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By J. R. Mihalisin

THE application of electron-microscopic techniques to the study of high-temperature alloys has met with considerable success.' This is due, in part, to the submicroscopic nature of the phases present in this type of alloy making high resolution methods necessary. Among the newer electron-microscopic techniques, the extraction replica technique' has proven to be of great value. This method allows phases to be examined in situ in the microstructure and permits their identification by means of electron diffracticn. This technique eliminates the main disadvantage in using electrolytic extraction of residues as a means of phase identification; that is, the uncertainty of relating constituents identified in the residue to what is observed microscopically. In the course of work relating microstructure to physical properties in high-temperature alloys, it was found that the formation of grain-boundary carbide phases and intragranular precipitation of an age-hardening phase greatly influence strength and ductility at high temperature. In particular, it was found that the formation of a unique type of precipitate in Nimonic "80" (a nickel-chromium-aluminum-titanium type superalloy), termed cellular or discontinuous precipitate, at grain boundaries generally results in poor ductility at high temperature. However, this mode of precipitation can be avoided by proper heat-treatment. It was assumed that this precipitate was either a carbide or age-hardening type of phase. Using various etching procedures with the extraction-replica technique, it was found to be possible to extract the carbide and age-hardening phases preferentially in this type of alloy. Previous work has shown that the age-hardening phase can be extracted from superalloys merely by

Jan 1, 1959

By N. F. Neumann, A. W. Schlechten

Metal chlorides were formed by reacting metal oxides and calcium chloride; the effect of additions to the reaction mixture was studied. It was found that by use of proper additions, metal chlorides could be prepared from mixtures that were not reactive under ordinary conditions. ManY recent metallurgical developments involve the use of chlorine or chlorides as primary reagents; good examples are found in the production of ductile zirconium and titanium by reduction of their chlorides with magnesium. Various methods of preparing metal chlorides are used and many others have been proposed. Some chlorides are formed by the direct combination of a metal or alloy with chlorine. Other processes react chlorine and metallic oxides; carbon or other reducing agents are usually employed to reduce the metal oxides and so promote chlorination. Metallic chlorides have also been produced by the exchange of chlorine between metal oxides and a chloride, such as sodium chloride. This type of reaction was the basis for the old process of chloride roasting in which metal ores were roasted in the presence of salt. Soluble chlorides thus formed

Jan 1, 1959

By R. F. Stewart

A key step in changing coals to fluid fuels and chemicals is the conversion of coal to synthesis gas by gasification with steam and oxygen. As oxygen represents one of the largest single expenses in gasification, its cost is a vital factor in the economy of the process. At present, the most economical method for producing tonnage oxygen is by the conventional rectification of liquefied air. Several alternate methods have been proposed for producing oxygen from air: (1) methods based on physical or chemical sorption of oxygen from air by liquids or solids or (2) the oxidation of certain inorganic com-pounds to higher oxides unstable at higher temperature levels. Economic limitations are discussed by which these methods may be evaluated. Chelated metals of the salcomine type are promising chemical sorbents of oxygen from air. This report covers a study of the reversible sorption of oxygen by salcomine and other chelates. The presence of water in the salcomine structure was verified; it is the loss of this water that causes slow deterioration of salcomine during cycling.

Jan 1, 1959

By Russell W. Hunt

The cave man of ages past took his wife-and family from the cave pointing to a fire he had built and beating on his breast said, "Look what I have done". Today man is taking his family back to a cave saying, "Come enter in because of what I have done". At the close of World War II Germany said if they had gone underground one year earlier with more of their operations, the war could have lasted four years longer with perhaps much of Britain devastated. The protection of the home front no longer rests with the soldier in actual combat. The battle will be won at home with the most careful kind of protection against missiles. After Nagasaki-Hiroshima Sir Winston Churchill said in substance "Up to now the Almighty has mercifully withheld from man the knowledge of these terrible weapons of destruction."

Jan 1, 1959

By H. Dolezal

A laboratory study of acid-ferrous sulfate treatment of low-grade manganese ores from the Cuyuna range, Minnesota resulted in 93-percent extraction of manganese as manganese sulfate with consumption of 3.8 pounds of H2S04 per pound of extracted manganese. Two types of ore were treated in consecutive stages. The first are contained carbonate minerals of manganese and iron, both soluble in H2S04 solution. The second ore contained manganese oxide minerals, insoluble in straight acid solution but soluble in the ferrous sulfate solution obtained from treating the first ore. Leaching data were obtained by countercurrent percolation of coarse (minus-1/2-inch) ore particles at room temperature and by agitating minus-65-mesh ore particles in heated solution. Extraction of manganese and acid consumption were the same, but the percolation leach required 6 days compared with 1 hour for hot agitation. Variations in the size of ore particles treated, leaching time, acid concentration, solution temperatures, and method of applying ferrous sulfate solution to the oxide ore were studied. The effects of several reagents for removing iron from solution and improving filtration were also studied.

Jan 1, 1959

By B. W. Naugle

This report describes the carbonizing properties of coals from the principal beds in Cambria County, Pa. Samples of coals from Upper and Lower Freeport and Upper and Lower Kittanning beds having estimated minable reserves of 50-million tons or more were studied by the Bureau of Mines. Cambria County coals rank either as medium-or low-volatile bituminous. A preparation study indicated that all coals tested in this county, except one sample from the Lower Freeport bed, were responsive to cleaning and would yield a product with satisfactory chemical properties for metallurgical coal. All coals tested from Cambria County yielded strong coke; however, they expand excessively when carbonized singly, and should be used only as minor constituents in metallurgical coking blends when carbonized in slot-type ovens.

Jan 1, 1959

By O. F. Kammerer, W. E. Miller, D. H. Gurinsky, J. Sadofsky, J. R. Weeks

Zirconium and titanium inhibit solution mass transfer of steels by liquid bismuth, mercury, and lead. It is shown that in bismuth and mercury, these adsorb on the surface of the steels and subsequently react with nitrogen and possibly carbon from the steels to form inert, adherent surface layers of ZrN, TiN, or TiN + Tic. Data are presented which describe the condition under which thase deposits form. These inhibitors decrease the solution rate of iron into bismuth, and require a higher supersaturation for precipitation of iron from bismuth. USE of the low-melting heavy metals (bismuth, lead, mercury, and their alloys) as coolants has been limited because solution mass transfer of steels occurs in these liquids; i. e., iron dissolves in the hot sections of the heat transfer circuit and deposits in the colder sections. The rate of solution of iron and the temperature coefficient of solubility are sufficiently great to cause complete or partial stoppage by the deposition in the coldest section of a closed circuit in finite time, even though the actual solubilities are extremely low. In the development of the mercury vapor turbine by the General Electric Co., Nerad and his associates1 discovered that the addition of as little as 1 ppm Ti or Zr to magnesium-deoxidized mercury reduced the mass transfer of ferrous alloys by mercury to a negligible amount. Reid2 reported that titanium was detected chemically on the surface of steels contacted with this mercury alloy in amounts varying from 2.0 to 2.6 mg per sq in., the greatest amount being found in the hottest portion of the circuit. Reid stated that the titanium forms the intermetallic compound Fe2Ti by reaction with iron on the surface of the steels. This compound was presumed to be highly insoluble in mercury. More recently, El-gert and Egan3 have reported a greater than 100-fold reduction in the rate of mass transfer of a 5 pet Cr steel by liquid bismuth upon the addition of titanium (in excess of 50 ppm) and magnesium (350 ppm) in the liquid metal, during experiments performed in thermal convection loops* over the temperature differential 700° to 615° C. Also, Shep-ard and his associates' have reported that the addition of titanium to liquid bismuth and Pb-Bi eutec-tic produced a marked decrease in the rates of solution of both iron and chromium from type 410 steel capsules under static conditions. This inhibiting effect increased with repeated reuse of the capsules. Tests performed in this laboratory under carefully controlled conditions have shown that the addition of zirconium and magnesium, or titanium and magnesium, to liquid bismuth or lead greatly reduces the rate of mass transfer of chromium alloy steels and carbon steels in thermal convection loops with a maximum temperature of 550°C.5-9 The present paper will review the data obtained to date at this laboratory on the behavior of iron and steels in contact with liquid bismuth alloys containing titanium or zirconium, and will attempt to explain the role of the above additives in reducing solution mass transfer. Reaction between the Zirconium or Titanium Dissolved In Liquid Bismuth and an Iron or Steel Surface Reaction between Zirconium Dissolved in Bismuth and the Surface of Pure Iron-—A small pure iron crucible (analyzed by the supplier to contain 0.8 ppm N was contacted with bismuth containing approximately 0.1 pet Mg and varying amounts of a radioactive zirconium tracer. The crucible was then inverted at the temperature of contact. The thin residual layer of adherent bismuth was dissolved in cold, concentrated nitric acid. The crucible surface and the solidified bismuth were then analyzed for radioactive zirconium. An analysis of the activity loss on the crucible surface and the weight loss of the crucible during the nitric acid treatment showed that the acid treatment removed the zirconium that had originally been dissolved in the adherent bismuth, but not any zirconium that may have reacted with the crucible surface. The crucible was then pickled in warm aqua regia to remove all surface activity, hydrogen-fired at 600°C, and recontacted with a new liquid alloy. The results of the experiments contacted 1 hr at 450°C show, Fig. 1, a Langmuir-type adsorption with an adsorption free energy of approximately 17 keal per g atom Zr.5 This deposit was estimated to contain 1 atom of zirconium for each 7 to 8 iron atoms on the crucible surface, assuming a surface roughness factor of the pickled crucibles to be five. Increasing the temperature to 520°C caused consi-

Jan 1, 1959

By J. E. Forciea, O. E. Palasvirta, L. G. Hendrickson

AH pilot and commercial plants working with Mesabi Range taconite employ wet magnetic separation. Progress is being made with a dry magnetic process, but this has not yet been applied to taconite except in the laboratory and pilot plants. Flowsheets in all five plants are similar, including multiple stages of grinding, each followed by magnetic separation, which rejects a finished tailing. The flowsheet in Fig. 1 is used in the preliminary and commercial plants of the Erie and Reserve mining companies and in Unit C of Oliver's Pilotac plant. At Erie the desliming operation is omitted. In the Reserve plants two ball mills are used with each rod mill. Pilotac uses flowsheet 2 in Unit A-B and has also tested flowsheet 3. Principal differences in the three flowsheets are the number of grinding stages and the type of roughing. The terms open-circuit roughing and closed-circuit roughing are best defined by the diagrams. Special Test Data Given in Table I: For the Erie and Reserve commercial plants, Table I reflects routine conditions. Pilotac, the experimental plant, has been run with several flowsheets, including those followed at Erie and Reserve's commercial operations. Pilotac data for these last two flowsheets are similar to commercial plant results and are not repeated in Table I; statistics are given, however, for special test conditions. using other flowsheets. when the objective was to 'to extra-grade concentrate, Variations Among Taconites: Although crude ore tributary to these plants is generally classified as taconite, there are important differences in mineralogy and fineness of dissemination.

Jan 1, 1959

By A. F. Henderson, C. F. Cornell, A. F. Dunyon, D. A. Dahlstrom

Ossi E. Palasvirta (Development Engineer, Oliver Iron Mining Diu., U. S. Steel Gorp.)—The authors are to be congratulated for their interesting article, which thoroughly illustrates the variables inherent in filtration of taconite concentrate. The work and the conclusions based thereon largely parallel the test work done by the writer at the Pilotac plant" and the experience gained with a commercial size agitating disk filter in the same plant. At Pilotac, however, a thorough study was also made of the effect of depolarizing (demagnetizing) the filter feed, and it is the purpose of this discussion to comment on the merits of depolarization of the magnetite concentrate prior to filtering. The work at Pilotac was done in three phases: 1) preliminary laboratory testing with a circular filter leaf of 0.047 sq ft, followed by 2) plant testing using a 4-ft diam, single-disk agitating filter that was purchased on the basis of the pilot tests on the 4-ft model. In the laboratory tests depolarization was achieved by slowly withdrawing' batches of thickened concentrate from a coil producing an alternating field of about 300 oersteds. In plant tests the standard Pilotac procedure' was employed, wherein the pulp falls freely through the depolarizing coil. The preliminary tests in the laboratory at first seemed to indicate that although depolarization of the filter feed decreases the cake moisture, it also tends to decrease the thickness of the cake, thus decreasing filtering rate. The tests with the 4-ft disk filter soon showed, however, that the compactness of the cake, attained during the form period because of depolarization, permitted a considerable decrease in drying time without any sacrifice in final moisture content. Thus, the filter could be operated at a much higher speed, and the overall capacity was higher than with magnetized feed. Because of the great compactness of the cake there was little shrinkage during the drying period, which prevented cracking and subsequent loss in vacuum. This in turn permitted operation with as thick a feed pulp as the diaphragm pumps could handle, eliminating the necessity of pulp density control. On the basis of these findings, the 6-ft agitating disk filter has been operated at 2 rpm, using feed pulps varying from 65 to 73 pct solids. Initially Saran 601 was used as medium, but it was later replaced with a relatively open, tight-twist nylon cloth. Filtering rates up to 750 lb per ft- er hr can be attained with feeds averaging about 70 pct- 270 mesh, and there is no trouble because of cracking. The cake moistures vary between 8.5 and 9.5 pct. To recapitulate, the merits of depolarizing the filter feed may be summed up as follows: 1) The well dispersed pulp shows less tendency to settle in the filter tank. 2) The homogeneous filter pool results in more even cake formation. 3) Because of absence of flocs, great compactness of cake is attained during the form period. 4) The cake does not tend to crack during the drying period. 5) A drier cake is produced. 6) A shorter drying period is necessary, permitting higher operating speed, which in turn results in increased capacity. 7) Density of the feed pulp can be kept as high as the equipment can handle. This increases capacity, since it is directly proportional to the percentage of solids in the pool. A few tests were also made to study the effect of chemical flocculants on filtration efficiency. Results showed that the effects of chemical and magnetic floc-culation were quite similar. Thus the use of a floccu-lant would impair rather than improve the filtering of magnetite concentrate. A. F. Henderson, C. F. Cornell, A. F. Dunyon and D. A. Dahlstrom (authors' reply)—We want to thank O. E. Palasvirta for his comments, particularly in view of the encouraging results obtained with demagnetized taconite concentrate. In our studies an attempt was made to evaluate the effects of depolarizing the feed to the plant filters by passing the slurry through a coil, similar to the method described by Palasvirta. Unfortunately, in our experiments there were no startling improvements in performance level, neither cake rate increase nor cake moisture reduction. However, when slow filter cycle speeds were employed, the filter cake tended to crack and the vacuum level dropped, resulting in an increase in cake moisture content. When demagnetized feed was used during slow speeds, no cake cracking was evidenced and the vacuum level remained constant. Thus the depolarizing coil was found necessary only in cases of cracking. It should be noted that most of our test work concerned a feed of 85 to 90 pct —335 mesh and about 60 pct by weight solids concentration. This contrasts with 70 pct —270 mesh and 65 to 73 pct by weight solids as noted by Palasvirta. Reviewing both sets of results, it might be concluded that depolarizing may be successfully employed to alleviate cake cracking tendencies and may markedly improve cake rates and moistures on the coarser taconite concentrates. Further investigations may disclose the exact relationship of grind and pulp density to the depolarizing action.

Jan 1, 1959

By D. F. Atkins, B. A. Rogers, E. J. Manthos, M. E. Kirkpatrick

A phase diagram of the uranium-columbium alloys is presented. The apparatus and the procedures used in obtaining the data are described. Data from which the diagram was drawn are given in tabular and graphic form. THE use of uranium in the production of energy from nuclear fission has given considerable im- petus to the investigation of the metal and its alloys. Accordingly, information concerning the phase diagrams of binary alloys of uranium with other elements is of interest to metallurgists engaged in nuclear-engineering activities. As a contribution to the knowledge of the binary alloys, the authors have attempted to establish the diagram of the uranium-columbium system. The reports of laboratories engaged in work for the Manhattan Engineering District and the U. S. Atomic Energy Commission contain a number of references to work on uranium-columbium alloys.

Jan 1, 1959

By F. D. Rosenthal, F. J. Dunkerley, G. J. Mills

Activities, free energies, and heats and entropies of mixing of liquid Pb-Zn alloys have been obtained by the electrode-potential method between 400° and 650°C. The large positive deviations observed from Raoult's law are in agreement with the phase diagram, which indicates a wide immiscibility field. A vapor-pressure method was used to extend the activity measurements to 900°C, allowing the maximum of the immiscibility gap to be estimated by thermodynamic calculation. Data on the mono-tectic and eutectic points compare favorably with previously existing work. SEVERAL long-standing methods have been in use for the study of phase diagrams from measurement of the activities of the component metals.' The use of thermodynamic analysis for interpreting equilibria data is comparatively recent, however. Such analysis is usually undertaken by first evaluating the principal thermodynamic functions as, for example, the enthalpy, entropy, and free energy of the alloy constituents. These, in turn, quite often can be correlated with the interatomic potential energies and atomistics of the system, from which a clearer understanding of the causes leading to deviations from ideal behavior is gained. The present study of liquid Pb-Zn alloys is concerned with a determination of these quantities by electrode-potential and vapor-pressure measurements, using these values in calculations involving phase equilibria and to obtain a theoretical insight into an alloy system exhibiting strong positive deviations from ideal metallic solution. A considerable portion of the previously reported work is based on thermal analysis. Supplemented by optical studies of solid alloys, these techniques have revealed the essential nature of the immiscible mixtures that are formed. It is difficult, however, using the phase-

Jan 1, 1959

By G. M. Gordon, J. W. Spretnak, R. Speiser

AT present, considerable research is being directed toward the development of high-temperature, oxidation-resistant columbium alloys. Columbium. along with molybdenum and tungsten, exhibits good high-temperature strength. Unlike molybdenum and tungsten. however. columbium does not form a volatig oxide below 1375°c.l Although the outermost oxide formed on pure columbium, Cb2O3 is stable in air at elevated temperatures, it is not of a protective nature. It is porous and voluminous, and

Jan 1, 1959

Jan 1, 1959

By K. U. Snowden, J. N. Greenwood

EARLY studies by Gough and sopwith' have shown that the fatigue resistance of certain metals increased when the test was carried out in a partial vacuum; lead showed this effect to a marked degree. This communication describes surface deformation differences between high-purity lead fatigued in air and in a vacuum of approximately 5 X l0-3 mm Hg. Both air and vacuum tests were carried out by the same alternating flexure machine at a frequency of 500 cpm. Flat cantilever-bend specimens with tapered sides were cut from strip, annealed at 100°C, and chemically polished.

Jan 1, 1959

By K. G. Gorling, S. J. Wallden, N. B. Lindvall

It is the policy of The Metollurgical Society to provide, in the TRANSACTIONS OF THE METALLURGICAL SOCIETY OF AIME, a prompt and accurate medium for publication of reports of significant new research in both the scientific and engineering aspects of metallurgy. Papers submitted to the Society are judged by competent reviewers according to established criteria for technical merit, accuracy, originality, and presentation. STAFF: Editorial Director, Rixford A. Beals; Associate Editor, James J. Burke; Assistants, L. Capria and R. K. Larkin. PUBLICATIONS COMMITTEE OF THE METALLURGICAL SOCIETY: A. W. Thornton, Choirmon; Dennis Carney, John Chipman, J. C. Fulton, J. H. Hollomon, H. tl. Kellogg, A. E. Lee, R. Maddin, J. D. Sullivan, and O. Swan. Review and selection of manuscripts is under the supervision of the following Publications Committees: Extractive Metallurgy Division T. B. King. Cha~rmon; S. J. Dickenson, R. P. Hermsdorf, R. Schuhmann, Jr.. and P. T. Stroup. Institute of Metals Division: Robert Maddin, Chairman. F. Lincoln Vogel, Jr., Vice-chairman, W. A. Backofen, R. W. Balluffi, J. H. Bechtold, M. B. Bever, R. S. Busk, C. G. Goetzel, Paul Gordon, C. D. Graham. Jr., Robert F. Hehe-mann, R. I. Jaffee, F. E. Jaumot, Jr., lrving R. Kramer, A. J. Leno, Horold Margolin, C. J. McHorgue, Russell A. Meussner, J. 6. Newkirk, H. W. Paxton, G. E. Pell~ssier, I. S. Servi, Alan U. Seybolt, A. J. Sholer, and Sack Wahsburn. Iron and Steel Division: J. C. Fulton, Chairman; T. B King, F. C. Langenberg, W. O. Philbrook, and T. B. Winkler. Published bimonthly by the American Institute of Mining Metallurgical and Petroleum Engineers Inc., 29 West 39th Street, New York 18, N. Y. Telephonne pennsylvania 6-9220.Petroleum Subscription Engineers$20 per year for non-AIME members in United States and North South and Central 6-9220.SubscriptionAmerica $25 toreign; $5 for AIME members. Single copies, $4.00, iinalo copies Southfpr;ign,andCentral $5 00. The AIME 'is $25not responsible for any statement made or opinion expressed in its publications Copyright 1958 1958 by the American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. . Registered coble address, AIME New York . . . Indexed in Engineering Index, Industrial Arts Index, ...and Chemical Abstracts . . . Application for second class mail privileges IS pending at New Yark, N. Y. Volume 212, Number 2.

Jan 1, 1959

At Black Lake, Quebec, Lake Asbestos of Quebec Ltd., a wholly-owned subsidiary of American Smelting and Refining Co., has opened a $36-million mining and milling operation which will produce about 100,000 tons of asbestos fiber a year and add 7 pct to the Free World's supply. The orebody once lay beneath Black Lake, and readying the ore deposit for open pit mining meant removing about 37 million cu yd of overburden- 30 million cu yd by dredging and pumping, and 7 million by power shovels and trucks. The enormous amount of material to be dredged, control of drainage during dredging, the need to cope with drainage problems in the area and to provide for flood control to replace the regulating effect of the lake, posed unusual engineering challenges and required tremendous capital investment.

Jan 1, 1959

By N. E. Hanna

The effect of small percentages of sodium chloride on the incendivity of permissible explosives was studied by the Bruceton up-and-down technique in gallery tests. Both the reduction in incendivity achieved by addition of sodium chloride and application of the test method to explosives evaluation are discussed. It is demonstrated that the up-and-down technique in gallery testing is suitable for distinguishing differences in incendivity between different explosive compositions and between lots of the same composition. The study also shows that addition of relatively small quantities of sodium chloride tends to reduce the incendivity of explosives to firedamp, but addition of sodium chloride cannot insure reduced incendivity. Any improvement attributable to the salt can be counteracted by undefined variations in the explosive. The need for experimental investigations of a number of factors that may affect the safety of permissible explosives is emphasized. ACKNOWLEDGMENTS Grateful acknowledgment is made of the assistance of Roy L. Grant in analyzing for normality of distribution of the data obtained by the up-and-down methods and to Harold E. Tubbs for numerous calculations.

Jan 1, 1959

By H. I. Aaronson

The nucleation of pearlite at proeutectoid ferrite is inhibited, to an increasing extent, at the following locations: At twin boundary-nucleated ferrite, between closely spaced ferrite sideplates, and at intragranular plates. These effects are discussed in terms of the influence of transformation strain energies and of the interfacial free energy of austen-ite:ferrite boundaries on the rate of pearlite nucleation. The growth of pearlite into the interiors of austenite grains from the region of the grain boundaries is markedly restricted when low reaction temperatures and large austenite grain sizes permit the development of interlocking networks of intragranular ferrite plates. PREVIOUS investigators have made extensive studies of the interactions which occur between the proeutectoid ferrite and the pearlite reactions from the viewpoint of the mechanisms through which pearlite interferes with the nucleation and growth of proeutectoid ferrite.1-3 In the present investigation, the processes through which proeutectoid ferrite (hereafter termed simply "ferrite") can reduce the rate of formation of pearlite have been explored in some detail. A steel with a relatively low carbon content, in which the ferrite reaction can compete successfully with the pearlite reaction over a wide range of reaction temperature, and exceptionally coarse-grained specimens, which further emphasize the role of the ferrite reaction, have been employed for most of this work. A brief examination also has been made, however, of the effects of smaller austenite grain sizes upon these processes. Experimental Procedure The steel employed had the following composition: 0.29 pet C, 0.76 pet Mn, 0.25 pet si, 0,007 pet S, and 0.005 pct P. This alloy was homogenized for 48 hr at 1250°C. The investigation was performed

Jan 1, 1959

By J. H. Field

The sulfur dioxide emitted in low concentrations in flue gases from the combustion of sulfur-containing coals and fuel oils is a significant factor in contamination of the atmosphere with sulfur dioxide. A review of methods for treating gases containing high concentrations of sulfur dioxide shows that they are seldom satisfactory for purifying flue gases. Processes developed specifically for treating flue gases using liquid absorbents are costly and may cause localized pollution, because the cooled flue gases can settle in the vicinity of the stack. Bench-scale research is being conducted to investigate the use of dry absorbents for sulfur dioxide removal at temperature levels of about 250°- 300° F. and 600°-650° F. Alkalized alumina has been found effective for treating simulated flue gas and Is regenerable by hydrogen, carbon monoxide, or producer gas. Other metallic oxides have been tested as absorbents also. Chemically impregnated activated carbons removed sulfur dioxide from the gas at 265° F. Vanadium pentoxide is effective as a catalyst for oxidizing of sulfur dioxide in the simulated flue gas at temperatures lower than have been used commercially for gases with higher concentrations of sulfur dioxide. Conversions of sulfur dioxide to trioxide wore studied as a function of temp- erature over a range of about 570° to 750° F.

Jan 1, 1959

By A. P. Young, F. C. Holden

IN many of the early investigations of the aging of titanium alloys, it was observed that the retained beta phase could be aged to a high hardness without an apparent change in microstructure; moreover, in some alloys it was found that even a very rapid quench produced beta having an anomalously high hardness. What appeared to be hard beta phase was designated as "beta prime," to distinguish it from the softer normal retained beta phase. Frost and co-workers'.' demonstrated that the increased hardness is caused by the formation of a metastable phase, omega, which can be identified from its X-ray diffraction pattern. This reaction also has been studied by Brotzen, et a1.,3 and the structure of the omega phase has been published by Silcock, et al.," and by Austin and Doig.3 The X-ray diffraction analysis by Austin and Doig indicated that omega is low in alloy content, approaching the composition of the stable alpha. The aging process proceeds by the path Thus, overaging results in the formation of alpha and the ultimate disappearance of omega. This is accompanied by a decrease in hardness and a recovery of ductility. The present work represents a study of the aging process in a high-purity Ti-6.4 Mn alloy, in which optical and electron microscopy, X-ray diffraction, and hardness data were correlated. The specimens, 1/8-in. sections cut from 1/4-in.-diam rod, were heated in argon to a temperature just into the beta field (810°C), held for 1 hr, and water-quenched. The aging samples were heated in air for 1 hr at 300 to 500°C. The specimens were ground and mechanically polished, finishing with alternate etching and polishing on a slow-speed wheel to remove disturbed metal from the surface. The surface finally was swab-etched, rinsed with tap water, and air-dried. The etchant used was an aqueous solution containing 1 1/2 pct HF and 3 1/2 pct HNO3. This procedure is identical with that used for preparing metallographic specimens, except that the optimum degree of final etching required for electron microscopy may vary from that used for light microscopy. Metal replicas, backed with silica, were prepared from plastic strip-pings for examination with the electron microscope. Complete details of the procedures used for preparing these replicas are available elsewhere." Fig. 1 shows a comparison between the structures revealed by the electron microscope and those obtained by conventional light microscopy. Hardness and X-ray diffraction data are listed in Table I. No evidence of a second phase is apparent in the optical micrographs for the as-quenched sample, or for the specimens aged at 300 or 400°C; fine alpha particles can be seen in the specimen aged at 500°C. In the electron micrographs, visible equiaxed pocks appear in the as-quenched specimen, and, with increasing density, in the samples aged at 300 and 400°C. After aging at 500°C, the structure becomes markedly coarser and develops an oriented appearance of a second phase, coincident with the appearance of visible alpha particles in the light micrographs. These observations are confirmed by X-ray diffraction and hardness data. In these specimens, aged for 1 hr, the intensity of the omega pattern increases to a maximum at the 400°C aging temperature, corresponding to maximum hardness and the maximum density of pocks in the electron micrographs. At this point the beta phase shows a definite enrichment in Mn. At 500°C, little or no omega re-

Jan 1, 1959