Metal Ejection Research Articles

Chemical composition and X-ray emission from starburst blown superbubbles

Abstract Recent observational results related to the X-ray emission from SB galaxies are reviewed. The results of calculations of the superbubble inner hot gas metallicity are presented. It is shown that supernova metal ejection leads to a high overabundance of the hot bubble interior, that allows for up to an order of magnitude higher X-ray luminosities compared with the standard model predictions.

Physics of solid armature launch transition into arc mode

The railgun launch of a solid armature is conventionally divided into two stages, namely, the initial stage, where a metallic contact is retained between the armature and the rails, and the second, starting at a velocity /spl sim/0.3-2 km/s, where the contact occurs through the arc plasma. While a variety of reasons for the transition were considered, no universally accepted physical picture supported by experiment has thus far been formulated. We showed experimentally that under usual launch parameters, 3D MHD instabilities form in the contact gap because of the absence of shear resistance, which result in the formation, collapse, and, eventually, explosion of pinch waists (see E.M. Drobyshevski et al. Tech. Phys. Letts., vol.25 no.3, p.245-7, 1999). The destruction of the pinch waists gives rise not only to termination of current flow from the armature to the rail through the metal and transformation of the metallic contact in the armature/rail interface into an arc gap, but to ejection of the liquid metal and dusty plasma from the gap forward and back into the railgun bore as well. Even in the absence of MHD instabilities, armature material can be shed due to very inhomogeneous distribution of fields of thermal, electric, and dynamic parameters in the armature body. Appearance of easily-ionized matter in the bore results in the formation of shunting arcs there, which naturally reduce the armature launching efficiency. The new physics revealed by the authors in the railgun solid-armature launch transition to the arc regime provides a basis for a search for ways of increasing the launch efficiency.

Extension of potentialities of millisecond pulsed Nd:YAG lasers in the welding technology

The dependences of the dynamic parameters of the growth of a vapour-gas channel and the depth of the melting zone on the shape of laser pulses and the spatial beam parameters are studied. Based on this study, the requirements are formulated to the characteristics of radiation providing a many-fold increase in the melting depth with respect to the depth that was previously considered as limiting. A new laser setup for deep high-quality welding was built. The role of the buffer volume of a melt in the suppression of ejection of molten metal from the laser-heated region upon deflection of the melt surface is substantiated. An increase in the rate of growth of a vapour-gas channel during an increase in its length (the self-concentration of a heat source) was experimentally observed. At the depths corresponding to the preferential vertical orientation of fluid flows, a large-scale vortex motion of the melt was observed. The dependence of the penetration depth of the melting front on the aperture angle β was experimentally found to have an extremum. The maximum penetration depth was obtained for β = 0.075 — 0.80 rad. Recommendations for designing pulsed laser technological systems for high-quality welding of metals are formulated.

Influence of gas composition on plasma arc cutting of mild steel

We report the results of a study on the influence of oxygen inthe plasma gas used in the plasma arc cutting process on cuts obtained inmild steel plates. Experimental results of shapes of kerfs and the leadingedges of the cut front formed while cutting a 6 mm mild steel plate at100 A with nitrogen, air and oxygen as plasma gases are presented. Theseresults are discussed in the light of the overall energy balance of theprocess. It is found that the exothermic reaction of oxygen in the plasmagas with the iron in mild steel enables the cutting of mild steel at higherspeeds with both air and oxygen than the maximum cutting speed attainablewith nitrogen. A comparison of the melting rates for oxygen with those ofair reveals that although oxygen can produce more exothermal energy byoxidation, oxygen is not superior to air in melting metal near the bottomof the kerf formed at high cutting speeds.The study shows that the dross formed at the bottom of the cut isdetermined by the shape of the cut-front surface over which the moltenmetal from the cut front flows to be ejected at the plate bottom. Anyimprovement of metal ejection to be gained with oxygen as the plasma gasmay be the result of enhanced superheating of the metal melted from thecut-front surface.

Intergalactic Dust and Observations of Type Ia Supernovae

Estimates of the cosmic star formation rate and of cluster metallicities independently imply that at z 0.5 the gas in the universe has substantial average metallicity: 1/10 Z/Z☉ 1/3 for Ωgas = 0.05. This metal density probably cannot be contained in known solar-metallicity galaxies of density parameter Ω* ≈ 0.004, implying significant enrichment of the intergalactic medium (IGM) by ejection of metals and dust from galaxies via winds, in mergers or in dust efflux driven by radiation pressure. Galaxies have a dust-to-metal ratio of ~0.5 in their interstellar media, but some fraction (1 - f) > 0 of this must be destroyed in the IGM or during the ejection process. Assuming the Draine & Lee dust model and preferential destruction of small grains (as destruction by sputtering would provide), I calculate the reddening and extinction of a uniform cosmological dust component in terms of f and the minimum grain size amin. Very small grains provide most of the reddening but less than half of the opacity for optical extinction. For f 0.3 and amin 0.1 μm, the intergalactic dust would be too gray to have been detected by its reddening, yet dense enough to be cosmologically important: it could account for the recently observed Type Ia supernova dimming at z ~ 0.5 without cosmic acceleration. It would also have implications for galaxy counts and evolutionary studies and would contribute significantly to the cosmic infrared background (CIB). The importance of gray intergalactic dust of the described type can be tested by observations of z = 0.5 supernovae in (rest) R-band or longer wavelengths and by the fluxes of a large sample of supernovae at z > 1.

Multiple superbubbles in the starburst nucleus of NGC 5253? Implications for mass loss from dwarf galaxies

ˇ4 arcsec, equivalent to 160 a200 ˇ80 pc. We consider the origin of the observed X-ray emission, concentrating on the sources expected to be associated with the starburst region: superbubbles, supernovae, supernova remnants and massive X-ray binaries. To assess the X-ray luminosity of a young superbubble blown by a single massive cluster of stars, we perform hydrodynamical simulations with realistic time-varying mass and energy injection rates. The predicted soft X-ray luminosity for a superbubble blown by an M, a 10 5 M( cluster during its Wolf‐Rayet period agrees very well with the luminosities inferred for the extended components seen by the HRI. We conclude that the extended X-ray components are most likely young superbubbles blown by individual young clusters in the starburst region. Although we do not rule out a contribution to the observed soft X-ray emission by supernova remnants and massive X-ray binaries, we argue that most of the emission comes from a few young superbubbles blown by the young stellar clusters in the starburst region. We discuss in detail the implications of multiple superbubbles for the efficiency of mass and metal ejection from dwarf galaxies by starburst-driven galactic winds. We suggest that the presence of multiple stellar clusters in starbursting dwarf galaxies and the resulting multiple superbubbles will reduce the total ISM mass ejected from dwarf galaxies, compared with the current models which consider only the blowout of a single

Starburst‐driven Mass Loss from Dwarf Galaxies: Efficiency and Metal Ejection

We model the effects of repeated supernova explosions from starbursts in dwarf galaxies on the interstellar medium of these galaxies, taking into account the gravitational potential of their dominant dark matter haloes. We explore supernova rates from one every 30,000 yr to one every 3 million yr, equivalent to steady mechanical luminosities of L=0.1-10 x 10^38 ergs/s, occurring in dwarf galaxies with gas masses M_g=10^6 - 10^9 solar masses. We address in detail, both analytically and numerically, the following three questions: 1. When do the supernova ejecta blow out of the disk of the galaxy? 2. When blowout occurs, what fraction of the interstellar gas is blown away, escaping the potential of the galactic halo? 3. What happens to the metals ejected from the massive stars of the starburst? Are they retained or blown away? We give quantitative results for when blowout will or will not occur in galaxies with 10^6 \leq M_g \leq 10^9 solar masses. Surprisingly, we find that the mass ejection efficiency is very low for galaxies with mass M_g \geq 10^7 solar masses. Only galaxies with M_g \leq 10^6 solar masses have their interstellar gas blown away, and then virtually independently of L. On the other hand, metals from the supernova ejecta are accelerated to velocities larger than the escape speed from the galaxy far more easily than the gas. We find that for L_38=1, only about 30% of the metals are retained by a 10^9 solar mass galaxy, and virtually none by smaller galaxies. We discuss the implications of our results for the evolution, metallicity and observational properties of dwarf galaxies.

The Metallicity of High‐Redshift Galaxies: The Abundance of Zinc in 34 Damped Lyα Systems fromz= 0.7 to 3.4

We report new observations of ZnII and CrII absorption lines in 10 damped \lya systems (DLAs), mostly at redshift $z_{abs} \simgt 2.5$ . By combining these results with those from our earlier survey (Pettini et al. 1994) and other recent data, we construct a sample of 34 measurements (or upper limits) of the Zn abundance relative to hydrogen [Zn/H]; the sample includes more than one third of the total number of DLAs known. The plot of the abundance of Zn as a function of redshift reinforces the two main findings of our previous study. (1) Damped \lya systems are mostly metal-poor, at all redshifts sampled; the column density weighted mean for the whole data set is [Zn/H] $= -1.13 \pm 0.38$ (on a logarithmic scale), or approximately 1/13 of solar. (2) There is a large spread, by up to two orders of magnitude, in the metallicities we measure at essentially the same redshifts. We propose that damped \lya systems are drawn from a varied population of galaxies of different morphological types and at different stages of chemical evolution, supporting the idea of a protracted epoch of galaxy formation. At redshifts $z \simgt 2$ the typical metallicity of the damped \lya systems is in agreement with expectations based on the consumption of HI gas implied by the recent measurements of $\Omega_{DLA}$ by Storrie-Lombardi et al. (1996a), and with the metal ejection rates in the universe at these epochs deduced by Madau (1996) from the ultraviolet luminosities of high redshift galaxies revealed by deep imaging surveys. There are indications in our data for an increase in the mean metallicity of the damped \lya systems from $z > 3$ to $\approx 2$, consistent with the rise in the comoving star formation rate indicated by the relative numbers of $U$ and $B$ drop-outs in the Hubble Deep Field. Although such comparisons are still tentative, it appears that these different avenues for exploring the early evolution of galaxies give a broadly consistent picture.

Dust formation in a BOF converter

Minimisation of waste and manipulation of residues to suit succeeding processes today is one of the steel works most important research areas. BOF dust is expensive to depose in landfills and difficult to recycle due to its zinc contents. The simultaneous loss of raw materials and cost increase makes it important to minimise the generation of dust. This can be done by employing better process control systems with regard to the mechanisms governing the generation. Four dust forming mechanisms can be considered in a converter: ejection of metal, ejection of slag, entrainment of charged material and vaporisation.In order to determine the importance of the four dust forming mechanisms and to characterise dust, with special emphasis to zinc, the off‐gas from a 100‐t BOF was sampled during twenty seven heats. The sampling equipment allows the sampling of both solid dust particles and vaporised elements. Samples from the first and the second part of blowing show significant differences both in chemical composition and in the origin of formation. The major dust formation mechanism is the ejection of metal and slag, respectively. Entrainment of solids plays an important role only during the first part of blowing. Vaporisation of elements from the bath is most important during the end of blowing. The formation of dust is influenced by process operation control, especially lance position, silica contents and time of charging of slag formers. Zinc is mostly found on the rim of ejected particles where a gradual transition of zinc oxide to zinc ferrite to iron oxide is found. At sampling temperatures of between 800 and 1000°C most of the zinc had already condensed.

A new method for film deposition in the discharge of target metal vapour

A new method for generation of a discharge in its own metal vapour of an r.f.-excited electrode is described. The method is based on the r.f. plasma jet (RPJ) system utilizing a small size r.f. nozzle in which a hollow cathode-type discharge is generated. The nozzle outlet (target) is sputtered and/or evaporated by the ion bombardment from the jet discharge. The power density at the nozzle outlet reaches the order of hundreds of watts per square centimetre even at reasonably low r.f. power supply levels (above 100 W). A dense plasma containing a large amount of the nozzle metal ions can be generated inside the nozzle. Depending on the nozzle material, at a definite critical value of the r.f. power the discharge character can change to a particular kind of arc (RPJ arc) in which metal ejection inside the self-heated nozzle is sufficient to generate a sustained discharge without any auxiliary gas. Experiments indicate that the generation of the RPJ arc can be considered as a combination of a distributed discharge (diffuse) arc and a high voltage arc. Optical emission spectra from an Mg RPJ generated plasma exhibit only Mg emission lines and Mg film growth rate reaches values above 4 μm min −1. Conditions for generation of self-sustained discharges in Ti and Cu nozzles are also discussed. The effect of the nozzle geometry on the generation of stable self-sustained discharges for deposition of thin films is explained. In most cases an enhanced thermionic electron emission from the metallic surface contributes to a positive feedback to maintain the dense metal vapour plasma discharge. Deposition of Ti films in a plasma containing Ti vapours, Ti + ions and low partial pressure of Ar at regimes close to the RPJ arc is described.

Ejection of Trace Metals from Volcanoes

Investigation of trace element content of snow which fell through the pyroclastic ejecta of the Hekla, Iceland eruption of 1991 revealed elevated concen t ra t ions o f a var iety o f elements. Laboratory rinses of pristine tephra and lava show similar concentrations as the snow when the water/rock ratio is 12.5. Many metals have concentrations higher than 100 ppb (Ti, Mn, Fe), between 10-100 ppb (Cu, Zn), and between 1-10 ppb (So, V, Cr, Co, As, Se, Sn, La, Sm) in the snow and tephra rinses. The light REE (LREE), that have the highest chondritic abundances, contain greatest values in the snow. The metals depict a positive correlation with CI-. No REE fractionation occurs during volatilization from the magma. It is proposed here that the metals are evaporated as chlorides during devolatilization of the magma in the eruption cloud. The metals form solid sublimates on the surface of the tephra and lava upon cooling. These halides are very soluble and are dissolved upon contact with the first rain that falls on the erupted solids.

The study of thermal processes in an electrode submitted to an electric arc

This article investigates the thermal phenomena that are occurring in an electrode submitted to an electric arc in air at atmospheric pressure. Our purpose is to get a better understanding of the electrode erosion phenomena concerning vaporization or liquid droplets ejection. For that we propose an original experimental device allowing the measurement of the liquid and vapor quantities created under the arc root. The principle of this device is based on the ejection of the liquid metal through centrifugal movement of the electrodes during the arc. Some results are given relatively to Ag, Cu and AgSnO 2 cathodes and anodes. Then we present a numerical modelling of the thermal phenomena induced in the electrode by the heat transferred from the arc root. We propose a method to solve the difficulties related to this kind of free boundary problems induced by the fact that the elecatrode material may undergo various phase changes. Finally we show how to use this numerical computation and the experimental results in order to estimate the power density input at a copper anode

Metal enrichment of the intracluster medium from protogalaxies and the gamma-ray bursters

view Abstract Citations (10) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Metal Enrichment of the Intracluster Medium from Protogalaxies and the Gamma-Ray Bursters Hattori, Makoto ; Terasawa, Nobuo Abstract Metal enrichment of clusters of galaxies by protogalactic star formation is discussed. We show that the observational requirement of metal ejection from protogalaxies into the intracluster medium (ICM) suggests pregalactic massive star formation bursts in the extended halo of protogalaxies. Our results predict that galaxies have an extended halo populated with a number of supernova remnants. The predicted large radius of the extended halo of our Galaxy is consistent with the distribution of γ-ray bursters observed by BATSE on the Compton Gamma Ray Observatory satellite, if neutron stars possibly formed in the extended halo of the Galaxy are the source of γ-ray bursters. Publication: The Astrophysical Journal Pub Date: April 1993 DOI: 10.1086/186785 Bibcode: 1993ApJ...406L..55H Keywords: Galactic Clusters; Galactic Evolution; Galactic Halos; Gamma Ray Bursts; Intergalactic Media; Star Formation; Astronomical Models; Metallicity; Supernova Remnants; Astrophysics; GALAXIES: CLUSTERING; GALAXIES: FORMATION; GAMMA RAYS: BURSTS full text sources ADS |

Mechanisms of dust generation in a stainless steelmaking converter

The four possible mechanisms of dust formation in converter steelmaking are evaporation of metal, ejection of slag, ejection of metal and entrainment of solids. In order to describe the relation between process operation and dust formation and take appropriate measures to minimize the quantity of dust, more detailed information is needed on the amounts contributed by the different dust generation mechanisms. For their determination, dust samples were taken from the off‐gas during refining of five austenitic heats in a modified 80‐t AOD converter. On the basis of dust, metal and slag analyses and process and product gas flow rates, the contributions of the different dust generation mechanisms were quantitatively determined for blowing step I (pure oxygen blowing) and reduction step R (pure argon blowing). The predominant mechanism is ejection of metal and slag droplets by bursting of bubbles at the bath surface. Dust formation via the vapour phase in AOD steelmaking is of less importance than previously expected, the relative amount is only about 3 %. During the addition of fluxes through the converter mouth, the entrainment of solids plays a role, too.

Pulsed Excimer Laser Photoablation by Backside Irradiation of Thin Metal Coated Polymer Films

AbstractBackside laser irradiation of metal coated quartz wafers can be used for transferring material imagewise to a target cleanly in absence of chemical vapors. However, the transfer of metal from a quartz surface requires a high energy, resulting in poor quality images in some cases.Use of a fluorinated polymer layer between the polycarbonate substrate and a Te-Se metal alloy is known for clean fabrication of metal holes in write-once-read-only memory media. Polymer thin films can be used similarly in backside laser irradiation for metal ejection from substrate surfaces.With an ArF excimer laser at 193 nm, gold and aluminum were ejected imagewise from Teflon AF, poly(methacrylonitrile) and quartz surfaces. The threshold fluences of 230 Å thick gold films from polymer surfaces were 7.9 to 9.7 mJ/cm2, whereas the threshold fluence from a quartz surface was determined to be 17.8 mJ/cm2. For aluminum on top of quartz and aluminum coated polymers, higher threshold fluences were found compared to gold ranging from 12.96 to 22.7 mJ/cm2.Also, interfacial reactions between the polymer films and the metal layer occured and have been studied by SEM and XPS.

Welding of plated, dissimilar metals for RF/EMI shielding

Plated beryllium-copper shield clips are used in the Motorola MicroTAC cellular portable telephone to provide interconnections between the RF ground and the mating shielded and compartmentalized housing cover. Outer shield clip attachment to the plated steel core of the circuit board is accomplished using a resistance weld in a narrow, space-limited area closely adjacent to conductor traces. The production welding process was characterized by widely varying weld strengths, the need for multiple welds to achieve adequate weld strength, ejection of metal during welding, frequent electrode dressing, and frequent electrode replacement. An investigation was performed with the purpose of developing a stronger weld and a more consistent welding process without the limitations mentioned above. It was determined that the process could be improved by (1) the use of projections, (2) larger, harder electrodes, (3) slightly softened shield clips, and (4) an angled top electrode to aid the operator. The improved weld was analyzed using cross sections, optical and scanning electron microscopy, and energy dispersion spectroscopy. >

Modeling of inhomogeneous film deposition and target erosion in reactive sputtering

Presented is a generalized microphysical model for reactive sputtering, taking into account inhomogeneities of both the target erosion and the deposition of films on condensing surfaces of substrates and chamber walls. The integral quantities, as the total metal ejection rate or the reactive gas consumption, can be treated as if the erosion and deposition were homogeneous but over properly determined effective areas. Conversely, the local quantities, as the target coverage by the compound or the film composition, are strongly influenced by the inhomogeneities. Both chamber wall area Aw and the substrate area As influence the system behavior. An increase of As and/or decrease of Aw leads to higher reactive gas content in films. This effect makes it possible to use a simple flow rate control for a high rate deposition of nearly stoichiometric films, as TiN, in the metallic mode of target operation.

電子ビーム溶接現象に関する研究 （第３報） 電子ビームによる母材の溶融過程とスパイクの形成機構

Melting process and spiking phenomenon have been investigated in electron beam welding. X-rays generated as a consequence of beam-metal interaction were measured at some specific sites of 3 mm in length along penetration using Xe-proportional counter simultaneously with taking highspeed photography of the molten metal flow to clarify a melting process.The results obtained were as follows.(1) Spiking phenomenon was most likely to occur when the electron beam .was focussed on the root portion of penetration.(2) Melting process and spiking phenomenon were dominated by the periodical flow of the molten metal.(3) Soon after the periodical ejection of the molten metal, the beam cavity was clear of the molten metal and the electron beam was free to drill the bottom causing the spike.(4) it is effective in monitoring spiking phenomenon to detect electrons emitted from interacting point using a probe biased 6V with respect to the specimen.

Electron stimulated desorption from CO and O adsorbed on clean and Cu covered W(110) surfaces

Electron stimulated desorption from CO adsorbed on Cu n W(110) with n = 0, 1, and 2 was carried out in order to compare cross sections and thresholds for CO, CO +, and O + desorption. It was found that the thresholds for all three products were virtually independent of the presence or absence of Cu, indicating very similar mechanisms; however cross sections for n = 1, 2 were appreciably higher than on clean W(110). The threshold for CO production is attributed to creation of a 5σ hole; absence of 2π b DOS for n ⩾ 1 rules out a 2 π b → 2 π a transition as the mechanism. CO + production could correspond to creation of 5σ −2. CO + formation near threshold may occur by creation of a 5σ −2 state. Arguments are presented to show that formation of 4σ −1 also corresponds to the CO + threshold and may lead to CO + desorption. O + production from adsorbed CO corresponds to formation of various 2 hole states. Comparison of yields of neutral CO from n = 0 and n ⩾ 1 also made it possible to obtain desorption and β-CO conversion cross sections for CO adsorbed on bare W(110). The ESD behavior of O/Cu n /W(110) layers for n = 0, 1–4 was also investigated. Only O +could be detected in all cases and there was no change in O coverage after prolonged electron bombardment. It is argued that O + comes from minority states corresponding to O adsorption on edge or corner metal atoms at steps and other imperfections. The thresholds are consistent with initial creation of a 2s hole on O, followed by filling of this hole by a metal electron and ejection of an O2p Auger electron. The resulting M +O + state leads to desorption of energetic O +. This process restricted to O bound to metal atoms in sufficiently poor contact with the rest of the substrate to give M + and O + the required lifetimes. None of the processes investigated showed openings of new channels at energies corresponding to creation of holes in substrate metal atoms.

Hydrodynamic stability threshold of liquid metal current collectors

A mechanism derived from hydrodynamic theory to explain the ejection instability of liquid metal current collectors is presented. The ejection mechanism is shown to be caused by the onset of the Kelvin–Helmholtz instability resulting from the gradient of azimuthal (primary) flow at the interface between the liquid metal and cover gas. This new mechanism differs from the previous theory developed by Eriksson [in Electrical Engineering Series, no. 48, edited by M. Luukkala (The Finnish Academy of Technical Sciences, Helsinki, Finland, 1982), who analyzed the onset of the Kelvin–Helmhotz instability resulting from the gradient of meridional (secondary) flow at the interface. Considering the solution to the linearized Navier–Stokes equations at the liquid metal and gas interface, the azimuthally driven (primary flow) instability mechanism for the onset of ejection is much more prevalent than the meridional (secondary) flow driven mechansim. Furthermore, Eriksson’s theory requires an empirical multiplicative fractional factor that is not physically justified to predict experimentally measured ejection points, whereas the present theory is more self-consistent. Calculations of minimum ejection values from both theories were compared with corresponding experimental ejection data. The present theory appears to give significantly better engineering estimates, both quantitively and qualitatively, for minimum ejection threshold than Eriksson’s theory. The basic mathemtical model presented can serve as the basis for developing a more complex mathematical model for liquid metal ejection.