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By A. U. Seybolt, D. H. Haman

The rate of oxidation of the lowest nitride of chromium, Cr2N, was measured to be equal to the rate of oxidation of chromium metal. It was found that, while the presence of Cr2N in chromium does not affect the oxidation mechanism, a long exposure at high temperature affects the morphology of Cr2N in chromium, causing a massive internal nitriding along chromium pain boundaries. Marker expen' -ments showed that the rate of oxidation of Cr2N layers on chromium is determined by the rate of chromium diffusion through Cr,03. The rate of formation of Cr2N is determined by diffusion rate of nitrogen through Cr2N. This rate at 1000°C is around thirty times faster than the rate of oxiahtion. Evidence is presented which suggests that nitrogen from the air reaches the chromium through the Cr2O9 by migration through pores or cracks rather than by a diffusive process. IT has long been recognized that, when chromium or alloys containing substantial amounts of chromium are oxidized in air, some chromium nitride (Cr2N) is formed under the oxide scale. Although the presence of this nitride layer has often been described, there appears to have been no systematic study of the role played by the nitride during the oxidation process. Indeed, there have been conflicting re-ports'92 on the kinetics of oxidation of chromium and chromium alloys in air and in oxygen. However, it is now well-established'-5 that the rate-controlling process during the parabolic oxidation of chromium to Cr2O3 is chromium-ion diffusion through Cr2O3. Because of the importance of chromium-containing alloys as oxidation-resistant materials, it seemed desirable to investigate the behavior of chromium during oxidation with and without the presence of chromium nitride. Since a semicontinuous Cr2N layer forms relatively early during the oxidation of chromium in the air, chromium atoms must either pass out of or through the Cr2N layer to become incorporated in the growing Cr2O3 scale. Therefore, it seemed desirable to examine the oxidation behavior of the pure nitride. MATERIALS AND EXPERIMENTAL PROCEDURE The chromium used in this investigation consisted of slices of an ingot made from "five-nine" iodide chromium which had been argon-atmosphere melted in a Y2O 3-stabilized ZrO2 crucible in an induction furnace. The only impurity of any significance was 625 ppm of 0, which was usually reduced to a microscopically invisible amount by hydrogen annealing at 1400°C. However, one sample of chromium was used with the as-cast oxygen level as explained below. The samples were used after abrading through 600 Sic paper and then washing in toluene and alcohol. Both nitriding and oxidation experiments were performed in a vertical tube furnace connected to a glass vacuum system. 'This system was equipped with pressure measuring instruments for the range of 10 p to 1 atm, and a cartesian-diver pressure-control device was used in conjunction with a needle valve to allow control of pressure in the range of about 10 to 760 mm. The nitrogen or hydrogen gas was purified by passing through hot copper chips at 600°C, anhydrous calcium sulfate (Drierite), and liquid nitrogen. Oxygen gas was dried through the Drierite column and a dry-ice trap (-78°C). Changes in specimen weight were followed by a Pyrex helix used in conjunction with a cathetometer which could reproducibly be read to +0.001 cm, yielding an accuracy of about +0.2 mg. The spring was maintained in the cool upper part of the furnace tube where the temperature did not rise above about 35°C. The nitride in equilibrium with metallic chro-

Jan 1, 1964

By Pol Duwez

The effect of the rate of cooling on titanium, zirconium, and thallium has been measured. For titanium-molybdenum alloys, it has been shown that for molybdenum concentration up to 8 pct the rate of cooling has no effect on the transformation temperature, but this temperature decreases progressively with increasing molybdenum content. HIGH strength to weight ratio and remarkable corrosion resistance have often been advanced as the main reasons for the present widespread interest in titanium. For the physical metallurgist, the existence of an allotropic transformation in titanium is another important factor. As in the case of iron, an allotropic transformation may be the fundamental property upon which the response of Ti-base alloys to heat treatment will depend. It is therefore important to study the mechanism of the allotropic transformation in pure titanium and the effect of alloying elements on this transformation. The existence of an allotropic transformation in titanium was reported in 1931 by Schulze.' Later, De Boer et al.' determined the transformation temperature from a discontinuity in the electrical resistivity at 882"42O°C. According to recent work," the transformation temperature is 882.5"&1°C. The crystal structure of the room temperature a phase is hexagonal close-packed and the high temperature fi phase is body-centered cubic.' It is well known that the high temperature /3 phase of pure titanium cannot be retained by quenching to room temperature. Several investigators'-' have shown that in alloys of titanium with metals which are soluble in the @ phase (for example, nickel, molybdenum, chromium, or manganese), the /3 structure can be retained, providing the concentration of the alloying element is greater than a certain critical value. Below this critical value, the alloys transform during quenching, at least partially, into a supersaturated solid solution having the a. structure. This behavior is very similar to that found in some iron binary alloys (Fe-Ni and Fe-Mh, for example) and is an indication that the transformation might occur by means of a shear mechanism analogous to that observed in the austenite-martensite reaction. The present investigation is mostly concerned with the effect of the rate of cooling on the /3 to a transformation. In the first portion of this paper, the results obtained on pure titanium are described. Two other pure metals, zirconium and thallium, were also investigated, because they both have an allotropic transformation like titanium, from an hexagonal close-packed to a body-centered cubic structure. For purposes of comparison, the effect of rate of cooling of the y to a transformation of iron was included in the experimental program. The second part of this paper deals with Ti-Mo alloys. The equilibrium phase boundaries involving the solid state reactions on the Ti-rich side of the system were determined and a study was made of the effect of the rate of cooling on the transformation of the high temperature /3 solid solution. Experimental Procedure Since the main object of the present investigation was the determination of the effect of the rate of cooling on a transformation temperature, the best technique available was that used by Greninger" in his study of the martensite arrest in carbon steels. This method consists of heating a very small sample of metal to which fine thermocouple wires are .attached, cooling the sample rapidly by means of a blast of helium, and recording the temperature vs. time curve on an oscillograph. The apparatus used in the present experiments was very similar to that described by Greninger, except that the heating coil was made of molybdenum wire (0.040 in. in diam) and the assembly was placed in a bell jar under vacuum of 10" mm Hg or less. The specimen con-

Jan 1, 1952

By Irwin Politziner F. M. Townsend, L. S. Reid

Recently published data indicate that the water vapor content of a gas, as determined by dew point measurement, is inaccurate when the gas has been dehydrated with diethylene glycol. Water vapor contents and dew point measurements of gases dehydrated with triethylene glycol have been obtained in this investigation in order to determine the magnitude of a similar error, if one exists. Experimental data show a very low concentration of triethylene glycol vapor in gases dehydrated at atmospheric ternperatures and pressures ranging from 500 to 2,500 psia and that the accuracy of dew point measurements is not impaired by the presence of triethylene glycol vapor. INTRODUCTION Nearly all natural gas transported by pipe line to northern and eastern markets must be dehydrated to a low residual moisture content in order to assure maximum transmission efficiency and continuous delivery under peak load conditions. Without dehydration, water vapor often condenses in pipe lines in quantities sufficient to restrict the flow3 and. under low atmospheric temperature conditions, gas hydrates may form and plug gathering. transmission and distribution facilities. Gas may be dehydrated to pipe line specifications by a number of methods. The most widely used methods are (1) adsorption of water vapor on a solid dessicant such as activated bauxite, alumina or silica gel,' (2) by absorption of water vapor by either diethylene or triethylene glycol-water solutions of high glycol concentration,11,13 and (3) by simultaneous expansion-refrigeration of very high pressure gas in which gas hydrates are purposely formed and then quickly decomposed.'"" Of these three fundamental methods, the adsorption and absorption processes provide the bulk of the dehydrated gas moving to market at the present time. The expansion-refrigeration process. a relatively new development, is gaining in favor because of its simplicity but is sharply limited in its application by available differentials between source and gathering system pressures. Where gas sale or purchase contracts contain a maximum water vapor content specification, the water vapor content is usually determined by measuring the dew point of the gas at system pressure. Knowing he dew point temperature and the system pressure, the water vapor content of the gas is determined from a graphical correlation of saturation, or dew point, temperature us the water vapor content of the gas which is customarily expressed as pounds of water vapor per million cubic feet of gas measured at 14.7 psia and 60°F. Dew points are usually measured with the U. S. Bureau of Mines Dew Point Tester. shown in Fig. 1, which is well suited for use at temperatures lower than 120°F and at pressurei; ranging from atmospheric to 3,000 psi. A number of correlations of dew point temperatures vs water vapor content are available,3,5,15 the most recent of which is that by McCarthy et al.4 Where natural gas is dehydrated by absorhing contact with concentrated diethylene glycol-water solutions. considerable difficulty is experienced in observing water dew points due to condensation of liquid hydrocarbon and glycol films on the mirrored surface of the dew point tester. Riesenfeld and Frazierl2 report that the dew point method for determining the water vapor content of a dietllylene glycol-treated natural gas is in error due to the glycol content of the condensate formed on the tester mirror, and that the water vapor content of the gas tested is actually lower than that indicated by the standard' dew point-water vapor content correlation. Extensive experience in testing gases dehydrated by concentrated triethylene glycol-water solutions lias not revesled difficulties of the nature cited above for diethylene glycol. Water dew points are clear and sharp and condensation of

Jan 1, 1951

By L. S. Reid, Irwin Politziner F. M. Townsend

Recently published data indicate that the water vapor content of a gas, as determined by dew point measurement, is inaccurate when the gas has been dehydrated with diethylene glycol. Water vapor contents and dew point measurements of gases dehydrated with triethylene glycol have been obtained in this investigation in order to determine the magnitude of a similar error, if one exists. Experimental data show a very low concentration of triethylene glycol vapor in gases dehydrated at atmospheric ternperatures and pressures ranging from 500 to 2,500 psia and that the accuracy of dew point measurements is not impaired by the presence of triethylene glycol vapor. INTRODUCTION Nearly all natural gas transported by pipe line to northern and eastern markets must be dehydrated to a low residual moisture content in order to assure maximum transmission efficiency and continuous delivery under peak load conditions. Without dehydration, water vapor often condenses in pipe lines in quantities sufficient to restrict the flow3 and. under low atmospheric temperature conditions, gas hydrates may form and plug gathering. transmission and distribution facilities. Gas may be dehydrated to pipe line specifications by a number of methods. The most widely used methods are (1) adsorption of water vapor on a solid dessicant such as activated bauxite, alumina or silica gel,' (2) by absorption of water vapor by either diethylene or triethylene glycol-water solutions of high glycol concentration,11,13 and (3) by simultaneous expansion-refrigeration of very high pressure gas in which gas hydrates are purposely formed and then quickly decomposed.'"" Of these three fundamental methods, the adsorption and absorption processes provide the bulk of the dehydrated gas moving to market at the present time. The expansion-refrigeration process. a relatively new development, is gaining in favor because of its simplicity but is sharply limited in its application by available differentials between source and gathering system pressures. Where gas sale or purchase contracts contain a maximum water vapor content specification, the water vapor content is usually determined by measuring the dew point of the gas at system pressure. Knowing he dew point temperature and the system pressure, the water vapor content of the gas is determined from a graphical correlation of saturation, or dew point, temperature us the water vapor content of the gas which is customarily expressed as pounds of water vapor per million cubic feet of gas measured at 14.7 psia and 60°F. Dew points are usually measured with the U. S. Bureau of Mines Dew Point Tester. shown in Fig. 1, which is well suited for use at temperatures lower than 120°F and at pressurei; ranging from atmospheric to 3,000 psi. A number of correlations of dew point temperatures vs water vapor content are available,3,5,15 the most recent of which is that by McCarthy et al.4 Where natural gas is dehydrated by absorhing contact with concentrated diethylene glycol-water solutions. considerable difficulty is experienced in observing water dew points due to condensation of liquid hydrocarbon and glycol films on the mirrored surface of the dew point tester. Riesenfeld and Frazierl2 report that the dew point method for determining the water vapor content of a dietllylene glycol-treated natural gas is in error due to the glycol content of the condensate formed on the tester mirror, and that the water vapor content of the gas tested is actually lower than that indicated by the standard' dew point-water vapor content correlation. Extensive experience in testing gases dehydrated by concentrated triethylene glycol-water solutions lias not revesled difficulties of the nature cited above for diethylene glycol. Water dew points are clear and sharp and condensation of

Jan 1, 1951

By Norman L. Newbern, Robert E. Green

An investigation of the effect of size on the deformation properties of metal single crystals made it desirable to grow from the melt cylindrical aluminum single crystals possessing exactly the same crystallographic orientation but varying in diameter. Methods for the growth of rather large (up to 3 in. diam) aluminum single crystals in molds of the desired shape are well known. However, when one applies the same techniques to the growth of smaller (less than 1/8-in. diam) specimens many additional problems arise. Two of the major problems are the construction of the molds to be used and the removal of the thin specimens from these molds without deformation after growth has been completed. Also the problem of the constraint forces exerted by the mold on the specimen is much more pronounced for the smaller specimens. The technique described herein is a zone-melting method in which no mold is used since the surface tension of the molten metal and its oxide is sufficient to retain the melt. The specimen is suspended vertically in a manner similar to that of Keck and Golay.2 However, while Keck and Golay supported the specimen from both ends, the method used here supports the specimen only at the upper end. The surface tension of the molten aluminum and aluminum oxide contains the melt and suspends a length of newly grown crystal that has already passed through the molten zone until the weight of the newly grown crystal is equal to the component of surface tension holding the specimen together in the molten region. When the weight of the newly grown crystal is equal to the component of surface tension holding the specimen together the specimen pulls in two in the molten zone. The length of crystal which can be grown before this separation occurs varies with the diameter of the specimen and the size of the molten zone. In order to prevent the specimen from pulling in two a tube of glycerine is placed beneath the furnace in such a manner that the newly grown crystal passes into the glycerine which provides sufficient buoyancy to allow aluminum single crystals in wire form to be grown to lengths determined only by the length of the tube containing the glycerine. A schematic diagram of the experimental arrangement is shown in Fig. 1. The furnace used is constructed as follows. High-resistance nichrome wire is coiled on a 3/8-in. diam fused quartz tube. The distance between the windings is much less over a length of about 3/8 in. at the center so as to develop a hot spot. This core is located in the center of a 4-in. diam steel cylinder 5 in. in height and insulated from it by Kayolite. The temperature of the furnace is controlled by means of a thermocouple located near the central hot spot and a Minneapolis-Honeywell temperature controller. Temperature ins,ide the furnace is measured with a thermocouple and a standard potentiometer in the usual manner. By the above method it is possible to grow high-purity (99.99 pct Al) aluminum single-crystal wires over a range of sizes. Crystals varying from 1/8 to 1/64-in. diam were grown by the authors. Since the tube containing the glycerine cannot contain a crystal longer than approximately 3 ft, the growth of crystals longer than this presents another problem. It was found that one could cut the newly grown crystal without deformation in the region between furnace and glycerine tube try means of a cutting torch and then by moving the glycerine tube slightly aside continue

Jan 1, 1962

By V. Patarini, M. Salkind

BECAUSE of its high strength and stiffness coupled with low density, continuous boron filament is showing great promise as a potential reinforcement for both metals and nonmetals. Of primary consideration for structural applications is the fatigue behavior of boron fiber composites. Composite fatigue behavior is dependent upon three factors: 1) fiber fatigue behavior, 2) matrix fatigue behavior, and 3) the effect of the interface and fiber ends. The purpose of this note is to describe the behavior of boron filament in rotating beam fatigue. The filament, described by Talley' and Galasso, Salkind, Kuehl, and Patarini,' was made by the hydrogen reduction of boron trichloride on a hot tungsten filament. Testing was performed using a commercial rotating beam wire fatigue tester* described by Votta.~ One end of the test sample is held in a chuck in a synchronous motor. The sample is bent around in a "U" shape, and the other end inserted into a carbide bushing. The maximum strain occurs at the bottom of the "U" where the radius of curvature is a minimum. The strain is adjusted by adjusting the length of the specimen and the location of the bushing. Samples were rotated at 3600 rpm and an automatic shutoff device used to determine the number of cycles to failure. The measurements were accurate to the nearest 360 cycles. The fatigue behavior is summarized in Fig. 1 for fifty-one samples of 4.8 x 10"3 in. diam fibers and ten samples of 3.2 X 10"3 in. diam fiber. The two sample groups represent two different filament production runs and two different nominal size groups. Both groups exhibited nominal tensile strengths of 400,000 psi. No significant difference in the fatigue behavior of the two sample groups is apparent. The scatter in the data is not unexpected for a brittle filament which exhibits a tensile strength distribution with a standard deviation of 10 to 15 pct. Because the test procedure provides a known outer fiber strain in the sample, the maximum stress was calculated assuming a Young's modulus of 58 x 10' psi. This value was selected as being representative of several nominal fiber sizes.2 All of the samples which failed exhibited sudden, catastrophic fracture, and no permanent deformation. One sample was stopped after 1.66 x lo8 cycles at *200,000 psi. The fiber exhibited no apparent damage or deformation. It is apparent that the fatigue resistance of boron filament is quite good. It can therefore be speculated that the fatigue behavior of boron fiber composites would be controlled by the "weaker links", namely matrix fatigue resistance and interface behavior. In fact, preliminary investigations have revealed that this is true for boron-reinforced aluminum? It should be noted that the data presented herein may not necessarily reflect the tensile fatigue behavior of boron filament. It is well-known that boron filament has a radial residual stress pattern with the outer surface in ~om~ression.~ Because of this fact, tensile failure is normally nucleated in the interior of the filament.5 Since the data presented herein is for a rotating beam test in which only the outer surface of the fiber is stressed to the maximum value, it would be incorrect to assume that the failure mechanism and fatigue behavior would be the same if the fiber were tested in tensile fatigue. The fact that many of the data are well above the nominal 400,000 psi tensile strength would tend to support this argument. The authors would like to express their appreciation to the United Aircraft Research Laboratories for supporting this investigation and for permission to publish the results. A portion of this effort was supported by the Air Force Materials Laboratory under contract AF33(615)-2125.

Jan 1, 1968

By T. Szaplonczay, D. E. Light

The auto-oxidation of sulfur dioxide to form sulfuric acid in commercially produced barren and recycle liquors, containing 1.66 and 4.56 gpl Fe respectively, from Elliot Lake was studied. A gas mixture, containing 3.5% SO2 and air was introduced into these liquors through a frit at a rate of 6.0g SO2 per hour per liter of solution. The barren and recycle were heated to 60°C. At the end of the first 24 hours of the process the concentrations of acid produced were 158 and 220 gpl H2SO4 for the barren and recycle respectively. Corresponding conversion efficiencies were 70 and 83%. In the period from 24 to 36 hours the rate of acid production decreased so that the H2SO4 concentrations at the end of 36 hours were 180 gpl for the barren and 260 gpl for the recycle; average conversions for the initial 36 hours were 55 and 68% respectively. Many investigators1'2'3 have considered the oxidation of sulfur dioxide to form sulfuric acid in aqueous solutions containing metallic ions. A summary of the work performed on this subject prior to 1946 has been presented by Keyes4 who described the auto-oxidation process as follows. Keyes also suggested that in this second reaction ferric ion serves as a catalyst for the conversion of sulfur dioxide to sulfuric acid. Neytzell-de Wilde and Taverner5 have reported on the use of auto-oxidation to produce a 4 to 5% sulfuric acid solution for use in a cyclic leach process at South African uranium plants. This paper describes investigations carried out to determine the feasibility of using the auto-oxidation process to produce sulfuric acid solutions of as high concentration as possible using commercially produced uranium plant barren and recycle liquors from the Elliot Lake region of Ontario. These liquors contained 1.66 and 4.56 gpl respectively of iron, chiefly in the ferrous state. This investigation is of particular interest to the uranium producers in Elliot Lake where the ores contain 3 to 4% sulfur, as sulfides. Flotation of these sulfides and roasting of same to produce SO, bearing gases have been successfully demonstrated using conventional methods.6'7 Barren and recycle solutions, as described previously, are also produced in large tonnages by these uranium producers. The experimental method and apparatus used to examine the auto-oxidation process will be described first. Then the tests carried out on laboratory prepared aqueous solutions containing ferric sulfate to determine optimum conditions will be presented. The next section will describe the tests using the commercial barren and recycle liquors. A final section will summarize the conclusions of the work. EXPERIMENTAL APPARATUS AND PROCEDURES Two types of solutions were used in the tests, a laboratory prepared aqueous solution containing definite amounts of ferric sulfate, and commercially produced iron bearing solution obtained from a uranium leaching plant in the Elliot Lake area. Two liters of a solution to be examined were placed in a 3 in. diam by 30 in. long glass cylinder with a cross-sectional area of 7 sq in. A mixture of air, and SO2 supplied from a lecture bottle for convenience, was introduced into the bottom of the vessel through a standard 30 mm glass frit, 700 sq mm in area. The temperature of the apparatus was controlled by a heating tape and variable transformer. Exhaust gases were vented to atmosphere. At the end of the test period the gas flow was shut off and the solution was analysed for H2SO4, Fe ++, and Fe +++, by conventional means. Four variables were examined using the laboratory prepared aqueous solution of ferric sulfate. First, the effect of SO2 concentration, from 1 to 1076, in the feed gas mixture was considered. Second, the temper-

Jan 1, 1964

By C. N. Reid

Slip-line studies on deformed chromium single cvystals showed the usual bcc behavior. At room temperatuve, cross slip was prevalent—slip was not confined to a given plane, but the slip direction was (111). At -10O0K, slip occuvred on (110) planes, twins on(112) planes, and cleavage on (1001 planes. A single-crystal tensile specimen with an axis close to [011] showed a pronounced yield drop and high strain rate sensitivity which zclere used to derive relevant parame tevs in a dislocation dynamics treatment. Transmission electron microscope studies confirmed the existence of (110) slip planes and showed ecidence of loops punched out by precipitates and of grown-in dislocations promoting tangling. OF recent years experimental studies have been made of the deformation characteristics of single-crystal molybdenum and tungsten, but very little has been published on the behavior of single-crystal chromium. During a study of the mechanical properties of chromium, single-crystal studies were made which have already been partially described.&apos; However, additional information was generated which was not directly relevant to the main theme of Ref. 1, and, therefore, was not reported. In view of the need for complete documentation of deformation modes, the experimental observations made on the deformation of single-crystal chromium are summarized here, together with an electron-microscope study of the associated dislocation structures. It was found that, in terms of the deformation modes, chromium is a conventional bcc metal, showing a very pronounced yield-point phenomenon. Further, it was found that the flow strength of these crystals is very sensitive to the strain rate. Finally, the crystals were observed to contain many unidentified precipitates, which often were associated with prismatic dislocation loops. EXPERIMENTAL METHODS Single crystals were grown from rods of wrought chromium by the method of zone annealing. Rods of "1/4in.-diam were supported vertically in an argon atmosphere while an induction coil was moved up the rod at 1 in. per hr. The power was adjusted to just below that required for melting, and the process produced single crystals in about 30 pct of the rods used. The orientations of the crystals, in general, lay near [011] and are summarized in Fig. 1. Before this treatment, the wrought material contained 35 pprn C, 68 ppm O, and 12 ppm N.* An analyzed single crystal *Usual metallic impurities found in iodide chromium are: Al, 5 ppm; Ca, A ppm; Cu, 2 ppm; Fe, 75 ppm; Yg, 0.5 ppm; Yn, < 3 ppm; Mo, < 3 ppm; Ni, 4 ppm; Si, < 20 ppm; Ti, < 1 ppm; V, 4 ppm; Zr, < 3 ppm. contained 10 pprn C, 79 ppm O, and 50 pprn N. Tension and compression specimens were shaped from the crystals by mechanical grinding, followed by the electrolytic removal of about 0.010 in. from the surface in a perchloric/acetic acid bath. All specimens had a gage length of 0.75 in., and tension specimens had a diameter of 0.100 in., while that of the compression samples was 0.200 in. Mechanical tests were carried out at a rate of 1.3 pct per min, and temperatures below 0°C were attained by means of a nitrogen cryostat similar to that of Wessel.2 EXPERIMENTAL RESULTS Modes of Deformation. In addition to the tensile properties of these crystals, which are described in Ref. 1, deformation markings on the surface were studied. Crystals A and F, Fig. 1, were deformed in tension at 300°K to 10 and 16 pct strain, respectively. The surfaces contained visible slip lines, about 1 C( apart, composed of both straight and wavy segments. They did not define a single plane, and so determination of the slip plane was not possible. However, the slip direction was deduced by comparing the axial orientations of the crystals before and after deformation. Fig. 2 is representative, and shows that the axis ro-

Jan 1, 1968

By R. D. Carter

Nurnerical .solutions are presented to some problems of unsteady-state radial flow of gas in which Darcy&apos;s law holds. These solutions are intended to aid in explaining the observed behavior of gas wells during drawdown tests. The variation of viscosity and Z-factor with pressure is accounted for in the solutions. Results are presented for three types of problems: (I) unfractured wells producing at a constant rate, (2) fractured wells producing at a constant rate and (3) unfractured wells producing through a critical flow prover. In the critical-pow-prover solutions, a correction of the calculated well-bore pressure to account for non-Darcy flow is made. A good correlation is shown between the solutions to the problem of Type 1 and the corresponding diffusivity-equation solution. Using this correlation, the diffusivity solution may be used to obtain gas-well solutions. The solutions to the problems of Type 2 illustrate the difference in drawdown-curve behavior to be expected between fractured and unfractured gas wells. Methods for estimatting fracture radius and flow capacity are presented and verified from solutions of Type 2. The solutions to the problems of Type 3 illustrate the differences to be expected between critical-flow-prover drawdown tests and constant-rate tests. An equation is presented for correcting critical-flow-prover data to constant-rate conditions. A description of the methods used in obtaining the solulions appears in the Appendix. INTRODUCTION It is necessary for many engineering purposes, such as predicting future deliverability performance, to be able to relate bottom-hole flowing pressure, formation pressure and flow rate for conditions of stabilized flow in gas wells. This information is customarily given as a plot of on logarithmic co-ordinates. It is desirable to be able to predict stabilized performance curves for gas wells based on data obtained from drawdown tests of short duration. Tests of long duration may be wasteful of gas, and low-permeability wells do not stabilize in a short-duration test. Although it is now commonly recognized that non-Darcy flow plays a significant part in gas-well behavior, it is believed that an understanding of transient behavior of systems obeying Darcy&apos;s law is still important in the interpretation of short-term test data, and the prediction of stabilized performance curves therefrom. In this connection, an equation for correcting Darcy flow It seems likely that solutions of the type presented herein, combined with the non-Darcy flow correction of the type of Eq. 1 and the usual laminar-flow skin factor, could provide a model which would adequately explain transient gas-well behavior for times after the non-Darcy flow region (which should be confined to a small area surrounding the well) has been established. The solutions presented in this paper are for three types of problems: (1) unfractured wells producing at a constant rate, (2) fractured wells producing at a constant rate and (3) unfractured wells producing through a critical flow prover. In the problems of Types I and 2, no corrections for non-Darcy flow were made in the results presented, since it was reasoned that the constant-rate boundary condition would facilitate such a correction if it was desired later. For the problems of Type 3, however, a condition of varying flow rate required that a non-Darcy flow correction of the type of Eq. 1 be included. This was done. Based on the numerical results presented, a number of approximations and a correlation are presented which may be useful in analyzing gas-well test data. It is assumed that the system can be described as a finite cylindrical gas reservoir produced by a single cylindrical well located at the center of the reservoir. Flow is strictly radial.

By R. J. Sherman, M. R. Achter

Creep rates have been measured for nickel at 1200°F in air and in vacuum, and related to the depth of surface cracks in the specimens tested in the two environments. The surface cracks were observed to grow faster in air than in vacuum in both short-time and long-time tests. Crack depths, however, could be correlated with creep rates only in the short-time tests. Although no cracks were observed in a relatively brittle Ni-Cr-A1 alloy creep tested at 1300°F, the appearance of alloy specimens fractured after interruption in creep indicated that there was a decrease of intergranular cohesion resulting from the diffusion of atmospheric gases into grain boundaries. PREVIOUS investigations1-3 have demonstrated that the effect of atmosphere on the high-temperature strength of nickel and nickel-base alloys may be reversed by changes in the stress or temperature of the test. At high stress and low temperature the creep-rupture life is longer in vacuum than in air, while at high temperature and low stress the relative strengths are reversed. A mechanism to explain this behavior was proposed based on two competing processes. Oxidation hardens and strengthens a metal, but adsorption of gas, by lowering surface energy, reduces the work required to propagate an intergranular crack. The controlling process is determined by temperature and stress. Basic to this mechanism is the concept that environment determines the ease of propagation of intergranular cracks and thus affects creep rate and rupture life. To explore the mechanism in greater detail, this investigation was undertaken to determine the effect of atmosphere on crack initiation and propagation rates in nickel1 and a relatively brittle Ni-Cr-A1 alloy.3 EXPERIMENTAL PROCEDURE The materials were the same as used previously. Nickel of 99.8 pct purity had the following impurity content: 0.02 pct Co, 0.03 pct Fe, 0.02 pct Mg, 0.03 pct Si, and 0.008 pct C. Rods were cold swaged from 1/2 in. to 3/8 in. in diam and machined into speci- mens with gage sections 1/4 in. in diam by 1-1/4 in. long. They were annealed in vacuum at 1600" F for 1 hr to achieve a grain size of 0.07 mm. The alloy was composed of 19.1 pct Cr, 3.6 pct Al, 1.7 pct Si, 0.57 pct Fe, 0.10 pct Mg, 0.027 pct C, 0.004 pct S, and the balance Ni. Sheet specimens of 0.500-in. width and 1.25-in. gage length were machined from 0.033-in.-thick strip and annealed in vacuum at 2000° F for 2 hr, resulting in a grain size of 0.036 mm. Large amounts of an intergranular phase were introduced as a result of the anneal. Creep tests on both materials, using equipment previously described by Shahinian; were conducted in air and in a vacuum of 1 x 10-5 mm Hg. They were continued to rupture and interrupted at various stages of the test. Although extensions were measured from dial gage readings of movement of the lever arm, it is considered that valid comparisons of creep rate may be made in this manner.l Two parameters were measured metallograph-ically* on longitudinal sections of nickel specimens interrupted during creep—the mean depth of surface cracks 2, and the density n as the number of cracks per unit length of surface. They were combined into one parameter by the relation p = n-d [1] As used here, p is equal to the total of crack depths per unit length of surface. RESULTS Nickel. It is well known that the incidence of intergranular cracking is increased with increasing rupture life. Indeed, it is evident in Tables I and I1

Jan 1, 1962

By R. L. Segall

AN unusual thermal etch figure in copper is described and an explanation in terms of twinning is suggested. A flat polycrystalline specimen of OFHC copper cut from a rolled sheet was electro-polished in orthophosphoric acid and annealed at 950°C in a vacuum of approximately 10-3 mm Hg for 2 hr. The specimen was found to be thermally etched, the markings on the surface being consistent with the assumption that they were the traces of the (111) planes which are developed preferentially because they have the lowest free energy. However, on one grain (the grain shown in Fig. 1) the traces formed an almost regular pentagon and at first sight it seemed unlikely that they could all be (111) traces. These traces were studied further because it was thought that they might be a type of growth spiral. A fringe pattern showed that this was not so, the grain being sensibly flat and the only features having steps were the striations and the faint curved line passing out from the center of the pentagons. To obtain some additional information, the specimen was deformed in tension. The effect of the stress was first to cause the appearance of lines running from the centers to the apexes of the pentagons and then to tilt the five segments so formed. At a much greater stress, appreciable slip appeared on the grain; these effects can be seen in Fig. 2. The micrograph was taken at a fairly late stage in the deformation and the tilting is quite marked. The magnification is the same as in Fig. 1, and although some slip can be seen it could be observed better by varying the illumination and using higher magnifications. In each segment of the grain, slip (which takes place on the (111) planes) was parallel to the side of the pentagon in that segment. The marked changes in direction of slip from segment to segment seemed to be incompatible with the presence of a regular array of subgrains. These results suggest that some of the five segments were twins. If this is so, since the twinning plane in copper is the (111) plane, the radial lines must be traces of the (111) planes on the surface. From the symmetry of the striations about the radial lines, these planes must be almost perpendicular to the surface. The angle between <III>directions in face-centered-cubic copper is 70&apos;32&apos;. If, in Fig. 3, OAB (triangle 1) is taken as matrix and OA, OB are (111) planes viewed edge on, then AB is in the correct direction to be the trace of either of the other two (111) planes on the surface. If triangle 2 is the twin (about the (111) plane perpendicular to the surface and containing OB) of triangle 1, then once again it can be shown that all lines are traces of (111) planes. Similarly, triangle 3 is the twin of triangle 2, 4 of 3, and 5 of both 4 and 1. (The sequence is, of course, quite arbitrary.) However, if this were the case there would be a discrepancy of 7&apos;20&apos; to be accounted for. It is suggested that the faint curved line passing outward from the center of the pentagon represents either a low angle boundary or a sixth small twin. The slight step shown by the fringes at this line might be an indication that the former is the case. This explanation does not account for the coincidence of obtaining a grain whose surface must be so close to (110) and obtaining the curious twinning described previously; it would be of interest to find a specific mechanism for this.

Jan 1, 1958

By Luiz C. Correa da Silva, Robert F. Mehl

A. D. Le Claire and R. S. Barnes (Atomic Energy Research Establishment, Harwell, Didcot, Berks., England)-—This much awaited paper admirably confirms that the Kirkendall effect is a true diffusion phenomenon and likely to be found in all diffusing systems. The most likely explanation put forward so far to account for the shift of interface is that the two components of the system, diffusing in opposite directions, do so with unequal rates so that there is a net loss of material from that half of the diffusion zone rich in the more rapidly diffusing component. This loss is accompanied, and at least partly compensated for, by a closing up or decrease in volume of this latter half of the diffusion zone and an expansion of the other half so as to tend to keep constant the overall volume per atom. This is manifest as a movement of the original interface. If this is a true picture of what is taking place then there are at least two important matters requiring further study."1—The quantitative relating of the observed shift with the independently measured separate diffusion coefficients of the two diffusing species."2—A detailed study of the mechanism and characteristics of the closing up process."We would like first to make a few remarks pertinent to these topics. In connection with the first of these, it is a pity that more and detailed measurements were not made on the Au-Ag system, the only one for which the separate diffusion coefficients of the two species have been measured.&apos;" One of us (A. D. Le C.) has calculated from Johnson&apos;s results the shift to have been expected in samples D.2 and D.3. Darken4 showed that the velocity v with which the markers move is related to the separate diffusion coefficients Dau, Dag, by the eauation:"dN"v = (Dag — Dau "dx"dN"where .is the concentration gradient at the mark-ax"ers. Under certain conditions,4, 20 it can also be shown that:"Xm"v = "2t"where x, is the total marker shift after time, t:"dN". . xm = 2t (Dag — Dau) [9]"dX"Johnson measured Dag and DAu in a chemically homogeneous alloy and so his reported figures represent the true or ideal diffusion coefficients"; the same quantities in eq 9 represent the actual diffusion coefficients as would be measured in the presence of a chemical concentration gradient, so we need to multiply Johnson&apos;s reported values of Dag and Dau by the"1 before insert-dlogN "ing them in eq 9. 7 is the activity coefficient of Ag at the concentration prevailing near the markers which we shall assume to be - 50 pct. The values of the thermodynamic factor for N = 0.5 and the temperatures at which D.2 and D.3 were annealed were obtained from thermodynamic data quoted by Darken.&apos; aN/ax was computed from the coefficient of inter-diffusion of Au and Ag given by Johnson on the assumption that in the samples D.2 and D.3, the concentration distance curve could be represented by the standard equation:""No is the original difference in concentration between the two halves of the couple, and + is the error or probability function."aN/ax at x = 0 is then given by:"adN/dx "2/nDt"and we assume that this represents the concentration gradient at the markers, although it is probable that the figure is slightly high."When all the appropriate quantities are inserted in eq 9, we find that the expected shifts are: for D.2, 0.0134 cm and for D.3, 0.0119 cm."The agreement between these results and those

Jan 1, 1952

By L. Hartsell Cash

INTRODUCTION Created in 1944 to help rebuild those economies, principally in Europe, which were seriously damaged or destroyed during the Second World War, the World Bank--or to use its correct name, the International Bank for Reconstruction and Development-began its operational phase by making a loan to the Government of France to accomplish two tasks: (i) to import coal for space heating purposes; and (ii) to buy new machinery and equipment to help rehabilitate its coal mines. Once the thrust of reconstruction in postwar Europe was largely accomplished, the World Bank Group (for today the World Bank has three separate lending windows) turned to mobilizing funds to improve living standards in developing countries, which remains its primary goal today. Over this period of time, the World Bank Group has continued to assist the world mining industry in various ways and, since 1955 the World Bank Group has financed mining or mineral processing projects with loans/credits totalling $1.5 billion. The World Bank Group consists of two institutions--the World Bank itself and the International Finance Corporation (IFC), which was founded as a separate institution in 1956 and three separate lending windows--the World Bank, the International Development Association (IDA), and IFC. The World Bank loans are provided at commercially-related interest rates but have grace periods usually of up to 3 to 5 years and repayment periods ranging from around 15 to 20 years. Since the World Bank raises its operating funds on the international capital markets in varying currencies and in varying interest rates, it relends a basket of currencies at floating interest rates which are fixed every six months to reflect the Bank&apos;s own borrowing cost. At the present time, the interest rate is just below 10% per year and in addition, a one-time front-end fee of 1/4 of 1% is charged. Also, a commitment fee of 3/4% per year is charged on the undisbursed amount of the loan itself. For loans to industrial and mining projects, it is normal to charge an additional guarantee fee of 1 to 1.5% in addition to the annual interest rate. This guarantee fee is payable to the government of the country in which the project is carried out since, by its charter, the World Bank is required to have the guarantee of the host government for each loan made in a specific country. By far the greatest source of lending funds within the World Bank Group is that of the World Bank itself and for the fiscal year ending June 30, 1984, the World Bank approved loans totalling $12 billion. The second lending window within the World Bank Group is IDA which performs the same functions as the Bank itself and has the same staff. Nevertheless, its loans (called credits) are made on much softer terms and are made to the poorest nations only. IDA funds are subscribed by the wealthier countries, usually as grants, and these are relent as credits to those countries with the lowest per capita income. IDA credits are made for 50 year periods, including 10 years of grace, to the government itself. The credits are interest free, but there is a service charge of 3/4% per year on the amount withdrawn and outstanding to defray the administrative costs of IDA. Credits approved during fiscal 1984 totalled $3.5 billion. The third lending window is IFC. While IFC is a separate corporation and operates quite separately from the World Bank and has its own staff and regulations, it works very closely with the World Bank on its overall approach to the mining sector and to a particular country. IFC&apos;s mission is essentially to supply venture capital and to stimulate development of the local private sector in capital markets as well as to promote the international flow of private capital to developing countries. Unlike the World Bank and IDA, the IFC does not lend directly to governments

Jan 1, 1985

By R. M. Asimow

Both smith1 and wells2 have shown that the dif-fusivity of carbon in austenite increases rapidly with increasing carbon concentration. Smith has shown, in addition, that part but not all of this increase can be attributed to the concentration dependence of the activity coefficient of carbon in austenite. From the work of Eshelby&apos;, it is known that, because of the image displacements, there is a uniform dilatation of the material in a body containing random centers of dilatation. It is thus tempting to explain the enhanced diffusivity as resulting from this apparent negative pressure caused by the interstitial carbon atoms.* That is, the activation free energy for diffusion is not directly a function of concentration if we consider that the alloy is subjected to a concentration-dependent pressure. To proceed with a quantitative solution, it is necessary to determine the activation volume AV for the diffusion process. An exact calculation of AV is quite a difficult problem and does not appear to have been solved as yet. A simpler procedure is to use the semiempirical, macroscopic theory of seyes&apos; which relates the activation free energy AG to AV. Keyes has shown that for many types of diffusion processes the following relationship is valid Where p is the Gruneisen constant and x the compressibility. This relationship is based on the assumption that AG can be identified with strain-energy terms. In general there will also be contributions to AG due to a change in the energy of the valence electrons of the metal; thus the relation must be considered largely empirical. Surprisingly, for self-diffusion where it is well-known that the electronic contribution is quite important,&apos; the Keyes relation works quite well for many systems. For interstitial diffusion where it might be expected that the relationship is on a firmer theoretical basis, the limited experimental data available is not in particularly good agreement as can be seen from Table I. However, it must be remembered that besides the uncertain basis of the Keyes formula there is considerable uncertainty in some of the experimental values of AV. The only real justification for using the Keyes formula in the present analysis is that it gives a result which satisfactorily solves the problem at hand and, further, there are no more reliable procedures for calculating AV available. The coefficient 3 in Eq. [I] is determined such that the room-temperature value for x is to be used. The activation entropy AS is estimated as 8.95 x 10"3 kcal per OK mole using the values in Table I1 and the Zener" relation AS = PAHIT, where p is a dimensionless thermal coefficient of Young&apos;s modulus which is to be evaluated at low values of T/T,, aH is the activation enthalpy, and T, is the melting temperature of the alloy. The resulting value of AG at 1000°C is 25.6 kcal per mole. The Gruneisen constant (p = 3cup/XC,), where p is the density, is evaluated from the room-temperature data in Table I1 after calculating C, from the relation. A value of p = 8.32 g per cu cm based on the value of a. in Table I is used. The result is C, = 5.0 x lo6 erg per g, H = 2.32, and AV = 3.41 cu cm per mole at 1000°C and infinite carbon dilution. It is assumed that the activation volume is not a function of carbon concentration. The theory could be refined to consider AV a function of concentration, but due to the uncertainties in the parameters there seems little justification for this. Carbon dissolved in austenite forms a nonideal solid solution, so that in writing an equation for. the diffusivity of carbon it is necessary to take into account the change in activity coefficient with concentration. The resulting equation is16

Jan 1, 1964

By G. A. Deitz, J. Halpren

The kinetics of dissolution of silver in cyanide solutions under oxygen pressure have been investigated over a wide range of conditions with a view to establishing the reactions involved and the factors which influence the rate. The results indicate that the rate is determined principally by the transport of reactants in solution to the silver surface. The thermodynamic features of the reaction with particular reference to the influence of pH and CN- are also discussed and summarized in the form of potential-pH diagrams. METALLIC silver is readily attacked and dissolved by cyanide solutions in the presence of oxygen. This reaction has long been recognized and extensively applied1 in the well-known cyanide process for the extraction of silver from its ores. While this process has been subjected in the past to a number of investigations2,3 both of a practical and fundamental nature, some features relating to the chemistry of the reactions involved, the role of oxygen, the nature of the rate-controlling step, and the effects of pH and certain reagents such as lime, are still not fully understood. It was felt that this situation justified a further investigation of the reaction, made with a view to obtaining a better understanding of its kinetics and mechanism. In the present investigation rate curves for the dissolution of silver were determined over an extensive range of carefully controlled reaction conditions. By carrying out the reactions in a pressure vessel, the partial pressure of oxygen, and hence its concentration, could be varied widely. The influence on the reaction of other variables including temperature, pH, and the concentrations of cyanide, peroxide, and other salts was also examined. The results of these kinetic studies are presented and discussed in this paper, together with a summary of available thermodynamic information relating to the possible reactions which can accompany the attack on silver by aqueous solutions of cyanide and oxygen. Chemistry and Thermodynamics of the Reaction The chemistry of the reactions of gold and silver with aqueous cyanide solutions has been the subject of several recent reviews.&apos;." It has been proposed&apos; that the following reaction occurs when silver dissolves in cyanide solutions in the presence of oxygen: 4Ag + 8CN- + 0, + 2H.0 -t 4Ag(CN); + 40H- [la] An equation of this form, for the corresponding dissolution of gold, was first suggested by Elsner." Bodlaender5 proposed a similar overall reaction, but suggested that it took place in two steps, 2Ag + 4CN- + O2 + 2H2O ? 2Ag(CN),- + 2OH- + H2O2 [2a] followed by 2Ag + 4CN- + H2O2? 2Ag(CN); + 20H- [3a] On the other hand, Janin- suggested that the dissolution of gold can occur with the liberation of hydrogen, rather than by reduction of oxygen. The corresponding equation for the dissolution of silver is 2Ag + 4CN- + 2H20 -t 2Ag(CN); + 20H + H2 [4a] All these reactions represent oxidation-reduction processes and may be resolved into the corresponding separate oxidation and reduction components. The oxidation step involves the formation of the argentocyanide ion and is the same for all the reactions, i.e., Ag + 2CN? Ag(CN)2 + e [51 However, reactions la, 2a, 3a, and 4a differ in the nature of the reduction steps which are, respectively, O2 + 2H2O + 4e ? 4OH- [lb] O2 + 2H2O + 2e ? H2O2 + 2OH- [2b] H2O2 + 2e ? 2OH- [3b] 2H2O + 2e? 20H- + H2 [4b]

Jan 1, 1954

By Peter M. Fozzard

The San Bartolomt silver deposit was discovered by a United Nations team of geologists working with a counter- part team of staff of the Ecuadorian Government&apos;s General Directorate of Geology and Mines (DGGM). The Phase I project over five areas of operation during which this discovery was made was financed through a United Nations Development Program contribution of $860,000 and an Ecuadorian Government participation of about $680,000 equivalent. Existence of mineralization at San Bartolomé was first recognized in 1966 when a reconnaissance geochemical stream-sediment program was carried out over a 10 500 km2 (4,054 sq mile) area centered around the city of Cuenca in southern Ecuador. Over the course of this project more than 10,000 samples of stream-sediment, soil, and rock materials were collected. Average costs per sample were $10.00, as follows: collection, $5; sample preparation, $1.60; assay work, $3.40. Initially in the program (1965-1966) sediments were collected along all motorable roads and tracks. Routine analyses, originally by colorimetry and later by AAS, were for Cu, Pb, Zn and occasionally As, Ni, and Co. Discovery geochemical samples from the San Bartolomé drainage area were among the first to be taken in 1965. As luck would have it, the road along which this traverse was taken passes only some 100 m (328 ft) downstream from the mineralized suboutcrop. The relevant two streams sampled are of inconsequential size, some 1 m (3.3 ft) in width, with a limited flow volume throughout the year. Original anomalies were recognized through cold-extractable Cu/Zn analyses. The pH of all river waters was also recorded at sample sites. Resampling the discovery sediments when AAS became available showed total extractable values of between 150 ppm-300 ppm Zn, 550 ppm Pb, and 10 ppm Ag. In 1967 the first followup was by rough-and-ready means. Dithizone field-kits (THM) were used to rapidly test soils from the surrounding area. The area has no outcrop. This work allowed the definition of an area of interest of some 2 km (1.2 miles) x 500 m (1640 ft). Six approximately 1 km (0.6 mile) to 1.5 km (0.9 miles) lines spaced at approximate 250 m (820 ft) intervals were established and used for IP surveys and soil sampling at 50 m (164 ft) intervals. Where one of the lines crossed the westernmost geochemical discovery creek a first-priority geophysical anomaly coincided with a major Zn/Pb (and later Ag) soil anomaly. A pit was sunk and encountered mineralized vein material at a depth of 1.5 m (5 ft). This lucky glory hole confirmed the geochemical discovery and prompted systematic followup. Immediately, costeaning of the west bank of the discovery creek, the Quebrada Ocashuaico, was carried out and exposed weathered and leached mineralization. Nearly 100 mineralized veinlets ranging in thickness from 0.5 cm (0.2 in.) to 8 cm (3 in.) were exposed across the 180 m (59 1 ft) costean. Sixty mineralized veinlets were determined over a 90 m (295 ft) wide zone. Sampling delineated minable widths averaging between 0.16 and 0.31 kg/t (5 and 10 oz per st) Ag with associated copper (very sporadic) lead and zinc. Over the period 1968- 1972 a considerable amount of detailed work was completed: detailed IP, EM Turam, magnetic and mise-a-la-masse geophysics, very detailed soil- sampling, trenching, drilling and glory-hole drifting, and cross-cutting. Numerous problems were encountered: the area was found to be a most difficult geoelectrical target; zero outcrop; pyrite (nonargentiferous zones) associated with faulting; mineralized groundwater; extensive clay development; loss of diamond drill-core, and no two-dimensional surface information. As the program developed the complexity of the structure was slowly unravelled, using a degree of good guesswork. Apart from photogeological and ground geological mapping at various scales, the following

Jan 1, 1985

By R. A. Harrington

THE structure of anodic films formed on aluminum and other metals under varied conditions is not well known despite the wide use of such films both as protective coatings and as the dielectric medium in elec-trolytic condensers. The present work was undertaken as a survey of the possibilities of electron diffraction in the investigation of anodic films, especially in comparing the properties of anodic films formed under dif-ferent sets of conditions and subjected to various subsequent treatments. In addition, an effort has been made to compare surface films formed on aluminum by anodic treatment with surface films formed by heating, immersion in chemicals, etc, The electron diffraction method in many cases has been successfully applied to the study of thin surface films. Its principal advantage is that it can be used without removing the films from the base material upon which they have been formed. The low penetrating power of electrons, in the "reflection" diffraction method which has been used in this work, prevents the appearance of diffraction patterns from substances at depths greater than about 100 Angstrom units (10-6 cm.). Different investigations of the structure of anodic films have shown widely varying results, depending on the methods used in preparing the films. Apparently under some conditions these films are crystalline and under other conditions they are amorphous, and it has been difficult to say which type of structure will be found in any particular case. Schmid and Wassermann&apos;s&apos; X-ray diffraction patterns of eloxal? films show two broad, diffuse bands, which these investigators attribute to finely divided cubic y-Al2O3-§ Burgers, Claassen, and Zernicke3 obtained sharp X-ray

Jan 1, 1940

TO THE BOARD OF DIRECTORS AND MEMBERS OF THE AMERICAN INSTITUTE OF MINING AND METALLURGICAL ENGINEERS GENTLEMEN: Submitted herewith are the report of the Treasurer for the year 1939 and reports for the same year of the following standing committees: Admissions, Membership, Papers and Publications, Mining and Metallurgy (Magazine), Library, Speakers for Local Sections and Student Societies, and Student Relations. These reports present additional details. Membership.-For the second year in Succession membership reached a new high level for all time, as indicated in the accompanying tabulation in which "Members" includes all categories except Student Associates. [END 1938 END 1939 NET GAIN Members9, 57 610, 163 587 Student Associates 2,898 3,760 862 12,474 13,923 1,449] Net gain in membership (aside from Student Associates) was 587 compared with 744 in 1938, despite the fact that applications received in 1939 exceeded those received in 1938 (1271 against 1162). The smaller net gain is accounted for in three ways: (1) A greater lag in enrollment of those elected in the last quarter of the year; (2) an increase in the number of applications involving change of status from Junior Member to Member; and (3) an increase of 167 in the loss by death by resignation and by suspension in 1939 as compared with 1938. Experience shows that at the end of a year of less prosperous conditions in the mineral industries, and, therefore, among engineers engaged in these industries, resignations and suspensions are more numerous. Business and industrial indexes all show 1938 to have been somewhat less prosperous than 1937; but the improvement in 1939 should be reflected in the record for 1940.

Jan 1, 1940

By Michael Tenenbaum, T. L. Joseph

In a previous investigation1 the authors studied the effect of pressure on the reduction of iron ores by hydrogen. With hydrogen as a reducing agent, the rate of reduction was increased substantially by increasing the pressure from 1 to 2 atmospheres. The results with hydrogen prompted the present study of the effect of pressure on reduction with carbon monoxide and with mixtures of carbon monoxide and nitrogen. Features of Reduction Process The gas stream in the lower part of the blast furnace always contains sufficient concentrations of reducing gases to complete reduction provided sufficient time is allowed for the reaction to proceed. Reducing gases react immediately with the iron oxide on the surface of lumps of ore. However, as the unreduced surface recedes from the easily accessible exterior of the lump, the reaction proceeds by virtue of the diffusion of the gases into and out of individual pieces. The rate of diffusion of gases, which undoubtedly plays an important role in the reduction of iron ores, depends on several factors, most important of which are: (1) molecular weight or density, (2) pressure, (3) temperature, (4) concentration gradient. Thus, the rate of reduction of a lump of iron ore at any temperature will depend not only on the specific reaction rate but also upon: (1) available surface of unreduced iron oxide, (2) rate of diffusion of the reducing gas to the reacting surface, (3) rate of effusion of the gaseous products of the reaction from the reacting surface, (4) adsorption of the gases on the reacting surface. The various features of the reduction process were discussed in previous work and need not be reviewed. However, in order to explain

Jan 1, 1940

By Michael Tenenbaum, T. L. Joseph

In a previous investigation1 the authors studied the effect of pressure on the reduction of iron ores by hydrogen. With hydrogen as a reducing agent, the rate of reduction was increased substantially by increasing the pressure from 1 to 2 atmospheres. The results with hydrogen prompted the present study of the effect of pressure on reduction with carbon monoxide and with mixtures of carbon monoxide and nitrogen. Features of Reduction Process The gas stream in the lower part of the blast furnace always contains sufficient concentrations of reducing gases to complete reduction provided sufficient time is allowed for the reaction to proceed. Reducing gases react immediately with the iron oxide on the surface of lumps of ore. However, as the unreduced surface recedes from the easily accessible exterior of the lump, the reaction proceeds by virtue of the diffusion of the gases into and out of individual pieces. The rate of diffusion of gases, which undoubtedly plays an important role in the reduction of iron ores, depends on several factors, most important of which are: (1) molecular weight or density, (2) pressure, (3) temperature, (4) concentration gradient. Thus, the rate of reduction of a lump of iron ore at any temperature will depend not only on the specific reaction rate but also upon: (1) available surface of unreduced iron oxide, (2) rate of diffusion of the reducing gas to the reacting surface, (3) rate of effusion of the gaseous products of the reaction from the reacting surface, (4) adsorption of the gases on the reacting surface. The various features of the reduction process were discussed in previous work and need not be reviewed. However, in order to explain

Jan 1, 1940