Gas formation rates

When this reaction rate was measured by the rate of molar gas formation in a Schwab type differential reactor 28, 28a) over silica-alumina catalyst, this rate was found not greatly affected by the introduction of a platinum component into the catalyst mass the observed gas formation rate remained controlled by the acidic activity alone. Yet, an analysis of the gas produced, and of the liquid product, showed a shift in product composition... 

ABSTRACT. The use of mass spectrometry to collect data on the decomposition chemistry of nitramine compounds and the relevance of the data to the processes occurring in these materials when they are used in actu propellant and explosive applications is discussed. The simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS) and time-of-flight (TOF) velocity-spectra techniques and then-application to the study of energetic materials are discussed. The means by which these techniques enhance the amount of information obtained from more conventional mass spectrometric experiments is illustrated with studies on the evaluation of the use of appearance energy measurements to study the thermal decomposition of HMX and on the identiHcation of the HMX pyrolysis products and the determination of their gas formation rates. 

After all of the pyrolysis products from the decomposition are identified, the STMBMS data are used to determine the rate of formation of each pyrolysis product by the general procedure illustrated in Figure 7, In this procedure the time-dependent mass spectrometry and microbalance data are used in conjunction with the reaction cell flow conditions to determine the time-dependent gas formation rates of the different products in the reaction cell. The gas formation rate is defined... 

Figure 14. Gas formation rates of the pyrolysis produas during the decomposition of HMX in a reaction cell with a 0.014 cm diameter orifice and at 212°C. The HMX sample size is 9.956 mg.

The STMBMS and TOF velocity spectra techniques enhance the use of mass spectrometry in the study of the decomposition of energetic materials. The careful control of the reaction environment in these experiments allows the identification of the pyrolysis products and accurate measurement of their gas formation rates to be made. Correlation between the observed products and the macroscopic and microscopic processes occurring within the reaction cell will allow qualitative models to be created that may explain the processes leading to the formation of the various products. Hopefully, these results may be correlated with the more limited results gathered from experiments conducted under more severe conditions (i.e. shock initiated reactions or quenched combustion experiments) to provide further insight into the mechanisms controlling the combustion of these materials under their operational conditions. 

The gas formation rates are defined as the rates that gaseous products appear in the free volume of the reaction cell. The time constant for the exhaust of gas from the free volume of the cell is 0.2 sec. Since gases that are formed within the particles may be released to the free volume of the reaction cell at some time after they were first formed, the data does not provide the time-dependence of the actual gas formation rates directly. Determination of the actual gas formation rates within the particles from the data will depend on properly modelling the release processes from the particles. 

The gas formation rates for the decomposition of HMX at 235°C is shown in Figure 5. The HMX reaches its isothermal temperature before little decomposition has occurred. Once the HMX reaches its isothermal temperature, the HMX vapor pressure within the cell remains approximately constant. However, the decomposition products exhibit the induction, acceleratory, and decay stages that are associated with condensed-phase reactions. It is also apparent from the data in Figure 5 that the temporal behaviors of all the products are not correlated with each other. 

Figure 5. Gas formation rates of the more abundant pyrolysis products formed during die decomposition of HMX. The sample reaches its constant temperature of 235 C at the hrst peak in the HMX signal.

Figure 6. Gas formation rates of H2O, CH2O, N2O, and HMX and their isotopic analogues during the induction period of the decomposition of unlabelled and deuterium labelled HMK. The HMX gas formation rate is determined by the HMX vapor pressure and the exhaust rate fiom the reaction cell.

A comparison of the gas formation rates of the major pyrolysis products for sample sizes of 8.6 mg and 27.9 mg, shown in Figure 9, indicates that the gas formation rates are proportional to the... 

Figure 8. Gas formation rate of the less abundant pyrolysis products formed during the decomposition of HMX as a function of the extent of sample decomposition X.

Figure 10. Gas formation rates of pyrolysis products from the isothermal decomposition of unlabelled and deuterium labelled HMX as a function of the extent of HMX decomposition X.

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