Temperature of Chemical Explosion

When an explosive detonates the reaction is extremely fast and, initially, the gases do not have time to expand to any great extent. The heat 

The temperature of explosion Te is the maximum temperature that the explosion products can attain under adiabatic conditions. It is assumed that the explosive at an initial temperature Tt is converted to gaseous products which are also at the initial temperature T,. The temperature of these gaseous products is then raised to Te by the heat of explosion Q. Therefore the value of Te will depend on the value of Q and on the separate molar heat capacities of the gaseous products as shown in Equation 5.14, where Cv is the molar heat capacities of the products at constant volume and E represents the summation of the heat capacity integrals corresponding to the separate components of the gas mixture  

The rise in temperature of the gases is calculated by dividing the heat generated Q by the mean molar heat capacity of the gases at constant 

Unfortunately, the heat capacities of the gaseous products vary with temperature in a non-linear manner and there is no simple relationship between temperature and Cv. The mean molar heat capacities of some gaseous products at various temperatures are presented in Table 5.15. 

Using this information, the heat liberated by an explosion at various temperatures can be calculated. Te can then be determined from a graphical representation of Te versus Q, as shown in the example below. 

The heat liberated by the explosion will raise the temperature of the gases, which will in turn cause them to expand and work on the surroundings to give a lift and heave effect . The effect of this heat energy on the gas can be used to calculate the temperature of explosion. 

---

When it is mixed with potassium nitrite in the melted state (440°C), ammonium nitrate detonates. The presence of rust decreases the temperature of the explosion to 80-120°C. This behaviour is linked to the chemical incompatibility of the nitrite ion and ammonium ion. 

A thermal explosion is the third type of chemical explosion. In this case, no reaction front is present, and it is therefore called a homogenous explosion. Initially, the material has a uniform temperature distribution. If the temperature in the bulk material is sufficiently high so that the rate of heat generation from the reaction exceeds the heat removal, then self-heating begins. The bulk temperature will increase at an increasing rate, and local hot spots may develop as the thermal runaway proceeds. The runaway reaction can lead to overpressurization and possible explosive rupture of the vessel. 

The pressure vessel test is used to examine the violence of thermal explosions. The test indicates whether a runaway reaction occurs when reactive chemicals in the vessel are heated by a fire or exposure to high temperature, or if the temperature of chemicals in the reactor rises abnormally. This test needs attention because the expulsion of chemicals from inside the vessel may mix with air and cause a mist explosion. 

Tables 16 and 17 Hst tke analytical test methods for different properties of interest. The Manufacturing Chemists Association, Inc. (MCA) has pubUshed the Chemical Safety Data Sheet SD 63, which describes in detail procedures for safe handling of use of toluene (46). The Interstate Commerce Commission classifies toluene as a flammable Hquid. Accordingly, it must be packaged in authorized containers, and shipping must comply with ICC regulations. Properties related to safe handling are autoignition temperature, 536°C explosive limits, 1.27—7.0 vol % in air and flash point 4.4°C, closed cup.

Common reaction rate v. temperature characteristics for reactions are illustrated in Figure 6.5. To avoid runaway conditions (Fig. 6.5a) or an explosion (Figure 6.5c), it may be essential to control the rate of addition of reactants and the temperature. The kinetics and thermodynamics of the reaction, and of possible side reactions, need to be understood. The explosive potential of chemicals liable to exothermic reaction should be carefully appraised. 

---