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By Glenn Keep

THIS paper is not an announcement of the successful conclusion of the Cerro de Pasco Copper Corporation's pacos-pyrite problems, but merely a description of the commercial-scale, intermittent-roasting operations conducted by the writer, J. H. Lucas and others of the staff. It was prepared by request, for presentation at the February meeting of the Institute. The results obtained in Peru confirm the 1-ton-a-day experiments completed about three years ago at Kearny, N. J. by C. C. Gordon and Mr. Lucas, where it was first demonstrated that a mixture of about 80 per cent. pacos ore with 10 per cent. pyrite ore and 10 per cent. salt could be roasted intermittently in a small 1-ton-a-day Holt-Dern furnace without extraneous fuel, producing porous calcine that could be leached rapidly. Mr. Keep and his staff, by successfully introducing improvements in the construction of the commercial furnace and in their handling of material, have established beyond doubt a low cost for roasting. The other steps in the process of treating pacos and pyrite ores have not as yet been demonstrated as sufficiently conclusive to warrant their acceptance for a permanent plant.

Jan 1, 1929

By H. W. Hardinge

DISREGARDING for the present the economic side of a new device, let us turn to that feature of the conical pebble-mill which is of interest from a scientific point of view, and consider the device as a puzzle in which the theories of the cylindrical type of mill have been increased. Many articles have been written on the theory of the tube-mill, and explanations have been made which do not explain.; but these have evolved suggestions of practice which have resulted in changes in the tube as to length, diameter, feed, discharge, speed of rotation, rotation on hollow trunnions, rotation on rings, and changes in the operation as to quantity and size of pebbles, charge of load above or below the axis, crushing by causing the larger pieces of the material of the charge to act as grinders, etc. The practical worker in crushing is first interested in the endeavor to reach an economic means of accomplishing a desired end; but the improvements in crushing-practice have been largely left to the manufacturer of machinery, who, as a rule, has little, if any, knowledge of the specific requirements-such as sizing for concentration without pulverizing the metals, instead of pulverizing the rock or gangue; the metals being the more friable, while the rock is tough and not so easily disintegrated. A reversal of this practice is the aim of sliming direct for cyanidation. In the ordinary cylindrical mill, having a diameter of 4 or 5 ft. and a length of from 15 to 27 ft., it has been found that the maximum size of the particles of the charge must not exceed 1 mm. (about 25 mesh), some of which, upon entering the mill, is immediately reduced to a slime. The work upon the individual particle having been finished, it should be passed out of the mill; but, instead of this, the finely comminuted material

Jan 7, 1908

By Arthur Notman

IN VIEW of the wide publicity given to the charges by the Couzens Committee of the United States Senate of discrimination by the Bureau of Internal Revenue in favor of the copper companies, it becomes a matter of interest to consider the basis for these charges. The point to be determined is whether they rest on a foundation of fact or are purely and simply matters of opinion. The whole question boils down to the purpose of the Tax Law as applied to mines, which is to afford the same protection to them as provided for all other taxpayers, namely: that they were to be allowed to pay back as depletion to their owners the values of their properties as they existed or were estimated to exist on May 1, 1913, free from tax. To determine these valuations it was? necessary to select from a wide range of possibilities a set of values for a number of essential factors.

Jan 1, 1925

By W. J. Taylor, H. J. Mutz, A. F. Brock

THE International Kickel Co. of Canada Ltd. operates five underground mines and an open pit. Four of the mines, the Frood-Stobie, Creighton, Murray, and Garson, are on the south range of the Sudbury Basin, map above, within a radius of 10 miles of the city of Sudbury, Ontario. The fifth mine, the Levack, is on the north range of the Sudbury Basin, 30 miles to the northwest of the city. The open pit is operating on surface ores of the Frood-Stobie orebody. Two pits were opened at the Frood-Stobie mine; the Frood section was started in 1938 and the Stobie section in 1942. To meet the heavy demand for nickel during World War 11, open-pit production was accelerated until it constituted over 40 pct of Inco's total tonnage. As a consequence open-pit ore was depleted considerably alhead of schedule; the Stobie pit was completed in the summer of 1951, and it is expected that mining at the Frood pit will be completed in 1953. The major program launched 10 years ago to develop additional underground production as a replacement of open-pit tonnage thus had to be greatly speeded up. This conversion to all-underground mining will be completed within the next two years, and the underground mines will then have an annual hoisting capacity of 13,000,000 tons. One of the new mines in the underground expansion program, the Murray, was brought into production in 1950. Ore production from the new Stobie section of the Frood-Stobie mine was commenced on a limited scale in 1951 and will be increased as the program progresses. Delivery of ore to the new Creighton mill was started in the summer of 1951 from the caving project launched at Creighton mine. When mining was started in the Sudbury district 65 years ago the ore deposits were opened on a small scale and mining methods conformed to a general pattern of small open cast pits, followed by open stopes as mining was extended below the pits. The open stoping methods used were heading-and-bench and shrinkage. In certain cases a type of cut-and-fill mining was used with drywall tramways and dry-wall chutes in the fill. As the mines were deepened,

Jan 1, 1954

By W. S. Owen, T. Bell

The variation ox the M, temperature with nitrogen concentration has been determined experinzentally. The free-energy difference between martensite and the parent y Phase at the M, temperature,is computed for Fe-C and Fe-N alloys using recent solubility data fm the Fe-N system and new data for the variatim of the activity of the interstitial solute in the y phase with concentration. The "geometric model" is considered also, and the importance of Zener ordering is noted. It is shown that, although at any chosen concentration the M, temperature and the activity are significantly different in the two alloy systems, the free-energy duference is the same within the limits of experimental error, thus Providing further evidence of the very close similarity between the martensite transformations in Fe-C and Fe-N alloys. TO estimate the free-energy change accompanying the martensite transformation in binary interstitial alloys it is necessary to know the variation of the Ms temperature with interstitial solute concentration and some thermodynamic data. To date, only the Fe-C system has been discussed because this was the only system for which relevant experimental measurements had been made, but even in this case the data available are insufficient to permit the free-energy change to be calculated without the assumption of a thermodynamic model for the y and a solid solutions. The last comprehensive discussion of the topic was by Kaufman, Radcliffe, and Cohen in 1.960.' Since that time Ellis, Davidson, and Bodsworth2 have redeter mined the activity of carbon in y iron as a function of carbon content and Atkinson3 has measured the activity of nitrogen in Fe-N austenite. The M, temperature of Fe-N is reported in the present paper. Thus, it is now possible to assess the free-energy change accompanying the martensite transformation in Fe-N alloys on the same basis as that used to assess the change in Fe-C alloys. This comparison is of interest because it has been shown recently4 that the structure of the martensite formed in Fe-N alloys changes with nitrogen content in a manner exactly parallel to the changes in structure in the Fe-C series and that the strain associated with the distortion of the iron lattice in either the y or the a phase by a nitrogen atom is the same as that produced by a carbon atom. The work to be described tests whether or not this close similarity between the two systems extends to the thermodynamics of the martensitic transformations. THE Ms TEMPERATURES FOR Fe-N MARTENSITE Bose and Hawkes5 found the M, temperature of a eutectoid Fe-N alloy (2.35 wt pct N) to be 35°C. This single determination appears to be the only reported measurement of the M, temperature of an Fe-N alloy. In the present work a series of more than fifteen different specimens containing between 0 and 2.7 wt pct N were prepared by controlled nitriding of pure iron wire 0.010 in. diam. The iron was supplied by B.I.S.R.A. and was designated ACN2. The nitriding procedure, all aspects of which are critical, has been described in detail elsewhere.' Each specimen was quenched from the austenitizing temperature into brine at 20°C without removing the specimen from the ammonia-hydrogen atmosphere in which it was ni-trided. Alloys containing up to 0.7 wt pct N were fully martensitic. More concentrated alloys contained progressively more retained austenite. At 2.34 wt pct N the specimen was completely austenitic after quenching to 20°C. The M, temperature of specimens with M, temperature above 20°C (those containing less than 2.35 wt pct N) was determined by a thermal arrest technique. For the more concentrated alloys (2.35 to 2.70 wt pct N) the variation of electrical resistance with temperature down to -196°C was used. Unlike Fe-C alloys, Fe-N alloys cannot be reaus-tenitized in vacuum or in an inert atmosphere because excessive loss of nitrogen occurs, even in short times, at high temperatures. Consequently, the alloys were reaustenitized in the ammonia-hydrogen mixture corresponding to nitrogen equilibrium at the temperatures used. The specimens were quenched in a blast of cold hydrogen gas and the temperature, measured by a thermocouple welded to the 2.5-in.-long specimen, was recorded on a high-speed recorder. In the first experiments 0.002-in.-diam chromel-alumel wire thermocouples were used but it was found that these gave erroneous readings due to contamination by nitrogen pickup. Pt-Pt 13 pct Rh wires of 0.002 in. diam were found to be satisfactory. Further details of the experiments are available in the original thesis.7 The cooling rate was controlled between 400° and 4000°C per sec by adjusting the hydrogen pressure. At least three cooling curves were obtained for each composition. Each specimen was analyzed for nitrogen after quenching. To aid in the accurate location of the martensite arrest points a series of cooling curves of 0.010-in.-diam platinum wire were recorded and these, which did not contain an arrest, were used as comparison standards. Four specimens, each in the form of a 3-in. loop, were prepared from each of the four alloys containing more than 2.35 wt pct N. One specimen was used for nitrogen analysis, one for X-ray diffraction, and two for resistance measurements below 20°C. The latter specimens were quenched from 20°C into constant-temperature baths at selected lower temperatures.

Jan 1, 1968

By Enrique Touceda

For a number of years prior to the world war, the firm of Geo. H. Thacher & Co., of Albany, N. Y., was engaged in the manufacture of marine and other gray-iron castings. At the outbreak of the war the firm decided to specialize in the manufacture of propeller wheels. It attacked the problem, therefore, from a foundry point of view, seeking to produce a casting that would be so accurate that no subsequent machining would be required on the blades, also from the point of view of the ship builder. There were two general methods of manufacture, the shortcomings of which have been freely acknowledged. In the sweep method, the nowel, or bottom half-mold, for each blade is swept up by a spindle beam and pitch race, while the top half-mold for each blade is built up individually. In the pattern method one individual blade, with the hub or hub portion, is mounted on a spindle and the individual blade mold formed, the pattern is then rotated on the spindle to the position for the next blade, etc. In rare cases wheels were made from a solid pattern. Owing to the cost of the pattern, its failure in many instances to be correctly made, and (when made of wood) its early and sure distortion the disadvantage of this pratctice is obvious, while metal patterns in most instances were prohibitive in cost. In these methods both green-sand and loam molding was practiced. The casting produced by either method can be considered only as a blank from which the propeller must be machined. The back surface of each blade must be chipped to the templet and through this procedure chipped to such accuracy as will be required for a static balance. Inasmuch as the work done by the machine tool is confined to the driving face of the blades, not only is perfection most difficult, but corrosion will be greater because of the removal of the dense skin of the casting and the local strains set up by the pneumatic tool in chipping. To produce a finished 9-ft. propeller for a Navy destroyer required from 8 to 21 days of foundry work and about the same length of time for the machining. Through the use of the Thacher process, only as many hours are required, besides it is possible to produce a finished casting in perfect conformity with any particular propeller-wheel design.

Jan 1, 1922

By Enrique Touceda

For a number of years prior to the world war, the firm of Geo. H. Thacher & Co., of Albany, N. Y., was engaged in the manufacture of marine and other gray-iron castings. At the outbreak of the war the firm decided to specialize in the manufacture of propeller wheels. It attacked the problem, therefore, from a foundry point of view, seeking to produce a casting that would be so accurate that no subsequent machining would be required on the blades, also from the point of view of the ship builder. There were two general methods of manufacture, the shortcomings of which have been freely acknowledged. In the sweep method, the nowel, or bottom half-mold, for each blade is swept up by a spindle beam and pitch race, while the top half-mold for each blade is built up individually. In the pattern method one individual blade, with the hub or hub portion, is mounted on a spindle and the individual blade mold formed, the pattern is then rotated on the spindle to the position for the next blade, etc. In rare cases wheels were made from a solid pattern. Owing to the cost of the pattern, its failure in many instances to be correctly made, and (when made of wood) its early and sure distortion the disadvantage of this pratctice is obvious, while metal patterns in most instances were prohibitive in cost. In these methods both green-sand and loam molding was practiced. The casting produced by either method can be considered only as a blank from which the propeller must be machined. The back surface of each blade must be chipped to the templet and through this procedure chipped to such accuracy as will be required for a static balance. Inasmuch as the work done by the machine tool is confined to the driving face of the blades, not only is perfection most difficult, but corrosion will be greater because of the removal of the dense skin of the casting and the local strains set up by the pneumatic tool in chipping. To produce a finished 9-ft. propeller for a Navy destroyer required from 8 to 21 days of foundry work and about the same length of time for the machining. Through the use of the Thacher process, only as many hours are required, besides it is possible to produce a finished casting in perfect conformity with any particular propeller-wheel design.

Jan 1, 1922

By J. Holms Pollok

The determination of specific gravity dates from such antiquity, and the various published methods of determining it are so numerous, that one may well be skeptical as to the value of a new means of obtaining so well-known a quantity. I make no claim to any great novelty for the little device here described, the principles, though not the convenient details, of which are more or less embodied in the publications of Mr.

Jan 1, 1900

By A. H. Larson, T. P. McNulty

RECENTLY, an investigation of the absorption of sulfur dioxide gas in molten binary copper alloys was conducted. A Sieverts-type apparatus, consisting of a mercury-filled gas dispensing buret and a mercury manometer, was used initially for determining the volume of gas absorbed as a function of pressure. The equilibration behavior of the alloys studied indicated that the mercury in the gas measuring system was absorbing sulfur dioxide. Owing to the widespread use of mercury as a displacement medium in absorption studies, an investigation was made to determine the nature and magnitude of the mercury - sulfur dioxide absorption effect. The gas measuring system was modified by substituting a Worden Quartz Products Type PDHV fused-quartz-spiral pressure gage for the mercury-filled dispenser and manometer. The dispensed gas volume at known temperature and atmospheric pressure was measured by evacuating a Pyrex vessel of known volume and by admitting sulfur dioxide into the vessel until the attached quartz pressure gage registered atmospheric pressure. Atmospheric pressure was measured concurrently with a separate mercury barometer. The volume of the empty sample chamber and its attendant apparatus was determined by measuring the equilibrium pressure accompanying the addition of a measured volume of sulfur dioxide into the initially evacuated system. The volume of the mercury sample was calculated from the density of mercury at the temperature of the study (25°C). Measured volumes of sulfur dioxide were then dispensed into the system and the equilibrium pressure accompanying each gas addition was determined. From the difference between the system volume and the mercury volume, the number of moles of gaseous sulfur dioxide remaining in the system at each pressure was calculated. The difference between the number of moles of gas dispensed into the system, denoted Enso2: and the number of moles of gas remaining in the system after absorption equilibrium had been attained, denoted nso2(g), was equal to the number of moles of absorbed gas, denoted nSO2. The number of moles of absorbed gas was then converted to absorbed volume, denoted VSo2, in cu cm at stp conditions of (PC and 760 mm Hg. Table I contains calculated values of Snso2, nSo2(g), and VSo2 for different sulfur dioxide pressures. In the original system, denoted Run I, volume limitations of the gas dispensing system prevented absorption studies at equilibrium pressures near atmospheric pressure, so a different gas dispensing system, denoted Run 11, was used for determining the last pressure reading in Table I. The data in Table I are expressed in terms of the absorption of sulfur dioxide in 49.68 cu cm of mercury. In Fig. 1, these data are expressed in terms of the absorption of sulfur dioxide in 100 cu cm of mercury. Since the absorption data plotted in Fig. 1 show a linear relationship, the volume of sulfur dioxide absorbed in mercury is a function of the first power of pressure. The absorption reaction is So2(gas) = SO2 (in Hg) The first-power pressure dependence, coupled with the fact that the sulfur dioxide could be removed from the mercury by applying vacuum, indicated reversible

Jan 1, 1967

D. F. HEWETT, Washington, D. C. (communication to the Secretary*).-I am not prepared to discuss the metallurgical use of manganese in the form of alloys. In connection with other work for the U. S. Geological Survey, however, I have been investigating incidentally, for about 5 years, the American as well as other sources of manganese. There are some conclusions that come out of this investigation that may interest those whose greatest interest lies in the use of the alloys. From a geological point of view, most manganese ore deposits may be regarded as concentrated masses of manganese oxides, as there are few masses of the other manganese minerals that are rich enough in manganese and low enough in silica to warrant smelting. The deposits of the Huelva district, in Spain, which are largely manganese carbonate and silicate, are exceptions to this statement. Some deposits of manganese oxides, such as those of Russia and Cuba, are bedded with ancient sediments, and although they are clearly concentrated under unique conditions, the source of the manganese cannot be determined. Probably 60 per cent. of the world's production of manganese ore, or 95 per cent., if that of Russia be excluded, is derived from the superficial parts of deposits that have undergone weathering and enrichment near the surface. In other words, the situation with the manganese ore supply is such as it would be with regard to copper, if instead of being derived largely from deep zones of deposits of deep-seated origin, such as veins, it were derived solely from the zone of secondary enrichment. Manganese oxide occurs in all rocks but is most abundant in igneous rocks, of which, according to Clarke, it forms an average of 0.10 per cent. It also forms 0.05 per cent, of the average limestone, but only traces are present in shales and sandstones. It is interesting that although many commercially important manganese deposits occur in rocks that are but slightly richer in manganese than the average, the most important deposits occur in rocks of unusual character that are much richer in manganese than the average. Thus, the most important deposits of India and Brazil overlie or occur near masses of rocks that contain excessive amounts of manganese garnet and pyroxene.

Jan 5, 1917

By C. H. Mathewson

(New York Meeting, February, 1916) DURING the past year considerable work dealing with the mechanical properties and microstructure following the anneal under uniform conditions of certain types of commercial rolled brass has been done in this laboratory. Since these experiments were conducted with the active cooperation of the Bridgeport Brass Co., involving free use of its product, and have thus furnished information which is characteristic of some of its special mixtures, full publication of the numerical relationships and comparative results encountered does not seem justifiable. Some of the more general features of this work are, however, available and it is our present purpose to use the material in question, along with some results of special tests, in discussing the characteristics of recrystallization as related to the degree of hardening by strain and the ordinary annealing variables. We desire to make acknowledgment of the many courtesies extended by Mr. Charles Ferry, Metallurgist of the Bridgeport Brass Co., and the value of his cooperation, which has greatly stimulated the study of brass in this laboratory. A clear and systematic presentation of the principal relations between temperature and time of anneal, the changing physical properties and microstructure and the degree of previous reduction by cold-rolling, was first made, in the case of rolled brass and copper, by the French engineer, C. Grard,1 in 1909, although much fragmentary information of this general character had appeared earlier and the main facts involved were undoubtedly known to many brass specialists through their own private research. From this work, it appears that in the cartridge mixture (67 per cent. copper, 33 per cent. zinc) the properties imparted by cold-working within the limits, 13 to 75 per cent. reduction of area by rolling

Jan 1, 1916

By V. C. Perini

The 1943 designation of districts for the Transactions† has caused some confusion because of the elimination of the West Central Texas district and the allocation of the counties of this district to the North Texas district and the North Central Texas district. The North Central Texas district as herein defined includes the counties of Brown, Callahan, Cole-man, Comanche, Coryell, Eastland, Erath, Fisher, Hamilton, Hood, Jones, Lampasas, Mills, Nolan, Palo Pinto, Parker, San Saba, Shackelford, Stephens, Stonewall, Summerville, Taylor, Throckmorton and Wise. These counties as listed are the counties of District 7B, State Railroad Commission. This district covers the south central crest and the west flank of the Bend flexure north of the Llano uplift. The west flank of the Bend flexure is on the east boundary of the Permian Basin of West Texas. The North Texas district, District No. 9, State Railroad Commission, includes the counties of Archer, Clay, Cooke, Foard, Hardeman, Jack, Knox, Montague, Wichita, Wilbarger and Young. The area of this district covers the crest and south flank of the Red River uplift and the north central crest of the Bend flexure. The greater part of the oil and gas produced in the past from the North Central Texas district has been from Pennsyl-vanian strata. Some oil and gas has been produced from the lower Permian (by the latest selection of the Pennsylvanian-Permian boundary') and minor amounts from the Mississippian and Ordovician sediments. Increasingly important quantities of oil and gas are to be expected from the older sediments by deeper development in proven fields and by new discoveries. Most of the oil and gas in the district has accumulated in localized, well-defined structural traps in limestone and sandstone reservoirs and in traps due to stratigraphic changes in sedimentation, mainly porosity traps in limestone and sandstone lenses, both usually associated with some structural feature. The Stripper Well Premium Plan as adopted by the office of the Federal Price Administrator has been an aid to the producers of stripper wells. The producers are pleased to receive the subsidy to prolong the plugging of wells, but they are not too pleased with the subsidy plan in principle. Most independent operators are in favor of, and think they are entitled to, an increase in the market price for oil. The price is not adequate to meet the requirements of the average independent operator with the continued advance in production, development and wildcatting costs. Old and new pipe lines for oil and gas leading out of the state are removing reserves at an alarming rate. Curves showing the rate of discovery versus production and pipe-line deliveries in and out of the state make a cross that sooner or later will be fatal to the state. Wildcatting not only needs a price increase but every other available incentive and encouragement.

Jan 1, 1945

By Clintford R. Jones, Om P. Pande

This chapter presents a survey of instrumentation and control systems used on ball mill circuits from the past to the present. It is based on the concept of optimization of plant practice, and addresses the influence of the circuit design on the control strategy and on the instrumentation philosophy. Methods of optimization of the grinding circuit, within the constraints of the mill design requirements, are reviewed. The modern use of automation and circuit optimization is critically reviewed for known and possible conceptual control loops. A comparative study of circuit variations due to instrument hardware, location and installation is provided. Future trends i.e., computer control (DDC) and the effects on both the control stratagems and the optimization stratagems are described.

Jan 1, 1982

By J. R. Finlay

The Cæur d'Alene silver-lead mining district of northern Idaho is probably best known to the general public as a seat of labor-troubles. So far as the writer is aware, little has been written and little is known about its geology and resources. People interested in lead-smelting are, of course, cognizant of the economic importance of the region, but they have not communicated much of their knowledge to the public. Exact figures as to the total output of the district are not obtainable, but the following estimates, covering the entire output of the 15 years during which the mines have been operated, are believed to be approximately correct: Group of Mines. Product. Wardner Group, including the Bunker Hill and Sul livan, Empire State-Idaho, Last Chance, Sierra Nevada, bur d'Alene Development Co... . $17,500,000 Cafion Creek Group, including the Gem, Frisco Con solidated, Granite, Standard, Mammoth, Hecla, Tiger-Poorman, Custer and Bell,.... 35,000,000 Mullan Group, including the Morning, You Like and Gold Hunter,........7,500,000 $60,000,000 This output covers the period of discovery and early struggles, and several periods of stagnation caused by strikes and other serious labor-troubles. In 1900 the output of the district was fully $10,000,000, and this figure would have been considerably increased in 1901 had not a curtailment of production been forced by the condition of the lead-market. In 1901 the product was about 150,000 tons of concentrates, with a gross. value of $8,250,000.

Jan 1, 1903

By P. G. Shewman, T. L. Wilson

Using published surface-diffusion (D,) data and published sintering equations, it is shouln that surface difusion should dominate the neck-growth stage of intering for all materials in which D, has been measured (six metals and A1as). Also, grain boundary diffusion can be expected to contribute appreciably to shrinkage and possibly to neck growth below some critical temperature of the order of 70 pct 01- the absolute melting temperatuve. In view of the widespread conclusion in previous sintering work that volume diffusion dowzinates neck gvowth, experiments were conducted using spherical copper powders to test this conclusion. Scaling studies on neck growth at 950°and 1020°C clearly demonstrated that suyface diffusion dorninates. Kinetic studies on shrinkage gave more equivocal results that indicated an increasing role of' grain boundary transport at lower temperatures. Five diarszeters from 100 to 300 u were used in the scaling sludy and a temperature range of -650' 10 950 C was covered in the shrinkage studies. All experiments were conducted in dvy hydrogen. In 1949, Kuczynski published his now classic paper on the determination of the transport mechanism in sintering from the time laws of neck growth. In the interim, these laws have been applied to many systems and slightly modified by several authors. Essentially all these authors concluded that, for crystal- line materials, the dominant transport mechanism in neck growth is volume diffusion. This stems from the observation that the neck radius increases about as t"5 and that the activation energy approximates that for lattice diffusion. A related but independent series of studies stems from Mullins' rigorous analysis of the growth of the groove formed where a grain boundary meets a free surface." xperimental work stemming from this analysis has shown that for each crystalline material studied (Au, Ag, Cu, Ni, Fe, Pt, Al2O3) surface diffusion was clearly the dominant transport mechanism for groove widths up to the order 10 to 20 p. The ratio of the quantity of material being carried by lattice diffusion to that carried by surface diffusion increases linearly with the groove width, so surface diffusion is dominant for all widths under 10 to 20 u. The analysis of the relative contributions of surface and volume diffusion to grain boundary grooving, and to neck growth in sintering, shows that they are quite similar. Thus, using the available surface-diffusion data and the approximate equations of Kuczynski, or the more rigorous recent equations of Nichols and Mullins, 3 it can be shown that the small necks between particles must grow almost entirely by surface diffusion. The purpose of this study was to re-examine the basis for the conclusion that the neck-growth stage of sintering proceeds by volume diffusion. Using spherical copper powders, of several different diameters, precise experimental measurements were made of both neck growth and shrinkage. Application of Herring's scaling laws to the neck-growth data clearly indicated that neck growth occurred by surface transport, even though the neck radius increased as or Using the recent analysis of Mullins and Nichols as well as published data on surface diffusion, it is shown that the observed time law, as well as actual rate of neck growth, can be satisfactorily explained by a surface-diffusion mechanism.

Jan 1, 1967

By Philip D. Anderson, Ralph Hultgren

Heat contents of extremely pure iron were measured over the range 300"to 1433"K, using a diphenyl ether calorimeter. Results from three samples containing widely differing impurities agreed with one another and with Previously reported results at higher temperatures (1184 ° to 1809°K) by Olette and Ferrier. From these data a table of heat contents of iron has been Prepared which is believed to be more accurate than those previously available. CP values have been derived which are consistent with these heat contents, with the best experimental Cp data, and with the thermodynamic conditions of equilibrium between bcc and fcc iron. The opinion is expressed that low-temperature extrapolations of presently known Cp values for y-Fe are not reliable. It would seem that the thermodynamic properties of iron, which is by far our most important metal, should have been well established long ago. This is not the case, however. As discussed by Olette and Ferrier,' there is objection to every earlier heat content measurement. While the best true Cp determinations agree well at temperatures below the Curie point, there is wide divergence at higher temperatures. Several investigators have examined available data and attempted to calculate thermodynamic functions for iron that are consistent with the two equilibrium temperatures of bcc and fcc iron. The two primary efforts were those of Austin' in 1930 and Darken and smith3 in 1948. The recommended values differ considerably; integration of Austin's Cp values leads to a heat content at 1100°K which is 300 cal per g-atom higher than the value recommended by Darken and Smith. The compilation of Fisher4 in 1949 was based on the selection of Austin. In 1956, Weiss and Tauer obtained yet another set of values by resolving Cp values into components due to dilation, lattice vibration, electronic excitation, and magnetism. The magnitude of contribution by each component and its dependence on temperature was estimated by semiempirical means. Their values are not self-consistent in that they do not form smooth curves when plotted vs temperature; moreover, their calculations cannot easily be repeated since they do not give the values of some of the parameters used. Clearly, experimental values for iron were in a most unsatisfactory state. The presently described measurements of the heat content of iron were therefore undertaken, covering temperatures as high as 1433°K. While the work was in progress, the high-temperature (1193" to 1789"K) heat content measurements of Olette and Ferrier' were published; in the region of temperature overlap the present results agree with Olette and Ferrier well within experimental accuracy. It is believed that the present results, combined with those of Olette and Ferrier, provide for the first time a reliable set of heat contents of iron from room temperature to the melting point. From these data, guided by available Cp measurements, it proved possible to derive Cp, entropy, and free energy function values for @-iron from room temperature to the melting point, and for y- iron in the temperature region of its stability. Exhaustive study led to the conclusion that extrapolations of y-iron functions to room temperature were not reliable enough to be useful; hence these have been omitted from the tables. EXPERIMENTAL Materials. Three samples of extremely high purity iron from different sources, containing widely different impurities, were measured. The first of these, designated "Chipman", was kindly supplied by Dr. K. K. Kelley of the U. S. Bureau of Mines from a lot which was made many years ago by Dr. John Chipman of the Massachusetts Institute of Technology. The second, designated6'Teddington", was supplied by the National Physical Laboratory, Teddington, England, from a lot zone-refined by them. The third sample, designated "Irsid", was supplied by the Institute de Recherches de la

Jan 1, 1962

By Henry J. Williams

The main difficulty in the determination of silicon in pig-irons containing very high percentages of that element, has been due to their almost complete insolubility in acids, or mixtures of acids. The object of the present paper, which presents no new principle, is to suggest a method of determination which has repeatedly given accurate results, and which obviates completely the tediousness and uncertainty of the usual slow solution in acids. This method has been tried with pig-irons containing from 7 to 14 per cent. of combined silicon, and properly called ferro-silicons. When reduced to an impalpable powder in the agate mortar, an 11 per cent. ferro-silicon was found to resist the action of all acids, or mixtures of acids, with the exception of sulphuric acid of about 1.25 specific gravity. But the action of this acid, even during long continued heating, was very slow, 72 hours being necessary to com pletely dissolve half a gramme of the metal. The complete decomposition of 1 gramme of the metal may, on the other hand, readily he effected in a few minutes by fusion with sodium carbonate in a covered platinum crucible over a blast-lamp —the idea being to dissolve the silicon, leaving the iron in condi tion to be readily attacked by acids. The silicon dissolves as soluble sodium silicate, and metallic iron remains in a very spongy and finely divided condition. The addition of a little hot water

Jan 1, 1889

By G. B. Kasik, George Sachs, George Espey

IT has been reported frequently that the hardness and strength vary over the cross section of cold-worked, particularly cold-drawn, material. Brass rod and wire usually has been found to possess a maximum strength and hardness near the surface.1,2 According to Sachs,1 the center fiber has about the same strength as a wire stretched by the same amount in a tensile-test machine, the strength increasing toward the surface (Fig. I). These differences are particularly large for wire given a small reduction on drawing through a die with a wide opening. However, with increasing reduction and hardness, a tendency to form a thin soft surface skin becomes apparent. On the contrary, copper wire has usually been found to possess a soft surface skin" and it has been reported by Harris3 that during the cold-drawing of hot-rolled wire the surface layer becomes increasingly softer than the core, while the layer of maximum strength moves toward the core, it being found near the surface at first. The increase of strength and hardness from the core to the skin is readily explained by the observation that, in addition to the stretching, the layers of a rod or wire are sheared more the closer they are to the surface.1,6-8 However, the presence of a soft surface layer can be attributed only to an annealing effect. The source of such a softening might be the extremely high temperature that originates from the friction between [ ]

Jan 1, 1941

By John Gross

THE deductions drawn in crushing and grinding operations have heretofore been based on a separation of the products into various sizes. A crushed product may be sized by sieving, by elutriation, and by aid of the microscope. To estimate the surface of each size the relation of the surface to the estimated average diameter must be assumed. Such a relation, owing to the irregularity of the particles, may involve two assumptions: First, a factor to convert average diameter to surface for one particular size; and second, a variation in the factor as the diameter of the particle changes. Obviously a surface measurement in which such assumptions and estimates are involved is questionable. In the first paper of this series1 a method has been given by which an accurate measure of surface of quartz can be obtained from its dissolution rate. By the use of this method, surface measurements have been made on a series of sieve sizes of crushed quartz, the results of which are given and discussed in this paper.

Jan 1, 1928

By Harry L. Washburn, Robert L. Llewellyn, W. J. Halvorsen

Many of the problems that occur in the preparation plant originate from practices in the mine. Impurities in raw coal can be in the seam itself or from extraneous material taken in mining from the roof or bottom. In the case of underground mines, the choice of mining equipment will affect the size consist and the amount of extraneous material included with the coal. Also, governmental regulations concerning the degree of rock dusting, gobbing underground, and cleanup have increased the dirt in raw coal. Sulfur dioxide emission standards, on the other hand, are pressuring the coal industry to clean coal more thoroughly. Coal supplied for coking purposes is nearly all upgraded by washing, while for the largest market, electric power generation, a high proportion is shipped as a raw product with processing, in whole or in part, only necessary when excess impurities are mined with the coal. This chapter will deal primarily with plants that process or wash coal to some extent (Fig. 1) and only incidentally with mines shipping raw run-of-mine coal crushed to a top size of, usually, 51 to 102 mm (2 to 4 in.), with little, if any, other treatment. JUSTIFICATION FOR COAL PREPARATION During the past decade, major changes have occurred affecting the market, profit, and long-range planning of the coal industry. Mining companies have become "partners" with consumers at many new and some old mines, both for steam and metallurgical coals. Coal properties have become "assigned" tonnages at mutually agreed upon conditions and prices. Lower unit-train tariffs have been instrumental in helping coal markets to compete against oil and nuclear energy. Coal prices for power plants are still on a Btu (British thermal unit)

Jan 1, 1981