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By Lester Tarnopol, Ralph Hultgren

A considerable interest in the subject of superlattices has been manifested by many papers and reviews that have recently appeared, both in physical and metallurgical publications. This interest is due largely to the apparent simplicity of the ordering process, which permits the explanation of many phenomena on the basis of elementary theory. Moreover, ordering may cause important changes in the physical properties of alloys. In this paper, we shall discuss the causes of superlattices in terms of simple properties of the elements that give rise to them, together with a series of experiments performed to test our conclusions. Evidence is presented that in some cases the process of ordering is more complex than might be supposed. While the different species of atoms are usually found in random positions in alloy lattices, in some cases unlike atoms tend to be nearest neighbors. Bethe's1 "order of neighbors" is a statistical measure of thib tendency. At suitable compositions it is possible for atoms in large regions to be regularly arranged, which causes superlattice lines to appear. in X-ray diffraction patterns. Bragg and Williams2 haw dealt with this "long-distance order" in their fundamental work 011 superlattices. Excellent discussions of superlattices are to be found in current reviews TheRmodynamic Considerations Thcrmal vibration tends to destroy order. The magnitude of the effect can be determined from the entropy of mixing, which is calculate from first principles. Since the ordered state has the lower entropy, it must also have a lower internal energy to be stable at any temperature. The difference in internal energy determines the critical temperature at which long-distance order disappears. According to the, theory of Bragg and Williams,~

Jan 1, 1939

By H. l. Burghoff

During the course of preparation of crystals of alpha brass for an investigation of their creep characteristics, a number of critically oriented crystals were produced. In each of these specimens, Po, the specimen axis, lay near some important crystallographic direction or on or near the border of two possible slip systems. Because of the unusual nature of their orientations, it was considered of interest to deform these specimcns in simple tension and to study orientation changes and any unusual occurrences, different from what would be expected for specimens ill which only one slip system had distinctly the highest maximum resolved shear stress. Choice of actual operating slip system in a crystal offering an immediate possibility of two slip systems would be expected to be due to chance., defeet, or some inhomogeneity. Even in an ideally perfect crystal so oriented, the natural oscillations of the atoms about their lattice positions would give rise to a condition wherein one slip system would be farored over the other at the critical shear stress. In the large, nonperfeet crystals of the present investigation, slip on both systems, but in different portions of the specimen, might occasionally be expected. Determination of Orientation and Operating Slip System Orientations of specimens before and after deformation were determined by Greninger&apos;s back-reflection Laue method.&apos; Elam2 has shown that deformation of alpha brass crystals proeceds as with crystals of aluminum and of copper; that is, the slip plane is a {111) plane and the slip direction is a <110> direction. There are, however, four possible slip planes of {111) form and each plane has three possible slip directions, so that there is a, total of 12 possible slip systems in a face-centered cubic lattjce. It is evident that the system for which the tangential component of shear is maximum will function

Jan 1, 1940

By Lester Tarnopol, Ralph Hultgren

A considerable interest in the subject of superlattices has been manifested by many papers and reviews that have recently appeared, both in physical and metallurgical publications. This interest is due largely to the apparent simplicity of the ordering process, which permits the explanation of many phenomena on the basis of elementary theory. Moreover, ordering may cause important changes in the physical properties of alloys. In this paper, we shall discuss the causes of superlattices in terms of simple properties of the elements that give rise to them, together with a series of experiments performed to test our conclusions. Evidence is presented that in some cases the process of ordering is more complex than might be supposed. While the different species of atoms are usually found in random positions in alloy lattices, in some cases unlike atoms tend to be nearest neighbors. Bethe&apos;s1 "order of neighbors" is a statistical measure of thib tendency. At suitable compositions it is possible for atoms in large regions to be regularly arranged, which causes superlattice lines to appear. in X-ray diffraction patterns. Bragg and Williams2 haw dealt with this "long-distance order" in their fundamental work 011 superlattices. Excellent discussions of superlattices are to be found in current reviews TheRmodynamic Considerations Thcrmal vibration tends to destroy order. The magnitude of the effect can be determined from the entropy of mixing, which is calculate from first principles. Since the ordered state has the lower entropy, it must also have a lower internal energy to be stable at any temperature. The difference in internal energy determines the critical temperature at which long-distance order disappears. According to the, theory of Bragg and Williams,~

Jan 1, 1939

By H. l. Burghoff

During the course of preparation of crystals of alpha brass for an investigation of their creep characteristics, a number of critically oriented crystals were produced. In each of these specimens, Po, the specimen axis, lay near some important crystallographic direction or on or near the border of two possible slip systems. Because of the unusual nature of their orientations, it was considered of interest to deform these specimcns in simple tension and to study orientation changes and any unusual occurrences, different from what would be expected for specimens ill which only one slip system had distinctly the highest maximum resolved shear stress. Choice of actual operating slip system in a crystal offering an immediate possibility of two slip systems would be expected to be due to chance., defeet, or some inhomogeneity. Even in an ideally perfect crystal so oriented, the natural oscillations of the atoms about their lattice positions would give rise to a condition wherein one slip system would be farored over the other at the critical shear stress. In the large, nonperfeet crystals of the present investigation, slip on both systems, but in different portions of the specimen, might occasionally be expected. Determination of Orientation and Operating Slip System Orientations of specimens before and after deformation were determined by Greninger&apos;s back-reflection Laue method.&apos; Elam2 has shown that deformation of alpha brass crystals proeceds as with crystals of aluminum and of copper; that is, the slip plane is a {111) plane and the slip direction is a <110> direction. There are, however, four possible slip planes of {111) form and each plane has three possible slip directions, so that there is a, total of 12 possible slip systems in a face-centered cubic lattjce. It is evident that the system for which the tangential component of shear is maximum will function

Jan 1, 1940

By William C. Maurer

A survey of 25 novel drills has shown that spark drills have potential for drilling oil wells and blastholes at higher rates than rotary drills. Available laboratory and field data were extrapolated to drilling rates of 70 to 280 fph for full-scale spark drills. Most of the data used in these extrapolations were from small-scale laboratory tests at atmospheric pressure. Accurate extrapolation of the small-scale spark drill tests to full-scale field drills was complicated by the fact that the effect of fluid pressure in the well bore and the effect of spark size were not known. In order to answer these questions and to more accurately evaluate the potential of spark drills for drilling blastholes and oil wells economically, a high-voltage spark discharge system was assembled. This equipment produced powerful sparks (10,000 joules) equivalent to those that would be used on a 100-kw full-scale field drill. These sparks are 100 times more powerful than those previously used on spark drills, thus eliminating extrapolation of the spark size. In addition, a pressure chamber was modified to enable using these sparks to produce craters in rocks at fluid pressures up to 15,000 psi, thus eliminating extrapolation from atmospheric pressure to the high pressure existing in deep oil wells. These tests have provided considerable information for more accurately evaluating spark drills for oil-field drilling. MECHANISM AND THEORY OF SPARK DRILLING Spark-Drilling Mechanism When a high-voltage capacitor is discharged across two electrodes, the dissipated energy produces a high-temperature, high-pressure plasma for a few µsec. When these sparks are discharged in air, they undergo considerable expansion (Fig. 1) and produce low-pressure pulses (103-

Jan 1, 1970

This story of the salting of a supposed diamond mine is a part of our Western history and deserves to be recorded in this book. It was more than a local affair, because it was concerned with persons in London and New York, as well as San Francisco. Part of the story has been told by Asbury Harpending in a little book published 12 years ago. Harpending (who died at New York in 1923) was in London in March, 1872, when he received a cable dispatch from William C. Ralston, the president of the Bank of California, stating that "a vast diamond field" had been discovered "in a remote section of the United States". Before starting for San Francisco, Harpending had an interview with Baron Rothschild, who showed a lively interest in the story, which was as follows: two weather-beaten prospectors went to the Bank of California and deposited some uncut diamonds and rubies for safe keeping; these precious stones were estimated to be worth $125,000. The men said that they had found the gems in "a desert portion of the West". They departed quietly, but the story was told in business circles; whereupon George D. Roberts, a mining engineer of wide experience and an associate of Ralston, sought an interview with the prospectors. One of them proved to be a man that had been in the employ of Roberts. Both prospectors, named Slack and Arnold, appeared "coy and cautious"; they were "simpleminded fellows", and were "afraid to trust anyone with the momentous secret ". They refused to divulge the place of discovery and declined "to part with their rights", but later "they became more amenable to reason" and expressed willingness to sell a half interest to

Jan 1, 1932

By L. S. Panyity

The Cleveland (0.) gas pool described by Frank R. Van Horn,&apos; is the northern extremity of the great "Clinton" sand gas development in Ohio. Numerous gas pools have been developed in this formation, which are now more or less connected, link by link, forming an almost continuous gas pool, starting at Cleveland, and running thence southward through Cuyahoga, Medina, Wayne, Ashland, Richland, Knox, Licking,

Jan 1, 1918

By Douglas W. Fuerstenau, Kalanadh V. S. Sastry

Based on an analysis of green pellet size distributions and kinetic data on ball growth with taconite concentrates, a ballability index has been developed to quantify ball growth behavior as a function of moisture and bentonite additions. The applicability of the ballability index to such other particulate materials as pulverized limestone and ground magnesite is shown.

Jan 1, 1973

By R. L. Boyer, F. Morgan, M. Muskat

In the last several years a type of application of the fundamental permeability-saturation relationships has been developed which offers great promise in the interpretation of general reservoir performance.l-&apos; In these developments no attempt is made to solve the detailed flow dynamics in actual oil and gas-producing systems. That problem still remains unsolved. But the permeability-saturation phenomena are incorporated in the analysis of oil-producing reservoirs in a manner such as to reflect the true role they play in controlling the gross reservoir behavior. In particular, they are introduced in such a manner as to determine the gas-oil ratio of the production at any stage of depletion, and, when combined explicitly with the so-called material-balance principles in differential form, one can obtain a differential equation describing completely the average pressure and gas-oil-ratio history of oil-producing reservoirs. While thus far they have been applied directly only to gas-drive reservoirs, they are susceptible of extension to partial water-drive systems, and qualitatively the same principles are of value in the study Of complete water-drive reservoirs. Moreover, in addition to giving a means for computing the variation of the reservoir pressure and gas-oil ratios vs. the cumulative production, they automatically lead to predictions of the gross ultimate recovery under natural depletion—and when properly extended they provide means for predicting the ultimate recovery under gas or water injection. The data required for such applications are the initial fluid distribution in the producing section, the pressure-volume-temperature data on the gas and liquid phases, and the permeability-saturation relationship for the oil-satuiated zone. The former can be obtained with reasonable accuracy by methods that are well established and available throughout the industry. The permeability-saturation data, however, involve techniques that are not at all standardized. In fact, only

Jan 1, 1947

By M. Muskat, R. L. Boyer, F. Morgan

In the last several years a type of application of the fundamental permeability-saturation relationships has been developed which offers great promise in the interpretation of general reservoir performance.l-&apos; In these developments no attempt is made to solve the detailed flow dynamics in actual oil and gas-producing systems. That problem still remains unsolved. But the permeability-saturation phenomena are incorporated in the analysis of oil-producing reservoirs in a manner such as to reflect the true role they play in controlling the gross reservoir behavior. In particular, they are introduced in such a manner as to determine the gas-oil ratio of the production at any stage of depletion, and, when combined explicitly with the so-called material-balance principles in differential form, one can obtain a differential equation describing completely the average pressure and gas-oil-ratio history of oil-producing reservoirs. While thus far they have been applied directly only to gas-drive reservoirs, they are susceptible of extension to partial water-drive systems, and qualitatively the same principles are of value in the study Of complete water-drive reservoirs. Moreover, in addition to giving a means for computing the variation of the reservoir pressure and gas-oil ratios vs. the cumulative production, they automatically lead to predictions of the gross ultimate recovery under natural depletion—and when properly extended they provide means for predicting the ultimate recovery under gas or water injection. The data required for such applications are the initial fluid distribution in the producing section, the pressure-volume-temperature data on the gas and liquid phases, and the permeability-saturation relationship for the oil-satuiated zone. The former can be obtained with reasonable accuracy by methods that are well established and available throughout the industry. The permeability-saturation data, however, involve techniques that are not at all standardized. In fact, only

Jan 1, 1947

By J. W. Cuthbertson, R. A. Cresswell

THE constitution of Cu-rich alloys with 1.5 to 13.5 pct Sn and 0.25 to 3.0 pct Be and the precipitation-hardening characteristics of alloys with 1.5 to 13.5 pct Sn and 0.25 to 1.0 pct Be have been examined. The hardness and tensile strength of the alloys examined increase markedly after solution treatment at 700°C followed by heat treatment at temperatures between 200" and 450°C. By a combination of cold work and heat treatment, hardness values similar to those exhibited by commercial Be-Cu alloys containing 2.25 pct Be can be obtained with ternary alloys containing 9 pct Sn and 0.75 pct Be and containing 10 pct Sn and 0.5 pct Be. Marked hardening effects occur with alloys containing even less beryllium. By heat treatment alone, a hardness value of 310 diamond pyramid hardness can be obtained from an alloy containing 10 pct Sn and 0.75 pct Be. Preliminary tensile tests have shown that an ultimate tensile strength of 110,000 psi with an elongation of 23 pct is obtainable by precipitation hardening an alloy with 8 pct Sn and 0.75 pct Be. The precipitation-hardening process has been followed microscopically for certain alloys and the inference is that, while the initial hardening effect is probably explained by the precipitation of the ß phase of the Cu-Be system, further hardening, proceeding at a much slower rate, also occurs, apparently as a result of precipitation of phases of the Cu-Sn system, particularly precipitation of the 6 phase at temperatures below 350". The presence of the e phase of the Cu-Sn system in certain alloys at temperatures below 350°C has been confirmed. Tin-bronzes are widely used in engineering applications where a combination of high strength and good resistance to corrosion is wanted. The maximum strength is induced in these alloys by cold working, and it would be an advantage for many purposes if high strength could be achieved alternatively by an age-hardening process. While Cu-Sn alloys have a good fatigue resistance they can be surpassed in this respect by Cu-Be, but the use of the latter alloy is limited by its high cost. If, by adding beryllium to tin-bronze, the properties of the respective binary alloys could to some extent be combined, a most attractive alloy should result. As pointed out by Raynor,¹ beryllium is on the borderline of the zone of favorable size factors for copper, and the solid solubility of beryllium in copper is consequently much more restricted than if the size factor were strongly favorable. The size factor is sufficiently favorable, however, to permit an increase in solid solubility with rise in temperature, and there is thus a composition range in which CU- Be alloys are susceptible to hardening by precipitation heat treatment. Although the a phase of the Cu-Sn system is similarly susceptible to precipitation treatment, the time necessary to establish equilibrium in commercial alloys of this type is usually so great that age hardening becomes impracticable. The addition of beryllium to Cu-Sn alloys would appear to offer a means of conferring on the latter useful age-hardening properties. Masing and Dahl² and others have, in fact, shown that the addition of beryllium to Cu-Sn a solid solutions renders these alloys susceptible to precipitation hardening and after such hardening confers on them an encouraging improvement in physical properties. If this improvement could be achieved by the addition of substantially smaller amounts of beryllium than are customarily found in binary Cu-Be alloys, the ternary alloys should possess economic advantages which might make them more attractive than the binary alloy for some applications. Binary Systems Copper-Tin: The constitution of these alloys is now reasonably well known and is summarized in the equilibrium diagram published by Raynor.³ The following observations, due to Raynor,¹ on the structure of those phases of the Cu-Sn system that are likely to be found in the ternary alloy system will facilitate the subsequent discussion on the examination of that system. The ß phase is an electron compound at the electron-atom ratio 3:2 and has a body-centered cubic crystal structure. This phase is stable only down to 586°C, at which temperature it decomposes eutectoidally into the a and y phases. The y phase has a structure that is also based on the cubic system. This phase is stable down to 520°C, at which temperature it decomposes eutectoidally into the a and d phases. The d phase is an electron compound (Cu³¹Sn8) which has a crystal structure analogous to that of 7 brass. This phase is stable from 590" to 350°C; on prolonged annealing at the latter temperature it breaks down into a mixture of the a and E phases. The e phase is an electron compound (Cu³Sn) having the electron-atom ratio 7:4. Its structure may be regarded as a superlattice based on the close-packed hexagonal system. This phase is stable from 676°C to room temperature. The primary solid solubility of tin in copper increases to a maximum of 15.8 pct as the temperature falls from that of the peritectic reaction to 586°C. The solid solubility remains constant from 586" to 520°C. At lower temperatures the solubility decreases progressively. Below 350°C the fall in solubility is pronounced and is associated with the precipitation of the e phase. This precipitation is very sluggish and does not normally occur under service conditions. Copper-Beryllium: The Cu-Be system has been investigated by Borchers&apos; and others. Raynor5 summarized the present state of information on it.

Jan 1, 1952

By O. Vartianen, R. T. Hukki

A preliminary investigation of the collecting effects of various fatty acids in tall oil has led to a conclusion that the collecting power of fatty acids used in flotation increases with increasing un- saturation of the hydrocarbon chain. Linoleic acid was found to be an excellent collector for oxide minerals. TALL oil is a mixture of fatty and resin acids extracted as byproducts in the sulphate pulp industry. In the field of flotation a well-known example of this type of product is Reagent No. 708 of the American Cyanamid Co. Its successful use as a flotation collector with many nonsulphide minerals has been described by Falconer and Crawford.&apos; The composition of crude tall oil varies within wide limits.&apos; " By a number of methods the crude oil may be refined to produce a variety of refined products. This investigation presents a preliminary comparative study of collecting properties of the fatty acids in tall oil. In Finnish tall oils these constituents are primarily palmitic, oleic, linoleic, and linolenic acids.:&apos; The first is a saturated fatty acid having 15 carbon atoms in its hydrocarbon chain, plus one in the carboxyl group. The others have 17-carbon-atom chains and are unsaturated. It is of particular interest to note that palmitic, oleic, lino-leic, and linolenic acids represent increasing degrees of unsaturation with 0, 1, 2, and 3 double bonds, respectively. To test the collecting properties of the four fatty acids separately, the vacuum flotation technique described by Schuhmann and Prakash4 was used. By this method the boundary between flotation and non-flotation conditions was approximately delineated, with the use of ilmenite and several other minerals. Collector concentration and pH were the principal variables. On the basis of information obtained, actual flotation tests were run on an ilmenite-bear-ing ore in a laboratory flotation cell. Through the courtesy of P. Kajanne from the Department of Chemistry, Finland Institute of Technology, the following reagents were obtained for this investigation: 1—Palmitic acid, of Judex, had a purity of 95 pct as determined by parallel iodo-metric and spectrophotometric measurements. 2— Oleic acid, product of May and Baker Ltd., indicated purity of 98 pct. By iodometric and spectrophoto-metric determinations the oleic acid content was found to be 83.8 pct. In addition, it contained 6 pct linoleic, 1 pct linolenic, and 9.2 pct saturated fatty acids.&apos; 3—Linoleic acid was prepared from soybean oil by low-temperature crystallization. Its linoleic acid content was 95 pct by the methods indicated above. 4—Linolenic acid was prepared from linseed oil by low temperature crystalIization. Its linolenic

Jan 1, 1954

By G. R. Frank, R. E. Willett, E. H. Hollingsworth

The most generally accepted equilibrium diagram for A1-Fe alloys has a eutectic system on the aluminum side with an essentially insoluble constituent of the formula, FeAl,, as the second phase. In 1938, Bradley and Taylor1 did report a phase change of FeAl,, but this change has never been confirmed. According to them, FeA1, is the stable phase only at higher temperatures; at lower temperatures, it is converted into Fe2Al7 and aluminum. It has now been found that there is, in fact, a phase change of the Al-Fe constituent on the aluminum side of the equilibrium diagram. This change, however, is not the one reported by Bradley and Taylor. The alloys used were cast by continuous processes and had these analyses: Fe - 1.98 to 2.02 pct, Cu-0.01 pct, Si - 0.01 pct, Mn - 0.01 pct, Mg - 0.00 pct, Zn - 0.00 to 0.01 pct, Cr - 0.00 pet, Ti - 0.00 to 0.04 pct. The constituent in these alloys was identified by X-ray analysis with a Guinier camera and by chemical and X-ray powder diffraction analyses. Two procedures were used to separate constituent for the last two analyses. In one procedure, it was separated by treating a sample with a solution of methanol saturated with iodine. And in the other procedure, it was separated by first applying, at 12 amp per sq ft in 15 pct sulfuric acid at 70°F, an oxide coating to a sample, and then dissolving this coating in a solution of 35 ml of 85 pct H3PO4 and 20 g of CrO3 per liter. Several observations directed attention to a phase change of the A1-Fe constituent. Differences that appeared too great to be accounted for by micro-structure alone were found in the voltages required to apply the same thickness of an oxide coating to products from rapidly and slowly chilled ingot. Even more striking was the difference in appearance of the coatings themselves. One applied to a product from a rapidly chilled ingot was dark gray in appearance, in fact, almost black, while one applied to a product from a slowly chilled ingot was essentially white. Also, even a short period of thermal treatment at an elevated temperature of products from rapidly chilled ingot led to the same anodizing behavior as that of products from slowly chilled in-

Jan 1, 1962

By Stanley C. Herold

At the present time five localities in the Argentine Republic are known to bear direct evidences of the presence of petroleum. The segregation of these localities is more or less arbitrary inasmuch as minor indications may be found to extend from one locality to the other at no regular distance apart, especially in the northern and western part of the republic. These localities are listed as follows: North Argentine-Bolivian region, Salta-Jujuy district, provinces of Mendoza and Neuquen, Comodoro Rivadavia, and the Gallegos-Punta Arenas region. Economic conditions attract us to the possibilities of developing these and other regions of countries in the southern hemisphere. Development work will, naturally, be undertaken first in such localities as present direct manifestations of the presence of petroleum; "hidden fields" may exist, but, unless discovered by accident, their development will be left to the last. The problems to be solved in the development of the petroleum resources of the Argentine republic are mainly of stratigraphy, structure, and transportation. We are not here concerned with the unfavorable climate of the countries to the north in the tropics where, for us of the "far north," life hangs by a thread ready to be severed by a mosquito, gnat, or tropical germ. North Argentine-Bolivian Region The North Argentine-Bolivian region has already been described by the author.&apos; Geographically and geologically this is admittedly one field extending from Argentine into Bolivia. It is not necessary to repeat here the various conditions pertaining to this field, though the summary may be quoted as follows: Extending from northern Argentine northward into central Bolivia is a belt of petroleum seepages. On account of the remoteness of the district it has, heretofore, been little considered by oil operators. The regional geology is comparatively well understood but the local features have not been carefully detailed. Development work in the past has been done on an unscientific basis and has led to failures. At the present time, access to the region is somewhat difficult but, no

Jan 1, 1921

By William E. Ford, Edward Salisbury Dana

1. Variations in the Forms and Dimensions of Crystals 2. Imperfections of the Surfaces of Crystals 3. Variations in the Angles of Crystals Internal Imperfection and Inclusions 264. The laws of crystallization, when unmodified by extrinsic causes, should produce forms of exact geometrical symmetry, the angles being not only equal, but also the homologous faces of crystals and the dimensions in the directions of like axes. This symmetry is, however, so uncommon that it can hardly be considered other than an ideal perfection. The various possible kinds of symmetry, and the relation of this ideal geometrical symmetry to the actual crystallographic symmetry, have been discussed in Arts. 14 and 18 et seq. Crystals are very generally distorted, and often the fundamental forms are so completely disguised that an intimate familiarity with the possible irregularities is required in order to unravel their complexities. Even the angles may occasionally vary rather widely.

Jan 1, 1922

By Luis Elek

DEVELOPMENT of the cement industry in Mexico began some 40 years ago. It has gradually reached great importance in the economic life of the country and has contributed greatly to the technical and economical advances which have been so noteworthy, particularly during the last 15 years. From a modest start, the industry now comprises 18 cement-producing plants having a potential annual capacity of approximately 14 million bbl. About half the plants were built and equipped with second-hand machinery during the last world war when no new machinery could be procured. They will hardly attain full production before being modernized and reconditioned, a job now under way in several of the plants. At present, the yearly consumption is only about 8 to 9 million bbl but is steadily increasing. This is only a fraction of the cement consumed in the U.S.A., which is about 250 million bbl per year, although on the basis of consumption per capita per year, the figure is 1/3 bbl for Mexico and 1 2/3 bbl for the U.S.A. Cement consumption in Mexico is well above the average of all other Latin American countries, with the exception of the Argentine, and considering the potentialities and undeveloped riches of Mexico, the road construction and irrigation works, it is fair to assume that the Mexican cement industry will still prosper and expand in spite of temporary setbacks in the future caused by-local events of economic or political nature. Portland cement is manufactured by burning a mixture of raw materials, one of which is mainly composed of calcium carbonates and the other of aluminum silicates. The most typical materials answering this description are limestone and clay, both of which occur in Mexico in many varieties. To be usable for cement manufacture limestone should contain at least 77 to 80 pct calcium carbonate. Lower grade limestone can be used for cement manufacture only if the lime content is increased by the beneficiation process, which has not yet been adopted by the Mexican cement industry. Most of the limestone used by Mexican cement plants has a calcium carbonate content of 90 to 95 pct and therefore requires addition of one or several correction materials. A typical composition of raw mix for cement manufacture is 85 pct limestone and 15 pct shale, clay or volcanic materials. Occasionally it is necessary to add a smaller amount of sand or other siliceous material to increase the silica ratio in the raw mix. Likewise, it is sometimes necessary to add 1 or 2 pct iron ore to facilitate fusion in the kiln and to obtain proper relation between alumina and iron oxide. After calcining and

Jan 1, 1952

By Rudolph G. Wuerker

With stepped-up work in rock mechanics, more and more data on strength and elastic properties of rocks has become available. Results of measurements of tensile strength, in addition to determinations of compressive strength, allow us to deter- mine, even if only in an approximate way, the third property influencing failure of a brittle material: shear strength. It is fairly generally agreed upon in rock mechanics, in drilling and blasting research, that Mohr&apos;s theory provides an acceptable method for explaining the failure of a brittle material. Mohr states that a material may fail either 1) through plastic slip when shearing stress Y in the planes of slips has reached a limiting value (which in general depends on the normal stress, X, acting normal to the surface), or 2) when the largest normal tensile stress has reached a limiting value. The mode of failure depends upon which of the two stresses is the smaller.

Jan 10, 1959

By Martin Mayers

FIVE-SIXTHS of all the coal that is mined in the United States is burned, without previous treatment other than screening, for the produc-tion of heat and power, so that its value is fixed by its suitability for this purpose. Nevertheless, the characteristics of individual coals that determine their fitness for use in particular pieces of combustion equip-ment are not yet well known. This condition is due not only to the small extent of our knowledge concerning coal itself, but also to our compara-tive ignorance of the nature of the combustion process. The following paper is an analysis of the combustion process as it occurs in industrial furnaces, based largely on the results of laboratory research on combus-tion rates. From this analysis it is possible to determine the characteris-tics of the fuel that limit the capacity of a given piece of combustion equipment. Limitations imposed by other factors than the attainable speed of combustion will not be considered, since they are subject to a different type of analysis involving the balancing of maintenance costs against fixed charges. In order to observe the relations among the various factors that affect the speed of combustion, representative particles of fuel will be followed through two types of furnaces. A pulverized-coal furnace will be con-sidered first, because the independence of the individual particles facili-tates the analysis of the effect of furnace conditions. The second example will be a grate-fired furnace in which ignition of the fuel takes place on the underfeed principle. This includes both underfeed and chain grate stokers,(8)? but does not include hand-fired furnaces and some overfeed stokers. The furnace will be considered to be large enough, the tempera-ture high enough, and enough air provided, to burn the fuel completely, without, for the moment, specifying these quantities more completely.

Jan 1, 1934

By E. L. Swarts

In the course of a program on high-temperature processing and electrowinning of uranium at the Knolls Atomic Power Laboratory,&apos;&apos; it became necessary to give attention to the interaction of molten uranium with graphite. Although it is known3 that a protective interface layer may form, details of this reaction have not been reported. Unfortunately it was impossible to complete the planned experimental program. However, the general problem is considered of sufficient interest to warrant reporting those preliminary results actually obtained. EXPERIMENTAL PROCEDURE Interface carbide layers were formed by melting samples of cleaned uranium metal in small closed graphite crucibles. Equilibrations were conducted in vacuo or in an atmosphere of dry helium at temperatures ranging from 1150" to 1400°C and for periods of from 24 to 240 hr.

Jan 1, 1960

By John M. McAnerney

In 1955, the U.S. Army started to experiment in Greenland with tunneling in glacial ice and later in frozen glacial moraine. By 1960, long adits and experimental rooms had been successfully excavated. Full mechanization with coal-cutting machinery was most efficient in ice but drilling and blasting were necessary in bouldery moraine. In 1963, the U.S. Army Cold Regions Research and Engineering Laboratory, (USA CRREL; redesignated U.S. Army Terrestrial Sciences Center July 1, 1968) started a tunnel in the frozen silt of central Alaska near Fairbanks. The original adit of 360 ft (109 m) was successfully driven in the permafrost by a twin-rotor tunnel-boring machine, the Alkirk Cycle Miner. The workings were enlarged in 1966 and 1967 by standard mining techniques in which jackhammers, steam points, and augers were compared. A mechanical coal cutter was tried to supplement drilling and blasting. In 1968, airblasting techniques were used successfully for breaking out the frozen silt. All mine products were loaded mechanically and hauled by self-dumping shuttle car. Pneumatic methods of transport were tried for both dust removal and for conveying blast products up to 3-in. maximum size. Studies of the effects of natural winter ventilation through a shaft showed that tunnel closure could be reduced by lowering the adjacent ground temperature. It is concluded that underground openings in frozen ground should be cut and maintained at well below freezing temperatures to hold deformation to a minimum. HISTORICAL BACKGROUND This chapter deals with aspects of tunneling not previously discussed in the conference papers in this book. The chief differences are that the three tunnels lie entirely within frozen material and are relatively small, since they were constructed mainly for research. The primary objectives of the research were to develop underground shelters for military per-

Jan 1, 1970