Search Documents

By M. Cohen, R. T. Howard

The purpose of this paper is to direct attention to the lower part of the austenite transformation diagram, or TTT curves, where considerable uncertainty still exists as to the blending of the bainite and martensite reactions. The dissimilarities between these two low temperature transforrnations have been summarized recently by Troiano and Greninger.' Of particular importance to the present work is the fact that martensite formation, unlike bainite formation, is not suppressed by the fastest quenching rates attainable. However, most of the investigations in this direction have been concerned primarily with the start of the martensite transformation (Mg) during cooling, rather than with the quantitative aspects of the subsequent reaction on either further cooling or isothermal holding. Several years ago, Cohen2 suggested a form of transformation diagram which reconciled, at least schematically, the isothermal characteristics of the bainite transformation with the insuppressible nature of the martensite transformation. In essence, the diagram consisted of a family of horizontal lines (representing the progress of the austenite-martensite reaction during quenching) which were interrupted in point of time by the bainite family of C-curves extending down from higher temperatures. This picture received later support by metal-lographic3 and dilatometric4,5 studies, but the techniques employed were not sufficiently critical to substantiate some of the details. Elmendorf6 and Grange and Stewardi have shown that the Greninger-Troiano metallographic technique8 may be used not only for M, determinations, but for studying the course of further austenite decomposition. In fact, the latter investigators have observed the amount of martensite formed as a function of temperature below M, in fourteen commercial steels. In the present paper, the Greninger-Troiano technique has been combined with the lineal method of Howard and Cohen9 to provide a unique, quantitative treatment of the austenite-martensite reaction. Furthermore, isothermal transformations have been similarly measured on holding at temperatures above and below M., thus permitting a fairly detailed presentation of the lower part of the conventional austenite transformation diagram. Experimental Details Materials The steels, listed in Table I, were selected for study because they exhibit a satisfactory range of M. temperatures and have not received as much attention as the lower carbon grades. They were prepared as 30 lb induction furnace heats in the laboratories of the Vanadium-Alloys

Jan 1, 1949

By M. Cohen, R. T. Howard

The purpose of this paper is to direct attention to the lower part of the austenite transformation diagram, or TTT curves, where considerable uncertainty still exists as to the blending of the bainite and martensite reactions. The dissimilarities between these two low temperature transforrnations have been summarized recently by Troiano and Greninger.' Of particular importance to the present work is the fact that martensite formation, unlike bainite formation, is not suppressed by the fastest quenching rates attainable. However, most of the investigations in this direction have been concerned primarily with the start of the martensite transformation (Mg) during cooling, rather than with the quantitative aspects of the subsequent reaction on either further cooling or isothermal holding. Several years ago, Cohen2 suggested a form of transformation diagram which reconciled, at least schematically, the isothermal characteristics of the bainite transformation with the insuppressible nature of the martensite transformation. In essence, the diagram consisted of a family of horizontal lines (representing the progress of the austenite-martensite reaction during quenching) which were interrupted in point of time by the bainite family of C-curves extending down from higher temperatures. This picture received later support by metal-lographic3 and dilatometric4,5 studies, but the techniques employed were not sufficiently critical to substantiate some of the details. Elmendorf6 and Grange and Stewardi have shown that the Greninger-Troiano metallographic technique8 may be used not only for M, determinations, but for studying the course of further austenite decomposition. In fact, the latter investigators have observed the amount of martensite formed as a function of temperature below M, in fourteen commercial steels. In the present paper, the Greninger-Troiano technique has been combined with the lineal method of Howard and Cohen9 to provide a unique, quantitative treatment of the austenite-martensite reaction. Furthermore, isothermal transformations have been similarly measured on holding at temperatures above and below M., thus permitting a fairly detailed presentation of the lower part of the conventional austenite transformation diagram. Experimental Details Materials The steels, listed in Table I, were selected for study because they exhibit a satisfactory range of M. temperatures and have not received as much attention as the lower carbon grades. They were prepared as 30 lb induction furnace heats in the laboratories of the Vanadium-Alloys

Jan 1, 1949

By M. S. Smani, P. Blazy, J. M. Cases

Investigations on the beneficiation of sedimentary Moroccan phosphate ores are reported in four separate parts. The first discusses electrochemical phenomena at the solid-aqueous solution interface for minerals of the apatite group. In the second part, the electrochemical properties of the calcareous gangue associated with the phosphate ore are investigated. The flotation of calcite and phosphate oölites, using both anionic and cationic collectors, is discussed in the third part. It is shown that selective recovery could be obtained for precise concentrations of collectors and pH ranges. Results of work aimed at optimizing depression of phosphate oölites during inverse flotation of the carbonate gangue with sodium oleate are reported in Part 4.

Jan 1, 1976

By D. S. G. Hanson

The Flin Flon Mine has been in production for over fifty years, and current mining is dependent on pillar and remnant recovery. One of the last major blocks of ore, and an important economic entity to the Mine, is the North Main Shaft Pillar. A rock mechanics program was initiated through under' ground instrumentation and other subsequent analyses, to establish the degree of instability as min¬ing progressed. Several studies have been and will be undertaken to evaluate the general stability, and possibly improve the chances of stability during pillar recovery. The North Main Shaft Pillar is immediately bounded by cemented cut and fill supporting rib stopes which inturn are bounded by slag and waste filled stopes. The min¬ing method involves a modified longhole open stoping and slag fil¬ling sequence for each mining block in a general mining upwards scheme.

Jan 1, 1983

By R. J. P. Lyon, A. E. Prelat, H. Lawrence

Introduction In 1977, the US Bureau of Mines awarded a grant to the state of South Carolina to explore the possibility of using Landsat multispectral scanner (MSS) data as an aid in monitoring surface mining activities in selected counties of the state. Work had been done in Aiken County prior to the grant by USBM and state personnel at the EROS Data Center using both the GE Image 100 and ESL IDIMS systems. The initial work on the 1:100 consisted of locating and measuring the areas of various kaolin mines. The results were excellent on location, identification, and accurate area measurements of several mines as compared with aerial photos of each mine. The effort also included locating and measuring the size of all mines (including sand and gravel) within two US Geological Survey (USGS) 7 % - min quadrangle maps. Line printer overlays using the IDIMS equipment and software resulted in the location of all known mines within an estimated error less than zt 91.4 m. Mine acreage was calculated by counting each symbol (which represented one pixel) and multiplying by 1.1 (the number of acres per pixel). [Fig. 1] shows a portion of one quadrangle overlay. [Table 1] gives a comparison of acreage measured for several mines from the 1-100 and IDIMS system vs. aerial photo measurements. The success of the preliminary work resulted in the South Carolina Land Resources Conservation Commission submitting a proposal to USBM for funding to expand the scope of work to other mineral mining operations within the state and determine if Landsat Imagery could be used to accurately locate and measure mining and reclamation activity on a continuing basis. Three separate tasks were proposed for selected kaolin mines in Aiken County: Task 1, to measure changes in active mine developments over the period 1974-77; Task 2, to measure reclamation activity, and, if time permitted, seasonal changes in mine signatures over the same period of time; and Task 3, to classify one complete mining operation (i.e., differentiate between active, spoil, overburden, water, reclaimed portions and surrounding terrain. The major effort was centered around J.M. Hubeis Richardson mine. Mining operations were progressing in a northerly direction and included three areas of reclamation: one prior to 1974; one started during early 1974; and one reclaimed during 1976. A discussion of all work done under the grant is available in the March 1979 Final Report listed under References. Computer compatible tapes (CCTs) containing MSS data from Landsat Path 18, Row 37, were purchased from the National Aeronautics and Space Administration (NASA) covering the period February 1974 through January 1977. The MSS data were processed on the General Electric Image 100 using parallelepiped classification at the EROS Data Center's Data Analysis Laboratory, Sioux Falls, SD, and at the Stanford Remote Sensing Laboratory, Stanford University, Palo Alto, CA, utilizing both an unsupervised classification (ISOMIX) and a supervised classification (sequential discriminant analysis). Studies at Stanford University Remote Sensing Lab (SRSL). In Feburary 1977, initial work was begun at Stanford using the STANSORT computer program running on a DEC PDP-10 (Honey, Prelat, and Lyon, 1974). This software is fully interactive and designed to study Landsat CCT data at high resolution (small areas) on a pixel-by-pixel basis (Lyon, 1977). Unsupervised Classification. The initial step was to locate the Richardson mine on the positive print of the full Landsat scene from CCT 1644-15252, dated 6/17/74. This was relatively easy due to a large abandoned kaolin mine and a long narrow pond clearly visible in the scene. Two unsupervised classifications of the Richardson mine were run using ISOMIX clustering (Honey, Prelat and Lyon, 1974). (ISOMIX essentially follows the interactive clustering procedures of ISOCLS Kan, Holley, and Parker. 1973). Although the classifications were successfully accomplished, it was apparent from the TV display that the results did not clearly define the mine areas. A supervised classification would have to be made in order to clearly separate each portion of the mine. Supervised Classification. This classification was done using the Stepwise Discriminant Program (BMDO7M) which is part of the BIOMED package (Dixon, 1970) and involved the following steps: Training group populations were selected and the digital

Jan 1, 1982

By J. O. Glanville, L. H. Haley

Ice frozen from a dilute chemical solution is mechanically weaker than ice frozen from pure water. This phenomenon is the basis of a practical method for reducing the strength of a mass of frozen coal. If a chemical additive is applied to moist coal prior to its shipment during freezing weather, the resulting frozen coal can be more easily broken than in the absence of the chemical additive. This greatly expedites the unloading and handling of coal during winter. There has been considerable research into the nature and mechanical strength of ice frozen from various solutions. In this paper, literature relating to this process as well as literature relating to the chemical treatment of coal and mineral particulates is reviewed. Some important articles are discussed and speculations made about the nature of the ice-weakening process. A laboratory evaluation of the effects of chemical additives on the mechanical strength of ice and frozen coal has been made. An apparatus designed for this purpose is described, and some results obtained with it are discussed.

Jan 1, 1983

By Arnold S. Epstein

Tlze green electroluminescence occurring at liquid-nitvogen temperature in epitaxial gallium phosphide diodes is exarnined using the donor dopants silicon and sulfur. Zinc is used as the p-type diffusant. Two tt~ain peaks are found, namely til 0.56 and 0.535 p. The intensity of the gYeen peak occurring at 0.56 is found to oary as -4"' wlzere Jf is the forward current density and to first order appears to be dependent on the concet~tvation of ionized donovs. Tile vadintive lifetinze fov this process is -10-'sec. The intensity of the 0.56-p lu~ninescence is nt least several ovdevs of magnitude greate,, at liquid-nitvogen temperature than that noted jor the 0.538 radiation for current densities up to about 35 amp per sq cm. The variation oj- the intensity of. the 0.538-p peak with current density caries according to the donor dopant. With sulfur as the donor one has a J12 dependence, whereas when silicon is the donov a J1.5 dependence is noted. Tl~e above can be fitted to a In molecular process (in first order) such as a band to band recombination. The constant B fir band to band vecombination) is found from our experitt~etlt to be of the order of 2 CZI cm per sec, zcl~ereas for tlze impurity vecombination peak (0.56 p]) tile A cotzstor~t is of the order of. 7 x 10-' cu cm per sec. The structuve o/. the diodes at liquid-nitvog-en tett~peruture is oj tlze double injection type, and by carefi~lly selecting. the thickness of the structure one can regulate the onset of the 0.538-p radiation. The diode clzavaclevistics follow an I-Vx laiv where x is >1. Llregatiue resistance in these structures con be correlated with saturation of tlze 0.56- peak. ThE development of high-purity, large single crystals of epitaxially grown gallium phosphide is the ultimate aim of the studies to be reported. While a number of papers and reviews' have been presented on properties of gallium phosphide grown from gallium solution and from the melt, less attention has been paid to the properties of epitaxial gallium phosphide grown from the vapor. In the studies to be reported we have examined the effects of shallow donor impurities, primarily silicon and sulfur, at liquid-nitrogen temperature, on both the electrical and green electroluminescent properties of carefully characterized single-crystal epitaxial Gap. I) EXPERIMENTAL PROCEDURES A) Material Preparation and Properties. The samules used in this investigation were single-crystal n-type epitaxial gallium phosphide. he single crystals were synthesized from the elements by vapor transport and epitaxial deposition on single-crystal gallium arsenide substrates. Typical transport agents used were chlorides. The growth procedures are described in more detail in Ref. 2. The samples were grown in the (111) orientation and had thicknesses up to 480 . Following the growth, the GaAs substrate was removed from the epitaxial Gap by etching in nitric acid. The Hall effect and resistivity of these n-type samples were measured as a function of temperature and analyzed for impurity content and compared with spectroscopic emission analysis. The results are given in greater detail in Ref. 3 but a summary is noted in Table I. In Table I, AED denotes the donor ionization energy, Nd is the donor impurity concentration, lvA is the acceptor impurity concentration, NI is the total impurity concentration, Rip vs temperature is the measured Hall mobility-temperature relationship from liquid nitrogen to about 400"K, n(77"K) is the measured carrier concentration at liquid nitrogen, and R/p(77'~) is the measured Hall mobility at liquid nitrogen. Good agreement is noted between electrical and emission analysis for the major donor impurity, silicon, in the two materials where it is a major constituent. In the case of the two samples SC90-6 and AP138-3(111) B which were sulfur-doped the ionization energy found from the electrical data is in good agreement with that reported for sulfur.4 The acceptor impurities are not known, although from the presence of magnesium in the samples as indicated by emission analysis and its known role as an acceptor in GaP,4 magnesium could be present as an acceptor. Similarly, since silicon is known to be an amphoteric impurity4 it may also be present as an acceptor in the Gap.* The *A small band has been noted at 0.625 11 in samples SC90-6, SC76-4, and SC77-4, suggesting according to Ref. 5 that sillcon could be present as an acceptor In these samples since these authors have found this peak to represent a donor-silicon emission. presence of calcium deduced from emission analysis is not correlatable with the electrical analysis and its presence as an electrically active impurity should be questioned. B) Sample Preparation and Diode Fabrication. The original slices were of the order of 2 sq cm in area witi the (111)B face up. The material was cleaved and sectioned and the best pieces selected (i.e., those which visually appeared to have the least strain and defects). The samples were polished, lightly etched, and cleaned in trichloroethylene. Zinc was diffused in a closed tube at 800°C to form a p-n junction. Diodes were made from these samples. The depth of junction varied, but did not exceed 10 p depth. The back side of the slice was lapped back and a low-resistance n-type contact was formed (at 600°C in forming gas) to an Au-Mo tab with a hole in the middle for

Jan 1, 1968

By John S. Johnson, Thomas Fraser

SIZING is the process of separating mixed particles into groups of particles all of the same size, or into groups in which all particles range between certain definite maximum and minimum sizes. In coal preparation, sizing is generally accomplished by passing the coal over screens. Separation by differential settling in air or water currents has been adapted to the special field of separating very fine sizes, and these processes are in commercial use to a relatively small extent in the coal industry. Separation with screens is a very old industrial practice. Agricola described the use of screens for ore treatment in the middle ages. In the literature of the British coal industry references were made to the screening of coal as early as 1589, but the practice of extensive sizing for the market did not become general until the last half of the nineteenth century. In America, the practice of sizing developed first in the Pennsylvania anthracite region, beginning with the use of rakes' in the mine working places to recover coarse coal. This mining procedure left the fines in the mine. Preparation outside the mine started with the installation of station¬ary cast-iron plates with 4 to 6-in. square holes. The run-of-mine coal was dumped upon the platforms, the large pieces of rock were picked out by hand, and the large lumps of coal were broken with hammers. The term "breaker," which still applies to the anthracite-preparation plant, originated with this practice, but the term is no longer descriptive of the entire function of the plant. In 1884, the first power-operated anthracite coal breaker' was erected by Gideon Bart at his colliery at Wolf Creek near Minersville, Pa. This plant utilized a system of rolls for breaking the coal and revolving screens for sizing. The plant was driven by a steam engine. It 'could handle

Jan 1, 1943

By Kurt Kennedy

A method is described by which three elements can be condensed simirltaneously on a common substrate in such a way that the composition varies with position on the substrate. Almost all possible combinations of three solid elements can be formed in a single evaporation. The three elements are heated by magnetically deflected electron beams. The alloys and cornpounds formed by this method generally correspond to those trade by other methods; however, many exceptions exist. Simple symmetric crystallographic phases tend to form in preference to more complex phases. The Nb-Sn. Cr-Fe-Nt, and other systems of alloys made by this method will be discussed. Phases that form very slowly, such as the o phase in Cr-Fe alloys, may be formed rapidly by this method when certain substrate temperatures are used. STUDYING all the mixtures and compounds of two or more elements by the preparation of individual samples forces the investigator to make sampling sufficiently close together so that the properties of the intermediate compositions can be inferred. A completely unknown system will require a dis c our aging ly large number of preparations in order to fully know all its properties. For the purpose of expediting this type of investigation, methods have been devised to prepare samples that have a continuous variation in composition over some predefined area. The code-position of two elements onto suitable substrates has been used to produce alloys or compounds that have variable compositions depending on their positions on the substrates Composition gradients have been formed by depositing a wedge-shaped layer of one element and then depositing a second wedge-shaped layer on top of it such that the total film thickness is kept constant. Concentration equilibrium perpendicular to the surface is then established by annealing.4 This paper describes a method for the simultaneous condensation of three volatile components on a substrate such that there is a regular variation of composition with position on the substrate. The arrangement of the evaporation sources and the substrate is shown schematically in Fig. 1. Materials to be evaporated are placed in three water-cooled crucibles located at the corners of a 10-in. equilateral triangle. Electron beams from cathodes located below the crucibles are bent 180 deg by magnetic fields and focused on the material to be evaporated. The cathodes are connected in parallel to a constant-current 12-kv power supply. The distribution of emission current from each cathode is controlled by filament temperature. When materials that sublime are to be evaporated, the electron beam is deflected by an auxiliary ac magnetic field so that the beam moves over the surface of the evaporating material rather than digging a hole in one spot. The substrate is a 10-in. triangle of 2-mil stainless steel or molybdenum which is stretched against a slightly curved heat sink by a frame as shown in Fig. 2. This frame and heat sink are located so that each corner is directly above an evaporation source. The heat sink has three radiant heaters at each corner that can be separately controlled permitting the

Jan 1, 1967

By Pei-Yung Huang, C. R. Hayward

In order to understand more fully the actual state of copper lost in copper reverberatory slags, a systematic study on the various reactions between certain metallurgically important copper compounds and synthetic copper reverberatory slags was undertaken by the authors in the Massachusetts Institute of Technology from 1942 to 1945.1 This paper, being only a part of the work completed, is published first because it furnishes the first experimental evidence of the formation of copper ferrite from reactions between cuprous oxide and copper reverberatory slags. Choice of Slag Composition The choice of the composition of the synthetic reverberatory slags to be used was much deliberated. Commercial copper reverberatory slags, neglecting minor constituents, avcrage :2,3 45 to 47 pct FeO; 38 to 42 pct SiO2; 5 to 6 pct CaO; 5 to 6 pct A12O3. Since the ternary system CaO-FeO-SiO2 has been much more thoroughly studied4 and is much simpler than the quaternary system CaO-FeO-SiO2-Al2O3, it was decided to use calcium oxide only instead of calcium oxide and alumina in the synthesis of the slags. Fortunately the composition of the average copper reverberatory slag with calcium oxide substituted for alumina lies in the region of the phase diagram clarified by the investigators. A survey of the phase diagram (Fig I) suggested two compositions: (I) the composition near the invariant point S, which is made up of 46 pct ferrous oxide, 37 pct silica and 17 pct calcium oxide; (2) the composition near the invariant point K with 45.5 pct ferrous oxide, 43 pct silica and 11.5 pct calcium oxide. Composition S has the advantage that the percentages of ferrous oxide and of silica almost exactly coincide with those of the average reverberatory slags, and that of the lowest melting point (1093º ± 3ºC) in the whole ternary system. The calcium oxide content, however, obviously is high. Since we have already substituted calcium oxide for alumina, and since calcium oxide is more basic than alumina, the fulfil- slag is decidedly too basic. Composition K has a slightly higher melting point (1150O + 3OC) and a higher silica content, but this is preferred because the slag is saturated with respect to tri-dymite and thus should not corrode siliceous refractories. Besides, it is less basic than composition S. The filial slag composition, therefore, was chosen to

Jan 1, 1949

By Edward Jeffrey

THE use of coke in metallurgy, to any important degree, dates from the middle of the 18th century. Its utilization came most opportunely for European civilization. The forests of Europe, except in the most remote and inaccessible regions, had been largely fed, in the form of charcoal, into the smelting furnaces. For a hundred years-the middle of the 17th to the middle of the 18th century-there was a stationary condition of population corresponding to the exhaustion of European forests. This situation, which was particularly evident in Great Britain, was due to the fact that the forests had been depleted and the practical utilization of coke had not begun. The coking industry is essential for our metallurgical industries, which in turn are basal to healthy economic progress. But coke is of great importance, not only on its own account, but for its byproducts, which enter fundamentally into all the arts of peace and war. The dyestuff industry and the manufacture of explosives are intimately connected with one another, as was shown by the recent war. The subject of coking coal, therefore, is well worthy the serious attention both of practical industry and the scientific investigator. The most valuable coking coals, from the metallurgical standpoint, are derived from the coals of highest ranks. Coals, for example, that have a carbon ratio of from 70 to 80 per cent. yield the most valuable coke for the blast furnace. The difficulty of investigating these coals, however, is great, for they are rather friable and delicate and possess a high carbon content, which makes them difficult to manipulate. They present, on account of their high carbon content, a considerable degree of opacity when examined, in thin sections, under the microscope. The tenderness of structure and blackness of such high-grade coking coals as those of Connellsville and the Pocahontas region make them extremely difficult to investigate.

Jan 1, 1925

Jan 1, 1943

By Joseph Singewald

INTRODUCTION FOR a number of years Russia, India and Brazil have outranked .all other countries as producers of manganese ores. During the 5 years immediately preceding the European war, the average annual production of Russia was 844,000, of India 694,000 and of Brazil 200,000 long tons. Since the outbreak of the war there has been a considerable falling off in the Russian and Indian production, particularly in the former, whereas the production of Brazilian ores has been greatly increased, amounting in 1914 to over 250,000 tons and in 1915 to nearly 350,000, with conditions favorable for a still larger production in 1916. Manganese is one of the few industrially important metals that are not produced in the United States in quantity commensurate with our needs, so that we have been compelled to import annually about 300,000 tons, having a value of over $2,000,000, and these ores have been obtained from the three countries mentioned above. Their rank as contributors to our imports of manganese ores was India, Russia, Brazil; and in 1913, Brazil contributed only one-fifth. During the past 2 years Brazil has furnished rapidly increasing quantities to this country, and, with the falling off of imports from India and Russia, has become our principal foreign source. In 1914, Brazil furnished two-fifths of the imports and more than India or Russia, and in 1915 over nine-tenths. The manganese ores of Brazil are consequently of more than usual interest to us at this time.

Jan 10, 1916

By C. Dirksen

This study investigates whether oxygen consumption during segregated forward combustion may be affected by natural convection. Linear theory indicates that thermal instability occurs in a horizontal porous medium when the modified Rayleigh number N 'Ra exceeds a critical value of about 40. Most experimental results, including those described here, indicate this value to be about an order of magnitude smaller. N ', is derived from "differential similarity" and the proper time scale factor is also obtained. The critical value of N'ra for a horizontal, water-saturated porous medium at atmospheric pressure subjected to a uertical temperature gradient was found to be about 3.0. The ambiguity in the value of N'R, arising when fluid properties cannot be assumed constant is indicated. Natural convection was observed for oblique systems below N 'Ra , while simultaneous horizontal flow did not affect N Racrit. The expected range of values for the various parameters pertaining to segregated forward combustion is indicated and the corresponding values of N 'Ra calculated. Only under very favorable conditions, such as high permeability, high pressure and low top temperature, can the critical value of N 'R, be exceeded. Thickness of the convection layer should not become too large, since the time required to obtain significant mixing is proportional to the square of the thickness. For an oblique combustion frant the conditions for significant mixing may be less strenuous. LNTRODUCTION Laboratory1,2 and field314 experiments have shown that a markedly upgraded oil can be produced by in situ forward combustion. Under certain conditions injected air may move through a high permeability, gas-saturated channel over the oil-saturated layer, while combustion takes place, exclusively, at the horizontal interface (Fig. 1). Such a channel may be a natural gas cap, or it may result from a forward combustion process in which injected air and combustion gases fingered through the top of the formation, causing a premature breakthrough at the production well. In this particular case of segregated forward combustion, the air stream moves parallel to the combustion front. Molecular diffusion and transverse mechanical dispersion will be insufficient to cause all the oxygen in the air stream to reach the combustion front. When the oxygen in the air stream is not completely consumed in the combustion process, it will reach the production well and create a serious fire hazard. In addition, the reduced efficiency may make the process economically unprofitable while also serious corrosion problems may be experienced in the production we11.3 This undesirable situation should, therefore, be prevented. However, in a situation as depicted in Fig. 1, an unstable temperature gradient exists in the gas phase. The combustion is taking place at the lower boundary at a nearly constant temperature that may be anywhere from 600 to 1,200F, depending on the conditions. The upper boundary of the gas phase is overlying, impermeable rock; its temperature might be around 100F, but may increase to 300F or higher due to conduction and convection as the combustion process continues. This represents a steep temperature gradient and it is conceivable that under those conditions free or natural convection will take place in the gas

Jan 1, 1967

By G. V. Raymor, James T. Waber, I. Rex Harris

The lattice parameters of a series of fcc alloys of cerium and thorium were measured at 93 " and 298OK. Lattice parameters were also estimated for 171OK. Substantial deviations, y, from Vegard's law were observed. Although y was negative at the two higher temperatures, it was positive and large at the lowest temperature. A variety of models, which have been proposed in the past, were considered, and the calculated values of y were compared with the observed values. The best agreement was achieved with values computed with Friedel's equation. THE purpose of this investigation was to determine the effect of temperature on the lattice parameter and on deviations from Vegard's law of Ce-Th alloys. A large negative deviation from Vegard's law was first observed independently by Weiner, Freeth, and Raynor' and Van vucht2 in the room-temperature lattice parameters of Ce-Th alloys that form a continuous series of solid solutions. This observation was confirmed by Evans and Raynor. The allotropy of unalloyed cerium was reviewed recently by Gschneidner, Elliott, and McDonald. In two subsequent papers,5" these authors reported the influence of various alloying additions on the y= transformation, which occurs below room temperature. Although other rare earths tend to stabilize the double-hexagonal phase, thorium, plutonium, and scandium as solutes tend to stabilize the normal fcc phase. With addition of sufficient thorium as a solute, there is evidence that the formation of is suppressed and it becomes possible to pass continuously with decreasing temperature from the room-temperature phase to the fcc a phase. Thus there is a closed loop which is similar in many ways to the y loop well-known in ferrous alloys. A closed field also occurs in the pressure-temperature "equilibrium" diagram of unalloyed cerium. Because of interest in the effect of thorium additions and their influence on the a and phases, lattice-parameter measurements were made at low temperatures on the fcc phase for a series of alloys ranging from 10 to 90 at. pct Th. The results obtained at three temperatures are shown in Fig. 1. Evans and Raynors analyzed the deviations from Vegard's law in Ce-Th alloys in terms of changes in the occupancy of the 4f electron level in cerium,

Jan 1, 1964

By Frank Corwin

It is the purpose of this article to give a brief account. of the experimental work and to show how the increase in efficiency was brought about. Part of the experimental work described in this paper was carried out by the writers, while in the employ of the Anaconda Copper Mining Co., under the direction of M. W. Krejci, Metallurgist, and Arthur Crowfoot, Chief Sampler. Complete records of all of the MacDougall testing work have been placed at our disposal through the courtesy of A. E. Wheeler, Superintendent. II. BRIEF HISTORY OF PRESENT MACDOUGALL PLANT. The first change from the Brueckner cylinders used for roasting concentrates at Great Falls was the construction of a MacDougall roaster of the Herreshoff type. This furnace was first started on June 15, 1898. It bad eight hearths, was lined with fire brick, and had an air-cooled central shaft, but no provision was made for cooling the rabble arms. It was operated for a while, and accomplished the work of roasting, but ran so hot that the rabble arms became twisted and distorted out of shape. To prevent the furnace from becoming too hot a device was then installed to draw the heated gases away from the hearths. This consisted of a pipe connected to alternate hearths of the MacDougall furnace and also connected to the flue. It was equipped with dampers, 'so that the hot gases could be drawn away from any one of the alternate hearths directly into the flue.

Jan 7, 1913

Jan 1, 1900

Jan 1, 1893

Jan 1, 1916

By M. J. Sinnot, J. C. Shyne

Low-frequency mechanical damping measurements were made to investigate internal friction in Fe-A1 alloys. The atomic ordering of the Fe-A1 system strongly influenced the stress-induced ordering internal friction. Magnetoelastic damping was also encounteyed and was shown to be reduced by the application of a static stress. THIS paper describes some damping experiments made on alloys of Fe and Al. Stress-induced ordering internal friction was measured with samples containing from 9.8 to 31.3 at. pct Al. Aluminum is soluble in a-Fe to about 50 at. pct and forms at least two long-range ordered structures, Fe3Al and Feu.' Stress-induced ordering internal friction is known to occur in many substitutional solid solutions, but few measurements of this damping effect have been made with alloy systems that have pronounced ordering tendencies. LeClair and Lomer developed expressions relating the relaxation strength of the damping process to the degree of atomic ordering and predicted that stress-induced ordering internal friction would be zero with complete ordering.' This concept was confirmed experimentally by Lulay and Wert using the system cd-Mg It is also consistent with the weak stress-induced ordering peaks observed in P -brass by Artman and in 16 wt pct Al Fe-Al by bert.' It was expected, therefore that the ordering characteristics of the system Fe-Al would strongly influence the stress-induced ordering internal friction exhibited by the experimental alloys. SAMPLE PREPARATION The alloys used in this investigation were induction melted under vacuum using high-purity melting stock. The iron was electrolytically refined Plastiron 101 which contained 99.85 wt pct Fe. The aluminum was a special 99.95 pct pure grade supplied by Alcoa. The only other raw material was spectrographically pure graphite which was used in small quantities as a deoxidant. The amount of carbon used was slightly in excess of the amount required to completely deoxidize the melt; this resulted in residual carbon contents of 0.01 to 0.02 pct in the finished alloys. The vacuum cast 2 1/2-in. diam ingots were hot rolled to 5/8-in. diam round bars. Portions of these bars were hot swaged and hot drawn to 0.050-in. diam wire. Straight pieces of the hot drawn wire were slowly heated to a temperature of 1300°C in a He atmosphere. After holding for 4 hr, the samples were allowed to cool in the furnace. This annealing treatment resulted in grain growth in the samples, the final grain size being about the same as the wire diameter. The grain boundaries were oriented perpendicularly to the wire axis, giving a bamboo grain structure. The existence of a preferred orientation could not be detected in these coarse grained samples. If the samples had a fiber structure, this probably would have been the same in all samples because of similar processing, thus the influence of crystal orientation on the relaxation strength would have been similar in all samples. The aluminum contents of the alloys are listed in Table I. EQUIPMENT The principle of the torsion pendulum was used for the internal friction measuring device. The

Jan 1, 1961