Very high pressure chemical reactions explosives

The heat of decomposition (238.4 kJ/mol, 3.92 kJ/g) has been calculated to give an adiabatic product temperature of 2150°C accompanied by a 24-fold pressure increase in a closed vessel [9], Dining research into the Friedel-Crafts acylation reaction of aromatic compounds (components unspecified) in nitrobenzene as solvent, it was decided to use nitromethane in place of nitrobenzene because of the lower toxicity of the former. However, because of the lower boiling point of nitromethane (101°C, against 210°C for nitrobenzene), the reactions were run in an autoclave so that the same maximum reaction temperature of 155°C could be used, but at a maximum pressure of 10 bar. The reaction mixture was heated to 150°C and maintained there for 10 minutes, when a rapidly accelerating increase in temperature was noticed, and at 160°C the lid of the autoclave was blown off as decomposition accelerated to explosion [10], Impurities present in the commercial solvent are listed, and a recommended purification procedure is described [11]. The thermal decomposition of nitromethane under supercritical conditions has been studied [12], The effects of very high pressure and of temperature on the physical properties, chemical reactivity and thermal decomposition of nitromethane have been studied, and a mechanism for the bimolecular decomposition (to ammonium formate and water) identified [13], Solid nitromethane apparently has different susceptibility to detonation according to the orientation of the crystal, a theoretical model is advanced [14], Nitromethane actually finds employment as an explosive [15],... 

Materials or substances, which, by themselves, are unstable and easily cause a violent chemical reaction without causing an explosion. This includes all substances that can easily engage in very exothermic transformations at high temperature and pressure. It also includes all substances that react violently with water or that can produce mixtures potentially explosive to water. 

The first recorded dust explosion occurred when a bakery storeroom exploded in a small city called Turin (Italy) way back in 1785. Such an explosion is also labeled as thermobaric , a chemical reaction that produces extremely high pressure and heat very rapidly. In the early 1960s, scientists began experimenting with this concept to produce a weapon that uses the same principle, but employs volatile gases and finely powered explosives. 

Most chemical reactions give off heat and are classified as exothermic reactions. The rate of a reaction may be calculated by the Arrhenius equation, which contains absolute temperature, K, equal to the Celsius temperature plus 273, in an exponential term. As a general rule, the speed of a reaction doubles for each 10°C increase in temperature. Reaction rates are important in fires or explosions involving hazardous chemicals. A remarkable aspect of biochemical reactions is that they occur rapidly at very mild conditions, typically at body temperature in humans (see Chapter 3). For example, industrial fixation of atmospheric elemental nitrogen to produce chemically bound nitrogen in ammonia requires very high temperatures and pressures, whereas Rhizobium bacteria accomplish the same thing under ambient conditions. 

Outside high vacuum systems we will have an ensemble of molecules that will exchange energy. Typically, thermal equilibrium will be maintained during chemical reaction. There are, though, important exceptions such as chemical reactions in flames and in explosions, as well as reactions that take place at very low pressures. 

An explosion is a sudden and violent release of energy. Usually it is the result, not the cause, of a sudden release of gas under high pressure. The presence of a gas is not necessary for an explosion. An explosion may occur from a physical or mechanical change, as in the explosion of a steam boiler, or from a chemical reaction. The explosion of a flammable mixture in a process vessel may be either a deflagration or a detonation, which differ fundamentally. Both can be very destructive. Detonations are particularly destructive, but are unlikely to occur in vessels. 

The original classification of explosives separated them into two very general types low and high, referring to the relative speeds of their chemical reactions and the relative pressures produced by these reactions. This classification still is used but is of limited utility because the only low explosives of any significance are black powder and smokeless powder. All other commercial and military explosives are high explosives. 

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