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By Dwight H. Seely, Louis R. Records

A process for low-temperature dehydration of natural gas utilizing Joule-Thomson effect in expansion through a throttling orifice has been tested in a full-scale field installation. The results of these tests are presented in the form of performance curves from which the process may be easily evaluated. The effect of separation temperature on condensate recovery from the process is also shown. INTRODUCTION The transportation of natural gas from producing well to the consumer has always encountered the problem of hydrate prevention. This problem has become increasingly important in the past ten years due to the rapid increase in produced gas volumes, production pressures, transportation pressures and distance from producing wells to consumer. Natural gas, as normally produced from gas or gas-condensate wells, is saturated with water vapor at well-head conditions of temuerature and pressure. The solution of the hydrate problem require; but one basic process — dehydration of the gas to a water content which will result in a water dew-point below the minimum temperature to be encountered from the producing well to the point of consumption. Much of the recent development of gas and gas-condensate reserves in the Gulf Coast Area has been in locations which are accessible only by water. High well-head pressures, pipeline construction and maintenance costs and the desirability of final central gas-condensate separation facilities have stimulated the development of dehydration equipment which can be installed at each well and which will permit hydrate-free transportation of both gas and condensate in the same line to central facilities. There are four types of natural gas dehydration processes now used: 1. Adsorptive processes. 2. Absorptive processes. 3. Chemical reaction processes. 4. Refrigeration processes. The first three of these processes are indirect in that they require use of adsorbents, absorbents or reactive chemicals. These materials require regeneration and part of the total gas stream is consumed in the regenerative process. Indirect processes have a wide range of flexibility as defined by allowable operating pressure and temperature, but most are not easily adapted to automatic operation. The refrigeration process described in this paper was designed for installation at the producing well-head. It requires no regenerative cycle and with normal well-head temperatures no external source of heat. The flexibility of this process is limited only by the pressure drop which may be allowed between well-head and transportation line. THEORY There are three basic physical concepts involved in the low temperature dehydration process. These are: 1. Formation of hydrocarbon hydrates. 2. Joule-Thompson effect resulting from the expansion of gaseous mixtures through a throttling orifice. 3. The equilibrium composition characteristics of water vapor and gaseous hydrocarbon mixture.. The chemical composition and physical structure of hydrate; have been described by several investigators.3,4,5,10 Specific conditions of temperature, pressure and composition as well as the requirements for turbulence and presence of free water necessary for hydrate formation have been described by Katz.6 Natural gas hydrates, as they are found in plugged gas pipe lines, have the appearance of packed snow. The mass of these hydrates has low continuous porosity and permeability. Joule-Thomson effect. or the reduction in temperature which occurs when natural gas is throttled throusll a restrictive orifice, is the basic phenomenon which permits efficient use of refrigeration for the purpose of dehydrating natural gas. Joule-Thomson coefficients for gafeous mixture; of methane with ethane and with butane have been reported by Buder.-I~olzer, Sage and Lacey.2 Brown1 predicted temperature drops for pressure drops from enthalpy-entropy calculations. Aside from this work there were no fundamental data found which would be applicable to natural gas mixtures of varying spe-

Jan 1, 1951

By B. P. Boisen

INTRODUCTION Application Measurement of rock deformation is essential to stability and behavioral monitoring of underground openings. The difficulties of obtaining adequate sample distribution, density, and orientation can frequently be overcome by the use of single and multiple position borehole extensometers. In its simplest form, a borehole extensometer consists of an instrument head, usually anchored in the collar of a borehole, and a number of in-hole anchors, each of which is fixed in place at a known distance from the collar. As rock adjacent to the borehole deforms, the component parallel to the borehole direction causes a distance change between adjacent in-hole anchors, as well as a distance change between individual anchors and the instrument head. These changes are measured by means of a mechanical link (usually wire or rod) extending to the instrument head from each anchor. The resulting data can be used to compute the distribution, magnitude, rate, and acceleration of deformation in the material intersected by the extensometer's borehole. Wire Vs. Rod Extensometers Since the early 1960s myriad varieties of borehole extensometers have become available through the combination of various special features of two basic instruments, the wire and rod versions of borehole extensometers. Recent publications have recommended shallow depth limitations for wire extensometers, and favor rod extensometers for a broad range of borehole inclinations and depths. There are three main reasons for using a deep wire system: its cost effectiveness; the fact that tremendous depth means tremendous rod weight which will cause the rod to buckle or rub against the borehole or casing wall; and users' attitude and proper understanding of how to install and apply a wire-type extensometer. Here experience plays a big role. Over the years, many have learned the hard way that untensioned rod extensometers are simple and inherently inexpensive, but limited to vertical up holes where sensitivity is not influenced by friction between the rod elements and the borehole wall or protective conduit, the inertia of the rod elements, or the direction of the movement to be measured. In deep, horizontal, or inclined holes, and in instances where compressive as well as tensile strains or displacements are anticipated, tensioned rod or wire systems are preferred. System Components Borehole extensometers are made up of at least the following five principal components: the instrument head; the collar anchor assembly; the downhole system of anchors and rods or wires; the signal cable if the head is equipped for electronic readout; and the readout apparatus, whether mechanical or electronic. These components are shown in Fig. 1. Borehole Requirements Most extensometers are designed for installation in nominal 75 to 57-mm (3.0 to 2.25-in.) diam drill holes. Either a diamond drill or a percussion drill hole is satisfactory, provided the variation in drill-hole diameter is within the tolerance of the standard anchor design. The basic system may be modified for other hole diameters by changing the dimensions of the collar anchor and downhole anchor assemblies. Some instrument heads and collar anchor assemblies require enlarged borehole collars, though usually not over 150 mm (6 in.) for a depth of 1 m (3 ft). It is desirable, although not essential, that holes be free-draining. Holes must be clean and free of debris before installation. Depth/Orientation of Extensometer Boreholes Extensometers are designed to measure axial strain components in the instrumented drill hole. As the drill hole is axially deformed, the distances between individual downhole anchors and the instrument head change, as do the distances between adjacent anchors. The distance changes measured by a multiple position borehole extensometer, for example, are reduced to functions of time, hole depth, anchor position, or other parameters of significance in terms of the structure under investigation.

Jan 1, 1982

By A. F. Witt, A. M. Gaudin, A. K. Biswas

Finite contact angles in the rutile-water-organic liquid system are traceable to contamination or are due to addition of a surface-active agent. Finite contact angles are invariably accompanied by hysteresis.1-7 Besides surfactant concentration and pH, the nature of the organic liquid is found to be a factor influencing the magnitude of contact angle hysteresis. In a recent paper the authors have reviewed principles and applications of measurement methods for contact angles and their hysteresis.22 In this paper, these methods are applied to a system consisting of rutile, an organic liquid (benzene, decane, or dode-cane) and water. Surfactant (dodecylamine hydro-chloride) was used at various concentrations and various pH values. MATERIALS A synthetic rutile crystal supplied by the Linde Co. was used. It is a cylinder 1/2 in. diam, with faces cut perpendicular to the c-axis. The crystal is stated to be alumina-free and to be 99.9% pure. Rutile is a high surface energy solid, its calculated average field strength being 2.7 x 105 e.s.u.,9 its dielectric constant10 is 114. The zero point of charge of rutile was measured11 and found to be at pH 6.0. The atomic distances and bond angles of the tetragonal crystal of rutile have been precisely determined.l2 The organic liquids were specially purified. Reagent grade benzene was repeatedly shaken with concentrated sulfuric acid to remove thiophene, then neutralized with sodium hydroxide solution, rinsed with distilled water, dried overnight over anhydrous calcium chloride and filtered. The refractive index of this chemically purified benzene was 1.4977 (at 25°C) - very close to that of pure benzene (n25 1.4979).13 Both n-decane and n-dodecane were washed with aqueous sodium hydroxide, concentrated sulfuric acid (repeatedly, until the acid layer was colorless) and again with alkali, to free the organic hydrocarbon from fatty acids and unsaturated hydrocarbons. The organic phases were subsequently washed with distilled water and dried over anhydrous sodium sulfate. The filtered hydrocarbons were then distilled under vacuum (9-10 mm pressure). Decane, thus purified, showed traces of unsaturated and of carboxylic compounds. On gas chromatographic analysis the purified n-dodecane showed the presence of two impurities. However, the relative retention times of these components did not change substantially when measured on a polar or a nonpolar column. This indicates that the compounds were probably in the same polarity class, i.e. the components were nonpolar like dodecane. Conductivity water has always been one of the liquids. Conductivity of the water used was 10-6 ohm-' cm". Dodecyl ammonium chloride was prepared from pure amine (supplied by Armour and Co., Chicago), by Li in the MIT Mineral Engineering Laboratory.14 The critical micelle concentration at 25°C is known, 0.0138 mol per liter15 or 3.06 gpl. All our experiments have been done at concentrations lower than the critical micelle concentration. The glass vessels, glass drop holder and the rutile crystal were all cleaned with hot chromic acid followed by distilled water, concentrated hydrochloric acid, and again distilled water, and conductivity water. During the experiments, a nitrogen atmosphere was maintained. For this purpose, commercially purified nitrogen was further purified by passing it over hot copper wire at 450°C, then through columns of acidic chromous chloride solution, concentrated alkali solution and distilled water. APPARATUS AND METHODS Hysteresis was produced by the "captive drop" or constant volume drop method as well as by the "expanding-contracting drop" or variable volume drop method. The image of the drop while it is expanding, contracting or moving is projected on a screen and photographed. The developed film is projected through an enlarger and the contact angles measured with a protractor.

Jan 1, 1964

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', 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' 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,' 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'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 M. J. Marcinkowski, K. S. Sree Harsha

A detailed numerical analysis has been made of the equilibrium configuration of partial dislocations in a blocked deformation twin under an externally applied stress. Twins made up of both pure screw and pure edge partials have been considered. The components of stress in the vicinity of the twin tip associated with each of these configurations have been plotted. It has been found that at some critical degree of oblateness the shear stress fields of the blocked screw or edge twin can both sPontaneously nucleate slip, whereas only the component of stress oxx about the edge twin can nucleate and propagate cracks. TWINNING becomes a predominant mode of plastic deformation at low temperatures and/or high strain rates. Fig. l(a) shows what must be the first step in the formation of a deformation twin, namely the formation of a loop of imperfect dislocation bounding a stacking fault. In an fcc crystal the partial dislocations have Burgers vectors of the type 1/6 a,(112) and the fault is of the intrinsic type while in the bcc crystal the partials have Burgers vectors of the type ao(lll). The stacking sequence of (111) planes in a perfect fcc crystal is given by ABC ABC, and so forth, and in one which contains a twin by ABCABACBA, and so forth. It is apparent that the stacking fault and twin give rise to no mistakes associated with adjacent close-packed planes; however, with respect to second-neighbor close-packed planes the faulted crystal has twice as many mistakes as the twin. The energy of the twin boundary may thus be taken to be one-half that of the intrinsic fault boundary. In the case of the bcc crystal the stacking sequence of (112) planes is given by ABCDEFABCD, and so forth, in a perfect crystal, by ABCDCDEFA, and so forth, in a crystal which contains a fault, and by ABCDCBAF, and so forth, in one which contains a twin. An analysis similar to that applied in the fcc crystal shows that both the fault as well as the twin involve no neighbor violations across adjacent planes. However, there are twice as many violations across second-neighbor (112) planes associated with the fault as compared to that of the twin. Thus once again the energy of the twin boundary may be taken as one-half that of the fault. It is important to note that, unlike the fcc, the faults in the bcc crystal involve first nearest-neighbor violations and are thus expected to be of much higher energy than those in fcc crystals. A more detailed analysis of the material discussed above can be found in Ref. 1. To a good approximation then, the lenticular twin shown in Fig. l(b) can be generated by adding partial dislocation loops on successive (111) planes for fcc crystals or (112) planes for bcc crystals in the manner shown, with no additional expenditure of chemical energy other than that required for the fault shown in Fig. l(a). In practice, deformation twins are much more extended than that shown in Fig. l(b) and more closely resemble one shown schematically in Fig. l(c). It is readily apparent that the free energy of the twin and matrix are identical. In those cases where the partials lead to a structural change, the free energy of the material contained within the dislocation array is lower than that of the matrix and we have the so-called martensite transformation. The present investigation is the first in a series of five major theoretical-experimental efforts which will deal with the static and dynamic behavior of twin nucleation and growth. There has been a recent surge in activity pertaining to the equilibrium shapes of twin lamellae2'3 and

Jan 1, 1969

By T. M. Kegley, J. H. Frye, D. L. McElroy, M. L. Picklesimer, E. E. Stansbury

Measurements of rate of growth, thermodymmic quantities, and partitioning of Mn are reported for high-purity eutectoid Fe-C and Fe-C-Mn steels for the auistenite-pearlite reaction. Evaluztion of the cotnstants of a derived-rate equation with these data indicate that Mn additions cause the decrease observed by increasivg the activation energy and apparent activation entropy or the movenment of complexes at the interface. A diffusion-controlled mechanism is not required. Appreciable partitioning of Mn to cementite occurs entirely behind the austenite-pearlite interface for more than 30°C of subcooling. ThE growth of pearlite from austenite has been extensively studied over a period of years. but the rate-controlling step in the process is not known nor is the mechanisrn of the effect of alloying elements understood. A comprehensive review of the subject has been given by Mehl and Hagel. The present study has been concerned with further considerations of the effects of alloying elements on the rate of growth of pearlite. Analytical relatioriships for the rate of growth of pearlite have been considered by Zener.2 Turnbull,3 Machlin,4 Cahn.5 Frye,6 and Frye et a1.7 The derived expressions in each case involve the free energy of the transformation. the interlamellar spacing. and some rate term of the nature of the diffusion coefficient. mobility or frequency of occurrence of some rate-determining step. The treatments. of course. differ in detail. Further consideration is given in the present paper to the equation of Frye, Stansbury. and McElroy which was derived from modified absolute rate theory without in any way specifying the mechanism of the reaction. This equation is r=c ? T ? F exp -?E*/RT [1] where r = rate of growth in mm/sec c = a constant AT = equilibrium transformation temperature minus actual transformation temperature "C ?F = free energy per mol of austenite minus that of pearlite ?E* = activation energy R= gas constant ?F in Eq. [1] is computed from the following: ?F=?H?T/To - ?T' dT' ?T' ?CdT"/T" [2] To To where AH is the enthalpy per mol of austenite minus that of pearlite at the equilibrium temperature, To, and AC is the difference in specific heat between austenite and pearlite per mol. Subsequently, Darken, Fisher, and Galligan8 have reported that a layer of ferrite separates pearlite from austenite at the growing interface (i,e., the advancing face of Fe3C is in contact with ferrite, not austenite) and the ratio of the thickness of this layer to the spacing of the pearlite has not been found to vary with alloy content or transformation temperature. This observation does not require any alteration in the above equation: however, it may require that a different significance be attached to the factor, AT. The AT term appears in Eq. [I] as a consequence of a factor for the amount of growth per complex transformed at the interface.* It is based *This is not the sole reason for expecting such a relationship. See Ref. 7._______________________________________________________ on a l/2 ?T dependence of the interlamellar spacing. Zener2 has developed a theory which leads to Soa 1/?V where So = the pearlite interlamellar spacing. This relation is as consistent with the data on interlamellar spacing as other relationships, although, as pointed out by Mehl and Hagel,1 the data are not sufficiently precise to consider the relationship as confirmed. The work of Darken, Fisher, and Galligan8 requires that the above be written where f = the thickness of ferrite layer between austenite and pearlite. The present paper is concerned with iron-carbon-manganese eutectoid alloys and reports experimental measurements of the following kinds: 1) the effect of

Jan 1, 1961

By R. S. Rickard, M. C. Fuerstenau

Anodic polarization curves for iron dissolution and cathodic polarization curves for copper deposition and ferric and hydrogen ion reduction were studied. These results were used to predict the relative rates of the reactions: The rates of the first two reactions were found to be first order with respect to the reacting ion, and the rale-controlling step was diffusion of the ions to the callzode surface. The rate of hydrogen ion reduction in an oxygen-free solution is dependent on the reciprocal of the square root of the hydrogen ion activity. In solutions containing oxygen, the rate of hydrogen reduction becomes dependent on the square root of the partial pressure of oxygen. At equal concentrations copper precipitation occurs about twice as fast as ferric ion reduction. In an air-saturated solution containing 0.01 M cupric ion at pH 2, the rate of hydrogen ion reduction zs about 10 times slower than that of copper precipitation. At pH values below 3, the rate of hydrogen reduction in oxygen-free solutions is very slozu. COPPER cementation has been utilized industrially for many years as a means of recovering copper from aqueous solutions. There are many different types of cementation plants, but all simply provide a means of contacting iron with relatively dilute copper solutions. In the past little or no attention has been paid to rates or mechanisms of the reactions involved. As a result, this and other studies'-3 have been undertaken recently to establish the important parameters in this system. The reactions involved in copper cementation by iron are: Since transfer of charge is involved in every case, these reactions should be considered from an electrochemical point of view. In any electrochemical system involving electrolytic conduction, passage of electrons necessitates ion transfer to the respective electrodes according to Faraday's law. The current in the system will be proportional to the rate of ion transfer, and, therefore, when the current in the galvanic cell is known, the rates of the reactions involved can be determined. Galvanostatic electrode measurements5" are applicable for these electrochemical studies, in that with this technique polarization curves (current density vs electrode potential) are established by impressing a constant current through an electrode and measuring the electrode potential. Once the current density, electrode potential, and reacting area are known for each reaction in this cementation system, the rates of the iron-consuming reactions can be determined. EXPERIMENTAL MATERIALS Several metal electrodes were used in this investigation; they are shown in Table I. Solutions were made with reagent-grade salts and conductivity water. Air, nitrogen, and oxygen were employed. All of these gases were saturated with water and degreased prior to use. EXPERIMENTAL PROCEDURE The experimental work was divided into two general areas. The first area involved galvanostatic measurements, which were used to determine the rates of reactions as a function of various parameters. The second area comprised actual cementation experiments to check the rates predicted from the electrode measurements. Galvanostatic Electrode Experiments. Polarization curves were obtained using a standard galvanostatic technique5'= with the apparatus shown in Fig. 1. The various electrode polarization experiments were run the same way except for changes in solution composition, polarity, and type of measured electrode. The general procedure involved the following steps: 1) a solution was made 0.5 M in sulfate ion and to the desired cation concentrations; this solution was placed in a constant-temperature bath and saturated with the desired gas; 2) the electrodes were cleaned and placed in the electrode holder; 3) the previously cleaned apparatus was assembled and immersed in a constant-temperature water bath (temperature controlled to ± 0.05"C); 4) the electrode was then positioned; the solutions were introduced, and the polarization meas-

Jan 1, 1969

By F. Liu, S. Rezaei, M. Muinonen, M. Barati, V. L. Lakshmanan, S. Marcuson

Canadian nickel-copper ore deposits have been a major source of nickel, copper, cobalt and precious metals for more than 100 years. The two main minerals of interest, pentlandite (Pn, (Ni,Fe)9S8) and chalcopyrite (Cp, CuFeS2), are usually accompanied by large quantities of pyrrhotite (Po, Fe1-xS). Until the 1950s, Po containing small amounts of nickel was routinely smelted as part of the valuable Ni concentrate. The rapid growth in Ni demand following the Second World War created impetus to treat the Po separately. This action would liberate a valuable smelting capacity for higher value Pn, allow for recovery of Ni locked in Po, convert the Fe to iron oxide or metallic iron pellets, and recover S as sulphuric acid or elemental sulphur. The roasting process also has the potential to produce energy due to the highly exothermic oxidation of Po. The Ni industry would then have a “waste-free” process. Both Inco (now Vale) and Falconbridge (now Glencore) developed processes and built large industrial plants for this purpose that operated with some success. But technical issues and tenuous economics were continual challenges. By the early 1980s these industrial operations were closed. Sophisticated froth flotation methods of rejecting Po were developed, and Po containing up to 1% Ni became a waste material reporting to the tailings stream. As part of a major study on possible processing methods of Po for both value recovery and waste remediation, this paper presents a historical perspective on Canadian Po tailings with regards to their generation, inventory, value, and attempts to process them.

Jan 1, 2017

By J. L. Fitch, B. G. Hurd

The presence of gypsum in samples subjected to standard core analysis introduces serious errors in the measurement of water saturation and porosity. The magnitude of these errors, depending upon the type of analysis procedure used, has been evaluated experimentally and theoretically. Water-saturated pore volumes determined by vacuum distillation or retort procedures may be too high by as much as 48 per cent of the volume of gypsum present. The maximum error in this value determined by Dean-Stark extraction with toluene is 36 per cent of the gypsum volume. If pore space is measured by a Boyle's law type porosimeter the maximum erorr due to gypsum is 38 per cent of the original gypsum volume present. The conscientious core analyst may eliminate the errors caused by gypsum by either of two methods. He may apply suitable corrections for the water of crystallization removed from gypsum, or take special precautions to prevent dehydration of gypsum during core cleaning and alzalysis procedures. These alternatives are discussed and methods for obtaining reliable core analysis data are proposed. Gypsum (CaSO4 . 2H2O) occurs as a common mineral in many of the world's sedimentary basins. In addition to its presence as primary bedded evaporitic deposits, it is often found as secondary replacement zones and pore-fillings in host rocks. That it may cause false indications in porosity, both on neutron logs and in standard core analysis, has been generally recognized. False porosity interpretations from neutron logs result because the chemically bound water in gypsum attenuates neutrons as effectively as free water. Errors in core analysis result when gypsum is dehydrated prior to or during the analysis. Vacuum retort procedures used by many laboratories to determine fluid saturation and porosity effect a complete removal of water of crystallization from gypsum. The crystal water, distilled and collected with free water from the sample, is counted as water-sat11rated pore space. Dehydration of gypsum results in a decrease in volume occupied by calcium sulfate and a corresponding increase in pore volume. Thus, if gypsum is dehydrated by sample cleaning and drying procedures, subsequent porosity measurements with gas expansion or compression instruments will be high. The qualitative effect of gypsum on porosity determinations by retort procedures was discussed in a recent article by Bynum and Koepl3. They concluded that since false porosity was interpreted as being water saturated, determinations of oil content were not affected. Others in the industry, however, have pointed out that porosity values are often used with values of water saturation determined independently, e.g., from electric resistivity logs in making reserve estimates. Values of water saturation calculated from the formation resistivity using the Archie equation, S4= are actually low if values of are high due to gypsum. In this case, false porosity values due to gypsum could cause serious errors in calculations of oil-in-place. This investigation was made to determine quantitatively the effect of gypsum on porosity values determined by different core analysis procedures. EXPERIMENTAL PROCEDURES Dehydration of Gypsum The extent and rate of removal of water of crystallization from gypsum under conditions encountered in core analysis procedures were studied. Taken for the experiments were three types of relatively pure, naturally occurring gypsum, viz. selenite, satin spar and massive gypsum. Although all samples probably contained trace chemical impurities, each type lost the theoretical amount of water upon complete dehydration. An automatic recording thermobalance, similar to one described by Mauer2, was used to obtain dehydration rate data for samples heated in dry air. Water

By D. Weinstein

Yieldilzg in annealed arc-cast molybdenunz in torsion was studied as a function of strain rate and tem-perature. The temperature dependence of the yield point for different strain rates was used to calculate a heat of activation for the yield point. The heat of activation was not a constant but was approximately a linear function of the stress at yield. It is proposed that the rate effect in yielding is determined in part by a site place-change of C (or other interstitial atom) in the metal. THE low-temperature embrittlement phenomenon in metals and alloys has been known to exist for a long time. Although a transition from ductile to brit-tle behavior has been observed in some close-packed hexagonal metals1 and a face-centered cubic alloy, the most common class of metals exhibiting this be-havior has a body-centered cubic lattice structure. For example, a ductile to brittle transition has been observed in iron,3 molybdenum,4 chromium,5 colum-bium,6 and tungsten.7 In the present investigation, molybdenum specimens were tested in torsion over a wide range of temperatures at three widely separated strain rates, and the temperature for onset of embrittlement was determined. Characteristic of body-centered cubic metals and closely associated with plastic deformation is the appearance of a sharp upper and lower yield point. Theoretical explanation of the yield point in iron and low-carbon steel is due to Cottrell,8 who attributes the phenomenon to the pinning of dislocations by the formation of impurity atmospheres around the dislocations. These atmospheres tend to lock the dislocations and make them more difficult to move. The stress required to move a dislocation and thereby cause plastic deformation is greatly increased, and thus an upper yield point is observed. In addition, theoretical analysis,9 as well as experimental observations, show that the upper yield point is strongly a function of temperature. The upper yield point is observed to decrease with an increase in testing temperature, and above a certain temperature (-700° K in iron) it no longer appears. This is consistent with the concept that thermal vibrations will help free a dislocation from its atmosphere, so that the external stress required to free a dislocation from its pinning atmosphere decreases with increasing temperature. Furthermore, with increasing temperature the equilibrium concentration of impurity atoms around a dislocation decreases exponentially with the result that the dislocation is less firmly pinned. In Cottrell's theory of yield point a static model is visualized in which the pinning atmospheres, particularly interstitial atoms, are immobile, and the dislocations are anchored to stationary positions in the lattice. However, experiments1,7 show the upper yield point to be time-dependent or a function of the rate of straining, a high strain rate causing a high upper yield point. Present theory does not adequately account for the rate dependence of the yield point, and the exact function of the interstitial atom is not under stood. Nevertheless, observation of the temperature dependence and rate dependence strongly suggests that the upper yield point phenomenon is due to the interaction between dislocations and pinning atoms, and that a diffusion mechanism is important in determining the yield point.

Jan 1, 1962

By P. Valicek, M. Farren, R. G. B. Pickering, G. Harrison, P. van Dorssen, W. Joubert, H. J. van Rensburg

Introduction In South African metalliferous mines, stoping operations are largely confined to narrow, tabular orebodies making mechanization extremely difficult. Limited flexibility in terms of stope width has necessitated drilling by means of hand held, pneumatic rock drills at most of our operations. As the largest producer of platinum in the world, we drill in excess of forty million stope blast holes per annum. Cleaning of the broken ore is also done by conventional means—utilizing scrapers and scraper winches. Conventional methods such as these carry high costs in terms of risk exposure as well as labour intensity. The purpose of this paper is to describe the development of a long hole stoping system suitable for the narrow platinum reefs. The new system had to be substantially safer and more cost effective than conventional mining. We selected a site that was conducive to mechanized mining and set out the parameters that we considered would meet our requirements. We then conducted a feasibility study to evaluate the conceptualized long hole stoping system in terms of specific goals. An analysis of the proposed system identified the Key Performance Indicators (KPIs). One of the most critical goals was to be able to create a man-freestope. This would mitigate the safety risk associated with normal stoping operations, as well as the inefficiency cost previously referred to. Other challenges included setting targets for long hole accuracy, stoping width reduction and specific blasting system performance for long hole stoping. We also modelled a critical span that we considered to be inherently safe and to ensure hangingwall stability, throw-blastcleaning and overall system productivity. Anglo Platinum Research and Development and Sandvik Tamrock entered into an agreement for the supply of a specialized long hole-drilling machine. The system was implemented and tested by the mine with the support of the other participants. The results achieved met our expectations. It was demonstrated that with this method of mining it is possible to have a man-free/support-free stope face and to achieve a reduction in shaft head cost per ton whilst reducing dilution. Key performance indicators assessed during the trial •Safety targets •Mining layout •Drill rig •Production targets •Support requirement •Explosives requirement •Services requirement •Ore removal and cleaning requirement •Training requirement Safety targets All persons involved with the project had to adhere to the mine’s safety programme including the zero-tolerance campaign, and were required to report all hazards observed immediately. Mine personnel and Tamrock carried out a full risk assessment on the drill rig before transporting underground. A further risk assessment was carried out when the machine was in position underground. Mining layout See Figure 1 and Figure 2 for a detailed description. Drill rig The drill rig was a combination of a Secoma P-Low LC 10long hole feed and an Axera low profile carrier. The choice of this equipment was made through consultation with Tamrock Sandvik. All relevant design perimeters of the area to be mined were taken into consideration. Production targets

Sep 1, 2001

By Milton E. Wadsworth, T. D. Chatwin

Bulk density variations can usually be minimized by properly mixing the material before moisture measurement. The measuring of moisture on material being with- drawn directly from storage bins requires some form of bulk density correction. In Bethlehem's pellet plants continuous automatic bulk density correction and uniform feed-rate control are obtained with Bethlehem's patented Bin Level Control System. With this sys- tem a single probe, suspended or inserted in the bin, senses whether material is at the proper level in the bin and automatically regulates filter speed to control the filter-cake discharge rate to maintain this level. The level of concentrate in the filter-cake bin can thereby be controlled to within ± 1/2 in. of the point of contact between the concentrate and the probe. Material thickness on the conveyor does not have to be controlled accurately and mix compositions can vary widely as long as they do not contain variable amounts of water-soluble electrolytes. In sinter plants, errors caused by changes in normal feed rate and bed height are minimized by counter-weights that permit the free-floating to maintain a uniform contact pressure on the mix. Large changes in mix resistance can be taken care of either by resetting the control point or by adjusting the calibration control.

Jan 9, 1968

By H. F. Webster, C. G. Dunn

Rolling md annealing procedures are described for developing the (110) preferred orientation in tantalum for use as a thermionic-emission materinl where electrodes of a uniform high work function are needed. The development of a (110) [001] annealing texture is also reported. A preferential growth process due to low (110) gas-metal surface energy is considered in explanation of the observed growth of (110) grains. ThE growth of (110)-oriented grains in thin strips of rolled zone-refined tantalum, previously discussed briefly,' is reported together with more recent information on the formation of a (110)[001.] annealing texture, i.e., one where the [001] direction of each grain lies close to the rolling direction. The development of tantalum sheet with a (110) preferred orientation (position of [001 ] directions unspecified) is of importance as a thermionic-emission material in thermionic-energy converters. Since therm ionic-emission properties of cesium-coated crystals vary over a wide range depending on (hkl) a2-7 a single (hkl) preferred orientation is more useful than either several preferred orientations or none. Furthermore, the (110) preferred orientation yields the highest thermionic-emission density for a cesium coverage of less than a monolayer.5-7 A consideration of the stability of the grain structure needed at high operating temperatures suggests that the preferred orientation itself should be produced by annealing processes. Information on annealing textures in tantalum, however, is rather limited. Pugh and Hibbard 8 obtained (111)[112] and (lll)[112] components in a 1400°C recrystallization texture in 95 pct cold-rolled foil; these components were enhanced on annealing at 2500°C. Muller9 rolled 99.97 Ta to 90 pct reduction in thickness in the final stage and noted only a slight sharpening of the rolling texture, with some intensification of the (111)[112] component upon annealing at 1200°C. The experimental procedure followed in the present work stemmed from the idea of using possible differences in (hkl) surface energies to provide a small driving force for growth of grains having the lowest (hkl) surface energy.l0* This would mean using high-purity tantalum processed into thin sheet form and annealed at high temperatures either in a noncontaminating atmosphere or in one producing additional sample purification. EXPERIMENTAL Zone-Refined Tantalum. National Research Corp. tantalum in the form of 1/8-in.-diam rod and of 99.98 purity (53 ppm 0, 15 ppm N, and 8 ppm C) was zone-melted four times. The traversing speed was 4 mm per min. Such treatment increased the resistance ratio, R293k/R20K , where R293K is the resistance of the specimen at 20°C and R20K the re-resistance at liquid-hydrogen temperature, from a value of 25 for the initial rod to 175 for the zone-refined rod (the increase in the resistance ratio provides a measure of purification11,12). Part of a zone-refined rod was rolled unidirec-tionally to a strip 0.003 in. thick and 0.28 in. wide. Samples were given anneals in the range 1300" to 2100°C using ac conduction heating in an oil-free vacuum system. Recrystallization to small grains appeared to be complete at 1300°C. Large grains were formed at higher temperatures, but these were not entirely strain-free, some grains showing asterism in Laue X-ray patterns and some displaying a range in orientation. Part of the difficulty was caused by thermal expansion of the tantalum strip as it was held between fixed supports. However, in a different arrangement with the tantalum freely suspended in a tantalum can, high-frequency induction heating in vacuo at about l0-6 Torr produced

Jan 1, 1964

By S. T. Yuster

An analysis has been made of the factors responsible for tilted fluid contacts in petroleum reservoirs. The factors are static and dynamic with the former being controlled by those variables responsible for the capillary rise of fluids, and the latter include rate of formation tilt and hydraulic circulation. The explanation that rate of formation tilt may be responsible for tilted contacts appears untenable. The role of some of these factors in the migration, fractionation. accumulation and possibly the prospecting for oil is indicated. INTRODUCTION While it is generally considered that the segregation of gas, oil, and water in a petroleum reservoir results in approximately horizontal planes separating these phases. there are factor; which modify this simplified picture to a very great extent. Some of these factors are static. and the departure of the fluid interfaces from horizontal may represent a static equlibriun. Some of these factors may be dynamic and the interface positions may be non-equilibrium and represent a steady .state condition. Of course combinations of these two situations may also exist. The reasons most commonly given for this behavior are hydraulic circulation of fluids, change in character of the formation, and a rate of tilt of the formations more rapid than the rate at which the fluids may re-establish an equilibrium. Russell's Principles of Petroleum Geology' contains an extensive discussion of tilted fluid interfaces and their importance in the migration and accumulation of petroleum. Russell cites examples of tilted water tables at Lance Creek, Wyo.; Rock River, Wyo.: Cut Bank. Mont.; Cushing, Okla.: and Graham; Okla. Also given was the Wasson Field of West Texas which has saucer shaped oil-water and gas-oil interfaces with the saucer being deeper in the case of the oil-water contact. The Bradford Field in Pennsylvania has a tilted water table. San Ardo. Coalinga None and some other California field.; have tilled contacts. A recent paper by King Hubbert discuses the effect of hydraulic circulation of the water underlying the oil in a given stratun and it- implications in the accumulation of and drilling for the oil. The foregoing would indicate that tilted fluid interfaces are not uncommon and that it would be of importance to underbtand the forces which are responsible. Further. it would be of interest to examine certain idealized models of situations which may cause tilting with the thought in mind of deriving relatinnships between the important variables. These relationships may only hold exactly for the model* assumed but the results may apply semi-quantitatively to actual formations and at least indicate trends. The discussion will be divided into the effect of static factors and the effect of dynamic factors. STATIC FACTORS It has already been mentioned that one reason given for tilted contacts is a variation in formation properties. Specifically this is a change in the pore size of the formation capilaries. If the internal surface of the reservoir is preferetially wet by water, capillarity will cause the water 10 rise to a greater extent above the free water table in a small capillary than in a large one. Consequently the water-oil contact will be higher in the lower permeability sands than in the higher permeability sand.;. The free water table may be defined as the position the oil-water interface would take if capillarity were absent. Since the phenomenon is the capillary rise of water in an oil environment, a derivation of this shold give a relationship between the variables. Fig. 1 is an idealized model of the situation with a uniform bore circular capillary ubstitttting for the tortuous non.circular formation pore. The upward force.; on the column of water will be equated to the forces downward to give the equilibrium situation. forces upward = force downward where r is the radius of the capillary in ceritimetera. a is the interfacial ten4on oil-water in dynes per centimeter, 0 is the

Jan 1, 1953

By B. F. Decker, D. Harker

The recrystallization reaction in OFHC and spectroscopically pure copper has been followed by X ray diffraction determinations of the amount of material with the cold-worked and recrystallized textures in specimens which had been given various heat treatments. The heats of activation for recrystallization are found to be: 29.9 kcal per rnol for OFHC copper and 22.4 kcal per rnol for spectroscopic copper. A reliable and speedy method for measuring the amount of recrystallized material in a piece of rolled metal, together with a new scheme for low temperature heat treatment, have made possible a determination of the activation energy for recrystallization in rolled copper. This method for studying recrystallization rates is different from others reported in the literature.' Oxygen free, high conductivity copper—OFHC copper—of purity 99.98 pct gave an activation energy for recrystallization of 29.9 kcal per mol with recrystallization data taken in the temperature range 208-245°C. Copper of purity 99.999 pct from the American Smelting & Refining Co. gave an activation energy for recrystallization of 22.4 kcal per mol with recrystallization data taken in the temperature range 43-135°C. The great change in activation energy for recrystallization as the small amount of impurity in the metal is decreased suggests that the motion of grain boundaries is conditioned by the impurities which must be concentrated in them. Thus the OFHC copper recrystallizes with an activation energy of the order of magnitude to be expected for the diffusion of the kind of impurities likely to be present. The high purity copper, on the other hand, recrystallizes with a much lower activation energy, in accord with the notion that the grain boundaries need not wait for the impurities to diffuse with them. Copper when strongly cold-rolled has a well-defined crystallite texture which can be described by saying that the [111] direction of the face- centered cubic crystals is aligned approximately in the cross-rolling direction and that faces of the form {110} lie approximately in the rolling plane. When such rolled copper is completely annealed the crystallite texture is quite different: the [loo] direction is in the cross-rolling direction and faces of the form (100) are in the rolling plane. At intermediate stages of annealing, the copper contains both textures. If a Geiger counter X ray diffraction spectrometer is set up so as to measure the intensity of the (200) Bragg reflection from the rolled surface of a piece of copper strip, this intensity increases from a very small value in the cold-worked state to a maximum as the specimen is annealed. The same would be true for (200) reflections from planes normal to the rolling or cross-rolling directions. In view of this fact, the amount of material in the copper which has recrystallized can be measured by comparing the intensities of one of these reflections just mentioned with the intensity from a similar specimen after complete annealing. In much the same way the intensity of (111) reflections from planes normal to the cross-rolling direction could be used to measure the amount of unrecrystallized material in the specimen. In the work to be described here the amounts of recrystallized and unrecrystallized material in partly annealed rolled copper specimens were determined in this way. Experimental Procedure Samples of oxygen free high conductivity (OFHC) copper, cold-rolled 99.7 pct to 0.002 in. thickness, were subjected to heat treatments for various chosen times at four different temperatures, and high purity copper samples, cold-rolled 98.0 pct to 0.0015 in. thickness, at six different temperatures. Each sample, after treatment, was placed in an orientation sample holder for use with a Geiger counter X ray spectrometer and a reading was taken of the intensity of the (200) reflection from planes perpendicular to

Jan 1, 1951

By A. Styka, G. Fischer, S. Tour

Described herein are the results obtained during research work involving coating titanium alloys with molybdenum by vapor-deposition methods. Results show that the method can be used successfully to deposit hard adherent wear-resistant coating of methodmetallic molybdenum on titanium or titanium alloys without changing the microstructure of the titanium base. PRODUCTION and use of titanium and its alloys have increased tremendously in the past few years. The physical, mechanical, and chemical properties of this engineering metal have caused considerable enthusiasm among metallurgists and engineers. However, as with all materials, there are some drawbacks. For example, titanium is susceptible to seizing and galling on wearing surfaces. In order to produce a good wear-resistant surface, many investigations have been conducted evaluating oxidizing, carburizing, nitriding, carbonitriding, sili-conizing, and chromizing of titanium. All of these processes require high temperatures for rather extensive periods of time. It has been possible to produce hard surfaces on titanium and its alloys by a number of these processes at the expense of a deterioration of the physical properties of the base material. A practical solution to the problem of providing titanium and titanium alloy parts with a satisfactory wear-resistant nongalling surface must be one that does not involve excessive temperatures for long periods of time. Sam Tour & Co. Inc. has completed a research and development contract for the United States Army Ordnance Corps on vapor deposition of molybdenum on titanium and titanium alloys. On the basis of results obtained from the research program, titanium alloys can be coated successfully with molybdenum to provide a hard wear-resistant surface without harm to their base mechanical properties. The remainder of this article is a description of the techniques used to apply the coating and the results obtained from wear tests on molybdenum-coated titanium. Theory Basically, the technique used was the application of molybdenum by a vapor-deposition method, thermal decomposition of molybdenum hexacarbonyl [Mo(CO)] with hydrogen as the carrier gas. The selection of this method was based chiefly on the following considerations: 1—low plating temperature which would minimize excessive grain growth, 2— low decomposition temperature of the carbonyl, 3— possibilities of controlling the hardness of the plate by adjusting the carbon content using the plating temperature and pressure as the primary variables, 4—use of high vacuum, thereby avoiding unnecessary oxidation and other complex reactions with the atmosphere. Free energy data1 show the strong tendency for titanium to combine with O2 N2 or carbon from normal temperatures to temperatures above its melting point. To maintain the titanium in a film free condition, the use of as high a vacuum as possible is indicated. The literature' indicates that the reaction product of hydrogen with titanium is unstable in vacuum at around 400°C. 5—Although it is indicated from the thermodynamic standpoint that there is little possibility of removing carbon from either titanium or molybdenum, the work of Lander and Germer -ndicates that the use of a suitable H,/CO ratio is somewhat effective in minimizing carbon deposition. 6—Availability of molybdenum carbonyl. In the simplest form, the conditions of equilibrium3 in chemical reactions involving decomposition of carbonyl are as follows: Mo (CO) ? Mo + 6CO 2CO * C + CO,. The plating rate is proportional to the rate of evolution of CO from the decomposed carbonyl, i.e., it is proportional to the pressure of the gaseous decomposition products. Carbon released from CO gas is the significant constituent for the variability of the physical properties of the product. High carbon deposition is favored by increasing pressure. Limitations are imposed in the selection of plating temperature and pressure. Excessive temperature re-

Jan 1, 1956

By J. H. O’Dette

BLISTER formation on wrought aluminum products has been a matter of concern to aluminum fabricators for many years. The fact that blisters make their appearance during the final stages of fabrication means that much time and effort have been expended before it is evident that the material must be scrapped. This and the loss of production are ample reasons for embarking on a research program to find out more about blistering and possible methods of control. Many excellent papers on this subject have appeared in the technical literature in the last few years. In one of the more recent papers, Kostronl gives a fairly complete review of the problem of gas in aluminum and blistering in general. From the work of the various investigators, a general mechanism for the formation of blisters has evolved and may be summarized briefly as follows: Hydrogen gas is usually present in the cast ingot, in the atomic or ionic state, in excess of the solid solubility. At room temperature the gas atoms are relatively immobile, but at elevated temperatures they become mobile and diffuse to free surfaces where they associate to form molecules. If these free surfaces are discontinuities within the ingot then the associated gas molecules collect and build up considerable pressure until equilibrium is reached with the dissolved gas around the discontinuity. Since the solubility of the gas is proportional to the square root of the partial pressure it is evident that large pressures may be built up at the discontinuities. When the metal is rolled to sheet the pressure of the gas in these, discontinuities is sufficient to deform the surface of the sheet and form a blister, particularly when the strength of the material is reduced during the annealing. Although the mechanism of the formation of blisters was fairly well known, the actual impor- tance of the individual roles played by the gas and the discontinuities was not so well established that positive methods for control of blistering were at hand. It was the object of the investigation to learn more about the nature of the discontinuities giving rise to blistering and to develop methods of control. The investigation was carried out in three stages as follows: a) A study of the more commonly used methods of removing hydrogen from aluminum, such as fluxing and holding, and their effects on blistering. b) Location of the discontinuities giving rise to blistering. c) A study, by indirect methods, of the movement of gas in the metal and its effect on blistering, and the development of methods of blister control during fabrication. Removing Gas and Reducing Blistering by Fluxing or Holding-—The work of removing gas and reducing blistering by fluxing or holding was carried out on metal of Alcan 2s (1100) composition with an artificially high gas content. The high gas content was obtained by introducing water into the melt prior to casting; the water reacted with the aluminum forming A12O3 and hydrogen. The procedure was to raise the gas content by introducing water into an aluminum melt and using half the melt to cast one ingot immediately. The remaining metal was treated again with water to make up for the reduction in gas content during holding, while the first ingot was being cast, and then given a fluxing or holding treatment and cast into an ingot. Samples for gas determination were cast from the molten metal before and after the gassing operation; before, after, and during fluxing, and while casting. Samples were also cut from sections of the ingots. Gas determinations were made on these samples using the well known vacuum fusion technique. All ingots were hot rolled at 500°C to 0.250-in. slab which, in turn, was cold rolled to 0.040 in. sheet. The sheet was coiled and annealed for 2 hr at 500 °C and then cut into 5-in. squares which were inspected for

Jan 1, 1958

By Chandrakala Kari, Divyang Shah, Lakshmi Kanth Reddy, Kaushik Vakil, Sanjay Sarkar, Bhavin Desai

Gases rich in sulfur dioxide generated as a by-product of smelting and converting operations of copper concentrate contain selenium apart from zinc, lead, copper, cadmium, bismuth, antimony, and arsenic. The gaseous stream is heat exchanged in waste heat boiler, dust collected in electrostatic precipitator followed by cleaning in reverse jet scrubber to remove fumes, halogens and fine dust before passing to DCDA Monsanto catalytic converter to produce commercial grade sulfuric acid. The gas cleaning section of the acid plant uses water to scrub the smelting gases. During scrubbing, precipitated solids, known as sludge, settles at the bottom of the reverse jet scrubber containing 30 to 40 wt% copper and selenium up to 40 wt% selenium. In the existing process, the sludge collected during scrubber cleaning process is directly recycled to the smelter for copper recovery. However, the selenium is expected to again vaporize due to high oxidation potential during smelting and converting, causing accumulation of selenium in sludge. In present investigation, a roasting process has been developed to recover the selenium from acid plant sludge before charging it to smelter for copper recovery. Selenium is associated with copper in acid plant sludge as copper selenide, as determined by X-ray diffraction and electron microscopy. Thermodynamic and thermo-gravimetry study revealed that the copper selenide phase present in the sludge was amenable to oxidation at 600°C forming oxides of copper and selenium (Cu-Se-O). However, the dissociation of selenium from the copper oxide was made possible by sulfatation using sulfur dioxide between 450°C to 600°C, resulting into the formation of CuSO4(s) and SeO2(g). Lab scale experiments were carried out in vertical tubular furnace to determine the optimum roasting conditions with respect to roasting time, temperature and molar ratio of O2:SO2. Using these optimum conditions, selenium up to 90 wt. % in the form of SeO2 vapors could be recovered from the acid plant sludge in a large scale commercial roaster. Roasted sludge free from selenium and containing oxides and sulfates of copper could now be recycled in the smelter for copper recovery. INTRODUCTION There is an increasing demand for minor metals due to their use in innovative technologies. Similarly, the increase in demand for selenium is expected due to disruption in sectors related to renewable energy and photovoltaic battery. Selenium is a chalcogen and a non-metal with black or red crystalline appearance. Selenium is used in the glass industry to decolorize glass and to make red-colored glasses and enamels. It is also used in solar cells and as a photographic toner. Selenium is used as a brasses in stainless steel to improve its machinability. Selenium sulfide is used in anti-dandruff shampoos. In spite of the toxicity of its compounds, selenium is also an essential trace element for humans and animals. Selenium occasionally occurs free in nature, but more often occurs as selenides of iron, lead, silver and copper. There is an urgent need for the development of new methods for selenium recovery from the existing resources. Commercially, selenium is obtained only from anode mud produced during electrolytic refinery of copper.

Jan 1, 2019

By Robert D. Pehlke, Robert G. Blossey

The solubility of nitrogen in liquid iron alloys containing chromium and nickel has been measured in the temperature range 1550° to 1700°C at nitrogen pressures to 1 ah. The solubility surface has been determined for the iron corner of the liquid metallic ternary to 21 pct Cr and 11 pct Ni. The nitrogen solubility increases markedly with increasing chromium concentration. The effect of nickel and the bilinear effect of chromium and nickel are less pronounced. The solubility data are presented, and interaction coefficients are determined from them. THE solubility of nitrogen has been determined in liquid Fe-Cr-Ni binary and ternary alloys. The work in this laboratory has been directed toward a relatively limited composition range, that is to 20 pct Cr and 10 pct Ni. Humbert and Elliott1 studied the entire ternary; but their investigation was, understandably, limited in this region. The region considered here is of the greatest commercial interest. Knowledge of the solubility in these alloys is important for accurate control of the nitrogen levels in various stainless alloys. Also, the solution behavior is of theoretical interest because of its deviations from ideal dilute solution rules at moderate chromium levels. The nitrogen solubility in the iron binaries has been reviewed extensively by Pehlke and Elliott,2 particularly with respect to the dilute solution interaction parameters. More recently, there has been some interest in accurate descriptions of solute interactions in non-dilute solutions. Most of the investigators have adopted a power series fit to accommodate any non-linearity of the data. The Taylor series expansion is adopted here, using Scimar's notation3 for the interaction coefficients. An alternate method, instead of requiring higher-order expansions, is to restrict the range of the composition variables. A planar solubility surface may be fitted to the data and its range of validity determined. If the axes of this region are displaced from the usual origin—the solvent pure iron—a change in standard state is required for the solution reaction. The standard state for nitrogen in iron is commonly taken as the hypothetical 1 wt pct solution of nitrogen in pure iron. However, for an alloy of appreciable solute concentration, e.g., 13 pct Cr or 18 pct Cr-8 pct Ni, it would be convenient to use that base composition as the solvent and redefine the solution reaction in terms of that particular solvent. A brief derivation follows, defining the free energy of solution in an alloy solvent. Following the treatment by Darken and Gurry,4 for a nitrogen pressure of 1 atm: N (pure component) = N (1 wt pct in solvent) [l] AG=RT ln100/ wt pct N in solvent Taking this reaction for an alloy solvent less the same reaction for a pure iron solvent the relation between nitrogen in pure iron and an alloy is: N (1 wt pct in Fe) = N (1 wt pct in alloy) [2] AG = RT[ln(wt pct N in Fe) - ln(wt pct N in alloy)] Adding ½ N2(g) to each side and subtracting N (1 wt pct in Fe) = ½N2(g), the total free energy for solution of nitrogen in an alloy, referred to nitrogen at infinite dilution, is given by: ½N2 (g) = N (wt pct in alloy) L3] AG°3 = -RT ln(wt pct N in alloy )PN =1 atm Interaction parameters have their usual meaning when ?G°/RT is differentiated with respect to the proper composition coordinate. If desired, the dilute alloy treatment may be utilized with the new reference composition as the solvent. This has. indeed, been done by Small and pehlke5 in their analysis of nitrogen solution in liquid 18-8 alloys. The Sieverts' technique was used for this investigation on an apparatus previously described.6 The materials used in this program were: Ferrovac-E iron, 99.95 pct, Crucible Steel Co.: chromium, 99.95 pct, Union Carbide Metals Co.; nickel, 99.9 pct, International Nickel Co. Recrystallized alumina crucibles were used with no evidence of crucible-melt reaction. RESULTS The locations of the ternary compositions investigated are shown in Fig. 1. The data of Turnock7 and small8 have been alluded to in other papers.5'6 There were no departures from Sieverts' law observed for

Jan 1, 1969

By M. E. Wadsworth, A. S. Peck

Infrared spectra disclose that oleic acid will not adsorb on the surface of pure beryl unless the mineral is first activated with HF. The adsorption of oleic acid on HF activated beryl is attributed to the hydrogen bonding of oleic acid monomers to F-surface bridging sites. These sites are formed as a result of the reaction of HF with chemisorbed water or surface hydroxyl. Characteristic infrared spectra of physically adsorbed oleic acid are correlated with flotation at different pH at temperatures of 25°C and 75°C for colloidal and -60-mesh particles. The usual mode of occurrence of the beryllium mineral beryl, Be3A12Si6O18, is in granite pegmatites as pale green, white, or yellow crystals. A dark green gem variety, emerald, may be found in the wall rock of pegmatite veins or in mica schist. The most important beryl deposits in the United States are in the Black Hills District of South Dakota, and several mountain ranges of central and west-central Utah contain potential commercial sources of this mineral. Several papers have been published concerning the flotation of beryl with different conditioning reagents. Kennedy and O'Meara1 reported on the essential use of HF in the flotation of beryl from different ores. The use of calcium hypochlorite to separate HF activated beryl from feldspar after flotation with an amine collector was made by Runke.2 A report on the activation of beryl with different cations using sodium oleate collector was presented by Viswa-nathan and co-workers.3 Flotation of beryl with sulfonate collector and different activating salts was employed by Fuerstenau and Bhappu.4 The role of the surface charge or zeta potential in the flotation of beryl with different collectors and salts was also extensively investigated.5"7 Previous infrared investigations by the authors8 disclosed that the orthosilicate beryllium mineral, phenacite, reacts with oleic acid to form a chemisorbed oleate monolayer on the mineral surface. Thus, chemisorption is the effective mode of adsorption in the phenacite-oleate acid flotation system. In contrast, neither chemisorption or physical adsorption of oleic acid occur on the surface of pure beryl as evidenced in this study. Efforts were subsequently made to determine the mechanism of activation and collector adsorption for HF pretreated beryl. EXPERIMENTAL PROCEDURES Large, white, terminated crystals of beryl were obtained from Madagascar through Ward's Co., Monterey, Calif. The crystals were broken into -60-mesh fragments in a porcelain mortar. Part of this prepared material was ground to a powder with a Fisher Grinder using an agate mortar and pestle. The powder was transferred to a graduated cylinder and mixed with 500 ml of distilled water. After 5 min, the colloidal suspension was separated from the settled particles by decantation and used as a stock for infrared test determinations. Adsorption tests were performed by first transferring 20 ml of colloidal suspension to 50 ml glass centrifuge tubes. The solids were then centrifuged out and the liquid was discarded. Then, the solids were pretreated with one molar HC1 or one molar HF. After 15 min, the solids were again centrifuged out. The mineral solids were washed free of residual acid by repeated centrifuging and water washing operations. Then, 20 ml of distilled water was added to the solids, and the resultant suspension was used for test purposes. In the preparation of mineral for flotation tests, 1.5 g of -60-mesh beryl was deslimed by removing the colloidal fraction by three successive water washes and decantations. Then, the coarse particles were pretreated with either one molar HCl or one molar HF for 15 min. The mineral was next washed free of acid with distilled water, and 20 ml of distilled water was added to the beryl prior to collector conditioning. The conditioning of mineral with collector was performed in 50 ml centrifuge tubes to which either NaOH or HC1 was added for pH modification. One drop (6.0 mg) of U.S.P. reagent grade oleic acid or 2 ml of 0.01 molar sodium oleate was added to the pulp and stirred at about 1500 rpm for 3 min at a

Jan 1, 1968