Search Documents

By M. E. Straumanis, R. P. Shodhan

LATTICE parameters of molybdenum of various purities are summarized in Table I. The latter shows that the parameter fluctuates between 3.1467 and 3.1475A. The room-temperature expansion coefficient a is also not well-known as values from 4.90 to 5.20 x 10-6 can be found in the literature.=-' It, therefore, seemed appropriate to repeat the measurements under exactly controlled conditions, using high-purity Hilger molybdenum powder (containing 0.0015 wt pct of Fe, 0.005 of Si and traces of other elements) and a 99.95 pct pure Sylvania Electric preparation (containing Cr, Fe, Ni, Si, Sn, and C in amounts of 50 ppm of each and in still smaller amounts Cu, Pb, Mg, and Mn). Of course, both samples could have contained at least 0.01 pct of oxygen in form of a surface oxide. However, oxygen, because of its small solubility in molybdenum, does not influence its lattice constant.g The determinations were made in a cylindrical precision X-ray camera, 64 mm in diam, the temperature of which was controlled within *0.05"C, by inserting it into a special thermostat." To exclude the film shrinkage effect (after the development of the film), the asymmetric film placement method was used." Absorption corrections (e.g., by extrapolation)" were unnecessary because of the use of a thin Li-B-glass fiber (about 0.08 mm in diam) which was fastened to the sample holder of the camera and dusted with the fine molybdenum powder. Cum radiation of the wavelength 1.389350 kX was applied because it produced in 30 min the line (420) having a high Bragg angle of about 81.6 deg. The conversion factor of 1.00202 gave the results in angstroms. To obtain the expansion coefficient a, exposures were made at various temperatures t, see Fig. 1, on at least two films at each temperature. The films were measured with a componator and the lattice constants a were calculated. The expansion coefficient was found from: where a2s is the constant at 25°C and A is the change in a and t. The same equation (knowing a) was used to reduce all the constants obtained at various temperatures to that of 25"C, Table 11. The probable error S507p (at a 50 pct confidence limit) was calculated from the reduced constants:

Jan 1, 1969

By W. A. Backofen, D. H. Avery, W. F. Hosford

Sheets of the magnesium alloys AZ31B, HK31A, and ZE10A in several different tempers were tested in tension and determinations were made of the ratio of width-to-thickness strain. A marked increase in the ratio with tensile straining and a dependence upon alloy and test direction are rationalized in terms of a balance between the amounts of basal and prism-plane slip. All such variations are related, in turn, to the prevailing crystallographic texture. Fracture appearance is explained on the basis of anisotropy in plastic flow, and implications for developing texture -hardening effects in these alloys are discussed. ThE crystallographic texture or preferred orientation of a given material is determined by details of processing history. Such texture is known to influence many aspects of material behavior, in particular both the yielding and strain-hardening characteristics which are of special interest in the present work. Traditionally, the resulting plastic anisotropy has not been regarded as especially desirable. Earing in drawn sheet is perhaps the most common example of an unwanted effect of texture. However, it has also been recognized that suitable textures may be usefully employed to improve drawability,1,2 as a specific example, and generally to control yielding resistance under combined-stress loading.374 Texture would seem to be a detail of structure not yet exploited to nearly the fullest extent. A convenient basis for characterizing anisotropy in plastic behavior is the ratio of width-to-thickness strains obtained in a tension test;5&apos;6 the parameter is frequently labeled "R" and its value is revealing with respect to the nature of the prevailing texture. R gives a useful measure of a material&apos;s "thinning resistance". For an isotropic material, R = 1. With R > 1 the increased through-thickness strength in a sheet means greater resistance to yielding under biaxial tension, or "texture hardening";3&apos;4 if R < 1 the result may be a "texture softening" under the same loading conditions.4 Most R data relate to steel sheets for deep-drawing applications. Values for steel and other materials of cubic structures are not often much greater than 1 and nearly constant with strain in testing.1,2,7,8 To explore the implications of plastic anisotropy further, it was felt that experiments with much more strongly textured materials would be useful, and this led to the choice of magnesium alloys. The "ideal" sheet texture for magnesium contains the (0001) plane in the rolling plane, which ought to lead to R values approaching infinity. However, departures from the ideal texture, the possibility of slip in non-close-packed directions, and deformation by twinning would all be expected to introduce some range of R. Accordingly, studies on these materials were undertaken. EXPERIMENTAL Alloys in sheet form, Table I, were selected to obtain a variation in crystallographic texture, in the expectation that this would be reflected in differences in plastic anisotropy. Pole figures constructed by the Schulz surface-reflection technique9 were provided with the experimental materials by the Dow Metal Products Co. Profiles of pole density along great circles through the rolling (0 deg) and transverse (90 deg) directions were prepared from the pole figures and are collected in Figs. 1 and 2; considerable departure from the "ideal" (0001) alignment in the rolling plane is evident, with the largest angular spread in both directions being found in the ZEl0 alloy. Results of tensile tests on full-thickness specimens of 6-in. gage length by 1/2-in. width are given in Fig. 3 as engineering stress-strain curves* in rolling and transverse directions. All tests but one were made at a constant drive rate of 0.02 in. per min, and the final values of percent elongation at fracture, over the initial 6-in. gage length, are noted at the ends of the curves; one test on ZE10A-

Jan 1, 1965

By K. Nassau

The Effect of tin and hydrogen on the C0 parameter of a titanium. specimens were capsule cooled in water to eliminate contamination by water. Deybe-Scherrer photograms were obtained in a 114.6 mm camera with CuKa radiation. The parameters shown in Table I and Fig. 1 were calculated from the 213 (8569°) and 302 (8173.5°) reflections? no attempt being made to correct for systematic errors. The principal difference in method of preparation of specimens between this investigation and that of Worner was the use of pickling by the latter to produce X-ray diffraction samples. The possibility that hydrogen introduced by pickling was responsible for the lower a and c-parameters was investigated with the same 80 pct HNO3- 20 pct HF solutions used by Worner. The 6 and 10 at. pct specimens, the parameters of which had already been determined, were pickled and the c-parameters obtained are also shown in Fig. 1. The a-parameters, not shown, are also diminished. The quality of the lines obtained from the unetched and etched samples was unchanged, being quite sharp in both cases. It is quite possible that if corrections for systematic error carried out that the parameters obtained for the unetched samples would approach the data of Worner. In any event, the parameters of the etched samples would be still lower. The data obtained here is evidence that hydrogen in solution has contracted the c and a -parameters. Crystallographic Angles of Calcium Tung-state (Tetragonal, c/a = 2.169) K. Nassau In connection with the preparation and orientation of single crystals of calcium tungstate (Scheelite -CaWO4), the need arose for a stereographic projection for this tetragonal material. There appear to be no tetragonal projections with a c/a ratio above that of indium1 (c/a = 1.522) in the literature. In addition to its use for calcium tungstate, such a projection might find other more general applications and is accordingly presented below. The most recent X-ray diffraction work on CaWO4 is that of Swanson, Gilfrich, and Cook,2 where a summary of previous work is also found. Lattice parameters given are: a = 5.242A, c = 11.372A, and c/a = 2.169. The material is tetragonal with space group Table I, giving angles between crystallographic planes (HKL) and (hkl), was calculated from the formula3

Jan 1, 1961

By J. Chipman, H. Towers, M. Paris

A simple radioactive tracer technique is used to measure the diffusion coefficient of calcium ion in molten slags. In a slag of 40 pct Ca0-40 pct Si0,-20 pct Al203, Dc " at 1450°C is 1.3x10-6 cm&apos; sec-&apos;. THE application of the principles of thermodynamics to steel and iron making problems has proved so fruitful that the kinetic approach has tended to be neglected. It seems probable that in some reactions the rate-determining step is the dif-fusivity of the reactants or of the products. But knowledge of the diffusion coefficients of the constituents of liquid slag and metal is singularly lacking. The present work was undertaken as a first step toward supplying such data for slags. Furthermore, any additional information on the physical properties of liquid slags might be expected to help in elucidating their structure. It is essentially a preliminary investigation, the course of which was determined more by the necessity of establishing a method than by the immediate intrinsic interest of the results. For example, the selection of calcium ion to be studied was dictated by the suitability of the isotope Ca45 in that it is a simple emitter with a long half-life. Of the other ions commonly encountered in slags, the isotopes of iron and manganese have relatively complex radiations as well as the normal disadvantage of requiring control of the oxygen potential of the atmosphere; Mg27 and Al29 have half-lives measured only in minutes; Si3&apos; has a simple decay process but its half-life of 2.8 hr is too short for preliminary studies; the only useful oxygen isotope is the stable O18; and there remain only sulphur and phosphorus both of which have suitable isotopes but were rejected as being of less fundamental interest than calcium. Similarly a lime-alumina- silica slag was used in preference to calcium silicate primarily because of its low melting point and its capacity to form a glass on fairly rapid cooling. Literature Review Very few studies of diffusion in liquid silicate systems have been reported. In order to determine the origin of diopside inclusions in felspathic rocks, Bowen1 investigated the diffusion between diopside and various mixtures of albite and anorthite. Platinum crucibles were used with diopside, the heavier of the two liquids, forming the lower half of the cell and diffusion taking place against gravity. Change in concentration along the diffusion path was found by measuring the refractive index of the quenched glass. Nearly thirty years later McCallum and Barrett2 used essentially the same method to determine the diffusion coefficient of lime in lime-alumina-silica slags. In this case the interest was to find the rate-determining step in the process of slag attack on refractory materials. In an investigation of the kinetics of the sulphur reaction, Derge, Philbrook, and Goldman8 determined the diffusion coefficient of sulphur in a typical blast furnace slag by the simple procedure of melting a slag containing 2 pct S over an identical slag sulphur-free. They make no claim to a high degree of accuracy but suggest that D, is of the order of 10-6 cm2 sec-l. Other high temperature liquid diffusion studies have been concerned with metals. Holbrook, Furnas, and Joseph4 determined the diffusion coefficients of silicon, phosphorus, sulphur, manganese, and carbon in liquid iron by immersing a small carbon crucible containing pure iron-carbon alloy in a large vessel containing iron with a high concentration of the particular element. Their results were confirmed by Paschke and Hauttmann5 using a similar method. Diffusion coefficients in silicates in the glassy state have been studied by Johnson, Bristow, and Blau6 Both Na24 and Ca45 were used as tracers but only the

Jan 1, 1954

By J. Kostuik, M. J. de Bastiani

The method of mining the uranium orebody at Denison mine in the Elliot Lake district of Ontario is discussed. Details of the development of haulage-ways and rooms are giuen, as well as methods of ore haulage. The milling and beneficiation stages are noted briefly. Located in the Elliot Lake mining district of Canada, the Denison mine lies between Sudbury to the east and Sault Ste. Marie to the west, Fig. 1. This area is overlain by Huronian sediments filling a basin in the Keewatin basement complex. Subsequent folding of these sediments developed a synclinal structure, known locally as the Quirke Lake Trough, which forms the northern portion of the now famous big Z structure, the geological trademark of this region. Plunging to the west and extending nine miles from the granite outcropping in the north to the Keewatin lava contact to the south, the syncline has dips of 10" to 45" on the north limb and 10" to 20" on the south limb, Fig. 2. The Denison orebody, located on the north limb of the syncline, lies between 800 and 3000 ft below the surface. The main ore zone is within 50 ft of the Missisagi-Keewatin contact (see Fig. 3), and it varies in thickness from 6 to 32 ft. This ore zone has a composite dip of 19" to the south and is composed primarily of two pyritized conglomerate beds separated by a band of pebbly quartzite stratum. The upper conglomerate bed of the main zone varies from 2 to 15 ft in thickness, while the lower conglomerate varies from 2 to 12 ft. Over extended areas, mining is carried out over the entire section comprising the two conglomerate layers and intercalated quartzite; in other areas, the conglomerates are selectively mined, depending on the thickness of the quartz-ite. The ore zone contains approximately 6 pct sulfides and 80 pct silica. The predominant uranium-bear ing minerals are brannerite, uraninite, and an unidentified mineral (probably thucolite). Some of the uneconomic metallic minerals identified to date are pyrite, pyrrhotite, and chalcopyrite. MINE LAYOUT Shafts: Underground exploration and development (Fig. 4) were performed through two shafts 1/2 mile apart. The No. 1 shaft, sunk to a depth of 1856 ft with the main station established at the 1600-ft ore level, is a 250-sq ft, 5-compartment shaft capable of handling 4500 tpd. Two 5x5-1/2-ft compartments serviced by a 12-ft diam double-drum hoist, are used for hoisting 190-cu-ft bottom-dump skips in balance. A 30-man cage, offset by a counterbalance, operates within a 5-1/2x11-1/2-ft compartment. The fifth compartment is used as a manway, pipe, and cable-way. This shaft is also provided with an intermediate pumping station used during the initial mining phase as well as loading-pocket and spill-pocket installations and pumping facilities. The 480-sq ft No. 2 shaft, located down-dip from No. 1 shaft, has a 2776-ft depth. Serving as the main hoisting shaft with a maximum capacity of 9000 tpd, it has eight compartments, four of which are used for hoisting ore in 10-ton capacity bottom-dump skips. These four compartments, measuring 5x6-ft in section, are serviced by two 12-ft diam double-drum semi-automatic hoists. A 50-man cage is operated in a 15x8-ft compartment, and it is counterbalanced by a 12-ton weight. Two compartments are used for ventilation, manway, electric cables, and pipes. A station was constructed at the 1325-ft horizon of the No. 2 shaft for relay pumping. The main sta-

Jan 1, 1961

By E. L. WOOD

IN ATTEMPTING to summarize briefly the reconstruction of the Hecla plant since the fire, three important facts must be held in mind; namely: a hurry-up job with the shadow of an insurance company in the background; restriction of working space in the narrow Burke Canyon; and building two-thirds of the plant on a filled area. Construction work was carried on without interruption through the winter season. These adverse conditions have contributed many obstacles not ordinarily encountered in mining work. The first problems immediately after the fire were organization and policy; the-former to create an efficient construction crew out of a mining organization; the latter to determine the type and extent of surface plant to be built. The new crew was organized from a nucleus of mine employees, 25 per cent. of the old crew remaining for construction work. Permanent fireproof buildings were decided upon, the general arrangement of the new plant to be similar to the old one as far as possible, at the same time enlarging it 100 per cent. in anticipation of the demands which would be made upon it when the Star Mine began operating. Cleaning up the wreckage was a big job, the extent of which is indicated by the fact that 30 carloads of scrap iron and steel were moved off the property. In re-establishing transportation facilities at the plant, a previous disadvantage of a steep grade on the high line was obviated by excavating 1600 yd. of solid rock; the fire having destroyed all town buildings below, made this work possible.

Jan 1, 1924

JOHN ALEXANDER MATHEWS, who has been awarded the Hunt Gold Medal for his paper "Austenite and Austenitic Steels," which was pre-sented before the Institute as the Howe Memorial Lec-ture for 1925, was born at Washington, Pa., on May 20, 1872. His interest in metallurgy may be said to be hereditary, as three generations of his Colonial forbears were gold and silversmiths. After graduating from Washington and Jefferson College in 1893, he entered Columbia University where he was successively assistant in assaying and tutor in chemistry and at the same time continued his work for the Ph. D. degree, which he received in 1898. He was at one time awarded a fellowship in chemistry, and for 1900, 1901 and 1902 re- ceived the award of the Ear- nard Fellowship for the En- couragement of Scientific Re- search, spending one year at the Royal School of Mines, in London, studying alloys un- der Sir William Roberts- Austen, another at Columbia under Henry M. Howe, and the third at Sanderson Bros. works, Syracuse. While in England, he was one of the first three, recipients of an Andrew Carnegie Scholarship of the Iron and Steel Institute of Great Britain, which later awarded him the first Car- negie Gold Medal for Re-search. He entered the employ of the Crucible Steel Company of America, at its Sanderson works, in 1902, as metal- lurgist and soon became as- sistant manager. In 1908 he ent to the Halcomb Steel JOHN A. Co., Syracuse, N. Y., as superintendent, later becoming general manager and president in 1915. In 1920 he returned to Crucible Steel Co. of America, first as vice-president and later became president from 1921 to 1924. He retired from the presidency in 1924, made a metal-lurgical trip to Europe, and returned as vice-president to resume his "favorite pastime" of directing research and development work in the production of special tool and alloy steels. He has taken a particular interest in the development of austenitic steels which, in addition to an extraordinary resistance to corrosive attack, show under fatigue, torsion, and tension tests superior qualities as compared with the ordinary engineering steels, and at elevated temperatures show remarkable resistance to oxidation and scaling and several times the strength of many of the complex alloys that are not of the natural austenitic variety.

Jan 2, 1928

By H. F. Beardmore

PETROLEUM consumption during 1946 broke all previous records and further increases are expected during 1947. U. S. consumption amounted to an average of 5,280,000 bbl a day, of which 4,745,000 bbl was domestic crude oil, with the rest from natural gasoline production and crude oil imports. World consumption during the past year, excluding Russia, is estimated at 7,200,000 bbl daily. Forecasts for 1947 indicate a U. S. consumption of 5,425,000 bbl daily of petroleum products. This is expected to be made up of 4,655,000 bbl of domestic crude oil production, 340,000 bbl of natural gasoline production, 400,000 bbl of crude oil imports, and the rest from stocks. Petroleum&apos;s principal use is still as a fuel. The field remains highly competitive, but petroleum has been continuously progressing. Less than fifty years ago, oil supplied only one twentieth as much of the nation&apos;s total energy as coal, but today it supplies over half as much.

Jan 1, 1947

By A. J. Ardell

SASS and cohenl (S-C) have recently reported some transmission electron microscope observations of an interesting effect which they call "veining". They observed veining in thin foils of solution-treated and (in certain cases) aged samples of a Ni-10.3 at. pct Ti-0.6 at. pct A1 alloy (assumed equal to 10.9 at. pct Ti). S-C suggest that veining in solution-treated samples is due to the selective electrolytic etching of titanium-rich regions in alloys which are otherwise homogeneous. They associate the veins with the discrete titanium-rich regions detected in a magnetic study of aging in this system by Ben Israel and Fine,&apos; and they also suggest that the initial strengthening of aged Ni-Ti alloys is due to these titanium-rich regions, rather than the formation of the coherent precipitate (Ni3Ti, L12 crystal structure).

Jan 1, 1970

By F. M. Drake

IN this paper I propose to describe a plant which I lately erected for the Mount Stewart Lead and Silver Mining Company of Leadville, New South Wales, Australia. I am indebted to Mr. W. F. Burrow, of the Roads and Bridges Department of New South Wales, for the drawings which I present herewith, he having reduced and assembled them from my working drawings. The works are situated on a sloping hillside, but sufficient fall mas not available to have the furnace as high as desired, and at the same time have a good slag-tip and sufficient depth on the ore-floor to store a supply of ore and flux. The ore is delivered on the ore-floor (which is of the full width of the furnace-building, and extends back into the hill a distance of seventy feet) by two overhead tramways (not shown in the drawings), one on each side. From these the ore-mixture is made up on one side, while it is being taken to the furnace from the other. The fuel also is delivered by these tramways. The fluxes are stored on a floor directly at the back of the boiler and engine room. The boiler is a Cornish one, 6 feet 6 inches in diameter by 25 feet long. Its flue is 3 feet in diameter and does not contain Galloway tubes. The working-pressure is 40 pounds per square inch. The engine is an old-fashioned one, with a cylinder 16 inches in diameter by 30 inches stroke. Both the engine and boiler had been part of the plant of a defunct gold-mining company. They were very extravagant in their consumption of fuel. The blast is supplied by a rotary pressure-blower, of the Baker pattern, made in England. It has a capacity of 60 cubic feet per revolution. The furnace, which has several novel points, is shown in detail in Figs. 1, 2 and 3. The jackets are of cast-iron, and are higher than those generally used. They are different, too, in that the feedwater inlet is through a hand-hole plate near the bottom. This plate is fastened to the jacket by stud-bolts, and is provided with a baffleplate, which prevents the cooling water from impinging against the inner plate. The outlet is by a goose-neck at the top, which dis-

Jan 1, 1893

By J. P. Nichols

Modern vibrating screening dates from about 1910 at which time the forerunner of the present day two bearing and four bearing circular motion inclined vibrating screens were first introduced. These simple machines consisted of a screen box holding some kind of a screening surface to which was attached an off-center shaft or a shaft with an off-center weight which was rotated. The rotation of these shafts caused a shivering motion to the screen box and produced the first vibrating screen. In the 1920&apos;s and early 30&apos;s, the box designs were improved and the mechanisms designs were also improved and by 1940, vibrating screens were an important part of most process plants. In the early days when the screen sizes were dictated by how much could be shoveled onto the screen box and by the force that a particular mechanism could produce, not much thought was given to the proper sizing of the particular units. As mechanism and body design improved the ability to predict vibrating screen capacity at various openings became more important. In the late 1930&apos;s, a set of empirical capacities came to be used. with few modifications, these capacities are still in use today, both by those companies that use a formula involving only the amount of fine material in a feed, and by those companies using a formula in which the total feed to a particular screen is used. In either method of calculation, the empirical values are based on these ideal conditions: (1) The material being fed to the screen contains 25% oversize. (2) The feed to the screen contains 40% half size material. (3) The material has a bulk density of 1.6 T/Cu.M. (100 lbs/cu.ft.). (4) The screening surface has an open area of 50%. (5) The material is dry, free flowing and relatively cubical. (6) The maximum screening efficiency required is between 90 and 95%. It is obvious that these conditions do not occur in natural or crushed size distributions. Therefore, modifications must be made to these empirical values to allow for the calculation of a vibrating screen for a particular set of conditions. Before we consider these various modifications, let us look at what happens to material as it is acted on by a vibrating screen so that we can better understand why the modifications are nec-

Jan 1, 1982

By Blair R. Benner

This paper describes the installation and operation of a Texas Nuclear on-line silica analyzer (NOLA) coupled with a Leeds and Northrup Microtrac particle-size monitor (Microtrac) at U.S. Steel&apos;s Minntac taconite concentrator. An automatic sampling system provides the NOLA with samples of final concentrate. After the sample is analyzed for silica by the NOLA, it is pumped to the Microtrac for size and surface area measurement. A sample is analyzed every six minutes, providing the control room with the silica concentration, the percent passing 270, 400, and 500 mesh, and an equivalent Blaine surface area number. When fed a slurry of final concentrate containing between 20 and 70% solids and 5 to 6% silica, the NOLA analysis is within ±0.2% of the wet chemistry silica. The agreement between the Microtrac output and standard screen analyses is ±1.2% at 270 mesh; ±1.5% at 400 mesh, and ±2% at 500 mesh. The poorer disagreement at the finer sizes is mainly due to inaccuracies in screening at 400 and 500 mesh. The agreement between Microtrac surface area a d laboratory Blaine surface area is about 9 ±80 cm 2/g. These instruments provide rapid and reliable feedback information to the concentrator and feed forward information to the agglomerator.

Jan 1, 1984

By Henry J. Schwellenbach

Lack of a system in scheduling the replacement of capital equipment can result in emergency purchases of units which may later be found unsuitable for the job. New York Trap Rock Corp., which produces crushed stone for use as construction aggregate, was faced with just such a situation some years ago. The company replaced capital equipment only when machinery in use was no longer serviceable, or when there was an obvious need for different equipment. Operating and maintenance costs were generally neglected because an efficient method was lacking. New York Trap Rock has four plants located along the Hudson River, all within 70 miles of New York City. Crushed stone output-6 million tons a year-is moved to markets in metropolitan New York, New Jersey, and Long Island areas by water transport. Customers are contractors with ready-mix concrete and asphalt plants located on the water.

Jan 10, 1959

By W. A. Eardley

FIFTEEN years ago the world&apos;s deepest oil well penetrated the earth about 7300 ft. That depth has now been more than doubled. Why has such deep drilling become necessary and how has it become possible? Three factors have had an important bearing: (1) Depletion of shallow zones, making it necessary to search for deeper producing measures. (2) The perfection of prospecting methods, which have been success- fully used to locate favorable buried structures, many at great depth. (3) Improvement in the quality of steels used for drilling.

Jan 1, 1940

By D. J. McAdam

As shown in three recent papers by the author,6,7,8 in two papers by McAdam and Mebs,9,10 and in a paper by McAdam, Mebs, and Geil,11 the technical cohesive strength of a metal, in any particular state as regards mechanical treatment and heat-treatment, cannot be represented by a single stress value, but must be represented by a diagram with the principal stresses? as coordinates. Each point on the boundary of such a diagram represents a technical cohesion limit. The technical cohesive strength thus comprises an infinite number of technical cohesion limits, each representing fracture under a specific stress combination. Moreover, neither the yield strengths nor the ultimate strength can be represented completely by a single stress value, but must be represented by a diagram with the principal stresses as coordinates. All combinations of the principal stresses may be classified in three groups as illustrated by Fig. I. Fig. Ia shows three typical stress combinations with no two principal stresses equal. The magnitude of each principal stress is indicated qualitatively by the length of the arrow. Arrows pointing away from the cube indicate tensile stresses; arrows pointing toward the cube indicate compressive stresses. Typical stress combinations with two principal stresses equal are illustrated in Figs. Ib and Ic. Such stress combinations would be produced by subjecting a cylinder to combinations of uniform axial and radial stresses. The uniform radial stress may be resolved into two equal principal stresses, with the mutually perpendicular directions rotatable around the axis of the cylinder. Fig. Ib shows stress combinations with S2 equal to Sa. The greatest principal stress is in the axial direction, and the stress combination tends to cause either absolute or relative increase in length.* Fig. Ia shows stress combinations with Ss equal to Sl. The greatest principal stress is in the radial direction, and the combination tends to cause either absolute or relative decrease in length. The complete representation of either technical cohesive strength, yield strength, or ultimate strength generally requires a three-dimensional diagram. When two of the principal stresses are kept equal, however, the strength of a metal may be represented by a two-dimensional diagram with the coordinates representing the axial and radial stresses.6-11 In this paper, attention will be confined almost entirely to stress combinations with two of the prin-

Jan 1, 1944

By R. N. Orava

TO the author&apos;s knowledge, only one satisfactory high-resolution technique for etch-pitting dislocations in Cu-Zn alloys has been published.&apos; In that account, pits in 70/30 brass single crystals were produced by etching electrolytic ally in a 30 pct orthophosphoric acid bath. Thereafter, observations were made from surface replicas by electron microscopy. The method of pitting and observation permitted the high resolution necessary for the distinction of individual dislocations in arrays of pile-ups. However, no comment was offered concerning the possibility of obtaining pits which are amenable to optical resolution. Moreover, for adequate results, the electrolytic pitting process is invariably preceded by a polishing stage which could obscure the surface features of interest. Consequently, it would be desirable to be able to delineate, by solely chemical means, dislocations which could be detected by both optical and electron metallo-graphic techniques. This was achieved by the simple expedient of modifying two etchants reported by young2 to reveal dislocations on the (100) planes of pure copper. Single crystals of 70/30 a brass, described previously,3 were sectioned to provide a surface parallel to a set of {100) planes, mechanically polished, and subsequently electropolished at 2.4 v in a solution comprised of 2 parts H3PO4, 4 parts ethanol, and 3 parts water. The inclusion of ethanol tended to inhibit nonuniform surface attack. Etch-pitting was effected by a 2 to 3 sec immersion in a 70 pct aqueous solution of HNO3. The samples were then washed in a fast-flowing stream of water, and rinsed further in distilled water, and ethanol, before drying. It is important to note that this reagent should be either used immediately after mixing, or, if allowed to cool, reheated to about 35°C prior to use. No pitting was obtained at room temperature. Typical results are shown in Fig. 1 where (a) is an optical view of the pitted surface and (b) is an electron micrograph of a silicon monoxide replica shadowed with tungsten oxide. The former is characteristic of a somewhat longer etching time (-6 to 8 sec) which varied with bath temperature. Similar pits accrued from a 1/10 aqueous dilution of another of Young&apos;s solutions2—2 M FeC1,6H20 and 7.8 M HBr.

Jan 1, 1968

By S. R. Maloof, W. R. Mitchell, J. A. Mullendore

Preliminary experimental evidence is presented to show that the metallic impurities aluminum, iron, and silicon, and beryllium oxide as found in commercially pure hot-pressed beryllium powder can be reduced to lower Concentrations by Zone -Purification techniques. The reduction in the concentration of aluminum to extremely low levels (10 PPm) is noteworthy, since earlier work demonstrated that aluminum is a major factor contributing to the hot-tearing of beryllium during fusion welding. On the basis of present findings, a method is suggested for producing beryllium metal of improved weldability. EXPERIMENTAL research now being conducted on the purification of beryllium indicates that several of the metallic impurities and beryllium oxide can be reduced to lower concentrations by employing standard horizontal zone-refining techniques. For the preliminary work, commercially-pure hot-pressed beryllium having a purity of 97.84 pct was used. The chemical composition is given in Table I. The hot-pressed beryllium was machined into bars 5/8 by 5/8 by 4 to 6 in. in length. Beryllium-oxide boats which had been conditioned by prior heating in a vacuum of 10"5 mm of Hg at 1100°C for 3 hr were used to hold the beryllium while it was zone melted. The boat with its charge, along with a smaller beryllium-oxide boat containing scrap beryllium to be used for gettering purposes, was loaded into a quartz tube and evacuated to 10-6 mm of Hg. Alter alternately evacuating and flushing three times with purified argon, the furnace tube was backfilled to a pressure of 1/6 atm of A and sealed off by means of a vacuum-tight stopcock. It was then removed from the pumping equipment and mounted on the traveling carriage of the zone-refining apparatus. Heating was accomplished with a 10 kw 450 kc induc- tion heating unit using an induction coil consisting of two turns of 3/16-in. diam copper tubing. Before starting to zone melt, the atmosphere in the furnace tube was gettered by heating the scrap beryllium in the smaller boat to above its melting point and holding at temperature for several minutes. The carriage was then shifted so as to locate one end of the beryllium ingot in the large boat within the induction coil. A molten zone approximately 3/4 to 1 in. was established by loading directly into the ingot. The molten zone was moved very slowly along the length of the ingot. Before each pass was made the procedure for evacuating, flushing, and backfilling, and so forth was repeatedI&apos; Speeds of 1 1/2 and 3 in- per hr were used with up to twelve zone passes. The appearance of a typical zone-refined ingot is shown in Fig. 1. After zone refining, the grains in the ingot appear to be elongated in the direction of zone travel, whilst before, they are essentially equi-axed. A microexamination revealed the presence of a network in the beryllium grains as seen in Fig. 2. Laue spots in back reflection pictures taken of the sample were not sharp, indicating the presence of subgrains in the structure. As can be seen, however, many of the network boundaries cross beryllium grain boundaries. It has been shown by Martin and Moore1 that beryllium solidifies as a bcc structure which then transforms to the hexagonal structure at about 1250oC.It is believed that the observed network is merely the outline of the bcc structure which formed from the melt and are not subgrain boundaries. In order to eliminate surface contaminants, approximately 1/16 of an inch of material was removed from the outer skin of each ingot after zone refining.

Jan 1, 1962

By A. C. D. Chaklader, Ashok K. Kakar

The basic density equation originally dericed &apos; to predict the increase in density of a compact of spherical particles with the progressive deformation at the points of contact has been further modified to include the yield strength of the material. This has been done by assuming that the contact areas grow to stable sizes under a fixed stress which is equal to three times the yield strength. The final equation has the form: where Do and D me the initial and final bulk densities of the compact, u is the applied pressure, and Y is the yield strength of the material. This equation was tested with the data obtained on spheres of lead, K-Monel, and sapphire. The calculated yield strength t~alues for lead and sapphire are within the range of values reported in the literature. A few of the earliest hot pressing models proposed to explain the mechanism by Murray, Livey, and williams2 and then by McClelland3 are based on a plastic flow mechanism. However, more recent investigations suggest that the overall densification process is a combination of several mechanisms, such as particle rearrangement, fragmentation, plastic flow, and stress-enhanced diffusional creep. While fragmentation and particle rearrangement are considered to be responsible for the densification in the early stages,"475 it has been concluded that the final stages of hot pressing are controlled by stress-enhanced diffusional creep.516 The manner in which the densification takes place, i.e., by fragmentation, particle rearrangement, plastic flow, or stress-enhanced diffusional creep, would depend upon the type of material, the temperature, and the stress level used during the hot-pressing experiments. Metal compacts can be expected to have a much greater contribution from plastic flow than ceramic oxides. Also, plastic flow would be a significant contributing factor to densification at high temperatures and high stresses. Most of these works, directed towards elucidation of densification mechanism, have dealt with kinetics of the process. The results of most of the authors vary from one another and they have proposed either new empirical or semiempirical equations to fit their data. The densification rate was found to vary with the type of the powder, shape and size of the powder, initial packing density of the compact, and a few other factors such as rate of heating, pressure, and so forth. Beyond the initial stages, the densification process has been considered to be as time-dependent flow, controlled by a diffusional process, e.g., Nabarro-Herring creep. Palm our, Bradley, and johnson&apos; have attempted to use modified creep rate equations to interpret the data of densification under hot-pressing conditions. Beyond the initial stages, however, the densification would be controlled by a process depending upon the temperature, pressure, and size of the powders. It is the authors&apos; belief that such densification cannot be exclusively controlled by a single process and so attempts should be made to study some observable phenomenon like microstructure, yield strength, and so forth. The emphasis of this work has been toward studying the densification problem from a more fundamental point of view. Some of the principal variables, like initial packing density, mode of packing, and size of the powders, have been controlled to a great extent. The total strain produced on pressure application (instantaneous) in such a case can be considered to be due to plastic and elastic deformation. The elastic component of the strain can be determined by decreasing the load to the initial value. The strain remaining then can be correlated with the contact areas produced by deformation and the corresponding applied load. In a previous paper,&apos; the possible deformation behavior of spheres in a compact has been theoretically analyzed and experimentally tested. The change in contact area radius a relative to the particle radius R was related to the bulk density and the bulk strain for simple and systematic modes of packing. Tt was found that a density equation relating the above parameters can be represented by: where D and Do are the bulk densities of the compact at any value of a/R and a/R = 0, respectively. This basic equation should hold for any material as it was derived from geometrical considerations alone. An attempt has been made in this work to include the yield strength in the above density equation, so that a knowledge of the properties of any material can be used in predicting the densification behavior during the hot-pressing process. THEORETICAL CONSIDERATTONS The deformation of two spheres in contact under a static load can be compared to the deformation occurring between a hard spherical indentor and the flat face of a softer metal. Tt has been shown theoretically by both ~encky~ and lshlinskyg and experimentally by ~abor" that, for a material incapable of appreciable work hardening, the mean pressure required to produce plastic yielding (for deformation occurring between flat face and a hemispherical indentor) is approximately equal to three times the elastic limit, Y, of the material (in tension or compression experiments). Tabor has further observed that the same relationship is valid in the case of work-hardening materials, if the elastic limit at the edge of the indenta-

Jan 1, 1969

By M. W. Lightner

IN 1947 the steel industry rebounded from its wartime effort and produced a record-breaking peacetime tonnage of steel ingots. During the first six months of the year the industry produced 42,000,000 tons of ingots and expected to produce 85,000,000 tons for the year. With a rated capacity of some 91,000,000 tons, production was at a rate of about 93 per cent of capacity. Credit must be extended to the steel producers who have maintained this steady state of operations while faced with many problems, not the least of which was a continued shortage of satisfactory scrap. Furthermore, the steel industry started a record-breaking peacetime expansion program at a total cost of more than $1,000,000,000. This program will increase the ingot-making capacity of the country by 2,500,000 tons and should be completed in 1948.

Jan 1, 1948

By Zay Jeffries

A SURVEY of rare metals and minerals for the past year places uranium as one of two partners, the other being the neutron, in what historians will probably say is the greatest discovery in physics at least during the year and probably for a consider- ably longer period. The uranium atom has been made to divide into parts somewhat after the style of reproduction of the amoeba. When an amoeba divides into two parts, however, it produces two amoebae substantially alike and each substantially like the parent: furthermore, there is no considerable change of energy when this happens. When the uranium atom divides it yields other atoms such as barium and krypton with the complete destruction of the original uranium atom but with the liberation of a tremendous amount of energy. This will be discussed more at length later.

Jan 1, 1940