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By William Johnson

IT is now recognized that several important types of reactions in metallic systems proceed by the formation of nuclei and the growth of these nuclei. The process, of freezing is a simple example of this, as Tammann pointed out years ago.1Tammann held that the rate of freezing is determined by a rate of nucleation, expressed as the number of nuclei formed per unit volume of unfrozen liquid per second, and a rate of growth of these nuclei, expressed as the linear rate of radial growth in units of length per second. For isothermal freezing the conception is simple; for ordinary freezing, extending over a range of temperature, it is not as simple, for the values of the two constants must change with change in temperature. There is ample evidence that the postulated mechanism is correct even though a quantitative derivation of the rate of isothermal or of ordinary freezing in terms of the two constants has been lacking. In recent years other reactions have been found to proceed in a similar fashion. It has been well established, particularly by Bain,2-8 that the formation of pearlite from the eutectoid decomposition of the solid solu-tion austenite proceeds in such a way, and Polanyi and Schmid, Tammann and Crone, Parnop and Sachs, and others'-1 have shown that the process of recrystallization proceeds in a similar way. Isothermal reaction rates have been determined for eutectoid decom-position by a number of investigators. Bain's2-8 work on the formation of pearlite from austenite is especially valuable in this respect-the type of isothermal reaction curve obtained, as illustrated in Fig. 13, showed an initial slow rate, accelerating to an intermediate maximum rate which then decelerated to the completion of the reaction; similar curves have been obtained by Wever and his collaborators.' Other eutectoid decompositions show similar behavior: for example, the decomposition of the beta eutectoid in the copper-aluminum system, studied by Smith

Jan 1, 1939

By W. R. Shimer

In his valuable report on Finishing Temperatures and Properties of Rails,l Dr. G. X. Burgess, Chief of the Division of Metallurgy, U. S. Bureau of Standards, has begun a line of investigation which should be continued by those interested in the subject, and who have proper facilities for carrying out the work. For the past year or more the Bethlehem Steel Co. has been conducting experiments to learn the effect of rail finishing temperatures on their physical properties and microstructure and the results are here given for the consideration of those interested in the rail situation. Considerable differences of opinion have been expressed by various authorities, in the past, as to the effect of large or small grain size and high or low finishing temperatures of steel rails on their physical properties and wearing qualities. Low finishing temperatures and, therefore, low shrinkage, have been advocated on the theory that the wearing qualities would be improved. Others have recommended high finishing temperatures. The generally accepted cause for rail failures, due to the development of transverse fissures, is excessive wheel pressure on hard rails. One of the causes advanced for hard rails has been that they contain too high percentages of carbon and manganese; another that the rails were finished at too low a temperature, i.e., at or near the critical point. In the experiments herein described the rails were rolled from reheated blooms. All the rail blooms were charged hot in a reheating furnace and brought up to about the original ingot-rolling temperature before rolling into rails. These rails gave better results in deflection, withstood a greater number of drops before breaking, and showed greater ductility than rails of identically the same composition and section which were rolled direct from the ingot. Rails rolled from reheated blooms, finished at somewhat higher temperatures than when rolled direct from the ingot, have a different microstructure, which the writer does not believe is due so much to the difference in finishing temperatures, as to the difference in

Jan 1, 1915

By Henry Louis

The present paper comprises two parts, which have but little con nection with each other. The first is practically a continuation of the investigation on the specific gravity of gold liberated by means of acids from its alloys, on which subject I had the honor of presenting a brief note to the Institute in 1893 (Trans., xxii., 117); the second describes a series of experiments on the behavior of amorphous gold under the action of heat. By the kindness of Prof. W. C. Roberts-Austen, C.B., F.R.S., chemist to the Royal Mint, I have been permitted to conduct these experiments in the mint assay-office, all the splendid resources of which institution were freely placed at my disposal. I desire at the outset to express my obligations to Prof. Roberts-Austen and to all the staff of the mint assay-office for their kind assistance at all stages of my experiments. I.—The Specific Gravity of Gold in Alloys. In the note already referred to, I published my discovery that the gold left on dissolving out the silver from an alloy of gold and silver (which I shall here term " residual amorphous gold ") has a higher specific gravity than ordinary molten gold. I also pointed out that I had worked on very small quantities of material and with balances and weights on the accuracy of which I could not implicitly rely, and that in so far my numerical data were inconclusive, although I had but little doubt of the correctness of the broad fact. The experiments now recorded were made under the most advantageous circumstances and with various refinements. Particularly, I found that the ordinary form of specific-gravity bottle was responsible for several small sources of error; and I accordingly designed an improved form (Journal of the Society of Chemical Industry, April 30,1894, vol. xiii., p. 322), which I used for this work. The

Jan 1, 1895

By Sydney H. Loram

The following notes have been compiled more for the reason that the district is little known to the outside world for its gold production, than for the hope of giving valuable information. The district of Canutillo lies about 15 miles south of the city of Freirina (1at. 28' 50' S. long. 70" 75' W.), and contains nine principal veins, all within a radius of a mile; 50 or more claims have been located on these veins, and this paper refers chiefly to those belonging to the Anglo-Chilean Exploration Go., Ltd., on which the greater part of the development work has been done. In all probability the mines were first worked by the Incas, who, under Tupac Yupangui, captured the country as far south as the Mauli river, between the years 1430 and 1470, and imposed a yearly tribut,e of gold and copper, which was forwarded by carriers on foot to Cuzco, the Inca capital in Peru. In the year 1535, soon after the time of the Spanish conquest, the stories of these consignments, together with those of supposed precious stones, led Diego de Almargro with a band of 400 soldiers to explore as far south as the Incas had gone, in the hope of finding the source of the precious metal, which he believed to have come from some definite point instead of being, as was afterwards proved, the collection of innumerable districts scattered over the entire length of the country. The method of winning the gold used by the Incas or by the natives whom they forced to work seems to have consisted in removing the ore by hard-wood wedges driven by stone-hammers, while a human shoulder-blade worn along its rounded edge, found in one of the mines, had evidently done duty to its second owner as a scraper or shovel. The mining was done by steep inclined workings sunk on the lodes at about 40" from the horizontal, the direction being reversed every 10 or

Jan 1, 1905

By Mary Louise Theodore, R. G. Aspden, D. A. Colling

T RACES of sulfur have a marked influence on the physical and mechanical properties of many iron-base alloys. The commonly used combustion method for the determination of sulfur content is not accurate enough at the 50 ppm level by weight and below to be useful in determining the influence of sulfur. Kriege and Wolfe' have described a method for the determination of sulfur in iron alloys in which the sulfur is evolved as hydrogen sulfide followed by reaction with N, N-dimethyl-p-phenylenediamine, and iron (111) to form methylene blue which is measured spectrophoto-metrically. This method of determining sulfur has been used to study the activity of sulfur in Fe-Si-S alloys,' but has not been previously applied to the determination of sulfur in Fe-Ni alloys because of the insolubility of nickel in dilute hydrochloric acid. Dissolution of nickel in dilute hydrochloric acid, however, can be greatly accelerated by the addition of a small amount of platinic chloride.3 By combining these two techniques in a procedure in which 0.005 pct platinic chloride in 1:l hydrochloric acid is used as the dissolving fect on the strength of the material. However, ductility is influenced by the presence of discontinuous precipitation. In Fig. 5, percent elongation data at room temperature and 1400°F is shown for two sets of specimens of Waspalloy which were solution heat treated at 1950°F and either quenched or slow cooled to the aging temperature and then aged for 100 hr at 1292" and 1598ºF, respectively. At room temperature the existence of a discontinuous precipitation cell at grain boundaries (see data point marked by arrow) has no apparent effect on ductility. However, at elevated temperatures a pronounced lowering of ductility occurs when discontinuous precipitation has occurred in the specimen. It would appear that the morphology of discontinuous precipitation "cells" at grain boundaries would be highly conducive to the initiation of cracks which in turn lead to premature "grain boundary" failure.

Jan 1, 1970

By K. M. Weigert

The position of the three-phase field between the alpha and the beta phases was established. The exact location differs from previous assumptions. The extremely high strength and hardness values were found near the phase boundaries of the ternary compositions. IN 1929, UenoL investigated vertical sections of the Ag-Cu-Zn diagram at constant silver and zinc values. From the evaluation of cooling curves and microscopic studies, he concluded that there was no evidence of a three-phase field in the solid state between the a and ,8 fields. The failure to find evidence for this field was due to the fact that it exists only in a very narrow range of compositions and requires special methods of heat treatment to establish phase equilibrium. In a later publication on the same subject Keinert2 rearranged Ueno's diagrams to conform with the basic phase rules. The existence of a three-phase field was postulated in the solid state between the a phases and the homogeneous ,9 phase between the Cu-Zn and the Ag-Zn binary border systems. The approximate location was based on a few microscopic observations of the structure and it was pointed out that the exact position could be determined only by a larger number of experiments. In the twenty years following these investigations alloys of Ag-Cu-Zn have become of general interest due to various technical applications, principally for brazing. In the course of an overall investigation of the physical properties of ternary Ag-Cu-Zn alloys the author found extremely high values of hardness and strength in alloys of compositions between the a and the yS fields. The exact location of the intermediate phase fields was established by the evaluation of more than a hundred cooling curves and microscopic mountings. Experimental Procedures Preparation of Test Samples: At the beginning of the investigation samples were chillcast into Vi in. diameter iron molds to determine hardness, strength, and the mechanism of primary crystallization. These

Jan 1, 1955

By W. R. Hamilton

THE knowledge of the existence of petroleum in Southern California dates back to the days of the missions. The presence of asphaltum and semisolid bitumen was reported at Santa Barbara in 1792, but no serious attempt was made to develop oil until Professor Silliman's optimistic report in 1865 started California's first oil boom. Wells were drilled in many counties of the State, but the equipment was unsuitable and the drilling difficult and no production was obtained except in Ventura County. Even there the production was of little importance commercially, and not until the early '80s did it become sufficient to again attract attention. In 1888 the production for the State had reached a total of about 700,000 bbl. per year, practically all light oil produced in Ventura County, Pico Canyon, Los Angeles County and in the Puente Hills. The production of petroleum attained the dignity of an industry in 1895 when the Los Angeles City and Coalinga fields were discovered. The subsequent development has been remarkable, and in 20 years the production has increased from 1,000,000 to 100,000,000 bbl. per year. The refining industry has kept pace with the production of oil. The Pacific Coast Oil Co., the predecessor of the Standard Oil Co. of California, was the virtual pioneer refining company of the State, having built a refinery at Alameda about 1880. When purchased by the Standard, about 1902, it was dismantled and the refinery at Point Richmond was built. The Richmond refinery is now one of the largest in the world, having a capacity in excess of 60,000 bbl. per day. A small refinery was built by the Union Oil Co. at Santa Paula in the early days of the industry and later many asphalt refineries were in operation in Southern California. The Pacific Coast Oil Co. was then, as has been its successor, the Standard Oil Co. of California, the principal refiner and marketer of light products, the most valuable of which was kerosene.

Jan 6, 1916

By Norman Maxwell

There was more activity in crude production in northwestern Pennsylvania in 1935 than for several years before, resulting in an increased oil production and also in the number of wells completed. Crude -production approximated 16 million barrels for the state, an increase of about one million barrels over 1934. Demand, indicated by refiners' runs to stills, increased proportionally, leaving stocks of available crude at the end of the year at the lowest point since the middle of 1934, when they reached an all-time low. The price of crude varied during the year from a low of $2.02 to a high of $2.27 at the end of the year for Middle district oil. The price of Bradford and southwest Pcnnsylvania oil changed accordingly. The average for the year would be a lower price than in 1934. A summary of the production data for the year 1935 is given in Table 1. In making up this table, 1935 figures were simply added to the table published by S. H. Cathcart last year1. A list of important wildcats is given in Table 2. Bradford Field Approximately 10,000 acres of the proven producing area of the Bradford field is in Cattaraugus County, New York, and it is possible, by differences, to distinguish the Pennsylvania production from the New York portion. The listed production for the Bradford field includes only that portion of the field situated in Pennsylvania, but also includes production from a small pool, locally known as the Mt. Jewett-Kanesholm pool, where the Bradford sand is being developed and flooded in precisply the same manner as that of the Bradford field itself. The Mt. Jewett-Kanesholm pool is not, strictly speaking, an extension of the Bradford field, but inasmuch as it is so closely allied with the Bradford field-—that is, the sand is the same and the production methods are the same—the production and drilling figures include this area.

Jan 1, 1936

J. S. UNGER,* Pittsburg, Pa, . (written discussion?).-The author of the paper has given an excellent description of the appliances used to cool parts of an open-hearth furnace, and some of the reasons why the refractories fail in service. Personally, I favor water-cooling, but to a limited degree. At one time I advocated more universal cooling than is now practised, but believe I must change my mind. Water-cooled, thin-lined blast furnaces have not proved as satisfactory as anticipated. While this may retard the building of many such furnaces, it will not prevent the use of regular tuyere- and bosh-cooling appliances. Water-cooling any furnace may be easily carried to the extreme. In an open-hearth furnace, excessive port or roof cooling, or cooling the working floors may preserve the lines of the furnace, lower the cost of refractories, acid to the comfort of the workmen, and necessitate fewer shutdowns for repairs, but it may not be good economy on account of the high first cost, the cost of cooling water, maintenance of cooling appliances, and the immediate reflection in a higher fuel cost. The question becomes a financial one, and is answered by using water-cooling devices up to the point at which they cease to show true economies. Open-hearth furnace bulkheads, roofs, and ports fail rapidly in about the order named. If they could be made to last indefinitely by water-cooling, the furnace would still have to be shut clown periodically for cleaning the slag pockets, regenerator chambers, and flues. Extra, or spare, pockets and regenerator chambers have been advocated to permit of continuous operation, but the space required, the cost of installation, and the fuel required to initially heat such cold chambers will largely prevent their adoption. Some particular fuels, as high-ash powdered coal, require frequent stoppages for cleaning, but for this particular fuel a special provision can' be made.

Jan 5, 1919

By Norman Maxwell

There was more activity in crude production in northwestern Pennsylvania in 1935 than for several years before, resulting in an increased oil production and also in the number of wells completed. Crude -production approximated 16 million barrels for the state, an increase of about one million barrels over 1934. Demand, indicated by refiners' runs to stills, increased proportionally, leaving stocks of available crude at the end of the year at the lowest point since the middle of 1934, when they reached an all-time low. The price of crude varied during the year from a low of $2.02 to a high of $2.27 at the end of the year for Middle district oil. The price of Bradford and southwest Pcnnsylvania oil changed accordingly. The average for the year would be a lower price than in 1934. A summary of the production data for the year 1935 is given in Table 1. In making up this table, 1935 figures were simply added to the table published by S. H. Cathcart last year1. A list of important wildcats is given in Table 2. Bradford Field Approximately 10,000 acres of the proven producing area of the Bradford field is in Cattaraugus County, New York, and it is possible, by differences, to distinguish the Pennsylvania production from the New York portion. The listed production for the Bradford field includes only that portion of the field situated in Pennsylvania, but also includes production from a small pool, locally known as the Mt. Jewett-Kanesholm pool, where the Bradford sand is being developed and flooded in precisply the same manner as that of the Bradford field itself. The Mt. Jewett-Kanesholm pool is not, strictly speaking, an extension of the Bradford field, but inasmuch as it is so closely allied with the Bradford field-—that is, the sand is the same and the production methods are the same—the production and drilling figures include this area.

Jan 1, 1936

By S. J. McCarroll

J. Bruce Clemmer, J. B. Rosenbaum, and C. H. Schack (U.S. Bureau of Mines, Salt Lake City)—We have watched with considerable interest Three Kids development of Manganese Inc. and have been impressed by the ingenuity with which management and staff have solved their many obstinate handling problems. Mr. McCarroll has been lenient in describing the difficulties faced by the company in developing a process for beneficiating Three Kids ore. The operation, equivalent in size to a 20,000-ton sulphide ore plant, is treating a unique ore by a flotation process pioneered by Manganese Inc. Perhaps the magnitude of the conditioning and flotation problems peculiar to Three Kids ore can be better appraised when it is pointed out that two-thirds to three-fourths of the ore is floated in the rougher step and that the four stages of cleaning which follow are equivalent to floating the whole plant feed two to three times. Our experience in both laboratory and pilot plant flotation of Three Kids and other manganese ores leads us to agree with Mr. McCarroll that suitable conditioning is a prime requisite for successful oil-emulsion flotation. The difficulties of proper conditioning were demonstrated in pilot plant processing of Artillery Peak manganese ore at our Boulder City, Nev., experiment station. Over three months of experiments and extensive plant revision were required before satisfactory conditioning was obtained in the 25-ton-per-day plant. Such factors as time, type and intensity of mixing, aeration, surface to volume relationship, and power input are still being studied by the Bureau of Mines in hopes of learning how best to condition manganese pulps for oil-emulsion flotation. Other factors affecting flotation of manganese with oil emulsion also deserve attention. A few of these are the influence of stability and proportion of ingredients in the collector emulsion, the feasibility of grinding

Jan 1, 1955

By Louis Katona

The practical execution of the design for rolling-mills presented by the writer at the Paris meeting* of thc Iron and Steel Institute in 1900 involves the determination of some questions not yet discussed, among which is the determinatioir of the amount of power required to perform the rolling of pieces of iron and steel of given dimensions. It is necessary to know this factor if we would put motors of proper capacity to the respective pairs of rolls, or, rcciprocally, if, having standard motors at our disposal, we would design grooves to suit them. Moreover, this factor is involved in giving right dimensions to every part of the rolls and housings. Expert designers of engines for driving rolling-mills of the present type receive very indefinite directions, such as: that the motor is to drive a light, medium or heavy train; that it must work with fly-wheel or reversing gear; that the number of revolutions per minute should not exceed 40 or 60, and that at a given speed the power developed should be from 100 to 200 H. P., or from 1,000 to 2,500 13. P. It frequently happens, however, that an cngine of 200 H. P. is forced under the circumstances to press or develop as much as 300 H. P., while, on the other hand, the ,1,500-11. P. engine may be rolling-stock which could be worked with a maximum expenditure of 60 to 80 H. P. Of course such variatior~s as these do not permit the best adjustment of parts or the best economy of power and fuel. The design of roll-trains is even more vaguely limited. Every part of a train, from the point where it connects with the engine to the last groove in the rolls, bears evidence that there are no rules for calculating even approximately the dimensions of the main-shafts, couplings, pinions, gears, rolls, trunnions,

Jan 1, 1904

By H. Case Willcox

AERIAL photographic surveying and mapping is not new or unknown to geologists. However, it has been utilized but little before, principally because it is only within the last few months that practical means of adapting this method to the requirements of petroleum companies have been discovered. No American aerial survey company has taken up aerial surveying and mapping as an engineering service to be offered to petroleum companies and their geologists for use in undeveloped and jungle-covered petroleum areas. This method of surveying and mapping, however, is used by the War Department, the U. S. Reclamation Service, and Geological Survey, and the corresponding Departments of the Canadian Government. ADVANTAGES OF AERIAL PHOTOGRAPHIC SURVEYING AND MAPPING The advantages of aerial photographic surveying and mapping to petroleum companies and their geologists are many. One of the most valuable is presented in the very first phase, or the exploration period. It is assumed that, when convinced that petroleum possibilities are present, a petroleum company has secured a concession of 8000 sq. mi. of unexplored area in Eastern Venezuela. The company may either have the entire area surveyed and mapped by the aerial photographic method, or send its chief field geologist up in an airplane so that he, from-an aerial reconnaissance, may reject certain portions that, for geological reasons, the company would not be interested in. He will then point out the regions that are to be surveyed and mapped. After the air-work is completed, the results are brought down, developed, and printed; then the resulting "contact prints" are given to the field geologist. They may be roughly assembled to give a general idea of the property in its entirety, or they are in shape to be examined in adjoining pairs under the stereo-scope. With this instrument, the geologist is enabled to make a minute examination of surface indications. The work of assembling and constructing a complete general or detailed map, according to the scales desired by the petroleum company and for the later office use, is continued by the aerial photographic company.

Jan 3, 1925

Bill S.1431 for the creation of a Department of Natural Resources has received a propitious hearing before the Senate Committee on Government Operations. Interior Secretary Rogers C. B. Morton was one of the prominent witnesses who testified in favor. The department had been proposed, Morton said, with "the conviction that the development of all natural resources would be harmonized with the most practicable possible means to protect and preserve the environment, consistent with the social and economic needs of the Nation." Another opinion on the pro side came from Atomic Energy Commissioner Clarence E. Larson, who said that a "total picture" had become essential to the establishment of a policy for developing energy resources in the best public interest. Commissioner James T. Ramey, on the other hand, was one of the AEC dissenters. Ramey said he believed the reorganization of resource responsibilities would hinder efforts to deal with energy-environmental problems and prevent the use of AEC "expertise and facilities" to the greatest advantage. As Arnold Weber, associated director of the Office of Management and Budget, pointed out, however, retiring AEC Chairman Glenn T. Seaborg is in favor of the new department. Another supporter, and one who can cast a vote on the bill, is Sen. Frank E. Moss. Final Standards for emissions from new stationary sources will be published by the Environmental Protection Agency on October 27. The initial proposals, appearing in the Federal Register on August 17, called for limiting emissions per million Btu of heat input (maximum 2-hr average) to 0.2 lb of particulate matter, and, where solid fuel is burned, to 1.2 lb of sulfur dioxide and 0.7 lb of nitrogen dioxide. While the new rules are mainly for new plants, the EPA is also proposing them for "existing plants which are modified in such a way as to increase or alter. . . their emissions."

Jan 1, 1971

By Robert Warner

WHEN a new mine is opened, and often when an operating mine must adapt itself to physical or economic changes, a mining system must be selected in complete detail. In the past the plan chosen was usually the product of the local staff alone, however limited the training and experi-ence of that staff might be, which often resulted in the introduction of methods that were familiar to the staff, but not so well suited to the con-ditions as others unknown to the local men. A new management, noting the difficulties with the existing layout, might make modifications or complete changes, so that many mines in their history have seen a whole series of mining systems, each somewhat laboriously grafted on to its predecessor. This should not be interpreted as a condemnation of the older staffs for sticking to the tried systems, such as open square-sets in the early days at the Homestake, because they knew it would work after a fashion, nor does the statement apply to the technically trained, and usually broadly experienced staffs of most present-day properties. The older miners did not have the variety of tools and methods, nor the present freedom of transfer of information as to what the other man is doing, and so did the best they could under the circumstances. Finally, the higher grade of the ores made the choice less vital. The ever-increasing need to mine low-grade orebodies, with a fixed or even lower price for the metal produced, has caused an increasing need for low-cost mining. In most new mines this has simplified the problem of selection by eliminating from consideration all of the high-cost systems, but it has also complicated the choice by the necessity for refinement in detail and a close adjustment of the plan selected to all the conditions at the property. In these low-cost problems any textbook division of mining systems as applied to "beds, veins or masses" avails little as a guide. It should be realized at the outset that to' be successful under modern competitive conditions a system of mining must be worked out with elaborate detail, with careful time scheduling and control of the various elemental operations, and that after it is introduced it must be run with a large amount of technical direction.

Jan 1, 1933

By P. H. Wendland

Calculations are presented for the design of a silicon photodiode in which the incident light beam makes multiple passes between the detector surfaces. Total internal reflection is used for this "light-trapping" effect. By this means, the optical path length can be extended to several millimeters, while the electrode separation remains less than 102 cm, as required for nanosecond response time. Data are presented for a Schottky barrier photodiode constructed on a multiply reflecting silicon base wafer. It is shown that the long-wavelength response is considerably extended in such structures without a corresponding sacrifice in high-speed response. The development of efficient and powerful lasers at 1.06 p has stimulated interest in detectors which operate at this wavelength. In typical silicon photodiodes, for detecting 1.06 p radiation, the requirements for high speed and high sensitivity are mutually exclusive. Since the absorption coefficient is only 25 cm-', a lo-'-cm path length is required to absorb 92 pct of the incident 1.06 p radiation. If the electrode separation is greater than 10 cm, however, the carrier transit time will be greater than 1 nsec. This problem can be solved by allowing the incident light beam to make multiple passes between the electrodes. The optical path length can then be extended to several millimeters, as required for complete absorption, while the electrode separation remains less than 10' cm, as required for nanosecond response time. In a typical photodiode geometry, one ohmic contact and one rectifying contact are formed on the two opposite surfaces of a base wafer, and the wafer thickness determines the electrode separation. The objective of the multiple reflection design is to allow all 1.06 p radiation to enter the detector front surface and to form the back detector surface so that no 1.06 radiation can exit. Total internal reflection at the back detector surface is well-suited for light trapping of 1.06 p radiation because the relatively large dielectric constant of silicon leads to a critical angle of 16.5 deg for total internal reflection. LIGHT TRAPPING It is well-known that, as light passes from one medium such as air into another medium such as glass or silicon, the angle of refraction is always less than the angle of incidence. In the limiting case, where the incident rays approach an angle of 90 deg with the normal, the refracted rays approach a fixed angle +, beyond which no refraction is possible: this is called the critical angle. It follows from Snell's law that where = critical angle, n - index of refraction of air, n' - index of refraction of the medium. Applying the principle of reversibility of light rays, all internal angles of incidence greater than +, will produce total internal reflection and "light trapping". The index of refraction of silicon at 1.06 p is 3.5,' and the critical angle is thus 16.5 deg. Fig. 1 shows these relationships for silicon. This very small critical angle in silicon is significant because all incident angles between 16.5 and 90 deg will produce total internal reflection and "light trapping". This effect can be implemented with a "prismlike" geometry, so that incident light can be introduced into the sample without loss and "trapped". PHOTOSIGNALS A precise knowledge of the absorption coefficient at 1.06 in silicon is of critical importance to the design of fast and efficient silicon photodiodes for 1.06 radiation. Dash and newman2 show a value of 25 cm-l, and our measurements have corroborated this value. Assuming that the collection of photoinduced minority carriers is perfect, the quantum efficiency of a photodiode is dependent only on the absorption coefficient. It then follows from Lambert's law that where QE is the quantum efficiency in pct, a is the absorption coefficient, d is the optical path length, and the reflectivity at the surface is assumed to be completely suppressed by an optical interference layer. Fig. 2 gives the maximum quantum efficiency for 1.06p radiation of a silicon photodiode with optical path length d, using Eq. [2]. The ultimate response time of a fully depleted photodiode to an incident light pulse can be considered to be the arrival times of all photoinduced carriers at the contacts, i.e., the minority carriers at the junction interface and the majority carriers at the oppo-

Jan 1, 1968

By V. O. Struebing, K. A. Johnson, F. H. Ellinger, C. C. Land

The system Pu-Ce-(Pu,Ce)Co2 has been investigated by thermal, micrographic, and X-ray diffraction methods. The principal characteristics of this system were found to be: 1) a "eutectic" valley extending across the phase diagram from the 6 Pu/Pu3 Co eutectic at 408°C to the 7 Ce/Ce24Co11 eutectic at 42Z°C, the maximum temperature in the valley being 443°C; 2) three ternary inter mediate phases, each having an appreciable mutual solid solubility for plutonium and cerium; 3) eleven four-phase equilibria comprising one eutectic, four peritectics, and six Class II reactions; 4) a pseudobinary section between the ternary phase A and the y Ce solid solution, and another such section between the 6 Pu solid solution and the 77 phase (Pu3 CO) containing cerium in solid solution. ALLOYS of plutonium that are completely molten at temperatures in the vicinity of 500°C are of interest for use in the liquid state as fast reactor fuels. Since exploratory work1,2 on Pu-Ce-Co alloys had indicated that a "eutectic" valley extended across the ternary system between the Pu-co[6 Pu/n (Pu3co)] and the Ce-CO[? Ce/? (ce24co11)] binary eutectics, thus allowing alloys of any plutonium concentration to be selected within the temperature limitation, the present investigation was begun for the purpose of accurately defining the "eutectic" valley. However, when the existence of three ternary intermediate phases and the consequent complexity of the liquid-solid equilibria were discovered, the investigation was expanded to cover the complete system, except for the corner between the isomorphous series PuCo2-CeCo2 and pure cobalt. 1) EXPERIMENTAL The purities of the alloy components are given in Table I. Alloy buttons, each weighing about 5 g, were prepared by arc melting the accurately weighed components (±0.1 mg) under a purified He-Ar atmosphere. Weight loss as a result of melting was usually less than 1 part in 1000; therefore, the buttons were not chemically analyzed. One half of each button was re-melted by induction heating in vacuo in a magnesia crucible and furnace-cooled, so as to produce a somewhat coarser microstructure than that of the rapidly cooled arc-melted button. About 20 g of each alloy to be examined by thermal analysis were remelted in vacuo in a tantalum crucible of the inverted thermocouple well type. The thermal, X-ray diffraction, heat treating, and micrographic methods used in this investigation were essentially the same as have been described in earlier reports.3,4 Two etchants for these alloys were found to be satisfactory: A) 8 (parts by volume) orthophosphoric acid, 5 ethanol, and 5 glycol; B) 7 tetraphosphoric acid, 36 water, and 57 2-ethoxyethanol. Etchant A was used at 5 to 6 v for 15 to 20 sec, and etchant B was used at 10 v for 10 sec. 2) THE LIMITING BINARY SYSTEMS 2.1) Plutonium-Cerium. The phase relationships of this system have been investigated by Ellinger, Land, and Cramer,5 and by Selle and Etter.6 The over-all agreement of their phase diagrams is good, but there are some discrepancies in the positions of some phase

Jan 1, 1967

By Vsevolod Krivobok

IT is generally recognized that "low temperatures" have a definite effect on the properties of metals and alloys. Furthermore, it is also generally understood that the effect is decidedly adverse. The possibility that the same low-temperature treatment might be employed for the purpose of improving certain properties of the .alloys has received less attention until recently, and the experimental and theoretical knowledge consequently is meager. The effect of low temperatures may be studied in two ways: by studying such properties as tensile strength, hardness, impact resistance, etc., at low temperature, and by studying the properties of alloys at room temperature after these alloys have been subjected to a low-temperature treatment. Even in the latter case, certain properties will differ materially from the same properties obtained on identical material but without cold treatment. In other words, subjecting alloys to cold treatment results in an irreversible change in mechanical properties. Changes of this character are usually indications of the appearance of a new phase or phases, and would be likely to occur in alloys which, either by virtue of their composition or by heat treatment, are retained at room temperature in a metastable condition. Consequently, studies of the effect of low temperatures logically should be conducted from the physicochemical point of view, since the results of such studies not only would furnish metallurgists with interesting theoretical data but would clearly indicate the classes of alloys that would hold promise of improvement, and, possibly, of new applications. As the present investigation deals with chromium and chromium-nickel alloys of iron of the stainless variety, it has been thought desirable to present the data concerning low-temperature properties of these alloys, available from the most recent and most comprehensive work of H: S. Russell.' A summary, of these data is given in Table 1. The data are confined to a limited number of alloys of the type dealt with in the present

Jan 1, 1931

By E. Gilpin

The Nova Scotian gold fields have yielded so little in comparison with those of the United States, that a lengthy description of them would almost appear unnecessary. However, not only are they interesting from a geological point of view, but experience has shown

Jan 1, 1886

By R. C. Patterson

In view of the circumstance that very few important changes have been made within the last 15 or 20 years in the equipment of rod and wire mills, the description of a new process introduced by Grenville Mellen, of LleweIIyn Park, N. J., to take the place of the present laborious system of producing rods of lead, zinc, brass, copper, aluminum, etc., may be interesting to members of the Institute. This new process consists in the production of cast rods at one operation in a small continuous casting machine. The hot liquid metal is transferred from the melting crucibles directly into an endless chain of mold blocks in the machine, where solidification takes place, and the rod comes out continuously in a solid form at one end as long as the molten metal is supplied. The operation of these mold blocks so as to produce a solid rod of uniform structure constitutes an important part of Mr. Mellen's invention. The machine (Figs. 1 and 2), 12 ft. in height over all, 2 by 3 ft. in horizontal cross-sectional area, and 6,000 Ib. in weight, has a framework of cast iron, holding in position two endless chains of mold blocks, which are made in sections and join in center alignment. The mold orifice is made up of these mold sections, into which the liquid metal flows. The molding chains are composed of steel blocks, grooved on one face to form the molding cavity, and linked together with flexible joints. Each block is carried on four rollers which guide the chain around the end sprockets and carry it in its course through the machine. The accuracy of alignment requisite to the production of a perfect rod in the mold groove formed by these sections is secured by careful machine work, and by building the four ways, down which the alignment takes place, so that two of the sides are fixed permanently, whiIe the opposite sides are held to their position by spring pressure. The guides carrying the molds, while in casting position, are water-cooled square tubes. The length of this machine is somewhat indeterminate. A certain amount of both time and cooling surface is required to solidify the metal jn the mold; and one may either use a long molding chain and run it fast, or a shorter chain and run it correspondingly slower. We have found,

Jan 1, 1916