Combustion behavior of TAL-1308 composite solid propellant for airbag applications

An experimental investigation on the characterization of the combustion behavior of a composite solid-propellant airbag formulation, TAL-1308, has been conducted. The major objective of this study was to experimentally determine several combustion characteristics of the TAL-1308 formulation, such as: 1) steady-state burning rates as a function of initial chamber pressure and propellant temperature; 2) temperature sensitivities; 3) temperature profiles in the condensed-phase; and 4) propellant activation energy. The experimental results were obtained using a high-pressure optical strand burner. Steady-state bum rates were determined for a pressure range of 20.8 to 41.5 MPa (3,000 to 6,000 psig) and initial propellant temperatures of 243 to 353 K. For the pressure and temperature ranges tested, the temperature sensitivity was on the order of 1 × 10^-3 K^-1. The pressure dependency on the burning rate was correlated using the Saint Robert’s law. The pressure exponent for the room temperature case (T_i = 25 °C) was 0.75. Also, the pressure exponent, n, was found to be a function of initial propellant temperature. An Arrhenius form burning rate correlation was also obtained for this propellant. The activation energy and the preexponential factor of the Arrhenius equation are E_a=2.735 kcal/mol and A=15.06 cm/s, respectively. The pressure deflagration limit (PDL) for this propellant was found to be in the range of 8.37 to 8.72 MPa (1,200 to 1,250 psig). Below 17.34 MPa (2,500 psig), the propellant did not regress in the layer-by-layer form. However, for higher pressures (above 20.8 MPa), the layer-by-layer regression of the propellant strand was observed. During combustion, small spherical particles as condensed phase residues were ejected and recovered from the test run. The higher the pressure and initial propellant temperature, the smaller the spherical particles. For pressures below 41.4 MPa, the size of the particles was on the order of 900 μm. For pressures around 84.4 MPa (12,500 psig), the bead size was much smaller, on the order of 300 μm. A chemical analysis on these particles using both the ESEM and the X-ray diffraction method was conducted. The X-ray diffraction results agreed well with the ESEM results and indicated that the material of the TAL-1308 beads was mostly sodium chloride, NaCl, with a small amount of silicon-containing compounds.