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By Charles S. Barrett, Robert F. Mehl, Dana W. Smith

The Widmanstatten figures found in the steels have been long recognized and in some aspects carefully studied,' especially as they occur in cast hypoeutectoid alloys. Aside from the practical importance of the structures obtained in the steels by various heat treatments, a study of the characteristics of these figures is interesting because of the rich opportunity the system affords to obtain new data on the mechanism of segregation from solid solutions. This opportunity is twofold: first, by changing composition within the austenite range the proeutectoid precipitate may be changed from that of ferrite to that of cementite, thus offering the same opportunity for changing the type of precipitate while maintaining the same basic lattice as that afforded by the Cu-Zn alloys;2 and second, the eutectoid inversion leads upon drastic quenching to the formation of martensite, a Widman-statten figure of unique interest from the crystallographic viewpoint, particularly in comparison with those formed on slow cooling.3 We have, therefore, two types of structure to study: that formed on slow cooling of hypoeutectoid and hypereutectoid alloys, and that formed on quenching hypoeutectoid, eutectoid, and hypereutectoid alloys. For each of these types of structure we require the crystallographic plane in the mother austenite along which the precipitate forms (we shall see that the precipitates in these alloys are invariably platelike in form), and also the orientation of the precipitate upon this plane. Some of these

Jan 1, 1933

By David W. James, Howard Jones, George M. Leak

Conditions are described for producing, by primary recrystallization, a matrix suitable for the growth of large grains near (110)[001] orientation in silicon iron strip by secondary recrystallizaliun in a steep temperature gradient. The orientation distribution of these large grains is expressed in terms of rotational deviations about the cross-rolling direction, the rolling direction, and the normal to the sheet, the deviational spread increasing in that order. With the aid of cowplenientary published data on the orientation dependence of growth rate, it is shown that this observation is consistent with the oriented-growth theory of recrystallization lextures. It is conclutled that growth-rate and orientation-distribution data obtained in a steep thermal gradient should be used with caution to account for isothermally Produced recrystallization textures. SEVERAL authors have reported methods of growing large grains by re crystallization of a small-grained matrix in silicon iron 1- B and pure a cr The present study was a preliminary in the growth of single crystals and bicrystals for surface relaxation," grain boundary mobility, and grain boundary diffusion studies. The method was to control the growth of a seed crystal into a suitable primary re crystallized matrix by feeding through a steep temperature gradient. The driving energy for growth derived from the grain boundary energy released as the seed crystals grew into the matrix. Thus, stability of the matrix against normal grain growth was considered to be essential for success. It was known that the manganese sulfide dispersion present in commercial silicon iron performs this function during secondary recrystallization to the (110)[001.] texture.12 Hence commercial, rather than high-purity, material was used throughout. The paper describes the growth conditions for grains large enough to be used as seed crystals for further growth into single crystals. The orientation distribution of the seed crystals is analyzed and its significance for the theory of recrystallization textures is discussed. EXPERIMENTAL PROCEDURE Strip material was supplied by the Steel Co. of Wales, Ltd. The chemical analysis in weight percent was Si, 2.90; C, 0.015; Mn, 0.059; P, 0.011; S, 0.027; Ni, 0.032; 0, 0.009; Fe, balance. A gradient furnace of similar design to one described previously4 was loaned from B.I.S.R.A. It consisted essentially of a vertical water-cooled copper slot projecting downwards into the hot zone of a molybdenum furnace. Hydrogen was passed through the furnace to protect both heating element and specimen from oxidation. Strip specimens up to 8 cm wide and 0.2 cm thick were sealed into the furnace at the mouth of the copper slot. A coating of light oil on the strip surface maintained the seal during translation of a specimen. The maximum temperature gradient in the region just below the copper slot was 500°C per cm over 1 cm, with the hottest point controlled at 1175°C. Several large grains would usually grow by secondary recrystallization from the primary matrix when a specimen was immersed in the hot zone for about 30 min. A back-reflection X-ray camera was constructed to facilitate rapid and accurate orientation determinations of the large grains produced. It was possible to reproduce a standard geometry, with regard to strip and camera, without the tedium of careful alignment on each occasion. Specimens, typically 4 cm wide and 75 cm long, were cut with the longitudinal axis parallel to the rolling direction of the original strip. The surfaces were cleaned by immersion alternately in a hot aqueous solution containing 2 pct hydrofluoric acid plus 10 pct sulfuric acid and in cold 10 pct nitric acid. The nitric acid etch was just sufficient to reveal the grain structure. Rolling and annealing treatments to prepare the matrix (discussed below) were followed by growth of seed crystals in the gradient furnace. The matrix was transformed to a single crystal by growth of a selected seed crystal connected to the matrix by a thin neck. 4,5 Growth was promoted by controlled feeding into the gradient furnace. Several single crystals of controlled orientation were grown successfully from seed crystals by twisting the interconnecting neck in a reorien-tation jig.4 EXPERIMENTAL RESULTS AND DISCUSSION Growth Conditions. A suitable matrix for growth of large grains was prepared starting from primary re-crystallized strip 1.9 mm thick. This was cold-rolled in two stages each being followed by a recrystallization anneal at 800°C for a few minutes. Such treatment gave the required growth matrix only if the two cold-reduction stages were each performed in several passes and in the following ranges: the first, 30 to 70 pct; the second, 10 to 50 pct. Immersion in the temperature gradient otherwise resulted in an equiaxed

Jan 1, 1967

By L. W. Pommier, F. B. Brien, A. K. Bhasin

The diflerential movement of solid particles through solid-liquid suspensions is very important to many branches of engineering. The flow of suspensions around immersed bodies is mainly of a turbulent nature. Problems are encountered when attempts are made, as is the general practice, to extrapolate the velocity and resistance relationships of Newton, pertaining to Newtonian systems, into non-Newtonian solid-liquid suspensions. The conventional velocity and resistance relationships for turbulent flow in fluids when applied to suspensions, do not take into consideration the two very important variables: suspension particle size and solid volume fraction. A study of the effect of suspension particle size (dgb) on the velocity of falling balls leads to the concept of a critical particle size (dgc) at which the suspensions will be Newtonian. This leads to the classification of static suspensions into two types: suspensions consisting of particle of diameter dgh > dgt, and those with dgh, < dgr. Separate velocity and resistance equations for these two types of suspensions have been proposed, taking into account both the solid particle size and solid volume fraction. The agreement between the velocities predicted from the proposed equations and the measured velocities, confirms their validity. The resistance force offered by suspensions to the movement of immersed bodies has been calculated from the proposed equations, and the effects of suspension particle size and solid volume fraction on the resistance force and velocity have been examined. The movement of immersed bodies in solid-liquid suspensions is of great importance in many areas of engineering such as minerals processing, oil well drilling, suspension flow in pipelines, and hydrometallurgy. A number of mineral dressing processes deal essentially with the movement of solids in suspensions—in particular, classification, thickening, filtration, ore washing, and gravity concentration—thus a study of the fluid characteristics of suspensions is of theoretical and practical interest.&apos; A rigorous analysis of the mechanisms of momentum transport of a solid-liquid system is complex indeed. The rheological properties of the suspensions deviate from those of liquids, varying, for example, with density, solid volume fraction, size and shape of the solid phase of the suspension, and with the density and viscosity of the liquid phase. The flow of suspensions around immersed bodies is mainly of a turbulent nature and hence studies of the turbulent flow characteristics of suspensions are of par- ticular importance. Problems are encountered when attempts are made to extrapolate the velocity and resistance relationships of Newton, pertaining to Newtonian systems, into non-Newtonian solid-liquid suspensions. Due to the numerous variables present in a suspension, certain limitations and assumptions become necessary in order to produce quantitative relationships for predicting their effects. The solid particle size and the solid volume fraction are two of the more important variables. By comparing the measured and calculated Newtonian velocities of falling balls in simple static suspensions, the existing velocity and resistance relationships have been modified to take these variables into account. In order to keep the study less complex, all other variables such as the characteristics of suspending liquid and shape of the particle are maintained constant. Objective The objective of the present investigation is to modify the Newtonian velocity and resistance equations in order to take into account the suspension particle size and solid volume fraction. Theory Liquids are classified on the basis of viscosity, which may be defined as the relationship between applied shear stress and resulting rate of shear.&apos; pure single-phase fluids composed of small light molecules behave as Newtonian liquids, having a single viscosity pa-

Jan 1, 1971

By F. Weinberg

Measurements have been made of solute segregation during dendrilic growth by using radioactive solute elements and ,measuring the activity of den(12-ites cut from decanted specimens. This has been done for both lead awl tin based binary alloys contaitzing the following solute additions: Ag, T1204, was dependet on ko, the equilibrium distribution coefficient in the following way Fay k &apos;c 0.1, C/C 0.6; for k0 >0.1. 0.6 <c,/c,< I. Qualitative obse?-vations were madc of dendritic segregation, by using autoradiographic techniques, for the Sn + Ag110 and Sn + Tlo4 systems. The observation were found to he in general agreement with the measurements ofCA/Co. Autoradiographic were also obtained of scctiolccl delzr11-iie stalks. These indicated that the stalks had a substructure, dclileated by solute corzetlt?atio?zs nlolg the substructure walls. A new dendrite growth direction <JI2> is reported for tila. SOLUTE segregation in dilute binary alloys has been investigated by Pfann,&apos; Smith, Tiller, and Rut-ter,&apos; and others. They considered the case of a slowly advancing plane solid interface, and derived expressions for the distribution of solute in both solid and liquid during solidification. To determine these expressions, they assumed no diffusion in the solid and either complete mixing in the liquid:&apos; or diffusion controlled solute movements in the liquid without any convective mixing.&apos; The present investigation considers solute segregation during dendritic growth, in which case the solid-liquid interface is not plane, and the growth rates are rapid. Segregation under these growth conditions has not been treated mathematically, because of the relative complexity of the system. It has been suggested by Chalmer, on the basis of preliminary results, that an alternative to the diffusion and heat flow controlled conditions during growth is &apos;diffusionless" dendritic growth in which solid is formed with the same composition as the liquid. He suggests this type of growth may depend upon a solvent-solute relationship that permits some solid solubility without excessive increase in internal energy, as is the case for solutions of tin in lead. On the other hand, Montariol,4 and others, have shown experimentally that some segregation does occur during dendritic growth in metals using etching and radioactive tracer techniques to indicate the concentrations of the solute. The present investigation was undertaken to determine, both qualitatively and quantitatively, the extent of solute segregation associated with dendritic growth in a series of binary alloys, as a function of solute concentration. PROCEDURE The solvent materials used were Vulcan Electrolytic tin (99.997 pct purity) and Tadanac lead (99.998 pct purity). The solute materials were Zn, Sn, and Sb (better than 99.998 pct purity), Ag and Co (99.5 pct purity), and T1 (Fisher "purified" metal sticks). Activation of the solute metals was carried out in the reactor at Chalk River, Canada. Master alloys were prepared by induction heating from the radioactive solute metal and the pure solvent, under argon, in graphite crucibles. Pieces of these alloys were then added to the solvent to give the required solute concentration. Dendrites were grown in essentially the same manner as that described by Weinberg and Chalmer, , in which controlled orientation single crystals were grown dendritically in horizontal graphite boats, and the liquid decanted. The crystals were grown and decanted in an atmosphere of tank argon. Before decanting, a sample of the liquid was drawn up in a glass tube and allowed to solidify rapidly. The orientations of the single crystals were such that <loo> was parallel to the growth direction, and (100) in the horizontal plane for lead, and [1101 and (110) respectively for tin. With these orientations long dendrite stalks formed along the bottom of the boat in the dendrite direction (<100> for lead and [I101 for tin) from which secondary branches grew. Only these secondary branches, which grew freely in the liquid from the dendrite stalk to the liquid surface, were used in the measurements. Accordingly, effects due to substrates and oxides on the surface of the liquid need not be considered. In order to measure the solute concentration C, of the dendrites, individual dendrite stalks were cut from the decanted specimens, remelted, and formed

Jan 1, 1962

By M. J. Pool

The partial molar heats of solution in liquid tin of cadmium, silver, tellurium, and zinc have been measured at 655°. 700°, and 750°K by liquid-metal solution calorimetry. Silver, cadmium, and zinc are endothermic at these temperatures while tellurium is exothermic. Only the heat of solution of silver depends on composition while all four elements show a temperature-de pendent heat of solution. The heat of solution of tellurium is constant up to 0.6 g-at. pct, becomes increasingly more exothermic, and reaches a limiting value at 1 g-at. pct Te. The limiting value has been used to calculate the heat of formation of SnTe at 750°K. The heat effects associated with the dissolution of the compounds Ag2 Te, CdTe, and ZnTe in liquid tin were measured at 750°K. These values are cotnOined with the measured hat effects at 750°Kfor silver, cadmium, tellurium, and zinc to detertrline the heats of formation of the telluride compounds. Cadmium lelluride exhibits a heat of dissolution which has a compositional dependence. THERE is a considerable amount of interest in the compounds of tellurium because of their electronic properties. Both cadmium and zinc tellurides are thermoelectric materials and considerable work has been done on their electronic properties but a limited amount of data is available on their ther-modynamic properties. This work was undertaken to elucidate the heat of formation data on cadmium and zinc telluride. Since both cadmium and zinc are in Group II it seemed to be of interest to compare the values obtained for them with the heat of formation of a Group I telluride. Silver telluride was selected for this comparison. In the course of the work it was also possible to determine the heat of formation of tin telluride and therefore to make a comparison of some of the Group I, 11, and lV tellurides with the metallic elements silver, cadmium, and tin being in the same period. There is also a great deal of interest in the energetic changes which occur upon addition of solute elements to a common solvent. This investigation provided an opportunity to study the partial molar heats of solution of silver, cadmium, tellurium, and zinc in liquid tin. The partial molar heats of solution are of theoretical interest because solute-solute interactions are a minimum in dilute solutions and application of solution models is simpli- fied. In order to complete the analysis of solute-solute and solute-solvent interactions the temperature dependence of the partial molar heats of solution was also measured. MATERIALS AND EXPERIMENTAL PROCEDURE All materials were of the highest purity available. The silver, zinc, cadmium, and tellurium were obtained from American Smelting and Refining Co. and were reported to be 99.999 pct pure. The silver telluride, zinc telluride, and cadmium telluride were obtained from Atomergic Chemetals Co., a division of Gallard-Schlesinger Chemical Manufacturing Corp., and were electronic-grade material of 99.999 pct purity. Tin used for the solvent bath and for calibration was obtained from the Vulcan Manufacturing Co. and was reported as being 99.99 pct pure. The liquid-tin solution calorimeter used in this work is similar in principle to the differential twin-type calorimeter described by K1eppa.l Two of three identical calorimeter wells are used together during any set of experiments, one well being active and the other being passive. The wells are positioned 120 deg apart in an aluminum calorimeter block. Each well contains a multijunction thermopile and a Pyrex test tube to hold the liquid metal bath. Forty-eight of the thermopile junctions are distributed over the surface of each calorimeter well adjacent to the test tube and serve to integrate the heat effects occurring. The other forty-eight are next to the aluminum calorimeter block. The thermopiles for the three wells are connected differentially so that any change in temperature at the outer junctions (which will be the same for both wells because of the high conductivity of the aluminum block) will oppose for the two wells and result in no shift of the zero. The electrical output represents the true temperature difference between the two reaction vessels. A reaction occurring in the active well gives a comparison with another body of very similar thermal properties. In this way, any spurious heat effects due to slight temperature drifts within the entire calorimeter block are eliminated. The output of the differential thermopile goes to a dc amplifier with multiple ranges of from * 10 pv to 1 30 mv. The output of the amplifier is then fed into a Leeds and Northrup strip-chart recorder. The adiabatic temperature change is then calculated using the technique of Howlett, Leach, Ticknor, and ever.&apos; The aluminum calorimeter block is contained in a cylindrical furnace with main and control heaters

Jan 1, 1965

Alfred Stansfield, Montreal, Canada:—In Professor Howe&apos;s paper on the position of Ae3, he shows its industrial importance in determining the temperature to which steel should be heated for " grain refining." Several years ago I carried out a research on the " burning " of steel and found that while hypo-eutectoid steel should be heated to Ae3, hyper-eutectoid steel that has been very much overheated must be reheated to the curve Sa on the carbon-iron diagram, in order to redissolve the pro-eutectoid cementite and thus to obtain recrystallization and grain-refining. This treatment was necessarily only partly successful, and I should like to ask whether the conditions of heat treatment for refining overheated high-carbon steels have been ascertained. Speaking of the &&apos;Persistence of Solidificational Segregation " Professor Howe quotes an experiment made by Mr. Stead in which a bar of 1.2 per cent. carbon steel was immersed in a large mass of molten blast-furnace slag and allowed to cool with it. The steel was heated ; above the solidus (curve An on the carbon-iron diagram), but below the liquidus (curve AB). A drop of eutectic carbon-iron alloy, rich in carbon, had liquated out and hung below the bar. This agrees exactly with my own observations on the burning of steel, but my interpretation differs somewhat from that of Professor Howe. Professor Howe considers that the fusion of a part of the metal (rich in carbon) shows that the solidificational irregularities of composition had persisted through the rolling and heat treatment of the steel, as otherwise no part of the steel would have been sufficiently fusible to melt. It does not appear to me that such an explanation is necessary. A piece of steel represented in temperature and composition by any point within the area ABa will ultimately resolve itself into a solid phase and a liquid phase in equilibrium with each other. It may appear that if the steel were absolutely uniform no fusion could take place, but, the smallest nucleus of high-carbon, fusible alloy would ultimately bring about this separation into liquid and solid phases, by diffusion of the carbon from the solid to the liquid areas. A nucleus sufficient for the purpose might be provided by an area of pro-eutectoid cementite which had not become diffused during the

Jan 1, 1914

By John Birkinbine

(Wilkes-Barre Meeting, June, 1911). MODERN advances in practically all lines of industrial development have occurred in such rapid succession, and have been accepted so readily as accomplished facts, that a retrospect surprises us, by showing how comparatively few of the acknowledged factors of improved conditions may be considered as old. While these advances have not been confined to any country, they have been more pronounced in some than in others, and nowhere more so than in the United States, the population of which, having multiplied nearly three-fold between 1870 and 1910, demanded a proportionately greater increase in materials, supplies, and manufactured products. It therefore appears desirable to discuss mainly conditions in the United States, as concrete evidence of industrial progress throughout the world. Looking backward for but three generations, we may trace the introduction and development of canal- and steamboat-navigation; railroad-transportation; artificial illumination beyond that furnished by candles and lard-oil; quick communication by mail, and subsequently by telegraph or telephone; the manufacture of iron, beyond forms of small dimensions; the production and utilization of steel in large quantities; the economic use of mineral fuel, oil and gas, etc. The practical coincidence of the fortieth anniversary and the 100th technical meeting of the American Institute of Mining Engineers, offers temptation to recall and compare the conditions of mining and metallurgy in or about the years 1871 and 1911. A complete resume would cover phenomenal changes in mining-methods and equipment by which the output of individual exploitation has grown from scores to hundreds and even thousands of units in equal time-intervals. Extension of operations in depth and area, demanding machinery of great power

Aug 1, 1911

By M. Metzger, L. E. Hendrickson

Grain boundary attack in 16 pct HCl was found to be substantially the same at low penetrations in zone-refined aluminum (individual impurities 0.1 at. ppm), superior electrolytically refined aluminum (51 at. ppm), and aluminum with various impurities at much higher levels. It was concluded that impurity atom segregation affecting corrosion would have been detected and that the corrosion susceptibility did not originate in this segregation but in the structure of the boundary. It was pointed out that the significance of most previous studies in this system had been obscured by an unrecognized autocatalytic copper reaction. Although general corrosion rate was also impurity-insensitive , there was shallow pitting attributed to iron seg-regation and a hillocked surface texture associated with copper; these were interpreted as due to cathodic damage affecting- cathode distribution. THE grain boundary corrosion suffered by high-purity aluminum in hydrochloric acid has been the object of some interest (the earlier work is summarized in Ref. 1). The central metallurgical question here is whether the corrosion susceptibility of a boundary originates in its structure or in impurity atom segregation. An attempt to study this question revealed large catalytic effects associated with small quantities of the copper impurity in the aluminum, 220 ppm, or in the corrodent, and these magnified the preferential boundary attack and obscured the intrinsic susceptibility question.&apos; After the catalytic effects had been examined,"&apos; test conditions could be designed to avoid them and methods developed for studying the shallow boundary penetrations prevailing when they were absent.= It then became possible to determine whether intrinsic boundary corrosion in aluminum involves impurity segregation. The older work provided no firm information on grain boundary segregation of specific solutes influencing corrosion although several studies suggested iron segregates.4,5 perryman4 found in 10 pct HC1 that the slowly developing (microns per month) grain boundary grooves were deeper in material of higher iron content (range 10 to 550 ppm, with 5 to 80 pprn Cu) but he did not measure the depths of general corrosion, which were probably several times greater, and his reference surfaces may have varied more than did the groove depths. Metzger and Intrater&apos;s results for 20 pct HC~,&apos; which yielded higher time-average rates (mm per month) and deeper penetrations, suggested that boundary segregation of iron (range 4 to 230 ppm, with 22 pprn Cu) decreased the penetration rate. However. in the stronger acid the autocatalytic l.E. HENDRICKSON, Student Member AIME ,and M. METZGER, Member AIME, are Research Assistant and Professor of Physical Metallurgy, respectively, Department of Mining, Metallurgy and Petroleum Engineering, University of Illinois, Urbana, Ill. Manuscript submitted March 11, 1968. IMD effect of the copper impurity is greater1,2 and it is now evident that their corrosion rates had been much magnified by this effect and did not provide a proper basis for the analysis of segregation. In exploratory studies of other solutes (made under the same conditions), 1000 ppm additions of Mg, Mn, or Si or 100 ppm Ca were without effect.1 Montariol6 noted that boundary attack in 22 pct HC1 persisted after zone refining although with fewer deep fissures (ranges 0.06 to 4 ppm Cu, 4 to 23 ppm Fe). Autocatalytic effects may have influenced these results also and those of Perryman.4 The present objective was, as a first step, to see whether quantitative tests designed to exclude autocatalytic influences would indicate the existence of low-level impurity effects on intrinsic boundary corrosion. Comparison of electrolytically refined with zone-refined aluminum of lower copper and iron contents revealed no differences in boundary corrosion, but certain impurity-sensitive differences in general corrosion morphology were noted and investigated further at higher impurity levels. I) EXPERIMENTAL PROCEDURE A) Material. A selection from commercially available material was made with the cooperation of several producers. An electrolytically refined lot (III-A, 1 ppm Cu, 2.4 ppm Fe) studied previously3 provided a starting point. Since material of substantially higher copper content could not be used if the autocatalytic corrosion reaction were to be avoided,2,3 a lot (III-B) of about the same purity was added as a check, two zone-refined lots (I-A and I-B) with copper and iron an order of magnitude lower were selected for comparison, and an intermediate lot (11) was included. Analytical data are given in Table I. For copper in I-B and iron in I-A and I-B, the actual concentration is thought to be near the limit given, i.e., about 0.1 ppm. For titanium, vanadium, and chromium in III-B, the actual amounts are thought to be, like those in III-A, substantially lower than in the zone-refined lots (these elements concentrate in the solid on freezing). Data are given later for some additional lots surveved. B) Specimen Preparation and Procedure. one by 3 cm blanks with a notched stem were cut from 1-mm cold-rolled sheet, annealed 24 hr in air at 650°C, and quenched in an air stream (42°C per sec initial cooling rate, 100 sec to cool to 100°C). The high annealing temperature maximized diffusivities and approach to equilibrium impurity distributions. A water quench, in principle more efficient in preserving the distribution established, was undesirable because the boundaries were almost plane and they tended to shear and migrate during the quench and thus to be separated from any existing impurity atmosphere. Test procedures, previously described,3 involved electropolish-ing, etching 2 min in 10 pct HF at 24.0°C, and expos-

Jan 1, 1969

By P. J. Dean

This Paper contains a comprehensive survey of the known electron-hole radiative recombination mechanisms in the family of III-V compounds. Because of space limitations, the luminescence properties of each III- V compound are not reviewed separately and exhaustively. Instead, the different known types of recombination processes are discussed in turn and exemplified with reference to the III- V compound in which they were first recognized, or are best understood. Electron-hole recombinations usually occur predominantly at impurities or lattice defects either introduced de1iberately or inadvertently present, but radiative intrinsic interband electron-hole recombinations, which occur in perfect crystals, have been observed. Recombination processes which involve the participation of impurities or lattice defects ("extrinsic" recombinations) considered include transitions in which a) free carriers recombine with carriers trapped at impurities ("free to bound" transitions) , b) electrons bound at donor impurities recombine with holes trapped at acceptor impurities ("donor-acceptor pair" recombinations), C) excitons bound to charged or neutral donor or acceptor impurities recombine radiatively (both "resonance" and "two-electron" "bound exci-ton" transitions have been observed), d) excitons bound to neutral donor or acceptor impurities recombine non-radiatively (an example of an "Auger" recombination), and e) excitons bound to impurities with the same number of valence electrons as the host atom which they replace ("isoelectronic " traps) recombine radiatively. In addition, Auger recombination processes involving one or more free carriers have been observed. These extrinsic processes all involve impurities which are present as point defects. Some apparently well-authenticated examples of the recombination of excitons bound to complex impurity-lattice defect centers including nearest-neighbor donor-acceptor pairs are also discussed. Identificalions of the transitions involved in stimulated emission from the direct gap III-V compounds are briefly reviewed. Although the examples of these recombination mechanisms are selected from the III-IV compounds ia this review, these processes have quite general relevance in semiconducting crystalline solids; irrdeed most of them have also been identified in the 11- VI compounds and elernental semzconductors. THE development of crystal growth and purification techniques in recent years and concurrent advances in the understanding of physical processes in solids has accelerated the development of a wide variety of solid-state electronic devices of proven utility. These de- vices are generally used for switching or amplifying operations in electrical circuits. Most solid-state circuit elements are very photosensitive. This photo-sensitivity is generally undesirable and the single-crystal chip forming the active portion of the solid-state device is mounted in an opaque container. The photosensitivity is made use of in phototransis-tors and photodiodes, which are among the most sensitive detectors of electromagnetic radiation particularly in the near infrared.&apos; In these devices, light is converted into electrical power. The solid-state lamp utilizes the inverse effect, namely the conversion of electrical power into light. There is an increasing tendency to use single-crystal diodes rather than the earlier electroluminescent cells in which the active material is present as a powder embedded in a suitable dielectric.&apos; The radiation is emitted at a rate far in excess of the thermal equilibrium rate for the frequencies and temperatures involved; i.e., luminescence occurs. The development of practically efficient solid-state lamps is at an early stage compared with solid- state circuit elements or even photodetectors. Considerable progress has been made in recent years, however.3 The present review is devoted to a survey of the radiative recombination processes in the semiconducting compound crystalline solids formed from elements in groups I11 and V in the periodic table. These materials exhibit the full range of known recombination processes in solids. In fact many of these processes were discovered in 111-V semiconductors. Nonradiative recombination processes, which control the lutninescence efficiency, are also discussed. Luminescence is efficiently excited in semiconductors through processes which produce large excess concentrations of free electrons and holes in the energy bands of the crystal. Transitions induced by lattice defects or impurities usually predominate in the recombination process. By contrast, luminescence in the conventional fluorescent lamp is excited by optical absorption at the luminescent impurity center itself (the activator) and/or at a second type of impurity center (the sensitizer). This latter type of photoluminescence process, occurring in doped ionic crystals with wide band gaps, is outside the scope of this review.4 I) ENERGY BAND DESCRIPTION OF ELECTRON STATES IN CRYSTALS The energy band description of the energy states available to an electron in a crystal forms the basis of our understanding of the empirical division of crystalline solids into metals, semiconductors, and insulators in accordance with their electrical and optical properties.&apos; Nonmetallic crystals have a finite energy gap between the highest energy band which is

Jan 1, 1969

By L. L. McDaniel

Copper smelters of various kinds have operated in the Morenci district since 1872, but all have been abandoned with the exception of the present Morenci Smelter of Phelps Dodge Corporation, which was completed in 1942. During the five-year period starting in 1937, the Morenci ore body was prepared for open pit mining, pilot mill test work was carried out, and a complete reduction works, of which the Smelter is a part, was designed and erected. Actual construction work on the Morenci Smelter was started in the fall of 1940, and warming up of the units began on April 1, 1942. Charging of the reverberatory furnaces commenced on April 18, 1942, and the first anode copper was produced on April 26, 1942. The smelter was originally designed to handle the production of the Morenci Concentrator on a 25,000 ton per day program, but by the time the smelter was in operation, plans were already underway to increase the smelter capacity to handle the production of the concentrator which was being enlarged to 45,000 tons a day capacity as a war-time necessity. This extension to the smelter was completed and the new units were put in operation toward the beginning of 1944. The original smelter consisted of a smelter crushing plant, bedding plant, two direct-smelting reverberatory furnaces with two waste-heat boilers on each furnace, three converters, an anode department, a stack, and all of the usual accessory smelting equipment. The extension consisted of increasing the bedding plant from three to five beds, the reverberatory department from two to four furnaces, and from four to eight waste-heat boilers, and the converter department from three to six converters. A third converter aisle crane was added and additions were made to the flue systems and conveyor systems throughout the smelter; but no change was made in the smelter crushing plant or the anode department, and the same stack was used for all additional Smelter units. A blister casting machine was installed at that time in the south end of the converter aisle to handle excess and emergency production above the capacity of the anode department and in 1947 a converter aisle skull breaker and a lime burning plant were added as the final units for a complete plant. The choice of direct smelting over calcine smelting for the Morenci Smelter was made after careful study by members of the Western organization of Phelps Dodge Corporation and after test runs on direct smelting of Morenci concentrate had been made at the Douglas Smelter of Phelps Dodge Corporation. The Morenci furnace charge is made up of comparatively high grade concentrate with no ores of smelting grade available and with only flux, a small amount of copper precipitate and the usual amount of smelter secondaries to be smelted with the concentrate. The simplicity of direct smelting for this charge and the large amount of waste-heat steam available from direct smelting operations were factors influencing the decision to adopt direct smelting for Morenci. The design of the Morenci Smelter and the type of units selected followed best experience at the Douglas Smelter of Phelps Dodge Corporation. A description of the original smelter before operations started was given in an article in the May 1942 issue of Mining and Metallurgy. The purpose of the present article is to describe the enlarged Morenci Smelter, with a discussion of metallurgy and operating practice and to show tabulations of operating and metallurgical results obtained. Because of beginning operations during the early years of World War 11, many problems caused by labor shortage were encountered, but no major difficulties developed in starting the new plant. However, because of labor shortage, full scale Smelter production was not reached until the fall of 1946. Fig 1 shows a general plan of the Morenci Reduction Works. The arrangement of the smelter equipment is shown in Fig 2, a sectional view of the smelter is shown in Fig 3, and the smelter flow sheet is shown in Fig 4. Metallurgy The metallurgy of direct smelting, being more or less fixed by the character of the charge, is not subject to the control available in calcine smelting. Slags may be modified by the addition of suitable fluxes, but the grade of the matte is determined almost entirely by the iron:copper ratio of the concentrate. The direct smelting operation involves distributing the wet concentrate along the sidewalls and in the bath of a reverberatory furnace by means of some suitable feeding device and raising the temperature of the charge so that first the moisture is driven off, then the first-atom sulphur is eliminated, and finally the sulphide portion of the charge melts and runs into the bath, carrying with it the non-sulphide portion which has been partially fluxed to form a suitable slag. The fusion of the non-sulphide portion is completed by contact with the irony converter slag which is regularly being poured into the reverberatory furnace. The smelting rate of the charge is influenced by the mineralogi-cal composition of the sulphide portion of the concentrate and by the composition and amount of the non-sulphide portion including the fluxes added. The copper in Morenci concentrate is chiefly in the form of chalcocite, intimately associated with pyrite, and non-sulphide content is very low so that

Jan 1, 1950

By J. Waldman, M. B. Bever, A. K. Jena

The heats of formation at 273°K of 6 silver-rich Ag-Cd solid solutions and the heat of formation at 78°K of one solid solution have been measured by tin solution calorimetry. The heats of formation are analyzed in terms of the quasichemical theory. If the enthalpy diffel-ence between a hypothetical fcc form and the hcp form of cadmium is taken into account, this analysis does not lead to the conclusion put forth in the literature that electronic effects make significant contributions to the heats of formation of silver-rich Ag-Cd solid solutions. The temperature dependence of the heats of formation is appreciable and negative near 78ºK, but decreases gradually to nearly zero abore 400°K. The relative partial enthalpies per grarn -atom of silver at 541°K and cadmium at 532" and 541°K in tin have also been determined. THE composition range of the silver-rich Ag-Cd solid solutions stable at room temperature extends to about 40 at. pct Cd. Heats of formation of these solid solutions at 308" and 723°K have been measured by solution calorimetry.1,2 Heats of formation for an average temperature of 800°K have also been calculated from vapor pressures.2,3 The heats of formation deviate from the values predicted by the quasichemical theory above about 30 at. pct Cd. This deviation has been attributed to electronic effects at the Brillouin zone boundaries.2 The heats of formation of Ag-Cd alloys are essentially the same at 308", 723", and 800°K; consequently the temperature dependence of the heat of formation d?H/dT = ?Cp is vanishingly small, although from the exothermic heats of formation a negative value would have been expected. In the investigation reported here the heats of formation at 273°K of 6 silver-rich Ag-Cd solid solutions and the heat of formation at 78°K of 1 solid solution have been measured by tin solution calorimetry. The results are analyzed in terms of the quasichemical theory and the dependence of the heats of formation on temperature is discussed. The relative partial enthalpies per gram-atom of silver in tin at 541" and cadmium in tin at 532" and 541°K were obtained in the course of this investigation. The values of the temperature dependence of the relative partial enthalpies per gram-atom of silver in tin derived from the data reported by various investigators2,4-9 are contradictory. The literature contains only a value for 517°K of the relative partial enthalpy per gram-atom of solid cadmium in tin.2 EXPERIMENTAL PROCEDURES Samples of Ag-Cd solid solutions were prepared by melting weighed amounts of silver (99.99 pct pure) and cadmium (99.95 pct pure) in graphite crucibles under a flux of molten potassium chloride.10 The solidified ingots were sealed in evacuated Vycor tubes and annealed at 775°K for 10 days. The ingots were swaged and drawn into wires. The wires, sealed in evacuated Pyrex tubes, were held at 725°K for 5 hr and cooled to 365°K at an average rate of 2.5ºK per hr, followed by furnace cooling to room temperature. Chemical analysis of samples taken from different parts of each ingot gave no indication of segregation. Metallographic examination showed the samples to be homogeneous. Samples of the solid solutions or of the component elements were added to tin-rich baths in a calorimeter." At the start of a run the bath consisted of pure tin. Silver was used in the form of wire of 0.01-in. diam as supplied and cadmium in the form of lumps. Gold (99.999 pct pure) was added with the samples in order to reduce the endothermic heat effect of additions of Ag-Cd solid solutions. Samples of only one composition were added in a run and the ratio of the weight of alloy to that of gold was the same in all additions of a given run. In each run several calibrating additions of tin were made from 273°K. The heat contents of tin were calculated from the following equation, which is based on published data:12 (HTºK- H279º) = 6.70 T - 72,300/T + 20 cal/gram-atom; 505°K < T < 650°K The heat effect of each addition was plotted against the average of the sum of the atom fractions of solutes in the solution before and after that addition. The total concentration of solutes at the end of a run was less than 2 at. pct. In this range the heat effect was a linear function of the atom fraction of the solutes. The heat effect at infinite dilution and the composition dependence of the heat effect were obtained from the plots. RESULTS AND DISCUSSION Evaluation of Data. The linear dependence on composition of the heat effects of additions suggests that in the dilute range the enthalpy interaction coefficients other than the first-order coefficients of silver, cadmium, and gold are negligible, as shown in a concurrent publication.13 The heat effects at infinite dilution and the values of the composition dependence of the heat effects are listed in Table I.

Jan 1, 1970

By Guy N. Bjorge, A. J. M. Ross, S. J. Staple, J. D. Johnson, J. F. Wiggert

In recent years the Homestake mine has been served by three shafts, the B. &. M., the B. & M. No. 2 and the Ellison, supplemented by an inside shaft, the Milliken, extending from the 2000-ft. level to the 3200-ft. level. In 1932, when a new operating shaft was under consideration, the bottom of the mine was at the 3200-ft. level. The B. & M. and the B. & M. No. 2 shafts were down to the 1550-ft. level and the Ellison was being deepened from the 2600 to the 3200-ft. level. All ore was hoisted at the B. & M. and Ellison shafts. Levels below the 2600 level, which were under development only, were served by the Milliken shaft. Below the 1550-ft. level, the mine was served only by the Ellison shaft from the surface. Within a few years, when ore reserves above the 1550-ft. level would be depleted, operation would be limited to the Ellison shaft and the auxiliary underground shaft. The Ellison shaft alone was not adequate for hoisting the entire output from the deeper levels and also handling all men and supplies. Furthermore, assurance of safety and uninterrupted operation required two fully equipped shafts to the deeper levels. Therefore a new operating shaft was authorized in November, 1932, and was named for A. J. M. Ross, the mine superintendent. Plans for New Shaft The B. & M. shaft, begun in 1878 before much was known of the form and extent of the orebodies, was too near the ore and was endangered by ground movement. In 1924 this shaft was seriously threatened and sinking of the B. & M. No. 2 shaft, to supplant it, was begun. The latter was completed to the 1550-ft. level in 1928. In the meantime ground movement at the B. & M. shaft had practically stopped and, though loss of the shaft constantly threatened, ore hoisting was con-

Jan 1, 1937

By J. B. DILWORTA

Ix estimating the investment-value of a mining-property or plant, the value of which decreases with operation, it is often necessary to know the sum which must be set aside periodically from earnings either to renew the plant at the end off its life, or to return the capital involved when the earning-power of the investment has ceased. In such cases it is manifestly incorrect simply to divide the total amount to be retired by the number of periods (usually years) during which the investment shall be active, as the sums periodically withdrawn have a certain interest-earning power varying with the length of time they are held and with the opportunities afforded for their investment. But though the interest may be considered to accumulate regularly year by year, yet the rules and tables for compound interest do not apply, owing to the addition of a fixed amount of new money to the total at the beginning of each period. Briefly stated, the problem of sinking-funds is, to find the amount of money which must be periodically set aside at a certain rate of interest, regularly compounded, to yield a certain sum in a given, length of time. In most practical cases the interest is compounded and the fresh amount added at the same time-usually once a year-and on this basis the problem may be solved as follows

Nov 1, 1909

By Harold V. Pearce

(Chattanooga Meeting, October, 1908.) THE fire which occurred in the fall of 1906, at the works of the Boston & Colorado Smelting Co., Argo, Colo., destroyed entirely the gold- and silver-refinery of the plant; and in view of the development of modern practice in the refining of copper-mattes, etc., the management decided that it would be inadvisable to rebuild that part of the works for the continued use of the process which had been conducted therein for so many years as a metallurgical secret. This decision probably removes altogether from the sphere of practice the " Pearce " method for the separation of gold. At all events, it removes the business reasons which have prevented hitherto the publication of the principles involved. At the suggestion of Dr. Raymond, Secretary of the Institute, my father, Richard Pearce, the former manager of these works, has requested me to prepare a brief description of this process for the benefit of our members. Since I severed my connection with the Boston & Colorado Smelting Co. some time ago, I am indebted for some practical details to the present superintendent, Charles Rees, whose friendly assistance I would gratefully acknowledge. With regard to the history of the inception and development of this process by its inventor, Richard Pearce, I cannot do better than quote freely from his own notes and papers. HISTORY OF THE PEARCE PROCESS.&apos; "In 1874 my entire time was directed to the improvements and additions to the plant at Black Hawk. The changes which I had made in the construction of the furnaces at Black Hawk proved so beneficial that I was requested to introduce the improvements at the branch works at Alma. These changes were carried out as speedily as possible, and proved of great advantage as compared with the old system. "The separation and refining of the gold from the matte now engaged my attention, and since previous experience in the treatment of gold-bearing matte and

Feb 1, 1909

By R. A. Kinzie

In a conventional cement plant, the drying and heating of the raw material takes place in the upper section of a cylindrical kiln where the heat exchange is poor. In a Lepol kiln this part of the process is carried out on a traveling grate where the heat exchange is efficient. The increase in fuel economy justifies the greater complexity of the installation.

Jan 1, 1950

By Don Rose

In the USA the cost of steel ribs for tunnels approximates $100 million each year. European practice has long since abandoned heavy steel ribs for tunnel support, and tunnel coats in Europe (normalized for wages) are about half the costs incurred in the USA. A feeling has existed for some time that the USA practices of supporting tunnels with heavy steel ribs have been overly conservative. The USA practice is based on rock load coefficients by Karl Terzaghi. In 1946, Karl Terzaghi published a tunnel rock classification system (Terzaghi, 1946), with the rock loads on tunnels predicted for each class of rock. No data on real rock loads were presented by Terzaghi and his rock load coefficients may have been largely intuitive. His classification system and associated predicted rock loads have been widely used in the USA. Each rock class, taken from Terzaghi&apos;s classification system, is assumed to generate loads of loosened rock resting as dead load. The dimensions of the loosened rock are described by rock load coefficients multiplied by the tunnel diameter. The resulting rock loads are used by design engineers, contractors and agencies to size supporting steel ribs. Terzaghi clearly stated that he had conservatively assumed high rock loads for his classes 4, 5 and 6 to take a presumed effect of groundwater into account. If the tunnel was not affected by ground- water, Terzaghi stated those rock loads should be reduced by 50 percent. Twenty two years later Tor Brekke (1968) wrote a paper clearly showing that based on observation of more than 250 tunnels groundwater does not affect tunnel rock loads. In 1969, Deere, et al., published measurements made on a number of tunnels, and a well-known curve was drawn by Deere to illustrate Terzaghios coefficients graphically. Deere&apos;s text stated that Terzaghi&apos;s predicted rock loads were too high and should be reduced. Cording and Deere (1972) more recently published data indicating that very large real rock caverns and chambers were being successfully built using rock bolts, which can take only a very limited rock load, thus indicating that real rock load is much smaller than Terzaghi or even Deere predicted.

Jan 1, 1982

By M. C. LAKE

THE industrial development of the United States has been stimulated by the presence of high-grade iron ore in the Lake Superior district. These great deposits have been susceptible to economical extraction and are conveniently located for cheap lake vessel transportation to the great consuming centers. The district furnishes from 80 to 85 per cent of the iron ore annually consumed in the United States, and a full understanding of the available supply of this great commodity is so important that it is well to consider whether or not the industrial supremacy and national independence attained as a result of the abundance of cheap ore are permanent. The enormous deposits of high-grade ore available in the Lake Superior district have been the foundation upon which the vast industrial structure of the steel and allied industries has been built. It is extremely important to the country as a whole, and especially to those States and communities now dependent on Lake Superior ore for their prosperity, that their industries shall retain the particular advantages with which they are now endowed, and that a generous supply of high-grade raw material be available for their consumption at a satisfactory cost. The steel industry is so basic and fundamental that any fluctuation in the cost of its finished products as determined by the supply and cost of the raw materials involved in its manufacture will necessarily affect the business of a wide variety of industries which are dependent on it.

Jan 1, 1926

By R. J. Woody

DESIGN of the most economic continuous counter-current decantation (CCD) circuit is based on selection of the number of stages and the wash volume that will give the minimum summation of the following items: 1) Capital and operating costs of the CCD circuit. 2) Capital and operating costs of the precipitation circuit. 3) Value of the dissolved product lost.

Jan 7, 1958

By B., Hoyaux

A first requirement for assessing the safety of a rock slope, either artificial or natural, particularly if the rock behaves in an elastic-brittle manner, is a proper knowledge of the distribution of stresses within the slope and their development with time and advancement of workings.

Jan 1, 1972

By Mark R. Lamb

THE treatment of slime is of special interest to those engaged in cyaniding gold- and silver-ores. The usual practice is to make as small a percentage of slime as possible. In many instances the slime is given no treatment, but is impounded in dams in the hope that the future will develop some method of economically treating this product. The filter-press was the first step upward from ordinary decantation, but, on account of heavy labor-charge and high cost, its use has been limited to high-grade material. The slime at the Combination mill at Goldfield averages perhaps $20 per ton, and although the values are quickly dissolved the filter-press installation was not entirely satisfactory, resulting in the erection of the canvas-cell filter, developed by Chas. Butters and his staff. This filter is a great improvement over the filter-press, and the following description of it will be of interest to those engaged in treating slime produced in crushing ores, especially in view of the fact that, by the use of this filter, slime can be treated at a lesser cost and with a higher percentage of gold- or silver-extraction than in the ordinary treatment of sand; and, moreover, the initial outlay for an all-sliming plant is less than that for the ordinary sand- and slime-plant. The economy of construction of the Butters filter-plant is clearly shown in Figs. 1 and 2, which illustrate the 20-frame filter of 40 tons capacity, now being installed by the Nevada Goldfield Reduction Co. In this construction the slime-pump is so connected that it can pump to or from either tank or the filter by changing the valve-settings-a combination which is necessary in this particular installation, since sufficient fall is not available for filling and discharging the filter by gravity. Ordinarily, a slime-plant comprises: a filter-box with frames

Jan 1, 1907