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By Murali Thirukkonda, Rahul Shah, Srinivas Tangrila, Shankar Rachakonda, Jan Kajuch, Arthur Gurson

"High-temperature superconductors have potential for a variety of applications such as power generators, superconducting magnets for mine sweepers or ship propulsion motors, and magnetic levitation transportation systems. Interest in the use of superconducting wires and tapes increased dramatically after the discovery of high-critical-temperature (high-Tc) oxide superconducting compounds, which offer operating temperatures above that of liquid nitrogen. Several techniques have been proposed to produce commercially viable high-Tc oxide based superconducting wires. One of the promising methods involves multi-pass powder-in-tube (PIT) wire drawing followed by rolling and heat treatment. This work focuses on the development of a numerical model to simulate the PIT drawing process for fabrication of long lengths of silver sheathed Bi-2212 superconducting wires. The finite element based model was used to predict densification of the oxide powder, wire drawing forces, and silver sheath thickness during drawing. A cap-type pressure dependent constitutive equation was implemented in the model to simulate the powder behavior. The model incorporated experimentally obtained material data for the silver and powder. Results indicate that powder densification is increased by decreasing the initial silver thickness and increasing the silver strength. Data from wire drawing experiments were used to verify model predictions. IntroductionSuperconducting wires and tapes can be used to carry large dc currents with no measurable loss due to resistivity. When used in superconducting magnets for power generators, motors, levitation devices, magnetic detectors, or energy storage devices, they could potentially result in significantly reduced energy losses. In the past, most prototypes were tested in liquid helium at 4.2K [1]. However, the necessity to provide liquid-helium cooling systems proved to be a serious limitation in commercialization. In 1986 high-critical-temperature (high-Tc) oxide superconductors were discovered [2], which could allow for higher operating temperatures above liquid nitrogen (77 K). Since then, both academia and industry have concentrated their efforts on the development of high-Tc oxide superconducting wires, tapes and coils. As yet, large scale fabrication of long lengths of these wires with the required current carrying capacity and mechanical properties remains an enormous challenge."

Jan 1, 1994

By Kenneth P. Michalek, James E. Kelly, Jonathan A. Dantzig

"Many investigations have been reported regarding the simulation of continuous casting with emphasis on in-mold heat transfer. These analyses have been limited, however, because they require either estimation or measurement of the characteristic heat transfer between the ingot and the mold. In this paper, a self-consistent model 'is presented for calculating the heat transfer between a solidifying continuous casting and the mold, in the context of the continuous casting of steel. Using both thermal and stress analyses, the air gap formed during continuous casting is calculated and used to compute the heat transfer coefficients. Iteration between the thermal and stress analyses is used to determine a self-consistent solution. IntroductionThe continuous casting process for steel is illustrated schematically in Fig. 1. Molten steel is tapped into a tundish from which it flows at a controlled rate into the continuous casting mold. The initial shell of the casting forms in the mold by transfer of heat from the metal through the mold wall to the cooling water. The remainder of the casting is solidified by application of water sprays, and/or radiation cooling below the mold.Heat transfer in the mold portion of the process is important because it controls the formation of various defects which are deleterious to subsequent processing. Examples of defects formed in this region are surface irregularities, such as cold folding and oscillation marks, and more serious defects, such as longitudinal or transverse cracks. A more catastrophic problem which may occur is a breakout, in which the shell ruptures and molten steel is discharged in an uncontrolled way."

Jan 1, 1986

By Norbert Steiner

For the desulfurization of weak SO2 gas streams, Degussa developed a process using dilute H2SO4 solution containing H2O, instead of conventional gas scrubbing with all solid absorbent medium (limestone, MgO). The process is based on fast reaction of H2O, with SO2 yielding H2SO4 up to 70% strength, depending on off-gas temperature. Compared to the conventional systems with typically < 95% efficiency, independent on the raw gas SO2 concentration, residual SO2 concentrations of less than 20 mg/Nm3 can be easily achieved, corresponding to nearly 100% removal. These features render the H2O, process a very attractive, low capital cost technology to retrofit existing conventional desulfurization plants.

Jan 1, 1996

By J. R. Bhamidipati, Nagy EI-Kaddah

"Over the years, mathematical modeling has been established as a viable tool for design and analysis of melting and solidification processes. Modeling of electromagnetic casting and melting systems involves three coupled problems -- determination of the containment field, the shape of the meniscus, and the temperature field -- which have to be solved simultaneously. One of the difficulties in numerical simulation of these systems is in defining and gridding the solution domain as the meniscus shape of the liquid region is not known a priori. This paper describes a methodology for solving these coupled problems in a two-dimensional electromagnetic containment field. This method is based on the solution of the electromagnetic, free surface dynamic, and heat transfer equations in a fixed domain in computational space by mapping the physical space into an invariant computational space during the search for the equilibrium shape using a variable non-orthogonal coordinate transformation. This approach, also, eliminates the need for regridding the liquid and solid regions during phase change. This methodology is demonstrated for two electromagnetic confinement systems -- the Magnetic Suspension Melting process and the electromagnetic casting of aluminum. The model predictions are in good agreement with available data for these systems. It is suggested that the methodology presented here is likely to provide a useful tool in the design, analysis, and optimization of electromagnetic confinement systems. IntroductionDuring the past decade, mathematical modeling has emerged as a viable tool for the design, analysis, and optimization of casting and melting processes /1-2/. It is generally recognized that the usefulness of modeling to study the interplay between the various process parameters without resorting to extensive experimentation relies heavily on accurate representation of the physical phenomena in these systems. In modeling electromagnetic confinement casting and melting systems, it is important that the model address all aspects of electromagnetic field interaction with the metal, if accurate predictions are to be obtained /3/. The electromagnetic field affects the heat transfer phenomena primarily through joule heating. In addition, the electromagnetic forces play a key role in heat redistribution in the molten pool via melt stirring, and, in confinement systems, support the molten metal pool."

Jan 1, 1994

By Anna Franzkowiak, Dean Gregurek, Alfred Spanring, Angelika Ressler

In order to determine the most suitable refractory products and improve the lining lifetime for the diverse furnaces used in the nonferrous metal industry, corrosion tests are performed at RHI’s Technology Center. The practical facilities include the cup test, induction furnace, rotary kiln, and drip slag test described in this paper, which enable a comprehensive understanding of the chemo-thermal brick wear on a pilot scale. The corrosion trials are performed with actual slags generated during operations at a customer’s plant. To determine the highest influencing wear parameter, every single test is combined with a detailed mineralogical investigation and thermochemical calculations performed using FactSage. Based on the results, tailored refractory solutions for the nonferrous metal industry can be provided in combination with trials conducted at the customer’s site.

Jan 1, 2014

By Tetsuro Sakai

Home appliance recycling law was put into force in April 2001 in Japan. Specified kinds of home appliances, such as air conditioners, television sets, refrigerators and washing machines, should be recycled according to the law. Mitsubishi Materials Corporation (MMC) in cooperation with home appliance manufacturers is operating five home appliance recycling plants in Japan. MMC established complete treatment system of recyclable materials generating from home appliance recycling plants, which is formed by unique collaboration among home appliance recycling plants, copper smelter and refinery, and cement plants. Recyclable materials containing copper and precious metals are only handled and treated within the MMC group. By using this lock-in system, safe treatment and traceability of materials are guaranteed as 100% materials recycle.

Jan 1, 2008

By Batric Pesic

Reactions of metallic iron were studied in several different aqueous solution systems: water, medium salt solution used for the growth of T ferrooxidans, ferric iron solution and solution containing T ferrooxidans. Each system was studied under abiotic and biotic conditions in the presence of T ferrooxidans and as a function of pH, particle size of iron powder, temperature, ferrous and ferric iron concentrations. It was found that metallic iron reacts with water differently than does with ferric iron in water. Surprisingly, T ferrooxidans were non-functional in the dissolution of metallic iron. Also, the reactions of metallic iron with pure water were indistinguishable from the reactions with water containing medium salts for bacterial growth. The reactions with ferric iron were also independent of medium culture compounds. The mechanisms of metallic iron reactions with ferric ions are different from the mechanisms of metallic iron reactions with water.

Jan 1, 2001

By P. Gray

Process and engineering development of the Warner Zinc Process over the past two decades has proceeded alongside the world-wide collection and analysis of operating and cost data of current processing practices from sulphide ores to refined metals. Study of these data shows that recoveries are dependent on mineralogical characteristics of the sulphide matrix and point to the inadequacy of differential flotation as a tool for preparing feed for smelters. The paid-for return at the mine on the combined metal values in zinc rich sulphide ores rarely exceeds 80% and increasingly runs as low as 50-60%. Surveying the possible alternative ways of improving these performances leads to the conclusion that the Warner Process is the only technology in sight that could meet a target of 90% paid-for recovery and that its development has now reached a point where it can be a fully practicable process for all mixed sulphide ores.

Jan 1, 2000

By M. Oliazadeh

The present study was performed to develop a process for solvent extraction of molybdenum and cobalt from an acidic solution generated by an electrodeposition process of nanocrystalline cobalt alloys. Solvent extraction is a common practice in hydrometallurgical and refining processes to produce metals; however its application for separation of molybdenum and cobalt from this specific solution is new, because molybdenum and cobalt are not commonly associated together in nature. Five commercial organic extractants were examined for extraction of cobalt and molybdenum from synthetic acidic solutions with pH ranging from 1 to 5. Preliminary results showed that at pH 2, any of the Cyanex 923, Alamine 336, Aliquat 336 and Hostarex A327 could be used to extract 99% of molybdenum from solutions, while from pH 3 to 5, Aliquat 336 was able to extract about 100% of molybdenum. Cobalt extraction, on the other hand, varied from 15% to 23% at pH 3 and 30% to 53% at pH 2 using different extractants. Based on results obtained, Aliquat 336 was applied on mixed solutions of cobalt and molybdenum at various pHs. The results showed that molybdenum could be extracted as much as 99% from a mixture of molybdenum and cobalt at acidic pHs, while less than 1% of cobalt was separated at pH 2 to 4 simultaneously.

Jan 1, 2003

By G. Upadhya

Of late, solidification modeling has progressed considerably to emerge as a viable simulation tool for the foundry engineer. A wide variety of tools exist in the commercial market to cater to the various needs of the design/ foundry engineer. In fact, recent developments in the area of solidification modeling have been so rapid that a comprehensive review of the state-of-the-art is very much needed. In this paper, an attempt is made to summarize the various issues of solidification modeling, at the same time addressing the historical evolution of the subject. The various phenomenological issues covered in this paper include: heat transfer, fluid flow during mold-filling, solidification kinetics and microstructural evolution, quick-analysis schemes for approximations, porosity prediction models, and the phenomena of fluid flow in the mushy zone. Modeling issues related to the development of solidification stresses which lead to defects such as hot tears and the development of artificial intelligence concepts in the area of rigging design are also discussed. Due emphasis is given to the various phenomena which add to the complexity of the whole subject, and the various alternatives available for solving a particular problem. For example, the heat transfer problem can be approached by the use of simple modulus schemes or by solving the conduction equation to obtain a more accurate temperature distribution. Similarly the microstructural evolution can be handled in a deterministic way by use of nucleation and growth models, or in a probabilistic way by use of empirical models. The main goal of this paper is to put the multi-faceted problem of solidification modeling in proper perspective so that it can serve as a guide for future developments in this area.

Jan 1, 1994

By Vojteh Leskov?ek

The tribological load is the load on forging tools resulting from the relative motions between the plastically deformed workpiece and the die. In comparison to many other forming processes hot die forging has an especially disadvantageous tribological system. The advantages of the application of hard coatings, which are well known for cutting tools, are to a much lesser extent explored for casting, extrusion, molding and forging tools. Increasing the lifetime of these tools is an important task in surface engineering because of the complex loading conditions and often complicated tool geometry. The plasma-assisted chemical-vapor-deposition (PACVD) technique is well suited to depositing hard coatings onto large dies and molds. The aim of this study is to present and discus results obtained on a duplex PACVD hard coating in an industrial application like the hot forging of automotive parts. A new generation of vacuum-melted and remelted (VMR) hot-work tool steels has been developed; these can reach a hardness of 58 HRc, and have a fracture toughness at this hardness equivalent to that of standard hot-work tool steels at 45 HRc. This offers one of two advantages: the steels can be used at the higher hardness to provide resistance to wear or deformation, or, when used at a hardness of 47?49 HRc for hot forging, to provide temper resistance, nitriding behavior and adhesive wear resistance. The results presented here are from a preliminary investigation. The experimental results indicate that the introduction of a proper duplex PACVD hard coating will lead to an improved wear resistance and a longer lifetime for the hot-forging dies. Furthermore, by using a hard, low-friction coating excellent anti-sticking properties can be obtained. At this stage of the investigation it is also necessary to carry out pilot trials to determine the wear resistance and the tool life in practice.

Jan 1, 2006

By I. Gaballah

The chalcopyrite ore&apos;s anodic and cathodic electrodissolution are studied using a Porous Pulsed Percolated Electrode (3PE) reactor. Stationary solid electrode experiments are also performed to explore the mechanism of electrochemical dissolution of chalcopyrite. Experiments with a low - grade natural ore have been carried out at 25 "C in solutions containing 1 M NaCl and 1 M HCl. Galvanostatic and potentiostatic conditions are employed. The influences of current and potential on selectivity of the chalcopyrite ore dissolution are assessed. Anodic oxidation of this ore leads to a preferential dissolution of iron bearing minerals, whereas cathodic reduction is more selective with respect to chalcopyrite. However, in both cases the electrochemical dissolution is incomplete and the current efficiency is low. Design of the actual reactor has to be modified to increase the bed conductivity and to allow continuous experimentations.

Jan 1, 1994

By David Hughes

The paper covers the utilization of on-line analysis in process control of solvent extraction in nickel leach solvent extraction processes in Finland and Australia and in copper heap-leach and solvent extraction in Chile. The goals of and requirements for controlling the solvent extraction stages of the processes are reviewed. The applications at three plants are compared. The development of the technology used is reviewed and design considerations are discussed. Requirements for on-line control and analyzer performance are compared. A new generation of analyzers and its effect on the set-up process of a project is introduced.

Jan 1, 2003

By A. K. Kyllo, N. B. Gray, B. N. McCurry

"Dynamic control of the formation of a solidified layer between a pipe wall and a flowing melt enables the flow rate to be adjusted in real time. This solidified layer can be generated by using a coolant on the outside of the pipe wall to remove the required heat. The coolant, and hence the solidified layer, can be controlled remotely. The dynamic behaviour of the solidified layer was investigated by both physical experiments and mathematical modelling. The mathematical model has been developed using a finite difference technique to describe conduction through the pipe wall and solidified layer. Results from the model were consistent with previous steadystate experimental results using molten lead. Experiments are currently being carried out using molten tin in a recirculating circuit with a cooling system that is instrumented for accurate computer control to validate the model. The circuit is designed for flowrates of up to 24 kg/s (86 tph) of molten tin. Steady-state and dynamic predictions were made for the current rig.Industrial SignificanceThe current method of choice for tapping slags, metals and mattes from many metallurgical furnaces is using an oxygen lance to open the taphole and using a clay plug to close it. There are, however, some significant drawbacks in this method. The heat generated by the oxygen lance erodes the refractory lining of the taphole, as well as the clay plug, and the furnace products themselves corrode the taphole. Using an oxygen lance is also a significant safety hazard to the operators as they must work in close proximity to the furnace and be subjected to a shower of sparks while opening the taphole. Also, the flowrate of material through the taphole cannot be controlled online as the diameter of the opening cannot be varied easily. This feature means that the level of product in a furnace cannot be kept constant."

Jan 1, 1999

By Matthew Jeffrey

Due to the increasing environmental and public concerns over cyanidation, there has been a large amount of research into viable alternative lixiviants. Despite these studies, there is little published data directly comparing the kinetics of gold leaching for each of these alternatives: most of the literature is concerned with gold extraction from ores. This paper presents a detailed kinetic study of gold leaching in cyanide, armmonia/thiosulfate and chloride/hypochlorite solutions. The gold leach rates were measured using a rotating electrochemical quartz crystal microbalance (REQCM). This instrument allows the mass of a gold sample to measured in?situ, with a sensitivity of less than 10 ng. From the results of these studies, it is possible to select experimental conditions where the leach rates of the alternative lixiviants are similar to that for the traditional cyanide system.

Jan 1, 1998

By Peter C. Hayes

"The high temperature reduction of solids through the use of reactive gas atmospheres has application in a wide range of industrially important processes. Whilst significant advances have been made in understanding and describing these processes, some key aspects of the chemical reactions and reaction mechanisms operating in these systems, for example, the transformation from metal oxide to metal, remain poorly understood. A number of different product morphologies have been identified in these reaction systems and the reaction rates have been shown to be critically dependent on the product structure.Theoretical examination of the elementary process steps taking place in the region of the gas/metal/metal oxide interface, combined with electron microscope studies of the resultant product microstructures, have enabled the key process and material variables responsible for the development of the various product morphologies to be identified. By considering i) established criteria for the stability of moving interfaces in a thermodynamic potential gradient, ii) the relative rates of chemical reactions on the oxide and metal surfaces, and iii) key process phenomena and physico-chemical properties of the solid phases, the mechanisms and conditions for the formation of various product morphologies are identified. Interestingly the analysis points to direct analogies between these phase transformations and, the phenomena and microstructures observed in metal solidification, and the potential to develop generic models of these fluid/solid reaction systems."

Jan 1, 2013

By Hong Ouyang

A unified computational model has been developed for the Bridgman growth processes of B-NiAI and CdTe crystals. To handle the geometrical and physical complexities, a two-level approach has been developed. At the gtobatlevel, conjugate heat transfer, phase change dynamics, and variable material properties along with the realistic geometries and thermal boundary conditions are accounted for inside the entire crystal growth system. Refined calculations are then made within the ampoule, with the boundary conditions supplied by the global simulations. This model can optimize the use of computational source, help understand solidification behaviors, and improve designs of crystal growth system.

Jan 1, 1996

By E. Fregeau-Wu

The major obstacle in recycling steelmaking slags to the blast furnace is their phosphorus content. Removal of the phosphorus, which is primarily associated with the silicate and phosphate phases, would allow for greater recycle of these slags for their iron, manganese, and lime contents. Calculations show that separation of the silicates from the oxide phases would remove nearly 90% of the phosphorus from the slag. The variable grain size of the as-received slag made liberation by fine grinding difficult. Therefore, slow-cooling experiments were undertaken to improve the grain size distribution. The grain size distributions were determined using in-situ image analysis. The samples were ground to their apparent liberation size and high gradient magnetic separation was used to separate the magnetic oxides from the nonmagnetic silicates and phosphates. Liberation analysis and modeling was performed on selected separation products for discussion of benefication characteristics.

Jan 1, 1995

By S. Shrivastava

A structure based model has been developed for the prediction of viscosities of K20-B20, melts. These melts exhibit an anomalous behavior of viscosity with continuous variation in B203 content. A maximum and a minimum are observed at low temperatures, which disappear on raising the temperature above the softening range. The addition of K20 to the borate melts causes two opposing phenomena: (1) depolymerization effects and the related breakdown of network structure resulting in the formation of singly bonded oxygens, which weakens the structure and hence causes a decreases in viscosity, and (2) the formation of four coordinated borons (BO4 tetrahedra) which strengthen the structure leading to an increase in the viscosity. The structural changes taking place in these melts on varying the temperature and the alkali content have been reviewed and are incorporated in developing this model. The predicted values are in excellent agreement with the experimental values over the whole temperature and composition range.

Jan 1, 1992

By KNona C. Liddell

Goethite is an important naturally occurring sorbent for divalent heavy metals and has often been used as a model compound in studies of adsorption on oxide mineral surfaces. Surface complexation modeling, surface spectroscopy, and electrochemical techniques have all been applied to goethite adsorption. Modeling studies have shown that usually several different sets of fitted parameters are equally successful in representing surface charging and adsorption data. Surface spectroscopic data are proving valuable in determining the nature of the surface sites, and refined models now incorporate structural information on interatomic distances and coordination numbers. Multisite surface complexation models can give very good fits to surface charging and adsorption data, but further improvements are needed to better represent surface reactions involving exchange of protons and divalent cations. Recent experimental and modeling studies on adsorption of divalent transition metals on goethite are described and the present status of the field is assessed.

Jan 1, 1999