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By G. E. McClelland

Introduction Many discoveries have been made during the-past decade of low grade gold-silver deposits in the western US. This has stimulated development of low cost cyanidation procedures for precious metal extraction. Heap leach cyanidation techniques possess considerable potential for application to these low grade ores, small ore bodies, mine strip waste, and tailing materials where fine grinding is not necessary for good extraction. For heap leaching to be successful, these resources must have good permeability to achieve uniform distribution of the cyanide solution throughout the heaps. Some of the most difficult of the gold and silver ores to treat successfully by heap leaching are those containing excessive amounts of clays, or fines generated by crushing. Presence of excessive amounts of slimes, -50 µm (-270 mesh), in the heap leach feed will slow percolation, cause channeling, or produce dormant or unleached areas within the heap. This may result in unreasonably long leaching periods and poor extractions. In extreme cases, the clays or slimes can completely seal the ore heap. This causes the leach solution to run off the sides of the heap rather than penetrate the ore bed. The problem of heap leaching ores with fines can be aggravated while preparing ore heaps because of the natural sorting of coarse and fine material that occurs. This phenomenon results in concentration or ore fines in the center of individual ore piles and concentration of larger rock fragments of the lower slopes and base of the pile. When the individual piles within the heap are leveled off for the installation of the sprinkling system, additional segregation occurs as the fines sift through the coarser ore particles. This results in localized areas or zones with marked differences in permeability. Consequently, the leach solutions follow the course of least resistance. They percolate down through the coarse ore regions and bypass or barely wet areas that contain large amounts of fines or slimes. Effective use of marginal gold and silver resources by heap leaching required development of new methods to achieve more uniform size distribution when preparing ore heaps and better slime control during leaching. Early methods Agglomeration and balling of crushed ore to produce a porous and more uniform feed material for heap leaching is a viable method for treating clayey ores. Researchers from the US Bureau of Mines in Reno, NV began agglomeration pretreatment research in the mid-1970s for applications to and exploitation of these poor percolating feed materials. Little attention had been given to such methods before the Bureau's research. In 1905, T. C. Scrutton developed a unique technique for obtaining rapid vat leaching of a clayey ore where the gold was finely disseminated. His technique consisted of rolling the ore down a chute inclined at 60° to form agglomerates or balls readily permeable by the cyanide solution. However, these agglomerates lacked rigidity. And, to ensure good percolation leaching and washing, they could not be bedded in layers more than 1 m (3 ft) deep. If this depth was exceeded, it is difficult to obtain uniform leaching and washing. This results in reduced gold recovery. Shepard and others in 1937 studied the addition of lime and carbon dioxide or calcium carbonate to gold-bearing tailings to form agglomerates suitable for vat leaching. Satisfactory percolation flow rates were achieved in 90 g (3 oz) scale experiments, but the reagent requirements were cost prohibitive. Agglomeration and pelletizing has been used in other segments of the mineral industry. This technique was first used successfully around 1911 for pelletizing iron ores. Since then, agglomeration

Jan 7, 1986

By J. A. Musselman, P. F. Gnirk

A study was made of indexed penetrations by a single dull bit tooth under statically applied loads into rock subjected to confining pressures from atmospheric to 5,000 p.si and atmospheric pore pressure. Experimental results obtained with a 45" wedge tooth over the above range of pressures are presented for two limestones and a sandstone, a variely of indexing distances and two degrees of tooth dullness. The optimum distance between successive bit-tooth penetrations required for maximum rock damage and chip formation decreases substantially with increa.sing confining pressure above the brittle-to-ductile transition pressure of a particular rock. However, the distance remains approximately constant for a variation in confining pressure below the transition pressure. At a given confining pressure, the bit-tooth force required lor chip formation is constant for indexing distances greater than optimum, but generally decreases linearly with decreasing indexing distance for distances less than optimum. The chip-formation force data obtained at confining pressures for which the chip-generation mechanism is macroscopic-ally of a pseudoplastic nature compare favorably with previous theoretical results for indexed dull hit-tooth penetrntion into an idealized, rigid, perfectly plastic rock. INTRODUCTION To study the cutting action of a roller-cone bit, the interaction of a penetrating bit tooth with craters formed in a rock surfacc by the passage of previous bit teeth must be considered. Current knowledge of the basic mechanics of bit tooth-rock intcract:on under simulated borehole environmental conditions has been extensively reviewed.',' Particularly of current interest are the effects of bit-tooth shape, distance between successive penetrations and differential pressure at the rock surface on the extent of the interaction. Pertinent to this paper are results of an experimental investigationb f the interaction between successive penetrations by sharp, wedge-shaped bit teeth. It was demonstrated that both bit-tooth angle and differential pressure influence the extent of rock damage between successive bit-tooth penetrations. Specifically, the optimum or minimum distance between successive penetrations required for maximum interact'on or chip generation tends to decrease with decreasing bit-tooth angle and increasing differential pressure. In addition, at differential pressures on the order of 2,000 psi for four va- rieties of limestones and sandstones, the macroscopic mechanism of chip formation exhibits a transition from brittle to ductile. In this paper, experimental consideration is given to successive or indexed penetrat ons by wedge-shaped bit teeth. Since pore pressure in a rock sample is maintained at atmospheric pressure, the differential pressure at the fluid-rock interface is equal to the confining pressure. The degrees of bit-tooth dullness include teeth with flat and round apexes (Fig. 1). Of primary concern in this paper are the bit-tooth forces required for chip formation, the macroscopic mechanism of chip formation and the minimum distance between successive penetrations, i.e., optimum indexing distance required for maximum rock damage, as functions of differential pressure. Of further interest is a comparison of actual bit-tooth chip formation forces at elevated differential pressures with calculated forces from previous theoretical results4 for indexed dull bit tooth penetration into a rigid-plastic rock. EXPERIMENTAL APPARATUS AND PROCEDURE The experimental apparatus consists of a pressure vessel equipped with a piston through the side of the vessel (Fig. 2). A single bit tooth inserted in the lower end of the piston is forced at a desired rate into the rock when the ram pressure chamber is pressurized. Electrical instrumentation incorporated into the apparatus yields a graphical plot of force on the piston as a function of bit-tooth penetration or displacement into the rock. Since the piston and ram assembly are in force equilibrium for a constant confining pressure in the main vessel, the fluid volume in the vessel remains constant during bit-tooth penetration. Hence, the force resisting penetration of the tooth is independent of the force exerted on either end of the as-

By Barry Hope, Javier Rico

"Goldcorp’s Hoyle Pond mine has recently completed several projects which have impacted the overall ventilation system. The project includes extending the Fresh Air Raise (FAR) to depth, development of a new Return Air Raise (RAR), and the installation of new sensors and ventilation controls throughout the mine. Two years after the completion of #2 Winze, the mine is ramping up its ore production to 1,300 tpd (up from 1,100). To ensure safe and profitable production, a reliance upon technology has been needed to provide the required ventilation to the work areas according to the mine plan. To systematically assess the mine’s ventilation in real-time, a significant increase in remote monitoring was required. This included installing additional flow, pressure, temperature and gas sensors. The first step in upgrading the existing monitoring was to purchase airflow and differential pressure monitors and install them in key areas of the mine. This paper presents the process of expanding the monitoring capability at Hoyle Pond mine, the selected equipment and the results of the implementation. The intended goal was to improve safety while minimizing capital and operation costs. The monitors were installed in strategic locations to provide immediate feedback on the impact of changes to the primary ventilation airflows. Comparing the available sensor technologies, installing them and systematically monitoring the ventilation served as a first step towards developing a mine wide Ventilation Control System. In addition, the initial state of the monitoring and control system, with final results and the chosen solution for the mine site, are presented. INTRODUCTION The Hoyle Pond mine is located in the City of Timmins, within the Porcupine mining district, Ontario, which has produced more than 70 million ounces of gold since 1910. Currently, approximately 60% of Porcupine Gold Mines gold production comes from the Hoyle Pond underground mine. Mechanized cut and fill and long-hole mining methods are used to extract the ore. The remainder of the ore comes from the Hollinger Open Pit mine. The Dome Underground mine ceased operations in 2017. Hoyle Pond is currently mining at 1820 meters below the surface and plans to go deeper. The average dry-bulb as wet-bulb temperature underground varies according to the depth and surface conditions which has extremes of –40°C in winter to +30°C in summer. The total airflow volume pushed down from surface is 240 m3/s to accommodate the diesel-powered equipment needed for normal operations. In order to improve the quality of air underground a program has been implemented to use diesel particulate filters, starting with the truck fleet and 6-yard scoops, followed by the intention to implement the rest of the functional diesel-powered equipment and eventually move to electric equipment."

Jan 1, 2019

By R. W. Fenn, H. A. Lepper, W. R. Hibbard

THIS paper reports the results of static tension and torsion tests made on single crystals of alpha brass for the purpose of determining its elastic coefficients. 70-30 alpha brass was chosen because it has been used extensively in the study of the plastic deformation and because it has the following desirable characteristics: (1) face-centered cubic structure, (2) marked elastic anistropy, (3) low elastic modulus. In 1928 Masima and Sachs' using static methods reported the following values for the elastic coefficients of 72-28 pct alpha brass: S11 = 19.4 X 10-13' cm2 per dyne S12 = —8.35 X 10"' cm2 per dyne S44 = 13.9 X 10-13= cm2 per dyne These values were obtained from the measurements shown in fig. 1. The experimental points for both tension and torsion lie consistently below the lines drawn to represent them. Fig. 2 shows the stress-strain curves for their specimens. Only a few points in the elastic range of these curves were available to obtain their values for Young's modulus. Therefore, it was considered that a re-evaluation of these data was desirable. In addition a variation of from 1.13 to 1.485 kg per mm2 was found in the values of the critical resolved shear stress for 70-30 alpha brass reported by Burghoff,² Treuting and Brick: Martin,4 Maddin, Mathewson and Hibbard5,6 and von Goler and Sachs.' Therefore, it was desired to evaluate the conclusion of Boas and Schmid8 that a constant resolved shear stress and not a constant elastic shear initiates plastic deformation. Theoretical Considerations*: The elastic deformation of cubic crystals may be defined by three elastic coefficients (S11, S12, S44,) or three elastic parameters (C,,, C,, C,,). These coefficients or parameters are sufficient to define the stress and strain relations for cubic crystals in the generalized form of Hooke's law referred to Cartesian coordinates. Elastic parameters and coefficients in the cubic system are related by the expressions: C11 —S11+S12/(S11-S12)(S11+2 S12) C12=-S12/(S11-S12)(S11+ 2 S12) (S11 — S12) (S11 + 2 S12) [2] C44 =1/S44 PI It is possible to determine all the elastic coefficients for a cubic metal by measuring two of the three elastic constants: Young's modulus (E), torsion modulus (G), or compressibility (S). The following relations exist between crystallographic orientation and E, G and S for cylindrical crystals of the cubic system: 1/E = S11 — 2 [(S11 - S12) — Su] (?1² ?2² + ?2²?83 + ?3² ?1²) [4]

Jan 1, 1951

By H. Stanley Benson

This report is an account of research conducted to improve the performance of and then further field test Draft Power Sensor (DPS) equipment, the use of which enables a bulldozer operator to optimize his machine's work rate. Significant improvements were made in DPS hardware, and extended field testing was conducted at two working strip mines: the Glenharold Mine of Consolidation Coal Company, near Stanton, North Dakota, and the Beulah Mine of Knife River Coal Company, near Beulah, North Dakota. This report documents the increase of bulldozer work production by greater than twenty percent while using the Draft Power Sensor when compared to baseline work production without benefit of the Draft Power Sensor. Research was done by Southwest Research Institute under contract with the Bureau of Mines.

Jan 1, 1980

The works recorded in this Test Report have been performed by Rade Roncar - Electrotechnical Institute of Zagreb, SFR Yugoslavia in collaboration with Bureau of Mines. The main objective of these investigations was to investigate the possibility of fabrication of thin-walled square enclosures of satisfactory safety factor in accordance with requirements of effective technical regulations. The results and the investigations can be divided in three main fields: - investigations of thin-walled enclosures with the view of determination of pressures causing technological deformations before performing tests in accordance with effective applicable regulations, - finding the safety factor by means of tests of metal-foam pressure vents, - comparison of enclosures with and without pretreatment by technological deformation.

Jan 1, 1987

Flotation of Smithsonite by Using Siloxane Cationic Surfactants as Collectors

Sep 13, 2010

The Significance of Internal Recycle in Froth Flotation

Sep 13, 2010

By Peter J. Huck, Swpan Bhattacharya, Madan M. Singh

This paper reviews the state-of -the-art techniques for estimating the duration of post- mining subsidence arising from different mining techniques and evaluates existing post-mining liability systems in the United States and abroad. For each mining technique (room-and-pillar and longwall) the mechanism of subsidence development is examined and the critical factors influencing the duration of subsidence are evaluated. These are followed by a comprehensive summary of field data on the duration of subsidence movements collected in various parts of the world. Using this information, graphical charts are developed to depict the relationship between the time duration and critical controlling factors. Also included are any mathematical relationships that may exist between the different variables. Finally, a survey of current state, federal and foreign legislation on mine operator liability time spans is provided. These laws are evaluated for their applicability in light of the data on duration of residual subsidence. On the basis of this evaluation, guidelines are suggested for the establishment of the mine operator liability structure for the United States.

Jan 1, 1986

By J. D. Appleton, J. Ridgway, K. B. Greally

Paper presented at the 28th International Geological Congress held in Washington DC, July 1989 (International geochemical mapping sessions). The results suggest that meaningful geochemical maps can be produced from very low-density surveys, and that existing data sets could perhaps be incorporated into such a map series with the use of a system such as Uniras software. There are still many problems to be resolved, however, including the compatibility of data derived from different analytical methods, and the precise methods to be employed will necessarily require international agreement. Sampling densities should be chosen on the basis of the scale of the geochemical and geological features to be distinguished and will vary from region to region. Reanalysis of selected samples from archives to increase the range of elements determined or to unify analytical methods is only likely to be effective if the original survey was at quite a low density

Jul 1, 1991

By Gary L. Mowrey

Visible and sometimes audible indications of excessive underground rock pressure such as pillar fracturing, squeezes on chocks, and "roof talk" are familiar to mining engineers. Such signs often precede rock failure on a larger scale and therefore may be used as a warning. Nevertheless, these subjective observations do not provide an adequate means of evaluating the existing rock pressure conditions in a mine. One method which appears to be extremely promising in determining the stability of geologic structures in general is that of monitoring their associated micro seismic activity. Mining engineers generally agree that during the process of rock deformation and failure small-scale seismic ("microseismic") vibrations are produced in the rock itself. These transient vibrations propagate through the rock structure and may be detected at a considerable distance from the failed rock by employing suitable electronic monitoring equipment. Hardy (1) has presented a detailed review of microseismic research in the mining, petroleum, and geoscience areas, and it is apparent that relatively little application of micro seismic techniques have been made in coal mines. This is especially true in North America since here most coal mines are fairly shallow and consequently are not generally subjected to excessive stresses. Furthermore, strict Federal and State mining laws limit the use of electrical equipment in coal mines complicating the use of the necessary monitoring facilities. In terms of both mine safety and economics, monitoring microseismic activity appears to be invaluable in the detection and location of over-stressed pillars and unstable roof conditions caused by development and production work. In 1970 The Pennsylvania State University Rock Mechanics Laboratory became involved in a research project, sponsored by the U.S. Bureau of Mines, to investigate the feasibility of using microseismic techniques to detect and to locate potential regions of instability around a longwall coal-mine operation [Hardy and t10wrey (2); Mowrey (3)]. In this study geophones (velocity gages) located in an array of shallow boreholes drilled from the surface above the active area of the longwall were employed to detect microseismic activity, and a mobile micro-seismic monitoring facility was used to condition and record this data for later analysis. This project is unique in that measurements were made from near-surface geophones rather than geophones installed on the mine itself. Two advantages are apparent, namely that (1) there are no electrical limitations on the monitoring system and that (2) mining operations can continue normally because there is no monitoring equipment or cables in the mine.

Jan 1, 1978

Caterpillar and Fortescue Metals Group have moved forward with the delivery, installation and support of a complete Cat MineStar System at Fortescue?s Solomon iron ore mine in the Pilbara region of Western Australia. The complete technology suite was implemented for the first phase of Solomon, the 20 Mt/a (22 million stpy) Firetail manned mine, in October 2012. As part of an autonomous mining solution for phase two, the 40-Mt/a (44-million stpy) Kings Mine, eight Command for hauling Cat 793F CMD trucks were commissioned and commenced operations in the second quarter of 2013. The mine plan calls for a progressive ramp up to 45 autonomous trucks during the next several years. In addition, other Cat MineStar System capability sets, Fleet, Terrain, Detect and Health, are being used across the mobile equipment fleet, including support equipment and light vehicles. Working closely with Fortescue and its mining contractor, Leighton Contractors, Caterpillar and the Cat dealer in Western Australia, WesTrac, are providing a full solution for managing, operating and supporting Cat MineStar System and Command for hauling. The greenfield Solomon Mine has brought together the skilled team from Caterpillar, Fortescue, Leighton Contractors and WesTrac to deliver an efficient, cost effective autonomous mining solution.

Nov 1, 2013

By G Sparrow

The Murray Basin is being heralded as the next major mineral sands province in Australia. Already exploration programs have delineated extensive commercial deposits and several companies are progressing with plans to produce zircon, rutile and ilmenite in the Basin. As these deposits are developed consideration will need to be given to several key issues of the Murray Darling Basin; the availability of fresh water and management of salinity in the area being two of them. In this paper ideas being developed in CSIRO that link the processing of mineral sands with the salinity problem in the Basin are presented. The proposal presented here is to process saline water to produce industrial minerals with large volume applications and to produce value-added products from the mineral sands in the Basin using reagents produced from the saline waters. Processes to produce titania pigment and zirconia consume chlorine, caustic soda, soda ash and hydrochloric acid, all derivatives of salt (sodium chloride). There may be a good economic incentive if these processing plants were located in the close vicinity of each other.

Jan 1, 2001

By D S. Stewart, K W. Keskimaki

The Henderson Mine has been utilising a continuous panel caving method to extract molybdenum ore since starting operation in 1976. In the past three decades since the mine was designed, many changes have taken place in underground technology as well as the general nature of the mining business. The impacts of larger scale underground equipment and automation are significant at Henderson and continue to reshape the nature of the enterprise. During the first years of operation in the 1970s, Henderson required almost 2000 employees to achieve full production, today only about 400 people are required to fully utilise the plantÆs capacity. The most recent change to the facility is the conversion from a rail haulage system to an underground crushing and conveying system that transports ore 25 km to the Henderson mill site. This change has required the introduction of large, rubber tired haulage trucks underground and the mining methods necessary to develop the large openings demanded by the trucks and underground crusher. The development of the underground crusher is also the first step to mining the final bottom horizon of the orebody. Along with this move comes an opportunity to almost triple the effectiveness of the mining effort, through higher draw columns and wider draw bell spacing. This final advancement to a totally trackless mine has positioned Henderson well for safe and efficient operation as it enters the 21st century.

Jan 1, 2000

By T. M. Bhatti

The main purpose of present study was to characterize the dissolution of uranium from low-grade black shale with indigenous isolated strain of Acidithiobacillus ferrooxidans (BSAF-01). The nature of shale is quartzite-schistose and contains uranium content of 0.005% U3O8 (50 ppm U3O8). Uranium is present in the tetravalent oxidation state (U4+) in the shale matrix. The main minerals identified are graphite, quartz, pyrite, mica minerals (phlogopite, biotite, sericite, and chlorite), microcline, K-feldspar and kerogen (hydrocarbon-compounds). Bacterial oxidation of pyrite was an acid-generating system and produced sulfuric acid and ferric sulfate during this biological phenomenon. A series of bioleaching experiments were conducted in shake flasks for leaching of uranium from black shale. The leaching experiments were performed at 50% pulp density using indigenous Fe- and S-oxidizing bacterium (Acidithiobacillus ferrooxidans). Bioleaching data revealed that about 90% ~ 95% U3O8 was leached out from black shale ore. Uranium dissolution from shale depends on pH (pH 1.5~1.9), redox potential (=500 mev) and the concentration of Fe2+ and Fe3+ ions in the leaching environment. The oxidative leaching of U4+ involves a redox reaction with Fe3+ as an oxidant and bacterial re-oxidation of Fe2+ in acidic leaching environment. Uranium leaching efficiency was attributed to the sulfuric acid and ferric sulfate production during bacterial oxidation of pyrite.

Jan 1, 2014

By Rak-lun Choi

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

Jan 1, 2003

By Michael L. Sorokin

The metallic nickel production by converting of nickel matte is analysed from the thermodynamic point of view using earlier developed thermodynamic models for sulphide, metal and slag phase. Three-suffix Margules equations are used to calculate thermodynamic properties of melts. Potential diagrams of Ni-FeS-OSiO2 system are calculated for various temperatures and Fe to Ni ratios. The diagrams used for consideration about possibilities of the direct one-stage metallic nickel production.

Jan 1, 1995

By A. H. Geisler, F. Keller

Although the subject of precipitation from solid solution appears to be one of the more profitable fields in metallurgy for study with the electron Microscope, few comprehensive studies have yet been made. Occasionally electron micrographs have been published that illustrated alleged precipitation in various alloys, but frequently the apparent size, shape and distribution of the particles do not fully agree with those expected from theory or from observations of the Precipitate when the particles have grown to a size resolvable with the light microscope. The presence of a Widmanstatten pattern for submicroscopic precipitate particles has been demonstrated for only a few aged a1loys.l The initial problem has been the development of suitable techniques for applying the transmission-type instrument to a field that has been inherently associated with reflection-type microscopes. The various techniques have been the subjects of numerous publications, and instead of describing them individually here it will sufficc to say that the oxide film method has proved to be the most satisfactory method yet found for studying the microstructure of aluminum alloys with the electron microscope. This method has the definite characteristic advantage that the actual surface layer of the specimen is examined and not a plastic or silica replica. Doubtless suitable methods for forming and removing the oxide film could be developed for alloys of other metals. The purpose of this report is to point out the characteristics of the oxide film method that have been observed during the studies of numerous aged aluminum alloys and to present the results of these studies. Preparation OF Specimens The oxide film method for preparing specimens of aluminum alloys for examination in the electron microscope has been described in detail previously,¹,² Briefly, the procedure consists of preparing the metallographic specimen, forming the film by anodic oxidation and removing the film from the prepared surface of the oxidized specimen, The specimen is polished accordillg to the usual procedure for microscopic examination.³ he specimen may then be etched to remove flowed metal but etching to attack the alloy constituents or to leave them in relief as in the replica processes is not necessary. Electrolytic polishing is not generally recommended, Deep-etched specimens are used frequently, however, since they provide information that is not revealed by polished specimens and frequently present the same information more clearly than do the polished specimens, The surface preparation of specimens to be deep-etched is not important, since specimens that have been subjected to the first wet PoliShing operation are generally used, but frequently the as-rolled surface is Suitable. These specimens are then etched using a suitable macroetching reagent.

Jan 1, 1947

By F. Keller, A. H. Geisler

Although the subject of precipitation from solid solution appears to be one of the more profitable fields in metallurgy for study with the electron Microscope, few comprehensive studies have yet been made. Occasionally electron micrographs have been published that illustrated alleged precipitation in various alloys, but frequently the apparent size, shape and distribution of the particles do not fully agree with those expected from theory or from observations of the Precipitate when the particles have grown to a size resolvable with the light microscope. The presence of a Widmanstatten pattern for submicroscopic precipitate particles has been demonstrated for only a few aged a1loys.l The initial problem has been the development of suitable techniques for applying the transmission-type instrument to a field that has been inherently associated with reflection-type microscopes. The various techniques have been the subjects of numerous publications, and instead of describing them individually here it will sufficc to say that the oxide film method has proved to be the most satisfactory method yet found for studying the microstructure of aluminum alloys with the electron microscope. This method has the definite characteristic advantage that the actual surface layer of the specimen is examined and not a plastic or silica replica. Doubtless suitable methods for forming and removing the oxide film could be developed for alloys of other metals. The purpose of this report is to point out the characteristics of the oxide film method that have been observed during the studies of numerous aged aluminum alloys and to present the results of these studies. Preparation OF Specimens The oxide film method for preparing specimens of aluminum alloys for examination in the electron microscope has been described in detail previously,¹,² Briefly, the procedure consists of preparing the metallographic specimen, forming the film by anodic oxidation and removing the film from the prepared surface of the oxidized specimen, The specimen is polished accordillg to the usual procedure for microscopic examination.³ he specimen may then be etched to remove flowed metal but etching to attack the alloy constituents or to leave them in relief as in the replica processes is not necessary. Electrolytic polishing is not generally recommended, Deep-etched specimens are used frequently, however, since they provide information that is not revealed by polished specimens and frequently present the same information more clearly than do the polished specimens, The surface preparation of specimens to be deep-etched is not important, since specimens that have been subjected to the first wet PoliShing operation are generally used, but frequently the as-rolled surface is Suitable. These specimens are then etched using a suitable macroetching reagent.

Jan 1, 1947

By Y. Huang, P. B. Prangnell

"An Al-0.1Mg alloy was firstly deformed at room temperature by ECAE to a true strain of 10, where a steady state deformation was established and further processing had little effect on grain refinement. The ECAE samples, with an average grain size of ~0.55µm, were then compressed in a channel die at 77K- 473K to various reductions. Microstructures were characterized by electron backscatter imaging and EBSD in a FEGSEM. Grain refinement to the ECAE submicron structure occurred during deformation at cryogenic temperatures of 77 – 213K, whereas coarsening took place during deformation at elevated temperatures. A steady state deformation was observed at all temperatures where a constant grain structure was developed and maintained upon further straining due to dynamic recovery. The mechanisms of dynamic recovery during steady state deformation at cryogenic temperatures are discussed.IntroductionSevere deformation processing (SDP) has been successfully used to produce submicron grain structures, and in some cases nano-scale crystallite sizes, in a wide range of alloys. However, the rate of grain refinement becomes increasingly inefficient at high strains as a steady state grain structure is approached [1-3]. Steady-state grain sizes have also been reported in other ultra-high strain deformation processes, like cryogenic ball-milling [4]. There is thus a minimum grain size achievable in a material by a given SPD process under constant deformation conditions.It is well documented that a steady state subgrain size is observed in warm deformation of metals due to dynamic recovery (e.g. [5]). In severely deformed alloys a constant grain size at ultra-high strains has similarly been attributed to dynamic recovery [1-3]. Mechanisms have been proposed, for rapid deformation induced grain growth including stress driven boundary migration and breakaway from solute pinning [2]. However, as pointed out by Humphreys et al. [2] the restoration processes are currently poorly understood, particularly at low temperatures, where the boundary migration rates required to maintain a constant grain size are orders of magnitude higher than can be satisfactory explained from diffusion controlled migration. Similar to the subgrain size, the steady state grain size obtained during SDP is generally related to the temperature compensated strain rate [2, 6]. Thermally activated restoration processes are thus expected to be suppressed by lowering the deformation temperature and a smaller steady state grain size can be achieved."

Jan 1, 2012