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

Abstract

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.

Towards understanding the catalytic properties of lead-based ballistic modifiers in double base propellants

“…In particular, a compelling theory is that the formation of this carbon soot layer, and its subsequent loss with increasing pressure, is responsible for the super-rate and plateau/mesa burning mechanisms in DBPs. 18,27 To test this hypothesis, layers of amorphous carbon have been deposited onto each of the most stable surface models identified in the previous section. The aim is to investigate the interaction between a carbon layer and the surface; if the bare surface remains intact then it becomes possible to define an adsorption energy (see ESI †).…”

“…1. 18 The b-PbO and b-PbO 2 surfaces have more accessible oxygen sites that take part in binding to carbon, and structural distortion effects are observed in both which render the calculation of carbon binding energies unreliable. For the latter model the oxygen atoms are ripped out of the surface to form part of the carbon matrix.…”

“…Much of the experimental work and theory development was documented in the 1950s-1990s, and has recently been summarised in a review article. 18 It is known that combustion of DBPs occurs in a succession of distinct zones, as depicted in Fig. 3.…”

“…5,7,9,11,[24][25][26] A compelling catalytic theory for the decomposition of DBPs with ballistic modifiers is that the initial formation of this carbon soot layer is responsible for modifying the burning surface and aiding super-rate burning; the subsequent loss of the carbon matrix with increasing pressure has then been proposed for inducing the plateau-burning effect. 11,18,27 As the available experimental evidence points towards the ballistic modifier decomposing to catalytically active clusters interacting at a solid/gas interface, a computational modelling investigation into the surface properties of various metal and metal oxides surfaces can offer fundamental insight into the nature of these catalytic processes. To this end, herein we simulate the electronic properties of the bulk crystalline materials of Pb, PbO and PbO 2 , which have demonstrated success as burn-rate modifiers when added to DBP formulations, and compare against Bi 2 O 3 and SnO 2 which, while capable of accelerating reactions at low gas pressures, have failed to support plateau or mesa burning effects.…”

The Auto‐Ignition Behaviors and Thermal Safety of the Composite Modified Double Base Propellants under Rapid Heating

“…Double-base propellants, which are based on nitrate esters (nitrocellulose, NC and nitroglycerin, NG), are known as smokeless propellants and are used for guns and rockets [1,2]. Extensive investigations have been conducted to study the characteristics of double-base propellants such as energy density, burning rate, and mechanical properties [3][4][5][6].…”