METALLURGICAL AND MATERIALS TRANSACTIONS B
ABSTRACTS
Volume 28B, No. 10, October 1997

This Month Featuring: The 1996 Howe Memorial Lecture; 1996 Distinguished Lecture in Materials & Society; Hydrometallurgy; Pyrometallurgy; Transport Phenomena; Process Control; Physical Chemistry; Solidification; Solid State Reactions; Materials Processing; Welding & Joining; Mathematical Modeling. View October 1997 Contents.

THE 1996 HOWE MEMORIAL LECTURE

Future Steelmaking Technologies and the Role of Basic Research
R.J. FRUEHAN
The steel industry is going through a technological revolution that will not only change how steel is produced but also the entire structure of the industry. The drivers for the new or improved technologies, including reduction in capital requirements, possible shortages in raw materials such as coke and low residual scrap, environmental concerns, and customer demands are briefly examined. The required response of the industry to these drivers will be new processes such as direct ironmaking, near net shape casting, and those to improve charge materials to the electric arc furnace (EAF).

The know-how for these process improvements and revolutionary technologies can be purchased, if it exists. However, since the U.S. industry has a unique set of drivers, it may be necessary to develop many of the new technologies through its own research and development. The current status of research and development in the United States and selected international producers was examined. As expected, it was found that the industry's research capabilities have been greatly reduced. Fur thermore, less than half of the companies that identified a given technology as critical have significant research and development programs addressing the technology. It is clear that, in many cases, these technologies must be developed collaboratively using all of the intellectual resources available, in cluding universities. Much of the basic process understanding and data for optimization can be obtained from basic research, which is highly focused on the requirements of the new process, thus eliminating some expensive pilot plant trials.

Examples of how basic research aided in process improvements in the past are given. The examples include demonstrating how fundamentals of reaction kinetics, improved nitrogen control, and ther modynamics of systems helped reduce nozzle clogging and how fluid flow studies reduced defects in casting. However, in general, basic research did not play a major role in processes previously developed but helped our understanding and aided optimization. To have a major impact, basic research must be focused and be an integral part of any new process development. An example where this has been done successfully is the AISI Direct Ironmaking and Waste Oxide Recycle projects, in which fundamental studies on reduction, slag foaming, and postcombustion reactions have led to process understanding, control, and optimization. Industry leaders recognize the value and need for basic research but insist it be truly relevant and done with industry input. From these examples, the lessons learned on how to make basic research more effective are discussed.

1996 DISTINGUISHED LECTURE IN MATERIALS & SOCIETY

Report from a Traveler: "A New Silk Road"
PETER CANNON
Dr. Peter Cannon currently serves as Managing Partner of VRE Company, an entrepreneurial and financial consultancy, and Advisory Director of Intec, Inc. Dr. Cannon is co-founder of Conductus, Inc., served 15 years as Rockwell International's Vice President and Chief Scientist, was an executive with General Electric's electronic businesses, and began his career at Proctor and Gamble. He began his career after graduating from the University of London with a Ph.D. in Physical Sciences. Dr. Cannon's academic teaching experience includes the Darden Graduate School of Business at the University of Virginia, the Graduate School of the Polytechnic University of New York and New Mexico State University. Along with publishing over 120 papers and patents on research, business, and policy matters, Dr. Cannon has served on several advisory panels, including the College of Engineering at Cornell University, the Division of Physical Sciences at the University of Chicago, and is a long-term visitor to North Carolina A&T University. His governmental service includes Chairmanship of the White House Initiative on the Historically Black Research Universities, various selection panels of NSF, Vice Chairman of the National Research Council's Board on Engineering Education, and Advisory Director of the Defense Reinvestment Program, which trains aerospace workers as classroom teachers in Los Angeles.

HYDROMETALLURGY

The Behavior of Thallium during Jarosite Precipitation
J.E. DUTRIZAC
Jarosite precipitation provides an effective means of eliminating thallium from zinc processing circuits, and a systematic study of the extent and mechanism of thallium removal during the precipitation of ammonium, sodium, and potassium jarosites was carried out. Thallium (as Tlp+) substitutes for the "alkali" ion in the jarosite structure. Nearly ideal jarosite solid solutions are formed with potassium, but thallium is preferentially precipitated relative to either ammonium or sodium. Approximately 80 pct of the dissolved thallium precipitates during the formation of ammonium jarosite; the extent of thallium removal is virtually independent of thallium concentrations in the 0 to 3000 mg/L Tl range and of the presence of 75 g/L of dissolved Zn. Although the deportment of thallium is nearly independent of (NH4)2SO4 or Na2SO4 concentrations >0.1 M, the precipitates made from more dilute media are relatively enriched in thallium. Likewise, the precipitates made from dilute ferric ion media are also Tl-rich. Low solution pH values or low temperatures both significantly reduce the amount of jarosite formed, but the precipitates made under these conditions are enriched in thallium. Furthermore, because thallium jarosite is more stable than the ammonium or sodium analogues, the initially formed precipitates are consistently Tl rich. The presence of jarosite seed accelerates the precipitation reaction, but dilutes the thallium content of the product. The results suggest that most of the thallium in a hydrometallurgical zinc circuit could be selectively precipitated in a small amount of jarosite, by carrying out the precipitation reaction for a short time in the absence of seed and from solutions having low alkali concentrations.

Object-Oriented Simulation of Hydrometallurgical Processes: Part I. Requirements and Implementation
C.T. KIRANOUDIS, N.G. VOROS, T. KRITIKOS, Z.B. MAROULIS, D. MARINOS-KOURIS, N. PAPASSIOPI, O. DIMITROPOULOU, I. PASPALIARIS, and A. KONTOPOULOS
Flowsheeting is an important engineering activity, arguably the most important, because it is the basis for analyzing process interactions within a specific flowsheet. An effective flowsheeting program can enhance the design procedure, and thus, improve the entire decision-making strategy. A number of requirements make the development of a flowsheeting system a complex task; useful and directed assistance requires a meaningful representation of process models to be kept in a computable form. The system should furthermore have the flexibility to provide support for exploration, evolution, cooperation, and integration. The described work addressed the preceding issues, and proposes solution for their achievement using a modular steady-state simulation tool (Process Integrated Simulator for Metallurgical Applications (PRISMA)) that is developed in order to model and simulate hydrometallurgical processes. A review of the simulator structure, along with its operation, is presented. Its development is based on object-oriented technology aspects appropriately analyzed and emphasized. User input to the simulator consists of flowsheet description, specification of the unit design variables and feed streams, as well as appropriate figures for the economic evaluation of the plant. The information introduced is passed to the simulator by means of an appropriate user interface developed in object-oriented code. Flowsheet computations are carried out by means of the execution part of the simulator.

Object-Oriented Simulation of Hydrometallurgical Processes: Part II. Application to the Bayer Process
C.T. KIRANOUDIS, N.G. VOROS, T. KRITIKOS, Z.B. MAROULIS, D. MARINOS-KOURIS, N. PAPASSIOPI, O. DIMITROPOULOU, I. PASPALIARIS, and A. KONTOPOULOS
The steady-state process simulator developed by Kiranoudis et al. has been used for the detailed simulation of the Bayer process flowsheet. It consists of the digestor/flash section as well as the precipitation and washing circuits. Advanced hydrometallurgical process models for the specific unit operations involved were developed and are appropriately described. The simulation studies mainly focus on studying the overall effects of certain design parameters on the entire plant efficiency. The overall performance of the bauxite digestion section is greatly and positively affected by the free-soda concentration of the feed liquor, the corresponding concentration of solid particles, and the operation temperature of the circuit. Precipitation of alumina in crystallizers is greatly affected by the corresponding soda concentration of the washing unit product stream, indicating the importance of this section. Furthermore, ambient temperature is important to the precipitation kinetics, influencing negatively the quantitative precipitation but resulting in particle populations of higher mean diameter.

Object-Oriented Simulation of Hydrometallurgical Processes Part III. Application to Leaching of Laterites and Pyrites
C.T. KIRANOUDIS, N.G. VOROS, T. KRITIKOS, Z.B. MAROULIS, D. MARINOS-KOURIS, N. PAPASSIOPI, O. DIMITROPOULOU, I. PASPALIARIS, and A. KONTOPOULOS
The steady-state process simulator developed by Kiranoudis et al. has been used for the detailed simulation of sulfuric acid pressure leaching of laterite ores for the extraction of nickel and cobalt, and aqueous pressure oxidation of pyrites for the recovery of gold. Advanced hydrometallurgical process models for the specific unit operations involved were developed and are appropriately de scribed. The simulation mainly focuses on studying the overall effects of certain design parameters on the entire plant efficiency. In the case of pyrites, the autothermal performance of the pressure autoclaves can be maintained by means of the oxidized recycle stream that greatly influences the fundamental heat balances of the reactor. Flashing the reactor pulp at the exit of the autoclaves results in further precipitation of solids related to ionic equilibrium reactions. The effect of grinding is important since most reactions are facilitated by small particle diameters. The ratio of feed pyrites influences the amount of precipitation of solids in the autoclave.

PYROMETALLURGY

Influence of Slag and Foam Characteristics on Reduction of FeO-Containing Slags by Solid Carbon
R.K. PARAMGURU, R.K. GALGALI, and H.S. RAY
The present study reports experimental results on the reduction of FeO in molten CaO-SiO2-Al2O3-MgO-FeO slags by solid carbon in an extended-arc plasma reactor. The reduction reaction was found to be controlled by mass transport of FeO in liquid slag. The CO gas generated stirs the bath to establish a convective mass transport system. CO also causes foaming. An analysis using dimensionless numbers provides correlations between the rate constant, k, as well as the foaming index, , with some properties of the slag such as viscosity, surface tension, and density. A correlation between k and is also developed using these parameters for slag characteristics.

Thermodynamic Modeling of Selenide Matte Converting
D.R. SWINBOURNE, A. YAZAWA, and G.G. BARBANTE
A by-product of the electrorefining of anode copper is a slime that contains significant amounts of silver, as well as selenium, copper, and other minor elements such as gold. Slimes are usually smelted to recover silver and gold. The thermodynamics of the smelting of such selenium-rich materials have received scant attention, and the little that has been done leads to erroneous predictions. In this work, a chemical potential diagram is developed that successfully explains previously published observations. The smelting of slimes was also modeled with a computational thermodynamics package. Despite the simplicity of the model, which assumed that the activity coefficients of all species remained constant throughout oxidation, it gave good agreement with experimental results published elsewhere for the compositions of all phases during smelting. The model was used to demonstrate that using air rather than pure oxygen significantly affected only the selenium content of the slag, reducing it to low levels. Smelting temperature in the range tested was shown not to be an important process variable.

Reduction Kinetics of Liquid Iron Oxide-Containing Slags by Carbon Monoxide
T. UTIGARD, G. SANCHEZ, J. MANRIQUEZ, A. LURASCHI, C. DIAZ, D. CORDERO, and E. ALMENDRAS
The reduction of iron oxides from liquid slags is important in the nonferrous as well as the ferrous industry. In the primary smelting of copper, the trend is to produce copper mattes with increasing contents of copper. This is accomplished by increasing the degree of oxidation, leading to more oxidized slags with higher copper contents. To recover this copper, the high magnetite content of these slags has to be reduced in a separate slag cleaning process. Laboratory reduction experiments on commercial copper slags using carbon monoxide-containing gases show that the reduction rate increases with increasing injection depth and slag temperature. The reduction rate was found to follow the relationship

Rate = 7.9 · 105 · e · pCO (Pa)

with an activation energy of 360 ± 20 kJ/mol.

TRANSPORTATION PHENOMENA

Experimental Studies of the Viscosities in the CaO-FenO-SiO2 Slags
F.-Z. JI, DU SICHEN, and S. SEETHARAMAN
In the present work, the viscosities in the CaO-FenO-SiO2 ternary system have been measured by the rotating cylinder method involving a spindle and crucible made of iron. Nine slag compositions in the ternary system have been chosen with CaO varying between 5.5 and 45.5 pct mass, FeO between 10.0 and 70.0 pct mass, and one measurement each in the binary FenO-SiO2 and CaO-SiO2 melts. The measurements have been carried out in the temperature range of 1423 to 1753 K. The viscosity in this system is described as a function of temperature and composition using the model approach developed earlier at the present laboratory. The isoviscosity lines have been predicated at 1573, 1673, and 1723 K. Good agreement between the calculated results and the experimental data has been obtained.

PROCESS CONTROL

A Study on the Improvement of the Sintered Density of W-Ni-Mn Heavy Alloy
MOON-HEE HONG, JOON-WOONG NOH, WOON HYUNG BAEK, EUN-PYO KIM, HUENG-SUB SONG, and SEONG LEE
Liquid phase sintering behavior of 90W-6Ni-4Mn heavy alloy has been studied. The present work takes into account the thermodynamic oxidation/reduction reactions of the constituent elements W, Ni, and Mn. The sintering cycle consists of heating under high purity nitrogen gas, holding at reduction temperatures after the atmosphere is changed to dry hydrogen, and sintering at 1260°C for 1 hour. As the reduction temperature increases from 1050°C to 1200°C, the relative sintered density increases from 92 pct, reaching 100 pct at temperatures above 1150°C. The relative density increases with increasing holding time at the reduction temperature and remains unchanged with heating rate. The sintered microstructure has been analyzed by a scanning electron microscope and energy dispersive X-ray spectroscopy. The relative density was compared with those obtained from other investigators. It is found that the formation of manganese oxide due to reducing reactions of W and Ni powders should be avoided in order to obtain a W-Ni-Mn heavy alloy without pores.

Arc Voltage Distribution Properties as a Function of Melting Current, Electrode Gap, and CO Pressure during Vacuum Arc Remelting
RODNEY L. WILLIAMSON, FRANK J. ZANNER, and S.M. GROSE
An industrial vacuum arc remelting experiment was carried out at Cytemp Specialty Steel Corp. (Titusville, PA) during which a 0.432-m-diameter Alloy 718 electrode was remelted into a 0.508-m-diameter ingot. The purpose of the experiment was to investigate the response of the arc voltage distribution properties (mean, standard deviation, and skewness) and the drip-short frequency to melting current, electrode gap, and CO pressure. The responses were characterized by recording and analyzing changes in the temporally averaged properties. Each independent variable was systematically varied in accordance with a modified Yates order factor space experimental design within the following ranges: melting current, 5000 to 11,200 A; electrode gap, 0.004 to 0.056 m; and CO pressure, 0.40 to 14.7 Pa. Statistical models were developed describing the correlation between the averaged arc voltage distribution properties and the independent variables. The models demonstrate that all of the voltage distribution properties, as well as the drip-short frequency, are directly related to electrode gap. An arc column model is presented to account for the mean arc voltage properties and the model is used to estimate the arc column pressure. The potential usefulness of the distribution properties as process diagnostics and control responses is evaluated.

PHYSICAL CHEMISTRY

Minimization of Hexavalent Chromium in Magnesite-Chrome Refractory
Y. LEE and C.L. NASSARALLA
The fundamentals on the formation of Cr6+have been studied from two points of view: thermodynamic and kinetic. Thermodynamically, the CaO-Cr2O3 phase diagram can be used as a guide to understand the formation of Cr6+ as a function of temperature and composition. The Cr6+ content, in the CaO-Cr2O3 phase diagram, increases with exposure to temperatures below 1022°C and with an increase in CaO (from 0 to 42 pct CaO). In kinetics, the chromite phase size also plays a major role in the formation of Cr6+. A decrease in chromite phase size increases the Cr6+ content in the refractory. The use of fused grains also decreases the formation of Cr6+. In the case of magnesite-chrome refractories, temperature, basicity (CaO/SiO2), and chromite phase size play important roles in Cr6+ formation. The formation of Cr6+ can be minimized by carefully controlling the amount of calcium oxide in the refractory and by avoiding the use of a fine chromite phase during brickmaking.

Thermodynamic Properties of Titanium and Iron in Molten Silicon
TAKAHIRO MIKI, KAZUKI MORITA, and NOBUO SANO
Titanium and iron in silicon are known as harmful "lifetime killer" impurities, which shorten the lifetime of excited carriers in silicon solar cell and disturb power generation. Therefore, the removal of titanium and iron is one of the most important topics for the production of solar grade silicon. Thermodynamic properties of titanium and iron in molten silicon were determined at 1723 K by equilibrating molten silicon-titanium alloys or molten silicon-iron alloys with molten lead, which has a limited mutual solubility for both alloys. The activity coefficients of infinite dilution, self-interaction coefficients of titanium and iron in molten silicon, and the Gibbs energy change of mixing for silicon- titanium and silicon-iron at 1723 K relative to pure liquid silicon, titanium, and iron were determined.

The Polynomial Representation of Thermodynamic Properties in Dilute Solutions
ARTHUR D. PELTON
Attempts to extend the interaction parameter formalism to higher-order polynomials and to render it thermodynamically consistent at finite solute concentrations have resulted in much confusion. The literature is reviewed with a view to clarifying the issues. The problem is best and most simply resolved through extension of the quadratic formalism, which has a sound theoretical foundation. A new and general set of equations for estimating higher-order parameters from binary parameters is derived. The applicability of using molar ratios rather than mole fractions in the polynomial expan sions is discussed. The formation of associate species (such as the formation of "AlO" associates in molten Fe) is treated. In such cases of strong solute-solute interactions, the usual practice of expressing the interaction parameters as linear functions of (1/T) is invalid. Finally, for more con centrated solutions, the advantage of using the Kohler or Toop interpolation models rather than the commonly used Muggianu model is shown.

Communication: Thermodynamics on the Formation of Spinel Nonmetallic Inclusion in Liquid Steel
HIROYASU ITOH, MITSUTAKA HINO, and SHIRO BAN-YA

Communication: Thermodynamics of Calcium and Oxygen in Molten Ti3Al
YOSHINAO KOBAYASHI and FUMITAKA TSUKIHASHI

SOLIDIFICATION

Particle Penetration during Spray Forming and Co-Injection of Ni3Al + B/Al2O3 Intermetallic Matrix Composite
D.E. LAWRYNOWICZ, B. LI, and E.J. LAVERNIA
Intermetallic matrix Ni3Al + B/Al2O3 composite, with 11 vol pct of Al2O3 particles incorporated into the matrix, was synthesized using a spray atomization and coinjection method. The penetration behavior of ceramic particles into atomized droplets during spray atomization and coinjection of Ni3Al + B/Al2O3 composite was investigated experimentally and numerically. It was found that the extent of incorporation of Al2O3 into Ni3Al + B droplets depends on the solidification condition of the droplets at the time of droplet/particle interaction. Penetration was observed only in fully liquid droplets or partially solidified droplets. No penetration was observed for droplets smaller than ~40 µm, because droplets in this size range were fully solidified at the point of coinjection, and pene tration was not possible for fully solidified droplets. The distribution of penetrated Al2O3 in the Ni3Al + B droplets was, in general, uniform, with no trends of segregation observed. However, it was noted that most Al2O3 particles were located at the grain boundaries inside the droplets, while some Al2O3 particles were trapped inside the droplets by primary dendrite arms resulting from a fast moving solidification front typically associated with rapid solidification processes such as spray atomization. Finally, it was believed that the Al2O3 particles facilitated nucleation upon penetration of the Ni3Al + B droplets either by means of thermal gradients or compatibility of preferred growth planes.

SOLID STATE REACTIONS

Minimizing Beta Flecks in the Ti-17 Alloy
CLIFFORD E. SHAMBLEN
Normal liquid to solid partitioning of Cr during ingot solidification for the Ti-17 alloy can result in the formation of a segregation anomaly called " flecks." These flecks can exhibit a significantly lower transus than the alloy; they may also present mechanical property issues. While the major thrust toward minimizing flecks is through melt process control, this article addresses the capability of reducing the extent of Cr segregation using a high-temperature field homogenization heat treat ment. The interdiffusion coefficients for Cr in phase Ti-17 were determined and used in diffusion equations to calculate the rate of dissipation of the segregated regions. Correlation is shown for the calculated, and critical experiment demonstrated, increase in the fleck transus temperature with the time and temperature of these homogenization heat treatments.

MATERIALS PROCESSING

Micropyretic Synthesis of Tough NiAl Alloys
G.K. DEY and J.A. SEKHAR
NiAl has been produced by micropyretic synthesis in a tougher state by adding Cr, V, and Fe. The mechanical properties of the alloys have been evaluated. Fracture toughness values as high as 9.5 M Pa have been obtained. The effect of different process variables like particle size, diluents, and extent of preheat on the process of synthesis and the microstructure have been ascertained. Diluents, when present in small quantities, have been found to enhance the combustion process in NiAl without significantly affecting the microstructure of the alloy. Preheating of the specimen prior to synthesis however had a profound influence on the microstructure. The microstructures of the alloys have been examined for chemical homogeneity and the defect structure. The sequence of steps leading to the formation of NiAl from elemental powders during the process of micropyretic synthesis has been determined.

The Effect of Silica-Containing Binders on the Titanium/Face Coat Reaction
C. FRUEH, D.R. POIRIER, and M.C. MAGUIRE
The interactions of CP-Ti and Ti-6Al-4V with investment molds containing alumina/silica and [chyttria/silica face coat systems were studied. "Containerless" melting in argon was employed and small test samples were made by drop casting into the molds. The effects of the face coat material and mold preheat temperatures on the thickness of the alpha case in the drop castings were evaluated with microhardness and microprobe measurements. It was found that the thickness of the alpha case was the same, whether a yttria/silica or alumina/silica face coat was used, indicating that the silica binder can reduce the apparent inertness of a more stable refractory, such as yttria. It was also found that the alloyed titanium castings had a thinner alpha case than those produced from CP-Ti, which suggests that the thickness of the alpha case depends on the crystal structure of the alloy during cooling from high temperatures. Furthermore, the small drop castings made in small yttria crucibles used as molds exhibited little or no alpha case.

Communication: Preparation of Fine Ceria Powders by Hydrolysis of Cerium(IV) Carboxylate Solutions
YASUHIRO KONISHI, SATORU ASAI, TETUYA MURAI, and HIROFUMI TAKEMORI

WELDING & JOINING

Interfacial Reactions in Molten Sn/Cu and Molten In/Cu Couples
LEE-HO SU, YEE-WEN YEN, CHAO-CHING LIN, and SINN-WEN CHEN
The interfacial reactions of molten Sn and molten In with solid Cu substrate were determined by studying their reaction couples. The annealing temperature was 300°C. The phases formed at the interface were examined by optical microscopy, scanning electron microscopy, and electron probe microscopy analysis (EPMA). The thickness of the reaction layers was measured using an image analyzer. For Cu/Sn couples, two phases, and , were found. Only the Cu11In9 phase was observed at the interface of the Cu/In couples. In comparison with the results of couples of solid Sn and solid In with solid Cu substrate, their phase formation sequences were similar; however, the interfacial morphology and the reaction rates were different. For the liquid/solid couples, the reaction rate was much faster and the interface was nonplanar. A mathematic model was also proposed to describe the dissolution of the Cu substrate and the growth of the intermetallic compounds. Fast dissolution of the substrate was observed in the beginning of the reaction and was followed by a relatively slow growth of the intermetallic compounds at the interface.

MATHEMATICAL MODELING

A Numerical Investigation of Gas Flow Effects on High-Pressure Gas Atomization Due to Melt Tip Geometry Variation
J. MI, R.S. FIGLIOLA, and I.E. ANDERSON
A parametric numerical study is presented on how melt feed tube geometry influences the gas flow field of a high-pressure gas atomizer (HPGA). The axisymmetric, turbulent, compressible Navier-Stokes equations are solved for the gas-only flow in the vicinity of the melt tip for a confined-feed, annular-slit atomizer. The numerical results indicate that a fully retracted melt tip can develop a high overambient base pressure over a wide range of operating pressures, while an extended melt tip can develop a subambient pressure, called an aspirating effect, which encourages melt to flow. Adding a taper angle to an extended melt tip decreases the aspirating effect. However, a melt tip can develop a radial pressure gradient along its base that forces the melt to move radially outward into a high-shear region of the flow, thus encouraging droplet formation. A fully retracted melt tip develops the highest such radial force, but this tends to decrease in magnitude with tip extension. Hence, a compromise must be established whereby the good aspiration character of a longer tip is balanced against the good pressure-driving force along the base of a shorter tip. The results provide details of the flow field and the effects due to variation of melt tip taper and extension.

Thermosolutal Convection and Macrosegregation during Solidification of Hypereutectic and Hypoeutectic Binary Alloys in Statically Cast Trapezoidal Ingots
M.A. RADY, V.V. SATYAMURTY, and A.K. MOHANTY
Thermosolutal convection patterns and evolution of macrosegregation during solidification of hy pereutectic and hypoeutectic NH4CL-H2O binary systems in trapezoidal side-chilled ingots with neg ative and positive slopes have been numerically investigated. The results have been compared with the base case of solidification in a rectangular ingot. During solidification of NH4CL-70 pct H2O hypereutectic alloy, channels and "A segregates" develop early in the solidification process. When the slope is positive, channels penetrate to a larger distance inside the ingot. Whereas, for negative slope, they are shifted outward toward the chilled wall and are vertically oriented. During solidifi cation of NH4CL10 pct-H2O hypoeutectic alloy, circulation cells which emerge in the narrow melt at later stages of the process are shown to be responsible for the development of V-shaped segregates in the final casting. The final degree of macrosegregation is higher for both positive and negative slopes of the ingot chilled wall compared to the rectangular ingot.

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