Search Documents

By Nobuyuki Higashiyama, Ikuo Yonezu

"Hydrogen-absorbing alloys containing rare-earth elements are used in high capacity nickel-metal hydride secondary batteries,' hydrogen storage systems for portable fuel cells, and refrigeration systems. New hydrogen-absorbing alloys containing rare-earth elements have also been developed and introduced into these applications. High performance in nickel-metal hydride secondary batteries is strongly demanded because of the remarkable advancements in portable electric appliances. A large hydrogen absorption capacity, high electrochemical reactivity and superior corrosion resistance in an alkaline solution are required for hydrogen-absorbing alloys used in nickel-metal hydride batteries. The aim of this investigation is to improve the performance of conventional LaNi5 type hydrogen-absorbing alloys. For example, Mm(Ni-Co-Al-Mn)„ type hydrogen-absorbing alloys with various non-stoichiometric compositions were developed. In addition, a new process of rapid quenching process was applied for preparing these hydrogen-absorbing alloys in order to improve their performance.IntroductionRecently, the trend in electronic appliances toward portability has increased the demand for high capacity of secondary batteries as power sources. Since nickel-metal hydride batteries were first commercialized in 1990 in Japan, they have become increasingly popular as power sources for cellular phones, portable computers, electric shavers, and other, products.The performance of a nickel-metal hydride battery, such as its discharge capacity, high rate capability, and charge-discharge cycle life, strongly depends on the characteristics of the hydrogen-absorbing alloy negative electrode. Many types of hydrogen-absorbing alloys have been developed so far. For a hydrogen absorbing alloy to be used as the negative electrode material, (1) it must allow a large amount of hydrogen to be absorbed and desorbed in an alkaline solution, (2) its reaction rate should be high, and. (3) it must have long term durability under repeated charge-discharge cycling. However, LaNi5, a typical rare earth-nickel type alloy, shows significant capacity deterioration during repeated charge-discharge cycling. Therefore the first step in its development was to obtain sufficient corrosion resistance of the LaNi5 alloy for its use as an electrode material. A partial replacement of nickel with cobalt and a substitution of the lanthanum- content with misch metal (Mm), a mixture of rare earth elements such as lanthanum, cerium, praseodymium and neodymium, were very useful in improving the charge-discharge cycle life. However, the discharge capacity of the alloy was still not sufficient for a practical battery. A study of the effect of the partial substitution of aluminum and manganese showed that the best alloy composition was Mm(Ni-Co-Al-Mn)x, as follows.The stoichiometry x of Mm(Ni-Co-Al-Mn)x largely affects the discharge capacity and cycle life. Theose alloys with non-stoichiometric alloys with the compositions of [Mm(Ni-Co-AMn)x: 4.7<x<4.8] have a large capacity and a long cycle life. Nogami' et al. reported that 'a non-stoichiometric alloy with a Mm(Ni-Co-Al-Mn)x (x=4.76) composition showed approximately 10% higher discharge capacity than the stoichiometric alloy (x=5) [1] and greater influence of x on the electrochemical properties of multi-component AB„ type hydrogen-absorbing alloys for batteries."

Jan 1, 2000

By Takahiro Miki

Soldering material widely used is Sn-Pb alloy, which have low melting point and excellent electrical, strength properties and wettability. However, Pb is one of the toxic elements, which is undesirable due to environmental and safety reasons, thus Pb-free alternative alloy is preferred for new soldering materiaL Sn-Ag and Sn-Zn based alloys have been viewed as very promising candidates, among many potential substitutes. Addition of third element to these alloys will decrease melting point of the alloys. Hence, Sn-Ag-In and Sn-Zn-Mg alloys are expected to be suitable for replacing Sn-Pb solder alloy. In order to dcsign new Pb-free soldering materials, it is crucial to understand precise thermodynamic properties and phase diagrams of alloy systems. In the present work, ion current ratios of Ag to In and Mg to Zn were measured for Sn-Ag-In and Sn-Zn-Mg alloys by mass spectrometry, respectively. Also, the authors reviewed the thermodynamic properties of terminal binary alloys determined by other researchers and evaluated a thermodynamic functions to express the excess Gibbs free energy of each binary alloy. Thermodynamic functions to express the excess Gibbs free energy of liquid Sn-Ag-In and Sn-Zn-Mg ternary alloys were determined, utilizing the assessed Gibbs free energy of terminal binary alloys with the measured ion current ratios using mass speetrometer.

Jan 1, 2003

By S. N. Lekakh

Experimental work and thermodynamic simulations of cast iron refining were carried out using various additions of alkali and rare earth metals. The refining reactions for sulfur and oxygen removal were studied for melts treated with Mg, Ca, and Ce. The measured data and the results of the computer simulations were in agreement. Experimental kinetic data, together with the thermodynamic calculations, were used for optimization of the amount and sequence of the addition of nodulizers for ductile iron production.

Jan 1, 2009

By Y. Y. Liu, H. M. Domanus, W. T. Sha

"Casting is fundamental to manufacturing of many types of equipment and products. Although casting is a very old technology that has been in existence for hundreds of years, it remains a highly empirical technology, and production of new castings requires an expensive and time-consuming trial-and-error approach.In recent years, mathematical modeling of casting has received increasing attention; however, a majority of the modeling work has been in the area of heat transfer and solidification. Very little work has been done in modeling fluid flow of the liquid melt. This paper presents a model of fluid flow coupled with heat transfer of a liquid melt for casting processes. The model to be described in this paper is an extension of the COMMIX code and is capable of handling castings with any shape, size, and material. A feature of this model is the ability to track the liquid/gas interface and liquid/solid interface. The flow of liquid melt through the sprue and runners and into the mold cavity is calculated as well as three-dimensional temperature and velocity distributions of the liquid melt throughout the casting process.IntroductionBower et al. (1), in their 1969 review of the evolution of some of the casting techniques, stated that:""The evolution of technology requires alternatives to be available so that choices can be made that lead to changes. The role of solidification science and other disciplines related to casting technology is to develop a better understanding of process and product, so that a wider range of alternatives is possible.Alternatives, whether from science or from invention, must lead to improvements in casting ""utility."" Utility, or economic advantage, must include consideration of total system costs, and final product value. The cost of materials, melt processing and finishing should be optimized with casting costs, since all are part of the production system. It is the favorable relationship between total processing costs and product value that makes a change in casting technology viable, but the best change is not possible unless technology has provided an understanding."""

Jan 1, 1986

By Nagy El-Kaddah, Thinium T. Natarajan

A modeling strategy is presented for computing the electromagnetic field and the shape of the molten metal in electromagnetic confinement systems. This strategy involves the use of a hybrid finite element/integral technique to calculate the electromagnetic field and force distribution in the melt. The free surface shape is determined from minimization of electromagnetic, gravitational and surface tension energies using the Lagrange method of multipliers. This approach was applied to model the electromagnetic levitation melting process. The model was found to accurately predict the measured shape of levitated droplets.

Jan 1, 2014

By Milton Manrique

The thermal decomposition of ilmenite 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 particle size was studied. Products were characterized by XRD, SEM, TEM and ICP techniques. Free energy minimization plots were used to predict the thermodynamic behavior of the system under different operating conditions. The results of this investigation showed a significant segregation process where titanium-rich products are collected in the reactor, while iron-rich products are collected in the quenching box and filter. The average size of the product is in the sub- micron range. Titanium nitride was formed and condensed in the reactor zone when using an argon-nitrogen mixture as the plasma gas.

Jan 1, 1998

By C. A. Silva

The kinetics of chlorination of titanium-bearing raw materials has been investigated. For comparison purposes pellets of controlled macro-porosity, made of analytical grade TiO2 and anatase concentrate (Brazil) , have been exposed to different combinations of gas composition - CO, CO2, C12 -, gas flowrate and temperature. A thermogravimetric technique and an adapted grain model have been used in order to assess the influence of the several experimental parameters upon the chlorination behavior.

Jan 1, 1997

By Patrick R. Taylor

This investigation studied the inflight calcination kinetics of nuclear waste simulant using a thermal plasma reactor. A series of experiments were performed to determine the conversion of insoluble aluminum compounds to the soluble compounds and the decomposition of complex organic and nitrite compounds present in the simulant waste. Thermodynamic calculations based on free energy minimization were performed to establish a theoretical basis for this investigation. A kinetic model to describe the conversion of gibsite to sodium aluminate has been proposed. The products of the calcination were characterized using XRD, Gas Chromatography, and chemical analysis by ICP. The results of this investigation indicated 85% gibsite conversion to sodium aluminate, 90% of nitrate decomposition, 52% TOC decomposition and 90% conversion of chromium to soluble compounds. A process is identified for inflight calcination of wastes. Key words: Plasma, waste, simulant, calcination

Jan 1, 1996

By Helmut Attlfellner

The selection of the best process for the oxygen generator for a metallurgical process requires the determination of all aspects which impact the economics of this facility. Concepts and features of modern air separation plants will be presented based on installed facilities for various metallurgical processes. The special features of advanced automation&apos; of oxygen generators with load following and optimization of power consumption, automatic restart and unattended remote controlled operation will be investigated.

Jan 1, 1992

By S. Kang, D. G. C. Robertson

Slag cleaning furnaces require extensive wall cooling because they involve the use of a superheated slag bath. This is in direct contrast to smelting furnaces, where the wall is usually (but not always) protected by "banks" of solid charge. In order to understand the heat transfer and flow in slag cleaning furnaces a number of model studies have been carried out using molten wax to simulate the slag. Wax is a good model fluid because, like slag, it has a high Prandtl number. Wax models cannot simulate the behavior close to the electrodes (DC arc or AC submerged), but they can and do give a good simulation of the flow and heat transfer at the wall. An understanding of these phenomena is of great importance for the design of cooling panels in the walls of the furnace. Since superheated molten slag will eventually wear away any refractory bricks over time, the wall cooling must be designed to form a frozen layer of slag, referred to as a "freeze lining". The heat flux density (Q/A) required to do this is given by Q/A = h* ?T, where h is the heat transfer coefficient in the slag phase at the wall, and Li T is the superheat (bulk slag temperature - liquidus temperature). Both Q/A and h vary greatly with position and both are usually a maximum at the slag line. In the experimental work, molten wax baths were heated by block heaters to provide similar energy densities to those encountered in commercial slag cleaning furnaces. This procedure was considered to be valid since most of the electrical energy into a furnace bath is dissipated as heat. Gas stirring was used to simulate the gas evolved at the electrode in real furnaces - the quantity of this gas could be estimated from a knowledge of electrode consumption. The similarity criterion was equal gas flow per unit area of surface, in model and prototype. Heat transfer coefficients were measured in the models as a function of power density, gas stirring, superheat, etc., and could be related to the full-scale operations by the use of dimensional analysis.

Jan 1, 1999

By Dewei Zhu

A general purpose computer model for describing the transport phenomena and resulting rate of deposition in Chemical Vapor Deposition (CVD) processes has been described. Partial differential equations describing the conservation of mass, momentum, energy and chemical species are solved by a computer program employing a finite volume method. The program allows for multiple chemical species and natural convection effects. In this paper, the deposition of silicon by the reaction of silicon tetrachloride and hydrogen in a vertical stagnation flow reactor with rotating substrate has been considered. The effects of reactor pressure and substrate rotation speed on the rate and uniformity of deposition have been studied. The predicted rates of silicon deposition along the substrate are in reasonable agreement with experimental results found in literature. The model can be used as a tool for design optimization of such reactors.

Jan 1, 1990

By James T. Staley

Quenching and aging are critical processing steps used to produce precipitation hardenable aluminum alloy products. This work describes personal computer programs that employ models to predict certain properties after quenching and aging and graphically display them. One of the programs allows the user to predict the attainable strength and toughness of aluminum alloy products after an arbitrary quench. Another program simulates the changes in strength and electrical conductivity occurring during second-step aging alloy 7050-T7X products as a function of thickness, furnace temperature set point, and furnace characteristics.

Jan 1, 1993

By Rashmi Kumar, Amit Chatterjee, Sanjay Chandra

The practice of adding alloying materials to a molten bath is an integral feature of many pyrometallurgical operations. However, very little is known about the dissolution rate and solution mechanisms of solid additives in liquid melts. In foundries where large tonnages of liquid metals are handled, there is considerable interest in achieving optimum metal quality at minimum cost. This objective is influenced by several factors and the solution is often plant specific. Though the amount, sequence and mode of ferroalloy addition vary from plant to plant, various fundamental factors determine how quickly these additions dissolve in the bath. At the Ingot Mould Foundry (IMF) in TATA STEEL blast furnace hot metal is used to cast ingot moulds. The composition of hot metal desired for making ingot moulds demands addition of 20 kg each of Ferromanganese and Ferrosilicon in the 12 T transfer ladles into which the blast furnace metal is poured at the IMF. Owing to low temperature of hot metal at the IMF, casting commences immediately and complete dissolution of the ferroalloys is often not possible. To study this aspect in detail and to evolve suitable corrective measures, a mathematical model for the melting of a solid particle in a liquid metal bath was developed at TATA STEEL. The model was validated using the data available in literature. In keeping with published work, two separate dissolution periods were identified - a "shell period" and a "free dissolution period". The maximum thickness of the crust formed around a spherical particle shortly after immersion, can be obtained by using the mathematical model which has been developed. The model can also be used to investigate the effect of various parameters such as superheat of the bath, size of the particle, etc., on the maximum crust thickness and the particle melting time. On the basis of this study, the addition of ferromanganese and ferrosilicon was optimized at the IMF in Tata Steel.

Jan 1, 1996

By Ian G. H. du Preez

It is illustrated how differences in the basic chemistry of individual metal ions can be exploited to develop new or improved separating agents. Factors like coordination number preferred by the specific metal ion, the degree of coordinate saturation reached by the metal ion and its relation to the phase transferability of the complex species, kinetic factors as opposed to thermodynamic factors controlling the success of the separation, the nature and type of the donor atom employed in a separating agent in relation to the preferences of the metal ion, the significance of stereochemical factors and the hydrophobicity of the media are some of the important factors which are discussed and applied for the development of pa1ladiwn(TI) and nickel(TI) specific separating agents, respectively.

Jan 1, 1999

By Carlos G. Levi

"The principles involved in the rapid solidification of supercooled metal droplets and existing numerical models are reviewed. The limitations of these models for studying alloy solidification are discussed in terms of the effects of alloying elements on the relevant heat transfer, thermodynamic and kinetic parameters. Analysis of the enthalpy-temperature diagram reveals how the extent of rapid solidification is hindered by the addition of solute. A solidification model incorporating thermodynamic and kinetic relationships into a Newtonian heat transfer formulation is used to analyze the thermal history and concurrent solute redistribution during recalescence. IntroductionIt is well acknowledged that microstructural evolution during solidification is intimately associated with the thermal history of the liquid-solid interface. Structural parameters like chemical homogeneity, morphology and size scale of the phases can be related to the interfacial temperature and velocity. These in turn change by the interaction of the interface with the thermal and solutal fields in its neighboring environment.The thermal history of powder solidification can be conveniently described on the enthalpy-temperature diagram for a pure metal shown in Figure 1 and discussed in detail elsewhere [1). A system can conceivably follow any path of decreasing enthalpy in the supercooled region of Figure 1 (~ < 1), starting at the nucleation temperature (oN < 0) on the liquid line, and ending at some point on the solid line. A vertical path represents an isothermal transformation, of which a limiting case is solidification without significant barriers to nucleation and growth, with the interface at the equilibrium temperature TM (path one in Figure 1). A horizontal path represents isenthalpic (or adiabatic) solidification whereby the system could form an amount of solid proportional to the initial supercooling of the liquid without further heat loss to the environment. A liquid that can completely transform to solid under adiabatic conditions is said to be ""hypercooled""."

Jan 1, 1986

By Zhou Jiemin

A mathematical model is developed to determine the economic thicknesses of refractories and insulations in rectangular furnaces, Both the heat loss cost and the lining investment are taken into account to achieve a minimum operation cost. For the sake of calculating the heat flux, the paper is particularly concerned with the simulation of the three-dimensional transient heat conduction processes in the lining and a Douglas-Rachford method is used to solve the finite difference equations, The model has been used to design an industrial electric resistance furnace operated periodically. the values of temperatures and power consumption measured from the furnace correspond with the model results.

Jan 1, 1991

By Gabriel Riveros

Fire refining of copper consists of two stages copper oxidation and copper reduction. Very frequently the capacity of the anode furnace is determined by the rate of copper reduction. The analysis of factors affecting the rate of the oxygen reduction from a liquid copper with solid carbon or injected hydrocarbons pointed out the role of the mass transfer in a liquid copper in final stage of the reduction. Experimental results of copper reduction with graphite and injected natural gas in laboratory- scale crucibles showed two stages of the reduction process with a sharp change of the controlling mechanism. The estimated dynamic surface area of gas bubbles based on the measured bubble frequency and the gas flowrate allowed for the detennination of the reaction constant as a degree of the partial pre-combustion of the air/natural gas mix. The variation of the used reductant as a function of the oxygen concentration and temperature has been evaluated based on the detennined kinetic model. The intensification of copper reduction in fire refining has been discusses on the basis of obtained kinetic data and analysis of various factors detennining the time of reduction.

Jan 1, 2003

By J. J. Rush

Neutron scattering and analysis techniques are extremely powerful, often unique, probes for the characterization of the amount, location, bonding states, and dynamics of hydrogen in all classes of materials. Developments over the past decade at the NIST Center for Neutron Research and elsewhere have greatly increased the sensitivity and dynamic range of neutron methods. In this paper, we provide a flavor of the capabilities of modem neutron instrumentation for the study of hydrogen in a number of technologically interesting systems, including metal hydrides, fuel-cell materials, fullerenes, and disordered carbons.

Jan 1, 2002

By Thomas Brynjulfsen, Merete Tangstad, Eli Ringdalen

Manganese ore fines cannot be added to the submerged arc furnace directly as they will prevent even gas flow through the burden. Low gas permeability in the burden will lower the degree of pre-reduction of ore subsequently increase the carbon and energy consumption of the process. In order to utilize manganese ore fines in the furnace, they are typically agglomerated into sinter. In this work, the melting and reduction properties of Gabonese sinter and Gabonese ore have been investigated in pilot scale experiments. Two experiments were conducted, one with 100% sinter as manganese source and one with 50/50 sinter and ore. Lime was used to achieve a charge basicity of 0.72 in both experiments. The composition of slag samples from the excavation of the furnace was established using EPMA(WDS), and the composition of the tapped slag and metal was found using XRF. It was found that while the coke-bed size would determine the tapped slag composition, the melting behavior of the Mn source would determine the mixing with lime.

Jan 1, 2014

By L. L. Tavlarides, N. V. Deorkar

"Recovery/Recycling of metal ions from industrial process waste streams is a preferred alternative to disposal by conventional techniques. This paper presents methods for preparation of inorganic chemically active adsorbents to be used in fixed bed adsorbers. Methods for immobilization of chelating agents on the inorganic supports are discussed. The prepared adsorbents are characterized to determine coverage density of functional groups, effect of pH on metal ion removal efficiency, regeneration efficiency and uptake capacity. Results from the laboratory scale and bench scale experiments are presented here.IntroductionRemoval of heavy metal ions from processing wastes in various industries is an important problem. Waste streams in electroplating, electronic, catalyst preparation and hydrometallurgical industries contain metal ions such as copper, nickel, chromium, lead, tin, cadmium, silver, gold and platinum. One major concern for the non-ferrous metal industry is secondary recovery of precious metals and cyanide from cyanide leachate from smelter residue and hydrometallurgical waste streams.Recovery methods recently considered include evaporation, electrolyte metal recovery, reverse osmosis (1), adsorption, ion exchange (2,3), membrane separation (4,5) and Solvent extraction. These processes have met with various levels of limited success. The use of liquid ion exchange molecules to selectively extract metal ions for on-site treatment of these waste streams is currently receiving substantial interest (6,7). This interest seems from an awareness of the advances made in the development of commercial extractants for metal ion separation in hydrometallurgical industries (8). However, separation by solvent extraction processes is generally considered to be economical in the range of aqueous metal ion concentrations from 0.01 to 1.0 mol/lit (9). In order to exploit the selectivity of chelating agents, the idea of immobilizing chelating agent into a solid matrix has attracted growing attention in recent years. Many supports such as inorganic oxides, organic polymers, cellulose powder and polyurethane foam can be used for immobilization of chelating agents. Over the last decade, considerable efforts have been directed toward attachment/introduction of chelating agents into a polymer matrix (10,11). Inorganic supports as compared to polymer supports provide high mechanical strength, chemical and thermal stability, and high reaction rates due to open pore structure. On the contrary, organic resins shrink and swell, thus affecting mass transfer (12). Many of the disadvantages of polymer supports can be excluded by the use of inorganic supports. Innovative use of immobilization techniques can produce inorganic chemically active adsorbents with comparable capacity, stability and reaction rates. Consequently, the objective of our program is the development of inorganic chemically active adsorbents to be used in a fixed-bed unit operation as an alternative heavy metal ion recovery process. Methods of preparation of inorganic chemically active adsorbents, (ICAAs) characterization and applications are discussed in this paper. A brief summary of the results from laboratory scale studies and bench scale studies is presented."

Jan 1, 1996