The fire extinguishing mechanism of ultrafine composite dry powder agent containing Mg(OH)2

• Published in: International journal of quantum chemistry Vol. 121; no. 24
• Main Authors: Hu, Wenhao, Yu, Rourou, Chang, Zhenxiang, Tan, Zhaoyang, Liu, Xiuwu
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 15.12.2021; Wiley Subscription Services, Inc
• Subjects: Ammonium dihydrogen phosphate; Chemistry; Decomposition; Decomposition reactions; Desiccants; Extinguishing; extinguishing mechanism; fire extinguishing agent; Free radicals; Magnesium hydroxide; Physical chemistry; Quantum physics; Reaction mechanisms; Thermal decomposition; Ultrafines
• ISSN: 0020-7608; 1097-461X
• DOI: 10.1002/qua.26810

Compound dry powder agent containing Mg(OH)2 is an efficient substitute for halon. Magnesium hydroxide and ammonium dihydrogen phosphate play an important role in chemical fire extinguishing substances. The reaction mechanism and thermal decomposition products of ammonium dihydrogen phosphate and magnesium hydroxide simulated by both molecule and cluster model were theoretically studied. Dense functional theory (DFT) was used to optimize the structure of the samples, and the reaction of the samples with free radicals H·, OH· and CH3· was calculated to prevent the combustion process. A fire extinguishing reaction mechanism that consisted of 13 elementary reactions were proposed. The most kinetically favorable mechanistic pathways in extinguishing reactions were identified. The direct reaction of Mg(OH)2 with H· free radical is the main pathway. Similarly, in the H3PO4 phase, the energy barrier of H3PO4 reacting with free radicals is smaller than that of self‐decomposition and the thermal decomposition of intermediates, indicating that the reaction of H3PO4 with free radicals is also the main route. In addition, the intermediate produced by the reaction will also combine with each other to form new fire extinguishing substances, which accelerates the fire extinguishing process. Therefore, the fire extinguishing effect of composite dry powder containing magnesium hydroxide is higher than the single powder extinguishing agent. H3PO4 and Mg(OH)2, the main components of composite powder fire extinguishing, first react with active radicals in the flame to produce a series of intermediate products (H2PO4,H2PO3,MgOH), part of these intermediate products continue to react with free radicals; another part of intermediate products react with each other to produce new substances (H2MgPO4,H2MgPO3), In addition, Mg(OH)2 clusters also react with free radicals in a cyclic manner to accelerate the fire extinguishing process.