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By A. J. Heckler, J. A. Peterson

A capsule technique was successfully employed to investigate the effect of nickel on the activity of nitrogen in Fe-Ni-N austenite in the temperature range 600" to 1200°C. This technique consisted of equilibrating nitrogen among various Fe-Ni alloys within a sealed silica capsule. Nitrogen transfer among the specimens occurred by N, gas at 900°, lOOO? and 1200?C. Nitrogen gas pressures within the capsules were estimated to be as high as 22 atm. The activity coefficient of nitrogen, fN , in Fe-Ni-N austenite is adequately described by the linear interaction equation: log . wt pct Ni where the standard state is chosen such that fN = I as wt pct Napproaches zero in binary Fe-N. This relationship was determined over the temperature range 873" to 1473°K and for nickel contents of 0 to 35 wt pct. ALTHOUGH chemical thermodynamics of liquid iron alloys have been extensively studied, experimental data for the solid state are needed. These thermody-namic data will provide a basis for understanding phase transformations, precipitation reactions, metal-gas equilibria, and so forth. The interaction of sub-stitutional alloying elements with the interstitial elements is of particular interest. In this investigation the thermodynamic behavior of Fe-Ni-N austenite has been studied. The solubility of nitrogen gas in iron austenite is known to obey Sieverts&apos; law up to about 65 atm.1-6 In addition, the solubility of nitrogen in Fe-Ni austenite has been investigated5"8 using the classical method of equilibrating Fe-Ni alloys with nitrogen gas at 1 atm. A capsule technique similar to that used to study the activity of carbon in alloyed austeniteg&apos;&apos;&apos; was employed in the present work to determine the effect of nickel on the activity of nitrogen in Fe-Ni austenite over the temperature range 600" to 1200°C. EXPERIMENTAL PROCEDURE A series of Fe-Ni alloys up to 35 wt pct Ni was vacuum melted and cast into 1 by 3 by 6 in. ingots. Chemical analyses at the top and bottom of each ingot demonstrated that the ingots were homogeneous with respect to nickel content. The nickel contents are given in Table I. Additional chemical analyses showed that wt pct Si < 0.05, s < 0.01, C < 0.01, Al < 0.006, 0 < 0.004, Mn < 0.002, and P < 0.002. A 2 in. section of each ingot was cold rolled to 0.015 in. The material was then decarburized to a carbon content of less than 0.004 wt pct. A portion of the material of each nickel content was nitrided to various levels in a H2-NH3 gas atmosphere to provide a source of nitrogen during subsequent equilibration. The experimental technique consisted of equilibrating the series of Fe-Ni-N alloys in a partially evacuated sealed silica capsule at the temperature of interest. Both Vycor and quartz capsules were used. In general, the final equilibrium nitrogen content for each Fe-Ni alloy was approached from both higher and lower nitrogen levels. The criterion for establishing that equilibrium was attained was that the final nitrogen content for each Fe-Ni alloy was the same irrespective of the initial level. A schematic drawing of the sample configuration in a capsule is shown in Fig. 1. The samples were arranged so that there was a minimum of physical contact. The samples were also dusted with a fine, high purity alumina powder to help prevent sticking. Several different types of furnaces were used in this study. In each case, a thermocouple was placed immediately adjacent to the capsule during equilibration and the temperature was controlled to within *4?C of that reported. At each equilibration temperature, the following times were found to be more than sufficient to attain equilibrium: 600°C-250 hr, 900°C-150 hr, 1000°C-150 hr, and 1200°C-50 hr. After equilibration the capsules were quenched in water and the nitrogen contents of the specimens determined by a Strohlein analyzer. Analyses of samples after equilibration at 1000" and 1200°C showed no silicon pickup from the silica capsules. RESULTS AND DISCUSSION Transfer Mechanism. The mechanism by which nitrogen was transferred among specimens in an initially hydrogen flushed and partially evacuated capsule equilibrated at 1000°C was investigated. After equilibration the gas in the capsule was collected over water and an estimate of the pressure at temperature

Jan 1, 1970

By C. G. Albert

The clay particles of 2 microns or less required for modern paper coating are predominantly flat plates, lying smoothly on the sheet and producing a high gloss. Operating speeds of today&apos;s coating machines necessitate a clay composition of 60 and sometimes 70 pct solids as against the 35 to 40 pct required in the past. Since clays in suspension may solidify in flow, only those of intrinsically low viscosity can be used as high coating solids. THE literature of paper technology contains a number of articles having reference to developments in the field of coating and filler clays for use in paper manufacture. Much of this information has not been included in mining publications and has therefore not been readily available to all in the mineral industry. Recent developments in this field, including spray drying of clays, are presented here. U. S. Bureau of Mines figures for 1952 indicate that the paper industry consumes more than 50 pct of all kaolin produced and sold in the U. S. As most of the kaolin used by the industry comes from Georgia producers, the fraction of their output destined for paper use is thus appreciably higher than 50 pct. Small wonder that the kaolin industry, especially in Georgia, is highly sensitive to the quality requirements of paper mills and must respond promptly to technological developments in paper manufacturing. The paper industry itself is not the ultimate consumer. For the greater portion of the clay the end product is the printed page, and the demands of printing and publishing have sparked some of the technological advances in paper making which have, in turn, brought about methods employed in the kaolin industry. As compared with the product of 20 or 25 years ago, one of the most striking characteristics of the graphic arts today is the mass production of quality printing of fine pictorial work, much of it in full color. During this time periodicals with printing standards close to those of yesterday&apos;s slick-paper publications that were printed on a slow schedule and for a limited circulation have grown to the point where they go out to many millions of readers, often at weekly intervals. The complexity of technological improvements brought about by this increased circulation is probably not appreciated even by technical people, unless they have had reasonably close contact with the industry. The advance has come about through developments not only in the art of printing, but also in the field of paper making and even at the level of clay mining and processing. The smoothness required for faithful reproduction of the kind of printed matter under consideration is attained with a clay-coated paper. Since the distribution expense of the publication will depend to a great extent on its weight, the paper used must not be too heavy. This means a lower basis weight than was normal for conventional clay-coated papers some 25 years ago. And for this mass production market it becomes necessary to provide a paper having these and all the other required characteristics at a very moderate price—not the premium price conventional clay-coated papers formerly demanded. This challenge has been met by a new method of producing coated paper. In the past, application of clay coating to paper was a conversion operation, performed separately from the making of the base sheet. The newer development is called machine coating. Here application of the coating is an integral step in a continuous process by which wood pulp, clay, and other ingredients are manufactured into a sheet of coated paper. Many more problems are involved in this procedural change than are apparent at a casual glance. The coating operation, for example, must function at much higher linear speed than could be obtained with coating mechanisms previously employed. The application machinery developed to meet this requirement necessitated changes in composition of the coating color.* This created new requirements, summarized below, for the clay employed as coating pigment. In addition to smoothness, a relatively glossy printing surface is needed, and to a large measure it is the function of the coating clay to make possible the development of both these surface characteristics. Traditionally, pigments such as satin-white, prepared by reacting lime with paper-makers&apos; alum, were used to assist in producing a high finish. However, economic considerations and others preclude large-scale use of such material in the new processes. In the 1930&apos;s Maloney&apos; discovered that a certain particle size fraction of kaolin, consisting

Jan 1, 1956

By James J. Bean

HE task of measuring the specific gravity of the -*- operating medium in a heavy-media separation system has never presented a particularly difficult problem because the medium is fairly stable and the overflow of the separatory vessel, as well as its underflow, can be sampled easily and accurately and the specific gravity of the suspension determined easily by weighing a known volume. However, while this method is simple and accurate it does require the operator to take the sample by hand and to weigh it and there is considerable temptation to avoid the periodic sampling if everything seems to be going well, or if something is occupying the attention of the operator. Furthermore all operators do not sample in exactly the same manner and considerable practice is required for two operators to be able to "check" each other to the last few hundredths, particularly if the sample is cut underneath the drainage screen where location of the point of sampling and load on the screens tends to influence the determination. While none of the above presents much of a problem, we have all recognized that some mechanical method of continuous measurement and recording would be advantageous since the operator would merely have to glance at the meter to check the gravity and to have an indication of the trend of any changes. Also if the instrument were of the recording type, a permanent record would be available for the guidance of the superintendent. The Eagle-Picher Mining and Smelting Co. was the first heavy-media user to actually install such a recording meter. In 1946 they installed in their Central Mill at Cardin, Okla., a specific gravity recorder manufactured by the Bristol Co. of Water-bury, Conn. R. A. Barnes, of the Bristol Co., working with E. H. Crabtree, Jr. and Elmer Isern, of Eagle-Picher, made the application and worked out the problems of sampling and measuring. Their attempts to measure the specific gravity of the medium in the cone itself were not entirely successful and they resorted to an outside sample tube for actually making the determination. Because of the particular flowsheet used, it was possible to tap off from the medium return pipeline a stream of medium and divert it into the sampling tube, which was provided with a constant level overflow and a spigot underflow, and into which the bubbler tubes dipped. The Eagle-Picher installation was successful and its possibilities were recognized by the Mineral Dressing Laboratory of the American Cyanamid Co. It was decided to install a similar unit in the heavy-media pilot plant to investigate further its possibilities. Chief among these was the continuous record which it was felt would be proof of the steadiness of the gravity in a heavy-media cone, something which is not always appreciated by POtential users. Because the heavy-media pilot plant is required to operate at a wide range of specific gravities, it was realized that the unit would have to record all gravities from 1.25 to 3.50, and do it to the nearest 0.01. It would not be necessary to record all of this wide range on a single chart and the method selected was to have 4 bands, each band range overlapping the other a small amount and calibrated so that with standard charts one division would represent 0.01 sp gr. A shift from one band to another could be arranged without alteration of the instrument itself, being accomplished by a simple change in the bubble-tube lengths, as described later. Accordingly, a recording type instrument was purchased and installed. Because there were some advantages in doing so, the first installation attempted to measure the gravity of the cone proper by placing the bubble tubes in the cone. This was not at all satisfactory and the second scheme utilized a fixed vertical screen at the surface of the cone, and an external sample-tube arrangement. We were particularly anxious to make this work as we felt it would be advantageous to measure the top level of medium where the separation was actually being made, but we were doomed to disappointment because it was impossible to keep the screen clean of float. Since the top gravity of the cone is the most convenient place to sample for control, a launder about 2 in. wide was installed longitudinally beneath the

Jan 1, 1951

By C. W. Sherman, N. J. Grant

The correlation of the high temperature chemical properties of slag-metal systems with some easily measured property of either slag or metal at room temperature has been the goal of both process metallurgists and melting operators for many years. There are several rapid methods for estimating various constituents in steel in addition to the conventional chemical methods which are quite fast, but these do not reveal the nature of the slag as a refining agent, which is of primary interest to the steelmaker. Furthermore, there are several methods for examining slag, the three principal ones being slag pancake, petrographic examination, and the previously mentioned chemical analysis. The main objection to the last two is the lime required to make a satisfactory estimate of the mineralogical or chemical components. The objection to the first is the inadequacy of the information obtained. A new technique has been developed by Philbrook, Jolly and Henry1 whereby the properties of slags are evaluated from an aqueous solution leached from a finely divided sample of slag. It is known that the pH or hydrogen ion concentration (of saturated solutions that have dissolved certain basic oxides, notably calcium oxide) will indicate a pronounced basicity. Philbrook, Jolly and Henry devised the pH measurement technique in order to supply open hearth operators with a fast, reasonably accurate method of estimating slag basicity. They offered the method as an empirical observation and made no claims as to its theoretical justification. The results were presented as an experi-metally observed relationship which applied over an important range of basic open hearth slags. They found that, in plotting the measured pH against the basicity, the best relationship existed between the pH and the log of the simple V ratio, CaO/SiO2. Extensive investigation also showed that there were several variables in the experimental technique that influenced the results and necessitated following a standard procedure to obtain reproducible pH readings. These variables were: 1. Particle size of the slag powder used. 2. Weight of sample used per given volume of water. 3. Time of shaking and standing allowed before the pH was measured. 4. Exclusion of free access of atmospheric carbon dioxide to the suspension. 5. Temperature of the extract at the time the pH was measured. In subsequent investigations of the pH method by Tenenbaum and Brown2 and by Smith, Monaghan and Hay3 the general conclusions of Philbrook&apos;s work were reaffirmed. It was the object of the present investigation to extend the technique to a point where it could be used to evaluate slags of all types. Experimental Results PARTICLE SIZK OF SLAG POWDER A large sample of commercial blast furnace slag of intermediate basicity (V-ratio 1.15) was selected for the study. The slag had been put through a jaw crusher until all of it passed through a 20 mesh screen. Five fractions of this crushed material were separated, -20 to +40, -40 to +60, -60 to +100, -100 to +200, and -200 mesh. A representative sample of 0.5 g was removed from each fraction and the pH determined using the method of Philbrook. Check pH analyses on the sample fractions varied due to the different amounts of shaking. To eliminate this variable, a mechanical shaker was employed. In order to know the exact time of contact between the slag and water, it was found necessary to filter the extract at the end of the shaking period. Using the mechanical shaker and a filtering apparatus, similar runs were made on the five fractions for contact times of 5, 10, 20, and 40 min. Random checks gave reproducible results within 0.02 pH. The data are plotted in Fig 1. It can be seen from the plot that each slag fraction is hydrolyzed to an extent that is roughly proportional to the surface area exposed to the water. The (—100 to +200) mesh material changed very little in pH after 10 min. shaking time. The curves are symmetrical and lie in proper relation to one another. The —200 mesh curve appears to be somewhat flatter than the others, but this can be attributed to the portion of very fine material that is not present in the other fractions. The closeness of the (-100 to +200) mesh curve to the —200 mesh curve and the fact that a —100 mesh sample would contain amounts of slag down to 1 or 2 microns in diam were considered sufficient reasons for selecting a —100 mesh sample as representative of the whole sample of slag for the purposes of this investigation.

Jan 1, 1950

By Robert F. Goss

OCAW appreciates the opportunity given to us by the sponsors of this Conference to present our position and policies on the issue of radiation hazards in mining. Our principal concern is the health impact that the mining of uranium has on our members. OCAW represents 1,500 underground uranium miners and more than 10,000 underground miners with 3,000 in the Rocky Mountain region. The U.S. Public Health Service has determined through mortality studies that the number one cause of death among uranium miners is lung cancer. It was also determined that exposure to radon daughters and mine dust correlates with the lung cancer experience of uranium miners. Data from the U.S. Mine Safety and Health Administration has also shown that not only uranium underground miners, but all underground miners, are exposed to radon daughters -- especially underground miners in the Rocky Mountain region. It is our position that any OCAW underground miner is at potential lung cancer risk. The dosages of radon daughters that our miners are exposed to are very many times the background levels of radon exposures in the communities where they live. We are also aware that cigarette smoking accelerates the onset of lung cancer; however, it has to be clear that the available scientific evidence shows that alpha radiation does initiate lung cancer and that cigarette smoke, as a recognized co-carcinogen, promotes cancer already initiated by radiation. It is true that cigarette smoke increases the risk of cancer significantly for miners exposed to radon, but nonsmoking miners have experienced lung cancer rates twice as high as the comparable members of the U.S. population. OCAW&apos;s position is that the occupational regulatory agencies should concentrate on the exposures that can be controlled; that is, occupational exposures rather than life-style exposures. Our Union has maintained a consistent posture in relation to carcinogens in the workplace -- that is, exposure to cancer-causing agents should be limited to the [lowest feasible level]. OCAW has interpreted lowest feasible level as the lower limit of detection of the collection and analytical method used to detect the carcinogen. Our posture is based on the available scientific information on carcinogenesis. We have asked the scientific community, many times, to provide us with safe levels of exposure to carcinogenic substances, including radon daughters. The answer has been: "We cannot determine levels of exposure low enough to assure that no cancer will occur." In short, there is not a "safe threshold" for any carcinogen. This statement does not come from one of the few so-called "pro-labor scientists," it comes from the National Cancer Institute and the National Institute for Occupational Safety and Health. I don&apos;t need to be a scientific sage, then, to conclude that the lowest level of exposure corresponds to the lowest risk of developing cancer. That is, then, our policy on exposure to carcinogens. It seems there has been an attempt to ignore the fact that lung cancer in uranium miners is the principal cause of death. Uranium miners are no exception from workers exposed to carcinogens. Our policy applies to them. Uranium miners should be exposed to the lowest feasible level of radon daughters and any decrease in the permissible exposure level is a decrease in their lung cancer risk. Accordingly, OCAW has petitioned the Department of Labor for a new permissible exposure limit to radon daughters in uranium mining, which lowers the current exposure standard from 4 Working Level Months (WLM) per year to 0.7 Working Level Months per year. We made our demand to the Department of Labor on April 20, 1980. We are still awaiting action from the Federal Government on our petition. OCAW is also very concerned with other important health impacts of uranium mining. We are concerned with a rate of disabling accidents and fatalities which is twice as high as the same rate in other underground mines, excluding coal. We are also concerned with the rate of respiratory disease fatalities among uranium miners which is almost four times the rate among a comparable U.S. population. We have expressed those concerns when the U.S. Senate proposed a Federal Compensation Act for uranium miners. That proposal, by Senator Dominici of New Mexico, found a quiet death in two Congressional sessions. In conclusion, our position on lung cancer induced by radon daughters is the same position we have taken with all other industrial carcinogens: The lower the exposure, the lower the risk. OCAW is demanding a drastic decrease of the permissible exposure limits. OCAW will never accept that a segment of our membership which mines uranium should take the lion&apos;s share of the risk while the uranium mining companies take all the benefits.

Jan 1, 1981

By W. Jacobi, B. Haider, D. Regulla, J. Huber

[Introductory Remarks] Thermoluminescence (TL) detectors are widely used for the dosimetry of X- and[ y]-rays. Also filter devices for radon daughter monitoring have been developed in which the a activity on the filter was measured with TL-detectors (Breslin et al., 1977). For this purpose normal LiF-tablets with a thickness of 0.4 - 1 mm were used. However the lower detection limit of such TLmonitors for radon daughters is relative high, especially in areas with a high [y]-background, due to the low [a /-y]-sensitivity ratio of such thick LiF-detectors. This [a/y]-sensitivity ratio can be increased if TL-detectors are used whose thickness is comparable with the range of [a]-particles. On the basis of this consideration we have developed a simple light weighted and sensitive TL-monitor for the measurement of the cumulative radon daughter exposure in air. [Description of the "Monitor] The monitor consists of two parts: The sampling pump with the accumulator, and the sampling probe which contains the air filter and TL-detector system. Both parts are connected with a plastic tube. For operation in mines a light weight, portable air sampler with a built-in accumulator (DuPont model 125 and 200, 400 g) is used which enables an adjustable, constant flow rate in the range of 7.5 -12 1/h. These air samplers allow a sampling period of 10 hours before recharging is necessary. For radon daughter measurements in houses this pump is replaced by a larger, netoperated pump with a flow rate of 180 1/h. Figure 1 shows a schematic cross section through the sampling probe whose weight is 40 g. The radon daughters are collected on a hydrophob membrane filter (Sartorius) with an effective filter diameter of 11 mm and a pore diameter of 3 µm; its collection efficiency for radon daughters is [>] 95%. Above the filter the detector system is mounted. It consists of two thin Tm-activated CaSO4-TL films of 8 mm diameter on a Al-carrier foil manufactured by Matsushita Inc., Japan. The thickness of the TL-film is 6 mg/cm2, which is comparable with the range of a rays. The first detector is faced in 3.5 mm distance above the filter; in addition to the ambient y background this detector is exposed to the [a] and ß radiation from the radon daughters on the filter. Between the first and the second TL-detector is an Al-absorber of 0.5 mm thickness which shields this detector against the [a] radiation and partly also to the ß radiation from the filter. Both detectors have the same [y] shielding. After air sampling both TL-detectors are read-out with a commercial, hot-air reader (Matsushita Inc. / Japan, Model 505 A). The glow-curves are identical for [a and y] rays (Regulla et al., 1980). The integral TLsignal from both detectors is displayed in mR-units (or mR-equivalent). The difference between the response of the unshielded TL-detector above the filter and the shielded TL-detector is proportional to the time-integral of the filter activity, integrated over the sampling period. Calibration and Intercomparison Measurements] The linearity of the a response was checked with a 241Am-source for an [a] fluence on the detector surface of 5400 [a&apos;s/cm2•s] in the range of 102 -105 mR-equivalent. Within the experimental error of 15% the response function is linear. The TLD-monitor was calibrated for radon daughters in air by comparison with a calibrated integrating, monitor (WLM-meter) equipped with a Si-surface barrier detector and a direct electronic read-out; this instrument was developed by us for area monitoring some years ago (Haider et al., 1976). The results of simultaneous measurements with the TL-monitor and the electronic WLM-meter in mine areas and in indoor air of houses are shown in figure 2. On the abscissa the mean potential [a] energy concentration (in WL) during the sampling period is given which was derived from the measurements with the electronic WLM-meter. On the ordinate the corresponding response of the TLDmonitor to radon daughters (difference between both TL-detectors) is displayed, expressed in terms of mRequivalent per liter sampled air. It follows from this comparison a linear relationship over the whole range of 0.005 - 5 WL with a standard deviation of 10%. The resulting calibration factor for the TLD-monitor is 18± 2 mRequiv per WL • 1.

Jan 1, 1981

By G. F. Leaming

The paper by R.V. Ramani and R.J. Sweigard is a wonderful description of the labyrinthine web that has been spun about the mining industry by energetic bureaucrats and politicians over the past 50 years. The remedy for the problem, however, is not more of the same, but less. That may be difficult for the industry to achieve, for it is not a technical solution but a political one. And the current fervor for more detailed planning at all levels of government and private enterprise has become deeply ingrained. The authors recommend the provision of more information about mining and mineral resources to "macro" (i.e., government) land use planners. They apparently overlook, however, the already strong tendency on the part of most government land use planners to consider themselves omniscient. Thus, giving them more information about the technical problems of mining will only make them want to get more and more involved in the "micro" (private, site specific) mine development and production plans of the individual mining firm. In fact, this has already happened at all levels of jurisdiction from municipal to federal government. Examples are legion. The most effective way to ameliorate the adverse impacts of government land use planning on existing and potential mining operations is to: (1) introduce greater flexibility in the definition of land use zones by local and state governments; (2) adopt realistic and relevant ambient environmental performance standards in governing relationships between mineral land uses and concurrent or subsequent nonmining land uses; (3) allow greater leeway for economic considerations in land use decisions in contrast to the explicit legalistic approach now in vogue; (4) recognize that all minerals are not the same and that sand and gravel mining should not be treated the same as underground metal mining, coal stripping, oil field production, or in situ leaching; and (5) eliminate the notion that mining operators should be responsible for determining in detail the use of land by subsequent owners of mined land. This last bit of conventional ethic really makes no more sense than requiring the builders of every shopping center or government office complex to provide detailed plans for the use of that land when its use for shopping or government is ended. Did the builder of Ebbetts Field plan for Brooklyn after the Dodgers went to Los Angeles? Should the developer of the Bingham Pit plan for suburban Salt Lake City after the copper mining goes to Chile? The nation&apos;s mining industry must address these questions before further bankrupting itself to provide more data to planners and spending thousands of dollars per acre to create land that when reclaimed is worth only a few hundred dollars per acre. ? Reply by R.V. Ramani and R.J. Sweigard We thank Mr. Learning for his valuable contribution. His views on the problems of land use planning and mineral resources are most welcome additions to our paper. As the title indicates, our paper was more concerned with the impacts of land use planning on mineral resource conservation than with the details of the planning process. On the whole, his five recommendations would be helpful for mineral resource conservation. However, we would suggest that the argument he presents for his final recommendation does not address the differences between mining as a land use and commercial or institutional uses. We believe that this difference is the crux of the issue. We share Mr. Learning&apos;s desire to ameliorate the adverse impacts of land use planning. Possibly the most detrimental impact is the loss of mineral resources. Any development, whether mineral or community, that does not give proper consideration to other resources can result in permanent loss or sterilization of resources. With proper planning, some of these losses can be avoided. As our paper indicated, one factor that limits the consideration of mineral resources, and ultimately leads to their sterilization, is the generally inadequate levels of resource characterization and understanding of the unique nature of mineral resources and mining operations. The last point raised by Mr. Learning is also important. In terms of reclamation and land use planning in mining districts, we certainly do not advocate spending more than what the results are worth. The main thrust of the paper was to explore the avenues for conserving the mineral resources so that, at some appropriate time, the issue of mining and reclamation can still be addressed. ?

Jan 1, 1986

By C. S. Smith, L. Guttman

It is shown, from a study of geometric probabilities, that the average number of intercepts per unit length of a random line drawn through a three-dimensional structure is exactly half the true ratio of surface to volume. Since the surfaces can be internal or external, the area of grain boundary or of the interface between any two constituents in a micro-structure can be measured. Other metric relations are tabulated that may be of use in studies of the microstructure of polycrystalline, cellular, or particulate matter generally. IN many fields of scientific investigation the structure of cellular aggregates or random arrays of discrete particles imbedded in some matrix is observed on a two-dimensional section and inferences are drawn therefrom as to the real structure in three dimensions. The biologist&apos;s microtome slice, the petrologist&apos;s thin section, and the metallurgist&apos;s plane polished and etched sections are common examples, although the problem is a general one. Scientists have commonly limited their thinking to the same dimensionality as their structures, and the few attempts that have been strictly three-dimensional in character have been laborious and noteworthy. From a metallurgical standpoint it is often of considerable importance to know, in addition to the volume fraction of two or more components in an alloy, the amount of two-dimensional interface between crystals. Such grain boundaries (which may separate either two identical crystals differing only in orientation or two crystals differing in structure, and possibly also in orientation) have a determining factor upon the mechanical behavior. It is at these boundaries that melting commences, that stress-induced corrosion occurs, and that various precipitates (harmful or otherwise) first appear. The boundary is doubtless of equal importance in nonmetallic crystalline aggregates such as rocks, ceramics, and concrete, and the biologist is deeply concerned with the area of cellular membranes. Many synthetic cellular foams involve similar structural problems. The very term structure usually implies the presence of interfaces and a complete understanding of structure involves nothing but an analysis of the geometrical, metrical, and topological relations between the various interfaces (zero, one and two-dimensional) that exist in a three-dimensional structure. Even systems lacking sharp physical interfaces often have interrelated gradients of composition or velocity (as cored crystals or turbulence cells) in which a neutral surface can be treated as a two-dimensional interface. In an earlier paper by one of the authors&apos; the question of cell shape was considered in terms of simple topological principles without regard to physical dimensions. The determination of the actual size of grains in two dimensions is carried out in a routine fashion in innumerable metallurgical laboratories (see, for example, the ASTM standard methods of grain size determination2), though this is done merely to check the uniformity of a product and has no relation to the actual three-dimensional shape or size of the grains. Some authors have discussed the three-dimensional problem but only on the basis of assumptions as to idealized grain shapes.:&apos;-&apos; Quantitative measurements of microstruc-tures to obtain the volumetric relations of various phases have been carried out by petrographers for many years and are of increasing popularity among metallurgists." The present paper will show how, on the basis of no assumptions other than randomness of sectioning (usually realizable in experiment), it is possible to learn a great deal about the three-dimensional structure. The relations to be derived will generally be used on random arrays of cells or other particles, although they are equally applicable to ordered arrays and even to isolated objects of complex shape provided that suitable random sections can be made. Total Area of Interfaces in a Sample Consider a typical microstructure of a single-phase polyerystalline metal, such as that shown pres- in Fig. 1. The plane cross section shown contains a network of lines which subdivides the area into two-dimensional cells. The lines, of course, represent merely the intersection of the two-dimensional plane of sectioning with the two-dimensional interfaces between adjacent three-dimensional cells. The structure also contains points at which two or more lines intersect: in three dimensions the points are, of course, lines. In the more general case there may be in three dimensions isolated particles surrounded by a single interface without contact with others, and both two and one-dimensional features which do not necessarily connect with others. On the two-dimensional section these will appear as areas delineated by a closed line (as at a and b, Fig. 2), as isolated lines

Jan 1, 1954

By J. P. Morris

PREVIOUS investigations1,2 have shown that alloying elements in liquid iron influence the thermodynamic activity of sulphur and thereby affect the partition of sulphur between metal and slag in the desulphurization process. For example, the greater efficiency of desulphurization in the blast furnace as compared to the open hearth can be attributed in part to a higher level of sulphur activity in blast-furnace metal due to the higher concentration of carbon and silicon. In the present investigation, a short study was made of the influence of manganese on the activity of sulphur in liquid iron and iron-carbon alloys. In contrast to carbon and silicon, manganese was found to decrease the activity coefficient of sulphur; and in iron-carbon alloys it counteracts to some extent the influence of carbon. However, at manganese concentrations normally present in the blast furnace or open hearth, the effect of manganese is small. Since manganese sulphide has a limited solubility in iron, manganese can act, under certain conditions as a desulphurizing agent. Considerable data on the manganese-sulphur product in carbon-saturated melts were obtained in the investigation and have been included in this report. The experimental procedure was the same as that used in the earlier investigations on the effect of silicon&apos; and carbon&apos; on sulphur activity. Briefly, the method was as follows: The molten alloy, contained in a graphite or sintered alumina crucible, was brought to equilibrium at a constant temperature with a mixture of hydrogen and hydrogen sulphide of constant composition by bubbling the gas through the metal. Samples of&apos; the melt were taken for analysis at regular intervals by suction through a 2 to 3 mm bore silica tube dipped into the metal. The experiments were run in a graphite spiral resistance furnace with melts weighing 50 to 60 g. The gas bubbling tubes were made of sintered alumina and were 5/16 in. OD, 1/16 in. ID, and 24 in. long. Equilibrium was assumed to have been attained when the sulphur content of the liquid metal reached a constant value. During an experiment there was a rapid loss of manganese from the melt by volatilization. To offset this loss, small additions of manganese were made periodically. The rate of manganese addition needed to maintain a constant manganese concentration was determined in preliminary tests. In all of the experiments, deposits of manganese sulphide formed above the melts in a cooler region of the furnace. Apparently, these deposits resulted from a reaction between manganese vapor and hydrogen sulphide in the gas. To prove that manganese sulphide did not volatilize from the melts to a measurable extent, an experiment was run in which helium was bubbled through liquid iron containing both manganese and sulphur. Although manganese volatilized rapidly in this test, there was no appreciable loss of sulphur. Volatilization of manganese sulphide from a melt would have led to an apparent equilibrium condition in which the sulphur content of the metal was lower than the true equilibrium value. The experimental results are shown in the first seven columns of Table I. The data in the last two columns were obtained from the previous work on the effect of carbon&apos; and show what the results would have been in the absence of manganese but with temperature, gas composition, and carbon content of the metal remaining the same. Comparison of the last four columns show that, in the presence of manganese, the sulphur content of the metal increased at equilibrium and the activity coefficient of sulphur decreased. However, the results show that, for manganese concentrations below 3 pct, the effect of manganese is small. The values for activity coefficient of sulphur given in Table I were calculated from the following relations: S (in liquid metal) + H2 (gas) = H2S (gas) [l] K ph2s/?s X %S X phg = 0.00251 [2] where K is the equilibrium constant for the reaction, PH2S and ph2 are the partial pressures of hydrogen sulphide and hydrogen, respectively, and ?s is the activity coefficient of sulphur. The standard state for sulphur was taken to be a 1 pct solution of sulphur in pure iron. The numerical value for K at 1600°C was determined in the earlier work. For the purpose of showing graphically the results of the tests run at 1600°C, the activity coefficients of sulphur were recalculated so as to correspond to a manganese concentration in the metal of 2 pct in each case. In the calculation it was assumed that the increase in sulphur content of the metal at equilibrium caused by the presence of manganese

Jan 1, 1953

By J. H. Swisher

When an Fe-Mn alloy is internally oxidized, the inclusions formed are MnO which contains some dissolzled FeO. In the internal oxidation reaction, not all of the manganese is oxidized; some remains in solid solution as a result of the high Mn-0 solubility product in iron. Taking these factors into consideration, the rate of internal oxidation of an Fe-1.0 pct Mn alloy is computed as a function of temperature, using available thermodynanzic data and recently published data for the solubility and diffusivity of oxygen in iron. The predicted and experimentally determined rates for the temperature range from 950 to 1350°C are in good agreement. ThE rates of internal oxidation of austenitic Fe-A1 and Fe-Si alloys have been studied extensively.1"4 Schenck et al. report the results of a few experiments with Fe-Mn alloys at 854" and 956C, and Bradford5 has studied the rate of internal oxidation of commercial alloys containing manganese in the temperature range from 677" to 899°C. When Fe-Mn alloys are internally oxidized, the inclusions formed are solutions of FeO in MnO, the composition depending on the experimental conditions. Since the thermodynamics of the Fe-Mn and FeO-MnO systems have been investigated,6"9 and since the solubility and diffusion coefficient of oxygen in y iron have been determined recently,&apos; it is possible to predict the rate of internal oxidation from known data. The calculations used in predicting the rate of internal oxidation will first be outlined, then the results of the prediction will be compared with the experimental results of this investigation. PREDICTION OF PERMEABILITY FROM THERMODYNAMIC AND DIFFUSIVITY DATA Oxygen is provided for internal oxidation in these experiments by the dissociation of water vapor on the surface of the alloy. The dissociation reaction is: + H2(g) + [O] [1] where [0] denotes oxygen in solution. The equilibrium constant for this reaction is known as a function of temperature:&apos; log As oxygen diffuses into the alloy, oxide inclusions are formed which are MnO with some FeO in solid solution. The reactions occurring are: [Mn] + [0] = (MnO) [31 and [Fe] + [0] = (FeO) [41 where [ Mn] is manganese dissolved in iron and (FeO) is iron oxide dissolved in MnO. The overall reactions may be written as follows: [Mn] + HOte) = (MnO) + H2(£) [5] and [Fe] + H20(g) = (FeO) + Hz(R) [61 The standard free-energy changes and equilibrium constants for Reactions [5] and [6] are known.6 Therefore the equilibrium constants for Reactions [3] and [4] may be obtained by combining known thermodynamic data for Reactions [I], [5], and [6]. For Reactions [3] and [4]: K = and For the present purpose, both the Fe-Mn7,8 and FeO-~n0&apos; systems can be considered to be ideal, i.e., [amn] = [NM~] and (aFeO) = (NM~~) = 1 - (NFeO) where the Ns are mole fractions. These relations, together with Eqs. [I] and [8], permit us to compute both the oxide and metal compositions as a function of temperature and oxygen potential at any point in the specimen. For cases where the oxygen concentration gradient between the surface and the subscale-base metal interface is linear, the kinetics of internal oxidation is an application of Fick&apos;s first law: where dn/dt is the instantaneous flux of oxygen into the specimen, g-atom per sq cm sec; 6 is the instantaneous thickness of the subscale, cm; Do is the diffusion coefficient of oxygen in iron, sq cm per sec; p is density of iron, g per cu cm; h[%O] is the oxygen concentration difference between the surface and sub-scale-base metal interface, wt pct. B6hm and ~ahlweit" derived an exact solution to the diffusion equation for systems in which there is a stoichiometric oxide formed. They showed that the oxygen concentration gradient is given by a rather complex error function relation. For the Fe-Mn-0 system and for most other systems that have been studied, however, variations in oxide compositions are small and rates of internal oxidation are sufficiently slow that the deviation from linearity in the concentration gradient of oxygen is negligible. The mass of oxygen transported across a unit area of the specimen for the total time of the experiment is given by the mass balance equation:

Jan 1, 1969

By J. Chipman, H. R. Larson

The data previously reported for the quantity as a function of oxygen pressure at 1550°C have been used to compute the activities of Fe, FeO, Fe2O3, and COO in slags of the ternary system. Activities of the first three have been obtained also for two quasi-ternaries involving fixed CaO:SiO2 ratios. IN a previous paper1&apos; the authors reported the results of an investigation into the effects of oxygen pressure on the composition of various simple slags analogous to some of those which are found in steel-making practice. The ratio of ferric iron to total iron was studied at 1550°C in iron oxide melts to which lime, magnesia, lime-plus-silica, and other oxides were added. The oxygen pressures involved those of air, carbon dioxide, and carbon dioxide plus carbon monoxide in several proportions. Although very low oxygen pressures could not be used, the slag-metal equilibrium studies of Fetters and Chip-man&apos; permitted extending the results to slags in equilibrium with iron. For the ternary system CaO-FeO-Fe,O, the oxygen pressure-composition relationship has been determined from zero percent lime to lime saturation over an oxygen pressure range from air to that represented by equilibrium with liquid iron. Lime and silica were added to iron oxide in the ratios 0.54, 1.306, and 2.235 to form three quasi-ternary systems which were also studied over the entire region of liquid melts at 1550°C. Ternary Gibbs-Duhem Equation Wagner" has developed a method by which the activities of two components of a ternary system can be calculated if&apos; the activity of the third component is known throughout the composition range being considered. The fundamental form of the Gibbs-Duhem equation for ternary systems is N, d In a, + N2 d In a, + N3 d In a3 — 0. Wagner has developed a usable form of this equation by introducing the term y = N3/(N3 + N1) and rearranging the equation to give (? In a1/?N2)x = -y/(1-N2)2 (? In a2/?y) x2 N2/1-N2 (? In a2/?N2) y To apply this equation to the slag system CaO-FeO-Fe,O,, the activity of one of these components must be known. However, the only activity which is known from the experimental data is the activity or pressure of oxygen in the gas phase with which the slag is in equilibrium. The activity of oxygen in the slag can be defined as the square root of the oxygen pressure. In order to use oxygen as one component, the composition of the slags must be converted to the basis Fe-O-CaO. Oxygen, exclu-sive of that contained in CaO, then becomes com-ponent 2 in Eq. 1, Fe is selected as 1 and CaO as 3. Then y = Ncao/(Ncao + NFe). Eq. 1 then becomes (? In a fe/? Nx) y = -y/(1-No)2 (? In ao/?y) xp - No/ 1- No (? In ao/ O No) y. In order to evaluate Eq. 2, the boundary conditions must be known. The obvious choice of a standard state for iron is to assign slags in equilibrium with iron an activity of one. Then In a,., or log aFe, which is substituted for convenience, is determined by integrating along a line of constant y from the slag in equilibrium with iron to the composition at which log a,, is to be determined. Mathematically this can be expressed as log aFe (Nlog y) = log a&apos;Fe + (? log a Fe/? No) dNo where the primes indicate equilibrium with liquid iron and a&apos;Fe = 1. When Eq. 3 is integrated along a line of constant y, the following is obtained: log a Fe (No, y) = - y No ?/ No ? y ( log ao/(1- No)2) No d No - No/1-No d log ao. Lime-Iron Oxide Slags Iron Activity: The oxygen pressure of lime-iron oxide slags is shown in Fig. 1 as a function of j, de-fined as j = Fe+++/(Fe++ + Fe +++) for various constant mol percentages of lime. The j values at 0 to 60 pct lime were then determined for oxygen pressures of 1, 10-1, etc. to 10-" atm. For purposes of calculation, the line for zero percent lime was extrapolated to

Jan 1, 1955

By K. E. Nelson

The effect of thorium and zinc variations on the strength and 100-hr creep characteristics of Mg-Th-Zn-Zr alloys was investigated. Optimum resistance to creep at 650° and 700°F are attainable within a certain range of thorium and zinc contents. This range does not conform to that which develops maximum tensile properties. RAPID advances have been made during the last few years in the development of magnesium alloys for elevated temperature applications demanding high resistance to creep. The beneficial effect of rare-earth metals on the creep resistance of magnesium alloys has been emphasized by a number of publications1-13 and such alloys are now in commercial production. The use of thorium as an alloying ingredient in magnesium was mentioned by McDonald and also in two Alien Property Custodian patent applications.10,17 The initial observation of Sauerwald that thorium contributes still higher creep resistance to magnesium than is attainable with rare-earth metals has recently been substantiated.&apos;" " In fact, it has been demonstrated that the useful temperature range of magnesium alloys is appreciably extended by the use of thorium. In all cases, it was observed that zirconium must be included in the alloys in order to render them fine grained and more readily castable. Several recent publications:2-27 indicate that a still further improvement in creep resistance and a further extension of the useful temperature range can be realized by the addition of zinc to alloys. The primary purpose of this paper is to present the results of a comprehensive study of the effect of zinc on the strength and creep characteristics of Mg-Th-Zr alloys. Compositions covering the range of thorium content from M to 6 pct and zinc content from 0 to 5 pct have been investigated. The creep characteristics at 650" and 700°F reported in this paper are based on results of tests of 100-hr duration. It is appreciated that creep tests of 100-hr duration might not yield adequate data for design purposes for parts with much longer expected life. However, for the purposes of the present discussion, it is felt that the combination of stresses and temperatures used in the 100-hr creep tests have yielded a clear representation of the compositional variation of creep resistance at the temperatures investigated. Creep tests of 1000-hr duration are now in progress on a few of the most promising alloys. Preparation and Testing of Alloys The alloys studied in this intensive investigation were prepared in 25 lb capacity mild steel crucibles. The thorium, zinc, and zirconium were alloyed and poured as described in earlier publications The thorium was introduced into the melt in the form of a Mg-Th hardener," the zinc added in the metallic form, and the zirconium alloyed in the form of the commercial hardener containing magnesium and 30 to 50 pct Zr.10, 26 Fluxing practices for melting and refining were the same as for magnesium-rare-earth metal-zirconium alloys. The melts were sampled for analytical determinations and poured into separately cast 1/2 in. diameter standard tensile bars. The test bars were given a precipitation treatment of 16 hr at 600°F in laboratory furnaces. It has been shown by other tests that a high temperature solution treatment followed by an aging treatment is unnecessary for the development of optimum properties in Mg-Th-Zn-Zr alloys. The selection of 600°F as the aging temperature was based on an attempt to achieve metallurgical stability without coalescence of the undissolved phases and the attendant loss in strength. The thorium, zinc, and zirconium contents of each melt were determined chemically. The zirconium contents are reported in two parts, "soluble" and "insoluble," referring, respectively, to the portions present in the alloy which are soluble and insoluble in dilute HCl acid. Distinction is being made between these two components of the zirconium content in the alloys because it has been found that only that portion of the zirconium content which is soluble in dilute inorganic acids affects the structure and properties of the alloys. The usual impurities consisting of copper, iron, manganese, and nickel were determined spectroscopically. The analysis for each melt is listed in Table I. A description of the methods of tension and creep testing has been detailed in earlier papers. The tests were performed with the cast skin re-

Jan 1, 1954

By W. A. Haley

The use of diesel engines in underground hard-rock mines dates back to the late 1940s. For the first several years, they were used only occasionally, being limited to a few metal mines that experimented with crawler¬mounted front-end loaders, tractor-trailer hauling units, a few tractors for drill-compressor mounts, and utility cleanup machines. By the mid-1950s, track loaders had become commonplace in limestone mines and uranium mines on the Colorado Plateau in the United States, as well as in Canada. Use of crawler-mounted tractors as drill and compressor mounts also increased. By the end of the 1950s, rubber-tired loaders and some haulers began to replace the track-type machines and rail-mounted cars that had been in use. About 1960, the rubber-tired machines brought about a new era of underground mining mobility and flexibility, centered on a method commonly known as "trackless mining." Ultimately, many of the underground rail-type systems for loading and hauling were replaced by the trackless mining technique. ECONOMIC CONSIDERATIONS The size and nature of mineral deposits, plus ground control techniques, historically had dictated small open¬ings to the surface from many underground mines. The small mine openings led to the development of special rubber-tired loaders and haulers designed specifically for access through the small openings. However, some mines, particularly those in massive mineral deposits, are able to excavate and maintain very large openings, and some use modified room-and-pillar systems. With the large mine openings, the use of larger, more produc¬tive equipment such as that commonly found in surface mining becomes economical. In fact, productivity gen¬erally increases at a more pronounced rate than machine size increases because many of the larger machines were designed for heavy-duty shot-rock applications in surface mines and construction sites where the handling of blasted rock is common. Table 1 can be used as a very Table 1. General Productivity Comparison for Conventional Machines In Underground Use (Shot-Rock Conditions) 2.3 m3 (3 cu yd) 4.6 m3 (6 cu yd) Loader Loader Expected Surface 230 t/h 540 t/h Production (250 stph) (600 stph) Expected Underground 90 t/h 270 t/h Production (100 stph) (300 stph) Expected Total Efficiency: Surface 40%-60% 50%75% Underground 25%.-40% 30%50% Expected Useful Machine 8000 hr 12,000 hr Life Before Replacement general comparison of the production and efficiency between small and large machines. Combining greater productivity often inherent in larger machines, with reduced downtime resulting from using fully developed machines with fast parts and service backup, some mine operators have been able to reduce material handling costs appreciably while reduc¬ing manpower requirements for operators and main¬tenance men. Large mine openings increase the amount of rock that must be handled in the development work, and they sometimes increase the dilution in stopes or rooms, de¬pending upon the dimensions of the ore zone. Providing adequate space for the unrestricted operation of large surface mining machines could, therefore, lead to more waste segregation and handling costs. It could also cause greater ore dilution that would result in a lower grade of ore being delivered to the processing plant. The tradeoffs between opposing cost factors must be reconciled and balanced to achieve the best overall cost of the crude ore, concentrates, or product. EQUIPMENT MODIFICATIONS Loaders and haulers designed for surface mining are seldom used underground in their standard con¬figurations without some modifications. If done, the modifications generally are made by the equipment dealer and/or the user, and the modifications usually include one or more of the following items: 1) The exhaust stack is lowered, and its direction is changed. Usually, it is repositioned horizontally to the rear, or it is fed into the engine fan to diffuse the exhaust gases. 2) The operator&apos;s position is lowered by either lowering the seat or changing the seat to a side mount. 3) The operator controls are adjusted to fit the new operator position. 4) Other components, such as the radiator and loader tower, are lowered. 5) Special bumper guards are mounted at the base of the radiator area. 6) An exhaust conditioner is mounted and con¬nected, using either a catalytic or a water-type condi¬tioner, or both. This usually is controlled by the safety and health regulatory authority having jurisdiction. 7) The positions of other components are rearranged

Jan 1, 1982

By H. I. Morrison, A. J. deVilliers, D. T. Wigle, H. Stocker

INTRODUCTION At the end of 1959, high levels of radioactivity attributed to radon and its daughter products were discovered in the fluorspar mines at St. Lawrence, Newfoundland. These levels were presumed to be the cause of an unusually high incidence of lung cancer among the fluorspar miners (deVilliers & Windish, 1964) (Parsons et al. 1964). The mining of fluorspar (calcium fluoride) began in 1933 as open pit operations but converted to standard underground mining procedures in 1936. During the second world war, production was greatly expanded as a result of increased demand for fluorspar used in the production of steel. Wet drilling was first introduced into general use in 1942. Ventilation was mainly by natural draft occasionally supplemented by small blowers. The amount of ventilation varied greatly between mines as well as over time. For example, one large mine, the Iron Springs mine, had only a single small raise to the surface some 600&apos; from the central shaft. Other mines, such as the Director mine, had a number of raises to the surface and, as a result, had far better ventilation. Mines also varied by the amount of ground-water which seeped into them. In the early 1950&apos;s, an unusually large number of lung cancer cases were diagnosed among the fluorspar miners. As a result, in 1956 and 1957, J.P. Windish of Canada&apos;s Department of Health and Welfare tested for possible causative agents in the mines. Unfortunately, radon measurements were not conducted until 1959 and 1960 when Windish tested Director mine as did the A.D. Little company in 1960. As a result of the high radon levels found, mechanical ventilation was introduced and the concentration of radon dauthers fell, on the average to well below 1 WL. During this period, lung cancer cases continued to be diagnosed with 29 lung cancer deaths recorded by 1964 and 71 by 1971. As of July 1981, 105 lung cancer cases had been identified (Hollywood, 1981). Previous reports concerning the fluorspar miners have dealt in detail with the factors in the occupational environment and discussed occupational mortality patterns. The purpose of this paper is to review further the mortality experience with particular reference to lung cancer in relation to cumulated radiation exposure and to describe briefly our ongoing study of this group. METHODS Occupational histories were prepared for men who had been employed by the mining companies at St. Lawrence during the period 1933 to 1977. The histories were compiled from company records except for the period 1933 to 1936, records for which were lost in a fire; however, the occupational histories for this period were completed by searching census records and interviewing company officials, ex-employees and others. In addition, occupational and smoking histories were also obtained for some miners during a survey conducted in 1978. Occupational records included name and date of birth as well as the type, place and hours of work by year. For each year prior to 1960, hours of work were converted to working months (1 WM = 167 hours) and were multiplied by the estimated average radon daughter concentration in working levels (WL) to yield the annual radiation exposure in working level months (WLM). Pre-1960 radiation levels were estimated on the basis of the history of mining methods employed, ventilation history of the mine, type and place of work and conditions under which the first radiation measurements were made in 1959 and 1960 (deVilliers and Windish, 1964). During the period from 1960 to 1967, the average exposure was about 0.5 WL. Beginning in 1968, radiation levels were measured more frequently, and, beginning in 1969, daily exposures for each worker were recorded based on radiation levels in the place worked on a given day. Mortality data were obtained from medical certificates of death. In a small number of cases, medically certified death certificates were unavailable. In these cases, probable cause of death were obtained from forms completed by the local clergyman (returns of death), parish records, information obtained from interviews with family members of the deceased and/or hospital information, before assigning a cause of death. Data obtained from these sources were found in Tables 1, 2 and 4, cover the time period 1933 to 1971. Data in Table 3 as well as in Figures 1 through 3 cover deaths from 1933 to 1977, and includes only those miners for whom medical certificates of death were available. Two medically certified causes of death were changed from other causes to lung cancer on the basis of pathology reports.

Jan 1, 1981

By Lawrence A. Roe

The magnetic reflux classifier, which utilizes the combined effects of magnetic fields and a hindered settling classifier, is a new tool for determining the quantity and quality of middlings in fine-sized magnetite concentrates. Results are given for processing a typical taconite ore, and a sketch of the apparatus is included. IN examining magnetite ores and beneficiated products it often becomes necessary to make critical studies of the amount of grinding necessary to produce the desired degree of magnetite liberation. In the past this has been accomplished by laboratory heavy-liquid tests, which provide a method for selectively removing middling particles and free magnetite from various-sized fractions. Examination of the various products under the microscope results in fairly accurate determination of the degree of liberation. The method is quite efficient on sizes coarser than 325 mesh. Thus the heavy-liquid method of middling separation was satisfactory until the advent of present day magnetic taconite studies. When magnetite concentrates ranging from 70 to 100 pct —325 mesh are studied it becomes apparent that older methods of determining liberation size are not satisfactory and that there is need for a new method. For example, some of the low-grade magnetite ores of the Wisconsin and Michigan iron ranges require grinding to 100 pct —325 mesh to produce a magnetic concentrate containing less than 12 pct silica. Examination of concentrates from such ores often reveals that many of the middling particles consist of only very minor proportions of iron mineral. Thus it becomes important to be able to determine the degree of grinding necessary not only for complete liberation, but also for liberation of only 80, 85, or 90 pct of the total iron mineral content. Actually, complete liberation is never attained, but is often used to designate that degree of liberation necessary for production of high-grade concentrates. A rougher concentrate, produced after elimination of a coarse-sized tailing, can usually be subjected to a second grinding stage and concentrated into a higher grade product than could be produced from the same crude ore with one stage of grinding resulting in the same overall size reduction. This fact adds to the importance of being able to determine partial degrees of liberation on any magnetite ore. Standard laboratory methods such as heavy-liquid separation, microscopic grain counts, Davis tube magnetic separation, magnetic flocculation, classification, flotation, and others often are not applicable, or are prohibitive because of time requirements when large numbers of fine-sized magnetite samples are investigated. The Davis tube magnetic separator is an efficient tool to use in rejecting the non-magnetic mineral particles from an ore sample. The middlings discarded by the tube separator usually are so low in iron content that they can be considered relatively unimportant in liberation studies. This condition is caused by the extremely high flux density used in the Davis tube. This flux density ranges from four to eight times the flux density produced by most of the powerful commercial machines in use today. Thus the problem resolves itself into a search for a method of selectively removing middlings from Davis tube magnetic concentrates which will be both rapid and efficient. Those methods showing most promise in the development of a process for isolating middlings from extremely fine-sized magnetic concentrates were flotation and magnetic flocculation. The use of flotation to remove middlings from magnetic concentrates is reported in the literature.&apos;.&apos; The flotation process is effective in removing middlings from a magnetite concentrate, but physical entrapment of fine-sized free magnetite in the silica-bearing froth is an undesirable feature. The flotation method of removing middlings requires time, effort, and precise control of many variables, and does not meet the required degree of middling isolation. Magnetic Flocculation Magnetic flocculation has long been resorted to"-" in efforts to upgrade magnetite concentrates. One of the new magnetic taconite plants now under construction on the Mesabi Range includes magnetic flocculation in the flowsheet&apos; as an accessory process to remove high-silica middlings and free silica which has been mechanically entrapped in magnetite flocs. The use of magnetic flocculation as a laboratory method of making precise separation of middlings was further investigated, since it offered a rapid, simple method of accomplishing the desired result. Magnetic flocculation involves the subjection of a magnetic concentrate to a strong magnetic field, passing the concentrate in a highly flocculated condition to a hydroseparator or other classifiers of various types, and removing free silica and middlings as overflow products. In an attempt to utilize simple

Jan 1, 1954

By A. E. Desrosiers, R. L. Kathren, D. L. Haggard, J. M. Selby

INTRODUCTION The radiological health significance of thorium-230 stems from its tendency to separate from the uranium238 parent, concentrate in bone tissues, and to subsequently irradiate the radiosensitive tissues lining the bone surfaces and the bone marrow. Indeed, thorium-230 may be the radionuclide which contributes the major dose following intake of natural uranium (Hartley and Pasternack 1979). This is reflected by the most recent recommendations of the International Commission on Radiological Protection, which specify the limits shown in Table I for the annual intake of radionuclides by occupationally exposed workers (ICRP 1979). TABLE 1. Occupational Annual Intake Limits (microcuries per year) for Selected Uranium Nuclides and Daughters (ICRP 79) [Radionuclide Ingestion Inhalation] [Uranium-238 200 0.05 Uranium-235 200 0.05 Uranium-234 200 0.03 Thorium-234 300 200 Thorium-230 3 0.02 Radium-226 2 0.5] Clearly, the relatively low annual limit of intake for thorium-230 shows it to be of greater radiological concern than its parent radionuclides. Because of the greater toxicity and different metabolism of thorium-230, monitoring only for uranium-238 does not satisfactorily identify the possible hazard from thorium-230 nor does it provide any real indication of the metabolism or biodynamics of these two radionuclides. Thorium-230 has a half-life of 80,000 years and can be detected by direct counting of the alpha particles or photons emitted during its transformation to radium-226. The 4.69 and 4.62 MeV alpha particles are distinctive and specific indicators of thorium-230 and are emitted with abundances of 76% and 24%, respectively. The principal photon, a 68 keV gamma ray, is emitted in only 0.37% of the transformations and is, therefore, not useful for low level measurements. The other photons emitted have even lower yields, or, in the case of radium L x-rays, are non-specific and, hence, useless for quantification. High sensitivity measurements of thorium-230 currently are usually accomplished by wet washing of the sample substrate, quantitative chemical separation of thorium atoms, and, finally, direct measurement of the alpha particles emitted from a massless deposition. This procedure is complicated, expensive, and time-consuming, and subject to interferences from uranium, other actinides, and other thorium isotopes. Recently, the feasibility of low-level measurement of thorium-230 by neutron activation analysis (NAA) was demonstrated (Kathren, Desrosiers and Church 1980). Two principal variations of the NAA method were used in this study: 1) instrumental NAA technique and 2) post-irradiation radiochemical separations (RCS). Instrumental NAA procedure is a nondestrucive technique which is preferred because of its simplicity. The procedure is as follows: after irradiation with a known neutron fluence, the samples are transferred to a clean container and quantitative gamma spectroscopy performed. With the radiochemical separations procedure, the sample is initially treated as in the instrumental technique. However, after irradiation, a known amount of "carrier" is added to the sample. The element(s) of interest are then separated from the rest of the matrix by distillation, precipitation and extraction techniques. The resulting sample, now free of interferring elements, is then ready for gamma-ray analysis. The use of a "carrier" is to determine the loss of element-of-interest during the chemical separations process. The neutron activation cross section of thorium-230 has an epicadmium resonance value of 1,010 barns (Mughahghab and Garber 1976) and a thermal neutron cross section of 23 barns. The 25.52 hr thorium-231 produced releases two photons of significance: an 84 keV complex, (6.5% yield) and 25.6 keV (15% yield) (Lederer and Shirley 1978). The 84 keV complex is particularly useful for quantification since neither natural uranium, thorium, their daughters, or activation products emit photons in this region. However, the higher yield of the 25.6 keV photon may result in increased sensitivity if there are no other photons of similar energy emitted by other radionuclides in the sample. PRELIMINARY STUDIES Thorium-230 standard stock solution was prepared from a pure sample of the oxide purchased from Oak Ridge National Laboratory. From this stock solution a series of samples were prepared for irradiation in the TRIGA Mark I reactor at Reed College. Various dilutions were prepared as well as thorium-230 spiked urine samples. Irradiation times varied from 1 to 54 minutes in a neutron fluence rate of 1.84 x 1012 n/ cu m-sec. The neutron spectrum was abundant in thermal neutrons, having a Cd ratio of approximately 10. Treated urine samples were also analyzed by the NAA instrumental method. Analysis of untreated urine samples was not possible due to the high background

Jan 1, 1981

By W. A. Sheaffer

Electric furnace installation and tough-pitch copper-casting operation at Canadian Copper Refiners Ltd. are described. General layout, power supply and control, refractories, induction pour hearth, casting equipment, metal temperature control, and oxygen-content control are discussed. E LECTRIC furnace at Canadian Copper Refiners Ltd. was put into operation in August 1949. The installation was designed primarily to melt electrolytic copper cathodes and to produce vertically cast tough-pitch shapes. To meet emergencies during reverberatory furnace shut-downs, provision was made for casting horizontal tough-pitch wire bars. Due to the ease with which metal temperatures, melting rates, oxygen content, and casting hours can be altered to suit production demands, the electric furnace has met the requirements admirably. General Layout The plant has been described by H. S. McKnight&apos; and by J. H. Schloen and E. M. Elkin.2 Since these papers were written, the electric furnace has been installed in a 140 ft extension of the original casting building. The extension, 264 ft in width, is divided into one 24 ft and four 60 ft bays, each a continuation of similar bays in the older building. Fig. l, a partial floor plan of the extension, shows the location of major equipment. Power Supply and Control Power for the electric furnace and its auxiliary equipment is delivered by Quebec Hydro over two 12 kv three-phase, 60 cycle pole lines. One line is in use, while the second serves as an emergency standby. Connections for the electric furnace from these lines, which also feed the refinery power house, are made to a substation on Canadian Copper Refiners Ltd. property. Connections between this substation and the furnace transformer room are in underground conduit. The are-furnace transformer, 550 v auxiliary-equipment transformer, and 12 kv switchgear are in the transformer room near the furnace. Stepdown from 12 kv to are-furnace voltages is done by a 7500 kva oil-immersed water-cooled three-phase 60 cycle transformer. This unusually high kva rating is available because the arc furnace and transformer were adapted from a steel-melting unit. Secondary voltages are available in 16 steps between 251 and 95 v (across phases). A four-position tap changer, operated from the furnace switchboard is connected to taps yielding 199, 164.5, 127, and 115 v, respectively. The transformer primary feeder is equipped with a General Electric Magne-Blast circuit breaker. The pour hearth, casting wheel, bosh conveyor, and other auxiliary equipment are fed by a 12 kv to 550 v, 750 kva three-phase 60 cycle transformer. Graphite electrodes, 14 in., with tapered nipples are held in the are-furnace electrode arms with steel wedges. The arms, fed from the transformer secondary busbars by flexible cable bundles, are actuated by winch cables. Direct-current motors operating the winches are supplied by a 250 v motor-generator set. Power input to the furnace is controlled from the furnace switchboard. The board has the usual combination of remote controls for the 12 kv breaker and transformer tap changer, meters, overload relays, automatic and manual electrode motion controls, switchgear, etc. When power is on the furnace, automatic electrode feed is used; the power draw on a given voltage tap then is governed by current-limiting rheostats. The rheostats work through a Westinghouse bal-lanced-beam control circuit which, in turn, operates reversing contactors in the winch motor circuits. Arc Furnace The arc furnace is a standard-type NT Pittsburgh &apos;Lectromelt with inside shell diameter 12 ft 3¾ in. By hydraulic-lift cylinders, the furnace can be tilted forward to 39 ½ ° and backward to 5" from horizontal. A roof-swing cylinder is also installed but not used. Fig. 2 shows refractory-lining details. With the lining as shown, operating life between repairs is 6 to 9 months of two-shift casting operation. Charge slot, skim door, and roof refractories then are replaced completely, and any necessary repairs made to side walls. Bottom life is longer and the original under courses are still in service, while the top course was replaced in October 1951. The launder is lined with high chrome-magnesite trough brick backed by fireclay and insulating brick. The trough is covered with fireclay brick and asbestos sheet. At intervals, openings 12x6 in. are left in the permanent covering. These are covered with

Jan 1, 1956

By G. W. Healy

Activities of oxides in the ternary FeO-MnO-SiO system are calculated from data on the binaries, using the Gibbs -Schuhmann method. These activity data are used, together with thermodynamic relations, to calculate the contents of oxygen, silicon, and manganese in liquid iron, and the composition of the corresponding oxide phases in equilibrium with it. Excellent agreement was found between calculated and experimental metal compositions, indicating that thermodynamic methods, such as those presented, can supply useful data on slag-metal equilibria, and are therefore capable of wider application. When molten steel containing oxygen is treated with a deoxidizer, the product of the reaction is composed of the oxides of the deoxidizing elements together with more or less iron oxide. This assemblage of oxides is presumably very close to equilibrium with the melt since it is formed directly from elements dissolved in it. Therefore, it is likely that metal analyses corresponding to a given oxide phase composition are calculable with considerable precision where sufficient information is available on activities in both phases. The present study was made to test this hypothesis in the case of deoxidation by silicon and manganese. Here experimental data on the relationship among oxygen, silicon, and manganese in the metal phase are available, as are activity data for the MnO-SiO2, FeO-SiO2, and FeO-MnO binary systems. A further objective was to demonstrate in a specific example how gaps in the data may be filled by judicious interpolation, and how the Gibbs-Schuhmann method is applied to obtain activities in ternary systems. The rigorous derivation of the latter, requiring considerable facility in handling partial differential equations, tends to mask the real simplicity of the method, and repel the very engineers and experimenters who would benefit the most from its use. I) GENERAL PROCEDURE Deoxidation of steel with silicon and manganese results in the formation of two phases, metal and oxide. The number of components is four—Fe, Mn, Si, and 0. The phase rule then gives the number of degrees of freedom: If temperature and pressure are fixed, 2 deg of freedom remain. Consequently, it suffices to fix the concentration of two of the components of the system for all the concentrations to be determined and, at least in principle, calculable. The practical problem is then to discover a straightforward method of calculation with a minimum of trial and error solutions. The type of reactions to be dealt with are like the following: Si (in steel) + 2 O(in steel) = SiO2(in oxide phase) The standard free energy of this reaction is readily obtained from the literature, so that the equilibrium constant can be calculated by the expression: Since the metallurgist is concerned with percentages rather than activities, a real solution requires information that will permit activities to be converted to concentrations. This information is fairly adequate for the elements dissolved in molten steel, but is not available for the FeO-MnO-SiO2 oxide system. Therefore, the first step in this study was to find the relation between activity and concentration for the three oxides making up the system. The next step was the calculation of slag and metal compositions that are in equilibrium with one another. As shown by the phase rule, it is sufficient to assume the values of two composition variables in order to calculate the rest. But which two are picked makes a vast difference in how difficult the calculation turns out to be, so that it is necessary to make preliminary trial of several routes to find the easiest one. A convenient method is to begin with the slag, and to pick FeO concentration and that of one of the other oxides. Starting with the relation between oxygen dissolved in the liquid steel and FeO in the slag permits a good first estimate to be made of the oxygen content of the steel in equilibrium with FeO, because the iron content being fairly close to 100 pct, Fe has an activity close to unity. Using this first estimate of oxygen activity, approximate values of the manganese and silicon contents of the melt are readily calculated from the appropriate equilibrium constants. A minor correction for the depar-

Jan 1, 1963

By Laurance S. Reid, Joe A. Porter

Gas dehydration plays an important part in the production of natural gas. Effective dehydration prevents formation of gas hydrates and the accumulation of water in transmission Systems,2,6,7 insuring uninterrupted gas deliveries at maximum efficiency under the most adverse weather conditions. At the present time, most gas companies require a maximum water vapor content of seven lb per million standard cu ft of gas. so that virtually all gas tendered for sale must he dehydrated to meet this specification. For a number of years it has been common practice to produce gas and gather it at a common point for dehydration prior to discharge into the transmission system.1,3,11,16,17 However, higher transmission line pressures, long gathering lines and relatively low ground temperatures have made it necessary to dehydrate gas at. or near. individual. wells in order to gather gas from a number of newly developed fields without unusual difficulty. Where gas has been dehydrated at pressures ranging from 300 to 800 psi in the past. future trends indicate that these processes may be operated at pressures as high as 2,000 psi. Economics of gas dehydration are of great importance, partitularly where facilities must he provided to process relatively small quantities of gas, such as the production from an individual well. Although the adsorption of water vapor from gas on a granular sorbent material such as activated bauxite, activated alumina, or one of the alumina-silica gels is highly effective and produces virtually "bone dry" gas, the cost of a small unit of this type is substantially greater than that of an absorption process which, through proper selection of the absorbing liquid, will dehydrate the gas sufficiently to meet pipe line specifications. For this reason, a great deal of emphacis has been placed on the development of small, inexpensive dehydration units8,24 and the search for more effective absorb. ent liquids has been intensified. A wide variety of methods for dehydrating gas are known&apos; and many of these have been used in industry. Earlier applications of the absorption process employed concentrated solutions of calcium and lithium chlorides as the absorbent. The severe corrosion problems inherent in handling these solutions and the relatively small dew point depressions obtained caused early abandonment in favor of, or conversion to. diethylene glycol when it was found that aqueous solutions of this organic liquid were more hygroscopic than the brines and were non-corrosive. Processes employing diethylene glycol-water solutions are widely used for gas dehydration at pressures ranging as high as 1,200 psi.13,14,15 At nominal pressures a dew point depression of 45° to 50°F may be be and the data of Russell et al." indicate that a minimum dew point is obtained from the effluent gas at a pressure of approximately 1,200 psi when the gas is in equilibrium contact with a 95 per cent by weight diethylene glycol solution. In a number of instances the dew point depression obtained with diethylene glycol-water solutions is not sufficient to produce a specification product without cooling the inlet gas. In a recent search for a better absorhent, triethylene glycol was used in a small commercial dehydration unit and subjected to rather exhaustive field tests.&apos; The data obtained were encouraging and indicated that, at pressures ranging from 300 to 500 psi, triethylene glycol porduced a substantially greater dew point depression than diethylene glycol. These results led to an investigation of the system natural gas-water-triethylene glycol in an effort to obtain vapor-liquid equilibrium data, to determine pressure limitations, and to develop other data pertinent to the design of gas dehydration processes. A review of the literature has failed to reveal any data which permit reasonably accurate calculation of the vapor-liquid equilibrium conditions for a solution of water and triethylene glycol in contact with natural gas at high pressure. Since these constituents form a non-ideal system, the Poynting equation18,21 or the usual combination of Raoult&apos;s and Dalton&apos;s laws19,20,22 would not be valid. Correction of Raoult&apos;s and Dalton&apos;s laws by the use of activity coefficients2&apos; is not feasible for available data are insufficient for the prediction of the actual increase in the ratio of the activity of one component in the vapor phase to its activity in the liquid. Therefore. experi-

Jan 1, 1950

By E. M. Kalar, I. Iwasaki, J. D. Zetterstrom

Several methods of removing fatty acid coatings from iron ore flotation concentrates were tested both on a Mesabi oxidized iron ore and on a magnetic taconite concentrate, and their effects on the duplex flotation process and on pelletizing were compared. Either acid or alkali alone could not remove the coatings, but a combination of such reagents as lime and quebracho, calcium chloride and pyrophosphate, or sulfuric acid and an organic acid (oxalic, malonic, or citric acid) was quite effective. The use of activated carbon was found to be particularly promising. The removal of fatty acid coatings from iron ores is of much practical interest when a pelletizing process is being considered for a concentrate floated with a fatty acid collector or when a duplex flotation process is being considered for upgrading an oxidized iron ore. A duplex flotation process is a fatty acid flotation of iron minerals followed by an amine flotation of the siliceous gangue from the rougher iron concentrate. Such a process is being used in the Florida phosphate fields.&apos; Although in northern Michigan mills fatty acid flotation concentrates have been pelletized successfully, at other locations fatty acid coatings on iron flotation concentrates have proved so undesirable in the agglomeration operation that other methods of concentration had to be sought.&apos; Since fatty acid coatings cannot be removed as readily with a simple acid or alkali treatment from iron oxide surfaces as from Florida phosphates, a combination of reagents, such as lime and quebracho,3 lime and alkali phosphate,4 or sulfuric acid and oxalic acid,&apos; has been proposed. It was also thought that activated carbon might be effective in removing fatty acid coatings due to its high adsorptive capacity. Activated carbon, with its enormous surface per unit of volume, is well known for its exceptional efficiency in removing organic pollutants from industrial effluents. This article presents the practical aspects of the above methods when they are applied to the duplex flotation process and to the pelletizing of iron flotation concentrates. The article also includes a preliminary investigation of the common parameters involved in the depressant activity of the reagents. EXPERIMENTAL WORK Initially, the experimental work was directed towards the optimization of each method for the removal of hydrophobic coatings from iron oxide surfaces floated with fatty acids. Subsequently, the methods thus optimized were tested in the duplex flotation process with an oxidized iron ore and in the pelletizing process with a magnetic taconite concentrate. Preliminary Flotation Tests: Although the three types of chemical treatment reported in the literature were briefly investigated for the purpose of comparison, major emphasis was placed during the preliminary flotation tests on the use of activated carbon because it was thought to have certain advantages over the chemical methods. LIME AND QUEBRACHO - To obtain a flotation concentrate for optimizing the lime and quebracho method of fatty acid removal, the magnetic taconite concentrate was used. The concentrate had a size consist of 90% passing 325 mesh and analyzed 64.5% iron. After a few preliminary tests the fatty acid flotation procedure with the magnetic taconite concentrate was standardized as follows. A 1200-g sample of the magnetic concentrate was pulped in a Fagergren laboratoy flotation cell to 40% solids, conditioned with 0.5 lb of soda ash per ton for 2 min, and then further conditioned with 1.0 lb of Acintol FA-2 per ton for 2 min. After 5 min of flotation, recovery was nearly complete, averaging 98.6% of the weight and 98.7% of the iron. The cell product, which amounted to 1.4% by weight and analyzed 63.2% iron, consisted mainly of relatively coarse middling particles. Since the repro-ducibility of the flotation concentrates produced by this procedure was vey high, the same procedure was used to prepare fatty acid concentrates for each of the six tests of the lime and quebracho method. To test the removal of the fatty acid from the magnetite surfaces by the lime and quebracho method, a fatty acid froth product was returned to the flotation cell, repulped by 30 sec of agitation, and then con-

Jan 1, 1968