Potential of molten lead oxide for liquid chemical looping gasification (LCLG): A thermochemical analysis

Molten lead oxide is revealed to have favourable thermodynamic performance for gasification in a new process employing chemical looping of a molten liquid metal oxide. In this process, the feedstock is partially oxidized with molten lead oxide in the fuel reactor, while the reduced molten lead is oxidized in the air reactor. As with other chemical looping processes, this avoids direct contact between air and fuel, which prevents the undesirable dilution of the gaseous product with nitrogen. The Gibbs minimization method was employed together with thermo-chemical equilibrium analysis to assess the feasibility of the gasification process using graphite as a surrogate for more realistic, but complex carbonaceous fuels, together with steam and/or carbon dioxide as the gasifying agent. It was found that both the reduction and oxidation reactions of molten lead oxide with carbonaceous fuel are spontaneous. Likewise, the ratio of H₂:CO can be as high as 2.5, while the carbon conversion can reach 94% based on the thermochemical analysis. An energetic performance analysis was also employed for the case of a supercritical steam turbine cycle to extract work from the hot gaseous co-products. On this basis, the first law efficiency of the power cycle was estimated to be up to 33.8%, while the syngas co-product stream for applications such as Fischer-Tropsch synthesis has a chemical exergy efficiency of 41%.     

Texture development and microstructure evolution in metastable austenitic steel processed by accumulative roll bonding and subsequent annealing

In this paper, microstructure and texture development in a Fe–24Ni–0.3C metastable austenitic steel processed by accumulative roll bonding (ARB) and subsequent annealing was studied. Microstructural observations and crystallographic analysis were carried out by FE-SEM/EBSD. The results showed that elongated ultrafine-grained austenite having 300 nm in thickness surrounded by high angle boundaries was obtained after 6 cycles of the ARB process. It was found that 1-cycle ARB-processed specimen exhibited Copper ({112} 〈111〉) component as main texture, while by increasing the number of ARB cycles, it deviated to S component ({123} 〈634〉) at 2 cycles or Brass component ({110} 〈112〉) at 6-cycle. Annealing of 6-cycle ARB-processed specimen at 873 K for 1.8 ks resulted in the formation of an austenite with mean grain size of 2.5 µm having strong Cube recrystallization texture ({100} 〈001〉).     

A study of the electro-catalytic oxidation of methanol on a cobalt hydroxide modified glassy carbon electrode

Cobalt hydroxide modified glassy carbon electrodes (CHM/GC) prepared by the anodic deposition in presence of tartrate ions have been used for the electro-catalytic oxidation of methanol in alkaline solutions where the methods of cyclic voltammetery (CV), chronoamperometry (CA) and impedance spectroscopy (IS) have been employed. In CV studies, in the presence of methanol the peak current of the oxidation of cobalt hydroxide increase is followed by a decrease in the corresponding cathodic current. This suggests that the oxidation of methanol is being catalysed through the mediated electron transfer across the cobalt hydroxide layer comprising of cobalt ions of various valence states. A mechanism based on the electro-chemical generation of Co(IV) active sites and their subsequent consumptions by methanol have been discussed and the corresponding rate law under the control of charge transfer has been developed and kinetic parameters have been derived. In this context the charge transfer resistance accessible both theoretically and through the IS studies have been used as a criteria. Under the CA regimes the reaction followed a Cottrellian behaviour.     

Electrodeposition of aluminum from molten AlCl3–NaCl–KCl mixture

Electrochemical deposition of aluminum from basic and acidic molten NaCl-KCl-AlCl₃ mixture on a graphite electrode at 140 °C was studied by voltammetry, chronopotentiometry and constant current deposition. The deposition of aluminum was found to proceed via a nucleation/growth mechanism in basic melt, while it was found to be diffusion controlled in acidic melt. The diffusion coefficient calculated for Al₂Cl⁻ ₇ ions in acidic melt by voltammetry was in agreement with the deductions of voltammetry. The morphology of the aluminum deposits was examined using a metallographic microscope and by SEM. It was shown that, depending on the current density (c.d.) and AlCl₃ concentration (acidic or basic melt) different aluminum morphologies were evident but a silver-bright, compact, and very stable metallic form of aluminum deposit was obtained in acidic melt with KI addition as surfactant.     

Study of the alloying additives and alkaline zincate solution effects on the commercial aluminum as galvanic anode for use in alkaline batteries

The corrosion behavior of different grades of commercial aluminum such as AA1040, AA5083, AA6060 and AA7075 in ZnO-containing 4 M NaOH has been determined by using open circuit potential-time measurements (OCP), galvanostatic and potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results of scanning electron microscopy (SEM) and energy dispersive analysis of X-ray (EDAX) reveal that ZnO produces the inhibition effect by the formation of a zinc-containing deposit layer on the surface of aluminum electrodes. Although the influence of zincating on the performance of aluminum alloys and considering the amount of alloying elements such as zinc, magnesium and manganese in AA7075 and AA5083 alloys is much more than AA6060 one, the AA6060 aluminum exhibits negligible corrosion rate. Alloying aluminum with other elements and modifying the composition of the electrolyte is a necessary condition for reducing the self-corrosion of the aluminum anodes, whereas the proportion of the amount of additive elements is sufficient and important condition. As AA6060 with a low amount of Zn and Mg, but the high value of the ratio of (Mg/Zn) content (>400) can serve as a good galvanic anode in the alkaline media.     

Effect of sub-layer temperature during HFCVD process on morphology and corrosion behavior of tungsten carbide coating

WC coating was deposited on the polished and cleaned 316L stainless steel by Hot Filament Chemical Vapor Deposition (HFCVD) technique at 400°C and 500°C. Field Emission Gun Scanning Electron Microscope (FEG-SEM) was used to study the corrosion morphology of the WC coatings. Energy dispersive spectroscopy (EDS) was used to analyze the chemical composition of the coatings. Coating porosity was measured by immersion in water. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were used to study the corrosion behavior of the coating in the solution of 1 mol/L H₂SO₄. Results showed that the WC coatings have a honeycomb microstructure where its porosity was increased at higher temperature of the sub-layer. Also, the WC coating significantly increases the corrosion resistance of 316L stainless steel. And increasing the sub-layer temperature in the HFCVD method reduces the corrosion resistance of the WC coating. Corrosion morphology was indicative of pitting corrosion of the WC coating.     

Automatic segmentation of newborns’ skull and fontanel from CT data using model-based variational level set

The newborn’s cranium is composed of flat cranial bone and fontanels forming together the envelope of the cerebral cavity. The fontanels are relatively flexible since they consist of fibrous membrane that ossifies during maturation becoming flat cranial bone as well. Fontanels give less contrast in computerized tomography (CT) images; they can be identified as gaps between the cranial bones. In this paper, we propose an automatic model-based method using variational level set to segment the skull and fontanels from CT images. In this approach, firstly a skull model consisting of cranial bones and fontanels is created and then used as constraint for level set evolution. Then, by removing the cranial bones from the segmented skulls, the fontanels are obtained. To verify the validity of the achieved results, automatically segmented skull and fontanels have been compared with the ones manually segmented by an expert using Dice similarity and Hausdorff dissimilarity measures, which show the good agreement between them. Furthermore, the surface areas of cranium and fontanel have been determined for these segmentations. The results for both, manual and automatic segmentation, are in good agreement.     

Two-time scale control and observer design for trajectory tracking of two cooperating robot manipulators moving a flexible beam

In this paper, we present two-time scale control design for trajectory tracking of two cooperating planar rigid robots moving a flexible beam, which does not require vibration measurement for the beam. First, the kinematics and dynamics of the robots and the object are derived. Then, using the relations between different forces acting on the object by the manipulators’ end-effectors, dynamics equations of the robots and the object are combined. The resulting equations show that the coupled dynamics including beam vibration and the rigid motion take place in two different time domains. By applying two-time scale control theory on the combined dynamics, a composite control scheme is elaborated which makes the beam orientation and its center of mass position track a desired trajectory while suppressing the beam vibration. For the controller algorithm, first a slow controller is utilized for the slow (rigid) subsystem and then a fast stabilizing controller is considered for the fast (flexible) subsystem. To avoid requiring measurement of beam vibration for the fast control law, a linear observer is also designed. The simulation results show the efficiency of the proposed control scheme.     

Particle‐Scale Investigation of Heat Transfer in Radiation‐Driven Char Gasification

A model of the steam gasification of a single char particle driven by high‐intensity radiation was developed and experimentally verified with available measurements in the literature. This was used to explore the sensitivity of the particle surface temperature and heat‐transfer mechanisms to variations in particle diameters, radiative heat flux, and the concentration of the gasification agent H₂O under typical conditions for solar gasification reactors. The results highlight the importance of the particle diameter in influencing solar‐to‐chemical energy conversion efficiency and assist in the selection of appropriate feedstock particles to match the conditions in specific solar gasification reactors.