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By G. D. Rieck, M. M. P. Janssen

Chemical diffusion coefficients and heats of activation for diffusion in the NizAh fy), NiAl (6), and Ni3A1 (E) intermetallic phases and the solid solution of aluminum in nickel (( phase) were calculated from layer growth experiments. No finite diffusion coefficient for the NiAl3 ((3) inter metallic phase could be calculated. The values of the diffusion coefficients are dependent both on the method of calculation and the type of diffusion couple. The heat of activation for diffusion in the y phase was found to be 47 kcal per mole in the temperature range oj 428" to 610°C. Heats of activation of 41, 12, and 48 kcal per mole were found for diffusion in the 6, E, and ( phases, respectively , in the temperature range of 655" to 1000°C. Experiments with markers in the diffusion zone demonstrate a very pronounced Kirkendall effect. It appears that only aluminum atoms take an active part in the diffusion process during the formation of the 0 and y phases at temperatures of about 600°C. During the formation of the 6, E, and < phases at higher temperatures only nickel atoms are moving. It is suggested that the great stability of the intermetallic compounds in the Ni-A1 system governs the Kirkendall effect. SOME factors controlling layer growth during inter-diffusion in the Ni-A1 system (phase diagram, see Fig. 1) were studied by Castleman and Seig1e.l&apos;~ They found the NiA1, ((3) and NiAl3 (y) intermetallic compounds to appear in the diffusion zone of Ni-A1 couples at annealing temperatures of 400" to 625°C; the NiAl (6) and Ni3A1 (E) intermetallic compounds appeared in y-Ni couples at annealing temperatures of 800" to 1050°C. These authors carefully examined metallographically Ni-A1 couples after 340 hr annealing at 600°C. Besides the (3 and y phases they found very thin layers of the 6 and E phases. ~n~erman~ and Castleman and Froot4 observed a much more rapid growth of the 5 and E phases at 600°C in Ni-A1 couples in case a crack was present at the /3-A1 interface. Numerous layer thickness measurements carried out by Castleman and Seigle on the y phase prove that the layer growth of this phase obeys the parabolic law after a certain transient period. From this they concluded that the layer growth of the y phase is controlled by volume diffusion. The growth of the 13, 6, and E phases appeared to be volume-diffusion-controlled also. The authors estimated that at 600°C and at atmospheric pressure Dp was 1.8 x lo-"ll sq cm per sec, D, 9.1 x 10" ™ sq cm per sec, Qp 27 kcal per mole, and Qy 31 kcal per mole. The present work was carried out to obtain more quantitative data about the kinetics of growth of the phases of the Ni-A1 system and the reactions that occur during the formation of these phases. Because in this system the diffusion process results in the formation of several distinct intermetallic compounds, the current term reaction diffusion is used in the title of this paper. In order to obtain layers of the fl phase compound of uniform thickness, a new technique for preparing diffusion couples was developed. The kinetics of growth of the y phase in 6-Al, E-Al, and Ni-A1 diffusion couples was studied at different temperatures. The kinetics of growth of the 6, c, and ( phases in Ni-y, Ni-6, and Ni-c diffusion couples was also studied at different temperatures. The calculation of the diffusion coefficients Dp and Dy by Castleman and Seigle are critically considered in this paper; by means of a revised method of calculation more reliable val-ues of , and Dg were found. These values are in good agreement with the values of the diffusion coefficients obtained by the method of Boltzmann-Matano. From the temperature dependence of the diffusion coefficients the heats of activation for diffusion were calculated by means of an Arrhenius-type equation. The investigation of the Kirkendall effect has been used to obtain information about the ratio of the intrinsic diffusion coefficients of the separate atoms5 and the mechanism of diffusion. Moreover porosity as a result of a distinct Kirkendall effect would be of practical importance in connection with the bonding of diffusion coatings. The analyses of the diffusion couples were carried out by metallographic methods. The values of the concentrations at the phase boundaries and the concentration profile in each of the phases, which are needed for the calculation of diffusion coefficients, were obtained by electron-pro be X-ray microanalysis. EXPERIMENTAL PROCEDURE A) Materials for Diffusion Couples. The intermetallic compounds 6 (50 at. pct Ni) and E (74 at. pct Ni) were prepared from the pure metals by high-frequency induction melting in argon atmosphere. Use was made of aluminum wire (99.99 wt pct Al) and nickel sheet (99.95 wt pct Ni). The 6 and E phase melts and the nickel shiet (thickness 0.1 and 0.5 mm) used for preparing diffusion couples were annealed for 64 hr at 1200°~ for homogenization and grain coarsening (final crystal size 1 to 3 mm). composition and homogeneity of the intermetallic compounds were checked by mi-crohardness measurements and X-ray diffraction. From the 6 and E phase melts discs of 0.5 mm thickness were prepared by means of a water-cooled rotat-

Jan 1, 1968

By Thomas L. Watson

A part of the field-seasons of 1900, 1901 and 1902 mas devoted by the writer to a study of the manganese ore-deposits of Georgia. A report embodying the results of this study is rapidly nearing completion, and when finished it will be published as a bulletin of the Geological Survey of Georgia. I believe, however, the importance of these deposits warrants a separate and earlier publication than that made possible by the Survey, in which the more important results of the study are briefly set forth. It is principally for this reason that the present paper has been prepared. Previous Work.—Some of the more important deposits of manganese occurring in the Paleozoic area of Georgia were studied to some extent previous to 1890 by Dr. Penrose;t and again in the early nineties by former State Geologist, J. W. Spencer. In a recent paper published in the Transactions, on the " Geological Relations of the Iron-Ores in the Cartersville District, Georgia," Dr. Hayes briefly mentions the manganeseores of the same district. Distribution of the Manganese-Ores.—Georgia is divisible into three geologically-distinct areas which, named in order from southeast to northwest, are (a), the Coastal Plain; (b), the Crys-

Jan 1, 1904

By L. Albert, A. M. Cameron, J. W. Gullick

International Nickel has 15 operating mines in Canada, and. 3 mines which are being maintained on a standby basis. Annual production is about 20 million dry short tons of ore, most of which is from underground mines, the remainder from open pit mines. Although some of the underground mines are served by ramps for trackless vehicles, most men, materials and ore are hoisted in vertical shafts. In addition to shafts and raises for ventilation and service purposes which are not equipped with hoisting plants, there are now 28 vertical shafts at Inco mines served by 47 hoists. Of these, 22 shafts and 36 hoists are located in the Sudbury District of Ontario, one shaft and two hoists are at the Shebandowan mine in Western Ontario, and 5 shafts with 9 hoists are located near Thompson, Manitoba. This paper describes the components of Inco hoisting plants-which have been applied at different times and under different conditions, and indicates the rationale for the various designs. Some engineering and maintenance practices, considered advantageous, are also described. MINE SHAFTS Many of the shafts sunk in the early days of the Sudbury District, on what are now Inco properties, were inclined shafts. Of the identifiable shafts sunk between 1885 and 1920, thirteen were inclined and at least four were vertical. Since 1920, thirty vertical and two inclined shafts have been sunk. All of the inclined shafts have been abandoned for hoisting purposes but the majority are still in use as service or ventilation ways. Shafts at Thompson- and Shebandowan are all vertical. The vertical shafts range from 2 or 3 compartment exploration and development shafts to 6 compartment shafts for ore, man and material hoisting. They vary in depth from 1,050 to 7,137 feet and in addition to hoisting compartments all contain manway and service compartments. Prior to 1948, unlined rectangular shafts with timber sets and guides were used. The rectangular cross-section was favoured since the rock is competent, the shape compatible with timber set framing, and since available shaft space could be used efficiently. Resistance to air flow was not of prime importance. Concrete linings were introduced for the first time at the Creighton No. 7 Shaft which was collared in 1948. All major shafts since that date have been concrete lined. Vertical set intervals were increased in steps, with the introduction of structural steel sets secured to the concrete linings. Whereas 7 foot set intervals were used with timber framing, this increased to 10 feet 6 inches with steel sets and more recently to 15 feet with steel and steel backed wood guides. With the advent of deeper shafts, or shafts which are expected to be deepened, the trend is to circular concrete lined shafts. The majority of shaft guides in service are of select Douglas Fir. This practice commenced as a component of timbered shaft design but continued as a

Jan 1, 1975

By Dorsey A. Lyon, Robert M. Keeney

Page I. Introduction..........234 I1. Chemistry oF Copper Smelting...235 1. Native Copper Ores.......235 2. Oxide and Carbonate Ores....235 3. Sulphide Ores.......236 (a) Elimination of sulphur ...236 III. Reverberatory Copper Smelting...237 IV. Substitution of the Electric Furnace for the Reverberatory Furnace..................... 238 V. Smelting of Fine Michigan Native-copper Concentrates in the Electric Furnace.................. 239 1. Conclusions.................240 VI. Proposed Process for Electric melting of Fine Native-copper Concentrates.................. 241 VII. OrdINary Copper Blast Furnace &apos;Smelting......... 245 1. Prerequisites.................. 245 2. Losses .................... 247 VIII. Experimental Data on the Electric Smelting of Raw Sulphide. Oxidized and Carbonate Ores............. 248 1. Vattier&apos;s experiment................ 248 2. Wolkoff&apos;s experiments................ 249 3. Experiments of Stephan.............. 250 (a) Conclusions of Stephan ............ 251 IX. Smelting of Sulphide Ores in the Electric Furnace...... 251 1. Ores Treated.................. 252 2. Conclusions................... 253 X. ELectric Furnace vs. the Reverberatory Furnace and Blast Furnace as a Melting Agent.............. 253 XI. Smelting of Sulphide Ores without Roasting or Partial Pyritic Smelting............254 XII. The Electric Blast Furnace vs. the Copper Blast Furnace for Partial Pyritic Smelting.......259 1. Metallurgical conditions......259 2. Mechanical considerations......259 3. Comparison of costs.......260 (a) General considerations .....260 (b) Cost of plant........260 (c) Amount of electrical energy...260 (d) Cost of smelting.......261 (e) Cost of electrodes........262 XIII. The Use of the Electric Furnace in the Smelting of PyRITIc ORES : 262 XIV. Summary...................... 264

Jan 1, 1914

By AIME AIME

JOHN ROY THOENEN, supervising engineer of the non-metal mining section of the U. S. Bureau of Mines, was one of the founding fathers of the Industrial Minerals Division. For the first three years of its existence, through 1937, he was its Secretary-Treasurer, and during 1938 serves as its Chairman. Jack was born in Ithaca, Mich., No\,. 8, 1886, attended high school at the Soo, and then spent a year and a half at Michigan State. Apparently this was when the mining bug bit him, for he set out for the Michigan College of Mines. After leaving Houghton in 1907 he tried the motion? picture business for a year and had he stuck to it might have been living in a Hollywood palace by now.

Jan 1, 1938

* A demonstration pipeline for transporting coal will be constructed by Pittsburgh Consolidation Coal Co, at the Georgetown strip-mining operation near Cadiz, Ohio, The 12-in., 17,000-ft line, special crushing and preparation equipment, and pumps especially designed for the operation will cost about $550,000. A slurry of fine coal and water will be fed into the line and moved through it under pressure. * Sulphur resources in the U.S. are being rapidly exhausted with no new major deposits being found, This common mineral may become one of the most strategic items during the next five years. Recovery of sulphur from pyrites is being considered in case of an emergency. Already the British have adopted stringent measures to conserve sulphur supplies.

Jan 3, 1951

By Henry Tobelmann

THE location, mode of occurrence of ore, and preliminary tests leading to the development of the present leaching process and the building of the present plant on the property of the New Cornelia Copper Co. at Ajo, have been described in previous papers presented to the Institute and in the, discussions thereof.1 It is sufficient to say that these tests began early in July, 1912, and were continued to the close of January, 1916; that small tests at Douglas were followed by the construction of a 1-ton plant at the mine; and this was followed by the operation of a 40-ton plant for 14 mo. In all about 15,000 T. of ore were treated experiment-.

Jan 2, 1919

By M. H. Merriss

IN THE last few years, there have been developed at the plant of the Nichols Copper Co., Laurel Hill, Borough of Queens, New York City, improvements in electrolytic copper refining by the series system that have materially increased the flexibility and economy of that system. The purpose of this paper is to discuss, as of interest to refiners and to those who have copper to refine, as well as to the engineering profession in general, the changes that have taken place resulting in wider application and increased efficiency of the series system. Copper is electrolytically refined in two ways, which are spoken of as the "multiple system" and the "series system." In both systems, the electrolytic tanks are in series electrically. In the multiple system the electrodes in a single tank are in multiple or in parallel, thus: In the series system, the electrodes in a single tank are in series, thus: There are two important adaptations of the series process, one represented by the series electrolytic tank room at the Baltimore Copper, Smelting & Rolling Co., Baltimore, Md., and the other by that of the Nichols Copper Co.&apos;s plant. At Baltimore, the anode is rolled to perfect

Jan 6, 1925

By R. J. De Angelis, J. B. Cohen, A. Nelson

In this note several recent results on twinning in copper shock-loaded with planar shock waves will be presented and the role of the twins in recrystalliza-tion will be discussed. The twinlike markings first observed in shock-loaded copper by smith1 were identified as twins by De Angelis and Cohen.2 This identification has been confirmed by others.3 In Ref. 2 it was also shown that there is an orientation dependence for twinning at low shock pressures, such that twins in a crystal loaded in [lll] form in the rarefaction or tensile wave but in

Jan 1, 1967

By James M. Riddle

INTRODUCTION Block-caving mines are generally large operations. Calculating the quantity and value of mineral present and determining the economic limits to mining are complicated processes requiring much time and effort. If these processes are to be worthwhile, they must be accurate and reliable. Success in planning may increase the economic returns significantly. Since capital investments in block-caving mines are generally quite large, and development may span several years, quicker and more accurate methods of mine layout are very worthwhile to the mining industry. The purpose of this study is to develop an approach to the evaluation and layout of block-caving mines. The study included development of a simple approach to modelling ore reserves and a rapid, dynamic programming solution for optimum ultimate mining limits. TRADITIONAL APPROACHES TO BLOCK-CAVING MINE LAYOUT General discussion of techniques of calculating and valuing ore reserves can be found in the literature, (1-4). Mining limit approaches have been investigated by many and follow five general methods: 1, Moving cone method (5) 2. Graphroriented technique (6,7) 3. Dynamic programming technique (7,8,9) 4. Network flow method (10,11) 5. Pillar method (12) Of these investigations, only two were developed for underground mining applications, those of Sharp (9) and Riddle (11).

Jan 1, 1977

By Allen L. Hatch

A survey of all phases of the world&apos;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&apos;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&apos;s and 1960&apos;s.

Jan 1, 1970

By Charles R. Keyes

PAGE I. Introductory............ 140 II. Location and History...........140 III. Surface-Relief of the District....... 141 IV. General GeoloGic Features........ 142 1. Main Relationships and Map....... 142 2. Résumé of Geologic History..143 V. Geologic Formations Represented...144 1. Broader Considerations......... 144 2. Geologic Section.......... 145 3. Nomenclature.......... 146 4. El Pasan Limestones..146 5. Santa Rita Limestone.... 146 6. Silver Shales........... 147 7. Bella Shales........... 147 8. Berenda Limestone..147 9. Grande Limestone... 148 10. Lake Valley Limestone........ 148 11. Sierra Limestone.......... 149 VI. Unconformities........... 149 VII. Geologic Structure.......... 150 1. Main Characteristics......... 150 2. Folding........... 1.50 3. Faultings........... 150 4. Relations of the Eruptives...153 VIII. Geologic Relations OF the Ore-Bodies...... 154 1. Governing Factom......... 154 2. Position.......... 154 3. Relations to Foldings...155 4. Relations to Lines of Dislocation... 15.5 5. Relations to Present Surface.Relief..156 6. Relations to Eruptive Rocks...157 7. Relations to Lithologic Nature of the Rocks.... 158 IX. MINERALOGIC CHARACTER OF THE ORES...... 158 X. Origin of the Ore.Deposits..159 1. General Statement......... 159 2. Original Source of the 0re.Materials...160 3. Contact-Metamorphism of the Region... 161 4. Process of 0re.Concentration..162 5. Lowering of Ground-Water Level..162 6. Formation of Cerargyritic Ores...163 XI. Recapitulation........... 168

Jan 1, 1909

By D. Dever, E. S. Fisher

Measurements of the temperature dependence of the elastic moduli in single crystals of hep ruthenium, rhenium, cobalt, dysprosium, and erbium were carried out for various temperature ranges so as to investigate the correlation, suggested by prior work, between the shear anisotropy ratio, A = C44/C66, and the occurrence of the hcp — bee phase transformation. These measurements confirm the suggestion that A has a positive temperature dependence in that group of hcp metals that undergo thermally induced transfornzations to the bee structure and a negative or zero temperature dependence in the other hcp metals. It appears, from indirect evidence, that the hcp -fee transformation in cobalt is preceded by a highly negative temperature dependence of A. These results indicate that elastic anisotropy is an important factor in determining the temperatures at which martensitic phase transformations occur. Two possible roles for elastic anisotropy are proposed: 1) the shear-modulus ratio within the habit planes must be nearly similar for the two phases and 2) a large anisotropy decreases the stress necessary for the movement of the transfornzation dislocations. FUCHS&apos; calculations of the elastic moduli in the alkali metals have shown that the high shear-anisotropy ratios, c/c&apos;, in certain bee metals and alloys are the result of large negative contributions to c&apos; = (c11 - c12)/2 arising from the nearest-neighbor repulsive forces.&apos; On this basis, and following Zener,2 the association between high c/c&apos; ratios and the martensitic phase transformations that occur upon cooling certain bee metals is explained as a unique characteristic of the bee structure. Recent measurements of the elastic moduli in hcp titanium and zirconium show, however, that a high elastic anisotropy also exists in these hcp structures at the temperatures at which they transform to bee upon heating3. If there exists a direct and consistent correlation between the elastic anisotropy in close-packed structures and the occurrence of transformations to the bee phases then there is evidently a need to re-examine the conclusions of Zener theory. Elastic anisotropy may also be the result of the effects of temperature on the stability of the low-temperature close-packed structures or it may play an important role in the mech- anism of the martensitic transformations. The present measurements were aimed at establishing the phenomenological correlation between elastic shear anisotropy in hcp structures and the thermally induced hcp —bee transformations that occur in the majority of the twenty-three hcp metals, as shown in Table I. Prior to the present work the temperature dependence of the anisotropy ratio, A = c44/c66, was known at various temperatures for nine of the metals listed. The data showed a negative temperature dependence of A for cadmium, zinc, magnesium, and cobalt, which do not transform to bee, and a positive temperature dependence of A for thallium, zirconium, titanium, hafnium, and yttrium. The correlation was, however, ambiguous in that these two groups of metals are also separated with respect to the c/a ratios as noted in Table I. There remained the possibility that the temperature dependence of A is a function of c/a and not consistently associated with the transformation. The measurements of the elastic moduli in rhenium and ruthenium, in which hcp —bee transformations do not occur, were needed to help decide this question. The studies of dysprosium and erbium were undertaken to determine whether the correlation holds for the heavy rare earth metals.

Jan 1, 1968

By George C. Stone

AS most of you probably know, Australia has had many strikes. The two places that had the worst reputation were the Broken Hill mines and Port Pirie, where the smelter was located. About four or five years ago, the smelter changed hands. The new proprietors - immediately endeavored to get on better terms with the men and made such progress in that respect that, the men came to them and said, "There is no use giving us any more money. You have just raised our pay one- bob a day, but the store-keeper and the boarding-house keeper have raised their prices. The boarding housekeeper raised our board three bob a week and the storekeeper took the rest of it and we are no better off." Learning that what the men needed most was firewood wood the company bought the wood on a tract of ground across Spencer&apos;s Gulf and- sent men over to cut it. The wood was brought to the works and given to a man to cut up. He thought he had an easy job and loafed, but when the committee representing the men discovered that his loafing added to the cost of &apos;the wood, it promptly disciplined him and made -him work as he had never worked before. The next question that arose was the distribution of the wood. The committee got bids from several cartmen whose prices varied from about two to five shillings. It gave the work to the next to the lowest bidder. The fact that if delivering the wood cost more, the user would have to pay for it, was an entirely new idea to the men.

Jan 1, 1920

By Hugh Rose

The properties of the company lie within the Pachuca district, State of Hidalgo, Mexico, connected by three railway lines with Mexico City, 55 miles southwest, and by two lines with Vera Cruz, 250 miles southeast. The ores were formerly divided by sorting into two classes, smelting and milling, the former averaging about 2 oz. gold and 335 oz. silver, the latter 0.12 oz. gold and 23 oz. silver. The smelting ores were sold to custom plants, principally the American Smelting & Refining Co. at Aguascalientes. The milling ores were treated by the patio process at the Guadalupe Hacienda, at Pachuca. This patio was probably the largest in existence at the time and continued in active operation up to March, 1910. In January, 1910, the mines and patio were sold to English interests, represented by Camp Bird Limited. Two new companies were formed, the Compania de Santa Gertrudis, S. A., to operate the mines, and the Compania Beneficiadora de Pachuca, S. A., to build and operate a custom cyanide milling plant. (Pig. 1.) Geology The historical geology of the Pachuca district is described by Fred J. Pope as follows: 1. The most recent sedimentary rooks in the district belong to the Cretaceous period. 2. The Cretaceous rocks were penetrated by large intrusions of ande-site (referred to hereafter as primary andesite) which occur as elliptical dome-shaped masses, striking northwest-southeast. These andesite bodies are from 8 to 15 miles long and from 6 to 10 miles wide. 3. A period of erosion during which the contour of the andesite domes was changed. 4. Andesite flows (secondary andesite) which rest unconformably on the primary andesites.

Jan 1, 1917

By Granville S. Borden

The fruits of industry are divided between capital, labor, and governments. Capital takes its redemption and remuneration through profits or dividends; labor takes its share through wages; governments take their share through taxes. Each must have a just share, and the question of what is a just share and the question of who-shall make the allocation are vital current political and economic issues. Certain political philosophies con- tend that government should take all the fruits and that some dictator or politician should have irrevocable discretion and power to distribute the fruits. Believers in democracy and free enterprise adhere to the view that capital is entitled to redemption and fair remuneration; that labor shall have a fair wage; and that governments shall make equitable levies. But since all human beings, both individually and in groups, are inherently selfish, there are many variable views in regard to the question of what ratios shall be applied in a division of the fruits and who shall have the power to fix these ratios. Perhaps all parties should devote more energy to means of increasing the crop, and not so much time to quarreling over a division of the existing crop. Moreover, all three parties must guard against killing the goose that lays the mineral eggs. For example, if the tax burden becomes oppressive and the taxpayer refuses to carry it, then business stagnates, with consequent unemployment, reduction of profits, and curtailment of government revenue. If a producer assumes the increased tax burden, marginal operations must be closed down, and again the consequences are increased unemployment and diminished government revenue. Quite often an increase in a rate of tax results in a reduction of government revenue. Perhaps the worst detrimental feature of selfishness and greed on the part of any one of the three distributees of the fruits of industry is the retardation of expansion of the enterprise. Growth means new jobs, more government revenue, better trade, and better standards of living. Explorations and discoveries have resulted in tremendous contributions

Jan 1, 1959

By Hugh Rose

THE properties of the company lie within the Pachuca district, State of Hidalgo, Mexico, connected by three railway lines with Mexico City, 55 miles southwest, and by two lines with Vera Cruz, 250 miles southeast. The ores were formerly divided by sorting into two classes, smelting and milling, the former averaging about 2 oz. gold and 335 oz. silver, the latter 0.12 oz. gold and 23 oz. silver. The smelting ores were sold to custom plants, principally the American Smelting & Refining. Co. at Aguascalientes. The milling ores were treated by the patio process at the Guadalupe Hacienda, at Pachuca. This patio was probably the largest in existence at the time and continued in active operation up to March, 1910. In January, 1910, the mines and patio were sold to English interests, represented by Camp Bird Limited. Two new companies were formed, the Compañia de Santa Gertrudis, S. A., to operate the mines, and the Compañia Beneficiadora de Pachuca, S. A., to build and operate a custom cyanide milling plant. (Fig. 1.) GEOLOGY The historical geology of the Pachuca district is described by Fred J. Pope as follows: 1. The most recent sedimentary rocks in the district belong to the Cretaceous period. 2. The Cretaceous rocks were penetrated by large intrusions of ande-site (referred to hereafter as primary andesite) which occur as elliptical dome-shaped masses, striking northwest-southeast. These andesite bodies are from 8 to 15 miles long and from 6 to 10 miles wide. 3. A period of erosion during which the contour of the andesite domes was changed. 4. Andesite flows (secondary andesite) which rest unconformably on the primary andesites.

Jan 8, 1916

By M. R. Lorenz

Efficient visible light emission from p-n junctions in semiconductors is currently achieved in the four materials, Sic, GaP, ]Ga1-xAs and GaAs1-x,. Recent advances in materials preparation and p-n junction formation are briefly reviewed. The radiative recombination processes in the different materials depend largely on the band structure and the impurity states of each material. The spectral distribution of the emission ranges from the blue in Sic, to green in Gap, yellow in Sic and red in Gap, Ga1-x AlxAs and GaAs1-x Px. The origin of the various processes are discussed. The conversion of the electrical power into optical power and the measurement of the conversion efficiency are reviewed. The currently maximum quantum efficiencies at 300°K are: 3 pct in GaP(red), 1 pct in SiC(yellow), 0.1 pct in GaP(green), 0.2 pct in Ga1-x AlxAs at 66001, and 0.1 pct in GaAs1-x Px at 6800. The brightness and the interplay of the quantum efficiency and the luminous efficiency are given detailed consideration. VISIBLE light generated by the application of a direct current to a semiconductor crystal was first observed by Lossev1 in 1923. Light emission came from naturally occurring junctions in Sic crystals but little was known then with regard to the mechanism of charge transport and light emission. Some nearly 30 years later and with a vastly increased understanding of semiconductors the phenomenon of electroluminescence was studied in more detail, for example in p-n junctions of germanium.2 In these early studies, the efficiency of converting the electron current into a photon current was very low and therefore aroused little interest toward practical application. More recently it became apparent that in certain materials, for instance GaAs, and under certain conditions, the conversion efficiency was not low at all.3 The subsequent discovery of the p-n junction laser4-6 provided the impetus for increased studies of electroluminescence. Light emitted from GaAs occurs in the infrared region of the electromagnetic spectrum and is not visible to the eye. At nearly the same time the use of GaAs1-xPx led to laser action at low temperatures which was visible to the eye.7 Later a red light emitting diode, made from Gap, was reportedS which emitted incoherent radiation at 300°K with an external quantum efficiency of about 1.5 pct. The fact that such efficient devices were obtainable led to a more concentrated effort in the search for highly efficient room-temperature semiconductor light sources. It is some of this later work on p-n junction luminescence with which we will be concerned here. Since our aim is centered on visible light, with hv =1.8 ev ( ?=7000?), only the wider band gap semiconductors are of interest, i.e., Eg 1 1.8 ev. Although many compounds meet this criterion, only a limited number of those are also good semiconductors, i.e. contain low resistance n and p regions. Some of the more promising candidates are listed in Table I. We will only be concerned with light generation from a p-n junction. This limitation excludes essentially the group II-VI binary compounds, although we will briefly review the case of ZnTe and the solid solution ZnTe1-xSex. As we will show they may contain a p-n junction but only of a special kind. Most of the discussion will deal with the four materials, Sic, Gap, Gal-xAlxAs, and GaAs1-xPx. These appear to be at the present time the best visible light emitting semiconductors. In the following sections we will briefly consider: 1) the electrical properties of p-n junctions; 2) some recent advances in materials preparation; 3) the formation of p-n junctions; and then in somewhat greater detail we will consider: 4) the various radiative recombination processes; 5) the measurement and observation of the external quantum efficiency; 6) the luminous efficiency; 7) the brightness of light emitting diodes (LED&apos;S). THE P-N JUNCTION The p-n junction in a semiconductor crystal is the interface between two differently doped regions. More specifically the p region is doped predominantly with acceptor impurities and the n region contains predominantly donor impurities. The energy band structure of a degenerate p-n junction at thermal equilibrium is shown in Fig. l(a). The excess electrons on the n side of the junction are confined to this region by the barrier potential Eg. Similarly the excess holes on the p-side of the junction are confined to the p-region by a similar potential barrier. If we now apply a dc voltage V such that the p region is made positive and the n region negative, the barrier potential EB is reduced by the applied voltage, V and the junction is said to be forward biased. With the barrier potential lowered, electrons and holes can drift toward the p region and n region, respectively, see Fig. l(b). The current voltage characteristics of p-n junctions in most wide band gap materials can be described by the relation: J = Joexp(eV/BkT) [1] where the functional form of Jo is determined by the recombination mechanism. Jo is generally a complicated parameter which depends on a number of different factors including temperature, junction width, bias voltage, and carrier lifetimes. The parameter B also depends on the recombination mechanism but

Jan 1, 1970

By W. H. Coghill, A. M. Gow, M. Guggenheim, A. B. Campbell

The object of this paper is to discuss the fundamental principles of ball milling and to present some observations which have been made in laboratory and plant investigations. The discussion will be limited to wet grinding of ores in cylindrical mills, but doubtless many of the principles involved will be equally applicable in the other fields of fine grinding in which mills of the same type are used. In the concentrators of the United States there are about 650 ball, rod, or pebble mills, operating or ready to operate, and these have about 100,000 connected horsepower. For grinding in cement plants there is about three times this connected horsepower, and other industries have an unestimated amount, all used for the general type of grinding that is to be discussed here. It is true that these figures do not represent stupendous amounts of power, but when one considers that ball milling is often the ((bottle neck" in a concentrator and that it often accounts for the largest single item in the cost sheet, the importance of a comprehensive understanding of the principles of ball milling can be appreciated. Much of the past literature devoted to the subject has been concerned with the Kick-Rittinger dispute over evaluating grinding, or with dissertations on ball paths and the closely allied impact versus attrition hypotheses, or with the exclusive consideration of certain specific variables, such as mill speed or circulating load, irrespective of the other factors in operation. Such subjects may be dismissed with but little discussion in what may be called, by comparison, a new philosophy in the study of ball milling. Briefly, this &apos;(new philosophy" consists of using power as an index of the mill operation, and investigating grinding from the standpoint of set and induced varisbles, with emphasis on the latter.

Jan 1, 1935

CONTENTS PAGE WARNER, ROBERT K.-Efficiency of Screening. Discussed by Robert C. Canby,Robert K. Warner, W. 0. Borcherdt, V. E. Flanagan 1 FAHRENWALD, A. W.-Surface Reactions in Flotation. Discussed by Arthur F. Taggart, A. M. Gaudin 7 Efficiency of Screening Discussion of the paper of ROBERT K. WARNER, presented at the New York Meeting, February, 1924, and issued, as Paper No. 1293-M, with MINING AND METALLURGY, January, 1924. ROBERT C. CANBY, Wallingford, Conn.-On page 2, the author speaks of the importance of using a testing sieve clothed with the same material as the screen being studied; does he regard this as essential? In practice, how does the screen efficiency calculated by the difficult-grain method compare with those computed by the usual undersize method? Is it possible by the author&apos;s method, to obtain a measure of efficiency that can safely be compared with that of another screen sizing a different ore? ROBERT K. WARNER.-The use of a testing sieve clothed like the mill screen being studied is desirable but not essential for routine work about a mill where the character of the feed varies little, as regards the shape of the grains and the sizing test. Close agreement in size of aperture between the sieve and the screen is, however, important if the data obtained are to be valuable to others working on a different feed. If the testing sieve is coarser than the mill screen, the efficiency will appear unfairly low; whereas if it is too fine one might get efficiencies greater than 100 per cent. because of the apparent oversize in the undersize. In either of these cases the usefulness of the difficult-grain method of calculation would be reduced. As screens wear, the undersize grows appreciably coarser so that it is desirable to test screens only when the cloth is new or else to provide testing sieves that are worn about the same amount. The futility of making efficiency observations on a. distorted or broken screen surface is obvious.

Jan 6, 1924