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By G. A. Mancini, V. Bharucha, J. W. Spretnak, G. W. Powell

The characteristics of the motion of the a interface during the "down" transformation was studied in zone-refined iron and dilute binary alloys containing nickel and molybdenum by means of the thermionic emission microscope and high speed photography. The frontal movements were found in all cases to be definitely discontinuous with time and an appreciable number of incremental jumps were found to proceed in the reverse direction (a to b). Molybdenum was found to be particularly effective in increasing the frequency of the increments of transformation from the stable to the metastable phase. A knowledge of the mechanism by which alloying elements affect the hardenability of a steel is desirable from both the practical and scientific viewpoints. It is well established that microstructures consisting of tempered martensite and lower bainite exhibit the best performance in terms of toughness and resistance to crack propagation. The presence of some upper transformation products, namely ferrite and pearlite, is in general undesirable. Various researches have indicated that the ferrite matrix grain structure is a very important difference between the upper and lower transformation products, namely equi-axed vs acicular. Any comprehensive theory of the decomposition of austenite should explain the dependency of the morphology of the matrix on undercooling. The contribution of various alloying elements to hardenability has been determined experimentally and catalogued in considerable detail. A rationalization of the basic mechanism or mechanisms by which individual elements affect the kinetics of the decomposition of austenite to products other than the phase "martensite" has not been evolved as yet. Interest in this problem was stimulated by the effects of minute quantities of boron in hardenable steels. This paper deals with one aspect of this problem, namely the characteristics of the ?-a transformation in high-purity iron and in two carbon-free iron binary alloys. A detailed historical account of the scientific developments in the study of the decomposition of austenite would be a prodigious undertaking and will not be attempted here. There are several excellent reviews in the literature on the formation of pearlite, martensitic reactions, and kinetics of solid-state reactions. The thinking on reaction mechanisms has been influenced to a large degree by the "classical" Tammann nucleation and growth model, in which an embryo springs into being by a fluctuation, and grows to a critical size through atom by atom deposition. Such a process is expected, accordingly, to be diffusion controlled. Considerable research attempting to relate the contribution of alloying elements to hardenability on the basis of their effect on the diffusivity of carbon in iron has not been productive from a mechanistic viewpoint. The formation of pearlite and ferrite has been treated in terms of nucleation and growth processes in which presumably the lattice transformation also occurs by a diffusion process. The other prominently considered mechanism is the "martensitic" or cooperative shearing mechanism. It seems generally, but not entirely, agreed that the phase "martensite" forms by this mechanism, and that it is involved to some extent in

Jan 1, 1962

By T. B. Counselman

PROBABLY the earliest concentration of iron ore in this country was carried on in the northeastern magnetite areas. Magnetic concentration was relatively simple and gave a concentrate that, after agglomeration, and in spite of being high in phosphorus because of the dry concentrating methods then in use, was satisfactory blast-furnace feed. Production from the northeastern magnetite area languished after the discovery and development of the Lake Superior ores, where there was seemingly an unlimited tonnage of high-grade ore, first the Michigan ores, and subsequently the still larger deposits of Minnesota. For years only the higher grade, direct shipping ores of the Lake Superior district were mined. Those of Michigan, and of the Vermilion Range in Minnesota, were hard ores and came principally from underground mines. The softer ores of the Mesabi came partly from underground mines, but mostly from the enormous deposits that could be worked by open-pit methods. The costs of ore from these open-pit deposits, even with the high initial cost of stripping, were so low that the underground mines of the Mesabi could hardly compete. The so-called Old Range ores, of Michigan and of the Vermilion Range of Minnesota, were hard and lumpy, and opened up the burden in the blast furnace, therefore making possible harder driving with greater output. Also, some of these ores were of such grade and physical characteristics that they were suitable for charge ore in the open hearth. These ores, therefore, commanded a price premium, and could compete with the softer, finer, but cheaper, Mesabi ores. The big tonnage reserves, however, are on the Mesabi, and it is these big open-pit deposits that constitute our stock pile of iron ore, from which we are drawing so heavily during this war period. On the western end of the Mesabi the ore was found to be high in silica, and not suitable as furnace feed. As early as 1902, attempts were made to concentrate this so-called wash ore and by 1910 the first washing plant was put into operation. The process was very simple, consisting essentially of a sizing and washing operation, with scalping screens, logwashers, and tables, which later were replaced by classifiers. Ore particles finer than 100 mesh were deliberately wasted, because these fines were undesirable in the furnace. Fortunately, these tailings were impounded, and already are being reworked. Before long some of the low-grade ores began to require more elaborate treatment than the simple washing operation and, tables having been discarded because of their low capacity, in favor of classifiers, jigs were next introduced. These were able to discard coarser pieces of tailing than classifiers. Jigs are in active use today, various improvements having been made in their design and application. Various other machines and methods of concentration have been tried from time to time, and have in turn been discarded for more improved processes. The latest and most important process that has been

Jan 1, 1943

By F. E. Harris

IT has been said that carbon is "ubiquitous" with reference to iron alloys. Certainly at temperatures where carbon and iron form the solid solution, austenite, it may be readily added to, or removed from, steel surfaces. Differences in concentration potential are the sole requirements for carbon flow. To measure the rate of carbon flow, a proportionality factor, D, is arbitrarily expressed in units of (length)2 X (time)-1. If the term used for carbon concentration is weight pct C, as is customary, then a factor must be found, changing this term to one of weight per unit volume when the diffusion coefficient, D, is used in flow formulae. The determination of D values for carbon is complicated since D varies with the concentration itself. The Matano method has often been employed for systems involving a variant D. This method expreses an evaluation of unsteady flow whereby .0 is given a relationship with the numerical value of C-X slopes. The author contends that this solution is incorrect, except when D is invariant. The primary purpose of this paper is to support this contention. Here diffusion is controlled under two conditions of flow. The first part deals with the steady state; the second part considers unsteady flow under definite restrictions. Beginning with the fundamental concept, the development is continued until equations for C-X curves are obtained. The solution is then subjected to experimental data. It is realized that a great amount of reliable data is required for a rigorous proof. No such research is claimed. Instead an attempt is made to set forth the physical significance of the diffusion mechanism, and particularly to express the factors which influence the flow of carbon in austenite. Of equal significance is the implication that gaseous media may be employed with reasonable accuracy in making these determinations. THE STEADY STATE DIFFUSION OF CARBON IN AUSTENITE The fundamental experiment defining diffusion in solid metals may be readily performed for carbon in gamma iron.1 For this experiment a thin plate of medium carbon steel is chosen. The surfaces of this plate may be taken as two parallel planes which may be considered infinite for points well in the center of the planes. These two planes are held at different concentrations of carbon at a constant temperature. This temperature, 1700°F for example, is one where the single phase, carbon in solution with gamma iron, exists. When these conditions are held for a sufficient time the concentration of carbon of the different points of the solid settles down towards its steady state value. At points well removed from the ends, the concentration will remain the same along planes parallel to the surfaces of the plate.

Jan 1, 1947

By Arthur S. Dwight

From the latest and best literature on lead-smelting, little can be learned concerning the present state of the art of mechanical feeding in the United States. H. O. Hofman, in his Metallurgy of Lead (5th ed., 1899), briefly describes the main features of the system in use at Pueblo, Colo., and later (p. 235) says " the only successful mechanical feeding, as far as the writer is aware, is that found at the works of the Pueblo Smelting and Refining Co." H. F. Collins, in his Metallurgy of Lead and Silver (London, 1899), covers American practice pretty thoroughly; but as to mechanical charging, he says: "The German plan of taking off the gases by means of a small iron pipe suspended in the center, and the plan of charging by means of cup and cone, as in iron blast-furnaces, have both been tried, but have not found favor, chiefly on account of the difficulty of obtaining free access to the furnace-shaft for barring, etc., with such devices."' . H. W. Hixon, in his Notes on Lead and Copper Smelting (3d ed., New York, 1900), gives a description and drawing of the Hixon feeding device, as originally installed at East Helena. Evidence that this system of feeding has passed its experimental stage, and deserves more serious consideration than it has heretofore received, is furnished by two large plants—the Pueblo and the East Helena—of the American Smelting and Refining Co., where mechanical feeding has been in continuous and successful operation for a considerable period; one new plant now erecting at Salt Lake City, Utah, and one old one belonging to the same company, the El Paso works, now being rebuilt after a disastrous fire, in both of which mechanical feeding is to be a prominent feature ; one new plant of an independent concern at Torreon, Mexico, which will adopt mechanical feeding; and a number of other smaller plants, among

Jan 1, 1902

By E. I. Larsen, E. F. Swazy, F. R. Hensel

EXPERIENCE has indicated that hard bronzes are not suitable for bearing applications where high bearing loads and speeds are involved. It is the general practice to utilize softer materials for these purposes, such as copper, lead, silver, babbitt, lead-base alloys, and more recently aluminum-base alloys, preferably supported by a steel backing. It was the objective of the present investigation to study a new material produced by powder metallurgical methods susceptible to precipitation-hardening. TEST MATERIALS Preliminary tests were made with compacts containing copper, nickel and silicon in quantities sufficient to form 3 to 5 per cent nickel silicide. It was found that this type of alloy was susceptible to the formation of a soft surface shell when sintered in tank hydrogen. The depth of the shell depended on the length of sintering time and sintering temperature, and varied in thickness from a few thousandths to as much as one eighth inch. This soft shell resulted from the preferential oxidation of silicon, thereby reducing the efficiency of age-hardening by the nickel silicide compound. The body of the sintered compacts below the soft shell could be precipitation-hardened to a hardness of 70 to 85 Rockwell B, by quenching from. 900°C. and age-hardening at 450°C. A series of tests was made with various addition agents, in order to decrease the rate of preferential oxidation, and it was found that phosphorus was most beneficial in this respect. After considerable experimentation, the following nominal composition was accepted as standard: 2.4 per cent nickel; 0.8 silicon; 0.3 phosphorus; balance copper. The physical properties and certain bearing properties of this alloy are described in the present paper. PREPARATION OF COMPACTS Several methods of incorporating the hardening ingredient (nickel silicide) were studied. Compacts formed from copper, nickel and silicon powders were found to be inferior to those fabricated from prealloyed nickel silicide master alloys, because of the rapid oxidation of pure silicon during sintering. The use of a prealloyed nickel silicide hardener containing 25 per cent silicon and 75 per cent nickel could be further improved by preparing a master alloy, incorporating nickel, silicon, phosphorus and copper, having the following nominal composition: 25 per cent nickel; 7 silicon; 3 phosphorus; 64 copper. This alloy is brittle in. the cast condition and can be readily powdered. SINTERING PROCEDURE The blended powders were pressed at 25 to 40 tons per sq. in., the pressure depending on the size and shape of the compacts. Sintering was carried out in hydrogen or cracked ammonia atmospheres at

Jan 1, 1946

By Joseph B. Umpleby

PROGRESS in the petroleum industry in 1929 has been characterized by outstanding accomplishments in the fields of new discovery of supply, economic control of production, increased efficiency and reduced costs of recovery, and lowered costs and greater flexibility in manufacture. Resources have been developed in an outstanding degree in the Kettleman Hills. California, the Oklahoma City field (which adds a large potential area in central Oklahoma), the discovery of Woodbine sand production in East Texas, and the discovery of Wilcox sand production in west-central Kansas. Engineering technique has progressed both along the lines of development and production, with a net result that costs have been reduced and extraction increased in notable degree, although it is impossible to give a close measure of either. In the field of re- fining crude oils variations to the end of promoting reduced cost and greater flexibility has been more important than genera! acceptance of innovations in practice.

Jan 1, 1930

By R. H. Atkinson

With the object of improving the melting, casting, and working of palladium and 95.5 pct Pd-4.5 pct Ru, the effects of different melting atmospheres (reducing, oxidizing, and neutral), crucible linings, and annealing atmospheres have been studied. Some interesting observations are included about the solubility and diffusion of gases in palladium. THE object of the present work was to ascertain the effect of oxidizing, inert, and reducing ambient atmospheres on the melting and casting of palladium and a Pd-Ru alloy commonly used for jewelry. The need for such a study was indicated during World War I1 when jewelers experienced difficulty in their attempts to make small castings of the torch-melted Pd-Ru alloy by the lost-wax process. When the metal was melted under oxidizing conditions similar to those used for platinum, the castings were gassy; on the other hand, if the melting atmosphere was reducing, the castings were hot-torn and brittle. General Experimental Procedure Pure palladium sponge (99.9 pct Pd) and pure ruthenium powder (99.8 pct Ru) were used for making small ingots (50 g) of palladium and 95.5 pct Pd-4.5 pct Ru by induction melting. The coil, 3 in. high by 2 in. ID with 16 turns, was energized by a 20 kva Ajax high frequency converter. The melting crucibles, so-called sand crucibles, which were made of a highly refractory fireclay, were lined with different materials, including proprietary magnesia, alundum, zircon, and zirconia

Jan 1, 1957

By Thomas G. Murdock

ETHIOPIA, the first country to be liberated from Axis domination, has recovered remarkably from the ravages of occupation and war. Mineral production has contributed significantly towards this recovery, as it has provided a means of obtaining foreign exchange and has given employment to hundreds of workmen whose maintenance otherwise would have presented a problem. Although primarily an agricultural country, never with a large mineral production, Ethiopia has within its borders a variety of minerals, both precious metals and nonmetallics. Some of these are important to the country as a national asset and others contribute greatly to local economy and can be expected to do so even to a greater extent in the future1 (Fig I). PHYSIOGRAPHY AND GEOLOGY The Empire of Ethiopia is essentially a mountainous and volcanic country, in northeast Africa, situated principally between latitude 4° and I5°N and longitude 34° and 44°E. It is bounded on the north by Eritrea, on the northeast by French Somaliland, on the southeast by Italian Somaliland, on the south by Kenya Colony, and on the west by Anglo-Egyptian Sudan. These European possessions thus completely surround the country. Its access to the Red Sea is through Eritrea; to the Gulf of Aden, through French or British Somaliland; and, to the Indian Ocean, via Italian Somaliland. These routes range in length from 40 to 250 miles. Ethiopia has an area of approximately 350,000 square miles, with a width from north to south of 625 miles, and a maximum length from east to west, along latitude 8°N, of about 875 miles. Physiographically the country is characterized by two very extensive sub-tabular plateaus: the Ethiopian Plateau to the northwest and the Somaliland Plateau to the southeast, separated by a long tectonic graben-the Rift Valley of the Galla Lakes and Danakil. The Ethiopian Plateau, deeply cut and notched by the drainage, slopes in a general northwest direction toward the Sudanese Plains and the valley of the Nile; the Somaliland Plateau slopes to the southeast, toward the Indian Ocean. The valley of the Galla Lakes and its extension to the northeast-the Awash River Valley, separates the plateaus, from Lake Rudolph to Danakil. This depression which constitutes a continuation or ramification of the Great Rift Valley of Central Africa joins in turn the trough of the Gulf of Aden and the Danakil-Eritrean Rift, continuations of the Red Sea and the Jordan Valley. The general basement of Ethiopia is made up of very old rocks, usually considered as Archaen.2 These rocks are represented by the metamorphic crystallines, such as gneisses, different kinds of schists, included lenses of crystalline limestone, and massive intrusives such as granites, diorites, and syenites, all cut by

Jan 1, 1947

By H. F. Perkins

CORROSION as an economic problem is growing rapidly in importance not only because it entails a replacement of corroded parts, but because it interrupts operation and causes hazards of damage and injury through failures of corroded equipment. Nearly all industries are interested in this subject. This paper, although concerned chiefly with corrosion in a complete refinery on the sea coast, discusses many of the various forms of chemical decomposition, most of which are found universally. The petroleum refining industry, in the writer's opinion, is seriously afflicted by the presence of sulfur in nearly all crude oils. The complete removal of sulfur from the crude as it enters the plant would cause such a relief from corrosion that this problem for research would seem to demand active attention. Next to sulfur the most troublesome corrosive agent is the saltmagnesium chloride, found in the water associated with crude oil, the last traces of which are so difficult to remove. This is much less serious, however, than the sulfur. Refinery corrosion can be tabulated as follows: Causes of Corrosion and Places of Attack in a Refinery CORROSIVE ELEMENTS MATERIAL ATTACKED Air: Pipe lines Moisture Tanks COQ Electric fixtures Sulfur gases Still towers Chlorine Condenser boxes Other acid-forming gases Ladders and stairs Smoke stacks Steel buildings All exposed metal Water: Alkali Fire lines and hydrants Acids Cooling water lines Air Condensers and coolers Other dissolved gases Boiler tubes Steam Steam pipes and valves Turbines Oil Sulfur compounds Tanks, pipes, valves, stills, towers MgCl2-Hydrochloric acid Condensers Air contamination

Jan 12, 1926

By A. E. Nehrenberg

R. A. Schmucker, Jr.—The writer wishes to point out that an acicular growth of austenite, similar to that described in the author's paper, was recently observed in an alloy steel of only 0.06 C content. This steel, which represents an 0.07 max C, 1.35 Cr, 0.55 Ni, 0.20 Mo analysis, combines the characteristics of minimum hardness in the annealed condition with maximum hardenability and is therefore suited primarily for cold-hobbing applications. The acicular austenite formation in this steel was observed accidentally during a determination of its Ac1 temperature. The samples used in this investigation represented as-forged bar stock which had been given a preliminary temper at 1300°F. The critical (Ac1) temperature was finally established at 1400 °F. Fig. 15 represents the microstructure of the sample which had been heated at 1450°F for ½ hr, water quenched, and tempered at 600°F for ½ hr (for the purpose of darkening the martensite). It will be observed from the distribution of the darkened areas of martensite that the parent austenite grains formed at 1450°F had grown in an acicular manner and still occupied only a small percentage of the total area. The remainder of the area contains the original equiaxed ferrite grains in which new austenite had as yet scarcely formed. However, the tiny isolated martensitic patches at several points where three or more ferrite grains intersect indicate that small austenite grains had formed and started to grow in an apparently equiaxed fashion. Fig. 16 represents the prior microstructure of an original sample in the as-forged and tempered condition, before it was heated -above the critical temperature. It is probable that there are two kinds of ferrite in this structure: (1) The equiaxed proeutectoid ferrite grains which separated from the austenite when the steel was cooled from the forging temperature, and (2) the acicular ferrite associated with the aggregate of fine carbide which is represented by the patches of

Jan 1, 1951

By Alan Probert

IN his inaugural address in 1949, President Truman made a policy declaration which launched the foreign technical assistance program known to the world as Point Four. Congress passed Public Law 535 defining the scope of the program and holding activities to certain limitations. It also provided $34.5 million for the first fiscal year. The Technical Cooperation Administration was established within the Department of State to coordinate and direct a program to include "economic, engineering, medical, educational, agricultural, fishery, mineral and fiscal surveys, demonstration, training and similar projects." The mineral programs of Point Four have been staffed and managed by two agencies of the Department of Interior, the Geological Survey and the Bureau of Mines. The Geological Survey is concerned primarily with water-supply problems, the discovery of mineral deposits, and the determination of habit, shape, and grade of mineral deposits. The Bureau of Mines is concerned with determining the commercial potentialities of mineral deposits, mineral technology, and the production and distribution of mineral commodities. Mineral projects comprised only 1 pet of the first year's budget. In spite of the relatively insignificant expenditure compared to those for food, agriculture, and health, a commendable record has been achieved.

Jan 1, 1952

By M. G. Corson

UNTIL recently, the characteristics of cast copper have seldom been studied and such study as has been made has been inadequate. The prevailing idea seems to be that since pure copper is infrequently used in the cast state, there is no reason for trying to establish precise data regarding the properties of the metal in that condition. On the other hand, wrought copper either in the shape of sheets or wire rarely fails in service, except as a result of the action of reducing gases at the annealing temperatures, so there is little incentive to study the properties of the cast shapes -cakes, bars, ingots and billets-for the sake of tracing the causes of failures of the wrought metal to the cast stock. However, about a decade ago, wirebars of American origin often cracked badly while being hot-rolled in mills in Germany. This led to four investigations: by E. Seidl and E. Schiebold,1 by P. Siebe,2 by 0. Bauer and G. Sachs,3 and by G. Welter.4 These authors came to the conclusion that failures in hot-rolling were due essentially to the presence of a' wide zone of columnar crystals between the thin layer of fine crystals near the surfaces of the bars and the large but more nearly: equiaxed grains of the central core. This macrostructural defect was explained in turn by the probable upward deviation in the temperature of the metal while it was being poured into the molds of the casting machine. More recently, cast shapes of copper were investigated by N. P. Allen5 and by C. Blazey.6 Allen examined vertically cast wirebars and horizontally cast wedge cakes of electrolytic tough-pitch copper, but only for the distribution of densities; i.e., porosity. Blazey was interested mainly in the mechanism of the variations in electrical conductivity due to cold-work and anneal, but gave introductively an account of the composition and average densities of the tough-pitch horizontally cast wirebars used. As far as the present writer can tell, no investigation was undertaken for the sake of presenting a picture of the distribution of mechanical characteristics in the wirebars of copper, tough-pitch or otherwise.

Jan 1, 1938

At the eastern end of the Mesabi Range, 70 miles due north of Duluth, is the vast plant of Erie Mining Co. Operated by Pickands Mather G Co. for the mine's four owners-Bethlehem Steel, Youngstown Sheet and Tube, Inter- lake Iron, and Steel Co. of Canada-Erie Mining Co, has earned just fame as a pioneer and a leader in the mining, beneficiation, and agglomeration of the lean iron ores of the Lake Superior district. Here is the story of Erie and the integrated operations that have made it such an outstanding member of America's iron ore industry.

Jan 5, 1963

By W. A. Oates, J. A. Lambert, P. T. GaIIagher

Monte Carlo methods have been used to compute the arrangements of interstitial atoms dissolved in tetrahedral sites in bcc lattices. It is assumed that the presence of an interstitial atom "blocks " a certain number of neighboring sites and prevents their occupancy. Sites "blocked" by more than one filled site are allowed for. The computed values of. the mean occupation number (defined as the ratio of the total number of sites blocked to the number of solute atoms are used to calculate the configurational entropies of the solutions. These entropies are compared with those resulting from previous theoretical studies of this problem and also with available experin~ental data for the p Zr-H, Nb-H, V-H, and Ta-H systems. Evidence is also given that the "blocking" explanation of low limiting compositions in these systems, rather than this being due to initial limitations on the number of sites available, is probably correct. THE ideal partial configurational entropy of mixing of an interstitial solute in a metal is given by: where p is the number of interstitial sites per metal atom and Xi is the atomic fraction of the interstitial. For the bcc lattice. which we shall be concerned with in this paper, the interstitial positions are shown in Fig. 1. It can be seen that for the tetrahedral sites, p=6. whereas for the octahedral sites, p = 3. Different emphasis has been placed on the relative importance of energy and entropy effects in determining deviations from ideality in interstitial solid solutions. In some cases the same system, e.g., Fe-C, has been described by the contradictory regular and athermal solution models indicating that the enthalpy and entropy functions, derived from equilibrium data, are frequently not accu.rate enough to differentiate between these treatments. However, for certain metal-hydrogen solutions the equilibrium data is available over sufficiently wide ranges of temperature and composition to permit a reasonably accurate determination of the compositional variation of the heats and entropies. Hoch&apos; has attempted to interpret the results of interstitial solid solutions in terms of a regular solution model. In the case of the Ta-H system where 13 = 6, this model entails fitting the experimental relative partial entropies of solution, asH, to the equation: where ASgs is the relative partial excess entropy of solution of hydrogen. Hoch found that the results of Mallett and Koeh1 could be fitted to this equation with an approximately constant value of AF up to XH = 0.25. However, it is apparent from the solubility isotherms in this system which become asymptotic to the composition TaH that, since (Xh /6 - ~Xh ) becomes infinite only at TaH6, it is necessary that AS<&apos; tends to infinity at TaH. In other words, the low saturation composition of TaH, instead of the anticipated TaH,, eliminates the possibility of applying regular solution theory to such systems. Rather large negative excess configurational entropies must exist at higher hydrogen concentrations in order to explain the lower saturation values. To account for these low limiting compositions and excess entropies two distinctly different approaches have been followed. Rees and many others1-l2 have assumed that not all interstitial sites are crystallographically equivalent with respect to the interstitial addition; that is, in Eq. [I] p is less than the value anticipated from geometrical considerations. To describe, say, a bcc metal-hydrogen system with a limiting composition of MH by this approach one would consider that p = 1 in the first instance instead of p = 6.&apos;j3 In some cases, nonintegral values of B have been taken in order to improve the fit with the experimental data over limited ranges of composition. The other approach which has been used to explain the low saturation compositions is to assume that, although all sites are available for occupancy, strong repulsive interactions exist between the neighboring interstitial atoms, and hence occupancy of any site excludes or blocks a certain number of neighboring sites from being occupied. Earliest treatments of this concept considered the exclusion of an integral number, of nearest-neighbor sites from being occupied at all concentrations. In this case, the partial configurational entropy is given by: These early treatments failed to allow for the overlap of the blocked sites which will arise at all but the very lowest concentrations. More recently attempts have been made to calculate the effect of this decrease in the number of blocked sites on the configurational entropy. Using the quasichemical treatment of interstitial solid solutions as given by Lacher and assuming that an infinite repulsive interaction energy existed between the solute atoms. atom obtained an approximate configurational entropy applicable to the blocking with overlap case:

Jan 1, 1970

By S. Skowronski

OvErpolEd copper, as commonly defined,- is copper which has been excessively reduced during the poling period of the refining process. Owing to its porosity, such coppcr is unfit for commercial purposes. The cause of this phenomenon is undoubtedly the lack of oxides in the copper, yet this does not completely explain it. Refined copper of the same "pitch" and "set" varies considerably in oxygen contents, and analyses of overpoled bars also show similar wide differences; moreover, it is possible to melt copper in &apos;crucibles so as to obtain bars that are practically free from oxygen although they show a "tough pitch" and "level set" surface. Frederick Johnson advances the following theory: The regulation of the quantity of oxygen in copper is the keynote of all copper refining. It is the presence of a well defined proportion of oxygen in the form of cuprous oxide, forming a copper-cuprous oxide eutectic, which enablcs copper to be cast free from blowholes. It seems that when oxygen is present, other gases are less soluble in molten copper; when oxygen is absent, or is present in insufficient quantity, the copper dissolves other gases, such as hydrogen and carbon monoxide, which are insoluble in the copper when solid, and, being rejected during the process of solidification, causes internal porosity and external ridges and excrescences.1 The "level set" of wire bars, etc., is entirely the result of a compromise between the occluded gases and cuprous oxide. With excess of the former the metal would be "overpitch" and spongy, while an excess of the latter would result in the metal being "underpitch" and brittle.2 The result of the absorption and subsequent expulsion of reducing gases, carbon monoxide and hydrogen,&apos; and the effect of this action on the overpoling of copper are in dispute; the literature on the subject is full of contradictory statements and will continue to be so until better analytical methods have been developed. Sulfur, however, is tangible. The refiner can see it in his button sample and consequently attributes to it any trouble that may happen during the melting of the copper.

Jan 1, 1919

By Thomas E. Howard

Recipient of the 1975 D. C. Jackling Award - "For his vision and initiative in defining, planning, directing, and accomplishing mining research programs; for his leadership in focusing worldwide attention on the need for research to improve underground excavation for mining and civil applications; and for his lecture. . ."

Jan 1, 1976

By Schrade F. Radtke

The future of lead and zinc, as with any material, will relate directly to their capability to remain competitive; that is, to demonstrate cost-performance ratios that are superior to those of competing materials. These cost-performance ratios are not static; therefore, it is necessary to develop improvements in products or processes to maintain present markets or to penetrate other markets. Perhaps the surest way to achieve these goals, if they can be achieved at all, is through research. The world lead and zinc producing industry established ILZRO as its cooperative research function to carry on both fundamental and applied research and development efforts aimed at the stated objectives. Current research efforts in the fields of die casting, galvanizing, finishing, chemicals, architectural applications, ceramics, and batteries are reviewed and potential impact assessed, some projections are given of possible new areas of research. Environmental research and its impact on future uses of lead and zinc are also discussed.

Jan 1, 1977

By G. J. Dickman, W. N. Thomas

The factors involved in selecting, a drive system for a grinding mill, including gearing arrangement, motor selection, and electric-supply system limitations are reviewed. Equipment costs are evaluated on a dollar per horsepower basis and starting performance is analyzed, the latter making use of a recently developed computer program. The present interest in large-diameter grinding mills and the rapidly rising cost of the drive in proportion to the cost of the mill establishes a need to explore the drive system in detail. The drive for a 7 to 8,000 hp mill will cost from $350 to $600,000 which represents nearly half the total cost of the mill package, and requires as much building space as the mill proper. Some of the drive components require a longer time to manufacture and the installation time and costs are equal to those for the mill. It is apparent that the drive has become a dominant factor in the overall mill design consideration. A new plant requires a tremendous investment in both time and money. With the high degree of competition in the mining industry, low capital cost is an exceedingly important factor in the development of a project. It is just as important, however, to insure that the equipment is going to perform satisfactorily for the anticipated life of the project without adding unplanned operating, maintenance, and replacement costs. This is the position in which the engineer or designer usually finds himself and is really one of his primary functionsestablishing a realistic compromise between cost and performance. Large primary grinding mills can represent a major portion of the cost of a plant and the drive system accounts for a substantial part of this cost. These facts justify a careful analysis of the drive requirements and all of the factors involved in ultimately arriving at the best system for the lowest cost. A number of excellent papers have been published on various aspects of mill drives. The authors have used information from these papers in making a study of a drive for a 7600-hp, 32 x 12-ft autogenous mill. This was a broad investigation, including mechanical and electrical design, layout, performance, and maintenance considerations, and overall economics leading to the selection of the optimum system for that mill. This paper was developed from the study and includes information applicable to large mills in general. For a successful and economical application, the drive must be considered as a system and all of the components analyzed to determine their effect on the system. This requires the participation of the mill designer, gear, and other mechanical component manufacturers, motor manufacturer, plant designer, and operator. A careful analysis of the mill torque requirements is first necessary to provide a basis for selection of the mechanical and electrical drive components. Because of manufacturing limitations on the size and capacity of gearing available for these low-speed applications, an evaluation of costs for various gear ratios and configurations in conjunction with motor speeds is required. Consultation with the power-supply company is necessary to determine limitations on motor-starting disturbances and to analyze operating costs on the basis of existing rate structures and low characteristics. Finally, consideration must be given to the drive arrangement and its affect on plant layout, space requirements, and location of auxiliary equipment for the selected process. There are presently three basic schemes for driving a mill. The first is a direct drive by a motor operating at mill speed with no gearing. The second is by a higher-speed motor through a trunnion-connected gear drive. The third is by a motor through the more conventional pinion and ring-gear with the option of an interposing gear box to permit greater motor speed than pinion shaft speed. [(Fig. 1.)] Several manufacturers have or are presently developing motors which drive the mill directly without the use of gears. One arrangement has the motor armature intimately surrounding the mill shell-discharge spout or extension of the trunnion journal. The motor stator is then supported independently and surrounds the shell or trunnion-mounted rotor. Another variation utilizes an independent mill-speed motor connected to the trunnion by a drive shaft and flexible couplings.

Jan 1, 1972

By H. H. Uhlig

Soon after general use of stainless steels began, it was observed in practice that certain combinations of factors tended to induce corrosion by pitting. For most applications this was a serious drawback, not SO much because the structural properties of the metal were impaired but because of the rapidity with which heavy sections of the alloys were penetrated by small elongated pits. These pits seemed to initiate readily in oxidizing metal salt solutions like ferric chloride and in chloride solutions like sea water. It was observed that in sea water pitting was more frequent in stagnant or polluted waters than in highly aerated, moving waters. The steels in these chloride solutions were observed to be sensitive to long contact with material such as sand grains or attached barnacles. At points of attachment or contact it was not uncommon to discover initiation of corrosion. Pits once begun at contact faces were observed to grow rapidly, usually elongating phenomenally in the direction of gravity until the metal was perforated. Hydrochloric acid and other nonoxidizing acids, on the other hand, were observed to corrode stainless steels generally; the weight losses often were higher, but the penetration less than for the pitting type of corrosion. The causes of pitting, a type of corrosion recognized as characteristic not only of stainless steels but of many additional metals and alloys, are important in corrosion studies. A possible explanation bears practical significance, for once it is known why pits begin where they do and continue to grow after initiation, intelligent direction can be given to diminishing corrosion. This can be done either by some alteration in the composition and treatment or&apos; the alloy or by some alteration in the environment. It appears foremost in importance to discover the nature of pit foci, for if initiation of pits can be discouraged their growth will be no longer a factor to be considered. In a multi-component alloy containing many impurities normal to production of such an alloy, each of which may play a part in pitting, and whose corrosion resistance is sensitive to heat-

Jan 1, 1940

By H. H. Uhlig

Soon after general use of stainless steels began, it was observed in practice that certain combinations of factors tended to induce corrosion by pitting. For most applications this was a serious drawback, not SO much because the structural properties of the metal were impaired but because of the rapidity with which heavy sections of the alloys were penetrated by small elongated pits. These pits seemed to initiate readily in oxidizing metal salt solutions like ferric chloride and in chloride solutions like sea water. It was observed that in sea water pitting was more frequent in stagnant or polluted waters than in highly aerated, moving waters. The steels in these chloride solutions were observed to be sensitive to long contact with material such as sand grains or attached barnacles. At points of attachment or contact it was not uncommon to discover initiation of corrosion. Pits once begun at contact faces were observed to grow rapidly, usually elongating phenomenally in the direction of gravity until the metal was perforated. Hydrochloric acid and other nonoxidizing acids, on the other hand, were observed to corrode stainless steels generally; the weight losses often were higher, but the penetration less than for the pitting type of corrosion. The causes of pitting, a type of corrosion recognized as characteristic not only of stainless steels but of many additional metals and alloys, are important in corrosion studies. A possible explanation bears practical significance, for once it is known why pits begin where they do and continue to grow after initiation, intelligent direction can be given to diminishing corrosion. This can be done either by some alteration in the composition and treatment or&apos; the alloy or by some alteration in the environment. It appears foremost in importance to discover the nature of pit foci, for if initiation of pits can be discouraged their growth will be no longer a factor to be considered. In a multi-component alloy containing many impurities normal to production of such an alloy, each of which may play a part in pitting, and whose corrosion resistance is sensitive to heat-

Jan 1, 1940