Search Documents

By Teruhisa HORITA

The durability of SOFCs is one of the critical issues to realize the SOFC systems. In order to improve the durability, a precise degradation mechanism should be clarified at the different functional ceramic interfaces in SOFC cells and stacks. This paper reviews the improvement of SOFC durability by the mass transport analysis especially at cathode/interlayer/electrolyte interfaces. We have made a precise analysis on the reaction of cathode with impurities. Especially at the (La,Sr)(Co,Fe)O3/CeO2/ZrO2 interfaces, a significant amount of SrCrO4 and SrSO4 were observed at the (La,Sr)(Co,Fe)O3 surface as well as inside the (La,Sr)(Co,Fe)O3 cathode, which suggested some process occurred for both poisoning. Possible degradation mechanisms were proposed based on the observation data.

Jan 1, 2016

By Guo Chen, Jin Chen, Jinhui Peng

In this paper, solving common problem of electrostatic precipitator (ESP), which was frequently ruptured of the cathode insulation in the production process were studied. The microwave heating airflow technology was introduced, which takes full advantage of its unique properties, solves the output problem of the high temperature air, achieves purpose of energy conservation, important economic significance and environmental significance. The mathematical models and designing of microwave high-temperature hot air system was calculated. The common forms of heat exchangers and comparative analysis were also introduced. The conditions found to be at the temperature of 240 °C. Under optimum conditions, the microwave heating power was 1482 W. Based on the mention results, this microwave heating method can be applied effectively and efficiently way for the production process of electrostatic precipitator.

Jan 1, 2015

By W. Murray Small

Nickel plays an important role in determining the properties of many stainless steels and superalloys. Cobalt also contributes significantly to the performance of certain grades of superalloys. A major technical aspect, in which both of these metallic elements are involved, concerns the solubility of nitrogen in these classes of alloys. Beyond certain content limits, dissolved nitrogen may contribute to the deleterious mechanical behavior by these alloys. It is therefore essential to control the level of this element during alloy processing. In this paper, results from several experimental studies have been assembled and are analyzed to describe phenomena related to the individual effects of nickel and cobalt on the solution of nitrogen in several groups of alloys. Both solid and liquid alloy systems are considered. This information may be used as a guide to limit or control the presence of this interstitial element in alloys.

Jan 1, 1993

By B. Erik Ydstie, Dimitrios I. Gerogiorgis, Sridhar S. Seetharaman

"Carbothermic production of aluminium is an important alternative to electrolytic processes and has in fact been identified several decades ago as a potentially feasible and profitable process. The cornerstone principle is to take advantage of the endothermic reduction reaction between carbon and alumina instead of resorting to extreme amounts of electric energy to ionize and reduce aluminium oxide to aluminium. Electric energy is necessary only for heating purposes.The present study focuses on constructing and solving a steady-state electrothermic model for obtaining the spatial distributions for electric potential, electric field intensity and temperature. The complex issues of reaction kinetics and multiphase flow are handled by an approximation and are not addressed at the present stage, due to the lack of complete validated models. Because of its inherent complexity, the reaction slag is considered a pseudohomogeneous layer.An electrothermic simulation encompasses important research challenges, due to the limited knowledge of thermophysical properties for high-temperature multi component molten slags. Therefore, thermophysical property modeling and a systematic compilation of published data is a necessary and major first step towards enhancing understanding of the process fundamentals. Models are obtained by analyzing measurement data from numerous literature references for the density, viscosity, thermal and electrical conductivity and specific heat capacity of the slag.The electric potential, field intensity and temperature distributions obtained reveal interesting maxima which indicate localized superheating and lead to important engineering conclusions. The temperature profile calculated will serve as the foundation for the flow problem solution. This computational study will form a basis for future research towards combining the scopes of microscale CFD modeling and mesoscale process modeling into a unified modeling approach."

Jan 1, 2001

By L. Béjar-Gómez

The aim of this research work is to study and characterize the precipitates in structural microalloyed steel by transmission electron microscopy and analysis by low resolution. Microalloyed steel with niobium was produced by casting in an electrical induction oven of 25 Kg capacity. Carbon content in steel was less than 0.1 % and 0.036% of niobium. Steel was processed thermomechanically; reheated to 1250 °C and hot rolled on a laboratory mill to a 13.0 mm thick plate with a finish rolling temperature of 900ºC and a thickness reduction of 80% . This work shows what precipitates are present in steel, the type of precipitates and their morphology. Analysis by transmission electron microscopy of low resolution was applied to obtain the chemical analysis of precipitates and the matrix. Spectroscopy of dispersive energy (STEM - EDS) was applied to obtain the element profile of precipitates. Particles of precipitates of NbC were found; with cubic morphology and size from 70 to 130 nm, circular morphology and size from 10 to 70 nm, polygonal morphology and size from 10 to 80 nm.

Jan 1, 2006

By G. A. Irons, G. S. Hanumanth

A three-dimensional mathematical model for the electric furnace of Cominco's Kivcet process was developed to compute the electric field intensity, power dissipation, temperature and velocity distributions in the furnace. A number of simulations of the electric furnace operation were carried out for various electrode immersion depths and electrode currents. The results showed that the current penetrated the bullion layer, generating high current densities in a layer approximately 0.3 m thick located in the slag/bullion interface region. An increase in the electrode immersion depth increased the furnace power as well as slag temperatures, and generated more vigorous bubble stirring and thermal homogeneity in the slag. For a given applied current, the computed power was in reasonable accord with the measured power input. The calculated temperatures were in rough agreement with the tapping temperatures of slag and bullion.

Jan 1, 2000

By Varadarajan Seshadri

The performance of mould fluxes in satisfying its quality requirements can have a significant effect on the efficiency of the continuous casting process and on the surface quality of the products. This performance is affected by various parameters including the characteristics of the mould fluxes, the quality of the steel being cast and the operational conditions of the caster. The extremely complex relationships involving the parameters mentioned above make it very difficult to have simple criteria for selecting mould fluxes for casting a certain grade of steel in a continuous casting machine. These difficulties led steelmakers and mould flux suppliers to select mould fluxes based mainly on plant trials. In the present work, a software to help in the analysis and development of mould fluxes for continuous casting was developed. This software includes several models for prediction of mould flux viscosity and consumption. A mathematical model was also used to predict the heat flux through the mould flux. The proposed methodology was applied to continuous casting of crack sensitive steels. Some of the results given by this software are presented, discussed and compared to plant data.

Jan 1, 2003

By J. E. Dutrizac

Mineralogical studies were carried out on nodulated copper cathodes from three primary refineries to characterize the nodular growths and to elucidate the causes of the nodulation. Nodulation is often initiated at the surface of the starter sheet or the stainless steel plating blank, although a layer of smooth copper sometimes is deposited before nodulation commences. In some instances, the "roots" of the nodules exhibit a pronounced dendritic texture that is associated with an abundance of cavities. Slimes particles are not usually associated with these growth features which lead to a globular surface deposit. The globules sometimes develop into larger nodules, and this type of nodulation is likely caused by improper addition agent concentrations. The nodules on most cathodes, however, exhibit "roots" at the contact with the substrate that are associated with microcavities and large clusters (>40 µm) of slimes particles. The slimes constituents are commonly Ag powder, PbSO4 and Cu2(Se,Te) but not AgCu(Se,Te) or Ag,(Se,Te). The size of the slimes clusters, rather than their composition, appears to be the important factor causing the copper to grow into nodules. Tiny individual slimes particles themselves do not appear to cause cathode nodulation.

Jan 1, 1999

By Tom W. Gonzales

Magma Metals Company commissioned a 3000 tpd Outokumpu flash smelting furnace in July 1988. Through September 1992 the PSP has smelted a first campaign record 4.1 million tons of concentrate. This paper discusses modifications made to the original process equipment to overcome design flaws as well as future design changes currently under consideration.

Jan 1, 1993

By Henry L. Ehrlich

This survey compares bioleaching and biobeneficiation by autotrophic bacteria with that by heterotrophic bacteria and fungi Some physiological principles are reviewed. Advantages and disadvantages of autotrophic and heterotrophic leaching are discussed. Principles of anaerobic leaching by autotrophs and heterotrophs are introduced. and the advantages? over aerobic heterotrophic leaching are discussed. Examples of useful organisms in the autotrophic and heterotrophic categories are cited.

Jan 1, 1991

By Natasa Mitevska

In the world, as well as in Republic of Serbia, conventional ore reserves are almost exhausted, so the problem of their shortage is more and more expressed. On the other side, there are many locations with significant reserves of polymetallic ores which present huge potential but cannot be classically processed. Each of these classes of materials has particular mineralogical characteristics which affect their processing. Because of that it is necessary to develop particular technology for each unconventional ore in order to extract valuable elements. The aim of investigation was to define technology for complex processing of the Blagojev Kamen sulfide concentrate by pyrometallurgical procedure in order to valorize valuable non-ferrous and precious metals present, and profit with absolute respect of environmental protection laws. The complex composition of the Blagojev Kamen sulfide concentrate with high content of non-ferrous (15.59% Pb, 9.05% Zn, 2.37% Cu) and precious (697 g/t Au and 744 g/t Ag) metals was the main factor for technological procedure and collector selection. Laboratory investigations are done in four series according to technological scheme: oxidizing roasting, charge preparation (flux addition and agglomeration), smelting under reducing conditions, lead bullion refining, Dore metal refining to final products. It is concluded that precious metals are concentrated in lead bullion (up to 97.95% of gold and 93.37% of silver), which has similar composition to lead bullion produced in lead metallurgy. In this case, simplified technology is used for lead bullion processing because of low content of arsenic, bismuth, etc.

Jan 1, 2006

By David Seymour

Newmont Gold Company (NGC) located in Northeastern Nevada has been processing carbonaceous and sulfide refractory gold ores through a chlorination circuit prior to cyanidation. A "Flash Chlorination" pilot plant was installed in 1987 in an effort to obtain higher chlorine utilization efficiency and increase gold extraction. The Flash Chlorination process oxidizes organic carbon and sulfide sulfur. It also deactivates preg-robbing carbon, making the ore amenable to cyanidation. Significant recovery improvements were observed using this new process. This scheme has also been instrumental in the processing of higher than normal grade ores at economic chlorine levels. The Flash Chlorination pilot plant has been successfully treating carbonaceous ore on a production scale since April 1988. This paper summarizes laboratory and pilot plant optimization test work, using conventional and statistical methods.

Jan 1, 1989

By Luísa Maria Abrantes

Environmental control is becoming more and more stringent. As conventional processes for zinc production are pollutant routes, alternative methods have become an important subject of research. In this regard, the leaching processes have aroused a considerable interest, namely the electrochemically induced approach. The behaviour of zinc concentrate ore in the leaching processesses is influenced by several parameters. Chloride concentration and leaching solution pH, time and temperature of reaction were studied in order to evaluate their influence on the zinc recovery. The efficiency of the leaching process for zinc extraction is performed by factorial design. The experiments were carried out by 23 and 22 factorial designs of the factors. Results show that all factors, except for the time of reaction have a significant influence on the optimisation process, within each experimental region.

Jan 1, 2001

Laboratory trials were performed in an induction furnace to study droplet formation during lance blowing. Compressed air was blown on a molten iron bath consisting of iron alloyed with carbon and silicon. Steel droplets were collected using a specially designed sampler. The average steel droplet composition and the oxide layer thickness were determined using scanning electron microscopy combined with energy dispersed spectroscopy. In addition, the concentration gradient of elements was determined using a microprobe. It should be noted that a special technique had to be developed in order to prepare the droplet sample. The size distribution and composition of the droplets was also determined using the microprobe. It was found that the carbon content in the droplets was lower than the carbon content in the bulk.

Jan 1, 2006

By Alexander I. Raitchenko

"Although one takes into account only thermal expansion usually at analysis of convection onset, the essential factors include magnetic and electric fields. If Lorentz-force originating from intercrossed electric and magnetic fields' action is directed downwards its effect strengthens gravitational action, and value of critical Rayleigh number (limit value for convection onset) must decrease; increasing of critical Rayleigh number should be observed in case of Lorentz-force directed upwards. Extent of such an influence is determined by relation of Lorentz-force to hydrostatic head in gravitational field. Competition between electromagnetic force due to nonuniformity of electroconductivity (on account of its temperature dependence) and electromagnetic buoyancy force may have ambiguous effect: both increase or decrease of critical Rayleigh numbers. Proposed conception is applicable to analysis of situations in liquid conductors and conductive gases.IntroductionStatic or dynamic situations in fluid media are determined besides properties of these media by a variety of external influences. However one correlate~ the onset of the convection and its development with influences of the minimum quantity of external causes frequently. Most known and usual factors are the gravitational and temperature fields. The number of processes includes heat generation in media volume, and theoretical analysis in these cases takes into account this interior heating together with boundary temperature conditions. But explanation of many natural and technical events is not complete and cogent within limits of thermo-gravitational terms. The whole complex of acting factors which influence convective processes in techniques and nature is greater in many cases. In particular the action of · electromagnetic nature often has not less importance than gravitation one. Stability or instability of a current layer in the plasma must be determined by non-uniformity of electroconductivity owing to non-uniformity of temperature [1]. The presence of Joule dissipation in the plasma through which the electric current flows stipulates initiation of origin of overheated instability [2]. It is known that electroconductivity of arc in the boundary zone changes sharply with radial distance [3], and this must influence its stability essentially. If the intercrossed electric current and magnetic field begin to act on an electroconductive fluid besides the non-uniform temperature field and the gravity, the conditions for the onset of the convection change radi- . cally: both the temperature field and their solutions have to be changed also. The analysis of equilibrium single-time correlation functions of fluctuations must be employed for situations with enlarged number of factors as this was in case for the Rayleigh-Benard problem where the object is a horizontal layer of liquid. This can be carried out by taking into account the detached forces' correlations [ 4, 5]"

Jan 1, 1999

By T. Malvik

Norway is a big producer of ferrosilicon and silicon metal. The raw material is quartz and quartzite and large quantities from both Norwegian and foreign sources are used. The demands maade on both the chemical purity and the thermomechanical qualities of the quartz/quartzite have increased in recent years in an attempt to reduce energy consumption and to improve utilization. Control of the chemical quality of the raw material is relatively easy by means of routine analysis, but it is more difficult to find a suitable method for testing the thermomechanical properties. A rapid test method to define high quality quartzite deposits for use in the metallurgical industry has been developed. The method is based on a combination of chemical analysis, dilatometry, thermosonimetry and cathodoluminiscence.

Jan 1, 1989

By E. T. White, Dean Ilievski

"Mathematical modelling of the precipitation process requires that the kinetics of crystal growth, nucleation and agglomeration be known. This paper reviews the current state of knowledge on these precipitation sub-processes (ie. growth, nucleation and agglomeration) and describes a number of experimental techniques for estimating their kinetics. The experimental methods used to generate the precipitation data and the data analysis techniques used to extract the kinetics information from the data are discussed separately. There is no universal ""best"" technique for determining the kinetics. However, studies on multi-crystal systems are more reliable for modelling purposes than are single crystal studies. The selection of a technique will depend on which sub-processes are present. A problem with all kinetics studies is that there is generally a large uncertainty in the estimated kinetic parameters. This stems from the scatter in the experimental data being further propagated by the mathematical techniques used to extract the kinetic parameters.IntroductionCrystallisation operations, including precipitation, are widely used in a number of hydrometallurgical processes to recover a desired component or to remove an undesired impurity. The goals of industrial precipitation processes are to maximise the recovery while maintaining product quality (generally product crystal size distribution, purity and morphology and product handling properties). Knowledge of the precipitation mechanisms and kinetics is invaluable for designing new precipitators or for improving existing units. The mechanistic and kinetic information is generally incorporated into mathematical precipitator models, which are then used for process design and optimisation."

Jan 1, 1996

By Charles L. Richman

The effect of the addition of Silver Sulfide on the rate of Chalcopyrite (CP) of Sulfuric acid (H2SD4 leaching is discussed, Although Ag2S in an expensive addition, a theoretical explanation of it's use will aid in the development of a economic substitution. We have used cyclic voltammography to show the presence reaction species at different potentials. Cyclic Voltammography maps the surface reaction current peaks on CP, to regions on the CP Phorbaix diagram. AC Electro-lmpedance spectroscopy (EIS) models the surface impedance properties, which control the rate of electron and ion transfer, and the surface kinetic reactions, with and with out light. EIS and other measurements show that AgCuS u Photo-reactive material- The EIS results are compared with the SEM and EDXA results to show the presence of diffusion pores, and diffusion controlled reactions during CP leaching without the addition of silver sulfate. We hypothesize that AgCuS is an ionic conductor like Ag2S. EIS shows an imposed negative leaching rate greatly. Our theory shows how the formation of Silver Copper (1) sulfide layer at open circuit potential gives an effect similar to negative potential, that is enhanced with illumination. We verify that AgCuAS is an N-type semiconductor that forms a diode type junction with the electrolyte with the Mott-Schoottly relation.

Jan 1, 2001

By Kathryn A. Mrotek

The textural growth patterns of nodules from two areas in the North Pacific and the South Pacific are characterized by mottled, columnar and compact-type zones. Amorphous material (mainly iron and manganese hydrox-ides) is a botryoidal-forming phase in the mottled and columnar zones. Crystalline material (platy crystals of birnessite and crystallites of todo-rokite) is found primarily in the mottled zones on botryoidal structures or as long-protruding structures growing onto that portion of the nodule in contact with the underlying sediments. The long-protruding mottled zones contain little or no biogenic debris, suggesting that these zones grew un-interruptedly within the underlying sediments. The coalition of spheroidal knobs comprising some of the nodules also suggests a relatively long residing time within the sediments. It appears that crystalline material (the usual host to associated valuable metals) forms in a quiet environment and as a result of direct nodule association with the underlying sediments.

Jan 1, 1982

By Larry Twidwell, Ed Rosenberg, Courtney Young, Sean Dudley, William Gleason, Maureen Chorney

Experimental and industrially produced polystyrene and silica resins are tested for recovery capabilities of Rare Earth Elements (REE). Testing regimes being used are typical of resin analysis. Inductively Coupled Plasma-AES results indicate that preferential separation and recovery is possible in the adjusted pH range of2 to 10, solution conditions, and resin type. Testing conditions are resulting in structure modification of the composite resin as indicated by X-Ray Diffraction, Differential Scanning Calorimetry, Scanning Electron Microscopy, Mercury Porisometry, and density analysis. Resin modification indicates both surface and internal structure alteration outside of reported standard behavior of resins. Structural changes have ramification for both Rare Earth Recovery RER and traditional resin operations. Analysis shows that the resin uptake of REE can be manipulated for concentration. Further analysis with SEM work indicates that widespread surface and interior modification is taking place as resins load with REE. This modification is leading to pore rupture and particle breakage. Further investigation is being performed to determine the mode of breakage.

Jan 1, 2015