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By Colin C. Harris, Nathaniel Arbiter

Flotation kinetics is the study of the variation in amount of froth overflow product with flotation time, and the quantitative identification of all rate con- trolling variables. With such variables maintained constant, the algebraic relationship between the proportion of mineral floated and flotation time is a flotation rate equation. This contains the constant values of all the rate determining variables implicit in one or more rate constants which must be evaluated from experimental data. The form or forms of the rate equation can either be deduced from assumptions or facts established about the mechanism of the process, or, more commonly, determined empirically or by analogy with similar rate process. (See pages 215 to 226 and 221 to 227.) The earliest contributions on flotation kinetics came in the mid- ~hirties,3,27,31 with interest increasing in recent years. The broad goal of these studies is the reduction of the total variability of a flotation system to equations among the individual variables, or among a lesser number of dimensionless groups.43 Although the goal is at present far from realization, its attainment will yield many practical advantages. The quantitative under- standing of the process should lead to improvements both in metallurgical results and flotation cell design. It should lead also to reliable methods for scaling-up* of laboratory and pilot plant results to full size operation without the need for expensive and time-consuming mill tests on commercial machines. Finally, this type of quantitative information will assist the automation of flotation cells and circuits as well as control by computers. Replacing present methods of control based on post-mortem assays and trial and error manipulation of reagents and cell variables by control through exact process analysis should yield higher levels of grade and recovery through reduction of the large variability of present-day results. CHEMICAL ENGINEERING ANALOGIES: Industrial flotation always involves flow of pulp through a series of stirred tanks. It thus bears formal analogy to many chemical engineering processes, the kinetics of which in flow systems has been studied for many de- cades.38,39,73,83 It will be useful to review these studies before considering flotation kinetics. Batch and continuous treatment are classified in Fig. 1. Batch operation in the true sense is unknown in flotation where concentrate is always removed

Jan 1, 1962

By P. V. Martin

Shortly after the middle of the nineteenth century, the invention of the regenerative open-hearth furnace and the development of the Bessemer process stimulated a rate of steel production whose magnitude created an unprecedented demand for pig iron. Revolutionary improvements in furnace design, auxiliary equipment, and operating technique enabled the blast furnace to keep abreast of the constantly increasing requirements of the steel mill. The development of improved blowing equipment, more adequate facilities for material handling, and particularly the general use of anthracitc and coke to replace the physically weaker charcoal, led to a rapid expansion in both the height and volume of furnaces. Beyond a doubt, however, the greatest single factor in blast-furnace improvement at this time was the use of the higher blast temperatures made available by the replacement of the recuperative iron pipe stoves by the regenerative Cowper brick stove. The increased blast temperature not only resulted in greater output but also reduced fuel consumption . far more than could be explained by the additional heat content of the blast. The progress of iron manufacturing was thus largely mechanical and thermal. Little attention was given the chemistry of the process until the publication of the investigations of Sir Lowthian Bell.1 Bell's painstaking experiments and investigations gave to the blast-furnace man his first real scientific conception of blast-furnace chemistry. Bell's recognition of the dual function of the carbon, the technical importance of reversible reactions and chemical equilibria, and his conception of the degree of oxidation of the carbon as shown by the analysis of the outgoing gases as a criterion of furnace efficiency, laid the foundation upon which has since been erected the structure of blast-furnace theory. Prominent among those availing themselves of Bell's data as .a basis of further study was M. L. Gruner,2 professor of the French School of Mines. His "Blast Furnace Phenomena," published in 1870, presented

Jan 1, 1940

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

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

Jan 1, 1945

By J. Lemish

Considerable research has been conducted in Iowa in recent years on carbonate aggregate reactions in concrete. Groups outside the state have become active in the past few years after recognizing that certain carbonate aggregates are reactive in concrete. The paper reviews the nature and extent of the problem and a summary is given of research by the author and his associates. In recent years considerable research has been conducted in Iowa on carbonate aggregate reactions in concrete. The research is part of a general study on the behavior of carbonate rocks as concrete aggregates sponsored by the Iowa State Highway Commission. Research on carbonate aggregates has not been extensive in the past. Laughlin1 published one of the first papers on carbonate aggregates in 1928 and was followed by others, notably H. S. sweet,' B. Mather et al.,3 and K. Mather4 who emphasized the petrographic and physical aspects of carbonate aggregates. The recognition that certain carbonate aggregates are reactive in concrete has led to increased participation in research in the past few years by groups outside of Iowa. Significant contributions have been made by Swenson and Gillot,5 Hadley,6 and Chaiken and Halstead7 in work which emphasizes the expansion of carbonate rocks in alkaline environments and the reaction of carbonate minerals or dedolomitization with alkalies. It is the purpose of this paper to review briefly the nature and extent of the problem and present a summary of the research by the author and his associates. EXTENT AND NATURE OF THE PROBLEM The problem is the deleterious behavior of certain carbonate aggregates in concrete. It was first recognized in Iowa over 20 years ago when poor service records of certain highways were correlated with aggregates produced from the Glory and LeGrand quarries. Deleterious behavior of carbonate aggregates have been reported in Canada and, more recently, in New York and Virginia. As more knowledge is gained concerning the problem, distress in concrete related to carbonate aggregates may be recognized over a widespread area. The problem may potentially exist in the Midwest, the Northeast, and other parts of the country underlain by thick sections of carbonate rocks readily available for utilization as aggregates. The nature of distress in Iowa highways is a general weakening and deterioration of concrete characterized by progressive cracking and spalling away from joints and edges (Fig. 1). The distress generally occurs after 15 years of service and becomes progressively worse. Specimens of such concrete lack the toughness of sound concrete and break easily under the hammer in the manner of a soft brick. The matrix is generally highly carbonated and dark borders, or reaction shells or rims outline the argillaceous carbonate aggregate fragments (Fig. 2). Cracks observed in cores cut across the aggregates and concrete matrix. Although localized volume change (expansion) is associated with spalling, there is no definite field evidence in Iowa that excessive growth of concrete slabs has occurred. The experience with carbonate aggregates in Iowa indicates that the concrete deterioration is not the same as that induced by the alkali-aggregate reaction associated with siliceous aggregates. The principal difference is that in Iowa the distressed concrete is weakened throughout the slab. In concrete affected by the alkali aggregate reaction, the

Jan 1, 1961

By John Norton

THE tremendous increase in the use of metals that have been prepared by the various cold-working processes during recent years has greatly stimulated the investigation of problems concerned with the fundamental nature of these processes. It has been observed in practice that different methods of bringing about the same dimension changes in a sample result in a rather wide range of properties. Cold working reduces the ductility of a metal, or what is perhaps more nearly correct, its "working capacity," and naturally the manufacturer wishes to produce an article that has as large a working capacity as possible, and to produce it with the smallest number of operations, It has also been known for some time that cold deformation produces a parallel alignment of the crystal grains of a metal, and that the type of this preferred orientation depends to some extent at least upon particular processes employed in the deformation. The present investigation has for its purpose the study of the relations between the various factors of a cold-working process and the preferred orientation of the metal crystals resulting from this deformation. The work is chiefly confined to a study of cold-drawn seamless tubing.

Jan 1, 1932

By George R. Elliott

Methods are presented for measuring and comparing "degree" of water drive, and for observing the control that rate of withdrawal exerts over decline of reservoir pressure. Degree of water drive is studied from pressure-production curves of 10 reservoirs; the method used to present these comparatively is to convert cumulative oil production from barrels to percentage of ultimate. Degree of water drive is also represented by a "water-encroachment factor," representing barrels of water influx per pound-month per acre-foot of oil reservoir. Pressure-production curves for the water-drive reservoirs after a period of declining pressure show a diminishing angle of slope, in some cases to the point where pressure ceases to decline or where it even increases; the shapes of these curves are in marked contrast to the dissolved-gas type of curve, which shows a general trend toward zero pressure at ultimate oil recovery. Yearly rate of oil production in percentage of ultimate oil recovery is correlated with pressure decline. The correct rate of production of oil with its associated gas and water sustains pressure in reservoirs having a high water-encroachment factor. For reservoirs having a low water-encroachment factor, it is necessary to inject the produced water and even inject large volumes of water from an outside source. The discussion of the actual reservoirs is preceded by a general review and is followed by a substantial bibliography. It is now generally accepted that water drive is capable of yielding 60 to 80 per cent of the original oil in place in most reservoirs, as compared with 20 to 40 per cent for dissolved-gas drive. There is no need to question the importance of controlling a reservoir in order to take advantage of such an efficient mechanism. What is a water-drive reservoir? Oil reservoirs usually combine two or more of the four basic mechanisms: dissolved-gas drive, gas-cap drive, water drive, gravity drainage. A water-drive reservoir is one in which water advances to take the place of the oil and gas produced. When the oil withdrawal rate is sufficiently low, the water will tend to maintain pressure. The maximum effectiveness is attained when the water follows the oil withdrawal so closely that little or no decline in pressure occurs. Oil in its underground reservoir is associated with water. This water is significant in the production of the oil according to the source of supply and the permeability of the surrounding formation. As oil is produced and the pressure is lowered, water can move in to replace the oil. With adequate supply and sufficient permeability, actual movement takes place on an extensive scale. The first movement of water takes place by expansion of the water and its associated fluids. While this expansion is of little importance in some fields, in others it is sufficient to supply all of the energy required for the production of oil. When a pressure differential has been established

Jan 1, 1946

Several of the current concepts of brittle fracture involve consideration of, the existence of defects or flaws. Griffith 1 observed that the tensile strength of brittle materials was several orders of magnitude less than might be expected from the calculated strength of the molecular bonds. He was able to show that the stress concentration at the tip of an elliptical crack is sufficient to raise the local stress level many fold. He therefore proposed that real materials do contain such stress risers in the form of minute cracks and that this accounts for the rather large difference between theoretical and actual strengths of brittle materials. The degree of stress magnification depends to a great extent upon the orientation of the crack with respect to the general stress system, and to the general geometry of the crack. It is but a small step to extend the theory to include flaws and defects of other sorts which, though they may be less tractable mathematically than cracks, may still function as stress risers in a real sense in real materials. Brace 2 proposed that the application of the Griffith theory to rock material could be tested in two ways: "(a) by finding the orientation of cracks from which macroscopic fractures have developed and (b) comparing failure strengths from tests at different conditions of loading." In 1963 the author and coworkers at the Bureau of Mines, Twin Cities Mining Research Center, working on a problem involving relationships between strength, sonic velocity, and microstructure "eveloped an experimental technique to examine several somewhat similar questions; namely. does the frequency of occurrence of actual or potential stress risers dictate the relative strength of the material as proposed by Weibull;4 can actual flaws or defects in the rock structure be identified and related to strength and perhaps other properties in accordance with Griffith's theory; and is the anisotropic strength and elastic behavior of certain rocks related to the preferred orientation of these actual or potential stress risers? The experimental approach developed to answer these questions appears equally applicable to the testing of Griffith's theory as proposed by Brace. Basically the approach consists of a series of point-load tensile tests followed by petrofabric examination of thin sections prepared from the specimens in order to identify and apply a quantitative measure to microstructural defects which may have contributed to the failure process. In the point-load test, tensile stresses are induced by a compressive load applied to the center of a disc-shaped specimen by means of two opposing hemispherical indentors. Failure generally occurs as a single fracture parallel to the axis of loading and bisecting the disc. Because of the geometrical symmetrical the induced tensile stresses are symmetrical about the loading axis

Jan 1, 1967

By A. R. Rosenfield, G. T. Hahn

The effects of adding 0.025 volume fraction of uniformly dispersed Tho2, particles (particle size -380A) to iron have been examined. The two-phase alloy is shown to have a lower transition temperature and higher cleavage stress than either the base metal or a solid-solution alloy (Fe-3Si). Enhanced cleavage resistance is thought to be a consequence of particles limiting the effective slip distance of dislocations and thus the ability of Pile-ups to act as stress concentrations. Further calculations predict that the highest cleavage strengths are attained with uniform dispersions, where the particle size is kept small (-250A) and the volume fraction is relatively large (-2 to 3 pct). ALTHOUGH a fine dispersion of second-phase particles is known to impart strength to an alloy, the possibility that it might also impart ductility has only recently been explored. Outstanding progress has been made in the production of ductile tungsten alloys containing Tho21,2or (Hf, Zr)C,= but the contribution of the dispersion to ductility has neither been optimized nor fully analyzed. The basis for such an analysis has now been developed1,5 and is discussed briefly below. Experiments on iron are also described that attempt to isolate one of the possible ductilizing mechanisms and test its effectiveness. In analyzing these experiments, it is important to remember that cleavage obeys a stress criterion, and that either a lower ductile-to-brittle transition temperature or a higher cleavage stress is evidence of enhanced resistance to cleavage. DUCTILIZING MECHANISMS Slip Blockage. Cleavage fracture of polycrystals may be initiated at the intersection of a slip band (or twin) and a neighboring grain or a large (-1 to 5 µ) particle. The slip band generates a stress concentration at its head, and either the grain boundary fractures, the particle fractures, or cleavage is initiated in a neighboring grain. Experimental evidence for this viewpoint is found in metallographic studies8-8 and from the observation that cleavage is usually preceded by yielding.8-11 The potency of a slip band as a stress concentrator

Jan 1, 1968

By R. W. Smith

There are many inconsistencies and gaps in available information concerning the mechanism whereby dodecylamine acts as a collector for quartz. The author compares the studies which have been made in correlating the contact angle with adsorption density on quartz over all pH ranges, and attempts to resolve some of the inconsistencies. In recent years much information has been obtained concerning the mechanism whereby dodecylamine acts as a collector for quartz. Fuerstenau,1 for ex- ample, has shown that adsorption density and zeta potential under some conditions, at least, can be correlated with contact angle and flotation rate. There appear, however, to be several inconsistencies and gaps in information available. One inconsistency involves trying to correlate contact angle with adsorption density on quartz over all pH ranges. Fuerstenau's correlation at a collector concentration of 4x10-5 moles per liter dodecylamine acetate and about pH 10 shows a contact angle of about 80 degrees occurring at approximately monolayer coverage. If Gaudin and Morrow's2 and Morrow's3 contact angle data for near neutrality (pH 6 to 7) are now compared with deBruyn's4,5 adsorption data on quartz in a similar pH range, it will be noticed that a contact angle of 38 to 40 degrees corresponds to complete monolayer coverage (at an amine concentration of approximately 10"3 molar). In fact even at an amine

Jan 1, 1963

By J. L. O’Brien, M. Suenaga, K. M. Ralls, V. F. Zackay

The effecls of aging a1 400°C on tile resistive transition at 4.2°K of a superconducling 70Zr-30Nb alloy are reporled. Microstrclural changes were studied by critical temperature, resistiue critical field, residual resistiuily, and microhardness measurements and by X-ray diffraction, optical microscoby, ad replication electron microscopy. The result of the aging treat- A defect-free Type 11 superconductor in a magnetic field above Hc1 cannot sustain a transport current runt is a fine array of w-phase pavticles with a mean center to center interparticle spacing of about 800A. At an aging time of 300 hr the maximum onset critical current density is rcached. The particle size at the maximum current density if about 4202. At times longer than 300 hr effective particle impingement leads to lower onset critical current densities. perpendicular to the applied field without power loss in the sample.'-3 This power loss is due to flux line motion caused by the Lorentz force and is manifested by a longitudinal voltage.4-6 When defects are present in the material, flux lines are pinned until the Lorentz force exceeds the "pinning force". That is, it is thought that flux lines reside in free-energy wells existing at the defects, and the critical Lorentz force is that which when integrated over distance will supply the free-energy difference necessary to move the flux

Jan 1, 1968

By Henry N. McCarl

Lightweight aggregates include a variety of mineral and rock materials used to provide bulk in concrete building units (block), light- weight structural concrete, and precast concrete units, as plaster aggregate, insulating fill, and other structural and/or insulation purposes. They are distinguished from other mineral aggregate materials by their lighter unit weight- 80 to 100 pounds per cubic foot (pcf) or less for loosely packed lightweight aggregates as compared to 125 pcf or more for crushed stone, sand, gravel, air-cooled slag, and other more common mineral aggregates. The various lightweight aggregate materials may be classified into four groups as follows: 1) Natural Lightweight Aggregate Materials-prepared by crushing and sizing natural rock materials such as pumice, scoria, tuff, breccia, and volcanic cinders. 2) Manufactured Structural Lightweight Aggregates-prepared by pyroprocessing clay, shale, or slate in rotary kilns or on traveling grate sintering machines. 3) Byproduct Lightweight Aggregates-prepared by crushing and sizing foamed and granulated slag, cinders, and coke breeze. With the exception of processed slag, this group is becoming less important as time passes. 4) Manufactured Insulating Ultralight- weight Aggregates-prepared by pyroprocessing ground vermiculite or perlite. This chapter will focus on the use of natural lightweight aggregates and manufactured insulating ultralightweight aggregates, and both the production and use of manufactured structural lightweight aggregates with some comments on byproduct materials. Detailed discussion of the production and use of both expanded and air-cooled slag is presented in a separate chapter in the utilization section of this volume, and there are separate commodity chapters on vermiculite, perlite, pumice, and volcanic cinders. Discussion of the commodities covered elsewhere in the book will be limited to observations on their utilization and relation to other lightweight aggregate materials. All materials considered as lightweight aggregates are derived from some initial natural raw material. While historical definitions have included such organic materials as straw and peat as lightweight aggregates, the discussion in this chapter will restrict itself to lightweight aggregates derived from mineral or rock materials. Thus while the actual lightweight material in use may be a manufactured product, it is derived from an ore or raw material that is obviously a mineral resource. In this context, then, the reserves of raw materials for lightweight aggregate use may include iron ore and flux stone (the components of blast furnace slag) as well as coal (the raw material from which cinders are derived) as well as those clay, shale, and slate deposits that display the characteristics of bloating or controlled expansion when subjected to elevated temperatures (1600 to 2400°F.).

Jan 1, 1975

By C. D. King

The key to maximum production of ingots for the war effort is maximum production of pig iron. For any given furnace and ore, the most important single influence on blast-furnace production is the quality of the furnace coke. It is generally recognized that undoubtedly deterioration of Pittsburgh coking coals will be accelerated by the depletion of some of the better grades of coal; the extension of mine mechanization, with attendant degradation of coal quality; and the opening of new coal fields, some of which are known to be fairly high in sulphur. All of these factors, contributing as they do to higher ash and sulphur, and not infrequently to inferior quality of coke, made it desirable that an extensive study be undertaken to determine the effect of washing some coals that closely approximate the average chemical composition of coking coals to be expected in the future by the subsidiaries of the United States Steel Corporation in the Pittsburgh district. It was deemed advisable to study the improvement obtained by washing such coals and to determine the need for supplementing the existing coal washery at Clairton to assure continued maximum production of pig iron from presently available furnace stacks. The existence of the coal washer at Clairton made it possible to conduct tests on coals used in raw form and on similar coals after washing. This study covers an investigation of the quality of furnace coke as affected by washing coking coals, and is confined to the use of 100 per cent high-volatile Pittsburgh seam coals from Fayette and Greene Counties in the manufacture of furnace coke. It covers the improvement in chemical and physical properties as well as the degree of uniformity in coke obtained by washing these coals, and includes the effect on blast-furnace production and practice. The test period involved is four months; the plants, Clairton by-product coke plant, and the Carrie No. 1 and No. 2 blast furnaces at Rankin, Pa., Carnegie-Illinois Steel Corporation. Clairton By-product Coke Plant and Coal Washer The Clairton by-product coke plant carbonizes 30,800 net tons of coal daily in 22 batteries containing 1482 ovens. Three oven sizes are used, commonly known as wide, medium, and narrow types, recognizing the difference in oven width, These ovens also differ in height and length. The present coal washer has a daily capacity of approximately 14,000 tons, leaving 16,800 tans to be carbonized in raw form. Washed coal is used on all the narrow ovens and on three of the six batteries with ovens of medium width, raw coals being used on all the remaining ovens. The customary arrangement is

Jan 1, 1944

By C. Ernest Birchenall, Robert F. Mehl

Application of diffusion laws in the customary form to experimental studies in binary metallic solid solutions has shown the diffusion cocfficient to vary with concentration for all systems investigated. The factors determining this variation have not been ascertained. However, the question of whether the diffusion coefficient would become a constant, independent of concentration throughout a single phase if the concentration gradient in the diffusion equation were replaced by an activity gradient has been an attractive subject for speculation. Wagner¹ derived an expression for the force acting on a diffusing particle in terms of the chemical potential. This was also the approach chosen by Jost2 in his monograph. From a somewhat different point of view, Eyring3 and his co-workers have used activity gradients when dealing with diffusion in concentrated nonideal solutions. The only actual test with experimental data is that given by Darken,4 though this is more qualitative than quantitative. Many others opposed the application in any way of thermodynamic concepts to kinetic phenomena, including diffusion processes. A rigorous examination of this principle requires good data expressing the relationship between activity and concentration for solid solutions for which reliable diffusion work has been done. The literature provides such information only for the interstitial solution of carbon in gamma iron (austenite) and for the substitutional copper-zinc solutions (alpha brass). Activity data for carbon in austenite at 800°C and 1000°C are available from the recent work of Smith5 on the equilibrium of hydrogen-methane and carbon monoxide-carbon dioxide mixtures with gamma iron. Combining these with the diffusion studies of Wells and Mehl6 makes possible a quantitative test for this interstitial solid solution. The vapor-pressure determinations for zinc over brass by Hargreaves7 allowed the calculation of activities in this system over a wide range of temperatures and concentrations. Extensive investigation of diffusion in this substitutional solid solution has been carried out by Rhines and Mehl.8 Activities in Brass9 If the vapor phase of zinc is assumed to behave as an ideal gas, any solid or liquid solutions that are in equilibrium with the same partial pressure of zinc at the same temperature have the same thermodynamic activity of zinc. In order to assign a numerical value to the activity azn, it is necessary to choose some standard reference state to which an activity value of unity is arbitrarily assigned. It is customary to choose the liquid or solid state of the pure material. Then azn is defined numerically by

Jan 1, 1947

By Sydney H. Ball

MINERALS used primarily for personal adornment and decorative purposes are called precious stones. To be so prized, the stones must possess beauty of color, must not be too common, and must be hard enough to withstand ordinary wear. If transparent, they must have brilliancy and fire. Almost one hundred minerals have been used as precious stones, the noble gems being the diamond, emerald, ruby, and sapphire; pearls are frequently included by courtesy. These gem stones, however, are sometimes equaled in beauty by fine opals, aquamarines, ourmalines, spinels, chrysoberyls (both cat's-eye and alexandrite), and spodumenes (hiddenite and kunzite). The Greeks, Romans, and medieval Europeans grouped together gem stones according to color and degree of transparency, and only as the niceties of mineralogy began to be known, about a century ago, was it realized how many different minerals have the beauty required of gem stones. Pliny, for example, did not distinguish between rubies and the red varieties of spinel and garnet, although he conjectured that the beryl and emerald were one mineral. GENERAL SURVEY Early man treasured bright colored berries, attractive shells, white teeth of wild animals and brightly colored pebbles, and used them as personal ornaments. In the eastern hemisphere, the earliest stones used were members of the quartz family (100,000 to 75,000 B.C.); then obsidian and amber (50,000 to 25,000 B.C.); the jade minerals, fluorspar and jet (22,000 to 7000 B.C.); turquoise (7000 to 3400 B.C.); lapis lazuli and garnet (prior to 3500 B.C.) ; emerald (2000 to 1800 B.C.) ; sapphire, ruby and diamond (800 to 500 B.C.). Indeed, gem mining is the oldest form of mining, and before any metals were known primitive man recognized about 18 gems and decorative stones. At first he sought them in stream gravels and residual deposits but by 3400 B.C. the turquoise mines of the Sinai Peninsula were operated. This was the world's first important hard-rock mining enterprise. The Afghanistan lapis lazuli mines may

Jan 1, 1949

By James A. Crookston, William D. Fitzpatrick

Committee C-8 of the American Society for Testing and Materials defines refractories as "material, usually nonmetallic, used to withstand high temperature," and it defines the term refractoriness thus, "in refractories, the capability of maintaining the desired degree of chemical and physical identity at high temperatures and in the environment and conditions of use.” The ability to withstand high temperatures is critical to classifying a material as a refractory. However, as the foregoing definition of "refractoriness" implies, the refractory material may be subjected to and is expected to resist not only high temperatures but a variety of other destructive forces incidental to its use. These include abrasion, impact, thermal shock, chemical attack, and high level loads at high temperatures. The various industrial applications of refractories represent an infinite variety of combinations and degrees of severity of these destructive forces, including high temperatures. Naturally, such a variety of application conditions leads to a need for a wide variety of refractory products to satisfy those conditions. The number of refractory products available is great enough that some form of classification is necessary to a discussion of refractories. Refractories may be classified in several ways, but the most suitable one is based on their general compositions and to lesser degrees on their physical condition and distinctive properties. The primary types of brick include aluminosilicate brick (fire clay and alumina), basic brick (magnesia and chrome ore, alone and in various combinations), silica brick, insulating brick, and special refractories (carbon, SiC, ZrO2, zircon, borides, and nitrides). Brick is, of course, preformed and usually is heat treated at high temperatures before use, but in some instances is unburned and/or chemically bonded, including the relatively new class of tar-bonded magnesia and/or dolomite brick. In addition to preformed refractories, another broad category includes the so-called specialty refractories, which are usually made in the same types as itemized for brick-bonding mortars and high temperature cements, hydraulic setting castables or refractory concrete, plastic firebrick, and ramming mixes. Refractory grains, such as fire clay and high alumina calcines, dead-burned magnesite and periclase, and dead-burned dolomite are also considered refractory products. Bricks are also classified on the basis of physical dimensions, as standard sizes and special shapes. The standard sizes are those which are of definite shape and design and are designated as 228.6 x 114.3 x 63.5 mm (9 x 4 ½ x 2 ½ in.) and 228.6 x 114.3 x 76.2 mm (9 x 4 ½ x 3 in.) straights and series. Bricks of nonstandard sizes are referred to as special shapes. These come about as a result of a particular need for a given furnace or for a particular application. Types and Classes of Refractories Fire Clay Refractories Classification: Fire clay refractories, as the name implies, are composed essentially of fire clay and/or calcined fire clay in varying proportions. The ASTM Standard Classification of Fireclay and High Alumina Refractory Brick, C27-70 (reapproved 1976), gives five classes of fire clay brick designated as super-

Jan 1, 1983

By C. E. Sims, G. A. Moore, D. W. Williams

During the past several years the steel casting industry has made studies of heavy castings in which the test bar has been taken from heavy sections rather than from attached or separately cast coupons. It has been noted that the ductility properties of these heavy sections are often lower than those normally expected. Such lowered ductility is usually accompanied by a spotty test bar fracture and the ductility values often can be greatly improved if a low-temperature aging treatment is given to the casting. A loss of ductility of this type is considered "abnormal," since it is not accompanied by an increase of tensile strength or hardness, and "temporary" when the ductility can be restored by aging, The cure of such an abnormal condition represents a real improvement in the quality of the steel. Some hundreds of previous investigations, largely qualitative in nature, have established beyond reasonable doubt that hydrogen is normally present in newly manufactured steel and that this gas, in small amounts, can cause a temporary ab- normal loss of ductility. The commonly observed association of high gas content and low ductility has given strong evidence for the presumption that hydrogen, possibly assisted by other gases, is the primary cause of the low ductility observed. Accordingly, the Steel Founders' Society of America has, since Nov. I, 1944, sponsored investigations at Battelle Memorial Institute whose primary objective is to obtain quantitative information on the relation of the amount of hydrogen and nitrogen in steel, together with associated methods of steelmaking and treatment, to low-ductility effects and porosity. In order that these investigations might proceed on a quantitative basis, hydrogen analyses of a precision considerably higher than any previously reported in the literature were necessary. 'The method chosen was selected entirely on the basis that it had the highest probability of freedom from uncontrollable errors and will be described in detail in another publication.' Briefly, the method used consisted of the hot extraction of solid pieces of steel weighing from 45 to 50 g in a highly evacuated quartz tube maintained at 1050°C (1925°F) for a period of approximately 40 hr. The greatest precautions were taken to eliminate blanks and insure a sound gas-collection system. vacuum and temperature conditions were maintained automatically. Mercury-filled risers were used for the introduction of samples in order that the System could be degassed thoroughly in

Jan 1, 1949

By D. A. Woodford

In a constant-load creep test, if the density of nlobile dislocations is assumed constant for strains exceeding that corvesponding to the minimum creep rate, it is shown that the creep rate may be approximated by the equation where E is the nominal strain, o0. is the initial stress, and a' the stress fov unit dislocation velocity. The constant C contains the mean density of mobile dislocations and n is a measure of the stress sensitivity of dislocation celocity. This equation is shoum to be applicable to published data on an alloy steel and on nickel. The degree of plastic instability and hence the creep ductility is dependent on the calue of n for these materials. When instability becomes gross and local macroscopic necking occurs, the assumptions are no longer valid. On the basis of this equation, and the strain-time relation derived from it, a method of predicting the creep behavior at different stresses is suggested. MOst analyses of creep data have been concerned with time-dependent transient creep or time-independ- ent secondary creep in constant-stress tests. The far more widely used constant-load test has been neglected in terms of a mechanistic approach. In general, since the strains involved are usually small, the same laws for transient creep may be applied to both types of tests. However, there is no steady-state creep in a constant-load test since the stress increases continuously. Any apparent steady state observed on a strain-time plot is either fortuitous or illusory, and is generally revealed as a continuously varying creep rate on a carefully constructed strain rate vs time plot.* Transient creep may be understood in terms of a simple differential equation representing the change in mobile dislocation density with time:' where p is the density of mobile dislocations. The first term on the right is related to first-order kinetics of dislocation multiDlication and the second to second-order kinetics of exhaustion. On the basis of this equation, several authors2-4 have found good agreement with experimental transient creep curves for a number of materials. When k1p = k2p2, a steady-state creep

Jan 1, 1968

By A. W. Gauger

It is with some trepidation that I approach my subject, for I know that I shall at once incur the suspicion of the mechanical engineer, with his concern for boiler tests and efficiencies; of the mining engineer, with his mechanization problems; and of the chemical engineer with his unit processes. Nevertheless, it must be recognized that the technology of fuels, the systematic body of knowledge relating to the production, processing and utilization of mineral fuels, has grown to such proportions and involves so many widely diverse applications of fundamental science and engineering that it behooves us to stop and consider just what its status is in relation to other technologies, as well as in relation to the present and future needs of the social order. The time has come when technologists, applied scientists and engineers must consider the possible effects that their achievements may have on Society. The development of a machine to - -replace -several hundred men is a fine achievement when considered solely from the point of view of creative endeavor. But what of the men who are displaced by the machine! Does not the responsibility for the development of this machine embrace as well the consequences of obsolescence and technological unemployment resulting from such development? I believe that it does and that we must recognize this fact in our practice of engineering and tech- nology as well as in the training of future engineers and technologists. Magnitude of the Fuels Industry Fuel technology is the body of knowledge that relates to the mineral fuels. The fuels industry is by far the most important of all Our mineral industries. The chart in Fig. I, reprinted from U. S. Bureau of Mines Information Circular No. 6643, indicates the compartive values of metals, fuels and other nonmetallic minerals for the year 1929. Of the grand total of 13¼ billions of dollars in value of minerals at the mines, the mineral fuels contributed 48 per cent. Coal, with 34.4 Per cent, exceeded the value of any other single mineral. In fact, the value of the production of the Pennsylvania anthracite mines alone anand exceeds the value of the gold production of the entire world. Petroleum and natural gas in 1929 contributed 14.3 per cent and 3.3 per cent, respectively, of the total value of world mineral production. So much for the world picture; let us now look at the situation in the United States. Over the 60-year period 1880 to '939, $46,409,727,000 of metal1ic products, $80,788,852,000 of fuels (coal, petroleum, natural gas, natural gasoline) and $27,871,-ooo,ooo of nonmetallic minerals other than fuels were produced. The mineral fuels have contributed 52.7 per cent of the entire mineral wealth produced over this period that has seen such tremendous industrial development in our Our As a matter of fact, our present industrial civilization has been made possible through the use of the

Jan 1, 1942

By M. F. Hawkes, R. F. Mehl

The rate of isothermal transformation of austenite to pearlite depends upon the rate of nucleation, N, and the rate of growth, G, of pearlite in austenite. Values of N are given in terms of the number of nuclei forming in unit time per unit grain boundary area of unreacted austenite; values of C are given in terms of the linear rate of radial growth. Variations in the isothermal rate with temperature result from variation of N and G with temperature. Depth of hardening of a steel depends fundamentally upon values of N and G; changes in carbon and alloy content effect changes in N and G and thus affect depth of hardening. Quantitative studies are available on N and G for the formation of pearlite in plain carbon eutectoid steels.3 Systematic studies in this field are necessary if the phenomena are to be well enough known to furnish a proper basis for full rationalization and for theory. Accordingly, the studies are continuing, both with respect to the effect of alloying elements upon the values of N and G in the formation of pearlite and to the values of N and G for the formation of ferrite in hypoeutectoid steels. The present paper is the first relating to the effect of alloying elements upon the values of N and G for pearlite. It offers special interest since cobalt is known to have an anomalous effect upon the rate of formation of pearlite, accelerating it, whereas all other elements retard it.4 It will be shown that cobalt increases both N and G for pearlite and that this effect is inherent in the Fe-Co-C system and not dependent upon factors relating to austenite heterogeneity nor upon any recognizable adventitious factor. Inasmuch as the rate of diffusion of carbon in austenite and the interlamellar spacing of pearlite are variables related to G and possibly to N (in a manner not yet certain), measurements of the effect of cobalt upon them are also reported here. In the course of the work, measurements were made on the effect of cobalt upon the marten-site temperature and these are given. COBALT AS AN ALLOYING ELEMENT IN STEEL Properties of Cobalt Cobalt resembles iron more closely than does any other chemical element. Its atomic number is 27, hence it is the element immediately following iron in the periodic system. The two differ in atomic structure only in the fact that cobalt contains seven electrons instead of six in the third, or transition, level of .the third shell. The next shell, which is the

Jan 1, 1948

By W. E. Remmers

The fact that gray iron increases in volume, cracks and distorts upon repeated heating and cooling is rather conlmon knowledge. In ingot molds, Diesel engine pistons, carburizing boxes, continuous furnace parts, grate bars, stoker parts, and all castings that are subjected repeatedly to high and low temperatures, the phenomenon of growth presents a vital problem. Ingot molds distort and produce cracks which result in seams or laps and later appear as defects in the finished product. The heads of Diesel pistons frequently fail by cracking in a stellar shape. This is attributed usually to the result of permanent growth. Distortion and change of dimension of furnace parts frequently renders them entirely unusable. In chain grate stokers, mechanical difficulties frequently are caused by the growth of the links. In proper operation these links should never attain a temperature sufficiently high to start growth; nevertheless, some have grown in. on an 8-in. length when improperly operated. Even though the phenomenon is generally known there still exists a deficiency in the explanation of the mechanism of this growth. The field of investigators of this subject has a decided variation in opinion concerning the causes. The problem is of sufficient importance therefore to warrant further consideration. Review of Published Work Since the published work, particularly the European, contains much detail, only the outstanding results and conclusions of the investigators will be reviewed. The pioneering investigations of Outerbridge in 1904 and 1905 brought forth the conclusion that growth was not a function of chemical or crystallographic changes but was a result of the formation of fine hair cracks. These cracks are supposedly due to a nonuniformity of thermal expansion and contraction which ruptures the structure of the material. More recently Benedicks and Lofquist presented a purely mechanical theory, which is similar to that of Outerbridge. These investigators believe the temperature gradient from the outside to the center of the cast piece causes a contraction of the outer layers on passing

Jan 1, 1931