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By C. Feng, D. W. M. Arrigan

Arsenic is often associated with gold mining operations and poses a significant health and environmental hazard. While a number of technologies are available for removing arsenic, none of them is effective under all conditions. Although adsorption is a promising approach, most methods focus on the purification of water under neutral or acidic conditions and tend to be less effective in gold mining process waters, operating under alkaline conditions. In this study, the removal of As (III) and As (V) from both arsenic-only solutions and simulated process waters using composite magnetic nanoparticles was investigated. The nanoparticles consisted of magnetite (Fe3O4) or maghemite (?-Fe2O3) cores covered by various metal oxides with Langmuir adsorption capacities of As (III) and As (V) ranging from 31.4 to 79.1 mg/g and 10.2 to 25.5 mg/g, respectively, in arsenic-only solutions at pH 9. Their adsorption capacities were further recognised by the adsorption tests conducted in simulated process waters. The ability to remove As (III) is of particular importance as it is harder to remove it from alkaline solutions. The magnetic cores allow simple and efficient magnetic recovery of the As-loaded nanoparticles.

Jan 1, 2017

By Oberlando Gonzalez, Claudia Serna, Andrea Alzate, Esperanza López, Maria Holuszko

This paper presents a systematic approach on gold recovery from electronic waste (e-waste) using ammonium persulfate. This process was developed as a response to the lack of hydrometallurgical systems capable of separating gold from its metallic substrate without material grinding, with minimum formation of pollutants, and achieving a lower reaction time. Computer memory boards, electronic processors and electronic pins and contacts were analyzed to determinate base metals (Ni, Fe, Cu) and gold (Au) using microwave plasma atomic emission spectroscopy (MP-AES). An aqueous commercial grade ammonium persulfate with oxygen and pressure was used to produce the persulfate anion (S2O82-) and the oxidative sulfate ion (SO42-), which partially oxidized and leached the base metals breaking the Au-Ni-Fe-Cu bonds and allowing gold to be recovered in its original non-leaching state. The influence of the oxidative parameters was evaluated using full factorial (FF) and central composite designs (CCD) with response surface methodology (RSM) and first and second order models were developed. Using RSM allowed to obtain a faster recovery of gold, minimizing the agent consumption. The findings presented suggest that optimized quantities of ammonium persulfate, oxygen, pressure, temperature and liquid solid ratio could be used for selective oxidization of the base metals and to extract more than 96% of gold from e-waste.

Jan 1, 2017

By James E. Fisher, Roger Cotton

"The legal background f or environmental issues, and the growing emphasis both from government and private concerns of corporate and management liability for environmental problems provides one of the driving forces behind the growing concern with environmental law for the future. One prime objective must be the identification and minimization of potential liability, both for the corporation and its officers, directors and employees.This paper will identify the basis for liability of individuals and corporations for environmental matters, focussing on current legal requirements, and the appropriate legal response to events of such potential liability. It will also consider the reduction of liability through the implementation of management systems and environmental policies in order to ensure due diligence both with respect to corporate responsibility and the responsibility of the individuals within the corporation.IntroductionConsolidated Professor Mines Ltd . and its predecessor have been exploring in northwestern Ontario for about sixty years . During the last twenty years, the company has been interested in developing a gold mine, the Duport Project, on Stevens Island in Shoal Lake . The lake straddles the border between Ontario and Manitoba and is a drinking water supply for Winnipeg and environs.The Duport Project involves the mining of 450 t/day grading an average of 0.35 oz Ault of ore . At the minesite, located on Steven s Island in Shoal Lake, only preliminary processing of the ore will take place, to produce gravity and flotation concentrates for final gold recover y at a mainland plant well removed from the Shoal Lake watershed. No hazardous chemicals will be used at the island site."

Jan 1, 1991

By Jessica Elzea, Haydn Murray

The term bentonite was first proposed in 1898 by Knight, a year after he had named this clay taylorite, because taylorite had been previously used for another mineral. The name taylorite was after the Taylor ranch, the site of the first mine, near Rock River, WY, and the name bentonite is from the Benton Shale in which the clay was thought at that time to occur. The Benton Shale was, in turn, named after Fort Benton, MT, located more than 640 km miles north of Rock River. Early in the 20th century, several geologists recognized that bentonite, mainly in beds in Cretaceous and Tertiary rocks, originated from transported volcanic materials. This recognition led to definitions based on origin, the one most widely quoted and generally accepted by geologists is the following definition by Ross and Shannon (1926): "Bentonite is a rock composed essentially of a crystalline clay-like mineral formed by devitrification and the accompanying chemical alteration of a glassy igneous material, usually a tuff or volcanic ash; and it often contains variable proportions of accessory crystal grains that were originally phenocrysts in the volcanic glass. These are feldspar (commonly orthoclase and oligoclase), biotite, quartz, pyroxenes, zircon, and various other minerals typical of volcanic rocks. The characteristic clay-like mineral has a micaceous habit and facile cleavage, high birefringence and a texture inherited from volcanic tuff or ash, and it is usually the mineral montmorillonite, but less often beidellite." The difficulty in applying the foregoing definition to bentonite as an industrial mineral commodity is that it is based on origin and is restricted to an ash, tuff, or volcanic glass parent material. Therefore, deposits consisting of the clay minerals required by this definition, but having uncertain origin or parent materials, cannot properly be called bentonite. Furthermore, many deposits in the western United States and in other countries that have formed from rocks other than the types required by the definition are being mined and sold as bentonite. Perhaps the best definition of bentonite as an industrial mineral is one given by R.E. Grim in a plenary lecture at the International Clay Conference (AIPEA) at Madrid, Spain, June 27, 1972. According to this redefinition, which will be used in this chapter, bentonite is a clay consisting essentially of smectite minerals (montmorillonite group of some usages), regardless of origin or occurrence. This definition solves the problem of the difference between the geologic and industrial usages of the term and overcomes the difficulty in assigning a name to smectite clay that formed from igneous rock other than ash, tuff, or glass, or those of sedimentary or uncertain origin. However, bentonite, when used with this meaning is still a rock term (consisting of more than one mineral), and it will not be possible to distinguish it from fuller's earth in many instances. One way of classifying bentonite is based on its swelling capacities when wet or added to water. Bentonite having sodium (Na+) as either the dominant or as an abundant exchangeable ion typically has very high swelling capacities and forms gel-like masses when added to water. Bentonite in which exchangeable calcium (Ca++) is more abundant than other ions has much lower swelling capacities than sodium varieties. Some calcium types swell little more than common clay, and most crumble into granular masses in water. Intermediate calcium-sodium bentonites, the so called mixed types, tend to swell moderately and to form gels of lesser volumes than equal masses of the sodium type bentonite. Because of the general relationship of swelling and exchangeable ion characteristics bentonite is commonly divided into the high swelling or sodium, low swelling or calcium, and moderate swelling or intermediate types. The term sub-bentonite (Davis et a]., 1940) is used inconsistently in industry for the low or moderate swelling varieties. The authors believe the use of this term should be discouraged because of its implication of low quality or low value and the lack of a mineralogical or use basis for it. In the United States bentonite is also classified by geographic location and the uses for which it is sold. Inasmuch as most of the low swelling calcium type occurs in states bordering the Gulf of Mexico, this variety is commonly called Southern bentonite. The largest high swelling sodium bentonite deposits and the major producing districts are in Wyoming and adjacent states. Therefore, this bentonite is commonly called the Wyoming or Western type. Such terms as drilling mud bentonite, foundry bond bentonite, and taconite bond bentonite relating directly to use are applied in marketing. Other terms including high and low yield bentonite, high and low gel bentonite, and high and low strength bentonite are also used to distinguish different grades. The varied classifications notwithstanding, bentonite occurs in so many different varieties that some cannot logically be classified according to any of the foregoing groupings. One of these types is hectorite, which is a high swelling lithium-bearing variety of smectite occurring mainly in California and adjacent states. It is, therefore, not a Wyoming type, and it occurs even farther west than the so called western bentonites. Others are bentonites having magnesium (Mg++) or hydrogen (H+) as the most abundant or dominant exchangeable ion. These types are neither sodium nor calcium varieties, and apparently some are low swelling, whereas others have rather high swelling capacities. Still another type of bentonite, the so-called potassium type, K-bentonite, or metabentonite, occurs in Ordovician and other Pa-

Jan 1, 1994

By Arcy A., J. G. Davis, D&apos Shock

Results of a pilot operation in the Carlsbad Basin are discussed. After hydrafracing between wells, a block of potash was removed by solution techniques. The distance between frac wells was about 200 ft, the thickness of potash mineralization, 5 ft. By proper manipulation, a feed of concentrate brine was obtained. The ex-periment showed that the thin-bedded potash could be removed by the solution techniques. The details of well construction, method of operation, and removal rates are discussed. Continental Oil Co.'s laboratory research on the fundamentals of potash solution mining has been expanded by means of a series of field tests, and subjects such as well completion and hydraulic fracturing were added to the investigation. Both single-well and multi-well systems were studied in the field work. Discussion Background: The current paper discusses one field test in which potash was solution mined by a two-well system from a thin sylvinite zone. The potential economic value of solution mining evolves from (1) the use of drilled holes and solution techniques instead of excavated shafts and caverns and (2) the ability to mine both land and marine deposits through any type of overburden geology and below conventional mining depths. Recent interest has been focused on potash' and other soluble minerals, such as trona. Solution extraction minerals, such as copper and uranium, are also worthy of important consideration. In addition, many of the techniques are directly applicable to the construction of horizontal underground storage carverns in salt. There are two general approaches to potash solution mining. The first is to mine on a single-well basis, in which the same well bore is used for both injection and production. This method is slow, and the areal extent may be quite limited in other than very thick ore zones. The second, and the preferred approach, is to mine on a multi-well basis in which the solvent is circulated between wells. This technique, if applied in a manner which allows the ore zone to be mined from the bottom upward, results in nearly all the solution taking place from the cavern roof. Salt removal rates, therefore, are very much higher than from a single-well system.l Wells can be interconnected into a multi-well pattern by several means. One is to join single-well caverns in the lower part of an ore zone. Another is to use the hydraulic fracturing techniques developed in the oil fields.' We preferred the fracture approach because of its potential for creating the greatest area of salt exposure. Test Site Description: The field tests were conducted in New Mexico's Carlsbad Basin, where the potash deposits are flat and uniform over reasonable distances. Here, 12 potash zones are present in the massive Salado Salt section. The specific target was the Third Ore Zone which is about 4 ft thick at our location and about 1150 ft deep. The test pattern was designed in the shape of an equilateral triangle with a fourth well located in the center, 200 ft from each of the vertex wells. This configuration allowed the ore zone to be hydraulically fractured from the center well with good assurance that the fracture would intersect the bore of at least one outside well. Several multi-well test patterns would be available if the fracture connected all wells. Well Completion: Surface casing was set in the top of the Salado Salt at 600 ft to shut off water flows from the surface sands, and the salt section was drilled and diamond-cored to a point below the Third Ore Zone. A drilling fluid made of diesel oil with a small amount of emulsified water was used to drill and core the salt. This fluid was highly successful in preventing enlargement of the drilled hole and in promoting good core recovery. The three outside wells were completed by setting 51/2-in. casing at the base of a streak of anhydrite about 20 ft above the ore zone. Pipe was set high so that the intersection point of the fracture could be detected even if the fracture migrated above the ore zone as it progressed outward from the center well. The center well itself was completed by cementing 51/2-in. casing through the Third Ore Zone. Cement bond logs run on the center well have shown excellent bonding. Fracturing Practice: A mechanical tool was used to cut a notch through the casing and into the salt at a point about 1 ft below the ore zone in the center well. The purpose of this notch was to fix the point of fracture entry into the salt. The fracturing was done with water at injection rtaes as high as 30 bbl per min. The salt parted at 1450 psi; and it required only 5 min for the fracture to reach the well which was 200 ft to the south. It took about 5 min more to reach the other two wells. Caliper surveys were run to locate the point of fracture entry in the three outside wells. The fracture appears to have drifted downward slightly, entering the outside wells at the top of a streak of carnallite 8 or 9 ft below the ore zone. A cross section of the wells selected for the multi-well test is shown in Fig. 1. The figure includes KC1 values based on core analysis and the trace of the fracture plane between the wells.

Jan 1, 1971

By W. W. Anderson, S. Razi

Electroluminescetrce of single crystals of terbium-(loped ZnS prepared by vapor-transport technique shows the sharp line specirum characteristic of the 4f— 4ft,ansitiotzs of the trivalent Tb3 rotz. V-I tt~easuverr~ents give evidence of space-ellarge-lirrlited curvent but the thrveshold for trap-filled law behavior is not iu agreement with Lampert&apos;s theory for. Single injection. Variations of &apos;brightness with applied voltage, the observation of double peaks its brightness because joms, and the spatial distribution oi electroLur?zir~escerrce indicate that the accelet~atiotz-collision mechanism involving the bst lattice and/ov shallow traps is most likely to be responsible fov excitation of&apos; electrolnminescence. Efficiency rtreusuver)~etits show the quantwn efficiency to be about 10 pct and powev efficiency about 0.05 pct. Effect of anr~eallng the crystal in sulfur vapor is to enluztzce llle rare-earth emission. It rs pvoposed tlzat sulfitv anr~ealing crreates acceptorr-lvpe defects with which the donor-type vare-eavtll ion can associate more readily vesulting in enhanced rare-earth emission. A&apos;o such e~zlznr~cerr~etrt is obserued when the crystal is atztrealetl in zinc vapor. Photolianinescence of ZnS doped nith a variety of rare earths also shows tile slurvp l~rze rwve-eavtlz erriission which in sorrretirr~es accompanied by broad band, stvuctureless lattice emission. Photo-atrd electrolutr~itzesce?~ce of ZIIS:Tb slw~rj do!rlit~unt rare-earth emission in the ~ticirzity of 54(3OA corre-sporrdit~g to the transition D* — Fj. Hoz~!el)er, the detailed line structuve of the luo spectvtr is cliffevet~t, irzdicutit~g that different sites are active in the two processes. Decay of rave-eartlr fluorescence in ZnS doped with any of sei!evul vuve eurtlzs car1 be described by a single exporleritial e.scepl joy ZrlS:lIo. Tl~is exceptiotr can be explaitred it~ tevrr~s of tlre closely spaced er~evgy 1e1:els Jov the HO~&apos; iorr. Decay lime measurertzekzts jov ZnS:Tb, using pulsed elect,-ical ar~d pulsed opticcll excitutiorzs, (11-e itz goor1 agrcetrier~t. LUMINESCENCE of rare-earth-doped materials has been a subject of interest for the past 20 years. Within the past few years there has been a considerable increase in rare-earth research motivated in search of new and more efficient laser materials and also due to the use of certain-rare-earth compounds in the preparation of color television screens. The purpose of this study has been to seek an understanding of some of the basic processes involved in exciting the rare-earth luminescence which is associated with transitions within the 4f shell of the trivalent rare-earth ion. Single crystals of ZnS doped with a variety of rare-earth ions have been prepared by vapor-transport technique described elsewhere.&apos; Photoluminescence was excited by a high-pressure short-arc mercury lamp together with suitable glass and chemical filters. For electroluminescence, sinusoidal and pulse excitations were used. 1) ELECTRICAL CHARACTERISTICS 1.1) V-I Measurements. Electroluminescence experiments were performed on crystals of terbium-doped ZnS. The samples were cleaned and etched and indium or In-Ga alloy contacts were alloyed on by heating in H2 atmosphere to 600°C for times ranging up to 10 min. Static voltage-current measurements were made on several samples. Fig. 1 shows the results for a typical sample. For voltage V < 20 v, the V-I relationship is linear giving a resistivity of 2.5 x 109 ohm-cm for this particular sample at room temperature. In the range of 20 to 250 v, I varies as V "3 and at still higher voltages (when electroluminescence is visible to the scotopic eye) current varies as Vs up to 600 v, all at room temperature. At 77"K, for V > 200 v, / I vge5 up to 1000 v. The V-I characteristics at room temperature follow reasonably well the behavior predicted by Lampert&apos; for one carrier space-charge-limited current in an insulator with traps although, as shown later, the expression derived by Lampert2 for the threshold for trap-filled law behavior Vtfl yields an unrealistically low value for trap density if we use the experimental value of 300 v for VtfL. Assuming the case for shallow trapping, the transition from Ohm&apos;s law behavior to space-charge-limited behavior occurs at voltage Vtr given by where no = thermally generated free carrier density, L = length of the sample, e = static dielectric constant, 6 = ratio of free to trapped electron densities, e = electron charge. For the ZnS:Tb crystal, L = 0.5 mm, E = 8.3 €0, Vtr - 20 v, and no = 5 x 10&apos; per cu cm, calculated from the ohmic behavior assuming electron mobility of 100 sq cm per v-sec. This results in 9 = 0= As more and more electrons are injected the Fermi level moves up in the forbidden gap toward the conduction band. If we assume a single-energy level for traps (which is not strictly correct, as we will show later), the current voltage characteristic is profoundly affected when the Fermi level crosses the trap level. The traps are now filled and injected carriers can no longer be immobilized in traps. Hence, current rises sharply with voltage. The transition from space-charge-limited behavior to the trap-filled behavior occurs at voltage VTFL given by

Jan 1, 1968

By Billy L. Crowder, John M. Fairfield

The implantation of B+ , P+, and As&apos; into silicon has been studied with the purpose of making shallow p-n junctions. The influence of such parameters as 1) ion energy, 2) target orientation and temperature, 3) total dose, and 4) annealing schedule was investigated. An energy range of 70 to 300 kev was used for boron and phosphorus implants and up to 500 kev for arsenic. It is found that the experimental projected range agrees well with theory and that shallow junction depths can be made reproducibly. ION implantation has received much attention recently as a technique for doping semiconductors. Specifically, it has the potential of supplementing or replacing the diffusion process as a method for making p-n junctions. In a few specific cases it has been used successfully to make semiconductor junction devices. Potential advantages of ion implantation doping over diffusion techniques are: 1) It affords greater control of shallow junction depths (< 0.2 µ) while maintaining high peak concentrations. This is particularly important for high-speed switching devices, since lower junction capacitances and resistances can be achieved. 2) More precise registration of small planar structures can be realized if proper masking procedures are employed. This advantage is especially useful in the design of high-density integrated circuits. It has been used to advantage in FET fabrication since the edge of the source or drain can be aligned precisely at the edge of the gate electrode.&apos; 3) Ion implanatation permits lower temperatures than diffusion techniques. This factor alleviates the problem of compatibility of diffusivities often encountered when designing multiple-junction structures. Also, the lower temperatures create fewer thermal defects and dislocations, which may account for the high efficiency of some ion-implanted solar cells.2 4) Impurity profiles can be more easily tailored to resemble ideal distributions. Successful exploitation of the potential advantages of ion implantation techniques will depend on increased knowledge and understanding of the subject. The factors likely to be influential in determining impurity distribution profiles in ion-implanted single-crystal targets have been reviewed by J. F. Gibbons.3 In addition to the mass and energy of the implanted ion, the total dose, target orientation, and target temperature are important parameters. The annealing temperature required for removing lattice damage and incorporating the implanted species on an electrically active site is very important. This paper describes an investigation of some of these factors. Implants of boron, phosphorus, and arsenic into silicon have been studied. Energy ranges of 50 to 300 kev were used for boron and phosphorus and up to 500 kev for arsenic. In addition to the implantation energy, the effects of total dose, target temperature, and post implant anneal have been investigated. EXPERIMENTAL PROCEDURE The implantation targets were silicon wafers cut from Czochralski-grown crystals, lapped, and chemically polished. The orientations were (111), (110). and (100) with misorientations of up to 7 deg from the principal axis. For this study, accurate target alignment (i.e., within 0.1 deg) was not available and quoted misorientation values should be regarded as approximate . The implantation equipment consisted of an ion source, a 300-kev linear accelerator tube, an electromagnetic separator, and the associated target supporting and beam focusing assemblies. The ion source was a simple oscillating electron type source,4 which has been described elsewhere.5 The gaseous compounds BF3, PF5, and AsH3 were used as ion sources for B+, P+, As+, and AS+&apos;. Analyzed current levels of up to 20 pamp could be obtained; however, for this investigation target current levels of 1-3 µ amp were usually employed. The analyzed ion beam was collimated through a double slit (1.4 x 0.4 cm) and swept perpendicularly to the long axis of the slit such that an area of about 2 sq cm on each target was covered. Dosages of around 1015 cm-2 were normally employed, but smaller amounts were also used for comparison. A uniform flux density over the bombarded area was assured by the continuous use of profile monitors similar to those described by Wegner and Feigenbaum.6 Post-implant annealing was accomplished in an argon atmosphere in a temperature range of 600" to 950°C. It was not part of the purpose of this investigation to study the annealing kinetics; however, some isochronal and isothermal anneal experiments were conducted to determine the time and temperature necessary to render a reasonably high portion of the implanted ions electrically active (i.e., higher than 50 pct). Post-implant anneal temperatures of around 900° and 600°C were required for boron, and arsenic and phosphorus implants, respectively. Arsenic and phosphorus implants increased in conductivity rather abruptly at the proper anneal temperature of the isochronal curve, but boron increased more gradually over a wider range. Isothermal anneal curves were reasonably flat after 10 min, so an anneal time of 1/2 hr was used for the experimental results described below. The profiling techniques were: 1) neutron activation analysis, 2) differential sheet resistance,7 and 3) junction staining.8 The differential sheet resistance technique is commonly employed in this type of study. Its principal disadvantage is the uncertainty of the ef-

Jan 1, 1970

By R. K. Ham, M. L. Wayman

TD-Nickel has been broken in tension and in fatigue at voom temperature. Rod specimens failed in tension by necking, with axial cracks attributed to voids elongated in the extrusion direction. Fatigue specimens failed in shear. Thin-film electron microscopy showed that the subgrain structure of TD-Nickel was very stable, and that particle-matrix detachment was very difficult, in tension and fatigue. TD-Nickel softened slightly during fatigue but had a high fatigue ratio (0.5at 10&apos; cycles). Fractography suggested that Stage I fatigue crack propagation is greatly extended in TD-Nickel. Td-NICKEL* is a dispersion of 2 pct by volume of thoria (ThO2) in nickel, produced by powder-metallurgical methods including compaction, sintering, and extrusion. The spherical thoria particles, which may have a mean diameter of a few hundred angstroms, are dispersed with a mean planar spacing of a few thousand angstroms. By a combination of cold working and annealing, a subgrain or cell structure of dislocations intimately associated with the dispersion can be produced.&apos; This gives the material useful tensile properties which are extremely resistant to exposure to high temperatures.&apos;-= At the same time, the material shows considerable ductility.3&apos;4 At the beginning of the present work, it was considered of great interest to investigate the mechanical stability of TD-Nickel under conditions of fatigue. On the one hand, materials which derive strength from a cold-worked structure are unstable in that they are susceptible to fatigue softening: in addition, the presence of discontinuities such as the particle-matrix interfaces might be expected to assist in the initiation and propagation of fatigue cracks, in that they may provide local concentrations of internal stress and sites for the initiation of voids." On the other hand, the substantial ductility of TD-Nickel suggests that if it obeys Coffin&apos;s relation8 (or the more refined form proposed by Manson9) it should have good fatigue resistance. The initial purpose of this investigation was to assess the importance of these factors. Also, relatively little fundamental work has been done on the mechanism of fatigue in dispersion-strengthened materials. Work on overaged A1-4 pct CU10-12 revealed a very large Bauschinger effect indicative of internal stresses at the particles, and very great fatigue hardening1&apos; presumably due to the multiple slip stimulated by these internal stresses, followed by softening which was initially due to softening in the matrix, but later might have arisen from cracking at the particle-matrix interfaces. The study of overaged Al-4 pct Cu could not settle this latter point by the electron microscopy of thin films, since the dispersion is too coarse. A previous study of the fatigue of internally oxidized copper13 was complicated by inter granular failure, attributed to oxide particles at grain bouhdaries; internal oxidation of single crystals, however, improved their fatigue properties.&apos;3 Investigations of SAP (sintered aluminum powder) are complicated by the complex particle shapes, and the possibility of continuous internal oxide films.14 It was hoped to avoid these difficulties with TD-Nickel, which had the further advantages that it was commercially available and suitable for study by the thin-film technique. 1) MATERIALS AND EXPERIMENTAL PROCEDURE TD-Nickel was purchased from the Driver-Harris Co. as 3/9-in.-diam rod which had been extruded, swaged, and "stress-relieved" (normally at 1010°C for 1 hr). Continuous-radius fatigue specimens with a minimum diameter of -0.1 in. were ground to shape and electropolished in 40 pct phosphoric, 35 pct sul-furic, 25 pct water at 25oC, with a stainless-steel cathode, at -6 v. Fatigue tests were carried out at room temperature with a Sonntag SF-1-U machine operating in push-pull at 1800 cycles per min, and in an Instron TT-C-L modified for reversed stressing at 26 cycles per min as described elsewhere.10 Round tensile specimens were ground with 0.85-in. gage lengths of 0.135 in, diam, electropolished, and tested in a Tinius Olsen hydraulic machine. The surfaces of fatigue specimens were examined with a Reichert metallograph. Discs for electron microscopy with a Siemens Elmiskop I were spark-cut 0.01 in. thick with a modified Servomet 11 employing a tool of moving molybdenum wire, cleaned in 50 pct acetic, 30 pct nitric, 10 pct phosphoric, and 10pctsul-furic at 85oC, and thinned by the window method in the electropolishing solution at -20°C and -6 v. Two-stage replicas (parlodion, then Pt-50 pct C self-shadowed at 40 deg) were taken from fatigue fracture surfaces for electron microscopy. Plane sections parallel to the specimen axis and containing the direction of fatigue crack propagation were polished, etched with Carapella&apos;s reagent, and examined optically. Transmission Laue X-ray photographs of as-received material electropolished to a point were used to determine preferred orientation. 2) RESULTS 2.1) The Structure of As-Received Material. Grains -1 µ diam and elongated 20 to 30 u in the direction of the rod axis were observed, With&apos; elongated "intergran-ular" voids (-4 p diam and -90 µ long and identified as such using longitudinal and transverse sections and

Jan 1, 1968

By N. N. Breyer

A specially built "hard" tensile machine with characteristics permitting the precise detertnination of the drop of the load at the yield point has been used to study the magnitude of the yield-point phenotnenon in prestrained martensitic 4340 steel. A new phenonzenon, the appearance of a secondary yield point, has been observed by holding the specimen at constant strain in the plastic region. Furthermore, it has been found that a series of yield-point drops could be introduced by successive constant strain holds in the plastic region. The isothermal kinetics of the development of the secondary yielding point lave been studied at four temperatures: 24° 0° -18°, and -79°C. From the results of the kinetic investigation, equations for the In a previous investigation1 it was shown that, contrary to generally held opinion, steels of medium carbon content, such as 4340, 4140, and 86B30, in the as-quenched martensitic condition, can be cold-drawn through a die with reductions in area of up to 10 pct without cracking. Tensile specimens of 4340 machined from bars quenched and prestrained in this manner exhibited tensile strengths of about 400,000 psi coupled with 30 pct reductions in area. In addition, it was found that each sample of such steels exhibited a yield point in the quenched, cold-drawn condition. Since these studies were conducted on a commercial hydraulic testing machine of a type which is not well-suited to detailed study of yield-point behavior, it was decided to study this phenomenon more thoroughly on a rigid straining machine. In this new investigation, use of such a "hard" machine not only allowed study of the magnitude of the yield-point drop but also revealed a new phenomenon—secondary yielding of the martensite introduced by stopping crosshead motion after plastic deformation of the sample had begun. The present paper is a report of these findings. MATERIALS AND PROCESSING The material used was a commercial 4340 steel of the composition shown below: 0.41 0.80 0.013 0.019 0.31 0.85 1.76 0.28 1 0.42 0.77 0.015 0.024 0.30 0.84 1.69 0.28 0.08 2 1 = Ladle analysis. 2 = Laboratory analysis. Bars of this steel were processed in the following way: 1) machined to predetermined diameters; 2) austenitized at 870°C for 1 1/2 hr; 3) oil-quenched; 4) cooled to -115°C for 1/2 hr; onset and increase in magnitude of the secondary yielding in this temperature region have been found to fit the relationship ?Ys = Atn where ?Ys is the magnitude of the secondary yield Point in psi, t is the time in seconds, and A and n are parameter characteris-tics of the material. Although the occurrence of the primary and secondary yield points could be rationalized qualitatively on the basis of stress-induced ordering of carbon atoms in the stress fields of dislocations, as postulated in an earlier paper, the kinetics of the secondary-yield-point development were interpreted to indicate that the ordering involves more than just single jumps of carbon atoms from high-energy to neighboring low-energy sites. 5) pickled and lime-coated; 6) drawn through a carbide die. The predetermined diameters were chosen so that drawing through the same die gave the various reductions desired. Tensile specimens of 0.252 in. diam with a 1 1/4 in. gage length were then prepared from the drawn bars and tested. In order to study the stress-strain behavior at the yield point in detail, a rigid tensile machine with a high spring constant was constructed. Columns of large cross section (relative to the specimen cross section) constituted the machine frame. A dc motor was used to drive a screw via a gear reducing train and a "crane" thrust bearing. In this relatively simple device small deformations could be observed un-blurred by the slow response and lower spring constant inherent in hydraulic machines.&apos; A strain-gage dynamometer permitted load changes as small as 8 lb to be read. RESULTS Tensile test samples machined from bars in the as-quenched condition with no subsequent drawing and samples from bars with 3.8 pct reduction after quenching gave stress-strain curves typified by those shown in Figs. I and 2. The time lapse between predrawing and tensile testing varied but usually ranged between 3 to 6 days at room temperature. The strain rate during testing was 0.003 in. per in. per min. The as-quenched curve is seen to have a broad serrated maximum whereas the stress on the specimen prestrained 3.8 pct rose linearly to point A, Fig. 2, fell abruptly to B, and then gradually to C. The abrupt drop to B was accompanied by evidence of incipient necking. The drop of the stress at the yield point in the prestrained samples (A to B in Fig. 2) changed with the percent prestrain, as illustrated on Fig. 3. Although the tensile strength increased continuously with the amount of previous cold drawing, the magnitude of the yield point drop first increased—up to about 6 pct prior reduction—and then decreased. Specimens from bars predrawn more than 8 pct broke in a brittle fashion in the elastic portion of the stress-strain curve.

Jan 1, 1967

By D. A. Nelson, Wedding. R. E.

"A planned production increase of 1.25 million tonnes per year at Domtar&apos;s salt mine in Goderich, Ontario required an increase in the underground mine ventilation system from 320,000 to 700,000 scfm, The design of the expanded facility included the addition of a 22-foot-diameter shaft to augment the existing production and service shafts.A preliminary review of the ventilation requirement s indicated that in order to pr ovide good economic design for the expanded system, a comprehensive ventilation survey of the existing system was required. The survey was completed in the latter part of 1980, and subsequent engineering design and equipment selection proceeded throughout 1981.This paper presents the methods used to carry out the survey. Particular attention is given to the numerous challenges presented in determining air flows in the large 45-ftwide by 43-ft-high airways. Emphasis is placed on practical field survey techniques.A mathematical model of the ventilation system using a computer program is described, and the application of this program to provide design data and assist in equipment selection is discussed. Economic sizing of airways and fan selection are analyzed considering horsepower and operating costs.IntroductionThe Goderich Mine of Sifto Salt Division, Domtar Inc., is located on the eastern shore of Lake Huron in the town of Goderich, Ontario, and has been operating since November 1959. The salt is extracted by a modified room-and-pillar method, and the workings advance at a rate of 1.5 miles per year by undercutting, drilling and blasting. The surface mine area consists of a 12-acre site in the Goderich harbour, at the mouth of the Maitland River, and the underground property consists of approximately 2,700 acres lying mainly under Lake Huron."

Jan 1, 1983

By J. Stachulak, M. Scobie

"This paper addresses the occurrence and indicated causes of conveyor fires in North American and European underground mines. Some significant convey or fires which have been experienced in recent years in Canadian hardrock mines are then reviewed. The nature of existing conveyor monitoring technology is considered in the context of such fire hazards. Experiences with new monitoring technology recently installed at several conveyor sites at Inca Ltd. mines are then reviewed.IntroductionFires associated with conveyors have long been recognized as a serious hazard in underground coal mines. Recently, however, there have been some significant conveyor fires in Canadian underground hardrock mines. These offer important evidence as to the nature and causes of potential hardrock mine fifes. They also warrant attention with a view to improving over-all mine design, ventilation and emergency preparedness.In addition, a new era in mine communications and monitoring technology has been entered which should offer improved capability to protect against such fires. This paper was motivated by the need to understand the causes and mechanisms of conveyor fires in order to improve their safety. This should be possible through implementing more effective monitoring systems, as well as improving conveyor design. Underground mines are becoming more intensively mechanized, with less human surveillance of equipment and a greater dependency on remote monitoring systems."

Jan 1, 1992

By M. C. Flemings, T. Z. Kattamis

Dendrite morphology and grain size were studied in bulk samples of iron and nickel base alloys under-cooled up to 300°C. In the alloys studied, dendrite morphology gradually changes with increasing undercooling from the usual dendritic structure to a structure composed of cylindrical dendrite arms. At a critical undercooling of approximately 170°C in these alloys there is an abrupt transition to a fine-grained structure of spherical morphology. Final dendrite-arnz spacing of melts nucleated at less than the critical undercooling decreases with increasing undercooling and with decreasing distance from a chilled surface. Grain size of melts nucleated at greater than the critical undercooling decreases similarly with these factors. It is concluded that structure coarsening, with reduction of surface area as driving force, is the principal mechanism determining final dendrite-arm spacing in melts nucleated at small undercoolings and grain site in melts nucleated at large undercoolings. IN solidification of highly undercooled melts, nuclea-tion and growth of the solid is accompanied by a rapid release of latent heat of fusion. The heat release is sufficiently rapid in bulk specimens that it takes place essentially adiabatically with respect to the surroundings; hence the specimen heats up ("recalesces") to some maximum recalescence temperature. For bulk liquid metals and alloys, a simple thermal balance shows the undercoolings obtainable in bulk samples are not sufficient to lower the maximum recalescence temperature below the equilibrium solidus temperature. Hence, some liquid always remains at the end of recalescence; this liquid must solidify by rejection of heat to the surroundings. Metals, including iron and nickel base alloys, normally freeze with only a few degrees of undercooling. In general, nucleation begins on impurity particles present in the metal, at a "heterogeneous nucleation temperature" that is quite close to the equilibrium liquidus temperature. Very small droplets of metal can be undercooled considerably before nucleation occurs,1-4 presumably because subdivision of the liquid reduces the probability of solid impurity in a given droplet. Following early work on metal droplets,&apos; a series of studies has shown that it is possible, without great difficulty, to undercool bulk samples of many metals and alloys. Undercoolings obtainable are approximately two tenths of the melting point for nickel, iron, copper, and other metals and alloys.5-9 Specimen sizes have generally been in the range of 50 to 500 g. Studies on undercooling to date have been concerned primarily with techniques of undercooling and with nucleation and growth kinetics. Only limited consideration has been given to dendrite morphology in under- cooled alloys. One such study, in bulk Cu-Ni alloy,8 showed that at small undercoolings a typical dendritic structure was obtained. At undercoolings the order of 175°C the structure of a Cu-40 pct Ni alloy became "ray or starlike", and a dense network of subbound-aries appeared. At still larger degrees of undercooling, of the order of 250°C, the structure became more random and included an ensemble of globular forms. Comparable results were obtained by walker10 on Cu-Ni alloys, and by Kamenetskaya et al.11 in research on Cu-Ni, Sb-Bi, Fe-Ni, and Fe-Cr alloys. In this work, study was made of the processing parameters influencing dendrite morphology and grain size in undercooled alloy melts. Experiments were specifically designed to show the effects of coarsening ("ripening") during solidification on final casting morphology. EXPERIMENTAL PROCEDURE Apparatus used was patterned after that of Walker,10 Fig. l(a). Melting was by induction under reduced pressure of helium. Two different types of crucible materials were used; there was no difficulty in obtaining substantial undercooling in both types of materials. Alumina crucibles were used for the bulk of the runs made, with a glass coating separating the metal from the crucible walls. Other runs were made using fused silica crucibles with or without slag coating. A graphite susceptor was employed around the crucible to aid in melting and to reduce melt stirring. The major portion of the experimental work was on

Jan 1, 1967

By G. Chi, W. J. Davis, S. Watters, D. Hoy, S. Castonguay

"The Poplar Mountain gold occurrence in western New Brunswick is hosted in the Poplar Mountain volcanic complex (PMVC), which is located along the southern segment of the regional Woodstock fault zone. The PMVC consists of three principal units including, in ascending order, a porphyritic felsic volcanic unit, a volcaniclastic unit, and a mafic volcanic unit. U-Pb dating of zircon indicates that the age of the volcanic rocks is younger than 459 ± 3 Ma, and 40Ar/39Ar dating of mineralization-associated sericite indicates that the age of mineralization is 411 ± 3.7 Ma. Gold-mineralized zones occur in all the lithologic units but mainly in the porphyritic felsic volcanic unit. Gold zones are not controlled by individual faults but are characterized by high-density brittle fracturing, thin carbonate-quartz veining, and intensive ankerite-sericite alteration, superimposed on an earlier chlorite-calcite- quartz alteration. Gold is associated with arsenopyrite, which mostly occurs as disseminations in the host rocks, and to a lesser extent with quartz-carbonate-sericite veins and quartz-cemented breccias.Geochemical data indicate that mineralization-associated alteration is characterized by enrichment of K, Rb, Cs, Ca, Sr, Ba, As, Sb, W, C, and S. Fluid inclusion data indicate that the mineralizing fluids are composed of H2O, salts, and CO2 with variable amounts of N2 and CH4; salinities range from 2.3 to 10.6 eq. wt.% NaCl, but mainly from 2.3 to 5.6 eq. wt.% NaCl, and homogenization temperatures lie mainly between 220° and 270°C. Fluid pressures at the site of mineralization are estimated to have been 770 to 1200 bars, corresponding to a depth of 2.9 to 4.6 km at lithostatic pressure. The d18OSMOW and d13CPDB values of mineralization-related ankerite range from +14.5‰ to +16.5‰, and -6.8‰ to -8.3‰, respectively. The d18O values of the ore-forming fluids are estimated to be 6.4‰ to 8.3‰ at a temperature of 250°C. These carbon and oxygen isotope data fall in the field of magmatic fluids and in part the field of metamorphic fluids.Considering the geological setting of the region, abundant granitic intrusions, the similarity between the age of mineralization (411 ± 3.7 Ma) and the nearby Pokiok batholith (402-415 Ma), and the enrichment of granophile elements in mineralization-related alteration, the ore-forming fluids were probably derived from a granitic intrusion underneath the PMVC. These fluids were focused along structures related to the Woodstock fault. The Poplar Mountain gold occurrence might be compared to some granitic intrusion-related gold systems based on the geochemical data presented herein. L’indice aurifère de Poplar Mountain dans l’ouest du Nouveau Brunswick est contenu dans le complexe volcanique de Poplar Mountain (CVPM), lequel est situé le long du segment sud de la zone de faille régionale de Woodstock. Les trois unités principales du CVPM sont, de la base au sommet, une unité volcanique felsique porphyrique, une unité volcaniclastique et une unité volcanique mafique. La datation U-Pb de zircons indique que les roches volcaniques sont plus jeunes que 459 ± 3 Ma, et la datation par la méthode 40Ar/39Ar de séricite associée à la minéralisation assigne à la minéralisation un age de 411 ± 3.7 Ma. Bien que les zones minéralisées en or soient présentes dans toutes les unités lithologiques, on les retrouve surtout dans l’unité felsique porphyrique. Les zones aurifères ne sont pas contrôlées par des failles individuelles mais sont caractérisées par une grande densité de fractures cassantes, de minces veines de quartz-carbonate, et par une altération en ankérite-séricite intense qui se superpose à une altération antérieure en chlorite-calcite-quartz. L’or est associé à l’arsénopyrite, laquelle est principalement présente à l’état de disséminations dans la roche hôte, et à un moindre degré avec des veines de quartz-carbonate-séricite et des brèches à ciment de quartz.Les données de géochimie indiquent que l’alté"

Jan 1, 2008

By A. H. Tousley, C. L. Vickers

The author presents a history of the development of the Port of Long Beach from its beginning in 1905 to the present construction of a new bulk loading facility. In describing this new facility, emphasis is placed on such aspects as rail car and truck handling, gravity yard, rotary car dumping, bottom dumping, car dumping equipment, feeding and conveying, ship-loader-stockpiler, stockpiling and reclaim, dust control, and construction problems. Development of the Port of Long Beach, Calif. (see Fig. I), began in 1905. In that year private Long Beach interests acquired 800 acres of marshland in the Inner Harbor area and initiated a program of channel dredging and land reclamation. Efforts to establish a municipal port began a short time later and culminated in the opening of Pier 1 in 1911. An event of even greater significance to the port future also occurred in 1911. This was the tideland grant enactment by the state legislature that conveyed to the city of Long Beach all of the state&apos;s rights in the tidelands located within the city boundaries. The grant stipulated that all revenue produced from the tidelands be used for the development of navigation, commerce, and fisheries. During the next 15 years up to 1926, the port&apos;s commercial growth was steady, although relatively slow. During this period, several fundamental steps in the development of a major harbor were accomplished. These included the creation of the Board of Harbor Commissioners in 1917, the dredging of the Inner Harbor and entrance channel to accommodate deep draft vessels, and the correction of a serious silting problem through construction of the Los Angeles River Flood Control Channel. These efforts bore fruit during the ensuing 10 years in the establishment of more than $30,000,000 worth of industrial plants and private marine terminals in the Inner Harbor. Commerce over municipal wharves also increased more rapidly, and it became necessary to start the development of the harbor in a seaward direction. In 1936, oil was discovered in the harbor area, and the first Harbor Dept. well was brought in 2 years later. It soon became evident that the city of Long Beach would receive substantial revenue that, under the terms of the state grant of 1911, must be used in the development of the port. It was further realized that to properly guide and coordinate such development, a long range comprehensive plan was essential. The Board of Harbor Commissions contracted with G. F. Nicholson and J. F. Collins, consulting engineers, for the preparation of such a report that was completed in 1940. The Nicholson-Collins report proposed the development of an East Basin, between the entrance channel and the Los Angeles River, and a West Basin in the area now occupied by the Long Beach Naval Shipyard. Twenty full-size berths were to be provided in the East Basin and more than fifty berths in the West Basin. The report recommended extensive modern terminal facilities for handling waterborne cargo. Attention was given to improvement of the street and highway system to give better vehicular access and to avoid congestion within the port. To a large extent the recommendations of the Nicholson-Collins report were followed in the subsequent development of the East Basin. This development was greatly accelerated by World War 11, with its need for increased oil production and additional shipping facilities. The wartime and immediate postwar construction was largely concentrated on Pier A, with the development of Piers B, C and D following in more recent years. An important factor in the planning of these piers was their dual function as oil drilling sites and cargo piers. The Navy&apos;s acquisition of the West Basin area made it necessary to depart from the Nicholson-Collins plan and find other areas for future expansion. At the present time only one Inner Harbor Port-owned area having protected deep water frontage remains undeveloped. This is the property fronting on Channel 2 in the Inner Harbor acquired in December 1957, from Pacific Dock and Terminal Co. The growth of the port has been in a southerly direction since the construction of the Long Beach Naval Shipyard in the West Basin area. Recent extension of Piers F, G and J into the ocean follows typical port construction methods developed during the expansion of the Middle Harbor during the last 20 years.

Jan 1, 1963

By E. J. Nielsen, P. R. Strutt

A study has been made of the progressive changes in the distribution of etch-pit structures occurring during high-temperature creep in copper + 7 wt pct Al single crystals oriented with a [113] tensile axis. The two equally stressed glide systems with the highest Schmid factor would be expected to form subboundaries of the type predicted by Kear.2 The alignments of etch-pits on sections parallel to different (111} planes consistent with these types of boundaries were not observed. However, they were consistent with planar subboundaries (on a macroscopic scale). From an analysis of Amelinckx1 it may be shown that stable cross-grid dislocation boundaries may form in the primary slip planes. These boundaries form when dislocations with a Burgers vector not in the slip plane move into the plane by combination of climb and glide. THE geometry of subboundaries formed by the interaction of dislocations of two glide systems has been analyzed by Amelinckx,1 and the particular types produced by deforming fee crystals are predicted by ear.&apos; In this paper types of boundaries which may be formed when climb as well as glide occur are discussed as this is relevant in high-temperature creep. It is assumed in the present investigation that the etch-pits observed in Cu + 7 wt pct A1 on surfaces parallel to {111} planes delineate the sites of dislocations. Although there is no direct evidence for this previous work on a-Cu/Al single crystals by Mitchell, Chevrier, Hockey, and Mon-aghan,3 would show this assumption to be reasonable. The alignments of etch-pits which form during creep are studied on sections parallel to each {111) plane. It is then deduced that these alignments are consistent with a specific type of planar subboundary. The Cu + 7 wt pct A1 single crystals had a [113] tensile axis and Fig. 1(a) shows schematically the relation of the slip planes and slip directions (as represented by tetrahedron ABCD) with reference to the tensile axis. The two equally stressed glide systems with the maximum Schmid factor namely ß-AD and (a-BD, from the analysis of Kear,2 would be expected to form the boundaries shown in Fig. l(a) and (b), also Fig. 5(a) and (b). EXPERIMENTAL PROCEDURE The a-Cu/Al single crystals were grown and annealed in a "gettered" argon atmosphere. Chemical analysis showed the aluminum content to be uniform in each crystal and the difference between crystals was maintained to an accuracy of ± 0.25 wt pct. The initial dislocation density and mean subgrain diameter after annealing was -106 cm-2 and 250 µ, respectively. Surfaces parallel to (111) planes were produced by specially developed electrolytic machining processes. The {111} faces were next electropolished for 5 min in a solution consisting of 25 g chromium trioxide, 113 ml glacial acetic acid and 40 ml water; the applied potential was 8 v. Dislocation etch-pits were revealed using l an etchant described by 1 ml bromine, 45 ml HCl, and - 250 ml water. RESULTS In crystals strained into secondary creep at higher stresses (443 and 750 g - mm-2 at 650° C aligned rows of etch-pits parallel to slip plane traces were evident in sections parallel to the (1111, (ill), and (111) planes, see Fig. 3. As well as the longitudinal alignments in Fig. 3, well formed randomly oriented arrays indicative of an equiaxed subgrain structure are evident. At the lower stresses (100 to 230 g . mm-2) only an equiaxed structure formed during creep. The sections in Fig. 3 are from a crystal crept for 70 hr at 650°C with a CRSS of 443 g.mm-2. Two identically oriented crystals were also deformed at the same temperature and stress for 5 min and 4 hr. In the crystal crept for 5 min, the etch-pits were randomly distributed with no tendency for directional alignment, see Fig. 2(a). As shown in Fig. 2(b) aligned arrays were evident after 4 hr creep but they were not nearly so well defined as in Fig. 3. The alignments (parallel to the arrows) in Fig. 3 are consistent with the existence of boundaries in the two main slip planes a and ß. The way in which this is deduced is seen by reference to Fig. l(c), where the existence of boundaries in the a and ß planes is verified by sectioning parallel to a,ß, and d. The (111) and ß(111) planes intersect the d(111) plane along BC [101 ] and AT [011] and alignments parallel to [101] and [011] are clearly evident in Fig. 3(c) in a section parallel to the d(111) plane. Similarly the a, and ß planes in Fig. l(a) intersect each other along DC [110] and hence there will be an alignment parallel to [110 ] in sections parallel to the a-plane and the ß-plane; this is evident in Fig. 3(a) and Fig. 3(b). It is interesting to note that alignments of etch-pits consistent with the boundaries predicted by Kear2 were not observed; see Figs. l(a) and l(b). The geometry of boundaries in {111} planes as shown in Fig. l(c) is discussed later. In Fig. 4(a) the individual etch-pits are resolved and the alignments are exactly parallel to the slip trace direction [101]. However, in some areas alignments deviate away from the slip trace direction by as much as 10 to 15 deg, this is evident in Fig. 4(b), and in Fig.

Jan 1, 1969

By G. R. Speich

The distribution of carbon and the type of substructure in iron-carbon martensites containing 0.02 to 0.57pct C has been studied in the as-quenched condition and after tempering at 25" to 700°C by using electrical resistivity, internal friction, hardness, and light and electron microscope techniques. in marten-sites containing less than 0.2 pct C, almost 90 pct of the carbon segregates to dislocations and to lath boundaries during quenching; in martensites containing greater than 0.20 pct C, appreciable amounts of carbon enter normal interstitial positions located far from defects. Tempering martensites with carbon contents below 0.20 pct at temperatures below 150°C results in additional carbon segregation to dislocations and to lath boundaries but no carbide precipitation whereas -carbide precipitation occurs in martensites with carbon contents exceeding 0.2 pct. Above 150°C, a rod-shaped carbide (either Fe3C or Hagg) is precipitated in all cases. At 400°C, spheroidal Fe3C precipitates at lath boundaries and at former aus-tenite grain boundaries. At 400" to 600"C, recovery of the martensite defect structure occurs. At 600" to 700°C, recrystallization of the martensite and Ost-waW ripening of the Fe3C occur. The effects of the carbon segregation that occurs during quenching and the subsequent substructural changes that occur during tempering on martensite tetragonality, hardness, and precipitation behavior are discussed. A mathematical analysis of carbon segregation during quenching is presented. RECENT studies of the strength of low-carbon martensitel-4 emphasize the importance of carbon segregation to the martensite lath boundaries and to the dislocations contained between them during quenching. Unfortunately, very few studies of the tempering of low-carbon martensites have been conducted, so the exact nature of this segregation is poorly understood. In fact, most early tempering studies5,6 were restricted to carbon contents greater than 0.20 pct. Moreover, these studies did not determine the amount of carbon segregated to the martensite substructure during quenching so that the initial state of the martensite was not established. Aborn7 studied the precipitation of carbide in low-carbon martensite during quenching but did not establish whether carbon segregation occurs prior to carbide precipitation, nor did he study the subsequent tempering sequence in detail. In the present work we have used electrical resistance and internal friction measurements, supplemented by electron transmission microscopy to establish the carbon distribution in as-quenched specimens. Specimens thin enough to avoid carbide precipitation (but not carbon segregation) were employed. The redistribution of carbon on subsequent tempering below 250°C was followed by measurements of elec- trical resistance. Additional studies were made on specimens tempered at 250" to 700°C to elucidate the overall tempering behavior of low-carbon martensites, including the formation of cementite and recrystalli-zation of the martensite. EXPERIMENTAL PROCEDURE Eight iron-carbon alloys with 0.026, 0.057, 0.097, 0.18, 0.20, 0.29, 0.39, and 0.57 wt pct C were prepared as 8-lb ingots by vacuum melting. Typical impurities in wt ppm were 40 Si, 20 Mn, 30 S, 10 P, and 10 N. These alloys were hot rolled to 3 in. plate at 1095°C) (2000°F). The hot-rolled plates were surface ground to remove scale and the decarburized layer, then cold rolled to 0.010 in. sheet. Specimens cut from the sheet were austenitized for 30 min at 1000°C (1830°F) in a vacuum tube furnace in which the pressure did not exceed 2 x 10-3 torr. Chemical analysis of specimens after austenitization indicated no decarburization at this pressure. Immediately before quenching, the furnace was filled with prepurified helium. The specimen was then pushed rapidly through an aluminum foil gasket, which sealed the bottom of the furnace, into an iced-brine bath (10 pct NaC1, 2 pct NaOH). The quenching rate at the M, temperature is about 104&apos;c per sec for 0.010 in thick specimens, as calculated from Newton&apos;s law of heat flow2 using a heat transfer coefficient of 25 ft-&apos;. This quenching rate is sufficiently high so that all the alloys transformed completely to martensite throughout the entire 0.010 in thickness and no carbide precipitation occurred in the martensite. All specimens were immediately transferred to liquid nitrogen after quenching and stored there until needed. Tempering below 250°C (480°F) was done in silicone oil baths thermostatically controlled to *;"C. Tempering above 250°C was done in circulating air furnaces or lead pots with the specimens contained in evacuated silica capsules. Electrical resistance was determined by measurement of the potential drop across both a standard resistance and the specimen, connected in series. All resistance measurements were made in liquid nitrogen (77K, -196°C) to minimize thermal scattering of electrons and thus maximize the contribution of impurity scattering to the resistance. Specimen dimensions were 5.10 by 0.19 by 0.025 cm. Although the precision in the electrical resistance measurements was +0.1 pct, the electrical resistivities could only be measured with an accuracy of +5 pct because of uncertainty in the specimen dimensions. Internal friction measurements were performed in an inverted pendulum apparatus at vibration frequencies of either 1.9 or 66 Hz. The specimen dimensions were 5.10 by 0.375 by 0.025 cm. Hardness measurements were made with a Leitz-Wetzlar microhardness machine with loads of 100 g. Specimens were examined by light microscopy after etching in 2 pct Nital and by electron transmission microscopy after preparation of thin sections by electrolytic thinning in a chromic-acetic acid solution.

Jan 1, 1970

By Antti J. Perala, Teemu J. Yli-Kovero

"Efficient use of land is constantly requiring more underground construction. Minimized execution time and disturbance to surroundings and nearby structures are essential benefits for all construction techniques. To meet the demands of a modern construction project, suppliers have to be able to provide high-quality and tailor-made products just on time. RD pile wall is a retaining wall based on drilled steel pipe piles which are connected to each other with special interlocking profiles. RD pile wall is a solution which enables penetration of overburden soil, dense fill layers including stones and boulders, and embedding into the bedrock in one single operation. Several test installations and laboratory tests have been made to develop the system and to test and improve the water tightness of the wall. Beside these tests, RD pile wall has also proven its reliability in almost 70 projects. Largest project so far has been Pasila Tripla project in Helsinki, Finland. A permanent retaining wall with surface area of 18,000 m2 (193,750 ft2), excavation depth of 21 m (68 ft) and over 17 m (56 ft) of water pressure was made with 711 mm (28”) and 406.4 mm (16”) pile sizes. Piles were delivered to site in one piece with lengths up to 33.5 m (110 ft).INTRODUCTIONExcavations in cramped city centers and in between of existing buildings and other structures are facing more and more challenges. Installation of sheet pile walls is often problematic or even impossible due to obstacles in ground from old structures and due to demand to extend the excavations to even deeper and harder soil layers. Also installations of secant pile walls are facing difficulties due to cramped construction sites and constantly tightening execution times.On the other hand, an efficient and reliable piling technique suitable for the demanding soil conditions described above, percussion drilling, has been developed since the 1960’s, and especially from the mid- 1990’s, when the concentric drilling method with the ring bit and pilot was introduced. A new retaining wall application, the RD pile wall, was developed by combining that drilling method with the widely used retaining wall solution based on steel pipe piles and welded interlocks (a pipe pile wall normally installed with vibratory or impact hammers).PRINCIPLE AND MAIN BENEFITS OF THE METHODRD pile walls can be used in all soil conditions. Most beneficial the system is in extremely demanding soil conditions where the installation of traditional retaining walls is challenging or even impossible. The RD pile wall is a combination of drilled steel pipe piles and interlocking sections as shown in Fig. 1.Individual RD piles are connected to each other with interlocks welded to the piles on the automated welding line at the workshop. The matching dimensions of the drilling system and interlocking sections allow the installation of RD piles through stones and boulders and even into the bedrock, if necessary, in a single operation. Installation is done by a down-the-hole (DTH) hammer using the centric drilling system and oversized ring bits or a drilling system consisting of a pilot bit and reamer wings shown in Fig. 2."

Jan 1, 2017

The Mine Safety and Health Administration (MSHA) defines an independent contractor as "any person, partnership, corporation, subsidiary of a corporation, firm, association or other organization that contracts to perform services or construction at a mine." Contractors that perform specific types of work are required to report the number of employees who perform work at coal mines and at noncoal mines.

Jan 1, 2004

By Luiz C. Correa da Silva, Robert F. Mehl

A. D. Le Claire and R. S. Barnes (Atomic Energy Research Establishment, Harwell, Didcot, Berks., England)-—This much awaited paper admirably confirms that the Kirkendall effect is a true diffusion phenomenon and likely to be found in all diffusing systems. The most likely explanation put forward so far to account for the shift of interface is that the two components of the system, diffusing in opposite directions, do so with unequal rates so that there is a net loss of material from that half of the diffusion zone rich in the more rapidly diffusing component. This loss is accompanied, and at least partly compensated for, by a closing up or decrease in volume of this latter half of the diffusion zone and an expansion of the other half so as to tend to keep constant the overall volume per atom. This is manifest as a movement of the original interface. If this is a true picture of what is taking place then there are at least two important matters requiring further study."1—The quantitative relating of the observed shift with the independently measured separate diffusion coefficients of the two diffusing species."2—A detailed study of the mechanism and characteristics of the closing up process."We would like first to make a few remarks pertinent to these topics. In connection with the first of these, it is a pity that more and detailed measurements were not made on the Au-Ag system, the only one for which the separate diffusion coefficients of the two species have been measured.&apos;" One of us (A. D. Le C.) has calculated from Johnson&apos;s results the shift to have been expected in samples D.2 and D.3. Darken4 showed that the velocity v with which the markers move is related to the separate diffusion coefficients Dau, Dag, by the eauation:"dN"v = (Dag — Dau "dx"dN"where .is the concentration gradient at the mark-ax"ers. Under certain conditions,4, 20 it can also be shown that:"Xm"v = "2t"where x, is the total marker shift after time, t:"dN". . xm = 2t (Dag — Dau) [9]"dX"Johnson measured Dag and DAu in a chemically homogeneous alloy and so his reported figures represent the true or ideal diffusion coefficients"; the same quantities in eq 9 represent the actual diffusion coefficients as would be measured in the presence of a chemical concentration gradient, so we need to multiply Johnson&apos;s reported values of Dag and Dau by the"1 before insert-dlogN "ing them in eq 9. 7 is the activity coefficient of Ag at the concentration prevailing near the markers which we shall assume to be - 50 pct. The values of the thermodynamic factor for N = 0.5 and the temperatures at which D.2 and D.3 were annealed were obtained from thermodynamic data quoted by Darken.&apos; aN/ax was computed from the coefficient of inter-diffusion of Au and Ag given by Johnson on the assumption that in the samples D.2 and D.3, the concentration distance curve could be represented by the standard equation:""No is the original difference in concentration between the two halves of the couple, and + is the error or probability function."aN/ax at x = 0 is then given by:"adN/dx "2/nDt"and we assume that this represents the concentration gradient at the markers, although it is probable that the figure is slightly high."When all the appropriate quantities are inserted in eq 9, we find that the expected shifts are: for D.2, 0.0134 cm and for D.3, 0.0119 cm."The agreement between these results and those

Jan 1, 1952

1. In 2002, a total of 7,125 sand and gravel mining operations reported employment to the Mine Safety and Health Administration (MSHA). The largest percentage of all mining sectors1 was sand and gravel mines (49.1%). Sand and gravel mines are found throughout all 50 states.

Jan 1, 2004