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By Andrew Mayer

EARLY in 1942 National Lead Co. was requested by the War Production Board to construct and operate a plant for the Government to produce magnesium by the ferrosilicon process which had been developed by Dr. L. M. Pidgeon in the laboratories of the Canadian National Research Council. A contract with the Defense Plant Corporation was concluded in May 1942 and Magnesium Reduction Co., a wholly owned subsidiary of National Lead Co., was formed to carry out this project. The capacity of the plant was rated at 10,000,000 lb. of magnesium per year, equivalent to an average production of about 14 tons per day. THE PROCESS The process, in brief, is as follows: The raw materials are dolomite and ferrosilicon, 75 per cent grade. The dolomite is calcined, the calcine and ferrosilicon are ground and mixed and the mixture is briquetted. The briquets are charged into tubular retorts of chrome-nickel steel set horizontally in a furnace with the open ends projecting outside the front wall. The retorts are then closed and evacuated. Magnesium is liberated according to the reaction 2(MgO, CaO) + Si = 2Mg + 2CaO, SiO2 It is distilled from the charge and condensed on a removable sleeve in the throat of the retort. Sodium and potassium, if present, are also liberated, distilled and condensed on a "sodium condenser" in the end of the retort. At the expiration of the distillation period the retorts are discharged and the cycle of operations is repeated. For the rated daily capacity of ±. tons of magnesium there are required approximately 170 tons of dolomite, equivalent to about 85 tons of calcine, and 16.5 tons of ferrosilicon. The retort residue, a bulky powder which at present is waste, amounts to about 87 tons. CHOOSING THE SITE The investigation to select the location of the plant was conducted by the Research Laboratories of National Lead Co. This work included geologic and economic surveys of a number of districts, examination of dolomite samples by chemical, spectrographic and petrographic methods and large-scale tests of dolomite from several of the more promising localities. In the last-named tests 2-ton samples were put through the ferrosilicon process in the pilot plant of the Canadian National Research Council, under the guidance of Dr. Pidgeon. The conclusions drawn from the investigation, in regard to the quality of dolomite to be used in the ferrosilicon process, were: First, the dolomite should contain not less than 21 per cent MgO

Jan 1, 1944

By J. S. Johnson, W. C. McCulloch

ALL phases of plant operation must be synchronized so that the number of interruptions in the flow of material may be reduced to a minimum. In the majority of plants operating under a labor agreement, time lost during the operating shift cannot be made up with overtime. With the work week restricted to 35 hr., the ratio of productive time to total time justifies extra effort in keeping the plant operating at capacity during the productive shift. This does not apply when central plants with adequate storage are operated by multiple shifts. In such installations the problems become similar to those of any factory or mill where added units parallel circuits, or excess capacity serve to maintain the average production during intervals of maintenance shutdown. These plants, by special agreement, may run continuously, barring mechanical interruptions. The control of plant operation is in those procedures that are practiced to obtain from the run-of-mine product a high recovery of clean coal products to meet adopted trade standards and consumer specifications at the lowest possible cost. Correlation of all factors for continuous operation requires more than mechanical perfection in the plant. The run-of-mine coal must be delivered to the preparation plant without delays and the clean coal and refuse products taken away. Power supply and water requirements must be adequate. Signal systems must be established for emergency stops and to facilitate resumption of coal flow. ORGANIZATION Probably the most important item for successful operation of a preparation plant is a capable organization interconnected with the mine organization. A typical organization chart for companies operating in the Pennsylvania anthracite region is shown in Fig. 1. The breaker foreman is in direct contact with the plant preparation operation and reports to the outside foreman, who, in turn, reports to

Jan 1, 1943

By J. S. Johnson, W. C. McCulloch

All phases of plant operation must be synchronized so that the A number of interruptions in the flow of material may be reduced to a minimum. In the majority of plants operating under a labor agreement, time lost during the operating shift cannot be made up with overtime. With the work week restricted to 35 hr., the ratio of productive time to total time justifies extra effort in keeping the plant operating at capacity during the productive shift. This does not apply when central plants with adequate storage are operated by multiple shifts. In such installations the problems become similar to those of any factory or mill where added units, parallel circuits, or excess capacity serve to maintain the average production during intervals of maintenance shut- down. These plants, by special agreement, may run continuously, barring mechanical interruptions. The control of plant operation is in those procedures that are practiced to obtain from the run-of-mine product a high recovery of clean coal products to meet adopted trade standards and consumer specifications at the lowest possible cost. Correlation of all factors for continuous operation requires more than mechanical perfection in the plant. The run-of-mine coal must be delivered to the preparation plant without delays and the clean coal and refuse products taken away. Power supply and water requirements must be adequate. Signal systems must be established for emergency stops and to facilitate resumption of coal flow.

Jan 1, 1943

By M. R. Geer, H. F. Yancey

INTRODUCTION The maximum yield of washed coal and the required ash and sulfur contents are the only performance factors of direct, immediate interest to any operator. Yet since the turn of the century coal preparation engineers have repeatedly sought more sophisticated performance criteria that could be used to draw comparisons between different cleaning operations and to permit generalizations about types of cleaning equipment or kinds of coal. Proliferation of efficiency formulas resulted. Hardly a year goes by, and certainly not an International Coal Preparation Congress, without the introduction of some new formula or some new concept of an existing criterion. This is merely the usual quest for improvement, because the performance criteria available today, although highly useful, are imperfect. Moreover, they are not as widely understood as they might be. The First International Coal Preparation Conference, which was held in Paris in 1950, accomplished a great deal toward establishing uniformity in terminology and methods of expressing cleaning results; the proceedings of that conference provide a wealth of detailed information on the various performance criteria, their uses and their limitations. For ease of discussion, the various performance criteria can conveniently be classed according to the degree to which they are dependent on the density composition of the raw coal treated. Some are directly dependent, some are only indirectly dependent, and some are, under certain circum- stances, essentially independent. DEPENDENT CRITERIA The yield and ash content of a washed coal are directly dependent on the washability characteristics of the raw coal from which it is derived. Thus, they are manifestly unsuited to comparing the performance of different plants, because no two plant feeds are the same. In fact, yield and ash content, by themselves, are inadequate for even routine day-to-day control. The continuous variation that occurs in the amount of impurity in raw coal, and sometimes in the float ash, make it impossible to tell whether a reduction in yield or an increase in the ash content of the washed coal results from any malfunction or misadjustment of the cleaning equipment. Recovery Efficiency For many years the most popular performance criteria that are only indirectly dependent on the washability characteristics of the raw coal have been efficiency formulas. Of the many that have been proposed, the one advanced by Fraser and Yancey in 1923 has had the widest accept-

Jan 1, 1968

By C. L. Ray, R. E. Baarson, H. B. Treweek

As an example of nonmetallic mineral flotation, the separation of several pegmatite minerals will be discussed in considerable detail, from both the laboratory-testing and plant-operation standpoints. The pegmatites have been chosen to illustrate the practicality of the selective separations of the minerals in a complex nonmetallic ore and, in so doing, to set forth a summation of the flotation art and technology which is applicable in part to the beneficiation of several less complex nonmetallic ores. In addition, a brief summary of descriptions of other nonnietallic mineral flowsheets and separations is included. Some of the industrial minerals now being concentrated by froth flotation methods commercially, or in the laboratory, are listed in Table 1. GENERAL CONSIDERATIONS There are two classes of chemicals that are normally utilized as collectors in froth flotation separations of nonmetallic minerals. These are defined as anionic and cationic and are typified by the fatty acids and amines, respectively. The fatty acids are selective to those minerals that have a high concentration of positive surface charges, such as the various calcium minerals typified by calcite, phosphate rock, and fluorspar. The amines are selective to those minerals with a high concentration of negative surface charges, such as silica sand and silicates. It should be noted, however, that by using various inorganic chemicals, a new or synthetic surface can be placed on specific minerals which produces different characteristics, thereby reversing the flotation reagent required for separation. The polar end of the collector attaches to the mineral surface either by chemical or physical adsorption; the nonpolar unreactive end is oriented away from the mineral surface. The result is a hydrophobic coating at the mineral surface which causes attachment to air bubbles. It is this surface condition that permits the floating of minerals which normally sink in water. In order to utilize these fatty acids and amine derivatives, several conditions .must be fulfilled. Before there can be a selective flotation process,

Jan 1, 1962

By McQuiston. F. W., E. C. Tveter

Sulfide mineral flotation has been applied to all naturally occurring sulfides and several synthetics. Of even more importance is the fact that economic separations are now being made between sulfides of essentially all the different metals. The variety of methods and minerals involved in such practice make it difficult to characterize them except in terms of general factors which influence the practices used. Ore grade and mineral composition are the major factors determining the processing method and the extent to which processing must be carried to achieve optimum economic return for a given ore. Since the choice of treatment is also affected by such factors as mine location, shipping charges, smelter schedules, each ore is a separate problem even though mineralization may be similar; The dissemination of minerals in the ore naturally determines the fineness of grind required for liberation. However, since grinding costs are a major part of most milling costs, emphasis has been placed on means of rejecting gangue minerals at the coarsest size possible. This has led to increased flotation of middling products or bulk concentrates for subsequent regrind and retreatment. Reagent development has also played an important part in present plant practice. Relatively few new frothers and collectors have found application during the past 25 years and many have disappeared. In general practice, re- agent combination choice is now fairly consistent with the type of collector being chosen on the basis of the mineral to be floated, the frother on the basis of pulp alkalinity, and the modifiers primarily on the basis of minerals to be rejected. REPRESENTATIVE FLOTATION PLANTS The milling operations described in this chapter have been selected primarily to illustrate these differences in ores and processing methods for the major types of ore minerals. The compositions of these minerals are shown in Table 1. These concentrators were chosen as representatives, both on the basis of geographic location and mineral content of the ore treated. At least one mill is included from each of the major producers, but the primary object was to show the practice employed for the various ore minerals and the different approaches to the middling problems encountered. The individual plants which have contributed data to this study are listed in Table 2, with a summary of their operating data, and are discussed in the order shown.

Jan 1, 1962

By Dale K. Fields

With today's technological advances in mineral processing equipment, there is an increasing demand for accurate system control. This can only come about through representative sampling. The purpose of this paper is to guide in the selection of sampling equipment and outline design parameters for the cutters used in dry and wet sampling without adding redundant mathematical probability formulas. Special attention will also be given to the equipment used in conjunction with samplers and sampling system, such as feeders, crushers, chutes, launders, and controls.

Jan 10, 1979

By Dale K. Fields

With today's technological advances in mineral processing equipment, there is an increasing demand for accurate system control. This can only come about through representative sampling. The purpose of this paper is to guide in the selection of sampling equipment and outline design parameters for the cutters used in dry and wet sampling without adding redundant mathematical probability formulas. Special attention will also be given to the equipment wed in conjunction with samplers and sampling system, such as feeders, crushers, chutes, launders, and controls.

Jan 1, 1980

By David R. Maneval, W. E. Foreman, J. Richard Lucas

INTRODUCTION The objective of this chapter is to inform the industry, as well as the public, of the challenges in dealing with problems associated with air and water contamination by coal preparation plants. The need for an informed industry is most important. It is hoped that some contribution may be given to a more efficient and economical approach to the problems of plant waste contaminants at individual plants. The problem has many facets, and consideration should be given to specific areas before any significant problems develop at a given plant. It is then possible to have a reasoned approach before the pressures of an emergency environment force hasty and incomplete solutions. It will be necessary to anticipate these problems in the design of new preparation plants, and advance consideration should be given to all problems concerned with contaminants.

Jan 1, 1979

By David R. Maneval, W. E. Foreman, J. Richard Lucas

INTRODUCTION The objective of this chapter is to inform the industry, as well as the public, of the challenges in dealing with the problems associated with the contamination of air and water from coal preparation plants. The need for an informed industry is most important. It is hoped that some contribution may be given to a more efficient and economical approach to the problems of plant waste contaminants at individual plants. The problem has many facets, and consideration to specific area should begin early before any significant problems develop at a given plant. It is then possible to have a reasoned approach before the pressures of an emergency environment force hasty and incomplete solutions. It will be necessary to anticipate these problems in the design of new preparation plants and advance consideration should be given to all the problems concerned with contaminants. The first part of the chapter will concern itself mainly with the contamination aspects of fine-coal cleaning and "black-water" disposal. Also attention will be given to the nature and formation of water from coal-mine drainage systems and the treatment of these waters for industrial use. Some attention will be devoted to the cost of installing and operating the various beneficiation systems for the removal of suspended solids. The second part of the chapter will analyze the problems of air contaminants from coal preparation plants. The nature and the effects of these contaminants and their potential for air pollution will be examined. One of the most critical is the measurement and analysis of these contaminants. As a result of identifying and determining the extent of the problem, better control can be planned. One of the most serious contaminants in air involves the element sulfur, and its elimination as a source of air pollution is one of the most challenging areas in coal preparation today. The last part of the chapter will emphasize the long-range problem of refuse disposal and control. Minimum operating and maintenance costs are functions of the proper selection and geometry of refuse disposal areas. Disposal procedures are varied but must be rigidly pursued or difficulties will result. Maintenance of refuse areas, including monitoring of burning refuse, is critical. It should be recognized that fine-solid refuse disposal systems must be carefully designed to minimize contamination. WATER CONTAMINANTS FROM PREPARATION PLANTS Pollution Aspects of Fine-Coal Cleaning and "Black-Water" Disposal The effluents from coal washeries and waters draining from plant-site surfaces inevitably contain fine coal and coal refuse materials in suspen-

Jan 1, 1968

By R. L. Curfman

In May 1960, six months after conversion of one- half of the Uranium Reduction Co. mill from acid to alkaline leach, severe corrosion was encountered in the 112 stainless steel wash baskets in the resin- in-pulp portion of the uranium circuit. Fortunately the corrosion was limited to the stainless steel screen cloth and bolts. The frames were not affected. Each resin-in-pulp wash basket serves as a container and a vehicle for approximately 40 cu ft of ion-exchange resin. Four baskets are installed in each tank through which uranium-rich solution flows as the baskets move up and down mechanically in the tank. The ion-exchange resin has an affinity for the uranium in the solution which causes it to be deposited on the resin in solid form. By reverse action with different chemical solutions, the uranium may be stripped from the resin for further processing and purifying. This section is the first step in the actual recovery of the uranium.

Jan 9, 1962

By J. A. Collins

THE process of plastic extension of face-centered cubic single crystal-line rods is so well understood, since the notable studies of Taylor and Elam,1 that the change in orientation of any crystal by slip and rotation may be predicted from the measured elongation. It is customary to assume a very homogeneous deformation, wherein gliding lamellae are free to rotate so that their slip direction continually approaches the axis of the rod, until a second slip system comes into operation; whereupon conjugate slip proceeds quantitatively to an end adjustment with the [112] direction in the axis of the rod. This process has been checked in many face-centered cubic materials and readily permits the preparation of specimens that have been sub-jected to various determinable amounts of shearing action. It is clearly of interest to study in such measurably strained specimens the development of a recrystallized structure on annealing and if possible detect the source of nuclei from which the new crystals grow. Strain-annealing experiments of this character have been performed by others but not in detail sufficient to permit a study, for example, of the number of recrystallized grains vs, the amount of shear. In the experiments now reported, this was done with a wide variety of orientations covering nearly the entire range of slip on a single system and corresponding to amounts of shear (ratio of shearing distance to distance between lamellae) at the conclusion of a test of from 0.08 to 0.57. A particular point was made of determining the crystallite rotation, or small angular range assumed by the octahedral slip plane after these various amounts of shear. The mechanism of recrystallization and the magnitude and effect of recovery on the recrystallization process was investigated.

Jan 1, 1940

By M. R. Pickus, C. H. Mathewson

THE study of the plastic deformation and recrystallization of metals has been the subject of many investigations. In regard to the simple deformational processes, such as tension and compression, the early knowledge gained from studies of polycrystalline material has been supplemented by many significant researches on the behavior of single crystals. Unfortunately, this has not been true for more complicated deformational processes. As far back as 1927, G. I. Taylor1 wrote: It is impossible in the present state of knowledge to do more than give a possible reason why (face-centcred cubic) crystals set themselves with a (110) direction in the plane of rolling, and at right angles to the direction of rolling. The explanation of why the orientation of the crystal axes round the transverse direction is what it is, must be left till the distortion of metals, and particularly single crystals of metals in the process of rolling, has been studied in greater detail. That this gap in the systematic study of deformation and recrystallization has not yet been filled was indicated by C. H. Samans,2 who wrote in 1934 that "only four investigations upon cold-rolled single crystals of any of the face-centered cubic metals have been reported in the literature." Of these four studies, only those of S. Tanaka3 and T. Sakao,4 both of whom worked with aluminum crystals, had quantitative significance. The other two, carried out by F. Wever5 and W. G. Burgers," were of a qualitative nature. It is our hope that the present investigation may contribute something to the knowledge necessary for a rationalization of the origin of rolling textures in terms of the known behavior of single crystals, and may add pertinent information concerning the recrystallization characteristics of deformed single crystals.

Jan 1, 1938

By M. R. Pickus

THE study of the plastic deformation and recrystallization of metals has been the subject of many investigations. In regard to the simple deformational processes, such as tension and compression, the early knowledge gained from studies of polycrystalline material has been supplemented by many significant researches on the behavior of single crystals. Unfortunately, this has not been true for more complicated deformational processes. As far back as 1927, G. I. Taylor1 wrote: It is impossible in the present state of knowledge to do more than give a possible reason why (face-centered cubic) crystals set themselves with a (110) direction in the plane of rolling, and at right angles to the direction of rolling. The explanation of why the orientation of the crystal axes round the transverse direction is what it is, must be left till the distortion of metals, and particularly single crystals of metals in the process of rolling, has been studied in greater detail. That this gap in the systematic study of deformation and recrystalliza-tion has not yet been filled was indicated by C. H. Samans,2 who wrote in 1934 that "only four investigations upon cold-rolled single crystals of any of the face-centered cubic metals have been reported in the literature." Of these four studies, only those of S. Tanaka3 and T. Sakao,4 both of whom worked with aluminum crystals, had quantitative significance. The other two, carried out by F. Wever5 and W. G. Burgers,6 were of a. qualitative nature. It is our hope that the present investigation may contribute some-thing to the knowledge necessary for a rationalization of the origin of rolling textures in terms of the known behavior of single crystals, and may add pertinent information concerning the recrystallization characteristics of deformed single crystals.

Jan 1, 1938

By Morris Steinberg, John Wulff, Robert Kamm

IN powder metallurgy it has often been observed that shrinkage may occur in one direction and growth in another during sintering. Even in long-time sintering experiments the rate of shrinkage may be different in different parts of the compact. In the fabrication of some parts requiring a constant permeability it is even questionable in some cases whether pressing from one direction should be attempted. These observations require for their interpretation a more detailed study of green or pressed density than has heretofore been available. Usually average density measurements of the whole compact are made and in some cases carefully cut sections are measured. A different approach to the problem was first mentioned by Rakowski1 and also used by Balshin.2 Balshin's diagram is reproduced in Fig r and schematically shows the result of pressing three layers of metal powder with fine intervening layers of graphite. The retarding effect of the die walls and a qualitative example of the density distribution is evident. More quantitative information about the distribution of density within a cold-pressed powder compact would be useful in showing the variation in density in compacts as influenced by the type of powder, shape of die, lubrication during the process, and other variables. Furthermore, information about the cracking of cold-pressed compacts may be obtained from an analysis of the stress distribution within a powder compact, and some information about the stress distribution can be obtained in turn from the density and strain distributions. A more detailed report on some of the present experiments appears in reference 3. PRESENT INVESTIGATION In order to ascertain the density gradients in cold-pressed metal powders, a deformable lead grid within the powder was employed. After pressing in cylindrical dies the ejected compact was radiographed, giving a pattern of the deformed grid. From the radiograph density and deformation from point to point is readily measured. From the radiograph strain distribution and stress trajectories were also determined. The latter also permits the determination of the coefficient of friction at the die wall. This technique indicates that the densest part of a compact pressed from one side is at the top outer circumference and the least dense region at the bottom circumference near the stationary plunger. For some heights of compacts the density at the axis is such that the lower density is at the top rather than at the bottom. So irregular a density distribution is due primarily to die-wall friction. As the ratio of diameter to height of compact is increased the die walls play a correspond¬ingly smaller role. More uniform density

Jan 1, 1947

By Samuel Hoyt

This paper gives a short account of plastic deformation as observed in single crystals of zinc, zinc having been selected for the experiments described herein because the phenomena are comparatively so simple and can be studied throughout such a wide range. It is hoped that the paper will serve to show the type of information which studies of single crystals afford and will contribute toward the solution of the general problem of metallic behavior. PRODUCTION OF ZINC SINGLE CRYSTALS The method of Czochralski,1 as modified by vow Gomperz,l was used to produce the crystals studied. The equipment is shown in Fig. 1. Molten zinc is held in a crucible at a temperature which is not far above its melting point, as measured by a pyrometer. A lava disc floats on the melt, and is provided with a central hole about 1 min. in diameter. A glass tube, drawn into a capillary at the lower end, is suspended from a string which is wound up by an electric drive at the speed desired. At the start, the glass capillary is let down into the melt and the hoist is started. The capillary brings up a small quantity of molten metal with it to a point just above the lava disc. At this point, a jet of hydrogen cools it and causes it to crystallize, with the result that a -small crystal forms. As the hoisting is continued, more molten metal is drawn up, in turn to be solidified by the jet of hydrogen. This additional metal continues the growth of the crystal already formed, and a long, cylindrical crystal results. The speed of hoisting used was generally between 0.1 and 0.5 mm. per sec., and the crystals were from 4 to 6 in. long and about 1 mm. in diameter. By varying the conditions, crystals of quite different orientations were obtained and were used in the study of the phenomena to be described.

Jan 1, 1927

By Samuel L. Hoyt

THIS paper gives a short account of plastic deformation as observed in single crystals of zinc, zinc having been selected for the experiments described herein because the phenomena are comparatively so simple and can be studied throughout such a wide range. It is hoped that the paper will serve to show the type of information which studies of single crystals afford and will contribute toward the solution of the general problem of metallic behavior. PRODUCTION OF ZINC SINGLE CRYSTALS The method of Czochralski,1 as modified by von Gomperz,2 was used to produce the crystals studied. The equipment is shown in Fig. 1. Molten zinc is held in a crucible at a temperature which is not far above its melting point, as measured by a pyrometer. A lava disk floats on ,the melt, and is provided with a central hole about 1 mm. in diameter. A glass tube, drawn into a capillary at the lower end, is suspended from a string which is wound up by an electric drive at the speed desired. At the start, the glass capillary is let down into the melt and the hoist is started.. The capillary brings up a small quantity of molten metal with it to a point just above the lava disk. At this point, a jet of hydrogen cools it and causes it to crystallize, with the result that a small crystal forms. As the hoisting is continued, more molten metal is drawn up, in turn to be solidified by the jet of hydrogen. This additional metal continues the growth of the crystal already formed, and a long, cylindrical crystal results. The speed of hoisting used was generally between 0.1 and 0.5 mm. per sec., and the crystals were from 4 to 6 in. long and about 1 mm. in diameter. By varying the conditions, crystals of quite different orientations were obtained and were used in the study of the phenomena to be described.

Jan 1, 1927

By C. H. Mathewson

CONSIDERABLE progress has been made during the last few years in analyzing the action of plastic deformation in metallic crystals. This is due largely to the development of X-ray spectrographic methods for studying changes in the orientation of single crystals, or of conglomerates, as they occur during the process of plastic deformation, but partly to the widespread knowledge of suitable technique for preparing large (single or variously combined) crystals for direct crystallographic observation under stress or in various conditions of strain. These two methods of studying changes in the crystalline structure of metals may of course be used in conjunction with features of mutual support, but unfortunately the advantage of direct crystallographic observation is lost when we proceed to the study of severely cold-worked structures, owing to the occurrence of real or apparent crystalline discontinuities which become more and more complicated as the amount of plastic action increases. Furthermore, the X-ray methods do not appear to be adequate, at least in their present stage of development, to fix definitely the character of structural alteration in the parent crystal lattice by plastic deformation. The principal question at issue concerns the nature of the crystalline particles that remain after plastic deformation. These are generally known in our American metallurgical literature as crystalline fragments,1 and they seem, indeed, to diffract as individuals causing the Hull pattern of a, severely cold-worked metal to resemble the pattern of a fine powder,2 with certain features of preferred orientation among the particles determined by the manner and intensity of cold working.

Jan 1, 1927

By C. H. Mathewson

CONSIDERABLE progress has been made during the last few years in analyzing the action of plastic deformation in metallic crystals. This is due largely to the development of X-ray spectrographic methods for studying changes in the orientation of single crystals, or of conglomerates, as they occur during the process of plastic deformation, but partly to the widespread knowledge of suitable technique for preparing large (single or variously combined) crystals for direct crystallographic observation under stress or in various conditions of strain. These two methods of studying changes in the crystalline structure of metals may of course be used in conjunction with features of mutual support, but unfortunately the advantage of direct crystallographic observation is lost when we proceed to the study of severely cold-worked structures, owing to the occurrence of real or apparent crystalline discontinuities which become more and more complicated as the amount of plastic action increases. Furthermore, the X-ray methods do not appear to be adequate, at least in their present stage of development, to fix definitely the character of structural alteration in the parent crystal lattice by plastic deformation. The principal question at issue concerns the nature of the crystalline particles that remain after plastic deformation. These are generally known in our American metallurgical literature as crystalline fragments,' and they seem, indeed, to diffract as individuals causing the Hull pattern of a severely cold-worked metal to resemble the pattern of a fine powder,2 with certain features of preferred orientation among the particles deter- mined by the manner and intensity of cold working. We must freely concede that there are conceptions of lattice alteration, apart from that of simple fragmentation, which would account for an increasing number of lattice positions according to X-ray spectrographic observation as the degree of deformation increased.

Jan 1, 1927

By Walter R. Hibbard

THE increased strength of a polycrystal-line metallic aggregate compared with that of its individual crystals generally has been associated with complex stress distributions at the grain boundaries resulting from atomic irregularity between grains. This disregistry, together with the necessity for adjacent crystals to deform 'compatibly regardless of the single crystal crystallographic strain mechanism, complicates this mechanism so as to increase the metal's resistance to deformation. Although Taylor1 has shown from purely mechanical considerations the requirement for at least five active slip systems to absorb the complexities during the homogeneous deformation of polycrystalline face-centered cubic metals, experimental studies by Barrett and Levenson2 indicate that this is feasible only in a qualitative sense because of deviations from homogeneous deformation. Seitz and Read in their review3 state: "Unfortunately . . . present knowledge of the grain boundary influence is not sufficient to complement the work in single crystals and provide us with a good foundation for treating polycrystals." The purpose of this investigation was to attempt to clarify the gap between single crystals and crystalline aggregates by an analysis of the effects of deformational stresses. Some of the results were described by C. H. Mathewson in his 1943 Campbell Memorial Lecture.21 PREVIOUS INVESTIGATIONS Since the performance of single crystals deformed under pure stresses has been relatively thoroughly investigated, the most significant researches are concerned primarily with deviations from single crystal behavior of large grained specimens. Qualitative grain boundary effects involving the observed amount of slip were reported by Carpenter and Elam5 in 1921. Individual crystals in a two or three grained aluminum specimen deformed by tension acted in the normal manner described by Taylor and Elam4 except for marked modifications at the grain boundaries. There the power to withstand deformation was considerably increased, leaving a ridge on the specimen where decreased slip occurred, often noticeable 34 in: from the boundary. Adcock,6 Yamaguchi,7 Seumel,8 Hirst9 and others have also reported this phenomenon as a qualitative trend. Yet attempts by O'Neill10 and Ljunggren11 to measure a difference in hardness at grain boundaries in undeformed specimens were unsuccessful. Miller12 measured quantitatively the reduction in slip near the boundary between the single crystal and polycrystalline areas of zinc specimens. These effects consisted of two parts: I. Next to the polycrystalline interface the distribution of stresses was so altered

Jan 1, 1948