Ignition thermal

Thermal ignition sources A source that will cause the ignition of a flammable gas, vapor, or dust, such as an electric spark, flame, or hot surface. 

Although the thermal-ignition theory was developed for double-base propellants, several investigators have attempted to correlate the ignition characteristics of composite propellants using this approach. Baer and Ryan (Bl) have correlated ignition data for a polysulfide-ammonium perchlorate... 

Two observations on the correlations can be made. First, these results tend to invalidate one of the major objections to the application of the thermal-ignition theory to composite propellants, namely that heterogeneous interfacial reactions within the solid phase are not possible. Secondly, the effect of pressure on propellant ignitability can be qualitatively explained. 

Peaking and Non-isothermal Polymerizations. Biesenberger a (3) have studied the theory of "thermal ignition" applied to chain addition polymerization and worked out computational and experimental cases for batch styrene polymerization with various catalysts. They define thermal ignition as the condition where the reaction temperature increases rapidly with time and the rate of increase in temperature also increases with time (concave upward curve). Their theory, computations, and experiments were for well stirred batch reactors with constant heat transfer coefficients. Their work is of interest for understanding the boundaries of stability for abnormal situations like catalyst mischarge or control malfunctions. In practice, however, the criterion for stability in low conversion... 

Although studied for agitated reactors, the phenomena of thermal ignition are probably of more interest in the non agitated high conversion reactors such as the polymerize-... 

Figure 2. Experimental temperature-time profiles for batch styrene polymerization with and without thermal ignition (S)...

It is obvious, then, that only the H2—Cl2 reaction can be exploded photo-chemically, that is, at low temperatures. The H2—Br2 and H2—12 systems can support only thermal (high-temperature) explosions. A thermal explosion occurs when a chemical system undergoes an exothermic reaction during which insufficient heat is removed from the system so that the reaction process becomes selfheating. Since the rate of reaction, and hence the rate of heat release, increases exponentially with temperature, the reaction rapidly runs away that is, the system explodes. This phenomenon is the same as that involved in ignition processes and is treated in detail in the chapter on thermal ignition (Chapter 7). 

With the physical insights developed from this qualitative approach to the thermal ignition problem, it is appropriate to consider the more quantitative approach of Frank-Kamenetskii [6],... 

Since (E/RT0) 1 is a small quantity not exceeding 0.05 for most cases of interest and (cvT0IQ) is also a small quantity of the order 0.1, the quantity (cvRT, /QE) may be considered to have a range from 0.01 to 0.001. Thus, the thermal ignition time for a given initial temperature T0 is from a hundredth to a thousandth of the reaction time evaluated at T0. Since from Eq. (7.28) and its subsequent discussion,... 

Our first example of a chain reaction, the decomposition of acetaldehyde to methane and CO, is endothermic so the reactor tends to cool as reaction proceeds. However, the oxidation of H2 is exothermic by 57 kcal/molc of H2, and the oxidation of CH4 to CO2 and H2O is exothermic by 192 kcal/mole of CH4. Thus, as these reactions proceed, heat is released and the temperature tends to increase (strongly ). Thus thermal ignition is very important in most combustion processes. 

In this section we consider a simple model that explains many features of thermal ignition processes. 

A. Ma ek, ChemRevs 62, 44-47 (1962) (Thermal decomposition of explosives including a thermal explosion theory) 14) A.M. Grishin O.M. Todes, DoklAkadN 151(2), 366-68 (1963) CA 59, 12585(1963) (Thermal explosion with heat transfer by convection and conduction) 15) P.G. Ashmore T.A.B. Wesley, "A Test of Thermal-Ignition Theory in Autocatalytic Reactions , lOthSympCombstn (1965), pp 217-226... 

P.G.Ashmore fit T.A.B.Wesley, A Test of Thermal Ignition Theory in Autocatalytic Reactions , 10th SympCombstn (1965), pp 217-26... 

A study of burning rate for a series of conventional thermite mixtures (Fe203[s]-Al[s] [micron-sized]) and nanocomposites (Fe203[s]-UFG[s] [nanosized]) indicates that nanocomposites appear to burn much more rapidly and are more sensitive to thermal ignition than conventional thermite mixtures. At the same time, it is interesting to observe that most of the nanocomposites are found insensitive during standard impact, spark and friction tests [103]. 

Another constituent of perchlorate explosives, ammonium perchlorate, unlike ammonium chlorate, is stable. It is also dissimilar to potassium perchlorate in being an explosive in the pure state, like ammonium nitrate. The greater specific gravity of ammonium perchlorate gives to explosives with which it is mixed a greater power than that of similar ammonium nitrate explosives. The former are also more sensitive than chlorate explosives to friction and impact and to thermal ignition. 

Molecular weight Decomposition temperature/°C Thermal ignition temperature/°C Crystal density at 20 °C/g cm 3 Energy of formation/kJ kg 1 Enthalpy of formation/kJ kg... 

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