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By K. A. Jackson, J. D. Hunt

A general theory for the growth of lamellar and rod eutectics is presented. These modes of growth depend on the interplay between the diffusion required for phase separation and the formation of interphase boundaries. The present analysis of these factors provides a justification for earlier approximate theovies. The conditions for stability of rod and Lanlellar structures are consitleved in terms of the mechanisms by which the structure can change. The mechanisms considered include both small adjustments to the lnnzellar spacing due to the motion of lamellar faults, and catastrophic changes due to instabilities. It is concluded that stable growth occurs at or near the minimum interface undevcooling for a gizierz growth rate. The conseqrlences of the existence of a diffusion boundary layer at the interface are discussed. The experimental results for the variation of growth rate, undercooling, and Lanzellar spacing are cornpared with the theory. We believe that the theory presented in this paper provides an adequate basis for understanding the complex phenomena of lanzellar and rod eutectic growth. The growth of lamellar eutectics has been the subject of several theoretical and many experimental studies. The foundations for the theoretical work were laid by zenerl and Brandt2 in their analyses of the growth of pearlite. Zener estimated the effect cf diffusion, and took into account the surface energy of the lamellar structure. He found that the lamellar structure could grow in a range of growth rates at a given undercooling provided the lamellar spacing was appropriate for the growth rate. Since pearlite grows with only one growth rate and one lamellar spacing at a given undercooling, there is clearly an ambiguity in the theory. Zener removed this ambiguity by postulating that the growth rate was the maximum possible at the given undercooling. He predicted then that the product of the growth velocity v and the square of the lamellar spacing A should be constant, i.e., A2v = const. Brandt2 started out by assuming that the interface between the lamellae and austenite was sinusoidal. Because of this, the ambiguity encountered by Zener did not arise. Brandt was able to obtain an approximate solution to the diffusion equation, but, since he did not take into account the surface energy, his considerations are incomplete. Tiller3 applied some of these ideas to the growth of eutectics, and proposed a minimum undercooling condition to replace the maximum velocity condition used by Zener. These conditions are formally identical. Hillert4 extended the work of Zener. He found a solution to the diffusion equation assuming the interface to be plane. Taking surface energy into account, and applying Zener's maximum condition, he was able to calculate an approximate shape of the interface. Jackson et al.5 used an iterative method employing an electric analog to the diffusion problem to refine the calculation of interface shape. It was found that the interface shape calculated from a plane-interface solution to the diffusion equation was negligibly different from the exact solution. The method provided an analog only for eutectics for which the volumes of the two phases are equal, growing from a melt of exactly eu-tectic composition. There has also been considerable experimental work on eutectics, Several experimenters8-10 found that A2v is constant as predicted by Zener.1 Hunt and chilton10 demonstrated that ?T/v1/2 is also a constant for the Pb-Sn system as predicted. Lemkey et al.11have recently found A2v to be constant for a rod eutectic. In the present paper, we present the steady-state solution for the diffusion equation for a lamellar eutectic growing with a plane interface, for the general case, that is, with no restriction on the relative volumes of the two phases, and with the melt on or off eutectic composition. A similar solution is also found for a rod-type eutectic. Expressions are obtained for the average composition at the interface and the average curvature of the interface. These equations for the average composition and curvature are similar in form to those derived by Zener1 and Tiller,3 and provide a justification for some of the approximations made by these authors. The mechanisms by which the spacing in a lamellar structure can change are considered. The important mechanism for small changes in lamellar spacing involves a lamellar fault. Examination of the stability of lamellar faults leads to the conclusion that the growth occurs at or near the extremum.* The insta- bilities which can develop in a rodlike structure are also discussed, resulting in the conclusion that this structure also grows at or near the extremum. Comparison of the conditions for rod and lamellar growth permits a prediction of the surface-energy anisotropy required to produce rods or lamellae for various volume-fraction ratios. The diffusion equation predicts the existence of a diffusion boundary layer at the eutectic interface unless the eutectic has 0.5 volume fraction of each phase and is growing into a liquid of eutectic composition. This boundary layer is such as to make the composition in the liquid at the interface approximately equal to the eutectic composition. This boundary layer permits changes in composition during the zone refining of eutectics. Photographs of the eutectic interface of a growing transparent organic eutectic system have been made. Both the components of this eutectic are transparent organic compounds that freeze as metals do.12 The in-

Jan 1, 1967

By G. M. BUTLER

TWENTY-ONE of the states in the Union, the Territory of Hawaii, and seven provinces of Canada now have in operation laws requiring that professional engineers be registered or licensed. In addition, two states require that civil engineers be registered, and one other state demands registration of structural engineers. Moreover, nearly every year sees additions made to the list. The registration movement, fostered by the American Association of Engineers, now has the powerful, energetic backing of the An1,erican Society of Civil Engineers, which is itself now fostering registration legislation, and there is a strong sentiment in favor of registration in the American Institute of Electrical Engineers and the American Society of Mechanical Engineers. Only in the American Institute of Mining and Metallurgical Engineers is anti-registration sentiment, strongly dominant, but many members of this organization are enthusiastic advocates of registration.

Jan 1, 1930

By Warren H. Westphal

For mining and exploration, and indeed the entire mineral industry, the first century of AIME has ended with far more problems than it began. Paradoxically, most of these problems have arisen not because, the industry has been unsuccessful, but rather because it has succeeded too well. Whatever the public demand for minerals over the past 100 years, it has somehow been met-and met at a price well within the public's ability to pay for the products. But as AIME moves into its second century, the past successes of mining and exploration are beginning to levy a tax on the future. Prospectors have already found most of the rich and ready ores, and miners have dug them out. New mineral assets grow progressively harder to come by, and as they do, the need for them grows inversely more pressing. How and where and at what cost can adequate supplies be found? How and at what cost can they be mined from heretofore inaccessible recesses deep underground and under the seas-or from vast surface tonnages containing only minor values? And once they are found or won, how can these assets be husbanded for generations to come? How also can they be extracted without injury to the land, air and water on which we and our successors must depend? And what constructive use can be made of the incidental materials now treated merely as wastes-sometimes at great expense?

Jan 1, 1971

By A. D. Hughes

A relatively small area in Malaya, about 200 miles long by 40 miles wide, is the most important source of tin in the world. Some tin is recovered in other parts of the peninsula. Of the tin mined, 98 pct is recovered from alluvial deposits. From 1935 to 1941 the average annual world production of tin was 190,000 tons. The average annual production from Malaya during the same period was 62,000 tons or about one third of the total. Other producing countries, in order of importance, were the Netherlands East Indies 34,000 tons, Bolivia 30,000, Belgian Congo, Nigeria, Siam, Burma, China, and a few others with smaller amounts. The serious shortage of tin during the war period was due to the fact that the Japanese were occupying Malaya, Netherlands East Indies, Siam, Burma, and China which, together, formerly were producing 65 pct of the world supply.

Jan 1, 1949

By C. F. Gates, H. J. Ramey

Recent literature shows that pronounced increases in oil recovery can result from the use of miscible systems in recovery operations. This literature also points out certain problems associated with maintaining miscibility, e.g., compositional changes resulting from alterations in pressure and temperature or from zone dilution. The purpose of the work described in this paper was to study miscible zones for possible use in waterflooding operations and examine the manner in which these zones break down. The fluid system selected for study was oil—terNary-butyl alcohol—water, which, because of its narrow range of miscibility, is ideally suited for investigation in short, linear systems. The laboratory-observed effects on oil recovery and zone stability of a number of variables are reported. Among the variables investigated were miscible zone size, viscosity ratio, length of travel, and interstitial water saturation. Results obtained with this system show that interstitial water adversely affects recoveries because of premature phase break. Salinity of the water further aggravates Ais situation. This effect, although pronounced for this system, would probably occur in any fluid system containing an alcohol. As expected, viscosity ratio has a decided influence on recovery efficiency and zone stability. The results also show that use of a suficieno zone size, even though the system has poor phase characteristics, yields higher oil recoveries than are obtained from straight water floods. Length-of-travel studies showed a square root relationship between zone growth and path length for favorable viscosity ratios. No such clear-cut dependence was observed under unfavorable viscosity conditions. INTRODUCTION As new oil reserves have become increasingly more difficult and expensive to find and develop, the oil industry has devoted more and more time and money to finding more efficient methods for exploiting known reserves. The increasing number of water floods is one manifestation of this attempt to improve oil recoveries from existing fields. Since considerable quantities of oil are by-passed by the waterflood process, it is only a partial answer to the problem. The search continues. Of late, several proposed processes have received the critical attention of investigators. Among them are gas drives, in situ thermal reactions and miscible displacements. The present paper is concerned with miscible displacements in conjunction with water floods. Recent literature1- reports that, under proper conditions, oil recoveries from LPG floods, propane sweeps, condensing gas drives, etc., approach 100 per cent of the oil in place in the region contacted by the flood. This literature also points out some of the problems associated with these processes, one of the main ones being the maintaining of miscibility. Compositional changes resulting from pressure and temperature variations or from zone dilution give rise to phase breaks and loss of miscibility, the conclusion being that, after loss of miscibility, much of the beneficial influence of the zone is lost.' The results of the subject work show that, if sufficient zone material exists ahead of a phase interface, considerable improvement in oil recovery can be obtained. In order to increase our understanding of the behavior of miscible systems as they degenerate into immiscible processes, a laboratory system having rapid deterioration characteristics was needed. The fluid system oil—ter tiary-butyl alcohol (TBA)—water possesses these properties and was the system investigated. Although these fluids are different from those generally employed in miscible studies, an understanding of their behavior can be applied to other miscible slug processes. However, under conditions where mass transfer maintains a miscible system through multiple contacts, e.g., enriched gas drive or high pressure gas drive, the observed behavior of alcohol zones would not be applicable. The variables of interest were zone size, viscosity ratio, length of travel, initial water saturation, rate and core characteristics. Of these, only the effects of the following on zone breakdown and oil recovery are reported in detail: (1) zone size, (2) path length, and (3) initial water saturation. The effects of viscosity ratio and core characteristics are discussed in conjunction with other variables. Although initial water saturation is not envisioned as important to the phase behavior of hydrocarbon systems, e.g., LPG, it is important in alcohol systems. The properties of the fluids and cores used are given in Table 1. As previously stated, this fluid system was selected because of the limited range of miscibility

By H. C. Schultz

CERTAIN local conditions were known to govern in large measure the successful adaptation of liquid-oxygen explosives to the large-scale blasting at Chuquicamata. The wide variation in hardness of the rock at this mine makes necessary the use of several types of explosives. A locally manufactured, relatively cheap black powder is used in blasting the softer waste and capping material, where a thorough displacement, breaks the ground sufficiently. Before the introduction of L. 0. X., an ammonia dynamite of about 65 per cent. strength was being used exclusively in the harder underlying orebody, where a strong disruptive as well as a displacement effect is required for breaking the ore. The L. 0. X., as developed for quarry work in the United States, has a practically pure carbon cartridge material, and the explosive has an extremely high rate of detonation, which should therefore cause it to usefully develop its full disruptive effect in hard ground. The individual blasts at Chuquicamata are large, black-powder shots which dislodge masses of rock averaging 250,000 tons each, and dynamite shots which dislodge masses averaging 80,000 tons each. It was desirable, therefore, to attempt to displace with L. 0. X. the faster, higher-cost ammonia dynamite used in the smaller blasts. It was not considered practical to attempt to displace the low-cost black powder with L. 0. X., as estimated costs showed no probable saving if this were accomplished. Since it was desirable to continue shooting relatively large blasts for effective operation, it was recognized that larger storage facilities than had been in use would be needed for the liquid oxygen. Because of the difficulty of transporting and discharging large storage containers of efficient design, the better plan appeared to be storage and discharge of the liquid at the place of manufacture, and transportation of the filled soaking boxes to the blast.

Jan 1, 1928

By C. N. Schuette

The material presented in this paper has been gathered by the writer during a long and varied experience on matters pertaining to the quicksilver industry. During the past 18 years he has visited practically all of the quicksilver mines of the United States and has had occasion to review the literature on quicksilver mining the world over. In a previous publication1 the conclusion was expressed "that the greatest opportunity for increasing the economy in quicksilver production lies in giving more attention to the geology of the deposits ... " The present paper is a contribution toward that end. Due to a lack of correlation of the observed facts, a great deal of confusion exists in the views of various writers concerning the mode of occurrence of quicksilver ores. This paper attempts to show that certain common factors underlie the formation of all quicksilver orebodies. It attempts to present a framework on which to marshall the observed facts and thus make clear the interrelation of various observations which at first sight appear to be contradictory. The material presented is fragmentary in many respects and it is hoped that readers familiar with the deposits mentioned may supply the deficiency. The reader is asked to refer to the publications cited for maps and additional information on the individual orebodies, as this review, in covering so much territory, must necessarily confine itself to a bare outline of the facts concerning each occurrence. The writer hopes that this paper will elicit comment and criticism from the many competent men interested in the quicksilver industry and to all of them he would express his indebtedness for the many courtesies that they have extended to him at various times in the past. Theory op Primary Concentration The mode of occurrence of any given orebody presents an individual problem to the miner engaged in exploiting it. No two orebodies are exactly alike in their geological relationships, therefore an understanding, in detail, of the geology is necessary if the orebody is to be exploited in the most economic manner.

Jan 1, 1931

By Carl Swartz

FOR many years kettles used in the melting and refining of lead and other nonferrous metals and alloys have been made of cast iron. The logic of this probably lies in the fact that cast iron has been known as a material of construction for vessels of this type much longer than steel, and satisfactory fabrication from it has been more easily accomplished and better understood. As the capacity of lead refineries has increased, it has been only natural to increase the size of kettles. Today kettles of 150 to 250 tons are not uncommon. As the size of the kettles increased and better shapes were designed, the uniformity of material of construction became more important. Records kept over comparatively long periods of time have shown that the length of service of kettles has not been uniform. Many causes contribute to this and the importance of each has not yet been evaluated. Kettle design, kettle setting, method of firing and material of construction have been changed from time to time to obtain better service, but the variation in length of service is still great. A kettle may fail during the first few heats or may last through more than one thousand heats. The purpose of this article is not to present the conclusions of a finished piece of research on kettle manufacture and use, but to present a series of observations made over considerable time in the hope that others will publish data and that all may be correlated into a logical scheme which will result in better service and longer kettle life.

Jan 1, 1931

Jan 1, 1902

By Roy McLellan

THE slags derived from the smelting of lead and copper ores are composed essentially of silicates. The problems arising from the smelting of these ores consequently involve the study of silicate fusions. In the absence of specific knowledge concerning the compounds occurring in slags, it has been the practice of metallurgists to treat them in terms of their total chemical composition. Slags have been classified as monosilicates, bisilicates, sesquisilicates, and subsilicates according to the relative amounts of oxygen in the acid and basic radicles of the hypothetical salt produced. While this has been a useful guide to metallurgists in computing the furnace charges, it falls far short of a basis for the scientific investigation of slags. In order to understand the nature of a slag as a whole it is necessary to learn the physical and chemical properties of the mineral compounds which go to make up that slag. The efficiency with which an ore is smelted in a furnace depends primarily on the physical properties of the compounds formed during the operation. When the melting points and fields of stability of each of the mineral compounds in slags have been established, it will be possible to determine the properties of any given slag by examining the nature and amounts of its mineral constituents.

Jan 1, 1930

By P. Beardmore, B. W. Howlett, B. D. Lichter, M. B. Bever

The heats of formation at 273°K of the compounds Mg2Ge, Mg2sn, and Mg2b, the heats of fusion and melting points of Mg2Sn and Mg2Pb, and the heats of solution of magnesium, germanium, and lead in liquid tin have been measured. The excess free energies of the liquid alloys and the free energies of formation of magnesium-Group IVB compounds at their melting points and their standard free energies of formation at 298°K have been calculated. The stability and bonding of the compounds are discussed with reference to these properties. Some thermodynatnic aspects of the liquid phases in the systems Mg-Sn and Mg-Pb are also considered. THE compounds of magnesium with the Group TVB elements, silicon, germanium, tin, and lead, have often been considered to constitute a nearly ideal homologous series. In particular, their thermodynamic stability has been assumed to decrease with increasing atomic number of the Group IVB element.' The binary-phase diagrams of the magnesium-Group IVB elements given by Hansen and Anderko2 have the same form. Each system has a single con-gruently melting compound of limited homogeneity range. The structures of these compounds, which have the formula Mg2X, are anti-isomorphous with the calcium fluoride structure. A recent investigation has found evidence of a second compound in the system Mg-Pb.3 The solid compounds Mg2Si, Mg2Ge, and Mg,Sn are semiconductors, while the conductivity of Mg2Pb approaches that of a metallic conductor. This difference suggests that other properties may also show a discontinuity. The investigation reported here is concerned with the thermodynamic properties of magnesium-IVB compounds and particularly their variations with the period of the Group IVB element. The heats of formation at 273°K of the compounds MgzGe, Mg2Sn, and Mg2Pb and the heats of fusion and melting points of Mg2Sn and Mg2Pb have been measured. The results, combined with published data, are interpreted in relation to the stability and the bonding characteristics of the compounds. Some thermodynamic aspects of the liquid phases in the systems Mg-Sn and Mg-Pb are also considered. In the course of the investigation the heats of solution of magnesium, germanium, and lead in liquid tin have been determined. 1) EXPERIMENTAL PROCEDURES 1.1) Samples. Samples of the compounds Mg2Ge, Mg2Sn, and Mg2Pb, supplied by Professor P. Aigrain, Compagnie Générale de Télégraphie Sans Fils, were used in measuring heats of formation, heats of fusion, and melting points. Samples of Mg2Sn and Mg2Pb, supplied by Dr. V. B. Kurfman, Dow Metal Products Co., samples of Mg2Sn, prepared at the Air Force Cambridge Research Laboratories, and samples of MgzPb, prepared in this laboratory, were used for additional measurements of the heats of fusion and the melting points. The samples were stored in evacuated Pyrex capsules or under nonreacting liquids. 1.2) Heats of Formation. The heats of formation at 273°Kof the compounds Mg2Ge, Mg2Sn, and Mg,Pb were measured by tin-solution calorimetry. In this method, samples of the compound and of a mixture of the constituent elements are added alternately from 0°C to a tin-rich bath. The difference between the heat effects, corrected for the change in composition of the bath, is the heat of formation of the compound. Details of the method have been given elsewhere. 4 The bath was maintained at 350°C for the dissolution of the compounds MgzSn and Mg2Pb. Since at this temperature the dissolution of Mg2Ge was too slow, a bath temperature of 400" or 450°C was used with this compound. At least three calorimetric runs, each of approximately six additions, were made with each compound. 1.3) Heats of Solution. The determination of the heats of solution of magnesium, germanium, and lead in tin was included in this investigation because they were not well-established at the time this work was started. To obtain the heat of solution, the difference

Jan 1, 1967

By George M. Fowler

THE Tri-State district, as outlined in this paper, refers to the entire mineralized area in southwestern Missouri, southeastern Kansas and northeastern Oklahoma (Fig. 1). The part of the district in Missouri and near Galena, Kans., is still sometimes referred to as the Joplin district (Fig. 2). The Picher-Miami area is that part of the Tri-State district located contiguously in Kansas and Oklahoma in the vicinity of Baxter Springs, Picher and Miami. This paper is confined almost wholly to the ore deposits of the Tri-State district and particularly to the Picher-Miami area. Our study of the ore deposits of this district dates from late in 1925 (by Fowler) and early in 1927 (by Lyden) to the present. Our work has been confined almost entirely to the search for ore for numerous companies and individuals. It was not possible for us to undertake numerous highly interesting investigations which presented themselves but which would not immediately help in finding ore. We particularly refer to the general structural geology of the Ozark uplift, the genesis of the ore, and other problems of a similar nature. The local and general structural problems of the district are being solved gradually as the work progresses. The factors that control the loci of the several orebodies are evident. This paper is based almost exclusively upon our own observations. Most of the important mines in the Picher-Miami area were studied in detail. A map (Fig. 5) is included which shows this area and the properties we have examined to date. When it was convenient we visited, studied and compared structural relations in numerous mines in states outside the district. Some of these observations are noted in this paper.

Jan 1, 1932

By Walter H. Bruckner, George B. Clark

SINCE the end of World War II interest has been increasing in the use of shaped charges in the mining industry and in other industries using explosives for blasting purposes. Shaped charges employ the principle known as the "Munroe effect," which was discovered by Charles E. Munroe more than 50 years ago (in 1888). Details of their design have been explained e1sewhere.l,2,3 Fig I shows the essential features of design of two types of shaped charges (with conical and hemispherical cavities) and a schematic sketch of their action upon detonation. The following discussion deals with the behavior of the metal in the cavity liners when they are subjected to intense pressures exerted when the explosive charge is detonated. Among the conclusions reached in research on shaped explosive charges, the following have been established concerning cavity liners: 1,2 I. The optimum wall thickness of a conical cavity liner is dependent upon the apex angle of the cone as well as on the base diameter of the charge. Acute apex angles require thinner walls for optimum performance and more obtuse angles require thicker walls for the same base diameter. 2. Cones were more effective in forming a penetrating jet when the walls were tapered; i.e., the thickness of the wall of the cone increased from the apex down. 3. The physical and mechanical proper- ties of metals have a marked effect upon their performance as cavity-liner material. Boiling point, ductility, malleability, tensile strength, and hardness are among the properties that influence the effectiveness of a metal used as a cavity liner. Lead, for example, makes a wide, flat crater in steel plates. Aluminum makes a deeper crater than lead, and an aluminum alloy having a high tensile strength makes a deeper hole, but slightly smaller in diameter. Cast iron makes a deep, narrow hole. These findings, together with the following analysis under Metallographic Survey of Slug, offer solutions to many of the problems involved in solving the mechanism of the formation of Munroe jets. It has been fairly well established that cavity liners collapse in a manner similar to that indicated in Fig 2. Conical liners are known to collapse upon themselves while hemispherical liners are believed to turn inside out in the process of jet formation. The first has been definitely proved by recovery of collapsed portions of cones, while liners from partly detonated charges show that hemispheres may turn inside out. Fig 3 shows a sketch of a recovered slug from a 6-in. shaped charge using a 45° cone made of cast iron. (This size of charge drilled holes up to 3 ft in depth in solid granodiorite.)

Jan 1, 1947

By Joseph S. Malesky

The discovery and development of explosives mark one of the most important findings in the history of civilization. Without explosives our vast economic enterprise concerning the mining of coal, copper, iron, aluminum, and various other ores could not function. Explosives are used in all kinds of construction works, in the razing of old buildings, blasting of trenches, driving of tunnels, and in many other instances common to our everyday life. For these reasons explosives are rightfully referred to as the forerunner of progress. An explosive may be defined as a substance (usually a mixture) that, when flame or shock is applied, yields readily to rapid combustion or oxidation, accompanied by the formation of such relatively large quantities of gases as to produce much violence and pressure which, in turn, react against their surroundings and cause what is termed an explosion. By their very nature the action of explosives is destructive and disruptive of adjacent materials. Decomposition of explosives can occur through deflagration, which is rapid burning or combustion, as in the case of black powder, or through detonation, which is an almost instantaneous disruption, as in the case of dynamites and blasting agents. HISTORY OF BLASTING WITH EXPLOSIVES At one time workmen obtained stone blocks for building by grooving the rock with crude picks, driving wooden wedges into niches in the rock, and pouring water on the wedges; the swelling of the wood forced out the blocks. As late as the 17th century, fires were placed against the face of rock to crack it, and water was sometimes dashed on the heated rock to shatter it by sudden cooling. The progress of our country is synonymous with advancement of the improved manufacture and extended use of explosives. Coal had been

Jan 1, 1981

By John T. Ryan

FOR the first ten months of 1942, on which data are available at the time this is written, the coal-mining industry achieved a most creditable safety record, and ha1 figures for the year may show a record surpassing that of 1941 in which the industry reached the best accident rate in its history. The ten- month accident rate for both bituminous and anthracite mining in 1942 was 2.197 fatalities per million tons of coal mined, compared with a revised rate of 2.271 for the same months of 1941. The bituminous rate decreased from 2.139 in 1941 to 2.039 for ten months of this year, and the anthracite rate shows a reduction from 3.707 to 3.699 for the same period.

Jan 1, 1943

By WILLIAM BOWIE

THE development of the isostatic idea during the last century would make an interesting paper in itself. But the various steps in the development have been covered in a number of papers and books which are readily available. Therefore this short paper should not give space to. the historical phases of the subject. Isostasy is really an old idea, but it is only in the last few decades that it has taken on any great prominence or importance in the study of earth phenomena. It is really remarkable how closely Dutton' sensed the isostatic principle 40 years or more ago. His general principles of isostasy as outlined by him have stood the test of time and fit in closely with the general ideas held today. It would seem, however, that some of his views with regard to the application of isostasy to geological processes must be modified or abandoned.

Jan 1, 1930

By George M. Fowler

DURING 1937 the subject of mining geology was probably given more attention and more mining geologists were usefully employed than at any previous time. Of the many contributing factors the most important were: (1) a higher degree of prosperity in many countries, (2) a. better understanding of geologic phenomena, and (3) the apparently diminishing reserves of several important minerals. Mining companies have come to look upon geology with a growing appreciation of its aid in the more effective exploration and exploitation of mineral deposits. Most of the larger and more active companies have one or more geologists permanently attached to their staffs and some have well organized and efficiently managed geological departments. Even the smaller companies, who feel they cannot afford to employ a geologist on a permanent basis, are seeking the advice of competent men in this field with increasing frequency. One of the most significant trends has been the growing tendency to base exploratory work on more thorough geologic studies instead of empirical "hunches,"on which so much off the work in the past has relied. Likewise, mining companies are apparently more willing to expend larger sums on the basis of geologic possibilities in a district.

Jan 1, 1938

By AIME AIME

EVEN though most of the program of the joint meeting at Easton, Pa., on Oct. 30 to Nov. 1. was devoted to the interests of combustion engineers rather than to coal-mining engineers, nevertheless the A.I.M.E. Coal Division was well represented, with 83, or close to one third of those in attendance giving this as their affiliation. The fuels division of the American Society of Mechanical Engineers had 108 representatives, and an equal number reported no society affiliation. Added to the men's total registration was that of some twenty ladies so the total attendance was in the neighborhood of 325, exceeding that of the last two joint meetings, at Birmingham and Columbus, and equaling the 1938 crowd at Chicago.

Jan 1, 1941

By J. T. Lapsley, I. I. Cornet, A. E. Flanigan, R. Hultgren, J. E. Dorn

WITH the greatly expanding use of magnesium during the war, it appeared necessary to the War Metallurgy Committee that procedures of heat treating common magnesium casting alloys be investigated systematically. Accordingly, the National Defense Research Committee of the Office of Scientific Research and Development placed a research contract with the University of California, supervised by the War Metallurgy Committee. Research on the solution heat treatment and aging of magnesium alloy AZ92, (formerly ASTM No. 17; also known as Dowmetal C or AM260) which was done under "Restricted" Project NRC-21, in 1942-1943, and reported, in detail in a final report to the OSRD on September 3, 1943, is the basis of this paper, which has been released for publication by the OSRD. American experience with magnesium alloys prior to World War II was limited, although some of these alloys had been in commercial use since 1909. Requirements of the aircraft industry for light alloys made it imperative to understand and utilize the advantageous strength-weight properties of magnesium castings. Magnesium casting alloys are commonly solution heat treated to increase their ultimate tensile strength and ductility; this treatment may be followed by an age hardening at elevated temperatures, which raises the tensile yield strength but diminishes the ductility. In the present investigation, AZ92 was studied to determine the effects on properties of various solution heat treatment and aging schedules. The principles of heat treatment of magnesium alloys are the same as for other non-ferrous alloys. The alloy studied, AZ92, has a nominal composition of 9 pct aluminum, 2 pct zinc, and minor constituents. Fig I shows, by the projection of isothermal sections on the concentration plane, the solubility surface1 of the ternary magnesium-rich solid solutions as determined by X ray analysis. From this figure it may be seen that above approximately 375°C (707°F), AZ92 alloy is a single phase alloy at equilibrium; below this temperature the equilibrium condition is a. two phase alloy. The beta constituent which precipitates from the solid solution exerts a hardening effect. Because the zinc concentration is only 2 pct, and because of its solubility relations, AZ92 resembles a binary alloy of magnesium with aluminum. The solubility curve1 of Fig 2 shows how rapidly the solubility of the beta phase decreases with decreasing temperatures. Unlike many aluminum alloys, magnesium alloys do not age harden at room temperatures; precipitation hardening of AZ92 alloy is performed at about 177°C (350°F). At this temperature about 3 pct aluminum

Jan 1, 1947

By Everett D. Jackson

The largest deposits of chromite in the United States occur in tabular layers in the lower part of the Stillwater Complex, Montana. Nearly 900,000 long tons of chromite concentrates have been produced from mines and mills in this area, and reserves equivalent to more than 2,500,000 long tons of Cr2O3 remain in the ground. Layered concentrations of chromite (known as chromitite zones) occur only within olivine-rich layers of the Peridotite member of the Ultramafic zone of the Stillwater. As many as thirteen chromitite zones, lying conformably one above another, have been found, but only five of them are thick enough to be of any conceivable economic interest, and only two of them have been mined to date. Individual chromitite zones can be recognized by their distinctive internal character and by their stratigraphic position in the Peridotite member. The chemical composition of chromite varies consistently between and within the different chromitite zones. The zones range in thickness from about an inch to more than 12 feet, and the Cr2O3, content of their chromite ranges from 36.6 to 49.2 weight per cent. In any given area, the G chromitite zone is the thickest, but the chromite of the H chromitite zone has the highest grade. Laterally, the thickness of the chromitite zones is related to the thickness of the Peridotite member; in general all are thicker in the eastern part of the Stillwater than in the western part.

Jan 1, 1968