Rajesh Shende

Generation of fast propagating combustion and shock waves with copper oxide/aluminum nanothermite composites

Nanothermite composites containing metallic fuel and inorganic oxidizer are gaining importance due to their outstanding combustion characteristics. In this paper, the combustion behaviors of copper oxide/aluminum nanothermites are discussed. CuO nanorods were synthesized using the surfactant-templating method, then mixed or self-assembled with Al nanoparticles. This nanoscale mixing resulted in a large interfacial contact area between fuel and oxidizer. As a result, the reaction of the low density nanothermite composite leads to a fast propagating combustion, generating shock waves with Mach numbers up to 3.

Nanoenergetic Composite of Mesoporous Iron Oxide and Aluminum Nanoparticles

Ordered mesoporous Fe2O3 was synthesized using cetyltrimethylammonium chloride (CTAC) and polyethylene glycol octadecyl ether (Brij 76) surfactant templates. The gel time was monitored as a function of the concentration ratio of precursor to the surfactant. As-prepared FeOOH gels were extracted in ethanol to remove the surfactant and calcined at 200–400°C for 6 h so that α-Fe2O3 is produced. The FTIR spectra of these gels reveal complete removal of surfactant and water impurities and the presence of Fe-O vibrations. TEM images show ordering of mesopores in the gels prepared using surfactant templating and no ordering of the pores in the gels prepared without surfactant. The gels after calcinations were mixed with aluminum nanoparticles to prepare nanoenergetic composites. The burn rate of the nanocomposites containing ordered mesoporous Fe2O3 mixed with Al nanoparticles was compared with the one containing Fe2O3 with no ordering of mesopores and Al nanoparticles.

A Novel On-Chip Diagnostic Method to Measure Burn Rates of Energetic Materials

ABSTRACT A novel on-chip diagnostic method has been developed to measure burn rates of energetic materials patterned on a 1 inch × 3 inch glass chip. The method is based on time-varying resistance (TVR) of a sputter-coated thin platinum (Pt) film, in which resistance of the film changes because of the propagation of ignition of the nanoenergetic material over it. The corresponding voltage differential is captured by a high-speed data acquisition system (1.25 × 106 samples/s). We have measured burn rates as high as 504 m/s for thermites of copper oxide (CuO)/aluminum (Al) and 155 m/s for bismuth oxide (Bi2O3)/Al nanoparticles using this method. We have provided an explanation for the change of resistance upon ignition, based on the microstructural characterization and energy dispersive spectroscopy.

Crystallization of amorphous silicon by self-propagation of nanoengineered thermites

Crystallization of amorphous silicon (a-Si) thin film occurred by the self-propagation of copper oxide/aluminum thermite nanocomposites. Amorphous Si films were prepared on glass at a temperature of 250°C by plasma enhanced chemical vapor deposition. The platinum heater was patterned on the edge of the substrate and the CuO∕Al nanoengineered thermite was spin coated on the substrate that connects the heater and the a-Si film. A voltage source was used to ignite the thermites followed by a piranha solution (4:1 of H2SO4:H2O2) etch for the removal of residual products of thermite reaction. Raman spectroscopy was used to confirm the crystallization of a-Si.

On-Chip Initiation and Burn Rate Measurements of Thermite Energetic Reactions

Burn rates of various nano-energetic composites were measured by two techniques; on-chip method and conventional optical method. A comparison is presented to confirm the validity of on-chip method. On-chip initiators were prepared using platinum heater films and nanoenergetic composites. Thin film Pt heaters were fabricated with different dimensions and ignition delay was studied using a nano-energetic composite of CuO nano-rods and Al-nano-particles. The ignition delay as a function of electrical power is presented for the same energetic composite. Heater with smaller surface area is found to be more efficient, which may be due to the lower heat losses.

Supercritical extraction of binder containing poly(vinyl butyral) and dioctyl phthalate from barium titanate–platinum multilayer ceramic capacitors

Supercritical extraction using carbon dioxide was examined for the removal of binder from multilayer ceramic capacitors. The binder contained poly(vinyl butyral) (PVB) and dioctyl phthalate (DOP), and the dielectric and metal electrode materials were barium titanate and platinum, respectively. At 40 MPa of carbon dioxide at 95 °C, approximately 55 wt % of the binder could be removed, and this was mainly the dioctyl phthalate component. The use of entrainers such as 2-propanol, methyl isobutyl ketone, and n-hexane was seen to have negligible effect on the degree of binder removal. The dielectric constant, loss tangent, and breakdown voltage of devices processed by supercritical extraction were similar as compared to devices processed by thermal oxidation alone. Although it was not possible to extract all of the binder with supercritical carbon dioxide, removal of the DOP fraction increases the pore space in the body by a factor of two. Transport model calculations indicate this partial removal of binder mitigates the buildup of pressure in the subsequent thermal processing step and can reduce the processing time for thermal removal of the remaining binder by a factor of 25.

Effect of porosity on the electrical properties of Y2O3-doped SrTiO3 internal boundary layer capacitors

Compositions of 0.8 mole % Y2O3-doped SrTiO3 were sintered over a range of temperatures of 1450–1550 °C for times of 1–15 h, and the resulting internal boundary layer capacitors had relative densities ranging from 92% to 98%. The effective dielectric constant and effective conductivity were highly correlated with each other, and both electrical properties decreased strongly with increasing porosity. To account for the effect of porosity on the two electrical properties, a scaling law model was developed, which takes into account the grain size, the thickness of the grain boundary region, the pore size, and the pore aspect ratio. The model predicts a strong decrease in effective dielectric constant and effective conductivity with porosity for internal boundary layer capacitors, which is in accord with the observed trends.