2. The charge transfer resistances of the Zn-Y2O3 and Zn-Y2O3-Al2O3 composite coatings are higher than that of the pure Zn coating (322.1 Ω cm2). Among them, the charge transfer resistance of the Zn-Y2O3-Al2O3 composite coating is the largest, which is 5947 Ω cm2, and it has excellent corrosion resistance.

3.7. Immersion Accelerated Corrosion Experiment

In order to further explore the corrosion resistance of the composite coating in an actual coal mine environment, an accelerated corrosion experiment of mine water immersion was carried out. The mine water used in the experiment was from the underground mining area of a mine in Lvliang City, Shanxi Province. The quality of the mine water is shown in Table 3.
The pH value of the mine water was 7.4, which is weakly alkaline. It can be seen from Table 3 that the mine water was rich in cations and anions, which improves the conductivity of the water and accelerates the corrosion process of the bolt. In addition, the mine water also contained a large number of corrosive ions, such as SO42− and Cl−, which can destroy the oxide layer on the surface of metal, promote the local anodic dissolution of metal, and further aggravate the corrosion of a bolt.
Figure 10 is the mass loss rate of the Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings immersed in the actual mine water environment for 7d, 14d, 21d, 28d, 35d, 42d, 49d, 56d, and 63d, respectively. It can be seen from the graph analysis that the mass loss of the three coatings increases with the increase in soaking time. After soaking for 63 days, the mass loss of the Zn-Y2O3-Al2O3 composite coating is the least, which is 11.2%, the mass loss of the pure Zn coating is the largest, which is 58.78%, and the mass loss of the Zn-Y2O3 composite coating is 46.19%. In addition to the corrosive ions SO42− and Cl−, the actual mine water also contained other metal ions. Their presence enhances the conductivity of the solution and promotes electrochemical corrosion.
The surface morphology changes of the three coatings after soaking for 7d, 21d, 35d, 49d, and 63d were recorded, respectively. The results are shown in Figure 11. It can be seen from the figure analysis that after 7 days of immersion, the surface of the three coatings showed different degrees of corrosion, and the surface of the Zn-Y2O3-Al2O3 composite coating was better than that of the Zn and Zn-Y2O3 coatings. After 35 days of immersion, the Zn and Zn-Y2O3 coatings fell off, and the matrix metal in some areas of the surface was bare, while the Zn-Y2O3-Al2O3 composite coating was preserved more completely. After 63 days of immersion, the Zn and Zn-Y2O3 coatings fell off in a large area, while the Zn-Y2O3-Al2O3 composite coating fell off, but the matrix metal was still completely covered and preserved. Therefore, in mine water, the corrosion resistance and durability of Zn-Y2O3-Al2O3 composite coatings are better than those of Zn and Zn-Y2O3 coatings.

4. Conclusions

In this study, aiming to address the problem of bolt corrosion in the process of coal mine production, the composite coating was successfully prepared by electrodeposition. The optimum preparation process of Zn-Y2O3 and Zn-Y2O3-Al2O3 composite coatings was determined by a single-factor experiment, and the surface morphology, phase composition, mechanical properties, and corrosion resistance of the composite coatings were investigated. The experimental results show that the addition of nano-Y2O3 and Al2O3 particles leads to a change in preferred orientation, increases the number of nucleation sites on the surface of the coating, prevents the growth of crystals, makes the surface of the coating denser, and reduces the formation of pores and cracks during the deposition process, thus improving the hardness and wear resistance of the composite coating. The excellent corrosion resistance of the Zn-Y2O3-Al2O3 composite coating was confirmed by electrochemical impedance spectroscopy, a Tafel analysis of the polarization curves, the static contact angle, the corrosion weight loss, and the morphology analysis. This is mainly due to the inert physical barrier constructed by the nanoparticles on the coating surface. The barrier effectively prevents the generation and expansion of corrosion defects in the coating, reduces the occurrence of pitting and localized corrosion, and significantly reduces the contact time and contact area between the coating and the corrosive medium, thus effectively isolating the contact between the corrosive medium and the steel plate. The Zn-Y2O3-Al2O3 nano-composite coating material has significant potential advantages in the field of corrosion resistance of underground anchor rods.

Author Contributions

X.F.: Conceptualization; Data curation; Funding acquisition; Methodology; Investigation; Project administration; Resources; Supervision; Writing—review and editing. F.Q.: Data curation; Formal analysis; Investigation; Methodology; Validation; Visualization; Writing—original draft. All authors have read and agreed to the published version of the manuscript.

Funding

This study was supported by the National Key R&D Program of China (Grant No. 2021YFC2902100), the Postgraduate Research & Practice Innovation Program of the Jiangsu province (Grant No. KYCX23_2810), and the Graduate Innovation Program of China University of Mining and Technology (Grant No. 2023WLJCRCZL039).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

All data are included in the article.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Abbreviations

The following abbreviations are used in this manuscript:
FSEMField Emission Scanning Electron Microscope
EISElectrochemical impedance spectroscopy

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Electrochem 06 00014 g001
Figure 1. Diagram of the experimental device.
Figure 1. Diagram of the experimental device.
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Figure 2. Single factor experimental results of Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings. (a) The effect of current density on the hardness of pure Zn coating. (b) The effect of nano-Y2O3 addition on the hardness of Zn-Y2O3 composite coating. (c) The effect of current density on the hardness of Zn-Y2O3 composite coating. (d) The effect of stirring speed on the hardness of Zn-Y2O3 composite coating. (e) The effect of nano-Al2O3 addition on the hardness of Zn-Y2O3-Al2O3 composite coating. (f) The effect of current density on the hardness of Zn-Y2O3-Al2O3 composite coating. (g) The effect of stirring speed on the hardness of Zn-Y2O3-Al2O3 composite coating.
Figure 2. Single factor experimental results of Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings. (a) The effect of current density on the hardness of pure Zn coating. (b) The effect of nano-Y2O3 addition on the hardness of Zn-Y2O3 composite coating. (c) The effect of current density on the hardness of Zn-Y2O3 composite coating. (d) The effect of stirring speed on the hardness of Zn-Y2O3 composite coating. (e) The effect of nano-Al2O3 addition on the hardness of Zn-Y2O3-Al2O3 composite coating. (f) The effect of current density on the hardness of Zn-Y2O3-Al2O3 composite coating. (g) The effect of stirring speed on the hardness of Zn-Y2O3-Al2O3 composite coating.
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Figure 3. (a) X-ray diffraction patterns of Zn coating; (b) X-ray diffraction patterns of Zn-Y2O3 coating; and (c) X-ray diffraction patterns of Zn-Y2O3-Al2O3 coatings.
Figure 3. (a) X-ray diffraction patterns of Zn coating; (b) X-ray diffraction patterns of Zn-Y2O3 coating; and (c) X-ray diffraction patterns of Zn-Y2O3-Al2O3 coatings.
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Figure 4. (a) FSEM images of Zn coating surface; (b) FSEM images of Zn-Y2O3 composite coating surface; and (c) FSEM images of Zn-Y2O3-Al2O3 composite coating surface.
Figure 4. (a) FSEM images of Zn coating surface; (b) FSEM images of Zn-Y2O3 composite coating surface; and (c) FSEM images of Zn-Y2O3-Al2O3 composite coating surface.
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Figure 5. (a) FSEM and EDS spectra of Zn-Y2O3 composite coating surface; (b) FSEM and EDS spectra of Zn-Y2O3-Al2O3 composite coating surface.
Figure 5. (a) FSEM and EDS spectra of Zn-Y2O3 composite coating surface; (b) FSEM and EDS spectra of Zn-Y2O3-Al2O3 composite coating surface.
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Figure 6. The friction coefficient of Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings.
Figure 6. The friction coefficient of Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings.
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Figure 7. The static contact angles of Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings were measured.
Figure 7. The static contact angles of Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings were measured.
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Figure 8. (a) The polarization curves of Zn, Zn-Y2O3, and Zn−Y2O3−Al2O3 coatings; (b) Self−corrosion current density and self-corrosion voltage obtained by Tafel fitting.
Figure 8. (a) The polarization curves of Zn, Zn-Y2O3, and Zn−Y2O3−Al2O3 coatings; (b) Self−corrosion current density and self-corrosion voltage obtained by Tafel fitting.
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Figure 9. (a) Nyquist plots of Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings; (b) Equivalent circuit model diagram.
Figure 9. (a) Nyquist plots of Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings; (b) Equivalent circuit model diagram.
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Figure 10. Mass loss rates of Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings immersed in mine water.
Figure 10. Mass loss rates of Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings immersed in mine water.
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Figure 11. Morphology changes of Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings immersed in mine water.
Figure 11. Morphology changes of Zn, Zn-Y2O3, and Zn-Y2O3-Al2O3 coatings immersed in mine water.
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Table 1. Bath composition and operating conditions.
Table 1. Bath composition and operating conditions.
CompositionConcentration (g/L)Parameters
ZnCl2150 (±0.01)Temperature (°C)25 (±2)
KCl50 (±0.01)pH3.8 (±0.1)
H3BO330 (±0.01)Plating time (min)45
Y2O30–15 (±0.01)
Al2O30–15 (±0.01)
Table 2. Equivalent circuit fitting results.
Table 2. Equivalent circuit fitting results.
SampleRs
(Ω cm2)		Q
(μΩ−1 cm2Sn)		nZWo
(μΩ−1 cm2Sn)		Rct
(Ω cm2)
Zn8.058.17 × 10−50.745.00 × 10−3322.1
Zn-Y2O36.891.60 × 10−50.891.21 × 10−31299.0
Zn-Y2O3-Al2O35.181.01 × 10−50.901.10 × 10−45947.0
Table 3. The main components of the mine water in a mining area of Lvliang City, Shanxi Province.
Table 3. The main components of the mine water in a mining area of Lvliang City, Shanxi Province.
Salt Ions and Heavy MetalsConcentration (mg/L)
SO42−1170
Cl−342
NO3−67
Na+102
Ca2+27.13
Mg2+10.54
Fe16.47
Pb0.14
As0.0512
Cd0.0126
Cr0.016
Mn1.93
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Feng, X.; Qiu, F. Study on the Corrosion Resistance and Application of Nano-Y2O3/Al2O3-Modified Anchor Rod Coatings Based on Electrodeposition Method. Electrochem 2025, 6, 14. https://doi.org/10.3390/electrochem6020014

AMA Style

Feng X, Qiu F. Study on the Corrosion Resistance and Application of Nano-Y2O3/Al2O3-Modified Anchor Rod Coatings Based on Electrodeposition Method. Electrochem. 2025; 6(2):14. https://doi.org/10.3390/electrochem6020014

Chicago/Turabian Style

Feng, Xiujuan, and Falong Qiu. 2025. "Study on the Corrosion Resistance and Application of Nano-Y2O3/Al2O3-Modified Anchor Rod Coatings Based on Electrodeposition Method" Electrochem 6, no. 2: 14. https://doi.org/10.3390/electrochem6020014

APA Style

Feng, X., & Qiu, F. (2025). Study on the Corrosion Resistance and Application of Nano-Y2O3/Al2O3-Modified Anchor Rod Coatings Based on Electrodeposition Method. Electrochem, 6(2), 14. https://doi.org/10.3390/electrochem6020014

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