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[en] The present work deals with the inhibiting effects of imidazole on the pure copper (Cu) corrosion in 1 M HNO3 solution analysing potentiodynamic polarisation curves, potentiostatic anodic current transient, AC impedance spectra and X-ray photoelectron spectra (XPS). By adding imidazole to HNO3 solution, the polarisation curves showed decrease in the corrosion current and the cathodic current, suggesting that imidazole acts as an effective cathodic inhibitor to Cu corrosion. From the measured anodic current transients, it is inferred that the protective Cu-imidazole complex film is simultaneously formed with the Cu oxide in the presence of imidazole during the early stage of the anodic polarisation. Analysis of the AC impedance spectra revealed that the values of the charge transfer resistance Rct obtained in imidazole-containing HNO3 solution were greater than that value in imidazole-free one and at the same time steadily increased with immersion time to the constant value. Contrarily, the capacitance value was abruptly lowered from the double layer capacitance Cdl to the complex film capacitance Ccf in the progress of immersion time. Furthermore, the Warburg coefficient σ value for the ion diffusion through the complex film was observed to increase with immersion time. This means that the Cu(N-OH) complex film becomes thicker during immersion in the HNO3 solution with imidazole through the inward growth of the N-rich outer layer to the O-rich inner layer, as well validated by XPS. Based upon the experimental results, it is suggested that the Cu corrosion in 1 M HNO3 solution is efficiently inhibited with the addition of imidazole by retarding both the charge transfer on cathodic sites of the Cu surface in the early stage of immersion time and the subsequent ion diffusion through the steadily growing complex film
[en] In the present study, electrochemical and surface analytical techniques were employed to study the mechanism of chemical mechanical planarisation (CMP) process for highly inert noble ruthenium (Ru) film in ceric ammonium nitrate (CAN) additives-containing acidic slurry. The steady-state polarisation curves with surface abrasion exhibited increment in the corrosion potential and cathodic current, suggesting that the partially exposed bare Ru acts as a cathodic site for CAN reduction on Ru2O3-covered Ru film as validated by X-ray photoelectron spectroscopy (XPS). Based upon the combined results of open-circuit potential (OCP) and anodic current transients, with scanning electron microscopy (SEM), we may assert that the mechanical removal of Ru2O3 enhances the local formation rate of RuO2 or RuO4 film, resulting in a loss of Ru by successive galvanic corrosion at the anodic sites. Using CAN-containing acidic slurry, Ru CMP process for manufacturing a bottom electrode for capacitors in DRAM device was satisfactorily accomplished as validated by SEM and atomic force microscopy (AFM)
[en] Shale gas has become an increasingly important form of hydrocarbon energy, and related technologies reflect the geographical characteristics of the countries where the gas is extracted and stored. The United States (U.S.) produces most of the world’s shale gas, while China has the world’s largest shale gas reserves. In this research, we focused on identifying the trends in shale-gas related technologies registered to the United States Patent and Trademark Office (USPTO) and to the State Intellectual Property Office of the People’s Republic of China (SIPO) respectively. To cluster shale-gas related technologies, we text-mined the abstracts of patent specifications. It was found that in the U.S., the key advanced technologies were related to hydraulic fracturing, horizontal drilling, and slick water areas, whereas China had a focus on proppants. The results of our study are expected to assist energy experts in designing energy policies related to technology importation. - Highlights: • We analyzed shale gas-related patent applications in the USPTO and SIPO. • We clustered shale gas patents by text mining patent abstract. • Differences were observed in shale gas technologies developed in the U.S. and China. • We proposed the policies of shale gas exploration and development based on patent analysis
[en] Large pulsed electron beam (LPEB) irradiation was used as a single surface finishing process for Ti−Al−7Nb. Nitrogen plasma gas and cathodic apparatus have been adopted to induce nitriding effect of Ti−6Al−7Nb during the electron beam irradiation. The atomic concentration of nitrogen atoms at the re-solidified layer could be t5achieved up to ∼18% by LPEB nitriding. Nano-hardness in the re-solidified layer was improved by ∼75% following the irradiation process, as a result of a phase transformation and the formation of TiN. The re-solidified layer induced by the LPEB nitriding, consisted of TiN, TiO_2, and TiO_xN_y, indicated significantly modified corrosion resistance showing a nobler corrosion potential, decreased corrosion current density, and improved charge transfer resistance. The increasing fraction of TiN at the re-solidified layer, induced by LPEB nitriding, was suggested as being responsible for remarkable improvement of mechanical properties and corrosion resistance, embedding uniformly noble and stable characteristics at the top surface. The corrosion-resistant surface layer with superior mechanical properties on Ti−6Al−7Nb has been successfully demonstrated by LPEB nitriding technique. - Highlights: • The nitrogen plasma source facilitated the formation of TiN at the re-solidified layer induced by LPEB. • The negative DC bias increased TiN fraction at the re-solidified layer. • The passivation of re-solidified layer enhanced corrosion resistance of Ti−6Al−7Nb. • The formation of uniformly stable oxy-nitride layer increased corrosion resistance. • Large pulsed electron beam irradiation with N_2 plasma source generated surface hardening.
[en] Highlights: • The numerical model of large pulsed electron beam irradiation process was developed. • A mechanism of energy transfer during the irradiation was specified. • An absorptivity of large pulsed electron beam was numerically investigated. • Experimental validations of the predictive temperature model were performed. • The numerical model of molten depths was well matched with the experiments. - Abstract: The pulsed electron beam irradiation process is a relatively advanced technique for surface modification, including surface hardening, corrosion protection, and wear inhibition. Due to increasing demand for surface modification processes on solid metals, many experimental studies have focused on electron beam irradiation processes. In this study, a three-dimensional numerical model of the large electron beam irradiation with a Gaussian-distributed heat source was developed. To reflect the natural interactions between accelerated electrons and solid substrates, the absorptance of the electron beam was evaluated with considering electron scattering, backscattering, and transmission. Predictions of temperature distributions were validated by measuring molten depths of engineering alloys after the electron beam irradiation. The effects of absorptance on the prediction accuracy of the molten depth were also explored, and the computational results were compared based on constant and calculated absorptance versus depth. The consideration of energy absorbing mechanisms resulted in more accurate predictions of molten depths, as demonstrated by the strong agreement with experimental results.
[en] Analysis of the initial stage of anodic dissolution and subsequent passivation on newly exposed bare surfaces of metals and alloys, which emerged from passivating oxide film breakdown, offers important information not only about localized corrosion but also the basic electrochemical behaviour. This article first introduced the historical development and principles of electrochemical techniques for the study of repassivation kinetics at passivating metals in the period 1973-1998. As compared with formerly established scratching electrode technique, the data acquisition period of the abrading electrode technique is quite sufficient for investigation into repassivation kinetics of passivating metals whose films instantaneously grow in the period of 5 ms. Thus, one gives more attention to the abrading electrode technique, which is widely used, than the scratching electrode technique in obtaining reproducible data. Finally, this article presented some recent results of repassivation kinetics of such passivating metals as pure Ni, Al, Al-Si-Cu alloy, pure Fe and 316L stainless steel reported from our laboratory using the abrading electrode technique
[en] A linear-response method based on plane-wave basis density-functional theory to calculate the effective Coulomb interaction (U) between closed-shell localized electrons is suggested and applied to the 3d closed-shell systems (Cu, Zn, and ZnO). Since the closed-shell localized states are far below the Fermi level, a large local perturbation potential (α) projected to the localized states is applied to induce a purposeful density response (Δn). From the α, the perturbation potential cost for the density response onset, by which the Δn begins to be induced, is removed. The main screening channel for the effective Coulomb interaction is the itinerant electrons deoccupied from the perturbed localized states. The Cu, Zn, and ZnO 3d electron binding energies are calculated based on the local density approximation plus U, with the U values being calculated from the linear-response and being found to be in good agreement with the experimental values.
[en] Based on first-principles theoretical calculations, we investigate the electronic structure of various defects in P-doped ZnO. We find that a PO impurity occupying an O site is a deep acceptor while a PZn atom at a Zn site is the dominant donor, causing a compensation of acceptors. Under O-rich growth conditions, Zn vacancies (VZn) are the main source of p-type conduction. Since VZn is mobile and strongly interacts with abundant PO and PZn defects, resulting complexes, such as PZn-2VZn and PO-VZn, which behave as acceptors, are likely to be formed under non-equilibrium growth conditions, and are responsible for the p-type conduction. We also investigate the effect of the strong Coulomb repulsion for the Zn d electrons on the electronic properties of various defects.
[en] In the reaction A + B →<- C, where A and B are ionic reactants having opposite charges, a B molecule approaching an A will experience a switching of the interaction potential when the A molecule is captured by one of the other B molecules in the medium. In the reversible case, the former B molecule still has a chance to react with the A, so that one needs to take into account the switched interaction between the reactant B and the product C as well as that between the reactants to treat the kinetics accurately. It is shown that this kind of interaction potential switching affects the relaxation kinetics in an intriguing way as observed in a recent experiment on an excited-state proton transfer reaction
[en] The objective of this study was to develop a spectral CT system using a photon counting detector and to decompose materials by applying a multiple discriminant analysis (MDA) to the energy-dependent attenuation coefficient ratios. We imaged cylindrical phantoms of Polymethyl methacrylate (PMMA) with four holes filled with calcium chloride, iodine, and gold nanoparticle contrast agents. The attenuation coefficients were measured via reconstructed multi-energy images, and the linear attenuation ratio was used for material identification. The MDA projection matrix, determined from training phantoms, was used to identify the four materials in the testing phantoms. For quantification purposes, the relationships between the attenuation coefficients at multiple energy bins and the concentrations were characterized by using the least-squares method for each material. The mean identification accuracy for each of the three materials were 0.94 ± 0.09 for iodine, 0.96 ± 0.07 for gold nanoparticles, and 0.92 ± 0.05 for calcium chloride. The mean quantification errors were 1.90 ± 1.58% for iodine, 3.85 ± 3.13% for gold nanoparticle, and 3.40 ± 2.62% for calcium chloride. The developed multi-energy CT system based on the photon-counting detector with MDA can precisely decompose the four materials.