Search Documents

By William M. Boorstein, Robert D. Pehlke

The rates of solution (of hydrogen in liquid pure iron and in several liquid binary iron alloys were meas-ured using a constant volume technique. The rates of absorption and desorption were found to be equal un-der all experimental conditions. increasing concen-trations of S, Si, or Te decrease the rate of hydrogen uptake but additions of Al, B, Cr, Cu, or Ni have no measurable effect up to concentrations normally en-countered in steelmaking practice. No relation ship was found between the effect of an alloying element on the equilibrium solubility of hydrogen in liquid iron and its effect on the solution rate constant. Mathe-rnatical analysis of the data indicates that under the present experimental conditions the rate of reaction of hydrogen with liquid iron is controlled by transport of gas solute atoms in the metal phase. Comparison of the present resuts with data on nitrogen taken un der similar conditions establishes that the hydrody-nurnic conditions which exist near the surface of a metal bath are best approximated mathematically by a surface renewal model for the case of rapid in-ductive stirring and by a boundary layer model for more quiescent melts. HYDROGEN has long been recognized as being a detrimental constituent in steel. If dissolved in the molten metal in excess of its solid solubility, hydro-gen can be evolved during solidification and cause bleeding or porosity in ingots and castings. In the solid metal, lesser amounts play a definite role in causing other defects such as hairline cracks, blisters, and embrittlement. For significant refinements to be made in metallurgical procedures designed to control or eliminate hydrogen from liquid iron or steel dur-ing processing, available equilibrium solubility data must be supplemented with reliable fundamental in-formation pertaining to the kinetic factors involved in the transfer of hydrogen to or from the metal. The scarcity of such information in the literature prompted the present investigation. PREVIOUS RESEARCH Whereas much of the existing data on the solution kinetics of gases such as nitrogen were obtained during the course of thermodynamic investigations, the solu-tion rate of hydrogen has been found too rapid to be accurately determined by conventional solubility meas-urement techniques. Consequently, little work on hy-drogen solution kinetics has been reported in the lit-erature. Carney, Chipman, and crant1 attempted to study the rate of solution and evolution of hydrogen from liquid iron by employing a newly devised sampling method. Although no significant quantitative data could be obtained, it was observed that the rate of solution was approximately equal to the rate of evolution of hy-drogen from the melt. Karnaukov and Morozov2 stud-ied the rate of absorption and Knuppel and Oeters3 the rate of desorption of hydrogen from molten iron by measuring pressure changes with time in a constant volume system. Karnaukov and Morozov determined the hydrogen pressures over their inductively stirred melts with the aid of a McLeod gage and therefore, were forced to work at pressures not in excess of 40 mm of Hg. Their experimental data conformed to a mathematical correlation based on diffusion control: and the rate coefficients calculated on this basis were shown to be independent of the initial absorption pres-sure. These authors reported the solution rate of hy-drogen to be eight-to-ten times higher than they had found for nitrogen in a previous study. They also re-ported that under identical conditions, hydrogen dis-solves somewhat more slowly in iron-columbium alloys than in pure iron. Knuppel and Oeters found that the desorption of hydrogen from pure iron at 1600°C was controlled in all cases investigated by diffusion in the metal bath as long as bubble formation was sup-pressed. This was substantiated by Levin, Kurochkin, and umrikhin4 who studied the kinetics of hydrogen evolution from liquid (technical) iron while applying a vacuum. Salter5 measured the rate of hydrogen ab-sorbed by iron buttons, arc-melted by direct current, as a function of hydrogen partial pressure in a hy-drogen-argon atmosphere. A carrier gas technique was used for analysis of the hydrogen absorbed. The initial rate of absorption was found to increase di-rectly with the square root of the partial pressure of hydrogen. EXPERIMENTAL METHOD Because of the rapid uptake and evolution of hydro-gen by iron-base melts, a constant volume technique was devised in order to obtain meaningful kinetic data over the entire course of the solution process. Apparatus. A schematic view of the experimental apparatus is given in Fig. 1. The hydrogen-liquid iron reaction system consisted of a gas storage bulb con-nected to a meltcontaining reaction chamber through a normally-closed solenoid valve. The gas storage bulb, an inverted 250 ml round-bottomed Pyrex flask was joined to the inlet port of the solenoid valve by a glass-to-metal seal. A more detailed illustration of the reaction chamber is shown in Fig. 2. The design of the Vycor reaction bulb was essentially that de-scribed by Weinstein and Elliott6 with the exception of a shorter, larger diameter gas inlet for this kinetic study. In position, the reaction bulb was closely by an eight-turn coil of water-cooled copper tubing which, when energized by a 400-kc oscillator, provided the inductive heating source. The walls of the bulb were maintained relatively cool by circulating cold water along their outer surface, thus preventing

Jan 1, 1970

By G. S. Cole, H. Biloni, G. F. Bolling

An experimental investigation of sovlze low .melting point alloys sJtows that a substvucture of isolated depressions can be the first manvestation of constitutional supercooling on solid-liquid interjaces veuealed by decanting. Electron-tni cvop vobe and wletallo gvaplic esanzinations, in tlze bulk belzind the interjace, oj the segregation associated with these isolated areas substantiate tlzei&apos;v depressed nature, since a solute of ko < 1 is enriched, and a solute of ko > 1 depleted. In contrast, the pox structuve, a set of projections often veported in the literature, leaves no trace oj. segvegation. These obserl;atims, accovlrpanied by a brief review of recent literature, point to inconsistencies between experirrental obsevvation and the idea that the fornzation of a projection is a causal step in the development of a cellular substructure. An argument is presented to show instead how it is plausible for substantial depvessiom to form in the pvesence of constitutional supercooling at dislocations threading the solid-liquid interjace. THE development of constitutional supercooling during growth from the melt leads to the formation of the cellular solidification substructure. This well-founded association between structure and instability has been basic in understanding cellular substructure and micro segregation; however, the initial formation of structure seems unclear. Rutter and Chalmers,&apos; in definitive experiments and theory, noted that in the presence of constitutional a planar interface might break down: "resulting in the formation of a small projection on an initially plane or uniformly curved interface." That is, the breakdown from a planar to a cellular interface was implied to be initiated via a projection into the unstable liquid. Later, Walton et (11. found that a structure of isolated projections, termed "pox", appeared at solid-liquid interfaces decanted under growth conditions near the onset of constitutional supercooling; the pox were taken as the indication of the instability promoted by the supercooling. Tiller and Rutter4 in their extensive work studied the shape transitions at decanted interfaces which were generally observed to proceed as— pox, "irregular cells", elongated cells, regular (hexagonal) cells, and so forth. The pox varied in size from lo-&apos; to 1CT4 cm, and tended to disappear as cells increased in number and regularity, but as noted,4 the first real array of cells did not seem to be a development from the pox. In fact these authors implied a lack of connection because they stated that the pox are denser on "irregular cells", and as cell boundaries increase in number (i.e., the cells become smaller) there is less need for the pox which do dis- appear. Thereafter, most authors dealing with either experiment or theory have accepted the reality of pox and have used them as a criterion for the onset of constitutional supercooling. In contrast, Spittle, Hunt, and smiths have now suggested that pox are irrelevant artifacts comprised of such things as entrapped oxide. This proposal invokes the observations of weinberg6 and chadwick7 each of whom have shown that the act of decanting leaves a residual liquid on a decanted interface; the remnant solid layer of the order 10 p may thus contain particles that might have been transported from the external surfaces, or elsewhere, during decanting. With the incentive of this suggestion,= some further experiments and a reexamination of the literature have been conducted, in order to question the validity of pox as evidence of an instability and to examine the initial development of the cellular substructure. 1) EXPERIMENTS Single crystals of zone-refined tin (-99.9999 pct) were grown from the melt in a controlled fashion with various, small concentration additions of lead and antimony, for which ko < 1 and > 1, respectively. The crystals were decanted at conditions near the onset of constitutional supercooling and were thus appropriate for observation of slight perturbations. It was possible to observe two types of small departure from smooth or "planar" interfaces in both cases of lead or antimony additions. Some were projections and others, if in regular array of any type, were depressions. The crystals were etched with suitable reagents progressively dissolving the decanted interface surface; projections left no record, but depressions were continuously associated with spotlike areas contrasting with the rest of the interface. Traverses were made with the beam of an electron microprobe across the regions of contrast; with lead addition the persistent spots were lead-rich, and with antimony addition the persistent spots were antimony-poor. This is consistent only with a dominant role for depressions, because if the projections had left spots but were incorrectly catalogued, a reversed observation should have been made; that is, the Pb(ko < 1) should have been depleted and the Sb(ko > 1) enriched. In the work of Cole and inegard, and elewhere, regular arrays of structure associated with the initial stage of instability have been shown, in photographs and represented as pox or projections. We believe this to be erroneous, by inference, since whenever a regular array was observed, in the present examination, it consisted of depressions, regardless of the nature of the solute, ko 1. Fig. 1 is reproduced8 as an ideal example of the possible optical illusion involved; the observer can satisfy himself from the distribution of illuminated areas that the markings are depressions. Fig. 2 from the present investigation is an interference photograph of an interface similar to that in Fig.

Jan 1, 1967

By R. E. Cech, J. H. Hollomon

KURDJUMOV and Maksimova reported experiments with manganese steels and high carbon steels&apos; and with an Fe-Ni-Mn alloy&apos; in which mar-tensite was formed isothermally over a range of temperatures. They found in some cases that mar-tensite formation could be suppressed by rapid quenching to liquid nitrogen temperature. From their microstructural observations of martensite formed isothermally, they concluded that the rate controlling step is nucleation rather than growth. Kulin and Cohen,3 in an attempt to reproduce these experiments, found that with a steel having the same composition as that reported by Kurd-jumov and Maksimova, the transformation to martensite was essentially complete above the temperature range of Kurdjumov and Maksimova&apos;s isotherms. The possible reasons for this disagreement were not considered. Recent papers by Das Gupta and Lement4 and Kulin and Speich5 report the formation of isothermal martensite in a high chromium steel and in an Fe-Cr-Ni alloy, but neither paper can be considered a verification of the original Kurdjumov and Maksimova results. Further, in neither case were the authors able to suppress the formation of martensite entirely. Because of the important bearing the Kurdjumov and Maksimova results have to an understanding of the mechanism of martensite reactions it was felt that an experimental investigation directly concerned with checking the validity of their results was in order. This paper describes the results obtained on the isothermal transformation over the temperature range from —79" to —196°C of an alloy of iron, nickel, and manganese. Experimental Apparatus A 15 lb heat of an alloy containing 73.3 pct Fe, 23.0 pct Ni, and 3.7 pct Mn was melted by induction and cast under argon. The ingot was forged to 1-in. bar and a portion rolled to 1/16x1 1/2-in. strip. This strip was pack-homogenized 300 hr at 1100" in a helium-filled sealed iron tube. The composition after homogenization was 73.2 pct Fe, 22.94 pct Ni, 3.73 pct Mn, 0.05 pct C, and 0.015 pct N. The strips were cut to 1/2-in. width for dilatometer and metal-lographic specimens. Only the center portion of the 11/2-in. strip was used in the present investigation. The dilatometer employed was similar in design to one described by Flinn, Cook, and Fellows." A concentric fused auartz rod and tube assembly with hooks for holding the specimen was mounted so as to transmit the specimen dilation to a 1/10,000 in., 1/10 in. travel dial gage. The dilatometer proper was mounted by means of extension arms to a counterweighted sliding member on a vertical standard. This method of mounting permitted rapid transfer of the dilatometer from the austenitizing furnace to the quenching bath and low temperature chamber. A small electrical vibrator on the dilatometer kept frictional effects of the quartz members at a minimum. The austenitizing unit was a vertical, molybdenum-wound, hydrogen atmosphere furnace maintained at a constant temperature ±3°C by means of constant power input. A 12-in. stainless steel jacketed copper liner having 1/2-in wall thickness acted to equalize the temperature in the hot zone of the furnace. This liner, closed at the bottom end and open at the top to permit entrance of the dilatometer and specimen, was kept filled with dry nitrogen gas. A chromel-alumel thermocouple was placed inside the tube to determine the temperature. The 4-in. dilatometer specimens in the chamber varied less than 1/2° across the specimen length except for a 1 1/20 drop at the end nearest the open end of the furnace. The low temperature isothermal holding bath was a double Dewar arrangement similar to one described by Turnbull7. The outer bath was filled with a refrigerant at a temperature lower than the desired holding temperature. The inner bath was filled with Freon "11" or "12" or a mixture of both, depending upon the holding temperature. This inner bath which tended to be cooled by the outer bath was kept at a constant temperature by introducing a small amount of heat with a manually controlled electric heater. Stirring was accomplished by bubbling dry air through the bath. A Leeds and North-rup type K potentiometer was used to measure the inner bath temperature as indicated by a five element copper-constantan thermopile. The bath temperature was maintained within ±0.2°C of the desired temperature by occasionally adjusting the heater current so as to keep the Leeds and Northrup galvanometer at zero deflection with a constant setting of the potentiometer. Isothermal tests were usually continued for 300 to 400 min and another reading made at approximately 1000 min if the bath, unattended overnight, had not deviated in temperature more than 5°C. Transformation curves are drawn dashed (Fig. 1) through the time region where temperature was not controlled precisely. Experimental Procedure Dilatometer specimens of 1/2x1/16-in. strip were cut to 41/2-in. length and holes were drilled for the quartz hooks with proper spacing to give a 4-in. measured length. A thermocouple consisting of 0.012-in. diameter chrome1 and alumel wires was spot welded to the specimen and threaded between the dilatometer rods to binding posts near the dial

Jan 1, 1954

By M. R. J. Wyllie

The relationship between the electromotive force (E.M.F.) across a shale barrier and the concentrations of sodium chloride solutions on either side has been investigated. It is shown that the action of a shale barrier is analogous to a glass membrane separating two acid solutions of different hydrogen ion concentrations. The shale behaves as a sodium electrode and is responsive to the activities of the sodium ions in the two solutions in such a way that the potential can be calculated by means of the Nernst equation. This conclusion is confirmed by laboratory experiments. In a borehole the total E.M.F. of a shale cell is the algebraic sum of the ~otential across the shale and a boundary potential. The relationship between total E.M.F. and the resistivity ratio of two sodium chloride solutions is indicated for a number of formation temperatures. The E.M.F. thus predicted is then compared with the .elf potential read from an electric log and good agreement is demonstrated. Based on both the self potential and resistivity curves of the electrical log. a method is given for calculating connate water content in a bed having in-tergranular porosity and containing both connate water and hydrocarbons. INTRODUCTION The first paper on electrical well logging by C. and M. Schlumberger and E. G. Leonardon in 1934&apos; attributed the self potential curve principally to streaming potentials, i.e. to electroki-netic effects. Almost immediately great difficulties were encountered in reconciling many of the curves they obtained with this interpretation. and a ~econd paper&apos; by the same authors soon appeared. In this second paper self potentials were attributed to the combined effects of streaming potentials and electrochemical potentials, the electrochemical potential being considered the result mainly of the interaction of fluids of differing salt concentrations, i.e. a boundary potential, and partly of potentials set up at the faces of impermeable materials. Some experiments involving a gray clay for the impermeable material were quated. The Schlumbergers and Leonardon deduced from the equation for a simple boundary ~otential that the electrochemical potential, as opposed to the electrokinetic potential, could be expressed in the form E=Klog- .......1 pe where K is a constant, pm the mud resistivity. p, the resistivity of the connate water in a porous bed. However, no general expression for the constant K was obtained. Although the literature between 1934 and 1943 contains a number of quotations of their results, the valuable work of the Schlumbergers and Leonardon was not extended so that the electrochemical potential has been generally attributed wholly to boundary potentials between the mud in the borehole and the connate waters in porous formations. Unfortunately, however, the fundamental premise of all these papers, that a boundary potential can give rise to current flow in a borehole, is thermodynamically untenable. As will be shown. the fact that the electrochemical potential can be fairly accurately express as E = K log pm/pc, a form in which a boundary potential may also be written, is partly fortuitous. The boundary potential is indeed an integral part of the expression for the electrochemical potential in a horehole, but in magnitude it represents only about 20% of the total potential. In 1943 an important step in the elucidation of electrochemical potentials was made by Mounce and Rust3 who showed that if a wall of shale separated two compartments which contained saline solutions of different concentrations, and if the two solutions were themselves brought into contact in the pores of a porous inert membrane (such as unglazed porcelain) a current flowed through the shale and saline solutions. The direction of positive current was from the shale into the more dilute solution. The paper of Mounce and Rust, while repeating some of the observations of the Schlumbergers and Leonardon, seems to be the first to show that the shale was the seat of a genuine electrochemical effect capable of causing current flow. In the same paper Mounce and Rust pointed out the similarity between the fundamental conditions of their experiment and the conditions which existed when a bed of shale in the ground was simultaneously in contact with a porous sand containing saline connate water and mud fluid of salinity different from that of the water in the sand. Since it is now generally recognized that the S.P. curve measures ohmic potential changes in the mud fluid in the well bore resulting from changes in current flow, it is apparent that currents having their origin in the electrochemical interaction of mud filtrate and connate waters with shale beds are a very important portion of the total S.P. The work of Mounce and Rusta and others appears to indicate that, in general, the electrochemical portion of a particular kick on a S.P. curve far exceeds any electrokinetic potentials resulting either from streaming potentials or Dorn effects. The Dorn effect, or sedimentation potential. arises when small particles are allowed to fall through certain fluids under the influence of gravity. a difference of potential being observe? between two electrodes placed at different levels in the stream of falling particles. The Dorn effect is unlikely to affect seriously the S.P. curve as now measured. A successful analysis of the electrochemical aspects of the S.P. log should

Jan 1, 1949

By G. P. Conard, E. H. Rennhack

The creep behavior of hot-rolled, hypoeutectic Zn-Ti alloys was investigated in the temperature range from 0.43 to 0.53 TM. Secondary flow was found to originate primarily from strain-induced gvain growth where grain boundary )nigvation served to relieve the strain energy of distortion introduced by slip, grain boundary sliding, and subgvain formation. The extent to which this recovery mechanism operated was determined by the ratio of grain width to the spacing between planar fibers of TiZn,, compound particles generated in these alloys during rolling. When this ratio was unity, creep resistance demonstrated a marked improvement. In this condition, which was fulfilled by annealing following rolling, structural stability was enhanced with decreasing grain size below the equicohesive temperature (-0.5Tm), while the reverse was true above this temperature. TITANIUM concentrations approaching the eutectic composition of 0.23 wt pctl have been shown to promote a significant increase in the creep resistance of rolled zinc,2 The alloying effect created with titanium is somewhat unique; a structure closely resembling that of a fiber-reinforced metal composite can be developed which selectively modifies creep strength in preference to other mechanical properties. In an earlier investigation,~ the present authors found that, while the fiber network, composed of individual TiZn,, compound particles, had a distinct influence on rolled texture, the crystallographic variations produced were of minor importance with respect to creep. Rather, creep resistance seemingly increased when the grain size appeared to coincide with the in-terfiber spacing. The work described here was undertaken to explore this effect in greater detail. EXPERIMENTAL PROCEDURE Three zinc-base alloys containing 0.05, 0.12, and 0.16 wt pct Ti were prepared from CP zinc and iodide titanium in the form of 4 by 2 by f in. chill-cast ingots. The melting and casting procedures for these alloys have been detailed el~ewhere.~ Individual ingots of each alloy were hot-rolled at 200°C (392°F) to total reductions of 10, 25, 50, 75, and 90 pct in from one to five passes, respectively, employing a 10-min reheat prior to each rolling pass. With grain, tensile-type creep specimens with a 1-in.-long, -in.-wide gage section were machined from the rolled strips for test purposes. Annealing studies to explore the influence of grain size on secondary creep flow were carried out at 400°C (752°F) in argon for times extending up to 60 min. The grain-size effect was evaluated in terms of average grain width and length values statistically derived from lineal intersection measurements.4 A similar method was applied in establishing the average interfiber spacing, i.e., average perpendicular distance between adjacent planar fibers. The creep characteristics of the alloys were investigated by means of constant-load and constant-stress creep tests. The former tests were conducted at 25°C (77°F) under an initial stress of 10,000 psi, while the latter were performed in the range from 25°C (77°F) to 90°C (194°F) at stress levels varying from 8000 to 22,000 psi. Total specimen strain, as determined with Budd HE-1161-B strain gages, was in excess of 0.10. Maintenance of constant stress was achieved through periodic load reductions made at 0.01 strain intervals to compensate for the attendant incremental reduction in specimen cross-sectional area. The maximum indicated error in the applied stress at these strain intervals was less than 3.0 pct. RESULTS AND DISCUSSION Constant-Load Creep. In an effort to clarify the in-terrelation between interfiber spacing and grain size with respect to the creep resistance of the Zn-Ti alloys, their separate effects on secondary creep rate were determined as a function of titanium content and rolling reduction. These results are set forth in Figs. 1 and 2, respectively. The average grain diameter plotted in Fig. 2 was resolved from average grain width and length values. No data are presented for reductions of less than 50 pct because of the inability to obtain consistent measurements on these strips. The curves of Fig. 1 indicated that, for a given titanium content, a decrease in interfiber spacing, as produced with increasing reduction, promoted a decrease in creep rate. Depending on titanium content, however, wide variations in creep rate occurred at the same interfiber spacing suggesting that interfiber spacing, by itself, has little or no influence on creep resistance. Grain size, on the other hand, decreased progressively with both increasing rolling reduction and titanium content, the effect of which led to a pronounced decrease in creep rate, particularly when the average grain diameter became smaller than 3.0 x 10"4 in., Fig. 2. The continuity of this relationship tended to support the view that grain size rather than interfiber spacing was predominant in controlling secondary creep. Annealing Effect. The observed dependence of creep flow on grain size suggested that a further contribution to creep resistance would result when the alloys were annealed to effect a coincidence between grain width and interfiber spacing, see Fig. 3(b). ~eiides creating an immediate barrier to grain boundary movement, annealing offered the possibility of providing increased structural stability by eliminating many high-energy, mobile grain boundaries.= To test this hypothesis, specimens from the Zn-0.16 Ti strips reduced 75 and

Jan 1, 1967

By Robert K. Steunenberg, Irving Johnson, James B. Knighton

The activity coefficient of plutonium in liquid magnesium, over the temperature range 650° to 800°C, was obtained from measurements of the distribution of plutoninm between a 50 mole pct MgC12-30 mole pct NaCl-20 mole pct KC1 molten-salt mixture and liquid Zn-Mg alloys. For dilute solutions (0.08 at. pct Pu) the activity coefficient of plutonium was found to vary from 10.1 at 650°C to 12.2 at 800°C. The activity coefficients of plutonium in dilute liquid solutions of plutonium in uranium, silver, lanthanum. cerium, and calcium were estimated to be. The distribution data indicate a value of about 0.1 at 800°C for the activity coefficient of PuCl3 dissolved in the above ternary salt mixture. LIQUID magnesium and several liquid alloys of magnesium with metals such as zinc and cadmium have been shown to be useful solvents in pyrochemical processes for the recovery of uranium and plutonium from discharged nuclear fuels,&apos; and for the separation of transuranium elements.&apos; The present study was undertaken to determine the activity coefficient of plutonium in liquid Pu-Mg alloys in support of process-development work. The activity coefficient of plutonium in liquid magnesium was determined from experimental data on the distribution of plutonium between a liquid ternary MgC12-NaC1-KC1 salt mixture and various liquid Zn-Mg alloys. The distribution data were used to calculate the ratio of the activity coefficients of plutonium in liquid zinc and in liquid magnesium. The activity coefficient of plutonium in liquid magnesium was then computed from the known activity coefficient of plutonium in liquid zinc. It was not necessary to know the thermodynamic properties of the molten-salt system explicitly. The major features of the Pu-Mg system have been reported by Schonfeld.3 At the temperatures of interest in the present study, i.e., above about 600°C, the phase diagram indicates the existence of a wide liquid-miscibility gap, with the plutonium-rich liquid containing about 8 at. pct Mg and the magnesium-rich liquid containing about 10 at. pct Pu at the intersection with the solidus regions. Additional data on the compositions of the two equilibrium liquid phases obtained in this laboratory4 have defined the miscibility gap up to the consolute temperature (at about 1040°C). EXPERIMENTAL PROCEDURE AND RESULTS Materials. The 50 mole pct MgC12-30 mole pct NaC1-20 mole pct KC1 salt mixture was prepared by melting the required proportions of reagent-grade NaCl and KC1 with anhydrous MgC12. The molten salt was then purified by contacting it with liquid Cd-30 wt pct Mg alloy (at 450°C) to reduce oxidizing impurities, followed by filtration through a stainless-steel frit (pore size, 65 µ) to remove solid MgO formed during the reduction. The purity specifications of the zinc, magnesium, and plutonium were 99.999, 99.8, and 99.85 pct, respectively. Apparatus. The liquid salt and metal were contained in a tantalum crucible inside a graphite secondary vessel. The crucible assembly was located inside a resistance-heated stainless-steel furnace tube. The furnace tube was closed by means of a stainless-steel cover, which was attached by bolts, with a neoprene O-ring serving as a gas-tight seal. The top of the furnace tube was water-cooled to protect the O-ring. The furnace-tube cover was provided with a tantalum thermowell, a tantalum stirrer, and a port through which sampling tubes could be inserted and materials could be added to the melt without admitting air to the furnace tube. Vacuum and an argon atmosphere were available through a side-arm on the furnace tube. The furnace temperature was regulated by a proportional controller that was actuated by a chromel-alumel thermocouple between the furnace tube and the heating elements of the furnace. The melt temperature was measured by means of a chromel-alumel thermocouple in the tantalum thermowell. The accuracy of temperature measurement was ±3°C. The salt and metal phases were intermixed by a motor-driven tantalum paddle positioned at the liquid interface. The tantalum crucible was provided with four baffles to increase the turbulence. The sampling tubes consisted of 1/4-in.-OD tantalum tubing that terminated in a tantalum frit (Kawecki Chemical Co.; average pore size, 30 µ). Procedure. The zinc, magnesium, plutonium, and salt were charged to the tantalum crucible; then the system was evacuated and filled with argon. The melt was brought to the desired temperature, and agitated for 1 to 2 hr. After allowing the salt and metal to separate, both phases were sampled. Filtered samples were obtained by immersing the end of the sampling tube in the liquid and increasing the argon pressure sufficiently to force the liquid salt or metal through the frit into the tantalum tube. The sample was then partially withdrawn into the cooler portion of the furnace tube and permitted to solidify before being removed. The temperature sequence for sampling at each magnesium concentration was 800°, 700°, 600°, 650°, and 750°C. The composition of the liquid-metal phase was varied by incremental additions of magnesium in a series of experiments at low magnesium

Jan 1, 1967

By W. D. Robertson, W. L. Phillips Jr.

Stress-strain curves were obtained for single crystals of alpha brass in tension and in direct shear. Specimens were strained various amounts in a given slip direction, unloaded, and immediately strained in a second slip direction 60°, 120°, or 180&apos; from the original slip direction. Crystals strained in tension and direct shear had comparable critical resolved shear stresses and stress-strain curves. The density of slip lines in direct shear and in tension was essentially the same. The stress-strain curves obtained in shear were independent of initial orientation, choice of {111 } slip plane, choice of <110> slip direction, prior annealing temperature, and rate of cooling after annealing. There was no recovery after annealing for 4 hr at room temperature or 200°C; recovery was observed after 4 hr at 400°C. The crystals showed no asterism and mechanical properties were completely recoverable up to 20 pct strain. It was found that there is a barrier to slip in all latent close-packed directions, and that the magnitude of these barriers, evaluated at 3 pct strain, is proportional to prior strain and independent of the choice of latent direction in the {111} plane. The formation of Cottrell-Lomer barriers is discussed as a possible explanation for the hardening of the latent systems. AN idealized concept of plastic deformation indicates that a single crystal should yield at some stress that is dependent on crystal perfection and it should then continue to deform plastically by the process of "easy glide," which is characterized by a linear stress-strain curve and a low coefficient, ds/dE, of work-hardening. Hexagonal metal crystals generally conform to this ideal concept of laminar flow. In face-centered cubic metals the range of easy glide is always restricted in magnitude and it is strongly dependent on orientation, composition, crystal size, shape, surface preparation, and temperature. Since one of the principal differences between the two crystal systems, both of which deform by slip on close-packed planes, is the existence of secondary (latent) slip planes in the face-centered cubic crystals, it has been proposed that the transition from easy glide to turbulent flow, characterized by rapid linear hardening, is due to slip on secondary planes intersecting the primary plane.&apos;-.; However, the characteristic differences between individual face-centered cubic metals remain to be explained; in particular, it is not clear why the range of easy glide should vary so greatly in different metals and alloys similarly oriented for single slip. An investigation and comparison of different metals with respect to latent hardening on the primary slip plane should provide some of the information required to specify the necessary and sufficient conditions governing the transition from easy glide to turbulent flow. But, in order to accomplish this purpose, plastic strain must be produced by simple shear in a chosen plane and in a predetermined direction by some form of directed shear apparatus, the results of which must be correlated with the corresponding tension experiments. Two such experiments have been performed previously with zinc and with aluminum. Edwards, Washburn, and Parker" and Edwards and Washburn7 found that the strain-hardening coefficients in two latent directions in the basal plane of zinc were the same as in the primary direction. However, to initiate and propagate slip in either the [2110] or the [1210] direction, following primary slip in the [1l20] direction, it was necessary to increase the stress above that required to continue slip in the primary direction; when the direction of shear was reversed 180 deg plastic strain began at a much lower stress than that required to initiate slip in the original direction and the stress to propagate slip in the reverse direction was lower than the stress to continue slip in the forward direction, indicating a permanent loss of strain-hardening. Rohm and Kochendorfer observed softening in aluminum for all latent close-packed planes and directions. They also found that the critical resolved shear stress obtained from their direct shear apparatus was 50 pct lower than the value obtained from conventional tension tests, that the stress-strain curve was linear at 50 pct plastic strain, and that slip lines were not visible at strains less than 30 pct. At present it is uncertain whether these diverse results correspond to real differences in work-hardening characteristics of the close-packed planes of aluminum and zinc or to differences in experimental technique. In view of Read&apos;s analysis &apos;" of the stress distribution in the experimental arrangement of Rohm and Kochendorfer, there is some reason to question the significance of the latter results. In order to resolve this problem it is necessary to re-valuate the direct-shear technique and either repeat the previous measurements or investigate a third system. The latter choice seemed most likely to produce significant results with respect to work-hardening, and accordingly, it was decided to examine the hardening characteristics of the latent slip directions in alpha-brass. The choice of alpha-brass was dictated by the fact that easy glide is more extensive in this alloy than in any other face-centered cubic metal or alloy and, presumably, more nearly like the idealized hexagonal system. Experimental Procedure Crystals were made in graphite by the Bridge-man method in the form of cylinders, 11/2 in. diam and 8 to 9 in. long. Material for the crystals was 70/30 brass containing the following impurities:

Jan 1, 1959

By R. S. Dean

JUST as the mineralogical name bauxite has come to include several minerals not known at the time the name was first applied, so the concept of bauxite as the one source of alumina must be enlarged during the war period to include the production of alumina from other, low-grade sources. Speaking in a narrow mineral logical sense, there is no such thing as bauxite, and similarly there is now no one source of alumina, and no one process for its extraction.

Jan 1, 1943

THE following letter from the Rector of Louvain University, addressed to Mr. Adams and the other delegates of the Founder Societies, will be of interest to members of the Institute. It is my duty, in the name of the University of Louvain and in my own personal name, to thank you and the representatives of the Founder Societies of the "United Engineering Society" for the very kind letter of congratulations which you sent to me from Brussels on the 5th of July.

Jan 1, 1928

The Howe Memorial Lecture, in memory of Henry Marion Howe, Past President of the Institute, was authorized in April, 1923, as an annual address to be delivered by invitation under the auspices of the Institute by an individual of recognized and outstanding attainment in the science and practice of iron and steel metallurgy or metallography, chosen by the Board of Directors upon recommendation of the Iron and Steel Division. The following were the Howe lectures and lecturers for the years indicated

Jan 1, 1929

The Government has for disposal a large stock of horse-drawn vehicles that were produced during the war to transport and handle all kinds of army supplies. These vehicles consist of escort wagons, also the axles and wheels; ambulances, model 1909; sprinkler, wagons, buckboards, combat wagons, hand carts, water carts, ration carts, and medical carts. These vehicles are adapted to numerous commercial purposes. All were produced under the strictest Government rules, specifications, and supervision and are first class in every way.

Jan 6, 1919

By C. B. Dudley

In a work published in 1838, De Morgan, the author of the article on " Probabilities," in the Encyclopedia Metropolltimn, says: " The method of least squares is not yet introduced iutb the affairs of common life,.....that many thi~gs which are denlonstrable only by the higher branches of mathematics are looked upon as useless." And he mentions an instance in which "a method was suggested for estimating the relative importance of boroughs, by considering their population and ~wntributions to the revenue con)-

Jan 1, 1881

By Benjamin Gildersleeve

Uniquely colored, thin-bedded quartzite is quarried between Crossville and Crab Orchard in Cumberland County, Tenn. It is produced in all sizes up to the limits of transportation from beds usually ranging in thickness from less than 1/2 in. to 6 in. The stone is very resistant to wear and weathering and is marketed throughout the country for many different purposes in exterior and interior construction. The annual production exceeds 36,000 tons, valued at nearly $1,000,000.

Jan 8, 1950

By The Staff of Dames & Moore

Five factors are required for the formation of uranium deposits: a source, transporting medium, host, trap, and preservation. Locating and evaluating uranium deposits requires ail integration of methods and techniques to determine if the above factors are present. A typical exploration program consists of selection of a favorable area, field reconnaissance, land acquisition, and target definition and evaluation. Target definition and evaluation utilizes a combination of geologic mapping, geochemical surveying, geophysical surveying, and drilling and logging. Each overlaps the others to some degree.

Jan 10, 1978

By Willard S. Morse

Referring to Mr. Rickard&apos;s paper on " The Limitations of the Gold Stamp-Mill" (Trans., xxiii., 137), and the discussions that have followed, and without entering into any controversy as to the relative merits of the " California " and " Colorado " types of stamp-mills, I wish to give the results obtained on ores from Lynx Creek district, near Prescott, Arizona, with a stampmill of the Colorado, or, more precisely, the Gilpin county, Colo., type. The mines of the district have been worked for nearly thirty

Jan 1, 1896

By P. A. Witherspoon, Y. W. Tsang

Normal stress-fracture closure variation and stress-dependent fluid flow rates were calculated for rock fractures of different aperture distributions. This study shows that both the mechanical and hydraulic properties of the fracture are controlled by the large-scale roughness of the rock fracture. Hence the typical large-scale undulation wavelength of the rock joint dictates the suitable sample size to be used in normal stress and fluid-flow measurements, if results due purely to sample size are to be avoided.

Jan 1, 1982

US 4,185,872-In the solution mining of uranium values from a subterranean uranium ore deposit, a lixiviant comprising sodium sulfate or other alkali metal sulfate and optionally minor proportions of an alkali metal carbonate or bicarbonate and an alkali metal hypochlorite is introduced into the ore to solubilize uranium therein. The pregnant lixiviant is recovered for processing. E.T. Habib, Jr., assigned to Mobil Oil Corp. Jan. 29, 1980. 5 pp (299-4). Filed- 8-18-78 (934,933).

Jan 1, 1982

By John F. Slonaker, Joseph W. Leonard

This note is a review of current research intended to increase the utilization of coal ash. Due to the magnitude of the fly-ash research program, some projects may be inadvertently omitted. Field research on fly-ash for use as an agricultural fertilizer is being monitored at Virginia Polytechnic Institute and State University. This research is directed at determining the plant nutrients that are available in fly ash as well as the quantities of fly ash that can be applied to agricultural soil.

Jan 1, 1975

By G. Richard Dreese, Harold L. Bryant

The coal mining industry has had a long history of successfully externalizing part of its costs. Thus the private or internal costs of coal mining have been minimized and the social or external costs have been ignored. The externalized costs have largely taken the form of water pollution from acid mine drainage and sedimentation of stream channels from eroding spoil banks and gob piles. The environmental problems created by strip mining are very conspicuous, so the public demand for legisla-

Jan 1, 1975

By D. W. Gentry, H. E. Sherer

Determining the age at which to replace a specific piece of mining equipment, and choice of the best possible replacement, is a problem common to nearly all mining operations. This paper examines the data required for intelligent equipment replacement decisions and discusses how to predict future repair cost from historic data, determine the total cost of various replacement alternatives, and evaluate the different replacement alternatives. Various operations research and computer methods were used to develop this easily-used, practical equipment replacement method.

Jan 1, 1984