Influence Of Surface Reactions Research Articles

Rapid Atmospheric Leaching of Chalcopyrite Using a Novel Reagent of Trichloroisocyanuric Acid

With the decrease in high-grade chalcopyrite resources, the copper extraction from low-grade chalcopyrite has attracted more and more attention. However, the kinetic rates of chalcopyrite leaching with traditional oxidants are usually very slow due to the formation of the passivation layer. In this study, a novel reagent of chlorinated oxidant, trichloroisocyanuric acid (TCCA), was used to leach chalcopyrite for the first time. The experimental results showed that when the initial oxidant concentration for TCCA was 0.054 mol·L−1, the leaching temperature was kept at 55 °C, and the pH of the pulp was controlled at 1, the oxidation efficiency of Cu can reach above 90% in less than 30 min. Various analyses of chalcopyrite mineral ore and its oxidized residues, such as chemical composition analysis, X-ray diffraction analysis, scanning electron microscopy analysis and X-ray photoelectron spectroscopy, were conducted, respectively. No obvious passivation layer was found on the chalcopyrite surface, though the sulfur product can also be generated during the leaching. Reaction kinetic analysis results showed that the different influence of surface reaction and diffusion process on the dissolution of chalcopyrite is little due to the fast leaching speed. After calculation, the activation energy of the whole leaching reaction is 9.06 kJ·mol−1, much lower than that in other reports. The mechanism was also proposed that TCCA was hydrolyzed in the solution to form hypochlorous acid, which is the strong oxidant, and cyanuric acid, which prevents the formation of a passivation layer. The processing in this study is expected to be applied as a novel method for atmospheric leaching of chalcopyrite.

Influence of Surface Reaction on Near-Wall Premixed Flame Behavior

To investigate near-wall flame behavior including effect of the surface reaction, two-dimensional direct numerical simulations (DNS) of methane/air, hydrogen/air and n-heptane/air premixed ignition and propagation between two parallel walls are conducted under several thermochemical conditions. From the DNS results, the flame front position defined by the OH gradient, and the flame displacement speed defined by the temporal evolution of the position are evaluated. The present analysis revealed following characteristics. (i) The flame speed takes a local minimum value near the wall. (ii) Under the conditions where the wall temperature equals unburnt gas temperature, this local minimum value corresponds to the laminar flame speed of the initial thermochemical condition. (iii) These characteristics do not depend on the ignition position, equivalence ratio, fuel types and presence/absence of surface reaction.

Kinetic Analysis of Copper Sulfide (Chalcopyrite) Dissolution by Moderately Thermophilic Bacteria

ABSTRACTThe objective of this study was to improve the basic understanding of copper sulfide minerals dissolution during bioleaching of flotation concentrate and to analyze the dissolution kinetic. The results show that the sulfide mineral dissolution kinetic changes with operation time. Both surface reaction and diffusion through product layer were found to be effective parameters for the rate of reaction with various degrees of influence. In other words, the whole dissolution process can be divided into two intervals. At the beginning, the effect of surface reaction on the reaction rate is obvious. With increasing operation time and formation of layer on the surface of copper sulfides, the influence of diffusion through the layers increases. However, the dissolution rate depends also on the particle size distribution index (d80) and pulp density. With decreasing particle size and pulp density, the influence of surface reaction on the dissolution rate is increasing more than that of diffusion through layers.

Effect of surface reactions on steel, Al2O3 and Si3N4 counterparts on their tribological performance with polytetrafluoroethylene filled composites

The influence of surface reactions on the tribo-performance of steel, Al2O3 and Si3N4 balls sliding against polytetrafluoroethylene/SiO2/epoxy composites was investigated. Al2O3 ball were found to exhibit the best tribo-performance, namely a low coefficient of friction and the lowest wear rates of both the composites and the counterpart ball, when sliding against the PTFE filled composites. The difference in the tribo-performance of the Al2O3 ball and the Si3N4 ball can neither be attributed to the different morphology of the worn composite surfaces nor to the amount of PTFE transferred onto the wear surfaces. Instead we found that the friction is greatly reduced in the case of the Al2O3 ball because two fluoro-terminated surfaces are sliding over each other; in fact, the formation of AlF bonding was confirmed by X-ray photoelectron spectroscopy.

F211 よどみ流予混合火炎のOH分布に与える表面反応の影響に関する実験的検討(OS-03:革新的技術のための燃焼研究(3))

F211 よどみ流予混合火炎のOH分布に与える表面反応の影響に関する実験的検討(OS-03:革新的技術のための燃焼研究(3))

プロパン-空気予混合火炎の燃焼特性に与える表面反応の影響に関する数値解析

プロパン-空気予混合火炎の燃焼特性に与える表面反応の影響に関する数値解析

The Influence of Surface Reactions, Bulk Diffusion, and Coherency Strain on the Kinetics of Intercalation in LiFePO4

not Available.

Influence of Surface Reactions on Complex Hydride Reversibility

Alkali metal hexahydride alanates, M 3 AlH 6 , are known to exist for M = Li, Na, and K. All three release hydrogen, forming MH and Al as the solid phase products. The reverse of this reaction, 6MH + 2Al + 3H 2 → 2M 3 AlH 6 , occurs without a catalyst for M = K, occurs only with a catalyst for M = Na, and has not been observed, even with a catalyst, for M = Li. Differences in the reactivities of the LiH, NaH, and KH surfaces may contribute to the observed differences in rehydriding. We have examined the reactivities of the low-energy MH(100) surfaces with respect to gas phase H 2 , H, O, O 2 , and H 2 O in order to test this hypothesis. We have found that H 2 weakly physisorbs and that H is unbound to all three MH surfaces, relative to gas phase H 2 . Atomic oxygen is very strongly bound to all three surfaces and O 2 dissociates without a barrier at low coverage on the LiH and NaH surfaces. The KH surface is more resistant to O 2 dissociation, but molecular O 2 strongly binds to the surface. We have identified dissociation pathways for H 2 O on all three MH surfaces, which results in the formation of surface metal hydroxide and gas phase H 2 . The zero-point energy corrected dissociation activation energies for H 2 O are 23.0, 13.8, and 18.4 kJ/mol for LiH, NaH, and KH, respectively. We have performed kinetic modeling of the H 2 O dissociation process resulting from MH surfaces exposed to vapor phase water at room temperature and partial pressures of 0.03 bar (100% relative humidity) and 10 -6 bar (1 ppm). In both cases, our modeling predicts that all three MH surfaces will be essentially completely covered with a monolayer of OH groups in less than 10 ms. We therefore conclude that there are no substantial differences in the reactivities of the MH surfaces that can account for the observed differences in their abilities to form the hexahydride alanate phase.

High‐Temperature Tribological Behavior of CrN‐Ag Self‐lubricating Coatings

The CrN‐Ag coating system is a promising candidate for high‐temperature lubrication, as it combines the wear and corrosion resistance of CrN with the lubrication properties of Ag. In this study, special emphasis is laid on the influence of surface reactions, like the formation of Ag agglomerates and/or surface oxidation, and on the high‐temperature tribological behavior at 600 °C. Characterization of the friction curves and the wear tracks provides an understanding of the relation between the out‐diffusion of Ag (forming agglomerates) and its lubricating effect.

Modeling of Infrared Radiation in a Space Transportation System Environment

An approach for modeling the infrared (IR) glow radiation about the space shuttle at low-Earth-orbit flight altitudes is examined. The study builds on the modeling and numerical techniques developed for understanding the visible glow of the Atmospheric Explorer. Because of the rarefied nature of the flow, a direct simulation Monte Carlo method is used. The study extends the earlier gas-phase reaction model to include NO vibrational-state-specific formation using cross sections derived from quasi-classical trajectory calculations. IR spectra are computed using the state-specific NO vibrational levels and an accurate line-by-line spectral model. The effect of internal and translational energy accommodation coefficients in the Maxwell gas-surface interaction model was studied. The translational energy accommodation coefficient affects the width of the NO overtone transition (Δν= 2) spectral peak, and a value less than unity is required to give good agreement between modeling and experiment. The vibrational energy accommodation coefficient significantly impacts the magnitude of the NO infrared spectra. The influence of surface reactions on the IR spectra was also examined and shown to be small. Finally, simulated spectra are compared with IR data obtained from shuttle space flight experiments. The comparison shows that the postulated gas and gas-surface phase models used in particle simulation enable one to predict quantitatively IR spectra at high altitudes.

The Characterization of Initial Growth of Polycrystalline Silicon Germanium Films on Zirconium Oxide

AbstractIn this study, the initial growth characteristics of a SiGe film realized by ultrahigh-vacuum chemical vapor deposition (UHV CVD) using GeH4 and Si2H6 on high-K gate oxide, ZrO2, has been investigated in the temperature range from 475°C to 550°C. The influence of surface reactions on growth characteristics such as the incubation of growth, roughness of the SiGe layer, and the interface reaction of the SiGe film with ZrO2were studied using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). From our analysis we conclude that ZrO2 reacts with Si and forms zirconium silicide in the temperature range between 500°C and 550°C. The surface roughness of amorphous SiGe layers increase from 0.5nm to 1.5nm by increasing Ge content from 0.1 to 0.3. A further increase of surface roughness is observed from less than 1nm to 5nm as SiGe layer transitions from an amorphous to a poly crystalline layer.

Influence of surface reactions and ionization gradients on junction properties of F16PcZn

Compared to unsubstituted phthalocyaninatozinc(ii) (PcZn), electron withdrawing fluorine atoms in hexadecafluorophthalocyaninatozinc(ii) (F16PcZn) cause a stabilization of the frontier orbitals of about 1.6 eV. This is concluded from photoelectron spectroscopy (UPS) at thin films on Au surfaces. From experiments at thin films [physical vapor deposition (PVD)] of PcZn deposited on top of F16PcZn under UHV conditions it is seen that a closed film of PcZn is formed at least within 5 nm average film thickness, that thermodynamic equilibrium between the films is achieved by charge transfer in redox reactions at the interface which, however, do not lead to a macroscopic space-charge layer. To study electrical device properties thin films of F16PcZn and PcZn were prepared in a range between 90 nm and 240 nm. Changes in electrical properties of ITO, Au|F16PcZn|metal (metal=In, Au) and ITO|F16PcZn|PcZn|Au devices have been studied in the dark and under illumination. Results of current–voltage characteristics and short-circuit photocurrent spectra of devices as prepared and measured under high vacuum (HV, 10–5–10–6 mbar) and after exposure to air are presented. In vacuum symmetrical I(U) characteristics were found for ITO|F16PcZn|Au devices. After exposure to air a decrease in dark conductivity, unsymmetrical I(U) characteristics and a considerable photovoltage (UOC) was measured under illumination. The magnitude of UOC as well as its direction can be clearly correlated with the exposure to atmosphere. This observation leads to a discussion based on a local asymmetry in O2 content as caused by slow diffusion into F16PcZn. O2 would lead to a decrease in the local majority carrier density as typically expected for organic n-type conductors. Rectification found in F16PcZn|In devices can be explained by a chemical reaction between the distinct electron acceptor F16PcZn and In as a donor. Photocurrent action spectra of devices with different thicknesses of F16PcZn layers in ITO|F16PcZn|PcZn|Au revealed detailed information about the site of charge carrier generation (photoactive area). The junction properties are discussed in detail based on the frontier orbital positions of PcZn and F16PcZn, and the work functions of the corresponding electrode materials.

Trends in ceramic breeder development

The paper summarizes the contributions on ceramic breeder development presented at ISFNT 2. Additionally a comparison with the state of the art is made. From this comparison conclusion in regard on further need in R&D are drawn. It is realized, that the knowledge of radiation defects and their influence on tritium release is unsufficient. Furtheron, the influence of surface reactions and dopants on the behavior of lithium ceramics needs further clarification. The design of blankets is far progressed. Now, critical points for further developments are identified. In this context the main emphasis in future will be on the increase of availability by improved designs using lesser welded joints and by improving the welding techniques itself.

Analytical models for growth by metal organic vapour phase epitaxy: II. Influence of temperature gradient

For pt.I see ibid., vol.5, p.16 (1990). Analytical descriptions are given of the growth rate in metal organic vapour phase epitaxy processes in the medium- and higher-temperature regions, where growth is controlled by diffusional transport through the gas phase and desorption of growth species, respectively. In continuation of part I, where only isothermal problems were considered, the temperature-dependent hydrodynamic behaviour is now investigated. A temperature gradient is introduced and the effect of thermal diffusion on the growth rate is studied, which is significant: a much ( approximately 40%) lower depletion is calculated if thermal diffusion is included. Furthermore the influence of surface reactions at high and low temperatures is investigated, resulting in a model in which the CVD number plays an important role. This model allows for the calculation of growth rates in both the diffusion-limited as well as the high-temperature region, where desorption dominates.

Reflection electron microscopy of surfaces

In surface science the direct imaging of the surface topography of single crystals is of great interest for the investigation of surface-changing processes. Imaging can be done in transmission electron microscopy (TEM) as well as in reflection electron microscopy (REM) using a diffracted beam with surface-sensitive intensity. Surface steps of atomic height can be imaged with both methods. The highest resolution is obtainable only in transmission; however, for the investigation of surface treatments, the reflection method from bulk single crystals is more suitable, even with a lack of resolution, since the thin TEM specimens are often not mechanically stable against surface treatments. With this technique the initial stage of epitaxy, the influence of surface reactions, corrosion etc. on the surface topography can be investigated. The application of REM requires that two important conditions be met, one concerning the specimen itself. Due to the small angle of observation the image is foreshortened.

Influence of surface reactions on the interface between liquid sodium and molten sodium chloride + calcium chloride mixtures

Influence of surface reactions on the interface between liquid sodium and molten sodium chloride + calcium chloride mixtures