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By W. F. Carew, F. A. Crossley

The stress for rupture in 500 hr at 1000° F has been reported to be about 13,000 psi higher for Widmanstitten than for equiaxed microstructures for the Ti-7A1-3Mo alloy.1,2 Also, limited data indicated Widmanstatten and equiaxed micro-structures to have approximately the same creep resistance at 1000°F.' Recently, data have been obtained which show Widmanstatten structures to be significantly more creep resistant than equiaxed structures at 1000°F, see Fig. 1. These data represent several ingots and several heat treatments of the solution treat and age type. The thermal history and tensile properties corresponding to the creep data are given in Table I. The creep data were taken from creep-rupture tests. The associ- ated rupture data are given in Table 11. It may be noted that total creep deformations are considerably greater for equiaxed structures. Previous evaluations of stability indicated that all of the structures tested are stable with respect to exposure to stress at elevated temperature.1,2 For a minimum creep rate of 10-4 in. per in. per hr the difference in stress levels is indicated to be about 17,000 psi. Holden,et found an irreversible contraction upon heating three a-ß titanium alloys in the equiaxed condition above their ß-transus temperatures. The alloys were: Ti-6Al-4V, Ti-155 A (5Al-1.3Cr-1.5Fe-1.2Mo), and C-130 AM (44-4Mn). The net contractions in length between the original equiaxed and the final Widmanstatten structures measured at room temperature were: 0.4, 0.4, and 0.7 pct, respectively. The greater creep and rupture resistance of the WidmanstStten structure of the Ti-7Al-3Mo alloy may be associated with the phenomenon

Jan 1, 1959

By V. Damiano, M. Herman

CELLULAR substructure observed in metal crystals grown from the melt. has been studied extensively'-' and is attributed to the existence of a constitutionally supercooled zone in the liquid ahead of the solidifying interface. The mathematical description of this process has been given in terms of the concentration of solute in the liquid phase, the rate of solidification, and the temperature gradien.t in the liquid as the only variables.5 This technical note presents some evidence of 1) the effect of crystal orientation on some aspects of cellular growth, and 2:) the degeneracy of these cells into dislocation arrays. The zinc single crystals used in these studies were alloyed with cadmium sufficient to produce the constitutional supercooled cellular substructure. Crystals containing 0.05 pct Cd exhibited substructure formation for a growth rate of 10 cm per hr and a temperature gradient of 15°C per cm in accord with the theory. The growing liquid-solid interface was examined after we liquid had been decanted away in a fashion similar to that described by Rutter and Chamers.' The cellular substructure was also observed after polishing and etching the surface directly behind the decanted interface with a solution of HNO, and water. Fig. 1 is a photomicrograph of a typical polished and etched surface revealing substructure, the cleavage plane, and twins. The crystal has been grown with its basal plane parallel to the direction of growth and the plane of the micrograph is per-

Jan 1, 1960

By Tkeoclore Marvi

IT is singular that an industry quite the antithesis of flying should record tremendous strides in the utilization of aviation through- out the entire depression period, .while in the same years private interests lagged and airplatie manufacturing plants closed to such an extent that he purchase of new planes of certain types was practically impossible. Though receiving little notice from aviation publications and national associations, this use of the airplane progressed by sheer merit. It saved money, conserved energies, and made minutes in the air the equal of weeks on foot or water. The advent of aviation into mining and petroleum operations dates back many years, yet it \vas not until the depression that this new facility of the mineral industry was put on its proper economic basis. There, by its possibilities for saving effort, time, and money, it takes its place equally with other great technical advances in nietl

Jan 1, 1934

I. PRESIDING OFFICERS. At all Business meetings of the Institute the President, or, in his absence, the Vice-President, or, in the absence of both of them, any other member of the Board of Directors to be chosen by the meeting, shall preside. At all other meetings of the Institute the President of the Council or, in his absence, one of the Vice-Presidents, if present, shall preside II. ORDER OF BUSINESS. At each Business meeting of the Institute the order of business shall be as follows 1. Reading of minutes of preceding meeting. 2 Report of the President. 3. Report of the Treasurer. 4. Report of the Secretary. 5. Election of Directors. 6. Election of Members of the Council. 7. Reports of Standing Committees. 8. Reports of Special Committees. 9. Special Orders 10. Miscellaneous business. This order of business may be changed by a vote of a majority of the Members and Associates present in person or by proxy. The usual parliamentary rules shall govern all meetings of the Institute except in cases otherwise provided by the Constitution or the By-Laws. At all sessions of the Institute other than business meetings, the order of proceedings and the time of adjournment, shall rest in the discretion of the presiding officer

Jan 1, 1923

By H. K. Najarian

This paper describes recent development work on the Wheaton-Najarian Vacuum Condenser for Zinc at Josephtown Zinc Smelter, wherein, to dissipate the heat of condensation, the "airlift" action of gases bubbling through the molten zinc in the condenser is utilized to circulate the zinc through an outside "cooling well" and cooling it continuously. AN earlier paper1 gave an account of initial development of the Wheaton-Najarian Vacuum Zinc Condenser at the Josephtown Zinc Smelter of the author's company. This paper is a progress report of further development work over the years directed toward improving the efficiency and increasing the capacity of the condenser. In this type of zinc condenser, zinc vapor with accompanying noncondensable gases from electro-thermic zinc smelting furnaces is passed upwardly through a mass of molten zinc confined in a refractory-lined U-tube. The zinc vapor condenses in the molten zinc and the noncondensable gases are drawn out of the condenser by suction applied over the surface of the molten zinc. The heat of condensation of zinc, amounting roughly to 1000 Btu per lb of zinc condensed, is absorbed by the molten zinc and, in turn, is dissipated continuously to keep the temperature of molten zinc in a range to permit effective condensation. At the time of publication of our first paper, we had at Josephtown Smelter five units of 69-in.-bore metal furnaces and one larger metal furnace having 96-in. bore. Each 69-in. metal furnace had a condenser with 22-ft overall length. The 96-in.-bore furnace had a condenser with overall length of 31 ft. Condensers were of circular cross section, with corrugated steel outer shell and carborundum lining. Diameter of these condensers was 32 in. inside the refractory lining. Molten metal in the con- denser was kept cool by spraying cold water on the outside of the condenser shell. Under good operating conditions, 22-ft condensers produced some 12 tons of metal per day; and the 31-ft condenser, about 22 tons. When the furnaces produced zinc vapor at higher rates, invariably the condenser temperature would rise to levels where excessive blue powder would form and accumulation of accretions in the condenser would be accelerated. We found that, with the system of cooling in use, we had to provide heat-exchange surface of some 150 sq ft to condense 1000 lb of metal per hr with reasonable efficiency. The wall of the condensers was made up of 5/8-in.-thick corrugated-steel shell having next to it several layers of mica and inner refractory lining of special carborundum shapes to fit the corrugation in the steel shell, and having a minimum thickness of about 2 in. Relatively low rate of heat transfer through the thick condenser wall and slow internal circulation of the molten zinc limited the rate of heat exchange between hot metal within the condenser and the cold water flowing over the outer steel shell. The thickness of the condenser wall was about minimum that we considered suitable for continuous operation. As we learned to operate the electrothermic furnaces with higher power input, producing zinc vapor at higher rates, it became apparent that we needed condensers having larger heat-exchange surfaces. Our 96-in.-bore furnace had 6 single-phase power circuits with transformers rated at 500 kva each and normally good for power input of 3000 kw.

Jan 1, 1959

By Walter R. Hibbard, George H. Eichelman, William P. Saunders

INTEREST in the various products of the austenite eutectoid transformation in iron-carbon alloys, particularly as produced by the isothermal sub-critical techniques introduced by Davenport and Bain,1 has resulted in the application of similar heat treatments to other eutectoid transformations. Studies2.3.4 of the beta copper-aluminum alloy eutectoid transformation revealed microstructures very similar to those found in iron-carbon alloys. Investigations5,6 of the kappa phase in the copper-silicon alloy system have established the eutectoid type transformation of this phase into terminal alpha and intermediate gamma phases. This transformation has been reported' as forming a eutectoid type structure in a very sluggish manner by a long time isothermal treatment. The purpose of the present investigation is to study the products of the kappa eutectoid transformation as affected by transformation temperatures by means of microscopic and hardness methods. PREPARATION OF ALLOYS The copper-silicon alloy equilibrium diagram is shown in Fig I. The kappa field converges to a minimum silicon solubility at the eutectoid composition and all other completely kappa alloys are hypereutectoid. Thus, kappa decomposition involves first the proeutectoid precipitation of gamma, followed by the eutectoid transformation of a lower silicon content kappa (5.2 pct). Smith5 has indicated that alloys containing between 5.4 and 5.7 pct silicon could be hot rolled, but that the latter composition was desirable in order to permit a wider kappa temperature range. The alloy was prepared by adding Baker's commercially pure silicon to an ingot of copper-silicon alloy containing 2.34 pct silicon remaining from the investigation of Brick, Martin and Angier.7 Following the casting techniques of Krynitsky, Saunders and Stern,8 the ingot was melted under a heavy layer of dried charcoal in a clay-graphite crucible in a gas-fired pot furnace. Small lumps of silicon were held under the melt surface with a graphite rod. After the silicon had dissolved, the alloy was chill-cast and then remelted without a cover, stirred thoroughly, skimmed and poured into a preheated cast iron mold. The cast microstructure is shown in Fig 2. The casting, 10 X 4 X ¾ in., was annealed at 750°C for 21 brand furnace cooled. About 1/16 in. was milled from all surfaces. The plate was cut in half longitudinally and the bottom half analyzed by A.S.T.M. methods.9 The composition by weight was as follows: copper 94.24 pct, silicon 5.56 pct, iron 0.11 pct.

Jan 1, 1948

By Wilford Stork

CERTAIN influences of oxygen on iron have been known for many years and it has always been considered one of the worst enemies of the iron and steel founders. Nobody had a good word for it, hence little was done to make use of this oxygen. In all the fields of foundry practice, the desideratum was "melt without oxidation of the metal." In the consideration of the influence of oxygen on cast iron, we must not confuse this condition with oxidized iron caused by poor melting conditions, due to a high bed, heavy charges, low coke ratio, excessive melting rate, high blast, or poor charging. It is admitted that oxygen absorbed by iron melted under these conditions has a deleterious effect on the properties of the iron. The writer has had experience both in the melting under such poor conditions and in remedying these bad conditions and considers the product far inferior to iron melted under normal conditions. As stated by Dr. Richard Moldenke,1 such iron has a higher melting point and high combined carbon, is sluggish, and contains slags and oxides in solution in the liquid, causing slag inclusions and gas occlusions, thus producing defective castings. This oxidized condition cannot be counteracted or removed by any of the known deoxidizers; it can be remedied only by proper melting conditions. Such iron is really burned, whereas the iron considered in this paper was melted under normal conditions with moderate blast, correct bed height, light charges of iron, and low coke consumption and is not in this category at all. In 1914, the late J. E. Johnson, Jr., startled the metallurgists of the world when he published his results on the advantages of oxygen on cast iron.2 His work is so convincing and so logical, in spite of the common and well-established notions on the subject, that nobody has been able to refute a single argument. Such an eminent authority on iron and steel metallurgy as Prof. H. M. Howe has accepted the work in all its details in his latest book3 The work of J. E. Johnson, Jr., has revolutionized

Jan 6, 1919

By C. Dean Starr

The physical basis of the equation correlating electrical conductizlity and temperature coefficient of resistance of solid solution alloys has been inzlestzgated and the nature of the constants evaluated. It is shaun that the same form of correlation is valid irrespective of the magnitude of the temperature coefficient. However, the effect of therma1 expansion and change in resistivity with temberature nust be considered when the magnitude of the temperature coefficient of resistance is near zero. In a comprehensive literature survey conducted at the Armour Research Foundation in 1950, it was found that a linear relationship exists between the electrical conductivity, K, and the temperature coefficient of resistance, a, for solid solution alloys. This was expressed by the equation where B, a constant, depends on the solvent metal but not the solute. A continuing investigation by Hansen, Johnston, and Parks showed this equation was generally appropriate for Cu, Ag, Au, Pd, Pt, and Co base binary solid solution alloys as well as for many ternary alloys of copper over a range of conductivities and temperature coefficient of resistances from 0.02 to 0.60 reciprocal pohm cm and-0.00015to0.004Q per 0 per "C respectively. Eq. [I] was not always valid for alloys that exhibited a change in state (magnetic to nonmagnetic) or for alloys that had a temperature coefficient of resistance near or below zero. For example, in nickel alloys, a simple linear curve as predicted by Eq. [l] was not obtained when the conductivity was plotted against the temperature coefficient of resistance. Hansen suggested that deviations observed were caused by transitions from a ferromagnetic to a nonmagnetic state. Subsequent and more extensive data by ronin on Ni-Mn alloys confirmed Hansen's postulate. While both states independently showed a linear relationship between K and a, the value of B was different for the two states. In some copper and gold base alloys, as well as the platinum and palladium alloys investigated by Hansen, the conductivity did not extrapolate to zero at zero a as demanded by Eq. [I]. This deviation can be readily corrected by simply adding a constant to Eq. [I.] whence Eq. [2] shows the K decreases as a decreases but that K has a positive value when a = 0 which is observed for commercial solid solution alloys as well as the experimental alloys tested by Hansen. While other methods of correlation of electrical properties have been made such as the one by Starr and Wang3 who found a linear relationship between resistivity and temperature coefficient of resistance for Ni-Cr-Al-Cu alloys, the data, in general, can also be correlated by a form of Eq. [2]. Thus, Hansen's empirical equation has considerable merit. The objective of this paper is to determine the physical basis for this equation and to examine the region near zero a in more detail. ELECTRICAL CONDUCTIVITY VS TEMPERATURE COEFFICIENT OF FU3SISTANCE The resistance of a metal or alloy is defined as

Jan 1, 1963

By John R. Gould

A mathematical treatment of multiple-pass floating-zone refining of semiconductors, including the evaporation of solutes from the melt at reduced pressure, is presented. Vapor pressures and evaporation rate constants for phosphorus, arsenic, and antimony in germanium have been determined from floating-zone experiments conducted at 10 mm Hg. Rate sensi-tivity of arsenic in germanium has been examined over the range of 1 to 10 in. per hr growth rate. The equilibrium value of the segregation coefficient of arsenic in germanium, as determined by an extrapolation of these data, was found to be 0.09. PFANN has treated the segregation of nonvolatile solutes in the zone-melting process, Bradshaw and Mlavsky2 considered the evaporation of solutes in a vacuum during the growth of crystals by pulling from the melt, and van den Boomgaard3 has shown that it is possible to bring a volatile impurity element homogeneously into an ingot by means of zone-melting under a constant pressure of that element. This paper is concerned with the volatilization of solutes during zone - melting in a vacuum. The mathematical analysis by Lord4 of multiple-pass zone melting is extended to include evaporation of solutes. A method is presented in which evaluations of vapor pressures, evaporation rate constants, and distribution coefficients may be derived from the variation of solute concentration in the floating-zone refining of germanium at 105 mm Hg. EXPERIMENTAL Ingots of zone refined germanium, approximately 1/4 in. in diam and 10 to 12 in. in length, were subjected to several floating-zone passes at 105 mm Hg in order to provide intrinsic material for these studies. These ingots were then seeded in a [Ill] direction and solid-doped to a constant impurity concentration of approximately 1015 atoms per cmS in a forming gas ambient (10 pct H - 90 pct A) at 1/2 atm gage. The resulting crystals were subjected to repeated floating-zone passes at 105 mm Hg and a concentration profile along the length made after termination of each pass. Concentrations were determined from four-point probe resistivity measurements, and proper precautions were taken to prevent contamination during handling. A constant zone length, crystal cross section, and growth rate were maintained during zoning. A stationary coil and moving crystal system were employed for floating-zone growth with neither the section of crystal above nor below the melt rotated.

Jan 1, 1962

By RUSSELL C. FLEMING

THE important advances that have been made of recent years in mining and milling methods and in mechanical equipment at mines need no re- telling, but there has been a remarkable growth in one type of equipment which has gone nearly unnoticed. That is the increasing use of storage-battery locomotives underground. Since the war the number of these locomotives and their field of use have increased tremendously; their growing acceptance represents an al- most complete reversal of opinion from an earlier period when they were generally looked upon as in- adequate for the strain of mine service. At the time when storage-battery powered units were first making their bid for recognition, the use of power in haulage had already passed through several phases; hand tramming, rope haulage, compressed air locomotives, even gasoline locomotives, had all been used, ending finally in the general adoption of the electric trolley locomotive for practically all power-haulage requirements. It was, and is, conceded that the trolley loco- motive met more adequately the varied and severe conditions of mine service than any previous type of haul- age unit. Subsequent developments have had to endure comparison and surpass in performance that type of haulage before changes would be considered.

Jan 1, 1930

By Simon D. Strauss

What are future prospects for U.S. mining? In many quarters the assumption is made that this country has passed its zenith as a mineral producer -- that it is in a period of decline and that it is becoming a have-not nation like Japan and much of Western Europe. These industrial rivals of ours must depend almost entirely on others for their mineral supplies. In trying to answer this question one must of course distinguish between resources and productive capacity. In today's volatile and competitive markets, the definition of what are reserves and what are merely identified resources becomes ever more difficult. Many large deposits have been found that are unlikely to be viable in the marketplace under normal conditions but that can be of significance to the nation's military and industrial security in times of emergency. I should like to draw on personal experience from World War I1 for illustration. 4fter Pearl Harbor great concern developed over the availability of a long 1ist of strategic materials for which this country was largely dependent on imports. Included were a number of minerals of which domestic deposits had been identified. Among these were chromite, manganese ore, mercury, mica and tungsten.

Jan 1, 1982

By M. W. Burkart, B. Lustman

Uranium-base alloys exposed to high temperature water fail either by uniform oxidation or by sudden cracking and disintegration of the metal. The disintegration results from the oxidation of a second phase which is precipitated during the corrosion process. The precipitate has been identified as a metastable hydride of uranium. URANIUM-BASE alloys consisting of the body-centered-cubic ? phase are susceptible to two different modes of corrosion failure when exposed to high temperature water. In the first process, a smooth oxide film is formed on the metal surface which continually flakes off during exposure and results in a uniform weight loss of the specimen. The oxide is present as a thin, adherent layer whose thickness remains approximately constant. As the metal oxidizes during corrosion, a nonadherent layer is built up on this film and continually sloughs off. Coincident with the uniform corrosion just mentioned, another process occurs which eventually leads to failure of the metal by cracking and general disintegration. The failure takes place during a relatively short time compared to the total exposure. To distinguish this type of failure from the uniform corrosion, the cracking or disintegration of the metal will be referred to as discontinuous failure. For the ? phase uranium alloys it is discontinuous failure rather than uniform corrosion that limits the useful corrosion life of the alloy. This paper will be concerned primarily with the mechanism of discontinuous failure. Physical Changes During Corrosion—The alloys used in this investigation were ? phase uranium alloys containing 7 to 12 wt pet Mo or Cb. The preparation of the alloys, the method of corrosion testing, and the actual corrosion results are presented in another paper.' The ? quenching treatment consists of annealing the alloy for 24 hr at 900°C in a sealed Vycor glass tube filled with helium and then water quenching to room temperature without breaking the tube. The corrosion behavior typical of a ? phase uranium alloy is shown in Fig. 1. This specimen was a U-12 wt pet Mo alloy tested in pressurized, degassed water at 650°F. The corrosion rate was practically constant at 0.28 mg per sq cm per hr or increased slightly until about 15 to 20 days of exposure, when the onset of discontinuous failure occurred in this particular sample, and the specimen soon began to crack and disintegrate. The simultaneous increase in the observed corrosion rate is a result of the increased area of exposure due to cracking of the specimen. The microstructure of a specimen that failed by cracking is shown in Fig. 2. The presence of a plate-like precipitate can readily be seen. Metallographic examination of corrosion specimens reveals that the onset of discontinuous failure is always preceded by the formation of a plate-like second phase in the ? uranium matrix. Hydrogen analyses of specimens periodically withdrawn from corrosion test reveal that the hydrogen content of the alloy increases on exposure to the high temperature water, as shown in Fig. 3. The hydrogen is available as a corrosion product resulting from the formation of UO2 by the reaction of the alloy with water. Specimens analyzed just prior to discontinuous failure contained as much as 1200 ppm H, whereas the plate-like phase appears to precipitate out at a hydrogen concentration of between 10 and 25 ppm. The observed increase in hydrogen content prior to and during the formation of the plate-like precipitate suggests that this constituent may be a hydride of uranium. Additional evidence linking the identity of this phase to a hydride is that it can be removed by vacuum annealing at temperatures of 100°C and above. Decomposition products of the ? phase would certainly not dissolve at such temperatures, nor could other likely products of corrosion, such as oxides, be dissipated at any of the test temperatures. The precipitation and growth of the second phase during corrosion is accompanied by an increase in hardness of the specimen. The hardness increase results from the dispersion of the harder precipitated

Jan 1, 1959

By D. B. Crouch, D. A. Poulter

The engineering and metallurgical assessment of the McLaughlin Project ore body concluded that an open-pit mine and cyanide leach mill process would be feasible, producing both waste rock and residual mill tailings. As a part of the planning and permitting process, site selection studies were conducted for the tailings and waste rock disposal. The site selection process began with a regional identification of potential disposal sites and proceeded through 1) regional screening, 2) elimination of sites with obvious fatal flaws, 3) qualitative ranking of site evaluation criteria, 4) quantitative ranking of sites, 5) field investigation, 6) evaluations of field data, and 7) selection of preferred sites. Based on this approach of site rankings and field evaluations, tailings and waste rock disposal sites were selected and recommended for the preliminary design phase of the permitting and project development process. The site selection study provided the documentation necessary to justify the use of these sites for waste disposal and enabled Homestake Mining Co. to anticipate and integrate environmental concerns with agency requirements into the planning process.

Jan 1, 1986

By W. E. Newell

The basic principles and assumptions involved in D. L. White's solution5 for ultrasonic wave amplification in piezoelectric semiconductors are summarized. If the gain per unit length is maximized at each frequency without regard to the drift-field power density, the gain increases linearly with frequency. Therefore it would seem that very high gain is possible for frequencies in the hundreds of megacycles. However, with present materials the resulting drift-field power density is so large that cooling would be a major problem. For this reason it is more realistic to judge the capabilities of an ultrasonic amplifier in terms of the gain that is possible with a specified power density. In this case the gain at high frequencies does not increase but decreases more rapidly than l/f. The calculation of the gain us frequency at a fixed power level involves the repeated solution of a cubic equation and is therefore tedious. For the purpose of comparing different materials, sufficient accuracy can be obtained from an approximate solution which may easily be plotted as three straight lines on logarithmic graph paper. This method is used to compare the Performances of CdS, CdSe, ZnO, and GaAs. At a power density of 10 watts per cu cm, the first three give maximum gains of 60 to 80 db per cm in the vicinity of 60 megacycles. At the same power density, GaAs has a maximum gain of about 7 db per cm near 150 megacycles. Although an increase in mobility usually increases the gain for a specified power density, it is shown that there is an optimum mobility above which the gain decreases. An approximate expression for the optimum mobility is established. It is well-known that the interaction between charged particles and an electromagnetic wave can be used to amplify the electromagnetic wave. In the conventional traveling-wave tube, electrons in a vacuum are caused to move at a velocity slightly greater than the wave velocity, thereby coupling energy into the wave.' In principle, the same effect would be evident in a solid except that repeated collisions prevent the electrons from attaining a velocity greater than that of an electromagnetic wave. However, the drift velocity of electrons can be made to exceed the velocity of an acoustic wave in a solid. In 1956, weinreich2 noted that the deformation potential provided one means of coupling energy from drifting electrons into an acoustic wave, but the effect was too small to be of any practical importance. It was not until 1961 that White and Hutson demonstrated that the piezoelectric effect provided a strong enough coupling to give appreciable amplification of an ultrasonic wave and awakened wide interest in electron-phonon interactions. Qualitatively the effect may be described as follows. An acoustic wave propagating through a piezoelectric material is accompanied by an electric-field wave. If the vibrations are properly oriented with respect to the crystal axes of a piezoelectric semiconductor, the local electric fields are axially directed and cause bunching of the charged carriers. If the drift velocity of these carriers is less than the velocity of sound, they tend to be dragged along by the acoustic wave. This electroacoustic effect results in a net potential appearing across the material and in attenuation of the acoustic wave. On the other hand, if the drift velocity exceeds the velocity of sound, energy is coupled from the carriers to the acoustic wave and amplification results. Related effects which are being investigated include ultrasonic amplification in semimetals6-' and semi-conductor, and current saturation in piezoelectric semiconductors.'4-17 There are various problems which hinder the immediate application of ultrasonic amplification in a practical device. First, there are the traditional problems encountered in the design of acoustic delay lines: attenuation in the electromechanical transducers, reflected waves (which can lead to self-oscillation in an amplifying device), mechanical tolerances necessary to maintain phase coherence, and so forth. Second, there is the problem of selecting the best material from among the various piezoelectric semiconductors as they become available in single-crystal form with a wide choice of characteristics. This paper deals with the second problem and shows that the most realistic way of comparing materials is in terms of the gain which can be obtained without exceeding a

Jan 1, 1964

By Robert H. Richards

My first paper, read at the Cobalt Meeting of the Institute,' July, 1907, dealt with the behavior of a small Wilfley table when collceiltrating galena from quartz, the table being fed with natural products, with sized products, and with classified products. Since galena, having a specific gravity of 7.5, is among the heaviest minerals ordinarily concentrated by Wilfley table, it was desirable that a similar set of tests upon a mineral of lighter weight should be made. Chalcopyrite, of a specific gravity of 4, would have been the best mineral for this purpose, on account of its great importance as an economic mineral, but in carrying out the test I was obliged to content myself with a cupriferous pyrite, the specific gravity of which was 4.68 and the content in copper 8.80 per cent. Through the kindness of H. 0. Cummins, this material was obtained from Shasta, Cal., in very pure, clean, homogeneous condition. It was broken by rolls to 2 mm. in size, taking care to make a minimum of slimes. The quartz used to mix with it was pure, white, New England quartz, broken in the same way to the same size. In studying the accompanying tables, it should be borne in mind that the material concentrated was of low copper-content, and in many cases the quantity fed to the machine was 1 kg. or less. As a consequence of the smallness of the quantity treated it was very difficult to adjust the table and get it in condition to do its best work before the feed became exhausted, and for this reason many results were obtained which appear irregular.

Jan 1, 1909

By L. Leibowitz, M. G. Chasanov, L. W. Mishler

A drop calorimeter system is described for use in measuring enthalpies to 3600°K. Data are presented for tungsten between 2800" and 3600°K. The enthalpy of tungsten in cal per mole between 2000° and 3600°K can be represented by the equation HºT- Hº298 = - 1.7622 X 103 + 5.7772T + 8.9861 where T is in degrees Kelvin. A tabulation of com -puted values is presented for heat capacity, entropy, and free energy function. A drop calorimeter has been constructed to carry out enthalpy measurements at temperatures to 3600°K. Samples are heated by induction1 and dropped into a commercial adiabatic calorimeter, modified for this purpose. The experimental temperature is limited by the melting point of container materials and compatibility of the container and its contents. Several high-temperature drop calorimeters have been described in the literature1-5 but none has been used at temperatures as high as those in the present work; our measurements of the enthalpy of tungsten range from 2800" to 3600°K. DESCRIPTION OF EQUIPMENT An overall schematic view of the equipment is shown in Fig. 1. Power for the induction coil is supplied by a 25-kw 250 kHz Ther-Monic generator coupled to an iron core RF transformer. The Sample capsule is suspended in the work coil by 10-mil diam tungsten wires which are wrapped around a horizontal 5-mil diam tungsten wire. The horizontal suspension wire is clamped between two massive copper electrodes which are fixed in an x-y motion device that allows adjustment of the position of the heated capsule from outside the vacuum chamber. The copper electrodes are connected by flexible copper straps to a 1250-joule (5 kv, 100 pfarad) condenser bank. When it is desired to release the capsule, the condensers are discharged through the horizontal suspension wire causing it to vaporize rapidly. Very reliable and precise release of the capsule is achieved in this manner. Experiments have shown that no heat correction is required for this discharge energy. As part of the temperature measuring system, two prism holders have been incorporated in the apparatus. The upper prism holder is in the main vacuum chamber itself, whereas the lower one is in a side arm attached to the drop tube below the gate valve. The upper prism is mounted on a rotary vacuum feed-through, and may be moved under a protective shield when not in use. This prevents deposition of vapors on the prism surfaces when temperature measurements are not being made. Similarly, the lower prism is mounted on a push-pull vacuum feed-through, and when not in use may be pulled into its side tube. The prism mountings are fitted with guides and stops so that they may be moved precisely into the desired position. The aim throughout is to minimize the time the prisms are exposed to vapors from the hot samples. At the high temperatures reported in this paper, only the lower prism was used. The upper prism holder in these cases was fitted with an additional radiation shield. By using a prism and viewport, the lower surface of the samples can be observed by an optical pyrometer. The measurements discussed in this paper were obtained with a Leeds and Northrup 8622-C-S series manual pyrometer which is estimated to be accurate to 0.5 pct. Pyrometer calibrations and prism and window corrections were carried out in the conventional manner6 using tungsten strip lamps calibrated by the National Physical Laboratory, Teddington, England. Prism corrections were rechecked after each use. All work to date has been done in vacuum, and no measurable change has been observed in the prism correction below -2300°K for the upper prism and below -2800°K for the lower one. The total time of exposure of the prisms is about 50 sec per run. At high temperature, the final temperature reading is corrected by using the final A value for the prism; see Ref. 6 for details of this procedure. The calorimeter is a modified Parr Instrument Co. (Moline, lll.), Series 1230 adiabatic calorimeter with automatic jacket control. Other authors5 have used a similar calorimeter with good results. The calorimeter jacket cover and calorimeter cover are attached to the drop tube which contains a radiation shield. This shield is a gold-plated copper disc which can be operated manually from outside the calorimeter. The receiver is attached below the radiation shield and is lined with tungsten. In a typical experiment, the calorimeter and its jacket water temperatures were adjusted to 0.000°K temperature difference. The sample was allowed to equilibrate in the furnace at the desired temperature for about 20 min. The initial calorimeter temperature was then recorded, the sample dropped, and appropriate shutters closed. After about 3 min, the drop tube and receiver were filled with helium to 60 torr. The final calorimeter temperature was recorded after it had remained constant over a 5-min period. The equilibration time in the calorimeter was about 25 min. Thermistor probes are used to operate a hot and cold water supply system to maintain the jacket temperature equal to the calorimeter temperature. For actual measurements of the calorimeter temperatures, a quartz thermometer was used (Hewlett Packard Dymec Thermometer, Model #2801A). This thermome-

Jan 1, 1970

By Harmon D. Nine

DISCONTINUITIES in the strain vs cycles to failure (S-N) fatigue curves have been reported for polycrystalline materials by Porter and Levy for copper,&apos; by Benham and Ford for mild steel,&apos; and by Williams and Stevens for 18/5 stainless steel.3 However, the considerable scatter of the points for polycrystalline materials have made a statistical analysis of the data necessary to confirm the discontinuities. By using oriented single crystals of high-purity material and low grown-in dislocation content, the reproducibility has been improved to a degree which makes statistical analysis unnecessary and clearly shows discontinuities in the S-N curves. A recent publication4 reports an abrupt change of slope in the S-N curve for ( 100) axially oriented copper single crystals fatigued in torsion. The reported discontinuities in the S-N curve, along with a different mode of failure in the two branches of the curve, have been interpreted as being due to two different amplitude-dependent mechanisms. Further work on copper single crystals of (111) axial orientation has now been completed which supports the existence of an amplitude-dependent change in the mechanism of fatigue. In the present study torsional-fatigue experiments were performed at room temperature in air on (111) axially oriented single crystals. The crystals were grown and prepared as reported in Ref. 4. Two different methods of growing the crystals also discussed in Ref. 4 produced crystals of two different perfections: Type I with dislocation density of >l06 per sq cm and Type I1 with dislocation density of <l05 per sq cm. In accordance with the accepted hypothesis that crystal flaws are primarily responsible for the scatter of fatigue lifetimes, particularly at low amplitudes, the values for the three lowest amplitudes for Type I crystal are believed to be uncertain. They are marked in braces in Fig. 1. On the other hand, at amplitudes above a surface shear strain (SSS) of *0.003, the data for both types of crystals are in agreement. Most remarkably the S-N curve for torsional fatigue of (111)-oriented single crystals is composed of three segments separated by rather large discontinuities, Fig. 1. Metallographic and X-ray measurements indicate that the lower branch corresponds to the low-amplitude (F) region of the (100) copper single-crystal results as discussed in Ref. 4, and the two upper branches correspond to the high-amplitude (H) region. The lower discontinuity in the (111) S-N curve and metallographic evidence give further support to the hypothesis that different mechanisms of failure operate for high and low strain amplitudes. Reference to the resolved shear stress diagram, Fig. 2, shows that the highest stressed systems in

Jan 1, 1965

By Kenneth C. Vincent, A. M. Gaudin

TEN years ago Taggart, Taylor and Ince1 described a workable, convenient apparatus for the measurement of contact angles between cleaved, ground or polished particles and captive bubbles. Wark and Cox2 and Wark and Sutherland3 have done an immense amount of experimental work with this apparatus. Their work has had as principal object the determination of "contact curves." Contact curves are cartesian charts in which pH (or some other variable) is plotted against quantity of modifying agent. The rectangular area is broken into two or more curvilinear areas separated by the contact curve. The curve indicates that a sharp demarcation exists between conditions that bring about sticking of particles to bubbles and conditions that do not produce sticking. The type curve appears in the TRANSACTIONS as Fig. 1, page 248, volume 112. Wark and Cox offer data to show that the contact angle has a value determined by and characteristic of the agent used. Wark and Cox also make the statement that they believe this value is independent of concentration (ref. 2a, p. 209). They say: It is suspected that, given sufficient time and provided that there are no disturbing factors, the full ethyl xanthate angle (corresponding to a complete xanthate film) would be obtained in every case where contact occurs. Such a conclusion, if correct, would tend to substantiate the hypothesis of flotation collection by metathesis championed by Taggart and his associates4-8 and would argue against the adsorption hypothesis now adopted by Wark7 and by one of us.8 However, the data of Wark and Cox do not bear out the conclusion that there is a sharp passage from conditions of contact to conditions of noncontact. Rather, they indicate the existence of a transition zone of reagent concentration across which the contact angle varies with changes in reagent concentration from zero to a value near the maximum. This may be seen, for example, from Fig. 195 in the new text by one of us (ref. 8, p. 380), which presents the data of Wark and Cox in graphical form. The object of this study has been to explore the nature of the transition from conditions of contact to conditions of noncontact. The data of Wark and Cox to which reference has been made as showing that a gradual transition exists are marred by the fact that the region of critical-agent concentration is at an extremely small concentration. This condition suggests that diffusion may have played such a preponderant role that equilibrium was not reached within the time alloted. In the Wark and Cox data, the critical concentration was at about one part of xanthate per million parts of water. To form a monolayer of xanthate on the mineral surface would therefore require depletion of xanthate in the liquid to a depth of the order of

Jan 1, 1940

By G. S. Tint, M. Herman, V. V. Damiano

Dislocation arrays and substructures were studied in cadmium doped zinc crystals using a newly devised etching technique. Cadmium precipitates delineating the dislocations were revealed by etching a surface closely parallel to the (0001) slip plane. Cinephotomicrography of the continuous etching process revealed the three-dimensional aspects of dislocations in the bulk crystal. Dislocation etch patterns were studied in both deformed and annealed crystals after suitable aging at room temperature. The effect of annealing was evidenced by a rearrangement of the dislocations into low-angle boundaries and hexagonal networks. ETCH pit techniques have been used extensively to study dislocations in both deformed and annealed bulk metal crystals. Ideally one hopes to obtain a one-to-one correspondence between the etch pits and the points of emergence of the dislocations at the surface. One then attempts to deduce the way in which dislocations are arranged in the bulk crystal from the arrangement of etch pits on the surface. It is clear that one can obtain only limited information of the dislocation configurations inside the crystal from etch pit studies of single surfaces. Considerably more information is obtained if one is able to follow the course of the dislocations through the crystal using progressive etching technique. Techniques of this sort were used by Gilmanl to study dislocations on the slip planes of NaCl crystals and by Damiano and Tint2 to study dislocation arrangement in zinc crystals grown from the melt. The present paper makes use of a technique first described by Tint and Damiano3 to observe and continuously record the dislocation structures which appear while a crystal surface was being progressively etched. Studies were made on cleaved (0001) surfaces to reveal the dislocations along their length on the surface closely parallel to the slip plane. The technique for revealing segments of dislocations along their length by etching is well known. Wilsdorf and Kuhlmann-wilsdorf4 revealed disloca- tions along their length in aluminum containing a few percent copper, when precipitates segregated along the dislocations. The technique was used by Low and Guard5 to study dislocation configurations on the slip plane in Fe-Si alloys containing carbon. In the present work the technique was applied to zinc containing cadmium since it was shown by Gil-man6 that a cadmium-rich phase could be made to precipitate from supersaturated solutions along dislocations in zinc. Segments of dislocations delineated by the precipitates were revealed by etching a surface prepared by cleaving the crystal. The three-dimensional nature of dislocations and substructures was thus studied from the cinephotomicro-graphic record of the continuous etching process. EXPERIMENTAL Single crystals of zinc containing the order of 0.1 pct Cd were prepared by slowly lowering a graphite crucible containing the melt through a temperature gradient of 15°C per cm at a rate of 1.5 X 10-3 cm per sec. "As grown" crystals were aged for periods of 1 month at room temperature, then cleaved in liquid nitrogen, and etched according to the procedure used by Gilman.&apos; The etchant containing 32 g of CrO3, 6 g of hydrated Na2SO3 in 100 ml of water behaved as a chemical polish for zinc and etch pits were produced at the site of precipitates or inclusions. After the precipitates or inclusions were removed from the surface, the etch pits left behind were eventually polished smooth. This behavior enabled one to continuously observe the surface while the specimen was immersed in the etchant. Best results were obtained when the specimen surface was vertical and the reaction products of polishing were continuously removed by gravitational convection. Some crystals were heavily deformed in excess of 25 pct strain, others were lightly deformed the order of a few pct by compression such that the deformation occurred essentially by basal glide. Some crystals were etched immediately after deformation, others were allowed to age at room temperature for several weeks prior to etching. Heavily deformed crystals were annealed at various temperatures and etched on the cleavage plane immediately after annealing, others were allowed to age at room temperature for several weeks prior to etching. The etched structures of deformed and annealed structures were studied. Similar experiments were conducted on 99.9999 pct pure zone refined Tadanac zinc crystals which

Jan 1, 1963

By M. E. Wadsworth, R. C. Peterson, W. M. Fassell

The temperature and pressure dependence of the reaction of tantalum in oxygen were investigated from 500° to 1000°C at pressures from 10 mm Hg to 600 psi total oxygen pressure. Tantalum was found to oxidize linearly under the above conditions. Three distinct regions of temperature dependence were found with different energies of activation. From 500° to 600°C the rate of oxidation of tantalum was found to be essentially independent of the oxygen pressure at the pressure investigated. The oxidation rate increases rapidly with an increase in pressure from 600&apos; to 800°C. The dependence of the oxidation rate on the bulk concentration may be expressed by V = k&apos;?, where k&apos; is the specific rate constant and ?=k1Co2/(l + K1Co2), where k, is the equilibrium constant for the adsorption of oxygen on tantalum. ONLY a limited amount of data has been presented in the literature on the oxidation behavior of tantalum metal. Some values of its oxidation rate were reported in the Corroston Handbook&apos; and by McAdams and Geil.&apos; The first extensive investigation of tantalum was the work of Gulbransen and Andrews." They determined the reaction rates of tantalum in O2 and N2. Their results indicate that this metal follows the parabolic law in the temperature range of 250" to 450°C in O2 at pressures of 7.6 cm Hg with an activation energy of 27,400 cal per mol. In nitrogen, the metal follows the parabolic law from 500" to 800°C at 7.6 cm pressure. All experimental determinations were of 2 hr or less duration and deviations from the parabolic rate conceivably could occur at longer times. A spectrophotometric study of the oxidation of tantalum by Waber, Sturdy, Wise, and Tipton&apos; indicated good agreement between this method and the microbalance technique. The experiments were conducted in air from 220" to 350°C. The metal was found to follow the logarithmic law up to 320°C and the parabolic law at higher temperatures. The activation energies in the logarithmic region were reported as 12.57 kcal per mol and 12.0 kcal per mol, respectively, for the microgravimetric and spectrophotometric methods. In the parabolic region the activation energy was found to be 27.2 kcal per mol, in good agreement with the value of Gulbransen and Andrews." The present paper is concerned with the behavior of tantalum from 500" to 1000°C in oxygen at pressures ranging from 1/2 to 40.8 atm pressure. Earlier preliminary data by McKewan5,6 indicated the following facts concerning the behavior of tantalum: 1—At temperatures from 500" to 600°C, the metal followed the linear law. 2—At 575°C the rate of oxidation was found to increase with O2 pressure. 3—The Arrhenius plot in this temperature region was nonlinear. The nonlinearity of the Arrhenius plot was indicative of a more complex behavior than originally suspected for this metal.

Jan 1, 1955