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By Jack White, Ralph B. Adair

The Mufulira mine in Northern Rhodesia is 13° south of the Equator and at an altitude of 4100 ft above sea level. The concentrator was planned in 1930 to treat about 10,000 tons of ore per day, but before construction work had gone very far the size of the plant was reduced to 1500 tons daily capacity. Then just as the construction was finished in December 1931, the price of copper did not warrant the commencement of operations and it was not until October 1933 that the mine re-opened. Extensions have been made to the plant in 1934, 1935, 1936, 1937, 1940 and finally in 1945. The capacity of the plant when the 1945 extension is completed will be 9500 short tons per day. The various extensions have been carried out with the minimum confusion and with great skill on the part of the designers and the erection engineers. In dealing with the plant in this paper it is proposed to give an outline of the present practice and only to refer to past practice when it is considered of particular interest. Ore Treated The ore consists of fine grained highly siliceous, felspathic and argillaceous quartz- ites, the latter containing graphitic carbon and locally termed graywacke. These rocks are considerably altered near the surface and on the fringes of the ore body. Despite extensive efforts at mixing, both underground and in the crushing plant, many sudden changes of ore take place in the mill feed. The minerals are chalcocite, bornite and chalcopyrite with relatively unimportant amounts of malachite, native copper, azurite, covellite and chrysocolla. Gold is present at about I oz to a thousand tons, and silver at about 2 dwt. per ton. With increasing depth the nonsulphide content or,, as commonly termed locally, the oxide content of the ore is decreasing and is now less than 0.25 pct against a high of 0.77 pct- Crushing Operations The first stage of crushing is done under. ground where the oversize from I2-in. grizzlies is fed to a 56 X 72-in. jaw crusher. At the Selkirk shaft two 10-ton skips deliver the run of mine ore at a rate of 450 tons per hour to the 400-ton capacity shaft bins. One 6 ft wide Ross chain feeder and one locally made air-operated finger feeder feed the two 30-in. McCully crushers. Ahead of each crusher is a 6 X 9-ft spring grizzley spaced at 5 in. on a 35O slope. Neither the Ross chain feeder nor the finger feeder is entirely satisfactory and for the wet, muddy and sticky ore that has to be handled it is planned to replace these with two 6-ft wide apron pan feeders. The McCully crushers deliver a minus 5-in. product, at a.rate of over 500 tons per

Jan 1, 1949

By F.S. Norcross

Manganese has long been considered one of the United States' most important strategic raw materials. Its indispensabil-ity in steel manufacture makes it vital to the nation's industrial life. Coupled with this indispensability is the fact that domestic producers have not been able as yet to supply more than a small part of the nation's manganese needs; consequently the United States has had to depend upon such distant foreign sources as the U.S.S.R., British India, the African Gold Coast and Brazil for the major portion of its ore. The great bulk of the mineral is consumed in the form of ferromanganese, an alloy that averages 80 per cent manganese and 20 per cent mainly iron and carbon. Manganese is used as a deoxidizer and desulphurizer in steel manufacture. By combination with the residual oxygen and sulphur of the bath, it helps to produce a clean, sound metal. Approximately 14 lb. of manganese, it is estimated, is used in making one ton of steel. For standard-grade ferromanganese, the ore should have a minimum of about 48 per cent Mn and preferably more. Beneficiation methods have not yet been developed for making the immense low-grade deposits in the United States salable at prevailing prices. Dependence upon foreign sources thrust the United States into serious difficulties during the World War. At the start of hostilities in 1914, the nation was obtaining about four-fifths of its ore from the Eastern Hemisphere. Domestic production had been negligible, amounting to only 3000 to 7000 tons a year. As the war continued, shipments from the East, endangered by sea attack and blockade, dwindled rapidly. Imports from Brazil mounted. In this grave emergency, the United States, starting almost from scratch and under the stimulus of high prices, succeeded by 1918 in producing a peak of 3II,000 tons, about 35 per cent of its consumption that year. Since the war, the United States has depended upon foreign sources for more than nine-tenths of its high-grade ore. During 1936, 1937 and 1938, imports for consumption averaged 736,000 tons a year. During the same period, domestic shipments averaged 21,000 tons a year. Of the imports, the U.S.S.R. accounted for an annual average of 280,000 tons, the Gold Coast 208,000 tons, India 74,000 tons, and Brazil 72,500 tons. But India and Brazil, which in 1936 ranked third and fourth in the list of importers, were displaced in 1937 and 1938 by a new and much nearer source—Cuba. From less than I per cent of United States imports in 1931, the island republic increased its shipments to more than 27 per cent in 1938. Cuba's average for this three-year period was 97,000 tons, and its total for 1938 was 131,000 tons. History The story of the economic development of manganese in Cuba dates back to the Spanish-American War days. John Green-way, then one of Theodore Roosevelt's

Jan 1, 1943

By F. S. Norcross

Manganese has long been considered one of the United States' most important strategic raw materials. Its indispensabil-ity in steel manufacture makes it vital to the nation's industrial life. Coupled with this indispensability is the fact that domestic producers have not been able as yet to supply more than a small part of the nation's manganese needs; consequently the United States has had to depend upon such distant foreign sources as the U.S.S.R., British India, the African Gold Coast and Brazil for the major portion of its ore. The great bulk of the mineral is consumed in the form of ferromanganese, an alloy that averages 80 per cent manganese and 20 per cent mainly iron and carbon. Manganese is used as a deoxidizer and desulphurizer in steel manufacture. By combination with the residual oxygen and sulphur of the bath, it helps to produce a clean, sound metal. Approximately 14 lb. of manganese, it is estimated, is used in making one ton of steel. For standard-grade ferromanganese, the ore should have a minimum of about 48 per cent Mn and preferably more. Beneficiation methods have not yet been developed for making the immense low-grade deposits in the United States salable at prevailing prices. Dependence upon foreign sources thrust the United States into serious difficulties during the World War. At the start of hostilities in 1914, the nation was obtaining about four-fifths of its ore from the Eastern Hemisphere. Domestic production had been negligible, amounting to only 3000 to 7000 tons a year. As the war continued, shipments from the East, endangered by sea attack and blockade, dwindled rapidly. Imports from Brazil mounted. In this grave emergency, the United States, starting almost from scratch and under the stimulus of high prices, succeeded by 1918 in producing a peak of 3II,000 tons, about 35 per cent of its consumption that year. Since the war, the United States has depended upon foreign sources for more than nine-tenths of its high-grade ore. During 1936, 1937 and 1938, imports for consumption averaged 736,000 tons a year. During the same period, domestic shipments averaged 21,000 tons a year. Of the imports, the U.S.S.R. accounted for an annual average of 280,000 tons, the Gold Coast 208,000 tons, India 74,000 tons, and Brazil 72,500 tons. But India and Brazil, which in 1936 ranked third and fourth in the list of importers, were displaced in 1937 and 1938 by a new and much nearer source—Cuba. From less than I per cent of United States imports in 1931, the island republic increased its shipments to more than 27 per cent in 1938. Cuba's average for this three-year period was 97,000 tons, and its total for 1938 was 131,000 tons. History The story of the economic development of manganese in Cuba dates back to the Spanish-American War days. John Green-way, then one of Theodore Roosevelt's

Jan 1, 1943

By K. E. Brown, F. W. Jessen

It is deemed feasible to store atomic reactor fuel wastes in salt dome cavities when the differential pressure acting on the cavity does not exceed 3,000 psi and the temperature is less than 400°F. Tests at pressure increments of 1,000 psi were conducted on a 2-in, cylindrical cavity contained in a 6-in. long X 6-in. diameter salt core. The cavity exhibited stability under pressures up to 3,000 psi and temperatures to 300°F. At temperature ranges of 100 to 400°F and with pressures of 5,000 psi and above continuous deformation of the cavity resulted. Initial movement of the salt was observed at all pressares. This was evidenced by vertical deformation and cavity size reduction. INTRODUCTION The development of storage techniques for safe disposal of atomic reactor fuel wastes is a goal of the Atomic Energy Commission. Salt domes have been used successfully for storage of liquefied petroleum gases and hence should prove to be suitable for liquid waste products of atomic reactors. The purpose of the following work is to evaluate the practicability of utilizing salt dome cavities for such wastes and to de-termine particularly the effect of pressure and temperature on a salt cavity. This work represents a part of a comprehensive study covering the over-all problem of storing re- actor fuel wastes in salt domes and/ or salt beds. The problem of accurately determining the stresses which exist in rocks in the earth's crust is indeed a complex one. Theoretical studies have differed widely in many of the basic assumptions about the physical properties of the rock itself. Some solutions of problems in underground stress analysis assume that rock is elastic, homogeneous and isotropic in character; others assume that rock possesses plastic, viscous, elasticovis-cous properties, or a combination thereof. Experimental evidence has shown that salt possesses plastic, viscous and elasticoviscous properties.' Recent work has shown that salt becomes more plastic with temperature.' APPARATUS AND PROCEDURE For experimental study a cylindrical cavity was chosen for analysis since it provided maximum volume per unit of depth with constant diameter. This particular cavity shape, allowing for irregularities, can be easily leached out of salt domes in field operations. For the purpose of approaching underground storage conditions as nearly as possible, the following factors were considered: (1) control of pressure and temperatures, (2) measurements of temperature gradients throughout salt mass, and (3) measurement of structural stability of salt cavities. In order to obtain triaxial pressure on the salt cavity without resorting to the application of fluid pressure directly on the salt mass, a system was designed whereby the same effect could be produced through axial loading only. By cutting a core to close dimensions to fit a steel test cylinder and applying axial pressure, a lateral pressure was obtained. This equipment is shown in Figs 1 and 2. A steel cylinder was made from

By R. E. Zimmerman

The separation of fine sizes of coal from its impurities by means of various flotation methods has become of increasing importance in the coal industry. This, no doubt, will be even more so in the future as the quantity of high grade coal is depleted, particularly that used for metallurgical purposes. The purpose of this paper is to describe and report the results of research work done under the auspices of the Pittsburgh Coal Co. to determine the amenability of their bituminous fine sizes of coal to flotation, to investigate the value of various reagents and factors affecting their use, and compare the results between froth flotation and bulk oil flotation. Compared with the preferential flotation of complex minerals, or ores, the flotation of coal is comparatively easy. However, this statement should not lull one into the feeling that there are no special problems involved. For instance, the separation of coal from pyrite in high sulphur coals is still far from being 100 pet successful. Size consist has considerable effect on reagent consumption and recovery. Other factors will be described and finally it must be remembered that in the flotation of coal a low priced material is being treated and thus economic considerations govern more closely its application than is generally the case in treating other minerals. As a result of the research work done by the Pittsburgh Coal Co. on the flotation of coal, it was concluded that it was practical to clean the —48-mesh coal commercially by froth flotation and after several different types of flotation units and circuits were investigated by means of pilot plants, large scale units were installed at their Champion Nos. 1, 4 and 5 Preparation Plants for the cleaning of —48-mesh slurries. These large scale operations have been recently described by D. H. Davis.' C. P. Proctor and C. B. Carlson2 in their chapter on Froth Flotation of Coal in the AIME Seeley W. Mudd series book on Coal Preparation describe some of the practical applications of our Pittsburgh Coal Co. laboratory work in actual plant practice as well as summarizing part of the investiga-tional work. The author presents this paper, however, as a supplement to their reports, and records the basic research accomplished in the laboratory investiga-tional work as well as the results of experiments using bulk oil flotation. In presenting this work the author wishes to state much more work must be done in applying the principles of flotation to cleaning coal, especially in view of recent studies and practices in other mineral beneficiation fields. Methods of Conducting Laboratory Tests The bulk of the research work was conducted in the laboratory of the Champion No. I Preparation Plant. This plant has elaborate facilities for sampling and analyzing coal and proved to be an admirable location for the investigational work. Four types of laboratory flotation ma-

Jan 1, 1949

By Jack White, Ralph B. Adair

THE Mufulira mine in Northern Rhodesia is 13° south of the Equator and at an altitude of 4100 ft above sea level. The concentrator was planned in 1930 to treat about 10,000 tons of ore per day, but before construction work had gone very far the size of the plant was reduced to 1500 tons daily capacity. Then just as the construction was finished in December 1931, the price of copper did not warrant the commencement of operations and it was not until October 1933 that the mine re-opened. Extensions have been made to the plant in 1034, 1935, 1936 1937, 1940 and finally in 1945. The capacity of the plant when the 1945 extension is completed will be 9500 short tons per day. The various extensions have been carried out with the minimum confusion and with great skill on the part of the designers and the erection engineers. In dealing with the plant in this paper it is proposed to give an outline of the present practice and only to refer to past practice when it is considered of particular interest. ORE TREATED The ore consists of fine grained highly siliceous, felspathic and argillaceous quartzites, the latter containing graphitic carbon and locally termed graywacke. These rocks are considerably altered near the surface and on the fringes of the ore body. Despite extensive efforts at mixing, both underground and in the crushing plant, many sudden changes of ore take place in the mill feed. The minerals are chalcocite, bornite and chalcopyrite with relatively unimportant amounts of malachite, native copper, azurite, covellite and chrysocolla. Gold is present at about 1 oz to a thousand tons, and silver at about 2 dwt. per ton. With increasing depth the nonsulphide content or, as commonly termed locally, the oxide content of the ore is decreasing and is now less than 0.25 pct against a high of 0.77 pct. CRUSHING OPERATIONS The first stage of crushing is done underground where the oversize from 12-in. grizzleys is fed to a 56 X 72-in. jaw crusher. At the Selkirk shaft two 10-ton skips deliver the run of mine ore at a rate of 450 tons per hour to the 400-ton capacity shaft bins. One 6 ft wide Ross chain feeder and one locally made air-operated finger feeder feed the two 30-in. McCully crushers. Ahead of each crusher is a 6 X 9-ft spring grizzley spaced at 5 in. on a 35° slope. Neither the Ross chain feeder nor the finger feeder is entirely satisfactory and for the wet, muddy and sticky ore that has to be handled it is planned to replace these with two 6-ft wide apron pan feeders. The McCully crushers deliver a minus 5-in. product, at a rate of over 500 tons per

Jan 1, 1947

By B. H. Caudle, A. B. Dyes

In a recent publication' it was shown that wells with a free surface in a homogeneous gravity-drainage reservoir have a hyperbolic decline with index n '. This paper reports efforts to extend this theory to practical field cases. As a first step in making the extension, a large number of lease production curves from gravity-drainage fields in the stripper stage were fitted with the general hyperbolic decline equation, q/q, = 1/(1 + y) y and n in each case being determined by statistical methods. It was found that this equation is reliable for decline curve extrapolation for periods up to at least 25 years. The resrilts obtained were disturbing in the sense that values for the index, n, were often smaller than one, which fact leads to the prediction that a well would produce all infinite amount of oil in infinite time. A theoretical investigation based on the results of the previous paper provides a suitable explanation for these low values of n. It suggests that these are obtained if production occurs from two or more layers of diflerent permeabilitv and thicktress or two lnyers having different skin effects. It is predicted that as the more permeable layers are exhausted, the index of decline, n, will rise from a value smaller than 2, to n = 2. A practical method is given for fitting the general hyperbolic decline Eq. 6 to production decline data. When this method is used, the index of decline observed in gravity-drainage reservoirs in the stripper stage when wing only data over early years 01 decline usually agrees quite closely with that determined using data over 25 years or more. This indicates that the hyperbolic decline equation is reliable for predicting behavior of such reservoirs. A method is also suggested for taking into account any changes in the value of the index INTRODUCTION As a result of both experimental work with models and theoretical deductions, it was recently concluded' that wells having a free surface in a homogeneous reservoir producing by pure gravity drainage should have a hyperbolic decline with n = 2. The present report details efforts to extend this work on ideal homogeneous reservoirs to actual field cases. It should be remembered that both the previous work and the present extension are based on the assumption that the reservoir is at very low pressure, and hence, nearly all the potential available for driving fluid to the well is the gravity head. Attempts to apply conclusions of this study to reservoirs which have considerable pressures supplementing the gravity drive may lead to difficulty. WELLS WITH NO FREE SURFACE In a dipping gravity-drainage reservoir such as that shown in Fig. 1, some of the down-dip wells have no free surface. The previous study' showed that the up-dip wells, which have a free surface, should follow Eq. 1. The following approximate analysis, of a type which was justified experimentally for up-dip wells in the work just mentioned, leads to results for the down-dip wells.

By N. P. Goss

Asterism appearing in X-ray Laue diagrams is an extremely sensitive index of changes in the internal structures of individual grains of polycrystalline metals. It indicates the existence of various forms of subboundary structure or subdivision within the grain. The present viewpoint is that the grain is made up of lattice blocks having substantially the same size and shape.l-4 When these blocks all assume exactly the same orientation, the crystal is perfect and asterism is absent. Cleaves and Thompson5 observed that the hardness of iron is virtually constant over a range of grain sizes. It is quite possible that the subboundary structure caused this, and that the latter is just as important as grain size itself. While the experiments reported here are not conclusive, they do support this viewpoint. Metals can, under certain conditions, be prepared entirely free from asterism, but this preparation does not necessarily require long heating or slow cooling, as will be shown here. In this paper a distinction is made between mosaic and distorted grain structures but the difference is only a matter of degree. In a previous paper9 it was shown that the grains can become distorted even during heat-treatment. The block structure exists inherently, even in a perfect crystal; the size and shape of these crystallites, or lattice blocks, varies, depending upon a number of factors. Goetz, for example: has shown that a metal before crystallizing from the molten state must go through a paracrystalline phase with oriented groups of atoms about 10-l4 to 10-l5 c.c., or 10-15 cm. in size. These crystallites, or blocks, appear to survive the most drastic cold-working, for it has been shown, and more elaborately by Wood's recent work," that cold-working cannot reduce the size of these crystallites smaller than of the order 10-5 cm. The interesting correlation brought out by the experiments of Goetz and Wood is that the block size after severe cold-working is of the same order of magnitude as the groups that formed in the metal just before crystallizing from the molten state. The work of Ewald and Rennenger17 and the now classical experiments of Darwin and James12,13 all strongly suggest the existence of a periodic structure of crystal. lites smaller than the grain itself. Related to this effect is the appearance of veinlike markings in the microstructures. Ammer-man and Kornfeld,16 in their experiments, did not observe any evidence of veining in specimens of alpha iron annealed below A3 and believed that veining was not due to impurities in the iron, as Northcott16 suggested; veining was observed by them only in specimens annealed above A3. Hanemann,16 Schrader and Tangerding found that annealing in hydrogen did not diminish veining and so it could not be caused by oxides. They concluded that veining was due to a slight difference in the orientation of ferrite lattice blocks. This viewpoint is well supported by the evidence presented here.

Jan 1, 1941

By B. G. Reisdorf

This paper describes the microstructural changes that occur when quenched ultrahigh-strength steels containing OA pet C and various amounts of nickel, silicon, and cobalt are tempered. The changes that occur in hardness, yield strength, and martensite diffraction-peak widths when these steels are tempered are related to the precipitation of the carbide phases. An unea$ectedly high silicon content (about 30 pct) was found in the E -carbide phase in a steel containing only 1.5 pct Si. TEMPERED martensitic steels have such wide-spread utility that they have been the subject of numerous investigations, and a sizable amount of literature has developed on this subject.M This investigation, which is a part of a larger program to correlate microstructure with mechanical properties at a variety of strength levels, is limited to the microstructural changes that occur when a quenched 0.40 pct carbon steel (USS Airsteel X-200 steel) is tempered, and to the effects of the alloying elements—nickel, cobalt, and silicon—on these microstructures. Used in this investigation were electron microscopy, electron-diffraction identification of the carbide phases, electron-probe micro-analysis of the carbides, X-ray determinations of retained austenite, and measurements of martensite X-ray diffract ion-peak widths. MATERIALS AND METHODS The chemical analyses of the eight heats examined eats No. 30 through 37) are shown in Table L Heat No. 30 has the chemical com~osition of Airsteel X-200, and the remaining seven heats contain various amounts of nickel, chromium, cobalt, and silicon. The heats were air-melted in an induction furnace and cast into 8 by 8 in. ingots that were subsequently heated to 2300 and rolled to 1-in.-thick plate. Oversize 0.505-in.-diam tensile specimens were rough-machined from the plates and austenitized in air at 1700° F for half an hour and oil-quenched. The specimens were then tempered in air at temperatures of 400° to 1000 for tempering times of 1, 4, and 16 hr, and finish-machined to 0.505-in.-diam tensile specimens. Electron micrographs were prepared from Formvar replicas of the midthickness of tensile-specimen shanks that had been electrolytically polished and etched in nital. Electron-diffraction patterns were obtained from carbon-extraction replicas. The replicas were prepared by etching the sample surface in the same manner as for microscopy, evaporating carbon on the etched surface, and re-etching the sample to free the carbon film and the precipitate particles. Electron-probe microanalysis was performed on some of the extraction replicas. To obtain adequate fluorescent X-ray intensities, several thicknesses of replica were exposed to the electron beam so that the results represent an average composition of the extracted particles rather than an analysis of single precipitate particles. The retained austenite contents of the specimens were determined by an empirical X-ray diffraction

Jan 1, 1963

By N. P. Goss

Asterism appearing in X-ray Laue diagrams is an extremely sensitive index of changes in the internal structures of individual grains of polycrystalline metals. It indicates the existence of various forms of subboundary structure or subdivision within the grain. The present viewpoint is that the grain is made up of lattice blocks having substantially the same size and shape.l-4 When these blocks all assume exactly the same orientation, the crystal is perfect and asterism is absent. Cleaves and Thompson5 observed that the hardness of iron is virtually constant over a range of grain sizes. It is quite possible that the subboundary structure caused this, and that the latter is just as important as grain size itself. While the experiments reported here are not conclusive, they do support this viewpoint. Metals can, under certain conditions, be prepared entirely free from asterism, but this preparation does not necessarily require long heating or slow cooling, as will be shown here. In this paper a distinction is made between mosaic and distorted grain structures but the difference is only a matter of degree. In a previous paper9 it was shown that the grains can become distorted even during heat-treatment. The block structure exists inherently, even in a perfect crystal; the size and shape of these crystallites, or lattice blocks, varies, depending upon a number of factors. Goetz, for example: has shown that a metal before crystallizing from the molten state must go through a paracrystalline phase with oriented groups of atoms about 10-l4 to 10-l5 c.c., or 10-15 cm. in size. These crystallites, or blocks, appear to survive the most drastic cold-working, for it has been shown, and more elaborately by Wood's recent work," that cold-working cannot reduce the size of these crystallites smaller than of the order 10-5 cm. The interesting correlation brought out by the experiments of Goetz and Wood is that the block size after severe cold-working is of the same order of magnitude as the groups that formed in the metal just before crystallizing from the molten state. The work of Ewald and Rennenger17 and the now classical experiments of Darwin and James12,13 all strongly suggest the existence of a periodic structure of crystal. lites smaller than the grain itself. Related to this effect is the appearance of veinlike markings in the microstructures. Ammer-man and Kornfeld,16 in their experiments, did not observe any evidence of veining in specimens of alpha iron annealed below A3 and believed that veining was not due to impurities in the iron, as Northcott16 suggested; veining was observed by them only in specimens annealed above A3. Hanemann,16 Schrader and Tangerding found that annealing in hydrogen did not diminish veining and so it could not be caused by oxides. They concluded that veining was due to a slight difference in the orientation of ferrite lattice blocks. This viewpoint is well supported by the evidence presented here.

Jan 1, 1941

By C. F. Clausen

"Cement" means binding agent or glue. It is derived from the Latin word "Caementum," the name of a limestone, chips of which were used in mortar more than 2,000 years ago in Italy. During the middle ages "cement" or "cement" generally denoted mortar. Today it means any binding material. The Thomas Register lists nearly 200 classifications for "cement" including automobile cement, household cement, rubber cement, etc. The material most commonly associated with this word, however, is portland cement which, when mixed with water and allowed to hydrate, is a ceramic binding material used to cement aggregates (crushed stone, gravel and sand) together in "concrete," the most universally used building material of today. It is estimated that more tons of concrete are used annually than all other building materials put together including steel, lumber, gypsum, bricks, tiles, aluminum and glass. Its use in foundations, building construction, sanitary work, dams, railroads, and highways, makes it difficult to conceive of modem civilization without concrete. A survey made in October 1955 showed the following uses of portland cement: [Percent Highways20 Nonresidential buildings20 Residential buildings15 Military construction10 Sewer and water works8 Public utilities10 Other (conservation, farm, and maintenance and repair)17 100] As of today, the percentage for highways is probably even higher. Ceramic binding materials have unquestionably been used in construction work for thousands of years. The mortar between the blocks of the great pyramids was calcined gypsum (plaster of paris). The use of calcined and slaked limestone goes back earlier than the Roman Empire. Gypsum, however, is relatively soft, and common lime mortar is not "hydraulic," i.e., it does not harden under water. The Greeks and Romans discovered later that an addition of a finely divided active siliceous material (Santorin earth or Pozzolana) would react with slaked lime to form a stronger, and hydraulic, cement. The Appian Way in Italy, Colosseum, and the great Aqueducts built by the Romans were made with this type cement, and some of these structures are still in existence today. However, not until 1756 did some serious research result in the development of better cements. In that year the English engineer, John Smeaton produced a stronger cement by burning a limestone containing considerable proportions of clayey impurities. Other investigations and improvements were made by Bryan Higgins, Bergmann, Joseph Parker, L. J. Vicat, J. F. John, James Frost, and I. C. Johnson.2 Traditionally, but perhaps unfairly to others, the invention of the prototype of today's portland cement is credited to the English mason Joseph Aspdin who in 1824 obtained a patent and gave the product its name, because in color the mortar produced from it resembled a natural building stone obtained from the British Isle of Portland. The contributions of Johnson and Aspdin were primarily the important step of preparing a synthetic mixture of lime and clay without depending on raw materials found in nature which might contain such elements in desirable proportions. However, even these early

Jan 1, 1960

By James C. Word, R. M. McLouski

This paper will describe the development and application of large-scale integration techniques employed in the fabrication of a germanium multielement array. The array consists of 100 by 228 PNP bipolar transistors fabricated on 5 mi1 centers. Back-biased p-n junction techniques are used for electrical isolation of the individual elements. The end use of the array is a high resolution, large area IR sensor. The monolithic array is fabricated in 1 ohm-cm p-type germanium epitaxially deposited on 6 ohm-cm n-type substrate. Epitaxy was accomplished through the hydrogen reduction of germanium te trachloride. Di-borane was used as the dopant. Base regions are achieved by the diffusion of arsenic from doped oxide or arsine sources. Oxide-masking of the arsenic im-pzlvity was achieved by the chemical deposition of a boron doped glass. The emitter is formed by an aluminum alloy diffusion technique. Vacuum deposited aluminum is used for the emitter, interconnections, and for the contact and bonding pads. ALTHOUGH a great volume of literature pertaining to the development of large scale integration techniques (LSI) has been published for silicon and in particular silicon imaging applications,' to date only a small number of similar devices have been constructed using germanium technology.' Since the physical and chemical properties of germanium are vastly different from those of silicon, the fabrication technology for integrated structures in germanium is also different from that of silicon. In particular germanium does not possess a stable oxide as can be grown on silicon by heating in an oxidizing ambient for masking of dopants and passivation. This paper describes the application of germanium LSI techniques employed in the fabrication of a multielement infrared sensor array. The array is used in a high resolution, large area infrared sensor for operation in the 0.8- to 1.5-u spectral range. Back biased p-n junction techniques are used for electrical isolation of individual elements. Discrete germanium devices have been fabricated routinely for some time. However, mainly due to the lack of a suitable mask for selective doping and the high current leakages inherent in germanium p-n isolation, few monolithic germanium structures have been constructed. THE INFRARED MOSAIC A cross-sectional view of the array is shown in Fig. 1. The monolithic structure consists of 12,800 PNP transistor elements in a 100 by 128 matrix fab- ricated on 5 mil centers. The emitters of each line of transistors are connected together using aluminum interconnects while the strip collectors are connected together in series at right angles to the emitter lines. The selection of this structure is dictated by the readout technique involved. Access to each element transistor is obtained by applying a bias voltage to a particular collector strip and separately interrogating each emitter row. A charge storage, i.e., an integration mode is used for reading out this particular array Construction techniques available for use with germanium do not include a selective p-type diffusion capability for surface concentrations greater than 10" per cu cm and junction depths greater than about 10 u. This fact limits the type of structure that may be used. Therefore, an array of PNP transistors that did not employ p-type diffusions was chosen. The structure was fabricated by growing a 1 ohm-cm p-type epitaxial layer on a carefully prepared 6 ohm-cm n-type substrate. N-type dopants were used for the isolation and base diffusions and alloyed aluminum was used to form the emitter junctions. The array was then completed by evaporation of aluminum interconnections and contact pads. SUBSTRATE AND SUBSTRATE PREPARATION Germanium substrates of (111) orientation grown by both Czochralski and zone leveling techniques were utilized for mosaic fabrication. Czochralski substrates were preferred because of the lower dislocation densities available in this type of material. Dislocation densities for the Czochralski material were typically less than 3000 per sq cm, while those for the zone leveled material were typically less than 5000 per sq cm. All substrates were uncompensated to minimize thermal conversion problems in subsequent epitaxial and diffusion processing. Both in-house and vendor polished wafers were used. The in-house polishing technique employed consisted of an initial gross chemical etch in CP4 to remove saw damage from both surfaces. This was followed by a chemical-mechanical polishing operation of one side of the wafer. The chemical-mechanical polishing solution used was Lustrox 1000 (Tizon Chemical Co.), and consists of zirconium dioxide, sodium hypochlorite, water and a surfactant. The wafer thickness before and after polishing was typically 0.020 and 0.010 in, respectively. THERMAL CONVERSION The problem of thermal conversion of both the substrate and epitaxial layer was particularly acute because of the relatively low carrier concentrations employed in both regions. This problem has been encountered by other workers in the past.3 Without special treatment before epitaxial growth substrate conversion (n-type to p-type) and changes in the re-

Jan 1, 1970

By R. Ebeling, M. F. Ashby

The paper is in two parts. The first develops the formulae and method needed to calculate the size, nu)nber, spacing, and volume fraction of hard or inert particles in the interior of a specimen from measurernents made on an extraction replica; throughout, the spread of- particle sizes in a single specimen is taken into account, and the extraction efficiency of the replica is considered. A method for testing whether the particles are randotnly distributed in space is described, and the spacing of randomly distributed particles is discussed. The second Part describes the application of the method to copper containing spherical particles of silica; the description includes an estimate of the errors involved, and a comparison of this with alternative methods. All parameters except uolume fraction can be determined satisfactorily, and the method offers advantages over other electron-,rzicroscopic techniques when dealing with hard particles in a softer matrix, or inert particles in a chem-ically less inert matrix. 1 HE experimental measurement of sizes and numbers of discrete particles of a second phase embedded in a matrix material from opaque, plane sections has been considered by many authors, notably by Fullman.' It is assumed that, when the specimen is sectioned, the particles are also sectioned, so that the diameters of the circles of intersection of particles with the plane of the cross section ("surface diameters") are measured. It is difficult to derive the distribution of true particle diameters ("volume diameters") from measurements of the distribution of "surface diameters" on a plane section. The measurement of size and numbers of small second-phase particles by transmission electron microscopy through thin foils of matrix containing the particles has been described by Cahn and ~uttin~' and by ~illiard.~ Because of overlap and the fact that particles which intersect the foil surface may be sectioned whereas those in the bulk of the foil are not, it is again difficult to measure the true distribution of particle sizes. The use of replicas for this sort of measurement has not been analyzed in detail. A replica made from an opaque cross section, thus replicating the circles of intersection of particles with the plane of section, is analyzed by Fullman's method and suffers from the same difficulties. Under certain circumstances, however, extraction replicas can be used, and offer a special advantage in that they make the determination of the true distribution of particle diameters particularly simple. It is the purpose of this paper to describe this extraction replica method. Consider the example of an alloy consisting of SiOz particles, whose mean diameter is about 1000A, dispersed in a copper matrix. When the alloy is sectioned and mechanically polished, the particles are not sectioned, because they are much harder than the matrix, and so will be either left in the surface or pulled out whole, and because the particle size is smaller than the abrasive size of even the finest abrasive. The particles are chemically inert in solutions which chemically etch or electropolish the matrix, so that chemical treatments do not section the particles either. (Experimental measurements of particle shape in this alloy confirm this—truncated particles are never seen.) Small, hard or inert, particles are therefore not sectioned when the specimen is sectioned and polished. An extraction replica taken from this polished surface shows the true "volume" diameter of each extracted particle; the distribution of diameters seen on the replica is the surface distribution of true "volume" diameters, and the volume distribution of true "volume" diameters is easily derived from it. The extraction replica method is not subject to the difficulties associated with sectioning of particles, and avoids the problem of overlap from which the transmission method suffers. The method is well-suited for studying hard particles in a soft matrix. Examples are provided by internally oxidized alloys, oxide-dispersion strengthened metals like T.D. Nickel, and carbides, nitrides, and strong intermetallic compounds in metals. It should be possible to adapt polishing techniques in alloys containing softer but inert particles to avoid sectioning the particles (say by electropolishing or etching). The method is tested and illustrated in Sections 8 and 9 by applying it to a dispersion of spherical SiO2 particles in a copper matrix. I) SYMBOLS Symbols are defined where they first appear in the text. Volume fractions of particles are denoted by the symbol f, particle diameters by x, center-to-center particle spacings by D, and numbers of particles by N. Mean particle diameters and standard deviations about these means are denoted by x and a. Both arithmetic (subscript A) and geometric (subscript G) means are employed. In this paper we measure the distribution of true diameters of particles which touch or pass through a random-plane section of the specimen. We may want to know the distribution of particle diameters in the

Jan 1, 1967

By G. H. Anderson

H. R. HANLEY*—I have been asked to discuss briefly the development of rotating cathodes for the electrolytic deposition of cadmium. The earliest recorded use of rotating cathodes was by Hoepfner at Frufurt, Germany about sixty years ago. He elec-trolized zinc chloride solution using diaphragms to separate electrodes. In the early experimental work of the Bully Hill Copper Mining and Smelting Co., Shasta County, Calif., rotating aluminum cathodes 4 ft in diam were used in the electrolysis of an acid zinc sulphate solution. Finished cathodes weighing up to 400 lb were produced. Because of mechanical difficulties, this type of cathode was abandoned for zinc, but was later used for cadmium because of the relative smoothness of deposit in comparison with stationary plates with comparable current densities. Cadmium sponge which forms on the cathode at moderate current densities (without special treatment) is entirely eliminated by a slow rotation. The rate of rotation of the cathode has an effect on the mechanical nature of the deposit. A high rate of rotation concentrates the adhering electrolyte on the shaft; a moderate rate appears to concentrate on the cathode a short distance out from the shaft tending to corrode the deposit in the form of a ring. At a very slow rotation (2 to 3 rpm) the adhering electrolyte gravitates nearly vertically, thus avoiding the cutting ring referred to above. The true explanation for the smoother deposits obtained on rotating cathodes may not be given definitely as the numerous factors involved are not thoroughly understood. Smooth deposits are obtained when the orderly growth of the metal crystals in the cathode lattice are disorganized. Thus the crystals form and grow for a very short interval when they are arrested and a new crystal forms. The continued growth of the original crystals provides large crystals and a rough deposit. Also if the acidity of the electrolyte is low, hydrogen gas bubbles adhere to the deposit. As the cathode is rotated the gas surface is brought into the atmosphere where they burst; thus the deposit is made on a surface relatively gas-free. An aluminum hub distance piece was riveted to each aluminum disk 4 ft in diam, slipped on a 4 1/2 in. steel shaft and pressed tight to prevent acid electrolyte seeping through to the shaft. The 9-cathode assembly was supported on insulated bearings. Electrical contact to the shaft was made through what was equivalent to a copper pulley. Sufficiently high conductivity brushes were placed on the face of the pulley to lead the current to the cathode bus bar. The assembly was driven by a link belt contacting a sprocket insulated from the shaft. The lead anodes were semicircular and supported on porcelain insulators placed on the bottom of the cell. Two anodes were provided for each cathode to permit an 8-in. space between them without increasing the ohmic resistance. This ample spacing permitted easy stripping of deposit with the assembly in place. Cathode cadmium was melted under 650 W cylinder oil. After casting, the primary slabs were remelted under molten caustic soda and cast into pencils 1 1/32 in. in diam. Rotating cathodes for deposition of cadmium are used at Risdon, Tasmania, and at Magdeburg, Germany. W. G. WOOLF*—This paper is very-interesting to me because in our work at the Electrolytic Zinc Plant of the Sullivan Mining Co. we had an exactly similar problem—that is, a method of producing cadmium from our purification residue, the recovery of the contained copper as a copper precipitate which could be sent to a copper smelter and the production of merchantable cadmium. It is interesting to me, not knowing of the work of the Risdon people, how closely we approximate them in their main metallurgy, diverging at several interesting steps which I would like to discuss for just a moment. For example, at Risdon they oxidize their purification residue. In our practice we take the current residue as it is produced in the purification department of the zinc plant and process it in the cadmium plant. The only oxidation that it obtains is the oxidation in the presses, the dumping of the presses and the collection and transportation of the residue to the cadmium plant. We find that the leaching of that residue does not necessarily require the oxidation step that the Risdon people evidently find necessary. The discussion of oxidation comes in again in the matter of the treatment of the precipitated cadmium sponge with zinc dust which again at Risdon is oxidized but which we do not attempt to oxidize except as it oxidizes itself in the storage. There is a partial oxidation which cannot be avoided, as Mr. David-sou pointed out, but we make no attempt to attain a complete oxidation and we dissolve the cadmium sponge in the sul-

Jan 1, 1950

By T. M. Morris, W. E. Horst

W. E. Horst—In regard to the flotation rate being described as "first orcler" for flotation of quartz particles below 65 p in size (or any size studied in this work) in this paper, it appears that the authors' conception of rate equations is not in agreement with cited references. A first order rate equation has as one of its forms the following: a In.=a/a-x=kt where a = initial concentration, a—x = concentration at time t, t = time, and k = constant. The constant, k, has the dimension of reciprocal time which is similar to the specific flotation rate, Q. described by Eq. 2 in the authors' article, as has been previously discussed by Schumann (Ref. 1 of original article). The plotted data presented in Fig. 4 of the article utilizes the specific flotation rate, Q (min.'); however, there is not adequate data given to indicate the order of the rate equation which describes the flotation behavior of the quartz system studied. Results from the experimental work indicate that the relationship between rate of flotation (grams per minute) and cell concentration (provided the percent solids in the flotation cell is less than 5.2 pct and the particle size is less than 65 p) is described by an equation of the first order (R, = k c+", n being equal to 1 in this size range) and the use of the first order rate equation does not apply. Similarly the relationship for other particle size ranges studied is expressed by equations of the second or third order depending on the magnitude of n. T. M. Morris—The authors are to be commended for the experiments which they performed. As they state in their discussion the concentration of collector ion In solution did change with change in concentration of solids in the flotation cell. Since for a given slze of particle, flotation rate increases with concentration of collector until a maximum is reached, the effect of concentration of particles in their experiments was to vary the concentration of collector ions. A collector concentration which insures maximum supporting angle for all particles eliminates the unequal effect of collector concentration on various sized particles and the effect of size of particles and concentration of particles upon flotation rate could be more clearly assessed. I believe that if the authors had increased the concentration of collector to an amount sufficient to attain a maximum supporting angle for all particles they would find that the specific flotation rate of particles coarser than 65 p would be constant with change in the concentration of solids in the flotation cell, and that a first order rate would apply to the + 65 as well as to the —65 p sizes. It might also be discovered when this change in collector concentration was made that the maximum specific rate constant would be shifted toward a coarser fraction than when starvation quantities of collector are used since this practice favors the fine particles and penalizes the coarse particles. P. L. de Bruyn and H. J. Modi (authors' reply)—The authors wish to thank Professor Morris for his kind remarks and for mentioning the influence of equilibrium collector concentration on flotation rate. With a collector concentration sufficient to insure maximum supporting angle for all particles, a first order rate equation may indeed be found to be generally applicable irrespective of size. Such a concentration would, however, lead to 100 pct recovery of the fine particles and consequently defeat the essential objective of the investigation to derive the maximum information on flotation kinetics. To establish absolutely the validity of any single rate equation for a given size range, the ideal method would be to work with a feed consisting solely of particles of that size range. Use of such a closely sized feed would also eliminate the possibility of the interfering effect of different sizes upon one another. The authors do not believe that increasing the collector concentration would shift the maximum specific flotation rate (Q) towards a coarser fraction. Experimentation showed Q to be independent of solids concentration for all particles up to 65 µ in size, whereas the maximum value of Q was obtained in the range 37 to 10 p. Professor Morris contends that the addition of starvation quantities of collector favors fine particles at the expense of coarse particles, but the reason for this is not entirely clear to the authors. The comments by Mr. W. E. Horst are concerned only with the concept of the term "first order rate equation." According to the usage of this term in chemical kinetics, time is an important variable, as is shown in the equation quoted by Mr. Horst. All the experimental results reported by the authors were obtained under steady state continuous operations when the rate of flotation is independent of time. To be consistent with the common usage of the "first order rate equation," it would be more satisfactory to state that under certain conditions the experimental results show that the relation between flotation rate and pulp density is an equation of the first order.

Jan 1, 1957

By A. L. Labbe

SOON after the Cottrell treater was placed in operation in the Murray plant in 1918 to treat combined lead sinter and Wedge roaster smoke, it was noticed that the power flowing through the treater did not remain constant. This was indicated by the varying milliamperes and also by the total amount of power consumed by the rectifiers. At times, for then unknown reasons, the treater current fluctuated through a wide range of from 40 to 300 milliamperes. Fortunately, these variations in power did not affect the treater's overall recovery, as this installation consisted of three independent units in series, a feature which made the Murray Cottrell an outstanding installation over many years of operation. Water conditioning of the smoke as a means of improving recovery was already known, but was not adaptable to this installation for reasons of excessive corrosion, which had been the case with other treaters using water as a conditioner exclusively. Tests conducted on the smoke had proved conclusively that water vapor played no part in the fluctuation of power, and the same was true of the SO2 contents and dust burden of the smoke. Neither did temperature variations of from 150 to 400°F have any effect on the power. Finally it was noticed that the variation in power taken by the treater, and the efficiency of recovery, had some definite relation to the number of Wedge roasters operating, and particularly to the sulphur contents of the charge. This observation soon led to the discovery that free sulphuric acid was the conditioner for Murray smoke and that variations in acid contents of smoke accounted for fluctuations of treater power. Analysis of recovered dust revealed that only a few hundredths of a per cent free acid was necessary to maintain a very efficient recovery. Once this knowledge was available, the roaster charge was adjusted as to sulphur contents to produce the necessary acid conditioner. For a number of years this practice was followed, but with improvements in the field of flotation, excess pyrites were eliminated from the smelting picture, so with a change in metallurgical practice we were confronted with the problem of providing the deficiency in acid by some other means. The situation was aggravated and our problem of acid conditioning made more difficult by the increase in the lead contents of concentrates roasted resulting from better flotation methods. The first step towards introducing acid vapors into the smoke stream by accessory means was accomplished by boiling sulphuric acid in cast iron pots placed in an open fire box. Acid fumes evaporated from the pots together with the combustion gases from the fire box were discharged into the flue through a cast iron pipe. Capacity of the iron pots was quite limited because of the comparatively slow rate of evaporation and the use of lump coal as a fuel, which did not lend itself to practical temperature control. This method of firing resulted in frequent pot failures due to overheating. In spite of these incidental difficulties, encountered in any new venture, the pot evaporator demonstrated the practicability of fuming sufficient acid to make up the deficiency in that naturally evolved in the Wedge furnace operation. As time progressed, less and less high sulphur material was available for Wedge roasting, and the necessity for accessory acid conditioning reached a climax when the supply of this material was entirely eliminated. Since the cast iron pots could only evaporate a few hundred pounds of acid per day, and were costly to replace, the logical thought presented itself of spraying the acid in a heated chamber. This new type of acid evaporator was simpler and more economical to operate and had sufficient capacity to fume several thousand pounds per day. The attached fig. 1 presents the outstanding features of the new furnace. A is the vaporizing drum, which is heated by the combustion gases of coal stoker fire box, B. Acid is sprayed into the hot gas stream within the drum through a number of air-acid atomizers, C, and the acid vapor, together with combustion gases, is introduced into the smoke stream through two cast iron pipes extending to different points in the flue. The operation of this type of furnace requires control of temperature inside the drum to prevent overheating, which dissociates the acid vapor to SO, and eventually to SO2, with resulting loss of acid. The dissociation to SO, at elevated temperatures is comparatively high, and in some cases accounts for as much as 60 pct of the acid sprayed into the drum. To reduce the loss of acid, through dissociation, some Cottrell plants, where the rate of acid sprayed reaches at times 9 ppm, use two evaporating units. Fuming the acid into the smoke stream is only

Jan 1, 1951

By D. L. Harris, A. M. Gaudin

Observations were made of the distribution of mercaptan containing S35 between aqueous solution and mineral and between aqueous solution and the gaseous phase. Although equilibrium may not have been attained, adsorption of the reagent was shown to occur reasily from air or aqueous solution on sphalerite, zincite, and willem-ite and to correspond to flotation. Adsorption on quartz did not similarly occur. THE following results, presented here in condensed form,' were obtained in a preliminary study of the adsorption of n-hexane thiol, hexyl mercaptan, on sphalerite, zincite, willemite, and quartz, from aqueous solution and from a gas. Interest in this subject was aroused by a Belgian report' of effective use of hexyl mercaptan for flotation collection of oxidized zinc minerals. The relatively low boiling point, 149°C, of the mercaptan3 suggested the desirability of extending the usual measurements of partition of collector between aqueous solution and gas and between gas and mineral. It is believed that this paper presents the first measurements of this type on a flotation system. Attempts were made to carry out the measurements at equilibrium, but as the work progressed it became increasingly doubtful that this desirable condition had been achieved. To control composition and extent of the gas phase, the apparatus was a wholly-enclosed thermally-controlled glass system. Because of these constraints and the desirability of dealing with pure minerals, a scale of operations was chosen in which a few grams of deslimed mineral were used in each test. It was also necessary to choose a particularly sensitive method for mercaptan analysis, and in fact a method that would permit the experimenters to follow the approach to equilibrium. For these reasons mercaptan marked by radiosulphur 35 was used. An analysis was made for the radiosulphur by a modification of the method of Gaudin and Carr. Coarsely-crystallized sphalerite was handpicked, stage-crushed in the dry state, wet-screened on a 200-mesh sieve, and deslimed in water at about 5 microns. Further treatment consisted of a wash in dilute aqueous hydrogen peroxide, drying, removal of the dark-colored fraction in a Frantz magnetic separator, washing in very dilute hydrochloric acid, repeated washing in distilled and conductivity water, and drying. The last washings showed a conductivity equivalent to a few ppm NaC1, that is, much more than would be provided, theoretically, by a saturated ZnS solution. The material was stored dry in sealed bottles. Analyses were as follows: Zn, 62.3 pct; Fe, 0.43 pct; Cd, 0.44 pct; S, 31.2 pct; Mn, 0.001 pct. The specific surface (BET method) was 2000 cm2/g. Zincite from Franklin furnace of the New Jersey Zinc Co. was hand-picked, dry-crushed, wet-screened at 100 mesh, and deslimed at about 10 microns. After drying, the associated zinc, manganese, calcium, and silicate minerals were removed in a Frantz magnetic separator. The purified zincite was washed in distilled water and conductivity water to a conductance of less than 2 ppm equivalent NaC1, dried, and stored. Analyses were as follows: Zn, 75.1 pct; Fe, 0.9 pct; Mn, 2.78 pct. The specific surface (BET method) was 1740 cm 2/g. Willemite, also from Franklin furnace, was purified similarly. Analyses were as follows: Zn, 52.5 pct; Fe, 0.12 pct; SiO², 27.3 pct; loss on ignition, 0.13 pct. The specific surface was 1760 cm 2/g. Conductivity water (double-distilled) and demin-eralized-distilled water were used in most of the tests. The specific resistance was not less than 600, 000 ohms, and usually above 1,000,000. Radiosulphur-marked hexyl mercaptan (1-hexane thiol) was synthesized by Tracerlab, Inc., Boston. Two lots were secured several months apart. The last lot, consisting of about 0.5 g of the mercaptan, had a total activity of about 10 millicuries. Tracerlab Co. guaranteed only the activity; hence a quasi -vapor pressure determination (based upon an S analysis) of the mercaptan was made. The calculated value, 4.2 mm of mercury at 25.5' C, has been compared with that of a sample of Highest Purity 1-hexane thiol from Fisher Scientific Co. The latter had a vapor pressure of 4.5 mm of mercury at 2.5 C. Analytical Procedures The sample containing radiosulphur-marked mercaptan was oxidized to convert the mercaptan sulphur to sulphate, carrier barium sulphate being added to provide a suitable quantity of total barium sulphate in a filter cake. The precipitate was filtered and dried, and counting was carried out either in a streaming-gas (Q-gas) counter for high sensitivity or with an end-window G-M counter for convenience. The oxidized and precipitated mercaptan gave a radioactive count of 65 counts per minute per microgram in the end-window Geiger-Mueller counter and 1100 counts per minute per microgram in a Q-gas counter. For standardization of the mercaptan solution, 15 replicate analyses were made. The average deviation per measurement was about 1600 cpm in 65,000 cpm, the probable error in the mean being 275 cpm. It

Jan 1, 1955

By W. C. Clarke

An empirical study of the nature of the embrittle-ment which occurs in martensitic and semiaustenitic precipitation hardening stainless steels upon exposure at temperatures of from about 550" to 875°F has been undertaken. This work was aimed at determining cazusation and means of controlling this phenomenon. A commercial copper bearing precipitation hardening alloy was used as a basic material for study. The effect of heat treatment variables was studied as was the effect of variations in analysis. It is concluded from the evidence that martensitic and semiaustenitic precipitation hardening stainless steels are subject to 885°F ernbrittlement similar to that observed in the straight chromium stainless steels. A characteristic of precipitation hardening stainless steels which has limited their use in certain applications is that they embrittle when held at temperatures in the range of from about 550" to 900°F. This is true to a more or less degree in all currently available alloys, either the basically martensitic type or the semiaustenitic type. The rate of embrittlement varies markedly with exposure temperature, being low at 550" to 600°F and in-creasing as the temperature increases. In spite of this embrittlement, these alloys with their unique combination of high mechanical strength, reasonable toughness, and good corrosion resistance are used in many hundreds of applications. Nevertheless, there are potential applications where the embrittle-ment described is a limiting factor. The purpose of this investigation was to study the embrittlement of these alloys and to find a way to control or eliminate it. GUIDELINES USED IN PRESENT WORK The work reported in this paper is based on a study of 17-4 PH*, a very widely used alloy. It has been used *Trademark of Armco Steel Corp., licensor. in pressurized water and boiling water atomic reactors operating at about 550°F for a number of years. As the life of such equipment is extended or operating temperatures are raised, the possibility of embrit-tlement becomes of increasing concern to materials engineers. Much investigation work was done with respect to the use of 17-4 PH at 550°F. K. C. Antony' states "Such estimation" (of an activation energy for the diffusion of chromium in iron) "would indicate W. C. CLARKE, Jr. is Senior Research Engineer, Advanced Materials Division, Armco Steel Corp., Baltimore. Md. This manuscript is based on a talk presented at the symposium on New Developments in Stainless Steel, sponsored by the IMD Corrosion Resistant Metals Committee, Detroit, Mich., October 14-15, 1968. significant secondary aging is improbable at temperatures less than 700°F within normal component service life". This statement is modified however by the recognition of the accelerating tendencies of applied stress and internal stress as well as the possible effect of irradiation. In this investigation of 17-4 PH, the H 1100 (1900°F-1 hr oil quench or air cool + 1100°F-4 hr-air cool) condition was used, partly because this condition is normally used in atomic reactors. As shown later, the precipitation hardening temperature has no real bearing on the rate of embrittlement. An exposure temperature of 800°F was selected since embrittlement at 800°F is rapid, permitting development of relative data in time periods of 400 to 500 hr. For those not familiar, a nominal present day analysis of 17-4 PH is: C Mn P S SiCrNiCuCbN 0.04 0.30 0.015 0.015 0.60 16.00 4.30 3.25 0.23 0.030 TYPICAL BEHAVIOR OF 17-4 PH Figs. 1 and 2 show the behavior of a commercial heat of 17-4 PH under the conditions defined. Characteristically, 800°F exposure causes a rapid drop in Charpy V-notch impact strength. Tensile and yield strengths gradually increase and a gradual loss of elongation and reduction of area occur, accompanied by an increase in hardness. Notched tensile strength increases to 125 hr exposure and then sharply decreases after exposure for 500 hr. The notched vs un-notched tensile ratio remains virtually constant to exposure for 125 hr (1.67 to 1.56) but drops to 1.15 after 500 hr. Tensile ductility is not alarmingly affected even after much longer exposure times than these. For example, samples aged at 1100°F for 1 hr exposed at 800°F for 4000 hr showed a drop in elonga-tion of from 13 to 11 pct and in reduction of area of from 58 to 37 pct. Notched impact is the property SmIgth KSI 3JJ[/__________^UTS-Nrteh 260 ;/- 240 —^ 200 UTS-Smooth________._, o ioo mo Sob" m Too Hours Exposure Fig. 1—Effect of exposure at 800°F for various times on notched tensile strength and smooth tensile and 0.2 pct yield strength of 17-4 PH in the H 1100 condition.

Jan 1, 1970

By C. D. Hall, F. E. Dollarhide

Conventional static tests of fluid-loss agents do not realistically simulate conditions in a fracturing treatment. The dynamic tests reported here show that fluid-loss volume is better represented as proportional to time, rather than as the square root of time. This leads to a different equation for fracture area. The leak-off rate increases with increasing shear rate at the fracture wall, but appears to approach a limiting value. Pressure effects are minor. Spurt loss ordinarily is not affected by the flow velocity in the fracture and is inversely proportional to concentration of agent. The filter cake, once it is well established, is resistant to damage by the flow of plain fracturing liquid (without fluid-loss agent). The latter two findings indicate that a treatment employing a high-concentration spearhead followed by plain fluid can offer a more economical treatment under suitable conditions. INTRODUCTION The successful design of hydraulic fracturing treatments depends on accurate knowledge of the fluid-loss properties of the fracturing fluid. Howard and Fast,' in giving the basic equation relating fracture area to fluid and treating parameters, described three mechanisms which might control the rate of fluid leak-off from the fracture. One mechanism usually is dominant in a given well treatment. For each mechanism, the leak-off velocity is inversely proportional to the square root of time, and the proportionality constant is designated as the fracturing-fluid coefficient. For the wall-building type of fluid-loss agent, the coefficient is determined by a filtration test in a pressure cell, usually with a rock wafer or core as the filter medium. In these static tests, the cumulative volume generally is proportional to the square root of time, after an initial spurt volume. The static-fluid-loss test is not representative of the con,-&tions under which a fluid-loss agent performs in a fratturing treatment. The marked difference between the dynamic- and static-fluid-loss behavior of drilling fluids reported in the literature2,3 implies that dynamic testing is also needed with fracturing fluids. We have therefore undertaken a study of the dynamic-fluid-loss behavior of fracturing fluids. The testing apparatus has also afforded opportunity to evaluate the resistance of the filter cake to removal or damage by flowing fluid containing no fluid-loss agent, with and without sand. The results of these studies offer a means for more accurate evaluation of fluid-loss agent performance, and point the way to a "spearhead" fracturing technique which may offer more economical treatment for some wells. EXPERIMENTAL METHODS The dynamic-fluid-loss testing method is applicable to any type of wall-building fracturing fluid. The present study aimed first at finding what phenomena are involved, and therefore has been limited in the number of materials tested. All of the results specifically reported herein are for kerosene containing a commercial solid fluid-loss agent, which is commonly used at 50 lb/1,000 gal of oil. Another agent in liquid form, used usually at 20 ga1/1,000 gal oil, has shown all the same phenomena in dynamic tests, and generally the same level of fluid-loss control as the solid agent. The dynamic-fluid-loss core cell used in all tests is shown in Fig. 1. The fracture was simulated by the an-nulus between a 2.03 in. OD sandstone core and the surrounding pipe. Annulus widths of 0.234 and 0.117 in. were used, and the core was 3.5 in. long. The annular geometry provides a uniform fluid velocity and a well-defined shear rate over the entire filtering surface, and permits a large filter area (144 sq cm) in a reasonably compact cell. The leak-off fluid passed into a 0.5 in. diameter axial hole in the core. A hollow steel rod through this hole was threaded into a rounded "streamliner" upstream of the core, and into a mounting stud downstream. The streamliner and the stud had the same outside diameter as the core. In all tests except those where sand was circulated, the mounting stud had protruding rings which constricted the annulus, to minimize any tendency for channeling of the fluid to the side exit port. The ends of the core were sealed by Neoprene, steel and Teflon washers. The leak-off fluid was conducted from the hollow rod to an exit tube, through a metering valve (a fine-pitched needle valve) and a quick-opening toggle valve in series, and into graduated cylinders for volume measurement; Two separate circulating systems were used in the experimental program. The extensive initial testing was done at 50 to 150 Psi. The fluid was circulated by a variable speed Moyno pump, and the flow rate was read by a rota-meter flow meter. The filtration Pressure was supplied by holding a back-pressure with a throttling valve. The discharge streamcould be diverted into any of four sections

Jan 1, 1965

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