Whether alkaline earth silicate fiber blanket will corrode when in contact with metal requires comprehensive analysis from three aspects: its chemical composition, environmental conditions, and the type of metal. Alkaline earth silicate fiber blanket is mainly composed of alkaline earth metal oxides such as calcium oxide (CaO) and magnesium oxide (MgO), and silicon dioxide (SiO₂), belonging to amorphous fiber materials. Its chemical stability is significantly affected by the composition ratio and structural morphology: when the content of alkaline earth metal oxides is high, the fiber's acid resistance is enhanced, but its alkali resistance may be weakened; crystalline fibers (such as those containing diopside or calcium silicate crystals) are more corrosion-resistant than amorphous fibers.
The chemical properties of the metal are the key factor determining the corrosion reaction. Active metals (such as aluminum and zinc) easily undergo electrochemical corrosion with the alkaline oxides in the fiber in humid environments. For example, aluminum may form a micro-battery with CaO or MgO in the fiber under aqueous conditions. Aluminum acts as the anode, being oxidized to aluminum ions and releasing electrons, causing the metal surface to gradually lose its luster and produce a powdering phenomenon. Inert metals (such as stainless steel and copper) readily form a dense oxide film on their surface, effectively preventing direct contact between fibers and metal, thus inhibiting corrosion. Furthermore, the purity of the metal also affects the corrosion rate; the presence of impurities can accelerate localized corrosion.
Environmental conditions catalyze or inhibit the corrosion process. High-temperature environments accelerate the dissolution and diffusion of alkaline oxides in the fibers, while simultaneously increasing the activity of the metal, making corrosion reactions easier to occur. For example, in high-temperature backing insulation scenarios in industrial kilns, if the fiber blanket is in direct contact with the metal support without protective measures, prolonged exposure to high temperatures may lead to a decrease in metal strength. Humidity is also important: in dry environments, the contact surface between fibers and metal lacks an electrolyte solution, making it difficult to form a corrosion cell; while in humid environments or environments containing corrosive gases (such as chloride ions and sulfides), an electrolyte film easily forms on the metal surface, promoting electrochemical corrosion.
The contact method between fibers and metal directly affects the uniformity of corrosion. Point contact or small-area contact easily forms localized corrosion pits, leading to stress concentration and accelerating metal failure; surface contact, on the other hand, may form an isolation layer due to the accumulation of corrosion products, thus slowing down the corrosion rate. For example, if the fiber blanket is not laid flat, the contact points with metal pipes may experience fiber wear due to long-term friction, exposing more alkaline components and further exacerbating metal corrosion. Furthermore, the softness of the fiber blanket also affects the contact effect: softer fibers can better conform to the metal surface, reducing gaps and lowering the risk of corrosion.
The manufacturing process of the fiber blanket has a significant impact on its corrosion resistance. Fibers prepared by high-temperature melting have a denser structure and better chemical stability than those produced by the sol-gel method. Post-treatment processes (such as surface coatings) can further enhance the corrosion resistance of the fibers. For example, coating the fiber surface with a layer of silicate or silicone resin can form a physical barrier, preventing direct contact between alkaline components and the metal. Simultaneously, introducing a small amount of alumina (Al₂O₃) into the fiber can refine the grains, increase the fiber density, and thus improve its corrosion resistance. In practical applications, targeted protective measures are necessary to prevent corrosion reactions between alkaline earth silicate fiber blankets and metals. In high-temperature industrial environments, a layer of high-temperature resistant ceramic paper or mica board can be laid between the fiber blanket and the metal as an isolation layer. For humid environments, hydrophobic fiber blankets can be used, or the metal surface can be galvanized or powder-coated to block the formation of electrolytes. Furthermore, regularly checking the integrity of the fiber blanket and promptly replacing damaged parts are also effective means of preventing corrosion spread.
The corrosion reaction between alkaline earth silicate fiber blankets and metals is not absolute; it depends on multiple factors, including fiber composition, metal properties, environmental conditions, and contact methods. By selecting appropriate materials, optimizing processes, and implementing protective measures, corrosion risks can be effectively controlled, ensuring the long-term stable application of fiber blankets in high-temperature insulation, industrial thermal insulation, and other fields.
