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By P. A. Larssen, P. R. Gage, R. W. Bartlett

The kinetics of formation of intermediate sili-cide compounds from MoSi2/Mo and WSi2/W couples were studied using a cylindrical sample configuration. Concentration profiles of the constituent metals were deter mined from electron-microprobe analysis of cross-sectioned samples after isotlzernzal diffusion annealing. These data also yielded hand widths of phases. Growth of intermediate phases depends on diffusionin them and obeys a parabolic rate law. The rates of formation of the intermediate phases decrease in the order Mo5Si3 > W5Si3 > Mo3Si. Crowth rates. for the isomorphous phases Mo5Si3 and W5Si3 had the same activation energy. 43 kcal per mole. SILICIDE coatings employed to protect refractory metals from high-temperature oxidation are usually formed by a diffusion process requiring concurrent transfer of silicon to the refractory metal surface. For a simple binary system and a coating thickness of one or two mils, the coatings on molybdenum and tungsten are primarily the disilicides WSi2 and MoSi2, respectively. During use of the coated re- fractory-metal system at high temperatures, in the absence of the silicon source, further diffusion causes growth of lower silicide compounds and depletion of the disilicides. Recent investigations have shown that the lower silicides are less effective than the disilicides in forming a glassy oxide film which impedes oxidation.' Consequently, failure of coatings at high temperatures may coincide with complete conversion of the disilicide phase. The purpose of this part of the study is to investigate the growth kinetics of the intermediate compounds in the W-Si and Mo-Si systems. There are three intermetallic compounds in the Mo-Si system: MoSi2 with a tetragonal structure

Jan 1, 1964

K. T. Aust and J. W. Rutter (General Electric Research Laboratory)—We find it difficult to reconcile the activation energies determined by Gifkins with his general conclusion that "migration during both creep and grain growth can thus be treated on the basis of the same model" (that of Lucke and Detert). Gifkins finds the activation energy for grain boundary migration during creep to be 24.5 kcal per rnol and that for grain boundary migration during grain growth to be 7.5 kcal per mol. The calculation carried out by Gifkins of the activation energy for grain boundary migration during grain growth, using the Lucke and Detert model, gives a value of 20 to 24.5 kcal per mol, rather than his experimental value of 7.5 kcal per mol. The theory of Lucke and Detert was developed to account for the rates of migration of grain boundaries in the presence of impurities during grain growth. The theory does not take into account the effect on the boundary migration of another, simultaneous process such as creep deformation and would be expected, therefore, to be applicable only to migration during grain growth. The fact that Gifkins measured a different activation energy for boundary migration during grain growth (7.5 kcal per mol) from that during creep (24.5 kcal per mol), although the specimens were of the same composition, shows clearly that such an effect exists under his experimental conditions; the presence of a simultaneous creep deformation markedly affects the boundary migration process in comparison with what would be observed under the same conditions but without the creep deformation. The failure of McLean's equation (Eq. [4] of Gifkins' paper) to give a satisfactory dislocation density difference for boundary migration during creep is not surprising, since the activation energy which must be used in this equation refers only to the elementary atom transfer process of grain boundary migration. This activation energy value is approximately 6 kcal per mol for zone-refined lead, as determined in both the grain boundary migration experiments of Aust and Rutter31, 32 and the grain growth experiments of Bolling and Winegard.33 Using this activation energy value, McLean's equation gives reasonable agreement with observed migration rates for grain boundaries moving free of the influence of impurities.31, 32 The value of 24.5 kcal per mol is probably associated with the presence of impurity atoms, as Gifkins suggests. It should be noted, however, that this value was obtained using lead of only one composition and measurements at only two temperatures. The work of Aust and Rutter3"' on the effects of tin, silver, and gold on grain boundary migration in zone-refined lead in the temperature range from 320" to 200°C, as well as the work of Bolling and Winegard34 on the effect of silver and gold on grain growth in zone-refined lead, shows that the measured activation energy is markedly dependent upon the kind and amount of solute present. Gifkins' work does not permit evaluation of the effect of the 8 ppm of impurities other than oxygen present in his specimens. One incidental point: the symbols used to designate the experimental points of Fig. 6 appear to be in incorrect order in the figure caption. As the caption is printed, it would indicate that larger grain sizes were obtained after annealing at 47°C than at 100°C, which does not agree with the text (point M, p. 1019). Finally, it seems clear from Gifkins' results that any serious attempt to determine whether grain boundary migration and grain boundary sliding during creep occur with the same activation energy, as Gifkins suggests and McLean rejects, must take into account the effects of impurities on these two processes, Although the work of Weinberg35 indicated that adding small amounts of copper, iron and silicon to aluminum did not affect the grain boundary shear behavior, it should be noted that his starting material contained approximately 60 ppm of impurities. Gifkins' results indicate impurity effects at an impurity level of 8 ppm, suggesting strongly that the most significant impurity range to be investigated lies substantially below that value. R. C. Gifkins (author's reply) — As Drs. Aust and Rutter suggest, the results under discussion may have to be reinterpreted in the light of their own work on grain boundary migration, which was not available to me when the paper was written. Because of their work, Aust and Rutter attach more importance than I did to the activation energy for grain boundary migration during annealing (7.5 kcal per mol) obtained from a "direct" plot of log-rate against the reciprocal of absolute temperature. At the time it was obtained, this value seemed rather low, although it was similar to the value obtained by Bolling and Winegard.36 It was then, and still is, difficult to accept this value because of the low value of the index in the power law for grain growth, which seemed to indicate the influence of impurities. It was also concluded that the low value of the activation energy might have arisen from the manner of selecting rates of grain growth which were truly comparable at the two temperatures. There were many other indications in these experiments and those on recrystallization during creep3? that an impurity, probably oxygen, was of importance. The model for grain-boundary migration which Lucke and Detert had proposed was an obvious possibility and its use yielded an activation energy for boundary migration during annealing of 20 to 25 kcal per mol.

Jan 1, 1961

By Robert E. Allen

The organized curtailment of California oil production is not yet one year old but during its first year it has accomplished so much that it is now firmly established as an agency of economic efficiency. The principle of cooperative curtailment has been adopted by other states and it is safe to say that the principle will continue as long as the demand for petroleum is notably less than the potential production. It' is interesting to note that this same principle of regulating supply to meet demand is now being urged for other industries, such as agriculture and mining. Since Oct. 31, 1929, when curtailment was instituted by the oil producers of Santa Fe Springs and Long Beach in an effort to avert the disaster of ruinously low prices which confronted them, there has been a constant and increasingly effective curtailment program in California. Prior to that time a notable effort toward the restriction of oil production was made under the direction of F. C. Van Deinse during the early summer months of 1929. A considerable reduction of oil output was recorded as the result of this effort, but because of incomplete cooperation and the discovery of still deeper zones at Santa Fe Springs the effort was abandoned; flush field production became unrestrained and prices soon fell to low levels. This initial curtailment movement was educational and experimental. It showed all operators a way out of their overproduction difficulties and developed the principles followed in later curtailment efforts. Thus it was that only a few days after their oil had been reduced to 60 c. per barrel, the operators of Santa Fe Springs got together and agreed to restrict their current production of more than 270,000 bbl. daily to not more than 150,000 bbl. daily. The operators at Long Beach followed the same course a few clays later and agreed to limit their production to not more than 110,000 bbl. daily. The Santa Fe Springs operators chose H. P. Grimm as umpire and director of their proration program. Neal H. Anderson was chosen umpire for Long Beach. Since that time, as the need for curtailment has increased, practically every field of the state has come under the curtailment of these two umpires. Curtailment of the Elwood and

Jan 1, 1931

By A. J. Opinsky

ThE superior performance of nonsag tungsten wire in lamps has been ascribed to the large-grained micro-structure that can be developed in it. The orientations of these large grains have been studied several times; most published data1-' appear to be similar to those plotted in Fig. 1. These new data were obtained by X-ray back-reflection Laue technique from all of the large grains occurring in thirteen different wires that had been heated at the lowest possible temperature for the formation of large grains. Here the wire axis is plotted in terms of the principal directions of the cube. Rosi decided that the preferred orientation of the large crystals could be described by a single ideal orientation, (531), being parallel to the wire axis.' Rieck2,3 and Mannerkoski' have essentially confirmed this finding. Opinsky, Orehotsky, and Seigle argued that the data suggest that (211) is parallel to the wire axis instead of a single ideal orientation.5 This {211} contains the (531) ideal orientation and would appear to be a more general case. Ahlborn and Wassermann report that their orientation data stretch from ( 110) through (531) to (311) 8 This is part of the locus of (211). All these investigators have determined the orientations of the large grains by back-reflection Laue techniques. They have all obtained essentially similar results. On the other hand, Swalin and Geisler, who obtained their data by neutron diffraction, indicated that the preferred orientation of the large grains in doped wire is (110) .7 These findings cannot presently be reconciled with the pole density data described in the previous paragraph. Rosi1 and Rieck2 have advanced arguments about how their orientations could occur. Nevertheless, the crystallographic link between the (110) (cold-worked) fiber texture and the preferred orientation of the large grains has remained missing. This link can be provided through the concept of coincidence-type boundaries. Such boundaries separate two grains that have a certain number of common lattice sites. Coincidence relationships that result from rotations about low index directions are given by Brandon et a1 .' What is desired is a calculation of those orientations that bear a coincidence relationship with the (110) fibers of the cold-worked matrix. This situation arises in the following fashion. Heating the tungsten wire for a combination of time and temperature falling short of the formation of the nonsag structure yields a structure that is still fibrous in nature and the preferred orientation remains (110). During grain growth, the growing grain is in contact with these fibers. It is hence possible that the entire process may begin by the passage of a coincidence boundary into a (110) fiber. The calculations were carried out analytically and checked graphically. Following Brandon et a1.,8 coincidence relationships from 1 in 5 to 1 in 19 have been considered. The results of the calculations are given in Fig. 2. Of the coincidences examined, some of those occurring upon rotation about ( 110) come closest to the experimental points in Fig. 1. Nineteen of the twenty-three data points in Fig. 1 can be attributed to the ideal orientations A, B, C, and D in Fig. 2. As determined analytically, three crystals lie within 4 deg of point A, four lie within 21/2 deg of point B, eleven lie within 5 deg of point C, and one lies within 1 deg of point D-a total of nineteen. The off-lying points are near the |110| point of the triangle.

Jan 1, 1968

By R. D. Satterley

THE Sherwood mine is an iron-ore mine owned and operated by the Inland Steel Co. in the Iron River district of the Menominee Range in Michigan. The property consists of an 80-acre tract in the village of Mineral Hills, about a mile north of the city of Iron River. The ore mined is a reddish brown, nonbessemer hematite and limonite. The ore bodies lie in a large syncline having an east-west strike and are associated with a rock structure that is folded in a complex manner. The two 40-acre tracts run north and south and the shaft is at about the center of the north forty. The shaft is 1286 ft. deep, with the principal operating level at a depth of 1000 ft. from surface. A new level at a depth of 1200 ft. is in process of development. The ore body at the 1000 ft. level is east and west at approximately the line between the north and south forties and at this elevation is from 50 to 250 ft. wide and extends above the level at varying heights of from 50 to 250 feet. The 1000-ft. haulage drift extends south from the shaft, through the east-west ore body to the slates on the south side of the body. The ore body was intercepted in the drifting at about 800 ft. from the shaft and was about 200 ft. wide at that point. A crosscut was extended to the east and west property lines along the south boundary of the ore body. This east-west ore body is laid out in areas 80 ft. wide for stoping with pillars 40 ft. wide. With this plan a stope is approximately 80 by 200 ft. and has a pillar on both sides that is approximately 40 by 200 ft. The ore has a height of from 50 to 250 ft. above the elevation of the level, therefore the height of the stopes varies in accordance with the height of the ore body at each location. From the crosscut, two main raises, each 6 by 7 ft., are put up into each 80 ft. stope area (Fig. I). One of the main raises serves as a manway and the other as an ore raise, through which the ore is transferred from the stope to the tramming equipment. The original layout was for scraping of the ore from under the stopes into the ore raises. The ore raise is put halfway (east and west) along the 80-ft. stope area and usually is in iron formation. The manway and ore raise are on approximately 15-ft- centers. These main raises are put up to a height of from 22 to 30 ft. above the level floor, then from the top of the ore raise a scraper drift (8 X 8 ft.) is driven across the width of the ore body, which is in the neighborhood of 200 ft. From the scraper drift, mill raises are put up at 12 ½ -ft. centers, staggered on opposite sides of the drift, and these are extended 23 ft. above the elevation of the scraper-drift floor. The sublevel connecting the top of these mill raises is called a mill "sub." Other sublevels are developed parallel to the scraper and mill subs at 25-ft. vertical intervals above the mill sub. The mill sub and the other subs above the mill sub are known as sublevels or dog drifts, and are 4 ft. wide and 6 ft. high. These dog drifts

Jan 1, 1945

The early history of coal in West Virginia is all included with that of Virginia in the few records available but for present-day readers it is much more convenient that the account of this area prior to the Civil War be grouped with that since then. West Virginia shares with Maryland in the first record of coal noted in the Appalachian fields. This was along the upper Potomac River, in the fall of 1736, and the data about it are given under Maryland, as most' of the development of the area was in that state. The next record of coal was left by John Peter Salley in his account of the expedition he made with Howard and others in 1742. (See p. 17.) The next reference found is that of Dr. Thomas Walker, in 1750, when he passed through the Pocahontas coal field. This has been described on page 18. Six years later, in March 1756, Capt. William Preston, who was with Major Lewis in his expedition down Big Sandy River, wrote in his journal: "Tuesday 2.... Moved down the branch and- came to the main creek where we camped. Put on half rations. Came into the Cole land; crossed the river 8 times."1 The party crossed from the head of Clinch River to Horse Pen Creek, then to Jacob's Fork and down it to Dry Fork of Tug River; the coal was seen in what is now McDowell County. The early settlers must have known of the presence of the great Pittsburgh bed in the northern part of the state, both along the Monongahela River and elsewhere, because the outcrops could easily be seen along streams in many. places. The report of the Commissioners for Adjusting Claims to Unpatented Lands, made in 1789, contains several references to coal in the names of streams, made years earlier. The earliest is one for 1,000 acres to James Walker, in Monongalia County, "adjoining his settlement on a branch of the right hand fork of Pappaw known by the name of the Stone Cole Lick made in the year 1773."2 Another of 400 acres in the same locality was settled upon in 1777.2 A third spoke of a tract "on the left hand fork of Stone Cole about three miles from the mouth," in 1783.1 Monongalia County then covered all of the northern

Jan 1, 1942

By Seymour G. Epstein

Using a modified capillary-reservoir technique, electromigration of dilute solutions of silver in liquid bismuth has been measured with relatively good precision. The effects of experiment duration, temperature. current density, and silver concentration have been investigated. Chemical diffusion coefficients of silver in liquid bismuth were also measured at temperatures ranging from 300°to 600°C. The effective valence of silver in bismuth was calculated as a function of temperature from a comparison of electric mobilities and diffusion coefficients. In an alloy containing 1 wt pct Ag, the electric mobility of silver increased from 1.65 x X sq cm per v-sec at 300°C to 2.38 x 10-4at 600°C; the diffusion coefficient in-creased from 3.0 to 17.5 x 10-5 sq cm per sec over the same temperature range. Calculated values of effective valence decreased from 0.28 at 300°C to 0.10 at 600°c. ALTHOUGH there has been considerable progress in the theoretical treatment of electron-transport properties in liquid metals, the mechanisms of mass-transport phenomena in liquid metals are still not clearly understood. This is especially true for the case of electro migration, alternatively termed elec-trotransport or electrodiffusion, which is mass transport induced by an applied electric field. A thorough knowledge of the mechanisms governing electromigration will considerably aid in understanding the electronic state of an impurity atom in a liquid metal. Electromigration has been long observed and studied in liquid metals and alloys. However, no satisfactory theory to explain the observed effects has been developed. The disparity in the present theoretical treatments, summarized by Verhoeven,1 has been attributed to the difficulty in describing the momentum transfer between electrons and ions and to the lack of precise measurements in liquid metals, especially at elevated temperatures. Prior to the last decade most of the electromigration studies were qualitative, in that only the direction of migration of alloy constituents was determined with any degree of reliability. These results have been summarized by schwarz,2 who was able to measure the electric mobility of several elements in mercury. More recently electromigration in liquid metals has been measured by a variety of techniques, with a varying degree of success. Mangelsdorf3,4 made precise measurements on dilute amalgams at room temperature, using a technique relating changes in composition to changes in alloy resistivity, but was unable to make measurements at elevated temperatures. Using a modification of this technique, Verhoeven and Hucke5 measured electromigration and resistivities in liquid Bi-Sn alloys. However, the resistivity technique is not sensitive to small composition changes and is impractical for very dilute alloys. Verhoeven and Hucke6 also measured electromigration of several solutes in liquid bismuth by adapting the capillary-reservoir method for determining diffusion coefficients in liquids. The reported precision of these measurements was poor, however, primarily due to the large uncertainties in the chemical analyses to determine concentration changes. Belashchenko7 has summarized the recent Russian investigations of electromigration, many of which, however, are of questionable accuracy. The present study was initiated to develop an experimental technique which would be both versatile and sufficiently sensitive to yield precise measurements of electromigration of solutes in dilute metal alloys at elevated temperatures. Using this technique, a comprehensive study of silver in liquid bismuth was made to determine the effects of experimental variables on the apparent electric mobilities. Chemical diffusion coefficients of silver in liquid bismuth were also measured over the same temperature range for comparison with the electromigration data. EXPERIMENTAL TECHNIQUE Electromigration Measurements. Electromigration of silver in liquid bismuth was measured by the capillary-reservoir technique, similar to that used by Verhoeven and Hucke,6 but modified to yield more

Jan 1, 1967

By Gunnar Almgren

Hole deviation has great consequences on mining economy, especially for long hole drilling technique. First of all the bore hole datas are concerned but also such factors as development, loss of ore and waste rock dilution are influenced. Hole deviation for sublevel open stoping is illustrated with examples from some mines. The deviations are indicated as mean values but also as standard deviation values, owing to their statistical distribution. The economic influence of the hole deviation is especially studied for steep, small lowgrade orebodies, mined with big hole blasting. Hole deviation can thus influence costs up to US$ 3-4 per ton for operating, development, losses of ore and rock waste dilution. This cost is of the same magnitude as the total operating costs for many sublevel stoping mines. The economic savings in accurate drilling are therefore substantial and are worth all attention.

Jan 1, 1981

By E. P. Chartkoff, W. P. Sykes

In 1926 one of the authors published researches on the determination and description of the iron-tungsten and iron-molybdenum systems,' including the equilibrium diagrams. In 1929, further work was carried on, including the examination by X-rays, which is recorded here. Meas-urements were made of changes in lattice parameters in the solid solutions. Precipitation from the solid solution and the accompanying changes in hardness were studied as well as the formation of the intermetallic com-pound phases upon sintering a mixture of metal powders. Materials All the specimens were prepared from the same quality of metals and by the same methods as were described in the determination of the constitutional diagrams. The metal powders as mixed and pressed were sintered or fused in a hydrogen atmosphere and subsequently treated as indicated in the titles of the figures. The formation of the iron-rich solutlon in the solid was accomplished by sintering in hydrogen for a period of 20 to 30 hr. at a temperature 25' to 50' C. below the melting point of the eutectic. The tungsten-rich and molybdenum-rich solid solutions of iron were prepared by adding the iron as a solution of iron ammonium oxalate to the oxide of tungsten or molybdenum, followed by a hydrogen reduction. This method results in a homogeneous alloy after sintering the pressed metal powder for 20 to 30 hr. at a temperature slightly below that of the peritectic reaction in the system involved. For X-ray examination the specimens were variously prepared, depending on the nature of the sample and what it was desired to show. For example, the iron containing tungsten or molybdenum in solid solution was cut with a file, the chips were put through bolting cloth, and this powder of filings formed the specimens for comparative study. The

Jan 1, 1930

By A. G. Jordan, W. Jeitschko, Paul A. Beck

The occurrence qf the V phase structure /Zr,Co,Ge, type) in ternary syste7ns (titanium, zivconium, niobium, lanta1urn) -(nickel, cobalt, iron)-(silicon, germanium) was incestigated. Nine V silicides and four V gertrlanides were found and their lattice constants are reporled. The lattice constants of twenty-one preri-ously identified E phases (TiNiSi type) are given. The average atomic volumes of these phases are discussed in relation to similar binary phases. ThE occurrence of a phase Ti4Ni4Si7 was first reported by Westbrook. DiCerbo, and peat' who gave it the name "V phase". They also reported the existence of an E phase TiNiSi. Subsequently a systematic study was undertaken in this laboratory to explore the occurrence of E' and V phases3 in related ternary systems. In the meantime the crystal structure of the E phase TiNiSi 4 and of the V phase Zr4CO4Ge 75,6 was determined. In the present paper the details of the V phase investigation and the lattice constants of the E and V phases are presented. V PHASES Alloy specimens of approximately 10 to 15 g were prepared by arc melting under argon (99.996 pct Ar) atmosphere. The starting materials were all of purity higher than 99.9 pct, with the exception of cobalt. which contained 0.14 pct Fe as the only major impurity. The weight losses were in all cases less than 2 pct, in most cases less than 1 pct. The samples were encapsulated in fused silica tubes with sufficient argon to yield about 1 atm pressure at the annealing temperature. After the homogenization anneal. Table I. the specimens were water-quenched. A representative portion of each specimen was then examined metallographically (etchant: 20 pct HNO,. 10 pct HF. 25 pct glycerine, 45 pct H20). Only minor amounts of second- and third-phase particles were observed in the specimens listed in Table I, with the exception of alloys Zr4Fe4Si7 and Ta,Fe,Si,. which contained an estimated 10 pct by volume of foreign phases. X-ray powder photographs were taken with a Seeman-Bohlin type focusing camera and Fe-KO radiation. Of the thirty possible combinations of elements in the ternary systems (titanium, zirconium. vanadium. niobium. tantalum)-(iron. cobalt, nickel)-(silicon. germanium) thirteen V phases could be identified. In the remaining seventeen ternary systems and also in the systems Cr-Ni-Si and (M0.W)-(Ni.Co)-Si no V phase was found at the composition 4:4:7 after annealing at temperatures between 900" and 1200'C. For the determination of the lattice constants of the V phases Debye-Scherrer photographs were taken using the asymmetric film arrangement and CrKcr radiation (ka1, = 2.28962A). Using the positional parameters, as determined6 for Zr,Co,Ge,. Table 11. intensity calculations were carried out for each of the V phases with the aid of a computer program.: Thus unequivocal indexing of the diffraction patterns was greatly facilitated. The lattice constants. Table I. were then computed by a least-squares fit of the high-angle lines with f (0) = cos2 Q as extrapolation function. Only few. if any. very weak impurity lines were observed, with the exception of the three iron alloys Zr,Fe,Si7. Zr4Fe,Ge7. and Ta,Fe,Si7. The agreement

Jan 1, 1970

By Phyllis A. Lyday

Jan 1, 1985

By H. R. Peiffer

Hardening of soft metals can be accomplished by dispersing finely divided hard particles in them. The dispersing of finely divided alumina in silver in the presence of oxygen yields a high strength material which is unusual in that its mechanical properties above the melting point of the continuous Ag-O alloy matrix are similar to other solids. The tensile strength is studied for two of these alloys, one of which contains 15 pct by weight alumina and the other 20 pct by weight alumina. The average fracture strengths above 960°C of these alloys were found to be 0.4 x106 dynes per sq cm and 3.8x106 dynes per sq cm respectively. The strengths appenred to be independent of temperature above 960° C. The creep behavior of the 20 pct alumina material was studied above 960°C. The initial creep rate, 6 , of this material can be represented by where s is the applied stress and E the activation energy for the process. This energy is of the order of 1.7 to 2.1 ev. HARDENING of soft metals by the addition of finely divided, hard particles has resulted in the production of materials with excellent creep resistance and with inhibited recrystallization.' It has been demonstrated that such composites have useful strength up to temperatures very near the melting point of the soft metals, but one might expect that the strengthening by the dispersed particles ceases to be of importance above the melting point of the softer phase. This, however, is not so.2 In this paper the strengthening of a liquid Ag-O solution by the presence of dispersed alumina is discussed and experimental data concerning the mechanical properties of such a material at temperatures above 960°C presented. EXPERIMENTAL PROCEDURE Specimens were prepared using powder metallurgical techniques. Finely divided silver oxide was mixed in the appropriate proportions with "Linde B" alumina. For these experiments the specimens contained 15 or 20 wt pct alumina in pure silver.* These alloys were used in these experiments since they were the ones that could be handled readily enough to yield experimental data. Silver oxide was used in preference to silver because it is readily available in a very finely divided form and because the presence of excess oxygen in the silver is important to the properties2 of the material. The powders were mixed wet, using alcohol as the medium, in an ordinary food blender until a uniform mixture was obtained. They were then dried and heated to reduce the silver oxide to silver. Only a fraction of the finely divided silver remains unoxi-dized upon removal from the oven since the finest particles of silver oxidize immediately upon contact with air. The remaining fine silver served as a binder during pressing. The mixture was then pressed at 20 tons per sq in. into shoulder-grip (reduced section 1/4 in. by l/4 in. by 1 1/4 in.) and rectangular bar specimens (l/4 in. by 1/4 in. by 2 in.). The green specimens were heated very rapidly in a globar furnace to 1000°C, held at temperature untic they had reached theoretical density and then furnace cooled. The strength of the two compositions at temperatures above 960 °C was determined by pulling shoulder grip specimens inside a furnace mounted on a tensile machine. Specimens were gripped by means of wires wrapped around the shoulders of the specimen. Temperatures were measured by means of a chro-mel-alumel thermo-couple placed in the vicinity of the specimen. Control of temperature (within ±°15C) was accomplished by means of a Weston Recorder-Controller. Before loading, specimens were held at temperature for approximately 15 min in order to insure uniform specimen temperature. The low loads were measured by a special load cell designed by Baldwin Lima Hamilton. All testing was performed on a FGT testing machine of the same com-pany. Creep studies were performed in bending utilizing rectangular specimens of the 20 pct alumina alloy. Specimens supported at both ends by knife edges of inconel were placed in a globar furnace, heated quickly to temperature, and the deflection of the beam measured optically as a function of time. The weight and size of the specimen were predetermined and the maximum stress on the beam calculated from

Jan 1, 1962

By W. C. Hagel, H. J. Beattie

Phases present at 2200° and 1500°F (1204° and 816°C) were identified in sixty wrought developmental austenitic alloys possessing wide compositional variations. The bases were iron-, cobalt-, and nickel-rich as well as a base with equal parts of each. There are only two structure types previously not found in similar alloys, viz .-the Co3 W and the Fe3Al types. A molybdenum-rich monocarbide decorates dislocations with unusual clarity. Other results provide correlations between alloy composition and phas e precipitation. Grouping intermetal -lic phases into three general classes : I) geometrically close-packed, 2) topologically close-packed, and 3) bcc derivatives, the nickel base prefers the first, the iron base the second, and the cobalt base the third—each base tending to shun the other two classes. Thus, a crystal-chemistry effect previously noted by Laves and Wallbaum can he expanded for these Group VIII elemental bases. There appear to he no quaternary or higher -order structure types requiring more than three atomic species. AFTER studying aging reactions in many diverse commercial austenitic alloys1-4 as a function of detailed time-temperature variations in heat treatment, it became apparent that matrix composition influenced structure types and morphologies to a large extent. These tendencies were related4 to a crystal-chemistry effect uncovered by Laves and Wallbaum.5,6 We have now directed our efforts to exploration of the whole ternary field, covering the standard base elements—iron, cobalt. and nickel— with 10 to 20 pct Cr and moderate amounts, up to 10 pct, of the usual alloy additions. Solutioning and aging treatments were held constant with major emphasis on X-ray identification of microconstituents. The possible existence of exceptions to the Laves-Wallbaum effect, or any new phases, was sought. Phases appearing in austenitic alloys can be classified as geometrically close-packed (gcp), octahedral or nonoctahedral interstitial compounds, topologically close-packed (tcp), semicarbides, and bcc derivatives. Crystal structures of the first four classifications can be visualized as a dense packing of semirigid spheres of different sizes, while the bcc derivatives represent a less efficient packing of spheres. The Laves-Wallbaum effect involves the gcp and tcp phases. Gcp phases possess both tetrahedral and large octahedral interstices; examples are Ni3Ti(n), NiSAl(y'), Co3W(E), and other ordered AB3 compounds where B atoms are smaller than A. Their precipitation is primarily intragranular, presumably coherent with an austenitic matrix, and a chief source of strengthening. Most octahedral interstitial compounds (e.g., CbC, Tic, TiN, Mo2C) have a gcp lattice of large metal atoms which accommodate small carbon or nitrogen atoms in the octahedral interstices. The compound Ti2SC, previously designated Y phase or T phase, can, with some reservation due to its partial co-valency, be placed in this category.7 The nonoctahedral interstitials (e.g., M7C3, Fe3C) represent close-packings of spheres in structures that provide larger triangular-prism interstices for carbon, since the octahedral interstices formed by chromium and iron atoms are too small. Tcp phases possess only tetrahedral interstices; examples are Laves (Fe2Ti, Fe2Cb, Fe2W...AB2), p(Fe7MO6, Co7W8.... A8B7), and (FeCr, Co2Cr3)

Jan 1, 1965

By B. D. Cullity

AS methods for measuring fiber textures become more exact, it becomes justifiable to scrutinize an observed pole-density curve for evidence of minor texture components. These are disclosed by minor maxima or abnormally broad major maxima. One possible source of these minor components is twinning of the main component. In cubic metals and alloys, there are two kinds of twins: 1) Annealing twins in face-centered cubic metals. These are reflection twins on {Ill), and they can be expected to be present in recrystallization textures. 2) Deformation twins in body-centered cubic metals. These are shear twins on (112). Although usually formed only by impact, they might conceivably be present in the deformation texture of severely cold-drawn wire. Fortunately, both kinds of twinning lead to the same orientation relationships. It thus becomes possible to prepare a single list of angles between various planes in parent crystal and twin, which is helpful in examining pole-density curves for evidence of twinning in any cubic metal or alloy. Such a list of interplanar angles is given in Table I. This table consists of three parts, corresponding to the three major texture components—<100>, <110>, and <111>-most commonly found in the fiber textures of cubic metals. The table lists the angle between the pole of {hkl}, in either the parent crystal P or the twin T, and the fiber axis <uvu>. The crystals with <uvw> parallel to the wire axis are here

Jan 1, 1959

By J. T. Norton, A. L. Mowry

S. J. SINDEBAND*—(1) Discussing the properties of the powders used, Mr. Rostoker mentioned a silicon powder as being between 150 and 325 mesh. We always had much difficulty in measuring particle size of silicon powder by screen analysis, because of its tendency to agglomerate. I would be interested in the method used to measure these particle sizes. (2) Mr. Rostoker maintains that the measurement of magnetic properties is more accurate in determining complete homogenization of an alloy, than is the X ray diffraction technique. I wonder whether this is really true. Even when diffusion is complete, magnetic properties will change during continuation of the heat treatment, due to change in density and pore shapes, as has been demonstrated by Mr. Rostoker himself. Which effect is faster, the diffusion of the alloy components or the attainment of final density, will, in my opinion, depend very much on initial material and sintering conditions used. For magnetic applications, of course, the magnetic measurements are most suited for determining the point at which equilibrium conditions are reached. (3) I was glad to see that Mr. Rostoker had used sample sizes which are similar to those I had used previously, and I believe that ring samples of about 2 in. od will become more or less standard samples for the determination of magnetic properties of powder metallurgy products. I should like to ask how the density was changed for the samples on which the effect of porosity was investi- gated, and, further, why the sintering temperature used for this series of experiments was so low. It is somewhat surprising that a 24-hr treatment at 850°C acts so much more to spheroidize the pores than a treatment for 1 hr at 1100°C. But the effect seems to be indisputable. I have made an investigation of the influence of sintering temperature for longer times on the maximum permeabilities of iron powder compacts which was presented at the International Powder Metallurgy Conference in Graz, in 1948, and I hope that these results will be published here within a short time. The results of this investigation are confirmed by Mr. Rostoker&apos;s findings that the change of time from 1 to 24 hr changes the permeability behavior considerably in the direction as indicated by Polder and Van Santen for spheroidiza-tion of pores. I do not quite understand Mr. Rostoker&apos;s explanation of the influ-

Jan 1, 1950

Jan 1, 1946

By J. Szekely, Robert J. Fisher

A formulation is Presented and solutions are given for the problem of transient heat conduction in a sphere that undergoes a spatially uniform radiative heat exchange with its environment. The solutions were obtained by the numerical integration of the appropriate Partial differential equation and are Presented in a graphical form by Plotting a dimensionless average temperature against the Fourier number with the radiation number as a paranreter, for various initial sphere and environment temperatures. In addition to these numerical results asymptotic analytical solutions are also given. PROBLEMS involving the transient heating or cooling of droplets and particles frequently arise and are of importance in metallurgical operations. Spray refining, vacuum degassing, high-temperature gas-solid reaction systems, and pebble heaters are but few of the numerous examples that may be quoted. The practical interest in these problems from a design or operational point of view is to evaluate the change in the particle temperature with the time given its physical properties, initial temperature, and that of the environment. At the high temperatures encountered the principal mode of heat transfer between the particles and their environment is by thermal radiation; in case of vacuum degassing due to the very low thermal conductivity of the gas space the convec-tive components are negligible and radiation is the only heat transfer mechanism. Although much work has been done on transient heat conduction problems, the special class mentioned here, in which thermal radiation is specified at the bounding surface, received little attention to date. One contributory factor to this situation may be the nonlinearity of the radiation term in temperature, which in general precludes the use of analytical techniques and requires numerical or analog solution of the appropriate differential equations. In fact the only solutions of general nature that are available at present pertain to semi-infinite media and slabs.&apos;-3 The work on which the paper reports forms part of a program aimed at the theoretical and experimental study of transient radiative heat exchange between particles and their environment. The purpose of the present paper is to develop a formulation and solutions to the problem of transient heat conduction in a sphere that undergoes a spatially uniform radiative heat exchange with its surroundings. The solutions, obtained by the numerical integration of the appropriate differential equations, will be presented graphically, by plotting dimensionless parame- ters covering the range of variables relevant to metallurgical interests, thus affording a ready reference for design calculations. In addition to these results, approximate analytical solutions are also given which represent asymptotes, corresponding to extreme values of the variables mentioned. FORMULATION Consider a spherical particle of radius, a, initially at uniform temperature, Ti (T measured on the absolute scale), having a thermal conductivity, k, density, , specific heat, C, and thermal diffusivity, a. At time = 0 let this particle be exposed to an environment which is at a temperature T, and subsequently let there be a purely radiative heat exchange between the particle and the environment resulting in a spatially uniform heat flux at the surface. If in addition to the above we make the assumptions that the sphere is a gray body radiator, homogeneous, isotropic, and opaque, and that the physical properties are independent of temperature, conservation of heat in the sphere may be written as follows: The boundary condition contained in Eq. [3] states that the initial temperature of the sphere is considered uniform, equalling Ti, whereas Eq. [4] is readily obtained from symmetry considerations. Eq. [5] expresses the continuity of the heat flux at the surface of the sphere, or in other words the condition that the rate of heat exchange between the sur-

Jan 1, 1969

GOD the Almighty has all things well ordered; in G particular, the effects and attributes of the seven planets whose reign and course (by the grace of God) determine for the most part not only our own life and death but also the growth and decay of vegetable and mineral life, so that the aforesaid planets generate and develop in a wondrous way the ores of gold and other metals in minerals, rocks, and earths. Specifically, the Sun develops the ores of gold, the Moon the ores of silver, Venus the ores of copper, Saturn the ores of lead, Jupiter the ores of tin and bismuth, Mars the ores of steel and iron, and so on. Since, however, no ore is made alone but each is made and wrought so that it is associated with other ores, it is necessary to know the art of separating the thus-made ores after they have become metals; as for instance, silver from lead and copper; gold from silver, and so on. [2]* If this is to be done usefully, you must be able to assay and must understand everything that is needed in connection therewith. It is obviously true and clear as light of day that some kinds of copper contain silver and some kinds of silver contain gold. In order that you may be able to separate them, so that each is obtained by itself and can be worked with profit and re ward you need first of all a true assay for the values of such metal. The assay, by revealing how great they are, whether the pure has been obtained separate from the worthless matter, and what the admixture is, advises you whether it would be worth the expense and the effort to start mining operations. Assaying also indicates how much silver there is in a centner of ore or how much copper and lead there are in

Jan 1, 1949

c

Jan 1, 1918

By L. W. Reynolds, R. F. Campbell, K. G. Carroll, S. H. Ballard

Based on metallographic and X-ray data probable equilibrium conditions from 1340" to 2400°F are presented for the composition range investigated. These are correlated with investigations of Takei and Kuo. Provision is made for existence of Mo, C and (Fe, Mo)2,C, carbides heretofore omitted in diagrams in this composition range. These carbides and (Fe, Mo),C, in equilibrium with ferrite and austenite, restrict the austenite and austenite + ferrite fields to lower carbon contents and higher temperatures than in the Fe-C system. OK groups of steel of different molybdenum content, but with approximately the same carbon variation in each group, Table I, were studied. The alloys were melted in an acid-lined 30-lb high-frequency induction furnace, and the ingots forged to l-in. rounds, which were then ground to 0.75-in. diam. To minimize chemical segregations a short length of each bar was given a high-temperature heat treatment as listed in Table I. Specimens 0.062 to 0.125-in. thick were thereafter cut from the homogenized bars for heat treatment to determine phase changes in the alloy. Heat treatments were performed in either a lead bath or muffle-type electric furnace, depending upon the temperature required. Maximum temperature variation was * 2" F in the lead bath and * 5"F up to 1900°F and +8"F above 1900°F in the electric furnace. Adequate protection of the specimen from the oxidizing atmosphere in the electric furnace was obtained by sealing the specimen in either a pyrex or a silica capsule which was evacuated or not as circumstances required. For austenitizing followed by quenching to an isothermal temperature, the specimen was placed in a closed-end refractory tube the mouth of which, extending beyond the furnace, was connected to a vacuum pump. The specimen could be withdrawn from this tube and quenched as desired. IDENTIFICATION OF PHASES The principal method of identification of phases was metallographic examination conducted on surfaces well removed from exposure to lead or atmosphere effects during heat treatment. Hardness measurements (Dph/lOkg) were also made on these surfaces. The etching reagents used and their effects are listed in Table II. Martensite and ferrite were readily recognized by their customary appearance after etching with saturated picral or 1 pct nital. The presence of liquid at high temperature was indicated by curved interfaces characteristic of boundaries between solid and melt, by intergranular pools of dendritic areas in a carbide matrix, and by a black network coincident with austenite grain boundaries. Examples of these structures are shown in Figs. l(a) and (0). The types of carbide which were attacked by the electrolytic chromic acid etch and the alkaline KMnO, etch, Table 11, were identified by X-ray analyses of extracted carbides of five alloys. Carbide residue was obtained from a metallographic specimen by etching the specimen for 24 hr in hydrochloric-picric acid in alcohol (grain-size reagent), after which the carbides, standing in relief, were scraped from the surface of the specimen and mounted on a glass slide. Diffraction patterns were obtained with a Philips spectrometer using iron-filtered cobalt radiation. Figs. 2, 3, 4, and 5 illustrate typical etching behaviors with chromic acid and alkaline KMnO,. Chromic acid attacked Mo,C as shown in Figs. 2(a) and (b)-but not (Fe, Mo),C, Fig. 3(b). Alkaline KMnO, attacked (Fe, Mo),C, Fig. 3(c), and also attacked M0,C. In accordance with these behaviors, a typical differentiation of coexisting Mo,C and (Fe, Mo),~ is shown in Figs. 4(a) and (b). The carbide (Fe, Mo),,C, could not be obtained free of other coexisting carbides for etching experiments. The behavior. however. of coexisting carbides identified by x-ray diffraction as Mo,C ind (Fe, Mo),,C, indicate that (Fe, Mo)23C6 is not etched by chromic

Jan 1, 1961