Search Documents

By Arnold Blaisonneau, Théophile Guillon, Xavier Rachez, Sylvie Gentier

"L’étude présentée ici vise à étudier l’influence, lors de stimulation hydraulique de puits dans les réservoirs géothermiques de type Enhanced Geothermal System (EGS), du comportement mécanique des zones de failles recoupant le puits sur la réponse hydraulique du réseau de fractures 3D. Dans ce but, un modèle 3D, basé sur la méthode des éléments distincts et dans lequel les zones de failles recoupant le puits sont modélisées par des fractures numériques 2D, est mis en oeuvre. Les modélisations présentées ici visent à caractériser l’influence du comportement mécanique (type de comportement, hétérogénéité) sur la cinétique de la stimulation hydraulique, ainsi que sur son effet spatial autour du puits. INTRODUCTIONPour le développement de l’exploitation géothermique de type Enhanced Geothermal System (EGS), la phase de stimulation conditionne grandement le succés du projet ; en effet, elle a pour objectif d’augmenter l’injectivité et la productivité des puits et doit permettre d’assurer la connexion entre les puits d’injection et de production garantissant ainsi la viabilité technique et économique de l’échangeur. Pour le site EGS de Soultz-sous-Forêts (France), parmi différentes techniques de stimulation, la stimulation hydraulique a été utilisée à cette fin en provoquant une augmentation irréversible de la perméabilité autour des puits. Dans ce type de réservoirs fracturés, le but des stimulations hydrauliques est de réactiver, plus spécifiquement en cisaillement, des structures hydrauliques pré-existantes (fractures, zones de failles etc.) dans le socle cristallin. La compréhension des phénomènes physiques durant la stimulation hydraulique est cruciale pour optimiser cette technologie et pour contrôler/limiter les risques associés (viabilité technique et économique des puits, sismicité induite etc.). C’est notamment le cas pour la relation entre le comportement mécanique des structures stimulées et les conséquences sur le comportement hydraulique dans un contexte tectonique spécifique."

Jan 1, 2015

By A. Jeffkins

Visibility is restricted when operating load haul dump vehicles resulting in a number of serious accidents in the Ontario Mining Industry. One of the leading causes of these accidents is the inability of the equipment operator to see clearly people, objects or hazards around the machine. Previous line of sight testing by the research team found specific machine characteristics were responsible for blind spots and impaired visibility. In order to identify feasible design modifications a computer simulation program, Classic JACK 3.1, was utilized. Program features include human factors analysis, which allows evaluation of line of sight and operator posture in order to decrease risk of musculoskeletal injury. Research within the virtual computer environment consisted of a Visibility Audit and a Target Audit in order to quantitatively determine how certain components of the LHD design affected the line of sight around the vehicle. Results indicate that modifying the LHD light brackets, engine profile, cab posts and other components will enhance visibility. The addition of cameras located on the front and rear of the vehicle were able to enhance the operator?s sight lines to previously obstructed areas. Modifications to seat height and the operators orientation both improved sightlines and decreased risk factors associated with back and neck musculoskeletal disorders.

May 1, 2003

By Eduardo A. Pérez, Alejandro R. Alonso, Rosa María Luna-Sánchez, Gretchen T. Lapidus

Rare earth elements have been widely used in various sectors, from the aerospace and steel industries, to electronic applications, particularly in displays and batteries for portable devices. The high demand for newer and better equipment, such as cell phones, tablets and lap tops, has increased the consumption of the rare earth elements and at the same time the need for its recovery from electronic wastes. For that reason, the recycling of batteries is important, principally the Ni-HM batteries, due to their elevated content of rare earths elements, in addition to the high concentrations of cobalt and nickel. The current processes are based on dissolution in strong acid solutions (sulfuric acid concentrations from 2 to 4 mol/L), and temperatures from 30 to 90°C. In the present work, electrodes from spent Ni-HM batteries were leached using 1 mol/L H2SO4, in the presence of ozone as the oxidant, where recoveries of 96% for La, Ce and Nd were obtained at room temperature. The separation of Ni and Co from the leach solutions was performed using an electrochemical reactor, after which rare earth elements were precipitated, obtaining a mixture of its hydroxides with impurities below 1%, according to EDS analysis.

Jan 1, 2014

By E. Rezaei

Glue is an animal protein that is used with other organic agent such as thiourea, in copper electrorefining. The concentration of glue has to be controlled carefully, because the electro-deposition process is often very sensitive to small fluctuation in the operating variable. This additive (glue) prevents rough and nodular copper cathode deposits. The nodular deposits may grow causing short circuits, which results in losses in production. Addition agents are effective in controlling metal growth; they modify the normal nucleation and lattice growth steps and refine the grain structure. In this research glue concentration was determined in an industrial copper electrolysis plant. A non-linear model with high capability was constructed and after optimizing its parameters, the accuracy and precision of the model were evaluated. For determination of glue concentration, electrochemical voltammograms in optimum condition (Differential pulse voltammetry technique, Hpulse=50 my, scan rate=10 mv/s) were plotted. Some information from voltammograms was transferred to the model as inputs and the calibrated model analyzed the information and the glue concentration was determined with high precision and accuracy. In this way there is no need to separate or add agents to remove interferences. This method has been successfully applied at Sarcheshmeh copper complex.

Jan 1, 2007

By Robert B. Parsons

"This month, Tax Notes focuses on two features which can potentially ""dress up"" a new issue of common shares to make the shares more attractive to investors. Attaching warrants to a share issue is a relatively common practice, and recent years have seen an imaginative variety of different kinds of warrants, some of which can be subject to somewhat different tax treatment . A less common financing strategy which certainly deserves some consideration involves the possibility of utilizing ""Share Purchase Tax Credits "" in conjunction with a new share issue.IntroductionPrevious subjects covered in Tax Notes have dealt with flow-through shares and other tax angles which can make equity issues more appealing to potential investor s. Two other techniques which can add zest to a new stock issue involve the utilization of warrants and ""share purchase tax credits"" (or SPTCs). This article takes a brief look at the better known subject of warrants and the lesser known matter of SPTCs.Of course, this paper presents only a relatively general summary of the income tax implications of warrants and SPTCs, and is not intended to be a definitive commentary on all of the detailed and complex tax issues that might be relevant in the circumstances."

Jan 1, 1985

By André Gobell

"La distribution des éléments majeurs dans une séquence de roches volcaniques felsiques, la formation de Waconichi, au sud de Chibougamau, indique que les roches pyroclastiques du secteur ouest de ce segment sont chimiquement anormales si on les compare à la composition moyenne des roches volcaniques de Chibougamau: elles sont caractérisées par une teneur anormalement élevée en f er, en magnésium et en potassium et une teneur anormalement basse en sodium et en calcium; ce chimisme caractérise les encaissants des dépôts de sulfures massifs d 'origine volcanique.Les coulées rhyolitiques massives sous-jacentes au gite de cuivre-zinc avec or et argent de Lemoine ne montrent pas ou très peu d’altération de ce genre. Le schéma de mise en place des dépôts de sulfures massifs d'origine volcanique et la nature des roches en présence permettent de croire que la zone d'altération mise en évidence à l'ouest de la mine Lemoine puisse être reliée à la mise en place de ce gisement d'ou l'im portance de tenir compte des caractères texturaux des roches lors de l'interprétation de données litho géochimiques."

Jan 1, 1980

By James Logan

BC Alkaline CuBC Cu--Au PorphyriesAu Porphyries ?Formed over narrow time interval ~205 Ma ?from silica deficientvsalkali-enriched magmas ?At shallowdepths ?Structuralcontrol ?Cu-Au-Ag, trace Mo ?Oxidized system anhydrite, magnetite ?Multipleintrusions & multiplemineralized centres

May 1, 2006

By Erik C. Westman

Knowledge of the orientation and relative magnitude of in-situ stresses at the mine scale is important for safe and efficient production from an underground mine. With this knowledge, stope location and scheduling can be optimized. Passive seismic tomography was used for imaging horizontal stress distribution at the mine scale. Microseismic measurements from the Creighton mine were used as input for the tomography calculations. The double-difference tomography algorithm was used, which provides the most precise results. The results clearly show a low velocity zone in the previously mined areas bounded by two high-velocity lobes located adjacent to the mined openings at locations consistent with those expected due to the horizontal stresses at the mine. The overarching goal of the research is to provide a tool that can augment both numerical modeling results and underground geotechnical measurements to allow the mine operator to produce in the safest and most efficient manner possible.

Jun 1, 2012

By C. Guo, R. J. Chalaturnyk, M. MacKinnon, J. D. Scott

The Mildred Lake Settling Basin (MLSB) is the largest disposal site for mature fine tailings (MFT) at the Syncrude Canada Ltd. oil sands plant. Over the past years (since 1996), there has been a marked change in the densification behaviour of MFT in the MLSB. Methane-producing microorganisms, known as methanogens, have become very active, and large amounts of biogas (mainly methane) have been produced. Continued field monitoring of the MLSB has provided convincing evidence of the rapid densification process (rapid water drainage from the tailings) at the area with intense microbial activity. This rapid densification has caused pumping challenges in the transfer of fine tailings from the Mildred Lake Settling Basin for the creation of composite tailings. It may also have potential positive effects in accelerating the reclamation of the oil sands fine tailings. A field and laboratory research program was carried out to study the mechanism leading to the rapid densification phenomenon. A review and discussion of the research program is given and some results from the field investigations and small-scale column tests are presented in this paper.

Jan 1, 2007

By K. Robertson, K. A. Scalise, K. C. Kocsis, M. B. Teixeira

"Many deep and highly mechanized underground metal mines require cooling. In many cases, appropriate working conditions might be fulfilled by ventilation alone, but some require the implementation of cooling systems. The most common cooling systems are bulk air cooling and localized cooling. These systems are effective, but they use considerable amounts of electricity. Ground source heat pumps (GSHP) can supplement existing cooling and heating systems, while geothermal systems can cool the mines in their entirety if there are significant sources of geothermal energy are present. A major advantage of geothermal and GSHP systems are their renewability, which reduces the carbon footprint of the mine.INTRODUCTIONThe western United States has abundant alternative energy sources including a high potential for geothermal energy. Geothermal utilization is a viable energy alternative that many areas throughout the world have access to because high geothermal potentials are located near areas of volcanic activity such as along plate boundaries, mid-oceanic ridges, rift valleys and hot spots (IRENA, 2017). There is significant potential to use geothermal energy for many applications. With constantly evolving and innovative technologies being developed, an increasing number of geothermal applications are becoming feasible. The western United States is an ideal candidate for alternative energy applications due to the geothermal availability and the emergence of modern technology. This paper investigates the incorporation of renewable methods and the alternative energy possibilities of Barrick Goldstrike, located in northern Eureka County, NV and Rio Tinto/BHP Billiton’s Resolution Copper mine located in Superior, AZ.RENEWABLE SYSTEMSGeothermal SystemsGeothermal temperatures are typically defined as either high or low temperature systems(Shengjun, Huaixian, & Tao, 2011). The high-temperature reservoirs (>220°C / 428°F) are feasible forlarge, commercial production of electricity with dry stream and flash stream systems (Shengjun, Huaixian, & Tao, 2011). Low temperature systems, below 220°C (428°F) (Shengjun, Huaixian, & Tao, 2011), aremuch more difficult to use for energy production. Low-temperature reservoir heat can be harnessedthrough the implementation of a binary cycle plant. The working fluid for a binary cycle plant is eitherorganic (Organic Rankine Cycle (ORC)) or an ammonia-water mixture (Kalina cycle). Organic fluids andammonia-water mixtures have low boiling points that allow for the recovery of heat from low-temperaturesources (Eymel Campos Rodriguez, et al., 2013). The efficiency of the binary cycle plant varies depending upon the fluid, thus the proper selection of the fluid is critical for maximum energy output"

Jan 1, 2019

By D. E. M. Plaumann

"The wet grinding of asbestos has attracted the attention of engineers for many years as a means of improving fibre liberation from the ore. Today, added impetus for wet grinding has resulted from a need to minimize worker exposure to asbestos dust in conventional dry mills using air, as well as a need to provide a cleaner, technically superior fibre for use by product manufacturers. However, high viscosities of asbestos slurries create transport and grinding difficulties which have been a factor impeding use of a wet grinding process.Laboratory evaluation of reagents to reduce viscosities of asbestos slurries found that one reagent, XFS-4272.00, reduced the viscosity of a 35% (by weight) slurry by 75%. The impact of XFS-4272.00 on actual grinding parameters were evaluated using a pilot plant rod mill. Slurries containing 78% solids and XFS-4272.00 were successfully milled and asbestos fibres from that milling compared favourably in liberation and relative surface area to asbestos fibres obtained from milling a 4% slurry without additives. IntroductionAlthough the use of asbestos has been declining over the last few years, the large deposits of chrysotile in eastern Canada (Quebec in particular) remain very important. Asbestos production in Canada stands ninth in volume for mineral production with over 740 000 tonnes produced in 1985. Of this quantity, 722000 tonnes were exported with a value of $446 million. Canada is second in world production of asbestos behind the U.S.S.R. The milling of asbestos ore has been done primarily by a series of steps involving crushing, dry-grinding and aspiration using large quantities of air to release the fibres. Contrast this process to those practiced in the purification of virtually every other mineral. Ores other than asbestos are crushed and milled using an aqueous slurry in rod, ball or pebble mills. The finely ground mineral, still as a slurry, undergoes beneficiation by froth flotation, heavy media separation, hydrocyclones or any of the other aqueous techniques currently employed in mineral processing.One of the driving forces behind the use of air instead of water as a means of separating asbestos is the nature of the aqueous asbestos slurry. While most slurries of minerals contain as much as 80070 solids and can still be pumped and transported, asbestos slurries become highly viscous with as little as 10070 solids. These high viscosities reduce the pumpability of the slurry and create severe handling problems. Mills become prohibitively large and uneconomical due to having to handle slurries containing only 10% rock and 90% water.Health-related issues have affected the use of asbestos in many countries. In Canada, the asbestos-producing provinces have introduced stricter occupational legislation to improve safety in the workplace. This primarily means strict control minimizing release of air-borne asbestos fibres . Quebec and Ontario have set limitations of airborne asbestos at 2 (2) and 1(3) fibre per cubic centimetre of air. With present milling technology, maintaining these low levels in the workplace requires constant vigilance."

Jan 1, 1988

By Adriana Ramirez, Bradford C. Wesstrom, Blanca Olave

The Freeport McMoRan El Paso Copper Refinery optimizes electrolyte quality using a number of systems. The facility controls copper, arsenic, antimony and bismuth using electro-winning cells within the Tank House and Nickel Carbonate Plant Liberator Circuit (NCP). The NCP manages sulfuric acid content utilizing recycled electrolyte in the slimes autoclave as well as operation of the Acid Purification Unit, APU. The El Paso Refinery removes common sulfates using metal hydrolysis with sodium carbonate. Finally, a Mechanical Vapor Recompression, (MVR), at the water recovery plant removes sodium sulfate generated by the NCP. This paper will provide a summary of these operations. INTRODUCTION In the mid 1920’s Nichols Copper Company, in Laurel Hill, New York, recognized the need for a modern copper refining facility in the southwest. Because of the many railroad heads, affordable power and abundant labor supply, and the close proximity to regional copper smelters in Mexico, Arizona, and New Mexico, El Paso became the ideal location. In December 1928, ground was broken for the joint venture refinery between the Nichols Copper Company, Phelps Dodge, and the Calumet and Arizona Mining Company. In September 1930, Nichols Copper Company became a part of Phelps Dodge Corporation after a stock exchange. In July 1938, Nichols Division officially became Phelps Dodge Refining Corporation. In March 2007, Freeport McMoRan Copper & Gold acquired Phelps Dodge. Water is a precious commodity in the desert southwest, making conservation of this natural resource an important goal for the El Paso Operations. In the 1980’s, work on the treatment of slimes was improved through the use of pressure leaching of the refinery slimes using an autoclave. Due to the high tellurium content in the leached slimes solution, it was crucial to implement a method for its removal before the solution returns to the tank house electrolyte. A copper telluride cementation operation was installed for tellurium recovery and the ability for the recycle of the leachate and wash water to the refinery electrolyte. In October of 1997, ground was broken for the construction of the water recovery plant using an MVR to reuse process water, reducing water consumption by 25%. In 2002, electrolyte purification was further improved with the installation of an Acid Purification Unit, (APU) (Sheedy, Pajunen, & Wesstrom, 2007). The APU recycles 90% of the acids (both sulfuric and arsenic acids) back to the tank house electrolyte. The solution that passes through the APU is treated with soda ash to precipitate metals out of solution as carbonates and generates a sodium sulfate solution. This sodium sulfate solution is easily processed in the new water recovery plant, where the majority of the water recycles back into the plant as pure condensate. In 2012, the power plant at the refinery upgraded its Reverse Osmosis System to provide RO water to the tankhouse. This insured that the refinery would not have to bleed electrolyte for metals contained in well water such as: calcium, magnesium, iron and sodium chloride.

Jan 1, 2019

By Grant L. Anderson, Richard C. Rice, Richard L. Jentgen

"Data for underground mine-hoist ropes determined in the Ontario Special Rope Tests were obtained, encoded and analyzed statistically. Prior 10 refined statistical analyses, these data were subjected la characterization studies and preliminary analyses to allow trends to emerge that could be used to guide and facilitate the refined analysis. The data were characterized by determining distribution s for a wide range of variables including remaining strength, service life in terms of lime and hoisting cycles, outer-wire torsion values, elongation during tensile testing, diameter reduction, location of strength loss and the strength lasses associated with corrosion rating and lubrication rating , This paper describes the more important relationships between remaining strength (or, conversely, strength loss) as the dependent variable and some of the principal independent variables mentioned above.IntroductionBoth productivity and safety in underground mines could be improved if mine-heist rope Iife and reliability could be predicted more accurately . As a result, hoist-rope failure processes and their effects on rope life and remaining strength need to be quantified and related in such a way that improved retirement criteria can be developed. This is true whether the failure is incipient or actual or whether the failure mode is by corrosion , wear, fatigue or a combination of these factors."

Jan 1, 1984

By E. P. Wiechrnann, C. M. Castro, G. A. Vidal

In copper Eta plants the optimal current density setpoint depends on the electrolyte composition and temperature. However, conventional plants operate with large standard deviations. A value of 14% with current densities offsets up to ±50% is typical. For worst, during opencircuit or shortcircuit events this variation can be from -100% to +200%. Naturally, energy consumption and copper quality are compromised. Several devices have been successfully employed to reduce set point deviations. Last developments include; Optibar Segmented Intercell Bars, Outotec Electrodes Arranging Method and NTC Selective Electrodeposition Enhancers. This paper researches and compares these technologies. It is shown that short circuits can be effectively reduced in occurrence and magnitude. Moreover, 95% of the electrodes can be forced to operate within ±10% of the set point. The specific energy consumption is reduced from 2,000 KW per Ton to values close to 1,900 KW per Ton.

Jan 1, 2011

By Hong Zhong, Shuai Wang, Gang Zhao, Lanqing Deng, Guangyi Liu

In this paper, three novel surfactants containing double reactive centers(-CONHOH and –CONH-), double hydrophobic groups were designed and synthesized as collector for separation of diaspore and aluminosilicate minerals, such as N-(4-(hydroxyamino)-4-oxobutyl)octanamide (HA-8), N-(4-(hydroxyamino)-4-oxobutyl)decanamide (HA-10) and N-(4-(hydroxyamino)- 4-oxobutyl) -dodecanamide (HA-12). The adsorption mechanism of N-(4-(hydroxyamino) -4-oxobutyl)alkylamides (HA) onto diaspore was also investigated by FTIR spectra, zeta potential measurement and DFT. The flotation results demonstrated that three collectors all exhibited superior collecting power to diaspore and selectivity against kaolinite and illite, and could effectively realize flotation recovery of diaspore from bauxite ores contained aluminosilicate minerals under neutral conditions. Moreover, HA-12 was a superior collector than other two collectors for bauxite separation. The results of XPS, FTIR spectra and zeta potential illustrated that at around pH 6.0, HA might chemisorb on diaspore surfaces through Al-O coordination bonds formed by binding its –C(=O)NHOH or –C(=O)NH– chelate groups with aluminum atoms on diaspore surfaces. HA’s unique properties, such as characteristic bond patterns onto diaspore surfaces, double hydrophobic groups, and intermolecular hydrogen bonds between neighboring HA molecules coated on diaspore surfaces, rendered it to be a superior flotation collector for diaspore.

Jan 1, 2016

By J. H. Pateson, D. C. Comrie, D. J. Ritcey

"Geopolymers are inorganic semi-amorphous three dimensional silico-aluminates of the poly(sialate) type (-Si-O-Al-0-) or of the poly(sialate-siloxo) type (-Si-O-Al-O-Si-0-). Polycondensation occurs at low temperatures with geopolymers being stable up to 12oo0 c. Research, development and application technology pertaining to geopolymers is being undertaken jointly with Dr. Joseph Davidovits of The Institute for Applied Archaeological Sciences of Florida, U.S.A. This joint focused upon the chemical Barry University in Miami Shores, research and development program has stabilization and solidification of various waste products through geopolymerization. Of particular interest is the geopolymerization of mine wastes including tailings and waste rock derived from the processing of base metals, precious metals, potash, coal and uranium deposits.INTRODUCTIOND. Comrie Consulting Ltd., in cooperation and technical liaison with CANMET, Ottawa has been testing the application of geopolymers to mining wastes. Corporate efforts to date have concentrated upon reactive acid tailings, principally from the abandoned Kam-Kotia Mine site, and dewatered paint waste sludges. Test work conducted to date has successfully yielded geopolymer treated materials and wastes with increased chemical and structural stability. Wastes containing heavy metals, cyanides, arsenic and sulphur dioxide have been successfully geopolymerized."

Jan 1, 1988

By J. Borlee, F. Sorrentino, A. Fleischanderl, M. Gimenez, W. Gebert, U. Gennari

Large quantities of solid by-products are generated by the steel industry and other important activity sectors in Europe (power plants, car dismantling companies, urban incinerators) with no or very limited potential for direct recovery. In the frame of a multi¬national project supported by the European Union, a consortium has been created to develop a treatment process able to turn these by-products into valuable metallic and mineral products. VAI has been responsible for the design, erection and start-up of the pilot plant for the new metallurgical process and for the execution of the test campaigns, with the targets defined together with the partners. Up to now, 9 campaigns comprising 60 heats have been performed successfully. By-products from C-Steel and stainless steel plants, as well as fly ash and auto shredder residues, have been used and defined products such as hydraulic binders for cement, metallurgical powders for De-S practice and recycled metal phase have been produced. The mineral products were positively assessed under industrial conditions. Results from cement tests and secondary metallurgy are reported, as well as a detailed characterization. The economic value of the products, credits from avoiding dumping and significant savings on CO2 emissions make the new process economically very attractive.

Jan 1, 2004

By J. W. Scott, G. G. R. Falkenberg

"The Syncrude project is an integrated complex designed to mine, extract and upgrade bitumen from the Athabasca tar sands to produce 129,000 barrels per day of synthetic crude oil. This paper provides a brief general description of the location, history and geology of the tar sands and the overall organization and structure of the project. The major emphasis and the bulk of the detail presented deals with the extraction plant; a material handling and mineral processing installation designed to treat 312,000 tons per day of tar sand feed.History of the Tar SandsThe Athabasca tar sand deposit was recorded in 1788 by Peter Pond, however the first serious geological mapping and exploration did not begin until 1915. Little interest was taken in the deposits until the Second World War, when the governments of Canada and Alberta conducted an extensive exploration program. In addition a number of pilot plants were sponsored during the 1940 -1950 decade. The hot water separation process was successfully demonstrated on the pilot plant scale during 1948 -49, and was established commercially in 1967 in the G.C.O.S. plant. The Syncrude plant, due to come on stream in April 1978, also employs the hot water separation process."

Jan 1, 1978

By B. B. Meadows

"The Minto-Chipman Strip Mining Reclamation Project was initiated to re-vegetate the spoil piles remaining from strip mining operations.All available information was studied by the team responsible, and areas being reclaimed in the U. S. were visited, Methods applicable to the N. B. Project were noted for future use.We have both surface and underground mining operations in New Brunswick, Both deface the natural landscape and reclamation varies in difficulty, Surface operation disturbances are the most difficult to correct.Some of the surface mining is carried out next to two main highways and the results are definite eyesores, With this in mind, it was decided to landscape the spoil ground next to the highways and plant “as is"" the ground remote from the public view.The landscaping entailed various degrees of bulldozing from complete levelling to contouring, smoothing and topping, Bulldozing is, of course, the most expensive part of any reclamation project.There are two phases to the planting program; experimental and operational--experimental both prior and, later, in conjunction with the operational planting.Initially in the experimental project, the pH and composition of the spoil was determined using a grid sampling system. Soil samples were tested in a laboratory at the University of New Brunswick."

Jan 1, 1970

By G. Avramovic-Cingara, H. J. McQueen

The microstructure of commercially pure aluminum was investigated by using polarized optical microscopy (POM), orientation imaging microscopy (OIM), and transmission electron microscopy (TEM) techniques. Specimens were deformed in torsion at 400°C and equivalent strain rate of 0.1 s-1, to various strains of 0.2, 0.5, 1, 4, and 6. The results indicate that POM can usefully reveal grain and subgrain structures over a large field in aluminum. TEM is most suitable to study dislocation substructure and evolution of subgrains. While TEM microscopy and OIM are capable of resolving individual subgrains, OIM can not reliably distinguish subgrains with small misorientations, particularly in samples with low strain. On the other hand, the OIM technique is very useful in the analysis of many regions surrounded by high, medium, and low angle boundaries (HAB, MAB, LAB). Various misorientation maps were studied using different data processing methods. The analysis revealed that the subgrain size is relatively insensitive to strain. The fraction of low LAB ( < 5°) decreased and HAB (>15°) increased conversely with increasing strain, whereas MAB (5-15°) remained stable. The development of an increasingly bimodal grain boundary misorientation distribution is consistent with the predominance of dynamic recovery (DRV) in the evolution of microstructure, combined with geometrical dynamic recrystallization (gDRX), now called grain-refining DRV.

Jan 1, 2006