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By Animesh Jha, Chris Dometakis

"Without the use of a flux, only a poor dispersion of ceramic phase can be achieved. A molten-flux-assisted ceramic phase dispersion technique for producing aluminium alloy metalmatrix composites has been developed. In this paper, we report the physical chemistry for the dispersion of TiB2 in molten aluminium. In particular, aspects of the interfacial energy and the thermodynamics of the dispersion reactions are briefly discussed for enhancing the volume of dispersion phase in the molten metal and for controlling their morphology. This investigation also addresses the role of molten flux in the fabrication of AI-alloy mmc using a casting technique. The morphological aspects of the dispersion are explained on the basis of the classical theory· of nucleation.IntroductionMetal matrix composites (MMCs), have long been recognised as an important class of material due to their greater wear resistance, specific stiffness and temperature capability when compared to conventional monolithic alloys. Particulate reinforced composites produced by melt casting techniques have been amongst the first MMCs to achieve commercial market viability. The advent of melt mixing techniques such as the Duralcan™ process have enabled low cost, easily fabricated composites based on the AI-SiC and AIAlz0 3 systems to be produced. In this process, uncoated ceramic particles with diameters 10ltm and larger, are incorporated into conventional monolithic alloys with reinforcement levels up to 25 volume percent. The AI-7Si-SiC metal-matrix composites have good wear resistance, high strength, low density and high thermal conductivity. The combination of these physical and mechanical properties has become a major attraction for the fabrication of light-alloy composite disc rotor brakes for the automotive sector2. However, in silicon-free alloys, SiC is thermodynamically unstable above the composite melting point and is extensively attacked by the melt to form aluminium carbide3 :"

Jan 1, 1996

By Y. Huang, P. B. Prangnell

"An Al-0.1Mg alloy was firstly deformed at room temperature by ECAE to a true strain of 10, where a steady state deformation was established and further processing had little effect on grain refinement. The ECAE samples, with an average grain size of ~0.55µm, were then compressed in a channel die at 77K- 473K to various reductions. Microstructures were characterized by electron backscatter imaging and EBSD in a FEGSEM. Grain refinement to the ECAE submicron structure occurred during deformation at cryogenic temperatures of 77 – 213K, whereas coarsening took place during deformation at elevated temperatures. A steady state deformation was observed at all temperatures where a constant grain structure was developed and maintained upon further straining due to dynamic recovery. The mechanisms of dynamic recovery during steady state deformation at cryogenic temperatures are discussed.IntroductionSevere deformation processing (SDP) has been successfully used to produce submicron grain structures, and in some cases nano-scale crystallite sizes, in a wide range of alloys. However, the rate of grain refinement becomes increasingly inefficient at high strains as a steady state grain structure is approached [1-3]. Steady-state grain sizes have also been reported in other ultra-high strain deformation processes, like cryogenic ball-milling [4]. There is thus a minimum grain size achievable in a material by a given SPD process under constant deformation conditions.It is well documented that a steady state subgrain size is observed in warm deformation of metals due to dynamic recovery (e.g. [5]). In severely deformed alloys a constant grain size at ultra-high strains has similarly been attributed to dynamic recovery [1-3]. Mechanisms have been proposed, for rapid deformation induced grain growth including stress driven boundary migration and breakaway from solute pinning [2]. However, as pointed out by Humphreys et al. [2] the restoration processes are currently poorly understood, particularly at low temperatures, where the boundary migration rates required to maintain a constant grain size are orders of magnitude higher than can be satisfactory explained from diffusion controlled migration. Similar to the subgrain size, the steady state grain size obtained during SDP is generally related to the temperature compensated strain rate [2, 6]. Thermally activated restoration processes are thus expected to be suppressed by lowering the deformation temperature and a smaller steady state grain size can be achieved."

Jan 1, 2012

By N. Moelans

A method using an ex-situ electrochemical measurement device was developed to determine the oxygen potential of non-ferrous metallurgical slags. The electrochemical cell consists of the molten slag sample, an inert Ir electrode, a stabilized Zr02 solid electrolyte and a NiINiO reference electrode. Different slags from non-ferrous pyrometallurgical processes were analysed at 1100 and 1200°C and pO2 values between 10-3 and 10.12 bar were obtained. The measurements were evaluated with? thermodynamic calculations and using processing considerations. It was found that the reproducibility and stability of the measurement was significantly improved by shielding the molten slag from the atmosphere by a thin layer of carbon, especially for slags with a low oxygen potential.

Jan 1, 2003

By Moelans. N.

A method using an ex-situ electrochemical measurement device was developed to determine the oxygen potential of non-ferrous metallurgical slags. The electrochemical cell consists of the molten slag sample, an inert Ir electrode, a stabilized Zr02 solid electrolyte and a NilNiO reference electrode. Different slags from non-ferrous pyrometallurgical processes were analysed at I 100 and 1200 °C and pO2values between 10-3 and 10-12 bar were obtained. The measurements were evaluated with thermodynamic calculations and using processing considerations. It was found that the reproducibility and stability of the measurement was significantly improved by shielding the molten slag from the atmosphere by a thin layer of carbon, especially for slags with a low oxygen potential.

Jan 1, 2003

By A. Lakschevitz

The Amazon region offers a large potential for gold extraction but its peculiar characteristics such as heavy rains, lacking of roads and general infra-structure, nature of the ore deposits, etc.. do require special care in plant design. REMETÁLICA has developed a know-how is designing leaching plants which have been demonstrated to be profitable under those tropical weather conditions. The solutions adopted are related to general process route, leach liquor distribution and flow pattern, conditioning of solids and effluent treatment. These plants, now operating in South America countries, demonstrate the success for the technology developed. A tipical plant with 800 t/day ore processing capacity, may require an investment of US$ 1.200.000,00, arid have? a pay back period of a few months, depending on ore grade.

Jan 1, 1989

By Sepp Härkki

The energy crisis in Finland after World War I1 together with a sharp rise in the price of energy caused Outokumpu Oy to consider replacing the electric furnace smelting of copper concentrates by some other method. The flash smelting method developed under these circumstances offered a considerable saving of fuel through the utilization of the reaction heat of sulphides and yielded a high recovery of sulphur in the form of acid. The pilot plant testing of the new process was carried out in the years 1947 - 1948. The process was adopted for the smelting of copper concentrates (1) (2) (3) on a commercial scale in 1949 and applied successfullv to the smelting of -nickel concentrates' at the Harjavalta Works in 1959 (4) (5) (6). In 1962 Outokumpu adopted another type of flash smelting where elemental sulphur is recovered from the gases after the thermal decomposition of pyrite in the flash smelting furnace (7) (8): In recent years, the copper-nickel flash smelter and pyrite process have been combined to produce elemental sulphur instead of SO2 from the smelter gases (9) (10). The basic idea of the Outokumpu flash smelting process for sulphidic ores is that the conventional methods with separate roasting and smelting operations are replaced by a combined roasting, smelting and part-converting process carried out in one unit. The heat generated from the exothermic reactions can thus be used for smelting the ore so that only a small amount of additional fuel is needed. The characteristic of the method is also that the dried, fine-grained concentrate is smelted in suspension, which offers the best conditions for rapid reactions. The recovery of waste heat from the furnace off-gases had been considered already in the original flash smelting system. A

Jan 1, 1976

By S. K. Varma, Miriam Regalado, Daniel Salas, Erica Corral, Erika Esquivel

"Age hardenable 2014 aluminum alloys and composites containing 0.10 and 0.15 volume fractions of alumina particles (VFAP) have been solutionized at 540 and 550°C for up to 20 hours. The solutionized samples, heat treated for 5 and 20 hours, have been subjected to room temperature rolling until cracking develops. The work hardening curves have been compared to determine the effect of solutionizing time on the rolling characteristics from both hardness and the microstructural evolution points of view. Solutionizing at two different temperatures results in differences in the extent to which the composites can be rolled until fracture. The microstructural characterization by TEM has been performed to understand the room temperature rolling behavior.IntroductionThe effect of solutionizing on the age hardening response of 6061 and 2014 aluminum alloys and composites reinforced with 0.10, 0.15 and 0.20 volume fractions of alumina particles (VFAP) have been reported in the literature [1-4]. A comparison of the monolith and composites indicates that particles promote the aging process through differences in the microstructures in solutionized condition. The first effect of solutionizing is to produce a grain growth process which follows a grain growth law (square of grain diameter as a function of solutionizing time). It appears that it is possible for vacancies to be emitted during grain growth period as they try to minimize the total grain boundary surface area by increasing their diameter. This may be common to both the monolith and the composites. However, the second effect must be exclusively considered for the composites. The particles generate dislocations during the solutionizing process due to the differences in the values of the coefficient of thermal expansion (CTE) between the particles and aluminum base metal. It has been determined [1] that the dislocation density increases with increase in solutionizing time in the composites of 6061 aluminum alloys reinforced with 0.10, 0.15 and 0.20 VFAP. The improved bonding between particles and matrix can give rise to additional generation of dislocations due to curvature effects [1] with the result that the dislocation density continues to increase with increase in solutionizing time even after the CTE effect is considered to have been stabilized."

Jan 1, 1998

By Larry M. Southwick

There is much ongoing work in research and development of new processes for the recovery and recycling of met.a.ls and other materials from various waste and scrap streams. Commercialization of such new technologies requires the bringing together and successful execution of a considerable effort involving a variety of activities. These include process conceptualization, research and development, detailed design and construction, and then plant startup and operation. Processes evolve through all of these steps by engineering due diligence, making objective and critical analyses of results, and troubleshooting processing steps to, hopefully, arrive at a sequence that has the best chance to succeed operationally and economically. After a summary review of the above steps, several processes will be described in more detail that provide mostly successful examples of the above procedures. Finally, some observations will be made on areas that will become critical in the near future to the success of new processes for wastes and residues.

Jan 1, 2000

By J. Priede, G. Gerbeth

"Two different instability mechanisms of electromagnetically levitated bodies are analyzed. The first is due to the virtual coupling between the electric current passing through the magnetic system and the variation of position of the body. This mechanism can result in unstable mass center oscillations of a levitated solid body. Another type of instabilities may occur because of the coupling between the motion and the electric currents induced in the body. This effect can cause a spontaneous rotation of the body setting in as the frequency of the alternating magnetic field exceeds certain critical threshold depending on the configuration of the field. This instability can be suppressed by an axial steady magnetic field of strength comparable to that of the levitating field. 1 IntroductionAn alternating magnetic field interacting with eddy currents induced in a conducting body causes repulsion between the body and the coil generating the field. Besides, the eddy currents provide a contactless heating of the body. In such a way metallic samples can be levitated and melted without a contacting crucible. This technique allows to avoid contamination of the melt with container material and so to achieve a considerable super-cooling of the melt before it solidifies. Nowadays electromagnetic levitation is widely used in material research for measuring of the thermophysical properties of molten metals (2) .It has been observed since early fifties when the first experiments on the electromagnetic levitation were done that under certain circumstances solid levitated samples start to rotate or oscillate [l]. Surface oscillations can appear in addition when the sample is melted. Such phenomena are undesirable because they often result in failure of the levitation. Recently we showed that rotational as well as oscillatory instabilities can have electrodynamic origin related to additional eddy currents induced by motion of the body in an alternating magnetic field [3] , [4].In the first part of the present paper we analyze another possible cause of oscillatory instability due to the coupling between the electric current passing trough the magnetic system with variation of the position of the levitated body. The second part of the paper deals with the origin and suppression of rotational instability in a uniform alternating magnetic field."

Jan 1, 1999

By Leonard J. Friedman

The recovery of sulfur dioxide from metallurgical gases for the production of sulfuric acid has been an effective means of reducing sulfur dioxide emissions from non-ferrous smelters. Sulfuric acid has been produced from gas originating from fluid bed roasters, electric furnaces, reverberatory furnaces, flash smelting furnaces, Pierce Smith and flash converters, sinter machines, etc. The gas from each of these sources has a unique set of variables that affect the design and operation of the sulfuric acid plant. In addition, the sulfuric acid plant itself has been evolving, with new equipment designs and materials. This paper will review each of the unit operations in the gas cleaning and contact sections of the metallurgical sulfuric acid plant, discussing various equipment designs, materials and the handling of gas stream variables and impurities. The paper updates to 2006 previous works on metallurgical sulfuric acid plants by the authors.

Jan 1, 2006

By Rubén J. Sánchez Rodriguez, Carlos M. Fontes Vieira, Carlos E. Gomes Ribeiro

Ornamental compound stone are produced by industry for decades, however, few published studies describe these materials. Brazil has many deposits of stone wastes and a big potential to produce these materials. This work aims to evaluate the chemical resistance of ornamental compound stones produced with marble waste and unsaturated polyester. An adaptation of Annex H of ABNT NBR 13818:97 standard, with reagents commonly used in household products, was used. The results were compared with those obtained for natural stone used in composite production.

Jan 1, 2015

By Patrick R. Taylor

Sub-micron sized boron carbide powders have been synthesized in a non-transferred arc thermal plasma reactor. Precursors for this synthesis are boric acid or boron oxide powders and methane. The powders produced were characterized in terms of size, shape and purity. Methods to increase the purity of the product were evaluated and included hot water leaching to remove unreacted oxides and controlled temperature, air roasting to remove excess carbon. Theoretical results are also presented on the thermodynamics and mechanisms of the synthesis reactions.

Jan 1, 1994

By J. H. Meza V

La Caridad operated at only 65% of design capacity during the first five years of operation. After the first major shutdown and repairs to the furnace in mid- 1992, the smelter quickly reached 95% of design capacity. Converter operation is now more efficient; blowing times have decreased from about 1.7 to 1.2 min/ton of matte. Anode copper production is now 15000 tons/month. The increased efficiency provided by better coordination and scheduling ensures La Caridad's ability to operate at present and expanded production capacity while simultaneously meeting environmental control standards.

Jan 1, 1993

By C. Ramasamy

The tariff reductions on imports, as a part of on-going liberalisation process in India, has fueled competition within and outside India and has, in turn provided an opportunity to reach global markets. This change calls for quality upgrades and cost-competitiveness without impairing the environment. In this context, gas based processes, contributing to improvement in quality and environment as well as processes where controls are applied when gases inimical to environment are involved, are discussed in a remelt/cast-house scenario. The impact of such processes on fabrication cost of sheet ingot is seen alongwith consumption and cost of materials and compared with a world class standard plant in North America.

Jan 1, 1996

By R. D. Lrwin, W. M. Mullins, S. Venugopa, J. C. Malas

"Physical models for acoustic emission (AE) are introduced and expressions are derived to predict AE activity from such parameters as applied stress, strain and strain-rate. These models are then incorporated into a visco-plastic finite-element simulation program, and the acoustic emission event rate generated during metal forming operations are predicted. Simulation results are presented for upsetting operations on a typical C-Mn type steel for various friction and die geometry conditions. The AE model predictions compare well with the limited available experimental results reported in the literature and demonstrate that AE signatures can be reliably simulated. The signatures predicted for metal forging are fairly insensitive to processing parameter changes. This suggests that AE event rate monitoring may not be well suited to process monitoring for forging. However, the size of the features is conjectured to influence the frequency content of the AE signals. Thus, since current simulations include only the ability to predict the number of events for a set of processing conditions, future work is required to simulate the duration and magnitude of acoustic events. Fourier analysis techniques may then be applied to investigate correlation with microstructural features.IntroductionThe open loop control system method for deformation processing design, as described by Malas et al. [1 ], consists of several steps in series to achieve the final design. The first step uses microstructure development models to determine the optimum deformation path to achieve the desired final microstructure. The second step, the process model, calculates the processing parameters required to achieve this deformation path. Finally, the metal-working system uses the required processing parameters to produce the part. Figure 1 shows this in block diagram form"

Jan 1, 1997

By V. J. Ramirez, A. M. E. Noguez, M. J. Navarrete, B. G. Salas, N. T. Robert

"The close die forging stress in truncated conical cavities is evaluated with dimensional analysis. Five dimensionless groups are proposed from the process variables in order to simplify the forging stress determination. These groups are experimentally related and graphically expressed. This methodology can be used to predict the actual forging stress in industrial close die forgingThe use of the dimensionless groups allow to comprise more cases than the presented here, provided similar geometries and operational conditions.Introduction.Closed die forging is essentially a plastic deformation inside a two piece mold (forging die) with the inverted shape of the actual forging geometry. This plastic deformation will always be the result of a compressive stress. There are theoretical models which include complex calculations for the analytical determination of stresses (1, 2, 3, 4). Results of these calculations are approximate, requiring generally ulterior tests to obtain the true operational conditions(5).In this paper, it is presented a simplified approach to the actual compression stress needed in the forging. A well known tool in engineering: the Buckingham's Pi theorem in conjunction with dimensionless groups and a working piece scale model is used. Dimensional analysis will give the dimensionless terms needed to experiment with a selected scale model geometry to make the stress determination. The results presented demonstrate the reliability of this methodology."

Jan 1, 1997

By H. Y. Sohn

A novel solvent extraction process in which the emulsion is generated by bottom gas injection rather than mechanical stirring has been developed. This process has a number of advantages over the mixer-settler unit or the spray column in terms of simple equipment configuration and the ease of cleaning and process control while providing a large interfacial area for mass transfer. The equipment consists of a horizontal cylindrical vessel in which the two immiscible liquids flow countercurrently. High-strength gas jets are injected from the bottom at certain intervals along the length of the vessel. The gas jet creates a plume zone consisting of an emulsion of the two liquids which contains a large interfacial area for rapid mass transfer. The two liquids then disengage and flow in the opposite directions before entering another plume zone. Thus, the process combines the simplicity of a cylindrical vessel, having no moving parts, with the contacting efficiency of a mixer-settler. The gas can be recycled in a closed loop, thus eliminating mist and other emission problems. These advantages would be especially significant for treating large-volume/low-value liquid streams which contain hazardous substances and/or suspended solid particulates.

Jan 1, 1996

By John A. Vallomy

"The CONSTEEL Process introduces a new concept in electric steelmaking by continuously feeding-preheating-melting and refining ferrous scrap or direct reduced iron. The process uses the furnace off-gas and fuel to preheat the scrap in a specially designed preheater. Thermal incineration of the flue gas reduces the carbon monoxide level to the more stringent requirements. Hot water or steam production from heat of flue gas is optional. The tap-to-tap time is set to match the cycle of the caster. The steel is treated via ladle metallurgy. The environment inside and outside of the steelplant is improved by decreasing levels of noise and hazardous emissions. Energy consumption decreases and disturbance to the electric network is eliminated. A CONSTEEL prototype was tested at Nucor Steel, Darlington, SC. A greenfield project is in the completion stage at the Florida Steel plant of Charlotte, NC, USA. The Process PhilosophyThe philosophy of the CONSTEEL Process is not solely to enhance efficiency; this was just a natural result of the change from a batch to a continuous practice. The primary objective in development was four-fold:1) 100% process control2) Rational use of available energy3) Improved environment inside and outside the plant4) Stability of energy input from the power systemIt was to make electric steelmaking more a science than an art and amenable to modern automation.The Basic Concept of CONSTEELThe concept of the process is shown in figure and includes basically a continuous feeding system, a preheater and a melting - refining furnace. A pre-established amount of heat is introduced into the scrap while traveling through the preheater using the sensible and chemical heat contained in the furnace off-gas and additional fuel. Melting-refining is carried out in the electric furnace. Slag formers, slag foaming additions and oxygen are injected to refine the melted steel continuously, to minimize the refractory erosion, to shield the arc, thus optimizing the transfer to the metal bath of the heat generated in the arc, to keep the bath homogeneous in composition and temperature and to produce carbon monoxide (CO) which is fuel for the preheater."

Jan 1, 1988

By D. Pradhan, R. G. Reddy

"Electrorefining of aluminum scrap was investigated from AlCl3 –1-Ethyl-3-methyl-imidazolium chloride (EMIC) (Molar ratio 1.65) chloroaluminate electrolyte using copper cathodes at temperature of 90±3°C and cell voltage of 1.5 V. The deposits were characterized using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The study was focused to determine the effect of electrode surface modification as well as deposition time on dendritic depositions of aluminum. Their effect on current density was investigated also. It was shown that the surface modification of electrodes reduced the dendritic depositions of aluminum. Pure aluminum (>99%) was deposited for all experiments with the current efficiency of 94-97%. The use of ionic liquids not only reduced the energy consumption but also minimized pollutant emissions (CO, CO2 etc.) compared to the commercial high temperature aluminum production.1. IntroductionAluminum electrorefining/recycling from aluminum scrap using ionic liquid electrolyte is an attractive process today because of the unique chemical and physical properties such as wide temperature range for the liquid phase, high thermal stability, negligible vapor pressure, low melting point and wide electrochemical window. But in conventional practice, melting of aluminum scrap and high temperature molten salt electrolysis makes this process more expensive and less energy intensive (average 13 kWh/ kilogram of aluminum) [1] . Although recycling scrap aluminum requires only 5% of the energy used to make new aluminum [1-2], but the green house emissions like CO2, CO and HF have to be counted for environmental reason. Approximately, 5.31 kilogram of CO2 emitted per kilogram of aluminum production in most of the US industries."

Jan 1, 2009

By Cailing Zhen, Jian Pan, Deqing Zhu, Xianlin Zhou, Yanhong Luo, Guixiang Huang

The grate-kiln process has been widely applied for oxide pellet production with the quick development of steel industry in China, but ring formation takes place which adversely affects the productivity and properties of fired pellets. Rotary kiln at high temperature seems a black box, and ring formation is difficult to measure directly by current technology. It’s of great importance to monitor ring formation during firing of pellets. Therefore, a method for estimating the thickness of ring formation in rotary kilns was studied, based on working out theoretically the relationship between ring thickness and the outside surface of the kiln, according to steady-state heat transfer across a cylinder, which provides a soft-sensing technique for ring formation at high temperature, and achieves stable pellet production .

Jan 1, 2015