Search Documents

By DeVerle P. Harris

Risk for most mineral investments is greater than that of average business ventures, because the physical and economic characteristics of the mineral deposit are never known with certainty. Inasmuch as the merits of a potential mineral investment cannot be fully appraised without consideration of the impact to the investor of the possible unfavorable events associated with the adoption of the project, methods of risk analysis are important in project evaluation and investment selection. The conceptual framework for risk analysis and the means by which some of the recommended practices might be implemented are examined. In addition to the normal business risk due to market forces, the physical and economic characteristics of the mineral deposit are never known with certainty, for only partial or indirect information is available, such as data from drill cores or surface and underground workings. Consequently, risk for most mineral investments is greater than that of average business ventures. Inasmuch as the merits of a potential mineral investment cannot be fully appraised without consideration of the impact to the investor of the possible unfavorable events associated with adoption of the project, methods of risk analysis are important in project evaluation and investment selection. This paper examines the conceptual framework for risk analysis and means by which might be implemented some of the recommended procedures. Utility Theory A discourse on risk and its impact upon investment selection quite often leads the reader into the concept of utility theory, for utility theory is a device constructed by economists to measure the satisfaction an individuai receives from a good; in the case of investment analysis, that good is the outcome of an investment. It briefly is reviewed here to describe the reaction of the individual to risk and as a stepping stone to other techniques more suited to risk analysis at the level of the firm. Utility theory proposes that an investor possess a utility map (curve), such as indicated in Fig. 1, which indicates the value in utiles of potential monetary rewards to an individual with some specific endowment of resources. Points on this map are obtained from the following relationship:

Jan 1, 1971

By D. J. McAdam

IN a recent survey of the literature, the author has found evidence incompatible with prevalent views regarding the technical cohesive strength and yield strength of metals. Some of the evidence regarding the technical cohesive strength was presented in a previous paper,21 and views were presented that are believed to be in better accord with the evidence. In that paper, it was shown that the technical cohesion limit (contrary to prevalent views) varies with the combination of principal stresses,† and that the influence of plastic deformation on the technical cohesive strength is not in accordance with prevalent views. In this paper, consideration will be given to both the technical cohesion limit and the yield stress as affected by the combination of principal stresses. Evidence will be presented that the variations of the yield stress and the technical cohesion limit with the combination of principal stresses are not in accordance with prevalent views. Consideration will also be given to ductility and work-hardening capacity, which depend on the initial difference between the technical cohesion limit and the yield stress. By the "technical cohesion limit" is meant the mean stress at actual or potential* fracture. An example of a technical cohesion limit is the "true" breaking stress of a tension-test specimen, the breaking load divided by the sectional area at fracture. The cohesion limit thus obtained for a ductile metal, however, has been greatly altered by the plastic deformation. It is important to consider the cohesion limit of the metal prior to this deformation, and the variation of the cohesive strength with plastic deformation. The relation between the cohesion limit and the corresponding flow stress† determines the ductility of a metal and the energy that it will absorb before fracture. In this paper, as in the previous paper,21 tensile stresses will be viewed as positive and compressive stresses as negative. The algebraically greatest principal stress will be designated S1, the least principal stress will be designated S3, and the intermediate principal stress will be designated S2. In the previous paper, attention was confined to stress combinations with two of the principal stresses equal (with the intermediate principal stress S2 equal either to S3 or S1). In this paper, consideration will also be given to the effect of stress combinations with all three principal stresses unequal. In the earlier sections of the paper (pp. 1 to 14), attention will be confined to stress combinations with

Jan 1, 1942

By W. C. Elmore

THE magnetic powder method, long used for roughly mapping mag-netic fields, has recently been refined 1,2 for investigating the microscopic variations in the surface magnetization of ferromagnetic crystals. Bitter2 first discovered regular powder patterns connected with the crystal structure of such specimens. Several other investigators3 have used Bitter's original technique, with slight modifications, to study the varia-tion of the patterns with variations in the magnetizing field applied parallel to the surface, and their dependence upon the state of strain, of polish and of crystal cut. All of the explanations-of these patterns on metallic ferromagnetics have been couched in general terms. In a preliminary report we have described an improvement in the powder technique which led us to the discovery of a new effect throwing con-siderable light on the magnetic secondary structure of alpha iron4 and of nickel5 single crystals. We now report additional evidence confirming the existence and stability of a magnetic block secondary structure.

Jan 1, 1935

By C. A. Stickels

The preferred crystallographic orientations developed during recrystallization of polycrystalline electrolytic iron sheet, cold-rolled 90 pct, were ivestigated. Recrystallization at 500° or 565° C for relatively short limes produces a texture which is similar to the rolling texture. A duplex partial fiber texture, significantly different from the rolling texture, is found when the annealing time is increased. Recrystallization at 700°C also produces a sequence of textures with increasing annealing time. In order of their appearance, these textures are: 1) the duplex partial fiber texture found at lower temperatures, 2) a four-component texture "near {322}(296)", 3) a {112)(110) +(111)(110) texture, and 4) a two-component "near {554)(225)" texture. Secondary recrystallization, or discontinuous grain growth, accompanies the development of the latter texture. However, the "near {554} (225)" texture was nol observed when secondary recrystallization occurred under other conditions. All of the ideal orientations found in recrystallization textures can be accounted for by the growth of minor components of the deformation texture. IN recent years there has been increased interest in improving the drawability of metals by controlling the preferred crystallographic orientation of the sheet.1-l3 Since more low-carbon steel is drawn than any other material, considerable attention has been focused on the properties of sheet steel. Efforts to improve drawability through texture control have been hampered by the lack of any published systematic study of the recrystallization textures developed in iron annealed below Acl. The purpose of the present work was to supply some of this missing information, specifically, the recrystallization textures obtained by isothermal anneals of polycrystalline iron, cold-rolled 90 pct. LITERATURE REVIEW—DEFORMATION TEXTURES Barrett14 reviewed and summarized the investigations of rolling textures in iron and low-carbon steel prior to 1952. The texture of heavily deformed iron (rolled 90 pct or more) is described as consisting of two partial fiber textures. The dominant fiber texture (designated here as fiber texture A) has a (110) fiber axis in the rolling direction and includes the orientations (001)[110], {112}( 110), and {111}(110). The secondary texture (designated here as fiber texture B) is described as having a (111) fiber axis in the sheet normal direction, and includes the orientations {111)( 110) and (111)(112). Since the publication of Barrett's book, there have been two detailed studies of the deformation texture in polycrystalline iron. In both instances, the more sensitive diffractometer methods of pole-figure determination were used. Bennewitz15 studied the cold-rolling textures developed in polycrystalline low-carbon steel and a 3 pct Si steel. He determined (110), (2OO), and (222) pole figures for specimens reduced 30, 50, 60, and 90 pct and analyzed his results in terms of partial fiber textures. He distinguished three stages in the development of the final deformation texture. 1) Grains rotate to form two incomplete fiber textures, with (110) fiber axes inclined 30 deg to the sheet normal toward the rolling direction (fiber texture B). After 50 pct reduction, the highest density of poles is near an ideal orientation {554}(225), the two components of which are members of this duplex fiber texture. 2) With increasing amounts of reduction, grains rotate about the former fiber axes toward ideal orientations of the type {112)( 110) (common to fiber textures A and B). 3) Finally, grains rotate about their ( 110) axis in the rolling direction, clockwise and counterclockwise from the orientations {112}(110). This produces the range of orientations from (111)(110) to (001)(110) commonly found in the rolling texture of heavily deformed iron (fiber texture A). No significant difference was found between the deformation textures of low-carbon and silicon steels. A few years earlier, Haessner and weik16 had determined (110) pole figures for carbonyl iron rolled to 30, 60, 80, and 90 pct reduction in thickness. heir data agree quite well with the more complete data of Bennewitz, but a somewhat different description of the evolution of the deformation texture was given. The appearance of (110) poles in the transverse direction is ascribed to a (100)[011] component rather than "near {554}( 225) " components, and the (110) fiber axes of fiber texture B are described as located 35 deg rather than 30 deg from the sheet normal. Both of these studies agree that the secondary texture present in heavily rolled iron, the duplex fiber texture B, has (110) fiber axes and not a single ( 111) fiber axis normal to the sheet, as

Jan 1, 1965

By L. C. Brown, E. B. Hawbolt

The formation of grain boundary precipitates has been studied in Ag-5.64 wt pcl Al alloys at 688°C. Large-grain specinzerzs were used and the boundary misorientation measured by X-ray diffraction. At low-angle grain boundrrries Primary sideplates form. u)hile abore a 17-deg misorientation lenticular precipitates predominate. Growth of the lenticular precipitates was studied on individual grain boundaries using a statistical technique. The thickening and lengthening rates appeared to be independent of &apos;pain boundary misorientation, indicating that grain boundary diffusion was not significant in this system. The precipitates grew urith constant shape, with both the length and thickness increasing parabolically with time. The parabolic lengthening rates were unexpected since previous theory and experimerztal results had indicated linear growth. By approximating the shape of the precipitate to that of an oblate spheroid grouling with constant shape an equivalent diffusion coefficienl was calculated. The zlalue obtained was in good agreement with nleasurements obtained fron, diffusiorz couples. IF a single-phase alloy is heated or cooled to a temperature such that the phase becomes supersaturated, there is a tendency for a second phase to precipitate from it in order to remove the supersaturation. Precipitation takes place initially on grain boundaries due to preferred heterogeneous nucleation, but subsequently Widmans kitten plates may form in the grain interiors if the grain size and supersaturation are sufficient. The type of grain boundary precipitate formed depends on the nature of the boundary. Aaronson1 and clark2 have shown that grain boundary misorientation can be characterized by the simple parameter R, where and X, Y, and Z represent the minimum rotations about three orthogonal axes required to bring the two lattices forming the grain boundary into coincidence. The maximum value for R is 60 deg. In using this parameter the orientation of the grain boundary itself is, of course, neglected. However it was found in both Fe-si3 and A1-Ag2 that the precipitate shape depended only on the parameter R. Clark found that the vast majority of precipitates formed were allo-triomorphs— lens-shaped precipitates that grew along the grain boundaries. At low-angle boundaries, however, (R < 15 deg) Widmanstatten sideplates nucleated at the grain boundaries and grew into the adjacent grains. It has been reported that the rate of growth of grain boundary precipitates is controlled by diffusion within the supersaturated phase.&apos; The theories which have been developed for growth rates have assumed the diffusion coefficient constant over the composition range of the supersaturated phase. This is a fairly good approximation if the composition range involved is not large. Thickening rates have been calculated using the theory developed by Zener4 and by Frank5 for the growth of planar precipitates. A parabolic growth law

Jan 1, 1968

By L. W. McKeehan

Jan 1, 1934

By G. R. Fitterer

By means of the C-Sic thermocouple1, liquid metal temperatures have been found to vary much more than was previously supposed, and fortunately these variations can be directly associated with some of our former knowledge which combined to form the "art" of liquid-metal manipulation. Commercial Development of This Device Several types of installations are operating in different plants. There are so many variables in steel plants in regard to operation, procedure, arrangement of pouring platforms, ladles, etc., that most of the installations now in service in this country are "tailor-made"; nevertheless, it is felt that satisfactory gains have been made, inasmuch as each installation has indicated some effect of temperature upon the metallurgical operation, and has pointed the way toward technical and financial benefits. In most cases, it has been necessary to accumulate the temperature data until sufficient metallurgical information is available for the drawing of conclusions. When mechanical difficulties have been eliminated, a distinct correlation of these factors has been obtained. The installations now in service are used for the determination of temperatures in the basic open-hearth furnace prior to tapping and in ladles from both acid and basic furnaces prior to pouring. Some of the installations are in shops making the higher priced steels; others are in "tonnage shops." The errors of human element, smoke screens and emissivity corrections connected with the use of the optical pyrometer do not affect the C-SiC thermocouple readings. The accuracy of the C-Sic thermocouple and the temperatures measured are discussed later in this paper. Temperature Variations or Liquid Pig Iron One well-known discussion between the blast-furnace and open-hearth (or Bessemer) departments has occurred intermittently for more

Jan 1, 1936

By G. R. Fitterer

By means of the C-Sic thermocouple1, liquid metal temperatures have been found to vary much more than was previously supposed, and fortunately these variations can be directly associated with some of our former knowledge which combined to form the "art" of liquid-metal manipulation. Commercial Development of This Device Several types of installations are operating in different plants. There are so many variables in steel plants in regard to operation, procedure, arrangement of pouring platforms, ladles, etc., that most of the installations now in service in this country are "tailor-made"; nevertheless, it is felt that satisfactory gains have been made, inasmuch as each installation has indicated some effect of temperature upon the metallurgical operation, and has pointed the way toward technical and financial benefits. In most cases, it has been necessary to accumulate the temperature data until sufficient metallurgical information is available for the drawing of conclusions. When mechanical difficulties have been eliminated, a distinct correlation of these factors has been obtained. The installations now in service are used for the determination of temperatures in the basic open-hearth furnace prior to tapping and in ladles from both acid and basic furnaces prior to pouring. Some of the installations are in shops making the higher priced steels; others are in "tonnage shops." The errors of human element, smoke screens and emissivity corrections connected with the use of the optical pyrometer do not affect the C-SiC thermocouple readings. The accuracy of the C-Sic thermocouple and the temperatures measured are discussed later in this paper. Temperature Variations or Liquid Pig Iron One well-known discussion between the blast-furnace and open-hearth (or Bessemer) departments has occurred intermittently for more

Jan 1, 1936

By Earl Hunner

IT is common knowledge that the iron orebodies of the Mesabi range lie nearly horizontal and are of trough or blanket-like types. These orebodies are from a few feet to several hundred feet thick and vary from a few acres in extent to the size of the largest one, at Hibbing, Minn., which is over 1 mile wide and 3 miles long. They are covered with sand, boulder and clay overburden and occasionally, shallow depths of ledge material, varying in total depth from about 20 to 200 ft. Large areas are not capped with overlying ledge material; the top of the ore lies directly underneath the surface material. Because of the comparatively great tonnage of ore, open-pit mining has made tremendous strides since the first open-pit ore was shipped from this range by the Merritt brothers, from the Mountain iron mine in October, 1892, and along with the great development of open-pit mining on the Mesabi range has gone a tremendous change in the character of equipment used.

Jan 1, 1930

By Arthur F. Taggart

The major portion of the work described in this paper was performed by R. W. Young, † a graduate student in the department of Mining and Metallurgy, Sheffield Scientific School, Yale University, working under a cooperative agreement between the Hardinge Conical Mill Co., the Sheffield Scientific School, and himself. Since this cooperative scheme is at present in effect in the case of a considerable number of other students in the department and since it is the hope of the school that the privilege thus extended may be utilized even more freely in the future by mining and manufacturing companies, it may not be amiss at this point to give a summary of the general plan. Briefly it is as follows: A graduate student, whose undergraduate work in this or other universities shows promise of ability to handle research work, is chosen by conference between the company and instructor involved. The aim of the company in the agreement then entered into is to obtain the solution of one or more of the technical problems with which it may be confronted, or, at the end of 1 or 2 years, to obtain as an employee a man especially trained in its work. As a means to accomplish one or both of these ends, the company furnishes the machine, apparatus, or material to be tested and pays the student during his graduate work a small salary, usually just sufficient to cover his living expenses, tuition and fees. The aim of the student is special training along a line in which he is particularly interested, the attainment of his advanced degree, and the chance to show to his future employer ability to handle such problems as may be presented to him. In return for the financial aid which he receives he agrees to devote at least half of his working time to the special problem submitted by his company. The other half is devoted to study of the collateral subjects required by the department for the granting of the degree which the student seeks. The student further agrees to enter the employ of the company in question at a wage not greater than that paid in like positions to recent graduates not specially trained and to remain with his employer at such wage for at east 1 year. If the student is to obtain a degree, the special work forming the basis of his investigation must be such as will involve real research and not mere routine manipulation. The subject is chosen by conference between the three parties to the agreement. The work is carried on under the direct supervision of the instructor involved. The school furnishes the general laboratory and library equipment essential to the pursuit of any extended investigation. In

Jan 1, 1918

By C. M. Tucker, K. R. Van Horn, W. P. Sykes

Recent investigations of the molybdenum-carbon alloys have been reported by Becker and Ebertl,‡ Westgren and Phragmén2, T. Takei3, and H. Tutiya4. Takei3 studied the Mo-C system by employing metal-lographic and X-ray methods, and the other publications described the determination of the crystal structure of the molybdenum carbides. In exploring this system by a technique previously applied to the tungsten-carbon series5, the results of Takei were confirmed with two definite exceptions; i.e., first the composition of the eutectic, and second the nature of the carbon-rich intermediate phase. Consequently, a more thorough examination of the molybdenum-carbon constitution was initiated in an effort to correlate the data supplied by the microstructures, diffraction patterns and chemical analyses. Metallographic Investigation A briquette of molybdenum powder when heated in a carburizing atmosphere at 1500" to 1600" C. for several hours develops the carbon-rich layer shown in Fig. 1. The carburization was accomplished by placing the briquette in a carbon tube, which was heated in the hydrogen atmosphere of an alundum muffle wound with tungsten resistor. While the macrostructure indicates two distinct shells, and suggests the possibility of two carbon-rich phases, no evidence of this condition could be detected by the microscope, which revealed but one high-carbon constituent. This carbide forms next to the molybdenum as a relatively dense, light-colored zone (Fig. 2) which passes abruptly into an outer layer of spongy texture. As will be noted later, only one intermediate phase was observed in the X-ray photograms prepared of different locations in the carburized zone. The metallographic structure at the inner border of the shell, reproduced in Fig. 3, shows a marked porosity accom-

Jan 1, 1935

By C. M. Tucker, K. R. Van Horn, W. P. Sykes

Recent investigations of the molybdenum-carbon alloys have been reported by Becker and Ebertl,‡ Westgren and Phragmén2, T. Takei3, and H. Tutiya4. Takei3 studied the Mo-C system by employing metal-lographic and X-ray methods, and the other publications described the determination of the crystal structure of the molybdenum carbides. In exploring this system by a technique previously applied to the tungsten-carbon series5, the results of Takei were confirmed with two definite exceptions; i.e., first the composition of the eutectic, and second the nature of the carbon-rich intermediate phase. Consequently, a more thorough examination of the molybdenum-carbon constitution was initiated in an effort to correlate the data supplied by the microstructures, diffraction patterns and chemical analyses. Metallographic Investigation A briquette of molybdenum powder when heated in a carburizing atmosphere at 1500" to 1600" C. for several hours develops the carbon-rich layer shown in Fig. 1. The carburization was accomplished by placing the briquette in a carbon tube, which was heated in the hydrogen atmosphere of an alundum muffle wound with tungsten resistor. While the macrostructure indicates two distinct shells, and suggests the possibility of two carbon-rich phases, no evidence of this condition could be detected by the microscope, which revealed but one high-carbon constituent. This carbide forms next to the molybdenum as a relatively dense, light-colored zone (Fig. 2) which passes abruptly into an outer layer of spongy texture. As will be noted later, only one intermediate phase was observed in the X-ray photograms prepared of different locations in the carburized zone. The metallographic structure at the inner border of the shell, reproduced in Fig. 3, shows a marked porosity accom-

Jan 1, 1935

By Arthur West

IT is the purpose of this paper to describe briefly some recent large power stations for blast furnaces, where the blast is exclusively supplied by gas engines using furnace gas. The stations are given in the chronological order in which they were designed, in order to indicate the various improvements suggested by experience. Fig. 1 shows the blowing-engine station of the Bethlehem Steel Co. at Bethlehem. Although the picture shows only five blowing engines, the house now contains 11 engines. In the diagrammatic. plan the arrow shows the position and direction of camera. This station handles five modern blast furnaces of 450 to 500 tons capacity each. In this, as in all the other stations described in this paper, each furnace is blown by-two single tandem gas engines. Ten engines are thus required for five furnaces, leaving one single tandem spare engine. This spare capacity has been shown by several years&apos; experience at Bethlehem to be adequate to insure continuous operation. The engines in the Bethlehem station are right hand and left hand, arranged in pairs. The outboard bearings of each pair are close together so that there is not room for passageway between them. On the right of the picture are shown the inclined drums communicating with the cold-blast lines outside of building, so that any engine may be operated on any furnace. The illustration shows four cold-blast gate valves with pipes passing through wall, but since the photograph was taken the drums have been extended to take care of a fifth valve for a fifth furnace. At the extreme back of the picture can be seen the tubs of three twin vertical-horizontal Southwark steam blowing engines, which, although of modern design and as good as new, are not operated because of the greatly reduced blowing cost shown by the gas blowing engines.

Jan 6, 1915

By Dale A. Vaughan, Oliver M. Stewart, Charles M. Schwartz

Solid-solubility limits at 1500°, l000q and 500°C for carbon, nitrogen, and oxygen in high-purity tantalum were determined by X-ray lattice-parameter methods. For carbon, the solubility was found to be 0.17 at. pct at 1500°C, and less than 0.07 at. pct at 1000°C. A nitrogen solubility of 3.70 at. pct at 1500° C decreases linearly with temperature to 2.75 at. pct at 1000°C, and 1.8 at. pct at 500°C. In the case of oxygen, the solubility was found to be 3.65 at. pct at 1500°C, 2.95 at. pct at 1000°C, and 2.5 at. pct at 500°C. The phases Ta2C, the low-temperature modification of Ta205, and Ta,N of unknown composition but which has a superlattice structure based upon the original bcc tantalum lattice have been identified as the initial precipitates in the respective systems. Metallographic methods were employed to verify the X-ray analyses. The etching behavior of Ta is discussed in terms of lattice i?rzperfections and precipitate phases. The excellent fabricability, high melting point, and nuclear properties of tantalum are responsible for interest in this refractory metal. Data on the solid solubility of the interstitial elements (oxygen, nitrogen, and carbon) in tantalum and on the precipitate phases are somewhat limited. The significant contributions are discussed below. Because the purity of electron-beam melted tantalum (only recently available) is considerably higher than that used in previous studies, the present investigation was initiated. Gebhardt et all-3 have investigated the tantalum-oxygen and tantalum-nitrogen systems with particular reference to the changes in physical properties and to the rates of reaction between these gases and the metal. The solubility of oxygen in tantalum was reported2 to be 3.7 at. pet at 1500°, 2.3 at. pet at 100O°C, and 1.4 at. pct at 750°C. Schonberg4 reported that several oxide phases (Ta40, Ta,O, TaO and Ta,05) exist while X-ray studies by Gebhardtl showed only two oxides, Ta,05 and an unidentified phase which was associated with a platelet-type precipitate. La-gergren and Magneli,&apos; however, questioned the existence of compounds other than the two allotropic modifications of Ta,05 for the tantalum-oxygen system. In the case of nitrogen, the solubility was estab- lished by Gebhardt3 to be of the order of 7 at. pct at 1800°c. The solubility was reported to decrease rapidly with temperature, and, although no limits were established, a precipitate phase was observed by Gebhardt except when the high-nitrogen specimens were cooled very rapidly from the reaction temperature of 1800c. He reported the initial precipitate phase to be a tetragonal distortion of the bcc tantalum lattice while Schonberg6 reported the phase lowest in nitrogen Jo be a cubic super-lattice with a cell size of 10.11 A. Two other nitride phases, Ta,N and TaN, were reported; these appear to be isomor-phous with the carbides of tantalum. The tantalum-carbon system was investigated by Ellinger7 and by Lesser and Braurer. Two compounds, Ta,C and TaC, were reported to exist, each with a range of composition. The solubility of carbon in tantalum was found to be practically nil at all temperatures. Thus, of the interstitial elements which are present in small amounts in high-purity tantalum, carbon might be expected to form precipitates. The present investigation was initiated to obtain additional data on the solid-solubility limits of these interstitials at 1500°, 1000°, and 500&apos; with particular emphasis on the distribution and the identification of the precipitate phases. EXPERIMENTAL WORK AND RESULTS In the present investigations of the solid solubility and of the precipitate phases in the systems tantalum-nitrogen, -oxygen, and -carbon, high-purity tantalum was reacted with high-purity gases, homogenized at 1800°c, and annealed at and quenched from 1500°, 1000,

Jan 1, 1962

By U. F. Kocks

The flow stress in some latent slip systems of aluminum and silver crystals after various deformations in single slip was investigated by transverse compression and supplemented by experiments on overshoot of the compression axis and the stability of corner orientations. Work hardening was found to be remarkably isotropic, the ratio of the flow stress in the latent system to that in the primary system being between 1.0 and 1.3. The strain-rate dependence was not significantly larger in the latent system. This low anisotropy suggests that specific dislocation interactions are not the direct cause of work hardening. Either the obstacles are essentially impenetrable so that only their distance enters, or a fairly random distribution of dislocations of all systems is. in fact. formed during single slip. The latter seems to he excluded by the observations on the strain-mte dependence and on the amount of secondary strain. The amount of seconzdary strains occurring in single slip was determined by shape-change mensurements and by a new method connected with the latent-hardening experiments. It is definitely less than 1/300 times the strain in the primary svstem. WORK hardening is due to dislocation interactions; this is a hypothesis, and possibly the only one, on which all present work-harden ing theories agree. About a dozen specific interactions have been considered, and it is unlikely that any essential one has been missed. Different work-hardening theories differ to a large extent in the specific interactions which are deemed most important. The presence or absence of any particular interaction, and its degree, depend on the geometrical relationships between the two dislocations interacting. Let us enumerate some examples. Two dislocations may react, with a varying reaction energy, to form a third dislocation, and this reaction product may be sessile or glissile. Two dislocations may intersect and a jog may be formed on both, on one of them, or on neither; this jog may be sessile17Z or glissile and it may, if moved nonconservatively, lead to the production of vacancies or interstitials. Finally, a dislocation may bypass another one and thus interact only with its stress field. All these interactions depend on the specific relation between the Burgers vectors and line directions of the two dislocations. Any dislocation generated during plastic deformation of fcc crystals belongs to one of twelve slip systems. Taking any one dislocation, its relationship to each of the other eleven can fall, by symmetry, into one of only five classes. These relationships are enumerated in Fig. 1 and Table I. Each slip system is represented in the stereo-graphic projection by two triangles, namely those in one of which the specimen axis would have to lie if the specimen were to deform in single slip on this slip system in a given sense, in a tension test. Let us represent the primary slip system by the shaded triangles. The other slip systems are classified only with respect to their relationship to this primary system. The code letters (initials of established names* in German) are explained in Table I. Three specific interactions are also listed in cases where they may be strong: the product of a reaction, the formation of jogs in either system, and the elastic bypass stress. The last column relates to the types of experiments reported in this paper and summarizes their results. To decide experimentally between the relative importance of the various interactions one would like to produce a group of dislocations in one slip system and then measure the stress necessary to force another group of dislocations of a specific second system through them. Hopefully, one can produce the first set of dislocations by plastically deforming the specimen in single slip. Then one can try to achieve single slip in a specific, previously latent system and measure its flow stress. If it is different from the virgin flow stress, there has been "latent hardening". Some types of latent-hardening experiments will be discussed in the next section. The strain-rate and temperature dependence of the flow stress is an indication of the importance of dislocation intersections. By extending an investigation of this dependence to the latent systems, one can determine how much more important forest contributions are here. seeger3 has used the as-

Jan 1, 1964

By John C. Martin

The discovery of a new gas reservoir demands that the planning of a sottnd well-spacing program be initiated early in the development stage. It is the purpose of this discussion to illustrate by actual field examples the application of basic well-spacing principles, previously developed for oil reservoirs, to the problem of well spacing in natural gas fields. These studies are presented for the field use of geologists and engineers who are concerned with the initial planning of the proper development of the newly discovered gas reservoir. INTRODUCTION The phenomenal growth of a vigorous natural gas industry emphasizes the increasing importance of natural gas as a source of energy, fuel, and raw materials to our nation&apos;s economy. Since 1945 marketed production of natural gas for the U. S. has increased 21/2 times to a record high of 10.6 trillion cu ft during 1957. As major participants in the gas industry, we share an added interest to develop and produce our natural gas reserves with constantly improved efficiency. The subject of well spacing is vitally important to the gas industry, for the well itself plays a significant role in the development of the natural gas reservoir and in control of the recovery process. Maximum utilization of wells is an integral part of sound conservation practices. The discovery of a new gas reservoir demands that careful choice of well location and well spacing be made and that the planning of a sound well spacing program be initiated early an the development stage. With the drilling of the first development well, efforts of the geologist and engineer must be directed toward acquisition of adequate technical evidence upon which a firm recommendation for a spacing program may be based. With this technical appraisal as a foundation, operators and state regulatory agencies jointly can go far in providing a framework for sound development of gas fields to achieve a program of conservation that avoids the unnecessary well. WELL-SPACING CONCEPTS Through laboratory and field investigations of the mechanism of the recovery of oil and gas, of fluid behavior, and of effective control of reservoir and well, a crystallization of ideas regarding reservoir behavior has emerged as a well-developed technology. Associated with a better understanding of the fundamental principles underlying reservoir and well behavior has been the growth of concepts concerning the role of wells and their spacing in the development and operation of an oil or gas reservoir. In addition to serving as outlets for the withdrawal of fluids from the reservoir, wells are recognized as having two other important functions: (1) providing access to the reservoir to obtain information concerning the characteristics of the reservoir and its fluids, and (2) serving as a means by which the natural or induced recovery mechanism may be effectively controlled. Beyond a minimum number of wells required to fulfill these two functions, additional wells will not increase recovery. With particular emphasis upon well spacing in oil reservoirs, many studies of the well spacing-recovery relationship have evolved the concept that the ultimate oil recovery is essentially independent of the well spacing.&apos; These fundamental concepts are no different when regarding the role of wells and their spacing in the natural gas reservoir. They are equally applicable to the consideration of well spacing in gas reservoirs. For the gas reservoir, the problem of well spacing then revolves around the question of drainage and the degree or extent to which a well may drain gas from its surrounding reservoir environment. Theoretical and Experimental Work During the past 30 years, theoretical and experimental work carried on to study the physical principles involved in the flow of fluids through porous media has shed light upon the matter of drainage. Fundamental mathematical equations have been derived to describe the mechanism of flow of oil and gas through porous rocks. With the recent advent of high-speed digital computers, attempts have been made with mounting success to develop solutions, employing numerical techniques, to mathematical expressions that describe more rigorously the physical behavior and mechanism involved in the unsteady-state flow of compressible fluids, such as a gas, through porous rock. In 1953, Bruce, Peace-man, Rachford and Ricez published a stable numerical procedure for solving the equation for production of gas at constant rate. The results of these calculations are significant with respect to this matter of drainage, for they indicated (1) that depletion of the gas reservoir resulted in a drop in pressure at the extremity of the

By John L. Burns

The object of this chapter is to present data concerning the effect of the introduction of relatively slight amounts of carbon and nitrogen into supersaturated solution in iron. The study is confined to the alpha temperature range of both the Fe-C and Fe-N systems. The age-hardening characteristics of these two systems are considered. These data are compared to those of other age-hardening alloy systems and a "classification" is essayed. A.—Relation of Lattice Parameter and Electrical Conductivity to Changes in Physical Properties Due to Aging of Fe-C Alloys Since Whiteleyl in 1927 showed that some of the iron carbide that is normally present in slowly cooled low carbon-iron alloys disappears on rapid cooling from just below the A, point, interest has been manifested in the possibilities of age-hardening in these alloys. Masing and Koch,~ and at the same time and independently, W. Koster,~ proved these alloys to be age-hardenable. A. A. Bates4 a little later also published an interesting paper on changes in physical properties due to the aging of low-carbon steels. Many other papers have appeared showing changes in physical properties in specific instances due to this same phenomenon.

Jan 1, 1934

By Y. A. Topkaya

The placer gold occurrences at Sart Çayl, Manisa, Turkey, the legendary River Pactolus of King Croessus, were evaluated in this study to determine if this deposit contains sufficient recoverable value to justify development and exploitation. The gold occurs both in the upper Neogene conglomerates and the alluvium derived from these conglomerates. The total reserve in the whole region is estimated to be 500 million cubic metres. Samples were taken of the upper conglomerate and in the alluvium in an attempt to determine the amount and the physical nature of the gold. The gold in samples was recovered by screening out barren oversize followed by washing the sand and gravel through riffled sluices. The resulting sluice concentrate was later panned and amalgamated at site. Laboratory cyanidation testing of some samples for control purposes was also done. The average calculated free gold was found to be about 90-100mg/m3 and the size of gold flakes found was quite small. The field as well as laboratory testing of the samples of Sart Çay1 indicated that the potential reserves in this region could only be developed as a sand and gravel operation and the gold could be recovered together with the heavy minerals as a byproduct.

Jan 1, 1984

Jan 4, 1950

By Kenneth K. Humphreys

INTRODUCTION What is automation? Why automate? Webster&apos;s New Collegiate Dictionary defines automation as "the automatically controlled operation of an apparatus, process or system by mechanical or electronic devices that take the place of human organs of observation, effort, and decision." This definition gives an implied answer to the second question, )"Why automate?" Automation, automatic control devices and process control equipment receive their justification in supplementing or replacing manpower, which results in decreased operating costs. In the past, processes were operated with a minimum of instruments for the purpose of merely guiding the operators. Processes were manually controlled by the operator on the basis of simple temperature, pressure, flow and level indications on a panel. Today the tendency is to design a new plant to operate in a fully automatic manner according to a preset pro- gram utilizing a minimum of manpower. In addition to this direct cost reduction savings in manual labor, increased equipment capacity results from uniformity of flow and uniform control of process variables. This control eliminates or minimizes surges and permits equipment to be operated at or near its ultimate capacity and, for a given material through- put, permits the use of smaller process equipment. Automatic control, therefore, be it in the field of coal processing or in any industrial field, is simply a problem of economics. Control equipment is justified in terms of its contribution toward increasing productivity, increasing profit margins or producing a new and saleable product at a profit. Instruments and control devices can be divided into two general groups: (1) units which measure, and (2) units which both measure and control a process variable. In coal processing, the first class of instruments, those which measure only, include analytical devices such as automatic ash, moisture and sulfur measuring units and the simple pressure, temperature, flow and level indicating devices mentioned previously. The second group of instruments, those which both measure and control, include a wide variety of units such as continuous weighing devices on conveyor belts and photoelectric cells which gauge the position of railroad cars on the track and insure that the cars are in the proper location for loading (see Chapter 15). The latter types of units as used in the coal industry differ from those used in other industries in one significant point. In coal processing these instruments need not be as highly sophisticated and accurate as in other industries; hence their cost is proportionately lower than in other industries. Because of the economic fact that coal sells for only a fraction of a cent per pound compared to dollars per pound for many chemical products, and

Jan 1, 1968