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By F. S. Turneaure, R. Gibson

The tin deposit of Monserrat, Bolivia, consists of one major vein 1600 m in length. The ore is unusual because of the notable quantity of teallite, even though cassiterite is the principal tin mineral. The deposit, formed at shallow depth under a wide range in temperature, may be classed as xenothermal. Polished sections reveal a complex history of replacement, with low-temperature minerals deposited before high-temperature minerals. THE Monserrat mine1'2 of the Compania Minera Monserrat is located 11 km east of Callipampa, a station on the Antofagasta and Bolivia Railway some 55 km south of Oruro. The mine lies in a group of low hills on the east slope of a broad valley of northerly trend. The valley is separated from the altiplano to the west by a prominent ridge that rises several hundred meters above the surrounding country (fig. 1). Callipampa is situated a short distance west of the ridge, near the east margin of the altiplano. The elevation at Callipampa is 3700 m and at the mine 4100 m. Monserrat is near the northeast limit of what may be called the Poopo-Pazna district, an area of northwesterly trend about 25 km in length and 15 km in width. The district includes the tin-silver prospects of Poopo to the north, the zinc-tin deposits of Salvador to the southwest, and the tin-tourmaline veins of Avicaya to the south. Along the prominent ridge already mentioned, which forms the western limit of the district, there are several tin and antimony prospects including the Trinacria mine, which is famous for its fine specimens of cylindrite. Although the principal ore mineral is cassiterite, the tin deposit of Monserrat contains an unusual amount of teallite. Cassiterite occurs in part as a finely granular mixture with sulphides of iron and zinc and in part as needle tin of late hypogene age. The regional structure is dominated by broad folds typical of the Andes of Central Bolivia and similar to those of the Llallagua district. The area adjacent to the Monserrat mine is underlain by thin-bedded shale somewhat variable in color but predominantly dark grey to black. The beds strike northwest and dip at low angles southwest, forming part of the northeast limb of a major syncline. A resistant sandstone formation, which underlies the black shale, crops out along a ridge east of the mine and also accounts for the high ridge to the west that was previously mentioned. No igneous rock of any kind is found at Monserrat. The nearest intrusive bodies known are the irregular dikes and masses of quartz porphyry at Avicaya about 10 km to the south. Mine Workings The Monserrat property includes one main vein, which can be followed on the surface for 1600 m, and two or three branch veins of distinctly minor importance. The principal haulage tunnel, referred to as the San Carlos adit or level III, extends northeasterly for 1700 m, following the main vein throughout most of this distance. Above the adit, there are

Jan 1, 1951

By J. C. Smock

The magnetic and polaric properties of magnetite, or magnetic iron ore: are fundamental facts in magnetism. The disturbing erect of this mineral upon the magnettic needle in land surveying must have been very early observed. The difficulties arising from this source are still almost insurmountable in making accurate surveys in districts where this ore occurs to any extent, either as a rock

By AIME AIME

MONDAY evening a reception, supper and bridge in honor of the guests of the Woman's Auxiliary was given by the New York Section in the Engineering Woman's Club. After supper, tables were made up for bridge. Some tried jig-saw puzzles, while others merely visited. On Tuesday morning the annual business meeting was called to order by President Bassett. Mrs. Bassett read a note from Mrs. Hoover regretting her inability to be present, and then gave her welcome and message: It gives me much pleasure to welcome you in this annual meeting, and I hope you will be able to come next year, and those who are not able to come this year I hope will be here next year.

Jan 1, 1933

By P. M. Blair

This paper presents numerical solutions of the equations describing the imbibition of water and the countercurrent flow of oil in porous rocks. The imbibition process is of practical importance in recovering oil from heterogeneous formations and has been studied principally by experimental means. Calculations were made for imbibition of water into both linear and radial systems. Imbibition in the linear systems was allowed to take place through one open, or permeable, face of the porous medium studied. ln the radial system, water was imbibed inward from the outer radius. The effects on rate of imbibition of varying the capillary pressure and relative permeability curves, oil viscosity and the initial water saturation were computed. For each case studied, the rate of water imbibition and the saturation and pressure profiles were calculated as functions of time. The results of these calculations indicate that, for the porous medium studied, the time required to imbibe a fixed volume of water of a certain viscosity is approximately proportional to the square root of the viscosity of the reservoir oil whenever the oil viscosity is greater than the water viscosity. Results are also presented illustrating the effects on rate of imbibition of the other variables studied. INTRODUCTION The process of imbibition, or spontaneous flow of fluids in porous media under the influence of capillary pressure gradients, occurs wherever there exist in permeable rock capillary pressure gradients which are not exactly balanced by opposing pressure gradients (such as those resulting from the influence of gravity). The importance of such capillary movement in the displacement of oil by water or gas was recognized in early investigations and described by Leverett, Lewis and True in 1942.1 Methods advanced by these authors for studying the process using dynamically scaled models were rendered more general and flexible by the research of later workers.2"4 The influence of capillary forces in laboratory water floods has also been discussed by several authors.6 While imbibition plays a very important role in the recovery of oil from normal reservoirs, Brownscombe and Dyes7 pointed out that imbibition might be the dominant displacement process in water flooding reservoirs characterized by drastic variations in permeability, such as in fractured-matrix reservoirs. In water-wet, fractured-matrix reservoirs, water will be imbibed from fractures into the matrix with a countercurrent expulsion of oil into the fractures. If the imbibition occurs at a sufficiently rapid rate, a very successful water flood can result; if the imbibition proceeds slowly the project might not be economically attractive. Scaled-model studies have demonstrated the vital importance of imbibition in secondary recovery in fractured reservoirs. It is therefore important in the evaluation of waterflooding prospects to develop a thorough understanding of the quantitative relationships of the factors which control the rapidity of capillary imbibition. The imbibition process serves reservoir engineers in still another important way by providing a technique for studying the wettability of reservoir core samples. Such experiments are usually conducted by observing the rate of expulsion of oil or water from core samples submerged in the appropriate fluid. Several papers have been 'published on the experimental techniques involved?? Although Handy has recently published a method for calculating capillary pressures from experiments with gas-saturated cores, it has not yet been possible to deduce quantitative information regarding water-oil relative permeability and capillary pressure characteristics of the rock from the experimental results. Thus a technique is needed for studying the quantitative dependence of imbibition rate on oil and water viscosity, initial water saturation, relative permeability-saturation, and capillary pressure-saturation relations. The development of such information, including saturation and pressure profiles by laboratory experiments, would be very difficult. However, recent advances in the applica-

Jan 1, 1965

By M. P. Tixier, F. Segesman

Explanations bused on theory and laboratory tests tire offered for certain unusual features of SP logs which may befog their interpretation, namely the "sawtooth" SP and the reduction or increase of SP with time. The sawtooth SP is frequently seen in SP recordings of thick, very permeable watcr. sands of the Louisiana Gulf Coast. Using SP data from a resistor network analog, this anomaly is explained on the basis of a thin shale streak within the sand. under which the invading filtrate accumulates by gravity segregcitiorr. The electromotive force then appearing across the shale streak gives rise to the anomalous SP. Reduction of the SP on successive logging runs Ira often been observed in very permeable sands when as indicated by the resistivity curves, the invasion depth has been reduced to practically zero. Laboratory results verify that this phenomenon may be due, to the presence of air electromotive force, across the mod rake when the fluids on either side differ in activity. Also, there is, in some cases; an increase of SP deflection on successive logging runs, because the emf initially present across the mud cake disappears as the somewhat saline water just behind the mud cake is progressively flushed out by the invading filtrate.. Field example and laboratory data are presented. I N T R ODUCT1ON Some unusual features are frequently observed on certain SP logs which make interpretation difficult. The purpose of this paper is to offer explanations of several cases of interest. All of these arc related to the conditions of invasion. The cases to be discussed are as follows. 1. The sawtooth SP anomaly which is frequently seen within the thick, highly permeable saltwater sands of the Louisiuana Gulf Coast 1. Reduction of the SP deflection from the usual sand line in very permeable sections when the depth of invasion is practically nil. As will be explained, such a reduction is attributable to a membrane electromotive force across the mud cake. 3. An increase of the SP with time just after the iormation is drilled as a result of progressive flushing of the invaded zone. FUNDAMENTALS OF SP PHENOMENA An explanation of SP phenomena must begin with the following basic ideas. 1. The SP log derives its character from ohmic potential differences in the hole produced by currents flowing through the mud.' These currents are driven by electromotive forces which are primarily electrochemical in origin. Other possible types of SP-producing electromotive forces may be disregarded for the purposes of this paper. 2. The electrochemical emf's associated with permeable formations are now understood to consist of liquid-junction emf's and membrane emf's.',' As schematically shown by thc battery symbols in Fig. 1, the liquid-junction emf, E,,,, exists at the contact between waters of different chemical activities, a,,,, (mud filtrate) and tr,,. (formation water); the shale membrane emf, lS.sn. exists across the adjacent shales whcn they separate waters of different activities. The emf's just cited are additivc in producing SP currents (arrowed circles of Fig. I). Thus, neglecting for the moment any possible membrane emf across thc mud cake, the total electrochemical emf, E,, will be given by their sum, where K,., -! K,q,, = 12 + 59, or 71 at 75 °F. In the log interpretations the SP of a thick sand (i.e.. the static SP) is generally related to the activities of the filtrate and formation water through Eq. 1. by setting the static SP equal to - E,.

By D. T. Peters

To better understand the Co-Mo interaction in maraging steels, the precipitate reversion behavior of two alloys closely related to the 18 Ni-250 grade has been studied. The reversion experiment is carried out by aging at a low temperature, T1 (preaging temperature), for some period of time and then aging at a higher temperature, T2, called the reversion tetnperature. Aging and reversion tmzperatures used were in the range 679 to 1050°F. Reversion is marked by an increase in resistivity and a decrease in hardness. It teas found that some reversion took place at all cornbinations of T1 and T2 but that pronounced rei3ersion resulfed for an Fe-18 pct Ni-5 pct Mo-8 pcl Co alloy exposed to preagz'ng' temperatures at or below 850°F. A similar alloy not containing cobalt exhibited no such discontinuity in reversion behazior with TI. The results are interpreted in terms of two types of molybdenum-rich precipitates, one nucleated at dislocations and the other in the matrix. The increased supersaturation resulting from the presence oj- cobalt evidently provides sufficient energy to nucleate the matrix phase. Anotnalies in the temperature dependence of the resistivity decrease and peak hurdness in the Fe-18 pct Ni-5 pct Mo-8 pct Co alloy as a junction of aging temperature noted in an earlier study are explained on this basis. SEVERAL investigatorsl-9 have studied the details of the precipitation-hardening reaction of the maraging steels. The great majority of conclusions have been drawn from transmission electron microscopy. Although much has been learned by this method, alternate techniques which will give information earlier in the aging process are needed for a more complete understanding of the series of precipitation steps probably involved in the aging reaction. Peters and cupp'' have recently shown, by measurements of the kinetics of precipitation, that an 18 pct Ni-Co-Mo maraging steel shows a distinct change in precipitation behavior at aging temperatures below 850°F. The results were interpreted in terms of the existence of two types of precipitates at low aging temperatures. Only one precipitate type is present at higher aging temperatures. The low-temperature precipitate was found to be a particularly effective strengthener. No evidence for the additional low-temperature precipitate was found in the 18 pct Ni-5 pct Mo ternary alloy. The object of this investigation was to study further the characteristics of the two types of precipitates and the interaction between cobalt and molybdenum characterizing this system. Some preliminary experiments indicated a difference in reversion behavior in specimens aged above and below 850°F. This suggested that knowledge of the reversion behavior might shed some light on these two questions. Hardy and Heal11 have defined reversion as the loss of hardness, electrical conductivity, or other properties caused by heating for a very short time at temperatures above the aging temperature. The precipitate reversion referred to in this paper is entirely distinct from "austenite reversion" often referred to in maraging steel literature. This latter phenomenon could more accurately be called the diffusion-controlled formation of austenite. Much has been written about reversion in several of the aluminum-base binary and ternary alloys.'2-16 Two explanations for reversion have been advanced. Based on the classical nucleation theory of Volmer-Weber-Becker-Doring,17 Konobeevski18 suggested that reversion was due to the size of the precipitate particles

Jan 1, 1968

By M. T. Simnad, R. F. Mehl, L. Yang

Techniques for studying marker movement in K-Rb interdiffusion have been worked out. The results indicate that Rb diffuses faster than K and that the ring mechanism of diffusion cannot be the dominant one operating in this case or probably in cases involving other alkali metals, despite their low ion core repulsive energies. SEVERAL theoretical attempts have been made in the past decade to elucidate the mechanism of diffusion in body-centered-cubic metals. No general agreement, however, has been reached by different authors. Zener,1 and later LeClaire,2 on the basis of a correlation between the entropy of activation for self-diffusion and the temperature dependence of the elastic constants, predicted that a ring mechanism should operate in the diffusion of body-cen-tered-cubic metals. Paneth3 calculated the activation energies of various ring, vacancy, and interstitial mechanisms for the self-diffusion in alkali metals and concluded that the most likely one was based on the linear motion of "crowdions," which is in fact a different form of interstitial diffusion. Fumi,1 however, showed that the experimental values of the activation energies for self-diffusion in the alkali metals could be better accounted for if the diffusion process in these metals was assumed to follow a vacancy mechanism. The same conclusion was reached by Kojima5 for the self-diffusion in lithium. Experimental evidences published during the past few years seem to exclude the ring mechanism as the predominating one in the diffusion of body-centered-cubic metals. For instance, maker movement has been observed in ß-brass, first in this laboratory" and later by Resnick and Baluffi.5 Shewmon and Bechtoldh also found marker movement in the body-centered-cubic system Ti-Mo and showed that the argument which led Zener and LeClair to favor a ring mechanism was not incompatible with a vacancy mechanism. In spite of this, it seemed to the authors that further experimental tests should be made by studying the Kirkendall effect in body-centered-cubic systems that characteristically have small ion core repulsion, such as the alkali-metal systems. Since the ion core repulsion term constitutes the main part of the activation energy needed for the rotation of a ring, such a test should be the most critical of all. The system K-Rb was chosen for experimental study because these metals form a continuous series of solid solutions. Experimental Investigation Owing to the extremely active nature of these two metals, a brass dry box (18 x 11 x 10 in.) was built for making the diffusion couple. It had a big lucite window on top, two side ports through which neo-prene-rubber gloves were inserted, and another side port covered with an optically flat-glass window for microscopic examination of the sample. Inside the box there were a circulating fan driven with a rotating horse-shoe magnet located outside the box, a heater used to generate potassium vapor for getter-ing the box, and a cold trap for keeping the inside of the box cool. Chemically pure grade K and Rb were triple distilled before they were transferred in vacuum into cylindrical steel molds kept in pyrex-glass ampules, Fig. 1. The latter together with the tools needed for making the diffusion couple were put into the dry box. After the box was flushed with purified argon and gettered with potassium vapor, generated from a heated steel crucible inside the box, the glass ampules were broken and the mound on the top of the alkali-metal ingot was cut off with a razor blade to yield a flat surface. To make the diffusion couple, one K ingot and one Rb ingot were pushed out of the molds together with their steel supports by screwing a metal plunger into the bottom of each mold. They were then laid on a brass cradle inside the assembling carriage (shown separately in Fig. 2) with the flat faces opposite to each

Jan 1, 1959

By O. C. Wheeler

Production in Colombia attained a new high during 1940 when it reached a total of 25,607,976 bbl. Of this amount, the Tropical Oil Co. produced 21;426,492 bbl., including 268,586 bbl. of petroleum condensate, and the Cololmbian Petroleum Co. produced 4,181,484 bbl. from its Barco property. The wildcatting program of different companies in the Magdalena Valley that was initiated during the previous year was continued but with results that were decidedly disappointing. Ten wells were drilled in the Magdalena Valley between the approximate latitudes of Puerto Wilches and Puerto Berrio and nine of these were dry; the tenth was a small producer of no commercial importance. The prospects of finding new fields in the Magdalena Valley thus received a serious setback, since some of the tests drilled were on well developed surface structures. The prospects of the Valley, however, have by no means been exhausted and drilling operations are being continued on other prospects. One additional wildcat was drilled outside the Magdalena Valley on the Colombian Petroleum Company's Barco Concession, which brought to 11 the total number of wildcats drilled in Colom-bia during the year. This well, known as

Jan 1, 1941

By C. T. Bischoff

DURING the past few years geochemical testing for traces of heavy metals in water, soil, rock, and vegetation has aroused increasing interest. Various techniques for field and laboratory determinations have been described in the literature, as have some of the results of application. However, little information has been published regarding application to glacial terrain. Over 90 pct of the Canadian Shield is overburdened, resulting in high costs for mineral exploration once the outcropping ore deposits have been found. This has been largely responsible for the widespread application of mining geophysics in Canada, permitting concentration of effort on area or zones considered most favorable. However, geophysical interpretation has its limitations, since at least 90 pct of the structures indicated thereby contain no valuable minerals. A more direct approach is therefore highly desirable. If underlying base metal mineralization can be detected by sampling soil or vegetation at moderate cost this should prove of great help in locating new discoveries or extending known ones. A large proportion of Canadian ore deposits contain appreciable copper or zinc, even where these are not the principal economic metals. Consequently the field of application is a broad one.

Jan 1, 1954

By O. C. Wheeler

Production in Colombia attained a new high during 1940 when it reached a total of 25,607,976 bbl. Of this amount, the Tropical Oil Co. produced 21;426,492 bbl., including 268,586 bbl. of petroleum condensate, and the Cololmbian Petroleum Co. produced 4,181,484 bbl. from its Barco property. The wildcatting program of different companies in the Magdalena Valley that was initiated during the previous year was continued but with results that were decidedly disappointing. Ten wells were drilled in the Magdalena Valley between the approximate latitudes of Puerto Wilches and Puerto Berrio and nine of these were dry; the tenth was a small producer of no commercial importance. The prospects of finding new fields in the Magdalena Valley thus received a serious setback, since some of the tests drilled were on well developed surface structures. The prospects of the Valley, however, have by no means been exhausted and drilling operations are being continued on other prospects. One additional wildcat was drilled outside the Magdalena Valley on the Colombian Petroleum Company's Barco Concession, which brought to 11 the total number of wildcats drilled in Colom-bia during the year. This well, known as

Jan 1, 1941

By F. H. Rhines, A. H. Grobe

The constitution of the indium-zinc alloy series has been investigated by Wilson and Peretti,1 who determined the liquidus and eutectic temperatures by the conven-tional method of cooling curves and the eutectic composition by analyzing eutectic exudations. Recent developments affecting the availability of indium and consequent increased interest in its applications make a more complete knowledge of the constitu- tion of its alloys desirable. As a part of a program far the reexamination of the constitution of indium alloys by precision methods, the indium-zinc phase diagram (Figs. I and 2) has been redetermined in its entirety. The eutectic temperature (I43. 5°C.) reported by Wilson and Peretti has been confirmed exactly, but their value of the zinc concentration at the eutectic, 4 per cent, was found to be high; the new value is 2.8 per cent of zinc. There is also a rather large difference between the forms of the liquidus curves of Wilson and Peretti and those found in the present studies. The solidus curves herein have been located for the first time and the limits of solid solubility have been tenta-

Jan 1, 1944

By A. H. Grobe, F. H. Rhines

The constitution of the indium-zinc alloy series has been investigated by Wilson and Peretti,1 who determined the liquidus and eutectic temperatures by the conven-tional method of cooling curves and the eutectic composition by analyzing eutectic exudations. Recent developments affecting the availability of indium and consequent increased interest in its applications make a more complete knowledge of the constitu- tion of its alloys desirable. As a part of a program far the reexamination of the constitution of indium alloys by precision methods, the indium-zinc phase diagram (Figs. I and 2) has been redetermined in its entirety. The eutectic temperature (I43. 5°C.) reported by Wilson and Peretti has been confirmed exactly, but their value of the zinc concentration at the eutectic, 4 per cent, was found to be high; the new value is 2.8 per cent of zinc. There is also a rather large difference between the forms of the liquidus curves of Wilson and Peretti and those found in the present studies. The solidus curves herein have been located for the first time and the limits of solid solubility have been tenta-

Jan 1, 1944

By A. H. Grobe, F. N. Rhines

THE constitution of the indium-zinc alloy series has been investigated by Wilson and Peretti,1 who determined the liquidus and eutectic temperatures by the conventional method of cooling curves and the eutectic composition by analyzing eutectic exudations. Recent developments affecting the availability of indium and consequent increased interest in its applications make a more complete knowledge of the constitution of its alloys desirable. As a part of a program for the reexamination of the constitution of indium alloys by precision methods, the indium-zinc phase diagram [ ] (Figs. I and 2) has been redetermined in its entirety. The eutectic temperature (143.5°C.) reported by Wilson and Peretti has been confirmed exactly, but their value of the zinc concentration at the eutectic, 4 per cent, was found to be high; the new value is 2.8 per cent of zinc. There is also a rather large difference between the forms of the liquidus curves of Wilson and Peretti and those found in the present studies. The solidus curves herein have been located for the first time and the limits of solid solubility have been tenta-

Jan 1, 1944

By F. G. Smith

A FEW years ago, the writer encountered a, problem that, at first, seemed to be due to peculiar conditions affecting grain growth. Large cups made from heavy metal failed in the first drawing operation in the process of making seamless tubes. The metal, as cast, appeared to be sound and strong; it rolled successfully and withstood the first cupping operation, but on the first draw it failed, with a crystalline fracture. The failure appeared in the slightly worked part of the bottom of the cup, and microscopic examination revealed exceptionally large grains. Knowing the general conditions governing recrystallization of brass, which were later published by Matthewson and Phillips, an investigation was outlined with the idea of including various conditions under which new grains might form, and which would include the effect that a previous anneal might have upon the anneal following. These conditions were produced by annealing specimens of brass at five different temperatures, indenting them with a 10-inn. ball under four different pressures, and then reannealing at each of the five temperatures five specimens each of which had been annealed at one of the five temperatures.

Jan 8, 1919

By AIME

Cores must be cut in half to secure workable samples for saturation, porosity, and permeability tests. They come from the field labeled as to the type of core, well, and depth from which they came.

Jan 1, 1948

By Earle Schumacher

THE solidus line above the solid solution field in the lead-antimony system was originally determined by Dean and his associates1 from heating curves. They did not regard this line as having been accurately fixed and in their more recent publications2 the curves drawn do not follow closely the original data. The precise location of the solidus line is of importance in the extrusion of lead-antimony cable sheath, as the temperature of the metal in this process must be less than the lowest temperature at which any part of the alloy in the lead-press charge becomes liquid. It is very desirable, however, to operate at as high a temperature as possible, as the rate of extrusion for a given pressure is approximately doubled for an increase of 10° C. in temperature. The precise location of this line is also important, in the investigation of ternary systems of lead, antimony and a third metal. For these reasons, and because of the differences reported in the literature, data were secured on the lead-antimony solidus line by the classical quenching-test procedure.

Jan 1, 1927

By D. H. Polonis, M. B. Kasen

AN unusual thermal etching phenomenon has been observed on the surface of a Cu-Si alloy. The observations were made during studies of vacancy condensation pit formation which were reported in previous papers.1,2 Figs. 1 and 2 are photomicrographs of the surface of a Cu-4.8 pct Si alloy after heating in vacuo (3 x X mm Hg) to 525°C and subsequently holding at that temperature for 16 hr in an impure (air-contaminated) argon atmosphere. Under these conditions preferential removal of silicon from the matrix by oxidation results in a surface which is entirely a phase overlying an a plus y structure. The light areas of Fig. 1 are regions in which very little thermal etching has occurred, while the majority of the surface has experienced severe etching. Similar regions in Fig. 2 are seen as plateaus above contours produced by net transfer of material from the specimen surface. Twin boundaries are also visible in Fig. 2. The difference in matrix mi-crostructure between Figs. l and 2 reflects the par- ticular orientation of low-index planes with respect to the surface of observation. Thermal etching contours of this type have been studied in detail by Hondros and Moore Both of the photomicrographs show that one or more dark spots are located approximately at the center of every protected area; where two spots are in close proximity, the protected areas have merged. The microstructures indicate that the anomalous resistance to thermal etching is related to the presence of these spots. Williams and Hayfield have shown that local regions of unusually high oxidation resistance can be caused by a surface monolayer of atoms with a work function higher than that of the base material. The result is an inhibition of the rate of electron removal from the base material and a decrease in the oxidation rate. The source of the protected layer may be either surface diffusion from contaminants on the specimen surface or pipe diffusion of solute atoms followed by migration across the surface. In the latter case the driving force is a difference in chemical potential resulting in a Gibbs adsorption phenomenon. In the present case, chemical polishing of the specimen surface precluded contaminants of a strictly surface nature. Consequently, diffusion of impurity atoms from within the lattice appears to be the most tenable explanation of the observed phenomena. The authors propose that the structures of Figs. 1 and 2 reflect the diffusion of impurity atoms along extended dislocations within the individual a phase grains prior to surface oxidation. The central spots within the protected regions are seen as sites of dislocation emergence which have become locally decorated with oxide in the manner discussed in Ref. 1. Williams and Hayfield observed protected regions adjacent to the grain boundaries of iron-contaminated copper which they attributed to the segregation of iron to the grain boundaries coupled with high dif-fusivity along the complex dislocation array at such boundaries. No evidence of such grain boundary protection was observed in the Cu-Si alloy; this

Jan 1, 1964

By R. J. Woody

Design of the most economic continuous counter-current decantation (CCD) circuit is based on selection of the number of stages and the wash volume that will give the minimum summation of the following items: 1) Capital and operating costs of the CCD circuit. 2) Capital and operating costs of the precipitation circuit. 3) Value of the dissolved product lost.

Jan 1, 1959

By J. L. Stokes, L. J. Demer

It has recently been shown' that epitaxial films of silicon carbide deposited on silicon single crystals possess desirable properties for semiconductor applications. There is one apparent disadvantage to such a system, however; since epitaxial deposition is a high-temperature process, it can result in plastic deformation of the silicon substrate. The accompanying Berg-Barrett X-ray diffraction photographs reveal plastic deformation in two silicon semiconductor crystals which occurred when the crystals were coated with an epitaxial layer of silicon carbide at 1150°C. Due to differences in thermal expansion between the silicon substrate and the epitaxial silicon carbide, the silicon was subjected to stresses while still in the plastic temperature range. Both crystals shown were 0.7 in. in diam and 0.0055 in. thick. The crystals were sliced from a larger crystal so that their polar axes were parallel to the [ill] direction. After cutting, the crystals were polished with diamond paste, and etched in HC1 vapor to remove surface damage re- sulting from the cutting and polishing operations. This provided clean, damage-free surfaces on which to deposit the silicon carbide. Figs. l(a) and l(b) are reflection and transmission photographs, respectively, of the same crystal. A smaller portion of the crystal is shown in the transmission geometry, because a vertical slit was

Jan 1, 1965

By Nelson P. Hulst

To those who have had the happy privilege of friendship with George W. Goetz, the announcement of his death has brought great sadness. He was born in Milwaukee, Wisconsin, February 17, 1855, and died January 15, 1897. In his boyhood days, when I first came to know him, his frank, trustful manner; his eyes brimming with truthfulness; his eagerness, never obtrusive, to gain knowledge from all whom he met; and his equal readiness to give without ostentation of his store, constituted a personality which at once commanded confidence and won friendship. I am told that as a scholar of five years he was conspicuous for brightness, a show-pupil, who was called on to recite when visitors were present at school. Yet this in no way spoiled him. His modesty was too strong a trait in his character to be overcome by any attention which might, be expected to arouse vanity. In his simple-heartedness he was pleased then, as he always was in his maturer years, to give of his knowledge for the gratification of his listeners, with never a thought of himself. So strong was this characteristic that in a brief autobiography, in the form of a letter to his wife and children, found among his papers, he excuses himself to them for recounting what he had accomplished in his life-work. As a preface to this autobiography (which, it seems, was prepared on the eve of a sudden journey to California, taken February, 1895, for his health) he says: " I am writing this rather hastily, and I

Jan 1, 1898