Insights into pyrolysis behavior of the typical condensed aerosol extinguishing agent forming compound: Interaction between its basic components

Abstract

The pyrolysis process of the condensed aerosol extinguishing agent forming compound (AEFC) is the key to improve its fire extinguishing efficiency. Therefore, a typical AEFC (homogenized K-aerosol) composed of potassium nitrate (KNO3), melamine and phenolic resin (mass ratio 7:2:1) was prepared by freeze-drying method. The pyrolysis process of homogenized K-aerosol is divided into three stages (stage 1 α:0–0.33; stage 2 α: 0.33–0.42; stage 3 α:0.42–1.00). The average activation energy (E) of stage 1–3 and the total pyrolysis process of homogenized K-aerosol are 123.94 kJ/mol, 97.344 kJ/mol, 149.194 kJ/mol and 135.01 kJ/mol, respectively. The stage 1 of homogenized K-aerosol is a one-step endothermic pyrolysis reaction of melamine with an average E, an average prefactor A and a reaction model of 123.94 KJ/mol, 6.21E10 min−1 and g(α)=(1−α)−2−1, respectively. And the pyrolysis in stage 2 and stage 3 of homogenized K-aerosol are of multi-step reactions. The TG-MS results show that the stage 2 is mainly the exothermic decomposition reactions of phenolic resin. And KNO3 in homogenized K-aerosol degrades in advance in stage 2. The stage 3 is mainly the thermal decomposition of KNO3 in homogenized K-aerosol. Therefore, the three components of homogenized K-aerosol interact with each other during its pyrolysis process. Firstly, melamine is pyrolyzed in advance and its pyrolysis is the main gas production process. Then, phenolic resin undergoes exothermic decomposition reactions, releasing reducing substances and catalyzing the pyrolysis of KNO3 in homogenized K-aerosol. Finally, a large amount of KNO3 is decomposed into K/KO free radicals which play a fire extinguishing role.