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By J. T. Norton, N. J. Grant, I. S., Servi

Coarse grained high purity aluminum was tested in creep at temperatures of 400° to 1200°F to develop subgrain structures. Measurements of subgrain size, distribution, and rotation were made from X-ray diffraction patterns. Subgrain size and distribution were checked metallographically and the size was compared with average slip band spacing. The slip family was determined for several specimens. THE interest and research recently evident abroad in the role of subgrain formation and polygon-ization as a contribution to the creep of metals at elevated temperatures is deserving of greater attention in this country. Such metallic subgrains can be defined as macroblocks existing within the grains. The general observation has been that the macro-blocks which belong to the same grain have a maximum difference in orientation of a few degrees. In spite of the considerable amount of work that has been done since Jenkins and Mellorl observed the "division of existing crystals into smaller units when deformation occurs at an annealing temperature," the subject of subgrain formation is only now receiving truly active discussion and investigation. The existence of subgrains has been revealed by metallographic methods, as in the work of Jenkins and Mellor,1 and by X-ray methods, first applied to this problem by Homes.' Hirst3 and Calnan and Burns4 applied the back-reflection Laue technique to the study of coarse grained specimens. Wood et al.5 and Greenough and Smith' examined the ring obtained with a back-reflection camera for the study of fine grained specimens. In addition to the above, the transmission technique was used by Wood.6 A special technique was developed by Guinier and Tennevin8 in order to improve the resolution. Metallographically, the subgrains have been observed directly on the surface of deformed specimens by Wood et al.,3 or have been made evident on repolished surfaces by applying a suitable etching reagent. The latter technique, first suggested by Lacombe and Beaujard,9 was then improved by Wyon and Crussard.10 Subgrains can be formed in single crystals after small amounts of bending followed by heating after this cold work, or during deformation at elevated temperatures. The first phenomenon was analyzed by Cahn11 for the simple case of pure bending followed by annealing. Cahn suggested a mechanism of subgrain formation based on the dislocation theory and called this phenomenon "polygonization." He extended this mechanism to the more complex case of local bending, such as the bending which may occur when a polycrystalline specimen is deformed in tension. Cahn's suggestion was later found quite consistent with the results obtained by Dunn and Daniels." An explanation has been presented recently regarding the formation of subgrains during deformation at elevated temperatures by Chang and Grant.'" In general, there are two schools of thought on the subject. One, according to Wood et al.,5 is that subgrain formation is a mechanism of deformation which is operative under certain conditions in the same way that the slip process is the mechanism of deformation which is operative under other conditions. The boundaries between the subgrains undergo a viscous flow which contributes substantially to the deformation of the material. The second, according to Cahn,13 Wyon and Crussard,10 and Chang and Grant,18 is that subgrain formation is the effect of simultaneous deformation and annealing and is,

Jan 1, 1953

air-lift and equipped with tapered tubing of proper design, we would have a gas input consumption of about 2500 cu. ft. per bbl., which at 3 to 4c. per 1000 cu. ft. would be 7 1/2 to l0c, per bbl., and there would be very infrequent loss of production due to stoppages. It has been demonstrated that with efficient design of air-gas lift, the production of wells can be increased much beyond that obtained with the former type of air-lift employed; also that small wells can be operated by air-lift with tapered tubing at a cost that places this method in competition with beam pumps in many fields. The next step in conservation that the writer expects to have an opportunity to demonstrate is that of restoring the pressure in a pool and producing by air-gas lift all of the oil possible to lift economically. This combined operation is probably the method toward which we shall eventually be working in recovering the maximum quantity of oil from pools where the oil is recovered through bore holes. General Discussion on the Air-gas Lift H. P. Porter, Tulsa, 0kla.—The papers presented at this meeting contain a great amount of valuable information. Wonderful progress has been shown in the development of air and gas-lifts. There has been nearly everything brought out that touches upon the subject. The real point that is lacking is exact knowledge of the velocity with in the flow column which will produce the best effect—that is the thing we must know more about. Velocity in Gas-lift Flow In other lines of industry the matter of velocity of fluids in pipe lines has been well analyzed and there are known laws by which to calculate velocity of flow; for instance, in irrigation work large pumps are designed with intake pipos to employ an intake velocity of 4 ft. per scc. By reduced cross-sect'ion the velocity is increased rapidly as it enters the pump and the discharge rate is at 12 ft. per src., which in turn is reduced in the discharge column to 4 ft. per sec. Crushed coal, grain and granular material is found to be best conveyed by air when a pneumatic conveyor is employed at 100 ft. per sec. As in the design of a pumping plant or a pneumatic conveyor, the velocity at the lower end of the column in the flowing well must be controlled within certain limits for best results. Mr. Griswold, I believe, stated that they had velocity as low as 15 it. per scc. and from that up to 78 ft. per sec. Mr. Pierce and Mr. Lewis showed an ideal flow column showing how the velocity increased as the fluid was carried up the column, hut did not give any figures as to the velocity. It would be well to take that sort of a diagram to establish an ideal velocity at the lower or intake end, and then calculate the velocity from expansion of the gas as it goes up. It may be that the, ideal intake velocity would vary, depending on the depth of the well, the quantity of liquid to be handled or the pressure which it may be desired to hold. The subject is one that might be worth much research.

Jan 1, 1928

By W. C. Winegard, W. J. Bratina

Internal friction characteristics and temperature dependence of the torsion modulus for iodide zirconium containing 2.4 pct Hf were investigated, using a low frequency pendulum technique. The internal friction curve consists of a background which increases as the temperature increases, a maximum at 860°C apparently a background due to the al-lotropic transformation, a maximum due to grain boundary relaxation with an associated heat of activation of 58,000 cal per mol, and an anomaly below 350°C which may be associated with a precipitation perphenomenon, Oxygen in below small amounts reduces the grain boundary maximum substantially. The variation of the torsion modulus at 20°C was found to be 3450 Kg per mm2 for the zirconium used in the present work. IT is well known that small amounts of certain solutes materially affect the ductility of zirconium. Lely and Hamburger,&apos; as early as 1914, found that high purity zirconium exhibited a remarkable ductility, while Fast&apos; has shown that oxygen and nitrogen can cause substantia1 embrittlement. Treco" has recently demonstrated that the ductility decreases sharply with the oxygen content, and that 2 atomic pct O2 embrittles zirconium to such an extent that cold working is impossible. The marked decrease in ductility is difficult to understand in view of the fact that Domagala and McPherson4 report the solid solubility of oxygen in zirconium to be 29 atomic pct at 500 °C. Another metal which behaves much the same as zirconium in this respect is titanium. Pratt et al." investigated the internal friction characteristics of titanium and the effect of oxygen on the internal friction values. It is evident that internal friction measurements are of value for studying grain boundary segregation, as shown by Pratt et al. for oxygen in titanium, by Pearson for oxygen in copper, and by Maringer and Schwope for oxygen in molybdenum. With this in view, the internal friction characteristics of zirconium and the qualitative effect of oxygen on the grain boundary relaxation phenomenon were investigated. Materials and Experimental Procedure The zirconium used in the present work was supplied by the Foote Mineral Co. in the form of wire 0.05 in. diam. The analysis supplied by the manufacturer indicates the amount of hafnium as 2.4 pct, less than 0.01 pct O less than 0.01 pct N,, less than 0.02 pct H,, and less than 0.001 pct C. Additional spectro-graphic analysis indicates the other main impurities as follows: 0.01 pct Fe, 0.05 pct Si, 0.008 pct Cu, <0.005 pct W, <0.001 pct Al, <0.05 pct Mg, <0.001 pct Ni, <0.02 pct Ca, and <0.01 pct Ti. Microscopic examination of the material in the as received condition revealed very fine grains with numerous twins. Specimens were annealed either in situ in the internal friction apparatus or in evacuated silica tubes in an auxiliary furnace. When the specimens were annealed in the auxiliary furnace, they were wrapped in identical zirconium wire to prevent contamination by the container. Metallographic sections were taken in all cases. Some were taken from the specimens used for internal friction measurements after completion of the experiments, while others were taken from control specimens at intermediate stages of the experiments. lnternal friction values were obtained by measuring the free decay of a low frequency torsion pendulum (1 cycle per sec), the suspension of which was

Jan 1, 1957

By N. F. Schulz, H. A. Lex, J. D. Zetterstrom

A green ball of iron ore faces many perils from the time it is formed until it finally emerges from the pelletizing furnace as a hardened pellet. For instance, if the rate of heat transfer into a ball is sufficient to produce vapor from either the free or combined water more rapidly than it can escape at a tolerable pressure, the ball may split, spall, or even explode, a failure commonly known as decrepitation. To avoid such failures, one must either limit the rate of heat transfer during the drying and preheating stages, at the expense of production rates, or improve the decrepitation resistance of the green balls. The latter remedy may often be accomplished through changes in ore preparation, balling procedures, or the judicious use of binders or other additives. INTRODUCTION Pelletization has become established as an especially desirable method for the agglomeration of fine taconite concentrates and it promises to be equally satisfactory for improving the physical structures of certain natural ores. A high-quality pelletized iron ore consists of uniformly sized spheres, usually about 1/2-in. diam, which are strong enough to resist abrasion and breakage during handling and which reduce well without disintegration in the blast furnace. The unfired agglomerates, "green balls", are subject to several destructive effects that must be avoided or minimized if a high-quality product is to be obtained by pelletization. Among these are abrasion and impact deformation or breakage during handling of the wet green balls, deformation and breakage by compressive forces in the bed of ore in the pel-letizing furnace, decrepitation during drying and preheating, wind erosion, and radial cracking at firing temperatures. Moisture condensation from the warm saturated gases downstream from the drying zone on wet, cool balls may cause bed collapse if it becomes excessive. Decrepitation is defined as the sudden disintegration of green balls, usually with an audible pop, that occurs when they are heated too rapidly during the drying or preheating stages of the pelletization process. The extent of ball disintegration may vary from merely splitting off a small fragment to almost total disintegration into the original ore particles making up the ball. Such ball destruction results in a decreased yield of pellets, and the fragments, which also tend to interfere by obstructing the gas flow through the bed, must eventually be screened from the fired product and recycled. The closely related type of ball failure that sometimes occurs during the high temperature firing stage, resulting in radial cracks without fragmentation, was not considered to be decrepitation for the purpose of this investigation. Failure by decrepitation is not usually a serious problem in the pelletization of taconite concentrates. The problem is significant, however, in the pelletization of some natural ores, especially those containing hydrous iron oxides. In some instances, economicd production rates cannot be maintained if the drying and preheating rates are slowed down enough to avoid decrepitation. OBJECTIVES This investigation was undertaken to: (1) Develop a practical laboratory means for quantitatively measuring the tendency for green balls to decrepitate in iron ore pelletizing furnaces, and (2) Investigate the causes and cures of ball decrepitation. MATERIALS Two iron ores were used in the work reported here: a taconite concentrate at 90% minus 325 mesh, containing 65.0% Fe, 8.4% SiO2, and no loss-on-ignition; and a crude oxidized ore at 54% minus 325 mesh, containing 59.1% Fe, 3.6% SiO2, 1.1% A12O3, and 9.5% loss-on-ignition. For a special test of effect of particle size distribution on decrepitation, two other

Jan 1, 1967

By R. E. Miner, J. K. Jackson, D. F. Gibbons

Internal-friction measurements were made during isothermal aging treatments of 18 pct Ni maraging-steel wires between 420° and 612°C. A sharp initial drop in the internal-friction level was interpreted in terms of a rapid dislocation recovery reaction. The rate of the recovery was found to be independent of temperature. Truncation of the recovery reaction was apparent in those systems that exhibited the rapid age-hardening characteristics of the maraging steels. It is proposed that this initial hardening response is the result of a low activation energy preprecipitation reaction involving molybdenum. A gradual rise in the internal-friction level at longer aging times was associated with the precipitation of a molybdenum-containing precipitate. CONSIDERABLE research effort has recently been devoted to the mechanisms responsible for the high strength and toughness of 18 pct Ni maraging steels. These bcc martensitic alloys are found to harden during aging at temperatures between 400° and 600°C. The aging response is very rapid with more than half the total hardness increase occurring within the first few minutes of aging, Fig. 1. Precipitate particles have been observed in the later stages of aging by a number of investigators.&apos;-&apos; While the identity of the precipitates remains the subject of some controversy, one or more of the intermetallic compounds, Ni3Mo, Ni3Ti, and Fe2Mo, are almost certainly involved. Heterogeneous nucleation of precipitates at dislocations has been noted8 and cobalt is believed to enhance the formation of fine, homogeneously distributed particles by lowering the solubility of the alloying elements in the martensitic matrix.3,7 Transmission electron microscopy studies of the initial hardening behavior have not been fruitful. Strengthening mechanisms based on atomic ordering have not been generally supported by X-ray and neutron-diffraction experiments.9 In the present investigation, the aging reaction was studied using isothermal-aging internal-friction measurements. The marked sensitivity of internal friction to short-range diffusion and precipitation processes has provided a convenient tool for the elucidation of the strengthening mechanisms operative in the maraging steels. EXPERIMENTAL PROCEDURE An upright torsion pendulum was used to measure the internal friction of several maraging steels during isothermal aging. The pendulum was placed in an atmosphere of helium at a pressure slightly less than atmospheric. To permit measurement of internal friction during the first minutes of aging, the specimens were rapidly heated by passing a current through them in a manner similar to that described by Ang and Wert.10 Thermal gradients in the specimen were largely eliminated by using specially designed specimen grips11 which produced temperature variations of less than 1 pct over 90 pct of the specimen length and less than 3 pct over the entire length at aging temperatures up to 620°C. A proportioning strip-chart program controller was employed to maintain constant specimen temperature during treatments of up to 36 hr duration. A number of vacuum-melted laboratory heats having compositions near that of a typical commercial 18Ni-7Co-5Mo-0.4Ti alloy were investigated. The amount of cobalt was varied from 0 to 7 wt pct in five of the heats. Either molybdenum or titanium was omitted in the remaining two heats. The alloy desig-

Jan 1, 1967

By M. C. Miller, M. R. Tek, D. L. Katz

Previous studies have shown the influence of geometric variations on the drawdown and buildup behavior of a well completed in a homogeneous, porous medium containing a single-phase fluid. Other papers have shown the influence of leakage across caprocks on drawdown tests on water wells and aquifers. This paper presents two additional cases: the influence of an adjacent, expansible source of fluid, and the effect of caprock leakage on the measured in situ permeability and compressibility. Methods are developed for evaluating the influence of these two deviations from a uniform aquifer upon the in situ permeability and compre.ssibility indicated by pump tests. INTRODUCTION In relatively uniform porous media, saturated with a single-phase fluid, the effective reservoir permeability and compressibility of the water porous bed system may be obtained from drawdown and build-up data on wells, such as the initial wells drilled in aquifer storage reservoirs (Homers and Katz et al.7). In considering the drawdown and build-up behavior of wells adjacent to storage reservoirs, or of wells in an aquifer adjacent to an unknown gas field, questions arise as to the quantitative effect of the presence of compressible fluid on the measured permeability and compressibility of the formation. The solution to this problem is presented, using a constant pressure line source at some distance from two wells, one of which is pumped and the other used as the pressure observation well. The solution is presented in terms of the geometry of the wells and their relationship to the constant pressure line. It is known that caprock leakage can interfere with the determination of an aquifer in situ permeability and compressibility (Mantush4, Hantush and Jacob3 and Witherspoon and Muellerll). This paper presents an added case of the effect of leakage through a caprock of known thickness and permeability on well tests starting with a reservoir of constant pressure above the caprock and contributing to the aquifer as a result of the pump test. Again, both a pumping well and an observation well are postulated. These two cases are presented together since both a compressible fluid nearby and. caprock leakage show similar deviations from expected in situ permeability and compressibility results, and the solutions are similar in form. EFFECT OF A NEIGHBORING CONSTANT PRESSURE SOURCE ON IN SITU MEASUREMENTS Bixel, Larkin and van Poollenl presented a paper showing the influence of a discontinuity of the properties of a fluid formation system on drawdown and build-up performance. Their case is related to the present study but may be distinguished from it in that their numerical work and resulting graphs relate only to the performance of the pumping well itself. Incorrect values for in situ reservoir properties may be obtained from pump test data if the skin effect of the well and after-flow are not considered. Analysis of this problem by the authors indicated that the more reliable method of evaluating the influence of an adjacent gas field or expansible source was to use one well for pumping and another well at some distance from it for observing the aquifer pressure performance. An expansible source of hydrocarbon near a pumping well may be approximated by a line of constant pressure for a pump test. Fig. 1 illustrates a pumping well and an observation well near a line of constant pressure. Pressure behavior of an observation well during a drawdown pump test near a line of constant pressure is given by the diffusivity equation:

Jan 1, 1967

By T. E. Scott, R. P. Zerwekh

The charactevistics of the deformatiotz of fcc thorium were examined between 78 and 473 K. Activation energy, actiuation volume, and the temperature dependence of the flow stress were determined and conlpared uith several theories for the rate-controlling mechnnistn of the tempemture-dependent component of the flou~ stress. It was established that the Cottrell-Stokes law does not hold, even approximately, for thorium. Through consideration of the above factors and other parameters, it was concluded that the vandom solute barrier theory proposed by Friedel demonstrates the best agreement with experimental observations of the deformation of thorium below ambient temperature. THORIUM, the first metal in the actinide series of rare-earth elements, is interesting and important from two points of view. In the more practical vein, it is a potential reactor fuel. As such, it is important to know its properties. Of specific interest here are the mechanical properties of thorium. Second, no detailed information concerning the deformation characteristics of the actinide elements has been gathered to date. In view of the interesting physical and chemical properties of these metals, their mechanical behavior might reveal characteristics which could improve our understanding of the mechanisms controlling deformation of the more common metals. For example, it has been shown1 that thorium exhibits a yield point which is greatly enhanced by interstitial solute elements such as carbon. This is not a normal occurrence in fcc metals. The goal of this investigation, therefore, was to characterize the deformation of polycrystalline thorium. MATERIAL AND PROCEDURES Thorium, made by the magnesium intermediate alloy process described by Peterson et al.,2 was rolled and swaged to 0.065-in.-diam wire. The metal analysis is given in Table I. After preparation, the oxygen and nitrogen contents had risen to 308 and 60 ppm, respectively. The 0.065-in.-diam wires were cut into 2-in. lengths and annealed in a vacuum of lo-&apos; Torr at 750°C for 1 hr, producing a grain size of 2735 grains per sq mm. The ends of the 2-in. sections were masked off so that a 1-in. gage length could be electropolished. Specimens were polished at 35 v in a solution of 6 pct perchloric acid in methanol which was maintained at 0°C . The gage diameters after polishing were about 0.0625 in. The tests were run on a screw-driven tensile machine at a constant crosshead speed corresponding to a strain rate of 0.005 min-&apos;. The strain rate was changed rapidly after each 0.01-in. extension between 0.005 min-&apos; and one of three higher strain rates which were selected in order to achieve strain-rate ratios of 5, 10, and 20. Tests were run at several temperatures from 78" to 473°K; most were tested at 423", 300°, 215", and 78°K. EXPERIMENTAL RESULTS Flow Stress vs Strain and Temperature. Typical true stress-true strain curves for thorium are shown in Fig. 1 for several temperatures over the range 473" to 78°K. The curves for 78", 215", 300") and 423°K were obtained from strain-rate change tests using the lower (0.005 min-&apos;) or base strain-rate values of stress. Additional tests, using the same base strain rate at different strain-rate ratios, gave curves which virtually superposed on those shown, indicating that strain-rate changes did not materially influence the work-hardening characteristics at the base strain rate. The curves for 273") 373") and 473°K were standard tensile tests at 0.005 min-&apos;. The behavior of the flow stress with temperature is

Jan 1, 1968

By William H. Mount

INTRODUCTION The requirements of mine ventilation demand the constant attention of the mine operator. Just as the physical mine structure changes with time, the ventilation requirements of a particular mine change considerably from season to season and even from day to day. No ventilation system can remain adequate indefinitely; and all systems require monitoring and adjustments to achieve proper ventilation. Instead of being given fore- thought and planning, mine-ventilation systems too of- ten are erected hastily, merely to correct an already un- healthy situation. The usual result is an inefficient and costly system that, in some instances, may prove in- effective in providing fresh air to the point of need. The ventilation of mines is a combination of both art and science. The fluid that must be moved is in- visible; its properties change drastically with temperature, barometric pressure, and humidity; and the methods of measurement are not precise. In part, ventilation engineering must rely upon the art of good industrial ventilation experience and sometimes even the trial-and- error method. However, the properties of air can be determined with relatively inexpensive equipment; with some care, measurement accuracies within 5% of the actual values can be obtained. Thus the art of ventilation gradually is being supplanted by improved engineering practices. Although the direction of flow and the volume may not be predicted correctly by airflow equations in every situation, it is better to try to predict the behavior of a given ventilation before installation than to proceed blindly with a system design. When used with the discretion that comes from education and experience, the basic laws of ventilation can provide sub-stantial insight into the design of an air-handling system; and they can prevent wasteful or even dangerous designs from being installed. Since the mine operators who read this text will have varying amounts of exposure to ventilation theory, the basic laws of airflow and of mechanical ventilation are presented in the first section. The emphasis has been placed on the interpretation and use of fan characteristic curves that are supplied by fan manufacturers. Considerable information can be obtained from these fan curves, particularly when they are used with a graphic model of the mine, drift, or duct in which the fan or fans are to be installed. A few minutes spent comparing the various characteristic curves can help the designer obtain the correct fan for the job. However, the under- standing of a few fundamentals is necessary; and this text has been prepared to provide ample and understandable information in a "how-to" style. In subsequent sections of this text, more down-to- earth subjects will be covered, including the problems of air recirculation, relative merits of installing fans in series or in parallel, expected maintenance requirements (vibration, lubrication intervals, etc.), fan noise and some remedies, effect of an inlet bell on the fan per- formance, basic air-measurement techniques and equipment, and similar miscellaneous items. Although this text is not intended to be a comprehensive bible of mine ventilation, it has been prepared as a guide that provides some useful information to individuals responsible for the quality of the underground environment. Every person working underground is en- titled to the safest environment that can be provided within the limitations of existing technology and at a reasonable cost. Adequate ventilation is well within both limits, provided that the system is designed intelligently, in conjunction with the mining plan, and not as an after-

Jan 1, 1982

By D. T. Peters

To better understand the Co-Mo interaction in maraging steels, the precipitate reversion behavior of two alloys closely related to the 18 Ni-250 grade has been studied. The reversion experiment is carried out by aging at a low temperature, T1 (preaging temperature), for some period of time and then aging at a higher temperature, T2, called the reversion tetnperature. Aging and reversion tmzperatures used were in the range 679 to 1050°F. Reversion is marked by an increase in resistivity and a decrease in hardness. It teas found that some reversion took place at all cornbinations of T1 and T2 but that pronounced rei3ersion resulfed for an Fe-18 pct Ni-5 pct Mo-8 pcl Co alloy exposed to preagz&apos;ng&apos; temperatures at or below 850°F. A similar alloy not containing cobalt exhibited no such discontinuity in reversion behazior with TI. The results are interpreted in terms of two types of molybdenum-rich precipitates, one nucleated at dislocations and the other in the matrix. The increased supersaturation resulting from the presence oj- cobalt evidently provides sufficient energy to nucleate the matrix phase. Anotnalies in the temperature dependence of the resistivity decrease and peak hurdness in the Fe-18 pct Ni-5 pct Mo-8 pct Co alloy as a junction of aging temperature noted in an earlier study are explained on this basis. SEVERAL investigatorsl-9 have studied the details of the precipitation-hardening reaction of the maraging steels. The great majority of conclusions have been drawn from transmission electron microscopy. Although much has been learned by this method, alternate techniques which will give information earlier in the aging process are needed for a more complete understanding of the series of precipitation steps probably involved in the aging reaction. Peters and cupp&apos;&apos; have recently shown, by measurements of the kinetics of precipitation, that an 18 pct Ni-Co-Mo maraging steel shows a distinct change in precipitation behavior at aging temperatures below 850°F. The results were interpreted in terms of the existence of two types of precipitates at low aging temperatures. Only one precipitate type is present at higher aging temperatures. The low-temperature precipitate was found to be a particularly effective strengthener. No evidence for the additional low-temperature precipitate was found in the 18 pct Ni-5 pct Mo ternary alloy. The object of this investigation was to study further the characteristics of the two types of precipitates and the interaction between cobalt and molybdenum characterizing this system. Some preliminary experiments indicated a difference in reversion behavior in specimens aged above and below 850°F. This suggested that knowledge of the reversion behavior might shed some light on these two questions. Hardy and Heal11 have defined reversion as the loss of hardness, electrical conductivity, or other properties caused by heating for a very short time at temperatures above the aging temperature. The precipitate reversion referred to in this paper is entirely distinct from "austenite reversion" often referred to in maraging steel literature. This latter phenomenon could more accurately be called the diffusion-controlled formation of austenite. Much has been written about reversion in several of the aluminum-base binary and ternary alloys.&apos;2-16 Two explanations for reversion have been advanced. Based on the classical nucleation theory of Volmer-Weber-Becker-Doring,17 Konobeevski18 suggested that reversion was due to the size of the precipitate particles

Jan 1, 1968

By C Placzek, E Beattie, K Blake

Channel iron deposits (CID) consist of ferruginous chemical sediments, and are an unusual subset of Phanerozoic ooidal ironstone deposits almost unique to the Pilbara, where they constitute around 19 per cent of the Pilbara’s iron ore exports. These deposits occupy many of the ancestral river channels of the Pilbara region, especially the Robe River palaeochannels, incising and meandering through the Precambrian banded iron formations (BIF) of the Hamersley Group and the underlying Fortescue Volcanics.This paper explores the factors underlying geochemical variation in CID, particularly the chemical properties of goethite. The selected deposits in the western Robe palaeochannel and its tributaries show little or no secondary reworking by later water tables. There is a total absence of aluminosilicate clays with all the deleterious elements such as aluminium and silica. Instead, these are associated with the goethite mineral lattice, either within or adsorbed to the cortices of pelletoids.A thickly vegetated environment, and the presence of the Maddina Volcanics as potential source rocks for these western Robe CID is offered as an explanation for relatively high aluminium in the deposits studied, and, in turn, as the reason most parts of the palaeochannel are preserved as inverted topography.CITATION:Beattie, E, Placzek, C and Blake, K, 2017. Dirty goethite – a geochemical characterisation of some western Robe River channel iron deposits, in Proceedings Iron Ore 2017, pp 489–502 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 24, 2017

The Earth?s population is approaching 6.6 billion people. More than half live in urban areas. And, as those figures continue to grow, the need to make wise use of the world?s natural resources as well as its living space will also grow. Thus, the concept of sustainable development ? meeting the needs of the current generation while preserving resources for future generations. The use of underground space is only one part of the sustainable development concept. But it is an important one. Tunnels and underground space are environmentally friendly and contribute significantly to sustainable development. But it takes years to plan and build tunnels and other underground infrastructure. And the demand for infrastructure in the world?s mega cities has grown significantly. In December, about 100 people representing several developed and developing nations spent a day at the United Nations (UN) in New York City discussing the future of underground space development throughout the world. The meeting was put on by the UN?s Department of Economic and Social Affairs and the International Tunnelling and Underground Space Association (ITA). The conference was titled ?The Use of Underground Space as an Unexpected Solution for Promoting Sustainable Development.? Its aim was to promote practical solutions to the use of underground space and tunnels as feasible alternatives to promote sustainable development throughout the world. A panel of speakers from government, academia, the UN and the ITA stressed that development is not sustainable without infrastructure. And, as the world?s population grows, there is now an urgent requirement to efficiently plan for the use of underground space to preserve it for the future benefit of mankind. The benefits of the use of underground space are many, they said. Among them: ? Tunnels channel clean water in and waste water out. This promotes health and sustainability worldwide, particularly in developing countries. ? The use of tunnels and underground space helps conserve energy and increases its efficient use ? the use of tunnels cuts commuting time and so saves energy. ? Tunnels, microtunnels and other underground structures promote the more efficient use of space in large cities ? the bulk storage of water, fuel and other goods. ? Underground structures are subject to less stress than surface structures, making them safe havens for natural and man-made hazards, including earthquakes. And, because underground structures are more durable, lifecycle costs are less than surface structures. ? Underground structures promote the multiple use of available land. Land owner-ship at several layers increases land use and provides more usable space. Han Admiraal is director of the Center for Underground Construction in the Netherlands. He said that urban planners need a new vision concerning the use of underground space. Going underground protects historical and archaeological surface facilities, he said. Underground space use can also protect populations located in adverse climates. And sensitive environmental areas on the surface can also be protected from development. In addition to the transportation of people, freight and water, underground development can also store water, as well as provide storage for waste, hazardous materials, carbon dioxide and geothermal energy. The upshot of this new awareness and vision for under-ground space is that its use should be considered before surface development, Admiraal said. And planners and developers are placing more emphasis on underground space development as part of their overall development plans for urban areas. That was not always the case, he said. In the past, underground space was not considered until after the surface space had run out, he said.

Jan 1, 2008

By D. F. Malan

This paper presents an overview of work conducted over several years to investigate the continuous stope closure profiles recorded in tabular excavations and the use of this data as a hazard indicator. In spite of the brittle nature of the rock, measurements in gold mines and intermediate depth platinum mines revealed a significant time-dependent closure component. Various approaches to simulate the time-dependent closure have been investigated. Viscoelastic theory is able to simulate the time-dependent closure behaviour, but there are subtle problems with the use of this theory as it cannot simulate the failure processes in the rock. To overcome these problems, continuum and discontinuum elasto-viscoplastic models were developed by the authors. Discontinuum models have the advantage of being able to simulate the creep behaviour of prominent discontinuities. Development of these models has led to useful insights into rock mass deformation and has made the numerical simulation of parameters, such as rate of mining, possible for the first time. A number of practical applications for the mining industry have been developed from this study. Among these are the delineation of geotechnical areas using closure data, use of the data as a hazard indicator and to give warning of large collapses in the platinum mines, identification of areas to be preconditioned in the gold mines, measurement of the effectiveness of preconditioning and improved da

Jan 1, 2007

By Lutz Markworth, Fernando Parra, Wolfram Jaspers

"The worldwide demand of iron ore and the depletion of the high-purity deposits make it necessary to recover ores in increasingly fine size fractions or low Fe content in the feed material. Impurities for Iron ore processing plants are mainly Silica, Al2O3 and Sulfides.There is a copper processing plant in Chile, which has a high content of Fe in its tailings. These tailings will be re-processed to recover the Fe and to produce a pellet feed concentrate. This challenging flotation process was developed by the customer in his own laboratory. Different flotation technologies were tested. The best results were achieved with the PNEUFLOT® (PNEUmatic FLOTation). For a feed capacity of approximately 600 t/h, a flow sheet of two flotation lines with a reverse two-stage Amine-Silica flotation followed by a single stage reverse Xanthate Pyrite flotation was developed.Because of the two impurities the process control is very critical. Not even the reagent dosing has to be flexible for changes in the feed material; also the flotation cell has to be adaptable. Continuous development of the PNEUFLOT® cell with their specific advantages and the elimination of dysfunctions in the PNEUFLOT® cell have led to a growing demand of this type of equipment worldwide for the iron ore industry within the past years.INTRODUCTIONThe worldwide increasing demand of iron ore is mainly caused by China. This has a major impact on all economics worldwide as the metal price indicates. However, not even the iron ore and steel price, but all other commodities prices and the precious metals prices are increasing by a high percentage. Figure 1 shows the iron ore (pellets) price increase for Fe and the import of iron ore by China. Figure 2 shows the imports of iron ore to China."

Jan 1, 2008

By J. Bakken, M. Th. Jonsson, G. Sævarsdottir

A typical three-phase submerged-arc furnace for production of silicon metal and ferrosilicon has arc currents ~100 kA, phase voltages ~100 V and total furnace power ~10 - 60 MW. The arcs burn in gas filled cavities or "craters", where the main atomic components of the plasma mixture are silicon, oxygen and carbon. Two quite different simulation models for high-current AC arcs have been developed: the simple Channel Arc Model (CAM), and the more sophisticated Magneto-Fluid-Dynamic Model (MFD). These models have been described extensively and results reported at INFACON-8 and INFACON-9, respectively. The coupling between the arcs and the AC power source is described by a complete three-phase Electric Circuit Model. Recent numerical modelling studies of industrial AC arcs show that the boundary conditions at the cathode and anode are critical for the simulation results. A novel Cathode/Anode Sub-Model for high-current AC arcs that treats both cathode and anode indicates a completely different cathode behaviour than previously assumed. A cathode spot which serves a high-current electric arc is shown to be dominated by the energy impact from the arc. This leads to lower cathode fall voltage than obtained from previously developed models. The anode fall voltage is negative, as the main function of the potential barrier is to repel plasma electrons. The cathode spot is diffuse in the sense that the arc in fact contracts away from the cathode. Simulation results are compared to measurements on both industrial furnaces and smaller scale pilot furnaces. An important conclusion, supported by our arc studies, is that the arc length in silicon metal and ferrosilicon furnaces does not exceed 15 cm and the arc may burn anywhere on the electrode, not necessarily beneath the electrode tip.

Jan 1, 2004

By Steve Cole

"The economic and strategic importance of PGE bearing deposits is fuelling renewed exploration and development efforts in the precious metals mining sector.This paper presents a review of the various techniques used in the processing of PGE bearing ores, from primary benificiation to processing routes for the different flowsheets that have been developed amongst current producers. Recent innovations such as preconcentration of ore using gravity separation, recent trends in flotation circuit design and the development of hydrometallurgical routes for the direct treatment of flotation concentrates without the need for smelting will be discussed. Data from recent projects will be presented to illustrate common characteristics of PGE ores and concentrates.INTRODUCTIONThe six platinum-group elements (PGE): ruthenium, rhodium, palladium, osmium, iridium and platinum, together with gold and silver, are considered to be ""precious"" metals. The recent spike in platinum and palladium prices coupled with the projected increase in demand for the metals has fuelled a spate of exploration and new projects in the PGE sector. Historically primary producers of PGE metals have controlled the flow of information relating to the mining and processing of these ores into the public domain. Very little published information relating to individual operations and processes is available in comparison to the abundant literature relating to other metals.The purpose of this paper is to provide a general overview of the issues relating to the processing of PGE ores. Each topic discussed could easily be the topic of a paper or book and so in many cases only the surface of the topic will be scratched. An attempt has therefore been made to provide as many references as possible.This paper discusses the classification and location of PGE ores, the mineralogical factors that affect recovery of PGE's, methods currently used for recovering PGE's and process trends in PGE metallurgy."

Jan 1, 2002

By J. Nell

An overview is given of the matte melting process used for the beneficiation of South African Platinum Group Metal (PGM) ores. Most producers use six-electrode furnaces to melt the concentrate and Pierce Smith converters to oxidize excess iron sulphide from the furnace matte. Concentrates from two reef-types (the so-called Merensky and UG-2 reefs) dominate the feedstock supply. Concentrate from the Merensky reef is low in chromium and do not pose significant melting problems. Concentrates from the UG-2 reef contain much higher levels of chromium, which results in the formation of chromium-rich spinels during melting. This is attributed to the low solubility of chromium in furnace slag under typical operating conditions (an oxygen partial pressure of 10-8-10-9bar at temperatures of 1550°C to 1600°C). During the converting process care is needed to avoid excessively oxidizing conditions, which result in cobalt, nickel and copper losses to the slag. High nickel losses result in the formation ofFe2NiO4(trevorite), which often forms solid solutions with FeCr2O4and Fe3O4. In future, the main challenge in the processing of South African PGM ores will be to cope with ever increasing levels of chromium in the concentrate. A short-term solution to the problem would be to melt the concentrate under slightly reducing conditions to promote the formation of CrO, which is more soluble in the slag than Cr2O3. A longer-term solution to the problem would be to abandon the current matte-smelting process in favour of an alloy-based process, which would offer total flexibility with respect to the amount of chromium that can be tolerated in the feed. Key words: Merensky, UG-2, furnace, slag, matte, converting, spinel, chromium.

Jan 1, 2004

By James M. Link

The first rule of mineral deposits always seems to be: the deposit is never close to the market. With gems and precious metals, this is not much of a problem. But with most of the mineral commodities used in today&apos;s world, transportation becomes a major part of the cost to the consumer. In Japan, for example, more than 60% of the cost of coal to the consumer may be attributed to transportation. The purpose of this article is to examine pipeline transportation, particularly mineral slurry pipelines, as a means of getting the mineral to market. Pipelines Today Regulated pipelines in the US totaled nearly 724 Mm (450,000 miles) in 1980 according to the Federal Energy Regulatory Commission (FERC). Worldwide, more than 210 Mm (125,000 miles) of new pipelines will start construction in 1982 at an estimated cost of more than $150 billion. According to the Bechtel Corp., the period between 1982 and 2000 will see major growth in pipelines of all kinds. In North America, major movements of crude oil from Alaska and synfuels from the Rocky Mountains will require the construction of nearly 16 Mm (10,000 miles) of new pipelines. Nearly 42 Mm (26,000 miles) of new gas transmission pipelines will be needed to tap both US and Canadian arctic gas fields and move the gas to major markets on both coasts. Other pipelines will be required to move additional quantities of natural gas from the Rocky Mountains to more populous regions. Bechtel says more than 24 Mm (15,000 miles) of slurry pipelines will be needed to transport coal from both eastern and western coal provinces to the Mississippi valley and coastal areas. In 1980, 125 companies delivered more than 1 km3 (6.5 billion bbl) of crude oil and 652 hm3 (4.1 billion bl) of products in the US. At the same time natural gas pipelines transported 498 km3 (17.6 trillion cu ft). The reported investment by these companies was nearly $20 billion at the end of 1980. Advantages of Pipeline Transportation The obvious success and vitality of the oil and gas pipeline industry is based, at least in part, on the fact that pipelines are a very efficient and low-cost method of transportation. This fact, coupled with the need for lower cost trans¬portation, has led to the marriage of oil and gas transmission technology and the bulk mineral solids transportation industry. The off-spring of this marriage is the mineral slurry pipeline. Slurry pipelines have a number of advantages over other transportation methods. One of these is the fact that they are buried-out-of-sight, out-of-mind. Second, they are relatively small users of labor because they lend themselves to automation and remote, or even computer control. Third, they offer an attractive economic alternative to other transportation systems. For example, for a 1000 km (621 miles) distance, rail costs of 1?/ km (1.7?/ton-mile) are about equivalent to slurry pipeline costs. But, as the distance increases, pipeline cost per t-km continues to drop while equivalent rail charges remain essentially insensitive to distance. Where existing rail, barge, or ocean ships are available, the cost of new construction associated with a slurry pipeline probably will render it noncompetitive. However, where new rail or other construction is needed, the cost of a slurry pipeline is very competitive. About three-fourths of the cost of a pipeline is in pipe, fittings, and construction. Nearly a fifth of the investment is in pump stations and the remainder is in right-of-way, surface facilities, utility acquisition, communication facilities, and other support areas. The fact that pipelines are capital intensive is, at the present time, a mixed blessing. For example, the delivered cost of coal in a hypothetical project doubles when the cost of money rises from 9% to 17.5% per year. The largest cost element for delivered coal in this example is in depreciation and finance charges. The next largest cost element is electricity to power the pumps, with labor making up the smallest increment of the delivered cost of coal. World Slurry Pipelines The idea of a slurry pipeline was probably first investigated in the latter 19th century, but the first ones were successfully built and operated in the US in the early 1900s. Today, they are fairly common worldwide. Table 1 shows a number of the world&apos;s slurry pipelines. An examination of these will further emphasize the fact that pipelines provide a cost competitive alternative where new construction of a transportation system is required. In each of the examples, the desired mineral commodity is located in a remote corner of the world, markets are at a great distance, value of the commodity is not great, and no other transport system is available.

Jan 10, 1982

By Frank C. Kelton

It is perhaps not widely realized that extraction and saturation processes carried out on oil well core samples alter the properties of these samples to varying degrees. On the other hand it is felt by some that quick-freezing of core samples increases their permeability and porosity significantly. Accordingly, laboratory tests were carried out on 49 pairs of horizontally adjacent samples in order to differentiate between the effect of quick-freezing per se on permeability and porosity of the samples, as distinguished from the effect of the identical saturation treatment on permeability and porosity of the companion samples. Also, additional field data were obtained on comparison of frozen vs unfrozen companion samples. LABORATORY INVESTIGATION OF FREEZING us SATURATION EFFECTS Procedure The samples used in these tests were two-cm cubes cut in horizontally adjacent pairs from cores from eight Gulf Coast and Mid-Continent wells, which cores had not previously been frozen. These samples were extracted with carbon tetrachloride, dried, and air permeabilities run in the conventional manner. They were then evacuated and saturated with brine of 25,000 ppm sodium chloride content, and porosities determined by gain in weight. The samples were partially desaturated by evaporation down to an average brine saturation of 68 per cent. One sample from each pair was quick-frozen by covering with dry ice after wrapping in a single layer of paper, and allowed to remain frozen for about two hours; the companion sample from each pair was not frozen. After thawing the frozen sample, all samples were immersed in tap water overnight in order to leach out most of the brine. Air permeabilities were re-run, and the samples were again saturated with brine to determine a second porosity value. For purposes of averaging of data, the samples were grouped according to four permeability ranges, from 0 to 10, 10 to 100, 100 to 1,000, and 1,000 to 3,840 md. Average permeability and porosity changes for the frozen vs the unfrozen adjacent samples are shown in Table 1. Discussion As may be seen from Table 1, the averages of the per cent permeability increases for the quick-frozen samples ranged from 3.8 to 12.9 per cent among the four permeability groups. The average changes among the four groups of unfrozen companion samples ranged from a decrease of 0.2 per cent to an increase of 9.3 per cent. There was no particular correlation of these changes with magnitude of permeability; however, the increase for each group of frozen samples paralleled the increase for the corresponding unfrozen samples. The differences between the two sets of values are believed to be a valid indication of the effect of the quick-freezing in itself, since the treatment of the two samples in each pair was identical except for freezing. The permeability changes which are strictly the result of the quick-freezing are shown in the sixth column of Table 1. These range from a decrease of 0.9 per cent to an increase of 4.0 per cent; the overall weighted average is 1.2 per cent, as compared to an average increase of 6.8 per cent caused by the saturation treatment of the samples not frozen. The average porosity changes are in general smaller than the changes in permeability, and range from a decrease of 2.3 per cent to an increase of 3.3 per cent. The overall weighted average change ascribed to the quick-freezing is 1.0 per cent of porosity. Many factors can contribute to the changes in permeability and porosity observed when subjecting cores to the simple processes used in these tests. Such are: hydration and swelling of clay, adsorption of ions, changes in surface structure and wettability, expansion and compression effects due to ice formation, shrinking and cracking, leaching of salts and colloids, displacement of particles resulting in either blocking or enlarging of pore openings. Whatever particular mechanisms are involved. however, it is apparent not only from this study but also from other investigations in the literature&apos; not directly concerned with quick-freezing, that the effects produced by commonly used extraction, saturation and drying techniques may be of considerable magnitude The results of this study indicate that for the particular samples and techniques used, such effects are of the order of five to six times the effect of quick-freezing. insofar as changes in permeability are concerned. It may be argued that these samples might not include extremely shaly material where the effect of freezing upon permeability may be much greater. However, had such material been available for these tests, it would undoubtedly have been very susceptible also to alteration by the extraction and saturation treatment used. To investigate this point further, the individual sample data were re-grouped according to the magnitude of the average per cent permeability increases for the pairs of samples, irrespective of permeability. The results

Jan 1, 1953

By E. W. Felegy

THE need for improved mine communication to increase efficiency and to insure greater safety has long been recognized. General and unrestricted communication between all points underground, and between the surface and all points underground, is probably the least advanced phase of the mining industry. An ideal system of mine communication must require no fixed wire installations. The equipment must be small, lightweight, and readily portable, and the power requirements low. A system that can be used not only under normal circumstances but also in an emergency, when the continuity of wires, tracks, and pipelines may be disrupted, must function independently of any aid furnished by standard installations. Radio communication offers possibilities of meeting all the requirements necessary for an ideal communication system in underground mines. Transmission of signals must be achieved through one or both of two mediums, through the air in mine openings or through the strata. The results or lack of results obtained by early investigators showed conclusively that radio communication by space transmission cannot be accomplished effectively beyond line-of-sight distances in underground passageways. A radio system underground therefore must depend solely upon transmission through soil and strata. The application of radio to underground mine communication was investigated by many individuals and agencies at different times in the last several decades, but little success was achieved before World war 11.2-0, The results of experiments during the war, and further knowledge gained in experiments with vastly improved communication methods and equipment after the war provided the background for additional research in radio communication in underground mines. During 1950 to 1.952 the University of Minnesota sponsored an investigation to determine the possibility of developing: a system of radio communication universally applicable in underground metal mines in the Lake Superior district. The possibility of using radio equipment to determine the imminence of rock bursts in deep copper mines in that district also was investigated. The investigation supplemented previous and concurrent emergency mine communication studies of the U. S. Bureau of Mines. Testing equipment and laboratory facilities maintained by the Bureau of Mines at Duluth, Minnesota, were used in the research program, which was conducted as a mining engineering graduate research problem by the present writer under the direction of T. L. Joseph and E. P. Pfleider. The radio units used in the research program were designed and built to specification solely to conduct tests of radio communication in mines. Two identical units were used in all tests. Each unit contained a transmitter section, a receiver section, and a power-supply section, mounted on a single chassis. The entire unit was enclosed in a single 10x12x18-in. metal case provided with a leather-strap handle for carrying purposes. The front of the case was hinged to open upward and provide easy access to the single control panel on which all controls were mounted. Storage batteries supplied the operating power for all tests. Standard 6-v automobile batteries were utilized to provide adequate capacity to conduct tests for a full day without exhausting the battery. A frequency range from 30 to 200 kc was covered in eight pre-fixed steps on each unit. The carrier frequencies were crystal-controlled and amplitude-modulated. The receiver employed an essentially standard superheterodyne circuit and was sufficiently sensitive to detect signal strengths of 5 micro v. A heterodyne circuit was employed in the transmitter to obtain the low-carrier frequencies used in the units. Power output of the transmitter, usually less than 2 w, rarely exceeded 3 w in any test. Tests were conducted in mines on the Vermillion iron range in Minnesota, the Gogebic iron range in Wisconsin, the Menominee and Marquette iron ranges in Michigan, and a copper mine in the upper Michigan peninsula. All tests were conducted when the mines were operating normally, and usual mining, maintenance, and transportation activities were in progress, so that any interference caused by normal production activities could be evaluated during the tests. Tests were made between different points underground in each mine, and between underground and surface points at some mines. Test readings obtained at any one mine were calibrated in the laboratory before another series of tests were begun at the next mine. The transmitter and receiver were separated by one or more levels in each test, and generally there was no other means of communication between test points. Two 100-ft lengths of rubber-covered wire were used for antenna wires on each unit in both transmission and reception. The ends of the wires were connected to ground points in one of several methods, depending upon physical conditions at each test site. The wires were clipped to metal rods about 200 ft apart in the back, side, or bottom of the mine opening where the character of the rock permitted driving rods. Both wires were clipped to points about

Jan 1, 1954

By T. B. Massalski, H. W. King

An hcp phase may be induced by cold working the ß&apos; phase of the Ag-Zn system. This phase reverts to ß&apos; on subsequent aging. No phase change occurs on cold working the o phase, but ß&apos; is formed when the deformed alloy is subsequently aged at room temperature. It is concluded that for alloys near 50 at pct Zn the ordered bcc ß&apos; phase is the equilibrium structure at room temperature. WhEN the disordered bcc ß phase of the Ag-Zn system is cooled to temperatures below 258o to 274oC, it transforms to a complex hexagonal phase <o.1,2 The nature of the o ß=o transformation has been the subject of some discussion,2&apos;3 and the structure of o has been described in detail.&apos; The latter phase appears to be stable on aging at room temperature but decomposes following cold work. When alloys containing approximately 50 at. pct Zn are rapidly quenched from the 0 phase field, the ß ? o transformation may be suppressed; but the ß phase undergoes an ordering reaction (ß ? ß&apos;). The ß&apos; structure may also be obtained as a result of cold working and aging at room temperature.4 Kitchingman, Hall, and Buckley4 have suggested that the decomposition of (o following cold work proceeds in two stages, (o ? ß followed by ß ? ß&apos;, but did not confirm this by experiment. When the ordered &apos; phases in the systems Cu-Zn5 and Ag-Cd6 are cold worked, they become unstable and transform to a close-packed hexagonal phase (( ) indicating that when order is destroyed in a ß&apos; structure the close-packed hexagonal phase may in many cases be more stable. It thus became of interest to study more closely the effect of cold work and annealing on the stability of both the ß&apos; and o phases in a Ag-50 at. pct Zn alloy. Predetermined weights of spectroscopically-pure Ag and Zn, supplied by Johnson and Matthey, were melted and cast under 1/2 atm of He in transparent vycor tubing. The ingot was homogenized for 1 week at 630°C and quenched into iced brine. Since mechanical polishing was found to induce a phase change, sections were first polished at room temperature, sealed in tubes under 1/2 atm of He, reannealed for several days at 630o or 200°C and then quenched into iced brine. Sections of the alloy thus prepared were found to be homogeneous when examined under the microscope. The sample quenched from 630°C (ß -phase region) was pink in color, whereas the sample quenched from 200°C (o-phase region) was silver. The latter sample showed the characteristic hexagonal anisotropy when examined under polarized light. Filings of the alloy were examined at room temperature, after various heat treatments, using an RCA-Siemens Crystalloflex IV diffractometer with filtered CuKa radiation. The X-ray reflections from flat powder specimens quenched from 630o and 200°C and sieved through 230 mesh were recorded graphically at a scanning speed of 1/2 deg per min. The resultant patterns are shown in Figs. 1(a) and 1(b) and may be identified as those of the 8&apos; and <02 structures respectively. The lattice parameter of the ß&apos; phase was determined as 3.1566Å.* This value compares very well withthatto be expected for a 50 at. pct Zn alloy from the data of Owen and Edmunds? and indicates that no loss of Zn occurred during casting. In order to study the effect of cold work upon the ß&apos; and o phases, filings made at room temperature and sieved through 230 mesh were mounted immediately in the diffractometer-i.e., without a strain-relief anneal. Changes in structure on subsequent aging were followed by scanning repeatedly over the regions of the low index reflections of the ß&apos; and o structures-i.e. , 28 from 35 to 44 deg. Immediately after filing the 8&apos; specimen, additional diffraction peaks were observed in the low-index region of the pattern, as shown in Fig. 1(c). These additional peaks do not coincide with those of the o structure, Fig. l(b), but may be indexed as the (10.0), (00.2), and (10.1) reflections of an hcp phase (<) with nearly ideal axial ratio. However, this hexagonal phase appears to be very unstable since within a very short time at room temperature it reverts back to the ordered ß&apos; phase, the reversion being complete within seven hours. The 5 ? ß&apos; reversion reaction is, therefore, very similar to those already reported in Cu-Zn5 and Ag-Cd6 7&apos;alloys. The action of filing caused the deformed surface of the originally pink ingot to become silver in color, indi-cating that the ( phase possesses similar reflecting properties to the o phase. Hence, the subsequent

Jan 1, 1962