Hysteresis loops of individual Co nanostripes measured by magnetic force microscopy

High-resolution magnetic imaging is of utmost importance to understand magnetism at the nanoscale. In the present work, we use a magnetic force microscope (MFM) operating under in-plane magnetic field in order to observe with high accuracy the domain configuration changes in Co nanowires as a function of the externally applied magnetic field. The main result is the quantitative evaluation of the coercive field of the individual nanostructures. Such characterization is performed by using an MFM-based technique in which a map of the magnetic signal is obtained as a function of both the lateral displacement and the magnetic field.     

Catalytic Decomposition of Methane Over M–Co–Al Catalysts (M = Mg,Ni, Zn,Cu)

Abstract  

The catalytic decomposition of methane over M–Co–Al (M = Mg, Ni, Zn, Cu) was studied. The samples were prepared by co-precipitation and characterized by S_BET, TGA, DTA, TPR and XRD. The carbon produced in the reaction was characterized by SEM and TPO. Activity tests were carried out in a thermobalance between 500 and 750 °C. The results show that the textural properties of the calcined samples did not change significantly with the partial substitution of Co by Mg, Ni, Zn or Cu. On the other hand, there were marked differences in the reduced samples. There was a strong influence on the reducibility of cobalt oxides in the presence of Ni or Cu. Nickel promoted the reduction of Co₃O₄ at the same temperature as the NiO phase, whereas copper strongly decreased the reduction temperature of both Co₃O₄ and CoAl₂O₄ due to a synergistic effect between Cu and Co. The sample containing Cu resulted in low catalytic activity in the whole temperature range because the reduction conditions promoted the formation of a Cu–Co alloy. In the reaction carried out at 700 °C, the observed activity was Co–Al > Mg–Co–Al > Ni–Co–Al. All the samples were deactivated by encapsulation under these conditions due to high rates of carbon deposition. The carbon produced was mainly carbon nanotubes, except for the Cu–Co–Al sample, which produced mostly amorphous carbon.     

High-Stable Mesoporous Ni-Ce/Clay Catalysts for Syngas Production

Abstract  

A mesoporous-type catalytic support was synthesized through the modification of a smectite with polyvinyl alcohol (PVA) and microwaves. Texture and micro-morphology of the support was determined. Several techniques were employed in order to describe the chemical environment of active species on the surface. Ni⁰ particle sizes were dependent on the structural site of reducible species. High stable Ni-Ce catalysts (calcined at 800 °C) were evaluated in the CO₂ reforming of methane reaction at 700 °C (WHSV = 96 L g⁻¹ h⁻¹, without dilution gas and pre-reduction). The catalysts have presented CH₄ conversions between 40 and 65%, CO₂ conversion between 35 and 65% and H₂/CO ratios between 0.2 and 0.4.     

Sliding-wear resistance of pure near fully-dense B4C under lubrication with water,diesel fuel,and paraffin oil

The sliding-wear resistance of pure near fully-dense B₄C is investigated, and the wear mode/mechanisms identified, under lubrication with water, diesel fuel, and paraffin oil. It is found that the wear is mild in the three cases, with specific wear rates (SWRs) of 10^?16–10^?17 m³/N m. Nonetheless, the wear resistance of the B₄C ceramic is one order of magnitude greater under oil lubrication (10¹⁶ N m/m³) than under water lubrication (10¹⁵ N m/m³), and twice as great for the specific case of paraffin oil than diesel fuel, attributable to the lubricant’s viscosity. It is also found that the wear mode is always abrasion, and that the wear mechanisms are plastic deformation and localized fracture with grain pullout. However, in agreement with the macro-wear data, the severity of the wear damage is lower under lubrication with paraffin oil, followed by diesel fuel, and lastly water. Finally, microstructural considerations are discussed with a view to enhancing the sliding-wear resistance of B₄C triboceramics.     

A COMPARATIVE STUDY OF KINETIC MODELS FOR ION-EXCHANGE USING MACROPOROUS RESINS AND CONCENTRATED SOLUTIONS

ABSTRACT

A “shallow bed” technique was employed for the study of the kinetics of K⁺ ? H⁺ exchange in concentrated solutions with a macroporous ion-exchange resin. Six kinetic models were applied to the experimental data. The fitting of the mathematical models and the behaviour of the kinetic curves when some variables change, show that there does not exist any model based on the Donnan exclusion principle suitable for explaining the experimental data. The best model in these extreme conditions is a modification of the Progressive Conversion mechanism. It can be easily applied to the design of industrial operations.     

Self-feed device behaviour evaluation designed for assessment of operability of coated electrodes

The objective of the present work is to evaluate the effectiveness of a self-feed device for coated electrodes. This device is able to eliminate disturbances from manual operation or the use of automatic control systems during the study of coated electrode behaviour. The conjugation of different methods such as short-circuit time statistical analysis and metallographic analysis (penetration, heat-affected zone, shape and mean distance between successive solidification fronts) together with the analysis of the electric arc and electrode melting parameters allows us to obtain relationships between arc behaviour, mass transfer processes and bead appearance. This permits the extraction of criteria to describe process stability and the behaviour of the feed device employed. An appropriate statistical methodology was obtained to process the ‘duration of the short-circuit’ parameter through an appropriate adjustment of empirical distributions to a log-normal model. The self-feed device for coated electrode welding allows the repeatable and reproducible execution of welding beads in the flat position, keeping the arc length based on physical and chemical characteristics of the electrode during welding trials using 125, 140 and 160 A.     

Exhaust emissions and electric energy generation in a stationary engine using blends of diesel and soybean biodiesel

The present work describes an experimental investigation concerning the electric energy generation using blends of diesel and soybean biodiesel. The soybean biodiesel was produced by a transesterification process of the soybean oil using methanol in the presence of a catalyst (KOH). The properties (density, flash point, viscosity, pour point, cetane index, copper strip corrosion, conradson carbon residue and ash content) of the diesel and soybean biodiesel were determined. The exhaust emissions of gases (CO, CO₂,C_xH_y,O₂, NO, NO_x and SO₂) were also measured. The results show that for all the mixtures tested, the electric energy generation was assured without problems. It has also been observed that the emissions of CO, C_xH_y and SO₂ decrease in the case of diesel–soybean biodiesel blends. The temperatures of the exhaust gases and the emissions of NO and NO_x are similar to or less than those of diesel.     

Sustainability assessment of bio-ethanol production in Brazil considering land use change,GHG emissions and socio-economic aspects

Three sustainability aspects of bioethanol production in Brazil were considered in this paper. Results show that the recent expansion of sugarcane has mostly occurred at the expense of pasturelands and other temporary crops, and that the hypothesis of induced deforestation is not confirmed. Avoided greenhouse gas emissions due to the use of anhydrous ethanol blended with gasoline in Brazil (E25) were estimated as 78%, while this figure would be 70% in case of its use in Europe (E10). Conversely, considering the direct impacts of land use change, the avoided emissions (e.g., ethanol consumed in Europe) would vary from −2.2% (i.e., emissions slightly higher than gasoline) to 164.8% (a remarkable carbon capture effect) depending on the management practices employed previous to land use change and also along sugarcane cropping. In addition, it was shown that where the bulk of sugarcane production takes place, in state of São Paulo, positive socio-economic aspects are observed. The general conclusion is that a significant share of ethanol production in Brazil can be considered sustainable, in particular regarding the three aspects assessed. However, as production conditions are extremely heterogeneous, a generalization of results is not possible.     

Catalytic performance of Ni-Pr supported on delaminated clay in the dry reforming of methane

Mineral clay modified with Al, polyvinyl alcohol (PVA) and microwaves was used as a support to obtain a Ni-Pr catalyst. This catalytic system was evaluated in the reforming of methane with CO₂. The experiments were carried out under drastic conditions for 300 min, with a 50/50 CH₄/CO₂ mixture, total flux of 80 mL min⁻¹, without dilution gas (WHSV = 96 Lg⁻¹h⁻¹) and without previous reduction. The effect of the calcination temperature of the materials was studied at 500 °C and 800 °C as well as the effect of Pr (evaluating nominal quantities of 0, 1, 3 and 5%). The calcination temperature of the solid influenced the formation of the NiO species which had an effect on the activity and formation of coke on the material. The Pr had a promoter effect on the activity of the catalysts increasing the conversions of the CH ₄ as well as the CO₂. The formation of coke for the catalysts calcined at 500 °C presented a correlation with the praseodymium content while for those catalysts calcined at 800 °C there was no formation of coke.