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By L. F. Mondolfo, F. A. Crossley

The mechanism of grain refinement by the addition of small amounts of titanium, molybdenum, zirconium, tungsten, and chromium to aluminum was investigated. The results indicate that the grain refinement is caused by the peritectic reaction which, by transforming the intermetallic compound into crystals of aluminum solid solution, seeds the melt with nuclei above the freezing point of aluminum. THE feasibility of reducing the grain size of aluminum alloy castings by the addition of small amounts of titanium, zirconium, molybdenum, tungsten, columbium, boron, and chromium has been known for a long time, and the use of some of these elements as grain refiners is common practice in the aluminum foundry industry. The purpose of the present investigation was to determine the mechanism by which these additions produce the grain refinement. Asato et al., on the basis of extensive work on copper, antimony, and silver alloys, presented a theory of grain refinement based on the occurrence of the peritectic reaction. Briefly, this theory states that during cooling of the melt crystals of the primary phase form, which react peritectically with the liquid upon further cooling. The peritectic reaction transforms at least partially the primary crystals into crystals of the secondary phase, which then act as nuclei for solidification of the remaining melt. As the peritectic reaction takes place the primary crys- tals break in pieces, and each piece acts as a nucleus. Fine dendritic crystals which can easily break are the most effective for grain refinement. Sicha and Boehm," in investigating the refining effect of titanium on an AI-Cu alloy, concluded that TiA1, crystals serve as nuclei to initiate crystallization, but did not offer further information on the mechanism of refinement. Bonsack in the discussion of their paper suggested that refinement was due to clouds of some solid in the melt, probably TiO² which hindered grain growth. Eborall,' after studying the effect of titanium, zirconium, vanadium, tungsten, columbium, chromium, and boron on some alloys, concluded that the peritectic reaction was not an essential feature of grain refinement. Her conclusion was based mainly upon the observation that under her experimental conditions (sand casting) the Al-Cr alloys, which undergo a peritectic reaction, did not show appreciable refinement. Cibula" investigated the mechanism of grain refinement and reported that two types of grain refinement exist: 1—Grain refinement produced by restriction of grain growth by the concentration gradient mechanism proposed by Northcott.' 2— Grain refinement produced by the presence of particles in the melt, upon which the melt crystallizes easily. He further concluded that very marked grain refinement results from a combination of the two mechanisms. Since Tic was found present in aluminum alloys refined by the addition of titanium, it was identified as the nucleating agent. In the case

Jan 1, 1952

By Walter Dake

THE mining engineer is being more generally called on to examine and report on properties where the introduction of mechanical loaders is proposed, and as the use of these labor-saving devices presents an entirely different problem from that of hand-loading, an outline of procedure is herewith pre¬sented based on five years of intensive field experience in making such studies. It is impossible to outline an examination which will cover every condition but the most important variables are noted and the re¬port may be amplified or abridged to suit individual mine requirements. There are, of course, exceptional cases in which a single minor variable will determine the final conclusion; the result of mechanical loader application can be, estimated within close limits by considering all variables listed and taking into account the sum of all those found to be applicable to the property under examination. It is necessary that a high degree of accuracy be exercised in the analysis of conditions, and that a relatively narrow margin be figured on all estimates of tonnage outputs and costs. In making an examination for this purpose the data as to company name, business address, name of mine, geographical location, rail or water connections, type of mine (whether shaft, slope, or drift), and the name of seam should, of course, be included, to be followed by the minimum, maximum, and average thickness of seam, a brief description of the charac¬teristics of the coal, the impurities contained, location of regular impurities or partings, together with nota¬tion as to quality, uses, and-markets for the coal. It is also necessary to make cross-sections of the seam so that face preparation may be studied in an effort to eliminate all regularly-occurring impurities at the working place. The possibilities for further cost re¬ductions by the removal and gobbling of partings under¬ground before mechanically ? loading out a face are sufficiently great to warrant careful study and analysis. The classification of the mine from the standpoint of gaseous or non-gaseous operation will determine the general type of electrical equipment needed. A notation regarding the power whether generated at the mine or purchased, together with the amount, voltage, and type of current available is necessary since these matters determine the exact type of elec¬trical equipment to be used. A brief description of the ventilating system, giving type of fan, amount. of air delivered, water gage, and whether force or ex¬haust type, will enable the engineer' to figure venti¬lating requirements per man under mechanical loading practices. The pitch of seam in degrees, the pitch of working faces, and a brief description of rolls or horsebacks should be included, as these affect the efficiency of mechanical loading and, therefore, the economic re¬sults obtainable. -Notations should be made as to the amount of water found in working faces, and whether pumping, sprinkling or rock-dusting methods should be considered. As the character of the floor affects the operation of the machine at the face if a cater¬pillar-tread type, its hardness should be determined, and also whether impurities consisting of floor ma¬terial are likely to be loaded with the coal. The char¬acter of the roof and overlying stratification determine the mining system and width of roof span at work¬ing faces. It therefore directly regulates the amount of tonnage to be loaded by machines without a move from one place to another.

Jan 12, 1927

By G. H. Kennedy, H. E. Criner

CYCLONE thickeners are "hydraulic centrifuges" designed either to produce a maximum practical separation between the water and solids of a feed slurry or to classify the slurry solids according to particle settling rate. The possibilities of utilizing the thickener to "close" plant water circuits have been investigated. Since the thickener becomes an integral part of the plant water circuit when installed, the basic means by which the solids content of all circulating water systems must be controlled is reviewed. All coal not separated from the circulating water by means of dewatering screens or settling devices must be bled from the plant at the same rate as they are being fed or created by degradation. If this were not true, the circulated volume would finally be completely filled with solids. If the rate of bleed is low, the solids concentration in the bleed and circulating water generally will be high. To keep a reasonable circulating water concentration, large amounts of fresh water must be supplied and the bleed rate must be high. These conditions are usually undesirable because of the difficulty in securing fresh water, the loss of large quantities of coal, and the pollution of nearby streams. Thickeners are the primary stage in the separation of the water contained in the bleed from the coal. Since a thickener, when operating with reasonable efficiency, usually cannot be expected to deliver an underflow containing less than 50 pct water, secondary dewatering devices such as a slurry screen or vacuum filter must be used to separate additional water from the bleed. The surface area required by the filter or screen will be nearly proportional to the total water which must be handled, and therefore the thickener becomes necessary to hold down the original cost. The water separated from the coal is then returned to the plant circuit to maintain the water balance and thus becomes the source of fresh water. It is not necessary to return clear water to the plant to maintain control of the circulating water concentration. It is only necessary that the bleed dewatering devices remove coal in all sizes at a rate equal to that at which these sizes are entering the circulating water. However, practically speaking, in order to maintain low solids concentration, it is usually necessary that the thickener have good recovery characteristics on bituminous coals in those sizes down to 400-mesh. The thickener can remove the smaller sizes from the closed-circuit system at the "solids in" rate and prevent their "build up" in the circulating water as shown in Fig. 1. With the portion of the feed water going directly to the underflow, comes the very fine solids not concentrated by the cyclone. All the larger solids are removed from the feed and delivered in a concentrated condition at the underflow. To apply thickeners with some reasonable assurance that operating requirements will be met, it is necessary to know the rate at which solids of all sizes must be removed from the circulating water and to know the thickener characteristics. The required removal rate of fine solids not recovered by other dewatering devices may be estimated from the size distribution and tonnage of the plant feed with a reasonable allowance for degradation in the circulating water system. A more reliable estimate may be secured by sampling the plant bleed water during a constant load period.

Jan 1, 1952

By William B. Senseman

FOR reasons well known to mining engineers, wet grinding is quite universal in plants having to do with the extraction of metallic values from crude ores. In the processing of the nonmetallic and industrial minerals, dry grinding is the more common method. The crude materials usually contain less moisture than is required for wet grinding and the products usually are marketed in dry form; most of them as powders. To grind wet, therefore, would entail the addition of water and an expense for drying the product, which is not justified. Furthermore, the material would be a dried cake that would still have to be pulverized or disintegrated before use. For producing fine products, air separators have largely replaced the earlier practice of sizing with screens and bolting reels. Mills in which the air-separating feature is an integral part of the design are now commonplace. Mill designs are many and air systems have developed along various lines, but for the purpose of this discussion, only the fundamental idea need be emphasized the idea of using air for sizing and removing pulverized material from a grinding mill. About 20 years ago, when the use of mills equipped with air separation had become common practice, heated air or gas was introduced to such a system for the removal of moisture. The purpose of this discussion is to outline the developments and trends that have followed this experiment. It is an important development, for mills equipped with air separation are now universally used for pulverizing not only nonmetallic and industrial minerals, but a great variety of other materials. All such mills are essentially the same. Dried material is pulverized, removed by an air stream, trapped in a cyclone collector, and relatively clean air from the cyclone is returned through a fan to the mill. There is no theoretical need for a vent from the system. The practical need is to vent the air that leaks into the system, and, since the cyclone is not 100 per cent efficient as a dust collector, this vented air carries some dust with it. The initial attempt. at drying was made on a system like that described, by the addition of a furnace. The minus pressure within the mill draws hot gas from the furnace. Infiltration air, along with the drying gases and evaporated moisture, is vented as before. The first application was made to a mill used for pulverizing coal. The coal contained very little moisture, so very little drying effect was needed for the success of this experiment. Actually, some calculated efficiencies of over 100 per cent were obtained before due allowance was made for the conversion of mill power into useful heat. When moisture is low,, the heat obtained from the conversion of mill power is an appreciable part of that required. That drying can be effected in the short time interval available in a grinding mill of this type is better understood by visual-

Jan 1, 1945

By H. R. Brannon, J. S. Osoba

The introduction of the scintillation counter into field use for gamma-ray well logging has provided a new tool with special utility for the deternzination of natural radioactivity of sediments. Previous subsurface gamma-ray measurements have indicated only the total amount of radioactivity of the sediments. With the scintillation counter, the relative amounts of the elements which emit gamma radiation can be determined. Sediments logged included 35 zones in wells located in the Teras Gulf Coast, East Texas, and West Teras. Although the data obtained from measurements made to date are not sufficient to evaluate the possibilities of spectral logging, it appears likely that spectral measurements will yield information of geologic value. INTRODUCTION Although variations in the natural radioactivity of sediments were recognized as early as 1909,1 the appli- cation of such variations to borehole logging was not made until almost 30 years later. A group of Russian workers in the early 1930's were successful in making crude measurements of natural gamma activity in an oil well borehole. The first practical gamma-ray logging system was developed by Howell and Frosch2 in 1939. Induced radioactivity, or neutron, logging appeared soon after the introduction of gamma-ray logging. After early work had demonstrated the potentialities of radioactivity logging, development of sensitive and stable logging equipment for field use followed, so that neutron and natural gamma logs are now run routinely and have proved to be extremely valuable in characterizing subsurface formations. Even though tremendous strides have been made in developing radioactivity logging, it is apparent that the ultimate in the method of logging has not been reached, for, until very recently1 in none of the commercially available logging systems has advantage been taken of the fact that gamma radiation is composed of a spectrum of rays, each ray having a distinct and characteristic energy. An individual gamma ray originates in a single element and has energy determined by the element. The inten- sity of radiation, or number of rays emitted from unit volume in unit time, is determined by the concentration of the element. If it were possible to sort out these gamma rays and assign them to their parent elements, thereby essentially analyzing for the elements, a wealth of new information descriptive of formation material and fluid content would be at hand. For example, if in natural gamma logging, the gammas due to potassium and to the thorium and uranium series were measured individually, data would thus be available on the concentrations of each of the three elements, adding materially to the information content of the log. In contrast, conventional gamma logs measure only a quantity proportional to the combined concentrations of uranium, thorium, and potassium. The naturally radioactive elements occur in sediments in concentrations dependent on source material of the sediment, and through their chemical characteristics, on conditions of deposition,' so that the individual concentrations may be diagnostic for particular formations. These concentrations, particularly if measured in situ, could lead to a powerful tool for correlation and for reflecting environmental conditions under which sedimentation took place. As a correlation tool, individual uranium, thorium, and potassium measurements

Jan 1, 1957

By B. Thomas Mansbach

INTRODUCTION The Overseas Private Investment Corporation ("OPIC") is a U.S. Government agency mandated to promote the economic development of the less developed countries ("LDCs") by assisting U.S. private investment in the Third World. Generally, investment decisions turn on the optimism or pessimism of the private sector's financial analysis of a project, with market price of product a major unknown in a very chancy set of projections. Discussions with American mineral companies, however, show that, more often than not, in developing country projects it is the political risks of investing in mineral exploration and extraction that pose the most serious deterrent to investment. In several of the projects described here, investments would not have been made if OPIC had not been involved providing support to the project sponsors and their funding sources. Clearly it is not OPIC's business to promote U.S. investment in a project which is not commercially viable, but OPIC's programs can neutralize the political uncertainties which act as disincentives to investment in otherwise commercially viable projects. That is to say, OPIC's programs are designed to reinforce market decisions and not distort them. Although OPIC is an independent agency of the U.S. Government, it is managed by a Board of Directors, the majority of whom come from the private sector. This, coupled with the statutory requirement that it be self-sustaining and operate with due regard for the principles of prudent risk management, requires that it operate on a business-like basis. Although established as a development agency, to the business public OPIC is both an insurance company and a lending institution, with two major programs which are available to U.S. investors in the minerals sector: its political risk insurance program and its finance program. Each has been specially tailored to the meet needs of the mining industry. The insurance program provides coverage against four basic types of political risk: Currency Inconvertibility, Expropriation, loss caused by War, Revolution and Insurrection and Interference with Operations as a result of an act of War, Revolution or Insurrection. Coverage against the risks of Civil Strife can be added to both War, Revolution and Insurrection coverage and Interference with Operations. Inconvertibility coverage provides protection against a deterioration in an investor's ability to convert local currency into U.S. dollars. This deterioration can be the result of either active or passive delays. Active delays consist of a change in exchange laws or regulations that leads to inconvertibility delays of 30 days or more. For example, if the exchange regulations at the time of contract execution allow an investor to transfer earnings equal to 18% of its registered capital per annum and the government of the host country later changes the law to allow conversion of only 12%, the insured would convert the 12% transferable under the new exchange regulations with the government foreign exchange authorities, delivering the remaining 6% to OPIC for conversion at 99% of the then prevailing rate of exchange. (OPIC does not cover devaluation risks.) Upon delivery of the local currency to OPIC, normally at the U.S. Embassy in the project country, the insured's account in the U.S. would be credited with dollars. Delays can also result from what is termed passive blockage, which includes administrative delays of more than 60 days (sometimes longer) caused by the bureaucratic tie-ups or pigeonholding of transfer requests, as well as delays suffered simply because the government of the host country does not have sufficient foreign exchange. The transfer procedure is the same as with active blockage - the local currency is delivered to OPIC in the project country and OPIC provides dollars in the United States at the then prevailing rate of exchange. The second coverage -- Expropriation -protects not only against the loss of the investment due to the well-known risks of expropriation, nationalization or confiscation by the host government, but also against

Jan 1, 1985

By S. A. Falconer

This paper deals with the practical application of the Dutch State Mines cyclone separator for fine-coal cleaning. The more important operating variables are discussed, and results of a number of continuous-scale tests on various fine coals with a 6-in. cyclone separator are given. Descriptions of the Cyanamid Pilot Plant and the 50 tph Cyclone Separator Plant at the Emma Washery in Holland are included. TODAY, as never before, the coal producers of this country are faced with the necessity for obtaining maximum yield of marketable coal of all sizes down to and including the finest. Particular interest is being displayed in a more effective means of recovering the finer sizes which in the past so often have been discarded to waste or treated by inadequate equipment. The reasons for this interest are easily understood. Rising mining costs have resulted in the increased use of mechanized equipment underground for full seam mining. This, in turn, means more refuse in the run-of-mine and also more fines in the feed going to the cleaning plant. Stringent antistream pollution laws now make it necessary at least to impound the fines, and usually it is a paying proposition to recover the coal from these fines before sending them to the storage area. Finally, the market and price of the finer sizes has increased, but at the same time specifications have tightened and the demand is for higher grade products. During the past four years a great deal of publicity has been given to this new process and apparatus for treating fine sizes of ores as well as coal. Excellent discussions of the apparatus itself and the theoretical aspects of the basic operating principles involved in its operation have been presented by M. G. Driessen,1-3 M. R. Geer and H. F. Yancey,4,5 J. W. Hyer6 and more recently by D. A. Dahlstrom8 as well as others.7,9-11 In view of this, it has been decided to include in the present paper only a brief description of the cyclone separator and its operating principles. This paper deals primarily with some of the more practical commercial aspects of the process and equipment required for its operation; the variables in the operation of the cyclone, their effect and means for control; and the results obtained with a 6-in. semicommercial size separator on a variety of fine coals, bituminous and anthracite, using finely ground magnetite for the separating medium solids. A description is included of the commercial-size cyclone separator pilot plant installed by the Dutch State Mines at its Emma mine in Holland, where finely ground slate is utilized as medium solids. Field of Application: The Dutch State Mines cyclone separator operates most efficiently on ores and coal in the size range of % in. to about 48 mesh. On some types of feed, effective separation can be made on sizes as small as 100 mesh, but up to the present, this may be considered exceptional. Depending upon the type of medium used, the specific gravities of separation can be varied within wide limits, up to as high as 2.70, if magnetite is used as medium. Early Development: The development of the Dutch State Mines cyclone as a separator, or cleaner, was the outgrowth of early experimental work by Dries-sen' and others in Holland, just prior to World War 11, in the course of which was discovered the effectiveness of the cyclone in reclaiming and thickening the dense medium used in the "Loess" process of

Jan 1, 1951

By S. A. Falconer

This paper deals with the practical application of the Dutch State Mines cyclone separator for fine-coal cleaning. The more important operating variables are discussed, and results of a number of continuous-scale tests on various fine coals with a 6-in. cyclone separator are given. Descriptions of the Cyanamid Pilot Plant and the 50 tph Cyclone Separator Plant at the Emma Washery in Holland are included. TODAY, as never before, the coal producers of this country are faced with the necessity for obtaining maximum yield of marketable coal of all sizes down to and including the finest. Particular interest is being displayed in a more effective means of recovering the finer sizes which in the past so often have been discarded to waste or treated by inadequate equipment. The reasons for this interest are easily understood. Rising mining costs have resulted in the increased use of mechanized equipment underground for full seam mining. This, in turn, means more refuse in the run-of-mine and also more fines in the feed going to the cleaning plant. Stringent antistream pollution laws now make it necessary at least to impound the fines, and usually it is a paying proposition to recover the coal from these fines before sending them to the storage area. Finally, the market and price of the finer sizes has increased, but at the same time specifications have tightened and the demand is for higher grade products. During the past four years a great deal of publicity has been given to this new process and apparatus for treating fine sizes of ores as well as coal. Excellent discussions of the apparatus itself and the theoretical aspects of the basic operating principles involved in its operation have been presented by M. G. Driessen,1-3 M. R. Geer and H. F. Yancey,4,5 J. W. Hyer6 and more recently by D. A. Dahlstrom8 as well as others.7,9-11 In view of this, it has been decided to include in the present paper only a brief description of the cyclone separator and its operating principles. This paper deals primarily with some of the more practical commercial aspects of the process and equipment required for its operation; the variables in the operation of the cyclone, their effect and means for control; and the results obtained with a 6-in. semicommercial size separator on a variety of fine coals, bituminous and anthracite, using finely ground magnetite for the separating medium solids. A description is included of the commercial-size cyclone separator pilot plant installed by the Dutch State Mines at its Emma mine in Holland, where finely ground slate is utilized as medium solids. Field of Application: The Dutch State Mines cyclone separator operates most efficiently on ores and coal in the size range of % in. to about 48 mesh. On some types of feed, effective separation can be made on sizes as small as 100 mesh, but up to the present, this may be considered exceptional. Depending upon the type of medium used, the specific gravities of separation can be varied within wide limits, up to as high as 2.70, if magnetite is used as medium. Early Development: The development of the Dutch State Mines cyclone as a separator, or cleaner, was the outgrowth of early experimental work by Dries-sen' and others in Holland, just prior to World War 11, in the course of which was discovered the effectiveness of the cyclone in reclaiming and thickening the dense medium used in the "Loess" process of

Jan 1, 1951

By M. P. Tixier, A. Poupon, M. E. Loy

Simple qualitative methods are explained for identifying those shaly sands in a well that are most likely to contain oil. A need for more precise measurement of the variables that enter shaly sand analysis is indicated. Field examples are given to illustrate the methods. A theoretical discussion of the quantitative interpretation of shaly sands is given as a basis for discussion and as a guide for the future. While not generally capable of practical application at the present time because of the lack of sufficient accuracy of the electric log data, these methods may become more feasible in the future as the result of the improved logging methods now being introduced. INTRODUCTION Experience has shown that for porous formations containing only a negligible amount of clayey material, reliable information on the fluid saturation and porosity of the reservoir rocks can usually be derived from the electrical logs. The interpretation is based on empirical formulae relating the true resistivity of a porous formation to its lithologic character, to the resistivity of the interstitial water, and to the proportions of water and hydrocarbons in the pores.' If the resistivity of the interstitial water is not known, its approximate value can be derived from the SP curve.2,3 The porosity can usually be determined to a good approximation from a MicroLog, or a MicroLaterolog.4,5 When the reservoir rocks contain an appreciable percentage of clayey material, an additional factor is introduced into the analysis. In a clean formation, the matrix is an electrical insulator, so that the ability of the formation to conduct current is due only to the conductivity of the electrolytes in the pores; in a shaly formation, the shale constitutes a part of the rock matrix able to conduct current, and influences the resistivity of the formation. On the other hand, the spontaneous emf's and the circulation of the SP currents are also responsive to the presence of the shaly material. All other factors being the same, the deflection of the SP curve opposite a shaly permeable formation is smaller than the deflection which would be observed if the formation were clean. The effects of the presence of shale on the resistivity and on the SP curves in a shaly formation are functions of the amount, of the specific resistivity, and of the geometrical distribution of the shaly material within the formation. The presence of shale therefore constitutes an important complication in electrical log interpretation. It is easy to realize, for example, that the presence of a large amount of clayey material in a sand may have such a predominant effect that the resistivity of the sand will not change very much, whether the pores are entirely filled with connate water, or contain a high saturation of hydrocarbons. Important research projects have been undertaken to investigate the influence of shales and to find a way to allow for this influence in the interpretation of a log. The problem of the SP in shaly sands was analyzed mathematically by H. G. Doll"' for the case of sands with shale laminations. Formulae expressing the resistivity of shaly formations were proposed by Patnode and Wyllie8 and de Witte.9 Other quite interesting theoretical and experimental results have been published by various authors.l0,ll,12,l3,14 The purpose of the present paper is to discuss an approach to electrical log interpretation in shaly sands. This approach is based partly on some of the theoretical and experimental data available in the literature and partly on observations made on actual field logs. Comparatively simple methods for qualitative and semi-quantitative analysis are described. These methods depend principally upon information provided by the electrical logs.

Jan 1, 1955

By G. Vaux, M. L. Fuller

AN apparatus and procedure for the determination by X-ray reflection of preferred orientation of crystals in rolled metal with the Geiger counter X-ray spectrometer was described by Schulz.' This is an excellent procedure and we have used it continually for several years. In our use of the procedure, two modifications have been made and used during most of this period. One of these provides for automatic scanning and recording of the reflections, and the other makes possible the application of the procedure to coarse-grained specimens and permits measurement of almost all orientations without resort to the transmission technique. The automatic scanning and recording are accomplished by a motor drive of the inner ring of the Schulz apparatus (see R, in Fig. 2 of his paper and R2 in Fig. 1 of this note) in synchronism with the chart recorder of the North American Philips 90" X-ray spectrometer. A rate of 10" per min is used. A scan of 180" is obtained corresponding to poles on the stereographic projection whose locus is a great circle. The modification for coarse-grained material is accomplished by allowing a larger area of the specimen to contribute to the X-ray diffraction. In the Schulz apparatus the incident X-ray beam is confined by a slit system to rays in the plane of the spectrometer. Schulz demonstrated that this restriction of the X-ray beam permits a survey of the X-ray reflections without correction up to about 80" on either side of that specimen position in which the specimen is perpendicular to the plane of the spectrometer. This is the angle + of rotation of the inner ring R2. One of these slits is horizontal and extends across the X-ray source side of the specimen. In the modification this slit is removed, thus permitting greater divergence in the X-ray beam and the irradiation of a larger area of the specimen surface. Fig. 1 shows the apparatus with the motor drive and with the slit removed. Discontinuities in the recorded X-ray intensity plot due to the few participating crystals in coarse-grained metal are much lessened. The increased divergence does not cause reflections from other crystal planes to enter the Geiger counter slit. An important advantage of the original Schulz scheme is thus lost and a system for correction is required. To do this, a compact of atomized copper powder was prepared and tested by the original Schulz method for the absence of preferred orientation. The horizontal slit was then removed and a curve recorded showing the variation of intensity with angle +. In our arrangement the intensity was uniform within the range + equals ±30°. Beyond this the intensity fell off rapidly reaching zero at ±90°. The curve thus produced is then used to correct measurements made on preferred orientation specimens. In practice this is accomplished by constructing from this calibration curve a family of curves which, as a transparency, can be superimposed on the recorder chart to read corrected intensity directly. Not only does this method permit the handling of coarse-grained material but it also makes possible the plotting of intensities almost to the circumference of the stereographic pole figure projection. Thus, nearly the entire pole figure can be plotted without the necessity of using the transmission technique. Moreover, intensities are much greater, an advantage when surveying crystal planes of poor reflecting power.

Jan 1, 1954

By H. L. Sauder, J. L. Newman, C. Waddell

An instrument capable of measuring subsurface flow rates is described. The instrument is self-contained and may be run on piano wire line. It detects flow by means of an impeller suspended between two torsion wires. The force of the well fluid striking the impeller causes the impeller to rotate, exerting a torsional force to the wires. This force is determined by recording the angle of rotation of the impeller on film using a battery-driven, clock-controlled camera. The impeller is sensitive to flow in either direction and the same instrument can be used to measure injection as well as production rates. Changes in direction of flow, such as might be caused by thief zones, are measurable and are indicated by a reversal of the direction of rotation of the impeller. Adjustment of the sensitivity of the instrument to measure a wide range of flow rates is accomplished by the use of different size torsion wires. An umbrella-type fluid trap, which contacts the casing or wellbore, diverts the flow through the flow tube. The fluid trap remains closed while rurrning in the hole and can be opened at any point in the well. The instrument with the trap closed is 1 3/4 in. OD and may be run through 2 in. tubing. Successful flow profiles have been made on wells with flow rates ranging from 60 BID to 4,000 B/D at surface pressure up to 4,500 psi. The instrument is designed for high-pressure and high-temperature operations. INTRODUCTION The need for an instrument that will measure flow rates in a wellbore is as old as reservoir engineering itself. A number of such devices have been designed within the past few years. Some of these have been described in the literature1,2,3,4,5,6 One of these devices1. a hot-wire anemometer type, made many successful jobs in dry gas producing areas. Difficulty was encountered when this flowmeter was used in wells producing liquids and development work was initiated to overcome this difficulty. The present flowmeter is the result of this work and provides an instrument with a wider range of application in the industry. Consider- able development work has been done on the tool involving many changes in the mechanics of recording the flow readings, however, the basic principle of flow detection has remained the same since its inception. PRINCIPLE OF OPERATION The basic principle of operation of the flowmeter is the utilization of a portion of the kinetic energy of flowing well fluid to impart a rotational force to an impeller suspended between two torsion wires. This impeller, Fig. 1, is a screw-type propeller with the blades having a pitch angle of 40. As the well fluid passes through the instrument it strikes the impeller. The resulting force rotates the impeller and twist\ the torsion wires to a balance point at which the torque imparted to the wires balances the force required for the impeller to deflect the well fluid. The impeller is symmetrical and a change in direction of the flow results in a reversal of the direction in which the impeller is deflected. Thus the direction of the flow as well as its velocity is indicated. A dial is attached to the impeller by means of a hollow tube through which the upper torsion wire extends. The angular position of the impeller is recorded by photographing the dial at frequent intervals. In any given set of torsion wires the modulus of shear and polar moment of inertia remain constant and the deflection varies directly with the applied torque. The deflection imparted to the torsion wires also varies as the square of the fluid velocity. Further, the velocities represented by any two given deflections hear the following relationships: and Where V = velocity of flow stream and O ;= deflection. This is the basic relationship which is used to calculate the relative velocities represented by a given set of deflections where the velocity represented by any one of the deflection readings is a known quantity. For a given torque, the deflection of the torsion wire varies inversely as the fourth power of the wire diameter. Wire sizes ranging from ,005 in. in diameter to .022 in. in diameter can be used. The range of

Jan 1, 1957

By H. D. Outmans

Present first-order theory for frontal stability and viscous fingering of immiscible liquids is improved by including the nonlinear terms in the equations describing conditions at the interface of the liquids. This leads to the revision of several conclusions which were based on first-order theory. They concern the growth rate and changing shape of a sinusoidal disturbance, particularly in relation to the wave number of this disturbance. Nonlinear aspects of effective interfacial tension are discussed and it is shown that this tension is not simply a positive proportionality constant in a linear relation between pressure difference and curvature at the interface. Scaling requirements are determined from the dimensionless groups which govern fingering. Gravity and interfacial tension invalidate a previously formulated conclusion that the shape of a finger after a given displacement is independent of the displacement velocity. Also, similarity of fingering (and, hence, of sweep efficiency in case of an unstable front) requires geometrical similarity of the initial disturbance in the model and the reservoir with a scale factor which is the same as the one for scaling down the dimensions of the reservoir. INTRODUCTION The critical velocity at which the transition zone in the vertical displacement of immiscible liquids becomes unstable was calculated by ill. More recently, the same was done for nonvertical displacements and it was also shown that the stability is affected by an effective interfacial tension between the liquids. 2-4 Although in the oil reservoir a stable front is always desirable from a recovery point of view, the necessary velocity may have to be so low that the corresponding production rate is not economical. In that case, a knowledge of the fingering unstable front is necessary for predicting recovery at break- through. Studies in this direction have not gone beyond the very moment at which fingering first occurs.5,6 Conclusions about stability and fingering in these references are all based on linear theory. In this theory the nonlinear terms in the equations describing conditions at the front are neglected. The usual justification for this lack of mathematical rigor is that the nonlinear terms can be made small relative to the linear terms and, supposedly, small causes produce only small effects. It has been recognized, however, that this is not necessarily true in the nonlinear problems of hydrodynamics.7 The hydro-dynamic stability and fingering of the front between two liquids, accelerated in a direction normal to the front, for instance, is strongly influenced by the nonlinearity of the boundary conditions.8-10 Since these boundary conditions are not unlike those arising in the problem of stability and fingering of the front during a slow immiscible displacement in porous media, it was thought that there, too, the nonlinear terms should be taken into consideration. A summary of the results obtained in linear theory and a comparison with experimental data precede the nonlinear theory developed in this paper. This summary serves to introduce some quantities which will be used in the further develop ment. It should also be pointed out that the method of higher-order approximation by which the nonlinear stability problem is solved has application in other reservoir studies.11 SUMMARY OF LINEAR THEORY 1. A plane interface remains stable if its velocity is smaller than a critical velocity. vc = (p2-p1)gn/(l/A2- l/A1 .........(1.1) This equation is derived for uniform flow in a thin layer inclined to the horizontal plane. The displacement takes place in a direction normal to the intersection of this layer and the horizontal plane. The undisturbed (line) interface is normal to the velocity. Fluid 1, the upper fluid (gas), is displacing Fluid 2 (oil). (VcQS would be the injection rate in cc/

By T. S. Lovering

GEOCHEMICAL prospecting extends the age-old method of searching out lodes with a gold pan and rationalizes the prospector's hunch that certain plants are associated with ore. It uses sensitive but cheap and rapid analytical methods to find the diagnostic chemical variations related to hidden mineral deposits. Exploration geologists can gain tremendous assistance from this new tool, although its optimum use is not simple. To bring out the geochemical pattern that reveals the presence of a hidden ore deposit with a minimum number of samples requires a combination of shrewdness, chemical knowledge, and exploration geology. The use of sensitive analytical methods for prospecting had its start in the 1930's in northern Europe, where Scandinavian and Russian geologists had some success in these early efforts. Very little geochemical prospecting was carried on in the United States at this time, and no sustained interest was manifest until the close of World War 11, when geochemical investigations were started by the Mineral Deposits Branch of the U. S. Geological Survey. The purpose of these investigations was to apply geochemical principles and techniques to surface exploration for mineral deposits. Both the research on analytical methods and the routine trace analyses for field investigations were at first conducted by a single group, but it later became apparent that the trace analyses could be done by men of less experience than that required for successful research on methods. For the past several years there have been two groups of chemists, and although their functions overlap, three of the chemists are chiefly concerned with research, while four to six other men make the trace analyses for field projects. The chemical investigations, as well as the field projects of the Geochemical Exploration Section, concern only those phases of the subject that are appropriate to a government organization; every effort is made to help private industry, but not to compete with it, in finding orebodies. The chief aim of the Section, therefore, is to develop new analytical techniques and publish the results promptly, to carry out field investigations of the fundamental principles of geochemical dispersion, and to field test promising- techniques under controlled conditions. Some routine geochemical exploration work is carried on in connection with DMEA loans, and in district studies where the project chief wishes geochemical information on certain areas for his report. It should be emphasized, however, that geologists of the Geochemical Exploration Section are primarily concerned with fundamental principles underlying the distribution, migration, and concentration of elements in the earth's crust. To facilitate the use of geochemical methods the USGS has published much information on its methods of analysis and has provided opportunities from time to time for qualified professional personnel to study these methods, to work in the USGS laboratory, or to attend demonstrations of the analytical techniques at the Denver Federal Center. Typical of the research carried on are the problems now being investigated: 1) Development of rapid and sensitive analytical methods suitable to the determination of traces of metals and other minor elements in various materials, such as rock, soils, plants, and water. At the present time attention is being concentrated on U, Bi, Cr, and Hg, and satisfactory rapid trace analytical methods are virtually perfected for U and Bi. Good methods are also available for: Cu, Zn, Pb, Ni, Co, As, Sb, W, Mo, Ag, Nb, Ge, V, Ti, Fe, Mn, S, and P. 2) The relation of geochemical anomalies in plant materials to the geochemical distribution of elements in soils surrounding the plant. 3) A study of the dispersion halos in transported sedimentary cover such as glacial drift and alluvium over known orebodies. 4) A study of the behavior of ore metals in the weathering cycle. 5) A study of the behavior of the ore metals during magmatic differentiation. This requires a study of the distribution of minor metals in fresh igneous rocks and their component minerals in a well established differentiation series and in adjacent country rock. 6) A study of the dispersion of metals in primary halos in the wall rock surrounding orebodies. 7) Regional and local studies of the metal content of surface and groundwater in mineralized and barren areas. Many field projects of the Mineral Deposits Branch also require the services of USGS chemists during their investigation of the geochemical environment of ore deposits. From the work that has been done certain general principles have emerged. Concentrations of an element that are above the general or background value of barren material are called positive geochemical anomalies or simply an anomaly, whereas values less than background are called negative anomalies. The anomalies most commonly investigated in geochemical prospecting are those formed at the earth's surface by agents of weathering, erosion, or surficial transportation, but more and more attention is being given to primary anomalies found

Jan 1, 1956

By W. O. Philbrook, R. S. Kaplan

Rates of oxidation were studied for levitation-melted samples of Fe-C, Fe-Si, Fe-C-Si, Fe-C-P, Fe-C-Mn, and Fe-C-S alloys oxidized by mixtures of either 5 or 10 pct O2, in helium at several temperatures in the range 1850o to 2050°C. The concentrations of the oxidized elements decreased linearly with time. Mass transport in the gas phase was found to be the rate-controlling step. Ilowever, a mulliple -film model was necessary to account for the flux of iron and manganese vapor counter to the oxygen flow. THE advent of the basic oxygen and spray-refining processes of steelmaking has generated considerable interest in the kinetics of reactions between oxygen-bearing gases and liquid iron alloys. The object of this research was the determination of the role of mass transport in the gas and metal phases and of surface chemical reactions in the overall oxidation process. Of the reactions for elimination of elements dissolved in liquid iron, the oxidation of carbon has been investigated most extensively. Studies by Fuji and Ura,1 Fuji,' and Gunji et a1.,3 done with pilot-scale basic oxygen furnaces, indicated that mass transport of gaseous oxygen was rate controlling when the metal carbon content was greater than 0.15 to 0.30 pct. When the carbon content was less than this critical amount, diffusion of carbon dissolved in the iron was thought to be rate limiting. L. A. Baker et a1.4,5 levitated samples of iron-carbon alloys and oxidized them in CO-CO2, CO-C02-He, and O2-He atmospheres at 1660°C. These investigators found that the metal carbon concentration decreased linearly with time and their samples exploded when the carbon content fell below about 0.8 pct. They concluded that the rate-limiting step was the transfer of oxidant to the gas-metal interface. A model based on this rate-limiting step predicted decarburization rates within a factor of two of those experimentally observed. The explosion of the samples was attributed to a shift in rate-controlling step from gas-phase mass transport to transport of carbon dissolved in the metal. L. A. Baker and R. G. ward6 and R. Baker7 used freely falling droplets to investigate oxidation kinetics. In both papers, the authors speculated that flame fronts may have been partially responsible for the lack of better agreement between experiment and theory. Swisher and Turkdogan8 oxidized liquid iron having an initial carbon content of 0.97 pct with CO-CO2 and CO-C02-Ar mixtures at 1580°C. They concluded that a surface reaction was the rate controlling step. Iron-silicon alloys have been oxidized by R. Baker7 and Filipov and Martynov.9 R. Baker 7 also studied iron-carbon-silicon alloys falling as liquid droplets through oxygen. He found that the rate of both carbon and silicon oxidation varied inversely with the drop radius. When the initial silicon concentration was greater than 6 pct, the samples cooled during their fall. Manganese oxidation has been studied by R. Baker,7 and by Filipov and Martynov.9 ward10 investigated the loss of manganese from liquid iron under vacuum. He found that mass transport of manganese vapor was rate limiting in argon atmospheres of 0.02 torr to 700 torr pressure. Iron-sulfur alloys were desulfurized with H2-He and H2-Ar mixtures by Peters et al.11 A model based on the transport of H2S from the gas-metal interface into the bulk gas gave fair agreement between the predictions of the model and the experimental results. EXPERIMENTAL TECHNIQUE Essentially, the technique consisted of using helium-oxygen gas mixtures to oxidize levitated samples of liquid binary and ternary iron-base alloys. The fused silica reaction tube is shown in Fig. 1. The coil design is similar to that of L. A. Baker et al.4'5 A Tef-lon-sheathed, ferritic stainless steel lifter (B) and an alumina pedestal (C) were used to support the sample in the coil prior to levitation and for the recovery of the sample. Samples were inserted into

Jan 1, 1970

By F. Weinberg

The relative concentration of 1" at grain boundaries in controlled orientation bicrystals has been examined by autoradiographic techniques, and by activity measurements of grain boundary surfaces exposed by preferential ,melting. The autoradio-graphs indicate that thallium is concentrated at grain boundaries in as-grown bicrystals, but not in zcell-annealed bicrystals. They also indicate that the solute concentration and the distribution on as-grown bicrystal surfaces are markedly different than that of the bulk material. The boundary surface measurements are in agreement with the autovadiographic evidence. On the basis of these measurements, as-grown bicrystals containing approximately 100 ppm of Tl, solidified at rates between 5 and 30 cm per hr and with tilt boundaries greater than 10 deg, exhibited grain boundary segregation equivalent to roughly 10 atomic planes of pure solute. Higher solute concentrations (equivalent to 140 atomic planes of pure solute) were obtained in bicrystals solidified slowly (0.6 cm per hr); slightly higher values were obtained in specimens containing a large angle nantilt boundary. Annealing for various times over a range of temperatures eliminated grain boundary segregation within the experimental uncertainty of the results (equivalent to 1 atomic Plane of pure thallium at the boundary). The results for the as-grown bicrystals can be qualitatively accounted for by assuming the presence of a groove on the solid-1iq;id interface, at the grain boundary. SOLUTE segregation at grain boundaries may be considered in two parts, namely, nonequilibrium segregation associated with the solidification process, and equilibrium segregation in fully annealed materials.' There is much indirect evidence for nonequilibrium segregation, based on preferential etching at grain boundaries and the mechanical properties of as-cast alloys. In addition, some direct observations have been reported in which radioactive tracers were used as solute additions and segregation detected at the grain boundaries by autoradiographic techniques. However, there is little detailed quantitative data on solute concentrations related to grain boundaries, particularly for different freezing conditions and grain boundary configurations. Equilibrium segregation at grain boundaries has been considered both theoretically and experimentally. cean' has made an estimate of the maximum equilibrium solute concentration that might be expected at a grain boundary, based on the lattice distortions in the boundary region. He arrived at a concentration which was equivalent t a monatomic layer of pure solute. A similar value, based on thermodynamic arguments, was calculated by Cahn and Hilliard for the segregation of phosphorus in iron. Experimentally, much higher values of solute concentration at grain boundaries have been reported recently by both Inman and iler' for phosphorus in iron, and Ainslie et 1.' for sulfur in iron. They observed concentrations equivalent to as much as 20 to 100 atomic layers of pure solute at the grain boundaries. However, in both cases it was shown that the observed segregation was not due solely to equilibrium segregation at the grain boundary. In the former case, precipitation effectss due to trace impurities in the material were believed to account for the large amount of solute present at the grain boundary. In the latter case it was shown that a high density of dislocations in the boundary region could provide a large number of additional sites for solute atoms, other than at the grain boundary. Thomas and chalmera have reported on the equilibrium segregation of po210 in grain boundaries of Pb-5 pct Bi alloys. Using autoradiographic techniques, they observed a concentration of polonium along the boundary trace on the surface of annealed bicrystal specimens grown from the melt. The concentration only appeared after annealing, and varied with boundary angle, increasing as the boundary angle increased. Their conclusions have been questioned by Ward," who pointed out that the segregation they observed along the boundary trace was much too wide to be compatible with the usual concepts of the thickness of a grain boundary of several lattice spacings. Also, Maroun et al.,l1 with specimens similar to those of Thomas and Chalmers, found that segregation could only be detected on the specimen surface, suggesting that Thomas and Chalmers' results were associated with an oxidation effect of polonium, and not equilibrium segregation. Thomas and Chalmers replied12 that they did observed segregation at the grain boundary in the bulk material and suggested further experiments were necessary to resolve the difference. The purpose of the present investigation was to examine both nonequilibrium and equilibrium grain boundary segregation in melt grown bicrystal specimens as a function of boundary angle, growth rate, and solute concentration, and to de-

Jan 1, 1963

By Robert E. Green, Kenneth Reifsnider

Several experiments have been performed in order to illustrate the application of a recently developed X-ray image intensifier system to metallurgical investigations. In the present work the system has been used to study the instantaneous alterations in Laue transmission X-ray diffraction patterns during tensile deformation of aluminum single crystals. Expem'mental results are presented which demonstrate the capability of the system for crystal orientation, for following orientation changes due to lattice rotation during tensile deformation, and for showing changes in the homogeneity of the lattice planes along the specimen length as a function of strain rate. RECENTLY, a new X-ray system has been developed which incorporates a cascaded image intensifier and permits direct viewing and recording of X-ray diffraction patterns produced on a fluorescent screen.1"3 In the present work the results of several experiments are presented which demonstrate the usefulness of this system for metallurgical applications. EXPERIMENTAL PROCEDURE A schematic diagram of the experimental arrangement is shown in Fig. 1. In this system a Machlett AEG-50-S tungsten target X-ray tube, normally operated at 50 kv and 40 ma, serves as the X-ray source. The X-ray tube is placed in direct contact with a 10-in.-long collimator, which transforms the X-ray beam from one with a circular cross section to one with a rectangular cross section 3 in. high and 1/6in. wide. By blocking off all but a small portion of the rectangular slit, it is possible to work with the more conventional "pinhole" collimated X-ray beam commonly used for obtaining Laue diffraction patterns. In the present work the test specimens were 99.99+ pct aluminum single crystal wires & in. in diam and 3 in. long. For the deformation tests the wire crystals were mounted in a special set of grips in a table model Instron machine so that diffraction patterns could be recorded during specimen deformation. For the orientation tests the wire crystals were mounted in a rotating goniometer so that diffraction patterns could be recorded during specimen rotation. At a distance of 3 cm from the specimen axis, a 6 in. diam DuPont CB-2 fluorescent screen is positioned to transform the X-ray image to a visible one. A Super Farron f/0.87 72 mm coupling lens, corrected for 4 to 1 demagnification, transmits the visible image to the image tube. The image intensifier used is a three-stage magnetically focused RCA type C70021A with an S-20 input photocathode and a P-20 output phosphor. The tube has unity magnification and useful input and output screen diameters of 1.5 in. The image on the output phosphor is of sufficient intensity to be viewed directly, to be recorded cine-matographically, or to be displayed by vidicon pick-up on a television monitor. The recording device most commonly used is a 16 mm Bolex motion picture camera fitted with a Canon f/0.95, 50 mm lens. The overall gain of the system is 16,000 for direct viewing and 2240 for recording on 16 mm movie film. The resolution of the system is limited to 1 line pair per mm which is approximately that of the fluorescent screen. This system has been used for cine recording of transmission Laue X-ray diffraction patterns with exposure times as short as 1/220 sec and for vidicon television pick-up and display at a scan time of 1/30 sec. Quantitative information may be obtained from each frame of the movie film, by either stopping the vertical slit down to a point source in order to obtain a conventional Laue photograph or else by retaining the linear beam and introducing fiducial marks as described in a previous paper.4 In either case, each frame may be enlarged to appropriate size for analysis by either using a photographic enlarger and making prints of the desired frames, or, more conveniently, by using a microfilm reader. EXPERIMENTAL RESULTS The first series of photographs which are presented in Fig. 2 serves to demonstrate the usefulness of the system for crystallographic orientation determination. This series of prints, made from enlargements of a 16 mm movie film, shows the dynamic Laue transmission patterns produced by an aluminum single crystal wire which was rotating about the wire axis when the patterns were recorded. The movie films were taken at 16 frames per sec and the crystal was rotated at a rate of 15 rpm.

Jan 1, 1970

By H. J. Tschirner, L. P. Davidson, R. K. Carpenter

HE electrolytic zinc plant of the American Zinc Co. of Illinois, at Monsanto, was expanded in 1943 to a capacity of 100 tons of slab zinc daily. This capacity was not attained because of inability of the leaching plant to deliver an adequate amount of solution for electrolysis. Changing the leaching method so that the acid was added to the roasted zinc material reversed the usual procedure and made it possible to attain the desired capacity. The conditions which prevented satisfactory work before this change and the difficulties which arose in reversing the usual leaching procedure are described. The "reverse" leach operation as now practiced is carried out as follows: All the calcine to be leached is fed continuously to a slurry mixing tank. About one third of the acid to be used is fed to the tank with the calcine. The slurry is discharged continuously to a Dorr duplex classifier in closed circuit with a Hardinge mill. The classifier overflow is pumped to any of six leaching tanks where the leach is completed. A finished leach is discharged through Allen-Sherman-Hoff pumps to Dorr thickeners, from which the overflow goes to the zinc dust purification and the underflow to vacuum filters. This change in leaching procedure from the usual one of adding calcine to a large amount of acid made it possible to provide an adequate amount of purified solution to the electrolyzing division and at the same time filter and dry all the residue produced. Operating savings in reagents and better metallurgical recoveries were also important benefits. The original flowsheet of the leaching plant provided leaching, sedimentation of the insoluble residue, and purification of the neutral zinc sulphate solution with zinc dust. The thickened residue was filtered and washed. The purification cake of excess zinc dust, precipitated copper and cadmium, and any insoluble residue was filtered off on plate-and-frame duplex classifier. Settlement in the thickeners was inadequate and the suspended solids in the thickener overflow gave rise to filtration difficulties after the zinc dust purification. Further, the filtration and washing of the leach residue was poor, and it became necessary to pump a large amount of unwashed or poorly washed residue to storage ponds outside the plant building. Two causes of the poor settling and filtration were determined: Soluble silica and ferrous iron in the calcine treated. The latter was a result of poor roasting and with more experience ceased to be a major problem. The silica was a normal constituent of the feed and the working out of the problem became a matter of controlling its solubility. The obvious method to render the silica insoluble was by intensive roasting. This, however, met with total failure as such roasting resulted in silicates, probably zinc, soluble in the 13 pct acid used for leaching. Attempts were made to coagulate the fine gelatinous slime with addition agents. Glue, lime, starch, beef-blood serum and others were tried without success. All the suggested tried-and-tested means of operating the thickeners gave no consistently good results. Variations in leaching time, in addition of calcine to the leaching tanks, "conditioning" of the pulp by prolonged agitation, immediate discharge of the leach upon completion to avoid breaking up flocs were all tried and given up as ineffective. Byron Marquis, of Singmaster and Breyer, worked with the plant staff on a beaker scale until a leaching procedure was developed which gave consistent results and a promise of overcoming the difficulties which had plagued the plant operation. It was suggested that the difference in solubility of silicates and zinc oxide in sulphuric acid could be made use of in a leaching method where the acidity was controlled carefully. Such control is possible when acid is added to a slurry of calcine. This process reverses the normal procedure of adding calcine to a vessel of acid, hence the term "reverse leach" was applied. In this way, the overall acid concentration can be kept very low. In the tests made, it did not exceed 0.05 g per liter free sulphuric acid. Numerous advantages were realized when no silicates were taken into solution and later precipitated as a bulky gel. The gel had made reasonable thickening and filtration of the leach pulp and practical drying of the residue impossible. When the gel was eliminated, thickening rates were increased as much as five times. The volume of residue after thickening represented about 10 pct of the total leach pulp and had been as high as 95 pct when the gel was present. The thickened pulp was filterable and the filtered cake was dried readily after washing. The zinc extraction from the calcine was slightly lower. This was more than compensated for by the increase in zinc recovered in solution from zinc which had been trapped in the gelatinous residue. The amount of copper recovered was lower. However, the amounts of other impurities, such as arsenic, antimony, and germanium, taken into solution were lower. This was particularly true of antimony. Since the inception of reverse leaching, no concentrates have failed to yield solutions free of antimony even when present in the calcine to the extent of 0.2 to 0.3 pct. Oxidation of ferrous iron is a problem of reverse leaching. Ferrous hydrate does not precipitate at pH 5.3 to 5.4 where a leach is finished. The usual oxida-

Jan 1, 1952

By J. F. Radavich

Many heats of steel of low carbon value have been known to produce brittle pieces of steel. The brittleness is believed to be due to the impurities located within the grain boundaries. Such brittle steels have been examined with an optical microscope to ascertain the nature and the amount of the impurities present at the grain boundaries. Due to the relatively low resolving power of the optical microscope, the impurities are not visible in fine detail. The writer obtained some sheet steel and proceeded to determine the location of the impurities and to show the application of the electron microscope to the study of grain boundaries. One sample was known to be capable of becoming embrittled, whereas another sample was believed to be much less susceptible to embrittlement. Treatment of Specimens The specimens were embrittled by annealing above the A3 point under mildly oxidizing conditions. One piece of ingot iron could not withstand a 90" bend, whereas another piece of ingot iron was not affected and could withstand a 90" bend. The brittle piece was then annealed at a high temperature in a hydrogen atmosphere. The annealed ingot iron was termed cured and could withstand a 90" bend very easily. The three specimens examined will be designated as brittle, good. and cured in the discussion that follows. Procedure The sizes of the specimens were as follows: one piece of brittle ingot iron-3/8 by 35 in.; one piece of good ingot iron-96 by 1/8 in.; one piece of cured ingot iron-36 by 54 in. The specimens were too small to be polished by hand and therefore were mounted in bakelite. The polishing procedure was carried out in the conventional manner with the use of 1/0 through 3/0 papers, and the final polish was done with alumina on a billiard cloth. The specimens were then etched in a 4 pct solution of picral in alcohol, and then they were examined through an optical microscope. An area was chosen that showed distinct grain boundaries, and an effort was made to keep near this area when pulling the replicas REPLICA TECHNIQIJE The replica technique used in the preparation of the replicas for examination under the electron microscope is described in Electron Metallography.' It consists essentially of the following steps: 1. Obtaining a suitably etched specimen. 2. Applying a swab of ethylene di-chloride on the surface. 3. Applying a formvar solution on the surface. 4. Placing a screen on any desired spot. 5. Breathing on the fornivar layer. 6. Applying scotch tape on the screen and film. 7. Pulling the film and the screen up with the Scotch tape. 8. Separating the screen from the Scotch tape. This replica technique is very similar to the one described by Harker and Shaefer. However, with the added step, the percentage of replicas removed is very much higher regardless of the length of the time from the etching of the specimen to the actual pulling of the replica. The replicas were then shadow cast with manganese at a filament height to replica distance ratio of 1 1/2:7. This produced a very high contrast replica for use in the electron microscope. One of the dificulties encountered with this study was the restricted area of the specimen. The width of the specimens was the same as that of the 200 mesh nickel supporting screen. In order to increase the effective area, the screens were cut down as shown in Fig 1. The arrow indicates the direction in which the replica was pulled. This operation made it possible to obtain a large percentage of good replicas. Fig 3 shows an electron micrograph of a brittle piece of ingot iron and a grain boundary that was polished mechanically. The surface is very rough probably due to the incomplete removal of the flowed layer by the picral etchant. The grain boundary does show evidence of impurities. It was decided to electropolish the specimens to obtain a much smoother surface than the one obtained by mechanical polishing. ELECTROPOLISHING The specimens were cut in half to expose the metal on the back side. The exposed metal had sufficient area to make good electrical contact and electropolishing was carried out easily. The conditions for electropolishing were 0.9 amp, 35 volts, and 25 sec. in an electrolyte composed of 850 cc of ethyl alcohol, 100 cc distilled water, and 50 cc of perchloric acid. The polished specimens were then etched in the 4 pct picral solution for a shorter time than was necessary for

Jan 1, 1950

By M. M. Wong, D. E. Couch, G. M. Martinez

The Bureau of Mines electrowon hafnium metal with an average oxygen content of' 150 ppm at 700°C from an electrolyte containing 27 wt pct LiCl, 62 wt pct RbCl, and 11 wt pct HfC14. The average anode and cathode current efficiencies were 90 pct at anode and initial cathode current densities of 86 amp per sq ft. Haf-nium metal with an average oxygen content of 440 ppm was electrowon at 800oC from an electrolyte containing 90 wt pct KC1 and 10 wt pct HfCl4. The average anode and cathode current efficiencies were similar to those obtained in the LiCL-RbCl-HfCl, electrolyte. The chlorine gas given off at the graphite anode was vented through either a silica or a graphite tube to prevent cell corrosion. THE current method for the commercial production of high-purity hafnium is the thermal decomposition of Hfl4.1 The iodide method is not adaptable to continuous process techniques. Nettle, Hiegel, and Baker2 studied the electrorefining of hafnium from hafnium sponge containing 800 ppm oxygen. They failed to obtain hafnium with 600 ppm oxygen in their initial deposits and obtained AEC specification for oxygen only after 75 pct of the soluble hafnium had been removed from the electrolyte. Calculations using their data indicated this was approximately 4 lb of hafnium. The electrolyte was then used to produce approximately 3 lb of hafnium with a low oxygen content. However, no data are shown concerning the amount of anode material initially used or what percent of it was dissolved, therefore, results are not suitable for evaluation of a continuous operation. In general, it was not possible to consistently obtain low oxygen content metal with the electrolytes described by Nettle, Hiegel, and Baker. Wong, Hiegel, and Martinez3 investigated the electrorefining process for hafnium and showed that even by strict control of electrolyte composition only relatively low oxygen reduction could be obtained. The oxygen contained in the hafnium anode material tended to transfer to the cathode deposit and only a limited purification was possible. Both the "iodide" and the "electrorefining" processes depend upon hafnium sponge as a starting material. The sponge is normally produced by magnesium reduction of HfC14 ' and does not meet AEC specifications for hafnium metal. Since only 30 pct of the anode feed could be utilized3 in the electrorefining cells, the Bureau of Mines developed an electrowinning process. HfC14 was used as the feed material for the electro-winning process described in this report. Many of the electrolytes used in the electrorefining studies3 ap- peared to be suitable carrier-electrolytes for HfC14. However, in the initial studies on electrowinning, it was desirable to use electrolytes that had low solidus temperatures and could be operated over a wide temperature range to investigate parameters of the process. Therefore, electrolytes containing LiC1, NaC1, KC1, RbC1, CsC1, and HfC14, in various combinations were explored. EQUIPMENT Chlorinator. Hafnium carbide was chlorinated to produce HfC14 in the batch-type chlorination shown in Fig. 1. Chlorination temperatures were measured with a thermocouple placed in the center of the HfC charge. A flow meter was used to monitor the helium and chlorine. The exhaust side of the silica chlorina-tor tube was equipped with a flask for collecting organic material released during the initial heating of the HfC. The temperature of an internal heater, which extended from the HfC14 condensing flask to the hot end of the chlorinator, was adjusted to prevent the HfC14 from condensing before entering the collection flask. Helium and excess chlorine were exhausted through the lid of the collection flask to an aqueous NaOH solution. Sublimer. Initial studies were conducted using a sublimer, Fig. 2, made by placing a 13/8-in. OD nickel thimble 11 in. long, inside a 11/2-in. ID nickel bell 12 in. long, and locking it in place. This unit was loaded with HfC14 and partially immersed in the molten electrolyte for sublimation directly into the electrolyte. In another sublimer shown in Fig. 3, the HfC14 was contained in a "resin reaction flask". Quartz wool, previously heated to 600aC, secured between two nickel wire screens, was placed just above the HfC14 powder. The lid contained a vacuum outlet, a gage, an argon inlet, and an air-cooled pipe for condensing the HfC14. This sublimer was evacuated and heated. The sublimation temperature was not critical and the sublimer operated satisfactorily at all temperatures between 250" and 350°C. Electrolytic Cell. The electrolyte chamber, Fig. 4, was made of mild steel 8-in. schedule 20 pipe, 30 in. long. The exterior was metallized with a Ni-Cr alloy. The electrolytes were contained in a 16 gage nickel or iron liner with a nickel heat shield on top. The cell was heated by a resistance furnace. A 21/2-in. ID by 25 in. long air lock was connected to one port of a two-port cell cover assembly through a slide valve. The cover assembly of the air lock was electrically insulated from the cell and was equipped with a rubber sleeve that provided for the passage of the cathode lead. This allowed the cathode deposits to be removed and a new nickel cathode to be introduced without allowing air to enter the cell. A tube-rod assembly was bolted to the other port on the cell cover assembly and was sealed by a packing seal. The tube-rod assembly consists of a graphite

Jan 1, 1970

Jan 1, 1947