Identification of Phases in Aluminide Coatings by Means of Interference Layer Metallography

Interference layer metallography was usedto identify the phases present in the aluminidecoating on superalloy IN738LC. They are: twointermetallic aluminides NiAl and Ni_3Al, y-solidsolution and a Cr-rich solid solution, twosulphides M_(23)C_6 and MC, and two sulphides(Al,Cr)_3S_4 and (Cr,Ti)_3S_4. ZnS and ZnSe areproposed to be vapor deposited onto the surfaceof the specimen to get good colour contrastand good light-dark contrast. The refractiveindex and absorption coefficient of all thesephases have been detemined.     

Control of Microstructure in Iron–Carbon Thin Films by Means of Electromigration

Herein, it is demonstrated that high DC electric current densities can be used to tailor the microstructure of iron–carbon thin films. Specifically, elongated ferrite grains can be formed in a nanocrystalline matrix via a process involving electromigration-induced carbide migration. Herein this article, the parameters that are required to produce and control elongated grain formation in the Fe(C) system are mapped out and they are interpreted in terms of carbon electromigration, and the flux divergences need to reach a critical carbon concentration for precipitate growth and migration. Possible approaches to allow more precise control of the elongated grains are discussed, as are the requirements for material systems where microstructure control through electromigration should be feasible.     

Study on Cure Behavior of a Model Epoxy System by Means of TTT Diagram

Duetotheirhighstrength,modulusandfracture toughnessaswellasgoodadhesionandthermalre sistance[1],epoxyresinsasmatricesarewidelyused inaeronautics,astronautics,transportation,sports andotherindustry.Standardepoxyresinsareusually basedonDGEBA(diglycidyletherofbisphenolA),whichneedsactivehydrogenorotheractivegroupsto opentwoepoxyrings.Four functionalepoxylike TGMDA(tetraglycidylmethylenedianiline)isoften usedforhigh performanceepoxymatrixcomposites becauseofitsrelativelyhighercross linkingdens…     

Comment on ‘Two-state Description of Total Polarization by Means of Singular Eigenvalue Problems’

We derive a formulation that can be used to determine the electromagnetic field distribution in the focal region of a wide-angle spherical mirror illuminated by an obliquely incident and linearly polarized plane monochromatic wave. The integrals representing the diffracted fields derived in part 1 [1] for the two cases of polarization of the incident field are first suitably expanded in series form. The integrals with respect to the azimuth 0 are then evaluated analytically with the help of some new integration formulae developed in this paper. The diffracted field components for the two cases of incident polarization are finally expressed in forms suitable for numerical computation. Our formulae can be used to determine the three-dimensional field distribution in the caustic region of the mirror for any obliquity of the incident beam. Simpler expressions for the field components for a few special cases of interest are also derived. In particular, it is shown that the series solution obtained for the case of oblique incidence reduces to the simpler results found by previous authors for the case of normal incidence.     

QCM Operation in Liquids: Constant Sensitivity during Formation of Extended Protein Multilayers by Affinity

The quartz crystal microbalance (QCM) is a well-established tool in mass-sensitive detection. Due to recent improvements in experimental procedures, QCMs are finding increasing attention for applications in liquids. One important application is bioaffinity measurements for analytical or research purposes. The effect of the formation of solid films at a QCM surface, especially in gases or vacuum, is well understood. However, the situation is more complex in bioaffinity applications due to the comparably high viscosity of the liquid and the softness of the biological overlayer. Typically frequency responses found for protein layers exceed the values expected from simple models. The use of a hydrogel extending several hundred nanometers from the transducer surface as interacting matrix is common in bioaffinity applications and further increases complexity. Pure mass-related effects as well as viscosity-mediated effects may contribute to the overall frequency response observed experimentally. To improve our understanding of the effects during the formation of extended biological overlayers we have investigated systematically the formation of protein multilayers with a QCM in situ. The attenuation of the QCM oscillation by the liquid leads to a broadening of the resonance frequency. We have overcome this limitation by frequency-dependent admittance analysis and by curve fitting of the resulting admittance. A time resolution of 5 s and a noise of 0.2 Hz has been achieved with 6-MHz AT-cut quartz crystals operating in liquids. Protein multilayers were formed by successive incubations with a biotin-albumin conjugate and streptavidin. Frequency responses for dry protein layers in air were in agreement with mass changes estimated from the Sauerbrey equation. However, in water, the corresponding frequency decrease was increased by a factor of 4, thereby indicating that significant amounts of water are embedded in the hydrated protein layer. Unexpectedly a constant frequency decrease per layer was found during the successive formation of up to 20 protein layers (～400 nm). Neither noise nor drift increased with the number of protein layers. These results indicate that, despite the high hydration of the protein layers, viscosity-induced effects play a negligible role and that the frequency decrease reflects primarily mass changes at the surface.     

Modeling of Gas Solubility Data for HFCs–Lubricant Oil Binary Systems by Means of the SRK Equation of State

The Soave–Redlich–Kwong (SRK) equation of state (EOS) is used to describe vapor-liquid (VLE) and vapor-liquid-liquid (VLLE) equilibria of mixtures containing environmentally friendly refrigerants (hydrofluorocarbons, HFCs) and lubricant oils (polyalkylene glycols, PAGs and polyol esters, POEs) at high pressures. For refrigerants, pure component parameters are used as they were found in refrigerant properties computer program Version 6.0 of REFPROP. For the PAG and POE oils, they are either predicted by group contribution methods or obtained from thermodynamic data. Extension to mixtures is performed by using the conventional quadratic mixing rule with only one parameter for each binary pair. The binary parameters are regressed from VLE experimental data available in the literature and subsequently used for prediction of VLLE. All results of the calculations are discussed, and the necessary parameters for prediction of thermodynamic properties of these types of mixtures for the SRK EOS are presented. The computations were performed using phase equilibria software (PE2000).     

HTS SMES Application for the Frequency Stabilization of?Grid-Connected Wind Power Generation System

Output power of the wind power generation system (WPGS) fluctuates due to wind speed variation and affects the frequency and voltage fluctuations of the utility. Superconducting Magnetic Energy Storage (SMES) can overcome these fluctuations because of fast response time for energy charging and discharging. To stabilize the frequency fluctuation, HTS SMES should be connected to the terminal of the WPGS. Ulleung island power network in Korea was modeled to demonstrate the effectiveness of SMES for frequency stabilization. Based on the simulation results using EMTDC, a toroidal-type HTS SMES cooled by conduction cooling method and a DC/DC chopper for current charging and discharging were fabricated for experiment. Power network including WPGS was implemented through a Real Time Digital Simulator (RTDS). The simulation and experimental results for frequency stabilization using real HTS SMES and RTDS are discussed in detail.     

Generation of Frequency Combs by Quantum Cascade Lasers Emitting in the 8-μm Wavelength Range

Technical Physics Letters - We have studied the generation of frequency combs by quantum cascade lasers (QCLs) emitting in the 8-μm wavelength range. Results showed the presence of a...     

Direct Generation of Intense Compression Waves in Molten Metals by Using a High Static Magnetic Field and Their Application

Compression waves propagating through molten metals are contributed to degassing, accelerating reaction rate,removing exclusions from molten metals and refining solidification structures during metallurgical processing of materials. In the present study, two electromagnetic methods are proposed to generate intense compression wavesdirectly in liquid metals. One is the simultaneous imposition of a high frequency electrical current field and a staticmagnetic field; the other is that of a high frequency magnetic field and a static magnetic field. A mathematical modelbased on compressible fluid dynamics and electromagnetic fields theory has been developed to derive pressure distributions of the generated waves in a metal. It shows that the intensity of compression waves is proportional to thatof the high frequency electromagnetic force. And the frequency is the same as that of the imposed electromagneticforce. On the basis of theoretical analyses, pressure change in liquid gallium was examined by a pressure     

Direct Generation of Internse Compression Waves in Molten Metals by Using a High Static Magnetic Field and Their Application

Compression waves propagating through molten metals are contributed to degassing accelerating reaction rate,removing exclusions from molten metals and refining solidifcation structures during metallurgical processing of materials,In the present study ,two electromagnetic methods are proposed to generate intense compression waves directly in liquid metals.One is the simultaneous imposition of a high frequency electrical current filed and a static magnetic field ;the other is that of a high frequency magnetic field and a static magnetic field ,A mathematical model based on compressible fluid dynamics and electromagnetic fileds theory has been developed to derive pressure distri-butions of the generated waves in a metal.It shows that the intensity of compression waves is proportional to that of the high frequency electromagnetic force,And the frequency is the same as that of the imposed electromagnetic force,On the basis of theoretical analyses ,pressure change in liquid gallium was examined by a pressure transducer under various conditions.The observed results approximately agreed with the predictions derived from the theoretical analyses and calculations.Moreover,the effect of the generated waves on improvement of solidification structures was also examined .It shows that the generated compression waves can refine solidification structures when they were applied to solidification process of Sn-Pb alloy ,This study indicates a new method to generate compression waves by imposing high frequency electromagnetic force locally on molten metals and this kind of compression waves can probably overcome the difficulties when waves are excited by mechanical vibration in high temperature environments.     

Development of FeSiB/CoSiB Bilayered Melt-spun Ribbon by?Melt-spinning Technique

The investigation addresses the bilayer melt-spun ribbons in which the positively magnetostrictive layer Fe_77.5Si_7.5B₁₅ is toward the free surface, while the negatively magnetostrictive layer of Co_72.5Si_12.5B₁₅ forms the one in contact with the quench wheel. Scanning electron microscopy (SEM) elemental scan showed drastic changes in concentration profiles of Co, Fe and Si across the bilayer, indicating the efficacy of rapid quenching by melt spinning. Crystallization onsets, saturation magnetization and dilatation studies of the single-layered alloys distinctly reflected the properties of the bilayered ribbons. The thermal variation of coercivity below crystallization onset in the case of a bilayer revealed a softening mechanism due to reduction of stresses. Ribbon deflection studies showed interesting results.     

Characterization of α ? β PbF2 phase transition by several techniques

X-ray Diffraction (XRD), Dynamic-Mechanical Analysis (DMA), Impedance Spectroscopy (IS), and Scanning Electron Microscopy (SEM) have been used to the study of phase transition in PbF₂ pellets pressed uniaxially in the 37 MPa–480 MPa range. A mixture of and phases is detected and the -phase content at room temperature is found to be dependent on the applied load. The dilation results on DMA, the phase identification by XRD, the ionic conductivity results by IS analysis and the SEM micrographs of -PbF₂ pellets show evidences for the increase in -phase content at the expense of the -phase. SEM analysis provided further evidence for specimen sintering under heating at approximately 498 K.     

Processing and characterization of TLCP fibers reinforced by 1?wt% MWCNT

A thermotropic liquid crystalline polymer (TLCP) blend with 1?wt% multiwall carbon nanotubes (MWCNTs) was prepared by melt compounding. Morphological observations of the blend show that the chemical-treated MWCNTs were well dispersed in the TLCP matrix with a good interface. MWCNTs have little effects on the thermal and rheological properties of pure TLCP. TLCP fibers with and without MWCNTs were prepared at certain drawing ratios by a melt spinning method. The degree of orientation of TLCP chains is enhanced by MWCNT micro-clusters during the fiber formation. The mechanical properties of TLCP/MWCNT fibers are significantly increased by 34.5?% for tensile strength and 38.0?% for tensile modulus in comparison with those of pristine TLCP fibers, due to the synergistic effects of MWCNT and TLCP.     

Andreev Reflection of Quasiparticles by a Vortex Tangle in Superfluid 3He-B?

We have made the surprising discovery that the thermal damping of a vibrating wire resonator in superfluid ³ He-B at ultra low temperatures is considerably depressed when a second wire in the vicinity is driven supercritically. The damping of a vibrating wire resonator at low velocities in the B-phase arises from the scattering of quasiparticle excitations and has a temperature dependence proportional to the Boltzmann factor exp(–/kT) at low temperatures. At higher velocities (v>v_L/3), the wire breaks Cooper pairs and emits a quasiparticle beam. At first sight it seems paradoxical that heating the superfluid can reduce the quasiparticle flux on a neighbouring wire. We can only understand this on the basis that vorticity emitted by the supercritical wire shields, via Andreev reflection, part of the background quasiparticle flux from reaching the other wire. If this interpretation is correct, these techniques will provide a sensitive probe of vortex dynamics in the ultra low temperature regime.     

Anticorrosion behavior of ultrafine-grained Al-26?wt% Si alloy fabricated by ECAP

Ultrafine-grained (UFG) Al-26 wt% Si alloy was obtained through multipass equal-channel angular pressing (EACP) procedure and subsequently tested in 3.5 wt% NaCl solution for the evaluation of electrochemical corrosion. The results show that the ECAPed alloy with increased number of pressing passes obtain lower mass-loss ratios, nobler E _corr and E _pit, lower I _corr values, and higher anode polarization. The improved corrosion resistance of the ECAPed alloy results from the homogeneous UFG structure with the breakage of brittle large primary silicon crystals, which contributes to a higher pitting resistance. The oxidation product with improved adhesion force and protection efficacy can be formed with greater ease on UFG alloys. It implies that grain refinement through severe-plastic-deformation can enhance anticorrosion behavior of hypereutectic Al–Si alloys, besides the well-known strengthening and toughening effects.     

Search for Enhancement of the Isobaric Thermal Expansion Coefficient of Superfluid 4He near T �� by?a?Heat Current

We report an experimental search for the enhancement of the isobaric thermal expansion coefficient (?? _P ) of superfluid ⁴He near the superfluid transition by a heat current (Q). The experiment was carried out using the hot volume technique at constant sample pressure of 1 bar. Liquid helium was contained in a thermal conductivity cell, and a constant heat current, Q=10 or 100 ??W/cm², was supplied from below through the sample column. We performed a sample density calculation based on existing helium properties known in the literature and a proposed enhancement ???? _P (Q). Both calculations, with or without the ?? _P enhancement, agree qualitatively with the measurement. The lack of definitive differentiation indicates that the ?? _P enhancement cannot be definitively resolved by our measurement in spite of applications of high-resolution thermometry and pressure regulation.