Alla N. Pivkina

Formation and characterization of metal-polymer nanostructured composites

Abstract Nanostructured metal (Pd, Sn, Cu)-polymer (poly-para-xylylene) and metal-oxide-polymer composites reveal synergism of properties of the initial components, which gives rise to specific electrical, mechanical, and optical properties related to an ordered distribution of nanoparticles over the matrix volume. Methods where polymerisation and formation of the nanoparticles are performed simultaneously are very promising. This paper reports on the experimental set-up for the production of nanocomposites by vacuum co-condensation of the metal and a monomer (paracyclophane) vapours. AFM studies reveal the metal nanoparticles to have a size of 7 to 10 nm. Depending on the metal concentration in as-prepared composites, three different types of surface morphology are distinguished. The percolation threshold of these systems is evaluated by measuring the temperature dependence of the electrical resistance. The type of Absorbance versus Wavelength dependency for the samples beyond the percolation threshold differs from that of the sample with a nano-metal content below the threshold.

Synthesis of 1- and 5-(pyrazolyl)tetrazole amino and nitro derivatives

n Regioselective introduction of nitro groups was studied in the case of pyrazoles containing a 1- or 5-tetrazole substituent at position 3(5). All the possible isomeric C-mononitropyrazoles were synthesized. The reduction of these compounds gave the respective 3(5)-amino-5(3)-tetrazolylpyrazoles, which were nitrated to 3(5)-nitramino-4-nitro-5(3)-tetrazolylpyrazoles. The reaction of 1-(nitropyrazol-3(5)-yl)tetrazoles with hydroxylamine-O-sulfonic acid produced the respective N-amino derivatives.

Synergistic Effect of Ammonium Perchlorate on HMX: From Thermal Analysis to Combustion

The thermal decomposition and combustion of binary mixture of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and ammonium perchlorate (AP) are investigated at various concentrations. Thermal stability was investigated by thermal analysis techniques, i.e., DSC/TGA, combined with FTIR spectrometry, and accelerating rate calorimetry (ARC). Twofold HMX/AP interaction result is observed: ammonium perchlorate as synergistic additive effectively (in 60 °C) reduces the onset decomposition temperature of HMX, whereas gaseous products of the HMX thermolysis, in turn, catalyze the AP decomposition. Burning rate of mechanical mixtures exceeds the HMX level at 4 MPa, when HMX content lies in the range close to above synergistic effect at thermolysis, and AP particle size is fine (10 μm). Addition of large AP particles to HMX does not enhance the burning rate. Comparative analysis of the combustion parameters of the mechanical mixtures and large HMX crystals covered with AP layer revealed that the direct contact between components is not a necessary condition for the HMX/AP interaction for compositions without binder, proving the gas-phase character of this effect. However, for compositions with active binder, the direct contact between components is important. Finally, the synergistic effect changes the decomposition pathway for mixtures with HMX content above 40 % and below 90 % and noticeably increases the burning rate of HMX-based compositions with active binder. Formulations with active binder and coated HMX provide higher burning rate than those ones with mechanical mixtures of HMX with fine AP. It means the possibility to use the considerably less amount of ammonium perchlorate to achieve the same level of the burning rate.

Catalysis of HMX Decomposition and Combustion: Defect Chemistry Approach

Abstract The influence of nanosized oxides of Ti, Al, Fe, and Si on the HMX thermolysis and combustion is reported. The following order of their catalytic efficiency in HMX thermolysis was obtained: TiO 2 xa0>xa0Fe 2 O 3 xa0≈xa0Al 2 O 3 xa0>xa0SiO 2 . The catalytic performance was analyzed and the key factors were shown to be specific surface area, content, and the acid/base properties of the metal oxide surface. Results reveal the burning rate increases and the pressure exponent decreases considerably by the addition of exceptionally nano-TiO 2 . Since in catalysis reactions occur at interfaces, point defects in the catalyst material are to be considered in the interfacial catalysis mechanism. Intrinsic and extrinsic point defects in TiO 2 are discussed. The presence of acidic or basic surface groups influences the space charges and hence the catalytic efficiency. Based on the experimental results, the physicochemical model (scenario) of the decomposition and combustion of the HMX/TiO 2 mixtures is elaborated.The influence of nanosized oxides of Ti, Al, Fe, and Si on the HMX thermolysis and combustion is reported. The following order of their catalytic efficiency in HMX thermolysis was obtained: TiO2xa0>xa0Fe2O3xa0≈xa0Al2O3xa0>xa0SiO2. The catalytic performance was analyzed and the key factors were shown to be specific surface area, content, and the acid/base properties of the metal oxide surface. Results reveal the burning rate increases and the pressure exponent decreases considerably by the addition of exceptionally nano-TiO2. n nSince in catalysis reactions occur at interfaces, point defects in the catalyst material are to be considered in the interfacial catalysis mechanism. Intrinsic and extrinsic point defects in TiO2 are discussed. The presence of acidic or basic surface groups influences the space charges and hence the catalytic efficiency. n nBased on the experimental results, the physicochemical model (scenario) of the decomposition and combustion of the HMX/TiO2 mixtures is elaborated.