Hydrogen evolution reaction in PTFE bonded Raney-Ni electrodes

This study is concerned with the hydrogen evolution reaction (HER) in several PTFE bonded Raney-Ni electrodes as function of temperature and treatments. The Mo-doped Raney-Ni catalysts are activated by hours of long cathodic polarization interleaved with few deep “charge - discharge” (polarity reversal) cycles. Moreover, the HER efficiency of the electrode requires additives which enhance conductivity and surface properties: with powders of Ni alloys (Ni-Ti, Ni-Cr, Ni-Fe) the electrode becomes also more stable, and almost insensitive to polarity reversal. The main effect of a temperature increase is the reduction of the Tafel slope, which is about 120 mV/dec at 25 °C, and about 60 mV/dec at 60 °C. A proper choice of additives yield electrodes which withstand polarity reversal and may be used in electrolysers which are intermittently operated, or have anodes which require periodic in situ re-activation by reduction.     

Activated carbon cloth as anode for sulfate removal in a microbial fuel cell

By employing the sulfate-reducing bacterium Desulfovibrio desulfuricans we demonstrate the possibility of electricity generation in a microbialfuel cell (MFC) with concomitant sulfate removal. This approach is based on an in situ anodic oxidative depletion of sulfide produced by D. desulfuricans. Three different electrode materials, graphite foil (GF), carbon fiber veil (CFV), and high surface area activated carbon cloth (ACC), were evaluated for sulfide electrochemical oxidation. In comparison to CFV and GF electrodes, ACC was a superior materialfor sulfide adsorption and oxidation and showed significant potential for harvesting energy from sulfate-rich solutions in the form of electricity. Sulfate (3.03 g dm(-3)) was removed from a bacterial suspension, which represented 99% removal. A maximum power density of 0.51 mW cm(-2) (normalized to geometric electrode area) was obtained with a one-chamber, air-breathing cathode and continuous flow MFC operated in batch mode at 22 degrees C.     

Morphology and texture of high-density polyethylene–polystyrene blends deformed by plane-strain compression

The blends of high-density polyethylene (HDPE) with atactic polystyrene (PS) were deformed plastically by plane-strain compression in a channel die. The samples were deformed up to the true strain 1.8 (compression ratio 6) in three temperature regimes: below, near, and above the glass transition temperature of polystyrene component. The morphology and the texture of crystalline component in the deformed blend samples were investigated by means of scanning electron microscopy and wide angle X-ray diffraction (pole figures technique). It was found that the deformation process in the blend of immiscible HDPE and PS does not differ markedly from the deformation of the one-component system from the point of view of the deformation mechanisms involved. The crystalline textures of the blend samples are qualitatively the same as in the plain HDPE deformed under similar conditions. The active deformation mechanisms are the same in deformation of both the plain HDPE and HDPE/PS blend. The mechanism identified are crystallographic slips: (100)[001], (100)[010], and (010[001] supported by the interlamellar slip. The presence of PS in blends modifies to some extent the deformation process and resulting orientation of the crystalline component of HDPE by modification of the stress distribution within HDPE matrix around PS inclusions. This influence is much stronger at low deformation temperatures, when PS is in a glassy state, than at temperatures above T_g of PS. © 1996 John Wiley & Sons, Inc.     

Optical excitation of nonidentical quantum wells in the active region of a vertical-external-cavity laser

Optical excitation of a semiconductor structure comprising two nonidentical quantum wells (QWs) separated by barriers absorbing the pump radiation has been numerically simulated. It is shown that the equalization of populations in the QWs can be achieved in two ways: (i) shift of the deeper QW to a region of weak carrier generation and (ii) introduction of a blocking layer preventing the transport of carriers.     

Low-temperature oxidation of pitch,petroleum, and shale semicokes

The oxidation of pitch, petroleum, and shale tar semicokes with air oxygen at 150–340°C was studied gravimetrically and by Fourier-transform IR diffuse reflectance spectroscopy. The oxidation led to a decrease in the intensities of the vibrational bands of aliphatic C-H bonds, and a noticeable reduction in the intensities of the vibrational bands of aromatic C-H bonds was observed for petroleum and shale tar semi-cokes. Below 200°C, oxygen enters to form largely ketone or/and aldehyde C=O groups; however, the carboxyl, anhydride, lactone, and C-O-C vibration bands appear as the oxidation temperature is increased.     

Production of petro/coal tar pitch by joint distillation of coal tar and heavy pyrolytic oil

The properties of petro/coal tar pitch and distillate fractions obtained in the joint distillation of coal tar and heavy pyrolytic oil from ethylene production are described. The petro/coal tar pitch is particularly reactive in heat treatment and air-blowing. The petro/coal tar pitch may be used as less carcinogenic binder and impregnating electrode pitch.