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By Ray Y. Lin, Randall A. Blue

"Joining of silicon carbide with infrared using a mixture of Si-30wt.%C as the brazing material has been investigated. Joining was performed at a temperature of 1500 °C in a flowing argon atmosphere for processing times ranging from 5 to 60 seconds. The joining filler materials include thin film silicon obtained by thinning down silicon wafers to about 70 /!m and graphite powder of a 15 /!m average particle size. Joint strengths were determined with a specially designed shear-in-compression jig for testing shear strengths of brittle materials. Cross section examinations of the joined specimens with optical microscopy, scanning electron microscopy and transmission electron microscopy have shown that all joints are essentially void free with excellent wetting between the base SiC and the brazing material. Silicon carbide in the B form has been identified as the reaction product in the joining zone with a transmission electron microscope (TEM) and selected area diffiaction (SAD) analysis. At 1500 °C with a joining time of 60 seconds, the joint has consisted of primarily SiC. With such a high SiC content in the joint, the joint strength is comparable to those by other joining techniques, such as diffusion bonding, as reported in the literature. A kinetic model for the formation of SiC from liquid silicon and carbon is proposed to explain the observed joint microstructural evolution.IntroductionSilicon carbide is of great interest for high temperature structural applications because of its excellent high temperature strength, wear resistance and anticorrosive characteristics [1]. Even though the interest in SiC is high, the use of the material has been limited by the high cost and difficulties involved in forming components of complicated shapes [2]. It is these limitations that necessitate the development of effective joining techniques that are cost effective and able to provide strong joints."

Jan 1, 1996

By Anand Kumar, Pradeep kumar Jha, Suman Kant, Pradeep Kumar

"It has been a major challenge to reduce the intermixed grade formation during ladle change-over operation in continuous casting process of tundish steelmaking. The F-curve generated by step input of the tracer (new grade steel) tells about the intermixed grade amount for different grade specifications. Use of flow modifiers is beneficial in reducing the intermixed grade because of the change in slope (in different time zones) and position of the F-curve due to their placement at tundish bottom. Present study aims at investigating the role of dam placed before the outlet in a multi-strand tundish with reference to the slope behavior of F-curve in different time zones during the teeming operation plays an important role in determining the intermixed amount.Introduction In Continuous casting process, the old grade steel remaining in the tundish (reservoir between ladle and mould) from the old ladle gets mixed with new grade steel from new ladle and leads to intermixed grade which is considered to be of inferior quality. Although formation of intermixed grade is inevitable with the sequential method of casting, its amount can be controlled by changing the flow behavior of steel inside the steel. Intermixing in a slab caster tundish was simulated using 3-D numerical model based on k-å turbulence equation and compared their result with that of water model experiment Yeh and Hwang [1]. Huang and Thomas [2] reported that quantity of residual fluid in tundish affects the composition distribution in the transitional slab and thus the intermixed length. Huang and Thomas [3] developed three sub models to predict mixing in tundish, liquid core of strand and solidification. Thomas [4] developed a one dimensional model to simulate the final composition distributions in slab caster of continuous casting and investigated the effect of process variables on the intermixing. Alizadeh mehdi et al., [5] simulated of the intermixing phenomenon for slab casting for three different sub models. Goldschmidt et al. [6] developed a numerical model that predicted the location of the intermixed steel in a four line round caster. Lan and Khodadadi [7] studied for the transient fluid flow of liquid steel, heat transfer and solidification during the flying tundish change process. Cho and Kim [8] developed a mixing model to predict the outlet concentration of the tundish during grade transition. Most of the work reported in the literature has dealt with intermixing in slab caster tundish. Billet caster units are more often being used by steel industries due to growing demand of billets. The multiple outlets lead to varying degree of intermixing with time owing to their different distance (location) from the inlet. Use of flow modifier to minimize the intermixed amount, however has also not been discussed in detail so far. Further no work has been reported regarding effect of slope of F-curves obtained through different outlets on intermixing. Hence keeping these objectives in mind attempt has been made by authors to analyze the slope of Fcurves after dividing them into three different time zones and the effect of these time zones on intermixing."

Jan 1, 2012

By Fatma Arslan

The lateritic nickel ore sample subjected to this experimental study was taken from Çalda ore deposit (Turkey) and contains 1.43% Ni and 0.105% Co. Mineralogical investigations showed that the ore sample contains asbolane, chromite, limonite, hematite, goethite, lepidocrocite, magnetite, serpentine, and clay type minerals together with chalcedon, quartz, calcite, and chlorite. In the acidic leaching experiments, the effects of temperature, acid (H2SO4) concentration, and leaching time on nickel leaching recoveries were investigated. Leaching recovery versus time curves showed a parabolic trend and increasing the temperature shifted that curves to the higher values. The dissolution of nickel from lateritic ore can be explained by a shrinking core model and the apparent activation energy was found as 47.34 kJ/mol in the range given by the literature. The highest Ni and Co leaching efficiencies as 90.2% and 96.8% respectively were obtained at 80°C temperature, 200 g/L H2SO4 concentration, and 8 hours of leaching time.

Jan 1, 2006

By Pascal Gardin

The purpose of the paper is the mathematical modelling of flows inside steel continuous casting mould. For CFD validation of flow oscillation prediction, unsteady calculations with a realizable k- model were performed in a billet caster with rectangular section. Self sustained and regular oscillations were obtained. Calculated flapping frequency is very close to what is mentioned in literature. For slab caster configuration, flow oscillation is influenced both by lower roll, which creates very small frequency oscillation (0.012 Hz for our water model), and upper roll, which creates slightly higher frequency oscillation (0.05 Hz). The two rolls interact and it is possible to detect both frequencies in the nozzle jet region. Numerical results are in good agreement with measurements for fluctuating velocity spectra and provide explanation for interaction of rolls. To improve flow stability inside the mould, it is established that gas injection in the nozzle has a very positive effect.

Jan 1, 2006

By R. G. Reddy

The effect of solid particles on viscosity behavior of Na2O-O-B2O3-SiO2 melts of composition XSio2/XNa2o =0.5 and in the temperature range of 900- 1150 K was studied. Samples were analyzed by X-ray diffraction and optical microscopy. The results showed that a crystalline phase (NaBO2) was formed and its amount increases with decrease in X,, from 0.50 to 0.25. The experimental viscosity values were compared with the predicted values using our viscosity model developed earlier. At low temperatures, for low content of B2O3 , the experimental values exhibits a large deviation from the predicted values. It was concluded that the deviation was due to the formation of solid particles in the molten slags. The existence of these solid particles increased the viscosity values significantly. A new viscosity model was developed to include the effect of solid particles.

Jan 1, 1993

By Sharon L. Eyer

"FTIR spectroscopy is employed to define mineable ore deposits based on exploration samples. The RAMBO (Robotic Assessment of Mineable Bauxite Ore) technology is operating successfully at an alumina refinery in K winana, Australia, for assessment of a number of critical ore attributes including available alumina, extractable organic carbon and total iron. Classical methods of analyses for these properties require laboratory-scale digestion of alumina ore (bauxite) or XRF analyses.Multivariate calibration is used in the RAMBO system to generate robust mathematical models that are able to estimate classical data from FTIR spectral data. Furthermore the models can highlight regions of ore that are relatively unusual. Unusual ore may be investigated for potential impacts on refinery processes well in advance of mining.The components of the technology are described and some results for an example application (bauxite) are presented. Challenges and difficulties are discussed. The potential to apply the technique to process control is introduced."

Jan 1, 1999

By R. Padilla

Enargite (Cu3AsS4) occurs normally associated with copper sulfides, mainly chalcopyrite. When the enargite content in chalcopyrite concentrates is high, direct smelting of the concentrate presents problems related to environmental pollution and contamination of the final metallic copper. Leaching processes are viable alternatives to treat copper concentrates with high content of enargite. Consequently, in this paper, the pressure leaching of enargite in sulfuric acid-oxygen system is discussed. The leaching rate was studied in the range 160 to 220 °C and partial pressures of oxygen of 74 to 200 psi. The enargite dissolution increased substantially with temperature increase. Complete dissolution of enargite was obtained at 220°C, and 100 psi of oxygen pressure in 90 min. The shrinking core model controlled by surface reaction was used to analyze the kinetics of enargite dissolution. Activation energy of 70 kJ/mol was obtained for the temperature range 160 to 220 oC.

Jan 1, 2008

By T. Ikeda, M. Maeda, K. Mita

Galvanized steel sheet is the major product for the automobile industry. Therefore, automotive recycling results in zinc-containing scrap that should be remelted in EAFs. Naturally, the EAF dust is a very important source of zinc for zinc recycling processes. The thermodynamic properties of the Fe-Zn intermetallic compounds formed on the surface of galvanized steel sheet should be clarified to make clear the evaporation mechanism of zinc; however, there are few reports on these compounds because of difficulties in their synthesis. There are various intermetallic compounds in the Fe-Zn system. We synthesized them at about 673K. A specimen was examined chemically and X-ray diffraction was applied to ensure the formation of intermetallic compounds. Material containing two phases was placed in a Knudsen type effusion cell and the mass spectrum studied to evaluate the vapor pressure of zinc. The thermodynamic property of intermetallics was then evaluated through measured intensity.

Jan 1, 2000

By Elli Miettinen

In Copper Flash Smelting operation disturbances may lead into dust build-up in the gas train and off-gas handling system causing reduced heat recovery efficiency and process availability. Flue dust of a Copper Flash Smelting process heat recovery boiler has been characterized and its thermal conductivity and diffusivity have been determined. Dust accretions consist of several layers possessing varying particle sizes, densities, and thermal properties, with the binding phase usually being sulphate. All the dusts can be regarded as effective thermal insulators with thermal conductivity values of less than 2 W/mK and thermal diffusivity values of less than 0.005 cm2/s. Porosity can be regarded as a fairly good indicator of the thermal transport efficiency of these types of materials, but the material microstructure must also be considered. The results can be used in the dimensioning of metallurgical heat recovery boilers and they also provide accurate input data for process models.

Jan 1, 2009

By E. Burgos Cruz

The behaviour of S, N and P during refining of Fe-18 wt%Cr-10 wt%Ni with calcium carbide was investigated. The effects of the initial contents of C and N in the metal phase, as well as the supply method of calcium carbide to the melt on the removal degrees of S and P were evaluated. Heats were carried out at 1873K, in MgO crucibles, using a laboratory induction furnace. It was observed that simultaneously with S and P, N and O have also participated in the reactions. It seems that, in fact, O governs the behaviour of the other elements dissolved in the melt and that N is had to the removal of P with calcium carbide. It was also noticed that high C content in the metal phase have not altered the dephosphorization and desuffirization degrees, but that the supply of calcium carbide done by injection led to a lower dephosphorization degree than the one obtained by dumping it.

Jan 1, 1995

By A. Alvarez

In this work, mesophilic and thermophilic cultures have been used in the presence of silver as a catalyst. Chalcopyrite and byproducts of bioleaching were characterized in order to: a) obtain information about the kinetics control of the process, and b) explain the different behaviour observed during the mineral attack. With thermophilic microorganisms (68°C and Norris medium as nutrient) the reaction stopped at approximately 65% copper extraction, with and without Ag ion addition as a catalyst. The remaining chalcopyrite appears surrounded by hydronium jarosite (with ammonium ion in substitution in the "alkaline site"), goethite and elemental sulphur. With mesophilic cultures (35°C and 9K medium as nutrient) the reaction stopped at approximately 25% copper extraction (without Ag) and approximately. 85% extraction (with Ag). In both cases, the remaining chalcopyrite was surrounded by agglomerates of ammonium jarosite (with hydronium ion substitution in the "alkaline site") and some iron oxides and/or hydroxides.

Jan 1, 1999

By A. K. Kyllo

The use of Composite Furnace Module cooling systems has been shown to give improved refractory performance in a number of above bath locations in WMC flash furnaces. To test the behaviour of modules in contact with a melt, a set of instrumented modules have been installed in the reaction shaft of a. nickel flash furnace. The location was chosen to provide a suitably harsh environment to ensure rigorous testing, while still allowing relatively easy access for module installation. The modules were continuously monitored to provide information on the module performance, as well as the temperature in the shaft itself. The shaft temperature showed significant transient behaviour, which resulted in heat fluxes through the modules ranging from 10 to 92 kW m-2. The modules were capable of handling the highest heat flux with no risk of the coolant boiling. This paper details the design and operation of the modules over a period of seven weeks.

Jan 1, 1999

By Stephen R. Brown

Current conditions in the copper market demand that mine and plant operators make budgeted production targets at the lowest possible unit costs. For those companies bringing new production capacity on-line, achieving budgeted production levels as quickly as possible after start-up is vitally important to minimize unit costs and to begin a positive cash flow. Whether the objective is to simply improve unit costs or successfully start-up a new, complex plant, success will be strongly influenced by .the skill levels of the operators :and supervisors. The only way to assure return on plant investment, and to survive during depressed metal prices, is to ensure that plant operators have the knowledge to effectively run the plant. Technology available in computer-based, multimedia training systems, including: interactive animation, videos, voice-overs, schematics, and text can now be used to train operators at their own pace using plant-specific information. Additionally, it has been shown that learning through multimedia provides a higher degree of long term retention than more traditional learning methods.

Jan 1, 1999

By E. A. Trillo, L. E. Murr, R. D. Flores, J. C. McClure, B. M. Nowak

Complex vortex and swirl-like solid-state flow phenomena have been observed in the residual microstructures characterizing the friction-stir welding (FSW) of copper to 6061 aluminum; 2024 aluminum to 6061aluminum,2024 aluminum to 1100 aluminum, 2024 aluminum to 7039 aluminum and 2024 aluminum to 2195 aluminum. These flow phenomena are characterized by intercalation lamellae composed of dynamically recrystallized grain structures of the dissimilar metals which provide a super-plastic-like mechanism for the FSW flow in the solid state; there is no melting and temperatures at the weld center do not exceed about 0.8 TM (where TM is the absolute melting temperature (K)). In experiments to be described and illustrated, optical or light metallography (LM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques are utilized in examining residual FSW microstructures corresponding to tool rotation (stirring) speeds ranging from 400 to 1200 rpm, and traverse (or actual welding) speeds of 1 to 2 mrn/s.

Jan 1, 1999

By Y. C. Avniel, T. E. Warner

"It is important to be able to measure sulphur and nitrogen in molten iron and steel on-line. Unfortunately, there are no solid electrolytes which are stable under oxidising conditions and in which the ions of these species are mobile. In this paper, novel applications of beta alumina electrolytes are described and the results compared with data in the literature. Excellent agreement was obtained confirming this approach as a viable method of detecting elements whose ions are not mobile in solid electrolytes.IntroductionIn the past two decades, the rate of many processes in steelmaking have increased substantially. The sophistication of chemical analysis has also increased but analytical equipment is frequently positioned a significant distance from the operating plant which dictates that time is spent taking a sample, sending it to the analytical facility, preparation of the analytical sample prior to insertion into the equipment. In many cases, the time taken for analysis can exceed the time taken for the actual process and is now the rate defining step. Furthermore, most analytical methods are unable to distinguish between the amount of element which is dissolved in the steel and that contained in precipitates. Even if the analytical equipment could separate these two, the distribution would have changed between the molten steel and the cast sample. It would be an advantage to analyse on-line for impurities in molten metals."

Jan 1, 1997

By Ray Y. Lin, Sunil G. Warrier

"Low cost processing of metal matrix composites is an essential requirement for this class of materials to be acceptable in commercial application. In an effort to reduce the cost of processing of metal matrix composites, an infrared pressureless liquid infiltration technique has been developed. The salient features of infrared infiltration are that it is rapid, simple and a low cost process. The rapid processing capability causes very little oxide formation on the alloy resulting in both improved wetting and flow characteristics and reduced oxygen contamination in the composite. Thus, vacuum is normally not required. Using infrared inflltration, aluminum and titanium matrix composites have been prepared under an ambient argon atmosphere. Reinforcements in these composites include carbon fibers, silicon carbide Nicalon fibers and Textron's SCS fibers. Microstructural and mechanical test results indicate that completely consolidated composites with good fiber distribution, limited interfacial reaction and high mechanical properties can be manufactured by this process. IntroductionAluminum and titanium matrix composites reinforced with ceramic reinforcements are strong candidates for numerous applications in the aerospace and automotive industries. Aluminum matrix composites are commonly fabricated by either solid state vacuum hot pressing, liquid state pressure infiltration or squeeze casting [1]. Although liquid state pressure infiltration and squeeze casting has significant advantages over solid state processes, the requirement for pressure makes these composites uneconomical for large scale industrial application. Titanium matrix composites are primarily fabricated by solid state diffusion bonding [2]. Pressureless liquid infiltration can significantly reduce the cost of fabrication in both the composite systems. However, during pressureless infiltration processes, several complications concerning the wetting characteristics and chemical compatibility arise."

Jan 1, 1994

By Ibrahim Yusufoglu, Cem Kahruman, Mert Zoraga

In this study, a strontium sulfate mineral (celestite) was converted to strontium oxalate in solutions containing ammonium oxalate as a reactant. The experiments were carried out under isothermal conditions. The effects of stirring speed, ammonium oxalate concentration, particle size and temperature on the conversion rate were investigated. During the conversion process, definite volumes of solutions were taken from the reactor after different reaction times for the determination of sulfate ions using ICPOES. Fractional conversions of strontium sulfate were determined at different times and fractional conversion vs time diagrams were generated. It was found that the conversion of strontium sulfate was increased by increasing the ammonium oxalate concentration and temperature in addition to decreasing the particle size. The effect of stirring speed was negligible on the reaction rate. It was observed that above 328 K, a protective layer of strontium oxalate was formed on the strontium sulfate particles. X-ray Powder Diffraction technique was used for characterization of solid substances.

Jan 1, 2014

By Ryosuke Matsuoka

Keywords: Tantalum capacitor, Scrap, Recovery, Titanium, Chlorination A recycling process for tantalum from capacitor scraps using an oxidation process followed by mechanical separation and chemical treatment was investigated. This study demonstrates that sintered tantalum electrodes inside the capacitor scraps can be mechanically collected after the oxidation of the scraps in air, and high-purity tantalum oxide powder (Ta2O5) was efficiently recovered after chemical treatment. By reducing the Ta2O5 obtained through magnesiothermic reduction, tantalum powder with 99 mass-% purity was obtained. Using the chlorination for tantalum recovery was also investigated, and the tantalum or tantalum compounds were reacted with chloride wastes such as FeClx. It was found that tantalum was effectively separated and purified when tantalum powder is reacted with FeClx at 1100 K under an argon atmosphere. This recycling process utilizing chloride scrap has now been extended to other reactive metals such as titanium.

Jan 1, 2004

By S. -H. Jeon, Y. -S. Choi

"The three dimensional current distribution on the rectangular cathode is predicted using a boundary element method with a linear element of trigonal type. The effect of cell geometry and anode shape on current distribution is simulated. Calculated results compare well with experimental results. The proper combination of anode size and distance between electrodes increase the current uniformity.The importance of electrodeposition as a fabrication technology in the electronics industry is large and growing. The main advantages of this wet processing method, in comparison to other dry processing methods, lie in its high yield, rapid processing and low cost. In nearly every application of electrodeposition the pursuit of deposit uniformity, especially thickness uniformity, has been technically imperative. The thickness uniformity of the deposit depends largely on the current distribution over the cathode. The current distribution is primarily determined by the geometrical characteristics of the electrodes and the cell. Also the polarization at the electrode surface and the mass transfer affect the current distribution.The current distribution is an important consideration for those involved in designing electrochemical systems and electroplating systems in particular. Although it is important, the common practice in industry is to use trial and error method to design the cell that optimize the uniformity of current distributions in electroplating. The purpose of this paper is to illustrate the useof boundary element method to predict three-dimensional current distribution in rectangular cell.The calculation of the current distribution is possible by various numerical techniques, which include the finite difference method (FDM)1, the finite element method (FEM)2, and the boundary element method (BEM)3,4. These methods of the numerical calculation have various problems, respectively, but the BEM is considered to be the most efficient. This is due to the fact that the BEM has the advantage of solving field equations only on the surface of a calculation domain. A good comparison between the BEM and the FEM for the secondary current distribution in a Hull cell was made by Matlosz et al.5The fundamentals on the theory of current distribution in electroplating are well-established in the literature by a number of authors.6, 7, 8 However, a small fraction of these works have been specially addressed to three-dimensional analysis, and, mostly thel·10 have focused on the problem qualitatively rather than quantitatively.Extending the previous work to three-dimension, we developed the program for the quantitative calculation of 3-dimensional current distribution using a boundary element method with a linear element of trigonal type. Integrals with singularity from the fundamental solution have been analytically computed and it is shown in detail in the Iiterature11. This paper deals with the three dimensional current distribution for the electrode position of copper in a cubic type cell and the effect of anode shape, size and the distance between electrodes on current distribution is studied."

Jan 1, 1997

By J. L. Bill

The capacity of the Mount Isa Mimes Limited Copper Smelter was expanded in 1998 from 180,000 tomes per year of anode copper to 265,000 tpy. It is based on the innovative Copper ISASMELT technology, which currently treats concentrate at up to 184 tph. Increasing lance-air oxygen enrichment increased the ISASMELT furnace feed rate from 102 to 184 tph. The increased feed rate was achieved without any modifications to the ISASMELT furnace. The first refractory campaign following the upgrade lasted for two years. Future campaign lives of four years or more--without water cooling-are possible. Other Copper ISASMELT furnaces are operating in the U.S.A., Belgium, and India, with additional smelters under construction in China and Germany. In addition, Lead ISASMELT furnaces are operating in the U.K. and Malaysia. The paper discusses the performance of the MIM Copper ISASMELT furnace and the Copper Smelter since the expansion, including operating data and refractory performance.

Jan 1, 2002