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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 R. Moreau, V. Uspenski, K. Messadek, Y. Delannoy

Experiments and numerical simulations have been carried out to investigate the properties of quasi-2D turbulence. A new mercury model experiment has been built and tested in a uniform magnetic field up to 6T, (Ha~ 1000), ensuring a better two-dimensional behaviour than earlier versions (Alboussiere et al., 1997), limited to 0.2T. The quality of the experimental results has been improved in order to get wave number spectra (instead of frequency spectra) and higher signal over noise ratio (due to the higher magnetic fields). In parallel, some two-dimensional "direct" numerical simulations were performed using a commercially available code to solve a 2-D motion equation involving a source term to model the Hartmann layer. This term is derived from the condition of closure of the electric current, which allows to transfer the Hartmann effect into the 2D-core flow without simulating the layer itself (Sommeria & Moreau, 1982). No subgrid scale modelling is needed in such a two-dimensional situation where most of the energy is carried by the large scales.

Jan 1, 1999

By Feng Gao

A general unsteady- state model, based on a cracked substrate, has been developed to account for reaction and diffusion within porous substrate during oxidation of Carbon Fiber Reinforced Carbon matrix (CIC) composites. The effects of several parameters, such as diffusion and reaction rate ratio, oxygen concentration, and composite density, on oxidation process are explored. Also, theoretical results for a set of parameter values of the CIC composites are compared with experimental data. It shows that the model predicted values agreed well with the experimental data in weight loss. Based on this model, quantitative predictions of oxidation of a composite with cracked substrate can be made.

Jan 1, 1993

By Yingtao Zhang, Shaofeng Du, Yiming Rong, Wenjun Zhao, Gang Wang

"20Cr2Ni4A steel is a kind of high quality steel mainly used for manufacturing high-duty gears in the world. The high-duty gear with good performance must have wear and fatigue resistance properties. In order to get the good properties, the high-duty gear needs a high hardness gear surface and a good hardness gradient along the depth direction. In this paper, the samples were designed and a vacuum carbonitriding process was put forward to improve the surface hardness of parts for 20Cr2Ni4A. The process contained carbonitriding, quenching, cryogenics, and tempering process. The surface hardness and hardness gradient of carbonitrided samples were measured and the good microstructure was gained. The surface hardness is 67.SHRC and the case depth is 1.2mm.IntroductionSteels are widely used in industry, but the fatigue strength and the wear resistance of steel is much low. So the heat treatment process is put forward to improve the mechanical properties of steel. It can be improved by high-energy heat treatment methods for medium-carbon and highcarbon steel. Those methods will not alter the chemistry of the base metal [ 1].For low-carbon steels, carburizing and quenching should be used to improve the steels' mechanical properties, especially the surface properties. Compared with the carburizing, carbonitriding has more advantages, such as a short production cycle, low temperature and small deformation of parts. Carbonitriding is a modified form of gas carburizing, rather than a form of nitriding. The modification consists of introducing ammonia into the gas carburizing atmosphere to add nitrogen to the carburized case as it is being produced. Nascent nitrogen forms at the work surface by the dissociation of ammonia in the furnace atmosphere; the nitrogen diffuses into the steel simultaneously with carbon. Typically, carbonitriding is carried out at a lower temperature and for a shorter time than is gas carburizing, producing a shallower case than is usual in production carburizing [2]. As a material surface strengthening technology, carbonitriding has been widely used in the production [3]. And vacuum carbonitriding process is better than carbonitriding, because the vacuum carbonitriding temperature can be higher than carbonitriding without surface oxidation."

Jan 1, 2014

By P. Louis

Gécamines is the world largest cobalt producer with about 60 % of the Western World production. During the last ten years, its annual production varied from 5,400 to 14,600 t/year. The actual cobalt production capacity of Gécarnines is 18,000 t/year and could be increased in the near future if necessary. Cobalt is presently produced at the Shituru plant by an old in-pulp electrolysis process and in Luilu, by electrolysis of a clear weakly acidic solution. The Shituru Cobalt quality is lower than the Luilu one. For that reason, part of the Shituru Cobalt is fire refined and cast into granules. Large efforts have been succesfully accomplished to improve the cobalt quality. This has been made possible by a better knowledge of the purification processes and of the electrolysis parameters.

Jan 1, 1988

By Liu Chunpeng

The new technological process developed is by means of thermal plasma arc smelting to obtain high grade Ni matte directly from Ni-Cu concentrates containing 6-7% nickel and 3-8% sulfur. In comparising with conventional smelting and converting processes the plasma arc smelting process has many advantages over conventional processes, such as lower energy consumption, lower capital investment and free from SO, pollution by transforming the sulfides into elemental sulfur with microwave irradiation under controlled oxygen potential, moreover, the process is simple and easily controlled due to less magnetite troubles in the operation. Therefore, this new technological process can be used as an alternative way to conventional process for Ni-Cu concentrate smelting. The main economical technical index is summarized in Tabal 1. Table 1 Main Ecnomic-technical Index

Jan 1, 1993

By Thomas A. Post

The methodology of determining the optimum SX pumper-mixer system based on bench top, pilot, or small-scale solvent extraction systems, is demonstrated. The design of small-scale SX-plants is different than a full-scale plant. The difference is explained here. The use of dimensionless parameters Nh, Nq, and Np that describe the head, flow and power of the pumper is shown and how to use them for the scale-up. Additional data is required to determine the optimum operating range. Applications of this methodology were used to design well known currently operating SX plants. The emphasis on the optimization of hydraulic efficiency will be shown on examples, including how the hydraulic efficiency is affected when the throughput of the system goes beyond the design. Designs of all sizes of equipment will be shown which optimize the hydraulic efficiency.

Jan 1, 2003

By Takayuki Ichikawa

Hydrogen storage properties of ballmilled mixtures composed of the hydrogenated nano-structured carbon (CnanoHx) and lithium hydride (LiH) were examined by thermal and optical spectroscopic analyses. LiH needs higher temperature than 600°C for hydrogen desorption even under vacuum condition, while CnanoHx, which was mechanochemically synthesized from graphite powder by ballmilling under hydrogen atmosphere, reveals hydrogen and hydrocarbons desorption in wide temperature range from 300 to 800°C. Nevertheless, the composite of CnanoHxand LiH prepared by ballmilling desorbs hydrogen in relatively lower temperature range from 150 to 450°C. These phenomena indicate that the thermally liberated hydrocarbon radicals immediately react with LiH and release hydrogen instead of hydrocarbons emission, because CnanoHx contains hydrocarbon groups at the edge of nano-meter sized graphenes, which are recognized as IR active C-H stretching mode, and LiH is well-known as an ionic crystal. Furthermore, it is of interest that a nanostructural feature persists in this composite even after annealing at 350°C, which shows excellent cycle properties as hydrogen storage media.

Jan 1, 2006

By Larry F. McHugh

Current sulfide ore processing methods involving mechanical sizing of ores, froth flotation, electro-winning, solvent extraction, smelting and roasting are quite effective but typically represent a significant energy and environmental cost. This paper is the subject of a recent patent application and development program involving major improvements in sulfide ore processing. This two-step ?looping oxidation? process effectively removes sulfur while producing materials of adequate purity in an energy proficient and environmentally friendly manner. The first step results in a metal sub-oxide and a highly concentrated sulfur oxide off-gas stream. This gas stream can be processed for recovery in a more effective manner regarding both energy and capital equipment costs. In the second step, this metal sub-oxide is further oxidized to efficiently generate energy that can be recovered and utilized without the typical complications of an ?acid gas? stream process. Additionally, a portion of the final fully oxidized product can be looped back to the first step as the oxidizing agent. This process will be described in detail and compared to existing technologies in the area of energy efficiency, and off-gas environment treatment energy requirements.

Jan 1, 2008

By Christoph Pichler

A special desulphurization slag accrues during the processing of iron ore to steel, which is needed to generate high quality steel. Sulphur removing is done by different technologies, but the most common one is the generation of a high sulphur containing slag by sulphur affine elements. Currently, this desulphurization slag is partly recycled, however, huge amounts are still dumped. To utilize this desulphurization slag for future purposes, a recycling process must be established. Therefore, first characterization of this material started some years ago at the Chair of Nonferrous Metallurgy, Montanuniversität Leoben. Subsequent trials in lab scale size were performed, also some investigations for different treatment steps were evaluated, starting with a parameter study in a hot stage microscope at various gas-atmospheres. Finally, the developed recycling process concept was verified in pilot scale trials to confirm the new recycling technology. Due to the successful treatment process, also a patent was applied.

By Zhang Yongzhu

The metallogeneticy and mineralogy of three types of Chinese refractory gold deposits (Au-As; Au-As-MeS; Au-As-C) which are somewhat different from those abroad are discussed. The modes of occurrence, the distribution of grain size, and the morphological features of gold in minerals and their influences on gold recovery by direct cyanidation are also discussed. According to the mineralogy of gold and minerals, bacterial leaching, pressure leaching and roasting technology are suitable for the pretreatment of arsenopyrite-Au, pyrite-Au and carbonaceous-clay-Au refractory gold ores prior to cyanidation, respectively. The most important sulfide pyrite bearing much gold is difficult to be oxidized, its crystalline structure, conduct-types , and minor elements in different mineralizing stages are also discussed. The pyrite aggregates in different deposits are very complicated and much different. Gold grade of arsenopyrite is much higher than that of pyrite for some deposits which have a high correlation coefficient of Au vs As.

Jan 1, 1992

By Viktor Ashikhin, Pavel Arkhipov, Yurii Zaikov

"Lead alloys electro-winning from chloride melts was under investigation. Impurities concentration in cathode lead is strongly depended on temperature, electrolyte composition, anode current density. The equilibrium electrode potentials of lead-antimony alloys with the various content of electropositive metal in the alloy were investigated in the wide temperature interval. Thermodynamic properties of Pb-Sb alloys containing 20-95 mol% of Pb were studied by EMF method in temperature interval 723-873K in molten mixture of potassium and lead chlorides. Partial and integral thermodynamic characteristics were calculated. Small negative deviations from Raul’s law were found. Anode processes were investigated. The lead dissolution was found to be the only process in certain interval of current densities and electropositive metal content in alloy.IntroductionAt present human race is facing the problem of pollution by lead and its compounds and also the pollution influence on population health all over the world. One of the solution ways is the recycling lead containing technical wastes by ecologically clean technologies.World scientific community pays much attention to the electrolysis of molten salts. The usage of salt mixtures, as electrolytes, discovers new possibilities in the production of metals, metal compounds and alloys. ?????????? of the electrolysis at the temperature 50 - 200 °? above the melting temperature of chosen salt mixture allow to unbreaks processes, that undergo in the pre-electrode layer. The rate of the electrodepositing of elements are much higher than in the water electrolytes. At present there are technologies developed for production of metals (Ta, Nb, Ti, Zr, Hf, Ca, Al, Mg, Be, Li and others) by the electrolysis of the melts. Electrolysis of melts might be used in order to convert different technological formations containing lead and other nonferrous metals, that produced by different enterprises. According to the level of the influence on the living organisms lead is in the group of highly dangerous substances alongside with arsenic, cadmium, mercury, selenium, zinc, etc. Toxity and ability to accumulate in the human organism are two main sources of danger for the human being."

Jan 1, 2008

By Riyad N. Ahmad-Bitar, Shadia J. Lkhmayies

"CdSi-xTex thin films were prepared by first producing CdS:In thin films by the spray pyrolysis (SP) technique and then annealing the films in the presence of Te vapor in nitrogen atmosphere. X-Ray diffraction (XRD) measurements showed that the films are polycrystalline with the wurtzite structure. Transmittance measurements were recorded at room temperature in the wavelength range 400-900 nm and used to deduce the absorbance. The first derivative of the absorbance was calculated and used to find the values of the bandgap energy, where more than one bandgap was obtained for each film. These results show that the films are inhomogeneous or the composition differs with location. The photoluminescence (PL) was recorded at T = 60 K and a deconvolution peak fit was performed for each spectrum. The results of the PL spectra are consistent with those obtained from the first derivative and confirm the inhomogeneity of the films.IntroductionPolycrystalline thin film CdS/CdTe solar cells are promising candidates for low cost and high efficiency photovoltaic applications. The CdS/CdTe interface plays an active role and a detailed knowledge of its properties is crucial for thorough understanding of the device. High efficiency devices have been obtained in spite of the large lattice mismatch (9. 7%) between hexagonal CdS and cubic CdTe. Interdiffusion at the CdS/CdTe interface is considered to affect the performance of the devices [1]. The formation of a mixed crystal or a graded layer at the interface causes a reduction in the lattice mismatch at the CdS/CdTe junction [2] and then a reduction in the number of interfacial states and recombination centers, thus enhancing the solar cell performance [3, 4].The objective of this work is to investigate the transmittance, photoluminescence (PL) and structure of CdSi-xTex thin films prepared by annealing the spray-deposited CdS:In thin films in the presence of tellurium vapor. X-ray diffraction (XRD) was used for exploring the structure. Transmittance is used to deduce the absorbance where its first derivative was used to find the bandgap energy which varies with composition. The evolution of the PL spectra as functions of tellurium concentration was evident and it confirmed the inhomogeneities of the films."

Jan 1, 2011

By E. A. Trillo, L. E. Murr, R. D. Flores, J. C. McClure, B. M. Nowak

Complex vortex and swirl-like solid-state flow phenomena have been observed in the residual microstructures characterizing the friction-stir welding (FSW) of copper to 6061 aluminum; 2024 aluminum to 6061aluminum,2024 aluminum to 1100 aluminum, 2024 aluminum to 7039 aluminum and 2024 aluminum to 2195 aluminum. These flow phenomena are characterized by intercalation lamellae composed of dynamically recrystallized grain structures of the dissimilar metals which provide a super-plastic-like mechanism for the FSW flow in the solid state; there is no melting and temperatures at the weld center do not exceed about 0.8 TM (where TM is the absolute melting temperature (K)). In experiments to be described and illustrated, optical or light metallography (LM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques are utilized in examining residual FSW microstructures corresponding to tool rotation (stirring) speeds ranging from 400 to 1200 rpm, and traverse (or actual welding) speeds of 1 to 2 mrn/s.

Jan 1, 1999

By Y. C. Avniel, T. E. Warner

"It is important to be able to measure sulphur and nitrogen in molten iron and steel on-line. Unfortunately, there are no solid electrolytes which are stable under oxidising conditions and in which the ions of these species are mobile. In this paper, novel applications of beta alumina electrolytes are described and the results compared with data in the literature. Excellent agreement was obtained confirming this approach as a viable method of detecting elements whose ions are not mobile in solid electrolytes.IntroductionIn the past two decades, the rate of many processes in steelmaking have increased substantially. The sophistication of chemical analysis has also increased but analytical equipment is frequently positioned a significant distance from the operating plant which dictates that time is spent taking a sample, sending it to the analytical facility, preparation of the analytical sample prior to insertion into the equipment. In many cases, the time taken for analysis can exceed the time taken for the actual process and is now the rate defining step. Furthermore, most analytical methods are unable to distinguish between the amount of element which is dissolved in the steel and that contained in precipitates. Even if the analytical equipment could separate these two, the distribution would have changed between the molten steel and the cast sample. It would be an advantage to analyse on-line for impurities in molten metals."

Jan 1, 1997

By C. Gasparrini

Mineralogy may be applied to the selection of appropriate separation techniques, as well as to assist in the evaluation of problems causing loss of metals and other economically important elements during plant processing. Mineralogic studies may thus help develop techniques to optimize metal recoveries. The present paper describes how such factors as the minerals in which the elements of interest are concentrated, their chemistry, the chemistry of the associated minerals, grain size and textural associations with other minerals in the ore, may affect decisions on separation techniques for the recovery of economic elements. A number of case studies are described in which the mineralogical observation of ore samples has revealed the cause of problems experienced in the extraction of select precious and base metals, or has been decisive in the choice of appropriate techniques for recovery.

Jan 1, 1981

By M. Tokumasu, T. Mutoh, Y. Sugawara

"In October 1986, a process computer was introduced in order to achieve an optimum combustion of pulverized coal at the reverberatory furnaces. The secondary combustion air volume is controlled based on the nitrogen oxide concentration of the off-gas from the reverberatory furnaces. The carbon monoxide concentration has strong relation with the concentration of nitrogen oxide under the situation of using alternative fuels, such as chipped tires and p,ulverized coal. Using this computer aided combustion control system, both nitrogen oxide and carbon monoxide concentrations were stabilized and conventional monitoring and controlling apparatuses were absorbed into this computer system. Due to this easily operated system, labor cost was reduced and the operation of the reverberatory furnaces and the off-gas treatment plant became stable.IntroductionOnahama Smelter and Refinery started its operation in April 1965 as a large scale copper smelter and refinery in Japan. The green charged reverberatory furnaces were introduced and bunker C oil was chosen as the fuel for the reverberatory furnaces. After the oil crises, Onahama was forced to use cheaper fuels such as coal and waste tires, i.e., alternative fuels instead of the expensive oil. As the amount of the alternative fuels fed to the reverberatory furnaces increased, the concentrations of nitrogen oxide and carbon monoxide in the off-gas became unstable. Consequently, the fluctuation of the combustion condition became not to be negligible in view point of a combustion efficiency and pollution regulations. A process computer has been introduced to overcome these off-gas troubles and to reduce the operating cost of the smelter.Outline of Operation HistoryInitially, the operation started by one reverberatory furnace and then the capacity was expanded almost twice by additional furnace in December 1972. As shown in Figure I, the smelting throughput was depressed after oil crises in 1973 and 1978. From 1983 to 1985, some copper mines stopped their operations because of low price of copper metal. During this period, Onahama suffered from the shortage of concentrate production levels were depressed."

Jan 1, 1989

By Carl W. Dalrymple

A wide variety of contaminants (heavy metals, suspended solids, colloids, oils, organics) have been successfully removed from wastewater using an electrocoagulation process. An innovative electrocoagulation system is described. This process involves a procedure which subjects dissolved and suspended wastewater contaminants to the simultaneous addition of metal ions in the presence of direct current. During the treatment process Ionic and other charged particles in the wastewater are neutralized with oppositely charged ions generating the coagulation of contaminants: The process Is called CURE, and' presented here with application to wastewaters containing mainly heavy metals.

Jan 1, 1995

By W. G. Davenport

H20 is present in many flash furnace inputs. Examples are: (a) moisture in concentrate and flux (b) humidity in blast (c) moisture in hydrocarbon fuel, particularly coal, Appendix IV. H20 may also leak into the furnace from damaged water-cooling jackets. H2O, especially that it be included H2O, exerts a strong cooling effect on the flash furnace. It is important our calculations. As will be seen from the calculations, gaseous and liquid H2O both increase flash furnace industrial oxygen and oil requirements. This is because gaseous H2O (humidity in blast) must be heated from its input temperature to the flash furnace off gas temperature. Liquid H2O must be evaporated and heated.

Jan 1, 2001

By Xiang Lan

A strain of Thiobacillus ferruuxidans No. 8 was isolated from the acidic mine water of an arsenopyrite deposit, South China. It has been found from the experimental results that the growth of bacteria was inhibited by flotation agents. The order of toxic effect of different flotation agents on the growth of Thiobacillus ferrooxidans is ethyl xanthate > butyat ammonium aerofloat > butyl xanthate ? isobutyt xauthate >? flother No. 2 oil. The bioteaching treatment of arsenic and antimony-bearing gold concentrate in Longshan mine, Hunan province, China, was influenced considerably by the presence of flotation agents. The possible causes of the influence of flotation agents were discussed and an improved method was suggested.

Jan 1, 1991