No abstract

1-D nanostructures of cubic phase silicon carbide (beta-SiC) were efficiently produced by combustion synthesis of mixtures containing Si-containing compounds and halocarbons in a calorimetric bomb. The influence of the operating parameters on 1-D SiC formation yield was studied. The heat release, the heating rate, and the chamber pressure increase were monitored during the process. The composition and structural features of the products were characterized by elemental analysis, X-ray diffraction, differential thermal analysis/ thermogravimetric technique, Raman spectroscopy, scanning and transmission electron microscopy, and energy-dispersive X-ray spectrometry. This self-induced growth process can produce SiC nanofibers and nanotubes ca. 20-100 nm in diameter with the aspect ratio higher than 1000. Bulk scale Raman studies showed the product to be comprised of mostly cubic polytype of SiC and that finite size effects are present. We believe that the nucleation mechanism involving radical gaseous species is responsible for 1-D nanostructures growth. The present study has enlarged the family of nanofibers and nanotubes available and offers a possible, new general route to 1-D crystalline materials.

Research on the effect of aluminum contents and of its particle size on detonation characteristics of RDX‐based compositions containing 15–60% aluminum was carried out. Measurements of detonation velocity for different charge diameters and confinements were performed. To measure the shock curvature of the detonation wave, X‐ray photography was applied. Unconfined charges and charges confined with a water envelope were tested. The radius of the detonation front curvature was determined. The cylinder test results were the basis for determination of the acceleration ability and energetic characteristics of the detonation products of the mixtures. The Gurney energy describing the acceleration ability was found. The detonation energy of the mixtures tested was also estimated from the cylinder test data.

Novel ceramic and carbon nanostructures have been created by thermolysis of mixtures containing polytetrafluoroethene (PTFE) and a pure metal or metal alloy in a calorimetric bomb. The influence of the stoichiometry was studied for Si-containing reactants for which the yield of the nanofibers was the highest. The process was monitored by measuring the heat of reaction and by differential thermal analysis/ thermogravimetric techniques. The reaction temperatures were measured, and the heating rates of the reactants during thermal wave propagation were estimated. Elemental analysis, X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray spectrometry were employed to characterize the chemical composition and structural features of the products. Well-crystallized elongated single-crystal Si nanofibers, coated with a thin SiO 2 amorphous layer, and crystallized carbon nanoparticles containing metals (e.g., Fe) and Si dominate. The highest yields of nanofibers and carbon particles were obtained from PTFE and Si-containing precursors, due to the volatility of SiF 4 .