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By Theodore Simons

The rapid and comparatively recent development of flotation has opened so fascinating a field for study and research that the older processes of gravity concentration no longer receive the attention they deserve. The early work of Munroel and Richards12 and the more recent contributions by Clevenger and Coe,3 Laist and Wiggin,4 Ammon,5 Bardwell,6 Crowfoot,' and Hayden8 (to mention only some which have appeared in our own Transactions) and by Schu1z,9 have furnished so much data that to offer something new seems a difficult task. It is still possible, however, to present known facts from a different point of view, and, with this in mind, the writer has undertaken to express basic principles of gravity concentration in terms of simple mathematics and mechanics; the conclusions thus reached will be found to correspond, in general, with those obtained by experimental methods. Rittinger, in his classic Aufbereitungskunde (1867)) reached analogous conclusions by way of intricate higher mathematics, for which reason his interesting investigations have remained a sealed book to most of us. The writer hopes that a more elementary treatment of the subject, based in part on Rittinger's metheds, may arouse new interest in the study of basic principles.

Jan 1, 1923

By Theodore Simons

The rapid and comparatively recent development of flotation has opened so fascinating a field for study and research that the older processes of gravity concentration no longer receive the attention they deserve. The early work of Munroel and Richards12 and the more recent contributions by Clevenger and Coe,3 Laist and Wiggin,4 Ammon,5 Bardwell,6 Crowfoot,' and Hayden8 (to mention only some which have appeared in our own Transactions) and by Schu1z,9 have furnished so much data that to offer something new seems a difficult task. It is still possible, however, to present known facts from a different point of view, and, with this in mind, the writer has undertaken to express basic principles of gravity concentration in terms of simple mathematics and mechanics; the conclusions thus reached will be found to correspond, in general, with those obtained by experimental methods. Rittinger, in his classic Aufbereitungskunde (1867)) reached analogous conclusions by way of intricate higher mathematics, for which reason his interesting investigations have remained a sealed book to most of us. The writer hopes that a more elementary treatment of the subject, based in part on Rittinger's metheds, may arouse new interest in the study of basic principles.

Jan 1, 1923

By AIME AIME

AT bottom of this page is a photograph recently taken by a student-John E. Stewart-of the most northerly situated college in the world, the Alaska Agricultural College and School of Mines. It is situated at College, near Fairbanks, Alaska, approximately on the 65th parallel of latitude, and therefore just south of the Arctic Circle. It is farther north than Hudson Bay, and in about the same latitude as southern Greenland.

Jan 1, 1932

By J. M. Adams

It is my purpose to give some of the results obtained by an experience of nearly seven years in working ores by the method frequently called the Washoe Process, and in several mills of which I have had charge, but principally in the Owyhee Mill, at Silver City, Idaho, which had twenty 650-pound stamps, and sixteen pans. I shall discuss here merely the mechanical details for working ores generally, subdividing the subject as follows : 1. Preparation of the ore for the stamps; 2. The crushing in the battery; 3. The settling of sand or pulp in vats or tanks; 4. The treatment in the pans; 5. The results obtained in settlers, agitators, and concentrators; 6. The straining of quicksilver, cleaning of amalgam, and retorting; 7. The saving of slimes and their subsequent treatment; 8. The loss of quicksilver. For descriptions of the various kinds of orebreakers, stamps, tanks, pans, settlers, etc., I must refer to the various works on these subjects, prominent among which are the reports of the United States Commissioner of Mining Statistics,and the volume on "Mining Industry," the third volume of the United States Geological Survey on the Line of the Fortieth Parallel through the gold and silver bearing regions of the great West, undertaken under the able guidance of Clarence King, assisted by Mr. James D. Hague and others. In this discussion it will be assumed that the general arrangement of the quartz mill is understood; and the question will be treated how to secure, from such a mill, the greatest economy in working, combined with the largest results. This place seems fittest for a single preliminary suggestion—namely, that there should be double "floors" throughout the mill, so that nothing can sift through and be lost.

By Robert H. Aborn, J. J. B. Rutherford

It is now well known that troublesome intercrystalline corrosion may occur in austenitic stainless steels following exposure of the metal to a temperature within the range 1000° to 1500° F. (540° to 815° C.). The present paper describes a satisfactory method of estimating the extent of such corrosion, based on the measurement of the electrical resistance of a specimen before and after attack. This new method enabled us to study quantitatively the effect of several factors upon intergranular corrosion in the 18 Cr, 8 Ni type of alloy. The results show that susceptibility to this attack increases with increasing carbon content and grain size and appears to pass through a maximum for certain combinations of temperature of sensitization and period during which the alloy was maintained at that temperature; and are in complete accord with our interpretation of the mechanism of this phenomenon. The method is probably applicable to other metals or alloys subject to intercrystalline attack, such as the aluminum alloys of the duralumin type. The methods hitherto in use for estimating the degree of intergranular attack fall into three types: (1) microscopic examinationll (2) macroscopic examination of fractures, and (3) determination of the time required for complete failure or disintegration.2 None of these lends itself very well to a measurement of the extent of corrosion. The first two are qualitative in nature and the third provides an arbitrary value largely dependent on individual judgment, since failure is a progressive phenomenon and not a sudden event. Our experience is that weight-loss determinations, although valuable in some types of corrosion investigations, bear no simple relation to intercrystalline corrosion in this type of alloy, as is to be expected since the phenomenon probably involves only the thinnest films between adjacent metallic grains. Measurement of electrical resistance has been used recently in the study of some types of corrosion,3 but seems not to have been applied to

Jan 1, 1932

By George W. Sargent

For the experiments here described a rod was used, 0.75 in. in diameter, and rolled from one ingot. Analyses of the ingot and rod showed them to have the following composition respectively: C. Mu. Si. P. 8. Percent. Percent. Percent. Percent. Percent. Ingot,. .. 1.150 0.328 0.223 0.020 0.016 Rod,. .. 1.033 0.327 0.223 0.020 0.016 Pieces 4 in. long were heated to various temperatures in a closed porcelain tube, within a gas furnace, and allowed to cool with the same; they were then turned, threaded, and subjected to physical tests in a Riehlé testing-machine. The elastic limit was determined by the drop of the beam. The elongation was measured in two inches. From the threaded ends of the testrpieces, disks were cut, and prepared by combined polishing and etching, using parchment stretched over a wooden block and moistened with a 2-per cent. solution of ammonium nitrate. The structure, as thus developed, and the fractures, were magnified and photographed. A cooling-curve was constructed, and the critical point was located at 675º-680º C. A thermo-electric pyrometer was used to make the measurements of temperature. The micro-constituents of steel have been so frequently and thoroughly described by others that I need only say here that the theoretical micro-structural constituents of this steel were : pearlite, 95 ; ferrite, 0 ; cementite, 5 per cent. The quenched metal would be expected to consist almost entirely of martensite—provided, however, the quenching be done at or near the proper temperature. Rapid quenching from a high temperature would give rise to austenite.

Jan 1, 1902

By Werner Ostertag

A series of rare earth cobalt compounds of the composition RCoa (r = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Ev, Tm, Lu) has been prepared. The compounds crystallize in space gvoup R3m and are isomorphous with PuNi3. Except for CeCo3 and PrCo, the series shows decreasing- values of a. and co. The relalively small parameters of CeCo, and PrCo, are explained by valencies of cerium or praseodymium which exceed the usual rare earth valency of three. The structure of the compounds is discussed as in-fillings of kagome nets in direct and staggered superposition. In the course of a systematic investigation of rare earth cobalt compounds"2 and their magnetic properties,, a series of alloys corresponding to the formula Rco3 has been prepared. The investigation of the Rco3 series was stimulated by our investigation of the yttrium cobalt system2 as well as by reports in the literature: Smith and Hansen4 reported the structure of YcO3 and Van vucht5 that of GdCo3; ceco3,6 Gdco3,7 and DyCo3 7 have been found to be single-phase during phase diagram studies. It was the purpose of this work to report crystallographic data on the entire Rco3 series and to interpret the structure of these compounds on the basis of general principles as discussed by Frank and Kasper.8 At the time this work was terminated, it was learned that a similar investigation has been carried out independently by Bertaut, Lemaire, and schweizer.9 Except for CeCo3 (ao = 4.952, co = 24.73') and NdCo3 (a0 = 5.067, co = 24.76') data of this work are in satisfactory agreement with their investigation. EXPERIMENTAL TECHNIQUES A series of samples having the composition Rc03 was prepared from stoichiometric amounts of the rare

Jan 1, 1968

By Donald Ofte

LIQUIDUS temperatures of molten alloys were measured in an oscillating-cup viscosimeter by observing the abrupt increase in the alloy viscosity when the apparatus was cooled below the alloy liquidus temperature. The liquidus transformation can be an elusive thermal effect in an alloy system where a small amount of material is involved in a low-enthalpy liquidus reaction, or where other unfavorable physical conditions interfere. Using the viscosity technique, liquidus temperatures were measured in binary alloys of plutonium with cerium, gallium, and iron, as well as ternary Pu-Ce-Co alloys. The previously described oscillating-cup viscosimeter1 is a torsion pendulum consisting of a right circular, cylindrical tantalum cup fitted to a rigid shaft which, in turn, is suspended by a torsion fiber in a highvacuum system. When the torsion pendulum is placed in oscillation the viscosity of the liquid contained in the cup is a function of both the decay of the oscillation caused by the viscous drag of the liquid contained in the sealed tantalum cup, and the period of the oscillation. The period is measured by a photo-electrically operated timer to the nearest thousandth of a second. Prior to each measurement, the apparatus is held at temperature between 5 and 18 hr to assure thermal equilibrium throughout the 8 to 10-cc alloy sample. When the cup, filled with a liquid metal, is oscillating. only a very thin outer layer of the fluid is in motion. This moving annulus represents the liquid's contribution to the moment of inertia of the torsion pendulum. When the viscosity increases, more liquid is placed in motion, and the slight increase in the moment of inertia causes a corresponding increase in the period of oscillation.

Jan 1, 1967

By AIME

BILL BREWSTER was a natural for the steel business. His family lived at Iron Mountain, Mich., when Bill was born on June 14, 1889, so that he had iron in his blood. Always he has looked toward the finished product, rather than the raw material, so that it was a fore-gone conclusion that he should work toward the steel end of the business. After preparing for college at Hotch-kiss Academy he entered the Sheffield Scientific School of Yale University from which he graduated in 1910 with the degree of Bachelor of Philosophy. No reunion of his class would be complete without Bill Brewster. Unlike many of us who try several jobs before settling down, Bill shot straight for the mark. After a summer's work at Iron Mountain, making sure of his background in the production of the raw iron ore, he entered the employ of Wisconsin Steel Works of the International Harvester Co. in September 1910 and has been there ever since. It wasn't much of a job to start with, just a laborer in the billet dock department, but soon there was an opening in the blast-furnace department, where he started as superintendent's clerk in December 1910.

Jan 1, 1946

Mr. John J. Porter, Chicago Ill. (communication to the Secretary†):—Mr. Baker's account of his experiences with stock-distribution has been particularly interesting to me, as it

Jan 1, 1905

By J. N. Ong, J. P. Ratledge, J. H. Boyce

Since German operators opened the Tsumeb mine in the early 1900's, continuous operation has been interrupted only by enforced shutdowns during two world wars and the depression of the 1930's. Original metallurgical practice was blast furnace smelting. This was applicable only to low zinc ore, leaving large tonnages of high zinc ore to be stockpiled on the surface. A gravity concentrator using tables, buddles, and jigs operated for several years, but differential flotation of the ore did not get beyond the experimental stage. When the property was put up for sale by the South African Custodian of Enemy Property there was an estimated 434,000 tons of ore on surface dumps. The dump material, assaying 4.48 pct Cu, 15.8 pct Pb, and 10.9 pct Zn, had become highly oxidized during a stay of many years on the surface. But these dump ores had to be used in evaluating possible metallurgy because the shaft became flooded after the 1940 shutdown and underground ore was unavailable. Many companies examined Tsumeb but quickly lost enthusiasm because of the formidable metallurgical problems presented by the dump ore. However, on the basis of extensive test work, the present company decided that differential flotation would be successful and purchased the property after competitive bidding.

Jan 4, 1955

By E. W. Johnson, M. L. Hill

Equilibrium concentrations of hydrogen in iron were measured at H2 pressures up to 136 atm and temperatures down to 145°C. Residual hydrogen was prominent near 600°C in air-melted but not in vacuum-melted iron. The diffusible hydrogen solubility is abnormally high below 390°C, confirming the hypothesis of hydrogen trapping.' It appears that the traps for hydrogen in iron form suddenly on cooling. The estimated H2 pressure in equilibrium with 5 ppm hydrogen in steel at room temperature is less than 1000 atm. It was shown previously1 that the diffusivity of hydrogen in a-Fe below 200°C is anomalously low, a behavior attributed to the presence in the metal structure of hydrogen "traps." The energy of the trapped hydrogen was computed as 4.8 kcal Per g-atom below that of the interstitially dissolved hydrogen. The strongest confirmation of the trap hypothesis should be obtainable from measurements of the hydrogen solubility at low temperatures. such measurements have been performed and are reported in this paper. The "residual hydrogen" effect1'' must be carefully controlled if valid measurements of the solubility are to be obtained, and such an effort was made in the present work. Previous data for the solubility of hydrogen in iron have been summarized by Geller and Sun.3 Their equation for the most probable solubility at 1 atm in a-Fe above 400°C is

Jan 1, 1962

By J. T. Eash, E. M. Wise

Many of the platinum metal alloys are hot-forged in the early stages of reduction from ingot and substantial quantities of platinum alloys are commercially employed at very high temperatures in ammonia oxidation units, orifices for forming glass rods and fibers and as cathodes in long-life thermionic amplifiers. They are used also for electrical heating resistors, safety blowout disks, thermocouples and crucibles. The tensile properties at elevated temperatures are important in many of these situations but data on the subject are limited. Creep data also are important, but will not be covered at this time. Scope and Conclusions Tensile tests were carried out at room temperature and elevated temperatures up to 1100" C. on previously well annealed samples of platinum. palladium and several of their important alloys with compositions shown in Table 1. The results are presented graphically in Figs. 1 to 4. The tensile strengths of platinum and the platinum-base alloys (with the exception of the 10 per cent rhodium-platinum alloy) at 1100" C. are from 16.6 to 18.8 per cent of the strengths of the same alloys (well annealed) at room temperature. The strength ratio of the 10 per cent rhodium-platinum alloy is 22.3 per cent, which is appreciably higher than that of the other materials tested. The tensile strengths of palladium and the palladium alloy at 1100" C. are from 10 to 11.2 per cent of the room-temperature values. The elongations of platinum and its alloys tend to increase at temperatures above 600" to 800" C., while the two samples of pure palladium show a maximum at 600" C.

Jan 1, 1938

By J. T. Eash, E. M. Wise

Many of the platinum metal alloys are hot-forged in the early stages of reduction from ingot and substantial quantities of platinum alloys are commercially employed at very high temperatures in ammonia oxidation units, orifices for forming glass rods and fibers and as cathodes in long-life thermionic amplifiers. They are used also for electrical heating resistors, safety blowout disks, thermocouples and crucibles. The tensile properties at elevated temperatures are important in many of these situations but data on the subject are limited. Creep data also are important, but will not be covered at this time. Scope and Conclusions Tensile tests were carried out at room temperature and elevated temperatures up to 1100" C. on previously well annealed samples of platinum. palladium and several of their important alloys with compositions shown in Table 1. The results are presented graphically in Figs. 1 to 4. The tensile strengths of platinum and the platinum-base alloys (with the exception of the 10 per cent rhodium-platinum alloy) at 1100" C. are from 16.6 to 18.8 per cent of the strengths of the same alloys (well annealed) at room temperature. The strength ratio of the 10 per cent rhodium-platinum alloy is 22.3 per cent, which is appreciably higher than that of the other materials tested. The tensile strengths of palladium and the palladium alloy at 1100" C. are from 10 to 11.2 per cent of the room-temperature values. The elongations of platinum and its alloys tend to increase at temperatures above 600" to 800" C., while the two samples of pure palladium show a maximum at 600" C.

Jan 1, 1938

By S. H. Moll, R. E. Ogilvie

The investigation of solid-state diffusion phenomena may lead to much information concerning binary alloys. In particular, a study of the concentration gradients present in multiphase diffusion couples can lead to the determination of the solubility limits of the single-phase fields in the phase diagram. The specific concentration gradient which results from the heat treatment of a diffusion couple depends not only upon the time and temperature of diffusion, but also upon the number of phases existing in equilibrium at the diffusion temperature. Such concentration gradients possess sharp discontinuities whose terminal points correspond to the solubilities existing at the limits of the two-phase field in the phase diagram at the diffusion temperature. In general, there will be a discontinuity in the concentration curve for each two-phase field which exists in the phase diagram between the concentration limits of the couple. A number of investigators have analyzed the gradients present in multiphase diffusion couples. 1-8 The iron-titanium phase diagram exhibits a y loop in the temperature range from 900" to 1400°C, and the limit of the a + y field lies at some composition which is less than 1 wt pct Ti for any temperature. It was felt that a diffusion study could yield values not only for the diffusion coefficients involved, but also for the chemical solubilities in the phase diagram. The concentration gradients were analyzed by an X-ray absorption technique developed by Ogilvie.6 The absorption of a monochromatic X-ray beam is measured in steps parallel to the diffusion direction and the resulting intensity gradients are transformed into concentration gradients by applying the laws of X-ray absorption in a binary system. This technique has been applied by ogilvie6 to the systems Ni-Au, Cu-Au, Fe-Cr, and Ni-Cr; by Gelles7 to the systems Be-Fe, and Be-Ni and by Hilliarde to the system Al-Zn. Linear X-Ray Absorption Analysis—The use of X-ray absorption analysis as a tool for determining concentration gradients arises from the fact that the beam is absorbed according to the quantity and species of elements present in the sample and not according to their state of aggregation. This method is more advantageous than the chemical analysis of machined layers since it is less time consuming and less expensive and can analyze a very small area. IF a homogeneous binary alloy (A + B) is analyzed with two different monochromatic X-ray beams I0(2) and lo(2) the following relation between the transmitted intensities, the intrinsic absorption coefficients of A and B for the two different radiations and the weight fraction of each element may be derived.' In (I/Io) (a+b) xa(u/p)a(2) + xb(u/p)8(2) Eq. [1] is independent of specimen thickness and density, but requires that either element A or B possess an absorption edge between the wavelength limits of the two monochromatic beams. I, is evaluated for each radiation by measuring the transmitted intensity through a varying number of foils of a suitable absorber. A plot of the natural logarithm of the transmitted intensity as a function of the number of foils, when extrapolated to zero foils, yields the value of I,. If a plot of the ratio in Eq. [ I] is calculated as a function of xA, then a master curve results. From

Jan 1, 1960

By Henry Rumfelt

8.1-1. History and Description of Shovels. The history of excavating machinery is not clearly defined but the machines seem to have been originally developed for dredging activities, principally involving rivers and harbors. The first, as far as can be determined, was a steam "spoon dredge" developed by Grimshaw of Boulton and Watt of Sunderland, England, in 1796. The land machine forerunner of the present-day power shovel was not developed until 1835. It was invented by William Smith Otis, a young partner of a Philadelphia contracting firm by the name of Carmichael and Fairbanks. The moving force behind this invention was the heavy activity in railroad construction. From this early start the power shovel has developed from steam powering to internal-combution-engine powering and to electric powering. In both directions it has developed to its present state of a finely engineered and precision-built tool. Through the interim the railroad-type shovel, about a half-swing arrangement designed especially for making railroad cuts and mounted on rails, was developed. The rail-mounted shovel gradually gave way to the full revolving shovel. It was high on the list in 1912 and was practically extinct by 1927. From the beginning, a few of the small revolving shovels designed primarily for the general contractors' market had found their way into quarry and mining operations. During this same period, the stripping shovel had been introduced-a 2 ½ cu. yd., 100-ton, full revolving stripping machine with a 41 ft boom. Although this shovel was designed especially for stripping, it was also used for heavy-duty, open pit mining service. In 1925 the heavy-duty, full revolving quarry and mine machine was developed. Strip mining shovels evolved through a somewhat separate path. Hand digging plows and mule-drawn slip scrapers were first reported used by Kirkland, Blakeney and Groves near Danville, Illinois for strip mining

Jan 1, 1968

By B. G. Bunting, D. L. Abata, J. Robb, J. H. Johnson

Toxic gases produced by the detonation of six explosives were measured in an underground hardrock metal mine during mining operations. The explosives included two semi-gelatin dynamites, three slurry explosives, and an ammonium nitrate, fuel-oil/ammonia dynamite combination. Explosives were detonated at the face of a drift and toxic gases produced by the detonation were trapped at the end of the drift by a bulkhead located a short distance away from the face. Toxic gas concentrations were then measured with direct readout instruments and together with the containment volume, the toxic gas volumes per mass of explosive were calculated. Toxic gas measurements were found in the following ranges (ft3/1bm): NO, 0.0100-0.035; N02, 0.003-0.019; CO, 0.08-0.30; SO2, 0.00-0.05; and CO2, 0.7-1.8. Results showed that toxic gas production (ft3/lbm) correlated with the densities (kg/m3) and energy densities (kJ/kg) of the explosives tested.

Jan 1, 1983

By James Gayley

The development of blast-furnace practice in America in the direction of large yields is mainly the history of our working since the year 1880, as the advancement that has been made in the last decade is greater than that in the third of a century previous. A new era in the manufactnre of pig-iron began in 1880 with the putting in blast of the Edgar Thomson furnaces. These furnaces at once leaped to the front as pig-iron producers, and have maintained that position—with but one brief interruption—ever since. I shall, therefore, confine myself mainly to a description of these works, showing the changes in design and practice by which these results have been achieved. In order to show more clearly the progress that has been made since 1880, I shall refer briefly to the best work that was done in the ten years previous to that time. The Struthers furnace, in Ohio, was one of the first to attract attention in the matter of large outputs. This furnace was 55 feet high, 16 feet in diameter of bosh, 9 feet in the hearth, and about 8 feet 6 inches at the stock-line. The fuel was raw coal. This furnace, in December, 1871, made 1602

Jan 1, 1891

By Robert Archer

THE proper material of construction for a given purpose is that material which meets the requirements satisfactorily at the lowest ultimate cost. It is consistent with this principle that most aluminum castings are made of an alloy containing about 8 per cent. copper. This alloy possesses mechanical properties satisfactory for general engineering purposes together with manufacturing characteristics leading to the production of finished castings at low cost. It is to the aluminum industry what gray iron is to the iron and steel industry. Just as some services require "semi-steel," malleable castings or steel castings instead of gray iron, there is a certain and growing demand for aluminum castings of superior strength or ductility, or both. Since the beginning of the industry producers and others have sought to develop alloys or processes by which such castings could be made. Out of these efforts have emerged many alloy compositions and special processes, of which only a few have had sufficient merit to survive. It is the purpose of this paper to describe those which seem to the authors to offer the greatest promise for the production on a commercial scale of aluminum castings of superior mechanical properties, with special reference to heat-treated castings. The suitability of an alloy or process for actual manufacture is affected by so many factors that the problem of appraisal is not a simple one. Since this is such an important part of the whole subject it is proposed to discuss briefly some of the requirements. The final verdict is of course the result of commercial trial and experience. It will therefore, perhaps, be profitable to employ a somewhat historical method of treatment in discussing the subject of alloy development.

Jan 9, 1926

By Peter Soo

Pvestrained Ferrovac E iron has been neutron-irradiated at approximately 90°C to an integrated flux of 1020 nut (E > 0.82 mev]. The irradiation was found to produce an incveased temperature dependence of the flow stress in addition to a greatly increased athemal stress. Measurements of the flow stress and stress relaxation, from which the activation volume and activation energy for slip were deduced, show that neutron irradiation changes the rate -controlling slip process to one based on dislocation interactions with tetragonal distortions which are Produced around submicroscopic interstitial loops in the lattice. The study indicates that without prestraining prior to irradiation the chances of detecting a change in the rate -controlling slip process are greatly reduced because in the initial stages of slip a substantial fraction of the radiation defects are swept out of the slip plane by gliding dislocations. Thus, activation parameters which are subsequently measured are representative of a greatly reduced defect density and would not differ appreciably from those for unirradi-ated material. The large increase in the athermal component of the flow stress is probably connected with the presence of depleted zones in the lattice which are introduced by irradiation. ALTHOUGH fast neutron-irradiation has not been observed to markedly alter the activation parameters for slip in bcc metals,' small but significant changes do occur. Most experimenters agree that irradiation predominantly increases the athermal component of the yield stress.'-= In addition to this, Laidler and smidt7 have shown that in iron irradiated to 5 X 10" nvt and molybdenum irradiated to 10" nvt, changes occur in the activation volumes for slip. A similar conclusion has been reached by Milasin and Malkin8 for irradiated iron. Work by Ohr et a1.5 shows that for Ferrovac E iron, irradiated to 1.2 X 1016 nvt, small increases in the activation energy for slip also occur. So far these changes in the activation parameters have not been explained on a firm theoretical basis. One important factor which would minimize the chances of detecting a change in the slip mechanism upon irradiation is the presence of "channeling" which has been observed in molybdenum,9 niobium,10 and iron.11These channels are formed by gliding dislocations which sweep irradiation defects out of the active slip planes and thereby create zones in which continued dislocation motion is encouraged. The activation parameters for the dislocations gliding in the defect-free channels would, therefore, be similar to those for unirradiated iron and a change in the rate-controlling slip process would be difficult to detect. In the present work, an attempt has been made to reduce the effect of uneven deformation on the measured activation parameters for slip in neutron-irradiated Ferrovac E iron polycrystals, so that a more realistic assessment of the effects of neutron-irradiation could be made. Primarily, the experiments involve the irradiation of specimens which had been prestrained to 9 pct elongation at room temperature prior to insertion into the reactor. It was hoped that the introduction of a large number of evenly distributed dislocations would substantially decrease any channeling effect which might otherwise occur. MATERIAL AND EXPERIMENTAL PROCEDURE The starting material was vacuum-melted Ferrovac E iron, an analysis of which is given in Table I. The standard tensile specimen had a gage length of 1.125 in., a cross-sectional diameter of 0.120 in., and a re-crystallized grain size of 1.2 x 10-3 in. All tensile tests were conducted on a floor model "Instron" tensile machine at a strain rate of 3 x 10-4 per sec. The irradiation of the prestrained specimens was performed in the Brookhaven High Flux Beam Reactor to an integrated flux of 1020 nvt (E > 0.82 mev) at a temperature of about 90°C. All specimens were excap-sulated in high-purity aluminum sheaths which were lightly swaged around the samples to ensure good thermal contact. Subsequent measurements on the irradiated specimens showed that within experimental accuracy the swaging had not deformed them. EXPERIMENTAL RESULTS Fig. 1 shows the flow stresses for a series of unirradiated control samples. In order to produce a comparable dislocation substructure throughout the test sm range, all specimens were prestrained

Jan 1, 1970