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By C. H. Li, R. J. Stokes, T. L. Johnston

Sodium chloride crystals are brittle in the presence of surface microcracks. Water immersion leads to an enhancement of ductility which is retained indefinitely in dry air providing the crystal is dried without leaving a surface precipitate. Storage in a damp atmosphere results in a surface reaction and consequent rembrittlement. Although elimination of surface flaws in ionic solids does not necessarily enhance ductility, there is always a change in the location of the fracture origin. EVER since the original experiments of Joffel there has been controversy over their interpretation and no satisfactory generalized explanation has yet been given. It is generally admitted that when sodium

Jan 1, 1961

By N. S. Stoloff, R. G. Davies

The annealing behavior of a heavily cold-worked FeCo-V alloy has been studied at temperatures both above and below Tc, the critical temperature for ordering. It was found that re crystallization and grain growth can take place below Tc in the ordered state and that, in agreement with results for fcc alloys, order retards grain growth. The activation energy for pain growth is -55 kcal per mole in the disordered condition; it was not possible to assign a value to the activation energy for grain growth below Tc because the degree of order is changing rapidly over the temperature interval investigated. Precipitation of an fcc y phase was observed upon annealing the cold-worked alloy at temperatures of 675°C and below. SINCE it is known that diffusion constants are greatly affected by long-range order,' it is not unreasonable to anticipate that order will influence the diffusion-controlled phenomena of recrystallization and grain growth. In the course of a study of strain aging of ordering alloys around the composition Ni3Fe Vidoz, Lazarevic, and cahn2 noted that a disordered cold-worked alloy annealed at a temperature T1 just below Tc will order but not recrystallize; Tc is the critical temperature for order. The same alloy annealed at a temperature T2 just above Tc, or an alloy of different (nonordering) composition annealed at either T1 or T2, will recrystallize after equivalent amounts of cold work. Initially Selisskii and coworkers,3,4 who examined a series of cold-worked and annealed bcc Fe- Co alloys, reported that alloys forming the B2 FeCo super lattice could not be recrystallized below Tc. However in a later paper5 it was shown that FeCo ordered alloys could be recrystallized below Tc. Thus the first question to be answered by the present investigation was whether or not a heavily cold-worked Fe-Co-V alloy could be recrystallized below Tc. When it was found that the alloy would indeed re-crystallize below Tc, the influence of long-range order upon subsequent grain growth was studied. EXPERIMENTAL PROCEDURE The grain-growth measurements were made upon FeCo-2 pct V wire of 0.031 in. diam; the alloy was the same as that used in an earlier study of the mechanical properties of FeCO-v.6 The wire was produced by cold swageing and drawing a rod 0.125 in. diam that had been quenched into iced brine from 850°C to disorder the alloy; the initial grain size was 0.05 mm. Rates of grain browth were measured after isother-mally annealing the wire in the temperature range 675° to 825°C; T, is -720°C. Grain diameters were measured on the transverse cross section of the wires. The line-intercept method of determining the grain diameter was used; conventional light photomicrographs were taken when the grain size was greater than 10 . Carbon replicas were produced and examined in the electron microscope if the grain size was less than Dislocation configurations after recrystallization anneals were studied by electron transmission microscopy of foils produced by cold rolling a 0.125-in.-thick strip of the quenched material to 0.012 in. The foils, after heat treatments similar to the wire samples, were thinned by electropolishing in a chromic-

Jan 1, 1967

By E. H. Dix

The work of Merical and other investigators indicates that the phenomenon of age-hardening in alloys of the duralumin type is primarily dependent upon the variation in the solubility of copper with temperature. In addition to copper, however, these alloys contain small amounts of magnesium, silicon, manganese and iron, which may affect the age-hardening either directly or indirectly. The effect of these elements on the solubility of copper and on the manner in which this solubility varies with the temperature is of considerable interest, therefore. The effect of magnesium is of especial interest because apparently it exerts a marked effect on the natural or room-temperature aging of alloys of the type described.2 A series of investigations3 has been in progress in the research laboratories of the Aluminum Company of America to determine the functions * Metallurgist, Aluminum Research Laboratories. f Metallurgical Division, Aluminum Research Laboratories. Formerly with Metallurgical Division, Aluminum Research Laboratories. 1 P. D. Merica, It. G. Waltenberg and H. Scott: Heat Treatment of Duralumin. U. S. Bur. Stds. Sn. Paper 347 (1910). 2 M. Gayler: Constitution and Age-Hardening of Alloys of Aluminum with Copper, Magnesium, and Silicon in the Solid State. Jnl. Inst. Met. (1922) 28, 213. W. Fraenkel: Vergutbare Aluminiumlegiengen. Ztsch. Melallkunde. (1920) 12, 427. E. H. Dix, Jr.: Note on the Microstructure of Aluminum-Iron Alloys of High Purity. Proc. Amer. Soc. Test. Mat. (1925) 26, Pt. 2, 120. E. H. Dix, Jr. and H. H. Richardson: Equilibrium Relations in Aluminum-copper Alloys of High Purity. Trans. A. I. M. E. (1926) 73, 560. E. H. Dix, Jr. and W. D. Keith: Equilibrium Relations in Aluminum-manganese Alloys of High Purity. Proc. Inst. Met. Div., A. I. M. E. (1927) 315. E. H. Dix, Jr. and A. C. Heath, Jr.: Equilibrium Relations in Aluminum-silicon and Aluminum-iron-silicon Alloys of High Purity. Proc. Inst. Met. Div., A. I. M. E. (1928) 164. E. H. Dix, Jr. and F. Keller: Equilibrium Itelations in Aluminum-magnesium Alloys of High Purity. Proc. Inst. Met. Div., A. I. M. E. (1920) 351. E. H. Dix, Jr., F. Keller and R. W. Graham: Equilibrium Relations of Aluminum-magnesium Silicide Alloys of High Purity. Trans. A. I. M. E., Inst. Met. Div. (1931) 404. W. L. Fink and K. R. Van Horn: Constituents of Aluminum-iron-silicon Alloys. Trans. A. I. M. E., Inst. Met. Div. (1931) 383.

Jan 1, 1932

By Otto Henry

THE purpose of this investigation was to determine the equilibrium diagram of the lithium-magnesium pair as a first step in studying the possible usefulness of these alloys as ultra-light structural materials. REVIEW OF THE LITERATURE The behavior of lithium towards magnesium was first investigated by Masing and Tammann.(I)? In order to prevent oxidation the alloys were made in iron tubes under an atmosphere of hydrogen; temperatures were measured with a glass-protected thermocouple. These investigators found that lithium and magnesium form two series of solid solutions separated by a miscibility gap between 85 and 95 per cent magnesium; that the alloys with 81 and 95 per cent magnesium showed a homogeneous structure under microscopic examination, while the alloy with 89 per cent magnesium contained two distinguishable crystallites; that the curve indicating the beginning of crystallization rises from the melting point of lithium to that of magnesium; and that no compounds of lithium and magnesium are formed. The equilibrium diagram was not plotted because no definite data were obtained for determining the solidus and the posi-tion of the miscibility gap in the solid state. The difficulties encountered in this investigation were: (1) that it was necessary to heat them as high as the melting point of magnesium in order to obtain homogeneous melts; at such temperatures the alloys attacked the glass protecting the thermo-couple; and (2) that at temperatures above 400° C. the lithium united

Jan 1, 1934

THE problem of reaction rates in the open-hearth process is essentially that of trying to form a fairly clear picture of the "chemical mechanisms" in the bath. Quantitative data on reaction rates would perhaps not be of much practical importance even if they were available; however, what few approximate data there are can be used in combination with data given in Chapters 16 and 17 to sketch a picture of the "chemical mechanics" of the open-hearth process that is consistent with essentially all the present available evidence. The result may later be found incorrect in many details but even so it will illustrate certain useful methods for obtaining a clearer understanding of the process. Consistent with the treatment in Chapter 15, but in simpler terms, we may say that chemical reactions in general involve the following elements or steps : 1. The reacting molecules are mixed together in space in such fashion as to favor collisions among them. 2. Units of what is usually an intermediate molecular arrangement called an activated complex are formed at a certain rate, depending on temperature and concentrations. 3. .These activated complex units decompose into the reaction products (this step usually assumed to be so rapid as never to limit the over-all process). 4. In any of these steps, heat energy may have to flow into, or away from, the reaction zone to permit the reaction to proceed. 5. The products of reaction will usually have to move out of the way to permit further reaction. The temperature factor enters mainly through step 2, and its effect is very marked. (What is called temperature is really the mean energy content of all the molecules of the substance involved; at any one temperature a certain proportion of the molecules will have much higher energy content than the mean value.) Various reaction rates measured at around room tem-

Jan 1, 1964

By J. C. Humbert, J. F. Elliott

The solubility of nitrogen in liquid pure Fe, Cr, and Ni, in liquid Fe-Ni, Fe-Cr, and Ni-Cr alloys and Fe-Cr-Ni alloys, has been measured by the Sieverts' type apparatus between 1500° and 1800°C. Tabulations and graphs of the solubility data and activity coefficients are shown. Heats of solution are reported. Interaction coefficients of the several elements in Fe. Cr, and Ni ave also reported. THE solubility of a gas in a liquid metal is usually measured by either the quenching technique or the so-called Sieverts' method. In the quenching method, 1-3 the melt is equilibrated at the desired temperature and pressure with the gas phase having a known fugacity of the gas being studied. The melt is sampled and the sample is quenched and analyzed chemically for its gas content. In Sieverts' method the melt is contained in a closed chamber. The apparent volume of this chamber, i.e. the "hot volume," is usually determined by introducing a known quantity of an inert gas having very closely the same physical characteristics as does the experimental gas. Alternatively, the experimental gas is used with an inert specimen having the same general physical characteristics as does the experimental melt. Subsequently, the experimental melt is equilibrated with the experimental gas by introducing a known quantity of the gas into the calibrated chamber. The solubility of the gas is obtained from P-V-T relationships. The quenching method suffers from' the limitation that some gas may be gained (as in the case of Cr-Fe alloys) or lost (as in the case of Fe-Ni alloys) during solidification and cooling of the sample. With Sieverts' method sampling and analysis are unnecessary. However, errors can result from the difficulty of determining accurately the "hot volume,"

Jan 1, 1961

By Jack A. Simon, M. E. Hopkins

GENERAL GEOLOGY Coal is defined as a combustible rock that originated in the accumulation and physical and chemical alteration of vegetation. Coal can be ignited and burned like the wood that was man's earliest fuel, but coal gives more heat than the same amount of wood and has many industrial uses. Unlike wood, coal is not generally found on the surface of the ground but is mined from the solid rock of the earth. Before taking up the occurrence, formation, and the unique character of coal in the rock sequence, let us briefly consider the general character of all rocks in the crust of the earth. Relatively little is known about the very earliest history of the earth, although a number of logical theories have been developed. Manned exploration of the moon and the rocks returned to earth continue to provide some answers to questions concerning the earth's origin and history. The period of earth history with which we concern ourselves here begins after great areas of water had evolved on earth and substantial land areas of once molten (igneous) rock existed. Weathering and other processes that attacked the surface of the rocks reduced them to small particles. Water provided by rainfall transported this material, ultimately, to large bodies of water where it was deposited. Thus was initiated the geologic sequence of sedimentary rocks that lie above the once molten igneous rocks. The crust and upper mantle of the earth are made up of several large plates along which differential movement (primarily horizontal) takes place. Such movements, although small, are occurring today. These horizontal movements are accompanied by vertical movements causing important changes in the relative position of the continents and oceans. Low-lying coastal swamps with favorable climates are ideal locations for coal accumulation and burial by river-borne sediments, and large areas

Jan 1, 1981

By F. R. Hensel

Up to the present time few attempts have been made to produce hard nonmagnetic materials by heat treatment of austenitic steels. The usual result has been to cause them to pass into the martensitic stage, thus destroying to a great extent the typical austenitic properties, since this involves a transition of a portion of the iron from a face-centered to a body-centered type of atomic arrangement. High-strength nonmagnetic materials such as might be provided by properly hardening austenite are required in the electrical industry for different machine parts. In Europe nonmagnetic retainer rings for restraining the end-turns of the rotor windings in turbo-alternators have been developed as a special application of high-strength austenite. In testing1 a 28,000-kva. three-phase Siemens turbogenerator running at 3000 r.p.m. at full load current, the losses in the short-circuit test were 450 kw. for the magnetic ring and 286 kw. for the nonmagnetic, and the difference should be attributable to the magnetic ring. The differences in temperatures during the same test are given in Table 1 and these show the advantage of a nonmagnetic over a magnetic retainer ring. Hardening in this case was obtained by cold working, such as hammering, rolling or some means for stretching the steel while at a temperature near 500" C. One means for stretching2 is to rotate the forged or rolled ring in a centrifugal machine so as to develop within it stress higher than

Jan 1, 1931

By P. K. Koh, L. S. Birks, J. M. Siomkajlo

Direct identification in situ of x and a phase precipitates in stainless steel is possible with the electron probe microanalyzer. Although particles in the 1 p size range are too small to yield absolute percent composition, the relative % Crfi Mo ratio can be used to distinguish the two phases with better than 95 pct confidence. Wet chemical analysis of extracted residues gives Cr/Mo ratios in good agreement with electron probe results extrapolated to the 4 to 5 p size range. WHEN stainless steels are subjected to extended heating in the temperature region around 1600°F, precipitation of the brittle 0 or x phases may occur and impair the properties of the material. Identi-

Jan 1, 1961

By Norman Patton

THE subject assigned is so broad that thorough discussion is well-night impossible within the space allotted, and further, few specific data are available upon which to predicate conclusions concerning the efficiency of present methods of distributing anthracite. This paper treats briefly the various agencies through which both primary and secondary distribution are effected, the methods of transportation and the general interrelation of production, demand, inventories and price. AVENUES OF DISTRIBUTION "Three distinct types of primary distribution are common in the marketing of anthracite. First, though not most important, is the sale by the producer, or operator, direct to the consumer. These sales, other than to employees and the local trade, are generally confined to steam sizes for industrial uses, and are consigned to the sidings or docks of the consumer. Sales of this type often are so closely priced to compete with oil and bituminous that the addition of even a small dealer's margin is sufficient to increase the cost to the point where the business might be lost. Second, the operator sells to a wholesaler or broker for subsequent resale, either to a retail dealer for clearance through his yard or direct to large consumers. Usually this method of distribution is employed by the smaller operators, who do not find it economically feasible to maintain extensive sales organizations. In most instances, the wholesaler retains some 5 per cent for his services, paid, of course, by the producing company whose anthracite he handles. He may, and frequently does, handle the output of several different companies, suited to the varying needs of the

Jan 1, 1935

By C. W. Washburne

Continued discussion of the paper Of ROSWELL H. JOHNSON, presented at the New York meeting, February, 1015, and printed in Bulletin No. 98, February; 1915, pp. 221 to 226. See also Bulletin No. 101, May, 1915, pp. 1157 to 1162, and No. 103, July, 1915, pp. 1449 to 1450. C. W. WASHBURNE, New York, N. Y. (communication to the Secretary*).-Mr. Johnson recognizes that connate waters must be driven, outward toward the earth's surface. He considers the ascent due to the settling and packing of the underlying sediments and to the formation of gas within the rocks, supplemented by abyssal pressures. The origin of the methane in the sedimentary strata probably is not simple. There are three possible modes of origin: (1) as marsh gas formed near the surface and entrapped in the sediments; (2) from abyssal sources; (3) by the decomposition of organic matter buried in the sediments. The abyssal source is generally negligible, and in all cases doubtful. The third origin is the most important in the gas fields. A fourth mode of origin, by the dissociation of liquid hydrocarbons, frequently has been suggested, but it is improbable, because crude oils are exothermic. Therefore they have no tendency, to split or decompose at low temperatures, as do endothermic substances, such as coal, which is geologically by the loss of methane, water, and carbon dioxide. This cannot happen to a hydrocarbon until its temperature of dissociation (" cracking point") is reached, which is over 250'.C. for the most easily cracked hydrocarbons and over 400° C. for others. Engler says that the dissociation of fats and waxes into oils is an endothermic process, thereby unconsciously nullifying his own theory of the dissociation of these substances at low temperatures. However, recently I have found reason to think that heat is liberated by the disruption of the molecules of fats and waxes, as it is in the molecular decomposition of the substances of wood, coal, etc. If this tentative opinion is correct, and Engler wrong, then it seems that the Engler-Höfer hypothesis of the origin of oil becomes not only possible, but even probable.

Jan 9, 1915

Discussion of the paper of W. A. Forbes, presented at the New York Meeting, October, 1913, and printed in Bulletin No. 82, October, 1913, pp. 2477 to 2514.. SAMUEL K. VARNES,* Steelton, Pa.:-We have a gas-cleaning plant consisting of a, centrifugal dry dust catcher, and two rain-type wet scrubbing towers, 25 by 60 ft. each, for rough cleaning of blast-furnace gas. This plant was put in early in 1910, with the intention of cleaning gas for use in hot blast stoves and under boilers, and was so used for several months. Soon after it went into service, the blast-furnace men complained that they could not get as high blast temperatures as they had obtained when using dirty gas. It was decided to run a series of careful tests to determine if this were true and to what degree the apparent results might be affected by other conditions. About 60 tests were run, covering a period of five months, and at the end we came to the conclusion that it did not pay us to scrub the gas for stoves and boilers. The tests were all run upon a single stove, no boiler tests being made, but the conclusions of the stove tests being applied to the boilers. The furnace burden was practically the same for all the tests and averaged: Per Cent. Daquari and other hard ores 57 Nodules 13 Raw Mayari ore 25 Mill cinder and scale 5

Jan 12, 1913

By Roland Kammel

For electrolytic recovery of silver from dilute aqueous solutions improved mass transfer is necessary to achieve favourable current efficiencies and high space-time yields. The many cell designs proposed for this application can be divided into two different groups: cells from which the silver must be redissolved and cells from which the deposit can be reclaimed as a metal. Introduction Electrolytic silver recovery methods have proven advantageous under technical and economic aspects for the treatment of rinse water, still rinses and spent silver solutions in the electroplating and surface finishing industry, of exhausted fixing baths from photographic processing, bleed electrolytes from silver refining processes and leach liquors. Examples of the compositions of typical dilute silver solutions are listed in Table I.

Jan 1, 1984

By D. J. McAdam

In 1917 Haighl presented evidence that under simultaneous corrosion and cyclic stress metals may fail at lower stresses than if the corrosion is prior to the cyclic stress. In 1926 the author, while investigating the cooling effect of water on the fatigue resistance of metals, found that under these conditions steel specimens fail at stresses far below the endurance limit.2 (By "endurance limit" is here meant the fatigue limit obtained with specimens as free as possible from stress concentration and corrosive influences.) This led to an investigation (at the Naval Engineering Experiment Station, Annapolis, Md.) of the influence of cyclic stress on corrosion. This investigation may be divided into three parts. The first part was a general survey of the conditions necessary to cause complete failure under corrosion and cyclic stress of relatively high frequency. The entire process by which metals fail under these conditions was called LLcorrosion-fatigue." Corrosion-fatigue limits" for a large number of metals were determined and the relationships of these limits to chemical composition, heat treatment and physical properties were established. The conclusion was reached that corrosion-fatigue is due to the accelerating influence of cyclic stress on corrosion. Results of this part of the investigation were presented in five papers.*-= The second part of the investigation was a preliminary study of the influence of cyclic stress on corrosion. Each experiment was conducted in two stages. The first was a corrosion stage in which the specimen was corroded under cyclic stress; the second was a fatigue stage, in which the previously corroded specimen was tested (without further corrosion) to determine its fatigue limit. The difference between this fatigue limit and the endurance limit was used as a criterion of the "damage" due to

Jan 1, 1932

United Engineering Society WALTER H ALDRIDGE J VIPOND DAVIES I V N DORR Engineering Societies Library Board SYDNEY H BALL ALEXANDER C HUMPHREYS GEORGE C SLONE JOHN H JANEWVAY Engineering Foundation Board H M BOYLSTON J VIPOND DAVIES GALEN H CLEVENGER Society for Promotion of Engineering Education WILLIAM KELLY ALLEN B ROGERS American Engineering Standards Committee GRAHAM BRIGHT GEORGE C STONE GEORGE E THACKRAY Alternates-RICHARD L LLOYD and HARLOWE HARDINGE

Jan 1, 1923

By Frank Wilder

THE most important process in a gypsum mill is calcining the crude mineral. There seems, however, to be little progress or change in calcining methods. This would not be surprising if the industry was not, in other ways, developing. The demand for gypsum in its various forms, however, is growing rapidly. The output has more than doubled in six years, while the value of gypsum products, through the introduction of higher priced specialties like wall board, has nearly trebled in the same period. In other industries, under somewhat similar conditions, calcining in rotating cylinders, either by direct or indirect heat, has replaced the method that still prevails in gypsum mills. Efforts were made to use rotary calciners in manufacturing plaster of Paris in the early days of the industry in America; 25 years ago rotary calciners were in use in Germany. At that time there was great diversity of opinion in regard to their merit. In 1923, the output of calcined gypsum in the United States was 3,101,378 tons. About nine-tenths of this material was calcined in kettles, the remainder in rotary calciners. The ratio was about the same 10 years ago. During these 10 years, rotary calcining made rela-tively no gains, and there were no important changes in the construction of kettles. In their manipulation, the only change of consequence was in connection with the length of time that the gypsum is left in the kettle. For wall-plaster purposes, all producers who had not previously done so changed from second-settled to first-settled calcined gypsum, thereby reducing production costs and improving the plasticity and sand-carrying capacity of their plaster. Nevertheless, in the few mills in which they were installed, rotary calciners continue to operate, with possibly one or two exceptions, and to be highly successful. In these 10 years, the Cummer type of rotary calciner has disappeared. All rotaries now used are of the cement-mill type with a diameter of 6 or 7 ft. and length of 80 to 120 feet.

Jan 2, 1925

By W. H. Adams

During the years when Americans were most active in investigations of the many substances containing nitrogen or ammonia, viz.: 1869 to 1875, my connection with certain chemical industries led me to experiments in the direction of the recovery of wastes from coal-gases. I take from my notes such memoranda as I think will be of interest, in the hope that some benefit may be derived therefrom by engineers at present attempting to utilize the waste products from coke-oven and blast-furnace gases. An examination of the conditions governing the manufacture of gas along the Atlantic seaboard, and an intimate knowledge of the mine-products used by the different large works, naturally led me at first to consider the well-known foreign methods of concentrating the available soluble salts in a modicum of water. The result was sufficiently promising to warrant a full line of experiments. At that time, no attention seemed to have been paid to the values of " gas-liquors." Nearly every gas-works in the United States wasted its wash-water in the sewers. The nitrogen in bituminous coals varies in quantity from 0.75 to 1.50 per cent. of the total weight. In the process of distillation in

Jan 1, 1887

By T. A. Dungan

The thermal processes for the production of metallic magnesium can be divided into two general classifications, the direct reduction of magnesia with carbon and the indirect reduction of compounds of magnesium by reducing agents that are themselves products of carbon reduction. The latter are so chosen as to cause reduction of magnesium compounds wherein only the magnesium is liberated in the vapor phase. Reducing agents used are: calcium carbide, silicon carbide, silicon, aluminum, various silicides or combinations of calcium, aluminum, silicon in iron. All of these are products of highly endothermic reactions and, with the exception of scrap aluminum, can be produced in an open, submerged arc furnace; that is, the arc is covered only by the charge itself. The more investment in energy required to prepare such a reducing agent, the less is the energy required in the subsequent step to reduce the magnesium compound to the metal. It is impossible, however, to avoid the laws of thermodynamics, no matter how much circumambulation is resorted to in the preparation of successively more powerful reducing agents. Since each such step carries forward its own inefficiencies, it appears evident that the ultimate status of such processes is dependent upon the development of by-products. The direct reduction of magnesium oxide by carbon has a decided appeal to both the scientist and the industrialist. The successful production of the carbo-thermic plant at Permanente is a significant fact in the substantiation of this concept. Like most developments, however, the history of carbon reduction of magnesia is not one of triumph after triumph, or immediate heady success to the investigators. It is understood that one of the early investigators conducted an experiment wherein he placed carbon and magnesia in one end of an evacuated tube and managed to heat this end to a temperature high enough that magnesia and carbon deposited at the other end of the tube. The charge, unreduced, appeared to have been completely transported from the hot to the cold end of the tube. This raised doubt for some time as to whether magnesia could be reduced at all with carbon. It was correctly suspected, however, that the magnesia was in fact reduced and the resultant magnesium vapor and carbon monoxide reacted upon one another upon reduction in temperature to reform the starting ingredients. Attempts were then made to dilute the two vapors by passing a considerable stream of hydrogen through an arc furnace charged with magnesia and carbon. Thus by dilution of the products it was' expected to obtain metallic magnesium. The results were positive and metallic magnesium was .0

Jan 1, 1944

By R. L. Bleifuss

The object of this study was to evaluate the oxidized taconites of the western Mesabi iron range and to establish a correlation between the various basic taconite types and their concentratability. The initial work included a study of the original mineralogical and stratigraphic facies of the fresh taconite and traced the oxidation and leaching patterns developed during the conversion of this material to oxidized taconite. Subsequent studies have extended this work to include the semitaconites and also the wash and heavy media ore types widely developed in the area. Each basic original mineralogical facies or taconite type produces during alteration an equivalent secondary oxidized facies which has a unique mineralogical composition and texture. These control the concentratability of the oxidized taconites. Actually the influence of the original mineralogical composition of the iron formation extends even further and determines whether the most likely product of oxidation and leaching will be a wash ore or a heavy media ore and even to the direct shipping ores where the ratio of hematite to goethite is largely determined by the original taconite type. The relationship between original taconite, oxidized taconite, semitaconites, and wash and heavy media ores is briefly summarized in Table I. The terms are not precise and in some instances tend to overlap. The table is intended to point out only the essential differences between the various materials. The original taconite was dominantly composed of mixtures of magnetite, iron carbonate, iron silicate, and quartz (chert). In a few thin stratigraphic units, hematite was present as an original constituent. The alteration of the original taconite to oxidized taconite has resulted from the circulation of ground waters through an initial fracture system related to minor structures in the iron formation. The chemical reactions have involved the oxidation and decomposition of original minerals such as magnetite, iron carbonate, and iron silicates to hematite or goethite. The alteration at this early stage is characterized by pseudomorphic replacement of the original minerals by oxidation products although retaining the major textural features of the original taconite. There was very little secondary migration of iron at this stage and the total iron content of the rock has been only slightly increased. Further alteration of this material to form a semi-taconite, a wash or a heavy media ore, involves extensive removal of silica in solution and significant redistribution of iron units. Wash and heavy media ores are developed by the growth of coarse secondary iron layers, dominantly goethite, coupled with the removal of silica in solution and decomposition of the cherty layers. This paper is concerned primarily with the materials classified as oxidized taconites which are characterized by oxidation of the original mineral constituents with little secondary enrichment. The area studied, shown on the index map, Fig. 1, extends some 30 miles along the strike of the Biwabik formation roughly from Hibbing to Coleraine. This study was greatly facilitated by the basic stratigraphic and mineralogical studies of Gruner1 and white2. The bulk of the material in this presentation represents a portion of the author's contribution to a study sponsored by the Great Northern Railway on the oxidized taconites of the western Mesabi.3 METHOD OF APPROACH A total of 106 drill holes, representing some 30,000 ft of drilling, were examined and sampled. The drill holes were logged and some 1500 composite samples were prepared for chemical analysis and bench scale metallurgical tests. These samples were analyzed for total iron and ferrous iron; and magnetite iron was determined by a standard Davis tube test at minus 200 mesh. Standard reduction roast tests using 150-gram samples of minus 10 mesh material were made on these 1500 composite samples with a mixture of H2, CO2, N2, and H2O at a temperature of 650°C. This roasted material was pulverized through 150 mesh and concentrated in the Davis tube. The iron recoveries and concentrate grades obtained on the roasted products were used to assess the concentratability of the oxidized taconites. Detailed mineralogical work was done on thin sec-

Jan 1, 1964

By J. M. Roberts, N. Brown

The stress-strain behavior of zinc single crystals was measured over a strain range of 10-6 to 10-2. The phenomenon of macroyielding was observed in detail and plastic strains were detected at almost zero-stress. Closed hysteresis loops were observed during loading and unloading in the strain region of about 10-5. From the hysteresis a frictional stress on the dislocation of about 6 psi was obtained. A preliminary analysis indicates that impurities are primarily responsible for the friction. Nonelastic Strains as much as 10 -4 were recovered depending on the amount of prior deformation. Part of the recovered strain occurs instantaneously upon unloading and the remainder occurs at zero stress. The time dependence of the recovered strain was measured. THIS investigation is concerned with the details of plastic deformation preceding the ordinary yield point as measured with the usual strain sensitivity of about 10-4. The approach leads to internal friction observations in the hitherto neglected frequency range below 10-1 cycles per sec. It is believed that if the phenomenon of macroscopic yielding is to be understood, then the stress-strain curve in the neighborhood of the macroyield point should be greatly magnified. It may then be possible to determine whether macroscopic yielding is a unique event or whether it is a process which begins gradually at a lower stress. In the case of low-carbon steel a unique event obviously occurs at the macroscopic yield point as indicated by a drop in the load, but copper appears to exhibit a gradual transition from the elastic to the plastic state. In zinc the yield point is rather abrupt although the data indicates that some plastic deformation precedes large scale yielding.' One of the purposes of this investigation is to determine whether there is an abrupt transition from the preyield microstrain region to the region of macroscopic deformation. Such a rapid transition would support the concept that there is a critical stress for yielding. The concept that yielding is a unique event associated with such phenomenon as activating a Frank-Read source, freeing the dislocation from solute atoms, dislocations cutting through dislocations, or dislocations moving freely by one another, has been expounded widely on theoretical grounds. It is hoped that highly sensitive measurements of strain in the neighborhood of the macroscopic yield point will shed some light on the event known as the "Yield Point". EXPERIMENTAL METHOD 1) Specimens—High-purity zinc was cast into spherical graphite moulds in air and grown into spherical single crystals by the Bridgman method under a positive pressure of Argon gas. Spectro-graphic analysis of cleaved sections from four crystals showed a purity of 99.994 pet Zn. The specimens were acid machined with an 1/8 in. gage section in a form similar to those used by Parker and co-workers.2 Bausch type grips were fastened to the specimen by Epon VI adhesive. The specimens were oriented so that only [1120] (0001) slip occurred. Fig. 1 shows two of the specimens in the grips. Prior to each test, the gage section of the specimen was given a concentrated HNO3 chemical polish followed by alcohol rinsing and air blast drying. 2) Test Method- The shear tests were performed on an Instron testing machine and the experimental set-up was made very "hard". Strain could be measured to a sensitivity of 10 -6 by means of a capacitance gage extensometer. The design and calibration of this type of extensometer to measure microstrain, as applied to pure shear and tensile tests of metals, will be the subject of a separate paper—therefore, only a brief account will be presented here. The method essentially consists of attaching a

Jan 1, 1961