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By Van C. Nyman

A time-sharing computer was tied in to Hecla in August of 1967. This has proven to be helpful in performing metallurgical and engineering calculations that were formerly tedious tasks. Metallurgy programs were written for applying two and three product formulas. Programs were expanded to make the monthly metallurgical balance calculations for each of the Hecla mills. The Hecla engineering department uses the computer for solving hoist duty cycles and for traverse analysis. Both Asarco and Bunker Hill Company in the Coeur d’Alene Mining District are tied to a time-sharing computer. Their uses for the time-sharing computer will be discussed. Asarco had the advantage in learning computer techniques during an extended strike. A comparison of Asarco computer use with that of Hecla's will show the advantage in having a person or persons spend full time on the use of computers. Bunker Hill has the versatility of five teletype units in their mine-smelter complex plus ability to tie in to their own computer.

Jan 1, 1969

By A. W. McReynolds

One characteristic of plastic deformation which distinguishes it from elastic strain is the essential inhomo-geneity of plastic strains. Elastic strain varies continuously through a material, and average relative displacements of initially adjacent atoms are only small fractions of their initial spacing, (strains of the order of 0.01 or less). On the other hand, plastic flow corresponds to the appearance of discontinuities in strain of the lattice, such as dislocations or slip bands, where local strain, on an atomic scale, is several orders of magnitude higher. These discontinuities are visible on a microscopic scale as the familiar slip lines (Fig 1). In spite of this obvious microscopic inhomogeneity, however, macroscopic measurements almost invariably show a smooth curve of stress vs. strain (Fig 2b) even if measurements of linear strains be made to an accuracy of one part in 107. This macroscopic homogeneity of strain indicates that the discontinuities in strain on slip planes occur in increments too small or too slow to be recorded individually, and further that they occur sufficiently independent of one another so that the small increments add at random to a smooth stress-strain curve. The present paper describes observations of plastic strain in aluminum of commercial purity and in high purity Al-Cu alloys, where there exists a strong coupling between slip in various regions of the specimen such that once initiated it spreads rapidly through a large volume. The total effect is that of relatively large, rapid, and regularly spaced steps of strain followed by periods of only elastic strain. Fig 2a illustrates the type of "stair-step" stress-strain curve which results. The properties of this cooperative slip phenomenon will be described further in the section on results: in par- ticular it will be shown that each step corresponds to the propagation of a wave of plastic deformation through the specimen. Some interpretations of the mechanism by which it occurs will be made in the following section. Although the type of plastic wave phenomena to be described has not previously been reported, there are numerous cases of related effects in the plastic yielding of metals: YIELD POINT PHENOMENA The most familiar of such effects is the "yield point" observed in low carbon steels, brass, duralurninum, and the like. It consists in the sudden termination of the elastic portion of the stress-strain curve by a large plastic strain. Since the usual tensile machine is such that yielding of the specimen relieves the load, the resulting curve is as shown in Fig 3. As the strain continues, deformation occurs at a lower stress for some time, then follows a rising curve, but with no further sudden yielding. This effect has been observed in brass by Sachs and Shojil and later by many others. Edwards, Phillips and Jones2 made extensive studies of the effect in steel, and of the role of various alloying elements. Although there seems to be fairly clear evidence that the yield point is caused by a hardening of the material by precipitation of impurities, no satisfactory explanation for the sudden yielding has been given. Winlock and Leiter3 have shown that the strain. level of the upper yield point depends strongly on the rate of loading, the yield point increasing by almost a fac- tor of two as the strain rate goes from 0.002 in. per in. per min. to 4.4 in. per in. per min. This effect would seem to imply an incubation period before yielding is initiated at a certain stress. On the other hand, by going to very slow loading rates, Edwards, Phillips and Jones2 showed that the yield point does not become lower and eventually disappear as might be expected, but, on the contrary, begins to rise at loading rates below about 25 Ib per in. per min. becoming much higher than at rapid loading rates. STRAIN AGING If, instead of continuing straining of a specimen after occurrence of a yield point, the load is removed and the specimen aged, resumption of the test results in occurrence of another yield point as shown by the dotted curve of Fig 3. The new yield stress is generally higher than the previous maximum applied stress. This hardening of the material by straining and subsequent aging is undoubtedly related to quench age-hardening resulting from the aging of a specimen quenched from high temperature. Since neither effect is observed in pure metals, it is generally accepted that quench-aging in all cases is the result of hardening by precipitation of a supersaturated alloying element, and that strain-aging is probably a similar precipitation, accelerated by disruptions of the lattice by previous strain. Pfeil4 has shown that strain-aging does not occur in iron from which all of the carbon has been removed, but that only a very small carbon content, around 0.003 pct, is necessary to cause strain-aging. In accord with this observation is recent work by Dijkstra5 in this laboratory showing that the solubility limit of carbon in iron is extremely low, less than 0.001 pct at 400°C. Edwards, Phillips and Jones2 have shown that the strain-aging effect is also removed by the addition of small quantities of elements such as Mo, Mn, Ti, and the like, which readily form carbides. Their results demonstrate the

Jan 1, 1950

By James W. Neill

Bituminous coal has for many years been used for the smelting of iron-ores in the blast-furnace. In some districts in Scotland it is used alone, in others it is used mixed with coke. The similar use of certain bituminous coals in the United States has been repeatedly mentioned in the Transactions. (See, for instance, as to the Hocking Valley coal, the papers of Dr. T. Sterry Hunt, Trans., ii., 275, and vii., 313; and as to Indiana "block-coal," the paper of Mr. J. S. Alexander, Trans., i., 225.) Phillips (Elements of Metallurgy, p. 250) says: " Raw coal for blast-furnace use must be of a non-cokiog kind, and, when of suitable quality, is perhaps the most advantageous fuel." In the first

Jan 1, 1892

By M. R. TECK, N. Rudd, L. K. Thomas, D. L. Katz

The authors are to be congratulated for presenting the first comprehensive paper on the theory and practice of threshold pressure determination in connection with underground gas storage. It is of particular value since most previous experimental work on this subject has been proprietary to the commercial laboratories engaged in such testing and to their clients. This dlscussion is presented in amplification of the subject paper, not in criticism, and is based upon our experience with approximately 5,000 threshold pressure determinations. Our comments are directed primarily to the experimental procedures as described by Thomas et al. It should be noted that, while clay mineral-rich lithologies are the most common caprock materials, the samples used (Table 1) include low permeability sandstones and carbonates, but do not include shales or other formations in which clav minerals exert a dominant effect. While our experience on samples analogous to those investigated by the authors generally confirms their findings, we have found that even more rigorous experimental conditions must be imposed where clay minerals are the controlling factor. These additional conditions result from the well-known molecular character of the clay minerals themselves in which water is interlaminated with, and bonded to, silicate sheets, thus becoming an essential component of the molecule. In many clay minerals the character of the intersheet bonding, and thus the dimension of the lattice, is strongly affected by variations in the identity and concentration of cations present in the intersilicate water. On a supermolecular scale, adsorbed water films on particle or "flakes" of shale provide much of the cohesive force necessary to maintain mechanical strength. The thickness of these films is variable and inversely proportional to intergranular pressure within the dimensional limits involved in caprock investigation. The thickness of the intersilicate water layers may also be subject to pressure under some conditions. These considerations are reflected in several necessary modifications of the experimental procedures described by the authors. Two of these are, in our judgment and experience, of such importance that they cast real doubt on the validity of data obtained on argillaceous materials without their application. The very careful resaturation procedures proposed by the authors should give good results in connection with the relatively "inert" lithologies used in their experiments. Our experience suggests, however, that they would create more problems than they would eliminate if applied to argillaceous materials. 1. Drying of the sample at the temperature and for the duration indicated by the authors not only will dessicate the sample with consequent shrinkage cracking, parting along bedding planes, and even total disassociation in the case of fissile shales, but it may also alter the character of the clay minerals themselves — in some cases irreversibly. 2. Prolonged evacuation to 2 microns Hg further dessicates the sample and is even more effective in reducing the intersilicate water content. 3. Resaturation with water differing in pH or chemical content from that existing originally in the sample also serves to alter the nature of the sample, particularly its structure and strength. 4. Our experience has been that, even with the thorough precautions proposed by the authors, complete resaturation of very fine grained materials is rarely obtained. Yet our experience confirms the

Jan 1, 1969

By G. R. Love, M. L. Picklesirner

THE use of color adds a new beauty, power, and versatility to metallography. This has been amply demonstrated in a number of public exhibits and on the walls of corporate, government, and university metallographic laboratories around the world. Indeed, in a number of cases, the color not only is of esthetic value but is scientifically essential to the competent examination of particular samples and systems. Optical strain analysis,' determination of true grain size in U-A1 alloys: phase identification in Nb-base alloys,3 analysis of transformation rates in heat-treated Nb-Zr alloys,4 measurement of solidification segregation in cast Nb-Zr alloys,' study of the intermediate phases in Nb/Sn diffusion couples,6 investigation of the oxidation kinetics at various surface orientations in single crystals,7'8 and a number of other research efforts9'10 would have been vastly more difficult without the extra clarity and distinction introduced by color—either the colors resulting from particular polarized light techniques or the interference colors obtained by oxidation. It is unfortunate that the beauty of colored micro-structures cannot be shared more widely, but the economics of publishing a technical magazine apparently prohibits color plates except under extraordinary circumstances. It is doubly unfortunate that no convenient, general method exists for communicating the information available in colored microstructures to the scientific community. True, in some instances the color changes observed are dramatic enough that direct black and white photography is adequate. In photoelastic stress analysis, several orders of interference fringes may be produced and it is frequently desirable to suppress the color effects (use monochromatic light) to simplify interpretation. On the other hand, relatively minute color variations may be readily detectable by eye, be of considerable assistance in interpreting a structure, and yet be enormously difficult to reduce to an unambiguous black and white print. In order to illustrate a possible compromise or solution to the above problems, we wish to show three black and white photographs of the same region of an Nb/Sn diffusion couple whose interpretation depends heavily upon use of color techniques. These micro-structures were obtained from a section through a rod consisting of commercial-purity niobium tubing filled with 99.995 pct Sn (melt-filled in 10"6 Torr vacuum). The composite rod, measuring 500 mm long, was bent into a hairpin shape and inserted into water-cooled copper grips in a vacuum high-temperature furnace. The rod was outgassed for 2 hr at a furnace temperature of 800°C and was further heated by self-resistance using a 2.2-kva ac power supply. The rod was raised to 1910°C over a 4+-hr period, held for 15 min, slow-cooled to 1500°C over a -hr period, and free-cooled to room temperature (all temperatures were measured with W5Re/W26Re thermocouple). Throughout the heat treatment the ambient pressure was kept below 8 x lo-' Torr. Metallographic preparation of the sample was completely conventional except that it was necessary to extend the grinding steps to remove damage in the brittle NbsSn phase introduced by sectioning. No satisfactory chemical or electrochemical etch has been found for these diffusion couples; of those which have been tried, any that attack the niobium-rich phases at all attack the tin-rich phases disastrously. However, the final polishing steps did produce a slight relief effect and this, coupled with anodizing, yielded excellent clarity in the microstructures for direct observation. The anodizing voltage was chosen to give maximum change in color per unit change in composition. In this case, indeed normally, this maximum sensitivity occurred in the blue-to-red color range. The pure niobium tube wall anodized to a relatively bright blue

Jan 1, 1967

By H. E. Stauss, E. I. Salkovitz, F. W. von Batchelder

EXISTING information regarding the structure of a spherulite in nodular cast iron is based on optical studies. According to these data, a nodule consists of an aggregate of graphite crystallites radiating from the center, with the closely packed basal planes at right angles to the radii. The c axes lie along the radii. This view faces some uncertainty in the fact that the c axis does not represent the accepted direction of fastest growth in graphite. To supplement the optical information, X-ray studies have now been made. The principle used was to screen the nodule in greater part from the X-ray beam and expose only a minor cap. As successively larger portions of the nodule were introduced into the X-ray beam, any differences in the X-ray patterns could be observed. Such photographs have been taken with chromium radiation and a Laue camera. The graphite nodule itself, about 0.010 to 0.025 in. in diam, was mounted with vaseline on a micrometer screw for control of the linear motion. The nodule rotated about 45" each time that it was translated linearly. The nodules were obtained from magnesium-treated hypereutectic iron by electrolytic solution of the iron in hydrochloric acid. In Fig. la is shown the pattern of the thinnest cap examined. In Fig. lb is shown the pattern of the same nodule moved 0.003 in. farther into the X-ray beam, and rotated 45" at the same time. Figs, la and lb indicate incomplete circles for graphite (the two outer circles arise from graphite) with the side arcs much weaker than the top and bottom ones. The arcs obtained are themselves not continuous in intensity but vary with maxima of intensity some 15" and 30" apart. The structure of the nodule that would give rise to such a pattern can be explained as follows. Basically the nodule consisted of small crystallites. The discontinuous character of the diffraction rings demonstrates that the nodule was not composed of randomly oriented crystallites. The strong vertical reflections and the weak lateral reflections show that the reflecting planes were roughly normal to the radii. The absence of sharp reflection spots suggests that the nodule did not contain large crystals. The sharpness of the diffraction rings in their radial direction shows that the variations in intensity along the arcs were not the result of line broadening resulting from extremely small crystals. In the diffraction patterns two rings corresponding to graphite were found. The third and inner ring in the figures originated in the vaseline. The graphite rings correspond to the a and ß lines reflected from the basal planes, showing that the radii of the nodules are the [0001] direction normal to the basal planes of graphite. The picture of the structure that is formed is, therefore, one of aggregates of crystallites. Within each aggregate the c axes of the crystallites tend to align themselves in the radial direction of the nodule, although these axes deviate somewhat in direction by a continuous variation of angle. Correspondingly the basal planes of the graphite crystallites are generally normal to the radii. It is a pleasure to acknowledge the assistance of M. C. Bloom and R. P. Dunphy of this laboratory.

Jan 1, 1952

By B. A. Shaw

Historically, microwave tubes have been fabricated from massive metal and ceramic components. The current trend is to lighten tibes for airborne applications. The reqciiremenls of light weight and also reduced cost have created a novel approach to tube structure in which thin-film technology plays a major role. Although the electrical requirements of thin-film circuits in microwave tubes differ from those required or se,niconductor integrated circuits. the technology is basically similar. The stringent requirements of the micvowave tube have created sophisticaled thin-film techniques thut are of interest to the integrated-circuit industry in general. This paper describes a nunzber of thin-jilm techniques recently developed and discusses in detail the application of the technology in microwave tubes. The particular areas of interest are: 1) ceramic mounted thin-film slow-wave structures; 2) thin-film secondary emitters; 3) suppression of tube environnental multipactor by semiconducting' thin films; and 4) age-hardenable and dispersion-hardened thin metal films. SEVERAL thin-film techniques specifically applied to microwave power tubes are discussed in this report. There are two reasons for this work. One is the necessity of reducing weight and cost of microwave tubes and the other is related to overcoming problems in the tube operation by the use of applied thin-film technology. The major emphasis of this work has been on tube slow-wave structures. Other work in the area of secondary emission, either its suppression or its enhancement, is continuing; the most satisfactory results to date have been by utilization of thin-film technology. The requirements of high thermal and electrical conduction together with greater strength than normally obtained with elemental materials have led to the development of dispersion-hardened films. The paper will discuss: 1) ceramic-mounted delay-line microwave tubes; 2) multipactor and secondary emission; 3) hardened films. I) CERAMIC-MOUNTED THIN-FILM SLOW-WAVE STRUCTURES In a conventional crossed-field microwave tube, the slow-wave or delay-line structure is produced from two carefully machined components. One half of the structure is shown in Fig. 1. The other half is the mirror image of the first but is rotationally offset by a half a period. The combined structure now forms an interdigital type of slow-wave structure and is the anode of the tube as shown in Fig. 2. The period and finger length of an interdigital slow-wave structure are prescribed by the desired dispersion characteristics. The typical design is as shown in the first figure; it can be noticed that the finger width is several times greater than the finger thickness. Even assuming that it were mechanically possible to produce free-standing fingers of extremely small cross-sectional dimension, for example, 0.002 in. thick by 0.005 in. wide by 0.500 in. long, decreasing this finger width would increase the tube efficiency but would also decrease the thermal-conduction path, causing an increased temperature rise from intercepted rf current which in its extreme could easily cause finger melting. Hence, for free-standing lines of this type, the design is a compromise between mechanical capabilities, tube efficiency, and thermal dissipation. These structures are also expensive and tend to be heavier than purely electrical considerations would demand. In the present approach, we have transposed the three-dimensional structure previously shown into an essentially two-dimensional structure as shown in Fig. 3. The linear structure is used here for clarity of detail. The support member is a ceramic material and the line is deposited copper. The final tube design is shown in Fig. 4. Because of the backwall sup-

Jan 1, 1967

By S. F. Shaw

THE principles involved in lifting oil in wells flowing naturally are identical with those underlying the flowing of wells by means of the air-gas lift, and information of a dependable nature obtained in the study of the air-lift can be applied to wells with natural flow. A well flowing naturally is one in which the lifting is done by means of the gas-lift, for which the gas is supplied entirely by the formation from which the oil is derived. In air-gas lift operations, there is insufficient gas supplied by the formation to lift the oil to the surface in an efficient manner, therefore additional gas for this purpose must be furnished from an outside source. There may, at times, be conditions obtaining in natural flowing wells different from those in wells flowed by gas-lift, but these differences do not at all conflict with the main principles of gas-lift work. One such condition is met with in wells in which the gas supplied by the formation is in considerable excess of that required to lift the oil to surface; this excess may be so great as to reduce the quantity of oil that can be lifted through the particular diameter of casing or tubing that has been lowered into the well. This same condition can be brought about, however, by supplying a large excess of gas from an outside source to an artificial gas-lift well, and a study of the effects obtained from injecting a large excess into the well can be applied directly to handling wells flowing naturally which have a large excess of gas supplied by the underground reservoir.

Jan 1, 1929

By N. W. Wickersham, Ward B. Blodget, Roberts R. Boyd

The year 1926 has seen few radical changes or developments in methods of drilling and handling oil wells, but it has been a year of steady progress and development in deep drilling and production methods. Probably the outstanding development of the year was recognition by the directors of the American Petroleum Institute of the importance of natural gas in the production of oil, and the Institute directors' resolutions in December, 1926, regarding regulation of gas production with oil by state legislation. This matter is extremely important and will receive the attention of the industry in 1927. Advances in Drilling Equipment The history of the progress of deep well drilling is the solution of problems as they have confronted the operator. As the prospects for deeper production have become apparent, methods of penetrating the earth to greater depths have been devised. Rotary Equipment Improvements in the construction and in the methods of operation of rotary drilling equipment have practically caused elimination of cable tools in California for all but shallow work. The rotary drill, from 1910 when it began to be a practical factor in California, has been making steady advances, first displacing cable tools for drilling to the oil sands in proved fields and later displacing the cable-tool outfit entirely. With the perfection of machinery for taking core samples of the formation penetrated, the rotary drill has become generally used for wildcat work, continuous coring being practiced when desirable. Deep Holes The use of the rotary drill has made commercially feasible the opening of oil fields at greater depths than was considered possible with cable tools. Heavier equipment has been promptly supplied as occasion has

Jan 1, 1927

By H. P. Reid

PORTLAND cement is manufactured under either of two general proc-esses, the wet or the dry. The raw materials in general consist of limestone, shells, marl, cement rock, clay, shale, blast-furnace slag, etc., so proportioned that when calcined the desired composition will be obtained. In the wet process the combined raw materials are ground to extreme fineness in the presence of water, to a resulting slurry of from 30 to 50 per cent moisture content. The moisture of the slurry may be reduced by thickening or filtering processes for feed to the cement kiln or the slurry may be fed to the kiln with its full percentage of water. The dry process differs from the wet in that the surface moisture of the raw materials is removed prior to grinding. For the drying of these materials heat is required and in most cases is produced by burning of raw fuel either on grates or stokers before the dryers or in suspension in the form of pulverized coal, oil or gaseous fuel. The power required for making the cement is sometimes purchased from outside sources; sometimes it is generated from the heat in the waste gases leaving the cement kilns, or generated at the plants direct from raw fuel. We have, then, as the possible requirements of fuel in the cement industry: (1) fuel for power generation, (2) fuel for drying raw materials, including coal before pulverizing, and (3) fuel for burning the raw materials to cement clinker. There is no essential difference in quality required in fuel for burning the materials by the wet and dry processes.

Jan 1, 1932

By H. Landsberg

THE curriculum presented here is an outgrowth of discussions by the Committee on Geophysics Courses of the A.I.M.E. in previous years. It had to be a compromise between the desires voiced by employers of geophysicists, professional geophysicists and the possibilities at an average college. There one has to face the questions of the available teaching staff, the inertia of administrators and teachers set in their ways, and the red tape involved in modernizing antiquated curricula. It is, of course, not ideal to have colleges and universities lag 10 years behind the times. Rather, instead of being prodded by industry, -they should be ahead of industrial needs. There should also be a certain amount of leeway for the student in any college curriculum. All these points had to be considered in drawing up a curriculum, which, instead of being narrowly termed "geology" or "geophysics" was rather called "earth science." It gives the student a chance to specialize in one of the various branches represented by teachers on the faculty of The Pennsylvania State College, giving as options Geology (with subdivisions of Mineralogy and Paleontology), Geophysics, Geography, and Meteorology. Table IA. represents the option of geophysics in the curriculum that envisages that a student may want to make his career in any of the fields encompassed by the American Geophysical Union or in geoexploration. This is, of course, only the start of an education that in most cases will have to be followed by graduate work for complete professional training. The outlined curriculum is definitely of an engineering type and is identical for all of the four options mentioned for the first two years. Specialization will start in the junior year but even thereafter the branches are kept as closely allied as feasible in order to permit a student to change from one to the other (e.g., because of a different aspect in the employment situation) with a minimum of additional work. Table IB shows the geophysics option according to subject matter, indicating the considerable amount of work in the fundamentals of mathematics, physics and chemistry with a liberal number of geology courses, and some engineering. The courses in the field of geophysics are limited-just two lecture courses as a general introduction and one field course, to permit the student a visualization of the correlation between mathematically analyzed physical data and the geological realities. Thesis work is considered essential to teach the student, while he is still in college, some things S. F. Kelly has mentioned as desirable: (I) following of instructions for somewhat independent work; (2) organizing of material, and (3) producing a readable report. This, together with the personal contact with the advising faculty member, will help in forming a student's personality. The seminar course attempts to get the student into the habit of reading current literature, so that he can keep abreast of the times.

Jan 1, 1941

By B. F. Oliver, C. W. Haworth

Pure tin and Sn-0.5pct Pb ingots have been frozen unidirectionally from the base. For quiescent melts that were initially undercooled, a transition from lower eqlciaxed structure to an upper columnar structure is found in the alloy ingots. Columnar to equi-axed back to columnar transitions are observed in superheated alloy ingots, but no such equiaxed band is observed impure tin. The reproducible equiaxed band is associated with a thermal undercooling followed by a recalescence. This undercooling is <5"C, whereas the critical (maximum obtainable) under-cooling for both the pure tin and the alloys used is -20°C. A similar undercooling is observed at the same position in the pure tin ingots, although in this case no clear transition in structure can be seen. The structure of the pure tin ingots is either entirely columnar or mixed columnar-equiaxed. A consideration of the detailed thermal history of the ingots indicates that the ingot macrostructures are determined by the occurrence of a local therlnal undercooling in conjunction with nuclei multiplication and transport mechanisrris. GENERALLY it is found that a pure metal ingot solidifies so as to produce an entirely columnar structure. Frequently an alloy ingot is found to have a columnar outer zone and an equiaxed central portion. Early systematic work to examine the factors controlling the formation of the equiaxed structure was reported by Northcott&apos; who showed that, for copper alloys frozen unidirectionally with a given ingot practice, the alloying element influenced the length of columnar crystals and the extent of the equiaxed structure. Northcott showed that alloys with a wider freezing range more readily produced the equiaxed structure. The nucleation process can be important in producing equiaxed structures; frequently an alloy which readily solidifies with an entirely columnar structure will produce an entirely equiaxed structure when a nucleating agent is added to the melt.&apos; The formation of the equiaxed structure was attributed by Winegard and chalmers3 to the presence of constitutional supercooling; that is, a region of liquid in front of the growing solid could have a temperature below its equilibrium liquidus temperature. Thus, with a small enough temperature gradient in the liquid, it was suggested that the presence of constitutional supercooling may be sufficient to bring about the nuclea-tion necessary for the formation of an equiaxed structure. Although this explanation is plausible, and may be relevant in many ingots, Walker has described an experiment&apos; for which constitutional supercooling seems to be an unlikely cause of nucleation. A Ni-20 pct Cu alloy, repeatedly undercooled more than 50"C, was crystallized and found to show the typical colum-nar-equiaxed structure. The separation between the liquidus and the solidus for the alloy is 40°C. Thus, in this experiment the nucleation required for the formation of the equiaxed structure must have come about in some other way than by the nucleation catalysis constitutional supercooling hypothesis. Chalmers has suggested more recently5 that nuclei (in a typical ingot) are present immediately after pouring and are prevented from redissolving by the constitutional supercooling effect. More recently Uhlman, Seward, Jackson, and ~unt&apos; have shown direct evidence using ice and organic materials that freeze dendritically that the "remelt mechanism" may be an extremely effective crystal multiplication process during the freezing of ingots under conditions involving dendritic growth. JSlia" experimentally demonstrated the detachment of dendrite arms. chernov14 has analyzed the dendrite arm detachment process as a coarsening phenomena driven by the minimization of interphase area. Katta-mis and ~lemings" working with undercooled steel melts give evidence supporting this mechanism. Mechanisms of dendrite arm detachment such as those assisted by convection are believed to be the origin of the macrostructures obtained in this study. This study makes no attempt to distinguish the relative contributions of these mechanisms. The object of the present work was to obtain accurate temperature measurements during the solidification of an ingot and to correlate these measurements with the formation of equiaxed grains in the resulting ingot structures. Similar previous work is very limited. The measurements carried out by Northcott are neither sufficiently extensive nor sufficiently accurate for any interpretation. Plaskett and winegard7 carried out experiments on A1-Mg alloys in which they observed values of the temperature gradient, G, in the liquid and rate of freezing, R (for a given alloy solute content Co), at the transition from a columnar to an equiaxed structure. They reported that equiaxed crystals were produced at values of G/G approximately proportional to the solidus composition. Similar experiments using Pb-Sn alloys carried out by £111011" showed a linear relation between G/R and the solidus composition. However, the thermocouples were in the mold wall rather than in the melt and, in one case, ingot surfaces were examined. There is ambiguity in the meaning of the values of G and R measured in all these experiments. APPARATUS AND EXPERIMENTAL PROCEDURE Alloys were prepared by induction melting 99.999 pct Sn and 99.999 pct Pb to form a Sn-0.5 wt pct Pb alloy in air in a graphite crucible and casting into a cylindrical graphite mold 6 in. long, 1 in. in diarn , and with a & in. wall thickness. This mold was mounted on a copper base through which cooling water could be

Jan 1, 1968

By G. W. Brownell, H. T. F. Lundberg, R. W. Pringle, K. I. Roulston

The rapid improvement of the airborne scintillometer and the perfection of its efficiency for counting low energy gamma radiation has made it possible to work out a technique to map in great detail the radiation pattern at the earth&apos;s surface. On such maps low radiation over certain areas appears to indicate the existence of oil accumulations, forming a pattern similar to that obtained by the geo-chemists. RADIOACTIVE analyses of samples from the surface of oil fields were carried out more than 10 years ago in Alberta by the alpha particle ioniza-tion chamber technique,&apos; but large enough tracts could not be covered in these investigations to make possible any evaluation of the method as a means of oil exploration. Considerable interest has recently been revived, however, as a result of certain striking advances which have been made in the instrumentation available -for the measurement of radioactivity. It is the object of this paper to indicate the nature of these improvements in radiation technology and then to describe the attempts that have been made to interpret the radioactive patterns obtained in the course of airborne recordings with the new instruments. Since the survey can be carried out from the air and records can be accumulated over vast areas in a short time, the result may easily lend itself to statistical treatment. Areas have been surveyed in Alberta, British Columbia, Saskatchewan, Quebec, Texas, New Mexico, Nebraska, Colorado, Utah, and Montana. Producing fields in Alberta and West Texas have been flown over several times in different directions, Fig. 1. The operations were then extended into unknown territory and drill holes were put down on the anomalies which looked promising. The results from these drillings were encouraging and have given hopes for the development of an entirely new method of oil exploration. Any large scale method for the survey of radioactive anomalies must be based on the measurement of gamma rays, as beta and alpha rays have much too short a range to be of any significance. Thus the essential improvement which has made the present stage of this work attainable is the development of new highly sensitive detectors for gamma radiation. In the past the only detectors of any consequence that were available were the ionization chamber and the geiger counter, but both of these suffer from the defect that only a small proportion of the gamma rays passing through the counter are detected, possibly 0.1 to 0.2 pct. The recent development of the scintillation counter2,3 has completely transformed the situation and has had a considerable impact on many branches of nuclear technology. The detection of alpha particles in zinc sulphide screens by visual observation of the individual scintillations which these particles produce dates back to the early spinthariscope of Rutherford and Crookes, but the combined use of an appropriate scintillating phosphor and photomultiplier tube had to await the technical development of the latter many years later. With this development came the modern era of the scintillation counter and a knowledge of phosphors which have a large light output under the bombarding action of gamma radiation. Some of these phosphors are relatively dense and are capable of stopping a large proportion of the incident gamma radiation. As the sensitive region is the whole volume of the crystal, a very high detection efficiency, 50 pct or more, can be obtained for medium energy gamma rays. Scintillation counters for geological purposes were first developed in 19494-6 in an attempt to utilize this remarkable improvement in efficiency, which has the attractive consequence that only a small portion of the normal background of the counter is due to cosmic radiation. In 1949 tests were made in northern Saskatchewan by Lundberg Explorations Ltd. with portable scintillation counters which gave excellent results in the search for uranium and served to indicate unknown uranium deposits in areas previously closely surveyed with geiger counters. Portable scintillometers (registered in Canada) are now commercially available and in regular use,&apos; and the adaptation of the instrument to radioactivity oil well logging has also been very successful.8 Initial attempts to measure radioactivity from aircraft with scintillation counters were made during this period in the same area and yielded most encouraging results. It would be appropriate to consider some specific requirements for airborne investigations. The essential problem to be met in the detection of any radioactive source is the necessity of obtaining a signal greater than the statistical fluctuations of the background counting rate for the instrument. It is possible to show that Nt>2k2 is the condition for detectability of a signal where N = average background counting rate for the detection. t = time constant of the counting rate meter, used to determine the average number of counts arriving in a certain predetermined time interval. N&apos; = average source counting rate at the detector. k = N/N&apos;, and N>>N&apos;. Sample values are given in Table I. Assume that the aircraft carrying the equipment is travelling at 120 mph, in which case it will cover 176 ft in 1 sec. Assume also, as a first approximation, that a point source target is in range when the air-

Jan 1, 1954

By E. H. Jr. Dix

OF all the alloying elements used in commercial aluminum alloys, copper stands out as by far the most important, and it is perhaps for this reason that the constitution of the aluminum-copper system has received the attention of a number of experimenters covering a period of approximately 20 years. It would be expected that during this time the equilibrium relations had been thoroughly and exactly worked out. In a general way this is true, but there is a surprising lack of agreement in the details of the high aluminum end of the diagram, particularly in regard to the solid solubility of copper in aluminum, which has been given variously as 2 per cent. to 5 per cent. at the eutectic temperature. The importance of this is much greater than might at first appear to one unfamiliar with modern commercial aluminum alloys. This is true because, with one exception, the susceptibility of the strong alloys to heat treatment depends, in part at least, upon the solid solubility relations of copper in aluminum. In 1919, Merica, Waltenberg, and Freeman1 published the first detailed information on these solubility relations. They found that the solubility of copper decreases with falling temperature from about 4 per cent. at 5.25° C. to about 1 per cent. at 300° C. and is apparently still diminishing at lower temperatures. In 1921 there was published a brief account of the results obtained in the National Physical Laboratory, Teddington, England.2 This laboratory, however, reported that 5 per cent. of copper is soluble in aluminum at 540° C., and that this amount decreases to about 3 per cent. at 20° C.

Jan 2, 1926

By R. R. Morral, F. M. Krill, K. T. Aust

THE occurrence of twins in aluminum ingots cast under certain conditions has been well established. For instance, Herenguel and Lacombe1,2 have observed a twinned columnar structure in 99.5 and 99.9 pct Al, solidified by continuous or semicontinuous casting. The structure, which they termed "basaltic," appears in the form of elongated crystalline fibers of alternating luster. Herenguel and Lacombe2 found sections of flat crystalline plates composed of twin crystal plates, in which the twin plane (111) and a [I121 direction contained in the twin plane are parallel to the principal heat gradient. This orientation relationship is different from the usual orientation texture observed in cast face-centered cubic metals, where the [100] direction is approximately parallel to the long columnar axes lying in the direction of growth." A large amount of twinning has also been observed by the present authors in semicontinuous cast aluminum of 99.2 pct purity, Fig. 1. Mondolfo4 has suggested that the twinned cast structure forms by a deformation twinning process as the result of uneven cooling stresses within the ingots. This suggestion appears to be inconsistent with the large amount of twinning observed in the semicontinuous cast ingots and with the large difference of dendritic

Jan 1, 1953

By William B. Plank

PRESENT enrollment of 182,361 students in the engineering schools of the United States and Canada represents an increase of 6.6 pct over the enrollment in these schools in 1951-52. Thus is brought to a halt the steady decrease in engineering enrollment that began with the close of the 1947-48 academic year, five years ago. The mineral engineering student picture is similarly encouraging. In the United States schools, 9453 students are preparing themselves for positions in the Mineral Industry. This is an increase of 8.3 pct over last year as compared with an increase of 6.6 pct in the total United States engineering enrollment. The rate of recovery for the mineral engineering group is thus more rapid than for the engineers as a whole.

Jan 4, 1953

By G. A. Baird

With the exception of eight wildcat completions, which were unsuccessful and abandoned, all of the 1935 new drilling was performed in the proven fields. As of Dec. 31, 1935, 22 drilling rigs were in operation, of which 9 were at wildcat locations and the remainder were being used in new drilling in proven fields; in addition, 25 workover rigs (exclusive of cleanout rigs) were operating, all in the major fields. Production of Crude Oil.—Notwithstanding the considerable decrease in new completions during 1935 as compared with 1934, crude production mounted to a new high of 148,893,225 bbl., clean oil at 60&apos; F., representing an increase of 12,532,579 bbl. over the previous record year, 1934, total of 136,360,646 bbl. This increase was due: (1) to the flush production

Jan 1, 1936

By G. A. Baird

With the exception of eight wildcat completions, which were unsuccessful and abandoned, all of the 1935 new drilling was performed in the proven fields. As of Dec. 31, 1935, 22 drilling rigs were in operation, of which 9 were at wildcat locations and the remainder were being used in new drilling in proven fields; in addition, 25 workover rigs (exclusive of cleanout rigs) were operating, all in the major fields. Production of Crude Oil.—Notwithstanding the considerable decrease in new completions during 1935 as compared with 1934, crude production mounted to a new high of 148,893,225 bbl., clean oil at 60&apos; F., representing an increase of 12,532,579 bbl. over the previous record year, 1934, total of 136,360,646 bbl. This increase was due: (1) to the flush production

Jan 1, 1936

By E. L. Vickers

Over the years, the pure theorist in economic analysis has accumulated a formidable array of facts in bringing his subject matter under control. Business managers and mining engineers are aware of the theorist&apos;s weapons, but the question of applying them to the mastery of practical problems seems hardly feasible, especially in view of the almost innumerable variables plaguing the everyday scene in the mining enterprise. One such sophisticated tool of long-standing in the theorist&apos;s arsenal is marginal analysis. Equally long-standing for the operating company and valuation engineer is the problem of defining the cut-off grade the point below which a mineral re- source ceases to be economically amenable to extraction. In other words, what part of a mineralized body of rock is ore and what is waste?

Jan 6, 1961

By Edward Saibel, W. T. Lankford

DURING the course of an investigation of the plastic flow of aluminum aircraft sheet under combined loads, several problems arose in which analyses of the conditions leading to unstable plastic flow were needed. In order to provide these analyses, and in the hope of attaining a better understanding of the general problem of unstable plastic flow, the present study was undertaken. It is well known that unstable plastic flow is associated with a form of mechanical instability frequently observed during the plastic deformation of ductile metals. This instability is characterized by the fact that, at its onset, plastic straining will proceed at a constant magnitude of the externally applied forces. It is further typical that the resulting unstable flow is generally accompanied by the formation of a neck, a local bulging, or some other form of heterogeneous deformation. Perhaps the most familiar example of unstable plastic flow to the metallurgist is the formation of the neck in the ordinary tension test. It is well known that in this test most metals exhibit a maximum in the externally applied load, followed by the process commonly referred to. as "necking down." Instability in the simple tension test has been frequently discussed and numerous investigators 1,2.3,12 have derived the criterion for instability in terms of a critical rate of strain hardening. It is the purpose of the present study to extend the criterion for unstable flow to the more general case where the body undergoing flow is subjected to combined loads. It is hoped that the problems considered will provide a more consistent picture of the general features of this important form of mechanical instability. The most practical implications of instability in plastic flow arise in connection with sheet metal forming operations. In the formation of a great many sheet metal parts, the deformations are produced primarily by stretching. If the conditions which lead to unstable flow are fulfilled in such a formation, and if the resultant instability leads to a pronounced localization of flow, then the useful limit of ductility of the material will have been reached. It is also essential that the effects of instability be taken into consideration in any study of the plastic flow and rupture of metals under combined stresses. In general, when unstable plastic flow is initiated, straining becomes localized, the geometry of the test specimen changes, and the state of stress in that portion of the specimen undergoing plastic flow is no longer under external control. In many past studies of the effects of combined stresses on flow and rupture, account has not been taken of the fact that, although a given test may be started under constant

Jan 1, 1947