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By John Wulff, Richard P. Seelig

THE importance of the pressing operation in the forming of articles by powder metallurgy depends to a great extent on the type of product to be made. While in some few cases the pressing is merely a means of compacting loose powder particles into a solid mass preliminary to a sintering treatment in most applications it constitutes a molding operation with the purpose of shaping the raw material in powder form into a certain predetermined, accurately defined part not altered in shape by sub- sequent sintering. In still other cases, no pressing at all but sintering in molds gives useful articles. A limited number of products are made by the simultaneous application of pressure and heat. The factors that control the product of the pressing operation are raw material, lubricant, type, size and shape of die and compact, magnitude and time of application of pressure, as well as temperature of pressing. All such factors need to be con- trolled; yet, depending on the function of the pressing operation, greater emphasis may be placed on processing factors other than the pressing operation. In any complete discussion of pressing, subsequent sintering cannot be disregarded. For the sake of brevity, the present paper has been limited to the mechanics of pressing and only occasionally refers to sintering. For the same reason, hot-pressing has been omitted as beyond the scope of this paper. In any survey of the literature on the pressing of metal powders, the 1938 paper of Balshin1 on the theory of the process of pressing deserves mention. The first attempts at an interpretation of pressing phenomena were made by Balshin1 and Rakovski.2 The experimental results of both are of great interest. Since the experimental results are not described, the work was repeated, using our own interpretation of the possible techniques, and is reported in the following pages. The basic theory of Balshin,1 based on a hydro- dynamic analogy, however, leads to but another way of plotting density and pres- sure against height of a pressed compact. Since it does not give any new insight into the phenomena, nor account for the influence of side-wall friction, a discussion of the theory has been omitted from this paper. DENSITY GRADIENTS IN COMPACTS The process of pressing metal powders in a die (disregarding for this consideration the powder filling and ejection operations) may be divided into three phases: (I) packing, (2) elastic and plastic deformation, (3) cold-working with or without fragmentation. It must be emphasized that these three steps do not follow each other in sequence; on the contrary, in practice

Jan 1, 1946

By F. M. Stewart

A paper by Hurst and van Ever-dingen in 1949 led to the practical solution of many nonsteady-state flow problems.' Subsequently, applications of this material have been discussed by several authors. The purpose of this note is to outline a simplified direct procedure for water-influx pressure predictions for pressures above the bubble point. The prcposed procedure is unique in that after the "time-conversion factor" and the "influx constant" are obtained, predictions are made without trial and error. The elimination of trial and error is made possible by expressing certain PVT characteristics as explicit functions of pressure. The procedure is applicable to fields producing at pressures above the bubble point and under radial water drive from an infinite aquifer. In the usual applications it is required to predict (1) withdrawals given future pressure history or (2) reservoir pressure, given future withdrawals or production. The theory, assumptions and conditions under which the nonsteady-state solutions hold are covered in the references and are not repeated. The simplified direct procedure outlined here has been developed from published solutions for the so-called "pressure case". A similar direct procedure for the same special conditions has been developed for the "rate case"; however, in this instance the procedure is lengthy and offers no advantage over the trial-and-error solution. Consequently, this paper covers only the procedure based on the pressure case. DISCUSSION Under the pressure case prediction of withdrawals from a water-drive field, given the future pressure history, involves the use of a nonsteady-state water-influx term together with the material balance equation. The solution of a particular problem requires the following steps: (1) division of past pressure and production data into equal time intervals; (2) computation of cumulative water influx vs pressure drop for each time interval of past history using the material balance equation; (3) determination of the best values for the "time-conversion factor" and the "influx constant" by equating the nonsteady-state influx term with the influx computed in Step 2 (this requires a trial-and-error procedure); (4) prediction of influx for a given pressure drop using the influx term and the computed factors from Step 3; and (5) calculation of fluids produced using the predicted influx in the material balance equation. A forecast of the water-oil ratio or water production rate is required to complete the calculation. It is assumed that a reliable estimate of original oil in place is available, as well as the production and pressure history, and data on reservoir fluid characteristics. If the original oil in place is unknown, it may be computed simultaneously with the tinie-conversion influx factors2,3. However, the oil in place so computed may be considerably in error3; consequently, it is usually preferable to use oil in place estimated from pore-volume data unless there is considerable doubt as to its accuracy. The Material Balance Equation Above the Bubble Point Above the bubble point the simpli-

By F. Louis Grammer

The following study of flue-dirt and the influences controlling it may be interesting to many. It is published because it represents observations at about thirty furnaces at different times. It may assist in giving an impetus to the making of similar observations elsewhere. Until ten years ago, the metallic waste in furnace-gases was not considered a problem of pressing urgency in iron metallurgy—certainly not in the blastfurnace end of it. Many plants at present ignore, or pay but little attention to, top-pressures. Prior to the introduction of Mesabi ore, the losses in escaping gases, if considered at all, were regarded as thermal losses, or losses of fuel (except by those interested in lead, zinc, silver, etc.). In a high-priced material like ferro-manganese, such losses were, indeed, considered important. But the behavior of the Mesabi ores, corning, as they did, in practically inexhaustible quantities, could not be disregarded by the furnaceman. These ores came to stay. The tables appended below have purposely been altered to disguise the plant, the company and the ores used. The comparative values are maintained. In these tables, the influencing elements and conditions which are constant, or practically so, namely, size of furnace, quantity of wind, fuel used, etc., are not mentioned. The figures represent observations consistently followed up for a long period. The weights of flue-dirt were obtained from cars on which no other dirt was thrown. The analyses and calculations are based on the best of sampling. The effects of slips are excluded. Slips should not occur at well-regulated or properly-constructed furnaces, excepting under unusual and rare conditions. Allowances are made for moisture, scrap charged and silicon in the metal. The cutting effect of Mesabi

Jan 1, 1904

By Ralph Hultgren

Few phase diagrams of alloys composed of two transition metals have been adequately studied, probably because of the high melting points involved. Transition metals are the elements that have inner shells incompletely filled with electrons. They comprise groups lIIa to VIIIa of the periodic table, including more than half of all metals. We have chosen to study two systems whose comparatively low melting points allowed the alloys to be melted in a molybdenum resistance furnace. The nickel-palladium system proved to consist of a simple series of solid solutions, but iron-palladium manifested several remarkable features. The main characteristics of the latter diagram were decisively established, but lack of time prevented precise determination of phase boundaries. The gamma to alpha transformation in this system is unusual and warrants further study. Grigorjewl determined the liquidus and solidus of the iron-palladium system by thermal methods. He found a minimum melting point, but no eutectic. He also found that palladium lowered the gamma to alpha and raised the gamma to delta transformation temperatures of iron, with a complete series of solid solutions existing between gamma iron and palladium. His measurements also indicated a compound or quptbr-lattice near the composition FePda. Jellinghausz found that annealing at 500" C. greatly increased 111 magnetic coercive force of an alloy of composition FePd. X-ray diffraction photographs showed that a tetragonal ordered phase had formed during the anneal. Hocart and Fallot made magnetic measurements over the entire range of composition. They found that less than 5 atomic per cent Pd

Jan 1, 1939

By Ralph Hultgren

Few phase diagrams of alloys composed of two transition metals have been adequately studied, probably because of the high melting points involved. Transition metals are the elements that have inner shells incompletely filled with electrons. They comprise groups lIIa to VIIIa of the periodic table, including more than half of all metals. We have chosen to study two systems whose comparatively low melting points allowed the alloys to be melted in a molybdenum resistance furnace. The nickel-palladium system proved to consist of a simple series of solid solutions, but iron-palladium manifested several remarkable features. The main characteristics of the latter diagram were decisively established, but lack of time prevented precise determination of phase boundaries. The gamma to alpha transformation in this system is unusual and warrants further study. Grigorjewl determined the liquidus and solidus of the iron-palladium system by thermal methods. He found a minimum melting point, but no eutectic. He also found that palladium lowered the gamma to alpha and raised the gamma to delta transformation temperatures of iron, with a complete series of solid solutions existing between gamma iron and palladium. His measurements also indicated a compound or quptbr-lattice near the composition FePda. Jellinghausz found that annealing at 500" C. greatly increased 111 magnetic coercive force of an alloy of composition FePd. X-ray diffraction photographs showed that a tetragonal ordered phase had formed during the anneal. Hocart and Fallot made magnetic measurements over the entire range of composition. They found that less than 5 atomic per cent Pd

Jan 1, 1939

By G. Cartaud, F. Osmond

We have already devoted two previous memoirs to this question. In the firstL we collated and discussed the existing literature on the subject; in the second: we described the crystalline forms obtained by the reduction, at different temperatures, of ferrous chloride by hydrogen or by zinc-vapor. The conclusion from these researches was that the three allo-tropic states of iron—a, stable below A2; , stable between A2 and A3; and , stable above A3—all crystallize in the cubic system. The differences observed were such as are customarily encountered in the crystallographic records of many minerals of which allotropic varieties or isomerides are not known, and did not conform to the ordinary definition of polymorphism. It is, however, improbable that allotropic transformations, which are placed beyond doubt by a series of positive facts, do not involve some changes in the intimate structure. As a matter of fact, the crystals we did obtain were too small to allow of a precise examination, and this might introduce an element of uncertainty in the firm establishment of our conclusions. Professor H. Le Chatelier mas even led to think from some of our results that r-iron could very well be a rhom-bohedron simulating a cube, and not a true cube, and it will be remembered that the crystalline form of bismuth was for a long time incorrectly regarded as cubic. Allotropy does not, however, necessarily involve such a deduction. Without departing from the cubic system at all, a whole

Jan 1, 1907

By H. C. Fiedler

The development of cube-on-edge secondary re crystallization texture in Si-Fe strip depends upon the ability of inclusions, such as manganese sulfide, to restrain nomal grain gvowth. The ability of inclusions to perform this function is shown to depend upon their size and distribution. The desired uniform dispersion of many small inclusions is obtained by controlling the cooling rate from above the solution tempmature of the inclusions or, alternatively, by drastic 'quenching from above the solution temperature followed by heat treating at a lower temperature. The development of the cube-on-edge secondary recrystallization texture in Si-Fe strip depends upon both establishing the proper primary recrystallization texture and having inclusions to restrain normal grain growth. It has been suggested that the first requirement is met with a texture which, though weak, is near (110)[001]. A mechanism for secondary recrystallization originally proposed by ielsen' is consistent with the presence of this primary texture. It is visualized that a secondary grain appears where two adjacent grains happen to be sufficiently similar in orientation to be capable of behaving as a single large grain. This pair of grains will grow at the expense of its smaller neighbors as a consequence of its having lower grain boundary free energy. Other explanations of the origin of the secondary recrystallization texture have been offered,' and it can be concluded that the mechanism is not fully understood. Nevertheless, it is apparent that operationally the necessary primary recrystallization texture is obtained simply by interposing an anneal during the cold reduction to final gage. The role of inclusions in the development of the secondary recrystallization texture has been demonstrated by May and Turnbull4 in a comparison of a high-purity heat and a heat containing manganese sulfide. They showed that the driving force for secondary recrystallization is inversely proportional to the diameter of the matrix grains and that the function of the inclusions is to maintain a small matrix grain size. Other inclusions, such as various sul- fides,')' silicon nitride,8 and vanadium nitride,' titanium carbide,'' and vanadium carbide," have been shown to be effective in promoting secondary recrystallization to the cube-on-edge texture. There is also evidence that silica inclusions in Si-Fe strip made by powder-metallurgy techniques perform this function.' This report is concerned with the second of the two requirements for secondary recrystallization, namely the importance of the metallurgical control of the size and therefore number of inclusions. While the concepts involved are simple, they are fundamental to the making of this material. EXPERIMENTAL PROCEDURE A heat containing 3.27 pct Si, 0.026 pct S, 0.06 pct Mn, and 0.004 pct C was made in an air induction furnace from electrolytic iron, 98 pct ferro-silicon, electrolytic manganese, and iron sulfide. The heat was divided between graphite and baked-sand molds with a cavity 2-5/8 by 5 in. and with walls 2-3/4 in. thick. Slabs, 1 in. thick and 2-5/8 by 5 in., were cut from the ingots and hot-rolled either in the as-cast condition or after one of the heat treatments described later. After pickling, the 80- to 100-mil-thick hot-rolled band was, unless otherwise noted, heat-treated for 5 min at 900°C before being cold-rolled to 25 mils. After a heat treatment of 1 to 3 min at 860°C, the strip was cold-rolled to 12 mils, the final thickness. The percent cube-on-edge texture was determined by dividing the maximum torque as averaged from four samples by the maximum torque of a 3-1/4 pct Si-Fe single crystal having the (110) plane in the plane of the sample. The torque measurements were made in a field of 1000 oe on 1-in.-diam disks. RESULTS AND DISCUSSION The importance of the thermal history of the ingot is evident in Fig. 1 from the appearance of strips heat-treated in a temperature gradient. The sample

Jan 1, 1964

By Edgar L. Collis

NO industry or group of industries is more deeply interested in the influence exerted by atmospheric dust than that concerned with the getting of coal and of metalliferous ores. The coal miner in the past has mainly been interested on account of the part played by coal dust in the occurrence of explosions; but investigation is revealing that coal miners experience, at least on certain coal fields, unduly high mortality ascribed to lung diseases, some part of which may reasonably be attributed to dust inhalation, and that a small group of men employed in sinking shafts and driving roads through sandstone rocks experience troubles identical with those that afflict many metalliferous miners. Coal Mining The Registrar General for England and Wales issues information every 10 years concerning the mortality experienced in various industries. The records dealing with coal mining are of particular interest, since they are given separately for each of the largest fields. When examined they exhibit the coal miner with a favorable death rate on the whole when compared with all other occupied males; but they reveal great differences on the different fields; thus the Lancashire miner in 1900-2 had a comparative mortality from all causes of 1006 as against a figure of 675 for the Nottinghamshire and Derbyshire miners, and in 1910-12 of 941 as against 570 for Nottinghamshire. When mortalities due to four only of the great causes of death are subtracted from the total the differences are greatly reduced; these four causes are phthisis, pneumonia, bronchitis and accidents. Thus for 1910-12 more than one-half of the mortality in Lancashire, 478 out of 941, is so accounted for, but less than one-third of the mortality in Nottinghamshire, 184 out of 570; the latter fraction compares with that for all males, 293 out of 790. Exactly why the accident mortality varies thus with those for the lung diseases has not been determined; the fact, however, points to an interesting association between health and so-called "accidental" occurrences.

Jan 1, 1927

By Eugene A. Stephenson

In most instances the fluids produced from underground reservoirs have been described as they appear at the surface, and usually it has not been necessary to distinguish between surface and reservoir phases. More recently it has become imperative to recognize the fact that changes in phase may occur between the reservoir and the receiving unit. The simple terminology of "wet" and "dry" gases and "crude petroleum oil" served our needs fairly well in the shallow, low-temperature and low-pressure fields. It has been left to the legislatures, regulatory commissions, and courts to decide whether a field is or was a gas field, an oil field, or both. This they have done by direct definition and also by implication. For example, in Texas:' (d) The term "gas well" is any well (a) which produces natural gas not associated or blended with crude petroleum oil at the time of production, or (b) which produces more than one hundred thousand (100,000) cubic feet of natural gas to each barrel of crude petroleum oil from the same producing horizon, or (c) which produces natural gas from a formation or producing horizon productive of gas only encountered in a well bore through which crude petroleum oil is also produced through the inside of another string of casing. (e) The term "oil well" is any well which produces one (1) barrel or more of crude petroleum oil to each one hundred thousand (100,000) cubic feet of natural gas. In the state of Louisiana, the same general result is achieved largely by the following paragraph :* Wells producing both oil and gas shall not waste or blow into the air an amount of gas of more value at three cents per thousand cubic feet, than the market value of the oil recovered. The Commissioner of Conservation shall allow a reasonable time to determine the status of any well. This means that for wells making both oil and gas, if n represents the price of oil in dollars, and x the allowable gas waste expressed in M cu. ft. Per day,

Jan 1, 1938

By R. H. Doremus

From measurements of carbide precipitation rates in a iron it was concluded that the carbides nucleated on dislocations in both strained and unstrained samples, except for the latter at lower temperatures and higher carbon concentrations, where there were more muclei than could form on the dislocations. The equation of Cottrell and Bilby for the segregation of atoms to dislocations was found to be inapplicable to this system. No satisfactory theory for the growth process is available. A study of the rate at which a second phase separates from solid solution can frequently reveal much about the mechanism of separation. There are still many features of the precipitation of carbon from a iron that are not understood, although this system has been examined extensively. To provide more insight into the mechanism of carbide precipitation in a iron, rates of this process were measured at different temperatures, carbon concentrations, and densities of dislocations in the iron. The concentra- tion of carbon in solution was followed from the height of the internal-friction peak; this height is directly proportional to the amount of carbon in solution and is not affected by the growing carbide particles. In this paper these rates are compared with those found by earlier investigators, and the mechanism of precipitation is discussed in light of these results as well as two earlier studies1, 2 and the electron microscopic work reported in the preceding paper. EXPERIMENTAL The amount of carbon in solution was followed by

Jan 1, 1961

By P. D. I. Honeyman

CHANGING trends in concentration, involving regrinding with the subsequent production of a finely divided, high-grade flotation product, presents a real problem to the modern copper smelter. In the treatment of such a material, handling difficulties are numerous and potential possible losses may be very great. In many plants, of course, preliminary roasting of the furnace charge remains an economical necessity. Under such circumstances, the operator has no alternative except to follow orthodox roaster reverberatory practice, though taking all possible precautions to avoid excessive dust losses and bad working conditions. In other plants, roasting is not only unnecessary but would be highly undesirable, and at best the charge would be merely dried before entering the reverberatory furnace. In the latter case the possibilities of raw charging loom large. The Miami plant of the International Smelting Co. handles the entire output of concentrates of the several mining companies operating in the Globe-Miami district. All of these companies produce a flotation concentrate which, at the Miami Copper Co. particularly, is all reground and is high in grade. In addition, the Inspiration Copper Co. ships a substantial tonnage of high-grade cement copper to the smelter from its leaching plant. Following the flow sheet of the original plant, all such material received was bedded, dried in Wedge furnaces and smelted in reverberatory furnaces. At times during the history of the plant it has been necessary to carry the drying operation further, to a partial roast, before reverberatory smelting. Since the charge contained over 80 per cent flotation concentrates, the handling of which in a dried condition was at best a dusty job, unusual precautions were taken to cut down dust losses. The Wedge furnace plant was equipped with a Cottrell treater and all hoppers and calcine cars were carefully designed to cut down dust loss in transferring the so-called calcine from hoppers to car and from car to furnace. In the furnace itself the dusting problem was a severe one. Arch erosion was very rapid and flues and waste-heat boilers rapidly filled up with a partly smelted flue dust.

Jan 1, 1932

By F. L. Vogel

Densities and distributions of dislocations in plastically bent germanium crystals before and after annealing were studied. In the bent and annealed crystals, the theoretical relationship between radius of curvature and density of dislocations is confirmed. Before annealing, however, more dislocations are present than required, and these are distributed with a minimum at the neutral axis and maxima at the top and bottom surfaces. On annealing, three significant changes occur in the bent bars: 1) the average dislocation density is reduced, presumably by the annihilation of opposite signs; 2) dislocations migrate from the high density outside regions toward the low density neutral axis, thus producing the equilibrium distribution of dislocations; and 3) a polygonized structure is formed by movement of the dislocations into walls normal to the slip plane. ETCHING to reveal edge dislocations'-" offers a unique opportunity to study, in germanium single crystals, the functioning of dislocations in plastic deformation. Plastic bending is ideally suited to this purpose because it produces a static array of edge dislocations in an ideally plastic material which is predictable from the theory." " Nye" has given a rather complete treatment of the geometry of bent crystals in terms of dislocations. The density of excess dislocations is related to the radius of curvature of the slip plane of a bent crystal, as shown in Fig. 1, assuming the absence of macroscopic elastic stresses. The curvature of any plane in the zone of the bend axis is found by resolving the Burgers vector into that plane, so that for the usual case where the slip plane is inclined at some angle 0 to the neutral plane of the bar, the equation applies, with T equal to the radius of curvature of the neutral plane of the bent crystal. Two predictions which are relevant to this study may be made from Eq. 1. First, in crystals bent to various radii, the average excess dislocation density is inversely proportional to the radius and second, for a bar bent to a radius which is large compared with its thick-

Jan 1, 1957

By J. J. Pye, J. B. Drew

The surface-diffusion coefficients of Ni63 diffusing on low-index planes of nickel single crystals have been measured over the temperature range from 400° to 1000°C using a precision autoradio-gvaphic technique. The activation energy for sur -face diffusion appears to he the same on the {111}, {110), and (100) planes and amounts to -0.60 ev. This is in good agreement with the value (-0.62 ev) reported for (111) planes obtained by mass-transport techniques. In an earlier paper, the authors have reported self surface-diffusion coefficients on silver.' In that work, a deviation of the diffusion coefficients from linearity in the Arrhenius plot was observed at high temperatures. This effect was attributed to a loss of tracer atoms into the bulk by volume diffusion. The purpose of the present work was to extend the technique developed to the nickel surface-diffusion system up to the point where volume diffusion would come into play. The nickel system especially lends itself to this technique due to the high efficiency of the isotope in darkening the film and the large absorption of the weak radiation (0.063 mev /3- particle of the trapped tracer atoms. The diffusion coefficients and ictivation energy for different orientations on nickel can also be compared with a report published by Blakely and Mykura 2 where a mass-transfer technique was used. This paper reports the self surface diffusion of nickel on the low-index planes over a wide temperature range using a precision autoradiographic technique. EXPERIMENTAL PROCEDURE The experiment is similar to that described in the earlier publication consisting of a radioactive needle as a source resting on a flat, smooth, chemically polished surface annealed in a dynamic dry-hydrogen atmosphere. The needle is held snugly on the surface by a holder fabricated from commercially pure nickel. The point source is made by grinding down a small-diameter nickel rod until a tip of approximately 0.1 mm radius is formed. It is then etched and the needle tip plated with the radioactive isotope Ni63. Nickel single crystals were used whose main impurities were spectrographically determined as Co 0.05, Fe 0.007, C 0.005, and S 0.003 pct. The surfaces, oriented to within 1/2 deg of the low-index planes, were carefully mechanically polished and etched in a 50-30-10-10 hot solution of acetic, nitric, sulfuric, and phosphoric acids giving a smooth polished surface. The crystals were then washed in distilled water and alcohol. Annealing temperatures ranged from 400° to 1000°C with a furnace arrangement in which the crystals could be brought up to temperature in times short compared to diffusing times. The temperature was maintained constant to ±10°C. In the temperature range investigated, the ratio of the surface-diffusion coefficient to the volume-diffusion coefficient (Ds/Du) was 105 or more and the mean bulk-penetration values, calculated from literature values of volume-diffusion coefficients,3 were on the order of 10-5 cm. After the diffusion anneal, the sintered needle is removed, and both the radius of the needle point and spot left on the crystal face are measured. The crystal is then placed on photographic film. Diffusion profiles are obtained by scanning the film with a recording microdensitometer which has a slit width of 10µ. DISCUSSION AND RESULTS The experimental conditions are such that the source strength and needle radius are essentially constant and the time is adjusted such that the mean bulk penetration is small. An exactly analogous heat-flow problem has been considered by Carslaw and Jaeger4 and the solution can be written in integral form as:

Jan 1, 1964

By Ronald D. Hill, Janet L. Auerbach

It is estimated that the mining industry generates over 2.1 petrograms per year of solid waste. These wastes are overburden, waste rock, low grade ore, concentrate (tailing), sludges from treatment facilities and wastes from support facilities. Concentrate wastes present the greatest environmental problem. Three recent federal laws impact the disposal of waste from mining: Resource Conservation and Recovery Act of 1976 (RCRA), Surface Mining Control and Reclamation Act of 1977, and Uranium Mill Tailings Radiation Control Act of 1978. RCRA specified a special study on mining waste which was to include an analysis of: (1) sources and volumes of waste produced, (2) present disposal practices, (3) potential dangers to health and the environment, (4) alternate disposal methods, (5) cost of disposal, and (6) potential for use of waste.

Jan 1, 1980

By J. D. Grozier, W. W. Mullins, H. W. Paxton

The morphology of the nucleation and growth of austenite into high-purity iron in NH3-H2, gas mixtzires has been studied. The growth rate of an austenitic rim (planar interface) from scratched surfaces of- polycrystalline iron specimens was determined as a function of temperature and percent NH3 and found to he in reasonahle agreement with growth-rate calculations based on a model which assumes the diffusion of nitrogen to he the rate-controlling step. Under certain conditions, austenite pew as platelets; growth rates of these along the surface of single crystals were found to he dependent on surface preparation, orientation, THE development of microstructures can conveniently be thought of in terms of nucleation and growth. The complex topic of nucleation in solid-solid transformations will not be discussed at length, although a few qualitative experiments were performed. Growth is determined by the mobility of the various possible interfaces under the available driving forces in a particular situation. In homophase transformations, it has been clearly demonstrated that the mobility is very sensitive to small amounts of impurities, to the kind of impurity, and to the orientation relations across the boundary.' A degree of quantitative knowledge has temperature and percent NH3. On electropolished surfaces with a (110) pole, the maximum growth rate of platelets was determined and found to be in agreement within a factor of 2 to 3 with theoretical calculations of the edgewise growth rate of a platelet. The calculations are based on a model which assumes that the diffusion of nitrogen in the ferrite in front of the moving curved attstenitic interface at the tip of the platelet is the rate-controlling step. The growth direction on the surface of the single crystal and resztlting habit plane of the platelets were determined and found not to he unique but to vary systematically with the pole of the surface. been obtained. In the case of heterophase transformations, which are significantly more complicated to treat, a comparison of theoretical and experimental studies often shows rather poor agreement.'-' The main purpose of the experiments discussed below was to obtain additional quantitative data on crystallographic effects on boundary mobility in a system which was otherwise as simple as possible, viz. the growth of iron-nitrogen austenite into fer-rite. In the course of the experiments, it became necessary to re-examine the theory for the growth of Widmanstatten plates, especially the influence of anisotropic interfacial free energy. Some other minor experiments in the Fe-N system were performed, and are described briefly. EXPERIMENTAL METHODS A) Material Preparation. The floating zone purified iron used for this investigation was supplied by Battelle Memorial Institute. The nominal composi-

Jan 1, 1965

By J. H. Rushton, L. H. Mahony

Principles of fluid motion and turbulence which have been found to be of use in mixing and agitation problems are discussed, as well as suggested applications in extractive-metallurgy processes. Various types of impellers are described, together with other conditions that affect flow pattern and turbulence. The choice of equipment for particular requirements is considered, and equations for power input are given. Modern heavy-duty mixing and agitation equipment can take an increasingly important part in such extractive-metallurgy processes as solids handling, crystallizing and leaching, chemical operations, and flotation. Application of mixing and fluid-mechanics principles to extraction methods can lead to greater process rates and a resultant saving in time and money. MIXERS are being applied with increasing frequency to problems in the metallurgical industries. The increase represents in part the modernization of mechanical equipment used through the application of unitized drives, modern electric motors and speed reducers, and recently developed materials of construction. Some applications have resulted from process changes and the use of techniques for operations similar to those that have been demonstrated and proven in the chemical industry. Still more applications are being developed through the use of fluid-dynamics principles not previously recognized as applicable to these operations. It is the purpose of this paper to describe those principles of fluid motion and turbulence which have been found to be of use in mixing and agitation problems, and to suggest applications for them in the extractive-metallurgy processes. Modern mixing equipment has been designed to provide the fluid motion consistent with that best suited to different operations.' When properly applied, these more efficient fluid-handling mixers result in lower process-production costs. Metallurgical operations usually involve large amounts of solids. The characteristics of the ore control the process and only enough liquid is added to provide sufficient fluidity for handling and processing. The reactive part of the ore, the mineral value to be extracted, is likely to be low in percentage, and the quantity of reagent required is similarly low, but excessive dilution makes additional reagent necessary and therefore is undesirable. Thus, the primary problems in minerals processing are to handle as high a concentration of solids as possible and to distribute reagents uniformly. These pulps, or slurries, are in a range of solids concentration where hindered settling rates apply, and care must be taken to agitate and mix sufficiently to maintain suspension and flow throughout the equipment. Such slurries have high densities which are the weighted average of the components and viscosities that are spoken of as "effective viscosities" but are difficult to evaluate. It is convenient to separate metallurgical operations involving mixers and agitators into three categories: solids handling, mechanical or physical operations, and chemical operations. In each of these categories fluid motion is required to maintain suspension, to distribute surface-active agents, to blend components and reactants, and to induce high rates of chemical reaction. After a discussion of some basic principles of mixing and agitation, examples of application to the three categories will follow. Fluid Motion The fundamental problems of mixing and agitation of liquids have to do with the mechanics of fluid streams and the means by which they are

Jan 1, 1955

By J. G. Hadley

IN THE early stages of the depression the Utah Copper Co. realized that an unemployment problem would he created which demanded an intelligent and sympathetic solution. The company recognized that as many men as possible must be kept at work on a basis which would ultimately permit of the most efficient reabsorption of displaced labor. The company therefore determined to distribute available work among the greatest number of men and to that end adopted a system of rotating employees on a part-time basis. An employer requires a certain number of days' or shifts' work during the month. Obviously one employee working thirty days or shifts a month is equal to two employees each working fifteen. In principle, therefore, where two employees equally fitted to do certain work are available the work could be divided between them on an equitable basis and twice as many persons would benefit. A rotation plan on this basis was adopted by the Utah Copper, Co. on Jan. 30, 1930. Some variations of the orig¬inal plan have been made from time to time, the reasons for which will be discussed.

Jan 1, 1932

By L. A. Roe, John Jan

Iodine is a soft, lustrous, grayish-black nonmetallic element with a density of 4.9. It is the least active of the four members of the halogen family. The other members are, in order of increasing activity, bromine, chlorine, and fluorine. Iodine is a solid at ordinary temperatures, while bromine is a liquid and chlorine and fluorine are gases. Iodine melts at 113°C and volatilizes at 184.4°C to a blue-violet gas with an irritating odor. It occurs in nature only as iodates and iodides or other combined forms. It was discovered by Bernard Courtois in France in 1811, who noticed its presence as an unknown substance in crude soda ash obtained from burning seaweed. Gay-Lussac recognized it as a new element and named it iode, from the Greek word "ioeides or iodes" for violet color (MacMillan, 1970). The world production is not known with any great certainty, but it is probably between 25 and 35 million lb per year, of which about 30% is consumed in the United States. Geology and Mineralogy Iodine compounds occur as a minor constituent as a mineral in the Chilean nitrate deposits and in solution in brines and seawater. According to the US Geological Survey, it is the 47th most abundant element in the earth's crust. The minerals lautarite, Ca (I03)3 (calcium iodate), and dietzeite, Cat (103)2 (CrO4), (calcium iodate-chromate) are found in Chilean nitrate deposits which are located in Antofagasta and Tarapaca provinces on the eastern slope of the coast range in a desert area. Various brines contain iodine compounds. Seawater contains about 0.05 ppm of iodine and some seaweeds will extract and accumulate it up to 0.45% on a dry basis. Some coals in West Germany also contain iodine compounds. The known and potential sources of iodine reported in 1968 are given in Table 1. Table 2 lists estimated world iodine reserves. Iodine has been recovered from brines in Java, Indonesia, France, England, and the USSR. Iodine has also been recovered from seaweed in Ireland, Scotland, France, Japan, Norway, and the USSR. The indicated reserves and future resources of iodine are large but have never been adequately measured. Analysis Iodine as the free element can be detected by the characteristic blue color it gives to a starch solution. Quantitatively it is determined as the free element by titration with standard thiosulfate solutions using starch as an indicator. Colorimetric methods are also applicable. Markets and Prices Iodine and its compounds are generally marketed in the form of: iodine, crude; iodine, resublimed; calcium iodates; calcium iodide; potassium iodide, sodium iodide, and numerous organic compounds. Product Specifications Crude iodine, World market: 99-99.5% 12. Crude iodine, US produced, average: 99.8% 12. Crude iodine, USP XVII Specs: not less than 99.8% percent I2. Resublimed iodine is usually 99.9% and ACS specifications call for not over 0.005% total bromine and 0.020% nonvolatile materials (Anon., 1971). Prices, c.i.f. United States, for iodine have been steadily increasing from $1.18 per lb of crude in 1967 to $6.37-7.27 in January 1981 (Anon., 1981). In 1980 the price of iodine increased by 50%.

Jan 1, 1983

By J. Tarwater

The torsional testing of cylindrical medium-carbon steel specimens, heat treated to a high strength level, revealed a stress-strain relationship that was dependent on the direction of torsional plastic pre-strain. This Bauschinger effect was observed in prestrained specimens both with and without subsequent elevated-temperature strain aging. Yield stresses in strain-aged specimens exceeded those of simply prestrained specimens and the difference in stress was greater when the prestrain direction opposed the test direction. This behavior is discussed in terms of the classical dislocation pile-up using Cottrell's equation, A plastically prestrained strain-hardenable member, loaded in a direction opposite to the direction of prestrain, produces a stress-strain relationship differing appreciably from the curve representing reloading in the prestrain direction. This phenomenon, referred to as the Bauschinger effect, will be discussed in terms of the stress differences ob- served at a specified strain. The effect, dating back to the 1880's, was first attributed to grain boundary stresses. When later work revealed that the effect was also present in single crystals, revised theories attributed the diminished applied reverse stress to assistance from internal long-range stresses. These stresses have been associated with dislocation pile-ups or with dislocation arrays having analogous stress patterns. The stress patterns are subject to alteration by interaction with interstitial solute atoms and acceleration of the interaction may be accomplished with elevated-temperature strain aging. As discussed herein, the interaction showed a directional effect with regard to the applied stresses necessary for small plastic strains. Aside from the rigorous Bauschinger stress-strai relationship, which compares prestrained members, it is interesting to compare the stress-strain curve of a member being prestrained with that of a prestrained member being reverse loaded. For small strains which are a fraction of the prestrain deformation, the applied stresses of the reverse reloaded member are smaller. However, as the reverse strain approaches the prestrain value, the stresses approach equivalence. It has been reported1 that the stress required to return a prestrained specimen to its initial "zero" position generally exceeds the prestrain stress because of the work hardening occurring on potential slip systems during prestrain.

Jan 1, 1963

By E. H. Kelton

The purposes of this paper are to describe the use of adjustable cut and draw tools as a control test of drawing properties and to point out that no other well-known test or combination of tests determines this quality in zinc and zinc alloys. Rolled zinc has been used for making drawn articles, particularly battery cans, for many years. The development of rolling treatments satisfactory for these purposes followed the usual course of trial and error experimentation depending upon cooperation with customers to determine what type of material was suitable. A quick test of drawing quality was highly desirable, of course. Scleroscope hardness and temperll having no apparent relation to drawing quality, were used simply to check the duplication of rolling treatment and grade of metal. The dynamic ductility1 test, on the other hand, was believed to be so like the drawing operation as to provide a reliable index and came to be taken as the criterion of good drawing properties. Faith in this test was strengthened by the fact that metal having the highest ductility was more satisfactory for operations, such as the manufacture of battery cups, that required several redraws. No distinction was made at that time in specifying metal as to whether it was to be subjected to simple cut and draw, redrawing or forming operations. It developed, however, that in some grades of metal the highest ductility did not coincide with the most satisfactory quality when the material was used for a single draw. When zinc-base alloys, with their wider ranges of effective rolling treatments, came into increased use, their dynamic ductility and drawing quality appeared to have no connection whatever. Furthermore, comparisons of known drawing quality with other physical properties of the metal, including tensile strength, elongation and dynamic cold bends, were fruitless in yielding any clear relationship. Almost any test value produced in one piece of metal could be duplicated by another rolling or annealing treatment with attendant different drawing characteristics.

Jan 1, 1934