Using thermochemical code EXPLO5 to predict the performance parameters of explosives

Thanks to the development of more powerful computers and efficient numerical techniques, numerical modelling has become a compulsory tool in solving various problems in the field of energetic materials. In cases where measuring techniques are still unable to measure a given parameter, numerical modelling may be the only option of obtaining a value. In addition, numerical modelling helps us to better understand some phenomena, particularly in understanding the influence of input parameters on output results, as well as saving time and money. The thermochemical equilibrium code EXPLO5 is such a tool which enables theoretical prediction of performance of high explosives, propellants and pyrotechnic compositions. The code is used by more than 80 research laboratories worldwide.

Exploring HNC and HCN line emission as probes of the protoplanetary disk temperature

Context. The distributions and abundances of molecules in protoplanetary disks are powerful tracers of the physical and chemical disk structures. The abundance ratios of HCN and its isomer HNC are known to be sensitive to gas temperature. Their line ratios might therefore offer a unique opportunity to probe the properties of the emitting gas. Aims. We investigate the HNC and HCN line emission in disks at (sub-)millimeter wavelengths and explore their potential utility for probing disk temperature and other disk properties. Methods. Using the 2D thermochemical code DALI, we ran a set of disk models accounting for different stellar properties and radial and vertical disk structures, with an updated chemical network for the nitrogen chemistry. These modeling results were then compared with observations, including new observations obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) of HNC J = 3−2 for the TW Hya disk and HNC J = 1−0 for 29 disks in Lupus. Results. Similar to CN, HCN and HNC have brighter line emission in models with larger disk flaring angles and higher UV fluxes. HNC and HCN are predicted to be abundant in the warm surface layer and outer midplane region, which results in ring-shaped emission patterns. However, the precise emitting regions and emission morphology depend on the probed transition, as well as on other parameters such as C and O abundances. The modeled HNC-to-HCN line intensity ratio increases from <0.1 in the inner disk to up to 0.8 in the outer disk regions, which can be explained by efficient HNC destruction at high temperatures. Disk-integrated HNC line fluxes from current scarce observations and its radial distribution in the TW Hya disk are broadly consistent with our model predictions. Conclusions. The HNC-to-HCN flux ratio robustly increases with radius (decreasing temperature), but its use as a chemical thermometer in disks is affected by other factors, including UV flux and C and O abundances. High-spatial resolution ALMA disk observations of HNC and HCN that can locate the emitting layers would have the great potential to constrain both the disk thermal and UV radiation structures, and also to verify our understanding of the nitrogen chemistry.

Rings, rings, rings: what does CN tell us?

CN emission lines are among the brightest, and have been observed in the last 20 years with single dish observations. With modern interferometers, we are now able to spatially resolve CN emission, which often shows ring-like structures. We investigate whether such structures trace the morphology of the disks, or if they have a chemical origin. By using the thermochemical code DALI, we conclude that CN formation is triggered by the existence of vibrationally excited H2*, produced by FUV pumping of H2. Herbig stars therefore generally have larger rings and higher CN fluxes than TTauri. Disks with higher masses and flaring also show stronger CN emission and larger rings. CN observations could in the future provide important constraints on some important disk physical parameters. The results of the models are well consistent with the spatially resolved CN observations to-date available.

Some nitrogen-rich heterocycles derivatives as potential explosives and propellants: A theoretical study

Four types of nitrogen-rich heterocycles substituted with -NO2, -NHNO2 and -C(NO2)3 explosophoric groups were explored as potential explosives and propellants materials. The calculated crystal density (?0)and the condensed phase heat of formation (?H?0f)for each of the twelve structures investigated shows that all these derivatives possess high (1.834-1.980 g cm-3)(?H?0f) and (605-2130 kJ kg-1) values. Interesting properties such as detonation velocity (D), pressure (P) and specific impulse (Isp) were calculated using the Kamlet-Jacobs method and ISPBKW thermochemical code. Detonation velocity and pressure in excess of 8.44 km s-1 and 32.87 GPa was obtained in all cases. Furthermore, trinitromethyl substituted derivatives shows performance exceeding that of HMX with an estimated D = 9.32-9.72 km s-1 and P = 40.61-43.82 GPa. Some -NO2 and -NHNO2 substituted derivatives were shown to be impact insensitive while retaining good detonation performance and thus are regarded as potential replacement for current RDX -based explosives. Finally, the calculated specific impulse (Isp between 248 and 270 s) of all investigated derivatives indicate that these energetic materials can be considered as possible ingredient in future rocket propellant compositions.