R. Meyer J. Köhler A. Homburg Explosives

Thermodynamic Calculation of Decomposition Reactions
2. Explosive and Porpellant Composition with a Negative
Oxygen Balance
Calculation of gunpowders.
The decomposition reactions of both detonation and powder combustion
are assumed to be isochoric, i.e., the volume is considered to be
constant, as above for the explosion of industrial explosives.
The first step is also the sum formula
CaHbOcNd
as described above, but now
c < 2a + 1
2 b
The mol numbers n1, n2, etc. cannot be directly assumed as in case
the of positive balanced compositions. More different reaction products
must be considered, e.g.,
CaHbOcNd = n1CO2+n2H2O+n3N2+n4CO+n5H2+n6NO;
CH4 and elementary carbon may also be formed; if the initial composition
contains Cl-, Na-, Ca-, K-, and S-atoms (e.g., in black powder), the
formation of HCl, Na2O, Na2CO3, K2O, K2CO3, CaO, SO2 must be
included. Further, the occurrence of dissociated atoms and radicals
must be assumed.
The mole numbers n1, n2, etc., must meet a set of conditions: first, the
stoichiometric relations
a= n1+2 n5
(1)
(carbon containing moles)
h=2 n2+2 n5
(2)
(hydrogen containing moles)
c=2 n1+n2+n4+n6
(3)
(oxygen containing moles)
d=2 n3+n6
(4)
(nitrogen containing moles);
second, the mutual equilibrium reactions of the decomposition products:
the water gas reaction
H2O+CO = CO2+H2;
the equilibrium is influenced by temperature and is described by the
equation
K1 =
[CO] [H2O]
[H2 [CO2]
K1: equilibrium constant
[CO2], [H2], [H2O] and [CO]: the partial pressures of the four gases.
318
(5)