Corrosion and time–dependent oxide film growth on AA5052 Aluminum alloy in 0.25M Na2SO4 solution containing H2O2 was studied using electrochemical impedance spectroscopy, potentiodynamic polarization, chronoamperometric and open circuit potential monitoring. It was found that sequential addition of H2O2 provokes passivation of AA5052 which ultimately thickens the oxide film and brings slower corrosion rates for AA5052. H2O2 facilitates kinetics of oxide film growth on AA 5052 at 25° and 60 °C which is indicative of formation of a thick barrier film that leads to an increment in the charge transfer resistance. Pitting incubation time increases by introduction of H2O2 accompanied by lower pitting and smoother surface morphologies. At short exposure (up to 8 h) to H2O2–containing solution, the inductive response at low frequencies predominantly determined the corrosion mechanism of AA5052. On the other hand, at prolonged exposure times (more than 24 h) to 0.25M Na2SO4+1vol% H2O2 solution, thicker oxide layers resulted in the mixed inductive–Warburg elements in the spectra. 相似文献
A new post-weld heat treatment (PWHT) cycle was designed for novel dissimilar linear friction welding (LFW) of selective laser melted (SLM) Inconel 718 (IN718) to AD730 forged nickel-based superalloy. The microstructure and hardness of the joints after the PWHT are investigated and compared with those of as-linear friction welded samples. The precipitation of γ′ + γ″ is determined as the main mechanism to increase the mechanical properties of SLM IN718 alloy. These particles coarsened during heat treatment at 1253 K and double aging. The results show that the thermomechanical history of linear friction welded joints can affect the microstructure of IN718 alloy such as the morphology of δ phase after solution treatment (ST) from the platelike in the weld zone (WZ) to the needlelike in the base material (BM). It was found that in AD730, nanometric size γ′ particles reprecipitated close to the weld line during rapid cooling after welding. The presence of ultrafine γ′ particles and coarsening of the remaining particles in the microstructure of the alloy, during PWHT, can enhance the strength and hardness. The developed PWHT resulted in uniform hardness across the new dissimilar joint.
The reductive benzylation of aromatic and aliphatic aldehydes with benzylic halides is reported using a nickel/zinc catalyst system. In addition to benzylic halides, the first report on the addition of benzylic triflates, acetates, tosylates and tritylates to aldehydes is also presented. By this new method a range of alcohols was synthesized efficiently from aldehydes and benzylic substrates at room temperature in moderate to high yields. The mild reaction conditions and good functional group tolerance make this nickel‐catalyzed process synthetically useful for the synthesis of diverse benzylic alcohols.
Rice crops are often subject to multiple abiotic stresses simultaneously in both natural and cultivated environments, resulting in yield reductions beyond those expected from single stress. We report physiological changes after a 4 day exposure to combined drought, salt and extreme temperature treatments, following a 2 day salinity pre-treatment in two rice genotypes—Nipponbare (a paddy rice) and IAC1131 (an upland landrace). Stomata closed after two days of combined stresses, causing intercellular CO2 concentrations and assimilation rates to diminish rapidly. Abscisic acid (ABA) levels increased at least five-fold but did not differ significantly between the genotypes. Tandem Mass Tag isotopic labelling quantitative proteomics revealed 6215 reproducibly identified proteins in mature leaves across the two genotypes and three time points (0, 2 and 4 days of stress). Of these, 987 were differentially expressed due to stress (cf. control plants), including 41 proteins that changed significantly in abundance in all stressed plants. Heat shock proteins, late embryogenesis abundant proteins and photosynthesis-related proteins were consistently responsive to stress in both Nipponbare and IAC1131. Remarkably, even after 2 days of stress there were almost six times fewer proteins differentially expressed in IAC1131 than Nipponbare. This contrast in the translational response to multiple stresses is consistent with the known tolerance of IAC1131 to dryland conditions. 相似文献
The paper proposes a concept configuration of reactors for coupling OCM and FTS, and presents systematic simulation results. FTS section is a combination of fixed bed and membrane fluidized bed reactor, and feed of the FT reactor is supplied by OCM. The reactor configuration is compared with the consecutive reactors of OCM and one fixed bed FT reactor. Effects of CH4/O2 ratio, percent of N2 in the feed, contact time, and input temperature on the yield of ethylene and valuable hydrocarbons are studied. The results show that compared with one FTS reactor configuration, the dual FTS reactor configuration is more effective and thus gives much higher product yields. Furthermore, a main decrease is observed in the formation of CO2 and CH4. 相似文献
Silicon-substituted hydroxyapatite (Si-HA) with up to 1.8 wt% Si content was prepared successfully by a hydrothermal method, using Ca(NO3)2, (NH4)3PO4 or (NH4)2HPO4 and Si(OCH2CH3)4 (TEOS) as starting materials. Silicon has been incorporated in hydroxyapatite (HA) lattice by partially replacing phosphate (PO43−) groups with silicate (SiO44−) groups resulting in Si-HA described as Ca10(PO4)6−x(SiO4)x(OH)2−x. X-ray diffraction (XRD), Fourier transform IR spectroscopy (FTIR), inductively coupled plasma AES (ICP-AES) and scanning electron microscopy (SEM) techniques reveal that the substitution of phosphate groups by silicate groups causes some OH− loss to maintain the charge balance and changes the lattice parameters of HA. The crystal shape of Si-HA has not altered compared to silicon-free reference hydroxyapatite but Si-incorporation reduces the size of Si-HA crystallites. Based on in vitro tests, soaking the specimens in simulated body fluid (SBF), and MTT assays by human osteoblast-like cells, Si-substituted hydroxyapatite is more bioactive than pure hydroxyapatite. 相似文献
Determination of diffusion coefficients of pure compounds in air is of great interest for modeling of air pollution control processes. In this communication, a Group Contribution (GC) method is applied to represent/predict the molecular diffusivity of chemical compounds in air at 298.15 K and atmospheric pressure. 4661 compounds from various chemical families have been investigated to propose a comprehensive and predictive model. The final model is resulted from coupling the Artificial Neural Network (ANN) with group contributions. Using this dedicated model, we obtain satisfactory results quantified by the following statistical results: Squared Correlation Coefficient=0.995, Standard Deviation Error=0.02, and Average Absolute Deviation=1.4% for the calculated/predicted properties from existing experimental values. 相似文献