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By Gopalakrishna B. Prabhu, David L. Bourell

"Three mol% Yttria-Stabilized Tetragonal Zirconia (YSTZ) was prepared by a sol-gel synthesis technique using zirconium tetrachloride and hydrated yttrium chloride precursors. After drying and annealing at 823K, the particle size was in the range 10 to 20 nm. The zirconia powder was sintered using a uniaxial hot press at an applied stress of 20 to 40 MPa. One hour, isothermal sintering was performed in air after initial heating at 50K/min. Theoretical density was obtained at densification temperatures above 1498K. After sintering, grain coarsening characteristics were studied using constant heating rate anneals followed by quenching, based on a model for grain coarsening in a linear heating rate cycle. The microstructural change was studied using SEM and TEM and the phases were determined using x-ray diffraction.IntroductionThe ability to sinter nanocrystalline materials to full density several hundred degrees below the normal sintering temperatures is one reason for their current interest. [1-5] Yttria Stabilized Tetragonal Zirconia (YSTZ) of grain size of about 300 nm has exhibited superplasticity, with elongations as large as 800%.[6-7] Fine grain size is critical for superplasticity. Retention of the fine grain size during sintering of nanocrystalline powder is important if a material is to exhibit superplasticity or to exhibit physical or mechanical properties associated with the ultra fine structure. This paper investigates the sintering behavior and the grain coarsening characteristics ofnanocrystalline YSTZ.Techniques for synthesizing nanocrystalline materials have been studied in great detail earlier. [8-12] The techniques used to synthesize nanocrystalline zirconia include alkoxide synthesis [9], the chloride method [11], the peroxide method [13] and the acetone-toluene method. [13] In this paper the method used in the synthesis of zirconia is the chloride technique. With this precipitation technique, either zirconium chloride or oxychloride and a corresponding yttrium salt or even pure yttria are used."

Jan 1, 1994

By T. Watanabe, T. Fujiwara, S-Wan Song, Y. Nakagawa, R. Teranishi, M. Yoshimura

"We have tried a new method to fabricate cobalt oxide films onto porous films directly by an electrodeposition method at low temperature. The porous substrate films (membrane-filters and paper) were placed between a LiOH solution and a CoSO4 solution and treated under electricalcurrents of ~1 mA/cm2 using carbon cathode and anode. Effects of temperatures, flow rates and electrical currents have been investigated. As a result, we found that the LiCoO2 films and Co3O4 films were successfully fabricated on paper and/or porous PTFE filters at 120 °C, while CoOOH films were deposited at 80 °C. Furthermore, LiCoO2 films did not cover whole the substrates, but was fabricated just over the anode. The chemical reactions of electrodeposition were also considered from these results.IntroductionRecent agreements on global environment require rapid progress of low energy and low waste processings for the fabrication of thin films that succeed to the mass production with the high consumption of the fossil fuels (such as physical vapor deposition°, chemical vapor deposition2), dip coating with firing3) etc.). The total energy consumption in aqueous systems should be the lowest among all these processing routes, because a much lager excess of energy is necessary to create melts, vapor, gas, or plasma than to form an aqueous solution at the same temperature4)The ""Soft Solution-Process"" (SSP) was one of the best concepts to realize the low energy and low waste fabrication of inorganic materials. 5) Generally speaking, SSP gives similar results to any other processing using fluids (such as vapor, gas plasma) and/or beam/vacuum processing. However, the total energy consumption of all these possessing routes should be the lowest in aqueous systems, because a much larger excess of energy is necessary to create melts, vapor, gas or plasma than to form an aqueous solution at the same temperature (Fig. 1). This idea can be easily demonstrated, using the simple example of BaTiO3. The energy diagram for the formation of BaTiO3 from various precursors is shown in reference 4. The driving forces (AG) for representative synthesis reaction of (1), (2), (3), (4) and(5) are 38, 727, 3685, 17 and —14kcal/mol, respectively at room temperature. 6' 7"

Jan 1, 2000

By Gökhan Hardal, Berat Yüksel Price

Nickel manganite based negative temperature coefficient (NTC) thermistors have good temperature sensor characteristics and electrical stability for temperature measurement applications. In this study, the electrical and microstructural properties of Ni0.5Co0.5Cu0.3Zn0.3Mn1.4O4 NTC thermistor were investigated. The samples were fabricated by the conventional solid-state reaction method. The powders were calcinated at 900 °C for 2 h and the samples were sintered at 1200 and 1300 °C for 5 h in air. The bulk density of samples was 5.07 and 4.96 g/cm3, respectively. The microstructure of samples was observed using a scanning electron microscope. The electrical resistance was measured in a temperature programmable furnace between 25 and 85 °C. The electrical resistivity of the Ni0.5Co0.5Cu0.3Zn0.3Mn1.4O4 sample increased from 52 Ω cm to 95 Ω cm when the sintering temperature increased from 1200 to 1300 °C. The material constant “B”, sensitivity coefficient “α” and activation energy “Ea” values were also calculated for the NTC thermistors.

Mar 1, 2017

By Herman Wotruba

Mercury emissions and other environmental impacts in small-scale gold mining are a world-wide problem. "Clean" or better: "Cleaner" technologies have -apart from being environmentally sound -to guarantee a higher income and better working conditions for the miners in order to have a chance for long-term acceptance. In small scale primary gold mining in several South American countries, a number of techniques have been adapted and improved so that they not only were accepted due to their efficiency and easy handling, but they could also significantly lower mercury emissions.

Jan 1, 2003

By H. -Peter Sattler

The laser sorting technique for replacing the handpicking of the non-ferrous metal scrap from auto shredders was first introduced 1990, The process is based on the use of atomic emission spectroscopy induced by lasers to identify the scrap particles and sort them with adequate systems into main fractions of Al-, Zn-and Cu-alloys, stainless steel and lead, In the meantime the handling technique for the scrap, i.e. the singling and sorting technique as well as the analytical detector were further developed for more efficiency and higher reliability, i,e. less maintenance, minor sorting errors etc. These developments were mainly based, on and initiated by operational experiences from the startup phase of a first production plant. Part of the on going research work was the development of an ,aluminium detector which makes it the first time possible to sort mixed aluminium scrap automatically into specific alloy fractions.

Jan 1, 1995

By W. Mueller

The function of a process mineralogist in the operation of a copper mine and plant is to assist in the identification and classification of the operation's main throughput. These include ore, concentrates, slag and matte, and to a lesser extent, refined products. In addition, a number of other products not normally thought of in association with mineralogy are examined. These include scales from submersible pumps, failed boiler tubes, acid plant, and shaft furnace; characterization of inclusions in failed compressor gear teeth as well as in copper rod; and flue dusts from a smelter, air transported particulates and coatings on passive copper anodes in the refinery. Techniques and equipment required for these studies include simple hand magnets to the high intensity Isodynamic separator, visual examination to electron microscopes, x-ray equipment, DTA, IR, heavy liquid separation, and contracted services of custom laboratories. Several examined products from Magma Copper Company have been selected to illustrate the range of techniques and equipment required by a process mineralogist.

Jan 1, 1981

By Manabu lshimaru

Solid-liquid interfaces as well as defect formation processes during crystallization of melted silicon (Si) have been examined by using molecular-dynamics (MD) simulations. The ordinary Langevin equation employing the Tersoff interatomic potential was used for the calculation of the atomic trajectories. A solid-melt interface has a tendency to form {]] I} microfacets during the crystal growth in the [001] direction, while it is essentially flat during the (Ill) crystallization. Because of the difference of the interfacial structures, the structures of grown-in defects and defect evolution depend strongly on the growth direction. We discuss defect structures and their formation processes within the context of our results as well as previous experimental observations.

Jan 1, 2001

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

By Hiroaki Kawamura, Takeshi Yoshikawa, Kazuki Morita, Yutaka Yanaba

"To develop an alternative metallurgical process for phosphorus removal in the production of solar-grade silicon (SOG-Si), slag treatment of metallurgical-grade silicon (MG-Si) was conducted, followed by acid leaching. Phosphorus-doped silicon alloy or MG-Si containing certain amounts of phosphorus and calcium was reacted at 1723 K and 1773 K with CaO--CaF2 of several compositions. Phosphorus removal from the molten silicon into the slag phase was confirmed by reduction to phosphide ions, P3-, and phosphate ions, P3-. These ions were separately determined using a wet chemical analysis method developed by ourselves. The highest phosphorus distribution ratio obtained was 2. 7 after reaction for 18 h with 17.5 mass% CaO--CaF2 slag. We then conducted acid leaching of the silicon and achieved removal of a large fraction (over 90 % ) of the phosphorus, which was much higher than that obtained by ordinary oxidizing slag treatment.IntroductionIn recent years, the production of solar cells has been increasing rapidly. Because of this, the demand for solar-grade silicon (SOG-Si) has also been growing rapidly. The development of lower-cost mass production processes is therefore needed to provide silicon feedstock. Phosphorus is one of the impurities in metallurgical-grade silicon (MG-Si). Because of its large segregation coefficient (kp = 0.35) [l ], it is difficult to remove phosphorus using a solidification refining process. Vacuum melting is considered to be a promising method for removing phosphorous from MG-Si [2], but the issues of high cost and large energy consumption have still to be resolved.Slag treatment is often used to remove impurity elements by oxidizing reactions during general oxidation refining processes. For example, phosphorus in molten steel is removed into a slag phase as phosphate ions, PO4 3-l-, by the following reaction:"

Jan 1, 2013

By Catherine Cai

A granular sorbent, prepared by gel-coating polyethyleneimine (PEI) on high surface area silica followed by crosslinking with a low-molecular weight diepoxide, has significantly higher uranium capacity, greater salt tolerance, and faster kinetics than the commercial resin Dowex 21K. Though having lower U(VI)/Fe(III) selectivity than Dowex 21K, the gel-coated PEI affords much higher sorptions of both U(VI) and Fe(III) and also their separation by selective stripping with acid.

Jan 1, 1999

By Tomás Vargas

The catalytic influence of a pure strain of Thiobacillus ferrooxidans (ATCC 19859) on the dissolution of natural pyrite crystals was studied using electrochemical techniques. The results showed that this microorganism catalyze the leaching of pyrite by both, oxidizing ferrous iron in solution and depolarizing the reduction of ferric ion on this sulfide. In addition, studies of bacterial corrosion under applied potential showed that pitting on the pyrite surface centers on weak sites of the sulfide structure in which bacteria has attached, but occurs only when the ferric iron in solution induces an adequate level of anodic polarization on the mineral.

Jan 1, 1992

By L. J. Davies

Refractories usage in furnaces for the extraction of nickel from both sulphides and lateritic ores is reviewed. Recent changes in raw materials and basic brick qualities developed to meet the increasing demands of existing and new processes are outlined. Examples of used brick examinations to establish mechanisms of wear are given. The importance of physical and chemical properties are discussed. The use of simulative laboratory testing to aid in refractories development and selection is described.

Jan 1, 1988

By Steve Johnston, Mowafak Al-Jassim, Fei Yan, Omar Sidelkheir, Alain Blosse, Katherine Zaunbrecher

"Imaging techniques are applied to multi-crystalline silicon wafers and solar cells throughout the production process. Photoluminescence imaging, both band-to-band and defect-band, is used to characterize defects and wafer quality at all process steps. These steps include bricks sawn from ingots, wafer sawing, cleaning and texturing, emitter diffusion, edge isolation and glass removal, anti-reflective coating/passivation, and metallization of finished cells. Bricks, wafers, and cells can be imaged at a rate commensurate with in-line measurement, giving spatial information to characterize quality and defect content. Photoluminescence images on silicon bricks can be correlated to lifetime measured by photoconductive decay and could be used for high-resolution characterization of material before wafers are cut. The defect areas in as-cut wafers are compared to imaging results from electroluminescence and lock-in thermography, and cell parameters of near-neighbor finished cells, showing correlations to efficiency, open-circuit voltage, and short-circuit current.IntroductionImaging techniques can rapidly characterize material quality and defect density. Photoluminescence (PL) imaging can be applied to silicon from the brick level to all wafer process steps [1-8]. At the brick level, material thickness allows for measurement and correlation to lifetime where surface recombination effects are minimized [6, 7]. At the as-cut wafer level where thin unpassivated wafers prevent accurate lifetime assessment due to surfaces, defects can still be categorized and quantified to predict finished cell performance [3-5]. Defect regions can be identified by recombination-limited band-to-band PL or by defect-band emission [9-12]."

Jan 1, 2012

By Teruhisa HORITA

The durability of SOFCs is one of the critical issues to realize the SOFC systems. In order to improve the durability, a precise degradation mechanism should be clarified at the different functional ceramic interfaces in SOFC cells and stacks. This paper reviews the improvement of SOFC durability by the mass transport analysis especially at cathode/interlayer/electrolyte interfaces. We have made a precise analysis on the reaction of cathode with impurities. Especially at the (La,Sr)(Co,Fe)O3/CeO2/ZrO2 interfaces, a significant amount of SrCrO4 and SrSO4 were observed at the (La,Sr)(Co,Fe)O3 surface as well as inside the (La,Sr)(Co,Fe)O3 cathode, which suggested some process occurred for both poisoning. Possible degradation mechanisms were proposed based on the observation data.

Jan 1, 2016

By Tapani Järvinen

Non-ferrous metals and metals in general are considered as being non-renewable natural resources. Metals are needed because of their excellent and irreplaceable properties. The consumption of metals, with the exception of carbon steel, is steadily growing by 1-3 % annually, and that of stainless steel as much as 3-6 %. This is a general trend, which is periodically disturbed by cyclical variations. In recent years so-called "New Economy" has become prominent in the public media and the market value of the traditional industry has been well below its real value and importance. Nevertheless, the modem society requires metals today and also in the future, and the companies using the most modern technology in a responsible way and innovative solutions not only in technology, but also in everything they do will survive. This paper describes the role of Europe as a producer of primary base metals and as a supplier of technologies in the base metals industry. It concentrates on the development and commercialization of technologies and project implementation in the metallurgical industry. As one example ofa European approach to these matters the paper presents Outokumpu's response to the future challenges in the base metals industry. Outokumpu Oyj is one of the leading metals and technology companies in the world of stainless steel, copper, zinc, and sales of technology in metals and minerals businesses. Outokumpu applies its knowledge of metals and processing to generate value for its customers and shareholder. Everything we do, we do in an economically, environmentally and socially responsible way.

Jan 1, 2003

By Tapani Järvinen

Non-ferrous metals and metals in general are considered as being non-renewable natural resources. Metals are needed because of their excellent and irreplaceable properties. The consumption of metals, with the exception of carbon steel, is steadily growing by 1-3 % annually, and that of stainless steel as much as 3-6 %. This is a general trend, which is periodically disturbed by cyclical variations. In recent years so-called "New Economy" has become prominent in the public media and the market value of the traditional industry has been well below its real value and importance. Nevertheless, the modem society requires metals today and also in the future, and the companies using the most modem technology in a responsible way and innovative solutions not only in technology, but also in everything they do will survive. This paper describes the role of Europe as a producer of primary base metals and as a supplier of technologies in the base metals industry. It concentrates on the development and commercialization of technologies and project implementation in the metallurgical industry. As one example of a European approach to these matters the paper presents Outokumpu' s response to the future challenges in the base metals industry. Outokumpu Oyj is one of the leading metals and technology companies in the world of stainless steel, copper, zinc, and sales of technology in metals and minerals businesses. Outokumpu applies its knowledge of metals and processing to generate value for its customers and shareholder. Everything we do, we do in an economically, environmentally and socially responsible way.

Jan 1, 2003

By Maria Salazar-Villalpando, Todd H. Gardner

"Efficient utilization of CO2 can help to decrease global warming. Methane reforming using carbon dioxide has been of interest for many years, but recently that interest has experienced a rapid increase for both environmental and commercial reasons. The use of CO2 provides a source of clean oxygen, which eliminates the need for costly oxygen separation plants. The product of dry reforming is useful syn-gas, which can be used to generate electrical power in a SOFC or in the production of synthetic fuels (hydrocarbons and alcohols). Hexaaluminate catalysts prepared at NETL may represent a product that can be utilized for the conversion of CO2 to syn-gas. In this work, transition metals dispersed in barium hexaaluminate have shown to be promising new catalysts for dry methane reforming. In this investigation, a series of BaNixAl12-yO19-d catalysts with varying Ni content were prepared by co-precipitation followed by calcination at 1400°C. CO2 reduction by dry methane reforming was carried out to determine catalyst performance as a function of temperature and carbon formation was also quantified after the reforming tests. Results of catalysts characterization, dispersion and surface area, were correlated to catalytic performance.IntroductionEfficient utilization of CO2 can help to decrease global warming. Methane reforming using carbon dioxide has been of interest for many years, but recently that interest has experienced a rapid increase for both environmental and commercial reasons. The use of CO2 provides a source of clean oxygen, which eliminates the need for costly oxygen separation plants. The product of dry reforming is useful syn-gas, which can be used to generate electrical power in a SOFC or in the production of synthetic fuels (hydrocarbons and alcohols). The dry reforming reaction has been known for a long time. Recent publications have reported studies over several catalysts. For example, the CO2 reforming of CH4 over mesoporous nanocrystalline zirconium powders (ZrO2–3%M2Ox; M: Ce, La and K) at 700ºC have shown methane conversion up to 60% (1). Similarly, the effect of Ni content (1–12 wt%) on the surface and catalytic behavior of bimetallic PtNi catalysts supported on ZSM-5 for reforming of methane with CO2 has been studied and report shows a maximum conversion of 16% and catalyst deactivation was observed during the first hour of time on stream (2). In another report, (3) Ni/a-Al2O3 catalyst was tested for syn-gas generation at 750ºC. The maximum methane conversion was 25%."

Jan 1, 2008

By Yuchun Wang

In principle, supported liquid membranes could be an exceedingly elegant separation process. However they tend to fail by displacement and emulsification of the organic solution in the pores, which allows mixing of the feed and strip solutions. We have stabilized supported liquid membranes comprising moctylamine in nylon and PVDF supports by covering the pores with semi-permeable polyamide films, using an in-situ polymerization technique. Scanning electron microscopy demonstrates that the polyamide films are sensitive to production conditions and the nature of the support. The transport properties of stabilized supported liquid membranes for Cr(VI) are compared with those of unstabilized membranes.

Jan 1, 1998

By Peter K. Liaw, Charlie R. Brooks, David C. Joy, Wei Zhao

In this paper, effects of oxidation, porosity and fiber-fabric stacking sequence on flexural strength of a continuous silicon carbide fiber (SiCr) fabric-reinforced SiC ceramic-matrix composite (CFCC) were studied. The failure mechanisms were correlated with flexural strengths of CFCC samples, both before and after oxidation. Microstructures and fractography were investigated using scanning electron microscopy (SEM). The chemical change after oxidation, such as Si, C, and 0, and their distributions, were detected by the SEM energy-dispersive X-ray spectroscopy (EDXS) line-scan chemical analysis technique. These effects on the strength of the CFCC can be attributed to following reasons: (i) The decrease in the flexural strength after oxidation is mainly due to degradation of the strength of Nicalon fibers and the damage of fiber/matrix interface both caused by high-temperature chemical reactions, (ii) Porosity is not too important in affecting the strength of the CFCC, when the bonding of the forced flow chemical vapor infiltration (FCVI)-SiC matrix is stronger than that of the fiber/matrix interface. However, a higher porosity content will be harmful, because higher porosity will both decrease the effective elastic modulus of the FCVI-SiC and make pore-linkage easier to occur, which is more likely to cause premature failure, (iii) The variation in the lamina stacking sequence of the CFCC changes the elastic stress distributions along the thickness direction of specimens, the magnitude of ceramic matrix-cracking stress, the effective elastic moduli of the laminate, and different crack initiation sites as well as different failure modes, and thus, leading to the scatter in the flexural strength of the CFCC.

Jan 1, 1998

By Roger Altman

The solubility of copper in primary spinel crystals encountered in reverberatory slag samples has been determined by electron microprobe analysis. These spinels, which ranged in composition from 22% A12O3 to pure magnetite, contained small quantities of dissolved copper (0-0.4%). Based on literature data it was estimated that the solubility limit of copper in solid magnetite is no greater than about 1% at 1200°C and about 2% at 1250°C. However, it was found that practically every spinel crystal examined contained significant amounts of matte inclusions. Further examination of converter slag revealed large quantities of irregularly shaped precipitated magnetite crystals which contained a large proportion of copper inclusions. Additional experimentation showed that the total copper content in reverberatory slag samples was greater than the sum of the estimated en- trained plus dissolved matte in the slag. This difference is believed to be significant and is due to the presence of matte inclusions in the spinel crystals. In the present reverberatory slag samples these inclusions accounted for about 1/2 of the amount of sulfide directly entrained in the slag.

Jan 1, 1976