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By Elmer W. Pehrson

Minerals have played a prominent role in the affairs of man and nations since time immemorial but with the advent of the industrial revolution, expanding use of the products of the mineral kingdom became synonymous with the material progress of mankind. Individuals and business groups have recognized this fact so have been aggressive in searching for and utilizing mineral resources, with notable success. Indeed, their achievements are primarily responsible for the present Machine Age. On the other hand, until recently the body politic has failed to grasp fully the essentiality of minerals although, at times, access to mineral supplies has been an important factor in the political maneuvers of nations. This chapter is concerned primarily with the broader political and economic relationships of mineral resources to the world economy, and with the internal and external actions of nations in the field of minerals. Many factors that condition the mineral economy of regions and the world as a whole, influence the internal and external affairs of individual nations. The more important of these are: 1. The nature of man's dependence on minerals. 2. The problems resulting from the unique characteristics of mineral occurrence. 3. Geopolitical concepts. 4. Minerals and world power. Actions of individual nations affecting their mineral economy seek two basic objectives: 1. Attainment and maintenance of prosperity. 2. Military security. Other objectives may be cited but on careful analysis they become integral parts or extreme phases of the two points noted above. For example, the twentieth century aggressions of the USSR, Germany, Italy, and Japan might be considered as direct bids for world power but they also can be interpreted as exaggerated or mistaken efforts toward military security and peacetime prosperity. Similarly, trade barriers, nationalization of industries, foreign exchange manipulations, taxation, monopolistic prac-

Jan 1, 1964

By Paul G. Shewmon

The migration of slightly solzrhle spherical particles through a solid under the infllrence of a temperature gradient is analylzed for the cases of various transport mechanisms. It is shown that the variation of the velocity of the particles with radius, r, depends on the dominant mechanism of matter transport around or through the inclusion. Thus the velocity varies as r-1 jor surface-dijf1~sion controlled migratzon. is independent of r for volume diffusion in either phase, and varies as if the rate is determined by an interfacial reaction (n is the order of the interfacia1 reaction). These same results hold tor the migration of a cvlinder of length much greater than its radius. and .for other types of potential gradients, e.g., an electrical field. These equations are combined with recent electron-microscopic ohservations to show that the rate of migratzolz of small helium-silled bubbles through copper is determined by surface diffusion of the metal atoms. With these equations and the temperature gradients attainahle in an electron-microscope joil, the dominant transpar/ mechanism (or any migrating pnrtzclos can he determined. AS a result of fission, rare-gas atoms are created in the hot fuel element of a nuclear reactor. These insoluble atoms precipitate to form bubbles of the gas in the fuel. The subsequent migration and coalescence of these bubbles is thought to play a dominant role in the swelling of fuel elements which in turn can limit the fuel-element life. As a result of this practical problem and because of the relative simplicity of the system, workers in several laboratories have imbedded rare-gas atoms in metals with the aid of an accelerator and studied the formation and behavior of the bubbles that form on annealing. Recently Barnes and Mazey have studied the migration of such helium-filled bubbles in copper foils using the electron microscope and the temperature gradient that can be induced in the foil by the electron beam. They found that the smaller bubbles moved faster than the larger ones. It is shown below that, if this is true, the rate-controlling step in their migration is surface diffusion of metal atoms instead of volume diffusion, vapor transport, or an interfacial reaction. The analysis given is in no way limited to gaseous inclusions so the variation of velocity with particle size for any relatively insoluble precipitate particles could be used to obtain information about the relative importance of surface diffusion, volume diffusion, and interfacial reaction in such two-phase systems. VOID MIGRATION IN A TEMPERATURE-GRADIENT ANALYSIS Barnes' studies indicate that helium does not dissolve or diffuse in metals to a measurable extent, so that when the voids move they must do so through the movement of metal atoms from the leading to the trailing sides of the void.' Thus voids might move by surface diffusion, diffusion of vacancies in the surrounding lattice, or vapor transport. We consider first the case of flow by surface diffusion alone. We assume that there is a force, in the sense of irreversible thermodynamics, tending to move the atoms around the bubble in a given direction. We designate this direction as the x axis and the force per atom as Fa. The net rate of flow of atoms from one side of the bubble to the other, under the influence of this force, is the surface flux, Js, times the cross-sectional area available for flow, A,. A, is taken as the circumference times the thickness of the high-diffusivity surface layer 6. Thus where 51 is the atomic volume. For bubbles to advance a distance dx, a volume equal to nr : dx must flow around the void so that The minus sign enters because the bubble moves in the direction opposite to that of the force on the atoms. Equations for volume diffusion and diffusion through the vapor can be obtained in the same manner. For vapor transport we have Ag = and the ratio of the densities of metal atoms in the gas and the solid (pg/pl) enters so that

Jan 1, 1964

From March to May of 1963, the Bureau of Mineral Resources carried out an experimental aeromagnetic survey at Cobar, New South Wales, to field test a proton-precession magnetometer installation in the Cessna aircraft VH-GEO. The Cobar area was chosen as considerable information was already held on the Earth's magnetic field there, which was known to provide a range of anomalous areas that are not excessively disturbed.A procedure for survey flying and methods for processing data were developed during the survey. Contour maps of the aeromagnetic results were produced in the field. The experimental survey was successful in outlining magnetic anomalies in detail.INTRODUCTIONSince 1951 the Bureau of Mineral Resources, Geology and Geophysics (B.M.R.) has carried out an airborne magnetometer exploration programme with DC.3 aircraft carrying fluxgate magnetometer equipment. Recently a proton-precession magnetometer was developed by the Design and Development Group of the B.M.R. for observatory use. One unit modified for airborne use was installed in the Cessna light aircraft, VH-GEO. The Cessna was modified structurally to take the magnetometer, associated bird, and winch gear.The proton-precession magnetometer has many good features.1. It utilises the transistor and associated solid-state devices in its electronics, and hence is light and small.This is the basic feature allowing its installation in a light aircraft. The transistor circuits have a high reliability factor and owing to the card sub-unit...

Jan 1, 1964

By Granville S. Borden, Frank H. Madison

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

Jan 1, 1964

Iron deposits of every major type except laterite occur in Quebec, and form one of the major iron ore resources of the world. The five principal types of ore described are: (1) hematite-goethite masses derived from iron formation through the oxidation and enrichment of iron by natural processes; (2) taconites consisting of fine-grained iron formation; (3) metataconites composed of coarse-grained iron formation; (4) iron and titanium oxide minerals in massive or disseminateed deposits within gabbro and anorthositic rocks; and (5) replacement or contact? metasomatic magnetite deposits associated with complex silicate and skarn mineral assemblages. Most of the ore, although relatively low grade, is easy to concentrate. The physical properties of the ores that affect the choice and efficiency of beneficiation methods are described. The extent to which iron ore from this area can be utilized in the future will depend on the continued use and improvement of highly efficient methods of beneficiation.

Jan 1, 1964

By C P. Gravenor

In 1953, a deposit of sedimentary oolitic iron ore was discovered in the Clear Hills area of northwestern Alberta. Since that time, detailed drilling has outlined reserves in excess of 200 million tons of ore grading 30 to 35 per cent iron. Attempts to physically beneficiate the ore to meet blast furnace or direct reduction feed specifications have been, in general, unsuccessful. In 1960, Premier Steel Mills Limited and the Research Council of Alberta jointly sponsored a pilot-plant test at the R-N Corporation at Birmingham, Alabama. About 5,000 tons of ore were treated, and briquettes containing 90 per cent Fe were produced, with 83 per cent recovery. At the same time that the R-N tests were being made, the Research Council initiated a program to produce high-purity powders by chemical methods. Several purification techniques were investigated; hydrochloric acid dissolution of reduced ore was finally adopted. Briefly, the steps involved in this acid process are as follow

Jan 1, 1964

Laboratory scale equipment was developed to recover zinc as oxide fume from granulated lead blast furnace slag. The cyclone furnace process is characterised by high treatment rates combined with continuous and independent operation.Results were sufficiently encouraging to warrant pilot plant scale trials being undertaken.INTRODUCTIONSince granulation of lead blast furnace slag started at Port Pirie in 1921 the stockpile of this material has increased to nearly 5 million tons which averages 17·5 per cent zinc by weight. Although a number of processes for recovering the zinc have been examined, economic considerations indicate that a slag fuming process is likely to be most suitable.In the conventional slag fuming process zinc is extracted by injecting pulverized coal and air into a molten slag bath. By maintaining a suitable air to coal ratio the oxidised zinc contained in the slag is reduced to metal. Volatilization of the zinc is followed by reoxidation in the gaseous phase with the addition of further air above the bath. The zinc oxide fume so produced is collected by normal gas cleaning methods.By examination of the thermodynamics of this process Bell, Turner, and Peters (1955) determined the zinc oxide activity of the slag over the duration of the fuming cycle.A combination of high temperature and high carbon monoxide/carbon dioxide ratio was found necessary for rapid zinc elimination.Since melting of the slag is an essential step in the slag fuming process, only two treatment methods appeared possible at Port Pirie until recently...

Jan 1, 1964

By J. Eldridge, K. L. Komarek

Activities of aluminum in solid Fe-Al alloys have been determined between 0 and 75 at, pct Al and 1100" and 1400°K by an isopiestic method in which iron specimens, heated in a temperature gradient, are equilibrated in a closed all-ceramic system with aluminum vapor. The activity of aluminum in these alloys shows a strong negative deviation from Raoult's law at low concentrations but increases rapidly above 40 at. pct Al. The enthalpy and entropy of mixing me both negative. For an alloy with equiatomic composition the values are: HM = -7300 cal and SM = -0.85 eu. Sodium chloride has been added at lower temperatures to accelerate the evaporation of aluminum. Equations have been derived to calculate activities of aluminum from experimental data. THE Fe-Al system has been the object of a great number of investigations.' Most of these studies have been concerned with the phase diagram and specifically with the order-disorder reactions in the range of solid solutions of aluminum in iron. The results have been compiled by Hansen2 and presented as a complete phase diagram, Fig. 1. More recently, Taylor and ones' have found that both ordered and disordered alloys can exist in the a field up to the solidus curve separated by a line starting at 18.75 at. pct Al at room temperature up to 37 at. pct Al at 1375°C. Chipman and coworkers4-7 have studied repeatedly the activity of aluminum in liquid dilute Fe-Al alloys. They have measured the distribution equilibrium of aluminum between liquid iron and

Jan 1, 1964

By J. E. Lawver, R. R. Beebe, J. L. Wright

This paper describes a separation coefficient Ks useful as a "measure of goodness" to be used in factorial and response surface methodology. The use and limitations of the separation coefficient is discussed, and a computer program for calculating the coefficient is presented (in Fortran). The application of the coefficient is illustrated in terms of electro-dynamic separation of Mesabi semitaconites. Present Mesabi wash ores and gravity concentrates with an iron to silica ratio of only 5 or 6 to 1 are no longer readily salable, for the steel industry now demands concentrates with an iron to silica ratio of at least 10 to 1 and a structure comparable to pellets. THE ELECTRODYNAMIC-FLOTATION PROCESS Wash ores and gravity concentrates consist largely of hematite, goethite, and quartz. Several methods of beneficiation are being tested at the University of Minnesota Mines Experiment Station with a view to improving the salability of these materials. A process that looks particularly promising from an economic view is the combination electrodynamic-flotation process shown in Fig. 1. This process is designed to upgrade gravity concentrates to a 5% silica content and to provide fines — from the flotation circuit —to permit agglomeration. Although electrodynamic concentration of specularite is an established and well-understood process, the electrodynamic concentration of Mesabi goethite-hematite gravity concentrates presents interesting and enigmatic problems. The gravity concentrates are by no means assemblages of clean, free mineral particles. Instead, the concentrates to be retreated consist of a great variety of middlings. More or less complete liberation would require grinding to minus 325 mesh, at which size only flotation could be expected to function, and even then grades and especially recoveries would not be satisfactory. A close examination of the gravity concentrates shows that grinding to 100% minus 48 mesh will produce a product which is approximately 70 weight % plus 325 mesh (see Fig. 1). The remaining 30 weight % can be deslimed and floated by conventional methods, but the resulting iron concentrate is

Jan 1, 1964

By Karl V. Lindell

Asbestos is not the name of a distinct mineral species, but rather the commercial term applied to the fibrous form of several minerals differing widely in composition. There are some 30 known varieties of asbestos but of this number only 6 are of economic importance, and these, in order of economic significance are chrysotile, crocidolite (or blue asbestos), amosite, anthophyllite, actinolite and tremolite. Chrysotile asbestos was formed by the introduction of hydrothermal solutions into fractures in serpentinised ultrabasic host rocks. These solutions dissolved magnesium silicate from the wall rocks, and with subsequent lower temperature and pressure they became supersaturated, and crystals of chrysotile asbestos formed. The chemical composition is variable but is classified as a hydrous magnesium silicate, containing a high percentage of magnesia and water, plus varying amounts of alumina and ferrous and ferric iron. Other asbestos minerals are formed by a similar process but with a different host rock e.g. crocidolite occurs only in iron' formation. The chemical composition of asbestos minerals other than chrysotile, shows a wide variation, but in general may be classified as silicates, or metasilicates, containing varying amounts of calcium, magnesium, sodium and iron.

Jan 1, 1964

By N. A. Eilertsen

Procedures of mining high-calcium limestone underground at the Kimballton mine of the Standard Lime and Cement Co. in Giles County, west-central Virginia, are described. Drilling and blasting procedures area discussed in detail, and direct mining costs are tabulated in percentage of total cost. Output, about 1,725 tons of limestone a day, is attained with heavy trackless equipment by the room and pillar method of mining modified by benching floors. Operating features include underground air compression, electric-eye control of curtained doorways, use of a single jumbo drill rig for all drilling, and an effective plan for maintenance of equipment. The company's safety program has contributed to an outstanding safe mining record. The mine is integrated with a plant on the property which converts the stone to metallurgical and chemical grade lime.

Jan 1, 1964

Jan 1, 1964

By G. Ansell, J. Weertman

G. Ansell and J. Weertman (Rensselaer Polytechnic Institute and Northwestern University, respectively) —The great increase in creep strength that you found in your indium-glass composites is quite striking. You ruled out a decrease in the dislocation source density as an explanation of the reduced creep rates. Could you tell in greater detail why you feel this is an inadequate explanation of the phenomenon. It appears to us that it is a reasonable one. Consider the spacing between the glass spheres in your composites. It is of the order of 10-3 cm. The spacing between dislocations in a (single-phase) annealed metal with a dislocation density of the order of 106 to 107 cm per cm3 also is of the order of 10-3 cm. Therefore it is not reasonable to expect that the arrangement of the dislocation lines is the same in the composite material as it is in pure indium. If the dislocation arrangements are different the density of the dislocation sources likewise will be different. Another way of saying the same thing is the following. The presence of the glass spheres reduces one of the dimensions of the metal phase to 10-3 cm. Thus the metal phase, in effect, is equivalent to a metal whisker or a thin metal film. These are strong because they have so few dislocation sources within them. T. D. Gulden and J. C. Shyne (authors' reply)—It is to be expected that the arrangement of dislocations in the indium-glass composites would be quite different than that observed in annealed pure metals. The dislocations probably exist primarily as segments connecting the dispersed particles. These segments and discontinuities at the very large area of particle-metal interface could act as dislocation sources. For this reason it was considered unlikely that the very high observed creep strengths were due to a low density of dislocation sources. A more likely explanation is that the distance a dislocation can glide is limited by the interparticle spacing. The particles averaged about twenty in diam and were less than 10 µ apart in the 40 pet composite. It seems reasonable to assume that a dislocation loop in a volume of metal surrounded by these relatively large particles would not bow out around them but would be restricted to the region between particles. A general expression for creep rate is given by the product of the dislocation source density, the average rate at which loops are generated from a source, and the average area swept out by a loop times the Burgers vector magnitude. Assuming that the area swept out is limited by the interparticle spacing and the rate of generation of loops is controlled by the rate of climb of loops over second-phase particles, as suggested by Ansel and Weert-men,9 a calculation of the dislocation source density may be made from the experimentally observed creep rates. The result comes out 10" to 10" per cm3 which seems reasonable in view of the assumptions involved. Thus it is concluded that the anomalously low creep rates that were observed were due not to a low dislocation source density but rather to a limitation on the area swept out by each dislocation loop.

Jan 1, 1964

By William Lodding

Unlike most ore minerals, the raw materials for lightweight-aggregate, such as clays and shales are abundant everywhere. In view of this ample choice, what are the reasons for many plant failures attributed to the raw material? How can we arrive at a proper choice of the raw material, the proper processing method for the chosen material, predict its behaviour in a plant and the properties of the final product? Determine the uniformity of the raw material and possible harmful impurities? One basic choice is sintered versus kiln-fired aggregate. It will be based on market preferences and availability of the raw material. Almost in every case a good raw material for one process is poison for the other.

Jan 1, 1964

By John W. Trammell

The White Pine Mine is situated in Ontonagon County, approximately six miles south of Lake Superior, in the Upper Peninsula of Michigan (Figs. 1 and 2). The ore body mined by White Pine Copper Company occurs in the lower - most 20 to 25 feet of the Nonesuch formation, a series of middle - to upper Keweenawan shales, siltstones, and sandstones. This paper elaborates on the solution of problems in ore grade control and mine planning arising from the presence of an essentially barren sandstone stratum within the ore body.

Jan 1, 1964

By H P. Tardif

This paper briefly describes some of the phenomena encountered when materials are submitted to extremely high pressures, such as those produced by the detonation of an explosive charge placed in contact with the material. It was found that extensive changes take place in the? microstructure of iron and steel. Diffusion-controlled processes, such as the transformation of lamellar pearlite, the recrystallization and grain growth of ferrite, and the homogenization of the pearlite-ferrite structure, can take place within micro-or milliseconds. Mechanical twins can propagate without deviation from ferrite to pearlite, thus indicating a proeutectoid ferrite-pearlite-ferrite orientation relationship. The propagation and interaction of intense stress waves in materials was demonstrated with the use of Armco iron. Finally, a comparison is made of the damage produced in metals by the formation of craters made by explosive shock and by hypervelocity impact. D DRING the last few years, exceptional development has taken place in the field of explosive metallurgy, i.e., the

Jan 1, 1964

By F. H. Vitovec, D. W. Hoeppner

Pusk-pull fatigue tests were conducted on copper tricrystals of 99.988 pct purity to ascertain the role of grain boundaries in the initiation and propagation of fatigue cracks. Significant differences in behavior were found for specimens which possessed different transverse-boundary misorientation. In speciwens with low boundary angles cracks initiated within the transverse boundary, while higher angles led to transcrystalline fatigue failure. It is suggested that at low angular misorientation moving dislocations may interact with dislocations of the boundary or dislocations present in adjacent pains on favorably oriented glide planes, thus initiating a fatigue crack. MANY fatigue studies have been concerned with fatigue-crack initiation within grains and the mechanism causing initiation and propagation1-3 Although the initiation of fatigue cracks in or near grain boundaries of pure metals has been observed and reported in the literature, the mechanism of this phenomenon has received little attention.4"11 EXPERIMENTAL PROGRAM Testing Procedure. To investigate the role of grain boundaries regarding initiation and propagation of fatigue cracks, copper tricrystals were tested in push-pull. Axial-stress tests were used to avoid the stress gradients introduced by stressing of some other nature. Copper was selected as the most suitable test material since extensive work has been done on the formation of fatigue-induced slip in copper. Tricrystal specimens were used to provide a grain boundary geometry with one boundary transverse to the principal stress axis and one or more boundaries nearly coincident with the direction of maximum resolved shear stress. The boundary energy and the slip characteristics in the vicinity of the transverse boundary depend on the relative orientations of grains across the boundary. Testing was done at room temperature, at a frequency of 700 cpm, in an atmosphere of either air or argon. It is known that the incidence of grain boundary cracking increases with increasing temperature and decreasing frequency.4 The fatigue machine applied a uniaxial tension-compression load to the specimen by a flat spring which was actuated by an adjustable eccentric. Use was made of an adjustable head and a load cell which had strain gages mounted at 120-deg intervals around its periphery, thus providing a means for eliminating any detectable superimposed bending moment. A clip gage was mounted between the gripping heads to record the cyclic strain amplitude applied to the specimen. Each specimen's hysteresis characteristics were recorded by supplying the load and strain signals to an oscilloscope. Microstructural changes were observed and recorded with an optical microscope which was mounted on the fatigue machine. Immediately prior to insertion in the machine, each specimen was chemically polished. Extreme care was exercised while inserting the specimen in the test machine to avoid either bending the specimen or introducing a mean load. Each specimen was stressed in the tensile direction first and subsequently the load was reversed. Specimen Preparation. Tricrystal fatigue specimens of 99.988 pct Cu were grown from the melt using a modified Bridgman technique. Ingots about 1 in. high were grown to the configuration shown in Fig. 1. Upon sectioning the resultant ingot, several specimens were provided with an identical shape and grain boundary orientation. Except for plane sectioning and final polishing, this method eliminated machining the specimens. The apparatus used for growing the tricrystals is shown in Fig. 2. A spectrographically pure graphite mold, Fig. 3, was inserted in a vycor tube which was mounted on a vertical zone-refining table. Prior to insertion in the tube the mold was assembled as follows. The insert and graphite rods were fixed in position in the mold. The copper was then placed in the mold and the entire mold assembly was positioned in the vycor tube, Fig. 2. At this point the tube was sealed, evacuated, purged with helium gas, and finally placed under a slightly positive helium pressure. The heating coil was then adjusted to melt the copper charge, after which it was raised at a speed of 4 in. per hr. It is also possible to use

Jan 1, 1964

By A. C. Barlow

The use of deep wells for waste disposal is not a new technique. The production phase of the oil industry has been using this method to dispose of unwanted oil field brine since the 1930's The adoption of this method by other branches of industry, however, to dispose of manufactured wastes is a relatively new development, but one which is finding increased use (2). Deep well waste disposal is not an ordinary technique even though it is finding relatively wide application. In fact, just the opposite is true; it is still a rather extraordinary measure. It is not now, nor is it ever likely to be a disposal method which can be assured of success before it is tried.

Jan 1, 1964

By H. R. Hardy

Whether the mining engineer is concerned with stress problems in a mine at depth, the development of a new drill bit, or the efficiency of a comminution process, the mechanical properties of the rock with which he must work are of the utmost importance. One of the most popular topics in rock mechanics circles today is ?Is it possible to utilize directly parameters determined from laboratory tests on rock specimens in the analysis of mining engineering problems?? It is the author's opinion that laboratory and .field investigations have not yet reached the stage of development where this question can be answered with any degree of certainty. At present, great difficulties are involved in applying the results of laboratory tests to a mining engineering problem. However, this is due in part to the lack of detailed measurements of stress and deformation in the field and in part to the lack of development of satisfactory structural theories to correlate laboratory and field measurements. Furthermore, if mechanical properties measured in the laboratory are to be directly applied to the analysis of mining engineering problems, the critical mechanical properties must be identified, reliable test procedures must be developed and extensive test programs must be carried out.

Jan 1, 1964

By Donald B. Evans, Robert D. Pehlke

The solubility of nitrogen in liquid Fe-B alloys has been measured up to the solubility limit for the formation of boron nitride. The activity coefficient of nitrogen increases with increasing boron content in the range 0 to 7 wt pct B. From experimen -tal data, values have been calculated for the B-N interaction parameter e3 at temperatures in the range 1550" to 1750°C. A value of 0.038 has been estimated for the boron self-interaction parameter eg at 1550°C. The standard free energy of decomposition of boron nitride into the elements dissolved in liquid iron has been determined to be: ?F° = 45,900 -21.25T in the range from 1550° to 1750°C. The nitride is assumed to be of composition BN. BORON nitride has an unusual combination of properties which make it appear attractive in a wide range of engineering applications. Some of its more important and most recent applications are in the nuclear area, particularly in connection with the liquid-metal cooled reactor concept now receiving considerable emphasis. Boron nitride has a high degree of stability at elevated temperatures. It also has excellent ma-chinability and the ease with which its crystals deform suggests applications as a lubricant. These properties stem from a hexagonal layer-type structure similar to the structure of graphite. One of its primary uses to date has been for seals in liquid-metal pumping systems. It is also used in nuclear reactors as an insulating layer to separate two solid metals which are not themselves compatible under the conditions of temperature and atmosphere in which they are used. Its inertness to liquid metals has also suggested use as a mold-release agent in casting processes. In addition to its excellent machinability and reported inertness to liquid metals such as iron, silicon, aluminum, copper, and zinc, boron nitride has high thermal conductivity and excellent thermal shock resistance. This combination of properties would make it appear ideal as a refractory crucible material for refining of high-purity liquid metals, for example high-quality steels. However, since it is known that concentrations of boron as low as 50 ppm can have a marked effect on the physical properties of certain steels,' in particular on the creep and stress-rupture properties, an investigation was undertaken to define accurately the chemical equilibrium among boron, nitrogen, and liquid iron in the range of steelmaking temperatures. EXPERIMENTAL PROCEDURE Two experimental approaches to this problem were employed: a Sieverts' method and a quenching method. In the first method, the Sieverts' technique was used to measure the equilibrium nitrogen solubility in liquid Fe-B alloys of 0 to 7 pct B as a function of nitrogen gas pressure over the melt. The solubility limit of the boron nitride phase formed was determined by the point of departure of the nitrogen absorption from Sieverts' Law. This technique has been applied to liquid Fe-Ti alloys by Rao and parlee,' to liquid Fe-A1 alloys by Evans and Pehlke,3 and to solid Fe-V alloys by Fountain and Chipman.4 In the second method a melt of liquid iron was held in a crucible of boron nitride under a known partial pressure of nitrogen gas. After thermodynamic equilibrium was attained, the melt was quenched in a stream of helium and then analyzed by wet-chemical methods for boron and nitrogen. The Sieverts' apparatus used in the first method was essentially of the same design as the one described by Pehlke and Elliott.5 The charge materials were vacuum-melted high-purity iron (Ferro-vac E) supplied by the Crucible Steel Co. and -325 mesh boron powder supplied by Cooper Metallurgical Associates of Cleveland, Ohio. The boron contained less than 0.02 wt pct O, according to supplier's analysis. Recrystallized alumina crucibles were used to contain the melt. Examination of solidified melts showed these crucibles to be satisfactory with no evidence of any reaction or physical penetration of the crucible wall by the melt. The melt temperature was measured by a disappearing filament-type optical pyrometer sighted vertically downward on the melt surface through a 1/4-in.-diam sight hole in the crucible lid. The pyrometer was calibrated against the melting point of pure iron in the same apparatus, taking the emissivity of

Jan 1, 1964