An analysis of surface erosion in electrical discharge machining

An analytical model for the computation of metal erosion by a single spark in electrical discharge machining is presented. The effect of plasma channel growth on metal removal was examined and good correlation was found between theoretical and experimental results. The model was further developed to study the effects of non-rectangular current pulse shapes on metal removal and relative electrode wear to establish the optimum current pulse form required to minimize relative electrode wear.     

Studies on curcumin and curcuminoids XVII. Variation in the content of curcuminoids inCurcuma longa L. from Nenal during one season

Summary The content of curcuminoids inCurcuma longa L. before, during and after a normal harvesting period was investigated. The plant material was grown in the Kathmandu area. Bis-demethoxycurcumin was found to be the main constituent. No significant change in the curcuminoid content was observed during a 17-week sampling period.

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Studien über Curcumin und Curcuminoide. XVII. Veränderung des Gehaltes an Curcuminoiden inCurcuma longa L. (Zingiberaceae) aus Nepal warend der Ernte

Zusammenfassung Der Gehalt an Curcuminoiden inCurcuma longa L. (Zingiberaceae) wurde vor, während und nach der normalen Erntezeit untersucht. Das Pflanzenmaterial stammt aus dim Kathmandu-Tal in Nepal. Der Hauptinhaltsstoff ist Bisdemethoxycurcumin. Im Laufe von 17 Wochen konnten keine signifikante Schwankungen observiert werden.

     

Modelling perforated mediated modified atmospheric packaging of capsicum

Perforation of a film would otherwise have a low permeability is an alternative to obtain optimum oxygen and carbon dioxide concentration in modified atmosphere packages. In present study, gas exchange was studied through a macroperforated packet containing capsicum having different number of holes, 1–4, of diameter 0.3 mm at temperatures of 5 and 25 °C. A model combining the Michaelis–Menten kinetics to describe the respiration rate of the product with mass transfer equation to describe the gas transfer across the package provided a good fit to the experimental data. Its applicability was further validated in a dynamic test, subjecting a package to a variable temperature programme simulating conditions in distribution chains. Model showed good agreement between predicted and observed values for both storage conditions with constant temperatures and variable temperature conditions of distribution chain, as mean relative deviation modulus (E) value was <10%.     

Studies on chemically modified cotton. V. Effect of zinc chloride solutions on swelling and other properties of cotton

This paper describes the effect of zinc chloride solutions of different molarity at different temperatures, viz., 10°, 25°, 36°, 55°, and 75°C, on various properties of cotton fiber such as degree of swelling, accessibility to water vapor and iodine absorption, infrared ratio, barium activity number (BAN), and leveling-off degree of polymerization (LODP). Zinc chloride solution caused inter- and intrafibrillar swelling in cotton fiber depending on conditions of treatment, viz., concentration of solution and temperature employed. Fibers treated in 10.07 moles/1. (M) solution of zinc chloride in slack state showed rapid increase in degree of swelling up to 2 hr, followed by a slow increase, reaching the maximum after 3 hr of treatment. Fibers swollen with fixed ends without allowing shrinkage showed gradual increase with maximum swelling after 6 hr of treatment. Cotton fibers treated in different molar solutions of zinc chloride at 55°C showed varying degrees of swelling (inter- and intrafibrillar) and a somewhat different trend compared to that observed at 10°C. Electron micrographs revealed mostly intercrystalline swelling in case of samples treated with 9.26M at 10°C, while the same concentration produced intracrystalline swelling at 55°C. Accessibility to water vapor, iodine absorption, and BAN of treated samples showed specific effect of temperature with regard to effectiveness of concentrations of zinc chloride solutions. Similar effects of temperature with regard to concentrations of reagent were observed on infrared ratio and LODP. Accessibility by iodine absorption and LODP correlate with BAN; also, the accessibility by iodine absorption correlates with the LODP.     

Zncl2 catalyzed flash hydropyrolysis of +525°C pitch from cold lake bitumen

Flash hydropyrolysis experiments have been performed on the vacuum bottoms fraction of Cold Lake bitumen, using zinc chloride as a catalyst. Milligram size samples of vacuum bottoms resid were heated rapidly (120–400°C/s) by passing a large electric current through the reactor tube. The variables studied included temperature, heating rate, catalyst/pitch ratio, vapour phase residence time and pressure. Temperature and catalyst/pitch ratio caused major changes in yields. In contrast pressure had little effect. It was found that high conversions could be obtained at hydrogen pressures which are much lower than those normally used in catalytically hydrocracking residual oils.     

Co-Extraction — Selective stripping for the recovery of nickel and copper from the leach liquor of ocean nodules

Ferromanganese deep sea nodules of the Indian Ocean have recently been recognised as a potential source of metals like copper, nickel, cobalt and manganese. For the treatment of the sea nodules following the reduction roast-ammonia leach process, the leach liquor containing copper, nickel and cobalt was processed to separate and recover these metals by solvent extraction (SX) using 25% LIX 64N in kerosene. Almost quantitative extraction of copper and nickel was realized in a continuous run. During nickel stripping, the small amount of copper in the nickel solution was removed by incorporating a copper extraction step using 10% LIX 64N in kerosene. The purified pregnant nickel electrolyte was electrowon in a non-diaphragm cell. Copper was similarly recovered by electrowinning (EW). A closed circuit of SX-EW was run to produce cathodes of nickel and copper with energy consumptions of 3.85 and 2.01 kWh/kg for the respective metals.     

Investigations of Ce3+ co-doped SbPO4:Tb3+ nano-ribbons and nanoparticles by vibrational and photoluminescence spectroscopy

Nano-ribbons and very small nanoparticles (size 2-5 nm) of SbPO4 doped with lanthanide ions (Ce3+ and Tb3+) are prepared at a relatively low temperature of 120 degrees C based on a solution method. Detailed vibrational and luminescence studies on these samples establish that these lanthanide ions are incorporated at Sb3+ site of the SbPO4 lattice. The excitation spectrum corresponding to the Tb3+ emission and the excited state lifetime of the 5D4 level of Tb3+ ions in the sample confirm the energy transfer from Ce3+ to Tb3+ ions in the SbPO4 host. The extent of energy transfer from Ce3+ to Tb3+ in these samples is found to be around 60%. Dispersion of these nanomaterials in silica matrix effectively shields the lanthanide ions at the surface of the nano-ribbons/nanoparticles from the stabilizing ligands resulting in the reduction in the vibronic quenching of the excited state. Our results show significant reduction in the surface contribution in the decay curve corresponding to the 5D4 level of the Tb3+ ions after incorporating the nano-ribbons/nanoparticles in silica. These nanomaterials incorporated in silica matrix can have potential applications in bio-assays and bio-imaging.     

Effect of impinging ion energy on the substrates during deposition of SiOx films by radiofrequency plasma enhanced chemical vapor deposition process

Radiofrequency (13.56 MHz) plasma enhanced chemical vapor deposition process is used for deposition of SiO_x films on bell metal substrates using Ar/hexamethyldisiloxane/O₂ glow discharge. The DC self-bias voltage developed on the substrates is observed to be varied from − 35 V to − 115 V depending on the RF power applied to the plasma. Plasma potential measurements during film deposition process are carried out by self-compensated emissive probe. The deposited films are characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation, nano-scratch test and thermogravimetric analysis. The characterization results show strong dependency of the SiO_x films properties on the energy of the ions impinging on the substrates during deposition. Analysis of Raman spectra indicates an increase in vitreous silica content and reduction in defective Si-O-Si chemical structure in the deposited SiO_x films with increasing ion energy impinging on the substrates. The increase in inorganic (Si and O) content in the SiO_x films is further confirmed from XPS analysis. The growth of SiO_x films with more inorganic content and defect free chemical structure apparently contribute to the increase in their hardness and scratch resistance behavior. The films show higher thermal stability as the energy of the ions arriving at substrates increases with DC self-bias voltage. The possibility of using SiO_x films for surface protection of bell metal is also explored.