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By J. B. Cheatham, R. B. Paslay

Rock stresses and steady-state flow rates induced by the pressure gradient associated with the flow of formation fluid into a borehole have been analytically determined for a permeable, elastic material saturated with an incompressible fluid. In this analysis, the material properties and loading are considered to be symmetric about the axis of the borehole and independent of axial position. For Case I the material is assumed to have uniform permeability in the radial direction, whereas for Case 11 the permeability is assumed to have been reduced in a localized region adjacent to the hole by either normal well completion and production operations or deliberate plugging during air drilling. Results of a numerical example indicate that, in the absence of plugging, the rock shear strength must be approximately two-thirds the formation fluid pressure in order to prevent rock failure. The required rock strength is high for small radial zones of plugging and decreases as the region of reduced permeability becomes larger; however, a depth of plugging can be reached beyond which there is no real gain in strength, although the flow rate can be further reduced. INTRODUCTION During normal production of oil from a well, it is often desirable to increase the production rate of the formation fluid by increasing the pressure gradient through the formation adjacent to the borehole. Depending upon the magnitude of this pressure gradient and strength of the rock material, this production-rate increase can cause sloughing of the hole wall. In many cases, the production - rate increase can result in excessive sand production, increased wear of production equipment, lost production time and expensive workover jobs. In addition, the phenomenon of increased rock bit penetration rate with the use of a gaseous instead of a liquid drilling fluid has been observed in oilfield drilling operations and experimentally demonstrated by various investigators for several years. The improvement obtained by employing this technique can be quite significant and offers apromising method for reducing drilling costs. However, air drilling is currently limited to geographical locations where high-capacity water-bearing formations are not encountered. This limitation has prevented widespread adoption of air-drilling techniques, because the water influx into the borehole interferes with efficient removal of the drilling cuttings and usually results in a condition such that the bit becomes "balled-up" or stuck in the hole. In an attempt to remove the water - intrusion limitation from air drilling, various chemical and mechanical water shut-off methods have been proposed. Goodwin and Teplitzl suggested one such proposal whereby the permeability of the water-bearing rock structure was reduced in the vicinity of the borehole. Although the development of a shut-off method based upon this approach would certainly be welcomed by the oil industry, it is conceivable that, under certain conditions of the pressure gradient, strength of the rock material and depth of the modified permeability zone, a stress field can be created that will result in an unstable hole. As part of their study, an analytical solution is given for stresses in an idealized model of a hole and the surrounding rock material. The purpose of the present study is to extend the analysis of Goodwin and Teplitz to gain more insight into the details and consequences of excessive production rates and formation water shut-off. In particular, simplified models of these problems have been analytically examined, which makes possible the evaluation of the type of stress fields that can be anticipated as a result of these production and drilling practices. Both problems solved concern the determination of the steady-state volume flow rate of the formation fluid and the resulting steady-state stress and displacement distribution in a hollow, cylindrical configuration. The cylinder of Case I, corresponding to the production-rate problem, consists of a material with a constant permeability from the inside surface to the outside surface; the cylinder of Case 11, corresponding to the water shut-off problem, consists of a material with a constant permeability from the inside surface to an intermediate concentric cylindrical surface and a second constant permeability from the intermediate surface to the outside surface-

By AIME AIME

AT the seventeenth National Metal Congress, held at Chicago, Oct. 1-3, the Iron and Steel Division and Institute of Metals Division participated with the American Society for Metals, American Welding Society, and the Wire Association in one of the most successful meetings ever held. The total attendance at the technical sessions and the scope of and interest shown in the exhibits at the Exposition were greater than at any of the "Metal Weeks" since the depression began. The Iron and Steel Division held two all-day symposia and one general session. The latter, at the International Amphitheatre, Wednesday afternoon, was the only one poorly attended. This was attributable, at least partly, to the location of the meeting roan.

Jan 1, 1935

By Luis Emylnn Salas

If the ordinary wet method be attempted for silver-bullion containing tin, much trouble is experienced, varying with the amount of tin present. Even with a percentage as low as 0.05, the end-point is masked by a persistent turbidity, while with amounts ranging from 0.5 per cent. upward, the determination of the exact end-point is impossible, owing to the finely divided or colloidal metastannic acid resisting all efforts to cause it to settle, or to give a clear supernatant liquid. The object of the following experiments was to seek a remedy for these difficulties, and to find the conditions whereby the Gay Lussac method might be applied directly to these bullions. Material containing tin is met with frequently in bullion from Mexico or Bolivia; and tin is carried (sometimes in large quantities) in jewelers' sweeps. 1. A bullion was prepared containing Ag, 74; Cu, 25; and Sn, 1 per cent. A weighed amount was treated by the humid assay-method as if it were an ordinary bullion free from tin. Ten cc. of HNO, (1.21) was added, and the bottle was heated until all traces of

Jan 1, 1913

By A.A. Grubb, F.L. Wolf

The tests here described were rrlade to obtain information regarding costs, efficiency, etc. of baking cores in an oil-fired oven and two electric ovens, which were installed, early in 1920, in the core room of The Ohio Brass Co. and were used almost continuously during the rest of that year. Operating costs were rather high so a complete test was undertaken early in 1921. The ovens will be referred to as Nos. 1, 2, and 3. Nos. 1 and 2 are electric ovens of different makes while No. 3 is an oil-fired oven made by the firm that made No. 2. The three arc. equipped with similar ventilating devices. They have full-height doors at front and rear. The cores are placed on iron racks, which arc lifted by Cowan trucks and rolled into the ovens through the front doors. When baked, they are removed through the rear doors. Fig. 1 shows the general plan of the elecric ovens while Fig. 2 shows the plan of the oil-fired oven. Oven No. 1 is 91 in. (231 em.) wide, 83 in. (210 em.) high. and 79 in. (200 cm.) deep, inside measurements. The walls are constructed ill panels about 18 in. (46 cm.) wide and 43/16 in. (10.6 em.) thick, packed with blocks of insulating material and covered with sheet iron. Thc concrete floor oil which the owns set is 13 in. (33 cm.) thick. 4 recess about 5 in. (13 cm.) deep was cut in the floor to provide room for the heating units. Channels and plates supported on I beams serve as supports for the trucks and racks. The ventilating system consists of a Sirroco No. 11/2 fan, connected so as to draw air from the top of the oven or from the room, through damper C, and to deliver it either to the bottom of the oven or to the floor; the delivery is controlled by the vane A. The fan 2nd pipes are covered with 1/4-in. (6.3 mm.) asbestos-cement lagging. The heating units have a capacity of 91.4 kw. and arc located along

Jan 1, 1923

By F. L. Wolf, A. A. Grubb

The tests here described were rrlade to obtain information regarding costs, efficiency, etc. of baking cores in an oil-fired oven and two electric ovens, which were installed, early in 1920, in the core room of The Ohio Brass Co. and were used almost continuously during the rest of that year. Operating costs were rather high so a complete test was undertaken early in 1921. The ovens will be referred to as Nos. 1, 2, and 3. Nos. 1 and 2 are electric ovens of different makes while No. 3 is an oil-fired oven made by the firm that made No. 2. The three arc. equipped with similar ventilating devices. They have full-height doors at front and rear. The cores are placed on iron racks, which arc lifted by Cowan trucks and rolled into the ovens through the front doors. When baked, they are removed through the rear doors. Fig. 1 shows the general plan of the elecric ovens while Fig. 2 shows the plan of the oil-fired oven. Oven No. 1 is 91 in. (231 em.) wide, 83 in. (210 em.) high. and 79 in. (200 cm.) deep, inside measurements. The walls are constructed ill panels about 18 in. (46 cm.) wide and 43/16 in. (10.6 em.) thick, packed with blocks of insulating material and covered with sheet iron. Thc concrete floor oil which the owns set is 13 in. (33 cm.) thick. 4 recess about 5 in. (13 cm.) deep was cut in the floor to provide room for the heating units. Channels and plates supported on I beams serve as supports for the trucks and racks. The ventilating system consists of a Sirroco No. 11/2 fan, connected so as to draw air from the top of the oven or from the room, through damper C, and to deliver it either to the bottom of the oven or to the floor; the delivery is controlled by the vane A. The fan 2nd pipes are covered with 1/4-in. (6.3 mm.) asbestos-cement lagging. The heating units have a capacity of 91.4 kw. and arc located along

Jan 1, 1923

By John S. Brown

The northeastern United States embraces that area of the Appalachian Mountains, and adjacent territory, beginning on the south at the Potomac River. It thus extends from the flat-lying Paleozoic terrane of the Appalachian plateau on the west, across the folded Paleozoics of the Great Valley and adjacent ridges (Paleozoic and Precambrian), over the Piedmont and New England metamorphic complex (mixed Paleozoic and igenous rocks), broken by the great Triassic rift remnants, onto the subdued coastal plain of Cretaceous and Tertiary sediments. Although not noted as a metal mining region, the area does contain numerous substantial and several outstanding mines, chiefly of the more prosaic metals, particularly iron, zinc, and copper, as well as many minor occurrences of these and a few additional items. These deposits occur to some extent in every subdivision of the area. The region to date (1966) has produced almost 500,000,000 tons of medium to lowgrade iron ore, especially magnetite, including ilmenitic magnetite; 50,000,000 tons of highgrade zinc ore; and 5,000,000 tons of lowgrade copper. In the past, it has yielded small amounts of chromite and nickel, and at present is a large producer of titanium. Precious metals are conspicuously absent, and so also are the Tertiary or Mesozoic igneous phenomena so commonly associated with mines of the West. Hence, a survey of the extensive mineralization · of this region should be instructive

Jan 1, 1968

By W. R. Clark, W. W. Cotter

Jan 1, 1946

By W. W. Cotter, W. R. Clark

Jan 1, 1946

By Cyril Wells, Robert F. Mehl

THE practical importance of a knowledge of the rates of diffusion of carbon and of alloying elements in steel has often been pointed out 1,13 This importance ties chiefly, though by no means only, in the study of carburizing and in the study of reactions involved in the eutectoid inversion in steel The present paper is one of a series in which the rates of diffusion of carbon and of alloying elements in y-Fe and their mutual effects are measured with precision The present paper reports the results of meas¬urements of diffusion coefficients D of manganese in -y-Fe over wide ranges of temperature, and concentration, and of the effect of carbon and impurities and of grain size upon these diffusion coefficients [$] Data on the rate of diffusion of manganese in y-Fe have been reported by Fry2 and by Paschke and Hauttmann 3 Claussen4 calculated the diffusion coefficient D from Fry's data as 3 X 10-10 sq cm per sec at 960°, which will be shown to be incorrect by many orders of magnitude Paschke and Hauttmann gave a rough value of 9 6 X 10-8 sq cm per sec at 1400° Neither of these workers considered the variation of D with concentration and with temperature, and neither studied the effect of carbon METHOD AND MATERIALS Method -The method employed is identical with that used earlier 5 Owing to the volatility of manganese and the consequent loss of manganese from the outer surfaces of the welded diffusion bars, these surfaces were discarded The diffusion anneals were performed in argon, except one (test 18) in which hydrogen was employed for purposes noted below The temperatures reported are accurate to about 3° and constant within I°C , the diffusion times are reported to the nearest half hour The specimens were furnace-cooled after the diffusion anneal at about 2° per min Layers, usually 0 004 in thick, parallel to the welded interface, were machined from the specimens after the diffusion anneal and analyzed for manganese to 0 01 per cent Mn, the distances of these layers from the interface was measured to ±0 0002 in The concentration-penetration curves obtained were analyzed by both the Grube and the Matano solutions e The D values calculated by these two methods do not differ appreciably 5 The Grube solution was used except in tests in which the effect of concentration upon D was greater than 50 per cent, in such cases the Matano method, which explicitly provides for the variation of D with concentration,1 is the more reliable In general, the number of layers machined from the zones of variable composition were large enough to permit the use of the average layer composition as that of the center of the layer In 3 of the 30 tests, however, this is not justified, and the D values

Jan 1, 1941

By E. R. Morgan, J. C. Shyne, V. F. Zackay

NITROGEN used as an alloying element in steel has received increased attention in recent years. Its merit as an austenite stabilizer and hot strengthener has long been recojinized, particularly by European investigators.' Recent work' indicates that nitrogen contents of 1/2 pet or more allow the addition of several percent of ferrite-forming hot strengtheners, such as molybdenum, without subsequent austenite decomposition at elevated temperatures. The room temperature properties of such alloys are characterized by high yield and tensile strengths with excellent ductility, even after cold working, as shown in Tables I and 11. The 1350°F creep-rupture properties of Cr-Mn-Mo-N steels are comparable to those of commercial alloys such as Timken's 16-25-6, containing 16 pct Cr, 25 pct Ni, and 6 pct Mo, as shown in Table 111. Cr-Mn steel containing 1/2 pet N must be made under pressure if ingot gassing is to be avoided. However, there are difficulties attendant to this practice. Pressure melting restricts the ingot size, and the equipment required is costlier and more complicated than comparable air melting facilities. An effort was made, therefore, to determine more economical methods of adding nitrogen. The pressures generated in centrifugal casting usually range from 5 to 10 atm and are sufficient to prevent the gassing of high nitrogen Cr-Mn steels. A centrifugal casting was made of an alloy containing 16 pct Cr, 18 pct Mn, 2 pct Mo, and 0.73 pct N. A risk, 8 in. diam and 11/2 in. thick, was cast at 1000 rpm. It has been calculated that a pressure of 9 atm was developed at the periphery of the disk at this speed. Metallographic inspection of specimens taken from the disk revealed no gas holes or other defects. The elevated temperature properties of radial and circumferential specimens taken from this casting are given in Table IV. The creep-rupture life of this cast nickel-free austenitic steel was equivalent to that of the wrought Cr-Mn-Mo-N steels. Although centrifugal casting appears to lend itself to the manufacture of high nitrogen austenitic steels, its applicability is limited to relatively small sizes. A process applicable to the production of large ingots of high nitrogen steels is suggested by low carbon rimming steel practice. Gas holes formed during ingot solidification are not detrimental so long as they weld shut during hot rolling. An economic advantage of gassing ingots is the increased ingot-to-slab yield, especially if the ingots are mechanically capped. Also, it is probable that higher nitrogen levels can be achieved with mechanically capped ingots than with hot-topped ingots. A series of gassy heats was made under both atmospheric and higher pressures, as indicated in Table V. Several of the air melted ingots were mechanically capped by chilling the molten ingot tops with a steel plate. The ingots were allowed to freeze in steel molds without hot-tops unless otherwise indicated. A comparison of Table 111 with Table V shows no significant difference in the creep-rupture properties of the gassy and the nongassy ingots after hot work- ing nor between the gassy ingots produced under different conditions. References 1 F. Rapatz: Application of Stainless and Heat Resisting Steels Alloyed with Nitrogen. Sinhl and Eisen ( 1941) 61, pp. 1073-1078. 'V. I?. Zackay, J. F. Carlson, and P. L. Jackson: High Nitrogen Austenltlc Cr-Mn Steels. Trans. ASM 119551 48, PP. 509-523.

Jan 1, 1957

By F. W. Bradley

MY first Nevada City mining reminiscence is one of seeing Capt. Thomas Mein, over 52 years ago, in the old Wyoming mill on Deer Creek about a mile below the town of Nevada City. Captain Mein was then superintendent of the Wyoming mine, where the old fashioned Cornish pump was used, as well as hurdy-gurdy water wheels for power. This mill was one of the typical, up-to-date mills of that time and consisted of stamps, fed by Chinese hand feeders, who also cobbed the ore down to a small enough size to be fed into the mortars. Stamps at that time were of light weight and crushed about one ton to one and a half tons to the stamp, the pulp going over plates, then into sluices with self-raising gates. When a sluice became full the pulp was shut off and directed into the parallel sluice, also with a self-raising gate. The concentrate thus collected in the sluice was shoveled out and carried to Cornish buddles and there cleaned up, preparatory to being sent to a local custom chlorination works.

Jan 1, 1929

By Frederic Dewey

(New York Meeting, February, 1913) This old and well-known method of determining, silver is, in bullion work, so far superior to the furnace-assay that it is looked upon with reverential awe by many, if not by most, users, and its-ease of execution, with proper equipment, commends it highly where much commercial bullion work on silver is required. The method is so thoroughly well known that a, description of it here may seem to be unnecessary, but many thousands of determinations are annually made by it in the U. S. Mint Service and its practice is there reduced to an art. This is necessary both for the sake of economy of time, acid because high-grade work with it requires constant practice. It is useless for a person who uses it only occasionally to expect to attain high accuracy with it, without spending more time upon a determination than is warranted in a busy commercial laboratory. It is always employed in the Mint service whenever possible, but its chief field is in the determination of silver in standard silver (ingots and coin), which is 900 fine in silver and 100 fine in copper, and I shall first briefly outline its use on this metal and then take up various points in detail, especially as related to the accuracy of the results obtained.

Jan 4, 1913

By Hermsdorf, Richard P. E.

AMONG the newer lead smelting and refining plants of the country is that of the United States Metals Refining Co., at Carteret, N. J. Not only is the technical practice here modern and efficient, but exceptional care is taken to assure healthful operating conditions for the employees. One large building houses the entire department, which includes, as its chief units, one reverberatory smelting furnace, one blast furnace, two softening furnaces, one utility reverberatory furnace, two Faber du Faur retorts, five 120-ton kettles, three 60-ton antimouial lead kettles, and one 5-ton kettle for experimental purposes. There is a 10-ton overhead crane in the kettle aisle, which is also used for shipping lead. Other auxiliary equipment is referred to in the outline of operations. A general plan of the plant is shown in Fig. 2, and a general view in Fig. 1. Primary smelting operations are conducted in a 30 by 11-ft. reverberatory furnace with bottom, roof, and upper walls of clay brick, magnesite

Jan 1, 1934

By J. J. Mulligan

Introduction Coal is found in every major geographic region through-out Alaska and in two offshore areas. Since about 1852, more than 100 small mines have opened and closed. In 1981 and 1982 production was almost entirely from one mine in central Alaska. Clearly, the utilization of Alaska's abundant coal resources presents political, economic, and technical problems that are far from solution. Location and Physical Features Figure 1 illustrates the geographical and geological similarity between Alaska and the western US. Alaska's Arctic region generally resembles Wyoming and the Dakotas. The Brooks Range is an extension of the Rocky Mountains. The central region of Alaska between the Brooks Range and the Alaska Range bears a general resemblance to the basin and range country of the western US. The southcentral and southeastern regions have a similar resemblance to the Sierra Nevadas and the West Coast. The Arctic, the central, and the southcentral regions have major coal fields. The southeast region has scattered occurrences. The topographic, climatic, and economic characteristics of each are different. These differences have a large effect on practical mining methods. Description of Alaskan Coal Coal deposits known in Alaska are almost all of Cretaceous or Tertiary age, much younger than the Carboniferous coal deposits of eastern and midwestern states. Consequently, most Alaskan coals have a higher moisture content and a lower heat value. Most Alaskan coals also have a much lower sulfur content. Low volatile bituminous, and anthracite coals occur in Alaska, but most Alaskan coals range downward in rank from high volatile bituminous to subbituminous and lignite. Alaskan coals are similar to coals of the northern Great Plains and the Rocky Mountains. Arctic Region Northern Alaska Coal Fields Northern Alaska coal fields are by far the largest group of coal deposits in Alaska (Fig. 2). Coal-bearing rocks extend from the foothills of the Brooks Range about 160 km (100 miles) northward to within about 80 km (50 miles) of the Arctic coast. The principal known occurrences are between the Colville River and the western coast. However, coal has been found eastward almost to the Canning River and westward under the Arctic Ocean. The northern Alaska coal fields are in a series of Cretaceous rocks that suggest a deltaic depositional environment. The beds tend to occur in series of up to eight or nine beds totaling 6-9 m (20-30 ft) of coal. However, beds 6-12 m (20-40 ft) thick have been reported, and beds 1-3 m (3-10 ft) thick seem to be relatively common. Including thin seams, coal in some places makes up about 10% of the stratigraphic section. However, no area has been explored in sufficient detail to block out any large body of reserves or to make reliable estimates of the total resource. Observation points in drill holes and along river and stream banks are few and far between. Coals in northern Alaskan fields tend to range in rank from bituminous, where moderately folded and faulted in the foothills, to subbittuminous in the gently folded rocks under the coastal plain. Coals toward the eastern extremities of the coal fields may be of Tertiary age and lower in rank, but the same general correlation between degree of folding and increase in rank can be expected. Some higher rank coals in the foothills belt are known to have coking properties but most, and possibly all, require

Jan 1, 1984

By Orson Cutler Shepard

RECENT research work in the flotation concentration of minerals has been concerned mainly with flotation reagents and the mechanism by which collecting reagents are held to the surface of certain mineral particles. The fundamental question of why air bubbles cling to properly prepared mineral surfaces is usually dismissed with the statement that the surface is air-avid or water-repellent. In my article in MINING AND METALLURGY for June, 1932, I showed theoretically that surface tension relationships govern bubble attachment in Rotation. This explanation has not been accepted by many; probably be¬cause the difficulty of measuring solid-solution surface tensions prevented obtaining experimental evidence. If the surface tensions involved in the system [solution, mineral, air bubble] are responsible for attachment of the air bubble to the mineral, any change in the surface tensions should cause a corresponding change in the attachment of the air bubble. An example in which the mineral-solution surface tension could be varied was found with mercury. When mercury is in contact with solutions of certain electrolytes the surface tension at the contact of mercury and solution can be altered by electrical polarization of the mercury. The surface tension rises to a maximum as the mercury is given an increasing negative potential and then decreases with further increase in potential. The theoretical relation between the surface tensions and the attachment of an air bubble is given by the following equation:

Jan 1, 1936

By Henry M. Howe

The object of the present paper is to suggest injecting into the hearths of iron blast furnaces, whose temperature has become unduly lowered, some form of fuel whose calorific intensity, under the peculiar conditions existing there, is considerably higher than than of liquid petroleum, the rose of this substance for melting out chills having grievonsly disappointed the high hopes which were at first entertained of it. A chill being a fall of the temperature below that needed for the complete liquefaction of the slag, which requires, according to Plattner, about 1800' C., one would suppose that the chief thing to be accomplished in curing it would be to raise the temperature in the crucible of the furnace. The most obvious ways of doing this seem to be to raise the temperature of the blast, and to increase the amount of fuel in the crucible itself. Simply increasing the rate at which the blast enters the furnace, if carried beyond a certain point, should lower the temperature in the crucible. The existence of a chill shows that the fuel is arriving too slowly at the tuyeres. If air be introduced so rapidly as to he in excess of that required for the combustion of the fuel, all that excess will simply lower the temperature around the tuyeres, carrying the region of intense heat upwards, and weakening its intensity by increasing its size. Up to a certain point, increasing the rate of introducing the blast will increase practically pari passu the rate at which the fuel reaches the tuyeres. But when mechanical obstructions, which so often accompany chills, retard the descent of the fuel, there must be a point beyond which this does not hold good, and beyond which farther

Jan 1, 1883

By W. J., Kroll

MOST people believe that rare metals are always, scarce in nature, expensive to make, and therefore useless despite some miraculous properties which might make them a cure-all. There are' some metals, which are quite frequent in nature, such as zirconium, which are called rare only because our present methods for making them are elaborate, thus forcing the manufacturer to sell them at a high price. There are also truly rare metals, such as gallium, which do not occur frequently in ores, but are easily reducible from their oxides. In these cases the price of the concentration operation is the decisive factor. The distribution of the elements in the earth's crust is no indication as to the availability of a metal; the concentration operation is the critical factor. Concentration is frequently obtained in the course of metallurgical operations for the extraction of other metals, and the rare metal may be enriched in by-products, flue dusts, mother liquors or precipitates from electrolyte purification as are indium, thallium, selenium, and tellurium. A periodic table of the rare elements may serve as a basis for discussion of their properties and to establish a program. (Table 1.)

Jan 1, 1946

By Albert Sauveur

(Winces-Barre Meeting, June, 1911.) THE instrument about to be described meets so perfectly the special needs of the metal microscopist that there seems to be little doubt but its merits must be readily appreciated by those who have had any experience in the microscopical examination of metals. The Microscope-Stand.-The microscope-stand proper, Fig. 1, consists of a microscope-tube, provided with both coarse and fine adjustments of the best construction, and with a draw-tube, rigidly mounted on a bar supported at both ends on substantial and firm cast-iron legs. The height between the table and the under side of the supporting bar is 5 in. and the distance between the supporting legs 12 inches. This arrangement' affords free space below the objective for the examination of large specimens of metals, such as full rail-sections, without detracting in the least from the value of the instrument when applied to the examination of the usual small specimen, as explained later. Many metal microscopists frequently have to examine bulky specimens, and this is altogether impossible with the ordinary microscopes as well as with the special metallurgical microscopes which have been designed and described from time to time. Recourse must be had to all sorts of makeshifts for the proper support of large specimens, or, more often, the microscopist gives up the attempt altogether, or else resigns himself to the cutting of the bulky samples into small pieces to -be laboriously polished and separately examined. It is believed that an instrument permitting the examination of large as well as of small specimens with equal ease and accu-

Dec 1, 1911

By Appendix by A. S. Goldoni, R. E. Tate, E. M. Cramer

The diffision coefficient for self-diffision of plutonium in the temperature range 350" to 440°C has been measured by using puZ3 as the tracer isotope. Autoradiopaphic techniques were used to inzlestigate the possibility of grain boundary diffusion, hut only evidence for volume diffusion was found. The least-squares fit of the data gives the .following equation for the diffision coefficient: The computer least-squares technique for fitting the nonlinear equations is outlined. DETERMINATION of the self-diffusion coefficient of the fcc 6 phase of plutonium is in principle a straightforward experimental task. However, the chemical reactivity, the intense @ activity, and the toxicity of plutonium put limitations on the experimental techniques. The technique selected included roll bonding for preparation of the diffusion couples and pulse-height analysis of the @-particle activity to determine the distribution of the PU tracer in the diffusion couples. EXPERIMENTAL PROCEDURE Couple Preparation. Cylinders about 0.5 in. in diam were cast from two special stocks of plutonium, one of which had been enriched in puZ3', as shown in the isotopic analyses listed in Table I. For each roll-bonded composite sheet, a cylinder 0.437 in. in diam and 0.190 in. thick was turned from each kind of plutonium on a lathe in a 98 pct He atmosphere. The two freshly machined cylinders were positioned face to face in a tube of commercially pure aluminum which had been sealed at one end by welding and the assembly was evacuated on a vacuum manifold overnight. The elapsed time between machining the faces of the plutonium cylinders and evacuating the loaded tube was about 15 min. After overnight evacuation of the assembly the indicated vacuum was 1 X 10"5 torr or better. The aluminum tube was then warmed and pinched off with a cold-welding tool. The pinched-off weld was also fusion-welded as an additional precaution against leakage of air into the evacuated assembly. The assembly was immediately heated for 30 min in a 250°C furnace and reduced in thickness by being passed through a rolling mill with rolls heated to 200°C. The rolling schedule (four passes of 100 mils each with a 10-min reheat after two passes) reduced the thickness of the assembly to 100 mils. The rolled assembly was allowed to cool normally in air. The rolled assembly was sheared at the edges and the aluminum peeled from the composite plutonium sheet. The elliptical sheet was about 0.060 in. thick and usually three 0.383-in.-diam disks could be punched from its central portion. The sheet was heated on a hot plate to the ductile low 0 range (140°C as measured by temperature-indicating pellets) before each disk was quickly punched. The quality of the bond in the disks was evaluated by metallographic examination of the scrap sheet adjoining the hole left by the punch. Only well-bonded specimens without oxide in the interface (as indicated by metallography) were considered satisfactory for further use. More than half of the specimens so examined contained sufficient oxide in the interface to be rejected. Diffusion Anneal. Each disk to be diffusion-annealed was wrapped in 1-mil-thick tantalum foil and sealed within a Pyrex capsule evacuated to 1 x 10~5 torr or better. This capsule was then sealed within another Pyrex capsule at a similar pressure. The diffusion anneals were carried out at temperatures between 350" and 440°C in Marshall furnaces adjusted to have a temperature gradient of not more than *1/2"C over a 5-in. length. This gradient was then further smoothed by using a nickel tube as a liner in the furnace. The liner was divided into three longitudinal cavities by a septum of nickel sheet to which two calibrated Chromel-Alumel thermocouples were attached. One thermocouple was used for controlling the furnace temperature by means of a Brown Pyrovane controller equipped with a Capaciline anticipation circuit; the second thermocouple was monitored twice daily with a Leeds and Northrup K-2 precision potentiometer.

Jan 1, 1964

By H. P. Allen

THE chloridizing mill of the Standard Reduction Co. is located about 75 miles south of Salt Lake City on the Tintic branch of the Denver & Rio Grande Western R. R. and 12 miles from the Tintic Standard mine. The daily capacity is 200 tons of a siliceous, low-grade, silver-lead ore from this property. It has operated continuously since it was started in January, 1921. The process consists essentially of a chloridizing roast followed by a percolating leach with a nearly saturated solution of common salt, acidified with sulfuric acid, the precipitation of silver on sponge copper and of copper and lead on tin-plate cuttings. The precipitates are shipped to a smelter. Some of the general ideas involved are said to have been used by Augustin in England, in 1840. A number of textbooks treat of the subject, especially the chloridizing roast followed by a leach with sodium hyposulfite or amalgamation. The process was revived in this district by Theo. P. Holt, N. C. Christensen, the Bureau of Mines, and others.

Jan 8, 1925