Question: Could you please suggest an epoxy resin, along with a hardener and accelerator, to use as a raw material in the production of a high-temperature-resistant adhesive? It may be a one- or two-part system. We need temperature resistance up to 500°C, and the adhesive will be applied to fill small gaps in a hot mild steel structure. The required initial setting time is 5 min.

Answer: That temperature is much too high for an epoxy adhesive. You almost certainly require an adhesive based on inorganic materials. In contrast to organic adhesives, where few can perform above 250°C, inorganic adhesives have been developed that offer a service temperature of over 2,000°C. These are based on inorganic binding compounds such as sodium silicates and various metal phosphates, with carbon, alumina, silica, magnesia, or zirconia powder fillers.

Ceramic adhesives can be formulated into one- or two-part systems and are often supplied as a water-based binder solution and ceramic filler that are mixed into a slurry for application as adhesives or sealants. Suitable selection of the binder and, more importantly, the filler allows the coefficient of thermal expansion of the adhesive to be matched to that of a substrate to minimize stresses during heating and cooling.

These adhesives are frequently used for very-high-temperature applications, particularly in bonding ceramics and ceramics to metals. Weaknesses of these adhesives often include brittleness, sensitivity to moisture, and lower adhesive strength than their organic counterparts.
 

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