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By Chu Bo-Yi

"This paper contains a comparison of creep-feed and shallow-cut grinding on ceramics with both neat oil and water-based grinding fluids. When a water-based grinding fluid was used in creep-feed grinding on ceramics the vertical forces and specific energies increased markedly fast with result that the wheel surface was damaged seriously. Creep-feed grinding on ceramics with neat oil not only produced much lower grinding forces and specific energies but also resulted in the wheel remaining in good condition and minimizing damage to the ground surface. This finding may lead to a deeper understanding of the behaviors of grinding fluids in grinding processes both on ceramics and metal as well.1. IntroductionAs advanced ceramics are obtaining more and more applications in the technical area, some machining processes are needed after the sintering to reach the accuracy and finish required by components. Because of higher hardness and brittle behaviors of modem ceramic many researches have been done in order to improve grinding efficiency and surface quality.In the grinding metals the concept of creep-feed grinding has been developed in industry as a real alternative to the normal method of shallow-cut grinding. In addition to the general economic advantages, dimensional accuracy and surface integrity are invariable improved using the creep-feed grinding technique.In grinding ceramics former studies have done many works on both creep-feed and shallow-cut grinding on ceramics with water-based grinding fluids since the water-based were thought to be better coolants than neat oil in most tests of grinding metals[l]. It was suggested that the specific grinding energies of ceramics are markedly higher in creep-feed grinding. The grinding force increases vary rapidly with time in the creep-feed case. In other words, so-called speed stroke grinding with high workpiece speed is considered more suitable for improving the grinding efficiency [2][3]."

Jan 1, 1998

By Akira Yazawa

The similarities and differences in copper, nickel and lead smelting processes are discussed based on the sulfur-oxygen chemical potential diagrams and the free energy minimization assessments using a thermodynamic software. The prominent features of copper smelting are ascribable to the fact that copper has a strong affinity for sulfur but weak for oxygen and the liquid phase immiscibility between Cu and Cu2S. During the oxidation of sulfides, nickel metal is not stable except at temperatures higher than 1500°C, well miscible with its sulfide, and is oxidized more easily than copper. Metallic lead looks as stable as copper during the oxidation of the concentrate but Pb and PbS. are much more miscible with each other and the vaporization loss is considerable. In the reductive smelting of oxides, the effects of oxygen potential and temperature on the copper contents in slag are not significant due to the monovalent character of copper and the reduction of copper content in slag is not easy in practice. The effect of the slag compositions on the oxidic metal contents of slag is much more significant for lead than either copper or nickel. Due to the immiscible nature between Pb and Fe, high grade lead bullion is easily obtained and lead is more tolerant to impurities.

Jan 1, 1998

By Katsuya Kase, Kaname Takeya, Keaji Ohmori, Yoshiyuki Asakawa

"The reduction-diffusion process (the R-D process) using Ca as a reducing agent has been practiced in industry in the production of the SmCos type, the Nd-Fe-B type and the 1b-Fe-Co type magnetic materials. The advantages of the R-D process are the generally high yield of rare earth metals and the single-stage conversion of a mixture of oxides and metal powders into a product of rare earth alloy powders. On the other hand, one of its disadvantages is the slightly high contents of oxygen and calcium. This disadvantage is remarkable in the Nd-Fe-B type. Singe-phase Nd2Fe14B alloy powders with low content of 0 and Ca, is obtained by choosing appropriate raw materials and performing the R-D process in a controlled way. These alloy powders are very suitable for the production of Nd-Fe-B sintered magnets and expected higher magnetic properties by adopting advanced magnet production method.IntroductionThe hard magnetic rare earth transition metal intermetallics, especially, have attained considerable technical importance. Examples are the alloys based on the intermetallics SmCo5[1], SmC017[2], NchFet4B[3], or the recently developed alloy SnuFe11Nx[4]. The reduction-diffusion process using Ca as a reducing agent has been well known as an economical method of producing rare earth based magnet materials[5]. The reduction-diffusion process has been practiced in industry in the production of the SmCos type, the Nd-Fe-B type and the 1b-Fe-Co type magnetic materials. The advantages of the reduction-diffusion process are the generally high yield of rare earth metals, the single-stage conversion of a mixture of oxides and metal powders into a product of rare earth alloy powders, the elimination of the crushing process of the alloy ingot, the inessentiality to special equipment, etc. On the other hand, one of its disadvantages is the slightly high content of oxygen and calcium. This disadvantage is remarkable in the Nd-Fe-B type. An outline of basic studies of the reduction-diffusion process was reviewed from the particular viewpoint of the production of magnet materials by Ogawa [6]."

Jan 1, 1998

By Mark Tjerkstra

In ,1993, the WMC Resources Ltd.-owned Kalgoorlie Nickel Smelter, underwent a capacity upgrade. This capacity increase was offset by .air quality control restrictions limiting the smelter's availability to 80%. As the direct. result of this limitation, WMC Resources Ltd commissioned a double absorption contact ,acid ,plant for the desulphurisation of furnace waste gas in August 1996. The history and the impact of the acid plant on S02 emissions and air quality is reviewed. General descriptions of the other aspects of the Kalgoorlie Nickel Smelter's Environmental Project are also included in the paper. Information on 'the design features? and operating practices that relate to or contrast with practices at operations visited by KNS personnel prior to acid plant commissioning provide the paper's focus. Smelter operation has changed markedly from unstable operation prior to 1997 to continuous" operation with little down time due to mechanical or process failures resulting in increased smelter availability to more than 90%

Jan 1, 1998

By Peter K. Liaw, Charlie R. Brooks, David C. Joy, Wei Zhao

In this paper, effects of oxidation, porosity and fiber-fabric stacking sequence on flexural strength of a continuous silicon carbide fiber (SiCr) fabric-reinforced SiC ceramic-matrix composite (CFCC) were studied. The failure mechanisms were correlated with flexural strengths of CFCC samples, both before and after oxidation. Microstructures and fractography were investigated using scanning electron microscopy (SEM). The chemical change after oxidation, such as Si, C, and 0, and their distributions, were detected by the SEM energy-dispersive X-ray spectroscopy (EDXS) line-scan chemical analysis technique. These effects on the strength of the CFCC can be attributed to following reasons: (i) The decrease in the flexural strength after oxidation is mainly due to degradation of the strength of Nicalon fibers and the damage of fiber/matrix interface both caused by high-temperature chemical reactions, (ii) Porosity is not too important in affecting the strength of the CFCC, when the bonding of the forced flow chemical vapor infiltration (FCVI)-SiC matrix is stronger than that of the fiber/matrix interface. However, a higher porosity content will be harmful, because higher porosity will both decrease the effective elastic modulus of the FCVI-SiC and make pore-linkage easier to occur, which is more likely to cause premature failure, (iii) The variation in the lamina stacking sequence of the CFCC changes the elastic stress distributions along the thickness direction of specimens, the magnitude of ceramic matrix-cracking stress, the effective elastic moduli of the laminate, and different crack initiation sites as well as different failure modes, and thus, leading to the scatter in the flexural strength of the CFCC.

Jan 1, 1998

By Peter K. Liaw, Niann-i Yu, Wei Zhao

"For a plain-weave Nicalon ™ fiber fabric-reinforced silicon carbide (SiC) ceramic composite, little attentation has been paid to the effect of fabric stacking sequence on its mechanical behavior. In this paper, fiber-fabric stacking sequence effects on the elastic stress distributions, ceramic matrix-cracking stress, effective elastic moduli, and flexural strengths of laminated flexural test bars are quantified. A quantification model is established based on the combination of classical laminated plate theories and a fiber undulation model developed by Chou et al. A FORTRAN program is compiled to implement the modeling, which can be run in a SUN work station. The mechanical performance of a continuous fiber-reinforced ceramic-matrix composite (CFCC) with a [0/30/60] lay-up was analyzed and predicted. The variation in the fiber-fabric stacking sequence can vary the elastic stress distributions along the thickness direction of specimens, magnitude of ceramic matrix-cracking stress, effective elastic moduli of the laminate, and crack initiation sites as well as fracture modes. Moreover, all these factors contribute to scatter in flexural strengths of the CFCC.I. IntroductionWith enhanced fracture toughness and the ability of non-catastrophic (graceful) failure behavior, CFCCs are currently under evaluation for high-temperature structural applications in heat exchangers, combustors, hot-gas filters, boilers components, first walls and high-heat flux surfaces gas turbines, space vehicles and nuclear reactors.[1-8] Extensive applications of CFCCs by industry are still hampered by an insufficient understanding of the mechanical behavior, and sometimes, the lack of a well-developed and widely accepted design philosophy, in addition to the high-production costs."

Jan 1, 1998

By Florian Kongoli

Non-ferrous smelting slags .can contain magnesia, which substantially increases the liquidus temperature. One option to counter this increase is to flux with calcia. In this work, experimental liquidus measurements including new measurements on industrial slags have been compared with a FACT-based thermodynamic model, which predicts the liquidus surface of multi-component iron silicate smelting slags containing both magnesia and calcia. The predictions, which agree well with experimental results, are summarized in both isothermal and non-isothermal diagrams to give a quantitative description of the liquidus surface.

Jan 1, 1998

By L. M. Bianchi

"Oxide, nitride and other compound coatings often do not have adequate properties for newer applications when produced using very high deposition rates and simple evaporation techniques. Solar control, abrasion resistance, low reflectance and barrier effective engineered coatings require exacting properties. Such properties can be obtained by adapting the activated reactive evaporation (ARE) technology to Web production processes. Adaptions of the HAD and MAD processes will be described along with data on the high deposition rates obtained. These fast production capabilities were developed in order to make the processes economically competitive.IntroductionThe Physical Vapor Deposition technique (PVD) has been used to coat steel strip for over 20 years. (1) However, its use as a production process has been very limited because of the high cost of the PVD coating process and because, in some instances, the properties of the coating were not good enough to meet the customers requirements. Nevertheless, the PVD process has found wide application in the airplane engine and electronic component markets. These production processes have stimulated further development and advances in the technology.In 1971, Profession R. F. Bunshah developed the Activated Reactive Evaporation (ARE) process which was then used to produce hard coatings such as carbides, nitrides, oxides and other refractory compounds. (2) The process from a fundamental viewpoint -produces a coating on the substrate via the evaporation of metal in the presence of a low pressure (typically around 1 millitorr) of reactive gas, with a plasma created in the space between the metal source and the substrate.The plasma may be created by many means but its function is two-fold. First, it activates the reaction between the metal vapors and the reactive gas atoms/molecules resulting in the formation of a compound that deposits on the substrate. Second, because the plasma is in contact with the substrate, it results in a negative bias on the substrate and produces bombardment of the growing film with ions and energetic neutrals from the plasma. This bombardment causes many significant changes in the microstructure, properties and appearance of the coating.Recently another new technology Pulsed Magnetron Systems (PMS) has been introduced into PVD. This new technology has been pioneered in production scale equipment by Dr. S. Schiller (3) and associates. The use of a pulsed power supply on the magnetron prevents the problem of the anode being coated with a insulating layer which will then lead to micro and macro arcing producing defects in the coating."

Jan 1, 1998

By Patrick R. Taylor

Coatings of TiCIFe have been produced by Reactive Plasma Spraying using ilmenite ore concentrate as the feedstock powder and methane as the reactive gas. A free energy minimization analysis of the ilmenite-methane system is presented. The coatings have been characterized by x-ray diffraction and SEM. The microstructure of the coatings indicates good interparticle cohesion. The composition of the coating is deficient in iron compared to the initial Fe to Ti ratio found in ilmenite.

Jan 1, 1998

By Kevin L. Gering

A detection method and apparatus have been developed to perform real-time measurement of aqueous free cyanide, C-. A laboratory prototype can measure cyanide ranging from 5 micrograms ,per liter to 100 milligrams per ?liter for analysis times as short as 2 minutes per measurement. Sample size per measurement is typically only a few mI, thus? minimizing the waste volume produced from spent samples. The basis for this detection device is a quantifiable, stable affinity between the electrode material and free cyanide in the sample; The electrode exhibits piezoelectric behavior, allowing it to be used as a microbalance. This technology 'has experienced two generations of laboratory prototypes, and has been thoroughly tested to determine the operational sensitivity toward process variables such as pH, competing reactions, etc. The speed and ,accuracy of this method make it superior to conventional wet chemistry methods used for quantifying cyanide levels in water. A device based on this technology could be useful in areas involving process monitoring and environmental compliance, .particularly in the cyanide-based leach mining industry. Interest for this detector has been shown by the gold mining industry and others. Patent application is in progress.

Jan 1, 1998

By Saskia Duyvesteyn

Small ion-exchange resin particles provide faster mass transport than conventional-sized beads. Unfortunately, high pressures are needed to pump solutions through columns containing small resin particles. It is preferable to disperse fine resins in the solution being treated. Screens have been used to separate the resin from the solution, but screens do not retain fines created by attrition of the resin particles. We have developed a separation process based on flotation, which relies on the surface characteristics of the resin, instead of size. The resin is conditioned with a surfactant before dispersing it in the solution to be treated; this increases the hydrophobicity of the resin sufficiently for froth flotation, without introducing surfactant directly into the solution. The surfactant adsorbed on the resin surface does not appear to impair the kinetics of metal ion removal. A flowsheet for an effluent treatment process is proposed; other applications are clearly possible.

Jan 1, 1998

By Olga A. Gomon, Alexey N. Lozhko

The technology of heat treatment for metal frequently includes multiple fast heating and cooling of the products surface. If the product is heavy-weight or long-size, its moving from a zone of cooling to a zone of heating and return require a long time. Other important condition of ensuring qualitative surface at heat treatment is intensification of cooling phase. It is known that turbulization of a flow activates heat exchange and increases efficacy of cooling without increasing volume flow rate of water. Additional difficulty is to ensure the regularity of heating and cooling on length of a product. The technology of cyclic heat treatment of rolling products, at which mobile zone of turbulent heat exchange is formed on the surface of a product, was developed and realized. The submission of water occurs through to face spray systems. Each of the systems has six long-range atomizers, which are located circularly. Two flows of water move towards one another along a surface of a product. When they collide, the right zone of turbulent heat exchange creates heat transfer in this zone of 10-15 time more intensive than on other surface of a product. The effect of moving turbulent zone on length of a product is reached by changing the proportion of volume flow rate of water, which is created by face sprays. The speed of movement for turbulent zone along a surface of a product is chosen so, that the cooling takes place on a small depth only. Then after passing the turbulent zone over a determined site of a surface, its temperature recovers fast owing to hot internal layers. The parameters of process were determined by mathematical simulation of cooling in an installation. The equations for dynamics of movement of collision point of flows, which were received this way, are interesting supplementary products of research. The experiments show that frequency of movement of turbulent zone is an important technological parameter. It defines mechanical properties of a surface and should be chosen depending on a profile of product and metal grade. The results of comparison of mechanical properties of a surface of various rolling products, which were received by developed and conventional technologies, are described in this report. Dependence of regularity of mechanical properties on frequency of movement of turbulent zone is adduced.

Jan 1, 1998

By Yuchun Wang

In principle, supported liquid membranes could be an exceedingly elegant separation process. However they tend to fail by displacement and emulsification of the organic solution in the pores, which allows mixing of the feed and strip solutions. We have stabilized supported liquid membranes comprising moctylamine in nylon and PVDF supports by covering the pores with semi-permeable polyamide films, using an in-situ polymerization technique. Scanning electron microscopy demonstrates that the polyamide films are sensitive to production conditions and the nature of the support. The transport properties of stabilized supported liquid membranes for Cr(VI) are compared with those of unstabilized membranes.

Jan 1, 1998

By Andre L. De Vegt

Hydrogen sulfide is an expensive chemical used in nickel, zinc and copper mining and metallurgical operations for selective recovery and concentration of metals, from leach water streams, acid plant blow down streams, refinery electrolyte bleeds and precious metal, plant bleeds. Hydrogen sulfide is either produced on site by catalytic reduction of elemental sulfur or transported to the site as liquefied hydrogen sulfide (H2S) or as a sodium sulfide solution (NaHS) Biologically produced hydrogen sulfide has economically very interesting, application possibilities in the mining and metallurgical industry. Converting sulfates from waste streams into usable hydrogen sulfide by biological reduction results in operational cost savings in existing lime treatment systems. H2S can be produced biologically for less-than $500/ton S. For the past ten years Paques has been engaged in the development and installation of treatment systems based on biotechnological processes to remove sulfur compounds from water, air and gaseous streams. Paques has designed and installed a groundwater treatment system for the Budelco zinc refinery in the Netherlands to remove sulfate and heavy metals. The hydrogen sulfide produced is used for recovery of metals,, mainly zinc, from the ground water stream. The system has been operating since May 1992 treating a flow of 5000 m3/d. At Kennecott's Bingham Canyon Utah copper mine, a pilot plant started operation in November 1995 to develop the process for selective recovery of copper from leach water using biologically produced hydrogen sulfide from sulfate containing groundwater. Other pilot plants are operated at DOE's Pittsburgh Research Center and at Cominco Research focusing on selective recovery of metals.

Jan 1, 1998

By Patrick R. Taylor

Titanium nitride has been synthesized in a thermal plasma reactor from ilmenite ore concentrate using methane and ammonia as the reactive gases. The product has been characterized by x-ray diffraction and SEM. Results show that a high concentration of methane favors the formation of iron, titanium nitride and titanium carbonitride. The formation of titanium carbonitride can be minimized by controlling the concentration of methane. The formation of TiN proceeds by the progressive reduction of the oxides of titanium to titanium, which is converted to titanium nitride.

Jan 1, 1998

By Toshiro Kuji, Masakazu Fujita, Tetsuji Saito

"The magnetic properties of the magnetic materials were deeply dependent on the microstructures. In this study, the novel technique to produce the desired microstructures in a controlled manner was proposed. The technique consisted of the production of the amorphous alloys and the control of the crystallization process. The technique was applied to improve the magnetic properties of Nd-Fe-B permanent magnets. The microstructural control of the magnets exhibited the excellently high energy-products of higher than 430 kJm-1. The relationship between the magnetic properties and the microstructures of the Nd-Fe-B permanent magnets was discussed.IntroductionThe intrinsic properties of the materials are basically determined by the properties of the constituent elements or the compounds. However, it is often noticed the difference between the observed properties and the theoretical values expected from the intrinsic properties of the materials. This indicates that the observed properties of the materials are determined not only by the properties of the constituent elements. In other words, the observed properties of the materials are also strongly dependent on the morphology of materials. This means that the microstructural control may creates a great improvement of the properties of materials.In Nd-Fe-B permanent magnets, the superiority arises from the uniaxial intermetallic Nd2Fe14B compound which has a large saturation magnetization and a high anisotropy field [1,2]. The magnetic properties of the Nd-Fe-B permanent magnets are dependent on the microstructure, that is, the size, shape and degree of the crystallographic alignment of the Nd2Fe14B phase. Currently, the Nd-Fe-B permanent magnets have been produced by either sintering or melt-spinning [3,4]. In the sintered magnets, alignment of the Nd2Fe14B phase is achieved by the prior green compaction of the crushed ingot powders in an applied magnetic field [3]. In the melt-spinning approach, alignment of the Nd2Fe14B phase is achieved by hot deformation [5]. Amorphous melt-spun ribbons are comminuted and then are consolidated into bulk form by hot pressing before hot deformation. As-hot-pressed magnets have randomly oriented Nd2Fe1~ grains [6]. Subsequent die upsetting of as-hot-pressed magnets gives rise to the crystallographic alignment of the Nd2Fe14B phase."

Jan 1, 1998

By Brian R. Green

Resin-in-pulp (RIP) technology has been developed for recovery of gold. It is now time to look forward to the potential for application of the technology to other situations. Some cases have been identified and have merited preliminary testwork. Four examples, which illustrate the potential of RIP, are dealt with in this paper. These include removal of metal-cyanides from pulps, recovery of manganese that is difficult to wash from filter cakes, recovery of nickel from low grade pulps, and recovery of zinc from process residues. The discussion includes descriptions of the problems, factors that affect the choice of resin, and factors that will affect the economics of the process.

Jan 1, 1998

By Craig A. Johnson

Cyanide speciation and behavior have been examined at three active heap leach operations, three heaps undergoing rinsing, and three sites with cyanide contaminated groundwater, all in the southwestern U.S. Data from these studies demonstrate that strong cyanometallic complexes of iron and cobalt can play ?an important role in cyanide behavior throughout the lifetimes of heap leach operations. In active circuits, we find evidence that significant amounts of cyanide combine with iron and cobalt to form strong cyanometallic complexes, and that these species can be adsorbed, probably onto iron hydroxides, or precipitated as insoluble cyanometallic compounds. When spent heaps are rinsed, the release of this cyanide is likely controlled by the slow kinetics of desorption from, or dissolution of, solids that have gone largely uncharacterized. We find evidence that strong cyanometallic complexes can give rise to transient free cyanide in some settings by rapid photo dissociation where heap rinse effluent is exposed to sunlight in open channels or translucent sample bottles. Thus, these species can complicate the ,preparation of spent heaps for decommissioning, even where regulatory standards ?are based on weak acid dissociable cyanide. There is a critical need for information on the form and stability of adsorbed and precipitated cyanide in spent ore heaps, on the concentrations of strong cyanometallic complexes in mineral processing effluents -particularly the complexes of cobalt, and on the natural attenuation of iron and cobalt cyanometallic complexes in both surface and subsurface waters.

Jan 1, 1998

By Federica Paglietti

In this work is presented SEX (Structural & Elemental X-Ray Instrument), the first spectrometer completely portable which make non-destructive X-ray fluorescence and diffraction analysis, in contemporary and in real time. This instrument has been realized using miniaturized detectors, the same model installed on the mission Pathfinder NASA, and X-ray microtubes. SEX allows the chemical and mineplogical characterization of all kind of solid materials and allows to make chemical stratigraphy and liquids analysis.

Jan 1, 1998

By Ignacy A. Lipiec

The advantage of microorganisms used in bioleach systems to conventional chemical reaction systems is that these apply the available energy more precisely where it is needed, either directly onto the mineral of interest or by efficiently catalyzing the production of a reactant. The literature cover the range from empirical models used in describing macro heat balance in heaps to detailed studies relating the micro heat effects of bacteria adhesion energy to the surface of minerals. In this paper, the heat effects are reviewed in a general way describing bioleaching in two macro systems, heap leaching and slurry bioreactors. The micro scale heat effects is the reactions and conditions at the microorganism scale, including the mechanism of leaching and bacterial behavior.

Jan 1, 1998