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By R. L. Orr, O. D. Sherby, J. E. Dorn

Creep data for pure metals at temperatures above those at which rapid recovery occurs (above about 0.45 the melting temperature) are correlatable by means of the equations and These correlations were applied successfully to data for aluminum, iron, nickel, copper, zinc, platinum, gold, and lead as well as for simple alloys. For a given metal, AH is a constant about equal to the activation energy for self-diffusion. THE early recognition that creep is stimulated by thermal activation prompted numerous investigators', ' to apply the same laws that are valid for the viscous behavior of liquids to analyses of creep data. To a good first approximation these laws are summarized by the equation were i is the creep rate; T, the absolute temperature; R, the gas constant in cal per degree per mol; T, the applied stress; AH, the activation energy in cal per mol; S', a constant dependent on the entropy of activation, the frequency of activation, and the contribution of each activation to the strain; and B', a constant dependent upon the size of the flow unit that is activated. Although Eq. 1 describes the flow of viscous fluids very accurately, its application to the creep of solids has been disappointing. Two reasons for the failure of Eq. 1 for creep are now known: First, the decelerating creep rates during primary creep demand that the internal structures of the metals are changing and that these changes might be reflected by changes in one or more of the three creep parameters S', AH, and B'. Consequently when the conventional methods of evaluating these parameters are employed by comparing the secondary creep rates at a series of temperatures and at a series of stresses, the true effects of temperature and stress are masked because of simultaneous changes in one or more of the creep parameters. Second, as will be illustrated more fully later, three distinctly different types of investigations have shown that the stress term for high temperature creep enters the analysis as and not as t/T. This rather unexpected result points sharply to a significant fundamental difference between the mechanisms for the viscous behavior of fluids and the high temperature creep of metals. More recent extensive investigations",'4 on the creep of high purity aluminum and several of its dilute a solid solutions have shown that where E is the total creep strain; temperature compensated time = for a constant temperature test; t, is the initial stress in a constant load test or the constant true stress in a constant stress test;" and t is the duration of test. • Eq. 2 is valid for either constant stress or constant load tests; but the total creep curve is difierent (i.e. the function, f, is differentl for each test. The fundamental origin of the validity of Eq. 2 is thought to arise from some equivalence of substructures in constant load creep tests at equal values of 0 or E. Both X-ray and metallographic examination revealed that practically identical lattice distortions and subgrain sizes are obtained for the same creep strain under the same load over wide ranges of test temperature.' Furthermore the room temperature tensile properties following equal creep strains at different temperatures under constant loads were also identical, illustrating that identical substructures were indeed obtained.' " A second type of correlation was obtained by differentiating Eq. 2 with respect to time, giving For the secondary creep rate, denoted by i,, But Eq. 2 reveals that 0, is a function of a, alone because the secondary creep rate in a given constant load test is always reached at a fixed value E,". Therefore where is the function that was introduced a number of years ago by Zener and Hollomon." Eq. 4 is not only valid for creep but will permit correlations between constant load creep and tensile data where e, is the rate of tensile straining and (TC is the engineering ultimate tensile strength.

Jan 1, 1955

By B. M. Larsen, W. E. Shenk

THIS paper describes a method of reversal control of the open-hearth furnace that obtains in practice those effects considered below as essential to a completely automatic control, without appreciable interference with the natural rise and fall in temperature of the regenerative portions of the furnace system. Growing out of some studies of radiation pyrometry in open-hearth regenerators, it was developed during 1934-1938, and has been successfully applied to a number of commercial furnaces. The goal of open-hearth furnace operation is the highest rate of production of steel of proper quality consistent with good refractory life and fuel economy. This requires rapid heat transfer from furnace to charge, which in turn is dependent upon heating the furnace refractories to the highest safe operating temperature. The greater the heat input to the melting chamber, the sooner this limiting temperature will be reached, so that control methods in general that are designed to protect against overheating of refractories should help to maintain maximum fuel input and production rate. For the typical open-hearth system, with fixed regenerator capacity and with rate of fuel input usually restricted in its range of variation, our basic assumption is the idea that the only other important variable that is, the time interval between successive reversals-should also be held constant or within a small range. The present reversal control was designed therefore so that, under normal operating conditions, no arbitrary limitation is imposed other than to keep the reversal interval within the optimum time range. However, since a near approach to completely automatic operation involves protection of refractories through the balancing of furnace end temperatures as well as emergency protection against temperature peaks above some upper limit, it was also felt essential to employ, as an integral part of the control unit, a temperature-measuring instrument to register the true temperature of the refractory surfaces at some critical region in the hot ends of the regenerative zones. As the basic elements of the control, we thus have one "maximum" and one "minimum" time relay and a potentiometer recorder-controller, combined with switches and relays to operate as follows: x. Reversal normally occurs within an optimum range limited by the maximum and minimum settings to about 4 to 6 min. variation, but the actual interval usually is less variable and closer to the minimum setting. 2. The margin between minimum and maximum time is utilized, together with a "floating temperature limit" in the potentiometric control instrument, to correct any

Jan 1, 1945

By J. W. Furness

THE utilization and collection of waste materials have gone on for centuries, and have become a habit of the human race. The degree to which the salvaging of waste plays a part in a nation's industry depends largely on the availability of raw materials within the political confines of the country itself, or its ability to purchase such material from outside. When purchase is necessary careful economical use of the raw materials results. These economies, as a rule, are represented by lengthening the life of the given article as well as much re-use. For many years the steel industry of Italy and Japan has depended largely on importations of scrap, yet both are important. As long as the expenses incident to the conditioning and marketing of materials manufactured from salvaged waste are less than the cost of virgin material, the salvaged material will be re-fabricated and in many cases will compete with primary materials. One of the most obvious methods for furthering the efficient utilization of our limited mineral resources is the salvaging of mineral wastes. This method, moreover, in¬creases the available supply of a given material. If the price depends on a balance of supply and demand and the recovery from wastes enlarges. the supply, there can be no question but that it influences the sales price of primary.

Jan 1, 1931

THE slag performs two useful functions in open-hearth steel- making. First, it is the means of disposal of all the impurities, save carbon, which are removed from the charge materials in refining the steel, so it must be suited to receiving and retaining as much as possible of undesirable elements with minimum loss of iron and useful alloying elements. Second, the slag serves as a buffer between the flame and the bath and transfers oxygen to the metal at a measured pace contrasted with the violent and difficultly controlled oxidation of the bessemer process. At the same time, the slag is a thermal insulator that limits the rate at which heat can be delivered to the metal from the flame, and a heavy slag blanket thereby serves as a brake on production rates. It has been said with justification that the secret of good steel- making is to make a good slag and the steel will take care of itself. In a broad sense, the subject of slag control includes not only the adjustment of the composition of the slag but also of its relative weight in terms of percentage of the metal-bath weight. The slag is made up essentially of: (1) oxides formed by oxidation of silicon, manganese, phosphorus, and iron in the charge, (2) Si02, MnO, MgO, and other oxides charged as such or introduced incidentally with ores or fluxes or by refractory erosion, and (3) lime charged or fed to the heat to neutralize the "acidic" oxides present (Si02 and P205). Obviously, if practically perfect control were possible over the composition of the charge as well as over the oxidation process during the melting period, both slag weight and composition would be very nearly predetermined; and the control problem would be solved. Unfortunately, only a somewhat imperfect control over these factors is possible, so the operator must begin during the lime boil and continue through the refining period to discover and correct departures from the normal pattern of slag development. To do this as the heat progresses, the first helper must be able to make quick estimates of the composition and physical state of develop-

Jan 1, 1964

By Kenneth C. Vincent, A. M. Gaudin

IN a study1of the action of amyl xanthate on chalcocite in water suspension, it was found that if the xanthate is added in relatively large quantity the xanthate group can be accounted for in three forms: (1) as xanthate ion remaining in water, (2) as benzene-soluble cuprous xanthate on the chalcocite, (3) as a benzene-insoluble coating on the chalcocite. Reduction in the amount of xanthate added leads to disappearance of form 1 then of form 2. With minute quantities of added xanthate, substantially all the reagent is of the "unleachable" kind. Yet this unleachable xanthate can be dissolved by pyridine to form a soluble cuprous xanthate complex, and it is sufficient in effectiveness to make chalcocite flotable even if insufficient in quantity to form a complete monomolecular film on the mineral. In that study it was also found that chalcocite abstracts cuprous xanthate from benzene solution, in what may (or may not) be a case of molecular adsorption. It seemed desirable, therefore, to study further the "unleachable" xanthate on the chalcocite, and particularly to ascertain whether it is formed as a result of the benzene leach or is actually formed during the conditioning of chalcocite in aqueous xanthate solution. A splendid tool to make such studies has recently been perfected; that is, the use of radioactive spies or tracer atoms. With this tool, it was thought possible to answer the problem stated above, but, unfortunately, this did not prove to be true. Answer to the flotation question was clouded by the existence of rapid and selective diffusion of copper atoms in the solid mineral-a phenomenon that was totally unexpected yet remains interesting and perhaps important. METHOD OF RADIOACTIVE SPIES The method of radioactive spies is discussed in many places. Two convenient references are the article by Evans2 and the book by Pollard and Davidson.3 The method was first developed by Von Hevesy and Paneth in 1913, when only natural radioactive isotopes were available. These isotopes are few in number, and so the method remained limited in scope. Recently the synthesis of over 350 active isotopes of all the known stable chemical elements4 has opened widely expanded possibilities for the method. A fundamental tenet of the method is that a radioactive atom and a nonradioactive atom are exactly alike until disintegration of the radioactive atom. Then, by its sudden death, the spy reveals its location. The relative abundance of spies at various locations makes it possible to ascertain the relative abundance of the corresponding nonradioactive atoms at the same times and locations. A second fundamental tenet of the method of radioactive tracers is that the radioactivity lies in the nucleus of the atom: transfer of radioactivity from one

Jan 1, 1944

By Mark David Rankin

This paper represents a general assessment of the primary factors driving the market for mobile offshore drilling rigs and the utility of those factors as choice variables for the offshore drilling program planner.

Jan 1, 1982

By Milton E. Wadsworth, J. Brent Hiskey

INTRODUCTION Fifteen years ago a distinguished electrochemist referred to electrochemistry as an "underdeveloped science " In the article in question, Professor Bockris (1) stated that many areas of.natura1 phenomena and applied technology are not perceived as being electrochemically based At that time, this was especially true for much of non-ferrous extractive metallurgy and was a particularly accurate description of hydrometallurgy During the last decade, there has been considerable advancement in applying the theory of electrochemistry to our know1 edge of hydrometallurgical processes and in understanding the mechanisms of underlying electrode reactions. Impressive as these advances are, there is still a growing need for electrochemical research of mineral systems and electrochemical engineering to apply this work in practical situations In a broad sense electrochemistry is defined as the physical chemistry of ions in solution and of phenomena which occur at the electrified interface. Bockris and Reddy (2) refer to electrochemistry as being divided into two fundamental domains, ionics and electrodics ionics is restricted to the behavior of ions in solutions, examples being many familiar redox processes Electrodics represents the main part of electrochemistry, and is the study of charged interfaces and the conditions governing charge transfer reactions across them. Considering hydrometallurgical applications, electrodics suggests the following relationship for a conducting solid (bulk or surface)

Jan 1, 1981

By A.S. Richardson

AIR conditioning, or air cooling, for the improvement of ventilation in the Butte mines has come into increasing use during the past 10 years. In part, the methods practiced have been described in previous publications of the Institute, but some improvements on earlier methods have been made and a number of new features have been developed. This paper is presented as a record of progress made, and for the sake of completeness describes all general features of the work. The need for air conditioning in the ventilation of mines in the district arises from the fact that the temperature of the ground and mine water has shown a very great increase with increase in mining depth, and has now reached a maximum of slightly over 130°F. The most difficult part of the ventilation problem is the maintenance of temperature and humidity of a satisfactory standard in the working places, especially on the lower levels. Although ordinary ventilation is adequate to maintain good conditions in most of the working places it is subject to a number of limitations at great depth. Most important among these limitations is that with increase in depth the air becomes heated before it reaches the working places, both by compression from increase in atmospheric Pressure and by heat transferred to it from rock at high temPerature, so that its capacity for lowering temperatures is greatly reduced before it reaches the operating zone. Increasing depth of mining also increases the distance traveled by the air in its passage through the mine, and this causes a corresponding increase in resistance to air flow, so that there is greater difficulty in maintaining even the same volume in circulation. Thus, in the face of a demand that the ventilating system have a very much greater capacity to remove heat from the mine, the tendency is for that capacity to diminish. The only evident alternatives were (I) the opening of additional air shafts to increase the volume of air in circulation, (2) an extension of the existing system that would be subject to the same limitations, or (3) the adoption of an entirely different method such as air cooling. Fortunately for an economic solution of the problem, the mean annual temperature of the surface atmosphere at Butte is about 40°F., with very low relative humidity in summer, so that there is unlimited natural cooling power at a temperature range adaptable to air-conditioning methods. Methods Two similar methods of air conditioning are used, as necessitated by service requirements and dependent upon the equipment available. In one, which is the more important and has the greater cooling capacity, water is circulated in a closed circuit, and, alternately, first absorbs heat from warm mine air and then dissipates it in the surface atmosphere by cooling at a cooling tower. The second

Jan 1, 1943

By A. S. Richardson

AIR conditioning, or air cooling, for the improvement of ventilation in the Butte mines has come into increasing use during the past 10 years. In part, the methods practiced have been described in previous publications of the Institute, but some improvements on earlier methods have been made and a number of new features have been developed. This paper is presented as a record of progress made, and for the sake of completeness describes all general features of the work. The need for air conditioning in the ventilation of mines in the district arises from the fact that the temperature of the ground and mine water has shown a very great increase with increase in mining depth, and has now reached a maximum of slightly over 130°F. The most difficult part of the ventilation problem is the maintenance of temperature and humidity of a satisfactory standard in the working places, especially on the lower levels. Although ordinary ventilation is adequate to maintain good conditions in most of the working places it is subject to a number of limitations at great depth. Most important among these limitations is that with increase in depth the air becomes heated before it reaches the working places, both by compression from increase in atmospheric Pressure and by heat transferred to it from rock at high temPerature, so that its capacity for lowering temperatures is greatly reduced before it reaches the operating zone. Increasing depth of mining also increases the distance traveled by the air in its passage through the mine, and this causes a corresponding increase in resistance to air flow, so that there is greater difficulty in maintaining even the same volume in circulation. Thus, in the face of a demand that the ventilating system have a very much greater capacity to remove heat from the mine, the tendency is for that capacity to diminish. The only evident alternatives were (I) the opening of additional air shafts to increase the volume of air in circulation, (2) an extension of the existing system that would be subject to the same limitations, or (3) the adoption of an entirely different method such as air cooling. Fortunately for an economic solution of the problem, the mean annual temperature of the surface atmosphere at Butte is about 40°F., with very low relative humidity in summer, so that there is unlimited natural cooling power at a temperature range adaptable to air-conditioning methods. Methods Two similar methods of air conditioning are used, as necessitated by service requirements and dependent upon the equipment available. In one, which is the more important and has the greater cooling capacity, water is circulated in a closed circuit, and, alternately, first absorbs heat from warm mine air and then dissipates it in the surface atmosphere by cooling at a cooling tower. The second

Jan 1, 1943

By T. Sterry Hunt

BUT little was known of the coals of Southeastern Ohio until the present survey of the State under Dr. Newberry began its work. The results of the geological investigations of Prof. E. B. Andrews in this region, and of the chemical investigations of Prof. T. G. Wormley, both of which appear in the reports of the survey for 1869 and 1874, and more recent special reports by the former, together with some data for which I am indebted to the kindness of Dr. Newberry, and my own limited observations, have served me for the preparation of the following notice of the coals lying on the western border of the great Appalachian coal-basin in the region drained by the Hocking River and its tributaries, and belonging to the Lower Coal-Measures. Some uncertainty exists as to the place in the succession of the lower coals to be assigned to the seams known and mined in the Hocking Valley. It is the opinion of Prof. Andrews that the inequalities of the original surface were such that we cannot identify in that region the lowest coals known in Northwestern Pennsylvania and the contiguous parts of Ohio, but that we must rather count from above downwards. These conclusions Dr. Newberry is not prepared to accept, and further researches will be necessary before certainty can be attained in this matter. Meanwhile it seems, from a study of its relations to the Pomeroy or Pittsburgh seam, that what is known as the great vein of the Hocking Valley, occupies the horizon of the Upper Freeport coal, E of the Pennsylvania survey, or No. 6 in Dr. Newberry's enumeration, counting from the base. This seam, in the region in question. assumes certain characteristics which, taken in connection with its geographical position, give it a great importance among the coals of the State. The area to be noticed includes the whole or parts of several townships in Perry, Hocking, Vinton, and Athens Counties, lying near the margin of the basin over which the vein in question assumes the character of a dry-burning or splint coal, and has a thickness varying from six to ten and even twelve feet. Its precise limit southward cannot at present be clearly defined, but it has been found as far south as the line of the Marietta and Cincinnati Railroad, with a thickness of six feet, and is mined at various points along the valley of the Hocking River, near Nelsonville, where it attains six or seven feet. To the northward, along the tributaries of this river, Sunday and Monday

Jan 1, 1874

By T. Sterry Hunt

But little was known of the coals of Southeastern Ohio until the present survey of the State under Dr. Newberry began its work. The results of the geological investigations of Prof. E. B. Andrews in this region, and of the chemical investigations of Prof. T. G. Wormley, both of which appear in the reports of the survey for 1869 and 1874, and more recent special reports by the former, together with some data for which I am indebted to the kindness of Dr. Newberry, and my own limited observations, have served me for the preparation of the following notice of the coals lying on the western border of the great Appalachian coal-basin in the region drained by the Hocking River and its tributaries, and belonging to the Lower Coal-Measures. Some uncertainty exists as to the place in the suc- ' cession of the lower coals to be assigned to the seams known and mined in the Hocking Valley. It is the opinion of Prof. Andrews that the inequalities of the original surface were such that we cannot identify in that region the lowest coals known in Northwestern Pennsylvania and the contiguous parts of Ohio, but that we must rather count from above downwards. These conclusions Dr. Newberry is not prepared to accept, and further researches will be necessary before certainty can be attained in this matter. Meanwhile it seems, from a study of its relations to the Pomeroy or Pittsburgh seam, that what is known as the great vein of the Hocking Valley, occupies the horizon of the Upper Freeport coal, E of the Pennsylvania survey, or No. 6 in Dr. Newberry's enumeration, counting from the base. This seam, in the region in question. assumes certain characteristics which, taken in connection with its geographical position, give it a great importance among the coals of the State. The area to be noticed includes the whole or parts of several townships in Perry, Hocking, Vinton, and Athens Counties, lying near the margin of the basin over which the vein in question assumes the character of a dry-burning or splint coal, and has a thickness varying from six to ten and even twelve feet. Its precise limit southward cannot at present be clearly defined, but it has been found as far south as the line of the Marietta and Cincinnati Railroad, with a thickness of six feet, and is mined at various points along the valley of the Hocking River, near Nelsonville, where it attains six or seven feet. To the northward, along the tributaries of this river, Sunday and Monday

Members Dues Resignations, Suspensions and Expulsions Institute Meetings Board of Director?s Meetings Directors and Officers Duties of Officers Committees Nomination and Election of Officers Publications Divisions, Local Sections, Affiliated Societies Amendments [As REVISED FEBRUARY 21, 19281 ARTICLE I MEMBERS-QUALIFICATIONS AND ELECTION , SEC. 1. The membership of the Institute shall comprise six classes, namely: 1. Members; 2. Honorary Members; 3. Senior Members; 4. Associates; 5. Junior Associates; 6. Rocky Mountain Members. All shall be equally entitled to the privileges of membership, excepting that Junior Associates, and all Members and Associates whose residence shall be outside of the United States of America, Mexico and Canada shall not be entitled to vote. SEC. 2. Members: A person to be eligible for election or transfer into the class of Member must be at least 27 years of age and must have had at least six years' employment in the practice of engineering, mining, geology, metallurgy, or chemistry, during at least three years of which he must have held positions of responsibility in one or more of these fields. This shall not apply to Rocky Mountain members.

Jan 1, 1928

By Pedro Bolsaitis, Paul M. Sullivan

The activities of zinc in liquid Zn-A1 alloys in the temperature range of 1000' to 1160°K were determined by means of the isopiestic technique. The results are in reasonable agreement with the previous values determined by the radioactive tracer dew point method. Slightly negative excess entropies of mixing were found. The measured activities suggest that the a function for these alloys is not a constant, as has frequently been assumed, but is better represented by two straight line segments of different slopes. THE thermodynamic data of Al-Z alloys have been the subject of investigation by many authors. However, in the recent compilation of such data by Hult-gren et al.,5 the conclusion is reached that none of the previous measurements are reliable or consistent with each other. Since then two new sets of measurements have been reported,2, 8 both laying claim to good accuracies, yet showing very significant disagreement in the measured activity coefficients of zinc in Zn-A1 alloys and in the magnitude and sign of the excess entropies of mixing. Information on the thermodynamics of the system is of particular interest for interpreting results of the Bureau of Mines research on refining of zinc by distillation of die cast scrap. The present study was undertaken as an independent check on the recent values obtained from dew point measurements 8 and electromotive force measurements.' The isopiestic method, first introduced by Herasy-menko,' was chosen because it is one of the few thermodynamic techniques which, in principle at least, is carried out under perfect equilibrium conditions. The disadvantage of the method is that data are obtained at various random compositions and temperatures, which makes the interpretation somewhat cumbersome. The random errors arising from temperature gradients and fluctuations appear to be comparable to those of other techniques, as evidenced by the magnitude of the estimated uncertainties in the calculated integral thermodynamic quantities. An advantage of the method is that each run provides a relatively large amount of data; thus, it is less time consuming than those methods where samples of each composition must be measured individually. EXPERIMENTAL PROCEDURE The activities of zinc in liquid Zn-A1 alloys were measured by the isopiestic method which uses the principle of the tendency toward equilibrium of a series of samples at various temperatures under an imposed vapor pressure of the more volatile component (i.e., zinc, in this case). The basic apparatus is shown in Fig. 1. The small graphite crucibles that contained the metal samples were 15 mm ID and 13 mm deep with approximately 3 mm wall thickness. Each crucible was notched at the top and bottom to allow easy passage of vapor from one to another. At the beginning of an experiment each crucible was weighed on an analytical balance. Zinc and aluminum of spectrographic purity (99.999 pct) were then weighed into the crucibles. The amounts of each metal added were such that initial compositions varied above and below equilibrium values. One crucible contained only pure zinc. After weighing, the crucibles were stacked with the pure zinc on the bottom (corresponding to the lowest temperature in the furnace) and richest aluminum alloys at the top. The entire stack of crucibles was then placed in the silica glass container "E" which was then sealed under vacuum. Sixteen to twenty calibrated Chromel-Alumel thermocouples were attached by wire along the length of the silica tube, one or more adjacent to each sample.

Jan 1, 1970

Sec. 1. The membership of the Institute shall comprise six classes, namely: 1. Members; 2. Honorary Members; 3. Senior Members; 4. Associates; 5. Junior Members; 6. Rocky Mountain Members. All shall be equally entitled to the privileges of membership, excepting that no member of any class whom residence shall be outside of the United States of America, except those residing in Mexico and Canada, shall be entitled to vote. SEC. 2. Members: A person to be eligible for election or transfer into the claw of Member must be at least 27 years of age and must have had at least six years' employment in the practice of engineering, mining, geology, metallurgy, or chemistry, during at least three years of which he must have held positions of responsibility in one or more of these fields. This shall not apply to Rocky Mountain members.

Jan 1, 1934

By K. A. Natarajan, I. Iwasaki

The effect of poisoning on the behavior of platinum electrodes in redox potential measurements in metallurgical systems was studied in the presence of such inorganic surfactants as cyanide and sulfide and such organic surfactants as dodecylammonium acetate, trimethyldodecylammonium chloride, potassium ethyl xanthate, and potassium diethyl dithiophosphate (Aerofloat®). These chemical species represent, more or less, typical constituents encountered in leaching, flotation, and sewage treatment systems. Triangular wave voltammetry was used as the experimental technique to study the nature of poisoned surfaces. Among the species studied hydrogen sulfide and dodecylamine were found to form a resistant surface film affecting charge transfer. Platinum electrodes appeared to have a weaker tendency to adsorb sulfide species in alkaline pH ranges, while cyanide, xanthate, and dithiophosphate affected the normal electrode behavior differently. Possible methods of reactivation of a poisoned electrode by mechanical cleaning are suggested.

Jan 1, 1974

By Robert W. Fullerton, Donald T. King

INTRODUCTION AND THEORY by Robert W. Fullerton In coal preparation plants, as in any industrial operation where raw materials are handled, nuisance problems arising from the generation of dust are inevitable. Devices for the control or collection of dust are there- fore essential components of the plant process equipment. The general term "aerosol" is applied to small particles suspended in a gaseous medium, usually air, whose velocity under the force of gravity is small enough that the particles remain suspended for a reasonable length of time. Aerosols can be classified as dust, smokes, fumes, mists or fogs. Dust includes particles originally formed by pulverization of materials by such processes as crushing, grinding, drilling, blasting and abrasion. Smoke includes particles formed from the burning of organic materials. Fumes are particles formed by processes such as condensation and sublimation, usually at high temperatures. Mists or fogs are particles formed by the condensation of water or other vapors on some nuclei. The size of aerosol particles is generally designated in units of microns, there being 1000 microns to a millimeter and 25,400 microns to an inch. Particles of about 10 microns or above are visible to the naked eye. Table 14-1 shows size characteristics of the general classifications of particles discussed above and includes typical examples of particles commonly en- countered. Table 14-1 also shows the relationship between micron size and standard screen mesh sizes. Smoke and fume are usually in the range of 0.01 to one micron, dusts are in the range of one to 400 microns, mists are in the range of 0.1 to 100 microns, and fogs are in the range of one to 100 microns. For purposes of dust control, particles greater than 10 or 20 microns in size are considered large, particles one to 10 microns are considered fine and particles below one micron are ultrafine. Sources of Dust Because coal is relatively friable, the mining and subsequent handling operations break part of the coal into dust that can be readily carried by currents of air. In a coal preparation plant mechanical handling operations such as unloading, transferring from one belt to another, screening, cleaning, and crushing in a dry state result in the generation and release of varying amounts of additional dust. The dust problem, of course, is much less serious in plants employing entirely wet processing. In addition to dust from handling operations, thermal drying of the fine coal product frequently presents another dust collection problem. Most coal driers are

Jan 1, 1968

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. B. NEALEY

MANY nonferrous smelting plants have recently adopted natural gas as fuel with resultant economies, both in cost and efficiency of utilization. Not only has this fuel been used for roasting, reduction, sintering, drossing, and smelting, but also for power. All of the three big smelters near Salt Lake City, Utah, have been changed over from coal and oil firing to gas. Among these is the plant of the International Smelting Co., Tooele, an Anaconda subsidiary, smelters of both copper and lead ores. In the roasting division at Tooele are 32 MacDougall six-hearth roasters, each 16 ft. in diameter and 19 ft. high. Two gas burners are installed on each furnace. These burners are of the single-valve, automatic gas-air proportioning type using high-pressure gas at 10 lb.

Jan 1, 1933

By E. Lifshin, R. E. Hanneman

QUANTITATIVE applications of the electron micro-beam probe frequently involve the evaluation of complex mathematical expressions and/or the analysis of large amounts of experimental data. The purpose of this communication is to describe briefly a versatile and useful computer program system that is applicable to analyze rapidly a wide variety of practical microprobe problems. This system consists of a group of ten FORTRAN programs that can be stored on tape, cards, or in the memory disc of the computer. These programs, or links, can be run individually or in any prespecified sequence without interrupting the operation of the computer or without destroying information which is being transfered from one link to another. For the program system described here a GE-235 computer with disc storage was used, so that the DCHAIN method of program linking was employed. Included in the library are programs to: 1) initiate analysis of a new set of data and transfer control between all other programs in any predetermined manner; 2) generate theoretical calibration curves of composition vs relative intensity; 3) generate empirical deviation parameters from least-square fits of experimental calibration data from standards of known composition; 4) convert raw X-ray data to corrected composition; 5) determine inter diffusion coefficients by Matano analysis of con centrat ion -distance data on a uniaxial diffusion couple; 6) determine activation energies and frequency factors of temperature-activated processes such as diffusion; and 7) generate calibration curves for determination of the thickness of thin films using microanalysis. A detailed description of these computer programs and their underlying principles is available on request from the authors."' The first program to generate theoretical calibration curves of corrected relative intensities vs composition uses the Poole and Thomas atomic number correction' and the Philibert absorption factor' with a voltage-dependent mass absorption coefficient for electrons in the alloy. A modified Castaing fluores- cence correction is also used which includes the effects of both Ka and KO radiation and over voltage.' Once the theoretical curves have been calculated in 1 wt pct intervals, these results are least-squares fit to obtain Ziebold deviation parameters' which are stored in COMMON in the computer memory. The net discrepancies between the original theoretical calibration curve and the regenerated curve using the Ziebold parameter are computed. Although this link is explicitly written for K-K fluorescent interactions, it can be applied to K-L, L-K, and L-L interactions as previously disc~ssed."~ Similar programs have also been written to utilize the Wittry fluorescence correction, Birks combined corrections, and various other corrections.' These modified programs have proved to be quite useful for quantitative comparisons of the results of the various theories. The program for conversion of raw X-ray data to corrected composition includes corrections for drift, backround, and instrumental dead time. The corrected intensities are converted to composition by use of the Ziebold equation"2 and parameter obtained from the program system. The results can be obtained for either atom or weight fractions. In addition to accurately computing interdiffusion coefficients the Matano analysis program calculates least-square smoothed values of concentration, concentration gradient, and curvature for each point on the raw input concentration profile. In order to obtain high accuracies a unique method of performing a least-square polynomial fit to incrementally advancing profile segments which overlap is used.' This program has been successfully modified for use in ternary diffusion problems3 and can readily be modified to handle analysis of diffusion profiles which include phase boundary discontinuities. This link is generally applicable to analysis of interdiffusion data obtained by other techniques as well as by the microprobe. The primary function of the next program is to least-squares fit experimental diffusion data to the normal Arrhenius function: D = Doexp(-Q/RT), to obtain values of Do and Q. In addition the probable error and one, two, and three u statistical confidence limits of DO, Q, and log D are evaluated. This program is also directly useful for analysis of any other simple temperature-activated processes including conductivity, and certain deformation and chemical processes. The program to generate calibration curves for film-thickness determination using the microprobe is based on a numerical integration of the equation derived by Cockett and ~avis.' Values of film thickness obtained by this program for copper on various substrates are in good agreement with measurements made by other techniques. Versions of the above program system have been prepared for use with or without a remote teletype connection to the computer for processing on either a real-time or time-share basis. The instrumentation coupling a microprobe to a teletype for automatic data collection and analysis by the presently described program system has been reported elsewhere by the authors.' If teletype equipment is not used to communicate with the computer, standard methods of card reading and tape reading can be used. In either

Jan 1, 1967

By S. E. Haszko

SEVERAL new XGa2 intermetallic compounds, Table 1, where X is a rare earth, having the AlB, structure were prepared as part of a continuing study of the magnetic and structural properties of rare-earth alloys.' In this note, the crystallographic results of these compounds are presented. Chart, Eq. 121 for the data in Fig. 1 can be adequately represented by The corresponding standard free-energy change is AF; = -4.576 T log K = -20,900 + 10.20T [5I At low nitrogen concentrations the ratio of mole fraction to weight percentage is a constant so that the mole fraction X of nitrogen is given by X = 0.0392 [%NJ. At low values of X, the activity and the concearation approach each other, hence K, = 0.0392 K,, where K, is expressed in terms of the mole fraction of nitrogen. Hence Eqs. [4]. and [5] become

Jan 1, 1962