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By Gerhard Derge, Harold Markus

The first paper1 of this series described a technique of careful surface preparation by means of which reproducible results may be obtained from potential measurements of the behavior of tin in carbonate solutions with a pH range from 8.4 to 11.2. It then went on to establish the behavior of pure tin electrodes under these conditions and showed that the metal remains active at all times, though the steady potential attained after several hours decreases from 1.12† volts at a pH of 12.6 to 0.6 volts at a pH of 8.4. This behavior may serve as a norm with which all other data can be compared. In the second paper,2 small amounts of other anions were added to the carbonate solutions and the conclusion was reached that the common impurities encountered in alkaline materials packaged in tin do not increase corrosion. In fact, in some cases these anions may actually promote the formation of protective films. The present paper rounds out this survey by presenting data on the influence of cations added to the carbonate solutions, as well as the effect of alloy additions to the tin. In many cases the potential data are supplemented with weight-loss measurements. Information is also presented on the effects of some additional anions, the influence of gases above the electrolyte, the behavior of high-purity tin, and the effect of atmospheric oxidation on the corrosion resistance of the above-named alloys. Analysis of the entire body of data discloses some general rules applicable to corrosion in carbonate solutions. The experimental methods used are the same as those previously described. Experimental Data Cations.—The carbonates of the cations K+, Li+, NH4+, which are soluble, were studied in the same way as the anions, by adding 0.01 mol of the metal carbonate to one liter of 0.1 M sodium carbonate solution, pH 11.2, or to 0.1 M sodium bicarbonate, pH 8.4. The other metallic carbonates are only slightly soluble, of the order of 10-3 mols per liter or less, and the sodium carbonate solutions were saturated by adding excess reagent several days before the experiment, shaking frequently, and filtering just before use. The chemicals were c.p. grade in each case except the indium salt. This salt was prepared by solution of the metal in hydrochloric acid and precipitation by addition of Na2CO3. These cations may be divided into two classes, according to their effect on the potential behavior of the tin: (I) normal, (2) passive. To offer a basis of comparison, curves I of Figs. I and 2 are given to illustrate the behavior of tin in carbonate solutions saturated with CaCO3. These curves are the

Jan 1, 1941

By Harold Markus, Gerhard Derge

The first paper1 of this series described a technique of careful surface preparation by means of which reproducible results may be obtained from potential measurements of the behavior of tin in carbonate solutions with a pH range from 8.4 to 11.2. It then went on to establish the behavior of pure tin electrodes under these conditions and showed that the metal remains active at all times, though the steady potential attained after several hours decreases from 1.12† volts at a pH of 12.6 to 0.6 volts at a pH of 8.4. This behavior may serve as a norm with which all other data can be compared. In the second paper,2 small amounts of other anions were added to the carbonate solutions and the conclusion was reached that the common impurities encountered in alkaline materials packaged in tin do not increase corrosion. In fact, in some cases these anions may actually promote the formation of protective films. The present paper rounds out this survey by presenting data on the influence of cations added to the carbonate solutions, as well as the effect of alloy additions to the tin. In many cases the potential data are supplemented with weight-loss measurements. Information is also presented on the effects of some additional anions, the influence of gases above the electrolyte, the behavior of high-purity tin, and the effect of atmospheric oxidation on the corrosion resistance of the above-named alloys. Analysis of the entire body of data discloses some general rules applicable to corrosion in carbonate solutions. The experimental methods used are the same as those previously described. Experimental Data Cations.—The carbonates of the cations K+, Li+, NH4+, which are soluble, were studied in the same way as the anions, by adding 0.01 mol of the metal carbonate to one liter of 0.1 M sodium carbonate solution, pH 11.2, or to 0.1 M sodium bicarbonate, pH 8.4. The other metallic carbonates are only slightly soluble, of the order of 10-3 mols per liter or less, and the sodium carbonate solutions were saturated by adding excess reagent several days before the experiment, shaking frequently, and filtering just before use. The chemicals were c.p. grade in each case except the indium salt. This salt was prepared by solution of the metal in hydrochloric acid and precipitation by addition of Na2CO3. These cations may be divided into two classes, according to their effect on the potential behavior of the tin: (I) normal, (2) passive. To offer a basis of comparison, curves I of Figs. I and 2 are given to illustrate the behavior of tin in carbonate solutions saturated with CaCO3. These curves are the

Jan 1, 1941

By J. W. Hickman

INTRODUCTION MOST of the electron diffraction studies of oxide films which form on metals and alloys have been carried out by oxidizing the specimens in an auxiliary furnace, cooling down to room temperature and then inserting the sample in the camera and taking a diffraction photograph. Prior to the investigations at the Westinghouse Research Laboratories, no systematic study of the oxidation of any metal or alloy had been made over a wide temperature range with photographs taken at elevated temperatures except the investigation of iron by Jackson and Quarrell.1 In order to interpret the electron diffraction patterns of the oxides which may form on alloys, it seemed advisable to make a comprehensive study of the oxidation of the purest metals available in the bulk form. Thus far studies have been completed on iron,2 cobalt,2 nickel,2 chromium ,2 Copper2, tungsten,3 molybdenum,3 beryllium ,4 uranium,4 thorium4 titanium5 and zirconium5 while investigations are in progress on tantalum and columbium, The next step in the study is concerned with the investigation of the oxides which form on binary alloys. Some of the alloys consist of a single, phase while others contain more than one phase. The identification of the oxides on the surface of a binary alloy may be more difficult than on the metals since oxides containing both metals as well as those of each metal separately may form. Furthermore, it is possible that solid solutions of the various oxides may occur. In these cases the electron diffraction method may not be able to identify the oxidation products unequivocally, Examples of solid solutions which may present difficulties are MoO2 and W02, Fe3O4 and FeO-Cr2O3 since the diffraction patterns are so similar. Since electron diffraction can determine only the structure of the oxide, the chemical composition must be inferred from the diffraction data based upon X ray diffraction investigations of specimens of known composition. It is possible in some cases to decide whether a given solid phase reaction can occur on the surface of an alloy by a study of available thermodynamic data. Table I lists the equations for the formation of most of the oxides from the elements together with values of log10 KR for the several temperatures. [OF°R = -RT In KR 0 and-~75T = logi°KR] [?F°R] and KR are the free energy and equilibrium constant of the reaction. Calculations may be made using the values given in Table I to determine whether a given solid phase reaction is possible thermodynamically. For example, a solid phase reaction should occur between aluminum and chromium' oxide to form

Jan 1, 1948

By Franc R. Joubin, D. H. James

Uranium exploration in the North Shore area of Lake Huron goes back to 1847 when J. L. LeConte, a distinguished American geologist, identified a pitchblende-like mineral which he called coracite from specimens sent from a locality north of Sault Ste. Marie. In 1948 a search for the LeConte occurrence resulted in discovery of the Camray field, some 70 miles north of Sault Ste. Marie. Prospecting the Camray field yielded about 30 pitchblende occurrences spread over approximately 200 sq miles. Almost without exception these discoveries consisted of narrow, short, pitchblende-filled fractures, within or along the contacts of diabase dykes cutting pre-Cambrian Archean granite and gneiss. Eight discoveries were diamond drilled and three were explored underground, but none proved to be of economic value. Uranium prospecting at this time spread far afield, and it was in 1949 that radioactive conglomerate was discovered in Long Township of the Algoma district midway between and 90 miles from Sault Ste. Marie and Sudbury. F. Joubin examined this discovery at that time but could not interest capital in its development.

Jun 1, 1956

By H. T. Shore, J. M. Schultz

A number of experimental rnethods—X-ray powder diffractometry, Laue photography, X-ray small-angle scattering, and transmission electron microscopy and dijfraction—have been utilized to examine the morphology associated with precipitation from the terminal, g, solid solution of a Zn-1 pct Cu alloy. A significant age hardening was observed in a 1 pct Cu alloy. X-ray and electron diffraction results showed that the structural inhomogeneities associated with the hardening were isotructural with the matrix. The average size and shape of the inhomogeneities were deduced from the electron microscopy and X-ray small-angle scattering. The preprecipitates are hexagonal platelets some 300? in diam. and some twelve unit cells thick. The orientation of the platelets was deduced from Laue photographs and electron diffraction. The platelet plane is (0001). When a large amount of pre-precipitation is present in a localized volume the new lattice is often disoriented by a rotation about (0001) of of the matrix. WhILE dilute Zn-Cu alloys have been commercially important for some 50 years, relatively very little is known metallographically about this material. The "Zilloys", zinc with about 1 wt pct Cu and sometimes a small addition of magnesium, are used to produce rolled zinc which is harder and stronger than that produced by other rollable zinc alloys.' According to the phase diagrams of the zinc-rich side of the Cu-Zn system, such dilute Zn-Cu alloys should age-harden;2-5 the solubility of copper in zinc, g-phase, at 424°C is 2.68 pct, while at 0°C it is only to 0.3 pct. However, the published literature on the aging of this system appears to be limited to a documentation of the contraction of 1, 2, and 3 pct Cu alloys aging at 95°c,6 and an attempt to measure changes in lattice parameters during aging.' In the latter work, no lattice parameter changes were detected, although a broadening of the highest-angle lines was detected and considerable diffuse scattering was observed. Micro-structural investigations have been limited to the latest stage of aging, wherein Widmanstatten precipitates are formed.3,47 These alloys are of interest for still another reason. The two most zinc-rich phases in the Cu-Zn system, 77 and E, are both hcp. Moreover, the change in a, between 17 and t for a 1 wt pct Cu alloy is onlv 3.64 -,~ct: the change in Co is 12.0 ict. It would be anticipated that precipitation in such a material might occur through metastable phases or G.P. zones with epitaxy along mutual 0001 planes. The goals of the present work are aimed at partially filling the void of knowledge concerning the early stages of precipitation from the g phase. In particular, we have attempted to document the magnitude of the age hardening of this system and to determine the size, shape, and orientation within the matrix of the elements of precipitation in an early stage of condensation. EXPERIMENTAL A) Specimen Preparation. Specimens were prepared In two somewhat different ways, one method being used for X-ray Laue and diffractometer measurements, optical microscopy, and Rockwell hardness measurements and the other used for electron microscopy and X-ray small-angle scattering. In the first case zinc and copper in the proper proportions to yield a 1 wt pct Cu alloy were melted together in a closed graphite crucible. Castings so made were free of apparent segregation or oxidation. The castings were then solution-annealed at 400°C for several days and then quenched in water to room temperature. Filings of portions of the specimens were made for use as X-ray powder diffractometry specimens. The electron microscope material was made as follows. Castings were made under vacuum with copper powder placed inside a hollow zinc cylinder to insure good contact of the materials. These 1 wt pct Cu pieces were then rolled to 0.1 mm with an intermediate anneal in vacuo. The rolled sheets so formed were then annealed for about 6 hr at 225°C. Finally the specimens were electropolished slowly until thin enough for transmission electron microscopy. The polishing is discussed in greater detail in the Results section. B) Measurements. X-ray measurements of three types were performed. A G.E. XRD-5 diffractometer was used to examine powders of the alloy for identification of second-phase material. A Kratky small-angle camera, also operating from a G.E. tube, was used to investigate the sizes of small precipitate particles. In both cases, nickel-filtered copper radiation was utilized. Finally, individual grains of the large-grained castings were examined in the back-reflection Laue geometry. Electron microscope studies were carried out with a J.E.O.L. Model 6A instrument. RESULTS A) Hardness Measurements. Hardness measurements performed at room temperature on the large-grained polycrystalline specimens showed a hardening which was essentially complete in 3 hr. Fig. 1 shows a typical plot of hardness vs aging time. The relative magnitude of the ultimate hardening varied from run to run between 150 and 200 pct of the value for the material immediately after quenching from the solution anneal. Most probably the variations reflect small changes in the time taken to remove the specimen from the vacuum furnace after the solution anneal.

Jan 1, 1969

By M. S. Abrahams

Germanium has been rolled in the temperature range of 700o to 800°C. The thickness has been decreased by as much as a factor of four, from a thickness of 0.032 in. to a thickness of 0.008 in. For deformations below 60 pet, the true strain per pass is found to be a constant; from the temperature dependence of this slope, an activation energy of about 2.5 ev is obtained. This energy agrees with that for dislocation climb in germanium . For reductions greater than 60 pet, complete rings are seen in the Lave photographs, new grains are observed in the microstructure, considerable softening occurs, and the hole mobility is very low. This evidence indicates that the recrystallization of gertnanium has occurred. GERMANIUM has been deformed in many ways1 including tension, compression, torsion, and bending since Gallagher2 first described its plastic nature at elevated temperatures. All of these studies indicate that the glide plane in germanium is (111) and that the glide direction is (110). Rolled germanium specimens were used by Kolm, Warekois, and Kulin3 in their X-ray study of deformed semiconductors, but no information is given on the rolling itself. The present experiments deal with the rolling of germanium at various temperatures and for different orientations. In all previous deformation studies, the phenomenon of recrystallization (i.e., the transformation of a single crystal into a polycrystal) in germanium has not been observed4 despite relatively large deformations at elevated temperatures. The proposed reason4 for this was that sufficient energy could not be stored in the deformed germanium lattice. In contrast to the earlier studies this work will present evidence indicating that recrystallization occurs in germanium during rolling at an elevated temperature. I) EXPERIMENTAL PROCEDURE A) Test Specimens. The samples used for rolling were in the form of rectangular parallelepipeds measuring 0.3 in. long, 0.06 in. wide, and 0.035 in. high. They were cut from an undoped single-crystal ingot of p-type germanium with a resistivity of 24.4 ohm-cm, a Hall mobility of 2300 sq cm v-' sec-l, and a hole concentration of 1.1 x 1014 cm"3 at room temperature. The surfaces of the specimens were metallographically polished prior to rolling. The initial dislocation density of the samples was about 10' cm-' as determined by etching in CP4. Two different specimen orientations were used. In the first case, the direction of rolling was parallel to (251), the surfaces in contact with the rolls were of the form (1021, and the normal to the third face was parallel to (211). The corresponding di-

Jan 1, 1964

By A. J. Lynch

There are two factors which are important in the development of automatic control systems for mineral preparation and concentrating processes. They are the availability of accurate and reliable on-line measuring instruments and an understanding of the effects of important variables on process behaviour. The state of automatic control for the different processes depends on the progress which has been made in these areas and this varies considerably. This is illustrated by discussion of four processes, wet ball milling and hydraulic classification, wet autogenous milling, sulphide flotation and dense medium separation in coal preparation plants. In each case the process characteristics, current control practice and future developments are discussed. Particular problems which have delayed progress are discussed.

Jan 1, 1984

By Robert C. Edmiston

The measurement of temperatures in exploratory drill holes yields information on regional and local geothermal gradients and mean surface temperatures. This data may be beneficial to the mining geologist interested in the occurrence and oxidation of metallic sulfide minerals or to the mining engineer interested in subsurface temperatures or water movement. Additionally, the estimation of mean surface temperatures by the projection of thermal gradients to the ground surface provides data on which to evaluate infrared imagery as an exploration tool. Temperature measurements in 30 diamond drill holes in the Silver Bell mining district of Arizona show that a regional geothermal gradient of 2.45°C per 100 m increases to 3.03°C per 100 m near the ground surface. It is also found that an anomaly in the mean annual surface temperature of 0.5°C is associated with the shallow occurrence of disseminated sulfides. Changes in the geothermal gradient due to topography, water circulation, and formation changes also occur.

Jan 1, 1976

By AIME AIME

THE Western States Joint Convention opened at Denver on Sept. 20, with about 400 registered the first day. Monday was devoted to the American Mining Congress, and the afternoon session was taken up with a discussion of the public land laws of the United States. Hubert Work, Secretary of Interior, and William Spry, Commissioner of the General Land Office, presented a comprehensive review of the origin and operation of the laws and argued against any general change in the system. Charles E. Winter, Congressman from Wyoming, marshalled the arguments in favor of turning over the public lands to the states within which they lie, and George H. Dern, Governor of Utah, presented a well-reasoned argument in favor of allowing the school sections to pass to the states regardless of their mineral or non-mineral character. The debate made it clear that in the West especially, there is strong feeling against any further development of the policy of reserving and leasing the public lands. Tuesday forenoon was devoted to the Silver Producers Association, F. H. Brownell and Charles A. Thomas being the principal speakers, and in the after- noon the American Association of Petroleum Geologists met with Alex. W. McCoy presiding, and Glenn C. Clark, J. V. Howell, and J. W. Beede presenting papers.

Jan 1, 1926

By G. D. Hobson, I. Mrosovsky

Material balance relationships for expansion-type reservoirs above the bubble point have been discussed in recent years by H. N. Hall and M. F. Hawkins, Jr. The former drew attention to the effects of rock compressibility, and the latter to the effects of the compressibility of any interstitial water. Hawkins derived a general relationship which took note of oil, water and rock compressibilities, and then by assuming first, the absence of interstitial water and secondly, no effects due to interstitial water or rock compressibility, obtained relationships symbolically of the same form as those previously derived directly by Hall. Hawkins defined his terms clearly, and noted an approximation, due to the omission of a term involving the product of two compressibilities, made in reaching his final equation. There is, however, possible ambiguity with regard to Hall's written definition of the oil production term. One interpretation would mean that the produced oil and initial oil-in-place, if both required as stock tank barrels, would be obtained by using different formation volume factors in the conversion in order to satisfy the conditions implicit in Hall's formulae. The other would involve an approximation which, if used, was not stated. In both Hall's and Hawkins' studies the effect of the approximation or inconsistency is very slight. Nevertheless, it may be justifiable to give a somewhat more consistent derivation, since the complexity of the final relationships is not thereby greatly increased. Let the initial pore volume be Vi and the volume after a pressure drop of Ap, V. Then V = V, (1 - ?p . cr), where c, is the rock compressibility expressed as change in pore volume/unit pore volume/unit pressure change, and is defined with the initial pressure as base. Suppose that the interstitial water saturation under the initial conditions is Sw. The total volume of interstitial water under those conditions will be ViSw. If the volume of the water after dropping the pressure by ?p is V., this will be given by Vw = ViSw (1 + ?p.c,w), the compressibility of the water being c, which is ex- pressed using the volume at the initial pressure as base. If Boi is the reservoir volume factor of the crude oil for the initial reservoir conditions, and B. the equivalent factor when the pressure has dropped by ?p, with N the initial amount of oil expressed as stock tank barrels. N.Boi = Vi - V,Sw If n is the amount of oil produced (in terms of stock tank barrels) as a result of the pressure drop ?p, the remaining subsurface volume of oil at the lower pressure will be Bw, and Bc can be related to the compressibi:ity of oil and the pressure drop, and if c, is the compressibility factor based on the initial conditions, The relationship derived by Hawkins was case to a standard at the lower pressure, while a term (Ap) had been dropped, because of its smallness arising from its dependence on the products of two compressibility factors. When there is no interstitial water and rock compressibility can be ignored, Eq. 1 reduces to:

Jan 1, 1957

By FREDERICK W. BRADLEY

MINING is one of the world's oldest industries and has pioneered the civilization of all new lands. Today, mining is not only one of the essential and basic industries of the world, but it is constantly growing in magnitude and becoming more important. We think that the most of our mining is done in the western portion of this country, but in the old State of Pennsylvania mines and products derived from minerals account for about two-thirds of the entire productive wealth of the State. As our forests are denuded, mining furnishes substitutes for timber in the way of concrete, gypsum board, etc. ; and as civilization increases the wants of mankind, mining is producing metals and minerals of every kind in increasing quantities. For example: during the past ten years the per capita consumption of copper in the United States has increased 49 per cent, to 14.56 Ib.; that of lead has increased 35 per cent, to 12.24 lb.; and that of zinc has increased 70 per cent, to 9.57 Ib. The consumption in European countries is about one-half of this, and there are other countries with large populations where there is virtually no consumption; so when all other countries catch up in consumption with our country, you can see what an enormous demand there is going to be for the metals, even to the extent of having to find substitutes for copper, lead, and zinc.

Jan 1, 1929

By Thomas M. Plouf

Getting optimal performance from flotation cells can, in many cases, be critical to a project's economic viability. Simple testing procedures can sound early warning signals as well as maintain optimum recoveries from the flotation cycle. The materials required for a simple testing laboratory include: (1) pH meter or pH paper, (2) bottles of reagents used in plant flotation, (3) stop watch, (4) calibrated eye droppers. (5) laboratory flotation machine (1000-g tank, open impeller), (6) froth collection pans, (7) magnifying glass, (8) sizing screen sufficient to retain 10% of the flotation feed coarse fraction, (9) sizing screen for the size particles at which desliming of the plant flotation feed is to take place, and (10) a set of screens covering the complete range of feed particle size.

Jan 4, 1978

By G. L. Oldright

DURING 1919, in the face of high cost for labor and supplies and a rapidly dropping copper market, the management of the Ohio Copper Co. of Utah was left with an orebody that had been shown to be very low grade, and a mill that could not make a satisfactory recovery, even by flotation, because a considerable proportion of the copper minerals was oxidized. About seven million tons had been mined by the use of a caving system, the best of the broken ore extracted and milled, and the nature and copper content of the rest of the orebody fairly well determined. The rock of the whole mine was shown to run between 0.3 and 1.3 per cent. in. copper. As, the Ohio Copper orebody lies at the contact of the original sandstone (now altered to quartzite) with the quartz monzonite intru-sion that was the source of the mineralization at Bingham Canon, the rock was thoroughly shattered. It was shown further that the rock was mostly quart-zite, with a few quartz-monzonite "fingers" projecting into it. Although some of the old cleavage planes had been healed by resilicification so as to leave some of the copper minerals disseminated in the rock, a large proportion of these minerals was distributed along the cleavage planes.

Jan 10, 1923

By G. Hasenfus, M. Karmis, G. Goodman

Surf ace subsidence is rapidly becoming an important environmental consideration of active as well as abandoned mining operations. The damages attributed to this phenomenon have been witnessed in both rural and urban areas and include land settlement and fracturing, structural damages to surface buildings or facilities and disruption or contamination of ground water supplies. The problem of mining subsidence has gained considerable emphasis in the Appalachian coalfield. The increased mining activity over the past few years and the particular topographic conditions, lithologic and structural environment, mining methods and hydrological patterns are all factors which have contributed to specific subsidence characteristics in this region. The objective of this paper is to discuss and review the most widely accepted methods of subsidence prediction above longwall as well as partial extraction systems in Appalachia. These include an accurate and easy to apply empirical method, which has been developed entirely from field information pertaining to the Appalachian coalfield and incorporates both geometrical and geological information of the panel in question. The second method is a development of influence functions and is founded on the zone area approach. Both methods, originally derived for longwall mining, have been expanded to include room and pillar applications and have been widely used by the mining industry in the Appalachian coalfield.

Jan 1, 1984

By R. M. Stewart

INTRODUCTION Requirements for achieving economic slope stability in open pit mining must not only be met during the operating stages but in all preceding stages of mine development. In many operating mines little or no emphasis was ever placed on evaluating the stability of possible slopes during the exploration and planning stages. The purpose of this discussion is to emphasize the necessary considerations that should be made in all stages of development in order to achieve the safest and most economic pit slopes. The most economic slopes may not always be the safest slopes and it is incumbent upon the mine operators and engineers to achieve an optimal combination of economics and safety. The stability requirements outlined are based on the profit motive and are, therefore, practically oriented. Long-term basic research or theoretical studies are considered important only to the extent that they can be shown to have a definite payoff. Consideration will first be given to the information required for stability analysis, which can be determined during the exploration and evaluation stage, followed by further stability work necessary during the mine planning and layout stage. Particular emphasis is then placed on the operating stage in which blasting, dewatering, artificial stabilization, and slope failure are discussed. Lastly, the importance of a logical and orderly research procedure is stressed. EXPLORATION AND EVALUATION STAGE The purpose of the exploration and evaluation stage in the mining scheme is to find and delineate a potential orebody. Discovery and delineation commonly involve drilling tens and in many cases hundreds of boreholes. These boreholes, which may cost as much as $20.00 per foot of depth for a cored hole, are usually abandoned once drilling is completed. Stability evaluation for a potential open pit should begin at this stage by taking advantage of the existing boreholes. Rock and soil properties, as well as hydrologic parameters, may be obtained from both the borehole and the core. Seismic velocity and neutron probes may be used to log the borehole to obtain elastic moduli data. A borehole dilation jack may also be used to give backup information on the rock and soil elastic parameters. Use of a core orientation system can result in the determination of fault and joint frequency and distribution. Before splitting or otherwise disturbing the fresh core, qualitative evaluation

Jan 1, 1972

By Duane E. Eubanks, David B. McDonald

The anticipated growth of western coal production over the next decade is expected to add approximately 274.3 million t/y (302.4 million stpy) to US capacity. The increased output, coming from both new mines and expansion of existing facilities, promises to bring with it a new set of problems for mine planners.

Jan 8, 1976

By E. F. Poncelet

Forty years ago A. A. Griffith developed a theory explaining why brittle materials displayed such low tensile strengths.' He based his views on two points. First, he found himself compelled to assume that all brittle materials are replete with flaws, cracks, and other defects that act, although quite invisible, as large stress raisers. Second, he applied the "theorem of minimum potential energy," which says that the total potential energy of a system must pass from the unbroken to the broken condition by a process involving a continuous decrease in potential energy. By this means he satisfactorily accounted for the noted low strength of such solids and also for the wide spread obtained in experimental measurement of these strengths. So successful has the theory been that it is favored by some to this day. Unfortunately this theory is of limited use beyond the explanation of these two noted phenomena and it is keenly felt that a better theoretical insight into the physics of the fracturing process is needed as the volume of experimental evidence accumulates. The author proposes in the following to build on the fundamentally sound concepts of Griffith and, with the help of increased theoretical knowledge over that available to Griffith, develop a mechanism for frac-ture which will provide far greater understanding of the experimental evidence accumulated to date than is possible from the original Griffith idea. THE GRlFFlTH THEORY Very little progress indeed can be made without accepting the first postulate of Griffith which supposes all brittle solids to be full of microcracks. It would be difficult indeed to find a better mechanism for the small strength of such brittle materials, in conjunction with the fact that the energy that must be expended for comminution is by no means small. The postulate of the existence of the microcracks permits the breakup of the various bonds a few at a time by concentrating the stress at the tip of the progressing crack, while the total energy expended is the same as if they all had been ruptured simultaneously. The only flaw in the argument is that no reasonable explanation has been proposed to account for the genesis of such cracks. Indeed their very presence is in violation of the Griffith second postulate, the potential energy theorem. This theorem is straightforward for isothermal processes, and, in spite of Griffith, there is some doubt that treating the problem isothermally is legitimate. The surface energy of bodies is a free energy, not a potential energy as stated by Griffith, and the production of new surface free energies is not necessarily an isothermal process. There is ample evidence to the contrary. Generally speaking, if heating a body increases its surface area, then, by virtue of Le Chatelier's principle, any increase of that area by other means will tend to lower its surface temperature. Lord Kelvin calculated the actual cooling that resulted in drawing out a film of liquid.2 R. A. Houston calculated the surface cooling that resulted in stretching a metal wire.3 These calculations were made by applying the Carnot cycle to the process and evaluating the thermodynamics thereof. IRREVERSIBILITY OF THE FRACTURING PROCESS While Griffith was very careful not to say so, the impression gained from studying his papers is that he considered the fracturing process as reversible, that is, a succession of quasi-equilibrium states. There is ample evidence that it is not. The indication that the new surfaces produced by the propagation of a crack are cooler than the original body points to an irreversible heat flow from the interior to the new surfaces to equalize the temperatures. If the process be reversible, any crack accidentally formed should immediately close up as, in the absence of any strain energy, the potential energy would thereby be lowered. The fact that they do not, constitutes a paradox. Such paradoxes are nothing new where certain phenomena that propagate from minuscule nuclei are assumed to be reversible. Such is, for instance, the condensation of a pure saturated vapor that is suddenly chilled by adiabatic expansion. At the beginning the tiny droplets that are formed should be only a few angstroms in size, but the vapor pressure at such droplets is so high that they should evaporate at once. A similar situation arises if a saturated pure solution becomes super-saturated upon cooling; the first tiny crystal nuclei should dissolve as fast as

Jan 1, 1964

By J. J. Pye, J. B. Drew

Mzasurements of the surface diffusion coefficients of metals have been made. Diffusion profiles for the Ag-Ag system were obtained by means of a radioactive point source and a precision auto-radiographic technique. The activation energy for silver self diffusion (=8.1 kcal per mole) is lower than that previously reported (-10 kcal per mole) on poly crystalline wire by Nickerson and Parker. The bresent data indicate an effect due to parasitic volume diffusion at temperatures above 500°C. RELATIVELY few measurements have been made of the surface self-diffusion coefficients of metals. Nickerson and arker' measured the diffusion of silver over the surface of poly crystalline wires and estimated that the activation energy was 10.3 kcal per mole. Winegard and chalmers2 carried out measurements on both polycrystalline and single crystal surfaces but did not report a value of the activation energy. They found, however, that at temperatures between 250" and 400°C the diffusion coefficients were on the order of lo-' sq cm per sec and that there was an acceleration of the migration of silver on the polycrystalline sample when a change of surface shape occurred. Winegard and Chalmers used an autoradiographic technique, hereafter designated ARG, and Nickerson and Parker used a surface scanning geiger counter in order to determine the diffusion profiles. More recently, Hackerman and simpson3 measured the surface self-diffusion coefficient of copper at a single temperature (750°C), and the value of the diffusivity (- 10-5 sq cm per sec) is in agreement with that given by jostein from his thermal grooving measurements. This paper reports the results of an investigation of the surface self-diffusion coefficients of silver over a large temperature range and describes the adaptation of autoradiographic (ARG) techniques for the determination of diffusion profiles obtained from a radioactive point source. EXPERIMENTAL PROCEDURE The experimental procedure is a modification of the method employed by Hackerman and simpson3 in their measurements on copper. A brief description of their technique is as follows: A radioactive needle which sinters to the surface during the diffusion an- neal serves as the source of diffusing atoms. After the diffusion run the needle is removed and the surface is scanned with a shielded counting arrangement. The diffusion profiles reported in this paper were obtained by a modification of the above procedure which employs a precision ARG technique. Previous investigations in this laboratory and elsewhere51B have shown that under carefully controlled developing conditions and by the use of calibration sources a linear relation exists between the concentration of the isotope and the photographic density for values below unity. The use of ARG under these conditions has advantages over the counter scanning method in that cumbersome shielding and requirements for great mechanical precision of the scanner are eliminated. Also the ARG gives a complete picture of the surface which is advantageous in studies of anisotropic diffusion. A recording microdensitometer having a 0.1 p wide slit was employed. At low temperatures the disturbing effects of subsurface radiations are negligible. The diffusion anneals are carried out in the cell shown in Fig. 1. The needle is formed by grinding down a 1.0 mm rod of high-purity silver until a tip of 0.2 mm radius or smaller is formed. This tip is plated withA"' which becomes the source of the diffusing atoms that are detected by ARG. The needle carrier and the crystal holder, Fig. 1 are constructed of quartz and ports are provided in the holder pedestal which allow free vapor circulation ((2.0 oz) and the carrier apron fits snugly over the crystal holder cap, insuring that the needle does not move and scratch the surface. Temperatures are provided by a stabilized tubular furnace which can be quickly positioned around the cell, thus bringing the crystal up to temperature in a time that is short compared to the diffusing times. The diffusion anneals range from 2 hr for the high-temperature samples to about 25 hr for those at the lowest temperature. The possibility of vapor transport of the radioactive metal as a contributing factor in the diffusion profile was investigated in two ways. One method was to suspend the needle directly over a dummy sample, raise the temperature, for periods of time equal to the diffusion times, and then take an auto-radiograph of the surface. Negligible radioactivity appeared. In the second method a thin slot in the crystal face on one side of the source provided a "cong path" for surface diffusion. If evaporation was the primary source of surface atoms the region of radioactivity around the source would be symmetrical. This was not the case. The profile dipped abruptly at the edge of the slot but on the other side of the source the usual diffusion profile appeared.

Jan 1, 1963

By C. R. Schumacher, W. H. Moyer

Cornwall, Pa. magnetite ore, containing recoverable sulfides in the form of chalcopyrite and pyrite, has been mined continuously since 1742 1 Beneficiation of the ore was begun in 1905, at the Lebanon concentrator located six miles from the mine. At first, only magnetite was recovered, using Grondal magnetic separators. In 1907, copper minerals were recovered by means of Wilfley tables. Copper flotation, attempted as early as 1912, was finally successful in 1919. In 1940, flotation of the cobalt- bearing pyrite was begun, and Cornwall ore became the major domestic source of cobait for many years. In 1916, the Bethlehem Steel Corp. began to purchase interests in the Cornwall mine and Lebanon concentrator properties, and by 1926 had acquired complete ownership. Metallurgical practice at the old Lebanon concentrator was good, but by today's standards the plant was outdated. The flowsheet was complex, due both to the mineral content of the ore and to the low capacities of much of the equipment. As the flowsheet developed, buildings were added and the plant was spread over a relatively large area, with resulting high manpower requirements. Another disadvantage was the six-mile rail haul from the mine to the Lebanon concentrator.

Jan 3, 1966

By John Dilworth

IN considering the valuation of industrial properties in general, and of developed coal properties in par-ticular, it is assumed as fundamental that they have but one true value regardless of the object for which they are appraised. As regards developed coal lands, this value is only very approximately indicated by the recent sale price of neighboring lands, for the reason that it is rarely possible to find a sale of a coal property sufficiently similar in essential mining conditions to the one under consideration to serve as a measure of its value; and if such a one is found there are frequently incidental conditions peculiar to this particular transaction which invalidate the use of the sale price as a measure of general values. The true measure of the value of a coal mining opera-tion is the amount and rate of earnings it will afford with intelligent and experienced management. Prac-tically all of the features of a property which are gen-erally recognized as affecting its value relate either to the cost of producing the coal, or to the price it will bring, and so are intimately associated with earnings. In practice it is customary to appraise those portions of a developed coal property which are produced -by the industry of man-mine plant, equipment, development, town, etc.-at their cost of replacement at prevailing prices of materials, machinery, and labor, with such deductions for age, condition, obsolescence, and lack of usefulness as conditions warrant. Surface is appraised at the estimated cost of similar land in the district. Coal value is the difference between the worth of the entire property; considered as an industrial unit and

Jan 9, 1927