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By Stanley M. Miller

The probabilistic nature of appropriate geologic variables can be included in analyzing the stability of potential slope failure modes. Random variables in the two-dimensional plane shear analysis of a specified structural discontinuity include the shear strength and waviness angle of the discontinuity and, in some cases, the rock mass density. Estimated probability density functions that describe these random variables are combined by Fourier analysis to produce an estimate of the safety factor probability density function, which appears to approximate a gamma distribution. The probability that sliding will occur along the specified structure is equal to the area under this density function where the safety factor is less than one.

Jan 1, 1982

By Robert J. Willard

The scanning electron microscope (SEM), became commercially available in 1966. Embodying some unique features not provided by conventional electron microscopes, this new electron-optical instrument offers the scientific community a new way of observing the surfaces of materials. In rock mechanics research, the SEM should prove a useful basic tool in characterizing rock fracture on a very small scale and thus contribute to a better understanding of rock behavior at larger scales. This article presents one example of how the SEM is being applied to such research at the Twin Cities Mining Research Center operated by the U.S. Bureau of Mines in Minneapolis. This research center conducts theoretical and experimental studies on a broad range of mechanisms that induce disintegration by the application of energy to rock.1 Some of these studies are concerned with the relation of microstructure to rock behavior and are carried out mainly with the petrographic microscope. At the same time, however, the center recognizes that this relation must be studied through several orders of magnitude, from lattice-size units of rock-forming minerals to field-size rock units. The SEM fits this scheme by extending the capability of the petrographic microscope into smaller orders of magnitude. However, because its resolution is limited to about 200 A at 10,000x, the SEM is not capable of resolving lattice-size units, and hence a conventional electron microscope with a much greater resolution capability is necessary at this order of magnitude.

Jan 6, 1969

By Ernest G. Enck

Expanding markets and technological investigations now in progress for commercial production of titanium metal and alloys, as well as expanding uses for the oxide, have resulted in greater production, increased prices, and accelerated search for additional commercial occurrences of titanium minerals. For more than 50 years rutile has been used in moderate quantities in ceramics, in the production of ferrotitanium, as well as nonferrous titanium alloys. During the early 1930's, use of pure titanium dioxide was introduced as an ingredient of coatings for electric welding rods. For technical and economic reasons rutile was soon found to be as good or better for mild steel welding rods, and this use continues to account for a good share of the rutile sales in the U. S.

Aug 1, 1956

By J. Walter Snavely

PRESENT-DAY processing in many industries, calcining, sintering, briquetting, beneficiation and nodulizing, increasingly calls for the handling of large volumes of hot bulk materials. Various types of conveyors have been employed. This discussion will cover the factors governing their selection. For temperature ranges up to 400°F, or approximately 200 °C, a wide range of conveyors is available. Special constructions of rubber conveyor belts, steel conveyor belts, vibrating and shaker conveyors, apron conveyors, and drag chain conveyors, all are used successfully. As temperatures go well above 400 2F, however, choice of conveyors is narrowly limited. This paper will consider the problem of handling bulk materials only where the temperatures exceed 400°F. The arbitrary selection of 400 °F as a dividing point undoubtedly can be challenged, as special conveyor belting constructions are available which are suitable for temperatures in excess of 400°F. However, when the relatively short life of such belts and the cost of their replacement, with the attendant down time, are balanced against the reliability and long service life of the properly designed steel constructed units to be discussed, there is little question in any operator's mind that the special belts are more expensive to use. Because the conveyors under study are for the handling of bulk materials, inevitably including a high proportion of fines, obviously wire mesh belts cannot be included for consideration. Even though this type of conveyor is widely used at high temperatures, i.e., for carrying glassware through a lehr, it is unsuited for the conveying of bulk materials, and therefore will be excluded from further discussion in this paper. Preliminary to the study of the conveyor itself is the determination as to whether the material is to be cooled while it is being handled, or whether the processing requires retention of all heat and the maintenance of a given temperature range. In the majority of cases cooling is incidental to or part of the handling process, when the handling, for example, follows completion of sintering, roasting, calcining, refining, or some other process. To meet such operating conditions successfully, the conveying medium used must have: 1—a construction capable of withstanding maximum initial temperatures of the material being handled. 2—a construction providing efficient heat transfer for cooling. 3—a construction providing dependable operation and long life with minimum service requirements, and 4—a construction providing controlled and efficient conveying. Under the usual conditions of cooling during the handling, the construction selected to withstand the initial maximum temperatures does not necessarily involve using alloys, as excellent results can be achieved with normal carbon steels and cast irons, when they are properly applied and proportioned. The earliest and simplest type of conveyor for handling very hot materials is the cast steel drag chain conveyor, still widely used for handling hot cement clinker, as illustrated by Figs. I and 2. Because of the rugged and generous proportions of the chain link design, low carbon steels are entirely suitable for the links. The pins, however, must be alloy steel. The simple, rugged construction of this type of conveyor makes it readily capable of withstanding high initial temperatures, even though the chain is operating buried in the material. The drag-chain type of conveyor has advantages and limitations. Although the efficiency of the heat transfer is relatively poor, the life of the conveyor is reasonably long, and because of its crude simplicity it does not require much servicing. However, as a conveyor, it is limited in capacity, and largely limited to horizontal runs. Furthermore, because of the crude design, heavy weight, and the chain operating at the temperature of the material, greatly reducing permissible operating chain pulls, this type of conveyor is limited to relatively short centers. Another type of conveyor that has been used for very hot materials is the cast pan conveyor. Because of its very generous proportions the cast pan, which is made of either cast iron or malleable iron, can withstand initial maximum temperatures. It also provides efficient heat transfer for cooling. Further, it is on efficient conveyor construction, which can be used for inclines. Because the chain employs rolling friction instead of sliding friction, and is not in the maximum temperature zone, much longer centers are possible. It is this type of conveyor that is frequently used in the casting of various metal pigs, pig iron, and aluminum; it is obvious, therefore, that very high initial temperatures are being handled. With this kind of conveyor the return run is frequently sprayed with water to accelerate heat transfer. The build-up of residual heat in the very heavy cast pans is thus overcome. The outboard roller steel pan conveyor is an improved pan conveyor' which provides high rates of heat transfer and substitutes formed steel pans for the heavy cast pans. It is a very efficient conveying medium. The details of this particular construction are clearly shown in Fig. 3. An early application of this type of conveyor is shown in Fig. 4. In this case the conveyor units are handling roasted phosphate rock at average temperatures of 1000" to 1500°F, and frequent maximum temperatures as high as 1900°F. Several widths are used. The capacity of the unit at a speed of 50 fpm is approximately 30 tph per inch of width at peak loadings, average capacity being about 1/3 of peak loading. The assembled conveyor is shown in Fig. 5, with views of both the top and the underside to show all the construction details. In particular, the following general design principles were carried out in this construction:

Jan 1, 1954

By Rixford A. Beals

It has been observed with considerable accuracy that if the major U. S. mines were moved to Mexico tomorrow, many of them would be losing money. But the companies would continue to operate, losses or not, because they would have to. And some of the newest and most promising low grade ore projects in the U. S. would never have "gotten off the ground" had they faced the equivalent of the mining taxes now in effect in Mexico. No one of the various mining taxes in Mexico seems prohibitive by itself. Taken together, on the balance sheet, however, the picture changes. Production and export taxes alone take from 20 to 40 pct of the gross product value for base and precious metals.

Jan 2, 1955

Bernard MacDonald, Guanajuato, Mexico (communication to the Secretary*):—Mr. Iceyes's paper is very interesting to me because of my personal experience with the development of the ore-deposits of Lake Valley.

Jan 1, 1909

By J. H., R. W. Guard, Westbrook

In 1953 Kornilov and Mints' presented data on thermal expansion and electrical conductivity of the compound Ni3A1 which indicated the possibility of a transformation in Ni3A1 at about 600°C. The present paper gives results of some observations

Jan 1, 1960

By William P. Blake

A recent paper by Prof. George P. Merrill, Curator of the Department of Geology of the U. S. National Museum, Wash-

Jan 1, 1897

By Vincent P. Gianella

Barite deposits are of widespread occurrence in Nevada but there are few producing properties; most of the latter are in northern Nevada. The production of the state is small at present-in the neighborhood of 15,000 tons annually-but is steadily increasing. The barite occurs in veins and also as replacement deposits in limestone. The bulk of the production has come from the replacement deposits. It is thought that the barite was deposited from rising hot waters similar to-and probably contemporaneous with-those responsible for some of the metallic ores of the state. This paper discusses only the deposits in northern Nevada. THE commercial mining of barite did not begin in Nevada until 1916 but although the production has been small there has been a rapid increase in tonnage during the past several years. Barite is widely distributed in the state and production comes from at least nine of the seventeen counties. Apparently this is not generally known, as only two counties are mentioned in a recent publication6 dealing with barite. The increase in output is due largely to recently discovered barite deposits in northern Nevada. The principal production has come from the northern portions of Lander and Eureka counties; smaller amounts from Elko County. The discussion in this paper is confined largely to the deposits in these counties. Most of the producing area is tributary to the Western Pacific and Southern Pacific Railroads, whose tracks lie along the Humboldt River. Barite is known from other northern counties but so far the production has been small. The output has come entirely from veins and replacement deposits, the latter largely in sedimentary rocks. In general, the barite from veins is white; that from the replacement deposits usually is dark gray to black, although some is light gray or white. Most of the veins contain sulphides and many barite-bearing veins have been worked for their content of base or precious metals. PRODUCTION The recorded production in Nevada to the end of 1938, according to the U. S. Bureau of Mines,3 is 66,424 short tons, of which 57,157 tons

Jan 1, 1940

By R. L. Fleischer, W. F. Hosford

Tensile data for coarse grained aluminum Polycrystals suggest that the "grain size" effect is not due to dislocations piled up at grain boundaries but rather is primarily a relative size effect due to surface crystals being weaker and less confined. STUDIES directed at interpreting hardening of poly-crystalline metals normally identify their strain hardening properties with those in some particular type of single crystal.1"4 The recent recognition in face centered-cubic metals of a nearly linear stage with rapid hardening occuring at comparable rates for both polycrystals and single crystals, suggested that the same process or processes determine both cases and hence that there exists some justification for the use of single crystals to understand polycrystals. Further evidence for the above view may be found by an approach initiated by Chalmers:5 By using bicrystals of controlled orientation it is possible to begin to assemble a polycrystal and also to study grain boundary effects in detail. In this way it has been found that a single grain boundary affects easy glide but not the subsequent stage II hardening.6 This result suggests that a sensitive way to observe grain boundary effects in polycrystals would be to vary grain size and measure easy glide. As will be seen, easy glide is only possible for coarse-grained samples, and hence the results will serve to fill in the gap in measurements between single crystals and bicrystals on one hand and fine-grained polycrystals on the other. One problem inherent in comparing single crystals with polycrystals is the uncertainty as to what slip systems are acting in a polycrystal. To compare the two types of samples, rates of shear hardeninn---L. on the acting -planes are needed. and these may be computed only if it is known what particular systems are active. The acting systems were examined for a coarse-grained polycrystal and it will be shown that the systems supplying the preponderance of slip can be determined with little ambiguity. EXPERIMENTAL PROCEDURE Twelve samples of aluminum were prepared by chill casting into a heated graphite mold, followed by annealing at 635° ± 5°C for 24 hr with an 8-hr fur- nace cool, and finally either etching7 or electropol-ishing.' The samples, with a 7 to 10 cm length between grips and 4.4 by 6.6 mm in cross section, were deformed at a strain rate of about 3 10 -3 . per min in a tensile device which has been described elsewhere.5 The composition was reported by Alcoa as 99.992 pct Al, 0.004 pct Zn, 0.002 pct Cu, 0.001 pct Fe, and 0.001 pct Si; nine samples were deformed while immersed in liquid helium and three in air at room temperature. The stress-strain curve for one of the samples (P-1) deformed at 4.2 "K has been reported previ~usl~.~ This sample was selected for determination of active slip systems. Eighteen of the crystals were examined by optical microscopy to determine the angles of slip line traces and by X-ray back reflection to determine orientation. By this means the slip planes were determined and the resolved shear stress factors for possible slip systems could be computed. Finally each sample was sectioned so that after etching, the number of crystals could be counted for each of ten newly exposed surfaces. The average of these ten values will be termed n, the number of crystals per cross section. Values of 11, varied from 1.9 (nearly bamboo structure) to 12.7. Sketches of typical cross sections appear in Fig. 1. RESULTS AND DISCUSSION: SLIP SYSTEMS 1) Determination of Acting Slip Planes—The stress axis orientation and operative slip planes in eighteen crystals of sample P-1, as determined by slip line traces and crystal orientation, are summarized in Fig. 2. For one of the crystals two planes had a common trace. so that the traces alone did not distinguish which plane or planes were slipping. However it was found that the stress resolving factor for the primary system was 0.386, .while that for the most stressed system in the other plane (indicated bv the dotted arrow) is 0.138. It will be assumed tgerefore that only the primary plane acted. Since the orientations were determined after extending the samples 4 pct, the stress axes may be rotated from their original value by as much as 2 deg in some cases. It is interesting to note that in five crystals only one slip plane acted, in eight two acted, and in five three planes were observed—an average of two slip

Jan 1, 1962

By K. G. Kreider, J. H. Brophy, J. Wulff

The technology of nickel-activated sintering of tungsten powder has been successfully applied to the densification of plasma-sprayed tungsten. Nickel was added by infiltration in a zinc solution followed by evaporation of the solvent. After sintering one hour at 1300°C density 95 pct of theoretical and transverse rupture strength of 74,000 psi were obtained. Shrinkage was found to be anisotropic and the mechanism of densification was comparable to that found in the nickel-activated sintering of tungsten powder. 1 HE use of a plasma spray gun for the fabrication of massive tungsten parts has become increasingly interesting. Applications now exist where a deposit in the as-sprayed condition is satisfactory. However, these deposits are generally characterized by a lamellar anisotropic microstructure containing 15 pct porosity of which, typically, two-thirds is open to the surface. Mechanically, the as-sprayed deposits fail at relatively low stress levels with a biscuit-like fracture. As a result of these problems the possibility of improving structure and strength by sintering treatments subsequent to spraying is particularly attractive. Preferably this sintering treatment should be adaptable to large bodies of sprayed metal. The similarity between the as-sprayed tungsten structure and that of a powder compact suggests that the relatively low-temperature activated sintering technique1 might be profitably employed in the densification of plasma-sprayed tungsten. It was the purpose of the present investigation to develop a technique for introducing the nickel-activating agent into the sprayed structure, to evaluate the amount and mechanism of densification obtained as a function of time and temperature, and to obtain an indication of the relative strength before and after sintering. EXPERIMENTAL PROCEDURE Powder used for spraying was purchased from the Wah Chang Corp. in several size fractions ranging from an average size of 4 to 150 . These powders were sized further for an explicit study of the influence of average feed size on densification. All powders were dried at 200°C before use. Spraying was accomplished with a Plasma Flame unit manufactured by Thermal Dynamics Corp. Several modifications of the unit were helpful in conducting the investigation. A variable speed auger feed mechanism coupled with the carrier gas mecha nism facilitated the use of fine particle sizes. A coil of ten turns of copper tubing in series with the arc power and concentrically would around the nozzle improved nozzle life and extended the range of operating currents available. The function of the auxiliary coil was to cause the arc to spin and to prevent impingement at only one point in the nozzle. Normally air sprayed deposits were made with an arc maintained at 400 amp at 50 to 70 v. The arc was blown by a gas mixture containing from 5 pct H, 95 pct N for the finest powder feed sizes ranging to 20 pct H, 80 pct N for the coarsest size. The flow rate was maintained at 100 cu ft per hr NTP through a nozzle of 0.25 in. ID. When apraying in air, the powder stream was directed toward an aluminum substrate for ease of mechanical removal of the deposit. The substrate was cooled by diverting the plasma flame with an air jet, and a second jet was directed on the deposit surface. In this configuration a gun-to-work distance of 2 to 3 in. was found to be satisfactory. Fig. 1 represents a typical as-sprayed deposit micro-structure. Laboratory studies of protective atmosphere spraying were carried out in cylindrical chamber 8 in. in diam by 18 in. in length. In operating the nozzle attached to such a chamber, particular care was required to avoid nozzle burn out due to reduced gas flow. The structure and density of the chamber sprayed deposits varied over wide ranges depending on substrate temperature. For the purposes of this investigation, flat deposits were made approximately 2 in. sq by 3/8 in. thick. From these deposits individual samples were cut an ground to a rectangular shape typically 1 1/2 in. by 1/8 in. sq such that the long dimension was perpendicular to the spraying direction. For the study of shrinkage anisotropy deposits up to one inch thick were produced. From these, rectangular samples were cut having a longer dimension parallel to the spraying axis. Prior to the addition of activating agent, the samples were deoxidized in hydrogen at 800°C for 20 min. No detectable dimensional or microstructural change was observed after this treatment. The addition of nickel was accomplished by infil-

Jan 1, 1963

By C. Laird, C. E. Feltner

May different kinds of dislocation structures have been observed in strain-cycled metals and alloys. In order to understand their pattern and causes, an experimental program has been carried out to determine the influence on the dislocation structures of the three variables: 1) slip character of the material, 2) test temperature, and 3) strain amplitude. The results show that at high strain amplitudes cell structures me formed when the slip character is wavy, and that these are progressively replaced by uniform distributions of dislocations as the stacking fault energy is decreased. At lower strains, dislocation debris is formed which consists primarily of dipoles in wavy slip mode materials and multipoles in planar slip mode materials. Temperature merely acts to change the scale of the structure, smaller cells, and clumps of dislocation debris being associated with lower temperatures. It is shown that the results for many metals fit this pattern, which Parallels that occurring in unidirectional deformation. DISLOCATION structures produced by cyclic strain (fatigue) have been examined in a number of metals by transmission electron microscopy. These studies have produced a variety of interesting and often seemingly conflicting results. For example, different investigators have reported such structural features as cells.le4 bands of tangled dislocations,4'5 dense patches or clusters of prismatic dislocation loops, planar arrays,4'10 and various combinations or mixtures of these different structures. Most of these observations have been made on materials which were initially annealed and cyclically strained at low amplitudes resulting in long lives. Recently we have reported observations of the dislocation structures produced in copper and Cu-7.5 pct Al cycled at large amplitudes, resulting in lives of less than 104 cycles.4 These results, examined in combination with those in the literature, have suggested that a common or consistent structural pattern exists. Variations in this pattern appear to be determined chiefly by the three variables, namely, the slip character of the material,4,11 test temperature. and the strain amplitude. To verify this interpretation, we have studied [he influence of the above three variables (in different combinations) on the resultant structures in cyclically strained metals. Copper, fatigued at room temperature, was chosen as a reference state to which all other observations can be compared. The effect of slip character has been investigated by employing fcc metals of different stacking fault energy. Thus aluminum which has a more wavy slip character than copper, and Cu-2.5 pct A1 having a more planar slip char- acter, have been examined. The aluminum samples were fatigued at 210°K thus making their homologous temperature equal to that of copper at room temperature. The influence of temperature has been evaluated by examining the structures in copper at room temperature and 78°K. Finally the effect of strain amplitude was studied by looking at the structures at amplitudes giving lives ranging from 104 to 107 cycles. All of the specimens were examined at the 50 pct life level at which stage the structures have reached a stable configuration.12 I) EXPERIMENTAL PROCEDURE Strip specimens, 0.006 in. in thickness, were prepared from base elements of 99.99 pct purity or greater. Specimens were fatigued by cementing the strips to a lucite substrate which was subjected to reverse plane bending. This method of testing has been described e1sewhere.7 After fatiguing, specimens were thinned and examined in a Philips EM 200 which was equipped with a goniometer stage capable of ±30-deg tilt and 330-deg rotation of the specimen. On the basis of separate calibrations,13 allowances were made for the relative rotation and inversions between the bright-field images and the diffraction patterns. II) RESULTS AND DISCUSSION The life behavior of the materials under different test conditions is shown in Fig. 1 in the form of plots of total strain range vs cycles to failure. Comparisons of structures produced in the different materials were made at amplitudes which produced equal numbers of cycles to failure. The influence of strain amplitude on the structures produced in the reference state material (copper tested at room temperature) is shown in Fig. 2. At the 104 life level the structure produced comprises cells similar to those previously observed.3,4 They are approximately 0.5 p in diam and the cell walls are generally more regular or sharper than those produced by unidirectional deformation.14 At the 10' life level the

Jan 1, 1969

By C. B. Manula, R. Venkataramani

Application of computers to present-day open-pit mining with bucket wheel excavators (BWE) is discussed. The development of the wheel excavators and their use in mining are discussed along with the necessity for building a computer model of the bucket wheel and the mathematical formulation of the problem. The simulation procedure, testing the model, and test results are summarized. Even though the mining industry in 1966 produced more ore than ever before, current extraction rates are only a fraction of what is expected in the later years of the 20th century. Nearly 90% of all metals and mineral products consumed last year was recovered by open-pit mining. This has placed great pressure on this segment of the industry which has, consequently, resulted in some spectacular developments. With increasing size of projects, the need for increased sophistication of engineering, planning, management, and administration of modern mining installations has never become more apparent. The design of complete systems for the mine and plant that fit the mold of today's business and social environments is undergoing an evolutionary process. Traditional concepts in mine development and operations are being sidestepped in favor of new ideas and principles. As the overburden thickness increases, materials handling presents a major problem to mining companies, especially those concerned with the mass production of ore and waste from low-grade deposits. The profit margin here is likely to be significantly less as to take chances with capital investment. Constant efforts are needed to improve upon productivity if the ore is to be economically mined. The development of vast low-grade deposits and thick overburden deposits calls for better tools to handle the enormous amount of materials. A natural solution to this problem is the use of bucket wheel excavators (BWE), which employ a continuous cutting head to feed the materials handling system. High productivity, versatility, economy of operation, and adaptability to most types of haulage systems combine to make BWE's attractive for large earth-moving operations. "Operating costs are being pushed down by the impact of giant haulage units, by high-speed conveyors, and computerized railroads. Matching all these with the continuous output of BWEs, one can visualize increased production at much lower costs." Historical Background The wheel excavator, which was patented in Germany in 1913, made its first appearance in an open-pit lignite mine in 1920. From this early beginning, however, BWEs were slow coming into practice. Initial developments were dampened by many design problems. From 1936 onward, major developments in design improved the wheel's ability, capacity, and versatility. A literature survey shows that wheel excavators are being used in Australia, Zambia, South Africa, the Congo, India, Indonesia, Czechoslovakia, Russia, Great Britain, Guyana, Yugoslavia, Morocco, Germany, Canada, and the U.S. for mining and loading chalk, lignite, clay, sandstone, phosphate, broken ore of iron, coal, shale, loose and semi-loose rock overburden.' A recent LMG* BWE at work in a German lignite mine weighs 6790 tons with an hourly capacity of 11,000 cu m. Although the BWE has wide applicability, its application to new mining areas poses a problem. Because of the large capital investment involved in BWE application and the narrow profit margins in mining low-grade ores or coal at depth, little margin of error can be tolerated in the selection, design, and operation of these machines. The questions that need to be answered prior to installation of a BWE for a mineable deposit are: 1.) What are the anticipated BWE performance characteristics? 2) Which method of BWE operation is most efficient? Attempts to answer these questions require a thorough knowledge of the mining system and the BWE operation. One approach is the building of a computer-ori-ented simulation model to determine how information and policy create the character of the BWE system under consideration. BWE Operation Modern BWEs generally excavate in blocks. Fig. la shows a BWE working in an established cut. The wheel is positioned to travel on the pit floor in line with the top edge of the old highwall. As it advances, a new highwall is exposed in the direction of excavation. Digging is done by rotating the wheel, swinging it from side to side in long parallel arcs, and "crowding" into the bank, by advancing the entire machine, or by the travel of the digging boom if an automatic crowd is available (Fig. lb). A second way by which the wheel can be advanced into the bank is by the falling cut method. A brief description of each of these methods follows. Cut with a Crowding Machine: At the end of every swing, the digging boom can be extended by the thickness of cut desired and the boom swung back in the reverse direction. Obviously, the thickness of bank excavated does not vary with the boom position; therefore, the slewing motion of the boom is fairly constant for uniform output. The thickness through which the digging boom can be advanced into the bank is theoretically calculated from the formula'

Jan 1, 1971

PITTSBURG MEETING The One Hundred and Ninth Meeting of the Institute, for the presentation and discussion of technical papers, will be held at Pittsburg, Pa., Oct. 8, 9 and 10, 1914. This meeting is to be under the auspices of the Iron and Steel Committee, the Committee on Petroleum and Gas, the Committee on Coal and Coke, and the Committee on Non-metallic Minerals. Thirty papers have been secured by these Committees and will be presented at the meeting. These papers will be published in the September and October Bulletins. The Local Committee of Arrangements for this meeting is as follows: SAMUEL A. TAYLOR, Chairman. FRANCIS C. PHILLIPS. GEORGE S. RICE. C. F. V. Rys. KENNETH SEAVER. JOHN S. UNGER.

Jan 9, 1914

By J. Chipman, N. J. Grant, B. M. Shields

The vacuum tin-fusion method of analysis for hydrogen, developed by Carney, Chipman, and Grant, has been modified to permit the analysis of the evolved gases for hydrogen by means of a thermal conductivity cell. A properly prepared sample can be analyzed in 10 min with a probable error of ±0.12 ppm. A study of various methods for storage of hydrogen samples shows that samples can be safely held in a dry ice-acetone bath as long as six days. Storage in liquid nitrogen is necessary for samples to be held one week or more. HE vacuum tin-fusion method, as developed by I- Carney, Chipman and Grant,' is the only analytical procedure which has shown promise of being fast enough for use in the control of hydrogen during steelmaking. It was felt that further simplification and faster speed of operation could be effected by the use of thermal conductivity measurements for analysis of the gases evolved in the tin-fusion method. The application of conductivity measurements to the tin-fusion method is possible because: 1—the evolved gas is essentially a mixture of hydrogen, nitrogen and carbon monoxide with a hydrogen content usually over 50 pct, 2—the evolved gas is collected at a relatively low pressure, and 3— the thermal conductivities of CO and N2 are practically identical while that of hydrogen is very much greater. The major part of this research program was devoted to the construction and calibration of a vacuum tin-fusion apparatus which analyzes the evolved gases for hydrogen by means of a thermal conductivity cell. The second phase of the problem was associated with the development of a procedure for storage of samples prior to analysis. With the rapid quenching method for hydrogen sampling,' which seems to be the most practical for steel mill use, it is necessary that the samples be stored safely during the interval between sampling and analysis if the hydrogen content of the molten metal is to be maintained in the supersaturated solid samples. The thermal conductivity bridge has been used for a number of years in the analysis of certain gas mixtures. An elementary discussion of the theory and practice of gas analysis by thermal conductivity measurements is given by Minter.3 A more comprehensive discussion of the theory and of the various measuring circuits is presented by Daynes.' A complete knowledge of the theory and properties of the thermal conductivity of gases and gaseous mixtures can be gained by a study of the standard textbooks on the kinetic theory of gases."' The existing data on the thermal conductivity of single gases are reviewed by Hawkins: that for a number of binary gas mixtures by Daynes' and Lindsay." The thermal conductivity method may be applied to the determination of the composition of a binary mixture if: 1—the thermal conductivity of the mixture varies monotonically with composition, and 2— the two gases have measurably different thermal conductivities. The greater the difference between the two gases, the greater the sensitivity of the method.10 he method is applicable to the analysis of multicomponent mixtures when all of the gases in the mixture except one have nearly the same thermal conductivity. Fortunately, the mixture of hydrogen, nitrogen, and carbon monoxide evolved by the tin-fusion analysis' falls in this latter classification. The thermal conductivities of nitrogen and carbon monoxide are practically equal; and the thermal conductivity of hydrogen is approximately seven times that of the other two. Therefore, the thermal conductivity of a gaseous mixture of hydrogen, nitrogen, and carbon monoxide at known temperature and pressure can be related directly to the percentage of hydrogen in the mixture by suitable calibration. Usually the thermal conductivity of a mixture of gases is measured at atmospheric pressure where the thermal conductivity is independent of pressure over a wide pressure range. At very low pressures (below 1 mm Hg), the thermal conductivity of gases varies with the pressure. This phenomenon has been utilized in the Pirani vacuum gage for the measurement of pressures in the range of 10" to 10-0 mm of mercury.= Very little has been published concerning the variation of thermal conductivity with pressure at intermediate pressures between 1 mm Hg and 1 atm. However, preliminary measurements indicated that the thermal conductivities did vary with pressure over the range of pressures (up to 10 mm Hg) at which gases are delivered from the vacuum pump. Therefore, the calibration of the thermal conductivity cell had to be planned to include the effects of both gas composition and pressure. Such a calibration chart is shown in Fig. 4. Most industrial applications of the thermal conductivity method of gas analysis have used a compensated Wheatstone bridge circuit containing two

Jan 1, 1954

By AIME AIME

It is with the deepest personal sorrow, and with the regrets of the Steel Company of Canada, that I report to you the death of one of our most valued associates, the late Frank B. McKune, superintendent of the Open-Hearth Department of our company. Many of you will remember Mr. McKune for his long attendance at these meetings, for the intelligent interest he took ill them, as well as for his innovations in steel-production practices.

Jan 1, 1940

Jan 1, 1907

By L. D. Clark

Pay-out, the ratio of capital expenditure to annual cash return can be very revealing when employed to gage the merits of a proposed mining venture. It is a quantity, numerically but not physically equal to a factor, by which cash return may be discounted to equal required investment. The fewer the pay-out years, the greater the average annual earning power of the project. Considerable material has been written in the past about the most important and difficult problem mining management faces in evaluation of a property: the optimum production rate for the venture. What daily capacity should be adopted for the proposed operation that it may be the most rewarding to those underwriting it? H.C. Hoover has said, "The most important objective is the least cost per ton mined; and minimum working costs can only be gained by the most intensive production." Theoretically and practically, the quicker the ore is removed, the more profitable should be the venture because of the saving in fixed charges, the consequent lower unit costs and the interest unearned by the profit from the unmined ore. Yet, such performance will be tempered by policy and a restraint imposed by the ratio of capital expenditure to annual cash return. * The 'Annual net profit after taxes but including depreciation and depletion allowances. former will be based upon an analysis of the economic climate anticipated, with its many ramifications including the demand for the product, prices, tax laws, the conduct of labor and related wage scales. The variables and intangibles involved in estimating the optimum production rate for a mine do not readily lend themselves to mathematical relationships or equations and the problem can become complex indeed. The more readily applicable and relatively faster appraisal method will be used which, in addition to being reasonably adequate in most cases, will serve as a guide, should a more expanded and detailed estimate be desired. The first question is what is company policy with respect to the rate of investment return? This will depend on that significant period of time referred to as the pay-out, which can be defined as the estimated interval during which capital investment is returned through application of annual cash return to its recovery. Expressed another way, it is the ratio of capital expenditure to the annual cash return. For example, if the capital investment is $C and the annual cash return is $A (after Federal tax), then $C/$A = the pay-out period in years. That is to say, if $C = $1,500,000 and $A = $214,000, then which is the mathematical expression for the period of time it takes to recover the funds originally invested in a mining enterprise. The relationship yp = $C/$A can be useful — an expression which requires only the significant tern yp to be fixed; in other words, the long range investment policy. For what is the pay-out period but an expression of that policy in terms of the speed, within practical limits, with which an individual or company may want to recover capital expenditure? A policy by which pay-out will be fixed is imperative. This ratio must lie within relatively narrow limits governed by what is economically feasible. It cannot be too low, rendering the ratio impractical or absurd, nor too great, delaying the return of capital for reinvestment beyond a commensurate interval. What pay-out will govern this policy? Federal corporate taxes would seem to present the best measure. Consider mining in Canada where new mines are exempt from Federal income tax for 3½ yr from date of first production. This exemption expressly allows The Act states: "A corporation . . . i s not required to include the profits . . . for the period of 36 months commencing with the day on which the mine came into production in reasonable commercial quantites." a company to recover capital expenditure during the early stages of production. With such an incentive, it is logical to strive for as much capital redemption as possible during this period. Thus, 3½ yr would be a major contribution to the pay-out in Canada. Furthermore, it generally takes from 1½ to 3 yr to develop

Jan 1, 1963

By S. E. Szasz, E. J. Moore, B. F. Whitney

An accurate value of formation water resistivity R, is essential in calculating formation porosity and fluid saturation from electrical well logs. In the cases where R, has not been measured directly, it must be obtained from other data, e.g., the SP curve. This paper deals with another approach: how to calculate R, from the chemical analysis of the formation water. INTRODUCTION It is known that the resistivity of aqueous solutions of pure salts depends on their concentration and on the temperature; the concentrations are given in MPL (mg of solute per liter of solution), or sometimes in ppm (mg of solute per kg of solution): MPL = ppm X specific gravity. Values for different pure salts are available in the literature, but not for solutions of mixtures which are of practical interest. The major component of the dissolved material in almost all formation waters being sodium chloride, it is customary to express the resistivity of formation waters in terms of equivalent sodium chloride concentration, i.e., the concentration of a solution of pure NaCl which has the same resistivity at a given temperature as that of the formation water under consideration. Thus, the problem of calculating R, from the chemical anaylsis can also be stated as how to convert the other constituents of the solute into equivalent NaCl concentration. Salts dissolved in water are at least partly dissociated into ions, and do not conserve their identity. If known amounts of several salts are dissolved in water, the solution does not necessarily contain the same salts in the original proportion, but perhaps some other combination of the ions, along with free ions in solution. This is why the chemical analysis of formation waters is often given in terms of ions, as if all dissolved salts were completely dissociated. Our problem then boils down to how to convert the concentrations of the various ions to equivalent concentrations of Na' and C1-. Dunlap and Hawthorne' have proposed to convert the concentration of all other ions to equivalent Na' and C1-concentrations by means of constant multipliers; e.g., 0.95 for Ca"; 2.0 for Mg"; 0.27 for HCO 3-; 0.5 for SO, -, etc. Their factors were based on measurements made at 68F on 26 formation water samples from the Texas Gulf Coast, ranging in concentration from 1,500 to 75,000 ppm. The Dunlap method is widely used in electric log interpretation, and is often extrapolated beyond its original concentration range. A comparison of R, values calculated by this method and values actually measured on formation water samples has shown large discrepancies, especially at higher concentrations. Therefore, two new methods were developed at Sinclair Oil Corp.'s Tulsa Research Center to calculate equivalent sodium chloride concentration from the chemical analysis of formation water samples. FUNDAMENTAL CONSIDERATIONS The resistivity of a solution, or its reciprocal the conductivity, at a given temperature is determined by the charge, concentration and mobility of the ions actually present. Monovalent ions such as Na' or C1- always carry the same charge. Compounds of polyvalent ions, however. may show incomplete dissociation, e.g., NaSO; + Na' instead of SO,-- + 2Na'. This happens especially in more concentrated solutions. Only very dilute solutions are completely dissociated, as assumed in the chemical analysis report. At higher concentration, the degree of dissociation depends not only on the nature and concentration of the particular salt under consideration but also on the nature and concentrations of the other solutes. Mobility of the ions depends on the viscosity of the solution. It also depends on the degree of hydration of the ions, which in turn is a function of the nature and the charge of the ions and also of the amount of free water available per ion, i.e., the total ionic concentration. The net effect is that the conductivity increases slower than proportional to the concentration, even if a solution contains only one salt such as NaC1, and is different for different salts (Fig. 1). Conductivity can even decline with a further increase in concentration, e.g., if additional salt is little dissociated but ties up some of the free water and/or causes an increase in viscosity. In solutions containing more than one salt, the contribution of one salt to the total conductivity depends not only on the fractional concentration of this same salt, but also on the concentration of all other solutes. A perfect method would give the conductivity or resistivity of a solution as a function of the concentrations of all solutes present. This is so complicated as to be impractical, and a simpler method must be found which is of acceptable accuracy. The Dunlap method, on the other hand. is too simple because it askmes that at any concentration the contrih-

Jan 1, 1967

Coal was found in many places in Montana by the early explorers and trappers but no commercial development was made until 1876, and very little coal was produced before 1885. All available data are given in Table 79 taken from U. S. Geological Survey Bulletin 356. [ ]

Jan 1, 1942