Begell House Inc.
High Temperature Material Processes: An International Quarterly of High-Technology Plasma Processes
HTM
1093-3611
4
3
2000
METALLURGICAL APPLIKATIONS OF HIGH POWER ARS HEATING SYSTEMS
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10.1615/HighTempMatProc.v4.i3.10
Dieter
Neuschutz
Lehrstuhl fur Theoretische Huttenkunde, Rheinisch-Westfalische Technische Hochschule (RWTH) Aachen, D-52056 Aachen, Germany
An overview is given on the present state and future trends of high power arc heating systems applied in iron and steelmaking, ferroalloys production and dust recycling. As arc generators, metallic torches with cold and hot electrodes are considered as well as graphite electrodes with and without gas-stabilization of the arc.
In practice metal plasma torches are only applied in limited cases to superheat the blast in cupola furnaces and, somewhat more frequently, to heat liquid steel in the tundish. In all other cases the electrode material in high power arc heating systems is graphite. Applications discussed are ore smelting in DC furnaces, submerged-arc furnace production of ferroalloys, stainless steel dust recycling and scrap-based steelmaking.
The production of steel in the electric arc furnace is steadily rising, its share of the total steel production climbing from modest 10 % in 1960 to 35 % in 2000 which will absolutely represent 280 mio t of steel produced in electric arc furnaces (EAFs) with 125 billion kWh or ca. 1 % of the world's annually generated electric power. Operating data of modern AC and DC EAFs are presented and discussed. New trends in furnace design are listed including twin-shell furnaces, scrap preheating and continuous scrap charging installations, DC furnaces with two electrodes and furnaces for high hot metal feed ratios.
OXIDATION OF STAINLESS STEEL PARTICLES WITH AND WITHOUT AN ALUMINA SHELL DURING THEIR FLIGHT IN A PLASMA JET
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10.1615/HighTempMatProc.v4.i3.20
Helene
Ageorges
University of Angers, LETP, 2 Boulevard Lavoisier, 49045 Angers Cedex, France
Pierre
Fauchais
Laboratoire Sciences des Procedes Ceramiques et de Traitements de Surface UMR CNRS 6638 University of Limoges 123 avenue Albert Thomas, 87060 LIMOGES - France
Investigations are carried out to study the oxidation of stainless steel particles collected after their flight in a plasma jet. In some tests, the injected particles are coated with an alumina shell. Particles are sprayed in Atmospheric Plasma Spraying (APS) and then collected in a concentric cylinder where they are quenched by argon jets. SEM observations of sprayed stainless steel particles show the formation of dark spots within their clear cross section, which displays the chromium and oxygen elements prominently. X-ray diffraction shows a chromium oxide phase which seems to be CrO. This is due to the convective movements within the particle renewing continuously fresh chromium at the surface and entraining the formed CrO inside the particle. It seems that, as for FeO, CrO is immiscible with liquid steel. On the other hand, alumina coated particles are less oxidized : cross sections present less oxide inclusions. Two types of particles were observed : some are still fully coated but the shell is broken due to the higher expansion of the stainless steel core. They probably result from particles where alumina has not been fully melted. Others have their alumina fused and entrained by liquid flow to the back of the moving droplet. Fused alumina droplets at the particles surface have coalesced creating a melted alumina cap. The two types of particles are probably due to the wide distribution trajectories within the spray cone which result in temperature differences. The particles with the alumina at the tail have probably traveled in the core of the plasma jet where temperatures are higher and then both materials have been melted, whereas the others have traveled in the jet fringes where the temperatures are lower.
ON THE OXIDATION OF Ni-23Co-17Cr-12AI-0.5Y-ALLOY SERVING AS BOND COAT IN THERMAL BARRIER COATINGS
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10.1615/HighTempMatProc.v4.i3.30
Reidar
Haugsrud
Centre for Materials Science Gaustadalleen 21,N-0371 Oslo, Norway
Ingard
Kvernes
Kvernes Technology AS., Munkedamsveien 96,P-box 2806 Solli, N-0204 Oslo, Norway
Erick
Lugscheider
Werkstoffwissenschaften Lehr und Forschungsgebeit der RWTH Jiilicher Sir. 342-352 52070 Aachen; Surface Engineering Institute (IOT), RWTH University of Technology Aachen, Augustinerbach 4-22, 52066 Aachen, Germany
Specimens of air plasma sprayed thermal barrier coatings with a Ni-23Co-17Cr-12Al-0.5Y bond coat have been oxidised in air at 900°C for 300-3000 hours. The oxide scale formed between the ceramic and the bond coat consists of essentially pure AI2O3, except at the interface with the ceramic overlay, where the composition of the oxide reflects that of the bond coat. The oxidation rate decreases with time and reflects growth of AI2O3, through inward grain boundary diffusion of oxygen. An inter-metallic phase identified as NiAl, precipitated during high temperature exposure. The thickness of the inter-metallic zone decreased with increasing oxidation duration. This was interpreted to reflect diffusion of Al toward the oxide and into the substrate. The amount of transient oxides at the surface was found to depend on the surface topography.
CONTACT ANGLE AND SURFACE TENSION MEASUREMENTS ON A METAL DROP BY IMAGE PROCESSING AND NUMERICAL CALCULATION
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10.1615/HighTempMatProc.v4.i3.40
V.
Leroux
L.M.C.T.S. - C.N.R.S. E.S.A. 6015 Universite de Limoges -123, av. Albert Thomas - 87065 LIMOGES Cedex
J. C.
Labbe
Faculte des Sciences et Techniques, L.M.C.T.S. - C.N.R.S. E.S.A. 6015 Universite de Limoges -123, av. Albert Thomas - 87065 LIMOGES Cedex, France
M.E.R.
Shanahan
Universite d'Evry-Val d'Essonne - Centre des Materiaux P.M. Fourt - E.N.S.M.P. BP 87 - 91003 EVRY Cedex
D.
Tetard
L.M.C.T.S. - C.N.R.S. E.S.A. 6015 Universite de Limoges -123, av. Albert Thomas - 87065 LIMOGES Cedex
J.F.
Goujaud
L.M.C.T.S. - C.N.R.S. E.S.A. 6015 Universite de Limoges -123, av. Albert Thomas - 87065 LIMOGES Cedex
The purpose of this work is to establish solid/liquid contact parameters : contact angle, surface tension and work of adhesion, for drops of molten metal on ceramic substrates. Referring to the literature, we can justify the use of the sessile drop method. After a judicious choice of the quantity of liquid for each drop, we have improved the performance of the measurement device. First, we have improved the definition of the drop picture. Then, we have rationalised the programs of exploitation of drop profiles for the calculation of the contact angle and the surface tension. Tests operated in various conditions such as high temperature show that the accuracy of the contact angle measurement is about one degree. This corresponds to a relative error of about 5 to 8 % on the work of adhesion when contact angle is around 150°.
HEAT TRANSFER FROM OXYGEN ATOMS RECOMBINATION ON SILICON CARBIDE: CHEMICAL EVOLUTION OF THE MATERIAL SURFASE
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10.1615/HighTempMatProc.v4.i3.50
P.
Cauquot
Laboratoire de Genie des Procedes Plasmas et Traitement de Surface - ENSCP -11, rue Pierre et Marie Curie - 75231 Paris Cedex 05
S.
Cavadias
Laboratoire Genie Precedes Plasmas - ENSCP 11, rue Pierre et Marie Curie - 75005 Paris- France
Jacques
Amouroux
Laboratoire de Genie des Precedes Plasmas Universite P. et M. Curie, ENSCP 11 rue P. et M. Curie 75005 Paris France
In order to quantify the energy transfer from the reactive flow to a surface, determination of recombination and accommodation coefficients (respectively γ and β coefficients) is required. The following work concerns atomic oxygen flow recombining on silicon carbide. The γ coefficient is measured in a pulsed oxygen plasma reactor in non equilibrium conditions, using an actinometiic method, whereas the β coefficient is determined in a micro-wave plasma reactor, using a calorimetric method. The βγ coefficient gives also the energetic transfer to the surface during the recombination reaction. The experimental study is undertaken on silicon carbide which presents interesting properties as refractory material. The measurements are performed on a large temperature range (300 - 1123 K) in order to point out a change in the recombination mechanism when the surface temperature rises. At the same time, the chemical structure of the material is followed by different analysis techniques (ESCA, SIMS and SEM) and shows a modification of the chemical composition of silicon carbide resulting from oxidation, ablation of the surface and diffusion of oxygen into the bulk material.
PLASMA-ASSISTED DEPOSITION OF NANOSTRUCTURED FILMS AND COATINGS
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10.1615/HighTempMatProc.v4.i3.60
Steven L.
Girshick
Department of Mechanical Engineering, University of Minnesota, 111 Church St. S.E. Minneapolis, MN 55455, USA
Recent work is reviewed on plasma-assisted deposition of nanostractured films and coatings. Several methods are being developed. These include conventional plasma spray in which nanostructure is induced in the coarse feed powder by mechanical milling before spraying; thermal plasma spray pyrolysis; plasma flash evaporation of fine powders injected into an RF torch; hypersonic plasma particle deposition; and low-pressure plasma synthesis and deposition of nanoparticles to produce thin films.
STANDARD THERMODYNAMIC FUNCTIONS OF DIATOMIC PRODUCTS OF THERMAL DECOMPOSITION OF SF6
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10.1615/HighTempMatProc.v4.i3.70
O.
Zivny
Department of Theoretical and Physical Chemistry, Faculty of Science, Masaryk University, Kotlarska 2, 611 37 Brno, Czech Republic
Standard thermodynamic functions of nine possible both neutral and single charged products of thermal decomposition of SF6 were computed by the method of direct summation and tabulated in form of approximation coefficients up to 20 000 K. Obtained results were discussed and compared With the existing literature data. Furthermore, influence of excited electronic states was briefly studied. Finally, the equilibrium composition was performed in the case of the decomposition of pure SF6 using the calculated data.
SOLAR THERMAL PRODUCTION OF ZINC: PROGRAM STRATEGY AND STATUS OF RESEARCH
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10.1615/HighTempMatProc.v4.i3.80
Aldo
Steinfeld
Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland; Solar Technology Laboratory, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
A.
Weidenkaff
Solar Process Technology, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
M.
Brack
Solar Process Technology, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
Stephen
Moller
Solar Process Technology, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
Robert
Palumbo
Solar Process Technology, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
The solar thermal production of zinc is considered for the conversion of solar energy into storable and transportable chemical fuels. The ultimate objective is to develop a technically and economically viable technology that can produce solar zinc. The program strategy for achieving such goal involves research in two paths: a direct path via the solar thermal splitting of ZnO, and an indirect path via the solar carbothermal and CH4-thermal reduction of ZnO. The chemical thermodynamics and kinetics for both paths are briefly reviewed. A vortex-flow solar reactor for reducing ZnO with CH4 is also described. Solar tests conducted at PSI solar furnaces in the temperature range 1000-1600 K yielded high chemical conversion to zinc.
SOLAR THERMOCHEMICAL PROCESSING: CHALLENGES AND CHANGES
14
10.1615/HighTempMatProc.v4.i3.90
Robert
Palumbo
Solar Process Technology, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
Stephen
Moller
Solar Process Technology, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
Aldo
Steinfeld
Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland; Solar Technology Laboratory, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
A strategy for conducting solar chemistry research is presented. It focuses on the development of technology and knowledge that offers society energy options from its current dependence on fossil fuels. The strategy shifts the traditional requirement from expecting a solar process to be economically competitive with current fossil fuel processes to being economically competitive with the best currently available sustainable energy options. The approach is illustrated with a current solar energy research program for producing Zn from ZnO.
PHASE EQUILIBRIA AND STRUCTURE IN THE Na3AlF6-Na2B4O7-TiO2 SYSTEM
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10.1615/HighTempMatProc.v4.i3.100
As part of the ternary system Na3AlF6-Na2B4O7-TiO2, the binary subsystem: Na2B4O7-TiO2 and the pseudobinary subsystem Na2B4O7-[Na3AlF6-TiO2]e were investigated. The phase diagrams established by DTA measurements evidenced a simple eutectic point for both systems except for the concentration range > 85 wt. % Na2B4O7 of the Na2B4O7-[Na3AlF6-TiO2]e system where the binary paragenesis rules are no longer obeyed. Additional information regarding the structure of the mixtures were obtained by X-ray diffraction and Raman spectroscopy. Both vitreous and crystalline state were evidenced, without any new compound formation. The presence of titanium, mainly as TiO4 tetrahedra, was also proved.
MULTISTEP PROCESSES IN THE ELECTRODEPOSITION OF REFRACTORY METALS IN MOLTEN CHLORIDES
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10.1615/HighTempMatProc.v4.i3.110
This paper deals with examples of complications arising during the electrodeposition process in molten salts of multivalent elements such as uranium, niobium and hafnium. The electroreduction process of U(IV), Nb(V) and Hf(IV) includes the intermediate formation of U(III), Nb(IV) and Hf(II) respectively, giving rise to secondary reactions such as disproportionation and adsorption. Each reaction of the overall process is characterized by using electrochemical criteria provided by chronopotentiometric and voltammetric measurements. Prereduction of U(IV) or addition of fluoride ions in the electrodeposition bath of hafnium have minimized the troubles due to these reactions.