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By Jamil M. Khalifeh, Shadia J. Ikhmayies, Bothina A. Hamad

"We computed the optical properties of the cubic niobium nitride (o-NbN) compound using the full potential linearized augmented plane wave (FL-LAPW) method within density functional theory (DFT). The complex dielectric function and optical constants, such as optical absorption coefficient, refractive index, extinction coefficient, energy-loss spectrum, and reflectivity, are all calculated and compared with experimental results. The behavior of the computed quantities is similar to that obtained experimentally, but the optical positions are shifted to lower energies. This shift was related to the strong interband transitions, which are located at energies higher than 5 eV for NbN- as they are for IV B transition-metal mononitrides- and they appear in the computed spectra and not in the experimental spectra. These interband transitions simply shift the position of the reflectivity edge or the screened plasma frequency to the longer wavelength side.IntroductionIn recent years, NbN, as a transition metal nitride, has become a very popular material due to its high hardness, melting point, wear resistance, chemical inertness and temperature stability, which makes it suitable for use as emission cathodes in microelectronics and sensors, optical films and micro-mechanics etc [l]. Niobium nitride has long been known as highly polymorphic material, for which several crystalline structures have been reported in the literature [2]. These structures include the well known super-conducting rock-salt (Fm-3m, or Bl) structure (o-NbN), the hexagonal structure with space group p63/mmc and prototype Fe2N (18fuN), the hexagonalstructure with space group p63/mmc and prototype NiAs ~-NbN) and others.There has been a lot of computational studies for the structural and electronic properties ofNbN [3, 4-7], but according to our knowledge there is not any computational work that has been devoted to study the optical properties of this transition metal compound. At the same time a number of authors had performed experimental work in this direction. For example, Xin-kang et. al [l] studied the microstructure and optical properties of magnetron sputtered NbN thin films. Torche et. al [8] studied the composition, structure, electrical and optical properties of nonstoichiometric niobium nitrides. Newport et. al [9] investigated the reflection and transmission spectra of cubic niobium nitride films, and Tanabe et. al [10] had investigated the optical parameters and reflectivity of reactively sputtered NbN thin films by using in situ ellipsometry."

Jan 1, 2013

By Wang Youlai

Sichuan province is the richest province for its waterpower resource in China, perfectly suited to develop a high consuming energy industry. Sichuan Aostar Group Company has two Aluminum smelters, Guangyuan Aostar smelter and Sichuan Aostar Smelter. The production capacity of Aostar Group was 240,000 tons in 2004. The construction scale of Sichuan Aostar Aluminum smelter is 250,000 tons per year. The first 168 GY-300KA pre-baked anode cells (125,000 tons/year) were put into production in 2003. This company has taken the lead in the use of the transfer gantry technology in China. Besides making the process of calibration the pot shell it has concentrated the efforts to construct cell lining elsewhere. This company also has taken the lead in China for using the EIRICH force mixing and cooling technology as well as in the world for the CP Company?s vertical ball mill technology that produces the pre-baked anodes. The carbon anode system completed its 190,000 tons/year production scale. This is the most advanced technology and the biggest scale pre-baking anode manufacture in China. Since the Sichuan Aostar 300KA cell was put into production, it runs normally and smoothly. Up to now the current efficiency is higher than 94% and the specific energy is only 13300kWh/T-Al.

Jan 1, 2006

Environmental and public concerns and the banned use of cyanide for the recovery of gold in some parts of the world have heightened the search for an alternative lixiviant to cyanide. Thiosulfate appears to be the most promising alternative to cyanide due to thiosulfate being non-toxic, relatively cheap compared to cyanide and generally gold recoveries are similar to those of cyanide. The most widely researched thiosulfate process is one where copper ions and ammonia are added to the solution. This paper reviews the leaching of gold in thiosulfate solutions and the contributions of the research at Monash University to the understanding of the gold oxidation reaction in thiosulfate solutions, the solution chemistry when copper ions, ammonia and oxygen are present, the influence of the changing solution chemistry on the gold leach kinetics, and the application of thiosulfate in the leaching of gold from ores. It is clearly shown that the gold oxidation rate is hindered in thiosulfate solutions. In the presence of copper ions the gold oxidation rate though is significantly enhanced and thus is why copper(II) is more effective than other oxidants in the thiosulfate leach system. The copper-ammonia-thiosulfate leach solution chemistry is shown to be very complex, especially in the presence of oxygen as the rate of thiosulfate oxidation increases and the majority of the copper ions are not maintained in the copper(II) oxidation state. The thiosulfate oxidation rate must also be maintained low as an intermediate thiosulfate oxidation product hinders gold leaching. In optimising the recovery of gold from ores with copper-ammonia-thiosulfate leach solutions it is important to evaluate and minimise any negative effect an ore may have on the leach solution chemistry and hence gold leaching.

Jan 1, 2003

By Jose Castro

The growing demand of scrap to supply the electric arc furnace has driven to search for new alternatives of raw material. The DRI produced using self-reducing pellets has become competitive due to the potential use of a wide range of carbonaceous materials such as coal, charcoal, biomass etc. In this context, the rotary kiln process using improved technologies such as post-combustion and self-reducing burden is a promising source of high quality raw materials. This paper presents a mathematical model of the rotary kiln process designed for self-reducing pellets and post-combustion. The model is based on the transport equation of two-phase flow, energy and mass transfer. The solid material is composed of a typical self-reducing pellet. The model considers the solid phase (C, volatiles, Fe2O3, Fe3O4, FeO, Fe, H2O, SiO2, Al2O3, MgO, P2O5, K2O, Na2O, FeS, CaO and gangue) and the gas phase (N2, O2, CO, CO2, H2, H2O, SO, SO2 and SiO). For each of the above components a conservation equation is solved and the mass and energy transport is accounted. The set of differential equations are coupled by the rate equations describing the kinetics of the several reactions, which take place within the rotary kiln. All the conservation equations are solved based on the finite volume method applied for a three-dimensional cylindrical coordinate system. Simulation results are presented for global parameters such as metallization degree, productivity, gas utilization ratio and calorific value. Inner conditions such as three-dimensional gas and solid temperature patter and compositions are discussed.

Jan 1, 2006

By Varadajan Seshadri

Torpedo cars have been extensively used for pig iron desulfurization although its geometry is not considered to be ideal as far as mixing and mass transfer are concerned. Complications arise from scaffolds formed through aggregation of flux, slag and pig iron during operation. Following industry demand a 1:6 torpedo car physical model was operated to assess the optimum refining conditions for pig iron desulfurization. Similarity between the model and prototype were established through Froude and turbulent Reynolds criteria. Mixing times were evaluated by pulse tracer addition and the kinetics of metal/slag interactions were assessed from experiments investigating iodine transfer from kerosene to water. The influence of parameters such as level of metal, gas flow rate, lance penetration, lance orientation, presence of scaffold were evaluated. Mixing times were found to be shorter than regular desulfurization time and also not very sensitive to scaffold presence. Scaffold contributes to the reduction of the useful volume only. Mass transfer at the permanent reactor is more effective when the torpedo is operated at its full capacity. The experiments also highlight the dominance of the transitory reactor as compared with the permanent reactor.

Jan 1, 2006

By Alex Moyano

At present, the Codelco Norte smelter processes in the Teniente Converter and the Flash smelting Furnace 1,420,000 t/y of its Chuquicamata concentrate with an arsenic content of up to 1.5%. In a near future Codelco-Chile is considering different processing options for a new projected concentrates from the Alejandro Hales mine (former Mansa Mina mine with an arsenic content of up to 6%). The main option is the possibility to process 3,000 t/d of mixing concentrates from the Alejandro Hales and the Chuquicamata mines, in the Teniente Converter. The main feature of this smelting unit will be high volatilization of arsenic when processing high arsenic-bearing concentrates. The CN smelter staff carried out a technical feasibility study to evaluate the processing of high arsenic-bearing concentrates directly in the Teniente Converter, thus the low arsenic-bearing concentrates can be processed in the FSF. Accordingly, laboratory scale tests were carried out at the Tohoku University facilities. The lab-scale results allowed an industrial scale test at the Codelco Norte smelter to smelt 2,300 tpd of high arsenic-bearing concentrates in the TC and evaluate the metallurgical impact in the smelting, converting and refining areas of the smelter. The main industrial-scale result confirmed the stabilization of the arsenic content at 0.5% in the 70% Cu produced white metal at the test condition.

Jan 1, 2006

By E. J. Peuraniemi

Recently commissioned Kennecott-Outokumpu flash converting was developed to replace the approved but environmentally outdated Peirce-Smith -converting to satisfy the globally tightening emission regulations. In the present study, dust formation and reaction mechanisms of two copper mattes with different experimental parameters were studied in lean suspension conditions. Both mattes had very high copper content of approximately 75 wt% and low iron content of 4.5 wt% and 1.2 wt% Fe. A laboratory scale, vertical laminar-flow furnace with a low feeding rate was used to simulate the phenomena taking place in the reaction shaft of a flash converter. Experimental conditions included temperature of 1300 °C with reaction gas oxygen contents of 20 vol%, 50 vol%, and 75 vol%. In the experiments, sieved particle fractions were fed to the furnace and sampled after short reaction time intervals by quenching them into a water film. Collected particles were analysed chemically for their main elements to define their removal rates. Also, optical and scanning electron microscopy with EDS-analyser were applied to determine phenomena occurring during reactions. Kinetics of oxidation as well as ignition of particles are discussed. Changes in particle morphology, size, and composition are reviewed to describe dust formation and reaction mechanisms.

Jan 1, 1999

By Luciano B. Oliveira, Angela O. Costa, Sergio N. Monteiro, Luis Guilherme C. Marques

"Biofuels are gaining a relevant role in today’s world not only as a solution for the decreasing petroleum reserves but mainly as a positive contribution to the efforts in global warming mitigation. In Brazil, since 1975, the replacement of gasoline by ethanol started a so-called PROALCHOOOL program, which is now being complemented with the replacement of petroleum diesel by biodiesel. This biodiesel program was officially created in 2005 with mandatory goals, supported by legislation, of 2% addition in 2008 and 5% addition in 2013 into all commercialized regular diesel. In this work, a critical analysis of the Brazilian biodiesel program is presented. The technical aspects related to the different raw materials, including wastes, available for biodiesel conversion as well as the economical conditions associated with production costs and market logistic are discussed. The environmental benefits associated with the retention of greenhouse gases are also discussed.IntroductionToday the commonly accepted fact that the petroleum world reserves are probably passing through a maximum and start declining in terms of the total amount that can be extracted by existing technologies is motivating significant changes in our society. The continuous increase in the price of gasoline and other liquid fuels is an immediate worrisome and visible consequence. However, more than an economical problem, our civilization is already facing the effects of global warming, due to CO2 emission from burning fossil fuels, mainly from coal and petroleum. It is now realized that a large scale solution for these problems demands the prompt substitution of non-renewable fossil fuels by others that, in addition of being renewable, have a relatively lower contribution to the greenhouse gases."

Jan 1, 2008

By Akita Ito, Sumio Kato, Mikio Sugai, Shinichi Nakata

"Spark Plasma Sintering (SPS) is a newly developed method for the sintering of metal and ceramic powders, and completes their densification at low temperature and in short period. The SiC powder was synthesized from diatomite and graphite or carbon black by heating at 1 450°C for 1 hr in an argon atmosphere. The synthesized SiC powder was heated at 1500-1800°C, 50 MPa for 15-18 min by SPS. The relative density of sintered SiC body increased with the rise in the temperature. The oxidation of the surface of the SiC particle and impurities in SiC from diatomite greatly influenced the sintering promotion of SPS.IntroductionThe SiC has high hardness because of the covalent bonding, and is also excellent in thermal and chemical stability. However, it is difficult to obtain a dense SiC sintered body by the combustion heating-method. Therefore, the dense SiC bodies have been made by the use of additives and I or the hot pressing (HP) method.In this study, the SiC powder was synthesized by using diatomite of natural products and graphite, and carbon black of reagent as raw materials, and the relationship between the properties of SiC powders prepared at various synthetic conditions and the density of sintered body by SPS was examined."

Jan 1, 2000

By I. Ohnaka

Although many works have been reported on the semisolid casting, the mold filling behavior of semi-solid alloys has not been so well understood. This paper compares the physical and numerical simulation results on the mold filling behavior. Physical simulation was performed by using solid-water mixture. The numerical simulation was made under the assumption of one phase flow with an effective viscosity. It was found that the solid particles stabilize the flow greatly if the kaction solid exceeds about 0.4, because viscosity increases greatly. The overall flow behavior can be estimated by the numerical simulation. Interesting flow behavior was also found which can not be observed in the case of one phase flow and which is difficult to simulate by the one phase flow assumption.

Jan 1, 1997

By David J. Krichten

A method of retrofitting air-fuel burners with oxy-fuel capability overcomes the potential problems associated with oxygen combustion in aluminum melting furnaces. The retrofit burner uses the existing combustion air connection, burner housing, and burner tile and replaces the gas tube with an oxy-gas burner. Maintaining a portion of the air flow to the burner reduces the potential for localized overheating. Proper design of the burner reduces NOx emissions by moderating the flame temperature with furnace gas recirculation. Economic analysis of using oxygen shows the benefits are increased productivity and reduced overall unit cost of melting. In practice, the melt rate in rotary furnaces increases by up to 50% and by up to 35% in reverberatory furnaces. Oxygen utilization reduces total melting cost by 112-314 cents per pound of aluminum melted.

Jan 1, 1997

By T. J. A. Smith

This paper provides an overview of some of the key issues in design of smelter gas handling systems, with particular reference to smelter smelting plants. In both primary smelting and converting, gas handling and treatment systems often represent the major capital cost component. There is also ample evidence that poor system design can be a major cause of smelter down time, lost production and unforeseen high maintenance costs. The paper discusses these issues and offers guidance for improved design.

Jan 1, 1992

By Frank A. Stephens

The process of converting iron ore (principally Fe,03 or Fe30,) into iron carbide (Fe,C) to be used as feedstock for steel-making yields complex mixtures of several Fe-containing compounds as a function of processing conditions. In addition to the above compounds (hematite, magnetite and cementite), the mixtures typically contain wustite (FeO) and metallic iron(Fe). Mossbauer spectroscopy has been developed into aquantitative analytical method for monitoring the degree of conversion to carbide from samples periodically extracted from a fluidized bed reactor type of pilot plant. Calibration of absolute quantities of the above five compounds is based on standards prepared from known mixtures of the high purity individual phases. The PC-based spectrometer allows fitting of the well-known spectral components of each of the five phases, the resulting spectral areas then being compared with the calibration curves via PC software to yield the weight fraction of each. Emphasis has been placed on standardizing and simplifying the analysis procedure for routine use in an industrial environment.

Jan 1, 1993

By M. O. Lai

"Metal matrix composite (MMC) with composition of Al-4.Swt.%Cu reinforced by IOwt.%TiB2 or ISwt.%SiC particulate has been successfully fabricated using powder metallurgy technique. Disk, compression and beam specimens were prepared with (a) layered structure containing ductile Al-4.Swt.%Cu with brittle Al-4.Swt.%Cu/TiB2 or Al-4.Swt.%Cu/SiC layers, and (b) homogenous constituent with composition of Al-4.Swt.%Cu/lOwt.%TiB2' The specimens for the fracture toughness measurement were built through three ductile-brittle-ductile alternating layers. For the beam specimens, the layers were built through brittle-ductile-brittle sequence. The brittle layer consisted of Al-4.S%Cu with fixed amount of reinforcement. Fracture toughness testing revealed an increase for layered composites although the total amount of the reinforcement was the same for all disk specimens. The increase in fracture toughness is due to the existence of ductile layers which manifests a strong influence on delaying the occurrence of fracture. It acts as a barrier to resist the propagation of crack and hence increases the fracture toughness of the layered MMC specimens, Delamination in the beam specimens was observed to be due to shear stresses. Fracture surfaces of both disk, compress and beam specimens were characterized using the SEM. IntroductionMechanical and thermal properties can be achieved by the incorporation of refractory secondary phases to constrain the plastic flow of the matrix in a metal matrix composite (MMC). The size of the reinforcement particulate incorporated must be in the range larger than the dislocation cell size and strongly bonded to the matrix (I). Particulate reinforced metal matrix composites hence provide high modulus, improved wear resistance and strength (2-4). Because of the incorporation of refractory phases which are generally brittle, the major limitation in the mechanical properties of MMCs is their limited ductility in comparison to their base metals. Cracks normally initiate from the reinforcement and voids (4, 5). Due to the lack of ductility, cracks propagate rapidly with increase in load. As a result, the interactions between reinforcement particles and propagating cracks have recently been of great research interest (6). In addition, volume fraction of reinforcement and aging condition of the matrix significantly affect the mechanical behaviour of MMCs. In the case of AI-3.5%Cu reinforced with varying volume fractions of SiC particulate, it has been found that the probability of particle fracture increased with increasing volume fraction of reinforcement (7)."

Jan 1, 1996

By Kazuhiro Nisizono, Takashi Kuroki, Nobuyuki Mori, Keisaku Ogi

"The improvement of critical current density and mechanical property is essential to the practical application of the superconductive oxides. A solidification technique is developed in this study for the growth of columnar or single Y123 crystal with finely dispersed Y211 and Ag particles through a monotecto-peritectic reaction of Li.(Ba-Cu-Ag-0 rich liquid)+ Y211-+ Y123+Lz(Ag rich liquid). The large solidification rate and temperature gradient can refine the Ag and Y211 particles. But Ag-free region is widely formed along the crystal growth direction in the central part of the Y123 cell. Since this phenomenon occurs because of the cellular growth, it is necessary to narrow Y123 cell width or to grow Y123 crystal with flat freezing interface. By controlling crystal growth direction using a seed crystal, Y123 columnar or single crystal with uniformly dispersed fine Ag particles are obtained. The· behavior of Ag and Y211 particles during the solidification of Y123 crystal is simulated by the peritectic growth model of faceted Y123 crystals.IntroductionY-Ba-Cu-0 superconducting oxide (YBCO) with high critical temperature also has excellent superconducting characteristic under the high magnetic field. The critical current density (Jc) has been enhanced by ·using unidirectional-solidification technique, which can overcome the weak-link problem at grain boundaries and control the crystal orientation and the distribution of Y211 particles which give effective magnetic flux pinning centers in the Yl23 matrix [1-4].In addition to improving superconducting properties, it is necessary to improve mechanical property for the practical application. The silver addition to the melt-textured YBCO superconducting oxide has been reported as the effective method to improve mechanical properties without degrading superconducting properties. Since the material properties are considered to be largely affected by silver particle size, form, dispersion state etc. in the Y123 phase, it is important to control Ag distribution in YBCO/Ag composites. Besides, it is also reported that the silver addition improve the corrosion resistance to the water and CO2 [5,6]. Nishizono et al. [7-9] have reported that the silver distribution in the YBCO/Ag composites is largely affected by the solidification condition, but yet some unclear points are also remained. YBCO has been also fabricated by the zone melting method [10-12], and Furuya et al. [5] and Hirano et al. [13] have reported the fabrication of silver added YBCO composites, but the distribution and behavior of Ag are not investigated in detail"

Jan 1, 2000

By A. Tsubouchi, F. Noguchi, T. Takasu

"A high current density operation is desired to improve the productivity in copper electrorefining. However, a lot of problems still remain such as passivation at anode, dendritic deposition at cathode and impurity behavior during the electro refining.Effects of the current densitY on the morphology of copper deposition on the cathode, and passivation at the anode were investigated at various fluid velocity of electrolyte in the present study.Although a granular appearance of the copper deposition was obtained with increasing high current density, it was depressed by an increase of the fluid velocity of the electrolyte. A uniform deposition on the cathode was also observed when the fluid velocity of the electrolyte become higher. It was ascertained that passivation at the anode was suppressed by circulating electrolyte during electrolysis. INTRODUCTIONIt is desirable to operate at high current density in copper electrorefining in order to improve plant productivity without enlarging the size of electrodes(1). However, there are many problems in copper electrorefining at high current density with the usual commercial practice, for example, anode passivation, dendritic deposition and an increase of impurities in the cathode.In general, it is effective to agitate the electrolyte in order to suppress these problems(2). Smith et a1.(3) have performed electro refining experiments at various current densities in the range of 8 to 32 Aldm2 and at electrolyte fluid velocities in the range of 40 to 120 mlmin, and they obtained well consolidated, void free copper even at high current density in a high electrolyte velocity. However, they did not discuss the recovery ratio and the passivation behaviour at the anode. Walsh et a1.(4)(5)(6) experimented with the rotating cylinder electrode, and ascertained that electrolysis can be carried out at high current densities under the condition of pure electrolyte.With regards to anode passivation, there are several papers by previous workers(7)(8). Our group ascertained the process of producing anode slime during electrolysis(9). However, these experiments were carried out without forced circulation of electrolyte. Therefore, in the present study, to solve these problems, we electrolyzed at current densities in the range of 4 to 50 Aldm2 with circulating electrolyte in the range of 0 to 48 mlrnin. The effect of electrolyte fluid velocity on the surface morphology of deposited copper at cathode and passivation at anode were investigated when electrolysis were carried out with circulating electrolyte at high fluid velocity and at high current density."

Jan 1, 1997

By S. N. Ojha, Gouthama, R. K. Mandal

"Spray deposition processing of liquid immiscible alloys, based on AI-Pb and Cu-Pb systems have been investigated. Process variables have been optimized to generate uniform dispersion of ultrafine second phase particles in· the matrix of the primary phase. Mechanisms governing the microstructural evolution in this synthesis methodology are discussed. Results of the present investigation are used to demonstrate that rapid solidification of atomized droplets initially provides a high nucleation rate of the second phase during the liquid phase separation. The solid matrix phase nucleates at a later stage and grows with a high velocity enabling trapping of the dispersed phase. Subsequent alteration in the size and size distribution of the second phase is suggested to arise further during deposition of high velocity droplets. Possible reasons for this effect are brought out. Microstructural features of atomized powders and spray-deposits of these alloys are presented to support the present approach of synthesizing composites. IntroductionIn recent years, synthesis of advanced materials with metastable microstructures and ultra fine dispersion of second phase particles has led to the development of novel techniques of materials processing. The other requirement of such a processing methodology is to achieve near-net shape geometries in less number of processing steps. The solidification processing method via spray deposition route qualifies these criteria. This process primarily involves atomization of a melt by high energy gas jets into spray of droplets which are subsequently propelled by the kinetic energy of the gas towards a deposition substrate to build-up a thick high density preform. Although the concept of spray deposition was pioneered by Singer [1] in the early seventies, the fundamentals of the deposition process has been understood only recently [2-4]. Several benefits of spray deposition processing are by now well established [5,6]. Rapid solidification effects are inherent in spray deposition processing due to high heat exchange rate at the droplet-gas interface and also on the deposition surface by force convection. Since considerable heat extraction occurs from the atomized spray prior to droplet consolidation, a relatively low processing temperature is ensured in this process. As a result deleterious coarsening phenomenon can be minimized. In addition, controlled maneuvering of the substrate provides the capability of the process in producing disc, sheet or tube shape preforms of difficult to work materials in a single operation. A significant improvement in properties, resulting from microstructural homogeneity and refinement in grain size induced by spray deposition has been reported for several alloy systems [7,8]."

Jan 1, 1994

By Jianhong Dong, Min Chen, Cuihuan Huang, Bo Li, Nan Wang

"Scale layer can be formed on the slab surface in the areas of secondary cooling and strand discharge during continuous casting process. From 1000 °C -1200 °C, the influence of steel composition on the stable oxide phases inside scale layer, particularly the types of alloying elements including aluminum, silicon and chromium, is investigated under different partial pressures of water vapor by the calculated predominance diagrams of iron oxide as well as its intermediate compounds formed with other metal oxides, and the stable oxide phase composition within scale layer under the working condition of secondary cooling is discussed. At lower partial pressure of water vapor, only a iron spinel (or ferrosilicate) phase is the stable phase with any alloying element contents in steel composition, whereas the stable phases are FeO and iron spine! (or ferrosilicate) inside the scale layer at higher partial pressures of water vapor .IntroductionOxide scale formation on the surface of cast and rolled products because of oxidation by the surrounding oxidizing atmosphere is a significant disturbance factor in steelmaking. The yield loss of iron because of scale formation is considerable during continuous casting and hot rolling process. Surface quality more often is impaired by scale property, which increasing the difficulty of quality assurance, dimensional accuracy and performance control. Furthermore, a potential source for subsequent surface cracking (hot shortness) can be caused by the enrichment of scrap residuals (Cu, As and Sn) at the steel substrate surface as a result of steel oxidation [1-2]. In flat products manufacture via thin slab casting technologies, these phenomena are particularly pronounced and require enhanced development efforts in descaling efficiency [3].Compared with the scale formation in continuous casting, the quantity of scale formed during hot rolling and reheating in the rolling mill is larger, and control of scale formation and descaling is a long-established task in hot rolling. Therefore, extensive research and development work have been carried out, including the effects of heating and rolling temperature on the thickness and microstructure of scale layer, heating time and furnace atmosphere, cooling mode, and steel composition on the scale formation, more attention has been given to the control of scale formation during reheating and hot-rolling process. On the other hand, hardly any specific efforts and countermeasures are taken in continuous casting, and very less research has been done despite the network-type crack on the as-cast strand surface caused by the subscale enrichment of scrap residuals [ 4-7]."

Jan 1, 2014

By M. Bhattacharya, A. Dutta, P. Barat

"Pinning of dislocations at nanosized obstacles like precipitates, voids and bubbles, is a crucial mechanism in the context of phenomena like hardening and creep. The interaction between such an obstacle and a dislocation is often explored at fundamental level by means of analytical tools, atomistic simulations and finite element methods. Nevertheless, such studies fail to predict the effect on the overall plasticity on account of insufficient information about the underlying statistics of this process comprising a large number of dislocations and obstacles in a system. Here we propose a new statistical approach, where the statistics of pinning at idealized spherical obstacles is explored by taking into account the generalized size distribution of the obstacle along with the dislocation density within a three-dimensional framework. The application of this approach has been demonstrated for dislocation pinning at nanovoids in neutron irradiated type 316-stainless steel.IntroductionPresence of nanoscale obstacles like precipitates, voids and bubbles play a crucial role in determining the deformation behavior of a crystalline solid on account of the interactions between the line defects and such localized obstacles. In the context of the glide motion of dislocations, the obstacles can offer resistance to a moving dislocation, thereby causing a hardening effect [l-3]. In some other cases, inclusions like voids and bubbles can affect the rate of dislocation climb through diffusive [4] and non-diffusive [5] mechanisms. Over the last few decades, numerous studies have been performed to gain an insight of the dislocation-obstacle interactions at a fundamental level. These include the interactions responsible for the hardening effect, in addition to those pertaining to the non-conservative motion of dislocations.Although the elementary mechanisms of the various dislocation-obstacle interactions have been vastly explored and understood by means of analytical theory and numerical simulations, it remains difficult to quantitatively understand their effects on the macroscopic deformation behavior. This is due to the fact that their influence on the gross plastic deformation of a bulk sample would be the collective outcome of a large ensemble of such interactions. As a result, it becomes infeasible to predict the bulk deformation behavior of a material until the statistics of pinning of the dislocations at the localized obstacles is available. In the context of precipitate hardening, some well known attempts to extract the pinning-statistics were made by Friedel-Fleischer [6] and Mott [7] by analytical means, which were later tested through simplified 2-dimensional in-silica modeling [8]."

Jan 1, 2014

By Hongmin Zhu, Suning Liu, Kai Huang

"Recovery of silicon particles from the cutting slurry for the manufacturing of solar grade silicon is very important to recycle this kind of special resource. The challenge is to separate the silicon particles from the mixed abrasive particles which contain SiC. Various methods such as sedimentation, centrifugation, and flotation have been conducted, while in present work, a simple and effective novel method was proposed to study the separation of Si and coexisting SiC particles in the cutting slurry. The new process is based on the size difference between the two kinds of microparticles. And the membranes with the different pore sizes of 1µm, 2µm, 3µm and 5µm were used to test the pass ratio and separation efficiency of the suspension. Results shows that the effective separation of Si and SiC microparticles was obtained under the optimal conditions, and indicating great potential of practical enrichment of Si from the coexisting abrasive particles.IntroductionWith the development of the world economy, energy shortage and environment problem is becoming more and more seriously. Solar energy, which is regarded as one of the most important new energy in the word, has received much attention and interest from the scientists [1, 2]. More than 80% solar cells are manufactured by the high purity polysilicon as the raw material. The main process of producing silicon wafer is by multi-wire slicing. In this slice processing, large amount of slurry is produced. The slurry contains more than 30% wt silicon powder, silicon carbide powder as the abrasive, scraps of metal chips, as well as cutting abrasive suspension polyethylene glycol (PEG). The high-purified silicon powders are worth recycling and reusing as the materials for preparing solar-grade silicon though it is a big challenge [3].Most of the current studies were focusing on the recycling of the silicon carbide and PEG, while work on the recycling of the high-purified silicon is not so been focused since there is lacking of very effective separation and recovery technologies till up now. Nishijima utilized the method of superconducting magnetic to recycle the abrasive [4]. Wang applied a combinational process of chemical treatment, high-gravity centrifugation, high-temperature precipitation technique and directional solidification to enrich the silicon [5]. And other purification methods, such as centrifugation [6], froth flotation technologies [7], electrical filed separation [8] and phase-transfer process [9] have been employed. The disadvantages such as using poisonous media or complex equipments decrease the feasibility and efficiency of the above mentioned techniques."

Jan 1, 2014