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By L. H. Schwartz, S. K. Lahiri, M. E. Fine, D. Chandra

WHILE the yield stress of solution treated Fe-Cu alloys increases rapidly with aging, a precipitate has only been directly observed in overaged samples.'-" This precipitate is essentially pure fcc copper, the E phase. Hornbogen2 suggested that the initial hardening is due to clustering of copper atoms in a bcc iron matrix. Hornbogen was not able to obtain direct confirmation for such bcc clusters by either X-ray diffraction or electron microscopy; however, he did observe analogous clustering in Fe-Au alloys7 where the scattering factor difference between iron and gold is more favorable than that for iron and copper. Fujii, Nemoto, Suto, and Monma4 recently observed diffuse electron diffraction scattering in a 2.5 pct Cu alloy aged at 500°C: for 30 hr. They suggested that part of the diffuse SCattering was due to a modulated structure of 26 to 42 wavelength parallel to the (110) matrix plane. This disappeared with further aging. However, 30 hr at 500°C is well beyond the peak strengthening in this alloy which occurred at less than I hr at 500oc.4 By transmission electron microscopy they could not distinguish between quenched samples and samples aged to maximum strength. The purpose of the present investigation was to try to obtain further confirming evidence for a precipitation stage preceding the formation of the fcc E phase. Change in Young's modulus was selected for study be- EXPERIMENTAL PROCEDURE The Fe-1.67 at. pct Cu alloy was supplied by the U.S. Steel Corporation in the form of a hot forged rectangular bar. The carbon and nitrogen contents of this alloy were 70 ppm and less than 10 ppm, respectively. The samples for Young's modulus measurements were made by cold swaging to & in. diam and cutting to 2 in. lengths. Tensile test samples 1 in. long were prepared by cold rolling to a thickness of 0.012 in. and then machining to gage dimensions of 0.5 by 0.012 in. For Mijssbauer studies, foils 1 mil thick were prepared by cold rolling. During fabrication the alloy was given intermediate anneals at 845OC followed by quenching. The specimens after preparation were solution treated at 1000°C (y field) or 845°C (a field) for 1 to 2 and 5 to 6 hr, respectively, in a dynamic vacuum of about 2 x lom6 torr. The tensile and modulus specimens were drop-quenched into iced brine through an aluminum foil which vacuum-sealed the bottom of the furnace tube. The MOssbauer foils were drop-quenched into helium gas cooled by passing through N2 (liq) in a copper coil. The grain diameter of the modulus and tensile specimens was between 0.025 and 0.035 mm. The samples were aged from 400" to 500°C in a dynamic vacuum of 2 x 10-6 torr and cooled by pulling into a water-cooled portion of the vacuum system. The dynamic Young's modulus was measured at room temperature using electrostatic excitation and detection of longitudinal vibrations.' Neglecting any length change during the aging, (this is expected to be comparatively small), the fractional change of Young's modulus (?Et)/Eav, is equal to twice the fractional change of the resonant frequency (?ft)/fav . ?ft =ft —fo where fo and ft are the resonant frequencies of a specimen before aging and after aging to time t. The measured f's, approximately 51,000 cps, were corrected to 25°C for any variation in the ambient temperature. The tensile tests reported were carried out at room temperature in an Instron with a 1000 lb full scale load cell. The flow stress reported herein corresponds to a strain of 0.002. The Massbauer spectra were taken in a constant acceleration model AM-1 NSEC spectrometer. The

Jan 1, 1970

By Theron Wasson

The state of Michigan showed considerable activity during 1935. The center of greatest interest was the Crystal field, which was unknown until March, 1935, and is an illustration of the effect of the unknown and unexpected on Michigan oil development. The fields of the state (Fig. 1) produced a total of 15,770,000 bbl. of oil in 1935, or about 5 million more than in 1934. In order to keep up this production 307 new oil wells were drilled, of which 88 were in the Crystal area, which produced 3,600,000 bbl. This field had a rapid development and reached its peak in October. Since that time increasing water encroachment has caused a rapid decline. The pay horizon at the top of the Monroe dolomite is only a few feet thick. Big producers were offset by dry holes or small wells. The discovery well, which was in section 11, Crystal township, Montcalm County, was drilled March 28, 1935. Its initial production was 5000 bbl. per day, and up to Dec. 31, 1935, had produced 350,000 bbl. of oil—dose to one-tenth of the total production of the field to that date. The Beaverton field, which was discovered at the close of 1934, did not develop rapidly. Four small producers were finished in the Dundee lime during the year. West Branch was active and at the end of the year had 97 producers, 72 of which were drilled during 1935. Most of the wells produce from the Dundee lime; a few are finished in the Traverse. The Birch Run field deserves special mention, for it is the one area where consistent production continues to be found in the Berea sand at about 1500 ft. Wells are small, 20 now producing a total of about 300 bbl. per day of oil of fine quality. The old Central Michigan producing area, extending from Nit,. Pleasant through Yost to Porter, continued to be the principal producing area of the state and accounted for 10,370,000 bbl. from 660 producing wells. Ninety-three new wells were drilled in this territory. The Porter field, at the southeast end of this producing trend, was outstanding from the standpoint of production. The old Leaton field of Isabella County added several new producers. Its production was greater than in 1934.

Jan 1, 1936

One of the best known of the early mining districts of Nevada was that at Eureka, where gold was first produced in 1864. While the most productive period for the district was during the early 1900s, production was maintained until World War II. During this time it is said that the Eureka district produced as much as $200 million from over 3,200 km (2,000 miles) of tunnels and workings. The Windfall Mine was discovered in 1902; and a 100 ton cyanide plant was operated there during the periods 1907 to 1912 and 1932 to 1940. Since 1974, however, Windfall Venture has been operating a unique heap leaching facility on the site of the old Windfall Mine. Gold at the Windfall occurs primarily in the Cambrian Hamburg dolomite which has been "sanded" and in which the original cementing material has been destroyed. The gold is micron sized and is accompanied by anomalous amounts of arsenic and mercury; however, the ore is low in base metals which distinguishes it from the typical Eureka district ores. Mining the ore causes it to break down into very fine sizes, approximately 50% minus 150 microns (100 mesh). Conventional heap leaching by spraying proved to be impossible; and extensive test work on alternate methods, aided by the United States Bureau of Mines, was conducted using 9 m (30 ft) high columns and then large tonnage heaps. The leaching procedure adopted was to build 10.6 m (35 ft) high heaps on a 50 mm (2 in.) asphalt pad covered with a layer of gravel for drainage assisted by perforated pipe drains and gravel-packed sumps. A berm is constructed around the top of each pad and cyanide solution is allowed to “pond” on top of the heap. The resulting percolation is at the rate of 24 liters per sq m per hr (0.6 gal per sq ft per hr), a figure about 2.4 times the average used in other heap leaching operations. The dolomite furnishes its own protective alkalinity and no lime or caustic is used in the solution which contains 0.4 kg per mt (0.8 lb per st) of NaCN. Pregnant solution from the heaps averages about 0.7 g Au per mt (0.02 oz per st) with a cyanide content of about 0. 2 kg per mt (0.4 lb per st) and a pH of plus 9. Addition of NaCN brings the pH of the leach solution up to 11 to 12. Carbon adsorption of the gold was originally done in six enclosed columns mounted in a trailer but five conventional columns have been substituted as the size of the operations has increased. Carbon stripping is with hot caustic, cyanide and 10% ethanol solution. The

Jan 1, 1981

By W. A. Gow, V. F. Harrison, H. H. Mccreedy

A semi-continuous bench-scale, countercurrent-decantation system, in which the ore was moved countercurrently to the flow of leaching solution, was used to conduct acid-leaching tests on uranium ore with the aid of bacteria. This method, which involved a low degree of agitation, was successfully applied to extract uranium in practical amounts and at practical rates. The acidity of the leaching solution was the main variable investigated in the bench-scale tests done at the Mines Branch, Ottawa. Over 90 11er cent of the uranium was extracted in a six-stage system. The results suggest that this technique could be ap-plied in the utilization of bacterial oxidation and leaching as a method for treating Elliot Lake uranium ore.

Jan 1, 1969

Jan 1, 1907

By S Kost, R Nievergelt, F Cortes

In recent years, the use of steel fibre-reinforced concrete (SFRC) for segmental tunnel linings has become increasingly popular due to numerous advantages including durability, resistance to spalling, reduced cracking at corners and edges and significant cost-saving potential. One of the key parameters for measuring the performance of SFRC is the residual (post crack) flexural strength. A problem often faced in design and quality control of SFRC is the high variability of results obtained by standard beam test methods, with reported coefficients of variability (CoV) in the order of 25 per cent. The high test variability results in a relatively low permissible design strength relative to the average flexural strength of the material and commonly leads to non-conformances with respect to residual flexural strength during production testing.This paper presents the implementation of an alternative testing method using large round determinate panels (RDPs) for quality control testing of the SFRC used in the segmental lining of the City East Cable Tunnel (CECT) in Sydney. The alternative RDP test method was found to correlate well with standard beam tests and significantly reduce the variability of test results, minimising the risk of outlying residual flexural strength results, with zero non-compliant test results reported during the production period.This successful implementation of an alternative test for post-crack flexural strength with lower variability in results constitutes a relevant precedent to demonstrate the feasibility of this approach which contributes to the development of more cost-effective concrete mixes and minimises the risk for non-compliant results and the contractual disputes that commonly arise from these.CITATION:Cortes, F, Nievergelt, R and Kost, S, 2014. Development of a segmental lining specification for steel fibre reinforced concrete flexural strength testing using round panel tests, in Proceedings 15th Australasian Tunnelling Conference 2014 , pp 461–468 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

The Effect of Grinding Aids on Laboratory Grinding of a Cassiterite-Polymetallic Sulfide Ore

Sep 13, 2010

Production of refined zinc (99.95 per cent) at the minesite without increasing greenhouse gas emissions is considered. As an example, exploitation of the full reserve of the McArthur River orebody is proposed, using the existing concentrator, whilst introducing radically innovative smelting technology. Bulk flotation of all the sulphide minerals is followed by smelting in a melt circulation reactor with tonnage oxygen. By smelting the high-energy pyritic concentrate and reacting the evolved sulphur dioxide with near-mine dolomite, a large amount of electricity can be generated. This is enough to supply all the requirements for the smelter itself, an air separation plant and a facility for compressing and liquefying carbon dioxide. Carbon dioxide is disposed of off-shore for enhanced oil recovery or by other means. The reacted dolomite fixes sulphur as an inert and environmentally acceptable solid residue. Treatment by these means leads to virtually zero gas emission smelting. The paper concludes with a vision for the future in which expansion of zinc smelting capacity is seen to be definitely needed.

Jan 1, 1998

By R. A. L. Black

Between March and June 1962, the privilege of holding a Carnegie Corporation Fellowship enabled R. A. L. Black to travel extensively in the northeastern and western U.S. and in Canada, seeing mining schools, mining research establishments and a cross-section of the American and Canadian mining industry. Visits were paid to 12 university mining schools, 7 research establishments and 19 mining operations. The author had previously spent two months in Britain in a similar manner and eventually returned to his home in South Africa after a short period studying mining problem in Australia. Thus, although the following remarks are mainly concerned with the educational problems of mining in North America, a comparison of impressions of American and Canadian conditions could be made with impressions gained from first-hand experience of other mining centers in the English-speaking world. The conclusion was reached that the problems and conditions of mining, research and mining education are very similar in all areas visited.

Jan 4, 1963

By A. Tremari, Paul I. Eimon

Photogrammetrists are studying with new interest the problems of mine mapping and mining engineers are beginning to see what photogrammetry can do for them. Administrators in a number of European and U. S. mines have tried photogram- metric methods and are finding that better maps and data, needed for mine development, can be produced with savings of time, men, and money. In addition to wide use in small scale mapping projects, photogrammetric methods are now used for producing large scale plans and maps in German coal and lignite mines, in some U. S. open pit mines, to inventory TVA coal stock piles, and to compute highway excavation volumes. In each case surveying and map compilation has been made more efficient and accurate by photogrammetry and at significant savings over ground methods.

Jan 5, 1959

OCHRE is a semimineral composed by Nature of earth and a tincture of yellow caused by a fumosity of lead ore. By itself it is a material without any [38] metal, although when it is used in smelting it helps to melt the harsh and sour ores of metals. I do not know that it has any other use, except to painters. Bole is also a red viscous earth which has a very astringent and drying nature. It has no very apparent smell or taste, and I think that the cause of its redness lies in the fumosities of iron ore, for it is a companion to this and is found in its mines. It is an efficacious medicine against any poison and in this capacity has an action like terra sigillata* or perhaps better. In

Jan 1, 1942

By J. B. Scuffham, G. A. Rowden

The use of ammonia as a leaching agent has been well-documented but only recently have its advantages been fully exploited on a commercial basis. When compared with conventional sulfuric acid leaching processes, the major advantage of ammoniacal systems is their ability to reject iron and many acid consuming gangue materials. Although metallic copper, nickel, zinc, etc. are dissolved rapidly in ammoniacal liquors at ambient temperature in the presence of air the sulfide ores of these metals are more resistant to this treatment. Sherritt Gordon Mines in Canada treats sulfide concentrates at its Fort Saskatchewan plant under pressure with ammoniacal am- monium sulfate solution to solubilize the non-ferrous metal values. Typical leach operating conditions are 80-95°C and 115- 128 psig. Although the metals present in the ammonical solution could be recovered via solvent extraction techniques, Sherritt Gordon Mines currently operates a pressure reduction process using hydrogen to yield metal powders directly from the ammoniacal solution. The basic Sherritt Gordon technology has been applied world wide for the treatment of nickel/cobalt concentrates.

Jan 12, 1973

By Douglas A. Anderson

Mine the Internet? You bet. Precious information resources are there to be found by those willing to explore. Of course, the stratigraphy and the exploration tools must be learned. This article is is designed to help learn those tools and how to find the information that can help the reader. However, beware the Internet. It can be addicting. On the other hand, information can be found that you never suspected. And users can make contact with people who might otherwise never have crossed their paths.

Jan 1, 1996

By Arnt Solbu, Jomar Thonstad

The reaction between CO, and aluminum in cryolite-alumina melts in contact with aluminum has been studied by passing CO2 over the melt. In unstirred melts a homogeneous reaction between dissolved metal and dissolved CO2 was observed. In stirred melts in which convection was induced by bubbling argon through the melt, the dissolved metal apparently reacted mainly with gaseous CO2. The rate of formation of CO increased slightly with increasing depth of the melt, and it did not depend on whether CO2 was passed over or bubbled through the melt. The rate of formation of CO increased with increasing area of the metal/melt interface and with the application of anodic current to the metal. It is concluded that the dissolution of metal into the melt is the rate-determining reaction. THE current efficiency in aluminum electrolysis is determined by the rate of the recombination reaction between the anode gas and the metal: 2A1 + 3CO2—A12O3 + 3CO [1] as originally stated by Pearson and waddington.1 The occurrence of this reaction in cryolite-alumina melts in contact with aluminum was first verified experimentally by Schadinger.2 Thonstad3 has shown that the reaction may proceed further to give free carbon: 2A1 + 3CO— A12O3 + 3C [2] Normally only a few percent of the CO formed undergoes such reduction. The mechanism of these reactions has not yet been clarified. Aluminum, as well as CO,, is soluble in the melt. The solubility of aluminum in cryolite-alumina melts at around 1000°C corresponds to 75 x 10- 6 mole A1 per cu cm,4 while that of CO2 is only 3 x 10-6 mole CO, per cu cm.5 Taking into account the stoichiometry of Reaction [I], the ratio between dissolved aluminum and dissolved CO2 available for the reaction in a saturated melt is about 40. Therefore, as will be shown in the following, the reaction probably mainly occurs between gaseous COa and dissolved aluminum. The dissolved aluminum presumably consists of subvalent ions of aluminum and sodium.4'6 Since the interpretation of the present results is not dependent upon the nature of this solution, the dissolved metal will be designated solely as Al+ in the following. The reaction can then be divided into four steps: A) dissolution of metal, e.g., 2A1 + Al3 — 3A1+ [3] B) diffusion of dissolved metal through a boundary layer; C) transport of dissolved metal through the bulk of the melt; D) Reaction [1]. If dissolved CO, takes part in the reaction, three additional steps embodying the dissolution and transport of CO2 must be added. schadinger2 observed, when bubbling CO2 through the melt, that the rate of formation of CO (in the following designated rfco) did not depend on the distance from the metal surface. The results also indicate that the rate of bubbling did not affect the rfco. When passing CO, over the melt, Revazyan7 found that the loss of metal did not depend on the depth of the melt above the metal or on the flow rate of CO2, and concluded that Step A is rate-determining. In an unstirred melt, however, Gjerstad and welch8 found that the rfCo decreased with increasing depth of the melt, indicating that step C was rate-determining. It thus appears that the rate control of the process depends on the experimental conditions, particularly on the convection. In the present measurements the reaction has been studied in unstirred as well as in stirred melts. EXPERIMENTAL AND RESULTS The experiments were carried out at 1000°C in a Kanthal furnace with a 10-cm uniform temperature zone (±0.l°C). The melts were made up of "super purity" aluminum (99.998 pct), hand-picked natural cryolite, and reagent-grade alumina. In experiments where alumina crucibles were used, the alumina content in the melt was close to saturation (13.5 wt pct9); otherwise it was 4 wt pct. Pure Co2 (99.85 pct) was passed over the melt, and the exit gas was analyzed for CO2 and CO by the conventional absorption method.3 From the weighed amount of CO (as CO2) the rfco was calculated as the number of moles of CO formed per min per sq cm of the surface area of the melt. The amount of carbon formed by Reaction [2] was not determined. As already indicated the rfco is much higher than the rfC, by Reaction [2]. Since the rfC probably is proportional to the rfco, the measured rfco should then the proportional to, but slightly lower than, the total rate of Reactions [I] and 121. In general the scatter of results obtained in duplicate measurements was ±5 to 10 pct, while within a given run a precision of ±3 to 5 pct was obtained. The various crucible assemblies that were used will be described below. Measurements in Unstirred Melts. When carrying out aluminum electrolysis in small alumina crucibles. Tuset10 observed that after solidification the lower part of the electrolyte was gray and contained free metal, while the upper part near the anode was white and contained no metal. One may test for the presence of free metal by treating with dilute hydrochlorid acid.

Jan 1, 1969

By R. G. Wayland

SINCE the installation at Kropfmuehl, Bavaria, of a modern flotation concentrator in 1938, the flake and fine graphite from the Passau area can now be delivered in about any normal specified carbon content of any size range up to a flake averaging about 0.7 mm. The graphite finds a wide German and export market for crucible manufacture, pencil leads, dry cells and other uses. A controversy over the origin of the graphite deposits is being resolved in favor of syngenesis rather than epigenesis. The syngenetic theory is newly supported by the yet unpublished work of Hartmann of the Bavarian Geological Survey. Development work and exploration for graphite in the area may be changed in direction as the syngenetic theory is accepted. Crystalline graphite is produced in the area east of Passau near the junction of Germany, Austria and Czechoslovakia, as shown in Fig. 1. This is the only graphite area of importance in Germany, and Gra-phitwerk Kropfmuehl AG is the only operating firm in the area. The plant and mine are located at Kropfmuehl near Hauzenberg, Kreis Wegscheid, about 10 miles east of Passau. A narrow gage railway from the mine connects with the German Railway at Schaibing Bahnhof. The Pfaffenreuth mines date from about 1730. Until the early 20th century mining operations were carried out in a haphazard fashion. During World War I graphite mining and milling was increased, since it had to cover almost all of the crucible needs of the Central Powers. Between the wars some 11 mines were operated by two large and several small companies, but under the Nazis these were consolidated by 1938 into the Kropfmuehl enterprise. Kropfmuehl built a modern flotation mill to treat its own ores and small amounts of custom ores and tailings from the area. Since Graphitwerk Kropfmuehl AG was an I.G. Farbenindustry subsidiary, it has been under Military Government Property Control and probably will be sold to private German capital. Geology The country rock of the graphite area is part of the "kristallines Grundgebirge," the series of old gneissic and schistose rocks that constitutes the bed rock of most of the Bohemian basin and rims the Sudeten-land. The gneissic rocks of the graphite area are considered to have been metamorphosed during the Carboniferous period. They are bordered on the north by granite stocks and penetrated by numerous smaller granite and pegmatitic intrusive rocks, as shown in Fig. 1. The gneiss is classed as a micaceous, coarse-grained cordierite gneiss by most investigators. It is much metamorphosed by the granite, particularly in the north near the larger granite bodies. Interbedded in the gneiss are the graphite seams and lenses, and also beds and lenses of crystalline limestone containing disseminated graphite in noncommercial quantities. The gneiss, together with the included graphite and limestone seams and lenses, is cut and displaced by a number of granite sills of medium to fine grain and by a large number of diorite lamprophyre dikes and a few syenite-pegmatite dikes. The lamprophyre dikes are of various mineral compositions and textures, but many are banded and richly impregnated with pyrite; while the syenite-pegmatite dikes are coarse-grained with good crystals of titanite, pyroxene, uralite and other green amphiboles. Most investigators and the miners speak only of diorite and granite dikes cutting the graphite seams. The diorite dikes are later than the granite and some of the faulting, as is evident from Figs. 1 and 2. Individual graphite seams and lenses may be mined for thicknesses of several feet up to several scores of feet, and for distances of several hundred feet. The aggregate thickness of a series of some 20 seams of graphite, limestone and interbedded gneiss at Kropfmuehl is stratigraphically about 450 ft. Laterally, the graphite in a seam may pinch out or grade into crystalline limestone. Graphite crystals also are found disseminated in the gneiss itself, although in unmineable concentrations. The faults that cut the graphite seams carry graphite for some feet or tens of feet away from the seams, apparently mechanically. Similarily, the graphite lenses themselves often contain mechanically introduced inclusions of wall rock, probably from flowage during folding. Graphite crystals make up 10 to 30 pct of the fresh, mineable graphite lenses at Kropfmuehl, averaging about 20 to 25 pct after hand-sorting by the miners. In weathered lenses, the graphite concentration is said to be as high as 50 pct. The associated primary and hydrothermal minerals are dom-inantly feldspar and calcite, plus quartz, pyrrhotite, pyrite, biotite and occasional garnet, hornblende, sphalerite and galena. Associated secondary minerals include kaolin, nontronite, mangano-oxide-silicates (mog), adularia and chlorite. The superimposed suite of siliceous cementation minerals present consist largely of opal, chloropal, chalcedony, jasper, and hyalite. The kaolin is of special interest since it too was mined as early as 1730 and was used in the well-known Nymphenburg porcelain from 1756 on. The kaolin is derived from the gneiss and the syenite pegmatites. The crystals of graphite vary in size within a given seam, but in seams more than a mile away from the granite on the north the average crystal-linity is less coarse, lowering the commercial value. The lenses in the Kropfmuehl-Pfaffenreuth area are the most developed, and are the only ones with deep workings now accessible. Other similar crystalline graphite lenses are known from older workings at Habersdorf, Oberoetzdorf, Ficht, Diendorf, and

Jan 1, 1952

By Wallace W. Roepke

The Bureau of Mines tested new designs of drag bit cutters with sintered diamond inserts instead of standard tungsten carbide tips. The bits were tested for orthogonal cutting forces, primary dust generation, and incendivity, with a standard plumb-bob type conical cutter (600 included tip angle) as the reference. Preliminary wear and impact-failure testing were also done. The results were mixed. Two new designs had forces similar to those of the reference bit, but one new design had about twice the normal force. This same design had almost twice the specific energy during shallow cutting but generated an equal or slightly lower amount of primary dust than did the reference bit. Incendivity was eliminated for two radial designs. One conical design had ignition only after more than 15 impacts, but the other conical design was incendive. Impact failure occurred, but not so quickly as anticipated. Over 7,500 impacts on a sandstone face, with a total cutting distance of more than 1,981.2 m, only scuffed the leading edge of the sintered diamond cutting face but put hairline cracks in the substrate mounting pad. Additional design and testing are needed to develop an optimum cutter, but prospects look good for this material.

Jan 1, 1983

By Rowe J

The case study is based on the largest ore deposit at Mt. Lyell; the Prince Lyell deposit, comprising a regular lensoid mass of dissemina- ted and vein pyrite-chalcopyrite mineralisation. Reserve estimation employs conventional techniques, based on diamond drill hole and relevant development sampling data. Probable ore reserves are estimated using the contouring (isoline) method an longitudinal projections for ore thickness and accumulation (m %Cu) at a '0.8% Cu' cutoff. Final stope and pillar res- erve estimates (proved ore) are derived from designed ring tonnages and contoured accumula- tion for individual mining units, following more intensive sampling. Systematic grade control procedures have been adopted and individual stopes and pillars reconciled against mill production. The proved ore estimates have been found to com- pare favourably with the reconciled production.

Jan 1, 1979

By J. Chipman, M. N. Dastur

The importance of dissolved oxygen as a principal reagent in the refining of liquid steel and the necessity for its removal in the finishing of many grades have stimulated numerous studies of its chemical behavior in the steel bath. From the thermodynaniic viewpoint the essential data are those which determine the free energy of oxygen in solution as a function of temperature and composition of the molten metal. A number of experimental studies have been reported in recent years from which the free energy of oxygen in iron-oxygen melts can be obtained with a fair degree of accuracy for temperatures not too far from the melting point. Certain discrepancies remain, however, which imply considerable uncertainty at higher temperatures; also several sources of error were recognized in the earlier studies. It has been the object of the experimental work reported in this paper to reexamine these sources of uncertainty and to redetermine the equilibrium condition in the reaction of hydrogen with oxygen dissolved in liquid iron. The reaction and its equilibrium constant are: H2 (g) + Q = H2O (g); K1 _ PH2O / [1] Ph2 X % O Here the underlined symbol Q designates oxygen dissolved in liquid iron. The activity of this dissolved oxygen is known to be directly proportional to its concentrationl,2 and is taken as equal to its weight percent. The closely related reaction of dissolved oxygen with carbon monoxide has also been investigated:3,4,5 co (g) +O = CO?(g); K _ Pco2___ [2] K2= pco X % O [2] The two reactions are related through the wat,er-gas equilibriuni: H2 (g) + CO2 (g) = CO (g) + H2O (g); K2 = PCO X PH2O [3] PH2 X PCO2 and with the aid of the accurately known equilibrium constant of this reaction, it has been shown5 that the experimental data on reactions [1] and 121 are in fairly good, though not exact, agreement. Experimental Method Great care was taken to avoid the principal sources of error of previous studies, namely, gaseous thermal diffusion and temperature measurement. The apparatus was designed to provide controlled preheating of the inlet gases and to permit the addition of an inert gas (argon) in controlled amounts, two measures found to be essential for elimination of thermal diffusion. A known mixture of water vapor and hydrogen was obtained by saturating purified hydrogen with water vapor at controlled temperature. This mixture, with the addition of purified argon, was passed over the surface of a small melt (approximately 70 g) of electrolytic iron in a closed induction furnace. After sufficient time at constant temperature for attainment of equilibrium the melt was cooled and analyzed for oxygen. GAS SYSTEM A schematic diagram of the apparatus is shown in Fig 1. Commercial hydrogen is led through the safety trap T and the flowmeter F. The catalytic chamber C, held at 450°C, was used to convert any oxygen into water-vapor. A by-pass B with stopcocks was provided so that the hydrogen could be introduced directly from the tank to the furnace when desired. From the catalytic chamber the gas passed through a water bath W, kept at the desired temperature by an auxiliary heating unit, so that the gas was burdened with approximately the proper amount of water vapor before it was introdvced into the saturator S. All connections beyond the catalytic chamber were of all-glass construction. Those connections beyond the water bath were heated to above 80°C to prevent the condensation of water vapor. After the saturator, purified argon was led into the steam-hydrogen line at J, and finally the ternary mixture was introduced into the furnace. THE SATURATOR The saturator unit comprised three glass chambers, as shown in Fig 1, the first two chambers packed with glass beads and partially filed with water and the third empty. Each tower had a glass tube with a stopper attached for the purpose of adjusting the amount of water in it. The unit was immersed in a large oil bath, which was automatically controlled with the help of a thermostat relay to constant temperature, ± 0.05ºC, using thermometers which had been calibrated against a standard platinum resistance thermometer. The performance of the saturator over the range of experimental conditions was checked by weighing the water absorbed from a measured volume of hydrogen; the observed ratio was always within 0.5 pct of theoretical.

Jan 1, 1950

By Charles H. Foreman

This paper describing the mining practice of the Hecla and Star mines, both located at Burke, Idaho, is one of a series being prepared by the Bureau of Mines on mining practices, methods, and costs in the various mining districts of the United States. It is partly a revision of articles by the author appearing in volume 72 of the Transactions of the American Institute of Mining Engineers, published in 1925, and in the June 1928, issue of the American Mining Congress Journal. About 26,000 tons per month of lead ore is produced at the Hecla mine. Costs at the mine are given for the year 1928. Stoping operations in the Star mine have covered such a short period, during which time the abnormal expenses of starting were incurred, that they are not given in this paper.

Jan 1, 1930

By L. Xu, N. I. Jayaraman, R. Bhaskar

The objective of this study is to develop a better understanding of the collection characteristics of dust measurement instruments used in mine dust control research with respect to properties of quartz and coal dust. Coal and quartz dust of narrow sues, with aerodynamic median diameters being approximately 2 µm, 4 µm and 10 µm, with quartz contents of l0%, 20%, 30%, 40% and 50%, were released in an aerosol characterization chamber using a fluidized bed aerosol generator. Dust was collected in MSA personal gravimetric samplers with l0-mm nylon cyclones, total dust samplers and Sierra 298 inertial cascade impactors. The samples were analyzed for mass and quartz content. A total of 21 experiments were performed for this study. The mass and quartz collection efficiencies of the total and respirable dust samplers and the impactor were determined. The data show that the amount of dust collected by the respirable dust sampler (respirable + oversize dust trapped in the cyclone pre-classifier) was, in general, less than the amount collected by the total dust sampler. The amount of dust collected by the impactor was higher than that collected by the total dust sampler. Quartz analyses of the airborne dust samples showed that the total dust and respirable dust samplers (including oversize dust) collect less quartz dust than at inertial impactor. The larger the median particle sire of the quartz and coal mixture, the lower the quart content of the dust collected in the samplers. For all three sires, the impactor was a better collector of quartz than the other instruments.

Jan 1, 1994