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By I. M. Richardson, M. Janssen, I. J. Bennett, V. A. Popovich

The most critical processing step during the manufacture of screen-printed crystalline solar cells is firing aluminium and silver contacts, which generates residual stresses and solar cell bowing. In this paper, an alternative Ag contact formation mechanism is proposed and aspects related to electrical contact properties, residual stresses and layer delamination are investigated. It is found that there are two main processing parameters affecting the uniformity and delamination of the Ag/Si interface, namely the peak firing temperature and the silicon surface roughness. Silicon surface polishing gives a better wetting of the silicon surface by the glass layer, resulting in a good contact and lower incidence of large voids, compared to the case of highly textured surfaces. The non-uniformity in the glass layer and large voids at the Ag/Si interface (in the case of a textured surface) are expected to have a negative effect on the mechanical strength of the solar cell.

Jan 1, 2015

By Deepak Gupta, R. Kageyamat, J. W. Evans

"In electromagnetic casting, a liquid metal pool is partly supported by electromagnetic forces resulting from the interaction between induced currents and an alternating magnetic field. Stability of the metal surface is of paramount importance if the cast ingot is to be free from surface defects. Prior work by Garnier and Moreau had suggested that the magnetic field has no influence on the surface stability, but a more complete analysis at Berkeley suggested that surface perturbations are destabilized by the magnetic field once a critical magnetic field is exceeded. More recently we have employed a modified version of the software SOLA to compute the behaviour of a melt surface in the presence of an alternating field. The computed results support the theoretical analysis in predicting an unstable surface. Experimental work is now in progress to examine the stability of a mercury pool in the presence of an alternating field. Introduction and Previous InvestigationsElectromagnetic casting (EMC) is a technique widely employed in the aluminum industry to produce ingot for subsequent rolling. It is a ""continuous"" casting technique (illustrated in Fig. 1) producing ingots several meters high (and perhaps 1m by 2m in horizontal dimensions) at a casting speed of one or two mm. per second. The technology has gained acceptance because the metal is solidified without contact with a mold. Consequently the surface finish of the ingot is usually smooth and the ingot can be fed directly to rolling without machining, the surface (""scalping""). Scalping is necessary with alternative technologies (e.g., DC casting) where a mold is used. Consequently any disturbances that result in surface imperfections of EMC ingot are a serious matter. One type of imperfection is waviness on the surface of the ingot; a line drawn along the crest of a wave would run horizontally around the ingot. This imperfection may be caused by waves on the surface of the metal pool. As the waves reach the solidification line at the periphery of the metal they cause alternate outward and inward bowing of the meniscus at that point with attendant small (but significant) changes in ingot width. Elimination of building vibrations and similar disturbances minimize the occurrence of these surface waves but it is interesting to speculate whether there are disturbances of the metal pool that arise from the electromagnetic forces supporting the liquid metal. These forces are generated by the interaction of currents induced in the melt and the magnetic field produced by the current imposed on the inductor surrounding the melt. The present investigation has been concerned with whether the alternating magnetic field destabilizes the melt surface."

Jan 1, 1994

By Vaughan R. Voller

"Numerical methods for dealing with a temperature dependent conductivity are discussed. An approach based on a local application of a Kirchhoff transformation at the discrete level is presented. The application of this transformation - that does not require any inversion- is demonstrated on solving a two-dimensional test problem.IntroductionMuch is said in the recent literature on the modeling necessity of obtaining appropriate thermo-physical properties; in particular the requirement to account for properties that are ""strong"" functions of the depended variables, e.g., Temperature. Of course obtaining appropriate thermo-physical properties serves no purpose unless they can be accurately integrated into a discrete numerical calculation. The purpose of this paper is to examine how temperature dependent conductivities that exhibit discontinuities or rapid changes can be handled in a numerical code.The discussion will be made in the context of a control volume finite element method [1]. After a brief outline of control volume finite element fundamentals basic methods of dealing with discontinuous or rapidly changing thermal conductivity are discussed. This is followed by the presentation of the recently proposed local Kirchhoff method [2,3], The paper concludes with an investigation of the performance of the various conductivity schemes in solving two dimensional problems. This testing clearly shows the advantages (accuracy and implementation) in using the local Kirchhoff method."

Jan 1, 2001

By W. D. Cho

The slag chemistry in steel processing plays an important role in terms of the removal of impurities including alumina particles. In the present study, the dissolution of solid alumina particles in CaO-based fluxes at the temperatures between 1450 and 1550 °C has been investigated to determine dissolution kinetics and mechanism. Alumina particles were added directly in the slags and the size of alumina particles was measured as a function of time using optical and scaru;ling electron microscopes. The dissolution rate has also been obtained as a function of Si02, CaF2, MgO and MnO contents in the slags. The diffusion boundary layer between alumina and bulk slag phase has been observed and analyzed using SEM and EDX. In addition, some experiments have been performed for the dissolution of alumina in BaO-based fluxes.

Jan 1, 2003

By C. J. Beyke

The U.S. Bureau of Mines has developed a process for the selective recovery of Pb metal from a mixed Pb-Zn concentrate. The concentrate was leached in recycled H2SiF6 at atmospheric pressure and 95° C with a redox potential of 570 mV (Eh). Eighty-five pct of the Pb was selectively leached from the concentrate while 87 pct of the Zn remained in the residue. Pressure leaching of the concentrate was slightly less successful, with 78 pct of the Pb leaching from the concentrate and 80 pct of the Zn remaining in the residue. Pure Pb metal was successfully electrowon from a purified PbSiF6-H2SiF6 solution with 96 pct current efficiency and 0.69-kW.h/kg energy consumption.

Jan 1, 1991

By W. D. Cho

The slag chemistry in steel processing plays an important role in terms of the removal of impurities including alumina particles. In the present study, the dissolution of solid aluimina particles in CaO-based fluxes at the temperatures between 1450 and 1550 °C has been investigated to determine dissolution kinetics and mechanism. Alumina particles were added directly in the slags and the size of alumina particles was measured as a function of time using optical and scanning electron microscopes. The dissolution rate has also been obtained as a function of Si02, CaF2, MgO and MnO contents in the slags. The diffusion boundary layer between alumina and bulk slag phase has been observed and analyzed using SEM and EDX. In addition, some experiments have been performed for the dissolution of alumina in BaO-based fluxes.

Jan 1, 2003

By Shadia J. Ikhmayies

CdSxTe1-x and CdS1-yTey solid solutions are usually formed in the interfacial region in the CdS/CdT thin film solar cells during the deposition of the CdTe layer and/or the processing steps of the device. It is well known that CdCl2 heat treatment encourages the formation of the CdSxTe1-x alloy which improves the solar cell performance. In this work, indium doped CdS1- yTey thin films are produced by first producing CdS:In thin films by the spray pyrolysis (SP) technique on glass substrates, then annealing the films in nitrogen atmosphere in the presence of elemental tellurium. The films are characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and transmittance measurements. The transmittance is used to deduce the optical parameters such as; the extinction coefficient, refractive index, besides to the real and imaginary parts of the dielectric constant. The dispersion parameters such as Eo (single-oscillator energy) and Ed (dispersive energy) of the deposited films are also estimated and discussed.

Jan 1, 2015

By Hui Zhang

The leaching behavior of palladium powder in aqueous solutions containing NaCI or N'H4Cl was investigated. Cupric ion was used as an oxidant for the dissolution reaction. The effect of a number of leaching parameters such as temperature, concentration, stirring speed and surface area on the leaching rate was studied. The leaching system containing chloride and cupric ion was found to be very effective for the dissolution of metallic palladium. Based on the experimental results the overall leaching rate was believed to be controlled by a chemical reaction step. The dissolution rate of palladium was found to be first order with respect to the concentration of cupric ion and second order with respect to the concentration of chloride.

Jan 1, 1996

By Katsuyoshi Tatenuma

"In order to mitigate the effect of global warming by preventing the accumulation of atmospheric CO2, a permanent fixation method of surplus CO2 as an insoluble mineral onto the sea bottom is proposed. As the proposed reduction method of atmospheric CO2, the concrete concept of this method is to form an insoluble carbonate mineral (CaCO3) by direct electrolysis of the seawater; Ca2++2HCO3 -+OH- ? ?CaCO3(insoluble)+CO3 2- (soluble)+H++H2O <not as coral reef reaction>, are directly disposed of itself onto the sea bottom. By this treatment, a concentration of carbonate is reduced in the section of superficial seawater, and therefore the absorption capacity of atmospheric CO2 increases depending upon the shift of chemical carbon equilibrium between the mass of superficial seawater and the atmosphere. As no additives are required, or no secondary waste are produced, the proposed method assuming as green-orientated, has possibility to resolve fundamentally the problem of global warming in a green orientate manner.IntroductionRecently, the amount of atmospheric CO2 has been exponentially increasing and it is a main greenhouse effect gas causing the global warming [1, 2]. The concentration of atmospheric CO2 has increased more than 30% (370ppm in 2001) during only last two centuries, therefore approximately 750 Gton-C of CO2 currently exist in the atmosphere, in which 180 Gton-C of CO2 are accounted for the increment during two centuries [1, 3, 4]. In order to avoid the progressive increase of CO2 global abundance, 3 Gton-C of the incrementing amount per year [4], have to be removed annually from the atmosphere."

Jan 1, 2008

By Hong Ro Lee, Seang Suk Cho, Byung Sun Chun, Chang Whan Won

"The preparation of Al203-SiC-TiC composite powders was studied by SHS process using silica (source of Si02) powder instead of Si which is expensive. And, aluminum powder was used as reducing agent of silica and charcoal activated was used as carbon source. Effects of the molar ratio in raw material mixtures and compaction pressure and initial temperature of reactant on the products and combustion process were studied. The most important variable affecting the synthesis of Al203-SiC-TiC was the molar ratio of carbon. The combustion reaction generated in powder state without preheating. But the unreactants exist in the product on all molar ratio. When the preheating temperature is over 400 °C, the combustion reaction was able to be generated in pellet state. Without preheating, the combustion reaction was possible by Ti02 addition. The optimum condition in this system was the molar ratio of Si02:Ti02:Al:C=2.5:0.5:4:3.1. INTRODUCTIONCeramics have demonstrated a capability as a cutting tool, especially in competition with WC-Co cermets (ceramic-metal composites) as inserts for metal turning and milling operation. The advantage of ceramics compared with carbides is retention of high hardness, strength, and chemical inertness to temperatures in excess of 1000 ·c . This allows use of the ceramics at much higher machining speeds than can be tolerated by carbides. However, the ceramics have lower toughness than the carbide materials, and have only been used successfully in the limited operations of turning and milling. There are several classes of cutting tools. The addition of TiC or PSZ, or both, and reinforcement with SiC overcame the poor fracture toughness and thermal-shock resistance that limited Al203 use in the past [1]."

Jan 1, 1998

By Hong N. Vu, Jitka Jandova

"Gypsum and limestone methods were examined in this study to process zinnwaldite wastes originating from dressing Sn-W ores mined in the Czech Republic. These wastes containing 0.20-0.30% Li and 0.10-0.20% Rb were subjected to magnetic separation to obtain a zinnwaldite concentrate with 1.36% Li and 0.94% Rb. It was observed that processing of the zinnwaldite concentrate with gypsum resulted in almost 96% recovery of Li into aqueous liquors, whilst rubidium extraction was only 25%. At the same time, it is possible to extract almost 92% Li and Rb from the identical zinnwaldite concentrate if the concentrate is processed by limestone method. Lithium carbonate, a final product of both methods was recovered from the refined sulphate solution using K2CO3 as a precipitation agent and/or from unrefined hydroxide solution using gaseous CO2. In the continuation of this study, rubidium will be separated from carbonate solutions after Li2CO3 precipitation as RbAl(SO4)2, an intermediate for Rb2CO3 production. IntroductionLithium is used as an alloying constituent in lightweight alloys, as a heat transfer medium in nuclear reactors and as a component in primary and secondary batteries. With the development of a new generation of electric vehicles, the lithium demand will dramatically grow. Lithium chemicals find extensive application in many industrial branches such as metallurgical, glass, ceramic and pharmaceutical industries. Rubidium compounds are predominantly used in psychiatry and medicine, in magneto-optic modulators, solid-state lasers, phosphors and components of electrolytes for fuel cells. The four most important lithium minerals are amblygonite, spodumene, petalite, and lepidolite. Spodumene LiAlSi2O6 (6.0-7.5% Li2O) and petalite LiAlSi4O10 (3.5-4.5% Li2O) belong to aluminosilcate minerals. Lepidolite (Li.Al)3(Al.Si)4O10(F.OH)2 (3.30-7.74% Li2O), lithium mica, is the most important representative of the mica minerals, a subgroup of the aluminosilicates. It frequently contains 3–5% Rb2O and eventually caesium. Zinnwaldite, which has the general formula K(Li.Al.Fe)3(Al.Si)4O10(F.OH)2 (2-5% Li2O), is regarded as a variety of lepidolite with a high iron content. Commercial amblygonite is a complex phosphate (Li.Na)Al(F.OH)PO4 (up to 9.88% Li2O), however, its deposits have not been commercially exploited because of their small size. Natural brines with a high lithium chloride content are important in the industrial production of lithium [l]"

Jan 1, 2008

By Zhenyang Wang, Xingle Liu, Xiangdong Xing, Shan Ren, Hongen Xie, Jianliang Zhang

"Non-isothermal combustion experiments of different additive amount of bituminous (0, 20, 40, 60, 80, 100 wt%) were conducted by synthesized thermogravimetry analyzer(STA409PC) from room temperature to 900°C in air. The changes of combustion characteristic parameters o f pulverized coals in different atmospheres are analyzed. The results show that DTG curves of coal combustion move to low temperature zones when the amount of bituminous increases. It indicates that both ignition and burnout temperature are lower, burnout time decreases, combustion characteristic index obviously increases, and combustion performance of blending coal are improved. The iso-conversional method involving Kissinger-Akah-Sunose (KAS) method was used for the kinetic analysis of the main combustion process. The results indicated that, when the additive amount of bituminous varied from 0 to 100 wt%, the value of activation energy which would sharply reduce if the additive amount of bituminous was under 60% increased from 133.94 kJ•mol-1 to 78.03 kJ•mol-1by using KAS method.IntroductionPulverized coal injection (PCI) to blast furnace (BF) is an important way for saving energy and reducing resource consumption during the ironmaking process. In order to acquire higher coal injection quantity, the relevant research topics in the field of pulverized coal combustion technology such as enhancing the efficiency of pulverized coal combustion, improving the combustion characteristics and reducing the harmful gas emissions and so on received extensive attention in recent years [1,2]. The combustion of blending coal when the appropriate proportion is selected for coal and also mixed well- distributed could give full play to the advantages of various types to make up the defects of single coal which is widely used throughout the world. So the blending coal injection to BF could produce a good impact on safety and economy for productive process. Therefore, a large amount of experimental researches on the combustion characteristic of blending coal for anthracite and bituminous were carried out by experts and scholars around the world [2-7].Nevertheless, the systematic research on the combustion behavior of anthracite with different content of bitumite in a thermogravimetric analyzer (TGA) is less. So in this paper, using the method of multiple scanning rate of conversion method, bituminous to promote the pulverized coal combustion reaction was studied to analyze its promotion mechanism of pulverized coal combustion reaction process, and the kinetic parameters of activation energy was also calculated, which to provide theoretical basis for the rationalization of resource utilization."

Jan 1, 2014

By Petrus Christiaan Pistorius, Farzin Fatollahi-Fard

The production of titanium oxycarbide – a consumable anode material used in molten-salt processes for electrowinning titanium – from heavy mineral concentrate, such as a high-titania leucoxene and natural rutile is described. The oxycarbide is prepared by carbothermic reduction of the oxide at elevated temperature. Particle size distribution (of the titanium oxide raw material) and temperature have large effects on the kinetics of the reaction, which seem to follow a “shrinking-core” model. It is anticipated that low porosity (in the anode pellets) would be advantageous during electrolysis. Particle size distribution, extent of reaction during carbothermic reduction, and sintering temperature are expected to affect pellet porosity after sintering, and are being tested experimentally.

Jan 1, 2015

By M. Krishna, Jayagopal Uchi1, Shanta Sastry, B. M. Satish

"A well-considered composite of ZA-27 reinforced with weight percentage 0, 2, 4, and 6% of alwninite particulate has been made by compocasting technique. The elastic properties of ZA- 27 /alwniniute particulate composite were determined by using U1M. The results showed that the modulus of elasticity and UTS of the composite gradually increases with increase in the wt.% of reinforcement. However, the overall ductility decreased monotonically with an increase in reinforcement. The results of these tests· as well as the predictions of several model~ for composite strengthening available in the literature were compared with experimental results. The data observed from Young's modulus by measurements studies were compared with theoretical results predicted by Eshelby model.IntroductionMetal matrix composites (MMCs) have received increasing attention in _the recent decades as engineering materials. The introduction of a ceramic reinforcement into a metal matrix produces a composite material resulting in an attractive combination of physical and mechanical properties that cannot be obtained with monolithic alloys. Particulate reinf9rced MMCs among the discontinuously reinforced MMCs have attracted quite a lot of attention both in the industrial sectors and the academic communities. There is an increasing need for knowledge about the processing techniques and mechanical behavior of particulate MMCs in view of their production getting enhanced and their commercial applications becoming wider [I]. Interest in particulate reinforced MMCs is mainly due to easy availability of particles and economical processing techniqu"

Jan 1, 2000

By Kuniaki Murase, Tetsuji Hirato, Yasuhiro Awakura

"Electrodeposition of CdTe was studied using aqueous ammonia-alkaline electrolytic baths in which Cd11-and Te1V-ions are dissolving as Cd11(NH3)/+ and Te1vol-ions, respectively. Ca-thodic polarization curves of the baths suggest the presence of strong interaction between the Cd11-and Te1V-ions; electrodeposition of tellurium is inhibited by the presence of Cd(NH3)/+ ions. The interaction makes it possible to electrodeposit CdTe films with stoichiometric composition. Polycrystalline CdTe thin film of about 1 µm thickness was electrodeposited at 343 K from ammonia-alkaline solutions (pH= 10.7) containing TeO32-(<20 mmol dm-3) and Cd(NH3)/+ ( < 60 mmol dm-3) ions. Increasing Cd(NH3)/42+/TeO32- mole ratio or decreasing total concentration of ammonia/ammonium-ion gave flat and smooth crystalline CdTe deposits at constant cathode potential-0.70 to -0.30 V vs SHE at 343 K.IntroductionCadmium telluride (CdTe) is well-known as a compound semiconductor whose band gap, i.e. 1.44 eV, is suitable for solar energy conversion with a photovoltaic cell. Various methods, such as CVD (chemical vapor deposition) and electrodeposition, of preparing CdTe thin films for solar cells have been investigated.Acidic sulfate solutions with a pH of 1-2 are usually employed for CdTe processing by electrodeposition.1-3) The electrodeposition of compound semiconductors is usually achieved (i) at a higher cathode potential than the redox potential of less-noble species, can in this case, and (ii) under the condition of diffusion-limiting current of a more noble species, Te1Y.4) There-fore, a suitable CdII/TeIV concentration ratio in the acidic electrolytic baths, resulting in the deposition of stoichiometric CdTe, is determined by the diffusion-limiting current density of TeIV- reduction, i.e. the concentration of HTeIVO2+ · Since the solubility ofTe1v species HTeIVO2+ in the acidic solutions is quite low, the rate at which CdTe is deposited from the acidic solutions is extremely slow."

Jan 1, 1998

By Peter Bates

"HIsmelt has faced and overcome many challenges in the understanding and development of injection technologies that satisfy process and engineering requirements for further scale up to a commercial plant.An overview of the design basis of bottom and top injection systems with plant results are described in this paper.IntroductionAn appropriate way to introduce this paper is to initially reflect on the genesis of the HIsmelt Process.It is appropriate that Professor Womer is the one we are honouring as it can be claimed that by the involvement of CRA in the WORCRA process that the concepts for irijection systems in iron and steel pyrometallurgical processes achieved significant attention by the company. The development of water cooled injection lances and their application injecting solids and gases with success was certainly a pre-cursor to the development of other injection systems commonly used today in arc furnaces and for top injection at HIsmelt.HistOrically it was the work of Savard and Lee in Canada with shrouded tuyeres and the subsequent commercialisation of this technology at the Maxhiitte Steelworks spawning the suite of bottom oxygen blown process as known as QBOP; OBM and the subsequent combined blowing process such as KOBM that first commercially succeeded in injecting solids under a molten metal bath. The next progressive step from the injection of calcined lime in the technology development was the injection of coal for coal gasification as developed by Klöckner technologies being called KG, KSG and KMS and also the injection of coal for increased scrap melting.A paradigm shift in thought process to leap from steelmaking and coal gasification to direct smelting by injecting coal and iron ore into a molten metal bath in the correct stoichiometric ratio to maintain the bath at a constant temperature and carbon level was the true genesis .of HIsmelt.A good overview of the state of the art of tuyere type injection technology is given in Ref. 1."

Jan 1, 1996

By Kenji Matsuzaki

A mathematical simulation model of the Imperial Smelting Furnace operation has been developed for purpose of improving the furnace operation. The model consists of top, shaft and bottom regions, Analysis in the shaft region is based on differential heat and materials balances taking account of reaction kinetics and heat transfer rates, and those in the top and the bottom regions are based on heat and materials balances under a steady-state condition, Longitudinal distributions of process variables such as temperatures of gas, sinter and coke, gas composition and fractional conversion under a practical operating condition were calculated, With this model, the furnace performance under various operating conditions also can be shown reasonably predicted,

Jan 1, 2003

By Malsuzaki. Kenji

A mathematical simulation model of the Imperial Smelting Furnace operation has been developed for purpose of improving the furnace operation. The model consists of top, shaft and bottom regions. Analysis in the shaft region is based on differential heat and materials balances taking account of reaction kinetics and heat transfer rates, and those in the top and the bottom regions are based on heat and materials balances under a steady-state condition. Longitudinal distributions of process variables such as temperatures of gas, sinter and coke, gas composition and fractional conversion under a practical operating condition were calculated. With this model, the furnace performance under various operating conditions also can be shown reasonably predicted.

Jan 1, 2003

By J. Leon-Torres, D. M. Stefanescu, P. A. Curreri, S. Sen

"Experiments were performed under terrestrial gravity (lg) and during parabolic flights (10·2 g) to study the solidification and macrosegregation patterns of Al-Cu alloys. Alloys having 2% and 5% Cu were solidified against a chill at two different cooling rates. Microscopic and Electron Microprobe characterization was used to produce rnicrostructural and macrosegregation maps.In all cases positive segregation occurred next to the chill because of the shrinkage flow, as expected. This positive segregation was higher in the low-g samples, apparently because of the higher heat transfer coefficient.A 2-D computational model was used to explain the experimental results. The continuum formulation was employed to describe the macroscopic transports of mass, energy, and momentum, associated with the solidification phenomena, for a two-phase system. The model considers that liquid flow is driven by thermal and solutal buoyancy, and by solidification shrinkage. The solidification event was divided into two stages. In the first one, the liquid containing freely moving equiaxed grains was described through the relative viscosity concept. In the second stage, when a fixed dendritic network was formed after dendritic coherency, the mushy zone was treated as a porous medium.The macrosegregation maps and the cooling curves obtained during experiments were used for validation of the solidification and segregation model. The model can explain the solidification and macrosegregation patterns and the differences between low- and high-gravity results."

Jan 1, 1999

By J. L. Jambor

Previous crystal-structure determination of magnesian annabergite (Ni,MgMAsO4)2 8H2O indicated that ordering of Ni and Mg occurs in non-equivalent octahedral sites; such ordering supports the possibility of miscibility gaps on the Ni3(AsO4)2 8H2O -MgiAs04)2 8H2O. (annabergite-hornesite) join. In a predecessor study based on analyses of natural specimens, it was proposed that solid solution is incomplete both for annabergite-hornesite and annabergite-erythrite [Co, (AsO4)2 8H2O]. In the current study, syntheses by use of a slow-addition technique and aging of the precipitates indicated that the annabergite-erythrite solid solution is complete, and that no miscibility gap is present on the annabergite-hornesite join to at least 58 mol % Mg. Thus, interpretation of the compositions of these phases in oxidized mill-tailings impoundments can be done with the normal precautions for homogeneity, and without the added concern of the possible presence of miscibility gaps in the ternary system.

Jan 1, 1995