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By Yong Zhao, Yan-hui Sun

Behaviors and evolutions of MgO·Al2O3 in non-oriented silicon steel during calcium treatment were investigated by thermodynamic calculations and high-temperature experiments. MgO·Al2O3 inclusions were the main type of inclusions before calcium treatment, which is also confirmed by the stability diagram of MgO/MgO·Al2O3/Al2O3 from thermodynamic calculations. After calcium treatment, the majority of original MgO·Al2O3 inclusions were mainly modified to CaO-MgO-Al2O3 system inclusions, this would be beneficial to improve castability and product quality of silicon steel. But there was no modification happening to some MgO·Al2O3 spinels which were directly surrounded by CaS inclusions. The content of Al2O3 occasionally existed a sudden increase besides a common decrease in the product layer of CaO·MgO·Al2O3. Then the evolution mechanisms of MgO·Al2O3 inclusions were proposed in present work. Thus, Al/Mg atom ratio had a significant influence on the modification of MgO·Al2O3 spinel.

Jan 1, 2016

By S. Sundarraj

The morphological transition between columnar and equiaxed structures is an important solidification phenomenon frequently observed in castings, especially complex parts with varying cross-section, The mechanical properties and the occurrence of defects such as hot tears are strongly dependent on the structure formed in the casting. Hence, it is important to understand the conditions leading to columnar or equiaxed structures. Although extensive work has been done in modeling solidification systems, almost all of the existing models are based on the assumption that the structure formed in the casting is either purely columnar or purely equiaxed. Prediction of the columnar-equiaxed transition (CET) requires a solidification model which accounts for the formation of both columnar and equiaxed structures, along with related microscopic and macroscopic solidification phenomena. In this paper a CET model is presented which: (i) takes account of both columnar and equiaxed structures, (ii) accounts for macroscopic heat transfer coupled with microscopic phenomena such as nucleation, growth and microsegregation, (iii) satisfies solute conservation, and (iv) is easy to implement in commercial finite element and finite difference software. The proposed model predictions of CET have been validated with available experimental results for a uni-directional solidification of an aluminum-copper alloy. A sensitivity analysis has also been carried out to determine the effects of various parameters on the CET model predictions. The model is being extended to other alloy systems and more complex geometries. This work will be published in due course.

Jan 1, 1996

By Jun Li

Rate processes of silver cyanidation were studied with the objective of understanding the reaction mechanism. The research was divided into three sections: anodic dissolution of silver in cyanide solutions, cathodic reduction of oxygen on silver surfaces and the direct leaching of silver in oxygenated cyanide solutions. The charge transfer steps plus the diffusion of reactants from bulk solutions to the silver surface were identified as rate-limiting and the rates of both anodic and cathodic reactions can be calculated using the Butler-Volmer equation and Fick's first law. Based on mixed potential theory and the results of electrochemical studies, a comparison of the rate obtained from direct leaching with that predicted from the calculation is made. Calculated results agree well with the experimental data.

Jan 1, 1992

By Mark Cross, Hadi Abou-Chakra, Nicholas Christakis, Mayur K. Patel, John Baxter, Ugur Tiizful

"In recent years significant effort has been put into using continuum mechanics for the description of granular flows. Although these models are partially successful in capturing some flow characteristics, they lack essential information on material properties, which are needed to account for the interactions between different particles. Thus, they are incomplete and can not be used to describe processes such as hopper filling/emptying and pneumatic conveying, where particle-particle interactions can lead to phenomena such as segregation, degradation and agglomeration. In this paper, a 3-D unstructured finite-volume framework is presented, which employs interface tracking techniques to solve for the individual material components of the granular mixture in the bulk and thus, determine the material-air interface. Various transport processes, arising from the micro-mechanical properties of the different particle species in the granular mixture, can be obtained through kinetic theory. The transport coefficients of each of the individual species can be determined and analysed in a micro-mechanical framework and the transport process parametrised in the form of constitutive models. These models provide the continuum theory with information on the micro-mechanics.This work describes the continuum framework and the micro-mechanical parametrisations, which are used to describe the processes and interactions at the microscopic level. Numerical simulations and comparisons with experimental data are then presented for the case of binary granular mixtures and conclusions are drawn on the capability of the model to realistically predict and quantify the main characteristics of granular flows."

Jan 1, 2001

By Greg Dowling, Jun Ge, George Shannon, Shufeng Yang, Yongfeng Chen, Lifeng Zhang

"Inclusions in 316L stainless steel ingots poured using two different upgate designs – a traditional upgate and a swirl upgate - were investigated using SEM and ASPEX automated inclusion analysis. The main inclusions were high SiO2 inclusions, MnS inclusions and SiO2-Al2O3-CaO inclusions. More inclusions were detected at the top of the ingot than other places in vertical direction, and more inclusions were at the edge of the ingot than other place in the radial direction. With swirling upgate there were more K- and Na- bearing inclusions than that with the traditional upgate indicating possible more serious flux entrainment with the swirl upgate.IntroductionIngot casting still is very important for production of special steel grades including high carbon chromium bearing steel, thick plate, seamless tube, forgings, bars, and wire rods [1] . During the bottom teeming process, molten steel enters the trumpet and passes through the spider into the runners. Molten steel then enters the ingot mold through an upgate near the end of the runner. In the early stages of filling a mold, a mold flux bag hung in the mold were burnt and the mold flux will cover the top of the rising steel to protect the steel from being reoxidized, acting as well as act as a thermal insulator. So far, some efforts on studying inclusions characteristics in the ingot have been reported. A review paper on the control of inclusions during steel ingot casting was published by Zhang et al. [2] Zhang also studied Inclusions in bottom-teemed ingots of plain carbon steel and found that the >20µm inclusions originated from either the entrainment of mold flux of the reoxidation during teeming process. [3] The results of Nagendra and Du showed that there were more inclusions in the centre part of the ingot [4]. Eriksson et al reported that the composition of inclusions was more complex in the mold samples in comparison to the ladle samples, and more inclusions in the mold were found than in ladle because of the reaction between the mold flux and the molten steel [5]. It was reported that SiO2-CaO-Al2O3 inclusions originating from mold powder with reoxidation product Al2O3 as a part, and there were more inclusions close to the side wall than the center of the ingot in the radial direction. [6]. A more recent investigation showed that four main types of inclusions in runner samples were classified: oxides, sulfides, complex and carbon-nitrides. [7] The flow pattern in the mold during filling has been found to be an important factor regarding inclusions in the ingot. In the early stages offilling a mold, steel enters the mold through the entry nozzle at a high velocity. The effect of the resulting turbulence on the meniscus can lead to the entrainment of mold flux. Efforts have been paid over the years to find methods to reduce the velocity of the molten steel entering the mold, such as using opening angle of the inlet nozzle [8], using swirl blade at the runner [9], using a divergent nozzle combined with a swirling flow generated in the nozzle [10-11]."

Jan 1, 2012

By Batric Pesic

Dissolution of gold with elemental bromine was studied by using a rotating disc technique. The main parameters studied were: bromine concentration, stirring speed, pH, and temperature. Additionally, effect of copper, iron, and manganese was also examined. A special attention was paid to elucidate the role of cations, primarily Na+, during gold dissolution. It was found that gold dissolution with bromine was characterized with two pH regions. Below pH=7, gold dissolution was independent of pH, and above this value, gold dissolution decreased with pH increase. Gold dissolution rates were proportional with concentration of bromine. Two regions, diffusional and kinetic, were observed with respect to stirring speed. with respect to the role of Na+, and cations in general, they play absolutely no role during gold dissolution with bromine, unless they are in their lower oxidation state and become oxidized by bromine. In that case they have a negative effect because of bromine consumption.

Jan 1, 1991

By Qiang Yu

This paper reports on a research project supported by NSF, which aims at developing a multi-scale methodology for systematic microstructure prediction in thermo-mechanical processing of metals. This methodology is based on combining mesoscopic microstructure models with macroscopic process formulations and involves the following three main steps: (I) based on the given global processing conditions, the gross deformation patternof the entire workpiece is modeled using a continuum-based algorithm, (2) the resulting parameters are then extracted from the continuum-based simulation, post-processed and passed on to the mesoscopic numerical module, and (3) the microstructural changes are finally modeled at the mesoscopic scale. This approach is expected to overcome the disadvantages of current microstructure prediction practice employing empirical relationships between microstructural features and processing parameters. Keywords: Thermo-mechanical processing, Microstructure, Grain growth; Recrystallization; Mesoscopic models; Finite Element Method

Jan 1, 2003

By Batric Pesic

Adsorption of gold on activated carbon from gold bromide solutions was examined as a function of pH, particle size, carbon amount, initial gold bromide concentration, bromine concentration, temperature, and various cations and anions. pH did not have any effect below pH=6. Above pH=6, pH had dramatically negative effect. The adsorption results satisfied a first reaction order model. The reaction rate constant was proportional to the inverse of carbon particle radius. It was also proportional to the amount of carbon, and independent of initial gold concentration. Temperature had a very little effect at pH=l. At pH=8, the activation energy was a function of the extent of a reaction, increasing with the extent of a reaction. Cu, Fe, Ca, Mg, and Na cations and sulfate, chloride and bromide anions did not have any effect on gold adsorption. Bromine had a very negative effect on gold uptake.

Jan 1, 1991

By J. Winters, L. Vos, C. Canoo

Committed to a sustainable development of zinc applications, Union Miniere is investigating processes for the minimisation of waste and residues originating from the classic hydrometallurgical zinc process. In that context, Union Miniere has developed a method for the cold inertisation and solidification of goethite, the Graveliet® process. The result is a hard and inert gravel that can be used in the building industry. During the past two years, a pilot plant for the production of Graveliet® has been built and operated. In the present paper, the Graveliet® process and the pilot plant are described after which the properties of the produced gravel are discussed, from both a mechanical and an environmental point-of-view. Graveliet fulfils the criteria for use as a secondary building material. The GravelietJ process is a viable technology to avoid stockpiling of goethite residues and it thus assures the long-term development of the hydrometallurgical zinc process.

Jan 1, 2000

By Leonid M. Lerner

High temperature aluminum Alloy 8009 is a rapidly solidified/powder metallurgy aluminum-iron-vanadium-silicon alloy. This alloy in combination with hard oxide aluminum film has unique engineering properties which may recommend its use in compressors and impellers for aerospace applications. Various anodizing processes (including Sanford Low Voltage DC+AC Process) for these task will be evaluated and normal chemical composition, physical properties, and macrostructures of 8XXX aluminum alloys will be presented.

Jan 1, 2006

By J. McKelliget, J. Szekely, Oreper. G. M.

"1. INTRODUCTIONThis paper is concerned with heat and fluid flow phenomena in arc welding operations. Fig. 1 shows a schematic sketch of a typical arc welding arrangement. It is seen that an arc is being struck between an inert electrode and a metal surface and that the resultant current and energy flow will case the formation of a molten weldpool.It is clearly appreciated that the weldpool shape and the nature of circulation in the weldpool may play an important part in determining the ultimate weld quality. It is known, furthermore,· that the weldpool behavior in turn will be affected by the spatial distribution of the current and the heat flux it receives from the arc. Indeed, the inherent coupling between the arc and the weldpool is a key feature of welding operations.Up to the present useful work has been done on the modelling of heat transfer and melt circulation in weldpools (1,2,3,4) and also on the description of arcs, including welding arcs (5,6,7,8). However, the coupling between these two sets of phenomena is relatively unexplored in a qualitative sense. The purpose of the present paper is to examine the interaction between welding arcs and weldpools. The actual material will be presented under the following headings:"

Jan 1, 1986

By Batric Pesic

The interactions of mineral-pyrite with T. ferrooxidans were studied by using a cyclic voltametry technique. The interactions with bacteria were examined during the entire growth stage of bacteria (fermentation), The pyrite ?surface invariably drastically changed ' its. properties at the second day of fermentation. Beyond two .. days of fermentation, the cyclic voltamograms were insensitive to convective diffusion produced by stirring. The product layer was examined by SEM,. X-ray diffraction and chemical analysis. The SEM study revealed that bacteria populated the pyrite surface at an extremely high density levels. The high density of bacteria, and the solid reaction products formed on the pyrite surface created conditions for pore diffusion which explained why the CVs became .insensitive to convective diffusion in solution (stirring). The x-r:ay diffraction study confirmed jarosite as a product layer. A mechanism of T. ferrooxidans cells serving as nucleation sites for jiarosite formation is proposed.

Jan 1, 1991

By V. Ramachandran

Under the Resource Conservation and Recovery ACT (RCRA), generators of listed or characteristic hazardous wastes must find satisfactory means for disposal. of wastes. Initially, for many this meant landfills and deep-well injection. Until recently, mining and metallurgical by-products have largely been exempt from RCRA, but now are coming under its jurisdiction. With the increasing closures of landfills, companies in the U.S. such as electroplaters, miners, metallurgical plants and others are turning to recycling as an alternative to treat their wastes. While the cost of recycling has been challenging, the long-term economics prove attractive because recycling interrupts the cradle- to-grave responsibility for the waste generator. The present paper describes the recycling of hazardous wastes at ENCYCLE/TEXAS. Encycle extracts marketable metals from metal-bearing sludges and wastewater using hydrometallurgical processes borrowed from the mining and metallurgical industry.

Jan 1, 1994

By T. T. Natarajan, Nagy EI-Kaddah

"Numerical simulation of electromagnetic confinement systems generally requires large CPU time due to the strong coupling between the electromagnetic and the free boundary problems. The present paper examines the accuracy and the computational efficiency of the most common numerical schemes used in modeling such systems. Levitation melting was taken as a test case. In this study, a comparison was made between the finite element and surface integral methods for electromagnetic field calculations. The computational efficiency of Lagrange and the modified Hestenes methods for solving the free boundary problem were investigated. The convergence of the Lagrange method was found to be much faster than the modified Hestenes method. It was also found that finite element method not only gives accurate solutions, but faster convergence to the final equilibrium shape than the surface integral method. The applications and the limitations of these techniques in modeling electromagnetic confinement systems will be discussed.IntroductionIn recent years there has been a growing interest in the use of electromagnetic forces for confinement of molten metals as a means to eliminate molten metal contamination during melting and to improve surface quality of cast products. Continuous casting of metal without contact of a mold is now a reality, and is being commercially applied for casting of aluminum slabs /1/, and copper rods /2/. New applications of electromagnetic confinement in melting and casting include containerless melting (Magnetic Suspension Melting) /3/, edge containment in twin roll casting, and meniscus shape control in continuous casting of steel /4/.Modeling of confinement systems involves the determination of the electromagnetic field and the equilibrium shape. These two problems are strongly coupled due to the dependence of the field on the shape of the melt. While significant advances have been made in computational electromagnetics /5/, the application of developed computational techniques to electromagnetic confinement problems is not a simple task. The principal difficulty in using these methods is that the solution domain is not known a priori. due to coupling between the electromagnetic field and the free boundary problems. These two problems have to be solved simultaneously, leading to an iterative solution procedure. As a result, numerical simulation of electromagnetic confinement systems are computationally intensive with computational time at least an order of magnitude larger than the fixed domain problems."

Jan 1, 1994

A simulation of a capper concentrate smelter was built with a capacity of 450,000 tons per year. The system's components to simulate were three : a Reverbetory furnace, a Wiente ' s modified converter ( TMC ) and two cranes. The system was classified as dynamic, stochastic and discrete. In the simulation language choice it was concluded that the most advantageous one was GPSS/H. The model verification was done through the interactive Debugger that the language has and the statistical validation was done through the result variables of sane activities, that as a whole characterize the system (charged matte and charged concentrate to the TMC, skimming white metal and skimning slag). The validation was done comparing the simulation results of these variables with the ones obtained for those variables in a specific month in the smelter. The comparison consisted in a difference of means test and in all cases the equality was accepted with a 95% of confidence. The animation tool was PROOF, a general purpose animator, that is used after processing the simulation.

Jan 1, 1994

By J. W. Holzenthaler

Teams continue to play a major role at the Phelps Dodge Mining Company El Paso Operations, especially during the present time of low copper prices. The El Paso Operations' teams have taken the initiative during this copper market downturn and have helped reduce operating costs significantly. Because of this, Phelps Dodge El Paso Operations has continued to grow within the team process by creating a total, non- exempt salaried workforce. In the last year alone, the El Paso Operations have implemented three major initiatives to accommodate the team process. The first was the creation of "guiding principles", a policies and procedures handbook. Second was the "zero and beyond" safety initiative. Third was team compensation. In addition, the Copper Products Company has now adopted a work-team environment, following the lead of the refinery.

Jan 1, 1999

By M. K. Patel, K. A. Pericleous, M. Molaei

"The future trading of carbon credits and increased financial cost necessitates substantial cuts in incidental C02 emissions in the production of metals (iron, steel, aluminum, zinc, lead). Although greener methods of production are being developed, in the short term the use of point-source C02 extraction using existing technology remains attractive. Accelerated natural carbonation, in a fluidized bed is a feasible technological route investigated in this research. CFD modelling has been used to study the efficiency of C02 capture in a fluidized bed reactor containing a CaO solid sorbent. A Lagrangian/Eulerian scheme describes describe CaO particle trajectories and exchange of mass, momentum and energy with the carrier gas, with a typical off-gas composition. Different reactor geometries are considered (with uniform, stepped and gradually expanding cross-section), to maximize conversion for a given particle loading and size distribution (100-200 microns). Removal efficiencies of up to 80% are demonstrated, making this a viable process.IntroductionBased on Intergovernmental Panel on Climate Change (IPCC) reports, the major cause of climate change and global warming is due to a high level of C02 concentration in the atmosphere resulting from fossil fuel combustion, particularly in coal-fired power plants [1]. Carbon capture and storage is therefore the most important action proposed to reduce C02 from combustion flue gases. In this process, carbon dioxide is captured and may then be regenerated as pure C02 and conducted to a permanent storage, or simply stored as a solid carbonate [2]. Capture and storage of C02 has an economic penalty and the main cost of this penalty is associated with the capture plant. Capturing C02 with a lime-based solid sorbent (CaO) is a very promising technique, due to the low cost and the wide availability of the reactant. In this process, the CaO reacts with C02 based on the following reaction in a reactor called a Carbonator:"

Jan 1, 2012

By R. K. F. Lam

Unacceptable levels of impurity were noted in high purity chromium melting. Analysis of recent melting data determined that oxygen content in chromium is the critical parameter. Thermodynamics studies identify zirconia to be the most stable oxide in the presence of liquid chromium, followed by alumina and silica. Iron oxide reacts readily with liquid Cr. A certain degree of chemical reaction between liquid chromium and oxides does occur, contamination by the crucible is therefore unavoidable. Equilibrium constants indicate that a chromium oxide addition decreases 'ceramic dissolution and reduces impurity contamination. Safe operating conditions with oxygen content between 1190 ppm and 2500 ppm were identified. Additions of chromium oxide (Cr2O3) of 161 grams and 264 grams to liquid chromium yielded acceptable levels of impurity, and oxygen content was respectively increased to 1624 ppm and 2 179 ppm. A new process of melting high purity chromium with chromium oxide addition for controlling the activity of Cr2O3 is recommended.

Jan 1, 1997

By Yong Kuk Park

The horizontal cold chamber die casting process can produce a wide range of near-net shape, non-ferrous castings with small dimensional variation, excellent surface finish and very complex geometries. However, top quality die castings can be achieved only when optimal performance of the cold chamber and plunger is maintained during the molten metal injection phase of the process. Cold chambers (shot sleeves) are known to deteriorate fast and sometimes fail catastrophically because of poor design. Catastrophic fracture and wear due to deformation are leading causes to degrade quality, increase downtime and thereby decrease productivity and profitability. Therefore, a systematic approach to minimize irregular and adverse conditions which prevent an intended injection profile, is highly desirable. To eliminate them, design criteria for shot sleeves were developed using analytical tools and available experimental data. The correlation between design and mechanical failures of shot sleeves was shown by the data obtained from the die casting industry. Also, the relationship between die casting process parameters and deterioration/ failure mechanisms were carefully evaluated.

Jan 1, 1996

By Riyad N. Ahmad-Bitar, Shadia J. Lkhmayies

"CdSi-xTex thin films were prepared by first producing CdS:In thin films by the spray pyrolysis (SP) technique and then annealing the films in the presence of Te vapor in nitrogen atmosphere. X-Ray diffraction (XRD) measurements showed that the films are polycrystalline with the wurtzite structure. Transmittance measurements were recorded at room temperature in the wavelength range 400-900 nm and used to deduce the absorbance. The first derivative of the absorbance was calculated and used to find the values of the bandgap energy, where more than one bandgap was obtained for each film. These results show that the films are inhomogeneous or the composition differs with location. The photoluminescence (PL) was recorded at T = 60 K and a deconvolution peak fit was performed for each spectrum. The results of the PL spectra are consistent with those obtained from the first derivative and confirm the inhomogeneity of the films.IntroductionPolycrystalline thin film CdS/CdTe solar cells are promising candidates for low cost and high efficiency photovoltaic applications. The CdS/CdTe interface plays an active role and a detailed knowledge of its properties is crucial for thorough understanding of the device. High efficiency devices have been obtained in spite of the large lattice mismatch (9. 7%) between hexagonal CdS and cubic CdTe. Interdiffusion at the CdS/CdTe interface is considered to affect the performance of the devices [1]. The formation of a mixed crystal or a graded layer at the interface causes a reduction in the lattice mismatch at the CdS/CdTe junction [2] and then a reduction in the number of interfacial states and recombination centers, thus enhancing the solar cell performance [3, 4].The objective of this work is to investigate the transmittance, photoluminescence (PL) and structure of CdSi-xTex thin films prepared by annealing the spray-deposited CdS:In thin films in the presence of tellurium vapor. X-ray diffraction (XRD) was used for exploring the structure. Transmittance is used to deduce the absorbance where its first derivative was used to find the bandgap energy which varies with composition. The evolution of the PL spectra as functions of tellurium concentration was evident and it confirmed the inhomogeneities of the films."

Jan 1, 2011