Search Documents

By R. Cavanagh

Studies relating to the fixation of sulfur by reaction of 4 to 8 mm diameter cylinders of calcined limestone or dolomite with high strength sulfur dioxide in the temperature range 880°C to 1020°C were undertaken. Dolomites are far superior in sulfate capacity and reactivity than dense limestones even at high strength SO2. The sulfation reaction was first order with respect to SO2 concentration below 100 percent. Zero reaction rate at 100 percent SO2 concentration indicates that sulfate was the exclusive reaction product and that sulfite had no role in the reaction. At relatively low SO2 concentrations gaseous diffusion through the reaction product layer has a marked effect on the rate. As SO2 concentrations were increased up to 100 percent more complex rate controlling mechanisms unfold. By sectioning partially reacted dolomitic limestone pellets a moving interface was observed. Reaction ceased because of pore plugging for dense non-porous limestones at 30% conversion. With dolomitic material virtually complete sulfation of the calcium was observed. S.E.M. analysis showed that the average atom ratio Ca:S was 1.01, thus supporting the argument that little if any of the magnesium was sulfated.

Jan 1, 1996

By Xirneng Zhu

The electrochemical behavior of Pittsburgh and Illinois coal pyrite in basic and neutral borate/sulfate solutions was investigated. In the transpassive region, aggressive oxidation of pyrite occurred. The reaction products in this region were Fe(III) oxide, sulfate ion and partially oxidized sulfur intermediates. The formation of sulfur and polysulfides was identified by in-situ Raman spectroscopy. The growth kinetics of the reaction product film, resulting from transpassive oxidation of coal pyrites, were studied using chronoamperometry measurement with both stationary and rotating disk electrodes. The reaction rate was well correlated by a paralinear rate equation. The effects of electrode rotation speed, solution pH and temperature were examined. The kinetics were compared to those for mineral pyrite.

Jan 1, 1994

By Makoto Suzuki

After hot rolling, stainless steel strip is processed by the Hot Rolled Annealing and Pickling line (HAP) , where H2SO4 or mixed acid of HNO3 and HF is normally used. In the pickling bath, metal oxide accumulates in the form of sludge, which should be removed from the bath regularly. A new automatic continuous sludge disposal system has been introduced at Chiba Works of Kawasaki Steel Corporation to increase sludge removal efficiency and improve the working environment. The elements of the equipment are as follows. a. Ejectors in pickling bath: to carry the mixed acid into the circulation tank through the piping system. b. Sedimentation bath : to sediment sludge out of the bath. c. Skip conveyer : to convey a specified volume of sludge into a kneading for device for neutralizing. The sludge removal efficiency of this system is very high. and the volume of sludge accumulation in the pickling bath has substantially decreased.

Jan 1, 1996

By Hui-Gai Li

The fine Ti oxide inclusions precipitated during solidification are favorable for intragranular ferrite nucleation. The oxygen content before solidification affects the composition and size of inclusions. The composition of precipitated inclusions in Mn-Ti alloyed steel was studied by means of thermodynamic calculation and experiment in this paper. The micro-segregation of Mn, Ti and O during solidification was considered in calculation and unidirectional solidification apparatus was employed in experiment to ensure that alloy elements diffused along solidification direction. The results showed that: inclusions are mainly Ti oxide when oxygen content is 10ppm; they are Ti oxide and Mn-Ti oxide when it is 20ppm; Mn-Ti oxide dominates when it is 30ppm. With the increase of oxygen content, the size of inclusions increases. The maximum oxides size is about 3µm from statistical results of experiment.

Jan 1, 2008

By Dian Adisty, Leiv Kolbeinsen, Eli Ringdalen

In Si and FeSi production, the main Si source is SiO2, in the form of quartz. Reactions with SiO2 generate SiO-gas that further reacts with SiC to Si. During heating, quartz will transform to other SiO2 modifications with cristobalite as the stable high temperature phase. Transformation to cristobalite has been investigated and shown to be a slow process where the rate varies between the investigated quartz types. The effect of quartz versus cristobalite as SiO2 source has been studied for reaction (1) 2SiO2 + SiC = 3SiO + CO, by heating of pellets with SiO2 + SiC in Ar-gas. The reaction was faster with cristobalite than with quartz. Initial experiments indicates that this is the case only in Ar and not in CO-atmosphere The higher specific surface area of cristobalite is believed to contribute to the higher rate. The industrial consequences of the observed difference between quartz types are discussed.

Jan 1, 2014

By Du Sichen, S. Seetharaman, J. A. Bustnes

"The present study deals with the kinetic studies of reduction of some selected transition metal tungstates with hydrogen. The measurements were carried out by the isothermal thermogravimetric method. Shallow powder beds were employed in order to avoid the effects due to transport phenomena affecting the reaction rate. In this way, the chemical reaction rates could be selectively studied. The experiments were carried out in the temperature range 873 - 1173 K. From the experimental data, the activation energies were evaluated and were found to be around 88 kJ / mol in the case of both iron as well as cobalt tungstates indicating the similarities in W-O bonds in both cases. The activation energies obtained are discussed in the light of the position of the transition metal in the periodic table as well as the thermodynamic stabilities of the various tungstates.IntroductionThe tungsten containing hard metals, characterized by high density, belong to a class of two-phase metal matrix composites. While these types of materials have traditionally found their applications within the defence industry as armour-piercing projectiles, counterbalance in helicopters and military aircrafts, outer casings of hand-grenades, etc., commercial applications for this class of alloys also exist, including radiation shields, penetrators for the oil industry, turbines for turbo-jet engines and a wide range of sports related parts. A possible route to the production of these alloys is to reduce the tungstates such as FeW04, Co W04 and NiW04 using a reductant like hydrogen or carbon monoxide. In order to have a better understanding of the processes involved in the production, it is important to have a knowledge of the reduction kinetics for these tungstates. According to the knowledge of the present authors, while the reduction ofNiW04 by hydrogen gas has been investigated earlier in the present laboratorypl no systematic reduction study has been carried out previously for the tungstates of iron, cobalt."

Jan 1, 1996

By V. Ramachandran

The Amarillo Copper Refinery, the newest and most modern copper refinery in the world, has been in operation for the last eleven years and has a rated capacity of 460,000 st/yr. The tankhouse - a structure that covers 500,000 ft2 under one roof - extends one-half mile in length and is a model of materials-handling efficiency. The use of recently developed and patented* reagent control technology, termed "Reatrol Process", has increased current efficiencies to an average of 98% and has considerably improved the physical and chemical quality of the cathode deposit. The present paper describes the current operations at the Amarillo Copper Plant with special emphasis on tankhouse operation.

Jan 1, 1987

By Luben Xie, Lin Hu, Qiang Wang, Min Gan, Tao Jiang, Wenqi Li, Xiaohui Fan, Zhiyuan Yu

"Crystal precipitation behavior of calcium ferrite (CF) during iron ore sintering process along with the effect of cooling rate, SiO2 and Al2O3 on crystalline condensation were studied. The results show that CF, has strong ability of precipitation. The precipitation is barely affected by extenal factors. It begins to precipitate when the liquid phase cools down to about 1200oC. CF could crystallize rapidly at the cooling speed of 150 °C /min. Furthermore, decreasing of the cooling rate favors the development of crystal. Binder phase transformed from CF system to silicate system when SiO2 content was increased to 5~6%, with a constant basicity (R) 2.0. Increasing Al2O3 content could promote the precipitation of CF and the development of crystal.IntroductionCrystalline condensation is the last stage of sinter mineralization. It includes the processes that crystalline substance and amorphous substance precipitate from high temperature solution phase and the consolidation of material when melt cools down. During the crystallization process, minerals precipitate following the order from high to low melting point coupled with the decreases of free energy. Most of binder phase minerals and part of iron oxides crystallize in this process, which have an important influence on mineral composition and microstructure of sinter. They finally determine the sinter strength and metallurgical properties."

Jan 1, 2011

By H. Y. Sohn, S. PalDey

"Fine particles of nickel aluminides and Ni4Mo were synthesized by reducing mixtures of, respectively, A1Cl3 + NiC12 and NiC12 + MoC12 vapors with hydrogen. Though thermodynamically favorable, the coreduction of NiC12 and A1Cl3 by H2 to form Ni3Al did not readily happen experimentally. The addition of a small amount of aluminum vapor was needed to initiate the coreduction reaction. The product particles as observed by TEM were very fine but usually agglomerated. The electron diffraction pattern of particles identified NiAl and NiA13 along with Ni3Al and metallic Ni. The content of Ni3Al was maximized at 52 mol% at 1050°C under the partial pressures ofH2, A1Cl3, and NiC12 at 57, 1.4, and 0.5 kPa, respectively. When a mixture of NiC12 + MoC15 was reduced by hydrogen, Ni4Mo particles with some Ni or Mo particles were obtained, the maximum content of Ni4Mo obtained being 93 mol % . The particle size was in the range of 100 to 200 nm. An Ni4Mo coating of 700 nm thickness on an Ni substrate was also prepared.IntroductionThe search for new high-temperature structural materials has stimulated much research on intermetallic compounds. Nickel aluminides have low densities, relatively high melting points, and good high-temperature strength properties. They show an increase, rather than a decrease, in yield strength with increasing temperature (1). Ni4Mo is also of interest as a high-temperature structural material. The major shortcomings of these intermetallics are their inherent brittleness at room temperature when they are in polycrystalline form. For much the same reason, the conventional casting of intermetallics is difficult. Ingot metallurgy and powder metallurgy are two other processing techniques. The first technique is quite energy consuming. In powder metallurgy, the powders of metals and alloys are consolidated in near net shape and then subjected to secondary processing. It would, therefore, be advantageous if intermetallic compounds can be produced in fine powder form from inexpensive raw materials, using less energy."

Jan 1, 1998

By F. D. S. Marquis

An investigation of the mechanisms of formation of two types of porosity-primary and secondary-their characterization, evolution during processing, and effects on the mechanical behavior (fracture, fatigue, and failure) of 7X50 and 2X24 alloys has been conducted. The mechanisms of formation of three forms of primary or cast porosity were investigated, and each form was characterized: (a) macroscopic shrinkage porosity-MSP); (b) microscopic interdendritic porosity (MIP); and (c) hydrogen gas porosity (HGP) or primary hydrogen porosity (PHP). The mechanisms of formation of four forms of secondary or thermal/thermomechanical porosity were investigated, and each form of porosity was characterized: (a) high temperature oxidation (HTO). internal hydrogen precipitation (IHP), or secondary hydrogen precipitation (SHP); (b) preheating blistering porosity (PBP); (c) eutectic melting porosity (EMP);and, (d) dissolution micro void formation (DMF). The evolution and interactions of the primary and secondary types of porosity (w.ith special emphasis on PHP and SHP) during industrial and laboratory processing and their effects on the fracture and failure behavior of both types of alloys (with special focus on fatigue crack initiation and propagation) were investigated.

Jan 1, 1996

By F. Shahbazian

attempt to systematize the knowledge on slag viscosities, the present work was carried out. The Among the physical properties of slags, viscosity is very important in understanding the mass out in the temperature range 1438-1762 Q The rotating cylinder method was used in the viscosity measurements. Crucibles and spindles made out of pure iron were employed. The transfer phenomena in metallurgical processes. The viscosities of fayalitic slags are of great interest in the non-ferrous metal industry, with special reference to copper production. In an slags were prefused before the measurements. In order to take into account the vaporization reactions involving CaF2, pre- and post measurement samples of the slags were chemically analysed and the compositions were ascertained. The results show that in the case of the CaO-SiO2 system, CaF2 additions tend to decrease the viscosity, in accordance with the expectations. In the case of the "FeO"-SiO2 system, at higher "FeO" / SiO2 ratios in the slags, a reverse trend was observed. The results are discussed on the basis of a viscosity model for silicate melts developed in the present laboratory as well as the structural considerations of silicates.

Jan 1, 2000

By E. A. van Dijk

Dusts from steel-making processes contain substantial amounts of zinc. Such dusts are also a hazardous waste and dumping them becomes unacceptable from environmental point of view. Therefore processes that can recover zinc and possibly other metals from steel-making dusts are being investigated. The aim of this paper is a contribution to the more fundamental kinetic aspects of zinc reduction from silica free calcium ferrite slags. The effects of alumina, lime and magnesium oxide contents of the slag, the COICO, ratio and the effect of initial Fe2O3/CaO ratio were studied experimentally at 1400°C The results indicated that the reduction of zinc from molten slag was possibly a first order reaction. As expected higher COICO, ratios increased both the extent and the rate of reduction. It was also observed that a higher iron content of slag improved the reduction of zinc from calcium ferrite slags. This fact seems to support the proposed mechanism that zinc is partly reduced by ferrous iron to zinc vapour and that ferric iron is reduced by carbon monoxide. The reduction rate of zinc in these slags was decreased by increasing alumina content of the slag. Alumina decreased the calculated optical basicity of the slag showing the fact that reduction of zinc oxide was more favorable in more basic slags. Probably the formation of complex ions by alumina and zinc oxide such as ZnAl2O32+ lowers the activity of Zn2+ ions in the slag and hence render them more difficult to reduce.

Jan 1, 1999

By S. E. Khalafalla

A method for preparing ferrochromium alloys containing less than 2 pct carbon has been devised in a single vacuum furnace reactor. This method can conserve chromium and should reduce the capital and energy requirements relative to chromite electrothermal reduction. Reduced products containing less than 2 and as low as 0.01 wt pct carbon were obtained by reacting pellets of chromite and carbonaceous reductant mixtures at pressures of 0.1 to 1 ton and temperatures of 1,230° to 1,320° C. The extent of reduction increased with increased temperature and decreased pressure; however, operating conditions were limited due to the onset of significant chromium vaporization at higher temperatures and lower pressures. Foundry coke, anthracite, and carbon black were found to be superior to graphite as reductants. The reduction of chromite to metallics was found to proceed via the carbide intermediates Fe3C or Cr3C2. Lime accelerates the. rate of solid state reduction of chromite and can shorten the furnacin1r time at 1,3000 C under vacuum from 13 hours to less than three hours. Additional lime and silica are added to the hot reduced chromite after releasing the vacuum and raising the furnace. temperature to 1, 700° C. Soaking the charge for about 20 minutes gave a button of low carbon ferrochromium alloy beneath a well-defined slag layer.

Jan 1, 1985

By M. Soltanieh

The liquidus surface? and tie-lines in the nickel-cobalt-sulphur ternary system have been determined between 1<273-1573 K. The experiments were conducted by equlibrating the liquid sulphide with the metallic alloy phase. The liquid sulphide phase was sampled and chemically analyzed. The alloy was analyzed by electrol} microprobe. Combining the present results with the.avai1abl~ literature data, the thermodynamic properties of this system were calculated.

Jan 1, 1998

By Petrus Christiaan Pistorius, Ming Tang

Magnetite concentrate is pelletized and then hardened by elevated-temperature oxidation to hematite, to produce pellets for ironmaking. Previous work showed that the rate of oxidation is under mixed control of gaseous mass transfer of molecular oxygen through the pellet pores, and solid-state diffusion into the oxidizing grains. Because of the partially limiting role of solid-state diffusion, concentrate size distribution strongly affects pellet oxidation. Previously, a simple mixed-control model was formulated to describe isothermal oxidation. In that model, the main effect of concentrate size distribution was on the plateau level of oxidation which is reached at a given temperature. However, the extent of plateau oxidation increases with increased temperature, requiring a more complex model for non-isothermal oxidation. In this paper, predictions of the non-isothermal model confirm the strong effects of concentrate size distribution and oxygen enrichment. In particular, a greater fraction of coarse magnetite particles would be beneficial, decreasing the size of the macroscopic unoxidized pellet core.

Jan 1, 2015

By Mick O'Meara

Metal Organic Chemical Vapour Deposition (MOCVD) is used in the production of computer circuit boards and metal shapes in nickel, gold, copper, cobalt, etc. All varieties of .MOCVD use the decomposition of a vapour of organometallic compounds to produce different forms of ultra-pure metals, or alloys. CVD Manufacturing's proprietary MOCVD process has been adapted and developed to produce commercially ultra-pure metal shapes, metal powders, and metal foams. Therefore, it is a purification process. The typical process has three steps. First, a volatile metal organic compound is produced from volumetrically contaminated metals, metal oxides, etc. Typical feed materials are metal powders, ores, concentrates, or a slurry of metals and contaminants. Secondly, the volatile. metal organic compound is purified by fractional distillation. Thirdly, the purified metal organic compound is decomposed into different forms of ultra-pure metals, such as net shapes, powders, or metal foams. A mixture of metals can be purified either by the selective production of volatile materials, or a separation can be achieved during the second step, in the fractional distillation stage. The purification and recycling of metals by the MOCVD process will be discussed, particularly with regard to nickel, aluminum, gold, the platinum group and other metals.

Jan 1, 2000

By Merete Tangstad, Fei Li

This paper studies the quartz and carbon black pellets at elevated temperature with varying temperature and gas atmosphere. High-purity quartz and commercial ultra-pure carbon black was mixed (carbon content wt.15%), and then pelletized into particles of 1-3mm in diameter. The stoichiometric analysis of the pellet during heating is studied in thermogravimetric analysis (TGA) furnace at different temperature in CO and Ar atmosphere. The microstructure, phase changes and element content of sample before/after heating is characterized by X-ray diffraction, scanning electron microscope, X-ray fluorescence and LECO analyzer. The reaction process can be divided into two stages. Higher temperature and argon atmosphere are the positive parameters for SiC formation.

Jan 1, 2016

By Michael K. Rhodes

A 120 tonne per day BacTech bacterial oxidation plant treating refractory gold concentrates for Gold Mines of Australia&apos;s Youanmi project in Western Australia commenced operation September 1994. This was the first commercial application of the BacTech process. A pilot plant trial on concentrates produced from Youanmi ore was carried out at BacTech&apos;s laboratory in Perth. Results and measurements from this trial were used by Signet Engineering Pty Ltd to design the commercial plant. This paper cover the results obtained from the piloting, their implementation in the plant design and the initial commissioning of the full scale plant.

Jan 1, 1995

By Patrick R. Taylor

Keywords: Thermal Plasma, Electroreduction, Electrolysis, Transition metals, Waste treatment, Molten oxides, Chromium oxide. An innovative process to treat transition metal oxide waste materials from diverse sources is presented. This technology involves using reverse-polarity DC plasma driven electrolysis in molten oxides. The process results in the recovery of the transition metal and other heavy metals from waste. By-products generated throughout the processing was converted to environmentally acceptable slag. The significance of this technology is that the treatment of the waste is accomplished in one step which in turn lowers the cost of remediation. Moreover, this process uses high temperature properties of thermal plasmas, which makes it possible to use molten oxides instead of halides as electrolytes. Chromium was successfully reduced from chromium oxide through the plasma driven electro-reduction process. It was shown that the selection of the appropriate ionic conducting oxides was critical for the formation of a slag that would enhance the reduction of chromium oxide.

Jan 1, 2004

By Javier Antoñanzas, Susana Caballero, Eduardo Fernández, Jorge Aragón, Juan Carlos Múgica, Lourdes Yurramendi

Air Pollution Control (APC) residues treatment by plasma was studied as a technology for vitrification. During the project a protocol to verify the plasma technology was developed and afterwards applied to a specific case study: the APC residues from Municipal Solid Waste Incinerators (MSWI). Different operational conditions were tested and the vitrified products obtained were analyzed using standardized leaching tests in order to evaluate their new properties concerning safety storage. Two leaching tests were used for the evaluation, the European EN 12457-4 compliance test for leaching of granular waste materials and the French XP X 31-211 test for the determination of the leachability of a solid waste material initially massive or generated by a solidification process. Finally, conclusions about the environmental performances of the technology were obtained.

Jan 1, 2008