Search Documents

By R. W. Smith

The flotation response and electrokinetic behavior of Chlorella vulgaris and Chlamydomonas sp . when using dodecylamine hydrochloride as collector were studied in the absence and presence of Pb(I1). Also, an electron microscopy study was made of the algae after Pb accumulation. The flotation behavior of the organisms after Pb accumulation appears at least partially related to the location of the abstracted Pb onto or into the organisms.

Jan 1, 1991

By S. G. Kumar

Experimental studies on high carbon steelmaking through LD Converter - Vacuum Arc Degassing - Bottom Pouring route to produce low oxygen steels were carried out. The results indicated that it is possible to produce steel with a total oxygen content of less than 15 ppm. Thermodynamic and mass balance calculations are made on low-carbon steels that are treated by a complex deoxidation practice based on primary deoxidation of aluminum, manganese and silicon additions; followed by secondary deoxidation of vacuum degassing with simultaneous additions of aluminum. The results showed that primary deoxidation is mainly due to aluminum and the effect of carbon under reduced pressures on deoxidation of molten steel that is already killed by aluminum is negligible. The effect of process parameters on total oxygen content of steel, like carbon content, slag composition and inert gas purging, are discussed.

Jan 1, 1994

By Shadia J. Ikhmayies

Polycrystalline CdTe thin films were prepared by vacuum evaporation on glass substrates. The I-V plots which were linear were used to find the resistivity. A value of 2.10×106 .cm was obtained. The transmittance was measured in the wavelength range 400-1100 nm. The bandgap energy was found to be 1.48 eV. X-ray diffraction pattern shows that the material deposits in the zinc blend structure with one strong reflection from the C(111) plane. The scanning electron microscope image shows a uniform surface with a small density of large (mµ1£) grains scattered on the surface.

Jan 1, 2009

By M. Jennings

In 1987, Echo Bay discovered a major silver/gold ore body at their McCoy property in Nevada, and quickly made a decision to build a 5000 tpd mill which was expanded during the design to 7500 tpd. Since the ore reserves consisted of cyanide leachable oxide as well as sulfide, the plant flow sheet involved an oxide leach, a gravity circuit, and lead sulfide and a pyrite sulfide recovery by flotation. The paper describes the process development, equipment selection, plant design and the startup of the oxide treatment.

Jan 1, 1990

By Zhang Yongzhu

Developments on bioleaching of low grade ores and refractory gold ores by T. Ferrooxidans in China are summarized. Effect of the ions on bacterial growth, bioelectrochemical reaction mechanism of sulfide minerals and bacterial reaction mechanism are also discussed.

Jan 1, 1992

By Toyohisa Fujita

The effect of variables on the gold extraction with ammonium thiosulfate was investigated on sponge gold and ore samples. The Effects of CUS04, (NH4hS203, NH40H, (N~hS04' pH, stirring speed and retention on gold leaching rate and thiosulfate oxidation (consumption) have been studied. Almost 100% of gold was leached from sponge gold and over 96% from ore sample at optimum conditions. Trioctylmethyl ammonium chloride was used to recover gold from thiosulfate pregnant solution. It was found that more than 99% of gold was recovered by the extractant diluted with n-octane at 01 A ratio of 1: 1 without the re-adjustment of pH or others. Also, the gold cementation was conducted without de-aeration by using zinc, copper and aluminum powders. The result indicated that the gold was effectively recovered from a solution of low ammonia and copper concentrations and higher thiosulfate concentration. The gold recovery process by using ammonium thiosulfate is an environmental friendly method comparing to conventional cyanidation process.

Jan 1, 2003

By D. Van Dooren

The final goal of the research project is to develop a 3D FEM model that is able to predict the kinetics and micro-structural evolution during the bainitic transformation. The input parameters consist of thermodynamic and atomic mobility data obtained from the ThermoCalc and mCTRA databases combined with structural mechanics data extracted from the stress-strain curves of the fcc and bee phases. In this paper the general principles of the model are outlined and some interesting preliminary results are shown and commented. The full implementation of the model has presently not been achieved yet. In the model the bainitic transformation is considered as a sequence of martensitic (re)nucleation and growth of a ferritic subunit followed by the carbon rejection into the surrounding austenite. The (re)nucleation of the subunits will be described through a non-classical martensitic nucleation criterion. Once a nucleus has been activated at a specific location in the material, a full-sized subunit is instantaneously formed through a displacive mechanism. The stress state in the system that arises due to the transformation strain can be calculated by a 3D FEM programming code. Immediately after the formation of the subunit, another 3D FEM programming code calculates the carbon diffusion from the supersaturated ferrite into the surrounding austenite. The resulting stress state and carbon profiles will be used to determine where and when a new subunit will nucleate based on a renucleation criterion. Keywords: Bainitic Transformation, Modeling, Eshelby, Carbon Diffusion

Jan 1, 2003

By P. M. Tyroler

At INCO's Copper Cliff Nickel Refinery, nickel is extracted by using the INCO Pressure Carbonyl (IPC) process. The resulting IPC residue containing copper, nickel, cobalt, iron, sulphur, precious metals, selenium and tellurium is further processed at a hydrometallurgical plant. This plant treats approximately fifty metric tons per day of IPC residue. The components of the feed are separated in a number of steps and a precious metals concentrate, nickel-cobalt carbonate, a selenium-tellurium intermediate and copper cathodes are produced. An iron-arsenic waste stream is also produced and discarded to tailings. The hydrometallurgical processes include pres- sure leaching, cementation, precipitation, thickening, filtration and electrowinning. This paper describes in detail the individual steps of the flowsheet.

Jan 1, 1988

By Andrzej Warczok

Liquid slags produced in smelting of copper concentrates contain copper in a dissolved form as well as mechanically entrained inclusions of copper matte. Coalescence and sedimentation of inclusions during slag cleaning plays a key role in copper recovery. Liquid matte inclusion in a molten slag presents a system of metallic conductor in an ionic solution. Constant electric field induces migration of the matte droplet along the current lines. Additional phenomena occur in a system under crossed electric and magnetic fields. Electromagnetic buoyancy force acting on the inclusion affects its settling rate. Electromagnetic buoyancy force of insulating and metal spheres has been measured in a liquid synthetic slag. It was found that depolarisation of the metal sphere, related to the electrode reactions occurring in the surface, plays an important role in the determination of the direction and magnitude of the electromagnetic force. On the basis of the existing theories and results of measurements a mathematical model describing the behaviour of metallic inclusions in the liquid slag under the influence of crossed electric and magnetic fields was developed. Simulation of behaviour of copper matte inclusions under crossed fields showed trajectory of motion in a liquid slag as a function of the slag properties and the inclusion size.

Jan 1, 2003

By Fujio Ishii

The deoxidation of liquid nickel and nickel binary alloys with silicon has been determined at temperatures between 1500°C and 1650°C using quartz crucibles in order to investigate the deoxidation of nickel based alloys. The equilibrium constant of the deoxidation reaction in liquid nickel and the effects of the different alloying elements such as chromium, molybdenum, tungsten, iron, cobalt and coppcr on the activity coefficient of oxygen in liquid nickel have been established.

Jan 1, 1993

By Z. M. Zheng

Cyclic voltammetry, potential step, and ac impedance techniques were applied to study the electrochemical reaction of arsenopyrite in chloride solutions. The relationship between anodic current density and time in potential step measurements indicates that the oxidation of arsenopyrite is irreversible. The results of the constant potential coulometry show that the stoichiometric factor of the total electron involved in the overall reaction is 14. It is proposed that the dissolution of arsenopyrite is retarded by coverage of sulfur produced in the reaction as an intermediate product. The measured results of ac impedance strongly support the proposition. The proposed reaction mechanism also explains satisfactorily the charging current density and Tafel slopes measured in potential step measurements.

Jan 1, 1995

By Milton Manrique

The thermal decomposition of zircon concentrates in a non-transferred arc thermal plasma flow reactor was investigated. The plasma torch was operated using argon-helium and argon-nitrogen mixtures as plasma gases. The effect of power, feed rate and zircon particle size was studied. Products were characterized by XRD, SEM, TEM and chemical analytical techniques. The average size of the product was in the submicron range. Free energy minimization plots were used to predict the behavior of the system under different operating conditions. A kinetic model to describe the different stages of the thermal decomposition process is proposed. The results of this investigation showed a significant segregation process where the zirconia-rich product is collected in the reactor while the silica-rich product is collected in the filter. TEM analysis indicated that silica vapor is condensed on the surface of the zirconia particles.

Jan 1, 1996

By Drew Sinha

Success of the environmentally benign semiconductor manufacturing depends on the cost-effective integration of the principles of reduce, recover, reuse and recycle from source material to final product disposal. Increasing demand combined with current shortage of polysilicon provided unique opportunities to recover the silicon waste, caused by various defects, in wafer manufacturing process. Current practices relating to recovery and reuse of waste silicon produced, from crystal growth process to finally polished and epitaxially deposited silicon wafer, at Mitsubishi Silicon America is presented. Future plan to recycle the process generated silicon fines produced during the intermediate steps of the wafer manufacturing process such as grinding, slicing, lapping and polishing is also discussed.

Jan 1, 1998

By F. J. Hogan

In early 1982 Atlantic Cement Company, a wholly-owned subsidiary of Newmont Mining Corp. will come on line with a new water granulating grinding facility at Sparrows Point, Maryland to produce 800, 000 tons a year of separately ground granulated blast-furnace slag. The process and product will be unique to the United States. This paper will review some initial investigations undertaken to evaluate the cementitious properties of granulated slag. The effect of slag fineness on strength development is discussed and data is presented showing a relationship between glass content and hydraulicity and grindability of slag.

Jan 1, 1982

By Hebi Yin

A coupled cellular automaton (CA) - finite element (FE) model was developed to calculate the growth of dendrites during the solidification of cubic and hexagonal metals. The model solves the conservation equations of mass, energy and solutes in order to calculate the temperature field, solute concentration and the growth morphology of dendrites, including the grain structure and the dendritic microstructure. Validation of the model was performed by comparing the simulation results with calculation results from previously published works, showing qualitatively good agreement in the dendritic morphology. Application to magnesium alloy AZ91 illustrates the difficulty of modeling dendrite growth in hexagonal systems, observed as deviations in growth direction caused by mesh-induced anisotropy. The model was applied to the simulation of small specimens with single- and multiple- equiaxed grain growths and columnar grain growth in directional solidification. The influence of cooling rate and some kinetics parameters on the grain morphology are also discussed.

Jan 1, 2009

By R. Hurman Eric

Within the Ag-Pb-S ternary system, the boundaries of the immiscibility region together with the tie-line distributions were re-established at 925°C by the equilibrium-quenching technique where samples were kept in evacuated and sealed silica capsules. Activities of Pb were measured by the dew-point method along the Ag-Pb binary at 925°C, 1100° and 1200°C. positive deviations were observed and the results were modeled by the Krupkowski formalism. Activities of Ag, Pb, and S, along the ternary miscibility gap were calculated at 925°C by utilizing the boundaries binary thermodynamics, phase equilibria and tie-lines. Activities of PbS within the pseudobinary Ag2S-PbS mattes were also measured by the dew-point technique and the results were again modeled by the Krupkowski formation Where negative deviations were observed.

Jan 1, 2003

By R. Hurman Eric

Within the Ag-Pb-S ternary system, the boundaries of the immiscibility region together with the tie-line distributions were re-established at 925°C by the equilibrium-quenching technique where samples were kept in evacuated and sealed silica capsules. Activities of Pb were measured by the dew-point method along the Ag-Pb binary at 925°C, 1100° and l200°C, positive deviations were observed and the results were modeled by the Krupkowski formalism. Activities of Ag, Pb, and S, along the ternary miscibility gap were calculated at 925°C by utilizing the boundaries binary thermodynamics, phase equilibria and tie-lines. Activities of PbS within the pseudobinary Ag2S-PbS mattes were also measured by the dew-point technique and the results were again modeled by the Krupkowski formation where negative deviations were observed.

Jan 1, 2003

By Shawn A. Cefalu, Matthew J. M. Krane, Kent J. VanEvery

"Segregation during electroslag remelting (ESR) of a nickel-chromium-molybdenum alloy (Ni-8 wt% Cr-25 wt% Mo) has been modeled. Features of the model include species transport and AC electromagnetic effects coupled with fluid flow, heat transfer, and solidification. The effect of varying ingot diameter and melt rate, on macrosegregation patterns, local solidification time, and liquid pool profiles obtained from this model are demonstrated. The results show that the macrosegregation in the ingots correlates to the filling velocity.IntroductionElectroslag remelting (ESR) is a secondary melting process used to refine the chemical composition and the microstructure of metals. Macrosegregation of solute elements causes defects in ESR ingots, including freckles and the maldistribution of phases. These defects are not correctable through heat treatment due to the large length scales over which they occur. However, the frequency and distribution of these defects may be minimized, or even prevented, through process control based on an understanding of the conditions that lead to their formation.In the past, studies have been conducted on the effect of the process parameters on the shape of the melt pool and the thickness of the mushy zone [1-7]. In these studies, the shape of the liquid pool is determined by consideration of the heat and fluid flow induced by electromagnetic (Lorentz) force and thermal buoyancy. The transport of solute and the resultant solutal buoyancy effects were not considered in these macroscopic models. Defect formation is tied to formation of secondary phases (e.g., freckling and white spots in nickel superalloys) [5,8]. In cases where secondary phase formation is calculated (e.g., [6]), phase fractions are determined using a micro-scale model given the local solidification time (LST) and local thermal history from the macroscale model.Using the local thermal history from the macroscopic transport model to predict microstructure increases the importance of the accuracy of those results. This investigation models the macrosegregation of molybdenum during the ESR of a Ni-Cr-Mo alloy. The effect of macrosegregation on pool shape and depth is demonstrated, along with its effect on the local solidification time. By comparing the relative effects of the melt rate and ingot radius, a better understanding of the factors that affect macrosegregation, and ultimately secondary phase formation may be obtained."

Jan 1, 2004

By Vadym Drozd, Yongzhou Sun, Shah Najiba, Jiuhua Chen, Andriy Durygin

"Phase transitions of the potential hydrogen storage compound, ammonia borane (NH3.BH3), was investigated using Raman spectroscopy and a diamond anvil cell at high pressures up to 9.5 GPa and low temperatures down to 90K. At room temperature, ammonia borane has three phase transitions in this pressure range. Upon cooling, four new phases were discovered through changes in characteristic Raman spectra. This result provides information about the stability of new bonding characteristics of this potential hydrogen storage material at low temperature and high pressure region.IntroductionDevelopment of hydrogen technology requires the safe, efficient and environmental friendly materials for hydrogen storage and hydrides have attracted much attention as hydrogen storage media. Among chemical hydrides, ammonia borane (BH3NH3) stands out due to its high gravimetric and volumetric hydrogen density ' "". Despite high hydrogen content, this compound is very stable. It releases hydrogen in several steps by thermal decomposition in the temperature range of 100°C to 500°C. Direct thermal decomposition also causes toxic borazine emission. Recent research interests on ammonia borane include destabilizing this compound to lower the dehydrogenation temperature with an enhanced hydrogen release rate using different techniques, e.g. the nanoscaffolds'', ionic liquids"" and acid'"" or transition metal catalysts' ""'. As a molecule of ammonia borane consists of protonic (NH) and hydritic (BH) hydrogens bonded by the polarized dative bond, thermal or catalyzed decomposition requires breaking of N-H and B-H bonding. Still now, the detailed information about the bonding characteristics of ammonia borane is not sufficient to understand details about its phases and structures. The development of methods to enhance hydrogen discharge rate from ammonia borane requires a detailed study about the structural and dynamical properties that control the stability and the intermolecular interactions of this material. This study is motivated to investigate the stability of the existing phases and also to explore the existence of any new phases at different temperatures and pressures which may have enhanced hydrogen release and uptake properties."

Jan 1, 2012

By Bingliang Gao, Junli Xu, Michal Korenko, Jinzhao Guan, Liangxing Li, Zhongning Shi, Zhaowen Wang, Aimin Liu

Al-Si alloy, a precursor of solar grade silicon, was prepared by direct electrolysis in cryolite molten salt at 950 oC using high purity silica as material, liquid aluminum as the cathode and high purity graphite as the anode. The electrochemical behavior of Si(IV) ion was investigated using cyclic voltammetry method. The electrolysis products were characterized by XRD, SEM/EDS and ICP. The results indicate that the reduction process of Si(IV) on tungsten electrode is a two-step process and there is about 0.6 V gap between the two steps. The contents of boron and phosphorus in the aluminum-silicon alloy are 3 ppmw and 8 ppmw, which will make the directional solidification purification effectively and reduce the cost of preparation solar grade silicon from metallurgical grade silicon.

Jan 1, 2015