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By S. N. Sinha

The distribution coefficients of lead and silver between copper and matte phases have been measured at two different temperatures. Experiments covered the ranges of 0.009-1.8, 0.07-0.13, and 0-11 wt pct lead, silver, and iron in matte, respectively. The distribution coefficients of lead have been measured at 1405 and 1505 K and correlated with lead and iron concentrations in metallic copper and matte. The values of the distribution coef¬ficient of lead between copper and iron-free matte, at infinite dilution of lead, have been determined to be 3.60 and 4,06 at 1505 and 1405 K, respectively. The distribution coefficient of silver between copper and iron-free matte is independent of silver concentrations and has been measured to be 2.13 and 2.21 at 1400 and 1500 K, respectively. For an iron-bearing matte, the distribution coefficient of silver has been correlated with iron concentration in the matte at both 1400 and 1500 K. From the measured values of distribution coefficients, the Raoultian activity coefficients of PbS and AgS0.5 in copper-saturated matte have been calculated. At infinite dilution, the following equations correlating the Raoultian activity coeffici¬ents of PbS and AgS0.5 with matte- composition and temperature have been obtained: log Y° PbS =1.515 + 1080/T 0.14 NFes lbS Fog YAgS = -0.074 - 425/T + 0.09 NFes. - 0.5

Jan 1, 1983

By N. Kanari

Kinetics of the carbochlorination of Cr2O3 has been studied with C12+CO gas mixtures between 500 °C to 900 °C using thermogravimetric analysis. The apparent activation energy is about 100 kJ/mol. Mathematical fitting of the experimental data suggests that the shrinking sphere model is the most adequate to describe the carbochlorination mechanism of chromium oxide and that is controlled by the chemical reaction. In the temperature range of 550 "C to 800 OC, the reaction order is about 1.34 and is independent of temperature. Changing the C12+CO content from 15 pct to 100 pct increases the reaction rate and does not affect the reaction mechanism. Similarly, changing the ratio of C12/(Cl2+CO) from 0.125 to 0.857 do not modify the carbochlorination mechanism of Cr203. In these conditions, the reaction rate passes through a maximum when using a chlorinating gas mixture having a Cl2/(C12+CO) ratio of about 0.5.

Jan 1, 1998

By Jorge Alberto Soares Tenório, Denise Crocce Romano Espinosa, Viviane Tavares Moraes

"The development of mobile phone technology has increased the replacement of outdated equipments for more modern models, transforming disposal of such devices into a serious environmental problem. Recycling appears as an attractive alternative to minimize the environmental impact of disposing such large quantities. Recycling can be accomplished by treating the printed circuit boards of used mobile phones by using the same techniques used in ore treatments with hammer mill; magnetic separation, electrostatic separation and grain size range. Before performing the recycling process a PCB characterization was performed to identify the fraction with the higher metals concentration/content. This study demonstrated that the electrostatic separation was not the best metals concentration of PCB aiming the recycling, while the non-magnetic residue had presented a more significant metal concentration. Furthermore, after the magnetic separation was possible to separate the following metals: iron and nickel.IntroductionPortable electronic devices have gained increasing acceptance over the last decades. Mobile phones sales in Brazil, for instance, have reached 104 million in 2007, and 128 million in 2008. It is estimated that, around the world, 100 million mobiles are thrown away every year, either because of loss of functionality or because newer models are launched in the market [1,2, 3]. Printed circuit boards in mobile phones are made of many materials, with approximately 83% in weight being metals and fiber-glass, and the balance being plastics pl. Several metals can be recovered from the electronics waste, such as copper, tin, iron, lead, nickel, titanium, aluminium as well as some precious metals such as gold, silver and palladium [4, 5, 6, 7, 8]. Concurrent with the increasing world demand for copper, there average metal content in ores has been decreasing. Economically interesting copper mines used to have 4% metal content, whereas presently, such content is around 1%, i.e., for every 1 ton of ore extracted, only 10 kg are copper [9, 10]. Approximately 33% of printed circuit boards (PCBs) composition is copper, that is, for every 1 ton of PCBs waste, 330 kg are copper [1]. Research in recycling PCB waste focuses on mechanical, electrometallurgy, pyrometallurgical and hydrometallurgical processes [3, 8]. Collecting and recycling obsoletes electro-electronic equipments is very important these days, in order to, not just preserve the non renewable natural resources but also to keep the environment and the population safe from the pollution caused by the toxic materials and heavy metals present in this kind of waste."

Jan 1, 2011

By Shadia J. Ikhmayies

"Tin oxide (SnU2) thin films of thicknesses in the range 100-600 nm were prepared on glass substrates by vacuum evaporation at ambient temperature. The films were characterized by transmittance measurements, X-ray diffraction (XRD), scanning electron microscope (SEM) observations and energy dispersion X-ray analysis (EDAX). It is found that the films have high transmittance and non sharp absorption edges. XRD diffractograms showed that the films are amorphous and the SEM micrographs showed that the surfaces are smooth, uniform and well covered with the material. The EDAX analysis showed that the films are deficient in oxygen. Indirect optical bandgap energy and Urbach tailing in the bandgap was observed, and the width of the tail, which is related with disorder and localized states, was estimated.IntroductionTin oxide is an n-type wide bandgap semiconducting material with a direct bandgap energy of 4 eV and an indirect bandgap of 2.6 eV [1], where inherent oxygen vacancies act as an n-type dopant [2], Tin oxide thin films have been used for transparent electrodes in photoelectric conversion devices namely amorphous silicon solar cells, liquid crystal displays, gas discharge displays, etc. [3]. Perfectly amorphous thin SnO2 films show good electrical response to reducing gases in air and could, hence, be applied to construct semiconductor gas sensors where the metal oxide films function as a monograin-eqivalent active layer [4]. Amorphous SnU2 can also be used in extended gate field-effect transistors (EGFET) as a pH sensor, where the sensitive part is made of the SnO2/Al structure. This device can be used to detect and to quantify any kind of substance that can produce or consume protons, like an enzymatic reaction, therefore showing a large range of applications as biosensors [5].There are different methods to prepare SnO2 films, such as atomic layer deposition (ALD) [6], reactive magnetron sputtering [7], chemical vapor deposition [8, 9], dip coating [10], spray pyrolysis (SP) [3, 11-14], and evaporation [8], The thermal evaporation method was chosen to produce SnO2 thin films in this work because deposition by this technique does not present any compositional problems. In addition, it is a low temperature technique, which increases the probability of producing amorphous films. To increase this probability, the films were deposited at ambient temperature."

Jan 1, 2012

By Masahiro Yoshimura, Sergiy Korablov

"Hydi-othermal corrosion ofTiN, TlAlN and CrN PVD films (3 µm thick) deposited on SUS-304 substrate was studied in 100MPa water in 20-950°C temperature range up , to 750h. The beginning temperature of their reaction was determined as 200°c for TiN and TiAlN and 500°C for CrN films, which are quite low in comparison with that of air oxidation of those powders. Very thin oxide scales. of TinO; n-I homologous series phases were formed above 300°C. TiO2 anatare. is observed for TIN and TiAlN films at 400°C. The· feature of hydrothermal corrosion of CrN films seems to be CrNxOy phase formation.Distinguishable weight changes were observed at higher temperature than 700°C for TiN, 750°C for· TiAlN and 800°C for CrN respectively. Hydrothermal corrosion kinetics .was constructed to calculate the activation energy of hydrothermal corrosions. On the base of obtained data, hydrothermal corrosion resistance was as follows: TiN – TiAlN - CrN. Facetted oxide crystals were formed at higher temperature than 500°C for TiN, TiAlN and 850°C forCrN.IntroductionThe metallic nitride (TiN; TiAlN, CrN) PVD films have high hardness, strength and wear resistance. Therefore these films are widely used in industry for wear resistij.nce application such as cutting tools and die molds. Their performances depend on not only the mechanical properties but also corrosion resistance of coated films. High temperature oxidation of metalliq nitride and nitride films was well studied [1-5]. However there are no reliable data concerning the .corrosion resistance of coated nitride materials. In high-temperature and high-pressure water. There are a few reports on hydrothermal corrosion of nitride films [6,7]. The increase of corrosion resistance of CVD films was observed in following succession TiC - TiCNO - TiCN - TiN at 300-680°C temperature interval and I 00 MPa pressure water according to data of the first report. Kawana et al. [7] have reported about excellent corrosion resistance of CrN films under 290°C and 8, 6 MPa water during I 000 h in the circulating type experimental loop. The films thickness was about 7-10 µm in both cases. However it remains unclear the chemical state of the surface species and especially in-depth distribution, oxide scale thickness and its growth, and defects formation in the oxide film."

Jan 1, 2000

By C. Alexandru Sonoc

Donnan Dialysis uses ion exchange membranes to extract and separate cations. The driving force is provided by differences in chemical potential, rather than by electric fields or pressure. A Donnan Dialysis based process to recover lithium, nickel, cobalt, manganese, and organic acid lixiviant from recycled lithium ion battery cathodes is under development. In this paper we present a model of Donnan Dialysis and results of simulations of the aforementioned process. The simulations show that 170 m2 of membranes can process 1000 L of leachate ([Li+] = 0.285 M, [Co2+] = [Ni2+] = [Mn2+] = 0.095 M, pH 2) in two days and recover 94.1% of the lithium (as lithium carbonate), 99.4% of the transition metals (as mixed sulphates ready for solvent extraction), and all of the organic acid using 423 mol of H2SO4 and 268 mol of KHCO3.

By T. A. George, David J. Sellmyer

"The concept of achieving a useful high-energy-product magnet through appropriate nanostructuring of known hard and soft phases has been tantalizing researchers since the idea was first proposed. The fabrication of exchange-coupled nanocomposite magnets faces several challenges including aligning the easy anisotropy axes of the hard-phase grains. Here we investigate experimentally two-phase nanostructures of hard Lio-ordered FePt and soft iron-rich/cc Fe(Pt). The Fe-Pt thin films were produced by epitaxial cosputtering onto MgO (001) single-crystal substrates which lead to strong (001) texturing. The measured hysteresis loops indicate nearly ideal exchange coupling. Excellent magnetic properties are obtained, with largest values of coercivity (51 kOe), saturation magnetization (1287 emu/ cm3, J, = 16.2 kG), and nominal maximum energy product (58 MGOe).1. IntroductionA key figure of merit for permanent magnets is the maximum energy product (BH)rrw.x. The achievable maximum energy product is determined by a magnet's saturation magnetization M, and its magnetic anisotropy. For example, it is well known that (BH)rrw.x :S 4n2M,2• In the past, record energy products have been the result of discovering new compounds with high values of magnetization and anisotropy. However, finding new compounds with better magnetic properties than the current record-holding magnet Nd2Fe14B has proven to be difficult. A different approach is to exploit the exchange coupling mechanism between known hard and soft magnetic phases to enhance the maximum energy product [1-5]. In such a composite system, high coercivity is achieved due to the anisotropy of the hard phase as well as a nanostructure which prohibits large-scale domain wall reversal mechanisms. Magnetization is enhanced by the soft phase and loop squareness results from texturing of the hard phase easy-axis as well as complete exchange coupling between the coexisting hard and soft grains."

Jan 1, 2012

By Mingming Zhang, Ramana G. Reddy

"Carbon dioxide (CO2) is one of the most common by-products produced during light metals production. It is considered to be the cause of greenhouse effects. Efficient reduction of CO2 can help minimize the rate of global warming and improving energy sufficiency. In this paper, a novel light metal production process was developed using ionic liquid electrolytes. This process has significant advantages compared to the traditional high temperature processes such as zero CO2 and CF4 emission, low energy consumption due to the low temperature operation and nonconsumable electrodes. Two types of anode materials (graphite, extruded carbon) were tested in electrolysis experiment. The results showed that both anode materials were stable (negligible weight loss). However, the extruded carbon was found to be superior to graphite in terms of current density and current efficiency. The calculated energy consumption for aluminum production was less than 10 kWh/kg at current densities up to 300 A/m2.IntroductionGlobal demand for ultra-light, ultra-strong, recyclable metals is growing as the world switches to low-emission vehicles, energy-saving devices and sustainable products. Aluminum demand is forecast to climb by 30 percent; magnesium demand by 200 percent, while for the emerging industrial light metal, titanium, the demand is expected to be at least double in the next decade. However smelting of light metals is the most energy intensive among all the steps of light metals production. For example, on an average it takes about 15.7 kWh of electricity to produce one kilogram of aluminum from alumina [1, 2, 3]. Advancements in energy efficiency have been steady, but slow, and most U.S. aluminum smelting production operates at 95% current efficiency. Besides high energy consumption, another major concern of the light metals smelting process is the emissions of greenhouse gases (GHG). Electrolysis green house gas emissions in the Hall-Héroult process can be split into three groups: 1) reduction reaction emissions, carbon dioxide (CO2) and carbon monoxide (CO); 2) process upset perfluorocarbons emissions; and 3) hydrogen fluoride (HF) formed from the moisture (H2O) present in the raw materials [2, 3]. Hydrogen fluoride gas can be captured and returned to the cells by the alumina dry scrubbing system used in modern facilities. A total of 5.31 kilograms of CO2 is generated from the reduction process for each kilogram of aluminum produced in the average U.S. primary facility. The perfluorocarbon emissions are related to the “anode effect.” If the concentration of alumina in the bath becomes too low, other reactions between the carbon anode and the bath occur and tetrafluoromethane (CF4) and hexafluoroethane (C2F6) are generated. These gases have high global warming potentials (GWP), which is a ratio developed to compare the ability of each greenhouse gas to trap heat in the atmosphere relative to carbon dioxide"

Jan 1, 2008

By Takeshi Ohgai, Hisaaki Fukushima, Tetsuya Akiyama, Joon-Seo Ki

"Recently, an intensive attention has been paid to the electrodeposition of Zn-Cr alloy in the field of the production of super-highly corrosion-resistant alloy plated steel sheets for the next generation. In this study the electrodeposition of Zn-Cr alloys from the sulfate baths was conducted to investigate the codeposition mechanism of Cr with Zn. As a result, Cr was codeposited with Zn at higher current densities in both polyethyleneglycol(PEG)-free and PEG- containing baths. However, PEG made it possible to reduce Cr+ to the metallic state and Cr existed in the form of Cr(III) hydroxide in the deposits obtained from PEG-free bath. The measurements of the partial polarization curve of Zn and the pH in the cathode layer revealed that PEG acted as a polarizer to shift the cathode potential to the reduction potential of the composited hydroxides of Zn and Cr formed due to the pH rise in the cathode layer.1. IntroductionRecently, much attention has been paid to the electrodeposition of Zn-Cr alloys because of its application to the production of super-highly corrosion-resistant alloy plated steel sheets for the next generation1Hl_ Some researches have already tried to commercialize this type of steel sheet. High corrosion-resistance of this steel sheet is brought about by codeposited Cr in the alloys. According to Piontelli's classification5l concerned with metal deposition from aqueous solution, Cr belong; to an inert metal and its deposition is associated with a large amount of hydrogen evolution. Therefore the current efficiency for Cr deposition is extremely poor. It has been also reported that Cr is unable to codeposit in the electrodeposited Zn film in the absence of a certain additive in the solution. 0-compounds group colloids7l, ether group organic compounds8), 9>, peptide based compounds10l, etc., have been found to be effective additives to induce the codeposition of Cr with Zn. However, few studies have been made on the codeposition mechanism of Cr with Zn. In this research, the fundamental electrodeposition behavior of Zn-Cr alloys from sulfate baths was investigated to clarify the codeposition mechanism."

Jan 1, 1998

By Anna Wasilkowska

The study concentrates on the effects exerted by microstructure, deformation history and uniaxial stress conditions (temperature, stress state, strain rate) on the mechanical properties offerritic TRIP-aided steels for automotive applications. In low-alloyed TRIP-steels it is quite difficult to separate the effect of the austenite to martensite phase transformation from the influence of the ferritic matrix contributing to the yield stress and uniform elongation. Investigation of transformation kinetics of retained austenite as a function of the deformation temperature show that using the parameter k to characterize the retained austenite stability allows to identify regious of different temperature sensitivity separated by a transition temperature of 10±5°C. The observed low strain-rate sensitivity of the flow stress is an intrinsic property of the ferritix matrix and points to defomtation governed by slip. The ultimate tensile strength is much stronger affected by temperature than the yield stress. The influence of the temperature on the elongation is complex, because of the heating of the specimens by 60-l20°C at moderate and high strain rates. The increase of the total strain can be understood in terms of thermal softening of the ferrite. On the other hand, the steep increase of the stress during dynamic testing is an effect of accommodated elastic and plastic strains in the matrix. The strain- hardening exponent is dependent on the conditions imposed during testing. The martensite transfomtation rate is lower and the critical stress for martensite nucleation is much higher under compression compared to tensile loading. In secondary tensile tests, the yield stress increases steeply, and the ultimate tensile strength and the total elongation depend linearly on the amount of pre-straining. The results confirm that in the range of 8=10-4 s-l the TRIP-effect governs room temperature plasticity. Keywords: TRIP-steels, mechanical properties, strain rate sensitivity, temperature sensitivity, austenite stability

Jan 1, 2003

By K. Narayana Swamy

The traditional approach to improving the operating efficiency of a metallurgical plant has been to study individual unit operations and focus on improving the poor-performing unit operations. The complex nature of most metallurgical plants call for a holistic approach that will consider the whole rather than just focus on the individual units of a plant. This holistic approach is part of the systems thinking principles. Numerous case studies highlight the importance of the need to apply systems thinking principles in improving the effectiveness of metallurgical operations. Improving the efficiency of one unit operation without considering its effect on the performance of other unit operations has in many cases lead to lower overall operational efficiency. Modeling and simulation are key to the application of the systems thinking principles. Standard flowsheet models are very useful in scenario analyses though they have to be supplemented with other models for useful predictions.

Jan 1, 2006

By M. I. Kalashnikova

Gipronickel Institute has developed the technology of treatment of difficult to concentrate sulphide Pb-Zn concentrates (Zn-19,9%, Pb-8,4%, Cu-0,34%, Fe-8,8%, Ba-6,8%, S-18,7%, Ag-106 g/tonne). The technology consists of pressure leaching, impurity removal from leaching solution, electrowinning and Pb-Ag containing cake treatment. Despite low zinc content in initial concen-trate the technology allows production of solution which is suitable, after standard procedure of impurity removal, for electrowinning with production of zinc grade SHG. Comparing to the standard technologies the flowsheet developed provides the lesser expenses per zinc unit because of decreasing of liquid to solid ratio at pressure leaching stage. The initial concentrate is characterized along with low content of principal metals by high con-tent of barite, which makes flotation of pressure leaching residue more difficult. That is why in this case the hydrometallurgical treatment was chosen. At optimal parameters of chloride leach-ing found during laboratory experiments the principal components extraction was 99.5% for Pb and up to 92% for Ag.

Jan 1, 2006

By Qingzhu Li

The adsorption process of Pb2+ from aqueous solutions by spent grains modified with Imol/L NaCI solution was investigated. The effects of solution pH, contact time, adsorbent concentration, initial Pb2+ concentration, particle size on Pb2+removal were also studied. The initial adsorption process was rapid and 90.35% of Pb2+ adsorption occurred within 30 min. The absorption equilibrium was obtained at 4h. When pH was 5.5, Pb2+ concentration in aqueous solutions decreased from the initial content of 20 mg/L to 0.0 I mg/L after 5 hours by application of IOg/L adsorbent at 25?C, Pb2+ removal efficiency reached up to 99.95% and the Pb2+ remaining in aqueous solutions was under China Sanitary Standard for Drinking Water (GB5749-85). Adsorption data fitted well with Lanf+muir and Freundlich models. However,Langmuir isotherm model was better to descnbe Pb- adsorplion than Freundhch model, mdlcatmg that the applicability of monolayer coverage of Pb2+ on the surface of adsorbent.

Jan 1, 2008

By Carlos Maurício Fontes Vieira

In the present work a ceramic body, fabricated using a mixture of clays and sand, for roofing tiles, produced in Campos dos Goytacazes, north of the State of Rio de Janeiro in Brazil, was characterized. Characterization was performed by X-ray diffraction, thermo analysis, chemical analysis, particle size distribution determination and plasticity. In addition, technological properties related to water absorption, linear shrinkage and flexural rupture strength were determined in samples fired at 700, 900 and 1100oC. The results showed that the investigated ceramic body has satisfactory plasticity and presents a refractory behavior during firing due to the predominantly kaolinitic nature of the clays.

Jan 1, 2006

By Jian Li, S. Penttila, W. Zheng

"Materials selection for Gen IV supercritical water reactor in-core components faces major challenges due to severe operating condition. Beside high-temperature mechanical properties, SCC and general corrosion resistance of commercially available materials are also major focuses in recent research. Recent reports suggest that certain types of surface modifications are beneficial to SCW corrosion resistance. In this study, the effects of surface modifications are investigated, and possible mechanisms for improved corrosion performance are discussed.IntroductionThe current Canadian pressure-tube supercritical water reactor (SCW) design specifies a core outlet temperature of 625°C under 25 MPa of pressure, with peak cladding temperature as high as 850°C. Challenges in materials selection include high-temperature mechanical properties, corrosion resistance, SCC resistance and radiation damage. Most of the SCW corrosion test results available are below 730°C. Early work by Allen [1] summarized the corrosion resistance of alloy groups including Ni-based super alloys, stainless and ferritic/matensitic (F/M) steels that can potentially be used for SCW reactors. F/M steels can only be used at low temperature sites (e.g. down stream piping). At 500°C and 25 MPa, F/M steels develop a thick but mechanically stable oxide layer. However, the long term stability of the surface oxide layer is largely unknown. Ni-based alloys appear to form very thin surface oxide, however pitting was observed in the vicinity of some intermetallic precipitates [2-5], and dissolution of major alloying components could pose significant problems for down stream piping [6]. In addition, concerns of Helium formation due to Ni transmutation prevented this alloy group to be used as fuel cladding. The corrosion resistant austenitic stainless steels (e.g. 316L) are found to be susceptible to localized corrosion such as pitting, intergranular attack and stress corrosion cracking (SCC) [7]."

Jan 1, 2012

By Dianyuan Dang, Guihong Han, Wenjuan Wang, Tao Jiang, Yanfang Huang

In this study reduction kinetics and swelling behaviors in "two-step process” were investigated by weight-loss technique and visualizing physical changes of pellet. Results showed that reduction degree (r) increased with increasing temperature and time. According to the dynamic calculation, when reduction temperature was lower than 1000°C the reduction process was controlled by chemical reaction with apparent activation energy of 72.27 kJ/mol. When reduction temperature was higher than 1000 , the equation of t/[1-(1-r)1/3] against [1+2(1-r)-3(1-r)2/3]/[1-(1-r)1/3] followed straight lines, demonstrating that reduction was mixed-controlled. Swelling experiments indicated that the maximum swelling index increased with the increase of reduction temperature and CO content.

Jan 1, 2016

By Helvio Pessanha Guimarães Santafé Jr.

The coir fiber extracted from the husk of the coconut has been extensively used as polymer composite reinforcement in a variety of industrial applications ranging from civil construction to automobile seat cushions. The hydrophilic coir fiber does not act as an effective reinforcement owing to its low interfacial strength with hydrophobic polymers. As a consequence, coir fiber composites display relatively low mechanical strength. The objective of this work was to investigate the effect of an acetylation treatment of the coir fiber surface on the mechanical behavior of epoxy composites with amounts of fibers up to 30% in volume. Coir fibers were immersed in an acid solution of acetic anhydride for one hour, washed and dried, before mixing with DGEBA/TETA epoxy to fabricate the composites. Flexural mechanical properties were obtained by bend tests. The results showed significant differences to similar composites with alkali treated coir fibers that have been previously investigated.

Jan 1, 2010

By Junmo Ahn

This study investigated leaching kinetics by alternative lixiviants for copper leaching from chalcopyrite (CuFeS2), the most abundant copper resource in the world. As a refractory sulfide mineral, chalcopyrite shows low copper extraction due to passivation on chalcopyrite surface. Also, decrease of copper grade with high portion chalcopyrite requires the alternative leaching procedure to increase copper recovery. Therefore, alternative lixiviants such as sulfurous acid and methanesulfonic acid (MSA) were tested for both concentrate and low grade ore to enhance copper extraction. Also, an oxidant, hydrogen peroxide, was compared to ferric to find out the improvement of leaching kinetic. In concentrate leaching tests, 30 g/L MSA showed the highest copper extraction (47%), compared to other lixiviants at 75 °C. Periodical H2O2 addition enhanced copper extraction, and above 90% of copper extraction was observed within 96 h by periodical addition of 0.6% H2O2 at 75 °C. The activation energy of chalcopyrite leaching by MSA and H2O2 achieved 40 kJ/mol, which is chemical reaction control. The results of low grade ore leaching tests indicates that no significant difference among lixiviants (H2SO4, H2SO3 and MSA) with ferric was observed, all of which achieved around 37% within 24 h at room temperature. However, significant increase of copper extraction (>80%) was observed at both 20 g/L MSA and 10 g/L H2SO4 conditions by the addition of 10% H2O2.

By Aureo D. V. Machado

An experimental study to obtain zirconia powders (ZrOz) from carboxylate zirconium solutions followed by hydrogen peroxide stripping and precipitation, has been carried out. Zirconium carboxylate was prepared by solvent extraction from a chloride aqueous phase using magnesium carboxylate as organic phase. The variables examined in the precipitation reaction were: Temperature: 25 - 90 ?C ? H202= concentration: 0.3 - 5% wt/wt - pH: 1 ? 9 Organic/Aqueous ratio (1/1) and reaction time (30 minutes) were maintained at constant levels. The optimum results (98% precipitation) were achieved at 25 °C, 5 % wt/wt H202=, and pH = 5. The precipitates were composed of large amorphous aggregates (<I00 micrometers). After calcination for 1 hour at 1000 OC, monoclinic ZrO2 with a large variation in particle size (1 -100 micrometers) was obtained.

Jan 1, 1991

By Toshiaki Tsuru, Takeshi Ohgai, Hisaaki Fukushima, Shigeo Kobayashi, Tetsuya Akiyama

"Electrodeposition behavior of Zn-Cr alloys from the methanol baths was investigated. In the methanol baths of low Cr3+ concentration, Cr (III) compound was incorporated in the deposits and no lusfrous Zn-Cr alloys was deposited. However, Cr was existed as metallic state in the deposits obtained from the baths of higher Cr3+ concentration. With an increase in water content in the baths, the chemical state of Cr in the deposits changed from metallic to trivalent state. Under the condition that metallic Cr can be electrodeposited, Zn deposition was significantly polarized to the potential of Cr deposition.INTRODUCTIONAn attention has been paid to Zn-Cr alloy plated steel sheet because of its excellent properties for body panels of automobile and electrical appliances [1]-[4]. This plating process can be operated using the sulfate solutions containing Cr3+ ion [1] - [6].In decorative single Cr plating, on the other hand, many attempts have been made to electroplate Cr from trivalent electrolytes, which is motived by environmental deficiencies of the presently used hexavalent process [7]. [8]. However, it has been reported that in the aqueous solutions the behavior of the electroreduction of 0 3+ is atypical due to the complicated nature of the chemistry and electrochemistry of cr3+ species [9]-[11]. Even in Zn-Cr alloy plating, it is difficult to codeposit metallic Cr with Zn in simple sulfate electrolytes [l]-[4], [12]. Therefore, it can be expected that the electrodeposition behaviors of Zn-Cr alloys as well as Cr are significantly changed when the electrodeposition is conducted in non-aqueous plating solutions.In this study, the electrodeposition of Zn-Cr alloy was conducted from methanol solutions to clarify the electroreduction mechanism of Cr3·-Cr0 in the alloy deposition process."

Jan 1, 2000