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By Vianey Garcia-Osorio

One of the problems in the carbothermic aluminum process is the substantial loss of aluminum compounds as vapors due to the high temperatures in the process. In order to solve this problem a Vapor Recovery Unit (VRU) is proposed. In this unit operation the aluminum vapor undergoes a series of heterogeneous non-catalytic reactions forming solid, liquid and gas products. In this work a model for the simulation of this unit was developed which includes heat and material balances as well as heterogeneous non-catalytic reactions. The model leads to a system of differential equations; its solution was implemented in Matlab giving as a result a stage-by- stage solid-fluid reaction model.

Jan 1, 2001

By H. Kamiya, H. Hasegawa, M. Nojiri, S. Matsui, Y. Fukuda, M. Tsukada

"The present paper focuses on the action mechanism of anionic polymer dispersants in dense Si3N4 and SiC suspension. An atomic force microscope (AFM) was used to determine the relationship between the macroscopic suspension viscosity and the microscopic adsorbed structure of a polymer dispersant at the solid / liquid interface. The surface interactions within the suspensions were analyzed in various dispersant pH and additive conditions. The addition of an anionic polymer dispersant decreased Si3N4 and SiC suspension viscosity and increased electro-steric repulsion force on the non-oxide surface in solution at pH> 6 which was the isoelectric point of the materials. It was assumed that the increase of repulsive force was promoted by a hydrophobic adsorption of polymer dispersant on the non-oxide particles.IntroductionThe surface of silicon nitride and silicon carbide powders in a water suspension system has quite a complex molecular structure. In the case of Si3N4, hydroxyl and ammonium groups form on the surface and the pH of the suspension is increased from neutral to about 10 due to surface oxidation. The particle surface is negatively charged in alkaline solutions (pH=10), because the isoelectric point of silicon nitride exists in the pH range from 5 to 6. However, in spite of charging the negative surface charge, an anionic polymeric dispersant is generally used for the reduction in slurry viscosity.In dense SiC suspensions, an anionic polymer dispersant is generally used in order to disperse aggregates and reduce the suspension viscosity, too. Since an anionic dispersant is used in alkaline solutions higher than the isoelectric point of silicon carbide, the dispersant adsorbed on the negative charged surfaces of SiC.Few researchers have discussed and estimated the adsorption mechanism and structure of anionic polymeric dispersants on silicon nitride and silicon carbide surfaces. This is because it is difficult to observe the structure and measure the interaction at the solid/liquid interfuce directly. However, new developments in surface-force measurement technology have enabled the determination of non-DLVO type interaction for analyzing aggregation behavior2. The use of the AFM for analyzing the effects of various surfactants and co-polymers on colloidal dispersions and solid surfaces has also begun to rapidly expand to characterize the interaction between solid surfaces."

Jan 1, 2000

By A. Andreas Hejja

Flow of slag and settling of matte in slag resistance electric furnaces are discussed in conjunction with furnace geometries, stirring action of the electrodes, buoyancy and electromagnetic effects. The rectangular electric furnace was regarded as a channel reactor and the mode of slag flow as a channel flow. The flow is affected both by buoyancy and electromagnetic forces, however the effect of electromagnetic forces is minimal. The flow velocity is made up of two components; (i) that developed by the action of the electrodes, and (ii) the bulk flow velocity determined by the smelting rate and the volume of the reactor. Slag samples were taken from various depths of the molten bath and were analyzed microscopically to determine the size and distribution of matte particles, The action of the electrodes was described by a simple mathematical formula indicating a balanced settling rate in the area of electrode action.

Jan 1, 1996

By Fang-Qui Zu

Understanding the nature of liquid structures and properties remains an open problem for many fundamental and applied fields such as materials sciences and processing. And as well known, there is no other defined phase line above liquidus (TL ) in phase diagrams of ordinary binary systems. However, via different experimental resorts, our research results on over 30 metallic melts including alloys and elements show a novel physical image: temperature induced liquid-liquid structure transition (TI-LLST) can occur hundreds of degrees over TL. On the other hand, the solidification behaviors and structures out of the melts experienced TI-LLST are distinct from those out of the melts before TI-LLST. In this presentation, some characteristic aspects of the TI-LLST and the effects on solidification behaviors and structures are briefly summarized, and the pertinent rules and mechanism are also analyzed.

Jan 1, 2009

By Devon A. Hannan

Thermodynamic modeling calculations were undertaken for the recovery of mercury from HgTe using a vacuum retort reactor. However, discrepancies were noted in the available thermodynamic data which introduced uncertainty in the model results. Consequently, a series of transpiration experiments were first undertaken on the thermal decomposition of HgTe into an inert carrier gas stream according to the following reaction: HgTe(s) Hg(g) + Te(s) From the measured weight loss of the HgTe samples, the Gibhs free energy change for the above volatilization reaction was determined as a function of temperature. The experimentally determined Gibbs free energy values were found to be approximately 30% larger (more posi-tive) than the values available in databases such as HSC Chemistry. By conducting a second-law analysis on the experimental data, the heat of formation of HgTe at 298.15 K and the en-tropyat 298.15 K were determined, which then formed the basis for a new database for the modeling calculations. The results of this study showed that HgTe was more stable at elevated temperatures than was generally indicated in the literature. The new database is given in a for-mat for direct insertion in HSC Chemistry. Using the new database, modeling calculations were conducted to examine the effects of the re-tort pressure and the molar ratio of purge gas to HgTe on the volatilization of mercury from HgTe. A diagram is presented that shows the minimum temperature for 100% volatilization of mercury from HgTe as a function of retort pressure for different molar ratios of purge gas (N2) to HgTe. For example, it was found that the minimum temperature for 100% volatilization could be decreased by 175 K, at a retort pressure of 0.05 bar, if the molar ratio ofN2 to HgTe is increased from 1.0: 1 to 100.0: I.

Jan 1, 2003

By C. Lupi

Electric arc furnace dust generated during the production of steels is regarded as hazardous waste because of the presence of leachable elements such as Cr, Pb, Cd .... Different processes are available according to the management policy chosen by the steelmaker: disposal. recycle and/or recovery. The feasibility of an hydrometallurgical Zn recovery process on fumes generated during the pyrometallurgical treatment of EAF dust has been investigated. The recovery of metallic iron, chromium and nickel as molten metal provides fumes very rich in zinc oxide ( 63.1% ) and poor in zinc ferrite. This secondary dust is still an hazardous waste and represents the raw material for the recovery of Zn and Pb. The waste material is first leached in 1.5 M sulphuric acid at 30°C to provide a Zn, Fe and Mn rich aqueous solution and a Pb and Ca sulphate rich sludge. The iron is eliminated by precipitation because is harmful to the following electrowinning process. The ftltered and purified leached solution is acidified in order to obtain good electrowinning conditions. A pure cathodic deposit of zinc is then produced in an electrolytic cell at laboratory scale.

Jan 1, 1996

By J. R. Sarazin

Density driven convection during solidification has been recognized for some time to result in macrosegregation particularly when lower density alloying elements are rejected into the interdendritic liquid. The resulting segregates are commonly referred to as channels, freckles or A-segregates. Buoyancy driven convection leading to channel formation has been examined in three model systems possessing somewhat different materials parameters. They are the Pb-Sn eutectic system, the transparent aqueous-salt NH C1-H 0 4 2 eutectic system and the transparent organic succinonitrile-ethanol monotectic system. Convection in these systems is controlled by a balance of buoyant and viscous forces, which are strong functions of composition and temperature. Composition, temperature and flow velocity were measured and elimination of channels through heavier ternary additions is discussed.

Jan 1, 1991

By S. Ozbilen, B. Erdogan, M. Erdogan

To study by thermal analyses the response of precipitation hardenable alloys of Al-Cu-Mg and Al-Li-Cu-Mg system to natural and artificial ageing, a series of ternary and quaternary Al-alloys with nominal compositions of Al-l.13wt%Cu-0:65wt%Mg (alloy-I), Al-1.15wt%Cu-0.57wt%Mg-0.07wt%Li (alloy-2), Al-l.19wt%Cu-0.56wt%Mg-0.75wt%Li (alloy-3), Al-2.0lwt%Cu-0.89wt%Mg (alloy-4), Al-2.14wt%Cu"0.56wt%Mg-0.07wt%Li (alloy-5) were used in the present investigation. Samples in the form of rolled sheets are subjected to water quenching at 25EC after solution treatment at 530EC for 20 min. Alloys were aged naturally at room temperature (25EC) up to 2 months and artificially at 190EC up to 2 days. By using differential scanning calorimetry (DSC) in the temperature range of25-300EC, differential thermal analysis (DTA) in the temperature range of25-600EC together with Vicker's hardness measurements, the response to natural and artificial ageing of the alloys used in the present study were investigated. It was observed that in these alloys, GPB(Cu, Mg) zones [Guinier-Preston zones with Cu and Mg] do form during water quenching at 20EC following solutionizing heat treatment. Natural ageing of the same alloys causes formation of more GPB(Cu, Mg) zones, which results in hardening in the alloys. Artificial ageing at 190EC up to l day results in GPB zone dissolution causing preliminary decrease in hardness values while two days of artificial ageing in the alloys cause S' (Al2CuMg) precipitation confirmed by DSC/DTA analyses resulting in an increase in hardness values. Li addition up to 0.75wt% helps T1 (Al2CuLi) and T 2 (Al6CuLi3) phase formation together with S' precipitation as DSC/DTA analyses show after the same heat treatment.

Jan 1, 1998

By Shijie Wang

In pressure oxidation leaching of copper anode slimes, than 65% of the tellurium is m' cxtraoted during decopperizing. About l0- 15% of the selenium is also dissolved simultane¬ously by severe leach conditions. Current operation for the treatment of the leachate is to constantly recirculate the leach solution through a bed of copper turnings. The tellurium and sele¬nium are precipitated from the leach liquor as copper telluride and copper selenide and sepa¬rated from the solution by filtration. In order to improve the reaction efficiency and reduce the process cost, viz, minimize the copper addition, cut retention time, and reduce the energy consumption; a chemical reducing agent is studied and the cementation process tested in the laboratory. In this paper, the test results are presented and the process chemistry is discussed.

Jan 1, 2003

By Scott Samson, Weidong Wang, Shekhar Bhansali, Vandana Upadhyay

"We present an improved design for the two-arm polysilicon thermal actuator. The classic thermal actuator design produces a localized hot spot at approximately the center of the thin actuator arm. This phenomenon limits the actuator efficiency, lifetime, and reliability. Since the actuator deflection is based on thermal expansion of the material, advantage may be gained by making the temperature profile more uniform along the hot-arm length. In our design, the geometry of the thin arm is modified by forming a nonlinear structure near the approximate location of the original hot spot. Electromechanical simulations of this design show an increase in deflection, due to a flattening of the temperature profile along the hot arm. The solid model generation, finite element analysis and simulations are carried out using PEA software. Experimental devices are in the process of being fabricated by using a polysilicon rnicromachining process.1. IntroductionMost active MEMS devices employ some kind of actuating mechanism to increase functionality. Various actuating mechanisms like magnetic, electrostatic, thermal, magnetostatic and piezoelectric have been investigated and incorporated for actuating microstructures. The primary features required from many on-chip actuating mechanisms are large deflection (>10 µm), low actuation voltage, low power.consumption, reliability, fast response, ease of design and fabrication, and small size. Thermal actuation is an attractive mechanism for rnicromechanical devices requiring high actuation forces, large deflections, good linearity and low actuation voltage. Thermal actuators, also known as ""electrothermal actuators"", ""heatuators"" or ""U-shaped thermal actuators"", have been largely used in MEMS based devices to provide both in-plane and out-of-plane actuation [l] .Thermal actuators are also easily compatible with standard CMOS circuitry due to their low driving voltage. However, high power consumption remains a major drawback of the thermal actuation mechanism."

Jan 1, 2004

By Xiang (Frank) Chen, Mikhail A. Sokolov, Randy K. Nanstad

"Nickel-base Alloy 617 is being considered as a structural material for application in the secondary heat exchanger of the New Generation Nuclear Plant, a very high temperature gascooled reactor. Thermal aging of Alloy 617 plate and welds is being performed with tensile, Charpy impact, and fracture toughness tests conducted at temperatures to 950°C. Results of testing for thermal aging to 5,300 h have been obtained and are presented; varying effects of thermal aging temperature and time on fracture toughness are observed. The 9Cr-1MoV (Grade 91) ferritic steel is a candidate for structural applications in the sodium fast reactor. Fracture toughness testing of unaged Grade 91 steel has been performed to evaluate specimen size effects in preparation for future testing of the material in the thermally aged condition. Results for material in the mill-annealed and heat treated conditions are presented and show that this heat of Grade 91 steel does not indicate a small specimen bias on the fracture toughness Master Curve reference temperature.IntroductionThe behavior of advanced engineering materials will be a critical factor in the performance of Generation IV reactors. In the case of materials utilized for reactor internals and pressure vessels, the effects of irradiation and long time thermal aging are major issues. The environmental conditions for some of the Gen IV reactors are generally beyond present day reactor technology, requiring new experimental data as well as analytical predictions of expected behavior of candidate materials at conditions for which there are only sparse or no experimental data. The radiation environments and several key materials issues for some Gen IV systems are summarized in Section 5 of [l] as a starting point for modeling and microstructural analysis of Generation IV materials. More detailed descriptions of materials research and development needs and recommended activities for the SCWR, VHTR, and GFR are provided in references [2, 3, 4], respectively. Mansur, et. al. provide an interesting comparison of materials needs for Generation IV reactors to corresponding needs for fusion reactors and spallation neutron sources in [5]. The two primary candidate reactor systems currently undergoing significant research and development by the U.S. Department of Energy (DOE) are the New Generation Nuclear Plant"

Jan 1, 2012

By S Ivanaj

Oxidation of chalcopyrite from a copper concentrate in an electrochemical cell having separate-anodic and cathodic compartments was studied by potentiodynamic, potentiostatic and galvanostatic experiments. Oxidation of chalcopyrite particles was mainly realized by in-situ electrogenerated FeIII and Cull ions. The use of an ion exchange membrane, in this experimental set, avoids the reduction of the ferric and cupric ions. The effects of particle size, current feeder potential, current intensity and pulp density were studied to optimize the oxidation parameters. Selective complete oxidation of chalcopyrite was achieved. Oxidation of pyrite was negligible. Mom than 85 % of sulfur was obtained in its elemental form. This may allow selective extraction- of copper from the chalcopyrite concentrate without sulfur dioxide emissions.

Jan 1, 1995

By C. M. Dentan

Conventional testing of crude kaolin ores emphasizes physical properties as they relate to end uses of kaolin products. This approach to evaluating crude ores does not reveal the basis of behavioral differences between typical coarse and fine kaolins from central Georgia. Optical and scanning electron microscopy in combination with XEDS have been employed to characterize both coarse Cretaceous and fine Tertiary kaolin in order to shed light on the reasons for the gross differences in their properties. Routine evaluation of various parameters was also carried out. Bulk densities were 1.48 g cc-l for the coarse clays and 1.53 g cc-1 for the fine clays. Surface areas were 15 m2 9-1 and 25 m2 9-1, respectively. Brookfield viscosities were low for the coarse clays at 70% solids, and high for the fine clays. The situation was reversed for Hercules viscosities. Sixty percent of the coarse clays had particles of less than 2 um and the fine clays had 90% less than 2 cm. Micrographs of thin sections prepared from blue-dyed epoxy-impregnated crude ores and of SEM fabric samples demonstrated vivid differences in texture. Cretaceous kaolins appeared to be completely recrystallized residual products of former aluminous sediments, while Tertiary kaolins retained their essentially sedimentary character. Differentiation of the coarse and fine kaolins is rapidly accomplished by both optical and scanning electron microscopy, and should be considered a valuable analytical technique in evaluating kaolin ores.

Jan 1, 1981

By K. S. Kawatra

In recent years, there have been several efforts to develop binder mixtures for iron ore pelletization. Some efforts have been fruitful, while others have encountered failure. For example, adding corn starch to bentonite is effective, while adding fly ash to bentonite is not. When binders are made with fly ash, a pozzolanic reaction occurs, but no such reaction occurs when bentonite and corn starch are used together. The authors analyzed which binders can be mixed, and which binders will succeed. The authors confirmed this analysis with several laboratory and plant studies. This paper presents this critical analysis, along with various combinations of binders for making Iron Ore Pellets.

By T. T. Chen

A mineralogical study of copper anodes and copper anode slimes was carried out to elucidate the silver phases present and the behaviour of silver during copper electrorefining. Most of the silver in the anodes is in metastable solid solution in the copper metal. As the copper dissolves, silver also dissolves, but is rapidly removed from solution by a variety of reactions. Some of the silver is precipitated as Ag by cuprous ions and some is precipitated as a complex CU-Ag-Pb-As-Se oxidate phase. Much of the silver, however, reacts with copper selenides to form, progressively, (CU,Ag) 2se, AgCuSe and Ag2se. The reaction commences at the periphery of the selenide grains and progresses inward; the result is commonly a silver-rich species on the outside of a silver-deficient core. Slimes collected periodically throughout the electrorefining cycle show a progressive silver enrichment of the selenides. Traces of Ag2Te also may be present, but the telluride seems to J:ie a rare constituent of most raw anode slimes.

Jan 1, 1989

By Wenxian Zhu, Patrick R. Taylor

"The small dimensions of nano-sized materials leads to novel and enhanced mechanical and physical properties. A thermal plasma reactor has been developed to study the formation of nanometer sized metal powders. A supersonic nozzle and a powder filter were designed and built. By vaporizing coarse metal powders in the plasma flame, and quenching the metal vapors through the nozzle at the rate of 107 K/sec, nanometric sized powders have been produced. The powders were collected in an airtight secondary quench-filter system. The particle size of the product power is 5 -20 nanometers, obtained through TEM analysis. The XRD analysis showed that the powder did not oxidize after the filter was handled in an inert atmosphere glove box.IntroductionNanostructured materials have been shown to exhibit improved physical and mechanical properties compared to conventional materials with larger grain sizes (1,2). There have been several methods proposed for preparing nanometer size materials. Thermally induced vapor-phase reactions have been used to produce a variety of powders. A common feature of these processes is the rapid production and cooling of condensable reaction intermediates and products, by gas-phase reactions, leading to the formation of a large number of very small particles. Thermal plasma synthesis of ultra-fine size particles has been attracting increasing interest (3,4,9-11), because it offers many advantages, especially in refractory materials processing, compared to conventional processes: (a) thermal plasma temperatures are very high(> 5000 K); (b) the rates of chemical reaction are much faster than those encountered in conventional processes; (c) high-purity materials may be obtained using fewer processing steps by collecting the product at temperatures where the by-products are in the vapor phase; ( d) the mean particle diameter can be controlled; (e) unifom sized particles may be produced with clean surfaces (these particles are particularly suitable for pressureless sintering); and, (f) high throughput per reactor volume can be achieved. In addition, the process used for generating particles determines the degree of sintering ability of the powders, since the process dictates the morphologies, the purity and its size distribution. In the future, thermal plasma synthesis nanometer size particles may play an important role in vapor phase reaction techniques and might be expected to be one of the first full scale commercial installations in the future."

Jan 1, 1998

By Jiakai Zhang

Many postconsumer electrical and electronic equipment wastes contain a considerable amount of rare earth elements (REEs); however, the current level of REE recycling from them is limited (<1%). Neodymium–iron–boron (NdFeB) magnets, used at both small- and large-scale, from computer hard disk drives and small tools to wind turbines and cars, are a good example of such waste materials that contain high content of neodymium (Nd) and dysprosium (Dy). These elements are considered critical metals because they are the main building block of emerging green technologies that will allow for GHG emission reductions. Because demand for these green products is increasing around the world, the demand for REEs is increasing quickly, putting their supply at risk in the near future. Thus, it is critical to develop efficient, robust, and cost-effective processes to recycle these elements from this class of electronic waste materials. Here, we performed a thorough characterization of a N52–NdFeB magnet to identify its composition, crystal structure, and morphology. Furthermore, we developed an efficient hydrometallurgical process to extract Nd and Dy with high efficiency (more than 95%).

By Erwin Flender, Preben N. Hansen, Peter R. Sahm

"Until now FDM-Techniques have been widely used for Modeling Solidification Processes in Castings. Often a rigid, regular type of enmeshment (cubes, , --) have been used. This has the advantage of low CPU-costs, but the disadvantage of a zig-zag presentation of the interface between the casting and the mold. The last point is the reason why FEM-Techniques, giving the possibility of a true presentation of the shape in the enmeshment, are increasingly used. The disadvantage is the high CPU-costs. In this paper, a technique is presented, which uses the FDM-Mesh with the zig-zag presentation of shape and ADI-Algorithms to calculate temperatures and gradients. The new idea is that the calculated parameters are not presented related to the mesh in which they are calculated, but displayed using the true shape of the casting. Such an advantage of both low CPU-costs and shape correct presentation of the calculated results are achieved. IntroductionThe main reason for using a regular type of enmeshment is that it gives the possibility, via ADI-Algorithms, of obtaining a very fast FDM-Technique. The technique presented by P.R. Sahm and P. N. Hansen (1984), and also used by E. Flender (1985), is numerically so stable that average time steps, at least 200 times larger than the limit given by the explicit FDM-Technique, can be applied. To obtain reasonably good results, average time steps in the range of 20 to 50 times the explicit limit seems to be applicable. It should be pointed out,however, that FDM-Techniques can be used on arbitrary nets, the disadvantages being the same as for the FEM-Techniques. This has, among others, been discussed by P.R. Sahm and P.N. Hansen (1984)."

Jan 1, 1986

By William Petruk

The capabilities of SEM/image analyzers for determining quantitative mineral data which have a bearing on extractive metallurgy have given applied mineralogy a new dimension. The capabilities include automatic mineral identification, unattended operation, search for rare minerals, and measurements of (1) mineral quantities, (2) grain and particle size distributions, (3) liberation characteristics of minerals in ground ores, and (4) mineral associations. Data on mineral quantities define the distributions of elements among minerals, provide background information on characteristics of the samples, and provide a data base for a mineral-materials balance. Size analysis data of the minerals in unbroken ores are used to predict the grind required to liberate minerals. Data on liberation analysis can be used in many ways. One application is to process the image analysis data for feed, concentrate and tails by a materials balancing technique to calculate the recovery of liberated and unliberated grains at each point in a circuit. The calculated recovery data define the behaviour of an ore in a concentrator, pilot plant or bench test, and indicate whether recovery improvements are possible and/or feasible for a particular ore.

Jan 1, 1991

By A. Dutta, B. Devulapalli, A. Mukhopadhyay, E. W. Grald

"Computational Fluid Dynamics (CFO) has matured over the past two decades as an analysis tool for conducting virtual experiments with significant time and cost savings. It complements and reduces physical testing. CFO has penetrated the diverse materials industry in much the same way as Computer Aided Design (CAD) did more than a decade ago. As the basic numerical algorithms used in CFO have steadily improved, so have the reliability, consistency and user-friendliness improved significantly, too. Other recent trends have also contributed to the rapid growth and widespread adoption of CFO. In this presentation, CFO applications from several materials processing industries will be presented using case studies. Emphasis will be on metals, glass and semiconductor applications.IntroductionThe term materials processing covers a diverse array of industrial applications and products today. From the continuous casting of steel, to the deposition of semiconductor materials atom by atom, to the extrusion of molten polymers, materials processing applications span an incredible range of length scale, process times, pressures, temperatures and velocities. The properties of the materials themselves, in terms of density, viscosity, thermal conductivity, etc., can be complex functions of temperature, shear rate, chemical composition and time. And the processing equipment may be very complicated in geometric shape.Computational fluid dynamics (CFD), the technique of solving the governing equations of fluid motion and other related phenomena using a computer, has enjoyed widespread and rapid growth, which started in the aerospace and automotive industries. More recently, CFD has also been successfully applied to a great many materials processing problems, in spite of the challenges described in the previous paragraph. The reasons for the growing usage of CFD in materials processing are many. Using CFD to test design options and reduce the number of physical prototypes can decrease the time and cost associated with new product and process development. CFD gives insight and provides detailed predictions of operating conditions in lieu of difficult, intrusive and often expensive experimental methods. CFD can be used as an aid to scale-up processes from lab or pilot scale to full production. Troubleshooting the performance of existing equipment is often carried out with the help of CFD. Determining how an existing piece of process equipment will operate under new conditions, or with new input ,materials, is also a common task for CFD."

Jan 1, 2004