Metal Free Surface Research Articles

Numerical Simulation of Casting Filling Process Based on FLUENT

Based on finite element theory, using FLUENT software and three-dimensional model to simulate liquid metal free surface and temperature field of casting filling process numerically. Boundary and initial conditions, such as velocity, pressure, temperature, etc., was reasonably set. The feasibility of using FLUENT to simulate three-dimensional casting was studied; the fluctuation of molten metal free surface was observed; the temperature distribution data on the end of filling was recorded, for further numerical simulation of casting solidification process which provided an accurate initial condition. This paper also predicted defects on casting filling process, and provided a basis for process optimization.

Orthogonal, metal-free surface modification by strain-promoted azide–alkyne and nitrile oxide–alkene/alkyne cycloadditions

In this article we present a fast and efficient methodology for biochemical surface patterning under extremely mild conditions. Micropatterned azide/benzaldoxime-surfaces were prepared by microcontact printing of a heterobifunctional cyclooctyne oxime linker on azide-terminated self-assembled monolayers (SAMs). Strain-promoted azide–alkyne cycloaddition (SPAAC) in combination with microcontact printing allows fast and effective surface patterning. The resulting bifunctional azide/oxime substrates could successfully be used for metal-free, orthogonal immobilization of various biomolecules by 1,3-dipolar cycloadditions at room temperature. Azide-decorated areas were modified by reaction with a cyclooctyne-conjugate using SPAAC, while benzaldoxime-decorated areas were activated by in situ oxidation to the reactive nitrile oxides and subsequent nitrile oxide cycloaddition with alkene- and alkyne-functionalized bioconjugates. In addition, orthogonal double immobilization was achieved by consecutive and independent SPAAC and nitrile oxide cycloadditions.

Suppression of Electromagnetically Induced Free‐Surface Instabilities in Liquid Metals

AbstractThe work presented is devoted to studies of foundations of the suppression techniques for electromagnetically induced instabilities of the free liquid metal surfaces. Such instabilities occur, for instance, in a number of technologies for requested refinement of materials like electron beam evaporation or levitation melting, in which the electromagnetic shaping technique is applied. The instability phenomenon in our case has following magnetohydrodynamic background. High‐frequency magnetic field causes Lorentz force density generation within so‐called skin‐layer in the liquid metal, which works as a surface pressure in turn. With increase of the electromagnetic pressure a destabilizing mechanism progresses within the liquid metal domain, which causes a bifurcation. In this paper we discuss application alternating magnetic fields to increase the bifurcation threshold by passive and active redistribution of the Lorentz force density in the near‐surface layers of the liquid metal domain. A novel stabilization system on the basis of a local electromagnetic influence on the liquid metal surface in the high frequency magnetic field is presented. The experimental results are discussed. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Transition of amorphous to crystalline oxide film in initial oxide overgrowth on liquid metals

It is important to understand the mechanism of oxidation in the initial stage on the free surface of liquid metals. Mittemeijer and co-workers recently developed a thermodynamic model to study the oxide overgrowth on a solid metal surface. Based on this model, we have developed a thermodynamic model to analyse the thermodynamic stability of oxide overgrowth on liquid metals. The thermodynamic model calculation revealed that the amorphous oxide phase is thermodynamically preferred up to 1·3 and 0·35 nm respectively, in the initial oxide overgrowth on liquid Al and Ga at the corresponding melting point. However, the amorphous phase is thermodynamically unstable in the initial oxide overgrowth on liquid Mg. The thermodynamic stability of amorphous phase in the Al and Ga oxide systems is attributed to lower sums of surface and interfacial energies for amorphous phases, compared to that of the corresponding crystalline phases.

Laser interferometer for measuring the mass velocity of condensed substances in shock-wave experiments on the TWAC-ITEP proton-radiographic facility

The results of development of a laser interferometer designed for measuring the mass velocity of condensed substances in shock-wave experiments in the field of high-energy-density physics are presented. The interferometer is incorporated in the measuring complex of the TWAC-ITEP proton-radiographic facility. The developed laser system allows measurements of the velocity of free surfaces of samples in shock-wave experiments with an error no worse than 10 m/s for the entire range of velocities attained experimentally. The time resolution of measurements is limited by the response speed of the used PMTs and amounts to 2.5 ns. Combined investigations of shock-wave loading of metal targets and scabbing-fracture and jet-formation processes on free metal surfaces were performed by the proton-radiography and laser-interferometry methods.

X-ray scattering: Liquid metal/vapor interfaces

We will review the principal x-ray scattering measurements that have been carried out on the free surface of liquid metals over the past two decades. For metals such as K, Ga, In Sn, Bi etc the surface induces well-defined layering with atomic spacing ‘d’ that penetrates into the bulk a distance of the order of the bulk liquid correlation length. As a consequence the angular dependence of the surface structure factor observed by x-ray reflectivity displays a broad peak at wavevector transfer ∼ 2π/d with a half width that is comparable to the width of the bulk liquid structure factor. Quantitative measurement of this surface structure factor requires correction for a singular Debye-Waller like effect arising from thermally excited capillary waves. For liquid metal alloys the layering is accompanied by chemical segregation (i.e. Gibbs absorption) that can be characterized from the energy dependence of the reflectivity. Particularly interesting are the temperature dependence and elasticity of the two-dimensional surface frozen phases that form on the surface of the Au82Si18 liquid eutectic. Surface freezing, although not observed near the eutectic points of alloys such as Au-Ge, Pd-Ge and Pd-Si, has been observed at the free surface of the glass forming alloy Au49Ag5.5Pd2.3Cu26.9Si16.3.

Oscillation Characteristics of Molten Metal Free Surface Under Compound Magnetic Field

The free surface waves of a molten low-melting point Sn-32% Pb-52% Bi alloy under the imposition of an AC and a static magnetic field were visualized and recorded by use of a laser displacement sensor and a high speed video camera. The Fourier analysis method was used to analyze the oscillation characteristics. The results show that at the center of the free surface, the azimuthal and radial oscillation mode can be found simultaneously owing to AC magnetic field. With increasing coil current intensity, the amplitude and the main frequencies of the oscillations increase, and the azimuthal fluctuation at the center of the free surface is also enhanced. The fluctuation characteristics are closely related to the turbulent flow induced by the alternating electromagnetic force. A series of regular traveling waves can be observed on free surface, and the main frequencies of oscillations at three-phase points decrease owing to superposing AC and static magnetic field. The static magnetic field can remarkably control the unstable swinging behavior of free surface. With increasing static magnetic flux density, the amplitude of oscillations at the center of free surface decreases firstly, and then increases, but the fluctuation amplitude at the triple-phase point always reduces and keeps within 1 mm, and the azimuthal waves at the center of free surface are weakened. Especially at 1.44 T, the radial waves are dominant. The static magnetic flux density should be controlled in an appropriate range to obtain more stable free surface. With compound magnetic field, even if the static magnetic flux density is above 1.0 T, the free surface still vibrates with lower amplitude and dominant frequency.

Elastic fields generated by a semi-spherical hydride particle on a free surface of a metal and their effect on its growth

The formation of a metal hydride is associated with a large increase of volume relative to the parent metal and therefore in large strain energies. Effects of elastic energy on the hydriding of metals are revealed in the microstructural evolution and kinetics of hydride growth on free surfaces. In the present work, we study in detail the elastic fields set up by a semi-spherical hydride particle growing at a free surface of metal with cubic symmetry, with and without an oxide layer. These systems combine geometric (structural) and material anisotropies.Three stages along the microstructural evolution on the surface of some hydride forming metals exposed to hydrogen at constant pressure were described experimentally. For these stages along hydride growth, correlations with the elastic fields are suggested as follows. (a) A hydride particle at the free surface generates regions of tensile and compressive hydrostatic stress in the surrounding matrix. This may induce a preferred nucleation of new hydrides and formation of clusters of hydrides precipitates, which is indeed observed experimentally. (b) Clustering, on the other hand, may contribute to the cease of growth due to competition on hydrogen. In addition, as the particle grows, changes in the stress fields may retard further diffusion from the surface and be another contribution to the cease of growth. (c) A growing hydride increases the stress in the oxide layer and may finely break it. Then the elastic energy per unit volume drops to its minimum value and the growth may accelerate. The formation of such “growth center” is favored for that hydride precipitate that grow alone and not in a cluster.

Experimental Investigation of Arc Plasma in GaInSn Liquid Metal Current-Limiting Device

This paper focuses on an experimental investigation of arc plasma in a liquid metal current-limiting device based on pinch effect. A specially designed experimental setup is employed to observe the dynamic process of arc initiation and arc evolution. From the frames obtained by high-speed photography, the mechanism of arc initiation is revealed. It indicates that the arc ignites due to the self-pinch effect, which starts from the free surface of liquid metal and develops in the form of gas cavities. According to the analysis of the subsequent stage after arc ignition, it can be concluded that the arc plasma should be a mixture of metal vapor and air. With the morphological changes of the arc, the arc evolution can be classified into four stages. The arc erosion on electrodes is observed during the arc process, and its causes are analyzed in detail. Using a liquid metal current-limiting device, the arc characteristics during the current limitation are investigated. It is found that the duration of the prearcing stage and the arc voltage are influenced by the pass-through current. As prospective current increases, the prearcing time reduces because of the acceleration of the pinch process and the arc voltage rise due to the adequate arc burning.

Heterogeneous “Organoclick” Derivatization of Polysaccharides: Photochemical Thiol‐ene Click Modification of Solid Cellulose

A simple and direct method for derivatization of solid polysaccharides is presented. The novel methodology is based on the combination of organic acid-catalyzed esterification or etherification and photochemical thiol-ene click derivatization of a heterogeneous polysaccharide. The solid cellulose was "organoclick" modified with aryl, alkyl and polyester groups, respectively. The modification allows for a highly modular and metal free surface modification of solid polysaccharides.

Complex Change in Superficial Layer Properties of Specimen Obtained by Metallurgical Powder under Vibration Process Method

The general purpose of the present work is based on an antifriction process to produce a metallurgical powder from nibs of iron powders base. Therefore, most of these processes used in motors and instruments industries, vehicles and agricultural mechanical engineering. Under normal operation conditions, which have stable climatic characteristics and exhibit to moisture, this increased the layer that exposed to corrosion. Metallurgical powder adsorbed moisture by determining the porosity which accelerates corrosion processes and increases at the free surface of metal, In this article, the results given for the materials of powders with bases on iron, zinc, aluminium and their alloys, in the same processes can be using it in the maintenance field to eliminate or modifying the surface of the work pieces treated which that increases the hardness.

10.1007/s11452-008-2007-3

Excitation of microplasma discharges in the interaction of a plasma flow with a metal surface partially covered with a dielectric film is investigated experimentally and theoretically. A new phenomenon—the excitation of microplasma discharges at the boundary between the free metal surface and the area covered with the film—is discovered. Microplasma discharges at the edge of the dielectric film are initiated by a strong electric field that arises between the free metal surface and the outer surface of the film in the interaction with the plasma flow. This field gives rise to surface breakdowns at the film edge, followed by the development of primary microplasma discharges. In turn, the dense plasma of primary microplasma discharges causes secondary microplasma discharges, which also arise at the edge of the dielectric film after the external plasma flow has already terminated. Microplasma discharges gradually evaporate the dielectric film, and the surface cleaned of the film acquires a microrelief due to the local melting and subsequent fast cooling of the metal at the sites of microplasma discharges.

EXTENDED FREE SURFACE FLOW MODEL BASED ON THE LATTICE BOLTZMANN APPROACH

The aim of this work was to extend numerical model of mould filling phenomena previously presented in [3]. Authors described some techniques for modeling single phase and free surface flows. Method, called "piston model", for modeling influence of liquid flow on gas behavior inside the mould and also, effect of local gas pressure on movement of metal free surface, was shown. In last part of this work, results from presented model were compared with data from the commercial simulation environment FLOW-3D.

Experimental Studies and Mathematical Modelling of Penetration in TIG and A-TIG Stationary Arc Welding of Stainless Steel

Experimental investigations of the kinetics of penetration of stainless steel in TIG and A-TIG welding, and theoretical analysis of thermal, electromagnetic and hydrodynamic processes occurring in the weld pool metal were conducted. The stationary arc welding process was chosen as the focus of investigation, in order to study physical-metallurgical peculiarities of metal penetration in TIG and A-TIG welding. This makes it possible to describe processes occurring in the weld pool within the framework of axisymmetric approximation. The conjugate model of heat exchange in the base metal and hydrodynamics of the weld pool, with the melt affected by the electromagnetic (Lorentz force), buoyancy (Archimedean force) and thermal-capillary (Marangoni effect) forces, was formulated. Comparative analysis of the impact of the electric characteristics of the arc (current, voltage, anode spot diameter) and different force factors causing motion of liquid metal on hydrodynamics of the weld pool and shape of penetration of stainless steel in TIG and A-TIG welding was carried out by the method of mathematical modelling. The relationship between the deformation of the free surface of the molten metal (due to changes in its density depending on the temperature) and energy characteristics of the arc was analysed. It is shown that in contraction of the anode region of the arc (with decrease in diameter of the anode spot, which is characteristic of A-TIG welding), the magnetic-hydrodynamic processes become the dominating factor, determining the penetration depth and formation of the weld as a whole.

CHANGE IN MICROSCOPIC HARDNESS DURING TENSILE PLASTIC DEFORMATION OF POLYCRYSTALLINE ALUMINUM AND TITANIUM

Microscopic hardness on free surface of polycrystalline metal during plastic deformation is closely related to the inhomogeneous deformation in respective grains. Uniaxial tensile tests were carried out on annealed pure aluminum sheet specimens with different averaged grain size and also on annealed pure titanium sheet specimen. The microscopic hardness was measured with the Vickers type micro-hardness testing machine. The increase in micro-hardness is larger at the grain boundary area than the central area of grains. The increase in the hardness is dependent on the averaged grain size of polycrystalline metals. The experimental results are discussed in relation to Hall-Petch relation concerning the grain size dependence of the yield stress or the flow stress.

Laser transfer of diamond nanopowder induced by metal film blistering

Blister-based laser induced forward transfer (BB-LIFT) is a promising technique to produce surface microstructures of various advanced materials including inorganic and organic micro/nanopowders, suspensions and biological micro-objects embedded in life sustaining medium. The transferred material is spread over a thin metal film irradiated from the far side by single laser pulses through a transparent support. Interaction of the laser pulse with the metal–support interface under optimized conditions causes formation of a quickly expanding blister. Fast movement of the free metal surface provides efficient material transfer, which has been investigated for the case of diamond nanopowder and diamond-containing suspension. The unique features of the given technique are universality, simplicity and efficient isolation of the transferred material from the ablation products and laser heating.

Physico-chemical analyses of Hispano-Moresque lustred ceramic: a precursor for Italian majolica?

The paper presents a comprehensive physico-chemical investigation on a series of Hispano-Moresque objects produced in the eastern Spain workshops between the XIV and XVIII centuries and fragments from XII century, in order to compare them with the Italian Renaissance majolica production. The techniques used are mainly non-destructive (ion beam analyses and X-ray diffraction), sometimes complemented by SEM observation and microanalysis, and electrothermal atomic emission spectrometry. Such methods allow a full description of the terra cotta, of the glaze and of the different surface layers which constitute the lustre decoration indicating individual elemental composition and thickness of each layer containing or not metallic nanoparticles. Principal results show the following: i) a constant source of supply for the eastern Spain terra cotta; ii) a significant change in the composition of the Spanish glazes around the XVII century, with the disappearance of the opacifying tin oxide addition; iii) significant evolutions in the structure and composition of the lustre layers, in particular related to the presence or not of a metal-free surface glaze film and its thickness; iv) interesting analogies and differences with the Italian majolica; v) confirmation of the change in the quality of blue pigment during XVI century, already evidenced by the authors in previous publications. A discussion about the transmission of the lustre technique between eastern Spain and Italy at the Renaissance period is proposed.

Initiation of microplasma discharges at the edge of a dielectric film deposited on a metal surface

Excitation of microplasma discharges in the interaction of a plasma flow with a metal surface partially covered with a dielectric film is investigated experimentally and theoretically. A new phenomenon—the excitation of microplasma discharges at the boundary between the free metal surface and the area covered with the film—is discovered. Microplasma discharges at the edge of the dielectric film are initiated by a strong electric field that arises between the free metal surface and the outer surface of the film in the interaction with the plasma flow. This field gives rise to surface breakdowns at the film edge, followed by the development of primary microplasma discharges. In turn, the dense plasma of primary microplasma discharges causes secondary microplasma discharges, which also arise at the edge of the dielectric film after the external plasma flow has already terminated. Microplasma discharges gradually evaporate the dielectric film, and the surface cleaned of the film acquires a microrelief due to the local melting and subsequent fast cooling of the metal at the sites of microplasma discharges.

Free‐surface instabilities during electromagnetic shaping of liquid metals

AbstractElectromagnetic shaping of free surfaces of liquid metals is a well‐known EPM technology used in a couple of metallurgic processes like cold crucible melting, semi‐levitation, and electromagnetic slit sealing, among others. However, the stability of such free surfaces is the most important problem and stability control is crucial for success. Within this context we investigate experimentally the stability behavior of liquid metal free surfaces submitted to a high‐frequency magnetic field. In this case, the induced Lorentz forces act as an electromagnetic pressure directly on the free surface of the liquid met al. We consider three experimental model configurations: (i) Sessile liquid metal drop (ii) liquid metal ring, and (iii) liquid metal disc. In each model experiment, upon increasing the feeding current beyond a certain threshold value, IC, we observe that the initial surface contour becomes unstable resulting in (i) drop oscillations (ii) electromagnetic pinching and (iii) static disc deformations. In each configuration the threshold value depends in a similar manner on the frequency of the applied magnetic field. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Liquid Metal Free Surface Motion Submerged in an AC Magnetic Field

Free surface motion of a liquid metal submerged in an alternating magnetic field has been examined. A copper vessel filled with a liquid gallium is set in a coil for the imposition of the alternating magnetic field. The alternating magnetic field penetrates into a liquid gallium only from an upper free surface because thickness of the copper vessel is larger than the electromagnetic skin layer of copper. Time variation of displacement of the standing wave loop excited on the free surface is detected by a laser level sensor. The standing wave was suppressed not only by intensification of the magnetic field magnitude but also increase of the magnetic field frequency.