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Volume 27B, No. 3, June 1996 This Month Featuring: The 1995 Distinguished Lecture in Materials and Society; Hydrometallurgy; Pyrometallurgy; Electrometallurgy; Transport Phenonema; Physical Chemistry; Solidification; Solid State Reactions; Welding & Joining; Surface Treatment; and Mathematical Modeling. View June 1996 Table of Contents.
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THE 1995 DISTINGUISHED LECTURE IN MATERIALS AND SOCIETY
Materials and Society--Impacts and Responsibilities
A.R.C. WESTWOOD
The needs of today's advanced societies have moved well beyond the requirements for food and shelter, etc., and now are focused on such concerns as international peace and domestic security, affordable health care, the swift and secure transmission of information, the conservation of resources, and a clean environment. Progress in materials science and engineering is impacting each of these concerns. This article will present some examples of how this is occurring and then comment on ethical dilemmas that can arise as a consequence of technological advances. The need for engineers to participate more fully in the development of public policies that help resolve such dilemmas, and so promote the benefits of advancing technology to society, will be discussed.
HYDROMETALLURGY
Bioleaching of Lateritic Nickel Ore by Ultrasound
R.N. KAR, L.B. SUKLA, K.M. SWAMY, V.V. PANCHANADIKAR, and K.L. NARAYANA
The bioleaching of nickel from lateritic ore of Orissa, India, using a native Aspergillus niger strain was studied with and without ultrasound. Different parameters, such as spore concentration, amount of dextrose in the medium, pulp densities, and sonication time, were studied for maximizing the extraction of nickel. Enhanced recoveries and reduction in leaching time were demonstrated using ultrasound. The highest amount of nickel, 95 pct, was extracted in 14 days with an inoculum size of 106 spore/mL and 2 pct dextrose in the medium under 30 minutes ultrasonic pretreatment using 43 KHz frequency at 1.5 W/cm2 intensity. It was also found that ultrasound assists in selective leaching of nickel over iron.
Electrochemical Behavior of the Dissolution of Gold-Silver Alloys in Cyanide Solutions
XIAOWEI SUN, Y. CHARLES GUAN, and KENNETH N. HAN
The dissolution behavior of gold and silver from Au/Ag alloys in aerated cyanide solutions has been investigated using rotating disc electrodes. The variables studied included concentration of cyanide, oxygen partial pressure, and rotating speed of the disc. The dissolution potential and the rate of dissolution were obtained in view of the anodic and cathodic current-potential relationships. The results were discussed in terms of the mixed potential theory. The results showed that the dissolution rate of gold and silver from the alloys was partially controlled by chemical reaction but largely controlled by transport of either oxygen or cyanide, depending on their relative concentrations under the experimental conditions employed in this study. The diffusion coefficient of free cyanide, DCN-, was found to be (1.25 +/- 0.05) X 10-5 cm2/s. The diffusion coefficient of oxygen, DO2, was calculated to be (1.29 +/- 0.02) X 10-5 cm2/s.
PYROMETALLURGY
A Kinetic Study of the Reaction of Zinc Oxide with Iron Powder
J.R. DONALD and C.A. PICKLES
Electric arc furnace (EAF) dusts contain significant quantities of zinc, mostly in the form of zinc oxide. This dust has been classified as a hazardous waste due to the presence of lead, cadmium, and hexavalent chromium. It is important that environmentally acceptable processes be developed to treat this waste. One possible alternative process would involve reacting the zinc oxide in the dust with either solid or liquid iron. In addition, in the carbothermic reduction processes, which have been designed to treat the dust, metallic iron is formed, and this iron can participate in the reduction of zinc oxide. In the present research, the reduction of zinc oxide by iron according to the reaction
was studied using a thermogravimetric technique. Briquettes of zinc oxide powder and electrolytic iron were reacted in the temperature range of 1073 to 1423 K in an argon atmosphere. First, a thermodynamic analysis was performed using the Facility for the Analysis of Chemical Thermodynamics (F*A*C*T) computational system, and then the effect of experimental variables on the reaction kinetics was determined. These variables included argon gas flow rate, reaction temperature, reagent particle size, iron to zinc oxide ratio, aspect ratio of the briquette, briquetting pressure, and alkali and alkaline earth additions. It was found that, initially, the reaction was chemically controlled with an activation energy of 230 kJ/mol. Additions, such as sodium chloride and calcium fluoride, promoted the reaction, and the activation energies were 172.5 and 188.7 kJ/mol, respectively. Once a product layer had formed, the reaction was limited by the diffusion of zinc gas away from the reaction interface. The experimental data were fitted to a parabolic rate law, and the parabolic rate constant was found to be
Chemical Potentials of Oxygen for Mixtures of CaO (s)+Ca4P2O9 (s)+{CaO+P2O5+FexO} Melts and Ca4P2O9 (s)+ Ca3P2O8 (s)+ {CaO+P2O5+FexO} Melts
HIDEAKI HOSHINO and MASANORI IWASE
Electrochemical measurements involving stabilized zirconia as solid electrode and Mo + MoO2 as reference electrode were conducted in order to determine the chemical potentials of oxygen for three-phase assemblages of CaO(s) + Ca4P2O9(s) + liquid and Ca4P2O9 + Ca3P2O8 + liquid within the system CaO + FexO + P2O5. The results for the former are
while for the latter,
The Use of Blast Furnace Slag and Derived Materials in the Vitrification of Electric Arc Furnace Dust
F.A. LÓPEZ, E. SÁINZ, A. LÓPEZ-DELGADO, L. PASCUAL, and J.M. FERNÁNDEZ NAVARRO
The electric arc furnace (EAF) dust was added to blast furnace granulated slag or a gel produced by dissolving slag in HNO3/EtOH followed by alkaline hydrolysis and gelification, and then it was vitrified. The proportion of EAF dust used was between 5 and 30 wt pct. The physicochemical properties of the glasses produced were studied by the X-ray powder diffraction technique, differential thermal analysis, and transmission electron microscopy (TEM). Thermal properties (dilatometric softening point, glass transition temperature, and thermal expansion coefficient) were determined. Finally, analyses were performed on leachability and ecotoxicity. The results suggest that the use of either slag or slag-derived gel produces a borosilicate glass with thermal properties similar to those of conventional soda-lime-silicate glass.
Oxidation-Reduction Equilibrium of Cu2+/Cu+ in Binary Alkaline Sulfate Melts
T. YAMAMOTO, N. YAMANO-UCHI, K. MASAMURA, M. TAMURA, and M. IWASE
Oxidation-reduction equilibria for a Cu2+/Cu+ couple in binary alkaline sulfate melts, Li2SO4 + R2SO4 (R = Na, K, Rb, Cs), were determined at temperatures of 973, 1023, and 1073 K by equilibrating these melts with gas mixtures of Ar + O2 + SO2. RedOx equilibria are well interpreted by the average ionic radii of alkaline metals: r(average) = X(Li2SO4) r(Li) + X(R2SO4) r(R), where r and X denote, respectively, mole fraction and the ionic radii of alkaline metal. The oxygen anion activities would increase with an increase in R2SO4 mole fractions of binary sulfates Li2SO4 + R2SO4.
Communication: Liquid State Infrared Processing of SCS-6/Ti-6Al-4V Composites
S.G. WARRIER, R.Y. LIN, and S.K. WU
ELECTROMETALLURGY
Fundamental Studies of Copper Anode Passivation During Electrorefining: Part I. Development of Techniques
XUAN CHENG and J. BRENT HISKEY
Anode passivation is an extremely important phenomenon in commercial copper electrorefining operations. Due to the electrochemical nature of the refining process, various electrochemical techniques have been applied to examine anode passivation behavior. In this investigation, cyclic voltammetry, linear potential sweep, and chronopotentiometry measurements were carried out on several commercial copper anodes, as well as on pure electrowon (EW) copper cathode, in synthetic electrolytes simulating the primary constituents for industrial operations. The important parameters associated with anode passivation were identified and compared for the three electrochemical techniques. Chronopotentiometry is an extremely sensitive technique and proved to be the most suitable for analyzing and characterizing copper anode passivation.
TRANSPORT PHENONEMA
A Statistical Analysis of the Effect of a Mixture Component on the Rheology of Alumina Feedstocks
K.C. HSU and P.C. TSAI
A statistical analysis based on the McLean-Anderson design method was carried out in studying the influence of each formulation component on the flow properties of alumina feedstocks. The formulations were composed of alumina powder (AL), polypropylene resin (PP), paraffin wax (PW), and stearic acid (SA). Fourteen different formulations were designed and their viscosities were measured using a capillary viscometer. The corresponding rheological parameters, i.e., fluidity, pseudoplasticity, and flow energy (
E) were evaluated and the effects of each ingredient in the mixture on them were analyzed. The studied ranges of AL, PP, PW, and SA were 87 to 89, 5 to 9.25, 3 to 7.25, and 0.75 to 1.5 wt pct, respectively. The results indicated that the lower alumina content or higher binder content would improve the fluidity of feedstocks. The order of increase in fluidity is SA > PW > PP. An increase of either AL or SA or a decrease of either PP or PW would cause less shear thinning in the resulting mixtures. Polypropylene resin is more effective than PW in enhancing pseudoplasticity. Finally, E of feedstocks first decreases, reaches a minimum value at AL of about 87.7 wt pct, and then increases with powder loading. Increasing SA or decreasing either PP or PW would make E smaller.
PHYSICAL CHEMISTRY
A Study of the Thermal Decomposition of BaCO3
I. ARVANITIDIS, D. SICHEN, and S. SEETHARAMAN
In the present work, the decomposition reaction, BaCO3 (solid) = BaO (solid) + CO2 (gas), was investigated by thermogravimetric analysis (TGA) and differential thermal analysis (DTA) methods. Both shallow powder beds and densely compacted spheres of the carbonate were employed. In the case of the shallow powder beds, TGA and DTA were carried out simultaneously. The DTA curves showed that BaCO3 exhibited two phase transformations, the transformation of orthorhombic to hexagonal occurring at 1079 K and that of hexagonal to cubic at 1237 K. The activation energy and the forward reaction rate constant of the decomposition of BaCO3 were evaluated from the thermogravimetric results of the powder beds. The activation energy of the decomposition was found to be 305(±14) kJ · mole-1. The experimental results obtained with the compacted spheres were compared with those corresponding to the powder beds. After the initial stages, the formation of liquid due to the eutectic reaction between BaCO3 and BaO appears to play an important role in the reaction kinetics.
Standard Enthalpies of Formation of Dysprosium Alloys, Dy + Me (Me 
Ni, Ru, Rh, Pd, Ir, and Pt), by High-Temperature Direct Synthesis Calorimetry
QITI GUO and O.J. KLEPPA
The standard enthalpies of formation of 13 dysprosium alloys with late transition metals have been determined by direct synthesis calorimetry at 1474 ± 2 K. The following values of H°f (kJ (mole atom)-1) are reported: DyNi, -(35.2 ± 1.5); DyNi5, -(27.4 ± 0.7); DyRu2, -(27.3 ± 0.9); DyRh, -(76.5 ± 2.0); DyRh2, -(62.3 ± 0.8); Dy7Rh3, -(56.8 ± 2.2); DyPd, -(83.3 ± 2.0); Dy3Pd4, -(86.6 ± 2.1); DyPd3, -(76.2 ± 1.5); DyIr2, -(69.9 ± 2.1); DyPt, -(109.4 ± 1.8); DyPt2, -(98.1 ± 2.8); and DyPt3, -(82.8 ± 2.2). The results are compared with predicted values from the Miedema model and with available literature data for DyNi, DyNi5, DyPd, and DyPt.
Reoxidation of Aluminum in Fe-Al-M (M = C, Mn, and Ti) Melts with CaO-Al2O3-FetO (3 mass pct) Slags
KWANG RO LEE and HIDEAKI SUITO
An Fe-0.01 to 0.5 mass pct Al alloy and an Fe-0.003 to 0.71 mass pct Al-1 mass pct M (M = C, Mn, and Ti) alloy were reoxidized with the CaO-Al2O3-FetO (3 mass pct) slags at 1873 K in an Al2O3 or CaO crucible for 5 and 60 minutes. The contents of acid-insoluble Al, total O, and alloying element M in metal as well as those of M and FetO in slag were measured as a function of total Al content. On the basis of the present and previous results for Fe-Al-Te alloys, the effect of alloying elements on the degree of supersaturation with respect to the Al2O3 precipitation was studied. As a result, the supersaturation phenomenon was observed in all experiments at 5 minutes, but in the experiments at 60 minutes, it was observed only in Fe-Al and Fe-Al-Ti alloys. No supersaturation was observed in the reoxidation of Si in Fe-0.13 to 0.98 mass pct Si alloys with the CaO-SiO2-FetO (3 mass pct) slags in a CaO crucible at 5 and 60 minutes.
Vacuum Evaporation of KCl-NaCl Salts: Part II. Vaporization-Rate Model and Experimental Results
LILY L. WANG, TERRY C. WALLACE, SR., FREDRICK G. HAMPEL, and JAMES H. STEELE
A model based on the Hertz-Langmuir relation is used to describe how evaporation rates of the binary KCl-NaCl system change with time. The effective evaporation coefficient (
), which is a ratio of the actual evaporation rate to the theoretical maximum, was obtained for the KCl-NaCl system using this model. In the temperature range of 640°C to 760°C, the effective evaporation coefficient ranges from ~0.4 to 0.1 for evaporation experiments conducted at 0.13 Pa. At temperatures below the melting point, the lower evaporation coefficients are suggested to result from the more complex path that a molecule needs to follow before escaping to the gas phase. At the higher liquid temperatures, the decreasing evaporation coefficients result from a combination of the increasing vapor-flow resistances and the heat-transfer effects at the evaporation surface and the condensate layer. The microanalysis of the condensate verified that composition of the condensate changes with time, consistent with the model calculation. The microstructural examination revealed that the vaporate may have condensed as a single solution phase, which upon cooling forms fine lamellar structures of the equilibrium KCl and NaCl phases. In conclusion, the optimum design of the evaporation process and equipment must take the mass and heat transfer factors and equipment materials issues into consideration.
SOLIDIFICATION
Effects of Forced Electromagnetic Vibrations during the Solidification of Aluminum Alloys: Part I. Solidification in the Presence of Crossed Alternating Electric Fields and Stationary Magnetic Fields
CHARLES VIVÈS
A new magnetohydrodynamic method of transmitting forced vibrations to solidifying aluminum alloy melts has been developed. Contrary to the case of the conventional mechanoacoustic systems, this device lends itself very well to a fundamental investigation. The relatively accurate knowledge of both the electromagnetic pressure and the local velocity peaks has enabled us to reveal the specific effects of the oscillatory flow and of the cavitation phenomena on grain refinement. It has been shown that the cavitation threshold depends both on the surface state of the crucible internal walls and on the electromagnetic pressure peak. In the presence of well-developed cavitation situations, a very fine and homogeneous microstructure has been observed throughout the ingot. A laboratory prototype of a new magnetohydrodynamic cavity resonator, allowing for significant energy saving and likely to be used for industrial applications, including the elaboration of metal matrix composites by means of a preform infiltration process, was also the subject of experimentation.
Effects of Forced Electromagnetic Vibrations during the Solidification of Aluminum Alloys: Part II. Solidification in the Presence of Colinear Variable and Stationary Magnetic Fields
CHARLES VIVÈS
The influence on grain refinement of electromagnetic vibrations imposed during solidification of various aluminum alloys has been examined. The vibrations were produced, without any material contact with the solidifying alloys, by the simultaneous application of a stationary magnetic field B0 and a periodic magnetic field b(t) of 50 Hz frequency. Extensive grain refinement has been observed in both continuous casting and batch-type mold casting. This investigation shows that the mean grain size obtained by this electromagnetic vibrational method is smaller than that produced by the variable magnetic field acting alone (electromagnetic stirring), particularly when the alloys are characterized by a narrow freezing range.
SOLID STATE REACTIONS
Kinetics of Sulfation of Chalcopyrite with Steam and Oxygen in the Presence of Ferric Oxide
SANJAY PRASAD, B.D. PANDEY, and S.K. PALIT
The kinetics of sulfation of chalcopyrite with/without ferric oxide addition has been studied in the fixed bed for the temperature range 673 to 773 K in the absence of external mass transfer effects such as particle size of ore and flow rate of oxidizing gases such as steam and oxygen. The sulfation reaction was observed to be topochemical. The activation energy value of 30.5 kJ/mol was found when no catalytic addition was made. The rate of sulfation increases with the addition of ferric oxide. The rate constant values obtained without and with 10 pct Fe2O3 were 5.5 X 103 min-1 and 7.00 X 103 min-1, respectively. The activation energy value for the roasting in the presence of the catalyst was 29.2 kJ/mol under these conditions. Examination of the kinetic data indicates that the reaction occurred on the surface of the mineral particles and proceeded through the reactant and product phase boundary. The sulfated products were also characterized by metallography, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and X-ray diffractometry (XRD) studies.
Extending the Compositional Limit of Combustion-Synthesized B4C-TiB2 Composites by Field Activation
H. XUE and Z.A. MUNIR
Composites of B4C-TiB2 with molar ratios B4C/TiB2 of up to 8 were synthesized by field activated combustion. The combustion wave velocity depended on this ratio and increased approximately linearly with the applied field. The effect of the field was analyzed and its contribution to the combustion temperature was calculated. X-ray and microscopic analyses showed the synthesis to be a two-step process. Titanium boride forms at or near the leading edge of the combustion zone and B4C forms at or near the trailing edge.
WELDING AND JOINING
Dilution in Single Pass Arc Welds
J.N. DuPONT and A.R. MARDER
A study was conducted on dilution of single pass arc welds of type 308 stainless steel filler metal deposited onto A36 carbon steel by the plasma arc welding (PAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and submerged are welding (SAW) processes. Knowledge of the arc and melting efficiency was used in a simple energy balance to develop an expression for dilution as a function of welding variables and thermophysical properties of the filler metal and substrate. Comparison of calculated and experimentally determined dilution values shows the approach provides reasonable predictions of dilution when the melting efficiency can be accurately predicted. The conditions under which such accuracy is obtained are discussed. A diagram is developed from the dilution equation which readily reveals the effect of processing parameters on dilution to aid in parameter optimization.
SURFACE TREATMENT
Improved Oxidation Resistance of Group VB Refractory Metals by Al+ Ion Implantation
J.M. HAMPIKIAN, M. SAQIB, and D.I. POTTER
Aluminum ion implantation of vanadium, niobium, and tantalum improved the metals' oxidation resistances at 500°C and 735°C. Implanted vanadium oxidized only to one-third the extent of unimplanted vanadium when exposed at 500°C to air. The oxidative weight gains of implanted niobium and tantalum proved negligible when measured at 500°C and for times sufficient to fully convert the untreated metals to their pentoxides. At 735°C, implantation of vanadium only slightly retarded its oxidation, while oxidative weight gains of niobium and tantalum were reduced by factors of 3 or more. Implanted niobium exhibited weight gain in direct proportion to oxidation time squared at 735°C. Microstructural examination of the metals implanted with selected fluences of the 180 kV aluminum ions showed the following. The solubility limit of aluminum is extended by implantation, the body centered cubic (bcc) phases being retained to ~60 at. pct Al in all three metals. The highest fluence investigated, 2.4 X 1022 ions/m2, produced an ~400-nm layer of VAl3 beneath the surface of vanadium, and ~300-nm layers of an amorphous phase containing ~70 at. pct Al beneath the niobium and tantalum surfaces. All three metals, implanted to this fluence and annealed at 600°C, contained tri-aluminides, intermetallic compounds known for their oxidation resistances. Specimens implanted to this fluence were thus selected for the oxidation measurements.
MATHEMATICAL MODELING
A Process Model for On-Line Quenching of Aluminium Extrusions
NIKLAS JÄRVSTRÅT and STIG TJØTTA
A complete process model for the cooling of aluminium extrusions is presented. It is capable of predicting both thermally induced distortions and possible strength reductions. The model consists of three parts: a thermal part, a metallurgical part, and a mechanical part. The thermal part includes heat-transfer and heat-conduction models and generates the temperature history needed as input to the other two parts. The metallurgical part consists of a kinematic model for the precipitation of nonhardening particles during cooling, and it predicts the resulting strength after subsequent aging. Finally, the mechanical part comprises the usual compatibility and consistency equations, as well as a unified material model that is very accurate both for rate-dependent material behavior at high temperatures and for the virtually rate-independent behavior at low temperatures. Water-cooling experiments have been performed, and finite element simulations were executed using the process model. The heat-transfer coefficient for water quenching is shown to be extremely sensitive to geometry and other cooling conditions. In addition, the cooling characteristics and the material model are factors of equal importance in the prediction of distortions.
Transient Thermal Model of the Continuous Single-Wheel Thin-Strip Casting Process
GUOWEI LI and BRIAN G. THOMAS
A transient heat-transfer model (STRIP1D) has been developed to simulate the single-roll continuous strip-casting process. The model predicts temperature in the solidifying strip coupled with heat transfer in the rotating wheel, using an explicit finite difference procedure. The model has been calibrated using strip thickness data from a test caster at ARMCO Inc. (Middletown, OH) and verified with a range of other available measurements. The strip/wheel interface contact resistance and heat transfer were investigated in particular, and an empirical formula to calculate this heat-transfer coefficient as a function of contact time was obtained. Wheel temperature and final strip thickness are investigated as a function of casting speed, liquid steel pool depth, superheat, coatings on the wheel hot surface, strip detachment point, wheel wall thickness, and wheel material.
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