Search Documents

By R. S. Rickard, B. Ball

INTRODUCTION Pyrite responds to the flotation reagents normally used in sulfide flotation systems. For example, it is well known that xanthates are good collectors for pyrite, and cyanide, sulfide and hydroxides are depressants. The particular response of pyrite to these and other reagents is used to advantage in several areas. By careful control of depressant and collector additions, pyrite can be separated from other sulfides by flotation. This is of obvious importance in base metal sulfide flotation where pyrite depression is often required to produce a marketable grade concentrate. Flotation of pyrite has long been employed in gold ore processing, and it appears that pyrite flotation from coal may become important in the future (1). It is probably a direct consequence of this relative ease of separation, plus the low economic value of pyrite, that detailed investigations on the chemistry of its flotation and depression are relatively limited. Gaudin (2, 3, 4) and others, in the mid-1950's published data on the flotation of pyrite, but detailed or consistent mechanisms were lacking. In 1955, Sutherland and Wark's book (5) was published, in which a large , amount of empirical information, especially earlier work of Wark and Cox, was presented. More recently, in 1968, significant contributions have been made by Fuerstenau et al. (6, 7) and Majima and Takeda (8). These papers introduced electrochemical explanations of the effects observed with xanthate and cyanide ions.

Jan 1, 1976

By Luis Toron, Salvador Cortes-Obregon

THE Oaxaca coal fields, shown in Fig. 1, are located in the Alta Mixteca region in the states of Oaxaca, Puebla, and Guerrero. Known outcrops are scattered over 3125 square miles. It is probable that further exploration will reveal a more extensive area of deposits. The region is of great importance to Mexico, as at present the only sources of coal are the fields near the U. S. border. Steel mills are also located in the North, and finished products must travel 600 to 800 miles to the area of consumption in central Mexico. The oaxaca coal, only 120 miles south of Mexico, D.F., lies close to several iron ore deposits. If this

Jan 1, 1955

By F. J. Mehringer, C. W. MacGregor

VARIOUS investigations have been carried out to determine the effects of cold-rolling on the common physical properties as represented by the yield strength, tensile strength, percentage of elongation and ordinary reduction of area. Very little information is available in the literature with reference to the effects of cold-rolling on the true stress-strain properties. Since the ordinary physical properties base both the stresses and the strains on the original dimensions of the test piece, which are greatly changed during the test, they are essentially empirical values and do not represent physically either true stresses or true strains. Consequently, they do not give an accurate picture of the effects of different conditions, both mechanical and metallurgical, on the strength and ductility of the material. It is not, however, the purpose of this paper to review the various advantages accruing from the use of true stress and true strain values, since these have been shown elsewhere,1-12 but to utilize them in representing the various effects considered. The true stress S and true strain (e = q') values mentioned above for the tension test are defined by1 [ ] where P, A, Ao are the axial load, the instantaneous area and the original area of cross section, respectively. From simultaneous readings of the axial load and the dimension or dimensions determining the instantaneous area of cross section, the true stress-strain curve is constructed by using the relations given in Eq. I. It is then the object of this paper to discuss the general effects of cold-rolling on the true stress and strain values for a low-carbon steel together with the effects of age-hardening and directionality on these properties. PRELIMINARY INVESTIGATIONS The material considered throughout the paper is a low-carbon steel of the following chemical analysis: C, 019 per cent; S, 0. 118; P, 0.092; Mn, 0.85; Si, 0.01. The stock was received in bars, 7 by 3/4 in., and was first annealed for one hour at 1650°F. followed by a furnace cool. Photomicrographs of this material showed considerable directionality even in the annealed condition. In view of the possible effects of the nonhomogeneity and directionality in this material, it was considered important to investigate their influence on the true stress-strain diagrams. In addition, the effect of strain-aging in this steel was also made the subject of a preliminary study. Elect of Aging on True Stress-strain Properties Since a certain time element would elapse between the cold-rolling operation and the final tension tests, it was determined to investigate the aging character-

Jan 1, 1945

[ ]

Jan 1, 1940

By R. E. Carter, F. D. Richardson

Self-diffusion coefficients have been measured for iron in wustite (700° to 1000°C) and for cobalt in cobaltous oxide (800&apos; to 1350°C) by means of radio-isotopes. Both sectioning and decrease of surface-activity methods have been used and a particular shortcoming of the latter method has been disclosed for wustite. The effects of oxygen pressure on the composition of cobaltous oxide and on the diffusion coefficient of cobalt in the oxide have been established. The effect of the preparation conditions of the cobalt-oxide specimens on the diffusion measurements has been determined. It has been concluded that diffusion of cobalt occurs via vacant cation sites and that a cobaltous-oxide disk reaches equilibrium with its environment in a time which is very short compared with that needed for diffusion of the radio-isotope. THE availability of radioactive isotopes in recent years has permitted the measurement of many self-diffusion coefficients which were hitherto impossible to determine. With the advent of radioactivity, the method of measuring diffusion coefficients has also changed. The earlier sectioning method by which the concentration profile of the diffusing species was determined in the diffusion specimen has often been rejected in favor of the decrease of surface-activity method first developed by Von Hevesy,&apos; and extended by Steigman, Shockley, and Nix,&apos; and Raynor, Thomassen, and Rouse." With the experimental arrangement where an infinitely thin deposit of tracer is diffused into a semi-infinite cylinder, the decrease in activity of the active face due to diffusion of the tracer into the specimen is measured by counting the active face before and after diffusion. Under these conditions, the appropriate solution of the diffusion equation is R = e*(l-<K/Z) [1] where R is the ratio of the counting rates after-to-before diffusion, $& is the Gaussian error integral of \/Z, and Z is defined as Z = p2Dt, p being the linear-absorption coefficient of the detected radiation in the diffusion specimen, D the self-diffusion coefficient, and t the diffusion time. In the older sectioning method the concentration distribution of the tracer is found after diffusion by analysing thin parallel sections cut from the active face of the diffusion specimen. As seen from the solution of Fick&apos;s second law for the distribution of an infinitely thin source after diffusion into a semi-infinite cylinder the log of the concentration plotted against x&apos; will be a straight line of slope log e/4 Dt. The diffusion coefficient thus can be calculated directly. The units of the tracer concentration are completely arbitrary, since any change in units does not change the slope of the log c vs x2 lot. Although both of the above methods have been widely used, a thorough experimental comparison does not appear to have been made. Birchenall and Mehl,&apos; during an investigation of the self-diffusion rate of a and r iron by the surface method using Fe" tracer, diffused and sectioned one welded couple. The diffusion coefficient from this run agreed with those by the surface method. Buffington, Bakalar, and Cohen," during an investigation on a and y iron

Jan 1, 1955

By J. Gurland

The strength variation ofWC-Co alloys with composition and particle spacing falls into two ranges. 1) Above a critical value of the mean free path, the strength follows a dispersion hardening relation; it is proportional to the volume fraction of WC and in-versely proportional to the particle size. 2) Below a critical value of the mean free path, the strength variation is based upon the Griffith criterion of fracture and is controlled by the case of crack propagation. The maximum strength is attained when the structure and load just satisfy the critical conditions for spontaneous crack propagation. THE relation between the strength and the structure of cemented carbides is of interest not only for its own sake but also for its contribution to the understanding of composite materials in general. The cemented carbides are essentially aggregates of a brittle carbide constituent and a ductile binder phase and, at certain structures of intermediate composition, the composite alloys attain strengths far higher than those of the separate constituents in bulk. It is this variation of strength with structure which will be discussed. The experimental procedures of sample preparation, mechanical testing, and quantitative metallo-graphic analysis have been described in Ref. 1. The reported strengths are the maximum fiber-stresses in bending calculated on the basis of completely elastic behavior. The plastic contribution to the over-all deformation is small and was neglected in the calculations (the elongation at fracture of the most ductile alloy, 50 pct WC-50 pct Co, is less than 0.5 pct).2 The pertinent structural parameters are: f, the volume fraction of tungsten carbide; p, the mean free path through the binder phase; the contiguity C, defined as the average fraction of surface area shared by a particle of wc with all neighboring particles of the same phase; and d, the average equivalent spherical diameter of the WC particles. The strength variation of WC-Co alloys with composition and particle spacing is shown in Fig. 1 and Table I, which are based partly on previously published data&apos; and partly on new experimental work which extends the range to higher values of the mean free path. Each data point represents the average of five samples. For a given composition, the transverse rupture strength reaches a maximum

Jan 1, 1963

By D. R. Wieland, A. N. Barron, A. R. Hendrickson

A definite relationship has been found between the reactivity of flowing hydrochloric acid and its shear rate in a carbonate fracture. Both flow velocity and fracture width affect the acid reaction rate. Laboratory studies were conducted on acid reactivity at different flow velocities through horizontal-linear fractures, using 15 per cent hydrochloric acid at 80&apos; F and approximately 1,100 psi. Fracture width varied from 0.02 to 0.20 in. These data provide a new basis from which the spending time and penetration of the acid can be estimated. Equations were derived expressing the relationship between injection rate, fracture width, acid concentration, time and fracture height, for linear and radial fracture systems. Because the penetration of the acid before spending is closely related to the extent of productivity increase resulting from an acidizing treatment, these data provide a valuable insight into some of the controlling factors that must be taken into consideration during treatment preplanning. INTRODUCTION Acidizing of carbonate reservoirs to improve production characteristics has been widely practiced since 1932. Originally, it was assumed that the acid uniformly penetrated natural formation pores and flow channels, enlarging them and thereby increasing their flow capacity. Little consideration was given to the reaction rate of the acid, or how far it would penetrate away from the wellbore into the formation, before spending. It has been shown recently&apos; that, unless fractures are present in the rock, very little penetration is attained before spending, and the benefits of the acidizing treatment are largely confined to the immediate vicinity of the well-bore. Therefore, acid treatments may be classified into two categories: (1) matrix acidizing, in which the acid flows through multiple: formation pores; and (2) fracture acidizing, in which the bulk of the acid travels through fractures in the rock, whether natural or induced. When acidizing treatments are conducted at pressures of sufficient magnitude to open and extend such fractures, it is often desirable to inject a propping agent to hold the fracture open after the treating pressure has been released, thus providing a highly conductive flow channel through the rock. In some cases where acid attack produces surface irregularities, the resulting flow passages can be sufficient to provide high conductivity without use of a propping agent. During injection, the acid dissolves the carbonate rock with which it comes in contact until it is spent. Deeper penetration of the spent acid into the formation produces no appreciable benefit (if no propping agent is used) because the unetched fracture faces will rejoin when treating pressures are released and the fracture will "heal", with negligible resultant conductivity. The spending time of the acid thus becomes important in determining how far from the wellbore the improved-conductivity zone extends. The spending time of acid after injection into carbonate rock depends on the rate at which the acid reacts with the rock. This in turn is controlled by a number of factors, as previously reported. 2-4 These include temperature, pressure, acid concentration, rock composition, injection rate and the area-volume relationship between the acid solution volume and the surface area of the formation flow channels through which it penetrates. Thus, in matrix acidizing, where an extremely large area is exposed to the acid, spending is rapid. In contrast, spending time is prolonged in open fractures, where the area-volume ratio is much lower. Thus, greatest penetration of the acid before spending will be achieved in acid-fracturing treatments where fractures are held open by hydraulic pressure. Perkins and Kern5 have presented equations for fracture-width determinations which, for hard formations such as limestone or dolomite, indicate that high injection rates and viscous fluids are required to create wide fractures. Increasing the injection rate will, in itself, produce faster reaction rates. Because this type of reaction can be considered to be first-order diffusion-controlled, &apos;-&apos; the rate of movement of fluid past the rock surface affects the thickness of the diffusion layer, in turn affecting the reaction rate. Staudt, et al,10 report the results of tests in which a rotating marble cylinder was immersed in acid, and the weight loss at different speeds determined. Such test conditions, however, are not truly indicative of the situation in a formation during an acid-fracturing treatment. This paper reports reaction-rate data obtained under

By D. Turnbull

RECENTLY it has been shown that aggregates of small liquid droplets of tin,&apos; mercury&apos; or gallium&apos; kept from intercommunicating by suitable films do not solidify at an appreciable rate unless the supercooling is very much greater than that usually necessary to cause a large continuous mass of the metal to solidify. For example oxide-coated tin droplets1 (1 to 10 micron diam) must be supercooled 100" to 110°C before their rate of solidification becomes rapid, although large continuous masses of liquid tin usually begin to solidify when supercooled 30" or less." These experiments have been interpreted&apos; on the hypothesis that nucleation of crystals in large continuous metal samples is almost always catalyzed by accidental inclusions. Therefore, if the metal is dispersed into a number of isolated droplets large in comparison with the number of inclusions, most of the droplets should not crystallize until a temperature sufficiently below the thermodynamic melt- ing point, T0, has been reached to permit an ap-preciable rate of homogeneous (noncatalyzed) nu-cleation. In general this temperature is very much less than the temperature at which the rate of heterogeneous (catalyzed) nucleation is appreciable. If this interpretation is correct then investigation of the kinetics of crystallization of small droplet aggregates should be one of the most fruitful methods of obtaining information about the homogeneous formation of crystal nuclei in liquids. In this paper the results obtained on gallium and mercury are reported more fully. In addition, results on the supercooling of aggregates of liquid bismuth and lead droplets are included. Experimental Procedure Some care must be exercised in the choice of a barrier to prevent the liquid droplets from coalescing lest the barrier itself catalyze the formation of crystal nuclei. From this standpoint, the most desirable barrier is vacuum or inert gas, but, because of the difficulty of experimental arrangement, solid compounds and adsorbed films have been selected. There are two guiding principles in the selection of compounds as barriers in addition to the requirement that they prevent coalescence of liquid droplets. First, the compound should be almost insoluble in the liquid metal and second, its lattice structure should be quite unlike that of the forming metal crystal. Even so, there is no a priori assurance that the solid compound film will not catalyze to some extent the formation of metal crystal nuclei. An adsorbed protective monolayer is less likely to be catalytic than a crystal compound film, but it is not often possible to find a monolayer that is stable under the experimental conditions. Also, it is desirable, though not generally essential, that the aggregate of droplets be prepared by breaking up the massive metal rather than from a powdered compound of the metal.

Jan 1, 1951

By H. F. Yancey, O. L. Furse

For several years the Bureau of Mines at its Northwest Experiment Station, in cooperation with the Mines Department. of the University of Washington, has been studying the breakage and degradation of coal. The first phase of the study was devoted to the determination of the friability of many coals of various ranks and comparison of various methods for estimating friability.&apos; A study of the relative ease or difficulty with which various coals are reduced to the fine size required for use as pulverized fuel followed the completion of this work. Baltzer and Hudson2 list twelve research organizations in the United States, two in England, one in Germany and one in Canada that are reported to be engaged on this problem; showing the general appreciation of the need for a simple method of estimating the grindability of different coals. Hardgrove,3 ho has advanced a method for estimating grindability, points out that pulverizer tests of different coals are incomplete and unsatisfactory. He compares such tests to that of a boiler test made without knowledge of the calorific value of the coal. Frisch arid Holder4 also stress the same point. They state that,

Jan 1, 1934

Discussion of the paper of M. B. YUNG, presented at the Pittsburgh meeting; October, 1914, and printed in Bulletin No. 93, September, 1914, pp. 2451 to 2458. T. T. READ, New York, N. Y.-I might .point out that this paper of Mr. Yung&apos;s is on a field that is comparatively little known. It is not as well known as the Kochiu tin field, of Yunnan, which is probably the third . in tin output of the world. This field under discussion is considerably further west and the tin which is produced here is, according to Mr. Yung, of somewhat higher grade than the Yunnan tin, and is used by the refiners at Hong Kong to improve the grade of the Yunnan tin. Most of you know that the tin from the Yunnan is shipped to Hong Kong, where it is refined and shipped to Europe. Mr. Yung points out that the Fu Chuan deposits are entirely alluvial and not found in any veins. They .differ in that from the Kochiu deposits, which Leclere says are "nullement alluvionels; leur origéne filonienne est de plus evidentes." Granite is the country rock here; doubtless the tin occurred in veins in the granite, and the deposits have resulted from the disintegration of the granite. This is a country of strong erosive agencies. The country is semi-tropical, and the rainfall is heavy, so that one would naturally expect deep surface erosion of this kind.

Jan 4, 1915

By William P. Blake

In the recent litigation for the possession of franklinite by one party and of zinc-ore by the other party, it was shown by the evidence of experts familiar with the original condition of the outcrops that at Mine Hill a more or less disticctly defined layer of red zincore underlay the heavier and larger body of the franklinite, so-called ; this layer or bed of zinc-ore dipping under the franklinite upon the western cropping, while at Stirling Hill, two miles south, the conditions were apparently reversed, the zinc-ore overlying the franklinite. An explanation being required, it was shown, first, that at both places, at Mine Hill on the north and at Stirling Hill on the south, the ore-bed lies in a synclinal or trough-like fold with the red zincore under the franklinite; and secondly, that at Mine Hill, we see chiefly the outcrop of the western part of the folded bed and at Stirling Hill the eastern part; the Mine Hill cropping being on the western slope, and the Stirling Hill cropping on the eastern slope of the hill. Thus the &apos;&apos;back vein" at Stirling (the western outcrop) corresponds with the front-vein at Mine Hill, and, like it, has the red zinc-ore on the foot-wall, while the front-vein or eastern cropping at Stirling corresponds to the back-vein or eastern cropping at Mine Hill in the part of the bed generally known as the " buckwheat-field vein." If the ore-bed were continuous in one synclinal trough between the two localities, no further explanation would be required. But it is not so ; and the synclinal folds at both places pitch steeply to the north, bringing the beds to the surface in horseshoe-like curves at their southern ends or croppings, and carrying the beds far below the surface northwards. This justifies a doubt

Jan 1, 1895

By D. A. Vaughan

COMPOUNDS in the U-N system have received little attention since the work of Rundle, Baen-ziger, Wilson, and McDonald in 1948.&apos; They described the three nitrides UN2, U2,N2, and UN as the only phases in this system. The region between UN and U,N, was reported to consist of the two phases while the region between U,N, and UN, is a homogeneous solid solution in which the U,N3, structure transforms with increasing nitrogen content into the UN, structure. This report presents the results of an X-ray diffraction study of the phases present in the region of the diffusion gradient on uranium reacted with nitrogen at several temperatures between 500" and 915°C. Several samples of uranium used in U-N gas-metal reactions by Mallett and Gerds were available for X-ray diffraction study of phase composition through the diffusion gradient. X-ray diffraction data were obtained using filtered iron radiation at intervals through the diffusion layer of the several samples on filings or turnings at approximately 0.001 in. increments down to the base metal. Representative X-ray diffraction patterns from various layers through the case on uranium after nitriding at 850°C are shown in Fig. 1. These data show that three different phases are present in the

Jan 1, 1957

By T. E. Leontis

Several publications1-7 during the past few years have demonstrated the markedly greater effect of cerium, as compared to all other alloying elements, in enhancing the strength and creep resistance of magnesium at elevated temperature either with or without the presence of other elements. In the work reported in Ref. 1-6, the cerium was added in the form of Mischmetal, which contains all the rare earth elements in essentially the same proportions as they occur in monazite sand, the principal ore of these metals. Mellor and Ridley7 have presented the creep characteristics at 200°C of magnesium alloys prepared both with pure cerium and with Mischmetal. Up to the present time, however, no comprehensive study of the effect of the various component elements of Mischmetal on the properties of sand-cast magnesium has been made. This hiatus in magnesium technology undoubtedly is associated with the difficulty in obtaining the rare earth metals separately. This investigation provides such a survey, the object of which was to determine which of the elements present in Mischmetal contributes the greatest effect in developing high strength and high resistance to creep at elevated temperatures. Toward this end the compositional variation of these properties has been determined as a function of temperature in the following alloy systems: 1. Magnesium-Mischmetal 2. Magnesium-cerium-free Misch- metal 3. Magnesium-didymiuin 4. Magnesium-praseodymium- lanthanum 5. Magnesium-cerium 6. Magnesium-lanthanum This designation, based on the names of the metals as furnished by the producer, is used throughout the paper in order to avoid the complicated system of listing all the elements present in the more complex alloys. The composition of the metals and the alloys is discussed in detail below. Preparation of Alloys ALLOYING INGREDIENTS The chemical composition of each of the six alloying ingredients used to prepare the alloys reported in this paper is given in Table 1. In each case, the percent total rare earths, percent cerium, percent neodymium, percent praseodymium, and percent thorium were determined in addition to the listed impurities. The percent lanthanum was determined by difference from the total rare earth content and consequently includes the other elements (samarium, terbium, yttrium, etc.) present in Mischmetal. These additional elements, however, seldom amount to more than 1 to 2 pet of the total rare earth content of Mischmetal. The iron content of the Mischmetal is considerably lower than that of the other metals. This grade of Mischmetal is now readily available. The metals are listed in the order of decreasing complexity. Elimination of the cerium from Mischmetal results in what the trade calls "Cerium-free Mischmetal." Carrying the separation a step further by eliminating the lantha-

Jan 1, 1950

By C. G. Rhodes, D. Kramer

High-field critical transport current density (J) measurements at 4.2 °K as a Junction of applied magnetic field (H) were made on samples of cold-rolled and annealed columbium with H parallel to J. Microscopic examination of the samples revealed a well-defined planar fiber structure produced by the cold rolling. J was found to he lower when fibers are parallel to the direction of magnetic field penetration than when they are perpendicular. This effect may he a consequence of the interaction of flux movement with fiber boundaries. THE severe changes in microstructure brought about by cold working superconductors leads to profound changes in their superconducting behavior. In particular, the ability of a superconductor to carry a transport current with zero resistance (the maximum value of this current density will be called "J" in the presence of large external magnetic fields (to be referred to as "H") is greatly influenced by the microstructure. In the case of columbium, LeBlanc and Little1 and Autler et a1.2 have observed an increase in J due to cold work. LeBlanc and Little also observed an anisotropy in J in cold-rolled columbium strips, which Hake et al.3-6 have shown to depend upon the angle between H (H ? J) and the rolling plane. An increase in J due to cold work has been found in a variety of high-field superconducting alloys3&apos;4&apos;7-9 as has the anisotropy effect.10 First explanations of why cold work raised J invoked the idea that dislocations carried the high-field supercurrents,8,11 since cold working drastically increases the dislocation density and presumably the number of supercurrent paths. However, recent ideas on the nature of high-field superconductivity together with new experimental evidence reveal that the bulk of certain superconductors can remain superconducting in high fields while carrying high transport currents. These later developments have been discussed by Berlin-court and Hake12 and a comprehensive review has been prepared by Berlincourt.13 According to the ideas of Gorter14 and Anderson,15 one would expect that the influence of microstructure on high-field supercurrent density will depend on tine interaction between microstructure and penetrating flux and on the direction of the Lorentz

Jan 1, 1965

By A. G. Guy

In a special type of electrodiffusion experiment the entire specimen is at constant temperature. The vacancies are then created at one end of the specimen and flow to the other end where they are destroyed. The energy required to operate the corresponding sources and sinks results in a super saturation of vacancies at one end of the specimen and an under -saturation at the other end. This gradient in vacancy concentration produces a chemical-diffusion flux, J(D), of vacancies in addition to the flux, J(E), caused by the electric current. Using the experimental data of Ch. Herzig,5 it is shown that a super saturation of 1 pct can cause J(D) to be about 25 pct of J(E), and thus account for the anomalous behavior of short specimens. THERE are advantages in a phenomenological treatment as contrasted to an atomistic one. For example, there are many reactions involving the element copper that are quantitatively and usefully understood from a phenomenological viewpoint, even though electron theory is not yet able to predict whether copper should be fcc or cph.&apos; Similarly, the lack of a complete atomic theory of vacancies need not prevent the development of a treatment based on thermodynamics and chemical kinetics. In the following discussion, models will be used for the vacancies and for the mechanisms by which they move or are created or destroyed, but the phenomenological treatments are not dependent on the details of these models. The important product of a phenomenological analysis is an equation that describes the relation among the measurable quantities determining the behavior of the system. Based on such an equation, experiments can be performed to study these quantities in detail. Eventually atomic theory will supply an adequate theoretical base for the phenomena in question. A chemical species whose chemical potential was invariant during reactions in binary and ternary systems of varying composition would indeed be an anomaly. Yet this is the role that has frequently been assigned to the vacancies in pure metals, in dilute solutions, and even in ordinary alloys. The weight of available evidence supports the view that supersatu-rations of vacancies are on the order of 1 pct in usual diffusion processes.&apos; Although it may seem strange that such a small deviation from equilibrium could significantly affect the thermodynamic properties of the vacancies, it is well known that the driving force for an ordinary chemical reaction is the departure of the components from their equilibrium state. Similarly, the reaction of vacancies that results in the formation of pores in various types of diffusion3 can reasonably be attributed to the supersaturation of vacancies. In the present paper, it will be shown that small degrees of supersaturation can significantly affect the kinetics of the diffusion process itself. ISOTHERMAL ELECTRODIFFUSION Two different experimental techniques are convenient for studying the behavior of vacancies in a pure metal in the presence of an electric field. Gilder and Lazarus4 studied self-electrodiffusion in a gold specimen in which only the central portion was at high temperatures. In this case the significant vacancy sources operate inside the specimen in the presence of a temperature gradient. In the laboratory of Th. Heumann a method has been devised for studying self-electrodiffusion at constant temperature.5 In principle, there is then no effect of thermodiffusion. It will now be shown why in this case the significant ATungsten disks \^^ ^^ ^Gold disks^^ ^^"T>.... "TTZA ? Up Iy&apos;7 markers ///// ////// initial plane p I y/y/y of joining \I 7//// V7//A_________I_________V//// -I 0 +I Distance from center of specimen (a) -— Direction of flow of electrons —Direction of flw of vacancies %yy} Matano I z~irkendall /%W, vy/A inlerfacej "interface ///// -} HfiK- +/ 0 Distance from center of specimen (6) Fig. 1—-Schematic illustration of the essential features of isothermal self-electrodiffusion. (a) Initial condition of specimen. (b) Condition of specimen after electrodiffusion.

Jan 1, 1970

By S. H. Ward, R. A. Barker

THE Juniper Prospect is in Carleton County, N. B., at approximately 46º 31&apos; north latitude, 67º 20&apos; west longitude. During the summer of 1955 an area in west-central New Brunswick was selected for aerial electromagnetic prospecting with American Metal Co.&apos;s helicopter-mounted equipment. Generalized, small-scale government geologic maps had suggested that this area was located along the western border of the northeast-trending granitic backbone of northwestern New Brunswick and might be underlain by the Ordovician-Silurian sediments and volcanics that are the host rocks for the recently discovered sulfide deposits of the Bathurst-Newcastle district.

Jan 1, 1958

By Walter Riethmeier, Arthur J. Lynch

The future of plant design in mineral processing and extractive metallurgy is discussed in relation to present trends and the future need to build plants that will treat larger tonnages and lower grades of ore. The future equipment and plant design of crushing, grinding, screening, classification, flotation, magnetic concentration, gravity concentration, hydrometallurgy, thickening, filtration, tailings disposal, health, safety, environment, and materials of construction are discussed. Future plants are expected to follow upon present evolutionary trends. The impact of escalation, energy costs, and increased regulation of the industry is foreseen as a major influence on plant design.

Jan 1, 1978

By Lynn B. Hales

The software systems which support the Pinto Valley Supervisory Control System are divided into three general categories. These are defined as the real-time operating system; a process data acquisition, reduction, and communication system; and a set of process-oriented systems which interface the operators and engineering staff to the process. The role of each of these three classes is reviewed. The software systems which provide reports, status displays, and trend graphs are discussed.

Jan 1, 1978

By Chi-shing Wang

The late Professor P. B. Bucky of Columbia University introduced the principles and techniques of barodynamic experimentation in early 1931 by the application of centrifugal loading to achieve dynamic similitude between models and prototypes of mine structures.1 Later, he and his associates introduced the combined experimental technique of photo- elasticity and the centrifuge to determine the stress distribution in civil engineering structures and mine workings by the use of transparent bakelite models.2,3 The photostress technique, also known as the birefringent-coating method of photoelastic stress analysis, dates back to 1930, when Mesnager published its principles.4 Since then it has been widely applied to experimental stress analyses in many industries. A practical method of observing the dynamic behavior of opaque mine models, which are made of prototype materials, by means of a combination of the centrifugal and the photostress techniques is a new experimental approach under development at the Henry Krumb School of Mines, Columbia University.5 This paper summarizes the development of the barodynamic photostress technique and presents the information obtained from a recent series of experiments in the study of the behavior of rock beams loaded by their own weight. THEORETICAL BACKGROUND Theory of Pure Bending In the general theory of strength of materials, the flexure stress at any point in a beam of any type of cross section which has a longitudinal

Jan 1, 1968

By W. E. Hess

At the Vesta mines of Jones & Laughlin Steel Corp. on the Monongahela River, 35 miles south of Pittsburgh, JCM Joy continuous miners and 6-SC shuttle cars are used for pillar extraction in the Pittsburgh seam. The entire output of the mine goes into coke production for blast furnace operation. Because this coal, which has high metallurgical qualities, is close to the place where it is ultimately used and because supplies with these properties are being rapidly depleted, complete recovery is essential wherever possible. With the introduction of the continuous miner into the Vesta mines, therefore, it was necessary to plan a project which would facilitate development and provide for future total recovery. Use of continuous miners under varying conditions has necessitated changes with regard to roof action, method of development, method of pillar attack, and innovations in mining. In the following pages these changes will be discussed.

Jan 2, 1955