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By A. S. Usrnani

Due to both turbulence and the highly variable geometry of castings, a realistic numerical simulation of the metal flow is prohibitvely expensive with current technology. However, when the chief purpose is to achieve realistic thermal fields a precise How simulation is not necessarily required. In this paper we assume a laminar flow regime and obtain the flow field by solving the incompressible Navier-Stokes Equations using a velocity-pressure segregated semi-implicit finite element method. The free metal surface is predicted by advecting a pseudo-concentration function via the computed How field. This involves an explicit finite element solution of a pure advection equation. The thermal field is calculated by solving the convective-diffusive energy equation by an explicit finite element method using the computed flow field and the location of the free surface. All the advection terms are discretized using a Taylor-Galerkin method. The interface between the metal and mould is modelled using special interface elements. The model is demonstrated by solving practical example problems. The results show that a sharp thermal front is maintained during the course of filling without excessive diffusion. The heat diffusion in the mould can be controlled by varying the metal mould heat transfer coefficient.

Jan 1, 1994

By Muhammad A. Imam, Ramana G. Reddy

This study provides a reasonable evaluation of the Mg-B binary system. Magnesium and Boron (Mg-B) alloys were investigated to determine their thermodynamic properties employing solid state electrochemical cells based on CaF2 electrolyte represented as –Pt; Ar= MgþCaMgF4 f gCaF2 k kf½Mg B alloy þ CaMgF4 g=Ar; Pt+ Investigations were performed over the temperature range of 773–873 K to measure the electromotive force (EMF), which was used to derive the partial Gibbs Free energies of the alloys in the composition range of XB = 0.07 to 0.95. The activities of Mg were also calculated from partial Gibbs Free energies. The activities of Mg in MgB2, MgB4, and MgB7 were expressed as a function of temperature respectively, ln aMg = 4.27–9.32 × 103/T, ln aMg = −7.54 + 6.67×103/T, and ln aMg = 4.93–19.57 × 103/T, where T is the temperature in K. From this expression, the activity of Mg for these intermediate phases can be extrapolated at a higher temperature to get the accurate phase boundaries for the Mg-B system.

Mar 1, 2017

By Guy Deschênes

In spite of the wide use of lead compounds to enhance cyanidation of free milling sulphide-bearing gold ores, an industrial control method was only implemented four years ago. This study presents the results of the investigation that led to the development of the on-line control technology. Two free milling sulphide-bearing gold ores and high purity minerals were used to develop and test the concept. The first ore contains 2.8 g/t Au, 6.2% pyrrhotite, 2.1% pyrite 0.6 % arsenopyrite, 0.1% chalcopyrite and 0.1% organic carbon. The second ore contains 10.4 g/t Au, 3.2% pyrite, 0.8% pyrrhotite and 0.38% chalcopyrite. The first ore showed a much higher oxidation rate in the pre-leach than the second one and consumed seven times more cyanide. A relation between the formation of thiosulphate and thiocyanate and the additions of lead nitrate were quantified. The ?reducing power?, a titration with permanganate, predominantly determines the concentration of thiosulphate and thiocyanate in cyanide solution. The relation between the reducing power and the addition of lead nitrate at various concentrations of pyrrhotite and chalcopyrite in the ores was established, providing a monitor/control strategy for lead nitrate addition.

Jan 1, 2006

By H. Itou, J. M. Toguri, T. Takasu

"Marangoni convection has a large effect on materials processing since it remarkably enhances heat and mass transport near a free interface. To have a better understanding of the behavior of Marangoni convection in molten salts, observation and calculation of the thermal convection in a column held between a pair of Pt disks (2mm in diameter) fixed to hot thermocouples, were carried out.Calculated flow patterns and absolute values of fluid velocity agreed well with the observed results. When the temperatures of both disks were set equal and the height of liquid column was 2.4mm, four vortexes were generated on the longitudinal plane with a typical velocity of 15mm/s . From the calculated isothermal lines, the behavior of the enhanced heat transport was obvious; fluid heated at the disks was conveyed to the free surface and the cooled fluid at the surface was conveyed to the inner region. Increase in the height of column and/or increase in the absolute value of applied temperature difference lead to increase in fluid velocity lineally in this calculation range.IntroductionIn the processing of many materials, fluid flow of melts has a large effect on refining capabilities and on the characteristics of the produced material. Marangoni convection is generated when a spatial gradient of interfacial tension exists on the free interface due to differences in temperature and/or concentration. This promotes heat and mass transfer locally near the interface.For example, Marangoni convection which are created following the dissolution of interfacially active materials, increases the local corrosion rate of refractories (1-3). In absorption and discharge of oxygen and/or nitrogen in a molten metal, the effective reaction rate of the gas components through the gas-liquid interface increases (4-7). Also in crystal growth, the distribution of defects and impurities in the crystal is affected and this can alter its quality (8-11 ). The temperature distribution is also affected and can greatly change the productivity. For these reasons, the effectiveness of Marangoni convection in refining should be quantitatively clarified and its control should be better understood."

Jan 1, 1997

By Sudhir C. Dhara

An attempt has been made on the concentration of Platinum Group Metals (PGM) from the converter matte material by microbial .leaching. Biological oxidation of base metal sulfides such as iron, copper, nickel and free sulfur present in the matte material using Thiobacillus ferrooxidans is an alternative method to concentrate the PGM-and gold. The method which produces a platinum group metals concentrate is comparable to chemical processes and electrochemical process.

Jan 1, 1995

By Michael L. Sorokin

The various methods of converter slag cleaning operation are analysed from the thermodynamk point of view: cleaning using coal, cleaning using combustion products of natural gas and cleaning in presence of matte. All calculations were done, applying the developing computer procedure based on the free energy minimisation algorithm. Three-suffix Margules equations were used to calculate thermodynamic properties of melts; The calculations resulted in recommendations for the practical appliance.

Jan 1, 1995

By Alexander I. Raitchenko

"An electroconductive viscous liquid may flow in laminar or turbulent regime under Lorentz-force generated by the intercrossed electric current and magnetic field. When there is a starting flat layer between hard and free boundaries with surface tension the spatial Lorentz-force can create a specific stationary regime of flow: the plane free surface will transform into the wavy one, and the movement in the depth will be not laminar and not turbulent, but this regime will be characterized by organized forms with indications of ""rolling of long cylindrical drops"". Wave-length is determined by the viscosity, the density, the surface tension, the average thickness of layer, and Lorentz-force. ·The limit of wavy regime is determined by most long of wave which is directly proportional to the critical value of specific flow and inversely proportional to the kinetic viscosity. The proper critical value of Reynolds number is determined by the dimensionless combination containing surface tension, density, viscosity, and Lorentz-force. The mentioned dimensio.nless combination in our case is some criterion substituting the known Kapitsa number for case of the thin viscous liquid layers under gravity. Spreading of admixture by mechanism of wavy regime is more rapid than by common diffusion or by laminar flow. The suggested conception can be a contribution into the theoretical basis for elaboration of some specific liquid metals technologies."

Jan 1, 1999

By Angus Hellawell

The application of the common tangent principle to free energy - composition surfaces is considered. It is shown that the construction requires that single phase surfaces on either side of a two phase volume must always exhibit the same sign of curvature - contrary to that shown in many published phase diagrams. In general, these curvatures will be such that the surfaces are mutually concave towards the more stable phase. A number of examples are discussed.

Jan 1, 1991

By Michael G. Mayer

Since its invention in 1859 various designs of lead batteries have evolved to meet commercial needs for traction applications and standby power. In recent years major developments have taken place in lead alloys and the chemistry and mechanical design of industrial lead batteries. These are reviewed in relation to their commercial application together with the new type of maintenance free gas re-combination lead-acid batteries which are opening so many new markets for lead.

Jan 1, 1990

By Xiang-dong XING, Zhen-yang wang, Jian-Liang Zhang

Distribution behavior of titanium between CaO-SiO2-MgO-Al2O3-TiO2 and hot metal was studied between 1350 °C to 1600 °C. Experimental results indicate that the reaction temperature influenced the activity coefficients of titanium and resulted in the variation of equilibrium constant. Finally, the Gibbs free energy formula of titanium carbothermic reduction was fit out using the thermodynamic model of Wagner and congregated electron phase models.

Jan 1, 2015

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

By N. Mizutani, S. Harada, Z. Asaki, T. Tanabe

"The development of lead-free solders is urgent in view of environmental standpoints. In this -work the wettability of tin-bismuth- silver solders on copper was studied. Three kinds of fluxes were used. The wettability of conventional eutectic tin-lead .solder exhibited an excellent level over the other solders of tin-bismuth systems. Poor wettability of the tin-bismuth solders may be caused by the growth or dendritic copper-tin compounds at copper/solder interface, in contrast to the case of tin-lead'· solder. The wettability was improved by the addition· of silver in the solder. In this tin bismuth- silver system, silver was abnormally concentrated at the copper I solder interface even in the initial stage of contact. The wettability of the solder and the thickness of compound formed on the copper have a good correlation; the solder containing 2% silver exhibited the best wettability and the formation rate of copper-tin· compound on the copper was slowest.IntroductionSocial demand to avoid lead use in the industrial fields has been recently promoted· (1) because of the environmental protection of water resources. Especially the lead-bearing solders have been widely used in electronics and automobile products, and it is urgent to replace them with nontoxic materials (2)-(4). Thus the development of lead-free solders becomes an indispensable subject to the new generations and many works (5)(6) have already been carried out on the research and development of new solders. New lead-free solders are expected to have some requirements, for example, moderate melting temperature, proper strength and integrity, and lower prices, as compared with conventional solders. There have been already several alloy systems developed. Among ·these alloy systems, tin-bismuth binary or tin-bismuth-silver ternary alloys have great advantages such as having a wide range of soldering .temperature by controlling con:ipositions, though they have such disadvantages as ""lift-off"" (7)-(9): It is said, on the other hand, that a frequently overlooked property of solders, or one that is typically ignored by the research scientist as an ""issue"" for the manufacturing or product engineer, is wettability (10), although a ·work on the wettability has recently been published (11). In this Work, therefore, the authors selected Sn-Bi-Ag solders and focused mi the effect of Ag-addition to wettability of the solder."

Jan 1, 2000

By M. Neises, M. Roeb, C. Sattler, S. Stenger

"A two-step thermo-chemical cycle process has been developed and investigated. It is based on metal oxide redox pair systems, which can split carbon dioxide as well as water molecules by extracting oxygen atoms and reversibly incorporating them into their lattice. If concentrated solar radiation is used as the heat source, a promising method exists to produce synthesis gas from water and CO2. An easy way of operation is gained by the combination of a ceramic substrate as the absorber structure, which can be heated to high temperatures with concentrated solar radiation, and of a metal oxide coating which is capable to carry out the redox reactions. The performance and kinetics of a ferrite based redox material coated on ceramic substrates were investigated in a laboratory set-up. CO2 could be reduced with significant conversions. In addition, several side reactions were observed like the formation of carbon and like the Boudouard reaction.IntroductionThe search for alternative energy carriers and for processes able to reuse carbon dioxide stimulates the research for sustainable routes of alternative fuel production. In the scope of this search thermo-chemical processes combined with sources of concentrated solar energy have become more and more attractive. Ideally, the only raw materials for such processes are water (H2O) and carbon dioxide (CO2) enabling not only a process free of emissions, but also allow to reduce emissions of other processes by reusing CO2 to provide synthesis gas, which itself can be applied to produce chemical commodities or even better synthetic fuels like methanol or petrol.In contrast to the direct splitting of those raw materials, thermochemical cycles split water and CO2 in several steps and enable hydrogen (H2) and carbon monoxide (CO) generation at temperatures controllable by today’s technical equipment. One of the most interesting thermochemical cycles is a two-step process using metal oxide based redox systems. During the first step of this cycle (the regeneration step) the metal oxide is reduced setting some of its lattice oxygen free according to reaction (1). In the next step (the splitting) the reduced and activated material is oxidised by withdrawing oxygen from water and CO2 and at the same time hydrogen and CO is set free according to reactions (2a) and (2b) respectively."

Jan 1, 2011

By David G. Dixon, Maziar Eghbalnia

"Gold and silver nanoparticles (NPs) were deposited on pyrite at ambient temperature from colloidal solutions prepared by reduction of hydrogen tetrachloroaurate or silver nitrate by sodium sulfide or sodium tetrahydridoborate. The nanoparticles were characterized using Ultraviolet-Visible (UV-Vis) spectroscopy and the experimental spectra were fitted using Mie - Gans modeling. The modified pyrite was investigated using Electrochemical Impedance Spectroscopy (EIS). Electrodes were prepared from both natural and modified pyrite samples and were modeled using an equivalent circuit (EC) based on the EIS data. The comparison of the results revealed a decrease in charge transfer resistance for the ferric ferrous redox couple associated with the modified pyrite. From this behavior it is concluded that the electronic transport between the nanoparticles and the electrode surface over distances in nanometer scale is enhanced. Nanoparticles below a certain size act as quantum dots due to electronic confmement. Decreased charged transfer resistance at the nanometer scale may be caused by electron transport through tunneling mechanism via quantum dots.IntroductionIn recent years, considerable attention has been focused on the synthesis and study of Metal nanoparticles due to their potential applications in the fields of physics, chemistry, biology, medicine, material science and their interdisciplinary fields[!]. When material is nano-sized, the physical properties deviate markedly from those of bulk material, however, this effect is highly dependent on the particle size, interparticle distance, and morphology of the nanoparticles [2].An extremely small region of space defmed in a semiconductor material in order of nanometers is called a quantum dot, a term coined by Reed [3]. The three dimensional confinement of quantum dots can change properties of the excitons in comparison to free excitons in a bulk material [4]. Nanoparticles behave electronically as zero-dimensional (restricted in all three dimensions) quantum dots when the de Broglie wavelength of the valence electrons and the particle are in the same size range.As Reed [3] explains electrons confined in a plane have no freedom to move the third dimension. Those confined in a quantum wire are only free to move in one dimension, and those confined in a quantum dot are not free in to move in any dimension. An electron inside a cube of material IO nm on a side is confined to a point."

Jan 1, 2012

By R. G. Robins

Metal separations based on the selective precipitation of phosphates have a potential application in many hydrometallurgical processes. This paper reviews the literature on the solubility of a number of both divalent and trivalent metal phosphates and presents the result of some additional experimental measurements. The systems examined have been modelled to obtain free energy of formation data for the various species. Computer generated solubility diagrams which are described can be useful in predicting a variety of metal separations.

Jan 1, 1991

By Patrick R. Taylor

Coatings of TiCIFe have been produced by Reactive Plasma Spraying using ilmenite ore concentrate as the feedstock powder and methane as the reactive gas. A free energy minimization analysis of the ilmenite-methane system is presented. The coatings have been characterized by x-ray diffraction and SEM. The microstructure of the coatings indicates good interparticle cohesion. The composition of the coating is deficient in iron compared to the initial Fe to Ti ratio found in ilmenite.

Jan 1, 1998

By S. N. Sinha

The distribution coefficients of lead and silver between copper and matte phases have been measured at two different temperatures. Experiments covered the ranges of 0.009-1.8, 0.07-0.13, and 0-11 wt pct lead, silver, and iron in matte, respectively. The distribution coefficients of lead have been measured at 1405 and 1505 K and correlated with lead and iron concentrations in metallic copper and matte. The values of the distribution coef¬ficient of lead between copper and iron-free matte, at infinite dilution of lead, have been determined to be 3.60 and 4,06 at 1505 and 1405 K, respectively. The distribution coefficient of silver between copper and iron-free matte is independent of silver concentrations and has been measured to be 2.13 and 2.21 at 1400 and 1500 K, respectively. For an iron-bearing matte, the distribution coefficient of silver has been correlated with iron concentration in the matte at both 1400 and 1500 K. From the measured values of distribution coefficients, the Raoultian activity coefficients of PbS and AgS0.5 in copper-saturated matte have been calculated. At infinite dilution, the following equations correlating the Raoultian activity coeffici¬ents of PbS and AgS0.5 with matte- composition and temperature have been obtained: log Y° PbS =1.515 + 1080/T 0.14 NFes lbS Fog YAgS = -0.074 - 425/T + 0.09 NFes. - 0.5

Jan 1, 1983

By Debbie Marshall

Nickel and cobalt in lateritic ores can be extracted by either a hydrometallurgical or a pyrometallurgical route. The high-iron limonitic fraction of a deposit is best processed' hydrometallurgically while the magnesium-rich transitional and saprolitic fractions are more suited for pyrometallurgical processing. During hydrometallurgical processing, it may be attractive, for economic reasons, to blend the limonitic component with transitional and saprolitic ores, which contain higher nickel levels. However, blending increases the concentration of magnesium in the feed, leading to increased acid demands. The decision on how much ore to process then becomes an economic one. Ore samples with different magnesium contents were prepared for the leach test program by blending limonitic and transitional ores. The ore samples were slurried in seawater and tested in the Falconbridge Hydrometallurgical Pilot Plant. As expected, acid consumption increased with increasing magnesium content of the ore. For target extractions of 95% nickel and 92% cobalt, the required residual free acid concentration increased from 30 g/L at 1.7% magnesium to 50 g/L at 2.7% magnesium. When the magnesium content was raised to 3.8% and 4.6% in subsequent pilot plant testing, the final free acid requirements did not increase beyond what was observed at 2.7% magnesium. Thus, the cut-off ore composition to maximize nickel units and minimize acid requirements is between 1.7- 2.7% magnesium. Keywords: high pressure acid leaching, laterites, magnesium

Jan 1, 2004

By William Petruk

A fully automatic image analysis system that consists of a microprobe, an energy dispersive x-ray analyzer, and an image analyzer was developed at CANME:I' to determine mineral behaviour that affects beneficiation. The interlacing between the instruments permits automatic identification and characterization of minerals in samples of unbroken ore pieces and of mill products. Different types of information are obtained for minerals in samples of unbroken ore pieces than in samples of mill products, and are used differently. For unbroken ore pieces size distributions are determined for discrete mineral grains to predict a grind at which they might be liberated, and other measurements are Irade to predict the percentage of mineral that occurs as nonrecoverable grains. For mill products the minerals are analysed to determine percentages that (1) are free, (2) are likely to be recovered in concentrates, (3) are likely to be lost to tailings, and (4) could be liberated with regrinding. The image analysis data for mill products are processed by a mineral-metals balance program to determine the distributions of free and unliberated mineral grains at each point in a concentrator, pilot plant or bench test. For samples containing trace minerals, such as gold, an automatic search technique is used to scan the entire area of the polished section for the trace mineral grains. The identified trace mineral grains are characterized with regard to size, liberation, and other properties.

Jan 1, 1988

By F. Rivard, L. Rao, P. Carabin

"Advances in thermal plasma torches have resulted in this technology becoming a commercially viable solution for chemical and metallurgical processes. The main advantages of plasma are its ability to control process chemistry and to build small footprint reactors due to its high energy density and reactivity of the free radicals that are produced. This paper focuses on thermal plasmas produced by DC torches and their applications for waste treatment, production of high purity metals, and nanomaterials. Both transferred and non-transferred torches have been used as either a source of heat or as a reagent in various industrial processes. Retrofitting plasma torches in place of fuel oil burners lead to lower operating costs, capital cost and greenhouse gas emissions.INTRODUCTIONPlasma technology has become an ideal solution for many industrial chemical, metallurgical and mechanical processes [!]. Thermal plasma powered systems are typical used for their unique characteristics such as high energy densities, high temperatures, small installation sizes, rapid start-up and shutdown features, controlled process chemistry and use of electrical energy as a heating source resulting in decoupling the heat source from the oxygen flow rate [2]. Depending on the nature of the main plasma forming gas used, thermal plasma systems offer a high temperature heating source coupled with a highly reactive plasma plume rich in free radicals and ions which promote otherwise hard to drive chemical reactions, as well as high heat transfer rates."

Jan 1, 2013