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By T. Reed Scollon

Coal reserves of the Rocky Mountain area are vast and are more than adequate to meet significantly increasing demands in the immediate future. Practically all of the increase in coal demand for the next decade or so will be in the electric power utility sector. All ranks of coal are available in the area, and from a technological viewpoint, all are suitable for electric power generation. Location of economically recoverable coal deposits, location of generating plants with respect to power demand areas and sources of cooling water, and availability and price of other fuels are the major factors which, individually or in combination, will determine the ultimate selection of Western coal deposits to be developed for electric power generation. The low sulfur content of most western coals and the non-urban location of many power plants should tend to minimize problems of air pollution. If projections for nuclear power prove correct, increases in demand for Rocky Mountain area coals beyond about 1980 will depend primarily on the extent of commercial development of synthetic fuel processes. Current research activities on the conversion of coal to liquid and gaseous fuels are promising. Most western coals range in rank from lignite through high-volatile bituminous coals and are particularly amenable to conversion. Vast reserves of Rocky Mountain coals have long lain dormant primarily because of their remoteness from major market areas. Recently, however, innovations in coal transportation and electric power transmission methods, combined with unprecedented demands for electric power in the West, have resulted in large-scale development of some of these coals. In the past few years, announcements of coal mine openings and transportation plans in the Southwest have been filled with superlatives: The Navajo mine in northwest New Mexico is expected to be the largest mine in the country in the near future. The largest single coal agreement ever made provides for coal shipment from northeast Arizona to Nevada via the largest and longest coal-slurry pipeline ever used. An 1100-mile haul of coking coal from northern New Mexico to California by unit train began last year. It is the purpose of this report to evaluate the coal resources of the Rocky Mountain area, and to project their potential utilization. In projecting energy demand levels on a national basis, the Bureau of Mines has developed some rather complex techniques to cope with uncertainties. Using these same techniques, an estimate has been made of consumption of Mountain area coal in 1980. No attempt was made to estimate coal consumption beyond 1980, but new market potentials are discussed briefly. The present and potential coal-producing fields of the Rocky Mountain area are in six states comprising the Mountain Region - Arizona, Colorado, Montana, New Mexico, Utah, and Wyoming. Since approximately 19% of the coal produced in these fields is shipped to the Pacific Region (Washington, Oregon, Cali-

Jan 1, 1969

By A. W. Dana, F. J. Shortsleeve, A. R. Troiano

The phenomenon of flake formation which may occur during cooling or room temperature aging of large steel sections is caused by a combination of hydrogen and stress. As such, the transformation characteristics of austenite in a particular section play a major role in the occurrence of flakes. Isothermal and continuous cooling studies demonstrated that flake formation is particularly sensitive to nature, distribution, and relative proportions of the microconstituents in the cooled sections. In the absence of transformation stresses, abnormally high hydrogen contents could be tolerated without flaking. Flakes were not found in the absence of transformation stresses. No correlation existed between average hydrogen content and flake formation where cooling stresses were low. Hydrogen in the steel was a necessary but not sufficient condition for flake formation. DESPITE a long history of laboratory and commercial investigations, the mechanics of hairline crack or flake formation in large steel sections remains unresolved. Recent publications1-5 emphasize that flaking is still a serious problem.* immediate cause of flaking is the pressure exerted by entrapped hydrogen gas that collects in small internal cavities or voids during cooling. When the temperature of steel is low enough to preclude extensive plastic flow, the cavity pressures cause local brittle fractures (flakes). 2—The microsegregation and transformation stress theory. According to this theory, flaking results from stresses arising from the volume changes accompanying the formation of martensite and/or low temperature bainite after a large portion of the section has transformed at elevated temperatures. The proponents of the hydrogen theory suggest that stresses from other sources may be additive to the stresses produced by hydrogen and may, in some cases, provide the increment of stress necessary to produce flakes. However, the critical aspect of this theory is that no stress, except that produced by hydrogen pressure, is believed to be sufficient in itself to produce flakes. For practical considerations, this means that the only safe thermal cycle is one that reduces the hydrogen content to some low critical level below which flaking will not occur regardless of the state of transformation. On the other hand, the transformation stress theory does not rule out the embrittling effect of hydrogen. This theory simply proposes that flaking does not occur in the absence of transformation stresses. With the transformation stress theory as a basis, commercial antiflaking cycles would be designed to complete the transformation of austenite prior to cooling to ambient temperatures. Both of these theories appear compatible with industrial experience. Antiflaking cycles, such as cooling at extremely conservative rates or soaking for periods of time in the upper subcritical temperature ranges prior to cooling to ambient temperatures, may allow the following: 1—diffusion of hydrogen out of the section and, as a consequence, reduction of the hydrogen content to some safe minimum value (hydrogen pressure theory) and 2—complete decomposition of the austenite at rela-

Jan 1, 1956

By Thomas Egleston

DURING the year 1873, my attention was called to the frequent accidents, resulting from the breaking of rails, on the different railroads in this' country, and I was requested to investigate the subject. The plan of investigation I proposed was to ascertain, in as many cases as possible, the exact hist* of broken rails, both in this country and in Europe; to collect information in Europe relating to the tests which rails used there were required to undergo, and to experiment upon the pieces of rails broken on the road, with a view to ascertain whether their fracture was due to their chemical constitution, bad manufacture, to a reduction in strength owing to temperature, or to physical changes in the constitution of the rail. The investigation was commenced by the collection of statistics, and for this purpose I spent several months in Europe, collecting information on the subject of broken rails, as well as the life of iron and steel rails generally, and inquiring into the systems of purchasing and of testing them employed by the railroads there, intending, on my return, to make a series of analyses of rails broken, both in this country and in Europe; to ascertain, if possible, how far great cold had an influence on the fracture; to examine whether the rail broken, either on the road or afterwards, underwent, at or about the fracture, any physical change, and to make a series of experiments on the strength of rails manufactured in the United States or sold in the American market. Unfortunately, the panic of 1873 came on, just before my return from Europe, and prevented the carrying out of the larger part of the plan proposed; as, however, I had collected in the meantime, a large number of statistics of different kinds from all parts of Europe, and had made a number of interesting experiments and investigations, I have thought it would be worth while to communicate some

By S. R. B. Cooke, S. W. Clark

Adsorption of calcium and magnesium by quartz was determined over a wide pH range using flame photometry for solution analysis. A parallelism was noted between calcium adsorption at alkaline pH and flotation of activated quartz by means of various fatty acid collectors. Abstraction of calcium from 100 ppm solutions increased above pH 10.5 until all of the calcium was removed at pH values between 12 and 12.5. Calcium was desorbed from the quartz over the pH range 12.5 to 13.0 and returned to the solution. Precipitation of magnesium hydroxide prevented measurement of magnesium adsorption above a pH of 9.9. A calcium adsorption isotherm determined at pH 9 matched measurements of barium adsorption by other investigators over the range where adsorption corresponded to the equation of a Freundlich adsorption isotherm. In accordance with the Gouy-Chapman theory for adsorption in the diffuse layer, adsorption of the divalent cations under these conditions was four times the adsorption of monovalent sodium. Activation of quartz by multivalent metal cations in flotation using anionic collectors has been studied by many investigators. The occurrence of activator cations in the water of flotation mills makes depression of silaceous gangue very difficult. Alternatively, in some flotation systems it is practical to cause activation of quartz so that it is floated from the desirable mineral values. The present study was initiated to investigate the activation of quartz by measuring adsorption of calcium and magnesium ions as a function of solution pH. Early empirical tests showed that quartz would be activated to flotation using anionic collectors if any of a number of divalent or trivalent metallic cations were present in the pulp.1*2 Subsequent studies by Clemmer,3 Cooke and Digre,4 Cooke,5 Schuhmann and Prakash,6 and Cooke, Iwasaki, and Choi,7-8 showed that flotation depended strongly upon the alkalinity of the flotation pulp, the concentration of the activating cations, and the chain length and structure of the organic collectors used. The concept of the electrical double layer has been applied to the case of the quartz-aqueous solution interface by Gaudin and Fuerstenau,9-10 and by de Bruyn 11 to explain the activation of quartz by multivalent metal cations. Studies of the surface of quartz by Gaudin and Fuerstenau9,10,12 and by Li " using the streaming potential technique contributed much information on the electro kinetic condition of the surface of quartz in the presence of various organic and inorganic ions. Measurement of adsorption of ac-

Jan 1, 1969

By T. Egleston

DURING the year 1873, my attention was called to the frequent accidents, resulting from the breaking of rails, on the different railroads in this country, and I was requested to investigate the subject. The plan of investigation I proposed was to ascertain, in as many cases as possible, the exact history of broken rails, both in this country and in Europe; to collect information in Europe relating to the tests which rails used there were required to undergo, and to experiment upon the pieces of rails broken on the road, with a view to ascertain whether their fracture was due to their chemical constitution, bad manufacture, to a reduction in strength owing to temperature, or to physical changes in the constitution of the rail. The investigation was commenced by the collection of statistics, and for this purpose I spent several months in Europe, collecting information on the subject of broken rails, as well as the life of iron and steel rails generally, and inquiring into the systems of purchasing and of testing them employed by the railroads there, intending, on my return, to make a series of analyses of rails broken, both in this country and in Europe; to ascertain, if possible, how far great cold had an influence on the fracture ; to examine whether the rail broken, either on the road or afterwards, underwent, at or about the fracture, any physical change, and to make a series of experiments on the strength of rails manufactured in the United States or sold in the American market. Unfortunately, the panic of 1873 came on, just before my return from Europe, and prevented the carrying out of the larger part of the plan proposed ; as, however, I had collected in the meantime, a large number of statistics of different kinds from all parts of Europe, and had made a number of interesting experiments and investigations, I have thought it would be worth while to communicate some

Jan 1, 1875

By C. H. Hewitt, J. T. Morgan

The Fry cocurrent in situ combustion project was carried out in a 3.3-acre portion of a lenticular body of Robinson sandstone of Lower Pennsylvanian age. This particular sand body is about 12,000 ft long and 3,500 ft wide; it varies in thickness from 0 to 55 ft, trends northeast-southwest, and occurs at depths between 880 and 936 ft. The reservoir is made lip of three distinct types of sandstone, each having characteristic reservoir properties. (See Table I.) Textural gradients, sedimentary structures, erosional basal contact, absence of marine fossils, and geometry of the sand body all indicate that the sandstone is of fluvial origin and part of an extensive complex of river-deposited sedirnents. Geographically oriented cores reveal that the direction of depositing currents was to the southwest, parallel with the sand-body trend. Directions of maximum pernleability also parallel the northeast-southwest trend. The layered nature of the sandstone reservoir and its directional properties have controlled the areal distribution of produced gas, the ignition behavior, and the vertical profile and horizontal extent of the conbustion zone. INTRODUCTION This paper is the first of a series of three papers that describe Marathon Oil Co.'s Fry in situ combustion test. This first paper contains the results of a detailed study of the geology and reservoir characteristics of the Robinson sandstone reservoir in which the Fry test was conducted. The second and third parts of this series report on the field operations' and performance. The geologic work reiated to cores cut through the combustion zone, and to the effect of reservoir properties on the combustion process is included in the third paper.' GEOLOGIC STUDY OF THE FRY RESERVOIR The close spacing of continuous cores in the Fry combustion site provided an unusual opportunity to study the details of distribution of lithology and reservoir properties within a petroleum reservoir. The objectives of the study were: 1. To determine the distribution of rock types within the Robinson sandstone in the Fry area; 2. To determine the relationship of porosity and permeability to rock properties and establish the distribution and homogeneity of reservoir properties; 3. To determine the origin of the Robinson reservoirs so that attempts could be made to predict the size, shape, distribution, extent and continuity of Robinson reservoirs; and 4. To determine what effects, if any, the reservoir rocks might have on the combustion process, so that the process might be better evaluated. AVAILABLE MATERIALS Continuous cores were cut from 14 wells in the vicinity of the Fry site. Ten of the cores are from within the 3.3-acre pattern; six of the 10 were cut prior to combustion, and four were cut through the combustion zone. Cores from the Emma Fry No. 15, Wampler 0-2 and Fry B wells (Figs. 1, 2 and 9) were geographically oriented by the Eastman Oil Well Survey Co. Maps, electric

Jan 1, 1966

By T. K. Perkins, O. C. Johnston

Because of the influence of dispersion on miscible-displacement processes, diffusion and dispersion phenomena in parous rocks are of current interest in the oil industry. This paper reviews and summarizes a great deal of pertinent information from the literature. Porous media (both unconsolidated packs and consolidated rocks) can be visualized as a network of flow chambers, having random size and flow conductivity, connected together by openings of smaller size. In such a porous medium, the apparent diffusion coefficient D is less than the molecular diffusion coefficient Do, as measured in the absence of a porous medium. For packs of unconsolidated granular material the ratio D/D, is about 0.6 to 0.7. For all porous rocks, both cemented and unconsolidated, the ratio of diffusion coefficients can also be represented as D/Do = 1/FF where F is the for- mation electrical resistivity' factor and 4 is the porosity. If fluids are flowing through the porous medium, dispersion may be greater than that due to diffusion alone. At moderate flow rates the porous medium will create a slightly asymmetrical mix zone (trailing edge stretched out), with the longitudinal dispersion coefficient approximately proportional to the first power of average fluid velocity (if composition is nearly equalized in pore spaces by diffusion). If the velocity in interstices is large enough, there will be insufficient time for diffusion to equalize concentration within pore spaces. In this region, longitudinal dispersion increases more rapidly than fluid velocity. At low velocities in interstices, transverse dispersion is characterized by a region in which transverse diffusion dominates. If the fluid velocity gets high enough, there will be a transition into a region where there is stream splitting with mass transfer but with insufficient residence time to completely damp-out concentration variations within pore spaces. There are several variables that must be con- trolled to get consistent longitudinal and transverse dispersion results, viz., (1) edge effect in packed tubes, (2) particle size distribution, (3) particle shape, (4) packing or permeability heterogeneities, (5) viscosity ratios, (6) gravity forces, (7) amount of turbulence, and (8) effect of an immobile phase. INTRODUCTION Diffusion and dispersion in porous rocks are of current interest to the oil industry. This interest arises because of the influence of dispersion on miscible-displacement processes. In a recovery process utilizing a zone of miscible fluid, there is the possibility of losing miscibility by dissipating the miscible fluid or by channeling or "fingering" through the miscible zone. Diffusion and dispersion are two of the mechanisms that may lead to mixing and dissipation of the slug. On the other hand, dispersion may tend to damp-out viscous fingers which may be channeling through the miscible slug. 58 Hence, dispersion may be detrimental or beneficial (if it prevents fingering through the miscible zone). Therefore, it is doubly important that we understand these processes. In this paper we review, summarize and interpret a great deal of information from the literature. In particular, we will briefly discuss molecular diffusion in miscible fluids. Then we will discuss what differences to expect for diffusion in a porous rock. If there is movement of the fluid through the rock, then there may be an additional mixing or "dispersion". Furthermore, the dispersion longitudinally (in the direction of gross fluid movement) and transverse to the direction of fluid movement will not be equal. We will discuss both types of dispersion as well as several variables which can affect dispersion (viscosity differences, density differences, turbulence, heterogeneity of media, etc.). This group of variables has sometimes led to difficulty when comparing literature data. DIFFUSION OF MISCIBLE FLUIDS If two miscible fluids are in contact, with an initially sharp interface, they will slowly diffuse into one another. As time passes, the sharp interface between the two fluids will become a diffuse

By E. H. Snow, B. E. Deal

Instability effects in semicanductor devices have long been attributed to the motion of charges on or within oxide layers on the surface. These effects are of critical importance in metal-insulator-semiconductor MIS) field-effect devices. For this reason, the capacitance-voltage or the conductance-voltage characteristic of these devices can be used as a sensitive detector to study charge transport and polarization effects in the oxide or insulator. A review is given of the results of such studies of thermally grown SiO2 as well as of other insulating films of importance in silicon technology. Three types of effects are distinguished. The first of these is the drift of mobile cations within the dielectric, examples being thermally grown SiO, which is often contaminated with sodium ions, and a variety of other glasses in which the mobile ions are a part of the glass composition. The second effect is a dipole-type polarization which occurs in phosphosilicate glass films obtained by reacting P2O5 with thermally grown SiO2. The third effect involves the transfer of charges between the dielectric and the silicon electrode. This occurs in silicon nitride and other deposited dielectrics. It is concluded that MIS studies have provided a powerful technique joy the study of charge transport and polarization effects in insulating films. The knowledge gained from these studies has led to an understanding of surface effects on conventional transistors and diodes as well as making possible stable MIS transistors. THE metal-insulator-semiconductor field-effect transistor is conceptually the oldest type of active semiconductor device.' The earliest attempts at making this device were frustrated because of high surface state densities at the interface between the semiconductor and the gate insulation.' However, by using a silicon substrate with thermally produced silicon dioxide as the gate insulation, this problem was solved and metal-silicon dioxide-silicon devices with good characteristics were made as early as 1960. 3 Yet it was still over 5 years before these devices became a commercial reality. This delay was largly due, not to surface states, but to stability problems associated with polarization effects within the insulating layer which caused the threshold voltage of the device to drift under temperature and bias treatments. The solution to these problems has not only made possible stable MIS devices, but it has added immensely to our understanding of failure mechanisms in conventional bipolar transistors and has added to the reliability of ali types of planar devices. In this review, we shall first describe the effects of various types of polarization phenomena on MIS device characteristics. Then, since thermally grown SiO, is by far the most important insulator used in these devices, we shall review historically the type of instabilities which have been observed in thermal oxides, the attempts at understanding and eliminating them, and the present status of the problem. We shall then turn our attention to the various deposited insulators which have been used, including lead glasses, phosphosilicate glass, vapor-deposited silicon oxide, and silicon nitride. Interestingly enough, many of these materials show polarization effects which are quite different from those generally observed in thermally grown SiO2. THE EFFECTS OF POLARIZATION PHENOMENA ON MIS CHARACTERISTICS The simplest MIS device and the one which has been most frequently used in the study of polarization effects is the MIS capacitor. Two modifications of this structure with single- and double-layer dielectrics are illustrated in Figs. l(a) and (b), respectively. The capacitance of this structure as a function of voltage applied to the metal gate electrode is plotted in Fig. 2 for the case of an n-type silicon substrate. When the silicon surface is accumulated (positive bias) the measured capacitance is just that of the insulating layer C. When the surface is inverted (negative bias), the capacitance is that of the insulator and a silicon depletion layer in series CoCs/(Co + Cs). Indicated on the horizontal axis of Fig. 2 is the voltage VT at which the silicon surface becomes strongly inverted. This voltage corresponds to the threshold or turn-on

Jan 1, 1969

By Brahm Prakash, R. Schuhmann

Chemical conditions for flotation and nonflotation of quartz with oleic acid as collector and barium, calcium, aluminum, iron, and tin as activators were studied using a simple vacuum-flotation technique in glass-stoppered graduates. The detailed study of barium activation led to an interpretation based on ideal Langmuirian chemi-sorption. FLOTATION of quartz is of practical importance as something to be avoided in soap-floating many types of ores. Clean, unactivated quartz is not floated with fatty acids and soaps, such as oleic acid and sodium oleate, in the quantities normally used for flotation. However, data in the literature indicate that almost any multivalent cation will activate quartz if given an opportunity. Thus, a common problem is to prevent activation of quartz by the various inorganic cations inevitably present in flotation pulps. Wark and his coworkers1 have demonstrated the reversibility of the chemical reactions and adsorptions involved in the activation, depression, and collection of the common sulphide minerals. The procedure in much of their work was to bring a mineral surface to equilibrium with solutions of known pH, collector concentration, and activator concentration, and then to test the floatability of the mineral by contact-angle measurement. From the data, graphs were constructed with pH and reagent concentrations as coordinates. These graphs show fields of flotation and fields of nonflotation, separated by narrow transition regions whose locations are shown by so-called contact curves. From the shapes and locations of the contact curves, which roughly separate fields of flotation from fields of nonflotation, a quantitative understanding of the interaction of the reagents with each other and with the minerals often can be deduced. The study of quartz flotation to be described in this paper follows in broad lines the approach of Wark and coworkers. That is, pH, activator concentration, and collector concentration were varied to find equilibrium conditions of flotation and non- flotation, and the results are presented graphically by means of contact curves. However, instead of testing for floatability by measuring the contact angle on a polished surface, a simple vacuum flotation technique was developed and used. Purified oleic acid was the collector and terpineol the frother. Barium activation was studied in some detail, and exploratory studies were made of activation with calcium, aluminum, ferric iron, and stannic tin. Preparation of Materials Quartz: Large lumps of high-grade vein quartz were crushed dry in a cone crusher and rolls. The —20, +28-mesh portion was screened out and used in the subsequent steps. This material was passed through a high-intensity magnetic separator to discard iron, then leached twice with hot concentrated HCl and washed repeatedly with distilled water. The cleaned sand was then wet ground with porcelain balls in a porcelain pebble mill, deslimed repeatedly by settling and decantation to discard —800-mesh material, and again washed with hot HCl followed by distilled water. The resulting stock of quartz was stored under water. Chemical analysis gave 99.8 pct SiO2. Table I gives the size analysis of the quartz used for flotation tests. Calculations from these data, using shape factors given by Gaudin and Hukki9 indicate a specific surface of about 500 cm2 per g. Blank flotation tests in distilled water, and in water with added frother, showed the prepared quartz to be completely nonfloatable and thus indicated the absence of organic contamination. Oleic Acid: The preparation of oleic acid was based on fractional vacuum distillation of methyl oleate2,3 followed by regeneration of oleic acid, and finally fractional crystallization of oleic acid from acetone solutions at low temperatures." The pure oleic acid was stored in a refrigerator. The iodine number of the oleic acid was found to be 90.0 (theoretical 89.93). Oleic acid was used in the form of a dilute water solution of sodium oleate, after preliminary flotation tests showed no effects of form of addition and order of addition of reagents when an adequate conditioning time (that is, 30 min) was provided. Other Reagents: Sodium hydroxide solutions low in carbonate were prepared by first making 1:1

Jan 1, 1951

By Allan Martin, R. A. Swalin

Diffusion rates of manganese, aluminum, titanium, and tungsten in nickel were measured at temperatures between 1100° and 1300°C. Activation energies, Q, and values of the frequency factor, Do, were calculated for each system. Values of Q were found to be within 15 pet of that for self-diffusion of nickel in agreement with present theories of diffusion. ONE of the most interesting problems in diffusion concerns factors governing the order of diffusion coefficients of various solutes in a common solvent metal at low solute concentrations. An early suggestion by Rhines and Mehl' was that diffusion coefficients might each approach that of the self-diffusion coefficient of the solvent itself. Later Thomas and Birchenall' pointed out correlations between the order of the diffusion coefficients and the freezing point depressions of the solvent by the various solutes. Other correlations have been sought. To settle this question it seems likely that much more data will be needed and, in particular, data collected at low solute concentrations. This type can be obtained by special analytical techniques as well as by use of radioactive tracers. The following study was made of diffusion of manganese, aluminum, titanium, and tungsten in a common solvent, nickel, at relatively low solute concentrations: 1—Production of alloys of nickel with manganese, aluminum, titanium. and tungsten at concentrations of the order of 1 atomic pet. 2—Use of pressure-welded diffusion couples in cylindrical form. 3—Diffusion anneals in the temperature range of 1100" to 1300°C. 4—Lathe sectioning of the diffused couples. 5—Spectrophotometric analyses of lathe turnings for the solute being studied. 6—Calculation of the diffusion coefficient for each of the solutes as a function of temperature. 7—Interpretation of results with current theories of diffusion. Experimental Work Materials—Two types of nickel were used in this research. The grade designated as Vacuum melted Mond nickel was used for all diffusion systems except the Mn-Ni system for which the Vacuum melted electrolytic nickel was used. Analyses of the two grades are given in Table I. The manganese used in making alloys was 99.9 + pet pure, aluminum 99.99 pet pure, titanium 99.9 pet pure, and tungsten of C.P. grade powder. Alloys used in this investigation were prepared by melting in vacuo or under a low pressure of argon. After melting, all heats except those of nickel-manganese were poured into a cylindrical copper mold 3 in. long and 1 in. ID. In the case of nickel-manganese, the alloys were solidified in the melting crucible. For nickel-aluminum heats alumina crucibles were used and for all other heats, zirconia crucibles.

Jan 1, 1957

By Richard H. Olson

"Rarely in our technological society does the discovery of a new class of inorganic materials result in such a wide scientific interest and kaleidoscopic development of applications as has happened with the zeolite molecular sieves." That opening sentence in a landmark volume on zeolite molecular sieves by D. W. Breck (1974), is, if anything, an understatement. Zeolites were recognized as a new group of minerals in the 1750s, but it was not until 1930 that the first analysis of the crystal structure of a zeolite mineral was made. In the late 1940s research workers at Union Carbide Corp. began a program of zeolite synthesis and study which has resulted in one of the major research achievements of all time. Naturally, with the vast research and development efforts devoted to the synthetic molecular sieves, Union Carbide became concerned in the mid-1950s about its position should minable deposits of natural analogues be discovered. Zeolite minerals have diverse origins, and even a brief discussion of these is beyond the scope of this paper. The early work on zeolites was confined to igneous rock occurrences (e.g., amygdules and veins) which were formed by "space-filling;" these crystals tend to be euhedral, thereby rendering them appealing to both mineralogists and collectors. During the first year or so of Union Carbide's exploration (which began in mid-1957) attention was devoted solely to such igneous, occurrences. A landmark paper by Bramlette and Posnjak (1933) heralded the potential significance of the occurrence of zeolite minerals as alteration products of vitric ash and similar materials. In the summer of 1958, full attention was directed by Union Carbide to the search for deposits of this type in the western United States. Since then, such exploration has been continuous by both commercial firms and private parties. The future economic potential for natural zeolite deposits seems to be restricted to those of the "open-and-closed system" types as described by Sheppard (this chapter). Therefore, this and the following discussions will concentrate upon these types; the other types of zeolites in sedimentary rocks (e.g., deep-sea sediments, burial metamorphic, and hydrothermal) will be, for the most part, ignored. Despite the relative cheapness of natural zeolite deposits as compared with the cost of synthetic molecular sieves, there has been minimal development of zeolite mining in the US over the past 25 years or so. Mumpton (this chapter) discusses the present commercial utilization of natural zeolites and their future potential in detail, but perhaps the following will serve as useful background. In the early days of synthetic molecular sieve research and production, the efforts were concentrated largely upon such high-value applications as physical separation of components in a stream (based upon molecular size and geometry) and in catalysis. Due to a number of reasons (some of which are difficult for an outsider to understand), natural zeolite ores (beneficiated or not) have not made substantial inroads upon the use of the higher-priced synthetic molecular sieves for the foregoing applications, but this is not to say that such a condition will exist forever. Furthermore, in view of the many other uses which are now known, or which loom in the future, the competitive position of the natural zeolites vs. the more expensive

Jan 1, 1983

By J. Chipman, J. C. Fulton

Reduction of Si from slag to carbon-saturated iron is a very slow reaction. The rate is nearly independent of stirring but is accelerated markedly by increased temperature. In a slag containing 45 pct SiO2, 38 pct CaO, 17 pct Al2O3, the energy of activation is approximately 130 kcal. AT temperatures of 1450" to 1600°C occurring in the hearth of the iron blast furnace, chemical reactions are normally expected to proceed with great rapidity. Many of the reactions of iron making are indeed quite rapid and attain a condition corresponding roughly to a state of equilibrium before metal and slag are tapped from the furnace. The one conspicuous exception is the reaction by which carbon in the coke or metal reacts with silica in the slag to deliver silicon to the metal. From the practical viewpoint the slowness of this reaction is indeed fortunate, for if it were fast enough to reach equilibrium during the time of contact, it would be difficult to produce pig iron of the desired low silicon content. The one other reaction which under certain circumstances can also be very slow is the transfer of sulfur from blast-furnace metal to slag. In their laboratory exeriments on this reaction, Hatch and Chipman found that at least 5 hr were required for the attainment of equilibrium in a small crucible and that the reaction was not accelerated by increasing the rate of stirring. Subsequently it was shown2 that the presence of a reducible oxide MnO greatly inhibited sulfur removal, and finally that SiO2 itself3 under some conditions has sufficient oxidizing Dower to interfere with sulfur transfer. The kinetics of sulfur removal are now rather well understood,4 and it has been shown3,5 that when the silicon content of the metal is high enough to prevent reduction of SiO,, the desulfurizing process is rapid. Thus the observations of slow removal of sulfur are associated with the coincident slow reduction of SiO2, a process which transfers both silicon and oxygen to the metal phase. It is, of course, the oxygen which interferes with sulfur removal. An explanation of the slowness of the silica reduction reaction has not been obtained. The sulfur transfer process has been shown by the authors5 to be at least partially transport-controlled in the absence of interference by silica. Under the experimental conditions. 99 pct of the total transfer at 1600" was accomplished within an hour. Under similar conditions the reduction of silica may not proceed half-way to equilibrium6 in 8 hr. It is scarcely imaginable that silica reduction could be transport-controlled when the slag contains 44 pct SiO2 and the metal about 1.4 pct C. The experiments reported here show definitely that it is controlled by a slow step or steps in the chemical reaction. One might expect to find such a slow step in the breaking of SiO bonds or in the slow removal of oxygen by carbon at the slag-metal or metal-crucible interface or by bubble formation. EXPERIMENTAL PROCEDURE The experimental procedure used in this investigation was similar to that used in the study of the kinetics of desulfurization.5 A sketch of the graphite crucible and stirrer used in the current work is shown in Fig. 1. The quantity of metal and slag used was adjusted so that the slag-metal interface was located between the top and bottom blades on the stirrer; the top of the slag layer was above the top blade. The stirrer shaft was hollow down to the metal level and served as thermocouple well or optical pyrometer target. Stirring speeds of 0 to 500 rpm were used. A carbon monoxide atmosphere was maintained in the furnace by flushing the gas over the slag surface, except in run No. 220 when it was bubbled

Jan 1, 1960

By O. Mellgren, A. M. Gaudin, P. L. De Bruyn

The adsorption density of ethyl xanthate on pyrite was determined as a function of xanthate concentration. Surface preparation of the mineral appears to have asafunctionsome effect on the subsequent adsorption process, A monolayer of xanthate on the surface is exceeded only in presence of oxygen. The effect of OH- , HS- (and x and CN- S=)and on the amount of xanthate adsorbed was investigated. Competition between OH- and X- (xanthate) ions for specific adsorption sites is indicated over a wide pH range. IN the flotation of sulfide ores, xanthates are most commonly used to prepare the surface of the mineral to be floated so that attachment to air takes place. The quantity of agent required to make the mineral hydrophobic is usually very small, of the order of 0.1 to 0.25 lb per ton of mineral. Details of the mechanism of pyrite collection are for the most part unsettled. Adsorption of collector has long been believed to involve an ion exchange mechanism as demonstrated for galena' and for chalcocite.2 In the work on chal-cocite it was also demonstrated that a film of xanthate radicals unleachable in solvents that dissolve alkali xanthates, copper xanthate, or dixanthogen was formed at the surface of the mineral. The unleachable product increased with increasing addition of xanthate up to a maximum corresponding to an oriented monolayer of xanthate radicals. Pyrite is extremely floatable with xanthate if its surface is fresh.9 ut the floatability decreases rapidly as oxide coatings increase in abundance. Pyrite shows zero contact angle when in contact with ethyl xanthate solution at pH higher than about 10.5;4 at neutrality, a contact angle of 60" is obtained at a reagent concentration of 25 mg per liter. Alkali sulfides and cyanides are pyrite depressants. In this study of pyrite collection the writers have sought to relate measured xanthate adsorption to the method used in preparing pyrite, to the presence or absence of oxygen, to concentration of hydroxyl, hydrosulfide, sulfide, and cyanide ions. The principal experimental tool has been radioanalysis," " using xanthatcx marked with sulfur 35. Experimental Materials Pyrite: Unlike most sulfides, pyrite is a poly-sulfide. The structure given by Bragg7 resembles that of sodium chloride, the iron atoms corresponding to the position of sodium and pairs of sulfur atoms corresponding to the position of chlorine. The edge of the unit cell in pyrite is 5.40 A and in halite 5.63 A. The S-S distance in pyrite is 2.10 A; the Fe-S distance, 3.50 A: and the Fe-Fe distance, 3.82 A. Natural pyrite from Park City, Utah, was used in this investigation. Pyrite 1 was obtained by hand picking pure crystals. Pyrite 2 and Pyrite 3 were obtained from finer textured crystalline material containing inclusions of silicates. The same cleaning technique was utilized for the preparation of Pyrite 2 and Pyrite 3, whereas a different cleaning technique was used for Pyrite 1. Pyrite 1 was prepared as follows: The crystals were ground in a porcelain ball mill and the 200/400 mesh fraction was separated by wet screening with distilled water, followed by washing for 1 hr with deoxygenated distilled water acidified with sulfuric acid to pH 1.5. The acid was removed by rinsing with deoxygenated distilled water on a filter until a pH of 6.0 was reached in the effluent. This filtration was carried out under nitrogen. The sample was then dried in a desiccator under nitrogen. The period of time for which this pyrite sample was in contact with water containing oxygen was about 4 hr. The specific surface as determined by the BET gas adsorption method was 582 cm2 per g. Final material assayed 53.12 pct sulfur and 46.5 pct iron (theoretical, for FeS,: S, 53.45 pct; Fe, 46.55 pct). After crushing, Pyrite 2 and Pyrite 3 were washed with 1 M HCl. rinsed, and fed to a laboratory shakinq table to remove the small amount of silicates. The concentrate obtained was ground in a laboratory steel ball mill. The 200/400 mesh fraction was separated by classification in a Richards hindered settling tube. This fraction was then given a final wash with 0.1 M HCl and deoxygenated water was filtered through the sample. The final effluent showed a conductivity equivalent to that of a solution having a salt concentration of 0.3 ppm. Aqueous hydrogen sulfide solution was then added to the sampln (about 100 ml saturated H,S solution to about 1000 g pyrite under a few hundred milliliters of water) which was stored wet under nitrogen. The sample stored in this manner showed no indication of formation of iron oxides, whereas iron oxides appeared

Jan 1, 1957

By T. E. Scott, D. H. Sherman, C. V. Owen

Mechanical properties and optical metallographic characteristics of vanadium containing 53 ppm (wt) H were investigated from, 77° to 298°K. A sharp ductile to brittle transition induced by the presence of hydrogen was observed between 238° and 223°K and a mar-tensitically formed hydride appeared at 200°K. While there appears to be a subtle relationship between the hydride formation and the ductile-brittle transition, it was concluded that the hydride per se was not sufficietzt to cause the severe em brittletnent. On the basis of the metallographic experiments and the results of a Petch analysis it is suggested that the mechanism of the embrittlement involves a reduction of the true surface energy, or cohesion, of the uanadiunz. THAT hydrogen can severely embrittle vanadium is well-documented;'-5 however, the mechanism by which hydrogen induces the observed embrittlement has not been established. It is not known whether the embrittlement of vanadium is caused by the formation of vanadium hydride or by a more subtle role of hydrogen. Until very recently6>' the solid solubility of hydrogen in vanadium at temperatures in the,range of the embrittlement was not known to a useful accuracy. In general, a severe embrittlement of the type produced by the presence of hydrogen in vanadium can be caused by changes in either of two properties of a metal. Either the yield stress of the metal is raised to the extent that plastic deformation at the tip of a crack cannot occur or the cohesive properties of the metal are reduced, at least locally, to the point at which cleavage is the natural response to applied loads. Of course a combination of these is possible. It is not known which of these properties of vanadium is influenced most by the addition of hydrogen. The purpose of this investigation was to determine the role of hydrogen in the embrittlement of vanadium. Accordingly, the solubility of hydrogen in vanadium in the temperature range where embrittlement is most severe was determined, the appearance of vanadium hydride was examined in relation to the initial ductile to brittle transition temperature, and an attempt was made to evaluate the effect of hydrogen on the yield stress and cohesive properties of vanadium. MATERIAL AND PROCEDURES Sample Preparation. The vanadium used in this investigation was prepared by the iodide refining process described by Carlson and owen.' Three ingots, 3 in. diam by 6 in. long, were cold-swaged to 0.096 in. diam, cut into short lengths, and then arc-melted under purified argon into one ingot. This process was repeated to insure a uniform composition in the final ingot. Chemical analysis of the metal is given in Table I. On the basis of work of Loria et a/ .' the following sequence of treatments was performed in order to obtain a uniform equiaxed ultimate grain structure: a) cold swage q-in.-diam ingot to 0.230 in. diam; b) anneal 6 hr at 1000°C in vacuum; c) by cold swaging reduce 81 pct in area in three steps: 0.230 to 0.187 in. diam, 0.187 to 0.150 in. diam, 0.150 to 0.096 in. diam. This sequence provided the desired grain structure after subsequent annealing treatments. Because annealing in evacuated quartz capsules resulted in contamination by oxygen, all anneals in this investigation were performed in a 304 stainless-steel chamber under a dynamic vacuum of 10- I Torr with the vanadium wrapped in tantalum foil. Prior to all annealing treatments the wires were electropolished for 1 min at 16°C in an 80 pct methanol-20 pct sul-furic acid electrolyte at 12.5 v. Following the final reduction the 0.096-in.-diam wire was cut into 2-in. lengths. A 1-in. gage section was reduced to 0.090 in. diam by electropolishing as above. Five different grain sizes were obtained by annealing the 2-in. samples at different temperatures for 8 hr to insure uniform grain size and residual hydrogen removal. The annealing temperatures used and the resulting grain sizes are given in Table 11. The final step in sample preparation was to charge half of the specimens of each grain size with hydro-

Jan 1, 1969

By A. D. McMaster, M. L. Gimpl, N. Fuschillo

There is interest in the use of rhenium metal films as resistive elements in thin-film circcits, and already some zvork has been done using er)aporated rhenium films. It has been found that rheniim films protected from the atmosphere by an evaporated layer of silicon monoxide show excellent electrical stability. Unprotected films, however, are subject to aging- effects, notably the increase in electrical resistivity as a function of time. This phenomenon can be understood as primarily one of oxidation of the thin films. This paper is concerned with the study of the oxidation and crystallization behavior of such unprotected films. It has been found that the oxidation rates are a function of the substrate temperatures used during the deposition of Lhe metal films. The strictures observed in the films are correlated with the film resistivities and some data are presented to establish the existence of the various types of oxides of rhenium. ThERE is some interest in the use of thin films of rhenium metal as resistive elements in monolithic, thin-film integrated circuits. Some work has been done using evaporated films and it has been found that such films, if protected from the atmosphere by an evaporated layer of silicon monoxide, show excellent electrical stability up to temperatures of 500"." Rhenium films unprotected from the atmosphere tend to age and the electrical resistivity of the films increases as a function of time. Rhenium films, of the order of <100A thick, prepared by electron-beam evaporation techniques are found to oxidize very readily when exposed to dry air at room temperature. It would seem, therefore, that this aging phenomenon could be attributed to the oxidation of the metal films. In this investigation, the oxidation and crystallization behavior of thin films of rhenium evaporated onto silicon monoxide substrates were studied as a function of the substrate temperatures used during the evaporation. The films were examined using electron-microscopy and electron-diffraction techniques. EXPERIMENTAL RESULTS Rhenium metal was evaporated onto suitable prepared substrates which were heated to various temperatures. The evaporations were performed in a vacuum of approximately 5 x 1CT5 torr. The evaporation was carried out at a rate of approximately 10A per omin. The final film thickness was approximately lOOA and the resistance ranged from 5000 to 10,000 ohms per square. The substrates used for supporting the metal films were made by evaporating 75A of silicon monoxide onto freshly cleaved mica. The silicon monoxide film was then floated off the mica by immersing the composite in water. The film could then be picked up on a clean nickel grid. Silicon monoxide substrates were chosen because of their similarity to quartz and glass substrates commonly used for making thin-film resistors. Fuschillo, Gimpl, and McMas-ter have also shown that silicon monoxide films have only minor structural changes at temperatures up to 800°C. This fact simplified the interpretation of any changes observed in the electron micrographs or electron-diffraction patterns obtained from the deposited rhenium films. After the evaporations were completed, the substrates were cooled to room temperature, except where noted differently, before the coated substrates were removed from the vacuum system. All aging of the deposited films was done in a desiccator. The evaporated films were examined in an electron microscope equipped with a hot stage that would permit continuous observations of the samples up to temperatures of 1000°C. RESULTS A series of electron micrographs of the rhenium films deposited on the silicon monoxide substrates are shown to Figs. 1 to 3. In all cases, the metal films are approximately 100A thick and the micrographs were taken 1 hr after the deposition was completed. here was no apparent structure in the films deposited on the substrates held at the higher temperatures. The

Jan 1, 1967

THE composition and quality of finished steel depend upon selection and proportioning of the raw materials of the charge as well as on control of furnace practice. This chapter deals only with those raw materials of the basic open-hearth process which are important in determining the composition of the steel or slag. They are the metallic charge, oxygen-bearing materials, fluxes, and alloying and deoxidizing additions. Refractories, which may also affect the slag composition, are discussed in the previous chapter. Wide variations are possible in the type and composition of charged materials, but in all cases certain fundamental relationships among the elements of the charge must be maintained. Since the process consists essentially of refinement by oxidation of undesired elements, a balance must be established between the sources of oxygen and the elements in the charge that are subject to oxidation (see Chapters II and VII). For example, if it is desired to use a high ratio of blast-furnace hot metal to scrap, it is necessary to add an oxygen-bearing material such as ore or mill scale to eliminate the excess carbon and silicon that are present in the hot metal. An example of the opposite extreme would be the use of a metallic charge composed entirely of steel scrap. With this type of charge, it is common practice to substitute burnt lime for limestone as a flux and to charge some carbonaceous material such as coke to avoid an excess of oxygen in relation to the elements of the charge that are subject to oxidation. Elements such as copper and nickel, which are not subject to oxidation or other reactions resulting in their elimination, may be introduced into the charge only to the extent to which they are permissible in the finished steel. An example of adjustment of the charge for elements of this type would be found in the use of steel scrap high in copper. In this case, metallic components of the charge other than the scrap should below in copper, or a sufficiently high ratio of pig iron to scrap should be charged to dilute the copper from the scrap, so that the average copper content of the melt will be below the required maximum.

Jan 1, 1944

By H. F. Silliman, Daniel R. Hull, John R. Freeman

In the normal operation of a brass-rolling mill, sheet and strip has, for the most part, been finished in comparatively thin gauges, involving a substantial amount of cold-work and a considerable number of anneals. This condition has been disturbed by the preponderance of cartridge brass, which is not rolled to thin gauges, and particularly by brass for artillery cartridge cases, on which the mill may finish its work at a thickness between 0.400 and 0.900 in. Obviously, the amount of rolling and the number of anneals to which such a product can be subjected are small compared with strip that is carried to a thickness of a few hundredths of an inch. As a result, critical examination into the internal condition of metal has been made on an extensive scale at a stage of manufacture that would not, in normal times, have been chosen for complete inspection. Under these conditions, a type of defect has been recognized that is not seen at thinner gauges. It might be more accurate to call it the appearance of a defect, since it refers to an apparently laminated, discontinuous structure, which, in fact, does not exist as such, and disappears after suitable treatment. For this reason it has been called a phantom lamination, which the authors consider an appropriate term. It is the purpose of this paper to describe the phenomenon and the conditions of its occurrence and, at least tentatively, to discuss its nature and cause. Great numbers of phantoms may be found in 2:r brass, either hot-rolled or cold-rolled. They are also found in 70-30 brass, sometimes when hot-rolled and generally when cold-rolled. It is not believed that phantoms are confined to these alloys but this paper is limited to them for the purpose of description. Hot-rolled 2:1 Brass For illustration, therefore, a typical cake of hot-rolled 2:I brass has been chosen. This was rolled to a slab 36 in. thick, from a casting 5 in. thick by 24 in. wide by 18 in. high, which was believed to have been sound. After hot-rolling and cooling, the slab was sheared and a portion of such a shear cut is shown in Fig. I. It would be difficult to convince anyone viewing this specimen that the metal was not unsound. The impression would be confirmed by the appearance of a tensile break, as shown in Fig. 2. This is an ordinary tensile-test piece from metal just described. Although there was nothing in its tensile strength or elongation that suggested unsoundness, it appeared run through with pipes and laminations. To question the reality of such a condition would imply questioning the obvious. But, considering the history of the metal, it would be difficult to believe that it could be so bad as it appeared. It seemed reasonable, though, that if the defects were what they appeared to be, they could be traced back from the sheared or broken face.

Jan 1, 1945

By J. E. Powell, F. H. Spedding

WHILE rare earths are reported to be widely distributed in nature and are not really rare," in practice, there are only a few minerals which are sufficiently rich in rare earths to serve as practical sources. Perhaps the best known of these is monazite which is a phosphate mineral containing rare earths and thorium. This mineral occurs as a dense brown sand in gravel beds and is particularly rich in the light rare earths of the cerium subgroup. This mineral is processed commercially for its thorium, cerium, and lanthanum content, and, consequently, furnishes rich concentrates from which neodymium, praseodymium, samarium, europium, and gadolinium may be obtained. Unfortunately, monazite is rather lean in rare earths heavier than gadolinium. A second mineral which is rich in the light rare earths is bastnasite, a fluoro-carbonate. Extensive deposits of this ore have been discovered in the western United States and have received considerable newspaper publicity in recent years. While bastnasite is very rich with respect to cerium, lanthanum, and neodymium, it contains even less heavy rare earths than does monazite. One of the better sources of heavy rare earths of the yttrium subgroup is gadolinite, a black silicate rock from which the rare-earth content can be extracted readily by acid leaching. It is obtained chiefly from Norway at the present time, although there are known deposits in the United States. Other sources of heavy rare earths include fergu-sonite, euxenite, and samarskite which are refractory tantalo-columbate ores. These minerals require caustic fusion or reduction to carbides with carbon before the rare-earth content can be extracted. All of the minerals which are rich in the heavy rare earths contain yttrium as a major constituent. After the rare earths have been extracted as a group from an ore by chemical means, it is generally convenient to precipitate them from acid media with oxalic acid in order to eliminate certain non-rare-earth impurities such as iron, beryllium, etc., which are usually present. The oxalate can then be readily ignited to R2O3. The oxide can be dissolved in acid and is the starting point for subsequent separation into the pure components. Perhaps the principal reason why the rare earths have not been studied as extensively as other elements of the periodic table, whose natural abundances are comparable, is that they are extremely difficult to separate from each other by the usual chemical means. Prior to 1945, the separation of one trivalent rare earth from another was a laborious process. All separations were based on repeated fractionation processes, i.e., fractional precipitation, fractional decomposition, fractional crystallization, etc. These processes were repeated from a few hundred to many thousands of times in order to obtain individual rare-earth salts of reasonable purity. Of course, mention should be made that, in the few cases where a rare earth could be oxidized or reduced to a valence state other than three, more conventional chemical means could be utilized to separate the oxidized or reduced ion from the other normally trivalent rare earths. The ionic states which deserve special mention are CeIV, SmII, Eu11, and Yb11. When it is possible to remove an element of the series efficiently, due to an optional valence state, its immediate neighbors also become easier to isolate. For example, binary mixtures of lanthanum and cerium, and praseodymium and cerium can be obtained by a relatively small number of fractional operations. The tetravalent state of cerium then allows the complete resolution of the binary mixtures by ordinary chemical means. Although the tetravalent state of cerium has been known for a long time, the divalent states of samarium, europium, and ytterbium were not used extensively in separations prior to 1930 because they are relatively unstable in aqueous media.&apos;-" No attempt will be made to give a comprehensive review of the extensive literature dealing with the separation of rare earths. Rather, this paper will be confined to a review of those methods which have been developed at Iowa State College during recent years, and which have proved extraordinarily successful for the isolation of highly pure rare earths in quantity. It was obvious that, if pure rare earths were to become generally available, methods would have to be developed wherein the thousands of fractional operations made necessary by the similarity of rare-earth properties could be performed automatically. The development of chromatographic techniques and ion-exchange resins appeared to offer a mechanism by which this objective could be accomplished. A number of early attempts were made to separate rare earths by these means; for example, Russell and Pearce12 passed a mixture of rare earths through a cation-exchange column and reported

Jan 1, 1955

By Richard P. Hight

Abrasives include the substances, natural or artificial, that are used to grind, polish, abrade, scour, clean, or otherwise remove solid material, usually by rubbing action but also by impact (pressure blasting for example). They do not include abrasive tools, for instance, lathe tools and files--or polishing agents such as waxes, which act by filling pores. Detergents and cleaners whose action is chemical rather than physical are omitted al- though some chemical-action polishes and cleaners may also contain solid abrasives, for example, many automobile and metal polishes. General Considerations The most important physical properties of materials that qualify them for use as abrasives are hardness, toughness (or brittleness), grain shape and size, character of fracture or cleavage, purity or uniformity. For making bonded abrasive products such as grinding wheels, additional important factors are stability under high heat and bonding characteristics of grain surfaces. The economic factors of cost and availability are always important. No one single property is paramount for any use. For some uses extreme hardness and toughness are needed, as in diamonds for drill bits; for others, the factors of greatest importance are hardness and ability to break down slowly under use, to develop fresh cut- ting edges when grains become worn-for example: in garnet for sandpaper neither highly cleavable or friable grains nor extremely tough grains are wanted. For still other uses, great hardness is objectionable; for example, abrasives for dentifrices and for glass-cleaning soaps. For the most efficient use in the more critical applications, the different types of abrasives are rarely completely interchangeable; thus, while crushed quartz and garnet are both used in sandpaper, the papers are not at all interchangeable in their use applications. In the last analysis, the choice of a high grade abrasive depends upon the quality and quantity of work done by the abrasive per unit of cost. Initial cost of an artificial abrasive may be much greater than that of a natural abrasive but the artificial abrasive may do so much better work than the natural one, and do it so much faster that the ultimate cost will be less. It is for this reason that artificial abrasives have largely replaced natural abrasives. Abrasive Value Mineralogical hardness or "scratch" hardness as expressed in Mohs&apos; scale is an important property in evaluating abrasive materials, but, as noted before, it is only one of several essential properties. The mineral hardness of pure crystal almandite garnet is about 7.5, but if the crystal is crossed by incipient fracture planes, or if it contains inclusions of other minerals, the apparent or useful hardness may be much lower. While the quartz grains in a sandstone have a hardness of 7, the bond holding the grains together may be so weak that the stone is valueless as a commercial abrasive. In artificially bonded wheels and stones, the hardness, strength, and character of the bond are fully as important as the hardness of the abrasive grains. Thus, in an overall consideration of abrasive hardness of loose abrasive grains, both "scratch" hardness and toughness must be considered. In naturally or artificially bonded abrasive stones, bond characteristics are a third factor, which is most important. The problem of abrasive hardness is further complicated by the inadequacies of methods of testing hardness and of expressing relative values. The Mohs&apos; scale is inadequate both because the methods of testing are very crude and

Jan 1, 1975

By F. A. Schaufelberger

METAL can be recovered from a leach solution either indirectly by precipitation as a compound that is later reduced or directly by electrolysis, cementation, or chemical reduction, for example, with hydrogen. The widely used electrowinning processes suffer from the inefficiency of converting fuel to low voltage dc and from low current efficiency when complete recovery is attempted. With the batch hydrogen reduction methods outlined here, a unit of fuel converted to hydrogen in modern gas reform plants will make two to three times as much metal as can be obtained with electrolysis. With continuous hydrogen reduction, four to six times as much metal is obtained. Precipitation by reducing a metal salt solution with H, has been known for almost 100 years.&apos; Commercial use of the process, however, awaited the research and development program initiated by Chemical Construction Corp. Within the last few years this program has brought about construction of commercial plants, listed on page 545. Ideal hydrogen reduction will precipitate a pure metal from a solution obtained by commercial leaching methods at a rapid rate without excessive temperatures and pressures. The metal precipitate will be of desired size and density, less than a percent left in the vessel being deposited on the wetted parts. The present discussion will outline Chemical Construction Corp.&apos;s early development program and will discuss the chemistry and mechanics of reducing copper, nickel, cobalt, and cadmium from solution by H2. Work on selective reduction of nickel from cobalt has been described earlier.&apos; The article is not concerned with precipitation of copper by disproportionation of cuprous solutions where yield is limited3 to 50 pet.* It does not discuss use of gaseous reducing agents other than hydrogen, such as SO2,4 which may lead to contamination with sulfur, or C0,5 which is considerably more expensive than hydrogen and produces a gaseous reaction product, CO2.† The article does not include use of other nongaseous reducing agents,7 which are far more expensive than CO. Also, notes on the history, engineering design, and performance of commercial plants have been given elsewhere.&apos; It will be shown that a pure metal can be precipitated by reduction with hydrogen from solutions obtained by commercial leaching methods when the solution composition is controlled and proper acidity, proper metal ion concentration through controlled complex formation and hydrolysis, and adequate agitation for suspension of metal and for transfer of reducing gas are maintained. Reasonable temperatures and pressures are used which are less excessive than those used by previous workers, although they are maintained at above equilibrium values because of process kinetics.&apos; It has also been found necessary to induce nuclea-tion and to control growth and agglomeration in order to get a powder product of suitable physical properties. Review of the Literature Muller, Schlecht, and Schubardt of I. G. Farben10 claimed a successive reduction of silver, copper, nickel, cobalt, and zinc from ammoniacal solution by applying progressively higher temperatures and hydrogen pressures. Metals produced by this technique were not pure, since no attempt was made to adjust the solution composition between the different reductions. It is doubtful that the zinc product contained any metallic zinc. The major contribution to the literature" was made by the Ipatiews,12 who prepared platinum, iridium, copper, nickel, cobalt, lead, tin, arsenic, antimony, and bismuth at often extreme conditions, up to the critical temperature of water (373ºC), at 1500 to 7500 psi, for as long as several days. Even cadmium and zinc were claimed to have been observed in trace quantities precipitated together with basic salts. In the early experiments solutions were not stirred. Extensive formation of oxides and basic salts occurred, probably long before sufficient hydrogen could be supplied in the unstirred liquid to decrease the metal concentration in solution by reduction. The importance of hydrogen pressure was

Jan 1, 1957