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The negative charges on diaphragms of quartz, tungstic oxides, stannic acid, acid dyestuffs, soaps, and glass have for a number of years been explained on the basis of chemical equilibria—a hydrogen ion or light metal ion passes into solution leaving the solid complex ion negatively charged. While there are a number of observations which indicate a proportionality between the ( potential and the streaming potential it should be recognized that all the experimental evidence thus far presented shows that if hydrogen ion concentration is kept at a constant value, electrokinetic phenomena are influenced by salts. The multivalent ions exert the greatest effect on the reduction of osmotic flow. In the interpretation of all electrokinetic data the assumption is made that the potential of the solid remains constant. That this is not true is evidenced by the values of [ potential for quartz in contact with conductivity water as reported by the several investigators and by the authors of this paper. It is apparent that the nonreproducibility of surfaces will always prevent the obtaining of exactly comparable data. At best the experimental technique described depends on a theory which is capable only of showing a trend—another quartz surface should exhibit similar but not identical potential curves. It seems entirely reasonable to assume that the negatively charged laurate ions should have little or no attraction for a negatively charged quartz surface. The weight of previous experience in selection of flotation activators points unerringly to the usefulness of the multivalent metallic ions. The primary reason why the divalent barium ion is not available to two negative charges on the quartz surface might easily be that of distance between such adjacent negative charges. Otherwise activation could not occur, and the quartz could not assume the remaining unit positive charge of the barium ion. For this case no electrical double layer theory seems necessary. Clearly this is, at the negatively charged quartz surface, a case of partial chemisorption of the cationically divalent barium ion followed by the anionic neutralization of the remaining cationic charge by the freely moving laurate ion. It is hoped that the authors will continue with this interesting technique and that their results will continue to indicate trendwise what is known about the

Jan 1, 1957

Belting worth thousands of dollars can be ruined in a few minutes because of careless maintenance or lack of maintenance. Proper belt conveyor maintenance means having a clean conveyor system at all times. The belt line should be visually inspected during each shift. Equipped with proper maintenance instructions, one belt man can patrol a belt line of 2 to 3 km (1.5 to 2 miles). His duties would be to lubricate drives and idlers (except sealed-for- life type), maintain belt and conveyor frame alignment, detect sticking idlers, and maintain an unobstructed right-of-way.

Jan 3, 1978

By Robert A. Brusca

OUTLINE Mineral Poor, but great primary inputs Net importer of most primary inputs • Copper • Zinc • Aluminum • Oil Problems for Japan • Supply Disruption • Currency Swings Remedies • Yen pricing of primary products • Long term contracts • Ownership of primary commodity producers Current Approach No Text Available

Jan 1, 1990

By Herbert H. Kellogg

Deposits of high-silica kaolinite clays occur at many places in central Pennsylvania. These white clays were formed apparently by weathering of argillaceous quartzite and limestone. Their geology, distribution and use have been reported by Leighton.1 The larger deposits have been mined from time to time, and the clay, after washing to remove coarse sand, has found use as rubber filler, foundry clay, and in white cements. In general, the clay from these deposits contains too much grit (quartz) to be useful as paper filler, and the silica content is too high to make it useful as china clay for ceramic ware. Gravity methods for the separation of quartz from these clays have failed because of the extremely fine size of the quartz grains, but by the methods of froth flotation described in this paper these sandy kaolins can be made to yield a purified kaolinite that has a chemical composition close to that of good-grade Georgia kaolins, and is free enough from grit to be used as a paper filler. As by-products of the separation, a fine ( — 325-mesh) sand assaying 95.5 per cent SiO2, and a very fine (—3-micron) clay are produced. The possible ceramic uses of these products are being investigated at The Pennsylvania State College. Experimental Procedure The Sample.—The clay sample used in these tests was obtained from a small mine near Tyrone, Pa. It had already been washed to remove coarse sand, and represented the finished product of this small mine and washery. Microscopic examination showed that the clay was composed almost entirely of the minerals quartz and kaolinite, and that the quartz was present mostly in particles larger than one micron, while the kaolinite particles generally were less than 20 microns in size. The kaolinite and quartz particles were physically separable by blunging the clay in water with a suitable dispersant. Preparation of Flotalion Feed.—By the addition of NaOH in an amount equal to 3 lb. per ton of solids, the clay was completely dispersed in water. Flotation feed was prepared by allowing a dispersed suspension (10 per cent solids) of the clay to stand for the period of time required for a 2.5-micron particle of quartz to settle from the top of the container to the bottom. After this settling period the suspension was decanted from the settled solids. The settled solids were redispersed in water and the separation was repeated once. The two fine fractions were then combined. Thus the clay was divided into a fine and a coarse fraction by size separation at approximately 2.5 microns.* The fine frac- . tion was found to have a considerably lower sand content than the raw clay (Table I), and was not treated further. The coarse fraction formed the flotation feed for all the tests described in this paper. A size separation of this type can be

Jan 1, 1948

By Herbert H. Kellogg

Deposits of high-silica kaolinite clays occur at many places in central Pennsylvania. These white clays were formed apparently by weathering of argillaceous quartzite and limestone. Their geology, distribution and use have been reported by Leighton.1 The larger deposits have been mined from time to time, and the clay, after washing to remove coarse sand, has found use as rubber filler, foundry clay, and in white cements. In general, the clay from these deposits contains too much grit (quartz) to be useful as paper filler, and the silica content is too high to make it useful as china clay for ceramic ware. Gravity methods for the separation of quartz from these clays have failed because of the extremely fine size of the quartz grains, but by the methods of froth flotation described in this paper these sandy kaolins can be made to yield a purified kaolinite that has a chemical composition close to that of good-grade Georgia kaolins, and is free enough from grit to be used as a paper filler. As by-products of the separation, a fine ( — 325-mesh) sand assaying 95.5 per cent SiO2, and a very fine (—3-micron) clay are produced. The possible ceramic uses of these products are being investigated at The Pennsylvania State College. Experimental Procedure The Sample.—The clay sample used in these tests was obtained from a small mine near Tyrone, Pa. It had already been washed to remove coarse sand, and represented the finished product of this small mine and washery. Microscopic examination showed that the clay was composed almost entirely of the minerals quartz and kaolinite, and that the quartz was present mostly in particles larger than one micron, while the kaolinite particles generally were less than 20 microns in size. The kaolinite and quartz particles were physically separable by blunging the clay in water with a suitable dispersant. Preparation of Flotalion Feed.—By the addition of NaOH in an amount equal to 3 lb. per ton of solids, the clay was completely dispersed in water. Flotation feed was prepared by allowing a dispersed suspension (10 per cent solids) of the clay to stand for the period of time required for a 2.5-micron particle of quartz to settle from the top of the container to the bottom. After this settling period the suspension was decanted from the settled solids. The settled solids were redispersed in water and the separation was repeated once. The two fine fractions were then combined. Thus the clay was divided into a fine and a coarse fraction by size separation at approximately 2.5 microns.* The fine frac- . tion was found to have a considerably lower sand content than the raw clay (Table I), and was not treated further. The coarse fraction formed the flotation feed for all the tests described in this paper. A size separation of this type can be

Jan 1, 1948

By Herbert H. Kellogg

DEPOSITS of high-silica kaolinite clays occur at many places in central Pennsylvania. These white clays were formed apparently by weathering of argillaceous quartzite and limestone. Their geology, distribution and use have been reported by Leighton.1 The larger deposits have been mined from time to time, and the clay, after washing to remove coarse sand, has found use as rubber filler, foundry clay, and in white cements. In general, the clay from these deposits contains too much grit (quartz) to be useful as paper filler, and the silica content is too high to make it useful as china clay for ceramic ware. Gravity methods for the separation of quartz from these clays have failed because of the extremely fine size of the quartz grains, but by the methods of froth flotation described in this paper these sandy kaolins can be made to yield a purified kaolinite that has a chemical composition close to that of good-grade Georgia kaolins, and is free enough from grit to be used as a paper filler. As by-products of the separation, a fine (-325-mesh) sand assaying 95.5 per cent Si02, and a very fine (-3-micron) clay are produced. The possible ceramic uses of these products are being investigated at The Pennsylvania State College. EXPERIMENTAL PROCEDURE The Sample.-The clay sample used in these tests was obtained from a small mine near Tyrone, Pa. It had already been washed to remove coarse sand, and represented the finished product of this small mine and washery. Microscopic examination showed that the clay was composed almost entirely of the minerals quartz and kaolinite, and that the quartz was present mostly in particles larger than one micron, while the kaolinite particles generally were less than 20 microns in size. The kaolinite and quartz particles were physically separable by blunging the clay in water with a suitable dispersant. Preparation of Flotation Feed.-By the addition of NaOH in an amount equal to 3 lb. per ton of solids, the clay was completely dispersed in water. Flotation feed was prepared by allowing a dispersed suspension (10 per cent solids) of the clay to stand for the period of time required for a 2.5-micron particle of quartz to settle from the top of the container to the bottom. After this settling period the suspension was decanted from the settled solids. The settled solids were redispersed in water and the separation was repeated once. The two fine fractions were then combined. Thus the clay was divided into a fine and a coarse fraction by size separation at approximately 2.5 microns.* The fine fraction was found to have a considerably lower sand content than the raw clay (Table I), and was not treated further. The coarse fraction formed the flotation feed for all the tests described in this paper.

Jan 1, 1945

By Albert G. Zima

ACCORDING to recently published statistics, it is predicted that as much oil must be produced during the next 16 years as has been produced during the past 75, in order to satisfy the high rate of consumption of petroleum products. During 1934, over 17,000 oil wells were completed in the United States, and it is expected that over 20,000 additional wells will be drilled during the current year. Were it not for the remarkable progress made during recent years in the improvement of drilling technique and in the development of equipment used in the production phase of the oil industry, it is doubtful whether sufficient oil could be produced to meet present requirements. A few years ago, wells seldom were deeper than 3500 to 4000 ft., owing to the limitations of the drilling methods and equipment employed.. Today, 'however, through the application of scientific drilling methods and the adaptation of modern equipment and improved materials, many wells range from 6000 to 8000 ft. in depth, and a few recent completions exceed 10,000 feet. DRILL TOOLS Modern rotary drilling tools are the product of ingenious design and careful selection and adaptation of materials used in their construction. They must withstand terrific abrasion and, because of their compactness, must be designed to resist exceedingly high unit stresses. In bits, core drills and reamers, the bodies are made of either forged or cast alloy steels, heat-treated to develop a combination of high strength and toughness. To provide sufficient strength to the threaded portions and to protect the threads from distortion or damage, the box or pin sections of the tools are hardened to approximately 310 to 330 Brinell hardness

Jan 1, 1935

By F. S. Buffington, Morris Cohen

THERE is little quantitative information available concerning the effect of applied stress, in both the elastic and plastic ranges, on diffusion kinetics. Accordingly, a program has been undertaken to determine the rate of self-diffusion in high purity iron, with the specimens subjected to stress during the course of diffusion. Results are reported here for body-centered cubic iron at a diffusion temperature of 890°C. The iron used was 99.97 pct Fe, the principal impurities being 0.002 pct C, 0.008 pct 0, and 0.02 pct Si. The surface-decrease method of self-diffusion analysis was employed, and Fe55 Mn x-radiation, 2.9 years half-life) was the tracer element. Details of specimen preparation and equipment are given elsewhere.' Disks of the high purity iron, % in. diam x 1/4 in. thick, were annealed at 890°C for 18 hr in dry hydrogen to produce large grains of a ferrite. The faces of the disks were then surface ground, and possible grinding stresses were relieved by annealing at 890 °C for 45 min in vacuum. A layer of radioactive iron 0.00186 cm thick was electroplated on one face of each disk. The self-diffusion coefficient was calculated from the ratio of the radiation intensities emanating from each of these faces, as measured before and after diffusion.' The heating was carried out in a vacuum furnace (10-5 mm Hg) controlled to ±1.5°C. The specimens were loaded in compression between two quartz disks during the diffusion runs by means of a lever system operating through a vacuum seal. Thus one quartz disk was pressed directly against the radioactive face of the specimen, minimizing the vapor loss of radioactive iron. Steady-state creep occurred in all instances where permanent deformation could be detected, but the specimens did not exhibit appreciable transverse barreling until natural strains of 0.2 to 0.3 were attained. Essentially, the diffusion took place under uniaxial stress. The plastic strain in each case was obtained at the diffusion zone by measuring the diameter d there before and after the run: e = 2 In — do Let Du equal the self-diffusion coefficient which would have prevailed at the given temperature if no stress had been applied. This was calculated from the temperature-dependence equation which had been previously determined: —59,800 D, = 6.2 exp ( I sq cm per sec* [I]

Jan 1, 1953

By Allen L. Hatch

A survey of all phases of the world's lead and zinc production in 1968 from ore through to refined metal was conducted by sending questionnaires to individual companies and the results of this survey are tabulated at the end of the paper. The paper goes on to review changes in the geographical distribution of the world's lead and zinc mine and metal production and in the trading patterns of raw materials, present and future utilization of metal production capacity, developments in metal smelting and refining processes and the growing importance of marketing, product development and research in the 1950's and 1960's.

Jan 1, 1970

By Clarence Balke

SMALL buttons of fused tantalum have been produced by are fusion in a vacuum, by drawing an arc between sticks of pressed tantalum and a tantalum-faced water-cooled copper block. However, ingots of appreci-able size can be produced only by the heat-treatment of bars pressed from powder. The following outline covering the production of finished bars of tantalum by the methods of powder metallurgy is also used for the production of columbium, taking into account the difference in the melting points of these two metals. PRESSING THE POWDER With possibly a few exceptions, a pressing operation is one of the essential steps in the practice of powder metallurgy. In fact, the author's experience with a number of high-melting-point metals and with numer-ous types of hard carbide compositions has led him to believe that this operation is often one of the most important in the- entire process, and frequently one of the most difficult to carry out in a satisfactory manner. Defects clue to improper pressing can readily lead to a defective finished product. It is the author's opinion that rarely is a bar or other article pressed from metal powder in such a way that all parts of the piece are uniformly pressed. The nearest approach to uniformity of pressing is possibly attained when the powder is contained in a flexible receptacle, such as rubber, and is pressed under a liquid by hydrostatic pressure. However, this method is not generally applicable. Hydraulic pressing in steel dies where one or two punches are forced into the die must usually be resorted to. As the pressure in such a die is built up, the powder begins to cling to the walls of the die with a tenacity dependent upon the nature of the powder, and this results in a bridging action, so that the layers of powder adjacent to the moving punch are pressed more heavily than those further removed in the mass. Frequently, as the pressure is carried higher, there may be a mass slippage of the powder upon itself, with the result that slip cracks are formed within the pressed

Jan 1, 1938

By Allen L. Hatch

A survey of all phases of the world's lead and zinc production in 1968 from ore through to refined metal was conducted by sending questionnaires to individual companies ad the results of this survey are tabulated at the end of the paper. The paper goes on to review changes in the geographical distribution of the world's lead and zinc mine and metal production and in the trading patterns of raw materials, present and future utilization of metal production capacity, developments in metal smelting and refining processes and the growing importance of marketing, product development and research in the 1950's and 1960's.

Jan 1, 1970

By E. T. Turkdogan, L. E. Leake

A number of measurements have been made on the vapor pressure of pure iron at 1600°C. Experiments were carried out by the transportation method in which a sample of iron is exposed in a furnace to a stream of pure argon, metered at a predetermined flow rate for a specified period of time. The vapor pressure was obtained from the weight loss of the sample. A detailed diagram of the apparatus used for the experiments is given in Fig. 1. It consisted of a horizontal molybdenum-wire-wound furnace fitted with a recrystallized alumina tube 1 1/8 in. internal diam. The boats, 1 by 3/16 by 1/8 in., were fired in argon at 1600°C to constant weight before use. After this treatment, subsequent heating of the boats to 1600°C gave little or no further change in weight, e.g. ±0.05 mg in 24 hr. The furnace and reaction tube were separately fed with argon from two independent flowmeters. These were connected to a common supply source via an argon purification furnace containing metallic titanium sponge at 700°C, and an anhydrone drying-tower. A rotary displacement-type meter was included in the gas train to provide a direct means of measuring the total volume of gas passed through the reaction tube. The material used was vacuum melted high-purity iron in the form of wire 2mm in diam. The following impurities were present in the iron: 0.008 pct C, 0.002 pct Si, 0.005 pct Mn, 0.008 pct S, 0.001 pct P, 0.01 pct Ni, 0.001 pct Cr, 0.006 pct Cu, and 0.001 pct Al. Samples consisting of three small pieces of this wire were laid end to end in a recrystallized alumina-combustion boat, and were separated by small fragments of alumina. The wire samples were then melted in argon to form spherical beads 2 to 3 mm in diam. After weighing, the boat with its contents was placed on the boat carrier and introduced into the cool end of the reaction tube. The entire furnace system was then flushed with argon for 30 min. At the end of this period, the flow of argon to both furnace and reaction tubes was adjusted to the desired level; then the boat was slid rapidly into the hot-zone of the reaction tube. After a known volume of gas had passed through the reaction tube, the boat was withdrawn quickly to the cool end of the furnace. When quite cool, the boat was removed from the fur-mace and placed in a desiccator for subsequent re-weighing. The semi-micro balance used in these experiments had a sensitivity of 0.005 mg. The above procedure was repeated at several flow rates within the range of 25 to 300 ml per min. The flow of argon in the annular space between the two tubes was at a rate of 300 ml per min in all experiments. During all the experiments the furnace temperature was maintained at 1600° ± 5°C by means of a temperature controller. The temperature of the reaction zone was measured with a Tinsley high precision disappearing filament pyrometer which was initially calibrated against a Pt-13 pct Rh/Pt thermocouple; the errors due to temperature measurements were within * 5°C. RESULTS Assuming that the iron vapor is in the monatomic state, the vapor pressure can be calculated from the weight loss of the sample and the volume of the carrier gas. The results obtained are plotted in Fig. 2 against the rate of flow of argon through the chamber containing liquid iron beads. At low flow rates, the thermal diffusion of iron gives an apparent high vapor pressure, but at high gas flow rates, the carrier gas is not saturated with the vapor, and therefore, low vapor-pressure values are obtained. This is now a well-known phenomenon. There is a distinct inflexion of the curve at about 120 to 160 ml per min rate of argon flow and the vapor pressure of iron within this

Jan 1, 1961

By W. Rostoker

The process of diffusion alloying of mixed powders offers attractive possibilities both commercially and experimentally. It avoids the fabrication difficulties arising from high alloy contents. Indeed, the process is facilitated by larger alloy additions. The direct formation of the part or test piece and the opportunlity to perform machining operations under more favorable conditions are of no small importance. However, it is necessary to make only brief mention of the interesting features. As yet there have been few attempts to study this process in detail and to carry it to completion, if such is possible. It was intended not only to measure the intermediate and optimum magnetic properties of sintered alloys but to use magnetic testing itself as a means of following the progress of alloying under various condi-tions. Having established that alloys could be successfully synthesized by this tech. nique, the opportunity was taken to study the magnetic properties of several alloys of iron and silicon which had hitherto been too difficult to prepare in suitable test piece form. While avoiding some of the difficulties inherent in the fabrication of alloys by orthodox methods, the diffusion alloying process introduces a few of its own. The first of these is the evaluation of the approach to homogenization. In recent years some notable contributions have been made to this question, but considerable uncertainty remains in its definition and evaluation. This work has concerned itself with further study of this problem and it is hoped that more light has been shed on it. The second of these difficulties arises from the presence of porosity. It is inevitable that in the consolidation of a loose bulk of powder, there should remain some voids unless extremely high pressures are repeatedly applied. It was therefore of importance to investigate their effect on magnetic properties. Recently this effect has been studied and certain predictions made of its behavior. It is believed that the experimental results presented here provide a sound substantiation of the theoretical treatment. The attempt has been made to synthesize five alloys of the iron-silicon system and three each of the iron-nickel and iron-cobalt systems. A series of experiments was also conducted on some of these alloys to test their susceptibility to heat treatment. Some unfortunate experiences have provided opportunity to report data on the deleterious effects of nitrogen on magnetic properties when present as a a in protective atmospheres. MateRIALS, PREPARATION OF SAMPLES and Testing The purest materials available were em. ployed for this work. A specially purified,

Jan 1, 1949

By D. C. Hilty, W. Crafts

A qualitative pseudoternary solidification diagram for the Fe-S-O system modified by manganese is proposed and supported by experimental derivation of an isothermal section at 1475°C and substantially 1 pct Mn in the solid-metal phase. The solubility of oxygen in liquid iron containing 1 pct Mn and sulphur contents up to 0.9 pct has been measured at 1600°C and found to increase as the sulphur content exceeds 0.15 pct. AS has been pointed out previously,' all oxide and sulphide inclusions in steel, excluding mechanically entrained matter, result from modifications of the basic Fe-S-O system. Therefore, one method of attack on the problem of the mechanism of deoxida-tion and inclusion formation is to examine the influence of deoxidizers on the Fe-S-O liquidus diagram. This approach has been adopted in work on the subject being carried out at the Metals Research Laboratories of the Electro Metallurgical Co. and has resulted in the postulation of types of solidification diagrams for the Fe-S-O system modified with common deoxidizers. This method has been of considerable assistance in interpretation of the factors affecting the formation of inclusions.' For the most part, however, these diagrams have been highly speculative. They were constructed primarily by inference from the pertinent binary and ternary systems and from the appearance of inclusions produced by specific deoxidizers. Moreover, since the systems contain four or more components, simplifying assumptions and qualifications were necessary in order to permit their representation as modifications of the Fe-S-O diagram. Consequently, experimental confirmation of the type of construction employed for these diagrams is desirable, and the present paper is concerned with such evidence. The addition of manganese to the Fe-S-O system was selected for initial investigation. Manganese is an important component of practically all steel and is, therefore, of fundamental interest. Because of its great affinity for sulphur, manganese has a more profound effect on the sulphide side of the Fe-S-O diagram than any of the other common deoxidizing eletments. In addition, more quantitative information pertaining to the contiguous binary and ternary systems involving iron, manganese, sulphur, and oxygen is available than for the other deoxidizers. Fe(Mn)-S-O Solidification Diagram Many of the side diagrams of interest in connection with this system are known. The Fe-Mn binary has been well established by several investigators;% the Fe-O system has been clarified by Darken and Gurry;' and FeO-MnO diagrams have been published by Herty,5 Andrew, Maddocks, and Howat,6 and by Hay, Howat, and White.7 The Mn-O diagram does not appear to have been derived experimentally, but the portion of 'it that is of interest can be visualized easily from a consideration of the melting points of Mn and MnO and the fact that a broad miscibility gap must exist between them. The ternary Fe-Mn-O diagram has been discussed by Benedicks and Löfquist,8 Wentrup,9 and by Körber and Oelsen.10 Experimental study of the Fe-Mn-O system has been carried out by Körber and Oelsen and to a lesser degree by Chipman, Gero, and Winkler,11 Hilty and Crafts," and others. On the basis of published information, then, an outline of the Fe-Mn-O liquidus diagram can be constructed as illustrated by Fig. 1. In this, as in all succeeding diagrams, transformations such as the ?-? reaction in iron have been ignored for purposes of simplification. The arrows denote falling temperature. The distinguishing feature of this diagram is the broad region of liquid immiscibility extending

Jan 1, 1955

By d&apos, L. Berenbaum, F. Heurle, R. Rosenberg

The structure of aluminum films obtained by evaporation was studied by electron microscopy, mostly by replica techniques and X-ray diffraction. The resistivities and stress conditions of the films were also determined. Film properties were studied as a function of source selection, substrate type, residual pressures of oxygen and water vapor, substrate temperature, and rate of growth. The formation of abnormal localized growths and whiskers resulting from annealing treatment subsequent to deposition was investigated. Films deposited onto single-crystal substrates were found to be epitaxially 0riented; for such films, relative orientations between films and substrates were determined. ALTHOUGH wide use has been made of evaporated aluminum films for the formation of conducting lines on semiconductor devices, relatively little has been reported concerning the structural characteristics of such films.1"9 The purpose of this study was to obtain an overall view of the dependence of these characteristics on film deposition and subsequent annealing conditions, which were similar to those used in silicon planar technology. Accordingly, most of this study was carried out using oxidized and bare silicon wafers as substrates, although some work was also done using alkali halide, magnesium oxide, and mica substrates. However, the main concern remained pragmatic. Emphasis was given to the study of the effects of deposition and annealing conditions on film characteristics such as structure, resistivity, and stress. I) EXPERIMENTAL PROCEDURES The films which were investigated in this study were deposited in 18-in.-diam glass chambers which were connected to the usual type of trapped diffusion pumps filled with silicon oil. Through the use of liquid-nitrogen-cooled Meisner traps and titanium sublimation pumps placed inside the deposition chambers, the pressure could be lowered to the lower portion of the 10- I Torr range and little increase in pressure would occur during the deposition cycle. Unless described otherwise, the substrates were 1-in.-diam p-type silicon wafers having a resistivity of 10 ohm-cm. The wafers were oxidized in wet oxygen at 975°C followed by a short dry-oxygen exposure at the same tempertture to a total oxide thickness of approximately 6000A. The wafers, backed by a layer of gallium, were mounted onto molybdenum discs brazed to a copper block.10 The latter was heated by imbedded commercial cartridge heaters. The substrate temperature could be maintained to within +10°C of a prescribed temperature during film deposition. The search for a satisfactory source for the controlled evaporation of aluminum has led to the use of 1-in.-diam crucibles" machined from rods of a commercially available, refractory composite* of Bn and

Jan 1, 1969

By Peter R. Drummond

THE final casting of refined copper has been re-J- stricted for generations by the following sequence of operations: Filling the reverberatory furnace, melting, skimming, blowing or flapping, and poling. The hoped-for 24 hr cycle, producing 300 tons or more, has been taken up largely with the necessary bat time-consuming tasks of cleaning the bath, sulphur elimination, and in turn removal of excess oxygen to produce tough-pitch copper. Incidental to comparatively slow melting under combustion gases, copper oxides react with the furnace lining, and the slag so-formed must be completely recycled. The three-phase arc furnace has eliminated some of the cycle stages, and telescoped the remainder into a continuous operation. Electrical energy, supplied to graphite electrodes enclosed in high grade refractories, rapidly melts copper cathodes and sustains a stream of metal, containing approximately 0.01 pct oxygen, without contamination from fuel. The arc was struck on the first large electric furnace for melting copper in the United States on April 13, 1949. The earliest use of this type of furnace was at Copper Cliff, Ont., in 1936, and an admirable description of their installation has been published? Copper, melted in the Baltimore furnace, is used to cast billets, and the installation differs somewhat from the Canadian, as will be described. The arc furnace is a heavy-duty, three-phase furnace, holding 50 tons, the general outline of which appears on Fig. 1. The steel shell is 15 ft ID with a bottom radius of 14 ft 2 in. The roof, separate and distinct from the body, consists of a 15-ft water-cooled, cast-steel ring of the same outside diameter as the furnace. The center line of the furnace lies 9 ft 6 in. from that of the trunnions, permitting a 5" backward tilt for skimming, and a 40" maximum nose tilt forward for complete draining. Normally, the furnace overflows by displacement, and the use of the forward tilt arrangement is restricted to covering charging delays. The charging slot, 3 ft 8 in. x 5 in., lies on the north center line, the tap hole on the south, and the 30x30 in. skim door 45" to the west of the slot. The original 20-in. graphite electrodes were replaced with 14 in. in December 1949. Three conventional direct current winch drives, governed by electrical controls, position each electrode which has individual mast supports and counterweights. An independent circulation supplies cooling water for the electrode glands, the roof ring, charge slot, and the skim door frame. Arc Furnace Refractories Hearth: Fused-in monolithic bottoms had been used in copper arc furnaces, installed prior to April 1949. These consisted of thin layers of periclase, successively fused in place over preliminary brick courses. Heat was obtained from the arc, using a T-like arrangement of broken electrodes resting directly on the periclase to be fused. The operation, taking weeks to perform, was very expensive. The chemically-bonded magnesite-brick bottom, installed at Baltimore, was the first of its kind and a radical departure from previous practice. It consists of a 1 to 6-in. layer of castable refractory laid on the steel shell, modifying it to a 12 ft 2 in. bottom radius. Two courses of 9x2 % -in. fireclay straights and keys follow. The third course is made of 9-in. magnesite blocks of special shape to form circles of an inverted arch. It was started by a four piece keystone with skew-backs forming the outer course. The fourth course also started on a central keystone, or button, of four 90" segments, 12 in. diam x 13 Vz in. deep, and continued with 13%-in. blocks. Skewbacks at the shell completed the course to produce a horizontal surface for the side walls with a single course of No. 2 arch fireclay against the steel. Dry chrome-magnesite cement was brushed over each course after laying, and a 1-in. expansion space between the brick and the shell was filled with the same mixture. The total bottom thickness, excluding the castable material, was 5 in. of clay plus 22% in. of chemically-bonded magnesite. Tap Hole: A 5-in. OD and 3-in. ID silicon-carbide tube constitutes the tap hole and is set tangential to the upper course of the furnace bottom. Molten metal fills the tube when the furnace is level and filled to capacity. Side Walls: The lining, against the shell, consists of a 9x4Y2x3 in. soldier course of fireclay, using straights and No. 1 arches to turn the circles. A second soldier course of 9x4'/2x2'/2-in. fireclay was laid in a somewhat similar fashion. Three courses of 13Y2x6x3 in. and 9x6~3 in. of final magnesite, laid flat, completed the lining, using Nos. 1 and 2 keys to turn the circles. Cardboard spacers were placed between every two bricks in horizontal courses, and a thin coat of chrome-magnesite cement filled the joints between the firebrick and magnesite. A sprung-arch spanned the skim door with jambs of suitable magnesite shapes. Charge Slot: The slot is 3 ft 8 in. wide x 5 in. high. A silicon-carbide sill of special shapes has a 30" slope to allow cathodes to slide easily into the bath. The original arch was flat, and composed of Nos. 1 and 2 wedge magnesite with a 6-ft radius. It projected 5 in. over the sill, and, being a flat arch, gave an 18 15/16-in. opening between the inner edge and the metal line. The whole assembly was later raised 9 in., and the flat arch replaced with an arch, the lower edge of which maintained the 5-in, width from the outer to inner edges as shown in Fig. 2. A water-cooled, cast-copper jacket protects the steel shell behind the slot.

Jan 1, 1952

By C. H. Bushell, M. Malnarich

REAGENT control in flotation is more an art than a science. Operators vary the amount of reagents used according to the metallurgy obtained. The amount of collector may be increased, for example, if tailings losses are high and decreased if concentrate grades are low. Often control decisions are based on only one assay, such as the tailings analysis by microscopic or quick assaying techniques. This method of control has given reasonably satisfactory results but is clearly far from perfect. No adjustment in reagent addition can be made until information is received that metallurgy has deteriorated, that is, until the optimum time for adjustment has already passed. The first adjustment probably will be an overcorrection or an undercor-rection, and time will be required to establish the best new addition rates. The seriousness of the problem depends on variability of the ore. In ore of continually shifting composition and complexity, mill results will shift back and forth from excessively high concentrate grades and high tailings losses to excessively low concentrate grades and low tailings losses. Economic incentive for improved control also increases with increasing size of mill. Even a small improvement in percentage recovery in a large mill pays for expensive control equipment. The Sullivan concentrator of The Consolidated Mining & Smelting Co. of Canada Ltd. at Kimberley, B. C., treats 11,000 tpd of complex lead-zinc ore, a scale of operations which justifies an extensive research program on automatic control. Work has followed two separate lines: 1) development of faster analytical methods for pulps, and 2) study of metallurgical control by measurement and control of reagent concentrations in flotation solutions. Although work is incomplete in both phases, a progress report can be given on the development of reagent control. The primary requirement in flotation is selective attachment of particles of one mineral to air bubbles while the other minerals remain detached. Hydrophobicity of mineral surfaces is established by the collector, which coats the minerals by adsorption. The requirement of selective affinity for air bubbles is therefore equivalent to requiring selective adsorption of a collector. Adsorption theory, supported by abundant experimental evidence, shows that the amount of a reagent adsorbed at a surface must be a function of its residual concentration in solution. As the concentration in solution rises, the amount adsorbed increases, usually following some type of logarithmic curve. Selective adsorption must depend on a natural difference in the minerals, but ordinarily the differences in affinity are not great enough to obtain complete coverage of one mineral while the others are completely uncoated. An optimum concentration will exist, below which coverage will not be great enough to float enough of the valuable mineral, and above which too much unwanted mineral will float. All other reagents, except some frothers, affect the amount of collector adsorbing at constant residual collector concentration in solution, either by adsorbing competitively with the collector, or by a

Jan 1, 1957

By K. H. Nimerick

A recent study has attempted to identify properties of hard-to-float coal that make them responsive to froth conditioning. Froth conditioning is the process of chemically enhancing the hydrophobic surface character of fine coal particles to improve their recovery by froth flotation. Since its introduction, froth conditioning has enabled recovery of an additional 1.9 Mt (2.1 million st) of coal. This study correlates field results to chemical, physical, and petrographic properties. The most direct correlation relates the coal's oxygen content to its response to froth conditioning. The higher the oxygen content, the greater the benefits of froth conditioning.

Jan 1, 1985

By Edward Judd

THE old Cerro de Pasco smelter at La Fundicion, near Tinahuarea, 9 miles. from the Cerro de Pasco. mines and at an elevation of 14,300 ft., has now been replaced by a thoroughly modern smelting plant at Oroya, the junction point of the company's private railroad with the Central Railway, of Peru. This site has the advantages of being closer to the Morochoca mines, as well as nearer to the port of Callao, and at the same time is 2000 ft. lower in elevation, which benefits not only the cost of transportation but also the tech-nical operation of blast furnaces , and converters. The Oroya smelter was designed with the idea of .smelting about 2500 tons of. ore per day, but having in mind the possibility of increasing its capacity, all departments of the plant can be extended within reasonable -limits; for instance, if it is found that reverber-atory smelting is cheapest, taking into consideration the cost of fine crushing and fuel, it is possible to extend the roaster and reverberatory plants accordingly. The ore handling system is modern, consisting of belt conveyors, reclaiming machines, and electrically driven calcine cars, all requiring the minimum of labor. Waste heat from the reverberatory furnaces is utilized in boilers for the production of power to operate the plant, and the power house is equipped with condensing units to obtain the highest economy. Shop installations for the making of all repairs required for the smelter are unusually complete, includ-ing iron foundry, steel foundry, forging and machine shops, carpenter and pattern shops, and an electrical shop. There is also a plant for the production of all clay and silica refractory brick used in the furnaces; this is situated on the smelter site and is conveniently arranged for receiving raw materials and delivering finished brick to the several departments of the smelter. The laboratory is in a wing. of the general office, which is a two-story brick structure, situated on the smel-ter site.

Jan 10, 1923

By Walter Crafts, C. M. Offenhauer

In a previous study of the carbide phase of chromium steels, it was shown that chromium carbide (Cr7C3) is 2 more stable carbide than cementite (Fe3C) at tempering temperatures above about 500°C. in quenched steels containing from about I to 7.5 per cent chromium. Below this temperature the carbide phase was found to consist of cementite in all of the steels examined. In the present investigation it was found that a similar change in the carbide phase takes place in molybdenum and in chromium-molybdenum steels at approximately the same tempering temperatures. The approximate ranges of occurrence of the alloy carbides Cr7C3, Cr4C, and Mo2C have been determined in steels containing up to 5 per cent chromium, I per cent molybdenum and 0.60 per cent carbon. The experimental steels were made in small high-frequency furnaces from Armco ingot iron, low-carbon ferrochromium and calcium molybdate and were poured into 2-in. ingots, which were forged to I-in. round bars. Sections of the bars were heated to the carbide-solution temperature and cooled rapidly to induce austenite transformation at relatively low temperatures. The steels were subject to some segregation, therefore comparatively high temperatures were necessary to dissolve all of the carbides. The microstructure of the quenched specimens was examined to verify the belief that the carbides had been dissolved, and also to determine the nature of the nonmartensitic structure of incompletely hardened steels. Ferrite and pseudo-martensite were present in some of the specimens, but all specimens were quenched at such a rate that pearlite was not formed, in order to ensure the formation of the carbides at temperatures lower than about 500°C. It had been found previously1 that in chromium steels the chromium carbide could be produced by transformation of austenite in the pearlite range above 500°C., and, in order to start the tempering treatment with the carbide present as cementite, the absence of pearlite was considered to be essential. The specimens were tempered for 64 hr. to permit the formation of the stable carbide. After tempering, the specimens were submitted to microscopic and X-ray examination. The carbides were separated either electrolytically in a 5 per cent HCl electrolyte or with an acidified copper-potassium chloride solution. The crystal structure of the carbide phases was determined by the Debye-Scherrer type of X-ray patterns. The X-ray patterns obtained from specimens near the boundaries between two types of carbides were generally weak and diffuse as compared with the other patterns. For this reason, and because the more soluble components may be masked, the boundaries between the phases could not be determined precisely. However, the X-ray analysis of electrolytically separated carbides has given consistently reproducible results

Jan 1, 1943