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By Edward C. Roper

Pegasus' Gold Ltd. operates two gold/silver heap leaching operations in the Little Rockies area of Montana. The Little Rockies has produced gold from underground operations on an intermittent basis from the 1880's to the early 1950's and from the open-pits on a continuous basis since 1979. Run-of-the-mine ore is drilled, blasted, sorted, loaded and hauled. The waste is dumped and compacted into 30 meter (100 foot) fills to be used for future leach pads. The leach pads have a central drain system and the impermeable membrane is constructed of bentonite and 30 mil PVC. The plants which have beenexpanded to 4900 Ipm (1300 gpm) capacity use the Merrill-Crowe process for gold and silver recovery. 4600 liters (1200 gpm) of the 9500 Ipm (2500 gpm) spray capacity is recycled through the old leach pads for upgrading before being processed. The gold/silver precipitate is smelted and the resultant dore' is shipped to a buyerhefiner. 1983 projected production is 2,177 kg (70,000 02s) of gold at a cost of less than $10/gm.

Jan 1, 1984

By Hsun Hu, R. S. Cline

In an earlier publication1 it was shown that a single crystal of Cu-4 wt pct Al cold-rolled in the (110)[112] orientation was stable up to 95 pct reduction, although the orientation spread was considerable larger than in a similarly oriented and cold-rolled copper single crystal. When rolled to 99 pct reduction, the copper crystal retained its initial orientation and a high degree of sharpness of texture, whereas the Cu-4 pct

Jan 1, 1969

PROF RICHARD ÅKERMAN Stockholm, Sweden ANDREW CARNEGIR New York, N.Y. DR. JAMES DOUGLAS New York, N.Y. PROF HATON DE LA GOUPILLIERE Paris, France PROF HANS HOEFER Leoben, Austria PROF HENRI LOUIS LE CHATELIER Paris France M FLORIS OSMOND Paris, France JOHN E. STEAD Middlesborugh, England PROF DIMITRY CONSTANTIN TSCHERNOFF St Petersburg, Russia CHARLES D WALCOT Washingtion D.C.

Jan 1, 1910

By Robert Maddin

crystal prior to, polishing in order to eliminate coring. This treatment may be accomplished by wrapping the single crystal tightly in very thin, dead soft, brass foil and annealing in the presence of air for 20 hr at 800°C. Since the wrapping encircles the sptcimen three to four times, only a very slight amount of oxidation occurs on the specimen surface. On unwrapping one of these cylindrical single crystals. in. in diam by ro in. long (72.75 pct cu, 27.23 pct Zn, 0.01 pct P11, 0.01 pct re), mall light-gray depnrrits in the form of circular arcs werenoted on the part nf the foil which had been in contact with the single crystal, Fig r. (By superim- approximatetl). These deposits, which, from their color, suggest the appearance of sublimated zinc, were found to coincide roughly with a set of octahedral planes nearly perpendicular to the rod axis. The pattern shorn in the figure held no relation to the profle of the sample since the markin~s on the crystal More annealing werc attributed to traces of cube planes. It seems very likely that the deposits were formed by sutllimation of zinc diffusing from octahrdral planes since diffusian would Eogically take place along planes of maximum atomic spacing. However, it is difficult to understand why a continuous sublimation of zinc should occur from a single crystat in contact with a wrapping roil OF the same composition, and why diffusion would take place along specific octahedral planes and in a regular pattern.

Jan 1, 1949

By C. E. MACQUICC

WITHIN a period considerably less than two decades, the engineering view of alloy steels has greatly changed-both as to their composition, and applications. Inasmuch as the elements used in manufacturing alloy steels are substantially the same as those which have been used for the past two or three generations, a statement like the foregoing may reasonably call for some explanation. The first commercial use of alloy steels in this country dates back to the sixties of the last century, when one of the earliest alloy steel patents, covering the use of chromium, was taken out by Bauer. About ten years later, German and French toolmakers began to introduce tungsten into tool steels. Developments along this line were more or less static for 25 years or more, the tool steel, compositions progressing along lines worked out by Mushet and one or two others in Europe. The next step in advance, made by Taylor and White inn the late nineties, consisted of heat-treating the alloy steels to enable much higher cutting speeds, thus introducing what soon became known as "rapid" or "high-speed" steels. All these developments being aimed toward the improvement of cutting tools, the compositions made were essentially of a hard, brittle nature. Following a different line of development started in the seventies, naval ordnance material began to embrace the nickel steels. These were rapidly popularized, became, and still are, with the addition of one or more elements, as chromium, molybdenum, vanadium, standard for heat-treated armor plate. During that period, however, no notable uses were made of alloy steels for engine parts or other high-stress parts where they are now considered indispensable; moreover, the present-day use of metals in the chemical industries was probably not even imagined. After the turn of the century, the necessity for making heavy-duty. machine parts, and especially the develop¬ment of the automobile, caused alloy steels to rapidly supplant plain carbon steels for engineering purposes.

Jan 1, 1930

By Kenyon E. Richard, James H. Courtright

SILVER Bell is situated 35 airline miles northwest of Tucson, Ariz., in a small, rugged range rising above the extensive alluvial plains of this desert region. Its geographical relation to other porphyry copper deposits of the Southwest is shown on the inset map in the lower left corner of Fig. 1. The climate is semi-arid. Altitudes range within 2000 and 4000 ft. Opening of the Boot mine, later known as the Mammoth, in 1865 was the first event of note in the district's history. Oxidized copper ores containing minor silver-lead values were mined from replacement deposits in garnetized limestone and treated in local smelters. Copper production had approached 45 million pounds by 1909 when the disseminated copper possibilities in igneous rocks were recognized. Extensive churn drill exploration carried out during the next three years resulted in partial de- lineation of two copper sulphide deposits, the Oxide and El Tiro. Although the then submarginal tenor discouraged exploitation of these disseminated deposits, selective mining of orebodies in the sedimentary rocks continued intermittently until 1930, providing a production total of about 100 million pounds of copper.

Jan 11, 1954

PRESIDENT OF THE COUNCIL ROBERT W. HUNT CHICAGO, ILL. (Term expires February, 1907 ) VICE-PRESIDENTS OF THE COUNCIL WILLIAM P. BLAKE TUCSON, ARIL. THOMAS F COLE DULUTH, MINN. IRVING A. STEARNS WLKES-BARRE, PA. (Term expires February, 1907 ) HENRY M HOWE NEW YORK, N. Y. J. B GRANT DENVER, COLO. JAMES D HAGUE NEW YORK, N. Y. (Term expires February, 1909 )

Jan 1, 1910

By H. P. Rassbach, E. R. Saunders

MUCH progress has been made in recent years in the theory and practice of making stainless steel. By effective utilization of oxygen for decar-burization and more suitable alloying agents, it has been possible to attain consistent production of very low-carbon stainless steel. In order to facilitate economical production of stainless steels, the Electro Metallurgical Co. has carried out an extended experimental program that has clarified some of the complex interrelations of temperature and composition under decarburizing and reducing conditions. These results'-:' have been founded in large part on small experimental heats, and in order to confirm their validity and significance under commercial conditions, a survey of stainless steel melting practice has been made with the cooperation of stainless steel producers. Conditions required for decarburization and associated oxidation of chromium, manganese, and iron have been fairly well established in relation to the beneficial effect of the highest practicable temperature. The recovery of chromium and manganese from highly oxidized slags by reduction with silicon has been indicated with somewhat less precision and this study has shown significant deviation in large commercial heats from the small experimental heats. In spite of an unsatisfactory degree of accuracy in estimating the conditions affecting reduction of metallic values, it has been possible to calculate a slag weight in reasonably good agreement with the results observed in large heats. While there still is much to be learned about both the qualitative and quantitative aspects of stainless steel melting, this survey has indicated the manner by which the efficiency of the production process may be measured. Oxidation Period In order to establish practices for the recovery of chromium and manganese from the slag the amounts of these metals oxidized should be known. Moreover, since reduction of oxidized chromium and manganese must necessarily be accompanied by similar reduction of iron, knowledge of the total quantity of metallics oxidized is essential. The relations between carbon, chromium, and temperature under oxidizing conditions were developed by Hilty in 1948.' While it had been realized previously that retention of chromium in the metal during carbon oxidation is favored by high temperatures, the Hilty relation provided quantitative information useful for evaluating melting procedures. For example, it was shown that decarburization to moderate carbon levels can be achieved while retaining substantial amounts of chromium. However, in decarburizing to the low-carbon level necessary for producing 0.03 pct maximum carbon stainless steel, very little chromium remains in the bath at the temperatures generally employed. For this reason, Hilty, Healy, and Crafts' later projected an extension of the chromium-carbon relation to the low-chromium region. Although this chromium-carbon-temperature relation defined the composition of a chromium steel bath at the end of the oxidizing period, it did not provide a direct means for estimating the total amount of metallic oxidation occurring during decarburization of a stainless steel heat. This subject was investigated by Crafts and Rassbach³ and, later, by Hilty, Healy, and Crafts" who demonstrated that metallic oxidation is a function of the chromium content of the initial furnace charge, the minimum carbon content attained, and the temperature. It was further demonstrated from data on 1-ton heats that an empirical relationship exists between the ratio of chromium plus manganese to iron in the slag (S) to the corresponding ratio of these components present in the metal bath. The following expression was derived to permit the calculation of the amount of metallics oxidized during decarburization of a given charge: W-2000 (Cr1 + Mn1)-(Cr2 + Mn2) 1 100s/s+1-(Cr3 + Mn2) where W is the pounds of chromium, manganese, and iron oxidized per ton of charge; Cr1, the percentage of chromium in the charge; Mn1, the percentage of manganese in the charge; Cr2, the percentage of chromium in the bath after oxidation; Mn2, the percentage of manganese in the bath after % Cr + % Mn oxidation; and S =%cr+ % Mn/%Fe in the slag after %Fe oxidation. In order to establish whether the slag ratios of commercial heats are consistent with those found in the experimental heats, the slag and metal analyses shown in Table I were evaluated. These data represent samples taken after the oxidation of two 1-ton and seven 15 to 25-ton heats of types 303, 304, and 304L stainless steel made in chromite, acid, and basic hearths. Fig. 1 illustrates that the results for the commercial heats correlate reasonably well with the relationship originally established for experimental 1-ton heats. It will be noted that in the range of metal composition of these heats, the slag values generally lie above the line. As was suggested by

Jan 1, 1954

By John G. Hall

The pumping operations at the Chief mine have been unique in the respect that for many years the entire flow of water into the mine has been disposed of by pumping into natural underground " caverns" or "sinks." Volumes up to 4000 gpm have been pumped into these caverns with no apparent tendency for the caverns to fill with water, and it has never been proven that any of the water returns to the mine workings. Major pumping operations have been carried on during two periods, the first from 1918 to 1927, and the second from 1942 to the present time.

Jan 1, 1949

By B. F. Oliver, F. Garofalo

Gas-metal heterogeneous reactions and zone-lrelting were sinultarneously employed to produce several high-purity irons with low interstitial contents in a levitating- zone melter. Successive zone-tneltitzg pusses were made in carious sequences of atmospheves which included prepuvified tank hy-drogeta, water vapor hydrogen, palladiuril-purified hydrogen, and vacuunm of 2 x 10-6 Torr. Different irons ranging in purity from 99.89 to 99.996 pct with residual curbon contents of 17, 8 to 10, and 3 to 5 ppm have been Drepared. No measuvable gradient in the residual carbon content was observed along the entire zone-melted length (6-10 in.) in I-ilz.-diameter bars. The absence of a carbon-concentration gradient in the solid indicates an apparent distvihution coefficient of 1, an unusual condition. Internal friction, solid-state extraction, and hot-hardness results indicate that the level of mobile carbon in a iron depends on the gas-metal heterogeneous reactions employed. Purification under an oxidizing atmosphere resulted in the immobilization of nearly all of the carbon present at leuels of 10 ppm or less. Continuation of purification in a reducing atmosphere veturued the carbon to a state of mobility which was aguin reversed by further purification in all oxidizing atmosphere. The immobilization of curbon at "vesidual levels " is believed to be associated with a strong interaction between carbon and oxygen atoms. frons with low carbon and nitrogen contetzts which did not exhibit a hot-hardness peak were produced after zone ynelting in vacuum. CARBON, nitrogen, and oxygen have strong and well-known effects on many properties of iron. These effects persist even at concentrations of 5 to 20 ppm. The intent of the present investigation was to establish procedures for the preparation of high-purity iron with concentrations of these elements in the range of 5 to 20 ppm and lower. The results reported here deal with the procedures employed to prepare high-purity iron, and with observations on the behavior of certain elements at "residual levels": particularly carbon. The details of the (levitating) zone melter in which the final purification steps are performed and the necessary control of the pertinent solidification variables have been described previously.1,2 MATERIALS AND PROCEDURES Commercial electrolytic iron was induction vacuum-melted and cast into 30-lb ingots. Melt additions and ingot analyses for carbon, oxygen, and nitrogen are noted in Table I. All ingots were melted in stabilized zirconia crucibles conditioned with one iron wash heat. Middle sections of the ingots were forged to 1-1/4-in. rounds, machined to 1-in.-diameter bars, then cut to 36-in. lengths. The zone-melting operations were performed on six iron bars (A to F) at a freezing velocity of 2 in. per hr with the freezing interface rotating2 at 200, 300, or 400 rpm. Liquid zones were passed through the bars in various sequences of atmospheres, Table 11, including prepurified tank H2, palladium-purified Hz, wet H2, and system vacuum of 2 x 1018 Torr. Wet-Hz atmospheres were obtained by bubbling palladium-purified Hz through water exhibiting a resistance of 3 megohms. This water was heated with a platinum-immersion heater and was degassed prior to use. Zone melting in a wet-HZ atmosphere resulted in oxidation of the elements which are oxi-dizable with respect to iron. Fine oxide particles were observed on the surface of the liquid zone, and were encased in the bar surface with the passage of the molten zone. Between each zone pass, the surface of the bar was removed by filing and deep etching; this was continued until the oxide formation ceased. The filings were magnetically separated and the residues analyzed by optical spectroscopy. These were especially high in silicon and manganese. Samples were removed from the iron bars, with few exceptions, following each zone-melting operation. A 0.08-in.-thick disc was cut with an Al2O3 cut-off wheel at a point 1/2 in. above the beginning of freezing. Material from each disc was used for hot-hardness measurements, resistivity-ratio measurements, and carbon, nitrogen, and oxygen analyses. Analyses for most other elements were

Jan 1, 1965

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 Thomas A. Simpson

THE Birmingham red iron ore district in Jefferson County, north central Alabama, Fig. 1, is bounded on the northwest by the Warrior and Plateau coal fields and on the southeast by the Cahaba and Coosa coal fields. The area of study includes the ridge and valley between Red Mountain and Shades Mountain, Fig. 2, approximately 70 square miles extending from Homewood in the northeast to Greenwood in the southwest. The district is one of the most important producers of hematite in the United States, with an annual production of about 7 million tons. The amount of hematite mined between 1870 and 1950 ranged from 6 to 16 pct of the nation's total annual production, and the iron and steel products from blast furnaces in the Birmingham district supply the entire southeastern section of the country.

Jan 1, 1955

By J. D. Sullivan, Chester R. Austin, J. L. Nunes

It is characteristic of most shales and surface clays that a bloated or vesicular structure is produced by burning to a sufficiently high temperature, usually about 150° to 200°F. above the normal maturing temperature used when making common brick of the same material. Early investi-: gators recognized this phenomenon and attributed it to the release or expansion of gases in the vitrified piece. A number of theories have been advanced on the source of the gas and the manner in which it is evolved, but none has been proved conclusively. T. E. Jackson's1 early theory that bloating was due to oxygen evolved by ferric oxide in forming ferrous oxide or ferrous silicate was never substantiated by - experimental work. Orton2 thought this explanation unlikely, as all clays should bloat at the same temperature, if this were true. He found that clays bloated in the range from IIoo° to 17oo°C. Also, many clays containing iron did not bloat at all, but fused. Orton also stated that oxida- tion of different types of carbon was a source of gas during burning of clay and should be expelled before vitrification was reached. Seger3 said that he had dissolved ferric oxide in glass with no apparent evolution of gas. Matson4 came to the conclusion that ferruginous clays burned ' to vitrification in an oxidizing atmosphere did not have the iron in a ferrous form. According to Wilson,= the gases responsible for bloating might be entrapped air, water, sulphur dioxide, carbon monoxide, oxygen, and hydrocarbons. He spoke of two causes of bloating: (I) incomplete oxidation below the vitrification temperature, and (2) decomposition of compounds and evolution of gases above the vitrification temperature. Decomposition of calcium sulphate was given as the principal example of the latter. Bleininger and Montgomery0 stated that if any time after vitrification began the evolution of gaseous matter was rapid enough so that pressure was produced within the clay, bloating was certain to take place, and a vesicular structure would be formed. They recognized that initial structure, rate of heating, kiln atmosphere, and many other variables affected bloating. Work done by the Emergency Fleet Corporation7 indicated that clays suitable for bloating should be high in compounds of metallic oxides, carbon, sulphur, sodium, potassium, or other equivalent compounds, which either act as a flux or give off gas. Orton2 studied the chemical status of the carbon, iron, and sulphur in clays during various stages of burning, using a Huron shale that bloated under oxidizing or reducing conditions. He found that only a small amount of sulphur remained in the clay and that it could be detected only by dissolving the clay in hydrofluoric acid; i.e., the sulphur was in combination with the silica. orton said that this sulphur was probably in the form of iron sulphide dissolved in the glass phase. The iron sulphide was not broken down by heating, but was dissolved in the basic slag or glass,

Jan 1, 1942

By J. D. Sullivan, Chester R. Austin, J. L. Nunes

It is characteristic of most shales and surface clays that a bloated or vesicular structure is produced by burning to a sufficiently high temperature, usually about 150° to 200°F. above the normal maturing temperature used when making common brick of the same material. Early investi-: gators recognized this phenomenon and attributed it to the release or expansion of gases in the vitrified piece. A number of theories have been advanced on the source of the gas and the manner in which it is evolved, but none has been proved conclusively. T. E. Jackson's1 early theory that bloating was due to oxygen evolved by ferric oxide in forming ferrous oxide or ferrous silicate was never substantiated by - experimental work. Orton2 thought this explanation unlikely, as all clays should bloat at the same temperature, if this were true. He found that clays bloated in the range from IIoo° to 17oo°C. Also, many clays containing iron did not bloat at all, but fused. Orton also stated that oxida- tion of different types of carbon was a source of gas during burning of clay and should be expelled before vitrification was reached. Seger3 said that he had dissolved ferric oxide in glass with no apparent evolution of gas. Matson4 came to the conclusion that ferruginous clays burned ' to vitrification in an oxidizing atmosphere did not have the iron in a ferrous form. According to Wilson,= the gases responsible for bloating might be entrapped air, water, sulphur dioxide, carbon monoxide, oxygen, and hydrocarbons. He spoke of two causes of bloating: (I) incomplete oxidation below the vitrification temperature, and (2) decomposition of compounds and evolution of gases above the vitrification temperature. Decomposition of calcium sulphate was given as the principal example of the latter. Bleininger and Montgomery0 stated that if any time after vitrification began the evolution of gaseous matter was rapid enough so that pressure was produced within the clay, bloating was certain to take place, and a vesicular structure would be formed. They recognized that initial structure, rate of heating, kiln atmosphere, and many other variables affected bloating. Work done by the Emergency Fleet Corporation7 indicated that clays suitable for bloating should be high in compounds of metallic oxides, carbon, sulphur, sodium, potassium, or other equivalent compounds, which either act as a flux or give off gas. Orton2 studied the chemical status of the carbon, iron, and sulphur in clays during various stages of burning, using a Huron shale that bloated under oxidizing or reducing conditions. He found that only a small amount of sulphur remained in the clay and that it could be detected only by dissolving the clay in hydrofluoric acid; i.e., the sulphur was in combination with the silica. orton said that this sulphur was probably in the form of iron sulphide dissolved in the glass phase. The iron sulphide was not broken down by heating, but was dissolved in the basic slag or glass,

Jan 1, 1942

By B. C. Raynes

IN the early part of 1952, under the auspices of the U. S. Atomic Energy Commission, Horizons Inc. undertook an investigation dealing with the preparation of high purity thorium metal in order to develop an economically competitive production process for this metal based on a recovery of the metal by a fused salt electrolysis, since a survey of the literature of thorium chemistry indicated that electrolytic methods had not received much attention, despite the consideration that electrochemical production methods often offer attractive commercial potentialities. Thorium metal has been prepared by methods which fall into four general categories: 1) reduction of halides or double halides; 2) reduction of the oxide; 3) thermal decomposition of halides; and 4) electrolytic methods. Some of the important results obtained by various investigators since about 1900 in recorded attempts to prepare pure thorium metal are summarized in Table I. A bibliography of pertinent literature is included in this paper. Thorium is strongly electropositive and possesses a great affinity for oxygen and nitrogen. As a result the prospects for the production of high purity thorium from aqueous media or oxygen bearing compounds are remote. The most promising and profitable area of investigation for production of thorium metal lies in fused salt electrolysis. Thorium has been produced previously by this technique from halide salts in fused alkali chloride eutectic mixtures. Until recently, however, the lack of known large uses for thorium has inhibited the investigation of these methods. The basic problem in an investigation into fused salt production methods for thorium is to develop a suitable fused salt system for the economic preparation of thorium. The first portion of the work in these laboratories was a small scale investigation of the electrolysis of potassium thorium fluoride, KThF5, under a variety of conditions. High purity thorium was prepared in this manner, but the process did not appear to offer the simplest and most attractive continuous commercial operation. The work reported here relates to an all-chloride system employing thorium chloride as the cell feed. ThCL4 was produced as an anhydrous material stabilized in molten sodium chloride. This product, further diluted in NaCl, was subjected to electrolysis. The electrolytic process has been studied in cells capable of holding up to 50 lb total salt charge. Ductile, pure thorium metal has been reproducibly obtained in this operation. Considerable experimentation was carried out in the preparation of ThCL as a cell feed free from moisture, oxides, and other impurities. Thorium was cathodically deposited as a coarsely crystalline powder interspersed with residual bath salts. Aqueous procedures for separating and recovering the metal were developed. The thorium metal powder obtained has been evaluated with respect to its hardness, chemical purity, and certain other physical properties. Preparation of ThC1,—Thorium chloride, and the chlorides of some other metals (aluminum, beryllium, tantalum, zirconium, etc.) cannot be obtained from aqueous solution by direct heating and evaporation. Evaporation and heating of a solution of thorium chloride yields a hydrated salt or partially hydrated salt, and finally Tho,. Anhydrous thorium chloride is obtained by forming a hydrated ammonium chloride complex salt in acidified water solution, dehydrating this compound, and finally decomposing the double salt and subliming the ammonium chloride component. Various methods for the preparation of anhydrous thorium chloride, in accordance with this concept, were investigated as indicated in Table I1 from hydrated thorium chloride (ThCl, . 3H2O), and from thorium oxycarbonate (ThOCO,). In the method found most satisfactory for this work, thorium oxycarbonate was dissolved in an excess of concentrated HC1 to give a clear yellow solution. At least 2 mol NH,Cl were added to the solution per mol of contained thorium. Ammonium thorium chloride hydrate was crystallized from solution by cooling and saturation with HC1. The resultant complex, (NH,Cl),ThCl;xH,O, was dehydrated by evaporation at 130° to 150°C and thoroughly dried at about 250°C. The dried ammanium thorium chloride was then mixed with sodium chloride in proportions to form NaThCL or to produce a ThCL4-NaCl mixture with a given thorium content. The ammonium chloride was sublimed off at temperatures above 500°C in an inert atmosphere furnace to give an anhydrous chloride source electrolyte, essentially free of Tho, and of NKC1.

Jan 1, 1958

By C. M. Schwartz, A. P. Young

ZIRCONIUM is noticeably embrittled at room temperature by hydride precipitate not only in notch-impact tests but also in tensile-impact tests.' The embrittlement in slow-strain tensile samples is much less severe. To understand better the relationship of the hydride precipitate to the strain-rate effect in tensile samples, the surfaces of chemically polished zirconium tensile samples strained at a slow rate (0.03 in. per min head speed) and at an impact rate (18.1 fps hammer speed) were examined in the light and electron microscopes. Vacuum-degassed samples and hydrogenated samples (100 ppm hydrogen) were examined. The hydrogenated samples were slow cooled from 800°C. The most apparent difference between slow-strain and impact tensile samples was the preponderance of twinning over slip in impact samples as opposed to relatively little twinning in slow-strain samples. The twin bands in hydrogenated samples often terminated on hydride needles as seen in Fig. 1. Almost opposite the twin terminus is a fine crack and a nearly round fissure. Holes near the areas where single lens-shaped twins or opposing pairs terminate on hydride particles also could be seen In the light micrbscope. Quite frequently, microcracks associated with a partial row of hydride particles were visible, as in Fig. 2, indicating that the crack was parallel to a row of hydride particles. Some samples were chemically polished after straining to remove metal with a minimum of disturbance of internal voids. Fig. 3 shows a crack in the interior of a hydrogenated impact sample. Holes along grain boundaries were seen after impact in both degassed and hydrogenated samples. Very few microcracks were seen in degassed samples after impact or slow strain, or in hydrogenated samples after slow strain.

Jan 1, 1959

By R. E. Smallman

R. E. Smallman (University of Birmingham, England)—Recently, Tedmon and Ferriss11 have determined the yield stress parameters oi and ky for tantalum by measuring the lower yield stress as a function of grain size 2d and fitting the results to a relationship of the form They report that although ky , which is taken to be a measure of the dislocation locking strength, is small (- 2 to 4 x 106 cgs units) a substantial yield drop is nevertheless observed in a normal tensile test. Niobium gives a similar result,12-14 as pointed out in the original work by Adams et a1.,12 and in order to check this apparent anomaly the yield-stress parameters of electron beam-melted niobium have recently been reanalyzed15 by the Luders strain technique. In this method the strain hardening part of the stress-strain curve is extrapolated to zero plastic strain; the intercept on the preyield portion of the curve is taken to give oi, whilst the difference between oi and the lower yield stress gives kyd-1/2. The results indicate that ky increases with increasing grain size and hence, a plot of vs d-112 yields an apparent ky, which is lower than the true value. A similar effect could account for the small ky found in the relatively pure tantalum used by Tedmon and Ferriss. The variation of ky with grain size shows that dislocations are more strongly locked in coarse-grained specimens than in fine-grained samples. In niobium, this may be attributed to the fact that the dislocation density in the fine-grained material is higher than that found in the coarse-grained samples which are given a sufficiently prolonged anneal to remove any residual substructure and, since the metal contains only a small amount of interstitual impurity, a variation in locking occurs. By contrast, application of both the grain size analysis and the Luders strain method to yield-stress data from commercially pure vanadium containing a large amount of interstitial impurity gives consistent values of oi and ky, with ky independent of grain size and temperature. Electron microscope observations show minor variations in dislocation density from grain size to grain size, but in any case in this material the dislocations are heavily locked with precipitate. On yielding new dislocations are generated and, as a consequence, the importance of any differences in dislocation density between the various specimens of different grain size is considerably reduced. It is perhaps significant that Adams and lannucci,16 working with a grade of tantalum containing a higher interstitial content than that used by Tedmon and Ferriss, prepared the specimens of different grain size by annealing in the temperature range 1500" to 2000° C to minimize any differences in dislocation structure, and found that ky had a value of 1.04 x 107 cgs units, independent of testing temperature. Such behavior is consistent with the dislocations being locked by carbide precipitates so that the generation of free dislocations is an athermal process. The recent work of Gilbert et al.17 also shows that in tantalum there is no significant variation of ky with grain size provided it contains 150 ppm of oxygen. In this case, however, the dislocations are not locked by precipitate and ky is temperature dependent. C. S. Tedmon and D. P. Ferriss (authors' reply)— We would like to thank Dr. Smallman for his interesting comments and discussion to our paper, "The Dependence of Yield Stress on Grain Size for Tantalum and a 10 pct W-90 pct Ta Alloy".18 It was suggested that perhaps the relatively small values obtained by us for ky of tantalum could be attributed to the same cause that accounts for the apparently small values of ky that result when it is determined by the Luders Strain technique. Since our values were obtained by plotting the lower yield stress vs the reciprocal of the square root of the grain size, it is not clear how this could be the case. The values of ky in this experiment have been calculated, using the Luders strain technique. With this method, values for ky on the order of 2 x 105 to 5 x lo6 cgs units were obtained. In spite of this rather large variation, the magnitudes are still small, and there appeared to be no good correlation between ky and the grain size or the yield stress, probably because of the difficulty in accurately extrapolating the work-hardening portion of the curve back to zero plastic strain. As was shown in the original data,18 there was little work hardening in any of the curves, at any temperature. In his discussion, Dr. Smallman also points out how ky has been observed to increase with increasing grain size, when determined by the Luders strain technique. There are at least two possible explanations for this. In the first case, if it is assumed that the bulk of the interstitial impurities are concentrated at the grain boundaries, then, of course, the available grain boundary area would decrease with increasing grain size, thus presenting less area for the interstitials, which would then presumably increase the concentration within the grains, thereby increasing the locking of the dislocations. In the second case, the increase in ky with increasing grain size would be attributed to the nature of the grain boundary itself. One of the several ways of deriving the Hall-Petch equation19 is based on the stress concentration arising from a pile-up of dislocations at the boundary. The ability of the stress concentration to unlock a source in a neighboring grain would depend on the strength of the grain boundary. As is well-known, the nature and struc-

Jan 1, 1963

Masjid-i-Sulaiman Field.—During the past year, drilling activities have been limited to repair work. No new developments of importance can be recorded in production technique. Fall of dome pressure is maintained at the 1 lb. per sq. in. per annum rate mentioned in previous reports. Acid treatment of wells is being increasingly used and for wells in fissured areas has been very successful. Such wells have been converted into first-grade producers with substantial drops in bottom-hole differential pressures. The effect of acid treatment has been to increase the flowing lives of wells so treated. The normal procedure consists of threo treatments of 500 gal. commercial acid diluted 100 per cent but success has been met with fewer applications. The policy of returning products to the resorvoir has been continued. The total quantity of products returned since the policy was commenced in 1929 now amounts to approximately 30 million barrels. Haft Kel Field.—The drilling of the main Haft Kel structure for production purposes has now been completed. Production and control wells have been completed to meet the rate of production anticipated over the next few years.

Jan 1, 1937

By E. W. Newman

During 1943 and 1944, there was an urgent need for certain grades of optical calcite (Iceland spar) for instruments for ' military uses. To find a supply of this material, prospecting was carried out in Montana, California and Colorado. Although some production was obtained by the work in California, the best results were from prospecting the large calcite veins of south central Montana. The bulk of the optical calcite mind during World War II has come from that area. The Bureau of Mines took an active part in the search for optical calcite in Montana. It examined most of the known calcite veins in the 70-mile distance between Wilsall, on the Shields River: and Absarokee, on the Still water River, and conducted exploration on several of the deposits. The Geological Survey also took an active part by mapping many of the veins. Actual mining of the calcite was performed at first by Calcite Operators, Inc., and later by the Metals Reserve Co., through an agent. A sorting plant was established at Clyde Park, where custom material could be sold. These activities stimulated mining by private operators. To be suitable for military uses, the calcite mined had to meet rigid specificstions as to both size and quality. Individual crystals had to be clear and transparent and if in the form of rhombs had to measure at least 7/8 in. on each edge. Some color and a few inclusions in the calcite were allowable, but material with incipient or developed cleavages, or showing twinning other than parallel to the base, was unacceptable. History of Deposits The existence of large veins of calcite in south central Montana has long been known, and for many years the farmers of this region have used the common vein calcite for producing grit for chicken feed. According to reports, the fist optical calcite produced from Montana came from the Cartwright deposit near Grey-cliff,' but until recently the mining of optical calcite in Montana has been limited to spasmodic searching for small crystals suitable for making nicol prisms for saccharimeters and microscopes, or for mineral specimens. The possible need of substantial amounts of optical calcite for military uses began to appear late in 1942 and early in 1943, therefore the Polaroid company began searching for a source of supply in Montana and California. Work on the Wade property near Clyde Park was started on a small scale in the fall of 1942, by .4. H. Hansen, of Clyde Park. During the winter and spring of 1943, a modest quantity of optical calcite was mined and shipped to the Polaroid Corporation, Cambridge, Mass. Most of this was produced from the "Hansen vug," which was found close to the surface. Early in the summer of 1943, mining on the Wade property was undertaken by Calcite Operators, Inc., a company organized for mining optical calcite from the

Jan 1, 1948

By E. W. Newman

During 1943 and 1944, there was an urgent need for certain grades of optical calcite (Iceland spar) for instruments for ' military uses. To find a supply of this material, prospecting was carried out in Montana, California and Colorado. Although some production was obtained by the work in California, the best results were from prospecting the large calcite veins of south central Montana. The bulk of the optical calcite mind during World War II has come from that area. The Bureau of Mines took an active part in the search for optical calcite in Montana. It examined most of the known calcite veins in the 70-mile distance between Wilsall, on the Shields River: and Absarokee, on the Still water River, and conducted exploration on several of the deposits. The Geological Survey also took an active part by mapping many of the veins. Actual mining of the calcite was performed at first by Calcite Operators, Inc., and later by the Metals Reserve Co., through an agent. A sorting plant was established at Clyde Park, where custom material could be sold. These activities stimulated mining by private operators. To be suitable for military uses, the calcite mined had to meet rigid specificstions as to both size and quality. Individual crystals had to be clear and transparent and if in the form of rhombs had to measure at least 7/8 in. on each edge. Some color and a few inclusions in the calcite were allowable, but material with incipient or developed cleavages, or showing twinning other than parallel to the base, was unacceptable. History of Deposits The existence of large veins of calcite in south central Montana has long been known, and for many years the farmers of this region have used the common vein calcite for producing grit for chicken feed. According to reports, the fist optical calcite produced from Montana came from the Cartwright deposit near Grey-cliff,' but until recently the mining of optical calcite in Montana has been limited to spasmodic searching for small crystals suitable for making nicol prisms for saccharimeters and microscopes, or for mineral specimens. The possible need of substantial amounts of optical calcite for military uses began to appear late in 1942 and early in 1943, therefore the Polaroid company began searching for a source of supply in Montana and California. Work on the Wade property near Clyde Park was started on a small scale in the fall of 1942, by .4. H. Hansen, of Clyde Park. During the winter and spring of 1943, a modest quantity of optical calcite was mined and shipped to the Polaroid Corporation, Cambridge, Mass. Most of this was produced from the "Hansen vug," which was found close to the surface. Early in the summer of 1943, mining on the Wade property was undertaken by Calcite Operators, Inc., a company organized for mining optical calcite from the

Jan 1, 1948