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By Corby G. Anderson

For over a century, the Sunshine Mine in Idaho has been a major producer of silver. An estimated 335,000,000 troy ounces of silver has been mined. This has established the Sunshine Mine as the largest single source of silver in the world. Because the dominant silver containing mineral is tetrahedrite, a copper and antimony sulfide, normal metallurgical treatments to recover the precious metal are not practical. Thus, over the course of the company's history, novel, hydrometallurgical technologies have been developed on-site to handle complex, precious metal containing materials. Recently, the use of Sunshine technology has been extended to the recycle of secondary materials. As well, the use of Sunshine technology by other organizations for treatment of both primary and secondary feedstocks containing precious and base metals is an area of growing interest. This paper will provide an overview of Sunshine hydrometallurgical technologies including the applicability of Sunshine technology to the recycling of precious and base metals.

Jan 1, 1995

By Peter Bauer, Klaus Gamweger

"Gas purging systems are well established in nonferrous metallurgy at multiple steps during metal production, including melting, converting, alloying, and metal cleaning. Since the kinetics of all of these stages are positively influenced by using gas purging systems the overall process benefits are substantial. In the aluminum industry, inert or reaction gases are blown into the melt using porous plugs to achieve improved metal grades, higher productivity, and more efficient energy utilization. To enable the most effective application of the process gases a complete package, termed AL KIN, was developed by RHI that includes porous plugs, refractory expertise, gas supply technology, and gas control equipment. This paper discusses the technological and economic advantages of this system and the specific benefits of fuel reduction, production time savings, decreased process gas consumption, and improved refractory service life and maintenance are illustrated using an aluminum slug plant in Austria.IntroductionIn addition to high quality production, increasing productivity is the main goal in many aluminum cast houses to maintain or even strengthen their market position. The Neuman Aluminium Group, based in Austria, North America, and based in Austria, North America, and China, is the largest slugproducer for tubes, cans, and automotive parts worldwide. Recently, a comprehensive improvement program was initiated at the Neuman Aluminium Austria slug plant in Marktl - the main factory and technological centre of the group. The principal goal of the optimization project was to increase the productivity of the strip-casting production. The investment included a gas purging system, ingot preheating equipment, a new insulated launder system, and optimized melting cycles. However, the introduction of the gas purging system was pivotal to the project and has accounted for approximately 50% of the benefits achieved. This paper describes the AL KIN gas purging technology and details the process benefits resulting from the improvements at Neuman Aluminium Austria."

Jan 1, 2009

By Suzanne Young

The effect of LiF additions on liqt.1id1.:1s temperature and electrical conductivity over a wide range of cryolite bath ratios (1.0 to 1.5 weight ratio) was investigated. Results did not agree with multi-regression equations reported by Dewing and Choudhary over the entire region. New regression equations were developed. Reasons? are given for the differences. The models are used to discuss the economic implications of LiF additions to Hali cell electrolytes.

Jan 1, 1985

By Katsuyoshi Kondoh

The utilization of silica particles originated in rice husks as reinforcements of magnesium composites was discussed. By using the solid state reaction of rice husk silica particles with magnesium powder, P/M magnesium based composites dispersed with the magnesium silicide (Mg2Si) and magnesium oxide (MgO) were fabricated. High-purity silica particles were originated from rice husks, one of the major agricultural wastes, via the citric acid leaching treatment and combustion in air. The effects of the silica particle characteristics such as size, crystalline and porous structures, on the reactivity of silica and magnesium to synthesize Mg2Si intermetallic were discussed. Amorphous silica was more useful for this reaction than crystalline one. The reactivity of rice husk silica was superior to that of the conventional mineral silica particles because of not only its amorphous structure but the larger specific surface area due to their pore structures. In the case of the green compact of the mixture of the rice husk silica and Mg powder, the silica particle size was not effective on the reactivity because the coarse particles were fractured into fine ones by cold compaction. The distribution of Mg2Si intermetallics of magnesium powder composites consolidated by SPS process was investigated by XRD and SEM-EDS analysis. Their mechanical and physical properties were also evaluated in detail.

Jan 1, 2009

By Brian Cochran, C. Edward Eckert

"EXECUTIVE SUMMARYINTRODUCTIONThe commercial incentives for using molten aluminum in casting operations are numerous and substantial. Although these incentives apply broadly to both shape castings (foundry) operations and wrought alloy production, the merit of a particular motive is indeed downstream processing sensitive. Melting cost reduction is a universal incentive that impacts on essentially all aluminum products. At a natural gas burner cost of $4.50 per therm, for example, the reverberatory furnace energy cost is at least $0.01 per pound of aluminum melted, exclusive of melt loss, fixed costs, and other expenses. The Aluminum Statistical Review' cited 3.188 million metric tons of secondary aluminum that was recovered by the industry in 1995. This represents a re-melt energy cost of over $70 million. Other incentives to use molten secondary aluminum include throughput enhancement, metal chemistry assurances, environmental considerations, and the avoidance of an in-house scrap processing operation.A traditional disincentive to use molten secondary aluminum is metal quality. If a particular secondary processing operation was successful in achieving and preserving an acceptable metal quality level prior to shipment, the subsequent metal transfer and ladle delivery events would frequently obviate these efforts. For example, a metal superheat on the order of several hundred degrees is required for an unheated transfer ladle to travel 3 to 4 hours to a customer location. The rate of the y-alumina formation reaction approximately doubles for every 120°F increase in temperature, therefore, the effect of excess superheat on melt loss and metal quality is considerable. Linear oxidation reactions, such as magnesia formation in magnesium containing alloys, are influenced to an even greater extent by temperature.The typical quality detractor events are:"

Jan 1, 2000

By Ramana. G. Reddy, Haoxing Yang

The electrodeposition of zinc from zinc oxide using urea and choline chloride mixture in a molar ratio 2:1 is investigated in different experimental variables, namely, the concentration of added [BMIM]HSO4, temperature, and applied cell voltage. The additive, [BMIM]HSO4, was determined to have beneficial effect on the current efficiency, energy consumed in the process and surface morphology of the deposits. The highest current efficiency (92.6%) and lowest energy consumption (2.92kWh/kg) was obtained for solution with 20mg/mL [BMIM]HSO4. The morphology showed the formation of absorbed additive layer on the cathode at higher concentration of additives. Experiments were conducted at different temperatures between 343K and 388K and at various applied cell voltages between 2.7V to 3.6V to determine the best experimental conditions. By varying temperature, highest current efficiency (91.3%) and lowest energy consumption (2.69 kWh/kg) was obtained at 373K. The electrodeposition process is enhanced between the applied voltage 3.0-3.3V by achieving lower energy consumption (2.75~3.06kWh/kg) and higher current efficiency (88.4~89.7%). SEM images showed grain size is significantly increased in higher applied voltages. While at higher temperatures, it seemed to generate particle growth as clusters at the outer deposit layer.

Jan 1, 2014

By Mary Cunningham

The EPA and DOE have collaborated on a series of studies to evaluate the effectiveness of treatment technologies at stabilizing bulk elemental mercury and wastes containing high concentrations (i.e., with greater than 260 mglkg total mercury) and multiple forms of mercury. The data from these treatment demonstrations are intended to help EPA to determine if regulatory revisions to allow a stabilization alternative for high-mercury subcategory wastes are warranted. In addition to mercury-contaminated wastes, the disposal of bulk elemental mercury is of concern because of the excess quantity of mercury in the Defense Logistics Agency (DLA) stockpile, as well as other potential sources of excess elemental mercury. The studies evaluated the effectiveness of several technologies at: I) stabilization of mercury in a "hard-to-treat" matrix; and 2) conversion of elemental mercury into a stable waste form for disposal. A surrogate waste was designed for the study on high-mercury wastes, which included an organic form of mercury, elemental mercury, and several mercury salts in an inorganic matrix. The surrogate waste and the bulk elemental mercury were treated by the vendors, and the treated waste forms evaluated for mercury Icachability, using both the TCLP and an automated, constant-pH leaching protocol. Constant pH leaching was conducted at pH 2,4,6,8 10 and 12 for 14 days at each pH. The leaching data demonstrate that the stability of the mercury in three treated waste forms varies widely across the pH range tested. Clearly, the stability of mercury in these treated waste forms will be highly dependant on the disposal conditions. The combination of site-specific disposal conditions and appropriate treatment technology must be considered as decisions are made about disposal of high-mercury wastes.

Jan 1, 2003

By T. Mutoh

Tellurium in raw slime has recently been recovered as copper telluride in Onahama Smelter & Refinery. The slime is decopperized with sulfuric acid solution in conventional leaching tanks. The pregnant leach solution containing 45 g/l of copper and 1 g/l of tellurium is introduced to a copper telluride recovering reactor. The tail solution from the reactor containing less than 20 mg/l of tellurium is recycled directly to circulation tanks of copper electrolysis. The impurities of the product copper telluride is kept below 1% without any purification.

Jan 1, 1990

By B. Mishra, W. A. Averill

"The application of various hydrometallurgical, pyrometallurgical and electrochemical processes in the extraction, purification and production of radioactive metals as well as the use of various materials, ego metals and alloys, ceramics, polymers, etc. in the process, construction and handling equipment in the nuclear industry has generated a large stockpile of radioactively contaminated waste material and scrap metal which can not be directly discarded, recycled or considered for long-term storage due to its volume and potential hazards, without the separation of radionuclides. This paper reviews the emerging methods that have been investigated and suggested for dealing with some of these wastes and scrap material.The separation technologies studied for the recovery of radioactive components from the pyrometallurgical and electrochemical processing wastes have been discussed in details with results from some of the recent theoretical and physical modeling work as well as the data obtained from the actual waste treatment. Specific processes shall be described in terms of its advantages and limitations. These emerging separation technologies are being considered by the US Department of Energy as alternatives for dealing with the issues of environmental management [EM] and decontamination and decommissioning [D&D].IntroductionThe high temperature carbothermic or metallothermic smelting reduction methods for metal production are associated with the generation of significant quantity of waste as slags, flue dusts, sludges, residues, effluent salts etc. Certain hydrometallurgical processes also generate lots of aqueous waste due to the inherent nature of the technique. Also, the gas-based reduction processes are not applicable to many stable metal compounds, such as alumina, titania, beryllia, lanthanide and actinide oxides, etc. due to thermodynamic considerations. All these methods cause substantial environmental hazard. There is a need to develop alternative processes which have low waste or ideally a ""zero-waste"" generation.Pyrochemical processes using molten salts provide a unique opportunity for the extraction and refining of many reactive and valuable metals either directly from the beneficiated ore (aluminum, beryllium, neodymium, plutonium, uranium, etc.) or from other process effluent that contain reactive metal compounds. The processes reduce metal compounds electrolytically (A12O 3 and BeCI2) on a carbon anode or by calciothermic reduction (Po, Nd). The by-product, in the latter case, is a calcium oxide saturated halide salt. The waste-treatment to recycle the halide has to be done as a separate step or stored as a contaminated waste. A successful separation technology can provide a new insight to the waste minimization strategy for the nuclear industry."

Jan 1, 1996

By Shen Shen, Paul R. Ohodnicki, Samuel J. Kemion, Vladimir Keylin, Alex Leary, Joseph F. Huth, Michael E. McHenry

"Recent DOE workshops highlight the need for advanced soft magnetic materials leveraged in novel designs of power electronic components and systems for power conditioning and grid integration. Dramatic weight and size reductions are possible in these applications through operating at increased frequencies. This manuscript discusses processing and composition design approaches for optimizing FeCo-based nanocomposites for higher frequency operation at 100 kHz and above. The proposed strategy involves starting with prior compositions known to exhibit high inductions, optimal field crystallization induced anisotropy, and excellent mechanical and high temperature magnetic properties. Proposed alloy modifications for the applications of interest would include increased amorphous phase resistance, optimum induced anisotropy, and minimized or carefully engineered magnetostriction. Relevant process developments would target reduction of ribbon thickness by optimizing the casting process or post-processing treatments such as chemical thinning or rolling. Three archetypes FeCo-based nanocomposites are described including near equiatomic FeCo-based, Fe-rich and Co-rich alloys.MotivationSilicon steels are widely applied for 60Hz utility-scale transformers [1]. For applications at high frequencies, however, Si-steels exhibit unacceptable losses and ferrites are typically used due to their high electrical resistivity and good soft magnetic properties [2]. However, the low inductions offerrites have limited their applications in power electronics. Developments in rapid solidification have led to amorphous metal alloys and controlled nanocrystallization processing has resulted in state-of-the-art amorphous/nanocrystalline nanocomposite soft magnets [3-5]. Commercial utility-scale transformers made with Fe-based amorphous materials have been demonstrated to result in significant energy savings with an associated reduction in greenhouse gas emissions [6]. DOE workshops held in 2010 emphasized a need for advanced soft magnetic materials for the next generation of power electronics. For advanced power conditioning and grid integration applications, frequencies of 20 kHz up to -1 MHz are of interest depending on the power level [7]. Here, we review previous work and discuss the approaches to optimize FeCo-based nanocomposite materials for high frequency applications."

Jan 1, 2012

By Varadarajan Seshadri

Geometallurgical characterization of iron ore which is a raw material for Iron making as in the case of charcoal blast furnaces operating in Brazil or for production of agglomerates such as iron ore sinter which serves as burden material for blast furnces of high productivity or pellets extensively used in the direct reduction processes all over the world in the iron and steel industry. Selection of proper raw material after due characterization should lead to an improvement of the productivity of the respective processes The usual classification of quality of iron ore is uniquely based on chemical analysis, granulometric and physical parameters. However not much emphasis has been given to the structural characteristics which also are important in the processes. Different typological categories of Brazilian iron ores have been used in the characterization . For instance, several kinds of hematite crystals like specularite, martite and microgranular hematite, etc with variable crystal sizes are found in the different ore types. They are also composed of different of fabrics and types of accessorial mineralogical constituents and have different porosities, pore diameters, etc which influence the cold and the hot agglomeration stages of the ore fines, and also chracteristics such as reducibility, decrepitation etc, important for assessment of quality of iron ores. . The first step for attaining a good characterization of ores is to know in detail about the structure of the deposit, shape of the body, types of iron ores and their distribution. This requires a geological-structural study and the mapping of the bodies using mineralogical criteria for typological classification of ores. followed by structural characterization of materials in stages of mining, comminution, screening and concentration processes. In this contribution a geometallurgical approach for quality control of Brazilian iron ores for sintering and pelletizing processes is highligted.

Jan 1, 2006

By lndu S. Das

An analytical simulation of the material characteristics of Inconel 718 is developed and bounds for mechanical and microstructural stability are obtained for isothermal and temperature-dependent cases. Experimental flow stress data using hot compression tests are reported for a wide range of temperature and strain at various strain rates. A parametric study of strain rate sensitivity, dissipation and entropy are presented. A complete set of processing maps delineating the stable and unstable regions are developed to help define the most efficient means of manufacturing an Inconel product.

Jan 1, 1992

By J. W. Lyman

Nickel-metal hydride (Ni-MH) battery electrodes have been developed as a substitute for cadmium-containing negative electrodes. Use of Ni-MH electrodes offers enhanced electrochemical properties in many instances as well as reduced environmental toxicity. Rechargeable batteries using Ni-MH electrodes are also strong candidates for electric vehicles. During the production and secondary reclamation of these battery types, recycling procedures will be needed to prevent environmental impact caused by these wastes as well as to recover the value inherent in the scrap. The U.S. Bureau of Mines (USBM) is investigating hydrometallurgical technology that separates and recovers purified metallic components from Ni-MH battery scrap of two types, AB, and AB,. An investigation of acid dissolution and metal recovery techniques has determined several processing alternatives that may be used to promote the successful recycling of much of the battery fabrication scrap and eventual secondary scrap. Although recovery techniques have been identified in principal, their applicability to mixed battery waste stream and economic attractiveness remain to be demonstrated.

Jan 1, 1995

By Robert E. Brown

Magnesium recycling has been used to recover both new scrap and old scrap. It was used extensively in Germany during WWII to expand the magnesium supply. There were a large number of magnesium recyclers in the US who got their start smelting old scrap, old airplanes and old waste dumps from the WWII build up. As the world magnesium industry dwindled, only a few companies were left that did magnesium recycling as a primary business. The sand foundries tended to recycle of their production scrap in their melting furnaces. Even the original die casters tended to put scrap directly back into melting furnaces at the die casting machines. As high purity alloys were developed and the use of die castings in automotive work increased, the tendency was to let the magnesium recyclers convert the scrap back to high quality ingot. Automotive use has grown because of the low density of magnesium. This property is the one of the biggest problems to overcome in shipping scrap. Gates and runners from die casting are very irregular shapes and it is very hard to load a truck with enough material to get a low shipping cost per pound. Recent new equipment companies have developed magnesium equipment that is specifically designed to recycle, refine and cast secondary magnesium metal. These melt cells are supplied as integrated units to magnesium casting sites. The cost and effectiveness of this approach will be discussed.

Jan 1, 2000

By G. Van Weert, A. van Sandwijk, O. W. J. S. Rutten

"Cathodic and anodic reactions in an acidic nitrate medium were studied in reference to the production of electrolytic manganese dioxide from pyrolusite' (Mn02) ores by reductive leaching. Two USA ores were investigated. The reductant for the pyrolusite ore is produced cathodically in an electrolytic cell and can either be nitrous acid (HN02) or nitric oxide gas (NO). In this work emphasis was placed on the nitrous acid leach. In a high-temperature leach in a nitrous/nitric acid medium, manganese and silver are solubilized and iron is not. Anodic electrowinning of manganese dioxide from the acidic manganese nitrate electrolyte yields flaky y-Mn02, similar to that produced from sulfate and chloride electrolytes. Cathodic regeneration of nitrorts acid was studied in a membrane cell in 1.0 M nitric acid and 0.0 to 0.1 M nitrous acid on a' platinized titanium cathode. At cathode potentials ranging from +950 to +700 mV (SHE), cathodic reduction to nitrous acid takes place, at cathode potentials < +700 mV, cathodic reduction of nitrous acid to nitric oxide takes place. A conceptual process is presented and discussed.IntroductionManganiferous-silver oresLarge reserves of manganiferous-silver ores are present in the Southwestern United States and Latin America. These ores are generally refractory to hydrometallurgical methods of treatment, due to the insolubility of the higher oxides of manganese (Mn 4+) in all common lixiviants such as cyanide solutions, dilute sulfuric acid, nitric acid, ammonia, salt solution, thiosulfates, etc. The silver is either bound by the insoluble manganese, or is rendered inaccessible to cyanide leach solution by the surrounding manganese mineralization.Higher oxides of manganese will dissolve if they are first reduced pyrometallurgically to manganous oxide (Mn2+). This is a widely used pretreatment for manganese dioxide ores and subsequent dissolution in sulfuric acid is common. In order to avoid the pyrometallurgical pretreatment with its large energy requirements and gaseous emissions, fully hydrometallurgical processes have been proposed. These processes are based on the presence of a reductant in solution, in order to reduce the insoluble higher oxides of manganese to soluble lower oxides. Aqueous S02 has been proposed and tested on industrial scale by the U.S. Bureau of Mines. After washing, silver could be extracted by cyanidation. The neutralization of the pulp prior to cyanidation however causes problems in filtration and the reagent consumptions are high [1]. More recently, acidified thiourea and bacteria were proposed for the solubilization of both manganese and silver in a single leach step. High extractions were obtained, but drawbacks of these methods are high reagent consumption or slow kinetics [2,3]. For the options of manganese recovery from the leach filtrate, precipitation with persulfate or ammonium carbonate and ion exchange have been proposed. The proposed options for silver reclaim are precipitation with either zinc or Na2S and adsorption onto activated carbon."

Jan 1, 1997

By Valerio Viti

In High Pressure Die Casting a molten metal is injected through a thin gate into the cast cavity. High injection pressures and high gate velocities create atomization phenomena which can negatively affect the final quality of the cast. In order to control atomization process it is essential to understand the atomization patterns and the two-phase flowfield that exist at the gate exit. In the present work, 2D numerical simulations of the flow of molten Magnesium through a high aspect-ratio rectangular gate are performed using a water analogue for an open and closed cavity. The numerical simulations made use of VOF-type (Eulerian) physical models and Lagrangian models. Further, a sub-grid scale model was implemented that, in conjunction with VOF-type equations can efficiently predict the general atomization pattern without the need for high-resolution grids. The numerical results were compared to experimental data for validation.

Jan 1, 2006

By Qionghua Zhou, Wei Liu

"Nanocrystalline silver bulk material with average grain size of 20.3 nm was prepared by warmvacuum- compaction method. The as-prepared nanocrystalline silver was characterized by X-ray diffraction (XRD), differential scanning calarmeutry analysis (DSC), thermogravimetric analysis (TG), and 6157 type Electrometer test, respectivily. The experimental results show that the average grain size and microstrain of the nanocrystalline silver are 20.3 nm and 0.088%. The melting point and melting enthalpy are 1228.7 Kand 82.34 Jig, which are lower than that of coarse-grained silver by 6 Kand 22.6 Jig, respectively. The electrical resistivity of nanocrystlline silver increases with higher temperature when the range of temperature is between 233K and 293K. The electrical resistivity at 293 K is 1.475xlO -7 Q·m, which is higher than that of coarsegrained silver by a factor of 9.IntroductionN anocrystaline ( nc) materials or nano structured ( ns) materials are three-dimensional (3 D) bulk materials with average grain size typically smaller than 100 nm. Ne materials have been of great interest for their unique properties, such as superior tensile strength [1-2], high microhardness [3- 4], superplasticity [5-6], magnetically quasi-isotropic [7-8] , and so on, making them one of the most promising nano-scale materials with wide applications. Ne materials with average grain size of 5-10 nm were firstly fabricated by Gleiter et al. [9] in 1980s, using inert gas condensation (IGC) method. Unfortunately, the large surface to volume ratio creates a high surface energy component in the total free energy of the system and results in a metastable state in the materials. Therefore, due to the signfica nt disordered grain boundary regions, nanomaterials are thermally unstable and are subjected to a strong driving force for grain growth. The grain growth even occurred at room temperature [10].The conflict or deviation of measured date, e.g. strength, microhardness, thermal stability, partly due to the grain boundary ratio or the distribution of grain size, and partly derived from imperfections such as voids and microcracks while earlier processing techniques are known to result in incomplete dens:fication [11-12]. Therefore, the higher quality samples produced in subsequently years still show such a general trend."

Jan 1, 2011

By Shilai Yuan, Huimin Lu, Zhijiang Gao, Panpan Wang

"Solvent refining of silicon through using Si-Al melts is a valid method to remove the impurities from metallurgical grade silicon (MG-Si) melt. The thermodynamic behavior of impurities Fe, Al, Ca, Ti, Cu, C, B and P in MG-Si during the solidification of MG-Si was studied based on the available thermodynamic parameters and experimental data. The morphology of inclusions was investigated by Scanning Electron Microscope (SEM). The chemical composition of inclusions in MG-Si and Al-Si melt was analyzed by EPMA. It is found that the amount of white inclusion reduces and most impurities are solved into the Al-Si melts. After solidification of Si–Al alloy using induction heating and acid leaching, impurities can be effectively removed. The solidification of silicon from the Si–Al melt is found to be more effective for purification than general silicon solidification.IntroductionPhotovoltaic energy is one of promising energy resources in a sustainable society because of its inexhaustibility and cleanliness. Although the production and installation of solar cells have increased significantly during the last decade, the cost of solar cell installation is still high. Multicrystalline silicon has now become the main material in the photovoltaic market because of its low production cost and because of the relative high conversion efficiency of solar cells made from this material, which has been studied for a long time [1-3].Electronic grade (EG) silicon (99.9999999% Si) is commonly used as the raw material to produce SOG-Si (99.9999% Si). Silicon produced from the chemical routes restricts the development of solar cells due to environment threaten, high energy consumption and low productivity. Purification of metallurgical grade silicon (MG-Si) is a low cost, environment friendly method. Although several metallurgical processes such as directional solidification, vacuum refining and electron beam melting [4], have been developed, the cost reduction and refining efficiencies for manufacturing silicon is still have to be further optimized.In the purification process, it is difficult to remove boron and phosphorus by the conventional metal refining method. The refining efficiency depends on the segregation behavior of different elements in solid silicon and the liquid phase. The segregation ratios of all investigated impurities were found to be much smaller than the segregation coefficients between solid and liquid Al-Si melts [5]. For instance, the segregation coefficient of B in Si is 0.8 at the silicon melting point (1687K), whereas it is around 0.2 when silicon is solidified from Si-Al melt at 1273K. For phosphorus the segregation coefficient is 0.06 when silicon is solidified from Si-Al melt at 973K°C, which is much less than 0.35 for recrystallization from liquid silicon. Since the segregation coefficient of boron in silicon is 0.8, it cannot be removed by directional solidification."

Jan 1, 2014

By Cao rong-jiang, Tang Xin-he

"In ordinary manufacture process of tungsten powder, a preferable intermediate product used is ammonium paratungstate (APT). The particle size of tungten powder made from it through W2OO58 is larger than 1. 0 um. In order to obtain ultrafine tungsten powder with narrow size distribution, a new type of tungstate, hydraziniull tungstate, was studied. Its formula is 5(N2H5)2O·12 WO.s , with tetragonal crystal structure of a=5.821 , c=18. 468. Three methods for preparing hydrazinium tungstate (ART) were set up and ART can be produced by current industrial APT process with little modification of operation and without any change of equipment.Under certain PH and operation condition of the solution from which ART was produced, an autoreduction of tungsten occured, which produced a lower valency tungstate with blue color when ART was heated at different temperatures, in N atmosphere, tungsten bronze, tetragonal W0290 and W02.7E could be obtained respectively. They all have the superiorities, in the production of tungsten powder, of superfine size and narrow size distribution [average size of 0.5um or even smaller.The rate of autoreduction of ART is very fast at elevated temperature. The reduction reaction, which gaves tetragonal WO290, could be handled smoothly without explosion. To research their behaviors at autoreduction temperatures and the products of autoreduction will be new advances of tungsten chemistry and may also serve tungsten industry with new processes and materials."

Jan 1, 1988

By Yichi Lu, Haydn N. G. Wadley, Douglas T. Queheillalt

"Using a 3-D ray tracing methodology combined with laser ultrasonically measured elastic constant data near the melting point, ultrasonic propagation in cylindrical single crystal bodies containing either a convex or a concave solid-liquid interface have been simulated and used to design new sensing concepts. Ray paths, wavefronts and time-of-flight (TOF) of rays that travel from a source to an arbitrarily positioned receiver have been calculated. Experimentally measured TOF data have been collected using laser generated/detected ultrasound on model systems with independently known interface shapes. Both numerically simulated data and experimental results have shown that the solidification (interfacial) region can be identified from ultrasonic transmission TOF data. Since convex and concave solid-liquid interfaces result in distinctively different TOF data. When TOF data collected in the diametral plane are used in a nonlinear least squares algorithm, the interface curvature has been successfully reconstructed and ultrasonic velocities of both the solid and liquid obtained. The reconstruction errors were found to be less than 5%.IntroductionMany of today's single crystal semiconductors are grown by variants of a vertical Bridgman technique in which a cylindrical ampoule of a molten semiconductor is translated through a thermal gradient, resulting in directional solidification and the growth of a single crystal, Fig. 1.1 It has long been recognized that during crystal growth the velocity and the shape of the solid-liquid interface, together with the local temperature gradient, control the mechanism of solidification (i.e. planar, cellular or dendritic), the likelihood of secondary grain nucleation/ twin formation (i.e. the loss of single crystallinity), solute (dopant) segregation, dislocation generation, etc. They thus determine the crystals' resulting quality.2-4 The solidification rate and the solid-liquid interface shape are also sensitive functions of the internal temperature gradient (both axial and radial) during solidification.5•6 This in turn is governed by the heat flux distribution incident upon the ampoule, the latent heat release at the interface, and heat transport (by a combination of conduction, buoyancy and surface tension driven convection, and radiation) within the ampoule. The solid-liquid interface's instantaneous position, velocity and shape during crystal growth are therefore difficult to predict and uncontrolled during growth, especially for those semiconductor materials with low thermal conductivity (e.g. CdTe).4-6 The development of technologies to non-invasively sense the interface position and shape throughout the vertical Bridgman crystal growth process has therefore become a key step toward developing a better understanding of the growth process, for enabling sensor-based process control, and thus ultimately for improving the yield and quality of difficult to grow semiconductor materials like CdTe."

Jan 1, 1997