Search Documents

By R. A. Greenkorn, R. C. Smith

Hele-Shaw cells are used to model creeping flow through porous media (where Darcy&apos;s law is valid). The effects of inertia on flow about obstructions in a Hele-Shaw cell can be calculated by a perturbation method if one can determine a solution to Laplace&apos;s equation. Results of a computer solution for flow about circular, square and elliptical obstructions are presented. These results show that or a modified Reynolds number of less than I, the inertia terms are small; and for values of less than 3, the average streamline predicts the ideal flow. Therefore, the analogy might be used for studying flow in porous media up to a modified Reynolds number of at least 3. INTRODUCTION The nature of fluid flow in porous media is of interest in the fields of soil mechanics, ground water flow, petroleum production, filtration and flow in packed beds. Because it is very difficult to study the phenomenological behavior of flow in porous media, homologs and analogs are used to study flow characteristics. A Hele-Shaw model, made of two closely spaced plates - usually glass — is often used as an analogy to two-dimensional flow in porous media. Hele-Shaw2 showed experimentally that the streamline configuration for creeping flow around an obstacle located between two closely spaced parallel plates is the same as for two-dimensional, ideal flow about the same obstacle. Stokes7 verified these observations mathematically. The usual equation of motion for flow in porous media is Darcy&apos;s law. The form of the mathematical statement of Darcy&apos;s law is identical, within a multiplicative constant, to the expression for the average velocity over the plate gap in the plane of a Hele-Shaw model. These models may be used to describe flow in both homogeneous and heterogeneous porous media. In the mathematical proof of the Hele-Shaw analogy it is assumed that the convective terms in the Navier-Stokes equations are negligible and that the equations of motion degenerate to Laplace&apos;s equation, with pressure the dependent variable. Whenever a Hele-Shaw model is used as an analogy to flow in porous media, .the validity of this assumption is in question. Riegels5 showed that if convection is not neglected, the velocity distribution around a cylindrical obstruction in the flow field depends on a Reynolds number, the plate spacing, and a dimension characteristic of the obstacle. Riegels&apos; solution, a perturbation solution, uses the boundary condition that the flow rate into the obstacle averaged over the plate gap at any point on the obstacle is zero. The method requires that a solution to Poisson&apos;s equation for the perturbation pressure be found. Riegels evaluated this solution for the case of the cylindrical obstruction. His method may be simplified by eliminating the need for solving Poisson&apos;s equation for the perturbation pressure. Instead, an analytic expression for the perturbation pressure gradient is obtained (valid for arbitrary shapes) and used to eliminate pressure from the equations for the perturbation velocities. The results show, for symmetrical shapes, that if NRe < 1, the convective acceleration terms are small, and that the average velocities represent ideal flow up to at least NRe = 3, where: L is a characteristic dimension of the obstacle perpendicular to flow, b is the plate spacing, u is viscosity, v, is velocity of approach and p is density. THEORY* Incompressible fluid flow through a Hele-Shaw model and a porous medium are analogous because the equations for the average velocity components in two-dimensional flow are identical if:

Jan 1, 1970

By D. M. Urich

New plant construction for pyrolysis and agglomeration during 1969 has been relatively quiet in the North American scene. U.S. pellet capacity approximates 52 million long tons and that of Canada 25.3 million tons. The foreign scene, however, has been extremely active during 1969, and this is expected to continue for the next several years. Changes in sinter practice have not been reported, other than a few changes towards increased bed depths and the increased use of screening facilities to size the product more closely. Interest in the field of briquetting in fields other than iron ore is high with a new fluorspar briquetting plant under construction at Brownsville, Texas. Considerable research appears to be pointed towards solving the problem of reclaiming steelmill waste products (flue dust, BOF dust, mill scale) by means other than sintering.

Jan 1, 1970

By Gary A. Kingston

Chromium resources in the United States are estimated at 1.8 million tons of recoverable chromium contained in 22.5 million tons of chromite-bearing material. Additional resource is presumed existent in large, but as yet undetermined, quantities of material containing less than 10 percent Cr203. No domestic resources are being mined presently (1969). Excluding transportation charges to domestic consuming areas, the total 1.8 million tons of chromim is estimated to be available, in ore or concentrate, at costs up to $0.64 per pound; 63 percent of the total is available under $0.11 per pound; and 38 percent under $0.08 per pound. It is judged that transportation from the resource areas to the existing market centers would add nearly $0.05 to the cost of a pound of chromium contained in ore or concentrate. Technically effective beneficiation methods have been developed for much of the known domestic resource, and further development might reduce costs of processing these materials. However, at present, domestic chromium resources are noncompetitive with foreign sources.

Jan 1, 1970

By B. S. Hickman

Using primarily quantitative single crystal X-ray techniques studies have been made of the precipitation of the metastable w phase in alloys of titanium with Mo, Mn, Fe, Cr, and Nb. It is shown that, in agreement with earlier work on the Ti-V system, the composition of the w phase during aging approaches a constant; the value varies from one system to another in a systematic manner with the electron concentmtion. Results relevant to the mechanism of w precipitation during quenching and during aging are presented and discussed. Results are presented to confirm that the w phase is coherent and the nzorphology of the Necipitates is described and discussed. PRECIPITATION of the metastable w phase in alloys of titanium is of interest because of its severe embrittling effect and also because of the enhancement of the superconducting properties which accompanies precipitation.1 The general features of w phase precipitation have been discussed by cuillan and by Bagaratskii et d3 The work described in this paper forms part of a general study of w phase precipitation which was undertaken to elucidate various unknown or controversial features of the process, namely: i) What is the mechanism of formation of the phase ii) How does its composition, morphology, volume fraction, and particle size vary with the type and content of the alloying element and with the heat treatment conditions? iii) What is the relation between the w phase and the equilibrium a phase? In a previous paper4 the results of a detailed study of w phase in Ti-V alloys were presented. It was shown that: U During aging the composition of the w phase approached a saturation value of 13.5 to 14.0 at. pct V. ii) w precipitated as cube shaped particles and once precipitation was complete, particle coarsening did not occur. iii) a phase formed initially by direct conversion of w-phase precipitates. In this paper similar measurements are reported on Ti-Mo alloys and some more limited data given on the Ti-Cr, Ti-Fe, Ti-Mn, and Ti-Nb systems. The results i.1 the six systems are then compared. It has been shown previously by electron microscopy that the w precipitates as ellipsoids in both the Ti-Nb system,&apos; and in i-o.&apos; Blackburn and williamsz3 have reported the precipitates in Ti-Fe, Ti-Cr, and Ti-Mn are cubic, i.e., similar to the Ti-V system.476 EXPERIMENTAL METHODS 1) Specimen Preparation. Samples of the compositions shown in Table I were prepared by arc melting. High purity electron beam zone refined titanium (Materials Research Corporation Grade I—total impurity content =250 ppm) was used; the other source materials are given in the table. A commercial Ti-8 wt pct Mn alloy was used for studies of this system. After homogenization the materials were rolled or cut into strip approximately 1/4 in. by 2 in.; the strip was then heated at temperatures of 1200" to 1300°C for several hours by passage of a direct current through the strip in an ultra high vacuum system (<10-torr) and then quenched by admitting high purity helium and switching off the current. This treatment resulted in crystals up to 2 in. by 2 in. by A in., almost all of which had a [100] direction nearly perpendicular to the plane of the strip. The crystals were cut from the strip by spark machining and their composition checked by lattice parameter measurements supported by chemical analysis. 2) X-Ray Diffraction Methods. Lattice parameter measurements were made using a modification of the single crystal spectrometer described by ond. In this technique the crystal angles for reflection on either side of a highly collimated primary beam are measured. Generally the 400 CuK, or the 400 CuKp reflections of the bcc lattice were used. In the as-quenched crystals a precision of 1 in 105 was obtained, but due to line broadening the parameters in aged materials could only be measured to 1 in lo4. This accuracy was, however, quite adequate for the purposes of these experiments and enabled the composition of the p phase to be obtained to 10.1 pct in all systems except Ti-Nb where the lattice parameter change with composition is very small. The precipitation and growth of the w phase was examined using a single crystal goniometer attached to a Phillips diffractometer. The relative intensities and line shapes of b-phase and w-phase reflections

Jan 1, 1970

By B. I. Ferber

Sodium chloride aerosol was employed to determine respirator filter penetration in a manner suitable for use in Bureau of Mines approval and certification procedures. The aerosol was produced by an ultrasonic generator and treated to yield the proper conditions of relative humidity, particle size, and concentration. Respirator filters were exposed to the aerosol; filter penetration (down to 0.02 percent) was determined with a flame photometer. Results are comparable with those obtained in another laboratory using different equipment.

Jan 1, 1970

By W. R. Bull, J. R. Roos

A method is described whereby the true financial value of each constituent of each concentrate can be calculated. Each value is then compared with what this value would be in a perfect separation. The difference in each case represents the loss incurred by each aspect of an inefficient separation. The relative magnitudes of these losses indicate those avenues of plant investigation and research that offer the highest potential reward. The metallurgical efficiency of a concentration operation is difficult to express because there are two criteria of performance, namely, grade and recovery. Neither of these alone gives any indication of the effectiveness of an operation and, if they are combined in some formula, it must be empirical and unreliable because of many external factors. Since milling is an operation performed as one step in the most profitable overall method of producing a metal or other end product, the main objective of mill operation should be to make a maximum contribution to this maximum profit. When concentrates are sold to custom smelters, the income from the operation, and the costs, may be calculated. When concentrates are further processed by another division of the same company, and there is no formal financial relationship between, say, the milling and smelting divisions of the company, the mill superintendent&apos;s job is less well defined. But even so, if the mill superintendent works as though he were selling his concentrates, and uses reasonable, if fictitious, conditions of sale, then he can get a good indication of the effectiveness of his operation by calculating his "Economic Recovery". ECONOMIC RECOVERY This is a method used as a basis of operation by several mills and has been described in the literature. Very briefly, the "standard" of operation is taken as that of a mill separating the ore into perfectly pure concentrates with 100% recovery of each mineral in its respective concentrate. For example, a 4%Pb, 4% Zn ore (galena and sphalerite), would provide a lead concentrate weighing 4.62% of the feed and assaying 86.6% Pb and a zinc concentrate weighing 5.97% of the feed and assaying 67.1 % zinc. These perfect concentrates are (hypothetically) shipped to the appropriate smelters, freight and treatment charges and payments calculated, and the net return obtained. This is the optimum financial return for the operation of the mill and is used as the standard. Now the return for the actual, real-life, mill operation is calculated in the same way, and the ratio of the two is termed the Economic Recovery. Many additions and modifications may be made in any particular case. For example, if the zinc mineral is marmatite, the optimum grade of the zinc concentrate may be set lower than 67.1%. If silver is present, it will be recovered 100% in the lead concentrate in the perfect operation. Similarly, cadmium will be recovered 100% with the sphalerite. Mr. Weiss&apos; paper&apos; mentions a case where, because of extremely fine intergrowth between the valuable mineral, chalcocite, and pyrite, the optimum grade of copper concentrate was taken as 45% Cu instead of the theoretical 80%. Each operation will present its own possibilities in this way.

Jan 1, 1970

By R. K. Agarwal

Transforming from a mere novelty field of science to a well-recognized branch of engineering, the scientific discipline of rock mechanics continues to mature. The past decade has witnessed an unprecedented in- fusion of scientific research approach into mine design. In the preceding year alone, there were six national and international congresses which also indicated the increased interest, in rock mechanics and participation by scientific personnel with diversified backgrounds. It may be presumptuous to conclude that the time, effort and money spent thus far on procedures for mine structure design have necessarily resulted in the evolvement of design techniques; but certainly the prospects of evolving such techniques art: more promising at present than ever before.

Jan 1, 1970

By M. J. Stewart, F. Weinberg

PREVIOUS investigations into convective flow in molten metals have examined systems in which the length-to-height ratio of the enclosure is large, usually using long graphite boats.&apos;&apos;2 In normal castings this ratio is generally small and it is not possible to extrapolate the results of previous work to casting configurations. The present investigation was undertaken to examine liquid flow in systems of low length to height ratio. The apparatus used for the experiments is shown in Fig. 1. The molten zone of tin is contained in an aluminum mold of inside dimensions 6.4 by 6.4 by 0.31 cm. A heating block containing a resistance coil is attached to one end of the mold and a cooling block is attached to the other end. These are used to produce a wide range of temperature differences across the mold. The mold is contained in a stainless steel tank which is heated from the outside by resistance heaters to give the required operating temperature during the experiment. Temperature measurements in the molten tin are made with an iron-constantan thermocouple PT equal to 5 atm. The phase diagram derived by us was the same as that found by Krivsky and Schuhmann, except for a similar discrepancy in one boundary line representing the gas composition in equilibrium with SO a. The vapor pressures of the pure components can be neglected at 1700°K, 1 atm and 2500°K, 5 atm. There-fore, in these cases PT is essentially the total pres-sure in the system. This is valid for all the diagrams presented by Krivsky and Schuhmann except for the one at 2500°K and 0.01 atm, where the vapor pressure of silicon is comparable to PT.6 This work was supported in part by the American Iron and Steel Institute. &apos;C. E. Wicks and F. E. Block: Thermodynamic Properties of 65 Elements, U S. Bur Mines, Bull. No. 605, 1963. R. P. Elliott: Constitution of Binary Alloys, 1st supplementary, McGraw-Hill Book Co., New York, 1965. 3W. A. Krivsky and R. Schuhmann, Jr.: Trans. TMS-AIME, 1961, vol. 221, pp. 898-904. 4M. F. Ancey-Moret, M. Olette, and F. D. Richardson: Mem. Sci. Rev. Met., 1964, vol. 61, pp. 169-76. 5J . F. Elliott and M. Gleiser: Thermochemistry for Steelmaking, vol. 1. Addison-Wesley, Reading, Mass. 1960. 6 J.Drowart, G. De Maria, and M. G. Ingraham: J. Chem. Phys., 1958, vol. 29, p. 1015. probe of 0.4 mm diam inserted into the open top of the mold. Radioactive sn113, in the form of a small sphere, was gently lowered into the molten tin at point A in Fig. 1 THERMOCOUPLE> WATER ARGON END HEATER QUENCH ARGON Fig. 1—Apparatus for detecting liquid flow. Point A indicates position the tracer was introduced.

Jan 1, 1970

By W. H. A. Timm

Lake Dufault Mines, Limited, is located ten miles north of Noranda, Quebec, Canada. Following discovery of a copper-zinc orebody late in 1961, metallurgical investigations of diamond drill core were conducted by Lakefield Research Limited during 1962 and 1963. These were followed by pilot-plant tests in May and June of 1964, utilizing underground development ore. Milling operations commenced on August 16, 1964, and reached rated capacity of 1300 tpd by October 1, 1964. Since that time, tonnage was gradually increased to a maximum of 1400 tpd and since January 1, 1968, gradually decreased to the present rate of 1100 tpd due to an increase in the hardness of the ore. The ore milled from start-up until January 1968, was mainly massive sulfides, consisting of a complex mixture of iron, Copper, zinc, and minor amounts of lead sulfides with important associated values in gold, silver and cadmium (average specific gravity of 3-8). From January 1968 until the present, the ore being processed is described geologically as a boxwork of sulfide stringers of chalcopyrite, pyrite, and pyrrhotite with some local dissemination in siliceous rhyolite (average specific gravity 2.9) supplemented by the massive copper-zinc ore. The limited size of the orebody and the mining method employed (open stoping by blasthole and slash benching methods) would have

Jan 1, 1970

By George S. Ansell, Thomas E. Davidson

It has been known for a considerable period of time that the ductility of even quite brittle materials can be enhanced if they are deformed under a superposed hydrostatic pressure of sufficient magnitude. The response of ductility to pressure, however, has been shown to vary considerably between materials. Prior work has shown that the effects of pressure upon the tensile ductility of Fe-C materials depend upon the amount, shape and distribution of the brittle cementite phase. In this current investigation, the effects of pressure upon the fracture mechanisms in a series of annealed and spheroidized Fe-C materials were examined. It was observed that the principal effect of pressure is to suppress void growth and coalescence, retard cleavage fracture and to enhance the ductility of cementite platelets in pearlite. Based upon the observed effects of pressure upon the fracture mechanisms, a proposed explanation for the enhancement in ductility by pressure and for the structure sensitivity of the phenomena is presented and discussed. THE effect of superposed pressure upon the tensile ductility of a variety of metals has been well documented.&apos;-&apos;&apos; Some of the results from several investigators are summarized in Fig. 1 where tensile ductility in terms of true strain to fracture (ef) is plotted as a function of the superposed pressure. As can be seen, a pressure of sufficient magnitude can significantly enhance the ductility of metals. However, Fig. 1 also demonstrates that the response of ductility to pressure and the form of the ductility-pressure relationship varies considerably between materials. Several explanations have been offered for the observed enhancement in ductility by a superposed pressure. Although no experimental evidence was provided, Bridgman13 and Bobrowsky10 proposed that the observed effect was due to the prevention or healing of microcracks or holes. Bulychev et a1.14 observed that cracks and voids in initially prestrained copper were healed in the necked region of a tensile specimen upon further straining while under a superposed pressure. Also, pugh5 observed that large cavities were suppressed in copper fractured in tension while under pressure. A second proposal has been forwarded by Beresnev et at al.6 This proposal is based upon the hypothesis that a material fails in a brittle manner because the normal tensile stress reaches a critical value before the shear stress is of sufficient magnitude to cause plastic flow. Since a superposed hydrostatic pressure will increase the ratio of shear to normal tensile stress, a sufficiently high hydrostatic pressure should favor plastic flow while retarding brittle fracture. Galli15 reported that a superposed pressure shifts the ductile-brittle transition temperature of molybdenum. This was explained based upon the reduction of the normal tensile stress by the superposed pressure. Pugh5 explained the occurrence of the observed pressure induced brittle-to-ductile transition in zinc in the same manner. Davidson et al.12 proposed an explanation for the enhancement of ductility by pressure based upon the effects of pressure upon the stress-state-sensitive stages of various fracture propagation mechanisms. Basically, they proposed that pressure will retard cleavage and intergranular fracture by counteracting the required normal tensile stress or will suppress void growth. They observed suppression of intergranular fracture and void growth in magnesium by pressure. Davidson and .Ansell16 reported ductility as a function of pressure for a series of annealed and spheroidized Fe-C alloys. Fig. 2, from this prior work, demonstrates that the effect of pressure upon ductility is structure sensitive in terms of the amount, shape and distribution of the brittle cementite phase. As shown in Fig. 2, in the absence of cementite or when the cementite is in isolated particle form (spheroidized), the ductility-pressure relationship is linear and the slope decreases with increasing carbon content. In the annealed carbon-bearing alloys wherein the cementite is in the form of closely spaced platelets (pearlite) or in the form of a continuous network along prior aus-tenite boundaries (1.1 pct C material), ductility as a function of pressure is nonlinear (polynomial relationship) in which the slope increases with increasing pressure. At the highest pressures studied (22.8 kbars), the slope of the curves for these materials tends to approach those for the spheroidized material of the same carbon content. In this current investigation the change in fracture mechanisms as a function of pressure for the materials shown in Fig. 2 has been examined. The possible connection between the observed effects of pressure upon the fracture mechanisms and the effect of pressure upon ductility is discussed.

Jan 1, 1970

By J. O. Wheeler

"DEFINITION OF THE REGION, ITS BOUNDARIES, AND PHYSICAL AND GE'OLOGICAL CHARACTERISTICSTHIS PAPER concerns the Western Cordilleran region, embracing most of British Columbia, the southern half of Yukon Territory and the southwesternmost part of the District of MacKenzie. It excludes Vancouver Island and the Queen Charlotte Islands, which are discussed in a background paper on the Pacific Continental Shelf. The region is bounded on the south by the northwestern United States, on the west by the continental shelf and Alaska, on the north by the front of the Ogilvie Mountains, on the northeast by the axis of the MacKenzie Mountains and on the east by the Rocky Mountain Trench.The region is dominated by two mountain chains that con tain icefields and glaciers: the St. Elias, Coast and Cascade Mountains in the west; the Selwyn, Pelly, Cassiar, Omineca and Columbia Mountains in the east. The Intermontane region between these mountain chains consists of lower mountains and plateaus. In the mountains, the region above the timberline and many of the steep valley-walls provide good exposures of rock, but these areas are subject to rockslides and landslides and in winter to snow avalanches. Much of the Western Cordillera was covered by ice-sheets at various times during the Pleistocene epoch. Consequently, the larger valleys in the mountains and much of the Intermontane region contain much glacial drift and alluvium and only limited exposures of rock. This same terrain in the Southern Cordillera, however, is the most favourable for agriculture. Parts of the region, particularly in the two mountain chains, are heavily forested. Elsewhere, the forest cover is less, with grassland prevailing in the south and tundra in the north."

Jan 1, 1970

By Bruce D. Sartwell

A program was written which utilizes a remote teletype input to a time- sharing computer to plot charged particle or X-ray energy spectra which are stored in the memory of multichannel analyzers. The program, written in FORTRAN V, accepts the data printed out by the pulse height analyzer on paper tape and then, after reading these data tapes into the computer, plots on the teletype the desired energy spectra on a scale automatically adjusted for the maximum number occurring in the data. The program is flexible enough so that the researcher can subsequently expand or contract the vertical (intensity) or horizontal (energy) scales. With a slight modification, the program will accept data printouts from scalers or analog to digital converters. The program also includes a feature for integrating the energy peaks obtained by pulse height analysis.

Jan 1, 1970

By S. S. Shen, M. J. Pool, P. J. Spencer

Heats of solution of gold and copper in dilute Au-Cu-Sn alloys have been determined using a liquid metal solution calorimeter. The self-interaction coefficient, Au - has been calculated at constant copper concentrations and n cu has likewise been determined at constant gold contents. Good experimental agreement is obtained between the interaction coefficients and nAu Cc thus demonsbating the reliability of the measured heat values. The measured data are compared with the Predictions of certain solution models. In previous publications,1,2 the results of calori-metric investigations of dilute Ag-Au-Sn and Ag-Cu-Sn alloys have been presented. The present work on the Au-Cu-Sn system concludes a program of studies of enthalpy interaction coefficients in dilute alloys of the Group IB metals with tin. Since the definition and derivation of an enthalpy interaction coefficient has been discussed previously,1,2 no restatement of this theory will be presented here. From the determination of the partial heat of solution of gold and copper in ternary alloys of various copper and gold contents, values of the interaction coefficients can be calculated. These coefficients give an insight into the various solute interactions that occur in the liquid solutions since changes in their magnitude and sign reflect bonding changes that are taking place in alloys of varying solute contents. EXPERIMENTAL Details of the design and operation of the liquid metal solution calorimeter used in this work may be found in a paper by Poo1.3 For the present studies copper of 99.999 pct purity was supplied by American Smelting and Refining Co., gold of 99.999 pct purity by A. D. Mackay, Inc., and tin of 99.99 pct purity by Baker Chemical Co. At the commencement of each series of experimental drops, a tin solvent bath consisting of between 70 and 90 g of the pure metal was inserted in the calorimeter. The weight of the bath was accurately determined and to it were added appropriate amounts of gold or copper to give alloys of the desired composition. For determinations of approximately 0.0015 g-atom samples of Cu were used and for measurements of ?HAu approximately 0.0025 g-atom additions of Au. The heat capacity of the bath was determined at regular intervals during a series of drops using tin calibration samples. Measurements were made of the heat of solution of copper in alloys containing a constant 0.01, 0.02, 0.03, and 0.04 mole fraction of Au, respectively, in order to determine ?HCu in each alloy, and the same mole fractions of copper were used to determine equivalent values for nAu at constant copper concentrations. The composition of the bath was maintained at the desired constant gold or copper content by making calculated additions of the appropriate solute throughout the experiments. The limiting values ?HAu in alloys of constant copper content and of %c, in alloys of constant gold content were studied as a function of the mole fraction of copper or gold respectively in order to determine and nCu. Heat content and heat capacity data used in calculating values of ?ºHAu and ?HCu at the experimental temperature of 720°K were obtained from Hultgren et a1.4 &apos; RESULTS AND DISCUSSION Determinations of ?HAu. The partial heat of solution of gold in pure tin as a function of gold concentration was determined in the previous study of dilute Ag-Au-Sn alloys1 and can be represented by the least-squares expression: ?HAu(l) =-8075 + 2413xAu [l] which is valid between XAu= 0.00 and xAu = 0.05. The standard error in the constant term, which represents the partial heat of solution of gold at infinite dilution in tin,?HºAu(l)is 35 cal per g-atom, while the standard deviation of the slope, which represents n Au is ± 619 cal per- agtom. Corresponding expressions for ?HAu(l) in alloys containing constant mole fractions of 0.01, 0.02, 0.03, and 0.04 copper were obtained from the data listed in Table I and are themselves given in Table II. Fig. 1 illustrates the partial heat of solution of gold as a function of its concentration in each of the alloys. For the four alloys of constant copper concentration, the values obtained for ?HºAU(l) (in order of increasing copper content) are -8141 i 36 cal per g-atom, -8210 ± 42 cal per g-atom, -8202 ± 46 cal per g-atom and -8268 ± 51 cal per g-atom. The corresponding values of the self-interaction coefficient, n Au, for these alloys are 3103 * 644 cal per g-atom, 2425 ± 676 cal per g-atom, 2574 * 717 cal per g-atom and 2523 ± 899 cal per g-atom. In Fig. 2 these values of n Au are plotted as a function of the copper content of the alloys and are seen to remain approximately constant within the experimental limits. The addition of increasing, small amounts of copper to dilute binary Au-Sn alloys thus has no apparent effect on Au-Au interactions in these dilute liquid solutions, although more exothermic values of ?HºAu(l) do result from an increase in the copper content of the alloys. Analogous behavior was observed with additions of silver to dilute Au-Sn alloys.&apos; By

Jan 1, 1970

By Albert J. Forney

A process for the manufacture of high-Btu gas from coal has been developed by the Bureau of Mines. The process consists of fluid-bed gasification of the coal, followed by the gas treatment steps of gas purification and methanation. Advantages of the system are that caking coals can be used directly, and more than half of the ultimate methane is made in the gasifier.

Jan 1, 1970

By J. B. Cohen, S. L. Sass

The nucleation process for y&apos;, Ni3Ti, is shou&apos;n to change from heterogeneous to uniform as the undercooling within the phase boundary increases. As unifornz nucleation beconres copious, (100) alignment is observed in the early stages of aging; howecer. whether or not the alignment is due to spinodal decomposition could not be determined. The presence oi a large-scale reversible segregation of titanium and not the intermediate precipitate y&apos; may be the cause of the initial strengthening in this alloy system and the discrete regions detected magnetically by Ben-Israel and Fine. Evidence is presented for the role of dislocations in the formation at long aging tines oJ the equilibrium precipitate . ThE nickel-rich portion of the Ni-Ti phase diagram consists of a terminal fcc solid solution of titanium in nickel called y.&apos; For temperatures below 1290°C if the solubility limit is exceeded and the temperature is high enough, the excess titanium will combine with nickel to form q, Ni3Ti, a four-layer hcp ordered structure with stacking sequence ABAC."~ Since a change in structure is involved, formation of q is slow and a metastable precipitate referred to as y&apos; forms. This metastable precipitate is an ordered cubic phase in the unconstrained state having a structure similar to Cu3Au (LIZ) with the composition Ni,Ti."&apos;5 From X-ray studies,8, 7 the following sequence is indicated for the precipitation reaction at low temperatures: 1) The appearance of satellites around low-index diffraction spots and splitting of high-index spots, indicating the formation of a slightly tetragonal phase in an imperfectly periodic arrangement. The tetragonal phase is y&apos; or the depleted matrix, depending on the volume fractions of matrix and precipitate (and hence, the alloy composition); tetragonality apparently arises from coherency strains. 2) The appearance of diffraction spots from the equilibrium second phase, q. Ben-Israel and Fine&apos;" used magnetic methods to measure the changes in matrix composition during aging, and to estimate the precipitate composition in a Ni-10.1 at. pct Ti alloy. They observed that the alloy, solution-treated at 1270°C and quenched, contained heterogeneities with discrete compositions which gradually vanished upon aging. It was suggested that y&apos; may initially form as a defect structure with several possible compositions deficient in titanium as compared to Ni3Ti; the composition Ni3Ti develops with prolonged aging. The initial composition was Ni6Ti which would require a very large deviation in stoichiometry for y&apos;. It was noted that at 700°C the precipitation reaction was 80 pct complete after 2 hr and that the volume fraction of second phase was 0.2 after 1 hr. Mihalisin and Decker&apos; suggested that the equilibrium precipitate, besides being nucleated at grain boundaries, could also form at stacking faults. ~errick" examined the formation of in Ni-Cr-Ti, and suggested that a collapsed vacancy cluster within y&apos; acted as a nucleus for intragranular q at high temperatures, 820" and 900°C. After long aging times at lower temperatures, 650" and 750°C, diffraction patterns taken from regions containing ribbons of stacking faults showed spots associated with q. Aging greatly enhances the mechanical properties of these alloys, even at high temperatures, and the metastable precipitate y&apos; is thought to be responsible.&apos; At 600°C the hardness of a Ni-10.1 at. pct Ti alloy increases rapidly during the first 20 hr of aging and continues to increase slowly thereafter.&apos;" At 700°C the hardness reaches a maximum at 1 to 2 hr and then decreases.l1 In this paper the kinetics of formation of y&apos; and the mechanism of transformation to in a Ni-Ti alloy are described. Evidence is presented that suggests that large-scale regions of titanium segregation are present initially and these may have an important influence on the initial strengthening of the alloy: these regions may be the heterogeneities detected by Ben-Israel and Fine. I) EXPERIMENTAL TECHNIQUES The Ni-10.3 at. pct Ti-0.6 at. pct A1 alloy was prepared by vacuum melting. Its chemical analysis is given in Table I. A 0.007-in.-thick strip was sandwiched between foils of the alloy and placed in an open Vycor tube with titanium chips (to get oxygen) and solution-treated for ; hr at 1150°C in a Globar Furnace under a flowing argon atmosphere. Following a quench into an ice-brine mixture at -5" to -2"C, a sample to be aged at temperatures up to and including 700°C was sealed in an evacuated Vycor capsule before being put into a fused salt bath. Aging above 700°C was carried out on bare samples in a salt bath. When removed from this bath and quenched into an ice-water mixture, the sample was normally coated with a thin layer of oxide easily removed with emery

Jan 1, 1970

By Warren E. Holland, Leon H. Robinson

The pore pressure must be included in any discussion of the state of stress within a rock. Rock cylinders at elevated stress levels, loaded uniaxially to a stress less than the yield strength, can be fractured by holding the constraints constant and increasing the pore fluid pressure. This can be described in terms of the Mohr envelopes using effective stresses. The effective stress concept can simplify data with various confining and pore pressures. When the pore and confining pressures are equal, the pore pressure appears to be totally effective in reducing the confining pressure effects. The area over which the pore pressure acts has been the subject of some prior discussions. Terzaghi 1 defined boundary porosity as ". . . the ratio of that part of the area of the potential surface which is in contact with the interstitial liquid and the total area of this surface." His method of calculation included a discussion of splitting failure which was objected to by Mr. Kessler, National Bureau of Standards. The values calculated by Terzaghi were close to unity. Leliavsky,2 using unjacketed cement cores, reported that the interstitial fluid pressure appeared to act upon about 92% of the surface of failure. He concluded: "The fraction of the area of cross-section over which the internal pressure acts can therefore have nothing to do with ordinary porosity, and the results of the experiments tend to support Professor Terzaghi&apos;s views." In 1947 Balmer3 determined the boundary porosity of concrete when the confining and pore pressures were equal. He also found values close to unity. In 1948 McHenry4 published some of the results from the same equipment and included the first data in which the pore pressure

Jan 1, 1970

By C. R. Clark, G. Swift, D. S. Roberts

The purpose of this investigation was to measure PVT behavior of various types and combinations of heavy hydrocarbon components from the paraffinic, naphthenic and aromatic classes where the relative proportions Of the various components were selected to approximate those of natural gas or gas condensate systems. Synthetic mixtures were used so that the compositions Of the various components could be measured accurately. n-Heptane, methylcyclohexane and methylbenzene were used to represent the paraffinic, naphthenic and aromatic components of the heavy fraction. In the mixtures studied, the heavy fraction composition was held constant at O. O5-mole lraction, the balance being methane except for one mixture where 0.10-mo1e fraction of an intermediate component, propane, was added. The PVT data for the mixtures were determined in a variable-volume, constant-mass apparatus at psuedo-reducedtemperatures from 1.84 to 2.00, over a pseudo-reduced pressure range from 2.3 to 12.0. The experimental results showed that, regardless of the type of heavy material (paraffinic, naphthenic, aromatic, or combinations thereof) mixed with methane or methane and propane, the compressibility factors at equal values of pseudo-reduced temperature and pressure varied by less than 2.2 percent. INTRODUCTION PVT data is used for natural gas and gas condensate fluids in determining reserves of reservoirs and performance of wells, in metering produced fluids, and in recombining samples for laboratory studies. While there are vast amounts of PVT data reported for natural gas and gas condensate systems from which useful correlations have been developed, &apos; the compositional analyses for these systems and the resultant correlations typically were made with components analyzed through some arbitrary carbon number, usually C6, with the residue reported as a lumped "heavy" fraction. The heavy fraction was stoichiometrically recombined on the basis of an apparent molecular weight to give the final compositional analysis. It is virtually impossible to make a systematic analysis of the effect that variation of the relative amounts of paraffinic, naphthenic and aromatic constituents of the heavy fraction of natural systems might have on PVT behavior. Because there is considerable latitude in the relative amounts of these constituents, one speaks of crudes or condensate liquids as being "paraffin base", etc. It is of interest to determine if changes in the relative amounts of these three types of hydrocarbons in the heavy fraction cause significant changes in PVT behavior. If so, steps should be taken to describe better the nature of the heavy fraction in PVT correlations. If not, more confidence can be placed in the correlations presently employed. DESIGN OF THE EXPERIMENTAL INVESTIGATION We attempted to determine if changes in the base of the heavy fraction would cause significant changes in the PVT behavior of gas or gas condensate fluids. Synthetic mixtures were used to enable us to systematically vary the base of the heavy fraction and to analyze accurately the fluids. We found that the heavy fraction of naturally occurring condensate systems seldom exceeds 0.05-mole fraction. Thus, the mole fraction of the heavy fraction in the synthetic systems studied was set arbitrarily at 0.05, to maximize whatever deviations in PVT behavior that might occur. Further, we judged that since the C7 hydrocarbons normally are present in greater quantities than higher carbon number hydrocarbons in naturally occurring systems, the use of n-heptane, methyl cyclohexane, and methylbenzene to represent the paraffinic, naphthenic, and aromatic species in the heavy fraction would be most appropriate. Finally, to enable us to compare our

Jan 1, 1970

By K. Thirumalai

This study forms a part of Bureau of Mines continuing research on thermal fragmentation of rocks. The potential of internal heating techniques for rock fragmentation is discussed. A concept of rock fragmentation with rapid inter¬nal heating of a localized inner volume of rock is advanced The energy required for rock fragmentation is made available by creating a required vol¬ume of localized heating. The fragmentation of rock using the proposed method is analyzed and qualitatively compared with the results of experiments with Charcoal granite, Dresser basalt, and Sioux Quartzite. High frequency dielec¬tric heating below 100 MHz is used in the study as an example to examine the working of the concept. The selection of operating conditions for the experi¬mental heating is explained. Fragmentation of Charcoal granite and Dresser basalt test rock blocks is achieved for localized heating below 550° C. The heated volume required for fragmentation is observed to be less than 2 percent of the test block volume and the electrical energy consumption is in the order of 3.5 to 6 5 kwhr/m3 The method offers a possibility for in situ fragmenta¬tion of rocks, favorable for internal heating. The method is highly dependent on rock properties governing internal heat generation The efficiency of dielectric heating in the experimental study is observed to increase with increasing dielectric loss of the rock material, ranging from about 10 percent in Sioux. Quartzite to about 50 percent in Dresses basalt

Jan 1, 1970

By N. Arbiter, C. C. Harris

In 1961, a research program started at Columbia into the mechanical aspects of flotation,* and certain ends are now in view. The purpose of this note is to explain these tentative conclusions in the hope of stimulating discussion and eliciting new data, especially industrial data, with which to test the views expressed. The variables presently under consideration are impeller rotational speed, N, volumetric air rate, Q, and impeller diameter, D, the latter being the parameter chosen to designate cell size. The most favorable *The latest work 1 references all previous publications. chemical environment is not under discussion since the procedures for establishing it are better understood than those for optimizing N and Q by virtue of a longer history of more intensive investigation. THE GRADE AND RECOVERY SURFACES With a given ore, chemical treatment, and flotation machine, both grade, G, and recovery, R, are functions of N and Q. The GNQ and RNQ relationships are best viewed in terms of three-dimensional surfaces (Fig. 1) which are experimentally determinate.2 TO maintain grade at an acceptably high level, it is necessary for N and Q to lie within certain limits, and similarly with recovery. However, the ranges of N and Q for grade on the one hand and recovery on the other are rarely the same. Selecting the single N

Jan 1, 1970

By J. B. Cheatham, M. D. Biggs

This paper presents a systematic method for determining the forces on a simplified roller bit. The kinematics of an actual roller bit drilling in rock is complex; nevertheless, it is desirable to obtain an accurate analytical model.. As a preliminary study, the roller bit is represented here by a simple two-dimensional bit and the rock by a Coulomb plastic material. Results from previous work, plus additional assumptions, are incorporated into a computer program to determine the forces required to move the bit in a specified manner. Example problems are worked by use of this program. By studying similar drilling problems and by supporting laboratory work, one could eventually obtain an accurate analytical model for drilling by an actual roller bit. This could lead to the compilation of a catalog of results that, in turn, would allow selection of the optimum drill bit for any given situation. INTRODUCTION

Jan 1, 1970