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.     

Power broadening of the Na-D lines in a flame—I. Time-dependent spectral and spatial properties of a flashlamp pumped dye laser

Prior to power broadening experiments on the Na-D lines in a flame (described in Part II), we investigated the time-dependent spectral and spatial properties of a flashlamp-pumped pulsed dye laser (pulse duration about 800 ns, FWHM), with Rhodamine-6G in methanol as dye liquid and an interference filter combined with a Fabry-Pérot etalon as bandwidth-restricting elements in the cavity. An experimental set-up is described that permits measurements of time-dependent spectra with a time-resolution of 10 ns and a spectral resolution of 2.5 × 10⁵. Results are given for different concentrations of the dye solution and for two different bandwidth settings of the laser. In general the spectral profiles at different moments during the pulse are well described by Gaussian curves. The spatial profiles at different moments during the pulse are best fitted by Lorentzian curves. At small concentrations of the dye solution, the time behaviour of the shift and the bandwidth are in (qualitative) agreement with theoretical predictions, i.e. a narrowing of the bandwidth and a shift to longer wavelengths of the line centre.     

Random walks with ‘spontaneous emission’ on lattices with periodically distributed imperfect traps

We study random walks on d-dimensional lattices with periodically distributed traps in which the walker has a finite probability per step of disappearing from the lattice and a finite probability of escaping from a trap. General expressions are derived for the total probability that the walk ends in a trap and for the moments of the number of steps made before this happens if it does happen. The analysis is extended to lattices with more types of traps and to a model where the trapping occurs during special steps. Finally, the Green's function at the origin G(0; z) for a finite lattice with periodic boundary conditions, which enters into the main expressions, is studied more closely. A generalization of an expression for G(0; 1) for the square lattice given by Montroll to values of z different from, but close to, 1 is derived.     

Some observations on small-size electrodeless discharge lamps for strontium used for Zeeman scanning of absorption line profiles in flames

Microwave-excited electrodeless discharge lamps (EDL) for Sr were produced and a technique was developed for stabilizing the microwave power. Some characteristics of the EDL were investigated. The lamps were compared with a normal (= non-boosted) commercial hollow cathode lamp (HCL).Half-intensity widths of the Sr-line at 4607.33 Å were determined by interferometry for EDL and HCL sources under various operating conditions. Moreover, with both sources peak absorption measurements were carried out in a flame with Sr vapor; the results obtained by either technique were partially mutually consistent. Selected samples of EDL gave half-intensity widths of about 7–10 mÅ, independent of microwave power.The line width of the HCL increased from about 7 to 20 mÅ with increasing current up to 26 mÅ (= maximum rating). The radiance of the EDL's (at 50 W) was about the same as that of the HCL, when the latter was operated at 10 mA to give a comparable half-intensity width of 10 mÅ. At maximum microwave power the radiance of the EDL appeared to be 15–20 % of that of the HCL at maximum current, but the EDL line width remains only 7–10 mÅ, whereas that of the HCL line is about 20 mÅ and the HCL line is heavily self-reversed. EDL's with radiance values 10–100 × higher than that of the HCL at 25 mA were also produced; the high radiance value is obtained by increasing the Sr content in the EDL drastically. The profile of the EDL line has then a width of about 60 mÅ and the line is heavily self-reversed. Some tentative results on stability and life of the EDL's are reported.     

Assessment of the regioselectivity in the condensation reaction of unsymmetrical o-phthaldialdehydes with alanine

One approach for the synthesis of isoindolinones, a privileged bioactive heterocyclic core structure, involves a condensation reaction of o-phthaldialdehydes with a suitable nitrogen-containing nucleophile. This fascinating reaction is revisited here in the context of the use of o-phthaldialdehydes that contain additional substituents in the aromatic ring leading to a detailed analysis of the regioselectivity of the reaction. Eleven monosubstituted o-phthaldialdehydes were synthesised and reacted with alanine. The regioselectivity observed across the eleven substrates led to the design of a disubstituted substrate that reacted with very high control. A gram-scale reaction followed by esterification gave one major regioisomer in high yield. In addition, the regioselectivity observed on reaction of two novel monodeuterated substrates led to an increased mechanistic understanding.