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By F. C. Frischknecht

Most early development and application of electromagnetic prospecting methods took place in Scandinavia, where geological conditions favor their use. In other parts of the world these methods have aroused cycles of interest, but in Scandinavia they have been used continuously and successfully since the 1920's. Electromagnetic methods may be classified into two general groups. One group includes methods in which the source of the electromagnetic field remains stationary while the receivers are moved about to explore the area. The other includes procedures in which the energizing and receiving systems are moved together. Other classifications could be based on the size of the energizing source, the particular components of the electromagnetic field which are measured, or the mode of transporting the equipment. The difference between fixed-source and moving-source methods, however, is of such great fundamental importance that it will be emphasized in this discussion. FIXED-SOURCE METHODS Essentially, a fixed-source method consists of the measurement of electromagnetic fields about the source. The mutual coupling between the source and the earth is constant, but the mutual coupling between the receiver and the earth (unless the earth is homogeneous) and also between the source and the receiver changes at each station. The results are usually normalized by relating the field data to the calculated free space or primary field. Turam and Radio Reference Signal Methods: The turam or two-frame* (see Fig. 1A) is probably * Turam means two-coil. the most common fixed-source method. The energizing source is an insulated cable grounded at both ends or formed into a large rectangular loop. Measurements are taken along a traverse at 5 to 50-meter intervals using two small receiving coils, the lagging coil being placed at the position previously occupied by the leading coil. The complex ratio (i.e., inphase and out-of-phase ratios) of the voltages induced in the two coils is measured. Operating frequency range is about 100 to 800 cps. In a typical turam survey a straight, grounded cable several kilometers long is laid out parallel to the probable strike of the ore deposits or conducting strata being sought. An area extending 1 or 2 km on each side of the cable, and within 1 or 2 km of the ends of the cable, is surveyed. Measurements are made at stations 5 to 25 m apart along traverses perpendicular to the cable. Measurements may be made along lines parallel to the cable to serve as base lines for the traverses or for other special purposes. Commonly the receiving coils are oriented with their planes horizontal so that only the vertical component of the field is measured. If additional information is required, one of the hori- zontal components may also be measured by orienting the coils with their planes vertical. In a modified turam technique developed recently for both ground and airborne measurements (Fig. 1B) the amplitude of the complex voltage induced in a single receiving coil is measured and its phase compared with that of a reference signal transmitted from the energizing system by a radio frequency carrier. Thus the un-normalized field is obtained directly, whereas with the turam method it is obtained by calculation from the ratios. The turam method and its modifications have a greater working depth than the other electromagnetic procedures used in ore prospecting. Under favorable conditions conductors have been located at depths of 200 to 300 m. A modified turam method with one of the electrodes grounded in the upper end of a plunging orebody was used to follow the extension of this body to a depth of 200 m beneath a layer of conducting schists. Straight grounded cables are usually preferred to insulated loops because they are easier to lay out and because they often make the method more sensitive. The greater sensitivity of a grounded cable is a result of ground return currents which may flow in the orebodies in addition to the eddy currents caused by induction from the current in the cable. Anomalies in the vertical field due to eddy currents are characterized by a correspondence between high values for the inphase component and positive out-of-phase components and/or low values for the inphase component and negative out-of-phase components. Also the inphase component may approach zero, but it does not become negative. In very long continuous conductors that are parallel to a grounded cable the effect of ground return currents may far exceed the effect of eddy currents. These ground return currents cause a lack of correspondence between the inphase and out-of-phase components and may cause negative inphase or anti-phase components. It becomes difficult to carry out the measurements and often difficult to interpret the results. Such results immediately suggest the presence of graphitic strata, however, since ore deposits are rarely extensive enough to accumulate sufficient ground return current to cause these results. A cable laid out perpendicular to the strike or an insulated loop is sometimes used in areas where graphitic schists and slates are present. Anomalies are then completely or almost entirely due to eddy currents and are easier to interpret. The measured voltage ratios are normalized by either subtracting or dividing by normal field ratios calculated from free space considerations. The normalized ratios are then plotted as individual profiles. When significant anomalies occur in the ratio measurements, the actual normalized fields are calculated by beginning with a measured or an assumed value for the field at a point near the cable and successively multiplying this value by the normalized ratios. There is a similarity between this process and a numerical integration of the ratio curve. Conversely, in many respects the ratio curve is similar to the first derivative of the field curve.

Jan 1, 1960

By D. S. Newton

Introduction Historically the production of zinc dust has been based upon residual and secondary zinc. Using horizontal retorts filled with diecasting scrap, galvanizers drosses and sweater billets, dust has been produced by condensation into static condensers on a 24 hour cycle. Although fairly flexible as regards input materials the process is not amenable to close control of the product, is labour intensive and unless carefully run can cause fume problems. With a steadily increasing demand for zinc dust of consistent properties and higher quality there is a demand for an improved method of manufacture in which dust can be produced continuously and which is capable of close control thus ensuring a minimum amount of oversize or unsaleable material. The Process in use in the works of Imperial Smelting Corporation (Alloys) Ltd. in England, and in Canada and Holland, satisfies the criteria stated above, and has proved to be easy to control with a minimum labour demand.

Jan 1, 1970

By O. P. Chisholm

Dross emerges from the blast furnace either with the lead through a lead well or by tapping from a forehearth or settler, but until a dozen years or so ago few dross reverberatories were used in western lead smelters because it was the usual procedure to circulate the dross from the drossing lead kettles back to the blast furnace. It was quite customary for lead smelters to produce matte in their blast furnaces, as this was the form in which copper could be collected, concentrated if necessary, and shipped to the copper smelters for further treatment. The main prerequisites for good matte formation arc., of course, a more or less definite amount of copper on the charge and sufficient sulphur. Such troublesome impurities as arsenic and antimony were ignored, in so far as possible, although they contaminated the bullion and thereby increased refinery costs. At the same time stocks of blastfurnace speiss containing gold, silver, lead and copper in addition to iron, arsenic and antimony, were being accumulated for want of a market to absorb them. As the dross was being fed back to the furnaces as rapidly as it was being produced, arsenic and antimony tended to build up until the arsenic could effect a combination with copper and iron and an alliance with lead, and the antimony a combination with copper and an alliancc with lead. Sulphur, being the most active agent in taking up the copper, left little of that element for the arsenic and antimony, so that on the whole a somewhat unsatisfactory metallurgy resulted. During this same period, certain lead plants were beginning to encounter trouble with zinc due to the replacement of crude ores of lot zinc content by concentrates containing high percentages of lead and zinc in sulphide form, the blast-furnace slags resulting from the smelting of such concentrates being characterized by a decidedly increased zinc content. It was soon realized that zinc plus sulphur was "poison" to a lead blast furnace and steps were taken to reduce the sulphur content,. At this stage some plants found that any substantial matte fall was out.

Jan 1, 1937

By David R. Mitchell, E. A. Reilly, G. R. Gardner, F. P. Lasseter

THE methods that may be applied to the treatment of slurries and water, as these are related to practical coal-preparation problems, are concerned essentially with the movements of solids suspended in water. It is assumed that there are no fundamental differences between the principles involved in the treatment of coal slurries and the phenomena encountered in general mineral-dressing practice, and the latter are-presented in some detail. Basic principles are correlated with present practice for both the anthracite and the bituminous coal fields, and methods are discussed which are designed to utilize best all the material subjected to treatment and suggest a sound approach to the solution of problems relating to the return of clear water to process or to streams. In order to approach the practical phases of the subject with sufficient understanding of the basic principles, it is necessary to discuss two types of phenomena that are applicable. The first is flocculation and the second is sedimentation. Descriptive matter is given covering the various methods and types of equipment employed to conduct these operations, with emphasis on their application to water and coal-slurry treatment. DEFINITION OF TERMS Definitions of terms are consistent with modern developments, and conform, in general, with their usage in mineral-dressing practice. Because of variations in coal-preparation methods, it is impossible to define a rigid upper limit of particle size for a coal slurry or sludge which will apply generally. Limits vary somewhat with the particular treatment method employed at a given plant. For purposes of definition, this limit is chosen as the particle size for which preparation methods such as Chance comes and jigs are usually dispensed with, and other methods, such as the Hydro-tator, tables, and froth flotation, are employed. Generally the limit will be 10 to 6 mesh.

Jan 1, 1950

By R. M. Brick

AN increased demand for information in regard to the effect of gaseous elements in steel has accompanied the recognition of the importance of grain size. Attempts to correlate grain-size characteristics with gas con-tent, particularly oxygen in solution or in the form of included metallic oxides, have not been universally successful. Certain definite effects of dissolved gases are recognized; specifically, the role of hydrogen in causing internal cracks or "flakes" and that of nitrogen in preventing excessive grain growth of ferritic chromium steels. When irregular behavior or properties are found in a well-known steel and no definite cause for the abnormality may be assigned on the basis of chemical and metallographic tests, dissolved gases are frequently blamed as the culprits. The solubilities of hydrogen1 and nitrogen2 in pure liquid iron are known but of the ternary systems, iron-alloying element-gas, only the Fe-Si-N3 and Fe-Cr-N systems have received attention and here the study was confined to liquid alloys. Krivobok4 published a curve show-ing the solubility of nitrogen in liquid Fe-Cr alloys but gave no informa-tion on the experimental procedure employed. The considerable experimental work reported on the Cr-N binary alloys has been reviewed by Hansen.5 It is generally agreed that the nitride CrN is a stable phase although the existence of nitrides within limited temperature ranges of stability, viz., Cr3N2 and Cr2N, has been disputed, Adcock6 and others7 have reported a eutectic between Cr and CrN at 1580°C., although the supporting evidence is not complete.

Jan 1, 1940

By C. N. J. Wagner, E. N. Aqua

The bee alloys of the terminal solid solution of rhenium in niobium were investigated by X-ray diffraclion methods. The analysis of the broadening of the powder pattern peaks from the niobium-rich alloys, cold-worked by filing, showed evidence for faulting on (211) planes. The alloys with larger rhenium concentrations were brittle, and fractured when filed. The analysis of the shapes of the diffraction profiles from powders produced by hammering with steel plates) of these brittle alloys indicated that the broadening was due predominantly to platelets bounded by clibe planes. This result was consistent with the Laue patterns from single-cleazlage facets which showed evidence for clearage fracture on {100} planes. The influence of faulting on the mechanical properties of face-centered cubic (fcc) metals and alloys, i.e., how faulting affects the various dislocation configurations in fcc metals, is well-known.' The important question is whether or not faulting occurs in body-centered cubic (bcc) metals and alloys, and, furthermore, if faulting does occur, to what extent it affects the mechanical properties. Theoretical calculations indicate that the stacking-fault energy is rather high in most bcc metals.2 The results of sev-eral studies using transmission electron microscopy have indicated that faults are present in well-annealed and lightly deformed bcc metals and alloys, such as tungsten,3 vanadium,4 and Mo-Re alloys.5,6 These faults, as have been observed, may be stabilized by the presence of interstitial (C,N,O) atom segregation to the extended dislocations. In addition, there is considerable X-ray diffraction evidence for faulting in bee metals,7-8 using the same techniques that were successful for the study of faulting in fee metals and alloys.7 This X-ray diffraction method is currently the only technique applicable for the investigation of faulting in metals with high stacking fault energies, i.e., when severe amounts of deformation are required to produce sufficient amounts of faulting to be detectable by X-rays. The thinned films of heavily deformed metals will become opaque in the electron microscope due to the high dislocation densities present. In a previous investigation of faulting8 in bee metals of group Vb and VIb, the authors observed that niobium was ductile when filed at room temperature, and showed the highest density of faults on the (112) family of planes. A niobium-base alloy system was therefore chosen to study the effect of alloying on the occurrence of faults in a bcc alloy. There is a large range of terminal solid solubility of rhenium in the alloys of the bee refractory metals. All of the Group VIb-rhenium alloys, i.e., Cr-Re, Mo-Re, and W-Re, exhibit solid solution hardening without loss of ductility.9 In fact, the ductility reaches a maximum for alloys with compositions near to the limits of solubility. This enhanced ductility has been attributed to the lowering of the stacking-fault energy in the alloy; i.e., the increased amounts of twinning provide an additional mode of deformation, resulting in the observed high ductility.' Because of this demonstrated effect of rhenium in bee alloys, it was decided to study a series of alloys of Nb-Re. Using the same X-ray diffraction methods as described in the previous investigation,' one is able to identify the possible causes of broadening of the powder pattern peaks, e.q., particle size, microstrains, stacking faults, and/or twin faults. The separation of these various contributions to the measured peak shape is accomplished by the Warren-Averbach analysis.7 I) EXPERIMENTAL PROCEDURE A series of seven bee solid solution alloys containing from 2.5 to 21.5 at. pct Re (remainder niobium) were prepared at the General Electric Research Laboratory. Buttons, weighing 25 g, were alloyed from electron-beam-melted niobium chips and random rhenium sheet by arc melting in a water-cooled copper crucible, under an argon atmosphere. The buttons were inverted and completely remelted to promote homogenization. The nominal alloy compositions are listed in Table I. Samples of the cold-worked alloys were obtained by filing to produce a powder for the X-ray study. Alloys too brittle to be filed were hammered with steel plates. The resultant filings or brittle impactings were screened through 150-mesh classifiers and compacted to the required shape for the diffractometer holder. The X-ray diffraction peaks were automatically recorded by fixed time counting at uniform 28 intervals, or by continuous registration with a ratemeter. In all cases, the (110)-(220) and (200)-(400) pairs of peaks and the (211), (310), (222), and (321) reflections were measured on a GE-XRD5 diffractometer using CuKa radiation with nickel filter or MoKct radiation and a LiF monochromator in the diffracted beam. The first part of the data reduction, completed with the aid of a series of programmed computations,10 was the analytical resolution of the Kol component of the diffraction profile. Subsequent computations were then made with reference only to the resolved Kol peak shape. These included the measurement of the

Jan 1, 1967

By E. C. Harder, D. F. Hewitt

Since early in 1916, when it became apparent that the steel industry of the United States could not depend for the duration of the war on several important foreign sources of manganese and might have to depend entirely on domestic ores, the U. S. Geological Survey, with the assistance of several cooperating organizations, has made a comprehensive investigation of domestic manganese resources. The work has included field studies in a number of states well as annual, quarterly, and monthly canvasses among operators concerning current and future production. In order that the interested public might have access to the important results of the studies, preliminary reports concerning the field work as well as periodic summaries of production were issued as promptly as possible. Although numerous summaries of production l2, l3, l4 have been prepared from time to time for the use of the several boards and committees responsible for the conduct of the war, it has been thought for some months that those engaged in the industry, as well as others, might be interested in a preliminary summary of the accumulated geologic and production data. The cessation of hostilities, in November, 1918, probably detracts from the usefulness of much of the material that is here presented, but apart from the historic interest in the performance of an important industry in war time, there is a possibility that some of the conclusions may be helpful to those who continue to exploit domestic deposits, as well as to those who wish to measure the country's independence in mineral supplies. Appropriate final geologic reports are being prepared by the geologists who did the field work. The present authors, having done but a small part of the recent field work, acknowledge with great appreciation the use of preliminary and unpublished reports and the cordial informal cooperation of the following geologists in the preparation of this paper: F. L. Ransome, G. W. Stose, F. C. Schrader, J. T. Pardee, E. L. Jones, Jr., H. D. Miser, Laurence LaForge, J. B. Umpleby, Arthur Keith, F. J. Katz, and E. S. Larsen, of the U. S. Geological Survey. Field work in Virginia was carried out in cooperation with the Virginia Geological Survey, T. L. Watson, State Geologist; in Georgia, with the Georgia

Jan 1, 1920

By Frederick N. Rhines, Robert F. Mehl

IT has been shown elsewhere1 that the data on the rates of diffusion in solid metals are fragmentary and in many cases unacceptable. As a result, relatively little is known concerning the factors determining rates of diffusion and the variations in these rates with temperature. The first form of Fick's law (equation 1 below), ‡ in which the diffusion coefficient D is assumed invariant with composition, has been recognized for many years as only an approximation. The differential equation representing the second form of Fick's law (equation 4 below) has only recently been integrated by Matano,2 and unfortunately only in cases where a full diffusion-penetration curve (concentration-distance curve) has been obtained can the Matano solution be applied. The proper analysis of diffusion data is thus confined to the data of Grube and Zedele and of Zedele.§ These data are essentially for one temperature alone and do not furnish any information on the variation of the activation heat of diffusion, Q, with concentration: no information exists on the variation of Q with concentration within a singles olid solution field. 11 Much of the argument concerning the properties of metals that determine D and Q has been drawn from data in which variations of the quantities with concentration are unknown, for these data have been taken from experiments that could not furnish this information. Speculation concerning the properties of metals that may be effective in determining D and Q on the basis of data in which the chosen D and Q values are averages over wide concentration ranges of values at particular concentrations, ranges often of 100 per cent, is likely not to be fruitful.

Jan 1, 1938

By George Sachs

THE process of recrystallization has not as yet been explained satis-factorily. Some definite conclusions could be drawn from recent investi-gations, such as, for example, that recrystallization is a process of nucleus formation and crystal growth 1and that the orientations of the nuclei correspond to some fragments of the original crystals, which have been considerably distorted during deformation.2 There are, however, a number of metals and alloys crystallizing in the face-centered cubic system, which form a particularly simple orientation if recrystallized as a sheet.3 Such a sheet is almost a single crystal with the cubic axes parallel to the rolling, transverse, and normal directions of the sheet. This preferred cubic or (100) orientation of the recrystallized sheet has been considered to be very different from the rolling structure of the same metals,4 but there are two reasons why this last supposition remains open to controversial discussion. The first reason is academic: In practically all cases except the one mentioned above, close correlations and similarities between rolling and annealing orientations have been observed; for instance, in iron and steel sheet.6 Secondly, no deformed metal actually forms a-simple orientation. In any thoroughly investigated case a number of different orientations and considerable scattering or deviations from the ideal orientations have been found., It is generally true that investigations on single crystals have shown that a definite orientation is approached in stretching or in compression of an originally undisturbed crystal.7 In the special cases, however, where the initial orientation was close to an important crystallographic direction that differed from the final "ideal" orientation, the resulting orientation changed very little by deformation, staying somewhere in the vicinity of the initial orientation." Such deviations

Jan 1, 1940

THE. extraordinary volume of work done in this period, and the multiplicity of subject matter, make a year-by-year historical account undesirable, if the account is not to be an assembly of unrelated fragments. We shall, instead, undertake to narrate the development in this period of each of the branches of the subject separately, hoping that their interrelations will be self-evident. There is a certain arbitrariness in the selection of subject matter in the following sections. The development of important engineering alloys-for example, high-speed steel-is disregarded, for it is the primary purpose of this account to relate the advances in ideas, the growth of the science of metals; other historical accounts relate these parallel advances. Nor are advances in techniques stressed, though occasionally the most important are noted; nor is the progress described in allied fields such as welding, cutting, etc.; for though these developments have very frequently made possible the advances herein related, they are far too numerous to recount in anything short of a ponderous volume. There is a more serious arbitrariness, however; it is not an easy matter to draw the boundaries of physical metallurgy, and some contiguous subjects have been omitted that perhaps should have been included, such as, for example, corrosion, gases in metals, the magnetic behavior of metals and alloys, and certain other fields in the physics of metals. REACTIONS IN ALLOYS--DIFFUSION Many of the reactions occurring in alloys proceed by the operation of the process of diffusion in the solid state: the annealing of mixed powders to form alloys, the homogenization of castings or forgings, the freezing of alloys, the treatment of clad metals, the loss

Jan 1, 1948

By J. L. Tokich, A. R. Troiano

INTRODUCTION SINCE 1921, when Hull' discovered that cobalt can exist in the face-centered cubic and hexagonal close-packed modifications, the transitions that occur in cobalt have been extensively studied. It is generally agreed that on heating the hexagonal lattice changes to the cubic structure at temperatures ranging from 400 to 500°C although considerable doubt exists as to the exact temperature. Data concerning the temperature of the transformation on cooling are much less concordant and their interpretation has not been satisfactory. The study is further complicated by the fact that many investigators have reported the existence of a high temperature allotropic change in the range 850 to 1020°C, at which the cubic lattice reverts to the hexagonal modification. The transition on cooling, which has been reported as occurring at various temperatures from approximately 400 to 100°C, is of particular interest. Troiano and Greninger2 have recently suggested and considered the possibility of allotropic transformations occurring in pure metals by a shear-type, diffusionless (martensite) transformation. The case of cobalt was specifically discussed and certain observations of previous investigators evaluated in terms of this type of transformation. Table 1 briefly outlines the methods and results of previous investigators of the transformation temperatures of cobalt. MATERIALS AND METHODS The major portion of this investigation was performed with cobalt sheet containing a total of 0.2 pct impurities with carbon present to the extent of 0.1 pct. After melting in an induction furnace under an atmosphere of hydrogen, the carbon content analyzed 0.03 pct. Some observations were repeated with hydrogen reduced cobalt compresses analyzing 99.9 pct pure. No significant variations in results were observed employing the as-received sheet, the remelted stock, or the cobalt compresses. Filings for X ray diffraction analysis were sealed in evacuated glass ampoules. Pyrex glass tubing was used for temperatures below 600°C and for higher temperatures clear fused quartz was satisfactory. After appropriate heat treatment at various temperatures, the specimen ampoules were furnace cooled, air cooled or quenched by crushing under distilled water. This allowed a range of cooling velocities from less than one degree C per sec to greater than 1,000°C per sec. X ray diffraction patterns were taken with a Debye camera and filtered characteristic cobalt K-alpha radiation. The proportion of the existing phases was roughly approximated by visual examina-

Jan 1, 1948

By Dr. O’Neil Thomas J., Donald W. Gentry

Pure gold was hidden in the quartz, they said, 'Twas proved by dreams and signs, and rods divining, By chemic tests, and spirits of the dead, In fact by everything-except by mining. " from R.E. White, "The Mining Town," Alta California, August 18,1873 Textbooks in mining engineering have traditionally covered ore reserve estimation and mine valuation in a single volume. Indeed, Examination and Valuation of Mineral Property by R. D. Parks (1957), having been the standard of the profession for over 20 years, is a classic example. However, the state of knowledge in these two fields has grown tremendously. Most mining engineering curricula now cover these topics in separate courses, and in practice, these tasks are usually performed by different individuals. Thus, this trend now suggests the need for separate, specialized publications rather than a single volume for both topics. Because of the separate development of the science of ore reserve estimation, it is important to state at the beginning what this chapter does not cover. It does not address in detail the design of sampling programs, sampling methods, or the processing of samples or sample data compilation. There are a number of suitable references available on these topics, including Peters (1978), Gy (1979), as well as the previously cited book by Parks. Furthermore, this chapter does not cover in any substantial detail either the traditional methods for using sample data to calculate ore reserves or the more recently developed geostatistical methods. The traditional methods are thoroughly covered by Popoff (1966) and more concisely by Barnes (1980). Among the more useful references for statistical applications in ore reserve estimation are Barnes (1980), David (1977), and Clark (1979). A thoughtful review of the entire science and art of ore reserve estimation is provided by King, McMahon, and Bujtor (1982). In spite of the fact that expansion of knowledge now calls for separate books on ore reserve estimation and financial evaluation, neither publication can ignore the important interrelationships between the two fields. In regard to this text, the unique and crucial role of ore reserves can not be omitted entirely; however, the field is now simply too extensive to treat here in any comprehensive manner.

Jan 1, 1984

[Note.—The paper of Mr. Hoffman on " Practical Results in the Magnetic Concentration of Iron-Ore " (page 602); that of Mr. Langdon on "The Use of Magnetic Concentrates in the Port Henry Blast-Furnaaces" (page 599); and those of Mr. Landis on "The Determination of Iron in the Tails from Magnetic Concentration " (page 609) and "Note on Sampling Iron-Ore" (page 611), were all prepared as contributions to this discussion.] The papers of Mr. Langdon and Mr. Hoffman were presented. W. H. Hoffman, Croton Mines, N. Y.: I will add a few remarks, by way of answer to inquiries for further details. The Croton Mines are particularly well located for cheap mining. The ore-bed is very large, and so lies in relation to the railway tracks of the Harlem and other railroads that a very large proportion of our mining for several years to come can be done above these tracks. The concentrating-mill is now 400 feet from where we are working in the quarry. In blasting we never remove less than 2500 tons at a blast,

Jan 1, 1892

By A. G. McGregor

IN THE Southwest a number of large steel chimneys discharge the gases from the copper smelting furnaces. Some of these chimneys show no deterioration after twenty years, others show serious deterioration after tour years service. A steel stack 20 ft. 7 ½ in. (6.3 m.) in diameter by 279 ft. (85 m.) high, Fig. 1, used for roaster gases only at the Calumet & Arizona Mining Co.'s plant at Douglas, Ariz., was lined to the top of the bell, 40 ft. (12 m.) from the base, with common brick placed on end, lime and cement mortar being used. Above the bell, the stack was lined with 4 by 4 by 8 in. (10 by 10 by 20 cm.) building tile, placed on end, making a lining 4 in. thick. The tiles were supported on angle-iron rings, riveted to the inside of the chimney shell about 15 ft. apart. The chimney was put into use in the latter part of 1913. Four years later, considerable of the tile lining had fallen out of place and mixed with the flue dust at the bottom of the chimney. About a year later, several . flattened and distorted sheets were noticed about 70 ft. below the top. An investigation showed that the thickness of these distorted sheets, which was originally ¼ in., had been reduced one half. One year later, or six years after the chimney went into use, several holes, a square foot and smaller in area, appeared near the flat spots mentioned. Soon afterwards, when the chimney was shut down for repairs, it was found that most of the tile lining for 125 ft. from the top had fallen out and that the steel shell was badly corroded; but where the lining remained in place the shell was undamaged. Many of the tile which had fallen out of place had become soft or flaky and crumbling, others were as hard as when placed. An analysis of the hard and soft tile is shown on p. 2. These tile were of a fireclay mixture, and were used instead of common brick on account of lower cost. The steel forming the upper 125 ft. (38 m.) was replaced, and a 4 ¼ -in. (11-cm.) lining of firebrick was laid from the bell to the top of the chimney. The brick were placed on end, wedges and keys being used. After each 8-in. course was set, keyed, and wedged tight, thin mortar -water, sodium silicate, and finely ground silica-was worked into the joints. The brick are supported on angle-iron rings, every 15 ft., in the same way as the tile.

Jan 1, 1921

By Arthur F. Colombo

The selective - deslime - flotation process developed by the Federal Bureau of Mines as part of its goal of maintaining an adequate supply of minerals to meet national economic and strategic needs is described. The operating parameters for the selective flocculation - cationic flotation of oxidized taconites from the western Mesabi range in Minnesota are discussed. Data from the operation of a 410 kg/hr (900 lb/hr) pilot plant employing reclaimed water are summarized for 2 types of oxidized taconites.

Jan 1, 1979

By Alan Morris

SEASON cracking of brass has received wide attention and there is a wealth of technical literature on the subject. Its causes are fairly well understood and means for its prevention are inexpensive and effective, .so that the frequency of failures from this source has diminished of recent years. But its sister phenomenon, the failure of annealed brass by reason of applied tensile stress plus a certain type of corrosion, has received less attention, though it has been responsible for occasional more or less troublesome cases of cracking of brass in service. The work described in the following pages was undertaken about two years ago to determine the relative resistance of various commercial brass mixtures to stress-corrosion cracking, and to learn something of the controlling factors. By stress-corrosion cracking we mean the cracking of brass free- from internal stresses by reason of applied tensile stress and simultaneous attack by certain corrosive agents. Rogers,1 in discussing a paper by Hatfield and Thirkell, says : "He had also applied a solution of mercuric salt to tensile test pieces of brass whilst they were under stress in the testing machine. At very moderate stresses such test pieces cracked, and very readily broke." Moore, Beckinsale and Mallinson2 subjected test pieces to simultane-us corrosion and tensile stress. In order to determine the minimum stress detectable in brass by the mercurous nitrate test, tensile samples were placed under stress and treated with mercurous nitrate solution. They found that brass stressed below a minimum did not crack.

Jan 1, 1930

By J. W. Halley, G. L. Plimpton

BECAUSE of the two distinct stages in the solidification of rimmed steel, segregation in the rimmed ingot is more complex than that in the killed or semikilled ingot. In the earlier stage, chemical reactions, resulting in evolution of gas and vigorous stirring of the metal, effect a degree of negative segregation unique to rimmed steel. The composition of this zone constitutes the principal quality advantage of this type of steel. In the later stage of solidification, after the evolution of gas has ceased, the segregation follows the general pattern of a more completely deoxidized steel. However, the composition of the liquid remaining after the first solidification stage varies markedly from that of the original melt, some constituents having been partially removed as reaction products while the concentration of others has been intensified by rejection from the metal solidifying in the first zone. The aim, from the standpoint of segregation, in rimmed steel of high quality is to effect a maximum negative segregation in the rim zone without excessive concentration of undesirable elements at the center of the ingot. To achieve this aim, the composition of the melt may be varied and the furnace and pouring practice may be adjusted within certain limits. It is the purpose of this study to discuss segregation in rimmed steel from the standpoint of the mechanisms that produce it and to survey the phases of open-hearth practice that influence those mechanisms. MECHANISMS PRODUCING SEGREGATION The mechanisms that determine the degree of segregation in the rimmed ingot are closely interrelated, making it difficult to select the primary factors and to determine a satisfactory order for presenting them. For instance, the question of sulphur segregation is relatively simple, since sulphur is not directly involved in chemical reactions in the ingot; but its concentration in the rim zone is dependent not only on its original analysis in the melt, its segregation coefficient, and the freezing rate, but also on the rate of its removal from the impure film on the solidifying surface. This washing action involves all the factors (such as freezing rate, the carbon-oxygen product, pressure, etc.) that determine the rate of gas evolution and hence the efficiency of film removal. Sulphur distribution between the rim and core is affected by the volumetric ratio between the two zones, and its segregation in the core is a function not only of the freezing rate of the core but also of all the foregoing factors that determine its concentration in the metal when solidification of the core starts. To simplify the presentation, it is proposed to treat the mechanisms affecting segregation independently in this section, reserving a discussion of their over-all effects for the section in which actual segregation data are given. The factors affecting segregation will be treated in the following order: (I) differential solidification, (2) removal of constituents as

Jan 1, 1944

By E. R. Parker, C. F. Riisness

That grain size has a great effect on the mechanical properties of metals has been recognized for a long time. Bassett and Davis1 in 1919 did excellent work in determining the effect of grain size on the hardness of brass. About the same time Jeffries2 and Sykes3 ascertained the effect of grain size on the strength and ductility of several metals at temperatures ranging from 80°K. to their melting points. When creep was recognized as an important property of metals, those engaged in the study of this property tried to determine the effect of grain size4-9 on creep rates. Unfortunately, most of the investigations were conducted on only two grain sizes, often designated simply as "fine" and "coarse." It is well known that at high temperatures coarse-grained test bars creep less than fine-grained bars. The relation between grain size and size of test bar, however, has been frequently overlooked. In his early work, Jeffries2 showed that the number of grains in the cross section has a more important influence on the properties of the material than the actual grain size. More recently Hanson and Sandfordl0 and Pell-Walpole,ll in their measurements of the creep and tensile properties of tin, tested a wide range of grain sizes and correlated the grain size with the strength. Hanson9 later established the relation between the number of grains in the cross section and the creep rate. At high temperatures, generally a coarsegrained structure is considered superior in creep to a fine-grained structure, but it is evident that for a given bar size continuously increasing the grain size will

Jan 1, 1944

By C. F. Riisness, E. R. Parker

That grain size has a great effect on the mechanical properties of metals has been recognized for a long time. Bassett and Davis1 in 1919 did excellent work in determining the effect of grain size on the hardness of brass. About the same time Jeffries2 and Sykes3 ascertained the effect of grain size on the strength and ductility of several metals at temperatures ranging from 80°K. to their melting points. When creep was recognized as an important property of metals, those engaged in the study of this property tried to determine the effect of grain size4-9 on creep rates. Unfortunately, most of the investigations were conducted on only two grain sizes, often designated simply as "fine" and "coarse." It is well known that at high temperatures coarse-grained test bars creep less than fine-grained bars. The relation between grain size and size of test bar, however, has been frequently overlooked. In his early work, Jeffries2 showed that the number of grains in the cross section has a more important influence on the properties of the material than the actual grain size. More recently Hanson and Sandfordl0 and Pell-Walpole,ll in their measurements of the creep and tensile properties of tin, tested a wide range of grain sizes and correlated the grain size with the strength. Hanson9 later established the relation between the number of grains in the cross section and the creep rate. At high temperatures, generally a coarsegrained structure is considered superior in creep to a fine-grained structure, but it is evident that for a given bar size continuously increasing the grain size will

Jan 1, 1944

By E. S. Greiner

STUDY of the plasticity of germanium or other semiconductor crystals affords unusual opportunities to extend our knowledge of deformation mechanisms. Crystals are available having extraordinary perfection and very high purity. They deform by slip on the systems {111} <110>,1-3 as do crystals of the simple face-centered-cubic structure. Dislocations generated in them during slip are easily revealed in the form of etch pits on either (111) or (100) surfaces.4,5 This fact alone makes possible more detailed studies of mechanisms than is usually the case with metals but, even further, the effect of deformation on their electrical conductivity is very large compared with metals. This comes about not only because the mobility of the charge carriers is reduced, as in deformed metals, but also because the number of these carriers is greatly altered. This latter effect seems closely related to the formation of both line and point imperfections during deformation and thus provides a needed tool for the study of the kinds and distributions of these imperfections. Other investigators have deformed germanium at elevated temperatures by bending,1, 6-8 compres-sion,6, 0,10 tension,2,3,6,11,12 torsion,23 and indentation." Wang and Alexander" have also reported successful indentation at room temperature. Dislocation etch pits consequent to deformation have been observed and studied.7,8,10,18,14,20 The experiments to be de- scribed here include principally the compression and the subsequent annealing of germanium with concomitant studies of etch pits, microstructures, and electrical properties. Both single crystals and heavily twinned specimens were used. Some indentation studies are included. Experimental Methods Plastic compression was effected in the apparatus shown schematically in Fig. 1. It consists of two tantalum platens contained in a helium atmosphere and so arranged that pressure can be applied by a hydraulic press. The specimen between the platens is heated by the surrounding furnace. The specimen is usually a small crystal cube about 0.30 in. on an edge. A control specimen is always inserted so, that it is subject to the same thermal cycle as the one being deformed. This serves to detect any impurity contamination that might accompany the thermal treatment. For high temperature work, where such impurity contamination often occurs, the specimens were first plated with gold whenever subsequent electrical properties were to be determined. This method" is effective in preventing significant contamination of germanium up to temperatures at least as high as 750°C, as evidenced by the constancy of the electrical conductivities of control specimens subjected to the same heat treatments. The total range of temperature used for deformation was from 375°C, the lowest at which significant flow was observed, up to 900°C. Microscopic examination was made after mechanical and chemical polishing and etching. Dislocation pits were revealed with CP-4 etchant by the tech-

Jan 1, 1958