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By Robert L. Gower, John H. Cash

Interconnections for integrated circuits operating at rnicrowaue frequencies rzust be formed as microwave transmission lines. This paper describes the fabrication of one type of microwave transmission line known as microstrip, which can be fabricated on momlithic integvated circuits by deposition of 0.1- to 2.0-mil-thick metal and dielectric films. A microstrip line consists of a narrow conducting strip separated from a gvound plane by a dielectric material. Thick films of good conducting materials are required for low loss at high frequencies. Vacuum-evaporation methods for depositing aluminum and silver films are described. The narrow conducting strip forming the top conductor is defined by photoresist-etching techniques after the thick rnetal film is deposited. Gold plating with a photoresist-masking technique is also used to forrrz thick metal conductors. The microstrip dielectric layer is formed by deposition of suitable dielectric films 0.1 to 2.0 mils thick. Several deposition techniques were investigated. Electron-beam evaporation of quartz is described. Electrical characteristics of deposited microstrip lines at microwave frequencies are included and the microwave power attenuation as a function of conductor and dielectric thickness is given. It is concluded that the deposition of microstrip transmission lines is a practical way to achieve low-loss interconnections in monolithic integrated circuits. CONNECTIONS between devices in low-frequency and digital circuits are usually made by connecting the devices with a length of conductor such as a metal lead oi- a wire. If this method were applied to microwave integrated circuits, the reactance of the connection due to the series inductance and parasitic capacitance would be very high, in fact too high to permit successful circuit operation. In addition, resonance and antenna effects would occur at high frequencies, especially when the connections approach the wavelength.' Connections which are sections of transmis- sion line will overcome these difficulties. The electromagnetic field is confined to the volume of the transmission line, parasitic effects are not present, and circuit design utilizes familiar transmission-line techniques. TRANSMISSION LINES One type of transmission line geometrically adaptable to integrated circuits is known as micrstri. A microstrip line can be generated from a coaxial line as shown in Fig. l(a). The outer conductor of the coaxial line is distorted into an ellipse (b) and finally separated at the extremities of the ellipse to form the strip transmission line shown in (c). One of the ground planes is then removed, leaving a conducting ground plane and a narrow conducting strip separated by a dielectric. Two configurations of the microstrip line were considered in this investigation, Fig. 2. Type (a) is fabricated from a semiconductor slice with the ground plane and top conductor deposited on each side of the slice. The semiconductor slice serves as the die lec-

Jan 1, 1967

By C. C. Henning

IN any line of human activity logical handling requires an amount of attention to each phase that is in keeping with the importance of that phase. In the complex and rapidly changing field of modern ferrous metallurgy it is difficult to allot the proper degree of attention to the various subjects, and it is not surprising that one or more subjects of major importance should for a time be neglected. Bessemer steel is a good example of a neglected subject. It is largely taken for granted, inferior physical quality is assumed for it, and there is a lack of interest in its technical development and commercial application. Availability of supply is limited. In spite of this technical indifference, limited source and lack of commercial exploitation, bessemer steel con-stitutes a large volume of tonnage in daily use. There is a fairly prev-alent idea even among technical people that bessemer steel survives mostly because of low cost and by reason of a dwindling residue of applica-tions sufficiently common to permit of its use. The difference in cost between bessemer and open-hearth steel is governed largely by the relative cost of manufacture of pig iron and the market price of steel scrap. During the past four years there have been long periods of time during which the price of steel scrap was low enough so that open-hearth steel was considerably lower in manufacturing cost than bessemer. As to application, it may be pointed out that thousands of tons of this material in the form of bessemer screw steel are applied for moving parts in automotive and other equipment. Some forging work and considerable heat treating, particularly carburizing, is performed on this grade.

Jan 1, 1935

By Chester Purington

PROBABLY no battleship of any great power save Japan could long remain in. the Pacific Ocean tinder present conditions, were it to depend for fuel supply on the hitherto developed coal or oil resources of any part of the adjoining lands in either hemisphere. This statement does not overlook the important but not inexhaustible oil fields of California, the bunker coals of British Columbia, nor the coals accessible and mined adjacent to Chinese water-ways. For both naval and merchant ships, however, modern practice seems to require high-grade Welsh or Pennsylvania bituminous even at great expense for transportation. Otherwise, we should not see British ships bunkering Welsh coal at Singapore nor the United States establishing a store of Pennsylvania coal at its naval base at Pearl Harbor, Hawaii. Compared with Atlantic coals, the best Miike and Nagasaki (Japanese) bunker coal, the Kailan coal of China, and the Welling-ton and Nanaimo coals of British Columbia, are dis-tinctly inferior, as one can soon learn from the chief engineers on Pacific liners. In addition to the coal used for steaming and bunker purposes, it is of increasing importance that an adequate supply of coking coal for metallurgical purposes should be made available at reasonable prices at industrial centers on the west coast of America, and at Japanese and Chinese coastal cities. The use of Chinese coking coals for smelting the iron of the lower Yang-Tse deposits is by no means so satisfactory as could be desired, while the poor quality. of Japanese coals for coking purposes is well known. If Russia, as seems not improbable, is to become a power on the Pacific in the course of the next few decades, she will doubtless develop an iron and steel industry in the Maritime Province, where an adequate and accessible supply of iron ore will necessitate a supply of coking coal.

Jan 9, 1923

By F. O. Garrabrant

Power is furnished to the Climax Molybdenum Co. by the Public Service Co. of Colorado over two 100,000-volt lines to a bank of three 3333-kva. transformers 100/13.8 kv. These transformers are so designed that with the addition of forced cooling their capacity may be increased 331/3 Per cent at 12,000-ft. altitude. Under present conditions, these transformers are operated at 140 per cent of their rating with forced air cooling. On the secondary side of this bank there is a 15-kv., 1200-amp. Westinghouse oil circuit breaker provided with automatic reclosing relays allowing three successive short circuits before lockout. From this breaker 13.8-kv. power is transmitted to a central switching station (Fig. I) where all circuits radiate to the different operations of the property. Each circuit is protected by a 23-kv., 600-amp. oil circuit breaker with by-pass and isolating disconnecting switches.

Jan 1, 1947

By Helmer Hedstrom

The purpose of this paper is to direct attention to the importance and the usefulness of phase measurements in electrical prospecting for ore, a subject about which virtually nothing has been published. The paper describes a new field method for ore prospecting, the "Turam" method, which makes use of phase measurements, and which has been used with great success for five years. Of the principal geophysical prospecting methods, the gravimetric and magnetic methods determine the direction and strength of the static fields of force of the earth. By seismic and electrical methods, fields of force are applied to the block of ground under investigation. By these methods a third parameter can be measured, besides the direction and strength of the field; namely, the time of arrival of the applied field at the different observation points. This time of arrival has been practically the only parameter measured in seismic work, while in electrical prospecting it has generally not been considered, the measurements having been limited to determination of direction and strength of the applied field. Phase Measurements In the most widely used of the electrical prospecting methods, those using alternating current, the time of arrival of the "electrical vibration" at the different observation points can be carried out as phase measurements. The phase angle measured then expresses, in part of one "vibration," or one cycle, how much the electrical vibrations at the observation point are out of step with those close to the source of the field. A phase lag of 45", for instance, means that the alternating field in the observation point is one-eighth of one complete " vibration," or cycle, out of step behind the field at the source. If the frequency is, say, 500 cycles per second, a frequency often used in electrical prospecting, a phase lag of 45' then means that the time required for the field of force to travel from the source to the observation point is 1/8 ' /500 = 1/4000 sec. Since the phase angle can be measured with an accuracy of a fraction, say one-tenth, of a degree, and the frequency can be considerably higher than 500, it is readily seen that the time of arrival can in this way be measured

Jan 1, 1940

By Helmer Hedstrom

The purpose of this paper is to direct attention to the importance and the usefulness of phase measurements in electrical prospecting for ore, a subject about which virtually nothing has been published. The paper describes a new field method for ore prospecting, the "Turam" method, which makes use of phase measurements, and which has been used with great success for five years. Of the principal geophysical prospecting methods, the gravimetric and magnetic methods determine the direction and strength of the static fields of force of the earth. By seismic and electrical methods, fields of force are applied to the block of ground under investigation. By these methods a third parameter can be measured, besides the direction and strength of the field; namely, the time of arrival of the applied field at the different observation points. This time of arrival has been practically the only parameter measured in seismic work, while in electrical prospecting it has generally not been considered, the measurements having been limited to determination of direction and strength of the applied field. Phase Measurements In the most widely used of the electrical prospecting methods, those using alternating current, the time of arrival of the "electrical vibration" at the different observation points can be carried out as phase measurements. The phase angle measured then expresses, in part of one "vibration," or one cycle, how much the electrical vibrations at the observation point are out of step with those close to the source of the field. A phase lag of 45", for instance, means that the alternating field in the observation point is one-eighth of one complete " vibration," or cycle, out of step behind the field at the source. If the frequency is, say, 500 cycles per second, a frequency often used in electrical prospecting, a phase lag of 45' then means that the time required for the field of force to travel from the source to the observation point is 1/8 ' /500 = 1/4000 sec. Since the phase angle can be measured with an accuracy of a fraction, say one-tenth, of a degree, and the frequency can be considerably higher than 500, it is readily seen that the time of arrival can in this way be measured

Jan 1, 1940

By J. H. Hollomon, J. C. Fisher

THE fundamental problem concerning the fracture of both crystalline and noncrystalline solids is the divergence between the actual and the theoretically computed fracture stresses; the stress required for fracture, computed from the forces between atoms, is many times that actually observed with commercially available materials. Computations have been made1, 2 indicating that the theoretical fracture stress should be from 100 to 1000 times that actually observed. There are other incidental problems that have arisen, perhaps the most important of which is the problem of size effect often observed in the measurement of the fracture stress of non-metallic solids, such as glass. Another effect concerns the relation between deformation and the stress required for fracture. Experiments recently made with pearlitic steels indicate that the tensile fracture stress increases with increasing tensile deformation and decreases with increasing prior compressive deformation. This marked anisotropy of the effect of deformation on the fracture stress is in contrast with the essential isotropy of the flow stress. Early experiments on rock salt crystals by Joffé, et a13 have illustrated the effect of tensile strain in increasing the tensile stress required for fracture. A consistent theory must be constructed that will explain not only the divergence of the measured fracture stress from the theoretical value, the size effect, and the effect of deformation; but will also explain and predict the effects of combined stress, of temperature, of strain rate, and of metallurgical structure. With respect to this last variable, it has now been relatively well established that the carbide particle is the element of structure controlling the fracture of steels. In steels carbide particles vary in shape from plates to spheroids. It has been found that not only does the magnitude of the fracture stress depend upon the size and shape of these particles, but also its dependence upon strain is affected by changes in shape and size of the particles. The precipitate resulting from the age hardening of duralumin also modifies the fracture stress of this alloy. Nonmetallic inclusions greatly lower the fracture stress of all metals. The magnitude of the lowering depends on the size and shape of the included particles. In glass, the major source of the low fracture stress has been fairly conclusively demonstrated by Griffith4 to arise from real flaws or cracks present in the material. He showed that the stress concentration at the end of a defect was of sufficient magnitude to raise the stress at this location to a value comparable with the theoretical strength of the material. If the cracks were reduced in size, Griffith showed that the observed fracture strength increased by virtue of the decrease in stress concentration. He also pointed out that cracks disposed perpendicularly to the applied tensile stress would be more effective in lowering the fracture

Jan 1, 1947

By J. Norman Bulkley

As electrical power is used to a greater extent on the Rand than in any other mining center, it is thought that a short description of the methods used and results obtained may be of interest. In comparing Rand practice with that on other fields, several general factors should be borne in mind: First, the mines are all working on large tonnages of low-grade ore (average. $6.50). The annual crushing rate is about 27,000,000 tons. Second, the mines are all grouped udder the financial and engineering control of mining houses, so that the results of a group, rather than an individual mine, are open for study, and practice follows more uniform lines. Third, coal of fair quality (about 12,000 B.t.u.) can be obtained for $2 to $3 per ton., Good supplies of condensing water are, however, scarce, and have to be carefully stored. Power Supply Power is supplied by the Victoria Falls & Transvaal Power Co., Ltd., and its subsidiary, the Rand Mines Power Supply Co. Both companies, which are practically one from an engineering point of view, operate the following stations, all feeding into the same system.

Jan 2, 1916

By Arthur Gates

INTRODUCTION RITTINGER'S law of the energy expended in crushing is, as roughly stated by Professor Richards,1 that the work of crushing is proportional to the reduction in diameter; or, as I have more fully expressed it: "The work done in crushing is proportional to the surface exposed by the operation; or, better expressed for this purpose, the work done on a given mass of rock is proportional to the reciprocal of the diameter of the final product-assuming that all the mass has been reduced to one exact size, which is only theoretically possible.?2 Kick's law is stated by H. Stadler as follows:3 "The energy required for producing analogous changes of configuration of geometrically similar bodies of equal -technological state varies as the volumes or weights, of these bodies." In other words, the energy expended is porportional to the volume reduction, instead of the diameter reduction. That these two laws would give widely different results may be shown by a simple imaginary case. A ton of 16-in. cubes is broken to 1 -in. cubes at the first operation, and these are broken to 1/16 -in, cubes at a second operation. Since the first operation produces only one-sixteenth as much new surface as the second, the ratio of energy expended in the two operations would be by Rittinger's law as 1 to 16. By Kick's law, since the volume-reduction ratio is the same in both cases, the ratio of energy would be 1 to 1. This discrepancy is great enough to challenge a test by actual experiment, of which there has been, hitherto, but little compared with the amount of argument. The present paper is the record

Jan 9, 1915

By Robert S. Archer, Zay Jeffries

It is about fifteen years since the development in Germany, largely by Alfred Wilm, of the aluminum alloy called duralumin. In this alloy, combining as it does the tensile strength of mild steel with the lightness and corrosion resistance of aluminum, a distinctly new material was presented to the engineering world. Despite the evident usefulness of this material, however, its commercial development has been slow, due in part to the difficulties involved in its fabrication. In view of the potentially great utility of strong aluminum alloys, it seemed desirable to find means of producing such alloys with better fabricating properties, and work was undertaken with this object in the laboratories of the Aluminum Company of America several years ago. This work has resulted in the production of two new types of aluminum alloy of the "strong alloy" class, having distinctly improved fabricating qualities. The knowledge gained has also made it possible to produce alloys of the duralumin type with greater strength and hardness than previously obtained. There have thus been made available some new engineering materials which it is the object of this paper to describe. These alloys, induding duralumin, are fundamentally wrought alloys. Castings of the same compositions heat treated in the same manner give inferior physical properties, particularly as to ductility. The statements made subsequently concerning properties and heat treatment apply to material that has received sufficient working to thoroughly break down the cast structure. The material referred to has, in general, undergone a reduction in section of at least 80 per cent, by mechanical working. It may be mentioned in passing that other compositions have been found that are suitable for the production of the maximum physical properties in heat-treated castings.

Jan 1, 1925

By A. L. Holley

IT has been customary at our opening sessions, for the presiding officer to address you on the general development of one or another of our several professions, or upon some important feature of Mining or Metallurgical Engineering. It is somewhat embarrassing to his successor that our former President, Dr. Raymond, expert as he is in every one of these professions, has been accustomed to keep them all, in their turn, prominently before you. In selecting for this occasion a subject necessarily connected with iron and steel, I have thought that a review of these manufactures, with reference to some of their more pressing needs for improvement, will be more timely than a general or statistical paper. I shall endeavor to confine my remarks to a few specific defects of practice and management, and to their equally specific and more or less developed remedies. That serious defects exist ; that they must be remedied ; that the manufacture is indeed already on the verge of transition, will be generally admitted. But it cannot be revolutionized all at once, however desirable the technical results might be, for that would bankrupt the business at large. We cannot afford to pull down and rebuild all our blast-furnaces that do not make a ton of pig iron with 25 cwt. of fuel ; nor to replace all our hand-puddling furnaces with revolving ones, even if we could select the best revolver. Although the soft steels promise to supplant iron for most structural purposes, there are neither money nor present market to warrant all at once replacing our iron works, or half of them, with steel works. Since, then, these manufactures can neither standstill nor be suddenly metamorphosed, their managers are saying to one another " We must feel our way into larger development ; we must work gradually into better practice; we must improve a little at a time." * President's address on the opening of the Cleveland meeting.

Jan 1, 1876

By Danforth R. Hale, R. E. Blair

Minerals for electronic and optical uses divide easily into two sections: (1) quartz and (2) minerals other than quartz. Quartz Quartz, having a great usefulness discovered by the radio communication enthusiasts about 1918, has become a subject of amazingly expanded interest in the US over the past decade as a man-made mineral and a multimillion dollar crystal-growing business. An economic summary of the commercial growing of quartz crystals has a place in a handbook directed to the mineral engineering industry when it is remembered that quartz crystals have long been an important commercial mineral, and that the raw material for "cultured quartz"-that is to say, quartz crystals grown through the ingenuity of man-is still natural quartz. Nearly all the natural crystals come from Brazil. The larger pieces which meet rigorous standards of quality are used for electronic and, to a lesser extent, optical components. Smaller pieces and fragments are used for vitreous silica. The need for high quality material in quantity led to US government-sponsored research programs in the 1940s that have resulted in the factory growing of beautiful crystals of prescribed shape, size, and quality. The development of the cultured quartz crystal is typical of man's success in adapting the product of the mine to increasingly sophisticated uses. A remarkable achievement perhaps, but foreshadowed by experiments in 1908 by Giorgio Spezia (1908), an Italian geologist studying the relative effects of temperature and alkaline environment on the solubility of quartz. Modern radio equipment is most often controlled as to frequency by the presence in the circuit of a separately added "crystal"-the 1918 discovery responsible for the existence and growth of the quartz industry. The "crystal" is quartz, but this component is a carefully oriented and prepared slice from a crystal, but not a crystal as recognized by a rock hound or seen in a museum. How quartz operates to control frequencies is not a proper subject for a handbook on industrial minerals, and references should be consulted (Cady, 1964; Mason, 1964). Quartz belongs to that class of materials called dielectrics: those that do not conduct an electric current but permit electric fields to exist and act across them. Quartz shows the "piezoelectric effect," which means that when a quartz plate is mechanically deformed against its natural stiffness, one of its surfaces becomes negatively charged, the other, positively charged. When the plate is released from the stress quickly, the charges disappear as the plate regains its original shape, but because of mechanical momentum the plate deforms in the opposite direction (to a lesser amount) and the surfaces correspondingly become charged in the opposite direction. By coating the two surfaces thinly with metal and attaching flexible wires, these charges may be brought into an electronic circuit. If the surfaces are suddenly electrically charged by movement of current through the wires, the "converse piezoelectric effect" occurs -the plate deforms. Carry the thought further and it is realized that an alternating current flowing through the wires responds to the mechanical oscillation of the plate and is keyed to this oscillation. By controlling the thickness of the plate its mechanical vibration frequency can be varied through a wide range. One type of quartz plate, called the AT-cut, having a precisely defined orientation with respect to the crystallographic axes of the crystal, vibrates on a microscopic scale much as a book would deform when placed flat on a table and the top cover moved parallel back and forth with the hand. There are at least 17 other orientations which have been studied, some of

Jan 1, 1983

By J. Moore Samuel

Before the year 1909, no measurements of dust losses and flue gases had been made at the Copper Queen Reduction Works, at Douglas, Ariz. At that time the "unaccounted" loss of the smelter had reached a figure that drew attention to the possibility of large stack losses. The measurement of dust losses had not been studied much at that time, and estimates of dust losses, with a few exceptions, were the results of tests by what has been termed '(chemical methods," that is, the aspiration and filtration through cotton, wool or some similar medium of a few liters of gas, the dust being weighed on a chemical balance, and the volume of gas computed from the volume of aspirator water. The possible error of this method is enormous, and the probable error much too large for reliable results. Since the object of these tests was to discover not only the extent of the dust losses, but also the possibility of profitably reducing them, it was decided that the method adopted must have the following characteristics: 1. The sample of gas taken for filtration must be representative of the whole volume of gas, that is to say, it must have the same dust content. This condition will be fulfilled in all cases if the gas sample is drawn off without change of rate of flow. Then it will contain the same proportion of entrained or suspended particles of dust as the original gas. In the case of flue gases which contain only fume, at a temperature above or near the sublimation point, this condition need not be adhered to since the fume will not behave as entrained particles, but more nearly as a true gas. Consequently the gas sample in this case only may be drawn off at any rate of flow. 2. The gas sample taken must be large enough (a) to yield sufficient dust to permit of accurate chemical and physical examination; (b) so that the ratio of the total volume of gas passing through the flue to the volume of gas sample taken shall not be too large.

Jan 1, 1917

By G. E. McElroy

Though air jets occupy only a minor role in the ventilation of mines and other enclosures, their importance in this respect is greater than is commonly recognized and may be considerably increased as our conception of their modes of operation becomes clearer. The object of this paper is to discuss some of the ways in which air jets are involved in mine ventilation and some possible applications to the ventilation of mines and other enclosed spaces. The mention of air jets ordinarily suggests the use of some form of an air injector, such as the Venturi blower occasionally used for auxiliary ventilation in mines, or the Saccardo (injector) system used to a limited extent for ventilating railroad tunnels. Actually, the term covers such common phenomena as the discharge of air from fan pipes and coal-mine line brattices, and even from smoke stacks and fans. A knowledge of the general mode of air entrainment by jets also helps to explain certain phenomena—some mine-gas explosions, for instance—that otherwise would remain obscure. Jet action has been involved in three recent series of Bureau of Mines experi-ments in which the author has participated: experiments on fan-pipe discharge, On the dilution of gases discharged from a stack and On the ventilation of a ship's hold. Available data on the discharge of jets into large openings and on the design and performance of air injectors have been analyzed in considerable detail and supplementary experiments are planned for after the war. The results of the fan-pipe experiments have been combined with the analyses of data on jet discharge into large spaces, and have been published.' The results of the stack-gas dilution tests, which refer to a jet discharged into a crosswind, have also been published2 and a paper on the design and performance of injectors has been prepared for publication.3 These technical experiments and analyses form the background and the documented evidence for the following nontechnical discussion of the use of air jets in mine ventilation. Jet Characteristics The jets commonly encountered are those in which the air is in turbulent— as opposed to laminar, or streamline-— motion. The characteristics under discussion apply only to such turbulent jets and have their basis in theories of the mixing of turbulent air currents. Such jets have basic characteristics that are present, though variable in form, regardless of whether the jet expands freely in space, whether the expansion is limited by adjacent walls, or whether the jet propels air through a flow circuit. They expand at definite angles and entrain the surrounding air, even though the entrained air must be obtained by recirculation of their own air streams. As the quantity of air in motion in the mixed stream increases, the average velocity of the stream decreases.

Jan 1, 1946

By J. David Lowell

For the first time in several years, Chile is again opening its doors to foreign investment. In its new investment code, the Chilean government has announced its willingness to become a partner in joint Chilean-foreign projects for a number of government-controlled porphyry copper deposits at the developed, semi-developed, or prospect stage; and, that it will allow privately owned deposits or deposits discovered by new exploration to be developed with up to 100% foreign ownership. Three deposits of particular interest are: El Abra, with at least 300 million mt of +100% Cu; Los Pelambres, with at least 428 million mt of 0.78% Cu and 0.03% Mo; and Andacollo, with 350 million mt of 0.70% Cu and 0.015% Mo. (El Abra is almost entirely government- controlled; but both Los Pelambres and Andacollo are mostly under private ownership.)

Jan 11, 1974

By R. R. Webster, H. T. Clark

The side-blown converter has been investigated as a possible commercial process for the production of low nitrogen steel. During this work, two converters of 3-ton and 22-ton capacity were operated on a pilot plant basis for a total of 214 heats. The steel made in these converters was low in nitrogen and possessed good cold working properties. Some problems of converter operation remain to be solved. IN plants operating with a high iron capacity, sev-eral different refining methods are used in the conversion of the molten pig iron to steel. These include various ore practices in stationary and tilting open-hearths, the duplex process employing the Bessemer converter and open-hearth, and the Bessemer process. At J&L, a considerable part of the iron produced is handled by the Bessemer process, either alone or in conjunction with duplexing, and therefore an appreciable portion of the steelmaking research effort has centered about the method. This paper covers research work on the development of the side-blow converter for the commercial production of low nitrogen ingots and includes descriptions of the operation of a 3-ton and a 22-ton experimental converter at the Aliquippa Works. The refining of iron to produce steel requires the removal of a large portion of the carbon and silicon and the control of manganese, phosphorus and sulphur which are present in the iron in varying amounts. The first large-scale means of refining iron was the acid Bessemer process which was brought into use almost 100 yr ago. This method, using compressed air as the refining medium, accomplishes substantially complete removal of carbon, manganese and silicon. Phosphorus and sulphur are not affected but, by choice of an iron composition sufficiently low in these elements, a commercial product can be produced. Since the process will handle large tonnages rapidly, operates without external fuel and with a minimum of additional equipment, it quickly became the major tool in the early expansion of the steel industry. Later, the basic open-hearth process, by affording control of phosphorus and sulphur and by consuming the large quantities of steel scrap that were becoming available, forced the acid Bessemer process into a secondary position in the industry. During the past two decades the demand for steel to be used in cold forming and drawing operations has gradually increased. Bessemer steel, because of its work hardening and aging characteristics, is not as suitable for these applications as basic open-hearth steel, consequently the decline of the process was accelerated. More recently, because of changing economic conditions, this long range trend appears to have been arrested or perhaps reversed. Ingot production data for recent years furnishes only an incomplete picture of the importance of the converter in the American steel industry; open-hearth furnaces utilize large tonnages of blown metal for which no published statistics are available. Metallurgical Aspects The fundamental difference between Bessemer and open-hearth steels apparently lies not in the method of manufacture but, rather, in the differences in chemical composition of the two steels. It is further believed that the principal features distinguishing Bessemer from open-hearth steel are the higher nitrogen and phosphorus contents of the former. Evidence supporting this position is supplied by tests on laboratory induction furnace heats that were made to contain varying amounts of phosphorus and nitrogen but were otherwise similar to normal low carbon silicon-killed steels. Fig. 1, 2 and 3, summarizing the test results, are taken from G. H. Enzian's paper titled, "Some Effects of Phosphorus and Nitrogen on the Properties of Low Carbon Steels."' Fig. l indicates that phosphorus has a marked effect on the cold work embrittlement of steel as shown by the work brittleness test of Graham and Work.' In the low nitrogen steels, which as a group have the better cold working properties, the effect of phosphorus variations is the more pronounced.

Jan 1, 1951

By R. R. Spencer, C. A. Campbell, R. J. Marcotte, A. S. Kromer, P. H. Ostlender

Calumet Div. of Calumet & Hecla Inc. is engaged primarily in mining, milling, and smelting the native copper ores of northern Michigan. The copper occurs in fragmental tops of lava flows and in certain interbedded felsitic conglomerates of Pre- Cambrian age. The most famous native copper ore- body in world history is the Calumet conglomerate, which outcrops between the villages of Calumet and Laurium for a distance of about 2 miles. The Osceola lode parallels the conglomerate lode and is mineralized for about 3 miles. Horizontal distance between the two is 750 ft. In 1932 the price of copper dropped to 54 per lb. Coupled with the high cost of obtaining copper from extreme depths, this low price made the venture un- profitable, and the mining unit was abandoned. After the shaft pillar copper was removed from several of the conglomerate shafts in a retreating operation, the mine was allowed to fill with water. In post-depression years, when the price of copper stabilized at about 12¢, Calumet Div. found it profitable to operate its remaining mines on other lodes, as well as its tailings reclamation plants.

Apr 1, 1956

By Ralph Hayden

I. INTRODUCTION. IN the wet concentration of ores there is always a certain amount of very fine material with which to contend, and which invariably carries such quantities of value that the treatment of it is worth while; commercially. This fine material usually contains that portion of the ore which hinders the separation of the mineral values: namely, the colloidal material resulting from the decomposition of certain constituents of the ore. The object of this paper is to show what efforts have been made to solve the slime problem as it occurs in the concentrator of the Washoe

Jan 8, 1913

By H. S. Chiang, S. S. Peng

INTRODUCTION Underground coal mining disturbs the original in-situ conditions which induces a series of strata activities and results in creating "mine pressures," the source of all ground control problems. Adoption of self advancing powered supports in modern longwall mining adds a new dimension to ground control problems and thus research. Roof stability, in general, refers to the integrity and stability of the immediate roof which is measured by the maximum exposed area and time duration without support. There are many factors that con- tribute to roof stability problems. In addition to mining height, rock property and stratum components and caving angle of the immediate roof, characteristics of joints and fissures and their degrees of development, faults and underground water, the operational techniques also play a very important role. This paper summarizes these operational techniques and methods of controlling stable and unstable roof. CLASSIFICATION OF THE IMMEDIATE ROOF There are many ways of classifying the roof (1). For practical purpose, the immediate roof in this paper is divided into three groups, i.e. unstable. medium stable and stable. Unstable Immediate Roof It has the following features (1) It consists of weak or soft carbonaceous shale, black shale, clay shale and well-jointed or fractures sandy shale

Jan 1, 1983

By Mark D. Tabak

Measurments of the transient photoconductivity in fillns of amorphous selenium with blocking- contacts haue been used in studying the transport properties. The results shozu that the transport of free carviers cannot be explained in terms of a model using bulk trapping. Measurments of the photocurrent-applied field characteristic as a unction of sample thickness do not pvoduce the scaling lau,s approps-iate lo a range-limited model. THE investigation described here was undertaken to explore the mechanisms of transport in amorphous selenium films. These films are used in xerography, where a photoconductor is charged electrostatically and then exposed to light to form a latent image. The sensitivity that one can expect when operating in this mode is directly related to the transport properties of the photoconductor material. The study of photoconductivity at high fields in insulating materials is often complicated by contact effects. Injection from the contacts can easily mask the fundamental transport processes that are being studied. A technique is described in this paper that allows a study of photoconductivity and transport processes in amorphous selenium films without the complicating effects introduced by contacts. Accordingly, the samples are prepared using insulating films between the sample and the metal electrodes, where the electrodes are capacitively coupled to the surfaces of the sample under study. A transient measurement is performed with pulsed light, and the photocurrent measured near the beginning of the pulse before the field is distorted by polarization at the blocking elec- trodes. A similar method has been described by Manyl using pulsed electric fields in studying the high field transport in insulating cadmium sulfide. EXPERIMENTAL It is possible to eliminate undesirable contact effects and maintain uniform high fields across the sample by using blocking electrodes and measuring the current-field characteristic under transient conditions. The sample configuration is shown schematically in Fig. 1. Each of the gold electrodes is separated from the amorphous selenium film by a layer of insulating plastic (Formvar) approximately 2000~ thick. The electrode on the front surface is semi-transparent to allow illumination of the sample. The whole configuration is mounted on a KEL-F substrate, which is a transparent insulating plastic having a thermal expansion coefficient that allows low-temperature measurements without cracking the selenium film. Fig. 2 shows a block diagram of the measurement apparatus. Light was obtained from a 450-w Xenon arc lamp, the intensity of which was controlled by stainless-steel screen filters and monitored by a pho-tomultiplier which was calibrated periodically against a thermopile. A camera shutter operated at 1/200 sec provided the light pulse and a synchronized signal to the oscilloscope. The photocurrent transient is ob-served with a high-speed picoammeter (response time of 1 msec) the output of which is displayed on an oscilloscope. The applied voltage is constant throughout the transient measurement. The selenium films were prepared by evaporation of four 9's pure selenium shot supplied by Canadian Copper Refiners. Spectrographic analysis showed about 1 ppm of Te and Fe, 5 ppm of C1, and 0.05 ppm

Jan 1, 1968