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By AIME AIME

THE report of the united. States Steel Corporation for the' year 1928 gives the, following ,figures of raw materials and' finished products . Raw materials, tons :

Jan 1, 1929

By B. H. Sage, W. N. Lacey

The growing background of experimental information concerning the volumetric and phase behavior of binary and ternary hydrocarbon systems is used as the basis for a comparison of these systems with naturally occurring hydrocarbon mixtures under conditions representative of underground petroleum reservoirs. The qualitative and semiquantitative similarities and differences between the two types of systems are considered in reference to the possibilities and limitations of using experimental data on binary and ternary systems for predicting the volumetric and phase behavior of naturally occurring hydrocarbon mixtures of low molecular weight. The possible influence on such phase behavior of water, hydrogen sulphide, nitrogen, and components of relatively high molecular weight is discussed. INTRODUCTION During the past two decades much effort has been devoted to the study of the volumetric and phase behavior of pure paraffin hydrocarbons and of binary and ternary mixtures of these compounds. Many of these studies were carried out with the direct objective of utilizing a knowledge of the detailed characteristics of binary and ternary mixtures of the lighter paraffin hydrocarbons for predicting the behavior of more complex mixtures. The ability to make such predictions with accuracy would be of great value in petroleum production and refining. Although the behavior of the methane-propane system' served at one time as a qualitative illustration of the probable characteristics of the more complex hydrocarbon mixtures found in nature, it' fell far short of requirements for quantitative predictions. The present paper endeavors to indicate the relation of the more recently accumulated information concerning the behavior of binary and ternary hydrocarbons to this problem. In discussing binary and ternary systems as examples pointing toward the behavior of multi-component systems no effort is made to present new methods of predicting the characteristics of natural hydrocarbon mixtures. Preliminary proposals have been made elsewhere for the prediction of volumetric phase equilibrium and thermodynamic data for multicomponent mixtures, utilizing as a basis the behavior of binary and ternary systems. Numerous other proposals have been made. That based upon the concept of a pseudo-critical state" has proved to be of value to the petroleum industry. Concurrently with this study of binary and ternary systems investigations have been made of natural hydrocarbon systems. Of the many publications reporting such experimental information only a few examples will be mentioned. A number of studies of black oil and natural gas have been made and much attention has been directed to extended and detailed investigations of the behavior of fluids in condensate fieldS 16,17,18,19,20. This work has been supplemented by some studies of the separation of bitumen from natural hydrocarbon liquids The over-all behavior of such systems has been used in predicting the volumetric and phase behavior of naturally occurring mixtures This background of experimental and correlated information concerning the behavior of multicomponent hydrocarbon systems also permits a direct comparison of the characteristics of binary and ternary aliphatic systems with those materials produced from underground reservoirs. PRESENTATION OF DATA The primary limitation encountered in using binary and ternary aliphatic hydrocarbon mixtures as examples of the characteristics of the fluids encountered in underground reservoirs lies in the existing lack of knowledge of the quantitative effect upon behavior of the presence of several important constituents, notably hydrocarbons of high molecular weight, water, carbon dioxide, hydrogen sulphide, and nitrogen. The presence of substantial quantities of hydrocarbons of fairly high molecular weight serves to increase the complexity of the phase behavior of natural systems. No simple systems yet studied give adequate guidance in this regard. The influence of such materials of high molecular weight was indicated earlier",?' to an extent which serves to show that definite limitations now exist in the correlation of simple and complex systems. However, significant progress is being made in filling gaps in the information. For example, similarities in the behavior of fluids in condensate fields with that of binary and ternary systems are becoming more systematically evident. A few studies of the behavior of water in paraffin hydrocarbon systems have been made Results of investigations of mixtures of carbon dioxide and the lighter hydrocarbons also are available Limited work has been reported con-

Jan 1, 1949

By E. A. Hopkin

Laboratory tests conducted by the author. together with actual field experience in Canada. have indicated the magnitudc of some of the factors affecting ability of drilling mud to clean the hole. A correlation was observed between funnel viscosity and particle slip velocity. A relationship was also observed between the Bingham yield value of the mud and the particle .slip velocity. Laburatury tests indicated little change in slip velocity with funnel viscosities up to ahout 80 sec/qt or to yield values of aboul 15 lb/100 .sq ft. The lip velocity of the partic1e.s. studied vuried from 160 ft/min with water to neerly zero for high mud viscositie. lncreasing the mud density, creating laminar annular mud flow or rotating the drill pipe Mlay also improve the carrying capacity of mud. Field tests indicated that during fast upper-hole drilling, the rate of cutting removal must he sufficien to maintain the concentration of cuttings in the annulus at less than 5 percent by volume to prevernt balled-up drill collars and .stuck drill pipe. INTRODUCTION In the Mid-Continent area, hole cleaning during rotary drilling normally involves the use of low-density drilling muds with funnel viscosities varying from 26 to 80 sec/qt. However, frequently it is necessary to raise the mud viscosity in excess of 200 sec/qt to clean the hole. In addition, field experience has indicated that during very fast upper-hole drilling, annular mud velocities considerably in excess of the maximum slip velocity of the cuttings (normally considered to be 120 to 150 ft/min) are necessary to prevent balling the bit and drill collars. In view of these variations in mud properties and circulation rates necessary to clean the wellbore, a study of factors affecting hole cleaning and the relative magnitude of each was undertaken. The study was also prompted by the knowledge that a drilling mud with properties close to those of water would drill at rates several times that of a viscous mud. The carrying capacity of these near-water muds was not clearly understood, however, and many drillers were reluctant to use them. DISCUSSION EFFECT OF MUD PROPERTIES ON DRILLING RATE The effect of mud properties on drilling rate has been studied by a number of investigators. 1t is clear from their work that mud properties close to those of water will significantly improve drilling rate and bit life. If the water-type mud will also effectively clean the hole and cause no logging or formation impairment problems, the choice of an appropriate drilling fluid is clear—use water. Often, however, a water-type drilling fluid is not capable of effectively cleaning the hole. THEORY OF PARTICLE SETTLING The forces acting on a particle that is allowed to settle through a fluid quickly reach equilibrium, and the particle settles at some constant velocity referred to as the slip velocity. The slip velocity of any particle depends upon a number of factors such as density and viscosity of the fluid, the volume, specific gravity, shape and roughness of the particle, and upon the shape and area of the projected face of the particle at right angles to the direction of relative fluid solid movement. Brown' expressed this relationship for spheres in Newtonian fluids in the following equation. where v, = slip velocity D, — diameter of sphere p, = density of spheye p, = density of liquid /a = friction factor g = constant. The friction factor f, varies as the size, shape, surface roughness and slip velocity of the body, and as the density and viscosity of the fluid varies. WaddelV ound experimentally that where dynamic similarity exists. f, was a function of the particle Reynolds number (NRe) of the sphere (Fig. 1). Fig. 1 shows that f, for spheres varies from over 10 for low NKe numbers to 0.44 for N,,. over 600.

By W. N. Lacey, B. H. Sage

The growing background of experimental information concerning the volumetric and phase behavior of binary and ternary hydrocarbon systems is used as the basis for a comparison of these systems with naturally occurring hydrocarbon mixtures under conditions representative of underground petroleum reservoirs. The qualitative and semiquantitative similarities and differences between the two types of systems are considered in reference to the possibilities and limitations of using experimental data on binary and ternary systems for predicting the volumetric and phase behavior of naturally occurring hydrocarbon mixtures of low molecular weight. The possible influence on such phase behavior of water, hydrogen sulphide, nitrogen, and components of relatively high molecular weight is discussed. INTRODUCTION During the past two decades much effort has been devoted to the study of the volumetric and phase behavior of pure paraffin hydrocarbons and of binary and ternary mixtures of these compounds. Many of these studies were carried out with the direct objective of utilizing a knowledge of the detailed characteristics of binary and ternary mixtures of the lighter paraffin hydrocarbons for predicting the behavior of more complex mixtures. The ability to make such predictions with accuracy would be of great value in petroleum production and refining. Although the behavior of the methane-propane system' served at one time as a qualitative illustration of the probable characteristics of the more complex hydrocarbon mixtures found in nature, it' fell far short of requirements for quantitative predictions. The present paper endeavors to indicate the relation of the more recently accumulated information concerning the behavior of binary and ternary hydrocarbons to this problem. In discussing binary and ternary systems as examples pointing toward the behavior of multi-component systems no effort is made to present new methods of predicting the characteristics of natural hydrocarbon mixtures. Preliminary proposals have been made elsewhere for the prediction of volumetric phase equilibrium and thermodynamic data for multicomponent mixtures, utilizing as a basis the behavior of binary and ternary systems. Numerous other proposals have been made. That based upon the concept of a pseudo-critical state" has proved to be of value to the petroleum industry. Concurrently with this study of binary and ternary systems investigations have been made of natural hydrocarbon systems. Of the many publications reporting such experimental information only a few examples will be mentioned. A number of studies of black oil and natural gas have been made and much attention has been directed to extended and detailed investigations of the behavior of fluids in condensate fieldS 16,17,18,19,20. This work has been supplemented by some studies of the separation of bitumen from natural hydrocarbon liquids The over-all behavior of such systems has been used in predicting the volumetric and phase behavior of naturally occurring mixtures This background of experimental and correlated information concerning the behavior of multicomponent hydrocarbon systems also permits a direct comparison of the characteristics of binary and ternary aliphatic systems with those materials produced from underground reservoirs. PRESENTATION OF DATA The primary limitation encountered in using binary and ternary aliphatic hydrocarbon mixtures as examples of the characteristics of the fluids encountered in underground reservoirs lies in the existing lack of knowledge of the quantitative effect upon behavior of the presence of several important constituents, notably hydrocarbons of high molecular weight, water, carbon dioxide, hydrogen sulphide, and nitrogen. The presence of substantial quantities of hydrocarbons of fairly high molecular weight serves to increase the complexity of the phase behavior of natural systems. No simple systems yet studied give adequate guidance in this regard. The influence of such materials of high molecular weight was indicated earlier",?' to an extent which serves to show that definite limitations now exist in the correlation of simple and complex systems. However, significant progress is being made in filling gaps in the information. For example, similarities in the behavior of fluids in condensate fields with that of binary and ternary systems are becoming more systematically evident. A few studies of the behavior of water in paraffin hydrocarbon systems have been made Results of investigations of mixtures of carbon dioxide and the lighter hydrocarbons also are available Limited work has been reported con-

Jan 1, 1949

By B. S. Butler

A. D. Mutch (Falconbridge Nickel Mines Ltd., Ona-ping, Ontario)—This contribution is prompted by the fact that the writer has recently published an article'!' which has in part the same general conclusions as B. S. Butler's, namely, the form of the standard mineral paragenesis in hypogene deposits and the parallel transition from early high temperature acid to late low temperature alkaline or neutral solutions. Since the writer also recognizes that he is not fully qualified to discuss the formation of ore deposits as a chemical problem, this discussion will be limited to summarizing other observations and will suggest how Butler's Table II might be made more effective. The form of Butler's table is not unlike that widely used by European geologists'" in which the various minerals are related to the types of ore fluids—peg-matitic, pneumatolic and hydrothermal. Thus the decrease in temperature and change in pH of the ore-bearing fluids as recognized by Butler may also be paralleled by perhaps even greater changes in composition, density, and character. W. H. Newhouse's article:" on the sequence of hypo-gene ore mineral deposition is still one of the most complete analyses of the problem. In it he makes four major observations: 1) The order of O, S, As, Sb is the same as their increasing atomic weights and the same as their melting points. 2) The order of the metallic elements is the same as the Schuermann series. 3) The general mineralogical order is paralleled by decreasing heats of formation. 4) The order is generally in decreasing hardness, higher metal content, and higher specific gravity. The order of 0, S, As, and Bi is also the same as their relative abundance. Another point worth mentioning about this series is that As, Sb, Bi, when abundant, often substitute for sulfur in the early pyrite-like minerals, whereas later in the sequence these elements appear to act more like metals. This behavior may be a further indication of the acid character of the early fluids. C. J. Sullivan"' has attempted to show that the sequence of the metallic elements is related to the order of their melting points and has discussed the interrelationship of the different types of bonding of sulfo-phile and oxiphile elements in minerals. Items 3 and 4 might best be summarized by saying that bonding of the minerals in the series appears to be from ionic to covalent to metallic, the early minerals being light in weight, hard, and near-transparent; the intermediate minerals of intermediate weight, semi-transparent, and semi-conducting; and the end minerals heavy, soft, and malleable, opaque and good conductors. A rapid fall in temperature has been assumed to be the cause of ore deposition in many deposits. Perhaps this in turn is the effect of a rapid release of energy in the form of pressure release and change of volume, the first minerals to form being those with the highest heats of formation which absorb the released energy the most rapidly. Butler's Table II could probably be streamlined and made more effective if the listed compounds were assembled as mineralogical groups as in Dana. Thus the sulfides, arsenides, antimonides, bismuthides, and sulfa salts could be arranged in AX,, AX, A2X2, etc. groups. Since these are continuous substitution series, in which the fields of stability and the heats of formation of the various individual minerals can be fairly regarded as similar, this should be accomplished with no loss of clarity. The occurrence of the individual minerals and the precise sequence of the mineral deposition in any one deposit is probably more dependent on the concentration and relative abundance of the component elements. The assembling of geological data in tabular form such as Butler's Table II will continue to be a very effective method of studying geological phenomena. The importance of this particular problem has been pointed out by C. F. Park,% who concludes that understanding of mechanisms of the standard paragenesis and interrelated problems of mineral zoning in space and time is one of the major keys to classification of ore deposits.

Jan 1, 1959

By G. Venturello, C. Antonione, G. Della Gatta

Results from work on the effect of inferstitials on recovery and recrystallization of' very pure iron (99.995 pet) doped with nilrogen up to 400 ppm are reported. Nitrided specimens were obtained by heating the iron in a static atmosphere of NH3 + H2. The samples were cold-rolled 80 pet, subjected to a series of isochronal and isothermal anneals, and submitted to examination by X-rays, micrographs, and hardness tests. Small additions of nitrogen show a strong effect in reducing recovery of' the mechanical properties of high-purity iron. At the temperatures of. the experiments, this effect proved greater than in the case of carbon. At 400°C pure iron recovers more than 50 pet of the total hardness increase, carburized iron vecovers 25 pet, and nitrided iron only 10 pet. On the other hand. the addition of nitrogen has, similarly to carbon, a very small effect on recrystallization; the effect is, however, slightly higher than that of carbon. When the concentration Of nitrogen is above the solubility limit in a iron at the temperattue of the experiments, an increase in the frequency of nu -cleation is also observed. THE object of the present work is to improve knowledge on the effect of interstitials both on recovery and on primary recrystallization of pure iron. In fact. at present there are no available data on the effect of nitrogen on high-purity iron. The only work which at present can be somewhat related to this problem is a work of Leak et al.1 in which grain boundary internal friction at high temperature in the presence of increasing amounts of nitrogen is studied by a torsion pendulum. The present work is a continuation of a previous one2 on the effects of carbon. EXPERIMENTAL PART Preparation of the Material. Pure iron was prepared following the same methods used in the pre- vious work2 and was nitrided using controlled quantities of ammonia in an apparatus similar to that used for carburizing. The apparatus consists essentially of a gas-tight quartz tube containing the specimens. The tube, maintained at constant pressure by means of a mercury seal, is placed in a resistance furnace. For nitriding, the NH3 + H2 atmosphere with a suitable concentration of NH3 was introduced into the tube, which had been previously carefully evacuated and degassed by heating at 600°C. The hydrogen used was carefully purified by passing it through a palladium filter. The ammonia required was prepared with the following reaction: CaO + 2NH4CI —CaCl2 + H2O + 2NH3 by heating the mixture of CaO and NH4C1 in a glass flask and then collecting the ammonia in a graduated Hempel burette. For each nitriding program a given amount of NH3 prepared by this method was introduced together with the H2 into the tube previously evacuated. Nitriding of the sample was then performed at 570°C for 48 hr. After this, to ensure a homogeneous distribution of nitrogen, the samples were further heated for 72 hr at 800°C. With this method which uses a static nitriding atmosphere, carefully controlled conditions of purity are obtained. Contrarily, with the conventional continuous-flow methods, using large quantities of circulating gas, there is a greater risk of introducing impurities into the samples. Furthermore, the required nitrogen concentration in the specimen is easily predetermined and obtained. A plot of the relation observed between the initial concentration of NH3 in the gas and the quantity of nitrogen introduced into the iron samples is given in Fig. 1. The data refer to samples of 1.2-mm thickness and to the nitriding conditions previously described. Furthermore, as a comparison, the data relative to two 0.5-mm-thick samples are reported. The presence of a reservoir in the cold zone of the reaction bulb made possible the gradual dissociation of ammonia on the sample in the hot zone. Internal-friction methods were used to determine the content of nitrogen dissolved in the iron samples. Some analyses were also carried out with chemical methods. The following table, Table I, shows a comparison of data obtained with chemical and internal-friction methods. The correspondence between chemical methods and internal-friction

Jan 1, 1964

By B. R. Berger

The Getchell area in the northern Osgood Range, Humboldt County, Nevada, was first prospected in the late 1800s for silver, copper, and gold; the first recorded mention of mining activity concerned a silver discovery. The September 17, 1874 edition of the Winnemucca Silver State notes that the Crystal Mining District was newly organized in the Fremont Range (as the Osgood Range was then called) to include discoveries of silver, lead, and antimony made on the Louisa claim. The name Crystal was derived from the plentiful quartz crystals found in-cavities near the prospects. This same area, occurring on the northwestern margin of the Osgood granodiorite stock, was later mined as the Richmond tungsten property, and crystals may still be found there in cavities in a massive garnet tactite. By 1878, how-ever, the name Crystal had been abandoned in favor of Potosi. The next flurry of activity in the Osgood Range was reported in 1899 when a copper strike on Granite Creek in the southern portion of the range received attention. The copper occukences were in a granite contact zone on the southeastern edge of the Osgood stock and, in 1916, the first tungsten in the district was discovered in the same deposit. During the last part of the nineteenth century, cattle and sheep were brought into the Kelly Creek Valley east of the Osgood Mountains by various ranchers. Alphonso and Adrian Bernard were among these ranchers, and in the first decade of the twentieth century, one of them recognized the altered rock where the Getchell Center it is now located. A 3-m (10-ft) deep prospect pit was dug on the outcrop, but the highest assay ran about $11/t ($10 per st). No further work was done on the gold-bearing rock. In 1934, Emmet Chase of Battle Mountain and Ed Knight of Golconda prospected in the area of the Bernard prospect pit and located several lode claims. At this time, Noble H. Getchell, a state senator, was looking for new mining opportunities to develop. He held interests in the Gold Circle Consolidated at Midas, which was becoming a losing venture. Chase and Knight brought their discovery to his attention, and he grubstaked them to prospect further in the area. In need of financial backing, Getchell solicited the help of George Wingfield, Sr., who held a minor interest in the Gold Circle. Wingfield was a successful banker and mine operator during the heyday of Tonopah and Goldfield, and he had become good friends with Henry C. Frick and Bernard Baruch. Wingfield let Baruch in on several very successful mining ventures in Goldfield, and Baruch returned the favor by underwriting the financing of the Getchell mine. Eleanor Roosevelt and Jack Dempsey were early stockholders in the Getchell operation. George Wingfield brought his brother-in-law, Roy A. Hardy, a consulting engineer who had constructed the American Flat mill near Virginia City, to look at the property. Upon inspecting the Chase-Knight claims, Hardy declared the whole area to be mineralized. A crosscut was driven to check the extent of the ore, and the results were better than anticipated. The locators were reportedly given $50,000 for the claims. The Getchell Mine, Inc., was organized on November 5, 1936. A small railroad that ran from Battle Mountain to Austin was purchased, and the ties and rails were moved to Getchell to be used in underground exploration. Enough reserves were found in the Center and South pit areas to construct a 40 t/d (44 stpd) mill. The financial and engineering help for the mill was provided by the Newmont Mining Co. for a 17 1/2% interest in the corporation. Newmont set about trying to solve the metallurgical problems with the sulfide ore, and also directed the early development work. Newmont wanted to grind the sulfide ore underground and oxidize it in the atmosphere by spreading salt on it. Detrital Flat in Arizona was purchased to provide salt for

Jan 1, 1985

By A. S. Michaels, M. C. Porter, A. Stancell

Previous laboratory studies have demonstrated that the injection of small quantities of reverse wetting agents during water displacement can increase oil recovery from unconsolidated porous media.9 In the present investigation, an attempt has been made to determine more fully the effects of reverse wetting treatments and to clarify the mechanism by which increased oil recovery is effected. Water-oil displacements were performed in beds of 140-200 mesh silica sand. Hexylamine slugs (injected after 0.25 pore volume of water throughput), when adequate in size and concentration, were effective in promoting additional oil recovery. Their effectiveness increased with the quantity of amine injected. However, slugs of sufficient size and concentration to stimulate oil production at water flow rates of 34 ft/day did not do so at 4 ft/day. Visual studies in a glass grid micromodel have shown that the stimulation of oil production, via ayueous hexylamine, is a result of transient changes in the oil wettability of the pore walls. if the amine slug is of sufficient size and concentration to induce significant changes in the adhesion-tension, large continuous oil masses will be formed. if the superficial water velocity is high enough to result in rapid desorption of the amine, a favorable "wettobility gradient" may be established across the masses; under such conditions, high oil mobility is observed, and increased oil recovery results. INTRODUCTION It is generally agreed that the efficiency of oil displacement by water in porous media is limited in part by capillary forces which cause the retention of isolated masses of oil — resulting in the so-called "irreducible minimum oil saturation". Recent estimates10 indicate that there are about 220 billion bbl of petroleum in United States reservoirs which are not economically recoverable with present techniques (such as water flooding). This amounts to almost five times the known recoverable reserves. It has been recognized for some time that a suitable alteration in the water-oil interfacial tension and/or the contact angle, as measured between the water-oil interface and the solid surface, should result in better displacement efficiency. Surface active agents can be used as interfacial tension depressants to accomplish this objective,1,2,7 but unfortunately, the additional oil recovery is seldom commensurate with the treatment cost. In contrast to interfacial tension depressants, the effect of contact angle alterations on water-oil displacements has received relatively little attention in the literature. It is known that the wettability affects the displacement process.3,4,11 Displacements in water-wet systems generally result in lower residual oil saturations than those in oil-wet systems. The effect of "'transient" wettability alterations concurrent with the displacement process have been investigated by Wagner, Leach and coworkers,4,11 wherein it has been demonstrated that the establishment of water-wet conditions during water flooding of oil-wet, oil-saturated porous media is accompanied by significant increase in oil displacement efficiency. Michaels and Timminss studied the effects of transient contact angle alterations resulting from chromatographic transport of reverse wetting agents through unconsolidated sand. It was demonstrated that chromatographic transport of short-chain (C4 through C8) primary aliphatic amines can improve oil recovery and that the recovery increases with the quantity of amine injected (i.e., with either the amine concentration or the volume of the slug injected). Circumstantial evidence indicated that the increased displacement efficiency resulted primarily from transient changes in wettability of the porous medium. In the Present investigation. additional information has been obtained on the effects of reverse wetting treatments and the mechanism by which increased oil recovery is accomplished. Hexylamine slugs of varying size and concentration were chromato-

Jan 1, 1965

By J. E. Owen

A model of a porous body is presented in which the pore space consists of a system of voids and interconnecting tubes. Relationships between porosity and resistivity formation factor are determined partly by calculation, partly by experiment. Con triction effects characteristic of the model are shown to be sufficient to account for high formation factors. It is shown that constriction may be combined with moderate amounts of tortuosity to give model pore systems exhibiting to a first approximation porosity and resistivity properties similiar to those of natural porous bodies. INTRODUCTION The relationship between the electric resistivity of a fluid-filled porous body and the geometry of its pore space is so complex that the calculation of the resistivity of a natural porous rock is a practical impossibility. Both the resistivity of a body and its porosity are measurable quantities, however, and previous successes at relating them have been reached by an empirical approach. Efforts at obtaining theoretically derived formulae relating them have generally been unsatisfactory. One of the reasons for this may lie in the pore geometry that has been assumed. THE TORTUOSITY CONCEPT A Parameter called the formation factor is useful in dis-cussing the resistivity of a fluid-filled porous body. This parameter is the ratio of the resistivity of a fluid saturated porous body to the resistivity of the saturating fluid. Formation factors are often available from measurements on cores or from electric logs, and many attempts have been made to correlate formation factors and porosities of geological formations. Whenever a successful correlation is found, the engineer working with electrical logs has a useful tool for the determination of porsities of pay section?. One of the more successful formulae applicable to these correlations is the familiar equation empirically obtained by Archie.' which F is the formation factor. $ is the porosity, and rn is an exponent called the cementation factor. When the for- mula applies, the cementation factor usually is found to be between 1.3 and 2.2. The values for formation factors experimentally obtained are often higher than simple pore geometry would lead one to expect. In an effort to account for such high values certain formulae have been derived based on a so-called "tortuosity concept." In deriving these formulae a synthetic porous body is usually assumed in which the solid material is an electrical non-conductor. and in which the pore system consists of three sets of fluid-filled tubes of uniform diameter connecting opposite faces of the body which, for convenience, is considered to be cubical in shape. The three sets of tubes account for the whole of the effective porosity of the body, and usually, it is specified that they do not interconnect. By considering that the pore tubes are not straight but tortuous, their resistance to the flow of electric currents can be made as high as needed to explain high formation factors. Such an explanation has some basis in fact, but it appears that the tortuosity concept is often incorrectly applied when other factors are largely responsible for observed high resistivities. Recently, Wyllie and Spangler have recognized that tortuosity as calculated by conventional formulae has little if any physical significance.' RESISTIVITY AND THE CONSTRICTION CONCEPT Any explanation of high formation factors which depends solely on tortuosity of uniform pore paths necessarily ignores the effect that variations in the cross-sectional area of the conducting paths have on the resistivity of a body. Although, as previously pointed out, the calculation of such paths for an actual body is impossible, it will he shown that a synthetic pore network can be devised which will yield to analysis, and lead to results in agreement with the experimental data represented by Equation (1). The porous body to be considered is assumed to be homogeneous and isotropic or, for present purposes, identical in its characteristics in the three directions parallel to its coordinate axes. It will he assumed to be built of identical unit cubes, each of which contains a single pore network connecting all faces of the unit cube. A unit of such a pore network is shown

Jan 1, 1952

By Leo Horvitz

Microanalysis of near-surface soils for hydrocarbons is the basis of a method for locating gas and oil deposits. To substantiate this technique, evidence of vertical migration of hydrocarbons from petroleum accumulations is presented. Tabulated data relevant to hydrocarbon surveys conducted in several petroleum provinces are included. PEROLEUM and natural gas are composed principally of the saturated hydrocarbons ranging from methane, the lightest, to nonvolatile liquids and solids containing approximately thirty-five carbon atoms. A technique for locating buried accumulations of these hydrocarbons before drilling obviously requires that some of the hydrocarbons leave the deposit and migrate toward the surface of the earth where they may be detected in their original form. Earliest attempts to link near surface hydrocarbons to petroleum at depth were apparently made by Laubmeyer' in Germany and by Sokolov in Russia. These investigators collected samples of soil air from boreholes one to two meters deep and analyzed them for traces of hydrocarbons. They found that soil air over producing areas is richer in these constituents than is soil air over barren areas. Since 1936 work on petroleum exploration techniques of this type has been going on in this country. However, instead of determining hydrocarbon content of soil air collected in the field, investigators analyze samples of the soil itself for adsorbed and occluded hydrocarbons, which are released by suitable treatment and found in larger amounts than are the quantities reported for soil air. Difficulties often encountered in collecting gas samples in the field, moreover, are eliminated when soil is used as the sampling medium. Field Procedure: Sample locations are first surveyed over the area to be investigated. Care is taken to locate the stations at considerable distances from roads, pipelines, drilling wells, and other sources of contamination. The borehole pay be dug with a bucket-type hand auger or with mechanical drilling equipment. Lubricants are avoided in either case. When the desired depth is reached, a sample is brought to the surface, placed in a pint glass jar or can, and securely sealed. Sample containers are carefully labeled and delivered to the analytical laboratory. Generally a satisfactory sampling depth range is 8 to 12 ft. In some regions, however, satisfactory data are obtained from samples collected at much shallower depths. Such is the case, for example, in areas of west Texas where the limestone and caliche near the surface occlude hydrocarbons and prevent their rapid escape to the atmosphere. In carrying out broad reconnaissance surveys in search of large features, considerable time is saved by first taking samples one-fourth to one-half mile apart along profiles about one mile apart. If the analytical data indicate a hydrocarbon anomaly of interest, additional samples are taken to produce a more dense and uniform sampling pattern within the interesting area. This sampling program is particularly adaptable to areas that are sectionized. In areas covered with a network of roads, sampling along these roads facilitates the reconnaissance survey. Actual sampling density used depends upon areal extent of features expected. When flanks of piercement-type domes where accumulations may be only several hundred feet wide are sampled, stations are often no more than 200 ft apart. Analytical Technique: Of the hydrocarbons composing petroleum, only the more volatile would be expected to reach the surface of the earth. The analytical technique, therefore, was developed to determine only those constituents that exert a vapor pressure at room temperature. Actually, in near-surface soils, only a very small part of the hydrocarbons are heavier than pentane. Details of the analytical technique have previously been reported. Only a brief description of the methods will be presented here. A weighed portion of the sample, about 100 g, is first treated with an aqueous solution of copper sulphate and then with phosphoric acid in a partial vacuum. The copper sulphate prevents the reaction of the acid with carbides that may be present because the sample has been contaminated by auger particles. Such a reaction may produce spurious methane. The role of the acid is to decompose any carbonates present, thereby helping to release the hydrocarbons. The carbon dioxide is removed with potassium hydroxide and the flask containing the

Jan 1, 1955

By Wallace W. Wilson

The Cook Ranch Field produces from a very permeable lens of Cook Sand of lower Permian or upper Pennsylvanian age, occurring at an average depth of 1.300 ft. The field was discovered in 1926, and has been operated with low pressure gas injection since July, 1927, one of the first such projects in Texas. Cumulative recovery to Dec. 31. 1950, was 14,701,131 bbl of crude oil, an average of 1,013 bbl per acre-ft of oil rection. and 72.5 per cent of the oil originally in place. Analysis of the reservoir performance indicates that grav-ity drainage has been an important factor in the producing mechanism. The high permeability and uniformity of the reservoir were extremely Favorable tor this type of operation. INTRODUCTION The Cook Ranch Field is the largest of a number of relatively small, shallow producing areas near .Albany, in Shackelford County, Texas. This field is one of the first to be operated by gas injection in Texas, and probably is the most successful low pressure gas injection project ever attempted. The field is owned entirely by Koeser and Pendleton, Inc., and Continental Oil Co., and has been operated by Roeser and Pendleton, Inc., since it was discovered. This study has been made possible through the cooperation of Roeser and Pendleton, Inc.. in making availahle a remarkably complete set of records covering all phases of their operations. The purpose of this paper is to present a summary of the history of the operations through Dec. 31, 1950, and to analyze some of the factors which appear to be responsible for the success of the project. Information concerning the physical plant and the early gas injection history has been presented in an earlier paper.' RESERVOIR CHARACTERISTICS production in the Cook Ranch Field is from a large lens of Cook Sand. of lower Permian or upper Pennsylvanian age, occurring at an average depth of 1.300 ft. The average dip of the sand body, as shown in Fig. 1. is only about 50 ft per mile to the northwest. The reservoir has an area of 930 acres and contains 15,512 acre-ft of Sand, consisting of about 14.512 acre-ft of produc-tive oil zone. and an estimated 1.000 acre-ft of primary gas-cap. The iso-pachous map (Fig. 2) was prepared from drillers' logs. Recent coring in the field has proven these logs to be quite accurate. The productive limits of the field are defined by shale on all sides but the southwest where a small zone of edgewater was encountered. This water does not appear to have encroached into the reservoir, and water production has been small. A smaller producing area to the south of the Cook Ranch Field also produces from the Cook Sand. but is separated from the reservoir under consideration by a band of shale. The sand consists of well sorted, coarse grained. rounded and subangu-lar quartz fragments. very poorly cemented. The analysis of 46 chip-core samples from two recently completed test wells indicates a range of porosity values between 12.5 and 28.2 per cent. wit11 an arithmetic average of 24.0 per cent. Air permeability values range between 50 and 2,300 md, with an arithmetic average of 1.200 md. The reservoir where cored is a Solid sand body. with no discernible major shale breaks or impermeable streaks. Vertical permeability appears to be of the same magnitude as the horizontal permeability. A core of the Cook Sand was cut ill the smaller field to the south, using lubricating oil as drilling fluid. The connate water content of the sand in this core was found to average about ten per cent, and the porosity and permeability were comparable with the values reported above. No analysis was made of subsurface or recombined hydrocarbon samples,

Jan 1, 1952

By F. D. Rosi, C. A. Dube, B. H. Alexander

The slip and twinning planes have been determined in deformed crystalsof titanium by an X-ray method of analysis. The slip planes are of the type {1010} and {1011}, while the twinning planes are of the type {1072}, {1121}, and (1122). In the case of the predominant (1010) slip, a type I digonal axis of indices <1120> was the effective slip direction. Microscopic observations on the appearance of the three twin types disclosed a distinct difference in their shapes, and an attempt was made to correlate this difference with the amount of twinning shear. The slip mechanism was discussed on the basis of the difference in c/a ratios for the common hexagonal close-packed metals. IT is a general rule that slip in metals occurs most easily on the planes of greatest atomic density and of the largest interplanar spacing, and that the direction of slip is a close-packed direction. Thus, of the hexagonal close-packed metals which have been investigated by the German school in the decade 1925 to 1935 (cadmium, zinc, and magnesium), it has been found that slip occurs on the basal plane (0001) and in a <1120> direction.&apos; In the case of magnesium above 225oC, slip occurs on a first-order pyramidal plane (1011) as well as on the basal plane.&apos; The hexagonal metals, moreover, deform in part by twinning, and, again with the exception of magnesium at elevated temperatures, the twinning plane has always been reported to be a second-order pyramidal plane {1012).&apos; In view of this consistency in the plastic behavior of these metals, it has been supposed that the same slip and twinning elements would be operative in the other important hexagonal close-packed metals (titanium, zirconium, and beryllium), although there are some reasons why this may not be so. Referring to the tabulation in Table I of the axial ratios of the important metals in this structural class, it may be seen that they can be categorized into three distinct groups depending on the value of their c/a ratios. In the first group are cadmium and zinc with large positive deviations from the ideal ratio for closest packing. This expansion in the direction of the c-axis would be such as to accentuate the basal plane as the slip plane, because it increases the interplanar spacing. The second group includes cobalt and magnesium, which closely approximate the ideal ratio. In the third group are zirconium, titanium, and beryllium whose axial ratios are decidedly less than the ideal. The lattice of the elements in this group is compressed along the c-axis which, in effect, tends to make the basal plane less favorable for slip inasmuch as it reduces the interplanar spacing and the atomic density of this plane. Thus, for metals in the third group, it may be said that there is a certain indefiniteness about the glide plane, in that planes other than the basal plane may be expected to operate. The fact that magnesium begins to exhibit planes other than the normal slip and twinning planes at elevated temperatures may indicate that this behavior will become more pronounced in metals of lower axial ratios. For this reason it might be expected that the slip and twinning behavior of zirconium, titanium, and beryllium would be different from that found in cadmium and zinc. One indication that there is a difference is reflected in the recent work which has been done on the deformation textures of these metals."&apos; As will be shown later, there is a significant difference between the rolling textures of cadmium, zinc, and magnesium on the one hand, and zirconium, titanium, and beryllium on the other, and this difference suggests that the mechanism of plastic flow is not the same in these two groups of metals. From these considerations, therefore, it may be seen that there are good reasons why it cannot be concluded that titanium will have the same crystal-lographic elements of slip and twinning as those exhibited by zinc and cadmium. For the complete determination of these elements it would be most advantageous to have single crystals. However, much valuable information can be obtained by using coarse grained polycrystalline specimens, provided the grains are sufficiently large to permit X-ray

Jan 1, 1954

By D. P. Kedzie, R. A. Dodd

The fatigue strength, fatigue hardening, and effect of fatigue deformation on subsequent age hardening of supersaturated Al(Cu) solid solutions have been determined as functions of alloy composition and temperature. The fatigue strength/tensile strength ratios, determined at 150°, 25°, and -195°C, decreased with increase in alloy content for all temperatures, but the F.S./U.T.S. ratios at -195°C decreased much more rapidly than did the ratios for 150" and 25°C. This suggested that strain aging and/or age hardening occurred during tests at higher temperatures. Additionally, the F.S./U.T.S. ratios at 150°C exceeded those at 25°C for all compositions, indicating greater strengthening during fatigue at 150°C. The effect of fatigue or tensile deformation at 150°, 25°, and -195°C on subsequent age hardening showed that the deformatzon increased the rate of precipitation and indicated that mechanically produced vacancies were probably formed during deformation. Fatigue hardening was studied at 150°, 25°, and -195°C, and the effect of room-temperature rests after 10 and 100 cycles was examined. The results confirmed that strain aging occurred at the higher temperatures . DURING the last 15 years various mechanisms of fatigue crack nucleation and growth based on dislocation and vacancy interactions, operating singly or collectively, have been proposed. The probable consensus of present opinion is that the fatigue process in pure metals essentially involves dislocation interactions, and that vacancies formed by such interactions play a minor or inconsequential role. However, there is some evidence that age-hardened alloys tend to overage during fatigue, probably by local vacancy-enhanced diffusion, and strain aging also might be important in selected cases. Furthermore, it has been established that the behavior of quenched-in vacancies in Al(Cu) and other solid solutions is composition-sensitive. Therefore, it seemed worthwhile to investigate various aspects of the fatigue behavior of supersaturated Al(Cu) alloys and to examine the results in terms of vacancy-enhanced effects. EXPERIMENTAL The alloys used in this investigation were prepared from 99.994 wt pet A1 and OFHC copper, the latter containing 0.04 pet 0 as the principal impurity. Six alloys were made, containing, by actual analysis, 0.58, 0.96, 1.96, 2.85, 4.45, and 5.51 wt pet Cu. They were induction-melted in air in graphite crucibles, cast as 7-in. by 7/8-in.-diam rods in graphite molds, and hot-rolled to 5/8 in. diam. The experimental work was a three-part program involving the determination of a) 10&apos; cycle fatigue stresses as a function of alloy composition and temperature; b) the effect of fatigue deformation on subsequent aging of the supersaturated alloys; and c) fatigue hardening as a function of alloy composition and temperature. For determining the 105 cycle fatigue stresses, a portion of the 5/8-in. stock was machined into Krouse rotating cantilever beam fatigue specimens, 2 in. in length by 1/4 in. minimum diameter. These were tested at +150°, 25°, and -195°C (liquid nitrogen) on a Krouse high-speed machine, with special weights to provide lower -than-normal loading ranges, this being necessitated by the small load requirements of those alloys of lower copper content. For the high-temperature tests a small resistance heater was designed to clear the collets and fit in between the chucks, while for the low-temperature tests a hollow nylon cylinder was used, having closed ends drilled to pass a fatigue specimen, and positioned similarly to the heater. A plexiglass container completely enclosed the fatigue machine; rubber gloves fixed to ports in the walls enabled the machine to be operated from outside the box. A tray of magnesium perchlorate dried the air in the container and prevented both atmospheric corrosion fatigue at room and elevated temperatures and troublesome ice build-up at low temperatures. A total of ten to fifteen specimens was used for each combination of alloy composition and temperature. The result of each test was plotted on a standard S-N diagram, and the next stress was selected on the basis of the trends indicated by previous specimens. In this manner a small portion of the S-N diagram was constructed, and the 105 cycle fatigue stress obtained. Small Krouse fatigue specimens were also used to study the effect of cyclic prestrain on subsequent

Jan 1, 1964

By C. L. Thornburg

FLANKING the Valley of Mexico on the northeast is a mountain range known as the Sierra de Pachuca. This northwesterly-trending range is about 30 miles long and 5 miles wide, its summit attaining an elevation of more than 10,000 feet above sea level, or 2000 feet above the valley floor. Pachuca, a town of 50,000 inhabitants, lies nestled at the southwest base of the range, 60 miles northeast of Mexico City. Three miles to the east, just over the summit and on the northeasterly slope, is the mountain town of Real del Monte with a population of about 20,000. These are the two principal towns in a 40-sq mile area whose yield has brought the district to its high rank among the world&apos;s silver producers. Total production probably exceeds 1.25 billion ounces of silver and 4.5 million ounces of gold. Exploitation by the Spanish was under way by 1530. As the mines were deepened operations became handicapped by the inadequate method of handling water with horse whims and bull skins. To offset this disadvantage a two-mile drainage tunnel was started in 1749 and completed ten years later. John Taylor of London acquired the mines from the third Count of Regla in 1824 and formed the Compania de Real del Monte y Pachuca. Two years later Cornish pumps were brought from England. A Mexican company purchased the British interest in 1848 and within a few years resumed an old project of driving a second, lower three-mile drainage tunnel, completing it in 1857. After American interests acquired control of the property in 1906 operations expanded to an unprecedented scale, despite periods of political strife, unstable prices, labor problems, and a growing burden of taxation. An idea of the scale of operations may be gained from records of the last two decades prior to 1947, the last year for which production information is at hand, during which time production ranged from 1.4 million to 1.1 million tons per year, and the combined development and exploration, exclusive of diamond drilling, amounted to about 18 miles annually. Pachuca differs from Zacatecas and some other Mexican silver vein districts that flourished and declined in earlier centuries in that a substantial part of its total production was made after 1900. While the district&apos;s accelerated activity in this century was largely due to the successful application of the cyanide process to the treatment of the ores, improved pumping methods, and new mechanical equipment, it was at the same time stimulated by the opening up of important new orebodies as a result of active and extensive exploration of the vein system. Some of these orebodies were found on veins which terminate upward far below the surface, and though these particular veins do not crop out, they show relationship with a type of alteration which may be their surface expression. The district has been studied by many able geologists, and a large store of information has been accumulated, much of which is recorded in published as well as private papers. Wall Rocks Extrusive Rocks: The Sierra de Pachuca is a thick accumulation of Tertiary eruptive rocks consisting mainly of flows, breccias, and tuffs. Numerous recognizable volcanic vents within the range itself manifest that the range was built up by material ejected from these vents. The maximum thickness of the volcanic pile is not known, but from deep exploration and from relationship with Mesozoic sediments to the north and east it is inferred that the average thickness in the main part of the district may be at least 6000 ft. The extrusive rocks comprise four general types, which in ascending order of age are: andesite, rhyolite, dacite, and basalt. The veins are confined largely to the andesite, the dominant rock of the region. Characteristically this rock is augite andesite, but it includes comparatively acidic as well as basic layers, the acidic strata being

Jan 1, 1952

By AIME AIME

AMONG the members of the Institute there are thirty-three who have been members for a half- century or-more Some time ago a professor of psychology made a careful study of a group of unusually brilliant children to determine whether there was any truth in the general belief that a brilliant mind is usually to be found in a physically sub-normal body. He definitely proved the exact opposite and it is now known that children who are above the average in mental capacity are also above the average in physical health and strength.

Jan 1, 1929

By Glenn S. Wyman

CHUQUICAMATA, located in northern Chile in the Province of Antofagasta, is on the western slope of the Andes at an elevation of 9500 ft. Because of its position on the eastern edge of the Atacama Desert, the climate is extremely arid with practically no precipitation, either rain or snow. All primary blasting in the open-pit mine at Chuquicamata is done by the churn drill, blasthole method. Since 1915, when the first tonnages of importance were removed from the open pit, there have been many changes in the blasting practice, but no clear-cut rules of method and procedure have been devised for application to the mine as a whole. One general fact stands out: both the ore and waste rock at Chuquicamata are difficult to break satisfactorily for the most efficient operation of power shovels. Numerous experiments have been made in an effort to improve the breakage and thereby increase the shovel efficiency. Holes of different diameter have been drilled, the length of toe and spacing of holes have been varied, and several types of explosives have been used. Early blasting was done by the tunnel method. The banks were high, generally 30 m, requiring the use of large charges of black powder, detonated by electric blasting caps. Large tonnages were broken at comparatively low cost, but the method left such a large proportion of oversize material for secondary blasting that satisfactory shovel operation was practically impossible. Railroad-type steam and electric shovels then in service proved unequal to the task of efficiently handling the large proportion of oversize material produced. The clean-up of high banks proved to be dangerous and expensive as large quantities of explosive were consumed in dressing these banks, and from time to time the shovels were damaged by rock slides. As early as 1923 the high benches were divided, and a standard height of 12 m was selected for the development of new benches. The recently acquired Bucyrus-Erie 550-B shovel, with its greater radius of operation compared to the Bucyrus-Erie 320-B formerly used for bench development, allowed the bench height to be increased to 16 m. Churn drill, blasthole shooting proved to be successful, and tunnel blasts were limited to certain locations where development existed or natural ground conditions made the method more attractive than the use of churn drill holes. Liquid oxygen explosive and black powder were used along with dynamite of various grades in blast-hole loading up to early 1937. Liquid oxygen and black powder were discontinued because they were more difficult to handle due to their sensitivity to fire or sparks in the extremely dry climate. At present ammonium nitrate dynamite is favored because of its superior handling qualities and its adaptability to the dry condition found in 90 pct of the mine. In wet holes, which are found only in the lowest bench of the pit and account for the remaining 10 pct of the ground to be broken, Nitramon in 8x24-in. cans, or ammonium nitrate dynamite packed in 8x24-in. paper cartridges, is being used. This latter explosive, which is protected by a special antiwetting agent that makes the cartridges resistant to water for about 24 hr, currently is considered the best available for the work and is preferred over Nitramon. Early churn drill hole shots detonated by electric blasting caps, one in each hole, gave trouble because of misfires caused by the improper balance of resistance in the electrical circuits. Primarily, it was of vital importance to effect an absolute balance of resistance in these circuits, the undertaking and completion of which invariably caused delays in the shooting schedule. Misfires resulting from the improper balance of electrical circuits, or from any other cause, were extremely hazardous, since holes had to be unloaded or fired by the insertion of another detonator. The advent of cordeau, later followed by primacord, corrected this particular difficulty and therefore reduced the possibility of missed holes. After much experimentation, the blasting practice evolved into single row, multihole shots, with the holes spaced 4.5 to 5 m center to center in a row 7.5 to 8 m back from the toe. Sucti shots were fired from either end by electric blasting caps attached to the main trunk lines of cordeau or primacord. The detonating speed of cordeau or primacord gave the practical effect of firing all holes instantaneously. Double row and multirow blasts, fired instantaneously with cordeau or primacord, proved to be unsatisfactory in the type of rock found at Chuquica-

Jan 1, 1953

The Institute conducts jointly with the American Society of Civil Engineers, American Society of Mechanical Engineers and American Institute of Electrical Engineers, certain activities as listed below, and is joint owner with them of certain properties. United Engineering Trustees, Inc. When Mr. Carnegie made his gift which made possible a home for the engineering societies, a separate corporation was organized to act as a holding company and to manage the common property. This was long known as the United Engineering Society but the name has now been changed to one which more nearly reflects the real function of the corporation. It holds title to the Engineering Societies Building and to various funds placed in its charge and is managed by a Board of Trustees of which three are chosen by each of the four societies, American Institute of Mining and Metallurgical Engineers, American Society of Mechanical Engineers, American Institute of Electrical Engineers and American Society of Civil Engineers, which own equal and undivided interests in the property. The land and building cost two million dollars. The interest of each of the Founders societies, aside from especial trust funds, is now valued at $493,352. The A. I. M. E. trustees are Arthur S. Dwight, J. V. N. Derr and George D. Barron. The President of the Board is Francis Lee Stuart and the Secretary, Alfred D. Flinn.

Jan 1, 1923

By M. J. Coolbaugh

Mining potash at depths of 3000 ft or more beneath thick water-bearing sediments in Saskatchewan presented a unique challenge to the North American mining industry. Potash is known to flow under pressure, but the knowledge of its flow characteristics at great depths was inadequate for safe design of mine workings and for assured protection from water above the salt formations. At the 3000-ft. depth of the Canadian mines, the potash is stressed beyond its elastic limit, and therefore mining design must deal primarily with its behavior as a plastic material. Recognizing that careful study would be required in order to assure safety and stability of mine workings in deep potash, IMC initiated an extensive rock mechanics investigation of structural properties of potash and salt under high-stress conditions. This presentation consists of a brief review of the development of some methods of testing potash in the laboratory and in the field; some of the rock mechanics concepts and principles derived; and their application to potash mine design. The mining of potash more than 3000 ft beneath the water-bearing sediments in Saskatchewan presented the unique challenge of designing stable mine workings and assuring protection from overhead water in a material that was believed to flow plastically, but whose behavior as a plastic material was not sufficiently known. Under the stress conditions ordinarily encountered in mining, most rocks behave as elastic materials; that is, they compress slightly under pressure, and rebound when the pressure is released. Salt and potash, however, are different. Even under the relatively low pressures encountered at shallow depths, these materials become slightly plastic and yield to stress by flowing.* The plastic properties become more pronounced at greater depth and pressure, and the question arises as to whether or not the plastic flow will be rapid enough and exert enough pressure to destroy underground structures or interrupt the mining process. It was found, however, that not only was there an insufficiency of information about the behavior of potash and salt, but conventional methods of testing these materials, such as determining the modulus of elasticity, Poisson&apos;s ratio, and uniaxial compressive strength, were inapplicable because of the high stress conditions prevailing at the 3000-ft depth. Potash under high pressure, for example, has practically no modulus of elasticity, its stress-strain relationship varies with time, and its compressive strength depends upon the degree of confinement. Elasticity and Stress/Strain Relationship: Fig. 1 shows a standard stress/strain chart for potash as made by the Department of Mines in Canada. Typically, when stress is applied to a hard-rock specimen, the specimen contracts, then expands to its original shape when the stress is withdrawn. This chart illustrates, however, that potash under stress yields to the stress by flowing, and does not expand when the stress is withdrawn. When the applied stress was held constant for 30 min, beginning at points A and C, the strain continued to increase and the potash flowed to points B and D, respectively. Points B, D, F, and H show that the potash did not return to its original shape when the stress was released. Thus it can be observed that potash has practically no elasticity and that the amount of strain depends upon the length of time that the stress is applied. Compressive Strength: The conventional method of determining the compressive strength of hard material is to find the maximum pressure that long slender specimens of the material can withstand without failing. As illustrated in Fig. 2,* line B, a standard 2-in. cube of potash subjected to a conventional type of uniaxial compressive test will exhibit a strength of about 5000 psi. However, the compressive strength exhibited can be made to change by changing the conditions under which the test is made. For example, if teflon plates lubricated with graphite are inserted between the press and the specimen, thus minimizing end constraint, the compressive strength is only about 2500 psi, shown in line A. If a specimen is cut in half, changing the width-to-height ratio to 2 : 1 instead of 1:1, and then tested without lubri-

Jan 1, 1968

By John D. Roach

DURING an investigation of the yttrium-hydrogen system aimed at producing solid yttrium hydride specimens containing various amounts of hydrogen, it was observed that yttrium containing approximately 2 wt pct H exhibited a tendency to crack and crumble to a powder on standing in air at room temperature. It was also observed that longer hydriding times, at a given temperature, increased this susceptibility to powdering without an increase in hydrogen content, also that moisture in the air is necessary for the observed effects to occur. Even if cracking did not occur, there was a continual formation of a light gray powder on the as-treated surface of the hydrided yttrium and this reaction continues until the entire hydrided piece has been reduced to a powder. Storing the hydrided specimens in the absence of air or removing the surface either by machining or grinding were effective means of preventing this disintegration of hydrided yttrium. In an attempt to determine the reason for this powdering phenomenon, the surfaces of a number of as-hydrided yttrium specimens were examined by X-ray techniques. In all cases the X-ray pattern obtained showed the major phase to be yttrium hydride (YH2) as would be expected since the specimens contained 2 to 2.2 wt pct H. In some cases a trace of yttrium oxide was observed. There was also a third phase present on the surface of these hydrided specimens which could not immediately be identified. This unknown phase was a face-centered cubic material, NaC1-type structure, with a lattice parameter of 4.855 and a calculated density of 5.914 g per cc. Very slight hand polishing of the surface of the hydrided yttrium specimens completely removed both the unknown phase and the traces of oxide so that only the yttrium hydride pattern remained. Based on the X-ray patterns the quantity of the unknown phase on the surface of the hydrided yttrium appeared to be directly related to the susceptibility of the material to powdering. Work at the Denver Research Institute on the yttrium-nitrogen binary system showed that yttrium nitride (YN) is a face-centered cubic material with a lattice parameter of 4.878A and a density of 5.890 g per cc. They also noted that this compound rapidly disintegrated to a powder on standing in air. The unknown pattern observed in the above specimens corresponds very closely to that of the nitride—fcc structure, 4.885 parameter, and density of 5.914 g per cc. The presence of this thin film of nitride on the surface of the hydrided specimens probably accounts for the observed powder formation and crumbling. The nitride reacts with the water vapor in the air (verified by private communication from Dr. C. Huffine, General Electric Co.) to yield yttrium oxide and ammonia. Ammonia is readily detected when hydrided yttrium specimens were allowed to stand in bottled moist air. The powder formed on the surface of the hydrided specimens was shown by X-ray analysis to be yttrium oxide. This reaction appears to occur primarily at the grain boundaries since discrete particles of yttrium hydride separate from the specimens during this powdering process. The reaction of yttrium nitride with water vapor is believed to be as follows: 2YN + 3H2O - Y203 + 2NH3. Despite the fact that this nitride is present only as an extremely thin surface film, if the above reaction is not prevented by removing this film from the surface either by machining or grinding, the reaction continues until the entire hydrided piece has been reduced to a powder. To account for this continuation of the reaction, it is believed that the following reactionalsooccurs: 2YH2 + 2NH3 -2YN + 5H2. The nitride produced by the latter reaction reacts in turn with water vapor. The reaction therefore becomes autocatalytic and continues until the hydride has been consumed and the entire piece reduced to oxide powder. The amount of nitride required to initiate this reaction is quite small and this nitrogen contamination can occur from a number of sources—hydrogen gas employed, minute leak in the hydriding apparatus or even from degassing of the reaction vessel itself. Longer hydriding times increase the possibility of nitrogen contamination and this is especially true when a dynamic gas system is employed in the hydriding process. The production of stable, solid hydrided yttrium is dependent on the complete absence of nitrogen contamination during processing. If such contamination does occur, powdering of the hydrided product can be prevented by removing the nitride from the surface e.g. grinding or by preventing access of air to the pieces e.g. sealing in wax or plastic. The author wishes to express his appreciation to General Electric Co. for sponsoring this research and for permission to publish the results of work under Subcontract AT-93.

Jan 1, 1962

By O. R. Morris, G. L. Hawkes

A galvanic cell, using as electrolyte a fused salt solution of calcium carbide and as electrodes carbon and a Fe-C alloy of known composition, has been set up to study the thermodynamics of Fe-C alloys in the temperature rmzge 800" to 1000°C. Time independence and reproducibility of the cell electromotive force were taken as evidence of the reversible behavior of the cell. Carbon was believed to be present in the electrolyte as the so-called acetylide ion, C;-. The plots of the cell electromotive force us temperature for a specific alloy composition were straight lines within the limits of experimental error. The average Partial molar enthalpy of carbon in iron relative to pure carbon was found to be +10,610 i 93 cal per g-atom C. Thermodynamic analysis of the data has led to the following equation for the carbon activity, ac, based upon pure carbon as the standard state: In ac = In Zc + 10,560/RT + (10.02 + 77O/T)ZC - 2.350 where ZC is the lattice ratio [nC/(nF, - nc )] and T is the absolute temperature. This equalion gives carbon activity values generally slightly lower than those from gas equilibration studies reported in the literature. METAL LOGRAPHIC examination of a polished cross section of the steel anode used in the electrolysis studies of fused salt solutions of calcium carbide by Morris and Harry revealed extensive carburization of the steel by the electrodeposited carbon. This carburization was reflected in the variability, with time, of the applied potential to the electrolysis cell, necessary to maintain a constant current density at the electrodes. This observation suggested the setting up of a galvanic cell of the "alloy concentration" type to study the thermodynamics of some metal-carbon alloys. Cells of this general type have been widely used for the study of alloy systems.2 In view of the availability of published data in respect of the austenite phase of the Fe-C system, it was decided to carry out measurements upon these alloys before proceeding to studies of less well documented systems. The galvanic cell may be written: where [C] is carbon dissolved in iron. The electrolyte was a fused salt solution of calcium carbide, containing some 5 to 10 mol pct of carbide. The cell reaction is believed to be: C(s)-[CI [I1 Carbon forms an interstitial solid solution in iron, with the atoms located in the octahedral interstices. In the fcc crystal structure of austenite there is one octahedral interstice per iron atom. Thus, the lattice ratio, ZC, shown by Gurney3 to be the fundamental concentration parameter in the context of interstitial solutions, is given by: where nc and nFe are the number of carbon and iron atoms, respectively. chipman4 has recently shown empirically the advantages of using this concentration parameter instead of the more usual atom ratio or atom fraction. The cell electromotive force, E, assuming reversible behavior, is related to the carbon potential or the partial molar free energy of carbon in the solid solution relative to pure carbon at the same temperature and pressure, GP at the composition ZC, by the equation: where z is the carbide ion valency and F is the Faraday constant. An activity of carbon, ac, in the solution relative to the value of unity assigned to pure carbon, and an activity coefficient, qC , are defined such that: where R is the gas constant and T the absolute temperature. GF is further related to the relative partial molar enthalpy Hm, and the temperature coefficient of the cell electromotive force, (aE/aT)Zc, by the equations: Measurement of the cell electromotive force thus enables calculation of the relative partial molar thermodynamic properties of carbon in iron, if z is known. At E = 0, the solid solution is in equilibrium with pure carbon. More convenient for many purposes is the standard state based upon the infinitely dilute solution, Henry&apos;s law. The relationship between the activity coefficient of carbon based upon this standard state, and that based upon the pure carbon standard state, qC , may be obtained by considering the free energy of transfer of carbon from the latter standard state to the former. The relationship is: where +:H is the activity coefficient of carbon in the hypothetical standard state based on a reference of

Jan 1, 1969