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By G. A. Swanquist, E. M. Morales

INTRODUCTION The idea of water management and control at the Church Rock Mill operations began to take shape in February 1979. At that time, we were already investigating the feasibility of decreasing the fresh water requirements so that the solids would become the limiting factor in tailings impoundment utilization. The area for solution evaporation could be kept at a fraction of the normal requirements under the standard process of full water usage. The Church Rock Mill is an acid leach circuit followed by solids/liquid separation with thickeners in counter current decantation, and solvent extraction. Following the normal design of acid leach circuits, reuse of tailings solution was not incorporated in the original mill process design. INITIAL WATER CONTROL INVESTIGATIONS The investigations to decrease the fresh water requirements centered around modifying the grinding circuit from the present semi-autogenous grinding (SAG) mill in closed circuit with hydrocyclones, to open circuit grinding with a rod mill. The open circuit grinding with the SAG mill and rod mill in series had the potential of decreasing the water requirements for grinding and leach dilution by approximately 50% or 1.4 m3/min (300 gpm). The grinding pulp density would be maintained at 70 to 72% solids, and the leach dilution to 50% solids would be accomplished with acid tailings liquor recycle. In such a grinding circuit arrangement, the SAG mill would provide the primary or coarse grind, and the rod mill would be used for the fine grind. By the SAG mill and rod mill series grinding method of water control and other secondary water controls in various places downstream from the grinding circuit, the required necessary evaporation area was estimated at 120 acres of liquid surface. A second method of water control at grinding was investigated. A two-stage cyclone classification circuit appeared to have a good potential of achieving the same water reduction at a much lower capital and operating cost. However, in retrospect, this would not have been a viable method since a high slime recycle load would have been established hindering classification. The use of reagents to neutralize the acid tailings solution was not considered seriously at that time, since it would have materially increased operating costs, although it would have also allowed more tailings solution recycle and consequently, less fresh water usage. However, with the tailings solution deposition area available at that time, it was not then necessary to incur the high cost of neutralization. The control expected by the series grinding of semiautogenous and rod mills would have been sufficient to maintain a water consumption/evaporation equilibrium well in line with the available land area. IMPLEMENTATION OF NEUTRALIZATION OPERATIONS During the summer of 1979, the UNC Church Rock Mill experienced a tailings dam breach which resulted in a prolonged mill shutdown. Upon resumption of operations at the end of October 1979, tailings deposition was restricted to a small portion of the tailings impoundment area. Figure 1 shows the general tailings area and the limits of the present deposition area in the central part including the borrow pits. These borrow pits had been excavated to provide materials for tailings dam construction. Immediately after resumption of operations, it became evident that it would be necessary to control the quantity of liquid to be evaporated because of the small confined area available for tailings solution deposition and to maximize the deposition time in the tailings area. The water control required had to be exercised on a large scale, and to be in operation as quickly as possible. An obvious solution was to reuse the tailings liquor in mill process. Immediate steps were taken to install the necessary equipment for tailings neutralization on an interim basis. Anhydrous ammonia was selected as the primary neutralization reagent since it was the quickest system that could be placed in operation. Previous laboratory tests indicated fair results with ammonia neutralization. Such a system required a minimum of installed equipment and handling. INITIAL NEUTRALIZATION OPERATIONS Actual neutralization operations began on November 26, 1979. The raffinate solution which normally would have been discarded was pumped to a 3.7 m (12ft) diam by 4.3 m (14ft) tank for reagent contact, see Figure 2. At this tank, anhydrous ammonia was added directly from the tanker trailers and controlled at pH 7.0 nominally. Agitation was provided by air sparging. The neutralized product formed a highly viscous slurry in the grinding circuit which resulted in pumping and cyclone classification problems.

Jan 1, 1982

By L. H. Reiss, J. Groult, L. Montadert

Many fields, where the reservoir is composed of sandy layers, show great complexity because of the lack of continuity which results from a particular type of seditnentation. This complexity may be a factor of prime importance in studying reservoir drainage, especially in the displacement of oil by water or gas. This paper describes work done to study this heterogeneity and its influence in the exploitation of the fields of the lower Devonian sandy shale in the Fort Polignac Basin in Algeria. Two lines of research were followed. 1. On the border of the hasin, a detailed sedimentological study established rules for the distribution of the sandy zones, which furnished hypotheses necessary for devising a geologic model of the reservoir. A certain number of sandy zones were recognized and characterized by their sedimentation. 2. In the interior of the basin, production logs deterrnined the productivity profile. Study of these point data led to a description of the distribution of oil and gas phases in the reservoir so that the continuity of different zones between the wells could be deduced. These techniques were applied to the study of the lower Devonian sandy shale reservoir of Zarzaitine. The sedimentological study guiding the correlation work, with the aid of the conventional static data (logs and cores), led to the establishment of a useful geologic model of the reservoir. Production logs, thanks to the contribution of dynamic elements, permitted corrobora-tion of the model. In particular, the logs confirmed separation, as proposed by the sedimenfological study, of two comparable sandy groups by revealing the continuity of a thin impermeable layer, invisible on conventional logs. INTRODUCTION The heterogeneity of sandstone reservoirs considerably influences the distribution of fluids, as well as their displacement in the reservoir. Rational development of a field and maximum recovery of hydrocarbons are closely tied to an exact and precise knowledge of the intern architecture. We will try to show how it is possible I refine the knowledge of the reservoir by seeking qui different and varied sources of information. Productic geology, the group of techniques which leads to idei concerning reservoir architecture and its geometric descris tion, furnishes the framework of this undertaking. Of these techniques. those used so far are qui varied. Descriptive as well as quantitative, the technique partake as much of classical geology as of reservo science. They include (1) geologic studies of the enti basin, especially a stratigraphic and sedimentologic study of the reservoir member at its outcrop, detail1 observations of cores taken from wells and, finall oriented cores; (2) interpretation of geophysical dat (3) interpretation of electric logs, nuclear and sonic lo and dipmeters: (4) petrophysical study of the reserve on samples taken from wells; (5) reservoir dynamics (stu of the production history and, in particular, interpretati of production logs); and (6) analysis of the fluids a thermodynamic studies. This incomplete list could also include (1) study the migration of the fluids, (2) geochemistry (chemi characterization of the oils), (3) regional hydrodynamii and (4) injection and detection of tracers. If most of these techniques are classic, attention i nevertheless be called to applying two of the techniql in conjunction: the study of the reservoir member its outcrop and the study of dynamic distribution fluid phases in the reservoir through use of product logs, used in the study of the sandy shale reservoirs the lower Devonian of the Fort Polignac Basin, Alge in particular, their application to the study of the 2 zaitine field where they have led to a new and satisfact model of the reservoir will be described. THE ZARZAITlNE FIELD Situated in the interior of the Fort Polignac 8 about 150 kilometers (km) north of the lower Devol outcrop, the Zarzaitine Devonian oil field was discovc On Ian. 28, 19'' (Figs. 1 and l8). It is in the fern a monocline truncated by two perpendicular fault: great throw, with a downthrown section to the north\: Erosion at the top of the structure has caused one of it to disappear. It is a reservoir with a gas cap an m coefficient on the order of 1:5, open to the aql On the northeast, with the oil zone covering an Of 106 sq km and with initial oil reserves of 222 mi

Jan 1, 1967

By C. E. McWhorter

IN underground mining recent trends toward mining large tonnages of low-grade ore have created, among other things, a need for cheaper and more flexible ore transport. A relatively new development has been the adaptation of shaker conveyors to meet this need. Although widely used in coal mining, only in the last few years have shaker conveyors been used in underground metal mining. The equipment consists of a driving engine, either electric or air powered, upon which is mounted a drive trough supported in ball-bearing frames. The trough line, or conveying medium, is made up of a number of sections, each section connected to another, usually with bolts. The length of each trough section is controlled by the length that can best be handled underground, but is usually from 9 to 13 ft over-all. The length of a complete conveyor line is determined by the character and weight of material to be handled as well as by the size of the ore body. Trough lines vary in lengths from 100 to 300 ft and the trough has a cross-section area of 127 sq in., and is 22 in. wide by 6 ½ in. deep.

Jan 1, 1948

By S. J. Leach

The possible solution of some of the problems raised in H. L. Hartman's article "Determining Ventilation Requirements for Continuous Miners," which appeared in the March 1962 issue of MINING ENGINEERING, is offered by recent investigative work done at the Safety in Mines Research Establishment, Ministry of Power, Sheffield, England. Highlights of this research are outlined here. Accumulations and layers of methane form in a mine roadway because it is difficult to mix methane with air beneath it by turbulent diffusion. Such mixing involves work contrary to buoyancy forces. In specifying requirements for good ventilation it is not, therefore, sufficient to state that the airflow must be turbulent in the absence of methane. Fundamental work at SMRE on the behavior of methane roof layers has led to the formulation of rules for controlling methane roof layers which specify the ventilation velocity needed to ensure adequate mixing in terms of the rate of flow of methane into the layer (V = cu ft per min) and the airway width (D = ft). A "layering number" for methane and air has been defined by [U37/V/D] where U is the mean ventilation velocity in ft/min in the upper half of the airway. In a horizontal airway there is no mixing by turbulent diffusion for values of the layering number less than about 2, resulting in extensive roof layers. But with a layering number of 5, the layer is "brought under control"-i.e., a further increase in the layering number will shorten the length of the layer only slightly, and a small decrease in the layering number will cause only a small increase in the length of the layer. In a sloping roadway with uphill ventilation, higher values of the layering number are needed to achieve this "controlled" condition; the values range from about 5 at small slopes to about 8 at a slope of 1: 10. In downhill ventilation it is possible for layers to "back" against the ventilation, i.e., to flow uphill. The critical condition for preventing backing can also be expressed in terms of the layering number. Backing will be prevented if layering numbers are about 3 for small slopes and about 4.5 for large slopes; these values for downhill ventilation also give good control of the layer.

Jan 10, 1962

By A. R. Troiano, W. J. Barnett

The existence of a grain size stabilization effect on martensitic type reactions as shown by Scheill in an iron-29 pct nickel alloy and by Troiano and Tokich2 in cobalt prompted a review of other martensitic reactions to determine if this stabilization effect is characteristic of all martensite type reactions. Preliminary work has shown this effect to be present both in the gamma —+ epsilon transformation in an iron-20 pct manganese alloy and the martensite transformation of SAE 4140 and 3 pct Cr-O.40 pct steels. No appreciable effect was found in an SAE 2340 steel. The M, temperature for the gamma —+ epsilon transformation was lowered from 380°F to about room temperature by varying the annealing treatment following cold work as shown in Table I. The effect of austenitic grain size on the M, of three steels is shown in Table 2. M, was deter- mined by the conventional quench-temper method of Greninger and Troiano. In a single crystal the change in external shape concomitant with the homogeneous shear mechanism of the martensite transformation can take place unhindered. In a polycrystalline specimen a restraint of these changes must occur at the grain boundaries. Therefore, the smaller the grain size the greater the shear strain energy necessary for the formation of a martensite crystal. The degree of lowering of M, due to the reduction of grain size is much greater when the change in crystal structure involves only a small energy change, such as face-centered cubic —+ close packed hexagonal (that is, CO and Fe-20 pct manganese alloy). The maximum lowering of M, observed in the steels investigated was 50°F with a change in the ASTM austenitic grain size of 1-2 to 8-9. In comparison, the crystal structure change face-centered cubic —+ body-centered tetragonal involves a considerable energy change. There is little doubt that with much finer grain sizes the increased grain boundary restraint would greatly enhance this stabilization effect. The implications of this phenomenon are multifold. Undoubtedly. under certain conditions it offers a method of stabilizing high temperature phases for room temperature

Jan 1, 1949

By P. W. Andrews, R. B. Toombs

ECONOMIC STRUCTURE OF MODERN INDUSTRIAL ECONOMIES The role of minerals in modern industrial economies may be examined in several ways. There are relationships with the various sectors of the economy: the primary, secondary, and tertiary industrial groupings and activities. Mineral supply and demand activities can be measured in terms of national accounts criteria. The economic policy objectives of the modem industrial economy are based to a considerable extent on the needs of the nation for economic supplies of miner- al materials. There is an important role for minerals relative to national security in peace and in wartime and many national policies are directed toward ensuring adequate sup- plies of minerals. Environmental control in the modem industrial economy is increasingly concerned with matters related directly to the production and use of minerals and these matters, in turn, bear importantly on conservation in mineral supply and demand. Mineral polices include specific provision for research and development activities concerned with the production and the use of minerals. In all, national policy objectives will be shaped in considerable part by the circum- stances of mineral supply and demand: the relative degree of availability from domestic and foreign sources, the state of the mineral-processing industries, and the degree of development of the mineral-using industries, and per capita and total changes in requirements. Goods made from mineral raw materials are the basis of all advanced societies and although this is taken for granted, every country is continually dealing with problems of mineral supply and demand. Considering that in the first 50 years of this century the consumption of mineral materials in a highly Industrialized country such as the United States increased by six times while the population was doubling, it becomes apparent that if a country is to enjoy rapid economic growth it must have access to huge and ever-growing supplies of mineral materials at lowest possible cost. Adequate supplies of mineral materials and wise usage of mineral resources have always been among the most important determents of a nation's survival The importance of access to adequate mineral supplies is increasing every year and this has significant international, as well as national, implications because of the unique locational characteristics of mineral resources. It is generally acknowledged that no particular type of natural resource is essential to a high level of national income or to economic progress. A country's endowment of natural resources need not exercise a determining influence on the course of its national income over time, provided it is able to trade. What is required for economic progress is the availability of a substantial quanti-

Jan 1, 1976

By M. R. J. Wyllie

The relationship between the electromotive force (E.M.F.) across a shale barrier and the concentrations of sodium chloride solutions on either side has been investigated. It is shown that the action of a shale barrier is analogous to a glass membrane separating two acid solutions of different hydrogen ion concentrations. The shale behaves as a sodium electrode and is responsive to the activities of the sodium ions in the two solutions in such a way that the potential can be calculated by means of the Nernst equation. This conclusion is confirmed by laboratory experiments. In a borehole the total E.M.F. of a shale cell is the algebraic sum of the ~otential across the shale and a boundary potential. The relationship between total E.M.F. and the resistivity ratio of two sodium chloride solutions is indicated for a number of formation temperatures. The E.M.F. thus predicted is then compared with the .elf potential read from an electric log and good agreement is demonstrated. Based on both the self potential and resistivity curves of the electrical log. a method is given for calculating connate water content in a bed having in-tergranular porosity and containing both connate water and hydrocarbons. INTRODUCTION The first paper on electrical well logging by C. and M. Schlumberger and E. G. Leonardon in 1934' attributed the self potential curve principally to streaming potentials, i.e. to electroki-netic effects. Almost immediately great difficulties were encountered in reconciling many of the curves they obtained with this interpretation. and a ~econd paper' by the same authors soon appeared. In this second paper self potentials were attributed to the combined effects of streaming potentials and electrochemical potentials, the electrochemical potential being considered the result mainly of the interaction of fluids of differing salt concentrations, i.e. a boundary potential, and partly of potentials set up at the faces of impermeable materials. Some experiments involving a gray clay for the impermeable material were quated. The Schlumbergers and Leonardon deduced from the equation for a simple boundary ~otential that the electrochemical potential, as opposed to the electrokinetic potential, could be expressed in the form E=Klog- .......1 pe where K is a constant, pm the mud resistivity. p, the resistivity of the connate water in a porous bed. However, no general expression for the constant K was obtained. Although the literature between 1934 and 1943 contains a number of quotations of their results, the valuable work of the Schlumbergers and Leonardon was not extended so that the electrochemical potential has been generally attributed wholly to boundary potentials between the mud in the borehole and the connate waters in porous formations. Unfortunately, however, the fundamental premise of all these papers, that a boundary potential can give rise to current flow in a borehole, is thermodynamically untenable. As will be shown. the fact that the electrochemical potential can be fairly accurately express as E = K log pm/pc, a form in which a boundary potential may also be written, is partly fortuitous. The boundary potential is indeed an integral part of the expression for the electrochemical potential in a horehole, but in magnitude it represents only about 20% of the total potential. In 1943 an important step in the elucidation of electrochemical potentials was made by Mounce and Rust3 who showed that if a wall of shale separated two compartments which contained saline solutions of different concentrations, and if the two solutions were themselves brought into contact in the pores of a porous inert membrane (such as unglazed porcelain) a current flowed through the shale and saline solutions. The direction of positive current was from the shale into the more dilute solution. The paper of Mounce and Rust, while repeating some of the observations of the Schlumbergers and Leonardon, seems to be the first to show that the shale was the seat of a genuine electrochemical effect capable of causing current flow. In the same paper Mounce and Rust pointed out the similarity between the fundamental conditions of their experiment and the conditions which existed when a bed of shale in the ground was simultaneously in contact with a porous sand containing saline connate water and mud fluid of salinity different from that of the water in the sand. Since it is now generally recognized that the S.P. curve measures ohmic potential changes in the mud fluid in the well bore resulting from changes in current flow, it is apparent that currents having their origin in the electrochemical interaction of mud filtrate and connate waters with shale beds are a very important portion of the total S.P. The work of Mounce and Rusta and others appears to indicate that, in general, the electrochemical portion of a particular kick on a S.P. curve far exceeds any electrokinetic potentials resulting either from streaming potentials or Dorn effects. The Dorn effect, or sedimentation potential. arises when small particles are allowed to fall through certain fluids under the influence of gravity. a difference of potential being observe? between two electrodes placed at different levels in the stream of falling particles. The Dorn effect is unlikely to affect seriously the S.P. curve as now measured. A successful analysis of the electrochemical aspects of the S.P. log should

Jan 1, 1949

By M. R. J. Wyllie

The relationship between the electromotive force (E.M.F.) across a shale barrier and the concentrations of sodium chloride solutions on either side has been investigated. It is shown that the action of a shale barrier is analogous to a glass membrane separating two acid solutions of different hydrogen ion concentrations. The shale behaves as a sodium electrode and is responsive to the activities of the sodium ions in the two solutions in such a way that the potential can be calculated by means of the Nernst equation. This conclusion is confirmed by laboratory experiments. In a borehole the total E.M.F. of a shale cell is the algebraic sum of the ~otential across the shale and a boundary potential. The relationship between total E.M.F. and the resistivity ratio of two sodium chloride solutions is indicated for a number of formation temperatures. The E.M.F. thus predicted is then compared with the .elf potential read from an electric log and good agreement is demonstrated. Based on both the self potential and resistivity curves of the electrical log. a method is given for calculating connate water content in a bed having in-tergranular porosity and containing both connate water and hydrocarbons. INTRODUCTION The first paper on electrical well logging by C. and M. Schlumberger and E. G. Leonardon in 1934' attributed the self potential curve principally to streaming potentials, i.e. to electroki-netic effects. Almost immediately great difficulties were encountered in reconciling many of the curves they obtained with this interpretation. and a ~econd paper' by the same authors soon appeared. In this second paper self potentials were attributed to the combined effects of streaming potentials and electrochemical potentials, the electrochemical potential being considered the result mainly of the interaction of fluids of differing salt concentrations, i.e. a boundary potential, and partly of potentials set up at the faces of impermeable materials. Some experiments involving a gray clay for the impermeable material were quated. The Schlumbergers and Leonardon deduced from the equation for a simple boundary ~otential that the electrochemical potential, as opposed to the electrokinetic potential, could be expressed in the form E=Klog- .......1 pe where K is a constant, pm the mud resistivity. p, the resistivity of the connate water in a porous bed. However, no general expression for the constant K was obtained. Although the literature between 1934 and 1943 contains a number of quotations of their results, the valuable work of the Schlumbergers and Leonardon was not extended so that the electrochemical potential has been generally attributed wholly to boundary potentials between the mud in the borehole and the connate waters in porous formations. Unfortunately, however, the fundamental premise of all these papers, that a boundary potential can give rise to current flow in a borehole, is thermodynamically untenable. As will be shown. the fact that the electrochemical potential can be fairly accurately express as E = K log pm/pc, a form in which a boundary potential may also be written, is partly fortuitous. The boundary potential is indeed an integral part of the expression for the electrochemical potential in a horehole, but in magnitude it represents only about 20% of the total potential. In 1943 an important step in the elucidation of electrochemical potentials was made by Mounce and Rust3 who showed that if a wall of shale separated two compartments which contained saline solutions of different concentrations, and if the two solutions were themselves brought into contact in the pores of a porous inert membrane (such as unglazed porcelain) a current flowed through the shale and saline solutions. The direction of positive current was from the shale into the more dilute solution. The paper of Mounce and Rust, while repeating some of the observations of the Schlumbergers and Leonardon, seems to be the first to show that the shale was the seat of a genuine electrochemical effect capable of causing current flow. In the same paper Mounce and Rust pointed out the similarity between the fundamental conditions of their experiment and the conditions which existed when a bed of shale in the ground was simultaneously in contact with a porous sand containing saline connate water and mud fluid of salinity different from that of the water in the sand. Since it is now generally recognized that the S.P. curve measures ohmic potential changes in the mud fluid in the well bore resulting from changes in current flow, it is apparent that currents having their origin in the electrochemical interaction of mud filtrate and connate waters with shale beds are a very important portion of the total S.P. The work of Mounce and Rusta and others appears to indicate that, in general, the electrochemical portion of a particular kick on a S.P. curve far exceeds any electrokinetic potentials resulting either from streaming potentials or Dorn effects. The Dorn effect, or sedimentation potential. arises when small particles are allowed to fall through certain fluids under the influence of gravity. a difference of potential being observe? between two electrodes placed at different levels in the stream of falling particles. The Dorn effect is unlikely to affect seriously the S.P. curve as now measured. A successful analysis of the electrochemical aspects of the S.P. log should

Jan 1, 1949

By AIME AIME

OPPORTUNITY may not be knocking but it, at least, is waiting for you, your family and your friends in that amazing republic south of the Rio Grande. For the first time we are able to publish the official itinerary for the forth-coming Mexico City meeting of 1936. As shown on Page 351, the deluxe special train leaves St. Louis on Thursday. Nov. 5 at 5:30 p.m., returning to St. Louis on Nov. 18 at 8:15 a. m. The schedule provides seven days and six nights in Mexico City with numerous excursions to nearby towns and resorts. The oldest surviving city in' North America is Mexico City, dating back at least to the twelfth century. It was the Aztec capital when Cortez arrived in 1519. The famous cathedral still standing was built on a foundation of sculptured Indian images and the remains of a great Aztec temple. Today it is a city of romance.

Jan 1, 1936

By H. M. Morse

During the year of 1940, wildcat wells were drilled in 32 counties of Mississippi; 85 wells in all. These were scattered over the state from the most northern county to the southern counties and from the Mississippi River on the west to the Alabama line on the east. Yazoo County, with 19, received the largest number. The average depth of all the wells was 5333 ft. The shallowest well completed as a dry hole was in Yalobusha County, aban-doned at 1392 ft. in the Selma. The deepest well drilled was in Scott County, abandoned at 10,365 ft. in the Lower Cretaceous Paluxy. G. C. Grasty drilled the Kentucky Lumber Company No. I well, sec. 7, T. 10 S., R. 10 E., Itawamba County, to a depth of 3530 ft. and bottomed his hole in the Ordivician. Tinsley Oil Field.—In the Tinsley oil field 104 wells were completed as producers during 1940. Five producing sands have been logged with a total average thickness of I57 ft. of oil sand. One of these sands is in the Selma, three in the Eutaw, and one in the Tuscaloosa. Vaughan-Pickens Field.—The Vaughan-

Jan 1, 1941

By H. M. Morse

During the year of 1940, wildcat wells were drilled in 32 counties of Mississippi; 85 wells in all. These were scattered over the state from the most northern county to the southern counties and from the Mississippi River on the west to the Alabama line on the east. Yazoo County, with 19, received the largest number. The average depth of all the wells was 5333 ft. The shallowest well completed as a dry hole was in Yalobusha County, aban-doned at 1392 ft. in the Selma. The deepest well drilled was in Scott County, abandoned at 10,365 ft. in the Lower Cretaceous Paluxy. G. C. Grasty drilled the Kentucky Lumber Company No. I well, sec. 7, T. 10 S., R. 10 E., Itawamba County, to a depth of 3530 ft. and bottomed his hole in the Ordivician. Tinsley Oil Field.—In the Tinsley oil field 104 wells were completed as producers during 1940. Five producing sands have been logged with a total average thickness of I57 ft. of oil sand. One of these sands is in the Selma, three in the Eutaw, and one in the Tuscaloosa. Vaughan-Pickens Field.—The Vaughan-

Jan 1, 1941

By R. R. Jones, R. W. Kraft

Zn-Mg2Znn eutectic alloys nzay freeze willr either rodlike or lanzellar rnorphology. Alloys with slighlly more than /he eutectic arrzount of rnagnesillrn usually contain three-cnned dendrjles of MgzZnll in a eutec-lic ttlulris. All three morphologies haue the same cryslallographic orientution relationship: (0UOl) zn - 11 (111) Mg2Znll and (2310)Zn 11(101) Mg2Znll, but u3ith different prej-erred groulth direclions. The lurnellae lo rods transifion in con/rolled ingols qf euleclic cotnposition occurs because lhe large kinelic undercooling due to MgzZnll minirrzizes /he ejj-ecl of the solid-solid inlerface energy. The eutectic morphology is influenced by the presence of lhree-nned dendrites 0-f MgzZn11 which may conlrol /he rricroslrccture by acting as nuclealion sites. In recent years there has been much interest in eutectic solidification and several theories have been proposed. One of the confusing factors is the existence of various morphologies in which the solidified phases may form. The lamellar microstructure seems to be most common in metal eutectics, and it has been claimed' that all regular eutectics should be lamellar if sufficiently pure. However, there still remain eutectic alloys which are not lamellar or which change their morphology as a function of growth conditions. The eutectic between zinc and the intermetallic phase Mg2Znll was chosen for this investigation because it has been found to solidify in more than one morphology. The diagram in anssen' locates the eutectic point at 3.0 wt pct Mg and 367°C. lliott gives 364°C as the eutectic temperature, leaving the phase compositions unaltered. Since the growth conditions determine the micro-structure of the solidified alloy, the factors controlling the transition from one morphology to another could be studied. The lamellae to rods transition is of particular interest. PROCEDURE Alloys were prepared from carefully weighed portions of 99.999 pct Zn and 99.97 pct Mg by melting in Pyrex containers under argon and casting into graphite boats. The resulting ingots were remelted under argon and solidified unidirectionally in a horizontal tube furnace at growth rates ranging from 2.0 to more than 50 cm per hr under a temperature gradient, measured over a 5-cm length, of 9" to 14°C per cm. The solid-liquid interface appeared to be planar at all growth rates although no attempt was made to confirm this by decantation or quenching. A few ingots were allowed to freeze uncontrolled. Most alloys were of the nominal eutectic composition, 3.0 wt pct Mg according to Hansen2 and lliott, but some contained as much as 3.35 wt pct Mg. Chemical analyses were not run since metallographic examination confirmed that the desired composition was achieved. Specimens were cut from the middle portion of the ingot normal to the growth axis, polished mechanically, and etched with 2 pct Nital. Suitable areas were selected for the determination of crystallographic orientation relationships by a tiontechniqueof described previously by one of the authors.4 The (2310) planes of zinc and the (8701, {944}? (1032) planes of Mg2Znll were found suitable for orientation determination; experimental error was on the order of 2 or 3 deg. RESULTS Three different morphologies were found in the unidirectionally solidified alloys: lamellar eutectic, rod-like eutectic, and a structure whose most predominant characteristic was the presence of three-vaned (cellular) dendrites of Mg2Znll. These dendrites were only found in alloys with more than the eutectic amount of magnesium. In some ingots fine hexagonal needles of Mg2Znll surrounding a core of MgZn2 were observed. They were probably due to incomplete alloying and seemed to have no effect on the eutectic morphology. In addition hexagonal spirals like those discussed by Fullman and wood5 and Hunt and acksonh ere observed in some ingots frozen without directional control. Both MgZZn,, and MgZnz were detected by X-ray diffraction in these alloys. Since the morphology could not be grown unidirectionally and no characteristic orientation relationship between the phases was found, further study was limited to the lamellar: rodlike, and three-vaned dendrite morphologies. Alloys of Eutectic Composition, No Dendrites. The mcrostructures of allovs with no three-vaned dendrites were either lamellar or rodlike depending on the growth rate. At rates below 10 cm per hr the morphology was lamellar, consisting of two sets of parallel plates intersecting at about 54 deg like the Mg-MgzSn eutectic described by raft.7 At growth rates faster than 14 cm per hr the microstructure showed rods of zinc in a matrix of MgnZnll, while intermediate rates yielded mixtures of rods and lamellae in small groups. The lamellar "grains" were often several millimeters in cross section, but contained small irregular areas which divided each grain into perfect islands 100 or 200 p in diam. Lamellae were parallel to each other throughout the grain in spite of these defects in the structure, Fig. 1. Rods, on the other hand, could only be produced in small groups arranged like fish scales and separated by irregular areas of appreciable thickness, Fig. 2. Alloys Not of Eutectic Composition, With Dendrites. In alloys with 3.1 to 3.35 wt pct ME,-. three-vaned dendrites bf MgzZnll were usually found surrounded by eutectic. At growth rates slower than about 10 cm per hr the dendrites were separated from each other by small areas of both lamellar and rod eutectic, Fig. 3.

Jan 1, 1969

By G. B. Misra

While investigating on the aerodynamic resistance of airways supported with peripheral timber sets, at regular intervals, the following theoretical equations were developed by the author to estimate the resistance coefficient of such airways: [ ] for S < 1, where f is Darcy-Weisbach resistance coefficient of the airway, C is modified drag coefficient of the supporting member, D is equivalent diameter of the bare airway, 8 is ratio of the approach velocity over the sets to the average velocity of the bare airway, A is cross-sectional area of the bare airway, a is projected frontal area of the sets, A., is cross-sectional area of the air stream at the vena contracta inside the set, S is spacing of the sets, f, is resistance coefficient of the bare airway, l is length of aerodynamic influence of sets, p is perimeter of the bare airway, p, is setted portion of the perimeter of the bare airway, pe is unsetted portion of the perimeter of the bare airway, and P shielding factor. The equations were verified experimentally in a model rectangular airway supported with one- (bars), three-, and four-piece sets of square-section timber of three different sizes and were found to hold true. The work has been further extended to one-, three-, and four-piece sets of round timber of 2.6, 3.2, and 3.8 cm diam with the same experimental set up. Tests have been carried out for spacings of 25, 50, 75, 100, 150, and 200 cm over a regime of flow defined by the Reynolds number (with respect to the equivalent diameter of the bare duct) ranging from about 1.5 X 106 to 5 X 106 using the same experimental techniques. The values of f are calculated in the manner indicated in [Ref. 1]. Unlike with square-section timber, the resistance coefficient f of the airway setted with round timber shows a distinct variation with the Reynolds number of flow. This conforms to observations made by Sales and Hinsley.2 In order to have a comparable value of f for all types of sets with all sizes of timber, it was necessary to select the value of f at a fixed Reynolds number of flow. Since f is chiefly a function of the drag coefficient of the sets, the appropriate Reynolds number RE is that with respect to the diameter of timber in the set. Considering the diameters of timber used and the regime of flow over which measurements were made, f was chosen at a value of RE = 20,000 in all cases. The f vs. S curves are maximal in nature and in conformity with theory, the f vs. 1/S curves are straight lines up to a value of S = 1 beyond which they show a distinct flexure. The observed values of 1, the length of aerodynamic influence of sets, agree with the relation 1 = 42 e, developed for square-section timber sets, thus suggesting that the shape of timber has little influence on the length of aerodynamic influence. The value of the modified drag coefficient CD for round timber was calculated in the same way as for square timber in Ref. 1, taking the contraction factor Z = 1.5 for round-edged constrictions. CD has an average value of 0.96 with a standard deviation of 6.08% as compared to the free stream drag coefficient of 1.2 at RE = 20,000 for long cylindrical obstructions The shielding factor [ ] is plotted against S/1 in [Fig. 1]. The curves are more or less independent of the size of timber, but are different for the different types of sets, possibly due to their different degree of symmetry. Values of f calculated by the author&apos;s [Eqs. 1 and 2], using experimental values of CD&apos; and [ ] and taking I = 42 e, are plotted in [Fig. 2] against experimentally measured values of f for different types of sets with different sizes of round timber. The values agree closely with a standard deviation of only 5%, thus establishing the veracity of the theoretical equations developed by the author for round timber as well. A comparison was made between the Xenofontowa4 equations (the only other reasonable relations available for the estimation of the resistance coefficient of supported airways) and the author&apos;s [Eqs. 1 and 2] by comparing in [Fig. 3] the values of the resistance coefficient f computed by the Xenofontowa relations with those experimentally measured by the author. In order to make

Jan 1, 1975

By J. W. Walker, G. J. Heuer, E. W. Hough

An improved apparatus is described for the deterrni-nation of interfacial tension* by the pendant drop method in the pressure range from 15 to 15000 psi and the temperature range from 100º td 280°F. The chief characteristics of this apparatus are reliability and ease of operation. Temperature control was accomplished by means of an electrically heated jacket which could he completely removed while cleaning the apptrratus. The cell was designed so that the camera could he placed about I in, from the window without overheating the carnera lens. Separate "0" rings employed to seal each window and corresponding window backup plate gave very reliable window operation at 10,000 psi. An extra pistorr-cylinder combination was added so that a high compression ratio could he attained when gas was employed as one phase in the pendant drop cell. Other essential parts of the system were similar to an apparatus already described.&apos; The interfacial tension for carbon dioxide and water varies from about 69 dynes/cm at 15 psi to about 19 dynes/cm at 1,250 psi for 100°F. For pressure.r between t,500 and 3,500 psi, the interfacial tension is between 32 and 24 dynes/cm at this temperature. The interfacial tension at 280°F varies from about 50 dynes/cm at 200 psi to about 17 dynes /cm at 10,000 psi. The maximum surface excess for carbon dioxide, assuming the surface excess of water to be zero, occurs at about 1,500 psi jor the 100°F isotherni and Itas a value of about -79 X 1014 mol/sq cm. At 160°F this maximum IS shifted to about 2,000 psi and has a value of about 10 X 1014 111ol/.sq cm. Other maxima, us well as several minima, are present at these and other temperatures. Judging from the data on the solubility of water in carbon dioxide at elevtrted pressures2,3, it appears that the principal maxinza natned are in regions of increasing solubility of the water in the carbon dioxide rich phase. INTRODUCTION AND APPARATUS A pendant drop interfacial tension apparatus which would accommodate an opaque liquid in a gas phase was constructed several ycars ago&apos; for industrial purposes. This apparatus was used as a starting point for the present development. The objective of the present development was to enhance reliability and convenience of operation. Other articles&apos;" have described pendant drop apparatus which could not accommodate a gaseous phase adjacent to the windows. A schematic diagram of the apparatus is shown in Fig. 1. The water used followed the path; A, intro-

By F. E. Werner, B. L. Averbach, Morris Cohen

THAT bainite formed near the M, temperature bears a striking r esemblance to martensite tempered at the same temperature has been shown by the electron microscope.&apos; By means of electron diffraction,&apos; it has been established that carbide and cementite are present in bainite formed at 500°F (260°C); these carbides are also found in martensite tempered at 500°F (260°C).&apos; The investigation reported here is concerned with an X-ray study of the matrix phases in lower bainite and tempered martensite. These phases have turned out to be dissimilar in structure; the matrix of bainite is body-centered-cubic while that of tempered martensite is body-centered-tetragonal. A vacuum-melted Fe-C alloy containing 1.43 pct C was studied. Specimens of 16 in. diam were sealed in evacuated silica tubing and austenitized at 2300°F (1260°C) for 24 hr. One specimen was quenched into a salt bath at 410°+7 °F (210°+4°C), held for 16 hr, and cooled to room temperature. The structure consisted of about 90 to 95 pct bainite, the re: mainder being martensite and retained austenite. A second specimen was quenched from the austen-itizing temperature into iced brine and then into liquid nitrogen. It consisted of about 90 pct martensite and 10 pct retained austenite. The latter specimen was tempered for 10 hr at 410°+2°F (210°+1°C). The specimens were then fractured along prior austenite grain boundaries (grain size about 2 mm diam) by light tapping with a hammer. Single aus-tenite grains, mostly transformed, were etched to about 0.5 mm diam and mounted in a Unicam single crystal goniometer, which allowed both rotation and oscillation of the sample. Lattice parameters were measured by the technique of Kurdjumov and Lyssak. This method takes advantage of the fact that martensite and lower bainite are related to austenite by the Kurdjumov-sachs orientation relationships Thus, the (002) and the (200) (020) reflections can be recorded separately, permitting the c and a parameters to be determined without interference from overlapping reflections. According to these findings, the matrix phase in bainite is body-centered-cubic and, within experimental error, has the same lattice parameter as ferrite (2.866A). On the other hand, martensite, tempered as above, retains some tetragonality, with a c/a ratio of 1.005t0.002. Most workers in the past have assumed that bainite is generated from austenite as a supersaturated phase, but the nature of this product has not been established. The question arises as to whether bainite initially has a tetragonal structure and then tempers to cubic, or if it forms directly as a cubic structure. If it forms with a tetragonal lattice, it might well be expected to temper to the cubic phase at about the same rate as tetragonal martensite. The martensitic specimen used here was given approximately the same tempering exposure, 10 hr at 410°F, as suffered by the greater part of the bainite during the isothermal transformation. About 50 pct bainite was formed in 6 hr at 410°F. On tempering at this temperature, martensite reduces its tetragonality within a few minutes to a value corresponding to 0.30 pct C.&apos; Further decomposition proceeds slowly, and after 10 hr the c/a ratio is still appreciable, i.e., 1.005. Thus, even if the bainite were to form as a tetragonal phase with a tetragonality corresponding to only 0.30 pct C, which might be assumed to coexist with e carbide, it would not be expected to become cubic in this time. It seems very likely, therefore, that bainite forms irom austenite as a body-centered-cubic phase and does not pass through a tetragonal transition. The carbon content of the cubic phase has not been determined, but it could easily be as high as 0.1 pct, within the experimental uncertainty of the lattice-parameter measurements. It has been postulated that retained austenite decomposes on tempering into the same product as martensite tempered at the same temperature. There is now considerable doubt on this point. The isothermal transformation product of both primary and retained austenite at the temperature in question here is bainite," and the present findings show that bainite and tempered martensite do not have the same matrix. Acknowledgments The authors would like to acknowledge the financial support of the Instrumentation Laboratory, Massachusetts Institute of Technology, and the United States Air Force.

Jan 1, 1957

By S. I. Liu

THE effects of strain histories, consisting of several prestrains in opposite directions, on the flow and fracturing characteristics of metals determined in a final test have been investigated previously.&apos;" Such strain histories vary from a single prestrain in tension or compression to the number of strain cycles leading to fatigue failure.&apos; Between these two limits, various strain histories could be visualized and some can be attained readily. One such example is a strain history consisting of a first prestrain in tension of various magnitudes and a second prestrain in compression also of various mag-nitude. In this investigation the strain history was extended to the combination of these two limits, i.e., a single prestrain in tension or compression followed by balanced strain cycles of a selected magnitude e, = k0.12. It was found in this case that only compressive initial prestrains could be investigated with sufficient accuracy.* Such strain histories can be considered also as (low cycle) fatigue tests of a metal subjected to various amounts of cold working. It appears from previous publications that cold working within a wide range of reductions usually raises the un-notched fatigue strength of many metals.&apos;-&apos; This effect, however, has been found to be inconsistent and sometimes reversed for other metals?.7 Furthermore, Ludwik reports that the yield strength of cold-worked specimens may be reduced by cyclic strains, while that of materials without cold work is generally increased in the initial cycles." " In addition to the above tests, a study was made of the effect of intermediate re-solution heat treatment on low cycle fatigue behavior. Such anneals should eliminate the strain hardening induced by the cyclic strains. As far as their effect on the fracture characteristics is concerned, a few previous tests seemed to indicate that the damage resulting from cyclic strains is retained only partially after heat treatment." A further investigation was made in which one specimen was subjected to repeated unbalanced tension cycles in which the strain interval was approximately $ 0.013. This repetition of plastic tension damages the material slightly. This result appears to confirm Ludwik&apos;s observations." " Commercial 3/4-in. rod of the aluminum alloy 24ST4 was selected for this investigation. The material was subjected to the following treatments before machining: 1—Re-solution treatment at 920" ± 10°F for 45 min, 2—water quench at room temperature, and 3—aging for four days at room tem-perature.? The treated material then was machined to desired specimen contour and tested. A coolant was used during machining to minimize any artificial aging effects of heating during machining. In some cases the 24ST4 specimens were reheat treated after having been strained. In these cases, the heat treatment was the same as the re-solution heat treatment described above. Procedure As shown in Fig. 1, threaded end specimens with a minimum diameter of 0.266 in. and a contour radius of 2 in. were used for prestraining to an axial compressive strain ranging from 6, = —0.10 to E, = —0.48. For large prestrains, two consecutive corn-

Jan 1, 1952

By W. A. Sheaffer

Electric furnace installation and tough-pitch copper-casting operation at Canadian Copper Refiners Ltd. are described. General layout, power supply and control, refractories, induction pour hearth, casting equipment, metal temperature control, and oxygen-content control are discussed. E LECTRIC furnace at Canadian Copper Refiners Ltd. was put into operation in August 1949. The installation was designed primarily to melt electrolytic copper cathodes and to produce vertically cast tough-pitch shapes. To meet emergencies during reverberatory furnace shut-downs, provision was made for casting horizontal tough-pitch wire bars. Due to the ease with which metal temperatures, melting rates, oxygen content, and casting hours can be altered to suit production demands, the electric furnace has met the requirements admirably. General Layout The plant has been described by H. S. McKnight&apos; and by J. H. Schloen and E. M. Elkin.2 Since these papers were written, the electric furnace has been installed in a 140 ft extension of the original casting building. The extension, 264 ft in width, is divided into one 24 ft and four 60 ft bays, each a continuation of similar bays in the older building. Fig. l, a partial floor plan of the extension, shows the location of major equipment. Power Supply and Control Power for the electric furnace and its auxiliary equipment is delivered by Quebec Hydro over two 12 kv three-phase, 60 cycle pole lines. One line is in use, while the second serves as an emergency standby. Connections for the electric furnace from these lines, which also feed the refinery power house, are made to a substation on Canadian Copper Refiners Ltd. property. Connections between this substation and the furnace transformer room are in underground conduit. The are-furnace transformer, 550 v auxiliary-equipment transformer, and 12 kv switchgear are in the transformer room near the furnace. Stepdown from 12 kv to are-furnace voltages is done by a 7500 kva oil-immersed water-cooled three-phase 60 cycle transformer. This unusually high kva rating is available because the arc furnace and transformer were adapted from a steel-melting unit. Secondary voltages are available in 16 steps between 251 and 95 v (across phases). A four-position tap changer, operated from the furnace switchboard is connected to taps yielding 199, 164.5, 127, and 115 v, respectively. The transformer primary feeder is equipped with a General Electric Magne-Blast circuit breaker. The pour hearth, casting wheel, bosh conveyor, and other auxiliary equipment are fed by a 12 kv to 550 v, 750 kva three-phase 60 cycle transformer. Graphite electrodes, 14 in., with tapered nipples are held in the are-furnace electrode arms with steel wedges. The arms, fed from the transformer secondary busbars by flexible cable bundles, are actuated by winch cables. Direct-current motors operating the winches are supplied by a 250 v motor-generator set. Power input to the furnace is controlled from the furnace switchboard. The board has the usual combination of remote controls for the 12 kv breaker and transformer tap changer, meters, overload relays, automatic and manual electrode motion controls, switchgear, etc. When power is on the furnace, automatic electrode feed is used; the power draw on a given voltage tap then is governed by current-limiting rheostats. The rheostats work through a Westinghouse bal-lanced-beam control circuit which, in turn, operates reversing contactors in the winch motor circuits. Arc Furnace The arc furnace is a standard-type NT Pittsburgh &apos;Lectromelt with inside shell diameter 12 ft 3¾ in. By hydraulic-lift cylinders, the furnace can be tilted forward to 39 ½ ° and backward to 5" from horizontal. A roof-swing cylinder is also installed but not used. Fig. 2 shows refractory-lining details. With the lining as shown, operating life between repairs is 6 to 9 months of two-shift casting operation. Charge slot, skim door, and roof refractories then are replaced completely, and any necessary repairs made to side walls. Bottom life is longer and the original under courses are still in service, while the top course was replaced in October 1951. The launder is lined with high chrome-magnesite trough brick backed by fireclay and insulating brick. The trough is covered with fireclay brick and asbestos sheet. At intervals, openings 12x6 in. are left in the permanent covering. These are covered with

Jan 1, 1956

By Raymond E. Byler

THE challenge of unprecedented need for more metals to meet present-day re-armament and domestic requirements is being met with minerals beneficiation projects of great number and variety, and with new and improved methods, techniques, and. equipment. Iron Range Developments Much attention has been given during the year to the tremendous program for beneficiation of taconites and intermediate iron ores which is progressing through large pilot-plant tests preparatory to full-scale production operations. The greatest activity has been directed toward concentration of magnetic taconites on the Mesabi Range. The Reserve Mining Co. has let $75 million in construction contracts for the 2 ½ million-ton-per-yr project (concentrates) at Beaver Bay, Minn., and is building a 300,000-ton-per-yr pilot plant to prove up the magnetic separation and pelletizing operations. Oliver Iron Mining Co. has a pilot plant under construction near Mountain Iron for concentrating magnetic taconites, and is operating experimentally a sintering and nodulizing plant on fine ore screenings and concentrates at Virginia to fully develop agglomeration technique. The Erie Mining Co. plant at Aurora continues its production of concentrates from magnetic taconites which was begun three years ago. No plans have been announced to treat the Mesabi Range nonmagnetic taconites, but F. D. Devaney, Pickands Mather and Co., is studying a new process for magnetically roasting lean ores to make them amenable to low-intensity magnetic concentration. W. R. Van Slyke, Cleveland-Cliffs Iron Co., calls attention to several noteworthy developments in the field of intermediate ores, perhaps the most significant of which has been the first commercial operation of a Dutch State Mines (DSM) cyclone plant at the Buckeye mine of the M. A. Hanna Co. The plant concentrates the +1/4 in. fraction by means of conventional heavy-media treatment after suitable crushing, screening, and washing. The -1/4 in. +65 mesh material is treated in two 12-in. cyclones, the -65 mesh fraction being sent to tailing storage. The plant is operating successfully on feed rates up to 120 tons per hr, and indicates that successful treatment of the fine fractions of Mesabi intermediate ores is imminent. Another commercial-size DSM plant was placed in operation late in the year by Cleveland-Cliffs at the Holman mine, and two additional ones are expected to be in operation next year. Various other methods are also in use at different plants for treatment of the fine fractions, including classification, abrasion milling followed by classification, jigging, and Humphrey spirals. Where it can be economically justified, it seems at present that heavy-media treatment of the -1/4 in. fine fraction will also come into increasing use on the intermediate ores. During 1951 a one-unit, heavy-media plant to treat hematitic crude ore was erected at the Ohio mine on the Marquette Range by Cleveland-Cliffs and plans for another plant at Humboldt to produce 2000 tons of concentrates annually is contemplated, as is also the construction of a plant for agglomera-

Jan 1, 1952

By J. Pinto, F. Galasso

THE current emphasis in preparing boron fibers by reduction of gaseous boron compounds on a resistively heated metal wire substrate has renewed interest in the borides of those metals which have relatively high melting points and are available as fine wires. A knowledge of the structures and properties of the borides, which are formed when boron diffuses into the metal core during boron deposition, can be of assistance in the understanding of the boron fiber formation process and the fiber properties. Many of these borides are well-known and their properties have been measured. However, when an unidentified boride is found in the core, it may be difficult to establish its composition because of the small amount of material available, the preferred orientation effects on the reflections in its X-ray pattern, and the possible overlap of X-ray reflections if several borides are present in the core. For example. the proper indexing of the X-ray pattern of WB4, which was formed in the tungsten substrate core during boron fiber formation, was accomplished only after small single crystals of this boride were grown and X-ray precession investigations were conducted.&apos; This note presents the results of a study of the phases formed in the core when tungsten, tantalum, and molybdenum metal wires were used as substrates in the boron fiber preparation process with particular emphasis on the identification and characterization of a higher boride of molybdenum analogous to WB,. Boron was deposited on resistively heated stationary 0.0012-in.-diam tantalum, tungsten, and molybdenum wires at 1050°C for various times up to 60 sec using boron trichloride and hydrogen as the reactant gases. After 60 sec of boron deposition the fibers were approximately 0.006 in. in diam. Examination of photomicrographs of fiber cross sections showed that the boron had diffused nearly to the center of the tungsten and molybdenum cores in 15 and 30 sec, respectively, and only halfway to the center of the tantalum core in 60 sec. X-ray diffraction photographs of the fibers indicated that it was also after 15 and 30 sec deposition times that the tungsten and molybdenum metal reflections, respectively, had disappeared from the X-ray patterns of the fibers. The patterns of the boron fibers produced using tantalum wire as a substrate showed that amorphous boron, TaB2, and tantalum metal were present after a few seconds deposition time and remained even after deposition times of 60 sec. Until a deposition time of 15 sec was reached, the tungsten substrate fibers contained amorphous boron,273 6WB, W2B5, and WB4 as well as tungsten metal, while the molybdenum substrate fibers contained amorphous boron, MoBa, Mo2B5, and molybdenum metal for deposition times up to 30 sec. Just before the molybdenum metal pattern disappeared, a pattern similar to that of WB, appeared, suggesting that a phase, MOB,, isomorphous with WB,, was present in the fiber. This same pattern was obtained from the product formed by heating a mixture of molybdenum metal and excess boron powder in a boron nitride crucible at 1960°C in an argon atmosphere. As was the case with the WBn pattern, this pattern could best be indexed on the basis of a hexagonal unit cell rather than the tetragonal unit cell Chrktien and Helgorsky reported for ~0~4,~ see Table I. The unit cell parameters for MoB4 were calculated to be a, = 5.214A, co = 6.358A. Assuming the space group P63/mmc and positions5 2M01 in 2b and 2MoII in 2c found for tungsten in WB~,&apos; a logical structure for MOB, was determined using geometrical considerations to place the boron

Jan 1, 1969

By William L. Fink, Dana W. Smith

Many investigators have attempted to determine the true nature of the internal changes taking place during aging. Merica, Waltenberg and Scottlt were the first to propose a theory of age-hardening. They attributed the age-hardening of duralumin to the precipitation of minute particles of the compound CuA12. Later Zay Jeffries and R. S. Archer2 augmented the above theory by suggesting that the small CuAl2 particles acted as "keys" causing "slip interference." Many other investigators3 have devoted much time to the mechanism of age-hardening, some corroborating the "precipitation" and "slip interference" theory, others coming to different conclusions because of effects that to them seemed unexplainable by the early theories; e.g., the increase of electrical resistance upon aging, the fact that no change in lattice parameter could be detected during the early stages of aging even at elevated temperatures, and the fact that the density did not change as would be predicted. In 1932, Merica revised4 his earlier precipitation theory to take care of these presumably anomalous effects. This revised theory, the "knot" theory, assumes that substantial age-hardening occurs before actual precipitation of solute as discrete particles. The assumed mechanism is one of diffusion of solute atoms into groups forming distorted regions which act as "hard" spots and cause slip interference. These "knots" are assumed to have approximately the same lattice arrangement as the solvent. The anomalous behavior of lattice parameter, density, and electrical conductivity, require a modification of the simple precipitation-hardening theory, only if it is assumed that the precipitation of minute particles during aging has the same effects on these properties as the formation of large particles under equilibrium conditions. Data obtained by the authors in the study of the aluminum-magnesium system5 indicated that

Jan 1, 1936