Search Documents

By Roland Blanchard

Recent discovery at Mount Isa of copper mineralization in commercial amount at a depth of 1000 ft., coinciding with downward termination of ore at about the same depth within the larger silver-lead-zinc lenses that have been the standby of Mount Isa's production to date, has been cited as an example in support of mineral zoning. A previous paper by the author and Graham Hall1 furnished a detailed description of the geology of the ore at Mount Isa as exposed up to that time, but necessarily dealt mainly with the silver-lead-zinc mineralization. Most of the geologic facts that constitute the first half of the present paper were set forth in the previous one in much greater detail, with full supporting evidence for the facts cited. The large amount of underground development (approximately 20 miles) and the extensive exploration carried out by diamond drilling (100,000 ft.) at Mount Isa, added to extensive microscope work conducted over a period of years, both by the company's staff and by others, had made possible the calculation within fairly close limits of mineralogical composition of the principal mineralized block of ground down to 1000-ft. depth, and had established closely the mineral succession, with reasons for deposition of the various minerals in the patterns now occupied by them. The geologic facts as outlined in the previous paper remain as stated; but because substantial development within the new copper ore body and further exploratory diamond drilling within the new silver-lead-zinc area (Racecourse) have taken place since that paper was written, statements and figures relating to those two areas in the present paper supersede those furnished in the previous one. The recent work likewise has established more clearly the paragenetic relationship between the chalco-pyrite and galena. Evidence confirming the relationship is furnished in the present paper. The facts of ore occurrence at Mount Isa show Accepted Zonal Succession Silver sulphantimonides Galena Sphalerite Tetrahedrite Arsenical sulphides Chalcopyrite Pyrrhotite Mount Isa Succession I In the main but prob- Silver sulphantimonides ably not wholly Tetrahedrite I contemporaneous Galena Pyrrhotite Sphalerite Arsenical sulphides They show further: (I) that instead of the silver-lead minerals yielding to increased zinc in depth, the zinc yields to increased silver-lead; (2) no dovetailing of the silver-lead-zinc sulphides into chalcopyrite takes place; (3) despite the large amount of pyrrhotite deposited in the district (estimated at upward of 100,000,000 tons), its deposition took place under moderately low temperature conditions; (4) no evidence has been found for increase in temperature of deposition, with depth, to deepest exploration in ore (1475 ft.). The anomalous condition at Mount Jsa, both as to the unorthodox mineral succession and the largely unorthodox patteru of mineral distribution, is explained in the present paper,

Jan 1, 1949

By Fred K. Stieler

The largest updraft sinter machine built has a roasting area of 132 sq.m. Sinter machines with an area of over 200 sq.m. are under consideration. These large machines require new techniques with regard to drive thrust and sealing mechanism. To optimize the results of sinter plants, the charge preparation systems and the return fines circuits were improved. Special crushers were developed for crushing return sinter of up to 800 ºC to a size of minus 6 mm. Strand cooling of Pb-sinter was investigated. Different methods for plant ventilation were compared. New processes, which might replace sintering in the future, are in the stage of large - scale testing.

Jan 1, 1977

By K. Tangri, M. Chaturvedi

The addition of 0.5 wt pct Cu to Zr-2.5 Cb alloy increases the as -quenched hardness of the hexagonal martensitic a' phase, produced by water-quenching bccß-Zr phase, by about 35 pct. This strengthening has been attributed to the solid -solution hardening of the matrix. On aging ternary martensite, a' phase reverts to equilibrium a and Zr2Cu and ß-Cb precipitate out, mainly at the twin and grain boundaries, causing a secondary hardening of the matrix. COLD-worked Zircaloy-2 pressure tubes have been in use in power reactors for a considerable period of time. The search for a better material led to the development of Zr-2.5 wt pct Cb alloy which in the quench-aged condition develops 50 pct more strength than that of cold-worked Zircaloy-2, however, its corrosion resistance in water and steam in the temperature range of 316" to 400°C, in absence of neutron flux, is inferior to that of zircaloy-2.' Work carried out by Ells et al.1 and Dalgaard2 has shown that the corrosion properties of Zr-2.5 wt pct Cb alloy can be considerably improved by the ternary addition of 0.5 wt pct Cu. This paper is concerned with the effect of 0.5 wt pct Cu on the formation of martensitic a and its aging characteristics in a Zr-2.5 wt pct Cb alloy. MATERIALS AND EXPERIMENTAL TECHNIQUES Zr-2.5 Cb-0.5 Cu (referred to as the ternary alloy) and Zr-2.5 Cb (referred to as the binary alloy) alloys, supplied by the Chalk River Nuclear Laboratories of the AECL were used. The detailed chemical analysis is given in Table I. Cold rolling and swagging with frequent intermediate anneal of 1000°C were used for the initial fabrication of the alloys. All the heat treatments were carried out after the specimens were wrapped in zirconium foils and encapsulated in silica tubes under a vacuum of 5 x 10-6 mm of Hg. For optical metallography and hardness measurements specimens were mechanically and then chemically polished in a 45 pct HNOj, 45 pct HzO, and 10 pct HF solution. Hardness was measured on a Vickers hardness tester using a 10-kg load. For each specimen at least fifteen indentations were made in order to obtain a representative value. The phase identification and structural analysis were carried out using X-rays and electron diffraction techniques. Wires of 1.5 mm diam reduced to 0.12 mm diam by chemical etching were used for making Debye-Scherrer powder patterns using Cu Ka radiation in a 114.6 mm diam camera. Carbon extraction replicas were prepared by etching the specimens, after depositing a layer of carbon on the metallographic specimen, in one part HF and thirty parts ethyl alcohol. Thin films were prepared by electropolishing heat-treated 3/4 by 1/2 by 0.005 in. thick strips using a modified Bollman-Window technique. The 10 pct perchloric acid-90 pct methyl alcohol bath was kept at -50°C and polishing was done at 5 to 10 V. The thinned specimens were washed in ethyl alcohol at -30º to -40°C and dried between filter papers. Replicas and thin films were examined in a Phillips 300 G electron microscope. For resistivity measurements thin strip specimens 0.02 by 0.3 by 10.0 cm long were used. The potential leads were spot welded to the specimens in order to maintain a fixed length for the initial and the final resistivity measurements. The resistivity was measured by a Kelvin bridge in a temperature controlled room. The temperature was maintained at 72º ±1°F and the accuracy of the resistivity measurements was 0.03 µa-cm. RESULTS As-Quenched Structures. In order to produce a homogeneous matrix to study the precipitation reaction the solution-treatments of both the alloys were carried out in the -field region. From the Zr-Cb phase diagram due to Lundin and cox3 ß/a + ß phase boundary for Zr-2.5 wt pct Cb alloy is 820°C. Ells et al.1 have reported this boundary for Zr-2.5 Cb alloy containing 1100 ppm 0 to be at 920°C. Also, the addition of 0.5 wt pct Cu reduces this temperature by 50°C. Therefore, the solution-treatments were carried out at 1000°C to ensure that the alloys were in ß-phase region. The soaking time was 1 hr and the specimens were water-quenched. The as-quenched hardness of the binary alloy was 245 Vpn whereas, that of the ternary alloy was 330 Vpn. The X-ray diffraction studies indicated that the as-quenched structure of both the alloys consists of martensitic hexagonal phase a', with a c/a ratio of 1.591, and some retained ß-Zr. The presence of a' phase was further confirmed by thin film electron microscopy. Electron micrographs of typical ß-quenched structures of the ternary and the binary alloys are shown in Figs. 1 and 2, respectively. Fig. 3 shows the diffraction pattern from an area similar to that shown in Fig. 1. Although, the as-quenched hardness of the ternary alloy is about 35 pct greater than that of the binary alloy, the structure of both the alloys seems to be the same. The matrix of both alloys is heavily twinned and shows very few dislocations. Furthermore, there is no evidence of any precipitation taking place in either of the two specimens during quenching from the solution-treatment temperature. Aging Behavior of Martensitic a'. The aging kinetics of the ternary alloy were followed by resistivity and hardness measurements. The as-quenched values

Jan 1, 1970

By John E. Riddell

This review is based on a questionnaire sent out in 1959 to 24 Canadian exploration companies, known to be active in the mineral exploration field, concerning their practice in the use of applied geo-chemical techniques in Precambrian terrains. Of the companies questioned, 21 returned completed questionnaires and of these, 15 companies stated that they had some experience in this type of work. Of the companies who stated that they had no experience in geochemical prospecting in glaciated Precambrian areas it is interesting to note that only three have reported that they do not use applied geochemistry at all. The others have reported that they make use of applied geochemistry in New Brunswick and in the Cordillera in areas of light glaciation. Their opinion is that it is a useful aid when accompanied by other techniques in evaluating mineralized areas. GEOCHEMICAL SURVEYS Table I reviews the type of geochemical surveys used by these companies, and the following points of interest should be noted.

Jan 11, 1960

By Arthur F. Colombo, David M. Hopstock

The Lake Superior region contains extensive deposits of potential iron ore in the form of fine-grained oxidized taconite. To help assure utilization of this resource in an environmentally sound manner, the U.S. Department of the Interior, Bureau of Mines, is conducting bench- and pilot-scale research using wet high-intensity magnetic (WHIM) separation. The advantages and disadvantages of WHIM separation in comparison with other feasible beneficiation methods are discussed. Pilot plant results are given for a flowsheet in which WHIM scavenging is used in conjunction with selective flocculation and flotation. A mathematical model for use in process optimization is given. Practical aspects of matrix selection and separator design for WHIM separation of fine particles are discussed.

Jan 1, 1980

By F. Robertson Jones

IF the tendency toward extending the scope of the workmen's compensation system to include life, health, accident, old age, and unemployment insurance for workers is not promptly altered, I believe there will be a complete breakdown of that system. This is not because of any objections, there may he to requiring industries to provide these additional forms of protection in whole or in part to their employees. It is rather because our workmen's compensation laws, their scale of benefits, and the administrative procedure under them are not adapted or suited to such situations. If the compensation principle is limited to its own proper sphere and is not enlarged so as to include all the ills that the flesh is heir to, it is practical, "workable, and beneficent. If it invades foreign realms, it is bound to grow into a veritable Frankenstein' which will harm principally those it 'is supposed to aid, and, at the same time, will promote waste, fraud, and Industrial demoralization. Compensation risks will become almost uninsurable; the cost to business will be intolerable; and the development of sound relief measures which will give to labor the protection now sought by the uneconomic device of enlarging the compensation law territory will be retarded.

Jan 1, 1934

By Gilbert Santoro

In this study tantalum carbide filaments of various compositions in the fcc region were prepared by heating a tantalum wire in a measured amount of hydrocarbon vapor. Such properties as tensile strength, transverse-rupture strength, microhard-ness, lattice parameter, electrical resistivity, and magnetic susceptibility were measured as a function of carbon content. Some of these properties showed a maximum or a minimum between a carbon-to-tantalum molar ratio of 0.80 and 0.85, the composition range at which the color changes from metallic gray to gold. The recent literature has shown that in the large homogeneity range for the fcc phase of the Ta-C system there is a marked variation for such properties as microhardness,' electrical resistivity, ' thermodynamic properties,z'3 lattice parameter and superconductivity. In addition to the technological interest of these variations within a single phase, important theoretical benefits may ensue from a continuous investigation of properties vs stoichiometry in tantalum carbide and other refractory defect compounds, for example the effect of the metal-metal distance and crystal structure upon bond formation and electronic structure. Whether there is a similar variation of the tensile strength is of practical importance. Of theoretical interest would be the knowledge of how the magnetic susceptibility varies with carbon composition. Both of these properties, as well as the transverse-rupture strength, were determined for tantalum carbide filaments in the fcc phase region. The lattice parameter, the electrical resistivity, and the microhardness were also investigated and compared with values appearing in the literature. EXPERIMENTAL PROCEDURE Material Preparation. Tantalum carbide specimens of various carbon content were prepared by statically carburizing high-purity tantalum filaments in measured quantities of pure hydrocarbon gas. The filaments, which were 10 mil in diameter and 20 or 40 cm long, were heated by their own resistance at temperatures from 1800" to 2200°C using alternating current in some cases and direct current in others. Tantalum wire from two sources was used. One had a reported purity of 99.96 wt pct Ta. The ingot from which this wire was drawn had been electron beam-melted as the final step in its purification. The reported purity of the other wire, which was prepared by a powder metallurgical process, was 99.88 wt pct Ta. The impurities of both tantalum sources are listed in Table I. Spec-trographic-grade toluene or research-grade propane was used as the source of carbon. The apparatus for the carburization of the filaments is shown schematically in Fig. 1. The system was evacuated to 1 x l0-' mm of Hg when using the electron beam-melted tantalum and to less than 1 p when using the less-pure tantalum. Neither the difference in the base vacuum, nor in the hydrocarbon gas, nor in the tantalum filaments resulted in any detectable difference in the properties studied in this work. However, only the carbides prepared from the higher-purity tantalum were used in the magnetic-susceptibility determinations. Once the base vacuum had been reached, the system was flushed with the hydrocarbon and re-evacuated. For any desired composition of the carbide, hydrocarbon gas was allowed to leak into a constant-volume flask to a predetermined pressure. These pressures were measured by a Cartesian diver-type mercury gage with a range from 0 to 20 mm and with a scale expanded to nine times. The hydrocarbon gas was allowed into the reaction tube and the filament was quickly raised to the reaction temperature. The slack in the filament due to thermal expansion was taken up by drawing out the movable electrode with a screw mechanism. The filaments were kept at temperature from a few minutes to 200 hr. In the majority of cases the heating time was 6 hr. The reaction tube was cooled by cascading water on its outer surface. By means of an ammeter and a voltmeter the electrical resistance at the reaction

Jan 1, 1963

By E. Tulcanaza

The practical significance of the in situ grade variability is usually neglected. Although recognized, often times it is either ignored or just considered as a vague guideline in many of the decisions dealing with exploration, reserve estimation, and mine planning. This paper stresses the significance of grade variability for exploration and mining, and illustrates its liaison to the structural features of the ore deposits, as well as to the mining parameters used for mine extraction. Some geostatistical results obtained from a silver mine, tungsten mine, and copper mine in South America are discussed.

Jan 1, 1985

By S. Acar, P. Somasundaran

The results obtained for the selective flocculation of natural ores do not usually agree with the corresponding properties of the constituent minerals when present alone. This is mainly due to the presence of dissolved mineral species which can interact in many ways with other components in the system and alter their behavior. In this paper, the effect of dissolved species on the flocculation and electrokinetic properties of sulfide minerals is discussed. Dissolved iron, copper, and nickel (Fe, Cu, and Ni) species are found to affect the properties of natural chalcopyrite and pentlandite in certain pH range. These effects are interpreted in terms of species adsorption leading to activation or depression of reagents, surface precipitation, and complexation of species

Jan 1, 1986

By B. Egeberg, H. B. Smith

Britannia metal is a white alloy consisting primarily of tin and antimony, the tin greatly predominating. The alloy usually contains a small amount of copper and occasionally very small amounts of one or two other metals, such as bismuth, zinc, and lead. It is capable of being cold-rolled, it takes a high polish, and it is fairly noncorrosive; properties which make it a popular metal for many household and traveling utensils. Britannia metal is similar in many respects to pewter and has largely replaced pewter in the arts, but it should not be confused with that alloy, because pewter is essentially a tin-lead alloy, while Britannia is a tin-antimony alloy. In view of the fact that so little has been published concerning Britannia metal, the authors feel justified in presenting the results of their investigation, particularly since the behavior of this alloy under cold rolling and heat treatment differs so greatly from that of other metals and alloys. The old craftsman, engaged in the making of ornaments or tableware, heated the cold-rolled sheet metal or his finished product to a straw color corresponding to about 375" I?., claiming to produce thereby a harder and more rigid article. The fact that possibly led him to this heating was that a reheated article or sheet made from Britannia metal has a distinct metallic ring when struck a sharp blow, whereas an unheated article or sheet has a leady, dead note. No doubt he has associated the metallic ring with a greater rigidity and strength, and justly so, as will be seen later. The approximate analysis of the metal we investigated was 91 Sn, 7 Sb, 2 Cu, and the molten metal was bottom-poured into an iron mold yielding an ingot 7 3/4 in. wide by 11 in. long and % in. thick, the casting temperature being 800" F. The ingot was cold-rolled to a sheet 0.032 in. thick, sufficiently large samples for experimental purposes being cut from the sheet at intermediate stages. The samples were all tested for hardness with scleroscope and Brine11 machine, then heated to 212" F. for 30 min., and again tested after cooling to room temperature. The same samples were heated successively at 300°, 400°, and 440" F., followed

Jan 1, 1929

By H. B. Smith, B. Egeberg

Britannia metal is a white alloy consisting primarily of tin and antimony, the tin greatly predominating. The alloy usually contains a small amount of copper and occasionally very small amounts of one or two other metals, such as bismuth, zinc, and lead. It is capable of being cold-rolled, it takes a high polish, and it is fairly noncorrosive; properties which make it a popular metal for many household and traveling utensils. Britannia metal is similar in many respects to pewter and has largely replaced pewter in the arts, but it should not be confused with that alloy, because pewter is essentially a tin-lead alloy, while Britannia is a tin-antimony alloy. In view of the fact that so little has been published concerning Britannia metal, the authors feel justified in presenting the results of their investigation, particularly since the behavior of this alloy under cold rolling and heat treatment differs so greatly from that of other metals and alloys. The old craftsman, engaged in the making of ornaments or tableware, heated the cold-rolled sheet metal or his finished product to a straw color corresponding to about 375" I?., claiming to produce thereby a harder and more rigid article. The fact that possibly led him to this heating was that a reheated article or sheet made from Britannia metal has a distinct metallic ring when struck a sharp blow, whereas an unheated article or sheet has a leady, dead note. No doubt he has associated the metallic ring with a greater rigidity and strength, and justly so, as will be seen later. The approximate analysis of the metal we investigated was 91 Sn, 7 Sb, 2 Cu, and the molten metal was bottom-poured into an iron mold yielding an ingot 7 3/4 in. wide by 11 in. long and % in. thick, the casting temperature being 800" F. The ingot was cold-rolled to a sheet 0.032 in. thick, sufficiently large samples for experimental purposes being cut from the sheet at intermediate stages. The samples were all tested for hardness with scleroscope and Brine11 machine, then heated to 212" F. for 30 min., and again tested after cooling to room temperature. The same samples were heated successively at 300°, 400°, and 440" F., followed

Jan 1, 1929

By Harold Price

PRIOR to Sept. 1, 1928, there had never been constructed what might be termed a long pipe line with electric-welded field joints. Nevertheless, by Sept. 1, 1929, within the period of a year, more than 2500 miles of electric-welded lines have been completed. These lines vary in diameter from 6 to 20 in., and in length from 50 to 700 miles. Before Sept. 1, 1928, no such line had been constructed .longer than 50 miles, and only one of nearly that length, a 40-mile 7-in. gas line in Louisiana. This was in reality the first pipe line to use electric-welded field joints. During the past year the following lines have been electric-welded by the Welding Engineering Co. alone: Texas Pipe Line Co.-157 miles of 8-in. line from Corsicana, Texas, to San Augustine, Texas. (This was the first electric-welded oil line.) Texas Pipe Line Co.-80 miles of 8-in. from Lafors, Texas, to Childress, Texas. Texas Pipe Line Co.-39 miles of 10-in. from Monahans, Texas, to Jal, New Mexico. Texas Pipe Line Co.-50 miles of 6-in, from San Antonio, Texas, to San Marcus, Texas. Texas-Empire Pipe Line Co.-424 miles of 12-in. from Cushing, Okla. to Chicago, Illinois. In addition to the field welding mentioned above,1 250 miles of 12-in. line was electric-welded into double joints at the pipe mill at Indiana Harbor, Ind.

Jan 1, 1929

By Walter Weeks

THE process of cooling air by allowing it to expand and do work in an engine is well known, but the theory of obtaining cold air by free expansion without the aid of an engine operating with cutoff has been little discussed. CASE I If compressed air is allowed to expand to the atmospheric pressure through an orifice in an air line that is supplied by a running compressor, no cooling results except the negligible one due to the Joule-Thompson effect, which will not be considered in this discussion. The effect of moisture will also be neglected.

Jan 1, 1937

By C. A. Zapffe

BOTH the foundryman and the theoretical metallurgist are now generally agreed that the anomalous "rising" or "bleeding" of certain ferrous castings of killed metal is primarily attributable to hydrogen. How and why the phenomenon occurs, however, have not been made clear. The following discussion is intended to harmonize foundry experience with metallurgical theory so that the foundryman may possibly improve his ability to prognosticate whether a certain casting may bleed or not. BLEEDING, RISING, AND PIPING The "rising" to be discussed here is not to be confused with the action in rimming ingots as a result of the carbon-oxygen reaction, although a conclusion will be drawn that may apply to the art of controlling the rimming action. Only killed metal is considered, which includes both steels and irons. In Fig. I, three killed, chill-cast ingots are shown: a porous ingot whose evolution of gas during late stages of solidification has ejected metal through the top; an ingot in which moderate gas evolution during solidification has lifted the mushy central metal, i.e., it has "risen"; and, third, a sound ingot with good piping characteristics. The first type is referred to as "bleeding," and generally infers that a solid skin had first formed through which the liquid metal later erupted. There is no fundamental distinction between bleeding and rising in reference to killed metal.* POROSITY Hydrogen appears as a cause of bleeding because the gas evolution simultaneously leaves a porosity of a type traceable to hydrogen. Twenty years ago, Melmoth1 noted that killed steel that rose unexpectedly in the mold, if returned while liquid to the furnace and heated further under a reducing lime slag, would again rise in the mold; but that if the ingot were allowed to solidify and was then remelted no rising occurred. A critical quantity of the responsible gas is therefore removed by the rising action. Melmoth associated rising with high silicon (0.7 to 0.9 per cent) and concluded that silicon increased gas absorption. Because silicon is a strong deoxidizer, oxygen must, therefore, be eliminated from consideration of the three common gases in steel-oxygen, nitrogen, and hydrogen. Butterworth2 later decided that pinhole porosity was caused by gases dissolved in the metal and that hydrogen was obtained from steam in the mold. Allen's classical work on copper castings,3 soon followed by

Jan 1, 1942

By W. F. Stowasser

A downdraft traveling grate process to agglomerate pelletized iron ore concentrates has been successfully demonstrated in a pilot plant at Carrollville, Wis. Work there followed several years of development in the Allis-Chalmers Mfg. Co. laboratories, and the pilot plant phase was carried out in co-operation with Arthur G. McKee & Co., consultants and engineers to the iron and steel industry. End result of the process is conversion of iron ore concentrates into a form which can easily be transported and smelted in the blast furnace.

Jan 5, 1955

By Perry Harrison

THE increased use of sintering for the beneficiation of iron ores and the reclaiming of flue dust creates a lively interest in sintering costs and, economics. The character of material sintered and geographical location of plants so radically alter sintering costs and economics that it is well to understand at least the basic elements which control such changes. The following cost factors are believed to be roughly approximated for large-scale Dwight-Lloyd 'continuously operated sinter-machine installations located anywhere. PER CRUDE TON Labor, supplies and repairs 0.15 Power 6.5¢ X kw-hr. rate ? Plant overhead and administration 0.05 Depreciation per ton annual capacity 0.05 Fuel: 6 per cent coke breeze or equivalent minimum ? 1 per cent coke breeze additional for each 5 per cent free and combined water in ore or dust ? Ignition distillate at 0.6 gal. per ton ? PER SINTER TON Royalty on Ore 0.10 Royalty on Flue Dust 0.15 PER CRUDE TON "Winter expense"; i. z., the cost of the five months enforced idle . period for plants tied in to Great Lakes transportation season 0.03 Using the foregoing data, it is possible to roughly approximate the cost of efficient sintering at any location for. any ore, viz:

Jan 1, 1932

By Roger Holmberg, Kenneth Mäki

This paper describe; open pit studies where blasting damage introduced in the remaining rock has been investigated. Results from two open pit mines are described and discussed. Parallel performed laboratory experiments, where simulated blasting damage has been introduced into samples before shear strength testing took place, are also reviewed. These studies are tied together in order to throw some light upon how the blasting damage influences the slope stability. A mathematical model is also described which will make it possible to optimize the blast design for a specified damage zone in the rock mass.

Jan 1, 1983

By S. Leber, R. F. Hehemann

Diffusion coefficients for the Cb-W system were measured using couples prepared from poly crystalline, commercially pure metals. The diffusion coefficients, measured in the temperature range between 1700° and 2300°C, decreased exponentially as the tungsten concentration was increased from 0 to 50 at. pct, then decreased abruptly at higher concentrations. A decrease of two orders of magnitude was observed over the entin? compositional range. The diffusion coefficients were in the range defined by the self-difiusion coefficients of the individual elements, indicating their general validity. An activation energy of 60,500 cal per mole was measured for the 20 pct W composition. Such low values, when compared with energies over 100,000 cal per mole for the pure constituent elements, indicated that transport mechanisnzs more rapid than volume diffusion were contributing substantially to inter dijfusion. Difference should, therefore, be expected between these data and the intrinsic diffusion coefficients. These differences should be significant in the kinetics of 'transport phenomena in practical systems. CONSIDERABLE attention has been devoted in recent years to the mechanical behavior and other properties of the refractory metals and their alloys. The Cb-W system has been of special interest as a base for the development of more complex compositions of commercial interest. In spite of the importance of mass transport to all aspects of elevated-temperature behavior, and especially to the production of alloys by powder-metallurgy techniques, little attention has been paid to diffusion in the Cb-W system. Results from a previous study of this system1 appeared to be anomalously high. The present investigation is, therefore, an attempt to obtain more accurate diffusion coefficients in this system. Intrinsic diffusion coefficients, of primary importance from the theoretical viewpoint, can only be obtained accurately from studies utilizing compositional gradients approaching zero. However, many practical problems involve diffusion under significant concentration gradients. The diffusion coefficients determined in this investigation were, therefore, obtained from couples prepared from elemental metals. The data obtained should be of value in the analysis of problems such as homogenization during powder-metallurgy alloying or reactions between base and clad in coated structures. In this vein, the investigation was conducted on poly crystalline materials of commercial purity. PROCEDURE Diffusion couples were prepared by sandwiching a columbium sheet between two sheets of tungsten. The composite was welded around all edges, the tungsten forming a protective can for the columbium. The composite was soaked for 4 min at 1600°C in a hydrogen-atmosphere furnace, quickly forged to 40 pct reduction in thickness, and then rapidly cooled to room tempera-

Jan 1, 1967

US 4,185,078-In the recovery of rhenium values from an aqueous sodium molybdate solution contained in the hydrometallurgical processing of roasted molybdenite, improved results are realized by using a described extractant consisting of a quaternary ammonium compound and benzene or other highly aromatic solvent which dissolves a quaternary ammonium-rhenium complex Essentially all rhenium is recovered from the solution and the extractant can be regenerated and recycled. This patent is a continuation-in-part of US Patent No. 4,049,771, dated Sept. 20, 1977. L R. Quatrini and M.B MacInnis, assigned to GTE Sylvania Inc. Jan 22, 1980. 6 pp (423-49). Flied. 7-19-78 (926,167).

Jan 1, 1982

By E. C. Truesdale

A FEW years ago H. M. Cyr, working in the Research Laboratories of The New Jersey Zinc Co., produced a few pounds of zinc1 of such purity that no other elements were detected in it by spectrographic analysis, using the facilities then available. This zinc contained less than one ten-thousandth of one per cent of metallic impurities.2 During the decade that followed upon the laboratory production of this "spectro-graphically pure" zinc, commercial developments brought about the production of large tonnages of zinc of purity exceeding 99.99 per cent, and today zinc of 99.999 per cent purity is produced and marketed as "chemically pure" zinc. Typical analyses of present supplies of high-purity zinc are given in Table 1. TABLE 1.-Typical Analyses Percentage by Weight Sum of Zinc Pb, Fe, Pb Fe Cd Al Cd Special High Grades 0.007b 0.005b 0.0056 none 0.0106 C.P. (chemically pure) <0.0002 0.0005° 0.000052 S.P. (spectrographically pure).. <0.0002d <0.00005d a A.S.T.M. Standard Specification for Special High Grade Slab Zinc (A.S.T.M. Designation: B 6-37). b Maximum. c Fe chemically determined. Pb and Cd are spectrographically determined. d Differences between composition of C.P. and S.P. zinc are discussed later in this paper. The availability of commercial tonnages of special high-grade zinc has been the basis for the development of the zinc-base die-casting alloy industry which, in the year 1936, consumed one-eighth of the zinc used in the United States for all purposes. This and the C.P. and S.P. grades have given impetus to scientific investigations into the properties of pure

Jan 1, 1939