Balance, oxygen

The amount of oxygen in each molecule of nitroglycerine (1) and TNT (4) can be calculated and compared with the amount of oxygen required for complete oxidation of the fuel elements, that is, hydrogen and carbon. 

When detonation of TNT (CvHsNsOe), 4, takes place the explosive is oxidized to give a mixture of gases such as carbon dioxide, water, and nitrogen (Eq. 12.20)  

Equation (12.20) is not balanced. The introduction of oxygen atoms (O) is needed to balance the equation (Eq. 12.21)  

TABLE 12.9 Balanced Reaction Formulae for Some Explosives 

The balance of the reaction formula for the combustion of TNT gave a negative sign for oxygen. This therefore indicates that TNT has insufficient oxygen in its molecule to oxidize its reactants full to form water and carbon dioxide. This amount of oxygen as percent by weight can now be calculated as shown in Eq. 12.21 [4]. 

The maintenance of an adequate oxygen balance in a mixture is a problem of high importance. Former German explosives of the Carbonit type, with incomplete combustion, have been banned. Modern mining explosives are required to have an oxygen balance equal to or higher than zero. Investigations in the U.S.S.R. have 

According to Soviet findings a concentration of carbon monoxide of less than 0.00025 % is admissible in the atmosphere of a coal mine, after ventilation of the shotfiring position. Before ventilation, -immediately after shotfiring, the content of CO should not exceed 0.02%. 

A positive oxygen balance markedly reduces the quantity of carbon monoxide formed. Assonov and Rossi [60] report the following results of experiments on the effect of the oxygen balance of explosives on the composition of the gaseous products of explosion (Table 99). 

Other agents also examined in the U.S.S.R. exert an influence on the combustion of the products of an explosion. According to Assonov and Rossi [60] increase in the moisture content of an explosive involves the increase in the content of gaseous products. 

Composition of gaseous products of explosion in explosives with a different oxygen balance 

If the amount of oxygen present in the explosive molecule is insufficient for the complete oxidation a negative oxygen balance will result this can be seen in the molecule TNT. Nitroglycerine, however, has a 

The equation in Reaction 5.1 needs to be balanced, and this can be done by introducing oxygen atoms (O) as shown in Reaction 5.2. 

Total molecular mass of oxygen atoms (O) in the products = — lOf x 16 = —168 

By considering the structural formula of TNT (5.1) and of nitroglycerine (5.2) the proportion of oxygen in each molecule can be 

The Chemistry of Explosives, 3rd Edition By Jacqueline Akhavan J. Akhavan 2011 

Explosive Formula Mol. wt. (g/mol) Blasting strength Oxygen balance (g/atom/kg) 

The detonation of an explosive is an oxidation reaction in which it may be assumed that all the carbon forms CO2, all the hydrogen forms H2O, and all the nitrogen forms N2. On this basis, an explosive with the composition CxHvOzNd will have an oxygen balance (OB) of 

The secondary explosives listed in Tables 14.3 and 14.4 represent the more common compounds. Some comments on a few of these will illustrate their relative characteristics. 

For substances containing only carbon, hydrogen, and oxygen, when the oxygen balance is zero, the reaction is simply  

More generally, the oxygen balance (OB) of a substance CxHyOzHj is expressed by Equation (2-6), when the nitrogen is assumed to evolve as N2  

This equation is not valid for substances containing other elements. 

It is known empirically that explosives with an oxygen balance close to zero are the most powerful [44]. This statement also holds for mixtures of reducing and oxidizing substances for which the OB is formulated as  

The energy that is involved in a reaction can be estimated by calculation if the enthalpies of formation of the reactants and of the products are known. The 

Let us consider the reaction of an oxidizer with the composition CjHbNcOjClgSf, as represented by 

The oxygen balance expressed in mass percent is given by 

For example, NG produces excess oxygen molecules among its combustion products according to 

The oxygen balance of any specified mixture of oxidizers can be obtained by assuming the nature of the oxidized products. Table 2.6 shows the oxygen balances [OB] and densities p of some energetic materials. 

Problem 1 Methyl nitrate, CH3NO3, is used as a rocket propellant. It explodes when heated to its boiling point, 64.5°C (148°F) 

This is a highly exothermic reaction releasing 646.8 kcal heat when 4 mol of methyl nitrate bnm. This is eqnal to 161.7 kcal/mol or 2.1 kcal/g. Also, in addition to such heat release, the above reaction shows that 12 mol of gaseons prodnct are formed, cansing a sndden and enormous increase in pressnre and, thns, an explosion. 

The explosive power or energy release of explosive chemicals that contain oxygen may be qualitatively assessed and predicted from 

TABLE X.2 Structural Features of Selected Classes of Explosive Compounds 

Azo compound Diazo compound Difluoroamino compound C—N=N— + C=N=N F -n( F Azoformamide Diazomethane 1,1-Difluorourea 

Some of them are described below largely following [41] 

Brisance is the destructive fragmentation effect of a charge on its immediate vicinity. The relevant parameters are the detonation rate and the loading density (compactness) of the explosive, as well as the gas yield and the heat of explosion. Brisance is a measure for the time required to build up the maximum explosion pressure. 

Loading density is understood to be the ratio between the mass of explosive and the volume available for the detonation. It depends on the production process, e.g. 

The oxygen balance is the quantity of oxygen, expressed in percent mass, released by complete conversion of the explosive. If all the oxygen bonded in the explosive is not sufficient to convert the explosible material completely, the oxygen balance is negative. In the converse case it is positive (cf. Table 2.31). 

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Shanley, E. S. and G. A. Melhem, 1995. The Oxygen Balance Criterion for Thermal Elaz-ards Assessment, Process Safety Progress, 14(1), 29-31. 

Hence the total contribution of water vapour to the combined form of hydrogen is 3x X2 Ku,o PtllX allowing for conuibutions to the hydrogen balance and the corresponding oxygen balance. A / is simply equal to the sum of the final number of molecules... 

Substances which have an adverse effect on the oxygen balance, particularly ammonia, nitrates The following metalloids and metals and their compounds ... 

An oxygen balance can be used to calculate water formed by the cniubus-tion ol coke ... 

Oxygen balance for an aerated system with activated sludge is defined by a dynamic model ... 

Making oxygen balance for the aeration tank, the dynamic transfer rate of oxygen is obtained ... 

Dividing the oxygen balance by the volume of the aeration tank and concentration of biomass, XV, the above equation will be simplified as follows ... 

Oxygen Balance of Common Explosives and Explosive Ingredients. 

In what follows OB wili always refer to oxygen balance to C02 unless otherwise stated. For convenience the % sign will not be used although it is to be understood that all subsequent OB s are in percent... 

Detonation Equilibria. Most of the commonly used expls are compds or mixts whose elemental compn consists of C, H, N, O. If the expl is reasonably oxygen-balanced (see Oxygen Balance in this Vol) then the detonation product... 

For nearly oxygen-balanced expls equilibrium (1) will dominate and control the compn of the detonation products. As already stated this equilibrium is expected to be independent of pressure if the gases behave ideally. But even for ideal gas behavior and an oxygen-balanced expl, no direct comparison can be made between theoretical detonation product calcns and observed products. This is so because measurements are made at temps much lower than detonation temps, and the products reequilibrate as the temp drops. Further complications arise because the reequilibration freezes at some rather high temp. This is a consequence of re-, action rates. At temps below some frozen equb... 

To anticipate some of the results to be presented later, it is instructive to compute the equilibrium compn ofPETN at 1600°K. PETN is nearly oxygen-balanced and as will be shown later its Tfr- 1600°K. The empirical formula for PETN is CgHs On. Let X be the number of moles of C03 at equilibrium, and C, H, O the original gram atoms of carbon, hydrogen and oxygen respectively. Then from mass balance and Raoult s law... 

Except for oxygen-balanced expls, the computation of detonation products depends strongly on the choice of the equation of state (EOS) for these products. In the US the BKW EOS (see Vol 4, D272-R) has been favored and most of the computed product compns below will be based on it. Some of these will be compared with the relatively few calcns based on a Lennard-Jones-Devonsnire (UD) EOS (see Voi 4, D287-L)... 

Unfortunately, chemical species produced by humans can react in ways that reduce the O3 concentration. For example, NO changes the oxygen balance through the following reactions NO + 03 NO2 + O2... 

GP 2] [R 2] Initial work with a steel multi-plate-stack micro reactor with micro-structured platelets made of polycrystalline silver (OAOR modified) confirmed a selectivity of up to 49% at conversions of about 12% (3 vol.-% ethylene, 50 vol.-% oxygen, balance nitrogen 5 bar 41 h 277 °C) [4, 26, 40]. 

GP 4] [R 11] For methanol conversion over sputtered silver catalyst, no catalyst deactivation at high oxygen methanol ratios (e.g. over 0.2 1) was observed, different from findings in the literature with conventional catalysts and reactors (8.5 vol.-% methanol 10-90% oxygen balance helium 510 °C 10 ms slightly > 1 atm) [72]. 

GP 9] [R 16] The reaction rate and activation energy of metal catalysts (Rh, Pt or Pd) supported on alumina particles ( 3 mg 53-71 pm) were determined for conversions of 10% or less at steady state (1% carbon monoxide 1% oxygen, balance helium 20-60 seem up to 260 °C) [7, 78]. The catalyst particles were inserted into a meso-channel as a mini fixed bed, fed by a bifurcation cascade of micro-channels. For 0.3% Pd/Al203 (35% dispersion), TOF (about 0.5-5 molecules per site... 

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