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By L. Béjar-Gómez

The aim of this research work is to study and characterize precipitates in structural microalloyed steel by transmission electron microscopy and analysis by high resolution (HRTEM). Microalloyed steel with titanium was produced by casting in an electrical induction oven of 25 Kg. capacity. Carbon content in steel was less than 0.1 % and titanium content of 0.04%. Steel was processed thermomechanically; reheated to 1250ºC and hot rolled on a laboratory mill to a 13.0 mm thick plate with a finish rolling temperature of 900ºC and thickness reduction of 80%. Analysis by High Resolution Transmission Electron Microscopy (HRTEM) identified precipitates in the steel; type and morphology. Energy Dispersive Spectroscopy (EDS) analysis was applied to obtain the chemical composition of precipitates and the matrix. STEM-EDS analysis was also applied to obtain the element profile of precipitates. The results showed the presence of carbonitride precipitates of titanium, Ti (CN), with a circular morphology and size of 10 nm and less.

Jan 1, 2006

By Chai Li-yuan

The anodic behavior of AZ31 magnesium alloy in NaOH alkaline solution was investigated in this paper. The effects of anodizing parameters, such as applied current density, concentration of NaOH and temperature of the solution on the formation, structure and surface morphology of the anodic films were also studied. The formation of the anodic film was analyzed by analyzing the anodic polarization curves, the potential-time curves and XRD, SEM graphs of samples obtained at different anodizing time. The results of corrosion resistance tests, XRD and SEM observation showed that the temperature greatly affected the formation and anti-corrosion property of the anodic film, but the concentration of NaOH not. The film with best anti-corrosion resistance was obtained at applied current density of 10mA/cm2, 353k in 1mol/l NaOH solution.

Jan 1, 2006

By S. V. Subramanian

The tool material and the machine design for high speed machining are well advanced over the last decade but the steel design has lagged behind. The paper examines the design of steel in order to control the sliding tribology for high speed machining under dry machining conditions. In high speed machining of steel, accelerated chemical wear of the tool occurs once atomic contact is established at the tool-chip interface, resulting in poor tool life even with high performance tools such as cubic boron nitride. Recent research has confirmed the occurrence of nanocrystalline grains in the interfacial layer of the chip at the tool-chip contact. The volume percentage of grain boundary is increased significantly (10 to 30%) as the nanocrystalline grain size is decreased well below 30 nm. The solubility of tool material into the nanocrystalline grain boundary is two or three orders of magnitude greater than in the crystal lattice. Further the kinetics of diffusion in the grain boundary is seven or eight orders of magnitude greater than in the crystal lattice. Enhanced nanocrystalline grain boundary diffusion occurring in the interfacial layer at the tool-chip contact causes the accelerated chemical wear. Significant improvement in tool life could be achieved by engineering glassy oxide inclusions in steel, designed to self-lubricate the tool-chip interface in-situ at higher cutting speeds. Thus the control of sliding tribological condition at the tool-chip interface is key to suppress nanocrystalline layer formation at the tool-chip contact and hence prevent accelerated chemical tool wear. Sulfide inclusions are designed essentially to promote chip fracture. In addition, sulfide inclusions are designed to act as a diffusion barrier at the tool-chip interface. The application of inclusion engineering concepts to enhance the tool life in high speed machining will be demonstrated with a suitable case history.

Jan 1, 2006

By Stanko Nikolic

Ferrous calcium silicate slags are potentially important for future practice in copper converting operations and processes and can be described by the ?Cu2O?-FeO-Fe2O3-CaO-SiO2 system. Despite its industrial importance the phase equilibria in this system have not been fully investigated. Characterization of this slag system is necessary to improve the design and optimization parameters of new processes, including fluxing and operating temperatures. Experimental methods have been developed to investigate the phase equilibria of these slags at copper saturation and without copper. This technique involved equilibration of samples at a fixed oxygen partial pressure, rapid quenching, and analysis of the compositions of phases using electron probe x-ray microanalysis (EPMA). Liquidus and solidus data are reported for the primary phase fields of spinel, wollastonite and tridymite at 1250oC and an oxygen partial pressure of 10-6atm. The resulting data has been used to construct liquidus isotherms in the ?FeO?-CaO-SiO2 system both in equilibrium with and without molten copper. The experimental results were compared with the predictions of a thermodynamic computer package utilizing a self consistent thermodynamic database. The predictions of the model were in good agreement with the experimental isotherms when projected onto the FeO-CaO-SiO2 section, however the copper concentrations in the liquid phase at copper saturation were lower than predicted using the current database of the model.

Jan 1, 2006

By Jackson Jenkins

The second survey of world copper SXEW plants has been completed. Solvent extraction and electrowinning data published in 1996 has been updated and leach data from seventeen plants is now included. The following pages list the results of the thirty- two plants that responded to the survey. Selected information is summarized in graphical form.

Jan 1, 1999

By I. Kim, J. C. Choi, W. D. Cho

"The effect of yttrium addition on the oxidation behavior of Fe3Al intermetallic compound was investigated in the range of temperature 800 to 1100 °C in 0.2 atm 02 in terms of oxidation rate and oxide adhesion. The oxidation rate of alloys, Fe-14.3 wt% Al and Fe-14.1 wt% Al-0.3 wt% Y, was nearly identical and the parabolic rate constant calculated as a function of temperature is Kp=5128 exp[-39506(cal/mol)/RT] mg2/cm4 hr.Rapid cooling and ultrasonic stress tests were carried out to test adhesion of scale formed on the alloys. While the oxide layer formed on the Fe-Al alloy without Y was found to be fragile and detached easily during the tests, the oxide layer formed on the Fe-Al alloy containing Y was protective, dense, and adhesive. The following two mechanisms were proposed to explain the adhesion improvement of Ah03 formed on the Fe3Al containing yttrium : (1) the addition of yttrium decrease generation of growth stress in alumina scale because the preferential diffusion of yttrium through grain boundary in alumina scale prevent internal oxidation of Al, one of main causes of growth stress, and (2) the second phase formed on the oxide scales prevents crack propagation through the scales, leading to better mechanical stability of the oxide scales.IntroductionIron aluminides have attracted the attention of many researchers as a candidate for use at high temperature because of their excellent oxidation resistance due to the formation of protective alumina scale. In order to resist aggressive environments at elevated temperatures, oxide scale formed on iron-uluminum alloy must satisfy the following three requirements : (1) thermodynamic stability (2) slow growth rate (3) adherence on substrate. According to Wallwork and Hed [l], the most suitable alloys for high temperature application are Fe, Ni, and Co alloys with the protection of Si02, Cr203, and Ah03 scales. While chromium oxide can vaporize as Cr03 above 1000 °C and silicon oxide may form low melting silicate [2,3], Alz03 has a high melting point and is the most stable among the three oxides thermodynamically [6]. In this respect, iron aluminides forming alumina seem to be most suitable for use at high temperature. However, alumina scale formed on the iron aluminum alloys tends to be easily spalled during oxidation due to the combination of growth stress and thermal stress."

Jan 1, 1998

By T. Maruyama

The Tamano Smelter of Hibi Kyodo Smelting CO. ,Ltd. went into operation in 1972. The Flash Smelting Furnace that was originally adapted was equipped with electrodes that were attached to the settler substitute of the slag cleaning furnace. Later the development of our own original coke combustion technology was promoted and a new Tamano Type Flash Smelting Furnace (T-FSF), without electrodes, was put into operation in 1988. The technology of coke combustion and combustion the burner have continued to improve. As a result the copper losses in the slag have been reduced as well as a stable operation has been achieved. Furthermore, this has been accomplished while increasing the concentration feed and the matte grade The current objective is to continue to strive for high matte grade operation and to raise production efficiency while paying attention to the important subject of copper losses in the slag. In this report, the data related to the copper loss in the slag reduction are presented along with the influence of the thickness, settling time and coke. The recent operation conditions of the T- FSF are also presented.

Jan 1, 2003

By J. Dille

Metallic cobalt exist in two allotropic forms : the hexagonal compact a which is stable at low temperature ( ( 420') and the cubic form 0 stable at higher temperature. This latest form is the only one which is ductile. During the electrode position of Co, in moderate acidic conditions, we noticed a code position of both a and B forms. The influence of several parameters on the B/a ratio in the deposit was investigated. High acidity and the presence of Fe increased its ratio; on the opposite, high temperature promote the a phase. No significant influence on the material were noticed. The differentiation of a and B forms of Co is rather difficult and the method of J. Scoyer was improved quite successfully.

Jan 1, 1988

By Chi-Ming Chang

Alloy powders are commonly used in the purification of zinc sulfate solutions for use in standard electrowinning practice. The primary goal of this research was to study the use of zinc-lead alloys for similar reactions in the galvanic stripping of impurities from organic solutions. The effects of various parameters on the electrochemical behavior of commercially produced zinc-lead alloy powders were determined. A qualitative evaluation and summary of the influence of the more pertinent parameters on iron removal from di-(2-ethylhexyl) phosphoric acid (D2EHPA) by galvanic stripping is given. Water concentration, oxygen content and reaction temperature were the principal factors affecting the reaction rate and process efficiency. Activation energies were also calculated and indicated that the reaction changes from chemical to diffusion control .with increasing temperature in the range of 35" to 45°C. The results showed that zinc-lead alloy gave faster reaction rates with less sensitivity to process variables than SHG zinc as a reducing agent for galvanic stripping. The role of lead could be as cathodic sites for the reaction which enhances the zinc dissolution or anodic half reaction. The morphology of the zinc-lead alloy surfaces, before and after the reactions, supports this assumption.

Jan 1, 1998

By I. Iwasaki

Flotation characteristics of pyrrhotite by itself and in complex sulfide ores are reviewed with respect to the effects of oxidation, grinding media and other electroactive minerals.

Jan 1, 1988

By Moelans. N.

A method using an ex-situ electrochemical measurement device was developed to determine the oxygen potential of non-ferrous metallurgical slags. The electrochemical cell consists of the molten slag sample, an inert Ir electrode, a stabilized Zr02 solid electrolyte and a NilNiO reference electrode. Different slags from non-ferrous pyrometallurgical processes were analysed at I 100 and 1200 °C and pO2values between 10-3 and 10-12 bar were obtained. The measurements were evaluated with thermodynamic calculations and using processing considerations. It was found that the reproducibility and stability of the measurement was significantly improved by shielding the molten slag from the atmosphere by a thin layer of carbon, especially for slags with a low oxygen potential.

Jan 1, 2003

By B. Yawney

A copper-nickel sulfide concentrate was leached in water at about 2000C under oxygen pressures of about 0.35 MPa. Oxidation of sulfide to sulfate was virtually complete in about 30 minutes, resulting in greater than 95% copper and 98% nickel extractions. Leaching temperature was shown to be the most important factor affecting metal extractions. Measured rates of oxygen consumption were used to develop batch kinetic data. Mini-plant continuous pressure leaching tests agreed with batch leach results. A proposed overall flowsheet is briefly examined.

Jan 1, 1976

By H. J. Thevik, A. K. Dahle

"A mathematical model that calculates the stress development in a coherent and stationary dendritic network due to interdendritic flow is proposed. The fluid flow is assumed to be related to the solidification shrinkage, and under the assumption of no porosity formation and unidirectional solidification, the shrinkage-induced flow within the mushy zone is calculated analytically. The interdendritic melt flow exerts a force on the solid network and an analytical expression for the stress build-up in the network is developed. Parameter studies illustrating the influence of cooling conditions, mushy zone length, dendrite coherency, fraction solid, volume fraction of eutectic, and solidification shrinkage upon the stress development within the solid network are presented. Comparing the magnitude of the calculated stresses to measurements of the strength in equiaxed mushy zones shows that it is possible for the stresses to exceed the strength, thereby resulting in reorientation or collapse of the dendritic network.IntroductionInterdendritic fluid flow is at present regarded as a very important mechanism for feeding of shrinkage during solidification of metal alloys. Solidification of many alloys is often characterised by heterogeneous nucleation of the primary phase on substrates in the melt with subsequent evolution of equiaxed dendrites. These equiaxed dendrites can initially grow freely, but impinge on each other and form a continuous dendritic network, ie. dendrite coherency, quite early in the solidification process. Measurements of the dendrite coherency point have shown that the dendritic network is established at solid fractions ranging between 0.1 and 0.5, and most often around about 0.2 [l]. Depending on the alloy composition this means that as much as 70 to 80% of the volumetric shrinkage has to be compensated by flow of liquid through the interdendritic network. Interdendritic flow occurs with a much larger resistance compared to free flow of the liquid and flow of a liquid with dispersed crystals. The pressure drop associated with the interdendritic flow increases rapidly with decreasing fraction ofliquid."

Jan 1, 1999

By Cevat Serdar Kucukkaragoz

The kinetics of prereduction of Chromite by carbon was studied under argon atmosphere at temperatures between 1000°C and 1300°C . The compacted and agglomerated specimens were reacted by using a TGA system. The mixing characteristics and the degree of compaction of the chromite and coke particles were the main parameters influencing the reduction kinetics. The reduction rate increased with temperature reaching to 81% reduction at 1300°C. The metallization started as the metallic nucleation around the particles which was first observed at 1100°C. The particles were surrounded by the metallic phase at approximately 40 % reduction obtained at 1200°C. At 1300°C, the reduction proceeded with a high rate during initial stages and with a low rate at final stages. The reduction was found to proceed in the sequence of Fe3+to Fe2+, Fe2+ to Fe(metal) and Cr3+to Cr(metal) with the formation of carbides.

Jan 1, 2006

By A. K. Riihimäki

The description deals with duplex stainless cast steels and austenitic high molybdenum steels used in pumps for severe condition service. The main modem nitrogen alloyed duplex cast steels are presented in the ASTM standard A-890. Two grades of high molybdenum austenitic stainless steels there are presented in ASTM A-744 (-96) standard i.e. CN-3MN and CK-3MCuN. The latest and most corrosion- resistant stainless steel grade is AVESTA 654 SMO?. Avesta Sheffield the trademark owner has granted Ahlstrom Pumps license to produce the material. This new stainless steel as pump material for severe service has improved properties in the hydrometallurgy and electrorefining processes of metal and especially in the copper industry compared to duplex stainless steels. The paper deals briefly with the foundry process to manufacture high alloy stainless steel pump castings. The AOD-method (AOD= Argon Oxygen Decarburization) is an important prerequisite for the melting of low carbon, high chromium and molybdenum alloyed nitrogen steels. The properties of these steels are included. The main topic is the corrosion resistance of the above-mentioned pump materials in severe service. Results of short-time erosion and corrosion tests are discussed and compared with the results of plant tests. Practical results of pump materials performance in severe service for the copper industry are given. The new high alloyed cast stainless steel (main elements; Cr-24%, Ni-22%, Mo-7,3% and N-0,5%) has shown improved corrosion and erosion properties as process pump material in several severe service applications e.g. in the metal industry.

Jan 1, 1999

By Yu-ichi Kanbe

It becomes more important to control the composition of inclusions with increasing the demand for quality of products in terms of cleanliness. Along with the development of refining technology to make inclusions harmless, a study was made to develop how to predict the quality of final products. At first, observations of a number of defects revealed that the defects were caused by inclusions larger than 100 m in diameter. Therefore it is required to detect relatively large inclusions in steel, whose existence is quite rare, to identify the quality. In order to estimate the maximum size of inclusions in a given sample, the method with statistics of extreme values has been applied for continuously cast (CC) slabs, hot-rolled coils and cold-rolled coils of type 304 stainless steel. For the CC slabs the diameter of inclusions, which were analyzed to be mostly silicate with globular shape, in the specimens was measured. For the coils, the width of inclusions was measured at the unit section perpendicular to rolling direction because it corresponds to the diameter assuming that the width of globular inclusions does not vary with rolled. Then maximum inclusion diameter in a specimen was calculated. As a result, the obtained values in the rolled coils are larger than in the slabs. This may imply that the measurement with the coils gives the values closer to the truth. Besides, the measurement with the coils is even faster than with the slabs due to its simplicity of preparation of the specimens.

Jan 1, 2006

By Leo Brewer, Kazuyoshi Shimakage, Mamoru Mitomo, Toshiyuki Nishimura, Yoichiro Uemura, Shinji Hirai

"In the synthesis process of ß -La2S3 via the sulfurization of La2O3 powder using CS2 gas, La2O2S was formed. This occurred at an initial stage of the reaction for sulfurization temperatures below 973K, and ß -La2S3 was also formed at a shorter period for higher sulfurization temperatures. It was found that the oxygen content in ß -La2S3 powders decreased gradually with an increase in sulfurization temperature. On the other hand, the carbon content in these powders increased gradually with an increase in the sulfurization temperature. Though it has been reported that ß -La2S3 was transformed to Y -La2S3 at 1723K± 50K, the sintered compact of double-phase Y -La2S3 and ß. -La2S3 was formed at a rather higher temperature of 1973K when the synthetic powder of ß -La2S3 containing a high amount of oxygen was used. However, phase transformation of -La2S3 to Y -La2S3 progressed preferentially with a decrease in the oxygen content of synthetic ß -La2S3 powder. The Seebeck coefficient of the sintered double-phase Y -La2S3 and -La2S3 was higher than that of the single-phase Y -La2S3, reported previously.Introduction La2S3 exists in three polymorphic forms that are similar to a series of Ce2S3, Pr2S3 and Nd2S3: a, ß , and Y'. The a -La2S3, which is stable at low temperature, is irreversibly transformed to ß -La2S3 of various compositions in the solid-solution range between La2S3 and La3S4, at 923 ± 50K. The -La2S3 may also be an oxysulfide of La10S14O2. Moreover, the ß .-La2S3 phase is transformed to Y -La2S3 ,which has a Th3P4 structure, at 1573 ± 100K. The melting point of Y -La2S3 is 2398 ± 30K where this temperature is similar to those of common refractory materials such as silica and alumina. Therefore, it can be predicted that y -La2S3 which has a high melting point and a thermodynamic stability due to the strong affinity of La for S, would have &high refractory character and chemical inertness in many molten metals. The y -La2S3, colored vivid faint yellow is stable up to 623K in air, where oxidation starts. y -La2S3 is frequently used as pigments for plastics and paints3. Furthermore, Y -La2S3 which is a semiconductor, is considered to be useful as a thermoelectric conversion materials, because it has a high Seebeck coefficient."

Jan 1, 2000

By Aichun Zhao, Rui Wang, Yihong Li, Yanping Bao, Yafeng Ji, Jiansheng Liu, Xiao Hu, Qingxue Huang

The slag entrapment under different conditions of 80t blowing argon ladle furnace was investigated by physical simulation. The water was used to simulate liquid steel and liquid paraffin was for slag. The processing of slag entrapment under different blowing structures was analyzed and the critical velocity and critical droplets diameter of describing it was obtained. Based on the experiments, the relationship between the interface flow velocity and the critical blowing rate CBR was deduced. In the real process, it is suggested that the bottom blowing rate is from 40 L/min to 180L/min when the interface tension is 0.12~1.2 N/m during the soft argon blowing.

Jan 1, 2016

By Rafael Padilla

The recovery of copper from chalcopyrite concentrates by leaching is difficult due to the slow dissolution kinetics of this mineral in most leaching media. However, recovery of copper from sulfidized chalcopyrite (a mixture of CuS and FeS2) by leaching is faster and could be selective depending on the leaching media. In this paper, the result of an investigation on the H2SO4-O2 pressure leaching of sulfidized chalcopyrite is presented. The variables considered in the study were stirring speed, concentration of sulfuric acid, temperature, and partial pressure of oxygen. The experimental data indicated that stirring speed over 500 rpm and sulfuric acid concentration over 0.1 M had very little effect on the leaching rate. An increase in temperature from 90 to 100 ºC increased both copper and iron dissolution; however, further increase to 120 ºC affected negatively the copper dissolution. Oxygen partial pressure was found to be the main variable that controls the copper/iron selectivity of the leaching. An increase in oxygen partial pressure increased significantly the rate of copper dissolution but deteriorated the copper/iron selectivity. The analysis for sulfur of the leaching solid residues indicated that most of the copper sulfide sulfur in the sulfidized concentrate oxidized to elemental sulfur.

Jan 1, 2006

By Alfonso Nájera

Turbulent flow of liquid steel and its control is studied using different geometries of turbulence inhibitors. Four designs of turbulence inhibitors were characterized through experiments of tracer injection I a water model and mathematical simulations using the Reynolds Stress Model (RSM) of turbulence. Geometries included octagonal-regular, octagonal-irregular, pentagonal and squared. A layer of oil was used to model the behaviour of tundish flux during steel flow. Fluid flows in a tundish using these geometries were compared with that in a bare tundish. Experimental and simulation results indicate that the flow in the bare tundish and a tundish using turbulence inhibitors open large areas of oil due to strong shear stresses at the water-oil interface but the squared inhibitor. These phenomena are explained by the high gradient of the dissipation rate of the turbulent kinetic energy using the squared inhibitor. Using this device the kinetic energy reports a high gradient from the tundish floor to the free bath surface as compared with other geometries.

Jan 1, 2006