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By Joseph D. McClung, L. G. Austin

INTRODUCTION Run-of-mine (ROM) coal generally falls into two major groups, that from underground mining (continuous mining machines) and that from strip mining. Continuous miners produce a finer product and strip mining a coarser product that is crushed to produce the desired size. Further size reduction depends on the proposed use or uses for the coal. For example, for pulverized coal power plants as a rough general rule, the coal is ground or pulverized to 80% less than 200 mesh (0.075 mrn) before it is blown into the boiler furnace as a coal-air suspension. For solvent-refined coal processes, the desired size is about <30 mesh ( <0.60 mm) ; in fluidized bed uses, the coal is typically < in. ( < 1.6 mm); for Lurgi pressure gasifiers, the desired size is 1-2 1/2 in. (25-63 mm). Coal preparation plants typically work with a coarse size fraction of 6x1 1/4 in. (15Ox32mm). It seems probable that the next decades will see much wider application of coal cleaning before use and that the stages of crushing and pulverization from ROM coal to end use will be integrated with coal cleaning processes. Since different cleaning processes work better with different ranges of coal size and the degree of cleaning possible is inti-

Jan 1, 1979

By G. E. Anderson

THE Asientos-Tepezala district is in the north of the State of Aguascalientes, about 30 miles north of the city of Aguascalientes, the capital. The district is reached by a standard-gage railway on the west side through the junction, Rincon de Romos, which is on the main line of the National Railways of Mexico from El Paso to Aguascalientes. The terminal is Tepezala. On the east side a narrow gage connects Asientos with the junction, San Gil, on the main line, Asientos to San Luis Potosi. Tepezala on the west side of the Asientos hills is about 2 miles from Asientos on the east side. The area between the two mining centers is separated by a low subued divide which forms the central part of the hills. The district is in a group of isolated hills surrounded by characteristic bolson plains. The hills rise above the surrounding plains about 6500 to 10,000 ft.; the highest peak is Alta Mira. The two mining districts lie somewhat upon the flanks of the hills at about the same elevation, 7200 ft. The district is an old one and has been known since early in the 17th Century when the mines were worked by the Franciscan Monks. Their mining operations which were limited to the oxidized ore above the water level, consisted chiefly in extracting silver from the Santa Francisca vein. To judge from the old workings and the remains of surface plant, the operations were on a large scale. By modern mining operations since about 1900, the various mines of the district have been one of the principal sources of ore for the smelter located at Aguascalientes.

Jan 2, 1926

By John Norton

IN spite of the very general employment of nitride hardening, there is still considerable doubt as to the real nature of the mechanism involved. Experience has shown that the addition of small amounts of hardening elements to iron or steel results in a wide variety of desirable properties in a nitrided case. Perhaps the foremost of these elements is aluminum and in this investigation an attempt has been made to study the behavior of aluminum during the hardening process. It is believed that the establishment of a complete atomic picture of the metal at various stages of the process will indicate the relationships between the several kinds of atoms and their individual influences on the physical properties in a clear and direct fashion. A consideration of the problem suggests a surprising similarity between the mechanisms of nitride hardening and of age-hardening. It is now generally understood that age-hardening may take place by one of two distinct processes, the first involving the precipitation of a finely dispersed phase and the other being concerned with the modifica-tion of an existing phase. Following much the same line of reasoning, two theories of nitride hardening have been suggested. The first expla-nation, which has been generally discussed, particularly by Fry,1 states in brief that the presence of aluminum causes the precipitation of alumi-num nitride during nitriding and that this finely dispersed phase is the primary cause of hardening. The second explanation, which has not been published but which has been freely discussed by those interested in the problem, postulates the substitution of aluminum atoms for certain of the iron atoms in the several iron-nitrogen phases in the same manner that the substitutional iron-aluminum solid solution is formed. The marked increase in hardness, as compared with the aluminum-free

Jan 1, 1934

By W. L. Honnold

(San Francisco Meeting, September, 1915) OWING to a unique labor situation and other unusual circumstances, the mining methods of the Rand are hardly comparable with practice elsewhere. They are&apos; of considerable interest, however, and their impor-tance is increased by the magnitude of the industry with which they are identified, gold of $166,186,000 value, say 40 per cent. of the world&apos;s production, having been recovered from 25,701,954 tons of ore milled in 1914. In the sketchy remarks to follow, attention will first be drawn to some influential factors of general bearing, after which certain features at two mines of the writer&apos;s group will be referred to. It is hoped that engineers associated with similar or different conditions and practice will contribute to broaden the discussion. Before proceeding, recognition is due the generous assistance of C. E. Knecht and F. A. Unger. GENERAL OBSERVATIONS The principal mines are situated along the northern limit of an irregularly shaped geological basin, and extend in almost unbroken continuity over a distance of about 60 miles. As the boundaries are defined by vertical planes there are both "outcrop" and "deep-level" properties, all differing in size and in technical features. So much has been written in regard to the geology of the Rand that only a few pertinent features need here be recalled. Briefly, the ore deposits are profitably enriched portions of certain conglomerate beds or "reefs," rarely more than three, which are interposed between quartzite, or quartzite and slate, and lie so closely together that where more than one are mined they are dealt with as a work-ing unit, although they may lie stoped separately. Their collective extension is locally referred to as "the Reef."

Jan 8, 1915

By G. R. St. Pierre, L. M. Adelsberg, R. Speiser

The rate of scale fot&apos;~I~ti0n on tantalum held in H20-Hz-Ar gns mixtures at temperatures between 840" and 1250°C is related to gas composition and ternpevature. It is found that water vapor partial pressure determines the oxidation rate at a given temperature and that the oxygen potential as fixed by the water vapor to hydrogen ratio Ins no significant effect on the oxidation rate. The Ta205 scale formed during oxidation is composed of an inner lattice-dijf~ision barrier and an outer layer of- cracked/porous oxide 1 HE oxidation of tantalum at temperatures less than 800°C is characterized by solution of oxygen into the metal,&apos;-&apos; the formation and growth of suboxides into the metal,&apos;)2~10-15 and the delayed nucleation of the highest oxide, Above 800°C, Ta205 is found to nucleate rapidly10, 11, 15, 16 except at low oxygen pressures:15 however, there is uncertainty regarding which does not retard the oxidation process. For each gas con~position and temperature investigated, the oxidatioz rate becomes constant after a short adjustment period. It is shozm that a constant oxidation rate nzay pre~?ail even though the tlzickness of the inner lattice-dijjitsion layer of Ta205 is clanging. TFze initial czcrz!ature of the typical &apos;Paralinear" oxidation curve may result froprz causes other than an increasing thickness of tlze inner protective layer. the detailed mechanisms of the high-temperature oxidation. Peterson, Fassell, and wadsworth17 observed linear oxidation behavior for tantalum in oxygen at temperatures between 600" and 1000°C. They reported that equilibrium adsorption of 0, occurs on a surface prior to the rate-deter mining step of the reaction. Cowgill and stringer1&apos; confirmed the observations of Peterson and his coworkers. They stated that the rate-determining step of the reaction could be either the incorporation of adsorbed oxygen into the anion lattice or the dissociation of 0, at the gas-oxide interface. The relative rates of the two surface reactions were proposed to be dependent upon the reaction temperature and the oxygen pressure. stringerlo subsequently reported that the reaction surface is located somewhere

Jan 1, 1968

By I. R. Kramer, P. D. Gorsuch, D. L. Newhouse

Although many methods have been suggested for the calculation of tensile strength and yield point from chemical composition, their usefulness has been limited to a particular cooling rate or section size. Further limitations have been imposed by failure to take into account many of the alloying elements that exert a considerable influence on the tensile strength or yield point. These systems, nevertheless, have filled an important need in many instances. The value of a system for the calculation of the tensile properties from the chemical composition and cooling rate is that it permits the prediction of the effect of alloying elements and heat-treatment on the mechanical properties, so that more efficient use of alloying elements may be made. Furthermore, it aids in the choice of steel for a given application aid tends to decrease the number of steels that otherwise would have to be tested. It is the purpose of this work to present a method of calculating tensile strength and yield point from the chemical composition and to suggest a method of correlating the tensile-strength and yield-point factors and cooling rate. Steelmakers have been interested for many years in the calculation of the tensile strength of hot-rolled steels. Quest and Washburn&apos; summarize several of the attempts that have been made to devise formulas. They show the inadequacy of each of these formulas and present one of their own. It is apparent from their work that a simple additive equation of the type TS = A + BX + Cy + DZ + . . . , where A, B, C, D, etc. are experimentally determined constants and x, y, z, etc., are the percentages of alloying elements present in the steel, is not adequate to analyze fully the situation encountered in the calculation of tensile strength. For example, it was found that the difference between the calculated and observed values became progressively greater as the carbon and manganese contents were increased. Therefore, the effect of manganese was given as a function of the carbon content. Grossmann, in his work on the harden-ability of quenched steels, and Walter, in his method of calculation of tensile strength of normalized steels, present two cases in which multiplying factors were successfully used to express the combined effect of alloying elements. The factors in both cases were obtained from the fractional increase in hardenability or tensile strength with increase of alloy content. Yield point often is more important in design than tensile strength. For quenched and tempered steels a linear correlation exists between yield 2nd tensile strength.4 This is not true, however, for normalized

Jan 1, 1948

By C. S. Sivil

To modern civilization the platinum metals are of inestimable value. Their distinctive properties, both physical and chemical, render them indispensable in an age in which the processes of the laboratory are becoming an essential part of the daily life of the world. Generally, their function, though vital to particular processes, is not spectacular, and so remains unknown to all except the operators. Early Methods of Manufacture The properties of platinum were recognized as of prime importance for scientific work at a very early date, probably between 1750 and 1760. The difficulty of making articles from it seemed almost insurmountable, because no means of attaining the temperature necessary to melt it were known at that time. It is true that solid platinum could be obtained by fusing the metal with a more volatile metal such as arsenic, which was subsequently driven off by baking, but such a method, at its best, would give only a very brittle product, which was totally unsuitable for the purposes for which it was intended. Little, if any, progress could be made until it was discovered that platinum sponge, heated to white heat and hammered in an iron or clay mold, would metallize and retain the shape of the mold. This was a process that could not be wholly satisfactory but from it developed the method of pressing the sponge in a mold and forging it at white heat into wire or sheet. At present a somewhat similar process must be used for fabricating articles of tungsten, molybdenum and other metals of high fusing point, as with these metals we face today the same problems that the scientists of the eighteenth century encountered with platinum, but possibly the next significant advance in the metallurgy of these metals will be the devising of means to melt and cast them. TO some extent this method of preparing platinum has survived, particularly in Europe. There are one or two objections to it, but they are not serious, as they can be surmounted with proper precautions. In the first place, the material is spongy and its millions of cavities contain entrapped air. Unless this is removed by thorough forging above 1000" C. the resultant sheet shows blisters. To give such a thorough forging,

Jan 1, 1931

By P. D. Gorsuch, I. R. Kramer, D. L. Newhouse

Although many methods have been suggested for the calculation of tensile strength and yield point from chemical composition, their usefulness has been limited to a particular cooling rate or section size. Further limitations have been imposed by failure to take into account many of the alloying elements that exert a considerable influence on the tensile strength or yield point. These systems, nevertheless, have filled an important need in many instances. The value of a system for the calculation of the tensile properties from the chemical composition and cooling rate is that it permits the prediction of the effect of alloying elements and heat-treatment on the mechanical properties, so that more efficient use of alloying elements may be made. Furthermore, it aids in the choice of steel for a given application aid tends to decrease the number of steels that otherwise would have to be tested. It is the purpose of this work to present a method of calculating tensile strength and yield point from the chemical composition and to suggest a method of correlating the tensile-strength and yield-point factors and cooling rate. Steelmakers have been interested for many years in the calculation of the tensile strength of hot-rolled steels. Quest and Washburn&apos; summarize several of the attempts that have been made to devise formulas. They show the inadequacy of each of these formulas and present one of their own. It is apparent from their work that a simple additive equation of the type TS = A + BX + Cy + DZ + . . . , where A, B, C, D, etc. are experimentally determined constants and x, y, z, etc., are the percentages of alloying elements present in the steel, is not adequate to analyze fully the situation encountered in the calculation of tensile strength. For example, it was found that the difference between the calculated and observed values became progressively greater as the carbon and manganese contents were increased. Therefore, the effect of manganese was given as a function of the carbon content. Grossmann, in his work on the harden-ability of quenched steels, and Walter, in his method of calculation of tensile strength of normalized steels, present two cases in which multiplying factors were successfully used to express the combined effect of alloying elements. The factors in both cases were obtained from the fractional increase in hardenability or tensile strength with increase of alloy content. Yield point often is more important in design than tensile strength. For quenched and tempered steels a linear correlation exists between yield 2nd tensile strength.4 This is not true, however, for normalized

Jan 1, 1948

By K. H. Adams, T. Vreeland

The basal stress-strain behavior, dislocation density, and strain vale sensitivity of the flow stress uqere measured at room temperature on single crystals oj-zone-refined zinc , 99.999 pct Zn, and zinc containing 0.0025 and 0.02 wt pct Al. No significant change in the stvain rate sensitivity of the flow stress occurs with the addition of aluminum. Changes in dislocation substructure and nonbasal dislocation density were obserrled with the addition of aluminum. The effect of aluminum on the basal slress-strain behavior is explained in terms of changes in nonbasal dislocation density which determines the separation distance of junctions between basal and nonbasal dislocations. The onset of basal slip is associated with the breaking of attractive junctions. The chunge in basal dislocation density was found to be proportional to the one-third power of the plastic shear strain, indepedent of purity. THE effect of impurities in solid solution on the stress-strain behavior of single crystals has been the subject of many theoretical studies. These studies have generally concentrated on the interactions between impurities and dislocations to explain the hardening effeet of impurity additions. The theories that have been proposed include those of yott and Nabarro,&apos;l&apos; Cott-re11; Suzuki; and Fisher. In practice, it is generally difficult to predict the relative importance of the vari- ous effects due to impurities. In addition, secondary effects of impurity additions such as induced changes in dislocation density and substructure in the as-grown crystals have received little attention. Many experimental investigations have been conducted on the effect of impurities on the stress-strain behavior of fcc crystals. Hcp crystals have not received much attention except for the extensive work of Levine et a1.= on magnesium alloy crystals. Stuwe~&apos;&apos; has studied the effect of copper impurity on the critical shear stress of zinc crystals and has interpreted the results in terms of the impurity atmosphere model of Cottrell and Jaswon. This report presents the results of an experimental study of the effect of aluminum additions to zinc on the basal stress-strain curve and the strain rate sensitivity of the flow stress. Etch pit techniques were used to measure and characterize the dislocation density and substructure in the zinc alloy crystals. EXPERIMENTAL PROCEDURE Specimen Preparation. Compression test specimens of four different purities of zinc were prepared from CP grade zinc of 99.999 pct purity obtained from the New Jersey Zinc Co. An analysis of this material furnished by the supplier indicated the following impurities in wt ~ct: Pb = 0.0002; Fe = 0.0002; Cd = 0.00005; other <0.60011. A quantity of material of this grade was further purified by zone refining. Zone refining was carried out under a helium atmosphere by passing a double &apos;One furnace Over a 6-ft-10ng charge at the rate of 2 in. Per hr. * total of ten double zone passes were made before the charge was removed from the furnace. The first one third of each charge was used to grow single crystals. Quantities of two

Jan 1, 1969

By I. R. Kramer

Single crystals of aluminum were pulled in tension in a solution of paraffin oil and stearic acid. The critical resolved shear stress did not change with the concentration of the stearic acid solution; however, the extents and slopes of Stages I and II were affected greatly. The observations lend evidence that the weakening effect of surface-active agents is controlled by the rate of desorption of the metal soap formed by the reaction of the surface-active agent and the metal surface. IT has been shown by various investigators1-" that surface-active agents markedly affect the mechanical properties of single crystals. (A surface-active agent, for the purpose of this report, is defined as a long-chain organic molecule which contains one or more polar groups. Usually, however, investigations have considered only molecules having one polar group.) In general, when single crystals are deformed in some solutions containing surface-active agents, the creep rate, Fig. 1, is increased and the yield strength is decreased. The fatigue strength has been reported to be affected also.ll Rehbinder and his asociatesl&apos; explained the "weakening" effect of surface-active agents in terms of physical adsorption. They assumed that a large pressure was created in microcracks which existed on the surface of the crystal." Harper and Cottrell,&apos; from their study of the effects of surface conditions, found that the deformation characteristics of zinc single crystals were not altered by a solution containing a surface-active agent unless the surface of the specimen had an oxidized surface. They concluded that the role of the polar molecule was to remove the strengthening effect of the oxide coating. Later, And-radeetBpresented additional evidence which appeared to agree with this conclusion. In contrast, Klinken-berg et al.7 reported data which confirmed the results of Rehbinder. Using zinc and cadmium crystals which had been cleaned by electrolytic polishing, a large increase in the creep rate was observed when Lle specimens were tested in a 1 pct oleic acid-paraffin oil solution. They also reported that the creep rate

Jan 1, 1962

By F. H. Parsons

At the time that converting or bessemerizing of copper matte first began to be practiced by the smelters in the copper industry, converters were lined by tamping the flux, usually siliceous ore, into the steel shell. About 1910, practice in several plants had demonstrated the superiority of a basic lining of nonfluxing material and the addition of flux through the mouth of the converter. Adoption of the new method by nearly the entire industry followed. Basic linings are made of refractory "magnesite" brick manufactured, usually, from imported dead-burned magnesite. Either the linings are laid up in the shell dry or the bricks arc bonded with some mortar dictated by the preference of the user. Foreign, usually Austrian, magnesite was the main source of supply for these bricks, although there were domestic sources, but it was not until costs began to rise a few years after the first use of basic linings that these domestic sources were investigated to any great extent. Exigencies created by the World War necessitated the use of the domestic magnesite during this period, but the brick manufacturers reverted to the use of the foreign product after the war, because the impurities therein made a brick with a better fire bond than the purer domestic magnesite. Therefore the domestic product became available at a favorable price for any metallurgical process that permitted its use. The United Verde converting practice using magnesite linings has resulted in a high consumption of magnesite because of the zinc content of the low-grade matte. It was realized that the cost of these linings represented a large portion of the cost of converting, and an investigation was started to find means by which these costs might be lowered. In the neighboring state of California rather pure magnesite was being mined and treated for the market. The product, however, was purposely made to simulate the dead-burned grain magnesite product from foreign sources by the addition of fluxing impurities before burning. It was learned that this dead-burned California grain magnesite could be laid down in Arizona at a price one-third that of the same tonnage of "magnesite" brick manufactured from foreign magnesite. It was also learned that at least one California producer was ready to supply the market with periclase, which was a grain magnesia produced by burning the

Jan 1, 1934

By A. Mitchell, M. Etienne

VARIOUS&apos;-3 reports on the electroslag remelting process refer to the "thin skin of slag" existing around the slag pool and the solidifying ingot, but none considers the various mechanisms by which this layer forms and thus influences the surface quality of the ingot. A vertical section4,5 of the Cao-CaF2-Al2O3 diagram is shown in Fig. 1 between CaF2 and 6Al2.CaO3 From this, it is seen that a typical "70:30" CaF2:A1a3 slag will solidify to produce 6Al2O3.CaO primary phase in a eutectic matrix. The commercial slags contain sufficient CaO to produce* this composition by both the

Jan 1, 1969

By F. M. Walters

IN order to isolate the effect of an element on some property of an alloy, the effect of the other alloying elements must be elimi- [ ] nated, either by reducing their quantity to the extent that they may be neglected or by determining the specific effect of each. The success of Grossmann1 in calculating [ ] hardenability from chemical composition by means of factors suggested such a

Jan 1, 1942

By Francis Foley

Small cracks in a plane normal to the axis of steels are found to be prevalent around the water hole of drill steels that have been in service for an unknown period of time. Cracks are not found on the exterior surface of the steels nor to any noteworthy extent even in the water holes of new drill steels. Undulations and serrations are found in the surface of the water hole in new steels; it is in the bottom of such defects that cracks appear to develop in used steels. The occurrence of the more serious of these cracks at the point in the steel to which it has been heated for forging or hardening is thought to account to a great extent for failures in that region. DURING the past, year, we have investigated the cause of 88 per cent, of the failures by breakage near the bit end of some 1-in. hollow, hexagon, drill steel used in a metal mine. This breakage in the region of the bit end of the steel was peculiarly interesting because we have been led to believe that breakage is most prevalent at the shank end of drill steels near the place where the steel is gripped in the chuck of the machine. Records from the mine showed, also, that the breakage was much more frequent in the short lengths of large gage than in the longer steels; this is shown graphically in Fig. 1. Because the shorter lengths of steels are usually those that have been made from broken pieces of long steels or from steels that have worn down in service, rarely being made from new stock, those who are wont to suspect steel of tiring and crystallizing in its old age through fatigue are quite apt to see in this instance an argument in favor of their idea. As usual, a careful examination of these steels reveals defects of a character hardly to be overlooked in favor of such a cause. The steel in question was rolled with a sand core and was of the usual drill steel composition: Carbon 0.85 per cent., manganese 0.60 per cent., silicon 0.25 per cent., phosphorus 0.02 per cent., and sulfur 0.02 per cent., with the exception that in some specimens there was vanadium, not exceeding 0.20 per cent.

Jan 3, 1924

By P. M. Robinson, M. B. Beaer

The heat of formation at 0°C of the intermetallic compound AgMg as a function of composition has been determined by tin-solution calorimetry. In this technique, the heat of formation is determined as the difference in the heat effects, at infinite dilution, on dissolution of the compound and a mixture of its components added alternately to liquid tin from a reference temperature, such as 0°C. The experimental technique and method of calculation have been described elsewhere.&apos; The compound AgMg is a 0 electron compound with a CsCl structure.2 In nonstoichiometric compositions of the compound, atoms of the excess component are substituted on the AgMg lattice.3,4 The homogeneity range is approximately 43 to 52 at. pct Mg at room temperature and 38 to 65 at. pct Mg at 500Oc.2 Single-phase alloys outside the homogeneity range at room temperature can be prepared by quenching. The specimens used in this investigation contained from 39.0 to 54.8 at. pct Mg. They were made available, together with analyses, by the Research Laboratory of the General Electric Co. Metallographic examination of the quenched specimens containing 39.0 and 54.8 at. pct Mg gave no indication of the presence of a precipitated phase. The measured heats of formation are listed in Table I. In a calorimetric run, four to six additions each of a specimen and the corresponding mixture of the components were made. One or two calorimetric runs were carried out with each composition depending on the amount of samples available. The limits stated in the table represent the experimental precision and not the absolute accuracy of the measurements. Thermodynamic investigations of the compound AgMg have been made by Trzebiatowski and Terpilowski 5 and Kachi.6,7 The heats of formation at 500°C derived from the combined electromotive-force values of these investigators8 are more exothermic than the heats of formation at 0°C reported here, Fig. 1. The differences cannot be explained by the difference in temperature. This is shown by the published heat capacity of the stoichiometric compound, which obeys the Kopp-Neumann rule from 0" to 500oC.9 The heats of formation derived from equilibrium data are generally considered to be less accurate than those determined by calorimetric methods because small errors in the change of the equilibrium values with temperature have a large effect on the calculated value of the heat of formation. The heats of formation derived from the combined published electromotive-force values reach a maximum at 56.0 at. pct Mg.8 Kachi reports a maximum of -4.7 kcal per g-atom at the stoichiometric composition.7 The present results also indicate a maximum at or near the stoichio metric composition, Fig. 1.

Jan 1, 1964

By J. L. Bruce

After six years of war-enforced idleness, Cyprus copper mines are operating again. This relatively long shutdown seems infinitesimal when compared with something like seventeen hundred years of inactivity that followed the important operations of the ancient Romans, and continued until the twentieth century. The historical records of the ancient operators are scarce but full of interest to those who realize that Cyprus copper production was important more than two thousand years ago. This paper, however, will give only a brief review of the ancient history and the evidence of ancient mining which have been quite fully covered in other publications.1-6 The purpose of this paper is to give a general sketch of the Cyprus Mines Corporation&apos;s enterprise in the Island of Cyprus, with special emphasis on those conditions and practices which are unusual. The picture is not intended to be complete, and many interesting details will be omitted. Some of these may be described in subsequent papers covering departmental practices. The principal operations of Cyprus Mines Corp. are in Cyprus, where it has leasehold concessions from the Cyprus Government covering about 50 square miles. It holds additional areas under "Prospecting Permits." The consideration for the concessions is a royalty on production, coupled with minimum annual rentals. Cyprus is a British Colony in the Eastern end of the Mediterranean with an area of about 3000 square miles and a population of about 400,000, of which 65 pct may be classed as Greeks on the basis of language, religious training, and traditions. About 25 pct are Moslems, principally of Turkish extraction. Prevailing languages are Greek and Turkish. A large proportion of the supervisory and administrative staff and practically all of the skilled and unskilled craftsmen and laborers are drawn from the native population. The "overseas" staff constitutes not more than 2 pct of the employees. The majority of these are from the United Kingdom, the British Dominions and Colonies. About one-third are from the United States of America. The topography of the Island is rugged, with mountains and foothills covering more than two-thirds of the area. Between the Kyrenea range rising to 3000-ft elevation, along the north coast, and the Troodos range (maximum elevation 6400 ft) occupying the southwest half of the Island, lies a cultivated rolling plain, the "Mesaoria," dry in summer and watered only by the winter rains and by scanty irrigation from small mountain streams and wells in the spring and summer. Climate and natural vegetation are characteristic of semi-arid conditions. The "urban" population, about one-fourth of the total, lives in the five port towns, Famagusta, Larnaca, Limassol, Paphos and Kyrenia, and in the capitol Nicosia, near the center of the Island. The suburban population lives almost entirely in villages or small towns, with very few people residing in isolated country homes.

Jan 1, 1949

By A. E. Nehrenberg

THE mechanism by which austenite forms in steels has received a great deal of attention in the literature in past years.&apos;-&apos;* Our present knowledge concerning this mechanism has been recently summarized quite concisely by Bain and Vilella,1 while a few years ago the literature was carefully reviewed by Roberts and Mehl.² The consensus is that any ferrite-carbide interface is a potential site for the nucleation of austenite during heating above the Acl temperature, and that the new austenite generally grows freely to produce approximately equiaxed grains, whether the carbides are initially present in the lamellar or the spheroidal form. In the case of eutectoid steels, growth of the new grains of austenite continues until contact is established with other grains. Then growth stops and an initial austenite grain size is established which does not change until the heating is continued to some high temperature at which grain coarsening begins. In the case of pearlitic steels which are not of eutectoid composition, the proeutectoid ferrite or carbide may interfere with the growth of the austenite if the temperature is not above that designated the A63 or the Acm, respectively. Although a large amount of work has been done to establish the mechanism of austenite formation in steels, it became clear to the present author while he was studying the transformation characteristics of a new 0.25 C Mn-Si-Ni-Mo hypoeutectoid steel" that the manner in which austenite grows in steels depends upon some factor, or factors, not previously considered. This was indicated by the fact that when this steel in the spheroidized condition was heated above the Ae1 temperature the new austenite which was formed did not envelop the carbides and grow in an equiaxed manner as described by Bain³ or spheroidized steels. Instead, in this steel, the austenite was observed to grow much more readily in certain directions than in others with the result that at temperatures within the Ac1-Ac³ ransformation range the austenite grains were acicular in shape. The excess ferrite was also found to be acicular with the distribution of these phases being such that a lamellar pattern was developed. This unusual directional growth of austenite in this new steel initially in the spheroidized condition is illustrated by fig. 1. A search of the literature revealed that this type of growth was not necessarily peculiar to this steel for similar microstructures had been observed by other investigators.4-8 However, the full significance of these microstructures does not appear to have been appreciated, and no work has been done to determine the conditions responsible for this directional growth of austenite or to arrive at an understanding of it. It was for this purpose that the work described in the present paper was carried out. Material: During the course of this investigation a total of 15 steels was studied. They consisted of hypoeutectoid, eutectoid and hypereutectoid carbon steels, and hypoeutectoid and hypereutectoid alloy steels, all of which were obtained in the annealed condition from commercial warehouse stock. As received, the carbon and alloy hypereutectoid steels had microstructures which consisted of spheroidal carbides in ferrite, whereas the eutectoid steel and the hypoeutectoid steels were pearlitic. The grades of steel represented were 1050, 1080, 10110, 3310, 4140, 4340, 4615, 6145, 8620, 9260, 9442,

Jan 1, 1951

By Manuel Eissler

The material presented in this paper is an abstract of a thesis submitted by the writer to the faculty of the Massachusetts Institute of Technology, as part requirement for the degree of Master of Science. The investigation was undertaken at the suggestion of Prof. H. 0. Hofman, and it was conducted, under his direction, in the laboratories of the Mining Department of the Institute. The purpose of the work was, first, to study some of the reactions that have been considered as a part of the mechanism of the chloridiz-ing roast, and second, to study the conditions under which nickel oxide and copper oxide may be chloridized. While the production of chlorine gas by various reactions during the chloridizing roast may not be primarily useful in the chloridation of metal oxides and compounds, it nevertheless serves a useful purpose in preventing the dissociation and decomposition of chlorides once they have been formed; for example, the dissociation of cupric chloride into cuprous chloride and chlorine. Therefore it was thought that a study of some chlorine-producing reactions would prove of interest, and the first series of experiments dealt with this phase of the subject. he object of the latter part of the work was to show the possibility of treating heavy sulphide ores, such as those of Sudbury, Ontario, containing much iron and small amounts of copper and nickel, by chloridizing and removing the copper, leaving an iron-nickel oxide product suitable for smelting in the blast furnace for nickel-bearing pig iron. The chloridizing of the copper would, of course, be preceded by a roast for the removal of sulphur, the sulphur oxides being available for the manufacture of sulphuric acid, if under the local conditions this product would be of commercial value. Reactions of the Chloridizing Roast Reaction of Sodium Chloride, Sulphur Trioxide, and Oxygen.—The first reaction studied was that involving the production of chlorine

Jan 1, 1915

By R. G. Gifkins

Mean boundary migration depended linearly upon creep extension under various conditions. Prolonged annealing or air-casting increased the proportion of immobile boundaries at a given stage of tests. Grain growth during annealing followed a power law. The linking of migration and sliding in creep and models for migration are examined; activation energies are calculated from these models. Segregation of oxygen to boundaries appears to be a controlling factor. THE idea that boundary migration and boundary sliding during creep are linked has often been suggested,&apos;-5 especially when evidence has been obtained for an alternation between the two processes. In simple bicrystals sliding can occur without any migration6 but in more complex bicrystals7 it is observed. McLean&apos; and Couling and Roberts 5 made measurements of both sliding and migration; McLean concluded that there was no linking of the two processes whereas Couling and Roberts supported the idea. McLean&apos; also developed a model for migration during creep and annealing. The present work was initiated as part of a study of the recrystallization of lead during creep9 but has been extended to examine some aspects of the mechanism of migration. MATERIALS AND METHODS Specially refined high-purity lead* was used; the total of impurities, excluding oxygen, was 0.0008 wt pct. Oxygen was removed as far as possible by melting in vacuo, treating at 550" to 600°C with hydrogen and then casting at 450°C under a vacuum of 10-2 mm Hg; the oxygen was then believed to be 0.00005 wt pct. Specimens were made from extruded strip and then annealed at the required temperature in an air oven, controlled to 5 lac. They were then polished in a mixture of acetic acid and hydrogen peroxide. At this stage some specimens were etched to give grain contrast and their grain sizes determined by the intercept method. Migration of boundaries during creep was measured on the surface of polished (not etched) specimens, directly loaded at room temperature (22°C) or 50°C (52"C) to initial stresses of 300 to 700 1b per sq in. Twenty six vacuum-cast hydrogen-reduced specimens were used and, in addition, two specimens were from material air cast after hydrogen reduction ("partial" air cast) and two from air-cast material not treated with hydrogen ("full" air cast). Duplicates were made in the majority of tests. At intervals through the creep tests, specimens were unloaded and the migration measured, normal to the direction of migration at the point of measurement, for each boundary along standard traverses. Usually between 110 to 180 boundaries were measured at each of some twelve stages of the tests. Migration was measured on the projected image (X100) using prism illumination. Fig. 1 illustrates the method of measurement and shows the kind of variation of migration found from boundary to boundary and along particular boundaries. Fig. 2 gives an example of more extensive migration. The mean value of distance migrated was generally reproducible to *10 pct but occasional points gave a scatter of *20 pct. The correctibn applied by McLean8 to allow for the contribution sliding makes to the apparent distance of migration could not be used, for the sliding at most boundaries was too small to measure with the equipment available. There were two reasons for supposing the correction unnecessary in the present work;

Jan 1, 1960

Jan 1, 1940