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By R. C. Ku, A. J. McEvily, T. L. Johnston

The microplastic response of a series ofas-quenched Fe-Ni-C martensites has been measured at 77°K. At strains less than JO'3 the flow stress is governed primarily by the transformation-induced dislocation structure of the martensite. Only at strains in excess of 10-3 is the influence of carbon manifested in the flow stress. At these macroscopic strains, typically 10-2, the solid-solution hardening is proportional to (wt pct C)1/3, and, in an alloy containing 0.39 wt pct C, amounts to 50 pct of the flow stress. THE technological significance of high-strength ferrous martensite has stimulated many investigations of its structure and properties. Although our knowledge of the characteristics of martensite has increased immensely, especially with the advent of high-resolution techniques, an understanding of the basic strengthening mechanism still remains elusive. The purpose of the present paper is to consider certain aspects of micro-plastic behavior of Fe-Ni-C martensite which we feel can help to resolve this important problem. Such alloys are particularly suitable for experimental investigation because their compositions can be adjusted to reduce the M, to a temperature low enough essentially to eliminate the diffusion of carbon in the freshly formed martensite.1 The mechanical properties in this condition are of interest inasmuch as they reflect a state that is free of the important but complicating influence of precipitation processes. In this virgin martensite the carbon is distributed as it was inherited from the parent austenite; i.e., it is present interstitially, and gives rise to tetragonality through strain-induced ordering.' In order to determine the source of strength of such alloys, Winchell and Cohen1 investigated the low-temperature macroscopic stress-strain behavior of a series of virgin martensites of increasing carbon content but of common M, temperature (-35°C). They found that the flow stress increased rapidly with carbon content up to 0.4 wt pct; beyond this point the flow stress increased at a much slower rate. It was concluded that martensite is inherently strong. To account quantitatively for the strength of virgin or as- quenched martensite in terms of the role of carbon, Winchell and cohen3 suggested that the carbon atoms, trapped in their original positions by the diffusionless martensite transformation, interfere with dislocation motion according to a model akin to that of Mott and Nabarro. 4 In this treatment, individual carbon atoms are considered to constitute centers of elastic strain and thereby generate an average stress resisting the motion of dislocations throughout the lattice. The additional stress necessary to move dislocations, over and above that necessary for motion in a carbon-free martensite, is given by where L is an effective length of dislocation capable of motion. L was assumed to be limited to the spacing between the twins that are an essential structural element of Fe-Ni-C martensites. They assumtd the spacing to be invariant and of the order of 100A. However, recent work5 has shown that L is variable and can be in excess of 1000Å, so that the assignment of an appropriate value of L is not straightforward. In contrast to the above conclusion that there is an intrinsically high resistance to plastic flow, it has been suggested by Polakowski6 that freshly quenched martensite is in fact "soft" in the sense that dislocations are initially free to move upon application of stress. The high indentation hardness and macroscopic yield stress of ferrous martensites are then a consequence of rapid strain hardening that depends upon carbon in solution. Consistent with this point of view are the results of Beau lieu and Dubé who measured the rate of recovery of internal friction as a function of aging (tempering) temperature in a freshly quenched steel containing 0.90 wt pct C, 0.37 wt pct Mn, 0.1 wt pct Cr, and 0.07 wt pct Ni. The kinetics were clearly consistent with the idea that many dislocations are unpinned in the as-quenched state and that during aging they become progressively pinned by carbon at a rate controlled by carbon diffusion in the body-centered martensite lattice. In order to provide a basis upon which to distinguish between the "hard" and "soft" interpretations indicated above, we have made studies of the initial stages of plastic deformation in Fe-Ni-C martensites similar to those'used by Winchell and Cohen. It will be shown that the results support the contention that dislocation segments in as-quenched material are indeed

Jan 1, 1967

By Daniel E. Sullivan

The recession of 1974 continued into 1975. Real gross national product (GNP), measured in 1972 dollars, declined significantly in the first quarter of 1975 but rose slightly in the second and increased sharply in the third quarter. Unemployment peaked during the second quarter and then declined slowly for the balance of the year. The inflation rate declined owing to reduced demand and smaller-than-1974 increases in energy and food prices early in the year. Recovery was clearly evident by yearend, though un-employment and inflation remained at high levels. Total output as measured by the GNP in current dollars rose 6.5% in 1975. Real GNP declined 2.0%, and inflation, as measured by the implicit price deflator, increased 8.7%. Real gross private domestic investment for residential structures declined 18.1% in 1975, which was a smaller rate of decrease than the 27% decline in 1974. Real State and local Government purchases increased 2.4%, and real personal consumption expenditures for services rose 1. 7 %. The Federal Reserve Board (FRB) index of industrial production declined 9.7%.

Jan 1, 1977

By N. Solak

CrN, TiN and Ti-B-N coatings were deposited onto H13 hot-working tool steel and alumina substrates by arc-PVD. The coatings were characterized with respect to their mechanical and structural properties. Oxidation behavior of the coatings on alumina substrates was investigated by TG/DTA. Samples coated on H13 substrates were oxidized in a tube furnace under atmospheric conditions at specific temperatures determined from TG/DTA tests of the same coatings deposited on alumina substrates. The oxide scale morphology was characterized by scanning electron microscopy and X-ray diffraction. Oxide scale thickness change and TG data were used to calculate oxidation reaction activation energies. It was determined that boron addition into TiN coating improves not only mechanical properties but also oxidation resistance. Depending on the substrate material different oxidation activation energy values for the TiN and Ti-B-N coatings were determined revealing the importance of film morphology on oxidation resistance.

Jan 1, 2006

By J. B. Cohen, S. L. Sass

The nucleation process for y', Ni3Ti, is shou'n to change from heterogeneous to uniform as the undercooling within the phase boundary increases. As unifornz nucleation beconres copious, (100) alignment is observed in the early stages of aging; howecer. whether or not the alignment is due to spinodal decomposition could not be determined. The presence oi a large-scale reversible segregation of titanium and not the intermediate precipitate y' may be the cause of the initial strengthening in this alloy system and the discrete regions detected magnetically by Ben-Israel and Fine. Evidence is presented for the role of dislocations in the formation at long aging tines oJ the equilibrium precipitate . ThE nickel-rich portion of the Ni-Ti phase diagram consists of a terminal fcc solid solution of titanium in nickel called y.' For temperatures below 1290°C if the solubility limit is exceeded and the temperature is high enough, the excess titanium will combine with nickel to form q, Ni3Ti, a four-layer hcp ordered structure with stacking sequence ABAC."~ Since a change in structure is involved, formation of q is slow and a metastable precipitate referred to as y' forms. This metastable precipitate is an ordered cubic phase in the unconstrained state having a structure similar to Cu3Au (LIZ) with the composition Ni,Ti."'5 From X-ray studies,8, 7 the following sequence is indicated for the precipitation reaction at low temperatures: 1) The appearance of satellites around low-index diffraction spots and splitting of high-index spots, indicating the formation of a slightly tetragonal phase in an imperfectly periodic arrangement. The tetragonal phase is y' or the depleted matrix, depending on the volume fractions of matrix and precipitate (and hence, the alloy composition); tetragonality apparently arises from coherency strains. 2) The appearance of diffraction spots from the equilibrium second phase, q. Ben-Israel and Fine'" used magnetic methods to measure the changes in matrix composition during aging, and to estimate the precipitate composition in a Ni-10.1 at. pct Ti alloy. They observed that the alloy, solution-treated at 1270°C and quenched, contained heterogeneities with discrete compositions which gradually vanished upon aging. It was suggested that y' may initially form as a defect structure with several possible compositions deficient in titanium as compared to Ni3Ti; the composition Ni3Ti develops with prolonged aging. The initial composition was Ni6Ti which would require a very large deviation in stoichiometry for y'. It was noted that at 700°C the precipitation reaction was 80 pct complete after 2 hr and that the volume fraction of second phase was 0.2 after 1 hr. Mihalisin and Decker' suggested that the equilibrium precipitate, besides being nucleated at grain boundaries, could also form at stacking faults. ~errick" examined the formation of in Ni-Cr-Ti, and suggested that a collapsed vacancy cluster within y' acted as a nucleus for intragranular q at high temperatures, 820" and 900°C. After long aging times at lower temperatures, 650" and 750°C, diffraction patterns taken from regions containing ribbons of stacking faults showed spots associated with q. Aging greatly enhances the mechanical properties of these alloys, even at high temperatures, and the metastable precipitate y' is thought to be responsible.' At 600°C the hardness of a Ni-10.1 at. pct Ti alloy increases rapidly during the first 20 hr of aging and continues to increase slowly thereafter.'" At 700°C the hardness reaches a maximum at 1 to 2 hr and then decreases.l1 In this paper the kinetics of formation of y' and the mechanism of transformation to in a Ni-Ti alloy are described. Evidence is presented that suggests that large-scale regions of titanium segregation are present initially and these may have an important influence on the initial strengthening of the alloy: these regions may be the heterogeneities detected by Ben-Israel and Fine. I) EXPERIMENTAL TECHNIQUES The Ni-10.3 at. pct Ti-0.6 at. pct A1 alloy was prepared by vacuum melting. Its chemical analysis is given in Table I. A 0.007-in.-thick strip was sandwiched between foils of the alloy and placed in an open Vycor tube with titanium chips (to get oxygen) and solution-treated for ; hr at 1150°C in a Globar Furnace under a flowing argon atmosphere. Following a quench into an ice-brine mixture at -5" to -2"C, a sample to be aged at temperatures up to and including 700°C was sealed in an evacuated Vycor capsule before being put into a fused salt bath. Aging above 700°C was carried out on bare samples in a salt bath. When removed from this bath and quenched into an ice-water mixture, the sample was normally coated with a thin layer of oxide easily removed with emery

Jan 1, 1970

By Douglas E. Wolfe, Jogender Singh, Robert Miller, Dong-Ming Zhu, Jeff Eldridge

This paper discusses microstructural changes produced by two novel approaches using electron beam physical vapor deposition (EB-PVD) in which periodic strain fields/microporosity was incorporated within the large columnar grains of Zr02- 8wt.%Y2O3 (8YSZ). The traditional columnar microstructure of partially stabilized zirconia has been slightly modified to produce a lower thermal conductive thermal barrier coating (TBC) by periodically interrupting the condensing vapor resulting in microstructural modifications with diffuse or sharp interfaces and morphological changes on the sub-micron scale without changing the composition of the TBC. These microstructural modifications resulted in a 20-30% reduction in the thermal conductivity, 28-56% increase in hemispherical reflectance, improved oxidation cyclic life (over 100%), and better strain tolerance as compared to standard ZrO2-8wt.%Y2O3 deposited on platinum-nickel-aluminide and CoNiCrA1Y bond-coated MAR-M-247 test samples. The TBC with tailored microstructures were examined by various techniques including scanning electron microscopy (SEM), x-ray diffraction (XRD), steady-state laser heat flux technique, and hemispherical reflectance.

Jan 1, 2004

The following is a, partial list of members and guests who called at Institute headquarters during the period Aug. 10, 1917, to Sept. 10, 1917. L. P. Barrett, Ann Arbor, Mich. Milo W. Krejci, Great Falls, Mont. H. J. Brown, Ridley Park, Pa. Chas. N. La Porte, Peoria, Ill. George M. Cheney, Guayaquil, Ecuador. Askin Nicholas, Bismuth, Australia. W. Lorrain Cook, Chicago, Ill. C. Edwin Nighman, Butte, Mont. John J. Croston, Atlanta, Ga. W. L. Remick, Norfolk, Va. A. F. Duggleby, Santiago de Cuba. T. C. Roberts, Jerome, Ariz. Geo. A. Easley, La Paz, Bolivia. Burr A. Robinson, New Haven, Conn. Burr J. French, Magdalena, Jal., Mex. J. L. Schueler, Peoria, Ill. A. D. R. Galloway, Komfrodua, W. Af. Walter L. Steele, Van Horn, Tex. P. R. Hines, Milwaukee, Wis. F. J. S. Sur, Denver, Colo. T. H. Jenks, Wickenburg, Ariz. C. A. Thomas, Dawson, Y. T., Canada. Paul S. King, Wilmington, Del. E. E. White, Ann Arbor, Mich. Harry Wolf, Golden, Colo. L. W. Bahney has left the Sheffield Scientific School, Yale, to become metallurgical engineer with the Scovill Manufacturing Co., Waterbury, Conn. H. B. Barling, formerly chief engineer of Breitung & Co., of New York, has been appointed manager of the mining department.

Jan 10, 1917

By Arnold O. Tanner

The domestic mining industry continued to be strengthened and revitalized in 1989. The healthy conditions and the industry comeback that began in 1987 continued to spread and became more established for many commodities. Relatively comfortable and stable commodity prices, still found predominantly in the metals sector, reinforced other operational factors in bringing vitality to the mining and mineral processing industries. New streamlined business practices, mine and plant modernizations, and the progressive use of new technologies successfully helped lower operating costs and increase efficiency during the past 5 to 7 years. An element common to these three factors of industry renewal and growth was the ever-increasing infusion of and growing dependence on constantly advancing computer technology applications. This trend of increasing computerization was occurring throughout the mining and mineral processing business while it similarly was in most facets of modern business and culture. Some commodities and companies still struggled to outlive sluggish prices and other unstable market conditions or to modernize their businesses, but increases in productivity and profits were more common. A trend toward increased mechanical excavation in nonsoil materials was beginning to surface as a substitute for standard cyclic mine development techniques, such as drill-and-blast and surface shovel-and-truck routines. More continuous mechanical excavation offered the potential for increased production, fewer people at the working face, better ground control, and generally improved safety. The main limitation was rock hardness. The construction industry had already recognized the benefits of tunnel-boring machines for long underground drives and mechanical planers for pavement removal. The Colorado School of Mines held a short course during the year entitled, "Mechanical Excavation Techniques in Mine Development and Production,'" which was at-tended by nearly 100 engineers from 12 countries. The consensus of attendees was that for the most efficient use of these machines and techniques, new mining plans needed to be developed beyond the simple adaptation of those excavators to existing mine plans.1

Jan 1, 1991

By J. M. Markowitz

The movement of hydrogen in two-phase Zircaloy-2 under the influence of a thermal gradient was studied in specimens of cylindrical geometry. A gross displacement of hydrogen toward the cooler regions of the specimen was observed with consequent copious precipitation of 6-ztrconium (ZrH) there. The kinetics of the diffusion are analyzed and discussed. X HE temperature-gradient redistribution of hydrogen in a-Zircaloy-2 has been treated both theoretically and experimentally Hydrogen moves toward the cold side of the temperature gradient until a steady state has been established; tendency for further hydrogen movement because of temperature differences is nullified by the tendency to move in the reverse direction because of the concentration gradient. The steady state condition is described by the equation in which iV is the concentration of hydrogen at a point in the specimen corresponding to absolute temperature T, R is the gas constant,k is a constant of integration, and Q is a parameter called the heat of transport, characteristic Of the particular system. The value of Q has been determined for hydrogen in Zircaloy-2 by several investigators, using Eq. [11. There is considerable variation in the results, the cause of which has not been resolved; reported values lie in the range 3 to 6 kcal per mole. The physical situation for two-phase thermal migration is much more complex. The -phase boundary for the solubility of hydrogen in Zircaloy-2 ranges from a concentration of 25 ppm at 200°C to a maximum of about 600 ppm at 550°C.4a Thus, if the concentration of hydrogen in Zircaloy-2 is sufficiently great (>600 ppm), the specimen will be entirely two-phase, consisting of a matrix of a-Zircaloy-2 surrounding particles of zirconium hydride. At time zero, with a temperature gradient imposed, the relative amounts of hydride and a-phase in each infinite-simally thin isothermal section of the specimen can be determined from the phase diagram by the lever rule. Moreover, the concentration of hydrogen in the matrix phase varies from point to point, following the a solubility line. Over most of this temperature range (<450°C) 6 phase, Fig. 3, has a constant concentration.5 The diffusion rate toward the cold side should be governed by 1) the slope of the a solubility line and 2) the temperature gradient, The extra complication of two-phase thermal diffusion lies in the fact that migration of hydrogen would leave the a-phase concentration gradient unaffected, since it is fixed at any temperature only by the solubility; gross concentration changes would reflect only the relative amounts of matrix and hydride, which could vary continuously at every point. Migration of hydrogen out of a region would lead to dissolution of hydride, and

Jan 1, 1962

The first meeting of the Naval Consulting Board was held at the office of the Secretary of the Navy, Washington, D. C., on Oct. 6, 1915. The Board organized by electing Thomas A. Edison, Chairman, Peter Cooper Hewitt, First Vice-Chairman, William L. Saunders, Second Vice-Chairman, and Thomas. Robins, Secretary. All of these officers are members of the American Institute of Mining Engineers. The other members of the Board are given below, and those who are members of the Institute are marked with an asterisk: *W. R. WHITNEY MATTHEW B. SELLERS. L. H. BAEKELAND. HUDSON MAXIM. FRANK JULIAN SPRAGUE. HOWARD T. COFFIN. BENJAMIN C. LAMME. ANDREW J. RIKER. R. S. WOODWARD. HENRY A. WISE WOOD ARTHUR GORDON WEBSTER. ELMER A. SPERRY. A. M. HUNT. *BENJAMIN B. THAYER. ALFRED CRAVEN. *J. W. RICHARDS. *SPENCER MILLER. *LAWRENCE ADDICKS. WILLIAM LE Roy EMMETT.

Jan 12, 1915

By Gordon E. Fletcher

This Bureau of Mines report outlines the atomic absorption analysis of oilfield brines for barium, calcium, copper, iron, lead lithium, magnesium, manganese, potassium, sodium, strontium, and zinc, using the method of additions. The advantages of using atomic absorption are discussed. The method of additions was chosen to overcome large matrix interferences usually found in brines; techniques of overcoming chemical, ionization, and background interferences are also described. The method was used to analyze several hundred oilfield brines and found to be rapid and reasonably accurate. A solvent extraction method was used to concentrate lead, copper, zinc, and iron in low-level samples.

Jan 1, 1974

By S. H. Ash

THE information obtained by examining and analyzing the core drillings from 15 diamond-drill holes shows that with the proper equipment little difficulty should be experienced while sinking the shafts at the 15 selected sites. Although a number of holes penetrated formations containing a high percentage of silica,, the health hazard from dust can be removed by using proper dust-control equipment. Methane was detected in small amounts in only one (hole 5) of the boreholes. The methane hazard should present no difficulty if adequate ventilation is employed while sinking the shafts.

Jan 1, 1952

By Roy E. Peterson

The Bureau of Mines conducted an investigation to produce metallized pellets from domestic iron ore superconcentrates using lignite and subbituminous coal as reductants. Feed materials for the metallizing process consisted of commercially indurated iron oxide pellets and green pellets prepared from upgraded domestic concentrates with graphite or limestone as internal additives. Durability of the green pellets during metallization was investigated in tests conducted in a 7-inch-ID rotating drum furnace. Test results indicated that the major cause of pellet disintegration with the concentrates used was the tumbling action during reduction rather than forces generated within the pellets. In larger scale tests made in a 34-inch-ID by 35-foot-long kiln, the previously indurated pellets were metallized with lignite at 1,030° C with little disintegration. A 96-percent level of metallization was obtained in pellets having an average compressive strength of 420 lb. In subsequent, similar tests using green pellets containing graphite or limestone, pellet disintegration was more severe, with 10 to 40 percent of the feed being lost as dust. The surviving pellets had metallizations ranging from 88.3 to 94.4 percent and compressive strengths ranging from 60 to 68 lb.

Jan 1, 1976

Safety Factor Characteristic Curves. Their Application to Mine Hoisting Ropes. (Paper by W. A. Boyer, Transactions AIME, 199, 989; Mining Engineering, October 1954. Discussion by B. E. Grant.) ............................................................................................................................. 1101 The Use of Wooden Rock Bolts in the Day Mines. (Paper by Rollin Farmin and Carville E. Sparks, Transactions AIME, 196, 922; Mining Engineering, September 1953. Discussion by Edward Thomas.) ................................................................................................................................. 1101 An Analysis of Mine Opening Failure by Means of Models. (Paper by Bernard York and John J. Reed, Transactions AIME, 196, 705; Mining Engineering, July 1953. Discussion by J. P. Zannaras.) ... 1102 B — Minerals Beneficiation Flotation and the Gibbs Adsorption Equation. (Paper by P. L. de Bruyn, J. Th. Overbeek, and R. Schuhmann, Jr., Transactions AIME, 199, 519; Mining Engineering, May 1954. Discussions by W. E. Ewers and Masayoshi Wada.)........................................................................................... 1103 Manganese Upgrading at Three Kids Mine, Nevada. (Paper by S. J. McCarroll, Transactions AIME, 199, 289; Mining Engineering, March 1954. Discussion by J. Bruce Clemmer, J. B. Rosenbaum, and C. H. Schack.)............................................................................................................. 1105 A Physical Explanation of the Empirical Laws of Comminution. (Paper by D. R. Walker and M. C. Shaw, Transactions AIME, 199, 313; Mining Engineering, March 1954. Discussions by Dimitri Kececioglu, George B. Clark, and Fred C. Bond.) ......................................................... 1106 F — Coal Underground Electrocarbonization of Coal and Related Hydrocarbons. (Paper by T. C. Cheasley, J. D. Forrester, and Erich Sarapuu, Transactions AIME, 199, 908; Mining Engineering, September 1954. Discussions by John G. Tripp and James L. Elder.)....................................................... 1108 Longwall Mining and Mechanization, with Special Reference to Nova Scotia. (Paper by Frank Doxey, Transactions AIME, 199, 701; Mining Engineering, July 1954. Discussion by Louis A. Turnbull.) ........................................................................................................................................ 1109 Cleaning Various Coals in a Drum-Type Dense-Medium Pilot Plant. (Paper by M. R. Geer, W. A. Olds, and H. F. Yancey, Transactions AIME, 196, 696; Mining Engineering, July 1953. Discussion by John Griff en.)................................................................................................................................. 1110 Frontiers in Heat Extraction from the Combustion Gases of Coal. (Paper by Elmer R. Kaiser, Transactions AIME, 199, 304; Mining Engineering, March 1954. Discussion by G. A. Vissac.) ............ 1112 Exploration of the Oaxaca Coal Fields in Southern Mexico. (Paper by Luis Toron and Salvador Cortes-Obregon, Transactions AIME, 199, 505; Mining Engineering, May 1954. Discussion by John D. Price.).................................................................................................................. 1113 H — Industrial Minerals Alkali Reactivity of Natural Aggregates in Western United States. (Paper by William Y. Holland and Roger H. Cook, Transactions AIME, 196, 991; Mining Engineering, October 1953. Discussions by Dexter H. Reynolds and W. L. Merritt.) ......................................................... 1114 Characteristics of Titaniferous Concentrates. (Paper by L. E. Lynd, H. Sigurdson, C. H. North, and W. W. Anderson, Transactions AIME, 199, 818; Mining Engineering, August 1954. Discussion by D. R. Grantham.)........................................................................................................................ 1116

Jan 1, 1955

An approximate rapid design system for tunnel liners and underground structures is presented which permits the effects of structure geometry and stiffness, rock quality in terms of its deformation modulus, and the applied system loading to be entered as data to produce direct designs conforming to stress limitations, optimum reinforcement requirements and restraints on section dimensions. An &apos;equivalent column&apos; concept is introduced for modelling the rock mass in contact with the structure. Only the rock treatment is given in detail but the results of sensitivity analyses, with reference to rock quality, for a typical liner design are given and these results related to a number of empirical design approaches.

Jan 1, 1976

By J. H. Sokolowski, R. I. MacKay

The level of Si and Cu in the 3xx series of alloys affects the volume fraction of the a-Al dendritic phase and the Al-Si eutectic phase. The volume fraction of these phases in turn affects the feeding conditions during solidification and ultimately the Area Fraction Porosity and Mean Pore Diameter measured in the as-cast structure. This work sets out to establish the relationship between the volume fraction of the a-Al dendritic phase and the Al-Si eutectic phase and the resulting porosity that forms on the Monotonic and High Cycle Fatigue properties. The alloys in question are the Al-9%Si-l %Cu and a Al-7%Si-4%Cu alloys which were cast into V8 performance engine block castings and then heat treated to achieve desired mechanical properties. The engine block castings provided the mechanical and metallographic test samples analyzed for this work.

Jan 1, 2006

By Y. Ren, B. Yang

The magnetic field characteristics due to electromagnetic stirring in the secondary cooling zone of an extra-thick slab during continuous casting are numerically determined using Maxwell's equations, with particular emphasis on the distribution of magnetic induction intensity and electromagnetic force, as well as the influence of process parameters on the magnetic field. The orientation of the electromagnetic force is the same when the electromagnetic stirrers at the 30° and 60° posistions of the arc-shaped slab are powered in the same direction; otherwise, the orientation is opposite. The magnetic induction at the centre of the section of the stirrer's central axis at the 30° positio, as well as the current, frequency, and fitting formulae, are as follows: B = {0.075I.(1/A)-0.3} mT and B = {-1.75f.(1/Hz)+22} mT. The electromagnetic force and current fitting formula at the central point of the B-B section is F = {0.03168I2.(1/A2)-03.762I.(1/A)+326.7} N/m3, and the fitting formula of electromagnetic force and frequency at the centre point is divided into two segments. The first takes the form of a parabola: = {-21((f-4.3).(1/Hz)2)+970} N/m3, and the second segment is negative linear: F = {-1.65f.(1/Hz)+51.5} N/m3.

Apr 16, 2024

By A. W. Fletcher

Report of discussion at February, 1971, IMM general meeting (Chairman: M. J, Cahalan President) of a paper published in Transactions/Section C (Mineral Processing & Extractive Metallurgy), vol. 79, December, 1970, pp. C247-52, and contributed remarks. Contributions are included from: Cahalan M.J., giving figures related to leaching Cu from pyrite at Rio Tinto 1880-1910; Noakes F.D.L.; Embling P.M.K.; Bradshaw A.V.; Le Roux N.W.; Kelly D.P.; and Tuovinen O.H. Questions were raised regarding impurity removal, effects of light and ultraviolet light on the bacteria, the economics of solvent extraction and the possibilities for other organisms or other metals

Dec 1, 1971

By Z. T. Yuan, S. L. Qi, Q. Y. Meng, G. X. Zou, L. X. Li, J. W. Lu

"The selective separation of pentlandite from serpentine was investigated using the magnetic coating-magnetic separation by conditioning slurry pH value, stirring speed, magnetic field intensity and controlling dosages of sodium hexametaphosphate (SHMP) and sodium oleate (SO). The optimal conditions were obtained as follows: the natural pH of 6.8-7.2, stirring speed of 2300 rpm, magnetic field intensity of 200 kA m-1, SHMP of 60 mg L-1, and SO of 400 mg L-1. Results showed that the Ni grade was 21.4% with the Ni recovery of 81.4% and MgO content of 3.8%. FTIR indicated that coagulant of SO preferentially adsorbed onto pentlandite and magnetite particles while hardly adsorbing onto serpentine particles when dispersant of SHMP was used. Thus, the selective magnetic coating of magnetite on pentlandite surfaces could be formed due to the formation of hydrophobic surfaces on pentlandite and magnetite particles. Calculations of DLVO (Derjaguin-Landau-Verwey-Overbeek) confirmed that interactions between magnetite and pentlandite particles were much stronger than that between magnetite and serpentine due to the existence of hydrophobic interactions with the addition of SO. Consequently, the pentlandite was successfully separated from serpentine. Therefore, this study exhibits the potential to separate pentlandite from serpentine minerals for practical applications and thus deserves further study.INTRODUCTION It has been well known that the separation of pentlandite from serpentine is a worldwide challenging issue in the processing of sulphide nickel-copper ores. Because the serpentine mainly causes the high pulp viscosity and slime coating on the pentlandite, which interferes with the flotation process of pentlandite (Cao et al., 2016; Feng et al., 2012). The fibrous mineral of serpentine preferentially attaches to the air bubble, forming bubble-macrofibers aggregates, which are easily floated into the nickel concentrates, resulting in the decline of Ni grade (Alvarez-Silva et al., 2016; Kusuma et al., 2014). In addition, the serpentine adheres to the pentlandite as hetero-aggregation or slime coating via the electrical interaction between a positively charged serpentine and a negatively charged pentlandite, which decreases the hydrophobicity of pentlandite and reduces the collector adsorption (Feng et al., 2013). In other words, the presence of serpentine or the occurrence of aggregates (including slime coating and bubble-macrofibers aggregates) seriously affects the flotation process and deteriorates the flotation of pentlandite. Therefore, we propose magnetic separation to recover pentlandite from serpentine with the magnetic coating technology, which is different from forth flotation."

Jan 1, 2018

By J. C. Gerdeen

A new analytical model for the shear stiffness at a joint of the fully-grouted resin roofbolt is developed using the Theory of Elasticity and an analogy to a beam on an elastic foundation, Gerdeen [2]. The model developed in this study treats the elastic foundation modulus of the resin as being composed of both an elastic rock and an elastic resin. All previous attempts have neglected the elasticity of the rock and treated only the resin. A three dimensional finite element model of the bolt-resin-rock system is developed also and comparisons are made between the predictions made by it and the analytical solution. It is found that the agreement between the two representations ranges between 1.2% and 10.5%, with the greater differences being observed for systems of very large or very small bolt diameters and resin annulus thicknesses. Since such configurations are not the rule in practice parameter studies are performed using the analytical solution with the finite element solution being used as a check. For a 0.75 in. bolt, a resin annulus thickness of 0.1375 in., a resin with E = 7 x 105 psi and -1) = 0.210, and a rock of modulus E = 6.8 x 106 psi and V = 0.159 the shear stiffness is found to be 1.220 x 106 lb,/in, from the analytical solution and 1.245 x 106 lb,/in, from the finite element model. Applying the finite element model to the problem of the axial stiffness of the fully-grouted resin roofbolt a value of 6.002 x 106 lb./in. is obtained which proves to be at least 50% higher than any of the now existing analytical predictions.

Jan 1, 1976

By H. Wen

"Taking the long flame coal, gas-fat coal and anthracite as samples, we tested the adsorption quantity to single component gas of N2, CO2 and CH4 under atmospheric pressure phase at different temperatures. Then we analyzed the adsorption characteristics and models of different metamorphic coals. The results show that metamorphic grade, temperature and gases species are main factors to adsorption quantity of coal. The higher and lower metamorphic grade of coal have greatly influence on adsorption capacity while moderate grade of coal has opposite result. The coal adsorption amount to three single component gases under the same experimental condition is CO2> CH4> N2.The simulation precision order of four adsorption models is quadratic curve model > Freundlich isotherm model> Langmuir model >logarithmic curve model. Quadratic curve model and Freundlich isotherm model both can accurately describe the adsorption behaviors of N2 and CH4, different isothermal adsorption curve of CO2 needs two kinds or more models to describe. This has a reference value to the study of adsorption characteristics and models to single component gases.INTRODUCTION Adsorption is the interfacial phenomena that concentration of single or multiple components in the interface layer is different from the bulk phase (1964). Adsorption model is mathematical models to describe the adsorption characteristics of the adsorbent, mainly reflected to fitting effect of gas adsorption isotherm, which contribute to deeply understand the adsorption characteristics of adsorbent. Many scholars have carried out extensively experimental studies of the coal adsorption process from different angles. Zhao (2010) studied the influence of coal metamorphism to pore development of coal seam through a variety of experimental methods. Zhang (2006) analyzed the adsorption capacity and the controlling factors from three aspects of the coal rank, maceral and coal mass deformation. Cheng et al., (2002) studied the influence of pore size distribution of different rank coals to adsorption constants. Zhong (2002) carried out varieties of isothermal assay and established the prediction method of coal seam adsorption affected by a variety of conditions. R. M. Bustin (1998) proposed that we could not simply describe the change law of coal adsorption capacity and maceral content by a fixed parameter, and the adsorption capacity of the same coal rank also has great change. C. R. Clarkson et al., (1997) used four different adsorption models to describe the coal methane adsorption process, and the fitting precision of adsorption models is D-A equation >D-R equation > BET equation> Langmuir equation. Gasem, K et al., (2003) found that the fitted isothermal adsorption curve of D-A equation and BET equation are better than Langmuir equation under high pressure condition, while D-R equation and BET model are better to CO2 adsorption. In recent years, scholars’ at home and abroad research achievements of coal adsorption focused on high-pressure stage (about 0~15 MPa), mainly for coalbed methane exploitation, carbon dioxide trapping and sealing technology development, but the study of coal adsorption under atmospheric pressure phase is little. In this paper, we analyzed the adsorption characteristics and models under atmospheric pressure phase, it has a reference value to the study of characteristics and models to single component gas."

Jan 1, 2015