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By Na Wang, Chao Du, Yao Zhang Shuqiang Jiao, Hongmin Zhu

"Na2NbAlO5 was synthesized using Nb2O5 and NaAlO2 as raw materials in molten NaCl-CaCl2 by a solid reaction. With an addition of sodium into the melts, Na2NbAlO5 was subsequently reduced to form NbAl3 intermetallic compound with a particle size of 50-300nm.IntroductionThe intermetallic compounds of niobium aluminides have been a subject of research interests as high temperature materials because of their properties such as high melting temperature, large specific strength at elevated temperature, good resistance to high temperature oxidation, low density and large ductility [1,2]. They are applicable for turbine blades in aircraft engines and stationary gas turbines [3,4].In recent years, the methods of powder synthesis have been widely discussed. There are many methods to synthesis intermetallic compounds such as conventional melting and solidification [5], powder metallurgy [6,7], reaction sintering [8] and reaction sintering with prior mechanical activation [9,10]. There is a prominent weakness in such methods that they use metal to produce intermetallic compounds by the means of diffusion reaction. Although the metal can diffusion sufficiently, it is still hard to avoid maldistribution of the constituents which impairs the properties of the materials."

Jan 1, 2012

By Sesha S. Srinivasan

Mechanochemical synthesis has been employed to prepare new light weight complex borohydrides, Zn(BH4)2. The thermal calorimetric and gravimetric analysis of these complex borohydrides shows the hydrogen decomposition temperature (Tdec) of about 100° C with theoretical capacity of ~8.0 wt%. This advanced materials based technology is considered to be suitable for attaining the US-DOE grand challenge technical targets. The powder x-ray diffraction analysis of the mechanically milled Zn(BH4)2 exhibits the presence of zinc borate and NaCl phase. The FTIR spectra of BH4-ion in NaBH4 has a characteristic band at 2290 cm-1,whereas in Zn(BH4)2, it occurs at ~2061 cm-1 (bridging B-H bonds) and ~2451 cm-1 (terminal B-H bonds) as well. The reversibility of hydrogen decomposition and recombination process is carried out by PCT measurements with multi-cycling procedure.

Jan 1, 2006

By Xiyun Yang

Magnetite was prepared by hydrogen reduction method. For a conversion to cobalt-modified magnetite, magnetite particles were suspended into a solution containing Co2+ and Fe2+ to precipitate a cobalt ferrite layer on the surface. pH value influences the particle composition directly, the desirable CoFe2O4 is obtained when pH value is 12. The coercivity increases with the increase of cobalt content, cobalt efficiency reaches a maximum value at cobalt content of 2.71wt%. With cobalt modification, magnetite particles have similar lattice constant and squareness ratio to that without cobalt modification. TEM and XPS analyses indicate that acicular morphology is retained during the coating process, the epitaxial growth layer consists of CoFe2O4and 0.3Co2O3CoFe2O4 at cobalt content of 2.71wt% and 5.03wt%, respectively.

Jan 1, 2006

By R. M. Luna-Sánchez

Electrochemical studies, particularly Evans? diagrams, have been employed in hydrometallurgy to simulate and explain the redox phenomena that take place at mineral and metal surfaces during operations such as leaching and cementation. However, despite their utility, in some cases, the combination of the cathodic and anodic branches, determined separately, does not reproduce the chemical environment present when both processes occur simultaneously on a specific surface. In the present paper, limitations of Evans? diagrams are analyzed through two examples: silver sulfide cyanidation and gold cementation on zinc. In both cases, the surface kinetics are sensitive to the local pH and cyanide levels. When the electrochemical oxidation of silver sulfide or the reduction of gold are performed in the absence of its corresponding redox reaction, the local pH obtained does not simulate the real situation and the combined reaction kinetics may be very different from those determined from the Evans? diagrams.

Jan 1, 2003

By Fuming Wang, Lifu Hu, Changrong Li, Ruipeng Pang

The solidification structure of 430 ferritic stainless steel has been calculated in the solidification process by using 3D-CAFE model under the condition of water cooling. The calculated results consistent with those obtained from experiment. Under watercooling condition, the solidification structure consists of chilled layer, columnar grain zone, transition zone and equiaxed grain zone

Jan 1, 2015

By John Sakala, Jeyapandian Sasikumar, Sydney Kwalela

The Isasmelt Furnace was commissioned in September 2006 with a concentrates treatment capacity of 850,000 tonnes per annum. However, the converter section became a bottleneck to the high throughput. Over 25% of the Isasmelt Furnace down time was attributed to lack of converter space. Factors that affected converter operations were low tuyere line campaign life (an average of 150 blows), high reverts generation, low conversion rates, and high converter cycle time. As a result of efforts carried out to improve converter operation, the average campaign life has increased to over 250 blows and reverts generation has been reduced from 22% of concentrate treated to 15%. Blister copper conversion rate has increased from 15 tonnes per hour to 19 tonnes per hour and blowing time per cycle has been reduced from 5.7 hours to 4.7 hours.

Jan 1, 2012

By Haldun Kurama, Cenk Karakurt, Ilker Bekir Topçu

"The usage of binders or pozzolanic materials in the production of concrete is not new. However, in recent years, the use of the pozzolanic siliceous material such as natural zeolite and coal combustion ash (CBA) has received re-attention due to the generated considerable interest in the economical use of both naturally occurring raw materials, recycling of the waste material and saved energy. In this study, the potential and utilization opportunities of natural zeolites and bottom ash (BA) in concrete applications were reviewed. Case studies, conducted to determine the possible usage of the natural zeolite and BA in concrete production, i.e. light weight concrete (LWC) were also presented. The physical and mechanical properties of cured concretes were examined to find out the competitive material usage on the final product properties. Autoclaved aerated concrete (AAC) with 1.1 nm tobermorite (5CaO 6SiO2 5H2O) as binder is a lightweight construction material that mainly uses in place of concrete to manufacture various building materials, including blocks, panels, slabs and the like. The material is a mixture of sand, lime, cement, gypsum, water and an expanding agent, which causes the raw material to rise like bread dough, with countless small air pores. AAC can be molded and cut into precisely dimensioned units and cured in an autoclave, which steam cures the concrete under pressure. During this process, the ingredients combine to form the calcium silicate hydrate gels that establish the special properties of the finished product. The process produces a material that is only one-fourth to one-third the weight of a conventional concrete block (bulk density of 400-800 kg /m3) of the same size. Regular AAC offers considerable advantages over other construction materials such as high thermal and sound insulation, excellent fire resistance, high resource and energy efficiency, low environmental impact, and finally outstanding structural performance (especially for earthquake zones) [1]. Its lightweight also makes it easy to use during construction, and its aerated structure gives it better thermal insulation and sound absorption properties than conventional concrete."

Jan 1, 2008

By W. G. Davenport

This chapter shows how flash furnace industrial oxygen and oil requirements are affected by different: (a) product temperatures (b) conductive, convective and radiative heat losses (c) electrical energy inputs (d) hydrocarbon fuels. The calculations of the chapter are all for production of 65% Cu matte from pure CuFeS2 concentrate. Blast temperature is? 298 K throughout.

Jan 1, 2001

By C. Peter Hayes

The world continues to change and with it the supply of minerals and metals, the location of centres of production of primary metal and the increasing levels of metals and materials recycling. New technologies are being developed to meet the ongoing search by industry for lower costs, cleaner production and new markets. To keep abreast with these changes, and to utilise fully, the potential benefits of these technical advances, the industry will need a professional workforce having different knowledge, skills and professional attributes than in the previous millennium. What are these skills and attributes? How to best attract and develop the metallurgists of the future, and provide for the ongoing educational and research needs of the industry?

By Karl-Heinz Daum

Outokumpu Lurgi Metallurgie GmbH, Oberursel, Germany ? give saleable by-products, ? not interfere with smelter performance, ? treat all gas streams simultaneously, and ? comply with environmental regulations. The latest developments in sulphuric acid plant design are presented.

Jan 1, 2002

By Sergio N. Monteiro

Polymeric matrix composites reinforced with coir fibers are being used in many industrial applications such as automobile interior panels and cushions. These composites have relatively low mechanical strength due to the weak fiber/matrix interface. The objective of the present work was to investigate the effect of a surface alkali treatment of the curaua fiber on the mechanical behavior of polyester composites with different amounts of these fibers. The treatment, also known as mercerization, was performed with distinct concentrations, 0.1 and 10% of NaOH at 1 min and 1 hour, before incorporation of the coir fibers into the polyester composite. The results showed no significant change in comparison to similar untreated coir fiber composites. A microstructure analysis revealed that, in addition to reducing the hydrophilic characteristic of the fiber,the treatment also affects the surface morphology and impairs the fiber/matrix interfacial strength.

Jan 1, 2009

By C. M. Acuña

At the Chuquicamata Division of Codelco-Chile high arsenic concentrates are produced, which at the smelter are processed via the Outokumpu Flash Furnace and Teniente Converters to obtain copper mattes. In the case of the Teniente Converters the production of matte grade near white metal composition is a common practice since the eighties and provided in the pyrometallurgical route no appropiate measures are taken, penalties have to be paid because of arsenic content in the anodes. During smelting huge volume of slag is produced and elimination of arsenic by slagging at this step is not economically attractive. Although during fire refining is possible to eliminate arsenic by use of mixtures of calcium and sodium carbonates this alternative is expensive, takes long process time and decreases the lifetime of the refractory lining. In spite of these facts a reasonably way to control arsenic in metal, and therefore in the anode, is taking, action in the converting step. The effects of oxygen and arsenic content in metal, arsenic in white metal and basicity index of the slag upon the distribution coefficient of arsenic between metal and slag were investigated at pilot and industrial levels. The best results are obtained for metals around 7,000 ppm oxygen and 0.3 basicity index slag, which results in a 5.7 distribution coefficient for a 5,800 - 7,100 ppm arsenic content in white metal, 18%-24% CaO slag at 1473 - 1523K. Furthermore, no significant/visible refractory wear has been realized.

Jan 1, 1999

By Fatma Arslan

The lateritic nickel ore sample subjected to this experimental study was taken from Çalda ore deposit (Turkey) and contains 1.43% Ni and 0.105% Co. Mineralogical investigations showed that the ore sample contains asbolane, chromite, limonite, hematite, goethite, lepidocrocite, magnetite, serpentine, and clay type minerals together with chalcedon, quartz, calcite, and chlorite. In the acidic leaching experiments, the effects of temperature, acid (H2SO4) concentration, and leaching time on nickel leaching recoveries were investigated. Leaching recovery versus time curves showed a parabolic trend and increasing the temperature shifted that curves to the higher values. The dissolution of nickel from lateritic ore can be explained by a shrinking core model and the apparent activation energy was found as 47.34 kJ/mol in the range given by the literature. The highest Ni and Co leaching efficiencies as 90.2% and 96.8% respectively were obtained at 80°C temperature, 200 g/L H2SO4 concentration, and 8 hours of leaching time.

Jan 1, 2006

By W. K. Tolley

The Bureau of Mines is investigating hydrometallurgical processing techniques to recycle metals from semiconductors and other advanced materials. Cadmium and tellurium were recovered from CdTe scrap produced in the manufacture of infrared optic devices. Sulfation, ferric chloride leaching, and oxygen-pressure leaching have been tested. Cadmium dissolution was achieved using oxygen-pressure leaching in dilute sulfuric acid. However, no satisfactory scheme for dissolution of the higher valued tellurium has been devised. Leaching the ground CdTe for 75 min at 110°C in 1.1M H2S0, under 120 psig 0, yielded 99.5% Cd extraction. Tellurium remained in the leach residue as TeO, and elemental tellurium; residual cadmium was less than 0.5%. The cadmium in the leach liquor was purified of coextracted metals such as gallium and iron by adjusting the pH. The cadmium was recovered as cadmium sulfate crystals by evaporating the solution. Recovery of by product metals, notably gallium, is possible.

Jan 1, 1991

By N. Solak

CrN, TiN and Ti-B-N coatings were deposited onto H13 hot-working tool steel and alumina substrates by arc-PVD. The coatings were characterized with respect to their mechanical and structural properties. Oxidation behavior of the coatings on alumina substrates was investigated by TG/DTA. Samples coated on H13 substrates were oxidized in a tube furnace under atmospheric conditions at specific temperatures determined from TG/DTA tests of the same coatings deposited on alumina substrates. The oxide scale morphology was characterized by scanning electron microscopy and X-ray diffraction. Oxide scale thickness change and TG data were used to calculate oxidation reaction activation energies. It was determined that boron addition into TiN coating improves not only mechanical properties but also oxidation resistance. Depending on the substrate material different oxidation activation energy values for the TiN and Ti-B-N coatings were determined revealing the importance of film morphology on oxidation resistance.

Jan 1, 2006

By C. M. Iheagwara

An overview of the scope and ramifications of scrap recycling in the Nigerian metallurgical industries has been presented in this paper. The modern state-of-the-art processing techniques and the operational strategies employed in the recycling plants are discussed. Optimization techniques for cost effective recycling operations are highlighted. As new units within existing metallurgical plants and new metal working plants approach commercial operations, expansion of existing recycling plants and the emergence of new ones have been showing to hold the key to their profitability from the raw material standpoint. The present economic predicament of the entire industrial sub-sector, lack of sufficient foreign exchange to procure new machineries and the emergence of a maintenance culture have triggered a phenomenal increase in the number of spin-off industries which depend on metal recycling activities. This, it is argued, widens the horizon for scrap processing/recycling.

Jan 1, 1992

By D. M. Hausen

Microscopic point-counting of polished sections, in combination with x-ray diffraction analyses of representative whole rock samples, provides an efficient means to compare the modal mineralogic composition of different rock types. Major gangue minerals, e.g., quartz, feldspars, micas, amphiboles, chlorite, clays, etc., are estimated semiquantitatively by x-ray diffraction techniques, utilizing optimum grind, gridded sample surfaces and a sample spinner during scanning. Opaque to semi-opaque oxide and .sulfide phases are estimated by microscopic "point-count" and "gross-count" scanning. Total mineralogic compositions are calculated and normalized to 100 percent from XRD and microscopic data by computer programming. Comparative mineral analyses for different rock types, as well as quantitative microscopic data for various parameters, including particle and crystal sizes, textures, degree of alteration, paragenesis, etc., provide useful guides in mineral exploration, both in early stages of geologic mapping and later stages of economic evaluation. Several case histories are described.

Jan 1, 1981

By Jian Li, S. Penttilä, P. Liu, W. Zheng, C. Bibby

"The materials selection for Gen IV supercritical water reactor in-core components faces major challenges due to severe operating condition. The current Canadian pressure-tube supercritical water (SCW) concept design requires core outlet temperature of 650 °C at 25 MPa with peak cladding temperature reaching as high as 850 °C. Aside from oilier challenges, there is currently very limited data on candidate stainless steels' corrosion resistance under this operating condition. Austenite stainless steels that include 316L, 304H, AL6XN and 3 l0S that cover a wide range of Cr contents are promising candidates for either direct in core applications or as base coating materials. However, their corrosion resistance has not been tested systematically under this stringent condition. In this study, these types of stainless steels are tested, and their corrosion resistances are compared.IntroductionThe Canadian pressure-tube supercritical water (SCW) concept will operate at a core outlet temperature of 650 °C at a pressure of 25 MPa, with potential peak cladding temperature reaching as high as 850 °C. High-temperature corrosion resistance is one of the key design requirements for fuel cladding components. As summarized by Allen [1 ], most testing to date has been carried out at temperatures below 730 °C. To date, SCW corrosion data above 600 °C is very limited. Even at relatively low temperature exposure to SCW (e.g. 500 °C), F/M steels develop a thick oxide layer rapidly, while some austenitic stainless steels develop thinner surface oxide. Ni based alloys appear to form very thin surface oxide, however pitting was observed in the vicinity of intermetallic precipitates [2-5]. Dissolution of major alloying components from all of these alloys could also pose significant problems for downstream piping [6]. Kaneda et al. [7] suggested some modified stainless steels provide better SCW general corrosion resistance, with no sign of SCC under the slow-strain rate test.Cho [8] suggested that as the Cr content increase, general corrosion resistance improved at 510 °C and 25 MPa. However, similar to Cho's work, most of the SCW corrosion resistance assessments were based on weight change measurement. This can be unreliable due to potential exfoliation of thick oxide film. Besides, there have been no systematic SCW corrosion resistance tests for candidate stainless steels under higher temperatures. SCW corrosion rate increase dramatically for alloys tested at 600 °C [1]. It is also important to understand the role of major alloying elements under this stringent operating condition, not only for fuel cladding components' materials selection, but also for coating materials development."

Jan 1, 2013

By Ralph P. Hackl

Bacterial leaching of the Doe Run Company?s cobalt/nickel-containing copper concentrate at low pH (pH 1.0-1.2) and high redox potential (>750 mV vs. SHE) enabled the cobalt and nickel to be preferentially dissolved over copper and iron due to the rapid passivation of the chalcopyrite component. Selective leaching of the cobalt and nickel was achieved with a mesophilic culture comprised mainly of Leptospirillum-like bacteria and Acidithiobacillus thiooxidans. This finding led to the conception of a novel hydrometallurgical process for passivating chalcopyrite and recovering the cobalt and nickel. The bacterial leaching process was tested extensively at the bench and pilot plant scales during 1997-1998. A pilot plant containing four leaching stages processed 30-40 kg/day of chalcopyrite concentrate continuously for 87 days. The cobalt extraction ranged from 75% to 86% during 6- and 8-day retention times respectively, whereas the copper extraction was limited to about 9%

Jan 1, 2003

By T. B. Braun

Cathode contamination is the principal factor affecting the quality of electrorefined copper. It is commonly accepted that annealability is unfavorably affected by the following elements, in decreasing order of adverse effect: tellurium, selenium, bismuth, antimony, and arsenic. Silver in cathodes has importance as it represents a nonrecoverable loss of silver to the refinery. Mechanisms for the contamination of cathodes by these elements are examined and the effect of operating variables on contamination, including anode composition, electrolyte composition, electrolyte temperature, addition agent practice, and electrolyte discard rate, are discussed.

Jan 1, 1976