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By Elwood G. Haney, R. N. Parkins

Stress corrosion cracking of two heats of 18 pct Ni maraging steel in rod form immersed in an aqueous solution of 0.6N NaCl at pH 2.2 has been studied on un-notched specimens stressed in a hard tensilf machite. Austenitizing temperature in the range 1830 to 1400 F has been shown to have a marked influence on the propensity to crack, the loulest austenitizing- temperature producing the greatest resistance to failure. In the nzosl susceptible conditions, the cracks followed the original austenile grain boundaries; but when tlze steels zcere heal treated to inproze their resistance to stress corrosion, the cracks becatne appreciably less branched and slzouqed significant tendencies to become trans granular. Electron metallography of the steels indicated the presence of snzall particles, possibly of titanium carbide, along- the prior austenite grain boundaries and these particles u:ere more readily detectable in the structures that were most susceptible to cracking. Crack propagation rates, which appeared to be dependent upon applied stress and structure, were usually in tlze reg-ion of 0.5 mm per hr and may, therefore, be e.xplained on tlze basis of a purely electrochetnical ,nechanism. However, there is some ezliderzce from fractography that crack extension may be assisted by ttlechanical processes. Anodic stit)zulation reduced the tiwe to fracture, although cathodic currents of small magnitudes delayed cracking-; further increase in cathodic current resulted in a sharp drop i,n fracture litne, possibly due to the onset of hydrogen ewbrittlement. THE use of the high strength maraging steels, with their attractive fracture toughness characteristics, is restricted because of their susceptibility to stress corrosion cracking in chloride solutions. Although this limitation has resulted in investigations of the stress corrosion susceptibilities of these steels, there have been few systematic studies aimed at defining the various parameters that determine the level of susceptibility. It is the case that the usual tests have been performed with the object of defining some stress or time limit, on unnotched or precracked specimens, within which failure was not observed,' but while such results may be of some use in design considerations, they are necessarily concerned only with the steels as they currently exist and not with their improvement to render them more resistant to stress corrosion failure. This omission may be considered unfortunate because the indications are that stress corrosion in maraging steels shows dependence on structure in following an intergranular path, and since experience with other systems of intergranular stress corrosion crack- ing is that susceptibility may be varied by modifying heat treatments, a similar effect may be expected with maraging steels. It is sometimes from such observations that a fuller understanding of the mechanism of stress corrosion crack propagation begins to emerge, leading in time to the development of more resistant grades of material. The present work was undertaken to study only one aspect of the influence of heat treatment upon the cracking propensities of the 18 pct Ni maraging steel, namely the effect of austenitizing temperature, although certain ancillary measurements and experiments have been undertaken. EXPERIMENTAL TECHNIQUES Most of the measurements were made on a steel, A, having the analysis shown below, although a few results were obtained on a steel, B, having a slightly different composition. Both steels were supplied in the austenitized condition, A as 3/8-in-diam rod and B as 1/2-in.-diam rod. Cylindrical tensile test pieces were machined from the rods: the overal length was 2 1/2 in., the gage length 1 in. and the diameter 0.128 to 0.136 in. The stress corrosion tests were carried out with the specimens strained in tension in a hard beam testing machine, the necessary total strain being applied to the specimen over a period of about 30 sec, after which the moving crosshead was locked in position and the load allowed to relax as crack propagation proceeded; the load relaxation was recorded. The load was applied after the specimen had been brought into contact with the corrosive solution, the latter being contained in a polyethylene dish having a central hole through which the specimen passed, leakage being prevented by the application of a film of rubber cement. The specimen was in contact with the solution for over half of its gage length and the solution was exposed to the air during testing. The solution was prepared from distilled and deionized water to which NaCl was added, 0.6N, and the pH adjusted to 2.2 by HCl additions. The composition of the solution

Jan 1, 1969

By Maurice C. Fuerstenau

INTRODUCTION The term, chelate, from the Greek for 'claw,' has its origin in the pincer-like representation of more than one atom of a single ligand bonded to the same metal atom, forming a ring-like structure. Depending on how many attachments exist on the sphere of coordination around the metal ion, ligands are referred to as bidentate, tridentate, tetradentate, pentadentate and hexadentate According to Calvin and Martell (1952) and Somasundaran and Nagaraj (1984), chelating agents must contain suitable functional groups, and their location within the ligand molecule must enable ring formation that is sterically possible. Typical structures that meet these requirements have been given by Fuerstenau and Herrera-Urbina (1988) and are listed in Figure 1. As noted, the functional groups of these reagents contain electron donor atoms such as oxygen, nitrogen and sulfur. Basic groups, such as amino (-NH,), are those that contain an atom with a lone pair of electrons. Acid groups are those, such as carboxylic (-COOH) which lose a hydrogen ion and coordinate with the metal atom. Examples of each of these types chelating reagents are given in Tables 1-4. The specificity of chelating agents for various metal ions has long been known and was utilized early in the search for new flotation collectors. In 1927, Vivian used ammonium nitrosophenylhydroxylamine as a collector for cassiterite. Holman (1929) tested dimethylglyoxime as a collector for nickel oxide. He also suggested taurin as a collector for oxidized lead ores. DeWitt and von Batchelder (1939) suggested the use of oximes as flotation collectors. Gutzeit (1946) conducted an extensive investigation on the use of chelating agents as collectors and as depressants for gangue minerals. The depressants are those reagents that form soluble chelates with metal ions that could function as

Jan 1, 2005

By A. N. Lasseigne

Hydrogenation behavior of the NaAlH4 intermetallics is investigated utilizing thermoelectric power and magnetic analyses. Using both thermoelectric power and magnetic susceptibility measurements on these intermetallics allows for confirmation and further insight into hydrogen's role in altering the material's electronic structure. The electronic and magnetic property correlations will indicate the direction for further alloy development to optimize hydrogen storage.

Jan 1, 2006

By B. W. Gandrud

The upper part of the Alabama deposits of crystalline graphite consists of an oxidized ore derived from the underlying unoxidized ore through prolonged Weathering. The degree of oxidation in different sections and at different depths within the bed is not uniform. The original ore is hard and blue-gray; the weathered product is soft and brown and is the only part that has been mined to any extent. Samples of both oxidized and unoxidized ores were obtained from two of the large graphite deposits of Clay County. Three additional samples of oxidized ore were obtained from different portions of a third property in the same region. In this report, ores 1 to 5 are of oxidized material and ores 6 and 7 of unoxidized.

Jan 1, 1934

By Jorge Ganoza

Algunos concentrados de plomo contienen contaminantes que afectan la comercialización del concentrado de cobre debido a aspectos ambientales, así como la calidad del producto final. En ese sentido, el presente texto busca la forma de minimizar la presencia del plomo y de bismuto en el concentrado de cobre, a través de la flotaciónpor chalcopirita. De otro lado, dado que el plomo y bismuto son elementos que tienen similar comportamiento durante la flotación, es factible aislar los minerales de plomo y bismuto.

Nov 1, 2012

By Homer W. Riley, C S. Jenkins

SMALL power-driven, toothed, cast-iron rolls were used first to break anthracite in 1844. Prior to that time, men with hammers, who stood on perforated cast-iron- plates, .broke the large lumps into commercial sizes. In order to convert run-of-mine into the various sizes required by the anthracite industry, about 20 million tons must be broken, annually, [ ] into smaller sizes. This phase of anthracite preparation is of major importance, because the degradation accompanying reduction in coal sizes should be kept at a minimum. The exclusive use of toothed rolls for that purpose indicates that comminution by rolls is the best solution of the problem. Many improvements have been made in tool design, but the most important was a reduction of the peripheral speed of the rolls from 1000 to 300 ft. per minute. The higher speed was based upon and approximated the velocity of a falling piece of coal when it entered the rolls. Exhaustive roll tests at the slower speed showed that the same size reduction could be affected with less degradation. The adoption, there- fore, of slow-speed, compound geared rolls, especially for breaking the

Jan 1, 1943

Carbon anode cells were studied by two-dimensional computer simulation to evaluate their suitability for alumina electrolysis at high superficial current densities. The most efficient anode arrangement was needed to overcome the electrochemical disadvantages of alumina's low solubility in chlorides. Cells with packed-bed anodes might provide practical superficial current densities greater than 0.67 A/cm2 when the granule size was less than 1 cm, but in the process of electrolysis the granules within the active zone would be consumed and become smaller, affecting alumina concentration transport. For zones of very small granules a concentration-dependent model should be considered; for more complete consideration a time-dependent model can be introduced to describe the variation of granule size and its influence on mass transfer and polarisation

Jun 19, 1905

By Thomas J. Martin, James W. Martin, Paul F. Martin

The conveyor belt is the basic building block of a broad range of material handling applications in modern mining systems. The mining plans and site conditions dictate basic system requirements but this is only a part of total design evaluation. The total system in the typical mining situation can encompass all the activities from the excavators at the mining face to the processing plant, site loadout facilities and/or a power plant. The number of alternative configurations which must be evaluated including subsystems and components is limited only by analytical time and creativity. The constraints and issues which must be addressed continue to expand, driven by reliability, environmental impact and cost competitiveness. All of the system requirements must be translated into specifications for costing, final design and construction.

Jan 1, 1993

By A. A. Bustos

A model was developed to simulate the blow-by-blow operation of the converting process. From the weights, compositions and temperatures of all converter feeds the model calculates the composition and tonnage of both converter matte and slag as well as bath temperature at the end of each blow. The development of the model and its application to the converter aisle operation are described. There is good agreement between model predictions and observed results. At the present time the model is being used to investigate different converting schemes and their effect on pay metal recoveries, slag chemistry and temperature of the bath. Future work involves the use of the simulation model as a process control tool for the converting operation.

Jan 1, 1988

By Jr. Matthews

The Candelaria copper-gold deposit is located in Region m of Chile, 805 kilometers north of the capital, Santiago. Candelaria was discovered in 1987, following a six month exploration program. In late 1986, induced polarization (IP) surveys outlined an anomalously high response within the area of interest. The first test hole bad three intersections totaling 49 meters, with an average grade of 1.97% copper. Drilling eventually outlined approximately 390 million tonnes, grading 1.09010 copper and 0.26 grams/tonne gold. Production began in early 1995 and is estimated at 120,000 tonnes copper and 80,000 ounces gold annually.

Jan 1, 1996

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 W. M. Deaton

The Keyes Helium Plant of the Federal Bureau of Mines was constructed under an expedited schedule, to supply the urgent and growing demand for helium in atomic energy, missiles, aerology, space exploration, shielded-arc welding, and low-temperature research. Construction began in December 1958 and ended in August 1959. The plant, near Keyes, Okla., processes 2 percent helium-bearing natural gas from the Keyes gasfield. In 1960 the plant produced and shipped 263 million cubic feet of helium (equivalent to an annual rate of 290 million cubic feet). Production cost was $9.11 a thousand cubic feet of helium. A low-temperature process involving two steps is used; the first separates a crude-helium product from the natural gas at about -250° F. and 225 pounds per square inch gage (p.s.i.g.); and the second purifies the crude helium to a high-purity product (Grade-A helium, 99.995 percent helium) at about -320° F. and 2,750 p.s.i.g.

Jan 1, 1961

Cokriging uses a sparsely sampled, but accurate and precise primary dataset, together with a more abundant secondary data-set, for example grades in a polymetallic orebody, containing both error and bias, to provide improved results compared to estimation with the primary data alone, as well as filtering the error and mitigating the effects of conditional bias. The method described here may also be applied in polymetallic orebodies and in other cases where the primary and secondary data could be collocated, and one of the data-sets need not be biased, unreliable, etc. An artificially created reference data-set of 512 lognormally distributed precious metal grades sampled at 25×25 m intervals constitutes the primary data-set. A secondary data-set on a 10×10 m grid comprising 3200 samples drawn from the reference data-set includes 30 per cent error and 1.5 multiplicative bias on each measurement. The primary and secondary non-collocated data-sets are statistically described and compared to the reference data-set. Variograms based on the primary data-set are modelled and used in the kriging of 10×10 m blocks using the 25×25 m and 50×50 m data grids for comparison against the results of the cokriged estimation. A linear model of coregionalization (LMC) is established using the primary and secondary data-sets and cokriging using both data-sets is shown to be a significant improvement over kriging with the primary data-set alone. The effects of the error and bias are filtered and removed during the cokriging estimation procedure. Thus cokriging using the more abundant secondary data, even though it contains error and bias, significantly improves the estimation of recoverable reserves.

Jan 1, 2014

By Joseph R. Stephens

Deformation substructures of' polycrystalline tungsten, W-2, 9, and 24 pct Re, and W-3 pct Ta were studied by tra?zsrnission electron microscopy. The stress-strain curve for unalloyed tungsten showed gradual yielding followed by work-hardening. Electron nzicrographs indicated a gradual increase in dislocation density with increase in strain up to 5.0 pct. Dislocations, although frequently jogged, were straight over moderate distances and were in a randorn array. Stress-strain curves for alloy specimens of W-2 and 9 pct Re and W-3 pct Ta exhibited a drop in stress at yielding followed by only slight work-hardening. Electron micrographs of these specimens after strains of 0.05, 0.1, and 0.5 pct revealed no change in dislocation substructure from the unstrained specimens. After 2.0 pct strain, the three alloys exhibited dense networks. W-3 pct Ta was characterized by straight, frequently jogged dislocations comparable with the dislocation structure in unalloyed tungsten after a similar amount of strain. In contrast, W-2 pct Re exhibited dislocations that contained widely spaced jogs, while W-9 pct Re had developed a cell structure after the relatively srnall strain of 2.0 pct. The W-24 pct Re alloy contained a few dislocations after 0.1 pct strain, while after 0.5 pct strain twins were evident. Dislocation slip bands apparently preceded the twins. The stress-strain curve for the alloy indicated that twinning commenced after approximately 0.25 pet strain. These results indicate that the primary effect of low rhenium concentrations (2 and 9 pct) in tungsten is to increase dislocation multiplication after macroyielding by reducing the Peierls-Nabarro force (lattice resistance to dislocation motion). The dislocation bands that precede twins in W-24 pct Re may be caused by localized internal stresses resulting fro a metastable structure, for example, clustering of rhenium atoms. The effect of high rhenium additions (22 a 65 pet* Rproperties of tungsten. Klopp, Witzke, and Raffo5 reported bend transition temperatures as low as -100°F (200°K) for dilute electron-beam-melted W-Re alloys tested in the worked condition. Recrystalliza-tion increased the bend transition temperature, but alloys with 2 to 4 pct Re were still markedly superior to unalloyed tungsten. Fractographic examinations of tungsten and W- 3 pct Re and W- 5 pct Re alloys by Gilbert 6 revealed that these low rhenium alloys showed a greater tendency toward cleavage failure than did tungsten. Garfinkle 7 showed that rhenium additions, up to 9 pct, to (100) oriented tungsten single crystals increased the proportional limit stress and decreased the flow stress and the rate of work-hardening. In addition, while deformation in unalloyed (100) oriented crystals apparently involved both (110)100) and (112) slip, crystals with rhenium contents of 5 andpct or more deformed primarily by (112) slip. The mechanism by which high and low rhenium additions affect the mechanical properties of tungsten is still not well-established. The present investigation was undertaken to determine by transmission electron microscopy the effects of low rhenium additions, 2 and 9 pct, and a high rhenium addition, 24 pct, on dislocation substructure in the early stages of deformation of polycrystalline electron-beam-melted tungsten. Unalloyed tungsten and a W- 3 pct Ta alloy were included for comparison. EXPERIMENTAL PROCEDURES Materials. Triple electron-beam-melted tungsten, W-2, 9, and 24 pct Re, and W- pet Ta were used for this investigation. Chemical analyses of the cast ingots are given in Table I. A description of the starting metal powders and melting and fabrication pro-cedures for unalloyed tungsten and the W-Re alloys is reported.5 The W-3 pet Ta alloy was processed in a similar manner. Compression specimens measuring 0.300 in. (7.6 mm) in length by 0.130 in. (3.3 mm) in diam were machined from swaged rods. All alloy specimens were annealed in a vacuum of 8 x 10- 6 Torr (10'2iVper sq m) for 1 hr at 3600°F (2255°K). The recrystallized grain size ranged from 0.06 to 0.08 mm diam for the alloy specimens. Unalloyed tungsten was annealed at 2400° F (1589°K) for 1 hr to produce a recrystallized grain diameter of approximately 0.12 mm. Specimens were electropolished in a 2 pet NaOH solution to a diameter of 0.125 in. (3.18 mm) to remove surface notches resulting from grinding and to improve reproducibility of t data. The ends o the compression specimens were ground flat, parallel to each other, and perpendicular to the longitudinal axes with 4/0 emery paper. Compression Tests. The compressive stress-strain apparatus used for compression tests is described in detail by Stearns and Gotsky.9 Room-temperature compression tests were conducted at a crosshead speed of 0.01 in. per min (0.25 mm per min).

Jan 1, 1969

By Hans Janzon, Ernst Buechi

INTRODUCTION The headrace tunnel in Amlach is part of a hydro electric power scheme near the city of Lienz in south west Austria. The project is owned and developed by Tiroler Wasserkraftwerke AG, the regional electrical supply utility. The construction work was divided into seven contracts for the entire scheme. The power output will be 60 MW, this being developed from a head of 370 m and water flows of 20 m3/s. The water will be tapped from the river Drau and lead through a 22 km long headrace on the south side of the Puster valley through the Lienzer Dolomiten mountain range. Contract No. 4, which is a joint venture between Mayreder, Züblin, Strabag, Rella and Innerebner, involves the construction of 13.5 km of the headrace. It was decided to bore this from one single adit, which probably makes it the longest pressure tunnel driven from one side by a TBM. (See Fig. 1.) For the tunnelling an Atlas Copco Jarva MK 12 TBM was chosen. The excavation diameter is 3.90 m, with the final lined diameter being in the range of 3.20 to 3.40 m. The back-up is a 145 m long single track rail system supplied by Mühlhäuser (Germany). Side-tipping cars with a capacity each of 8.2 m were used for removing the muck. One California switch was attached to the back-up after 3,000 m, and a second fixed switch was installed after 8,000 m of boring. 3 m long

Jan 1, 1987

By Gary A. Perry

Cyprus Sierrita produces copper and molybdenum from its Sierrita and Twin Buttes open pit mines south of Tucson, AZ. Both pits were started in the late 1960s and are more than 460 m (1500 ft) deep. Sierrita has used a Caterpillar 992C Remote Controlled Loader since January 1993. The loader was justified to increase safety and profits at Sierrita. It has exceeded all expectations. As of June 1993, the 992C had produced additional profits of more than $1.5 million. Safety and Geotechnical The safety of Cyprus personnel and equipment is always of prime concern. The remote controlled loader removes personnel from the active raveling area. But it requires prudent operation. The remote controlled loader discussed here is always intended to be used in a safe manner under a managed slope. Any increase in slope angle or use of any equipment under a critical slope is taken only after careful analysis of the specific

Jan 1, 1994

By Fred N. Kissell, Jon C. Volkwein

In This Chapter [How inert gas works to prevent methane explosions How inert gas is generated and delivered at highwall mines Volume and quality requirements for inert gas at highwall mines How an inert gas system is operated and Precautions to take during mining to prevent methane explosions] This chapter discusses a method, originally developed by Volkwein and Ulery [1993], to prevent methane explosions during highwall mining. In highwall mining, a horizontal auger or a mining machine enters the coal seam from a surface mine pit at the bottom of a highwall, and the coal is mined out from a series of parallel holes. Explosions can be prevented by injecting inert gas into each hole as it is mined. Coal near the surface has lost most of its methane gas over time. However, in recent years, surface mining has been used for deeper reserves of coal. This trend toward mining deeper reserves has increased the chance of encountering methane, and methane explosions at highwall mining operations have resulted in injuries. HOW INERT GAS WORKS TO PREVENT METHANE EXPLOSIONS A methane explosion requires the presence of sufficient amounts of both methane and oxygen, as well as an ignition source. If the methane cannot be reduced and the ignition source cannot be eliminated, then explosions may be prevented by adding an inert gas, which contains little to no oxygen, to the mixture [FWQA 1970]. Just how much inert gas must be added depends on the mining rate, as well as the composition of the inert gas. An explosibility diagram can be used to show whether a methane mixture is explosive after inert gas is added [Zabetakis et al. 1959] (Figure 10–1). This diagram indicates that gas mixtures fall into one of three range categories—explosive, explosive when mixed with air, and nonexplosive—depending on the percentage of methane and percentage of “effective inert.” Effective inert is calculated from the percentage of “excess nitrogen”3 and percentage of carbon dioxide in the mixture.

Jan 6, 2006

By Ralph W. Crosser

The emergence of residuals management as a planning and management tool in the mineral industry has been recently accelerated by the proliferation of environmental regulation and its associated costs. Residuals management practices allow for the early determination and integration of both production and environmental goals in the development of management strategies to arrive at the most cost effective, environ- mentally sound solution. The term residuals management was in actuality derived from the substitution of the word residual for the term ?pollutant? or ?waste?. A residual can be defined as a non-product output having no value in existing markets or a value less than the cost of marketing it. The values of the residual can be determined by time, technology, government policy, market conditions, etc. Residuals basically fit into two classes -- materials which are composed of liquid, gaseous or solids; and, energy, which mainly consists of heat and noise. These residuals are interrelated and can be modified by adding materials and/ or energy, which also may become a residual; thus, lending themselves to alternate disposal schemes to control the adverse effects.

Jan 1, 1979

By Ingvar Bergqvist

El presente texto describe el uso de los explosivos desde el siglo XVII hasta la actualidad, así como los factores a considerar dentro de la minería. Entre estos tenemos la velocidad de detonación, potencia, seguridad en el manejo, estabilidad de detonación, calidades de manejo, densidad, resistencia al agua, congelación y los aspectos médicos. Asimismo, los tipos de explosivos se dividen en los basados en nitroglicerina y los libres de ello, ANFO y slurry.

Jul 1, 1977

In November 1999 Waihi Gold Mining Company commissioned its new crushing and conveying plant used to transport both ore and waste from the Martha Mine to its ore processing plant and also its tailings dam construction area. To date, a record monthly throughput of 854 000 tonnes throughput has been achieved. This paper outlines the measures taken subsequent to the commissioning of the system to achieve greater than design throughput and to mitigate the environmental and safety issues associated with operating the system in the middle of a town.

Jan 1, 2001