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By Pol Duwez, Paul Pietrokowsky

The crystal structure of the compound TisGeS has been determined from X-ray powder diffraction data. Related silicon and tin compounds have been found to be isomorphous. Unit cell dimensions, axial ratios, and parameters for equivalent atomic positions are given. THERE is, at present, only meager information pertaining to the solid state reactions of titanium with the elements in group 4B of the periodic table (silicon, germanium, tin, and lead). The only two compounds whose crystal structure has been established are TiSi² and TiGe² (references 1 and 2 respectively). These two compounds are isomor-phous and have an orthorhombic symmetry D242h— Fddd. The titanium-rich regions of the constitution diagrams of titanium-silicon, titanium-tin, and titanium-lead have been investigated by Craighead et al.³ While valuable information concerning the alpha solid solubility of these three elements in titanium was obtained, no light was shed on the existence or nature of the titanium-rich compound in these systems. The present study is concerned with the crystal structure of the intermediate phases Ti5Si ?, Ti³Ge³, and Ti5Sn³, which were found to be isostructural. The alloys were prepared by mixing the pure metal powders in the desired proportions, pressing the mixture into pellets, and melting them in an electric arc furnace in the presence of a helium atmosphere.& After melting, the specimens, weighing approximately 5 g, were sealed in evacuated quartz vials, homogenized at 1038°C for three days, and quenched from that temperature. Powder diffraction patterns were made with a 143.2 mm diam Debye-Scherrer X-ray camera in which the Ievins and Straumanis film arrangement was utilized. Filtered copper radiation was used throughout the entire investigation. A study of the powder patterns of a series of alloys of various compositions indicated the presence of a compound around a composition corresponding approximately to a ratio of 3 titanium to 2 silicon, germanium, or tin. From a visual examination of the diffraction patterns, it was evident that the silicon and germanium alloys were iso- morphous. For small angle reflections, the powder pattern of the tin compound was analogous to that of the silicon and germanium compounds, but after the first ten reflections, the similarity was no longer clear. The powder pattern of the germanium compound was selected for indexing, since it exhibited a weak small angle reflection and clearly resolved doublets in the back-reflection range. Good agreement between observed and calculated values of (1/d)² was found by indexing the pattern on the basis of hexagonal symmetry. For the hexagonal system:

Jan 1, 1952

By James A. Barr

The writer's first experience with flotation was during World War I, in the bene-ficiation of Alabama graphite schist ores. One plant used a cone with a peripheral overflow; dried ore was distributed by a rotating disk onto the surface of the water. No reagents were added' The flake-graphite film floated along with some fine silica. Dewatering screens separated the flake. Naturally unit capacities were low but results were satisfactory. Minerals separation mechanical flotation machines were used in another graphite mill. pine oil was added directly to the head cells, with very good results. All the graphite concentrates from both types of flotation were carefully refined after drying by passing through burr mills, followed by very close sizing on sifters. In March 1927, the writer ran a very successful flotation test on minus 28-mesh, deslimed, Tennessee brown phosphate "sand,"† using a mechanical laboratory machine built in the shops of the Anaconda Copper Mining Co., through the courtesy of Ernest Klepetko. The machine was soon converted to a subaeration type, with improved results. This phosphate research program was greatly enlarged and led to the formation of the phosphate Recovery corporation. The development of nonmetallic flotation followed rapidly. The first flotation machine for bene- ficiation of phosphate was installed in January 1928, in a pilot mill, by International Minerals and Chemical Corporation, at Mulberry, Florida. These machines were Minerals Separation, 24-in., sub-,,,tion types, with weir control of pulp between cells. The sand bleeders were very small—about 1¼-in. diameter. As the feed flake. Is to 25 per cent plus 28-mesh material, the cells choked up frequently. This was corrected by cutting a 2 by 6-in. bleeder opening above the impellers, at grid level, which short-circuited the coarse fractions directly into the feed of the next cell. The matter of size classification and grinding was a considerable problem, which does not come within the scope of this article. Because of the troubles noted above, cascade-type roughers were installed in the second flotation plant, built about 1930. Experimental cells had been tried in 1928. General plant layout is shown in Fig. 1 and details of the cascade construction in Fig. 2. The cascade installation in plant NO. 2 gave good results and eliminated troubles due to choke-ups and coarse feed. The capacities and metallurgical results equaled those of the modified 24-in. Minerals Separation flotation machines in plant No. I The objections to the cascade installation are the floor space and mill height required. In 1939 an improved Minerals Separation machine was tested in parallel with the cascades. Extensive tests indicated

Jan 1, 1947

By James A. Barr

The writer's first experience with flotation was during World War I, in the bene-ficiation of Alabama graphite schist ores. One plant used a cone with a peripheral overflow; dried ore was distributed by a rotating disk onto the surface of the water. No reagents were added' The flake-graphite film floated along with some fine silica. Dewatering screens separated the flake. Naturally unit capacities were low but results were satisfactory. Minerals separation mechanical flotation machines were used in another graphite mill. pine oil was added directly to the head cells, with very good results. All the graphite concentrates from both types of flotation were carefully refined after drying by passing through burr mills, followed by very close sizing on sifters. In March 1927, the writer ran a very successful flotation test on minus 28-mesh, deslimed, Tennessee brown phosphate "sand,"† using a mechanical laboratory machine built in the shops of the Anaconda Copper Mining Co., through the courtesy of Ernest Klepetko. The machine was soon converted to a subaeration type, with improved results. This phosphate research program was greatly enlarged and led to the formation of the phosphate Recovery corporation. The development of nonmetallic flotation followed rapidly. The first flotation machine for bene- ficiation of phosphate was installed in January 1928, in a pilot mill, by International Minerals and Chemical Corporation, at Mulberry, Florida. These machines were Minerals Separation, 24-in., sub-,,,tion types, with weir control of pulp between cells. The sand bleeders were very small—about 1¼-in. diameter. As the feed flake. Is to 25 per cent plus 28-mesh material, the cells choked up frequently. This was corrected by cutting a 2 by 6-in. bleeder opening above the impellers, at grid level, which short-circuited the coarse fractions directly into the feed of the next cell. The matter of size classification and grinding was a considerable problem, which does not come within the scope of this article. Because of the troubles noted above, cascade-type roughers were installed in the second flotation plant, built about 1930. Experimental cells had been tried in 1928. General plant layout is shown in Fig. 1 and details of the cascade construction in Fig. 2. The cascade installation in plant NO. 2 gave good results and eliminated troubles due to choke-ups and coarse feed. The capacities and metallurgical results equaled those of the modified 24-in. Minerals Separation flotation machines in plant No. I The objections to the cascade installation are the floor space and mill height required. In 1939 an improved Minerals Separation machine was tested in parallel with the cascades. Extensive tests indicated

Jan 1, 1947

By A. K. Jena, M. O. Bever

The thermodynamic behavior of dilute solutions of copper, silver, and gold in liquid tin is not explained by current solution theories.1-3 The relative partial gram-atomic enthalpies, or heats of solution, of silver, gold, and platinum in liquid lead at 623°K have been measured in the investigation reported here. Their interpretation requires a modification of the regular-solution theory although lead-rich solutions may be expected to be simpler than tin-rich solutions. The liquid metal solution calorimeter used has been described.4 At the start of a run the bath consisted of 621 g of reagent-grade lead. Several calibrating additions of lead were made during a run; a value of 3.48 kcal per g-atom5 was taken for H623°K - H273°K Two runs were made with each of the solutes silver, gold, and platinum. Annealed wire samples of 99.999+ pct purity were used. Four to six samples each weighing 0.5 to 1,0 g were added from 273°K to the bath at 623°K and the associated heat effects were measured. The samples dissolved in approximately 3 min. No serious experimental difficulties were encountered. The heat effects of the additions in a run plotted against the average atom fraction of solute before and after each addition314 were linear functions of the concentration in lead of silver, gold, and platinum, respectively. By subtracting the difference between the heat contents of a solute element at 623° and. 273°K5 from the measuredheat effects, the partial gram-atomic enthalpy relative to the solid solute was obtained. The relativ: partial gram-atomic enthalpy at infinite dilution and the concentration dependence of the partial gram-atomic enthalpies obtained from the plots of vs atomic fraction x are listed in Table I. The relative partial gram-atomic enthalpy at infinite dilution of silver in lead of 5.46 kcal per g-atom at 623°K compares with values at 723°K of 5.74' and 5.765 kcal per g-atom. These data yield a temperature coefficient of 3.0 cal per g-atom-OK. The partial gram-atomic enthalpy at infinite dilution of gold in lead at 623°K is 0.89 kcal per g-atom compared with 0.85 kcal per g-atoms (obtained by extrapolation) and 0.95 kcal per g-atom.5 By combining these values for 623°K with those for several other temperatures5" the temperature coefficient of was found to be 3.2 cal per g-atom-OK. No thermodynamic data are

Jan 1, 1968

By R. S. Shoemaker, F. W. McQuiston

REFINERY SECURITY "Highgrading, " a polite word for stealing gold and silver, has been a way of life since the metals in native form have been mined or produced. Unfortunately, in the past, highgraders were not always severely prosecuted or even looked upon unfavorably in their communities. Recent high metal prices with attendent world wide publicity, however, has made highgrading or thievery again a serious problem in mines and plants. When a small button of gold the size of the end of ones little finger has a value equal to about one week's wages, the safe-guarding of gold production by enforcing tight security measures becomes a prime responsibility of management. The higher the gold price, coupled with unrestricted owner- ship, the greater the temptation to “get-your-cut”, and diligence by management must become an integral part of plant security. Primary security begins by knowing the expected gold production and the sampling of a gold ore mill feed for this determination has proved not reliable. However, solution flows can be accurately sampled and measured thereby closely predicting the gold recovered each day as precipitate. The progressive record of total ounces of gold contained in the precipitation press, referred to in cyanidation plants as I1solution calll1 predicts the accumulated production. The "callH is an important adjunct to security and extreme caution must be used so that the pregnant solution meter and sample are confined in a security area. It should be recognized that this key sample may be the target for Ifdoctoring" by trusted insiders (assay office employees) as a preliminary step for stealing precipitates and/or metal. Security measures similar to the following were adopted after one operation experienced a sizeable theft of gold precipitate and metal by trusted employees. The refinery area where precipitates are handled and melted to bullion and all other gold products are kept should be completely enclosed with a tight security fence preferably of solid construction. Access to this enclosure should be through one of two electrically controlled gates, one for personnel and another for occasional truck entrance. Admittance should be restricted to essential personnel who are required to sign a register in and out with the date and time. I£ there is a "back gate" to the restricted fenced area, it should remain locked except in an emergency and then opened only by a supervisor. Television monitoring cameras viewing the gate entrance and other sensitive areas connected to a viewing screen located in the general office afford visual observation at all times.

Jan 1, 1975

By E. C. Franz

IN an effort to understand high cycle fatigue, as well as to study the mechanism of fracture in general, a number of researches have been undertaken whereby the fracture properties of a metal have been determined under conditions of repeated cyclic prestsain employing high strains with relatively few cycles. Liu, Lynch, Ripling, and Sachs' showed the effect of a definite strain history consisting of small increments of tensile or compressive prestrain upon the flow and fracture characteristics of metals after a limited number of repeated loadings. Liu and SachsW emonstrated by cyclic straining of the aluminum alloy 24s-T4 that the least reduction in ductility was obtained when the compressive stress was nearly equal to the tensile stress. Attempts have been made to correlate the reduction in ductility under such prestraining with conventional fatigue data, as was done by Liu and co-workers.' The following research was conducted to determine if such reduction as has been noted could be correlated with conventional fatigue data or whether the effect resulted from causes extraneous to the basic mechanism of fatigue failure such as strain aging. It might be pointed out in this connection that the reduction in ductility has occurred in alloys that might be susceptible to strain aging or similar behavior, such as alloy 24s-T4. In the present investigation, the test specimens were prepared from the aluminum alloy 75s-T6 and annealed electrolytic copper. Alloy 75s-T6 is a complex precipitation hardenable alloy, whereas electrolytic copper would not be expected to exhibit strain aging effects, particularly at room temperature. The experimental procedure consisted of prestraining test specimens repeatedly by increasing tension in small increments to various total prestrain values, followed by testing to failure in a tension test. The prestraining as well as the final testing was performed on a tensile machine using special fixtures9 0 maintain concentricity of the specimens. After prestraining, the specimens were unloaded as rapidly as possible and immediately reloaded so that the total time lapse between strains was held to a few seconds. Logarithmic or true natural strain was used in all calculations. The results are presented in Figs. 1 and 2. In Fig. 1, the retained ductility, area after prestrain area at fracture is plotted against the tensile prestrain, initial area area after prestrain as abscissa with the number of stress reversals executed to attain the required prestrain plotted as parameter. Several specimens that fractured during

Jan 1, 1955

By M. E. Wadsworth, I. B. Cutler, R. W. Bartlett

The oxidation kinetics of ZrC was studied between 450" and 580°C in oxygen pressures from 6.5 x 10-to 1 atm using a ther mogravimetric apparatus and sized powder samples. Two parallel rate controlling processes were observed. A surface reaction occurring at the ZrC-ZrO2 phase boundary accounted for most of the oxidation and had an activation enthalpy of 46 kcal per mole. The other process, believed to be diffusion of oxygen into the ZrC lattice partially replacing carbon, had an activation enthalpy of 53 kcal per mole. The enthalpy for chemisorption of O2 on ZrC was determined to be —13 kcal per mole. Water vapor in the presence of oxygen accelerated the surface reaction rate. THERE has been little reporting of formal rate studies or attempts to ascertain the mechanism of oxidation of carbides. MacDonald and Ransley1 studied the oxidation of titanium carbide which has the same structure as zirconium carbide, fcc. They observed an initial increase in rate with increasing temperature followed by a rapid decrease through a rate minimum and a subsequent second increase at higher temperatures. The discontinuity in the rate rise was attributed to a phase change in the oxide which changed the rate determining step from the surface reaction at the carbide-oxide interface to diffusion through the oxide layer. Samsonov and Golybera 2 studied titanium carbide and reported that during the initial period of oxidation a dense film of Tic-TiO was formed followed by the formation of less adhering layers of higher oxides. The purpose of this investigation was to study the kinetics of oxidation of zirconium carbide and to attempt to gain some knowledge of the mechanism by which oxidation occurs. EXPERIMENTAL PROCEDURE Measurement of the weight gain associated with the oxidation of ZrC was used to determine oxidation rates. The principal experimental parameters were surface area, temperature, and oxygen pressure. Although moderately sized crystals of ZrC can be grown by the Van Arkel method, the only commercially available ZrC is a powder. In using powders, the surface area must be controlled either by fabricating the powder into a sintered pellet with a measurable surface area, relatively fixed during oxidation, or by using sized unconsolidated powder and applying appropriate geometric considerations to the shape of the grains to correct for their diminishing surface areas as they oxidize. Both techniques involve some difficulties. pellets of binder-free zirconium carbide can be made by hot pressing, but it is difficult to obtain densities greater than 90 pct of

Jan 1, 1963

By Luther W. Bahney

(San Francisco Meeting, October, 1911.) LIME is the alkali that is almost universally added to the solutions in the cyanide process of gold- and silver-extraction for maintaining the so-called, protective" alkalinity. It is produced by the burning of limestone. The value of lime for this purpose depends upon the percentage of calcium oxide contained, which is determined by three factors : 1, purity of the limestone used; 2, degree of the burning-temperature and the period of burning; and 3, length of time of storage of burned material and the condition stored, and whether it has been damp or wet during the storage. These three factors render uncertain the quality of lime bought in the open market. In the United States, lime bought from reliable manufacturers, who thoroughly burn a pure limestone and deliver at once to the consumer from the kilns, may be of a fairly-high and uniform composition ; but in Mexico and Central America, where it is purchased from many small producers, who often start with a poor grade of limestone and burn it in small crude kilns with as little fuel as possible, the quality of the product is quite variable. In consideration of the foregoing, it is apparent at once that there is a great need for a rapid technical method for the valuation of the lime to be used in a cyanide-plant. The determination of calcium by the gravimetric method, with the necessity of determining also the proportion of carbon dioxide, silica, and iron, requires too much time, and is usually out of the question for an isolated plant unequipped with a skilled chemist and, the necessary apparatus. The calculating of all the calcium so found to calcium oxide, although sometimes done, is manifestly very inaccurate.

Nov 1, 1911

By S. W. Miller

DURING the examination of welds made in steel by the oxy-acetylene and electric-arc processes, the writer has met with some unusual structures, which he has not encountered elsewhere. They seem to be quite closely associated with the welding methods used, and characteristic of them, and would seem to be worth noting, especially as the references to them in the literature are few, and their explanation not clear or complete. An introductory word or two about fusion welding may not he out of place. The oxy-acetylene process is based on the great and very local heat generated by the burning of acetylene in the presence of commercially pure oxygen, the two gases being thoroughly mixed before combustion. The theoretical temperature is somewhat under 4000° C., but on account of various losses, the actual maximum temperature is probably about 3000° C. 1 The electric-arc process, using a metal electrode, which is also the filling rod, generates a still higher and more local temperature. The actual temperature of the positive crater of the carbon arc is given as 3500° C.2 No figures have been found for the temperature of the arc using a metal electrode, but it would probably not be very different from that of the carbon arc, and probably higher than that of the oxy-acetylene flame. The greater localization of the electric arc is due to the fact that it is not surrounded by a large envelope flame as well as to its higher temperature; while the oxy-acetylene white cone, or welding flame, in which the carbon of the acetylene is burned to CO, is surrounded and preceded by -a long envelope flame, itself of quite high temperature, in which the CO is burned to C02, and the hydrogen of the acetylene to

Jan 2, 1918

By T. D. Thomas

CONTENTS PAGE T. D. Thomas-Misfires in Anthracite Coal Mines 3 W. H. Forbes-Misfires in Bituminous Coal Mines 12 A. W. Worthington-Misfires in Non-metallic Mining (Limestone) 18 Misfires in Anthracite Coal Mines BY T. D. THOMAS,* LANSFORD, PA. (New York Meeting, February, 1929) IN THIS paper, major attention is given to misfires in mines where electric multiple shot-firing is the system used. Misfires are sometimes caused by one action or condition and at other times by a combination of two or more. They may be divided into two classes: (1) those caused by workers in the mines, (2) mechanical or manufacturer's causes. The second cause will be discussed first. MISFIRES CAUSED BY FAULTY DETONATORS The important part of an electric blasting cap, to the user where multiple shot-firing is done, ass in the steep-pitch, thick-vein, anthracite mines, is the bridge wire. In single shot-firing this factor is not apparent, but in mines where multiple firing is done any variation in the resistance of the bridge wire, where full or even rated battery capacity is required, will most likely cause a misfire The reason for this is obvious. If the resistance in the bridge wires is not the same, some of the detonators will fire because of their greater comparative resistance. Variance in resistance of bridge wires is caused by a slight difference in the diameter of the bridge wire, also to a difference in the composition of the bridge wires. Again, where the bridge wires have become rusted, there will be a variance in resistance. About the year 1922, one of the large coal companies was greatly alarmed by the number of serious and fatal accidents caused by misfires. The general manager issued an order that these accidents must be greatly reduced, and if possible, entirely prevented.

Jan 1, 1929

By John T. Norton, V.G. Mooradian

The diffusion of metal atoms into the crystal lattice of another metal and the assumption of regular positions to form a homogeneous alloy are some of the most fundamental phenomena of structural metallurgy. The mechanism of this process has been the subject of a great deal of study from many viewpoints, but the picture is still far from complete. It is generally believed that if one metal is to diffuse into another, the first must have some solubility in the second1. This means that the solvent must be able to accommodate the stranger atoms, either on points of its own lattice or in the interstices between, without losing its own crystal-lographic identity. It is also a general observation that cold-working is a distinct aid in the diffusion process, causing it to take place with greater rapidity at the same temperature or with the same speed at a lower temperature. There is considerable doubt, however, as to the real significance of the deformation in its effect on the diffusion mechanism. Several factors associated with the cold-working may be responsible for the increased diffusion rate. The plastic deformation causes a distortion of the solvent lattice, which may be an aid in the assimulation of atoms of another kind. There are many references2 in the literature that suggest that some distortion or "loosening" of the lattice is necessary for atomic migration and that diffusion cannot take place in the undis-torted lattice. On the other hand, it may be that the cold-working causes an increase in surface of contact between the two metals through fragmentation or provides a more intimate contact that is necessary for diffusion. If it is true that lattice distortion is an important factor in diffusion, it seems as if there should be some particular relation between

Jan 1, 1935

By J. B. Morrow, D. H. Davis

THERE are two general approaches to the problem of increasing profits from an operation. One is to lower expense; the other is to raise income. Mechanical preparation of coal may be used for either purpose but a prudent consideration of many details must precede any decision lest the results be negative instead of positive. It is quite possible that any net gain will result from a combination of the two. Since mechanically prepared coal invariably is a better product qualitatively than a hand-picked coal from the same mine, it is a reasonable expectation that the customer will be willing to increase the producer's income by paying a higher price. Or there may be the possibility that a combination of mechanical mining plus mechanical cleaning will give a lower over-all production cost for the coal in the railroad car. More likely, there will be found a combination of these two factors. From the customer's point of view, the competitive delivered cost per B.t.u. considered in relation to such incidental factors as dust nuisance, handling properties, ash disposal, and ash fusibility determines what he will pay. In-a bulk tonnage such as coal, freight is a very considerable part of the delivered fuel cost, and obviously freight paid on incombustible ash has no economic attractions. INCENTIVE FOR CLEANING Coal is prepared in four major ways: l (1) by screening or sizing, (2) by mixing or blending, (3) by cleaning, including hand picking and mechanical cleaning, (4) by dustless treatment. By a combination of any or all of these methods, coal can be prepared to standard specifications. It is easily possible to have good cleaning and still get a poor final product because of faulty screening or mixing, while it is possible to produce a very acceptable product from mediocre cleaning if the coal is well screened and mixed.

Jan 1, 1950

By V. G. Mooradian, John T. Norton

The diffusion of metal atoms into the crystal lattice of another metal and the assumption of regular positions to form a homogeneous alloy are some of the most fundamental phenomena of structural metallurgy. The mechanism of this process has been the subject of a great deal of study from many viewpoints, but the picture is still far from complete. It is generally believed that if one metal is to diffuse into another, the first must have some solubility in the second1. This means that the solvent must be able to accommodate the stranger atoms, either on points of its own lattice or in the interstices between, without losing its own crystal-lographic identity. It is also a general observation that cold-working is a distinct aid in the diffusion process, causing it to take place with greater rapidity at the same temperature or with the same speed at a lower temperature. There is considerable doubt, however, as to the real significance of the deformation in its effect on the diffusion mechanism. Several factors associated with the cold-working may be responsible for the increased diffusion rate. The plastic deformation causes a distortion of the solvent lattice, which may be an aid in the assimulation of atoms of another kind. There are many references2 in the literature that suggest that some distortion or "loosening" of the lattice is necessary for atomic migration and that diffusion cannot take place in the undis-torted lattice. On the other hand, it may be that the cold-working causes an increase in surface of contact between the two metals through fragmentation or provides a more intimate contact that is necessary for diffusion. If it is true that lattice distortion is an important factor in diffusion, it seems as if there should be some particular relation between

Jan 1, 1935

By Julian Kennedy

THINKING that it may prove of interest to the Institute, 1 have prepared a short; account of the blowing in and subsequent working of the "A" furnace of the Edgar Thomson Steel Works. This furnace was built for the purpose of making spiegel, but has been started and is now running on Bessemer iron. The shape and size of the furnace are shown in the accompanying drawing. It will be seen that the section is formed of lines making very small angles with each other. In fact, an arc of a circle can be drawn, from the top to the tuyeres, which will nowhere deviate more than two inches from the lines given. In building, also, great pains were taken to gradually round the angles, so that the most careful observer, standing in the crucible and looking upward, could not tell at what points the slopes changed. It will also be seen that the widest part of the furnace is almost exactly midway between the bottom and the stock line. The flattest slope is maintained for 20 feet above the crucible, and is about 18 inch to the foot from the perpendicular. The furnace is lined with small brick throughout, and has six tuyeres four inches in diameter, which project seven inches inside of crucible. There are three Siemens-Cowper-Cochrane stoves, each 15 feet in diameter by 50 feet high. Blast is furnished by an upright engine with 32-inch steam cylinder, 84-inch air cylinder, and 48-inch stroke. The steam cylinder has balanced poppet valves, working horizontally. The steam valves are worked by a Porter link-movement in order to obtain a variable cut-off. The exhaust valves are worked by a separate eccentric. It is intended to attach a governor to the cut-off, but at present it is set by hand. The steam cylinder is

Jan 1, 1880

By Foster Fraas

MOST commercial electrostatic separators utilize the electrical property of conductivity, but although based on the same principles, they are constructed in a variety of forms, a common one being the simple roll type. Some information obtained during an investigation of that type of separator, and which indirectly is applicable to other types, is presented here. NUMERICAL RELATIONSHIP In Fig. I material discharged from hopper 6 is fed onto grounded rotating roll 2. Electrode 3 is at a high electrical potential with respect to roll 2, and any conductive particle in contact with roll 2 therefore acquires an electrical charge of such polarity that, when present in the electrical field, the force on it is in the direction of electrode 3. A detailed description of the charging by conductance as utilized in electrostatic separators may be found in a previous publication.1 As a result of this force, the path of the projected particle is changed in increasing amounts in the direction toward region C as the magnitude of the charge is increased. With the dividing edge 4 the projected particles may be divided into two fractions -those in region C designated as "deflected" or " deflectant " and those in region B designated as "residue." [ ] When material is passed over the roll only once, a complete separation is seldom obtained, therefore most commercial separators contain several roll-separator units in series, and some practical machines use as many as 12. In this paper a "pass" means the passage of material over a single-roll unit. The procedure is to repass either residue B with a low potential on electrode 3 or deflectant C with a high potential on 3. Most electrostatic separations follow a flowsheet of roughing and cleaning either the concentrate or the tailing, on both. In a specific instance, a dry, heated mixture of wet cleaned chromite and garnet from an

Jan 1, 1942

By G. S. Morison

I have bad considerable experience with the testing-machine at the Watertown Arsenal, having had broken there sixteen large steel eye-bars, besides quite a number of iron bars and two compression members. So far as accurate mid satisfactory results are concerned, the machine is all we could ask for, and the officers who have it in charge, together with their civil assistants, are thoroughly conversant with it 1 details, and entirely competent to make the tests required. The principal defect is that the force is very inadequate. As the machine is arranged, tile weighing apparatus is at one end and stationary, the measure of strain being carried from this to the scale-beam by the fluid in a tube m small that it looks like a wire. At the other end is placed the hydraulic press by which the power is applied; this press is mounted on a small carriage and held by two eight-inch screws about four feet above the floor, which arc of course strained in compression during tensile tests, and in tension during' compression tests. When the stretch of the material has exhausted the throw of the plunger it is necessary to relieve the strain, draw back the plunger, and move the carriage along, which is done by nuts turned by steam working on the large screws. Every specimen placed in the machine must be lifted above the large screws and lowered into position. To do this, crabs, running on travellers, which span the entire room, are placed over the machine, and by these the specimen can be lifted and put in place. The actual time required to make a test depends largely on the amount which the material stretches, bat it may generally be said, that for specimens which will stretch from two to three feet the

Jan 1, 1882

By Foster Fraas

MOST commercial electrostatic separators utilize the electrical property of conductivity, but although based on the same principles, they are constructed in a variety of forms, a common one being the simple roll type. Some information obtained during an investigation of that type of separator, and which indirectly is applicable to other types, is presented here. NUMERICAL RELATIONSHIP In Fig. I material discharged from hopper 6 is fed onto grounded rotating roll 2. Electrode 3 is at a high electrical potential with respect to roll 2, and any conductive particle in contact with roll 2 therefore acquires an electrical charge of such polarity that, when present in the electrical field, the force on it is in the direction of electrode 3. A detailed description of the charging by conductance as utilized in electrostatic separators may be found in a previous publication.1 As a result of this force, the path of the projected particle is changed in increasing amounts in the direction toward region C as the magnitude of the charge is increased. With the dividing edge 4 the projected particles may be divided into two fractions -those in region C designated as "deflected" or " deflectant " and those in region B designated as "residue." When material is passed over the roll only once, a complete separation is seldom obtained, therefore most commercial separators contain several roll-separator units in [ ] series, and some practical machines use as many as 12. In this paper a "pass" means the passage of material over a single-roll unit. The procedure is to repass either residue B with a low potential on electrode 3 or deflectant C with a high potential on 3. Most electrostatic separations follow a flowsheet of roughing and cleaning either the concentrate or the tailing, on both. In a specific instance, a dry, heated mixture of wet cleaned chromite and garnet from an

Jan 1, 1942

By James Norman

SEPARATION of minerals by froth flotation is rightly called an art. It can truthfully be said that no two ores separate in the same way. The difference in results obtained when natural and synthetic mixtures of minerals are separated is so great that such tests frequently have been worthless in attempting to select conditions in which a natural mixture will separate. With a few rare exceptions, the natural mixture is much more difficult to treat than a synthetic mixture, and a much poorer separation is obtained. Perhaps several experimenters have wondered why 10 or 20 per cent of a mineral being floated from an ore does not float and is different from the 90 or 80 per cent that is recovered. In experimental tests on pure sphalerite, observers1 have noted that varying amounts of sphalerite may be froth-floated with pine oil alone, the amount recovered in the froth depending apparently upon the source of the sulphide. The only explanation of results such as these, barring insufficiency of frother or time of flotation, is that the surface of the mineral floated is different from that of the mineral depressed. This difference often has been found to be caused by natural contamination of mineral surfaces, apparently brought about by weathering and exposure to natural solu-tions. There is virtually no rock that is absolutely unweathered. One of the writers had an exceedingly instructive experience in 1931 while working with United Verde copper-zinc iron sulphide ore in Arizona. Nonselective flotation of chalcopyrite and sphalerite away from some of the pyrite was all that could be accomplished. All known depressants produced only slight effect. Sodium cyanide showed some effect, but so much had to be used that only a small amount of chalcopyrite could be

Jan 1, 1939

By J. E. Harris, J. A. Whiteman, A. G. Quarrell

The graphitizing reaction has been studied in a number of Fe-C-Si alloys in the temperature range 550° to 725°C. The TTT relationships exhibit "C" curve behavior except where nuclei, either foreign or graphite itself, are present before the start of the reaction. It is suggested that the rate -controlling process is diffusion of carbon through ferrite. For the reaction to proceed at the observed rate it is calculated that the matrix surrounding the particles must deform plastically; experimental evidence for this deformation is presented. It is well-established that the decomposition of austenite to pear lite occurs at a maximum rate at an intermediate temperature.l-5 This "C curve" be- havior, which has been reported in a number of other systems,5-10 is a consequence of the relatively low rate of nucleation of the pearlite at small degrees of undercooling of the austenite. The cemen-tite phase in the pearlite is, in turn, metastable with respect to graphite and if steels are held for prolonged periods at elevated temperatures decomposition of the pearlite occurs. It is difficult to predict the shape of the subcriti-cal graphitization TTT (time, temperature, transformation) diagram for, in this case, undercooling does not occur. However, the free-energy change for the reaction does decrease with increasing temperature" (Fig. 1) and it is thus anticipated that the rate of nucleation will fall as the temperature approaches that of the eutectoid. In addition, a decreasing growth rate with increasing temperature is predicted in some circumstances with pure Fe-C alloys. However, apparently similar conditions exist for first-stage graphitization in the austenite range (malleabilization) but no evidence for C curve behavior has been presented in the extensive liter-

Jan 1, 1965

By Donald Ofte

LIQUIDUS temperatures of molten alloys were measured in an oscillating-cup viscosimeter by observing the abrupt increase in the alloy viscosity when the apparatus was cooled below the alloy liquidus temperature. The liquidus transformation can be an elusive thermal effect in an alloy system where a small amount of material is involved in a low-enthalpy liquidus reaction, or where other unfavorable physical conditions interfere. Using the viscosity technique, liquidus temperatures were measured in binary alloys of plutonium with cerium, gallium, and iron, as well as ternary Pu-Ce-Co alloys. The previously described oscillating-cup viscosimeter1 is a torsion pendulum consisting of a right circular, cylindrical tantalum cup fitted to a rigid shaft which, in turn, is suspended by a torsion fiber in a highvacuum system. When the torsion pendulum is placed in oscillation the viscosity of the liquid contained in the cup is a function of both the decay of the oscillation caused by the viscous drag of the liquid contained in the sealed tantalum cup, and the period of the oscillation. The period is measured by a photo-electrically operated timer to the nearest thousandth of a second. Prior to each measurement, the apparatus is held at temperature between 5 and 18 hr to assure thermal equilibrium throughout the 8 to 10-cc alloy sample. When the cup, filled with a liquid metal, is oscillating. only a very thin outer layer of the fluid is in motion. This moving annulus represents the liquid's contribution to the moment of inertia of the torsion pendulum. When the viscosity increases, more liquid is placed in motion, and the slight increase in the moment of inertia causes a corresponding increase in the period of oscillation.

Jan 1, 1967