Search Documents

By W. R. Ingalls

Jan 1, 1922

By W. R. Ingalls

Jan 1, 1922

By James W. Wade

THIS discussion of the future supply of lead refers only to the next ten-year period. Beyond that no prediction can be made that would be of sufficient accuracy to serve any purpose. When any commodity is by an unsatisfied demand forced to a higher price level, and the profits of those who are able to produce the commodity are greatly increased, there is awakened a new interest in the commodity on the part of both producer and consumer. The consumer attempts to reduce his costs by developing substitutes or assisting in the development of new sources of supply. Lead is now going through this stage. The lead producer is increasing development expenditure and searching for new mines. The consumer is developing substitutes as illustrated by the increasing use of zinc oxide as a pigment, and the use of dry batteries in radio sets. The search of the Ford interests for lead, by prospecting in Missouri and Idaho, is induced by the effort to develop a new source of supply. Considering the index figures of the Department of' Commerce, it is evident that lead is on a substantially higher price level. For February, 1926, the index figure of lead is 209, while the general commodity price index is only 156, 100 being taken as the base for 1913.

Jan 1, 1926

By AIME AIME

T. E. PURCELL, general chairman . of the local committee, opened the seventh meeting of the Fuels Division A.S.M.E. and the Coal Division A.I.M.E., at the William Penn Hotel, Pittsburgh, Oct. 28-29, by introducing Harry M. Moses, president, H. C. Frick Coke Co., who welcomed the 500 registrants to "our town." Mr. Moses, in his brief talk, declared that in the postwar period each of the new centers must have a reason for existence. Pittsburgh, he said, has no iron ore, or bauxite, and limestone is scattered and not near by; but Pittsburgh does have low-cost fuel within reasonable distance. Its problem is the economical utilization of the low-cost fuels that remain, as the high-quality fuels are gone. Mr. Moses expressed confidence in this group in the solution of the problem and looked forward to what they would do. Harold V. Coes, the first A.S.M.E. president to attend one of these conferences, responded. He thoroughly believed in these joint meetings - in the cross-fertilization of ideas. Each Division learns from the other. Mr. Purcell then turned the meeting over to J. E. Tobey who presided over the coal research session that followed.

Jan 1, 1943

By Ovid W. Eshbach

ENGINEERING education has been powerfully affected by the impact of war, just how powerfully can be better understood after considering the postwar problems regarding students, staff, and plant. In time of war no one will question the necessity of expediency of military training. With the cessation of hostilities, expediency gives way to the evolutionary process of strengthening engineering education as need is exemplified by experience. During the war, except for the Navy V-12 program, engineering education was at its lowest ebb of the century. Freshman enrollments were largely limited to those graduating from high school at the age of seventeen; and the upperclass, to those disqualified for active service. In most schools the experienced staff was either in service or government and industrial research. Many may never return to their former occupations. The most immediate problem is that of maintaining and building a staff to meet the enrollment of returning veterans. It is estimated that out of the eleven

Jan 1, 1945

By John R. Lotz

DEVELOPMENTS in Iran currently arousing interest in a considerable portion of the world, particularly on the part. of that country's immediate neighbor on the North and in our own country, an inseparably related to and largely dependent upon the government's attempts to strengthen its economy and improve the standard of living of its people. These efforts are encompassed by provisions of the Seven-Year Development Plan recently enacted and not, in the process of implementation. It is a fine example of what one financially sound but extremely backward and poorly equipped country has undertaken to do on its own account and with its own resources. This Seven-Year Plnil was formally authoriztld by an act of the Iranian Parliament in February 1948. Its stated objects are to carry out such plans for the development of the country and its economy as ail1 raise the standard of livinc: and standard of education of the people, and re- duce the cost of living. A seven-yrar program for carrying out the work within the limits of appropriations was assigned under the law. The total amount to be expended during the seven- year period was fixed at the equivalent of $670 millioil at current rates of exchange.

Jan 1, 1950

By L. S. Cates

THE war is now behind us. We in the mining industry feel a just pride in the part that our industry and our men and our products played in defeating the enemy on the fighting fronts around the world. In five years of mobilization and actual combat, our mines and oil wells produced over 3 billion tons of coal, a billion tons of petroleum, 500 million tons of iron ore, 21/4 million tons of lead, 31/2 million tons of zinc, 5 million tons of copper, 14 million tons of bauxite, 17 million tons of sulphur, 68 million tons of salt, and 3 million tons of potash. It was an unparalleled performance. But what of today? Why the present low production and high costs? Among the black clouds in the mining sky none are so black as that presented by the labor situation. We know it is the result of the legislation and the interpretation of that legislation in the past ten or fifteen years. Since the passage of the Norris-LaGuardia Act in 1932, we have had nothing but a succession of laws, regulations, and decisions that have intensified the strength of the unions and made the operators of the mines and the sources of their financing prartirally impotent

Jan 1, 1946

By J. V. W. REYNDERS

FIRST of all let me express my affectionate gratitude for the cordiality and good will of your reception. On the part of the men I venture to interpret the character of your greeting, not only as a recognition of the position to which you have been good enough to elect me, but also as an expression of your friendly attitude. However, I cannot pass over the tribute of the ladies so casually: Nor does it seem possible to do justice to my sentiments in addressing them collectively. I would feel more equal to the task if I could have the opportunity to talk to them singly, in doing which I know I may count upon their good sportsmanship not to compare notes. There has been some discussion between Mr. Kelly and myself as to our respective duties on this occasion: The precedents are not clear as to whether the retiring or the incoming president is expected to speak at length. Mr. Kelly's argument was that as the incoming president confines himself to promises for the future his field is a broad one and his opportunities for extending his remarks correspondingly unlimited.

Jan 1, 1925

By Clyde E. Williams

MODERN steelmaking has gradually evolved from an inefficient small-scale operation, utilizing tiny units, to a highly efficient one utilizing large units almost completely mechanized. The leading position of the United States in the steel industry is due to the possession of easily assembled high-grade raw materials and large-scale highly developed plants. Modern integrated steel operation is largely one of material handling. Mining and transportation of iron ore, coal, and fluxes, coking the coal in by-product ovens, smelting the ore with coke and limestone in blast furnaces, converting the resulting pig iron into steel in the Bessemer, or in the open hearth when supplemented with scrap, and fabricating the resulting steel ingots in the shapes of commerce all are done on a huge scale, mostly by machinery, most of the labor being employed either in operating the machine or keeping it in repair. At the same time the quality and uniformity of the product have been greatly increased by the development of scientific knowledge and operating skills. Thus, the steel industry in this country is highly developed both mechanically and technically.

Jan 1, 1942

By Arthur Mitchell

POSSIBLY in no other of the non-ferrous mining districts of this country has the use and develop-ment of mechanical loaders been carried to such an extent as in the "lead belt" of Southeast Missouri. It has become apparent to the four mining companies in the district that it is imperative to apply satisfactory mechanical methods to the chief remaining stage of the entire operations-mining, milling, smelting and refining-in which manual labor is still largely used to handle material in process. With increasing wages and with the reduction of the metal divisor by the extension of mining into lower-grade orebodies, the shoveling cost per ton of lead produced has become relatively so large that in an effort to reduce it there is ample justification for considerable capital expenditure. Hand shovelers load about 18 tons of ore per shift and the average grade is less than five per cent. lead. Further, the ore is relatively heavy, about 21 cu. ft. to the ton when broken, and is often so coarse and so closely compacted after shooting that it requires much more block-holing, sledging, and muscular effort to shovel than, for example, does the cherty and more granular ore of the Joplin district or the finer ore in the headings of a drift mine. No mining company desires to pay for mere back muscles if it be economically feasible to avoid it, and labor saving machinery should be susceptible of operation by older employees, who are no longer capable of the more strenuous manual occupations.

Jan 4, 1923

By P. H. Turnock, R. D. Pehlke

The effects of mutual interactions between elements on the solubility of nitrogen in liquid iron alloys containing chrormium, columbium, molybdenurn, nickel, or silicon have been determined. The equilibrium nitrogen solubilities in the liquid iron alloys were measured by the Sieverts method. The second-order effects caused by the presence of chrormium, columbium , or silicon in the melt were found to be significant. The solubility of nitrogen in liquid iron alloys containing several alloying elements has also been measured as a function of melt temperature and nitrogen pressure. The heat of solution of nitrogen in microcomponent iron alloys has been found to be a function of the logarithnz of the activity coefficient of nitrogen, irrvespectilje of the composition of the melt. The heat of solution of nitrogen in pure liquid iron was determined to be 1265 ± 450 cal per g-atom of N over the temperatxue range 1600° to 1800°. Sieverts ' law was obeyed for all melt compositions studied in the pressure interval 0.4 to 1.0 atm. The solubility of nitrogen in liquid pure iron and in many dilute binary liquid-iron alloys has been the subject of many investigations. Pehlke and Elliott' made a comprehensive investigation on this subject in which they summarized and compared previous researches. However, the practical application of these solubility studies requires prediction of the nitrogen solubility in the multicomponent alloys encountered in operating practice. The interaction parameter as defined by wagner2 has been used to predict the behavior of a solute in a complex alloy, and a modification of this approach has met with reasonable success in several instances.'1"5 The necessity for extending the nitrogen solubility data on binary alloys is caused by the lack of direct measurements of the solubility of nitrogen in molten alloy steels. A direct comparison between measured solubilities and those predicted for multicomponent alloys based on data in binary systems has been made in only a few instances, and most of these were reviewed by Langenberg,6 who developed a graphical technique for predicting nitrogen solubilities in multicomponent iron alloys. The solubility of nitrogen has also been studied over the entire Fe-Cr-Ni ternary system by Humbert and Elliott.? Both studies compared the solubilities computed from binary iron alloy data with those measured in ternary alloys in the liquid state at 1600°C. Most of the nitrogen solubility measurements referred to above were for iron alloys at 1600°C; thus, the ability to predict nitrogen solubilities in molten iron alloys has been restricted primarily to alloys at 1600°C. Recently, Nelsson8 devised an approximate method for calculating the change in nitrogen solubility in molten iron alloys as a function of temperature, but an assumption of regular solution behavior limits the applicability of the method. Chipman and Corrigan9,10 have developed an empirical correlation. based on the activity coefficient of nitrogen in the iron alloy at 1600°C, which facilitates the estimation of nitrogen solubilities at higher temperatures. This method also has limitations, due to the necessity of calculating the activity coefficient for nitrogen in a multicomponent iron alloy at 1600°C from the nitrogen solubility data for binary iron alloys. The shortcoming of such a straightforward approach to the problem of predicting nitrogen solubilities is the disregard of mutual interactions between elements in a complex iron melt. This investigation was conducted in an attempt to provide a more reliable method of predicting nitrogen solubilities in multicomponent iron alloys. The effects of the mutual interactions between chromium, nickel, silicon, molybdenum, or columbium in iron were studied, using the Sieverts' technique1,7 to measure the effects of alloy composition, temperature, and pressure on the solubility of nitrogen in ternary liquid iron alloys.

Jan 1, 1967

By R. M. Rose, K. A. Jones

Resistive measurements ulere made on superconducting niobium single crystals in transverse magnetic fields. Crystals were grouln in both high and ulfrahigh vacua, doped with stnall quantities of oxygen, and annealed in ultrahigh vacua at temperatures from 900' to 1350°C. Maxima in the fluxoid pinr~ir~g force were observedfor the [100] and [210] directions. The increase of the critical current density with dissoved oxygen was seen to saturate at relatively low concentration. This behavior, and the variation of J, and residual resistivity (as a function of oxygen content and annealing) of both clean and dirty gassy) crystals, is seen as a consequence of the formation of clusters with (210)~b habit planes and (200)ffo common boundaries. These suboxide clusters are apparenlly stable at high temperatures and very low oxygen concentrations. It is generally known that dissolved oxygen at concentrations well below the solubility limit sharply increases the critical current density of superconducting niobium.' Such a result would not be expected if Nb-0 solutions were random, not even as the result of segregation on the scale usually encountered in solid solutions. According to the Kim-Anderson theory of flux creep,' the critical transport current density is determined by the pinning force Fp associated with some feature of the microstructure. As the Lorentz force. a or (J X R), of the transport current in the magnetic field approaches Fp, flux creep and then flux flow occur. The pinning force is expected to be quite small if the heterogeneity involved is significantly smaller than tte range of coherency which for niobium is circa 250~.~ Although the strain field of an individual oxygen atom in the niobium lattice is relatively large, it does not seem plausible that individual atoms could be so effective as to account for the data. Also, ~ramer~ found that straining and strain aging specimens containing small amounts of oxygen on occasion decreased the residual resistivity. A possible explanation for the above behavior may be found in the work of van Ooijen and van der Goot,= who found that annealing changed J, for niobium foils containing oxygen, and they attributed the changes to ordering of the oxygen atoms. This phenomenon has been observed by other investigators using X-ray and PROCEDURE Cylindrical 4-in.-diam niobium single crystals with axial orientations [ill], [110], [112], and [oo~] were grown from pure niobium, see Table I for analysis, in an ion-pumped ultrahigh-vacuum system using the electron beam floating zone technique. Total pressure during growth was lo-'9 torr: the oxygen partial pressure was less than lo-" torr, as determined by a mass spectrometer. These crystals will be referred to as the "clean" crystals. Similar crystals were also grown in another system at a pressure of 5 X 10"6 torr. These crystals will be referred to as the "dirty" crystals. Specimens 14 in. long were cut from the as-grown crystals and one end was polished down to no. 600 carbide paper smoothness. A back-reflection Laue photograph was then taken in order to fix the crystallo-graphic directions transverse to the crystal. The critical current density J,, the current density necessary to produce a voltage drop of 1.0 pv between voltage leads placed a in. apart, was determined as a function of the magnitude and direction of the transverse magnetic field and of the oxygen concentration. The technique and experimental arrangement was essentially similar to that of Tedmon et al.' In the remainder of this paper, the azjmuthal angle $ for the field H is referenced to the [ I101 direction in all four crystals, and oxygen was added in small equal increments by anodization and annealing.7 The resistivity ratio, RR, of the resistance at room ternperature to that at 4.2"K (H =7.00 kG) was determined as well.

Jan 1, 1970

By H. A. Wriedt

Zinc-vapor pressures in equilibrium with bcc solutions of zinc and iron at 703.5", 757", 793", and 900°C were measured by an isopiestic method. Thermody-na?nic properties of zinc in these solutions were derived directly and those of iron with a Gibbs-Duhem integration. Zirzc and iron exhibit large, positive, and moderately temperature-sensitive deviations from ideality. Excess enthalpies and Gibbs energies are positive in the ranges studied. It has been establzshed in relating published phase equilibria to the Gibbs energies of forming solid solutions that positive departures from ideality also exist in the fcc solutions. Tlze stability, as defined by Darken, of the bcc solutions is small but positive at 703.5"C. Its decrease with decreasing temperature indicates that a miscibility gap may exist in the stable or metastable bcc solutions at lower temperatures. The changes of thertnodynanlic properties relatable to changes in magnetic state are minor compared to other changes due to alloying. The accuracy with which the relation between lattice parameter and composition of the bcc solutions is known has been improved. Zinc increases the lattice parameter of a iron by O.ZOZA per unit atom action zinc to at least NZn = 0.25. TO our knowledge, only Ciganl has previously investigated thermodynamic properties of the bcc solutions of the Fe-Zn system. He measured zinc-vapor pressures in the temperature range from about 320" to 360°C by an effusion technique. We have measured the vapor pressures of zinc in equilibrium with bcc solutions of zinc and iron at 703.5", 757", 793", and 900°C by an isopiestic technique. This investigation and the pursuant thermodynamic computations are part of a program for studying several properties of these solid solutions. In the appendix we report a remeasurement of the relation at room temperature between the lattice parameter and zinc content. Related work not reported herein embraces measuring the diffusivity2 of zinc in ferrite at 700" to 900°C and the Curie point temperature3 as functions of composition. EXPERIMENTAL METHOD AND APPARATUS Purified iron at a series of constant temperatures was saturated with zinc at a series of constant zinc-vapor pressures, the range of conditions being so limited that the equilibrated solid solutions were ferri-tic. The equilibration was conducted in long capsules, Fig. 1, that had been evacuated, gettered with titanium, and sealed. The purified iron, part of a vacuum-melted ingot of electrolytic-iron stock (Glidden Co. 1044-grade), had the impurity contents listed in Table I. It was used in the form of millings about 0.001 in. thick. A zinc of 99.999 pct purity (United Mineral and Chemical Corp.) and later one of 99.9999 pct purity (Cominco Products, Inc.) were used, with no observed difference in results. Sufficient zinc was placed in the capsule (separate from the iron and kept at a different temperature) to supply the vapor phase and the iron alloy, while leaving a pool of pure liquid zinc throughout the run. The imposed temperature of the residual zinc pool fixed the vapor pressure of zinc throughout the capsule; condensation was avoided at other locations by making this the lowest temperature in the capsule. Two common complications of nonisothermal systems were, we believe, effectively absent from ours: first, molecular species other than monatomic have no appreciable concentration in zinc vapor at 700" to 900~~: second, the development of zinc-pressure differentials in the capsules was suppressed by use of relatively large-diameter tubing and the absence of diluents in the zinc vapor other than desorbed impurities. The specimens and zinc pool were located at two isothermal zones (each ranging within 1°C over several inches) of a wire-wound, 37-in.-long vertical-tube furnace. The required temperature distribution was achieved by external adjustment of the currents in three electrically isolated windings. The temperatures of the isothermal zones were controlled independently by ther-

Jan 1, 1968

By F. H. Deily, Jean M. Quets, Milton E. Wadsworth, John R. 222-000-000-012 Lewis, D. S. Rowley, R. J. Howe

Samples of synthetic magnetite were reduced in hydrogen-water vapor atmospheres in the temperature range 450o to 900oC. The reaction was always surface controlled, indicating the final products of reaction are nonfirotective. Three separate cases have been identified from the kinetic results: Case I, reduction of magnetite to iron below 570°C; Case II, reduction of magnetite to iron above 570°C; and Case 111, reduction of magnetite to wustite above 570 oC. In Cases I and 111 the kinetics have been explained by the formation of oxygen anion vacancies in the magnetite surface followed by associated diffusional processes. In Case 11 the observed kinetics have been related to the concentration of iron cation vacancies in the wustite layer formed, followed by associated steady-state diffusional processes. The concentration of cation vacancies in the wustite is maintained constant by the magnetite-wustite equilibrium. THE reduction of the oxides of iron has been a subject of study and interest for many years. However, few attempts have been made to interpret the results in terms of the mechanism of reduction of an iron oxide by either hydrogen or carbon monoxide. Stalhane and Malmberg' using CO, H2, and CO-Hz mixtures, developed the rate expression: where m = mass of oxide reduced, t = time, k = a constant, s = surface area, P = partial pressure of of CO or H,, and P, = partial pressure of the reducing gas at equilibrium. The rate of reaction per unit area was proportional to the difference between the partial pressure of the reducing gas and its pressure at equilibrium. Hansen, Bitsianes, and Joseph2 studied the reduction of pellets of hematite to magnetite with mixtures of CO-CO,. They concluded that below 450°C the reaction proceeded according to a model in which CO reacts with the hematite surface producing an oxygen ion vacancy. The rate controlling step was then assumed to be oxygen ion diffusion through vacancies resulting in the formation of magnetite. They derived an expression giving the rate of reduction proportional to the cO/CO, ratio. Recently McKewan3 published results for the reduction of magnetite spheres in atmospheres below 570°C. He explained his results by an equation of the form where K, is the equilibrium constant for wustite-iron equilibrium attributed to the formation of wustite as an intermediate in the reduction of magnetite. According to McKewan, Kp is an equilibrium constant for H, -HO adsorption in which oxygen is deposited on the surface from the H,Oand subsequently acts as a poison for reduction by hydrogen. Sample Preparation and Experiments. In this work the authors used the same apparatus and experimental procedure employed in the hydrogen reduction of magnetite. Sintered disk samples weighing approximately 1.5 g and measuring 1.2 cm in diameter and 0.25 cm in thickness were prepared by a method described previously.4 Partial pressures of hydrogen and water vapor were controlled by bubbling hydrogen through a series of flasks containing distilled and deionized water maintained at constant temperature in an oil bath. The total flow rate of the reacting gases—hydrogen and water vapor—was approximately 0.5 liter per min. The entire external system was maintained at a temperature above the oil bath to prevent condensation of water vapor. This was accomplished by wrapping electrical resistance elements over all surfaces. The glass column containing the weighing system-a McBain balance suspended from a gold chain-was enclosed in an aluminum tube heated by nichrome resistance wire enclosed in an insulating material. The temperature of the glass column was held constant by means of a series of thermocouples connected in parallel to a Leeds and Northrup temperature controller. This was necessary since variations in temperature resulted in expansion and contraction of the glass column and could be readily observed with the cathetometer. The spring extensions were measured through a window with a gaertner cathe-

Jan 1, 1962

By G. R. Speich, D. J. Mack

The transformation of was studied by isothermal methods. At all temperatures, the ß transforms quickly to fine grained ß" which develops silver-rich striations. At higher temperatures the striations disappear, the final structure being Widmanstatten a in ß'. At lower temperatures, the striated ß" is consumed by pearlite nodules of a + ß' which in turn form the Widmanstatten a in ß'. The transformation is unlike any previously reported for a eutectoid. AS part of a general program of study on the eutectoid reaction, the Ag-Cd eutectoid seemed particularly attractive because the ß phase which undergoes the reaction is another of the typical "electron compounds," AgCd, having the disordered body-centered cubic structure. This work deals with the eutectoid which occurs at 50.5 wt pct Ag, and not with the eutectoid which has been reported at 42.9 pct Ag.' There has been no work reported specifically on the Ag-Cd eutectoid which was studied. The only information available on this eutectoid is that work done in the determination of the phase diagram. For the most part, the terminal portions of the diagram, Fig. 1, are well established; however, the region from 40 to 60 pct Cd is still somewhat in doubt. The X-ray evidence'..' in this region is in conflict with the results of thermal analysis. X-ray analysis3 does not show a polymorphic transformation at about 240°C as indicated by thermal analysis.1,5 Even the X-ray evidence, within itself, is confusing in this region of the diagram. One investigator2 reports the ß phase as hexagonal close-packed and has found three phases in the one-phase ß field. Other X-ray investigators"' ' report the ß phase as body-centered cubic. The authors believe that much of the confusion resulted from incomplete homogenization of the alloys. It was found that it takes almost a week to produce a completely homogeneous two-phase structure at 370°C. Another possible source of error is the volatilization of cadmium from the surface and cracks of the specimen during annealing with the possible formation of a cadmium-poor phase. The only metallographic data available on this eutectoid alloy are those of Durrant1 and Fraenkel and Wolff.5 his information is very limited. The phase diagram chosen as most nearly correct is that in the Metals Handbook," which is almost identical with the phase diagram suggested by Durrant.1 Materials and Procedure The alloy was prepared from high purity silver (999.5 plus fine) and high purity cadmium (0.02 Pb, 0.005 Cu, trace Fe). The metals were melted in carbon under a nitrogen atmosphere. Some cadmium was lost by volatilization but by remelting several times and adding cadmium a 200 g ingot of approximately eutectoid composition was obtained. Because the CdO fumes are quite toxic, the exit gas from the furnace was led through a water trap to condense the CdO. The ingot was homogenized at 650°C for 24 hr, no attempt was made to prevent decadmiumization. This resulted in a narrow decadmiumized rim on the ingot which was removed. Filings for analysis were obtained from cross sections of the ingot. Silver was determined by the Volhard thiocyanate method,? cadmium by difference. The ingot analyzed 50.8 pct Ag at the top of the ingot and 50.7 pct at the middle and at the bottom of the ingot. This alloy was only slightly hypo-eutectoid compared to the accepted value of 50.5 pct Ag and was used for the isothermal studies. It was felt that further attempts to adjust the composition might be futile because of the volatility of the cadmium. The ingot was sectioned to specimens approximately 3/4 x 3/4 x 1/8 in. These specimens were "austeni-tized" for 3 hr in air at 650°C to yield homogeneous ß and then quenched into a salt bath held at constant subeutectoid temperatures where the transformation

Jan 1, 1954

By N. Jaffe, J. E. Dorn

This investigation is concerned with the possibility that the creep resistance of metals might be reduced as a result of recovery at the creep temperature when the applied stress is reduced. For this purpose the effect of stress on the recovery of the creep behavior of pure polycrys talline aluminum was investigated in the cross-slip temperature range where the activation energy for creep is 28.000 cal per mole. Before recovery all specimens were given the same substructure by creeping them under a stress of 7800psi to a strain of 0.218. Recovery was then accomplished by holding the specimens at the creep temperatures of 327" and 337°K under a series of reduced stresses for various periods of time. When the original stress was reapplied the specimens crept more rapidly than when the original stress was first removed, illustrating that recovery did take place. The extent of recovery could be indexed in terms of the UNDER certain conditions of test, the creep rate decreases over the primary stage of creep often by as much as a factor of 10~B. Since the external variables of stress and temperature are held constant, such pronounced and significant changes in the creep rate must be attributed to various substructural modifications that are introduced as a result of creep itself. At the secondary stage of creep, over which the creep rate remains constant and the substructure no longer changes, a balance must be achieved between the rate of increase in creep resistance due to creep straining and the rate of recovery of the substructural modifications. The general validity of these concepts on substructural changes has already been shown,' including the corollary that a more creep-resistant substructure is introduced under a more rapid creep rate arising from a higher applied stress.' In spite of these well-documented facts, very little progress has been additional strain undertaken by the recovered specimen to achieve the same strain rate as the unrecovered specimen. It is significant that the higher recovery stresses gave the most rapid rates of recovery. Over the high range of reduced stresses, where some creq took place during recovery, the activation energy for recovery equaled that for creep, namely 28,000 cal per mole. But for stresses during recovery below 0.80 of the original creep stress, no creep was detected during recovery and an activation energy for recovery of about 72,000 cal per mole was obtained. Whereas the activation energy of 28,000 cal per mole suggests that cross-slip of dislocations is responsible for this recovery, the mechanism for the 72,000 cal per mole process is not known. This activation energy, however, is about twice that for self-difhsion. made in determining, in satisfactory detail, precisely what substructural changes so effectively modify the creep rate.' Up to the present, electron microscopy has failed to uncover, in a satisfactory quantitative manner, the mechanistic processes involved. Since, however, creep, at least at moderate and high temperatures, arises from one or more types of dynamic recovery processes, it should be possible to shed additional light on the total problem by investigating the recovery of creep resistance. The importance of such an investigation becomes apparent when the fact is recognized that there has yet been no direct experimental proof that the rate of softening due to substructural changes as a result of recovery equals the rate of hardening due to creep-induced substructural strengthening over the secondary stages of creep. Furthermore the problem of what happens to the creep-strain induced strengthening when the material recovers either at zero or some reduced operating stress has significant engineering consequences. It was for these reasons that the present investigation on the recovery of creep behavior was initiated. Inasmuch as a substantial background has now developed on the creep of high-purity aluminum, this material was again selected for the current investigation. Furthermore extensive evidence is now

Jan 1, 1963

By R. F. Hehemann, R. H. Goodenow

Thermal arrest, hot-stage microscopy, and transtnission electron microscopy techniques have been employed to study the transformations in low-carbon iron and Fe-9 pct Ni alloys. In continuous cooling experiments, each alloy transforms at an essentially constant temperature for cooling rates below the critical rate required for martensite formation. However, high-tenzperature transformation in pure iron takes place by a different mechanism than that in the 9 pct Ni alloys. Pure iron exhibits an equi-a a structure with a low and random dislocation density while the 9 pct Ni alloy exhibits a cell or lathlike substructure analogous to that of low-carbon martensite. This same substructure characterizes upper bainite in higher-carbon inaterials. UNTIL relatively recently, diffusionless transformations have been considered to take place by the same mechanism and have been termed mar-tensitic transformations.l-3 The most characteristic feature2 of this mode of transformation is the shape change produced by a shear deformation and growth of the product phase frequently occurs at an extremely high velocity approaching that of an elastic wave.4'5 A different mechanism of diffusionless transformation was recognized first in Cu-Ga and other copper-base alloys.6,7 From the absence of surface tilting in these alloys, it has been concluded that transformation is not accomplished by the cooperative shear displacements that occur in mar-tensitic reactions. Transformation presumably takes place by the rapid movement of an incoherent interface which is capable of propagating across parent grain boundaries. Although the transformation is diffusionless in the macroscopic sense, advancement of these interfaces is accomplished by an atom by atom rearrangement. Transformations of this type therefore require thermal activation and are generally operative only at high temperature. Although requiring short-range diffusion at the interface, propagation still occurs so rapidly that the reaction cannot be suppressed with normal cooling rates.7 The resulting microstructures exhibit large, irregular-shaped regions of the product phase, which are essentially free of crystallographic features. Consequently, these reactions have been termed massive transformations. Transformation by the massive mechanism has been reported to occur in ferrous systems involving pure iron and binary alloys of iron with nickel, chromium, and silicon by Gilbert and owen.' The Fe-Ni system is of special interest in that the massive transformation was observed in alloys with less than 15 pct Ni while alloys having more than about 28 pct Ni transformed by the conventional mar-tensitic mechanism. By employing cooling rates substantially higher than those used by Gilbert and Owen, Swanson and Parr have been able to suppress the massive transformation in alloys with 0 to 10 pct Ni9 and produce martensite as revealed by surface relief. The massive transformation in the alloys having less than 15 pct Ni was identified by the lack of surface relief and an irregular rather than clearly acicular microstructure.' Speich and Swann, using thin-foil electron microscopy, identified three distinctly different structures10 in quenched binary Fe-Ni alloys. From 0 to 4 pct Ni the structure consisted of blocky grains of a with a low and random dislocation density. Alloys with 4 to 25 pct Ni exhibited a cell structure with a high dislocation density; and at greater than 25 pct Ni the structure consisted of internally twinned plates. The structural change at approximately 4 pct Ni suggests that alloys with low nickel content transform by a different mechanism than those with intermediate nickel contents and the transition from the cellular to the internally twinned structures at approximately 25 pct Ni is analogous to the transition from needles to internally twinned plates that occurs over a narrow range of carbon contents in Fe-C martensites.11,12 Conventional bainitic and martensitic modes of austenite decomposition operate in ternary Fe-C-Ni alloys having less than 10 pct Ni. This investigation was conducted in order to explore the conditions under which the massive, bainitic, and martensitic transformations occur and the relationships between these modes of decomposition.

Jan 1, 1965

By I. M. Bernstein

The steady-state creep behaviov of zirconium and zivcaloy-2 was examined in the temperature vatlge 520° to 620°C A1 low stresses the creep rates were cimracterized by a linear stress dependence; at highev stresses the stress dependence was much more pronounced. Temnperature-cycling tests yielded values for the aclivation enevgy for creep. Various tlzeories were examined in the ligltt of- the experimental re-sults and it mas concluded that the low-stress creep behavior is the result of the stress-direcled diffusion of vacancies along gain boundaries. It has been observed,"&apos; usually under conditions of high temperature and low stress, that creep deformation can occur for which the steady-state creep rate is linearly dependent on the applied stress. For magnesium and certain magnesium alloys, Harris and ones&apos; and ones&apos; have argued that this type of creep occurs by mass transfer as a result of the stress-induced generation and migration of vacancies, along a gradient defined by the stress direction. Jones&apos; demonstrated that the rate-controlling diffusion path is sensitive to grain size and temperature, and that by suitable control of these variables creep could occur by vacancy diffusion either predominately along grain boundaries or through the lattice. Recently, Jones3 suggested from an examination of limited high-stress data for zircaloy-2, composition in Table I, that significant diffusion creep could occur at low stresses, at least between 375" and 500°C, controlled by grain boundary vacancy diffusion. This process could have an important implication in assessing the role of zirconium alloys as a structural or cladding material in certain classes of nuclear reactors, since it predicts creep deformation far in excess of any estimates based on extrapolating slip creep data from higher stress levels. If the diffusion creep process occurs it should be possible to describe the total steady-state creep rate of zirconium and its alloys as the sum of two terms, Eq. [I]; the first term relates to a slip creep process important at high stresses and which is manifested by a much more pronounced dependence of creep rate on stress4 than diffusion creep and the second to a process controlled by mass transfer,5&apos;6 dominant at low stresses: where A and BI are parameters which can depend on structure, Ql and Q2 are the activation energies for the particular creep process occurring, and n describes the sensitivity of the creep rate on stress. It is the purpose of this paper to present some direct experimental evidence in support of this view. It is recognized that other analytical approaches have been proposed to explain data of this kind and these will also be discussed. 1) EXPERIMENTAL PROCEDURE Flat creep specimens (gage length 1 by 0.25 by 0.02 in. approx) were prepared from cold-rolled, argon-remelted, crystal bar zirconium and cold-rolled commercial-grade zircaloy-2, the analyses of which are given in Table I. The specimens were annealed at a pressure of < 10-5 Torr at temperatures from 625" to 675°C for 2 hr and slow-cooled. This treatment produced stable grains of average size (defined here by the average linear intercept) of for zirconium and -4xin. (-10 p) for zircaloy-2. The specimens were tested in a dead load tensile creep rig. The stress was maintained constant by adjusting the applied load after approximately each 1 pct of strain. The specimen temperature was controlled to better than +1°C. This system had a small thermal lag, so that rapid temperature changes were possible. To minimize corrosion, the specimens were tested in high-purity (99.95 pct) argon, further dried,

Jan 1, 1968

By Paul A. Farrar, Harold Margolin

The Ti-Al-V system has been delineated from 50 to 100 wt pct Ti and front 600 to 1400°C by X-ray and ntetallographic techniques. Isothermal sections were delineated at 600, 700, 800, 900, 1000, 1100, 1200, 1300, and 1400°C. X-ray and metallographic evidence indicated the presence of two phases and in addition to those reported by previous investigators of the ternary system&apos;-3. T HE titanium-rich region of the Ti-Al-V system as originally proposed by Rausch et UZ, and Jordan and Duwez3 was based on the binary Ti-Al diagram as proposed by Bumps et uZ. As additional phases have been shown to exist5-&apos; in the region previously thought to be all a, the titanium-rich region of the Ti-Al-V system is open to serious question. Therefore, in order to determine the effect of the indicated changes in the Binary Ti-Al system on the ternary Ti-Al-V system the present investigation was initiated. EXPERIMENTAL PROCEDURE The experimental procedures in this investigation are the standard techniques used in the study of titanium-alloy systems which have been described in detail previously.1° Consequently, only details pertinent to the present work are discussed. The alloys employed for the delineation of this system were prepared from titanium obtained from the Bureau of Mines (73 BHN) 99.99 pct Al and 99.7 pct V, by the consumable arc-melting technique. The titanium was premelted into buttons of 25 g because spattering during the first melt caused uncontrollable loss of alloying constituents. Typical analyses of the material used have been reported elsewhere Attempts to hot roll the alloys prior to heat treatment were made on the first series of alloys prepared, but as the area of extensive hot workability was fairly restricted, see Table I, this practice was discontinued. The times of isothermal annealing are given in Table 11. A preliminary heat treatment of 96 hr at 1000°C was used prior to heat treatment at lower temperatures. The standard techniques used for polishing specimens involved belt-grinding, grinding on emery paper, polishing electrolytically, and etching with Remington "A" etch. In the low-alloy region it was found that the oRo etch, developed by Ence and Margolin,o gave better contrast between phases. Where this procedure did not differentiate between phases clearly, the method of stain etching developed by Ence and was used. It has been previously reported15 that filing of titanium alloys is not desirable for producing X-ray powders, since the powder becomes contaminated by the file material. Therefore, for those samples not brittle enough to Crush, the procedure described below was used. The specimen was wrapped in molybdenum sheet and placed in a vacuum system and evacuated to 0.03 p. Palladium-pur if ied hydrogen was then admitted to the system until a partial pressure of 5o Cm of H was reached. The specimen was heated in the system to the temperature of original heat treatment and was slowly cooled over a period of 3 hr to 400°C while the partial pressure of hydrogen was maintained. The sample was removed from the system after it had completely cooled and was crushed to a powder of 230 to 270 mesh. The powder, wrapped in molybdenum sheet, was dehydrogenated at the temperature of original heat treatment until a partial pressure of 0.03 p was maintained in the system for at least 1/2 hr. The tube containing the powders was quenched in iced brine while still connected to the vacuum system. After dehydrogenation, the powder, except for the

Jan 1, 1962

By J. M. W. Mackenzie

The interactions between oil drops and mineral surfaces have been examined for the cetyltrimethylammonium bromide (CTAB)-quartz and sodium dodecyl sulfate (SDS)-hematite systems. The results have been interpreted using a electrical double layer interaction model, a "sweeping-penetration" model based on steric interactions and a free energy of adhesion model. The adsorption of long-chain ions at the mineral interface was also studied and found to follow a Fuerstenau-Modi model of combined Coulombic and chain-chain interaction forces. The basis of the emulsion flotation process and the feature which makes it differ from conventional flotation is: encounter, followed by adhesion, between oil drops and mineral particles which are suspended in an aqueous environment. The manner in which the adhesion between these two phases contributes to the flotation process may be through the formation of min-eral-oil drop-mineral linkages, mineral-oil drop-air bubble linkages, or a combination of both. Possible flotation mechanisms derived from these adhesion processes are shown schematically in Fig. 2 while Fig. 1 shows an example of the first mechanism for quartz particles which have been floated using a cetyltrimethyl-ammonium bromide (CTAB)-Nujol emulsion as collector. In Fig. 2 the three phases, mineral, oil, and air, for convenience have been shown as having approximately equal size. This would not always be the case in an actual emulsion flotation operation. For the flotation of sand-sized particles of approximately 0.5 mm diam, the mineral particles would be at least ten times the size of the largest emulsion drops present in the system, while in the flotation of —10u slime particles, the mineral phase may be of the same order of size as the oil phase. The air bubbles in a flotation cell are normally about 1 to 2 mm in diam and therefore, in general, would be larger than the oil drops. Although the relative size of the three phases does not alter the basic adhesion processes between oil drops, mineral particles, and air bubbles, which depend on the physical and chemical properties of the interfaces involved rather than on the extent of these interfaces, it does alter the degree of deformation of the oil drops and air bubbles which will occur on adhesion. For mechanisms 1 and 2 to take place, the oil-water and mineral-water interfaces must be partially replaced by a mineral-oil interface while in mechanism 2 there is the additional requirement that the oil-water and air-water interfaces must be replaced by an oil-air interface. In view of the importance of the oil drop-mineral particle encounter and subsequent adhesion stages to both of the emulsion flotation mechanisms discussed, a study has been made of some physicochemical factors which control these processes for Nujol-cetytri-methylammonium bromide (CTAB)-quartz and Nujol-sodium dodecyl sulfate (SDS) -hematite systems. Experimental Electrokinetic Measurements.—The zeta potential of mineral particles was measured using a streaming potential technique similar to that described by Fuerste-nau.1 The streaming potential was measured using a multirange electrometer while the plug conductivity was measured using a 50 cycle sec1 bridge. Measurements were made on 28 x 65 mesh particles. Contact Angle Measurements.—A captive bubble technique was used to measure the contact angles for air bubbles and oil drops. The angles were measured on fracture faces of unmounted minerals which proved easier to clean than polished mounted specimens and should more closely represent a flotation system. Reagents: These have been described in a previous publication.0 Minerals: Rock crystal quartz from the New England district, N.S.W., was used for contact angle and streaming potential measurements. The quartz was hand

Jan 1, 1971