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By W. C. Ellis, E. S. Greiner, M. E. Fine

Discontinuous changes of Young's modulus, internal friction, coefficient of expansion, electrical resistivity, and thermoelectric power are evidence for a transition in chromium near 37OC. Although the X-ray diffraction pattern gives no clue, a difference between the thermal expansivity and the temperature dependence of the lattice parameter suggests a crystal-lographic change. Young's modulus data disclosed another transition near THE thermal dependence of a number of proper- ties of chromium indicates a transition occurring over a temperature range near room temperature. Bridgman' noted this first from a minimum in the electrical resistivity near 12°C. In a sample of greater purity, Sochtig' observed the minimum at 41 °C. Erfling3 reported an inflection in the thermal expansivity curve at 36°C. These temperature-dependence curves are reversible with no hysteresis being detected. No discontinuity or inflection has been observed in the heat capacity' or the paramagnetic susceptibility.' Likewise, no one has noted a change in crystal symmetry. In the present investigation Young's modulus, internal friction, coefficient of expansion, electrical resistivity, illustrated in Fig. 1, lattice constant, Fig. 2, thermal electromotive force, Fig. 3, and paramagnetic susceptibility, Fig. 4, were measured over an extended temperature range. The samples were prepared in two ways: (1) By cold pressing a sintered electrolytic powder compact,' and (2) by electroforming from an aqueous solution. The electroformed samples were prepared by R. A. Ehrhardt and G. Bittrich by plating on copper or nickel tubes from an aqueous solution according to the method of Brenner, Burkhead, and Jennings.' The pressed powder samples (method 1) were finally annealed at 1400°C in purified helium: the electroformed samples, packed in powdered chromium, were vacuum-annealed at 1000°C. From the composition of the original powder' the purity of the pressed powder samples is estimated to be 99.8 pct Cr. Spectrochemical analysis furnished by E. K. Jaycox, revealed only slight traces of impurities in the electroformed sample (less than 0.001 pct), neither iron nor nickel being detected. Chromium deposited by this method is reported to contain approximately 0.05 pct 0.- Methods and Data Young's Modulus: For measurement of Young's modulus, an annealed, pressed powder sample, 0.114 x0.237x1.845 in., and an electroformed sample, 0.10 in. od, 0.01 in. id, and 1.86 in. long, were prepared. The resonant frequencies of the rod samples in forced longitudinal vibration were measured at a series of temperatures from —192" to 200°C by a method previously de~cribed.6,7 Because the samples were nonferromagnetic, iron- silicon or molybdenum permalloy tips (0.013 in. thick) were soldered to the ends. The softening temperature of the solder limited the temperature of measurement. Young's modulus, E,, of chromium at temperature, T, may be calculated from the resonant frequency of the composite rod, f,; the thickness of the tips, t; the length of the chromium sample at 25°C, l,.; the density of chromium at 25°C, pc (7.20 g per cc);5 and the thermal expansivity, Al/l25. Modulus differences for two temperatures, ET and E, are accurate to +0.002x10" dynes per cm2. ET = 4PAlc+2tyf Young's modulus at 25°C, Fig. la, is 28.2~10" dynes per cm' (40.8xlO" si) in wrought chromium (upper curve). The modulus of the electroformed sample is apparently lower due to cracks. From the modulus measurements two transitions were observed: one with a critical temperature at 37°C, the other at —152°C. Internal Friction: The internal friction, 1/Q, was determined from the width, Af, of the strain amplitude-frequency curve at 0.707 times the strain amplitude at resonance;' the internal friction, 1/Q, then equals Af/f. Fig. lb shows a sharp peak in internal friction at 38°C. The internal friction of the electroformed sample had a similar maximum. Thermal Expansion: The expansivity measurements, shown in Fig. 2, covering the temperature range —195" to +400°C were made by D. MacNair in an interferometric dilatometer8 sing a sample consisting of three pyramids 0.25 in. high prepared from wrought electrolytic chromium. Below —120°C the experimental points deviated up to ±2x10 from the drawn expansivity curve in Fig. 2 because of decreased precision of the quartz wedge thermometer at low temperatures. Near 38°C the thermal expansivity curve, Fig. 2, goes through an inflection corresponding to a minimum in the coefficient of expansion, Fig. ld, and a relative volume decrease on heating. Electrical Resistivity: The variation of electrical resistivity with temperature measured by the po-tentiometric method is also shown in Fig. l. The resistivity of the wrought chromium (upper curve) at 20°C is 13.6 microhm-cm; of electroformed chromium (lower curve) 12.8 microhm-cm. The lower value reflects higher purity and agrees closely with a published value." A minimum at 40°C occurs in the resistivity curves of both samples. No conclusive evidence for a transition near — 150°C was observed, but the points, Fig. 1, appear to deviate from a smooth curve between —120" and —160°C.

Jan 1, 1952

By C. W. Phillips, D. N. Frey

A commercial Ti-Fe-Cr alloy, Ti-150, exhibits a martensitic transformation on cooling and two nucleation and growth reactions, one above and one below the Mg-Mf region, on isothermal holding below the single-phase ß temperature range. The reactions were followed by metallographic, X-ray diffraction, and microhardness methods. THE rapidly expanding engineering application of titanium and its alloys makes increasingly urgent an adequate knowledge of the effect of heat treatment on this material. The work herein reported is an attempt to determine certain aspects of the behavior of a commercially available alloy, Ti-150, during heat treatment. The alloy, with a nominal composition of 2.7 pct Cr, 1.3 pct Fe, 0.25 pct 0, 0.02 pct N, and 0.02 pct C, was received in the as-rolled condition as a 3/4 in. round. Slugs 0.11 to 0.12 in. thick were cut under a coolant using a silicon carbide wheel. Preliminary work established that the alloy consists of two phases, a (hexagonal close-packed) and /3 (body-centered cubic), at temperatures below 1750" to 1775"F, and of only /3 phase at higher temperatures. The slugs were heated for 1 hr in air at 1800°F to form a single-phase /3 matrix, then transferred to molten tin (1250° to 1650°F) or lead (1150°F and below) for isothermal holding. Holding temperatures ranged from 700° to 1650°F, times from 0.001 to 23 hr. The treated slugs were then sectioned, one part for metallographic examination and diamond pyramid hardness, the other, after deep etching to remove the high oxygen surface,' for comparative lattice parameter determination and X-ray phase identification. Hardness measurements were taken on the lightly etched surfaces of the metallographic specimens; a 1000 g load on a 136° diamond pyramid was used. Five impressions on each sample were made and the average of the hardness calculated. The use of microhardness measurements to follow the course of an isothermal transformation reaction is undesirable because of the possibility of wide differences in microconstituent hardness.' They were used in this case, however, because of the small amount of material available. At the higher transformation temperatures, where the above-mentioned objection was apparent, the readings were proportioned to correspond to the estimated ratio of transformed and untransformed constituents present. At lower temperatures, resulting in much finer microconstituents, the microhardness measurements were more uniform. The standard deviation of the mean of five impressions calculated from these latter values was 4.2 DPH. Employing 2a limits (probability 0.95) the experimental error of the hardness measurements averages was 8.4 DPH. The etchant used was composed of one part glyc-erol and one part 48 pct hydrofluoric acid." Of a number of etches tried, this one appeared most satisfactory. All micrographs were taken at 500X magnification and with oblique lighting to permit easier identification of the acicular structure resulting from rapid cooling. No advantage was gained by using polarized light for metallographic examination. Phase identification and lattice parameter measurements were made with a North American Philips high angle spectrometer in conjunction with a recording potentiometer. Considerable difficulty was encountered with some of the lattice parameter measurements because of the extreme broadness of the few diffraction lines obtained from samples consisting mainly of strained, untempered, quenched structures.

Jan 1, 1953

By Adam L. Wesner, A. C. Richardson

DURING World War II the demand for electrode carbon was greater than could be met by the supply of petroleum coke available for this use. It was believed that coke made from an extremely low-ash coal might be a suitable substitute for petroleum coke. Requirements for electrode carbon to be used for the production of aluminum are that the silicon plus iron content shall be not more than 0.14 pct of the coke. However, during the period when petroleum coke was in short supply, it appeared that relaxations of the specifications might be allowed to permit 0.4 pet iron plus silicon in the coke. For this work, the specifications were that the coal should contain less than 1 pet of ash, and the combined iron and silicon content of the coal should not exceed 0.28 pct. Heavy-liquid separations made on a number of coals showed that if certain size fractions of some coals were separated at low specific gravities the resulting float products would meet the required specifications. The objective of this work was to develop a continuous, commercially feasible process for producing low-ash coal. After consideration of various processes, the method chosen was a float-and-sink separation using a solution of calcium chloride as the separating medium. Eagle Seam coal was used for the experiments. The -10 +35 mesh fraction was found to be the most promising feed for producing the low-ash [ ] content coal. A batch of 30 tons of -3/8-in. coal was screened at 10 and 35 mesh; the yield of -10 +35 mesh was 20 pct of the feed. This fraction comprised the feed for the separation tests. In spite of the fact that this portion was screened a second time at 35 mesh, the coal still contained 16 pct that was finer than 35 mesh. Three-fourths of the undersize was in the -35 +48 mesh range. A representative portion of the -10 +35 mesh fraction was subjected to batch float-and-sink separations to determine the best gravity to be used in the continuous tests to obtain a high recovery of low-ash content coal. The heavy liquid used was a mixture of carbon tetrachloride and benzene which assured complete wetting of all of the particles. As usual in batch separations, adequate time was allowed for each separation so that even the near gravity particles had ample time to separate. The separations were made at increments of 0.01 sp gr from 1.25 to 1.28 and also at 1.32 and 1.59. Each specific-gravity increment was assayed for ash content. From these data it was concluded that 1.27 sp gr was best for the continuous separation of the coal. The products from the batch separation were composited into float 1.27 and sink 1.27 sp-gr fractions; these were assayed for ash, iron, and silicon. Table I shows the results of the batch separations. The composite float 1.27 fraction contained 66.04 pct of the total weight, and had an analysis of 0.79 pet ash, 0.073 pct iron, and 0.112 pct silicon, or 0.185 pct iron and silicon combined. These data are indicative of the results possible if a perfect separation is made at 1.27 sp gr under static conditions. Inasmuch as the method under investigation is a dynamic system these results could not be obtained. It remained to be determined, however, just how close to the theoretical results the actual continuous separation would be.

Jan 1, 1952

By D. W. Smith

THE beta solid solution phases of the systems copper-zinc, copper-aluminum, copper-tin and silver-zinc are structurally analogous.1 R. F. Mehl and 0. T. Marzke2 have shown that the a phase upon segregating from the 0 phase in the system copper-zinc takes the form of needles lying parallel to a [111.] direction or some similar direction, such as [556], of the parent solid solution, and that the a phase upon segregating from the ß phase in the system copper-aluminum also takes the form of needles. By analogy they assume that in this case also the segregate needles lie parallel to the [111] or [556] direction in the ß lattice. The purpose of this investigation is to determine whether the structures resulting from segregation of the a phases from the respective 0 phases of the systems copper-tin and silver-zinc are analogous to those obtained by Mehl and Marzke in the systems copper-zinc and copper-aluminum.

Jan 1, 1932

ALABAMA. Aldrich, Aldrich, W. F. Anniston, Noble, A. E. Auburn, Brown, R. L. Bessemer, Abbott, C. E., Ferguson, V. Birmingham, Aldrich, T. H., Aldrich, T. H., Jr., Allen, A. W., Bowron, J., Burbidge, T. A., Crawford, G. G., Crockard, F. H., Davis, F. H, Dimmick, F: D., Ellis, E. E., Geismer, H. S., Hiller, E., Johnson, G. R, Ludwig, C. P., McCormack, G. B., McCrery, Peters, R, Jr., Phillips, W. B., Pill, J. R., RamSay, E. Coal City, Pattberg, 0. F. E-msley, Wil¬liams, E. P. Helena, Squire, J. Holt, Shook, J. W. Huntsmlle, Moss. Ironton, Hudson, J., B. Lehigh, Toulmin. Bock Bun, Garvin, J. M. Woodward, Wood¬ward, A. H.

Jan 1, 1910

By Edward Wisser

The Pachuca silver district, situated about 100 kilometers northeast of Mexico City (Fig. l), covers roughly the southeastern half of the Sierra de Pachuca. The latter is a mountain range with northwest trend, and forms a part of the northeastern rim of the topographic basin known as the Valley of Mexico. The length of the Sierra proper is about 50 km., its greatest width about 9 km., and it rises to a maximum of 600 meters above the general level of the basin floor. The Pachuca district consists of two contiguous subdistricts, the Pachuca area and the Real del Monte area. The center of the Real del

Jan 1, 1937

By Olav Klomstadlien

The lean, but extensive iron ore deposits of the Dunderland Valley north of Mo i Rana, Norway, are the raw material base for Rana Mines, a division of the state-owned A/S Norsk Jernverk steel mill. The iron bearing minerals are magnetite and specular hematite. The magnetite/hematite ratio varies considerably both within each deposit and from one deposit to another. The ore bodies that lend themselves to mining have generally a thickness of 30-60 m grading 30-35% Fe and 0.15-0.25% P. The grain size varies from 0.05 to 2.5 mm. The fine grained ores are hard while the coarse grained ores are soft and easy to grind. The A/S Norsk Jernverk steel mill operates both a sinter and a pellet plant, and this necessitates production of two types of concentrates. The present flowsheet is shown in [Fig. 1]. The crude ore from the pits is crushed in a 1.07-m gyratory crusher with an open side setting of 12.7 cm. The crusher product is transported by rail to the concentrator located 25 km from the mines. The ore is fed by twelve 1.22 X 1.83 m vibratory feeders onto conveyor belts which carry the ore to a surge bin ahead of the autogenous mills. The feed rate is automatically adjusted to maintain a set power load at a level suitable for the ore type being processed. The mills operate in closed circuit with twelve dual-drum screens equipped with a 0.8-mm screen cloth. Oversize is returned by gravity to the mill feed while undersize flows to the gravity separation section which consists of Humphrey spirals in three stages. The ores are very heterogenous and analysis may vary quite considerably. The quantitative need for concentrate in the steel mill may also change rapidly. The process in the concentrator must therefore be easily changed, and consequently alternative process lines have been established. This is indicated with the dotted lines in the flowsheet. Apatite is removed by flotation by fatty acids to give a final sinter concentrate of 63% Fe and 0.020% P or less. Pellet concentrate contains about 65% Fe and less than 0.020% P. The fineness is about 1500 Blain.

Jan 1, 1981

By B. S. Blakeney, E. P. Abrahamson II

The effect of the transition elements in binary solid-solution additions upon the recrystallization temperature of iron has been investigated. All these elements immediately raised the temperature, the majority having their greatest effect in less than 0.10 at. pct. A correlation is noted between the rate of change of recrystallization temperature with atomic percent solute and the electron configuration of the solute element. THE work of Abrahamson and rant' on binary chromium-base alloys indicated that a correspondence existed between the effect of each solute element on the brittle-to-ductile transition temperature of chromium and the ground-state electron configuration of the element added. This was felt to be a bonding phenomenon and would be expected to be observed in measurements of other properties involving the breaking or exchange of atomic bonds. From this work it was postulated that a like correspondence should be found for other properties of binary alloys, such as recrystallization. This study is an effort to check this postulation using binary solid-solution iron-base alloys. Previously, the majority of recrystallization studies were carried out on steels. However, Tammann2 investigated the recrystallization of iron as effected by Co, Ni, Si, Mn, Mo, and Cr and stated that elements with the same crystal structure at room temperature as iron appeared to be more effective in raising the recrystallization temperature. Austin, Luini, and Lindsay3 studied the effects of Ni, Cr, Mn, Co, Si, and Mo on cold rolling and annealing, but noted no trend. Abrahamson and rant,' in their work on the effect of both substitutional and interstitial elements upon the brittle-to-ductile transition of chromium, have shown that the outer electron configuration in the ground state of the solute element appears to be the prime determinant of the transition temperature. PROCEDURE All alloys were made using 99.95 + pct Fe with 0.02 wt pct 0, 0.004 pct C, and 0.001 pct N. All alloying elements were 99.9 + percent pure. Metal-lographically the alloys, out to at least 0.1 at. pct, appeared to be in solid solution. Though several published phase diagrams tend to dispute this.4 All alloys were arc melted six times and cast into square 400-g ingots under an argon atmosphere.

Jan 1, 1961

By G. P. Walters, W. C. Fuller

THE production of thin films of beryllium became essential early in the irradiation program at Harwell in order to study the fundamentals of irradiation damage in this metal. In common with other metals, electron-microacope specimens of beryllium can be produced by different techniques. The techniques used to produce thin-film specimens varied according to the starting material. Most of the starting material was -0.060 in. thick. Large-area specimens (1 in. long by 0.5 in. wide) were chemically thinned to -0.005 in. thick in a solution containing 85 pct orthophosphoric acid, 10 pct chromium trioxide, and 5 pct sulfuric acid at 70°C prior to electropolishing. Small-area specimens, Fig. 1, had to be mechanically thinned prior to electropolishing because chemical thinning considerably reduces the area as well as the thickness. Mechanical thinning tends to produce a worked layer about 0.002 in. deep and hence this method cannot be used to thin bulk specimens below about 0.005 in. thick. Mechanical thinning is carried out by mounting the specimen on perspex then carefully polishing on wet grinding papers. Polishing is continued until about half the initial thickness is removed; the reverse side is then polished in a similar manner. After the bulk specimens have been mechanically or chemically thinned to -0.005 in. they are elec-tropolished in the solution shown in able I at 50" to 80°C. This solution should be prepared by adding the chromium trioxide to the orthophosphoric acid and then the glycerol last. The glycerol should be added slowly because a vigorous effervescence can occur. Electropolishing is carried out by holding the specimen in stainless-steel tweezers and gently agitating in the solution. Masking or "window" techniques are not required for beryllium, good microscope specimens being obtained from the edges of elec-tropolished foils. A stainless-steel beaker should be used, acting as the cathode and solution container. A closed circuit voltage of 30 v is used for polishing. Too low a voltage produces a matt surface and pitting occurs when it is too high. The solution temperature is important. If it is too low, the solution is viscous and bad polishing results and, if too high, etching of the specimen occurs. After electropolishing, the foils are thoroughly

Jan 1, 1963

By W. A. McCurdy, Joseph W. Leonard, William F. Lawrence

INTRODUCTION Utilization from the Point of View of the Preparation Engineer The primary interest of the coal preparation engineer is in process design, operation, and maintenance to produce an acceptable product that can be sold at the greatest possible profit. Because of emphasis upon these interests, attention to other potential values of coal is sometimes neglected. The intent of this chapter is to alert the preparation engineer to the utilization possibilities of the product as well as the tributary coal flow moving through a modern coal preparation plant. The basis for any unrealized potential derives directly from the coal seam itself. Most coal seams consist of coal bands and benches sandwiched together in layers that differ visually from each other in physical structure and luster. Randomly selected physical and chemical ranges determined from layers of coal in a single seam can easily differ by as much as 30 Hardgrove grindability indices, 0.30 of a specific gravity point, 20 percentage points of ash, 6 percentage points of dry volatile matter, and 10 percentage points of total su1fur.l Similar wide variations exist for calorific value, seam moisture content, and, undoubtedly, for any other conceivable coal test parameter that might be used for comparative purposes. These observations all point to the long-established fact that coal is not homogeneous, as conventional analytical methods might tend to indicate, but is instead a highly heterogeneous substance.

Jan 1, 1979

[NORTH AMERICA UNITED STATES ALABAMA ADAMSVILLE U. S. Steel Corp. Neason, James E. ALBERTVILLE Thompson Floral Co. Loudermilk, E. L. ANNISTON No Data Supplied Bonnichsen, Bill BESSEMER U. S. Steel Corp.-TCI Div. Beck, Adolph W., Jr. Boyle, James R. Cofield, William H. *Evans, James D. F., II *Guyton, Jesse C. Johnson, Leland H. Tetley, Albert L. No Data Supplied Crockard, F. H. Fisher, Joe T. Griffin, Joseph M. McFarland, E. A. Mohr, Henry E. Neal, George M. Walker, Wilber D.]

Jan 1, 1961

By W. Wanjokow, H. O. Hofman

In the metallurgical treatment of most metallic sulphides it is usually necessary to carry on a roasting-operation. In some cases the raw ore will have to be roasted; in others the intermediary product, matte, produced in smelting the ore; again, both ore and matte may have to be subjected to oxidation at elevated temperatures. Most metallic sulphides, when given an oxidizing-roast, pass through the state of sulphate before they are converted into oxides. All metallic sulphates are completely decomposed by heat, with the exception of those of lead and bismuth, but the temperatures at which decompositions take place vary with the metals. Some metallic sulphates are converted directly into oxides, others first form basic salts. Alkali-earth sulphates show a behavior similar to that of metallic sulphates, while alkali sulphates do not part with their sulphur trioxide even at elevated roasting-temperatures. The older data on the decomposition of metallic sulphates by heat are only approximations. Thus Kerl' gives the order in which metallic sulphates are decomposed with increasing temperatures as (Ag2, Fe, Cu, Zn, Ni, Co, Mn, Pb) SO,. More recent statenlents give definite temperatures and modify the formerly accepted order of decomposition. But the temperatures given by various observers do not agree. The reasons for this are to be found mainly in the method and manner of carrying out experiments. Four methods have been used: 1. Heating in an evacuated tube; 2, heating in a tube closed at one end, without air-cur-

Jan 1, 1913

By Charles W. Dickson

CONTENTS. [ ] I.THE RELATION OF NICKEL TO PYRRHOTITE. Introduction. The Sudbury district is to-day one of the two great sources of nickel in the world. The peculiar geological relations of

Jan 1, 1913

By C. M. Haight

The mines of the New Jersey Zinc Co. in New Jersey, are situated in the northern part of Sussex County, at Franklin, formerly Franklin Furnace, and also at Ogdensburg. The mine at Ogdensburg is still in the development stage, but the, mine at Franklin, with which this paper deals chiefly, has been a steady producer of high-grade zinc ores for many years. The town is about 50 miles from New York City, among the foothills -of the Kittatinny Mountains. It is equipped with water supply (filtered and chemically treated), good roads, electric lights, efficient police protection and excellent schools, including a new vocational high school. For a mining community, the conditions and location are far above the average. Franklin Furnace Folio, No. 161 of the U. S. Geological Survey, describes the geology and mineralogy of the district in detail, so that merely an, outline of the main characteristics of the orebody need be given. The

Jan 10, 1917

By J. W. Downey, A. E. Dwight, M. H. Mueller, H. Knott, R. A. Conner

Sixty new ternary equiatomic compounds are reported with a hexagonal crystal structure that is isostructural with or very similar to Fe2P, D3h-P62m. HoNiAl is a typical example, with a, = 6.9893 ± 0.0003Å, C, = 3.8204 ± 0.003Å, and c/a = 0.54 7. Three holmium atoms occupy (g): x,0,1/2 three aluminum atoms occupy (f): x,0,0; one nickel atom occupies (b): 0,0,1/2; and two nickel atoms occupy (c): 4, + , 0. The nonequivalent 1(b) and 2(c) sites give rise to two sets of unequal interatornic distances (i.e., Ho-Ni and Al-NL in the case above), which account for the prevalence of Fe2P-type tertmry compounds and the scarcity of binary examples. Unit-cell constants are presented for the sixty compounds and density measurements on the compounds HoNiAl and UFeGa confirm that three formula weights are present per unit cell. Neutron and X-ray powder diffraction intensity measurements were made on CeNiAl and HoNiAl, respectively. The atomic posiLiotml parameters in CeNiAl were determined from neutron data to be x = 0.580 5 0.001 for cerium and 0.219 5 0.001 for aluminum. An investigation of the quasibinary section between the binary compounds CeNi2 and CeA12 revealed a new ternary compound CeNiAl. The compound has a hexagonal structure and is isostructural with the prototype compound Fe2P. Additional examples discovered or confirmed in this investigation provide a total of sixty ternary compounds that are isostructural with or closely related to Fe2P. Previous investigators1'2 reported the unit-cell constants for the hexagonal compounds UFeA1, UCoAl, UIrA1, ZrNiAl, ZrNiGa, HfNiAl, and HfNiGa and the present investigation has confirmed that the compounds are isostructural with Fe2P. Independently, Steeb and petzow3 reported the same structure type for UCoAl, UIrA1, and UNiA1. However, the present results suggest a different atomic site occupancy for the component atoms in the three compounds. A detailed investigation of the relative positions of the three kinds of atoms in the compounds CeNiAl and HoNiAl will be discussed. EXPERIMENTAL PROCEDURE The equiatomic alloys were prepared from elements of 99.9+ pct purity by arc melting under a helium-argon atmosphere. After homogenization at temperatures from 700" to 900' C, a metallographic examination was performed by conventional methods, and density measurements were carried out by the immersion method in CCl4. A powder sample was prepared for diffraction studies by crushing a portion of the annealed button. X-ray diffraction patterns were obtained with a Debye-Scherrer camera, in which the annealed powder was glued to a quartz filament, and indexed with the aid of a Bunn chart. Unit-cell constants were calculated from the computer program of Mueller, Heaton, and Miller4 and d spacings were obtained by the program of Mueller, Meyer, and Simonsen.5 The intensity values were calculated from the relation I, ~ (m)(L.P.)F2 by a computer program written by Busing, Martin, and Levy.6 The absorption and temperature correction factors were neglected. An X-ray study of HoNiAl was carried out to take advantage of: large differences in atomic scattering factors for holmium and aluminum, X-ray patters free of background darkening, negligible oxidation at room temperature, and negligible weight loss in the preparation of this alloy. The neutron diffraction studies were made on a powder sample of CeNiAl contained in a -in. diam V tube and a pattern was obtained with neutrons of wavelength The neutron scattering factors employed (x 10-12 cm). In contrast to the scattering amplitude for X-rays, cesium does not have the largest cross section, however, there is a sufficient difference in the neutron scattering amplitudes to distinguish between the atomic species. The neutron transmission was high, 86 pct; therefore, absorption corrections were not necessary for the cylindrical sample. Most reflections could not be observed individually, because of the relatively large unit cell (a = 6.9756 and c = 4.0206Å) and relatively short neutron wavelength; therefore, the intensity of grouped reflections was considered. The Kennicott modification7 of the Busing-Martin-Levy program6 was employed to determine the identity of the atoms at the various lattice sites and the positional parameters. RESULTS A structure for the prototype compound Fe2P was first reported by Hendricks and Kosting;8 however, the structure was in error. The correct structure, as reported by Rundqvist and Jellinek,9 is as follows. The unit-cell constants and volumes per formula weight (V/M) are given in Table I for the sixty compounds examined in this investigation and classified as Fe2P-type compounds. The structure type was determined initially from a comparison of the unit-cell constants of HoNiAl with other known examples of this structure type1' and from the density of HoNiAl, given in Table 11. The density indicated that three formula weights comprised a unit cell, as in the prototype compound Fe2P. The assignment of the three species to lattice sites was made initially on the basis of atomic size. The large holmium atoms were assigned to the 3(g) sites that have a relatively large interatomic distance to nearest neighbor positions, the small nickel

Jan 1, 1969

By M. J. Duggin

Structural similarities between the E, X, and iron carbides are illustrated. Experimental evidence regarding phase transformations occurring during ternpering reactions in finely divided carbides, thin-film carbides, and carbides which occur in steels is considered and possible mechanisms for the E — x and x — 9 transformations proposed. HOFER1 has shown that within the appropriate temperature ranges carbon monoxide will react with finely divided a iron to form either iron carbide or x iron carbide. He has shown that at an elevated temperature the E iron carbide will transform to the x iron carbide (Hagg carbide) which, upon further elevation of temperature, will transform to 9 iron carbide (cementite). Jack,2,3 using X-ray diffraction methods, has observed that during the tempering reactions occurring in steel the E iron carbide formed in the first stage of tempering passes into two-dimensional platelets of 0 iron carbide during the second stage of tempering. The three-dimensional form of the 0 carbide is formed during the third stage of tempering. Jack suggested2 that the two-dimensional platelets of 0 carbide could be related to the faulted x iron carbide. Okada and Arata4 investigated a Swedish steel containing 1.05 wt pct C and approximately 1.0 wt pct Mn using permeability measurements at low field strength. A Curie point of 360°C was observed in the quenched steel, which indicated the presence of E iron carbide. On tempering at 400°C the specimen developed a Curie point at 230°C, indicating the presence of x iron carbide, and on tempering at 700°C the specimen developed a Curie point at 190°C which was assigned to 0 iron carbide. The carbides were extracted electro-lytically and the use of X-ray diffraction techniques4r5 indicated the carbide with a Curie point of 230°C to be x iron carbide. The Curie points of the carbides are 10 to 22°C lower than the accepted values which is probably due to the presence of manganese in the carbides, since it has often been observed (e.g., Ref, 6) that a partial substitution of manganese for iron in cementite will lower the Curie point of this carbide. Hofer' summarizes additional evidence of the tempering reactions in steel in which E iron carbide, formed during the first stage of tempering, transforms to x iron carbide during the second stage of tempering. During the third stage of tempering, the x carbide disappears as the 0 carbide is formed. By carburizing thin iron films in a CO gas stream, ~a~akura' has been able to produce the E, X, and 0 iron carbides. He found that below 250°C the E iron carbide was formed; between 250" and 350°C the x iron carbide was formed and above 350°C the 0 iron carbide was formed. He has shown that the E iron carbide transforms to form x iron carbide at 380" to 400°C and that the x ir°n carbide transforms to form the 0 iron carbide at approximately 550" C; both of these phase transformations are irreversible. Hofer' presents a review of evidence to show that the sequence of reactions occurring during tempering processes subsequent to the formation of E iron carbide formed by the direct carburization of finely divided a iron is the same as the sequence of reactions which occur during the tempering processes subsequent to the formation of E iron carbide in steel during the first stage of tempering. It is evident from Nagakura's work that identical tempering reactions are found in thin films of iron which have been carburized to form iron carbide. The purpose of this paper is to discuss the structural similarities between the E, X, and 0 carbides and to suggest a possible mechanism by which regions of the E carbide, formed during the first stage of tempering, may transform to the x carbide during the second stage of tempering. For the finely divided or thin film carbides a mechanism will be proposed for the transformation of the x carbide to the 0 carbide during the third stage of tempering, although it will be suggested that there is evidence that such a transformation may not occur in steels. STRUCTURAL DATA OF THE E, X, AND 0 IRON CARBIDES € Iron Carbide. It is evident from X-ray diffractions and electron diffraction', investigations that the metal atoms in the E iron carbide form an hcp structure with lattice constants ah = 2.752A, ch = 4.3534, using electron diffraction, reports the lattice paramet$rs of the superlattice cell to be a = 4.767A, c = 4.354, c/a = 0.9134. He finds that the carbon atoms occupy the octahedral voids in the metal atom structure so as to form a hexagonal stacking sequence with its basal plane parallel to that of the metal atoms. Considerable long-range disorder occurs in the positioning of the carbon atoms, however, which is in agreement with the possible range of composition Fe2C-Fe3C discussed by Hofer.' Barton and ale" have made X-ray diffraction measurements on a sample of E iron carbide extracted from a catalyst in an organic process. Although there were few reflections recorded on the obtained X-ray powder diffraction pattern, they have proposed that the structure could belong to one of the three possible space groups p3m1, P63/mmc, or Pbcn if one assumed the composition to be Fe2C. Nagakura, using electron diffraction data, suggests a space group of P 6322 for a specimen of c iron carbide of apparent composition Fez.&. x Iron Carbide. The x iron carbide has been studied by Duggin and Hofer" and by Jack and wild,' who

Jan 1, 1969

By E. F. Koch, J. L. Walter

In a study of the structure and properties of tungsten wire used for lamp filaments, it became desirable to perform transmission electron microscopy on the wire in the annealed as well as in the drawn condition. Wire used for lamp filaments is generally drawn to diameters less than 0.010 in. which is too fine for the preparation of transmission samples from single wires. Thus, it is clear that some assembly of wires must be used to form a "wire sheet" similar to that used by Glenn and Duff.' Also, because recrystallized tungsten wire is brittle at room temperature, the "wire sheetJ' must be rigidly contained during any subsequent grinding and polishing operation. With these conditions in mind, a technique was devised for thinning tungsten wire of 0.001 to 0.010 in. diam for transmission electron microscopv. Sample Preparation. The commercially doped (218) tungsten filament wire was obtained from the Lamp

Jan 1, 1969

By Paul M. Tyler

Mineral raw materials, because they are essential to our industrial prosperity and military strength, must be made available in substantial quantities regardless of cost. Variations in the cost of procuring minerals, as compared with the cost of obtaining other commodities, and changes in the cost of production of different minerals relative to one another, will naturally influence the quantities of a given mineral item that can be marketed readily. However, in the last analysis, the cost of winning minerals from the ground usually constitutes only a small fraction of the value of the end-use products and services derived from them. The miner's share of the cost of a typewriter, telephone circuit, or even a modem office building, is almost insignificant. Far more important to the ultimate consumer, therefore, than any minor saving in cost is the assurance of ample supplies of the minerals needed to aliment our expanding economy. To create a successful metal mining operation involves (1 ) the discovery and systematic development of a mineral deposit, (2) extraction of the ore, (3) the mechanical and metallurgical processing to eliminate worthless or harmful impurities, and (4) the profitable disposal of the product. The fist step of the technological process belongs chiefly in the realm of the geologist, the second is a mining engineer's job, the third is mainly up to the millmen and extractive metallurgists; whereas the fourth and equally important step poses a commercial problem that has aspects in common with the marketing of other products. Ore finding is far from being an exact science. There is no mathematical criterion for evaluating the efficiency of prospecting and exploration. Lady Luck shares the honors or assumes part of the blame along with the prospector and geologist. Marketing like- wise involves factors that seemingly defy engineering analysis. Although the other steps can be measured with some degree of mathematical accuracy, even they tend to vary so widely in basic principle, as well as in

Jan 1, 1964

By R. Hadfield

Last year this institute was good enough to accept some remarks by the writer regarding sound steel, entitle Plant for Hadfield Method of Producing Sound Steel Ingots…

Jan 1, 1915

By d&apos, K. Mukherjee, C. R. Antonio, R. J. Maciag, G. J. Fischer

Tensile data indicate that over the range of strain rates 10-5 to 10-1 sec-1 and in the temperature range 298° to 743°K the flow stress at a given temperature may be expressed as: C0 = Cem where m changes abruptly at a critical strain rate of 10-2 sec-1. The Zener-Hollomon parameter was tested and found to be invalid except at temperatures exceeding 700° K. Values of AH calculated for temperatures above 700°K ranged from 30 to 47.5 kcal per g-mole. ThE flow characteristics of aluminum and aluminum alloys as a function of temperature and strain rate have been of interest to various experimenters for many years. Trozera et al.1 determined tensile flow curves for pure aluminum and concluded that the combined effect of temperature and strain rate on the flow stress could be related using the Zener-Hollomon parameter. More recently, Hockett2 proposed a relationship between compressive flow stress, temperature, and true strain rate which could be represented by a surface. Holt et al.3 studied strain rate effects on flow stress in a number of aluminum alloys at room temperature. It was determined that there is a critical strain rate above which a strain rate effect is observed. It was also reported that the strain rate sensitivity was significant in aluminum alloys in the "0" condition only. In a recent review paper McQueen4 has considered a number of mathematical expressions which have been used to describe the relationship between stress, strain rate, and temperature. These expressions have been applied to the flow characteristics of a number of different metals and alloys including aluminum. In the present work the strain rate sensitivity of 7075-0 aluminum was determined in the temperature range of 298° to 743°K. The tensile flow stress at 0.2 pct offset was obtained over a nominal strain rate range of 10-5 to 10-1 sec-1. EXPERIMENTAL Threaded tensile specimens were cut from a single heat of 7075-T6 aluminum. The composition of this heat is given in Table I. The test bars had a gage section 1.5 in. long by 0.250 in. diam and conformed to ASTM specification E-8-57T. After machining, the bars were annealed at 413° ± 10°C for 2 hr. They were then cooled to 260°C in 3 hr, and finally air cooled to room temperature. This treatment is commonly used to produce the "0" condition. Load-time curves at constant crosshead speeds were obtained at various temperatures using an Instron testing machine. Crosshead speeds ranged from 0.002 to 40 in. per min. A three-zone resistance tube furnace was used for the elevated-temperature tests. Temperatures were measured at three points along the gage length by means of suitably placed thermocouples. Each tensile bar was held at temperature for 30 min prior to testing and the maximum temperature variation along the gage length was kept below 1°C. In all, 275 samples were tested and each data point plotted is an average of at least two tests. In many cases the point represents up to six tests. RESULTS AND DISCUSSION Values of the flow stress at 0.2 pct offset at six different temperatures are plotted vs strain rate on log-log coordinates in Fig. 1. Over discrete ranges of strain rate, the data for each temperature fit the expression:

Jan 1, 1969