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By H. B. Pulsifer

This paper outlines a method for rapid production of flat,, granular surfaces on many of the medium hard alloys. Grinding wheels and fabrics on wheels are not used; the purpose is accomplished by rubbing on emery papers and on fine abrasives heaped on hand boards. The advantages of chromic acid in the solutions for etching nickel and copper alloys are explained. Steels may require an additional step in the mechanical smoothing owing to the lack of an ideal etchant. Chloric acid is a rapid etchant for steel. Thirty-six photomicrographs illustrate the steps in smoothing and the clearness with which structures can be rapidly exposed. New structures in low-carbon steels are announced. After a little practice, many materials can be finished within two or three minutes. CUPRONICKELS In the previous papers on the metallography of copper and magnesiurn which the author has presented to this Institute there has been an attempt to demonstrate the advantages of minimizing the mechanical work of surfacing and depending more on chemical means; the present paper continues the research into a still wider field. It is obvious that the success of a chemical method for smoothing and etching depends almost entirely on the use of a suitable reagent. The etchant must remove the surface granulations and outline the structures. A very special type of reaction between reagent and metal must be displayed. Promiscuous corrosion or the intensification of the attack about local couples formed by impurities or components must not be in evidence. There are several reagents that etch highly polished nickel and copper alloys very well. Acidified ferric chloride solutions, concentrated and dilute nitric acid solutions, and nitric and acetic acids in acetone have been used to good advantage for the purpose. However, if they are expected to etch rather deeply—that is, smooth as well as characterize— the results may be far from satisfactory. Advantages of Chromic Acid In a protracted series of experiments it has been found that the addit,ion of chromic acid may be of the most surprising benefit. The function

Jan 1, 1929

By H. B. Pulsifer

This paper outlines a method for rapid production of flat,, granular surfaces on many of the medium hard alloys. Grinding wheels and fabrics on wheels are not used; the purpose is accomplished by rubbing on emery papers and on fine abrasives heaped on hand boards. The advantages of chromic acid in the solutions for etching nickel and copper alloys are explained. Steels may require an additional step in the mechanical smoothing owing to the lack of an ideal etchant. Chloric acid is a rapid etchant for steel. Thirty-six photomicrographs illustrate the steps in smoothing and the clearness with which structures can be rapidly exposed. New structures in low-carbon steels are announced. After a little practice, many materials can be finished within two or three minutes. CUPRONICKELS In the previous papers on the metallography of copper and magnesiurn which the author has presented to this Institute there has been an attempt to demonstrate the advantages of minimizing the mechanical work of surfacing and depending more on chemical means; the present paper continues the research into a still wider field. It is obvious that the success of a chemical method for smoothing and etching depends almost entirely on the use of a suitable reagent. The etchant must remove the surface granulations and outline the structures. A very special type of reaction between reagent and metal must be displayed. Promiscuous corrosion or the intensification of the attack about local couples formed by impurities or components must not be in evidence. There are several reagents that etch highly polished nickel and copper alloys very well. Acidified ferric chloride solutions, concentrated and dilute nitric acid solutions, and nitric and acetic acids in acetone have been used to good advantage for the purpose. However, if they are expected to etch rather deeply—that is, smooth as well as characterize— the results may be far from satisfactory. Advantages of Chromic Acid In a protracted series of experiments it has been found that the addit,ion of chromic acid may be of the most surprising benefit. The function

Jan 1, 1929

By Harmon F. Fisher

In the course of a comprehensive investigation for the development of the electrical process for the dehydration of oil-field emulsions, the writer has had an unusual opportunity to direct and execute a number of related, parallel studies concerning crude oil emulsions and extending over a period of nearly six years. Among these was an investigation utilizing the microscope for studying both the general characteristics of crude oil emulsions, the nature of their electrical charge and the action of an alternating current field in causing coalescence of the finely dispersed, more or less permanently suspended, emulsion particles into larger droplets of such mass that subsequent dehydration would follow by the ordinary process of settling, further agglomeration of the water droplets and, finally, separation into commercially dry, pipe line oil and a clean water discharge. It is not the purpose of this paper to enter into a detailed discussion of the highly specialized subject of microscope technique, nor into a theoretical discussion concerning the origin of the electrical charge on the emulsion particle or concerning the mechanism of the electrical phenomena occurring during the electrical treatment of oil-field emulsions. In a short paper of this character one can hope to touch on only a very limited discussion of the theoretical aspects of crude oil emulsions. The subject of emulsions and colloids is comprised in a comparatively young science in which, however, very rapid progress is being made and consequently it is undergoing many changes; a tentative conclusion valid today may be overthrown tomorrow. Nor would it be a simple science even if it were no longer undergoing this rapid progress; a thorough study of emulsions is based upon a knowledge of such fundamental subjects as molecular structure, ionization and other electrical phenomena, surface chemistry, surface and interfacial tension phenomena, viscosity and other factors too numerous to discuss here and the fundamental theories of which are still undergoing more or less change. Therefore this paper will confine itself largely to a generally descriptive discussion, a sufficiently detailed outline of the microscope technique and a brief comment on

Jan 1, 1931

By Paul Foote

SEEBECK discovered, in 1821, that if, in a closed circuit of two metals the two junctions are at different temperatures, an electric current will flow in the circuit. In the case of an iron and a copper wire, for example, current will flow from copper to iron at the hot junction, or from iron to copper at the cold junction. Two factors combine to cause the current. An electromotive force exists between the two metals, the magnitude of which, depends upon the temperature and upon the metals; this is called the Peltier e.m.f. If a single wire of homogeneous material is heated at one end, an electromotive force is developed between the ends of the wire, the magnitude of which depends upon the metal and upon the difference in temperature; this is known as the Thomson e.m.f: The total e.m.f. acting in the circuit is the sum of the Peltier e.m.f. at the two junctions and the Thomson e.m.f. in each wire, consideration being given, of course, to the algebraic signs of the four e.m.f.'s. The total electromotive force thus depends upon the difference in temperature of the two

Jan 9, 1919

By H. Larson, J. Chipman

The ferrous and ferric oxide concentrations of slags, expressed as j = Fe+++/(Fe+++ + Fe++), have been established through gas-slag equilibrium at 1550°C in a range of oxygen pressure of 10-I to 10-9 equilibriumatm. The value of j is increased by basic additions (BaO, CaO, MgO, MnO) and decreased by acidic oxides (SiO2 and TiO2). Oxygen pressure is shown graphically as a function of composition for slags which are analogous to those at the slag-gas interface of the open hearth furnace. THE progress which has been made in recent years in understanding the chemistry of metallurgical slags has been based largely on studies of slag-metal and slag-gas equilibria. There is a considerable body of knowledge which is applicable to reactions occurring at the slag-metal interface in open hearth steelmaking. There is little information concerning reactions of the slag with the furnace atmosphere and hence little basis for an understanding of the transfer of oxygen, sulphur, or hydrogen between gas and slag. The oxygen pressure of the open hearth atmosphere is normally of the order of 10-1 to 10-3 atm which differs by several orders of magnitude from that of about 10" atm at the slag-metal interface. The chemical properties of the slag, for example, the ratio of ferric to ferrous iron and the ability of the slag to hold sulphur in solution, are greatly affected by changes in oxygen pressure. This investigation was undertaken to enlarge our knowledge of the effect of oxygen Pressure on steel-making slags. Using air or controlled mixtures of CO a CO2 a range of oxygen Pressures from 10.' to 10.' was covered. Review of the Literature There are only a few references in the literature which pertain directly to this investigation. The most important is that of Darken and Gurry1,2 on the system iron-oxygen. This work included the determination of the phase diagram of the system and also a study of the field of homogeneous melts and their oxygen pressures. Their apparatus and procedure were very similar to that used in this study. Iron oxide was melted in a platinum crucible under an atmosphere of CO2:CO, CO2:H2, H2O, CO2, air or O2 depending upon the partial pressure of oxygen desired. After equilibrium was reached, the sample was quenched and analyzed for ferrous and ferric oxide. By appropriate calculations these authors were able to determine the oxygen and iron activities in the various slags, heats of formation of the oxides of iron, and heats of solution of iron and oxygen in the liquid slags. In a subsequent paper' the same authors made a less thorough investigation of the effects of additions of lime and manganese oxide on the composition of iron oxide melts. Only a few experiments were made and those in a narrower range of temperature and oxygen pressure. Darken' has investigated the fusion temperature of iron oxide in contact with silica under various atmospheres. He found that the temperature changes from 1120° to 1447°C as the gas composition changes from CO2/CO equal to 20.8 to pure oxygen. A comprehensive paper by White" predates the work of Darken and Gurry. The decomposition of ferric oxide into oxygen and lower oxides of iron was studied from 1000° to 1650°C and under oxygen pressures from 2 to 76 cm of mercury. The effect of

Jan 1, 1954

By Kirtland Marsh

THE manufacture of gas masks by the Chemical Warfare Service, U. S. A., required preparation of the carbon used in the canisters. The largest plant for the production of this carbon was situated at the works of the Astoria Light, Heat and Power Co., at Astoria, N. Y.; this paper will deal1 with the pyrometry equipment at that plant. Commercial charcoal was found unsuitable for use in gas masks because of its low power of absorption and its poor resistance to abrasion. The best raw material for the production of carbon was found to be coconut shells, but any kind of nut shells or fruit pits were used when sufficient quantities of coconut shells could not be obtained. The shells were first carbonized in retorts, the carbon was then crushed and screened between 8 and 16 mesh, and finally submitted to a special heat-treatment in air; steam treatment was later substituted for treatment in air. The production of gas-mask carbon on a commercial scale was begun at Astoria about Aug. 1, 1917. Temperature control was essential during the initial carbonization of the shells, as well as during the air or steam treatment, and pyrometers were installed for this purpose. The installation and maintenance of all pyrometry equipment was done by the pyrometry department, consisting of an officer in charge, an assistant, and two men. A special pyrometry laboratory was maintained in which all repairs were made.

Jan 9, 1919

By Frederick M. Becket, Russell Franks

In a recent article,l which described the softening effect of columbium in plain high-chromium steels, the authors stated that their investigations had shown columbium to be also a particularly valuable inhibitor of intergranular corrosion in steels of the 18 per cent chromium, 8 per cent nickel type. It is the purpose of the present paper to record some of the results obtained through the introduction of columbium to the austenitic chromium-nickel steels. The damaging effects of this type of corrosion have become so widely known as to restrict considerably the applications of the steels under consideration, and therefore there is little question of the importance of the goal to be attained. Numerous contributions concerning the susceptibility of the austenitic chromium-nickel steels to intergranular corrosion have appeared during the past few years, and among others who have dealt constructively with the subject are such well-known authors as Strauss and Houdremont of Germany, Hatfield of England, and Bain in the United States. Different theories have been propounded as to the cause of intergranular corrosion, and various remedial measures have been proposed, the majority of which involve the use of addition agents. Titanium is the addition agent at present most generally employed, as suggested by Houdremont and modified as described by Bain, Aborn and Rutherford. Little has been published on the effects of holding these steels for long periods at the relatively lower temperatures in the presence of corroding media, and the effects have mot been fully realized by producer and consumer.

Jan 1, 1934

By Alexander R. Troiano, Eugene P. Klier

SINCE the very early work on quenched structures, where the products of the martensite transformation had been recognized, this transformation has provoked much interest and study. Theoretically it was desirable to account for the extreme changes in physical properties resulting from the formation of martensite, as that information might lead to results of practical importance. Desirable information, therefore, was on the kinetics of transformation from austenite to martensite as well as on the physical constitution of the martensite. It has been known for years that certain steels quenched to room temperature will contain persistent austenite as well as martensite. Other important and now well- established features of the martensite reaction are the progress of the reaction on cooling only and the independence of Ar" with cooling velocities exceeding the critical velocity. These facts have been experimentally determined by various methods and investigators. Notable among the early investigators were Tammann and Scheill and Wever and Engel.2 Unfortunately, all investigators did not fully interpret their results, which, coupled with several investigations that yielded conficting results, caused a state of confusion that was not clarified until quite recently. X-ray investigations of martensite in steels3-6 indicate it to be a supersaturated solid solution of carbon in alpha iron. This supersaturation is evident from the appearance of a body-centered tetragonal structure with the addition of sufficient carbon. The dimensions of this tetragonal structure are alinear function of the carbon content within the limits of accuracy of the determinations. Slight tempering of tetragonal martensite leads to the destruction of the tetragonal structure, which is converted to a body-centered cubic structure. This phenomenon has precipitated a controversy concerning the nature and mechanism of the tempering of martensite. The facts in the case have been outlined by Epstein7 and more recently by Antia, Fletcher, and Cohen.8 The significance of Ar" on theoretical grounds is not clear, however, although considerable study has been devoted to its determination. The precise position of Ar" as a function of carbon content was first stated by Greninger and Troianos for steels covering a range of approximately 0.7 to 1.8 per cent carbon. The effect of alloying elements on Ar" has recently been the subject matter of investigation by various methods.

Jan 1, 1945

By J. L. Gregg, C. W. Kuttner

ReceNtly there has been considerable interest in the production and use of extra hard alloys composed primarily of tungsten and carbon. Dr. Hoyt's recent paper1 gives a good description of these alloys and describes their performance when used as tools. There are a number of these alloys on the market sold under various trade names, and it is the purpose of this paper to describe the results of an investigation of the structure of five of these alloys by means of microscopic and X-ray methods. The samples studied were in the form of small tools or wiredrawing dies, which were either purchased or supplied as samples. They were in some cases not supplied by the original makers but were furnished by the agents in this country, and we wish to call attention to the fact that they may not be truly representative of the materials supplied under the various trade names No performance data are given and no inference as to the inferiority of one alloy as against any other is made. K. Schröter2 recently described methods for polishing alloys of this type for microscopic examination and has presented photomicrographs of several alloys. However, he did not identify their constituents or describe methods for their identification. Constituents and Their Identification As far back as 1915 attempts were made to utilize tungsten carbides commercially, but the great brittleness of these carbides made these first attempts unsuccessful. Later, successful dies were made by sintering the powdered carbides with small amounts of iron, nickel, or cobalt. Due to the high melting points of the tungsten carbides (2600" to 2800" C.), it is difficult to melt the carbides without volatilizing almost quantitatively the added element of the iron group. Inasmuch as the added metal does not exceed 20 per cent. and is usually present in much smaller amounts, some understanding of the tungsten-carbon equilibrium dia-

Jan 1, 1929

By C. W. Kuttner, J. L. Gregg

ReceNtly there has been considerable interest in the production and use of extra hard alloys composed primarily of tungsten and carbon. Dr. Hoyt's recent paper1 gives a good description of these alloys and describes their performance when used as tools. There are a number of these alloys on the market sold under various trade names, and it is the purpose of this paper to describe the results of an investigation of the structure of five of these alloys by means of microscopic and X-ray methods. The samples studied were in the form of small tools or wiredrawing dies, which were either purchased or supplied as samples. They were in some cases not supplied by the original makers but were furnished by the agents in this country, and we wish to call attention to the fact that they may not be truly representative of the materials supplied under the various trade names No performance data are given and no inference as to the inferiority of one alloy as against any other is made. K. Schröter2 recently described methods for polishing alloys of this type for microscopic examination and has presented photomicrographs of several alloys. However, he did not identify their constituents or describe methods for their identification. Constituents and Their Identification As far back as 1915 attempts were made to utilize tungsten carbides commercially, but the great brittleness of these carbides made these first attempts unsuccessful. Later, successful dies were made by sintering the powdered carbides with small amounts of iron, nickel, or cobalt. Due to the high melting points of the tungsten carbides (2600" to 2800" C.), it is difficult to melt the carbides without volatilizing almost quantitatively the added element of the iron group. Inasmuch as the added metal does not exceed 20 per cent. and is usually present in much smaller amounts, some understanding of the tungsten-carbon equilibrium dia-

Jan 1, 1929

By H. Landssberg

Subsidence caused by mining operations has been a matter of interest for the mining engineer for just 111 years, since the Belgian committee for study of subsidence in the city of Liege submitted its first report in 1825. This interest is fairly expressed in the enormous amount of literature that has since appeared on this subject. A bibliography, probably far from being complete, which preceded this study as a preliminary survey, comprises more than 800 titles. In spite of this fact the problem remains today as acute as it has ever been. The questions of as good a recovery as possible of the national resources, the safety of the operations, and the protection of private and public property are the important angles from which to look at the problem. The Problem To systematize an investigation regarding the effects of mine excavations two different aspects have to be dealt with: (1) the subsidence of the immediate roof above the workings, affecting the safety of the workers and the progress and efficiency of the operations; (2) the subsidence of the surface, which is also, from the point of time, the second event. The immense importance of surface subsidence as regards the impairment of surface structures of every kind in a mining area is self-evident. Both effects result from reactions of the strata overlying the excavations and they depend mainly on the extent of the excavations and the structure and geological condition of the strata. It has been stressed repeatedly, in this country principally by G. S. Ricel,† that for the understanding of the phenomenon of subsidence accurate surveys are the most urgent necessity. In the past, however, at least in the normal course of mining operations, these surveys have been very crude. The control of the roof in the mine is left to the observation of the behavior of the timber, warning cracks and sounds in roof and walls and to the general judgment and experience of the worker and his supervisors. In any given case this may or may not be sufficient to prevent fatalities but certainly it does not give any accurate information as to what is happening in roof and strata. On the surface, principally in endangered areas, surveys have been conducted more frequently, but also in this case usually weeks or even

Jan 1, 1936

By H. Landssberg

Subsidence caused by mining operations has been a matter of interest for the mining engineer for just 111 years, since the Belgian committee for study of subsidence in the city of Liege submitted its first report in 1825. This interest is fairly expressed in the enormous amount of literature that has since appeared on this subject. A bibliography, probably far from being complete, which preceded this study as a preliminary survey, comprises more than 800 titles. In spite of this fact the problem remains today as acute as it has ever been. The questions of as good a recovery as possible of the national resources, the safety of the operations, and the protection of private and public property are the important angles from which to look at the problem. The Problem To systematize an investigation regarding the effects of mine excavations two different aspects have to be dealt with: (1) the subsidence of the immediate roof above the workings, affecting the safety of the workers and the progress and efficiency of the operations; (2) the subsidence of the surface, which is also, from the point of time, the second event. The immense importance of surface subsidence as regards the impairment of surface structures of every kind in a mining area is self-evident. Both effects result from reactions of the strata overlying the excavations and they depend mainly on the extent of the excavations and the structure and geological condition of the strata. It has been stressed repeatedly, in this country principally by G. S. Ricel,† that for the understanding of the phenomenon of subsidence accurate surveys are the most urgent necessity. In the past, however, at least in the normal course of mining operations, these surveys have been very crude. The control of the roof in the mine is left to the observation of the behavior of the timber, warning cracks and sounds in roof and walls and to the general judgment and experience of the worker and his supervisors. In any given case this may or may not be sufficient to prevent fatalities but certainly it does not give any accurate information as to what is happening in roof and strata. On the surface, principally in endangered areas, surveys have been conducted more frequently, but also in this case usually weeks or even

Jan 1, 1936

By G. P. Conard, E. H. Rennhack

The generation of fibers composed of individual TiZn15 compound particles and their influence on crystallographic orientation in chill-cast, hot-rolled hypoentectic Zn-Ti alloys were explored. Metallo-graphic examination and X-ray diffraction data show that such fibers form a planar network after 50 pet reduction which eventually tends to suppress twinning at some critical reduction level (-90 pct) where the grain size approaches the interfiber, spacing. This leads to the development of a duplex-type projerred orientation through slip rotation consisting of an al-most ideal (0001)(2iiOj texture and a (0001) (1010) rotated component. Correlations between basal-plane rotation and secondary- creep rc11e sugg-est, however that prejerred orientation does not contribute in a major way to the creep resistance of these alloys. EFFORTS to improve the creep resistance of zinc through alloying without incurring a loss in fabricating properties have achieved only minor success with the exception of the very effective addition of titanium. Anderson, Boyle, and Ramsey,l for example, demonstrated that increasing the amount of thiselement from 0.05 to 0.23 wt pct produced a progressive, 45-fold increase in the inverse creep rate of hot-rolled

Jan 1, 1967

By A. J. Lynch, E. V. Manlapig, J. S. Hall, G. C. Thorne

Modelling of industrial sulphide flotation based on data collected in several flotation plants is discussed. A mechanistic approach is used in which it is recognised that flotation is a two stage pro- cess with concentration occurring both in the pulp and in the froth. The important features of the model, which is a kinetic model, are – 1. for each particle species there is a range of flotation rates which corresponds to the range of particle sizes, 2. the flotation rates of the liberated gangue particles which have no hydrophobic properties are dependent on the flotation rate of water and are controlled by variables such as the air and frother addition rates, and the pulp level, 3. as an approximation the valuable sulphide particles may be regarded as being present in two groups with high and low flotation rate constants, 4. increase in the addition rate of collector tends to increase the proportion of sulphide particles which are in the high flotation rate constant group. The actual flotation rate of each group of particles is a combination of an "inherent" flotation rate and a flotation rate which is dependent on the flotation rate of water, 5. at particular air and frother addition rates and pulp levels there is a physical limit to the rate at which particles can be transported into the concentrate and this is recognised in the model. The model has been used to study the steady state and dynamic properties of flotation circuits in operating plants. The assessment of the behaviour of composite particles is difficult because of the problem of quantitatively describing the surfaces of mineral particles. A method which is being developed to measure unpolished particles is described briefly.

Jan 1, 1976

By W. L. Dennen, W. W. Wirth

Research looking toward the reduction of the cost of roof support by substitution of longer-life materials for wooden timber is fully justified by the fact that roof support is an important element of all production costs. Permanent or semipermanent roof support will reduce the expense of timber-maintenance crews during steady operations, but even more markedly during idle periods. The management, therefore, is faced with the important problem of timber renewals, which in times of regular operation are frequently obscured by more urgent problems of production. Increased use of timber in the Anthracite Region of Pennsylvania is caused mainly by increased percentage of coal obtained from robbing areas, which requires more timber for safety than development work, and maintenance of long haulageways through crushed ground despite the fact that less coal is transported over them. The timber reserve in the immediate vicinity of the mines has been depleted to such an extent that it is necessary to secure 70 per cent of the timber requirements from distant sources. Originally, mine timbering in this region was done by largely utilizing round props or legs with round collars. The whole cross section of the tree from which timber was cut was utilized by forming the joints between the legs and the collars with saw and adze, using plank or round saplings for lagging behind the legs and over the collars to prevent material falling between them. The Mine Inspectors' report of 1898 records an important digression from the use of round timber, when two tunnels at the Babylon colliery, near Pittston, Pa., were timbered with 12 by 12-in. square timber sets with mud sills, through quicksand for distances of 425 and 160 ft., respectively. The timbers were lagged with 3-in. plank to control sand. An early step toward the permanent type of roof support was the installation of "brick pillars or perfect arched brick rooms" instead of

Jan 1, 1940

By W. L. Dennen, W. W. Wirth

Research looking toward the reduction of the cost of roof support by substitution of longer-life materials for wooden timber is fully justified by the fact that roof support is an important element of all production costs. Permanent or semipermanent roof support will reduce the expense of timber-maintenance crews during steady operations, but even more markedly during idle periods. The management, therefore, is faced with the important problem of timber renewals, which in times of regular operation are frequently obscured by more urgent problems of production. Increased use of timber in the Anthracite Region of Pennsylvania is caused mainly by increased percentage of coal obtained from robbing areas, which requires more timber for safety than development work, and maintenance of long haulageways through crushed ground despite the fact that less coal is transported over them. The timber reserve in the immediate vicinity of the mines has been depleted to such an extent that it is necessary to secure 70 per cent of the timber requirements from distant sources. Originally, mine timbering in this region was done by largely utilizing round props or legs with round collars. The whole cross section of the tree from which timber was cut was utilized by forming the joints between the legs and the collars with saw and adze, using plank or round saplings for lagging behind the legs and over the collars to prevent material falling between them. The Mine Inspectors' report of 1898 records an important digression from the use of round timber, when two tunnels at the Babylon colliery, near Pittston, Pa., were timbered with 12 by 12-in. square timber sets with mud sills, through quicksand for distances of 425 and 160 ft., respectively. The timbers were lagged with 3-in. plank to control sand. An early step toward the permanent type of roof support was the installation of "brick pillars or perfect arched brick rooms" instead of

Jan 1, 1940

By George Bain

METHODS of mining building stone of any sort are planned to pro-duce as few fractures as possible, and present a strong contrast to methods of mining metallic ores, which must be crushed eventually and have fractures produced in as great profusion as possible. Shocks transmitted to a stone invariably make it more porous and more permeable and reduce its effective life, therefore methods of mining building stone involve as FIG. 1. THE SUPREME COURT BUILDING, WASHINGTON, D. C. This building illustrates the fine detail of workmanship, unprotected sharp corners and thin edges, and tall narrow columns characteristic of marble structures. These features require exceedingly coherent stone, and preservation of these features for decades or centuries demands many special quarrying precautions to keep absorption to 0.14 per cent or less, a detail not essential to stone for coarser architectural types. few shocks as possible. This is singularly true for marble because marble structures are intended to have long life, greater delicacy of line, more gracefulness and fineness of sculpture than those made from any other structural material (Fig. 1). So that delicate lines may remain in almost perfect preservation for decades, or even centuries, it is important

Jan 1, 1935

By A. V. Deforest, A. R. Anderson, C. W. MacGregor

ONE of the important problems in the design of structures and machine parts subjected to rapidly applied loads is the determination of the strength and ductility of the material itself under such conditions. Realizing the need for such information, many investigations have been carried out in the past. Most of these experiments have been made using notched bars in bending either with the Charpy or Izod impact machine. While yielding valuable data on the effect of notches in the energy absorption of the material and on the condition of heat-treatment, this form of test does not lend itself readily to a determination of fundamental stress-strain relations. For this and other reasons, more attention has been paid recently to the tension impact test. An extensive literature already exists on the subject and only those investigations somewhat closely related to the present paper will be mentioned. For a more comprehensive list, the reader is referred to the Symposium on Impact Testing of the A.S.T.M., 1938. The work of Mann,1 Clark and Dätwyler,2 Nádai and Manjoine,3 Winlock and Leiter,4 Deutler,5 and Brinkmann,6 however, deserve especial mention. In most of the previous investigations on the subject, when stress-strain relations were obtained under high rates of loading, it was the common procedure to determine stresses based on the original area and strains based on the original length. Stress-strain curves were then constructed by plotting [So = ooT as a function of eo =o] where A o and Lo refer to the original area and gauge length, respectively. At present there exists a paucity of true stress-strain data in the impact problem. The advantages of constructing so-called true stress-strain curves in order to reveal the fundamental physical properties of the material for the tension test were discussed recently by one of the authors? It was shown that the true physical behavior of the material in the tension test could best be represented by plotting the average true stress, [S = P] as a function of [e = q' = log A-le = log Lo] where P, A, L, S, [e], and q' refer to the load, the cross-sectioned area while the load P is applied, the actual gauge length, the average true stress, the true strain and true reduction in area, respectively. Besides giving a better physical representation, the method has certain additional advantages in that the stress-strain curve so plotted becomes a straight line from the maximum load point to fracture. The construction of such curves, however, while comparatively simple for the slow rates of loading customarily used in the tension test, presents certain difficulties for tensile impact in that both loads and diameters are required throughout the test. The continuous measurement of test-piece

Jan 1, 1941

By R. W. Fountain, M. Korchynsky

The precipitation phenomena occurring in cobalt-tantalum alloys have been investigated in the temperature range frm 500" to 1050°C by correlating the results of metallographic, X-ray, micro-and macrohardness, and electrical resistivity studies. The property andmacrohardness,changes were found to depend on 1) general precipitation, and 2) lamellar precipitation. Two new intermetallic phases have been identified: 1) a Co3Ta, a metastable ordered face-centered-cubic compound, and 2) a stable ß Co3Ta phase of hexagonal structure. In addition, the previously reported Co2Ta phase was found to exist in two allotropic modifications: the hexagonal MgZn,-type and the cubic MgCu2-type Laves phases. SINCE a large variety of structures can result as a consequence of the decomposition of a solid solution, predictions on the nature of property changes are difficult, if not impossible, to make. For any rational attempt to correlate properties and structures of a precipitation-hardenable alloy, a detailed understanding of the kinetics of decomposition and morphology of phase separation, as well as knowledge of phase relationships, appears to be prerequisite. Information of this type has been accumulated in the past for many alloy systems, both of theoretical and pastforpractical importance.1,2 Although the presence of intermetallic compounds has been reported in cobalt-base alloys,3 the amount of published information on precipitation-hardenable cobalt-base systems is very limited. A survey of the binary phase diagrams of cobalt indicates that cobalt-tantalum alloys might be of interest as typical of other cobalt-base systems in which Laves phases of the A,B type can be precipitated from solid solution. The present work has been undertaken, therefore, to study the kinetics and morphology of the precipitation reaction in this system and to establish a base for a correlation between the structural aspects and properties in this class of alloys. PREVIOUS WORK The only available phase diagram of the cobalt-tantalum system is based on the work of Koster and Mulfinger. According to these authors, the maximum solubility of tantalum in cobalt is about 13 pct (at 1275°C) and. less than 7 pct at room temperature. Tantalum additions lower the temperature of allotropic transformation of cobalt (about 420°C), and at 7 pct Ta, the high-temperature face-centered-cubic modification (ß cobalt) is retained at room temperature. The precipitating phase was originally designated as Co5Ta2 compound (55.2 pct Ta, about 1550°C melting point), but subsequent investigations by wallbaum5" identified this constituent as the A,B-type Laves phase. Wallbaum's data indicate that there are two modifications of this intermetallic compound: one richer in cobalt (Co2.2 Tao.8)of the hexagonal MgNi, type; and another of a higher tantalum content (Co2Ta) of the cubic MgCu, type. On the other hand, Elliott7 found that the cobalt-rich alloy (CO2.10,Tao.~l) was predominantly the cubic MgCu, type at 800°C and a mixture of both the MgCu2 and the hexagonal MgZn,-type Laves phases at 1000°C. At 1200°C, Elliott found only the MgZn, type while at 1400°C, he observed only the MgCu2 type. At the stoichiometric composition, Co2Ta, Elliott reported only the cubic MgCu2-type Laves phase in the temperature range of 600oto 1600°C. The precipitation of the cobalt-tantalum intermetallic compound is accompanied by a marked increase in hardness. According to Koster's4 data, the Brinell hardness of an 8 pct Ta-Co alloy increases from 230 to 340 upon short-time aging at 800°C. EXPERIMENTAL PROCEDURE The binary cobalt-tantalum alloys investigated contained 5, 10, and 15 pct Ta. The range of tantalum additions was thus slightly broader than the reported minimum and maximum solid solubility limits of tantalum in cobalt (7 and 13 pct, respectively)4 The alloys were vacuum-induction melted in a magnesia crucible using cobalt rondelles and technically pure tantalum sheet as raw materials. Deoxidation of the melt was accomplished with carbon, and the chemical analysis of the alloys is given in Table I. The effect of isothermal aging treatments on the progress of precipitation was studied on samples cut from cast ingots. These samples were solution treated for 2 hr at 1250°C and water-quenched. Aging was conducted in the temperature range from 500" to 1050°C for periods between 15 min and 1000 hr and followed by water-quenching. To prevent contamination from the atmosphere, all samples were sealed in evacuated Vycor or quartz tubes for heat-treatments. For solution treatment, argon at 0.2 atmospheric pressure was introduced prior to sealing of the capsule to prevent collapse at high temperature, and titanium sponge was placed at one end of the capsule to act as a getter. MACROHARDNESS The effect of aging on Vickers hardness (Dph) of

Jan 1, 1960

By C. E. Mills

Studies of ground movement and subsidence resulting from mining operations cover a broad field. It is also a very important consideration and one that eventually affects nearly every mining operation of any extent. The damage to surface buildings, removal of mine surface plants and replacements of main hoisting shafts must reach an astounding expenditure were these cost figures available over a period of years. Were the subject one of mathematical formula and dependent only on the angle of draw of the walls or country rocks, the problem would be relatively simple. Consideration must be given to depth and extent of workings; structural conditions of the orebodies and enclosing country rock; physical properties of these same rocks, including schistosity, bedding, jointing, slips, dikes, faults, and other structural weaknesses. The method of mining, extent of openings, supporting pillars, and amount of moisture or water underground are other pertinent factors. With such a large number of variable factors, it is apparent that the subject of subsidence is one that must be based largely on experience and results at other mines where conditions are somewhat comparable. In presenting this paper, it is the intent to describe the progressive results of past ground movements at the United Verde, to bring out physical conditions largely responsible for this movement, but to refrain from theorizing on the ultimate extent of subsidence resulting from future mining operations. Geology and Structure1 The ore deposits of the United Verde are of the massive sulfide, schist-replacement type. A structural anticline formed by the intrusion of diorite between bedding planes of steeply dipping and severely folded greenstones and porphyry localized the deposit of sulfide. The mineralized zone is of great horizontal extent varying from 200,000 to 400,-000 sq. ft., and extends from the surface to the lowest levels at a steep dip of from 50° to 75. The irregular interfingering of the sulfide with

Jan 1, 1934