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By William Metcalf

ONE of the first questions that naturally occurs to one who handles steel is," Why does steel harden ?" To answer this question the chemist and physicist have devoted much thought and experiment, and while they have enriched our store of knowledge of the nature and composition of steel, it cannot be said that they have yet solved the problem involved in its hardening. In this communication I desire to direct attention to a line of investigation yet new, in the hope that it may receive the attention of those who have the time and ability to pursue it. I refer to magnetism. There are so many parallels between the action of magnetism on iron and steel and their behavior under different processes of manipulation that it would seem as if there must be some connection between the forces at work in the different cases, if, indeed, there be not an identity of force in all of these cases. Magnetism, as we know it, may be merely the visible manifestation of forces, which may serve as a guide to lead us to an exact knowledge of the structure, the strains, and the resistances with which we have to deal in iron and steel. If a magnet be brought close to a pile of iron filings, the little pieces of iron will fly to the magnet and attach themselves to it, with their longer axes lying in the direction of the force. If molten cast iron be poured into an iron mould,-a chill,-the iron upon crystallizing will form needlelike crystals, with their long axes normal to the surfaces of the mould. If the iron is at the proper temperature and the quantity small, compared to the mass of the mould, the whole of it will be chilled, or set, in' the hard needlelike crystals

Jan 1, 1881

By Arthur Lake

Within the past few months I have had occasion to visit and examine the area of country in Gunnison county locally called the Gold Belt and extending from the Cebolla river on the west to the head of Taylor Park and the Sawatch range on the east. The region including the "belt" may be hided topographically into two parts, a northern and a southern one. The former is characterized by lofty mountains and deep canons, with occasional parks and wide valleys. Most of it is included in the granitic system of the Sawatch range, with local patches of the Palaeozoic sedimentary rocks, more or less traversed by great bodies of porphyry and other eruptive rocks. The southern portion, on the other hand, is characterized by comparatively low, rounded hills of schist and sahistose gneisses, underlain by coarse, massive granite, which outcrops locally in small, and sometimes in large, patches. These hills also sometimes form table-lands by reason of overflows of lavas, such as andesitic breccia, rhyolite, trachyte and basalt. The leading geological feature is that of a schistose area of width and extent unusual for Colorado. These schists and gneisses are of pre-Cambrian age; but whether assignable to the Algonkian or to some older system has not been determined. The granite which occasionally outcrops from beneath these schists is, I think, of true eruptive character, since its mode of occurrence indicates a once molten, or at least highly viscous or plastic, condition. Thus, we may observe, included in its mass, numerous fragments of schist, almost like a coarse, volcanic breccia. Again, at its immediate contact with the schists, which often stand vertically upon it, the pediments of the latter are fused into the granite, and granite tongues and veins run up amongst the schists, as only a molten or viscous

Jan 1, 1897

By C. L. Dake

Many proposals have recently been made regarding the broadening of engineering education, often with little consideration of the problems their application involves. The chief purpose of this paper is to point out how many and how complex are the questions that absolutely must be answered, in any conscientious effort to solve the problem of liberalizing engineering curricula. Among proposed additions, more training than is now given has been urged in public speaking, report writing, business law and contra s, general finance, money and banking, scientific management, gene ' economics, economic and financial history, social problems, labor pre lems, public ownership, psychology and similar related subjects. T urge in this direction is widespread and persistent. In discussing the blem, the following questions must be given careful consideration, an he absolutely definite conclusion reached: 1. The Present Curriculum Load.—Is this load actually too heavy? In the face of this load, is there room to add broadening subjects to our curricula? Can elimination of present subject matter make room for such additions? Can an elective system accomplish the desired end? 2. Problem of Early Specialization.—Is early specialization a weak ness? Is industry forcing early specialization? Do our varied degrees demand early specialization? Can broadening be harmonized with the present degree of specialization? 3. Graduate Work to Solve the Broadening Problem.—Can we add the desired work in the graduate school? Are the proposed additions of graduate caliber? Is it desired to reduce graduate standards? Can present undergraduate work be removed to the graduate school, to make room for desired broadening courses? Is graduate work normally broadening, or is it specialization ? 4. Importance of Proposed Additions.—Will they increase entrance salaries? Will they increase the engineer's efficiency? Will they raise

Jan 1, 1934

By William Metcalf

One of the first questions that naturally occurs to one who handles steel is, " Why does steel harden?" To answer this question the chemist and physicist have devoted much thought and experiment, and while they have enriched our store of knowledge of the nature and composition of steel, it cannot be said that they have yet solved the problem involved in its hardening. In this communication I desire to direct attention to a line of investigation yet new, in the hope that it may receive the attention. of those who have the time and ability to pursue it. I refer to magnetism. There are so many parallels between the action of magnetism on iron and steel and their behavior under different processes of manipulation that it would seem. as if there must be some connection between tile forces at work in the different cases, if, indeed, there be not an identify of force in all of these cases. Magnetism, as me know it, may be merely the visible manifestation of forces, which may serve as a guide to lead us to an exact knowledge of the structure, tile strains, and the resistances with which me have to deal in iron and steel. If a magnet be brought close to a pile of iron filings, the little pieces of iron will fly to the maguet and attach themselves to it, with their longer axes lying in the direction of the force. If molten cast iron be poured into an iron mould,—a chill,—the iron upon crystallizing will form needlelike crystals, with their long axes normal to the surfaces of the mould. • If the iron is at the proper temperatare and the quantity small, compared to the mass of the mould, the whole of it, will be chilled, or set, in 'the hard needlelike crystals

Jan 1, 1881

By Edwin S. Johanson, Ronald H. Wolk, Clarence A. Johnson, Harold H. Stotler, Katherine C. Hellwig

The H-Coal process, an ebullated bed reactor system for converting coal to liquid fuel, is described. Results from long-duration continuous flow bench-scale operations with Wyoming Wyodak, Arizona Black Mesa, and Utah Kaiparowits Plateau coals are presented. Economic data on the conversion of these coals to liquid products are given. The potentials of the H-Coal process in regard to coal from western producers is stressed.

Jan 1, 1974

By Benj. Lyman

The Institute, in June, 1881, visited Low Moor in Alleghany County, Virginia, on the Chesapeake and Ohio Railway, seven miles easterly from Covington. Having occasion myself, a few days later, to make a very hasty geological reconnaissance of the iron-ores there, and finding them to be somewhat different in age from what was said to be the opinion of some of those who were there with the Institute, I have thought it worth while to bring the matter up again at the present meeting. According to the opinion quoted, the principal ore-banks belong to the Oriskany sandstone; and that seems to be the view entertained of the same ore in that region by Prof. Wm. B. Rogers in his reports of 1837 and 1838. it is likewise given by Prof. J. L. Campbell in a paper on the Rich-patch iron region in The Virginias for December, 1880 (vol. i., p. 189). A comparison, however, of the section at Low Moor with sections in Pennsylvania, shows clearly that the main ore-bed is the same as that of the bottom part of the Marcellus shales (part of Pa. and Va., No. VIII), a short distance above the top of the Oriskany sandstone (No. VII). The Upper Helderberg limestone is absent at Low Moor, as indeed it is at many places in Pennsylvania, and that is perhaps the reason why the ore has been thought to belong to the Oriskany sandstone. The ores and their accompanying rock-beds, are exposed in three or four folds near the Low Moor iron-mines on Fork Rim and, as described and pointed out by Mr. Geo. T. Wickes, who had in his management of several years' duration become well acquainted with them, are as follows, from above downwards:

Jan 1, 1886

E. R. Buckley, Flat River, Mo. (communication to the Secretary*) :—Some statements in the paper of Mr. Keyes relative to the nature and formation of the Ozark lead- and zinc-deposits seen1 to me erroneous and misleading, and I respectfully present the following criticisms, placing Mr. Keyes's original statements in quotations. Referring to the Ozark dome: (p. 192.) "It is a region that has been repeatedly upraised and planed off, until in the middle portion the oldest known rocks only are exposed." Does he mean that the St. Francois mountains, which have always been considered as lying on the eastern flank of the Ozark dome, are the middle of the dome ? Or does he mean that the Cambrian rocks of the generally-accepted middle are the oldest known rocks ? Certainly not the latter, and if the former, his idea of the middle of the dome is not in accord with that of others who are familiar with the region. (p. 203.) "... the ore-deposits are definitely associated with, or localized by, geologic structures of some kind that produce in effect basins in which the underground waters are impounded, or their flow retarded." This statement does not appear to be altogether consistent with the facts, since the ore bodies of the Joplin district, as the rule, occur in those parts of the Mississippian formation which have a tendency to accel erate the flow of ground-water rather than retard it. I migh name the open, brecciated ground near Joplin, Webb City, and Oronogo as especially noteworthy illustrations. The ore-bodies, everywhere, occur in positions where there must have been a free and copious circulation of dilute lead- and zinc-solutions in the presence of reducing constituents. The inequalities in the distribution of the ore-deposits are

Jan 1, 1910

By Harry M. Conger

It is a pleasure for me to keynote this first Western Regional Minerals and Coal Conference here in the Black Hills of South Dakota. It is pleasing for two main reasons. First, Homestake Mining Company has been associated with the Black Hills since 1875 when gold was discovered following Custer's trek through the Hills during 1874. Second, the future mineral development of the Black Hills will depend, to a great extent, on minerals and metals covered in this conference. The metals and minerals that are featured in this conference have unique similarities--and important differences--and therefore, will be of great interest to all who are involved in our industry in this area of the country. Precious metals have always been, and likely will always be, subject to political influence; they are only partially affected by the demands of our industrial economy. Energy minerals, while more directly affected by industrial stimulus, are also politically sensitive. In this regard, the need for a minerals policy affecting the energy sphere has been made very clear to us in the last five years. More importantly, the lack of a national policy and purpose relating to our total future energy needs has severely affected the overall economy and security of this country. Very briefly today, I would like to outline for you my thoughts on the future of these most important minerals. I will start by a discussion of precious metals, primarily my favorite precious metal, gold. A brief history of gold will be helpful in setting a perspective for forecasting its future although it is difficult to give a brief description of a metal that has been prized by man for over 6,000 years. Until recently, as you know, gold was held by the Federal government as a metal to be owned by the government only and

Jan 1, 1983

ST. LOUIS LOCAL SECTION Executive Committee ARTHUR THACHER, Chairman R. A. BULL, Vice-Chairman WALTER E. MCCOURT, Secretary-Treasurer, Washington University, St. Louis, Mo. H. A. BUEHLER R. R.-S. PARSONS HERBERT A. WHEELER On the afternoon of May 1, 1915, 42 members of the St. Louis Section, as the guests of E. S. Catch, President, and his associates in the Granby Mining & Smelting Co., visited the new zinc smelter of that company at Roselake, Ill. The annual meeting, which was preceded by a dinner at the St. Louis Club, was attended by 54 members and guests. The Chairman, H. A. Wheeler, presided. The Chairman rendered a report on the activities of the Section during the past year and the Treasurer presented a financial report. The following Executive Committee was elected: Arthur Thacher, Chairman; R. A. Bull, Vice-Chairman; W. E. McCourt, Secre-tary-Treasurer; H. A. Buehler, R. R.. S.. Parsons. H. A. Wheeler, as retiring Chairman, retains membership in the committee. W. L. Saunders, President of the Institute, made an address. H. W. Gepp, of Australia, described the lead and zinc deposits of Broken Hill, Australia, and V. H. Hughes, of Tulsa, spoke on the geology of the Cushing oil pool, Oklahoma. WALTER E. MCCOURT, Secretary.

Jan 6, 1915

NOW continuing with the preparation of the moulds I say that it is necessary to give the greatest attention to the differences of the clays as well as to the differences of those things that you wish to mould; and to know that every concavity in the mould produces a convexity and every convexity a hollow following the shape of the original pattern that you have. The pattern should be a body of a harder mated than the thing [78] you wish to mould with and of a substance that is not swollen or disintegrated by moisture. Its archetype may be of marble, bronze, lead, or any other metal, or also of wood, wax, tallow, gypsum, sulphur, or other plaster compositions-in short, of whatever you may have or whatever succeeds best for you, depending on whether the works are large or small and easy or &cult to mould. If you wish to cast them in bronze, you must mould them with loam, covering them with it and then drying it. There are some things in which it is enough to form only one part, such as half- or bas-reliefs. These are easy if they have no undercuts. Some other patterns that are easily handled are formed in two halves, or in three or four pieces, if they are of a hard material. There are also moulds for large statues, which, if one desires to make them of bronze, are first made of wax according to the ordinary procedure. I have in mind to describe every one of these processes in their own place. There are like- wise some moulds that are difficult to make, like scenes on a plane to which figures in full relief are attached, or twisted ornaments or other detached things that cannot be withdrawn from the mould without break-

Jan 1, 1942

By Cyril Stanley Smith, Earl W. Palmer

STRIP of any of the metals used for deep drawing operations occasionally yields cups that are defective because of a rim that varies in height around the cup in a wave-like manner Some such defects are traceable to tools or other press factors, but when the protuberances formed (usually four in number on brass and other copper alloys) are symmetrically disposed with respect to the rolling direction of the strip, they are invariably attributable to the metal The effect is known as "caring" and the protuberances are called "ears" Other terms frequently heard are "tips," "scallops," and "corners " It is recognized that the effect is most commonly a result of a directional crystal structure produced by rolling and annealing operations in the manufacture of the metal strip Numerous papers dealing with various aspects of the caring effect have appeared in the literature, those listed in the references' being especially interesting and valuable An investigation of the factors influencing caring of brass cups has been in progress in the laboratories of the American Brass Co for several years, and it was thought desirable to make some of the results generally available in summarized form The present paper discusses many factors that do and do not contribute to ear formation In addition, a section is devoted to methods of minimizing the caring tendency of brass sheet by proper selection of the cold-rolling and annealing schedule by which it is produced In the space available, it is impossible to quote detailed experimental procedures and numerical results However, the authors make no statement that they do not believe to be properly substantiated, either by experimental evidence obtained under laboratory conditions or by experience in the actual production of deep-drawing brass in the brass mill MECHANISM OF EAR FORMATION It must be clearly understood that the formation on cups of symmetrical ears, four or more in number, is attributable solely to the strip metal, and results from the strip having different deformation characteristics in different directions The tools used in the drawing process, or the type and completeness of lubrication of the strip, have nothing to do with the problem of ears, although they do, of course, greatly affect the "drawing quality" of the strip and the general appearance of the cup A single tip may be drawn up on the rim of a cup because of misalignment of the tools, or because the gauge of metal varies from side to side of the strip The two-ear form that sometimes appears is also traceable to gauge variations However, the four-ear and six-ear symmetrical forms that we are concerned with here are caused by factors inherent in the structure of the metal itself

Jan 1, 1942

Alfred E. Hunt, Pittsburgh, Pa. (communication to the Secretary): Mr. Blue's statement (page 576) that, " owing to the presence of iron and other impurities, makers of aluminum. assert that native corundum is unsuited for the production of that metal," is somewhat incorrect, at least so far as it may refer to any objection made by the officials of the Pittsburgh Reduction Co. to the Canadian corundums. We recognize corundum as among the richest and purest of the ores of aluminum, and the material furnished from Canada would offer for us the advantage of a supply near to our works for the manufacture of aluminum at Niagara Falls. The real difficulty which we find in the use of corundum for this manufacture is the cost of the raw material as compared with that of native bauxites. In this item we include not only, the price of the corundum as it has been offered to us, but also the expense of grinding it to an impalpable powder, which must be done before it can be used directly in the manufacture of aluminum, and the cost of preliminary chemical treatment for purification—which latter operation, however, is also required for bauxite. I agree with Mr. Blue that the introduction of new and irnproved processes has greatly reduced, during the past ten years, the cost of manufacturing aluminum; but I am inclined to believe that any further improvements, facilitating the use of corundum for this purpose, would apply, in equal or greater degree, to the common clays (silicates of aluminum) which exist in all parts of the world, are more easily mined and handled, and are likely to be always cheaper per unit of aluminum than any corundum.

Jan 1, 1899

By Horace Pops

ThE shape of the primary solid-solubility limits in copper-rich Cu-Si-Zn alloys has been discussed recently1 in terms of the atomic size effects and the electron concentration, e/a. Although these limits are parallel to lines of constant e/a near the Cu-Zn binary system, they deviate and become sharply restricted near the Cu-Si binary system. Hence, it appears that the primary solid solutions with higher silicon contents are restricted by the presence of the intermediate phases, [, X, and p, which follow them in the ternary system. owever, a similar restriction in solid solubility might also result from an interaction in the copper matrix between silicon and zinc. Evidence for such possible interactions has been observed, for example, in the Al-Mg-Si systion.A where a contraction of lattice spacings in the ternary solid solution appears to correspond to an electrochemical interaction between the two solute elements, magnesium and silicon. The observed contraction is associated with restricted solid solubility. It was also shown1 that the extent of the primary solid solubility did not follow the trends predicted by the lattice-distortion oncept." This again suggested that the solubility limits are strongly affected by the stability of the intermediate phases, I, 1, and X . In order to test the above hypotheses, lattice-parameter measurements of the fcc @-phase alloys were determined within the ternary system at a constant electron concentration (e/a = 1.30) and also at a constant zinc content. Alloys of predetermined composition were prepared from high-purity metals and melted and cast under reduced pressures of helium in quartz capsules. Since the weight losses were very slight and did not exceed one part in 2000, the nominal compositions listed in Table I were accepted without chemical analyses. The ingots were homogenized

Jan 1, 1964

By Lo-Ching Chang, J. Chipman

C. B. POST*—Just what are you showing that has not been shown by fixing the attention on molecular species and choosing the molecular species to give you a perfect solution? J. CHIPMAN (authors' reply)—In general a fairly satisfactory thermody-uamic treatment of slag-metal equilibria can be worked out on the basis of assumed molecular species in the slag. This has been the method used by Shenck and more recently by White. Winkler and I also used it in studying dephosphoriza-tion. Darken and Gurry found that it did not fit satisfactorily in the case of their data on iron oxides. The ionic formulas used here conform to the data much better and probably correspond somewhat more closely with the actual structure of the slags. C. B. POST—It does seem to be similar to you? J. CHIPMAN—It is alternative, and may lead to a more complete understanding. C. B. POST—Have you had a chance to talk to glass technologists on this? Have they been using this type of set-up for glass solutions? J. CHIPMAN—Yes, and the ionic formulas have given them a little better understanding of what liquid glass is like. C. B. POST—Nelson Taylor always said we were going- about slag reactions from the wrong viewpoint when using molecular species. Evidently the glass technologists use ionic species exclusively when dealing with liquid glass reactions. J. CHIPMAN—I agree that it seems more rational and more accurate to use ionic rather than molecular formulas. We should be cautious, however, and not suppose that we really understand the structure of a slag just because we are able to fit its reactions by ionic equations.

Jan 1, 1950

By Persifor Frazer

IT was my intention to have directed the attention of the members of the Institute to a complete series of rocks representing the older and middle formations represented in Pennsylvania, but time has been insufficient for the purpose, and I have been unable, in the first attempts to reduce the sections of those rocks, which I have brought with me to this meeting, to the requisite thinness necessary for exhibiting the peculiarities of their constituent minerals. The rocks represented here belong to the various horizons already mentioned, and include gneiss, ferruginous gneiss, chlorite slate, quartzites, and hydro-mica slates, limestones, dolomites, ferruginous conglomerates, quartz conglomerates, "Potomac marble" (nether member of the Mesozoic series), dolerites, and a syenite. The order in which these are named is, roughly, the order -of geographical position in a section line from southeast to northwest, commencing at the intersection of the Northern Central Railroad with the Maryland line, and ending a few miles from the town of York, and a short distance within the marginal outcrop of Mesozoic red sandstone. In such a geographical section all the rocks above mentioned would be encountered in the given order except syenite, about which a few words are to be said in a moment. (But this is far from representing the rocks in their geological sequence.) There is nothing of unusual interest to present to your notice in these slates and quartzites. The limestones were carefully searched under 450 diameters microscopic power, but they show no signs of organic remains. One section of a fine-grained Triassic sandstone contains a very beau¬tifully banded plate of quartz. But the objects of greatest interest at present are the specimens of trap. The more fine-grained and compact traps were collected from

Jan 1, 1875

Discussion of the paper Of NOEL CUNNINGHAM, presented at the New York meeting, February, 1915, and printed in Bulletin No. 99, March, 1915, pp. 601 to 608. C. H. POIRIER, New York, N. Y. (communication to the Secretary*). -Mr. Cunningham's paper, written from the standpoint of a stamp advocate, while commenting more or less favorably upon the installation of ball mills in the Vipond plant, does not, in my opinion, give as much emphasis to the comparatively new departure as the installation of ball mills in the place of stamps justifies. This discussion is based upon my personal and intimate practical work for several years with stamp mills, and for the past three years with Hardinge ball and pebble mills. The fact that the Vipond mine contains about equal quantities of the A and B classes of ore mentioned by Air. Cunningham, and the further fact that I have had a most intimate knowledge of the working of both classes of ore in the Porcupine district in stamp mills and ball mills, justifies upholding my final decision to use ball mills in the place of stamps, and defends my present further action in now increasing the present Vipond capacity by the addition of another 6-ft. Hardinge ball mill, in which action the directors of my company concur. This is one of the strongest evidences I can possibly offer in substantiation of my opinion that the ball mill exceeds the efficiency of the stamp, both in metallurgical and mechanical economy. It is hardly fair to compare a 100-ton per clay plant with a mill handling several times this amount, yet it is my belief that the cost per ton. of grinding in the ball mill is far less than that of any stamp mill in the district, where capacities run up to 400 tons per clay.

Jan 5, 1915

Discussion of the paper of C. A. HEBERLEIN, presented at the New York meeting. February, 1915, and printed in Bulletin No. 98, February, 1915, pp. 497 to 504. H. D. PALLISTER, State College, Pa. (communication to the Secretary).-Mr. Heberlein gives some valuable information concerning a branch of mining and metallurgy which has been neglected during the last few years. His results with fine grinding and Deister tables suggest the possibility of the mining and concentration of a number of low-grade cinnabar deposits. Can Mr. Heberlein give us some idea as to the loss of quicksilver during this concentration? The advances in the metallurgy of quicksilver have been few and far between in recent years. Most miners prefer to go on in the old way with the Scott furnace and the large brick condensers. The large brick condensers are expensive to build and to keep in repair, and on account of the thick walls are extremely slow in cooling the gases; and further, the joints between the bricks offer passages for the quicksilver vapors unless great care is used in building the condensers.. The escape of vapor at the top of the furnace is another source of loss and I see the people at the Oceanic mine have overcome this in a very ingenious way. I recently returned from the Terlingua quicksilver district of Texas, where the only operating company, the Chisos Mining Co., is operating a 20-ton furnace of the Scott type. They had considerable difficulty with getting a good extraction, clue to too high heating in the furnace with its .resulting diffIculties. Recently they have been running with ashpit and fire doors closed and have been able to keep the heat lower, thus getting much better results and practically verifying the results obtained at the Oceanic mine.

Jan 5, 1915

By Rex O. McLellan

The formation of a monovacancy in a metal is simulated in an elastic model by the displacement of the surface of a small spherical cavity in a large elastic continuum. The application of linear elasticity to this distortion results in a well- known formula for the energy and an expression for the concomitant entropy change due both to the shear strain in the continuum and also to the dilation of the solid resulting from the boundary conditions at the surface of the solid. Elastic data (the sliear modulus and its temperature coelficient) are used to calculate the entropy and energy of formation for many metals. Despite the simplicity of the assumptions involved, the agreement between the calculated entropies and energies and experimental values is remarkably good. In recent years there has been a large increase in measurements of the absolute concentration of mono-vacancies in metals as a function of temperature. Hence new data for both the energy and the noncon-figurational entropy of formation of monovacancies has become available. Recent measurements&apos; of the anomalous (non-Arrhenius) self-diffusion in many bcc metals has also focused interest on the prediction of the thermodynamic parameters of mono- and multi-vacancies in those metals for which no data are available. Damask and Dienes&apos; have discussed the various theoretical calculations of the energy of formation EL, of a monovacancy. These include simple models involving the breaking of atomic bonds on moving atoms from the interior of a crystal to the surface, models combining elastic calculations with surface-energy terms and detailed quantum mechanical calculations. The simler models give the correct order of magnitude of &, but tend to overestimate it by a factor of about two. The quantum mechanical calculations4"7 have been carried out for the noble and alkali metals with generally reasonably good agreement with the available Ef data. The calculation of entropy of formation Sfv14 lnvolves a fundamental calculation of the perturbation of the phonon spectrum caused by the creation of a vacancy. Huntington, Shirn. and wajda8 have given an approximate evaluation of sJV by considering an Einstein model for the localized vibrations in the immediate neighborhood of the defect and then using elastic theory to calculate the entropy associated with the shear stress field in the distorted crystal (as originally proposed by Zenerg). They also included a term due to the dilation of the crystal. They obtained a value of 1.47k for copper, in good agreement with the experimental value (1.50k). However, Nardelli and Tetta- manzi1° have recently shown that neglecting the coupling between atoms (Einstein Model) may lead to a serious error so the agreement may be somewhat fortuitous. In this work simple linear elastic theory is used to calculate the entropy and energy of formation of mono-vacancies. Despite the simplicity of some of the assumptions involved, the agreement with the available experimental data is remarkable. However. the reasonable degree of success in the application of linear elastic calculations to the excess entropy of a solute atom in a dilute solid solution1&apos; indicates that the application of elastic theory to vacancies. where the interaction of different atomic species is not involved, may not be inappropriate. THE ELASTIC MODEL The metal is assumed to be a spherical elastic continuum. A small spherical cavity of volume V = 4i;v:&apos;/3 is cut from the center. removed. and dissolved rever-sibly in the bulk of the material. TO a good approximation no net atomic bonds are broken and the material does not undergo a volume change although the externally measured volume of the body would increase by V. The radius of the sphere of metal is much larger than r Next a negative pressure is applied to the cavity causing its surface to be displaced inward by an amount simulating the relaxation of the lattice around a monovacancy. In this model the energy and entropy accompanying the distortion are taken as 4, and <. As a first approximation the equation of state for the solid is taken as: r = ro(i + *~D LiJ where K is the bulk modulus. P the hydrostatic pressure. Vo the volume of the material at 0°K and zero pressure. and d+/dT = 30. where 0 is the linear thermal expansion coefficient. The variation of entropy with hydrostatic pressure is given by the Maxwell equation: These equations give the entropy change resulting from increasing the hydrostatic pressure from 0 to P as: and since • we have: This is the entropy arising from the dilation resulting

Jan 1, 1970

By John L. Miles

John L. Miles (Arthur D. Little, 1nc.)—Pollack and orris" have reported measurements on electron tunneling through A1-A12O3-A1 sandwiches in which the oxide was formed by gaseous oxidation in a glow discharge. From these measurements they deduced the asymmetry of the barrier and, since this is small, conclude that the mechanism suggested by Mott19 for the growth of oxide in thin A12O3 films is inapplicable. In earlier papers20 Pollack and Morris report similar work for oxide films grown thermally. In this case they find a greater asymmetry and conclude that the Mott mechanism is valid. I would like to point out that both these conclusions are quite unjustified. Mott suggests that the growth of the oxide film on aluminum results from the passage of ions through the already present film of oxide under the action of an electric field. This field results from a constant voltage which is in effect a contact potential between metal on one side of the barrier and adsorbed oxygen ions on the other side of the barrier. The theory does not require that the oxide grown is nonuniform either in stoichiometry or structure. It does however specifically assume that the partial layer of ionized oxygen on the surface remains adsorbed on the surface of the growing oxide. In other words, the so-called "built-in field" remains in the oxide only as long as the ionized oxygen is present. When a counter electrode of aluminum is deposited on the oxide, it will react with the adsorbed oxygen on the surface of the oxide, thus forming a small additional amount of oxide. It is clear, then, that there is no requirement in the Mott theory of oxide growth which would necessitate tunneling currents through an Al-A1203-A1 sample to be different when the polarity is reversed. Neither does the theory eliminate the possibility that some additional mechanism could cause the tunneling barrier to be asymmetric and hence tunneling currents to be a function of polarity in such a sandwich. Thus these tunneling-currents measurements are not germane to the question of whether the Mott mechanism is the true method of growth of aluminum oxide films. In fact, it is not surprising that there should be a difference between the oxide properties at the two interfaces (with resulting asymmetry in the tunneling barrier) since the growth conditions and growth rates must have been quite different at these two positions. S. R. Pollack and C. E. Morris (authors&apos; reply)— The point raised by Miles above is one has caused some confusion in the past. The following is an attempt to clarify this point. The built-in field which is responsible for the growth of the thermal oxide at low temperatures arises, according to Mott, because of the passage of electrons from the Fermi surface of the oxidizing metal to surface states introduced by the adsorbed oxygen. It is assumed that the energy of these surface states lies below the Fermi energy of the metal. Electrons therefore continue to flow from the metal to the surface until the built-in electric field raises the potential energy of the surface states to the value of the Fermi energy in the metal, at which time equilibrium is obtained between the surface states and the metal. That is in equilibrium as many excess electrons pass from the metal to the surface per unit time as vice versa. The surface of the oxide prior to deposition of a metallic counterelectrode can then be pictured as follows. The Fermi energy lies in the energy gap of the oxide and is essentially pinned at the energy of the oxygen surface states. The vacuum work function of the oxide is then given by the sum of the electron affinity of the oxide (i.e., the difference in energy between the vacuum and the conduction-band minimum) plus the energy difference between the conduction-band minimum and the Fermi energy. The deposition of a metal onto the surface of the oxide can result in a transfer of electrons across the extremely thin oxide only if there is a contact potential difference between the deposited metal and the parent metal or oxide. That is if the vacuum work function of the deposited metal differs from that of the parent metal, then charge can be redistributed across the oxide in order to equilibriate the Fermi energy across the structure. (It should be

Jan 1, 1965

By S. D. Baumer, P. M. Hulme

IN the late thirties, the National Carbide Co. cooperated with C. E. Wood, of the U. S. Bureau of Mines, in his investigation of the relative merits of various desulphurizers, including soda ash, caustic soda, and calcium carbide. Laboratory tests showed that carbide, when it could be made to react, is an excellent desulphurizing agent for molten iron. Sulphur content can be driven to lower levels and higher extractions obtained with carbide than with actionsany of the more common reagents. Wood&apos;s results1 are shown in Table I. Unfortunately, as the Handbook of Cupola Operation puts it, the chemical fact that carbide is a good desulphurizer was of only academic interest because it was found to be extremely difficult to devise a practical means to make it react with molten iron. Calcium carbide is formed in the electric furnace at 4000°F and above, and its softening point is probably at least 500 °F above the usual working temperatures encountered in iron and steel practice. Consequently, carbide does not form a true slag but floats as a dry powder on top of the metal and only a very small portion of it ever comes in actual contact with the iron. Stirring with a rabble, or pouring the metal over the carbide, increases the efficiency only slightly. Extractions of 20 to 30 pct can be obtained in this manner, but conventional soda slag treatment can do better than this and do it more cheaply. All attempts to lower the melting point of carbide in order to obtain a reactive, liquid slag have so far proved fruitless. Directly under the arc in a metallurgical electric furnace, carbide becomes highly reactive. Excellent sulphur removal can be obtained without any slag other than a thin layer of carbide." imilarly, good results are obtained by adding small amounts of carbide to the finishing slag in double-slag arc furnace practice. To react a liquid with a solid, it is axiomatic that the liquid has to wet the solid before anything can happen. If the solid is heavier than the liquid, the problem is easy, but it becomes more difficult when the solid is much lighter than the liquid, as in the case of carbide and liquid iron. Wood recognized this problem and solved it in a unique fashion. The results shown in Table I were obtained by spinning the carbide beneath the surface of the molten iron by means of a refractory centrifuge. This technique allowed each particle of the finely divided carbide to come into intimate contact with the metal and to be wetted thereby. Wood&apos;s centrifuge technique was successful in the laboratory where it achieved excellent and consistent results. Some attempts were made to expand this method to commercial practice, but serious difficulty was encountered in obtaining a refractory centrifuge head that would be economically feasible. About this time the war intervened and the project lay dormant for several years. In 1944, it was revived. It was suggested that the carbide could be blown into the metal with a carrier gas in an attempt to eliminate the necessity for the expensive and brittle centrifuge. The idea was first tried out in a fairly large ladle of iron using natural gas as the carrier. Considerable sulphur was removed, but it was quite obvious that the use of natural gas was not practical. Attempts then were made to blow carbide into molten iron using, in turn, nitrogen, argon, carbon dioxide, air, and oxygen. The latter two gases proved unsatisfactory. Calcium evidently prefers oxygen to sulphur because in the tests calcium oxide and carbon dioxide were produced, the sulphur still being untouched in the iron. Nitrogen, argon, and carbon dioxide gave much better results, although the efficiencies and extractions were erratic, and only a few isolated tests approached the results obtained by Wood. Table II shows typical results obtained with these gases. The sulphur removals were interesting, sometimes even encouraging, but it is evident that such erratic behavior could not be tolerated in commercial practice. A number of different types of equipment, such as sand blasting machines, refractory guns, and the like can used to blow the solid into the metal. All types required relatively large quantities of gas in order to maintain the flow of solid carbide through the system and into the metal. It was observed that the bubbles of gas breaking through the surface of the metal contained quantities of unreacted carbide. The liquid metal never came in contact with these particles and if it cannot wet them it cannot react with them. The initial work had shown that carbide had great possibilities as a desulphurizer. In practice

Jan 1, 1952