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By D. C. Reynolds

Recent experiments with II-VI compounds have shown that they hazle considerable potential for laser applications over a broad region of the optical spectrum. It may be possible to cover the spectrum continuously from 3200A (ZnS) to the far infrared (CdHg:Te) since HgTe is a semimetal. At this writing laser action has been observed in ZnS, Zn0, CdS, CdSe, CdS:Se, CdTe, and some of the CdHg:Te alloys. Of particular interest are those lasers operating in the zlisible and near ultraciolet regzons of the spectrum where detectors of high sensitivity are available. The lasing transitions in II-VI compounds are bound exciton transitions some of which have been identified in auxiliary experiments. High efficiencies and low thresholds for lasing hare been achieved almost exc1usively in plutelet-type crystals. The greater crystalline quality exhibited by the phtelet-type material is shown to result from the crystal growth habit. Phonon scattering- of conduction electrons to the ground-state exciton is discussed ill relution to Lou thresholds and high efficiencies for lasing- observed in the CdS:Se solid solutions. The first successful semiconductor laser operation was achieved in the III-V compounds. It is possible to choose a material in this group that will operate between approximately 0.65 and 8.5 . There are at least two reasons why one would like to have a laser operating at shorter wavelengths. First, it would be easier to experiment with a laser operating in the visible region of the spectrum, and also more desirable to have high-in tensity visible light sources. Second, the most sensitive photomul-tiplier detectors are available in the visible and near ultraviolet regions of the spectrum. It is known that II-VI compounds are direct-band-gap semiconductors and as such offer the potential of operating at any specified wavelength between 3200 (ZnS) and 7772A (CdTe). Light emission from II-VI compounds has been the subject of numerous investigations for many years. These investigations were all primarily concerned with noncoherent emission. It has been only recently that coherent emission from these compounds has been observed. To date, laser operation has been demonstrated in CdS, CdSe, and the solid solutions of CdS:Se, ZnS, ZnO, and CdTe. These compounds cover an appreciable portion of the optical spectrum from the ultraviolet to the near infrared. In considering laser applications, the use of lasers in communication's systems offers many desirable features. In any operation of this type one must consider the losses in transmitting the radiation from the source to the detector. Atmospheric absorption in the visible and near ultraviolet is variable and greater than in certain regions of the infrared. It might be concluded that for long-range communication systems an infrared laser operating in a spectral region that is coincident with a transmission window in the atmosphere would be preferable. However, one cannot overlook the possibility of operating a system in the sensitive region of a highly sensitive photomultiplier detector or other light-amplifying system. LASER CONSIDERATIONS To produce a source of coherent radiation it is necessary to achieve a population inversion. In the case of semiconducting materials it is necessary to raise the electrons from one energy state to a higher-energy state relative to it. In semiconductors, this population inversion can be achieved by three different techniques: 1) Current Injection. This technique uses a p-n junction biased in the forward direction. Large numbers of electrons are injected from the n region into the p region, and recombination occurs close to the junction. An inverted population is obtained in this region and the recombination radiation propagates parallel to the junction. This type of pumping has been used in the GaAs junction-type lasers but has not been successfully employed in the II-VI compounds. 2) Optical Pumping. In this case, one uses photons to obtain a population inversion by exciting electrons to higher-energy states. The pump sources are flash lamps or arc lamps and, occasionally, other laser sources when such sources have the appropriate energy for exciting the electrons. The disadvantage of this type of pumping is that flash lamps put out a rather broad spectrum of radiation, whereas the laser material has a rather narrow region of absorption. This results in an inefficient process. Laser sources provide efficient pump sources but the number of usable wavelengths is limited. 3) Electron Beam Pumping. In this technique, the laser sample cavity is bombarded with electrons having energies in the range from approximately 10 to a few hundred kv. The bombarding radiation excites electrons from valence to conduction band states in the semiconductor, giving rise to an inverted population. This type of pumping has been used successfully in several 11-VI compounds.

Jan 1, 1968

By Sauer P

The features of Banana screens have been known for some considerable time and recently considerable interest has been generated in the performance of these units. This paper reviews screening principles on Banana and conventional units and demonstrates the capacity and effic- iency of these units. Furthermore, the behaviour of modern Banana screens and modem screens in general, are examined with respect to life, vibration isolation, noise emission and maintenance requirements.

Jan 1, 1978

By R. Harris, M. Misra

Column flotation technology has a demonstrated potential for recovering clean coal from high-ash waste fines. The effect of different variables such as air flow rate, frother addition, depressant addition, percent solids and particle size on the quality of separation are discussed. Results indicate that air flow rate and depressant addition are the important variables which control the selectivity in the flotation of fine coal in a column cell. Separation efficiency achieved with column cells is significantly better than that with conventional flotation cells. Under appropriate experimental conditions with a deep column, more than 80 percent coal can be recovered in the concentrate containing 10 percent ash from waste fines containing over 60 percent ash.

Jan 1, 1988

By J. E. Smith, P. B. Crawford, B. L. Laudrum

A method is presented by which the displacement efficiency of a steam-injection process may be determined. The method consists of a determination of the position of the steam front at a particular time and the application of the Buckley-Leverett theory to the hot and cold regions of the reservoir with the appropriate hot or cold fluid properties. A uniform, linear flow system is assumed for this study. The method is applied to a number of reservoir conditions. The primary properties which affect the results of a steam-injection process are the oil viscosities at steam and reservoir temperatures, injection rate, pay thickness and oil saturation. The efficiency of steam injection is compared with that of water injection for a 10-acre, linearly flooded reservoir. In reservoirs where the oil viscosity is about 35 times the water viscosity, the steam process yields recoveries about 20 per cent higher than the water flood. Where the oil viscosity is near 500 cp, the steam process may recover from three to four times as much oil as a water flood. INTRODUCTION In a previous paper,' a method was suggested for evaluating a steam-injection process. Emphasis was placed upon the determination of the steam-front position in the reservoir at various times. In the present paper, the displacement process is studied in more detail. The approach is essentially that employed by Jordan, Rayne and Marshall3 in their study of hot-water injection. The steam-injection process is quite complex, and an exact description of the process has not been found; however, a qualitative description can be made. When a quantity of steam is injected into a relatively cold reservoir, the leading edge of the steam front continaally flows into cool sand, and some steam condenses. As more and more steam condenses, a bank of condensed water will form which is augmented by displaced connate water. The reservoir may be divided in three regions—(1) a region containing displaced fluids at reservoir temperatures, (2) a region contain- ing water at reservoir temperature and (3) a region occupied by steam. The reasons for the lack of a region of hot water or oil of any appreciable size have been discussed.' A method has been presented by which the location of the steam front can be determined even when heat losses to the regions surrounding the reservoir are sizable compared with the amount of heat injected. It remains to show the effectiveness of steam injection in increasing the ultimate oil recovery. To illustrate the technique for determining the increase in displacement efficiency and, hence, the increase in ultimate production, two sets of hypothetical reservoir conditions will be studied in detail.

By Mehdi Asgharifar, Rouzbeh Sarrafi, Radovan Kovacevic

"The surface treatment of aluminum alloys using atmospheric-pressure of low intensity DC plasma arc discharge is investigated in terms of surface properties. With respect to the conventional surface treatment processes for aluminum alloys mostly based on chemical etching or sand blasting, this process is very environmentally friendly and cost-effective. The effect of two processing parameters, the current and the plasma torch scanning speed, on the surface morphology is studied by using a scanning electron microscope. The effects of cathode spots within the tested range of process parameters are determined, and the limiting factors of the process (such as surface cracking) are discussed. The topographical studies of the treated surfaces have suggested potential enhancement of surface properties for different applications, such as preparing surface for painting and adhesive bonding.IntroductionIn the last decade the aluminum alloys are finding broad applications in automotive industry. In order to successfully execute the joining process of aluminum alloys such as arc welding, laser welding, and adhesive bonding, there is a need to remove oxides for welding and texture the surface for bonding along the join line. A number of surface treatment techniques such as chemical etching, sand blasting, and plasma treatment have been used by industry. It is shown [1] that plasma surface treatment is characterized as environmentally friendly, lower cost, and easier to control process. Bogaerts et al. [1] mention that when an adequately high potential difference is applied between cathode and anode, electrons are accelerated toward anode by an electric field coming in collision with gas atoms. The gas breaks down into positive ions and electrons, giving rise to gas discharge. The DC electrical discharges used in industrial plasma sources can be related to their location on the voltage-current curve as shown in Figure 1.It is generally believed that dark discharges other than coronas, and arc or torch plasmas are not very good candidates for surface treatment because oflow or high power density and active species flux. However, the glow discharge plasma is used for plasma surface treatment applications because of its proper power density and active-species flux [2]. Our objective is to investigate the feasibility of using low intensity DC plasma arc discharge as a surface treatment method without damaging the cathodic non-thermionic workpiece."

Jan 1, 2011

By Charles S. Barrett, Robert F. Mehl

A study of the structures arising from the decomposition of the ß solid solutions in the Cu-Zn and the Cu-A1 systems is of peculiar interest in the study of the mechanism of precipitation from solid solutions. It is possible in these alloys, by varying the composition within the ß field, to precipitate from the same basic lattice phases having different lattice structures. It has been rather generally assumed heretofore that the type of structure originating from the decomposition of a solid solution— the Widmanstätten structure—-is determined by the lattice structure of the parent solid solution alone. In the first paper of this series1 evidence was advanced which threw doubt upon this hypothesis; but definite proof of the correctness or incorrectness of the hypothesis should be forthcoming from a study of these alloys, for if the structures originating, for example, from the precipitation of the a phase from ß and of the ? phase from the ß in the Cu-Zn system should be shown to be crystallographically different, the hypothesis would necessarily be held as definitely disproved. Furthermore, the newer proposal enunciated in the first paper of this series—that the origin of the Widmanstätten structure lies in a cooperation between the lattice of the parent solid solution and that of the precipitate-—which at present seems the only a1ternative hypothesis, would in such an event be given added weight. The work here reported shows that the Widmanstätten structures originating in the precipitation of the a phase from the ß and in the precipit'at.ion of the y phase from the y in the Cu-Zn system are indeed crystallographically different; and incidentally presents some new descriptive information on the Widmanstätten structure from a more general point, of view.

Jan 1, 1931

By R. Frenette, A. W. Mo, H. A. Hamza

Fine particles present major technical and economic problems to those who deal with solid/liquid separation processes. In the coal industry the problem is compounded by the large amounts of produced fines such as those present in Western Canadian coals. Flocculants in the form of high molecular weight water soluble polymers are commonly considered an effective solution for the enhancement of the separation process. These reagents are relatively expensive especially when considering a low-price commodity such as coal. Optimization of the use of these reagents is therefore an operational necessity. Six polymers were evaluated as to their effectiveness in flocculating a fine coal tailing. Results were compared with those for a reference flocculant, in-use at that time in the washery. It was shown that, in general, flocculants significantly improve the solid/liquid separation process. The ranking of the flocculants as to their effectiveness in settling and filtration indicated that the best flocculants for settling were not necessarily the most effective for filtration. Flocculants that showed the best filtration improvement were generally cationic and those best for settling were anionic.

Jan 1, 1988

By R. L. Lewis

The White Pine Mine is a large underground copper mine located in the Upper Peninsula of Michigan. A numerical ground water flow model of the White Pine Mine was constructed to evaluate potential engineering controls that would reduce the rate of mine-water discharge after closure. Of the passive controls evaluated, the placement of bulkheads within the mine workings was predicted to offer the greatest benefit, reducing the rate of discharge by as much as 35%.

Jan 1, 1997

Mining and reclamation procedures that meet the requirements of SMCRA are illustrated on pages 8 and 9 for each of the three major surface coal mining methods -- area mining, contour mining, and mountaintop removal mining. The three methods involve the same basic steps: clearing the land of trees and other vegetation, removing topsoil and overburden, mining the coal, and reclaiming the land. Although all three methods would not usually occur on any single site, the illustration facilitates comparison of mining and reclamation methods and aids basic understanding of the reclamation processes that take place under SMCRA. Area Mining The area mining method is commonly used to mine coal in the flat to moderately rolling terrain found principally in the western and midwestern states. After the overburden is excavated down to a coal seam, the mining area is enlarged horizontally to expose more coal for removal. In the West, where coal seams are commonly 10 to 20 feet thick (and range up to 100 feet thick in the Powder River Basin of Wyoming), the life of some mines maybe more than 50 years. In the Midwest, coal seams are typically 3 to 7 feet thick and 75 to 100 feet below the surface. Because of the large expanse of area mines and their relatively unrestricted sites, enormous equipment is used to remove overburden and reconstruct the land. The area mining operation in the illustration is on land that was formerly used for farming. The drawing shows that the agricultural use is being reestablished immediately following reclamation. Mining is proceeding across the land toward the left side of the site. The initial excavation was made far enough away from the stream along the right edge of the site to prevent damage to the water supply. The coal under most of the site has been removed, and reclamation has been completed on some of the land. For example, some of the cattle in the foreground and those in the feedlot behind the silo are grazing on reclaimed land that has been mined. At the far left of the illustration, topsoil from the unmined area is being removed by scrapers, transported across the area of active mining, and immediately spread on the land on the right, which is being reclaimed. (Reclamation of mined land as soon as practical, as required by the Act, is called contemporaneous reclamation.) A

Jan 1, 1992

By I. H. Warren, E. A. Devuyst

The selective dissolution of pyrolusite (MnO2) in presence of goethite (FeO•OH) in aqueous ammoniacal ammonium carbamate solution has been investigated: various reducing agents were studied, in particular sodium sulfite (Na2SO3,) and hydrazine hydrate (N2H4•H2O). Sodium sulfite was found to be an unsatisfactory reducing agent for both goethite and pyrolusite, for the leaching rate decreased steadily with time to an impractical level because of the limited solubility of the reactions products. Hydrazine hydrate was an effective reducing agent for pyrolusite even at low temperature, whereas goethite required much higher temperatures for any appreciable dissolution. A 1-hr leach at 35°C dissolved 90% of the pyrolusite but only 0.1% of the goethite. An activation energy of 17.0 Kcal per mole was found for the dissolution of pyrolusite with hydrazine. A reaction mechanism for the leaching of pyrolusite with hydrazine is proposed in which a reduction reaction on the surface of the mineral is the rate-determining step. The application of ammonium carbamate to the beneficiation of ilmenite is briefly described.

Jan 1, 1973

By Longworth C. R

This paper descrioes a case history of a coal mine which developed un'tahle roof conditions due to mass sliding of the overburden strata on a claystone band within the coal seam. The sliding is believed to have been initiated by stress relief associated with the removal of overburden alongside the entry portal of the underground workings. Once in motion, the roof block was kept moving by bulking due to roof collapse in the normal underground goafing operations. Control measures in the form of an earth and rockfill buttress against the entry portal and a sequential mining plan to create goaf areas alongside the entry portal have been initiated to attempt to limit movement. The operation has been continually monitored and a gradually decreasing pattern of movement is being re, orded.

Jan 1, 1981

By Morris A. Dodd

The nodulizing process described converts finely divided zinc calcine into a dense purified nodule. These zinc nodules are suitable for direct use in zinc reduction furnaces, especially the horizontal retort type, for the production of metal or American process zinc oxide furnaces for producing lead free zinc oxide. The basic reactions are carried out in a rotary kiln fired with fuel oil or natural gas. The combustion gases travel countercurrent to the flow of the zinc bearing material. Volatile impurities are carried out of the kiln with the combustion gases and a small portion of the finely divided feed material. The gases are cooled and the larger solid particles are separated from the stream before the resultant fume is collected in a conventional cloth filter baghouse. The fume collected can be further processed by conventional wet processes for the recovery of metallic values such as lead and cadmium. In order to nodulize the calcine properly it is elevated to a point of incipient fusion. The agglomerated material falling from the kiln is cooled and then sized by passing through a screening and crushing system consisting of a jaw crusher and a roll crusher in closed circuit with a vibrating screen.

Jan 1, 1970

By Jing Zhou

2-hydroxy-3-naphthoy hydroxamic acid code name F203 is a good collector of cassiterite, 1-hydroxy-2-naphthoy hydroxamic acid code name ZJ-3. F203 and ZJ-3 are similar series of isomers. They have similar naphthye, and similar series of functional OH and ?CONHOH, but the seat of OH and ?CONHOH group are different, on the F203 is 2.3; on the ZJ-3 is 1.2, ortho position too. According to Isomeric principle ZJ-3 is a good collector of cassiterite slime too. Using ZJ-3 as collector flotation -10µm occupies 90%, grade 1.16% Sn cassiterite slime of Da Chang Chehe concentration plant, pass one coursing flotation, two cleaning and one scarenging flotation, and obtains grand 18.26% Sn, recovery 92.68% cassiterite concentrate. The result proves the Isomeric principle of flotation reagents is correct again. This principle may supply to synthetize new flotation reagents reference. Keywords: F2O3, ZJ-3, cassiterite flotation, Isomeric principle, Isomeric principle of flotation reagents

Sep 1, 2012

By Jorge Ganoza

Hay varios ejemplos recientes de proyectos que no han llegado a los niveles de producción o a los resultados del modelo financiero desarrollado durante el estudio de factibilidad. Las personas responsables de decidir la inversión en los proyectos deben poder percibir los problemas potenciales y los grandes riesgos, cuando hay decisiones mal tomadas en el estudio de factibilidad y en la etapa de construcción inicial. Si bien es cierto que no hay diseño de ingeniería perfecto, los problemas pueden evitarse si —tal como propone este artículo— se siguen las etapas de estudio necesarias, desde la toma de muestras hasta la ejecución e interpretación de los resultados de las pruebas metalúrgicas.

Nov 30, 2018

By Calvin L. Stevenson

The probability of a particle passing through a maze is predictable and consistent. This principle may be utilized to effect a particle size separation of materials by presenting a physical maze to a stream of material that will allow the fine particles to pass, while deflecting the coarse particles. A maze is effective even though all apertures encountered are many times larger than the particles being separated. By designing a machine that allows the probability parameters to be controlled and varied without changing physical dimensions, probability sizing becomes a useful tool for the separation of granular materials.

Jan 1, 1967

By Kelly C. Strebig

Laboratory tests were conducted by the Bureau of Mines to determine the effect of depth of cut and bit type on respirable coal dust generation. Apparatuses were constructed to contain the coal samples, measure the linear cutting forces, and analyze the dust generated. Single-bit tests were conducted in Illinois No. 5 and Pittsburgh seam coals with five bit types at four depths of cut. The results showed that bit type did not significantly influence dust production. On the other hand, deep-cutting bits were more efficient and generated substantially less respirable dust per pound of coal broke than shallow-cutting bits.

Jan 1, 1975

By C. Z. Serpan, L. J. Wittenberg

The density of liquid plutonium was determined, by a pycnometm'c technique, from 664 to 788°C and exhibited a temperature dependence, which could be expressed as:. P= C17.63 - 1.52 x 10-"t] +0.04 g per cc where t = OC. These density values compare favorably with the values previously obtained by a technique utilizing Archimedes' principle. The apparatus and method were evaluated when the densities 0.f molten tin and bismuth were measured and found to be in agreement with accepted literature values. PLUTONIUM or an alloy of plutonium in the liquid state has been proposed as a fuel for a fast-breeder type nuclear power plant.' Since knowledge of the liquid density of plutonium is required for the proper design of such a system, this study was undertaken. In addition, the density and volume expansion coefficient of liquid plutonium are of interest for comparison with these same properties of the six allotropic modifications of the solid metal. Comstock and GibneyZ were first to report a value for the density of liquid plutonium. The value for only one temperature, 665"C, was calculated from data obtained by the radiography of the meniscus, Fig. 3. Recently, the density at a series of temperatures has been reported by Knight,3 who obtained his values by using a differential volumeter, and by 01-sen, Sandenaw, and Herrik, who obtained their values from measurements of the loss in weight of a tungsten bob immersed in the liquid. The density of liquid plutonium reported here was determined by a vacuum pycnometer method. In an evacuated system, the tips of calibrated tantalum pycnometers were lowered beneath the liquid sur-

Jan 1, 1962

By Klaus Schoenert

In the analysis of comminution processes, it is necessary to have a detailed knowledge of such subprocesses as: transportation of the particles to the zone where they are stressed; the stressing of particles to a level high enough for breakage; removal of the fragments that are smaller than the limit size from the grinding zone; and prevention of agglomeration of the fine fragments. Breakage phenomena of particles is the most difficult subprocess to understand. It can be understood only by applying the principles of fracture physics to obtain information about the stress-strain field in particles which are loaded either by compression or by impact, and by using this theoretical knowledge to interpret experimental results obtained from single particle crushing studies. Two important features of the "Science of Communition" are discussed: the fracture physics and crushing under controlled conditions with special reference to single particle crushing, packed bed crushing, measurement of energy needed for fracture, fragment size distribution, and new surface area produced. The important features of these aspects are detailed, namely, energy balance of a crack, influence of environment, specimen size problems, and energy utilization in single particle crushing.

Jan 1, 1973

By John D. Smith, Robert J. Mitchell

"There is a world-wide trend toward underground bulk mining methods employing hydraulically placed backfill. This trend is recent and therefore there is little in the literature to assist an operator in the design of backfill properties, the design of drainage facilities, the calculation of the operating forces on a bulkhead, and the control procedures considered necessary before, during and after pouring. This paper presents recommended procedures that are based on over to years of experience in the various aspects of backfilling large openings. Free-draining timber or concrete block bulkheads are shown to be a viable alternative to massive reinforced concrete bulkheads for the containment of backfill pours. Hydrostatic pressures cannot develop in backfills provided adquate drainage facilities are installed.IntroductionThe increasingly adverse relationship between mining costs and mineral values has led mining companies to develop more productive, lower-cost, bulk mining methods. This has led to the increasing use of large, more or less continuous, hydraulically placed backfill pours to enable the recovery of a higher proportion of pillar ore. The success of any bulk mining method depends on the degree of stability maintained during the stoping operations with reference to the mining rate, the performance of the backfill with respect to the per cent extraction of pillar ore, and the control of the mine structure with respect to safety and productivity. One such method has been previously described(I) where a steeply dipping orebody is being mined with a sub-level method that employs large, hydraulically placed tailings pours for delayed pillar recovery. The paper describes the rock mechanics analysis undertaken to establish the stope and pillar geometry and the approach taken to establish backfill strength requirements to prevent dilution during pillar recovery. Production with this method started in 1970 and because few, if any, large bulk pours had previously been used in- this way (judging by the lack of information in the literature), design data and criteria were needed for several aspects of the work. Methods to establish backfill quantities and pertinent ""in-place"" fill properties are described in 2, 3 and 4 in the list of references. Results of field measurements taken to establish fill pressures for bulkhead design purposes are described in 5 and 6. Laboratory large-scale model tests undertaken to confirm a fill strength design equation, which takes into account fill arching, have recently been completed. A paper describing these tests and the results will be forthcoming in the near future."

Jan 1, 1982

By A. D. Unsted

The Premier mine has been in existence for over 75 years and is closely woven into the glamour of the history of South Africa. A note on the geological formation of the diamond pipe and the gabbro gives a clearer overall picture of the mine. Mining methods for operations above and below the gabbro sill are briefly discussed. Ventilation arrangements for mining above the sill are briefly described and possible ventilation arrangements for mining below the sill are discussed in more detail. Note: conversions to S.I. units are not exact as rounding has been done.

Jan 1, 1980