A diffuse interface method for solid-phase modeling of regression behavior in solid composite propellants

Solid composite propellants (SCPs) are ubiquitous in the field of propulsion. In order to design and control solid SCP rocket motors, it is critical to understand and accurately predict SCP regression. Regression of the burn surface is a complex process resulting from thermo-chemical-mechanical interactions, often exhibitingextreme morphological changes and topological transitions. Diffuse interface methods, such as phase field (PF), are well-suited for modeling processes of this type, and offer some distinct numerical advantages over their sharp-interface counterparts. In this work, we present a phase-field framework for modelingthe regression of SCPs with varying species and geometry. We construct the model from a thermodynamic perspective, leaving the base formulation general. A diffuse-species-interface field is employed as a mechanism for capturing complex burn chemistry in a reduced-order fashion, making it possible to model regressionfrom the solid phase only. The computational implementation, which uses block-structured adaptive mesh refinement and temporal substepping for increased performance, is briefly discussed. The model is then applied to four test cases: (i) pure AP monopropellant, (ii) AP/PBAN sandwich, (iii) AP/HTPB sandwich,and (iv) spherical AP particles packed in HTPB matrix. In all cases, reasonable quantitative agreement is observed, even when the model is applied predictively (i.e., no parameter adjustment), as in the case of (iv). The validation of the proposed PF model demonstrates its efficacy as a numerical design tool for future SCP investigation.

Graphene-based Composites for the Thermal Decomposition of Energetic Materials

Owing to its remarkable mechanical, electrical and thermal properties, graphene has been a hot area of composites research in the past decade, including the field of energetic materials. Graphene has been widely applied in enhancing the physical properties of energetic materials, such as solid composite propellants. Through the way of adding different forms of graphene into the matrix of solid propellants, their thermal decomposition performance can be effectively improved. In this paper, we reviewed the status and challenges of the application of graphene in the thermal decomposition of composite solid propellant. Moreover, the main preparation methods and material structures of graphene are reviewed. We can conclude that graphene and its derivatives can enhance the catalytic effect remarkably, which can be attributed to the large specific surface area of graphene that makes the uniformly dispersed catalyst particles and the more catalyst active sites. Meanwhile, graphene possesses the high thermal conductivity, making the rapider heat diffusion, which can promote the decomposition reactions of the energetic components in solid propellants. Graphene and catalyst work synergistically in their thermal decomposition. More than this, the main methods to improve the thermal decomposition of energetic components of composite propellants and their effects on decomposition temperature reduction are systematically summarized, respectively.

[(3-Nitro-1H-1,2,4-triazol-1-yl)-NNO-azoxy]furazans: energetic materials containing an N(O)N–N fragment

A novel class of energetic compounds with a N(O) N–N fragment, [(3-nitro-1H-1,2,4-triazol-1-yl)-NNO-azoxy]furazans, which exhibit good thermal stability and high experimental enthalpies of formation are estimated as possible components of solid composite propellants.

Nose-only inhalation exposures to alumina nanoparticles / hydrogen chloride gas mixtures induce strong pulmonary pro-inflammatory response

Background: Combustion processes, especially in aerospace and defense fields, can lead to complex aerosols emission containing gases and nanoparticles (NPs). Alumina (Al2O3) NPs and hydrogen chloride gas (HClg) are for instance present in high concentrations after solid composite propellants use. Exposure to these pollutants mixtures by inhalation is thus possible but literature data towards their pulmonary toxicity are missing. To specify hazards resulting from these combustion aerosols, an inhalation study was implemented.Male Wistar rats were exposed by nose-only to Al2O3 NPs (13 nm) and/or HClg aerosols for 4h (unique exposures ; UE) or 4h a day for 4 days (iterative exposures ; IE). Bronchoalveolar lavage fluids (BALF) content and lungs histopathology were analyzed 24h after exposures.Results: Iterative co-exposures (IE) increased total proteins and lactate dehydrogenases (LDH) concentrations in BALF indicating alveolar-capillary barrier permeabilization and cytolysis. Early pulmonary inflammation was induced after IE to Al2O3 NPs ± HClg resulting in polymorphonuclear neutrophils (PMN) and pro-inflammatory cytokines increases (TNF-α, IL-1β, GRO/KC) in BALF. Moreover, after exposure to Al2O3 NPs ± HClg aerosols, both exposure scenarios induced early pulmonary histopathological lesions, among which vascular congestions, bronchial pre-exfoliations, vascular and interalveolar septum edemas. Lung oxidative damages (8-hydroxy-2'-deoxyguanosine ; 8-OHdG) were observed in situ following UE in each experimental condition, suggesting early oxidative stress induction by aerosols inhalation. However, no 8-isoprostane concentration increase was simultaneously found in animals BALF.Conclusions: Biological effects of the studied aerosols are dependent on both aerosol content and exposure scenario. Results showed an important early pro-inflammatory effect of Al2O3 NPs/HClg mixtures on rats lungs following iterative inhalations (IE). Taken together these data raise concerns towards potential long term pulmonary toxicity of combustion mixtures aerosols, and highlight the importance for workers to wear individual protections.