Figure 8 Potential energy diagram of the reactions between R125
and H·, OH·.
In order to further explore the fire extinguishing mechanism of R123,
the reactions of R125 with H· and OH· radicals are also calculated as a
comparison (Figure 8). The same as R123, R125 and free radicals mainly
undergo substitution reactions and abstraction reactions. For the
reaction of R125 with H·, three additive reaction paths are
theoretically exhibited, with P17 (path 17), P18 (path 18) and P19 (path
19) separately generated via TSd1, TSd2 and TSd3 by consuming 164.9,
148.6 and 59.8 kj·mol-1. And two substitution
reactions occur about R125 with OH·, which consumes 304.0 and 296.6
kj·mol-1 respectively, these reactions can generate
more F· atoms. However, the product
of R123 contains not only F· atoms but also
Cl· atoms, Cl· atoms are easier to
generate than F· and CF3· atoms, and the energy barriers
that need to be overcome are lower, so the fire extinguishing
performance of R123 is better. The introduction of fluorine-species
reactions and chlorine-species reactions in literature, it is indicated
that fluorine-species reactions have less sensitive to the burning
velocity. For the chlorine-species reactions, the burning velocity is
sensitive to three reactions of the initial break-down of R123, such as
CF3CH2Cl=CF3+CH2Cl,
CF3CHCl2+H=
CF3CHCl+HCl[18]. And two of the reactions in the
catalytic radical recombination cycles (HCl + OH = Cl +
H2O, and Cl + HCO = CO + HCl) are affecting the burning
velocity[36, 37]. In general, the chlorine-species reactions have
more obvious inhibitory effect on the burning velocity.