Corrosion phenomena in life have brought many safety hazards and economic losses. Coating anticorrosion has been widely used because of its simple operation and remarkable effect.

In recent years, due to its own structure and excellent physical and chemical properties, fly ash has attracted widespread attention as a filler material in anti-corrosion coatings. The addition of fly ash replaces or partially replaces the material substances in the anti-corrosion coating, which greatly reduces the economic cost of raw materials and improves the utilization rate of solid waste resources. Combining the basic properties of fly ash, the author first discusses the principle of its corrosion resistance from the three aspects of physical shielding effect, mechanical properties and electrochemical protection of the coating, and clarifies the role of fly ash in it.

In recent years, great progress has been made in the research on the structure and properties of fly ash as a solid waste resource, the physical and chemical properties and working principle of fly ash-based anti-corrosion coatings. The fly ash-based anti-corrosion coating achieves the effect of corrosion resistance through the interaction of various components in the coating.

1 Anticorrosion mechanism of coatings
The most common corrosion phenomenon in life is electrochemical corrosion. Metals are often destroyed by the chemical and electrochemical effects of surrounding substances in daily life. In our daily life, corrosion is mainly caused by environmental factors such as water vapor, oxygen and electrolytes. The corrosion process of metals can be approximated as a short-circuit galvanic reaction. The metal loses electrons as the anode, and the corrosion medium gains electrons as the cathode. The whole process belongs to the oxidation-reduction reaction.

2 Fly ash epoxy resin anticorrosion coating
Epoxy resin has excellent mechanical properties, chemical properties and design properties, so it has important application value in the field of anti-corrosion coatings. It has corrosion resistance and stable chemical properties. However, epoxy resins have defects such as microporosity during the curing process and cannot provide long-term shielding effect for metal substrates. Studies have found that adding inorganic fillers to epoxy resin can effectively improve the compactness of the coating and block the penetration channels of corrosive media, thereby improving the corrosion resistance of epoxy resin coatings.

3 Fly ash silicate anti-corrosion coating

Compared with organic epoxy coatings, inorganic silicate coatings are alkali-resistant and environmentally friendly, and are high-tech replacement products that meet environmental protection requirements. Inorganic silicate is the most common inorganic coating binder, which has the advantages of strong cohesive force, film-forming ability, rich source of raw materials, no pollution, and low cost. At present, the commonly used inorganic silicate film-forming substances in inorganic silicate coatings are mainly potassium silicate, lithium silicate, sodium silicate and ammonium silicate. Due to its volcanic ash effect, it reacts chemically with alkaline substances such as Ca(OH)2 in the environment to form gelling substances such as calcium silicate hydrate, which improves the anti-corrosion effect of the concrete matrix.

In recent years, the application of fly ash is mainly concentrated in the construction field. How to rationally and efficiently utilize fly ash on a large scale has become an arduous task for scientific researchers to break through. Laboratory research results show that the anti-corrosion coating prepared by using fly ash shows excellent corrosion resistance in 3.5wt% NaCl solution. The corrosion rate of the coated substrate is significantly reduced, and some coatings even reach 0.328nmyr-1. Electrochemical test results also show low corrosion current density and high impedance value, and the corrosion inhibition effect can reach more than 50%, and some research results can even reach 99.999%. However, the research on the use of fly ash for anti-corrosion coatings is still at the laboratory scale at this stage, and it is difficult to achieve large-scale industrial application due to cost and process reasons. During the research process, it is also a challenge to use fly ash to prepare multifunctional coatings with synergistic properties such as anti-corrosion, self-healing, self-cleaning, and anti-pollution. To gain insight into the protective mechanism of fly ash-based coatings at multiple scales, in-depth studies using advanced experimental studies and theoretical approaches are required. At the same time, multidisciplinary cooperative research should be carried out to achieve a breakthrough in the field of anti-corrosion coatings of fly ash.