Search Documents

By G. W. Cullen

Niobium-tin has been prepared on insulating suhstrates hby simultaneous hydrogen reduction of gaseous niobium and tin halides. Stoichiometric material is greater than 98.8pct theoretical density, appears to he single-phase, and has a total impirity level less than 0.3 at. pct. Transition temperatures and lattice constants may he related to composition. Typical current densities in various fields and orientations are given. IT is known that Nb3Sn carries large current densities in high fields, 1 and exhibits an unusually high transition temperature2 and critical field.3 For these reasons high-field solenoids have been constructed of this material.4 Because of the emphasis on solenoid fabrication, much of the materials research has been directed toward development of wire geometries wherein the brittle Nb3Sn is supported by a more malleable metal or alloy. There are, however, basic studies and applications that can be carried out only on Nb3Sn supported by an insulator. Insulating substrates are desirable for a number of reasons: the substrate does not interact with applied or induced currents and fields; diffusion of metallic species into the de- posit is avoided, both during the preparation and during subsequent heat treatment; irradiated samples are not more active than the deposit itself. Unsupported Nb3Sn geometries may also be prepared by preferential chemical dissolution of the insulating substrate. This report describes the preparation and properties of Nb3Sn deposits on ceramic substrates. Experiments currently utilizing material prepared in the manner described in this report include the following: dependence of current-carrying properties on field strength and orientation 5,6 radiation damage,7,8 tunneling,9 thermal conductivity (substrate removed),1° microwave surface impedance," tube magnetization,6,12 resistivity as a function of temperature,13 and current density and transition temperature as a function of annealing.14 Possible practical applications include magnetic shielding, superconductor generators, and frictionless bearings. PREPARATION Methods for the deposition of elemental niobium and tin by hydrogen reduction of the gaseous metal halides have been known for some time,15,18 but only recently a procedure was developed in this laboratory17 for the codeposition of these two metals on a hotwire as the intermetallic compound, Nb3Sn. This method of simultaneous hydrogen reduction of the gaseous niobium and tin chlorides is used for the preparation of Nb3Sn On ceramic substrates. The procedure differs from that employed on a hot wire in that insulating substrates cannot conveniently be heated to temperatures greater than their surround-

Jan 1, 1964

By R. T. Gallagher, C. G. Brennecke

This paper is the result of a research program entered into cooperatively by the General Reinsurance Corporation and Lehigh University in January 1944. The research program was instituted to find a more positive method to determine the presence of hazardous roof conditions in mining operations. The co-authors, together with Mr. R. D. Currie, Engineer for the General Reinsurance Corporation, started working on the project in January 1944, first undertaking a library search; second, a preliminary study based on some existing equipment; third, the design of new and more suitable equipment; and finally, the field testing of equipment and methods. PURPOSE Any study of the accident statistics of mining operations will disclose the rather startling fact that approximately 50 to 60 per cent of all fatal underground accidents in the anthracite and bituminous mines are caused by falls of roof and coal, the metal and nonmetal mines showing only a slightly smaller percentage. Advancements in safety engineering have produced definite results in the decrease of accidents due to blasting, haulage, electricity, and explosions but no such decrease is shown in those caused by falls

Jan 1, 1946

By S. F. Emmons

This mine is situated upon the western slope of the Meadow Valley mountains, about 70 miles by road from the present end of the railroad-track, which is at Uvada, on the UtahNevada boundary. This boundary-line marks fairly well a certain change in type of scenery from western Utah to eastern Nevada,—from a region in which the desert valleys predominate over the mountain ranges to one in which they are in about equal proportion. The railroad from Salt Lake City runs somewhat W. of S., for the most part along the bottom of the ancient Lake Bonneville. The latter part of its present course follows the axis of the southern arm or bay of that lake, now known as the Escalante desert. Along this bay, its line is a mathematically straight one, with no perceptible change of level for two " tangents " of more than 30 miles each, varying but a few degrees in direction. In the four or five hours re-

Jan 1, 1902

By E. F. Bailey, L. S. Birks

The effect of stress on the austenite to ferrite transformation in carbon steel was studied by X-ray diffraction techniques. Tensile stress was found to cause reorienta-tion of austenite above the transformation temperature, to accelerate equilibrium conditions at the transformation temperature, and to cause precipitation of large carbides at a critical value of stress. IN the past, a number of papers' have discussed the effect of stress on the austenite to martensite transformation at relatively low temperatures. In general, it has been shown that tensile stress induces some transformation at a given temperature, while compressive stress retards the transformation. Very little work has been reported on the effect of stress on the transformation from austenite to ferrite plus carbide near the A, point in steel. One of the few papers in the literature2 reports an increase in A1 of about 1°C in pearlitic steel upon the application of tensile stress. In this paper, the effect of tensile stress on eutec-toid steel at, and above, the A, point was studied in

Jan 1, 1956

[NORTH AMERICA UNITED STATES ALABAMA Birmingham Cord, Richard H. Dlsmukes, Edward B. Hunter, Robert A. Citronelle Perrin, Huey P. Fairfield Pagel, Herbert Ervin Fairhope Ruffles, William R. Huntsville Eng, Harvard Kelley, Dean W. Waggoner, J. B. Weber, Thomas C. Mobile Hankins, James D. Horner, William L. Petroutson, Peter C. University Cudworth, James R. Jones, Walter B. Mason, William L.]

Jan 1, 1961

By A. G. H. Anderson, Eric R. Jette

During the period from 1910 to 1920, there was a lively interest in the subject of grain growth and many papers were published, followed by interesting discussions. Questions dealing with the fundamentals of grain growth—why and how it occurs—were treated in papers by Howe,' .Jeffries,² Sauveur,² Chappell,4 Beilby,5 Mathewson and Phillips,6 Mc Adam,7 Carpenter and Elam,8 Stead and Carpenter,9 Ruder,l0 as well as others. Since that decade, much indeed has been done regarding the practical control of grain size, and it is now possible to order material having a size sperified in the American Society for Testing Materials classification. Also, one hears the term "spliced boundaries" used in connection with certain tungsten lamp filamentsl1 wherein it is important to prevent "sagging" between consecutive turns of the helix.12 This practical use of a certain knowledge as to the things that influence or even control grain growth should not be taken as an indication that the subject has been thoroughly explored and that nothing more can be learned from fundamental studies. It is with this thought in mind that a report of some observations and experiments on abnormal grain growth is believed justified. Abnormal grain growth is met with in heat-treating high-carbon steels in the austenitic range,'? in the hardening treatments of high-speed steels,14'15 and in the low-temperature annealing of strained low-carbon steels as in sheet and wire material. Entirely aside from these instances of exaggerated grain growth, which some might consider as freakish, it is thought that abnormal growth is simply a case where the growth forces and the forces tending to prevent growth are almost, but not quite, evenly balanced. Information relative to grain-growth characteristics in general may be obtained from a study of abnormal growth conditions, which may be looked upon as vantage points. Reflection will show at once that if growth forces are great in comparison to inertia or resistance to growth, many crystals start to grow and, for that reason, none becomes very large, whereas if inertia is

Jan 1, 1938

By Eric R. Jette, A. G. H. Anderson

During the period from 1910 to 1920, there was a lively interest in the subject of grain growth and many papers were published, followed by interesting discussions. Questions dealing with the fundamentals of grain growth—why and how it occurs—were treated in papers by Howe,' .Jeffries,² Sauveur,² Chappell,4 Beilby,5 Mathewson and Phillips,6 Mc Adam,7 Carpenter and Elam,8 Stead and Carpenter,9 Ruder,l0 as well as others. Since that decade, much indeed has been done regarding the practical control of grain size, and it is now possible to order material having a size sperified in the American Society for Testing Materials classification. Also, one hears the term "spliced boundaries" used in connection with certain tungsten lamp filamentsl1 wherein it is important to prevent "sagging" between consecutive turns of the helix.12 This practical use of a certain knowledge as to the things that influence or even control grain growth should not be taken as an indication that the subject has been thoroughly explored and that nothing more can be learned from fundamental studies. It is with this thought in mind that a report of some observations and experiments on abnormal grain growth is believed justified. Abnormal grain growth is met with in heat-treating high-carbon steels in the austenitic range,'? in the hardening treatments of high-speed steels,14'15 and in the low-temperature annealing of strained low-carbon steels as in sheet and wire material. Entirely aside from these instances of exaggerated grain growth, which some might consider as freakish, it is thought that abnormal growth is simply a case where the growth forces and the forces tending to prevent growth are almost, but not quite, evenly balanced. Information relative to grain-growth characteristics in general may be obtained from a study of abnormal growth conditions, which may be looked upon as vantage points. Reflection will show at once that if growth forces are great in comparison to inertia or resistance to growth, many crystals start to grow and, for that reason, none becomes very large, whereas if inertia is

Jan 1, 1938

By R. N. Woody, S. J. Work

Crushing development at Duval Corp.'s Sierrita concentrator in Sahuarita, Ariz., has been a continuing effort since plant startup in January 1970. The original crushing system was designed to produce 65 000 t/d (72,000 stpd) of ore. However, in the summer of 1970 the Sierrita plant was averaging only 43 000 t/d (47,000 stpd) due to coarser than expected secondary crushing plant feed, lower than design crusher operating availability, and inability to achieve design tertiary crusher power draught at an acceptable hydraulic support pressure.

Jan 4, 1979

By E. P. Pfleider, D. H. Yardley

Layers of magnetic taconite of above average magnetic iron content extend down dip on the Mesabi Range to depths beyond the reach of open pit mining. A selected layer with thickness of 75 to 100 ft underlies many square miles. Such a selected layer can provide over 50 million tons of recoverable concentratc per square mile, at lower concentration ratios than in the present open pit taconite operations. The system contemplated would consist of large scale underground quarrying by a lane and pillar method. Working heights would be 60 to 100 ft; room widths, 50 to 75 ft; and productivity targets, about 40 tons per man-shift. The most critical problems would he roof control and blasthole drilling. The successful operation of large open pits and concentrating plants for treatment of magnetic taconites indicates that the basic techniques and economic problems of pellet production have been solved. The open pit reserves are large, but they are not necessarily available in sufficient quantity or quality to provide an adequate raw materials base for all potential producers. Furthermore, as the more easily available open pit crudes are used up, the pits will become deeper, stripping costs per ton of concentrate will increase, and recoveries will decrease as leaner crudes are utilized. The time will come when supplementary and replacement reserves of magnetic taconite will be required. One way these can be obtained is by underground mining of the down-dip extension of the Mesabi magnetic taconites, especially those layers averaging well over 25% recoverable iron. A key point in such a proposal is the possibility of realizing substantial savings by beneficiating an ore of 30% magnetic iron at 2.5 to 1 ratio of concentration. This contrasts with current practice in Mesabi commercial taconite plants, where the ore averages 22 to 25% magnetic Fe, with concentration ratios of about 3.0 when producing 61% Fe pellets. Two factors which favor the eventual development of underground taconite mining are: 1) the desirable physical structure and high grade of taconite pellets in general and 2) the improved engineering techniques in underground mining. Experience in large scale room and pillar mines demonstrates that, given strong rock strata immediately above a high grade mining

Jan 1, 1963

By William E. Greenawalt

Ever since electrolytic copper refining gave promise of success, about a half century ago, efforts have been made to apply the idea to the extraction of copper from its ores. The methods of attack have, usually, been to leach with a dilute acid and then to deposit electrolytically the copper from the resulting solution with the simultaneous regeneration of the solvent used in the process. Many efforts have been made, and many patents have been taken out, both in the United States and abroad, to give this idea practical application, but only within the past few years have the difficulties been surmounted. Leaching and electrolysis, as applied to copper ores, are among the most promising fields in modern metallurgy. New conditions are arising, which will bring the wet methods into prominence; while high freight rates and increasing cost of fuel will tend to limit smelting to highly favored localities. The possibilities offered by the installation of hydroelectric plants and the greatly enlarged range of power transmission will greatly widen the field of electrolytic methods. Electrolytic methods are ideally adapted to hydroelectric development, for the load is constant throughout the full twenty-four hours, and the cost of both installation and operation of hydroelectric plants is not appreciably greater when operating for twenty-four hours than when operating for eight or ten hours; whereas, in fuel-power generation, as also in smelting, the cost is more or less in proportion to the fuel and power used. Nevertheless, fuel-power generation presents advantages in electrolytic methods, as the power plant may be located in a favorable place while the leaching and electrolytic plants may be located at the mine. The ultimate possibilities of the wet methods have yet to be determined. The possibilities of smelting have been thoroughly worked out; there is no unsolved major problem in copper smelting, and it has practically reached the limit of its possibilities. It seems hardly probable that any future improvement, either of method or apparatus, will greatly

Jan 1, 1924

By R. R. Estill

THE rank of the Ruhr coal ranges from a high volatile bituminous coal to an anthracite, depending to some extent on the original depth of the seam. The average Ruhr coal corresponds to a soft bituminous American coal of a coking quality. The average thicknesses of individual coal seams being mined are also comparable (59 in. against 65 in. in the United States). However, consideration of seam conditions and mining conditions other than those just mentioned emphasizes differences rather than similarities with United States soft coal. In general, the Ruhr seams now being mined are much more folded and inclined than American seams. Dips of 20" and 30" are common in seams now being worked, and 30 pct of the coal reserves in the district are in seams dipping more than 35". Only on the tops and bottoms of folds do we find rather flat coal seams. In addition to the folding there is extensive displacement by cross faulting plus a certain amount of strike faulting of an overthrust nature, which results locally in doubling or omission of seams. Because of the long history of mining in the Ruhr, nearly all coal lying near the surface has long since been mined out, and we find that the average depth of mining is at present about 2300 ft below the surface. Deep mining, folding, and faulting result in seam conditions requiring a great deal more roof support than one finds in American soft coal mines. In fact only in the anthracite district and the Rocky Mountain and Pacific coal fields do we find somewhat similar conditions. It is easy to say, therefore, that the problem of mechanization of coal cutting and loading in the German mines is quite different from that which we have so effectively met in America with our mobile cutters and loaders, duck bill loaders, and a room and pillar system of mining our drift and slope mines.

Jan 12, 1950

By Charles Fettke

IN THE present day manufacture of glass nearly pure quartz sands are used almost exclusively as the source of the silica, which is the major constituent of all common varieties of glass. Ordinary soda-lime, such as bottle, common tableware, plate, and window glasses, contain from 65 to 75 per cent. of silica. OCCURRENCE Glass sands occur in nature either in the form of loose, unconsolidated sediments or in deposits in which the individual grains have been more or less thoroughly bound together by some cementing agent so as to form sandstones. While deposits of sand and sandstones occur both widely and abundantly distributed, deposits that are sufficiently free from other constituents than quartz grains, so that they can be employed in the manufacture of the better grades of glass, are, comparatively speaking, of rare occurrence. The major portion of the glass sand produced in the United States comes from sandstones. In order to be suitable for glass sand, they should be rather friable. The rock should break down readily along the cementing material between the grains and should not break across the grains rather than along the bond. Some of the sandstones used are so friable that only light shots of slow-burning dynamite are necessary to disintegrate them sufficiently for hydraulic mining, while others have to be passed through crushers in order to disintegrate the rock into its individual grains.

Jan 2, 1926

By R. A. Harrington

THE structure of anodic films formed on aluminum and other metals under varied conditions is not well known despite the wide use of such films both as protective coatings and as the dielectric medium in elec-trolytic condensers. The present work was undertaken as a survey of the possibilities of electron diffraction in the investigation of anodic films, especially in comparing the properties of anodic films formed under dif-ferent sets of conditions and subjected to various subsequent treatments. In addition, an effort has been made to compare surface films formed on aluminum by anodic treatment with surface films formed by heating, immersion in chemicals, etc, The electron diffraction method in many cases has been successfully applied to the study of thin surface films. Its principal advantage is that it can be used without removing the films from the base material upon which they have been formed. The low penetrating power of electrons, in the "reflection" diffraction method which has been used in this work, prevents the appearance of diffraction patterns from substances at depths greater than about 100 Angstrom units (10-6 cm.). Different investigations of the structure of anodic films have shown widely varying results, depending on the methods used in preparing the films. Apparently under some conditions these films are crystalline and under other conditions they are amorphous, and it has been difficult to say which type of structure will be found in any particular case. Schmid and Wassermann's' X-ray diffraction patterns of eloxal? films show two broad, diffuse bands, which these investigators attribute to finely divided cubic y-Al2O3-§ Burgers, Claassen, and Zernicke3 obtained sharp X-ray

Jan 1, 1940

By Jacques Steininger, Robert E. England

Single crystals of ZnTe and ZnTe1-,Sex with x up to 0.13 have been grown from the elements by temperature gradient solution zoning using excess tellurium as a solvent. Best results have been obtained with charges with the compositions 45/55 at. pct Zn, Te, for ZnTe and increasing amounts of selenium for ZnTe1-xSex. The temperature in the molten zone was maintained at about 1070°C with a gradient of about 10°C per cm. Chemical analyses of quenched ZnTe ingots show tellurium concentrations in the molten zone as high as 70 pct with concentration differences across the zone of 1 to 2 at. pct Dark dots which are observed by transmitted light microscopy in as-grown crystals can be removed by annealing in zinc vapor at 900 C. INTEREST in wide band gap semiconductors has led to a new study of ZnTe and ZnTel-xSex crystal growth. ZnTe is the only II-VI compound with a wide band gap (2.3 ev) that can be made p type with low resistivity. Attempts to make it n type with low enough resistivity to be useful for p-n junctions have so far been unsuccessful.1 ZnSe has a band gap of 2.65 ev but can be made n type only. However, ZnTel-xSex solid solutions with x as low as 0.36 have been made both highly n and p type2 with a minimum band gap around 2.12 ev3 at room temperature and appear to hold the best promise for efficient injection electroluminescence in the visible. ZnTe has the lowest melting point of the zinc chal-cogenides (1295°C) and consequently attempts have been made to grow crystals from both the liquid and the vapor phase.4 Complicated apparatus is required for growth from stoichiometric melts because of the high vapor pressures of the elements at the melting point of ZnTe and because of the problem of quartz devitrification. Small crystals have thus been grown in high-pressure equipment by Fischer5 and by Narita et a1.6 with pressures of the order of 50 atm of argon to prevent excessive evaporation from the melt. Large crystals of ZnTe can be obtained by growth from the vapor phase4 but they often present numerous dislocations and inclusions. An improvement in the quality of vapor- grown ZnTe crystals was reported by Albers and Aten7 by equilibration of mixtures of small crystals with compositions lying on either side of the solid single-phase field at fixed temperature. The same technique was later applied by Aten8 to the growth of ZnTe1-xSex crystals with less than 1 pct inhomo-geneity. Because of the higher liquidus temperatures of the solid solutions and the high vapor pressure of selenium, previous attempts to grow ZnTel-xSex from the melt have been limited and unsuccessful.9 The phase diagram of the Zn- Te system is reproduced in Fig. 1, based on data from Kobayashi10 and Kulwicki.11 Carides and Fishher12 have reported lower liquidus temperatures on the tellurium-rich side, but their data would require confirmation. The liquidus temperature on the tellurium-rich side decreases rapidly with increasing tellurium concentration and the Te2 vapor pressure over the liquidus also decreases accordingly.'3 The decrease in liquidus temperature and vapor pressure therefore makes it possible to use conventional apparatus if there is a sufficient excess of tellurium in the melt. Single crystals of ZnTe have thus been grown by Kucza,14 in a modified Bridgman technique, from solutions containing up to 60 at. pct of Te by lowering unsupported quartz ampoules through a temperature gradient at about 1200°C. Under these conditions, the phase diagram indicates that the entire charge is initially molten. Crystal growth can therefore proceed by normal freezing and rejection of excess tellurium into the melt. The modified Bridgman technique has several major limitations. Because of the rejection of excess tellurium into the melt during freezing, the melt composition and the temperature at the growth interface vary continuously. They tend to follow the liquidus until the eutectic which is very close to pure tellurium (447°C, >99 pct Te). Since the solidus composition also varies with temperature,15 crystals grown by this method are inhomogeneous. They present small variations from stoichiometry which may affect their structure and physical properties. The simultaneous increase in tellurium content and decrease in melt temperature also combine to reduce the rate of diffusion of tellurium away from the growth interface, thereby causing constitutional supercooling and possibly dendritic growth. To minimize these effects, the initial melt composition is in practice kept relatively close to stoichiometry (less than 60 pct Te). This however limits the possibilities of operating at low temperatures and pressures. This paper describes a modified method of crystal growth by temperature gradient solution zoning (TGSZ) which is an adaptation of the temperature gradient zone-melting technique developed by pfann16 and of the traveling solvent method of Mlavsky and weinstein.I7 The TGSZ method now applied to the growth of ZnTe and ZnTel-xSex crystals is characterized by its very simple experimental arrangement and sample preparation technique. Unlike the modified Bridgman technique, there is no increase in the tellurium concentration in the melt and therefore it is possible to operate at lower temperatures and pressures. This method is also suitable for maintaining a constant temperature at the growth interface.

Jan 1, 1969

For the US coal industry, 1978 was a nightmarish recurrence of 1977 as the United Mine Workers strike cut into production during the first three months of 1978, followed by the strike against the Norfolk and Western Railway during the summer and early autumn. Coking coal production was floored by the one-two punch of environmental constraints on US coke ovens and competition from low-cost, high-quality imports. At the same time, US ex orts of coal fell to their lowest level since 1962. And in the face of all of this, steam coal consumption was sluggish as utilities burned huge amounts of oil to conserve coal stockpiles during the UMW strike. This was followed by decreased electrical demands due to mild summer weather in many parts of the country and dramatically improved availability of hydroelectric power.

Jan 5, 1979

By Paul A. Farrar, Harold Margolin

The system Ti-Cr has been re investigated From 40 to 100 pct Cr. The high-temperature modification of TiCr, was found to exist in the temperature range from 1365 where it terminates in the eutectoid reaction TiCr,(TI)* — HE chromium-rich region of the Ti-Cr system was investigated by Vogel and Wenderott,' Mc Quillan,' Van Thyne et dl.,' and Cuff Duwez and Taylor determined the crystal structure of the low-temeperature modification of TiCr, to be fcc a = 6.943A and Levinger' discovered the existence of a second (high-temperature) modification of TiCr, and determited its crystal structure to be hexagonal a = 4.932A, c/a = 1.617i. No information was obtained as to the temperature range over which each modification of TiCr? existed; therefore the present investigation was initiated. I) Experimental Techniques Alloys employed for the delination of this system were prepared from iodide titanium and high-purity chromium. The purity of these materials is as follows: Iodide titanium: purity 99.99 pct; major impurities—carbon 0.0001 pct; oxygen 0 to 0.002 pct; nitrogen 0 to 0.002 pct; silicon 0 to 0.005 pct; manganese 0.001 pct; copper 0.001 pct (Foote Mineral Co., Lot 609-29). Chromium #1: metallic purity 99.997 min.; interstitial content—oxygen 0.27 to 0.46 pct; hydrogen 0.028 to 0.038 pct; nitrogen 0.0002 pct (Ave-quipo Inc.). Chromium #2: purity 99.9 pct; major impurities—carbon 0.01 pct; oxygen 0.013 pct; nitrogen 0.02 pct; silicon 0.01 pct; sulfur 0.03 pct; iron 0.01 pct (Fulmer Research Institute Ltd.). A total of sixteen alloys of thirteen different compositions was prepared in the range from 40 to 95' *All percentages are given in weight percent. pct Cr. The compositions of the alloys prepared were as follows: Ti-40, 45, 50, 60, 62, 64, 66, 68, 70, 80, 85, 90, and 95 pct Cr. Two buttons were prepared of the 66, 90, and 95 pct Cr alloys. The 40 pct Cr and one of the 66 pct Cr alloys were prepared from the chromium # 2. All the other alloys were prepared from chromium #1. The alloys were arc-melted as 25-g buttons in a copper-hearth glass-walled furnace7 under an inert atmosphere of high-purity helium. The alloys were sintered at 250 amp and melted twice at 350 amp for 30 sec with the buttons being turned over between melts. Weight losses during melting were determined and in the range 45 to 68 pct Cr they were found, in all cases, to be less than 1.25 pct of the total alloy weight. A number of the high-chromium alloys shattered during cooling from either the first or second melt, which made the weight loss considerably larger than usual. The 70 and 80 pct alloys lost approximately 5.7 pct of their total weight, the 85 pct alloys 1.5 pct, the 90 pct alloy 2 pct, and the 95 pct alloy 3 pct. However, it is felt that the actual composition of the alloys in this region is probably within approximately 1 pct of the intended composition, as a large portion of the material lost was that due to shattering after melting. Nominal compositions were therefore used in plotting data and referring to the alloys. The alloys were cut into specimens, wrapped in molybdenum sheet, and encapsuled in argon-filled quartz or Vycor tubes for heat treatment. The heat-treatment times and temperatures are given in Table I. The specimens were quenched in iced brine (I.B.Q.) following heat treatment. The standard techniques of grinding, polishing., and etching were used in preparing the specimens for metallo-graphic examination. For alloys below 68 pct Cr

Jan 1, 1963

By D. G. F. Hedley, S. N. Muppalaneni, J. W. Roxburgh

A stope and pillar method is used to mine the gently-dipping uranium bearing reefs, to a depth of 1000 m, at Elliot Lake, Ontario. A few isolated rockbursts have been reported in the 11 mines in the area during the first twenty-five years of operation. However, in March 1982 a series of rockbursts were initiated in the old mined-out workings at the Quirke Mine of Rio Algom Ltd. Detailed records of pillar deterioration and size of the affected area were kept both prior and subsequent to the occurrence. Seismic instrumentation was installed before and convergence stations shortly after the start of bursting. Observations indicate that the squat pillars failed violently where- as the slender pillars exhibit a less violent failure mechanism. Floor cracks and heaving are common, but the massive quartzite hanging wall strata is relatively undamaged although some roof falls have occurred due to local structure. The microseismic system accurately locates seismic events to f 20 m within the geophone array and it has been found that an accelerating convergence rate coincides with and in some cases precedes an increase in seismic activity. Displacement discontinuity and boundary element computer models have been used to estimate pillar stresses and areas of high stress concentration in an effort to determine the causes of rockbursts. Mine and pillar stiffness and energy balance concepts are used to explain cases of gradual and sudden pillar failures at Quirke Mine.

Jan 1, 1984

By Walter Knox, J. D. Doherty

IN 1939, at the request of The Koppers Coal Co., the Koppers Company Research Department established a Stoker Coal Research Laboratory for the purpose of investigating the performance characteristics of stoker coals in typical domestic stoker installations. Fig. I is a photograph of part of the laboratory. The material in this paper deals with the performance of one coal in a single installation. Presented are details of this installation, mechanical characteristics of the stoker, and the results of a series of burning tests in which adjustments were systematically varied. SUMMARY OF RESULTS Mechanical Features I. A large percentage of the total power consumed by a domestic stoker is used to operate the gear case and motor (Fig. 3). 2. The power consumption per ton goes down with an increase in rate of coal feed (Fig. 4). 3. The automatic air control in this stoker showed advantages over manual control (Fig. 5). 4. The air velocities through the retort tuyeres were uniform around the retort, but varied between the rows of tuyere rings (Fig. 6). 5. The crushing of coal with this stoker increased the minus 1/8-in. from 1 1.6 per cent to 19.2 per cent. There was a noticeable segregation of coal as it came from the retort and distribution was not uniform (Fig. 7). 6. Measurement of air entering over the fire showed that with some not uncommon adjustments this air may he a high percentage of the total air supply (Fig. 8 and Table I). Operating Performance I. The removal of clinker was shown to give a period of poor performance characterized by a high fuel-bed resistance and a high percentage of carbon monoxide in the flue gases (Fig. 10). 2. The fuel-bed resistance was found to decrease as the fuel bed built up in a normal response to heat demand after a prolonged hold-fire (Fig. II). 3. With intermittent operation the burning rate was almost always less than the feeding rate. The wide variations were found to be greatly dependent upon the length of the On period and the length of the intervals between On periods (Fig. 12). 4. The maintenance of a low furnace draft led to less fly ash, better clinker formation, and higher efficiencies (Fig. I3). 5. The maintenance of a minimum of excess air also resulted in less fly ash, better clinker formation, and higher efficiencies (Fig. 14). GUIDING PRINCIPLES In planning the investigations, the following principles were adopted: Selection of Healing Equipment.-Use only standard models of stokers and furnaces representative of those widely used.

Jan 1, 1942

By J. B. Newsom

IN the September 1936 issue of MINING AND METALLURGY the pioneer work of boring a 5-ft. shaft to a depth of 1125 ft. at the Idaho Maryland mine in California was described. Later, a Bureau of Mines Information Circular (No. 6923) gave additional data. In re¬cent months still further progress has been made in this technique through the sinking of a 5 1/2-ft. shaft for Pickands, Mather & Co. at their Zenith mine, Ely, Minn. The present work was done with new carefully designed equipment and several experienced men so that progress, as shown below has been much better:

Jan 1, 1938

By William L. Fink, H. R. Freche

The constitution of the aluminum-cobalt alloys has been the subject of relatively few investigations. Brunckl analyzed the residue which remained after treating the 17 per cent cobalt alloy with dilute hydrochloric acid. The results of the analyses indicated the existence of a compound Co3Al13. Guillet2 published a liquidus for the aluminum-cobalt system which contained two maxima corresponding to CoA16 and CoAl2 and two eutectic points at 30 and 74 per cent Co. The most extensive investigation of the system was carried out by Gwyer13 whose results are summarized in Fig. 1. It will be noted that at the aluminum end there is a suppressed eutectic at 644' C. By extrapolation of the duration of the eutectic arrest to zero, the composition of the compound was placed at Co3Al13. Another thermal arrest was noted at 550" C., which Gwyer attributed to a peritectic reaction. The present investigation of the aluminum end of the aluminum-cobalt system is the eleventh of a series dealing with the constitution of aluminum-rich alloys prepared from electrolytically refined a1uminum.l Preparation of Alloys.—The alloys used in this work were all prepared from electrolytically refined aluminum, the analysis of which is shown in Table 1. In preparing some of the alloys, metallic cobalt (98 to 99 per cent) was used either directly or in the form of an intermediate alloy, the composition of which is given in Table 1. In order to obtain alloys of higher purity, cobalt was introduced into some of the alloys by means of chemically pure cobaltous chloride which was readily reduced by the aluminum. A small electric furnace with nickel-chromium heating elements was used in the preparation of the alloys. Chemical Analysis.—An analysis sample from each melt was chill-cast in the form of a plate 3/16 in. thick. In all cases the casting temperature was well above the liquidus. Cobalt was determined electrolytically in all alloys containing more than 0.05 per cent cobalt and by the nitroso-

Jan 1, 1932