INVESTIGATING THE CORROSION BEHAVIOUR OF ZX10 MAGNESIUM ALLOY IN VARIOUS CORROSIVE MEDIA AND THE CORROSION RESISTANCE OF MAGNESIUM OXIDE COATINGS

At present, magnesium alloys are receiving considerable attention in the fields of computer parts,automotive,aerospace components, and biomedical applications because of their low density, high specific strength and bio-compatibility. Among them, the ZX10 magnesium alloy exhibits excellent mechanical properties. However, due to their poor corrosion resistance and insufficient mechanical properties when exposed to different aggressive environment, the engineering application of magnesium alloys is limited and requires appropriate surface treatment. This study, therefore, focused on the degradation behaviour of ZX10 magnesium alloy in different corrosive media at room temperature and the development of protective MgO coating on ZX10 magnesium alloy. The degradation behaviour and corrosion rate of ZX10 magnesium alloy in different aggressive media with varying pH values, were investigated by employing the Tafel curve and electrochemical impedance techniques, and analyzed with the Scanning Electron Microscope (SEM). The chemistry and diffraction phases of adhering corrosion products were also investigated by utilizing the X-ray diffraction (XRD) technique. MgO coatings were electrodeposited on magnesium alloy using cathodic electrolytic method and subsequent calcination at different temperatures to improve the corrosion resistance. The protective performance of the MgO coatings was investigated by potentiodynamic polarization, and electrochemical impedance spectroscopy and a correlation was drawn between calcination temperature of coatings, corrosion resistance, and mechanical hardness. A modeled calcination mechanism, as it relates to barrier performance at low and high thermal conditions, has been illustrated based on collected experimental evidence. Results showed that magnesium alloy demonstrated varying rates of corrosion and passivation within a range of pH of corrosion media. The acidic systems showed the highest rate of metal corrosion while the lowest corrosion rate was observed for the alkaline systems. Localized corrosion has been observed by SEM, while electrochemical impedance spectroscopy and potentiodynamic polarization techniques reveal increased anodic polarization and charge transfer, respectively. The metal uniformly corroded for each examined corrodent over an extended period of time; however, the early corrosion stages reveal localized formation of oxide films at grain boundaries. The protective MgO coating was successfully developed and optimized on ZX10 magnesium alloy. The internal tensile stress was produced in electrodeposition because of the occlusion of hydrogen atoms in the coatings. Results showed that at calcination temperature of 250 o C, the internal tensile stress was released leading to crystallization of oxide coating layers with compact and continuous multi-layered micro-structures. At higher temperatures (around 500 o C), recrystallization of the MgO coating increased coating porosity and broadened inter-diffusion at micro-defects. Surface and bulk pores and cracks have been observed at 500 o C as clear evidence of the consequence of over-calcination. Enhanced corrosion resistance was observed for the MgO coatings obtained at 250 o C calcination temperature after chloride-induced corrosion tests and its corrosion current density is one thousand times smaller than that of bare magnesium alloy

Assessment and Spatiotemporal Variation Analysis of Water Quality in the Zhangweinan River Basin, China

AbstractSpatiotemporal variation analysis of water quality and identification of water pollution sources in river basins is very important for water resources protection and sustainable utilization. In this study, fuzzy comprehensive analysis and two statistical methods including cluster analysis and seasonal Kendall test method were used to evaluate the spatiotemporal variation of water quality in the Zhangweinan River basin. The results for spatial cluster analysis and assessment on water quality at 19 monitoring sites indicated that water quality in the Zhangweinan River basin could be classified into two regions according to pollution levels. One is the Zhang River basin located in northwest of the Zhangweinan River basin where water quality is good. Another one includes the Wei River and eastern plain of the Zhangweinan River basin, and the water pollution in this region is serious, where the pollutants from point sources flow into the river and the water quality changes greatly. The results of temporal cluster analysis and seasonal Kendall test indicated that the sampling periods may be classified into three periods during 2002-2009 according to water quality. Results of temporal cluster analysis and seasonal Kendall test indicated that the study periods may be classified into three periods and two different trends was detected during the period of 2002-2009. The first period was the year of 2002-2003, during which water quality had deteriorated and serious pollution was observed in the Wei River basin and eastern plain of the Zhangweinan River basin. The second period was the year of 2004-2006, during which water quality became better. The year of 2007-2009 is the third period, during which water quality had been improved greatly. Despite that water quality in the Zhangweinan River basin had been improved during the period of 2004-2009, water quality in the Wei River (southwestern part of the basin), the Wei Canal River and the Zhangweixin River (eastern plain of the basin) is still poor. These results provide may useful information for better pollution control strategies in the Zhangweinan River basin

Relationship of land use/cover on water quality in the Liao River basin, China

AbstractA total of 76 sampling sites were selected in the Liao River basin (21.9×104km2). During the period of 2009-2010, 58 water samples were collected in 2010 and 42 were collected in 2009, physical-chemical variables were analyzed to investigate their spatial-temporal variability in particular the relationship with land use /cover. The results indicated that physical and chemical properties showed obvious spatial heterogeneity in the Liao River basin. Taizi River and Hun River are located in the southeast of the basin, the water quality for two sub-basins: water quality in upstream is better than that in downstream, water quality level in downstream was classified into IV-V. There were no obvious features in the East Liao River basin, water quality in downstream was classified into III level. West Liao River run for many years, water quality was classified into IV. Big Liao River basin was located in middle and east of the Liao River basin. Water quality was classified into V. Correlation and regression analysis indicated that BOD5, COD, sediment, hardness and nitrate–nitrogen (NO3−–N), total dissolved particular (TDP) were significantly related to land use for forest and agriculture

Finite Size Scaling, Fisher Zeroes and N=4 Super Yang-Mills

We investigate critical slowing down in the local updating continuous-time Quantum Monte Carlo method by relating the finite size scaling of Fisher Zeroes to the dynamically generated gap, through the scaling of their respective critical exponents. As we comment, the nonlinear sigma model representation derived through the hamiltonian of our lattice spin model can also be used to give a effective treatment of planar anomalous dimensions in N=4 SYM. We present scaling arguments from our FSS analysis to discuss quantum corrections and recent 2-loop results, and further comment on the prospects of extending this approach for calculating higher twist parton distributions.Comment: Lattice 2004(spin), Fermilab, June 21-26, 2004; 3 pages, 4 figure

Acoustic phonon transport through a double-bend quantum waveguide

In this work, using the scattering matrix method, we have investigated the transmission coefficients and the thermal conductivity in a double-bend waveguide structure. The transmission coefficients show strong resonances due to the scattering in the midsection of a double-bend structure; the positions and the widths of the resonance peaks are determined by the dimensions of the midsection of the structure. And the scattering in the double-bend structure makes the thermal conductivity decreases with the increasing of the temperature first, then increases after reaches a minimum. Furthermore, the investigations of the multiple double-bend structures indicate that the first additional double-bend structure suppresses the transmission coefficient and the frequency gap formed; and the additional double-bend structures determine the numbers of the resonance peaks at the frequency just above the gap region. These results could be useful for the design of phonon devices.Comment: 13 pages, 6 figures, elsart.cls is use

Landau Transport equations in slave-boson mean-field theory of t-J model

In this paper we generalize slave-boson mean-field theory for $t-J$ model to the time-dependent regime, and derive transport equations for $t-J$ model, both in the normal and superconducting states. By eliminating the boson and constraint fields exactly in the equations of motion we obtain a set of transport equations for fermions which have the same form as Landau transport equations for normal Fermi liquid and Fermi liquid superconductor, respectively with all Landau parameters explicity given. Our theory can be viewed as a refined version of U(1) Gauge theory where all lattice effects are retained and strong correlation effects are reflected as strong Fermi-liquid interactions in the transport equation. Some experimental consequences are discussed.Comment: 19 page

Aerosol particles at a high-altitude site on the Southeast Tibetan Plateau, China: Implications for pollution transport from South Asia

      Bulk aerosol samples were collected from 16 July 2008 to 26 July 2009 at Lulang, a high-altitude (>3300m above sea level) site on the southeast Tibetan Plateau (TP); objectives were to determine chemical characteristics of the aerosol and identify its major sources. We report aerosol (total suspended particulate, TSP) mass levels and the concentrations of selected elements, carbonaceous species, and water-soluble inorganic ions. Significant buildup of aerosol mass and chemical species (organic carbon, element carbon, nitrate, and sulfate) occurred during the premonsoon, while lower concentrations were observed during the monsoon. Seasonal variations in aerosol and chemical species were driven by precipitation scavenging and atmospheric circulation. Two kinds of high-aerosol episodes were observed: one was enriched with dust indicators (Fe and Ca2+), and the other was enhanced with organic and elemental carbon (OC and EC), SO42−, NO3−, and Fe. The TSP loadings during the latter were 3 to 6 times those on normal days. The greatest aerosol optical depths (National Centers for Environmental Protection/National Center for Atmospheric Research reanalysis) occurred upwind, in eastern India and Bangladesh, and trajectory analysis indicates that air pollutants were transported from the southwest. Northwesterly winds brought high levels of natural emissions (Fe, Ca2+) and low levels of pollutants (SO42−, NO3−, K+, and EC); this was consistent with high aerosol optical depths over the western deserts and Gobi. Our work provides evidence that both geological and pollution aerosols from surrounding regions impact the aerosol population of the TP

Two-dimensional negative donors in magnetic fields

A finite-difference solution of the Schroedinger equation for negative donor centers D^- in two dimensions is presented. Our approach is of exact nature and allows us to resolve a discrepancy in the literature on the ground state of a negative donor. Detailed calculations of the energies for a number of states show that for field strengths less than \gamma=0.117 a.u. the donor possesses one bound state, for 0.117<\gamma<1.68 a.u. there exist two bound states and for field strengths \gamma>1.68 a.u. the system possesses three bound states. Further relevant characteristics of negative donors in magnetic fields are provided.Comment: 7 pages, 1 figur

Multiple superconducting gap and anisotropic spin fluctuations in iron arsenides: Comparison with nickel analog

We present extensive 75As NMR and NQR data on the superconducting arsenides PrFeAs0.89F0.11 (Tc=45 K), LaFeAsO0.92F0.08 (Tc=27 K), LiFeAs (Tc = 17 K) and Ba0.72K0.28Fe2As2 (Tc = 31.5 K) single crystal, and compare with the nickel analog LaNiAsO0.9F0.1 (Tc=4.0 K) . In contrast to LaNiAsO0.9F0.1 where the superconducting gap is shown to be isotropic, the spin lattice relaxation rate 1/T1 in the Fe-arsenides decreases below Tc with no coherence peak and shows a step-wise variation at low temperatures. The Knight shift decreases below Tc and shows a step-wise T variation as well. These results indicate spinsinglet superconductivity with multiple gaps in the Fe-arsenides. The Fe antiferromagnetic spin fluctuations are anisotropic and weaker compared to underdoped copper-oxides or cobalt-oxide superconductors, while there is no significant electron correlations in LaNiAsO0.9F0.1. We will discuss the implications of these results and highlight the importance of the Fermi surface topology.Comment: 6 pages, 11 figure

Anomalous Heat Conduction and Anomalous Diffusion in Low Dimensional Nanoscale Systems

Thermal transport is an important energy transfer process in nature. Phonon is the major energy carrier for heat in semiconductor and dielectric materials. In analogy to Ohm's law for electrical conductivity, Fourier's law is a fundamental rule of heat transfer in solids. It states that the thermal conductivity is independent of sample scale and geometry. Although Fourier's law has received great success in describing macroscopic thermal transport in the past two hundreds years, its validity in low dimensional systems is still an open question. Here we give a brief review of the recent developments in experimental, theoretical and numerical studies of heat transport in low dimensional systems, include lattice models, nanowires, nanotubes and graphenes. We will demonstrate that the phonon transports in low dimensional systems super-diffusively, which leads to a size dependent thermal conductivity. In other words, Fourier's law is breakdown in low dimensional structures