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By Rak-Jun Choi

Plasma-induced damage of InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) has been studied in terms of forward turn-on and reverse breakdown voltages, together with etch rate and surface morphology. The physical degradation of sidewall along with rough surface morphology of n-GaN caused by increased ion scattering induced the deterioration of the forward and reverse voltages. It was found that the turn-on voltage is sensitive to the surface roughness of the etched n-GaN and the breakdown voltage is strongly affected by the sidewall contamination. Annealing under nitrogen after the mesa etching improved the electrical properties of the InGaN/GaN MQW LEOs. Efficient blue light-emitting diodes (LEOs) were fabricated using InGaN/GaN triangular MQWs. The LEOs with triangular QWs showed a lower operation voltage and 2.4 times higher light output power than those with the rectangular MQW LEOs at 20 rnA and 20 "C. The intensity of electroluminescence (EL) at 20 mA was almost independent of ambient temperature in the triangular QW LEO, but decreased substantially in the rectangular one.

Jan 1, 2003

By S. W. Marcuson

Smelting of nickel-copper sulfide ores at Vale Inco’s Sudbury operations commenced in 1888 and the first converting plant went into operation in 1892. As the demand for nickel grew, the smelting operations expanded and by the 1960’s the Copper Cliff Smelter featured the longest converter aisle in the world with space for nineteen Peirce-Smith converters. During this long period, different converting techniques and vessels were employed. The evolution of converting is reviewed with special emphasis on the modifications made to the Peirce-Smith vessel to accommodate the metallurgical and process needs of the changing times.

Jan 1, 2009

By Bingchen Chen, Zhitong Sui, Junwei Ma

"In the blast furnace slag, titanium disseminated in various mineral phases Titanium could be concentrated mainly in perovskite, which could be selectively precipitated and grown by optimizing the operation factors like the slag composition, temperature of heat treatment and additive agents. This study aims at establishing the titanium slag mineralogy and its distribution in the treated slag and the as-received slag, as well as the methods of perovskite separation. After heat treatment, the grain size was grown from 5 - 20µm to 80 - 200µm, the distribution of Ti02 in perovskite was increased from 48% to 81 %, the morphology was changed from snow-shaped grain to coarsening dendrites or equiaxed crystals. A concentrate were produced by gravity separation analyzing 35.25% Ti02 with a recovery of 68.28% and a tailing analyzing 9.53% Ti02 , and a possibility of flotation upgrading was discussed. I INTRODUCTION CHINA is rich in mineral resources of titanium, 92.4% of which is vanadium-titanium bearing magnetite. About 53% titanium were in iron concentrate after mineral processing, by which the blast furnace slag containing about 25% TiO2 were produced[11 • The content of TiO2 in such slag is too low to separate titanium dioxide, and it is also too high to produce slag cement[21. It has been accumulated to 50 million tons so far, which is still increasing at a rate of 3 million tons per year, and results in a waste of titanium resources and pollution of environment. Due to the dispersed distribution of titanium component in various mineral phases, very fine grain(<10µm) and complex interfacial combination, it is very difficult to recovery titanium component from the slag by traditional separating technique. In this paper, a novel technique to recovery titanium from the waste slags was proposed [3H4l, on which three continuous processes were involved: selective concentrating, selective growing and selective separating. Perovskite was designed as a titanium-rich phase, in which the most titanium was concentrated promptly, then perovskite could be selectively grown and coarsened by optimizing the heat treatment and the appropriate additives [ 5l[6l. The grain size of perovskite phase was larger than 80 µm, and the crystals appeared as coarsening dendrites or equiaxial grains like lump."

Jan 1, 2000

By Rak-lun Choi

Plasma-induced damage of InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) has been studied in terms of forward turn-on and reverse breakdown voltages, together with etch rate and surface morphology. The physical degradation of sidewall along with rough surface morphology of n-GaN caused by increased ion scattering induced the deterioration of the forward and reverse voltages. It was found that the turn-on voltage is sensitive to the surface roughness of the etched n-GaN and the breakdown voltage is strongly affected by the sidewall contamination. Annealing under nitrogen after the mesa etching improved the electrical properties of the InGaN/GaN MQW LEDs. Efficient blue light-emitting diodes (LEDs) were fabricated using InGaN/GaN triangular MQWs. The LEDs with triangular QWs showed a lower operation voltage and 2.4 times higher light output power than those with the rectangular MQW LEDs at 20 mA and 20 °C. The intensity of electroluminescence (EL) at 20 mA was almost independent of ambient temperature in the triangular QW LED, but decreased substantially in the rectangular one.

Jan 1, 2003

By Yang Jian-guang, Deng Zi-xiang, Zhang Xu-liang, Li Jun-yuan

"Hyperaccumulator biomass harvested after heavy-metal phytoremediation must be considered as hazardous waste that should be contained or treated appropriately before disposal or reuse. As a potential method to detoxify the biomass and to convert this material to a suitable bio-energy resource, the hydrothermal upgrading process was applied to remove heavy metals and upgrading crude bio-oil from Pteris vittata stems and leaves harvest. Parameters such as material granularity, temperature, Liquid/Solid (L/S, ml/g), pressure, duration and catalysts were examined for their effect on the removal efficiency of heavy metals and upgrading efficiency of crude bio-oil. Maximum heavy metal removal efficiency of>99% and crude bio-oil upgrading efficiency of 83% were attained with an 200 mesh (75 µm) granularity, LIS 40:1and23 MPa at 380°C in the presence ofO.l mol L-1 K2C03 for 30 min. GC-MS analysis results show that the resulting bio-oil mainly consists of benzene 11 %, ketone 42%, alcohols 14%, alkene 15% and ester 11 %, etc., and the relative molecular weight distribution lies in 94-282, carbon number distribution lies in 6-18, calorific value is 32MJkg-1.IntroductionPhytoremediation of soil or water with hyperaccumulator has been extensively explored in recent years [1-4]. Living plants can clean up soils or waterways. This approach exploits the ability of various plant species to thrive in high metal environments where large amounts of toxic elements are accumulated, such as heavy metals, and is particularly appropriate when slow remediation of relatively low metal concentrations is acceptable. Advantages compared with existing remediation methods include the minimal site destruction and destabilization, low environmental impact, and favourable aesthetics; advantages compared with biosorption include continuous in situ regeneration of the biomass, and the ability of living plant cells to supplement passive sorption of metals with metabolic mechanisms of metal uptake and detoxification [5-8]."

Jan 1, 2014

By Laurentiu Nastac, Ruslan Mudryy

"This paper investigates the solidification of cast energetic materials. An active cooling and heating (ACH) technology and a mechanical vibration (MV) technology were applied to achieve unidirectional solidification during casting and to reduce cracks, gas pores, and shrinkage defects. The design parameters of these technologies were developed via Computational Fluid Dynamics (CFD) modeling and thermal stress analysis. Concerning the ACH technology, the number of cooling/heating sections and their temperature profiles and time sequences were optimized based on the thermo-physical properties of the energetic material as well as the riser and mold diameter, thickness and type. The ACH technology will also decrease the thermal stresses during casting of energetic materials and therefore minimize the formation of potential cracks that may form during the casting process. The MV technology will help to remove air entrapped during pouring process and decrease the detrimental gap size between the projectile and the solidified energetic material.IntroductionCasting processes are widely employed in the manufacture of products with intricate shapes and, in particular, in applications where the material of the final product is sensitive to machining. It is especially useful in processing of energetic materials. The cooling conditions applied in the casting process can affect the quality of the final cast in terms of void formation, residual stress distributions, and mold separation. Substantial shrinkage is also observed due to the density change upon solidification [1-3]. Residual stresses are known to be closely related to the formation of cold cracks and hot tears during casting. The formation of a gap between the mold and the cast material is of critical importance due to its deleterious effect on heat removal and on crack formation. In the casting of energetic materials all these defects can significantly impair the detonation velocity, Gurney energy, and insensitive munitions characteristics of the formulation, and lead to catastrophic accidents in explosives handling [ 4-5]. Imposition of carefully controlled cooling condition is thus critical in optimizing the cast quality that could help avoid such destructive effects."

Jan 1, 2013

By M. Kawakami

In relation to the designing of a new-type blast furnace, the reaction of carbonaceous materials with CO2 is expected to occur at as low temperature as possible. In order to get a highly reaetive carbonaceous material at low temperature, the reaction kinetics was investigated by measuring such quantities as the reaction rate from weight loss, the amount of CO adsorption and specific surface area by BET method. The reaction rates were large in the order of the Bintyo char, metallurgical coke, graphite and glassy carbon. If the rate was converted to the rate per unit area, however, those of the Bintyo char was smaller than that of graphite. Thus, it is suggested that the rate of the Bintyo char is influenced by the pore diffusion of CO2. The rate had a positive relation with the amount of CO adsorption, showing that the rate determining step would be the desorption of CO from the active side on the surface. The rate independent of surface area was derived, combining all the obtained data.

Jan 1, 2003

By Sui Xue

A process has been developed from laboratory-scale experiments for the aqueous processing of various lead-bearing wastes. The process exploits the limited solubility of lead in sulfate-rich solutions to effectively separate lead from other metals. The lead sulfate is then completely converted to lead carbonate using sodium carbonate and ammonium carbonate. The effectiveness of this conversion was observed to be sensitive to the solution pH and carbonate concentration. The final stage of the process uses low temperature calcination of the lead carbonate to form PbO. Yellow lead oxide (massicot) is readily formed if calcination is conducted at a temperature at or iibove 50G°C, wlule red iead oxide (iitharge) is formed at temperatures near 450°?C. A complete economical analysis of the process will be discussed.

Jan 1, 1996

By Chidchai Loyprasert, R. A. Stoehr

"A computer model has been developed to predict grain structures in alloys solidified under unidirectional flow using a combination of three techniques -- solution of the equations for flow of an incompressible fluid bounded by curved surfaces by the SOLA-SURF algorithm, calculation of heat flow by a finite difference method, and simulation of grain formation by a two-dimensional cellular automaton (CA) model. The changing rigid surface has been taken into account. Heterogeneous and homogeneous nucleation are considered, and the growth kinetics of a dendrite tip are evaluated by the Kurz-Giovanola-Trivedi (KGT) model. These calculations were applied to solidification of an Al-4.5% Cu alloy flowing over a chill on the bottom of a channel, a system for which experimental results were available. Using a variety of flow rates and superheats, agreement between the computed and experimental results were very good including transitions between columnar and equiaxed grains, the aspect ratio of the grains, and the inclination of the grains to the flow.IntroductionModeling of casting and solidification processes has developed over the years along two distinct tracks: (1.) modeling of macroscopic heat transfer and fluid flow for design purposes, and (2.) modeling of microscopic processes such as nucleation and growth in order to improve the scientific understanding of the phenomena involved. The present work is an attempt to combine the macroscopic and microscopic approaches for the solidification of an alloy flowing over a chill. The specific case chosen is that of an aluminum-4.5 % copper alloy flowing linearly over a water-cooled copper chill for which experimental results were available over a range of flow rates and superheats. For the macroscopic calculations, the SOLA-SURF algorithm for solution of the twodimensional fluid flow equations was combined with the finite difference method (FDM) for calculating heat transfer. For the microscopic calculations, heterogeneous and homogeneous nucleation were considered, and the growth kinetics at the dendrite tips were evaluated. The cellular automaton (CA) technique was used to apply the microscopic kinetics to the temperature and .flow conditions."

Jan 1, 1999

By S. R. Reddy, R. G. Reddy

"The Margules equation is used for interpreting excess Gibbs energy of several ternary systems. In the present study activity coefficient of a dilute solute, 2, in a binary solvent 1-3 was derived. The derived expression is used to interpret logarithmic activity coefficient of oxygen and sulfur in several metallic systems. Self interaction parameter of the solute is derived from the partial function of solute using constant compositional path. An expression for logarithmic activity coefficient and self - interaction parameter of solute is also derived using Maclaurin infinite series. The derived equation is based on Maclaurin infinite series used successfully to deduce thermodynamics of self interaction of oxygen as a interstitial atom in two metallic systems. The predicted thermodynamic parameters values using Maclaurin infinite series and Margules equations, are in excellent agreement with the experimental data and also our predictions are far more accurate than the predictions made by other models.1 IntroductionIn most of the pyrometallurgical high temperatures processes, interactions of solutes such as oxygen, nitrogen and sulfur, with the solvent atoms are most important during refining processes. There are numerous theories are developed [1-25] to interpret the thermodynamics of solutes in multicomponent alloy systems. Which are mainly developed using statistical or Quasichemical equations.Wagner [4] developed one energy parameter ideal solvent model based on activity coefficient of solutes compositional dependency. He used one energy interaction term which is not able to account for interaction energy parameters for the same solute concentration at different solvent compositions and also it is ineffective model to predict for strong interacting systems."

Jan 1, 1996

Acid generation from reactive sulphide mineral tailings has become a major environmental problem in the mining industry. Initiation of chemical and biochemical oxidation reactions of the sulphide mineral leads to acid generation. A novel concept of safe disposal and utilization of reactive fine mill tailings is presented in this paper. The paper also presents the results of a preliminary laboratory experimental .study of the concept. The tailings are agglomerated using portland cement as a binder. The cold bonded agglomerates are encapsulated with other chemical additives to act as acid neutralizers, oxygen and ironoxidizing bactericides., The primary. factors influencing the choice of bacterfoides to inhibit the acid generating bacteria are their costs, toxicity and environmental friendliness. The paper discusses the utilization of agglomerated&apos; products as aggregates for underground backfill, or as gravel for surface land cover.

Jan 1, 1991

By Gabriel Riveros

Fire refining of copper consists of two stages copper oxidation and copper reduction. Very frequently the capacity of the anode furnace is determined by the rate of copper reduction, The analysis of factors affecting the rate of the oxygen reduction from a liquid copper with solid carbon or injected hydrocarbons pointed out the role of the mass transfer in a liquid copper in final stage of the reduction. Experimental results of copper reduction with graphite and injected natural gas in laboratory-scale crucibles showed two stages of the reduction process with a sharp change of the controlling mechanism. The estimated dynamic surface area of gas bubbles based on the measured bubble frequency and the gas flowrate allowed for the determination of the reaction constant as a degree of the partial pre-combustion of the air/natural gas mix. The variation of the used reductant as a function of the oxygen concentration and temperature has been evaluated based on the determined kinetic model. The intensification of copper reduction in fire refining has been discusses on the basis of obtained kinetic data and analysis of various factors determining the time of reduction.

Jan 1, 2003

By Gabriel Riveros

Fire refining of copper consists of two stages copper oxidation and copper reduction. Very frequently the capacity of the anode furnace is determined by the rate of copper reduction. The analysis of factors affecting the rate of the oxygen reduction from a liquid copper with solid carbon or injected hydrocarbons pointed out the role of the mass transfer in a liquid copper in final stage of the reduction. Experimental results of copper reduction with graphite and injected natural gas in laboratory- scale crucibles showed two stages of the reduction process with a sharp change of the controlling mechanism. The estimated dynamic surface area of gas bubbles based on the measured bubble frequency and the gas flowrate allowed for the detennination of the reaction constant as a degree of the partial pre-combustion of the air/natural gas mix. The variation of the used reductant as a function of the oxygen concentration and temperature has been evaluated based on the detennined kinetic model. The intensification of copper reduction in fire refining has been discusses on the basis of obtained kinetic data and analysis of various factors detennining the time of reduction.

Jan 1, 2003

By T. M. Dreher

The difficulties associated with the operation of a classical rhodium refining process have prompted many attempts to develop a viable solvent extraction flowsheet for rhodium. Recent investigations at McGill University have involved the activation of rhodium prior to its solvent extraction. The role of activation is to convert the aquochloro complexes of rhodium to a form extractable by conventional solvent extraction reagents. In the novel separation scheme identified, chloro complexes of rhodium are converted to bromo complexes, which undergo aquation to a lesser extent, making them more easily extracted. Rhodium is then extracted using Kelex 100, and stripping is achieved by use of a concentrated chloride based solution. Separation of rhodium from iridium is achieved by either prior reduction of Ir(IV) to Ir(III), as the latter is not extracted, or via co-extraction and differential stripping. A conceptual flowsheet for the refining of rhodium using this method is proposed.

Jan 1, 1998

By Takeo Fujino, Nobuaki Sato, Junichi Hasegawa, Masato Nakazawa, Kohta Yamada

"Tantalum oxide thin films were deposited on quartz substrates by laser ablation of Ta2O5 target using Nd:YAG pulse laser. Deposition-was observed when a laser light energy higher than 200 mJ and its repetition rate higher than 3 Hz. A thin film of 0.1 µm thickness was obtained by the ablation using a laser light of 300 mJ and 6 Hz for 2 sec. The thickness of the film increased with increasing energy, repetition rate and irradiation time of laser. By the SEM observation, it was found that many island-like particles were deposited on quartz substrate forming a thin film. The obtained thin film, which was identified as ? Ta-O by X-ray diffraction, was oxidized to Ta2O5 by the heat treatment in air at I273 K for 3 h.IntroductionTransition metal oxides have a potential to show special characteristics in electrical, magnetic and/or optical properties. When such compounds are fabricated in the form of thin film, the special properties would be improved or new characters would appear in comparison with bulk materials. Tantalum penta-oxide is widely used as a capacitor since Ta2O5 shows high dielectric constants up to high temperatures. The tantalum solid capacitor has been fabricated by the electrical oxidation of sintered Ta metal cylinder followed by MnO2 film coating. However, further improvements, reduction and layered structure formation, are required for compacting the devices. The layered structure of thin films would be applicable for the above requirements. The formation ofTa2O5 film by low pressure CVD1), photo CVD2) and magnetron sputtering3l were reported. The laser ablation -method is one of the most convenient techniques for the deposition of thin films from their compounds, such as oxides. Formation of Ta2O5 film by pulse laser deposition (PLD) method using ArF excimer4), Nd:YAG (533nm)5) and TEA CO2 6 lasers was reported. In these PLD studies, ablation was carried out in relatively high oxygen pressures resulting in formation of Ta2O 5 film. In this paper, the deposition of tantalum oxide thin film by the laser ablation of Ta2O 5 using Nd:YAG pulse laser was examined at a viliety oxygen pressures ranging from 10-8 to 10 Torr. The morphology of the films was also investigated in relation with substrate temperature and oxygen pressure."

Jan 1, 2000

By Robert R. Beebe

On the night of August 1&apos;9-20, 1995, seepage was seen at the toe of the Omai tailings dam in Guyana. The mill was immediately shut down, and within two hours the flow, then mostly water, was diverted into an inactive mining pit nearby. At about the same time a second more serious break occurred at a point where water and solids could flow directly into the Omai River. By the time Ii coffer dam could be completed in the early morning of August 24, some 4.2 million cubic meters of tailings water and solids had escaped from the dam, of which nearly2.9 million cubic meters had reached the Omai River. This paper outlines some initial Process considerations and operational decisions which might have contributed to the dam&apos;s failure, describes how the Government of Guyana and the operator, Omai Gold Mines Limited, cooperated in dealing with immediate problems and shows how the Government set about investigating the accident. In particular, the paper details the work of a Process Review Committee comprising Guyanese and foreign experts convened to assess the gold processing and effluent management systems at Omai, and to recommend actions where appropriate.

Jan 1, 1998

By E. S. Peterson

The selective separations of trace metals- and organics from water are processes of importance to industry. The application of a new metals capture technology coupled with polymer membrane technology has proven to be one avenue to accomplish such selective separations. The polymers used in these studies are polyphosphazenes. Polyphosphazene polymers consist of an alternating backbone of nitrogen and phosphorus atoms. The polymers have high thermal and chemical stabilities. Experiments at the Idaho National Engineering Laboratory demonstrate that polyphosphazene membranes coupled with Chromato Chem,"Chelation Chromatography" process are capable of removing both chlorinated hydrocarbons and metal ions from process streams. These results point to a wide range of potential industrial and environmental applications for such systems. Data will be presented which show the efficiency and selectivity of separations, postulated separation mechanisms, and the initial designs of industrial demonstration units which are currently under construction. Parts of this work have been performed under a Cooperative Research and Development Agreement (CRADA) between ChromatoChem, Inc. and Idaho National Engineering Laboratory (INEL). The work at INEL was been sponsored by the United States Department of Energy&apos;s Office of Industrial Technologies

Jan 1, 1995

By E. C. L. Cardoso

Hydrocarbon polymers, as PP, made from cheap petrochemical feedstock are important in many branches of industry. However, they have an undesirable influence on the environment and cause problems due to waste deposition and utilization. Polymeric materials composites account for an estimated from 20 to 30% of total volume of solid waste disposed. Thus, there is a tendency to substitute such polymers by those ones that undergo biodegradable processes. Polypropylene (PP) is a commodity, with high melting point, high chemical resistance, low density, with a balance between physical and mechanical properties and easy processing at low cost. Nevertheless, PP shows limitations for some special applications in automotive industry and civil construction. In order to minimize this deficiency, related to rheological behavior of polymer melt, especially referring to viscosity in processing temperature, a 50% mixture with HMSPP (High melt Strength Polypropylene) was used. PP/HMSPP was blended with 10, 15, 30 and 50% of natural (sugarcane bagasse) and synthetic polymers (PHB and PLA) aiming to partially biodegradable materials. The admixtures were subjected to gamma-irradiation at 50, 100, 150 and 200 kGy and then further assessed by mechanical tests in order to evaluate their degradability.

Jan 1, 2015

By Shaohua Ju, Feng Jiang, Chuanhua Li, Jinhui Peng, Libo Zhang

A T-junction microchannel is proposed to overcome the existing problems in conventional solvent extraction of indium from zinc hydrometallurgical process. Experiments were performed to separate In3+, Fe3+ and Zn2+ from sulfate solutions using Di-(2-ethylhexyl)phosphoric acid (D2EHPA) as the extractant. The effect of parameters such as pH, microchannel size and contact time on the extraction behavior of In3+, Fe3+ and Zn2+ was investigated. At contact time of 2.52 s and initial solution pH of 0.48, the extraction efficiency of In3+, Fe3+ and Zn2+ was 99.13%, 8.31% and 2.45%, respectively and separation factor of In3+/Fe3+ and In3+/Zn2+ were almost 1229.54 and 4864.98, respectively. Then, the loaded organic phase was stripped in T-junction microchannel. At contact time of 33.6 s, 99.64% of stripping efficiency of In3+ and stripping equilibrium were reached, while concentration of Fe3+ and Zn2+ was lower than 0.01 g/L with good separation of In3+ from Fe3+ and Zn2+.

Jan 1, 2016

By R. G. Reddy

Viscosities of alkaline metal oxide-silicate melts were estimated using our previously developed mathematical model. The structural based model considers depolymerization effects and related breakdown of the silicate network structure, on the addition of metal oxides to the melt. The developed expression: n =4.9x10 9 NO 0 T ½ exp(E/RT) poise was used to calculate the viscosities of various binary silicate systems such as, CaO-SiO,, MgO-SiO, and MnO-SiO,, as a function of temperature and composition. Excellent agreement was obtained between the calculated and experimentally determined viscosities.

Jan 1, 1991