Rates of Gas Evolution

This section deals with the radiation-induced decomposition of the azide sublattice as detected by nitrogen-gas evolution from both large and small band gap azides. The two groups of azides, which are shown in other sections of this chapter to have different radiation-induced disorder, also have different gas-evolution properties. Another significant difference is the photocurrent which accompanies decomposition in the small band gap azides but has not been observed in the large band gap azides. 

Early studies dealt almost exclusively with the rate of gas evolution as a function of time. In these experiments sample purity, particle size, age, etc.. 

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The possible gas evolution M and the rate of gas evolution (dM/dt) (or corresponding derived parameters) of the reaction or possible decomposition... 

The change in the rate of gas evolution is sometimes not clear, especially when the temperature of the hood is high. When the change is recognized distinctly, the addition of hydrogen cyanide solution may be stopped at this stage. 

With reference to Fig. 6.7, note there is no photocatalytic activity without Ft loading [99] the rate of gas evolution increases with increasing Ft content reaching a maximum at 0.3 wt%. Other metals have shown similar trends in photocatalytic activity. Therefore, it is suggested that metal loading is one of the essential requirements for photocatalytic decomposition of liquid water. However the back reaction of evolved gas on the Ft particles increases with Ft loading. To suppress the backward reaction of H2... 

Semiconductor Loading (metal Rate of gas evolution (umol/li) Ref... 

The vacuum stability test (VST) is considered the most acceptable test for measuring stability and compatibility of explosives, worldwide. This is an empirical test in which rate of gas evolution is measured under isothermal conditions and a limit of 01 cm3 of gas per gram of an explosive is set for explosives heated at 120°C (150°C for RDX) for 40h (25h for PETN). A similar test but at somewhat lower temperatures, is used to assess compatibility of an explosive with other explosives or with non-explosive materials such as binders (polymers), plasticizers etc. 

For the gas-measuring device, the submitters used an inverted, calibrated 10-1. bottle, filled with saturated sodium chloride solution, resting in an enamel bucket big enough to hold the volume to be displaced. The checkers used a gas meter. However, the rate of gas evolution can be estimated by using a simple gas bubbler. 

The peak rate of gas evolution in the reactor can be calculated using an equation from Annex 2 ... 

Qv and Qg should be evaluated at the same temperature and pressure, usually the relief pressure. QG, the volumetric rate of gas evolution, can be obtained from measurements in a calorimetric test by the use of equations (A2.3) or (A2.4) (see Annex 2). Qv is the volumetric rate of vapour generation and can be calculated, as follows, from the rate of temperature rise in a closed calorimetric test or in an open test with a high superimposed containment pressure (see Annex 2). 

The information required for relief sizing for gassy systems is the rate of gas evolution, Qg, (for the full-scale vessel), as a function of temperature. This can be calculated from the rate of pressure rise in the small-scale test by means of one of the following equations111,121. Equation (A2.3) is the more general equation and is best used for data from closed tests ... 

As the mass increases in volume due to the production of gas, a competition between the gas pressure and the gel strength of the polymer ensues. If the former is higher than the latter, a point will be reached at which the foam will collapse. The easiest way to demonstrate this is by increasing the temperature. The reason relates to the activation energies of the two reactions (polymerization and abstraction of CO2). If the temperature is increased, the rate of gas evolution increases faster than the polymerization or gelation. 

Heat flask 1 with the flame of a gas burner through an asbestos gauze and estimate the rate of gas evolution according to the number of bubbles in wash bottle 2. When a uniform stream of gas is established, carefully wear eye protection heat the bottom part of vessel 3 with the open flame of a burner. Do not let the products clog the gas-discharge tube. The amount of the aluminium chloride condensing in the upper part of the apparatus should be insignificant. 

Farmer s experiments were repeated and extended by Garner and Hailes [41]. They examined the behaviour of mercury fulminate at about 100°C and came to the conclusion that during the initial induction period, decomposition is accompanied by a slow evolution of gas at a constant velocity (linear decomposition). At the end of this phase the main decomposition period begins with an increased rate of gas evolution. The authors noticed that if the fulminate is finely ground, rapid evolution of gas begins at once, without any initial period. 

Fix the leak rate and thus p . Allow the ribbon to come to a steady state at any value of 7 c, i.e., 7 c..id. Determine 9 by the flash-off method. Call this 6, or steady-state 9. Again let 0 increase to 0 at T = 7. Now reduce the leak rate to a very low value and wait until the pressure in the system reaches a new low value of p . This will be determined by the rate of gas evolution from the glass walls and the pump speed. Now suddenly raise the ribbon temperature to 7 i, at which the evaporation rate E is to be determined. From a preliminary test this T, should be so chosen that p will rise to about 100p . Record p vs. time t. E at any time t can then be calculated from the following equation ... 

No. Semiconductor Loaded metal Rate of gas evolution/yUmol Ir1... 

Semoicon-ductor Loaded material Rate of gas evolution/jumol h 1 in Na2C03 sol. in pure water h2 o2 h2 o2 ... 

Catalyst Rate of gas evolution (/imol h, g 1) Optimun condition pH of the solution... 

The rate of gas evolution of Tetryl exhibits the characteristic autocatalytic shape as shown in Fig 1 (Ref 23)... 

Results46 on the rate of gas evolution on stirring dialkylmercurys with concentrated aqueous hydrochloric acid are hence not included, since in this case the reaction medium is probably heterogeneous. 

The process of delivery of propellant gases at a predetermined rate involves the selection of a propellant composition with the required burning rate at the operating pressure of the firearm, and then designing the propellant granules so that the necessary burning surface is available to provide the required mass rate of gas evolution, that is, the necessary time/pressure relationship. 

PVC-U foams incorporate sodium bicarbonate and the results are available of an investigation into controlling the rate of gas evolution and heat of decomposition (281). 

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