Search Documents

By J. J. Kramer, K. Foster

The orientation distribution of surface-energy -induced secondary recrystallized grains was determined. This work was conducted on thin sheets of a 3 pct Si-Fe alloy annealed under environmental conditions that furor grouth of grains with a (100) plane in the surface of the sheet. The texture was found to be extremely sharp and almost independent of sheet thickness. The distribution varied exponentially with the angular deviation from the {100} plane. It was possible to relate the distribution to the nu-cleation rate of the secondary rains as influenced by the surface-energy difference. THE role of surface energy in the secondary grain growth of cube-oriented grains (grains with a (100) plane in the plane of the sheet) in thin Si-Fe sheets has been previously discussed.1-4 In high-purity sheet material normal grain growth usually occurs until the grains have extended through the sheet. Further grain growth is inhibited by the thermal grooving of the boundaries at the sheet surface. However, additional growth of cube grains can occur by a secondary grain growth process under conditions where the (100) plane has a lower surface energy than other orientations. Apparently for these alloys, cusps exist in the polar plot5 of surface free energy with the lowest cusp energy occurring at the (100) orientations. This has been reported to be the result of preferential adsorption of sulfur on the (100) planes.6 As a result of this process, a distribution of orientations could arise from two possible mechanisms. First, when a cusp is present in the polar plot of surface free energy, there are orientations inside the cusp that have a lower surface energy than elsewhere on the polar plot. Also, at sufficiently high temperatures, flat surfaces whose orientations are inside or just outside the cusp (depending on its shape) can often thermally etch, yielding a microscopically stepped surface of even lower surface energy. As a result, grains oriented close to cube would also have a lower surface free energy, either because of the cusp shape or by thermal etching, and could possibly grow as secondary grains by the surface-energy phenomenon. One should thus observe a distribution in the surface orientation of the cube grains comprising the secondary structure. It is the purpose of this paper to investigate this orientation distribution experimentally and to discuss the factors involved in its formation. For this purpose, the surface orientations of a large number of secondary grains in various sheet thickness were determined by means of the Laue back-reflection X-ray technique. PROCEDURE A vacuum-melted 3 pct Si-Fe alloy containing a nominal impurity content of 0.005 wt pct was processed into strip. A single cold-rolling step of 90 pct reduction was used for each strip regardless of the final sheet thickness. Final strip thicknesses of 0.60, 0.30, 0.15, and 0.075 mm were used. Care was taken to insure that the final strip surface was smooth and flat. All strips of a given thickness were annealed together at 1200°C in dry hydrogen (dew point -70°C) to develop the desired secondary structure and to insure identical environmental annealing conditions. The annealing time was selected to develop a complete secondary structure in the thinner sheets but to permit the thicker sheets (0.60 mm) to have residual primary grains remaining. This was necessary to determine whether growth impingement could lead to one secondary grain consuming another at a greater angular deviation. For the X-ray determination of the surface orientation of the secondary grains, a special specimen holder was used. The camera and holder arrangement could be aligned by X-raying a grain in three positions rotated 180 deg to each other. Thus, with a small beam X-ray focus (1 mm), the surface orientation of any grain could be determined to within one-half a degree. The surface orientations of one hundred cube secondary grains were determined for each sheet thickness. The criteria of a secondary grain were its size relative to the sheet thickness and the number of sides of the grain observed in the sheet surface. (A primary recrystallized grain extending through a sheet will generally have six edges visible in the plane of the sheet, whereas a secondary grain will have many more when growing entirely into primary grains.) Grains were selected as randomly as possible by X-raying every secondary grain found along a line drawn on the strip. No attempt was made to determine the exact orientation of the planes of the surface, as many strips from randomly selected sheets were used. On1y the angular deviation of the surface plane from {100} was measured. In order to assess the volume distribution in the

Jan 1, 1965

By R. Schuhmann

Distribution of material in the fine sizes of a comminution product generally is well represented by the empirical equation' y = 100 (x/k)a [1] in which y — cumulative percent finer, x = particle size, a -= distribution modulus, and k = size modulus. Charles3 found that the energy consumption in comminution is usefully expressed by another empirical relation, E = Ak(1-D) [2] in which E = energy input per unit volume of material, A = a constant, k = size modulus based on Eq. 1, and n = a constant; (1-n) is the slope of a plot of log E vs log k. Holmes3 has presented energy equations similar to Eq. 2. The constants a and n in Eqs. 1 and 2 have been shown to depend both on the nature of the material and on the comminuting device. Moreover, Charles showed that within experimental error a and n are a — n+1 = 0 [3] Combining Eqs. 2 and 3, E = A k-a [4] In the first sections of this article it is shown that the energy equation, Eq. 4, can be derived directly from the size distribution equation for the fine sizes, Eq. 1. The derivations are made without assuming any of the specific relationships between energy and particle size which have been common in previous literature. For comminution processes in which Eqs. 1 and 4 adequately represent the experimental data, the constant A in Eq. 4 is found to be a simple and useful inverse measure of grindability. That is, A is the energy consumption per unit volume of comminution product finer than unit size as determined from the straight line portion of the log-log plot of the size distribution. These considerations all lead to a unifying hypothesis of comminution mechanism from which both Eq. 1 and Eq. 4 can be derived. Finally, it is pointed out that this hypothesis raises serious questions as to the significance of the Rittinger hypothesis, the Kick hypothesis, and other theories in which energy numbers are systematically assigned to various size fractions of comminution products in order to calculate theoretical energy consumptions. Derivation of the Energy Equation from the Size Distribution Equation: For simplicity, consider the comminution of 100 volumes of a feed material of relatively uniform particle size. The comminution process may be considered as the summation of many individual and independent comminution events. The extent of comminution is most easily expressed as the number of comminution events, z. In the first derivation, the key assumption is that the characteristics of the comminution events in a given crushing or grinding process are substantially constant and do not vary with the progress of the comminution process. Accordingly the characteristics of an average comminution event may be defined. In one such event, a quantity of energy $E is applied to a single particle of size f and volume $v. The crushing of this particle produces fine particles with a size distribution similar to that given by Eq. 1: yw=100(x/ka)a0 [51 In this equation yo, a0, and k0 are used to characterize the product of an individual comminution event rather than the product of the comminution process as a whole. In using Eq. 5, we will not be concerned with values of x close to the feed size f and will therefore assume only that the equation is applicable to the finest sizes of the material. In 100 volumes of total product, the actual volume of product finer than x from a single comminution event, or dy, is given by The total volume of material below size x, resulting from z events, is then given by y = z(dy) =z(dv) (x/ka)a0 =" Eq. 7 reduces to Eq. 1 when we let a, = a and [8a] z =100/dv (ka/k )1 or k = ka (zdv/100)-1/a [8b] Eq. 8a shows that the distribution modulus of the comminution product is the same as for the product of an individual comminution event. Eq. 8b shows how the size modulus of the comminution product k varies with the extent of comminution as measured by the number of events, z, or as measured by the fraction of the feed actually subjected to com- minution1 zdv/100. The energy input to 100 volumes of total feed, or 100E, is the sum of the energy inputs for all the comminution events: 100E =z (dE) [9]

Jan 1, 1961

By J. O. Brittain, E. P. Lautenschlager, D. A. Kiewit

Compression tests were run in the temperature range of 700° to 900°C ox 0' phase NiAl intermetal-lic alloys of several grain sizes. At these temperatures the minimum strengths were observed at the stoichiometric composition. While significant increases in strength occurved in both the low-nickel (vacancy) and high-nickel (substitutional) regions, the highest strengths were found in the high-nickel region. During deformation serrated flow was sometimes observed in the low-nickel alloys. After deformation transgranular cvacking and deformation striations were observed in all compositions tested. AS part of a general investigation of the properties of NiAl inter metallic compounds, a preliminary study of the role of point defects upon plasticity was made by high-temperature compression tests on ß' NiAl specimens of several grain sizes and compositions. ß' NiAl is an intermetallic compound having a CsCl structure and a rather wide range of composition from A1-45 at. pct to 60 at. pct Ni.1 According to Bradley and Taylor2 and to cooper,' it possesses a defect lattice in which departures from stoichiometry in the direction of decreased nickel content lead to the presence of vacant nickel sites (although Cooper's work indicates that a small amount of substitution also occurs) whereas departures on the high-nickel side lead to substitution of nickel on aluminum sites. NiAl forms congru-ently from the melt at approximately 1650°C,1 and thus has a higher melting point than either of its component elements. Up to this time, although this and other high-melting intermetallic compounds have been suggested for elevated-temperature usage,4 only the hardness4 and a few tensile-strength measurements5 have been reported for NiAl at high temperatures. In the present investigation the effects of composition upon the compressive-strength properties in a range of 700° to 900°C have been measured for NiAl of several grain sizes. EXPERIMENTAL PROCEDURES The alloys were made as described elsewhere6 from an A1-46.8 at. pct Ni master alloy furnished by the International Nickel Co. with additions of high-purity nickel and aluminum. The charges were vacuum-induction-melted in A12O3 crucibles with small amounts of helium added to the atmosphere to suppress vaporization. They were cooled slowly from the melting temperature to achieve uniform grain size. In order to refine the as-grown grain size a special rolling technique was developed. Alloys were packed into 0.10-in. wall-type 302 stainless-steel tubes which were partially filled with magnesium oxide to prevent bonding between the alloy and the steel jacket. The ends of the tubes were closed by hot forging, and the packets were then hot-rolled. The alloys with greater than 50 at. pct Ni were rolled at 1100°C, but it was found necessary to increase the temperature to 1350° C before alloys with less than 50 at. pct Ni would roll without cracking. With these temperatures, reductions as high as 48 pct were achieved in a single pass. The rolled alloys will hereafter be referred to as "fine grained" whereas the as-grown material will be designated "coarse-grained''. The compression specimens were made by cutting square cross-sectional pieces, approximately 3/16 by 3/16 by 1/2 in., with a water-cooled diamond cut-off wheel from the as-grown or the rolled alloys. Specimens were ground to their final dimensions by polishing through 3/0 grit silicon carbide papers. The final shape was a rectangular parallelepiped of square cross section having a height-to-width ratio of 3:1. Compression testing was carried out in a compression rig of our own design mounted on an In-stron Floor Model. The specimen chamber could be heated to 1000°C and was controlled within ±2°C. The compression rig was enclosed within a bell jar and was maintained at a 50 µ of mercury vacuum throughout the duration of the test. The test cham -ber was heated from room to test temperature within 15 min. Specimens were then held at the test temperature 30 min prior to testing. Previous experiments indicated that no grain growth would occur within this time. An Instron Variable Crosshead speed unit was used to adjust for small variations in specimen lengths in order to have a constant initial strain rate, €, for all specimens of a group. For the fine-grained specimens the strain rate was changed rapidly at constant temperature by a factor of 10 with the speed lever on the Instron. For a given € the compression data was analyzed in terms of true plastic strain (E) and true compressive stress (0).

Jan 1, 1965

By J. A. Burkhardt

Field measurements and theoretical studies have been made of pressure surges—momentary variations in fluid pressure—produced by movement of pipe in mud-filled boreholes. Pressure measurements were recorded by five pressure gauges located at various positions in the borehole. An important positive pressure peak was found to occur as the casing moved with maximum velocity. Important negative peaks were found as the casing was lifted from the slips and as brakes were applied to stop pipe movement. A rigorously formulated theory has successfully predicted the sequence and magnitudes of these positive and negative surges and has established a basis for understanding how they occur. Both the measurements and theory indicate that the most important pressure surge is usually due to viscous drag of the flowing mud. The theory of viscous-drag pressure surges has been approximated by simplified graphs and calculation procedures to facilitate ready use in field operations. Comparison of measured results with those predicted by the simplified theory shows that the magnitude of this surge can be predicted accurately. INTRODUCTION It is widely recognized that raising or lowering pipe in a fluid-filled borehole produces momentary variations in fluid pressure, commonly called pressure surges. Both negative (or "swabbing") surges and positive (or "fracturing") surges may occur. In 1934, Cannon1 measured the negative surges and showed that they could be large enough to cause flow of formation fluids into the well-bore and, in extreme cases, lead to blowout conditions. Later, Coins2 measured the positive surges associated with lowering pipe. His results and subsequent field operations strikingly demonstrated that pressure surges could be an important factor in some cases of lost returns. In addition, although the evidence is less clear than in the case of blowouts and lost returns, other investigators 3, 4 feel that pressure surges probably play a part in many instances of minor gas cutting, salt-water flow and other hole trouble. The importance of pressure surges in drilling operations led naturally to attempts to explain the physical causes, nature and magnitude of the surges. Cardwell5 was the first to publish a theory which allowed the quantitative prediction of momentary pressure variations. He assumed that the drilling fluid was a 300-cp Newtonian fluid in turbulent flow. Most field muds have a considerably lower viscosity and are generally believed to be Bingham plastic in nature.6 However, card-well's results were useful because they were presented in a form convenient for field use and, in some cases, gave a reasonably accurate predicted value for the maximum pressure surge. Subsequently, Ormsby7 published a more comprehensive theory of pressure surges. He discussed both laminar and turbulent flow and considered the theory of mud-bypass devices for reducing pressure surges. As a consequence of his more rigorous approach, his results were more accurate but more complex and difficult to use. Further, both Ormsby and Cardwell considered only the pressure surge arising from viscous drag of the moving mud. Clark later published idealized graphs of surges and presented equations for predicting their magnitudes. In addition to pressure variations arising from viscous drag, he considered those caused by inertial effects. His theory was in this respect more complete than those of Cardwell and Ormsby, although he did not discuss pressures due to breaking of the gel. Furthermore, his equations, while not exceptionally complicated, were too complex for ready use at a drilling location. One difficulty common to all three theories is that none was tested rigorously by direct comparison with measured pressure surges. Their accuracy, therefore, could, not be demonstrated. Further, the two theories based on most realistic assumptions (Ormsby and Clark) required the solution of one or more rather complex algebraic equations. The research described in this paper was undertaken to supplement that described and to overcome some of the difficulties noted. It seemed obvious that a fully satisfactory study of pressure surges should encompass three main phases. 1. A valid theory useful in all field situations must be developed. This theory must be based upon realistic assumptions, must be formulated rigorously and should lead to clear concepts whereby the nature of pressure surges can be easily understood. 2. The theory, however complex and involved, ultimately must be presented in simplified form for convenient field use. This may involve extensive machine computations and the use of figures and empirical equations. 3. The accuracy of the simplified equations must be established by comparing measured pressure surges with those predicted by the theory. These must agree both in their characteristic nature and in magnitude. 'This means that careful measurements of surges occurring in actual field operations must be made.

By G. R. Pickett

Examples are presented which show that the velocity~ amplitude, attenuation and apparent frequency of several acoustic waves can be recorded in the borehole. Examination of such recordings, termed "character" logs, indicates that the wave types observed include a refracted compressional wave and a wave which travels with formation shear velocity. Laboratory data are used to show that compressional and shear wave velocities are dependent on porosity, effective stress and lithology; but that the change in reciprocal velocity per unit change in porosity is larger for shear waves than for compressional waves. We, therefore, conclude that. the accuracy of porosity determinations can sometimes be improved by use of shear wave velocities, provided that the shear wave amplitudes are large enough to delineate the shear arrival from the preceding compressional arrival on the character log. Borehole data are presented which show that the difference between shear wave and compressional wave reciprocal velocities can be used to predict porosities. This is a refinement which may allow the prediction of porosities from single-receiver acoustic logs without introduction of errors from borehole fluid traveltimes. Laboratory and field data are presented to show that the relationship between compressional and shear wave velocities can be used to indicate lithology. An example is presented to show that fractures usually cause a greater reduction in borehole shear wave amplitudes than in compressional wave amplitudes, an effect which may offer a more reliable means of detecting fractures. The complexity of the borehole acoustic wave train can rake presently available cement bond logs highly sensitive to the gate and bias settings used. The character log offers a means to circumvent possible misinterpretations by recording all amplitudes, from which the interpreter can select the appropriate data for evaluating the cement bond. Character logs may also be used as a quality control for open-hole transit-time logs when existence of small compressional wave amplitudes interferes with the proper functioning of bias-controlled timing devices. Evaluation of the potential uses of character log data is not complete; but a character log presented in a form convenient for routine use would be a desirable addition to currently available logs. To summarize, possible applications for such a log in formation evaluation include the following (1) quality control of transit-time logs, (2) refinement of porosity predictions, (3) determination of lithology, (4) improvement of fracture detection and (5) improvement of cement bond evaluation. Suggestions are made regarding the requirements for a suficient but practical character log for routine use. INTRODUCTION Acoustic logs have become a widely used porosity tool in formation evaluation. In addition, there is a growing application of acoustic logs in cement bond evaluation and fracture detection. These applications have mainly involved the use of logs of first-arrival transit times and amplitudes and have not included detailed studies of the complete signal. The purpose of this paper is to show that significant benefits in formation evaluation can be gained by a more complete use of the acoustic wave train generated in the borehole by an acoustic logging tool. We hope that this discussion will also stimulate further development of logs suitable for routine use so that these benefits may be realized. Examples of acoustic wave train logs, termed "character" logs, are presented to show that several identifiable acoustic waves are present in the borehole. The measurable characteristics of these acoustic waves and some of their relations to formation properties of interest are also discussed. The more obvious potential uses of character logs are listed, and some suggestions are made regarding the requirements for a sufficient but practical character log for routine use. CHARACTER LOGS Some 10 years ago, Vogel' and Summers and Broding' noted that the signals received uphole from an acoustic logging tool located in a borehole had a number of interesting characteristics. The logging tool consisted of two or more pressure transducers spaced on an acoustically insulated body (Fig. la). One of the pressure transducers was used as a transmitter to generate pressure waves in the borehole fluid. The other transducer served as a receiver to detect any pressure waves reaching it in the borehole. The receiver then converted these pressure waves to electrical signals which were transmitted to the surface and displayed on an oscilloscope as a record of time vs receiver-signal amplitude. Fig. lb is a schematic representation of a typical record. The interesting characteristics seen in the earlier' and subsequent experiments were (1)

By C. F. Allen, G. B. Walker

The sink-float methods designated by heavy-media separation processes were pioneered by C. Erb Weunsch for the treatment of base metal ores as an improvement over jigs. The work of Weunsch was further developed by Victor Rakowsky and The American Zinc, Lead and Smelting Co. Early in the development of the processes, the inherent unsuitability of galena as the solid constituent of the medium was recognized and ferrous media amenable to magnetic recovery and control were developed. The high efficiency and low cost of magnetic recovery and cleaning of ferrous media regardless of particle size, slime contamination, or surfacial oxidation had led to the adoption of ferrous media by all of the sink-float plants operating under the heavy-media separation processes patents controlled by American Zinc, Lead and Smelting Co. Approximately 2,000,000 tons of base metal and nonmetallic minerals are treated each month by these methods. Heavy-media separation processes are a modern practical and economical adaptation of the well-known laboratory procedure for separating a mixture of two solids by immersing the mixture in a liquid having a specific gravity intermediate the specific gravities of two solids. The lighter solid floats while the heavier sinks. This method of separation has been attempted on a commercial scale, but the high loss and high cost of the organic liquids halted the development of the process. Many attempts have been made to simulate a heavy liquid by using a suspension of a finely divided solid in water. If the solid phase of the suspension is ground fine enough, the suspension can be made stable or so slow settling that a substantially uniform specific gravity can be maintained from top to bottom of the bath. However, any material separated by such methods will inevitably be contaminated by some slime which will eventually accumulate in the bath and cause a viscous medium at the expense of separating efficiency. Therefore, it is necessary to provide means for continually cleaning a portion of the medium to eliminate slime at the same rate at which it is introduced to the medium. The problem of efficiently cleaning the medium limits the minimum grain size of the solid of the suspension in the case of the Chance sand process for cleaning coal, because de-cantation is the only cleaning method available. If the sand is too fine, it will be lost along with the slime. Therefore, coarse sand must be used, and to maintain a semblance of a uniform suspension, it is necessary to use strong rising water currents. The combination results in a separation based more on hindered settling classification than on sink-float principles. As previously mentioned, galena was used as the solid constituent of the medium during the early stages of the development work. The high specific gravity of galena made it suitable for the preparation of medium for high specific gravity separations. Galena can be cleaned by either decantation or by froth flotation. As with sand, de-cantation limits the minimum particle size of the media that can be cleaned without excessive loss. Froth flotation for cleaning galena medium has been used, but the problem of floating fine galena that has been exposed to extensive oxidation is well known to be a most difficult one. Last year the largest heavy-media plant m the world, and the second plant to be installed, converted from galena medium to ferrous medium despite the fact that the ore contains galena which can be used as medium. The change to ferrous medium has been beneficial in many ways. Today all the heavy-media plants have been converted from galena to ferrous media. Unquestionably, ferrous media have the widest application of any media developed, for the following reasons: 1. Ease of recovery and cleaning by magnetic means. Particle size or surface condition not a factor. 2. Low consumption per ton of ore treated. 3. Resistance to abrasion. 4. Widest range of media densities, including higher workable densities (1.25 to 3.4) than have been found possible with nonferrous media. 5. Space required for recovery and cleaning of ferrous media is considerably less than that for nonferrous media. 6. Ferrous media require lower capital investment and operating costs for media recovery and cleaning. Advantages of Heavy-media Separation Processes Heavy-media separation processes offer the following positive advantages, amply demonstrated on a wide variety

Jan 1, 1950

By W. Rostoker, R. F. Domagala, R. P. Elliott

The phase equilibria of the Hg-Th system over the composition range 0-100 pct Th and temperatures up to 1000°C have been studied for a small-volume, closed system. The solubility of Th in liquid Hg is about 5 pct at 300°C and decreases sharply with decreasing temperature. Two intermediate phases occur, Hg3 Th and HgTh. The structures of these are hexagonal (nonideally close-packed) and face-centered cubic, respectively. The HgTh phase decomposes eutectoidally at 400°-500°C. The solubility of Hg in solid thorium seems to be negligible. AFULL-phase diagram for this system would have to be defined on temperature-composition-pressure co-ordinates. This paper describes the pseudo phase diagram of a closed system, that is, where the alloy enclosed in a small volume equilibrates with a vapor pressure of mercury dictated by composition and temperature. Because of the experimental difficulties in studying a system of this nature, many of the phase relations can only be sketched. Alloy Preparation Alloys over the full range of composition were made from triple distilled mercury and one of two grades of thorium. For the bulk of the work, a calcium-reduced metal in sintered pellet form of reported 99+ pct total thorium content was used. Arc-melted specimens of this thorium gave a hardness of 135 VPN. The microstructure showed small primary dendrites of ThO2. A number of alloy compositions were made with a high-purity, iodide-decomposition thorium metal. The are-melted hardness of a button of this material was 35 VPN. Although the microstructure of the arc-melted specimens showed no dendrites of ThO2, there was definite evidence of an unidentified phase enveloping the grain bound-aries. There were no distinguishable differences between the constitution of alloys made with the two grades of thorium metal. Under normal conditions thorium is not wetted by liquid mercury. The film of ThO2 on all thorium metal cannot be penetrated by either liquid or vaporous mercury. It was therefore necessary to comminute thorium in the presence of mercury under such conditions that oxide films could not reform on the newly exposed metal surfaces. This was accomplished by the use of a high-speed, carbide-tipped rotary cutter incorporated in a chamber purged with argon and connected at the bottom to a demountable Vycor bulb containing a weighed amount of mercury. This experimental device is fully described in a separate paper.1 Alloy compositions were calculated by weighing the empty bulb, the bulb containing the mercury, and the bulb containing the mercury and the thorium chips. Many alloys were analyzed chemically for thorium and/or mercury after subsequent homogenization; the agreement between analyzed and calculated compositions was invariably very close. Bulbs containing the requisite amounts of mercury and fine thorium chips were clamped off, removed to a sealing unit, evacuated and sealed. Amalgamation under these conditions proceeded rapidly even at room temperature. To insure homogeneity, the specimens were annealed to 300-400°C. Alloys containing less than 30 pct Th remained pasty after all treatments, indicating an equilibrium condition of liquid plus solid. Alloys with more than 30 pct Th were transformed into a dark powdery product. These latter specimens were annealed for times of up to 1 week to complete interdiffusion. Many of the alloy compositions are pyrophoric. On exposure to air they oxidize with considerable evolution of heat to a mixture of ThO2 and free mercury. It was mandatory that alloy specimens be handled in a "dry box" purged thoroughly with argon. All X-ray diffraction specimens were powdered, screened, and sealed in capillary tubes within the dry box. Experimental Procedures Thermal analysis experiments, useful only in the mercury-rich region of the system, were conducted with the alloys in their original containers. A reentrant thermocouple well formed an integral part of the bulb. These bulbs were heated in a silicone oil bath and cooled in a dry ice-acetone mixture. The rates of heating and cooling were slowed by immersing the specimen bulb in a larger tube containing silicone oil. This provided a suitable thermal lag. In all tests, pure mercury was run as a basic standard. While the invariant reaction at about the melting point of mercury was detected by thermal analysis, the heat effect at the liquidus was not sufficient to produce an inflection in the cooling curve. It was necessary to determine the liquidus temperatures at the mercury-rich end of the system by "breaks" in electrical reslstivity versus temperature curves for individual alloys. The apparatus for this purpose consisted of a pyrex tube about 2 in. diam and 12 in

Jan 1, 1959

By P. A. Witherspoon, S. P. Neuman

Evaluating the permeability of a caprock overlying a potential gas storage reservoir is a very critical problem. Pumping water from the reservoir can be used as an evaluation tool in analyzing this problem. Fluid level changes that occur in the aquifer us well as in the caprock can be measured with appropriately placed wells. If the leakage of water from the caprock into the aquifer is considerable, the effects will be apparent in the aquifer. If the leakage is slight, however, it will not be possible to detect it with certainty from observations in the aquifer alone. Fluid level measurements in the caprock must be relied upon. and improved methods of analyzing such effects have been developed which are based on a theoretical analysis of fluid flow through a caprock of infinite thickness. An example applying these methods to field data is discussed. INTRODUCTION One of the most critical problems in evaluating an aquifer gas storage project is determining the tightness of the caprock overlying the formation to be used as the storage reservoir. A formation that has previously held oil or gas obviously has a suitable caprock, but an aquifer that contains only water gives no such assurance. A number of aquifer projects in the United States have been troubled by gas leaking out of the intended storage zone, and the ensuing difficulties have led to the development of new evaluation methods. One of these new methods is pump testing wherein water is removed from the aquifer at some controlled rate prior to injection of gas. This fluid withdrawal causes a pressure drop to move out through the aquifer for considerable distances in a matter of days or weeks. Depending on the properties of the caprock, a pressure transient can also pass upward (as well as downward) through the caprock layers adjacent to the aquifer. Thus, if the operator has placed observation wells at appropriate distances from the pumping well, the rapidity with which the pressure transients reach different points in the system can be used to investigate the fluid transport properties of both the aquifer and its caprock. The usefulness of pump testing has been recognized by groundwater hydrologists for many years as a means of determining the potential yield and properties of aquifers used in water supply They have introduced the term "leaky aquifer" for a system in which an aquifer is overlain (or underlain) by semipermeable caprock layers. The ease with which water leaks into the aquifer during pumping can, of course, be very beneficial in bringing additional water to the pumped well. Hydrologists have therefore devoted considerable attention to this prob-lem. From the gas storage standpoint, however, the tighter the caprock layers that overlie the intended storage reservoir, the better are the conditions for minimizing or eliminating any vertical migration of gas. Thus, after a suitable geologic structure has been found, the emphasis in aquifer storage projects is in determining that the caprock is tight. Attention has recently been focused on the use of pump testing as one approach to solving this problem.23,24 This paper presents a further development on evaluating the permeability of a slightly leaky caprock when the caprock is of infinite thickness. From the practical standpoint, this means that the caprock layers are thick enough that pressure transients do not reach the outer boundaries of the system during the pumping test. In a subsequent paper, an analysis of the case where the caprock is of finite thickness will be presented. PREVIOUS WORK ON LEAKY AQUIFERS Jacob" developed a partial differential equation describing the flow of water in an aquifer of permeability k that is overlain by a leaky caprock of permeability k'. Fig. 1 shows a schematic cross-section of the system under consideration. One of his principle assumptions was that if k > > k', the direction of flow is essentially vertical in the caprock and horizontal in the aquifer. Neuman19 confirmed the validity of Jacob's assumption using a mathematical model. Another assumption was that a permeable source layer overlies the caprock (Fig. 1) and is able to maintain a constant hydraulic head at the upper boundary of the caprock. By neglecting the effects of compressibility within the caprock, Jacob1* developed a solution for a bounded circular aquifer. Later, Hantush and Jacobx5 used the same assumptions to solve the case of an infinite radial aquifer that is pumped at a constant rate. Their solution may be expressed in di-mensionless parameters by

By H. D. Hodges, J. K. Godbey

In order to better understand the fracturing process, bottom-hole pressures were measured during a number of typical fracturing operations. A recently developed system was used that allows simultaneous surface recording of both the bottom-hole and wellhead pressures on the same chart. The results from six fracruring treatments are summarized on the basis of the pressure data obtained. Al-though no complete analysis is attempted, the value of accurate pressure measurements is emphasized. Important characteristics of the bottom-hole pressure record do not appear at the wellhead because of the damping effect of the fluid-filled column. In four of the six treatments described, the formations apparently fractured during the initial surge of pressure with only crude oil in the well. The properties of the fluids used during the treatments are given and the fluid friction losses are obtained directly from the pressure records. This technique is also shown to be adequate for determining when various fluids, used during the process, enter the formation. INTRODUCTION Hydraulic fracturing for the purpose of increasing well productivity is now accepted in many areas as a regular completion and workover practice. Numerous articles have appeared in the literature discussing the various techniques and theories of hydraulic fracturing'. In general, three basic types of formation fractures are recognized today. These are the horizontal fracture, the vertical fracture, and fractures along natural planes of weakness in the formation'. Any one or all three of these fracture types may be present in a fracturing operation. However, with only the wellhead pressure record as a guide, it is difficult at best to determine if the formation actually fractured, and is almost impossible to determine the type of fracture induced. These difficulties arise in part because the wellhead pressure record, especially when fracturing through tubing, does not accurately reflect the pressure variations occurring at the formation. Several factors contribute to this effect and preclude the possibility of using the wellhead pressure as a basis for accurately calculating the bottom-hole pressure. These factors are: 1. The compressibilities of the fluids which damp the pressure variations. 2. The changes in the densities of the fluids or apparent densities of the sand-laden fluids. 3. The flowing friction of the various fluids and mixtures, which is dependent on the flow rates and the condition of the tubing, casing, or wellbore. 4. The non-Newtonian characteristics of a sand-oil mixture and its dependence upon the fluid properties, the concentration of sand, and the mesh size used. 5. The unknown and variable temperatures throughout the fluid column. Because of these reasons it was determined that in order to obtain a more accurate knowledge of the nature of fracturing, the bottom-hole pressure must be measured along with the pressure at the surface during a fracturing treatment. Even with accurate pressure data, a reliable estimate of the nature of fracturing is still dependent upon knowledge of the tectonic conditions. However, the hydraulic pressure on the formation is basic to any approach to a complete analysis. In order to accomplish this objective a system was developed to record the wellhead and bottom-hole pressures simultaneously at the surface. By recording both pressures on a dual pen strip-chart recorder, it was possible to greatly expand the time scale so that rapid pressure variations would be faithfully recorded. By such simultaneous recording, time discrepancies inherent in separate records are eliminated, thus overcoming one of the most difficult problems associated with bottom-hole recording systems. This paper illustrates the results obtained by using this system during six typical fracturing operations. All of these tests were taken in wells that were treated through tubing. By a direct comparison of the wellhead and bottom-hole pressures, the importance of obtaining complete pressure information during a fracturing treatment is emphasized. THE INSTRUMENTATION AND PROCEDURES The bottom-hole pressure measuring instrument consisted of a pressure-sensing element, a telemetering section, and a lead-filled weight or sinker bar. The pressure-sensing element used was an isoelastic Amerada pressure-gauge element. By using an isoelastic element, no temperature compensation was necessary in the tests described, since the temperature was believed to be well below the maximum temperature limit of 270°F. The rotary output shaft of this helical Bourdon tube element was coupled to a precision miniature potentiometer. The rotation of the pressure-gauge shaft thus changed the resistance presented by the potentiometer

By P. Pietrokowsky, T. E. Tietz, J. E. Dorn

The amount of solid solution hardening in aluminum alloys was found to be dictated by two factors: the lattice strain, and the change in the mean number of free electrons per atom of the solid solution. To obtain this correlation it was necessary to assume that aluminum contributes two electrons per atom to the metallic bond. WHEN the modern scientific method of analysis was first being formulated, Francis Bacon recorded in his "Essays" (circa 1600) that "an alloy . . . will make the purer but softer metal capable of longer life." During the intervening centuries voluminous data have been reported which demonstrate that the additions of alloying elements do in fact increase the hardness and strength of the pure metals. Nevertheless, the significant details of this problem on the unique effect of each element toward enhancing the mechanical properties of alloys only recently have been subjected to systematic scientific scrutiny. The major objective of this investigation is to determine how minor additions of alloying elements affect the plastic properties of polycrystalline aluminum alloys. By means of such studies it is hoped to provide not only data on the solution strengthening of aluminum alloys, but also a body of facts which will supplement the knowledge already available on the factors responsible for solution hardening in general. A review1"10 and analysis1' of the existing data on the effect of solute elements on the plastic properties of solid solutions reveal that our current knowledge on solid solution hardening is somewhat meager, inconsistent, and inconclusive. Many of the inconsistencies are undoubtedly attributable to the influence of unsuspected factors, such as purity; or uncontrolled factors, such as grain size, on the plastic properties of alloys. Nevertheless the following conclusions might be tentatively accepted: 1. Addition of solute elements invariably increases the yield strength, tensile strength, and hardness of the host element. 2. The rate of strain hardening, in general, increases with the concentration of the alloying element. 3. The strengthening effect in ternary alloys is the sum of the individual strengthening effects of the two solute elements as measured in their binary alloys. 4. The lattice strain is one factor that affects the strengthening of the alloy but it is not the only factor. 5. A second factor might be the difference in valence between the solute and solvent metals. All of the available evidence is in complete agreement with the first conclusion; the remaining conclusions, however, are not in agreement with all of the published data, but, in each case, the major weight of the existing evidence favors these deductions. Additional investigations will be required before most of these tentative conclusions can be accepted without reservation. In the following report an extensive investigation of the plastic properties of binary aluminum alloys is described. This work was undertaken in an attempt to shed more light on the general problem of solid solution hardening. Materials for Test: Aluminum was selected as the solvent metal for the present investigation on the effect of solute elements on the plastic properties of alloys. This choice was made for several reasons: (1) There appears to be little fundamental data in the published literature on the effect of solute elements on the properties of high-purity aluminum alloys. In view of the ever increasing economic importance of aluminum, such data would be of basic interest to the metallurgists concerned with the development of new aluminum alloys. (2) Aluminum is thought to be only partially ionized in the metallic state1' and consequently it might provide more complex relationships of the mechanical properties with the concentrations of the solute elements than more simple fully ionized solvents would reveal. (3) The data on aluminum alloys will provide a broader basis for correlations between the mechanical properties of metals in general and the concentration and atomic properties of the solute elements than is now available. Some complications, however, attend the selection of aluminum: The solubility of the various elements in the alpha aluminum phase are quite restricted, and not always well known. Consequently, only dilute solid solutions are available for study. This, however, may be somewhat advantageous because the dilute solution laws presumably are simpler than those applying to concentrated solutions. In addition, strain-hardened pure aluminum is known to recover at atmospheric temperatures. Very likely its alloys exhibit slower recovery rates. Thus, the secondary factor of effect of alloying elements on recovery might complicate the data. Such compli-

Jan 1, 1951

Background Carbon monoxide (CO) is an odorless, colorless gas that can cause illness and death by asphyxiation. Although the toxicity of CO is understood, CO exposure can occur from unrecognized sources. On April 2, 2000, a couple and their newborn infant were poisoned by CO migrating through the ground from blasting at a nearby coal strip mine into their home near Kittanning, Armstrong County, PA. They were treated at the hospital and diagnosed with CO poisoning. The infant had a carboxyhemoglobin level of 31%, the father 28%, and the mother 17%. Carboxyhemoglobin is the compound formed in the blood when CO is breathed. Persons not exposed to CO have carboxyhemoglobin levels of 0.3%-0.7%, and cigarette smokers have levels of up to 9%. Following release from the hospital, the family installed a CO detector in the basement of their home with the help of the local fire department. This Technology News briefly describes this incident to help increase awareness of the problem. It is discussed in more detail by Eltschlager et al. [2001]. Figure 1 shows the coal strip mine believed to have generated the CO. The initial suspect for the source of the CO was the furnace in the house. Only later did it become apparent that blasting at the nearby strip mine might be the culprit. A State investigation concluded that CO had migrated approximately 500ft from the blast, through the ground, and into the home. Figure 2 shows the locations and order of blasts at the mine. Initially, the mine did not plan to blast. Overburden generally consisted of weathered shale that could be dug without blasting. However, the mine decided to blast when hard sandstone that could not be dug out was encountered within 3 ft of the coal top. The blasting was intended to break up the sandstone. Blasting was done using bulk ammonium nitrate-fuel oil (ANFO) in 6.25-in holes 25-30 ft deep on a 16-ft by 16-ft pattern, with charge weights ranging from 17 to 170 lb. The closest blast to the home was 430 ft on April 17, 2000. The distance from the home to the blast area on the day when CO was first reported (March 31, 2000) was 500 ft. Twenty blasts were detonated at the mine between March 7, 2000, and April 20,2000. The blaster was careful to prevent fly rock since another home was only 150 ft away and a garage was 50 ft away. The quantity of explosive used in the blasts was sufficient to break the sandstone, but was less than would normally be used to blast overburden. The holes were typically one-third explosive and two-thirds stemming, with powder factors averaging 0.43 lb/yd3. Additionally, the muck was not immediately excavated after each blast. The heavy confinement on the explosive acted to prevent the typical release of blasting fumes into the atmosphere. Instances of CO migrating from blasts into homes have occurred before, but generally the distances involved were under 150 ft. It is believed that the blast design contributed to the confinement of CO in the ground, and discontinuities in the ground strata facilitated migration toward the residence. Upon inspection of the blast pitwall, a regular system of joints was observed. These joints are oriented roughly from the blast pit toward the house (figures 3-4).Blast-generated CO appears to have been driven into the joint system, displacing the air. When the joint system was saturated, the next succeeding blast pushed the CO into an uncased well next to the house (a high level of CO has been measured in the well shortly after a blast). From there, the CO entered the French drain system and then the basement of the house. The joints are vertical cracks through rock layers that occur on a regular spacing (figure 3). They are most common near valley slopes and are caused when valley walls converge as the stream cuts down through the rock layers. Often called hill seams, they roughly parallel the valley walls, but can curve and split, creating a pathway for gas movement (figure 5). These fractures are often encountered when underground mining proceeds close to outcrop. The system of fractures at the Kittanning blast pit was well developed and provided a path for transmission of CO both through the sandstone and up and through the overlying shales. Blasting engineers should be able to distinguish naturally occurring fractures from blast fractures and note the frequency, development, and orientation of the hill seams and their proximity to occupied houses. The limits of transmission of

May 1, 2001

By E. C. Hopkinson, A. H. Youmans, R. A. Bergan, H. I. Oshry

A new log has been developed for quantitative formation evaluation which is based on a measurement of the length of time slow neutrons survive before they are captured in the rocks and fluids. The logging instrument employs a cyclically pulsed neutron generator and a gated scintillation counter which is synchronized with the source. The source emits short, intense bursts of 14 mev neutrons once every 1,000 microsec and is quiescent between bursts. During the period the source is quiescent, the detector is electronically actuated for two independent preselected intervals. A comparison of the counting rates during these two intervals gives a measure of the rate of decay of the slow neutrons and of the associated gamma radiation. The average neutron lifetime in most earth formations is in the range from 50 to 500 microsec. It can be measured during a continuous logging operation at conventional logging speeds. The design of the logging instrument is described and the results of tests are compared with theoretical predictiom. Formulas are developed which give the relationship between log response and formation properties. It is shown that the method is particularly sensitive to formation fluid salinity, and that salt water saturation can be measured accurately in either cased or open hole. The measurement can be made independent of borehole size, fluid type, casing and tool position in the hole by properly selecting the intervals during which the measurements are made. The results of tests with a prototype logging tool are given. INTRODUCTION A new nuclear logging system has been developed which employs the Accelatron,* an accelerator-type neutron source, and accurately measures formation brine saturation in an entirely new way. It has produced a type of formation log with better sensitivity, greater sampling depth and simpler quantitative interpretation than any other nuclear log thus far suggested. The new Neutron Lifetime Log* employs a pulsed electromechanical neutron source and a synchronously gated radiation detector. A prototype instrument has been field tested during recent months to demonstrate the operability of the apparatus and the feasibility of the method. Tests in wells and simulated boreholes have confirmed theoretical predictions and have shown that formation param ters can be measured independent of casing and other borehole parameters. Preliminary results of field tests have indicated that the log may have important and widespread applications. BASIC PRINCIPLE OF NEUTRON LIFETIME LOG The Neutron Lifetime Log is based on the fact that neutrons emitted by a source in a well are rapidly but not instantly captured by the material around the source. Their capture is a matter of statistical probability; the greater the number of capturing nuclei and the greater the "capture cross section", the greater is the probability that a neutron will be captured quickly. The average life of a thermal neutron in vacuum is about 13 minutes, but in common earth materials, the average neutron life ranges between extremes of about 5 rnicrosec for rock salt and perhaps 900 microsec for quartzite. The Neutron Lifetime Log responds to variations in this average neutron life. The theoretical basis for a log of this general type has been well understood by nuclear logging experts in many laboratories both in America and in Russia, and develop mental work along these lines has been in progress for many years. The Russian literature has reported both theoretical and experimental work1,2 but in this country there have been no published reports of progress toward a practical logging instrument. The logging instrument is designed to measure radiation produced by slow neutrons during selected intervals when no neutrons are being emitted by the source. The source is arranged to emit neutrons in bursts or pulses. During the quiescent interval between the pulses, it is possible to observe the exponential "decay" of the neutrons and the neutron-induced radiation as the individual neutrons progressively disappear due to capture by atoms in the formation or the borehole. When a short pulse of 14 mev neutrons is emitted by a source in a borehole, the individual neutrons are slowed to thermal energy within a few microsec. Thus, a cloud of "slow" neutrons is formed around the source within 10 to 50 microsec after the pulse. This cloud is most dense within a few inches of the source, and is progressively less dense out to a radius of about 3 ft, where radiation from the source is practically undetectable.

Jan 1, 1965

By R. R. Estill

THE rank of the Ruhr coal ranges from a high volatile bituminous coal to an anthracite, depending to some extent on the original depth of the seam. The average Ruhr coal corresponds to a soft bituminous American coal of a coking quality. The average thicknesses of individual coal seams being mined are also comparable (59 in. against 65 in. in the United States). However, consideration of seam conditions and mining conditions other than those just mentioned emphasizes differences rather than similarities with United States soft coal. In general, the Ruhr seams now being mined are much more folded and inclined than American seams. Dips of 20' and 30" are common in seams now being worked, and 30 pct of the coal reserves in the district are in seams dipping more than 35". Only on the tops and bottoms of folds do we find rather flat coal seams. In addition to the folding there is extensive displacement by cross faulting plus a certain amount of strike faulting of an overthrust nature, which results locally in doubling or omission of seams. Because of the long history of mining in the Ruhr, nearly all coal lying near the surface has long since been mined out, and we find that the average depth of mining is at present about 2300 ft below the surface. Deep mining, folding, and faulting result in seam conditions requiring a great deal more roof support than one finds in American soft coal mines. In fact only in the anthracite district and the Rocky Mountain and Pacific coal fields do we find somewhat similar conditions. It is easy to say, therefore, that the problem of mechanization of coal cutting and loading in the German mines is quite different from that which we have so effectively met in America with our mobile cutters and loaders, duck bill loaders, and a room and pillar system of mining our drift and slope mines. Partly because of more limited coal reserves, the traditional German mining system is largely the longwall method, which gives an almost complete coal recovery. Backfilling must be extensively practiced to protect the longwall faces, the over and underlying seams and workings, and especially the surface industrialized areas and barge canals. The German engineers have accordingly concentrated their efforts on the design of cutters, loaders, and conveyors suitable to longwall methods rather than room and pillar methods. Undercutters with cutter bars like American models have been in use in the Ruhr since well before World War 11. In 1941 they accounted for 8.5 pct of the production. This percentage, of course, includes coal which was undercut but nevertheless had to be broken down with air hammers or with explosives. The most common of these cutters is the Eickhoff Standard cutter (see fig. 1). This machine does about 95 pct of the undercutting in the Ruhr today, and is available with either compressed air or electrical power and in at least four different sizes. A variation of the cutter is this one with two cutter bars (fig. 2). At the end of 1947 about 200 of these machines and similar cutters were accounting for 13.2 pct of the total production, a production which was, however, only 60 pct of the 1941 production rate, so that the actual cutter tonnage was only up to a small amount over 1941. In 1941 about 3 pct of the production was accounted for by shearing machines making their cut perpendicular to the longwall face. They were similar to those used in the States. These machines are today considered obsolete and now account for only 0.7 pct of the total production. They are located at only a few mines and at present do not seem to have much of a future in the Ruhr. For the future, the Ruhr miner is looking forward to rather extensive mechanization of face work, with two major types of equipment being developed almost simultaneously. On one hand there is the development of cutter loaders for use in relatively hard coal. They represent the further extension of ideas developed after relatively long experience with the Eickhoff cutter. On the other hand there has been since 1942 an intense interest in the Ruhr in the development of face-stripping methods, particularly by the Kohlenhobel (coal plow) and its modification. At the end of 1947 these cutter loaders, Kohlen-hobels and scrapers together were actually accounting for only about 1.4 pct of total production while air hammers still broke 77.1 pct and as much as 1.2 pct was actually broken by hand picks. However,

Jan 1, 1951

By R. R. Estill

THE rank of the Ruhr coal ranges from a high volatile bituminous coal to an anthracite, depending to some extent on the original depth of the seam. The average Ruhr coal corresponds to a soft bituminous American coal of a coking quality. The average thicknesses of individual coal seams being mined are also comparable (59 in. against 65 in. in the United States). However, consideration of seam conditions and mining conditions other than those just mentioned emphasizes differences rather than similarities with United States soft coal. In general, the Ruhr seams now being mined are much more folded and inclined than American seams. Dips of 20' and 30" are common in seams now being worked, and 30 pct of the coal reserves in the district are in seams dipping more than 35". Only on the tops and bottoms of folds do we find rather flat coal seams. In addition to the folding there is extensive displacement by cross faulting plus a certain amount of strike faulting of an overthrust nature, which results locally in doubling or omission of seams. Because of the long history of mining in the Ruhr, nearly all coal lying near the surface has long since been mined out, and we find that the average depth of mining is at present about 2300 ft below the surface. Deep mining, folding, and faulting result in seam conditions requiring a great deal more roof support than one finds in American soft coal mines. In fact only in the anthracite district and the Rocky Mountain and Pacific coal fields do we find somewhat similar conditions. It is easy to say, therefore, that the problem of mechanization of coal cutting and loading in the German mines is quite different from that which we have so effectively met in America with our mobile cutters and loaders, duck bill loaders, and a room and pillar system of mining our drift and slope mines. Partly because of more limited coal reserves, the traditional German mining system is largely the longwall method, which gives an almost complete coal recovery. Backfilling must be extensively practiced to protect the longwall faces, the over and underlying seams and workings, and especially the surface industrialized areas and barge canals. The German engineers have accordingly concentrated their efforts on the design of cutters, loaders, and conveyors suitable to longwall methods rather than room and pillar methods. Undercutters with cutter bars like American models have been in use in the Ruhr since well before World War 11. In 1941 they accounted for 8.5 pct of the production. This percentage, of course, includes coal which was undercut but nevertheless had to be broken down with air hammers or with explosives. The most common of these cutters is the Eickhoff Standard cutter (see fig. 1). This machine does about 95 pct of the undercutting in the Ruhr today, and is available with either compressed air or electrical power and in at least four different sizes. A variation of the cutter is this one with two cutter bars (fig. 2). At the end of 1947 about 200 of these machines and similar cutters were accounting for 13.2 pct of the total production, a production which was, however, only 60 pct of the 1941 production rate, so that the actual cutter tonnage was only up to a small amount over 1941. In 1941 about 3 pct of the production was accounted for by shearing machines making their cut perpendicular to the longwall face. They were similar to those used in the States. These machines are today considered obsolete and now account for only 0.7 pct of the total production. They are located at only a few mines and at present do not seem to have much of a future in the Ruhr. For the future, the Ruhr miner is looking forward to rather extensive mechanization of face work, with two major types of equipment being developed almost simultaneously. On one hand there is the development of cutter loaders for use in relatively hard coal. They represent the further extension of ideas developed after relatively long experience with the Eickhoff cutter. On the other hand there has been since 1942 an intense interest in the Ruhr in the development of face-stripping methods, particularly by the Kohlenhobel (coal plow) and its modification. At the end of 1947 these cutter loaders, Kohlen-hobels and scrapers together were actually accounting for only about 1.4 pct of total production while air hammers still broke 77.1 pct and as much as 1.2 pct was actually broken by hand picks. However,

Jan 1, 1951

By Irving B. Cadoff, Ernest Levine

The crack formation and propagation in the single -phase Cu-4 pct Ag alloys were studied. The alloys were loaded in mercury to various stress levels, the mercury was removed, and the specimen examined for cracks. Cracks were found to develop below the fracture stress; the frequency of such cracks increased with increasing stress level. Some cracks were nmpropagative. Fracture in mercury was found to occur by the link-up of cracks formed at various stress levels rather than by the growth and propagation of a single crack. If the mercury environment is removed prior to a critical amount of crack formation, then continued loading results in ductile fracture. The appearance of the cracks at selected grain boundaries is related to the relative orientation of the boundaries, as are the propaga-tive characteristics of the crack. The mercury interaction appears to be one of lowering the strength of the metal-metal bonds in the high-stress area of the grain boundary. GRIFFITH'S microcrack theory1 proposed a critical crack size above which a crack in an elastic material grows with decreasing energy at a stress of From his theory it was proposed that the presence of a liquid tends to lower the surface energy of the microcrack faces2 leading to a decrease in the critical crack size necessary for spontaneous fracture propagation. stroh3 proposed that the stress concentration at a grain boundary due to pile-up may initiate a microcrack at the grain boundary. petch4 and Stroh5 evaluated the stress distribution at the head of a pile-up in a polycrystal-line material and deduced that the critical crack size and hence of is dependent on the grain size. Experimental verification of this dependence was found by petch6 for hydrogen embrittlement of steel. Studies in stress-corrosion cracking7 have provided a picture of fracture which shows that initial separations occur in a scattered, independent fashion in regions of high tensile stress. A minimum or threshold stress is necessary to produce a sufficient stress concentration to initiate frac- ture. These separations join up to form a crack. The extension of fracture is largely discontinuous and consists of a joining up of cracks. In recent worka evidence of this scattered crack network was found in a Cu-Ag alloy embrittled by mercury. For the Cu alloy-Hg couple, the crack path has also been found to be dependent on the orientation of adjacent grains, and with the addition of zinc to mercury a reduction in embrittlement along with a change in fracture morphology was found.9 In this present study, a mercury-dewetting method was used to observe crack initiation and fracture morphology when a Cu-4 pct Ag alloy is deformed in mercury and Hg-Zn solutions. PROCEDURE Specimens of Cu-4 pct Ag were prepared as in previous crack-path studies.' The specimens were heated at 770°C for 24 hr and water-quenched Tension tests using a table-model Instron were carried out in mercury and in various concentrations of Hg-Zn. Loading was in steps up to the fracture stress, with the load being removed and the specimen examined for surface cracks at each step. The specimens were dewetted after each load to permit examination of the surface structure and rewetted prior to continued loading. The specimens were wetted by electro polish ing in phosphoric acid, rinsing in alcohol, and then immersing in a pool of mercury. Dewetting was accomplished by flame heating the specimen for 30 sec in a vacuum. Some surface contamination was found, but not enough to obscure crack configurations and grain boundaries. RESULTS Fracture Characteristics in Mercury. Fig. 1 is a stress-strain curve showing the progressive step-wise loading of the specimen. As may be seen from the graph, the first position stopped at a is at a stress 5000 psi below the expected fracture stress of 25,000 psi. Examination of the specimen after removal of mercury showed only one crack. The appearance of this crack at a stress far below the fracture stress of this alloy in mercury did not affect the stress-strain curve in any manner. The specimen was then recoated with mercury and deformation was continued (curve b, Fig. 1) raising the stress by 4000 psi, and the same procedure re~eated. The initial crack was located and appeared as in Fig. 2 (crack lb). In this figure the crack is

Jan 1, 1964

By J. L. Gillson

Historically, rock deposits and sand deposits of titanium minerals came into production about the same time, although there may be some argument as to what is meant by production. Beach deposits of heavy minerals in India (Figs. 1-4) and Brazil (Figs. 5) were worked for monazite about the turn of century, but as there was then no market for titanium minerals, these were thrown away. The rock rutile deposits at Roseland, Va., Fig. 6, were worked to supply rutile for titanium chemicals and for coloring ceramics long before there was a titanium pigment business. The pigment industry started about the middle twenties, both in Europe and the U. S., and almost simultaneously the rock deposits at Ponte Vedra Beach near Jacksonville, Fla., were worked for titanium content. Since those days, production from both types of deposits has continued to grow at a rapid rate; many deposits of both types have been found, and reserves have grown to very large figures. In total tonnage of reserves, there is no doubt that the rock deposits are far ahead of the sand deposits; nevertheless there is a very large tonnage of commercial sands available. It is the quality of titanium mineral in the sand and the relatively lower costs of operating sand deposits that have kept them abreast, at least in annual tonnage produced, with the rock deposits. The principal titanium mineral used is ilmenite, but as soon as that mineral began to be sought as a titanium ore, it was obvious that there are ilmenites and ilmenites. Textbook ilmenite should have the composition FeOTiO2 and should analyze 52.6 pct TiO2 and 36.8 pct iron as Fe. The Indian ilmenite, for almost a generation the standard ore for manufacturing pigment in the U. S., was found to analyze about 60 pct TiO, and only 24 pct. Fe, and most of the iron is in the ferric condition. The whole process of pigment manufacture in the U. S. was built up on the use of a raw material of that grade, and the American chemical engineers who operate the pigment plants shuddered at the thought of using a rock ilmenite with 45 pct or so of TiO, and nearly 40 pct Fe. Intensive search was made around the world to find other deposits of rich black sand, like the Indian beaches, but although a few were found, there was some objectionable feature about each. A deposit in Senegal, south of Dakar (Fig. 7), was worked for a while, but an organic coating on the grains made attack by acid difficult. Modern practice would have included a scrubbing operation, in a caustic soda bath, to eliminate the organic coating. Brazilian deposits were numerous, but individually small, and shipping from them difficult. Deposits on the east coast of Ceylon had many attractive features, but the ilmenite analyzed only 54 pct TiO2 and could have been used only with a penalty. Sand deposits with 2 pct ilmenite, like those now worked in Florida, would not have been considered commercial ore, even if they had been known at that time. Most rock ilmenites are associated or mixed with hematite or magnetite, which accounts for the lower titanium and higher iron values than in the sand ilmenites. The Norwegians, English, and Germans, with cheap Norwegian rock ore at hand, learned to install in their pigment plants adequate capacity on the black side, as it is calltd, and counterbalanced the extra cost of plant, and larger amount of acid used, by the lower cost of ore. When World War II arrived, two of the largest pigment manufacturers in the U. S. had to learn how to use the Adirondack ilmenite, but one of them very gladly went back to sand ores when the Florida deposits came into large-scale production after the war. The other continues to use Adirondack ilmenite and finds it commercially attractive to do so. Rutile is not a raw material for titanium pigment manufacture by the sulfate process, since it is insoluble in sulfuric acid. In addition to its small consumption in chemicals and ceramics it began to be used in quantity in welding rod coatings. With the outbreak of World War 11, and the tremendous need for welding rods in shipbuilding and other structural steel construction, rutile suddenly became in heavy demand. The sand deposits on the eastern shore of Australia (Fig. 8A) which had been worked in a small way since 1934 were brought into production, and some stream placers in Brazil were worked and rutile concentrates shipped to American

Jan 1, 1960

By A. T. Iannacchione

Synopsis Underground stone mining Is an emerging sector of the U.S. mining industry. As this expansion takes mines under deeper cover, and as more efficient mining methods are utilized, effective stone pillar design methods will become even more Important. Current design practices are examined and a discussion of safe mine layouts is presented as a first approach towards weighing the demands for increased production against increased risk. Risks to underground stone-mine workers include rib Instabilities, pillar failures and roof falls. Seventy-two stone-mine pillar designs were examined. Pillars with width to height ratios of less than 1.5 appear more likely to fail when subjected to excessive stress levels. When width to height ratios fall below 1.0 defects in the pillars, such as through-running discon¬tinuities, can have a significant influence on stability. Discontinuity persistence, dip, material properties and orientation are also important determining factors in pillar strength. During the past three years the number of active underground stone mines in the U.S.A. has ranged between 90 and 100. This number is expected to increase as the crushed stone industry responds to growing demands for its products.1 As more of the industry moves to benefit from the advantages of underground mining production from underground stone mines is expected to increase above its current level of approximately 66 000 000 r/year. Parker2 identified four advantages of underground mining operations: (1) surface developments, zoning laws and environmental concerns are often less of an issue; (2) stripping and restoration requirements are eliminated; (3) additional reserves are often available beneath the quarry floor, under pit slopes or under an adjoining property; and (4) space is created for secondary use. Underground mines enjoy the added benefits of work in a constant underground climate, rather than in the variable surface climate, minimization of community concerns by placement of the crushing, sizing and stowing operations underground and reduction of surface vibration concerns through smaller blasts. The drawbacks of underground mining include added health and safety hazards for the stone miners, whose health can suffer from increased exposure to falls of ground, airborne contaminants and fog in large underground openings. Injuries from falls of ground in stone mines have occasionally exceeded the incidence rates for other mineral resources mined underground. 3 Existing underground stone operations, by comparison with stone operations a decade ago, mine more stone at a faster rate and with larger equipment. Because of high demand mines face increased pressure to yield more stone per production blast. A majority of the miners use the V-cut blasting pattern, which limits the depth or pull for each shot to about 4 m. Therefore, to produce more stone, either the mines must work more faces or existing faces must be enlarged. The enlargement of underground openings poses problems in the maintenance o€ strata stability, First, the widths of the mine entries partially control the amount of sag or deflection that any given roof beam can withstand before failure. This deflection can take pi ace quickly after an opening is excavated or much later as weathering processes form additional, thinner beams. Because increased deflection increases the potential for roof beam failure, there is a limit to how wide a room can safely be made. These limits depend on local geological and stress conditions and, to some extent, the cost effectiveness of roof-bolting. Given these room width limitations, underground stone mines have placed more attention on expansion of production through benching where mining thicknesses permit. The heights of rooms partially control the strength characteristics of adjacent pillars: as the room height increases for a given pillar width the pillar width-to-height ratio (w/h) decreases. In general, stone pillars are very strong, but when the width-to height ratio diminishes the potential for pillar rib instabilities and pillar failures increases (see Fig. 1). [ ] In the underground environment the desire to utilize wider rooms, higher benches and multi-level mining results in the potential for unstable ground conditions. Although the number of failed pillars is currently very low, the potential for additional failures will grow if more slender pillars are developed, especially under deeper cover, with wider mining sections and in multi-level operations. It should also be noted that the passage of time acts to decrease the strength of many existing pillars. An examination of current design practices

By H. C. Rogers

A phenomenological study of the failure of polycry stalline ductile metals at room temperature was carried out using light and electron microscopy. Tensile fractures as well as sections of partially fractured bars of OFHC copper in particular were examined. The initiation and growth of the central crack in the neck of a tensile specimen occurs by void formation. After the formation of the central crack the f'racture may be completed in either of two ways: by further void formation or by an "allernating slip" mechanism. The first leads to a "cup-cone" failure; the second, to a "double-cup" failure. In the past decade or decade and a half there has been a great deal of emphasis on the solution of the problem of the brittle fracture of metals, particularly those which normally exhibit considerable ductility such as steel. Since the problem of the fracture of metals after large plastic strains has less immediate commercial or defense significance, there has been considerably less effort expended in describing the details of the phenomenology and determining the mechanism of this type of fracture. The present research was undertaken to increase our knowledge in this area. The problem of ductile fracture has not been neglected completely, however. Ludwik1 first found by sectioning a necked but unbroken tensile specimen of aluminum that fracture began with a large internal crack which appeared to have started in the center of the neck. Examination of the fracture indicated that the crack had propagated radially with increasing deformation until a point was reached at which the path of the fracture suddenly left this transverse plane and proceeded at approximately 45 deg to the stress axis until the surface was reached. This gives rise to the commonly observed cup-cone tensile fracture. When MacGregor2 was attempting to demonstrate the linearity of the true stress-true strain curve from necking until fracture, he found that copper was anomalous in that the stress dropped off markedly from the straight line value before fracture occurred. Radiography indicated that in the copper an internal crack was formed long before the final fracture, the stress decreasing during the growth of this crack. One of the most significant advances in the understanding of ductile fracture was the result of work by Parker, Flanigan, and Davis.3 By the use of etch-pit orientations they were able to demonstrate conclusively that the fracture surface at the bottom of the cup, although on a gross scale normal to the tensile axis, did not consist of cleavage facets as had been previously supposed by many investigators. Recently, Forscher4 has shown evidence of porosity near the tensile fracture of hydrogenated zirconium which he attributes to hydride decomposition. The workers at the Titanium Metallurgical Laboratory5 have also shown evidence of porosity in a number of the commonly used metals after heavy deformation. Many metals have relatively low ductility during creep tests at high temperature. The fractures are intercrystalline, resulting from the nucleation and growth of grain boundary voids. The work in this area has been recently reviewed by Davies and Dennison.6 It is possible that some of the observations and conclusions may have a bearing on the present study? especially since at least two studies7,' have been extended down to room temperature and below using magnesium alloys. However, since magnesium does exhibit low-temperature cleavage, these results may not be pertinent to the present one. The use of the electron microscope as an aid to the study of fractures has been extensively exploited by Crussard and coworkers.9 The examination of direct carbon replicas of the fractures of a large number of metals and alloys showed that the bulk of the fracture surface was covered with cup-like indentations of the order of 1 to 2 µ in size. These frequently had a directionality by which Crussard claims to be able to tell the direction of the crack propagation. With this rather disconnected background of information, this investigation was undertaken in the hope of presenting a unified picture of the initiation and propagation of a fracture in a ductile metal. To this end all of the techniques previously used were employed simultaneously so that there might be a good correlation of the data obtained by different techniques. EXPERIMENTAL PROCEDURE The metal which was chosen as the starting material for this investigation was OFHC copper. Of the dozen or so materials considered, it best fulfilled the requirements of commercial availability in large sizes, good ductility, relatively high melting point compared with room temperature and

Jan 1, 1961

By R. S. Sherwin

The extractive metallurgy of primary aluminum from its ores is discussed with special attention to the production of alumina from high grade ores by the Bayer process, including differences between American and European practice and a brief description of some processes for lower grade ores and the electrolytic reduction of the oxide to aluminum. METALLIC aluminum is not found in nature, but the oxides, hydroxides, and especially the silicates are plentiful. The estimated percentage of in in the crust of the earth is about 8 pct while that of iron is about 5 pct. By far the larger portion of this is combined with silica in the form of various clay minerals and igneous silicate rocks. From the point of view of extractive metallurgy of aluminum, these are low grade ores while the better qualities of bauxite are the high grade ores. There have been various definitions of bauxite but perhaps the best definition at the present time is that bauxite is a rock or earth commonly used as an ore of aluminum or its salts in which the aluminum is present predominantly as a hydrate or a mixture of hydrates and hydrous oxides. It contains varying amounts of oxides of silicon, iron, and titanium and traces of compounds of some of the less common elements. The silica is mainly combined with alumina as clay or clay minerals which are hydrous aluminum silicates, although a part of it may be present as quartz sand. On the American continents, the alumina is mainly present as gibbsite, Al2O3 . 3H2O, and the same may be said of the best known deposits of the Dutch East Indies and some of the deposits in India. In France and other countries in Europe as well as in Africa, the alumina is present mainly as boeh-mite, A12O3 . H2O, but in some of these deposits it is mixed with minor amounts of gibbsite. Some other deposits, such as those in the islands of Haiti and Jamaica, evidently contain two or more hydrates or hydrous oxides of alumina in varying proportions. Perhaps the main portion of the alumina may be present as gibbsite and boehmite with the proportion between the two varying rather widely. In the silicate minerals, including clay, the alumina is chemically combined with silica and has not been separated satisfactorily by mechanical or physical ore-dressing methods. Low grade bauxites are mixtures of hydrates, usually gibbsite or boehmite, with clay, iron oxides, etc. In some low grade bauxites, it is possible to separate a portion of the gibbsite or boehmite, which may be present as relatively hard and coarse particles, from soft or finely divided clay minerals by log washing or similar methods. This has been applied to the product of some mines or parts of them, but on other ores it is not applicable. In some cases the gibbsite or boehmite is almost as fine and soft and of nearly the same specific gravity as the clay minerals so that washing and gravity separations are not successful. The iron oxide, the clay minerals, and a part of the titanium minerals are often so finely dispersed in the ore that any of the physical mineral separation methods, including separations by gravity, particle size, flotation, and electrostatic or magnetic separation, have not been commercially SUCCESSFUL except on relatively small lots of ore. For these reasons, the only available methods of separation on the general run of ores have been methods which would be classed as chemical rather than physical or mechanical separations. Aluminum oxide can be reduced by carbon at temperatures above 1800°C to form metallic aluminum and aluminum carbide or nitride. The temperature for rapid reduction of aluminum oxide to metallic aluminum is about the boiling point of aluminum and above the temperatures necessary to reduce iron, silicon, and titanium so that the direct reduction of an aluminum ore with carbon will produce an alloy of aluminum, iron, titanium, silicon, etc., which may be mixed with carbides and nitrides. Also a large amount of the reduced aluminum may be lost as a vapor except in the presence of some alloying agent such as copper or other metals. While it is possible to refine such alloys or mixtures so as to produce commercially pure aluminum, the methods which have been found are too expensive for the present market. One direct reduction method which found limited commercial use in Germany during World War II was the direct reduction of a mixture of clay containing very little

Jan 1, 1951

By D. A. Dukelow, K. Li, G. C. Smith

Decarburization in the Fe-C system by oxygen top blowing has been studied in laboratory -scale experiments. It is shown that equilibrium models fail to explain or predict either the course of refining or endpoint conditions, giving results which either are incompatible with the chemistry of the system or do not satisfy material balance requirements. Also the path of decarburization was found to vary even for heats made under apparently identica1 conditions. A promising approach to analyzing the decarburization results is to relate oxygen efficiency fm carbon removal to bath carbon content. This relationship for Fe-C heats shows the same range of oxygen efficiencies as is obtained in pilot-plant and commercial heats using hot metal-scrap charges. This implies that oxygen transfer is primarily controlled by the decarburization reaction itself, independent of other refining reactions. Therefore, it should be possible to study separately decarburization and slag-metal reactions. DECARBURIZATION is probably the most important reaction in steelmaking. Not only is it a main reaction in the refining of iron to steel but it also provides the stirring action in the bath necessary for the diffusion processes to proceed at reasonable rates so as to make a steelmaking process practical. Kinetics of decarburization in the open-hearth process has been a subject of investigation for many years.&apos;-B It is generally accepted that at steelmaking temperatures the rate of homogeneous C-0 reaction is extremely high and cannot constitute a rate-controlling step. Diffusion of oxygen through a boundary film in the metal phase has been suggested by arken&apos; as rate-determining. Recently, Larsen and sordah16 concluded from experiments in a laboratory furnace that, with oxygen supplied from air or combustion gases, the rate of "steady-state" carbon boil is controlled essentially by a diffusion process of O2, Co2, or H2O through a film of nitrogen above the slag surface. Displacing this diffusion film by a stream of nearly pure oxygen produced a ten-fold increase in the rate of carbon boil with the rates of slag-metal oxygen transfer, bubble nucle-ation, and other steps all apparently able to keep pace. In the top-blown basic oxygen process, however, the transport of oxygen takes a more direct route. and the state of bath agitation is much more turbulent than in the open-hearth process. In addition, direct contact of the gas with the metal phase provides opportunity for direct oxidation of carbon. It is likely that the rate-limiting factor for the decarburization reaction will be different. However, only a few descriptive discussions of the subject have been reported in the literature.10-l2 Studies of the decarburization kinetics based on plant or pilot-plant data are necessarily complicated and are influenced by other refining reactions which occur simultaneously. In order to investigate the mechanism of decarburization, experiments have been conducted in which carbon-saturated iron melts were top-blown with pure oxygen over a range of conditions. It is hoped that this study will form a foundation on which a more basic understanding of this important reaction may be built. EXPERIMENTS One group of blowing experiments was made in a standard 200-lb induction furnace and another group in a 500-lb induction furnace. The furnaces were modified to the general shape of a basic oxygen furnace by adding a rammed refractory cone section to the regular crucible body. Crucible and cone were of high MgO (95 pct) material. A water-cooled lance, 1/2 in. in diam and threaded at one end to take a nozzle, was used for blowing oxygen. The lance with its water and oxygen lines was supported on a cantilever arrangement so that it could be moved up, down, or sideways. Oxygen of 99.5 pct purity was supplied from a cylinder and metered through a rotameter equipped with pressure and temperature gages. Another pressure gage was located at the top of the lance. A schematic diagram of the assembly is shown in Fig. 1. Before each experiment, a weighed amount of ingot iron, containing 0.02 pct C, < 0.01 pct Si, 0.10 pct Mn, 0.019 pct P, and 0.015 pct S, was charged in the furnace and melted down by induction heating. Graphite was then added to the molten charge until it became saturated. When the temperature of the charge reached the desired level, the lance was lowered to a predetermined height above the bath

Jan 1, 1964