Albert S. Tompa

Thermal analysis of liquid and solid propellants

Abstract Kinetic constants from differential scanning calorimetry data using heat evolution and variable heating rate methods were obtained for the thermal decomposition of a liquid monopropellant; good agreement was found between the observed and predicted half-life for the first order decomposition reaction. The rate of volatilization of nitroglycerin in a crosslinked double base propellant was investigated by isothermal and dynamic thermogravimetry and was found to be first order. The effect of sample size, atmospheric environment, aging and crosslink density of the propellant on the volatilization rate was determined. It was observed that the rate increased as (1) the sample was changed from a cylindrical plug to a powdered form, (2) the atmosphere around the sample was changed from nitrogen to helium to vacuum, (3) as the thermal stability of the sample decreased, and (4) the relative crosslink density was changed from a higher to a lower value. A kinetic compensation effect was found for cylindrical plugs but not for powdered samples.

DSC and TG study of the stability in vacuum of ferrocenyl compounds and their compatibility with ammonium perchlorate

Abstract Ferrocenyl compounds are used as burning rate modifiers for propellants containing ammonium perchlorate. An admixture of a ferrocenyl compound and ammonium perchlorate is highly sensitive to an electrostatic discharge. When ammonium perchlorate is added to a propellant mix, a cloud of ammonium perchlorate dust is formed above the mix, and if the ferrocenyl compound is volatile at the mixing temperature of 150°F and at 5 mm vacuum then a potentially hazardous operation may exist. A simple, fast, isothermal and dynamic thermogravimetry method was developed to determine the stability and half-life of the ferrocenyl compound under processing conditions. The half-lives of nine ferrocenyl compounds were found to range from one hour to over one year in vacuo at 150°F. Dynamic DSC showed interactions between the components in the mixture. In a vacuum, individual ferrocenyl compounds and ammonium perchlorate showed endothermic peaks due to decomposition and sublimation, respectively. In the mixture exothermic decomposition peaks were observed for the moieties at lower temperatures than those for the neat components. The activation energies for the thermal decomposition of the ferrocenyl compounds were decreased by 20% in the mixtures.

Effect of energetic materials on the thermal stability of polymers

Abstract The effect that energetic additives, such as ammonium perchlorate, ammonium persulfate, cyclotetramethylenetetranitramine, triaminoguanidine nitrate, plastisol nitrocellulose, and a nitrate lacquer at the 5% level, had on the thermal stability of polyacetals, aliphatic and aromatic polyesters, and polyamides was investigated by isothermal and dynamic thermogravimetry in a nitrogen and air atmosphere. Activation energies were determined for some of the admixtures; the additives were found to lower the activation energy by 30–88%. The effect of a series of ammonium and potassium salts on the thermal degradation of polyacetals was determined. It was found that the more acid character the cation and anion moieties had, the more effective the substance was in decreasing the thermal stability of polyacetals. Thermal instability of an admixture of polymer and additive was observed as a shift of the thermogravimetry curve to a lower temperature or by an increase in the rate of volatilization. Dynamic thermogravimetry studies of polyacetal admixtures offered a novel method for distinguishing between the acid strengths of the additives.

A TG study of the solvolytic breakdown of a crosslinked double base propellant

Abstract The solvolytic breakdown and dissolution of obsolete crosslinked propellants may be carried out with surprising ease with subsequent recovery of expensive constituents in high yields. An approach was adopted in which degradation was initiated in composites while they were swollen in an appropriate solvent containing additives capable of reacting with and cleaving chemical bonds located in the polymer chain. A kinetic study of the solvolysis reaction of the urethane linkages in a crosslinked double base propellant in ethanolamine solution was followed by thermogravimetry. Kinetic data were obtained using the propellant fraction reacted, which was expressed as the product of the TG fraction at 200°C and the molarity of the ethanolamine solution. First-order rate constants for the reaction were found to be higher in the mixed solvent of toluene-isopropanol compared with isopropanol probably because of their differences in swelling behavior. Activation energies for solvolysis were about 5 kcal mole −1 in toluene-isopropanol and about 8 kcal mole −1 in isopropanol. Nitroglycerin present as a plasticizer in double base propellants was extracted prior to kinetic analysis because it was found to react with the ethanolamine. The solvolytic degradation of the propellant binder with nitrocellulose was about three times as fast as the binder without nitrocellulose. A variable heating rate study showed that the binder with or without nitrocellulose had the same activation energy for thermal decomposition. Kinetic data indicates that nitrocellulose appears to catalyze the solvolytic degradation but not the thermal degradation of a crosslinked double base propellant binder.

Effect of additives and particle size on the hydrolysis of aluminum at 100° to 110°C

Abstract The reaction of aluminum powder with water at 1000 to 110oC was carried out in glass pressure bottles and was followed by the change in gas pressure as a function of time. It was observed that as the particle size of aluminum increased, the percentage reacted decreased. The proportions of aluminum found to react under conditions used in solid propellant degradation was of minor significance. Hydrogen was involved, however, in sufficient quantity to form explosive mixtures with air and to raise the pressure of closed systems by an atmosphere or more. In the presence of oxidizing salts some of the hydrogen was oxidized and chloride was formed from ammonium and potassium perchlorates. Nitrates were reduced to ammonia. The proportion of these salts reduced was small, however, and was a linear function of the concentration of the additive. The effect on the hydrolysis rate of aluminum by Perchlorate and halide salts solution appeared to correlate with the ionic radius of the additive cation when the anion was held constant and with the additive anion when the cation was held constant. As the radius decreased the hydrolysis rate increased. The effect of some oxidants on the hydrolysis rate of aluminum appeared to depend upon the final pH of the solution; the rate increased in highly basic solution and decreased in slightly acidic or neutral solution compared to water alone. A slight reaction of aluminum powder with alcohols was observed at 1000C. The rate of reaction increased as the dielectric constant of the alcohol increased.