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By R. E. Pollard

The National Bureau of Standards received, in August 1940, a number of samples of bridge wire taken from the cables of the General U. S. Grant suspension bridge over the Ohio River at Ports- mouth, Ohio. These cables were 7% in. in diameter under the wrapping and each was made up of 1458 ungalvanized wires of No. 8 gage in 3 parallel-wire strands. The choice of ungalvanized wire was based on the previous satisfactory performance of similar wires in other bridges over periods of 20 to 50 yr. of service(1).2 After about 12 yr. of service a number of breaks were discovered in the Portsmouth bridge cables, most of them at the anchor- age shoes, and they were replaced by cables made up of galvanized wire(2).

Jan 1, 1945

By J. B. Reed, T. A. Read, H. Rosenthal

Although the season cracking of brass has been a subject of experimental investigation for more than thirty years, the mechanism that is responsible for this phenomenon is still obscure. While at- tempts to elucidate the stress-corrosion cracking of some alloys have been relatively successful, the principal accomplishments made in the studies of the season cracking of brass have consisted of improved techniques for the fabrication of articles of alpha brass, which reduce the danger of season-cracking failure in service. The primary purpose of the present paper is to collect the published experimental data which appear to be of importance to the development of an adequate theory of the mechanism of the season cracking of brass. Some of the possible mechanisms which have been proposed will also be discussed, together with some promising avenues of future attack on the problems. Several excellent survey papers on season cracking are available, including the recent ones by Croft and Sachs(1)2 and by Gibbs(2). The principal facts concerning season cracking, as presented in these papers, may be summarized as follows. The season cracking of alpha brass is a special type of stress-corrosion failure, which may occur in atmospheres containing ammonia, air, and water vapor. The stress causing failure may be either the

Jan 1, 1945

By Bernard G. Carbajal

The dielectric properties and thermal stability of glow-discharge polytnerized films of styrene, chloro-benzene, and other organics and photoresist filrns are presented. Variations in the glow-discharge polymerization procedure are related to thermal stability. Thermal treatwzents to improve the dielectric properties of both positive (A2 340) and negative (KMER) photoresists are given. THIS study of the dielectric properties of thin organic polymer films is part of a program to investigate the electronic applications of organic materials. Thin organic polymer films have been produced in an ac glow discharge,13 with a low-energy electron-beam process,4 and in an rf dicharge. A process has been developed during the course of this program for forming thin organic polymer films in a dc glow discharge. These glow-discharge polymerized (GDP) films exhibit some useful dielectric and insulative properties. Variations in the properties of the GDP films can be induced by changes in the source material (monomer) andor in the conditions of the glow discharge. Thin organic polymer films can also be produced from typical positive and negative photoresists. Some variations in the properties of the photoresist films can be induced by suitable post-application treatments such as thermal crosslinking. The properties of interest in this study are dielectric constant, dielectric strength, resistivity, and thermal stability. POLYMER FILM PREPARATION I) GDP Films. The GDP films were prepared in a dc glow discharge in an atmosphere of organic monomer vapor. The details of the glow-discharge procedure have been presented previously.6 Briefly, under the influence of a dc glow discharge organic vapors can be polymerized in the vapor phase and the resultant polymer (GDP film) deposits on and in the vicinity of the cathode. Substrates placed behind a screen cathode can be uniformly coated over all exposed areas. Pattern definition can be achieved using normal mask stencil techniques. Table I presents the pertinent parameters in the preparation of GDP styrene. Conditions of Forrrzation of GDP Styrene. The rate of deposition for GDP films was monitored using a current-time integrator. The thickness of the deposited film for a given set of experimental conditions was a function of the current-time integral. The fifth row in Table I is a compilation of the deposition rate of GDP styrene films. Other organic monomers behave in a similar fashion. With the exception of the highly halogenated saturated hydrocarbons, all organics subjected to the conditions of the glow discharge form GDP films. 11) Photoresist Films. Photoresists are normally recognized to exist in two forms, a low molecular weight, soluble polymer form (A) and a high molecular weight, crosslinked insoluble form (B). Typical negative photoresists are applied in the low molecular weight form A and converted to the high molecular weight form B by the action of light. (Positive photoresists are applied in form B and converted to form A by the action of light.) Eastman Kodak Metal Etch Resist (KMER) has been chosen as a typical negative photoresist. Polymer film samples were prepared in the same configuration used for GDP films. The KMER was applied in the usual fashion using a 120°C drying step (infrared-lamp heating) and a 180°C post-bake. Care must be taken to completely remove the solvent in the drying step and to properly develop and postbake to exposed photoresist. If the photoresist film is not properly dried and postbaked, severe blistering and peeling will occur during subsequent elevated-temperature exposure. Thickness can be controlled by varying the viscosity of the form A photoresist and the spin rate at application. AZ 340 was chosen as a typical positive photore-

Jan 1, 1967

By Norman P. Goss

It is generally agreed that cold-working mechanically refines the grains into smaller fragments and with continued working these are oriented with certain crystallographic directions bearing a relation to the direction in which the metal is worked. Some of the energy expended on the metal during plastic deformation appears in the form of heat, but a very small portion remains in the metal as stored energy. The entropy, specific heat capacity, temperature at which recrystallization will just begin, density, ductility, elasticity, tensile strength, and resistance to corrosion are affected. These properties have been studied extensively and some of the changes in the physical properties due to cold-working were attributed to lattice distortion.l-8 The broadening of the Ka lines on the X-ray diffraction diagrams of plastically deformed metals is believed to indicate lattice distortion, and consequently the existence of internal stresses. The evidence supporting this theory rests solely upon the observed experimental fact that the diffraction lines are broadened and the Ka doublets are completely diffused. Elam9 has reviewed the matter of lattice distortion in relationship to the hardening of metals by plastic deformation. The X-ray diagrams of plastically deformed metals differ in general from annealed metals. The hardening of a metal was believed due to lattice distortion.9 The resolution of the doublet is lost when a metal is cold-worked and the Laue spots are elongated. At one time this elongation was thought to indicate the elastic bending of the crystal planes. However, more careful work showed that the asterism was due to new orientations developed within the fragmented grains during plastic deformation. Some theories attributed the hardening to fragmentation of the grains into smaller units. Jeffries and Archer,ll after carefully considering the problem of work-hardening from many angles, came to the conclusion that cold-working mechanically refines the grains into smaller crystal fragments, some of which at least differ in orientation from the parent grain. The increase in

Jan 1, 1940

By Norman P. Goss

It is generally agreed that cold-working mechanically refines the grains into smaller fragments and with continued working these are oriented with certain crystallographic directions bearing a relation to the direction in which the metal is worked. Some of the energy expended on the metal during plastic deformation appears in the form of heat, but a very small portion remains in the metal as stored energy. The entropy, specific heat capacity, temperature at which recrystallization will just begin, density, ductility, elasticity, tensile strength, and resistance to corrosion are affected. These properties have been studied extensively and some of the changes in the physical properties due to cold-working were attributed to lattice distortion.l-8 The broadening of the Ka lines on the X-ray diffraction diagrams of plastically deformed metals is believed to indicate lattice distortion, and consequently the existence of internal stresses. The evidence supporting this theory rests solely upon the observed experimental fact that the diffraction lines are broadened and the Ka doublets are completely diffused. Elam9 has reviewed the matter of lattice distortion in relationship to the hardening of metals by plastic deformation. The X-ray diagrams of plastically deformed metals differ in general from annealed metals. The hardening of a metal was believed due to lattice distortion.9 The resolution of the doublet is lost when a metal is cold-worked and the Laue spots are elongated. At one time this elongation was thought to indicate the elastic bending of the crystal planes. However, more careful work showed that the asterism was due to new orientations developed within the fragmented grains during plastic deformation. Some theories attributed the hardening to fragmentation of the grains into smaller units. Jeffries and Archer,ll after carefully considering the problem of work-hardening from many angles, came to the conclusion that cold-working mechanically refines the grains into smaller crystal fragments, some of which at least differ in orientation from the parent grain. The increase in

Jan 1, 1940

By Edward Keller

Jan 1, 1906

By E. D. Fields, R. W. Sayers, M. C. Tippett

The Duval Corp. porphyry copper deposits at Copper Canyon and Copper Basin, though widely separated, form an econornic unit requiring integrated exploitation. Contrasts in mineralization, host rocks, and mode of occurrence present unique mining and milling problems. Mixed oxide-sulfide ore is treated in extensive dump leaching facilities in both areas. Complex Cu-Au-Ag ore is treated in a 4000-tpd mill at Copper Canyon. In both areas, hypogene metallization occurs within large aureoles of metamoiphism and hydrothennal alteration related to quartz monzonite intrusions of mid-Tertiary age. Supergene processes fitrther altered the rocks and enriched the hypogene protore. At Copper Canyon, hypogene copper and iron sulfides with gold and silver occur in fractures, as partial replacement of favorable beds, and as disseminations in Paleozoic sedimentary rocks. The lower part of the Pennsylvanian Battle formation was a particularly favorable host. Metallization occurs to a lesser extent in quartz monzonite. Metal zoning is well-developed. The deposits at Copper Basin consist principally of supergene copper minerals in arenites of the Cambrian Harmony formation. Oxidation of hypogene copper and iron sulfides in tactite zones has formed at least two commercial deposits; intersections of fractures with favorable beds exerted important ore controls. Recently, the Copper Canyon and Copper Basin properties of Duval Corp. have been added to the list of porphyry copper mines in Nevada, marking the first new copper open pit in this state in 15 years. The properties are situated in the Battle Mountain

Jan 1, 1970

By Thomas Kesler

THE Cartersville mining district, 35 miles northwest of Atlanta, Ga., has been of varying but continuous importance in the southern mineral industry during the past century. Noted chiefly for its production of brown iron ore, manganese oxide ores, barite, sienna, and magnesian limestone, the district and its environs have produced brick and tile clays, slate, gold, bauxite, and graphitic schist. Minor deposits of serpentine, sericite schist, copper ore, and red iron oxide have been prospected. The obvious deposits of brown iron ore, together with some associated specular hematite, were mined out years ago, although a little ore was left in the workings. Moderately steady production of sienna reached a peak about 1930, then declined rapidly. Manganese mining passed through a relatively active period from the World War to 1931, but has subsided to a small but rather constant output for the Birmingham market. How-ever, the White Manganese Corporation has prepared for possible increased production by constructing a new washer capable of handling about 300 tons of ore per day. Principal activity in the district proper has centered for some years in the production of barite and magne-sian limestone.

Jan 1, 1940

By William L. Fink, L. A. Willey

Since so many different curves have been published for the solid solubility of zinc in aluminum, it seems desirable to definitely establish the correct curve by two or more independent methods. The curve published in part I1t was based entirely upon X-ray measurements because the other methods employed at that time were not satisfactory. The present paper (the seventeenth of this series on high-purity aluminum alloys) describes the determination of the solid solubility of zinc in aluminum by the measurement of electrical resistivity at temperature and by microscopic examination. Since the publication of our part I in 1932, an investigation of the solubility relations in the aluminum-zinc system has been reported by Schmid and Wassermann2, who obtained their solubility results from lattice-parameter measurements on heat-treated and quenched specimens. The diagram that they published is shown in Fig. 1. In this investigation they also found by X-ray measurements that the parameter of the gamma phase changed continuously with zinc content and at such a rate that it would be identical with that of the beta phase at 60 atomic per cent zinc. It was concluded therefore that the beta and gamma phases, from the point of view of structural relationship, are one single phase. They also suggested a gap of immiscibility between 270" and 350" C. The complete boundary in this region could not be determined satisfactorily by the method employed and therefore was not shown in their diagram. Aluminum-zinc Alloys Materials Used.—Electrolytically refined aluminum3 was used in preparing the alloys for the work reported in this paper. Chemical analysis showed the following impurities: 0.004 to 0.005 per cent silicon, 0.006 to 0.008 per cent iron and 0.005 to 0.006 per cent copper. Also,

Jan 1, 1936

By Persifor Frazer

The '(author's edition" of the following paper, "subject to re vision," was received by him, and copies sent to Professor Geikie and others about two weeks before the date of the meeting at which it was to be read. A telegram, and subsequently a letter (both of which unfortunately arrived too late), apprised the present writer that the Director General objected to certain views ascribed to him as the reverse of those which he really held. These views, however interesting, had no very important bearing on the object of the fol lowing notes, which, as must be evident, are devoted to the conside ration of the close analogies between the Welsh and American rocks. Without being able, therefore, to account for the circumstance which Professor Geikie has mentioned, it is thought better in the present revised edition to omit all allusion to Professor Geikie, or Mr. Peach, or their views, except in this place, where I desire to thank them for their courtesy during the time which I had the pleasure of spending in their society. It appears sufficiently throughout the body of the paper that the writer had not the slightest intention of entering the controversy, which was about to commence, concerning the proper horizons of the St. David's rocks, for many reasons; and amongst others because he did not feel that a sojourn of a few days in a difficult region, which had been already studied by many of the foremost geologists of England, would warrant him in adding to the literature on the sub ject. The discussion of the analogies between these rocks and those of the Eastern Appalachians, which he has studied for twelve years, of which eight were spent in the service of the Second Geological Survey of Pennsylvania, was much more to his taste as it was more within his ability, and if he has added anything to the evidence of these analogies, the paper, however imperfect, will not have been written entirely in vain. Right or wrong, he assumes the entire responsibility of what follows.

Jan 1, 1883

By F. F. Schmidt, H. R. Ogden, E. S. Bartlett

ThE solubility of carbon in tantalum has been reported to be very low at temperatures below 1500 C,1'2 increasing to at least 0.02 wt pctl at the eutectic temperature of 2800°C. The solubility limits at low temperatures were based on metallo-

Jan 1, 1963

By Joseph Kuti

Longwall mining is the term used for the underground extraction of a wide and deep panel of coal. Such a panel may be blocked out by one or more entries on either side ("head" and "tail") of a longwall face. If all the entries are pre-driven, the panel extraction is termed longwall retreat mining. With one exception, all the longwall faces in the United States are of this type.1 Prior to the general decline in the rates of production with Continuous Miners, the development of the multiple entries generally kept ahead of the longwall extraction rate. This is no longer the case: longwall extraction rates far exceed the rate of development. In addition to this problem, in newly established mines, the development of a haulage and bleeder system based on multiple entries results in a lead-time of three years or more before longwall mining can be applied.

Jan 11, 1979

[Murray and Renard: chondres on ocean floor, XLI, [155]. Musconetcong Iron Works, Stanhope, N. J., blnst furnace, XL, 467. MUSSEN, H. W.: Discussion on The Bogoslovsk Mining Estate, XXXIX, 897. death, XLIII, [Ixxvi]. Muzo, CoIombia: emerald deposits, LV, 910. emerald mine, XXXIX, 317. minerals, LV, 925.]

Jan 1, 1918

By George D. Dub

INTRODUCTION OWENS LAKE is at present a source of important nonmetallic minerals, sodium carbonate (soda ash, Na2CO3); sodium sesquicarbonate (trona, Na2CO3.NaHCO3.2H20) and borax, (Na2B407.10H2O). Owens Lake is a closed basin in the southern part of Inyo County, California, at the southern end of Owens Valley, east of the Sierra Nevada Mountains and west of the Coso and Inyo Mountains. Broadly considered, it is in the Great Basin area, but at no time was it a part of Lake Lahontan. CLOSED BASINS Closed basins are phenomena of arid or semiarid regions where outflow is considerably less than inflow and where accordingly soluble salts concentrate in residual liquid. When inflowing waters originate in areas where the rocks are predominantly marine sediments, the residual basin liquid is primarily a chloride brine; if the rocks are largely igneous, the residual brine tends to be alkaline containing carbonates, and sometimes borates as well. Since normally, both types of rocks occur in regions contiguous to closed basins, residual liquids do not often fit into the two broad divisions mentioned. No two residual brines are exactly alike, just as no two ore deposits are exactly alike. Even out of the same closed basin, it is possible to get widely different analyses of liquids since underground and surface flows, as well as local evaporation rates and other conditions might have a marked influence on residual-liquid compositions. At Searles Lake, The American Potash and Chemical Corporation is building a plant to process a lower-level brine which is considerably higher in sodium carbonate and borax, and lower in potassium chloride, than that company has processed for many years. F. W. Clarke1 has classified waters of closed basins as follows: I Chloride type; largely sodium chloride (NaCI) and of oceanic type, such as Great Salt Lake. Related is the Dead Sea, a bittern residue of magnesium, potassium and sodium chlorides. 2. Sulphate type; largely sodium sulphate (Na2S04) with considerable sodium chloride such as Sevier Lake, Utah; Laramie Lakes, Wyoming; Dale Lake, California. 3. Carbonate type; high in carbonates and fairly high in sulphates, such as Moses Lake, Eastern Washington; and the Nebraska Potash Lakes. 4. Carbonate-chloride type; lower in carbonates than type 3 and about equally rich in sulphates, such as Pyramid Lake, Nevada. 5. Sulphate-Carbonate type; quite high in sulphates and carbonates, such as Pelican Lake, Oregon. 6. Triple type; considerable quantities of carbonates, sulphates and chlorides

Jan 1, 1947

By P. R. Sperry, M. L. Holzworth, P. A. Beck

The basic work of Z. Jeffries 1,2,3 has long ago established the main features of grain growth in the presence of a dispersed second phase. Working with sintered specimens of initially fine grained tungsten, to which various amounts of thoria had been added, Jeffries found that grain growth was inhibited, that is, practically prevented, up to a certain annealing temperature. When this temperature, which increased with the thoria content, was exceeded, extremely large grains developed abruptly from the fine grained matrix. such a a temperature" was later found by Gross-mann~3,14 in certain types of steel, while ~~i~ showed15 that in other steels grain growth was gradual, without inhibition and abrupt coarsening. Later work demonstrated the connection between coarsening and aluminum additions. The viewpoint that the direct cause of inhibition and coarsening in aluminum killed steels is a fine dispersion of aluminum oxide21 appears to be held quite generally, although some doubts have been voiced even very recently, 20 In steels with Ti additions the titanium carbide phase is considered responsible for the inhibition effects found.20 The coarsening temperature increases with the titanium content. That coarsening may occur, as a result of, certain heat treatments, even in low carboil rimmed sheet steel, was shown by Samuels. He also detected coarsening in a steel ingot of similar composition, after giving it the same heat treatment as that used by him for the sheet material. In this instance the identity of the inhibiting phase has not been determined. However, Tangerding found23 that even the few small carbide particles, which occur in carbonyl iron, have a very marked inhibitive effect. As a result of an oxidizing anneal at 850°C, large grains begin to form at the surface of the carbonyl iron specimen, and gradually grow inward as the subsurface oxidation of the carbide particles progresses and eliminates the obstruction. The carbide particles Can be removed also by annealing in hydrogen, with similar results. But if the oxidizing anneal of 10 hr at 850°C in air is followed between in hydrogen for 75 hr at the Same temperature, grain growth is more hibition usually the whole specimen is transformed into a single crystal (approx. 1.5 cm X 5 cm). The reversed procedure, that is, hydrogen annealing followed by oxidizing annealing leads to smaller grains. Tangerding arrived at the logical conclusion that there must have been in his specimens some additional obstruction to grain growth hibition from a minor impurity, other than carbon. It seems likely that this obstruction was caused by an oxide formed during the oxidizing anneal and gradually reduced rtain the subsequent hydrogen-annealing. Other instances of grain growth inhibition of varying severity, associated with a dispersed second phase, have been described by several authors. Notable examples: lead with 0.06 pet Cu or Ni,24 cartridge brass with 0.12 pct Cr,25 or with up to 0.15

Jan 1, 1949

By J. A. Jargon, H. K. van Poollen

Flow of slightly compressible fluids through porous media can be described by linear equations. Many mathematical solutions- are available for the boundary conditions of constant terminal pressures or constant flow rates, or a combination of both. Various techniques of formation evaluation use drastic rate changes, such as sudden shut-in. Other methods require that the well be produced at a constant rate. In practice, one is not always able m fulfill these rigid requtirements. This report shows a methor1 by which varying-rate data can be converted to a constant-rate pressure response, called the unit response function. After obtaining the unit response function, one may analyze it, using techniques described in the literature. The method uses tile principle of superposition. Necessary data is a time history of pressure and production. If pressure changes and/or rate changes are very drastic, the unit response function becomes erratic and oscillates The erratic and oscillating results are obvious, and under those circumstances, no answer can he obtained. It appears, however, that a response function without oscilla-tion will not contain any appreciable errors —- one gets either good results or no results. This report includes a mumber of examples of converting constant-rate data to constant terminal-pressure data and vice versa. In addition, a number of field-test applications are given. This method should be useful in converting mathematical solutions from one boundary condition to another. It already has proven useful in converting varying-rate data to constant-rate conditions. INTRODUCTION Pressure drawdown tests are performed on production wells to determine various reservoir characteristics, including permeability, distances to discontinuities, reservoir continuity and wellbore conditions. An ideal drawdown test is performed at a constant production rate with pressure observation during the drawdown period. A typical drawdown curve for a constant rate of production is shown in Fig. 1. In practice, a constant production rate cannot always be maintained. Fig. 2 shows a pressure drawdown curve for a varying rate. Usual methods of analysis are not applicable to tests such as this. It is, therefore, necessary to convert the varying-rate data somehow, before usual analytical techniques can be applied. This report describes a method of obtaining a response function. A response function can be defined as the relationship between pressure and time for a well producing at a constant unit rate. Such a response function can be analyzed by the usual analytical techniques. Hutchinson and Sikora' first approximated a resistance function (response function), and by applying the superposition principle, pressures were calculated using the varying rates. If no match was obtained, adjustments were made to the response function and the closer approximation was used again in an attempt to match calculated and observed pressure behavior. If a good match was obtained: the response function was then used to extrapolate the future aquifer behavior.

Jan 1, 1966

By J. W. Pamplin

SOME 40 miles east of Tampa is the center of the Florida pebble phosphate deposits. These are of Pliocene age and consist of several members of the Bone Valley formation.' Physically the phosphate-bearing formation, locally called the “matrix," varies in thickness from nothing to about 25 ft., usually averages 10 ft., and consists mainly of clay, quartz and phosphate pebble, the latter particles varying in size from colloidal to one inch diameter. The pebbles range in color from dark gray, through white, to cream, and in hardness from that which must be broken with a hammer to that which can be scratched with the fingernail. They assay from 66 to 80 per cent bone phosphate of lime (called "B.P.L." in the trade) or tricalcium phosphate (Ca3P2O8) and are secondary apatites. They form from 15 to 50 per cent by weight of the matrix. Over the matrix lies a varying thickness (5 to 40 ft.) of overburden composed of quartz and clay. Briefly, mining consists of two operations2 in open pits about 200 ft. wide by ½ mile or more in length. In the first step overburden is removed by large electric draglines at the rate of about 700 cu. yd. per hour. This is followed closely by hydraulic mining of the matrix at the rate of about 300 cu. yd. per hour. This matrix yardage is moved from an improvised sump in the floor of the pit to an ore-dressing plant, some- times a mile distant, by one, two or three "pit-cars" (pumping units) working on a 12-in. pipe line called the "rock line" to distinguish it from the high-pressure water line feeding the hydraulic giants, which is known as the “hydraulic line." This 700 yd. of overburden and 300 yd. of matrix-1000 yd. in all- amounts to about 1500 tons of material moved each hour. The over- burden is dumped into the mined-out pit alongside the pit being mined. The matrix moves to the ore-dressing plant at the rate of about 7 ½ long tons in 4000 gal. of water per minute-a ratio of approximately one to two by weight, or one to six by volume. This constitutes the "mill heads," but in the pebble district it is called the "matrix."

Jan 1, 1938

By R. E. Somers

1. INTRODUCTION 1. Location, Topography, and Climate The Burro Mountains are located in the southwestern part of New Mexico, in Grant County. The group is made up of two distinct moun-tain masses, known as the Little Burros and the Big Burros, the former lying about 6 miles southwest of Silver City-, and the latter about 9 miles farther in the same direction. They are separated by the valley of the Mangas River, a tributary of the Gila, and a stream only in name, except after a heavy down-pour of rain. . The Little Burros attain an elevation of 6,625 ft. above sea level, and the Big Burros 8,054 ft., with the surrounding country averaging about 6,000 ft. To the south of these mountains stretches the desert plain, while to the north are the more frequent elevations of the mountainous country.

Jan 5, 1915

By D. L. Albright, R. W. Kraft

Solidification experiments were conducted with the objective of testing the theory of eutectic colony formation. Appropriate control of variables in tests on a series of high-purity aluminum-copper specimens of eutectic composition resulted in the observation of three types of eutectic microstructures, these being a unique structure consisting of lamellae essentially parallel to one another, a banded structure, and the colony structure. Lamellar faults, which are morphologically similar in many respects to edge dislocation models in crystals, produced a complex substructure in these specimens. SOLUTE rejection at the advancing solid-liquid interface of a unidirectionally solidified single-phase metal can cause the liquid immediately in front of the interface to become constitutionally super-cooled below the equilibrium liquidus temperature. Constitutional super-cooling occurs if the solidification rate, R, is too rapid, or if the thermal gradient in the liquid at the interface, G, is too low. 1 This constitutionally supercooled layer in turn stabilizes a cellular rather than a planar interface.&apos; A similar cellular interface has been observed when lamellar and other types of eutectics were unidirectionally solidified, and it has been shown that the cellular interface led to the formation of eutectic colonies.&apos; The lamellar structure is fan-shaped at the edges of colonies (which correspond to valleys or grooves in the cellular interface) because the lamellae grow normal to the local interface. One of the possible mechanisms which might cause the formation of the cellular interface, in the case of solidifying eutectic alloys, is constitutional supercooling of the liquid with respect to a third component rejected by both phases of the eutectic.3,4 On the basis of the analogy between the solidification of single-phase metals and binary eutectics, a eutectic alloy should solidify with a planar interface if the ratio of G/R is sufficiently high to compensate for any impurity which might be present and causing constitutional supercooling. The fan-like microstruc-ture of eutectic colonies should not occur under these conditions and the lamellae should be parallel to one another and to the solidification direction for extended distances. The experiments conducted in this investigation were designed to test these ideas. Following a resume of the experimental procedure, the various microstructures observed during the study are described, and their relationship to the growth conditions which produced them is discussed. EXPERIMENTAL PROCEDURE The eutectic between an aluminum solid solution and 0 phase (approximate composition CuA12) was chosen for this work for the following reasons: it was known that a lamellar structure forms, the eutectic temperature is low enough to facilitate experimental work, and the components can be procured commercially in a very pure form. High-purity copper (est. 99.999 pct Cu, obtained from National Research Corp.) and spectrographic aluminum rods, having impurities other than copper estimated to be Zn-15 ppm, Mg-10 ppm, Fe-3 ppm, Na-2 ppm, Cd-1 ppm, and Mn < 1 ppm, were melted in a stabilized zirconia crucible in a vacuum induction furnace at a pressure of 10 pof Hg. The melt was superheated to about 1000°C to assure mixing, cooled to 780°C and cast into an investment mold which yielded sixteen cylindrical specimen blanks 1/2 in. in diam and 5 1/2 in. long. The casting was allowed to solidify under vacuum. This master heat had an analysis of 32.6 wt pct Cu and 67.4 wt pct A1 by difference. The cylindrical specimen blanks were remelted and solidified unidirectionally in an apparatus illustrated schematically in Fig. 1. An RF induction coil heated

Jan 1, 1962

By H. H. Uhlig

Soon after general use of stainless steels began, it was observed in practice that certain combinations of factors tended to induce corrosion by pitting. For most applications this was a serious drawback, not so much because the structural properties of the metal were impaired but because of the rapidity with which heavy sections of the alloys were penetrated by small elongated pits. These pits seemed to initiate readily in oxidizing metal salt solutions like ferric chloride and in chloride solu-tions like sea water. It was observed that in sea water pitting was more frequent in stagnant or polluted waters than in highly aerated, moving waters. The steels in these chloride solutions were observed to be sensi-tive to long contact with material such as sand grains or attached bar-nacles. At points of attachment or contact it was not uncommon to discover initiation of corrosion. Pits once begun at contact faces were observed to grow rapidly, usually elongating phenomenally in the direc-tion of gravity until the metal was perforated. Hydrochloric acid and other nonoxidizing acids, on the other hand, were observed to corrode stainless steels generally; the weight losses often were higher, but the penetration less than for the pitting type of corrosion. The causes of pitting, a type of corrosion recognized as character-istic not only of stainless steels but of many additional metals and alloys, are important in corrosion studies. A possible explanation bears prac-tical significance, for once it is known why pits begin where they do and continue to grow after initiation, intelligent direction can be given to diminishing corrosion. This can be done either by some alteration in the composition and treatment of the alloy or by some alteration in the environment. It appears foremost in importance to discover the nature of pit foci, for if initiation of pits can be discouraged their growth will be no longer a factor to be considered. In a multi-component alloy containing many impurities normal to production of such an alloy, each of which may play a part in pitting, and whose corrosion resistance is sensitive to heat-

Jan 1, 1940