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By Edward W. Mehal

This paper presents a review of the technologies which have been used in the application of III-V compound semiconductors to integrated circuits and arrays. These materials have properties which make them useful for various devices such as: light emitters, sensors, microwave sources, and microwave diodes. Technologies for incorporating these devices into integrated circuits have been reported and processes developed for fabricating planar devices using selective epitaxial deposition or selective diffusions. Isolation methods utilizing semi-insulating GaAs, oxide isolation, and ceramic insulation have also been reported. These techniques, and the devices and circuits produced or proposed are discussed. AFTER the invention of the silicon-integrated circuit, methods for utilizing compound semiconductors for integrated circuit applications were proposed. The scope of applications was potentially much broader because of the range of properties available from these materials. There also was the opportunity of coupling these properties with germanium and silicon devices to realize functions and circuits which could not be produced with silicon monolithic circuits. Table I exemplifies the range of electrical properties available in III-V compound semiconductor materials which are currently being widely used. A wide range of sensor and emitter applications result from the range of band gap. The band structure of GaAs and GaAsxP1-x permits their use as microwave oscillator source, and the high electron mobilities further facilitate their utility in microwave devices. The concept of "integrated functions"1 results from the availability of these materials and methods for utilizing their special properties. Heteroepitaxial growth allows the fabrication of a monolithic block of these materials. Semi-insulating GaAs permits the attainment of electrical isolation between components in a monolithic block without resorting to p-n junction biasing or oxide isolation methods. An "integrated function" is a unit which can perform a system or subsystem role and perform a number of electromagnetic functions. These functions could include sensor or input transducer, signal processing, interconnections, and control or output function. Two examples which demonstrate this concept are an optoelectric processor and a microwave receiver front end. The optoelectronic processor, Fig. 1(a), would consist of a light sensor, signal processor, and output emitter. The sensor could be InSb or InAs which would be IR-sensitive. The signal from this sensor would then be amplified and transmitted to the light emitter. The amplifier could utilize GaAs bipolar or field effect transistors. A Gap emitter would then produce visible radiation. The microwave receiver front end, Fig. l(b), would consist of a local oscillator section and a mixer section. A signal input from an antenna is mixed with the signal from the local oscillator. The local oscillator signal is produced by a Gunn oscillator. The single-ended mixer utilizes one Schottky barrier mixer diode. The IF signal would then be amplified further and suitably displayed. A further extension of the capability of utilizing the

Jan 1, 1969

By William Fink

THE constitution of the aluminum-cobalt alloys has been the subject of relatively few investigations. Brunck1 analyzed the residue which remained after treating the 17 per cent cobalt alloy with dilute hydrochloric acid. The results of the analyses indicated the existence of a compound Co3Al13. Guillet2 published a liquidus for the aluminum-cobalt system which contained two maxima corresponding to CoAl6 and CoAl2 and two eutectic points at 30 and 74 per cent Co. The most extensive investigation of the system was carried out by Gwyer,3 whose results are summarized in Fig. 1. It will be noted that at the aluminum end there is a suppressed eutectic at 644° C. By extrapolation of the duration of the eutectic arrest to zero, the composition of the compound was placed at Co3Al13. Another thermal arrest was noted at 550° C., which Gwyer attributed to a peritectic reaction. The present investigation of the aluminum end of the aluminum-cobalt system is the eleventh of a series dealing with the constitution of aluminum; rich alloys prepared from electrolytically refined aluminum.4 Preparation of Alloys.-The alloys used in this work were all prepared from electrolytically refined aluminum, the analysis of which is shown in Table 1. In preparing some of the alloys, metallic cobalt (98 to 99 per cent) was used either directly or in the form of an intermediate alloy, the composition of which is given in Table 1. In order to obtain alloys of higher purity, cobalt was introduced into some of the alloys by means of chemically pure cobaltous chloride which was readily reduced by the aluminum. A small electric furnace with nickel-chromium heating elements was used in the preparation of the alloys.

Jan 1, 1932

By O. Hyvärinen

The treatment of anode slimes at Outokumpu Pori Copper Refinery comprises the following process stages: copper leaching by air oxidation, nickel removal by digesting slimes in concentrated sulphuric acid at 200 °C, and dissolving of the formed nickel sulphate into water, roasting of the slimes in controlled gas atmosphere at 600 °C for selenium removal, smelting of slimes in a Doré furnace, electrolytic refining of silver, sulphuric acid and aqua regia leaching of slimes from the silver cells followed by the reduction of gold and platinum metals. The paper discusses operational experiences and recent developments of the process.

Jan 1, 1984

THE story of Miami really is two stories. First, that of an excellent Porphyry Copper mine, ably managed as a business enterprise, and always among the leaders in technical progress. Concentrating its first ore in 1911, it had by 1925 paid dividends totaling $30,000,000 or $40 per share on stock that had cost the public $5 per share in March, 1908. The ore, containing 2.5 per cent copper at the start, had become progressively leaner but the recovery had tended to improve. Production costs had gone up during the World War and the early post-war period; and had come down again. In all these respects it had followed the norm. If the mine had been abandoned as exhausted and the company had been liquidated late in 1925 (a program that had been given earnest consideration in 1924), Miami would have gone down into history a first-rate mining venture; as an active and progressive participant in the great Porphyry achievement. But Miami was not liquidated in 1925; instead it started to write the record of its second and really amazing story. Near the old mine was a large body of low-grade ore containing, in place, less than 20 lb. of copper to the ton, and without, incident- ally, any considerable sweetening of gold and silver. Any method of underground mining that was cheap enough would certainly entail some dilution, so that ore as sent to the concentrator necessarily would average much less than 20 lb. As a matter of record, the average for 1929 was 16.6 lb., from which 11.726 lb. was recovered as concentrate. As already said, the exhaustion of the older orebody during 1925 was foreseen; but in 1924 the decision was reached to enlarge the concentrator and develop a new mine. An expenditure of $2,500,000 was entailed in this program. By October, 1925, the

Jan 1, 1933

By Thomas T., Read

ALTHOUGH the first colonists in the area that is now the A United States, whether Spanish, French or English in nationality, were usually keenly interested in the possibilities of mineral wealth, it is a curious and interesting fact that none of them happened upon the mineral deposits that eventually were to make this the greatest mineral-producing country; up to 1800 it would probably have been rated as rather poor in minerals. Spanish explorers traversed the southeastern United States with- , out finding the Appalachian gold deposits that aroused so much interest in the early nineteenth century; Coronado sought in vain for the seven golden cities of Cibola; and the important gold \ deposits of California were not discovered until the political sovereignty of the region had passed from Mexico, which had held it for three centuries. The French also held Canada for nearly two centuries (and the British for another century) without finding the mineral deposits in Ontario and Quebec that now are so important. Though they knew of the copper of the Keweenaw peninsula, the lead ores. of Wisconsin and Missouri, and the coal of Illinois in the seventeenth century, these deposits were all too remote for exploitation. In the area held by Great Britain, iron smelting was planned at Jamestown as early as 1619 and was actually begun at Lynn, Mass., in 1643. The industry grew slowly, at first, but had reached considerable importance before the Revolution. Commercial bituminous coal mining began about 1750 in Virginia but anthracite mining in Pennsylvania was not started until 1800. As a result there was naturally little interest in the technical aspects of mineral prodnction here before 1800 by any except the few people who were actually engaged in it. Students of natural science were much interested in minerals, however. The activities of those who rank as geologists are so thoroughly covered in

Jan 1, 1941

By A. B. Boghani, R. H. Trent

A computer program has been developed to simulate evacuation of a mine in various configurations. The simulation input variables include characteristics of the mine, expressed in the form of a network of passages, properties of hoists and hoisting strategies, initial miner positions, ventilation and compressed air velocities, stench warning system and self rescuer capabilities. The simulation can be carried out for cases in which there is no fire, i.e., fire drill simulation, or for cases in which there is a fire at any arbitrary location. The fire is assumed to generate gases which impede movement of miners in the gaseous region. However, the thermal effects of the fire are not considered. The simulation output include the evacuation time for each miner, movement of the hoists, propagation of smoke through the mine passages and smoke exposure of the miners. Several illustrative simulations have been carried out to verify validity of the program and to demonstrate its capabilities. The computer program has been able to predict evacuation time, within 5 percent, for an actual fire drill. It is believed that this program can be used to evaluate evacuation performance of a mine, identify problem areas and demonstrate improvements due to the recommended corrective actions.

Jan 1, 1977

By Homer W. Riley

ANTHRACITE SMALL power-driven, toothed, cast-iron rolls were used first to break anthracite in 1844. Prior to that time, men with hammers, who stood on perforated cast-iron plates, broke the large lumps into commercial sizes. In order to convert run-of-mine into the various sizes required by the anthracite industry, about 20 million tons must be broken, annually, into smaller sizes. This phase of anthracite preparation is of major importance, because the degradation accompanying reduction in coal sizes should be kept at a minimum. The exclusive use of toothed rolls for that purpose indicates that comminution by rolls is the best solution of the problem. Many improvements have been made in tooth design, but the most important was a reduction of the peripheral speed of the rolls from 1000 to 300 ft. per minute. The higher speed was based upon and approximated the velocity of a falling piece of coal when it entered the rolls, Exhaustive roll tests at the slower speed showed that the same size reduction could be affected with less degradation. The adoption, therefore, of slow-speed, compound geared rolls, especially for breaking the larger sizes, became quite general after 1912. A high-speed roll is shown in Fig. 1 and a slow-speed roll in Fig. 2. Anthracite Crushing Problems.-Crushing anthracite presents the problem of selecting a series of rolls that will produce the greatest percentage of the prepared sizes of nut and over. The size distributions to be expected are shown in Table 1. Coal breaking and crushing practices in anthracite breakers involve the use of equipment for comminuting the following classes of material: 1. Run-of-mine-plus 6 ½ -in. coal. 2. Sized coal-steamboat, broken, egg, stove, nut, and pea. 3. Flat coal--coal that is flat and hence not suitable for the market. 4. Bone--a piece of laminated coal and slate, crushed for the purpose of reclaiming the coal. 5. Breaker refuse, reduced to a size suitable for flushing into a mine for back-filling purposes.

Jan 1, 1950

By R. G. Coyle

This paper describes a model of operating policies in an underground metal mine. The purpose of the model is partly that the problem of controlling a mining operation in the face of shocks from its economic environment is interesting in its own right, and also as an input to a larger research project on policy-making in mining companies. The model includes, mining, development and milling sectors together with cash flow and finances. In particular, it shows how the policies used to control the various sectors in the face of environmental shocks from metal prices and changing state of the system are connected by feedback loops. The use of feedback theory differentiates the model from 'ordinary' simulation and assists in the design of 'robust' policies which always achieve effective control. This model is the first stage of a major project and approximations have been made, simply to get the model going. The purpose of this paper is to show the kind of output this type of model produces, to lay our explicitly what is in the model and above all, to invite contributions from mining people on what the model should show and what should be put into it. We claim no virtues for this model. It is just a research tool so that later models will be more worthwhile and useable in practice.

Jan 1, 1977

By A. Steiner, E. Miller, K. L. Komarek

Equations have been derived to calculate the chemical potentials of the components of liquid binary alloys from liquidus and enthalpy data. The equations are applicable to systems with intermetal-lic compounds of limited solid solubility. The liquidus curve of the Mg-Sn system was accurately redetermined, and the melting point of the compound Mg2Sn was found to be 770.5° * 0.3°C. The thermo-dynamic properties of the liquid alloys were calcu -lated from the liquidus data. The activity of tin shows both positive and negative deviations from Raoult&apos;s law and the relative integral entropy is positive. THE phase boundaries in an equilibrium phase diagram are functions of the thermodynamic properties of the coexisting phases. Specifically, the shape of the liquidus curve near an intermediate compound is determined by the properties of the compound and the liquid phase. Hauffe and wagnerl have derived an equation for the chemical potential differences (ui) of the liquid alloys near the congruent melting point when the heat of fusion of the compound and the liquidus curve are known. In their derivation the temperature dependence of the ui value was neglected, and liquid of stoichio-metric composition was chosen as the reference state. To obtain chemical potentials over the ntire composition range of the phase diagram with the pure components as the reference state, equations have been derived which incorporate the temperature dependence of the chemical potentials. Such a thermodynamic analysis can be carried out when the liquidus curve and the enthalpy values are known. The equations have been applied to the redetermined liquidus curve of the Mg-Sn system to obtain the thermodynamic properties of liquid Mg-Sn alloys. The Mg-Sn phase diagram has been studied by various investigators and the results have been compiled and critically assessed by Hansen.2 Preliminary thermal analyses showed that the basic features of the diagram were correct. The system has one congruent melting compound, Mg2Sn, two eutectics, and some solid solubility of tin in magnesium. However, the published liquidus temperatures show considerable scatter. In order to perform an accurate thermodynamic analysis, the liquidus curve between the magnesium-rich and tin-rich eutectic compositions was therefore redetermined by careful thermal analysis using highest-purity starting materials. EXPERIMENTAL PROCEDURE The magnesium metal (Dominion Magnesium Ltd, Toronto, Canada) had a purity of 99.99+ pct with the following impurities (in ppm): 20 Al, 30 Zn, 10 Si, <1 Ni, <1 Cu, <10 Fe; tin (Cominco Products, Spokane, Wash.) contained 99.999+ pct Sn. The graphite crucibles were machined from graphite rods (United Carbon Products Corp., Bay City, Mich.) which had an average total ash content of less than 30 ppm. All the graphite parts were baked out in vacuum at 950" to 1000°C for a minimum of 24 hr to remove volatile organic materials. The graphite crucibles (3 in. long, 1-5/8 in. OD, 1-3/8 in. ID) were tightly closed with a threaded cover (1/2 in. thick) which had a central thermocouple well (2-1/4 in. long, 5/16 in. OD, 3/16 in. ID). Cover and thermocouple well were machined from one piece of graphite. A thin sheath of quartz was inserted in the well to protect the thermocouple

Jan 1, 1964

History of Reverberatory Smelting in Montana, 1879-1933. By FREDERICK LAIST (Trans, vol 106 31,800 words ) The development of the art of reverbera¬tory smelting from 1879, when smelting first started in Butte, up to the present time is described. The paper traces the development of the reverberatory furnace, as regards both constructing and operating, from the initial 10-ton furnaces to the present-day 600-ton furnaces and the changes in operating practice which accom¬panied the gradual enlargement of the furnaces and the reasons therefor are described and explained The results obtained from an investigation (made in the course of the Carson litigation) into the various methods of charging reverberatory furnaces are given These investigations proved that the method of charging a reverberatory had very little to do with its performance It was also found, at the same time, that the depth and extent of the bath maintained in the furnace had very little to do with its performance Numerous operating results are included and the article is illustrated Development of Copper Converting at Butte and Anaconda. BY WILLIAM KELLY AND FREDERICK LAIST (Trans , vol 106 4400 words.) This paper is based on recollections of one of the authors, W M Kelly, who has been identified with the development of smelting and converting at Butte and Anaconda since early times The article starts with a description of the circumstances surrounding the first intro¬duction of copper converting at the Parrot Works in Butte under the Manhes patents It briefly recounts the difficulties which were encountered and the steps taken to overcome them Among these were the absence of means for punching tuyeres in the original converter This difficulty was overcome crudely by drilling holes in the windbox opposite the tuyeres, said holes being closed by wooden plugs Later these plugs were replaced by steel slides and still later by the Dibblie ball valve, which has remained standard ever since The development of the converter from both struc¬tural and operating standpoints is traced from the early beginning to the present day Developments in Lead and Copper Converting at Tooele. BY B L SACKETT (Trans, vol 106. 3900 words) This paper shows the development at this Utah lead and copper smelter from separate converting of the two kinds of matte produced to a more efficient and economical treatment of the combined mattes This was accompanied by the use of relatively large amounts of silicious ore in the converting of lead matte as well as copper matte, which greatly improved the quality of converter slag produced, both from the standpoint of its copper content and its desirability for

Jan 1, 1935

By Gail F. Moulton

The production of petroleum in Illinois in 1928 was approximately 6,500,000 bbl., a decline of about 500,000 bbl. from the previous year and of about 1,500,000 bbl. from 1924. Production increased about 200,000 bbl. in Indiana to slightly less than 1,000,000 bbl. Production for 1929 is estimated at approximately 6,000,000 bbl. for Illinois and 1,000,000 bbl. for Indiana. Illinois Because production from most of the wells in the state has declined to a small daily average and the low prices for crude oil discouraged wildcatting, the number of wells drilled fell below that for any previous year since the development of commercially important production in the state. The Ohio Oil Co. discovered a pool of apparent commercial importance in southwestern Illinois near Dupo, in St. Clair County, and favorable showings of oil were encountered in a well in southeastern Illinois, near Harrisburg in Saline County. New production from the Dupo area is expected to check the rate of decline for the state. Thc following tablel summarizes field developments for 1927 and 1928 (for important detail by counties see notes at foot of table): 1027 1928 Completions........................................... 162 145a Initial production, bbl.................................. 2244 1840b Dry holes........................................,.... 66 58" Gas well completions................................... 13 8d 0111 wells abandoned.................................... 45" a Crawford, 44; Lawrence, 28; Wabash, 40. b Crawford, 501; Lawrence, 403; St. Clair, 165 (4 completions); Wahash, 668. o Crawford, 12; Wabash, 19. d Crawford, 6. b Lawrence, 21; Wabash, 15. The discovery well in the Dupo field in St. Clair County, produced about 150 bbl. per day from the Trenton lime at 660 ft. It is located in a northern extension of the Columbia-Waterloo anticline on which the Waterloo pool was developed in 1921. The best information on the.

Jan 1, 1929

By Horace Winchell

AN EXAMINATION of the Pachuca and El Oro. districts in July, 1920, although cursory and incomplete, disclosed facts of more than passing interest to the student of ore deposits; and inasmuch as the literature on these districts is limited and some of their features are little understood, a brief account may prove valuable as reconnaissance observations to be amplified by more thorough and competent observers in the future. Where no complete monograph of important mining camps has been published a partial presentation of the data is often useful, as it sometimes leads to fuller and more accurate descriptions, by stimulating discussion. The following notes are presented with the consent of Mr. A. F. Main, managing director of the El Oro Mining and Railway Co., whose fund of information and wide acquaintance with both districts alone made it possible to cover so much ground in a short time. I have also to acknowledge gratefully the aid of Messrs. C. A. Lantz and D: S. Calland of the Santa Gertrudis and Real del Monte companies, respectively, in connection with permission to inspect geological features of interest in their mines.

Jan 6, 1921

By A. Lee Barrett

SO commonplace that they are seldom noticed, mining-machinr, bits have a definite and important bearing on the cost of coal production. At the average mine many thousands of bits are used during the year. The actual cost represented by the purchase of the bits used, as well as that of sharpening and handling them, represents a considerable sum of money. From the point of view of indirect costs they are important, as the lack of good bits at a mining machine can seriously impair production. Good bits tend to ensure an adequate supply of coal. Classes OF Bits Mining-machine bits may be divided into three general classes, based on shape and method of use: (I) chisel, (2) pick-point and (3) one-use. The chisel and pick-point bits are shown in Fig. I. The so-called "chisel" bits were made of steel of various sizes and were sharpened to a wide chisel cutting edge. Few of this type of bit are used, except in places where coring is very bad. Sometimes chisel bits are used with standard bits to help cut out the core. The "pick-point" bit is widely used today. Normally it is made from ½ by I-in. steel, is about 4½ in. long when new, has a rake angle of about 25°, a front clearance of about 23O, a side clearance of approximsteji 8".&apos; There are many variations in the shape of this bit, depending on the ideas of the individual that may be dressing the dies of the bit machine. This bit has been generally used for many years and at present, in one form or another, is by far the most popular bit used in coal mines. This bit usually is made from 0.85 carbon steel, although in recent years some alloy-steel bits have made their appearance. At present, carbon-steel bits are frequently tipped in. hard facing materials. A third class of bits might be called the L&apos;one-use" bit; that is, a small bit that is used once and then thrown away. These bits have two or three points, are usually made from 0.85 carbon steel and sometimes from higher alloys. Recently some. of them have been tipped with hard facing material. Most of them were used at first with special

Jan 1, 1942

By A. Lee Barrett

SO commonplace that they are seldom noticed, mining-machinr, bits have a definite and important bearing on the cost of coal production. At the average mine many thousands of bits are used during the year. The actual cost represented by the purchase of the bits used, as well as that of sharpening and handling them, represents a considerable sum of money. From the point of view of indirect costs they are important, as the lack of good bits at a mining machine can seriously impair production. Good bits tend to ensure an adequate supply of coal. Classes OF Bits Mining-machine bits may be divided into three general classes, based on shape and method of use: (I) chisel, (2) pick-point and (3) one-use. The chisel and pick-point bits are shown in Fig. I. The so-called "chisel" bits were made of steel of various sizes and were sharpened to a wide chisel cutting edge. Few of this type of bit are used, except in places where coring is very bad. Sometimes chisel bits are used with standard bits to help cut out the core. The "pick-point" bit is widely used today. Normally it is made from ½ by I-in. steel, is about 4½ in. long when new, has a rake angle of about 25°, a front clearance of about 23O, a side clearance of approximsteji 8".&apos; There are many variations in the shape of this bit, depending on the ideas of the individual that may be dressing the dies of the bit machine. This bit has been generally used for many years and at present, in one form or another, is by far the most popular bit used in coal mines. This bit usually is made from 0.85 carbon steel, although in recent years some alloy-steel bits have made their appearance. At present, carbon-steel bits are frequently tipped in. hard facing materials. A third class of bits might be called the L&apos;one-use" bit; that is, a small bit that is used once and then thrown away. These bits have two or three points, are usually made from 0.85 carbon steel and sometimes from higher alloys. Recently some. of them have been tipped with hard facing material. Most of them were used at first with special

Jan 1, 1942

By F. W. Bloecher

D ETERMINATION of the surface area of finely divided minerals is of interest to mineral engineers engaged in flotation, comminution, and dewatering studies. In the industrial minerals field, many materials are classified as to fineness according to their specific surface (surface area per unit weight). A method of surface area determination has been tested and used in the Richards Mineral Engineering Laboratories at M.I.T. It involves low temperature krypton adsorption measurements using the technique described by Beebe.1

Jan 3, 1951

By D. C. DERINGER

METALLURGISTS and mill operators appreciate, in a general way, .the economic or commercial relationship between recovery and grade of product but few have correlated in detail fluctuating metal prices with the metallurgy. They know that many factors such as metal price, dedusiions for returning charge, transportation, percentage of metal in head ore, etc.; all affect the commercial relationship between recovery and grade of product. In practically every mill some one at some &apos; time has calculated the amount of recovery that can be sacrificed for each percentage increase in grade of concentrate and from this calculated ratio the commercial or ., economic tail has been established. Such a ratio finally becomes a well-entrenched rule by which the progress of the metallurgy is judged.. When once established, these-, ratios are but seldom corrected to changes of metal prices for each possible grade of concentrate that may be produced. The calculation is tedious when often repeated. Other methods have been suggested and used to correlate the commercial with the metallurgical phase. A factor .derived ,by multiplying the grade of concentrate by recovery is often used, but is of little importance because it does not possess a single commercial quantity. The percentage monetary recovery calculated by dividing the gross value of the ore into the net smelter return gives a good economic index and, is to be commended, but it is difficult to correlate exactly and quickly the work of each day on a commercial basis.

Jan 1, 1931

By AIME AIME

ALBERT PORTEVIN, distinguished French physical metallurgist .and savant, has been added to the Institute&apos;s list of Honorary Members. Professor Portevin&apos;s work in collaboration .with A. M. Garvin represents one of the greatest steps ever made in understanding the heat-treatment of steel and the function of steel-alloying elements. In addition, he has published the results of important work, on the castability of ternary alloys, on the determination of oxygen and-oxides in steel, and on high-temperature oxidationn and scaling of steel. Notable also are his studies on methods of testing metals, on the constitu¬tion and structure of alloys, on founding and welding, and on alloys of aluminum, magnesium, and copper. Professor Portevin was horn in Paris in 1880, entering

Jan 1, 1938

IDO not want to omit anything in which fire or its operation has a part, if I know or can tell it, and have already told you so many other useful, powerful, and ingenious effects (finally of powder and other&apos; fire deadly and very injurious to all living things, indeed, composed for the destruction of those who possess it as well as those who do not) but I do not want the end of my writing to be in tragedy. Therefore I wished to tell you how, from these fires composed of forceful and horrible mate¬rials bringing harm and terror to men, a happy and pleasing effect is also produced and, instead of fleeing from it, the people willingly go to see it. Among others I remember that it was once customary to use these in Florence and in Siena, more than elsewhere. The chief feast day celebrated. by one of these cities is the day of the birth of Saint John, and the other is the Assumption of Our Lady, on the fifteenth of the month of August. In the morning they visit the shrines with great devotion and solemnity, displaying their pomp as much as possible, and later they hunt lions, wild bulls, untamed horses, and many other animals. In the same public squares there was also erected as a decoration an edifice fixed in the ground in the middle of this space, or hanging from a heavy rope crossing between the loftiest points of equal height that could be found in that place. This they have done and still do, and perhaps in time to come will continue to do when opportune. This structure was usually of wood; indeed it is necessary that the latticework of its construction be made only of this. It was covered and en¬larged by tying and fastening hay on top to bring it almost to completion and then papier-mâché was applied. [165v] The figures were first appropriately painted and made of a combination of vessels one above the other, developing various decorative figures in relief which should represent some fable or history and should not appear haphazardly made or without understanding. Now the master proceeded to arrange these figures in a composition according to his skill or art of design, and likewise planned

Jan 1, 1942

By K. A. ACKLEY

The petroleum industry experienced a year of satisfactory accomplishment in Oklahoma during 1945. Crude oil production was increased, a new record for recent years was established in well completions, and refinery operations were maintained at a maximum level. Daily average crude oil production increased to 382,000 bbl., reflecting a 13.5 per cent gain compared with production during the previous pear. Total wells drilled during 1945 amounted to 2556, a gain of 28.7 per cent over 1944 Refinery throughout averaged 187,500 bbl. daily, an increase of approximately 4 percent over the preceding year.

Jan 1, 1946

By W. A. Backofen, B. C. Wonsiewicz

The Plasticity transition in magnesium was studied by plane-strain compression of single crystals and polycrystalline material at temperatures from about 20" to 307°C. Reduction of single crystals along the c axis was accommodated by twinning on {1011) and retwinning on (10 12}, followed by basal shear in the doubly twinned volume. Deformation in that mode can result in sufficient independent shears for arbitrary shape change. Fracture in c axis compression, below about 100°C, has been related to excessive shear caused by unloading from the stress for {1011} twinning (-50 ksi at 20°C) to that for slip within the twin (-3 ksi); ductility follows from heating because the stress difference is lowered and the twin volume, in which elastic strain energy is dissipated on unloading, is increased. The stress for (1011) twinning is strongly temperature-dependent but not given by a critical resolved shear stress law. The latter is attributed to the influence of stress concentration from prior intersecting shear on nonbasal planes, the former to the temperature dependence of the preliminary slip. THE basic symmetry of hcp crystals has the effect of limiting the number of independent slip systems and making twinning an important deformation mechanism. The general result in wrought polycrystalline aggregates is a more or less sharply developed texture (or preferred orientation) which underlies a strong anisotropy in mechanical behavior. Knowing how the one influences the other is essential background for the use of such materials. Magnesium was of interest in this work because of the unexplained plasticity transition that it undergoes somewhere in the neighborhood of 200°c.&apos;&apos;~ At lower temperatures plastic deformation before fracture in polycrystalline material is limited, while at higher temperatures extensive deformation is possible. The transition temperature commonly determines the lower limit of the range in which magnesium is worked. The limited ductility can be traced to a lack of independent crystallographic shears. A minimum of five are required for arbitrary shape change.&apos; Around room temperature, however, slip on all known systems provides only four.&apos; In each case, the slip direction is in the (0001) basal plane so that slip does not allow strain along the c axis. With increasing temperature, more slip occurs on the ( 1011) pyramidal plane and the ( 1010) prism plane but without change in direction.&apos;?&apos; Thus, that development alone cannot explain the transition temperature.

Jan 1, 1968