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Article

Research on Interface Modification and Thermal Insulation/Anticorrosive Properties of Vacuum Ceramic Bead Coating

by
Jin Gao
1,*,
Taiyang Zhu
1,
Zhi Zhang
1,
Yuan Kong
1 and
Xin Zhang
2,*
1
Corrosion and Protection Center, Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, China
2
Testing Center of University of Science and Technology Beijing Co., Ltd., Beijing 100083, China
*
Authors to whom correspondence should be addressed.
Coatings 2022, 12(3), 304; https://doi.org/10.3390/coatings12030304
Submission received: 8 January 2022 / Revised: 11 February 2022 / Accepted: 15 February 2022 / Published: 24 February 2022
(This article belongs to the Special Issue Syntheses, Properties, and Applications of Organic Dyes and Pigments)
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Abstract

:
The thermal insulation effect of the coating was closely related to the content of the thermal insulation filler, but too much filler would cause interfacial compatibility problems of various substances in the coating, micro-defects in the coating, and affect the anti–corrosion performance of the coating. Therefore, solving the interface problem was the key to preparing a coating with heat insulation and anticorrosion functions. In this study, organic–inorganic hybrid polymer was used to modify the surface of vacuum ceramic microbeads, and epoxy–silicone resin was used as the film–forming material to prepare a heat-insulating and anticorrosive coating that can withstand 200 °C. The SEM morphology showed that the interface compatibility of the vacuum ceramic beads modified by the organic–inorganic hybrid agent and the film-forming material were improved, the dispersibility was significantly improved, and the beads were tightly arranged; the thermal conductivity of the coating reached 0.1587 W/(m·K), which decreased by 50% after adding 20% ceramic beads, ANSYS finite element simulation showed that the coating has good thermal insulation performance; after the coating underwent a thermal aging test at 200 °C for 600 h, the microstructure was dense, and the low-frequency impedance modulus was still around 109 Ω·cm2. There was no obvious defect in the microstructure after the alternating cold and heat test for 600 h; the low-frequency impedance modulus was still above 108 Ω·cm2, and the low-frequency impedance modulus of the coating was 1010 Ω·cm2 after the 130d immersion test, indicating that the coating had good heat resistance and anti-corrosion performance.

1. Introduction

Much equipment, such as petrochemical industry and thermal pipelines, have been in service at approximately 150 °C. The insulation layer is easy to be thermally aged and cracked under service temperature, which provides a path for the infiltration of corrosive media. A large number of infiltrated corrosive media are accumulated and held between the insulation layer and the protective layer [1,2,3], and the anti–corrosion layer on the surface of metal pipelines will soon fail [4,5,6]. Therefore, the development of thermal insulation and anti–corrosion coating is of great significance for this field.
Thermal insulation coating is a functional coating that can effectively prevent heat conduction, improve working environment, and reduce energy consumption, and which is widely used in buildings, industrial equipment, aerospace, and military fields [7,8,9]. At present, the work of thermal insulation coating focuses more on the research and development of thermal insulation coating and studies the influence of the type and content of thermal insulation filler on the thermal insulation performance of the coating [10,11,12]. Microspheres, such as hollow glass microspheres and ceramic microspheres, have attracted the attention of scientific researchers because of their advantages of low density, low thermal conductivity and good thermal stability [13,14]. Researchers have conducted in–depth research on the thermal insulation effect and thermal insulation mechanism of microbeads [15,16]. S. Montazeri et al. [17] found that the coating has good thermal stability and thermal insulation effect when the content of glass microbeads was 7%, and the thermal conductivity of the coating dropped to 0.29 W/(m·K). S. Kiil et al. [18] established a mathematical model based on the experimental data of the thermal insulation performance of insulating glass microbead coatings and found that the calculated results of the model were in good agreement with the experimental data. T. Jin et al. [19] established a heat transfer model on the basis of Fourier heat law, which could better explain the thermal insulation mechanism of glass beads. However, as an inorganic material, microbeads are difficult to be infiltrated by resin; the interfacial compatibility with organic resins is poor, which leads to micro–defects in the coating, resulting in a decrease in the overall performance of the coating. Therefore, in order to realize the functions of thermal insulation and long–term anticorrosion of the coating, the problem of interfacial compatibility between microbeads and other components must be solved, and surface modification of microbeads is an idea. Some researchers used silicone sol, zinc phosphate, and other substances to coat it [20,21,22], and the thermal insulation performance and mechanical properties of the prepared coating were improved, but these methods had little improvement on the anti–corrosion performance of the coating. Therefore, the research on the interface modification of vacuum ceramic beads and the coating with thermal insulation and anti-corrosion performance is of great significance for petrochemical, thermal pipeline and other fields.
Based on this, the surface of vacuum ceramic beads was modified with a self-made organic–inorganic hybrid agent, and the changes of vacuum ceramic bead coating structure before and after modification were analyzed by scanning electron microscope; through thermal conductivity test and ANSYS software to explore the thermal insulation performance of the coating; the micro-morphology, adhesion and EIS changes of the coating after being subjected to environmental tests under different conditions were tracked, and the thermal resistance and anti-corrosion performance of the coating were analyzed.

2. Experimental Details

2.1. Materials

Tetraethylorthosilicate (TEOS, 99.99%, Macklin), ethanol (99.7%) and acetic acid (HAc, 99.5%) were purchased from Shanghai Macklin Biochemical Co., Ltd., Shanghai, China. Glycidoxypropyltriethoxysilane (GPTMS) was supplied by Chuangshi Chemical Co., Ltd., Nanjing, China. Epoxy–silicone resin was purchased from Hubei Xinsihai Chemical Co., Ltd., Zhaoyang, China, and the specific parameters are shown in Table 1. Cardanol curing agent was provided by Anhui Meidong Biomaterials Co., Ltd., Hefei, China. Vacuum ceramic microbeads were purchased from Shanghai Huijingya Co., Ltd., Shanghai, China. Dispersant, defoamer and other additives were purchased from BYK Additives (Shanghai) Co., Ltd., Shanghai, China. Titanium dioxide and mica powder were provided by Henan Borun Materials Co., Ltd., Zhengzhou, China.

2.2. Sample Preparation

2.2.1. Interface Modification of Vacuum Ceramic Beads

The organic precursor GPTMS was dissolved in absolute ethanol at room temperature (25 °C), water and acetic acid were added for hydrolysis under the condition of pH = 4.0 and stirred for 0.5 h, then TEOS was added and stirred at 25 °C for 2.0 h to prepare the organic–inorganic hybrid modifier. The vacuum ceramic microbeads (vcb) were soaked in it for 0.5 h, filtered and dried at 60 °C for 2 h to obtain the modified vacuum ceramic microbeads (Mvcb).

2.2.2. Preparation of Vacuum Ceramic Microbead Slurry

The preparation process of the vacuum ceramic microbead coating is shown in Figure 1. Firstly, titanium dioxide, mica powder and other fillers (15%) were added to epoxy silicone resin (60%), and stirred at the speed of 1500 r/min for 1 h, during the stirring process, dispersant (0.5%) and defoamer (0.5%) were added dropwise. After that, different contents of Mvcb (0, 10%, 20% and 30%) were added, and the vacuum ceramic bead coating was prepared after stirring them for 3 h at the speed of 800 r/min, during the stirring process, dispersant (0.5%) and defoamer (0.5%) were added dropwise.

2.2.3. Coating

Cardanol was added as a curing agent (10%) to the vacuum ceramic microbead coating and matured for 10–15 min. The prepared Q235 carbon steel (75 mm × 50 mm× 1 mm) was coated with a self-made anticorrosive primer of 100 μm, then coated with vacuum ceramic microbead coating after 24 h and cured at a high temperature of 120 °C for 2 h. The thickness of the vacuum ceramic microbead coating after drying was about 500 μm.

2.3. Performance Test Method

2.3.1. Thermal Conductivity Test

The Hot Disk TPS 2500 (Uppsala, Sweden) was used to measure the thermal conductivity of the paint film by referring to ISO22007–2 standard (“Determination of thermal conductivity and thermal diffusion rate of plastics”). The thickness of the sample was set below 2 mm, and the thermal environment temperature was set as 21 °C.

2.3.2. Finite Element Simulation of the Thermal Insulation Effect

ANSYS 14.5.7 finite element software was employed to establish the geometric model of the thermal pipeline during the work process according to SH/T 3010–2013 standard (“Petrochemical Equipment and Pipe Insulation Engineering Design Code”). The model was composed of a thermal pipeline, vacuum ceramic microsphere thermal insulation and anticorrosion coating and thermal insulation layer. The temperature in the pipeline was set as 150 °C to analyze the thermal insulation effect of the vacuum ceramic microsphere thermal insulation and anticorrosion coating at that temperature.

2.3.3. FT–IR Test

The Fourier Transform Infrared Spectroscopy (FT–IR) instrument (PerkinElmer, Waltham, MA, USA) was used in the ATR mode. The incident angle was 10–15°, and the wave number ranged from 4000 cm–1 to 400 cm–1.

2.3.4. EIS Test

The M2273 electrochemical workstation (Princeton Applied Research, Oak Ridge, TN, USA) was adopted to perform the EIS test on the samples at each test stage. The test frequency range was 10−2–105 Hz, and the amplitude of the sine wave excitation signal was 20 mV. The test utilized a three–electrode system comprising a saturated calomel electrode (reference electrode), a metal platinum sheet (auxiliary electrode), and a Q235 steel plate with coating (working electrode). The working area of the test was 3.14 cm2, and the electrolyte was the 3.5% NaCl solution.

2.3.5. The Adhesion Test

The adhesion test was according to the ISO 4624–2002 standard (“Paints and varnishes–Pull–off test for adhesion”). The PosiTest automatic pull–out adhesion tester produced (DeFelsko, New York, NY, USA) was used for the adhesion test.

2.3.6. Micro Morphology

QUANTA 250 environmental scanning electron microscope (Thermo Fisher Scientific, Waltham, MA, USA) was utilized to characterize the microstructure of the vacuum ceramic beads; KEYENCE 200 series laser scanning confocal microscope was used to observe the surface morphology of the sample during the 200 °C thermal aging test and the 200 °C alternating cold and hot tests, zoom in the multiple was 200× and the Keyence VK–200 confocal microscope system (Osaka, Japan) was used for data analysis.

3. Results and Discussion

3.1. Microstructure

The appearance of the vacuum ceramic microspheres which were used in the test were white, loose, closed hollow spheres, as shown in Figure 2. The spherical structure makes them better than general sheet, needle, or irregularly shaped thermal insulation fillers. Fluidity can effectively and evenly disperse and bear the external impact and stress [23,24] so that the coating film has higher strength. Moreover, the inside of the vacuum ceramic beads is a vacuum hollow structure, as shown in Figure 2c, there is no air conduction, so it can play a good thermal insulation effect. EDS analysis of vcb showed that the main elements were O, Si and Al, which also proved that the main components of vcb were SiO2 and Al2O3.
Although vacuum ceramic beads had a good thermal insulation effect, they had dispersion and compatibility problems in epoxy silicone resin when used as thermal insulation filler. Therefore, organic–inorganic hybrid [25,26] agent was used to modify their surface. The micro morphology of the coating before and after modification was shown in Figure 3. It could be seen that the dispersion of vacuum ceramic beads in the coating before surface modification was poor. After surface modification, the dispersion of vacuum ceramic beads in the coating was improved, the beads were evenly arranged, and the double graded bead ratio made the structure more compact. The cross-sectional morphology showed that the beads were accumulated in the coating, and there was no extrusion between the beads. After modification, the interfacial compatibility of vacuum ceramic beads in resin was significantly improved, and the dense structure had a strong blocking effect on thermal energy.
FT–IR analysis was performed on the vcb and Mvcb, as shown in Figure 4. It could be seen that the structure of the microbeads changed significantly after modification. 460 cm−1 was the bending vibration peak of Si–O–Si, 800 cm−1 and 1100 cm−1 were the symmetrical and asymmetric stretching vibration peaks of Si–O of SiO2 [27], these groups indicated the main ingredient. The spectrum of Mvcb showed completely different results from vcb at 1730 cm−1, 2920 cm−1 and 3450 cm−1. Near 2920 cm−1 was the absorption peaks of –CH3 and–CH2 [28], and 3450 cm−1 was the vibration absorption peak of –OH. The peak intensity increased significantly, and all of this indicated that the groups generated by the hydrolysis of the organic–inorganic hybrid agent were attached to the surface of vcb, and 1730 cm−1 was the characteristic absorption peak of the ester group [29]. The appearance of the ester group indicated that the part of the –OH produced by the hydrolysis of the organic–inorganic hybrid agent chemically reacts with the –OH on the surface of the vcb, which changed the surface structure of the vacuum ceramic microbeads. The groups on the surface of Mvcb, such as –OH, could react with –OH groups in epoxy silicone resin segments, which reduced the possibility of agglomeration of the microbeads and reduced the porosity in the resin, so that the microbeads could be well dispersed in the coating system and the coating has a dense structure.

3.2. Thermal Insulation

The vacuum structure of the microbeads could significantly reduce the thermal conductivity of the coating. The lower the thermal conductivity of the coating, the better its thermal insulation performance [30], and the arrangement of vacuum ceramic microspheres was more conducive to improving the thermal insulation performance of the coating. The thermal conductivity of the vacuum ceramic microbead coating by adding different contents of Mvcb was measured, and the result is shown in Figure 5. It could be seen that the thermal conductivity decreased gradually with the addition of the Mvcb content. When the amount of Mvcb reached 20%, the thermal conductivity was significantly reduced, and the thermal conductivity of the coating film was almost the same as when it was 30%, indicating that the packing density of the microbeads at this time was relatively tight, and the heat transfer method between the film-forming substance and the microbeads was host. Too much content might lead the ceramic microbeads to squeeze and break each other and affected the performance of the coating. Therefore, the content of Mvcb in the coating was determined to be 20% when the thermal insulation coefficient showed little difference.
When the heat flow was transmitted inside the coating, it would propagate along the substrate with low thermal impedance. Different from the solid structure of ordinary ceramic microbeads, which could transfer heat flow, vacuum ceramic microbeads had a vacuum hollow structure, and there was no air inside to conduct heat, which had a great blocking effect on heat flow transmission [31,32], as shown in Figure 6b. Therefore, heat flow could only conduct along the outer wall of the vacuum ceramic microspheres and the resin matrix. Given that heat flux travels longer in the vacuum ceramic microbead coating than the ordinary one, the thermal insulation effect of the former was better than that of the latter. Moreover, within a certain range, the more vacuum ceramic beads were contained in the coating, the higher the packing density of the beads would be. This phenomenon increased the path of heat flow transmission and thermal impedance of the coating, and thus enhanced the heat insulation effect of the coating. However, with the further increase in the amount of vacuum ceramic beads, it was possible that the adhesion will decrease due to uneven dispersion or micro-defects in the coating. Therefore, the influence of ceramic beads on the mechanical properties of the coating needed to be balanced in the preparation of thermal insulation coatings.
ANSYS finite element software was utilized to establish the geometric model of the pipeline axial profile of the uncoated and coated vacuum ceramic microsphere thermal insulation and anticorrosion coatings (Figure 7). The model was used to simulate the temperature distributions between the inner wall of the pipeline and the outer wall of the insulation layer at 150 °C and after the coating was applied. Subsequently, the thermal insulation effect of the vacuum ceramic microsphere thermal insulation and anticorrosion coating at 150 °C was analyzed. According to the relevant standards for domestic thermal pipelines, the temperature of the outer wall of the insulation layer cannot exceed 50 °C. The internal (d1) and external (d2) diameters of the thermal pipeline were set as 40 mm and 44 mm, respectively, and the thermal conductivity of the pipeline (λ1) was 45 W/(m·K). The thickness of the coating applied outside of the pipeline (δ1) was 2 mm, with a corresponding thermal conductivity (λ2) of 0.15 W/(m·K). The thermal conductivity of the insulation layer (λ3) was 0.2 W/(m·K). The temperature of the inner wall of the thermal pipe (t1) was 150 °C. The convective heat transfer coefficient between the hot water in the pipe and the inner wall (λ4) was 180 W/(m·K). The atmospheric temperature outside the insulation layer (t2) and the temperature at the interface between the insulation layer and the atmosphere (t3) were 25 °C and ≤50 °C, respectively. The convective heat transfer coefficient between the atmosphere and the outer wall of the insulation layer (λ5) was 10 W/(m·K). The length of the heat pipe (L) was 100 mm.
The finite element simulation results of the radial temperature distribution of the pipeline with and without heat insulation and anticorrosion coating are shown in Figure 8. The temperature of the outer wall of the insulation layer was 49.21 °C when no coating was applied outside the pipeline and the thickness of the insulation layer was 55 mm. When the thickness of the coating and insulation layer was 2 and 50 mm, respectively, the temperature of the external wall of the thermal insulation layer was 49.41 °C. The thermal insulation effect of the two models was identical and satisfies the requirements of domestic pipeline standards. Therefore, a 2 mm. thermal insulation coating could reduce the use of a 5 mm. thermal insulation layer, which not only achieved the thermal insulation effect, but also reduced the aging under the thermal insulation layer.

3.3. Heat Resistance and Corrosion Resistance

3.3.1. Anti-Corrosion Performance after Thermal Aging Test

Considering the service environment of petroleum pipelines, not only better heat insulation performance was required, but also the heat resistance performance of the coating was also a test. The vacuum ceramic microbead heat-insulating anticorrosive coating was subjected to a 200 °C thermal aging test of 120 h, 240 h, 360 h, and 600 h. The microscopic morphology changes are shown in Figure 9. It could be seen that the coating was completely bright after heat aging at 200 °C for 600 h, the microstructure was still dense, and there were no microscopic defects, such as holes and cracks in the coating. The coating had excellent heat resistance at 200 °C, which is for the organic–inorganic hybrid agent that made the vacuum ceramic beads, the film-forming material had a strong interface bond, and the epoxy silicone resin, which was used in the coating, had good heat resistance at 200 °C.
In order to further judge the heat resistance of the coating, the EIS test was carried out on the samples after the 200 °C heat aging test for 120 h, 240 h, 360 h, and 600 h, the test result was shown in Figure 10. It could be seen from the Nyquist diagram that the radius of the capacitive arc was continuously reduced during the entire aging process. The compactness of the coating to begin to decrease for the polymer chain of the coating bond was broken out at high temperatures [33], but during the test, the capacitive arc always showed a time constant, indicating that the coating was still a complete dense layer at this time, and the corrosive medium had not penetrated into the substrate; in the Bode diagram, as the test progresses, the low frequency of the coating The impedance modulus value continues to decrease, especially after the aging test after 600 h; the low-frequency impedance modulus value dropped significantly, but it was still above 108 Ω·cm2, indicating that the coating still had good protective performance at this time and could effectively block external corrosion and hinder the corrosive medium which infiltrated into the surface between the matrix and the coating [34]. It could be that the coating had excellent protection nature and excellent heat resistance even at 200 °C from combining with the analysis of microscopic morphology and electrochemical performance.

3.3.2. Anti-Corrosion Performance after Alternating Cold and Heat Test

The service environment of alternating cold and heat would bring greater internal stress to the coating. Cracking and warping would occur when the internal stress of the coating was greater than its adhesion with the substrate. Therefore, the heat and cold alternate test was used to simulate and accelerate the effect of internal stress on the failure of the thermal insulation and anticorrosive coating. The sample was placed at 200 °C for 6 h, and then quickly transferred to room temperature water (25 °C) to quench for 2 min, and the sample was placed again at 200 °C. 6 h, then transferred to room temperature water to quench for 2 min. This is a hot and cold cycle. The micro–morphology changes of the coating after 10 (120 h), 20 (240 h), 30 (360 h), and 50 (600 h) cycles are shown in Figure 11. It could be seen that the microstructure of the coating was still dense after 600 h without microcracks, indicating that the coating was excellent. The coating had a strong resistance to internal stress because it had good heat resistance and ductility, which the epoxy silicone resin was introduced to the coating.
It was the EIS changes in Figure 12 that the coating was after the alternating cold and hot test. It could be seen that the arc radius of the Nyquist diagram continues to decrease as the cold and heat alternate test, especially after 360 h and 600 h, the arc radius decreased sharply. This was because the high temperature and thermal stress exists in the cold and hot alternate at the same time, the cleavage of the polymer chain occurred faster, the coating produces tiny holes, and the compactness of the coating decreases, simultaneously, the second time constant in the EIS diagram was not observed, indicating that the corrosive medium has not penetrated into the substrate and the corrosion reaction of the base metal did not occur; the Bode diagram showed that the low-frequency impedance modulus of the coating was continuously decreasing as the test was carried out, but it was still more than 108 Ω·cm2 after the alternating cold and hot test for 600 h, indicating that the coating still had high shielding ability at that time. The good protection performance under the alternating cold and heat test was derived from the chemical bond between the vacuum ceramic beads and the film-forming material, which brought strong cohesion to the coating, so that the coating was still maintaining good compactness and effectively blocking the infiltration of external corrosive medium.
Adhesion reflected the interface between the coating and substrate, which was related to the protective effect and protective time of the coating [35]. The adhesion of the coating after the 200 °C thermal aging test and the 200 °C alternating cold and hot test was analyzed, as shown in Figure 13. It could be seen that the change of adhesion after the two tests showed different laws. Firstly, the initial adhesion data was 4.6 MPa, indicating good bonding and compatibility between coatings. Secondly, after the thermal aging test, the adhesion first increased and then decreased with the increase of aging time. The reason was that under the action of short-term high temperature, the crosslinking and curing of the polymer chain of the coating was further intensified, the bonding between coatings was increased, and the polymer chain was degraded with the further increase of aging time. The cohesion between coatings was affected under the action of high temperature for a long time so that the adhesion decreased gradually, but it remained at about 4 MPa after 600 h, indicating that the coating still had good interface bonding with the substrate at that time. The adhesion of the coating after the 200 °C cold and hot alternating test decreased with the increase of test time, which was quite different from that after the 200 °C thermal aging test. First, the huge temperature difference in the cold and heat alternating process made the coating heat unevenly and produced temperature strain, resulting in residual stress in the coating, which weakened the adhesion of the coating. Second, because the cooling condition was in the immersion environment, water molecules penetrated into the coating, further weakening the bonding between the coatings. However, in this harsh environment, the adhesion was still 2.6 MPa after 600 h, indicating a good interface between the coating and the substrate.

3.3.3. Anti-Corrosion Performance after Immersion Test

The sample was immersed in 3.5% NaCl solution, and the electrochemical behavior of the coating after immersion for 18 d, 64 d, 80 d, 100 d, and 130 d was followed to investigate the shielding ability of the coating to the medium. Figure 14 shows the EIS change of the coating during the immersion test. The Nyquist diagrams were all single-capacitive arcs with a large radius as the test is carried out, which was characterized by a time constant. However, as the immersion time increases, the radius of the arc was also decreasing, indicating that the charge transfer step after immersion for 130 d was a control step. Although water, oxygen and other corrosive media were constantly penetrating into the coating, which had not penetrated into the metal substrate, and the coating was still a complete shielding layer. The Bode diagram of the coating was always a straight line. Although the low-frequency impedance modulus was decreasing with the increase of time, the one of 130 d still remained above 1010 Ω·cm2, indicating that the coating structure was still dense after long-term immersion, which had a strong shielding ability to the corrosive medium [36].
The electrochemical impedance spectroscopy data was fitted with an equivalent circuit to further analyze the changes of the coating during the immersion test [37]. The equivalent circuit of the heat-insulating anti-corrosion coating during the immersion process is shown in Figure 15a. Rs was defined as the solution resistance, Rc was defined as the coating resistance, and Cc represented the coating capacitance. Both Rc and Cc reflected the impermeability of the coating, and the fitting results of the two are shown in Figure 15b. It could be seen that with the increase of the test time, Rc was continuously decreasing, indicating that the protective ability of the coating was continuously weakening, but still remained at a higher order of magnitude; Cc was generally increasing, indicating that water molecules continuously penetrated into the coating in the test, and the high dielectric constant of water caused the overall capacitance value of the coating to increase [38]. However, the change rate of Rc and Cc was slower because the diffusion and penetration of water were restricted, which reflected the good shielding ability and anti-corrosion performance of the coating.
The above environmental test showed that the vacuum ceramic bead coating had excellent anti-corrosion performance, which was inseparable from the structure of the coating. Firstly, the vacuum ceramic microbeads modified by the organic–inorganic hybrid agent produced a chemical bond connection with the film-forming material, which enhanced the interface bonding between the vacuum ceramic micro-beads and the film–forming material, and reduced the micro-defects in the coating; and the usage of the organic–inorganic hybrid agent increased the cohesion of the coating and greatly reduced the impact of the internal stress caused by the alternation of cold and heat on the cracking of the coating; in addition, the use of a two-level model design made the vacuum ceramic microspheres tightly packed. In addition, the flaky fillers arranged in parallel in the heat–insulation and anti–corrosion coating were partially accumulated in the pores between the microbeads, so the prepared coating had a dense structure, which effectively blocked the infiltration of external corrosive medium and protected the substrate for a long time.

4. Conclusions

1. The dispersibility of the vacuum ceramic microbeads modified by the organic–inorganic hybrid agent in the film-forming material was improved, and the arrangement of the microbeads was uniform and compact;
2. The thermal conductivity of the coating reached 0.1587 W/(m·K), which decreased by 50% after adding 20% Mvcb. The finite element simulation of the radial temperature distribution of the petrochemical pipeline showed that the coating had good thermal insulation performance, and a 2 mm. coating can reduce the usage of thermal insulation layer by 5 mm;
3. The coating had good heat resistance and corrosion resistance after the environmental simulated test in the paper. The microstructure was dense, and the low-frequency impedance modulus was still around 109 Ω·cm2 after the coating undergoes a thermal aging test at 200 °C for 600 h; the low–frequency impedance modulus value was still above 108 Ω·cm2, and there was no obvious defect in the microstructure after the alternating cold and heat test for more than 600 h (heat test time cumulating 600 h at 200 °C); the low-frequency impedance modulus value of the coating was 1010 Ω·cm2 after the 130 d immersion test.

Author Contributions

Conceptualization: J.G.; methodology: J.G., X.Z. and Z.Z.; investigation: T.Z., Z.Z. and Y.K.; resources: J.G.; experimental work: T.Z., Y.K. and Z.Z.; writing: T.Z.; review and editing: J.G. and X.Z. All authors gave final approval and agree to be accountable for all aspects of the work. All authors have read and agreed to the published version of the manuscript.

Funding

The authors wish to acknowledge the financial support provided by the National Natural Science Foundation of China (No. 51771030).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data sharing is not applicable to this article.

Acknowledgments

The authors wish to acknowledge the financial support provided by the National Natural Science Foundation of China. The comments provided by the reviewers are greatly appreciated.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Preparation of vacuum ceramic bead coating.
Figure 1. Preparation of vacuum ceramic bead coating.
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Figure 2. Morphology of vacuum ceramic beads: (a) macroscopic; (b) microscopic; (c) cross-section; (d) EDS analysis.
Figure 2. Morphology of vacuum ceramic beads: (a) macroscopic; (b) microscopic; (c) cross-section; (d) EDS analysis.
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Figure 3. Micromorphology of vacuum ceramic microbead coating: (a) before modification; (b) after modification and; (c) cross-section morphology after modification.
Figure 3. Micromorphology of vacuum ceramic microbead coating: (a) before modification; (b) after modification and; (c) cross-section morphology after modification.
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Figure 4. FT–IR spectra of Mvcb and vcb.
Figure 4. FT–IR spectra of Mvcb and vcb.
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Figure 5. Effect of bead content on thermal conductivity of coating.
Figure 5. Effect of bead content on thermal conductivity of coating.
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Figure 6. Schematic diagrams of the heat insulation effect of (a) ordinary ceramic beads and (b) vacuum ceramic beads.
Figure 6. Schematic diagrams of the heat insulation effect of (a) ordinary ceramic beads and (b) vacuum ceramic beads.
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Figure 7. Pipe model (a) without coating and (b) with thermal insulation anticorrosive coating.
Figure 7. Pipe model (a) without coating and (b) with thermal insulation anticorrosive coating.
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Figure 8. Finite element simulation results of the radial temperature distribution of the thermal pipe (a) without coating and (b) with coating.
Figure 8. Finite element simulation results of the radial temperature distribution of the thermal pipe (a) without coating and (b) with coating.
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Figure 9. Laser confocal micromorphology of the coating after (a) 120 h, (b) 240 h, (c) 360 h, and (d) 600 h of the heat aging test at 200 °C.
Figure 9. Laser confocal micromorphology of the coating after (a) 120 h, (b) 240 h, (c) 360 h, and (d) 600 h of the heat aging test at 200 °C.
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Figure 10. EIS change of coating during 200 °C heat aging test: (a) Nyquist and (b) Bode.
Figure 10. EIS change of coating during 200 °C heat aging test: (a) Nyquist and (b) Bode.
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Figure 11. Confocal laser confocal microscopic morphology of the coating after the alternating cold and hot test: (a) 120 h; (b) 240 h; (c) 360 h; (d) 600 h.
Figure 11. Confocal laser confocal microscopic morphology of the coating after the alternating cold and hot test: (a) 120 h; (b) 240 h; (c) 360 h; (d) 600 h.
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Figure 12. EIS changes during the alternating cold and heat test of the coating: (a) Nyquist; (b) Bode.
Figure 12. EIS changes during the alternating cold and heat test of the coating: (a) Nyquist; (b) Bode.
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Figure 13. Change of coating adhesion after the 200 °C thermal aging test and the 200 °C alternating cold and hot test.
Figure 13. Change of coating adhesion after the 200 °C thermal aging test and the 200 °C alternating cold and hot test.
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Figure 14. The EIS change of the coating during the immersion test: (a) Nyquist; (b) Bode.
Figure 14. The EIS change of the coating during the immersion test: (a) Nyquist; (b) Bode.
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Figure 15. Fitting circuit result of immersion experiment: (a)Fitting circuit model; (b)Fitting circuit results of Rc and Cc.
Figure 15. Fitting circuit result of immersion experiment: (a)Fitting circuit model; (b)Fitting circuit results of Rc and Cc.
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Table
Table 1. Specifications of epoxy–silicon resin and cardanol.
Table 1. Specifications of epoxy–silicon resin and cardanol.
MaterialEpoxy–Silicone ResinCardanol
AppearanceLight yellow transparent liquidOrange transparent liquid
EEW/(g/eq)1000–1250/
AEW/152
Viscosity/(mPa·s)1000–15003000–4000
Solid Content/wt%6095
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Gao, J.; Zhu, T.; Zhang, Z.; Kong, Y.; Zhang, X. Research on Interface Modification and Thermal Insulation/Anticorrosive Properties of Vacuum Ceramic Bead Coating. Coatings 2022, 12, 304. https://doi.org/10.3390/coatings12030304

AMA Style

Gao J, Zhu T, Zhang Z, Kong Y, Zhang X. Research on Interface Modification and Thermal Insulation/Anticorrosive Properties of Vacuum Ceramic Bead Coating. Coatings. 2022; 12(3):304. https://doi.org/10.3390/coatings12030304

Chicago/Turabian Style

Gao, Jin, Taiyang Zhu, Zhi Zhang, Yuan Kong, and Xin Zhang. 2022. "Research on Interface Modification and Thermal Insulation/Anticorrosive Properties of Vacuum Ceramic Bead Coating" Coatings 12, no. 3: 304. https://doi.org/10.3390/coatings12030304

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