Analysis of the combustion kinetics and thermal behavior of an intumescent system

The combustion kinetics of a laminate with intumescent behavior were determined by thermogravimetry for heating rates between 5 and 20 K/min and a final temperature of 873 K. The devolatilization stage consists of three consecutive first-order reactions that can be associated with the release of (1) water vapor (from aluminum trihydrate), (2) HCl (from polychloroprene), and (3) a gaseous mixture (from expansible graphite), followed by charring. The corresponding activation energies are 114, 140, and 83 kJ/mol. The second stage is the heterogeneous combustion of the active part of the intumescent char. This process is described by a one-step reaction whose rate presents a power-law dependence (n = 1.98) on the solid conversion and an activation energy of 182 kJ/mol. The thermal response of a composite system that uses the intumescent material as a coating for thin steel slabs was also investigated. For external temperatures of 625-1025 K, the sequential chemico-physical changes undergone by the intumescent coating highly affect the dynamics of steel heating.