Effect of depithing on pulps from egyptian bagasse

Egyptian bagasse was pulped by the prehydrolysis-soda process followed by multi-state bleaching. Raising the concentration of sodium hydroxide used in the second step of bleaching improved the chemical characteristics of the pulp. Depithing had to be applied to improve the degree of pulping and to reduce the ash content. The minimum ash content (0.07%) was arrived at either by carrying out depithing before prehydrolysis to the extent of 2%, or after prehydrolysis to the extent of 10%. Depithing before prehydrolysis was superior as it resulted in a better yield, higher alpha cellulose, and higher degree of whiteness.     

Kinetics of Carbon Dioxide Reforming of Natural Gas Using Different Catalysts

Abstract

The Kinetics of CO₂ reforming of natural gas to produce synthesis gas (CO + H₂) has been investigated using 2 g of 0.5% wt of each of the catalysts; rhodium, ruthenium and iridium supported on γ-alumina. The experiments were carried out in a tubular reactor at three temperature levels namely 600, 700, 800°C and four gas weight hourly space velocities; 18000, 36000, 45000, and 60000 ml g^?1 h^?1. The reaction was found to obey first-order kinetics for the depletion of both of the reacting components; CH₄ and CO₂ on all the investigated catalysts. At the same temperature, CO₂ had a higher reaction rate constant, k', as compared to CH₄ for all the catalysts. This was more pronounced for Rh/γ-alumina catalyst, which occupied the highest reaction rates. Activation Energies were calculated from the Arrhenius relation.     

Optical,Structural, Electrical Characterization of (Polyvinyl Alcohol–Carboxymethyl Cellulose-Manganese Dioxide) Nanocomposite Fabricated via Laser Ablation

Polyvinyl alcohol (PVA)/Carboxymethyl cellulose (CMC)/Manganese dioxide (PVA/CMC/MnO₂ NPs) nanocomposite were produced by one-pot laser ablation route. PVA/CMC/MnO₂ NPs nanocomposite were prepared with different content of manganese dioxide nanoparticles. The formation of MnO₂ is confirmed by appearing diffraction peaks at 2θ?=?26.4°, 28.4°, 37.2°, 42.5°, 56.4°, 72.2° according to JCPDS No. 24-0735 which agreed with previous literature. The increasing of laser ablation time causes a change of all bands intensities. All the above conclusions affirmed the formation of Mn–O and their complexation with PVA/CMC blend. The ultraviolet and visible (UV/Vis.) measurements showed enhanced in the optical properties as the ratio of Manganese dioxide nanoparticles enhanced. The absorption edge is changed towards lower photon energy sides when MnO₂ NPs are added to the PVA/CMC. The AC conductivity was enhanced after the addition of MnO₂ NPs. The values of the ε′ and ε? of the synthesized samples increased as the ratio of Manganese dioxide nanoparticles increased, which is attributed to an increase in the current films' ion conduction. The obtained results demonstrate the benefits of using MnO₂ NPs as a filler to improve polymeric systems and suggest it for optical and electrical applications.

     

4-layer inductive grid FSS at 45° incidence

Transmission/reflection-band centre ratios of about 1.3 can be attained with multiple layers of inductive or capacitive grids, or with single-layer arrays of more complex elements. The copolar losses and the linear crosspolar performance of a 4-layer inductive grid and a 2-layer array of concentric rings are compared to illustrate some of the problems that can arise experimentally.     

Microstructural and mechanical properties evolution of magnesium AZ61 alloy processed through a combination of extrusion and thermomechanical processes

In this work, the microstructures and tensile properties of a commercial magnesium alloy “AZ61” processed by a combination of hot extrusion and thermomechanical processing (TMP) were investigated. The TMP was consisting of two or three hot rolling steps with large reductions per pass, thus allowing significant grain refinement. The microstructural evolution has been studied by means of optical and scanning electron microscopes, as well as X-ray diffraction analysis. The as-cast material is extruded in the form of a cylinder with initial diameter of 250 mm to a final diameter of 110 mm (80% reduction in cross-sectional area). Then hot rolling regimes were performed at 300 °C with different percentage of strain per pass. Tensile and hardness tests were performed in the samples (as-cast, extruded, and rolled) at room temperature in order to evaluate the mechanical properties of the material. The results of experiments demonstrated that fine grain size might be achieved in magnesium alloy AZ61 by using a two-step processing route involving an initial extrusion step followed by thermomechanical processing with large reduction in thickness per pass. This two-step process, designed to achieve average grain sizes of 10–20 μm.     

Modification and development of the optical,structural, thermal and electrical characterization of Chitosan incorporated with Au/Bi2O3/Mo NPs fabricated by laser ablation

The molecular structures of pure polymer (chitosan) incorporated with ternary metal nanoparticles (Au/Bi₂O₃/Mo) synthesized by laser ablation have been performed ia FT-IR and XRD. The surface of the synthesized samples has been investigated ia SEM. Thermal, electrical, and dielectric haracterization have been performed to utilized in energy applications. XRD patterns display the amorphous nature of chitosan (Cs), characterized by two hump peaks at 2? =11.34^o and 2? =19.57^o, which disappeared by doped with Au/Bi₂O₃/Mo NPs. FT-IR spectra revealed that thereare complexation between Cs and Au/Bi₂O₃/Mo NPs took place in amorphous regions. SEM displays grains with rectangular shape after adding different filling nanoparticles, and rod-shaped formed on the surface of the samples.TGA curves obtained the enhancement in the thermal stability of samples . The AC conductivity of the samples increased by the addition of Au/Bi₂O₃/Mo NPs. The results confirm that nanocomposite of Cs/metal have excellent thermal and electronic haracterization, which may suggest the utilization of these nanocomposites in energy storage.

     

Effect of different cooling rates on thermomechanically processed high-strength rebar steel

The present article is dealing with 0.2% C, 0.1% V and 0.02% Nb steel. Billets with 130 mm × 130 mm cross-section were austenitized and hold at 1080 °C. The billets were hot rolled to 22 mm bar diameter. Hot rolling was finished at 980–1000 °C. The final bars were air-cooled. On a parallel way, an experimental hot deformation investigation, on the same steel, was carried out at deformation temperature range 1200–800 °C with the same amount of deformation (97% reduction in area). However, cooling regimes after deformation were air cooling, water quenching to 600 °C followed by air cooling, and water quenching to room temperature. Microstructure investigation was done using both optical and scanning electron microscopes. Further evaluation was done using mechanical testing. The industrial trial has unsatisfied results with poorer yield strength with higher ultimate strength. Bainitic aggregates are detected in the hard phases islands. Air cooling after pilot hot deformation creates banded ferrite–pearlite microstructure with 9.11 μm ferrite grains. However, quick water quenching to 600 °C followed by air cooling develops tempered and softened coarse bainite phase. On the other hand, water quenching to room temperature develops fine bainite texture. Water quenching to 600 °C followed by air cooling is the best regime creating accepted mechanical properties.     

Dissolving pulps from Egyptian bagasse. II. Low temperature cooking

Bagasse was pulped by the prehydrolysis-soda process. Increasing the concentration during prehydrolysis or pulping had a favourable effect on pulp properties. Further improvement in these properties was attained when the increase in concentration was accompanied by lowering the temperature. The effects of increasing the concentration and lowering the temperature of prehydrolysis and pulping were compared.