Search Documents

By Oliver Bowles

"Rhodesian asbestos is of high quality and is much in demand by American consumers. Production in Rhodesia was first reported in 1909. The production for this and each succeeding year is shown in the following table:The serious curtailment in production for the years 1912 and 1913 was occasioned by transportation difficulties. In 1914 a railway was projected to Victoria and thereafter production increased greatly. Up to 1916 asbestos was obtained,from the Victoria district only, but thereafter the Bulwayo district became an important,producer with minor quantities from Gwelo.In the Bulawayo district the productive area is about 2 1/2 miles long, with Shebanie mine at the north-west end, the Nil Desperandum at the south end, and the Birthday claims between them."

Oct 1, 1920

By W. van der Knapp

A theoretical and experimental ana1ysis is given of the change in volume of a porous medium due to changes in external and internal pressures. The result enable one to deduce directly the effect of large increlents in stresses. It is shown that the three-dimensional representation of the volume of a nonlinear porous system is a cylindrical rules surface, the generating lines of Which have a slope according to the solid rock compressibility. Analytical expression for such a ,surface is very simple. It follows that the bulk and pore compressihilities depend only on the difference between pore fluid and external hydrostatic pressure, i.e., the effective rock frame pressure. From measurements on a number of sandstones as well as limestones it can be conduded that for practical values of this effective frame pressure the pore compressibility falls in the range between the compressibility of water and that of undersaturated crude oil. In general, pore compressibility is found to be higher the lower the porosity. For a particular limestone reservoir pore compressibility and porosity could he related by means of a simple empirical formula. Results from the described study find a direct applicxtion in material balance calculations and in prob1ems of liquid flow through porous media. Since the elastic constants of the rock bulk material enter into equatiorls for velocity of acoustic waves, the results are also of importance for calculating rates of wave propagation in these media. It is shown for sandstones with 1.5 to -10 prr cent porosity that laboratory measured porosities may differ from those lender reservoir conditions by about I per cent of their value. The difference for low porosity limestotnes can be of the order of 10 per cent. The subsidence caused by elastic deformation of reservoir rock is shown to he very small. General formulas relating pore and bulk volume to external and internal pressure can be derived, as has been shown by Biot1, Gassmann2 and Geertsma.2 Their theories describe the differential change in volume caused by a variation in pore fluid tension and external hydrostatic tension. It has been known for a long timei that the stress-strain relations of a packing of spheres are essentially noninear. Our experiments show that for almost all reservoir rocks which arc elastically deformable the relation between volume and loading is also a nonlinear one, resembling that of a packing of spheres very closely. The behavior of these media is often described by using the linear stress-strain relations for small incremental stresses and strains in the vicinity of a pre-stressed condition." The present study differs from these considerations in that it enables one to deduce the effect of large increments in the stresses directly. In analogy to the stress tensor for a homogeneous body the stress tensor for a porous body can be written in the conventional way: where the tensor components, o, and t, represent the total forces acting on the faces of a unit cube of porous material. This tensor can be split into two parts. a hydrostatic and a deviatoric part, as follows2,3,1 where the component of the hydrostatic stress system, a. equals The hydrostatic stress causes a change in volume whereas the deviatoric stress system gives rise to a change in shape only. One of the difficulties in describing changes of volume occurring in reservoir rocks is that the relations connecting these volume changes with external and internal stresses are essentially non-linear. A complete description requires the bulk volume, V,,, as well as the pore volume,V,,. to be known as a function of both the changes in pore fluid tension (v) and the hydrostatic tension on the outer boundary.

By G. W. Neighbor, M. S. Abrahams

The actice slip plane in InSb is found to be of the {111} type by using the method of two-tmce anulysis. Measurements of the rotation of the tensile axis with increasing plastic shear strain indicate that the tnacroscopic slip direction is a <110>. Recrystal-lization is first observed at a sheav strain of about 70 pct for a crystal deformed at a temperatzcre of 473° C and at a shear strain rate of 2.90 times 10- %ecc-I; the dislocation density corresponding to this value of the strain is 1 x 108 em-&apos;. At a shear strain of about 170 pct, the recrystallization process is complete. This appears to be the fimt time re-crystallization has heen observed in a semiconductor. V HE operation of the {Hi} glide plane in Ge was first noted by Gallagher.&apos; This finding was confirmed by Treuting who also extended the result to Si. Using X-ray techniques, Treuting3 demonstrated that the macroscopic slip direction in Ge was of the <110> type. The choice of the (111) <110> slip system in Ge is exected since in the diamond-type structure the {Ill7 plane is the plane of highest density and the <110> direction is the direction of closest packing.4 There is little reason to expect that the glide elements of InSb are different from those of Ge, since the zinc-blende structure characteristic of InSb is quite similar to the structure of Ge. With regard to InSb, Allen5 has indicated that the glide plane is the {111} type. There appears to be no quantitative determination of the glide direction, however. The present work was undertaken to establish both the glide plane and glide direction in InSb and also to see if recrystallization occurs at large shear strains. EXPERIMENTAL PROCEDURE Mechanical Deformation. The single crystals of InSb used in this investigation were deformed in uni-axial tension. The tensile axis of the specimens was [145] and the periphery was bounded by (111) and (321) planes as shown in Fig. 1. The metallographi-cally polished specimens were deformed in a dynamic atmosphere of He, using an Instron machine. The tensile tests were performed at temperatures in the range of 300°C to the melting point (525OC) and at shear strain-rates varying between 1.94 X 104 sec-&apos; to 1.94 x 103 sec-&apos;. Additional details concerning the preparation and deformation of the specimens have been presented previously.&apos; Analysis of the Glide Elements. The traces of the active slip plane in both (111) and (321) planes were analyzed according to the usual method of two-trace analysis." The macroscopic slip direction was determined by measuring the rotation of the tensile axis as a function of plastic strain,8 These measurements were made from Laue back-reflection X-ray photographs. The X-ray beam was perpendicular to the (111) plane. A given crystal was used for only one measurement of the rotation of the tensile axis after it had been strained to a predetermined value. Therefore, care was taken at all times to insure that the X-ray beam was parallel to the [Ill ] direction of all the samples. RESULTS AND DISCUSSION Glide Plane. After 3.4 pct plastic shear-strain, at a temperature of 369°C and a shear strain-rate of 1.94 x 104 sec-&apos;, the slip traces on the (111) and (3.21) planes appear as in Figs. 2(a) and 2(b), respectively. The results of an analysis of these glide markings demonstrate that the slip plane is (111). The operation of this plane is expected on the basis of the orientation of the specimen, since glide on this plane and in the [I011 direction will result in

Jan 1, 1962

By B. Gaucherand

Dado que en los últimos años, la industria de los fosfatos ha visto diversificado los procedimientos de enriquecimiento a nivel industrial -esto debido al agotamiento de los yacimientos más ricos y a la evolución de las leyes exigidas de los concentrados-, se revisa los procedimientos para el enriquecimiento de los minerales fosfatados a través de un esquema de estudio para los nuevos yacimientos. En este sentido, el texto revisa las propiedades de cada fosfato y busca incrementar la produción de la industria fosfatera a partir de la explotación de nuevos yacimientos, rentabilizar al máximo el tratamiento de las reservas y eliminar los riesgos de contaminación del entorno por la utilización de productos.

Nov 20, 1978

By F. Paredes, W. R. Holman, R. W. Crawford

The diffusion coefficient for hydrogen in the ß titanium alloy containing 13 pct V, 11 pct CY, and 3 pct A1 was measured over the temperature range 20° to 500°C. Results fit the expression: D= 1.58 x lgs exp-------==-----) cm2,sec THE diffusion coefficient for hydrogen in the metastable ß-phase titanium alloy containing 13 pct V, 11 pct Cr, and 3 pct A1 was measured as part of an investigation of the effects of hydrogen on the mechanical properties of titanium alloys. Several theories on the mechanisms of hydrogen embrittle-ment include diffusion of hydrogen at ambient temperature as an important step in the embrittling process.&apos;-5 In hydrogen-contaminated a-ß titanium alloys, it has been postulated that the rate-controlling step may be the rate at which hydrogen diffuses from the ß phase to stress- or strain-nucleated brittle hydride platelets at the a-ß interface.&apos; However, embrittlement of the all-ß alloy investigated in this work may proceed by a different mechanism, since this alloy can be embrittled without the formation of detectable hydride platelets.6 Troiano has suggested that in this case the mechanism of delayed failure or embrittlement is similar to that proposed for high-strength steel, i.e., repeated crack initiation caused by a decrease in bonding energy as hydrogen diffuses to points of high tri-axial stress at the root of a notch. In both types of alloy the rate of embrittlement is believed to be controlled by diffusion of hydrogen in the ß phase. Accurate hydrogen-diffusion data in the vicinity of room temperature should therefore be of some assistance in understanding the mechanisms of embrittlement in these two classes of titanium alloys. Diffusion of hydrogen in pure titanium has been studied by Wasilewski and Kehl7 at temperatures above 500°C. Their measurements on diffusion in the ß phase were extended below the ß-a transformation temperature (882°C) to approximately 600°C. This was possible because of the 8 stabilizing effect of hydrogen. No results at lower temperatures have been published and there are no data in the literature on hydrogen diffusion in the ß -phase alloy used in this program. Hydrogen diffusion in metals is generally investigated by measuring the rate of transport of hydrogen past a solid-gas interface, i.e., by absorption, permeation, or degassing-rate measurements. These methods produce accurate diffusion data when bulk diffusion is the rate-determining step in the over-all process. However, at the lower temperatures of interest in hydrogen-embrittlement studies or under conditions where surface films are present, the measured rates may be surface-controlled and the calculated diffusion coefficients will be in error. Surface effects were eliminated in the present work by using a modification of the common welded-couple technique m which two bars with uniform but different compositions are joined before the diffusion anneal." The same type of step change in the initial concentration vs distance curve was produced by electrolytically hydrogenating thin-strip specimens which had been electrically insulated over half of their length. Concentration vs distance curves were determined, after appropriate diffusion-annealing treatments, by vacuum-extraction analyses of transverse samples sheared from the strips. Diffusion coefficients were calculated by the methods of Grube.M This technique was feasible because of the large concentrations of hydrogen which can be charged into p -phase alloys without the formation of hydrides15&apos;16 and because of the extremely low degassing rates observed when hydrogenated titanium alloys are heated in air. EXPERIMENTAL WORK The diffusion couples were cut from a 0.022-in.-thick mi ll-annealed sheet.* Strips 8 in. long by 1/2

Jan 1, 1965

By H. E. Cline, T. H. Alden

A study zvas made of rate-sensitive plastic deformation and superplasticity in alloys of lead and tin. These alloys (lead, PO-19 pct Sn, Sn-38 pct Pb, Sn-2 pct Pb, tin) were extruded, aged at room temperature, or melted and resolidified to produce a variety of ~nicrostrnctures. Flow stress us strain rate data were obtained frorn tension tests for strain rates between 10-6 and 1 min-1. The curve log o .us log £ was S-shaped jor fine-grained materials and approxinzately linear for coarse-grained nzaterials. At constant grain size, the behavior was relatively insensitive to conposition. High rate sensitivity (d log o/d log k) and superplasticity occurred at intermediate strain rates in fine-grained materials and are believed to be associated with a transition with strain rate in the mode of plastic flow. This transition was shifted to higher strain rates with increasing temperataire or decrensing grain size. The high rate rneclzanisrn is presunzed to be slip, while rnetallographic evidence sug-gests that the low rate lnechanism is pain boundary sliding. PEARSON&apos; discovered that extruded eutectic alloys of Pb-Sn and Bi-Sn could be elongated as much as 2000 pct in tension. The ability for stretching decreased with aging time or annealing to increase the grain size. At high strain rates, or if the material was in the cast condition, normal ductility was observed. Following deformation of the extruded Pb-Sn eutectic at low rates, Pearson observed an equiaxed granular structure on an initially flat surface, while rapid straining produced elongated grains. He attributed the large deformation in the extruded alloys to the persistence of extremely small grains to a temperature sufficiently high for inter granular flow. Avery and backofen2 measured the strain rate sensitivity of the flow stress, m = d In old In 6, in the Pb-Sn eutectic and established a correlation between m and the tensile elongation. In the extruded eutectic alloy the strain rate sensitivity was 0.1 to 0.2 at rapid rates and the elongation was small, while at low rates m increased to 0.4 to 0.6 and superplastic elongation was observed. They also noted a grain size effect. In the case of the cast Pb-Sn eutectic the strain rate sensitivity remained at 0.1 over the range of strain rates of their experiment (3 x 10"3 to 2 min-I). These authors suggested that diffusional (Nabarro-Herring) creep was the mechanism by which deformation occurred at low strain rates, while climb-controlled creep occurred at high rates. Two predictions of this model are that, at low strain rates, the strain rate sensitivity approaches 1, i.e., Newtonian viscosity, and that the strain rate at constant stress varies as D/L2, where D is the coefficient of self-diffusion and L the grain size. More recently, a mechanical and microstructural investigation of the dilute superplastic alloy, Sn-5 pct Bi, has been done.3 The results show that the high strain rate sensitivity is associated with a transition with strain rate of the mechanism of plastic flow. At low strain rates, grain boundary sliding and its associated accommodation processes were evident, while at high strain rates quasi-uniform slip was concluded to be the dominant deformation process. The following experiments were performed to extend our knowledge of the phenomena of superplasticity to a larger range of strain rates, compositions, temperatures, and microstructures in the Pb-Sn alloy system. The question of why a cast structure does not exhibit viscous behavior although it appears to have a fine microstructure2 was investigated.

Jan 1, 1968

By K. Mukherjee

Instantaneous resistance change during martensitic transformation in Fe-30 at. pct Ni alloy has been studied using a low-noise electronic system. The smallest signals recorded in this investigation were of the order of 10 pv. These small signals did not show the initial increase reported by earlier investigators to support a double shear mechanism.&apos; A variety of pulse shapes and sizes was observed during "burst" transformations, and these signals were neither a linear function of the size of martensite plates nor of the volume fraction transformed. Even the smallest signals, presumably from single plates, showed complications resulting from elastic and/or plastic deformation, shock wave propagation, and so forth, which are inherent in the growth process of a martensite plate. The time of formation and interface velocity determined froni this experiment agree very well with the pioneering work of Bunshalz and Mehl.&apos; AN Fe-30 at. pct Ni (c0.005 pct C) alloy was used to study the time of formation of martensite plates. Martensitic transformations, unlike the nucleation and growth processes, are usually characterized by an extremely fast reaction rate. During the transformation, the crystal structure changes and this change is propagated through a finite volume of the parent crystal lattice within a very short time interval. The interface between the two phases probably consists of moving dislocations, and the time of formation of the plate depends on how fast this dislocation interface can move. Knapp and Dehlin~er or Cottrell and Bilby mechanisms, or similar dislocation models, can be used to calculate the time of formation of a martensite plate of a given size. In the past, conventional photographic technique475 as well as electrical resistivity techniques"~-" have been used to measure the time of formation of a martensite plate. The specific resistance of the martensitic phase in Fe-30 at. pct Ni alloy is lower than that of the austenite phase. Therefore if a current is passed through a small austenite sample in series with a large external resistance, then one would observe a voltage change across the sample as martensite is formed. Such dc measurements are shown in Fig. 1. The initial large voltage drop in Fig. 1, at the M, temperature, is due to a "burst" transformation where a large number of plates are formed in a cataclysmic manner within a very short interval of time. Even during the later stages of transformation as shown in Fig. 1, one can observe discontinuous voltage changes due to small bursts. In order to resolve the time scale of such discontinuous stages, the voltage signals are amplified and fed into a highspeed oscilloscope. In this investigation a low-noise amplifier was used for the first stage of amplification. The signal to noise ratio was further improved by the design of a pulse transformer. This transformer was capable of amplifying the signal by a factor of six. Voltage signals were studied over a wide time scale ranging from 2 sec to 0.1 psec. I) EXPERIMENTAL PROCEDURE A) Specimen Preparation. Specimens were cut from induction-melted Fe-30 at. pct Ni (<0.005C) alloy and cold-rolled to 0.2 by 1 mm cross section and an average length of 5 cm. During mechanical shaping, the specimens were strain-annealed at 950°C for 24 hr in vacuum. Finally the finished samples were vacuum-annealed at 1000°C for 6 hr and water-quenched to room temperature. The average grain diameter was 0.02 cm. B) Cooling System. The M, temperature of the alloy was -55°C. Fig. 2 shows the arrangement which was used to cool the specimen at a slow rate. The specimens were mounted inside a i -in.-diam hole in the 2-in.-long section of the copper specimen holder. This cavity was filled with silica gel. A dummy specimen was used under identical conditions for

Jan 1, 1969

By L. Xia, B. Hart, J. Nigim, Z. Chen

"Grinding ore is an important step in the flotation process. Not only does grinding reduce particle size and liberate minerals, it also creates conditions for reactions to occur on particle surfaces that can aide or inhibit flotation. There have been numerous studies examining various grinding regiments and the effect on flotation pulp chemistry, including autogenous grinding and using media of variable composition. There have been however, few studies looking at the effect of variability in grinding media size on pulp chemistry and subsequent flotation. This study attempts to link changes in pulp chemistry in response to variations in grinding media size to flotation recovery. It uses probes mounted in the grinding chamber (pH, Eh, DO, and conductivity) to monitor pulp chemistry changes during grinding of a Cu-Zn ore. Surface chemistry analysis by ToF-SIMS was performed on sphalerite from the mill discharge. Activator and depressant species were monitored on the mineral surfaces and their presence was evaluated in the context of variability in pulp chemistry linked to differences in grinding media and its ball size.INTRODUCTIONIt has been widely recognised that not only does grinding reduce particle size and liberate minerals but the grinding environment has a large effect on the flotation of sulphide minerals. This effect is attributed to Eh change, iron hydroxide coating on surfaces, oxygen reduction, precipitation from solution and galvanic coupling (Grano, 2009). As early as 1960, it was reported that after grinding the ores in an iron mill the natural floatability of sphalerite was reduced significantly (Rey and Formanek, 1960). Kocabag and Smith (1985) studied on the industrial circuits showing that the depression of sulphides flotation in a steel mill is possibly due to the coating of iron oxidation products. Peng, Grano, Fornasiero, and Ralston (2003a, 2003b) found that iron contamination from grinding media plays a dominant role in depressing galena and chalcopyrite flotation. Huang, Grano, and Skinner (2006) reported the same observation in the flotation of arsenopyrite."

Jan 1, 2016

By Eugene F. Broome, Hugh A. Walls

Self-diffusion coefficients were measured using the modified shear cell technique over a temperature range from 31" to 401°C. These data agree within experimental error with those of Petit and Nachtrieb, which were determined from 30°to 99°C. LIQUID self-diffusion behavior in gallium has been studied previously by Petit and Nachtrieb&apos; using their shear cell technique.&apos; Data were obtained in that investigation over temperatures ranging from 30.6 to 98.7"C, and these comprise the only published data for liquid gallium. In the work reported here, diffusion data were obtained from 30.8 to 400-9.Cusing a shear cell technique different from that of Petit and Nachtrieb. This modified shear cell method and the mathematical analysis for diffusion in a finite capillary geometry have been previously described.3 PROCEDURES AND ANALYSIS The segments of the modified shear cell were fabricated from types 304 and 316 stainless steel. No corrosion problems with gallium were encountered until attempts were made to obtain data at 500°C. The diffusion capillary diameter was 1.59 mm and capillary lengths for the four sets of cell segments used are given in Table I. Gallium with a purity of 99.999 wt pct was obtained from Var-Lac-Oid Chemical Co. The gallium-72 isotope used to measure the self-diffusion coefficients was produced from this inert gallium by irradiation in The University of Texas Reactor Facility, and was checked for radiochemical purity. Following a period of isothermal diffusion controlled to within 0.0l°C, the contents of each capillary section were emptied into a counting planchet, weighed to assure that gallium had not been lost during handling, and the radioactivity determined by windowless gas-flow proportional counting. Great care was taken to obtain a reproducible counting geometry for the samples. Diffusion coefficients were obtained from the solu-tion3 to the diffusion equation for the modified shear cell problem, viz.: in which B2= C2(t)Li + L2)- CSL1-COL2 P* (C0-Cs)(L1+ L2) and L, and L2 are the capillary segment lengths. The step-function initial concentration distribution was expressed as C(x,O) = C, for -L1 = x < 0 and C(x,O) = Co for 0 < x 5 L?. Also, C2(0 = ^- fcix,t)dx Computation of the diffusion coefficients was done numerically as described in our earlier paper.3 Because of the short half-life of gallium-72 (14.1 hr) and the relatively long counting times taken to give a precise value of the diffusion coefficient, it was necessary to account for the radioactive decay both during the actual count and between counts for different samples (before and after diffusion). Thus, the average count rate Cz(t) for a second sample counted from times t3 to t4 can be made consistent with the average rate Co determined for a first sample counted from times t1 to t2 by the relationship: N(e-»i-e-M») , , C2(f) " &-«,)(*-«.-«-»«) [21 in which N is the total number of counts taken and is the decay constant. RESULTS AND DISCUSSION The self-diffusion coefficients determined in this investigation are listed in Table 11. Values of the parameters used to calculate the coefficients are given in the table, as are values of the random counting error &apos; for the concentration ratio pz and the corresponding expected random variation AD in the diffusion coefficient. The quantity is calculable from: &apos;Cg — C2(t)} , „ ,2 .-„¦, M co-csl(ACs)J W in which AC is the error in the individual count rate. The mean values of the diffusion coefficients within each temperature group are also given in Table 11. Such temperature groupings of data are reasonable because of the small variations between the temperature~.~

Jan 1, 1970

By E. J. Koval

Practical miscible displacement processes will be characterized by lingering of the solvent into the oil. The lingering process is brought on by viscosity differences, and can be accentuated by channeling and longitudinal dispersion. The effects of these factors on the efficiency of unstable completely miscible displacements are combined in what is called the K-factor method. This method, analogous to the Buckley-Leverett method, predicts recovery and solvent cut as a function of pore volumes of solvent injected. Experimental data are included and show excellent agreement with theory for a wide variety of sandstone cores and viscosity ratios. INTRODUCTION Theoretical considerations,1 laboratory experiments,2 and pilot tests3 lead to the conclusion that miscible displacements in the field will be unstable In an unstable miscible displacement, the solvent fingers through the oil. This fingering leads to early breakthrough of the solvent and an extended period during which both oil and solvent are produced. For such a system, there appear to be four principal factors which bring about or accentuate the effects of instability: longitudinal dispersion (including geometrical effects), channeling, viscosity differences and gravity differences. Other factors, such as diffusion and flooding rate, can also influence the effects of instability, but at the flooding rates considered in this report, circa 15 ft/D, they are unimportant. Longitudinal dispersion can be thought of as a spreading of the solvent front caused by the presence of microscopic inhomogeneities. Channeling of the solvent occurs when a porous medium has macroscopic inhomogeneities; i.e., gross permeability variations. Viscosity differences lead to fingering of the less viscous solvent. This difference in viscosity accelerates the growth of fingers along paths previously developed because of permeability variations. Gravity differences lead to overriding by the usually less dense solvent. Al- though gravity effects are generally small at a flooding rate of 15 ft/D, they would, nevertheless, unnecessarily complicate the interpretation of flooding experiments. For this reason, all the experiments reported herein were done with matched density fluids. Fingering and the resultant poor areal sweep were recognized early as the dominant influences on the efficiency and the economics of miscible displacement processes. Much research effort has been spent on ways to minimize fingering and increase areal sweep such as the use of graded viscosity slugs4 or water slugs. Some researchers attempted to work out ways to prevent fingering completely; i.e., to achieve a stable displacement through gravity or latitudinal dispersion stabilization. l Others did not attempt to control fingering but obtained an economic process by merely recycling the solvent and sweeping pattern by pattern.6 During this period, all aspects of fingering came under close scrutiny. Some researchers reported on how fingering looks2 and how it is affected by viscosity ratio,7 geometry,7 and slug size.2,* Peaceman and Rachfordg suggested a mathematical approach to the prediction of unstable miscible displacements in relatively homogeneous sand packs, but their work cannot be extended conveniently to heterogeneous systems. Hence for a heterogeneous system, no method is presently available for predicting solvent cut and recovery as functions of pore volumes of solvent injected. The purpose of this investigation was to attempt to fill in the gap in our knowledge concerning the prediction of performance of unstable miscible dis placements. Necessarily, the system selected for study was a relatively simple one. The restrictions placed on the system were: (1) The system was linear; (2) The solvent was miscible in all proportions with the oil in place; (3) The solvent was continuously injected into the porous medium; (4) Gravitational effects were eliminated by matching densities and (5) All the flood rates were high and constant at 15 ft/D to avoid any small rate effect and to minimize any diffusion effects. To simplify and to indicate that both longitudinal dispersion and channeling arise from permeability variations, the effects which they cause or influence have been termed heterogeneity effects. The use of

By R. M. Goldhoff, J. W. Spretnak

IN connection with establishing the mechanism by which boron enhances the hardenability of heat treatable steels, this research work has been undertaken. Spretnak and Speiser1,2 indicated the need for studying high temperature effects in boron steels and, chief among these, the possible nonhomogeneous distribution of boron in iron grains. The occurrence of this effect may be of significance in explaining the mechanism of enhancement of hardenability by boron as well as in explaining some of the observed characteristics of boron steel behavior. Primarily, then, this work was undertaken a) to establish whether or not boron is adsorbed in ? solid solutions, b) to determine the nature of any such adsorption effects, i.e., whether it is positive or negative as well as its temperature coefficient, and c) to establish the magnitude of any such effect. While past literature on this specific subject is rather sparse, a number of authors have postulated that the observed temporary loss of hardenability as well as the occurrence of the characteristic boron constituent in these steels is due to the nonuniform distribution of boron in austenite.3-0 Experimental Techniques Attempts to obtain direct evidence of grain boundary effects in boron steels have been unsuccessful, both by using the technique of Chalmers&apos; in which small concentrations of solute made radioactive by irradiation are detected by autoradiographic means, and by means of studying cleavage fractures with the electron microscope.8 The present study attempts the design of experiments to measure the effect of boron on properties which might be subject to variation because of grain boundary effects. A study of the theoretical aspects of grain growth indicates that such studies may be pertinent. Another valid type of experiment involves the measurement in polycrystalline materials of properties whose values depend on the bulk of the grain, being negligibly influenced by grain boundaries. One such property is the lattice parameter measured by X-ray diffraction. The value of the lattice parameter reflects the average conditions which obtain over a relatively large number of atoms in a fixed crystalline lattice, and is therefore mainly dependent on bulk grain material. Measurement of lattice parameter variation over the austenite range of temperature in iron with and without boron should give evidence of concentration variations in the bulk grain material if adsorption effects are significant. Finally, use is made of the Grange and Garvey3 metallographic test for boron in which a characteristic boron constituent can be developed in austenite grain boundaries. The very occurrence of this phenomenon suggests grain boundary enrichment of boron and a study of the occurrence of this constituent and its varation with austenitizing temperature should help to detect grain boundary effects. Materials One lb ingots of pure iron, an Fe-B alloy, an Fe-C alloy, and an Fe-C-B alloy were prepared. The melting technique included an initial melting of electrolytic iron under vacuum followed by remelting under hydrogen and, finally, by melting under argon with the addition of alloying elements. Each ingot was surface machined between meltings. A quantitative spectrographic analysis was obtained on the pure ingot and, in addition, oxygen, nitrogen, and carbon were determined by the vacuum fusion method. The results of these analyses are given in Table I. Semiquantitative spectrographic analyses were performed on the alloy ingots, while quantitative determinations of the alloy additions were obtained. These analyses are shown in Table 11. The cast ingots were subjected to the following sequence of fabrication treatments: forging to 5/8 in. bars, swaging to 0.300 in. rounds, drawing to 0.025 and 0.010 in. wire. Portions of each ingot were retained in the swaged condition for experimental use. For certain portions of the work typical commercial steels were used. These materials were supplied by the Republic Steel Corp., Canton, Ohio, and correspond to AISI 8640 and AISI 86B40 compositions.

Jan 1, 1958

By Thom Mambe, Angelo Fernando

The objective of this work was to identify key parameters related to the reduction of the sulphur content in ammonium diuranate (ADU), and the identification of solid products being formed under various operating conditions. A laboratory-scale, continuous ADU precipitation circuit was assembled using a glass reactor vessel immersed in a temperature-controlled water bath. A pre-prepared uranium feed solution was fed continuously using a peristaltic pump. Anhydrous ammonia mixed with compressed air was metered and pumped using a double-headed peristaltic pump. An over-head mixer was used to keep the solids in suspension. The precipitated ADU slurry was removed from the reactor at the same flow rate as the feed solution. The slurry was sampled to generate ADU solids for chemical and physical analysis after four hours of continuous operation to ensure steady-state conditions. The following variables were studied to determine their influence on the sulphur content in the resulting ADU. (a) sulphate:uranium molar ratio in the reactor (1:1, 1:5, 1:10 and 1:20) (b) precipitation pH ( pH 6, 6.5, 6.9, 7.5 and 9) and (c) precipitation temperature (40C and 60C) A total of 18 tests covering the above parameters were conducted, and the results indicated that the sulphur content in the resulting solids was highly dependent on the reaction pH. Out of the pH levels tested, tests completed at pH 6.9 and 7.5 generated solids containing the lowest sulphur contents, between 0.5 to 1.5% S uranium basis (UB). The sulphur content in solids was found to vary linearly with the sulphate:uranium ratio in the feed solution, showing a statistically valid correlation. The impact of temperature was minor between 40°C and 60°C, with a slight advantage at higher temperatures. Tests at a sulphate:uranium ratio of 1:1 produced solids with the lowest sulphur contents. The influence of pH or temperature on sulphur content in solids was almost non-existent at this sulphate:uranium ratio. Precipitation pH is the major factor influencing ADU sulphur content, followed by the uranium to sulphate ratio.

Jan 1, 2020

By Jaime Fernández Concha

El presente texto señala la ubicación, fisiografía, geología general y cubicación del depósito de Fierro del Cerro Tarpuy y Cerro Mirador ubicado en el departamento de Arequipa.

Jul 1, 1956

By G. Archer

ASARCO, a large and diverse producer of nonferrous metals, is involved primarily in the smelting and refining of lead and copper. Lead-antimony alloys, antimony trioxide, bismuth, cadmium oxide, selenium, tellurium, silver and gold are among products which result from processing by-products of smelting and refining. The complex mixture of concentrates at some smelters and the high impurity loads at some refineries result in various drosses, sludges, dusts and slags. In this paper, the complex interplant and intraplant transfer of by-products is addressed. These by-products result in an exchange of metals between the lead circuit and the copper circuit. Examples of the transfer of by-products and the prospects for the recycle of valuable products from wastes generated by customers and unrelated processors are also discussed.

Jan 1, 1992

By R. F. Steigerwald

The effects of heat transfer on the corrosion behavior of type 304 stainless steel in boiling water have been studied. Heat transfer conditions increase the tendencies of the stainless steel toward stress-corrosion mucking when the water is contaminated with Cl-. Surface preparation is the most important variable in determining the severity of the stress-corrosion problem in water with a given Cl- content. Heat treatment, chemical cleaning, and degree of wet film boiling also affect the corrosion of stainless steels used as heat transfer surfaces in boiling water. An up-paratus for corrosion testing under controlled heat transfer conditions is described. THE principal objective of this investigation was to study the corrosion behavior of AISI Type 304 stainless steel in boiling high-purity water under conditions of heat transfer. The principal variables in the study were: a) boiling conditions: limited boil, agitated boil; b) metallurgical structure: annealed or sensitized; c) surface condition: rolled, pickled, or ground. The results of the study should elucidate the role of heat transfer in the corrosion of stainless steel in boiling high-purity water and provide a base line from which to assess the severity of this type of corrosion. Although there has been an investigation of the effect of heat transfer on the corrosion behavior of stainless steels in alkaline waters,&apos; work on the corrosion of stainless steels under heat transfer has been largely confined to various acid solutions.&apos;-4 Furthermore, the study of the corrosion of stainless steels in high-purity water has been generally restricted to auto-clave and instream testing in superheated (e.g., 300°C) water and steam.5&apos;6 Cooling water problems led to this study of the corrosion behavior of type 304 stainless steel in high-purity water at its atmospheric boiling point. In addition to the effects of heat transfer, this study also considered the influences of the type of boiling,7 metallurgical structure, and surface condition on the corrosion behavior of stainless steel in high-purity water. Two boiling conditions were investigated in this study: a) limiting boiling, i.e., when the heat-transfer surface had just reached the boiling point and boiling nucleated randomly over the specimen surface and b) agitated boiling, i.e., when a mild degree of superheat had been achieved on the specimen surface and boiling occurred generally over the specimen surface. Both boiling conditions are broadly classified as wet-film boiling. Originally, this program included the study of a third type of boiling, dry-film conditions. At dry-film boiling the temperature of the heat transfer surface is high enough so that it is covered with a continuous film of steam. Experimental difficulties made it impossible to study this kind of boiling with the available apparatus. Since surface condition affects heat transfer rates, three typical surfaces were chosen for study: a) as-rolled, the 2B finish received from the supplier, b) as-pickled, 30 min in 8 pct HNO3-1 pct HF, and c) as-ground on 120 grit paper. In order to evaluate the effect of improper heat treatment or welding on hot wall corrosion, both annealed and sensitized mi-crostructure were included in this study. EXPERIMENTAL Test Apparatus. The particular problems of interest in this investigation required a knowledge of the thermal gradient through the test specimen. From this gradient, the heat flux to the surface and the surface temperature could be determined. In order to satisfy this need, an apparatus similar to the boiling-disk apparatus of Fisher and whitney2 was designed. The solution is contained in a thermally-insulated, steel pipe lined with TEFLON resin. A stainless steel _______;________________________________________

Jan 1, 1970

By J. R. Long

The investigations described herein are concerned with a portion of a systematic research, by the Federal Bureau of Mines on ductile titanium. The Bureau&apos;s work on the metal has resulted in development of a semi commercial process for the preparation of titanium and has also made available significant information on the fabrication and physical properties of this new strong, light, corrosion-resistant metal. Considerable interest has been aroused by this work, and a number of other laboratories have begun similar investigations. However, the necessity for Consolidating titanium by normal powder metallurgy methods presents difficulties in producing commercial forms and shapes on a large scale. This investigation was therefore undertaken for the purpose of improving the technique for consolidation of titanium powder into solid nonporous metal.

Jan 1, 1949

By M. C. Flemings, A. A. Tzavaras

Analytical and experimental procedures are descrihed for quantitative determination of volume-fraction microporosity in metals by mimorarlio-graphg. The analysis assumes spherical pores but allows for the observed fact that pores or portions of pores smaller than a given thickness do not project an image on the film. Volume-fraction microporosity was measuured in cast low-alloy steel and shown to vary from 0.6 x 10-4 to 10 x 10 depending on mode of solidification and on whether the material was air- or vacuum-cast. The aim of work described herein was to develop a method of quantitative measurement of the volume fraction of microporosity in cast metals. Microporosity, present in nearly all castings and ingots, is always interdendritic in nature and may be large enough to be seen on a polished surface with the naked eye. More generally, it is smaller in size, and its detection more difficult. Three techniques might be considered for measurement of microporosity: 1) lineal analysis of a polished metallographic surface, 2) density measurement, or 3) quantitative microradiography. As will be shown later, volume fractions of porosity in directionally solidified castings may be the order of 10-4 to 10-3; such small amounts of porosity are difficult to identify and measure on a polished surface. Density measurement is also not a suitable technique (for alloys) when the volume fraction of porosity is low. This is because the density of the base metal is often not known within the necessary accuracy, due to microsegregation or partial phase transformations. In general, it is not possible to completely eliminate microsegregation without also altering the porosity. Because of the limitations of the foregoing techniques, quantitative microradiography was employed to determine amount of porosity. In recent work, microradiography has been found to be useful for qualitative measurement of porosity, including determination of size and shape of individual pores;&apos;)&apos; however, quantitative determination of amount of porosity has not been attempted. I) CALCULATION OF VOLUME-FRACTION POROSITY The following analysis employs procedures similar to those of Cahn and Nutting3 and Hilliard.4 Major simplifications are that pores are assumed to be spherical and to be present in sufficiently small quantities that no overlapping occurs. A basic difference from the previous treatments is that the limited "sensitivity" of microradiography is considered. Assume first 1) cavities are spherical and of uniform diameter, 2) cavities are randomly distributed, 3) volume-fraction porosity and specimen thickness to pore radius ratio are sufficiently small that overlapping of the projected images of cavities is negligible, 4) sensitivity is limited (i.e., holes or portions of holes of less than a given thickness do not project an image on the film). The sensitivity, is defined as: where 5 = minimum thickness of void from which an image will be projected on the film and t = specimen thickness. Now, from Fig. 1, it is possible to distinguish between two different types of holes. These are 1) holes whose centers lie within the region t/2 > X > 6/2, where X is distance from one surface of the specimen (positive into the specimen), and 2) holes whose centers lie within the region (6 — r) < X < 6/2, Holes whose centers lie outside X = (6 -r) project no image on the film. These two types of pores are considered separately below. Type 1 Pores. When 6 is greater than 0, the image of a spherical cavity of radius r appears on the film as a circle of radius a which is smaller than r. From geometry, Fig. 1: a2=r2-52/4 [2] where a = radius of image of pore on film and r = radius of pore. Since the pores are randomly distributed and spherical V =4/3pr2Nv [3] where V = volume fraction of voids and Nv = number of pores per unit volume and the number of images of Type 1 pores per unit area of film, N&apos;A, is

Jan 1, 1965

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 Sidney A. Hiscock

INTRODUCTION Lead and zinc are today rightly regarded as sister metals. Historically, however, they differ markedly with lead being known and in general use as the metal since 3000 BC in several countries which at that time might have been described as mature economies. Zinc was not isolated and recognised as an industrial metal with distinct and valuable properties until about 1700-1800 AD (although it had, of course, been utilised as a constituent of brass for some 2000 years previously). c were well established as industrial metals by the beginning of the 20th century. The present paper briefly reviews the overall growth in world consumption* and changes in the three main areas which today represent the mature economies or industrialised areas, i. e. ,Europe, the United States and Japan. Trends in overall consumption are determined by the demands for the individual uses for lead and zinc. The changes in patterns of use in the industrialised areas - individually and collectively - and reasons for the changes are also considered. LONG TERM TRENDS - 1900-1984 The World Picture Since the beginning of the 20th century the world consumption of lead (3.9 million tonnes in 1984) has grown almost fourfold and that of zinc (4.7 million tonnes in 1984) is almost eleven times greater than it was in 1900. The long-term trend has been one of continuing expansion for both. metals although the pattern has been severely disturbed at certain periods, for example in the years immediately following the two world wars and at times of marked recessions in industrialised areas. Apart from such major setbacks, new levels of consumption have been established regularly every few years. Recently, however, consumption has not really grown and with only a slow and partial recovery in world industrial activity at present, there is no indication that the peak consumptions of 4.2 million tonnes of lead, set in 1979, and 4.8 million tonnes of zinc (1973) will be exceeded in the near future. The growth in world lead and zinc consumption since 1900 is shown in Figure 1 (which includes changes in copper and aluminium for comparison). Overall growth over the period 1900-1984 has been about two percent a year for lead and about three percent for zinc (annual growth for copper has also been about three percent). Increases in tonnage consumption and growth rates by decade for lead and zinc are summarised in Table I. However, the growth rates by decade sometimes conceal very large individual annual increases and decreases. For example, in 1975 lead consumption fell by 13 percent and zinc consumption by 22 percent compared to 1974. In 1976 consumption of lead and zinc rose by 12 percent and 18 percent respectively. The years when consumption &apos;landmarks&apos; (ie one, two, three and four million tonnes) were first reached are shown on Table 2. Clearly, the pattern of shorter periods being required to attain each extra million tonnes of consumption was broken in the 1970&apos;s. The consumption of zinc overtook that of lead for the first time in 1940, and since 1946 has always been at a higher level. Trends in industrialised areas The two key industrialised areas at the beginning of the 20th century were Europe and the United States which between them accounted for some 95 percent of world lead consumption and 98 percent of zinc consumption. Figures 2 and 3 show the growth in lead and zinc consumption, and Figures 4 and 5 the percentage shares for each area since 1900. Europe has usually been the major user of lead except for some years in the 1920fs, most of the 40&apos;s and early 50&apos;s when consumption in the United States was larger. In 1900, Europe accounted for about 64 percent of world lead consumption and the United States just over 30 percent. Currently, Europe takes about 40 percent of world consumption and the

Jan 1, 1986

By McHenry Mosier

The diamond-drill method was tried at the site selected for driving a 5- by 6 -foot air shaft at the east end of the Bellefonte mine . This method of sinking consisted , first , of drilling a 5-3/4 -inch-diameter cut hole from the surface , then drilling parallel 1.5 - inch ( EX ) holes around it at appropriate distances for a balanced blasting round . The cut hole was not charged with explosive but served as a relief chamber for the incipient expansion of the ground broken by. blasting the surrounding 1.5 - inch holes . The length of each hole was 236 feet , which was the finished depth of the shaft . The nature of the work in the air shaft was largely experimental , and many difficulties arising from the lack of special equipment and proper technique for precise alinement of the drill holes caused expensive delays before they could be overcome . Drilling the 5-3 /4 - inch hole , which was impeded by frequent core blocks in the core barrel , required 10 shifts . average advance per shift for an EX hole was about 150 feet . The The holes were charged and fired from the surface . The length of the section blasted in one cycle was 10 feet . Blasting progressed from the bottom of the shaft upward . The broken stone dropped into a chute , from which it was drawn into cars on the haulage level . The Bellefonte mine is an underground limestone mine.3/ The primary objective in undertaking the research on shaft sinking by diamond drilling was to perfect a method for driving connections between levels of the mine .

Oct 1, 1948