Search Documents

By R. W. Nelson

The theoretical basis is presented for energy dissipation methods of measuring permeability in saturated heterogeneous media. Analysis starts with the equation for single-phase flow in heterogeneous porous media which is a first-order partial differential equation in the unknown permeability. This equation is reduced to a system of characteristic equations useful in deriving a differential expression for the permeability as a function of the known potential distribution. For steady flow systems the expression is integrable, giving the permeability integral for direct calculation of the distribution along successive streamlines. The boundary condition in permeability is presented and includes a discussion of the special requirement to assure uniqueness. Theoretical results and necessary computations are incorporated into two general computer programs capable of determining the permeability distribution in two- and three-dimensional steady flow systems. Results are then presented for an energy dissipation analysis using the methods and soltware to determine a field permeability thickness distribution. INTRODUCTION Theoretical work leading to the description of fluid flow in heterogeneous porous media has developed slowly and somewhat sporadically, although the areas of engineering applications predominantly involve flow in nonhomogeneous media. The lack of accurate and economical methods for measuring field permeability distributions has been a major limitation to realistic description of natural flow systems. The economical measurement of permeability using energy dissipation methods may overcome this limitation. Among other things, any permeability measurement method involves consideration of energy dissipation; as used here, "energy dissipation method" denotes the following general approach. The areal energy distribution is measured on an existing flow system in porous media. Then through appropriate analysis of the dissipation of energy in the flow system, the permeability distribution is determined throughout the region using the minimum boundary conditions required to assure a mathematically unique result. This paper presents the theoretical basis for such a method, as well as the techniques and computer software needed to carry out the analysis. The method and techniques are then used in a preliminary field application. EQUATIONS DESCRIBING FLOW IN HETEROGENEOUS MEDLA Heterogeneous as used here implies differing in kind, having unlike quantities or possessing different characteristics. Accordingly, a heterogeneous porous medium has unlike quantities or differing characteristics at different locations. More precisely, if a porous medium is heterogeneous with respect to some property, then that property is functionally dependent on the spatial location. (Media properties are considered here as macroscopic.) Specifically considering permeability k,** then k = G(x, y, z) ,............(1) or the permeability is a scalar function G of the location (x, y, z). Spatial variation of several other properties, of which porosity, dispersivity and medium compressibility are but a few, is implied by the broad title of heterogeneous porous media. The term will be used hereafter to imply only heterogeneity with respect to permeability. The porous medium is considered isotropic as implied by G being only a scalar function. Anisotropy

Jan 1, 1969

By Albert E. Reed

The development of the modern highspeed vibrating screen, together with the increasing availability of long-lasting stainless-steel screen cloth for relatively fine-mesh separations, means that more screen circuits will be used in the future. It seems pertinent therefore to examine a few characteristics of screen-circuit products, and especially the points of difference as compared with products of classifier circuits. The most noticeable change that takes place when substituting screening for classification in a grinding circuit is a substantial drop in the circulating load, owing to the greater ease with which the "fines" leave the circuit. Where circulating loads of 500 to 600 per cent are considered fairly normal in classifier grinding circuits, the grinding circuit equipped with screens for equivalent work will have a circulating load of only 20 to 75 per cent. As a result, the products of screen circuits will show a minimum of overgrinding or sliming as compared with a classifier circuit. The desirability of this characteristic will naturally vary according to the metallurgical requirement in each case. Because screen separations make a sharper division according to particle size, the products of screen circuits can be expected to show greater crowding of particles near the point of separation. These changes in product characteristics are so important that other factors, both in the grinding and concentration processes must be adjusted if the operator is to take full advantage of the increased tonnages and higher efficiencies available to him through the use of the screen circuit. One factor that too often is overlooked when changing to screen circuits is the importance of adjusting the ball-mill or rod-mill charge, to compensate for: (I) increased tonnage of new feed, (2) decreased circulating load, or (3) more granular character of feed. These same factors should also be taken into consideration for their effect on the various types of concentration or flotation equipment that may follow the screen circuit. Over a period of years, this equipment has generally been designed and adjusted to the product of the classifier, therefore it seems obvious that some research on the adjustment and adaptation of concentrating and flotation equipment to screen-circuit products will be most profitable to the operators. To illustrate the points mentioned above, the results from three recent installations follow, with data on the comparative characteristics of screen and classifier circuits. A range of separation from 10 to 48 mesh has been chosen, using two general types of screening equipment and two types of classifiers. The first of the installations of which the results are to be examined is that of an iron-ore installation where eastern magnetite was being concentrated prior to sintering. Fig. I shows the original grinding circuit, using classification, while Fig. 2 shows the same circuit equipped with a

Jan 1, 1947

26. G. H. S. Price, S. V. Williams, and G. J.O. Garrard: Heavy alloy, its production. properties and uses. Metal Industry (1941) 599 354s 372. 394. 27. R. Kieffer and W. Hotop: p. 320 of ref 12. 28. F. R. Hensel. E. I. Larsen, and E. F. Swazy: Physical properties of metal compositions with a refractory metal base. Chap. 42, 483, Powder Metallurgy, ed. by J. Wulff (1942) Cleveland. 29. R. Kieffer and W. Hotop: p. 290 of ref. 12. 30. H. Freundlich: Kapillarchemie. 211 (1923) Leipzig. 31. W. Ostwald: Zisch. f. Phys. Chemie. (1900) 34, 503. 32. G. A. Hulett: Zisch. f. Phys. Chemie. (1901) 37. 385; and (1904) 47, 357. 33. J C. Chaston: Discussion to Price, Smithells and Williams, p. 257 of ref. 4. 34. W. Dawihl: Untersuchungen ueber die Vorgaenge bei der Abnuetzung von Hartmetallwerkzeugen. Ztsch. f. techn. Phys. (1940) 21 336. 35. W. Dawihl and J. Hinnueber: Ueber den Aufbau der Hartmetallegierungen. Kol-loidzlsch. (1943) 104, 233. 36. F. Skaupy: Dispersoidchemische und verwandte Gesichtspunkte bei Sinter-hartmetallen. Kolloidzlsch. (1942) 98, 92; and (1943) 102, 269. 37. F. C. Kellcy: Cemented tantalum car- bide tools. Trans. ASST (1932) 19, 233. 38. E. W. Engle: Cemented carbides. Chap. 39, 436, Powder Metallurgy, ed. by J. Wulff (1942) Cleveland. 39. W. Dawihl: Zlsch. f. Melallkunde. (1940) 32, 320. 40. P. M. McKenna: Tool Materials (Ce- mented Carbides). Chap. 40. 454. Powder Metallurgy, ed. by J. Wulff (1942) Cleveland. 41. G. A. Meerson. G. L. Sverev, B. Y. Osinovskaja: Zhurnal Prikladnoi Khimii. (1930) 139 66. 42. A. G. Metcalfe: The mutual solid solubility of Tunesten Carbide and Titanium carbide- Metal Trealmenl (1946) 13, 127. 43. P. Schwarzkopf: Powder Metallurgy. 196-201 and 354-356 (1947) New York. 44. H. Burden: The manipulation and sintering of hard-metals. Special Rep. No. 38, p. 78. Iron and Steel Inst.. 1947. London. 45. W. D. Jones: Principles of powder metal- lurgy. 150. (1937) London. 46. J. E. Drapeau: Sintering of powdered copper-tin mixtures. Chap. 32. 332, Powder Metallurgy, ed. by J. Wulff (1942) Cleveland. 47. H. E. Hall: Sintering of copper and tin powder. Metals and Alloys (1939) 10, 297. 48. F. Sauerwald: Present status of powder metallurgy. -.Melallwirlschafl. (1941) 20, 649. 671. 49. H. L. Wain: Powder metallurgy; influence of some processing variables on the properties of sintered bronze. Report ACA-25. Australian Council for Aeronautics (1946) Melbourne. 50. S. L. Hoyt: Constitution of copper-tin alloys. Metals Handhook, 1364. (1939) Cleveland. 51. T. Ishikawa: Studies on the interdiffusion of copper, tin and graphite powders. Nippon Kinzoku Gakkai-Si (1937) I, 226. 52. A. Carter and A. G. Metcalfe. The struc- ture of porous bronze bearings. Special Rep. No. 38, p. 99. Iron and Stecl Inst. (1947) London. 53. R. P. Koehring: Sintering atmospheres for production purposes. Chap. 25, 278. Powder Metallurgy, ed. by J. Wulff (1942) Cleveland. 54. C. G. Goetzel: Some properties of sintcred and hotpressed copper tin compacts. Trans. AIME (1945) 161, 569. 55. J. W. Lennox: The production of some non ferrous engineering components by powder metallurgy. Special Rep. No. 38. p. 174. Iron and Steel Inst., 1947, London. . P. Duwez and H. E. Martens: The power metallurgy of porous metals and alloys having a controlled porosity. TP 2343, Metals Tech. April 1948. This volume. p. 848. 57. E. A. Owen and L. Pickup: X-ray study of the interdiffusion of copper and zinc. Proc. Royal Soc., London, Series A. (1935) 149, 283. 58. C. G. Goetzel: Sintered and hotpressed compacts of copper-zinc powder. Chap. 34. 352, Powder Metallurgy, ed. by J. Wulff (1942) Cleveland. 98, R. Chadwick. E. R. Broadfield, and S. F. Pugh: Observations on the pressing. sintering, and properties of iron-copper powder mixtures. Special Rep. No. 38, p. 151, Iron and Steel Inst. (1947) London. 60. A. Squire: The properties of iron-copper compacts. Watertown Arsenal Lab. Rep. WAL No. 67101. 61. F. C. Kelley: Properties of sintered iron- comer uowder. Iron Age (Aug. 15. 193) 158 57. 62. G. H. Howe: Sinterinn of Alnico. Iron Age (Jan. 11. 1940) 14.5, 27. 63. R. Kieffer and W. Hotop: p. 359 of ref. 12. 64. W. Hotop: Permanent magnets from sintered iron-nickel-aluminum. Stahl und Eisen (1941) 61, 1105. 65. P. R. Kalischer: Some experiments in the production of aluminum-nickel-iron alloys by powder metallurgy. Trans. AIME (1941) 145, 369. 66. S. J. Garvin: Production of sintered per- manent magnets. Special Rep. NO. 38. p. 67. Iron and Steel Inst. 1947, London. 67. F. C. Kelley: Discussion to P. R. Kalischer. p. 375 of ref. 65. 68. R. Kieffer and W. Hotop: p. 357 of ret, 12. 69. C. H. Howe: Sintered alnico. Chapter 48, 530, Powder Metallurgy, ed. by J. Wulff (1942) Cleveland. Powder Metallurgy Seminar (C. G. Goetzel presiding) C. G. Goetzel—The seminar has been opened by a man who has been active in the field for over fourteen years and has made, since then, some major contributions to the advancement of the art. After having been associated with the Moraine Products Division of General Motors Corporation for over ten

Jan 1, 1949

By John W. Weeton, Max Quatinetz, Robert J. Schafer

Nickel powders of 1-, 0.4-, and 0.2- average particle size were combined with 0.05- p MgO powder. Oxide was added in quantities of 4, 12, and 20 vol pct. The mixtures were vacuum hot pressed and extruded at 2100°F. In spite of a general tendency to growth of oxide particles during processing, dispersions of fineness comparable to those of Sintered Aluminum Powder, SAP, were achieved. A small amount of oxide considerably improved 1800°F stress-rupture strength, but further oxide addition resulted in a decrease of strength. RECENTLY there has been much speculation concerning the requisites for strong and stable dispersion-strengthened alloys. The nature of the dispersed phase, the stability of the alloys, and variables influencing the mechanical properties of alloys have been given consideration. Such topics have been reviewed by Bunshah and Goetzel. Of the many parameters related to the mechanical properties of dispersion alloys, mean free path between dispersed particles (a measure of the fineness of the dispersion), particle size, and vol pct of the dispersed phase have been shown to be very important. Generally, strength increases with decreasing mean free path, and there is an optimum vol pct of dispersed phase. Just how fine a dispersion ought to be is somewhat open to debate, but Irmann, Lenel, Backensto, and Rose, Gregory and Grant,4 and others have shown in the original SAP-type alloys, aluminum plus aluminum oxide alloys, that better strength is generally obtained with finer dispersions and the best strengths were obtained when the mean free path was less than . Further, Cremens, and rant' showed that in nickel plus aluminum oxide alloys, stress-rupture strength at 1500°F was definitely increasing with decreasing mean free path. In their investigation, however, the finest dispersions that were produced were about 2.0 mean free path. To determine the potential of the nickel plus oxide type of product, it would be neces- sary to obtain dispersions analogous to those of SAP alloys; namely, ones where the mean free path between oxides is less than . Unfortunately, however, it is very difficult to produce extremely fine dispersions of oxides in metals other than those which naturally form refractory oxide skins. There are several approaches to this problem including such procedures as mechanical mixing, internal oxidation, reduction of mixed oxides, and metal deposition from solution. Work at the Lewis Research Center has shown that metal powders 0.1p or finer could be produced by ball milling, when selected grinding aids were utilized.' Because these unusually fine powders were available, it was an initial objective of this study to determine if by mixing of these fine Ni powders with various amounts of MgO (0.05) a fine dispersion of MgO in Ni comparable to those in Al-Al203 might be achieved. A second objective was then to attempt to relate the parameters of structure to 1800°F stress-rupture strength of the alloys. Nickel powders of 1-, 0.4-, and 0.2-p average particle size were combined with 0.05- average particle size MgO powder. This oxide was added in quantities of 4, 12, and 20 vol pct. The mixtures were hot pressed and extruded at 2100°F.

Jan 1, 1962

By R. J. Arsenault

The yield drop that occurs in tantalum, Cu-AZ. and Ag-Al was investigated as a function of strain rate and at several temperatures. From the strain-rate dependence of the yield drop an activation volume was calculated and found to agree with that obtained from differential strain-mte tests. The temperature dependence of the yield drop can he explained in terms of the parameter temperature divided by activation volume. The yield drop is attributed to the rapid multiplication of dislocations during their motion. THE yield-point or yield-drop (upper yield stress minus the lower yield stress) phenomenon has been the subject of numerous investigations1-9 in both bcc and fcc metals. Also, there is no dearth of theoretical explanations10-20 to account for the yield-point phenomenon. The present explanations can be divided into two categories: the concept of dislocation locking and subsequent unlocking and the concept of multiplication of dislocations due to their motion. The Vottrell10,11mechanism of locking and unlocking, as applied to bcc metals, is the best known of the three proposed locking mechanisms. The two additional mechanisms, short-range order (SRO)7,16,17 and Suzuki-type locking,14,15 have been employed to account for the existence of yield points in fcc metals. The experimental evidence supporting the locking of dislocations, especially in bcc metals, is well-established. The dependence of the yield point on interstitial concentrations,' the kinetics of strain aging,2 and the observations by electron-transmission microscopy18 are some of these experimental results. The number of experimental observations supporting dislocation locking in fcc metals is not as extensive as in bcc metals. The unlocking of dislocations, which actually is supposed to account for the yield drop, is by no means well-established by experimental results for either bcc or fcc metals. The similar temperature dependence6 of the yielding and plastic flow is one of the experimental factors that cannot be explained in terms of the unlocking of dislocations. The mechanism based on the rapid multiplication of dislocations has been proposed by several investigators. 18-20 Johnston and Gilman19 have proposed a detailed model of yielding, which was later employed by Hahn21 to predict quantitatively the yield drop in iron. This mechanism was discussed in a previous paper22 and several limitations were pointed out. In the same paper it was shown that an activation volume could be obtained from the strain-rate dependence of the yield drop and that a correlation existed between the activation volumes obtained from the yield-drop tests and from differen-

Jan 1, 1964

By D. L. H. Forbes

The application of the cyanide process to complex sulphide ores for the extraction of the gold and silver is no longer a novelty; but, as an example showing modern teudencies in this direction, the following description of the new milling process at the Lucky-Tiger mine is offered: The extraordinary richuess of the ore in the upper workings of this mine made any thought of milling in its early days seem unnecessary. Its location in an almost inaccessible part of the rugged mountains just south of the Arizona boundary-line, and 60 miles from the town of Douglas, made the expense of bringing in machinery and sopplies a very serious consideration. But, after the property had been shipping high-grade ore on mule-back for a few years, there remained in the mine a considerable tonnage of vein-matter that mas too low in value to ship, but which it wag thought could be milled near the mine at a profit. The first milling-experiment consisted in the installation of Nissen stamps in conjunction with concentrating-tables and Frue vanners, but, as the ore from the upper workings contained most of its silver in the form of cerargyrite, this type of mill mas not successful. The proximity of the mine to the great copper-concentrating mills of Cananea and Moctezuma naturally made the influence of copper-milling ideas felt in the company's next instdlation. At considerable expense a stage-crushing concentrating-mill, with a capacity of 100 tons per day, was built. This mill was modeled along the lines of the most approved practice in copper-concentrators at that time, the main idea being that crushing by stages .in rolls was necessary in order to prevent losses from " sliming." Largely owing to the fact that, when the mill

Jan 1, 1913

By G. L. Oldright, T. B. Brighton, C. M. Dice

The base bullion from the lead blast furnace contains varying amounts of the impurities left in the smelter feed by the concentrator, regardless of the method of smelter operation. These impurities may be held in part in mechanical suspension rather than being present as true alloys. However, usually there is little free space in the crucible in which to separate these drosses before the bullion is taken from the lead well. When such a dross is melted in a laboratory crucible and allowed to cool, the products obtained are lead bullion, speiss, and matte in well separated layers. Typical analyses of layers are: Analyses. Per Cent Element Bullion Speiss Matte Pb.............................................. 92.0 41.2 38.3 Cu.............................................. 2.4 36.3 40.6 As............................................... 4.0 16.5 4.3 Sb............................................... 0.7 0.2 0.4 S................................................ 0.6 1.9 13.1 Fe............................................... 0.0 0.0 0.0 Totals......................................... 99.7 96.1 96.7 The absence of iron in these products drossed from the blast-furnace bullion proves that the impurities for the greater part are not simply finely divided blast-furnace speiss or matte that has been dissolved or dispersed in the lead, but are held in solution by the liquid metal and rise to its surface as infusible compounds when the temperature of the bath is lowered. In general, the drosses made locally are metal sulphides and arsenides and not oxidized compounds. The large content of metallic lead also does not seem to be retained because of oxidized compounds

Jan 1, 1937

By G. A. Mancini, V. Bharucha, J. W. Spretnak, G. W. Powell

The characteristics of the motion of the a interface during the "down" transformation was studied in zone-refined iron and dilute binary alloys containing nickel and molybdenum by means of the thermionic emission microscope and high speed photography. The frontal movements were found in all cases to be definitely discontinuous with time and an appreciable number of incremental jumps were found to proceed in the reverse direction (a to b). Molybdenum was found to be particularly effective in increasing the frequency of the increments of transformation from the stable to the metastable phase. A knowledge of the mechanism by which alloying elements affect the hardenability of a steel is desirable from both the practical and scientific viewpoints. It is well established that microstructures consisting of tempered martensite and lower bainite exhibit the best performance in terms of toughness and resistance to crack propagation. The presence of some upper transformation products, namely ferrite and pearlite, is in general undesirable. Various researches have indicated that the ferrite matrix grain structure is a very important difference between the upper and lower transformation products, namely equi-axed vs acicular. Any comprehensive theory of the decomposition of austenite should explain the dependency of the morphology of the matrix on undercooling. The contribution of various alloying elements to hardenability has been determined experimentally and catalogued in considerable detail. A rationalization of the basic mechanism or mechanisms by which individual elements affect the kinetics of the decomposition of austenite to products other than the phase "martensite" has not been evolved as yet. Interest in this problem was stimulated by the effects of minute quantities of boron in hardenable steels. This paper deals with one aspect of this problem, namely the characteristics of the ?-a transformation in high-purity iron and in two carbon-free iron binary alloys. A detailed historical account of the scientific developments in the study of the decomposition of austenite would be a prodigious undertaking and will not be attempted here. There are several excellent reviews in the literature on the formation of pearlite, martensitic reactions, and kinetics of solid-state reactions. The thinking on reaction mechanisms has been influenced to a large degree by the "classical" Tammann nucleation and growth model, in which an embryo springs into being by a fluctuation, and grows to a critical size through atom by atom deposition. Such a process is expected, accordingly, to be diffusion controlled. Considerable research attempting to relate the contribution of alloying elements to hardenability on the basis of their effect on the diffusivity of carbon in iron has not been productive from a mechanistic viewpoint. The formation of pearlite and ferrite has been treated in terms of nucleation and growth processes in which presumably the lattice transformation also occurs by a diffusion process. The other prominently considered mechanism is the "martensitic" or cooperative shearing mechanism. It seems generally, but not entirely, agreed that the phase "martensite" forms by this mechanism, and that it is involved to some extent in

Jan 1, 1962

By T. S. Lundy, R. E. Pawel, F. R. Winslow, C. J. McHargue

The volume-diffusion coefficients of Nb-95 and Ta-182 in niobium have been measured over the temperature range 878° to 2400°C. High-temperature specimens (T 21500°C) were sectioned by conventional lathe and grinding techniques while low-temperature specimens were sectioned by an anodizing and stripping technique previously described. Over a range of more than ten orders of magnitude in diffusivity, the self-diffusion data is well-represented by the equation: D = (1.1+ 0.2) exp [- (96,000 * 900)/RT ] cm2/sec Upward deviations from this line are explained by short-circuit diffusion in combination with the loss of resolution of the sectioning techniques. Oxygen contamination within the range 100 to 450 ppm was found to have little or no effect on the self-diffusivitj 01 niobium. In a limited number of measurements, the diffusivity of Ta-182 in niobium was found to be about half that of Nb-95 in niobium. These data may be described by D = (I.0+0.90.5)exp [- (99,300 * 2400) /RT ] PREVIOUSLY reported studies of self-diffusion in niobium were by Resnick and Castleman1 and Peart, Graham, and Tomlin.2 The data of Resnick and Castleman over a temperature range 1585" to 2120°C show considerable scatter but. can be represented by D = (12.4 *0.8) exp [-(105,000+3OOO)/RT] cm2/sec The limited data of Peart, Graham, and Tomlin follow the equation D = 1.3 exp (-95,00O/RT) cm2/sec In view of recent diffusion data for ß zirconium3 and 0 titanium4 in which Arrhenius-type plots do not yield straight lines and of the potential high- temperature uses of niobium and its alloys, we thought it important to investigate the diffusion behavior of this bcc refractory metal over a large temperature range. This has recently been done for molybdenum,5 chromium,6 vanadium,"" and tantalum.9 Niobium was a particularly suitable material for this study largely because of the development of an anodizing and stripping sectioning technique which enables diffusivities as small as l0-19' sq cm per sec to be determined accurately.10 In addition to self-diffusion data, data were obtained for the diffusion of Ta-182 in niobium and for the effect of varying oxygen content on self-diffusion. I) EXPERIMENTAL PROCEDURE Materials. The niobium was obtained from three sources: 1) melting stock from Shieldalloy Corp., 2) electron-beam melted single crystals, 1/2 in. diameter, from Semi-Elements, Inc., and 3) oxygen-doped, electron-beam melted single crystals from Materials Research Corp. The melting stock was electron-beam melted and specimens 5/8 in. diameter by 1/2 in. long were machined from the center of the bar. The analysis supplied by the vendor and an interstitial analysis of one of the specimens are given in Table I. The single crystals (type 2 above) were cut with a jeweler's saw to specimens about 3/8 in. long. The interstitial analysis of this material is given in Table 11. This material was used

Jan 1, 1965

By J. O. Brittain, E. P. Lautenschlager, F. Felberbauer

This investigation was undertaken to evaluate the effect of a dispersed phase in a iron upon the strain hardening and the stress dependency of dislocation velocity as inferred from the strain-rate sensitivitv. Experiments were made in a-iron specimens with controlled amounts of carbon and/or A12O3. They were tested at various temperatures between 195' and 373 'K under a variety of conditions oj-concentration, strain rate, and quench aging. The resulting yield strength, flow strength, and strain hardening increased with addition of Al2O3. The parameter m, measured from changes in strain rate, was xsed to describe the stress dependency of the dislocation velocity. m was found to increase with additions of A12O3, increasing carbon in solution, and with increasing temperature. When applied to a recent model for yielding based upon dislocation multiplication and velocity characteristics, the values of m alone did not successfully predict yielding for the materials of this investigalion, but had to be adjusted with a consideration of the number of unlocked dislocations nucleated heterogeneously at discontinuities or inclusions. The change of yield strength with Al2O3 Interpar-ticle spacing appeared to obey a theory of Orowan. EVER since the concept of dislocations has been introduced to explain plastic deformation in crystalline materials, the origin of dislocations and the source of the number of dislocations required to account for plastic deformation have been persistent questions. Ruling out the possibility of homogeneous nucleation,' Gilman2 drew attention to the various cases of heterogeneous nucleation as the source of dislocations, whereas Frank and Read3 introduced the Frank-Read source. However, Gil-man found that the Frank-Read sources did not play a dominant role in the deformation of LiF crystals, but that small precipitates are often, if not always, associated with the nucleation of dislocations. In LiF crystals, however, most of the dislocations arose through the multiplication of moving dislocations in a mechanism described by Koehler4 and Orowan,5 Thus, relatively few precipitates could account for a large number of dislocations. A similar observation of dislocation nucleation at inclusions of precipitates was made by Stein and LOW' on Si-Fe crystals. Their crystals contained

Jan 1, 1964

By Charles W. Henderson

THE influence of mineral production on the development of the western United States has been profound. From 1848 to 1860, there was only gold production, the effect of silver began in 1860, and from then on both had a powerful influence. Lead production started in 1863, copper in 1863, and zinc in 1885, but was small until 1898. Gold alone was therefore the stimulus of the early settlement and exploration of the Western States.. But mineral deposits caused neither acquisition of territory nor determination of boundary lines. Arizona, California, Nevada, New Mexico, and parts of Utah, Wyoming, and Colorado were formally acquired from Mexico fourteen days after the actual date of the discovery (January 19, 1848)1.2 of gold at Sutters Mill, near the present town of Coloma, California (a discovery which, with the immediate new discoveries, aroused the world several months later) ; but the acquisition was by treaty (under negotiation for some time but signed February 2, 1848)3 in settlement of a war involving the boundaries of the grassy plains of Texas, an area at that time not known to contain any metals, and to date found to have but few metal deposits.4 The international boundary at 49º latitude for the far northwest states was determined by causes other than mineral deposits.

Jan 1, 1933

By J. E. Fox Jr., J. L. Lummus, J. P. Gallus

Fresh water or brine drilling fluids may be kept free of suspended drilled solids by the addition of a water soluble acrylamide-carboxylic acid copolymer at the flowline. Addition of from .01 to 0.2 lblbbl of the polymer solution to drilling fluids containing less than 5 per cent clay solids by weight causes the solids to flocculate and settle rapidly to the bottom of the pits. Solutions of the polymer injected at the pump suction reduce the loss of water to permeable formations without impairing the permeability to oil. The use of drill-itlg fluids clarified with the polymer has resulted in increased drilling rates, extended bit life, and lower drilling fluid costs. INTRODUCTION Field experience and the results of a number of investigations have established that the accumulation of solids in drilling fluid reduces drilling rate.'-' Drilling with water makes possible higher drilling rates than can be achieved with mud but in many areas drilling with water may not be feasible because of the possibility of encountering high formation pressures or by-dratable formations. To combat these conditions, the drilling fluid must possess certain physical properties such as viscosity, density, fluid loss, etc., which require the presence of solids. The current trend in drilling fluid treatment is to maintain as low a percentage of solids as is possible without harmfully affecting the mud properties needed for drilling. Mechanical separating devices such as wet cyclones and decanting-type centrifuges are proving to be an economical means of controlling the percentage of solids and thereby maintaining low solids muds. Also: special muds have been developed for the purpose of retarding the hydration of drilled solids so that they may be more easily removed by shale shakers or settling pits. In some areas, such as West Texas, the characteristics of some formations will permit drilling with water. However, because of the dispersion of drilled solids, it is usually not possible to maintain clear water even with the aid of mechanical separators, or by utilizing large settling pits. For this reason the commonly used term "water drilling" is a misnomer since the water usually contains some solids. Because of the improved drilling rates and other benefits which might be effected, a laboratory and field study was made of the use of flocculating agents for maintaining clear water for drilling. PROCEDURE Laboratory—Solids Settling Two techniques were employed to determine the effectiveness of flocculating agents in settling solids from drilling mud. First, the rate of fall of solids was measured in graduated beakers containing mud treated with various flocculating agents. Natural gum, oil-in-water emulsions prepared with ethoxylated nonyl phenols and diesel oil. and a powdered synthetic acrylamide-carboxylic acid copolymer* (hereinafter referred to as "polymer") were tested as flocculating agents in both fresh water and salt saturated muds containing 4 per cent solids. The polymer was not added in the powder form directly to the muds but was first dissolved in water in a concentration of 3.5 lb/bbl. The polymer solution was then added directly to the mud. The concentration of the flocculating agents, including the polymer, was varied. High rates of fall of the solids indicated high flocculating efficiency. A second technique consisted of measuring the time in minutes required to obtain clear water at the pump suction after addition of the various flocculating agents at the flowline. These tests were made using a model mud circulating system having a total volume of approximately 10 gal. The natural fresh water and brine muds used contained 4 per cent solids. A sketch of the circulating system appears in Fig. 1. The circulating rate

By J. J. Gilman, T. A. Read

FOLLOWING the deformation 01 zinc monocrys-tals, sharply bent basal planes are observed near several types of inhomogeneities. Three of these in-homogeneities have characteristics which are quite regular so that they can be studied and analyzed. These are compressive kink bands, "deformation bands," and the inhomogeneities near end restraints. The present paper describes experiments in which "deformation bands" were artificially produced, and bend plane phenomena are discussed in terms of dislocation theory. Also, two new bend plane phenomena are described. The importance of bend plane phenomena in the deformation of crystals is not widely recognized. Many phenomena may be explained in a manner similar to the discussion in this paper. Jillson1 has pointed out that the "punching effect" in zinc is a bend plane phenomenon and is not caused by prismatic slip.' Bowles3 has suggested that they may be involved in diffusionless phase changes. Cahn4 has discussed the role of bend plane formation in the polygonization of zinc. Experimental Work Tensile Kink Bands: Because of the geometrical similarity between "deformation bands" and "kink bands" (compare Fig. 1 of this paper with Fig. 1 of the paper by Hess and Barrett"), the band shown in Fig. 1 of this paper will be called a "tensile kink band," and that shown by Hess and Barrett will be called a "compressive kink band." It is felt that the term "deformation band" should be reserved for banded structures in polycrystalline materials such as iron." Tensile kink bands seem to form spontaneously in aluminum crystals deformed by tensile loading.7-10 In zinc and cadmium crystals they do not form in good, carefully loaded specimens.'." However, tensile kink bands can be produced artificially in zinc crystals. The present authors did this by scratching one of the flat surfaces of triangular crystals transversely with a sharp needle. Natural tensile kink bands caused by inhomogeneities sometimes appeared in deformed crystals which were identical in appearance with the artificially produced ones. Zinc monocrystals were grown by the Bridgman method in graphite molds. Chemically pure zinc (99.999+ pct Zn) was used and the molds were sealed inside evacuated pyrex tubes during growth. The crystal cross sections were equilateral triangles with a typical base of 0.210 in. The artificial kink band shown in Fig. 1 is typical of tensile kink bands in zinc. The band lies between two bend planes which run from upper right to lower left and is inclined oppositely to the slip bands which are sharply bent at the two bend planes. The general form of the artificial tensile kink bands was independent of the scratch depth (1 to 5 mils deep) and also independent of which side was scratched. These variables did cause variations, however. Deep scratches produced more localized kink bands than light scratches. Also, if the angle between the slip plane traces and a transverse scratch varied appreciably among the three sides, then localization of the resulting kink bands also varied. Furthermore, if the slip direction lay nearly parallel to the scratched side, the band was more developed near the scratched side than at the opposite edge. Scratches produced tensile kink bands for crystal orientations from xo = 15" to x, = 75". Fig. 2 shows a scratched crystal after deformation. One triangular side lies in the plane of the photograph. The right hand tensile kink band was produced by a transverse scratch on the upper right side. The next two kink bands were the result of scratches on the front surface. The kink band at the left was caused by a scratch on the lower back side. All four bands have the same general form. A longitudinal scratch was also made on the crystal shown in Fig. 2 to determine the effect of a scratch on the critical shear stress. The critical shear stress of the scratched region was 33.9 g per sq mm compared to 24.4 g per sq mm for the un-scratched region above it. Fig. 3 shows Laue patterns of the crystal shown in Fig. 2. Fig. 3a shows the pattern of the undeformed crystal. The orientation was x, = 21°, A, = 31". After deformation, Fig. 3b was made of the homogeneously deformed portion of the crystal. The spots are compact but split into two halves. This region was elongated 45 pct and its orientation was x = 14", X = 20"; the sine law predicts x = 14", A = 20.5". Fig. 3c was taken near the center of the middle tensile kink band of Fig. 2. The pattern shows a range of orientations and polygonization in this region. The spread in orientation was due to the fact that the basal planes were curved (see Fig. 1) rather than flat as in the ideal case. Some may also have been the result of elastic distortions and "local curvatures." The orientation range was x = 23" to 32", A = 30" to 42". It is apparent from Fig. 3 that the material inside and outside the kink band rotated in opposite directions with respect to the tension axis during deformation. The orientation calculated from the ideal configuration of Fig. 9,

Jan 1, 1954

By Lee Hillard Meltzer, Ralph E. Davis

INTRODUCTION During the past few years emphasis has been placed upon methods of estimating the future expectancy of gas production from natural gas fields. Before technical methods were applied, the production expectancy over future years was based upon the knowledge of gas well behavior, learned through long experience and embedded in the "know-how" of men long in the gas producing business. It is doubtful that a technical study of future expectancy of a gas field or a group of fields was ever prepared for the preliminary planning of a natural gas pipe line system built prior to about five years ago. The decline in well production capacity was naturally recognized by all familiar with the business since its earliest beginnings more than 75 years ago. In 1953, the Bureau of Mines published Monograph Number 7, "Back-Pressure Data on Natural Gas Wells and Their Application to Production Practices," which gave to the industry the first technical analysis of the decline in production of individual gas wells. This method affords a means of estimating the future production in relation to decline in reservoir pressure. The demand for technical determination of expectancy of future gas productivity from fields or a group of fields led technical men to the application of the knowledge of well behavior to the problems. The decline in a well's ability to produce as pressures declined could be estimated by the use of the curve known as the "back-pressure potential curve" as developed by the Bureau of Mines. A field containing few, or even numerous, wells could be analyzed on the basis of the sum of potentials of all wells. In most studies of this nature, the problem is to estimate the rate of production that can be expected, not only from present wells but also, from wells that will in the future have to be drilled into the reservoir being studied. The "back-pressure potential" method requires that the following data be known or estimated: (1) Proved gas reserves. (2) Current shut-in pressures and rate at which shut-in pressures change with production. (3) Back pressure potential data on wells in the source of supply. (4) Ultimate number of wells which will supply gas, and their potential. (5) Limitations on productivity such as line pressures against which the wells will produce, friction drop in the producing string, and so forth. It is evident that the resulting estimate of gas available in each year for a future of say, 20 years, contains many uncertainties. While the method may have considerable merit for a field that is fully developed, it cannot be completely dependable in fields that are only partially developed. In such cases, some of the data upon which it is based can only be estimated or assumed. In the study of this problem during the past few years, a method has been developed which we believe has great merit, especially when applied to fields subject to substantial future drilling, and when applied to the study of fields which, on the average, appear to have characteristics similar, in general, to the average of the fields used in the development of the "yardstick" outlined herein. From an analysis of the production history of 49 reservoirs which are depleted, or nearly depleted, a curve has been constructed which shows the average performance of the reservoirs during the declining stages of production. When properly applied, this "average performance curve" can be used to determine the stage of depletion at which a reservoir or group of reservoirs will no longer be able to yield a given percentage of the original reserves. "AVAILABILITY" AND "AVAILABILITY STUDIES" The rate at which. a reservoir will yield its gas depends basically upon physical factors, such as the thickness and permeability of the sand, the effect of water drive, if any, and other conditions, and upon economic factors, such as the number of wells drilled. Within the ranges set by the physical conditions, a rate of delivery tends finally to become established. The rate (or range of rates) represents a balance between the interests of the operator, who desires the maximum return from his property and of the pipe line owner, who desires to maintain a firm supply for his market. This balance, which is influenced by the terms of the contract, determines the capacity which will be developed by the operator, and the time and rate at which the decline in production is permitted to occur. Thus the "availability" of gas

Jan 1, 1953

By G. Cartaud, F. Osmond

We have already devoted two previous memoirs to this question. In the firstL we collated and discussed the existing literature on the subject; in the second: we described the crystalline forms obtained by the reduction, at different temperatures, of ferrous chloride by hydrogen or by zinc-vapor. The conclusion from these researches was that the three allo-tropic states of iron—a, stable below A2; , stable between A2 and A3; and , stable above A3—all crystallize in the cubic system. The differences observed were such as are customarily encountered in the crystallographic records of many minerals of which allotropic varieties or isomerides are not known, and did not conform to the ordinary definition of polymorphism. It is, however, improbable that allotropic transformations, which are placed beyond doubt by a series of positive facts, do not involve some changes in the intimate structure. As a matter of fact, the crystals we did obtain were too small to allow of a precise examination, and this might introduce an element of uncertainty in the firm establishment of our conclusions. Professor H. Le Chatelier mas even led to think from some of our results that r-iron could very well be a rhom-bohedron simulating a cube, and not a true cube, and it will be remembered that the crystalline form of bismuth was for a long time incorrectly regarded as cubic. Allotropy does not, however, necessarily involve such a deduction. Without departing from the cubic system at all, a whole

Jan 1, 1907

By L. T. Lloyd, H. H. Chiswik

The operative deformation elements in a-uranium single crystals under compression at room temperature have been determined as a function of the compression directions. The deformation mechanisms noted may be arranged with respect to their frequency of occurrence and ease of operation in the following order: 1 — (010)-[I001 slip, 2—{130} twinning, 3—{~172} twinning, and 4bunder special conditions of stress application, kinking, cross-slip, {.-176) twinning, and (011) slip. The composition planes of the (172) and (176) systems were found to be irrational. Cross-slip was shown to be associated with the major (010) slip system, coupled with localized interaction of slip on the (001) planes. The mechanism of kinking was found to be similar to that observed in other metals in that it occurred chiefly when the compression direction was, nearly parallel to the principal slip direction [loo] and was associated with a lattice rotation about an axis contained in the slip plane and normal to the slip direction: the [001] in the uranium lattice. The resolved critical shear stress for slip on the (010)-[100] system was found to be 0.34 kg per mm2 In a single test it was shown that under compression in suitable directions twinning on the (130) also occurs at 600°C. DEFORMATION mechanisms of large grained polycrystalline orthorhombic a-uranium have been studied by Cahn.1 A major slip system identified as the (010) with a probable [loo] slip direction and a minor slip system on the (110) planes were reported; the slip direction of the minor system was not determined. The twinning systems that were identified experimentally included the (130) and the irrational (172) composition planes; observations of other traces which were not as frequent and which did not lend themselves to positive experimental identification led Cahn to postulate on the basis of indirect evidence that twinning also occurred on (112) and (121) planes. In addition to the foregoing slip and twinning mechanisms, Cahn also observed kinking and cross-slip in conjunction with the major (010) system; the cooperative cross-slip plane was not identified. The availability of single crystals to the present authors has enabled them to check these results, particularly with reference to the doubtful mechanisms and the preference of operation of any one mechanism in relation to the direction of stress application. The tests were confined to compression only, primarily because of experimental limitations imposed by the size and shape of the available crystals. The tests were performed at room temperature except for one crystal compressed at 600°C. The compression directions were chosen to obtain a representative coverage of one quadrant of the stereo-graphic projection. To test the existence of some of the deformation elements that were reported by Cahn, but were not found in the present study, several additional crystals were compressed in specifically chosen directions considered most ideal for their operation. Experimental Techniques The single crystals were obtained by the grain coarsening technique described by Fisher? They grinding and polishing on rotating laps, with final surface preparation performed in a H3PO4-HNO3 electropolishing bath. A typical crystal readied for compression is shown in Fig. 1; their dimensions were rather small and depended upon the testing direction. Crystals isolated for compression in a direction close to the [010] axis, which lay roughly parallel to the longitudinal axis of the polycrystalline rod, were about 3 to 4 mm long and 5 mm2 in cross-section, while those prepared for compression in other directions were smaller. Most of the crystals were free from twin markings and showed no evidence of Laue asterism. Several crystals, however, contained twin traces prior to compression; these were identified prior to compression so as to clearly distinguish them from those initiated during deformation. The origin of the twin markings prior to deformation may be ascribed to two sources: thermal stresses and specimen handling during isolation and preparation. Two other types of imperfections in the crystals should be mentioned: inclusions, which were probably oxides or carbides. and three of the crystals contained a small number of spherical included grains (<0.01 mm diam), which were remnants of unabsorbed grains from the coarsening treatment. The volume represented by these imperfections was small, and their presence presented no difficulties in the interpretation of the macrodeformation processes during subsequent compression. Two compression fixtures were employed: crystals A, B, C, E, and G were compressed in a hand-operated screw-driven jig whose compression platens were designed to minimize axial rotation;

Jan 1, 1956

By W. H. Bassett, J. C. Bradley

Beads of metal frequently appear at the ends of cast-copper wire bars and on the sides of wedge cakes near the top. These are richer in cuprous-oxide than the rest of the casting. A micrographical study of these exudations has been made. 11 is suggested that the materical is forced through the surface while the copper is solidifying. If not eliminated in process of manufacture, it shows on the finished polished sheet copper in patches differing in color from the main body of the shad. Figures 1 to 4 show the copper exudations, at different magnifications, as they appear on the ends of cast wire bars, and on the sides, usually near the top, of wedge cakes. Sometimes the exudations are in fine "drops;" at other times, large masses of the material are found. Microscopic examination of the copper exudation indicates that it is high in oxide and of eutectic proportions. Because of the difficulty of securing a suitable sample, the protuberances have not been analyzed chemically; but the spectroscope shows no indication that there are any more metallic impurities present than in the balance of the copper. The lowest copper plus silver content of the coppers studied for this paper was 99.914 per cent.; the highest, 99.966 per cent.; so the oxygen content of the whole casting would be well under 0.07 per cent. Structure of Protuberances The segregation of oxide between grains in the interior of the cast bar, not far from the "set," is shown in Figs. 5 and 6. In general, the amount of cuprous oxide begins to increase at a point about 0.01 in. below the normal surface of the casting, i. e., the base of the drop; but it does not attain maximum concentration in the main body of the metal. Vertical sections, Figs. 7 to 12, show that there is a definite line of large cuprous-oxide globules at the base of the drops. Horizontal sections at this place show that these large globules lie in a thin billowy

Jan 1, 1926

By Clarence A. Seyler

The technical difficulties of cutting thin sections of coal for examination by transmitted light have hitherto restricted the investigation of the important subject of the microstructure of coal to the few possessed of the requisite skill and time. Apart from this, the method fails with anthracites and other coals rich in carbon, owing to the opacity of the material. Occasional use of the method of polishing a surface, with or without etching, has been made, but it was not until Winter&apos; published an account of his results that attention was seriously directed to the method. In May, 1923, a specimen of dull anthracite came into my hands; I tried Winter&apos;s method on it and the presence of megaspores and other vegetable structures became clearly visible. A preliminary notice was published by me;2 but I soon abandoned the use of Schulze&apos;s solution, having found that a mixture of chromic and sulfuric acids gave far better results. In the meantime Turner and Randall, in America, had independently developed the method of flame etching, as applied to anthracite, with great success. I have spent a year studying the method of chromic etching, which gives excellent results with bituminous coals and camels, as well as with anthracite. For anthracites, I have used the chromic method and Turner&apos;s method of flame etching, whichever was the more convenient or as a check one on the other. The polishing is done, according to metallurgical practice, by the use of a polishing machine and successively finer emery paper, followed by polishing on cloth moistened with a suspension of levigated green oxide of chromium, and a final rubbing on "selvyt" (a cotton velvet polishing cloth) moistened with alcohol. The polished sample is examined by reflected light with a 2/3 and 1/6 in. objective. Bituminous coals usually show considerable structure, and even anthracites show it faintly in places. The sample is then etched by immersion in a boiling solution made by adding 10 c.c. of concentrated sulfuric acid to 30 C.C. of a saturated solution of chromic acid; enough water is then added to dissolve

Jan 1, 1925

By E. S. Machlin, Morris Cohen

The isothermal formation of martensite in a 71 pct Fe, 29 pct Ni alloy is found to take place mainly by the nucleation of new plates rather than by the growth of existing ones, and is dependent on the temperature and time of the isothermal hold, the amount of atherrnal martensite present, the state of internal strain, and the application of tensile stress. The conclusion is reached that the isothermal nucleation is activated by thermal fluctuations superimposed on localized regions of very high strain. The reaction-path concept, involving martensite nucleation at strain embryos by athermal activation on cooling, or by thermal fluctuations on holding, reconciles the athermal and isothermal modes of transformation, and offers a unified picture of the kinetics of martensite formation. THE phenomenon of isothermal martensite formation has been the subject of considerable study lately,&apos;-&apos; and its reality has been thoroughly established. The existence of such isothermal transformation has been claimed to confirm the nucleation and growth hypothesis as applied to the martensitic reaction.1 " However, the isothermal formation of a martensitic phase is also compatible with the reaction-pathw escription of the transformation. The purpose of this investigation is to examine the isothermal mode of the martensitic reaction, both theoretically and experimentally, in order to test the likelihood of the above two mechanisms. Material and Methods The alloy used in this study contained about 71 pct Fe and 29 pct Ni. The complete analysis was 29.5 ± 0.2 pct Ni, 0.036 pct C, 0.02 pct N, 0.19 pct Mn, 0.09 pct Si, 0.008 pct P, and 0.006 pct S. The amount of isothermal transformation was determined by electrical resistance measurements using a Kelvin double bridge. The specimens were in the form of rods 1/16 in. diam x 4 in. long. Aus-tenitizing was performed at 1095°C for % hr either in a pre-purified nitrogen atmosphere or in an evacuated Vycor tube, followed by oil quenching to room temperature. After this treatment, the samples were completely austenitic, and the transformation studies were conducted at subatmospheric tempera- tures. Lineal analysis and X-ray determinations of retained austenite were used to calibrate the electrical resistance changes in terms of the percentage of martensite. The martensite range curve for this alloy is given in Fig. 9 of ref. 6. The M, temperature occurs at about -18°C (255°K). Reaction-Path Theory The nucleation and growth description of the martensitic transformation that occurs isothermally has already been given by Kurdjumow.&apos;,&apos;2 However, no comparable treatment exists using the reaction-path concept." Consequently this section presents the reaction-path description of the isothermal mode of the martensitic transformation. According to the latter theory, there is a reaction path (a strain) which describes the relative motion of the atoms during their transference from the austenitic to the martensitic state. The possibility exists, therefore, that the nucleation of a martensitic plate is accomplished by an embryo that comprises a state intermediate between that of austenite and martensite. This state may be attained within a finite volume by means of a homogeneous strain of the austenitic matrix. There is a free-energy barrier (F.) along the reaction path, corresponding to a critical strain in a critical volume. When activation is achieved, a spontaneous increase in strain and volume of the embryo takes place to generate the full-size martensitic plate. This mode of nucleation is to be distinguished from the more conventional mode involving embryos of the martensitic phase that merely grow in size by an interface motion. There are two ways whereby embryos in the austenitic phase can achieve the critical state of strain for isothermal nucleation: 1—through the formation of internal strains by plastic deformation or by stress; and 2—through thermal fluctuations, preferably superimposed upon existing internal strains. The activation free energy F,, must be supplied either mechanically by internal strains or thermally by energy fluctuations, or by a combination of both.

Jan 1, 1953

By K. G. Wikle, W. W. Beaver

The factors which control the rate of dissolution of pure gold in cyanide solution were studied both directly and through measurement of solution the current-potential curves for the anodic and cathodic portions of the reaction. The mechanism of dissolution is probably electrochemical the reaction in nature, and the rate is determined by the rate of diffusion of dissolved oxygen or cyanide to the gold surface, depending on their relative concentrations. The significance of the results and the effects of impurities are considered. ALTHOUGH the dissolution of gold in aerated cyanide solutions has been used as an industrial process for treatment of gold ores since the late nineteenth century, the factors which determine the rate of the reaction have never been identified unambiguously. Studies of the rate of dissolution by Maclaurin,1 White,2 Christy,3 Beyers,4 Thompson,6 and others are contradictory in their conclusions; some claiming that diffusion of the reactants to the gold. surface controls the rate, and others that the chemical reaction is inherently slow and related to high activation energy for the reaction. Christy3 and &apos;Thompson" both suggest that the reaction is electrochemical in nature and that the dissolution of gold proceeds at local anodic regions while the oxygen is reduced at cathodic regions on the gold surface. Although their studies are ingenious and do indicate an electrochemical reaction under the conditions of study, their experiments were of limited nature and failed to identify the rate-controlling process in the system. The importance from an industrial viewpoint of a knowledge of the mechanism and rate-controlling factors in gold dissolution can be illustrated as follows: If the rate is controlled by a slow chemical reaction rather than by diffusion of the reactants, then an increased temperature should have a marked accelerating effect; agitation of the slurry should have no effect on rate: and increased concentration of reactants should cause acceleration of the rate. If the rate is controlled by the diffusion of one or the other of the reactants to the gold surface, then increased agitation should increase the rate; increased temperature will increase the rate, but not as much as for the case of a slow chemical reaction; increased concentration of the reactant which is diffusion limited will increase the rate; and the concentration of other reactants should be without effect on the rate. It may be concluded that for design of a commercial process for gold leaching, the rate-controlling factors of the reaction should be understood so that an intelligent choice of the conditions of agitation, temperature, and reactant concentration may be made. The experiments described here lead to the unambiguous conclusion that in a system of pure gold and a pure aerated cyanide solution the rate of dissolution is controlled either by the rate of diffusion of dissolved oxygen or cyanide to the gold surface, depending on the relative concentrations of each. There is also ample, but not conclusive, evidence that the mechanism of the reaction is identical to that of electrochemical corrosion. The practical significance of these conclusions will be discussed later in the paper. Experimental The experimental method used in this work was to employ an electrolytic cell which performed the overall gold-dissolution reaction, and to study the anodic and cathodic reactions of this cell as to their nature and the rate-controlling factors. Simple experiments on the rate of dissolution and the potential of the dissolving specimen also were performed under conditions of agitation, temperature, and concentration identical to those used in the electrode studies. Analysis of the electrode studies by well established theories of electrochemical corrosion were made, and the results were found to bear a one-to-one relation with actual rate and potential measurements. Electrode Studies: The Anodic Reaction: The gold specimen used for all of the electrode studies and the rate determination consisted of a sheet of 99.99 + pct Au wrapped around a lucite rod and sealed at the edges with plastic cement, thus forming a cylinder of gold of known and constant area (8.0 sq cm). The lucite rod was threaded into a brass spindle which could be rotated at speeds of 100, 300, and 500 rpm. For the electrode studies electrical contact between the gold cylinder and the brass spindle was made by means of a gold strip covered with plastic. The anodic dissolution of gold was studied by immersing the electrode in a solution containing known concentrations of KCN and KAu(CN)2 but free of oxygen, and by passing an anodic current through the gold electrode. The pH of the solution was maintained between 10.5 to 11.0 in these and all other tests by addition of KOH. The pH was measured before and after each test by means of a glass-elec-

Jan 1, 1955