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By J. P. Heller, H. B. Bradley, A. S. Odeh

It is an accepted procedure to represent oil field displacement problems in which the pressure is relatively constant by a potentiometric model. Variations in reservoir permeability thickness product are represented in the model by proportional variations in electrolyte depth. It is shown that significant errors are present wherever these variations are of such magnitude that the consequent differences in the electrolyte depth in the model or any regions therein are appreciable in comparison with their respective horizontal dimensions. To demonstrate the order of magnitude of this error, a hypothetical linear oil field in which permeability varies linearly with distance was treated both analytic.ally and by potentiometric model. The results obtained from the model are compared with the exact solution for various configurations of linear geometry. Deviations in flow times up to 11 per cent were observed. It is confirmed that these discrepancies can be reduced by increasing the areal scale and/or decreasing the vertical scale of the model. It is the purpose of this work to assist in the design of potentiometric models by indicating the relationship between this error and the chosen scale factors. INTRODUCTION The fundamental geometrical criterion which determines whether the pressure distribution in an oil or gas reservoir may be simulated in a conventional potentiometric model is the requirement that all reservoir parameters be constant along any vertical line between its upper and lower boundaries. This situation never obtains exactly; nevertheless, it is usually assumed that there is no permeability stratification within the section of interest, that all wells completely penetrate the sand, that there are no gravitational effects, and that variations in thickness of the sand are small compared to the horizontal extent of the field. In these ways the reservoir problem is reduced to two dimensions in which there is no variation of pressure in the vertical direction within the limits of the sand. Variations in sand thickness and/or horizontal pesmeability may be taken into account as described by Muskat, by considering the fluid conductivity of the reservoir in its horizontal plane to be proportional to the product of permeability and sand thickness. If the variations in sand thickness are small compared to the horizontal dimensions of the reservoir, then it is a good approximation to consider the reservoir problem to be essentially two dimensional. The same approximation, however, is made in the simulation of the assumed two-dimensional reservoir by the electrolytic model. The model, if it is to take into account variations of permeability-thickness product, must of necessity be made in three dimensions, that is, with variable depth. Most potentiometric model studies and theoretical treatments reported in the literature to date2,3,4,5,6,7,8 are those in which either an average permeability was used or a constant permeability was assumed. This is understandable since detailed permeability data are not usually available for the majority of reservoirs. Many investigators have recognized that the failure to incorporate permeability variations within a reservoir in model studies leads to serious error in predictions made

Jan 1, 1957

By Immo H. Redeker

Through close cooperation with geophysical and geological test work by Texas Gulf Sulphur Co. in Beaufort County, the Asheville Minerals Research Laboratory assisted in the evaluation of North Carolina's most valuable mineral resource, the Pungo River phosphate deposit. After a core evaluation study, the flotation process for the concentration of North Carolina phosphate was demonstrated in a 500-lb per hr pilot plant in Asheville. Tonnage samples of phosphate concentrate were produced for customer evaluation in the United States, Europe, and the Far East. Plans for a larger pilot plant to be erected at the plant site at Lee Creek were prepared for TGS. The larger pilot plant was operated by TGS in conjunction with a test dredging operation which led to the adoption of a dragline dry mining method to move 90,000 tpd of material for the production of 10,000 tpd of phosphate concentrate in the all-flotation phosphate concentrator. Calcining, dry grinding, and byproduct studies complimented the construction of one of the world's largest and most modern fertilizer raw-feed complexes on the eastern North Carolina seaboard.

Jan 1, 1972

Discussion of the paper of Leonard Waldo, presented at the New York meeting, February, 1911, and printed in Bulletin No. 76, April, 1913, pp. 555 to 559. HERBERT HAAS, San Francisco, Cal. (communication to the Secretary*):-Referring to Leonard Waldo's paper on Temperature Conversion Tables, I believe the following formulas can be easily remembered, and by reference to the thermomter scales of Fahrenheit (F.), Celsius (C.), and Réaumur (R.), their derivation and relation are at once understood n° F. = 4/9 (n°-32) R. = (n°-32) C. n° C.=(9/5 n° + 32) F. = 4/5 n° R. n° R.=(9/4 n° + 32) F. = 5/4 n° C. As the freezing point of water is at 32° F., corresponding to 0° C. and 0° R., 32 must be deducted from the Fahrenheit degrees when these are converted into C. or R. degrees. Likewise, to C. or R. degrees converted into F. degrees 32 must be added. The fractions 4/9 and 5/9 and their reciprocals are obtained thus:

Jan 5, 1913

By G. H. Enzian

W. C. Ellis—The intergranular fracture observed by these authors in brass seems to be characteristic of metals when tested under similar conditions. It has been observed by us in room temperature tests on lead alloys subjected to constant stress when the stress has been low enough to afford a small strain rate. If, however, the test be carried out at a high stress and therefore at a large strain rate, a characteristic, tapered, transcrystalline fracture is obtained. The same change of fracture has been observed by others with decrease of strain rate and increase of temperature for other metals—for example aluminum—and may be presumed, as the authors point out, to be general for metals. These findings suggest a plastic flow mechanism under conditions of small strain rate and high corresponding temperature differing from classical block slip. The required conditions point to a process fundamentally diffusive in nature—a less organized process than block slip. Nabarro18 has shown that plastic flow can occur by stress induced diffusion of vacant sites— a process of self-diffusion. Movements of a pseudo-viscous nature at grain boundaries are suggested in the work of Ke.15 Deformation near to a grain boundary by other than a slip mechanism appears necessary to Boas and Hargreaves.19 Wood and Rachinger20 report a cellular structure in slowly deformed alumi- num—the cell size is larger, the higher the temperature and the slower the strain rate. Presumably in the latter case diffusive movements occurred in the cell boundaries. In any case the nonslip mechanism seems somewhat obscure and further work is indicated. Such studies will undoubtedly clarify the nature and behavior of lattice imperfections—the very core of the strength and plastic properties of metals. F. H. Wilson and E. W. Palmer (authors' reply)—It is certain that the metallic behavior which has been termed "creep" includes many interdependent phenomena of which a nonslip type of plastic flow may well be one. The reports to which Mr. Ellis refers are illustrative of the many different observations that must be correlated for a complete understanding of creep. The list could be extended considerably. For example, we ourselves have been impressed by the sensitivity of creep phenomena to the presence of minor impurities and feel that this aspect of the problem warrants more thorough study than it has yet received. References 18 F. R. N. Nabarro: Report of Bristol Conference on Strength of Solids. P. 75, (1948) London. 19 Boas and Hargreaves: Proceedings Royal Society. (1948) 193. 89. 20 wood and Rachinger: Journal Institute of Metals. (1949) 17, 237.

Jan 1, 1951

By R. G. Woolery

INTRODUCTION Since 1975, Union Carbide Corporation has been conducting uranium exploration in southwestern South Dakota. This program has resulted in the discovery of an ore body about eight miles north of Edgemont in Fall River County. The site which was previously mined for uranium in the 1950's and 1960's consists of 950 lode claims (approximately 20,000 acres) and is within the Black Hills National Forest. Preliminary development plans indicate that fewer than 200 surface acres will be involved in the mining and heap leaching of the ore. The ore occurs in both the Fall River and Lakota formations. The exploration to date has developed something in excess of two million tons of ore averaging -0.1% U308. About 75% of the ore is expected to be mined from underground with 25% coming from five to seven small pits. The surface mining will be extensions of previously mined areas with a disturbance of 35-40 new acres near 35-40 previously disturbed acres requiring a total reclamation of 70-80 acres. Several options for processing the ore including conventional milling by UCC, conventional milling in joint venture with another producer, and heap leaching are under consideration. This paper is concerned with the preliminary assessment of the heap leaching option based on the limited test work conducted on surface samples and on available cores from the deeper ones. The final design for a commercial operation will not be available until an underground bulk sample has been obtained and evaluated. Union Carbide has been operating heap leach facilities commercially since 1973 at Gas Hills, Wyoming and Maybell, Colorado. During this period, we have made considerable progress in heap construction

Jan 1, 1983

By H. B. Charmbury, D. R. Mitchell

Recovery of fine coal from solids reporting to wash water has become increasingly important. These solids range from about 28 mesh to 0 and constitute 3 to 7 pct by weight of the feed tonnage to a coal preparation plant. In the past they were usually wasted to streams, but present clean stream legislation makes it necessary to remove them from the wash water and, if economically possible, recover the associated coal as a saleable product. Where these solids are not wasted to streams or to slime ponds they are recovered by thickeners and filters. Since filter cake is often high in ash or sulfur, or both, it is not readily marketed or used. Common practice is to mix it with other plant products, generally slack or cleaned run-of-mine. Uniform blending is difficult, not only because the impurity is usually high, but also because during certain operating periods it is possible to get a concentration of this filter cake in a railroad or barge.

Jan 2, 1959

By V. F. Zackay, W. A. Goering

ALLOYS of iron and aluminum up to 35 wt pct aluminum are single-phase solid solutions, and are of potentially wide applicability.1-3 In spite of early and continued interest1-4 little progress has been made until recently in the preparation and evaluation of sound alloys containing more than 6 wt pct aluminum. Vacuum-melting techniques for the production of ductile Fe-A1 alloys have been described recently.1-7 A. procedure for air melting these alloys is presented here. Low-carbon iron is induction melted without a slag in a rammed magnesia crucible. At the beginning of melt-down, aluminum pig (99.95 pct Al), charged in a clay-graphite bottom-pouring crucible is placed in a pot furnace at 1800°F. The primary deoxidation of the molten iron after melt-down is effected by the addition of 0.1 pct aluminum and 0.5 pct manganese. (Hilty and Crafts" have reported a significant increase in the deoxidation efficiency of the aluminum and manganese combination over that of the aluminum alone.) A more drastic deoxidation designed to reduce the oxyen content to the lowest possible level is accomplished by plunging metallic calcium to the bottom of the melt. This is done by wiring small cubes of the metal to a steel rod. A circular shield larger than the diameter of the crucible opening is attached to the rod so that any spa'ttering of the molten metal will not endanger the operator. Since the temperature of the molten metal is above the boiling point of calcium, the bath is vigclrously purged by calcium vapor. It is believed that the calcium-vapor treatment permits a homogeneous distribution of calcium in the melt. Owing to the vigor of the reaction the temperature of the molten metal should be kept below 2900°F prior to the calcium addition. A total of 0.05 pct calcium is added in two stages in this manner. The second calcium deoxidation is made just before charging the molten aluminum into the iron, in order that an excess of calcium be present for the remainder of the melt. The aluminum, which has been removed from the holding furnace, is then hydrogen degassed by bubbling chlorine through a quartz tube immersed in the molten aluminum. The hydrogen-chlorine reaction is an exothermic one preventing the solidification of the aluminum during the 5-min chlorination. Approximately 0.1 pct calcium, based on the amount of aluminum, is then added to the aluminum. A further excess of calcium is introduced into the melt in this manner. The oxide dross is removed, fluorspar is added to the molten iron, and the molten aluminum is poured through the fluorspar slag. The fluorspar should be dried thoroughly prior to its use, as any water present will react with the aluminum. Aluminum oxide formed during the pouring operation reacts with the fluorspar slag to form gaseous aluminum fluoride and calcium oxide. A forced-draft ventilating system is required for this operation as aluminum fluoride is toxic. As soon as the molten aluminum has been added, vigorous manual stirring of the melt is required because the slag-aluminum oxide reaction is highly exothermic and tends to take place near the top of the melt. The combination of high temperature and the slagging action of the fluorspar quickly erodes the crucible at the slag line if the aluminum is not stirred uniformly into the melt. It has been found that at least 4 min of manual stirring combined with induction stirring are necessary to ensure homogeneity. The power is shut off 1 min prior to pouring to allow metal and slag to separate. As much slag as possible is removed from the melt, which is then poured directly into cast-iron molds. A mold wash of aluminum oxide is used to prevent ingot sticking. For slab ingots which are to be rolled into sheet, a carbon-tetrachloride vapor atmosphere or a chlorinated-pitch mold wash is desirable, as the aluminum oxide formed in the pouring operation is subsequently removed by the chlorine in the presence of carbon." As in vacuum melting, a pouring temperature of about 2900°F is recommended. Adequate hot-topping is important as iron-aluminum ingots are subject to very deep piping. Ingots are removed from the molds and buried in vermiculite, where they are allowed to cool slowly to room temperature. The ingots are radiographed,

Jan 1, 1959

By BARONJUPTNER VON JONSTORFF, Andrew A. Blair, GUNNAR DILLNER

IT is a well-known fact that the results of different analysts, when operating on the same identical sample of steel or iron, are far from concordant, and it not infrequently happens that great annoyance and trouble in the commercial community are occasioned by these discrepancies. Attempts have been made at various times to investigate the causes of such differences and to obtain more reliable methods of analysis. The most important of these was made by the British Association in 1889: The following gentlemen, with Sir W. Roberts-Austen as Chairman, and Professor T. Turner as Secretary, were constituted as a committee to investigate the question, viz.: Sir F. A. Abel, Mr. Edward Riley, Mr. G. J. Snelus, Mr. John Spiller, Professor J. W. Langley, and Professor Tilden. Average .samples of steel were prepared in America under the superintendence of Professor J. W. Langley. The steels, in the form of turnings, were divided and distributed to sub-committees in Great Britain, America, France, Germany, and Sweden. In Sweden Professor Åkerman acted as Secretary to the Swedish committee. The Government Department of Tests was appointed in Germany; Mr. Ferd. Gautier in France; the British Association Committee in England; Messrs. William

Mar 1, 1905

[James C. Gray, President W. B. Stephenson, President-Elect A. B. Cummins, Past-President E. G. Fox, Eastern Regional Vice-President H. C. Weed, Western Regional Vice-President Donald W. Scott, Central Regional Vice-President John Cameron Fox, Secretary 29 W. 39 Street New York 18, N. Y. After September 7, 1961 345 East 47 Street, New York 17, N. Y. D. R. Tone, Assistant Secretary Nathaniel Arbiter, Treasurer]

Jan 1, 1961

The United States Coast and Geodetic Survey has announced the completion of a new outline map of the United States on the Lambert conformal conic projection, scale 1-5,000,000. This map is intended merely as a base to which may he added any kind of special information desired. The shore line is compiled from the most recent Coast and Geodetic Survey charts, state names and boundaries, principal rivers, capitals, and the largest cities in the different states are also embodied. The value of the new outline map on the Lambert projection can best be realized when it is stated that it shows that throughout the largest and most important part of the United States, that is, between latitudes 30 ½ and 49°, the maximum scale error is only 0.5 per cent. This amount of scale error of 0.5 per cent. is frequently less than the distortion due to the method of printing and to changes from the humidity of the air. Only in southernmost Florida and Texas does this projection attain its maximum error of 233 per cent. The map measures 25 inches by 39 inches and will be sold by the Government at 25 cents.

Jan 7, 1919

By B. A. Cheadle, C. E. Ells

The ovienlalion of hexagonal a-zirconium crystals in cold-drawn Zircaloy-2 tubes and in both as-extruded and heat-treated Zr-2.5 wt pcl ND tubes has been rrleasured using the inverse Pole - figure technique. Uniaxial tensile tests hare shown the Zil-caloy-2 lubes to hare highly anisotropic delovmation behavior whereas heat-treated Zr-2.5 wt pet Nb tubes are nearly isotropic. The differences in deformation behavior are esbloilred from the observed textures of the tubes and the deformation systems known to oberate in Zircnloy,-3. Tlze vcsults lead to an explanation of the high effective strain observed fov the Zircaloy-2 tubes as colrzpared to heat-treated Zr-2.5 wt pet Nb tubes in restrained end burst tests at 280° to 300°C. THE Zr-2.5 wt pct Nb alloy. when heat-treated by quenching from temperatures slightly below the (a + p)/P phase boundary and subsequently aged at 500°C, has tensile strengths about 50 pct greater than those of 20 pct cold-worked Zircaloy-2.1 There is. therefore, considerable economic incentive to replace Zircaloy-2 with the heat-treated alloy in some in-reactor applications. notably for pressure tubes, where strength is a prime consideration. However, when tubes of Zr-2.5 wt pct Nb fabricated by extrusion and drawing prior to heat treatment were subjected to restrained end-burst tests at 300 °C. the circumferential expansion at failure1 was only 10 pct that of cold-drawn Zircaloy-2 tubes in similar tests,2 Table I. This result was not predicted from uniaxial tensile tests in which the ductilities of the two materials were quite similar.' The detailed requirement for ductility in pressure vessels has not yet been worked out. and comparison of the relative merits of cold-worked Zircaloy-2 and heat-treated Zr-2.5 wt pct Nb is further complicated by the irradiation-induced loss of ductility and hydrogen pickup each will undergo from reactor operation.1,2 Nevertheless. the lower circumferential expansion of the Zr-2.5 wt pct Nb tubes raised serious doubts on the advisability of their use as pressure vessels. For this reason, an investigation to determine the cause for different ductilities of the two types of tubes was initiated. From a study of uniaxial tensile properties and crystallographic orientation it has been found that the fracture ductilities observed in the burst tests can be related directly to the crystallographic ori-

Jan 1, 1965

Electrowinning U.S. 4,066,520 - Recovery of copper from copper sulfide ore. Finely divided ore concentrate is leached with moderately strong sulfurous acid to solubilize copper ions, the leach solution treated with calcium sulfite to reduce the copper ion concentration by forming copper-precipitate solids therein, the solids filtered off, and and the filter cake dewatered to obtain a slurry of copper-precipitate solids amenable to direct electrowinning of copper therefrom using a described electrolysis apparatus which utilizes high current flow with a minimum of mechanical agitation. R. C. Emmett, Jr., J. K. Dicksa. B. C. Wojcik and F. A. Baczek, assigned to Envirotech Corp. Jan. 3, 1978. 14 pp. (204- 108). Filed: 9- 1-76 (7 19,867).

Jan 1, 1979

By J. B. Hiskey, W. J. Schlitt, W. G. Pitt

Aqueous SO2 (sulfurous acid) is an interesting chemical compound. It functions as a reagent in various hydrometallurgical systems, but also represents an undesirable constituent in gyro- and hydrometallurgical effluent solutions. When present in such streams, SO2 can be oxidized to the more stable sulfate form to avoid exsolution of SO2 as a source of fugitive emissions and to simplify standard water treatment plant operation. This study provides information on the stoichiometry, kinetics, and mechanism of SO2 oxidation using oxygen and an iron salt catalyst with solutions containing 0.05-20 g/L (0.002-0.7 oz per gal) SO2. The effects of iron salt concentration, oxygen pressure, temperature, degree of agitation, and pH on SO2 oxidation are also described.

Jan 1, 1984

By D. R. Maneval

The Surface Mining Act of 1977 required a study by the National Academy of Sciences regarding the special mine reclamation requirements of Alaska. The status of mines operating and planned in Alaska will be presented. New mines opening in Alaska must establish a baseline inventory of plants and animals in the mine site area as well as determine pre-mining air and water quality. Current work in these areas will be summarized. Reclamation practices in Alaska and other Arctic countries as practiced currently will be described. A summary of current research in Alaska dealing with revegetation on surface mined lanais, re-establishment of animal populations, and water treatment processes necessary in this pristine environment will be discussed. Included will be future predictions of the direction of mine reclamation in Alaska as more mines enter the industry.

Jan 1, 1984

By John Dodd

This paper reviews advances in the technology of abrasion resistant iron and steels, which could help combat abrasion and wear in mining operations. With the recent progress in high chromium alloy iron development, high temperature heat treatment of massive castings can be eliminated, aloy cost reduced, and cracking problems avoided. Data on erosion-corrosion resistance of these irons; trends in the development of improved cast steels; and factors influencing toughness and abrasion resistance of manganese steels are all considered. The 7% Mn. 1% Mo manganese steels are shown to combine toughness and abrasion resistance, and composite castings are a means of combating abrasion in applications involving severe impact. A brief appraisal is given of recently developed martensitic wrought steels with improved weldability.

Jan 1, 1982

By William E. Ford, Edward Salisbury Dana

The Niobates (Columbates) and Tantalates are chiefly salts of metaniobic and metatantalic acid, RNb2O6 and RTa2O6; also in part Pyroniobates, R2Nb2O7, etc. Titanium is prominent in a number of the species, which are hence intermediate between the niobates and titanates. Niobium and tanta¬lum also enter into the composition of a few rare silicates, as wöhlerite, låvenite, etc. The following groups may be mentioned: The isometric PYROCHLORE GROUP, including pyrochlore, microlite, etc. The tetragonal FERGUSONITE Group, including fergusonite and sipylite. The orthorhombic COLUMBITE Group, including columbite and tantalite. Also the orthorhombic SAMARSKITE GROUP, including yttrotantalite, samarskite, and ånnerodite. The species belonging in this class are for the most part rare, and are hence but briefly described.

Jan 1, 1922

By Felix B. Shay

THE Agua Fria mine is in eastern Honduras at Lat. 140° 06' N., Long. 86° 36’ W. Danli, the seat of the local municipal government, is the nearest town. The property is approximately 44 miles east of Tegucigalpa, the terminus of a truck road from the Pacific coast. The mine lies at an altitude of 3300 ft. with surrounding elevations as high as 6000 feet. For 20 years the oxidized croppings of the Agua Fria vein had been worked intermittently when in 1927 an attempt was made to open the property. A shaft was sunk 300 ft. and considerable ore was blocked out, but before a mill could be installed financial difficulties arose and the mine reverted to the original owners. Erle P. Halliburton, of Los Angeles, purchased the property in 1934. At that time a careful consideration of all factors involved showed that air transport was the only practical method of moving the equipment and machinery necessary to commence production. The other alternative was by muleback, which required sectionalizing all equipment to a maximum load of 200 lb., and during the rainy season this type of freighting was subject to serious delays. It was decided to purchase a trimotor Ford powered by three Pratt and Whitney Wasp B motors developing 400 hp. each. There were several reasons for the choice: (1) this type of plane was available at a reasonable price, owing to its replacement by faster models on most of the airlines in the United States; (2) the ship was capable of carrying a pay load of 3000 lb. over the required distance; (3) since this airplane had been widely used there would be no difficulty in securing competent personnel or in purchasing spare parts. It was necessary to rebuild the plane for cargo service. The windows were removed and the fuselage was entirely covered. A hatch was cut in the top of the fuselage to receive heavy crane loads and pieces of freight that were too large or too long to go through the rear door. The seats were removed and the interior of the plane was lined with Duralumin sheets. A heavy-duty landing gear was installed and the floor was reinforced. The nearest site for an airport was two miles north of the mine. The necessary grading was done by a small track-type tractor with a wheeled grader, which was brought in overland. Six weeks was required for bring-

Jan 1, 1940

No. 349.-A Canadian university wishes to engage a man to teach non-ferrous metallurgy and ore-dressing as well as to direct research work. The instruction work covers 7 months but the research work is continued throughout the year. To a suitable man the rank of professor will be granted. Applicants are requested to state education, experience, salary desired and any other particulars that might assist in selecting a man for this position. No. 354.-Wanted, for Northern Nigeria, one chief and two assistant mining engineers, competent surveyors, with good knowledge of alluvial tin mining and dressing of tin concentrate. Preferably with previous Nigerian experience, and exempted or able to. secure passport. Apply in writing, stating qualifications, experience and salary required.

Jan 12, 1918

By Eugene S. Meieran

The effects of methods of crystal growing, wafer sawing, polishing, routine handling, diffusion, and epitaxial growth on the defects in GaAs are reviewed and studied using reflection and transmission X-ray topographic techniques. In general, it was found that boat-grown crystals exhibited fewer defects than Czochralski crystals, although all crystals showed large numbers of precipitates visible when examined in the electron microscope. Mechanical surface treatments such as sawing and mechanical polishing introduce damage to a depth of about 5 µ, most of which can be removed by suitable chemical or chem-mechanical polishing. In addition, defects can be introduced through routine handling of wafers, for example with metallic tweezers. These defects can be quite severe, and have been observed 20 µ below the wafer surface. Defects can also be introduced through diffusion and epitaxial growth. These defects, which include precipitates, growth pyramids, stacking faults, dislocations, and so forth, can be detrimental to device fabrication. It is shown that wafers or films which appear defect-free optically can contain defects visible in the X-ray topographs. WHILE the use of GaAs in the semiconductor industry has increased very rapidly in the last few years, due mainly to the recent development of many important GaAs devices,1,2 the major limit to the production of commercial quantities of many GaAs devices remains a severe lack of suitable materials technology. This lack is apparent in two critical areas. First, production quantities of high-quality GaAs crystals, reproducibly doped and precipitate-free, simply are not available commercially, although some reasonable quality material is available on a limited first-come, first-serve basis. Second, in comparison to silicon technology, little is known about the effects of processing variables on the defects either present in as-grown GaAs or introduced through processing and handling of wafers. These areas are now receiving some attention from semiconductor device manufacturers, who are studying defects in GaAs in order to better understand how either to prevent their occurrence or to cope with their existence. Most investigations of the defects in GaAs have been made by optical microscopy3-5 or transmission electron microscopy techniques.'-' Recently, however, the imaging techniques of X-ray topography, electron mi-croprobe analysis, and scanning electron microscopy are being applied to the study of GaAs.9-14 In the case of X-ray topography, a one-to-one image is obtained that must be photographically enlarged. In compensa- tion, the defects within entire wafers may be imaged by simple scanning (Lang technique15) if the wafer is reasonably perfect, or by using the scan oscillation technique developed by Schwuttke16 if the wafer is warped or distorted. The purpose of this paper is to both review and extend the general application of X-ray topographic techniques to GaAs. Emphasis will be placed on the effects of growth and process variables on the quality and perfection of both bulk and epitaxial GaAs. Reference to optical or electron microscopy results will be made when useful. Since the effects on defects of a wide variety of processing variables such as crystal growing, sawing, polishing, diffusion, and epitaxial growth will be somewhat superficially reviewed, a fairly extensive bibliography of the most important recent results in these areas is included. However, for completeness, important defects will be illustrated here, although such defects have been previously shown by others. While this paper is concerned with defects rather than with the physics of X-ray scattering, the mechanisms of contrast formation in the topographs will of necessity be briefly mentioned. EXPERIMENTAL GaAs crystals, both boat-grown18 and Czochralski-grown,'8 containing a variety of dopants of various concentrations, were purchased from outside vendors. Wafers were sliced from the crystals using a Hamco ID saw and were mechanically polished using 1 µ diamond paste. Chem-mechanical polishing was done in bromine-methanol as described by Sullivan and Kolb.18 Chemical polishing was done using a modified sulfuric-peroxide solution, 11 parts H2SO4, 1 part 30 pct H2O2, 1 part DI water.5 Zinc diffusion was carried out in a closed tube, using a 10 pct Zn-In source at 825°C for 1 hr. Oxide masking techniques were used to select the area to be diffused. Epitaxial wafers were either purchased or prepared here. All epitaxial runs prepared here were carried out using a Ga-GaAs-AsC13 source in a closed tube at a substrate temperature of 750°C. Wafers were chem-mechanically polished and gas-etched prior to deposition. The X-ray topographs were taken on a Krystallos Lang camera, operating in the transmission scanning geometry (Lang technique15) or in the reflection scanning geometry (modified Berg-Barrett technique20,21). MoKa, radiation was used for all transmission topographs using a Jarrell-Ash 100-µ spot focus. CuKal radiation was used for all reflection topographs using a General Electric CA-7 1-mm spot focus X- ray tube. Topographs were printed from an intermediate contrast inversion film, so the contrast shown in all figures here is the same as that of the original 50-µ-thick emulsion L4 Iiford nuclear plate used to record the topograph.

Jan 1, 1969

By L. F. Bryant, J. P. Hirth, R. Speiser

The surface, gain boundary, and twin boundary energies, as well as the surface diffusion coefficient, of cobalt were determined from tests at 1354°C in pure hydrogen. A value of 1970 ergs per sq cm was calculated for the surface energy, using the zero creep method. It was possible to measure the creep strains at room temperature because the phase transformation was accompanied by negligible irreversible strain and no kinking. Established techniques based on interference microscopy were used to obtain values for the other three properties. The gain boundary and twin boundary energies were 650 ad 12.7 ergs per sq cm, respectively, while a value of 2.75 x l0 sq cm per sec was determined for the surface dufusion coefficient. In the course of a general study of cobalt and cobalt-base alloys, information was required about the surface energy of cobalt. Hence, the present program was undertaken to measure the interfacial free energy, or, briefly, the surface energy, of the solid-vapor interface of cobalt. The microcreep method was selected for this measurement because other surface properties could also be determined from the accompanying thermal grooving at grain boundaries and twin boundaries. A brief summary of the methods for determining the various surface properties follows. At very high temperatures and under applied stresses too small to initiate slip, small-diameter wires will change in length by the process of diffu-sional creep described by Herring.1 The wires acquire the familiar bamboo structure and increase or decrease in length in direct proportion to the net force on the specimen. For a specimen experiencing a zero creep rate, the applied load, wo, necessary to offset the effects of the surface energy, y,, and grain boundary energy, y b, is given by the relation: where r is the wire radius and n is the number of grains per unit length of wire. The first results obtained from wire specimens were reported by Udin, Shaler, and Wulff.' udin3 later corrected these results for the effect of grain boundary energy. The grain boundary energy is determined from measurements of the dihedral angle 8 of the groove which develops by thermal etching at the grain boundary-free surface junction. For an equilibrium configuration: Measurements of the angle 8 can be made on the creep specimens4'5 or on sheet material, as was done in this investigation by a method employing interference microscopy.= If the vapor pressure is low, the rate at which grain boundary grooves widen is determined primarily by surface diffusion and, to a lesser extent, by bulk diffusion. The surface diffusion coefficient, D,, is obtained from interferometric measurements of the groove width as a function of the annealing time, t. As predicted by Mullins~ and verified by experiment, the distance, w,, between the maxima of the humps formed on either side of the grain boundary increases in proportion to if grooving proceeds by surface diffusion alone. For this case: where fl is the atomic volume and n is the number of atoms per square centimeter of surface. When volume diffusion also contributes to the widening, the surface diffusion contribution can be extracted from the data by the method described by Mullins and shewmon.8 Where a pair of twin boundaries intersects a free surface, a groove with an included angle of A + B (using the groove figure and notations of Robertson and shewmong) forms by thermal etching at one twin boundary-free surface junction. If the "torque terms", i.e., the terms in the Herring10 equations describing the orientation dependence of the surface energy, are sufficiently large, an "inverted groove" with an included angle of 360 deg-A'-B' develops at the other intersection. The angles A + B and A' + B' are measured interferometrically. When the angle, , between the twinning plane and the macroscopic surface plane is near 90 deg, the twin boundary energy is calculated from the relation: 1) EXPERIMENTAL TECHNIQUES Five-mil-diam wire containing 56 parts per million impurities was used for making ten creep specimens. These specimens had about 15 mm gage lengths with appended loops of wire and carried loads (the specimen weight below the midpoint of the gage length) ranging from 3.7 to 149.8 mg. The wires were hung inside a can made from 99.6 pct pure cobalt sheet. Beneath the wires were placed small specimens of 20-mil-thick, 99.9982 pct pure cobalt sheet from which the relative twin boundary and grain boundary energies and the surface diffusion coefficient were measured. All the specimens were annealed at a temperature of 1354" i 3°C which is 92 pct of the absolute melting point of cobalt. The furnace atmosphere was 99.9 pct pure hydrogen that was purified further by a Deoxo catalytic unit, magnesium perchlorate, and a liquid-nitrogen cold trap. As a precautionary measure the gas was then passed through titanium alloy turnings which were heated to 280" to 420°C and replaced after every test period. The hydrogen was maintained at a

Jan 1, 1969