Non-expansive fire retardant coatings, with their non-combustibility, low thermal conductivity, and physical insulation mechanisms, play a crucial role in fire protection of steel structures, concrete, and other substrates. However, their chemical corrosion resistance is often reduced by environmental factors such as acids, alkalis, salt spray, and solvents, leading to coating peeling and performance degradation. Improving their chemical corrosion resistance requires a comprehensive approach encompassing material selection, formulation optimization, process improvement, and environmentally adaptable design.
Optimization of inorganic substrates is fundamental to the chemical corrosion resistance of non-expansive fire retardant coatings. Traditional coatings often use inorganic materials such as gypsum, cement, and silicates as base materials. While these materials possess high fire resistance, their high porosity makes them prone to adsorbing chemical media. Introducing nanoscale fillers such as silica and alumina can fill the substrate pores, forming a dense structure and reducing the penetration pathways of corrosive substances. For example, uniformly dispersing nano-silica in gypsum-based coatings can significantly improve the coating's impermeability and acid/alkali resistance while maintaining its thermal insulation properties. Furthermore, selecting inorganic cementing materials with higher chemical stability, such as phosphate-based or aluminate-based cementitious agents, can further enhance the stability of the coating in extreme environments.
The synergistic effect of flame retardants and corrosion inhibitors is crucial. Non-expansive fire retardant coatings often add phosphorus-based, halogen-based, or boron-based flame retardants, but some flame retardants may reduce the chemical resistance of the coating. For example, halogen-containing flame retardants may release acidic substances in high-temperature or humid environments, corroding the substrate. Therefore, it is necessary to screen for flame retardants with good compatibility with the substrate, such as phosphorus-nitrogen composite flame retardants, whose decomposition products are neutral or weakly alkaline, with low corrosiveness to metal substrates. Simultaneously, compounding corrosion inhibitors such as zinc powder, zinc phosphate, or organic amine compounds can inhibit corrosion reactions by forming a passivation film or neutralizing acidic substances. For example, adding zinc powder to fire-retardant coatings for steel structures can simultaneously provide cathodic protection and flame retardancy, extending the coating's service life.
The introduction of surface treatment technologies can significantly improve the chemical resistance of the coating. By adding silane coupling agents to coatings, chemical bonds can be formed at the coating-substrate interface, enhancing adhesion and reducing peeling caused by corrosion. Furthermore, using low surface energy substances such as fluorocarbon resins or polysiloxanes as surface sealing agents can form a hydrophobic and oleophobic protective film, preventing direct contact between chemical media and the coating. For example, spraying a thin layer of fluorocarbon resin onto a non-expansive fire retardant coating surface can improve its acid and alkali resistance while maintaining its original fire resistance.
Optimized coating structure design is also an important means of improving chemical corrosion resistance. Multi-layer composite coatings, through functional layering, can address both fire protection and corrosion resistance requirements. The bottom layer uses an inorganic zinc-rich coating with excellent chemical resistance to provide cathodic protection; the middle layer is a non-expansive fire retardant coating, providing thermal insulation protection; and the top layer uses a weather-resistant organic coating to form a sealing layer. This structure can block corrosive media from the top layer, and even if the top layer is damaged, the flame-retardant function of the middle layer can still be maintained. Furthermore, increasing coating thickness can extend the penetration path of corrosive media, but a balance must be struck between cost and performance to avoid cracking due to excessive thickness.
Environmental adaptability design requires adjusting the formulation according to specific application scenarios. For example, in marine environments, coatings need excellent salt spray resistance, which can be achieved by adding corrosion inhibitors such as molybdates and tungstates to suppress chloride ion corrosion of the metal substrate. In chemical environments, the coating's solvent resistance needs to be improved; high-crosslinking density resin systems, such as epoxy resins or polyurethane resins, can be selected to reduce solvent molecule penetration. Additionally, adjusting the coating's pH value to near neutral can reduce sensitivity to acidic or alkaline environments.
Proper application procedures also affect the coating's chemical resistance. Before application, oil, rust, and old coatings on the substrate surface must be thoroughly removed to ensure good adhesion between the coating and the substrate. During application, ambient humidity and temperature must be controlled to prevent blistering or decreased adhesion due to residual moisture. After application, adequate curing is necessary to allow the coating to fully harden and form a stable chemical structure. For example, non-expansive fire retardant coatings applied in high-temperature and high-humidity environments require extended curing times to ensure stable coating performance.
Through comprehensive measures such as inorganic substrate optimization, synergistic effects of flame retardants and corrosion inhibitors, surface treatment technology, coating structure optimization, environmental adaptability design, and standardized construction processes, the chemical corrosion resistance of non-expansive fire retardant coatings can be significantly improved. This not only extends the coating's service life and reduces maintenance costs, but also expands its application range in harsh environments such as petrochemicals, marine engineering, and power facilities, providing more reliable protection for building safety.
