Search Documents

By Mehmet Bu daycı, Onuralp Yücel, Ahmet Turan, Murat Alkan

In this study, iron based alloys (Fe, Fe-Cr-Ni-Mo, etc.) were produced by using metallothermic methods starting from Mill Scales obtained continuous casting processes. During the process, the combustion was realized by ignition and the produced wave propagates throughout the reactant mixture yielding the desired product. In this work, Mill scale used as an iron source, which includes +2, +3 values iron oxides. Aluminum, Magnesium and Silicon were used as reductants. In these metallothermic experiments, different ratios of reductants were examined, and their effects on the metal recovery and alloy compositions were investigated. The samples were characterized by using chemical analysis (AAS), XRD and XRF techniques.

Jan 1, 2016

By Rashmi Ramesh

Zinc oxide nanoparticles and nanostructures form an active area of research in the recent years. It can be doped to modify electronic, optical and other properties. Synthesis and characterization of zinc oxide is of extreme importance in order to understand the structure property relationship in this material which is now being considered of importance next to carbon nanotubes. Microstructure of zinc oxide nanomaterial is extremely sensitive to the preparation conditions. Nanocrystalline pure and Mn and Mg doped zinc oxide samples were prepared by wet-chemical method under different growth conditions. The samples were investigated for crystalline phase, microstructure, morphology and luminescence characteristics. The effect of Mn and Mg doping on the characteristics of ZnO have been discussed.

Jan 1, 2010

By NRMR Bhargava

With the increasing use of lead-free solder alloys, low melting point alloy is often required due to the heat- sensitive parts or substrates in modern electronic devices. For such demand of low melting point, the nanostructure lead- free solder alloy, having excellent metallurgical characteristics and a melting point of <215oC, were developed by mechanical attrition of conventional lead free solder alloys (Sn-Ag-Cu, Sn-Ag and Sn-Cu). The decrease in melting point due to nanosize effect was calculated theoretically as function of particle size and the theoretical results were compared with experimental values measured by differential scanning calorimetry. The newly developed alloys have eutectic composition of Sn-3.5Ag-0.7Cu, Sn-3.5Ag and Sn-0.7Cu and the melting point depression found to be 5.10C, 4.10C and 6.20C when the bulk alloys reduced to 80 nm, 92nm and 96nm sizes respectively.

Jan 1, 2009

By Sutham Niyomwas

Keywords: Al2O3-SiCW, Ceramic Matrix Composite, Carbothermal Reduction, Kaolin The formations of Al2O3-SiCw composite have been obtained in situ by carbothermal reduction of a mixture of kaolin and activated carbon. The reaction temperature was controlled at between 1400°C to 1600°C. The synthesized products were mixtures of alumina and silicon carbide in the form of whiskers. The effects of milling time of precursors and reaction temperature are presented. XRD and SEM analyses indicate complete reaction of precursors to yield Al2O3-SiC as product powders, with the SiC having porous and whisker morphology.

Jan 1, 2005

By J. P. Bellot

During the non-ferrous metal processing, the melting step under vacuum or under rarefied gas leads to volatile metal losses. It is the case of the metallurgical processing of the nickel-based, titanium-based or zirconium-based alloys where the evaporation losses don&apos;t allow a sufficient control of the alloy chemical composition. A theoretical approach has been carried out involving both a continuum description in the liquid phase and a molecular approach in the rarefied gas phase. The finite volume method is used in order to solve the coupled transport equationsin the liquid, whereas the Boltzmann equation is modelled by using a Monte Carlo method. At the liquid metal and metallic vapor interface, the volatilization and recondensation fluxes link up the two calculations. Simulation results are given for the melting and refining of reactive metals such as titanium alloys where the control of the chemical composition remains a major difficulty. The validity of the kinetic Langmuir&apos;s law is discussed for different operating conditions.

Jan 1, 1996

By A. Deneys

An experimental technique has been devised for studying the reaction kinetics of the reaction: ZnO + 2Fe0 = Zn(g) + Fe203, by which zinc evolution can occur from a molten slag bath in the absence of a carbonaceous reductant. When studying the reaction kinetics by heating from room temperature, solid state reactions and poorly defined melting points may obscure the starting point of the reaction. In order to eliminate this problem, an experimental technique was devised whereby two molten slags could be melted independently, and then mixed, to provide a well defined starting point from which to begin taking measurements. Two crucibles were mounted in a vertical reaction cylinder. The upper, mild steel, crucible had a bottom pouring plug which was sealed by a steel stopper rod. A fayalite mixture was contained in this crucible. The lower crucible contained an A12O3-CaO-SiO2-ZnO solution. Once the two slags had been melted, the steel stopper rod was removed from the upper crucible. The upper, reduced slag (fayalite in equilibrium with the upper steel crucible), drained into the lower crucible where the two slags were mixed by submerged argon stirring. Dip samples were taken to measure the zinc content of the final mixture as a function of time. The experimental procedure will be described, as well as results of experiments which were conducted on synthetic slags. The system investigated was similar to the lead blast furnace slag which is produced by the primary lead smelters of Missouri, USA.

Jan 1, 1997

By C. J. Newman

Production levels at the Kidd Creek copper operation increased during the 1980&apos;s by expansion of both the smelter and refinery and by major modifications to equipment which was causing bottlenecks. As a result, there was a significant reduction in the unit cost, some manpower reductions and hence a significant increase in productivity. In the last two or three years, there have been no major expansion projects leading to unit cost reductions and yet these have still been attained. This has been achieved by the development and implementation of various techniques designed to maximize the inherent potential of the operators and maintenance employees. This paper will initially describe the operation but will then place emphasis on employee involvement through such methods as idea awards, incentive schemes, loss control and continuous improvement programs. Organizational changes are discussed, particularly with reference to changes from the traditional operator role to one which encompasses maintenance skills and to cross-training of maintenance employees into multi-discipline fields. The effect of these changes are discussed by a review of the salient plant parameters of safety, production levels, cost and quality.

Jan 1, 1993

By James A. Voigt

The efficient separation of metal species from aqueous streams by precipitation techniques requires &apos;a fundamental understanding of the various processes that occur during precipitation. These processes include particle nucleation, particle growth by solute deposition, agglomerate formation, and agglomerate break-up. The application of the population balance approach has been used to develop a kinetic model that accounts for these competing kinetic processes. The usefulness of the model is illustrated through its application to the precipitation of yttrium hydroxynitrate, YHN. The kinetic parameters calculated from the model equations and system-specific solution chemistry are used to describe several aspects of the effect of pH on the precipitation of the YHN. Implications with respect to the simultaneous precipitation of more than one cation type are also discussed through use of example systems: The effects of solution chemistry, precipitator design, and solvent choice are considered.

Jan 1, 1996

By S. Tanaka

The Tamano Smelter of Hibi Kyodo Smelting Co. Ltd. was commissioned in 1972. Since start up, the anode production capacity has increased from 101,000 tpy to 290,000 tpy, as a result of the application of continuous improvements at each phase of the expansion projects. The Tamano Smelter had developed several innovations, including the original coke combustion technology for Flash Smelting Furnace operations (T-FSF), and has also been able to extend the operating life of the Peirce-Smith converters. This paper will present several improvements implemented at the Tamano Smelter, and will discuss relevant P-S converter operation.

Jan 1, 2005

By Zhuokun Cao

Manufacture of aluminum foams still suffer from nonuniformity and poor reproductively for there is lack of basic knowledge of foaming process. In this paper, carbon fibers are used as novel stabilizing additive for aluminum foams, and the structure evolution of aluminum foams with different fiber content was studied. A laser rangefinder was used to detect the expansion rate of different al foams. Al foam samples are solidified at different foaming time to determine its relative density and cell size distribution. Results indicate that the cell size of foams linearly increases with the decrease of density, and the slope of the line is influenced by fiber content. The relationship between expansion ratio, density and cell size of the foams is discussed. It is concluded that the density of resulting foam is influenced by the rate of gravity driven drainage, and its cell size is determined by expansion ratio and foaming time.

Jan 1, 2010

By W. K. Collins

Engineered Scavenger Compounds (ESCs), developed by the U.S. Bureau of Mines, are a novel class of compounds that can selectively recover a desired element from a solid or molten alloy. Lithium titanate (Li2Ti3O7 or L&apos;20-3T&apos;02) is being used as an ESC to recover lithium (Li) from Aluminum-Lithium (Al-Li) alloys. X-ray diffraction measurements have shown that lithium titanate undergoes a phase change from an orthorhombic structure to a hexagonal structure. This change is due to the incorporation of Li in the matrix of the material and the effect of temperature. Although both are metastable, the hexagonal phase that forms during the scavenging of Li from Al-Li alloys appears to be the more stable phase. Recovering Li from the ESC by electrodeposition does not cause the structure to revert to the orthorhombic phase. Both the orthorhombic and the hexagonal structures of Li2Ti3O7 have similar scavenging capacities for Li. This paper proposes a new mechanism for the phase transformation.

Jan 1, 1993

By W. D. Riley

Engineered Scavenger Compounds (ESCs), developed by the U. S. Bureau of Mines I are a novel class of compounds that can selectively recover a desired element from &apos;a solid or molten alloy. Lithium titanate (Li2Tip7 or Li20&apos; 3TiO.) is being used as an ESC to recover lithium (Li) from Aluminum-Lithium (AI-Li) alloys. X-ray diffraction measurements have shown that lithium titanate undergoes a phase change from an orthorhombic structure to a hexagonal structure. This change is due to the incorporation of Li in the matrix of the material and the effect of temperature. Although both of the structures are metastable, the hexagonal phase that forms during the scavenging of Li from AI-Li alloys appears to be the more stable phase. Recovering Li from the ESC by electtodeposition does not cause the structure to revert to the orthorhombic phase. Both the orthorhombic and the hexagonal structures of Li.Til07 have similar scavenging capacities for Li. This paper proposes a new mechanism for the phase transformation.

Jan 1, 1991

By Harsh Deep Chopra, Jason N. Armstrong, Susan Z. Hua

"Existence of anisotropic Curie temperature materials [E. R. Callen, Phys. Rev. 124, 1373 (1961); J. Appl. Phys. 32 S221 (1961)] is a longstanding prediction - materials that become paramagnetic at a lower temperature along certain crystal directions while remaining magnetically ordered in other directions up to a higher temperature. Validating Callen's theory, we show that all directions within the basal plane of monoclinic F e1Ss (pyrrhotite) single crystal remain ordered up to 603 K while the c-axis becomes paramagnetic at 225 K. Results prompt a re-evaluation of existing magnetic materials with a focus on magnetic characteristics along different crystal orientations above instead of below the ordering temperatures. Theoretical guidelines for identifying new materials with large anisotropy of Curie temperature are also given, and analysis protocol to characterize them in a self-consistent manner is discussed. Materials with such a large directional dependence of Curie temperature open the possibility for uniquely new devices and phenomena, including energy storage and spintronics devices.IntroductionThis paper is an overview of our recently published work on anisotropic Curie temperature materials [l]. As a background, ferromagnetic and ferrimagnetic materials are characterized by a critical temperature below which magnetic interactions prevail over thermal agitation, leading to the appearance of a spontaneous magnetization. Above this critical point, called the Curie temperature, thermal energy eventually overcomes magnetic interactions and the material becomes paramagnetic.It is less well known that the Curie temperature varies with the orientation of the crystal. In ordinary ferromagnets this orientation dependence of Curie temperature is negligible because of the vanishingly small ratio of anisotropy to exchange energy, i.e., the spherical or isotropic exchange term dominates. Thus Curie temperature in ordinary ferromagnets appears to be an isotropic property, and assigning it a single characteristic ordering temperature suffices. However, a 'small' difference is not equivalent to being the 'same', and under appropriate set of conditions the anisotropy of Curie temperature is predicted to become appreciable, as discussed in the following.In formulating the theory of 'anisotropic magnetization' [2, 3] E. R. Callen and H. B. Callen first discussed the ""interesting possibility"" of anisotropic Curie temperature [2] or ACT; Callen and Callen noted that it was W. J. Carr, Jr. who initially raised this question, and they discussed it in detail at the Conference on Magnetism and Magnetic Materials (NY, November 1960), see footnote on page 320 of Ref. [2]. Soon thereafter, E. R. Callen developed the theory underlying the anisotropy of Curie temperature and conditions conducive to its observation [4, 5]."

Jan 1, 2013

By Phillip A. Armstrong, Charles A. Lewinsohn, John H. Gordon

"This paper describes the opportunity offered by employing systems based on mixed conductive ceramics, in particular, ceramics conductive to oxygen ions and electrons, in reducing CO2 emissions from metallurgical production. Membranes based on these mixed conducting properties enable commercial viability of several attractive metallurgical processes. One of these processes utilizes modular, ceramic-membrane structures for the generation of pure oxygen, in tonnage quantity. The membrane-based systems offer significant capital savings and operating efficiencies in various metallurgical processes. The current status of this technology is summarized below.IntroductionCryogenic oxygen supply technology is currently the state-of-the-art for applications that require large quantities of oxygen (hundreds to thousands of tons per day). Cryogenic technology, however, requires substantial energy inputs and, hence, adds significant costs and emissions to processes. Furthermore, cryogenic oxygen supply technology is mature and there is relatively little potential for substantial capital cost reduction or efficiency improvement in coming decades. Non-cryogenic technologies offer a means to reduce the environmental footprint and cost of the oxygen supply facility in various applications.Ion Transport membranesCommercially available non-cryogenic air separation technologies, such as adsorption-based and polymeric membrane-based methods, do not afford the economies of scale that the cryogenic distillation enjoys. Therefore, industrial gas industry researchers began searching for alternatives to the relatively inactive and unselective polymeric membrane materials available. In the late 1980’s, Air Products began developing a new class of highly selective membrane materials with exceptionally high activity for oxygen transport. The materials constitute a class of oxide ceramics, and conduct both oxygen (as oxygen ions) and electrons in the same membrane, separating oxygen from air electrochemically. Numerous detailed process economics studies have shown that, based on these ion-transport membranes (ITM’s), the cost of oxygen can be reduced by approximately one-third relative to that obtained from state-of-the-art cryogenic oxygen supply technology, through a combination of capital cost savings and efficiency improvements. [1,2,3]"

Jan 1, 2008

By T. Shi, Q. Yuan, S. P. Vanka, B. G. Thomas

"The quality of continuous cast steel is greatly affected by fluid flow in the mold region, especially involving transient phenomena. Mathematical models are being applied to investigate many different aspects of these phenomena, but their accuracy must be validated before they can be applied with confidence. As part of a long-term effort to develop and apply comprehensive models of the continuous casting process, this work evaluates the relative accuracy of models of three different fluid flow phenomena in continuous casting through comparison with measurements.Firstly, transient flow simulations of velocities in the mold region are compared with digital particle image velocimetry (PIV) measurements in a single phase water model. Large-eddy simulations (LES) are found to reasonably match the flow measurements, including transient flow variations, except at long time scales, which could not be modeled owing to the excessive computation costs. The standard K-e model produced very good agreement with time-averaged velocities for relatively little computation time, although it is inaccurate at predicting the transient variations. Secondly, particle trajectory calculations are compared with water model measurements to study the distribution and flotation removal of inclusion particles. The LES model was able to match the measurements both qualitatively and quantitatively. Thirdly, steady, multi phase flow computations are compared with flow patterns observed in both a water model and an operating steel caster with argon gas injection. For the same conditions, the water model and steel caster produced very different flow behavior. The computational model was able to match the measured flow patterns in both cases.This work suggests that computational flow modeling has the potential to match real processes as well or better than water models, especially when complex related phenomena such as particle motion and multiphase flow are involved. Much work is still needed to further improve the models and to apply them in parametric studies."

Jan 1, 2001

By M. I. Brasileiro

The use of experimental design to the study of mixtures has found a wide range of applications, even in laboratory scale or in industrial development works. The aim of this work was to maximize granite sawing waste content in ceramic tiles using experimental design. Based on the raw materials, specific formulations were developed using the experimental design. The raw materials were mixed and sample bodies were produced using uniaxial pressing. The sample bodies were fired and characterized in terms of water absorption, mechanical strength and X-ray diffraction. Regression models were adjusted relating the water absorption and mechanical strength with the amount of raw materials. The results showed that the methodology of experimental design maximize the content of wastes incorporated in ceramic tiles formulations. Formulations containing up to 40% of waste can be used for the production of ceramic tiles.

Jan 1, 2009

By Frame Ritzert, Dennis Keller, Vijay Vasudevan, David Arenas

"An investigation was conducted to describe topologically close packed (TCP) phase instability as' a function of composition in the advanced ·Ni-base superalloy Rene N6. TCP phases are detrimental to overfill high-temperature performance of Ni-base superalloys because of their brittle nature and because they deplete the Ni-rich matrix of potent solid solution strengthening elements. Thirty-four variations of polycrystalline .Rene N6 determined from a design-of-experiments approach were cast and homogenized at 13 l5°C for 80 hours followed by exposure at 1093°C for 400 hours to promote TCP formation. The alloys had the following composition ranges in atomic percent: cobalt 10.61 to 16.73, Mo 0.32 to 1.34%, W 1.85 to 2.52%, Re 1.80 to 2.11%, Ta 2.36 to 3.02%, Al 11.90 to 14.75%, and Cr 3.57 to 6.23%. Physical and chemical characteristics of all microstructures obtained were described using various analytical techniques. From these observations, a mathematical description of TCP occurrence (s and P phase) was generated for polycrystalline Rene N6.IntroductionNi-base superalloy single crystals represent the state-of-the-art for turbine engine airfoil application as they offer the best balance of properties to allow for the high operating temperatures required: for efficient engine operation.1 Current trends in alloy design take advantage of improved creep rupture strength with the addition .of higher levels of refractory elements. 2 In .particular, the addition of significantly higher levels of Re in third generation superalloys is key for both microstructural stability and creep rupture strength. 3 While the presence of the refractories is thought to provide strength benefits from solid solution hardening, a tendency for alloy instability in the form of topologically-close-packed (TCP) phases or secondary reaction· zone (SRZ) ·phenomena accompanies the high refractory content. 3 The formation of these phases in sufficient amount is detrimental to the overall high temperature performance of Ni-base superalloys because of their brittle nature and because they deplete the Ni-rich matrix of potent solid solution strengthening elements.4 The tendency for a particular composition to form TCP may not be immediately known since the precipitation of TCP phases in Ni-base superalloys is nucleation controlled, thereby requiring long times at elevated temperatures to precipitate. 5 They preferentially nucleate along the octahedral planes of the Ni-base superalloys, usually in areas of refractory metal enrichment at grain boundaries or inside dendrites.5-6 In Rene N6, two closely related TCP phases, a and P, have been observed.2"

Jan 1, 1998

By Gary A. Wickham

In the zinc industry, this past decade has seen both prosperity and depression. Significant changes have occurred throughout the world in mining, smelting, refining, and marketing. This paper will review many of the industrywide changes of recent years and the potential impact for 1990s. In addition to an historical review of supply and demand are discussion of technology considerations for zinc and zinc based products, effects of geographical shifting of markets, and projections for the 1990s.

Jan 1, 1990

By Zhang Duomo

A novel homogenous precipitation method, including microwave heating, solution conductivity controlling and freeze drying, was developed for the preparation of US nanoparticles. The effects of the precipitation conditions on the structure and morphology of CdS particles were discussed individually. It was found that under the experimental conditions the particle sizes were controllable in the range of 14nm to 100nm. Blend-type CdS was obtained from nitrate or sulphate solution and the more stable wurtzite-type US was obtained from chloride solution, which was ascribed to the coordination of C1 and Cd2+ altering the supersaturation of the solution as well as the different growth units and their connecting patterns, In the precipitation process the surface of US nanoparticles were surface modified with CH3CHSCOOH. The results demonstrate that the bifunctional thiols of thioglycolic acid modified the surface through Cd-S coordination bonding and the induced counter ion AOT-SO3 as the balance charge further increased the stability and dispersity of US nanoparticles. This surface-modified US nanoparticles had been used to prepare nonlinear optics and self-assemble catalysts.

Jan 1, 2003

By Tang Chaoho

Laboratory research on the reducing and matte smelting of Jamesonite concentrate has been carried out. The influence of the process conditions such as the smelting temperature, the amount of pyrite cinder (the agent of fixed sulfur) and the amount of additives on the smelting process have been studied. Under the optimum condition the direct recovery ratios of antimony and lead are 83.26% and 68.50% respectively. The ratio of fixed sulfur is 98.97% but more than 15% lead and 30% silver remained in the ferrous matte. The key problem to be solved of this new process is how economical and effective is the recovery of silver and lead in ferrous matte.

Jan 1, 2003