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There is a basic need for the health and safety manager to know what work he or she is to do and how to do it in a more professional way. Peter F. Drucker in The Practice of Management said, "The ignorance of the function of management, of its work, of its standards and its responsibilities is one of the most serious weaknesses of an industrial society-and it is almost universal." The biggest need in mining today is for its managers to have a thorough understanding of the management control activity.

Jan 11, 1979

By D. E. Munson, P. R. Dawson

An empirical model is developed that predicts accurately the transient response of salt creep to incremental and decremental changes in stress and temperature. Even though the model is empirical, it is derived from a firm theoretical framework for the micromechanical deformation processes of both steady-state and transient creep. In the model, the transient creep functions modify the steady-state creep behavior, which in turn is based upon creep mechanisms and the def ormation-mechanism map. The model is applied successfully to experimental stress-drop results obtained for salt.

Jan 1, 1982

SAMUEL L. HOYT.-The question of adding the ferromanganese to the ladle or to the furnace involves both theoretical and practical questions and its discussion might very easily occupy the rest of the day. One of the points to be kept in mind is the desirability of obtaining uniform steel. If ferromanganese is added to the ladle, it is necessary first to melt the manganese and then to distribute uniformly throughout the heat. The only heat available for this purpose is that of the molten steel itself. No doubt sufficient heat is present, but in our desire to pour the steel as quickly as possible there is hardly sufficient time allowed, many times, for the proper distribution of the manganese. In other words, this is an operation which takes a certain amount of time and any undue shortening of the time allowed must affect the quality and uniformity of the steel. Again, this particular method does not lead to as efficient a use of the manganese as might be desired; a contention which is based on theoretical grounds. In concentrated solution, manganese will completely reduce all the ferrous oxide, the presence of which I hypothecate and produce, as the reaction product, manganese oxide. In dilute solution, the manganese only partly reduces the iron oxide, but the manganesee oxide which does form dissolves the iron oxide in simple solution. The dissolution of ferrous oxide in the manganese oxide will result in a more economical utilization of the manganese and an equal purification of the heat. This whole point, at present, has not been definitely proved and its answer will involve very difficult research work. On the other hand, if the manganese is added to the furnace, the heat of the furnace is used to melt the alloy and there is plenty of time during tapping for the manganese to be very uniformly distributed throughout the steel. By distributing the alloy throughout the charge we can secure a better utilization of the manganese than is possible if the addition is made to the ladle. Certain other points, such as the recovery, have been dealt with at greater length in the paper.

Jan 4, 1919

By D. F. Stein

In spite of the apparent usefulness of autoradiography in demonstrating segregation, it has had very limited success in demonstrating grain boundary segregation. Because of this limited success, a model system amenable to mathematical analysis was devised to determine which variables in the experiment are most important. As a result of these calculations, it was concluded that autoradiograPhy is a rather insensitive technique to measure grain boundary segregation. The range (energies) of the emitted particles (ß and a) must be low, and the concentration of the radioactive speczes at the grain boundary must be (in general) two or three orders of magnitude greater than the concentration within the grain. Because of these very restricted conditions , the limited success of the technzque is not surprising. In spite of the apparent usefulness of autoradiography in demonstrating segregation, it has had very limited success in demonstrating grain boundary segregation. Sulfur segregation in iron1 and possibly polonium segregation in Pb-5 pct B1 2 alloys are the only autoradi-ography experiments that have demonstrated segregation to grain boundaries in metals without the formation of a second phase. Segregation to a boundary without the formation of a second phase is often called Gibbs' absorption and is discussed by McLean in Chapter 5 of Ref. 10. There are several394 experiments showing grain boundary diffusion of a radioisotope, but this type experiment is not representative of equilibrium between the concentration of an element at a grain boundary and that in bulk, so it will not be discussed in this paper. In an attempt to determine if temper embrittle ment of low-alloy steels was associated with segregation of antimony to grain boundaries, a program to use auto-radiography (using Sb-125) was initiated. Even though other measurements strongly suggest that segregation is occurring during embrittlement, no evidence of grain boundary segregation was observed in the auto-radiography experiments. An attempt was also made to detect segregation of carbon (using C-14) to grain boundaries in iron during slow cooling. There is again strong indirect evidence7 that segregation occurs during such a treatment, but the autoradiography experiment gave no evidence of such segregation. Because of the failure of these experiments and the general lack of success by our metallographic unit in measuring grain boundary segregation using autoradi-ography, a model system amenable to mathematical analysis was devised to determine which variables in the experiment are most important. MODEL SYSTEM The model system is illustrated in Figs. 1 and 2. It is a semi-infinite bicrystal with a single grain boundary perpendicular to the top face. The width of the grain boundary, W, is defined as the region to which segregation has occurred and it is assumed that this region is of constant composition. The assumption of an infinite dimension is for mathematical reasons but the results of such an analysis (as will be demonstrated later) are valid for even very small specimens. It also is assumed that the measurement is not limited by means of detecting the radiation (photographic emulsions, counters, and so forth) but that the means of detecting radiation is linearly sensitive to the radiation and has infinite resolving power. The distance y is the perpendicular distance from the center of the grain boundary to the point at which the background radiation is measured and x is the integration variable. CALCULATION FOR BETA PARTICLES Two values of the intensity of radiation will be calculated, the intensity at the center of the grain boundary and the intensity far from the grain boundary. The radiation at the center of the grain boundary can be calculated in the following way. Assume a grain boundary of width W having a uniform concentration equal to Cgb + Cb where CGb is the excess concentration of the element under consideration at the grain boundary and Cb is the bulk concentration. The intensity of radiation, IgB, at the center of the grain boundary, is a consequence of the amount of radioactive material, decay rate, absorption, and geometrical factors which can be represented mathematically by the following expression:

Jan 1, 1968

By P. H. Wendland

Calculations are presented for the design of a silicon photodiode in which the incident light beam makes multiple passes between the detector surfaces. Total internal reflection is used for this "light-trapping" effect. By this means, the optical path length can be extended to several millimeters, while the electrode separation remains less than 102 cm, as required for nanosecond response time. Data are presented for a Schottky barrier photodiode constructed on a multiply reflecting silicon base wafer. It is shown that the long-wavelength response is considerably extended in such structures without a corresponding sacrifice in high-speed response. The development of efficient and powerful lasers at 1.06 p has stimulated interest in detectors which operate at this wavelength. In typical silicon photodiodes, for detecting 1.06 p radiation, the requirements for high speed and high sensitivity are mutually exclusive. Since the absorption coefficient is only 25 cm-', a lo-'-cm path length is required to absorb 92 pct of the incident 1.06 p radiation. If the electrode separation is greater than 10 cm, however, the carrier transit time will be greater than 1 nsec. This problem can be solved by allowing the incident light beam to make multiple passes between the electrodes. The optical path length can then be extended to several millimeters, as required for complete absorption, while the electrode separation remains less than 10' cm, as required for nanosecond response time. In a typical photodiode geometry, one ohmic contact and one rectifying contact are formed on the two opposite surfaces of a base wafer, and the wafer thickness determines the electrode separation. The objective of the multiple reflection design is to allow all 1.06 p radiation to enter the detector front surface and to form the back detector surface so that no 1.06 radiation can exit. Total internal reflection at the back detector surface is well-suited for light trapping of 1.06 p radiation because the relatively large dielectric constant of silicon leads to a critical angle of 16.5 deg for total internal reflection. LIGHT TRAPPING It is well-known that, as light passes from one medium such as air into another medium such as glass or silicon, the angle of refraction is always less than the angle of incidence. In the limiting case, where the incident rays approach an angle of 90 deg with the normal, the refracted rays approach a fixed angle +, beyond which no refraction is possible: this is called the critical angle. It follows from Snell's law that where = critical angle, n - index of refraction of air, n' - index of refraction of the medium. Applying the principle of reversibility of light rays, all internal angles of incidence greater than +, will produce total internal reflection and "light trapping". The index of refraction of silicon at 1.06 p is 3.5,' and the critical angle is thus 16.5 deg. Fig. 1 shows these relationships for silicon. This very small critical angle in silicon is significant because all incident angles between 16.5 and 90 deg will produce total internal reflection and "light trapping". This effect can be implemented with a "prismlike" geometry, so that incident light can be introduced into the sample without loss and "trapped". PHOTOSIGNALS A precise knowledge of the absorption coefficient at 1.06 in silicon is of critical importance to the design of fast and efficient silicon photodiodes for 1.06 radiation. Dash and newman2 show a value of 25 cm-l, and our measurements have corroborated this value. Assuming that the collection of photoinduced minority carriers is perfect, the quantum efficiency of a photodiode is dependent only on the absorption coefficient. It then follows from Lambert's law that where QE is the quantum efficiency in pct, a is the absorption coefficient, d is the optical path length, and the reflectivity at the surface is assumed to be completely suppressed by an optical interference layer. Fig. 2 gives the maximum quantum efficiency for 1.06p radiation of a silicon photodiode with optical path length d, using Eq. [2]. The ultimate response time of a fully depleted photodiode to an incident light pulse can be considered to be the arrival times of all photoinduced carriers at the contacts, i.e., the minority carriers at the junction interface and the majority carriers at the oppo-

Jan 1, 1968

By Clark Millison

The core recorder, a mechanical instr-ent for determining the exact depth at which core is recovered, drilled up or lost, is described. Examples of charts from the recorder are explained and interpreted. The uses of the core recorder are discussed. INTRODUCTION In the experience of geologists and engineers during coring operations on drilling wells, many will recall the times when a full core was not recovered and particularly when the requirement was urgent that they know exactly what part of the core was lost. To make this determination, the core recorder was designed. Its uses are many, and only the most obvious will be presented here. Although this discussion will be limited to drilling wells for petroleum, the core recorder can be used in any type of coring operation. The principle of the core recorder is the proportional reduction of the motion of core entering or dropping out of the core barrel to a stylus moving in such a manner as to record the reduced motion on a chart. The time element is registered on the same chart by the revolution of a clock which turns the chart drum. Thus the exact amount of core entering or dropping out of the core barrel is charted and the time of such entry or exit from the core barrel is precisely correlated to the depth at which the core is recovered or lost. Lack of movement of the stylus which is revealed by the continued revolution of the chart drum indicates that no core is entering the barrel. The principles are accomplished by an instrument placed inside of the core barrel. A cylinder which contains the clock and mechanical apparatus has a diameter smaller than that of the core barrel. Near the top of the cylinder is an eighteen hour clock which turns the drum that contains the chart. Near the bottom of the instrument is a serrated wheel which by friction against the inside of the core barrel is turned as core enters or drops out of the barrel.

Jan 1, 1949

By Clark Millison

The core recorder, a mechanical instr-ent for determining the exact depth at which core is recovered, drilled up or lost, is described. Examples of charts from the recorder are explained and interpreted. The uses of the core recorder are discussed. INTRODUCTION In the experience of geologists and engineers during coring operations on drilling wells, many will recall the times when a full core was not recovered and particularly when the requirement was urgent that they know exactly what part of the core was lost. To make this determination, the core recorder was designed. Its uses are many, and only the most obvious will be presented here. Although this discussion will be limited to drilling wells for petroleum, the core recorder can be used in any type of coring operation. The principle of the core recorder is the proportional reduction of the motion of core entering or dropping out of the core barrel to a stylus moving in such a manner as to record the reduced motion on a chart. The time element is registered on the same chart by the revolution of a clock which turns the chart drum. Thus the exact amount of core entering or dropping out of the core barrel is charted and the time of such entry or exit from the core barrel is precisely correlated to the depth at which the core is recovered or lost. Lack of movement of the stylus which is revealed by the continued revolution of the chart drum indicates that no core is entering the barrel. The principles are accomplished by an instrument placed inside of the core barrel. A cylinder which contains the clock and mechanical apparatus has a diameter smaller than that of the core barrel. Near the top of the cylinder is an eighteen hour clock which turns the drum that contains the chart. Near the bottom of the instrument is a serrated wheel which by friction against the inside of the core barrel is turned as core enters or drops out of the barrel.

Jan 1, 1949

By P. Gianella Vincent

Barite deposits are of widespread occurrence in Nevada but there are few pro-ducing properties; most of the latter are in northern Nevada. The production of the state is small at present-in the neighborhood of 15,000 tons annually-but is steadily increasing. The barite occurs in veins and also as replacement deposits in lime-stone. The bulk of the production has come from the replacement deposits. It is thought that the barite was deposited from rising hot waters similar to-and probably contemporaneous with-those responsible for some of the metallic ores of the state. This paper discusses only the deposits in northern Nevada. THE commercial mining of barite did not begin in Nevada until 1916 but although the production has been small there has been a rapid increase in tonnage during the past several years. Barite is widely distributed in the state and production comes from at least nine of the seventeen counties. Apparently this is not generally known, as only two counties are mentioned in a recent publications dealing with barite. The increase in output is due largely to recently discovered barite deposits in northern Nevada. The principal production has come from the northern portions of Lander and Eureka counties; smaller amounts from Elko County. The discussion in this paper is confined largely to the deposits in these counties. Most of the producing area is tributary to the Western Pacific and Southern Pacific Railroads, whose tracks lie along the Humboldt River. Barite is known from other northern counties but so far the production has been small. The output has come entirely from veins and replacement deposits, the latter largely in sedimentary rocks. In general, the barite from veins is white; that from the replacement deposits usually is dark gray to black, although some is light gray or white. Most of the veins contain sulphides and many barite-bearing veins have been worked for their content of base or precious metals.

Jan 1, 1940

Discussion of the paper of Norman B. Braly, presented at the Butte meeting, August, 1913, and printed in Bulletin No. 80, August, 1913, pp. 1881 to 1906. GEORGE A. PACKARD, Butte, Mont.:-I would like to ask Mr. Braly if he has any information as to the relative efficiency of the sinking pump, using it as he refers to it, discharging the exhaust into the water column or otherwise. MR. BRALY :-I have never gathered any information on that point. It is a question of getting the work done. In driving the shaft, using that method, we find it easier on the men and everything else. In the bottom of the shaft, if you exhaust back into your column, it is a quiet. shaft. Another thing is the freezing: if you are sinking with air in your pump, you will find it is liable to freeze, and in that case as the air is still under compression it will not freeze the pump. The difference is very small if there is any. But, as might be expected, the pump is a little less efficient when exhausting the air into the column. MR. PACKARD :-I suppose all of us know what a pump in the bottom of the shaft is. My experience has been, although I have no figures, that the capacity of a pump is quite considerably decreased if you are pumping, say, from a depth of 200 ft. through a No. 7 Knowles pump, when you exhaust the air into a column, but, on the other hand, it is also my impression that we can raise the water to a little greater distance. I would like to get some figures from somebody who has made actual tests.

Jan 11, 1913

By J. D. Audley Smith

Heine's " blue test" for copper, as described by the authorities generally, calls for a set of standard colors; and there has been some discussion concerning the relative superiority, for this purpose, of sulphate and nitrate solutions. The whole matter evidently hinges on the preservation of the standard colors in well-stoppered bottles. The apparatus described by Q. L. Heath* cannot be much improved, when very accurate readings are required. The following method was devised for the purpose of doing away with preserved sets of standard colors, by making a fresh standard for each batch of assays. The solutions are prepared in the usual way, each ammoniacal solution being filtered into its separate bottle, and then filled up to the containing-mark and thoroughly mixed. A similar color-bottle, with an " S " etched upon it, to distinguish it from the other bottles, which are numbered to correspond with the samples, is kept to run the standard. About 150 C.C. of water is put into it, and then the amount of acid (sulphuric or nitric) present in each determination, followed by 30 C.C. of ammonia (s. g. 0.90), which should make the mixture strongly ammoniacal. The liquid is now made up almost to the containing-mark (200 c.c.), say within 1 C.C. The lowest assay is selected first and placed alongside the standard, which, at the beginning, contains no copper. A copper-solution is then dropped into the standard from a burette ; and after each addition the bottle is well shaken and compared with the assay-sample. This operation is repeated until the two shades match exactly, when the burette is read and the assay-result is calculated. The assay next in order of depth of color is now taken and treated in the same way, and so on, until the batch is completed. It

Jan 1, 1901

By James Harding

THE usual method of sampling mineral deposits is to drill holes and assay the sludge or core. Though the results thus obtained may not represent the true average value of the deposit, it is on these results that estimates of practically all large orebodies are made. In a large number of cases, the results of exploitation fall far short of the estimated value of the orebody. The standard method of making these estimates is to find the cubic contents of triangular prisms, in the apexes of which the drill holes are placed, .by multiplying the surface area by the average depth of the ore in the three drill holes and then multiplying the cubic contents by the specific gravity of the ore or rock to find the tonnage. The assay value is found by dividing the sum of the products of the depth of ore in each hole and the corresponding assay value by the sum of the depths of the ore in the three holes. As the latter part of this method is subject to many mathematical errors, it should not be depended on.. Some engineers, therefore, use a discount factor, but as this factor is either arbitrarily selected or is obtained by obscure methods, the results are no better than guesswork. The standard method is correct when the drill holes are so laid out that the triangular prisms are equilateral in cross-section. But as ore deposits cannot always be drilled into at regular intervals and because of the human factor, if many holes are drilled, triangular prisms of all degrees of angularity are produced. In such cases, it is necessary to assume that the influence of the different holes is not the same in all directions, which assumption of course is absurd.

Jan 1, 1921

By Reino Kurppa

The Pyhäsalmi mine of the Outokumpu Co. is located in central Finland (Fig. 1). The deposit was discovered in the autumn of 1958. Construction of the mine was started a year later, and production began on Mar. 1, 1962 (Fig. 2). At present, 750,000 metric tons (mt) of ore and a nearly equal amount of country rock are mined annually. Slightly over one-half million tons of various concentrates are produced per year, of which 85% is pyrite concentrate, 10% zinc concentrate, and 5% copper concentrate. The pyrite concentrate is treated in the company's pyrite smelter,1 yielding elementary sulfur, sulfur dioxide, and iron-oxide cinders, as well as electric power. Thus all the sulfides, totaling 75% of the ore, are of economic value. This is a fact which had a bearing on the development of the stoping method. GEOLOGY The ore is of breccia type containing fragments of country rock of varying sizes. It is coarse-grained pyrite ore containing sphalerite and chalcopyrite as a matrix between the pyrite grains. Only small amounts of pyrrhotite have been observed in certain marginal parts of the orebody. The ore averages 0.85% Cu, 3.0% Zn, 38% S, and 33% Fe. The orebody extends from the surface down to at least 500 m, which is the lowest level from which present information has been obtained. Horizontally, the orebody is 650 m long. It is 75 m wide at its central part, narrowing towards the ends (Fig. 3). At a depth of 115 m, the orebody suddenly narrows down to a thickness of 25 to 30 m. In the northern part of the orebody, the dip is 50° to 70°, but elsewhere it is almost vertical (Fig. 3).

Jan 1, 1969

By Charles H. White

Methods in colorimetry are based on the assumption that the intensity of the' color of a definite volume .of solution is directly proportional to the quantity of the color-producing substance present. In the preparation and examination of colored solutions there are three ways in which the depth of color may be varied. These variables are : (1) the quantity of' the coloring matter; (2) the quantity of the solvent, or the dilution ; and (3) the thickness or depth of that portion of the solution examined. With these three variables as a basis, three general methods in colorimetry have been devised, all of which have been used in the determination of carbon in steel. In the first method, the quantity of the solution is kept the same for both the unknown steel and the standard, and the sections compared are of equal thickness, while the quantity of the standard is varied until the color obtained is of the same intensity as that produced by a definite quantity of the unknown steel. In laboratories where this method is used there is prepared and kept for permanent use a series of solutions with varying amounts of the standard, representing the percentages of carbon from the lowest to the highest demanded in that laboratory. These standard solutions are kept in bottles or test-tubes of equal diameter, and are arranged in series from the faintest to the most intense color, so that it is a simple matter to find the place of the unknown steel in the series, when the solution is of a definite volume and is contained in a tube of the same diameter as the standard tubes. In the second method, equal quantities of the standard and of the unknown steel are dissolved, the standard is diluted to a definite volume, and the solution of the unknown steel is di-

Jan 1, 1907

By Peter I. Brooker

Elementary estimation methods in which blocks are assigned values according to a geometrical area of influence concept are investigated for a tabular deposit. This quantitative assessment of the estimation technique is made using Matheron's geostatistics which allows the variance of the error between actual block values and estimated values to be found once the semi-variogram is known. For the deposit in question it is shown that the elementary technique makes poor use of the available information. There is a 20% relative error associated with it, whereas by using the optimal technique of kriging this can be reduced to 9%. An infill drilling program, which might have been suggested on area of influence results, would reduce the estimation variance only marginally over that of the current campaign; the relative error being lowered to 6%. Thus the geostatistical analysis shows this would be an unnecessary expense. The accuracy of an earlier drilling stage is also studied and it is shown that with the information available at the earlier stage block values could have been known with a relative error of 13%. Drilling could have stopped then if this were reckoned a tolerable error level. These results are all obtained for blocks whose size is dictated by the mining engineer and is set at the current grid size. In the area of influence approach smaller blocks are considered as the grid becomes finer and a study of the accuracy of area of influence estimates and kriged estimates for differing block sizes is presented. Between drilling stages more information from which the semi- variogram is calculated becomes available. The sensitivity of the estimation to changes in the semi-variogram parameters between earlier and current drilling programs is investigated.

Jan 1, 1977

FREQUENTLY the careful engineer puts the word porphyry in quotation marks or precedes it with "so-called," when he writes of the Porphyry Copper mines. This is done by way of serving notice that he is aware that the term is not a precise one, though no one who is informed on the subject would in any event misinterpret it. The name originated from the fact that the rock containing the copper at Utah Copper, Morenci, Nevada Consolidated, and Braden-the first four to be developed-was in each instance known as porphyry. The term was convenient; and when Ray, Miami, and inspiration came along they fell into the Porphyry category even though the ore consisted essentially of a rock called schist instead of porphyry. The word is not inclusive enough; nor as a matter of fact is it sufficiently exclusive. Numerous copper deposits occur in porphyry rocks that are not Porphyry Coppers, paradoxical as it may seem. Desiring to be more accurate and at the same time to use a word that is in some degree descriptive, various engineers have adopted the expression "disseminated copper deposits." This alludes to the characteristic scattering of grains or specks of copper minerals more or less uniformly throughout the mass of the rock. Yet here again the implication is not entirely accurate, for the following reason: in some of the ores, the proportion of copper minerals "peppered" in the rock is small, compared with that which coats the walls of cracks and minute fissures; and that which is found as veinlets along planes of fracture. Many geologists have extended their interpretation of the term disseminated to include both types of mineral occurrence. One of the most striking features of the Porphyry ores is the intense shattering and fracturing that the rock underwent at some period or periods prior to the deposition of the copper

Jan 1, 1933

By Albert B. Horn, J. J. McKetta, O. L. Culberson

Since water is present in natural gas and petroleum reservoirs, it is of engineering value to have accurate experimental data regarding the behavior of water in hydro-carbon systems. Since experimental data of this nature are so scarce in literature, a program is under way at the University of Texas to obtain experimental data regarding the distribution of water in petroleum hydrocarbons. This initial paper is subdivided into three parts: A. The apparatus and analytical procedure are discussed. B. The equipment has been checked by comparing the experimental data with data of literature on the solubility of methane in water at 77°F and pressures to 10,000 psia. C. Experimental data are presented at 100, 160, 220, 280, and 340°F on the solubility of ethane in water at pressures to 1200 psia. As the temperature is increased the solubility of ethane in water first exhibits a minimum and then a maximum solubility. The range of applicability of Henry's Law is discussed. INTRODUCTION Although considerable experimental data have been published on water-hydrocarbon systems in the hydrate region, the information on these systems in the vapor-liquid and the vapor-liquid- 'References are given at end of paper. Manuscript received at the office of the Petroleum Branch August 31. 1949. liquid regions at elevated pressures is extremely scarce. A survey of the literature on hydrocarbon-water systems at elevated pressures was presented by McKetta and Katz12,13,14 showing the systems and phases investigated. In addition to these existing published data, Poettman and Dean" have reported the water content of propane in the three-phase region (only the propane-rich liquid and the vapor phases were studied) and Michels, et al.15 have reported the solubility of methane in water at pressures to 6800 pounds per square inch at 77°F and at pressures to 1500 psia at temperatures to 300°F. It has been shown12,14 that the presence of water will materially affect the phase equilibrium of hydrocarbon systems. In order to make experimental studies on the quantitative effect of the presence of water in naturally-occurring hydrocarbon systems, it is desirable to have data available on binary hydrocarbon-water systems. A program is underway at this laboratory to determine the phase relations of the hydrocarbon-water systems. Initially the investigation will be limited to binary systems with water as one of the components. Later ternary and complex systems will be investigated and reported. EQUIPMENT AND ANALYTICAL PROCEDURE Apparatus In order to avoid a description of the methods employed in each subsequent paper, a description of the apparatus and the analytical procedure will be given here. The apparatus is shown schematically in Fig. 1. The numbered items in Fig. 1 represent the high pressure valves. The equilibrium cell is of the totally enclosed type, with a volume of 550 cubic centimeters. The cell is mounted in an air bath which in turn is mounted on pillow blocks and connected to a rocking mechanism so that the cell and bath will oscillate approximately 30 degrees above and below the horizontal at 35 oscillations per minute. The air bath is heated by two resistance heaters. The first or primary heater is 250 watts and is controlled by a thermoregulator; the second heater is of 500-watt size and is manually controlled to aid in bringing the cell to equilibrium temperature. Air circulation in the bath is accomplished by means of a fan. the shaft of which is concentric to the heaters. The walls of the bath are insulated with 2-in. thick blocks of 85 per cent magnesia. Temperature observations are made with three calibrated thermocouples. One couple is sealed in a well provided within the equilibrium cell, and is used as the criterion of the cell being at the equilibrium temperature. The other two thermocouples are located on opposite sides of the cell to indicate temperature uniformity within the air bath. The thermoregulator, used in conjunction with a relay, gives a variation in the temperature of the air in the bath of plus or minus one degree Fahrenheit. However, since the equilibrium cell weighs approximately 55 pounds, the

Jan 1, 1950

By G. P. Tiwari

Recrystallization and grain growth in thoria dispersed nickel and nichrome were recently studied by Webster as a function of temperature and deformation. The unexpected part of these results was that specimens which had received heavier deformation developed greater resistance to recrystallization. Retardation of recrystallization was accompanied by the formation of voids around thoria dispersion. To explain these results, Webster suggested that the formation of void around the particles increased the effective size of thoria particles. This resulted in greater impediment to the grain-boundary migration and as a consequence the recrystallization of the matrix is retarded. In the present note an alternative and more probable explanation for the effect of voids on recrystallization is presented. The exact mechanism of void formation in thoria dispersed nickel or nichrome is not known. However, it is reasonably certain that it must be preceded by the stress concentration in the matrix around thoria dispersion during the deformation.'' The resulting stress concentration must be sufficient enough to supply the surface energy for the new surfaces created. Further, the decrease in the strain energy of the matrix surrounding the potential void nucleus must be larger than the surface energy of the newly created surface. The release of strain energy due to formation of crack results in a strain free cylinder of the material around the voids.13 If the void formation is not localized, at few points only (as is the case here), this process may lead to considerable amount of release of strain energy of the matrix. The pattern of recrystallization behavior of single phase homogeneous matrix as well as the matrix having a second phase dispersion is same except for the fact recovery and recrystallization are more clearly delineated.14 In general, the recrystallization temperature is lowered (i.e., recrystallization is easier) with increase in the amount of cold work. This is due to the increase in stored energy in the matrix with increasing amount of deformation. If somehow there is a relaxation of strain energy in the matrix, the recrystallization should become difficult because of the decrease in the amount of stored energy available for recrystallization. Since the formation of voids leads to a decrease in the strain energy of matrix, the recrystallization of the matrix would be inhibited due to the formation of voids during deformation prior to recrystallization. It has been observed by earlier workers15'16 that the presence of preexisting voids in a matrix retards the recrystallization. The essential issue here is how do the voids act to produce this effect. If the voids influence recrystallization only by blocking the grain boundary migration, then the effect should be maximum when they are present almost exclusively along grain boundary. These conditions are obtained during high temperature deformation. However, the voids produced due to creep along grain boundary are not able to prevent recrystallization17 suggesting that they are not effective in blocking grain boundary movement. Recently it was shown by Davies and Williams that the voids can act as sinks for vacancies." As a result the processes dependent on vacancy diffusion like recovery, recrystallization, dislocation climb, and so forth, will be hindered. This fact may be responsible for inhibition of recrystallization during subsequent deformation and annealing cycles. It is to be noted here that there is a large difference between the density of voids in creep experiments and the other experiments where retarding effect of voids on recrystallization is seen. The voids in former may number up to l04 to l05 per sq cm whereas in latter cases the voids density is typically around 1010 to 1013 per sq cm. It appears that the decrease in supply of vacancies in creep is insufficient to adversely affect the recrystallization due to low void population. The author is grateful to P. Das Gupta and S. P. Ray for helpful discussions. Author's Reply D. Webster Tiwari appears to have misunderstood the nature of grain boundary-particle interactions. Tiwari (quoting Cahn) states that second phase particles become more effective as they become smaller, therefore as the voids in TDNiC make the thoria particles effectively bigger their ability to resist grain boundary movement is impaired. This particle size argument was originally proposed in the form of an equation by Zener 20 years agol9 and is not necessarily valid as is discussed below. However, assuming it is valid, it predicts a greater boundary restraining effect by smaller particles simply because their combined cross sectional area is greater at a constant volume. If the number of particles remains the same and their effective size increases, as in the present case, Zener's equation predicts a greatly reduced grain size. This is because the effect

Jan 1, 1970

By F. X. Tartaron

This paper deals with basic physical phenomena, which when combined and interpreted, lead to the same mathematical equations that describe comminution phenomena. Thus, a physical model is described that corresponds to the mathematical model presented in the writer's previous papers. '12 In the mathematical model, the energy consumed in breakage is related to the volume or weight of material broken and the size of particles broken. The equation E=2.303 Ck-a log x1/x2 was derived by multiplying the volume or weight of each size in an ideal Gates-Gaudin-Schumann size distribution by an energy factor. The product of these two factors gives the energy distribution among the different sizes in a single size distribution. The energy of breakage of a specific constant weight of one size distribution to another size distribution is given by the equation E = constant/kn-1. In this case, where the volume or weight is constant, the energy is proportional to the size factor 1/kn-1. In what follows, a physical theory will be presented showing that the energy consumed in comminution is proportional to the volume or weight of the material broken and to the reciprocal of the size of this material raised to a constant exponent. THE VOLUME FACTOR The atomic theory of matter reveals that in solids, atoms or ions are arranged so as to be in equilibrium at specific distances from one another. Although the atoms or ions are oscillating, there is a definite determinable mean distance between them and this distance is a balance between repulsive and attractive electrical forces. It therefore requires force to separate the atoms or ions and when an outside force is applied, it first produces strain in increasing the distance between the atoms or ions. This strain increases to the breakage limit on application of sufficient force. In brittle materials, there is negligible plasticity and when an elastic limit is exceeded, breakage takes place. The work done is the force applied per unit area times the cross sectional area of the ideal particle multiplied by the maximum strain per unit length at right angles to the area times the length of the particle. Thus the work done is proportional to the area times the length, which is equivalent to the volume of the ideal particle. If more than one feed particle is considered broken, each particle must be subjected to sufficient strain so that the breakage limit of its contained atoms or ions is reached in order for the particle to be broken. Thus, the energy of breakage is proportional to the total volume of the particles broken. If the particles are of different sizes, the size factor must be included to get a correct determination of energy of breakage. In the preceding, it has been assumed that there is a constant binding force between the atoms throughout the volume being strained. This, of course, is not true. It is known that there are many irregularities in the structure of matter and the binding force differs markedly in different portions. But the differences are only discernible by examining extremely small subdivisions of matter. In one order of magnitude of volume, cracks can be discerned separately from non-cracked neighboring material. In a smaller subdivision of volume, lattice dislocations can be isolated. When these situations are brought into focus, mechanisms of their behavior can be learned, leading to a fuller understanding of phenomena that occur in larger scale subdivisions of matter. Very often, however, the mechanisms that operate in small scale subdivisions have negligible effect in those of large scale, and there still is a place for deriving a mechanism for large scale conditions. The quantum theory is extremely valuable for use with photons and electrons, but is of negligible use with ordinary atoms and molecules. This paper deals with relatively large scale subdivisions of volume present in comminution phenomena. Hence, the effects of cracks, lattice dislocations, misplaced atoms, etc., are smoothed out in an average, constant for each relatively large subdivision of volume. This attitude is supported by experience. If two 10 cc samples of the same ore were ground identically, the same product would be obtained. However, if two samples, each a cubic micron, were conceived to be broken, then one sample might contain a crack and the other not, hence a different product would be obtained. Experience shows that ordinary samples used in comminution, behave as though no irregularity existed

Jan 1, 1964

By Adrian E. Ross

Diamond drilling through caving formations at depths greater than ZOO0 ft has long presented serious difficulty, generally solved either by casing or cementing. Casing is permitted only when the resulting smaller hole is acceptable, and cementing is frequently a problem at depth. A new method that injects cement under pressure at the desired location is an aid in diamond drilling deep holes. DRILLING through caving formations in diamond drill holes at depths greater than 2000 ft has long been a serious problem. These caving formations are normally passed only by casing the hole or by cementing the hole. Casing the hole is possible only when a resulting smaller hole is acceptable. In as much as only a limited number of reductions are economically practical, cementing is frequently considered the only method suitable for solving these problems. Cementing either by pumping a slurry into the hole or by dropping cylinders containing cement has proved satisfactory on holes under 2000 ft. In holes substantially deeper than 2000 ft these methods are not satisfactory, since during the pump- ing process cement separates out, whereas cylinders usually break before the bottom of the hole is reached. A new procedure, the injector method, apparently solves these problems.* With this method, cement is lowered in the hole in a cylinder, the cement being

Jan 1, 1953

By Adrian E. Ross

Diamond drilling through caving formations at depths greater than ZOO0 ft has long presented serious difficulty, generally solved either by casing or cementing. Casing is permitted only when the resulting smaller hole is acceptable, and cementing is frequently a problem at depth. A new method that injects cement under pressure at the desired location is an aid in diamond drilling deep holes. DRILLING through caving formations in diamond drill holes at depths greater than 2000 ft has long been a serious problem. These caving formations are normally passed only by casing the hole or by cementing the hole. Casing the hole is possible only when a resulting smaller hole is acceptable. In as much as only a limited number of reductions are economically practical, cementing is frequently considered the only method suitable for solving these problems. Cementing either by pumping a slurry into the hole or by dropping cylinders containing cement has proved satisfactory on holes under 2000 ft. In holes substantially deeper than 2000 ft these methods are not satisfactory, since during the pump- ing process cement separates out, whereas cylinders usually break before the bottom of the hole is reached. A new procedure, the injector method, apparently solves these problems.* With this method, cement is lowered in the hole in a cylinder, the cement being

Jan 1, 1953