Coupled thermo-physical behaviour of an inorganic intumescent system in cone calorimeter testing

This article examines the thermo-physical behaviour of an inorganic-based intumescent coating, tested with bench-scale cone calorimetry, in order to promote the understanding of its intumescence and to contribute to the optimisation of its thermal insulation performance. In the test, the specimen underwent the following phenomena simultaneously: (1) thermo-kinetic endothermic water vaporisation; (2) formation of micro-scale pores in its internal volume; (3) expansion of its volume; (4) variations in thermal boundaries. These simultaneous phenomena cause several changes in internal-external conditions given to the test sample: (1) loss of mass (water molecules); (2) reduction of effective thermal conductivity owing to its porous structure; (3) increase in length of the conductive heat transfer path across its expanding volume; (4) irradiance intensification and additional heat transfer generation on its moving boundaries, exposed to the heat source and surroundings. This interacting thermo-physical behaviour impedes the heat transfer to the underlying substrate. It is therefore comprehensively explained by finite element analysis, associated with the experimental data obtained from a thermogravimetric analyser, differential scanning calorimetry, electric furnace and cone calorimeter tests. The numerical predictions agreed with the physical measurements with consistent accuracy, in terms of both histories of substrate temperature and coating-thickness expansion. This combined numerical-experimental approach enables clear interpretation on the process of intumescence, the impediment mechanism of heat transfer and the critical factors of the material's behaviour.