Hydrogen permeation during zinc-manganese alloy plating

Electrodeposition of metals from solution is usually accompanied by the simultaneous discharge of hydrogen ions or water molecules. When hydrogen is liberated at an iron/steel surface during electrodeposition, a portion of the hydrogen is absorbed by the metal surface and then diffuses into the interior. The diffused hydrogen produces some detrimental effects, such as reduction in ductility and loss in mechanical strength, leading to hydrogen embrittlement. The present paper reports investigations on hydrogen permeation measurements in zinc-manganese alloy deposition using a modified electrode clamp for easy removal and fixing of the electrode. Hydrogen permeation studies indicate that the porosity of the deposit increases in the following order:Zn-Mn(14.3%), Zn-Mn(2.4%), Zn-Mn(24.8%) and Zn-Mn(37.5%).This is in agreement with the corrosion data obtained which indicates that Zn-Mn alloy deposits with low manganese content show better performance than pure zinc deposits.     

Optimization of Microwave-Vacuum Drying of Button Mushrooms Using Response-Surface Methodology

Button mushrooms (Agaricus bisporous) were dried in a microwave-vacuum dryer up to a final moisture content of around 6% (d.b.). The effect of microwave power level (115 to 285 W), system pressure (6.5 to 23.5 kPa), and slice thickness (6 to 14 mm) on drying efficiency and some quality attributes (color, texture, rehydration ratio, and sensory attributes) of dehydrated mushrooms were analyzed by means of response surface methodology. A rotatable central composite design was used to develop models for the responses.Analysis of variance showed that a second-order polynomial model predicted well the experimental data. The system pressure strongly affected color, hardness, rehydration ratio, and sensory attributes of dehydrated mushrooms. A lower pressure during drying resulted in better quality products. Optimum drying conditions of 202 W microwave power level, 6.5 kPa pressure, and 7.7 mm slice thickness were established for microwave vacuum drying of button mushrooms. Separate validation experiment was conducted at the derived optimum conditions to verify the predictions and adequacy of the models.     

Hydrogen generation in a Pd membrane fuel processor: Productivity effects during methanol steam reforming

Performance analyses are carried out for the palladium membrane fuel processor for catalytic generation of high purity hydrogen. The reactor model includes detailed particle-scale multi-component diffusion, multiple reversible reactions, flow, and membrane transport. Using methanol steam reforming on Cu/ZnO/Al₂O₃ catalyst as the test reaction, a systematic examination of the effects of operating and reactor design parameters on key performance metrics is presented. Single particle simulations reveal a complex interplay between nonisobaric transport and the reversible reactions (methanol reforming and decomposition, and water-gas shift), which impact overall reactor performance. An analysis of characteristic times helps to identify four different productivity controlling regimes: (i) permeation control, encountered with thick membranes and/or insufficient membrane area; (ii) catalyst pore diffusion control encountered with diffusion of reacting species in larger particles; (iii) reaction control, encountered when intrinsic catalytic rates are too low because of inadequate activity or catalyst loading; and (iv) feed control, encountered when the limiting reactant feed rate is inadequate. The simulations reveal that a maximum in the hydrogen productivity occurs at an intermediate space velocity, while the hydrogen utilization is a decreasing function of space velocity, implying a trade-off between productivity and hydrogen utilization. The locus of productivity maxima itself exhibits a maximum at an intermediate membrane surface to volume ratio, the specific value of which is dependent on the particle size, membrane thickness and reaction conditions. At moderate temperature and total pressure (, 10 bar), particles smaller than 2 mm diameter, Pd membranes with thickness less than , and membrane surface to volume ratio exceeding are needed to achieve viable productivity . A comparison between the packed-bed membrane reactor and conventional packed-bed reactor indicates a modest improvement in the conversion and productivity due to in situ hydrogen removal.     

Organic nitrogen transformations in a 4-stage Bardenpho nitrogen removal plant and bioavailability/biodegradability of effluent DON

Nitrogen species, specifically, the fate and occurrence of organic nitrogen (ON) within a 4-stage Bardenpho process bioreactor producing low total nitrogen (TN) effluents were investigated in this study. The results showed release of ON in primary anoxic zone and no ON release in the first aerobic zone of the process. The research included investigation of biodegradability/bioavailability of wastewater-derived effluent dissolved ON (DON). The final-effluent DON utilization was evaluated by two different bioassay protocols in the presence and absence of nitrate. About 28–57% of the effluent DON was bioavailable/biodegradable. Bioavailable (to algae and bacteria) DON (ABDON) and biodegradable (to bacteria) DON (BDON) results did not show significant differences in terms of quantity, but DON utilization rates by ABDON (0.13 day⁻¹) protocol were higher than that of the BDON (0.04 day⁻¹) protocol in the nitrate-removal samples. As a result, ABDON requires a shorter time to exert the bioavailable fraction due to symbiotic relationship between algae and bacteria. In the nitrate-containing samples, it appears that nitrate competes with labile DON as a nitrogen source to microorganisms in both ABDON and BDON protocols. The first order decay rate of DON in the presence of nitrate was 0.11 day⁻¹ and 0.02 day⁻¹ for ABDON and BDON, respectively.     

Molecular Characterisation of Flavanone O-methylation in Eucalyptus

Flavonoids are ubiquitous polyphenolic compounds in plants, long recognised for their health-promoting properties in humans. Methylated flavonoids have received increasing attention due to the potential of methylation to enhance medicinal efficacy. Recently, Eucalyptus species with high levels of the O-methylated flavanone pinostrobin have been identified. Pinostrobin has potential commercial value due to its numerous pharmacological and functional food benefits. Little is known about the identity or mode of action of the enzymes involved in methylating flavanones. This study aimed to identify and characterise the methyltransferase(s) involved in the regiospecific methylation of pinostrobin in Eucalyptus and thereby add to our limited understanding of flavanone biosynthesis in plants. RNA-seq analysis of leaf tips enabled the isolation of a gene encoding a flavanone 7-O-methyltransferase (EnOMT1) in Eucalyptus. Biochemical characterisation of its in vitro activity revealed a range of substrates upon which EnOMT1 acts in a regiospecific manner. Comparison to a homologous sequence from a Eucalyptus species lacking O-methylated flavonoids identified critical catalytic amino acid residues within EnOMT1 responsible for its activity. This detailed molecular characterisation identified a methyltransferase responsible for chemical ornamentation of the core flavanone structure of pinocembrin and helps shed light on the mechanism of flavanone biosynthesis in Eucalyptus.     

Aminotetryls: Synthesis,spectral characterization,thermal decomposition and explosive properties

This paper describes the synthesis and spectral investigations of two amino derivatives of N-methyl-N-(2,4,6-trinitrophenyl)nitramine (tetryl). Also discussed are the results from thermal decomposition studies on the three explosives, viz. tetryl, 3-aminotetryl (3 AT) and 3,5-diaminotetryl (3,5 DAT) and preliminary work on the explosive properties of the last two compounds. The aminotetryls have been prepared by the amination of the corresponding chlorotetryls. The yield was 87% for 3 AT, but was only 33% for 3,5 DAT, probably due to steric crowding around the benzene nucleus. The mass spectra show interesting differences in the electron impact fragmentation patterns of the three tetryls with the M⁺ ion relative intensities following the order 3,5 DAT > 3 AT > tetryl, which could be due to (a) resonance stabilization and (b) hydrogen bonding effects. Evidence for the latter is also found in the infrared spectra of these compounds. Arrhenius kinetic parameters derived from thermal decomposition studies of the three compounds are presented and show that 3,5 DAT is thermally less stable than 3 AT. Explosive sensitiveness tests indicate that the diamino compound is the most sensitive, the trend being 3,5 DAT > 3 AT > tetryl. This is contrary to the generally found desensitizing influence of NH₂ groups on the thermal stability and explosive sensitiveness of trinitroaromatic energetic molecules. Mechanisms to account for the observed thermal decomposition behaviour and explosive sensitiveness patterns are discussed.     

Fed batch enzymatic saccharification of newspaper cellulosics improves the sugar content in the hydrolysates and eventually the ethanol fermentation by Saccharomyces cerevisiae

The newspaper is comprised of (w w^?1) holocellulose (70.0%) with substantial amount of lignin (16.0%). Bioconversion of the carbohydrate component of newspaper to sugars by enzymatic saccharification, and its fermentation to ethanol was investigated. Of various enzymatic treatments using cellulase, xylanase and laccase, cellulase enzyme system was found to deink the newspaper most efficiently. The saccharification of deinked paper pulp using enzyme cocktail containing exoglucanase (20 U g^?1), β-glucosidase (60 U g^?1) and xylanase (80 U g^?1) resulted in 59.8% saccharification. Among additives, 1% (v v^?1) Tween 80 and 10 mol m^?3 CoCl₂ improved the enzymatic hydrolysis of newspaper maximally, releasing 14.64 g L^?1 sugars. The fed batch enzymatic saccharification of the newspaper increased the sugar concentration in hydrolysate from 14.64 g L^?1 to 38.21 g L^?1. Moreover, the batch and fed batch enzymatic hydrolysates when fermented with Saccharomyces cerevisiae produced 5.64 g L^?1 and 14.77 g L^?1 ethanol, respectively.     

Palladium dispersed multiwalled carbon nanotube based hydrogen sensor for fuel cell applications

Palladium nanocatalysts supported on surface-oxidized multiwalled carbon nanotubes (MWNT) were prepared by the aqueous solution reduction of _PdCl2${\mathrm{PdCl}}_2$. MWNT have been synthesized by catalytic chemical vapor deposition (CCVD) technique. Pyrolysis of acetylene using a fixed-bed catalytic reactor over rare earth (RE) based _AB2${\mathrm{AB}}_2$ alloy hydride catalyst, obtained through hydrogen decrepitation technique, has been performed to synthesize MWNT. Structural, morphological and vibrational characterizations have been carried out using XRD, SEM, TEM and Raman spectroscopy, respectively. In situ electrical resistance measurements for thin films of MWNT obtained by spin coating samples were carried out by two-probe technique in a chamber with provision to introduce known concentration of hydrogen in constant air flow. Investigations of hydrogen sensing properties of Pd–MWNT ensembles have been carried out. The stability of Pd–MWNT thin films after several cycles of adsorption and desorption was studied. The change in electrical resistance due to hydrogen adsorption is reversible, with increase to saturation on exposure to hydrogen gas. The results demonstrate that chemically treated MWNT functionalized with nanostructured Pd show good _H2${\mathrm{H}}_2$ sensing response at room temperature.     

Laser diagnostics of soot precursors in a heavy-duty diesel engine at low-temperature combustion conditions

To better understand in-cylinder soot formation processes for modern, low-emissions, low-temperature combustion (LTC) operating conditions in diesel engines, soot and its precursors are imaged by laser diagnostics in a heavy duty optical engine. Virtually simultaneous images of planar laser-induced incandescence of soot (soot-PLII) using 1064 nm excitation and combined soot-PLII and planar laser-induced fluorescence of poly-cyclic aromatic hydrocarbons (PAH-PLIF) using 532 nm excitation reveal the temporal and spatial evolution of soot and its precursors during combustion. With increasing dilution of the intake air stream by various levels of nitrogen to simulate the use of exhaust-gas recirculation (EGR) to achieve LTC, the residence time of PAH increases as soot formation is delayed. At zero dilution (21% intake oxygen), soot appears nearly simultaneously with PAH, while at higher dilution (12.7% or 9.5% intake oxygen), soot formation is delayed by hundreds of microseconds to a millisecond or more. At all dilution levels, at its onset, PAH rapidly fills most of the downstream cross-section of the jet, with a relatively uniform fluorescence intensity distribution. The spatial evolution of soot, however, shifts from a relatively rapid filling of the downstream head of the jet at low dilution, to inception at the midstream periphery of the jet followed by a gradual progression downstream at high dilution. Effects of fuel-bound aromatics are also explored by comparing soot and PAH formation for a representative diesel fuel containing 27% aromatics by weight to that for neat n-heptane. The residence time of PAH before the onset of soot is slightly longer with the non-aromatic fuel, but otherwise the spatial and temporal evolution of PAH-PLIF and soot-PLII are indistinguishable from that of the diesel fuel at LTC conditions. Spectral analysis shows a characteristic soot emission spectra from 1064 nm excitation, while 532 nm excitation yields significant short-wavelength emission that cannot be attributed solely to soot incandescence, and is likely due to fluorescence of large PAH soot precursors. No narrow spectral features, such as from C2 or C3 emission, are apparent in the spectra, even at high laser fluence.     

Hall current effects on MHD flow of chemically reacting fluid through a porous medium with heat source

We considered the magnetohydrodynamic (MHD) free convective flow of an incompressible electrically conducting viscous fluid past an infinite vertical permeable porous plate with a uniform transverse magnetic field, heat source and chemical reaction in a rotating frame taking Hall current effects into account. The momentum equations for the fluid flow during absorbent medium are controlled by the Brinkman model. Through the undisturbed state, both the plate and fluid are in a rigid body rotation by the uniform angular velocity perpendicular to an infinite vertical plate. The perpendicular surface is subject to the homogeneous invariable suction at a right angle to it and the heat on the surface varies about a non-zero unvarying average whereas the warmth of complimentary flow is invariable. The systematic solutions of the velocity, temperature, and concentration distributions are acquired systematically by utilizing the perturbation method. The velocity expressions consist of steady-state and fluctuating situations. It is revealed that the steady part of the velocity field has a three-layer characteristic while the oscillatory part of the fluid field exhibits a multi-layer characteristic. The influence of various governing flow parameters on the velocity, temperature, and concentration are analyzed graphically. We also discuss computational results for the skin friction, Nusselt number, and Sherwood number in the tabular forms.