Detection of autocatalytic decomposition behavior of energetic materials using APTAC

Characterization of autocatalytic decomposition reactions is important for the safe handling and storage of energetic materials. Isothermal differential scanning calorimetry (DSC) has been widely used to detect autocatalytic decomposition of energetic materials. However, isothermal DSC tests are time consuming and the choice of experimental temperature is crucial. This paper shows that an automatic pressure tracking calorimeter (APTAC) can be a reliable and efficient screening tool for the identification of autocatalytic decomposition behavior of energetic materials. Hydroxylamine nitrate (HAN) is an important member of the hydroxylamine family. High concentrations of HAN are used as liquid propellants, and low concentrations of HAN are used primarily in the nuclear industry for decontamination of equipment. Because of its instability and autocatalytic decomposition behavior, HAN has been involved in several incidents.     

Ultrafast magneto-optics in nickel: magnetism or optics?

Several magnetic and optical processes contribute to the magneto-optical response of nickel thin films after excitation by a femtosecond laser pulse. We achieved a first complete identification by explicitly measuring the time-resolved Kerr ellipticity and rotation, as well as its temperature and magnetic field dependence in epitaxially grown (111) and (001) oriented Cu/Ni/Cu wedges. The first hundreds of femtoseconds the response is dominated by state filling effects. The true demagnetization takes approximately 0.5-1 ps. At the longer (sub-ns) time scales the spins are found to precess in their anisotropy field. Simple and transparent models are introduced to substantiate our interpretation.     

Facial selectivity in the nucleophilic additions of vinylmagnesium bromide to bicyclo[2.2.2]oct-5-en-2-one derivatives

The levels of diastereoselection attainable by addition of vinylmagnesium bromide to a selection of bicyclo[2.2.2]octenone derivatives 1-6 in the presence of various Lewis acids such as LiBr, CeCl3, TiCl4, ZnBr2, MgBr2, and Et2AlCl have been determined. The 1,2-addition of ketone 1 with vinylmagnesium bromide in THF provided a mixture of anti- and syn-isomers. The reactions of 2 with vinylmagnesium bromide at room temperature afforded anti- and syn-isomers with preference to anti-isomers in most cases. These reactions in the presence of Lewis acids afforded anti-isomers as the major product with an excellent stereoselectivity or as single isomers in some cases. The ketones 3 gave surprisingly different results providing anti-isomers predominantly even in the presence of Lewis acids. The bicyclic ketones 4 and 5 and all-carbon tricyclic ketone 6 furnished the syn-isomer as the main product. There is no significant effect of Lewis acid catalysis in the nucleophilic addition reactions of 1, 4, 5, and 6. The use of a preformed vinylmagnesium bromide-CeCl3 reagent for the addition reactions of 2d-f and 3d-f provided almost exclusively syn-isomers. The substituents and reaction conditions can influence facial selectivity in the nucleophilic additions to the bicyclo[2.2.2]oct-5-en-2-one derivatives.