Synthesis of metal iodates from an energetic salt.

Iodine containing oxidizers are especially effective for neutralizing spore forming bacteria by generating iodine gas as a long-lived bactericide. Metal iodates have been shown to be strong oxidizers when combined with aluminum fuel particles for energy generating applications. One method to produce metal iodates in situ is by using metal oxides and an energetic salt: aluminum iodate hexahydrate (Al(H2O)6(IO3)3(HIO3)2), which is called AIH. In this study, the thermal stability and reactivity of AIH with metal oxides commonly used in energetic formulations was investigated. Three metal oxides: bismuth(iii) oxide (Bi2O3), copper(ii) oxide (CuO), and iron(iii) oxide (Fe2O3) were investigated because of their different oxygen release properties. Each metal oxide powder was combined with AIH powder. Thermal stability and reactivity were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) and reactive properties calculated to supplement experimental observations. Powder X-ray diffraction (XRD) was also used to identify the product species at various stages of heating corresponding to exothermic activity. Results show that AIH decomposition is entirely endothermic but, with the addition of metal oxide powder to AIH, exothermic reactions transform metal oxides into more stable metal iodates. This analysis provides an understanding of the compatibility of AIH with metal oxides and contributes to the development of novel energetic composites that have the advantages of both thermal and biocidal mechanisms for spore neutralization.

Single Particle Combustion of Pre-Stressed Aluminum.

An approach for optimizing fuel particle reactivity involves the metallurgical process of pre-stressing. This study examined the effects of pre-stressing on aluminum (Al) particle ignition delay and burn times upon thermal ignition by laser heating. Pre-stressing was by annealing Al powder at 573 K and quenching ranged from slow (i.e., 200 K/min) identified as pre-stressed (PS) Al to fast (i.e., 900 K/min) identified as super quenched (SQ) Al. Synchrotron X-ray Diffraction (XRD) analysis quantified an order of magnitude which increased dilatational strain that resulted from PS Al and SQ Al compared to untreated (UN) Al powder. The results show PS Al particles exhibit reduced ignition delay times resulting from elevated strain that relaxes upon laser heating. SQ Al particles exhibit faster burn times resulting from delamination at the particle core-shell interface that reduces dilatational strain and promotes accelerated diffusion reactions. These results link the mechanical property of strain to reaction mechanisms associated with shell mechanics that explain ignition and burning behavior, and show pre-stressing has the potential to improve particle reactivity.

Ray tracing calculations in simulated propellant flames with detailed chemistry.

Optical measurements in propellant flames are necessary to understand the combustion physics, yet these conditions provide challenges in probing the flame and may introduce uncertainty into the measurement. This work reports the use of simulations of an ammonium perchlorate propellant flame with finite rate chemistry to understand the role of ammonium perchlorate particle size and pressure on the uncertainty of imaging-based measurements on propellant flames. A two-dimensional ray tracing code was developed to incorporate the effects of the species concentration and temperature gradients on ray refraction within propellant flames. It was determined that the effects of the flame structure based upon pressure and oxidizer particle size increases the amount of ray deflection particularly at high pressures explaining a cause for challenges of aluminum agglomerate measurements at elevated pressure. This framework shows promise for understanding limitations and uncertainties of optical measurements for reacting and turbulent flows.