Search Documents

By John J. Schanz

INTRODUCTION The two prior Seeley W. Mudd books on mineral economics devoted their final chapters to themes having to do with the future. In 1932, the last chapter in Mineral Economics8 was "The Future Value of Mineral Property" by J. R. Finlay. Both the first edition (1959) of Economics of the Mineral Industries7 and the slightly revised second edition (1964) closed with "Minerals and Man's Future" by Zay Jeffries. We are not inclined in this third AIME volume on mineral economics to ignore the tradition of the prior volumes. Moreover, it always is fitting and proper to close a book about the mineral industries by examining in a rather general way the challenges and uncertainties that are perpetually strewn in our path as we pick our way into the future. Unlike its predecessor volumes, which were written to acquaint the nonspecialist with the economic characteristics of mineral resources and to provide data about the mineral industries, this edition was also designed with the mineral economics student and practicing specialist in mind. Thus it is anticipated that it will be both a reference as well as suitable for use as a textbook. Consequently, this closing examination of our changing perspectives about mineral resources devotes some space to the past events and current status of mineral economics as a field of study. The fears and forecasts of the past can be a perceptive and usually deflating way to begin an examination of the future. As we look up and down the track of time from the 1975 platform, we find that many of the past views of the future were transient in character, others were imperfect in their prognosis, while others were based on fears that now seemed unfounded. But down through the years some of the observations or expressions of concern have a persistency which perhaps reflects some elemental characteristics of mineral resources. On these "truths" rest our contemporary understanding of the economics of the mineral industries. The uncertainties and priorities for the next 25 or more years, not surprisingly, have a somewhat different mix than those that seemed most compelling to our predecessors in 1932 or 1959. So it is appropriate that we review how the perspective of the mineral economist has changed over the span of a half century. In light of the particular interest of AIME on the role technology must play, it is fitting that we close with some observations on that topic. THE EMERGENCE OF MINERAL ECONOMICS AS A FIELD OF STUDY The publication of Mineral Economics by the AIME in 1932 as a Seeley W. Mudd volume marked the end of emerging interest in

Jan 1, 1976

By A. S. Yue

The interface morphology of the Mg-32 wt pct A1 eutectic has been studied in terms of the freezing rate, the temperature gradient, and the impurity content. For the impure eutectic it has been found that for a given temperature gradient a fast freezing rate favors the formation of a cellular intwface with sub-grain strucfure. This cellular interface can be changed to a planar interface of the same substructure either by decreasing the freezing rate or by increasing the temperature gradient. For the eutectic of highest purity, as purified by zme-refining, no cellular interface was found for any growth condition and only a planar interface with subgrain structure was observed. Furthermore, a layer of liquid adhering to the interface during de-cantation freezes with shapes and sizes of the phase particles different from those in the main eutectic solid. WHEN a molten metal or a binary eutectic liquid with zero freezing range is solidified unidirec-tionally, a cellular interface is usually formed-3 This interface is schematically represented by Fig. 1. The profile of the solid-liquid interface has a corrugated shape, as shown in Fig. l(a), while the decanted interface consists of cells, as shown in Fig. l(b). The cell boundary in a frozen eutectic is distinguishable from the cell interior by changes in particle shapes, as shown in Fig. 4. The formation of a cellular interface, according to Weart and ack,' is attributed to a layer of constitutionally supercooled" liquid generated at the advancing interface by the simultaneous rejection of an impurity by the two phases of the eutectic mixture, which then permits freezing over an appreciable temperature range. This concept has been further elaborated by Tiller, who predicts that even in the absence of an impurity the rejection of solute ahead of each lamella of the eutectic may promote the formation of a cellular interface. More recently, Chilton and Winegard, and

Jan 1, 1963

By R. T. DeHoff

Saltykov's meihod for the determination of the size distribution of spherical particles from measurements made on random plane sections is extended to particle shapes which are not equiaxed. The analysis permits the deterrrzination of the size distribution of aggregates of ellipsoidol particles provided all particles have tlze same shape. V ARIOUS solutions to the problem of the determination of the size distribution of spherical particles from measurements made on random plane sections have appeared in the literature since the original solution was first published by Scheill in 1934. Solutions have been offered utilizing measurements of the diameter1y2 or area3'4 of circular sections that result when a test plane is passed through an aggregate of spherical particles, and the length of intercept5y6 that results when a test line is passed through the aggregate. To the best of the knowledge of the author, no method has been proposed which permits the determination of the size distribution of particles that are not equiaxed. The purpose of this paper is to develop a method which permits the determination of the size distribution for a specific class of particle shapes which cover awide range of axial ratios; namely, ellipsoids of revolution. In the interests of simplicity, it is necessary to limit consideration to aggregates of particles which are all similar in shape; that is, the ellipses which, by rotation about one of their axes, generate the particles, all have the same axial ratio. The size distribution, which is to be determined by the analysis, is arbitrary. It is also assumed that the section, or sections, upon which the measurements are made represent the average of all possible sections through the structure. This ideal condition can be approached as nearly as may be desired by observing a sufficient area of sections taken at random positions in a randomly oriented aggregate, and in random positions and orientations in an aggregate that has one or more axes of orientation. SIZE DISTRIBUTION FOR PROLATE ELLIPSOIDS Consider an aggregate of cigar shaped, geometrically similar particles (prolate ellipsoids), dispersed in an opaque matrix. Let the size of each particle be specified by the length of its minor axis, By Fig. 1, and the shape, q, be defined by the ratio of its minor to its major axis, B/A. Let the index, j, refer to dimensions of ellipsoids in a particular size class, and the index, i, to dimensions of an ellipse resulting from the intersection of a test plane and a particle. The size of such a section is specified by the length of its minor axis, b. Let the particles be arbitrarily divided into k size classes, and let the increment of size between each class be A, where A = &,$, B,,,being the minor axis of the ellipsoids in the largest size class. Since all sections are represented on the test plane, the minor axis of the largest of the sections observed, results from the intersection of the test plane with an ellipsoid in the largest size class at its center, and is therefore equal to Bmax Thus the increment, A = The final result will consist of the k numbers which represent the number of particles in each size class per unit volume of aggregate:

Jan 1, 1962

The classification here used is one of convenience only; it is not intended to include all known types of ore deposits. The characteristic features of the several well-marked types of primary mineralizations are described without reference to the ultimate source of their metals. The minerals of many deposits of obscure origin were probably introduced through fissures that are now healed, or are due to the migration of metals from such deposits. [ ] It is not within the scope of this book to enter into a general discussion of the genesis of ore deposits but, in view of the progress being made in our comprehension of the conditions under which ore deposits were formed, mention should be made of recent work. J. E. Spurr's two volumes, "The Ore Magmas," are recommended as crystallizing the views of those who are inclined to ascribe the origin of most ore deposits to a differential precipitation from magmatic rock masses and to the migration and precipitation of the viscous, liquid or gaseous exhalations from those masses. He has especially emphasized the role

Jan 1, 1932

By T. A. Rickard

Among the gold-deposits discovered in recent vears none is more extraordinary in richness or interesting in structure than that of the famous mine at Mount Morgan. At a time when but few Australian mines were known to the world outside the colonies, Mount Morgan was quoted as an occurrence, unusual not only in its origin (for it was said to be dye to geyser-action) but also in the purity of its gold. The mine is situated just within the tropics, twenty-six miles southwest of Rockhampton, in central Queensland. Queensland attained in 1889 the first place among the gold-producing colonies of Australasia, a position previously always held by Victoria. In that year Queensland produced 737,822 ounces, while Victoria cape second with 614,838 ounces. Of the four chief mining districts Rockhampton stood first, as the following figures show: Quartz crushed, Yield,. Average per ton, Tons. Ounces. Oz. Dwt. Rockhampton ,....81,138 340,669 4 4 Charters Towers,.. .. 109,328 165,551 1 10 Gympie,.....106,625 112,847 1 1 Croydon,.....29,423 51,156 1 15 It should be added that Queensland has but little alluvial mining, the total output from this source in 1889 being only 5044 ounces, none of which came from the four principal gold-fields. Leaving out Rockhampton, the output of which is practically that of the Mount Morgan mine, it will be noted that the more northerly goldfields show the highest average (Gympie being furthest from and Croydon nearest to the equator). This is largely explained, however, by the increased cost of milling, due chiefly to the want of water for batteries and the consequent economical necessity of selecting high-grade material only for crushing. During the year ending November 30, 1889, the Mount Morgaq

Jan 1, 1892

By Claus G. Goetzel

Pressing of powdered metal parts is best done in the direction of the shortest extension of the piece, to avoid too great a loss of pressing force through internal iriction. As long as curved surfaces, re-cessej, or offsets occur only parallel to this shortest axis of pressure, no special difficulties arise: the cross sections, perpendicular to the pressure, do not vary, nor does the shape of the parts change during compression except for a gradually reduced thickness (Fig. IA). The problem becomes more dificult, however, when the curved surfaces or recesses are perpendicular to the shortest axis of the part (Fig. IB) Two processes for molding uniformly dense parts with complicated shapes from powdered metals are described in detail in this paper. Both can be employed successfully by those trained in the art. The first refers to curved parts; the second is especially adapted to parts having one or more recesses or steps. Both methods, as set forth here, are applied under the condition that presents the more difficult problem. For clarity, before description of the two practical methods, the variable factors in molding powdered metal parts will be reviewed, then an idealized procedure will be considered briefly. Variable Factors in Molding Powdered Metal Parts Compression Ratio Compression ratio is defined as the proportion of the final relative density of the compact to the apparent density of the powder. For iron powder of an apparent density of 3.0, for example, a compression ratio of 2 1/2:1 would be required to produce a compressed compact of 7.5 density; whereas for another iron powder having an apparent density of only 1.5, a compression ratio of 5:1 would be required to produce the same density. The lower the powder's apparent density, the greater must be the compression ratio for pressing compacts of high density.

Jan 1, 1946

By Claus G. Goetzel

Pressing of powdered metal parts is best done in the direction of the shortest extension of the piece, to avoid too great a loss of pressing force through internal iriction. As long as curved surfaces, re-cessej, or offsets occur only parallel to this shortest axis of pressure, no special difficulties arise: the cross sections, perpendicular to the pressure, do not vary, nor does the shape of the parts change during compression except for a gradually reduced thickness (Fig. IA). The problem becomes more dificult, however, when the curved surfaces or recesses are perpendicular to the shortest axis of the part (Fig. IB) Two processes for molding uniformly dense parts with complicated shapes from powdered metals are described in detail in this paper. Both can be employed successfully by those trained in the art. The first refers to curved parts; the second is especially adapted to parts having one or more recesses or steps. Both methods, as set forth here, are applied under the condition that presents the more difficult problem. For clarity, before description of the two practical methods, the variable factors in molding powdered metal parts will be reviewed, then an idealized procedure will be considered briefly. Variable Factors in Molding Powdered Metal Parts Compression Ratio Compression ratio is defined as the proportion of the final relative density of the compact to the apparent density of the powder. For iron powder of an apparent density of 3.0, for example, a compression ratio of 2 1/2:1 would be required to produce a compressed compact of 7.5 density; whereas for another iron powder having an apparent density of only 1.5, a compression ratio of 5:1 would be required to produce the same density. The lower the powder's apparent density, the greater must be the compression ratio for pressing compacts of high density.

Jan 1, 1946

By Walter Herd

Fox the past eight years No. 2 mine of the Cumberland Railway & Coal Co., Springhill, Nova Scotia-a subsidiary of the Dominion Coal Co., Ltd.-has had an unenviable reputation for bumps. As the workings extended in certain directions under a greater cover, these bumps increased in severity and it became apparent that some change in the system of extraction was necessary if the mine was to continue to operate. In September, 1924, following several fatalities resulting from bumps, the Mines Department of Nova Scotia requested from the U. S. Bureau of Mines the services of George S. Rice, Chief Mining Engineer of the Bureau, to report on the conditions then prevalent in No. 2 mine, Springhill. This request was promptly and courteously granted. Mr. Rice made a full investigation and a comprehensive and helpful report, which is embodied in the 1924 Annual Report of the Department of -Public Works and Mines, Nova Scotia. Prior to 1925, the room and pillar method was employed and in January of that year (there being a cessation of work from March to August due to labor troubles) longwall retreating on the west side, on a limited scale, and in a small section on the east side of the mine was started. The major portion of the east side was not operated on this system till August, 1926, as there was developed a considerable area ready for pillar extraction between an arbitrary boundary and a point up to which bumps of any consequence, had not been experienced. In the interval development work for longwall retreating below the 5900-ft. level was vigorously- pushed. This longwall retreating system was suggested by Mr. Rice as a possible remedy and was heartily endorsed by the company officials. This paper describes the conditions and happenings subsequent to Mr. Rice's report and more especially the results with the longwall retreating system of mining under the peculiar circumstances pertaining to mining. No. 2 Seam, Springhill, at depth, and records the 'conclusions which experience with several severe bumps under this mode of extraction would suggest. Except where necessary to make the paper intelligible as an entity any duplication of Mr. Rice's report will be avoided.

Jan 1, 1929

By F. A. Veer, W. G. Burgers, B. H. Kolster

Starting-- from Cu-Si diffusion couples a study of diffusion in the intermetallic compound Cu3Si of the Cu-Si system has been made. Mmker experiments showed copper to be the diffusing element. From the rate of growth of the Cu3Si phase diffusion coefficients were derived. The activation energy for diffusion is 18.6 kcal per mole. The couples show some interesting microscopic features, for which a tentative explanation is given. THE synthesis of dimethyldichlorosilane, (CH3)2SiC12, an important compound in the manufacture of methyl-silicones, takes place at the surface of a thin Cu3Si layer deposited on a mass of silicon particles."' By passing CH3C1 vapor at about 350°C, silicon atoms are consumed from Cu3Si in forming the volatile silane molecules, thus leaving copper atoms at the surface. It is well-known that copper acts as a poison for the above-mentioned reaction by catalyzing the dissociation of methylchloride.' However, no poisonous effect is observed, at least not before most of the silicon from the particles is converted into silane.3 This would be understandable, if either the copper atoms diffuse through the Cu3Si deposit to the underlying silicon or silicon atoms diffuse in the reverse direction to the copper, both processes resulting in the formation of new Cu3Si and so ensuring the proceeding of the reaction. In this paper experiments are described, demonstrating copper to be the diffusing element. Also a very low activation energy for the diffusion is observed. EXPERIMENTAL The silicon used contained 1 ppm Mg and 1 ppm Cu; the copper was spectroscopically pure (Fe: 2 ppm; Ag, Mg, Si: 1 ppm). The copper and silicon samples were prepared in the form of blocks of approximately 10 by 10 by 5 mm with two parallel sides by spark-machining. The blocks were ground on emery paper (grit 600), etched (copper with nitric acid, silicon with a 4:l nitric acid:hydrofluoric acid mixture), and cleaned with alcohol. As the brittleness of the silicon did not allow a welding procedure to prepare the diffusion couples, the copper and silicon blocks were pressed together in a steel clamp. The pressure exerted by the clamp brought about contact between the parts of the couple and so ensured proceeding of the diffusion. The couples were heated in a vacuum furnace (about 10"5 Torr). The temperature was stabilized within 1 pct. After a heat treatment a section parallel to the direction of diffusion was examined in the microscope and in the X-ray scanning microanalyzer. To determine whether copper or silicon is the diffusing element marker experiments were carried out using tungsten wires with a 20-p diam. EXPERIMENTAL RESULTS Figs. 1, 2, 3, and 4 give micrographs of diffusion zones of Cu/Si couples. Analysis by the electron mi-croprobe of the Cu/Si samples after a definite heat treatment revealed the existence of only one intermetallic phase as can be seen from the line scan shown in Fig. 5. From the X-ray diffraction pattern it could be deduced that this phase was CU 3 Si.4 Even when diffusion zones of considerable width (up to 600 p) were obtained, no other phases occurring in the Cu-Si system could be detected, neither by the electron microprobe nor by X-ray diffraction analysis. The optical anisotropy of the Cu3Si phase made it possible to observe the columnar shape of the crystal-

Jan 1, 1969

By Raymond D. Sloan

During 1944, substantial gains were recorded in practically every phase of the petroleum industry in Oklahoma. With the spotlight of activity focused on other states during the more recent years, the production momentum that was achieved in Oklahoma through the discovery and development of such outstanding pools as Oklahoma City, Fitts. and major pools in the Seminole area during the late 1920's and early 1930's was practically spent by the end of 1943. However, with much of the industry's exploratory efforts greatly reduced in Illinois, Indiana and Kentucky, the strong demand for Mid-Continent crude and the optimism created by some discoveries in the state toward the end of 1943, Oklahoma has again become the recipient of much activity and interest, with its 1944 drilling activity, production and refinery runs to stills registering substantial gains over the preceding year. Development and Exploration Since the discovery of the West Edmond pool in April of 1943, with the substquent drilling and development boom, the scene of exploratory activity has shifted from the central. south and east portions of the state to the general trend of the . Granite Ridge, where leasillg and wild-catting were greatly activated within a wide radius of this high subsurface feature. Leasing activity, however, jumped the confines of the Granite Ridge trend and extended into all of the northwestern counties in the state. Seismograph activity at once began following and keeping pace with this shift in the leasing and exploration locale, by the concentration of a large number of seismograph crews in the area. At one time during the year,35 crews were concentrated in Oklahoma, the majority being west of the Granite Ridge and extending into the northwestern counties. To illustrate the increase in geophysical work done in the state during the year, records indicate that 377 crew months were worked in 1944, which is a 21 per cent increase over the 311.5 crew months activated in 1943. With the discovery in 1943 of several encouraging prospects and the finding of West Edmond as an incentive, drilling operations increased some 54.3 per cent, for a total of 1986 completions during the year. This is compared with a figure of 1287 for wells drilled in 1943, an increase of 699 wells. The industry, with a total of 1064 oil producers, enjoyed a success percentage of 53.6 per cent. Gas wells completed were 223, while 699 dry holes were drilled. In 1943, completions included 587 oil wells, 127 gas wells, and 573 dry holes. The number of oil producers completed during the Year was almost double the numher of wells in 1943. Of the total drilling wells completed in the state, 350, or 17.6 per cent, were wildcat operations—an increase of 5.1 per cent over the 194.3 total of 333. The wildcat success percentage was 13.4 per cent, 47 successful wells being completed for an average initial potential of 160 bbl. In the state, 23 gas wells were completed with an average initial production of

Jan 1, 1945

By E. L. Mann

Asbestos is the generic name given to a group of fibrous mineral silicates found in nature. They are all incombustible and can be separated by mechanical means into fibers of various lengths and cross sections, but each differs in chemical composition from the others. The commercial grades of asbestos consist of a spectrum of lengths and sizes and are not definitive as are most organic fibers. It is generally recognized that there are two main groups of asbestos. The first only contains the fibrous serpentine called chrysotile and comprises about 94% of the world production of asbestos. The second group contains five minerals in the amphibole series-crocidolite, amosite, anthophyllite, tremolite, and actinolite. The latter two have no commercial importance. Properties Physical The structures of asbestos fibers have been studied intensively over a number of years. X-ray diffraction patterns have been used as a means of identification and classification. Low angle X-ray scattering techniques have shown that chrysotile fibers are "hexagonally close packed" and parallel to each other, having cross-sectional diameters varying from 18Å to 300 Å units, while the amphibole fibers are many times larger in cross section, have considerably smaller surface areas, and the fibers are less symmetrical than those of chrysotile. Electron micrographs of the more common types of asbestos are shown in Figs. 1-4. Fig. 1 illustrates the softness and flexibility of chrysotile which make it suitable for textile-type products. For a number of years there was considerable controversy over the exact nature of chrysotile fiber, but the photographic evidence in Figs. 5-7 clearly show that it is tubular in structure. The curvature is the result of the mismatch in the dimensions of the silica [Si2O5] and brucite [Mg(OH)2] layers which are on the inside and outside, respectively, of a double sheet. This curvature had been predicted by Pauling (1930) years ago based on the molecular dimensions of the two component structures. In contrast to this, the structure of the amphiboles consists of two ribbon chains based on Si4O11 units separated by a band of seven cations with two hydroxyl groups attached to

Jan 1, 1983

By James O. Lewis

Gravity drainage is the self-propulsion of oil downward in the reservoir rock. Under favorable natural and operational conditions, it has been found to effect recoveries comparable to water displacement. With modern technical knowledge, the operator can often make a choice between dissolved gas drive, water drive and gravity drainage as the principal recovery agent in a reservoir. It is desirable that the opeator be able to determine which of the three agents will be most effective under each set of conditions. So far, gravity drainage has received less consideration than the other two. In this paper. an endeavor is made to set forth some of the principles of gravity drainage, to point out the types of reservoirs favorable for it, and to show how it may be applied in them. Field examples are described and discussed. Introduction Since early in the history of the oil industry, it has been recognized that gravity is one of the three important natural forces for expelling oil from the reservoir rock. As knowledge of the technology of oil recovery progressed, ideas changed with respect to the relative importance of the three forces and with respect to the manners in which they functioned. For a time, disproportionate emphasis was placed on the importance and function of gas and the need for conserving gas pressures. More recently, disproportionate emphasis has been placed on encroaching edge water. Only lately has there been evidence that the function and importance of gravity was to receive due consideration. Study of this neglected phase of oil recovery is needed to round out our knowledge of reservoir behaviors and to gain a balanced viewpoint of the interplay of forces that may operate in varying importance in reservoirs. The purpose of this paper is to discuss mainly in a qualitative way, the functions of gravity, to present some concrete instances where it has been important and to raise some questions that should be investigated further. Oil-recovery Agents The important natural agents for effecting oil recovery that may be originally available in a reservoir are gas, both dissolved in the oil and free in gas caps, encroaching edge water and gravity. Each of these agents can act in a dual capacity—physically to overcome the surface energies that hold the oil within the pores and mechanically to overcome viscous . resistance and to propel the oil through the porous reservoir rock to the wells. Advancing edge water displaces the oil from the pores and lifts it updip to structurally lower wells. Gravity drains the oil from the pores and flows it downdip to the wells. Gas displaces oil from the pores, entrains it in the gas stream and flows it to the wells, but gas in solution also affects the physical properties of the oil and thus can influence oil recovery by the other agents, whether or not the mechanical energy in the gas is utilized. Of the two functions of these agents, the more important is the ability to dis-

Jan 1, 1944

By James O. Lewis

Gravity drainage is the self-propulsion of oil downward in the reservoir rock. Under favorable natural and operational conditions, it has been found to effect recoveries comparable to water displacement. With modern technical knowledge, the operator can often make a choice between dissolved gas drive, water drive and gravity drainage as the principal recovery agent in a reservoir. It is desirable that the opeator be able to determine which of the three agents will be most effective under each set of conditions. So far, gravity drainage has received less consideration than the other two. In this paper. an endeavor is made to set forth some of the principles of gravity drainage, to point out the types of reservoirs favorable for it, and to show how it may be applied in them. Field examples are described and discussed. Introduction Since early in the history of the oil industry, it has been recognized that gravity is one of the three important natural forces for expelling oil from the reservoir rock. As knowledge of the technology of oil recovery progressed, ideas changed with respect to the relative importance of the three forces and with respect to the manners in which they functioned. For a time, disproportionate emphasis was placed on the importance and function of gas and the need for conserving gas pressures. More recently, disproportionate emphasis has been placed on encroaching edge water. Only lately has there been evidence that the function and importance of gravity was to receive due consideration. Study of this neglected phase of oil recovery is needed to round out our knowledge of reservoir behaviors and to gain a balanced viewpoint of the interplay of forces that may operate in varying importance in reservoirs. The purpose of this paper is to discuss mainly in a qualitative way, the functions of gravity, to present some concrete instances where it has been important and to raise some questions that should be investigated further. Oil-recovery Agents The important natural agents for effecting oil recovery that may be originally available in a reservoir are gas, both dissolved in the oil and free in gas caps, encroaching edge water and gravity. Each of these agents can act in a dual capacity—physically to overcome the surface energies that hold the oil within the pores and mechanically to overcome viscous . resistance and to propel the oil through the porous reservoir rock to the wells. Advancing edge water displaces the oil from the pores and lifts it updip to structurally lower wells. Gravity drains the oil from the pores and flows it downdip to the wells. Gas displaces oil from the pores, entrains it in the gas stream and flows it to the wells, but gas in solution also affects the physical properties of the oil and thus can influence oil recovery by the other agents, whether or not the mechanical energy in the gas is utilized. Of the two functions of these agents, the more important is the ability to dis-

Jan 1, 1944

Until the end of 1960, the small primary aluminum industry in Australia was run by the government. The entire operation was at Bell Bay on the north coast of Tasmania. It consisted of an alumina plant and smelter, owned jointly by the Commonwealth and the State of Tasmania. Apparent domestic demand that year was about 48,000 long tons; 11% thousand came from Bell Bay; the rest was imported. By March 1964, Australia had two fully integrated aluminum companies. The government has stepped out of the picture and the key word of the industry from bauxite to metal is "growth." Present annual capacity of the two companies for making aluminum metal totals 92,000 long tons a year. Australian demand is about 60,000 tons. By 1968 Australian consumption should be 90,000 tons and by 1970 it is expected to reach 107,000 long tons per year. Export markets for bauxite, alumina and metal are developing.

Jan 10, 1964

By L. C. Raymond

Valuations in the mineral industry differ from those of other enterprises because mines and oil wells have a definite life so cannot be considered a perpetuity. This requires that in any mineral-property evaluation the recovery of invested capital is necessary during the life of the property. Capital writeoffs for nonextractive industries are assumed to be continuously plowed back to sustain the operation and produce yields on the capital invested. The extractive or mineral industry, however, generally attempts to return to the investor both interest and principal during the life of a property. Normally this is done currently and the dividend includes both items. Where the mineral properly possesses large reserves and the life factor approximates a perpetuity, the return on investment is generally comparable to that of industrial stocks. The valuation of a mineral property, at best, is based on educated estimates and judgment factors. This is particularly true as it relates to estimating selling prices over a long term or assessing the quality of management. Also, it is possible to make various assumptions as to rapidity of working out the deposit, varying time for start-up of operations, varying earning rates, so as to obtain different results with the same basic facts. Thus it is not surprising that two engineers, irrespective of their abilities, may not agree exactly even when given the same facts, but their results should be close enough to be used in establishing a fair value for trading purposes. The valuation is no better than the source of basic data and the soundness of judgment factors. Fundamentally the basic principles of mineral valuation are similar for base metals, sulphur, oil, or any other mineral. Each mineral, however, requires an engineer to have a knowledge of such factors as its occurrence, distribution, mining and processing methods, and marketing problems in order to gather and analyze all the facts and data that have a bearing on the earning potential of the property. PRESENT VALUE OF A MINERAL PROPERTY In essence the present value of a mineral property is a sum of money in today's dollars that future earnings from the property are worth. It differs

Jan 1, 1964

By E. T. Turkdogan, P. Grieveson

Molten silver is equilibrated with silicon nitride at 1400°C in nitrogen + hydrogen gas mixtures, and from the solubility data the activity coefficient of silicon is found to be 1.76 at silicon concentrations below 1 pct. Using this value, and that available from the silicon cmbide solubility measurements, together with those derived from the phase equilibrium diagvam, the activities of silver and silicon are estimated for the entire composition range. The main feature of the activity data is that there is a pronounced positive deviation from ideality. The activity of silver in molten silver containing up to 5 pct Si was determined by Schadel, Derge, and Birchenall1 by measuring the vapor pressure of pure silver and of the alloy over a temperature range of 850º to 1050°C. They deduced from their results that there is a positive deviation from Raoult's law and that the activity coefficient of silver increases with decreasing temperature. However, as pointed out by Kubaschewski and Catterall,2 their activity coefficients are much too high, giving silver activities greater than unity. At a later date McCabe and Birchenal13 showed that the previous vapor pressure data on silver4 were high by a factor of about 1.3; presumably a similar error must have occurred with the vapor pressure measurements on the Ag-Si alloys. The activities of silicon and silver calculated by tager' from the phase diagram and by Gibbs-Duhem integration, respectively, show a positive deviation from Raoult's law for silicon activity and positive and negative deviations for the silver activity. According to these computations, at infinite dilution of silicon ygi = 1.12 at 1420°C. d'Entremont and chipman6 measured the solubility of silicon carbide in molten silver at unit carbon activity; the equilibrium silicon content is found to be Nsi = 0.017 ± 0.002 atom fraction for 1420°C. Using the data of Grieveson and Alcock7 for the free energy of formation of silicon carbide from pure silicon and graphite, the activity of silicon for unit activity of carbon and of silicon carbide is asi = 0.0308 at 1420°c; therefore for the above solubility data on silver, YSi = 1.81, which is somewhat higher than that given by Hager. Use is often made of silver alloys in the measurements of activities of solutes in metals where silver has a very low solubility; in fact, Ag-Si and Ag-A1 alloys have been used in the past for such purposes. In an attempt to gain more thermodynamic data on molten Ag-Si alloys, measurements have been made in the present study on the solubility of silicon nitride in molten silver; the results on these solubilities are given in this paper together with a detailed discussion of activities of silver and silicon. SOLUBILITY OF SILICON NITRIDE The standard free energy of formation of silicon nitride is known with a reasonably high degree of accuracy. According to the measurements made by Hincke and Brantle8 and by Pehlke and Elliott,' the following are the free energy data for the standard states of solid Si3N4, liquid silicon, and Nz at 1 atm pressure:

Jan 1, 1963

By William Phillips

THE possible sources of potash salts in the United States have been considered from many points of view during the last several years, but it is only within the last two or three months that the situation has become acute. We import from Germany, the only source of large supply, more than $10,000,000 worth of potash salts annually, and this business has been badly crippled by the European war. If there was ever a time in our industrial existence when the necessity of providing for our own needs was more acute than it is now, we are not aware of it. One has only to study the price, lists of chemicals sent out by the large supply houses to see the change wrought within a very short time. Whether or no these prices are to maintain for a considerable time, no one can say; but it appears to be probable that we shall not see prices materially lower for a period of uncomfortable length, to say the least. It is not my purpose at this time to discuss the various sources of supply of potash salts that have been suggested or recommended. Some of them might afford a pleasing relief but all of them combined would not affect the situation seriously. If we are to have our own sources of potash salts, they will have to compare, in some efficient manner, with the sources upon which we have drawn during the last 20 or 30 years; i.e., they must exist-in minable quantities. It seems to me to be quite idle to speculate upon our domestic sources of potash if those sources are not of a character similar to those upon which we have so long depended. A few thousand or, perhaps,, a few hundred thousand dollars' worth of chemically derived 'potash may be produced under the stress of present conditions, but when we consider that each year demands more than $10,000,000 worth, we must look to underground sources; we must look to mines similar to the famous Stassfurt and Halle deposits. If we cannot mine potash salts, we shall have to do without them for a while.

Jan 2, 1915

By Charles S. Barrett

THIS paper is a progress report covering metallographic applications of the electron microscope that have been made during the past year at Carnegie Institute of Technology. An account is presented of the techniques that have been most satisfactory, the difficulties encountered, the resolution obtained, and the peculiarities that have been noted in the microstructures. About 12m exposures have been made during the year on the instrument, which is an RCA type B2 transmission microscope,1 and a number of these have been selected to illustrate the results obtained. Prints are also included showing the common types of falsities-to borrow a term from the biological field, the "artifacts." In brief, the paper is a record of our attempt to determine the value of the electron microscope in the study of the structure of metals and alloys. n addition to comments on techniques and the quality of photomicrographs obtainable with them, the paper discusses the nature of the etch attack on a few metals, and the possible relation between the fine structure revealed by etching and the mosaic block structure of the grains. Since numerous papers and reviews are available on the subject of imperfection in crystals, the comments here may be very brief; in fact, are restricted almost entirely to points having to do with recent theories relating the strength of metals to imperfections and to spacings of slip lines. SPECIMEN PREPARATION AND PHOTOGRAPHS Mechanical polishing by hand was used throughout this work. Precautions that must be taken in microscopy at high magnification, which have been well explained by Vilella in his book on Metallographic Technique for Steel, are likewise important with the electron microscope. This applies particularly to the need for repeated polishing and etching (each successive polish becoming less severe and each etch lighter), since the final etch should in general be no heavier than is used for oil-immersion optical microscopy and in many instances should be much lighter (compare Figs. 6a and 7a, 6d and 7b). An extremely light etch, of course, is incapable of cutting through a flowed layer of appreciable thickness. Unquestionably it would be very advantageous in each instance to compare the structures obtained by electrolytic polishing with those obtained by mechanical polishing, but difficulties with the electrolytic method have prevented this in the following collection of prints. The choice of etchant is important, of course; for example, picral proved superior to nital for tempered martensite. With the exception of Figs. Ib and IC, the replicas used were of silica, deposited up0n polystyrene and floated from the polystyrene in ethyl bromide according to polystyrene in ethyl bromide according to the method of Heidenreich and Peck.2 The samples were mounted in Bakelite, polished and etched, then the polished Bakelite

Jan 1, 1943

By William D. Klopp, Joseph R. Stephens

ThE phenomenon of high ductility associated with a phase transformation, termed super plasticity, has been reported for a number of alloy systems. Abnormally high ductility has been observed during tensile testing of cast eutectic alloys of Pb-Sn and Mg-cu.1 Brasses of Cu-37 at. pct Zn and Cu-40 at. pct Zn elongate up to 180 pct when tested near their transformation temperature.' Enhanced ductility was also observed in Cu-47 at. pct Zn tested near the order-disorder transformation temperature. The most remarkable super-plastic effect reported to date is for the eutectoid alloy A1-60 at. pct Zn, where elongations up to 1000 pct have been reported.3 underwood4 has recently summarized the conditions that normally accompany the superplastic effect which are: 1) a phase transformation or allotropic change or order-disorder transformation; 2) an externally applied stress; 3) presence of an interface between two phases; and 4) a metastable structural condition. In addition, higher ductility is observed when the specimen is tested at slow deformation rates rather than under impact. The purpose of this note is to present evidence of the superplastic effect in a Cr-30 at. pct Co alloy. In addition, low-temperature bend ductility data are given for the alloy in the quenched, metastable, single-phased condition and in the slow-cooled, two-phased, near-equilibrium condition. Sixty-gram alloy ingots were prepared by noncon-sumable arc melting of iodide chromium and electron-beam-melted cobalt. These were cast into rectangular ingots and fabricated to 0.035-in. sheet by rolling at 2300°F. Attempts to roll at slightly lower temperatures invariably resulted in severe cracking, apparently due to presence of the brittle a phase below the transformation temperature of 2230°F. Tensile specimens with a 0.25 by 1.0 in. reduced section were cut from the sheet by electrical discharge machining. The specimens were heated at 2400°F for 1/2 hr to obtain a recrystallized, bcc, single-phased structure. Temperature of the specimens was subsequently raised or lowered to the desired test temperature and held for 10 min prior to testing at a crosshead speed of 0.01 in. per min. Fig. 1 shows the chromium-rich side of the Cr-Co phase diagram.6 The alloy composition investigated is near the point of maximum solubility of cobalt in chromium, and the alloy is two-phased when in equilibrium at temperatures below 2230°F. The results of tensile tests conducted at temperatures indicated by X's in Fig. 1 are summarized in Figs. 2, 3, and 4. Tensile elongations shown in Fig. 2 increase from 11 pct at 1900°F to a maximum of 160 pct at 2250°F. The elongation then decreases to 44 pct as the test temperature is further increased to 2600°F. The proximity of the temperature of highest elongation and the solvus temperature suggests that a superplastic effect is present in Cr + 30 at. pct Co similar to that observed for other alloys that show anomalous ductility. The variation of upper yield stress with temperature is shown in Fig. 3. A small peak in yield stress occurs at 2250"F, coincident with the maximum in

Jan 1, 1967

By N. Mungan

Laboratory imbibition and displacement experiments were performed using crude oil and cores drilled with water and preserved under anaerobic conditions. The purpose of these tests was to determine reservoir rock wettability and to find out if more oil could be recovered by use of NaOH solution than by conventional waterflooding. The preserved cores were found to be oil-wet. Contrary to work in the literature, these cores changed to water-wet upon contact with air. After exposure to air for a week, the cores yielded more oil by waterflooding than when preserved under exclusion of air. At reservoir temperature of 160F, flooding the preserved cores with 0.5N NaOH solution recovered more oil than an ordinary wa-terflood, and additional oil when following a waterflood. When the caustic solution was used from the beginning, all the extra oil was obtained before breakthrough; when the caustic followed a conventional waterflood, the extra oil was produced in the form of an oil bank ahead of the injected caustic. The increase in oil recovery resulted from wettability reversal. Also, use of caustic reduced the volume of injection required to flood out the cores. At room temperature, however, the caustic solution did not reverse the wettability and gave no additional oil recovery. Cores which had become water-wet by air exposure or caustic flooding were restored to their original oil-wet state when saturated with crude oil and allowed to equcilibrate at reservoir temperature for two weeks. Therefore, in the absence of preserved cores, it may be possible to restore weathered cores to their original wettability for use in laboratory floods. INTRODUCTION Waterflooding has been in use since 1865, and is by far the simplest of secondary recovery methods. Unfortunately, most waterfloods are inefficient in recovering oil, often leaving half or more of the original oil in place un-recovered. The low oil recovery generally results from low sweep efficiency and low displacement efficiency. Consequently, to increase oil recovery by waterflooding, sweep and displacement efficiencies should be improved. Sweep efficiency is primarily affected by reservoir heterogeneities and mobility ratio, while displacement efficiency is affected by the capillary forces between fluids and rock surfaces. For petroleum reservoirs, the capillary forces are expressed in terms of interfacial tension and wettability. If oil recovery is to be improved significantly in water- flooding, the capillary forces holding the oil in the raervoir porous matrix must be reduced or eliminated. One way to reduce capillary forces is to inject commercial surfactants ahead of the injection water into the reservoir. Laboratory tests of this method have shown no promise of an economical process yet, and no increase in oil recovery was obtained in the field trials which have been reported. Work is continuing in many companies to find surface-active agents which, in workable concentrations, can yield substantial added oil recovery. Another way to change capillary forces operating in petroleum reservoirs is by changing the pH of the injected water. Wagner et al.' showed that change in the pH sometimes activates the surface-active materials natural to some crudes and brings about gross wettability change. Since pH alteration can be obtained with cheap chemicals, such as hydrochloric acid or sodium hydroxide, the process shows promise of being economical in a field application. Pan American Oil Corp. reported oil recovery by use of caustic solution from a flooded-out reservoir.' Their test, conducted at a small additional cost, yielded results which were so sufficiently favorable and encouraging that the wettability reversal flood was expanded to portions of the field not previously flooded.13 It is important to bear in mind that changes in the pH of the water not only can reverse wettability but also can lower the interfacial tension between water and crude oil. Reisberg and Doscher4 have studied the pH dependency of the interfacial tension of Venture crude using sodium hydroxide solutions of various concentrations. Their data show that the interfacial tension was lowered from 23.0 to 0.02 dynes/cm by increasing the NaOH concentration from 0.005 to 0.5 per cent by weight. Thus, the use of NaOH may lead to additional oil recovery due to both wettability reversal and lowering of interfacial tension. Whether alteration of pH results in wettability reversal from oil-wet to water-wet and increases oil recovery depends on wetting properties of the reservoir rock and the crude. This necessitates delicate laboratory experiments, with suitable core and fluid samples from a field. Although many investigators have studied wettability reversal floods in the laboratory,1,2,5,6 these studies have been carried out with synthetic porous media, refined laboratory fluids and surface-active chemicals to simulate the process. The study presented in this paper is the first time that wettability reversal by pH alteration has been accomolished in laboratory core floods using carefully preserved natural cores, live crude and with experiments performed at reservoir pressure and temperature.

Jan 1, 1967