COMPARATIVE STUDY OF Ag2O/CO3O4 CATALYSTS PREPARED BY THE SOL-GEL AND CO-PRECIPITATION TECHNIQUES: CHARACTERIZATION AND CO ACTIVITY STUDIES

In this study effects of the preparation method on the characteristic properties and CO oxidation activities of Ag₂O/Co₃O₄ catalysts were investigated. Catalysts were prepared by two different methods: sol gel and co-precipitation. N₂ physisorption measurements, X-ray diffraction, and scanning electron microscopy measurements were used to characterize the catalysts. CO oxidation activity tests were carried out under 1% CO, 21% O₂, and the remainder He feed condition between 20° and 200°C. According to the N₂ physisorption measurements, catalysts prepared by the co-precipitation method have a higher surface area than the catalysts prepared by the sol-gel method. Co₃O₄ and AgCoO₂ phases were obtained from catalysts prepared by both techniques. In addition to these phases, metallic silver peaks were obtained by increasing calcination temperature. SEM micrographs of the catalysts showed that catalysts have uniform particles. Increasing the calcination temperature caused the formation of different-sized agglomerates and an increase in the gaps between agglomerates. The best activity was obtained from the Ag₂ O/Co₃ O₄ catalyst calcined at 200°C and prepared by the co-precipitation method. This catalyst gave 50% CO conversion at 106°C. The other two catalysts gave 100% CO conversion at a higher temperature of 200°C.     

Electrocatalytic oxidation of sodium borohydride on metal ad-atom modified Au(111) single crystal electrodes in alkaline solution

The electrochemical oxidation of borohydride was investigated by using various ad-atom modified Au(111) electrodes in alkaline media in comparison to Au(111) single crystal, polycrystalline Au, Pt and Zn electrodes. The catalytic activity of gold towards borohydride oxidation has tended to increase in more alkaline media as reflected in the oxidation peak in the concentration range of NaOH (0.01-2.0 M) studied. Additional shift on the oxidation peak potential of borohydride on Pt and Zn ad-atom modified Au(111) electrodes was observed for both ad-atom modified electrodes to more negative potentials compared to that of bare electrodes, respectively. The ad-atom modified Au(111) electrodes surfaces do not only provide a superior electrical contact, but also accelerates electron transfer as proven by the increase in peak current and positive shift in the peak potential.     

Prediction of flow fields and temperature distributions due to natural convection in a triangular enclosure using Adaptive-Network-Based Fuzzy Inference System (ANFIS) and Artificial Neural Network (ANN)

Artificial Neural Network (ANN) and Adaptive-Network-Based Fuzzy Inference System (ANFIS) were used to predict the natural convection thermal and flow variables in a triangular enclosure which is heated from below and cooled from sloping wall while vertical wall is maintained adiabatic. Governing equations of natural convection were solved using finite difference technique by writing a FORTRAN code to generate database for ANN and ANFIS in the range of Rayleigh number from Ra = 10⁴ to Ra = 10⁶ and aspect ratio of triangle AR = 0.5 and AR = 1. Thus, the results obtained from numerical solutions were used for training and testing the ANN and ANFIS. A comparison was performed among the soft programming and Computational Fluid Dynamic (CFD) codes. It is observed that although both ANN and ANFIS soft programming codes can be used to predict natural convection flow field in a triangular enclosure, ANFIS method gives more significant value to actual value than ANN.     

Electrolytic recovery of copper from dilute solutions considering environmental measures

The electrolytic recovery of copper is one of the methods of preventing the formation of sludges generated by conventional treatments. Electrolysis of metal ions in dilute solutions using vertical electrodes results in low recovery. Therefore, a design consisting of a rotating tubular bed reactor with extended cathode surfaces was developed to improve the mass transfer in the cell. The electrolytic conditions were fixed in a Hull cell prior to the actual electrolysis in the reactor. Two types of copper solution obtained from actual industrial sites were used. This process allowed the copper concentrations in the solutions to be reduced to low levels. More importantly, a combination of electrolytic and ion exchange treatments further reduced the copper content below the p.p.m. levels. This technique not only recovers more copper but also protects the environment with additional economic savings.     

Electrocatalytic Reduction of Oxygen on a Pd Ad-Layer Modified Au(111) Electrode in Alkaline Solution

Oxygen reduction was studied on palladium, cadmium and zinc ad-atom modified single crystal Au(111) electrodes. The electrodes were modified by underpotential deposition process and their activity towards oxygen reduction was studied in alkaline media by voltammetry. The reduction peaks obtained were compared with those of bare Au(111), Pd disc and bulk deposited Cd electrodes. Enhanced catalytic activity of the Au(111) electrode in the presence of Pd, Cd and Zn ad-layer can be attributed to a change in surface charge and energy by ad-layer formation. In oxygen saturated medium a well defined sharp reduction peak was observed at ?0.12 V for 1/5 ML Pd ad atom modified Au(111) electrode while it was positioned at ?0.18 V on a Pd disk electrode. The best shift in reduction peak potential was obtained with 2/5 ML Pd ad atom modified Au(111) electrode with similar current density of Pd disc electrode.     

The effect of liposome on dyeing mohair/wool blends

The aim of this study was to examine the use of liposome in the dyeing of wool and mohair fibres with acid dyestuffs. Soybean lecithin and cholesterol were used to form the liposome membrane utilised in the dyebath. Liposome production was performed according to the thin lipid layer method (Bangham Method) using a rotary evaporator. Two different forms of liposome were used for dyeing wool and mohair fibres. In its first form, liposome was utilised as an auxiliary agent, where it was added to a conventional dyebath at the beginning of the process. In its second form, dyes were encapsulated with liposome and then used in dyeing. The effects of these two different forms of liposome were compared with conventional dyeing. Dyeing was carried out at depths of shade of 0.5%, 1.0% and 2.0% using three different concentrations of liposome (0.33%, 0.66% and 1.33%). An analysis of K/S values, fastness to washing, and the alkali solubility of fibres was conducted. The fibre samples dyed in the presence of liposome exhibited very good fastness to light (grade 8). The wash fastness test results of the liposomal‐dyed samples were significantly better (grade 4‐5) than for those samples which were conventionally dyed. In the presence of liposome, the tensile strength of fibres was 20 gf, whereas it was 11 gf without liposomes.     

Prediction of Heat Transfer Coefficient in Saturated Flow Boiling Heat Transfer in Parallel Rectangular Microchannel Heat Sinks: An Experimental Study

This study focuses mainly on the prediction of saturated flow boiling heat transfer in microchannels. A wide range of experiments has been carried out with de-ionized water to obtain a comprehensive data set. Experiments of mass fluxes of 51–728.7 kg/m²s, wall heat fluxes of 36–221.7 kW/m², vapor qualities of 0.01–0.69, liquid Reynolds number of 7.72–190, aspect ratios of 0.37–5.00 (with a constant hydraulic diameter of 100 µm) and hydraulic diameters of 100–250 µm (for constant aspect ratio = 1). A new correlation including the aspect ratio effect is proposed to predict the heat transfer coefficient for saturated flow boiling in microchannels. The proposed correlation shows very good predictions with an overall mean absolute error of 16.9% and 86.4%, 96.2% and 99.5% of the predicted data falling within ±30, ±40 and ±50% error bands, respectively.     

Non-Newtonian laminar pulsating heat and fluid flow in plane duct

In the present study, laminar pulsating power-law momentum and heat transfer in a uniformly heated plane duct is studied analytically. Assuming that fully developed conditions exist both hydrodynamically and thermally, a perturbation series method is utilized to derive analytical solutions for the momentum and energy balance equations, and the amplitude is prescribed as the perturbation parameter. For varying values of the power-law index ( $n$), representing pseudoplastic, Newtonian, and dilatant fluids, effects of dimensionless amplitude ( $ϵ$) and frequency ( $F$) on periodic and period-averaged friction factor and Nusselt number are obtained. The results obtained for Newtonian fluid are shown to be in good harmony with the corresponding findings in the open literature.