Experimental investigation of paraffin-based fuels for hybrid rocket propulsion

Solid fuels for hybrid rockets were characterized in the framework of a research project aimed to develop a new generation of solid fuels, combining at the same time good mechanical and ballistic properties. Original techniques were implemented in order to improve paraffin-based fuels. The first strengthening technique involves the use of a polyurethane foam (PUF); a second technique is based on thermoplastic polymers mixed at molecular level with the paraffin binder. A ballistic characterization of paraffin-based hybrid rocket solid fuels was performed, considering pure wax-based fuels and fuels doped with suitable metal additives. Nano-Al powders and metal hydrides (magnesium hydride (MgH2), lithium aluminum hydride (LiAlH4 )) were used as fillers in paraffin matrices. The results of this investigation show a strong correlation between the measured viscosity of the melted paraffin layer and the regression rate: a decrease of viscosity increases the regression rate. This trend is due to the increasing development of entrainment phenomena, which strongly increase the regression rate. Addition of LiAlH4 (mass fraction 10%) can further increase the regression rate up to 378% with respect to the pure HTPB regression rate, taken as baseline reference fuel. The highest regression rates were found for the Solid Wax (SW) composition, added with 5% MgH2 mass fraction; at 350 kg/(m2s) oxygen mass flux, the measured regression rate, averaged in space and time, was 2.5 mm/s, which is approximately five times higher than that of the pure HTPB composition. Compositions added with nanosized aluminum powders were compared with those added with MgH2, using gel or solid wax

Effect of Mechanical Activation on the Reactivity of Composites for Flameless Heaters

The work is devoted to the activation of metal powder mixtures suitable for use in flameless food heaters. Four activated powders have been manufactured starting from the reference material using a standard technique. Activated powders exhibited a significant increment of the reactivity for the reference mixture. Experimental tests were carried out to characterize the resulting composites in terms of the combustion rate. The oxidation reaction at a low heating rate was monitored using a SEIKO EXTAR II thermal analysis machine and its tests were carried out at open air in temperature range starting from room temperature up to 1150 °C at the heating rate of 10 °C/min. Powders activated by mechanical activations and the initial mixture of materials were characterized in terms of apparent density, absorbed surfactant with the mass of sizing, i.e. granulometry, oxidation properties at a low heating rate. With increase the grinding time, the color of the powder switches to dark tones. Powder granulometry was performed on a MALVERN laser granulometer MASTERSIZER 2000 using dry block SCIROCCO. Three measurements for each sample were performed and the results were averaged. The tests were recorded and processed by digital technology to make the combustion rate of the powders, also the experimental setup used for investigations was presented. The sample AlS-AlF_MnO2_SiO-150 is characterized by the lowest metal content, and by the most regular combustion propagation. The powder AlS-AlF_MnO2_SiO-50 features the highest metal content, but the less regular combustion propagation. The use of mechanical activation allows increasing the number of nanoscale materials, which contributes to the synthesis of highly effective flameless food heaters

Dynamic anoxic ferruginous conditions during the end-Permian mass extinction and recovery

The end-Permian mass extinction, ~252 million years ago, is notable for a complex recovery period of ~5 Myr. Widespread euxinic (anoxic and sulfidic) oceanic conditions have been proposed as both extinction mechanism and explanation for the protracted recovery period, yet the vertical distribution of anoxia in the water column and its temporal dynamics through this time period are poorly constrained. Here we utilize Fe–S–C systematics integrated with palaeontological observations to reconstruct a complete ocean redox history for the Late Permian to Early Triassic, using multiple sections across a shelf-to-basin transect on the Arabian Margin (Neo-Tethyan Ocean). In contrast to elsewhere, we show that anoxic non-sulfidic (ferruginous), rather than euxinic, conditions were prevalent in the Neo-Tethys. The Arabian Margin record demonstrates the repeated expansion of ferruginous conditions with the distal slope being the focus of anoxia at these times, as well as short-lived episodes of oxia that supported diverse biota