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By David S. Butts

There are many solution mining operations that use solar ponds as a mineral recovery step. Other locations in the world are now under investigation to recover minerals by solution mining but require the cheap energy of solar ponds to make the recovery viable. This paper shows a step-by-step material balance system that can be used in both simple and complex solar ponds. Use of this system will help the engineer determine if solar ponding efficiency can be improved or if solar ponding will work at all with a given set of conditions. Even the most complicated solar pond can be reduced to six flow streams. These are (1) feed, (2) exit, (3) leakage, (4) entrainment, (5) salts, and (6) evaporation. The equations developed in this paper will allow the solar pond engineer to easily evaluate the effect of each of the flow streams on the mineral production of a pond or pond complex.

Jan 1, 1985

By D. F. Toner, P. E. Gage, D. J. Mack

MUCH work has been done on the decomposition of the p phase at the eutectoid composition, 11.9 pct Al, in the Cu-A1 system by Smith and Lind-lief,' Mack,' Klier and Grymko,3 Haynes,4 and others. In all of the mechanisms proposed by these workers for the decomposition of the ß phase, it was stated that the a phase must precipitate rich in aluminum with respect to the equilibrium composition of 9.4 pct A1 at 565°C. To check this hypothesis, it was necessary to have a master curve relating equilibrium aluminum content of a to lattice parameters of a. A number '' binary Cu-Al alloys of increasing amounts of aluminum were prepared by Ampco Metal Inc. These alloys, received as-cast, were given a 30 pct reduction of area by hot-working and then annealed at 900°C for homogenization and slowly cooled in the

Jan 1, 1956

The Second Pan-American Scientific Congress will be held under the auspices of the United States Government in Washington, D. C., Dec. 27, 1915, to Jan. 8, 1916. The organization officers are John Barrett, LL. D., Director General of the Pan-American Union, Secretary General; Glen Levin Swiggett, Ph. D., Assistant Secretary General; the headquarters of the Congress are the Pan-American Union, Washington, D. C. The program of the Congress is divided into nine main Sections, which are given below with the name of the Chairman of each Section: 1. Anthropology, William H. Holmes, B. S., Smithsonian Institution, Washington. 2. Astronomy, Meteorology, and Seismology, Robert S. Woodward, Ph. D., Carnegie Institution, Washington, D. C. 3. Conservation of National Resources, Agriculture, Irrigation and Forestry, George M. Rommel, B. S., Bureau of Animal Industry, Department of Agriculture, Washington, D. C. 4. Education, P. P. Claxton, LL. D., Bureau of Education, Washington, D. C.

Jan 12, 1915

By Thomas D. Henderson, Donald E. Crowell

INTRODUCTION This paper presents a "case history" of the steps taken to estimate capital and operating costs for a typical porphyry copper concentrator of ±9,070 metric tons (10,000 short tons) per day capacity. The concentrator described herein is hypothetical, but is based on experience and is, in effect, a composite of several actual projects. The numbers used are illustrative only and do not represent actual costs at any particular concentrator. These numbers are, however, representative of typical milling costs at one point in time, and. are sufficiently accurate to illustrate the cost estimating procedures described in this paper. It is not possible to publish actual, current milling costs and, in any event, actual cost figures quickly become meaningless in today's economic situation with various costs all rising at different rates. The paper is divided into three parts: (1) order-of-magnitude estimate, (2) feasibility study estimate, and (3) discussion of differences between estimated and actual costs.

Jan 1, 1978

By George W. Lower, Robert B. Booth

The use of cyanides in the extraction of gold and silver is well known1 Such extractions employ concentrations of cyanide in the range of 0.02-0.25% sodium cyanide equivalent in leaching cycles of 24-48 hr and frequently longer. Copper minerals, even though minor components of precious metal ores, dissolve in these cyanide leaching solutions, consume cyanide, cause fouling of mill solutions, and thus interfere with the precipitation and recovery of gold.2,3,4 This paper presents a summary of laboratory investigations on the use of cyanide solutions as extractants for copper from various copper-bearing ore fractions. In view of the metal contents involved, it will be apparent that larger quantities of cyanide are required to extract copper than for the extraction of precious metals. In cyanide solutions of concentrations generally favorable to copper extraction, sulfide and oxide copper minerals were found to dissolve rapidly at room temperature and atmospheric pressure.

Jan 11, 1965

By Charles Catlett

(San Francisco Meeting, October, 1911.) WHILE the occurrence of phosphorus in coking-coal has assumed less importance with the development of the open-hearth method of steel-making, it may not be without interest to note the form in which phosphorus exists in one particular coal-seam. In the examination of what is known as the Big seam, which outcrops a few miles west of Columbiana, Ala., my attention was called to the distribution through the coal, in the form of minute veins and particles, of a resinous-looking substance. A small amount of this was selected, and was provisionally identified as evansite (Al6, P2 014. 18 Aq). Subsequently, through the courtesy of Dr. Sharshall Grasty of the Geological Department of the University of Virginia, I was able to secure an additional amount of material, which was purified down to about 0.3 g. This was examined by Prof. John J. Porter of the University of Cincinnati, and gave the following partial analysis

Nov 1, 1911

The Motor Truck Sections of the 20th Annual Automobile Shows of 1920, to be held in the 8th Coast Artillery Armory, New York, Jan. 3 to 10, 1920, and in the International Amphitheatre, Chicago, Jan. 24 to 31, 1920, will he the largest and most comprehensive exhibitions of the kind ever held. Approximately 125,000 sq. ft. of exhibition space has been alloted at each place and upward of seventy makes of motor trucks, together with trailers, pacts and accessories will be dis-played. In conjunction with these expositions, Highway Transport Conferences will be held, with sessions each afternoon and evening. Every important phase of highway transportation will be discussed by men recognized as qualified authorities. Various talks will he il-lustrated by motion pictures and stereoptican slides. Members of the Institute may apply for complimentary tickets to-S. A. Miles, Manager, 7 East 42d Street, New York City.

Jan 12, 1919

The Bureau of Mines extends. a cordial invitation to all members of the Institute to visit Pittsburgh, Sept. 29 to Oct. 1, to participate in the dedication of the Mines Experiment Station. Accompanying this will be a nation-wide participation in a First-aid and Mine Rescue Contest. The Pittsburgh Chamber of Commerce will cooperate. The Institute will be represented by a special delegate appointed by the President. MONDAY 8:30. A. M. Bureau Building open for inspection. 10:30 A. M. Dedicatory Ceremonies in rear of Main Building, .4800 Forbes St. 2:00 P. M.. Special Train and Automobiles to Experimental Mine near Bruceton, Pa. 3 to 6 P. M. Mine Explosion and Inspection of Experimental Mine . and of Explosives Testing Plant near Bruceton, Pa. 6:00. P. M. Return by Special Train and Automobiles to B. & 0. Station, Pittsburgh. 8:00 P. M. Informal Reception and Organ Recital Carnegie Music Hall. Arranged by Carnegie Institute of Technology.

Jan 9, 1919

By F. R. Van Horn

WALLACE MCKEEHAN, Douglas, Ariz. (communication to the Secretary*).-In going over this report, which I have done very carefully, I find that the summary as composed deals with the various problems almost entirely from the employer's standpoint and that practically no consideration is given to the employee's point of view. An experience of 3 ½ years as safety inspector, and almost 30 years as workman-and official, has convinced me that any plan for the betterment of working conditions which will achieve any degree of success must give the workmen their share of responsibility and allow them full participation. The company may finance and direct the movement, but its ultimate success depends upon the support given by the workmen. The cooperation of the men doing the actual work is so essential that all writers insist that this must be secured, but they do not agree as to how this can best be done.

Jan 4, 1917

By Harold F. Yde

Hydraulic tailing fill in the Butte deep-level mines resulted from studies made in 1958 by The Anaconda Co. Mining Research Department. At the time of the study, dry mine tailing was hauled via rail cars from the Anaconda tailing ponds, 25 miles distant, to the tailing fill plants of the underground mines at the Leonard, Anselmo and Mt. Con mines. Presently, tailing from the Weed concentrator in Butte is delivered to the Kelley shaft via pipeline and stope filling has become automated. Tailing at 30% solids is pumped 8000 ft horizontally and upward from the concentrator to the Kelley fill plant, where it is dewatered and deslimed by three Krebs cyclones. These discharge the material into the cased and grouted mine delivery boreholes at desired densities of up to 70% solids. The vertical boreholes and 4-in. rubber-lined Victaulic pipe carry the material downward to horizontal distribution lines, which in turn tap into the 3-in. stope-filling, unlined Victaulic pipelines.

Jan 1, 1970

Plans for the fall meeting of the AIME, to be held in conjunction with the Centennial of Engineering -marking the 100th anniversary of the Society of Civil Engineers-indicate that the Chicago gathering will be one of the most significant in Institute history. Headquarters for the six divisions represented will be the Palmer House. Twenty technical sessions will be held from September 3 to 6, with papers of industry-wide impact to be presented. The papers will follow the theme of the celebration-a century of engineering progress. The MBD will start the ball rolling with morning and afternoon sessions Thursday, September 4. A luncheon also will be held. MBD has scheduled morning and afternoon sessions for the following day as well. MGGD, Iron and Steel, and the Coal Div., will hold sessions Friday afternoon. The Industrial Minerals Div. plans an executive meeting, 5 pm, Friday. Geology Subdivision is slated for morning and afternoon sessions Saturday. The Coal Div. will meet again Saturday morning.

Jan 1, 1952

By R. S. Handy

The No. 2 unit of the West Mill of the Bunker Hill & Sullivan Mining & Concentrating Co., which went into commission Apr. 17, 1912, is structurally a twin of the No. 1 unit, which was started Nov. 9, 1909. Up to the point where the ore enters the concentrating-de-partment, it follows precisely the process described by G. Cae-tani in his article entitled, Milling of Lead-Silver Ores,' under the heading, Preparation of the Mill-Ore. The process from this point forward, in the No. 2 section, is outlined on the accompanying flow-sheet. In describing it I shall attempt to analyze the products of each separate process. The constancy of the tonnage and the uniformity of the quality of the feed render this practicable. No. 1.—550 tons of feed, all having passed 30 mm., is washed into two 15-mm. trommels, 4 ft, in diameter, 60 in. long, 17 rev. per min., 1 in. slope, 3/8-in. gauge steel.

Jan 1, 1913

By Frederick Prime

AT the last meeting of the Institute, Mr. A. L. Holley read a paper on "Steel," in which he proposes for it a definition so opposed to the one generally received, as to call for some remarks. Until within the last five or six years there has been no dispute on the subject, and it seems worth while to investigate the matter. For not only does a proper tax on all importations depend on a proper appreciation of the term steel, but it is necessary to know whether steel, or wrought-iron, or homogeneous iron are requisite in all processes of manufacture in which malleable iron is employed, on account of cost, strength, etc. Karsteu* says : " Iron may be obtained, either as an unforgeable, unweldable metal, which melts at a high heat, termed cast-iron; or as a ductile, weldable, soft metal, which can only be melted at the * Karsten, Handbuch der Eisenhüttenkunde, 3d ed., vol. i, p. 6. Berlin, 1841.

Jan 1, 1876

By O. D. Gonzalez

Existing measurements for the steady-state permeation of hydrogen in a iron above 100°C have been examined for contribution of determinate errors. The analysis leads to a recommended equation for the permeability of hydrogen in a iron: o= (2.9 ±0.5) x 10-3 exp - (8400 ± 400)/RT cu cm (ntp H2) cm-1 sec-1 atm-1/2 THE permeability of a iron to hydrogen has been the subject of numerous investigations over the past 40 years, and at present there are thirteen sets of published results for the rate of steady-state permeation of hydrogen in a iron above 100°C. The numerical values in each set of results are entirely self-consis-tent, but the spread among the sets is too large to be attributed solely to experimental error, i.e., to error other than in the specimen itself. Several reasons have been advanced to explain the disparities, but to date the relative importance of experimental inaccuracy to the spread remains uncertain. The purpose of this report is to examine in detail the sources of determinate errors inherent in the experiments and to assess as far as possible the contribution of the errors to the results. The ultimate goal is the selection of values for the permeability and heat of permeation most nearly representative of hydrogen in a iron. The analysis is limited to those experiments in which the permeation rate was observed at steady state—a condition in which traps for hydrogen within the metal are filled to a fixed level15 so that the trapping mechanism is not reflected in the rate of passage of the gas. Furthermore only data are examined in which surface processes are judged to have little or no influence on the flow. It is hoped with these restrictions to obtain values of the permeability and the heat of permeation which will be as closely related as possible to the mechanism of lattice diffusion. I) DEFINITION OF TERMS; UNITS In this report the data for permeation are given in terms of a coefficient oj permeability, ?, which is defined by the equation: jt=?A/?x{p1/2-po1/2) [1] where jt is the total flow of gas normal to the surface of a membrane of planar geometry, e.g., a disc, of area A and thickness ?x; pi and po are the pressures in the input and output sides, respectively. For flow radial to the walls of a membrane of cylindrical geometry, e.g., a tube, the corresponding equation is: where 1 is the length of the cylinder, and ri and ro are the inner and outer radii, respectively. The flux normal to the surface is given by Fick's law: j= -D(dc/dx) [3] At steady state the concentration gradient will be constant, and integration of Eq. [3] gives for the total flow through a disc of area A and thickness Ax: h =-DA(co - ci) [4] where c, and ci are the concentrations of solute at the output and input surfaces, respectively. When surface control is absent, co and ci are given by Sievert's law c = Kp1/2, and substitution therewith into Eq. [4] gives directly Eq. [I] where ? = DK. Integration of Fick's Eq. [3] in cylindrical coordinates will give Eq. [2] where again ? = DK and is thus shown to be independent of geometry (provided that surface control is negligible). The coefficient of permeability, or simply the permeability,* must be expressed in proper units. In *The term permeability will refer in this report always to the coefficient defined above; permeation will be used to specify the general phenomenon of gas passage through a membrane. this report ? will be expressed in the units of cu cm (ntp H2) cm-1 sec-1 atm-1/2. The variations of D and K with temperature are given by D = Do exp(-Ea/RT) and K = KO exp(-?Hs/RT) where E, is the activation energy for diffusion and AH, the heat of solution, each usually expressed in calories per mole of solute. The variation of permeability with temperature will thus be given (for conditions where surface control is negligible) by ? = ?o exp(-?Hp/RT) where ?0 = DoKo and ?Hp = Ea + ?Hs. The units of ?0 are the same as those of 6, and??Hp will be expressed in calories per mole H. 11) SUMMARY OF PERMEABILITY RESULTS Table I gives the values reported to date for the permeability of H2 in a iron in terms of ?o and ?Hp. Except where noted the parameters listed were taken directly from the numbers reported by the various investigators with only a change in units. The temperature limits within which the listed ?o and ?Hp hold are given in column 7; the limits marked in parentheses in this column indicate the entire temperature range covered in each investigation. The listed values of ?o and ?Hp are those giving a linear plot of ln? against T-1 at the higher temperatures in each set of measurements, and thus presumably represent the case for which surface control was negligible. Column 6 gives values of 9 at a representative tem-

Jan 1, 1970

By N. L. Svensson

The model developed by Tuylor for the calculation of Polycrystalline yield strength has been applied to the case of an aggregate hawing a preferred orientation. In general this procedure requires the specification of texture by means of weighting factors applied to specific orientations. The problem to which the model has been applied is that of the yield-strength aniso-tropy of cold-rolled aluminum whose rolling texture was described as a combination of (110)[112] and (311) [112] In this case yield-strength anisotropy is defined by the rutio of yield strength measured at an angle 8 to the rolling direction to that measured along the rolling direction. The method of calculation of yield-strength ratio as a function of ? is described and the results show good agreement with experimental values. The orthotropic yield criterion suggested by Hill has been applied to the results and the strain ratio R also calculated as a function of ?. This has been compared with calculations using the method suggested by Elias, Heyer, and Smith which does not exhibit suck good agreement with observation. one deficietlcy of the method presented is that the strain ratios used by are those applying to iso-Irobic materials. The method should therefore be reg-clrded only as a first abbroximation to the prediction of anisotropy. THE problem of calculating the stress-strain characteristics of polycrystalline aggregates from the properties of single crystals has attracted attention for a number of years. The most important contributions to this study have been those due to: Sachs,' Cox and sopwith,2 Taylor,3 Kochendorfer,4 Batdorf and Budiansky,5 Calnan and Clews,6 Bishop and Hill,7,8 Kocks,9 Budiansky, Hashin, and sanders, 10 Kroner,11 Cyzak, Bow, and payne, 12 Budiansky and Wu,13 and Lin.14 While the earlier work has been largely superseded, recent developments tend to support Taylor's solution" within the restriction imposed by his assumptions. The essential features of Taylor's approach were: 1) the material is rigid-plastic; 2) each grain experiences the same strain components as the aggregate as a whole (the problem was that of uniaxial deformation with principal strain components in the ratio 3) all regions of each grain deform uniformly; 4) work hardening occurs equally on all slip systems. While Bishop and Hill7 have generally validated this approach, there has been some criticism offered. Kocks? as pointed out that since multiple slip must occur the single-crystal data must be determined from orientations arranged such that polyslip takes place. Boas and Hargreaves,15 and others, have shown experimentally that the strain distribution within grains is not uniform, the strains in the vicinity of grain boundaries being less than those in the center of the grains. Both of these criticisms can be largely offset by the suitable choice of single-crystal critical shear stress. However, for the problem analyzed below, the critical shear stress is not directly used and, consequently, these criticisms lose their importance. The more recent contributions have attempted to obtain a more complete analysis by considering an elas-toplastic material and considering interactions between grains of differing orientations. Lin14 has considered the early stages of yielding for a polycrystalline aggregate having specific regions of defined slip plane orientations. On the other hand, Budiansky and Wu13 have allowed for these interactions for randomly disposed grain orientations and have calculated the polycrystalline stress-strain curves for crystals exhibiting either elastic-ideally plastic or kinematic hardening characteristics. This work has shown that yielding commences when the macroscopic stress is 2.2 times the critical shear stress for slip in a single crystal (7,). The yield stress-strain curve then rises becoming asymptotic to a value of 3.072 7,. This is close to the value obtained by Bishop and Hill (3.06) in their confirmation of Taylor's method. This, of course, is to be expected since, at large strain values, the elastic strains are negligible and the rigid-plastic model is satisfactory. The results of Budiansky and Wu indicate that the result obtained by Taylor is 7.7 pct high at a plastic strain which is two times the elastic strain at the initiation of yield. By defining the anisotropy in terms of relative values, the ratio of yield strength at orientation ?, to that measured in the rolling direction, the effect of the discrepancy in Taylor's solution is considered to be of lesser consequence. Therefore, it is anticipated that an analysis based on Taylor's solution, which can be quite straightforward, should provide a reasonable estimation of the anisotropy of materials having a preferred orientation texture. OUTLINE OF TAYLOR'S METHOD In fee metals there are four possible slip planes (the octahedral planes) and in each there are three possible slip directions (the edges of the octahedron), that is a total of twelve possible slip systems. von Mises16 has shown that at least five independent slip systems must become operative in each grain of the polycrystalline aggregate in order to preserve continuity of strain. With this geometrical requirement as basis and the assumptions previously listed, Taylor determined the operative slip systems for a number of orientations of the tensile stress axis specified in the unit stereographic triangle. For the ith slip system, the critical shear stress

Jan 1, 1967

By T. K. Redden

Protective coatings based on the formation of a surface coating of nickel aluminide (NiAl) were applied to the nickel-base superalloys IN 100, SEL 15, and U-700. Coated specimens were exposed to an oxidizing environment at temperatures between 1600 and 2200 F for times up to 1000 hr. The oxidation resistance and stability of the coating were evaluated by weight gain measurements, metallographic examination, and X-ray diffraction study of surface oxides and coating. The composition of the coating and diffusion zone was determined by electron microprobe traverse of samples before and after high-temperature exposure. Intermediate phases formed in the coating and diffusion zone were identified by X-ray diffraction in situ and after electrolytic extraction. The outer coating was found to consist of the inter-metallic compound, NiAl, while the diffusion zone contained MC, M23C6 or M6C carbides, and a phase in a matrix of NiAl + Nidl. Oxidation resulted in formation of an A1203 n'ch scale containing some Tz02. Depletion of aluminum during oxidation resulted in degradation of the outer coating to Ni3Al and the nickel alloy matrix. Diffusion of aluminum into the base metal was found to be slight and did not influence coating life significantly. The o formed in the diffusion zone during coating decomposed during elevated-temperature exposure to form stable carbide phases characteristic of the base metal. Diffusion zone phase changes were found to have no effect on the life of the aluminide coating in the oxidizing envzron?nent. THE oxidation resistance of many high-strength nickel-base superalloys is inadequate for extended exposure at temperatures above about 1600°F. In addition, some applications for these materials require that they be exposed to environments containing sulfur compounds and sodium salts which can cause surface attalk known as sulfidation or hot corrosion. In order to provide the necessary corrosion resistance to the high-strength alloys, protective coatings based on an aluminizing process have been developed. These processes, usually based on a pack cementation technique, result in the formation of a NiAl-rich outer coating layer either during the coating process or by a subsequent diffusion treatment. The performance of the aluminide coatings is affected by interactions between the coating layer and the base metal both during the coating process and during subsequent exposure at elevated temperatures. Knowledge of these interactions is required to guide the development of coatings capable of longer life and improved reliability. Goward et al.' recently reported the metallurgical factors which influence coating per- formance on MAR-M200. The present work is concerned with correlating the interactions and performance of coating compositions on several representative materials. EXPERIMENTAL PROCEDURES Materials. Three cast nickel-base superalloys which are used for turbine buckets in air-breathing engines were studied: IN 100, U-700, and SEL 15. Their chemical compositions are given in Table I. The alloys were vacuum-induction-melted and cast to slabs approximately 0.3 in. thick from which rectangular specimens 0.25 by 0.5 by 1 in. were machined. Coating Procedures. The machined specimens were coated by CODEP processes which were developed at the author's laboratory. These are based on pack cementation in various media to deposit either aluminum or aluminum in combination with titanium. The coating process which deposits only aluminum is designated CODEP-C, while the CODEP-D process deposits titanium in combination with aluminum. The CODEP-D process was applied only to IN 100. Both CODEP processes are applied at 1950" or 2000°F for 4 hr without need for a subsequent diffusion treatment. An outer coating about 1 mil in thickness is produced by these processes. Test Procedures. Coated specimens were exposed to static oxidation for periods ranging from 24 to 1000 hr at temperatures of 1600" to 2200°F. Terminal weight gain measurements and visual examination were used to evaluate oxidation resistance. including oxide spalling and coating failure. Both as-coated and exposed specimens of each alloy were studied by metallographic examination, electron microprobe analysis (EMA), and X-ray diffraction analysis either of the exposed surfaces or of phases extracted from the coating and diffusion zone. RESULTS As-Coated Condition. The microstructures of as-coated conditions were generally similar, irrespective of base materials or the particular coating process. They are typified by IN 100 coated by CODEP-D as shown in Fig. 1. The predominately single-phase outer layer, area A, Fig. 1, was identified by X-ray diffraction as the intermetallic compound NiA1. The NiAl zone extended inward to the original base metal interface. The diffusion zone, area B, Fig. 1, included carbide phases, a lamellar phase oriented perpendicular to the base metal surface, and a matrix phase consisting of a mixture of NiAl and Ni3Al. The phases in the diffusion zone were electrolytically extracted using a 10 pct HCl in methanol solution at approximately 1.3 amp per sq cm. The extracted phases were found to be M6C, MC, or M=C6 carbides and o as shown in Table I1 for each of the alloys. The d spacings from a typical diffraction pattern are

Jan 1, 1969

By W. E. Quist, R. Taggart, D. H. Polonis, C. J. van der Wekken

An intermediate compound that has been identified as Niab is observed to form as a decomposition product from supersaturaled Ni-Nb solid solutions during aging at temperatures between approximately 300" and 500°C. On the basis of data from electron microscopy and selected-area diffraction, the structure of this compound has been determined as fct with a = b - 3a0 and c = a, wlzere a,, is the lattice parameter of the parent solid solution. The compound consists of close-packed layers with triangular ordering, where the niobiutrl atoms are separated by two nickel atoms ([long- close?-packed directions. A nine layer stacking sequence is required to describe the proposed structure. STUDIES of the Ni-Nb binary system have been limited primarily to phase diagram determinations,'-4 investigations of high-temperature equilibrium phases,5"1 and the determination of the influence of deformation on the structure of the equilibrium compound.8 The nickel-rich portion of the binary system is reported to be of the simple eutectic type in which the maximum solubility of 12.7 at. pct Nb occurs at 1282"c.' The two-phase field below the eutectic temperature is bounded by the a fcc solid solution and an orthorhombic Ni3Nb compound. No metastable phases have been reported in previous investigations. In transformation studies of certain nickel-base commercial alloys that contain niobium, two ordered metastable compounds containing niobium have been shown to precipitate from the solid solution, both of which have been identified as y' and have the composition NisNb or Ni,Nb. One compound has been reported to have the bct DOz2 type Al3Ti structure" and the other the cubic LI2 type Cu3Au structure.9,11 In the present work on Ni-Nb binary alloys a metastable y' compound has not been detected after conventional quenching and aging treatments. An anomalous behavior was noted in electrical resistivity measurements. in alloys containing between 7 to 12 at. pct Nb when aging treatments were performed below 500°C after fast quenching from 1250°C. Transmission electron microscopy has shown that this behavior is caused by the formation of a low-temperature precipitate of unreported structure type and composition. EXPERIMENTAL METHODS Several Ni-Nb alloys, containing up to 11.5 at. pct Nb. were prepared by either levitation melting and casting in copper molds or by induction melting in alumina crucibles; both techniques employed purified helium gas as a protective atmosphere. The purity of the nickel and niobium used to make the alloys was 99.98 wt pct Ni and 99.9 wt pct Nb. The composition and homogeneity of the alloys were checked by weight measurements and by electron microprobe analysis. The induction-melted alloys were homogenized for 100 hr at 1100°C. The resistivity specimens were prepared from rods swaged to 2.5 mm and the electron microscopy specimens were cut from sheet that was rolled to 0.4 mm and thinned using a modified Bollmann technique." The elevated-temperature solution treatments were carried out in a purified helium atmosphere followed by direct quenching into a 10 pct NaCl solution at 23°C. Additional protection against oxidation of the samples during solution treatment was accomplished by using tantalum foil as a "getter" in the furnace. The specimens were aged at various temperatures in salt baths controlled to +2oC. A Leeds and Northrup K5 potentiometer was used to make electrical resistivity measurements on specimens immersed in liquid nitrogen. Electron microscopy and diffraction studies were carried out with JEM-7 and Philips EM-200 microscopes operating at 100 kv. RESULTS AND DISCUSSION Ni-Nb alloys containing between 7 and 11.5 at. pct Nb that have been solution-treated in the range 1220" to 1280°C and quenched to 23°C undergo a precipitation reaction when aged in the temperature range 300" to 500°C. Precipitation was detected by selected-area electron diffraction after aging a specimen for as little as 30 sec at 350°C) whereas the reaction was well-advanced after aging for 150 hr at 475°C. Electrical resistivity measurements were used to monitor the progress of the precipitation reaction. In the present experiments the nucleation process for precipitation required a high solution temperature and a rapid quench into brine. The presence of aluminum, iron? and carbon in amounts totaling less than 1 wt pct was found by electron diffraction to completely suppress the formation of the low-temperature precipitate that has been detected in the binary alloy. Electron diffraction techniques were used to determine the structure of the precipitates that formed during the decomposition of the Ni-Nb supersaturated solid solutions. Figs. l(a) through l(d) show electron diffraction patterns oriented to the [loo], [110], [lll], and [I031 zone axes of the matrix. Areas of reciprocal space between these sections were investigated by slowly varying the orientations of the crystal under study; this procedure revealed no reflections other than those depicted in Fig. 1. The presence of super-lattice reflections at points coincident with the matrix reflections was confirmed by the examination of an almost completely transformed structure. On the basis of the accumulated diffraction data, the reciprocal lat-

Jan 1, 1970

By W. W. Anderson, S. Razi

Electroluminescetrce of single crystals of terbium-(loped ZnS prepared by vapor-transport technique shows the sharp line specirum characteristic of the 4f— 4ft,ansitiotzs of the trivalent Tb3 rotz. V-I tt~easuverr~ents give evidence of space-ellarge-lirrlited curvent but the thrveshold for trap-filled law behavior is not iu agreement with Lampert&apos;s theory for. Single injection. Variations of &apos;brightness with applied voltage, the observation of double peaks its brightness because joms, and the spatial distribution oi electroLur?zir~escerrce indicate that the accelet~atiotz-collision mechanism involving the bst lattice and/ov shallow traps is most likely to be responsible fov excitation of&apos; electrolnminescence. Efficiency rtreusuver)~etits show the quantwn efficiency to be about 10 pct and powev efficiency about 0.05 pct. Effect of anr~eallng the crystal in sulfur vapor is to enluztzce llle rare-earth emission. It rs pvoposed tlzat sulfitv anr~ealing crreates acceptorr-lvpe defects with which the donor-type vare-eavtll ion can associate more readily vesulting in enhanced rare-earth emission. A&apos;o such e~zlznr~cerr~etrt is obserued when the crystal is atztrealetl in zinc vapor. Photolianinescence of ZnS doped nith a variety of rare earths also shows tile slurvp l~rze rwve-eavtlz erriission which in sorrretirr~es accompanied by broad band, stvuctureless lattice emission. Photo-atrd electrolutr~itzesce?~ce of ZIIS:Tb slw~rj do!rlit~unt rare-earth emission in the ~ticirzity of 54(3OA corre-sporrdit~g to the transition D* — Fj. Hoz~!el)er, the detailed line structuve of the luo spectvtr is cliffevet~t, irzdicutit~g that different sites are active in the two processes. Decay of rave-eartlr fluorescence in ZnS doped with any of sei!evul vuve eurtlzs car1 be described by a single exporleritial e.scepl joy ZrlS:lIo. Tl~is exceptiotr can be explaitred it~ tevrr~s of tlre closely spaced er~evgy 1e1:els Jov the HO~&apos; iorr. Decay lime measurertzekzts jov ZnS:Tb, using pulsed elect,-ical ar~d pulsed opticcll excitutiorzs, (11-e itz goor1 agrcetrier~t. LUMINESCENCE of rare-earth-doped materials has been a subject of interest for the past 20 years. Within the past few years there has been a considerable increase in rare-earth research motivated in search of new and more efficient laser materials and also due to the use of certain-rare-earth compounds in the preparation of color television screens. The purpose of this study has been to seek an understanding of some of the basic processes involved in exciting the rare-earth luminescence which is associated with transitions within the 4f shell of the trivalent rare-earth ion. Single crystals of ZnS doped with a variety of rare-earth ions have been prepared by vapor-transport technique described elsewhere.&apos; Photoluminescence was excited by a high-pressure short-arc mercury lamp together with suitable glass and chemical filters. For electroluminescence, sinusoidal and pulse excitations were used. 1) ELECTRICAL CHARACTERISTICS 1.1) V-I Measurements. Electroluminescence experiments were performed on crystals of terbium-doped ZnS. The samples were cleaned and etched and indium or In-Ga alloy contacts were alloyed on by heating in H2 atmosphere to 600°C for times ranging up to 10 min. Static voltage-current measurements were made on several samples. Fig. 1 shows the results for a typical sample. For voltage V < 20 v, the V-I relationship is linear giving a resistivity of 2.5 x 109 ohm-cm for this particular sample at room temperature. In the range of 20 to 250 v, I varies as V "3 and at still higher voltages (when electroluminescence is visible to the scotopic eye) current varies as Vs up to 600 v, all at room temperature. At 77"K, for V > 200 v, / I vge5 up to 1000 v. The V-I characteristics at room temperature follow reasonably well the behavior predicted by Lampert&apos; for one carrier space-charge-limited current in an insulator with traps although, as shown later, the expression derived by Lampert2 for the threshold for trap-filled law behavior Vtfl yields an unrealistically low value for trap density if we use the experimental value of 300 v for VtfL. Assuming the case for shallow trapping, the transition from Ohm&apos;s law behavior to space-charge-limited behavior occurs at voltage Vtr given by where no = thermally generated free carrier density, L = length of the sample, e = static dielectric constant, 6 = ratio of free to trapped electron densities, e = electron charge. For the ZnS:Tb crystal, L = 0.5 mm, E = 8.3 €0, Vtr - 20 v, and no = 5 x 10&apos; per cu cm, calculated from the ohmic behavior assuming electron mobility of 100 sq cm per v-sec. This results in 9 = 0= As more and more electrons are injected the Fermi level moves up in the forbidden gap toward the conduction band. If we assume a single-energy level for traps (which is not strictly correct, as we will show later), the current voltage characteristic is profoundly affected when the Fermi level crosses the trap level. The traps are now filled and injected carriers can no longer be immobilized in traps. Hence, current rises sharply with voltage. The transition from space-charge-limited behavior to the trap-filled behavior occurs at voltage VTFL given by

Jan 1, 1968

By B. W. Christ, P. M. Giles

Mossbauer effect measurewents have been made on I-mil-thick foils of commercial 1 wt pct C steel and Fe-2 wt pct C alloy. The experimental method required about 3 to 5 vol pct of a phase in the nzultiphase steel sample for detection. Room-temperature Md&apos;ssbauer patterns obtained on austenitized atid quenched samples exhibit fifteen, and possibly twenty-one, lines. A sharp parama&tetic singlet and a quadrupole doublet, poorly resolued from the singlet, are attributed to austenite. Remaining lines are due to tnartensite. Accurate evaluation of austenite line paranzeters is not feasible if significant amounts of other phases such as carbides or martensite occur simultaneously with austenite. This is demonstrated by comparison of hyperfine interactions determined for austenite in multiphase high-carbon samples with those reported for Fe-C austenite in a nearly 100 pct austenitic sanple. Lines from carbides are incompletely resolced from austenite lines, as demonstrated by comparison of austenite line positions with carbide line positions calculated frow published values of hyperfine interactions. One martensite line overlaps an austenite line in the pattern for commercial 1 wt pct C steel. Results of this study suggest that the usefulness of e M6ssbauer pectroscopy for quantitatizle analysis of austenite in bulk samples of quenched and tempered high-carbon steels is restricted by poor resolution. Use of Mossbauer spectroscopy for phase identification and for evaluation of atomic and electronic structures appears quite feasible, however, The Mijssbauer effect has been widely discssed,&apos;-and e Mossbauer effect measurements have been reported on materials of metallurgical interest.7"20 In particular, it has been proposed that e Mossbauer patterns of commercial steels and laboratory-made Fe-C alloys, in the quenched condition, are composed of lines originating in two phases, Fe-C austenite and Fe-C martenite.-&apos; Evidence accumulated in this study demonstrates that three absorption lines found in the central region of the e Mossbauer pattern obtained on quenched steels are attributable to retained austenite. This interpretation is supported by parallel decreases in the intensity of these three lines caused by subambient cooling of commercial 1 wt pct C steel samples after water quenching to room temperature. A second result of this study is to clarify effects of line resolution and sensitivity in the Mossbauer patterns of multiphase steels on the accu- rate determination of austenite line parameters. Experimental line widths (full width at half height) are generally 1.5 to 3 times larger than the natural line width of 0.19 mm per sec. At least two lines, and sometimes more, from a single phase such as cementite (Fe3C), other carbides, martensite, and austenite fall in the energy band, i0.85 mm per sec. hhis band width is employed simply for convenient reference. It represents approximately the energy interval between the + 112 to 112 transitions in ferrite and is expressed as the velocity needed to Doppler shift a 14.4kev 7 ray to the aforementioned ferrite energy levels. This energy band is referred to as "the central region of the Mossbauer atttern:: in this paper. Hence, due to the large number of lines from different phases in a multiphase steel falling in a relatively narrow energy band, absorption lines from the different phases may overlap. Analysis of available data, presented below, indicates that this occurs to a significant extent for phases which commonly occur in quenched and quenched and tempered high-carbon steels. One consequence of limited resolution in the Mdssbauer patterns from multiphase steels is difficulty in accurate determination of such line parameters as position, width, and intensity. In fact, it appears that quantitative analysis for retained austenite in quenched and tempered high-carbon steels is not practical with the present experimental method. Line resolution is influenced to some extent by sensitivity. We point out below that atom or volume fractions of less than about 3 to 5 pct are not detected by the present experimental method. Thus, the presence of a multiplicity of phases does not always lead to impaired resolution. Finally, we report in this paper room-temperature MGssbauer parameters determined for austenite in a freshly quenched, commercial 1 wt pct C steel and in a freshly quenched laboratory heat of an Fe-2 wt pct C alloy. These parameters are compared with others reported in the literature. Three types of hyperfine interactions are detectable in a Mossbauer effect measurement: isomer shift, quadrupole interaction, and magnetic dipole interaction. These interactions are evidenced by one, two, and six line patterns, respectively.&apos;-4 More than one type of interaction has been reported in certain metallurgical phases thus far studied by this method. Isomer shift is the experimentally measured displacement of line position from some arbitrarily defined reference position. In the case of a multiline pattern, isomer shift is given by the displacement of the centroid (center of gravity) of that pattern from the reference position. All isomer shifts measured at finite temperatures contain a second-order Doppler effect characteristic of that temperature. The isomer shift is related to the total s electron density at the nucleus, becoming more negative with increasing s electron density. The first-order quadrupole effect arises from the interaction between the nuclear quadrupole moment and any axially symmetric electric field gradient in

Jan 1, 1969

By G. R. Speich

The interlarnmelm spacing, growth rate, and degree of segregation that accompany cellular precipitation in four Fe-Zn alloys containing 9.7, 15.2, 23.5, and 30.5 at. pct Zn have been determined in the temperature range 400" to 600°C. The chemical free-energy change for the reaction was calculated from the available thermodynamic data and the known compositions of the phases. The fraction of the chemical free-energy change for equilibrium segregation that is converted into interfacial free energy decreases from 0.43 to 0.08 as the magnitude of this free-energy change increases from 35 to 270 cal per mole. At constant temperature the cellular growth rate is proportional to the cube of the dissipated free energy. At 600°C newly 100 pct of the equilibrium segregation is achieved during cellulm precipitation whereas at 400°C only 85 pct of the equilibrium segregation is attained. During cellular growth, mass transport of zinc occurs by grain boundary diffusion; excess zinc remaining in the a! phase after the completion of growth is removed slowly by volume diffusion. A modified Cahn theory of cellular precipitation predicts the observed interlamellar spacing within a factor of two. In cellular precipitation reactions such as pearlite formation or discontinuous precipitation, the basic problem is to predict the variation of growth rate G, interlamellar spacing S, and degree of segregation P with composition and temperature. To accomplish this we need three independent equations relating these quantities. One of these equations comes from the diffusion solution. To obtain two additional independent equations, some assumptions must be made. cahnl has suggested recently that two plausible assumptions are 1) that growth rate is proportional to the dissipated free energy and 2) that the spacing which occurs is that which maximizes the dissipated free energy. According to the first assumption, this spacing also maximizes the growth rate and the rate of decrease of free energy per unit area of cell boundary. The present work was undertaken to test these assumptions. To test the first assumption it is necessary to study a cellular reaction over a wide range of supersatura-tions to establish a relationship between G and the dissipated free energy at constant temperature. This is possible only in discontinuous precipitation reactions since in pearlite reactions constituents other than pearlite form if the composition of the parent phase deviates even slightly from the eutectoid composition. The Fe-Zn system was chosen for study because 1) discontinuous precipitation proceeds to completion over a wide temperature and concentration range, 2) the degree of segregation within the cell can be measured by lattice parameter measurements,2 and 3) the thermodynamics of this system have recently been determined by Wriedt.3 In this system the cells consisting d alternate lamellae of a and r phases form from supercooled iron-rich a phase. The a phase within the cells is bcc as is the original a phase, cia, but has a different orientation and a slightly lower zinc content than the original a phase. The r phase has a zinc content of about 70 at. pct and a crystal structure isomor-phous with T brass. EXPERIMENTAL PROCEDURE Four Fe-Zn alloys with 9.7, 15.2, 23.5, and 30.5 at. pct Zn were prepared from carbonyl-iron powder (400 mesh, 99.8 wt pct Fe) and zinc powder (200 mesh, 99.99 wt pct Zn). The powders were ball-milled together and cold-pressed under 60,000 psi to discs $ in. thick by $ in. diam. The cold-pressed discs of the alloys with 9.7 and 15.2 at. pct Zn were sealed in evacuated silica capsules and heated slowly to 1100°C over a period of 1 week (3 days at 600°C, then 3 days at 80O°C, then 1 day at 1100°C). The alloys with 23.5 and 30.5 at. pct Zn were treated similarly except that the final homogenization temperatures were 1000" and 85O°C, respectively, to prevent melting. The alloys were quenched in iced brine from the final homogenization temperature. Specimens of each alloy were subsequently aged in salt pots at temperatures of 400°, 450°, 500°, 550°, 600°, and 650°C for times that varied from a few minutes to several hundred hours. At a late stage of this work, an alloy containing 11.2 at. pct Zn was prepared by vapor-impregnation of iron foil with zinc vapor at 890°C. This alloy proved useful for electron microscope studies because it was free of porosity. The homogenization and aging conditions were based on the recent Fe-Zn phase diagram of Stadelmaier and Bridgers4 rather than the earlier diagram of ansen.5 They consist of a homogenization heat treatment in the homogeneous a field followed by an aging treatment in the two-phase a + r field. The aged specimens were metallographically polished and etched in 2 pct nital and the radius of the largest cell in the microstructure determined. This radius plotted vs time gave a straight line whose slope is the boundary migration rate or growth rate G of the cell. To determine the interlamellar spacing, specimens were examined by surface-replica and thin-section electron microscope techniques. Because of the irregular nature of the lamellae within the cell, the average interlamellar spacing S .of the cell was measured by the method of Cahn and Hagel,6 where S is defined by:

Jan 1, 1969