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By Ma Keyi, Yang Xianwan, Zhu Xiaoyun, Guo Zhongcheng, Zheng Yanping

"The oxidation of the Multifunctional Electrodeposited RE-Ni-WP- SiC Composites at high temperature is investigated. The results show that during high temperature oxidation the relationship between the mass change of pure Ni , Ni-W-P, Ni-W-P-SiC or RE-Ni-W-P-SiC coating and the oxidation time follows a mixed curve, i.e. it is approximately a linear relationship when the oxidation time is less than 60 mins while it is a power function relationship when the oxidation time is over 60 mins. The order for the oxidation rate of the four coatings is Ni> Ni-W-P> Ni-WP- SiC>RE-Ni-W-P-SiC. The mass change of Ni-W-P, Ni-W-PSiC or RE-Ni-W-P-SiC coating increases exponentially with a rise of oxidation temperature. The high temperature-oxidation resistance of RE-Ni-W-P-SiC composite coating is 3-4 times that ofNi-W-P alloy coating. The cross section morphologies and Xray diffraction patterns indicate that the high temperature oxidation resistance of RE-Ni-W-P-SiC composite coating is better than any other coatings.1. IntroductionWith the rapid development of modem industries the products in engineering industry are continually challenged by the requirements of long-term and stable working at higher temperature, pressure, speed and under adverse conditions. Consequently, the surface properties of the products, such as the resistance to oxidation at high temperature, the resistance to wear and the resistance to corrosion, should be improved continually."

Jan 1, 2000

By Bing Li, Miao Shen, Qiang Wang, Yuqi Chen

Electrochemical methods including cyclic voltammograms, square wave voltammograms, chronopotentiometry are applied to characterize the reduction potentials of Na+ and Li+ ions in LiCl-KCl melts. According to theoretical calculation, the reduction potential for Na+ is slightly more negative than Li+ in NaCl-LiCl-KCl melts at 450℃. However, by electrochemical measurements, the reduction potential of Na+ is slightly more positive than Li+ in the above melt and the potential difference between Na+ and Li+ reaches 0.16-0.2V on an inert W electrode in 1.0-2.0 wt% NaCl-LiCl-KCl melts. An active Pb electrode is used to improve the removal rate of Na+ from LiCl-KCl melts. The reduction potentials for both Na+ ions and Li+ ions on a Pb electrode shift to more positive values and the reduction currents become larger. After 6h electrolysis on a Pb electrode at -3.0V, the practical removal efficiency of Na+ ions reaches 90.12% and the reduced products contain metallic Na and Li with a Na/Li mass ratio of 4.25/1.

Jan 1, 2015

By K. P. Nishad

The origin of many casting defects can be traced at the mold filling stage. Entrapped air/gas pockets and oxide film formation are notable examples. In the present work, the mold-filling process is simulated using a mathematical model, built on a multi-physics based commercial package PHYSICA. The simulation code has the capability to solve multi-phase problems. The numerical model addresses a complicated dynamics of filling operation including free surface flow and subsequent flow behavior and is based on conservation of mass and momentum. The Free surface is modeled using the scalar equation method (SEM). The model is validated with benchmark experimental results from the literature. The role of turbulence and the pouring rate on variables affecting sites prone to oxide film formation are investigated using a simple but novel technique. Key findings of the work are presented.

Jan 1, 2006

By C. A. Nogueira, F. Pedrosa, F. Margarido, R. N. G. Guerra

"A hydrometallurgical process for recycling spent Zn-MnO2 batteries was developed, involving leaching with sulfuric acid, purification by precipitation and metals separation for further recovery. Leaching of zinc oxide was easily attained while for manganese oxide was rather difficult depending on temperature and acid concentration. At 90°C and with the liquid/solid ratio of 20 L/kg, more than 95% of zinc is recovered in 30 minutes with 0.5M H2SO4. To attain similar recovery for manganese, higher levels of acid concentration and time are needed (e.g 0.7 M and 2 hours). After leaching a purification step is necessary to remove iron co-dissolved through Fe(III) precipitation. Separation of zinc from manganese by solvent extraction with 1M DEHPA follows in the process route. The countercurrent multistage separation diagram developed allows the production of a zinc electrolyte with 120 g/L Zn and 0.005 g/L Mn, and a raffinate with 16 g/L Mn and 0.013 g/L Zn.IntroductionThe recycling of spent Zn-MnO2 batteries is carried out by dedicated recyclers using several process alternatives [1]. Most of the running processes use pyrometallurgical technologies [2] based on zinc distillation. Alternative treatments by hydrometallurgy have been reported [3-5] but its application is scarce.In order to contribute to the development of alternative solutions, a process for recycling batteries based on Zn-MnO2 systems has been studied. The process is based on the hydrometallurgical treatment of spent batteries in sulfuric acid media (Figure 1). The process starts with the physical processing by shredding using cutting grinders, where the batteries are opened and size reduced, allowing the liberation of the interior electrode particles or pastes. The fines can be then separated and the coarse material containing the steel scrap can be treated to remove the remaining aggregate electrode. The final scrap also contains some plastics and other non-metal materials and can be further valorized."

Jan 1, 2008

By Sven Reutzel

Investigations show that Co-based melts embedded by glass flux in a crucible can be under- cooled nearly as strong as samples processed containerlessly by electromagnetic levitation. This allows to measure magnetic susceptibility on undercooled melts while combining the use of a Faraday-balance and undercooling technique. The magnetic susceptibility of Co and Co-based alloys (such as Co-Pd and Co-Cu) is investigated as a function of temperature from superheated to undercooled state. This is done by measuring the change of magnetic force F, on a sample in a constant magnetic field Bo and an additional gradient field by means of a Faraday-balance. When liquid Co-based alloys are undercooled the magnetisation steeply rises if temperature approaches the Curie temperature. The magnetisation is measured for some Co-based alloys in liquid state as a function of alloy system and its concentration. The results show that the magnetic susceptibility of the liquid undercooled samples follows a Curie-Weiss behaviour, from which Curie temperature and magnetic moments for the liquid state are inferred.

Jan 1, 2002

By Xiao-hui Fan, Xu-ling Chen, Xiao-xian Huang, Gui-ming Yang

Grate-kiln-cooler is a predominant process of producing iron ore pellets in China. Since this process is of multi-variant, strong coupling and large hysteresis characteristics, a reliable performance monitoring is thus essential to ensure product quality and economic benefits. Aiming to efficiently monitor the pellet induration within this process, this study proposed an approach that combines statistical analysis and quality soft-measurement. Soft-measurement of pellet quality was accomplished based on the predicted time-temperature profile, and the soft-measured indices were on-line monitored using statistical control charts. Based on the proposed approach, a monitoring system for grate-kiln-cooler thermal process was developed for a domestic pelletizing plant. Running results demonstrate that our system can assist in the detection or diagnosis of abnormal thermal state and finally helps to stabilize the pellet production.

Jan 1, 2016

By Che Xin, Liu Tianlong, Bi Hongyun, Chen Lijia

"High-cycle fatigue experiments were conducted at 800°C in laboratory air for three ferrite stainless steels including 15CrNbTi, 15CrMoNbTi and 18CrNbTi, where the stress ratio of 0.l was adopted. The experimental results show that at 800°C, the fatigue limit of the 15CrMoNbTi steel is the highest, the fatigue limit of the 15CrNbTi steel is slightly lower than that of the 15CrMoNbTi steel, and the fatigue limit of the 18CrNbTi steel is the lowest. At the same maximum stress, the 15CrMoNbTi steel has longer fatigue lives than the 15CrNbTi steel in the low stress area, while the 18CrNbTi steel has the shortest fatigue life. In addition, the observations on the fracture surfaces of fatigue specimens reveal that the fatigue cracks initiate transgranularly at the free surface of the specimens and propagate in a transgranular mode.IntroductionIn modem automotive industry, the manufacturers have paid great efforts to clean exhaust gas and to improve fuel economy. It is thought an effective way to increase the temperature of combustion chamber in automotive engine. And thus, the manifold closed to the engine in automotive exhaust system can suffer high temperature up to approximately 1000°C. Because of their relatively low thermal expansion coefficient, high yield strength at elevated temperature and good fatigue resistance, ferrite stainless steels, especially added with alloying elements such as Mo, Nb and Ti, are increasingly used for automotive exhaust systems [1-3]. In fact, exhaust manifold operated under high frequency vibration and exposed to high temperature exhausting gas also requires good fatigue resistance at elevated temperature. Some studies on the high temperature fatigue characteristics of stainless steel have been documented. It has beeen found that the fatigue limit of four ferrite stainless steels including 409L, 436L, 429EM and 444 (18Cr- 2Mo) reduces significantly with increasing temperature [4, 5]. In the research concerning the effect of a-phase embrittlement on fatigue behavior in a high-chromium ferrite stainless steel, it is noted that the precipitation of brittle a-phase will reduce the crack initiation and growth resistances and result in a decrease in fatigue limit [6]. In this investigation, the high-cycle fatigue behavior of three ferrite stainless steels including 18CrNbTi, 15CrNbTi and 15CrMoNbTi at 800°C have been studied to address the mechanical aspect of high-cycle fatigue behavior for ferrite stainless steels and to provide the theoretical reference for the safe design of automotive exhaust system."

Jan 1, 2013

By Timothy W. Skszek, Adrian S. Sabau, Hebi Yin, Gerard M. Ludtka, Xiaoping Niu

"A constitutive model has been developed to predict the yield strength aging curves for aluminum casting alloys during non-isothermal age-hardening processes. The model provides the specific relationship between the process variables and yield strength. Several aging heat treatment scenarios have been investigated using the proposed model, including two-step aging recipes. Two-step aging heat treatments involve a low temperature regime to promote nucleation of secondary phases and a second step at higher temperature for the growth of the secondary phases. The predicted results show that a yield strength of approximately 300MPa might be obtained in a shorter aging time, of approximately 30 minutes. As a result, better mechanical properties can be obtained by optimizing the time-temperature schedules for the precipitation hardening process of heat treatable aluminum alloys.IntroductionA356 is one of the commercially heat treatable aluminum casting alloys, and T6 is one of the heat-treated conditions to improve mechanical properties. The first stage of a T6 temper is solution treatment at an elevated temperature, generally in the range of 480 - 540°C. After solution treatment, the cast part is typically quenched in water/air to retain the solute-rich homogeneous matrix chemistry at room temperature. Subsequent ageing treatment stages capitalize on this super-saturated solid solution to generate controlled dispersions of very small strengthening precipitates within the matrix of Al grains [l]."

Jan 1, 2013

By Yotamu Stephen Rainford Hara

"The study focuses on the reduction mechanisms of copper, cobalt and iron during carbothermic reduction of copper-cobalt mineral sulphide concentrates in the presence of lime, in the temperature range of 1073K and 1273K. We have used three types of mineral concentrates which were derived from froth flotation from the Copperbelt region in Zambia. The reduction mechanisms were studied using thermogravimetric analysis in which selected reactions were stopped at different times for characterising the reaction mechanism using optical microscopy, XRD and SEM-EDX analyses. Using SEM-EDX analysis, we have analysed in details the stages of metallic phase formation during reduction process. Metallic cobalt and iron were embedded into copper, thereby permitting magnetic separation of the reduced metals even though copper is diamagnetic. Methods of preferential reduction of metal values were investigated by analysing the metallic phase formation.IntroductionIn conventional smelting or converting of copper sulphide minerals, metallic copper forms by giving off S02 gas on. Although in terms of overall energy balance the selective oxidation for metal production has major advantages, the process suffers from drawbacks in smelting complex concentrates containing copper, cobalt and iron sulphides minerals and these are: (i) cobalt and iron are oxidised, and consequently cobalt is lost into the slag phase. (ii) The volume of S02 gas produced is in low concentrations, which is insufficient for extracting sulphur or manufacturing sulphuric acid. The release of dilute S02 causes serious environmental pollution. The major cause for the loss of cobalt and iron into the slag, is due to that fact that the oxides of these metals are more stable than their sulphides. Since cobalt and copper are more valuable than iron, reducing conditions are required in a separate slag treatment reactor using electric arc melting for recovering the lost metal oxides from slag. This energy-intensive step makes metal making expensive.During chemical beneficiation of mineral sulphides (Cu2S, CoS, FeS) in the presence oflime (CaO), two types of equilibrium conditions may be set up either by forming CaS under reducing conditions, or by stabilizing CaS04 under oxidising conditions [l]. By comparison in the presence of carbon, CaS and metallic phases form, enabling the recovery of metals from sulphide minerals, which have been investigated by a number of authors [2-9]. During reduction of metal sulphide in the presence of lime and with carbon, it has been proven that the overall reaction le proceeds via two main steps: [5, 8, 9] (i) the anion exchange reaction between metal sulphides (MS) and CaO as shown in equation la, followed by (ii) the reduction of metal oxide (MO) via reaction lb."

Jan 1, 2013

By M. Bhattacharya, A. Dutta, P. Barat

"Pinning of dislocations at nanosized obstacles like precipitates, voids and bubbles, is a crucial mechanism in the context of phenomena like hardening and creep. The interaction between such an obstacle and a dislocation is often explored at fundamental level by means of analytical tools, atomistic simulations and finite element methods. Nevertheless, such studies fail to predict the effect on the overall plasticity on account of insufficient information about the underlying statistics of this process comprising a large number of dislocations and obstacles in a system. Here we propose a new statistical approach, where the statistics of pinning at idealized spherical obstacles is explored by taking into account the generalized size distribution of the obstacle along with the dislocation density within a three-dimensional framework. The application of this approach has been demonstrated for dislocation pinning at nanovoids in neutron irradiated type 316-stainless steel.IntroductionPresence of nanoscale obstacles like precipitates, voids and bubbles play a crucial role in determining the deformation behavior of a crystalline solid on account of the interactions between the line defects and such localized obstacles. In the context of the glide motion of dislocations, the obstacles can offer resistance to a moving dislocation, thereby causing a hardening effect [l-3]. In some other cases, inclusions like voids and bubbles can affect the rate of dislocation climb through diffusive [4] and non-diffusive [5] mechanisms. Over the last few decades, numerous studies have been performed to gain an insight of the dislocation-obstacle interactions at a fundamental level. These include the interactions responsible for the hardening effect, in addition to those pertaining to the non-conservative motion of dislocations.Although the elementary mechanisms of the various dislocation-obstacle interactions have been vastly explored and understood by means of analytical theory and numerical simulations, it remains difficult to quantitatively understand their effects on the macroscopic deformation behavior. This is due to the fact that their influence on the gross plastic deformation of a bulk sample would be the collective outcome of a large ensemble of such interactions. As a result, it becomes infeasible to predict the bulk deformation behavior of a material until the statistics of pinning of the dislocations at the localized obstacles is available. In the context of precipitate hardening, some well known attempts to extract the pinning-statistics were made by Friedel-Fleischer [6] and Mott [7] by analytical means, which were later tested through simplified 2-dimensional in-silica modeling [8]."

Jan 1, 2014

By Kenji Monden

A simple technique is presented to evaluate optical property of biomimetic microlens array (BMA) as an antireflective surface on a polydimethylsiloxane (PDMS) sheet. The integration of these structures is done by a thermoforming process. We have only UV-VIS spectrophotometer for optical evaluation apparatus. The transmittance of the sheet is measured with angled sample holder. The 50 deg. transmittance of 270nm pitch BMA on PDMS sheet increases from 87 to 92% after the moth-eye structure is introduced. The transmittance of 350nm pitch BMA on PDMS sheet increases from 87 to 96% after the moth-eye structure is introduced. The transmittance increases with increasing pitch of BMA. The results obtained using UV-VIS spectrophotometer with handmade sample holder.

Jan 1, 2015

By John K. Wright

The segregation process involves heating oxide-type ores with a halide salt in the presence of a solid reductant. By a complex series of cyclic vapour-phase reactions, the desired metal is extracted from its original position in the ore and segregated to the vicinity of the reductant. In this form it is then amenable to concentration by physical methods. In this work the segregation behaviour or eight different nickel laterite ores has been examined using a laboratory rotary kiln. It was found that the silicate (serpentine) ores responded better to the segregation conditions used than did the limonitic ores. An examination of the segregated metal particles showed that they consisted of ferro-nickel. The concentration of nickel in the metallics was sensitive to the ore types and the segregation roasting conditions.

Jan 1, 1994

By Hideya Sato

Refractory wear caused by melts is one of the major determining factors for the interval of shut-down repair of the metallurgical furnaces in general. Calcium ferrite slag employed by M it subishi Continuous Copper Converter, shows hi& fluidity and corrosive characteristics against most of the refractories. In order to improve the corrosion resistance of the refractories, the mechanism of MgO-based refractory wear by the calcium ferrite slag was intensively studied. The dissolution behavior of the refractory into the molten slag and the penetration of the molten slag into the refractory were observed by crucible tests and newly developed oscillating furnace tests. It was found that the wear of MgO-based refractories by the calcium ferrite slag is mainly dominated by the internal structural failure caused by the penetration of CaO-Cu20 rich slag which is formed as a result of the preferential absorption of FeO, from original slag by the spinel of the refractory.

Jan 1, 1999

By Hideharu Fukunaga, Jin Pan

"The recognition of Metal Matrix Composites (MMCs) as a means of providing high specific strength, high specific stiffness, excellent wear resistance, low thermal expansion and improved high temperature properties has led to a number of new processing, not previously used for plastic and ceramic matrix composites. As a primary fabricating process, the liquid methods are the major ones, which are reviewed briefly from the view of processing terminology. One of them, squeeze casting process is the most traditional and well-developed, because it is rapid, versatile and near-net shape production of materials. Two of new squeeze casting processes are presented to offer the hardness· controlled MMC and the· functionally graded MMCs as well as a newly developed whisker preform.I .IntroductionA large number of liquid processes and techniques including semi-solid liquid process are proposed. The most primitive process is ''pressure infiltration casting” of liquid metal into the fiber preform. It is called as follows depending on pressure and its source squeeze casting (1-4) by hydraulic ram, gas pressure infiltration casting (5, 6), vacuum infiltration, centrifugal casting (7), Lorentz-force-driven infiltration (8). The pressurizing on the liquid metal requests a large and stiff equipment, so pressureless infiltration technique has been developed using K2ZrF6 flux (9,10) while the mechanical properties are not high enough, and using H2 gas with Mg alloying element called pressureless infiltration casting (11-13), spontaneous infiltration process (14) and PRIMEX (15). In those processes, no severe reaction occurred between the reinforcement and matrix molten metal. In early l 990's, the reactive processing with pressure or without pressure, in which one material is totally transformed into another of the required shape, eq. assisted oxidation, has been developed, called reaction squeeze casting (16,17), DIMOX (18) reactive infiltration casting (19,20), and in-situ process (21,22). Die casting of SiCp/Al alloy (23,24) and thixocasting of SiCp/Mg alloy (25) are also applied to produce the machine component of MMCs."

Jan 1, 2000

By Tian Tang, Sergio D. Felicelli

"The laser cladding is an important surface treatment for enhancing resistance against corrosion, abrasion, and wear. The focus of the present study is to develop a three dimensional finite element model to analyze the temperature history and thermal stress evolution during multi-pass laser cladding process on H13-H13 tool steel sample. A sequentially coupled thermal-stress analysis methodology was adopted in this study. The thermal model was firstly established to investigate the temperature history of the laser cladding process. Then the temperature history was used as input to mechanical model to calculate the thermal stress evolution during the process and the residual stress after the sample completely cooled down to room temperature. The influences of process parameters including the scanning speed and scanning strategies on temperature history, thermal stress evolution, and residual stress were investigated in details.IntroductionLaser cladding is an advanced material process technique, which is often used to improve mechanical properties or increase corrosion resistance, repair worn out parts, and fabricate metal matrix composites. In this process, the injected powder or wire feedstock material and a thin layer of substrate are melted and consolidated by use of a laser in order to coat part of a substrate or fabricate a near-net shape part.Numerous mathematical models have been established for analyzing the effects of process parameters, microstructure evolution, and thermo-mechanical behavior of laser cladding. Zhou et al. [1] established an analytical model to investigate the laser induction hybrid rapid cladding for Ni-based WC composite coatings. Huang et al. [2] also developed an analytical model to theoretically investigate the interaction between the laser beam and the powder stream of laser cladding process. A simple and realistic model of laser cladding was proposed by Picasso et al. [3]. The cladding layer is very sensitive to cracks due to the accumulation of residual stress, caused by non-uniform temperature changes, which have limited the wide application of laser cladding technique in industry. Recently, fmite element method has been increasingly used to simulate the laser cladding process [ 4-6]."

Jan 1, 2014

By Ying Mao, Zhancheng Guo, Long Ma, Huiqing Tang

"A new 2D computational fluid dynamic (CFD) model was developed for the gaseous reduction of iron ore fines in an innovative reactor-multilayer moving-fluidized bed. The solution of the proposed model was performed by integration of FLUENT and PHOENICS. Numerical results of cold state were compared with the experimental data and the agreement between them was good. A hot case-gaseous reduction of iron ore fines using syngas with this reactor was simulated using the present CFD mode. Results indicate that under the given simulation conditions, total pressure drop is 90 Pa less than that under cold state though the gas supply rate is increased about 4m3 under hot state. Gas temperature decreases from 1073 K at the bottom to 500 K at the top, Utilization efficiency of the gas reduction potential is about 27 %. For ore fines reduction, the final reduction fraction could reach 0. 70 and solid temperature 900 K.IntroductionWith the development of coal gasification technology, various coals could be converted to Syngas with air or steam. Therefore gaseous reduction of iron ore fmes becomes an acceptable alternative process for iron making besides blast furnace route[!] and moreover it still has some advantages in processing low grade iron ore fines[2]. Gaseous reduction using fluidized bed technologies is the most competitive in all direct reduction iron-making processes up to now. It has the advantage that ore fines can be directly charged to the process without prior treatment while its disadvantages are particle agglomeration and high gas/solid ratio[3]. To avoid these advantages, a new reactor, multilayer moving-fluidized bed reactor has been developed for carrying out the gaseous reduction. Hydrodynamic behaviors of gas and fines in the reactor were studied and the results were satisfying[4]. However, due to its unique structure of the multilayer moving-fluidized bed and unique gas-solid flow pattern, models of multiphase flow as IPSA, DPM and Eulerian Model could not give a satisfying solution. The current paper is developed a new CFD model and a new solution approach for simulation of the reactive gas-solid flow in the multilayer moving-fluidized bed for its optimization, design improvement and future scale-up."

Jan 1, 2013

By Cashman R. S. Mason

Removal of halides (fluoride, chloride) from metallurgical solutions can reduce corrosion rates and improve hygiene from decreased anodic chlorine evolution. This is particularly true for zinc sulphate electrowinning solutions. This paper describes the chemistry of a new process for the removal of halides from such solutions by solvent extraction ? the Teck Cominco Halogon? process, for which patents are pending. In this process, the halides are loaded directly from commercial zinc sulphate solutions and are stripped into a form suitable for disposal. Sulphate extraction efficiency is variable while maintaining halide extraction efficiency. The method of optimizing the solvent composition is demonstrated.

Jan 1, 2003

By V. T. Taniguchi

A process for large scale chromatographic separations using a continuous chromatography technique is described. The process combines the advantages of large scale batch fixed column displacement chromatography with conventional analytical or elution continuous annular chromatography (CAC) to enable large scale displacement chromatography to be performed on a continuous basis (CDC). Such large scale, continuous displacement chromatography separations have not been reported in the literature. The process is demonstrated with the ion exchange separation of a binary lanthanide (Nd/Pr) mixture. The process is, however, applicable to any displacement chromatography separation that can be performed using conventional batch, fixed column chromatography.

Jan 1, 1989

By Guohui Zheng

The ever increasing quantities of solid wastes generated by various industries are at the source of the growing need for proper waste disposal methods. Thermal treatment of combustible wastes is a proven technology which permits the reduction of hazardous material having to be landfilled. However, this method is not universally applicable to waste disposal. For example, the transferal of heavy toxic metals into the thermal remediation products is a major issue of public concern. This paper focuses on the analysis of morphology changes from solid sludge to ash which is a product of the sludge combustion. The morphological parameters analyzed were particle size and external surface. They were determined using Jeol 840 Super Probe. The experiments were conducted in a computer-controlled high-temperature combustion system consisting of the thermogravimetric furnace coupled with Fourier transform infrared spectrometer (TGA-FTIR). Sludge particles were made of complex fibers trapped in the aluminosilicate matrix. At low temperatures, up to 680 K, the solid residue looked similar to the initial sludge. Between 680 K and 1180 K the sludge underwent intensive burning and steadily changed into powdered ash. At the temperature of 1050 K the ash was composed of separate, flat flakes with sizes ranging from 5 to 20 um. At 1470 K the flakes aggregated into large particles. The surface observed at 1670 K was a mixture of mullite crystals. Such structure could result from the solidification of the ash material after its melting. Morphological changes influenced the distribution of metals in the solid residue. For example, Cr was concentrated in small aggregates. Such distribution should allow for recovery of valuable metals from the solid waste residue.

Jan 1, 1996

By K. S. Raja, M. Misra, S. K. Mohapatra

"Ordered arrays of TiO2 nanotubular photocatalysts were prepared by a simple anodization process. Band gap states of the TiO2 were altered by controlling the anodization electrolyte composition and thermal annealing conditions that resulted in enhanced photo activity. These nanotubes were used for reducing CO2 to methanol either by photochemical or photo electrochemical routes. Pd nano-particle loaded TiO2 nanotubes were employed for photochemical reduction of CO2 to methanol that showed a conversion rate of 12 x 10-3 mol m- 2h-1. Carbon modified TiO2-xCx type nanotubes were used as photo anode and Ti as cathode for photo electrochemical reduction of CO2. The potential of Ti cathode was maintained at -0.5 V SCE. The formation rate of methanol was determined as 13 x 10-3 mol.m-2h-1.1. IntroductionGlobal warming due to emission of carbon dioxide is a serious environmental concern. The atmospheric concentration of CO2 is about 384 ppm by volume and about 3 x 1012 tonnes by weight. Burning of fossil fuels and deforestation are the leading causes for increase in the anthropogenic CO2. More than 32 x 109 tonnes of CO2 are released per year (based on 2006 data) worldwide from the fossil fuel. Pumping CO2 from the fossil fuel power plants into deep ocean basin is one of the most discussed disposal options. The other potential option is converting this green house gas into valuable fuels.Carbon dioxide feed stock can be converted into fuels of solid, liquid or gas phase by chemical, electrolytic, photocatalytic and photo-electrocatalytic methods. Reduction of CO2 to fuel form of any phase requires energy. The reduction process should be energy efficient so that we do not spend more energy and emit more (indirect) CO2 in the process of converting CO2. From this point of view, conversion processes occurring at room temperature look attractive.Electrolytic conversion of CO2 into various forms such as methane1, ethane2, ethylene3, methanol4,5, ethanol6, n-propanol, formic acid7, and formaldehyde has been widely reported. The standard equilibrium potential (at pH: 0) for reduction of CO2 to methanol is 0.14 VSHE and to methane is 0.2 VSHE which is thermodynamically more favorable than hydrogen reduction. However, the gas phase reduction is kinetically complex requiring effective electrocatalyst. The major issues with electrolytic conversion of CO2 to useful products are:"

Jan 1, 2010