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By J. Steininger

The Hallimond tube flotation of sphalerite and pyrite with sulfhydryl collectors has been found to be inhibited near neutral pH in the presence of copper salts. Alkalimetric titration studies of the reactions between collector and activator indicate that this effect is apparently related to the formation of basic copper collector complexes. The conditions of formation of these compounds and their stability are in good agreement with the depression observed in flotation experiments. The general procedure employed in the flotation of zinc sulfide minerals requires activation of the mineral surface by heavy metal ions, usually copper, which react more easily than zinc with the common short-chain ionic sulfhydryl collectors.' Commercially, zinc flotation is carried out under alkaline conditions (pH 7 to 10.5), but small-scale experiments indicate that zinc sulfide minerals can also be activated and collected under acid conditions. Selectivity, however, becomes poor at low pH and undesirable materials such as pyrite, silicates and carbonates tend to report in the float. Several years ago, Wark and Sutherland~, measured the contact angles of air bubbles on copper-activated sphalerite immersed in various sulfhydryl collector solutions. When represented, as in Fig. 1, on pH-sodium cyanide diagrams, the results are characterized by 'islands' of non-contact near neutral pH and

Jan 1, 1969

By W. H. Chang

The phase identification results on several Mg-base alloys are presented. These results have been correlated with strength data and microstructural studies to indicate that carbide dispersion may contribute significantly to raising the recrystallization temperature and strength of Mo alloys. Evidence is presented to show that the degree of carbide dispersion, and hence the extent of strengthening, is governed by the "metal/carbon" ratio which, in turn, depends on both the carbon content and the presence of stable -carbide-forming alloying elements. IN recent years, Mo-base alloys containing small additions of C, Ti, and/or Zr have been developed, which exhibit much higher recrystallization temperature and strength than those of unalloyed Mo. The superiority of these alloys undoubtedly results from simultaneous operation of more than one strengthening mechanism. In the present paper, the strengthening effect of carbide dispersion will be discussed. Although the role of carbide dispersion is being increasingly recognized, the nature of the carbides has, to the author's knowledge, not been well es- tablished. In Table I are presented some of the phase identification results on representative Mo alloys. These results have been obtained by X-ray diffraction of residues electrolytically extracted from an ethyl alcohol solution containing 7 pct HC1.

Jan 1, 1961

By C. E. MacQuigg

In this paper it is impossible to more than touch on many of the commercial alloys of iron, chromium, and carbon, therefore the discussion is confined to the properties of some of the less well-known alloys with upwards of 20-per cent. chromium. The discussion has been based largely on the strictly engineering aspects of the alloys. Chromium has well-defined effects when added to the iron-carbon system. These effects depend on the amount of chromium added and on the composition of the iron-carbon alloy to which the addition is made, i.e. whether low- or high-carbon steel, cast iron, etc. In the case of the low-carbon steels, the chromium addition, when not in excess of several per cent., appears to exert an influence on the properties by its influence on the critical range. In the higher chromium alloys, the physical properties are influenced chiefly by the formation of new complexes, such as iron-chromium solid solutions and, with higher carbon contents, iron-chromium carbides of great hardness. Examination of the published data1 on the critical range phenomena of chromium-bearing steels up to several per cent. chromium indicates an agreement on the following points:

Jan 1, 1923

By C. E. MacQuigg

In this paper it is impossible to more than touch on many of the commercial alloys of iron, chromium, and carbon, therefore the discussion is confined to the properties of some of the less well-known alloys with upwards of 20-per cent. chromium. The discussion has been based largely on the strictly engineering aspects of the alloys. Chromium has well-defined effects when added to the iron-carbon system. These effects depend on the amount of chromium added and on the composition of the iron-carbon alloy to which the addition is made, i.e. whether low- or high-carbon steel, cast iron, etc. In the case of the low-carbon steels, the chromium addition, when not in excess of several per cent., appears to exert an influence on the properties by its influence on the critical range. In the higher chromium alloys, the physical properties are influenced chiefly by the formation of new complexes, such as iron-chromium solid solutions and, with higher carbon contents, iron-chromium carbides of great hardness. Examination of the published data1 on the critical range phenomena of chromium-bearing steels up to several per cent. chromium indicates an agreement on the following points:

Jan 1, 1923

By F. W. Bowdish

A theoretical and experimental laboratory study has shown that the rate of breaking of oversized particles in a ball mill is proportional to 1) the concentration of such particles, and 2) the area of the balls, provided that the balls are larger than a certain size relative to the particles. If all undersized material were removed as formed, the rate of breaking would be almost independent of the quantity in the mill. Rate equations are given which are similar to those for zero, first, and second order reactions. Deviations of small balls from the equation for a second order phenomena are quantified by a factor called "nipping efficiency." Some data are correlated by a dimension-less equation, which is used to estimate nipping efficiencies from data not in the correlation. The investigation described here was undertaken after a literature survey revealed that little was known concerning the mechanism of breaking of particles within a ball mill and the effect of this mechanism upon grinding rates. One paper, by Roberts1 , offered a theory concerning the mechanism of breaking, and a rate equation for the breaking of particles larger than some size to particles smaller than that size. That paper provided the starting point for a theoretical and experimental investigation of grinding under carefully controlled conditions. THEORETICAL CONSIDERATIONS In his paper on the probability theory of ball mill grinding, Roberts theorized that "... a given expenditure of power leads either to a certain number of point to point blows per bp-hr or to a certain distance of line contact per hp-hr ..." He assumed that the balls touch each other during each blow or during moving contact. Then he said that a volume of pulp, dependent upon the size being considered, would be covered per minute within which all oversized particles would be crushed to particles smaller than that size. Naturally, the higher the concentration of oversized particles in the pulp, the higher the rate of which they would be broken. From this reasoning Roberts obtained the differential equation -dC/dt = k hp/ton C (1) where k is a constant for any size of particle, density of particle, and moisture content of pulp. C is the percentage of oversize in the material to be ground, t is the time, and hp/ton is the power input per ton of material in the mill. He then integrated the equation to log Co/Ct = k/2.3 hp/ton t , where Co and Ct are the percentage of oversize at time zero and t respectively. By always using the same quantity of material in a mill and assuming that it required constant power to run the mill, he was able to combine the horsepower per ton factor with the other constants to give an equation for a first order rate.

Jan 1, 1961

H. G. Haemers (Ghent University, Belgium)—The authors claimed "the results of their work indicate that the metals can be arranged in a sulfation series similar in its application for selective sulfation tot the electromotive series for displacement of metals from solution". The series as stated in decreasing order for tendency of SO3 give up, is the same as that stated by free energy diagrams. Indeed, the degree of stability of a sulfate is measured by the free energy of sulfate formation out of the corresponding metal oxide and SO3. The more negative the value of the free energy (-DG) the greater the stability of the sulfate. As a second consequence this statement results in a relative aptitude for capture of SO3 by each metal oxide when brought in contact with the sulfate of other metals. Let M1 and M1 be the two metals, and — DG1 and — DG2 their free energy values at temperature T. Both sulfates are stable at temperature T if - DG1 < O and — DG2 < O. In case where — DG1 < — DG2 the stability of M1SO4 is greater than that of M2SO4, and when M1O (oxide of

Jan 1, 1958

By S. P. Burke

THE presence of gas in coal mines necessitates the use of costly ventila-tion arrangements and the use of expensive mining methods. On the other hand, the gas itself in many instances is of considerable intrinsic value, and its separate recovery might conceivably be a profitable under-taking. This paper is concerned with a study of the movement of gas in coal strata with the object of determining the laws governing gas move-ment and thus making at least a preliminary step toward the solution of the more practical problem of its control or recovery. Naturally, so important a subject has received much attention from scientists and engineers. In most cases, however, the studies have been concerned with the origin1?, the amount2, the composition3 and the method of retention4 of the gas in coal; or, from the more practical side, have been concerned with the phenomena and conditions associated with outbursts5 or explosions and their control. Numerous studies also have been made of the permeability of coal to gas6, of gas pressures measured in coal seams, etc. The authors are unaware, however, of any attempt to present a consistent or complete picture of the laws governing the movement of gas through the coal.

Jan 1, 1935

By R. C. Emmett, R. P. Klepper

The industrial practice of concentration of solids and production of clear solution by gravity sedimentation is an old technology. Through the years, many devices have been designed and built to aid this process One of the more significant developments was a revolving rake mechanism to convey settled material to a central discharge point of a circular tank, patented in 1907 (Dorr). In recent years, clarification systems employing parallel inclined plates have appeared on the market; the original device utilizing this principle was patented in 1886 (Gaillet, et al.) Numerous other methods have been invented, tested, discarded, and sometimes reinvented, all with the specific intention of improving the capacity of a particular settling area. Sedimentation theory, as expressed in Stokes&apos; Law, shows that the rate of settling of a panicle is directly proportional to the difference in density between the particle and the surrounding liquid and, more significantly, proportional to the square of the panicle diameter. While this latter effect is less pronounced with larger particles, anything that can increase the diameter will greatly assist sedimentation and, as a result, flocculation always has been an integral part of sedimentation. Most materials suspended in aqueous media are naturally flocculent to some degree and, hence, are readily concentrated by sedimentation, although sometimes very slowly.

Jan 1, 1981

By Henry Fay

THE CHAIRMAN (ALBERT SAUVEUR, Cambridge, Mass.).-In forcing us to face and to discuss the important question of erosion of steel guns, Prof. Fay is performing a public service. His investigation has been fruitful and his results illuminating and suggestive. It is not in a spirit of adverse criticism, therefore, that I venture a few remarks suggested by his paper, but rather to add my mite to the discussion in the hope that it may not be entirely without value. Prof. Fay considers it conclusively demonstrated that the hard layers forming in the inside of guns of large calibers after they have been fired a number of times consist of martensite. Still, he admits that he never was able to detect in the hard layers the structural characteristics of martensite. This leads him to conceive the existence of amorphous martensite. We may well hesitate before accepting this theory on the strength of the evidence offered. Martensite, as we know it, is essentially a crystalline condition assumed by a close association of iron and carbon, possibly if not probably of the nature of a solid solution. Lacking this crystalline character we are hardly justified in calling it martensite on the ground, merely, of its being very hard.

Jan 4, 1917

By R. J. Watson, A. H. Juch

About half a million sucker-rod pumps are installed in oil wells in the U. S. alone. In Venezuela, too, the system is widely used; some 5,000, or 90 percent, of Cia. Shell de Venezuela&apos;s wells produce a total of 400,000 BOPD by this method. Most of the crude pumped is viscous, gassy and contains relatively small amounts of free water. API gravities vary from 90 to 16O; dead oil viscosities vary from 10 to 10,000 cp at the pump; and GOR&apos;s range from 100 to 2,000 cu ft/bbl. Pumps are set at depths ranging from a few hundred to 6,000 ft; the average setting depth is about 2,500 ft. From the literature, it appears that although recent years have seen significant progress toward understanding the rod pumping system as a whole, relatively little attention has been paid to those key items, the sucker-rod pump and the subsurface gas separator or gas anchor. Perhaps because of proration in the U. S., pump manufacturers have seemingly concerned themselves more with the durability of their product, achieved mainly through robust design and metallurgical know-how, than with its working efficiency. In 1963, CSV commenced a major rehabilitation and expansion of its heavy oil fields along the Bolivar Coast. The advent of the more efficient gravel-packed completion and of large-scale thermal recovery (mainly steam soak) operations resulted in well potentials *Now with B. I. P. M., The Hague, The Netherlands. greater than pump capacities. Hence, an urgent need arose to improve over-all pump efficiencies and to attack those special problems related to the production of both the extremely viscous and the hot, steam-laden crudes that formed an increasing proportion of the total stream. There followed a detailed investigation and testing program, carried out in close cooperation with a major pump manufacturer. This culminated in the introduction to the oil industry of a new line of sucker-rod pumps. Early Investigations and Experiments Field Tests Extensive field tests were carried out in three primary Bolivar Coast wells with an in-situ dead oil viscosity ranging from 400 to 6,000 cp. In these installations provision was made to (1) monitor bottom-hole pressures below, in and above the pump by means of pressure transducers, and record casing- and tubing-head pressures continuously; (2) measure accurately the annulus gas, as well as measure the tubing gas and liquid production from the well; (3) take special PVT samples of the well fluid; (4) measure power consumption of the prime mover; and (5) measure the rod loads at the polished rod. A typical test installation is illustrated in Fig. 1. It was established from the pressure transducers that with viscous oils, there is considerable flow resistance across the pump and gas anchor assembly. Pressure surges were observed over each pump cycle,

Jan 1, 1970

By Lawrence H. Van Vlack, Alfred S. Keh

The distribution of sulfur in iron was found to be dependent upon the time and temperature of the treatment as well as the chemical composition of the sulfide. With higher temperatures, the sulfide phase spreads more extensively between the iron grains. A complete network, however, does not form until approximately 1300°C (2372°F), ot which temperature the dihedral angle approaches zero. Silicon has little effect on this change. Aluminum, oxygen, and manganese all modify the temperature of sulfide network formation to a higher value. The microstructures which result and have significance in relation to hot-shortness are discussed. SULFIDE inclusions in steel were recognized by metallurgists before the turn of the century. Considerable attention has been paid to them, and numerous studies have been made on the working properties of steel as affected by them. It has been suggested that ho t-shortness of steel is due to the presence of an enveloping liquid sulfide film at the grain boundaries of the steel in the range of the hot-working temperatures. However, several facts have been observed in commercial steels which do not seem to be completely consistent with this explanation: 1) the frequent absence of continuous films of sulfide as observed under the microscope, 2) the absence of hot-shortness in some high sulfur and resulfurized steels, and 3) the limitation of hot-shortness to a definite temperature range. The role that manganese plays in steel to eliminate hot-shortness is well known, but the theory behind it is still under question. Moreover, the effect of de-oxidizers such as aluminum and silicon, and the effect of oxygen are still not clearly known. In this study, the effect of heat treatments and of additions of manganese, aluminum, silicon, and oxygen upon the distribution of sulfide inclusions in iron was investigated. Both the as-cast and the heat treated structures were studied, using microscopic and autoradiographic techniques. Part of the results were interpreted in terms of Smith&apos;s&apos; concept of microstructure. Review of Literature Metallurgists used to consider sulfide inclusions as suspended particles. It was Wohrman&apos; who first pointed out that sulfide inclusions are soluble in liquid iron. Many observed facts may be understood on the basis of this concept of solubility. Wohrman found that small castings contain small inclusions. and larger castings contain larger ones. Also, inclusion sizes are smaller near the chilled surface. For the same size ingot, the average inclusion size in a given heat of steel depends upon the rate of solidification. That is, with slow solidification, enough time for precipitation and agglomeration of these

Jan 1, 1957

By J. Mason

In order that the use of continuous mining machines be most economic, the equipment must be operated at rated capacity as much of the time as possible and downtime for repairs kept at a minimum. A large factor influencing any proposals for maintenance programs is the complexity of the machines—often the intricacies of the precision-built equipment requires engineering knowledge byond the scope of mine maintenance personnel. A training program is part of the answer; there are others. In addition to investigating a joint company-manufacturer equipment-design improvement program, Mountaineer Coal Co. has launched a detailed preventive maintenance program to combat extensive downtime often encountered when continuous miners are used. Everyone in the coal industry knows the importance of operating continuous miners at their rated capacity as much of the time as possible. The potential capacity of the miner is such that l-min. delay means from 3 to 8 tons of coal lost. Today&apos;s miner is a well designed, precision-built machine, complicated with hydraulic and electrical equipment and complex mechanical assemblies with all possible combinations of gears, levers, and rods. As the machine becomes more complex, the problem of maintenance becomes more acute. The transition from conventional to continuous mining has taken place so rapidly that the mine mechanic has been unable to keep pace. When there is a machine failure, the maintenance man usually employs either the trial-and-error or the play -it-by-ear method of repair, but this represents an expensive proposition. Mine mechanics, maintenance superintendents, and mine managers complain about the complexity of the machines and how difficult it is to keep them running. There is no shortage of skill in the design offices. Machines are designed by good engineers, but for engineers. What&apos;s the answer? Better trained maintenance men—better maintenance instruction—better field service. These are all good corrective measures, but the real cure is to provide for the men at the do it level. Designers have got to cooperate with men to simplify maintenance on the increasingly complex machine. The designer must be aware of how his machine can be maintained. Sometimes a simple design change in a bearing, oil seal, or a bushing will correct recurrent breakdowns. Parts such as filters, hydraulic cylinders, hoses, and pivot pins can be better arranged on the machine to make them accessible so that the mine mechanic can easily keep the machine producing. Therefore, to get our maintenance off on the right foot, the program must begin back in the design office, before the machine is delivered to the mine property. Realizing the importance of this aspect, our company set out on a joint company-manufacturer equipment-design improvement program. This is a formal program in which quarterly reports are written covering machine defects, design weakness, and general problems relating to machine maintenance and performance. The manufacturer in turn comments on each and every item appearing in these reports, indicating the action he proposes to take. In addition to the written reply, meetings are scheduled with manufacturer representatives to discuss further the outlined problems. The benefits realized from this organized program are both substantial and far reaching. Good maintenance begins with a good design. The subject of preventive maintenance is not a new one. Volumes have already been written on the subject. It consists primarily of doing the maintenance work when you want to rather than when the machine demands it. However, a preventive maintenance program can be overdone. Theoretically, if carried to ridiculous extreme, all working time could be spent inspecting and repairing the machines and no time would be left for production output. Our goal in maintenance is to maximize running time for all machines, and to prevent or at least minimize production downtime. INSPECTION AND REPORTING The center of any preventive maintenance schedule is regular and systematic inspection, but it must be

Jan 1, 1961

By Leo F. Reinartz

It was with humility that I accepted the invitation of the Board of Directors of our Institute to deliver the Twentieth Howe Memorial Lecture. Many previous lecturers could speak from personal experience of the great work done by Professor Howe. It was not my privilege to be one of his students but, indirectly, I came under the influence of his work many years ago. My mentor in Metallurgy at Carnegie Institute of Technology, Prof. Fred Crab tree, was an ardent admirer of Professor Howe and his work. Professor Crabtree taught me early to appreciate Professor Howe&apos;s love of truth and keen desire to find a scientific reason for every metallurgical phenomenon. In this early search, Professor Howe encountered many unexplainable facts. Nevertheless, in the classic text, "The Metallurgy of Steel," published in 1891, he indicated that he believed Research could light the way. Under the heading of "The Treachery of Steel" he said: "In the early use of Bessemer and Open Hearth Steel, many then unexplained and hence mysterious failures occurred. With our present knowledge, an easy explanation of most of them would probably have been seen. But even today certain unexplained and apparently inexpli- cable failures occur in steel; inexplicable in spite of full and intelligent investigation." Then Professor Howe continued to talk about "the trustworthiness of steel" in the following manner: First, the steel-maker has learned by experience. He knows today far better the effects of a high percentage of carbon or of phosphorus; of cracks, pipes and blow-holes; of segregation and imperfect mixing; of over-heating; of finishing too hot or too cold. Knowing, he guards against them more effectually, and keeps at home much steel that he would formerly have sent into the market. Those who would not, or could not learn and do, have been driven out of the business; the conditions necessary for producing good sound steel by the acid Bessemer and the acid Open Hearth processes have been mastered. By and by, the basic process came along with new conditions, new liabilities to unsoundness, a great hue and cry about mysterious fractures followed, and Lloyd&apos;s register provisionally forbade the use of basic steel. Much basic steel was irregular and brittle throughout; too much carbon, too much phosphorus, too cold teemings—imperfect mixing. Still there was little doubt that, with further experience, these difficulties of the basic process would be mastered as those of the acid process had been. This shows that Professor Howe could not take anything for granted. Believing that careful research would find the answer to all mysterious phenomena, he was several generations ahead of the practical acceptance and adoption of this principle.

Jan 1, 1943

By Leo F. Reinartz

It was with humility that I accepted the invitation of the Board of Directors of our Institute to deliver the Twentieth Howe Memorial Lecture. Many previous lecturers could speak from personal experience of the great work done by Professor Howe. It was not my privilege to be one of his students but, indirectly, I came under the influence of his work many years ago. My mentor in Metallurgy at Carnegie Institute of Technology, Prof. Fred Crab tree, was an ardent admirer of Professor Howe and his work. Professor Crabtree taught me early to appreciate Professor Howe&apos;s love of truth and keen desire to find a scientific reason for every metallurgical phenomenon. In this early search, Professor Howe encountered many unexplainable facts. Nevertheless, in the classic text, "The Metallurgy of Steel," published in 1891, he indicated that he believed Research could light the way. Under the heading of "The Treachery of Steel" he said: "In the early use of Bessemer and Open Hearth Steel, many then unexplained and hence mysterious failures occurred. With our present knowledge, an easy explanation of most of them would probably have been seen. But even today certain unexplained and apparently inexpli- cable failures occur in steel; inexplicable in spite of full and intelligent investigation." Then Professor Howe continued to talk about "the trustworthiness of steel" in the following manner: First, the steel-maker has learned by experience. He knows today far better the effects of a high percentage of carbon or of phosphorus; of cracks, pipes and blow-holes; of segregation and imperfect mixing; of over-heating; of finishing too hot or too cold. Knowing, he guards against them more effectually, and keeps at home much steel that he would formerly have sent into the market. Those who would not, or could not learn and do, have been driven out of the business; the conditions necessary for producing good sound steel by the acid Bessemer and the acid Open Hearth processes have been mastered. By and by, the basic process came along with new conditions, new liabilities to unsoundness, a great hue and cry about mysterious fractures followed, and Lloyd&apos;s register provisionally forbade the use of basic steel. Much basic steel was irregular and brittle throughout; too much carbon, too much phosphorus, too cold teemings—imperfect mixing. Still there was little doubt that, with further experience, these difficulties of the basic process would be mastered as those of the acid process had been. This shows that Professor Howe could not take anything for granted. Believing that careful research would find the answer to all mysterious phenomena, he was several generations ahead of the practical acceptance and adoption of this principle.

Jan 1, 1943

By J. J. Bikerman

In a recent study&apos; of the martensitic transformation of Cu-Zn ß-phase alloys, it was noted that the MS temperature at the surface was raised due to the loss of zinc by volatilization. It seems likely, therefore, that the MS temperature may serve as a guide for the measurement of composition. From a knowledge of the dependence of the transformation temperature on composition, 2 it should be possible to detect variations in zinc content which are less than 0.1 at. pct by measuring the MS temperature throughout the sample. It is unlikely that an electron microprobe analysis could detect accurately such small zinc losses because the presently accepted limits of accuracy of the micro-probe analysis in simple ternary systems are of the order of 2 to 5 pct of the amount present.3 In the present study, a composition gradient was produced by precipitating the a primary solid solution, and reheating for a very short time within the 0-phase field. The nominal composition, in atomic percent, of the ternary ß-phase alloy used, 64.2 Cu, 34 Zn, 1.8 Si, was selected because it had an MS temperature of +4°C, thereby simplifying the experi-

Jan 1, 1968

By A. M. Gaudin, T. P. Meloy

Based on the equation for single fracture, a formula has been obtained for repeated fracture. Solution of this equation is obtainable analytically for a few examples and numerically for all others. Graphs of the size distribution equations have been obtained; they agree broadly with the experiments of others. In another paper1 we have considered a model and a comminution distribution equation for single fracture of brittle materials. Most comminuting devices, however, depend on the occurrence of repeated fracture. This is especially true of continuous cylindrical mills of the ball, tube, or rod type. But even in primary crushers there is some repetition of the breaking process, so that this paper should be of interest in connection with all comminuting devices. HALF LIFE AND PROBABILITY OF FRACTURE To facilitate the study of fracture it is useful to introduce the concept of the half life of a particle, In the ball mill, for example, we may start with 10,000 feed particles. The time, 7, by which one half of these particles have been broken is the half life of the feed under the prevailing experimental conditions. The probability of breakage bears an inverse relationship to the half life. In a ball mill, for instance, it can be shown that the

Jan 1, 1962

By A. M. Gaudin, Olav Mellgren, P. L. De Bruyn

In commonly used to prepare the surface of the mineral to be floated so that attachment to air takes place. The quantity of agent required to make the mineral hydrophobic is usually very small, of the order of 0.1 to 0.25 lb per ton of mineral. Details of the mechanism of pyrite collection are for the most part unsettled. Adsorption of collector has long been believed to involve an ion exchange mechanism as demonstrated for galena&apos; and for chalcocite. In the work on chalcocite it was also demonstrated that a film of xanthate radicals unleachable in solvents that dissolve alkali xanthates, copper xanthate, or dixanthogen was formed at the surface of the mineral. The unleachable product increased with increasing addition of xanthate up to a maximum corresponding to an oriented monolayer of xanthate radicals. Pyrite is extremely floatable with xanthate if its surface is fresh,,&apos; but the floatability decreases rapidly as oxide coatings increase in abundance. Pyrite shows zero contact angle when in contact with ethyl xanthate solution at pH higher than about 10.5; at neutrality. a contact angle of 60° is obtained at a reagent concentration of 25 mg per liter. Alkali sulfides and cyanides are pyrite depressants.

Jan 1, 1956

By Horace Pops, Jorge E. Kittl

In a recent study&apos; of the martensitic transformation of Cu-Zn ß-phase alloys, it was noted that the MS temperature at the surface was raised due to the loss of zinc by volatilization. It seems likely, therefore, that the MS temperature may serve as a guide for the measurement of composition. From a knowledge of the dependence of the transformation temperature on composition, 2 it should be possible to detect variations in zinc content which are less than 0.1 at. pct by measuring the MS temperature throughout the sample. It is unlikely that an electron microprobe analysis could detect accurately such small zinc losses because the presently accepted limits of accuracy of the micro-probe analysis in simple ternary systems are of the order of 2 to 5 pct of the amount present.3 In the present study, a composition gradient was produced by precipitating the a primary solid solution, and reheating for a very short time within the ß-phase field. The nominal composition, in atomic percent, of the ternary ß-phase alloy used, 64.2 Cu, 34 Zn, 1.8 Si, was selected because it had an MS temperature of +4°C, thereby simplifying the experi-

Jan 1, 1968

By N. J. Grant, Masao Adachi

A number of Cu-SiO, and Cu-A1203 alloys of low oxide content, produced by internal oxidation of copper-silicon and copper-aluminum dilute solid solutions, were exposed at temperatures up to 1050°C for fairly long times to bring about partial or total re crystallization. The creep-rupture properties of these re crystallized alloys were compared to those in the as-extruded condition at 450° C. Some of the alloys were cold worked after re crystallization to note changes in creep-rupture properties, also at 450OC. SINCE the introduction of the SAP alloy in 1949,~ many studies have been carried out on similar oxide and intermetallic dispersion hardened alloys to determine properties and to establish the mechanisms involved in the strengthening process which led to stable, high-temperature behavior.&apos;-&apos; To date, it has been indicated that, however achieved, the structure should be composed of a continuous ductile metal matrix in which is dispersed a fine, submicron size, hard, insoluble second phase (or at least, essentially insoluble at temperatures very near the melting point), with a submicron or near submicron interparticle spacing. Stored energy, obtained by a high strain rate deformation process appears desirable, as an additional strengthening means beyond pure dispersion.=

Jan 1, 1961

By C. Jackson, J. J. Harrington

The pH control system at Kennecott Copper Corporation&apos;s Nevada Mines Division concentrator consists of two independent systems, lime dilution and lime addition. Lime dilution is accomplished in a mixing tank where slaked lime and water are introduced proportionately. The desired dilution of the milk of lime is determined by the electrical inputs provided by eight pH probes, one per grinding section. The inputs are averaged and applied to a time base generator. The summation output of the time base generator determines the proportion of lime and water that are to be mixed and applies this input to a voltage sensitive switching device. The switching device provides a signal to one of two relays which will add either slaked lime or water, dependent upon the summation output. The entire cycle is based on a 2-min repetition rate to allow for sufficient mix time. Responsivity is controlled by maintaing a limited maximum solution level in the mix tank. Lime addition is controlled independently within each grinding section. The electrical input from the pH probe in a given section controls the solenoid valves which provide lime to each of the ball mills. The valves remain open within a time range capable of maintaining the pH of flotation feed at a given set point.

Jan 1, 1978