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By D. H. Baldwin, R. E. Reed-Hill

DURING the course of experiments involving oxygen equilibrations with a high-purity Pd-5 at. pct Rh alloy, the appearance of a subscale was noted. Most of the heat treatments in a pure oxygen atmosphere were performed at 900°C. The presence of the subscale was noted when the oxygen partial pressure was in excess of approximately 95 mm, up to 1 atm, the highest pressure used. According to available thermodynamic information' on the free energy of formation of Rh2O3 (the only reliably reported solid oxide of rhodium), this oxide should not be stable under these conditions, nor, of course, any oxide of palladium. Extraction of the subscale from the matrix was affected by treatment with aqua regia, and the resulting X-ray diffraction powder pattern is shown in Table I. This pattern is not that of Rh2O3, nor that of any known rhodium or palladium oxide. It can be indexed on a hexagonal lattice with a. = 5.22Å and co = 6.0Å. In addition to this unknown material, there was a weak Rh2O3 pattern. An X-ray fluorescence analysis of the powder gave 3214 palladium counts per sec and 5381 rhodium counts per sec, thus indicating the likelihood of a double oxide of palladium and rhodium. In view of the fact that the above result was obtained on a single sample, it is perhaps best not to insist upon the above ratio of about 0.6, but possibly to tentatively assume 0.5 or 1/1. The small amount of Rh2O3 in the X-ray pattern might have occurred on cooling, and it seems possible that the double oxide, below some temperature level, is not as stable as Rh2O3. To examine this point, some of the extracted double oxide was heated on a sheet of pure palladium in air at 900°C, and allowed to furnace-cool over a period of several hours. The X-ray diffraction pattern of the powder showed approximately the same intensity of Rh2O3 and the "hexagonal" oxide as before, but, in addition, a rather faint pattern of another crystalline species made its appearance. This finding again suggests partial transformation of the major (double) oxide to other oxides on cooling from 900°C. Application of the phase rule shows that only one equilibrium oxide (subscale) could have been present at temperature. Vacuum-fusion, oxygen analysis of the extracted subscale showed 7.7 ± 0.7 pct O. Combining this information with that of the X-ray fluorescence analysis suggests the formula PdRhO. This compound should have an oxygen content of 7.07 pct, which is within the range of error of the oxygen analysis. However, until a more careful stoichiometric study is made, it is suggested that the formula be written

Jan 1, 1965

By E. E. Gardner, P. A. Schumann

A description of a new four-point probe configuration which permits measurement of epitaxial layer resistivity is given. An analytic solution to the potential distribution due to a point current source on a multilayered structure is briefly described. Typical solutions for this probe configuration are presented. Probe spacing, layer thickness, substrate resistivity, and substrate thickness enter into the calculation. Correction factors for typical cases are given. A brief description of the construction of a probe which can achieve a small spacing of 15 is presented. The prohe is constructed so that all points are adjustable by micrometers and the probe spacing and configuration can be easily altered. Measurements of layer resistivity with the four-point probe are compared with those taken with the three-Point probe and diode-capacitance techniques. TWO techniques of obtaining profiles of N/N+ epitaxial structures are given. The reproducihility of the probe spacing and resistivity measurement is discussed. The effects upon the resistivity measurement of errors in the measurement of the lager thickness, substrate resistil)itv, and substrate thickness are presented. SINCE its introduction by valdes' in 1954, the four-point probe has been the most widely used tool for determining semiconductor resistivity. Its usefulness ranges from the evaluation of bulk semiconductor ingots to the characterization of impurity profiles in diffused structures. In general the four points, two current probes and two potential probes, are placed on one surface of the material being tested either in an in-line array or in a square array. Numerous correction factors1 8 have been worked out for these configurations which are dictated by the finite geometry of the sample being tested. One method of evaluating thin wafers has been proposed which has two probesg on each side of the wafer. Further modifications have added a fifth'' and a sixth" probe. One paper1' has discussed the accuracy of the four-point probe and the precautions necessary in its use. With the exception of the method where two points are placed on opposite sides of the wafer, the four-point probe is restricted to evaluation of wafers with a homogeneous resistivity or to the case where an isolating junction exists between the substrate and the layer (epitaxial or diffused) being evaluated. Due to the relative resistivities and thickness, the resistance of the epitaxial layer is much greater than that of the substrate, and consequently a majority of the current flows through the substrate. The potential distribution at relatively large distances from the current sources is determined by the substrate resistance, and hence the AV/I value is a measure of the substrate resistivity and not that of the epitaxial-layer resistivity. In the immediate vicinity of a current source the potential distribution is determined by the layer resistivity among other factors. Consequently, if the potential probe is placed very close to the current source, then with appropriate correction factors it is possible to determine the layer resistivity. This was the theoretical basis for using two closely spaced probes on opposite sides of an epitaxial wafer. However, due to mechanical problems, it is desirable to place the four probes on the same side of the wafer. This paper discusses the potential distribution in

Jan 1, 1965

By J. M. Dahl, L. H. Van Vlack

STAFF: Editor, Gerhard Derge Associate Editor, Paul G. Shewman Carnegie lnstitute of Technology Schenley Park Pittsburgh, Pa. 15213 Editorial Assistant, M. A. Redmerski Production Editor, Otto T. Johnson THE METALLURGICAL SOCIETY: Jack H. Scoff, President; Richard C. Cole, Post-President; Harold B. Emerick, President-Elect; Ralph L. Hennebach, Treasurer; Robert W. Shearman, Secretary; Donald A. Parks, Assistant Secretary; Leslie S. Wilcoxson, Assistant Secretary. PUBLICATIONS COMMITTEE OF THE METALLURGICAL SOCIETY: R. E. Lund, Chairman; T. E. Dancy, H. B. Emerick, P. R. Gouwens, R. E. Grace, J. H. Jackson, H. H. Johnson, A. E. Lee, Jr., R. R. Nosh, R. D. Pehlke, and Paul Queneau. Review and selection of monuscripts is under the supervision of the following Publications Committees: Extractive Metollurgy Division: R. E. Grace, Chairman; G. M. Bell, D. W. Bridges, J. M. Cigon, G. W. Healy, T. A. Henrie, R. D. Holli-day, C. E. O'Neill, C. S. Sami s, A. W. Schlech-ten, and Charles Shull . Iron and Steel Division: R. D. Pehlke, Chairman; T. P. Floridis, Arnulf Muon, G. R. St. Pierre, E. T. Tuckdogon, L. H.Von Vlack, and J. M. Uys. Institute of Metals Division: H. H. Johnson, Jr., Chairman; J. B. Clark, Vice Chairman; M. R. Achter, G. F. Bolling, J. O. Brittain, G. P. Conard, II, L. A. Girifolco. G. T. Hahn, J.P. Hirth, L. Himmel, G. T. Horne, George Krauss, C. F. Leitton, Jr., J. D. Livingston, R. D. Monning, H. M. Otte, S. V. Radcliffe, R. E. Reed-Hill, H. C. Rogers, O. Sherby, M. T. Simnod, G. R. Speich, E. A. Steigerwold, R. A. Swolin, W. A. Tiller, W. R. Upthegrove, J. B. Wagner, Jr., Derek Walton, H. W. Weart, W. W. Webb, and D. WiIsdorf. Published monthly by the American lnstitute of Mining, Metollurgicol, and Petroleum Engineers, Inc., 345 East 47th Street, New York, N. Y. 10017. Telephone PLAZA 2-6800. Subscription $30 per year for non-AIME members in United States and North, South, and Central America; $32, foreign; $7.50 for AlME members. Single copies, $6.00, single copies foreign, $6.50. The AlME is not responsible for any statement mode or opinion expressed in its publications . . . Copyright 1965 by the American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. . . . Registered cable address, AlME New York . . . Indexed in Engineering Index, lndustrial Arts Index, and Chemical Abstracts . . Second class postage paid at New York, N. Y., and Ann Arbor, Mich. Volume 233, Number 1.

Jan 1, 1965

By Martin J. Hughes

The Eagle Mountain Mine of the Kaiser Steel Corporation is located in the California portion of the Colorado Desert at a distance of about 60 miles east of Indio, California. At the present time, this mine is producing at the rate of 5,000,000 tons of concentrate per year. A total of 1,000,000 tons of ore per year is presently being sold on the Japanese market while the remainder is consumed by the Kaiser Steel Company blast furnaces at Fontana, California. A new Pellet Plant and Concentrator is presently under, construction with completion scheduled for May or June 1965. This plant will have a rated capacity of 2,200,000 tons of pellets per year and essentially all of this production will be sold to Japanese steel companies.

Jan 1, 1965

By John D. Verhoeven

A technique has been developed for carrying out normal freezing experiments with a current density of 2000 amp per sq cut passing through the solid-liquid interface. The equation relating the effective distribution coefficient to the equilibrium distribution coefficient in electric field-aided solidification, originally developed by Huckc et al.,1 has been modified for the case of concentrated solutions. Preliminary experiments on the Sn-Bi system give qualitative agreement with the equation. The data are analyzed by a slightly novel use of the normal freeze equation which allows one to determine the effective distribution coefficient more easily. Very extensive mixing in the liquid was found at these high current densities and it is postulated that the mixing results from a vertical component of the magnetic Lorentz force generated by the electric current. In the search for techniques of obtaining ultrahigh-purity metals the inefficient but very effective technique of electrotransport has received little attention. Electrotransport is most effective in the liquid state and a natural application, therefore, is to apply an electric field across the liquid zone of a zone-melting experiment. The present investigation was undertaken to study the effect of an electric field upon solidification of metals, so that the usefulness of electrotransport in such solidification experiments as zone melting could be determined. In zone-melting and normal-freezing experiments it is difficult to achieve complete mixing in the liquid in the immediate vicinity of the solidifying interface. Consequently a solute build-up will occur at the interface in the portion of the liquid where complete mixing does not occur (an equilibrium distribution coefficient, ko, less than one, and unidirectional atom motion will be implied throughout). This local solute build-up produces a corresponding rise in the solute concentration in the solid so that the ratio of the solute concentration between the solid and the bulk liquid is larger than the equilibrium distribution coefficient. This ratio is defined as the effective distribution coefficient, k,. The differential equation describing the solidification process may be derived by applying the continuity equation to an expression for the net solute flux at the interface. The solution to this differential equation then allows one to determine the solute distribution in the liquid and the relationship between k0 and ke. One of the most useful solutions to this equation was first derived by Burton, Prim, and Slichter,' in which they assumed that a) the equilibrium distribution of solute was maintained on the plane of the interface, 11) the solute build-up ahead of the interface in the liquid disappeared at a distance 6 from the interface, and c) the solute distribution in the liquid was invariant with time. The following well-known relation between ko and ke was then obtained, where R is the rate of solidification and D the diffusion coefficient of the solute in the liquid. This equation appears to correlate the data from a number of different types of solidification experiments very well. Application of an electric field across the solid-liquid interface can produce an additional flow of solute atoms as a result of the electrotransport. When the polarity of the field is such as to direct the electrotransport flux away from the interface the solute build-up may be diminished, even to the point of producing a solute depletion and a consequent ke smaller than ko. The quantitative description of this process and the resulting form of Eq. [I] was first given by Hucke et al.1* and then inde- where E is the electric-field intensity and U is the differential mobility, i.e., the velocity of the solute atoms with respect to the solvent atoms per unit electric field. Both authors follow the method of Burton, Prim, and Slichter in their derivation, the only difference being the additional electrotransport term in the flux equation. It has been pointed out1,3 that Eq. [2] predicts the possibility of a noticeable increase in the purification of materials by solidification in an electric field. The validity of Eq. 121 has not been checked experimentally and it is possible that other factors' arising from the presence of an electric field across

Jan 1, 1965

By G. W. Birge

Fifteen coal samples, representing the Winifrede, Chilton, Alma, No. 2 Gas, Powellton, Eagle, Douglas, Sewell, Beckley, Pocahontas No.4, and Pocahontas No.3 beds in Wyoming County, and five samples, representing the Fire Creek, Pocahontas No.6, and Pocahontas No.3 beds in Mercer County, W. Va., were carbonized at 9000 C by the Bureau of Mines-American Gas Association (BM-AGA) method, and yields of products and physical properties of cokes were determined. Expansion characteristics of the majority of samples were determined in the Bureau of Mines sole-heated oven. Chemical analyses and agglutinating values were determined for all coals. The coals were mostly strongly coking and low in ash and sulfur content. Dry, mineral-matter-free fixed-carbon content of the Wyoming County coals ranged from 63.0 to 83.4 percent. The Mercer County samples were all low volatile in rank. Yields of carbonization products were generally in accord with yields from similar rank coals of the Appalachian region. Because of their expanding tendencies, most of the medium-and low-volatile coals would require blending with lower rank coal for normal coke production.

Jan 1, 1965

By H D. Smith

T HE production of coal in Canada was slightly higher in 1964 than in the immediate past, and the major users continue to be the electric utility and metallurgical industries. There are continuing trends toward the increased use of cokes and chars in various metallurgical applications. Geological Research During 1964, the coal drilling program of the Research Council of Alberta (RCA) was concentrated in the extreme south of the Province (notably in the Milk River area and the region immediately to the northeast of this area). Field work commenced on June 1 and was completed at the end of September, by which time a total of 376 holes, aggregating some 48,500 ft., were drilled in 132 townships. Although no new major coal occurrences were intersected, the pro-gram yielded useful data for defining the extent of the known coal deposits in the area. Detailed results will be analyzed during the winter and reported in due course. Meanwhile, a full report on the

Jan 1, 1965

By Edwin M. Thomasson

HELIUM SHIPMENTS in 1964 exceeded the volume shipped during the previous year for the 15th successive time. Shipments from Bureau of Mines helium plants were 667.4 million cubic feet,2 about 6 percent more than in 1963. Production at Bureau of Mines plants totaled 784.5 million cubic feet. An additional 3,193.1 million cubic feet, which was produced by private companies participating in the helium conservation program, was purchased by the Bureau and stored underground for future use. The Bureau of Mines continued to sell helium at $35 a thousand cubic feet, the price established in 1961. Substantial railway freight rate reductions for tank car shipments of helium went into effect during the year, resulting in a lower delivered price for helium. As the Nation moved ahead in the space age, it became increasingly apparent that helium would continue to play an essential role in research, in technology, in defense, and in industry.

Jan 1, 1965

By Lippe D. Sadwin

This report describes a high-speed streak camera technique for measuring the lateral shock pressure generated by a cylindrical explosive charge detonated from one end. Experimental data show that the magnitude of the lateral pressure is approximately 50 percent that of the pressure generated from the terminal end of the charge for three explosives studied.

Jan 1, 1965

By R. M. Goldhoff, H. J. Beattie

The high-temperature properties of a 1 Cr-Mo-V forging steel are described. A series of controlled heat treatments was designed to delineate the effects of austenitizing and tempering treatments, temile strength, and grain size on such properties. Studies indicate that the mechanical properties and their varlations under creep can be described by the initial metallurgical structures and their changes droPirzg exposure, particulavly the carbide reactions. Such structures are described and correlated with the mechanical properties. FOR many years the large steam turbine industry has relied on the 1 Cr-Mo-V type forging steel for critical applications. Because of its adequate heat resistance and relative economy, it is currently in use in the temperature range up to about 1050" to 1075°F. Attempts to understand the large property variations attainable in this steel involve the structural modifications due to the wide latitude in its heat treatment. The heat treatment essentially involves a two-step process which includes solution-ing of carbides in the austenite range followed by a suitable tempering treatment below the critical to adjust the level of properties. The latter step is referred to as "secondary hardening" and is basically an ordinary aging reaction involving carbides. In the commercial heat treatment of large components of such steel, homogenizing and stress-relief anneals may be included and have some importance in determining subsequent properties. Several studies of the engineering properties of this steel as a function of transformation micro-structure have been reported.1 3 However, in this steel the carbide reactions, which are a function of composition and heat treatment, appear to be the property-controlling factor rather than the micro-structure defined as a transformation product. Thus, the tempering resistance of this type of alloy steel is mainly a function of the size and distribution of alloy carbides.4 However, it is also necessary to consider the stability of the microstructure and the effect of dynamic carbide reactions on subsequent properties. It is the purpose of this paper to show the interdependence of properties and corresponding structures, particularly carbide reactions, developed for a limited set of controlled heat-treatment conditions applied to 1 Cr-Mo-V steel. MATERIALS AND PROCEDURE The material for this work came from a large production forging whose chemical composition is shown in Table I. The property data accumulated on this steel as a function of heat treatment were room-temperature tensile and smooth- and notch-bar creep rupture at 1050°F (notch geometry: shank diameter = 0.357 in., depth = 50 pct, radius = 0.005 in.). To achieve controlled structural variations the temperature and time of both austenitizing and tempering were varied in a manner to produce a series of eight steels each at one of two grain sizes and one of two hardness levels in proper combination for valid comparisons. This will be clear upon examination of Table I. Structural studies involved the use of optical and electron microscopy as well as X-ray and selected-area electron diffraction. To reveal the nature of carbide precipitations, electrolytic extraction techniques were used with subsequent analysis of the residue by X-ray diffraction. Weight losses of the steel specimens during electrolysis were measured and successive chemical fractionations of the residues were applied and checked by X-ray examination. The details of fine structural distributions, morphologies, and crystallography of the precipitates as well as dislocation distributions were investigated by examining in the electron microscope three common types of preparation. a) Relief Replicas. Mechanically polished sections were etched in 2 pct nital, replicated with a nitrocellulose film, which was shadowed by chromium vapor deposited at a glancing angle of 20 deg. b) Extraction Replicas. A thin film of carbon was vapor-deposited on the polished and etched surface. The carbon films were then etched off and gathered on electron-microscope supporting grids. The carbides left imbedded in the carbon replica in their original distribution were then examined crystallo-graphically by selected-area electron diffraction. c) Thin Films. Specimens were mechanically ground and polished down to a thickness of 0.001 to 0.003 in. Final thinning was done electrolytically in a "chrome-acetic" electrolyte. When holes began to appear in the foil, the voltage was interrupted and applied in several 1-sec bursts. Sections of the foil between holes were thin enough to pass a 100-kv electron beam that carries an image.

Jan 1, 1965

By K. G. Davis, P. Fryzuk

WEINBERG,' in an investigation of solute distributions along unidirectionally solidified rods of dilute silver in tin alloys, concluded that, for rods of 2 mm diameter or larger, a very high degree of convective mixing takes place in the melt ahead of the advancing interface. Suggested causes for this mixing were (1) thermal convection, (2) convective currents set up by changes in fluid density associated with concentration gradients, and (3) currents set up by changes in volume during freezing. Evidence was presented that causes (2) and (3) were not primarily responsible for solute mixing. Further, convective mixing took place in horizontal rods with temperature gradients as low as 6°C per cm, putting doubt on the importance of thermal convection. In the present work, convective mixing is examined in melts with known initial solute distributions. The absence of a moving solid-liquid interface eliminates convection caused by volume changes on solidification. In the first experiment, three silica tubes 2 mm in diameter and approximately 20 cm long were filled with an alloy of 100 ppm Ag in tin (99.999 pct purity), placed adjacent to one another in a horizontal furnace, and solidified from one end at 1 cm per hr. A110, a Y emitter, was used as tracer. A few centimeters at the start of the rod were left un-melted, to determine the initial concentration Go. After solidification was complete, one sample was removed. The hot furnace was then brought back to

Jan 1, 1965

By Klaus Detert, Joseph Ziebs

The progress of primary recrystallization has been studied in alloys of nickel with 0.01, 0.1, and 1.0 at. pct Ta. It can be shown that in one particular alloy containing 0.1 Ta and 0.02 02 a large grain structure (0.5 mm diameter) could he developed by primary recrystallization in thin sheetswhich were cold-worked to 97.5 pct reduction in thickness. Electron transmission microscopy demmstrates that this phenonmena was linked to the occurrence of fine precipitates at subboundaries. A discussion of how fine precipitates can exert under certain circumstances a rather distinct retarding effect on nucleation rate is included. IN a former investigation, the recrystallization and texture formation in a series of binary nickel alloys including pure nickel were studied.' Nickel alloys with some tantalum added displayed peculiarities during primary recrystallization which have been studied in more detail by the present investigation. The alloys were prepared by powder-metallurgy techniques similar to the previous investigations.' Pure metal powders were thoroughly mixed to obtain alloys with 0.01, 0.1, and 1.0 at. pct Ta, referred to as alloy A, B, or C, respectively. The metallic impurities were kept below 0.005 at. pct except iron and cobalt with slightly higher values, by using highly purified nickel and tantalum powders.' The mixtures were pressed into bars and sintered at a temperature of 1300°C. The sintering atmosphere was either high vacuum, dry hydrogen, or wet hydrogen. The sintered rectangular bars were rolled 60 pct to a thickness of 3 mm, then annealed under dry hydrogen at 1000°C and again cold-rolled to about 97.5 pct reduction of thickness. After this heavy deformation, the sheet thickness was 0.07 5 mm. In order to study primary recrystallization which occurred in measurable times between 400" and 600°C, samples of the rolled sheets were annealed in a salt bath at various temperatures for various times in order to study the progress of recrystallization by hardness measurements and microscopic examination. For optical observation, the samples were polished and etched in a solution of 65 cu cm HNO3, and 18 cu cm acetic acid in 20 to 100 cu cm H2O, depending of the particular sample and annealing treatment. For transmission electron microscopic observations, thin foils were prepared by the combined window and Bollmann techniques.273 The electrolyte consisted of 23 pct perchloric acid and 77 pct acetic acid held at 15°C. Polishing was performed at a current density of 0.4 amp per sq cm. The examination of the thin films was accomplished by a Siemens Elmiscope-type electron microscope operating with an accelerating voltage of 100 kv. RESULTS The progress of primary recrystallization was very accurately followed in these alloys in order to establish the time when recrystallization started and ended during an isothermal anneal. Table I gives some of the data obtained by these studies. The time for beginning is a mean value, where somewhat less than 5 pct of the matrix has recrys-tallized. The end of recrystallization is the time when at least 95 pct of the matrix has recrystal-lized. Listed are three different B alloys, with 0.1 Ta distinguished by different sintering atmospheres which influence the rate of primary recrystallization. By the above method, the state of the grain structure when primary recrystallization was completed, but grain coarsening had not started, could be clearly defined. The average grain diameter of the recrystallized matrix is also given in Table I. The grain size did not depend on the temperature of the isothermal anneal. With one exception the grain size of the primary recrystallized matrix was found to be rather fine

Jan 1, 1965

By Joseph A. Cavallaro

This report describes the timed release analysis technique that was developed to serve as a tool for assessing the froth flotation cleaning potentials of fine-size coals. Using this developed technique, 16 coals from 10 different coalbeds were tested. All of the coals included in this study were quite amenable to froth flotation with float coal yields ranging from 80.7 to 99.5 percentage points. Float-and-sink analyses of the coals tested are shown to be of limited value in predicting froth flotation cleaning potential. Generally the float-and-sink analyses indicated a better product could be obtained than froth flotation could provide; although, in four of the coals tested froth flotation results were superior to those expected from the gravimetric analysis. The fixed carbon content of the samples collected was found to correlate with the floatability of the coals. The higher rank coals were the most readily floatable coals while the lower rank coals did not respond quite as well to flotation.

Jan 1, 1965

By J. M. Stuve

Calorimetric data for the dissolution of scandium sesquioxide and scandium trichloride in 4.360 molal hydrochloric acid were used to evaluate the standard heat of formation of ScCl3(c). The heat of reaction for Sc(c) + 1.5Cl2(g) = ScCl3(c) at 298.15° K was computed as -225,440 ±340 cal/mole.

Jan 1, 1965

By W. M. Wojcik, R. F. Kowal

Oxygen and sulfur distributions in commercial, 5-ton ingots of killed, medium carbon steel are described. Oxygen distribution is found to vary with deoxidation practice. Irregular distribution of oxygen within ingots makes necessary special precautions in sampling of rolled products for analysis of oxygen. Oxygen distribution is discussed in terms of recently published solidification concepts which had been successfully applied to simpler cases of segregation. These concepts have been found inadequate to explain observed oxygen distributions. Convective movements of the liquid metal, as determined by tracer elements, are shown to be capable of accounting for the observed distributions of oxygen. IN an effort to explore the origin of surface and subsurface imperfections in pierced steel products, a study of oxygen and sulfur segregation was made on ingots cast in open-top and hot-top molds. The results of our previous investigations1"3 have indicated the importance of the location and amount of oxide inclusions in an ingot. Inclusions close to the surface of the ingot have been found to contribute greatly to the formation of imperfections in the surface of finished products. This study of the effects of deoxidation and casting practice on segregation and the resulting oxygen distribution in ingots was initiated to determine the parameters controlling the location of inclusions in an ingot. Segregation of solute elements during solidification of low-melting binary alloys has been studied in the past.1, 5 Formation and growth of inclusions in iron melts have been studied under specific conditions."- In spite of these and other recent studies,10-12 segregation during solidification of commercial, killed steel ingots is not well understood. Consideration of solidification rates, of segregation during solidification of the chill, dendritic, and central zones, and of material balances for the segregated elements has indicated that a simplified theoretical solidification model is not adequate. However, the observed high oxygen contents in localized volumes of the dendritic zone can be rationalized if additional effects of convection currents in the ingots, precipitation, and rapid growth of new phases are considered. EXPERIMENTAL PROCEDURE Steelmaking and Processing. A group of nine killed. medium carbon steel heats having compositions listed in Table I have been studied. The deoxidation and mold practices used were varied to give a wide range of steel oxygen contents. The amounts of aluminum added to the ladle and the ingot casting practices (hot top and open top) were the main variables. The steel was made by a duplex practice in 160-ton tilting basic open-hearth furnaces. All nine heats were top-cast into 24 by 24 in. big end down, fluted molds, to a height between 60 and 76 in., using both open tops and exothermic hot tops. The deoxidation practice and the tapping and teeming details for each heat and ingot studied are given in Tables II and III, respectively. Hot-top practice is indicated by the letter H following the heat designation. Furnace and ladle temperatures were measured by standard disposable-tip, Pt/10 pet PtRh thermocouples. Teeming-stream temperatures were obtained as described by Samways et al.,13 by immersing a Pt/10 pet PtRh thermocouple, covered by a silica sheath, into the teeming stream under the nozzle. The output of this thermocouple was recorded with Leeds & Northrup Speedomax potentiometer. Calibration of the latter thermocouples was based on the freezing point of a pure iron/oxygen alloy (2795°F). The accumulated errors of measurements were within ±10°F. The thermocouple measurements were supplemented in this investigation by continuous recording of a ratioing, two-color pyrometer (Shawmeter), protected from smoke by a blast of clean air within the sighting tube, and calibrated to read with better than ±10°F accuracy. Following teeming of three heats, P, R, and T, tracer elements were added to the steel in the molds to obtain a record of the progress of solidification. As soon as the teeming stream was shut off, a 0.010-in.-thick steel can containing a mixture of crushed standard ferro-titanium and ferro-vanadium (0.05 pet of each alloy element) was plunged into the middle of the steel pool to a depth of 6 in. In about 30 sec no indication of the can or its contents remained. The surface of the open-top ingots solidified in 20 to 30 sec. A study of liquid metal movement and the precipitation of oxides was facilitated materially by use of the tracer technique as titanium has a low distribution coefficient between solid and liquid steel while vanadium has a high distribution coefficient.

Jan 1, 1965

By Frank A. Jerabek

Problems of mine backfilling and fill material deposited underground, the characteristics and relationship between the deposited fill material and overlying ground, and the practical applications and limitations of hydraulic backfilling as ground support are discussed. A great variety of materials ranging from coal washery refuse to concentrator tailings is used as hydraulic fill. Some materials will solidify and cement; others will resemble quicksand, Hydraulic fill as ground support is more efficient in inclined mine openings than in horizontal mine openings, where it cannot be placed tightly to the back. This and other deficiencies of hydraulic backfilling led to the development of pneumatic stowing. Research work in hydraulic backfilling at the Pennsylvania State University is also discussed. This research work includes the investigation of segregation in the discharged fill slurry, the quantity of solids escaping in the drain liquid, the relationship of escaping solids to slurry concentration and discharge rate, and the compressibility of fine fill material.

Jan 1, 1965

By B. B. Letson

The heats of formation of lithium chloride and lithium oxalate were determined with the aid of a Bureau-developed, glass Dewar-type solution calorimeter which uses thermistors as its temperature sensing element. Values obtained at 298.15° K were -98.38 ± 0.54 kcal/mole for lithium chloride and -329.02 ± 0.79 kcal/mole for lithium oxalate, using graphite as the standard state for carbon.

Jan 1, 1965

The principal activities of the Bureau of Mines Explosives Research Center from July 1, 1962, to June 30, 1963, are described briefly in part 1. Part 2 gives short abstracts of publications that appeared during fiscal year 1963; in general, the research reported in these publications antedates the report period.

Jan 1, 1965

By G. W. Tuffnell, S. Floreen

Three Fe-18 pet Ni-base ternary alloys cortaining carbon, molybdenum, or cobalt were aged to pgroduce hardening by carbides, Ni3Mo, or ordering, respectively. Each alloy was tested in rotating-beam fatigue tests after hardening to 195 ksi ultim.ate tensile strength. The fatigue properties of three alloys soere essentially identical. The results suggest that tlze fatigae strength of an igron-base alloy should depend primarily upon the tensile strength, and not iipon the hardening mecaanisrn. THE fatigue strengths of many steels have been found to be directly related to their ultimate tensile strengths. For ultimate strengths below 200 ksi, the fatigue endurance limit at 107 to 10' cycles is approximately half the ultimate strength. Essen- tially all of the steels that have been tested, however, have been hardened by carbon. Thus it is not certain whether the relationship between fatigue and ultimate strengths is a general one that applies for other types of hardening in steels, or whether it applies only for the particular method of hardening by carbon. The recent developments of the martensitic precipitation-hardened stainless steels and the marag-ing steels have shown that it is possible to achieve high strengths in iron-base alloys by other hardening mechanisms than that due to carbon. Therefore, it is now possible to compare the fatigue properties of several iron alloys having the same ultimate strengths but hardened by different mechanisms. For the present study a binary Fe-18 pct Ni martensite was selected as a base material. This particular matrix composition has been found to have deformation characteristics very similar to pure iron.' Three ternary alloys were prepared by adding either 0.23 wt pct C, 5 wt pct Mo, or 20 wt pct Co to this base composition. After suitable heat

Jan 1, 1965

By I. R. Kramer

In his technical note entitled "Specimen Temperature During Electropolishing of Aluminum Crystals" Dr. Nakada 1 reported that the temperature of his aluminum specimen increased 65°C when it was polished electrolytically; he therefore concluded that the temperature of the specimens used in our work (Nakada's Refs. 4 and 5) similarly increased by this amount. From this he further concluded that the change in plastic-flow characteristics associated with the removal of the surface by electropolishing during deformation were due solely to a temperature effect. We believe that these conclusions are not justified. It is, of course, realized that the amount of the temperature increase is associated with the total heat transfer of the entire system, including the efficiency of the stirring action, heat flow through the grip on the specimen, and so forth. Of great importance is the type of electrolyte used for polishing. For example, in Dr. Nakada's experiment a methanol-perchloric acid solution was used. This solution has a relatively low conductivity and for the current densities of 0.3 amp per sq cm the electrical input appears to be 30 to 40 w. In our research a methanol-nitric acid solution was employed and for the size of specimen employed by Dr. Nakada the power never exceeded 7 w. There are major differences in his test apparatus which also appear to affect the temperature rise. In our case a steel specimen holder was used in order to provide a good heat sink and conduction path. The cathode was a coiled aluminum tube through which a coolant was passed to provide additional cooling capacity near the specimen. The stirrer was placed in a position to obtain maximum cooling efficiency. On the other hand Dr. Nakada used a teflon grip to support the specimen at one end only and a flat copper cathode, thus providing a much less efficient heat sink as compared with the metal grips used in our studies. The relationship between current density and the temperature increase for two sizes of aluminum crystals tested in our tensile apparatus is shown in Fig. 1. The temperature measurements were determined from a thermocouple spot-welded to the surface of the specimen. The thermocouple was protected from the acid by means of a thin film of stop-off lacquer which covered just the outer surface of the thermocouple junction. Whereas Dr. Nakada reported a time delay of 8 min to obtain thermal equilibrium, our temperature change occurred in less than 15 sec. This emphasizes the importance of the heat transfer in the entire system. However, readings were taken over a period in excess of 5 min to assure thermal equilibrium. The data given in Fig. 1 were also confirmed by determining the thermal expansion of the specimen in a sensitive creep apparatus. As may be seen, for the smaller specimen the increase in temperature is 8°C for a current density of 1.5 amp per sq in. The majority of our data on the effects of surface removal on the plastic behavior of aluminum were obtained at current-density values at or below this value. Above 1.5 amp per sq in. the temperature rise is uncertain; for under certain conditions, especially in the vicinity of 2 amp per sq in., the anode can become polarized and the current flow is erratic. This condition is easily recognized because wide fluctuations in the creep and stress-strain data make it virtually impossible to obtain reliable results, a condition which was always avoided in our work. The temperature increase for the larger specimen is less than that of the smaller specimens below a current density of 1.5 amp per sq in. At a current density of 2 amp per sq in. the temperature increased 13°C. The above temperature data are in accord with observations made during creep experiments. Using a transducer capable of detecting strain in the order of 10 -6, temperature changes in excess of 8°C were not detected when the current density was increased to as high a value as 1.5 amp per sq in. Finally we wish to point out that our experimental data cannot be explained solely in terms of a heat effect. For example in Fig. 1 of Ref. 2, the change in slope of Stage II as a function of the rate of re-

Jan 1, 1965