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By Zay, Jeffries

THE effect of thoria (ThO2) on grain growth in tungsten was discussed in some detail in a paper presented before this Institute by one, of the authors in 1918.1 In that paper it " was assumed that the, thoria was present in the tungsten entirely as a mechanical mixture. There was no indication in the experiments described that even a trace of the thoria was in solid solution in the tungsten. Langmuir,2 however, observed that thoriated-tungsten filaments under certain conditions showed electron emissions many thousand times greater than unthoriated tungsten at the same temperature. He concluded from his studies that a slight amount of the thoria had dissociated on heating the filament to a temperature near 220°. C. At this temperature and higher, part of the thorium diffuses to the surface of the filament where it evaporates at. a much faster rate relatively, than the tungsten, and also at a rate, nearly as fast as it is brought to the surface by diffusion: If the temperature is lowered to say 1800°,. C., diffusion of the thorium atoms to the surface is more rapid than evaporation, sown adsorbed film of thorium atoms is produced on the surface of the tungsten filament. The electron emission is governed by the outside layer of atoms so the emission from such a filament might be expected to approxi¬mate that of a thorium filament at the same temperature. PRESENCE OF METALLIC THORIUM IN THORIATED TUNGSTEN If the filament containing the adsorbed film of thorium. is heated to a sufficiently high temperature, the thorium atoms evaporate: rapidly and the electron emission becomes more nearly that of tungsten. On cooling again to 1800° C., or thereabouts, the emission 'builds up gradually to a maximum. The filament containing the adsorbed layer of thorium atoms is said to be "activated." By studying the rates of activation under different conditions of prior thermal treatment and at different temperatures, Langmuir was able to arrive at an estimate of the

Jan 1, 1927

By A. L. Benham, W. E. Dowden, W. J. Kunzman

The mechanism involved in creating a miscible fluid displacement of typical reservoir fluids through porous media by light hydrocarbon mixtures usually involves a number of mixing and separation stages in the contact area. This mechanism has been illustrated on ternary diagrams for miscible displacement of reservoir fluid by rich hydrocarbon gases. A relatively simple method has been devised for calculating the approximate conditions for a miscible displacement of reservoir fluid by rich, light hydrocarbon gases or by LPG mixtures. Miscibility is favored by increased pressures, decreased temperatures, light reservoir fluids and light hydrocarbon-displacing fluids rich in the heavier components. The conditions for miscible displacements of five typical reservoir fluids by various light hydrocarbon mixtures were determined for a range of temperatures from 70" to 260°F and pressures from 1,000 to 3,000 psia. A correlation of these conditions was obtained using the variables of temperature, pressure, C,+ molecular weight of the reservoir fluid, C,+ molecular weight of the displacing fluid, and mol per cent methane in the displacing fluid. This correlation has been applied to data appearing in the literature with very good success. A partial check of the correlation has been made using a step-wise procedure with a windowed PVT cell. INTRODUCTION The term, "miscible fluid displacement", may be defined as any oil-recovery displacement process where there is an absence of a phase boundary or interface between the displaced and displacing fluids. A water flood would not be a miscible fluid displacement, although cycling in a condensate reservoir would be. Another example is displacement of oil by gasoline. Not so obvious, however, are the conditions under which fluids (such as propane, mixtures of propane and methane, or other similar systems) will give a miscible fluid displacement of oil. There are four standard miscible-fluid-displacement processes being used for the recovery of oil from an "nderground reservoir—(1) high-pressure dry-gas miscible displacement, (2) rich-gas miscible displacement, (3) miscible slug using a slug of LPG followed by a lean dry gas under miscible conditions, and (4) gas driven-slug process using a slug of LPG followed by a lean dry gas under immiscible conditions. The first problem faced by the engineer designing a miscible displacement process is to determine the conditions for miscibility. A number of papers have included discussions of the process of obtaining miscibility in these processes.1-8 However, methods for calculating the conditions for miscibility have not been published. This paper includes a method for calculating the conditions for a miscible displacement of reservoir fluid by a rich gas (LPG diluted with methane or natural gas). In this paper, a rich-gas miscible displacement process is defined as an oil-recovery process in the reservoir. The cost of a rich-gas miscible displacement will be decreased by diluting the LPG with methane or natural gas as much as possible. Therefore, it is important to be able to predict the maximum dilution for miscibility. MECHANISMS The mechanisms for obtaining miscibility between a displacing mixture of light hydrocarbons and displaced reservoir fluid often involve a number of displacing and mixing stages. As stated previously, the cost of a rich-gas miscible displacement is decreased by diluting available LPG with natural gas. The problem is to predict the maximum dilution allowed while maintaining miscibility. To get a picture of the displacing and mixing stages, it is helpful to consider these complex hydrocarbon mixtures as pseu do-ternary systems. Graphical representation of a complex system as a pseu do-ternary system can be thermodynamically rigorous if enough variables are used to describe the character of each pseudo-component in one of the phases. However, even if the characterization of each pseudo-component is not complete, pseudo-ternary representation does serve to illustrate the mechanism for obtaining miscibility and can be used to make some general conclusions concerning the conditions for obtaining miscibility. A phase diagram for the ternary system, methane-

By S. H. Ash

Safety records in the mineral industry for 1954 will do well to hold their own as compared with 1953, because of the poorer rate in the coalmining branches, even without the recent mine explosion at the No. 9 mine of the Jamison Coal & Coke Co., Farmington, W. Va., that killed 16 persons. .The cause of that disaster has not yet been ascertained. The metal-mining branch appears to have improved its record over the last year, however. Health Diesel equipment continues to be favored in non-coal mines. Equipment includes locomotives, trucks, tractors, and muckers. Of major concern and interest is the establishment of a new threshold limit for oxides of nitrogen-5 ppm as compared with 25 ppm. This gas is the most harmful component of diesel-engine exhaust gas

Jan 3, 1955

By R. L. Schmidt, J. D. Verhoeven

The diffusion coefficients and electrotralzsport mobilities of aluminum, gallium, and arsenic have been determined in molten germanium with the capillary reservoir technique. The diffusion coefficients are slightly higher than those determined by the solidification technique of Brirton et a1.1 It was found that aluminium and gallium migrate to the cathode in molten germanium) whereas arsenic migrates to the anode under an electric field. A possible technique for producing p-n junctions by means of electric field freezing is discussed in view of the experimental data. In the past decade or so the literature has abounded with articles concerning the solid-state properties of the semiconducting elements germanium and silicon. It is surprising by comparison how little has been published concerning the liquid-state properties of these materials. In the production of doped germanium or silicon the diffusion coefficient of the dopant in liquid germanium or silicon is an important quantity. Yet, to the best of our knowledge, no one has ever made a direct measurement of the diffusion coefficient of solutes in either molten germanium or silicon. A number of authors'-4 have determined some diffusion coefficients by the indirect technique developed by Burton et al.1 This technique appears to give numbers of the correct order of magnitude but it does depend upon a number of assumptions in the analysis and also requires prior knowledge of the viscosity of the melt. In the present work a more direct measure of the diffusion coefficients of arsenic, gallium: and aluminum in molten germanium has been made. It has been shown independently by two groups of authors5, 6 that, when an electric current is passed through the interface of a solidifying metal containing an impurity, the resulting electrotransport in the liquid boundary layer at the interface offers a mechanism for control over the redistribution of the impurity accompanying the solidification. These authors show that the degree of control is proportional to the mobility, U of the impurity atoms in the liquid boundary layer, where the mobility is defined as the drift velocity relative to the solvent per unit electric field. In principle the results apply to the solidification of a doped semiconductor and offer an interesting technique for control of the doping of a semiconductor. In the present work the mobilities of aluminum, gallium, and arsenic were determined in molten germanium in order to evaluate the potential usefulness of electro-transport as a technique for solute control when applied to the solidification of doped germanium. EXPERIMENTAL PROCEDURE Both the diffusion coefficients and the mobilities were measured using high-purity alumina capillaries and a resistivity technique for analysis. A schematic diagram of the electrotransport apparatus is shown in Fig. 1 and the details of the cell design are shown in Fig. 2. For the mobility experiments electrical contact with the bottom of the capillary was made with graphite, as shown in Fig. 2. In order to prevent electrical contact with the melt the graphite was coated with a thin layer of alumina using a plasma spray torch. The cell assembly, a graphite electrode, and another assembly containing two blank capillaries were fastened to the lavite disk shown in Fig. 1. To make a run the system was evacuated and the doped germanium was outgassed at the operating temperature of 1030°C. The cell and blank capillaries were then submerged beneath the melt and a slightly positive pressure of helium was introduced to fill them. After passing current through the cell for a given time the cell and blank capillaries were raised from the melt and the furnace was shut off. The temperature of the cells dropped below the freezing point of germanium within 1 to 2 min after the furnace was shut off.

Jan 1, 1968

BASIC open-hearth slags have no obviously unique features when compared with slags from other metallurgical operations. Open-hearth slags form and exist at temperatures ranging from 2500 to 3100 F (1370 to 1700 C). In the course of an open-hearth heat, the liquid slag changes slowly and continuously in chemical analysis-the changes reflecting changes in temperature, changes in metal analysis, solution of charged materials, solution of feed additions, and solution of refractories. Through- out the process, the slag performs specific primary functions that are responsible for a large measure of the technical and economic importance of basic open-hearth steelmaking. It is intended in this chapter to present the chemical reactions by which the primary functions of basic open-hearth slags are carried out, to describe the physical and chemical principles governing the extent to which these reactions proceed and can be regulated, and finally to indicate the limitations imposed on other features of the process by the fulfillment of the primary functions. Basic open-hearth slags perform three primary functions. First and foremost, the slag provides a means of removing phosphorus from the liquid metal. The ability to remove phosphorus is largely responsible for the widespread use of the basic open- hearth process. Second, the slag serves as a controlling factor in transferring the oxygen required for the other oxidizing reactions. Third, the slag provides a means of eliminating some sulfur from the open-hearth bath. While the extent of sulfur removal is not comparable to that of phosphorus, the ability to remove some sulfur contributes much to the value of the process. The effectiveness with which the slag fulfills its functions varies with temperature and composition. Since operating temperatures are fixed largely by the specified nature of the product and the equipment, the speed and extent to which the functions of the slag are carried out depend largely on its composition. The necessity for regulating slag composition to accomplish the re-

Jan 1, 1951

By J. D. Embury, R. M. Fisher, A. S. Keh

An investigation of the defect structure and properties following large strain deformation has been carried out using transmission electron microscopy and mechanical testing for a range of ferrous materials and for copper. It is shown that, for a variety of ferrous materials, a cellular substructure is developed during the initial stages of working and on further deformation the dimensions of this substructure are reduced. Quantitative measurements of the flow stress and the scale of the substructure indicate that the strength of heavily worked materials is largely determined by the spacing of cell walls. These cell walls act as dislocation barriers in a manner analogous to grain boundaries. FCC materials do not harden as extensively as bcc after cold working and the present observations on copper indicate that the dimensions of the substructure in fcc materials are not markedly reduced on deformation. The differences between the fcc and bcc structures produced by large plastic strains are ascribed to differences in the extent of dynamic recovery. It is tentatively proposed that the greater stability of substructural barriers in bcc structures results from strong interstitial Pinning effects. It is proposed that for large plastic strains the work-hardening process may be considered in terms of the reduction of substructural-barrier spacing during the working process. This pvovides a simplified hut useful analysis of the strain hardening occurring during mechanical processes. THE mechanisms of strain-hardening processes have occupied the attention of numerous investigators over the past three decades and a multitude of theories have emerged in this field. The majority of previous work has been concerned with the development of a description of the plastic behavior of single crystals in terms of dislocation theory.'" In contrast, scant attention has been given to the strengthening mechanisms operative during mechanical working processes such as rolling and drawing. The large plastic strains involved in these processes make it difficult to correlate the observations with any elementary dislocation theory. Further, as Bullen and coworkers3 have opined, for large plastic strains both hardening and recovery occur simultaneously and thus it is extremely difficult to estimate the effect of plastic strain on the ambient internal stress field. It is probable that for large plas- tic strains any theoretical estimate of the internal stress field must be made in terms of complex dislocation groups. Although some valuable theoretical work has been done toward calculating the elastic properties of dislocation groups4 any detailed self-consistent model for large plastic strain is as yet impossible. With these limitations in view it is still of value to examine the mechanical properties of highly strained materials as a function of their substructure. This relationship is explored in the present communication for a variety of materials subjected to rolling, drawing, or swaging. The primary object of this investigation has been to establish the validity and the limitations of the substructural strengthening mechanism proposed by Embury and eisher' for drawn pearlitic wire and by Meieran and Thomas for drawn tungsten wire. No attempt has been made to delineate the basic interaction mechanism which occurs between a slip dislocation and the substructure and the authors believe that a great deal more experimental evidence must be compiled before these fundamental aspects can be explored. Also, no specific attention has been given to the detailed formation of substructure during working. Experimental Details. A variety of materials were used in this investigation, the compositions and heat treatment of which are tabulated in Table I. The commercially pure iron is referred to throughout this report as Ferrovac E. The mechanical working processes were all performed at room temperature. The wire drawing was performed on a manual drawing bench. Reductions of between 10 and 20 pct in area per pass were used in both swaging and drawing. The experimental parameter used to evaluate the mechanical properties of the materials was the 0.2 pct proof stress. This was determined for wire samples using an Instron tensile machine at a crosshead speed of 0.02 in. per min. The techniques for preparation of samples for transmission electron microscopy have been described previo~sl~.~ Specimens from wire samples were prepared from longitudinal sections and in some cases from transverse sections. To evaluate the substructural characteristics of rolled materials, thin foil samples were prepared of both the face and edge sections. Results. One of the more familiar ways of expressing work hardening in mechanical working is by the flow stress as a function of reduction in cross-sectional area. Fig. 1 shows such a plot for Ferrovac E eutectoid carbon steel and for copper. The curve for Ferrovac E is characterized by an initial stage of rapid work hardening and a final stage of rapid work hardening separated by an intermediate stage with a low rate of work hardening. This behavior is typical of many ferrous materials and the drawn pearlite wire previously investigated by Embury and Fisher is a more pronounced example. Copper shows an initial

Jan 1, 1967

By Charles Wraith

THE property of the Roan Antelope Copper Mines, Ltd., is situated at Luanshya, north-central part of Northern Rhodesia, and is connected with the main line of the Rhodesia Railways, Ltd., by a 24-mile branch line from N'dola. Most of the material and supplies that are not available in Africa are shipped into the country via Beira, on the East Coast of Africa, a distance of 1473 miles from Luanshya and the nearest ocean port. The output of copper is shipped by rail to Beira and thence by boat to the market. Passenger travel is mostly via Cape Town, a distance of 2162 miles from Luanshya. Excellent passenger trains operate on regular schedules between Cape Town and Northern Rhodesia. Luanshya is 13° south of the equator at an elevation of 4000 ft. above sea level, and has a mild healthful climate. During the rainy season, from October to March, the rainfall averages 53 in. The area is pro-fusely covered with vegetation. An ample supply of water for industrial and domestic purposes is available throughout the year. The more important supplies for smelting purposes, such as wood, coal, limestone, silica, quartzite, and clay for "dolly" mud, are con-veniently available. Excellent grades of coal, coke and firebrick are obtained from the Wankie Colliery Co., Ltd., Southern Rhodesia. The Wankie colliery has just completed the erection of equipment for the manufacture of silica brick. An ample supply of quartzite of good grade is available for this purpose. Silica brick is also obtained from the Belgian Congo and from India. Limestone is quarried from a large deposit a few miles from Bwana Mkubwa, which is 30 miles by rail from the smelter. An abundant supply of clay for "dolly" mud and for lining launders is available within a short distance of the smelter.

Jan 1, 1933

By Fathi Habashi

Nickel, copper, and elemental sulfur can be recovered from a low-grade pyrrhotitepentlandite type concentrate by leaching with HNO3 in a pressure reactor at moderate temperature and pressure. The bulk of iron is converted to an oxide. Same results can be achieved by leaching in an open vessel under a reflex condenser for an extended period of time.

Jan 1, 1974

ASHBEL WELCH, Lambertville, N. J.: Dr. Dudley has given the wear of steel rails under four different conditions. He arrives at the conclusion that the softer rails, or those that from their composition ought to be softer, wear better than the harder. But there is another condition which has an important bearing on the subject, and should not be overlooked,—the weight on a wheel. With the lighter weights of the past, the softer rails may have worn best; with the heavier weights of the future, the harder may wear best. Weights will probably be increased up to the capacity of steel to bear; then doubtless the harder steel will wear best. A leaden rail with ten pounds on a wheel might carry millions of tons, but with one hundred pounds on a wheel, it would be destfoyed by a few thousand tons. So in the days of iron rails, my experience was that the softer rails under light machinery stood better than some of the harder; but under heavy machinery the softer were muqh the most rapidly destroyed. It is doubtless the same with steel. The pounding motion of the wheels loosens or spreads the particles of a thin film of steel; the pull lengthwise on the rail de-

Jan 1, 1881

Jan 1, 1925

By G. M. Schwarz

There has been considerable controversy regarding the structure and mineral constituents produced when iron ore is sintered. This investigation was undertaken in order to establish the fundamental reactions that take place in the sintering process by determining the nature of the resulting minerals. The writer's immediate interest in the subject arose mainly from the request of E. W. Davis for information based on a microscopic study of sinter submitted by him in May, 1926. In the author's preliminary work, samples of iron-ore sinter were secured from the Minnesota School of Mines Experiment Station and from commercial plants. These were polished by the usual methods for polishing opaque ores. In order to study these surfaces satisfactorily, it is necessary to magnify them rather highly, a range from 100 to 1000 dia. being used. For the higher magnifications oil-immersion lenses and an intense source of light are necessary. After the preliminary study had shown the problems involved, a series of small samples were sintered under carefully controlled conditions and with analyzed materials. Variations in the relative amounts of ore, coal and water were made in order to study the effect of each constituent. The attempt has been to arrive at a clearer understanding of the sintering process and the reactions involved without reference to any preconceived notion as to sinter. It is clear that the study of polished surfaces has yielded results not possible with thin sections alone. The thin sections made in this work were found unsatisfactory at magnification greater than 75, whereas magnifications of 1000 were easily studied with reflected light on carefully polished surfaces. A rather complete statement of observed facts is made so that the reader may form his own conclusions. The writer's interpretations are suggested. It is to be hoped that a more complete understanding of the structure arid composition of iron sinter, as well as the changes which go on during

Jan 1, 1929

By Robert J. Ramsey, Robert D. Jeppson

Introduction The Utah Copper Division of Kennecott Copper Corporation will present its contribution to the A. M. Gaudin Flotation Symposium in four parts. The first two segments will discuss briefly the historical development of the Utah Copper Division and describe the ore body. The third segment will review the facilities and operating procedures for the Utah Copper division's newest plant, the Bonneville Concentrator. The fourth segment describes flotation process circuitry, including molybdenite recovery procedures, at the Arthur and Magna concentrators. (The Bonneville concentrator is a crushing and grinding unit and does not have its own flotation plant). I. Historical Development Progress through change has been the key to the successful operation of the Utah Copper Division for more than 70 years. As the original low-grade copper operation, the pressures to remain competitive and profitable have dictated the timing and extent of each change. Much of the change has occurred through technological and economic advancements in the area of ore concentration. The Utah Copper Division of Kennecott Copper Corporation had its origin June 4, 1903, when the Utah Copper Company was organized. The initial mill of 300 tpd (tons per day) capacity was built at Copperton a few miles below the present Bingham Canyon mine site. From 1904 to 1910, the Copperton mill was expanded to a capacity of 1,000 tpd, and all of the known apparatus for gravity concentration were evaluated.

Jan 1, 1976

By H. G. Moulton

The increasing scale of mining operations over the past decade, particularly in connection with the exploitation of large bodies of comparatively low-grade copper ores, has made necessary the study of the behavior of rock under failure. When extractions of as high as 40,000 tons a day are reached in steam-shovel operations and as high as 20,000 tons per day in underground mining operations, it is evident that excavations soon become of such size that the behavior of the rock will often be dependent on fundamental principles applicable to more or less homogeneous materials under stress, rather than on weathering or local planes of weakness. In the ordinary rock excavations encountered in civil-engineering practice, such as excavations for subways, highways, railroads, etc., rock faces are not carried to depths sufficient to develop any pressures, or consequently any failures, except those due to loose masses resulting from local planes of weakness. When, however, orebodies whose tonnage is measured by hundreds of thousands are to be extracted by steam-shovel operations in open pits, it is necessary to determine if possible in advance the slopes that the sides of the pits will assume, for these slopes influence the shape of the excavations and thereby the amount of ore that may be extracted by the open-pit method. When large orebodies are mined underground at depths of 300 to 500 ft. (91 to 152 m.) by caving methods, the surface subsiding as the ore is withdrawn, it is necessary to determine in advance the outermost limits of fracture in the subsiding surface, for on the delineation of these limits depends the location of surface improvements, mills, smelters, etc. and also the location of development work, such as hoisting shafts, main haulage levels, and all other underground openings that must remain undisturbed during the period of ore extraction. Heretofore, in civil-engineering practice, it has been assumed that earth and rock behave differently in failure. For the calculation of earth pressures, formulas are used in which the assumption is made that earth banks fail by sliding along the slope determined by the frictional resistance of the material. The line of failure and the resulting pressure is held to be dependent on the angle of repose, which is different for varying

Jan 1, 1920

By A. H. Underwood, M. –Ls. Trépanier

INTRODUCTION The King and Beaver mines of Asbestos Corporation Limited (ACL) were joined in 1957 to form the King-Beaver mine. In 1964, ACL purchased the Johnson's Asbestos Company. The combined underground workings are a part of the King- Beaver mine. Asbestos ore is mined at the rate of 4080 metric tons per day (mtpd) to provide 15% of the company's daily requirement in the Thetford Mines area. Figure 1 shows the location of Thetford Mines. Two shafts service the underground. No. 3 shaft, 457 m deep, is used for personnel and material transportation, downcast ventilation, and ore hoisting. No. 4 shaft, 820 m to the south, is 389 m deep. It is used for material transportation and upcast ventilation. Figure 2 shows the relative locations of the shafts and the underground workings. The ore is mined by block caving. HISTORY The orebody outcropped at surface and was first mined as an open pit. Underground mining commenced when open pit mining became impractical. Shrinkage stoping, used initially, was unsatisfactory in the highly fractured ore. Sublevel stoping improved ore recovery and safety, but did not overcome the adverse effects of the un- stable rock. Observations of the rock failures indicated that block caving would be satisfactory. This was confirmed by careful investigation and testing. A method of block caving similar to that used at the Miami Copper Company was adopted. The first block commenced production in June 1933. BLOCK CAVING General A large block of ore is undercut above pre- pared drawpoints. The ore above the undercut caves by its own weight. Caving progresses up- ward as the caved ore is drawn. A large proportion of the rock breaks up in the caving action so that it will pass through the drawpoints. Oversize blocks are broken by drilling and blasting or mudcapping. Figure 3 shows the progressive stages of block caving. In the central part of the ore zone, the vertical dimension of a block is determined by the 132 metres between production levels. When isolated ore pockets are developed, the vertical dimensions of a block depend on the extension of the ore zone above the undercut. The minimum horizontal dimension of an under- cut determines the cavability of the overlying block. When necessary, caving is assisted by drilling long horizontal holes into the block above the undercut and blasting them. This procedure speeds up or restarts caving. It will not ensure complete caving of blocks having undercuts less than 30 m wide. Orebodies suitable for block caving are highly fractured and wide enough to cave freely without excessive dilution. Undercutting must

Jan 1, 1981

By J. P. Carson

THE Croton water-shed furnishes the source and storage of watersupply to both the old and the new aqueduct. The Croton river rises in the southern part of Dutchess county, about 68 miles from the lower end of New York city. Its three main branches, called the East, Middle and West branches, flow southward across Putnam county, joining, near its southern boundary, to form the Croton, which continues thence in a general southwest direction across Westchester county to the Hudson river at Croton Point, about 35 miles north of the city. The water-shed above the proposed site of the Quaker Bridge dam extends about 33 miles north and south, with an average width of 11 miles, making in all about 362 square miles, from which, by complete storage, an average daily supply of 250,000,000 gallons may be collected—sufficient for the needs of the city, probably, for the next fifteen years. The water-shed above the Croton dam is 23 square miles smaller, and furnishes the present daily supply of 100,000,000 gallons. By referring to the map it will be seen that the shortest approximately straight line between the proposed site of Quaker Bridge

Jan 1, 1891

By G. S. Cole, G. F. Bolling

A series of Al-Cu alloys has been cast from constant superheat to solidify either with a hot top or with a free liquid/air interface. All the other variables which affect relative fluid motions were kept constant except the imposition of slow rotations m oscillations of the mold. Depending upon the exact circumstances, evi-dence could be found for the nucleation of equiaxed grains from dendrite bits detached from the columnar zone, or from the free surface, or from solid bits induced at pouring; a special experiment showed the solute buildup during ingot solidification and by inference the reality of constitutional supercooling. All methods of grain nucleation are thus supported. When solidification is arranged in a static mold the columnar- to-equiaxed transition occurs by one of these nucleation paths, subject to the natural decay of temperature gradients which promotes nucleation or the survival of nuclei. But when solidification is forced under special fluid flows it may display odd transitions. In one of these the equiaxed zone is synihesized from. dendrite bits detached from the solid/liquid interface. These survive under the concurrent lowering of temperature gradients and eventually cause transition by impeding columnar growth. GRAIN structure control is desired because real experience shows that specific properties are associated with specific cast grain structures. But since control is thus a matter of need and does not require understanding, much of casting remains art. For example, the manipulation of relative fluid motions in simple ingots provides a control of grain structure development,1-4 but theoretical insight is not required in order to broaden its potential applicability. Fortunately, however, once a variable like fluid flow is recognized it can also provide paths toward new insight. New observations using this variable have provided an insight which is curious. All the theories or descriptions of the columnar-to-equiaxed transition (CET) seem to be supported as long as the appropriate experiment is carried out. In order to develop this idea, let us ignore segregation, the chill zone (until a later section of this paper), and the origin and development of the columnar zone.= The details of questioning how equiaxed material forms in a casting may be divided in two. The first part is simply a questioning of the origin for equi-axed grains: are there fresh nuclei from heterogeneous nucleation, or dendrite bits broken off or melted from the columnar zone or elsewhere,6 or other solid bits surviving from the outset of freezing? The second is more complex, a questioning of the CET: does columnar growth slow down and allow the dominance of equiaxed grains, however they are formed, or do equi-axed grains take over and force columnar growth to stop? This "chicken-or-the-egg" second question can be quite useful, especially because it allows us to delineate the ordinary or NATURAL EQUIAXED ZONE and the induced or SYNTHETIC EQUIAXED ZONE. A natural equiaxed zone occurs if solidification proceeds in the absence of disturbances or extraneous forces such as ultrasonics, stirrings, and so forth. Both the CET theory proposed by Winegard and Chal-mers, 7requiring constitutional supercooling, and the CET theory suggested by Chalmers,8 requiring nuclea-tion only on pouring, pertain to the natural equiaxed zone. The best collating evidence to date for both these theories is contained in the work by Biloni and Chal-mers;9,10 the former theory7 is supported by special versions of the unidirectional growth experiment performed by Plaskett and winegardl1 and the latter theory' is supported in detail for the solidification of small ingots. An equiaxed zone can be synthesized when disturbances caused by forced fluid flows2-4 or other artificial means9,10 break off or melt off dendrite tips from an advancing solid/liquid interface,* if (and only if) temperature gradients in the melt are (forcibly) reduced enough to ensure the survival of these bits of dendrites, 2'3 Willful disturbances even so trivial as those produced by rapping a mold might be included here; as will be shown for example, this follows Southin's suggestion that the free liquid/air interface

Jan 1, 1970

By J. Steininger

The Hallimond tube flotation of sphalerite and pyrite with sulfhydryl collectors has been found to be inhibited near neutral pH in the presence of copper salts. Alkalimetric titration studies of the reactions between collector and activator indicate that this effect is apparently related to the formation of basic copper collector complexes. The conditions of formation of these compounds and their stability are in good agreement with the depression observed in flotation experiments. The general procedure employed in the flotation of zinc sulfide minerals requires activation of the mineral surface by heavy metal ions, usually copper, which react more easily than zinc with the common short-chain ionic sulfhydryl collectors.' Commercially, zinc flotation is carried out under alkaline conditions (pH 7 to 10.5), but small-scale experiments indicate that zinc sulfide minerals can also be activated and collected under acid conditions. Selectivity, however, becomes poor at low pH and undesirable materials such as pyrite, silicates and carbonates tend to report in the float. Several years ago, Wark and Sutherland~, measured the contact angles of air bubbles on copper-activated sphalerite immersed in various sulfhydryl collector solutions. When represented, as in Fig. 1, on pH-sodium cyanide diagrams, the results are characterized by 'islands' of non-contact near neutral pH and

Jan 1, 1969

The organization of the American Institute of Mining Engineers, 75 years ago, parallels the beginning of present-day steel-producing methods in the United States. This early association with the industry is emphasized by the fact that the first open-hearth furnace constructed and operated in this country was then only three years old, and the first commercial bessemer converter was just seven years old. Total steel production in the year 1871, as recorded by the American Iron and Steel Institute, was 84,000 net tons, of which 2,000 tons was produced by the open-hearth process, 45,000 tons by the bessemer, and 37,000 tons by the crucible, puddled iron, and other processes. The bessemer process had thus become the major source of steel production. Its capacity expanded progressively during the following decade, and by 1880 was the source of approximately 86 pct of total steel production. Most of this tonnage was made in eastern Pennsylvania and used in rail manufacture. At about this time, however, important changes began to occur which gave impetus to the production of steel on a much larger scale. The development of Lake Superior ores from 1870 to 1890 and the exploitation of the Mesabi Range in 1892 provided the industry with great quantities of high-grade ores. The abundance of coking coals and limestone in the region adjoining western Pennsylvania and the development of cheap water transportation on the Great Lakes tended to shift the center of iron and steel manufacture to an area west of the Allegheny Mountains. Encouraging these new develop-

Jan 1, 1948

By W. T. lsbell

HERCULANEUM, MO., about thirty miles south of St. Louis on the Mississippi River, is the site of the lead smelter of the St. Joseph Lead Co. The lead concentrates come by rail from the Flat River district and from three properties in Madison County, Missouri; from the Balmat division in St. Lawrence County, New York; a small tonnage from the Tri-State district; and occasionally from the Aguilar property in Argentina. The average grade is 67 to 68 percent lead and 1 to 3 oz of silver. The bulk of the material is flotation concentrate, with some gravity or table concentrate. No secondary metals, outside drosses, or any materials high in bismuth, arsenic, or antimony are treated. All concentrate is received in box-caps and is unloaded directly from a trestle into the concentrate bins at the roaster plant. Flux, coke, and any miscellaneous lead-bearing material is either unloaded directly into bins or unloaded with a locomotive crane. All moving and switching of cars is done with two thirty-ton steam locomotives. Shipping facilities for the plant are provided by the Missouri-Illinois Railroad. Water for the plant and for fire protection is obtained from a dam built in a near-by creek. Drinking water both for plant and town is obtained from

Jan 1, 1947

By Eric R. Jette

In order to control a chemical process by other than empirical, rule of thumb methods, two types of knowledge concerning the reactions involved must be available: (1) the thermodynamics of the reactions, and (2), by no means less important for efficient operation, the mechanisms and kinetics of the reactions. Information on the thermodynamic side enables the operator to decide upon initial and final conditions, whether heat must be added or removed from the system, whether the reactions proceed farthest in the desired direction at high pressure or low, etc. Knowledge of the mechanisms involves the determination of the individual steps by which an initial set of reactants, under given conditions, proceed to give the desired final products and kinetic studies upon which the mechanisms are based give the speed at which each of these reactions or steps take place. Thus thermodynamic studies of a reaction enable the operator to control the direction and extent to which the reaction can proceed, while kinetic studies enable him to control rates and thus the time efficiency of the operations. The thermodynamics set the limit to which the reacting system approaches; the kinetics tell how fast the system actually approaches this limit. The two types of information are complementary and not antagonistic even though in discussing the mechanism the introduction of thermodynamics is entirely needless and generally of no assistance, while in thermodynamic studies mechanism need not even be mentioned. Heterogeneous Reactions The thermodynamic side of metallurgical reactions has received much attention in the past; the mechanisms, relatively, very little. The main reason for our present lack of information on the mechanisms of these reactions lies in the fact that every one of importance is a heterogenkous reaction; i. e., the substances involved in the reaction exist in more than one phase, while, if we neglect the large amount of work which has been

Jan 1, 1931