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By John J. Gilman

BECAUSE of their layerlike structure, zinc crystals exhibit strong anisotropies for almost all physical and chemical properties. This should, and indeed does, greatly influence the plasticity of zinc for various crystal orientations. At low temperatures, the investigator of this plastic anisotropy is plagued by the great variety of deformation modes that operate. However, at high temperatures (250° to 419°C) only two deformation modes predominate: basal (0001) and prismatic (1010) glide. Furthermore, since strain hardening is virtually absent at high temperatures, the plasticity for these two modes of deformation can be very simply described by means of two equations of state. It is the purpose of this paper to describe the experimental behavior of basal and prismatic glide in zinc crystals, and to interpret this behavior in terms of other physical properties (in particular, the thermal expansion coefficients and the elastic constants) using the theory of dislocations. Fig. 1 defines the two planes of the zinc structure that will be discussed. Glide occurs very readily on the basal planes at all temperatures, and there is a very large literature on this subject. Much of the literature has been reviewed by Schmid and Boas;' it will not be reviewed here. Kolesnikovl was the first to show that if basal glide is circumvented by stressing a zinc crystal parallel to the basal planes (giving zero shear-stress on the basal planes) then, at temperatures above about 320°C, glide on the first-order prism planes occurs. His results have recently been confirmed by Cahn, Bear, and Bell." These previous workers have established the existence and crystallographic elements of prismatic glide; the present paper is concerned with the stress, strain rate, and temperature relations of prismatic glide as contrasted with basal glide. Experimental Methods The crystals were square ones, 6x6 mm, that had been grown in precision Pyrex tubes by a method that is described in detail elsewhere.' Most of the crystals were 99.999+ pct Zn (New Jersey Zinc Co. CP grade). Some were alloyed with 0.1 -+-0.005 atomic pct Cd, and chemical analysis showed that almost all of the added cadmium persisted through the crystal-growing process. For measurements of nonbasal glide, crystals were oriented with their basal planes parallel to both the rod axis and one of the flat faces of the square cross section. However, the orientation of the close-packed directions [1210] with respect to the rod-axis was variable. For basal glide measurements, the angle between the basal plane and the specimen axis was 35". The orientations were measured by the Gren-inger back-reflection X-ray method. The problem of finding a suitable method of gripping the crystals was the most serious experimental obstacle that arose. Because of the large plastic anisotropy of zinc, the usual gripping methods were unsatisfactory. Some methods that were tried were: high melting-point solder, making heads on the ends by locally melting a crystal, and electroplating nickel on the ends to form enlarged portions. For all these methods, the regions of the grips were weaker than the crystals themselves. Finally, two methods were decided upon: bend tests and direct machining of tensile specimens. In the bend tests, specimens were loaded as simple beams so that gripping was not a problem. The beams were 1 in. long and the axis of bending was parallel to the hexagonal axis of the crystals. For the crystals that were machined into tensile specimens, brass bars with slots in them were used to support the crystals, and thereby minimize the distortions due to machining. The crystals were glued into the brass bars with plastic cement which was later dissolved away with acetone. See Fig. 2, left. No clamps were used near the crystals and the machining was done using a milling machine with a fly-cutter. The tool bit was very sharply pointed to minimize burnishing. The feed was less than 1 mil per cut. The depth of cut was 2 mil for roughing cuts, and % mil for the finishing cuts. This machining method produced surface layers of tiny recrys-tallized grains only 2 to 3 mil deep, and the bodies of the crystals were not measurably disturbed. After the crystals had been machined and removed from the brass holders, they were chemically polished until about 5 mil had been removed from all their surfaces. The polishing reagent consisted of equal parts of concentrated HNO,, 30 pct H3O and ethyl alcohol; it is described in detail elsewhere." A typical crystal is shown in Fig. 2, right. The I-shaped faces are normal to the hexagonal axis of the crystal; otherwise the projections at the ends would simply shear off when the crystal was loaded. The cross section in the 2?-in. gage length is 0.215x0.115 in. It was found that the polished

Jan 1, 1957

By J. T. Lapsley, I. I. Cornet, A. E. Flanigan, R. Hultgren, J. E. Dorn

WITH the greatly expanding use of magnesium during the war, it appeared necessary to the War Metallurgy Committee that procedures of heat treating common magnesium casting alloys be investigated systematically. Accordingly, the National Defense Research Committee of the Office of Scientific Research and Development placed a research contract with the University of California, supervised by the War Metallurgy Committee. Research on the solution heat treatment and aging of magnesium alloy AZ92, (formerly ASTM No. 17; also known as Dowmetal C or AM260) which was done under "Restricted" Project NRC-21, in 1942-1943, and reported, in detail in a final report to the OSRD on September 3, 1943, is the basis of this paper, which has been released for publication by the OSRD. American experience with magnesium alloys prior to World War II was limited, although some of these alloys had been in commercial use since 1909. Requirements of the aircraft industry for light alloys made it imperative to understand and utilize the advantageous strength-weight properties of magnesium castings. Magnesium casting alloys are commonly solution heat treated to increase their ultimate tensile strength and ductility; this treatment may be followed by an age hardening at elevated temperatures, which raises the tensile yield strength but diminishes the ductility. In the present investigation, AZ92 was studied to determine the effects on properties of various solution heat treatment and aging schedules. The principles of heat treatment of magnesium alloys are the same as for other non-ferrous alloys. The alloy studied, AZ92, has a nominal composition of 9 pct aluminum, 2 pct zinc, and minor constituents. Fig I shows, by the projection of isothermal sections on the concentration plane, the solubility surface1 of the ternary magnesium-rich solid solutions as determined by X ray analysis. From this figure it may be seen that above approximately 375°C (707°F), AZ92 alloy is a single phase alloy at equilibrium; below this temperature the equilibrium condition is a. two phase alloy. The beta constituent which precipitates from the solid solution exerts a hardening effect. Because the zinc concentration is only 2 pct, and because of its solubility relations, AZ92 resembles a binary alloy of magnesium with aluminum. The solubility curve1 of Fig 2 shows how rapidly the solubility of the beta phase decreases with decreasing temperatures. Unlike many aluminum alloys, magnesium alloys do not age harden at room temperatures; precipitation hardening of AZ92 alloy is performed at about 177°C (350°F). At this temperature about 3 pct aluminum

Jan 1, 1947

By O. W. Ellis

The question of the influence of gases upon the properties of copper has received the attention of a number of investigators, among whom Sieverts,' Iwase,2 Lobley and Jepson3 stand preeminent. Solubility of Gases in Copper Sieverts and Iwasé concerned themselves with the solubility of a variety of gases in the metal in the solid and liquid states. They determined the absorption coefficients of these gases and in all cases found a sharp change in solubility at the melting point of the metal. In this respect they disagree with Lobley and Jepson, who have based their opinions upon the appearance of small ingots of the metal which had been fused in an atmosphere of one or other of three gases and had then been rapidly cooled, while surrounded by gas, to the freezing point (rate—possibly 30" to 60" C. per sec.). The ingots that had been fused and cooled under nitrogen and carbon monoxide were free from blowholes and it was assumed that these gases were not absorbed in amounts much in excess of those which would dissolve in the solid metal; the ingots similarly treated under hydrogen were full of blowholes and it was assumed in this case that gas was ejected on solidification of the copper. The effect of varying the rate of freezing upon the character of the test ingots was not examined by these investigators; otherwise, it is felt, their views might have been subject to modification. Sieverts' most important contribution is that the solubility of a gas in any metal is proportional to the square root of its pressure or concentration. Knowing then the absorption coefficients of the various gases in copper, it should be possible to determine the analysis of the

Jan 1, 1929

By O. W. Ellis

The question of the influence of gases upon the properties of copper has received the attention of a number of investigators, among whom Sieverts,' Iwase,2 Lobley and Jepson3 stand preeminent. Solubility of Gases in Copper Sieverts and Iwasé concerned themselves with the solubility of a variety of gases in the metal in the solid and liquid states. They determined the absorption coefficients of these gases and in all cases found a sharp change in solubility at the melting point of the metal. In this respect they disagree with Lobley and Jepson, who have based their opinions upon the appearance of small ingots of the metal which had been fused in an atmosphere of one or other of three gases and had then been rapidly cooled, while surrounded by gas, to the freezing point (rate—possibly 30" to 60" C. per sec.). The ingots that had been fused and cooled under nitrogen and carbon monoxide were free from blowholes and it was assumed that these gases were not absorbed in amounts much in excess of those which would dissolve in the solid metal; the ingots similarly treated under hydrogen were full of blowholes and it was assumed in this case that gas was ejected on solidification of the copper. The effect of varying the rate of freezing upon the character of the test ingots was not examined by these investigators; otherwise, it is felt, their views might have been subject to modification. Sieverts' most important contribution is that the solubility of a gas in any metal is proportional to the square root of its pressure or concentration. Knowing then the absorption coefficients of the various gases in copper, it should be possible to determine the analysis of the

Jan 1, 1929

By Walter Crafts

Structural steels containing chromium have become widely used in the last 20 years. In the earlier part of this period the major applications were in chromium-molybdenum aircraft tubing and similar special high-strength steels. During the past 10 years there has been a notable expansion in the use of chromium-bearing steel for structural purposes when welding was utilized for fabrication. The chromium-bearing steels introduced by Saklatwallal (chromium-copper), Kinzel2 (chromium-manganese-silicon), and Schultz3 (chromium-copper) are being extensively used at the present time. General Effects of Chromium Chromium is so widely known for its carbide-forming tendency that its capacity to stabilize oxygen, nitrogen, and phosphorus is often overlooked. In low-carbon steels of the structural type these so-called secondary characteristics become more prominent. For this reason also, chromium in structural steel is definitely a toughening agent. As the carbon content is increased, the more widely known hardening effect becomes more evident. In low-carbon steels chromium increases the notched-bar impact strength substantially. This property persists at subzero temperatures and is utilized for low-temperature service in chromium-copper steel.4 Chromium also reduces any tendency to strain-aging embrittlement. In addition to improving the toughness of steels with the usual impurities, chromium has the specific property of counteracting the brittleness induced by high phosphorus.5,6 In steels low in carbon and alloys, chromium has an almost negligible effect on tensile strength, and a hardening influence is noticeable only in the stronger steels. The ductility of welds adjacent to the base plate is also improved by chromium, both in the range of foolproof welding steels having strengths of less than 80,000 lb. per sq. in. as well as in the higher strength steels.

Jan 1, 1939

By Walter Crafts

Structural steels containing chromium have become widely used in the last 20 years. In the earlier part of this period the major applications were in chromium-molybdenum aircraft tubing and similar special high-strength steels. During the past 10 years there has been a notable expansion in the use of chromium-bearing steel for structural purposes when welding was utilized for fabrication. The chromium-bearing steels introduced by Saklatwallal (chromium-copper), Kinzel2 (chromium-manganese-silicon), and Schultz3 (chromium-copper) are being extensively used at the present time. General Effects of Chromium Chromium is so widely known for its carbide-forming tendency that its capacity to stabilize oxygen, nitrogen, and phosphorus is often overlooked. In low-carbon steels of the structural type these so-called secondary characteristics become more prominent. For this reason also, chromium in structural steel is definitely a toughening agent. As the carbon content is increased, the more widely known hardening effect becomes more evident. In low-carbon steels chromium increases the notched-bar impact strength substantially. This property persists at subzero temperatures and is utilized for low-temperature service in chromium-copper steel.4 Chromium also reduces any tendency to strain-aging embrittlement. In addition to improving the toughness of steels with the usual impurities, chromium has the specific property of counteracting the brittleness induced by high phosphorus.5,6 In steels low in carbon and alloys, chromium has an almost negligible effect on tensile strength, and a hardening influence is noticeable only in the stronger steels. The ductility of welds adjacent to the base plate is also improved by chromium, both in the range of foolproof welding steels having strengths of less than 80,000 lb. per sq. in. as well as in the higher strength steels.

Jan 1, 1939

By Clifford Wilson

SCREENED pipe is designed with the view of restraining the fine, free-running sands of the production zone from entering oil wells. Its successful use is dependent on a number of factors. The nature and effects of some of these factors can be determined through experiment and observation, but some of the elements that have a distinct bearing on the use of screened pipe can be evaluated only by estimate. The important subsurface conditions which affect the use of screened pipe are: 1. Depth of production zone. 2. Extent of production zone. 3. Reservoir pressure. 4. Character and relative quantity of oil and gas. 5. Character of sediments a. Consolidation of beds. b. Variation in beds. c. Grain-size gradation of sands. d. Free-running characteristics of sand from different levels. Aside from the use. of mechanical equipment and tools, the measures to be taken in the installation of screened pipe involve: 1. Size of liner. 2. Length of liner. 3. Design and mesh of screen. 4. Portion of liner to be screened. 5. Manner of setting liner. 6. Preparation of or washing of the well before or during the setting of the screen. 7. Manner of bringing in the well. 8. Manner of flowing the well. Values applicable to the actual subsurface conditions that exist at any well can only be approximated. The accuracy of the estimate will be measured by the amount and quality of the evidence at hand and the personal factor of ability to interpret the evidence fairly, whether

Jan 1, 1932

By Y. H. Liu, G. W. Powell

Thin foils made from the gold-rich region of- short (0.15 mm)Au-Ag diffusion couples annealed at 880°C for 1 hr were examined in ax electron microscope and the structures were compared with that of pure gold subjected to identical heat treatments. The couples underwent Plastic deformation (bending) during the diffusional anneal. The foils prepared from the diffusion zone have a higher dislocation density and incidence of subboundaries than pure gold. The plastic bending of the couple can be interpreted in terms of the climb of edge dislocations, which are pavallel to the bend axis, along the direction of diffusion. THE interaction of lattice defects during interdiffu-sion between two metals has been considered by several investigators. In particular, da Silva and Mehl,1 Barnes,' and Bardeen and Herring3 have proposed models based on interactions between point and line defects to account for the Kirkendall effect (marker movement). Each of these models is based on dislocation climb, which can either add or remove lattice planes, induced by an under- or supersaturation of vacancies. A theoretical treatment of the nucleation and growth of voids by the condensation of vacancies has been presented by Seitz.4 Stresses can arise in a binary diffusion couple as a result of the vacancy flux and the gradient in the lattice parameter. rinkmman' has investigated the effects of diffusion-induced stresses on void formation; the results of his analysis suggest that voids can form and grow under the influence of these stresses in the absence of an excess vacancy concentration. The relationships between vacancy supersaturation and diffusion-induced stresses and void formation have been elucidated also by Balluffi and seigle6 who concluded that the stress generated by a vacancy supersaturation aids the growth of voids. Experimental evidence which indirectly shows that stresses are produced by chemical diffusion has been obtained by several researchers.2,7-9 This evidence consists in part of the observation by light microscopy of the formation of subgrains, a process characteristic of the high-temperature deformation of some metals during creep.'0 More striking, however, is the plastic bending of short (0.2 mm) Cu-Ni couples observed by Barnes2 and of boron-doped silicon crystals reported by Queisser.9 Diffusion-induced dislocations in iron and silicon have been investigated by Ainslie et a1.11and Schwutte and Queisser,12 respectively, the former using transmission electron microscopy and the latter an X-ray transmission technique. Matthews and Crawford13 observed the formation of boundaries by the climb of interfacial misfit dislocations in thin, vapor-deposited Au-Pd couples diffused in situ in an electron microscope. In order to obtain additional information on the phenomena associated with defect interaction and diffusion-induced stresses in binary couples, an electron transmission study of foils prepared from the diffusion zone of short Au-Ag couples was undertaken. The initial objective was to investigate the processes occurring at various points of the diffusion zone. Subsequent research demonstrated that foils could be prepared only from the gold-rich region of the diffusion zone using the technique described herein. EXPERIMENTAL PROCEDURE Preparation and Annealing of the Diffusion Couples. The couples were made from annealed, high-purity (99.999 pct). polycrvstalline gold and silver sheets (0.075 mm thick). Shall (0.075 by 5 by 17 mm) elec-tropolished coupons of gold and silver were pressure-bonded by heating the two metals in a graphite device to 770°C and holding at this temperature for approximately 30 min. The quality of the bond was ascertained by metallographic examination at 150 times. Each couple subsequently was annealed at 880°C for 1hr; under these conditions, the extreme portions of the

Jan 1, 1968

IN the early period of steelmaking, ingot structure and segregation were of no practical importance. Crucible melting required very small ingots that gave little segregation, and a small inserted hot top prevented pipe. As larger ingots were poured from bessemer converters and open-hearth furnaces, segrega- [ ] tion, piping, and gas evolution became increasingly important. The techniques of making semikilled and rimmed ingots were developed with little knowledge of the actual mechanism of the process. The first studies of solidification were made by the Brearleysl and Gathmann,2 who used stearine to show the effects of shrinkage and mold shape. Fig 11-1 is a picture of a series of stearine ingots at various stages of solidification. These studies showed that the liquid solidifies at a nearly uniform rate from the sides and bottom of the mold and demonstrated the formation of

Jan 1, 1951

By Edwin B. Johnson

The success of self-fluxed sinter in enhancing the operation of the blast furnace during the past few years has reasonably led to the assumption that the use of self-fluxed pellets might result in even greater furnace efficiencies. A great share of development work in agglomeration has been directed towards techniques related to the production of self-fluxed pellets, but no appreciable tonnage of self-fluxed pellets had been produced on a commercial scale until this past year when The Cleveland-Cliffs Iron Co. produced 35,000 tons of such pellets by the grate kiln system at the Republic mine during the period May 21-June 5, 1962.

Jan 3, 1963

By R. B. Muter, W. C. Grady, T. D. Wheelock, D. G. Chedgy

INTRODUCTION Topics of special interest, such as preparation plant flowsheets and noise pollution, are described in this chapter along with a discussion of non- state-of-the-art processes such as chemical cleaning, high intensity magnetic separation, and bacterial oxidation. PREPARATION PLANT FLOWSHEETS by RICHARD B. Muter In determining the layout or combination of unit operations to be utilized in a modern preparation plant several factors must be taken into account.

Jan 1, 1979

By J. J. Rutledge

On Sept. 4, 1914, Mine No. 1 of the Union Coal Co., Adamson, Oklahoma, suddenly caved, entombing thirteen miners whose bodies were never recovered. The seam of coal mined, the Lower Hartshorne, averaged 5 ft. in thickness and dipped at an angle varying from 22" to 30n. The strata overlying the coal seam were sandstones and shales. The mine was worked by the pillar-and-room method, the rooms being driven directly up the dip of the seam. All coal was blasted off the solid. Rooms were turned on short centers and room pillars were thin and irregular, as shown in Fig. 1. Fig. 2 is a cross-section of the form; showing the mine workings. Some cracks had been observed on the surface, it is said, at least a month before the squeeze occurred, but the collapse of the mine workings came very suddenly. As is usual when squeezes occur on such steep dips and the pillars fail, the crush progressed rapidly down the dip until it reached solid coal; there was a line of break, or draw, over in the solid coal. Several well-defined cracks appeared on the surface, after the mine had squeezed, but there was no appreciable subsidence of the surface, the weight seemed to be thrown entirely to the dip. About one year after the squeeze, and after the workings of the adjoining mine, NO. 4, had been retimbered and made safe, the writer inspected the tenth north (right) entry, or lift, off of No. 4 slope, which was below and fairly near the lowest caved portion of mine No. 1. The roof shale was composed of thin layers, which had been bent in somewhat the same manner as the leaves of a book having flexible covers are bent when the book is folded or rolled up in the hands. Though the mine workings are immediately beneath the streets and buildings of the mining town of Adamson, business was not disturbed by the squeeze, so far as any subsidence of the surface was concerned. No surface monuments were available and no elevations were taken, but the mine workings had been accurately surveyed and traversed, and the streets of the town overlying the mine workings had been carefully platted on the mine map, so that it was possible to locate accurately the cracks on the surface.

Jan 1, 1923

By J. J. Rutledge

On Sept. 4, 1914, Mine No. 1 of the Union Coal Co., Adamson, Oklahoma, suddenly caved, entombing thirteen miners whose bodies were never recovered. The seam of coal mined, the Lower Hartshorne, averaged 5 ft. in thickness and dipped at an angle varying from 22" to 30n. The strata overlying the coal seam were sandstones and shales. The mine was worked by the pillar-and-room method, the rooms being driven directly up the dip of the seam. All coal was blasted off the solid. Rooms were turned on short centers and room pillars were thin and irregular, as shown in Fig. 1. Fig. 2 is a cross-section of the form; showing the mine workings. Some cracks had been observed on the surface, it is said, at least a month before the squeeze occurred, but the collapse of the mine workings came very suddenly. As is usual when squeezes occur on such steep dips and the pillars fail, the crush progressed rapidly down the dip until it reached solid coal; there was a line of break, or draw, over in the solid coal. Several well-defined cracks appeared on the surface, after the mine had squeezed, but there was no appreciable subsidence of the surface, the weight seemed to be thrown entirely to the dip. About one year after the squeeze, and after the workings of the adjoining mine, NO. 4, had been retimbered and made safe, the writer inspected the tenth north (right) entry, or lift, off of No. 4 slope, which was below and fairly near the lowest caved portion of mine No. 1. The roof shale was composed of thin layers, which had been bent in somewhat the same manner as the leaves of a book having flexible covers are bent when the book is folded or rolled up in the hands. Though the mine workings are immediately beneath the streets and buildings of the mining town of Adamson, business was not disturbed by the squeeze, so far as any subsidence of the surface was concerned. No surface monuments were available and no elevations were taken, but the mine workings had been accurately surveyed and traversed, and the streets of the town overlying the mine workings had been carefully platted on the mine map, so that it was possible to locate accurately the cracks on the surface.

Jan 1, 1923

By Craig R. Barrett, Oleg D. Sherby

The creep characteristics of four pure metals with widely Varying stacking-fault energies (silver, copper, nickel, and aluminum) were evaluated above 0.5Tm. Creep tests were performed under conditions of constant atomic diffusivity and constant stress over the elaslic modulus. The sleady-state creep rate, Es, was found to he a funclion of the THE most common empirical representation of the steady-state creep rate, Es, at high temperatures and intermediate stresses is of the form where a is the applied stress, E is an elastic constant, A and n are constants (n is typically stacking-fault energ, y, such that Es is proportional to y3,5. In addition, it was uncovered that the primary creep strain and the strain to fracture increased with increasing y, and that the ratio of initial to steady-state creep rate decreased with increasing y. about 5), Q is the activation energy for creep (usually equal to that for self-diffusion), and kT has its usual meaning. sherbyl and McLean and ale' have used this expression to correlate creep data for a number of pure metals. An interesting aspect of Eq. [I] is the absence of any dependence on the stacking-fault energy. While most creep data seem to obey the stress and temperature dependence predicted by Eq. [I], when data for several metals are put on a master plot they do not fall on a common line but form a band. The width of this band corresponds to a variation in Es of 102 to l03. sherbyl attempted to explain this band by assuming that a grain-size effect was present which led to the observed variation. On the other hand, Felt-

Jan 1, 1965

By C. G. Fink

A PART of the material incorporated in this paper was derived from the studies of ancient metal objects examined by the authors from time to time for museums and art collectors, in order to verify the age of the metal. The data thus accumulated during several years was systemati-cally surveyed and supplemented by new material obtained in examina-tion of a set of specimens that had been generously donated by museums for this study. Altogether over 50 pieces were investigated, of which 39 are described in this paper. Every specimen is at least 1500 years old; the majority are considerably older. Exact conditions to which these bronze and copper objects were exposed in the ground are unknown, unfortunately. It is safe to say that exposure conditions did not remain constant during the long period of burial. Although the collection of specimens studied represents a wide variation in location and age of the objects, as well as in the nature and composition of the metals, it was found that fundamental changes in the metal structure were limited to a few typical cases which, therefore, may be considered as more or less general. The authors' chief aim was to study the effect of extremely long periods of corrosion on the structure of bronze and copper.

Jan 1, 1936

By M. R. Geer, J. D. Davis, H. F. Yancey

ALTHOUGH the mechanical cleaning of coal is carried out at plants on the surface, preparation is actually begun at the face in the mine. Here the character of the coal and the amount, character, and distribution of the impurities within the bed may be seen. Blasting methods, dust-allaying procedures, location of mining cut with respect to bands of impurity, and the practice of discarding segregated impurities underground, all have an important bearing on the successful operation of surface cleaning units. The most important single characteristic of both coal and its associated impurities from the standpoint of cleaning is specific gravity. Other characteristics related in one way or another to the preparation of coal are rank, petrographic composition, structure and hardness, and friability. These and still other coal properties are discussed in the first section of this chapter and impurity characteristics in the second. COAL CHARACTERISTICS RELATED TO PREPARATION Rank As a result of work done over a period of several years by committees of the American Society for Testing Materials and the American Standards Association, standard specifications are now available showing the classification of coals according to rank and quality of grade. The term "rank" expresses the degree to which the original coal-forming material has been changed by metamorphism through successive stages from peat to anthracite. Table 1 shows the classification of coals according to rank as devised by the committees of the organizations mentioned. The basic scheme of classification for the higher-rank coals is according to fixed carbon content, calculated to the dry, mineral-matter-free basis. Groups of lower rank are divided

Jan 1, 1950

By J. H. Bucher

The effect oj strengthening by the precipitation of CbC on the toughness offerrilic steel (0.11 pct C, 0.74 pct Mn, 0.02 pct Cb) was stlrdierl. A g-veater degree of pvecij~itatiotz strengthning is ohtaznable by aging the so11ution-treated steel rtt velaticely Low temperature was (1050" to 1l0O3F) than at higher temperatures (I150" to 1200°F). Tlzis ),eslrlts because a finer dispersion of CbC is obtained. However, the ductile-brittle transition te~ripertltlo.e is raised approximately tlzjeee tirues as IFLIIC~ perv a given yield stress increase) by aging in the lower tempareture range, as opposer1 to the Irigher temperaturee range. This is proposed to result pl-iir~avily because different precipitation distributions ar-e associated with the different aging -treaments. For tile steel aged at 1050" and 1100 F, heavy: precipitation on disloccctions occurs resulting in a high degree of rlislocution pinningh tl~us lowevirzg- the toilguiess. in tll c(.rise of the steel aged at 1150 'a?zd 1300"F, Pvecipitatiol~ is irzove g-enerally distributed throughout the matrix rather limn preferentially on dislocations.; and Ike detlsitj, oj mobile dislocations is not sttyong-ly affected. THE most effective means of strengthening hot-rolled ferritic steels are grain refinement and precipitation hardening. It is well-known that grain refinement increases both the strength and the toughness. However, the upper limit of yield strength obtainable by grain refinement alone is about 60,000 psi,'12 i.e., without the formation of acicular structures of lower toughness. The most economical means of obtaining higher strengths is the addition of small amounts of elements such as columbium, vanadium, and titanium which form carbonitrides. These precipitates are very effective in increasing the strength, but the ductile-brittle transition temperature is is Although it is agreed upon that precipitation decreases the toughness, there has been little effort to isolate the causative aspects of embrittlement. The purposes of this research are to assess quantitatively the embrittlement associated with different precipitate distributions and morphologies, and to correlate the degree of the embrittlement with the microstruc-ture. In this manner, a more fundamental insight into the mechanism of embrittlement may be gained. The steel selected for this purpose was a low-carbon, columbium-bearing steel which, after solution treatment, was aged in various time-temperature cycles while attempting to hold all other microstructural variables constant. MATERIALS AND PROCEDURE The composition of the steel used in this investigation is given in Table I. Starting with commercially hot-rolled material 0.074 and 0.280 in. thick, tensile blanks were cut from the thinner material and sub-size Charpy blanks from the thicker stock. The steel had been rolled using a low finishing temperature and rapid cooling after hot rolling to produce grain refinement. Also, chemical-extraction analysis and electron-microscopic examination revealed that the cooling was rapid enough to suppress any significant precipitation of CbC. Therefore, the as-rolled steel is essentially in the solution-treated condition in terms of the precipitation reaction, and it was used as the base material in this investigation. The room-temperature tensile properties of the as-rolled steel aged at 1100", 1150", and 1200°F for various time intervals were determined, see Table 11. The ductile-brittle transition behavior was studied for smooth and notched tensile specimens, and longitudinal half-size (0.200 in. thick) Charpy V notch specimens aged at 1100" and 1150°F for various times, also Table 11. In addition, tensile specimens aged for single times at 1050" and 1200°F were evaluated with respect to their ductile-brittle transition. Only one 1050°F treatment was used because of the extremely slow kinetics of precipitation at this temperature and because no significant difference between 1100°F aging was observed. Only one treatment at 1200°F was used because aging at this temperature alters the shape of the grain boundary cementite particles present in this steel and complicates analysis. The design of the tensile specimens is given in Fig.1.

Jan 1, 1968

By J. Charles Miller

NATURAL carbon dioxide has recently been exploited in the United States in consequence of oil and gas developments in the Western States and the growing demand by transcontinental and transoceanic shippers for solid carbon dioxide. The discovery by drilling of commercial deposits resulted in consideration of its geographic and geologic distribution and occurrence. Its wide distribution in nature is evidenced by its occurrence in the atmosphere, hydrosphere and lithosphere. The question of origin of carbon dioxide involves consideration of theories similar to those concerning natural hydrocarbons, although available evidence favors an inor-ganic rather than an organic source. Areas favorable to development of commercial production appear to be those in proximity to igneous rocks or in the vicinity of decadent volcanic activity, where, it has long been known, the gas is evolved either free or dissolved in the waters of furnaroles, geysers or mud pots. Structure contour maps are presented showing the Wagon Mound anticline in New Mexico and the Farnham anticline, Utah. A well drilled on the latter supplies gas to a 20-ton plant manufacturing solid carbon dioxide at Wellington, Utah, on the Denver and Rio Grande R.R., whence it is shipped to surrounding territory and to the West Coast. Before funds are invested in a plant for the manufacture of liquid or solid carbon dioxide, whether supplied by wells or springs, an effort to ascertain the volume of gas available is advisable. The use of present methods of estimation of gas reserves with modifications to account for the quantity absorbed by any water present in the produc-ing formation is recommended. The Farnham anticline is used as an example and computations are made of the probable volume of gas originally present in the struc-ture. No attempt was made to compute reserves in the Niland area, California, for the reason that in such areas it is believed the volume is indeterminate.

Jan 1, 1937

By Hans Lundberg, Theodor Zuschlag

Based upon an instrumental improvement, a new development has taken place in the art of electrical prospecting, and some remarkable results have already been obtained with regard to potential exploration. In order to visualize the importance of this development, it is deemed advisable to review briefly the fundamental facts about potential surveys. Potential exploration may be carried out qualitatively or quantitatively. Qualitative investigations are made by determining and plotting on a map points of equal potential, whereby any anomalies are revealed, without, however, much clue to their magnitude. Quantitative investigations determine the variations of potential or potential drop, and thus show not only the location of the anomalies, but also their magnitude. Figs. 1 to 6 illustrate the influence of simple types of ground inhomo-geneities, assuming one effective exciter potential only. Such a condition can be closely realized by connecting an electric current source to two electrodes, one of which is located at a great distance. Assuming uniform ground resistivity, the resultant potential distribution mar be represented by concentric spheres. Any change from the normal condition causes a characteristic distortion of the spheres, which becomes different for different types of resistivity variation. The series of Figs. la to 6a illustrates schematically results of qualitative investigations and series lb to 6b results of quantitative investigations. Figs. 1 and 2 picture the well-known case of local resistivity variations normally encountered in ore prospecting. Figs. 3 and 4 show the reactions caused by more or less vertical resistivity contacts and Figs. 5 and 6 refer to the problem of ground-water and bedrock investigations where the resistivity contact is horizontal or nearly SO. It is evident from Figs. 5a and 6a that qualitative measurements do not permit an identification of such general geological features as widespread horizontal strata, because the resultant contraction or expansion of the equipotential circles at the surface cannot be recognized without quantitative determinations. On the other hand, qualitative measurements are well suited for the exploration of local or lateral resistivity

Jan 1, 1932

By Mark Malamphy

DURING colonial times, Brazil was famous for the richness of her alluvial gold deposits. Paul Ferrand has estimated that the gold produced during the period from 1700 to 1820 was the equivalent of some 64 million pounds sterling. Since that time, most of the more prolific alluvial deposits have been exhausted. A few gold mines are still func-tioning, notably the Morro Velho mine, which is one of the deepest mines in the world. Today, the gold production of Brazil is insignificant when compared with world figures, but there are still many gold-bearing regions and it is probable that in at least some of them profitable returns would result from an exploitation program taking advantage of all the most modern innovations in gold mining and ore treatment on a large scale. In order to demonstrate the value of some of these abandoned pros-pects and stir up interest in increasing the national gold production, the government has stimulated research. Experimental plants have been and are being established in various places, and tests on large quantities of ores are being carried out on a semicommercial basis. The Geological Survey of the State of Minas Geraes is very active in this line and the Federal Institution is also showing an increased interest in the matter. One of the lesser known gold-bearing regions of Brazil is in the vicinity of Lavras, in the State of Rio Grande do Sul. Gold was first reported from this region in the early part of the nineteenth century. In 1811, D. João VI sent an experienced prospector from Minas Geraes to investi-gate the validity of the reports. According to the reports of Baron

Jan 1, 1934