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By R. M. Hudson

The removal of nitrogen from a nitrogenized low-carbon sheet steel that contained 0.011 wt pct N was determined during heat treatment in Hz-N, mixtures. TIze process followed a first-order rate law; that is, plots of the logarithm of nitrogen content in steel were linear with the time of treatment at a given temperature. The rate of removal increased with an increase in temperature from 900" to 1300°F. By 1400°F the rate in dry hydrogen had decreased to a value intermediate between the rates at 1200" and at 1300°F; in wet (2.47 vol pct water vapor) hydrogen the rate at 1400°F was less than the rate at 1300°F and nearly the same as the rate at 1200OF. The rate at a given temperature increased as the 3/2 power of hydrogen concentration in the atmosphere. While wet atmosplzeres were generally more effective than the corresponding dry atmosplzeres, the effect of water vapor was much less pronounced than the influence of hydrogen content. NITROGEN is the principal agent in the strain aging of ferrite, the effect of carbon being secondary.' To eliminate the return of the yield point after straining and aging, it is claimed2 that the amount of nitrogen in solution in steel must be reduced to 0.0002 wt pct. Strong nitride-forming elements (titanium, vanadium, zirconium, and aluminum) can act to eliminate strain aging by combining with nitrogen. It is extremely difficult to decrease the nitrogen content in commercial steels to the low level required by conventional coil annealing because of the poor contact between the strip surface and the reactive atmosphere. However, a variety of gas-metal reactions can be effected by use of the open-coil annealing method,3 in which the metal surface is fully exposed to the atmosphere. With this possibility in mind, the Applied Research Laboratory has studied the influence of time, temperature, and atmosphere composition on the removal of nitrogen from low-carbon sheet steel. MATERIALS AND EXPERIMENTAL WORK Samples from a commercial nitrogenized low-carbon steel (0.010 in. thick) in the cold-reduced condition were used. The chemical composition of this steel is given in Table I. The gas mixtures used are listed in Table 11. The moisture content in the "wet" annealing atmospheres was controlled at a +70°F dew point (2.47 vol pct water vapor) by passing the gas mixture through a glass tube packed with a solid mixture of 10 pct anhydrous oxalic acid and 90 pct oxalic acid dihydrate held at 127°F; this technique has been described previously.4 For "dry" atmospheres, the gas mixtures were passed through a cold trap immersed in liquid nitrogen. A hinged-top Hevi-Duty electric furnace was used with a Vycor-glass furnace tube. When the furnace was at the desired temperature, the gas mixture was passed through the furnace at a flow rate between 1.1 and 1.2 cfh; coupons (size 3 by 3/4 in.) of the steel were pulled into the center of the Vycor-glass

Jan 1, 1964

By R. T. Hukki, P. Voutilainen

This paper describes a new apparatus for continuous wet fine-screening. Its preferred size range seems to be from 0.1 to 1 mm. The supercritical trommel screen is a short cylindrical trommel of wedge-bar type construction operated at a speed greater than the calculated theoretical critical speed and at a speed lower than the speed at which particles introduced into it will centrifuge. The paper describes results obtained with the prototype supercritical trommel screen in pilot plant scale. The results point to a high capacity and simultaneously to a high sharpness of screening. Finally, an analysis is presented of the forces acting in screening on a supercritical trommel screen. In the era of high speed, high capacity processing of raw materials the conventional slowly rotating trommel screen is often considered a relic from the times passed. A typical trommel screen is the cylindrical trommel rotated about a horizontal or slanting axis at a relatively low speed. Its screening characteristics are well known. Trommel screens of various types of construction, methods of operation, performances and other characteristics have been described in detail by Taggart.1 The theoretical critical speed of a trommel screen is defined by the same well known equation as that applied for grinding mills: where ncritical = the numerical value of the theoretical critical speed in rpm, D 1 = the inside diameter of the trommel in feet, and D2 = the inside diameter of the trommel in meters. ncritical corresponds also to the centrifuging speed provided that the coefficient of friction f between the trommel surface and the outer layer of the charge is = 1.0. In a general case: From Eq. 2 it is seen that in all cases where f < 1.0 the centrifuging speed of the trommel is greater than the theoretical critical speed. The supercritical trommel screen concerns screening operations within that speed range which is between the theoretical critical speed defined by Eq. 1 and the centrifuging speed defined by Eq. 2, under conditions such that the coefficient of friction f<1.0. It is reported by Taggartl that the optimum speed of a conventional cylindrical trommel screen 36 in. in diam was experimentally found to be about 16 rpm. From Eq. 1, the critical speed of this trommel is 44.2 tpm. The indicated optimum speed corresponds to (16/44.2) x 100% = 36.2% of the theoretical critical speed. The optimum speed range based on information available seems to vary from 33% up to 45% of the theoretical critical value. The trommel screen operated at a supercritical speed: operates at a speed greater than the calculated theoretical critical speed; operates at a speed lower than the speed at which the charge introduced into it will centrifuge; operates within the supercritical speed range in such a way that the coarse fraction of the charge must slide in respect to the inside surface of the trommel; the outer layer of the said fraction next to the screen tends to proceed in the same direction as any selected point on the trommel surface, but now at a lower speed, and indeed at a subcritical speed; allows to a certain degree adjustment of the maximum determining particle size x of the fine product simply by a variation of the speed of the trommel within the supercritical speed range. With increasing trommel speed, finer and finer material only will get the opportunity to find its way into the fine product while the screen opening remains constant. In conventional practice, the low speed trommel is generally used for sizing of coarse and medium coarse material, but seldom for fine screening. The characteristic feature of the product passed through the conventional trommel is that the determining size x of the biggest particle is barely smaller than the nominal size of screen opening. The supercritical trommel screen, on the other hand, is best suited for sizing of relatively fine material. Furthermore, the characteristic determining size x of the biggest particle in the fine product can be substantially smaller than the nominal width of the screen opening or slot. In the trommel screen best suited for the applications

Jan 1, 1965

By R. R. Sayers

TWO serious hazards from coal dust confront the bituminous-coal miner- -a physical or safety hazard and a physiological or health hazard. The first threatens the miner with loss of life from coal-dint explosions, and the second with loss of health and earning capacity from inhaling large quantities of the dust. Studies by the Bureau of Mines have shown that coal dust, except some grades of anthracite dust, is capable of initiating an explosion when no explosive gas is present and that its property of extending or propagating an explosion has been responsible for nearly all the widespread explosions that have occurred in bituminous mines in the United States in the present century. For years many mining people believed that low-volatile coal dust was not explosive but not only is it explosive but if the source of ignition is intense, it is as explosive as the dust of many high-volatile coals because the war is creating increased pressure for greater coal production and because of the trend toward greater mechanization in mines, explosion and health hazards from coal dust are likely !n increase considerably.

Jan 1, 1943

By Philip J. Shenon

IN 1947 the mining industry strove desperately to regain operating normalcy. During the first part of the year the industry in this country was plagued with labor shortages, strikes, and portal-to-portal lawsuits. Then followed the uncertainty of Government policy with respect to subsidies and tariffs; and the long and bitter controversy as to whether we are a nation of mineral "haves" or "have-nots." As the year progressed the labor supply impoved somewhat and the Taft-Hartley law brought partial relief to strike-troubled industry. The uncertainty with respect to tariffs was partly answered by President Truman on April 29 when he announced the suspension of the 4¢ import duty on copper until March 31, 1949, and later, near the close of the year, by the announcement of the tariff agreement signed by the United Nations at Geneva. By this agreement tariff rates are to be adjusted downward, or "bound" at their present levels, for three years, on commodities amounting to some 60 per cent of United States trade. Effective Jan. 1, 1948 the rate of duty will be substantially reduced on ores, concentrates, or metals of zinc, aluminum, copper, manganese, tungsten, iron, steel, barytes, nickel, cadmium, and antimony.

Jan 1, 1948

By J. L. Gillson

Andre Hubaux: In the writer&apos;s opinion, more stress should be put on field and microscope observations, as J. L. Gillson does. His discovery of relics of big labra-dorite feldspars from the Marcy anorthosite in all the other rocks is proof enough that previous field observations have been inadequate. The writer&apos;s field experience with anorthositie massifs is limited to the Egersund-Sogndal district in southern Norway; however, this is a very large and well exposed area. It seems to have so many points in common with the Adirondack region that a detailed comparison should be beneficial. This comparison was not possible 20 years ago, owing to the scarcity of geological data, at least for Norway. Both regions are now far better known—the Norway district because of the work of Professors Bugge and Barth 33-35 and especially because of the extensive field and microscopic research of P. Michot,30-35 who introduced me in the field to the problems of that region. In a particular unit of the Egersund district, a sodi-fication of the plagioclase, very similar to what Gillson calls "andesinization," has taken place. 12&apos; The percentage of anorthite in the plagioclase has dropped from 42 to 43 pct in the original norite down to 27 pct, but never below that level. This metasomatical transformation is a part of a whole series of processes of mig-matitization which have produced, above the level of granitization, concentrations of Mg, Fe, and Ti and among them, patches and parallel bands of ilmenite and magnetite. Thus both regions present somewhat comparable features and the theories to explain them have several points in common. However, as there seem to be differences between some American conceptions and the views commonly accepted at the University of Liege, I would like to make some comments about J. L. Gill-son&apos;s article. The author speaks of the garnet as being an anti-stress mineral. However, garnet may be found in schists, where its helicitic texture, when present, demonstrates its formation during differential movement. Furthermore, the whole concept of stress and anti-

Jan 1, 1959

By F. M. Lewis, J. F. Myers

W. I. Garms-—The authors state that when they added 11 tons of balls to the 45 pct volume ball load, the power needle did not budge. The question arises as to whether any increase in capacity accompanied the 11-ton addition. It is hardly conceivable that all of the balls making up the 11-ton addition were sterile. However, as the work done in the ball mill is not by kilo-watthours per se or balls per se but by kilowatthour-balls, it is possible that the kilowatthourballs in the mill before the 11-ton addition had a different amperage, voltage or robustage than those in the mill after the addition and that the overall outcome was that equal work was done before and after the addition. The authors can keep the efficiency that they got with the 45 pct volume 1-in. ball charge and get additional capacity by putting more kilowatthourballs to work in the form of the addition of 11 tons of 2-in. balls to the present ball charge, and subsequent makeup additions by weight of 20 pct 2-in. balls and 80 pct 1-in. balls. J. F. Myers (authors&apos; reply)-—Mr. Garms points his finger at the 11 tons of "sterile" balls added to the Tri-cone mill. A fact so interesting to us that we felt it should be reported. Clearly, ball slippage at the existing mill speed prevented any further transfer of power from the shell to the ball mass. We agree that the kilowatthourballs would increase, were we charging rough 2-in. balls as suggested by Mr. Garms. The assumption is, of course, that we would get a corresponding increase in work done. Our reported data (CIME meeting, Vancouver, 1946) shows a gain of work accomplished of 7.6 pct as we decreased the ball size from 2 in. to 11/2 in. and a further gain of work accomplished of 2.1 pct when we went from 11/2 in. to 1 in. The small ball results reported by H. R. Banks at Chapman Camp are also very convincing. In the case of 2-in. balls they would take the conventional ball path and start cascading. They would thus destroy the classifying pool over the "foot" of the

Jan 1, 1951

By J. F. Myers, F. M. Lewis

W. I. Garms-—The authors state that when they added 11 tons of balls to the 45 pct volume ball load, the power needle did not budge. The question arises as to whether any increase in capacity accompanied the 11-ton addition. It is hardly conceivable that all of the balls making up the 11-ton addition were sterile. However, as the work done in the ball mill is not by kilo-watthours per se or balls per se but by kilowatthour-balls, it is possible that the kilowatthourballs in the mill before the 11-ton addition had a different amperage, voltage or robustage than those in the mill after the addition and that the overall outcome was that equal work was done before and after the addition. The authors can keep the efficiency that they got with the 45 pct volume 1-in. ball charge and get additional capacity by putting more kilowatthourballs to work in the form of the addition of 11 tons of 2-in. balls to the present ball charge, and subsequent makeup additions by weight of 20 pct 2-in. balls and 80 pct 1-in. balls. J. F. Myers (authors&apos; reply)-—Mr. Garms points his finger at the 11 tons of "sterile" balls added to the Tri-cone mill. A fact so interesting to us that we felt it should be reported. Clearly, ball slippage at the existing mill speed prevented any further transfer of power from the shell to the ball mass. We agree that the kilowatthourballs would increase, were we charging rough 2-in. balls as suggested by Mr. Garms. The assumption is, of course, that we would get a corresponding increase in work done. Our reported data (CIME meeting, Vancouver, 1946) shows a gain of work accomplished of 7.6 pct as we decreased the ball size from 2 in. to 11/2 in. and a further gain of work accomplished of 2.1 pct when we went from 11/2 in. to 1 in. The small ball results reported by H. R. Banks at Chapman Camp are also very convincing. In the case of 2-in. balls they would take the conventional ball path and start cascading. They would thus destroy the classifying pool over the "foot" of the

Jan 1, 1951

By William O. Hotchkiss

IN COMMON with every other good citizen I long for conditions that will make perpetual peace a reality throughout the world. I have studied the statements of our public men relating to what we must do to bring this about after this war is over. In most of these I find one common error. They always build their plans on the unstated, subconsciously accepted premise that there can be such a thing as an ideal nation whose citizens are possessed of infinite wisdom and actuated only by motives that are above reproach. This heavenly vision fails to correspond with the facts. We wish it could be true but we are forced sadly to admit that the human beings that will live here after this war is over are going to be much like the fallible race that has occupied our planet for the past centuries.

Jan 1, 1943

By P. A. Tucker, T. B. Rhinehammer, D. E. Etter, J. E. Selle

The Ce-Cu phase diagram was investigated by differential thermal analysis and rnetallography. Two congruent melting compounds, CeCu2 (817°C) and CeCua (938°C), and three incongruent cornpounds, CeCu (516°C), CeCu, (796°C), and CeCu, CERIUM and copper have been suggested as possible diluents in a liquid-plutonium fueled reactor. As part of the determination of the Ce-Cu-Pu ternary phase diagram, a review Of the Ce-Cu system (798°C), are present in this system. Eutectics exist at 28 at. pct Cu (424°C), 74 at. pct Cu (756°C), and 91 at. pct Cu (876°C). The purity of the cerium used has an important effect on the results obtained by differential thermal analysis. was considered necessary. Previous work by Hanaman was conducted with relatively impure metal: 96.7 pct Ce with 2.5 pct other rare earths and 0.5 pct Fe as major impurities. The metal had a melting point of 715°C as compared to the melting point for pure cerium of 804°C as reported by Spedding and Daane.2 Results presented in this work were obtained primarily by differential thermal analysis (DTA) and metallographic examination of slow-cooled or quenched samples.

Jan 1, 1964

By R. W. Olson, A. L. Benham

Viscous fingering was studied as it occurred in an open Hele-Shaw model (1 ft x 4 ft x 1/16 in.); it was also studied in the same model packed with 80-mesh glass beads during miscible displacements under unfavorable viscosity ratio conditions. It was determined that the lengths of 20 elements of the front were distributed normally around the average position of the combined elements under all conditions. Represented by the normal distribution, the length of the viscous fingers grew linearly with the distance traveled from the point of finger formation, increased with displacement velocity, and increased with increasing mobility ratio. Results obtained during the first few inches of displacement were of little or no use in predicting finger growth and/or finger length throughout the 4-ft model since the point of finger initiation cannot be predicted and would often occur several inches from the point of injection with either positive or apparent negative coordinates. The fingering occurring during a miscible slug displacement was much greater than would be predicted based upon the actual mobility ratios between in-place fluid and slug and between slug and following fluid, using the results described above for miscible displacement in the absence of a slug. Many of the experiments in the packed model showed that the rate of growth of the viscous fingers was diminishing toward the end of the displacement in the 4-ft long model, indicating that microscopic mixing, such as diffusion or dispersion, was decreasing the viscous fingering effect. INTRODUCTION Viscous fingering is a manifestation of a finger-shaped interface between displaced and displacing fluids occurring during typical miscible displacement projects for oil recovery. Its cause may be traced to the instability of a viscous fluid being displaced by a more mobile fluid. Viscous fingering takes on important significance in the miscible slug process 1.2 where it may be a dominant factor in determining minimum slug size. Experimental1-3 and theoretical4-7 studies of viscous fingering have been made by other investi- gators. However, an exhaustive study of the variables affecting viscous fingering had not been made. The present study was undertaken in an effort to determine the effects of some of the more obvious variables—such as mobility ratio, displacement velocity, distance displaced, and packing—upon viscous finger length and growth in a small laboratory model. It does not necessarily follow that conclusions reached by studying the results of this model study may be applied to the field. Future studies would have to evaluate the effect of model size on extension of these results. EQUIPMENT AND EXPERIMENTAL PROCEDURES A flow diagram for the equipment used in this study is shown in Fig. 1. Basically, it consisted of (1) a constant-rate pump for the injection of displacing fluid into (2) a model made up of two flat transparent plates spaced a small distance apart and (3) provisions for the production of fluid into a calibrated graduate. The displacing fluid contained a dye which allowed visual observation of finger spacing and length. The pump performed at rates from 2.5 cc/hr to 480 cc/hr, while pumping a light mineral oil into a bladder in a closed glass container holding the displacing fluid. The model was made up of two plates of 1-in. Plexiglass with dimensions 1-ft wide by 4-ft long. These were spaced 1/16 in. apart so that the internal model dimensions were 1-ft wide x 4-ft long x 1/16

By John Hays Hammond

IT was but a few years ago that the mining engineer, and his confreres, the civil, mechanical and electrical engineer, were stigmatized by politicians of the parish? pump variety as advance agents of unprincipled exploiters of backward countries. Today he is recognized as a most important missionary of civilization in opening up new territory to contribute its mineral wealth and incidentally its other resources for the needs of mankind. An engineer, it is now conceded, is not only a benefactor of the world at large, but is a primary factor in the betterment of conditions of the inhabitants of those countries developed by his skill and indomitable courage-for courage is requisite in pioneering and his indefatigable industry. The engineer will, I believe, become a real "Ambassador of Good Will," when the slow-consenting academic mind realizes as it must that beneficent deeds are more enduring and more convincing than mere gestures of professed amity.

Jan 1, 1929

By AIME AIME

THE time of the Section delegates was economized this year by providing the section reports in mimeo- graphed form, together with the reports of the officers and committees of the Institute, for their consideration on arrival. The meeting was called for Thursday forenoon and despite a certain amount of oratory managed to get through before all the luncheon was gone. In all, nine section delegates and one from the Iron and Steel Division attended and took part. One delegate, who had come many miles, got lost in the complication of the program and failed to attend. Six appointed dele- gates failed to attend and two sections neglected to make appointments.

Jan 1, 1929

By J. J. Gilman

Examination showed that characteristic cleavage step patterns are observed on the cleavage surfaces of undeformed, slipped, bent, twinned, compressed, and indented zinc crystals; and the effect of temperature is discussed. Dimples were seen to produce cleavage steps in a treelike pattern in otherwise undeformed crystals. The steps seem to originate when cracks intersect screw dislocations. IT has been known for a long time that the path of fracture in polycrystals may be discontinuous (see Jaffe, Reed, and Mannl for review). Recently, Kies, Sullivan, and Irwin2 have proposed, and given evidence, that crack propagation is discontinuous within individual crystals as well. Other evidence has been given by Low.&apos; When discontinuous cracks within a crystal join together to make a macrocrack, the lamellae between each set of two cracks are torn somewhere, forming small cliffs. These cliffs appear as lines when the cleavage surface is observed microscopically.4,5 The lines have been called vein, tree, and riverlike markings by various authors, and they have sometimes been mistaken for fissures. The descriptive term cleavage steps is used in this paper. Cleavage steps vary in height over a wide range of values, from molecular dimensionsG to lor. and larger. Kies, Sullivan, and Irwin,2 as well as George,&apos; have shown that the gross cleavage step patterns for plastics, polycrystalline metals, and for mono-crystals are sometimes similar. Thus, they depend mostly on the mechanical variables that prevail during cleavage and are relatively insensitive to the structure of the material. For example, parabolic markings2,7,8 sometimes result when cracks open up ahead of, and not coplanar with, the main crack front. If the advance crack has the same velocity as the main crack, their intersection line is a parabola, otherwise it is a hyperbola or an ellipse. The patterns are strongly affected by differences in crack velocities. This results in chevron patterns which point to the place of origin of the main crack. It is the purpose of this paper to demonstrate the existence of a mechanism of cleavage step formation which is a continuous rather than a discontinuous process. Also, certain characteristic step patterns are described, and the strong effect of temperature is shown. The specimens were zinc monocrystals (grown from 99.999+ pct pure metal). These were cleaved at room temperature and at — 196°C. Results and Discussion Cleavage step patterns are highly variable from point to point on a given specimen, as well as from one specimen to another. Although the patterns shown in the photographs are typical, they have been selected for graphic illustration. Figs. la and lb compare undeformed crystals that were cleaved at —196 °C and room temperature, respectively. Cleavage at room temperature (Fig. lb) resulted in a higher density of high steps (dark black lines) and enhanced the visibility of the fine background markings. Deformation by simple slip caused no marked change in the step patterns until the glide strain reached about 1.0. But, as Fig. lc shows, the density of high cleavage steps was greatly increased by large glide strains. Corrugations lying perpendicular to the slip direction may also be seen in Fig. lc. These are caused by deformation bands. The cleavage resistance of the crystal of Fig. lc was very high compared to undeformed crystals (estimated by the force on a needle required for cleavage). Striking and varied cleavage step patterns were observed on bent crystals. Two characteristic patterns that were observed on crystals bent at 25°C, and cleaved by reverse bending at —196°C, are shown in Figs. 2a and 2b. The first, Fig. 2a, consists of V-shaped lines similar to the parabolas of other materials2,7 Fig. 2b shows a pattern that is the equivalent of Fig. la, consisting of faint background lines with a few higher step markings. Cleavage of bent crystals at room temperature resulted in Figs. 2c and 2d. Now, the cleavage step lines show a strong tendency to follow one of two perpendicular paths. In Fig. 2c (bent once), many of the cleavage step components that lie parallel to the bend axis are assembled into irregular lines. In Fig. 2d (bent twice), the cleavage steps again tend to consist of two perpendicular components, but neither of the components is assembled into lines. Also, the step density is higher.

Jan 1, 1956

By D. N. Seidman

In the course of a study of the electronic and thermodynamic properties of Pb-Se alloys it was found necessary to have an accurate knowledge of the phase diagram. However, the literature is in disagreement as to whether or not a monotectic reaction occurs in the lead rich portion of the phase diagram. Pelabonl reported only a two-phase region consisting of lead-rich liquid and solid PbSe extending from almost pure lead to the compound PbSe, and gave the melting point of PbSe as 1065°C. The data of Friedrich and Leroux2 are in general agreement with this type of diagram, with the melting point of the compound being 1088°C. However, Nozato and Igaki by inverse rate thermal analysis observed a monotectic reaction isotherm exlacing at 860°C with a monotectic composition of 20.5 at. pct Se. The miscibility gap in the liquid state extends from 7.5 to 20.5 at. pct Se. Hansen and Anderko4 accepted Nozato and Igaki&apos;s phase diagram in the region of the lead-rich monotectic. To reinvestigate this portion of the phase diagram, both thermal analysis and metallographic examination of various compositions were performed. The thermal analysis apparatus was constructed according to the specifications of the National Bureau of Standards. A t/t-l pct Rh thermocouple was calibrated against the melting point of copper (NBS), zinc (NBS), and antimony (A. D. Mackay), the emf being measured with a Rubicon Type B potentiometer sensitive to lpv. The absolute accuracy of the thermal analysis obtainable with this system is ± 0.5oC. Starting materials were semiconductor grade lead and selenium purchased from the American Smelting and Refining Co. Both elements were 99.999 pct pure with only trace impurities detected upon spectroscopic examination. One hundred galloys were sealed in quartz crucibles with a central thermocouple well under a vacuum of less than 1 p. This procedure prevented any composition change due to vaporization during the run. Cooling curves were obtained on the alloys listed in Table I. Data was taken by the direct method at cooling rates ranging between 1/2 to 2°C per min. The alloys were heated well above the liquidus and shaken vigorously to insure homogeneity. No evidence of an arrest indicative of the monotectic reaction was observed, and the two-phase region reported by Pelabonl and Friedrich and Leroux? was confirmed in general, although our data give higher liquidus temperatures than Friedrich and Leroux. The melting point of stoichiomet-ric PbSe determined for two different samples was 1080.7 0.5oC. The results of this investigation are compared with Nozato and Igaki&apos;s data in Fig. 1. To Complement the thermal analysis data, an 86 at. pct Pb specimen was examined microscopically. This composition was in the center of the miscibility gap reported by Nozato and Igaki.3 The alloy was heated to 1000°C, held for 1/2 hr, and water quenched. The specimen was polished using standard metallographic techniques for lead. The alloy was etched with an acetic-nitric acid etchant for 10 min at 45°C. Microscopic examination did not indicate the existence of two separate layers or solidified droplets imbedded in a matrix, as would be expected if a miscibility gap were present. The mi-crostructure shown in Fig. 2 consists of uniformly dispersed, dendritic PbSe in a lead-rich matrix.

Jan 1, 1962

By K. Thirumalai, D. P. Schlick

Longwall Technology has a potential of resulting in safety and productivity improvements of U.S. underground coal mining similar to those experienced by the introduction of continuous miner systems. The study presents a comprehensive national evaluation of longwall technology to assess the potential of longwalls to improve health and safety and coal productivity. The study was conducted by the authors during the spring of 1980 as part of MSHA New Technology Coordination activities and with a view to examine the factors that may limit the acceptance of longwall technology in the U.S. coal mining operations. The study points out areas where adjustments need to be made in MSHA regulations and enforcement to help Longwalls. A two-entry longwall system appears to offer a practical method of improving underground coal productivity and safety. Applying regulations that are primarily designed for room and pillar methods to longwall mining, in some instances, reduces the effectiveness and productivity benefits feasible by new technology application. Controlling dust is the single predominant problem in the design and operation of longwalls in the United States. The results of this study points out a need for a coordinated program between government and industries on dust control technologies for examining acceptable technological options to control dust in longwalls without restraining the production capability of the system.

Jan 1, 1981

Attention! Engineers! Geologists! Here is your Opportunity to be of Professional Service The war has interrupted the supply of many minerals, which were normally imported. In view of present transportation conditions, a serious shortage exists in certain materials and will soon develop in others. Some immediate action is imperative. The first thing is to take a careful inventory of American resources. We must know where the ore deposits are, what has hitherto hindered their utilization, what methods must be used, and what equipment will be needed if an emergency demands their rapid development. Many properties must be re-examined from a new point of view, that of present necessity rather than of normal profit. When the shortage is realized, the preliminary steps for relief should have been completed. It is a necessary and patriotic form of mineral insurance. Will you have a part in it? Do not forget that these are war times, and that what may have been valueless a year ago may be a "life-saver" now; an abandoned copper prospect of 1913 might make a successful pyrite mine in 1917. We are fighting an autocratic enemy who knows his resources to the last pound, and uses them with most efficient organization. We have no Kaiser, so each of us must do his share to put our Government in the same situation. The Government needs your facts.

Jan 8, 1917

By G. Thodos, R. B. Grieves

A method has been developed For predicting the critical temperatures and critical pressures of binary mixtures of carbon dioxide, hydrogen sulfide, nitrogen, hydrogen, carbon monoxide and oxygen with the normal paraffin hydrocarbons. For carbon-dioxide and hydrogen-sulfide systems, relations are presented that take into account the peculiar behavior of mixtures with closely boiling components, such as carbon dioxide-ethane and hydrogen sulfide-propane mixtures which exhibit minimum critical temperature points. For hydrogen, nitrogen and carbon-monoxide systems, the extreme critical behavior caused by wide differences in pure component properties is established In addition, those fixed gas-paraffin systems which resemble paraffin-paraffin systems are also accounted for. For a mixture of known composition, the pure component critical temperatures, critical pressures and normal boiling points are all that are required to determine its critical point. Graphical relations are presented relating Tc and PC , of the mixture to the pure component properties. From the treatment of 12 carbon-dioxide and hydrogen-sulfide systems reported in the literature (74 mixtures), the expected error lor the critical temperature is approximately 1.5 per cent, and for the critical pressure, approximately 2 per cent. From the treatment of six hydrogen, nitrogen and carbon-monoxide systems reported in the literature (30 mixtures), the expected error for both the critical temperature and critical pressure is approximately 2.5 per cent. The relationships, which have been developed with only normal paraffins as the hydrocarbon components, may be extended to those isoparaffins and olefins which fall within the allowable volatility ranges. INTRODUCTION Many of the fixed gases — carbon dioxide, hydrogen sulfide, nitrogen, hydrogen, carbon monoxide and oxygen — occur in natural mixtures with hydrocarbons. Carbon dioxide and hydrogen sulfide are frequent components of the fluids produced from underground petroleum reservoirs. Nitrogen, carbon dioxide and hydrogen sulfide are present in varying quantities in most natural gases and gas-condensate well effluents. Hydrogen mixtures are of considerable interest in many phases of refining processes of petroleum. The determination of the critical temperatures and critical pressures of such mixtures is of value in vapor-liquid equilibrium studies, for the prediction of the characteristics of underground reservoirs, and for reduced-state correlations of PVT, transport and thermodynamic properties. The accurate estimation of the critical point for binary mixtures is an important initial step toward a complete analysis for the establishment of the critical temperatures and pressures of multi-component mixtures. Methods for predicting the critical temperatures and critical pressures of binary hydrocarbon systems have already been presented in the literature.8 It is possible to apply these existing methods to fixed gas-paraffin mixtures, but due to their unusual critical behavior, values calculated deviate considerably from experimental values. For systems containing trace quantities of the fixed gases, these methods are acceptable; however, for systems containing more than 5 mol per cent of the fixed gases, these utterly fail to produce reasonable critical values. Consequently, in this study a method has been developed for handling such binary mixtures over the entire composition range. CARBON-DIOXIDE AND HYDROGEN-SULFIDE SYSTEMS The critical behavior and the vapor pressure behavior of mixtures of carbon dioxide and hydrogen sulfide with paraffinic hydrocarbons may be quite similar or quite dissimilar to that of paraffin-paraffin mixtures, depending on the volatilities of the components involved. The critical temperature and normal boiling point of carbon dioxide are very close to the corresponding values for ethane, while its critical pressure is considerably higher than that of ethane. The normal boiling point of

By J. F. Smith, J. E. Davison

The heat capacity of CaMg2 was measured over the temperature interval, 4.8° to 287°K, by the technique of low-temperature adiabatic calorimetry. Heat content measurements were performed with a drop calorimeter over the temperature interval, 273" to 673°K. From these data the thermodynamic functions, (FT - H0)/T, ST - So, and & - Ho, were evaluated. A third-Law calculation of the standard entropy of formation of CaMg2 yields a value of -0.25 * 0.06 cal per (°K g-atom) , and the free-energy function derived from this study when combined with existing equilibria data yields a value for the standard enthalpy of formation which is in agreement with direct calorimetric enthalpy measurements. The accompanying paper&apos; shows that the enthalpy of formation of CaMg2 has been determined with good precision by three different calorimetric techniques.&apos;-= TWO independent determinations of the Gibbs free energy of formation of CaMg2 have also been made; both determinations were based on vapor pressure measurements, being in one case hydrogen vapor pressures over ternary Ca-Mg-H alloys4 and in the other case magnesium vapor pressures over binary Ca-Mg alloys.5 The present determination of heat capacity of CaMg2 below room temperature and of the heat content of CaMg2 above room temperature was undertaken to provide supplementary data. These data are useful in their own right but can in addition be used to evaluate an entropy of formation for CaMg2 which, because of the interrelation of free energy, enthalpy, and entropy, can be used as a check of the self-consistency of the composite of the presently available information. LOW-TEMPERATURE HEAT CAPACITY The heat capacity of CaMg2 was measured over the temperature interval 4.87° to 286.64°K in an adiabatic calorimeter. The physical details of the calorimeter and the experimental procedure for measuring the heat capacity of a specimen have been adequately described by Gerstein et a1.6 The source and purity of the calcium and magnesium are described together with the methods of sample preparation and chemical analyses in the accompanying paper.&apos; Results of chemical analyses of the material which was used in the present investigation are shown in Table I. These analyses show that, on the basis of the published phase diagram,7 the heat capacity sample contained a slight excess of a calcium while the heat content sample contained a slight excess of magnesium. However, in both cases the excess was small, and X-ray diffraction patterns showed reflections which were without exception attributable to CaMg2. The sample which was used for heat capacity measurements weighed 69 g while the sample container and addenda weighed 132 g. The sample was in the form of annealed powder, 50 to 60 mesh, and was sealed into the sample container under 0.1 atm of helium. Copper fins inside the sample container facilitated thermal equilibrium of the powdered Sample. Time intervals of the order of 10 min were required for thermal equilibration, and such times are normal for this calorimeter regardless of the form of the sample. The observed heat capacities were corrected for the small excess of a calcium through use of the heat capacity values tabulated by Hultgren et a1.8 The corrected heat capacities are tabulated as a function of temperature in Table II. The free-energy function and the absolute entropy of CaMg2, which were calculated from the experimental heat capacity data, are listed in Table 111. A smooth curve was fitted to a plot of the experimental values of the heat capacity and in only two instances above 30°K did the plotted points deviate from the curve by more than 0.2 pct. Below 10°K the deviation of several of the points was as much as 50 pct. These large percentage deviations were attributed to the small value of the heat capacity and to the low sensitivity of the platinum resistance thermometer in this temperature range. The deviations in the region of 10°to 30°K were less than 5 pct. Although the percentage deviations of some of the low-temperature measurements are large, the actual value of these deviations is small since the magnitude of the heat capacity in that temperature range is small. The error in the value of the third-law entropy at 298.15°K was estimated to be less than 0.01 cal per (°K g-atom). A value of -0.25 ±0.06 cal per (°K g-atom) was obtained for the standard entropy of formation at 298.15°K from the relation:

Jan 1, 1969

By H. W. Gillett

Many of the parts of motor cars, aircraft, etc., that require strong light construction, hence must be made of high-quality steel, are stressed to the maximum limit only in a very small volume. In parts subject to bending stress a line or even a point may take the maximum stress. A series of endurance tests under repeated bending in progress in the U. S. Bureau of Mines laboratories, like similar tests by other investigators, has shown the great difference in life of sister bars of the same stecl, handled in the same way and tested at the same nominal stress. It is known that a surface notch or scratch greatly increases the local stress over the nominal calculated stress; internal notches, such as those formed by inclusions or sonims, probably have a similar effect. From the tetss made by the Bureau of Mines, the cleanliness of the steel at the dangerous section, or point of maximum stress, seems to be one of the most important factors in determining the life of the piece. The more localized the stress, the more does chance, rather than the average properties, dctermine the life of the steel. The usual test, a tension test of a bar taken longitudinally, is not sensitive to the local drop in strength (or tendency to increase the true local stress over the nominal) because of inclusions, which probably have a more injurious effect in hard heat-treated steels, such as must be used when great strength is sought, than in softer steels. Users of steel who make transverse tests find surprisingly low ductility on transverse bars of dirty steel, though the longitudinal tests may be good. Bending tests, reverse bending tests, and notch-bar impact tests,

Jan 1, 1923

By H. W. Gillett

Many of the parts of motor cars, aircraft, etc., that require strong light construction, hence must be made of high-quality steel, are stressed to the maximum limit only in a very small volume. In parts subject to bending stress a line or even a point may take the maximum stress. A series of endurance tests under repeated bending in progress in the U. S. Bureau of Mines laboratories, like similar tests by other investigators, has shown the great difference in life of sister bars of the same stecl, handled in the same way and tested at the same nominal stress. It is known that a surface notch or scratch greatly increases the local stress over the nominal calculated stress; internal notches, such as those formed by inclusions or sonims, probably have a similar effect. From the tetss made by the Bureau of Mines, the cleanliness of the steel at the dangerous section, or point of maximum stress, seems to be one of the most important factors in determining the life of the piece. The more localized the stress, the more does chance, rather than the average properties, dctermine the life of the steel. The usual test, a tension test of a bar taken longitudinally, is not sensitive to the local drop in strength (or tendency to increase the true local stress over the nominal) because of inclusions, which probably have a more injurious effect in hard heat-treated steels, such as must be used when great strength is sought, than in softer steels. Users of steel who make transverse tests find surprisingly low ductility on transverse bars of dirty steel, though the longitudinal tests may be good. Bending tests, reverse bending tests, and notch-bar impact tests,

Jan 1, 1923