The mechanism of super-rate burning of catalyzed double base propellants

Lead-based compounds are the current industrystandard ballistic modifier for double-base propellants, but there is a pressing need for alternatives as incoming European legislation will soon ban their use. This review article introduces the main concepts and terminologies in the combustion chemistry of double-base propellants, and critically evaluates the four theories put forward in the literature to account for the ballistic modifier effect, namely (i) photochemical, (ii) chelating/complex, (iii) carbon soot, and (iv) free radical theories. We also review the literature on current trends in ballistic modifier research and note the emerging potential of oxide nanoparticles (in particular Bi 2 WO 6) and Cu/Bi encapsulated in carbon nanotubes as lead-free ballistic modifier additives.

Section: Combustion Reactions and The Five Combustion Zonessupporting

confidence: 78%

Section: Combustion Reactions and The Five Combustion Zonesmentioning

confidence: 59%

Section: Combustion Reactions and The Five Combustion Zonesmentioning

confidence: 99%

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A Review of the Catalytic Effects of Lead‐Based Ballistic Modifiers on the Combustion Chemistry of Double Base Propellants

Warren

Zi-Xuan

Pulham

et al. 2020

“…There are mainly three factors that are believed to have an influence on this:t he heat loss data treatment applied for the closed vessel results has an impact on the burning rates and givent he impact of the volume reducing sleeve on heat loss, this might have influenced the pressure exponent.H owever,g iven that the heat loss is comparable for every propellant, the validity of the comparison between the propellants is unchanged. Secondly,t he nitrocellulose used in the propellant formulationh ad slightly different nitrogen content compared to the referenceu sed: 13.25 %i nt his work compared to 12.56 % [ 18].F inally,t he reference from which the formulation was taken presented mostly strand burnerr esults and some variation is to be expected between strand burner and closedd ata due to the difference in pressure. It is unknown, which factor or combination of these factors is responsible for the difference in The general effect of either of the two bistetrazoles on the burn rate of the propellants followed the same trend, which is an increase of the pressure exponent along with ad ecrease of the b coefficient at low concentrations.…”

Section: Burning Ratesmentioning

confidence: 69%

Burning Rates and Thermal Behavior of Bistetrazole Containing Gun Propellants

Lavoie

Petre

Paradis

et al. 2016

The influence of two selected bistetrazoles, 5,5′‐bis(1H‐tetrazolyl)‐amine (BTA) and 5,5′‐hydrazinebistetrazole (HBT), on the combustion behavior of a typical triple‐base propellant was investigated. Seven propellant formulations, one reference and six others incorporating 5 %, 15 %, and 25 % of either HBT or BTA compounds, respectively, were mixed and extruded into a cylindrical, no perforations, geometry. The resulting propellants showed high burning rates, up to 93 % higher than the reference formulation at 100 MPa. However, the increase in burning rates came at the cost of higher burning rate dependency on pressure, with a pressure exponent as high as 1.4 for certain formulations. HBT‐containing propellants showed notably lower flame temperature when compared to the reference formulation, with a flame temperature reduction of up to 461 K for the propellant containing 25 % HBT. The thermal behavior of the propellants was also investigated through DSC experiments. The addition of bistetrazoles provided lower decomposition temperatures than the pure nitrogen‐rich materials, indicating that the two compounds probably react readily with the −ONO2 groups present in the nitrocellulose and the plasticizers used in the formulation. The onset temperature of all propellants remained within acceptable ranges despite the observed decrease caused by the addition of the bistetrazole compounds.

“…The methods of burning rate measurements and manufacture of these thermocouples are described in Ref. 5. Burning rates were measured at 243 K, 293K, and 343K, which gave a lOOK temperature difference for the initial propellant temperature.…”

Section: Burning Rate and Thermachemical Analysismentioning

confidence: 99%

Combustion Mechanism of Azide Polymer

Kubota

Sonobe

1988

Self Cite

154

The combustion wave structure and thermal decomposition process of azide polymer were studied to determine the parameters which control the burning rate. The azide polymer studied was glycidyl azide polymer (GAP) which contains energetic – N3 groups. GAP was cured with hexamethylene diisocyanate (HMDI) and crosslinked with trimethylolpropane (TMP) to formulate GAP propellant. From the experiments, it was found that the burning rate of GAP propellant is significantly high even though the adiabatic flame temperature of GAP propellant is lower than that of conventional solid propellants. The energy released at the burning surface of GAP propellant is caused by the scission of NN2 bond which produces gaseous N2. The heat flux transferred back from the gas phase to the burning surface is very small compared with the heat generated at the burning surface. The activation energy of the decomposition of the burning surface of GAP propellant, Es, is determined to be 87 kJ/mol. The burning rate is represented by r = 9.16 × 103 exp(–Es/RTs) where r (m/s) is burning rate, Ts (K) is the burning surface temperature, and R is the universal gas constant. The observed high temperature sensitivity of burning rate is correlated to the relationship of (∂Ts/∂T0)p = 0.481 at 5 MPa, where T0 is the initial propellant temperature.