Erosion wear on Francis turbine components due to sediment flow

Aslam Noon, A.,Kim, M.H. Elsevier Sequoia [etc.] 2017 Wear: An international journal on the science and Vol.378 No.-

<P>Sediment particles flowing through the turbine components erode the surface in interaction. Erosive wear of hydro turbine components generally depends on different parameters such as concentration, size and shape of the sediments particle, velocity of flow, properties of the base material of the turbine components and operating hours of the turbine. Tarbela Dam Hydel Project (TDHP) located in the Himalayan range in Pakistan is facing the same problem. The sediments particle have caused damage to the plant equipment, mainly to the turbine components; stay vanes, guide vanes, runner and draft tube. As a result, these components are disassembled and refurbished almost every year. Analysis have been performed on one of the Francis turbine units to predict the effect of sediment particles concentration, size and shape on erosion rate. Gradual removal of the base material has changed the profiles of various components of the turbine and also has weaken its structure. One of the major concerns of these effects is the continuous loss of turbine hydraulic efficiency. The governing equations of fluid flow are solved numerically on an unstructured grid using FEM based software ANSYS CFX. Finnie erosion model is used to compute average erosion rates. Simulation results are compared with the actual site data. The CFD analysis showed good agreement with the results of experimental work done previously using similar kind of geometries and operating conditions. (C) 2017 Elsevier B.V. All rights reserved.</P>

Microstructure and electrical properties of XInZnO (X=Ti, Zr, Hf) films and device performance of their thin film transistors-The effects of employing Group IV-B elements in place of Ga

Moon, M.R.,Jeon, H.,Na, S.,Kim, S.,Jung, D.,Kim, H.,Lee, H.J. Elsevier Sequoia 2013 Journal of alloys and compounds Vol.563 No.-

In this study, we systematically investigated the effects of employing Group IV-B metals (Ti, Zr, and Hf) in place of Ga in GaInZnO films by fabricating XInZnO films (X=Ti, Zr, or Hf) with a various ratio of the Group IV-B elements. Materials characterization using various analytical methods (including transmission electron microscopy and X-ray photoelectron spectroscopy) elucidates that upon the addition of a small amount of the alloying elements, while the microstructure turned into amorphous from nanocrystalline, the oxygen vacancy concentration decreased systematically along with the carrier concentration. The device characteristics (threshold voltage and field-effect mobility) of the transistors fabricated from the films sensitively reflect the changes in the film properties (carrier concentration and bulk mobility). The bias stability enhanced with the increase of the ratio of the alloying elements to an extent that apparently increases in the order of Ti, Zr and Hf, which is reverse to the order of the electronegativity.

Synthesis, structure, and magnetic properties of the halide-bridged dimeric complex [(bpmaL₁)Fe(μ-Cl)Cl]₂

Yang, M.,Kim, E.,Jeong, J.H.,Min, K.S.,Lee, H. Elsevier Sequoia [etc.] 2013 Inorganica chimica acta Vol.394 No.-

Complexation of FeCl<SUB>2</SUB>.4H<SUB>2</SUB>O with N,N-Bis{(1-H pyrazole-1-yl)methyl}aniline [bpmaL<SUB>1</SUB>] gave air-stable dichloro-bridged binuclear iron(II) species (1a) having five-coordinated iron, which was characterised by X-ray crystallography and magnetic susceptibility. The geometry at each iron centre of 1a is a distorted trigonal bipyramid with two equivalent half-molecules providing overall C<SUB>i</SUB> symmetry. One of the pyrazolyl nitrogen atoms (N1) and a chlorine atom (Cl2)<SUP>#</SUP> form one apex of the distorted trigonal bipyramid. The magnetic parameters indicated only a weak antiferromagnetic coupling, despite the presence of two chloro ions, and dominant zero-field-splitting parameters. The relatively long Fe...Fe distance of 3.8118(6)A within the chloro-bridged dimer excludes direct interaction between the iron(II) ions. Thus, the antiferromagnetic coupling between the two iron(II) ions of 1a is attributed to superexchange through the chloride ions. Compared to the analogous cobalt complexes, the activity of α-olefin polymerization towards ethylene, norbornene, 1-octene and methyl methacrylate (MMA) was virtually zero, 1a is the first bis-pyrazole based dinuclear and five-coordinated iron(II) complex.

Effects of stretching and cycling on the fatigue behavior of polymer-supported Ag thin films

Sim, G.D.,Lee, Y.S.,Lee, S.B.,Vlassak, J.J. Elsevier Sequoia 2013 Materials science & engineering. properties, micro Vol.575 No.-

The fatigue behavior of silver films on polyethylene-terephthalate substrates is studied for various levels of film thickness, pre-stretch, sample width, and applied strain range. Films with large pre-stretch have a shorter fatigue life, with failure caused by strain localization (films thicker than 100nm) or intergranular crack formation (100nm film). There is a significant effect of film thickness on how the strain range affects the fatigue life - we observe 'smaller is better' behavior for films subjected to a total strain range of Δε<SUB>t</SUB>=1.0%, while the opposite is true when the total strain range increases to 2.0%. We attribute this difference to a shift in failure mechanism with strain amplitude from typical fatigue failure to a more ductile-type failure. Our experimental results are well described by the Coffin-Manson relationship and a failure mechanism map is drawn based on the experimental results. Considering stretchability and long-term reliability, design suggestions are made to optimize the fatigue life of coatings subjected to uniaxial stretch and fatigue.

Microscopic residual stress evolution during deformation process of an Fe@?Mn@?Si@?Cr shape memory alloy investigated using white X-ray microbeam diffraction

Kwon, E.P.,Sato, S.,Fujieda, S.,Shinoda, K.,Kajiwara, K.,Sato, M.,Suzuki, S. Elsevier Sequoia 2013 Materials science & engineering. properties, micro Vol.570 No.-

Microscopic residual stress evolution in different austenite (γ) grains during shape memory process in an Fe@?Mn@?Si@?Cr alloy was investigated using the white X-ray microbeam diffraction technique. The use of high-energy white X-ray microbeam with small beam size allowed us to measure the microscopic residual stress in coarse γ grains with specific orientation. After tensile deformation large compressive residual stress was evolved in γ grains due to the formation of stress-induced ε martensite, but upon recovery heating it almost disappeared as a result of reverse transformation of martensite. The magnitude of compressive residual stress was higher in grains with orientations close to <144> and <233> orientations than in a grain with near <001> orientation. Analysis of the microstructure of each grain using electron backscattering diffraction suggested that the difference in the magnitude of compressive residual stress could be attributed to different martensitic transformation characteristics in the grains.

Polyvinyl alcohol/carbon coated zinc oxide nanocomposites: Electrical, optical, structural and morphological characteristics

Chandrakala, H.N.,Ramaraj, B.,Shivakumaraiah,Lee, J.H.,Siddaramaiah Elsevier Sequoia 2013 Journal of alloys and compounds Vol.580 No.-

Polyvinyl alcohol (PVA) films doped with different concentrations viz., 0.5, 1.0, and 2.0wt.% of the carbon coated zinc oxide (C-ZnO) nanoparticles were prepared by solution casting method in order to investigate the effect of C-ZnO addition on the electrical, optical, structural and morphological properties of PVA matrix. The electrical properties such as dielectric constant (ε'), dielectric loss (ε''), dissipation factor (Tan δ), electrical modulus (M', M'') and AC conductivity (σ<SUB>ac</SUB>) of the PVA/C-ZnO nanocomposites have been performed with reference to weight percentage of nanofiller (i.e., 0.5, 1.0, and 2.0wt%) and frequency (20Hz to 1MHz). It is observed that the dielectric constant, dielectric loss, and electrical conductivity gradually decrease with filler concentration. Microstructural property of the nanocomposites is studied by using X-ray diffraction. XRD profiles demonstrated the semi crystalline nature of the composites. SEM photomicrographs of the PVA/C-ZnO nanocomposites reveal the uniform distribution of nanoparticles within the polymer matrix. Differential scanning calorimetry (DSC) thermograms of nanocomposites clearly indicates that the influence of nanofillers on their melting temperature (T<SUB>m</SUB>) is insignificant.

Photosensitization of novel ruthenium-functionalized photoconductive polymers: Effect of ruthenium complex as photosensitizer

Moon, J.S.,Kim, C.,Kim, W.G.,Kim, I.,Kyhm, K.,Oh, J.W.,Kim, N. Elsevier Sequoia 2015 Journal of photochemistry and photobiology. A, Che Vol.310 No.-

Owing to their efficient photo-charge generation, ruthenium derivatives are emerging as an important class of photosensitizers. Despite their promising characteristics, several deficiencies, such as the relatively low quantum yield and short lifetime of the lowest energy metal-ligand charge transfer, have limited their applications. Here, we present new photoconducting polymers that contain ruthenium complexes as a photosensitizer. Ru(phen)<SUB>2</SUB>(m-COOH)(PF<SUB>6</SUB>)<SUB>2</SUB> complexes, which covalently bind the poly(N-vinyl carbazole) (PVK) side chain, provided a high quantum yield and sufficient lifetime of the lowest energy metal-ligand charge transfer state for photo-charge generation. A series of PVK-Ru(phen)<SUB>2</SUB>(m-COOH)(PF<SUB>6</SUB>)<SUB>2</SUB> complexes were thus prepared with various concentrations of Ru. We employed a helium-neon (HeNe) laser (633nm) and a xenon lamp to measure the photo-charge generation efficiency and photoconductivity of the studied complexes. The wavelength dependence of the photo-charge generation efficiency and photoconductivity was found to be similar to their metal-ligand charge transfer absorption spectra. This suggests that the Ru complexes can extend the photosensitivity of the conductive polymers to longer wavelengths due to the lowest metal-ligand charge transfer energy. The photo-charge generation efficiency and photoconductivity of these polymers was found to be greater than those of PVK-Ru-complex composites.

Synthesis of and ethylene oligomerization with binuclear palladium catalysts having sterically modulated bis-imine ligands with methylene spacer

Budagumpi, S.,Liu, Y.,Suh, H.,Kim, I. Elsevier Sequoia 2011 Journal of organometallic chemistry Vol.696 No.9

Sterically modulated bis-imine ligands (L<SUP>1</SUP>-L<SUP>3</SUP>) were prepared by reacting 4,4'-methylene bis-(2,6-dialkyl aniline) and antipyrine-4-carboxaldehyde in a 1:2 stoichiometric ratio. The reactions of L<SUP>1</SUP>-L<SUP>3</SUP> with dichloro(cycloocta-1.5-diene)palladium(II) [PdCl<SUB>2</SUB>(cod)] yield the corresponding binuclear palladium complexes with the general formula Pd<SUB>2</SUB>Cl<SUB>4</SUB>L (L = L<SUP>1</SUP>, L<SUP>2</SUP>, and L<SUP>3</SUP>). The binucleating ligands bind to the palladium ion via the lone pair on the imine nitrogen and amide oxygen atoms, resulting in a square-planar geometry around the metal center. All the palladium catalysts efficiently oligomerize ethylene to produce C<SUB>4</SUB>-C<SUB>20</SUB> fractions at activities of up to 1308 kg-oligomer mol-Pd<SUP>-1</SUP> bar<SUP>-1</SUP> h<SUP>-1</SUP> at 30 <SUP>o</SUP>C in combination with ethylaluminum sesquichloride. The formation of active sites by the change in geometry of the metal complexes could be traced using spectroscopic and electrochemical techniques.

Comparison of mechanisms of advanced mechanical surface treatments in nickel-based superalloy

Gill, A.,Telang, A.,Mannava, S.R.,Qian, D.,Pyoun, Y.S.,Soyama, H.,Vasudevan, V.K. Elsevier Sequoia 2013 Materials science & engineering. properties, micro Vol.576 No.-

Mechanical surface enhancement techniques are used to introduce compressive residual stresses to enhance the fatigue life and corrosion resistance of metallic components. In this study, we compare the effects of three advanced mechanical surface enhancements treatments: laser shock peening, cavitation shotless peening and ultrasonic nano structure modification on residual stress, hardness, plastic deformation and changes in near surface microstructure introduced in a Ni-Base superalloy, IN718 SPF(Super plastic forming). Coupons of the alloy were peened using two different conditions of each treatment and results compared to achieve a better understanding of underlying mechanisms of these techniques. Results indicate that there are significant differences in mechanisms of these surface treatments leading to differences in material response.

Phase behavior of some mono-substituted ferrocene- and [3]ferrocenophane-containing nematics with the cyclohexane ring in the rigid core

Kim, S.Y.,Kadkin, O.N.,Kim, E.H.,Choi, M.G. Elsevier Sequoia 2011 Journal of organometallic chemistry Vol.696 No.11

Generally, incorporation of the cyclohexane rings into the rigid core of rod-like mesogens leads to improved technological parameters, i.e. low viscosity, ambient transition temperatures and stability of the nematic state. Taking this into consideration, a series of novel cyclohexane-containing derivatives of ferrocene has been synthesized. The effect of various structural factors on liquid crystalline behavior of the synthesized ferrocene-containing nematics has been examined. Ferrocenophane compounds exhibited enhanced liquid crystalline properties in comparison with the derivatives of unbridged ferrocene. Depending on thermal prehistory of the samples, some of the synthesized ferrocenomesogens showed remarkable migration of the phase transition temperatures. In one case such behavior led to stabilization of the initially monotropic nematic mesophase in subsequent heating cycles. In another case, the phase transition shifts caused the lowering of the crystal-to-nematic transition temperature and the broadening of the mesophase range. There was also a case of alteration from the initially enantiotropic to monotropic behavior. The obtained novel metallomesogens are important footsteps toward the development of low-viscous and low-temperature materials for liquid crystal applications possessing a chromophoric, redox-switchable, polarizable and chemically stable superaromatic ferrocene unit.