Search Documents

By John Mitchell, C. C. Hanninen, L. D. Clark

INTRODUCTION Certain rock types can be fractured thermally by spallation and thermal cracking. Spalling occurs in the regions subjected to thermal shock temperatures and cracking takes place in the adjacent cooler regions. The analysis of the heat-affected zones requires that heat transfer calculations be made where the thermal conductivity of the rock is a function of temperature and direction. Generally, accurate thermal conductivity data is not available for the high temperatures and rise rates associated with most thermal rock breaking methods. This paper describes a method for determining the thermal conductivity of an orthotropic material whose conductivity is a linear function of temperature. The necessary data is obtained from one test which makes it especially useful for in situ applications. The properties data are determined through an iterative process of comparing theoretically computed values of temperature for assumed conductivity parameters with data measured in the laboratory. The conductivity of the rock is determined when the results of the assumed parameters yield computed temperatures which agree with those obtained experimentally. Transient temperatures are computed using the explicit numerical method at given points in a three-dimensional semi-infinite solid whose surface is symmetrically heated on a circular spot. The thermal conductivity is assumed to be a linear function K = [a] + Bt; however, if necessary, any reasonable linear or non-linear function might just as well be used. The stability, convergence, node size,

Jan 1, 1971

By J. R. Finlay

Every business man who has reached the age of forty, or perhaps even thirty, must know from his own experience that there are occasional periods of "good times'' and others of "bad times "-booms and panics. Those who give to business some complexion of science have invented a semiscientific name for these alternations-the business cycle-indicating that it is a normal phenomenon which by its own nature repeats itself. The longer one lives and the more one enlarges his own experience by the study of history, the more of these cycles he knows and the more disposed he becomes to take their recurrence for granted. If these alternations can be put into the category of common- places, why not treat them as such? We are in a sharp depression right now, why worry about it? Is there not a certain average value for business that can be depended upon in spite of depressions? By way of rejoinder one might answer that war is the great commonplace of history, but when we get into one we generally find it worthy of attention. In the present case, many a man has lost two-thirds of his income, and he is extremely nervous about finding it again. The Southern Pacific Railroad earnings have dropped 75 per cent in the past year; Pennsylvania, 60 per cent; United States Steel Corp., about the same. The drop in current earnings is

Jan 1, 1932

By Charles A. Mitke

Excluding top-slicing and sublevel caving, large production caving methods may be divided into two general classes, the branch raise, or undercut caving method, and the combined shrinkage and caving method, each of which has a number of variations, the result of continual efforts towards obtaining lower costs and better extraction, by the introduction and substitution of minor improvements and modifications. Early Caving Methods Present caving methods are the cumulative result of developments covering a period of many years, with the most rapid growth during the past 15 years. They originated, presumably, from early English stoping methods, and, as far as is generally known, were first introduced in the Michigan iron district. They have had their greatest expansion and application in the large low-grade porphyry coppers. In their present form, they are probably a development and combination of sublevel caving and shrinkage (back stoping on ore) with gravity handling of broken material. Sublevel caving, as practiced in the Michigan district today, is a combination of drift, or crosscut, mining, with top-slicing, and caving, supplemented by later refinements in the shape of mechanized handling of broken ore. A height of anywhere from 16 to 20 ft. is generally taken, and the ore is drilled and blasted along the drift or crosscut for half this height (say 8 to 10 ft.), after which the upper 8 to 10 ft. caves and breaks of its own weight, with comparatively little assistance from drilling. This

Jan 1, 1928

By H. M. Howe

It has seemed to the writer that one important, and indeed sufficient reason, for our slow progress in learning the relation between the chemical composition and the physical properties of cast-iron, has been that the problem has not been attacked properly. It would be well to select the most probable working hypothesis which we can find, and proceed to test that hypothesis by comparison with observed facts, and by making new observations specially designed for such a test. Our first step, then, is to select the most probable working hypothesis ; and to attempt this selection, to state the hypothesis and its immediate corollaries, and to take some first steps toward testing it, is the object of the present paper. Its chief purpose is to bring the hypothesis to the attention of those who are more familiar with the evidence than the writer can pretend to be, and in a better position both to present new evidence and to discuss it. The hypothesis here selected is, that composition governs properties in the case of cast-iron, in the same general way and for the same reasons as in the case of steel, mutatis mutandis. This hypothesis, which of course makes no claim to originality, certainly seems reasonable and probable; its exposition and discussion are made easy by our existing knowledge of the constitution of normal or " carbon " steel; it therefore seems worthy of consideration.

Jan 1, 1902

By R. L. Stephenson

IN plants casting electric-furnace ingots and converting them immediately into blooms, billets, slabs, bars or forgings, the criterion of quality performance is the soundness of the semifinished or finished product. When rejections are necessary, it is not always obvious whether the defects were caused by an unsound ingot or by improper treatment during the heating and forming operations. To evaluate the effects of the numerous factors involved, it is necessary to accumulate a large number of detailed observations and to analyze and interpret these data properly. Even after a thorough investigation has been conducted, it is impossible, in some cases, to isolate the cause of the defect and say that it is definitely the result of an unsound condition in the ingot or mistreatment of the ingot during further processing. Two factors that are extremely difficult to evaluate are the chemical composition of the steel and time from finish pour to charge in the soaking pits or "track time," and it is necessary to evaluate their combined effects before many other factors can be studied. Plain carbon, fine-grained steel in the range of 0.18 to 0.23 pct carbon, is very susceptible to cracking and the longer the elapsed time between the pouring of the ingots and stripping for charging into the soaking pits, the higher the billet rejections for cracks are found to be. Below 0.15 pct carbon and above 0.30 pct the track time

Jan 1, 1947

By Marshall D. Himes

The Pima mine, Pima County, Ariz., a 53,500-tpd copper mine, is located 17 miles south of Tucson, Ariz. The mine is in a sequence of Paleozoic and Mesozoic sediments striking east-north-east and dipping southeasterly. These sediments are intruded by a Tertiary quartz monzonite porphyry. The Paleozoic Permian (?) dolomites, limestones, and sandstones have been altered to calc-silicate skarn, marble, and quartzite. The overlying Mesozoic Triassic (?) clastic sediments have undergone some recrystallization and hydrothermal alteration. The clastic metasediments are divided into three distinct lithologic units: lithic arenite, arkose, and interbedded and overlying black argillite. Three types of hydrothermal alteration in the clastic rocks are propylitic alteration (epidote, chlorite, and quartz, with or without sericite), quartz-sericite alteration, and potassic alteration (K-feldspar, quartz, and sericite, with or without chlorite and calcite). The porphyry has undergone potassic alteration. Dominant structures are an east-west postmineral fault in the western part of the pit, and strong low angle faulting and shearing which truncates the ore body at depth. The two joint sets, one parallel to bedding and the other at right angles to bedding are prominent in the mine. Faulting is in two dominant directions, one striking northwest, dipping northeast, and the other striking northeast, dipping northwest. Economic mineralization is prediminantly disseminated pyrite and chalcopyrite, and molybdenite-quartz veinlets. There are less important amounts of magnetite, hematite, sphalerite, galena, tennantite, and bornite. Mineralization is believed to be both structurally and chemically controlled.

Jan 1, 1974

By Wilbur I. Duvall, Thomas C. Atchison

Over the past ten years a series of investigations have been conducted to determine some of the physical processes involved in breaking rock with confined concentrated charges. Detailed discussions of many of these investigations have been published elsewhere.1-6 Laboratory experiments made by other investigators using Hopkinson pressure-bar techniques have shown that solid materials are fractured in tension by the reflection of an incident compressive stress pulse at a free surface.7-12 In these tests a small charge of explosive is placed in contact with one end of a bar. Detonation produces some plastic flow and crushing of the bar near the charge and generates a compressive stress pulse that travels along the length of the bar. At the free end of the bar the compressive stress pulse is reflected back into the bar as a tensile stress pulse. If the tensile strength of the bar is exceeded during this reflection process, a tensile fracture normal to the length of the bar is produced, and the broken end of the bar moves forward with a constant velocity equal to the average particle velocity trapped in the broken fragment. The new surface formed by the fracture becomes the new free end of the bar that reflects the remaining portion of the incident compressive stress pulse. This process is repeated any number of times until all of the incident stress pulse is reflected.

Jan 6, 1959

By G. B. Gould

EVERY mathematical statement of a measure of anything (as distin-guished from a count) is followed by a qualification always implied if not explicity stated--that the statement is only an estimate, which may vary from absolute accuracy within certain limits, according to the accu-racy of the measuring instrument. This basic fact, so obvious to engineers, is not so well understood by many that make use of laboratory coal tests. The tolerances that must be allowed in measurements of coal quality are very important in both their commercial and engineering applica-tions-and the significance of these tolerances depends upon the use made of the laboratory coal test. Only in recent years has there been any intensive study of this ques-tion of tolerances as applied to measurements of coal quality. There is very little in our published literature on the subject, and what has been published is not, readily comprehended by those who sell coal, or buy coal and use it, unless they happen to have made a study of the subject them-selves. There is great need for more widespread understanding of what has been discovered and how it applies to the use of laboratory coal tests. What follows is an attempt to condense into a few pages the results of the major investigations so far reported, and to explain their meaning in simple nontechnical language, with the addition of some recent illustrative experiments.

Jan 1, 1937

By C. A. Heiland

GEOPHYSICAL methods are playing an ever increasing part in various engineering fields. About ten years ago, geophysical exploration was first applied in civil engineering to the study of foundations and the location of construction materials and water. Its usefulness is now being extended into the field of structural engineering. Almost every structure has to be so designed that it will withstand any force to which it may be subjected. Such forces may result from its own weight, applied loads, pressures of various kinds, including those due to wind and water, ground subsidence and vibrations. The last two, problems involving the nature and dynamic behavior of surface and subsurface formations, are within the scope of geophysical investigations. In the design of any structure, the disposition and dimensions of its members as well as their materials must be so selected that they will withstand any or all of the forces enumerated above. In other words, its "resistance" to such forces must be sufficient, allowing for a definite margin of safety. Often a static treatment of the problem leads to satis-factory results, but the static method entails serious errors when vibra-tions are involved, as in resonance with an impressed vibration the displacements of a structure or parts thereof may dangerously exceed the allowable values. The principle of "dynamic design"? is, therefore, avoiding or reducing resonance by suitable selection of the natural frequency of a structure, or by the provision of damping.

Jan 1, 1939

By G. R. Gohn, S. M. Arnold

The results of stress-corrosion tests upon several non-ferrous sheet metals are presented in this paper. The metals include tough pitch copper, five binary brasses, two leaded brasses, one copper-silicon alloy, two tin bronzes, and two nickel-silver alloys. The tests indicate that for most of these sheet metals, externally applied bending stresses below the yield point (0.01 per cent offset) do not result in stress-corrosion cracking as determined by the A.S.T.M. Tentative Method of Mercurous Nitrate Test for Copper and Copper Alloys (B 154-41T).~ Only in the cases of low brass, high brass and medium leaded brass, all cold-worked 4 B & S numbers hard, was any corrosion cracking observed below the yield strength, and in all cases such failures occurred at stresses above the proportional limit for these materials. However, when some of the same materials which showed no evidence of stress-corrosion cracking at stresses below the yield strength, are stressed beyond the yield point, stress- corrosion cracking is quite apt to occur. Since experience has shown that some of these materials, particularly the brasses, are susceptible to stress-corrosion cracking under service conditions, these tests would indicate that, besides externally applied stress and corrosion, plastic deformation in addition to that resulting from the original cold working of the material is also required to produce conditions conducive to stress- corrosion cracking.

Jan 1, 1945

By N. B. Gray, R. V. Culver, W. S. Boundy, N. W. Stump

The kinetics of sulfation of single crystals of lead sulfide to lead sulfate have been studied between 969" and 1073°K in gas atmospheres of known composition using a thermobalance technique. The data are described by an equation derived on the basis that diffusion outward through the Product layer is the major controlling step. The rate of sulfation is linearly related to the logarithm of the sulfur trioxide partial DESPITE its industrial significance the oxidation of lead sulfide has received limited attention. The oxidation reactions have been studied using beds, briquettes, single crystals, or thin films of lead sulfide. Lead oxide and lead sulfate (PbSO,) were formed when Mclntoshl and Gardner2 roasted beds of galena pressure and the temperature coefficient of reaction is 40 ± 5 kcal per g mole. Gold marker experiments show that the sulfate layer grows by outward movement of ions through the sulfate layer. Initially the PbSO, adheres to the PbS but later forms an irnpewious spheroidal envelope; PbS vaporizes and pb2' ions diffuse through the envelope to react at the external surface. in air at temperatures up to 800°C. In a more extensive investigation, Tchizhykov3 obtained Pb, PbO, and PbS04 in accordance with Eqs. [1] to [4], when a bed of -200 mesh galena was oxidized in O2-N2 mixtures at 700° to 900°C.

Jan 1, 1968

By L. B. Underwood, C. J. Distefano

NORAD, when completed, will be housed in large chambers excavated out of the granite beneath the Cheyenne Mountain near Colorado Springs. A room and pillar layout for the chamber excavation was selected and executed. Many complex problems arose in designing a rock bolt system; this paper includes discussions on: rock strengthening following excavation, excavation and ground support problems, orienting rock bolts with respect to jointing systems, conducting pull tests, four-way chamber intersection problems, the need for grouting rock bolts, and loss of tension and permanency of anchorage in a rock bolt system. In the event of a sudden nuclear attack upon the United States, it is imperative that vital command and control centers have a high probability of survival. One such vital facility is the North American Air Defense Command Combat Operations Center at Colorado Springs, Colo. Known briefly as NORAD, this installation when completed will be housed in large chambers excavated out of granite beneath the eastern slope of Cheyenne Mountain (Fig. 1). The NORAD COC, a U.S. Air Force sponsored project, will serve as the primary collection and evaluation center for data concerning unknown aircraft, missiles, or space vehicles, which might bring destruction to North America. The data will be fed into high-speed computers and electronic equipment from outpost sources: radar, ballistic missile early warning stations and picket ships throughout the world. Electronically controlled display boards will make it possible to evaluate the tracking data instantaneously and to take appropriate defensive action.'

Jan 1, 1968

By Paul D. Merica, O. B. J. Fraser

PROBABLY the first metallic objects used by man were nickel alloys. In search for flints suitable for the fashioning of their rude tools, our paleolithic ancestors, some 25,000 years ago, quite likely may have come upon some of those heavy, metallic fragments that we now know as meteorites, which consist of an alloy of nickel and iron containing usually from 5 to 15 pct of nickel. Whether paleolithic man ever did discover and use meteoritic fragments, his sketchy records do not actually disclose. We do know, however, that such fragments have been found and used by peoples, particularly the North American Eskimos, for weapons and implements in just the same manner as stones, and prior to any knowledge by those peoples of the reduction of metals from ores. Meteoritic showers were recorded frequently in earliest times and the meteorites often were found and fashioned into useful objects. The ancient Arabic and other myths of "invincible swords fallen from heaven" seem thus to have had a very definite basis in fact, and such weapons, of meteoritic material, have actually been re- covered from archeological excavations. It thus seems probable that meteoric nickel-iron was found and used long before iron was recovered by smelting iron ores (perhaps about 1200 B.C.) and probably even before there was knowledge and use of bronze and gold. Although many centuries were to pass before nickel was first isolated, in 1751, from Swedish ores and recognized as an elemental

Jan 1, 1953

By Earl Bardwell

(Butte Meeting, August, 1913.) THE structural relations existing between cuprous oxide and copper were first systematically studied by Heyn1, who suggested that a study of the microstructure of refined copper might be substituted for the analytical methods in vogue for determining the oxygen content of copper coming .;from the refining furnace. Hofman, Green and Yerxa,2 in their paper A Laboratory Study of the Stages in the Refining of Copper, working along the lines suggested by Heyn, showed that a study off the microstructure could be made to yield a correct estimate of the oxygen content of the specimen of refined copper under examination. In order to determine the oxygen content of the specimen of refined copper under examination a photomicrograph was first made. From the relative areas of copper and eutectic, the percentage of cuprous oxide and the corresponding percentage of oxygen were then readily calculated. It was found that the values for oxygen thus obtained corresponded closely with the analytical results. With the idea of utilizing, this method of determining the oxygen content of each charge dipped from the refining furnaces at the Boston & Montana Reduction Plant, the physical testing laboratory was equipped with suitable apparatus for carrying out the work. It may be of interest to describe certain of the methods which have been worked out in, this connection and give such data as have been obtained bearing on the effect of the oxygen content of refined copper upon its conductivity.

Jan 7, 1913

By J. H. Klepinger, C. W. Goodale

I. Introduction....................567 II. Character oF the OrE................568 III. Old FluE System..................572 IV. Tests on Old FLUE System..............575 1. Aspiration Tests................. 575 2. Tests with Steel Settling Chamber........... 575 3. Test with Experimental Brick Flue........... 583 4. Testa on Blast Furnace Geses............. 591 V. Design of New FluE System.............. 597 VI. Main Dust Chamber................. 605 VII. Some DetailS of Construction ............. 609 VIII. THE Chimney.................... 616 IX. Operation of New FluE System............. 624 X. Temperatures and DraFTS............... 630 XI. Velocities and Volumes................ 632 XII. TeStS on the New FluE System............. 637 XIII. Conclusion..................... 643 I. Introduction. In the summer of 1909 the Boston & Montana reduction department of the Anaconda Copper Mining Co. completed a new flue system, at a cost of about $1,100,000, and as this includes the largest and highest chimney in the world, and some new features of flue construction, a description will be of interest. At the Spokane meeting of the Institute in September, 1909, a brief mention was made of this flue system, in discussing Mr. Brunton's presidential paper on the Progress of Metallurgy in the West, and a promise was given that when a long enough time had elapsed, so that operating results could be given, a paper would be offered. The smelting plant includes blast furnaces, MacDougall roasters, gas-fired reverberatories, and converters.

Jan 1, 1914

By J. R. Bell, W. J. Childs, J. H. Bucher, G. A. Wilber

A technique for determining recrystallization times as short as 0.10 sec was developed utilizing the "Gleeble", a commercially available testing system designed for the study of short-time, high-temperaLure themal and mechanical processes. The procedure consisted of heating a small tensile specimen to a given temperature of hot deformation, loading to a given reduction in area, unloading, delaying various intervals at temperature, and then reloading- to failure. The magnitude of the ultimate load obtained upon reloading decreased with delay lime as recrys-lallization proceeded. The technique was applied to austenite recrystallization in AISI 1010 and AISI 1010 uith 0.02 pct Cb steels. For each steel the reduction in area given the specimen on the first pull was mainlairred at 30 ± 5 pct and recrystallization times deterntined at various temperatures. The results indicaled a significantly slower rate of recrystallization for the columbium-modified composition, suggested the presence of- a recovery stage in the softening process , and indicated a greatly increased softening rate at a temperatuve where significant allotropic transformation to a partially ferritic Structure could occur. In recent years increasing attention has been paid to the fact that the process of recrystallization of austenite deformed at elevated temperatures is far from instantaneous at many practical hot-working temperatures.1-3 This realization has given rise to such terms as hot cold-working1 or warm-working,2 These terms generally describe processes where the recrystallization rate at the temperature of deformation is slow enough to have an appreciable effect on mechanical properties despite a relatively high deformation ternperature. The mechanical properties of interest can be either the properties at the deformation temperature as in hot-workability studies4 or the room-temperature properties after cooling as in the many recent studies of various thermomechanical processes172 where heat treatment and deformation are intentionally combined to give a unique set of room-temperature properties. Because of this interest in processes where the austenite recrystallization kinetics can be an important variable, the development of quantitative methods of following the course of short-time, high-temperature recrystallization has received increasing attention.l,3,5 The experimental methods to date have, in general, relied upon rapidly deforming the austenite, holding at temperature for various brief intervals, quenching as G.A.WILBER and W. J. CHILDS, Members AIME,are Research-Fellow and Professor, respectively, Rensselaer Polytechnic Institute, Troy, N. Y. J. R. BELL and J. H. BUCHER, Member AIME, are Research Engineer and Research Supervisor, respectively, Graham Research Laboratory, Jones & Laughlin Steel Co., Pittsburgh, Pa. Manuscript submitted March 13, 1968. IMD. rapidly as possible, and then using room-temperature measurements to follow the recrystallization process. Although such methods can be successfully applied to certain alloy steels, the existence of the allotropic transformation during cooling of plain-carbon or low-alloy steels tends to obscure the results. Thus, such room-temperature measurements as hardness and X-ray line widths do not correlate well with the extent of austenite recrystallization before quenching,5 and results based on room-temperature microstruc-tural observations are dependent upon the success in correlating the observed structure with the prior aus-tenitic grain structure.1,3,5 The purpose of the present work was to develop a quantitative method for the determination of short-time, high-temperature recrystallization rates, based on measurements made at the temperature of deformation. EXPERIMENTAL TECHNIQUE The basic technique consisted of heating a small tensile specimen to a given temperature of hot deformation, loading to a given reduction in area, unloading, delaying various intervals at temperature, and then reloading to failure. The data were obtained in the form of traces of load and elongation as a function of time. Due to the high deformation temperature, the strain hardening introduced during initial loading was progressively annealed out with holding time after unloading and the loads obtained upon reloading decreased as this softening proceeded. Although the value of the second load at any Consistent point On the load-elongation curve could have been used as a measure of the degree of softening, the most convenient to use was the ultimate load. The softening indicated by the decrease in the second ultimate load with time is essentially a process of annealing of cold-worked material at a high deformation temperature. Although some recovery grain growth may contribute to such a softening process, it is generally considered that the major softening which must take place to achieve complete removal of substantial Strain hardening will occur by the formation of new, stress-free grains. As the results of this work indicate that essentially complete removal of strain hardening did in fact occur. the primary softening process will be attributed to recrystallization, and specific reference made where it appears that other mechanisms may be contributing to the total observed softening. It would, of course, be of interest to attempt to correlate the results of this work with the actual austenite fraction recrystallized as determined by other techniques. This was not attempted in the present work because it would have required running a large number of additional specimens and, as discussed previously, there is limited assurance that the results would accurately reflect the prior austenite fraction recrys-

Jan 1, 1969

By J. A. Jaekel, W. C. Aitkenhead

Uranium deposits in the Spokane Indian Reservation, as well as those around Mt. Spokane, are essentially low grade, much of the ore containing less than 0.2 pct U3O8. The Mining Experiment Station of the Division of Industrial Research, State College of Washington, has been engaged in intensive research on the amenability of these low grade ores to froth flotation. The results: successful flotation of autinite, chief mineral constituent. At the outset of this work the goal was a concentrate of 1 pct U3O8 with a 90 pct recovery from ores containing less than 0.2 pct U3O8. Most of the work has been done on argillite ore from the Midnight mine on the Spokane Indian Reservation. The goal has not been attained using this ore, but samples of the granite ore from Mt. Spokane yielded successful results. For example, a concentrate containing 11.2 pcl U3O8 was produced from a Mt. Spokane high grade ore containing 1.27 pct U3O8 with a recovery of 97.8 pct. Another Mt. Spokane ore yielded a concentrate of 5.0 pct U3O8 from an ore containing 0.13 pct U3O8. with a recovery of 85 pct. This same ore gave a recovery of 93.5 pct when the grade of concentrate was reduced to 2.0 pct. It has been concluded that a successful method for floating autunite has been developed and that the mediocre results from the Midnight argillite ore are probably caused by the presence of some other uranium mineral or minerals less amenable to these reagents. The experimenters tested a third type of Washington ore, found on the Northwest Uranium Mines Inc. property on the Spokane Indian Reservation. This is a conglomerate of pebbles and small boulders of partially decomposed granite and is shot through with autunite. Its characteristics lie between those of the Midnight ore and the granite ore from the Spokane district. It responds better than the ore from Midnight but not as well as that from Mt. Spokane. As the fatty acids are the only type of collectors showing promise, investigation has been concerned with these acids and the optimum conditions for their use. The first method for treating the argillite ore from the Spokane Indian Reservation made use of Cyanamid's R-708 as a collector, a tall oil product described as a substitute for oleic acid. Although the investigators proved that R-708 is a collector for autunite when mixtures of autunite and silica sand are used, results on the ore were mediocre. Tests of other fatty acids revealed that the solid fatty acids of the saturated series are collectors for autunite and that their collecting power increases with the length of the carbon chain. The even carbon members of the whole series were tested from the 10 carbon acid (capric) to the 22 carbon acid (be-henic). The least expensive collector, stearic acid (18 carbon), proved to be a good one, so this was used in most of the tests. In first attempts with stearic acid, the collector was dissolved in various hydrocarbons and the solutions were added to the flotation cell. Cyclohexane, gasoline, fuel oil, kerosene, and other solvents were tried. Small amounts of high grade concentrates could be brought up, but recoveries were low. Finally emulsions of stearic acid were tried. It was discovered that stearic acid alone has little collecting power except when conditioning is carried out at high temperature. When hydrocarbon solvents were also present, it proved to be an excellent collector. An example of one emulsion that proved satisfactory for some ores is given as follows: 1 part stearic acid by weight, 1 part sodium oleate by weight, 1.2 parts kerosene by weight, 100 parts water. In some successful tests part of the stearic acid was replaced by oleic acid. The emulsions were made by agitating the stearic acid and sodium oleate together with hot water, then adding the kerosene and agitating while cooling. In the five tests reported in Table 1, 650 g of ore were ground with 650 cc water in a laboratory rod mill. The pulp was filtered to eliminate excess water and the ground ore transferred to a stainless steel beaker for conditioning at high pulp density. In most of the tests sodium hydroxide was added to the conditioner during agitation, then the collector emulsion, and finally the sodium silicate. The amount of alkali was adjusted to give a pH of 8.5 to 9.0 in the flotation cell. After conditioning the pulp was transferred to a laboratory flotation cell and the test completed in a normal manner. It is interesting to note that a deposit of high grade concentrate forms on the conditioning agitator and in the conditioning vessel, and at times on the agitator of the flotation cell itself. A few grams of concentrate running as high as 4 pct U3O8 were recovered from the conditioner when Midnight ore containing less than 0.2 pct U3O8 was treated. In the examples given in Table I this conditioner concentrate is calculated as part of the total concentrate. The authors have not yet fully explored the possi-

Jan 1, 1960

By W. J. Slatosky

W. 0. Philbrook (Cairiegie Institute of Technologyogv—Mr. Slatosky has presented an interesting and constructive paper that represents another step along the way of converting steelmaking from an art to a science. I am confident that his computer will be practical and successful and that with a very few months of experience it will provide a significantly better degree of control than his record of 65 pct of heats within range obtained with the slide-rule calculator . A paper such as this, with a lot of symbols and condensed mathematics, is difficult to comprehend quickly. Since I have had an opportunity to study it carefully, perhaps my evaluation of its validity and accomplishments will save time for others. Mr. Slatosky has correctly used standard principles of stoichiometry and heat balances, which are available to anybody, but he has also brought to them two original contributions: 1) He has developed from operating data some empirical relations for predicting the final FeO content of the slag (at 0.5 pct C end-point) as a function of slag basicity, lance height, and scrap, ore, and scale in the charge. This improves the accuracy of prediction of temperature or scrap requirement compared with assuming an arbitrary, constant FeO content at the end of each heat. There is no assurance yet that exactly the same relations will hold for other furnaces or practices, but similar correlations can be expected. 2) He has combined calculations that are ordinarily carried out laboriously as a number of individual steps into a single, simple linear equation that can readily be fed into a machine. This involved a tremendous amount of painstaking detail work as well as the imagination to see the possibility and work out the steps. While his particular Eqs. [3] and [6] are valid only for the furnace design, charge weight, and blowing time used at Aliquippa Works, only a few numerical values have to be changed to adapt it for other conditions. In order to arrive at a useable solution, Mr. Slatosky had to make some basic assumptions about the process that are similar to those used by others. He neglected variation in some process variables and assumed an arbitrary average value for waste gas analysis and temperature for want of more exact information at the present time. All of these judgments are clearly stated. In addition, some thermody-namic data presently available are not adequate for the job, notably in relation to heats of formation and sensible heat in slag, and some expedient has to be adopted to get around the difficulty. Other people might prefer slightly different judgments about these details and hence obtain somewhat different numerical solutions. This is not of serious importance, however, because the errors accumulate in the "heat loss" term and are largely self-compensating for a constant heat time. Although the extended Eq. l(a) in Appendix I was set up as a rate equation originally, for convenience in using an analogue computer as stated in the paper, the time dependence was removed by later mathematical manipulations and assumptions about the process. The final result is an integration of element and energy balances from initial to final states; this procedure is as legitimate here as in any other form of heat-balance calculation. The formal handling of stoichiometry and thermochemistry appears to be correct, and it is assumed that any arithmetical errors would have come to light in applying the calculations to furnace practice. Mr. Slatosky's approach is not necessarily unique, in that other people might start with apparently different equations or prefer another form of final equation for another type of computer. However, he has presented an accomplished result that appears to be a theoretically sound and practically useful way of applying scientific principles and rapid computation for better control of steelmaking. His success will undoubtedly encourage himself and others to improve on the mathematical model and its use as better informatioq becomes available. John F. Elliott (Massachusetts Institute of Teck-t2ology)-The last comment by Mr. Richards that a calculator is quite unnecessary for an L-D operation ?-equi??es a rebuttal. The L-D furnace is a very high capacity process which places a premium on close control. When one is making steel at rates between 100 and 200 tons per hr, one cannot afford the luxury of an extra 5 or 10 min at the end of a heat correcting for an error that should never have been made in the first place. Mr. Slatosky's paper is a very sound application of the simple principles of stoichiometry and the energy balance. It is a satisfactory and valuable start, but only the start of the development of methods of control for this process. An analysis of the process shows that it should be very suitable to control by a computer. This is especially the case when various grades of steel are to be made. In fact, it would seem that the organizations who are planning new and bigger installations of L-D vessels should consider carefully the advantages that would stem from computer control of a vessel with the operator present to do little more

Jan 1, 1962

By Malcolm McColl, C. A. Mead

Thin films (of mica have unique attributes that are exceptionally good for studies of high-field conduction mechamisms in thin-film insulators and the quantum mechanical tunneling of electrons from metal to metal. The principal advantages of using mica films are that the films are crystalline and the cleavage planes occur every 10Å. This property results in films whose thicknesses are integral multiples of 10Å and whose surfaces are uniformly parallel over sizable areas. Hence, very well-defined metal -mica-metal structures are possible. Furthermore, the fact that the insulator is split fro??! a bulk sample allows the index of refraction, dielectric constant, forbidden energy gap, and trapping levels and their density- to be obtained directly from measurements performed on thick samples Of mica rather than requiring that these properties be interred from the conduction characterrsties alone. In the work to he described, all the cleaving was done in a high vacuum just prior to the evaporation of metal elertrodes so as to avoid air contamination at the interfaces. Results of these studies indicate that the current through the 30 and 40Å films exhibited quantitative agreement with the theoretical voltage and temperature dependence derived by Strallon for the tunneling of electrons directly from metal to metal. Thicker films at room temperature exhibited volt-ampere curves suggesting Schottky emission of electrons from the cathode into the conduction band of mica. However, the thermal activation energy was smaller than that found from other measurements, and the experimsntal Schottky dielectric constant was larger than the square of the index of refraction. These facts would indicate that the electrons were being injected into polaron stales ill the iusulator. At low temperatures and high fields, the current through the thicker films did not exhibit the Fowler -Nordheim dependence as would be predicted by a simple extention of the theory of field emission into a vacuum. THE mechanism of electrons tunneling through insulating films has received considerable attention in the last few years due to the devices possible utilizing tunneling'-4 and the success of tunneling in the study of superconductivity.5,6 Until the recent paper by Hartman and chivian7 on the study of aluminum oxide, there had been no reported successful quantitative experimental fit to the theory. Their method of fabrication necessarily results in a polycrystalline insulator, the stoichiometry of which is nonuniform from one side to the other. This structure also introduces complications to the shape of the barrier which is set up by the insulator since the insulator possesses a spatially nonuniform band structure and dielectric constant. Due to these facts an analysis of the data in terms of a pviori barrier shape is of questionable validity. The use of muscovite mica not only overcomes these disadvantages but, as an insulating thin film, provides physical properties (dielectric constant. trapping levels and their densities, forbidden energy gap, and so forth) that are identical to the easily measured values of the bulk sample. Furthermore, it is a single-crystal insulator whose cleavage planes (10Å apart8,9) provide uniformly parallel surfaces of well-known separation. This material is therefore ideally suited to the study of electron-transport phenomena. Von Hippel10 using a 6.5-µ-thick sample was the first to observe the high-field conductivity (=5 x l06 v per cm) of mica. No attempt was made to develop an empirical formula, but Von Hippel concluded from intuitive arguments that the current was being space-charge limited by trapped electrons. Mal'tsev11 in a more recent investigation at high fields observed a dependence of the conductivity a on the field F of the form exp(ßF1/2). This dependence was attributed to the Frenkel effect,12,13 a Schottky type of emission from filled traps. No mention in the English abstract was made of the thicknesses of his samples or, and more important, of how well the value of ß fit Frenkel's theory. In 1962 Foote and Kazan14 developed a technique for splitting mica to a thickness of less than 100Å and observed a dependence of the current density j on the field of the form j = jo exp(ßF1/2) on a thin sample thought to be 40Å thick. Assuming that this was a Schottky emission process and that the appropriate dielectric constant for such a mechanism would be closer to a low-frequency value of 7.6, Foote and Kazan calculated from ß an independent thickness of the mica of 36Å. No further investigation was made of the phenomenon. However, the work reported in this paper indicates that the film measured by Foote and Kazan was probably 60Å thick, the error arising from the measurement of the very small metal-insulator-metal diode areas that were used, along with the diode capacitance and dielectric constant, to calculate the thickness. In the research reported in this paper, Foote and Kazan's technique was modified to cleave muscovite in a vacuum of 10-6 Torr, immediately after which metal electrodes were evaporated creating Au-mica-A1 diodes. Aluminum was chosen because of its strong adhesion to mica, as necessitated by the

Jan 1, 1965

By F. F. Craig

Many full-scale waterflooding operations are preceded by pilot floods, one purpose of which is to provide an estimate of recoverable oil. A laboratory model study was made to determine the influence of the producing wells' effective productivity on the oil recovery efficiency of single five-spot pilots, as well as single injection well pilot floods. The effective productivity is indicated by the value of Condition Ratio, defined as the actual well productivity to that of on undamaged and non-stimulated, normal-sized well in the same formation. The effects of initial gas satrcration and mubility ratio on recovery eficiency were also investigated in this model study. Model test results skowed that at favorable mobiliry ratios, a five-spot pilot flood can provide a direct quantitative estimate of the recoverable oil in the pilot area. If the pilot producer's Candition Ratio is 2.2 or more, upwards of 90 per cent of the recoverable oil in the pilot area is recovered from the inside producer, regqrdless of the mobility ratio or initial gas saturation. This Condition Ratio can be achieved with preyent fracturing techniques. Model studies also showed that over the range of imposed injection pressure differences and regional pressure gradients normally encountered in field operations, there was no effect on the recovery efficiency of a five-spot pilot waterflood. Model studies of single injection well pilot waterfloods showed that with no initial gas saturation, the total oil recovery at the offset producing wells can indicate the oil recovery possible by full-scale waterflooding. It is essential that the Condition Ratios of the offset wells be above 1.4. If an initial gas saturation exists prior to water injection, the recoverable oil cannot be directly evaluated by a single injection well pilot flood. However, the production per formance of such a flood can be used to provide information on volumetric sweep efficiency. INTRODUCTION Oil reservoirs are conlplex structures and cannot always be fully studied in the laboratory. Therefore, many operators consider it prudent to evaluate a waterflood prospect by means of a pilot flood. Pilot waterfloods generally involve one of two well arrangements: a single five-spot pilot waterflood, involving four injectors and an internal pilot producing well; and a single injection well pilot flood (sometimes called an inverted five-spot pilot) having one injector and four sur- rounding pilot producers. Some pilot floods are composed of multiple five-spot pilot patterns. To yield information applicable to field-wide performance, the pilot must be located in a representative portion of the reservoir. Pilot floods generally are conducted for one or more of the following reasons: (1) to determine whether water could be injected at desirably high rates, (2) to determine whether an oil bank or zone of increased oil saturation is formed by water injection, and (3) to estimate the oil recovery by waterflooding. Many of the early pilot water-floods were conducted for only the first two reasons. As soon as a buzz in oil production was obtained in the pilot, water injection was initiated throughout the entire lease or field. A number ot laboratory studies have been directed toward determining conditions under which a pilot flood could yield a quantitative estimate of the oil recovery possible by full-scale pattern flooding. One of the early studies of single five-spot pilot flooding' showed that well damage to the inside pilot producer could reduce the total amount of oil recovered. In a study of the single injection well pilot flood pattern,' the results indicated that if the model boundaries were no closer than a half-well spacing beyond the pilot pattern, the pilot performance in the laboratory is unaffected by these boundaries. In another study,? he effect of initial gas saturation and mobility ratio on the ratio of production to injection rate for various groupings of five-spot patterns was defined by mathematical and analog methods. In a study4 involving both potentiometric and flow model experiments at a mobiliry ratio of unity, four different pilot patterns were studied. These included a single five-spot, a single injection well pilot, a cluster of four single injection well pilots and six inverted five-spots. In this study the ratio of well diameter to the distance between injection and producing wells was held constant at 1:1000. The effect of the 7 ratio-—the ratio of the pressure drawdown at the producing wells to the pressure build-up at the injection wells on the pilot performance-was studied. The values of 7 ratio ranged from 0 to 0.34. Results showed that both the total oil recovery and the total fluid production from the pilot relative to the cumulative injection increased with increasing values of the 7 ratio. The effect of both the ratio of injection to producing rates and mobility ratio on the oil recovery performance of a liquid-saturated single five-spot pilot flood was studied in a series of flow model tests.5 Rate ratios ranged from one to four, and mobility rates ranged from 0.1 to 10. Resulls of these tests showed that at low rate ratios, the pilot producers may recover up to four times the recover-

Jan 1, 1966