Liquid Explosive Mixtures - Liquid Explosives - page 298

7.1 Nitro Liquid Explosive Mixtures

7.1.1 Nitromethane-Based Liquid Explosives

Nitromethane was only recognized as an explosive featuring typical explosion
characteristics in the past 30 40 years. Particularly, in 1958, two explosion inci-

dents took place in the railroad tank cars that were transporting nitromethane in the
US, proving that nitromethane could be a liquid explosive with strong power.
Nitromethane is a colorless transparent liquid with a boiling point of 101.2

-

° C and

C. Its density is 1.138 and 1.124 g/cm 3 at 20 and 30

freezing point of 28.55 ° ° C,

−

respectively. The temperature coef cient of the density of nitromethane (d ρ /dt)is

C − 1 .
The heat of combustion for nitromethane is 708.1 kJ mol − 1 under standard
conditions, and the enthalpy of formation for liquid nitromethane at 25

0.001377 g/cm 3 °

−

° Cis

0.63 kJ mol − 1 , whereas the one for gaseous nitromethane is only

112.99 ±

−

74.65 kJ/mol − 1 at the same temperature.
Nitromethane can form azeotrope with many organic solvents. Additionally, it can
dissolve certain polymers, nitro compounds, and nitrate compounds. Nitromethane is
partially miscible with water; at 20

−

C, the solubility of nitromethane in water is
9.5 % (by volume) or 10.5 % (by mass), meanwhile, the solubility of water in
nitromethane is 1.75 % (by mass). Generally, the miscibility of nitromethane
increases with the rise of temperature. Dry nitromethane is a neutral substance, thus it
possesses excellent storage stability. After being stored for certain period of time, wet
nitromethane will become acidic, which making it capable of corroding metals,
however, adding a small amount of phosphoric acid or phosphate can effectively
inhibit corrosion.
Low-carbon nitroalkanes have similar physical properties as nitromethane, but
they are comparatively more dif

°

cult to detonate, exhibiting inferior detonation
properties, therefore, they are mainly used in liquid explosive mixtures to lower the
freezing point of nitromethane. Table 7.1 listed the physical properties of four low-
carbon nitroalkanes including nitromethane (NM), nitroethane (NE), iso-nitropro-
pane, and nitropropane.
As shown in Table 7.1 , increasing the number of carbon atoms in nitroalkanes
can lead to the rise of density, which in turn would increase the dif culty of

detonation, ultimately dampening detonation properties.
Nitromethane is an extremely insensitive explosive. Heating or burning nitro-
methane in thin-walled containers would not lead to detonation. Explosion would
only take place when nitromethane is heated to 300

C or above in a sealed thick-
walled container. The sensitivity of nitromethane to mechanical shock is closely
related to whether it contains bubbles. Using no.8 detonator alone cannot detonate
nitromethane at ambient temperature, and booster pellets must be employed. The
detonation sensitivity of nitromethane increases with the rise of temperature, while
its critical diameter is reduced. Figure 7.1 showed the effects of temperature on
critical diameter and detonation velocity of nitromethane sealed in tubes [ 31 ].

°