In view of the appropriate physicochemical characteristics and environmental friendliness of the trans-1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz(E)) substance, the thermal-decomposition mechanism as well as the fire-extinguishing mechanism and performance of this agent were systematically studied by employing both experimental and theoretical methods in this work. We found that the HFO-1336mzz(E) agent not only has promising thermal stability at room temperature but also exhibits pronounced fire-extinguishing performance, which is comparable to that of HFC-236fa and even better than that of HFC-125 extinguishant. Additionally, the promising fire-extinguishing performance of HFO-1336mzz(E) may result from the physical and chemical extinguishing effect of its thermal-decomposition products including HFO-1336mzz(Z), HCCCF3, CF3CCCF3, and CF3H, which makes a significant contribution to capturing the free radicals in the flame, as well as cooling and diluting the combustible fuel-air mixture. Both experimental and theoretical results suggest that the HFO-1336mzz(E) agent is a highly recommendable candidate for Halon extinguishant, which is worthy of further investigation and evaluation of its practical applicability in fire-suppression utilization.
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.
Due to the serious destruction of Halon to the ozone layer, it is significant to explore the fire‐extinguishing agent with zero ozone depletion potential (ODP). At the molecular structure level, Octafluoro‐2‐butene has a special arrangement of fluorine atoms, endowing itself with better potential to replace Halon than the reported perfluoroalkanes and hydrofluoroethylenes (HFOs). However, as a new Halon substitute, the fire‐extinguishing mechanism of Octafluoro‐2‐butene has not been studied. In this paper, the thermal decomposition and fire‐extinguishing mechanism of Octafluoro‐2‐butene were studied by density functional theory (DFT) and the rate constants of each reaction path were calculated for the first time. The calculation results show that Octafluoro‐2‐butene produces a large number of fire extinguishing groups and the rate constants of the main fire extinguishing paths are fast. Noteworthy, there is no combustion radical produced during extinguishing. In addition, the thermal decomposition of Octafluoro‐2‐butene mostly produced halogenated alkane with the better ability to react with chain radicals. The theoretical results show that Octafluoro‐2‐butene is a promising Halon substitute, and its practicability can be further studied and comprehensively evaluated.
As Halon extinguishers impose severe damage to the stratospheric ozone layer, Halon substitutions are urgently desired and explored. In this paper, the thermal decomposition mechanism, the fire‐extinguishing performance and mechanism were experimentally and theoretically investigated for Trifluoroiodomethane (CF3I). The theoretical results direct that CF3I and its main decomposition products (CF3· and I·) can react with OH· and H· to block the combustion chain reactions. Besides, reaction kinetics analysis also direct that CF3· and I· are more easily generated during the interaction between CF3I and the flame. And the minimum fire‐extinguishing concentration (MEC) of CF3I in extinguishing methane‐air flames is 3.42 vol%, which is lower than those of representative HFCs and HFO‐1336mzz(E) and even comparable to that of Halon 1301. Both the experimental and theoretical results suggest the promising applicability of CF3I in practical Halon replacement and the necessity of its further evaluation.
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