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By Michael Epstein, Daniel E. Rosner

Fume nucleation sufficiently close to vaporizing suvfaces can augment net vaporization rates into cooler environments. Environmental conditions favoring large vaporization rate enhancements are briefly discussed and a previous theoretical treatment of this nucleation phenomenon is generalized to account for the self-regulating effect of condensalion-heat release within the boundary layer. Despite kinetic limitations on homogeneous nucleation, and latent heat release, non-diffusive condensate removal processes appear to make possible large enhancements in steady-state vaporization rates, provided surface temperatures are well below the boiling point. When condensed phases vaporize (or dissolve) into cooler media, the diffusion-limited mass loss rate can be strongly influenced by the process of nucleation/con-densation (or precipitation) within the thermal boundary layer. This condensation process (which typically leads to mists or fumes in the case of evaporation into cooler gases) has the effect of steepening the vapor pressure profiles near the evaporating surface, since the condensation zone acts as a vapor sink. However. the resulting enhancement in the diffusion-limited evaporation rate can be estimated (as first done by Turkdogan1 for the case of molten iron/nickel alloys evaporating into helium) only if one has independent knowledge of the critical supersaturation, sCrit(T), required to homogeneously nucleate the vapor.* In a recent reformulation and generalization of the theoretical model of Ref. 1 it has been shown that, when log sCrit is approximately linear in reciprocal temperature, rather simple expressions can be derived4 for the ratio of the actual rate of vaporization j" to either the minimum (no condensation) rate j"min, or the maximum (equilibrium condensation) rate j"max In the present communication we wish to briefly report on further developments and implications of the formulation of Ref. 4, with emphasis on i) environmental conditions favoring large enhancements in vaporization rate, and ii) the self-regulatory influence of condensation heat release (neglected in Refs. 1 to 4) on predicted vaporization rates. Additionally, we take this opportunity to correct several misprints appear- ing in Ref. 4, and comment on Elenbaas's recent criticism5 of Ref. 1. MAXIMUM POSSIBLE VAPORIZATION RATE IN PRESENCE OF CONDENSATION A nonequilibrium theory is of interest because of the very large difference between the minimum (no condensation) and maximum (equilibrium condensation) vaporization rate. The magnitude of this maximum possible enhancement can be shown quite clearly by combining a result of Refs. 3 and 4 with the fact that for most liquids there is a simple relationship between the molar heat of evaporation, A, and its boiling point, i.e., A/(RTBp) = C, where the constant C, often called the Trouton ratio, takes on values not very different from 11.* More generally, for any substance (including The Trouton ratio (which for water is 13, for methane, 10, and so forth) will be recognized as the ratio of the molar entropy change upon vaporization (at TBP or Ttransf) to the unlversal gas constant R. Its near constancy reflects the fact that the change in atomic order upon vaporization depends only weakly on the kinds of molecules involved. those that sublime under ordinary conditions) we can define a characteristic transformation temperature. Ttransf, by a relation of the form Ttransf =A/(CR), and then examine the maximum possible evaporation rates as a function of how far removed from Ttransf are the surface temperature, Tw, and ambient temperature, T. Subject to the assumptions: 1) equilibrium vapor pressure, pv,eq, everywhere small compared to prevailing total pressure, p, and 2) negligible effect of condensation heat on temperature profile, the maximum enhancement ratio was found (Eq. [17], Ref. 4) to be: where, for most vapors, Nu/NuD (the ratio of heat transfer coefficient to mass transfer coefficient for the same configuration) is a number near unity.* Ex- *An alternative derivation of the Nu = NuD special case of this equation. revealing its validity for arbitrary velocity/temperature profiles in a laminar boundary layer, is given in Ref. 3. amining this result for a "Trouton substance", one obtains the results shown in Fig. 1, constructed for C = 11. Since we are concerned with vaporization enhancements (j'max/J"min > 1) at surface temperatures below Ttransf, this area of interest is shown unshaded. One notes that at a fixed ambient temperature (hence, T/TtranSf) there is a unique surface temperature, 2T , at which j"max/j"min attains its peak value; moreover, the peak enhancement ratio, see dashed locus. Fig. 1, is: (NuA/NuD)(C/4)(Ttransf/T,). Hence, if Nu = NuD, when the ambient temperature is less than 1/4 of TtranSf the peak enhancement exceeds the Trouton

Jan 1, 1969

By C. H. Mathewson, A. U. Seybolt

As is well known, many questions affecting the properties and uses of a metal cannot be answered without careful consideration of the state of purity realized in the various operations of preparation, refining, or special treatment that have brought the product to its final state. The occurrellce of an impurity in minute quantity offers no guarantee that its effect will be inconsiderable because dissolved substances often modify the properties of a metal quite out of proportion to their concentration. In such cases the determination of solid solubility must be accepted as a problem of considerable difficulty, requiring the use of especially purified materials and methods not ordinarily used in the metallurgical laboratory. This aspect of the equilibrium between metals and their oxides is especially important and a search for fundamental data reveals little except conflicting opinion even concerning the systems of common occurrence and interest. Rhines and Mathewson1 in 1934 studied the solubility of oxygen in solid copper by annealing to equilibrium in air and gave reasons for the failure of other methods, notably the ordinary procedure of heat-treatment followed by microscopic examination, to yield reliable results. In this paper, a similar study has been made of the solubility of oxygen in cobalt. The simple theory of this method is outlined below. Conditions of Equilibrium between a Metal and Dissolved Oxide at Different Temperatures and Pressures The general conditions of equilibrium in any system are conveniently summarized in a projection of the triple curves of the P, T, X space

Jan 1, 1935

By A. U. Seybolt, C. H. Mathewson

As is well known, many questions affecting the properties and uses of a metal cannot be answered without careful consideration of the state of purity realized in the various operations of preparation, refining, or special treatment that have brought the product to its final state. The occurrellce of an impurity in minute quantity offers no guarantee that its effect will be inconsiderable because dissolved substances often modify the properties of a metal quite out of proportion to their concentration. In such cases the determination of solid solubility must be accepted as a problem of considerable difficulty, requiring the use of especially purified materials and methods not ordinarily used in the metallurgical laboratory. This aspect of the equilibrium between metals and their oxides is especially important and a search for fundamental data reveals little except conflicting opinion even concerning the systems of common occurrence and interest. Rhines and Mathewson1 in 1934 studied the solubility of oxygen in solid copper by annealing to equilibrium in air and gave reasons for the failure of other methods, notably the ordinary procedure of heat-treatment followed by microscopic examination, to yield reliable results. In this paper, a similar study has been made of the solubility of oxygen in cobalt. The simple theory of this method is outlined below. Conditions of Equilibrium between a Metal and Dissolved Oxide at Different Temperatures and Pressures The general conditions of equilibrium in any system are conveniently summarized in a projection of the triple curves of the P, T, X space

Jan 1, 1935

By D. Mizer, J. B. Clark

In a recent investigation of the entire magnesium-yttrium phase diagram, Gibson and Carlsonl report the maximum solid solubility of yttrium in magnesium as 8.0 wt pct Y at 1050°F (565°C). However, independent studies of the precipitation in magnesium-yttrium alloys, 2 conducted prior to the publication of the above phase diagram, indicated a greater solid solubility of yttrium in magnesium. Accordingly, the magnesium-rich region of the diagram was re-investigated to determine more accurately the liqui-dus, solidus, and solvus of the magnesium solid solution in this system. Metallography and thermal analysis were chosen as the best corroboratory methods for accurately determining this region of the diagram. A magnesium-yttrium master alloy was prepared from yttrium of 99.9 pct purity and singly sublimed magnesium of 99.9 pct purity. Subsequently, the twelve magnesium-yttrium alloys shown in Fig. 1 were prepared using standard alloying procedures for magnesium. Metallographic samples of the alloys were heat treated under an SO, atmosphere in an electric furnace capable of control within ±3oF of the desired temperature. Alloy samples for the metallographic determination of the solvus, and for the precipitation studies were solution treated at 1000° F for 16 hr. Subsequent aging times for the solvus determination varied from a minimum of 6 hr for the higher temperatures up to 816 hr for lower temperatures. Periods of 30 min at temperature were used to generate liquation for the metallographic placement of the solidus and eutectic horizontal. The liquidus and the eutectic horizontal were determined by thermal analysis. Simple time-temper- ature heating and cooling curves were obtained from 10-g alloy samples heated and cooled in a well-insulated electric furnace. An Iron-Constantan thermocouple was placed in direct contact with the sample. The thermocouple did not contaminate the alloy sample since metallographic examination showed that the alloy melt did not wet or attack the thermocouple. The heating and cooling rates were approximately 5 to 8OF per min. The standard metallographic procedures for magnesium were used in polishing and etching the magnesium-yttrium alloys studied. Glycol etchant* was etchant was used to reveal precipitate in the solvus determination. The redetermined magnesium-rich region of the magnesium-yttrium diagram is shown in Fig. 1. The

Jan 1, 1962

Prof. J. C. BRanner, Stanford University, Cal. (communication to the Secretary): On p. 398, Mr. Hedburg mentions Marionite and Brannerite as ores of zinc. Neither of these has been authoritatively recognized as a distinct mineral species. Marionite, originally described by Elderhorst, was subsequently determined to be nothing else than hydrozincite. Analyses of the so-called Brannerite were sent by me to Prof. Penfield, who says it is a mixture of Smithsonite with some other mineral. On p. 398, Mr. Hedburg says the zinc-bearing formation of North Arkansas " is recognized as the Upper Silurian." So far as my observation goes, the ores occur both in Lower Carboniferous and in Ordovician or Lower Silurian rocks, but nowhere in rocks known to be of Upper Silurian age. If Mr. Hedburg has any paleontological evidence of the Upper Silurian age of these rocks, or of any of them, he will confer a favor upon geologists by making it known. On the same page is another statement in which I cannot concur. He says that in this region, " it can easily be seen that the largest fissure-deposits have been eroded and washed away, leaving here and there a few patches adhering to the hillsides." I am compelled to say that in many years' study of the geology of the region in question, I have never been able to recognize such a state of affairs as Mr. Hedburg here describes. The patches which he regards as remnants of fissure-veins, " adhering to the hillsides," I have found to be either the edges of bedded deposits, or portions of the zinc-bearing breccias, formed along old drainage-lines, and laid bare by the ordinary processes of erosion. That fissure-deposits have been partly removed by the same agency, goes without saying; but it is, in ,my judgment, no more true of North Arkansas than of any other mining-region that erosion has selected and washed away " the largest " deposits. My own views of the region in question are given in detail

Jan 1, 1902

By Marie Kinzel

LOS ALAMOS, New Mexico, the birthplace f the atomic bomb, is one of the most famous-and mysterious-places in the world. It leaped into fame on Aug. 6, 1945, when the first atomic bomb burst over Hiroshima. Unheard of until that day, its present life is as hidden from most people as was its very existence in pre-Hiroshima days. Then, those who did know of it dared not breathe their knowledge. "What do you tell your wife when you go to Shangri La?" was the favorite quip of the few consultants who made regular trips from east or west to Los Alamos during the tense months when the bomb was in the making. Security regulations made it impossible even to hint at the rigid secrecy surrounding the project. The puzzled wives in question knew only that their husbands had top priority on airplane flights to Albuquerque. When they had verified the safe arrival of the flight, they undoubtedly breathed a sigh of relief. If they could have visualized the rest of the trip, the sigh of relief would have been replaced by a state of tizzy, until a telegram came saying "Arriving home on Flight X" (on a nice safe airplane).

Jan 1, 1946

By Verne C. Fryklund, S. Warren Hobbs

The Coeur d'Alene district in the panhandle of Idaho is one of the major lead-zinc-silver producing areas in the world. The value of recorded production to date has exceeded $2 billion. Country rock comprises six formations of the fine-grained, highly siliceous, and slightly metamorphosed Precambrian Belt Series. Small stocks of monzonitic rocks and several varieties of dikes intrude the sediments. The district is at the intersection of a north trending major anticlinal uplift and the west northwest-trending Lewis and Clark line of which the Osburn fault is the dominant feature. The district structure is complicated and comprises folds, some of which are overturned, and a complex of faults of diverse ages and directions of movement. Late Cretaceous stocks but are also probably Cretaceous in age. The productive veins are localized within a series of 12 subparallel, straight mineral belts that trend approximately N65°W and that appear to be controlled by deep fractures in the basement rocks. The mineral belts are in two groups, separated by 15 miles of post-mineralization movement on the Osburn fault. Veins and ore shoots are variously disposed within each mineral belt. Many crop out at the surface, but others apex several thousand feet beneath it. Local controls that influence the position of ore shoots within the mineral belts include the brittle character of host rock attitude of bedding relative to the mineralized fracture, and the amount and direction of movement on faults. Depth appears to have had little effect on the occurrence or type of ore. Ore occurs in a series of steeply dipping replacement veins of relatively simple mineralogy. Six periods of mineralization, ranging from Precambrian to Tertiary in age, are recognized. The productive galena sphalerite-bearing and tetrahedrite-bearing veins-of the main period of mineralization-are younger than the

Jan 1, 1968

W. H. Blauvelt, New York, N. Y.—One thought lias been running through my mind during the wholc of this meeting and that is that the scientific and the practical men must recognize very clearly their interdependence. The value of scientific classification of coal is going to be of the very greatest importance to the users, the practical men. Is not the scientific investigation and the great amount of work that is being done in a measure at least lost to the world? Therefore the scientific investigations and the practical needs of the users should bo brought as close together, and the work should be done as closely together, as possible; that is, the scientific man should know what the practical man needs, and the practical man should not feel that the scientific man is merely a theorist. Scientific investigation is going to have a great effeet and be of great valuc to the practical man who is trying to solve his problems. In the subject which I discussed' for instance, we must look to the scientific man to tell us why coal cokes in one way and not In another and why certain coals will do certain things and others, which appear on the surfacc to be generally similar, do not act in the same way. Need or Physical Data on Coal H. J. Rose, Pittsburgh, Pa.—There is a subject which is a sort of hobby of mine; that is, the need for what might be called critical tables of constants for coal. The chemist has big volumes giving constants, such as the density, solubility, specific heat, thermal conductivity and all other physical and chemical data that have been determined for chemical compounds. Data arc also available on many common materials, for example, the density, hardness, modulus of rupture or maximum crushing strength of swamp white oak as compared with some other wood. In fact, physical data for practically cvery hype of wood commercially produced in the world can he found. In the same way the metallurgical man has handbooks giving the properties of alloys, etc., but we havc very little tabulated information about coal. Our principal reference works are the volumes published by the U. S. Bureau of Mines on the proximatc and ultimate analysis and calorific values of coals of the United States. That is 3 pioncer work of enormous value, but we have reached the point where we need more diversified information. Mr. Fulweiler raised the question of the relative strength of the different coals and cokes. Dr. Campbell and Dr. Ashley wanted to have some information on the resistance of coal to air slacking. It was brought out in the discussion that we want to know something about the coking properties of coal. There are any number of physical tests that we need, such as the thermal conductivity of certain coals, the coefficient of expansion, or the coefficient of friction; or other constants. A smattering of such information is scattered through the literature; for instance, a research worker in Wales will report a coefficient of expansion on Wclsh coals and one in South Africa will report something else for one or two kinds of African coals, hut it is difficult to find the information that is needed on our own coals. Would it not be worth while to consider collecting reliable critical

Jan 1, 1930

By A. J. Shaler, J. Prieto Isaza, John Wulff

TANTALUM metal has a number of unique properties which give it widespread application in modern technology and in research. In electronic apparatus involving high temperatures in vacuo some of the refractory metals become brittle. Tantalum retains its ductility at elevated temperatures, and this property, together with its low vapor pressure and its ability to absorb gases, make it important in this field. Its chemical inertness in the presence of acids, halogens, and other corrosive media, makes it useful in chemical apparatus and in neuro and orthopedic surgical applications. As an addition to tungsten carbide in steel-cutting grades of cemented-carbide tools, the carbides of tantalum and of its sister element columbium have found considerable use. The present-day method1 of manufacturing tantalum is to sinter a powder compact of the metal in vacuo. Because tantalum- columbium alloys are difficult to work and since tantalum ores almost always contain columbium, the two metals must be separated chemically, the products of the separation being generally in the form of potassium tantalum fluoride and potassium columbium oxyfluoride. These salts are used in fused-salt electrolytic baths from which coarse metallic powder is deposited as a sponge at the cathode. Finer powder can be made from the coarse product or from tantalum scrap by first submitting it to an embrittling heat treatment in hydrogen and then crushing it. The fine hydrogen- containing powder may subsequently be degassed in vacuo at a high temperature. Prompted by the success of others2,3 in the magnesium reduction of titanium and zirconium halides, one of the authors under- took4 an investigation of the thermo- chemistry of the reaction between solid magnesium and gaseous tantalum penta-chloride, a subject which had not previously been studied. He found that the heat of formation of tantalum pentachloride is approximately 364,250 cal per mol at temperatures lower than the melting point of magnesium. A value of 83 units was found for the standard entropy at these temperatures. With these values, it was shown that magnesium and tantalum pentachloride are capable of reacting exothermically at temperatures less than the melting point of magnesium, and that no great violence is to be expected when these substances are heated together. The exothermic nature of the reaction indicated that the process should be efficient and should not require much externally applied energy. Tantalum pentachloride is not commonlv made commercially, and any process using it therefore involves the subsidiary problem of producing and handling this substance. A series of experiments was carried out in which dried chlorine saturated with carbon tetrachloride was passed over heated tantalum, either in the metallic state or combined

Jan 1, 1947

By B. W. Frazier

This interesting application of the laws of thermodynamics to metallurgical practice has not been discussed by any writer, within my reading, except the late Prof. Callon of Paris. In his Cours de Machines," Prof. Callon has given a short but lucid discussion of this subject in the admirably clear style for which he was remarkable. Although the interest attached. to the subject is rather theoretical than practical, I have thought that an attempt to explain the mechanical action exerted in the hot-blast oven might not be entirely devoid of utility, especially in the suggestions which it involves. The statement, that the mechanical work performed in heating the blast is, when high temperatures are produced, considerably greater than the work performed by the blowing-engine, may seem incredible to many who are practically acquainted with the subject, appearing, as it does, to conflict with the results of their experience. It is, nevertheless, literally true, and I shall attempt in this paper to prove it, and to explain why it has not rendered itself palpably manifest in practice. Before proceeding to the mathematical demonstration, it will be well to recall to mind the definitions of some terms employed by writers in mechanics and thermodynamics. The actual energy of a moving body, as defined by Rankine, is the work which it is capable of performing against a retarding resistance before being brought to rest, and is equal to the energy which must be exerted on the body to bring it from a state of rest to its actual velocity. The value of that quantity is the product of the weight of the body into the height from which it must fall to acquire its actual velocity.

Jan 1, 1879

By Pradeep K. Rohatgi, Clyde M. Adams

Dendritic aggregate of ice formed on freezing of aqueous soluitions has been studied. Chlorides of sodium, potassiutn, lithiunz , and hydroget1 were used as solutes. The spacing between ice platelets or den-drites was experimenlally found proportzonal to the square root of freezing time when the freezing rate was constant from beginrting to end of solidification; the constant freezing rates were obtained during freezing of small droplets of aqueous soliitions surrounded by relatively large heat sinks. The transverse growth velocity of the ice platelets is proportional to the square root of the freezing rate. During unidirectional freezing from a constant temperuture chill, the solution at each location is subjected to a spectrum of freezirtg rates. The freezing rate is ini- FREEZING of solutions has been a subject of investigation in many disciplines. Aqueous solutions offer the advantage of transparenty; their study is of special significance due to the increasing interest in freezing processes for desalination. In addition dendritic solidification of aqueous solutions is in many ways analogous to freezing of metallic solutions. Aqueous solutions of most ionic salts freeze with tially low, passes through a maximum, and then decreases until solidificatimz is complete. The den-drite spacing increases linearly with the distance from the chill surface; it is inversely profiortional to the square root of the maximum freezing rate. The dendrite spacings in the two systems (the constanl freezing rate and the varying freezing rate) are equal, when the maximum freezing rate of the varying freezing rate system equals the average freezing vale of the constant freezing rate system. Mass transport in interdendritic liquid duriug solidificatiotz is analyzed; the experimental observations indicate that maximum concentration difference (AC) and supercooling (AT) in the interdendritic liquid are indepexdent of freezing rate. the separation of practically pure ice crystals from the liquid phase; with very few exceptions there is no solid solubility of ionic salts in ice. As an ice crystal grows there is rejection of solute from the moving interface into the liquid. Since the rejected solute moves primarily by diffusion, concentration gradients are established in the liquid. The highest solute concentrations are found in liquid immediately adjacent to liquid-solid interfaces and lowest concentrations farthest from the interface. Two-phase equilibrium obtains only at the solid-liquid interface; at other locations the liquid becomes supercooled because temperature gradients are negligible compared to concentration gradients. This is an immediate consequence of the fact that thermal diffusivities are considerably higher than mass diffusivities.

Jan 1, 1968

By Reginald S. Dean

THE widespread occurrence of manganese in low grade oxide and carbonate ores not amenable to mechanical concentration has led to extensive investigations of hydrometallurgical methods for producing a pure manganese compound suitable for further treatment. Manganese carbonate is the preferable compound. This product when fully crystalline and of not too fine crystal size is easily filtrable and stable in air. It can be converted to other compounds such as the oxides by heating in air or can be reacted with acids for producing salts. A useful hydrometallurgical process must produce relatively concentrated solutions that can be purified easily, reagents must be cyclically used, and heat requirements must be small. Neither the ammonium sulphate nor sulphur dioxide leaching processes that have been tested extensively fulfill these 'requirements. Other hereto-fore proposed processes have obvious limitations and have not been tried on a large scale. The present process is based on the discovery by the writer of a new group of aqueous manganese-ammonia complex solutions highly concentrated in ammonia, which permit rapid solution of manganous oxide to concentrations of 80 to 100 g Mn per liter and from which a fully crystalline, easily filterable manganese carbonate is precipitated by the addition of carbon dioxide and partial ammonia removal. Although the process may be carried out with many ammonium salts, commercial advantages dictate the use of ammonium carbamate, which is obtained when CO2 is passed into concentrated aqueous solutions of ammonia. If the carbamate is used, the only reagents, ammonia and C02, are volatile and may therefore be recovered from solutions and residues by heating, thus eliminating washing and extensive evaporation. Impurities are controlled easily as most metal oxides are either insoluble in the lixiviant or fail to precipitate with the manganese carbonate. Others are controlled by sulphide addition. The process has been tested extensively on a small scale on a wide variety of ores; including Three Kids, Artillery Peak, Cuyuna, and Chamberlain; as repre-

Jan 1, 1952

By JESSE L. MAURY

DEVELOPMENT of new gold mines in Canada since the price of that metal was increased in 1932 and 1933 has been of interest and importance to many of us. The day-by-day story has given an impression of aggressive effort and enough good luck so that the spirit of enterprise has been encouraged. It is the purpose of this article to report the results of a statistical appraisal which give emphatic numerical confirmation to this impression, together with certain side lights on the costs of development and equipment of new mines. The data presented have been taken from all readily available published sources up to the close of 1938 and are representative of that year. A. B. Bower did a large part .of the spadework and Weston Thomas offered many helpful suggestions.

Jan 1, 1939

By Harry L. Washburn

Use of coal thermal dryers has steadily increased since 1928 when one of the predecessor companies of the present Consolidation Coal Cu. constructed a complete preparation plant with thermal dryers. Today there are about 25 additional preparation plants that, all together, use over 65 individual thermal dryers of almost every type. The thermal dryer is a heat generator and the unit may have a separate furnace or a firebox that is an integral part of the dryer. It is also a materials handling device that allows an intimate mixture of wet coal and hot gases with instrumentation for temperature control and. in some cases, the more difficult flow rate of hot gases. The materials handling portion of the dryer is subject to the normal wear and teal of any similar device plus effects of heat, water vapor, moisture: and, sometimes, acid. With present emphasis on air pollution. most fine coal dryers have wet scrubbers.

Jan 8, 1963

By Zay, Jeffries

THE effect of thoria (ThO2) on grain growth in tungsten was discussed in some detail in a paper presented before this Institute by one, of the authors in 1918.1 In that paper it " was assumed that the, thoria was present in the tungsten entirely as a mechanical mixture. There was no indication in the experiments described that even a trace of the thoria was in solid solution in the tungsten. Langmuir,2 however, observed that thoriated-tungsten filaments under certain conditions showed electron emissions many thousand times greater than unthoriated tungsten at the same temperature. He concluded from his studies that a slight amount of the thoria had dissociated on heating the filament to a temperature near 220°. C. At this temperature and higher, part of the thorium diffuses to the surface of the filament where it evaporates at. a much faster rate relatively, than the tungsten, and also at a rate, nearly as fast as it is brought to the surface by diffusion: If the temperature is lowered to say 1800°,. C., diffusion of the thorium atoms to the surface is more rapid than evaporation, sown adsorbed film of thorium atoms is produced on the surface of the tungsten filament. The electron emission is governed by the outside layer of atoms so the emission from such a filament might be expected to approxi¬mate that of a thorium filament at the same temperature. PRESENCE OF METALLIC THORIUM IN THORIATED TUNGSTEN If the filament containing the adsorbed film of thorium. is heated to a sufficiently high temperature, the thorium atoms evaporate: rapidly and the electron emission becomes more nearly that of tungsten. On cooling again to 1800° C., or thereabouts, the emission 'builds up gradually to a maximum. The filament containing the adsorbed layer of thorium atoms is said to be "activated." By studying the rates of activation under different conditions of prior thermal treatment and at different temperatures, Langmuir was able to arrive at an estimate of the

Jan 1, 1927

By P. W. Ramsey, D. P. Kedzie

INCREASING demand for improved strength-weight ratios made on aircraft structures has resulted in a gradual increase in the tensile strength requirements for steels used in such applications. As the cyclic loads often are more critical than static loads, and the fatigue properties are generally the design criteria, the question arises as to whether an improvement in fatigue properties accompanies the increased tensile strength. The present investigation was undertaken to determine the relationship between fatigue and tensile properties for an aircraft quality steel in the 155 to 280 ksi (1000 psi) tensile strength range, using the Prot method of fatigue testing. Procedure and Results After preliminary work to establish proper heat treating procedures for this heat of aircraft quality electric furnace steel (a Ni-Cr-Mo-V steel," AMS- Prot Fatigue Testing Method—The determination of the endurance limit by the conventional Wohler method can be time-consuming and easily require 20 specimens when statistical variance is to be established. This is also true when endurance limit loads are determined on actual parts or subassem-blies, and the desirability of a reliable accelerated method has been evident for some time. The primary advantage of the Prot method of fatigue testing is in reducing the number of specimens and the time required for each test. Unlike the Wohler method, every Prot specimen tested con- tributes to the determination of the endurance limit, and the authors have been able to duplicate Wohler results obtained with 20 specimens with only half the specimens and a fourth of the total cycles. This new technique for defining the endurance limit was proposed in 1948' by Marcel Prot and consists of progressively increasing cyclic stress until fatigue failure occurs. By varying the load rate, a, a useful relationship is found to exist with failure stress, so that for steel the failure stress appears to

Jan 1, 1958

By Ralph W. Marsden

The natural iron ores of the Lake Superior Region in the United States are being replaced by iron-ore concentrates produced from magnetite- or hematite-rich horizons in the Precambrian cherty iron formations. The production of natural ores will soon be less than one-half of the total ore shipped annually. The tonnage of natural ore produced will continue to decline until it is a minor percentage of the ore shipped. The natural ores include (1) soft ore, (2) hard ore, ( 3) conglomerate ore and ( 4) siliceous ore. The soft ores are the important ore type and are sometimes termed "Lake Superior type ore". These ores are in situ deposits of hematite and limonite formed by the leaching of silica and other gangue materials in the iron formations. The leaching is believed to have been done by downward moving surface waters. In deep ore deposits, generally over 1000 feet below the present surface, circulation and leaching action may have been assisted by hydrothermal activity. Hard ore deposits occur on the Vermilion and Marquette ranges where hematite or magnetite has replaced the silica (and possibly some silicates) in cherty iron formation. These ores commonly occur in structural situations favorable for the movement of hydrothermal waters. The ores are believed to be the result of hydrothermal action with iron, possibly from the iron formation, transported by hydrothermal waters to areas favorable for the replacement of silica by iron oxides. Certain stratigraphic horizons of the Lake Superior Precambrian cherty iron formations contain sufficient iron as magnetite or hematite, with a grain size and texture that will give adequate mineral liberation, to yield an ore-quality product after grinding and concentration. The magnetite-rich deposits are termed magnetite taconites. These ores occur on the Mesabi, Gogebic, and Marquette ranges. Magnetite taconite ores are unenriched cherty iron formation and are the result of the sedimentary deposition of the iron formation and the metamorphic history of the rock. The commercial quality hematite-rich iron formations in Michigan are termed jasper ores. The jasper ores are being mined on the Marquette and Menominee ranges. These ores are composed of specular or granular hematite associated with quartz and iron silicates. The jasper ores appear to be recrystallized iron formations in which iron, prior to recrystallization, occurred as hematite.

Jan 1, 1968

By T. F. Bower, M. C. Flemings, H. D. Brody

A series of experiments are reported which show thai reasonable assumptions for analysis of solute redistribution in solidification of castings and ingols illclr(de: negligible undercooling before nuclcation of solid phases, negligible increase of solute in advance of the tips of growing dendrites, complete diffusion within the Liquid oer distances the order, of dentrite arm spacings, platelike dentrite t/o?$holog?.. Qzmli/ali,e and periment is obtained JOY Al-Cu alloys front measurements of amount of nonequilibrium second phase, minimum solute content at the centers dentrites arms (after solidification), and 3) change in minimum solute content in dentrite arms during solidification. In a previous paper' analyses were given describing solute redistribution in dendritic solidification. The analyses were undertaken primarily to permit prediction of "severity of microsegregation" in a casting or ingot after solidification and cooling to room temperature, but can also be used to predict "local fraction solid' as a function of temperature in the solidifying alloy. Numerical results were given for Al-Cu alloys. The aims of this paper are to examine the validity of some of the assumptions of that analysis, and to compare predictions of the theory with experiments. All experiments reported are on Al-Cu alloys, the bulk on Al-4.5 pct Cu alloy. EXPERIMENTS Experiments conducted were on small ingots, 41/2 in. in diam by about 10 in. high. solidified in a controlled thermal environment (i.e., in a resistance-heated, re-circulating air furnace, whose temperature could be controlled to 1°C). In one series of experiments, the ingots were solidified very slowly (solidification time was varied from 8 to 1000 hr) and at constant rate of heat extraction. In a second series of experiments the ingots were solidified ( 'unidirectionally". Fig. 1 is a sketch of the method of making the two different types of ingots. The unidirectionally solidified ingots were fully columnar, and the slowly solidified ingots had equiaxed structures, Fig. 2. In making the slowly solidified ingots, the mold employed was carbon steel, coated with inert refractory. Typically the mold and its environment were heated to 700°C. The molten alloy was then poured into the mold and the temperature of the system equilibrated above the liquidus. The environment of the mold was next cooled with a controller responding to a differential thermocouple that measured the difference between the temperature of the melt and the temperature of the mold environment. The differential thermocouple consisted of one chromel-alumel junction in the melt connected in opposition with a second junction in the furnace. The potential across the differential thermocouple was input to the controller which acted to keep this potential at a set. constant value; hence the temperature difference between the two junctions was maintained nearly constant. Major resistance to heat flow in the above apparatus was between the metal surface and the furnace atmosphere, not in the metal itself. By maintaining a constant temperature difference between the metal and the furnace atmosphere, the controller maintained an essentially constant rate of heat extraction during solidification, regardless of amount of heat released by the metal per unit temperature change. When the metal temperature dropped just below the eutectic temperature. the ingot was removed from the furnace and water-quenched. The unidirectionally solidified ingots were cast in a similar mold to the foregoing except that provision was made to extract heat through the bottom face of the mold by passing air or water through the mold base, Fig. 1. For these experiments, metal and mold temperature were again equilibrated above the liquidus. Temperature of the mold environment was then held

Jan 1, 1967

By J. B. Dyess

TARNISH films on some of the common metals (particularly on copper and silver) have been of much scientific and commercial concern for a long time, but before the development of the electrical method1 of measuring film thicknesses there was no satisfactory quantitative approach by which to study the separate parts of these complex films. This method has been adapted to the measurement of duplex (cuprous-cupric) oxide films on copper .2 In the present work it has been used to measure tarnish films on copper when they were mixtures of cuprous oxide and cuprous sulphide, and also when they contained cuprous oxide, cupric oxide and cuprous sulphide, each component part being measured at a different potential value. Oxide-coated copper specimens, prepared by heating copper in air at chosen temperatures for given periods, were exposed to moist hydrogen. sulphide in air to form the various oxide-sulphide films studied. The comparative resistances afforded by (1) different thicknesses of oxide films, and also (2) equal thicknesses of oxide and sulphide films, against severe attacks of hydrogen sulphide were measured. The electrical method requires that the time be observed for the cathodic reduction of each part of the film substance, and these respective time values multiplied by the constant current give the corresponding quantities of electricity expended. Then each millicoulomb per square centimeter represents a film thickness of T= MX10 8 2D X 96,494 X 103 (a) where M is weight of oxide (or sulphide) giving one gram-atom of oxygen (or sulphur) for cathodic reduction, D is density of the oxide (or sulphide) and t is the thickness in Angström units per millicoulomb per square centimeter. The value of t for cuprous sulphide (cubical) is 14.27, and is obtained by substituting 5.78 for D and 159.20 for M in equation a. Previous values2 of t for cuprous and cupric oxides (12.36 and 6.39, respectively) were used in the present work.

Jan 1, 1939

By J. Szekely, V. Stanek

Heat and gas flow interactions in nonisothermal packed beds were examined in the paper. A study was made of the response of the system to a step or pulse change in the inlet gas temperature, with a fixed value of the overall pressure drop across the bed. Under these conditions the heat flow and fluid flow transients are coupled because the convective heat transfer rate is alfected by the mass flow rate of the gas which, in turn, for a fixed pressure drop will depend on the temperature profile in the system. The Problem was stated in terms of differential equations, which were integrated numerically. The parameters used in the computation were so chosen to reflect the operation of the stack region of blast furnaces and sinterbeds. The computed results showed that the pressure drop-flou1 relationships and the rate of progress of the temperature fronts (waves) were strongly interrelated and were also markedly affected by variations in particle size and in void fraction. MANY metallurgical processes involve the contact of solid particles with a gas stream in a packed bed arrangement under nonisothermal conditions. Examples are shaft furnaces, regenerators, pebble heaters, and the sinter process. Although the heat and mass transfer aspects of packed bed processing have been extensively studied, the associated flow phenomena and in particular the effects of nonisothermality on the flow, have received little attention to date. :In fact, most of the previous workers considered the flow rate of the carrier gas time invariant and independent of the heat or mass transfer processSzekely and carr2 have shown that the pressure drop-flow relationships in nonisothermal packed beds may be strongly affected by the temperature profile within the system. These authors have devised a method for relating the pressure drop to flow for a given temperature profile. thus providing an extension of the Ergun equation to steady nonisothermal systems. Finally, in a recent paper willmot3 examined the response of regenerators to externally imposed changes in the gas flow rate. Both these investigations were somewhat specialized since, in general, neither the temperature distribution nor the gas flow rate may be regarded as truly independent variables, thus the heat transfer and the fluid flow problems have to be solved simultaneously. The work reported here is divided into two parts: in Part 1 the general formulation is given and a detailed discussion is presented of fixed bed systems. Part is devoted to systems in which a gas and particulate solids are contacted in a counter flow arrangement. FORMULATION Consider a nonisothermal fixed packed bed, extending from through which a gas is flowing. The problem is to develop a relationship between pressure drop and gas flow (with the gas flow being the dependent variable) and to evaluate the rate at which a change in the gas temperature, imposed at the inlet, travels through the system. Let us consider an infinitesimal section of the bed and establish differential heat, mass, and mechanical energy balances over this region. In addition, relationships are needed describing the temperature dependence of gas density (equation of state) and the temperature dependence of viscosity. These may be written as: where c, and are constants. It is noted that in this formulation we neglected any temperature gradients within the solid particles, thus assuming these to be either sufficiently small or of sufficiently high thermal conductivity to meet this condition. The justification and consequences of this assumption will be mentioned in the discussion.

Jan 1, 1970