Search

It is hoped, in conclusion, that the practical experience with the tube digester proves: 1. There is not waiting time required for extraction, and it is sufficient to heat pulp to the temperature proper to the bauxite. 2. The sojourn time can be reduced to 150 sec to this end. 3. The tube digester, in many respects, has a better duration function than the autoclave series with corresponding consequences for the transmutation. 4. The desilication is complete. 5. The quartz does not appear to be more attacked than in autoclaves. 6. The settling behavior of the red mud is often much better than low temperature red mud.

Some well-known methods for calculating the round-off error in floating-point addition are analyzed in this paper. The methods have been introduced by Moller [16], Kahan [11] and Knuth [12]. The necessary and sufficient conditions under which these methods produce the value of the round-off error, for rounding, truncating and parity arithmetic, are given. The computer-oriented parity arithmetic is not commonly known, but it has some desirable properties, as this paper will demonstrate. Some experimental results are also reported.

In the first part of this paper the optical absorption of amorphous films of PbCl2, formed by quenching condensation, is shown and compared to the spectrum of PbCl2 in its normal state. The sharp exciton band of crystalline PbCl2 in the long wavelength region is considerably broadened in the spectrum of amorphous films. The transition from the amorphous state to the normal crystalline state is indicated by an abrupt, irreversible change in the absorption curve at 260‡ K. This comparatively high temperature of crystallisation seems to be due to the complicated structure of PbCl2. In the second part of this paper the optical absorption curves of evaporated films of the system TlCl-KCl are measured. A shift of the absorption bands as a function of the composition is found. The 3,46-eV-maximum of pure TlCl is coordinated to the A-band of the KCl∶Tl-phosphor. On the other hand there is no connection between the 5,82-eV-maximum of TlCl and the known bands of KCl∶Tl.

This paper describes the application of a new interferometric method by holography to photoelasticity. Interferometric photoelasticity is a well established and elegant method; however, its use is still not commonplace in laboratories engaged in stress-optics. In the past few years, there has been a rapid growth in holographic activities. The stress-optic method described in this paper shows an alternate (holographic) method for determining both isochromatic and isopachic interference families, thus enabling a relatively easy and quick solution to plane-elasticity problems. It is also shown how the two material constants which are required can be determined simultaneously with a single calibration test.

The following four papers were presented during the February 1968 AIME Annual Meeting, at a symposium sponsored by the Pyrometallurgy Committee of the Extractive Metallurgy Division of The Metallurgical Society. The single theme of the symposium was copper converters—their history, modern construction and operation, and process by-products. Additional papers from this symposium will be published in the September issue.

In this paper we prove a variational inequality which gives a necessary condition for a minimum of a certain in general non-differentiable function. This inequality is applied to problems of best approximation and optimization to deduce global conditions for a minimum.

Infiltrability of a porous TiC compact, produced by powder metallurgy technique, depends on the capillarity of the compact and the surface condition and nature of the individual particles. Capillary forces raise the liquid metal infiltrant into the interconnected pores of the compact and the complete filling of these pores is a function of their geometry as well as the wettability of the TiC particles. The paper deals especially with the improvement of this wettability through surface conditioning of the TiC particles.

This paper contains solutions of the differential equation of diffusion in binary alloys if the diffusion coefficient is an exponential function of the concentration of one of the components.

By condensation of metals from the vapour onto a cooled substrate an especially high degree of disorder can be frozen in. Such strongly disordered films show essential changes of their properties. This paper deals with optical studies of such films of Bi, Ga, Sn and Ag. Reflectivity and transmission and their changes during annealing are measured in the spectral range from 0,25 to 4 microns. There is reasonable agreement with results of other measurements e.g. Hall-voltage, electrical resistance and electron diffraction. Optical constants and their changes during annealing are calculated in the range from 0,8 to 4 microns by approximation formulas. The high disorder produces similar anomalies of the optical constants as observed so far at extremely thin films. Concentrations and collision frequencies of free electrons are determined by means of the Drude theory. These values, obtained by a purely optical method are compared to results of electrical measurements and show satisfactory agreement.

This paper is an account of a detailed examination of the reaction by which nickel can be precipitated from aqueous ammoniacal nickel sulfate solutions by hydrogen at elevated pressures and temperatures. The thermodynamics of the reactions are discussed and the behavior of ammonia is illustrated. A mechanism is proposed to account for the catalytic effect of ferrous salt additions, and the effect of variables on the autocatalytic nature of the reduction is described with particular reference to the dependence of the reaction rate on the available surface area of nickel metal.

The paper presented below offers a detailed examination of some of the more pressing problems facing technology today. Offered by one of the country’s foremost authorities in the field, the study causes both reader and participant to take a long, hard, look into the current situation, and perhaps, in the offing, be taken with a certain resolve.

This paper describes a method and equipment developed and used for the growth of single crystals of high purity zinc, of substantial size and of various orientations, in substantial numbers, together with the results of some tests of the degree of perfection of the product.

The paper presents the results of experiments on the anelastic behavior of gold, as manifested by grain boundary relaxation. Two grain boundary internal friction peaks are found for 99.9998 pet Au. It is found that the peaks are associated with primary and secondary recrystallization. However, the existence of two discrete peaks cannot be explained on the basis of grain size and shape alone. It is suggested that grain boundary stability, as determined by orientation, plays a role in the observed effects.

Some aspects of Boltzmann’s solution for one-dimensional diffusion in an infinite medium when the initial distribution is a step function are clarified. Thus, the fact that the concentration is a function of the single variable x/t1/2 is established by a dimensional argument. The basis of the Matano-Boltzmann method for determining diffusion coefficients from concentration curves is discussed, and a new way of applying the method is derived and illustrated. As in the work of Hall, emphasis is placed on the curve obtained when (in effect) concentration is plotted against position on probability paper. This curve is approximated by a polynomial, and the diffusion coefficient is calculated by using an equation in which the coefficients of the polynomial appear as parameters. The new procedure makes the judgment of the effect of errors in concentration measurements easier than do the graphical methods frequently used.

The internal field emission (Zener-tunneling) is examined from two directions, using a onedimensional model. In section I the transition probability is calculated using the Houston expansion, but without perturbation theory, as has been used in previous papers by other authors. The calculation permits an examination of the various perturbation approximations. It is found, that the validity of the first approximation depends critically upon the residue of the interband coupling function. This residue contains the Keldysh factor, which is determined here. In section II the transition probability is calculated using free electron functions, again without perturbation theory. The same transition probability is obtained in both cases.

In a series of charts this paper presents the composition of all gas mixtures, composed of the elements carbon, hydrogen, oxygen and nitrogen, which at temperatures from 1000° to 1800°F are in equilibrium with (1) austenite of various carbon contents, (2) iron and iron carbide, (3) graphite, (4) iron and its oxide.

It was found that a critical boron content exists which yields the maximum boron-hardenability effect in hypoeutectoid steels, as was predicted from the mechanism proposed in a previous paper. The hardenability of boron steels with boron contents between 0.00005 and 0.0017 pet was dependent on the boron content, austenitizing temperature, quenching temperature, and austenite grain size. The effects of these variables on hardenability can be explained by the mechanism previously proposed for the boron effect.

The performance of welded structures is closely associated with the ductile-to-brittle transition temperature of the steel from which they are made. A low transition temperature is desirable because it indicates that the steel is less likley to fail suddenly at low ambient temperatures. Structures such as bridges, ships, storage tanks, and pipelines are usually made from hot rolled semikilled steel. Changes in rolling practice or chemical composition appear to be the most practical methods for improving the toughness of such materials. This results from the fact that production is likely to be seriously curtailed if improvements were obtained by recourse to heat treatment or complete deoxidation. This paper discusses the effect of variations in carbon and manganese contents on the properties of semikilled steels. The transition temperature, a property to which considerable importance is attached, varies with specimen configuration, testing method, and criterion of performance. Both the Navy tear test and the keyhole Charpy test were used in the investigation. According to the terms used by Vanderbeck and Gensamer, the tear test was used to measure a fracture transition and the Charpy test to measure a ductility transition. In either case the specimens absorb considerably less breaking energy in tests below the transition temperature than in tests above the transition temperature. Decreasing the testing temperature of notched-bar specimens seems to be equivalent in its effect to increasing the severity of loading on fabricated structures. Therefore, structures built from steels exhibiting lower transition temperatures in laboratory tests are expected to be less susceptible to sudden brittle fractures in service. Consequently, changes in composition which lowered the transition temperature of the experimental steels were judged desirable.

For almost 100 years after their discovery, rubidium and cesium were considered laboratory curiosities. Recent reductions in cost have stimulated interest in these metals. This paper describes their occurrence, extractive metallurgy, and known and possible uses.

The paper reviews the efforts made to utilize powder metallurgy to solve problems encountered when using alloys at high temperatures. The following subjects are discussed: comparison of wrought and sintered super alloys, sintered aluminum powder, porous materials for transpiration cooling, molybdenum, and cermets.

From the early work on the gas turbine to today’s efforts to obtain materials for service at over 2000°F, the processing of high-temperature alloys has been a tough, up-hill fight. The AIME High-Temperature Alloys Committee reviewed this progress at the Annual Meeting in February, and the Journal of Metals here presents three of the papers from this session.

This paper describes the results of studies to improve the effectiveness of Na2SO4 for removing copper from molten iron. These studies included the use of sulfate mixtures, recycling of used slags, and additions of Na2SO4 in lump form versus powder. The results can be summarized as follows

A simple method of obtaining multistage batch separations by crystallization was described recently. Known as zone-refining, it comprises passing short molten zones through a long solid charge. This technique can now be used on a continuous basis by means of the zone-void method described in this paper. Feed enters, at an intermediate point, a column down which molten zones travel, and waste and product leave at the ends. Materials move in the column through the agency of voids, which are introduced at the ends and travel toward the feed inlet. The voids and molten zones are moved by external heaters in a simple manner, and the principle of reflux is utilized.

Sound metallurgical approaches toward understanding, as well as eliminating, the persistent problem of brittleness in beryllium metal are described in this paper.

Two particles in mutual contact form a system which is not in thermodynamical equilibrium, because its total surface free energy is not a minimum. If such a system is left for a certain period of time, the bonding of the two particles will take place in order to decrease the total surface area, even though the temperature is lower than the melting point. This phenomenon of bonding of two or more particles with the application of heat only and at temperatures below melting point of any component of the system will be called sintering, although the powder metallurgists use this term in a broader sense, including the presence of molten phase and pressure. It is the objective of this paper to study this process and the mechanisms involved in it.

The chief limitation in using beryllium as a structural material, brittleness, is analyzed on the basis of the preferred orientation of slip plandes of single crystals. Solutions to overcome beryllium's lack of ductility, alloying, texture and grain size control, and obtaining high-purity metal, are described and evaluated. Fabrication methods are listed and evaluated with specific regard to the brittleness problem of beryllium. (auth) A review is presented on information published during 1962, both published papers and technical reports, in the field of diffusion in solids. Diffusion mechanisms, solutions of the diffusion equation, diffusion in ternary systems, self- diffusion, diffusion in pure metals and alloys, the effect of strain on diffusion, the effects of temperature and pressure gradients, interfacial diffusion, diffusion in nonmetals, and diffusion in liquids are all included. 138 references are included. (P.C.H.)

An apparatus is described, which enables us to measure the thicknesses of films immediately after condensation at low temperatures and in different stages of annealing by means of a multiple beam interferometry technique (Tolansky). The film thicknesses are also measured by the temperature dependence of the electrical resistance. Measurements of Pb- and Cu-films are given as an example, and the sources of errors are discussed. In the case of Pb-films both the methods give the same thicknesses at any condensation temperature. This leads to the conclusion that Pb-films have a density of the compact material. At low condensation temperatures the disorder in the films turns out to be thickness dependent, and the distribution of defects seems to be inhomogeneous. Cu-films condense at low temperatures with high porosity. This may be the cause of the often observed getter effect of freshly condensed Cu-films. The filling factor of Cu-films is studied at different condensation temperatures. The temperature dependence of the resistivity of thin metallic films is discussed in the appendix of this paper.

Recent investigations have shown that the poleward flux of angular momentum across latitutde 30° N can be regarded essentially as an edey flux due to macroturbulence. Since the principal source region of atmospheric angular momentum is the frictional layer in the trade-wind zone it is necessary to have a mechanism which explains the transport of the angular momentum up to the upper troposphere and the tropopause level and into the planetary jet stream aroundlatitude 30° N. In the present paper it is shown that this transport can easily be explained by assuming the existence of a mean meridional circulation between the Equator and latitude 30°N. The mass transport in this meridional circulation cell can be computed from the empirical data for the poleward eddy flux of angular momentum presented byY. Mintz. The same data can then also be used to estimte the excess of precipitation over evaporation in the equatorial zone of the ascending branch of the circulation.

A tentative U-Si phase diagram was determined by the present authors about 10 years ago. A description of the experimental work has not been published in the open literature, although the resulting phase diagram did appear in the National Nuclear Energy Series.1 In 1949 Zachariasen2 published crystal structure determinations for the U-Si intermetallic compounds and came to the conclusion that several of the formulas assigned to the compounds by Kaufmann et al. were in error. The purpose of the present paper is to describe the original work done in 1944 and, in particular, to discuss some of the properties of one of the intermediate phases, known as ϵ, whose formula is approximately U3Si.

Unique combinations of low density, high strength properties have made beryllium and its alloys extremely important in space applications. This paper presents an evaluation of beryllium intermetallic compounds.

The magnesium-rich corner of the 375°, 200°, and 100°C isothermal sections of the Mg-Li-AI system as developed by metallographic and X-ray diffraction studies is presented in this paper.

Our discussion has covered a great deal of ground and that in rather cursory fashion, but it is hoped that it will serve as an introduction to the subject which will aid the interested reader in the assimilation and assessment of the very large number of papers available in the literature. The basics of the behavior of pores, both voids and bubbles, in solids, with and without driving forces, appear to be well-established. Quantitative agreement between theory and experiment has been obtained in several instances, all involving a dominant driving force, either curvature or thermal gradient. On the other hand, when no driving forces exist, the restraining effects of structural defects must be carefully considered in any “random-walk” analysis. Also, the effects of faceting of pores due to anisotropy of surface tension become very important. Further effects of possible significance include strain field interactions between pores or between pores and surfaces. In short, when no driving force is applied, many normally small effects take on great importance and are extremely elusive of quantitative analysis. On the other hand, the presence of a strong driving force may well “swamp out” these effects and thus provide results in agreement with predictions of an idealized theory.

From the exciton spectrum of the alkali halides it can be shown that theP-function of the alkali atom seems to be necessary, if one wants to construct certain excitons by means of atomic orbital functions. A relation between the ionisation energy of the exciton and the optical dielectric constant has been obtained from the experiments. This is consistent with a hydrogenic model of the exciton, which we have used in an earlier paper.

In this paper the ratioHc3/Hc2 is calculated for all electron mean free paths. Correction terms to the standard resultHc3/Hc2=1,695 are obtained both in the Ginzburg-Landau region and in the dirty limit at all temperatures. In the clean limit our results are identical with those obtained earlier byLuders.

A three ton per day blast furnace using blast temperatures up to 2200°F was operated to recover manganese from open-hearth slag and manganiferous iron ore. The spiegel product containing 12 to 24 pct Mn was blown in a basic converter to high manganese oxide slag as described in the paper which follows this one.

The paper presents isothermal recrystallization curves for 0.08 and 0.15 pet C steel at subcritical temperatures following small amounts of plastic deformation. The effects of deformation, temperature, and aging on nucleation and growth rates are described. The free energy of activation for grain boundary migration in steel is given.

Treating a complex nickel-copper-cobalt sulfide concentrate in a leaching operation has required the development of special techniques for the separation of nickel and cobalt. The process described in this paper can be applied with only minor modifications to a wide range of nickel and cobalt bearing solutions.

This paper reports the distribution of sulphur between iron and titanium in Fe-Ti-S alloys and in Fe-Ti-C-S alloys. The compound TiS was found, which exists as a separate phase at temperatures below 1200°C. Titanium in steels reacts with sulphur in preference to carbon.

This paper discusses the exploratory application of holography to photoelasticity. It is shown that the two-beam holographic method may be used to record the birefringent pattern of a standard two-dimensional photoelastic specimen. A special type of polariscope is required. A discussion is presented of the various arrangements required to produce isochromatic, isoclinic, isopachic and combined isopachic and isochromatic fringe patterns. The three-dimensional nature of the holograph is utilized to separate the principal stresses by means of oblique incidence. Both normal- and oblique-incidence fringe patterns are recorded on a single hologram. A brief discussion of the extension to the dynamic case is presented.