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By W. G. Oldham

By monitoring the capacitance of abrupt p-n junctions it is possible to follow the motion of substitu-tional impurities. A p-n junction is formed by growth of silicon from an Al-Si alloy on an n-type silicon sutstrate at a temperature in the range 650" to 750°C. The diodes are etched and sorted for consistent V-I and capacitance behavior and separated into groups. After irradiation, each set with an unirradiated control set is annealed to various temperatltres for 10 mm and the capacitance remeasnred. For very heavily doped diodes (-1019 per cm3) observable capacitance changes occur at neutron fluences of >1015 per cm 3. The results may be interpreted in seceral ways, the simplest of which is to assume simple vacancy diffiision with small impurity -racancy interaction (at the diffiision, i.e. annealing temperature of 700°C). In this interpretation it is found that a typical vacancy makes about 1024 jumps and travels about 10-5 cm before disappearing. The required effective annihilation center density is about 1016per cm3 . Estimates of the vacancy-impurity interaction can be made and the above numbers correctecl, but for arty reasonable assumptions the number of vacancy sinks connot be much reduced. ThE complete annealing of radiation induced defects requires that the vacancies and interstitials either recombine, travel to the surface of the crystal, or travel to an annihilation center, e.g., a dislocation or a precipitate. If the interstitial is ignored except as a possible vacancy annihilation center at low temperatures,* the motion of vacancies may be followed by monitoring the corresponding motion of substitutional impurities. pfister2 has measured the enhanced diffusion of impurities in an asymmetric shallow diffused silicon structure by optically monitoring the junction movement. In these experiments we monitor instead the capacitance of a heavily-doped deep symmetric p-n junction. The sensitivity for this method is several orders of magnitude higher than in Pfister's technique, mainly for two reasons: 1) the junction capacitance of a heavily-doped junction is sensitive to impurity movements in the Angstrom range* com- and 2) the junction may be far from the surface which is a major annihilation center for vacancies. THE EXPERIMENT A p-n junction is formed by the epitaxial growth of silicon from an A1-Si alloy on a silicon substrate at a temperature in the range 650° to 750°C. The technique used is the transport of an aluminum melt through a temperature gradient.4 A 10-mil thick aluminum disc is sandwiched between two silicon wafers and the assembly raised to about 650° C with a temperature gradient normal to the sandwich. After about 8 hr the upper (hotter) wafer has been entirely transported and deposited epitaxially on the substrate wafer. The substrate and overgrowth resistivity are measured with a 4-point probe. The as-grown structure is lapped until the wafer is about 1/2 mm thick with the junction in the center. Contacts consisting of electroless nickel covered by electroplated rhodium are applied to both the p and n sides. The wafer is diced into square dice 1/2 to 1 mm on a side and the dice are etched sufficiently to remove approximately 1 mil of silicon. The following results are all for aluminum (p-side) and antimony (n-side) doped specimens with NA =3x 1018 per cm3, ND = 2-8 x 101A per cm3. The diodes are sorted for consistent V-I and capacitance behavior and separated into groups. After irradiation, each set with an unirradiated control set is annealed and the capacitance remeasured. A special capacitance measurement method is used to insure a low sensitivity to shunt resistance. The diode is voltage driven and the current monitored by a phase lock amplifier. It is possible to adjust the detector phase to a point where shunt resistances as low as 100 O have no effect on the reading. The diodes in this study have a capacitance in the range 1000 to 5000 picofarads and a shunt resistance in the range 100 to l06 O depending on the stage of the anneal. THEORY The theoretical problem is twofold: 1) The computation of the amount of impurity diffusion and hence the impurity profile resulting from a given amount of vacancy motion, and 2) the computation of the capacitance from the impurity profile. A comparison of the theoretical and experimental capacitance (in particular the changes) yields the amount of vacancy motion. Vacancy Motion. A convenient parameter to measure the total amount of vacancy motion is Jv the total number of vacancy jumps per unit volume. Although this parameter varies with position in the crystal, owing to vacancy annihilation at the surfaces, it is approximately independent of position far from the surfaces, i.e. in the junction region. In terms of the number of vacancies per unit volume Nv and the vacancy diffusivity given by

Jan 1, 1970

By R. K. Iyengar, G. C. Duderstadt

An investigation was carried out to determine the effect of Ca-Si additions on the dissolved oxygen content of liquid steel. An apparent equilibrium was reached after holding the melt for some time when the total oxygen content of the melt was identical with the dissolved oxygen. Results of the investigation show that for deoxidation with silicon and manganese the apparent equilibrium is reached after 8 to 12 min and the oxygen content of the melt is in good agreement with values reported in the literature for similar steel compositions. Ca-Si additions decrease the dissolved oxygen content appreciably below that obtained with Si-Mn deoxidation. It is postulated that some calcium dissolved in liquid steel at the time of its vaporization combines with dissolved oxygen to form CaO which then fluxes the manganese silicate, thereby lowering the activity of the deoxidation products. Slow flotation of calcium silicate inclusions is attributed to their slower growth rate. An addition of aluminum (to yield <0.005 pct Alsol) prior to introduction of Ca-Si improves the kinetics of removal of resulting deoxidation products. WITH the introduction of continuous casting of billets and blooms, application of calcium-containing alloys for deoxidation purposes has gained new interest. More so than in conventional ingot casting, the degree of control of the dissolved and total oxygen contents in steel for continuous casting can determine the success or failure of the operation because these affect both surface (pinholes) and internal quality of the billets. Of the available deoxidizers, only silicon has so far found wide application. However, in the typical range of application (0.20/0.30 pct Si), it is too weak a deoxidizer to suppress pinhole frequency to the level desirable for all but the least demanding appli-cations (approximately 10/50 pinholes per sq ft, de-pending on degree of subsequent reduction). On the other hand, Vincent&apos; has shown that it requires ap-proximately 0.007/0.008 pct A1 soluble in the steel to suppress pinhole formation to <10 pinholes per sq ft. In view of the difficulty of consistently maintaining this aluminum level and the associated problem of tundish nozzle constriction2 when aluminum is added to the ladle, steelmakers have searched for other de-oxidation alloys to circumvent the problem. Calcium-containing alloys offer such a possibility. When employed as a partial substitute for silicon, CaSi (30 pct Ca/60 pct Si) additions are reported to yield adequate pinhole contro1.3 Its use simultaneously preserves the "fluidity" of the steel and ensures good castability.4 Oxygen contents as low as 0.007 to 0.014 pct have been obtained with CaSi additions varying between 3 to 8 lb per ton.5-7 Due to the high degree of vaporization of calcium at the temperature of molten steel and the different methods used to introduce it into the liquid, the reported results show considerable scatter and lack of consistency. According to several investiga- deoxidation tors, the flotation characteristics of CaSi products are not as favorable as those found for alumi-num but are similar to those established for silicates with low alumina content.678 Thus, cleanliness ratings were improved when CaSi was replaced by a com-bination of Si + A1 followed by CaMnSi additions.5,9 In view of the lack of a comprehensive description of the deoxidation potential of CaSi alloys, a study was undertaken of the effect of CaSi additions on oxygen content in comparison to Si + Mn and Si + Mn + Al. The alloy chosen for this study contained 63 pct Si, 32 pct Ca, <3 pct Al, and 2.5 pct Fe. EXPERIMENTAL PROCEDURE The experiments were divided in three groups as shown in Table I. In each group, the CaSi addition was increased successively while maintaining the melt composition constant. The experiments in the third group were designed to determine the effect of prede-oxidation with small amounts of aluminum. Ingot iron, containing 0.02 to 0.03 pct C and 0.03 to 0.05 pct Mn, was melted in a 100-lb magnesia crucible. Pig iron was added to the melt under air in an induction furnace to attain the desired carbon content of 0.05 to 0.15 pct and thereby control the initial oxygen content of the melt between 0.04 and 0.015 pct. After removal of the slag, the furnace was sealed and argon was introduced through an opening in the graphite cover, Fig. 1. When the desired temperature was reached, electrolytic manganese was added to the melt and pin samples were taken (7 mm silica tubing) to establish initial oxygen content. To obtain maximum efficiency, CaSi and metallic silicon were introduced in a sealed steel pipe into the bath. This procedure assured minimum loss of calcium through vaporization as the deoxidants were always released at the bottom of the melt. Samples were taken at regular intervals and quenched in water. Temperature of the bath was measured with a Pt/Pt-10 pct Rh thermocouple. Portions of the pin sample were used for oxygen analysis; five determinations per sample were made to obtain average oxygen content. Oxygen analyses were made by the inert carrier gas fusion method with frequent cross checks with the vacuum fusion method.

Jan 1, 1970

By M. Duclos, A. Sawatzky

A simple model has been developed which describes the steady-state solute distribution in Ti-H type systems above the eutectoid temperature in the presence of a temperature gradient. The solute distribution is dependent on the shape of the phase boundaries. An interesting result, and one that is not observed at steady state in thermal diffusion below the eutectoid temperature, is the existence of a two-phase region. The heat of transport for hydrogen in a titanium, Q*a, over the temperature range 275" to 650.C is determined to be 4500 * 230 cal per mole. The heat of transport for hydrogen in B titanium, QB* over the temperature range 320" to 590.C is found to be 630 ± 200 cal per mole. It is also shown that thermal diffusion provides a method by which phase bounduries above the eutectoid may be determined in Ti-H type systems. IN modern technology materials are being used at constantly increasing temperatures under greater temperature gradients. Thus atomic migration in metal alloys due to a temperature gradient (thermal diffusion) may in some cases occur to an observable extent. The thermal diffusion of hydrogen in zirconium has in recent years received considerable attention1-&apos; because of the use of zirconium alloys in nuclear power reactors. The thermal diffusion kinetics below the eutectoid (547°C) are fairly well understood. At steady state the solid solution, a, and hydride, 6, phases are completely separated with the hydride precipitating at the lower temperatures. No experimental work has been carried out in the a + B region although Droege4 suggested that a complete separation of the two phases, as observed at temperatures below the eutectoid, might not always occur. In the present investigation a simple model has been used to determine the steady-state solute distribution under a temperature gradient in Zr-H type systems heated above the eutectoid temperature. The solute distribution is shown to be dependent on the shape of the phase boundaries in the constitutional diagrams and several typical cases are discussed. The model has been applied to Ti-H. This system was chosen in preference to Zr-H because of its much lower eutectoid temperature (-300°C as compared with 547.C), thereby reducing experimental errors due to oxidation and hydriding. The heats of transport for hydrogen in the a and B phases of titanium also have been determined since they were required to compare the proposed thermal diffusion model with experiment. THEORY In the presence of a temperature gradient the atomic flux in a single-phase region of a two-com-ponent system of which the atoms of only one component are diffusing is given by:&apos; J = - U\dx + RT3 dx) which can be written as: j-D(dn/dt +Q*n/RT2)dt/dx [11 J - -D\dT + RT2)dx [1] where D = diffusion coefficient, n = solute concentration, T = absolute temperature, R = gas constant, dT/dx = temperature gradient, and Q* = heat of transport. At steady state (J = 0) Eq. [I] leads to the solute distribution: n = noexp Q*/RT where no = a constant depending on total solute content. The heat of transport Q* can be experimentally determined from the steady-state distribution. In the present paper we shall determine the solute distribution in systems having the constitutional diagram exemplified by Ti-H shown in Fig. l.&apos; As shown, N,(T) and NB(T) are the equilibrium solute concentrations in the a and 0 phases at temperature T. Lines AA&apos; and CC&apos; define the region of interest to us. The following assumptions are made: 1) Steady-state conditions prevail. 2) In a single-phase region all points on an isotherm have the same thermodynamic potential so that the composition over an isotherm is uniform. If a two-phase region exists, thermodynamic equilibrium is found only at phase interfaces. However, we assume the component of the concentration gradient along an isotherm to be small so that the composition in each phase is approximately the same as at the interface and is given by the constitutional diagram, Fig. 1. 3) There is appreciable diffusion of only one component. 4) We shall consider only the case where Qa*, QB*, and Qg*, the heats of transport for solute diffusion in the a, B, and 6 phases, respectively, are positive. This has been observed for the thermal diffusion of hydrogen in zirconium3 and titanium.10 We will show that the steady-state solute distribution above the eutectoid is primarily determined by the heats of transport and the temperature dependence of Na(T) and Np(T). It may be quite different from the steady-state distribution below the eutectoid. For example, we will see that, under certain conditions,

Jan 1, 1970

By John N. Dew, William L. Martin, `

This paper describes the results of a laboratory investigation conducted to obtain data for an evaluation of the in situ combustion process as a method of producing crude oil from reservoirs. Air and fuel requirements, rates of advance, com-bustion temperatures, and coke and fluid distributions are presented. The mechanism of oil recovery by in stiu combustion is discussed. Five crude oils ranging in gravity from 10.9 to 34.2"&apos; API were prodrrced from a semiadiabatic, uncon-.solidnted sand pack by in situ combustion. Experimental conditions were varied over a wide range in order to determine the inter-relation-.ships of process variables. The mini-mum air flux requirement for self-sustained combustion was found to he less than 10 scf/hr-ft&apos;l. The rate of advance of a self-sustained combustion zone was found to be nearly proportional to the air flux at the combustion front. The effects of presrure and injected air flux were studied in a series of experiments using a 21.2" API crude. A minimum air require-ment was observed at an air .flux of 20 scf/hr-ft&apos;. The oil saturation con-sumed as fuel averaged 5.5 per cent of pore volume. The effect of air pressure was, found to be .small for experiments having high combustion eficiencies. This study should promote a better understanding of the problems and mechanisms involved in labora-tory investigations and field applications of the in situ combustion pro-cess. The data presented will be use- ful in the interpretation of results of field tests. When tempered with volu-metric sweep efficiencies, the data can be used in making preliminary economic appraisals of the process as applied to reservoirs containing high porosity unconsolidated media. INTRODUCTION The purpose of this work was to obtain laboratory data for an evaluation of the in situ combustion process as a method of producing crude oil from reservoirs. In situ combustion basically consists of (1) injecting air into a reservoir through selected input wells to create an air sweep through the reservoir, (2) igniting the crude at the injection well, and (3) propagating the combustion front through the reservoir by continued air injection. By this means, oil is swept toward producing wells in the area. The fuel for combustion is supplied by heavy residual material (coke) which has been deposited on the sand grains during distillation and cracking of the crude oil ahead of the combustion front. Recovery of petroleum by a combustion or heat wave process is not a new idea. F. A. Howard was granted a patent in 1923 on a process in which air and a combustible gas were pumped into an injection well and ignited.&apos; Russian engineers reported on field experiments with a crude oil gasification process in 1935&apos;. Other known early field tests include those conducted near Bar-tlesville and Ardmore, Okla., in 1942." More recently completed field tests include an inverted seven-spot by Sinclair Oil Co. in the Delaware-Childers field, Nowata County, Okla.&apos;; a three-well and an inverted five-spot test by Magnolia Petroleum Co. in Jefferson County, Okla."."; and a test by California Research Corp. in the Irvine-Furnace field in Kentucky. The Worthington Corp. has completed a test in cooperation with the Forest Oil Corp. in Clark County, 111.l Several field tests are now in progress. Sinclair has acquired a 600-acre lease in the Humboldt-Chanute field, Allen County, Kans., and is under way with a large-scale operation. Three field tests are under way in California. The General Petroleum Corp. is conducting an inverted five-spot pattern test in the South Bel-ridge field in Kern County under a cooperative agreement with 11 other companies, including Continental Oil Co. California Research Corp. is conducting a four-well pattern test in Midway-Sunset field near Maricopa, and Richfield Oil Corp. is under way with a test in the Ojai field in Ventura County. Although the published information is valuable concerning results of field tests, little laboratory data other than that reported by Kuhn and Koch5 are available to aid in appraising the tests from a technical or economic standpoint. Engineering data needed to evaluate the process include the amount of air required per barrel of oil recovered, minimum injection rates which will support combustion, rates of advance, air required per unit volume of reservoir cleaned, amount of oil recovered, and amount of oil consumed as fuel. The present laboratory investigation was undertaken to provide these data for that portion of the reservoir swept by the combustion zone. The first phase of this investigation was exploratory in nature and was conducted at injection pressures less than 100 psig. Data were ob-

By Arthur Baker

The orebodies are long bedding-plane lenses of chalcopyrite and sphalerite, associated with garnetite masses. Most of the orebodies are within a 50-ft thickness of Cambrian limestone; other Paleozoic limestones and dolomites are locally metamorphosed but only slightly mineralized. Pre-mineral faults are numerous, but shallow folds were the main ore-localizing structures.

Jan 12, 1953

By James W. Guider

Of all the technology available to the iron blast furnace operator, raw materials preparation [(Fig. 1)] is by far the most important. Superior raw materials have been basic to the success of the Japanese steel industry, and they are just as essential to the American steel industry in winning its competitive battle against foreign government subsidized steel imports. Therefore, the mine operator and the ore beneficiation engineer must strive to produce the highest quality raw materials possible to meet the precise demands of the modem blast furnace and steel plant.

Jan 1, 1982

By Leo Horvitz

PETROLEUM and natural gas are composed principally of the saturated hydrocarbons ranging from methane, the lightest, to nonvolatile liquids and solids containing approximately thirty-five carbon atoms. A technique for locating buried accumulations of these hydrocarbons before drilling obviously requires that some of the hydrocarbons leave the deposit and migrate toward the surface of the earth where they may be detected in their original form. Earliest attempts to link near surface hydrocarbons to petroleum at depth were apparently made by Laubmeyer1 in Germany and by Sokolov2 in Russia. These investigators collected samples of soil air from boreholes one to two meters deep and analyzed them for traces of hydrocarbons. They found that soil air over producing areas is richer in these constituents than is soil air over barren areas.

Jan 12, 1954

By C. W. Nicolson

THE Tri-State zinc and lead-mining district is in the northeast corner of Oklahoma, the southeast corner of Kansas and the southwest corner of Missouri. The area throughout which active mining has been conducted is about 45 miles long and about 5 miles wide, extending northeasterly from Commerce, Okla., to Alba, Missouri. Although the lead ores were mined on a very small scale in the vicinity of Joplin, Mo., as early as 1848, nothing of any importance was done in the district until 1870, since when both mining and smelting have been prosecuted with considerable vigor. In the beginning the lead ores only were exploited, but within a few years extensive deposits of zinc ores were found and since that time the production of zinc ore has far exceeded that of lead. Both the surface and mineral rights in Missouri and Kansas were under individual ownership by the time ore was discovered. Although some of these rights were purchased by mining companies, most of the mining has been done under leases covering small areas, usually 40 acres, although in the past many leases were given on much smaller tracts. In Oklahoma most of the mineral land had been alloted by the Government to various Indian tribes and although the title to some of these lands had been acquired by various white men before the discovery of the rich Picher field, the title to most of the land has remained with the Indian tribes and the leasing of the mineral rights has been done by the Federal Government for the benefit of the Indians. The Indian allotments were of 200 acres each and some of the mining leases covered entire allotments, although many leases were granted for only 40 acres or even less.

Jan 1, 1938

By Ma Guang, Huang Jinshou

In this paper we briefly describe measuring techniques and their practical use in the mining industry of China. A strain coefficient matrix of triaxial strain cell for a flat ended borehole is also introduced.

Jan 1, 1983

By Thomas T. Read

ONE of the major purposes of the Institute is to "maintain ... a library of books relating to subjects cognate to the sciences and arts of mining and metallurgy." In conformance with this purpose the Institute maintained its own library for a number of years until 1912 when it was merged with the libraries of the other Founder Societies. At that time the A.I.M.E.&apos;s share of operating expenses was wholly covered by the income from a $100,000 gift from James Douglas. But interest on the Douglas Library Fund has declined from 51/2 per cent to 31/4 per cent; the library has grown from some 50,000 volumes in 1913 to more than 170,000 in 1945, with consequently increased costs; and its costs nave otherwise risen. The Institute today contributes to the library annually about 65c per member, of which about 25c is income from the Douglas Fund, or a net charge, from regular income, of 40c per member. The annual library budget runs about

Jan 1, 1946

By William Wraith

1. INTRODUCTION. AT the Washoe smelter,. Anaconda, Mont., the blister-copper from the converters is transferred, by means of a crane, to a refining-furnace,, in which it is brought to proper pitch by means of air and poles. From this furnace the refined copper, containing gold and silver, is poured into cast-iron molds placed on a platform-conveyor, giving an anode 36.75 in. long, 28 in. wide, and 21 in. thick. By reason of a disagreement between the smelter and the refinery, in reference to the silver-content of the anodes, it became necessary to investigate the methods of sampling used. II. SMELTER METHOD OF SAMPLING. At the smelter the sampling is done by " spotting " into water a small portion of the molten stream of copper as it flows from the furnace, by batting" the stream with a wooden paddle. The first sample is taken 30, min. after the pouring is started, three. other samples being taken at 1-hr. intervals, each sample weighing from 4 to 6 oz. The samples are dried, examined for particle&apos;s of burnt wood, screened on a 10-mesh screen of No. 8 wire to remove the fines, the oversize then screened on a 4-mesh screen of No. 20 wire to remove the coarse, the undersize of this screen being taken as the sample. Teh four portions thus obtained are thoroughly mixed and spli in half by passing over a 16-slot splitting-device, slots being 0.5 in. wide. One-half of the sample is sent to the laboratory for analysis and one-half kept as a duplicate. III. REFINERY METHOD OF SAMPLING. The method used at the refinery and also used in this investigation is the one developed by Dr. Edward Seller, of

Mar 1, 1910

By Jacques B. Wertz

Among the parameters to be considered in the continuous search for new base-metal deposits, there often is a stratigraphic controlling factor that seems instrumental in the localization of ore. In British Columbia, for instance, the Upper Triassic as well as Lower Jurassic volcanics mixed with sediments are a useful indication in the search for copper while, in some parts of Australia, rhyolite bodies seem to be the favorable indicator, and this always within the geosynclinal environment. In Arizona, this stratigraphic factor becomes highly significant and it will be shown here that a large number of ore deposits are to be located around the flanks of ancient calcareous basins or depressions, preferentially corresponding to a certain optimum thickness as revealed by isopachs. The Martin limestone, of Devonian age, is already known for its basal O&apos;Carroll bed which coincides with mineralization at places, and this is a relatively minor control. However, several limestone basins outlined by isopachs are in reality of greater importance as they localize mining districts. Indeed, most mines are found to coincide with a specific thickness of limestone while occurring simultaneously close to major, regional fracture intersections. The regional fractures in question were interpolated and extrapolated from known, important fault expressions, integrating quite well with the existing geology and further confirmed by minor criteria such as contacts, igneous plugs, axes of elongation of batholiths, dikes, etc. Although elements of subjectivity remain, this grid of fractures can be used quite successfully as a working hypothesis in the search for ore. Results of the present study which superposes major structural

Jan 1, 1971

By Carl R. Christiansen

Since the first pay hole in Missouri&apos;s "New Lead Belt" was drilled in 1955, this district has become one of the world&apos;s leading sources of lead. The belt extends from north of Viburnum in a southerly direction to near Eminence, a distance of about 35 miles. The St. Joseph Lead Company was the discoverer and first to develop new mines in the Viburnum area. Since the discovery of the New Lead Belt, many companies have engaged in exploration programs and several major companies have become active in development of new mines. These include Cominco American, Inc., which operates a joint venture with Dresser Industries; Ozark Lead Company, a subsidiary of Kennecott Copper Company; and Missouri Lead Operating Company, a joint venture of Arnax and Homestake. St. Joseph Lead Company, with over 100 years of experience in the Old Lead Belt, has served as a leader in development of equipment and mining techniques, making its properties some of the most efficient mining operations in the world. The new producers give the district the benefit of fresh viewpoints, as their engineers are mostly from outside of Missouri and their previous experience has been considerably different from conventional lead belt practices. While all operations are similar in that they are room-and-pillar, the diverse experience of the operators has produced a group of mines that employ a variety of equipment and mining techniques to give increased efficiency

Jan 1, 1970

By R. F. Mehl, J. T. Ransom

For many years the Metals Research Laboratory of Carnegie Institute of Technology has been concerned with the statistical nature of the engineering properties of steel from an experimental viewpoint, particularly those properties representing ductility.&apos; In the past three years new work has been directed toward evaluating the statistical nature of the endurance properties. It has been shown that both the fracture curve and the endurance limit in fatigue are markedly statistical in nature. The S-N curve (and the endurance limit) of ferrous materials is often determined with specimens which number as few as ten. The common procedure is to test the first specimen at a stress well above the expected endurance hmit. Each succeeding specimen is then tested at a progressively lower stress, until, after five or six tests, a specimen runs ten million or so cycles without failing. Two or three more specimens are then used to find the highest stress at which failure will not occur; the limiting stress determined in this way is called the endurance limit. It has now been found, however, that the variability in the fracture curve and in the endurance limit in heat-treated alloy forging steels is so great that S-N curves must be drawn on the basis of distribution curves which can be appraised only by statistical methods. Two methods have been adopted in this study: (1) straightforward statistical studies of cycles to fracture of a number of specimens at each of a series of stress levels, and (2) a new abbreviated statistical method, known as "staircase testing."2 The latter corisists in testing a series of specimens, one by one, with the test stress for any given specimen automatically

Jan 1, 1950

By S. Kobayashi, A. E. Armenákas, C. Mylonas

Earlier work1-4 has shown that commercial mild steels under static loading at the lowest natural operating temperatures fracture in a brittle manner only when damaged by a suitable history of straining. Notched and then compressed plates have fractured in subsequent tension at loads as low as 10 pct of the limit load and precompressed smooth bars at a subsequent extensional strain as low as 0.01. The comparison of the average net fracture stress with the flow limit stress was shown to be an excellent criterion of brittle or ductile behavior of mild steel structures when only loads and general stress levels are known. The present investigation shows that the deformation at fracture is a far more sensitive measure of brittleness than the fracture stress. Both criteria, deformation and stress, are used to determine the amount of uniform precompression of two mild steels, ABS-B and Project E-steel, resulting in brittle fracture under the strong constraint of a subsequently machined severe circumferential groove. The fracture stress equaled or exceeded the theoretical flow limit Ól = 2.680., (&apos;based on the elevated yield stress at each prestrain) up to prestrains of about 0.20 and then fell off to about 1 at prestrains of 0.60. Yet a prestrain of only 0.05 reduced the elongation at the shoulders by a factor of about 4. The total plastic elongation of a region surrounding a sharp notch in prestrained steel deternines whether or not fracture will be initiated in large structures, hence is a direct and realistic measure of the remaining ductility and provides an excellent test of the material&apos;s resistance to embrittlement. ALMOST all engineering structures of mild steel which failed in service in a so-called "brittle" manner exhibited appreciable local plastic deformation (more than 1 pct) and a mixture of "cleavage" and "shear" fracture surfaces. Furthermore, the peak local stress in an advancing crack is always high. Such simple criteria as pure cleavage, absence of plasticity, or fracture stress, so useful in other fields, are insufficient to characterize brittleness in engineering structures at ordnary temperatures. The "brittle)&apos; behavior of engineering structures is caused by the limited ductility at cracks or notch regions, as shown by recent work at Brown University summarized and extended in Refs. 1 to 4. It was also shown that the local ductility of mild steel may be catastrophically reduced by a suitable strain and temperature history similar to those which may occur in real structures. Localized yielding begins at the notch roots at low loads but is contained by surrounding elastic regions. The plastic strains are hence small. They increase slowly with the load up to the flow limit or limit load for an ideally plastic material. Unrestricted plastic flow then occurs. At such strains the real material locally st rain-hardens and fractures. With work-hardening materials no flow limit exists, and the transition from low to high plastic strains is gradual but increases more rapidly at loads close to the flow limit of an equivalent perfectly plastic material. When the available ductility is sufficient for reaching the limit load, the behavior is normal or "ductile". With insufficient ductility, fracture will occur at a low load and will be defined as "brittle". Accordingly the sufficiency or not of the ductility at a notch is reflected in the magnitude of the fracture load or average net stress as compared with the limit load or flow limit. The application of this criterion gave surprising results. Service failures under semistatic loading occurred mostly below the limit load, hence were "brittle". On the contrary all static tests with undamaged commercial mild steels reached the limit load in spite of the deepest notches and temperatures below Charpy impact transition (say about -30°F or higher). Notched bars showed no brittleness even under fully dynamic axial loading up to 1.5 x107 psi per sec at -23°F and about 2.5 x l06 psi per sec at -ll0°F, but broke in a brittle manner at -200°F and l03 psi per sec.&apos; To propagate a fracture at low load, experimenters had to trigger it by superimposing a strong dynamic impact at a notch cooled by liquid nitrogen as in the Robertson5 or Esso tests.&apos; Once started the cracks would run through warmer regions of smaller stress. Obviously the ductility of the apparently undamaged commercial steels was "sufficient" in the laboratory tests but not in the service fracture, where it must have been reduced by some embrittling procedure of fabrication or service. These conclusions were confirmed by the achievement of low static stress (brittle) fracture initiation in unwelded steel after a local reduction of ductility by simple prestraining. Symmetrically notched plates of undamaged mild steel cooled below the Charpy V-notch transition range were tested in central static tension: Undamaged plates withstood loads of limit intensity, but when subjected to prior in-plane com-pressive prestraining perpendicular to the notch axis and to accelerated aging, the plates fractured completely or partially at very low static loads, as low as one-tenth of the flow limit.2-4 However, damage could not be easily related to the strongly variable prestrain around a sharp notch. To obtain easier strain measurements, it was decided to use axially precom-pressed bars and bent bars. Final testing was done by

Jan 1, 1970

By Dan White

Stress measurements taken at Climax, El Teniente, Henderson, Lakeshore and Urad mines indicate that the deposits cited are generally subject to an inclined stress field that can be highly anisotropic. The horizontal stresses vary significantly between deposits and exceed the measured vertical stresses at Henderson and El Teniente mines. Experience at Henderson, Lakeshore and Urad mines is used to suggest a relationship between cavability and the premining stress. In poorly fractured, high strength rock masses, high stresses can assist the caving process. In well fractured, low strength rock masses, caving is ensured by breakage along fracture planes. The relationship between ground weight and the premining stress is also investigated. Ground weight problems appear to be most related to the competence of the ground rather than the magnitude of the premining stress as supported by experience at Climax and El Teniente mines. Recent developments in block caving favor the extraction of poorly fractured, high stressed rock. Accompanying the development of these deposits are new problems such as rock bursts. These pose particular problems to mine designers in that no experience currently exists in combatting rock burst problems at block caving mines.

Jan 1, 1984

BENEFICIATION AND CONCEN&apos;TRATION; FROTH FLOTATION U.S. 4,069,144 - In the froth flotation beneficiation of phosphate rock using at least an acid flotation step and an amine flotation step, the crude ore is dried either during transport or storage or by air circulation immediately prior to classification, and the dried ore mixed with water and classified prior to flotation The preliminary drying substantially eliminates the usual problems with clay slimes G. C. Johnson and A. E. Schweizer, assigned to Mobil Oil Corp. Jan 17. 1978. 4 pp (209- 11) . Filed 1 1-19-75 (633,535).

Jan 1, 1979

By William P. Blake

Postscript to the paper read by Prof. William P. Blake at the Lake Superior meeting, September, 1904. POSTSCRIPT.*-Since the publication of my paper upon the blackening of the surface of rocks in desert regions, I have noted that similar views of the origin of superficial discoloration in the case of certain rocks from the Salt Lake basin of Utah have been expressed by Prof. George P. Merrill. In the pamphlet, he described the brown-coated weathered boulders from Tooele county, reaching the conclusion that the discoloration was due to the solution of the manganese and iron compounds &apos;in the interior of the boulder, while they were in the water, and the gradual bringing of this material to the surface through capillarity and its oxidation when exposed.

Mar 1, 1905

Jan 1, 1967

By Robert W. Hunt

THE first pump of this character, made by H. R. Worthington, and, so far as the writer is informed, the first and only one of this kind ever constructed, is now in daily use in the above-named works. The water-pressure necessary for the working of the hydraulic machinery of this plant had been supplied, up to the time of the building of this pump, by two Worthington Duplex High Pressure Pumps, having steam-cylinders of 20 inches diameter and 12-inch stroke, with water-plungers of 72 inches diameter; eight inlet and eight outlet valves of 22 inches diameter, and pumping into a 6-inch pipe. These pumps required a large amount of steam, and, in consequence of the various additions to their duty, their capacity became far short of the work required. In preference to putting in another engine of the same class, it was decided to accept Mr. Worthington&apos;s proposition to build the compound one under description, he guaranteeing that it should be equal to the demands of the works, and at the same time cause a saving of from 5 to 6 tons of coal per day from the amount required to run the two old pumps. The new engine has been in operation about one month, and so far has exceeded the most sanguine expectations. It consists of two high-pressure cylinders of 21 inches and two low-pressure ones of 36g inches diameter, by 36-inch stroke, with water-plungers of 91 inches diameter. There are two air-pumps of 20 inches diameter by 18-inch stroke; the condenser being 24 inches diameter by 60 inches high. Both cylinders are jacketed with wood and felt, and the low-pressure cylinder also with live steam. The high and low pressure steam-cylinders are in line and immediately adjoining each other, while the inconveniences attending an internal stuffing-box are avoided by having two piston-rods for each of the low-pressure cylinders, running through stuffing-boxes on the outside of the smaller high-pressure ones. The steam-valves are very ingeniously designed balanced

Jan 1, 1876