Crystallization of Stoichiometric SbSI Glass

Congruent crystallization of antimony sulphoiodide (SbSI) glass of stoichiometric composition, which is prepared successfully for the first time using rapid melt‐quenching, has been investigated using differential scanning calorimetry (DSC). The results for glass powder show a glass transition at 127°C and two separate exothermal peaks with maxima around 140°C and 190°C. The ratio of the intensities of the exothermal peak at ~190°C to the peak at ~140°C increases as the particle size and heating rate are increased, but their total enthalpy remains constant at 62 ± 2 J/g for all DSC runs. Surface heating of the glass induced by a 520 nm CW laser shows two contracted regions: needle‐like crystalline formations at low temperature and bulk crystallization at high temperature. The observed phenomena and DSC results suggest two different kinds of crystallization of the SbSI phase: one‐dimensional crystallization at low temperature which starts from the sample surface and three‐dimensional bulk crystallization that continues the transformation to crystalline state at higher temperatures. The origin of the two different crystallizations can be traced to the strong anisotropy of the SbSI crystal structure due to the weak van der Waals interaction between covalent‐ionic chains (Sb₂S₂I₂)_n.     

Dendrimer as nanocarrier for drug delivery

Dendrimers are novel three dimensional, hyperbranched globular nanopolymeric architectures. Attractive features like nanoscopic size, narrow polydispersity index, excellent control over molecular structure, availability of multiple functional groups at the periphery and cavities in the interior distinguish them amongst the available polymers. Applications of dendrimers in a large variety of fields have been explored. Drug delivery scientists are especially enthusiastic about possible utility of dendrimers as drug delivery tool. Terminal functionalities provide a platform for conjugation of the drug and targeting moieties. In addition, these peripheral functional groups can be employed to tailor-make the properties of dendrimers, enhancing their versatility. The present review highlights the contribution of dendrimers in the field of nanotechnology with intent to aid the researchers in exploring dendrimers in the field of drug delivery.     

Propellant Gas Phase Chemical Kinetics

An adiabatic constant pressure chemical kinetic study of the AP gas phase is conducted. The objective is to examine the importance of chemical kinetic studies for propellant deflagration modelling in general and for AP in particular. A reaction mechanism consisting of ninety five elementary reactions involving twenty one chemical species is developed to represent the AP gas phase. An important parameter that can be obtained from the kinetics is the time rate of change of temperature of the gas phase at the condensed phase-gas phase boundary (dT/dt at t = 0). This is directly related to the heat feedback from the gas phase to the condensed phase. Comparison with earlier work indicates that the use of a one-step overall reaction could lead to underestimates of heat feedback from the gas phase by a factor of about four. In addition it is found that the rate of decrease of dT/dt at t = 0, with pressure is much larger at lower pressures, suggesting a possible gas phase role in the low pressure deflagration limit. Further, the kinetic study does not support the conclusion of a constant fraction of AP reacting in the condensed phase in the pressure range 20–100 atmospheres. These results are at variance with what is obtained by use of a one-step overall reaction. Thus, the one-step overall reaction cannot represent even qualitatively several gas phase characteristics important for deflagration studies, and its use leads to erroneous results. It is concluded that a full reaction mechanism representation of gas phase chemical kinetics is essential to AP deflagration modelling. The same conclusion is probably valid for propellant deflagration modelling in general.     

Fabrication and optimization of polypyrrole/cerium oxide/glassy carbon sensing platform for the electrochemical detection of flupirtine

Journal of Applied Electrochemistry - In spite of single nanomaterials, nanocomposites have come to be the superior modifying materials for electrochemical sensing. Herein, the highly...     

Energetics of Propellants,Fuels and Explosives; a chemical valence approach

A simple approach involving the chemical valences of the fuel and the oxidizer elements present in a combustible mixture is described to evaluate the energetics related parameters of propellants, fuels and explosives. It simplifies the stoichiometric balancing of complex combustion equations, and provides an easy method of calculating the elemental stoichiometric coefficient. The method correctly predicts whether a mixture is fuel-lean, fuel-rich or stoichiometrically balanced. The calorimetric value of various stoichiometrically balanced combustible systems has been shown to be linearly dependent upon their total oxidizing (or reducing) valences. This relationship has been used successfully to evaluate the calorific value of fossil fuels. For fuel-rich explosives, a new valence dependent parameter has been derived which is found to be related with properties such as detonation velocity, heat of explosion and impact sensitivity.     

Identification and tackling of a parasitic surface compound in SiC and Si-rich carbide films

Silicon carbide and silicon rich carbide (SiC and SRC) thin films were prepared by PECVD and annealed at 1100 °C. Such a treatment, when applied to SiC/SRC multilayers, aimed at the formation of silicon nanocrystals, that have attracted considerable attention as tunable band-gap materials for photovoltaic applications. Optical and structural techniques (X-ray photoelectron spectroscopy, Reflectance and Transmittance, Fourier Transformed Infrared Spectroscopy) were used to evidence the formation, during the annealing treatment in nominally inert atmosphere, of a parasitic ternary SiO_xC_y surface compound, that consumed part of the originally deposited material and behaved as a preferential conductive path with respect to the nanocrystal layer in horizontal electrical conductivity measurements. The SiO_xC_y compound was HF-resistant, with composition dependent on the underlying matrix. It gave rise to a Si-O related vibration in FTIR analysis, that may be misinterpreted as due to silicon oxide. The compound, if neglected, can affect the structural and electrical characterization of the material.To overcome this problem, a procedure is analyzed, based on the deposition of a sacrificial capping a-Si:H layer that partially oxidizes, and is removed by tetra methyl ammonium hydroxide (TMAH) after annealing. XPS analysis revealed that the resulting surface is mainly made up of SiC regardless of the composition of the underlying SRC layer. Subsequent SF₆:O₂ dry etching results in a porous SiC-rich surface layer. The proposed method is effective in controlling the SRC surface configuration, and allows the performance of reliable optical and electrical characterization.     

Correlation between the milling time and hydrogen storage properties of ZrCrFe ternary alloy

Laves phases with AB₂ compositions are common type of topologically close packed structure. Furthermore, lave phases are capable of dissolving considerable amounts of ternary alloying additions. ZrCr₂ crystallized in the hexagonal C14 type of structure is one of interesting candidate among them, but it is not used as storage compound due to its excessive stability, at 323 K the equilibrium pressure is only 1.2 kPa. However the substitution of chromium by other elements can modify the crystal structure, the hydriding capacity and dissociation pressure of hydrogen. In this work Fe has been chosen as a substitute material for Cr and ZrCrFe ternary alloy is prepared using arc furnace. The mechanical alloying process has been introduced to produce nanocrystalline material. This paper presents comprehensive study on structural aspects of ball milled ZrCrFe alloy. On comparison of the XRD data, the broadening was found in the peak width with the increase of milling time which is clear indication of refinement of crystallite size. This refinement could also be confirmed from the SEM analysis also. PCT measurements were performed for a temperature range 303 K–373 K.