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By K. Pagalthivarthi, P. V. Desai

"During solidification of alloys, many inter-related physical processes, such as melt convection, mass diffusion, heat transport, macrosegregation and melt-undercooling occur. Several research workers have studied one or more of these effects separately. To answer important questions on solidification behavior, an overall approach interrelating the processes is necessaryAs a first step toward accomplishing the overall modeling, the freezing of a binary liquid metal is examined. The various stages during freezing of the alloy are critically described to build a continuum model for the entire process. Diffusive mixture theory is used to write the conservation equations for the liquid and the mushy zones. The concept of local thermodynamic equilibrium in the presence of curvature effects is used to restrict the number of degrees of freedom within the mushy zone. Constitutive equations relating flux quantities and affinities, the governing differential equations and boundary conditions are discussed briefly for the freezing process.IntroductionA solidification study encompasses such facets as solifidication time, microstructure, macrosegregation of the solute, shrinkage effects and soundness of the casting. Influence of one or more of the coupled heat and mass transfer phenomena such as local solute redistribution, thermosolutal convection, melt undercooling at dendrite tips and heat dissipation to the ambient have all been previously examined [1-3J. Several studies have examined the individual facets of alloy solidification as isolated processses. In fact, the transport processes occur simultaneously and a comprehensive model should include their inter-relationships. In particular, some of the existing studies of the mushy zone [4-6J do not emphasize thermodynamic completeness. This work represents an attempt to develop a thermodynamically consistent model of the entire solidification process on physical grounds."

Jan 1, 1986

By Shi Yuan

Molten copper was deoxidized using a one-end-closed yttria-stabilized zirconia (YSZ) tube. A thin layer of porous Ni-Zr02 cermet electrode was deposited on the inner wall of the YSZ tube. The outer surface of the tube was in contact with the melt and the inner surface with a flowing reducing gas. Without applying external EMF, the melt was deoxidized by short-circuiting the melt with the cermet electrode. The deoxidation process was analyzed and the rate controlling steps were identified. These experiments were also conducted at different temperatures to evaluate the effect of temperature on the deoxidation kinetics.

Jan 1, 1994

By Noritaka Horii, Katsuyoshi Kakinuma, Hiroshi Yamamura

"ZrO2 and Y2O 3-doped ZrO2 gel film were obtained by spin coating of sol from Zr-n-propoxide, n-propanol, acetylacetone, nitric acid, and water on a silica glass as a substrate. ·Dried gel films crystallized to monoclinic, tetragonal, cubic and their mixed phases, depending on the chemical composition of sol, .firing temperature, and coating cycles. ZrO2 films with highly preferential orientation were successfully obtained from a solution containing a large amount of n-propanol. The highly oriented ZrO2 film was found to have high transparency compared with non-oriented 'films. Electrical conductivity of 8 mol% Y2O 3 doped ZrO2 film was also measured.Introduction3 mol% Y2O 3 doped ZrO2, which has a tetragonal symmetry is ·well known to have a strong mechanical property and a high toughness. (1) On the other hand, 8 mol % Y 2O 3-doped ZrO2 is high oxide-ion conducting material and is applied to oxygen sensor, oxygen pump, and solid oxide fuel cell (SOFC). (2) Sol-gel methods using metallic alkoxide are widely applied for synthesizing ceramics such as high-purity fine particles, thin film, and fiber. (3) For ceramics films, many reports have been made on SiO2, (4) TiO2, (5) and PZT. (6) Several case studies have been done on zirconia film based on the sol-gel method, (7) - (11) but very few on preferentially oriented film and on systematic Y zO3 doping. Almost zirconia ceramic· films reported were prepared by means of dip-coating. Kamiya et al. (12) and Ganguli et al (13) converted zirconia into fiber. Sol from Zr alkoxide is usually very unstable, and a stabilizing agent such as glycol or ß-keton is used beforehand (7) (14)."

Jan 1, 2000

By Seshadri Seetharaman, Nurni N. Viswanathan, Haijuan Wang

"In order to make the stainless steel making process efficient and environment friendly, it is essential to minimize the loss of chromium to the slag phase. With a view to investigate the advantages of using CO2 to attain moderate oxygen partial pressures in the oxidant gas during the decarburizations of stainless steel, the present experiments were carried out to understand the oxidation kinetics of Fe-Cr alloys and Fe-V alloy with gas mixtures containing CO2. In the present work, the oxidation behavior of Fe-Cr and Fe-V was examined by thermogravimetric analysis (TGA). Various mixtures of O2 and CO2 were used as the oxidant gas and the oxidation rate was followed by the weight changes as a function of time.The experiments demonstrated that the oxidation rate is independent of temperature at present experimental situation, but has strongly related to the Cr-content of the alloy as well as the oxygen partial pressure in the oxidant gas mixture. The wetting of alumina by the iron drop and the change of the drop shape during the course of the oxidation were investigated by X-ray radiography."

Jan 1, 2010

By A. V. Tarasov, V. M. Paretsky

"A mathematical model of the low-temperature (soft) nickel oxide reduction (SNOR) in a tubular kiln has been developed including an equation describing changes in the nickel oxide content of the solid material along the length of the kiln; an equation describing the changes in the content of reagents ensuring nickel reduction (i.e., hydrogen and carbon monoxide) in the gas phase along the kiln length; as well as the temperature along the kiln length. The kinetic relationships used for the development of the model had been determined based on experiments conducted specially for this purpose. Model investigations were conducted to determine the distribution of such parameters along the length of the kiln as the contents of metals oxides in the solids, partial pressure of hydrogen and carbon monoxide, variations of the temperature depending on the SNOR process conditions, including the kiln rotation speed. Based on the data obtained, a simplified regression model of the reducing roasting process was developed.IntroductionAt the SeveroNickel complex (Russia) a technology has been developed and is being introduced on a commercial scale for low-temperature (soft) nickel oxide reduction (SNOR) in tubular kilns.The SNOR process has a number of advantages, the main of which are the higher degree of metallization and higher chemical activity of reduced nickel oxide attributable to the lower fusion of the surface of the grains of reduced material due to lower process temperature (800-1000°C) and improved reducing ability of the gaseous phase. However, the fact that the process is conducted in a gaseous phase sets higher requirements to the consistency of its composition necessitating careful continuous monitoring and control of the main process parameters."

Jan 1, 2001

By William E. Frazier

The presence of minute amounts of sulfur (10ppm) in nickel-base superalloys has been associated with reduced oxidation resistance and the premature spallation of protective coatings. Removal of sulfur by annealing these alloys in a hydrogen atmosphere has been successfully attempted by several researchers. This paper examines the fundamental thermodynamics and kinetics governing hydrogen desulfurization of elemental nickel. Limiting conditions for successful desulfurization are delineated. Assuming that the diffusion of sulfur is the rate limiting process of desulfurization, the effectiveness as well as time associated with hydrogen desulfurization is explored.

Jan 1, 1994

By Aureo D. V. Machado

An experimental study to obtain zirconia powders (ZrOz) from carboxylate zirconium solutions followed by hydrogen peroxide stripping and precipitation, has been carried out. Zirconium carboxylate was prepared by solvent extraction from a chloride aqueous phase using magnesium carboxylate as organic phase. The variables examined in the precipitation reaction were: Temperature: 25 - 90 ?C ? H202= concentration: 0.3 - 5% wt/wt - pH: 1 ? 9 Organic/Aqueous ratio (1/1) and reaction time (30 minutes) were maintained at constant levels. The optimum results (98% precipitation) were achieved at 25 °C, 5 % wt/wt H202=, and pH = 5. The precipitates were composed of large amorphous aggregates (<I00 micrometers). After calcination for 1 hour at 1000 OC, monoclinic ZrO2 with a large variation in particle size (1 -100 micrometers) was obtained.

Jan 1, 1991

By G. A. Eltringham, A. F. Sarofim, A. A. Shook, M. P. Heap, B. R. Adams, K. A. Davis

This paper discusses the use of a reacting CFD model to determine chalcopyrite kinetics in a drop tube furnace and to predict the reaction of a chalcopyrite concentrate in the reaction shaft of an industrial smelter. Reacting CFD codes can be applied to determine the consequences of the interaction of gas with particles and therefore improve the ability to derive kinetic parameters that take into account the different temperature and oxidation histories that different particles will see. This paper describes the application of such a model to derive improved kinetic parameters for the pyrolysis and oxidation of chalcopyrite. The improved kinetic parameters derived from the drop tube studies are used to simulate chalcopyrite concentrate reactions in the reaction shaft of an industrial smelter. The reaction shaft model includes the effects of turbulent fluid mechanics, entrained flow mixing, turbulent particle dispersion, heterogeneous particle reactions, radiative and convective heat transfer, and surface and bath deposition rates. Particle reaction and composition characteristics are predicted as a function of particle trajectory and deposition and are used to aid in evaluating shaft performance.

Jan 1, 1999

By Sung Tae Kim

The viscosity is one of the most critical properties of slags and thus its influence on the physicochemical phenomena in metallurgical processes has been issued for last decades. The viscosity of ferrous- and non-ferrous metallurgical slags can be understood via structural investigation with spectroscopic methodologies including x-ray photoelectron spectroscopy, infrared- and Raman spectroscopy, and solid state nuclear magnetic resonance spectroscopy, etc. Therefore, the reaction kinetics such as desulfurization in ladle metallurgical furnace, reduction of FeO and MnO in electric arc furnace is strongly dependent on the viscosity of the slags. The rates of oxide (inclusion and refractory) dissolution into the slags and fluxes are governed by the viscosity. Alternatively, the structure of aluminosilicate melts also affects the thermochemical properties such as sulfide capacity, etc. These diverse applications of the viscosity-structure relationship to ferrous- and non-ferrous metallurgical processes were reviewed.

By Dinesh Agrawal

Microwave energy has been in use for variety of applications for over 50 years. These applications include communication, food processing, wood drying, rubber vulcanization, medical therapy, polymers, etc. In the last two decades microwave heating has been also applied very effectively and efficiently to heat and sinter ceramic materials. Microwave heating is recognized for its various advantages, such as: time and energy saving, very rapid heating rates, considerably reduced processing cycle time and temperature, fine microstructures and improved mechanical properties, better product performance, etc. The most recent application of microwaves has been in the field of metallic materials for sintering, brazing/joining and melting. Several common steel compositions, pure metals and refractory metals have been sintered in microwaves to nearly full density with improved mechanical properties. Many commercial powder-metal components of various alloy compositions including iron and steel, copper, aluminum, nickel, Mo, Co, Ti, W, Sn, etc., and their alloys have also been sintered in microwaves producing better properties than their conventional counterparts by using a 2.45 GHz multimode microwave system. This work has been further extended to join and braze bulk metal pieces, especially super alloy based turbine blades. Further, in a specially designed microwave cavity, even the bulk metals can be made to couple with the microwave field and melted. The implications of these findings are obvious in the field of powder metal technology.

Jan 1, 2006

By Dengfu Chen, Huabiao Chen, Yunwei Huang, Mujun Long, Youguang Ma, Lintao Gui

In the current work, a three-dimensional model coupling turbulent flow, heat and solute transport was developed to investigate the solute transport and redistribution in the mold of slab continuous casting where the Reynolds number is very high and the molten steel flows strongly. The conservation equations of momentum, energy and species for a multicomponent system which includes solute element C, Si, Mn, P, S were solved with the commercial software ANSYS Fluent. The parameters used in the model are based on the actual continuous casting. The fluid flow, temperature distribution and solute elements distribution were analyzed. Results showed that negative segregation occurred near the strand surface, and the species concentration reached a peak value at the solidification front during solidification. The segregation degree of solute element S is higher than the other solute elements because of its lower equilibrium partition coefficient. The species concentration in the liquid pool is homogeneous because of the turbulent flow effect.

Jan 1, 2015

By Zhang Hengzhong

Ni-P-Fe slag is the by-product in the production of phosphate fertilizer in blast furnace with nickel contained serpentine ore as the raw material. It contains nearly 5-7% Ni, 65-7( Fe, and 10-12% P. The slag is very hard to process, it neither dissolves in aqueous ammonia, nor in sulphate acid. In the stiff the technique to treat the slag in order to extract valuable nickel was developed, it essentially consisted of the processes of roasting, leaching, separation and purification. Nickel sulphate was prepared with this method.

Jan 1, 1993

By A. J. Davidson

A novel sensor is described for the measurement of the copper content of copper matte. Due to the high copper concentrations found in matte, potentiometric sensors are not sufficiently sensitive. A highly sensitive sensor has been developed based on a modification of the amperometric technique using a copper ion conductor, Cusicon. The results correlate closely with the theoretical predictions.

Jan 1, 1998

By Geir Wedde, Anders Sorhuus

"Vast quantities of energy are released as heat to the environment from industrial operations. Many countries target waste heat recovery to mitigate CO2 emission. Exhaust gases from industries such as primary aluminium smelting, carry a substantial portion of the waste heat generated. For a cost efficient capture of more valuable heat (higher exergy), heat exchangers should operate on the exhaust gases upstream of the gas treatment plants. Heat exchange surface would be exposed to dust laden gases with risk of fouling. Heat exchangers of innovated design and operation have overcome the potential of excessive fouling rates. Heat exchangers of the ""shell and tube"" design have been demonstrated for exhaust gases from ferroalloy as well as primary aluminium smelters. In addition to the heat recovery, gas cooling results in smaller gas treatment plants with lower costs and reduced emission. The aluminium experience is exampled in the paper.IntroductionIndustrial usage of energy continues to grow as a result of increasing volumes of production, a trend that is likely to continue in the coming decades as living standards keep rising globally. World energy consumption (Figure la) is to grow 49 % by 2035 (ref. 2010) as reported by EIA [1]. The industrial sector consumes somewhat more than 50% of the total world energy consumption predominantly the energy increased demand comes from non-OECD countries in Asia. The industrial consumption by production of metals iron and steel accounts for 14 % and for non-ferrous metals 3 % mostly for aluminium production (Figure lb). Aluminium production will be discussed in this paper as an example of an industry with large quantities of waste heat to recover"

Jan 1, 2012

By Krzyszof Borowiec

With the aim of determining the thermodynamic conditions for sulfation of impurity elements, in particular magnesium, in titaniferous slags the equilibrium gas composition for the sulfation reaction: MO + so2 + 1/2 02 = MS04 has been studied by an EMF technique with a solid zro2 + Cao electrolyte. Here M denotes the impurity elements: Mg, Ca and Mn, and the following _oxide systems have been studied: Ti02-MgO-Fe2 o 3 , Ti02-MnO-Mn2 o 3 , and Ti02 -CaO-Si02 , all in the . temperature range 700-1000ºc. Reproducible EMF values were obtained by adding small amounts of -Na2so4 to the oxide-sulfate mixture. From the observed results the Gibbs energy of formation of the phases Mg 2Ti04 , MgTi03 , MgTi 2o 5 , MnTi03 , CaTi03 , and CaTiSio5 , as well as the activity of MgTi05 in the solid solution with Fe2Ti05 have been calculated. The results show that, from a thermodynamic viewpoint, sulfation of these impurities in titaniferous stags i:s favorable- at around and below 800ºC.

Jan 1, 1985

By Seong-Jong Kim

The formation behavior and corrosion characteristics of anodic oxide films on pure Mg and Mg-AI alloys were investigated focusing on the effects of anodizing potential, Al content, temperature and NaOH concentration. Pure Mg and Mg-AI alloys were anodized for 10 min at 3, 10, 40, and 80 V in NaOH solutions. Mg(OH)2 was generated by an active dissolution reaction at the surface of the specimen and the product was affected by temperature while MgO generation increased with NaOH concentration. Moreover, the current density after anodizing for 10 min at a constant potential decreased with increasing AI content in Mg-AI alloys,

Jan 1, 2003

By F. Leuzzi

Asbestos is a natural mineral fibre which has been known and utilized commercially for about a century. From the forties, it was employed on an ever-increasing scale throughout the mechanical engineering, building, paper-making and plastics sectors, to name but a few. There are essentially five minerals which provide fibres for industrial applications, namely, the chrysotile variety of serpentine and the amphiboles such as riebeckite, anthophyllite, cummingtonite-grunerite (amosite) and tremolite. About a fifth of the world&apos;s asbestos output was once taken by Europe for the manufacture of asbestos-cement products, reinforced plastics, paper and cardboard, panels, soft insulation and spray-on powders. However, in the sixties and seventies the hypothesis regarding the pathogenic nature of asbestos fibres started to gain ground. Moreover, between the sixties and eighties the EU issued a series of regulations designed to bring about a steady decrease in asbestos consumption. This line of action has culminated in recent years in a whole set of directives banning the use of asbestos in all products. This created a major problem, namely, how to clean-up the several million tons of various types of asbestos products in various states of conservation existing in Western Europe. CORDIAM (Pat. RM95 A 000269 and Pat. RM96 A 000782 in the name of ECOTEC S.r.1.) is one of the thermal inertization techniques recently proposed for this purpose. The process provides for the low-temperature ceramization of the toxic-harmful material. Of course, with such a great variety of waste materials and the volumes to be treated, as well as the need to ensure the correct dimensional design of the thermal sections of the treatment plant, it is necessary to know as much as possible about the thermal behaviour of the wastes concerned. This paper details the steps taken firstly to ascertain the thermal behaviour of such materials as may be encountered in day-to-day practice and secondly to examine the influence of the main process parameters on the preliminary design of gas- or fuel-oil-fired rotary kilns of the kind used for waste treatment.

Jan 1, 1999

By M. O. Lai

"Metal matrix composite (MMC) with composition of Al-4.Swt.%Cu reinforced by IOwt.%TiB2 or ISwt.%SiC particulate has been successfully fabricated using powder metallurgy technique. Disk, compression and beam specimens were prepared with (a) layered structure containing ductile Al-4.Swt.%Cu with brittle Al-4.Swt.%Cu/TiB2 or Al-4.Swt.%Cu/SiC layers, and (b) homogenous constituent with composition of Al-4.Swt.%Cu/lOwt.%TiB2' The specimens for the fracture toughness measurement were built through three ductile-brittle-ductile alternating layers. For the beam specimens, the layers were built through brittle-ductile-brittle sequence. The brittle layer consisted of Al-4.S%Cu with fixed amount of reinforcement. Fracture toughness testing revealed an increase for layered composites although the total amount of the reinforcement was the same for all disk specimens. The increase in fracture toughness is due to the existence of ductile layers which manifests a strong influence on delaying the occurrence of fracture. It acts as a barrier to resist the propagation of crack and hence increases the fracture toughness of the layered MMC specimens, Delamination in the beam specimens was observed to be due to shear stresses. Fracture surfaces of both disk, compress and beam specimens were characterized using the SEM. IntroductionMechanical and thermal properties can be achieved by the incorporation of refractory secondary phases to constrain the plastic flow of the matrix in a metal matrix composite (MMC). The size of the reinforcement particulate incorporated must be in the range larger than the dislocation cell size and strongly bonded to the matrix (I). Particulate reinforced metal matrix composites hence provide high modulus, improved wear resistance and strength (2-4). Because of the incorporation of refractory phases which are generally brittle, the major limitation in the mechanical properties of MMCs is their limited ductility in comparison to their base metals. Cracks normally initiate from the reinforcement and voids (4, 5). Due to the lack of ductility, cracks propagate rapidly with increase in load. As a result, the interactions between reinforcement particles and propagating cracks have recently been of great research interest (6). In addition, volume fraction of reinforcement and aging condition of the matrix significantly affect the mechanical behaviour of MMCs. In the case of AI-3.5%Cu reinforced with varying volume fractions of SiC particulate, it has been found that the probability of particle fracture increased with increasing volume fraction of reinforcement (7)."

Jan 1, 1996

By Munyaradzi Kwatara, Ron Schonewille, Edgar Peek, Juzer Tayabally

"The potential recovery of nickel from a South-American saprolitic laterite ore using the segregation roasting technique was investigated. The ore was heated to temperatures that ranged between 900 and 1 000°C in a rotary kiln. In all the tests, the laterite ore was first mixed with a predetermined amount of calcium chloride and either coal or coke. By varying the temperature, calcium chloride and reductant in the different tests, a preliminary set of optimal conditions was established for the specific laterite ore that was tested. A combination of chemical analysis and electron-probe-micro-analysis (EPMA) were used to determine and evaluate the effectiveness of segregation roasting on the recovery of nickel. The present paper describes the test procedure and the results that were obtained.IntroductionIt is known that laterite ore resources account for an estimated 72% of the world's nickel resources, with sulfide sources accounting for the remaining 28%. Yet sulfide resources account for 58% of the world's primary nickel production while laterite resources account for the remaining 42% [I]. There are numerous reasons for this discrepancy, but the most important one is the mineralogical and compositional complexity that is associated with laterite ore deposits. For example, this complexity currently offers only limited opportunities for upgrading, thereby creating capital intensive whole ore processing facilities. It then follows logically that the identification and application of a low-cost processing option for the treatment of laterites could potentially open up an opportunity for exploiting these vast untapped laterite resources.To this end, a preliminary screening investigation was initiated by Xstrata Process Support to evaluate the potential application of the so-called (nickel) segregation process as a unit operation that could potentially be integrated into a laterite processing flow sheet. Laboratory bench tests were performed on this segregation process and this paper details some of the findings from this preliminary investigation."

Jan 1, 2011

By R. K. Mehta

Microorganisms have been increasingly used in applications such as-metal solubillzation, precipitation and recently being used as flocculants. Optimal control and on-line monitoring of these processes occurring in microbial reactors are of extensive interest but often difficult because of the unavailability of a mechanistic model of the process and on-line direct sensors. In this paper a dynamic populatlon balance model of microbial desulfurization will be presented. The influence of certain physical and biological parameters on the leaching rate will be illustrated via computer simulations and an extended continuous-discrete Kalman filter will be Implemented for estimation of unknown states.

Jan 1, 1991