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By W. Shockley

THIS lecture can best begin with a statement of the chief conclusion: The metallurgical industry will find profit in supporting fundamental research on dislocations. This support should be done both in their own laboratories and in universities. My lecture consists of an exposition of the basis for this conclusion. The experience on which I base it is drawn largely from two fields in solid state physics—one field is transistor electronics and the other is dislocation theory. At present the relationship of solid state physics to technology is different in these two fields. In electronics without question, the physics has led the technology. In metallurgy, on the other hand, the technology in the form of metallurgical art is far ahead of the fundamental science. In transistor electronics, physics has suggested and can still suggest previously unachieved combinations of matter that will have new and useful properties; that is, the physicist can make specific predictions. The physicist can also have some confidence that the predicted devices will actually come into existence in a matter of months or years and that they will live up to the predictions. In metallurgy, the physicist cannot to a comparable degree make predictions and have the same hope that they will lead to something new and valuable. There are a number of reasons for this difference. The first is simply historical. Transistor physics is young. It may be regarded as dating from the announcement of the transistor, in which case it is about four years old, or from the first real control of semiconductors as materials (this was accomplished largely by metallurgists, by the way) in which case it is about ten years old. Metallurgical art, on the other hand, is thousands of years old. There is no doubt that the advance of this art has been and will be hastened by a good fundamental understanding of the quantum theory of atomic phenomena. It, is too much to expect, however, that theory will soon catch up with the lead that practice has gained in a thousand years, and that theory will then point out specific pathways to better materials. It seems more probable that modern atomic theory will serve to interpret and organize information much as thermodynamics has done through phase diagrams. In this lecture, I shall emphasize an important feature common to both solid state electronics and to metallurgy. This common feature is the harmonizing principle that justifies discussing electronics and metallurgy as related topics in solid state physics. In both cases the important properties of the materials arise from imperfections. By imper- fections I mean deviations of the materials from perfect single crystals. The imperfections may be of many forms. From the point of view of utility they may be either good or bad, and a given type may be good or bad depending on circumstances. The technical material of my lecture will be divided into two parts. The first will be chiefly concerned with four types of imperfections in germanium crystals. The control of these imperfections makes possible the fabrication of useful electronic devices. A good example of such control is the junction transistor, which I shall discuss from this viewpoint later. The junction transistor, as some of you may have heard, can be used as an amplifier of electrical signals and in a number of respects surpasses what has hitherto been achieved with vacuum tubes. The second part of my technical material will be concerned with dislocations. For about fifteen years the theoretical physicist has had dislocations in mind as the most important kind of imperfection in metals. He has, however, until recently had experimental material of a highly speculative nature to back up his assertions. I am fortunate in the timing of this lecture to be able to describe some recent results that put dislocations on a far more definite basis than has been the case in the past. In fact there are now some experiments which reveal the characteristic properties of dislocations almost as clearly as experiments in transistor physics reveal the properties of holes and electrons, properties that I shall soon describe. It is this advance in the status of dislocations that emboldened me to make my initial assertion that the metallurgical industry will profit from supporting fundamental research on dislocations. Transistor Electronics In order to discuss imperfections in semiconductors, it is necessary to visualize a reference condition that may be regarded as perfect. In the cases of silicon and germanium, which find application in transistor electronics,' the perfect structure is the diamond structure shown in Fig. I. In this structure, each atom is surrounded by four neighbors with which it forms four covalent or electron-pair bonds. These bonds use all of the four valence electrons possessed by each of the silicon or germanium atoms. The electronic structure of the crystal is thus complete and perfect. A crystal of silicon or germanium with a perfect electron-pair bond structure would be an insulator, In order for electrical conduction to occur, it is necessary for imperfections to arise in the electronic structure. In this lecture, I shall discuss four possible imperfections whose symbols and relationships are indicated in Table I. We shall consider first, as an example, a crystal of silicon containing an arsenic atom as an impurity.

Jan 1, 1953

By C. S. Herzig

In the Engineering and Mining Journal of Jan. 27, 1900, there appeared an article by Fred T. Greene, describing a method of measuring stopes by the use of strings, a clinometer and a tape. In the early part of 1899 I had occasion to use a somewhat similar method, for the purpose of accurately ascertaining the volume of a very irregular drift connecting two mines. This drift was an important factor in a lawsuit for $150,000, in which it was necessary to determine accurately the volume originally occupied by the material extracted from the drift. While it is unnecessary to give all details of the controversy, some explanation of the conditions is required for a clear understanding of the following description. This drift was started by the a E." Co. from its workings, in about 7 ft. of ore, and headed toward the " G " property, the plan being to extract all the ore between foot- and hanging-walls, but to take out nothing but ore. As the " G." workings were approached; the ore-body became very irregular and much thinner. It was, however, very closely followed, and where the drift broke through into the " G." workings, the hole was only 11 inches high by 14 inches wide, or just about the size of a man-hole in a boiler.. Thus, this connection-drift tapered sharply; and the very irregular foot-wall sloped toward the " G." workings, and entered them at a place where the stope was only about 3 ft. high, and the ground had already commenced to cave. It may be added that the ore-body was a nearly flat deposit of lead carbonate in limestone, the ore and gangue being quite soft. I was called upon by the " G." people to make the survey

Jan 1, 1901

By J. T. Crawford

ALTHOUGH nearly 10 pct of the total tonnage of coal produced annually within the United States is handled by bulk freighters on the Great Lakes, very little of the detail connected with it has been published other than occasional newspaper stories and publication of tonnage statistics. Of the total tonnage floated on the Lakes each year some 10,000,000 is stored and distributed from the port of Duluth Superior, at the western end of Lake Superior commonly known as the Head of the Lakes. This port has the largest single area concentration of coal docks in the world. Since this area contains the largest ore docks, the largest movable material handling bridge, the largest and highest grain elevator and the largest coal briquetting plant in the world, it is entirely fitting and proper that here also should be located the largest coal dock and what we believe to be the worlds largest clam shell. Of the sixteen coal docks operated by ten companies, five are owned and operated by the North Western-Hanna Fuel Co. which has two docks on the Superior, Wis. water-front and three docks in Duluth, Minn. It is with these five docks that we are primarily concerned. GENERAL HISTORY In the summer of 1871 a small sailing vessel entered the harbor of Duluth Superior with the first commercial coal cargo. All the coal brought up that first year did not amount to more than 3000 tons. During the year 1877 the first dock equipped for handling coal was built in Duluth. Coal receipts increased to 52,785 tons in 1879 the first year for which an official record was kept. Since then the volume of water-borne coal to the Head of the Lakes steadily increased to a maximum of 12,688,321 tons in the year 1923. This tonnage was nearly equalled in the year 1927 and the next highest tonnage recent year was in 1946 when 10,105,703 tons were unloaded. The average annual bring-up over a ten year period 1938 to 1947 was 8,605,231 tons. Approximately 30 pct of the coal unloaded at the Head of the Lakes is handled over the docks of the North Western-Hanna Fuel Co. Competition of other fuels coupled with expansion of coal fields in the mid-west have held coal receipts for Duluth-Superior at a relatively constant figure during the last eight years although the total tonnage of coal floated on the Great Lakes has more than doubled in the past 25 years. From the shovel and wheelbarrow method of unloading early cargoes to the horsepowered windlass derrick with a wooden tub was but a short step. The first movable coal handling, steam operated,

Jan 1, 1948

Pumping coal to market may help Appalachian coal operators increase their share of the eastern seaboard fuel business. Transporting it by pipeline is already an accomplished fact, but until recently it had to be dewatered to be used in boiler furnaces. The campaign for these eastern markets was begun in earnest last November by the widely publicized announcement of successful plant-scale firing of a central station boiler with coal slurry pumped to the burners. This latest advance makes coal similar to oil and gas in convenience in handling and controlling at the consumption end of the pipeline. Slurry could be considered a new commodity for the fuel market. HUGE POTENTIAL MARKET The heaviest concentration of power plants in the U.S. is along the line Washington, Baltimore, Philadelphia, New York and Boston which makes this region the best hunting ground for selling pipelined coal brought from western Pennsylvania and northern West Virginia. Furthermore, if this region is assumed to consume 125 million tons of coal annually, on a comparable basis, the consumption of oil and gas would be about 180 million tons. Even if all of this fuel is not consumed in central stations, it is still a very big market for coal at the right price. Consolidation Coal Co. and Texas Eastern Transmission Co. are trying to line up customers in this area so that a pipeline can be built. This is not to say that there are not many other areas in the U.S. that could not be supplied advantageously by a mine-to-market pipeline.

Jan 1, 1962

By John M. Lovejoy

I take pleasure in transmitting herewith "Petroleum Development and Technology in 1927," in which we have attempted to set out in a series of 40 papers with attendant discussions the advances made in Production Engineering and Refinery Engineering during the year. The volume also contains a digest of round table discussions on Petroleum Engineering Research problems and Petroleum Engineering Education. In addition to the above we set out in 16 papers a review of production of each producing area of the United States and of the more important foreign countries, together with a review of the world's production and forecasts for 1928. We also include 8 papers on the Economics of the oil industry. The papers and discussions included herein represent the contributions of more than 200 engineers, including the foremost in each line. These papers were presented at technical sessions held in Fort Worth in October, 1927, and at the annual meeting in New York in February, 1928. We desire to express our thanks and appreciation to all those who have contributed to this volume. As in previous years, we have attempted to emphasize the value of both written and impromptu discussions. -We have made a practice of returning all impromptu discussions to the authors for correction and amplification, and because of this practice we feel that the discussions contained herein are in very presentable and readable form. It was decided by the nominat,ing committee when meeting for thc purpose of nominating officers for 1928 to eliminate the vice-chairrnanship for Transportation Engineering, as that branch of the industry seemed to come more naturally under the activities of the American Petroleum Institute. It was also decided by this committee to institute a new vice-chairmanship for Petroleum Engineering Research. Wc have had heretofore round table discussions on engineering research, but through the newly created vice-chairmanship, to which Mr. L. C. Uren was elected, we expect to have more comprehensive sessions on engineering research than heretofort.

Jan 1, 1928

By E. R. Brownscombe, Francis Collins

The pressure distribution in a reservoir producing an incompressible fluid by radial flow in a horizontal structure is a simple logarithmic function' used daily by reservoir engineers. The assumption of an incompressible liquid is equivalent to assuming that pressure is maintained constant at the well radius and at some external "radius of drainage," or, in other words, that the entire flow into the well passes across the external radius. In most cases a well is surrounded by other wells draining adjoining areas so that the "radius of drainage" is not a line of constant pressure with flow equal to the flow into the well but rather a contour of zero pressure gradient across which no flow occurs, production being due to the expansion of the liquid within the area. The radial flow steady state pressure distribution for this case does not seem to be extensively used despite the fact that the mathematical analysis has been given in detail' and the results are simple and generally applicable. 'The object of this discussion is to develop this result from a physical rather than a mathematical viewpoint, thereby aiding intuition in judging circumstances to which it may be applicable. If the production rate at a well in an unsaturated reservoir is maintained constant while no flow occurs across the outer radius a steady state will soon be reached in which the flow rate or pressure gradient is constant with time at all points in the reservoir. To preserve such a condition it is necessary that the pressure decline at the same rate at all points in the reservoir, that is, the curves of pressure versus radial distance at successive times are all parallel. Then each unit volume of oil is expanding at the same rate and contributing an equal share to the production. The rate of flow q across any circle r is thus proportional to the volume of the reservoir between r and the external radius re, or q = qw (I-r2/r2e) ......(1) where q, is the production from the well and it is assumed that rw is very small compared with re. This equation can be combined with the differential form of Darcy's law for radial flow, 2phkr dp q =—— ........(2) aµß dr ( where q is not a constant as in the incompressible flow case but is a function of r given by Equation (1). If Equation (1) is substituted in Equation (2) the variables p and r can be separated and the result integrated to obtain the pressure distribution p = pw +--------In------------- 2pkh[ rw 2re2] ......(3) This equation differs from the incompressible case only in the addition of the term proportional to the square of the radius

Jan 1, 1950

By T. F. Archbold, R. E. Grace

The use of interference colors is the simplest experimental way to determine the approximate film thicknesses of oxides formed on liquid metals. A large amount of data under various conditions can be obtained easily and quickly. The oxidation of liquid lead has been studied by several investigators,1-5 but all of these studies have been on thick oxide scales. The purpose of- this work was to investigate the range 0 to 2000A film thickness. By using electron diffraction, Jenkins concluded that the surface of the film on molten lead is yellow orthorhombic PbO with the (110) planes parallel to the surface. This was confirmed by Shimaoka and Yamai7 who also used electron diffraction from the melting point of lead to 730°C. The rate of oxidation of pure liquid lead in air was measured in the temperature range 453" to 643°C by observing the rate of formation of interference colors on static lead baths. Approximately 170 g of lead (99.999 pct) was placed in a refractory dish having a working surface of 13.8 sq cm. This crucible was placed in a deep-well resistance furnace open to the atmosphere. The times at which the various interference colors appeared, after wiping the molten metal surface clean, were determined at 453", 533°, 600°, and 643°C. Elapsed times were determined with a stopwatch and all colors were estimated by eye. Bath temperatures

Jan 1, 1959

By G. G. Gunther, C. L. Boeke

THE zinc deleading processes at the Parral and Santa Barbara mills are described separately to provide a basis for comparison. Although the two procedures are fundamentally alike, there are some differences in application to meet specific conditions. The Asarco mill at Parral in the State of Chihuahua is a flotation plant treating 1450 metric tons per day of complex sulphide copper-lead-zinc ores. In general, the procedure used for selective separation of the minerals into a copper, a lead, and a zinc concentrate follows the usual practice. First, a bulk copper-lead concentrate is floated and then separated into a final copper and a final lead concentrate by the sulphurous acid process. A small tonnage of high grade gravity lead concentrate is tabled from the bulk copper-lead cleaner tailing before it is reground so as to avoid undesirable over-grinding and sliming of this portion of the lead mineral. Next, a zinc concentrate is floated from the lead rougher tailing and, as described later, is separated into a final lead product and a final zinc concentrate. Finally, the zinc rougher tailing receives a strong scavenger float to remove all recoverable middling values for regrinding and return to the flotation circuits. The slime is separated from the scavenger flotation product, and only the sand portion goes to the regrind section. The minerals in the separated slime are extremely resistant to all methods of selective separation and pose one of the major problems awaiting solution. Nevertheless, the slime shows a profit when mixed with either the lead or the zinc concentrate, except when metal prices are very low, so it is accepted as a final product for lack of a more profitable method of handling it. In contrast, the minerals in the reground sands of the

Jan 1, 1953

By M. M. Fine

Normally the U. S. produces less than 10 pct of its annual manganese requirement. About 95 pct of domestic consumption is used by the steel industry.' The strategic and critical nature of manganese has been recognized by its inclusion in the national stockpile and by intensified research directed toward cataloging and evaluating domestic manganiferous deposits. The USBM has participated in these activities for many years with field and laboratory studies to assess the extent and potential utilization of domestic manganese ores. One area of particular interest is in the vinicity of Batesville, Ark., where deposits have been mined since 1849 for both manganese and ferruginous manganese ores. Production is centered in Independence County, but deposits are also found in Sharp, Izard, and Stone counties in north-central Arkansas. Miser has described the geology and manganese mineralization in some detail.'. * "he rocks of the area are sedimentary, consisting of sandstone, limestone, shale, and chert. The two formations of greatest importance,' Fernvale limestone and Cason shale, are host rocks of the primary manganese mineralization. Through 1955 the district produced some 230,000 long tons of manganese ore (35 pct Mn or more) and 236,000 tons of ferruginous manganese (10 to 35 pct Mn).5 Most of the ore has been mined from deposits of manganese oxides in residual clays resulting from weathering of the two formations noted above. Concentration methods have been primitive, consisting for the most part of washing. hand picking, and jigging. A significant accomplishment in the district in recent years was the USBM recognition and investigation of the huge manganese potential represented by unaltered Fernvale limestone. systematic reconnaissance of manganiferous limestone and other occurrences has been in progress since 1953 to delineate the extent and tonnage of manganiferous materials. Results of that survey have appeared in two recent publications,1-5 which ascribe to the district an inferred reserve of 166 million long dry tons at a grade of 5 to 6 pct Mn. Most of this was mancaniferous limestone with an estimated content of 5 pct Mn. Specifications: Beneficiation was carried out on a group of manganiferous limestones to develop a way to recover commercial-grade concentrate from this extensive resource. The following chemical specifications were established by the GSA for metallurgical manganese ore acceptable for delivery to the national stockpile: Size specifications were not considered, as it was assumed that the concentrates could be pelletized or sintered. Manganiferous Limestones: Of the 11 samples tested to date, six were taken by cutting vertical channels across beds of limestone outcrops. Diamond drilling through overlying barren chert into unex-posed limestone provided four samples, and the last was a churn drill sample. In general, the samples were dlrk, fossiliferous limestone containing small amounts of braunite, hausmannite, rhodochrosite, massive and micaceous iron and manganese silicates, quartz, barite, and glauconite. The braunite and other manganese oxides partly to completely replaced some of the calcite and fossil material. The calcite was generously stained with mangenese and iron oxides. Phosphorus was present in all samples as collophanite grains, calcium phosphate fossil replacements. or an unidentified manganese-bearing carbonate. The difficulty in separating this complex array of minerals was further complicated by a very intimate association. Although some manganese grains as large as Ik in. were noted, grinding to subsieve sizes would have been necessary to liberate the components. Figs. 1 and 2 are micrographs, at X100, of typical polished sections in which white areas are manganese. gray is gangue, and black areas are surface depressions. By comparison with the 100 mesh opening, it is seen that some of the grains are coarse enough to respond, perhaps to tabling or flotation, but many are obviously beyond the scope of ohysical processing. Partial chemical analyses of the eight samples that were ultimately amenable to concentration are presented in Table 1. BENEFlClATlON RESEARCH Tabling: To take advantage of the presence of sand-size grains, both jigging and tabling were considered at the outset. Jigging was largely ineffective, but tabling achieved a partial recovery from most samples. As an example, the surface material from Baxter Hill was crushed to —28 mesh, hydraulically classified, and the coarsest spigot fraction was tabled to yield a concentrate, middling. and tailing. The latter two were reground to pass 48 mesh, combined with the primary fines, re-classified, and retabled. The middling and tailing were again ground, this time to pass 150 mesh, and deslimed at 20µ in a 3-in. hydraulic cyclone. The cyclone underflow was returned to the table to reclaim a small amount of high-grade manganese. An interesting facet of the gravity concentration developed on certain samples in which braunite was the principal manganese constituent. Since braunite has a Mohs hardness of 6 to 6.5, while the host rock, limestone. is only 3, a differential size reduction took place during crushing, and the

Jan 1, 1960

By L. R. Plitt, E. O. Lilge

Tests carried out with both kaolin and silica slurries show that flocculants of the polyacrylamide type can be used to improve the thickening performance of hydrocyclones. This thickening improvement demonstrates that contrary to previously held theories, flocs can be formed which are capable of resisting the shear forces in a hydrocyclone. For the 1.25-in.-diam cyclone used, optimum thickening occurs when the flocculant solution is injected into the slurry stream at or near the feed inlet. Hydrocyclones offer many distinct advantages over gravity thickeners. These advantages include simplicity, low initial and operating costs, small space requirements, and flexibility of operation. In spite of these advantages hydrocyclones have not been widely used as thickeners. The main reason for their lack of application is that hydrocyclones are unable to efficiently remove semicolloidal particles (less than 5 microns) from the suspending solution. In gravity thickeners, the fine particles can be induced to form particle aggregates, or flocs, which have the settling characteristics of large particles. In the hydrocyclone, however, it was always assumed that the existence of shear would prevent the formation of flocs.1-3 Thus, if no floc structure is retained, the thickening hydrocyclone must be designed so that its separation size is below the size of the smallest particle to be recovered. To obtain a very small separation size requires the formation of very high centrifugal forces, which necessitates the use of small-diameter cyclones. Small hydrocyclones have, in turn, very low throughput capacities which render them impractical for many industrial thickening applications. Thus, if the effects of flocculation cannot be utilized, the usefulness of hydrocyclones as thickeners remains limited to pulps which contain no very fine particles. It is well established that most substances acquire a surface electric charge when brought into contact with an aqueous medium. The repulsive interactions between similarly charged particles act to prevent flocculation. One method of flocculating a dispersion is to neutralize the repulsive surface charges by the addition of an electrolyte. The reduction of the electrostatic surface charge (Zeta potential) then permits the universal van der Waals attractive forces to operate between the atoms of the various particles and form particle aggregates. The lime additions used by thickener operators promotes flocculation by this mechanism. A second method of flocculating a dispersion is by the addition of long-chain macromolecules. In this case flocculation is brought about by a bridging mechanism in which the molecules are adsorbed with part of their length on two or more particles, thus forming a molecular bridge between the particles.4,5 The molecules also form bridges between themselves when a single particle is bonded to several polymer molecules. The type of bonding between the flocculant molecule and the particle may be hydrogen bonding, chemical bonding, or electrolytic attraction.6 The flour and glue which are used as thickener additives are believed to promote flocculation in this manner. In the past decade synthetic long-chain polymers with extremely high flocculating capabilities have been developed. The flocs formed by these new polymeric flocculants are larger and more shear-resistant than those formed by the presence of electrolytes.7 The advent of these flocculants raises the question: Are the flocs formed by these synthetic polymers stable enough to resist the liquid shearing forces in a hydrocyclone? The investigations reported in this paper were carried out in order to provide some answers to this question. EXPERIMENTAL WORK For the bulk of the test work a 5% slurry of commercially available kaolin with an average particle size of 5 microns was used. An initial evaluation of the available flocculants was carried out to determine which flocculant formed the most shear-resistant flocs. A combination of the techniques used by Healy7 and Booth8 was used for this purpose. This initial study revealed that the neutral high-molecular weight polyacrylamides produced the most shear-resistant flocs. One of these flocculants, Separan MGL*, was selected and then used for all the hydrocyclone tests. The flocculant was dissolved in water and added to the hydrocyclone as a dilute solution.

Jan 1, 1968

By Ernest F. Burchard

In connection with the work of testing structural materials for the use of the U. S. government at the laboratories of the technologic branch of the U. S. Geological Survey at St. Louis, Mo., from September, 1904, to April, 1909, and since then at Pittsburg, Pa., large quantities of sand, gravel, and crushed stone have been needed from time to time, besides samples of building-stone, clays, and other quarry-products. In many instances it has been necessary to obtain single samples of sand, gravel, or crushed stone in lots of a car-load or more. For obvious reasons all these collections have had to be made by a representative of the Survey. As the work progressed it was found essential that numerous geologic data should be gathered regarding the materials collected, in order that they might be properly classified as to kind of material, source, geologic age, etc., and that they might be rated according to quantity available, accessibility to transportation facilities, approximate costs, suitability for special purposes, etc., and that notes might be taken regarding undeveloped deposits of possible value. Furthermore, it mas desired that the selection of materials for tests should be made broadly, so as to cover, first, the representative types of material, and later, if possible, the typical materials of the more important building-centers in the United States. In order to insure a certain degree of uniformity in this work and economy of effort and expense, it was decided that as much of the sampling as was practicable should be done by a member of the geologic branch, whose regular field-trips could be combined conveniently with those necessary for procuring materials for the laboratory. During parts of the last three years 1 have been engaged in field-work of this sort.

Jan 1, 1911

By M. Cohen

THERE seems to be a natural urge for the human mind to wonder about the beginning of things. When an explosion occurs, we immediately inquire "what set it off?" If a person contracts a disease, we are likely to ask "how did it happen?" On a much loftier plane, when we reflect about the universe, there is the inevitable question "what, or rather Who, started it all?" In principle, these varied queries have at least one attribute in common: they are attempts, whether earnest or casual, to search out the origin of events in nature. Accordingly, they involve not only scientific, but philosophical and even re1igious matters of deep concern. It is evident that, in a broad sense, the phenomenon of nucleation is enmeshed in this enticing concept of "the beginning", but we must extract the scientific component of the problem for our present purposes. Nucleation, as in the case of phase transformations, is best regarded from the standpoint of kinetics. There are then two main steps, which may come in either order: (a) Experimentally, one attempts to measure the frequency with which transformation centers spring into existence; and (b) theoretically, one seeks a model that will account for this observed birth-rate. Temperature, composition, strain, and prior history are some of the important variables that must be considered both experimentally and theoretically when dealing with nucleation in the solid state. Such interaction of theory and observation is an integral part of science in general, but it is particularly significant in the nucleation problem because the very beginning of a phenomenon invariably occurs on too localized a scale in both space and time to be detected with available techniques. Thus, there is little hope of making direct measurements on the nucleus during its birth or to ascertain the exact nature of the process; one can only infer the details of nucleation from the model whose predicted behavior seems to harmonize best with the measured rate of nucleation and its dependence on known parameters. In the field of solid-state nucleation, both theory and experiment call for much ingenuity, but somehow the conceptual schemes have spawned faster than they can be tested by observation. This is not to say that there are many basically new ideas in modern nucleation theory; rather, as we shall see, it is because the required fine-scale measurements are of immense technical difficulty. Quite likely, some of the nucleation models existent today have survived only because of the latitude permitted by meager data. There is great need to bring theory and experiment into better balance in this important area of physical metallurgy. Although one can

Jan 1, 1959

By Richard H. Jahns

Gem materials, comprising those minerals and closely allied natural substances used for personal adornment, for the fashioning of ornamental objects, or for other decorative purposes, have been valued in human commerce for thousands of years. Amber, jet, natural glasses, and at least 15 mineral species were sought and used by primitive man, and most of the materials in common use today were known well before the time of Christ. Their variety is remarkably great, and the traceable relationships among their respective sources, modes of occurrence, properties, and histories of production, preparation, and valuation are extremely complex. Their uses have been affected by numerous shifts in fashion, and from time to time by superstition, by decrees of church and state, by personal interpretations of religious significance, and by various presumptions concerning medicinal value and influence on human behavior (Ball, 1935, 1950; Kunz, 1913; Pogue, 1915, Whitlock, 1946). Thanks to their durability, portability, and relative scarcity, some gem stones have been employed as media of exchange, and the investment value of the more precious stones has long been recognized and exploited, especially in Asiatic and European countries. Demands for gem materials have stimulated trade among various peoples for centuries, and they also were responsible for much early geographic exploration. During more recent times they have prompted numerous geological studies and a considerable amount of research on the growth and properties of crystals. Apart from decorative uses, some naturally occurring gem materials also are employed directly in numerous fields of industry. Substances that are manufactured for gem or industrial uses are termed synthetic gem materials; most of these correspond in composition and crystal structure to certain minerals found in nature. Imitation materials are those whose use is based upon their resemblance to substances of different composition and greater intrinsic value. Gem stone is a designation commonly restricted to those materials suitable for personal adornment, and the complementary term ornamental stone is applied to the remaining materials not used industrially. This distinction is arbitrary and somewhat inconsistent, owing to numerous geographic differences and historical shifts in end uses. Further, there is a complete gradation between the category of ornamental stones and that of dimension stone. Substances that lose their identity in use are excluded from the gem category; thus a transparent crystal of beryl would not be classified as a gem stone if it were processed as a source of beryllium metal. The adjectives precious and semiprecious have been employed as a means for distinguishing different gem materials on the basis of recognized value. Diamond, emerald, ruby, and sapphire consistently have been regarded as precious stones, and in cut form they commonly are referred to as the noble gems. Opal, pearl, turquoise, and chrysoberyl also have been classed as precious at various times. In recent years, however, it has been increasingly recognized that no satisfactory distinction can be based upon assessed value or any group of specific properties, and now all gem stones normally are referred to as precious. Indeed, the tendency is to extend this term to include many of the so-called ornamental stones, and the designation semi- precious has been essentially discontinued. Unlike most mineral commodities of economic value, gem materials are little altered in processing for end uses. Some stones are used in essentially their natural form, and most are reshaped and polished without significant changes in their fundamental properties. Thus the preparation of gem and ornamental stones is intended chiefly to emphasize or enhance

Jan 1, 1975

By Henry Howe

THE brilliant and very original matter in Professor Jeffries' discussion ? should rank not only as an independent paper, but as a most important one. In particular, the explanation which it gives of the remarkable Sauveur phenomenon, over which so many of us have puzzled long and hard, is so clear, complete, and cogent as to go far toward establishing Professor Jeffries' hypothesis. The very features of Professor Sauveur's photographs which fit this hypothesis so exactly are reproduced in Chappell's photographs of steel coarsened under somewhat different conditions. 1 The ideas developed by these discoveries are so novel that conven- ience of language seems to call for new conventional terms for expressing them. In, what follows here I propose certain terms for this end, for criticism and improvement, and I attempt to generalize from Professor Jeffries' hypotheses. Generally speaking, a given set of grains which undergo no growth in the cold will, when the temperature is raised progressively, start to grow on reaching a certain temperature, and will continue growing at all higher temperatures. The "germinative" temperature is that at which growth begins, quite as the conditions which cause a seed to grow are "germinative." We have then. an inert temperature range below the germinative temperature, and a growth range above it, the germinative temperature being the limit between these two ranges. So, too, a germinant grain is one which is at its germinative temperature, and hence beginning to grow, while inert grains are those below their own germinative temperature, and the term "growing grains" includes those which are germinant and those which are above their germinative temperature. These last could be called "supergerminant" if the distinction should be needed.

Jan 12, 1916

By Frank W. Cramer

THE operator's panel is the control center f or the operation of the electric-arc furnace. It contains the switches and meters that control and indicate the power supply and in a way gives a picture of what is going on during the meltdown and refining periods. Regardless of manufacture, these panels are very similar with respect to equipment and position of apparatus. A typical panel is shown in Fig I. The three lights at the top of the panel are connected from the electrodes to ground and give a visual measure of the voltage across each arc. The ammeters underneath the lights show the current passing through each electrode. Directly underneath are the voltmeter, the watt-hour meter and the wattmeter and under these the three current-adjusting rheostats. In the center of the panel is the master electrode-control switch, which controls the movement of all three electrodes, with the individual electrode-control switches directly underneath. Next from left to right is the six-position voltmeter switch, which can be positioned to show on the voltmeter above the voltage between phases and to ground, the tap-changer switch with its indicating lights, and the main circuit-breaker control switch.

Jan 1, 1947

By James C. M. Li

The thermodynamics of the set of functions including the activation enthalpy. the activation free energy, and the activation entropy for the motion of dislocations at low temperatures is formulated without a specific model or a mechanism. The behniiior near absolute zero of all these functions and of other relevant quantities related to dislocation mobility Is examined in the light of the third law of thermodynamics. The velocity measurements of Stein and Low for edge dislocations in Si-Fe are used .for illustrotion. In the plastic deformation of crystalline materials, a fundamental assumption, which is supported by direct measurements using etch-pit techniques,'-4 is that the average velocity of a certain mobile dislocation is a single-valued function of temperature and the effective shear stress exerted on the mobile dislocation: Sometimes under certain assumptions, even without direct dislocation-velocity measurements, an activation volume can be obtained from a change in strain rate in a simple tension test. Similarly an ac tivation enthalpy can be obtained by changing the temperature in a creep test. However, the assumptions involved should be studied carefully before using the results of these tests. Consider, for example, a tensile specimen at some stage of deformation with a distribution of mobile dislocations. Let the total length of dislocations of type i be pi per unit volume. The Burgers vector of these dislocations is hi which makes an angle ?i with the tensile axis. With respect to the same tensile axis, let the normal of the slip plane of these dislocations

Jan 1, 1965

By Richard Amberg

While the old-time melter was satisfied to bring his metal out in the desired condition, and therefore took care to have the slag liquid enough, the importance of a thorough knowledge of the slag is at present recognized in all up-to-date melting-shops. Formerly slag or cinder was considered a necessary evil, accumulating in some mysterious way wherever a man was striving to produce a clean metal. Nowadays we deliberately aim at a well-defined slag, which varies with the nature of the process and the product. In steel-making we need slag for two main purposes, namely, refining and protecting the metal. To refine metal, essentially oxidizing and reducing processes are required, while to protect the metal we need a reducing or, still better, a neutral atmosphere. Although an absolutely neutral condition between steel, on one side, and the containing vessel and the slag, on the other, is an imaginary conception, the various furnaces in use for the production of liquid steel maybe arranged with respect to the attainment of this ideal in about the following order of merit: converter, open-hearth, crucible, and electric furnace. In dealing with the subject we will find it convenient to avail ourselves of the terms of physical chemistry, which yield a simple conception of the matter and an expedient way of expression. Slag and metal at large are not mixable with each other, and we will therefore call them the two " immiscible phases," though there are certain compounds which dissolve in both phases under conditions to be considered later. Reactions be-

Jan 1, 1913

RAYMOND M. Howe (author's reply to discussion*).-Dr. Unger states that magnesite will hardly supersede dolomite in fettling after a heat; that it is hard to believe a slag composed of oxide of iron containing about 6 per cent. of phosphorus is the active corroding, agent in a boil in a furnace; and that boiling cannot be said to be the result of the chemical action of a high-phosphorus slag on a basic bottom. These are well-established facts that no one would venture to question. The authors were misinterpreted in the statement that "in the summary, it is claimed that magnesite low in lime, or of greatest purity, ranks first in resistance to slaking," etc. On the contrary, the position has been taken throughout that while a low lime content is advantageous, the presence of several per cent. of iron oxide (an impurity), is necessary in order to confer the proper bonding and sintering properties in dead-burned grain magnesite to be used for furnace hearths. We cannot subscribe to the view that pure magnesia is no better fitted for a refractory than pure lime,' nor that the pure natural varieties of magnesite; such as Grecian or Washington, must necessarily be burned with silica and oxide of iron to produce a satisfactory material. On a small scale, pure magnesia has been satisfactorily used as a refractory in the form of crucibles. In the production of dead-burned grain magnesite from the Grecian or Washington mineral, iron oxide is added but the addition of silica is neither customary nor desirable. It is possible to manufacture brick of good quality from both the Grecian and the Washington material without adding either silica or iron oxide, providing they are burned at a sufficiently high temperature. This is regularly done on a commercial scale both in America and abroad when brick of. exceptionally high refractoriness or special purity are desired. The following analysis is of an English brick of Grecian magnesite which is extremely low in all impurities.1

Jan 6, 1919

By H. H. Rachford, J. Douglas, D. W. Peaceman

A numerical solution of equations describing two-phase flow in porous media shows promise in providing a technique for predicting the displacermet from satlds of oil by water or gas. The description includes the influence of relative permeability, fluid viscosities and densities, graviry, and capillary pressure, and, tholrgh tested ortly for two-dimensional cases, should be eqlmlly applicable in three-dimensional geometry. Two memorical methods ore presented: the first method is quite general in its applicability; the second method can be used only with certain types of boundary conditions but requires less computing. Comparisons of computed results with data from Inhoratory models are presented. These data were taken on a water flood of a strarified model and on water floods of a five-spot model for favorable and unfavorable mobility ratios. On the stratified model, excellent agreement with recovery at breakthrough was obtained; agreement with recovery after breakthrough was poor. In the five-spot model, good agreement was obtainecl with recovery at and after breakthrough. The purpose of this paper is twofold: first, to present a reservoir engineering method requiring knowledge only of rock geometry and the normally measured rock and fluid properties for calculating the multi-dimensional flow of water displacing oil from porous, water-wet rock containing connate water; and, second, to investigate the validity of the method by comparing results of calculations with previously observed displacements in laboratory models. The availability of such a verified technique of reservoir analysis would afford major advantages. First, it would demonstrate that the fundamental macroscopic concepts of two-phase fluid mechanics, i.e., relative permeability and capillary pressure, yield an adequate description of the physical process. Also, since most reservoir rocks appear to be water-wet and contain connate water along with oil, it would provide a method of technical and economic value for calculating the course of oil displacement by water directly from measured reservoir and fluid properties. It is important to emphasize that the calculation is subject only to the limitations of detail and precision of reservoir information, but not to limitations introduced by simplifying assumptions. Further, it would providc almost the only means of examining the influence of factors such as the size and extent of reservoir inhomogeneities and uncertainties in the basic reservoir data. Knowledge of this influence is essential in stating quantitatively the detail required to define a reservoir and in establishing the relation between the uncertainty in the definition of reservoir properties and the reliability of predicted performance. Moreover, in the process of solving a particular problem much detailed information would become available about the displacement process. For example, at each point in the reservoir for all stages of the displace ment. the calculations would yield not only the water and oil saturations but also the direction and magnitude of fluid velocities and the local fluid mobilities. Such dctail is potentially of great value in giving insight into the mechanics of particular displacements. The development of such a method has long been the goal of research in the application of numerical an-alysis to petroleum reservoir enginecrinz. The most complete treatment of the displacement process published to date is that of Douglas. Blair, and Wagner,' which, however, was limited to flow in a single dimension. The method presented in the present work is hascd on the numerical solution of a finite difference analogue of the multi-dimensional differential system describing the displacement process. Although current work has considered only displacement of oil by water from water-wet sands, the differential system for other immiscible displacements, such as gas displacing oil with which it is in phase equilibrium, is quite similar. It should therefore be expected that the technique described will be applicable to displacement by gas as well. The description of the simultaneous flow of fluids through porous media in terms of relative perrncability and capillary pressure has been adequately discussed in the literature and standard textbooks. Sec, for exampje, Muskat. Chapter VII.'

By Thomas Downing

WHEN examining a coal property it is customary for the engineer to take channel samples at several coal faces. In doing so the extraneous matter, or partings, which can be removed by hand, or mechanically, with the facilities at hand, or proposed, is rejected. Where there is doubt concerning a stratum it is usually rejected from the main sample but part is taken for separate analysis. The samples are forwarded to a chemist for proximate analyses and determination of British thermal units, and, sometimes, ash fusion. Consideration is given all available commercial analyses but frequently the owner presents only the favorable ones. From the results thus obtained a general evaluation is made, monies are loaned or expended, markets are determined, and realization is estimated. In many instances, such grades are not substantiated and it is time we looked deeper for a basis which will prove more practical. Institute committees are working hard on analytic and use classifications and much valuable information has already been assembled and distributed. However, no single grade can be applied to any particular bed or region. Much study has been given the Pittsburgh No. 8 seam, yet that bed is subject to material differences in a single section; i. e., some strata of a face may differ from others in structure and analysis, particularly in sulfur content. From some localities it yields a good carbonization fuel, while in others it is chemically unfit for such use. Traveling south to the Logan, W. Va., field we find the Cedar Grove (Island Creek) seam a hard, gray splint coal. In the same field, and not far distant, the same bed changes, both structurally and chemically, and consists of excellent gas coal. In Illinois the moisture content of a bed may vary greatly in different localities. We have seen mines in which part of the coal is excellent for special purpose use but is spoiled by the product from another part of the same mine.

Jan 1, 1931