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By William G. Pariseau

The flexure of geologic strata, a phenomenon of interest to geologists and mining engineers alike, is examined as a sheet bending problem in Coulomb plasticity. Fonnulae for the distribution of stress, strain, and displacement increments; volume change; change in the length of the central surface; and power of dissipation, as well as for the neutral surface shift are given. Strains of any magnitude are considered. The analysis shows that deeply buried strata may bend and develop "tensile" cracks under generally compressive states of stress. It is also shown that bed separation and high capacity props are desirable in mechanized longwall mining, a result in keeping with operating experience. Although speculative at this time, the analysis provides a rational working hypothesis as regards the problem of strata flexure and control. | he purpose of this paper is to present an analysis of the flexure of geologic strata as a problem in the bending of a sheet of material failing in accordance with a Mohr-Coulomb criterion. The flexure of strata has an obvious academic interest to the geologist concerned with the mechanics of folding. It is of interest to the economic geologist as it relates to the structural control of certain types of ore deposits. It has an intimate association with mine subsidence phenomena, and is of concern to the mining engineer. Strata flexure is also the dominant feature of roof behavior about longwall workings. An improved understanding of strata flexure through a rational mechanical analysis thus appears desirable not only from the academic view but from the economic one as well. In the field, the most commonly observed feature of folding, subsidence, and longwall roof behavior is the permanent and therefore inelastic nature of the strata movement. Fig. 1 illustrates the physical disposition of strata in the vicinity of a longwall face. Inasmuch as most rocks (with the possible exception of certain evaporites) do not exhibit significant viscoelastic behavior, at least not over time spans of engineering interest, a plastic analysis is indicated. The analysis is meant to apply to strata whose deformation is dominantly that of bending such as might be expected in the remote roof about a longwall face.

Jan 1, 1970

By Edward F. Winter, C. E. Ruoff

A silicon solid-state array image scanner is described. This paper deals with structural and performance properties of the array which basically consists of PIN photo and gating diodes, and low capacitance isolation diodes. Each chip of the array is composed of an 8 by 9 matrix of photo detector cells; each cell contains one each of the three diode types mentioned. This x-y matrix is read a column at a time with an access delay of approximately 100 nsec per column. It is designed to detect the presence or absence of illumination within 10-mil diam image spots located on a 15- by 15-mil grid. Radiant power level of an illuminated spot is low; of interest is the range around I uw with a of 8400g Structural improvements to the original array which will result THE purpose of this paper is to describe the results of a solid state scanner exploratory development activity. The scanner is intended to sense the presence or absence of low-level illumination falling upon a matrix of 10-mil wide squares arranged on a 15- by 15-mil x-y grid pattern. The light of interest has a wavelength of 8400, characteristic of radiation emitted from a GaAs lasing diode. This wavelength matches well the spectral absorption of silicon,' thus the well-developed silicon processing technology can be applied to fabricating large integrated arrays of PIN photocells to sense the radiation. The illumination state of the cells of the array is read, one column at a time, by addressing a drive line of the particular column in question and examining the state of those sense lines which are orthogonal to the drive Lines of in greater sensitivity at various wavelengths, both above and below 8400Å, and in greater speed are presented. These include variations in diffusion depth, resistivity of N and P regions, isolation techniques, and packaging. Trade-offs between access speed, cycle frequency, and sensitivity are discussed. A packaging approach to achieving an array composed of several chips is described. Requirements on this package are: 1) maintenance of 15- by 15-mil pitch of the light sensitive cell position, therefore positional accuracy of mounted 8 by 9 cell photo detector chips; 2) maintenance of inherent high array speed even though signal levels are low through high density close proximity mounting of monolithic sense amplifier circuitry. the array. One bank of N sense amplifiers is required, where N is the number of photodiode cells in each column of the array. CELL AND CHI" STRUCTURE A photograph of a single monolithic cell is shown in Fig. 1. Each cell is composed of three junctions, an isolation junction, a logic or blocking diode junction, and a photodiode junction; all of these junctions are connected electrically by a common N region. An electrical schematic of four cells of the array is shown in Fig. 2 with the associated driver and sense amplifier circuits in block diagram form. Note the common cathode configuration of the three diodes of each cell. Fig. 3, a diagram of the cell vertical struc ture, illustrates how the electrical configuration of

Jan 1, 1970

By Lyman Johnson

Single crystals qf copper in "single slip" orientatiorzs have been deformed in compression. During defortnation all of the independent deformation parameters have been measured. These parameters consist of thefive strain components and three components descrihing the lattice rotation. By a finite strain analysis these pararmeters , forrming a deformation gradient martrix, are related to the amounts of slip on each of the twelve slip systems. The results show that the amount of secondary slip is about equal to the amount of primary slip. This is an order of magnitude larger than has been believed previoutsly. ACCORDING to early theory and experiments, when a single crystal of a fcc metal is deformed in tension or compression it should deform by slip on only one slip system until the stress axis reaches a symmetrical orientation.' However. the observation of a large increase in the secondary dislocation density during ..single slip" makes it clear that some slip does occur on secondary systems. Knowledge of the amount and distribution of this secondary slip is essential to a complete understanding of the mechanisms of single-crystal deformation. Ahlers and Haasen 2 and Mitchell and Thornton1 have tried to detect the amount of secondary slip in single crystals of silver and copper, respectively. Each simultaneously measured the angle A, between the tensile axis and the primary slip direction and the length 1 of a gage section of the specimen after incremental amounts of deformation in tension. The measured A, was then compared with the theoretical single slip angle hp. given by sin Ap = j sin . hO where ?o was the initial angle between the tensile axis and the primary slip direction and lo was the initial gage length. In both sets of experiments a small but systematic difference between ?e and ?p was found. This difference must be due to the occurrence of secondary slip. However, as Mitchell and Thornton1 pointed out. nothing quantitative can be said about the amount and distribution of this secondary slip from the measurements that they made. The reason that no quantitative conclusions could be made is because no unique solution for the distribution of slip on the twelve fcc slip systems can be determined from only two measured deformation parameters such as A and 1. There are, in fact, eight independent macroscopic deformation parameters that can be measured when a single crystal undergoes a homogeneous deformation. Physically these can be thought of as the five finite strain components and the three angles describing the crystal lattice rotation. All eight of these parameters were measured by Taylor4,5 for aluminum deformed in tension and compression. At that time the concern was to show that slip occurs on {111 (110) systems in fcc metals, and the mathematics were not available to determine what slip distributions were compatible with the measurements. In this paper the mathematics6,7 are developed that allow the slip distribution to be determined from these measurable macroscopic deformation parameters. The analysis is applied to the measurements of the strain and lattice rotation of copper single crystals deformed in compression. The results show that the amount of secondary slip is an order of magnitude larger than had previously been thought. CRYSTALLOGRAPHIC DESCRIPTION OF A HOMOGENEOUS DEFORMATION The deformation of a solid body can be represented by a transformation matrix F that transforms the un-deformed state into the deformed state. Consider a vector X connecting two material points in the unde-formed material and the vector x connecting the same two material points after deformation, where both vectors are referred to the same set of Cartesian axes. The final vector x is related to the initial vector X by the equation: X = FS. [2] Eq. [2] can be considered as the equation defining F, which is called the deformation gradient matrix. Its components are: If the deformation is homogeneous, the transformation is linear and the components of F are constants. Using subscript notation, if P is the unit vector in the initial direction of a material line, the components of the unit vector p in the direction of the same material line after deformation are given by:

Jan 1, 1970

By G. P. Marino

The "conductivity ", Kr, of a spherical void in a linear temperature gradient due to radiation is calculated by integration of the general expression for diffuse radiation between two gray surfaces of arbitrary orientation. The spherical geometry allows an exact evaluation of the phenomenon without resorting to up-proximate expressions for the radiant heat flux. The resulting expression for Kr is three quarters of the approximate value obtained by Loeb. IN the determination of the thermal conductivity of porous materials such as sintered UO2 and ThO2 fuel pellets, the magnitude of the thermal conductivity in the pores due to radiative heat transfer across the pore, Kr, may be important in assessing the total conductivity of the pellets. Loeb' has calculated Kr for various pore geometries by approximating the net flux of heat between two surfaces of temperature difference AT as 4eT~AT and obtained: K,=4yoet3odp [1] where a is the Stefan-Boltzmann constant, E is the emissivity of the radiating surface, To is the average absolute temperature of the region across which radiation occurs, dp is the largest dimension of the gap in the direction of heat flow, and y is a geometric factor. That is: y = 1 for laminar pores and cylindrical pores with axes parallel to the heat flow direction, y = 2/3 for spherical pores, y = /4 for cylindrical pores with axes perpendicular to heat flow direction. It was the purpose of this work to obtain an exact expression for K, in spherical pores by integration of the general expression for the net heat transfer between two incremental areas on the surface of a spherical pore. This procedure yields a value of Kr 3/4 of that obtained by Loeb. I) CALCULATION OF Kr Fig. 1 illustrates the general geometry which defines the problem. The total emissive power for a gray body is given by: E = EoT4 [2] where E is the radiated energy per unit area of the radiation surface per unit time, T is the absolute temperature, o is the Stefan-Boltzmann constant (o = 5.67 X lo- '' watt per sq cm-"K1), and E is the emissivity of the surface. Although Eq. [2] gives the exact expression for the total emissive power of any gray body, all practical problems involve the net exchange of thermal radiation between a body and surrounding bodies. The two major considerations in the solution of such problems are a) shape and relative position of the surfaces and b) the emissivities of the surfaces. In this work it shall be assumed that all incremental areas on a pore have the same emissivity and, further, that little or no reflection occurs (i.e., the radiation hitting a surface is either absorbed or transmitted). Thus, the solution of the stated problem requires only that consideration a be satisfied. Consider two incremental surface areas dA 1 and dA2 of the same material in a general orientation to one another. Let dAl be at temperature TI and dAz be at T2. Fig. 2 illustrates the geometrical parameters involved. That is, 71, is the normal of dA, n2 the normal of dA2, r the line connecting the centers of each area, 81 the angle between nl and r, and Q2 the angle between 7,2 and r. Using Eq. [2] and the Lambert cosine law of diffuse radiation it is easily shown that:293 WdAf- dA, = ecr T*------^fpi------" dAidA2 [ 3a 1 and

Jan 1, 1970

By G. Sandoz, D. A. Meyn

The fracture surfaces of specimens of titanium a1loys which exhibited susceptibility to subcritical crack growth in a wide variety of environments, including aqueous solutions, alcohols, hydrocarbon gases, carbm tetrachloride, and dry air, were examined. The dominant and characteristic fracture mode was cleavage. which became mixed with an increasing porportion of ductile fracture modes (dimples. and so forth) as the applied KI was increased. The cleavage plane in all the alloys was oriented at 15 deg from (0001) of the a phase. No indices could be assigned to the 15 deg cleavage Plane because of uncertainty as to which zone it belonged to. SLOW crack growth and delayed fracture take place in certain titanium alloys at stress intensity (KI) lower than the critical values for complete fracture (KIc) found in short-time tests for plane strain fracture toughness.' Such crack growth may take place in very dry air on sustained loading if the alloy contains a sufficient amount of hydrogen and if the stress intensity factor is higher than a threshold value designated KIH.2 Similarly, a number of environments such as water, alcohols, and hydrocarbons may cause slow crack growth provided the stress intensity factor exceeds the threshold value KISCC. In this paper it is intended to examine some fracto-graphic and crystallographic details of this subcritical crack propagation process as related to alloy composition, environment, and stress intensity. It has been previously reported that subcritical crack growth takes place in titanium alloys in aqueous environments by cleavage.2"6 The observations to be described here indicate that in the alloys investigated the mode of subcritical crack propagation is more dependent on the stress intensity during cracking than on the environment. The fracture mode is illustrated with photographs of the fracture surfaces at a wide range of magnifications. The crystallographic character of the cleavage mode is also presented and the results discussed. EXPERIMENTAL APPROACH The studies were made on four titanium alloys— Ti-8A1-1Mo-lV, Ti-5A1-2.5Sn, Ti-7Al-1Mo-lV, and Ti-0.350. Of these four alloys the first two were mill annealed and fine grained. The latter two were noncommercial and coarse grained, having been prepared for other experimental purposes. The crystallographic studies required a large-grain size. Consequently the fine-grained alloys were an- nealed in a vacuum at 1950°F and furnace cooled to produce samples for these studies. This treatment did not alter the microstructure significantly except for grain size. All the aluminum-containing alloys showed primary a with a network of ß-phase particles within the a grains; Figs. 1 and 2 show this microstructure for the specific case of fine-grained Ti-8A1-1Mo-1V. The cracks in the figures will be discussed later. Fractographic studies were made on all the alloys, but the electron fractographs displayed herein are from the Ti-8A1-1Mo-1V alloy in the fine-grained condition. Emphasis was placed on this commercial alloy because considerable information was available on the stress-corrosion cracking characteristics in a variety of environments. Sufficient supplementary studies of the alloy after the anneal to produce large grains were conducted to establish that the stress-corrosion cracking susceptibility and fractographic characteristics were not changed significantly. Thus it could be inferred that the crystallographic data obtained exclusively on large-grained specimens would apply also to fine-grained specimens. Fracture surfaces for study were obtained using precracked cantilever beam specimens loaded as described by Brown. The precracked section of a specimen was immersed in the environment of interest. Values of initial stress intensity factor Kli were chosen slightly higher than KISCC in order to obtain a fairly extensive region of slow crack growth. Fracture surfaces representative of a variety of stress intensity levels could then be examined because in the cantilever beam test KI increases as the crack propagates.

Jan 1, 1970

By Mayumi Someno, Kazuhiro Goto, Masahiro Kawakami

The apparent rates of decarburization of liquid alloys of Fe-C, Fe-C-S, Ni-C, and Co-C systems and the rate of oxidation of solid graphite with pure carbon dioxide gas and with gas mixtures of carbon monoxide and carbon dioxide have been measured in the temperature range of 1000° to 1600°C. The cotnposition of carbon dioxide and carbon monoxide gas at the reaction surface has been measured by oxygen concentration cells with the ZrO,-CaO solid electrolyte. 1) The apparent rates of the carbon removal are essentially the same for all the cases of solid graphite, Fe-C, Fe-C-S, Ni-C, and Co-C systems under the same experimental conditions. 2) The apparent rates are independent of the carbon content in the high carbon concentration range but very much affected by the flow rate and the gas composition of the CO-CO2 reactant gas mixture. The ratio of the gas consumed by the reaction to the total quantity of the supplied gas is very large under the present experi~nental conditions. 3) There is a concentration gradient of' carbon dioxide in the vicinity of the reaction surface and the content of CO, becomes extremely small at the reaction surface. 4) A large time fluc-tuation of the gas composition was observed. This jluctuation implies the presence of unstable flow in the gas phase in the vicinity of the reaction surface. THE decarburization of molten steel by an oxidizing gas or by slag may be one of the most important chemical reactions in steelmaking processes. Nevertheless, the kinetics of this heterogeneous chemical reaction do not seem to be well-solved even with the previous studies. Although the conditions for the reaction in steelmaking processes are quite different from those in the laboratory scale, some critical experiments may give information on the mechanism of the decarburization. From the previous work,'-' it is known that the rate of the decarburization is independent of the carbon content in liquid iron with more than about 0.2 wt pct C when the oxidizing gases are supplied to the surface of liquid Fe-C alloys on a laboratory scale. Two rate-controlling steps have been proposed for the decarburization of liquid iron with the high carbon content: one is the surface reaction control proposed by Swisher and Turkdogan;' the other is that the rate is controlled by the gaseous diffusion through the gaseous stagnant layer. proposed by Baker. Warner, and Jenkins.7 and also by .Ito and Sano.2 In the present study, some experiments have been carried out for the evaluation of these rate-controlling steps in the decarburization of liquid iron with high carbon content. The apparent rate of decarburization of liquid iron has been compared with the rates of carbon removal of liquid Ni-C, Co-C, and solid graphite under the same experimental conditions. The composition of carbon dioxide and carbon monoxide gas at the reaction surface has been measured by oxygen concentration cells. I) EXPERIMENTAL PROCEDURE Fig. 1 shows the schematic diagram of the reaction chamber. Solid graphite and liquid metals were contained in an alumina or magnesia crucible of 32 mm ID and 35 mm in height. The samples were heated by high-frequency induction and the temperature was measured by the calibrated optical pyrometer. The temperature was held constant to within 10°C. The re-actant gases were supplied to the surface of the samples through the quartz tube of 8.0 mm ID. The distance from the end of the quartz tube to the surface was 20 mm. The block of high-purity graphite was cut and shaped to the inner profile of the crucible. The height of the shaped graphite was 18 mm, which corresponded to the depth of the liquid iron of 100 g. About 100 g of Fe-C alloy (4.20 to 4.40 pct C), Ni-C alloy (1.84 pct C), Co-C alloy (1.85 pct C), and Fe-C-s alloy (4.35 pct c, 0.5 or 1.0 pct S) were melted in the crucible. The reactant gases were pure CO, and gas mixtures of CO-CO,: the flow rates were controlled by capillary flowmeters with bleeders.

Jan 1, 1970

Jan 1, 1970

By Ben-Zion Weiss, Melvin R. Meyerson

Chromium diffusion coatings on commercial Armco iron lead to carbide precipitation at the grain boundaries in and below the coatings. High compressive stresses are introduced into the coating and, as a result, tensile stresses are introduced into the base material below the coating. In coated samples, fatigue cracks form at the grain boundaries below the coating after only a limited portion of the total lifetime (5 to 10 pct). Residual tensile stresses and a stress concentration caused by precipitated carbides seems to be responsible for early crack nucleation. Stage I of Propagation may be divided into two substages: I-a in which the crack Propagates along grain boundaries, and I-b in which the crack propagates along slip boundaries according to a shear mode. In uncoated samples, the cracks form at slip bands after 40 to 50 pct of the total lifetime. In coated samples the Propagation process takes longer than in uncoated samples because of the moderate rate of crack extension until the crack breaks through the coating. The chromium-diffusion coating causes little if any increase in fatigue life. CHROMIUM diffusion is one of the most popular processes used to apply coatings to iron alloys. This popularity stems from the fact that the diffusion treatment is comparatively easy to carry out, and it improves certain surface properties such as corrosion and wear resistance as well as some other properties. Very little effort has been devoted to the investigation of the effect of chromium-diffusion coatings on mechanical properties and particularly on fatigue properties. Since the chromium coating usually represents a small fraction of the total volume of the base material it is generally assumed that the macro properties are dependent principally on the base material rather than the coating. Insofar as fatigue is concerned, there are indications that the fatigue life of the chromium coating is not less than that of the basic material and the fatigue properties are generally not reduced by it.' But chromium diffusion causes drastic structural and chemical changes in the region of the material surface2-4 which introduce additional residual stresses. Such changes must affect fatigue crack nucleation and may sometimes affect the initial stages of propagation. Furthermore, it is conceivable that the secondary stages of the crack propagation could be influenced by some irreversible structural changes in the core of the material, which stem from the long-time heat treatment at high temperatures required to apply the coating. This paper analyses the structural and compositional changes produced in commercial Armco iron by a chromium-diffusion coating and the effect of the coating on fatigue crack initiation and propagation. EXPERIMENTAL PROCEDURES The investigations were carried out with commercial Armco iron. The chemical composition of the iron, the number of specimens tested, the grain size produced during chromizing and heat treating, and the thickness and microhardness of the chromized layers are shown in Table I. Samples were chromized by a gas diffusion process. The temperature and time of the diffusion coating process were chosen according to a previous grain growth study. It had been found that at a temperature of 970°C and a holding time of between 3 and 9 hr there are practically no changes in grain size. To describe the grain size more accurately the ASTM method5 was supplemented by a statistical analysis of the mean volume diameter as outlined by Fullman6 and The The mean volume diameter was deter- mined from D = p/2m where D is the mean volume diameter, and m is the mean reciprocal value of grain diameters as seen on the micrograph. The shape and the size of the asymmetrical sample, see Fig. 1, were chosen so as to facilitate the study of fatigue crack initiation. Before coating, the samples were machined and the surface of the groove was polished. After chromizing, the two side surfaces were machined and polished so as to retain the coating only on the top surface of the groove. Residual stress in the chromized layer was measured on the top of the grooved section of the specimen after the diffusion process. The inclined incident X-ray beam procedure was used.9'10 The computations were performed with the initial assumption of a zero surface normal stress component. An electron microprobe analyzer was used to obtain the relative amounts of chromium and iron con-

Jan 1, 1970

By W. O. Philbrook, K. Natesan

The oxidation kinetics of spherical pellets of zinc sulfide made from Santander concentrates were studied using a thermogravimetric technique. The experiments covered a temperature range-. of 740" to 102O°C, 0-N mixtures varying from 20 to LOO pct O2, and pellet diameters between 0.4 and 1.6 cm. Mathematical models were formulated to Predict the reaction rate on the assumption that a single transport or interface reaction step was rate -controlling. Analysis of the data indicated that the process of oxidation was predominantly controlled by transport through the zinc oxide reaction-Product layer. ROASTING processes, which are reactions between solids and gases, are very important because they are employed in the production of a number of basic metals. These processes are highly complicated, and one needs to consider the transport phenomena of heat and mass between the solids and gases in addition to the kinetics of various chemical reactions involved. Because of such complications there is a lack of knowledge concerning the rate-limiting factors, which may strongly depend on temperature, particle size, gas composition, and solid structure. The oxidation of zinc sulfide, which is of commercial importance in zinc production, falls into this class of reactions. The major goal of this work was to elucidate the roles played by different process variables, such as reaction temperature, gas composition, pellet size, and pellet porosity, on the kinetics of oxidation of single pellets of zinc sulfide. Roasting of zinc sulfide single particles has been a subject of both experimental and theoretical investigations.&apos;-&apos; The reaction is exothermic and may be considered to be irreversible. Such a reaction has been found to proceed in a topochemical manner. In other words, as the reaction proceeds, a progressively thicker outer shell of zinc oxide is formed, while the inner core of unreacted sulfide decreases. It has been found experimentally, both in the present work and in the previous investigations,1-9 that the particle retains its original dimensions and the process requires transport of gaseous oxygen across the porous product layer for continued reaction. The reaction may be represented by ZnS(s) + 3/2 O2(g) = ZnO(s) + SO2(g) [1] The solid product considered here is only zinc oxide, since the diffraction patterns of zinc sulfide pellets oxidized partially at &apos;798" and 960°C showed K. NATESAN, Junior Member AIME, formerly St. Joseph Lead Fellow, Department of Metallurgy and Materials Science, Carnegie-Mellon University, Pittsburgh, Pa., is now at Argonne National Laboratory, Argonne, Ill. W. 0. PHILBROOK, Member AIME, is Professor of Metallurgy and Materials Science, Carnegie-Mellon University. This paper is based on a them submitted by K. NATESAN in partial fulfillment of the requirements for the Ph.D. degree in Metallurgy and Materials Science at Carnegie-Mellon University. Manuscript submitted December 2, 1968. EMD lines corresponding to original zinc sulfide and the newly formed zinc oxide. OXIDATION MODEL The generalized model for gaseous oxidation of zinc sulfide is illustrated in Fig. 1. This depicts a partially oxidized sphere of zinc sulfide in a gas stream surrounded by a laminar film of gas. The spherical sample of zinc sulfide of unchanging external radius r0 is suspended in a flowing gas stream of total pressure PT and composition specified by the partial pressures of the individual components. Partial pressures of the gaseous species in the bulk gas phase, at the exterior surface of the pellet, at the ZnS/ZnO interface, and at equilibrium for Reaction [I] are identified by the superscripts b, o, i, and eq, respectively. The overall reaction involves the following ~te~s:&apos;~&apos;~&apos; Step 1. Transfer of reactant gas (oxygen) from the bulk gas stream across the gas boundary layer to the exterior surface of the pellet and the reverse transfer of the product gas (sulfur dioxide). Step 2. Diffusion and bulk flow of oxygen from the pellet surface through the product shell (ZnO) onto the ZnS/ZnO interface and the reverse transfer of sulfur dioxide. Step 3. Chemical reaction at the interface, which results in consumption of oxygen gas and generation of sulfur dioxide gas and heat; at the same time the _________ PARTICLE SURFACE / x^^^^n^X / MOVING INTERFACE core-----/ sJSNxy " /T^T^02 \ V\V$\ ^NWX/ "*/— GAS BOUNDARY x. \\ZnO SHELLV/ / \^ . / &apos; ^ BULK GAS --------N_______ _____,------p£ w \ P« / (f> \ / a \ <i) / <----------------- _(o) ^^--------------(b) °- pso, pso2 ro ri 0 ri ro RADIAL POSITION Fig. 1—Generalized model for oxidation of a sphere of zinc sulfide.

Jan 1, 1970

By C. A. Rowland, R. C. Nealey

Until recently there were very few dry grinding rod mills used. The early installations performed as anticipated. In the last seven years a number of dry grinding rod mills have been made, most of which have been used for grinding iron ore. The recent installations have not operated as anticipated in accordance with practices learned from wet rod milling. The paper does not establish any definite rules for the application of dry grinding rod mills but does attempt to establish some guidelines that can be followed. The paper reviews a number of flowsheets describing the problems encountered and some of the solutions found. Completely dried compared to partially dried feed is reviewed. Problems encountered in scaling up from pilot plant to production-size mills are described. Rod sizing, effect of rod length, rod bending, rod breakage, and rod tangling are discussed. While wet grinding rod mills have been used for 50 years to grind ores and make specifications sands, dry grinding rod mills have only recently come into significant use in the mineral industries. Among the materials now being processed in dry grinding rod mills are (1) lead sinter, lead slag, and limestone; (2) iron ore; (3) silica; (4) cement clinker; and (5) coke. Because the application of wet grinding rod mills was well understood at the time that dry grinding rod mills were introduced, the criteria and guidelines for selecting the former were carried over to the selection of the latter - in some cases with the anticipated results, but in many cases not. It is the purpose of this paper to describe, through a series of flowsheets, some of the recent problems encountered with dry grinding rod mills, to point out the solutions to these problems, and to set forth some guidelines for the selection and application of these mills. When dry grinding rod mills came into use, the following facts about their wet grinding counterparts were already well established: (1) The performance of large-sized mills can be accurately predicted from the performance of rod mills 5 or 6 ft in diameter. Wet grinding mills as large as 14 ft in diameter (inside shell) by 20 ft long with rods 19.5 ft long can operate satisfactorily.

Jan 1, 1970

By L. A. Tarshis, H. E. Cline

A stability criterion for a lamellar eutectic interface was derived previously1 assuming that the wavelength, A,. of the perturbation which grows most rapidly is much larger than the lamellar spacing. A. This assumption was required to permit averaging of both the interface temperature and composition over the complicated geometry of a lamellae. If this assumption is invalid, as has been suggested.2,3 then the problem becomes too complicated to solve completely. The first of these analyses1 did not calculate the wavelength. A,. of the initially unstable perturbation. whereas the more recent analysis.&apos; which led to a contradiction of this assumption. did not include one of the key factors for determining this wavelength. To rigorously determine the wavelength, the effect of the curvature of the perturbed interface (not considered by either of the above treatments) must be included. By omitting this term, one would be led to an incorrect conclusion regarding the magnitude of A,. but to an accurate criterion for stability as evidenced by the excellent agreement with experimental observations.&apos; In the case of single-phase alloys. the critical wavelength. A,. for instability can be calculated from the Mullins and Sekerka4 (M.S.) analysis which includes the effects of capillarity. In the following discussion, the M.S. analysis is applied to lamellar eutectics and the critical wavelengths calculated for reasonable growth conditions in Pb-Sn eutectic alloys. In order to apply the M.S. analysis to eutectics. one may substitute i) the effective liquidus slope.1 m*. for the single-phase liquidus slope and ii) the ratio of the bulk alloy composition. C,. to the average interface composition in the liquid (Ci = CE where CE is the equilibrium eutectic composition) for the distribution coefficient to give:

Jan 1, 1970

By Peter Hood

Data on worldwide geophysical activity in mining exploration programs is collected annually by the Geophysical Activity Committee of the Society of Exploration Geophysicists as part of a continuing service to the industry. The data is obtained by sending out questionnaires to all organizations (which are) known to be carrying out mining geophysical work; the organizations canvassed include mining companies, contractors, government departments and universities. The questionnaire is divided into three sections, namely ground methods, airborne methods and research. In 1968, 515 questionnaires were circulated throughout the non-Communist world and 283 replies were received which is a 55% return. A 67% return was received from the U. S. organizations surveyed so the statistics quoted in this report for the United States are reasonably reliable. This report is published in condensed form, but with emphasis on the United States statistics, with the permission of the Society of Exploration Geophysicists. It was presented at the 39th Annual International Meeting of the SEG in Calgary, Alberta, on September 15, 1969. Worldwide utilization of mining geophysical methods reached a new high in 1968 with total expenditures of United States $41.4 million, compared lo $32.3 million in 1967, representing a 28%, increase. The expenditure distribution by area and type of activity is shown in the graph on page 64. In terms of money spent, ground geophysical surveys accounted for 49% of the total, airborne survey&apos;s 36% and research 15%. The percentage of the money spent on ground geophysical surveys fell by approximately 7% from 1967, that for airborne surveys, increased by 5%, and for research the amount increased by 2%. Industry accounted for 79°1% of the total monies spent on mining geophysical activity in the world in 1968 and governments and universities 21 o%.

Jan 1, 1970

By W. E. Quist, R. Taggart, D. H. Polonis, C. J. van der Wekken

An intermediate compound that has been identified as Niab is observed to form as a decomposition product from supersaturaled Ni-Nb solid solutions during aging at temperatures between approximately 300" and 500°C. On the basis of data from electron microscopy and selected-area diffraction, the structure of this compound has been determined as fct with a = b - 3a0 and c = a, wlzere a,, is the lattice parameter of the parent solid solution. The compound consists of close-packed layers with triangular ordering, where the niobiutrl atoms are separated by two nickel atoms ([long- close?-packed directions. A nine layer stacking sequence is required to describe the proposed structure. STUDIES of the Ni-Nb binary system have been limited primarily to phase diagram determinations,&apos;-4 investigations of high-temperature equilibrium phases,5"1 and the determination of the influence of deformation on the structure of the equilibrium compound.8 The nickel-rich portion of the binary system is reported to be of the simple eutectic type in which the maximum solubility of 12.7 at. pct Nb occurs at 1282"c.&apos; The two-phase field below the eutectic temperature is bounded by the a fcc solid solution and an orthorhombic Ni3Nb compound. No metastable phases have been reported in previous investigations. In transformation studies of certain nickel-base commercial alloys that contain niobium, two ordered metastable compounds containing niobium have been shown to precipitate from the solid solution, both of which have been identified as y&apos; and have the composition NisNb or Ni,Nb. One compound has been reported to have the bct DOz2 type Al3Ti structure" and the other the cubic LI2 type Cu3Au structure.9,11 In the present work on Ni-Nb binary alloys a metastable y&apos; compound has not been detected after conventional quenching and aging treatments. An anomalous behavior was noted in electrical resistivity measurements. in alloys containing between 7 to 12 at. pct Nb when aging treatments were performed below 500°C after fast quenching from 1250°C. Transmission electron microscopy has shown that this behavior is caused by the formation of a low-temperature precipitate of unreported structure type and composition. EXPERIMENTAL METHODS Several Ni-Nb alloys, containing up to 11.5 at. pct Nb. were prepared by either levitation melting and casting in copper molds or by induction melting in alumina crucibles; both techniques employed purified helium gas as a protective atmosphere. The purity of the nickel and niobium used to make the alloys was 99.98 wt pct Ni and 99.9 wt pct Nb. The composition and homogeneity of the alloys were checked by weight measurements and by electron microprobe analysis. The induction-melted alloys were homogenized for 100 hr at 1100°C. The resistivity specimens were prepared from rods swaged to 2.5 mm and the electron microscopy specimens were cut from sheet that was rolled to 0.4 mm and thinned using a modified Bollmann technique." The elevated-temperature solution treatments were carried out in a purified helium atmosphere followed by direct quenching into a 10 pct NaCl solution at 23°C. Additional protection against oxidation of the samples during solution treatment was accomplished by using tantalum foil as a "getter" in the furnace. The specimens were aged at various temperatures in salt baths controlled to +2oC. A Leeds and Northrup K5 potentiometer was used to make electrical resistivity measurements on specimens immersed in liquid nitrogen. Electron microscopy and diffraction studies were carried out with JEM-7 and Philips EM-200 microscopes operating at 100 kv. RESULTS AND DISCUSSION Ni-Nb alloys containing between 7 and 11.5 at. pct Nb that have been solution-treated in the range 1220" to 1280°C and quenched to 23°C undergo a precipitation reaction when aged in the temperature range 300" to 500°C. Precipitation was detected by selected-area electron diffraction after aging a specimen for as little as 30 sec at 350°C) whereas the reaction was well-advanced after aging for 150 hr at 475°C. Electrical resistivity measurements were used to monitor the progress of the precipitation reaction. In the present experiments the nucleation process for precipitation required a high solution temperature and a rapid quench into brine. The presence of aluminum, iron? and carbon in amounts totaling less than 1 wt pct was found by electron diffraction to completely suppress the formation of the low-temperature precipitate that has been detected in the binary alloy. Electron diffraction techniques were used to determine the structure of the precipitates that formed during the decomposition of the Ni-Nb supersaturated solid solutions. Figs. l(a) through l(d) show electron diffraction patterns oriented to the [loo], [110], [lll], and [I031 zone axes of the matrix. Areas of reciprocal space between these sections were investigated by slowly varying the orientations of the crystal under study; this procedure revealed no reflections other than those depicted in Fig. 1. The presence of super-lattice reflections at points coincident with the matrix reflections was confirmed by the examination of an almost completely transformed structure. On the basis of the accumulated diffraction data, the reciprocal lat-

Jan 1, 1970

By D. de Fontaine

A convolution procedure is described for obtaining an analytical expression for the composition profiles of solute concentration:; in binary solid solutions. The free energy of solutions containing such compositional inhomogeneities can then be evaluated and the stability of spherically symmetric clusters (G.P. zones, for short) us a function of their radii and central compositions can be studied accordingly. Two characteristic zone radii are defined: the minimum radius (RM) corresponding to the smallest zone for which growth is energetically favored over dissolution, and the critical radius RK) corresponding to zones associated with the minimum work of formation. The values of RM and RK coincide at the two classical limits of nucleation and growth and spinodal decomposition. As the spinodal is approached, however, RM and RK diverge increasingly and it is proposed that the initial] decomposition morphology is governed more closely by the minimum, rather than by the critical radius since the former possesses no singularity within the m eta stable phase boundary. Reversion is briefly discussed in the light of the foregoing and it is shown that a set of reversion temperatures located between the coherent miscibility gap and the coherent spinodal must correspond to a given distribution of low temperature zones. SINCE the early works of Guinier1 and preston,2 the kinetics and morphology of GP zones have been studied extensively, see Ref. 3, for example, for a recent review. Nevertheless, a completely satisfying theoretical treatment of the decomposition of meta-stable or unstable binary solid solutions is still lacking due to the almost unsurmountable mathematical difficulties that one encounters in attempting to solve the pertinent diffusion equation which, in principle, describes the whole process. This equation, first derived by Cahn for the initial stages of spinodal decomposition,4 is a nonlinear partial differential equation of the fourth order in anisotropic space, a general analytical solution of which is completely out of the question. From this equation, some prediction can be made, however, concerning the later stages of spinodal decomposition5 and a recent numerical solution6 of the equation in the case of one- and two-dimensional composition modulations of a solid solution inside the spinodal has led to the following considerations: the sinusoidal morphology7 is to be expected only for solutions of average composition c, located near the center of the coherent miscibility gap.8 For solutions with co closer to the spinodal decomposition, depleted shell zones9 should constitute the first recognizable decomposition product, later evolving to iso- lated, enriched preprecipitates in a uniformly depleted matrix as this must, in all cases, constitute the final metastable morphology, barring, of course, loss of coherency and change in crystal structure. In agreement with the qualitative description of Bonfiglioli and Guinier,l0 it thus appears that the various models discussed by previous authors are, in fact, idealized successive stages of the general decomposition process. Unfortunately, corresponding calculations for a solid solution outside the spinodal are not yet available because of two additional difficulties: it is essential that the diffusion equation be solved in three-dimensional space, and furthermore, one must include in the equation an appropriate "source term" describing the statistics of the creation of composition fluctuations required to trigger the nucleation events. At present, a general treatment of this problem does not appear to be tractable. Nevertheless, by using a modelistic approach, i.e., by selecting a priori certain composition variation profiles and by evaluating their associated free energies, one can draw certain conclusions relative to the stability of these isolated composition modulations or "zones", both outside and inside the spinodal. This is the object of the present investigation. THEORY We shall now describe a standard four-parameter spherically symmetric GP zone, evaluate its free energy according to the Cahn and Hilliard11 formula (Eq. [5], below), and plot the corresponding energy surfaces as a function of zone amplitude and radius as

Jan 1, 1970

By B. Ladanyi, B. Hoyaux

One of the most important problems in underground works is the assessment of the stability of underground openings and the determination of loads on eventual supporting structures. Under certain stress conditions, a hard and sound rock around an unlined opening may show a tendency to rock bursting, which can be prevented by appropriate measures. On the other hand, a less competent rock even if it fails in a less violent manner may give rise to a rock load because within limited regions surrounding the opening, the failed material may have a tendency to flow into the opening; this condition should be prevented by designing a proper supporting structure. The stability of the opening, as well as the value of the design loads acting on the supports in the latter case, depends clearly on the shape, extent, and location of the failed regions, which are often called “plastic zones.” It has been known for some time how the plastic zones develop in some very simple cases, such as in the case of a circular opening in an elastic ideally plastic medium subjected to a nongravitational stress fie1d.l However, to the knowledge of the authors, no information has been available up to now about the extent of the plastic zones in a more general case and for rocklike media. ASSUMPTIONS ON ROCK BEHAVIOR MADE IN THE CALCULATION The solution shown in this chapter is valid for a horizontal tunnel of circular cross section driven through a rock medium at a finite depth.

Jan 1, 1970

Grad, the abbreviation for Graduate Resume Accumulation and Distribution, is a computerized information retrieval system operated on behalf of college placement officers around the country by the non- profit College Placement Council, Inc. Grad is free to all engineering candidates (regardless of the number of years of experience) and is a means of getting together college alumni who are seeking new employment and prospective employers. Who is Qualified? Candidates must have at least a bachelor&apos;s degree from a four-year college or university, or. in lieu of this, be accredited by a professional institute such as AIME as a full Member.

Jan 1, 1970

By John V. Beall

Spots Goblenski fluffed up his pork chop sideburns, checked the angle of his wide brim Stetson and ambled off the airplane. The pert Braniff hostess stood smartly at the door. "Goodbye now, take care," she said in the special airline stewardess voice superimposed on a Texas drawl. Spots smirked, "You betcha, Peaches, you too." It was a crystal clear, sunny day which New York can have at any season of the year (but rarely gets credit for) and being in high spirits Spots did not mind being captured by a cab driver. That is the cab driver brushed aside all other conversation to give a continuous colorful commentary on New York politics, revealing in the process that only the very wealthy and cab drivers share the same political views in that city. After installing himself in the fading opulence of the Hotel Roosevelt, he finished the day with a steak dinner with baked potato under sour cream and hearts of lettuce salad with Roquefort dressing at the Black Angus restaurant. The next morning he had an appointment with Hemphill, Frye and Louderdock. The offices of this prestigious firm of management consultants are high in the Pan Am Building. He was courteously received by a lacquered receptionist and was soon escorted into the presence of Mr. John Smith. "Ah, Mr. Goblenski; Spots, isn&apos;t it? Hope you had a good flight. Lovely weather we are having. Just make yourself comfortable over there, Spots." Smith seemed cordial and Spots slipped comfortably into the interview. He had always thought that management consultants were evolved from the "efficiency experts" made famous by the radio team, Amos and Andy. He associated the modern version with computers, PERT and other systems approaches. He was surprised that one of these firms was apparently acting as an employment agency. "Of course" continued Smith, "in evaluation of basic criteria of performance moduli, the human element enters, Spots, and that brings us to you." Spots sat up and focused his attention.

Jan 1, 1970

By Bruce A. Kennedy

The long awaited new Mining Engineering Handbook is taking shape under the leadership of A. B. Cummins, Chairman of the Editorial Advisory Board for the SME Mining Engineering Handbook, and Ivan Given, Editor-in-Chief. The last Mining Engineers&apos; Handbook, the Peele edition, published by John Wiley and Sons, was last revised in 1941. This book was and still is a virtual mine of information although a good deal of its content, especially the cost tables, is becoming rather antiquated. The new one-volume work will contain approximately 1600 pages and be divided into 36 sections. A brief summary of the sections follows: The Place and Contribution of Mining, Mining Costs: Mining Geology-Minerals and Mineral Deposits; Minerals Discovery-Prospecting and Exploration Methods and Equipment; Site Exploration and Selection; Minerals-Mining Design; Soil and Rock Mechanics; Design of Excavations; Opening and Development: Underground Mining Systems and Equipment; Roof and Ground Control; Groundwater and Groundwater Control: Open-Pit and Strip-Mining Systems and Equipment: Underwater and Ocean Mining; Fragmentation-Cutting, Drilling, Blasting; Underground Haulage: Hoists and Hoisting Systems; Surface Haulage, Hoisting. Lowering Pumping and Drainage; Ventilation: Mine Surveying; Ore and Coal Processing; Mill Design; Industrial Minerals-Specifications and Markets: Power; Maintenance plant and Equipment; Supply Service; Health and Safety; Reclamation and Surface Restoration: Administration and Management; Operations Optimization (Systems Engineering) : Mint, Costs and Control: Mine Examination. Valuation. Reports; Engineering Terms: and Consulting Engineering.

Jan 1, 1970

By C. J. Sparks, J. C. Ogle, E. A. Starke

DEFORMATION of cold-rolled fcc metals and alloys produces one or the other of two types of rolling textures, usually referred to as the copper type or the brass type. The pure fcc metals, with the exception of silver, develop the copper-type texture when rolled at room temperature. Silver, brass, and many other alloys develop the brass-type texture. Transition from one texture type to another can also occur. Solute additions to pure copper cause a transition from the copper-type to the brass-type texture.&apos; Varying the deformation temperature also produces texture transitions. Copper rolled at -196°C developed the brass-type texture2 and silver rolled at elevated temperatures, 200°C, developed the copper-type texture.374 The work of Haessner,&apos; Smallman and Green,6 and Hu and coworkers3&apos;4 seems to have established an apparent correlation between the type of rolling texture (and the texture transition) and the stacking-fault probability. Thus materials with low stacking-fault energies are thought to develop the brass-type texture while high stacking-fault energy materials develop the copper-type texture. Mikkola and cohen7 measured by X-ray diffraction techniques the stacking-fault probability, a, in the ordered and disordered fcc alloy Cu3Au. Unexpectedly, ordered specimens showed about twice the stacking-fault probability as the disordered ones. Marcinkowski and Zwe118 also found stacking faults in ordered Cu,Au, but not in the disordered CusAu. More recently, Camanzi and coworkers9 have shown that the intrinsic stacking-fault energy of Cu3Au undergoes a considerable decrease (approximately 100 ergs per sq cm) when passing from the disordered to the ordered phase. In general, deformation reduces order&apos;&apos; but some of our measurements showed that some long-range order still remains in Cu3Au after cold reduction by rolling 80 pct. From the above considerations Cu3Au offers the possibility of studying the texture transition in fcc alloys without varying either the temperature or the composition. If the stacking-fault energy correlation is correct, an initially ordered alloy should develop the brass-type texture during rolling while a disordered alloy should develop the copper-type texture. The present communication describes some initial results of experiments designed to investigate this possibility. The rolling textures of ordered and disordered Cu3Au samples were determined after various amounts of deformation. The ordered sample had an initial long-range-order parameter of S = 1, determined from X-ray diffraction. The grain size of both the ordered and disordered samples was the same, and the initial textures of both were also identical and approximately random. No obvious differences in the deformation textures of the ordered and disordered materials were detected up to 35 pct reduction and the (111) pole figures of Fig. 1 resemble that of pure copper. However, with reduction larger than 35 pct and less than 50 pct, a marked deviation from the copper texture was noted in the ordered material. The newly developed orientation was close to the (110)[i12] ideal orientations re-

Jan 1, 1970

By R. S. Shrode, R. F. Bunting

Transportation is one of several important increments in the total market cost of most commodities. On a national average it has been reported that transportation accounts for about 25% of the total cost of a product at the market place. And industrial minerals are no exception. In fact, the proportionate cost frequently exceeds the 25% average. Further, it may actually determine the economic value of a deposit. Transportation possibly may be thought of as a specialized subject, of concern only to a traffic manager and of only nominal interest to the mining engineer, the geologist or other technically oriented member of a mineral producers&apos; staff. However, in the industrial minerals field, interest is not commonly confined to exploration, development, production or marketing, but is in contrast an overlapping one. In a very real sense this broad area of interest in the total economics of the business is the specialty of the industrial minerals man. And transportation is a vital part of the total picture.

Jan 1, 1970