Brief introduction to the technology of high solid

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A brief introduction to the technology of high solid wear-resistant, heat-resistant and heavy-duty anti-corrosion coatings


China has successfully developed a variety of industrial anti-corrosion coatings, which have played an important role in the anti-corrosion of metal structures. However, so far, the development of heavy-duty anti-corrosion coatings in China still cannot meet the needs of large-scale engineering construction. The high-tech anti-corrosion coatings have a large gap with the actual demand in terms of variety and quality, and the problem of short validity period is widespread. The anti-corrosion coatings with special performance, especially the high solid and solvent-free heavy-duty anti-corrosion coatings, cannot meet the needs of a large number of marine and coastal facilities, water conservancy projects For the long-term anti-corrosion needs of petrochemical engineering and Metallurgical Construction Engineering [1, 2], it is necessary to strengthen the research and development of protective coating system with long service life to meet the needs of heavy anti-corrosion coating for major engineering construction in China

1 experimental part

1 1. Raw materials and instruments

modified epoxy resin; Various ceramic powders; Aluminum tripolyphosphate antirust pigment

xgp portable specular glossometer; Jm-3 coating abrasion tester; Electron microscope

the instruments used in the electrochemical experiment are m273 potentiostat and m5210 lock-in amplifier produced by PE (Platinum Elmer company) in the United States. The electrochemical impedance spectrum is analyzed by M398 impedance test software. 3% NaCl solution is selected as the soaking solution

1. 2 formula design

the relationship between the gloss of the coating film prepared by different coating formulas and the formula PVC is shown in Figure 1 [3]. It can be seen from the figure that the gloss of the coating film changes with the PVC of the coating formula, and the inflection point coordinate is (0.30 ~ 0.329), that is, the CPVC value is about 0 30 ~ 0. 32 。 When the type of filler is fixed, the change curve of the gloss of PVC film with the formula PVC

the experimental results show that the PVC value is 0 The test piece of 5 bubbles first, and then the PVC value is 0 25, PVC value is 0 The last blister of 35. This is because when PVC CPVC is used, the amount of resin is relatively small, which can not fill the whole volume between pigments and fillers, and there are gaps in the film, so the water permeability resistance of the coating is poor; In the case of PVC CPVC, there is "excess" resin in the coating film, and the close accumulation degree of the coating film must be lower than that of the coating when PVC = CPVC, and the water permeability resistance of the coating must also be reduced, prior to the damage of the coating when PVC = CPVC. Considering the test error range, it can be determined that the CPVC range of the coating is basically consistent with the above

1. 3. Process

the test determines that the process for preparing the coating is as follows:

(1) after the analysis and test of raw materials are qualified, weigh the solvent and resin according to the formula and mix them until the epoxy resin is dissolved

(2) add additives, antirust pigments and troubleshooting methods: please check whether the sensor selection in the "online" setting is correct. Add ceramic powder to the above (1) mixed solution and stir it at high speed to disperse

(3) put the above (2) mixed slurry into the sand mill, adjust the sand mill to the best speed, grind for 48 h, and filter and pack after passing the inspection

1. 4 performance test

1 4.1 abrasion resistance

the abrasion resistance of the coating shall be measured with jm-3 coating abrasion tester, the standard template with a diameter of 100 mm shall be fixed on the rotatable base, and the rubber grinding wheel shall be pressed down to contact the coating surface according to the standard requirements. When the load is 1000 g (including its own mass), the sample plate rotates slowly, and the counter records the required number of revolutions. The wear resistance of the coating is measured by the method of weighing the mass. The sample mass before and after wear is weighed by an analytical balance. The difference is the coating loss mass, and this value represents the quality of the wear resistance

1. 4.2 anti corrosion performance

with the same basic formula, add 14 6% 、 9. 8% 、 6 . 5%, 4.9% and 0% of the antirust pigments were made into samples (the corresponding formula numbers were C1, C2, C3, C4 and C0). The change of the impedance spectrum of the coating with the soaking time was tested to study the effect of the antirust pigments on the corrosion resistance of the coating. Ceram -kote 54 coating with good comprehensive performance (produced by American comprehensive application engineering company) is selected, and the actual use is up to 10? The 036 oil resistant and corrosion-resistant coating with more than years of experience was compared with the ceramic wear-resistant, heat-resistant and heavy corrosion-resistant coating

2 results and discussion

2 1 corrosion resistance

electrochemical impedance spectroscopy [] EIS (electrochemical impedance spectroscopy) was first applied to metal corrosion research by ebelboin in 1971. Through coating pretreatment, various impedance spectra (Bode diagram, Nyquist diagram) of the coating at different AC frequencies were measured, and the impedance spectra were analyzed to obtain coating capacitance and resistance values to study the protective effect of organic coatings on metals []. The water absorption of the coating can be measured from the capacitance value, the corrosion resistance of the coating can be measured from the resistance value of the coating, and the corrosion rate can be estimated from the electrochemical corrosion charge transfer resistance of the metal under the coating, so that the change of the coating performance can be tracked and the coating performance can be evaluated. Based on the above principles, the influence of antirust pigments on the corrosion resistance of coatings was investigated by measuring the changes of impedance spectra of coatings under different soaking times, and compared with similar coatings at home and abroad

2. 1.1 effect of antirust pigments on corrosion resistance of coating film

from the change of impedance spectrum, it can be seen that in a very short time (0.8 d), the time constant of C1 impedance spectrum changes from one to two (in which the high-frequency part reflects the information of coating, and the low-frequency part reflects the information of base metal corrosion), and the low-frequency part is a severely deflected arc, which indicates that the corrosion medium soon infiltrates into the coating/metal interface, At this time, due to the uneven distribution of metal defects and the influence of corrosion products, there is a dispersion phenomenon, which appears as a semicircle with deflection in the low-frequency part on the impedance spectrum. Then, with the increase of immersion time, the low-frequency part appears a shape of arc connected with a diagonal line, and the radius of the arc gradually increases, which indicates that the corrosion resistance of the base metal increases with the extension of immersion time. This change indicates that the antirust pigment has an effect, that is, in the process of the corrosion medium penetrating the metal surface through the coating, some antirust pigments dissolve and penetrate the metal surface with the medium, acting with the metal, A dense saponification layer is formed, which makes up for the defects of the coating and blocks the transmission of corrosive media such as oxide skin and metal debris. The control step of metal reaction is the diffusion process of oxygen, which slows down the corrosion of metal. At the 45th day, the arc radius of the low-frequency part decreased significantly, and the coating resistance was 104 Ω, so the coating had lost its protective effect. The change process of Nyquist diagram of other formulas is similar. The corrosion resistance of C1 is weaker than that of C0. The main reason is that the amount of antirust pigment is relatively large and the resin content is relatively small, which increases the porosity of the coating and destroys the compactness of the coating film, so that the impermeability of the coating film is weakened and corrosion occurs soon. The slow down of the corrosion rate in the later stage is due to the role of the antirust pigment, but the amount of the antirust pigment is limited, which eventually leads to the failure of the film. Therefore, the amount of such antirust pigments must be controlled

2. 1.2 corrosion process of coating

it can be seen from Figure 2 that the resistance of coatings containing different antirust pigments changes with soaking time. In general, the coating resistance decreases with the immersion time. This is because the electrolyte enters the coating through the pores in the coating and gradually establishes a micro conductive path, resulting in the decrease of coating resistance. The resistance of C1 coating is significantly lower than that of other formulas. This is mainly due to the high amount of antirust pigment in the coating, which leads to the lack of coating base material, but leads to the high porosity of the coating and affects the corrosion resistance of the coating. On the macro level, the coating appears obvious rust spots after soaking for 20 days. The R P values of the other three specimens were greater than C0 at the early stage of immersion, which reflected that the antirust pigment played a certain role; In the later stage, the coating resistance of C4 and C0 intersected, indicating that the role of antirust pigment was weak at this time, which was mainly caused by the insufficient addition of C4 antirust pigment. The resistance values of C2, C3 and C4 fluctuate with time. Among them, the resistance of C3 coating fluctuates obviously, which is mainly due to the formation of saponification layer on the substrate due to the release of complex ions from antirust pigments, and the accumulation of metal corrosion products, which blocks the pores of the coating, increasing the resistance of corrosion medium through the coating, The decrease of coating resistance is due to the increase of pore size, conductivity and the emergence of new micro channels due to the corrosion of micro channels by corrosive media. C2 resistance changes slowly and is always at a high resistance level, which is the result of the good proportion of resin, base material and antirust pigment in the formula

is the change of capacitance of C0, C1, C2, C3 and C4 with time at different soaking times. The capacitance value of organic coating is closely related to the amount of water molecules entering the coating through micro defects. The greater the amount of water molecules penetrating into the coating, the higher the capacitance value of the coating. Therefore, the water permeability resistance of organic coating can be inferred. It can be seen from Fig. 3 that the capacitance of the test piece with antirust pigment is significantly lower than that of the test piece without antirust pigment, except that C1 is prematurely damaged due to excessive addition of antirust pigment, indicating that the antirust pigment plays a role in delaying corrosion. On the whole, the change of coating capacitance with soaking time is small, especially C4 and C2 have basically no change, and the general change order is C1 μ C0 C3 C2 ≈ C4 。

change curve of resistance value of antirust pigment coating with different content with immersion time

change curve of capacitance value of antirust pigment coating with different content with immersion time

difficulty of electrolyte solution penetrating into organic coating (i.e. water permeability resistance of organic coating) is a performance index closely related to the protective performance of organic coating. Since electrolyte penetrating into organic coating will cause changes in coating capacitance and resistance, in turn, It is also possible to understand the degree of penetration of the medium into the organic coating from the changes of the coating capacitance and resistance. Brasher D. m and Kingsbury l put forward the formula of water absorption volume fraction of organic coating:

x V%=l00 lg[C C (T)/C (0)]/LG (80)

where XV% is the water absorption volume percentage of organic coating; C C (0) and c c c (T) are the coating capacitance before and after soaking time t. After analyzing the impedance spectrum data to obtain C C (0) and C C (T), the water permeability of the coating can be obtained by using the above formula. In this experiment, the change of coating water permeability is shown in Figure 4. It can be seen from the figure that, except for C1, the coating film is prematurely damaged due to excessive addition of antirust pigment, the change of coating water penetration rate during immersion is very small, indicating that the coating has strong protective ability

variation curve of water penetration rate of antirust pigment coating with soaking time

2 1.3 comparison experiment with relevant coatings at home and abroad

the electrochemical impedance method was used to compare this coating with two other coatings that have been used for a long time and proved to have excellent anti-corrosion performance

3 kinds of coatings were soaked for 108 days at the same time. During the whole soaking period, the Nyquist diagram of the coating is a time constant, indicating that the coating has not been damaged, but from the change of the impedance value of the coating in the same period, their protective performance is still different. The change of the coating resistance is

the change curve of the resistance value of different coatings with the soaking time

note: sample 1 ceramic wear-resistant, heat-resistant and heavy corrosion-resistant coating, referred to as ceramic coating

sample 2 American comprehensive application engineering company

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