Search Documents

By D. G. C. Robertson

The thermodynamics and kinetics of the reactions involved in fuming zinc from oxide slags using coal or coke were first studied in 1955 and have been the subject of many investigations since that time. The key reaction is ZnO(in slag) + CO Zn(g) + COl. This paper will review the some of the recent work, and will add new insights obtained in experiments carried out by the authors. In the first series of experiments it was shown that the reaction 2Fe2+ + ZnO = 2Fe3+ + Zn(g) or 2FeO + ZnO = Fe2O3 + Zn(g) does not occur at an appreciable rate, as is expected from thermodynamic considerations. In the second series of experiments it was shown that zinc does not fume from the slag at a significant rate unless a reductant has been added. This again is in accord with thermodynamic considerations, but is in contradiction to some of the experimental results reported in the literature. A third series of experiments was carried out with excess coke being present, so that the rate of supply of reductant was not in any way controlling the rate. The kinetics of zinc oxide reaction were then found to be independent of the zinc oxide concentration, but increased with increasing basicity, and temperature. The presence of high concentrations of FeO in the slag also improves the kinetics. At low zinc oxide concentrations iron oxide reduction occurred in parallel with zinc oxide reduction. We propose that (under the conditions of this work) the kinetics were controlled by a chemical step, namely the rate of desorption of an adsorbed CO2 species. This is the same mechanism as reported by Belton and co-workers for the kinetics of the reduction of FeO. This explains why the reduction of metal oxides in slags by hydrogen is often faster than by CO.

Jan 1, 2003

By C. E. M. Meskers

Electronic and Electric Equipment contains a range of components made of a wide variation of metals, plastics and other substances. Up to 60 elements can be found in complex electronic equipment: base metals, precious metals and special metals in circuit boards and batteries. Because of its amount WEEE represents a considerable metal resource with a higher special and precious metal content than found in ores. The Umicore integrated smelter and refinery recovers and supplies back to the market 17 different metals from EEE. Pre-treated materials enter state of the art, material and energy efficient metallurgical processes for environmentally sound recovery of metals and treatment of off gasses and hazardous substances. The organics in the feed function as reducing agent and alternative energy source during smelting for precious metal recovery. Lithium-ion batteries are treated using a dedicated process. As a result the environmental footprint of metals produced from EEE is much smaller than primary production.

Jan 1, 2009

By Yunyan Wang

Diagrams of pc-pH for the complex ions concentration and pH value and -g- for activity coefficient and ionic strength ln±MnSOI4had been drew based on the thermodynamic principle of coordination chemistry and combined with Pitzer theory at 298.15K. The diagram of -g- indicated that -gincreased sharply from 0.0000 up to 1.2147 when I changed from 0.00 ln±MnSOIln4±MnSO4to 0.09; The increase of -gbecame slowly when I was more than 1.00 and less than 1.69; kept still when I ln±MnSOln4-g±MnSO4was more than 2.25 and less than 4.00. Diagrams of pc-pH illustrated that the minimum solubility of Mn(OH)2(s) increased with the increase of I, the pc increased from 6.5 to 5.5 when I increased from 0.00 to 4.00; The pH of the minimum solubility of Mn(OH)2(s) increased with the increase of I, the pH increased from 11.80 to 12.76 when I increased from 0.00 to 2.89, the pH kept still when I (I was less than 4.0) increased. There is single function relationship between the minimum solubility of Mn(OH)2(s) and relevant pH in different I.

Jan 1, 2010

By Changqing Su

A batch incubation experiment has been carried out to investigate the optimal condition for the microbial remediation of hexavalent chromium (Cr(VI)) in soils contaminated by chromate ore processing residue at Hunan Iron-Alloy Factory in China. The optimal condition was obtained by comparing the remediation efficiency of Cr (VI) by indigenous bacteria under different culture media, the quantity of nutrient sources, the pH and the temperature. The results indicated that glucose and yeast extract was the optimal component of culture medium and the quantities of the above components were 8 g L-1 and 13 g L-1, respectively. The optimal temperature and pH value were 30_ and 10.0, respectively. A bioreactor was operated under the optimal condition to evaluate the efficiency of Cr(VI) remediation in the contaminated soil. The result showed that water soluble Cr(VI) in soils was reduced from 320 mg kg-1 Cr(VI) of the initial concentration to below detection limit after 30 h in a bioreactor. Thus, there is a large potential to make bioremediation for the reduction of Cr(VI) to Cr(III) by the addition of optimal culture medium under aerobic condition.

Jan 1, 2010

By S. N. Lekakh

Phosphorous segregated at grain boundaries during solidification and heat treatment dramatically decreases low temperature toughness of precipitation hardened Fe-Mn-Al-C austenitic steel. A thermodynamic analysis was performed to evaluate the possibility of decreasing P and subsequent segregation by Ca- and Ce-additives in the melt. It was shown that the predicted probability of forming a P containing compounds depends on melt composition and treatment sequence. Experimental heats were performed and several micro- and macro-structural effects of Ca- and Ce-additives were recognized by using an automated inclusion analysis technique.

Jan 1, 2010

By C. Hennesmann, D. Maijer, S. L. Cockcroft, P. Yo

"Die cast aluminum wheels are one of the most difficult automotive castings to produce because of stringent cast surface and internal quality requirements. As part of a collaborative research agreement between researchers at the University of British Columbia and Canadian Auto Parts Toyota Incorporated, work has been underway to predict heat transport and porosity formation in die cast A356 wheels. The basic heat transfer equations have been solved using the commercial finite element package ABAQUS to which specialized routines have been added to predict porosity. Preliminary work on predicting porosity formation focused on using the Niyama parameter as a measure of the probability of porosity. The latest version of the model incorporates a new fundamentally based porosity criterion, which takes into account the effect of hydrogen concentration. The development of this model together with its application to a series of cylindrical test castings as well as a production cast wheel are presented.I. IntroductionDie cast aluminum wheels are one of the most difficult automotive castings to produce because of stringent cast surface and internal quality requirements. Microporosity, in particular, is a common defect that can adversely affect wheel quality. The mechanism of microporosity formation in aluminum alloys is complex owing to its dependence on the interaction of a number of phenomena occurring during solidification including the decrease in hydrogen solubility, the decrease in volume, the development of the solidification structure, and the increase in difficulty in interdendritic feeding [1]. As a result, the amount, size, and distribution of microporosity is affected by a large number of casting parameters including thermal variables, melt composition, grain structure, modification, and inclusion content, making optimization by trial-and-error methodologies difficult.The use of criteria functions, based on thermal conditions during casting, offers a relatively simple approach to predicting microporosity. In practical terms, they are useful because they provide a straightforward method of assessing the impact of varying casting parameters on porosity through various thermal parametersl21 such as thermal gradient, cooling rate, solidification time, and solidus velocity. Drawbacks of criteria functions include insensitivity to varying hydrogen concentration and the limitation to qualitative predictions. Consequently, in aluminum alloys, attempts have been made to develop models incorporating the effects of hydrogen gas and microstructure evolution. However, these types of models represent a significant increase in complexity and sacrifice the simplicity and ease of application of the thermally based criteria functions."

Jan 1, 2001

By Jay S. Gunasekera

Since great emphasis is being placed on the manufacturing science and processing science programs in the Department of Defence and other government research agencies and industries; currently, extensive research on computer aided design(CAD)/ computer aided manufacturing (CAM)/ and computer aided engineering (CAE) is being conducted at Ohio University (OU) . OU has invested over a million dollars in CAD/CAM hardware and software. Design and analysis packages like ALPID, NIKE, STREAM, SHEAR, POLY_FLON, RINGROLL have been developed or modified at OUusing finite element method, finite difference techniques or enhanced slab analysis. Packages like ABAQUS, FLUENT, and NASTRAN have been extensively used.

Jan 1, 1990

By Alicia Esther Ares

The family of Zn-Al (ZA), Zn-Ag and Zn-Al-Ag (ZINAG) alloys offers high mechanical properties, ease of finishing, the advantage of low energy and pollution-free melting. Also, present alternatives to the well developed alloy systems, such as brasses, bronzes, cast irons and aluminum alloys. The main objective of this paper is to measure thermal parameters in ZA, Zn-Ag and ZINAG hypoeutectic and hypereutectic alloys directionally solidified which present columnar, equiaxed and columnar to equiaxed transition structures (CET). Also, estimate the mechanical properties, such as microhardness and tensile parameters and correlate these with the thermal (cooling rate) and structural parameters (grain size and dendritic spacing). The different types of structures were analyzed with optical and scanning electron microscopy. The results showed the influence of concentration, microstructural arrangement and thermal conditions during solidification on the mechanical properties. The results of the present investigation are compared with previous experiments.

Jan 1, 2010

By Omid Lashkari

Keywords: SEED, SSM materials, Microstructural evolution, Rheology, Swirling Speed SEED (Swirled Enthalpy Equilibration Device) is established itself as a new technology amongst the many Semi-Solid Metal (SSM) processes, where swirling of the mush plays an important role in modifying the dendritic structure of as-cast parts. A range of semi solid metal structures, dendritic, rosette and/or globular morphology of primary phase, can be prepared using SEED. The current article reports on the application of rheological tests in characterizing microstructural evolution during SSM processing of 356 Al-Si foundry alloy. A simple parallel plate test machine, designed and constructed at our labs, was used to determine viscosity values for each structure and identify the optimum structure with superior die filling characteristics. Such findings have important technological and economical implications during high pressure die casting of semi- solid metals. The strain-time graphs for 356 Al-Si foundry alloy indicated lower viscosity values for globular microstructure, i.e. improved die filling.

Jan 1, 2005

By Dale T. Peters

Conductivity, both electrical and thermal, are attributes accounting for about 70% of the applications of copper and its alloys. This paper presents results of on-going research into two new applications that depend on copper's excellent conductivity. The Copper Development Association (CDA), together with materials and motor company partners, is working toward a solution to the key problem preventing pressure die casting copper for the conductor bar/end ring structure of the induction motor rotor, i.e., lack of a durable high-temperature mold material. Work is showing that a combination of high- temperature materials and elevated temperature processing gives much improved mold life compared to die steels. Substitution of copper for aluminum in the rotor can result in a 20% decrease in electrical losses in motors consuming 35% of electrical power generated in the U.S. The second development uses the excellent thermal conductivity of several high-strength high-copper alloys to simultaneously improve productivity and part quality in the injection molding of plastic parts.

Jan 1, 1999

By Othon do Rêgo Monteiro Neto

[The present study has investigated the extraction of copper from a chalcopyrite flotation concentrate using an adapted strain of Thiobacillus ferrooxidans and shake flasks, tank leaching and Warburg respirometer techniques. From the shake flask experiments, the activation energy and the frequency factor have been determined to be ?ka = 59.4 kJ and A = 3.3 x 105 S-1, respectively. The temperature coefficient was found to be Q10 = 2.2 in the range of 20 to 35°C. It was suggested that the reaction mechanism of chalcopyrite leaching by T. ferrooxidans involves the formation of an activated complex. whose thermodynamic values have been calculated to be ?G? = 92.1 kJ, ?S? -148.8 J K-1 and ?H$ = 47.8 kJ. The maximum volumetric oxygen mass transfer coefficient for the reactor leaching was found to be achieved by using an optimum air flow rate of 1970 cm min l at a rotational frequency of 1000 min-1. The highest copper extraction in tank (reactor) leaching experiment was 86.8% after 17 days of leaching, while in the sterile runs the corresponding copper extraction was only 40.1%. The copper extraction was suggested to be diffusion controlled. The power requirement of the aerated reactor was calculated to be Pg = 2.02 watts. During leaching, the oxygen saturation concentration was found to be C* = 6.70 mg dm-3. Using the gassing out method the critical oxygen concentration was assessed to be CCrit 0.05 mg dm 3. From the Warburg experiments, the kinetic parameters of the Monad equation were derived with a new evaluation technique to be Vmsp = 9.0 µm3 02 min-1 mg protein-1 and K = 7.4% pulp density for the effect of substrate concentration. The order of reaction and the overall reaction rate constant were determined from the modified van't Hoff plot to be n = 0.0 and k = 1.49 p dm3 02 min-1 mg Protein -1 for the chalcopyrite concentrate oxidation by T. ferrooxidans. On the basis of this experimental work, a preliminary flow sheet has been proposed for the bioextraction of copper from flotation concentrates.]

Jan 1, 1985

By Sven Eck, Andreas Ludwig, Menghuai Wu

"Phase separation is a frequently occurring phenomenon during solidification accompanied by melt convection, sedimentation or, in the case of two unmixable liquids, a Marangoni driven motion. In order to describe these phase separation phenomena a two-phase volume-averaging model was employed for globular equiaxed solidification of binary alloys and decomposition and solidification of hypermonotectic alloys. The model considers nucleation and growth of equiaxed grains or second phase droplets, motion and sedimentation of grains or droplets, feeding flow and solute transport by diffusion and convection. It allows the prediction of macro segregations and the distributions of grain size or droplet size. Evaluations were made by comparing the numerical predictions with experimental results. For example it is shown that the numerically predicted grain size distribution in a plate casting (Al-4wt%Cu) agrees reasonably well with the experimental analyses.IntroductionModeling of metallurgical processes is a rapidly expanding field and the research activities in the last decades cover a wide range of areas including melt pre-treatment, solidification and subsequent manufacturing routes. Among those activities solidification stands in the central position, because the primary structure of the materials, and even many defects such as porosity, (macro or micro) segregation and inclusions form during solidification. Those primarily formed structures or defects once existing are difficult to be removed or modified by the subsequent material processing.Solidification is a multi-disciplinary field involving thermodynamics, fluid dynamics and solid mechanics, heat and mass transfer, and other disciplinesr1 -31• One of the most challenging problems in solidification modeling is the complex interactions between physical phenomena occurring on different length scales ranging from atomic rearrangement over single crystal-melt interactions to heat extraction, momentum and species transport at the system level. Modeling an industry process on atomic scale is umealistic, even on grain scale (e.g. phase field method) it would need another 40 years to be able to model the exact grain morphology in a casting space envelope of 10x10x10 cm3 [ 4]. Therefore, the realistic models for industry process are based on the solution of the macro transport equations (mass, momentum, enthalpy and species) on system scale. The microscopic phenomena such as thermodynamics, nucleation law, crystal growth kinetics and interactions at the liquid-solid interface are considered with simplified models, which are coupled with the macroscopic transport equations."

Jan 1, 2004

By Xiao Caimei

The method of Substance Flow Analysis (SFA) provides a helpful tool for the study of the industrial metabolism of a certain metal within a regional level, such as copper, lead etc. In this paper the flows and inventory of cobalt in China, 2008, were traced with the STAF model, and the situations of production, fabrication and manufacturing, use and waste management in China were introduced. The result revealed that the resource of cobalt in China was so poor that a large amount of cobalt material or cobalt products needed to be imported, and there was lack of recycling of cobalt resources.0

Jan 1, 2010

By Eulogio Velasco, Jose Nino, Marcos Cardoso

"Recycling of aluminum scrap for production of secondary alloys used for automotive applications is increasing continuously. Automotive alloys require a strict control to remove alloy impurities, inclusions and excess of magnesium. The advantage of aluminum is its recyclability with large energy and emission savings with minimal loss in material properties. The aim of this work is to study the magnesium removal from recycled aluminum by chlorine injection in a reverberatory furnace, and removal by an oxidation process at high temperature in an industrial rotary furnace.The magnesium removal by gas injection is carried out by the reaction between chlorine and magnesium, with its efficiency associated to kinetic factors. In the rotary rapid oxidation of aluminum and magnesium elements at high temperature is characterized by the formation of surface films composed of magnesium oxide. Additionally this work reviews the benefits of an efficient demagging process.IntroductionThe advantages of using light alloys for automotive applications include fuel economy improvement, greenhouse gas reductions and polluting emissions. These characteristics makes the aluminum alloys an attractive option for automotive components such as powertrain products and other critical parts like cylinder heads and blocks. [1]Aluminum alloys coming from recycled automotive components, used beverage cans (UBC) and wrought alloys have positive effects in the energy savings and current environmental trends. Producing a scrap recycled aluminum ingot consumes approximately 5% of the energy required to produce a primary aluminum ingot from bauxite ore. [2]"

Jan 1, 2011

By W. Kunda

Silver nitrate solution is a very common product in hydrometallurgical processes involving the treatment of various silver bearing materials. Silver is recovered by electrolysis. The alternative method for the recovery of silver from aqueous solutions is the precipitation by hydrogen at elevated temperature and pressure. A previous study by the authors revealed the feasibility of this technique for the silver ammine sulfate system. Further study showed different behavior for silver in the silver ammine nitrate system and a systematic study was initiated to establish the optimum conditions for the process. The study showed that the process can be controlled by (1) composition of the feed solution, (2) temperature and (3) hydrogen pressure. The recovered silver product was in the form of very fine powder.

Jan 1, 1989

By Tianjiao Luo

The electroless copper plating process for continuous carbon fiber using CuSO4?5H2O as the main salt and formaldehyde as reducing agent was experimentally studied, including the effects of pH values and concentration of chelating agents, stabilizing agents and reducing agent on the electroless plating process. The surface morphology and the composition of coating were investigated by means of Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS), and deposited the coating thickness was measured by way of dissolution. The results indicated that the pretreatment of carbon fiber before plating was so important. This pretreatment could prevent the formation of the black cores, furthermore, it could form many active absorption cores with Ag as the center on the carbon fiber surface. Used the optimized parameters in this process, which led to a stable solution for plating, a homogeneous copper coating was conducted with the carbon fiber plated with favorable mechanical performance and high adhesion strength.

Jan 1, 2006

By A. J. Sideris

It is known that Mg can act as a catalyst/solvent in the high pressure high temperature diamond synthesis. However, above pressure levels of the order of 7 GPa, and temperatures from 1700 ? 1800oC, it was not possible yet to use Mg for the industrial production of diamond. A possible alternative is the use of MgNi based alloys. However, owing to the great Mg reactivity, it was consider, so far, a difficult task to deal with such alloys. The present work presents successful results regarding the production of MgNi alloys, with different composition, at high pressure conditions. The behavior of the alloys and their microstructural characterization is analyzed.

Jan 1, 2006

By Anne Kvithyld

Silicon solar cells, that convert the energy of sunlight into electric energy, are attractive sources of energy. In the production line wafers of solar cells are sliced from a multicrystaline ingot solidified unidirectionally. Recycling scrap from top and sides of such ingots is addressed. SiC and Si3N4 inclusions are a major problem. Scrap from Scan Wafer ASA is melted in a high vacuum furnace at around 1500ºC. The filters, from commercial producers, are C and SiC with 10, 20 and 30 ppi. Characterisation of inclusions before and after filtration, and in the filter itself, is performed by microscopy. Dissolution of silicon in acid and counting of the un-dissolved inclusions is also carried out. In the filter Si3N4 needles and SiC inclusions were identified. The amount of these inclusions in the filtered silicon is much less than in the input. In conclusion, filtration using SiC and C filters in vacuum system in argon atmosphere removes SiC and Si3N4 inclusions from solar cell scrap. Flow of metal through the filters is not a problem. These results are promising with scale-up to industrial application in mind.

Jan 1, 2006

By Hector Carreon

Due to elevated temperatures, excessive stresses and severed corrosion conditions, turbine engine components are subject to creep processes that limit the components life such as a turbine bucket. The failure mechanism of a turbine bucket is related primarily to creep and corrosion and secondarily to thermal fatigue. As a result, it is desirable to assess the current condition of such turbine component. By using eddy current images, it was shown that the eddy current technique could be used to monitor creep damage in a nickel base super-alloy. The eddy current results also show a significative variation in the electrical conductivity on the creep damage zone with respect to the background zone in nickel-base super-alloy samples. In addition, the absolute thermoelectric power coefficient show also a strong dependence associated with creep damage in nickel base super-alloy samples using a copper hot tip reference. The eddy current and thermoelectric power techniques seems to show promise as nondestructive evaluation tools for monitoring the level of creep damage in metallic alloys.

Jan 1, 2010

By Karel Van Acker

The automotive is a sector where energy consumption during the use phase prevails over the production and the end-of-life phase. Therefore, a lot of research and innovations at replacing classical steel parts by lighter materials like light metals and polymer composites. While composites are very attractive for the use phase of cars, their introduction suffers from the limited end-of-life options for composite structures. An extensive life cycle analysis for a reference car design has been conducted to study the effects of replacement of conventional steel structures by lightweight carbon fibre composite alternatives. The study also takes second order effects in the design of the car into account. The opportunities and treats of the trend towards more intensive use of carbon-fibre composites in car design are identified. A discussion on the potential of other types of composites for the automotive in terms of sustainability considerations is added.

Jan 1, 2010