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By Royal B. Jackman, Carle R. Hayward

Two comprehensive papers have appeared regarding the forms of copper that occur in smelter slags, one by Frank E. Lathe1 and the other by C. G. Maier and G. D. Van Arsdale.2 These authors comment on other published results and draw conclusions from their own investigations. The development of X-ray examination of minerals and improvement in high-power microscopic methods make it possible today to get additional evidence by means that were not available to earlier investigators. The present work was confined to reverberatory slags obtained from five different plants. Some definite conclusions were reached regarding the forms of copper present in these slags. In most cases these agree with some of the findings of Maier and Van Arsdale but new methods of attack were used in the investigation. Conclusions of Previous Investigators Various important conclusions reached by previous investigators are summarized in the following paragraphs, arranged chronologically. William A. Heywood:3 Slag losses increase with grade of matte but with the same grade of matte losses decrease as the acidity of the slag increases. Lewis T. Wright:' Slag losses are only partly due to prills of matte. It is suggested that part of the copper is dissolved in the slag. J. Parke Channing9 A considerable part of the copper enters the slag as silicate or oxide and not as sulfide. C. A. Grabill:6 Slag losses are both physical and chemical. Physical losses, due to poor settling, gas flotation and slight differences in specific gravity, are small under normal conditions. Chemical losses may- be due to formation of oxides or to solution of metals and sulfides. The last is considered the most important. John W. James:' The copper in converter slag is largely the oxide and as such enters the reverberatory slag when converter slag is added to the charge.

Jan 1, 1934

By R. L. Bleifuss

Most pellets swell only slightly during reduction, but some swell so enormusly that their increase in size is termed catastrophic. Since catastrophic swelling produces irregularities in blast furnace operation, an understanding of the phenomenon is of practical as well as theoretical interest. Observations have shown that catastrophic swelling is characterized by the growth of a network of fine iron filaments. Evidence is presented to show that the growth of these filaments is promoted by the presence of calcium in the magnetite lattice of the original ore. During reduction, the limited mutual solubility of CaO and FeO produces an unstable condition that inhibits the uniform nucleation of metallic iron. Other elements in the magnetite lattice whose oxides are continuously soluble in FeO in the critical temperature range have no effect. Magmatic segregation or pyrometasomatic replacements are the most likely deposits to contain calciferous magnetite. Over the past few years there has been an increasing concern throughout the iron and steel industry over the tendency of pellets to swell during reduction. Although the tendency for swelling is only one of several attributes that determine the behavior of pellets in the blast furnace, swelling-reduction tests are now part of the normal evaluation procedure of many pellet consumers. During a swelling-reduction test, pellets display either the moderate increase in size known as normal swelling, or the enormous expansion known as catastrophic swelling. This paper is concerned with the origin and control of catastrophic swelling and how it is enhanced or inhibited by the presence of minor elements. Swelling Behavior The swelling behavior of pellets during reduction is indicated in Fig. 1. The lower curve represents normal swelling and the upper curve catastrophic swelling.' During the initial stages of reduction, that is, up to about 20-25% reduction, the two curves are considered to be equivalent. Beyond this point normal pellets undergo a gradual decrease in size with increased reduction. By contrast, pellets which exhibit catastrophic swelling show a second dramatic expansion between 25 and 70% reduction. The initial normal swelling develops as the hematite of the pellet is successively reduced to magnetite, and then to wustite. Work by Edstrom' and others has shown that the reduction of hematite to magnetite is accompanied by a 25% volume increase, whereas the magnetite to wustite stage shows a volume decrease. The volume increase overlaps the wustite field because magnetite is formed simultaneously with the wustite during topochemical reduction of the pellet. The catastrophic expansion is clearly related to the wustite, to

Jan 1, 1971

By A. S. McLatchie, R. A. Hemstock, J. W. Young

Much attention has been given in the past few years to methods of increasing the recovery of oil from proven reserves. Numerous laboratories have made investigations to evaluate the possibilities of increased oil recovery by high-pressure injection of dry gas, injection of a propane slug followed by dry gas, solvent flooding. and by the injection at relatively low pressures of gases enriched with ethane and propane. Several years ago, Whorton and Kie-schnick' published the results of laboratory studies on high-pressure gas injection which showed that, in the case of light oils, recoveries could be considerably increased by sweeping the reservoir with dry gas at pressures in excess of 3,000 psig. The increase was attributed by those authors to the vaporization of oil at the invading gas front and viscosity and solubility effects produced at the front by the invading gas. Later, Stone and Crump' presented the results of a series of displacement experiments in which a light under-saturated crude oil was displaced from sand-packed columns with unusually high recoveries when the displacing gas was a rich condensate or a dry gas enriched with ethane or propane. They also conducted similar experiments at higher pressure on heavy undersa tu rated crude oil, although in this case the increase in recovery was not as great as in the case of the light oils. In both cases, viscosity reduction and swelling of the by-passed oil behind the invading gas front were believed to be responsible for the more favorable recovery of the original oil in place. Within the past year, other investigators", ' have presented the results of laboratory studies of miscible slug and solvent flooding recovery processes. This paper describes the laboratory methods developed for evaluating benefits to be obtained by enriched gas drive in specific reservoirs, and presents the results of several displacements of crude oils which possess a wide range of physical properties. The displacements were conducted at reservoir conditions of temperature and pressure. The apparatus used in the following experiments consisted of a sand-packed tube which served as the model reservoir, a cylinder of injection fluid, and a mercury pump. The stainless steel tube, 8 ft long and 0.53 in. I- was packed with a graded quartz sand. The high-pressure pump discharged mercury into the bottom of the injection fluid cylinder at a constant rate as low as 1 cc/hr. The average porosity and permeability of the sand column were 34.6 per cent and 3.25 darcies, respectively. In each case the tube was charged by the displacement of salt water by the reservoir oil under consideration. Recently a project was initiated to evaluate oil recovery by enriched gas drive from three oil reservoirs. Samples from a fourth reservoir (in this case high-viscosity oil) were studied with a view to obtaining recovery information of general applicability to low-grade, high-viscosity crudes. The oils from these four reservoirs exhibited a wide range of physical properties, and the reservoir conditions of pressure and temperature simulated in the laboratory represented several typical field conditions under which enriched gas drive might be employed. One of the reservoirs selected for laboratory displacement experiments produced an intermediate-gravity crude (29.6" API) by solution gas drive and a weak water drive. A low recovery in the range of 10 to 20 per cent was anticipated. Four displacement experiments were made to determine the effect of injection gas composition and initial gas saturation upon recovery of oil from the laboratory model. Two types of reservoir oil were used in these experiments. In the first run, a desaturated crude with a bubble point of 395 psi was charged to the tube. In the three subsequent runs, a simulated original reservoir oil was charged at 2,000 psi and produced by solution gas drive to 300 psi before beginning gas injec-

By James J. Bean

HE task of measuring the specific gravity of the -*- operating medium in a heavy-media separation system has never presented a particularly difficult problem because the medium is fairly stable and the overflow of the separatory vessel, as well as its underflow, can be sampled easily and accurately and the specific gravity of the suspension determined easily by weighing a known volume. However, while this method is simple and accurate it does require the operator to take the sample by hand and to weigh it and there is considerable temptation to avoid the periodic sampling if everything seems to be going well, or if something is occupying the attention of the operator. Furthermore all operators do not sample in exactly the same manner and considerable practice is required for two operators to be able to "check" each other to the last few hundredths, particularly if the sample is cut underneath the drainage screen where location of the point of sampling and load on the screens tends to influence the determination. While none of the above presents much of a problem, we have all recognized that some mechanical method of continuous measurement and recording would be advantageous since the operator would merely have to glance at the meter to check the gravity and to have an indication of the trend of any changes. Also if the instrument were of the recording type, a permanent record would be available for the guidance of the superintendent. The Eagle-Picher Mining and Smelting Co. was the first heavy-media user to actually install such a recording meter. In 1946 they installed in their Central Mill at Cardin, Okla., a specific gravity recorder manufactured by the Bristol Co. of Water-bury, Conn. R. A. Barnes, of the Bristol Co., working with E. H. Crabtree, Jr. and Elmer Isern, of Eagle-Picher, made the application and worked out the problems of sampling and measuring. Their attempts to measure the specific gravity of the medium in the cone itself were not entirely successful and they resorted to an outside sample tube for actually making the determination. Because of the particular flowsheet used, it was possible to tap off from the medium return pipeline a stream of medium and divert it into the sampling tube, which was provided with a constant level overflow and a spigot underflow, and into which the bubbler tubes dipped. The Eagle-Picher installation was successful and its possibilities were recognized by the Mineral Dressing Laboratory of the American Cyanamid Co. It was decided to install a similar unit in the heavy-media pilot plant to investigate further its possibilities. Chief among these was the continuous record which it was felt would be proof of the steadiness of the gravity in a heavy-media cone, something which is not always appreciated by POtential users. Because the heavy-media pilot plant is required to operate at a wide range of specific gravities, it was realized that the unit would have to record all gravities from 1.25 to 3.50, and do it to the nearest 0.01. It would not be necessary to record all of this wide range on a single chart and the method selected was to have 4 bands, each band range overlapping the other a small amount and calibrated so that with standard charts one division would represent 0.01 sp gr. A shift from one band to another could be arranged without alteration of the instrument itself, being accomplished by a simple change in the bubble-tube lengths, as described later. Accordingly, a recording type instrument was purchased and installed. Because there were some advantages in doing so, the first installation attempted to measure the gravity of the cone proper by placing the bubble tubes in the cone. This was not at all satisfactory and the second scheme utilized a fixed vertical screen at the surface of the cone, and an external sample-tube arrangement. We were particularly anxious to make this work as we felt it would be advantageous to measure the top level of medium where the separation was actually being made, but we were doomed to disappointment because it was impossible to keep the screen clean of float. Since the top gravity of the cone is the most convenient place to sample for control, a launder about 2 in. wide was installed longitudinally beneath the

Jan 1, 1951

By J. W. Leonard, B. A. Donahue

A method is described for incorporating coal petrography into mining and preparation plant quality control based on conventional analyses. Complete analyses are made of each of the uniform and relatively distinct petrographic bands in a coal face. With this information it is possible to develop petrographic standardization curves. These curves permit diverse coal characteristics to be rapidly monitored by application of a few standard coal tests. Single seam quality control is discussed in this paper. Inquiries continue to be made about coal petrography, and specifically, about whether coal petrography should be applied more extensively in the coal industry. Coal petrography is the study of the distinct physical, optical, and chemical increments which make up the organic rock mixture which we know as coal. Petrography can be applied by any coal company or at any coal mine where conventional coal analytical facilities are available and where additional resources can be allocated for an increased number of determinations. This first paper of a two part series includes (1) a proposed conventional approach to single seam petrography based on the development of petrographic standardization graphs and (2) some informative and supplemental interrelationships involving coal characteristics developed as a result of this research. In the second part of this series, to be published at a later date, those petrographic characteristics of bands taken from many different coal seams located over wide geographic areas which can be closely related to each other will be considered. These findings will be examined looking toward the development of a comprehensive, conventional approach to coal petrography which can be used as a common basis for multi-rank petrographic standardization graphs. Implicit to the understanding of coal petrography is the well established fact1,2 that the individual analyses of distinct petrographic bands often differ widely from the average analysis which is used to characterize a whole coal seam. In fact, a distinct and minor banded increment of coal in a high volatile seam may actually be a medium or low volatile coal with an analysis similar to the average analyses of seams located in distant coal fields. During the mining of coal, much degradation is caused which tends to randomly scatter coal bands. The degraded, scattered, and physically separated constituents of distinct petrographic bands are processed side by side in the coal preparation plant as distinct petrographic fractions with particles grouped according to a narrow size range (which derives in part from common hardness), specific gravity, and-or surface chemistry. Tile data obtained from numerous analyses made on each of the bands of any given coal seam, although diverse, can be readily interrelated. Indeed, these interrelationships can be developed into a series of nomographs or petrographic standardization graphs to serve as a basis for developing a conventional petrographic* program. Thus, by analyzing one property (for example, ash) of a selected petrographic fraction collected or separated from the flow of coal in a preparation plant, it should be possible to estimate the other physical, chemical, and thermal properties of this fraction by referring to the petrographic standardization graphs. It follows that any or all petrographic fractions in the total coal flow originating from a single coal seam can be rapidly monitored for many properties on the basis of a single analysis run on each fraction. In recent years coal petrographic research has concentrated heavily on that phase of this work which involves microscopic reflectance measurements made at many minute and selected points on a coal briquette surface.3,4 Thus, the percentage of the total number of reflectance measurements that fall into each of a consecutive series of arbitrarily chosen reflectance classes are used to characterize coal. This procedure is analagous to using the face of a coal briquette to represent the reflectance characteristics present at the face of a coal seam. Moreover, by analyzing petrographic fractions of known and uniform optical properties it is possible to closely relate reflectance to other coal characteristics. For example, reflectance has long been known to be related to such

Jan 1, 1968

By R. E. Zimmerman

The separation of fine sizes of coal from its impurities by means of various flotation methods has become of increasing importance in the coal industry. This, no doubt, will be even more so in the future as the quantity of high grade coal is depleted, particularly that used for metallurgical purposes. The purpose of this paper is to describe and report the results of research work done under the auspices of the Pittsburgh Coal Co. to determine the amenability of their bituminous fine sizes of coal to flotation, to investigate the value of various reagents and factors affecting their use, and compare the results between froth flotation and bulk oil flotation. Compared with the preferential flotation of complex minerals, or ores, the flotation of coal is comparatively easy. However, this statement should not lull one into the feeling that there are no special problems involved. For instance, the separation of coal from pyrite in high sulphur coals is still far from being 100 pet successful. Size consist has considerable effect on reagent consumption and recovery. Other factors will be described and finally it must be remembered that in the flotation of coal a low priced material is being treated and thus economic considerations govern more closely its application than is generally the case in treating other minerals. As a result of the research work done by the Pittsburgh Coal Co. on the flotation of coal, it was concluded that it was practical to clean the —48-mesh coal commercially by froth flotation and after several different types of flotation units and circuits were investigated by means of pilot plants, large scale units were installed at their Champion Nos. 1, 4 and 5 Preparation Plants for the cleaning of —48-mesh slurries. These large scale operations have been recently described by D. H. Davis.' C. P. Proctor and C. B. Carlson2 in their chapter on Froth Flotation of Coal in the AIME Seeley W. Mudd series book on Coal Preparation describe some of the practical applications of our Pittsburgh Coal Co. laboratory work in actual plant practice as well as summarizing part of the investiga-tional work. The author presents this paper, however, as a supplement to their reports, and records the basic research accomplished in the laboratory investiga-tional work as well as the results of experiments using bulk oil flotation. In presenting this work the author wishes to state much more work must be done in applying the principles of flotation to cleaning coal, especially in view of recent studies and practices in other mineral beneficiation fields. Methods of Conducting Laboratory Tests The bulk of the research work was conducted in the laboratory of the Champion No. I Preparation Plant. This plant has elaborate facilities for sampling and analyzing coal and proved to be an admirable location for the investigational work. Four types of laboratory flotation ma-

Jan 1, 1949

By E. P. Klier, S. M. Grymko

The transformations in eutectoidal systems have been extensively studied as they occur in steels.&apos; As a consequence of these studies the martensite, bainite and pearlite reactions found for most steels are widely recognized. Further, because of the work of Smith and Lindlief2 and of Greninger and Troiano3 these reactions, except for the bainite reaction, are considered as typical for all eutectoidal systems. The primary alloy studied by Smith and Lindlief2 was a CuAl alloy of near eutectoid composition as was the alloy more recently studied by Mack.4 The transformations in these alloys were, for the most part, studied metallo-graphically, while an X ray analysis of structures was essentially wanting. It has appeared desirable, therefore, to investigate selected CuAl alloys at and slightly away from eutectoid composition. For this purpose three alloys were prepared containing 10.5,11.9 and 13.5 pct A1 respectively. The results of a metallographic and X ray analysis of structures obtained for isothermal transformation of the ß-phase are reported here for the 11.9 and 13.5 pct A1 alloys. Introduction The phase equilibria in the CuAl alloys of immediate concern are indicated in the equilibrium diagram section presented in Fig 1.5 The equilibrium and transition structures which have been reported in this system are as follows: a = copper rich terminal phase (f.c.c.) ß = high temperature eutectoidal phase (b.c.c.) r2 = aluminum-rich intermediate phase (r-brass structure) a&apos; = modified a-phase postulated by Bollenrath and Bungnrdt.26 ß1 = ordered ß (b.c.c.) ß&apos; = martensite structure: A1 < 13 pct (near h.c.p.) ß" = ß&apos; of Smith and Lindlief2 7&apos; = martensite structure: A1 > 13.5 pct (h.c.p.); ß2 of Bollenrath and Bungardt.26 The eutectoid transformation can be suppressed at sufficiently high cooling velocities. The ß-phase is then retained to about 500°C where ordering sets in. The ordering interval is not satisfactorily known but indirectly appears to be non-suppressible. Subsequent to the ordering reaction and consequently at lower temperatures, the ordered ß1 decomposes to a marten-sitic structure. The kinetics of these reactions and in particular those of the martensite reaction have an important bearing on the results obtained in this investigation. Since some confusion exists concerning certain reported aspects of these reactions, they will be considered in some detail. THE MARTENSITE REACTION The martensitic structure is formed on cooling through a critical range6

Jan 1, 1950

By J. C. Sarace, S. M. Sze, C. R. Crowell

Thin films of tungsten 077 n-type germanium, silicon, and gallium arsenide were obtained by reacting tungsten hexafluoride with the semiconductor surface in an argom atmosplrere at temperatures between 325° and 400° C. Capacity-voltage, current-iloltage, and photoelectric measurements were used to investigate the characteristics of the tungsten -semiconductor diodes thus Produced. The junctions are shown to he very close to ideal Schottky barlp/ers with barrier heights measured with respect to the Fermi energy of 0.18, 0.65, and 0.78 1.1 jar W-Ge, W-Si, and W-GaAs, respectively. The electrical properties of the W-Si interface show no deterioration when heated to 1000°C in dry forming gas for 5 min. A theoretical value of the Richardson constant, A, appropriate to the semiconductor-hand structure has been used in evaluating the current-voltage characteristics. ThE W-Si surface-barrier diode was initially proposed for investigation because the eutectic temperature with silicon (1400°C) is much higher than that in the Si-Au system 1370°C).1 This would permit more flexibility in heat treatment and possibly provide greater reliability at elevated temperatures. The lower work function of tungsten (4.54 ev)2 compared with that of gold (4.78 ev)3 also suggested that a lower barrier height would be obtained with tungsten and hence a lower forward bias and lower minority carrier injection ratio for a given current density. The investigation was extended to include the characterization of W-Ge md W-GaAs surface-barrier diodes. The tungsten films have been produced by reacting WF6 with germanium, silicon, and GaAs surfaces in an argon atmosphere at temperatures from 300° to 500°C.4 This process is a very satisfactory alternative to the relatively difficult process of evaporating tungsten films in vacuo. To ensure an adequate electrical characterization of the tungsten-semiconductor interface, three types of barrier-height measurements have been performed. The mutually consistent results obtained lead to the conclusion that the tungsten-semiconductor junctions are indeed of the Schottky type. EXPERIMENTAL PROCEDURE The apparatus used for producing tungsten films is shown schematically in Fig. 1. It consists of an argon carrier gas line to which metered amounts of tungsten hexafluoride can be rapidly added. The mixture passes through a heated reaction tube containing the semiconductor slices and is exhausted to a hood. The argon is purified by passage through a 6-in. column of titanium turnings maintained at 800°C. The tungsten hexafluoride dispensing arrangement was designed by V. C. Garbarini and W. R. Bracht.4 A measured amount of liquid tungsten hexafluoride is injected into the argon stream and vaporizes. The mixture passes through a sodium fluoride absorption cell to remove traces of hydrogen fluoride, then into the nickel reaction tube. The tube is 12 in. long with an inside diameter of 1/2 in. The center section is heated by a furnace of the self-supporting wire-filament type. It was chosen for its rapid heatup and cooling. The wall thickness is 10 mils except for a 3-in. hot zone which is 30 mils thick to reduce thermal gradients along the length. The samples to be coated are placed on a sapphire plate and centered in this section. The tungsten is deposited with the following sequential steps: the loaded reaction tube is flushed with argon at a rate of 500 cu cm per min and heated to 370°C. Then 0.45 g of liquid tungsten hexafluoride is injected into the argon stream. The samples are held at this temperature for 2 min. The tube and samples are then cooled to room temperature and the samples removed. Tungsten films were grown on (111) faces of silicon and germanium polished with Linde A abrasive and lightly etched with HF-HNO3. The GaAs surfaces were (100) faces chemically polished with a H2SO4-H2O2 solution. The films have typical sheet resistances of 0.2, 8, and 15 52/0 when grown on germanium, silicon, and GaAs, respectively. After the tungsten deposition, ohmic contacts were alloyed on the back surfaces of the wafers. Ohmic contacts to the germanium and silicon were obtained by alloying Au-Sb at 370°C, ohmic con-

Jan 1, 1965

By P. Greenfield, P. A. Beck

The phase is a hard and extremely brittle material with a tetragonal crystal structure, containing 30 atoms per unit cell&apos; It occurs in many binary and ternary alloys of the transition elements. The existence of twelve a phases has been reported in binary alloys of metals from the group vanadium, chromium, molybdenum, and tungsten with metals from the group manganese, iron, cobalt, and nickel. It is a characteristic fact that the composition of the o- phases in the various binary systems is not the same. Rather, there is a gradual shift in composition, for instance in the series of chromium a phases, approximately as follows: CrMn,, FeCr, Cr3Co,. In recent years several ideas have been put forward to account for this variability of composition. SullyZ proposed that a was a type of electron compound, characterized by 1.7 electrons per atom in excess of the number required to fill the Pauling atomic orbitals. These excess electrons were supposed to just fill the first Brillouin zone of the u structure. However, later work indicated that the phase is ferromagnetic at low temperatures, so that a- is unlikely to be a full zone compound.~ Another proposal,* which is also based on the structure of the transition elements advanced by Pauling, and in fact leads to essentially the same a compositions as Sully&apos;s theory, suggests that the u phase is characterized by a constant number of electron vacancies per atom. The electron vacancy numbers N,. used were originally the same as those in the Pauling theory, but were later modified empirically vn order to bring about better agreement with data for the p phase in certain ternary systems. For alloys, N,, was calculated on the assumption of simple additivity from the electron vacancy numbers of the components, as follows: N,. = 4.66 (Mo + Cr + V) + 3.2 (Mn) + 2.2 (Fe) + 1.71 (Co) + 1.6 (Ni). On this basis a reasonably constant value of N, = 3.4 was obtained for all of the binary u phases and a fairly constant value of N,, = 3.1 for the various p phases. More recently, Bloom and Granta pointed out that a similar correlation with the total number of 3d and 4s electrons per atom is also fairly well fulfilled and concluded that no reference need be made to the Pauling theory. This proposal does not lead to the same binary a compositions as the one described above, so that the relative merits of the two proposals may be determined on the basis of direct comparison with experimental composition data. The purpose of the present paper is to provide such a comparison. Since the experimental data for the composition ranges of several of the known u phases were rather incomplete, it was decided to carry out new experimental determinations for many of the binary systems. Experimental Procedure The alloys were prepared by induction melting in recrystallized alumina crucibles, either in vacuum or in helium atmospheres. Some aluminum was picked up from the crucibles in the alloys of high vanadium content, but this was minimized by keeping the alloys in the molten state for as short a time as possible. The maximum aluminum impurity was 0.13 wt pct by chemical analysis, in an alloy containing over 50 wt pct V. In general, the as-melted compositions agreed accurately with those obtained by chemical analysis. In the case of manganese, however, losses inevitably occurred; consequently all manganese alloys were analyzed. Specimens of all alloys were annealed at temperatures ranging from 1000" to 1300°C in an atmosphere of purified 92 pct helium and 8 pct hydrogen mixture. All manganese alloys were sealed in quartz tubes under vacuum before annealing. The specimens were held at temperature for between four and eight days before being quenched into cold water. Alloys were prepared for microscopic examination by mechanical polishing, usually followed by electrolytic etching. X-ray diffraction specimens were prepared by crushing the homogenized alloys, and by reanneal-ing the obtained powders in evacuated quartz tubes for a few hours at the temperature of the lump anneal. X-ray diffraction patterns were made with unfiltered chromium radiation, using an asymmetrical focusing camera of high dispersion. Using microscopic and X-ray techniques jointly, the accuracy

Jan 1, 1955

By Richard H. Jahns

GRANITIC pegmatite deposits are the chief source of commercial feldspar, sheet mica, beryllium, tantalum-columbium, and lithium minerals, and certain types of kaolin. They also have yielded significant quantities of cassiterite, gems, scrap mica, molybdenite, tungsten minerals, uranium-thorium and rare-earth minerals, and zircon, either directly or as the sources of placer deposits. The output from pegmatite mines in the United States is small as compared to other mineral products in terms of bulk or value, and much of it comprises minor metals and nonmetals. Nevertheless, pegmatite minerals play a vital part in domestic industrial economy, particularly in the ceramic and electrical industries. Numerous special purpose uses also are important, even though they require small quantities of raw materials. Never was United States dependence upon pegmatite mining more clearly emphasized than during World War 11, when greatly expanded demands and uncertainties of foreign sources of supply caused much concern. Such commodities as beryl, tantalite, and sheet muscovite remained high on the critical list for months at a time, and for some minerals there was a real struggle to achieve and maintain a favorable ratio of supply to demand. Satisfactory stock piles of certain sizes and qualities of sheet mica, for example, were not built up until late in 1944, when wartime requirements already had begun to level off or even to decrease. Production of all the strategic pegmatite minerals from domestic deposits during World War I1 constituted only 10 pct or less of the total domestic consumption of these minerals, but the importance of this contribution should not be minimized. Domestic production often represented the difference between increase and further reduction of existing stocks of commodities already in seriously short supply, and in the early stages of the war it was the only assured source if imports were cut off. During the recent war period, the U. S. Geological Survey carried on a program of pegmatite studies in the New England and Southeastern States, in the Black Hills area of South Dakota, in the Rocky Mountain region of Wyoming, Colorado, and New Mexico, and in various parts of Washington, Idaho, Utah, Nevada, Arizona, and California as shown in Fig. 1. Several papers and reports already have appeared as an outgrowth of this work,&apos;-= and others are in preparation. This paper outlines some results of data obtained by the writer during the period 1942 to 1946, when he was engaged in studies of pegmatites in the Southeastern, Southwestern, and Rocky Mountain States. Beryllium Minerals Beryl is the present commercial source of beryllium metal and beryllium compounds, which are used in ceramics, in the preparation of X-ray tubes and fluorescent lamps and screens, in special processes of paint and textile manufacture, and in the optical systems of some electrical instruments. The metal also is used in nuclear physics, chiefly as a source of neutrons. Beryllium is alloyed with aluminum for certain light-metal uses and is a constituent of some nickel and iron alloys. Currently the chief demand, however, is for copper-base alloys, which are exceptionally resistant to fatigue and wear, are responsive to hardening treatments after

Jan 1, 1952

By D. W. Mitchell

INE operators have a choice of several classi- fications of mechanical loaders. Within each classification there are many types and makes available. Table I lists loaders on which manufacturing data as to operating characteristics are available. This paper discusses the conditions met in a mine as they affect these characteristics. It is assumed that management will provide satisfactory engineering, supervision, power, maintenance, loader service within a concentration of workings, and a balanced working cycle served by balanced production equipment. These are factors which affect the optimum operational efficiency of a loader. The conditions which determine loader choice are: Height of Vein—The main limitation to the use of a loading machine is the height to which the vein is mined; i.e. a loader cannot be higher than the place in which it is to work unless rock is taken. Since there are several low vein loaders being developed and successfully applied, this does not appear to be a requisite of an efficient mining operation. The maximum useable height of a loader should be equal to the working seam thickness less a working clearance for travel and operation. A—Working seam thickness = B—Artificial roof support thickness = C—Safe headroom below support = (generally about 6 in.) D—Height of roadway = E—Total of B + C f D =_______________________ A—E = maximum loader height F—Distance from top of roadway to bottom of roof support = G—-Height of loader&apos;s coal or ore line (see Table I) = H—Difference between F and G = Size of largest broken particle + a safety factor of 2 to 3 in. H is a loadability factor and is important because the clearance over the top of the conveyor chain to the roof or roof support must be greater than the largest broken particle or else the particle and/or the conveyor chain may be broken. From this standpoint it might be desirable to use a lower height machine even though it may have a smaller capacity, though this is warranted only when increased lump realization offsets lower man-day and machine pro- duction rates. Ivan Given has stated, "Loading should not be handicapped by securing lump only to grind it in the breaker." Width of Working Place—The width of a working place is the greatest width a place may be safely driven. The working place includes not only the face but the roads the loader must tram when mucking out more than one face. The width is limited by the system of placing props with sufficient room between them for the machine runner (about 2 ft). Maximum width of place in which the loader will operate at maximum efficiency is determined by the type of mounting. With track-mounted loaders, maximum width of place is determined by maximum angular swing of the loading head and proximity of track to the face. The use of double track leads to added expense and operational complexities. Several mines that have used double-track systems have found that a substantial saving is made by the use of machines that load out wider places. Trackless loaders may work in rooms of any maximum width. Minimum width of place in which a loader will operate is determined by width of the loader plus a safe movement area for the operator. Often a barodynamic study of the mine will show that either an increase in room width and/or a change in the system of propping may be made by using roof bolting, full or part-width room timbers, removable aluminum I-beams at the face, etc. Increasing the width of a working place will, in general, increase loader operating efficiency by providing more material per fall and by decreasing the preparation and moving time per ton. A change in the system of propping that would increase the minimum width might permit the use of a higher capacity loader with safer working conditions. Proper face tirnbering is necessary to insure safety from roof falls and because the speed of preparation and loading generally increases since the men work with greater assurance and there is less chance of kicking out posts. Maximum Room Length—With the exception of the scraper and the duckbill, the limit to room

Jan 1, 1952

By Martin Weinstein

A technique is described for preparing finegrained lead telluride by ultrasonic agitation of a solidifying melt. Material prepared by this technique is dense and chemically homogeneous. N-type PbTe, containing 0.03 mole pct PbIz, has been made and its thermoelecCric Properties have been measured as a function of temperature. For comparison, the properties of similarly doped PbTe made by cold pressing and sintering, and by extrusion, have also been measured. The ultrasonically prepared material compares favorably with the others in its thermoelectric-efficiency factor. Comparison of compressive-flow curves for the three kinds of PbTe show that the ulhasonically prepared material has much superior ductility. The cleavage strength of the ultrasonic material is related to the grain size, D, by the Petch relation:Extrapolation to infinite grain diameter yields a fracture strength of 5000 psi for single-crystal PbTe. WHEN metals and semiconductors solidify in a mold they normally assume one of three cast structures illustrated in Fig. 1.&apos; Solidification in a casting starts at the mold walls where a large number of fine crystals of random orientation can be nucleated to form the chill zone. Because of the anisot-ropy of the growth rate, those crystals whose direction of maximum linear growth is parallel to that of the heat flow grow faster and crowd out the crystals of less favorable orientation. A second zone, having a preferred orientation, called the columnar zone, thus forms adjacent to the chill zone. The speed of growth of the columnar grains will depend, in the case of limited undercooling of the melt, on the rate at which heat can be abstracted. The columnar zone can extend to the center of the casting, Fig. l(a), but it is frequently followed, in solid-solution alloys, by another zone of equiaxed randomly oriented grains in the central portion of the casting, Fig. l(b). The equiaxed structure in Fig. l(c) represents the completely grain-refined case where the equiaxed grain size is small. The third type of structure is the most desirable because it imparts a somewhat higher strength for all except high-temperature applications, it reduces segregation of the doping constituent, and it reduces the possibility of hot tearing (the separation of grains due to the melting of a low-melting point constituent in the grain boundaries). In order to obtain fine-grained castings, the nu-cleation frequency must be increased and grain growth must be restricted. Various techniques have been employed for obtaining this end, namely: rapid cooling, vibration, and inoculation of the melt. The success of these techniques depends upon the characteristics of the metal species and on factors controlled by heat transfer through the crucible walls. Recent studies2" have shown that the application of ultrasonic energy to the solidifying ingot is an extremely powerful tool in the improvement of the crystalline structure of metallic castings. Both the mechanical properties and homogeneity of the ingots are improved. Ultrasonic oscillations may affect the crystallization process by 1) permitting subcritical nuclei to agglomerate and thus form nuclei of sufficient size to cause crystallization, 2) changing the state of surface adsorption of various catalysts found in the liquid melt, 3) breaking pieces of solid from the solidified surface near the supercooled region thereby increasing the number of possible nuclei, 4) causing temperature fluctuations to occur in certain parts of the melt thereby increasing the supercooling at specific points in the liquid, and 5) decreasing the critical nucleus size by increasing the pressure at specific points in the melt.&apos; Various investigators have concluded that the effectiveness of the ultrasonic oscillations results from cavitation which disrupts the growing solid-liquid interface The present paper describes the application of ultrasonic oscillations to the crystallization of the semiconductor N-type PbTe. The purpose of this study is to prepare crystalline

Jan 1, 1964

By Alfred V. de Forest

WE are now assembled in this hall for the eighteenth lecture in honor of the memory of our greatest American metallurgist, Henry Marion Howe. Many of his most intimate contemporaries, led, as was fitting, by Professor Sauveur, have described his vital accomplishments in three fields: as a leader in technical industrial development; in theoretical research; and finally as a teacher and source of inspiration for nearly two generations of students. In 1914 Professor Howe had retired from active teaching, but maintained his laboratory at Columbia University under the care of Arthur G. Levy, with whom he published many of the papers that later were incorporated into his last book, "The Metallography of Steel and Cast Iron." My position at the time was that of personal assistant to Professor Campbell-no pay, no duties, but the great privilege of preparing specimens, taking pictures and attending to some of the current consulting work. Whenever possible, I visited Howe&apos;s laboratory to chat with Levy and gather ideas about the wonderful field of metallography-in which I was a rank amateur, rescued by the quiet enthusiasm of Donald Smith of Princeton from an instructorship in civil engineering. Levy let me act as a fly on the wall during the Professor&apos;s occasional visits. Busy as he was, Professor Howe took the time and trouble to encourage my interest, as he had done for hundreds of others. He told me how he went about gathering his own information speculating as to causes, considering experiments, and verifying his conclusions. I ventured to mention some tests I had run on the irregular stretching of wires of different metals. He read the small volume I had prepared of ill-assorted facts and fancies and remarked: "Nobody cares for your theories or the history of your tests. Describe what you found as briefly as possible and perhaps I can help you to publish." Curiously enough, among my discards were some autographically recorded load-versus-electrical-resistance measurements. Taken with inadequate knowledge and equipment, these curves did not reproduce consistently, but if the relationship between strain and resistance had then been explored, the latest type of strain gauge might have been in useful service for the past 25 years. Professor Howe was a gifted teacher, perhaps because he was primarily an ardent and assiduous student. His own eagerness to learn and his willingness to revise and extend his opinions constantly encouraged those of his environment to be diligent and painstaking in the pursuit of knowledge. In honoring his memory, I also wish to bring to mind the kindly, humorous and quiet Levy, and join his name again, as it was for too brief a space in the past, with that of many-sided Henry Marion Howe. FACTORS OF IMPACT STRENGTH The subject chosen for the Howe Memorial Lecture by Dr. Gillett last year

Jan 1, 1941

By R. I. Jaffee, C. M. Craighead, G. A. Lenning

THERE has been considerable discussion among A metallurgists and others interested in the development of titanium alloys as to the nature of the fine line markings which appear in the microstruc-tures of unalloyed titanium and a titanium alloys. These markings have been variously called x phase, etching pits, and twins. Figs. 1 to 3 show typical examples of the line markings as they appear, respectively, in high purity iodide titanium, commercial purity titanium rod, and a high purity a alloy containing 0.2 pct N. The commercial purity titanium sample, shown in Fig. 2, contains both line markings and some spheroidal retained-ß phase. The ß phase seen in this micrograph should not be confused with the line marking, since it originates from the iron present as an impurity in the sponge metal. It will be noted that the line markings seem to have a definite orientation pattern with respect to the grains and in titanium noticeably resemble the precipitation occurring in artificially aged high purity Al-Cu alloys. This similarity led to the hypothesis that the line markings observed in titanium and a titanium alloys resulted from precipitation of some unknown phase. With the work of Hägg1 and McQuillan2 as background, there was little reason to suspect hydrogen of being responsible for the line markings. Hagg reported that up to 33 atomic pct H was soluble in a titanium, and McQuillan reported an a solubility of up to 8 atomic pct. Furthermore, McQuillan examined metallographically a 5.1 atomic pct H alloy quenched from 300°C and stated that the structure appeared to be a single-phase a solid solution. Line markings have been observed frequently and were first noted by Jaffee and Campbell3 in 1949. They did not observe them in vacuum-annealed titanium and a Ti-O and Ti-N alloys, but did observe them in Ti-H alloys containing 0.25, 0.5, and 1 atomic pct H. They stated that it was doubtful that the markings were a second phase based on hydrogen, because 1 atomic pct was far from the accepted solid solubility of hydrogen in titanium. Finlay, Resketo, and Vordahl,4 in 1950, concluded that the markings were a true second phase as a result of observations on their etching characteristics. Anderson5 Commenting on these markings in titanium was inclined to associate them with hydrogen, but was loath to call them titanium hydride, because of the reported high solubility of hydrogen. Work at Battelle Memorial Institute for the Navy Bureau of Aeronautics," done concurrently with the work described in this paper, provided information on the experiment converse to that described by Jaffee and Campbell in 1949. This work showed that the amount of line markings in unalloyed titanium could be decreased by vacuum annealing at elevated temperature. It was suggested that this was the result of removal of hydrogen; previously, the data of Jaffee and Campbell9 howed that the markings appeared when hydrogen was added. Recent work at Battelle for the Ordnance Corps, Department of the Army, which is described here, now establishes the identity of the markings as a titanium hydride phase. A sample of high-purity titanium rod 1/4 in. diam, 0.009±0.001 wt pct H (0.43 atomic pct), Fig. 1, was resistance heated in a 0.05 micron vacuum for 41/2 hr at 1500°C. During the early states of heating, the pressure increased to 150 microns, indicating that gases were being evolved. After cooling in vacuum, the iodide titanium rod was analyzed for hydrogen. Vacuum-fusion analysis showed 0.0006 ±0.0003 wt pct H (0.03 atomic pct) to be present.* Metallographic examination of the vacuum-annealed rod showed only a transformed ß structure. There was no evidence of fine line markings, Fig. 4. A section of this vacuum-annealed rod was cold rolled to 0.040 in. thick sheet and annealed for 1 hr

Jan 1, 1953

By Benjamin Lustman, Robert F. Mehl

The study of the high-temperature oxidation of pure metals, intensively pursued experimentally since the pioneer work of Pilling and Bedworth1 and supplemented by the recent theoretical work of Wagner2 is now well advanced. The important field of low-temperature oxidation—i.e., oxidation extending only through the temper color range of thicknesses with the formation of thin oxide layers in the range from 0 to 1000-2000 ?ngstroms—has not, however, reached so satisfactory a state, owing largely to the experimental difficulties that attend the formation and study of thin films; most of the work has been performed on abraded specimens whose surface irregularities approximated the thickness of the films formed. It has been pointed out that the rates of oxidation of different crystal faces are different and that the difierence may be related to the orientation relationships that obtain between the metal crystal and the superimposed oxide crystal; it has also been suggested that this orientation dependence should manifest itself in rates of oxidation and perhaps also of corrosion in aggregates bearing preferred orientations.3&apos;4 An attempt to measure the rates of oxidation of different crystal faces of alpha iron demonstrated this difference in rate,4 but the dependence of rate on orientation was not simple; the method of measuring thickness, consisting of a color comparison with barium stearate multi-films of known thickness, was not wholly satisfactory. For these reasons it was felt that a study of the rate of oxidation of single crystals prepared with surfaces as smooth as possible, using a sensitive method giving true film thickness, should be profitable. Copper was chosen because of the ease of reduction of the primary oxide film and because the orientation relationships between metal and oxide and the composition of the oxide films formed at low temperatures are known; for thin films formed at low temperatures, Cu2O alone occurs.22-24 Experimental Procedure Various methods of surface preparation were attempted in order to obtain a surface that would oxidize uniformly and repro-ducibly. Electrolytic polishing by the method of Jacquet5 and electrolytic and mechanical polishing followed by annealing in vacuum and in purified hydrogen at various temperatures were tested. The procedure finally adopted consisted in a fine metallographic polish followed by an anneal in purified hydrogen at temperatures of 900° to 1000°C. for 12 hr. or more. The surface so produced was very bright and smooth, with no trace of specular etching (though some grain-boundary etching was observed); indeed, fine scratches produced by the final polish were entirely removed by the high-temperature anneal. After this treatment, the specimens were cooled in hydrogen to room temperature and placed in the oxidation furnace, where

Jan 1, 1941

By Richard D. Hagni

Abstract-Although the ore microscopist routinely examines polished sections to determine the mineralogy and texture of ores, his importance to the solution of problems peripheral to geology is not always fully realized. The techniques which he uses can be applied with little modification to the solution of a wide variety of beneficiation problem. By extending his studies beyond those normally considered to be of interest to the geologist, he can include examinations of polished sections of selected mill products. This is a logical extension, because the minerals and textures in the polished sections of ores are the same as those in mill Products. The mill dressing engineer should be more aware of the types of beneficiation problems that can be solved by the ore microscopist and what the ore microscopist can do for him. A greater degree of cooperation between the ore microscopist and the mill dressing engineer can be of significant mutual benefit. Ore microscopy holds an advantage over chemical analysis, because the interrelations and combinations of the mineral constituents of an ore or mil1 product can be visually determined. This advantage provides solutions to many beneficiation problems. Locking is a type of beneficiation problem that is particularly amenable to ore microscopy. The percentage, type, and distribution of locked particles can be readily determined with the aid of an ore microscope and an estimate made of the extent of additional grinding required for liberation. The extent of intimately locked types, which no reasonable amount of grinding will liberate, can also be evaluated. Mineral coating conditions, free particles of a deleterious mineral, and free particles of a valuable mineral held in floculated clusters of gangue are other features that can readily be observed. In some instances, visual examination may show that the problem is not one of locking. Photomicrographs illustrate the variety of beneficiation problems for which the ore microscope is applicable. These problems and their resolution demonstrate the importance of the instrument and show the value of close coordination between the mill dressing engineer and the ore microscopist.

Jan 10, 1978

By L. J. Ingvalson, Roy H. Miller

IN 1948, as part of a program to expand the copper tube mill facilities of the American Brass Co. plant at Kenosha, Wisconsin, plans were formulated to convert the 100 ton capacity anode casting furnace at the Great Falls, Montana plant of the Anaconda Co. to the production of 3 in. phosphor -ized billets. The furnace was rebuilt completely and construction was started on an addition to the building. Members of the Great Falls staff visited various billet casting plants to draw upon the experience of other producers of this type of casting. Many features of other plants were incorporated into the Great Falls plant but, in addition, many new designs were made and perfected to make the plant the most advanced of its type. Construction was begun in 1949, with the intention of having the plant in production in the early part of 1951. In January 1951, as the plant was being rushed to completion, the government placed restrictions on the production of copper tubing. As a result, work was halted and the plant lay idle for two years. Interest was reactivated in May 1953 with the lifting of restrictions on copper. Plans were laid to go into production in July and the first charge was taken out July 1, 1953. Basically the plant is designed to produce from cathode copper a 3 in. diam billet, 50 in. long. weighing 110 lb, and containing 0.013 to 0.036 pct P, at a rate of 150,000 Ib per operating day. These billets are to be pierced and drawn into tubing. Furnace The furnace is a 100 ton capacity reverberatory type, gas fired furnace; 21 ft long and 9 ft wide. Gas is introduced to the furnace through two 38 hole Mettler gas burners. These burners are of chrome nickel alloy with four jets per hole. The furnace is charged with cathodes from the Electrolytic Copper Refinery plus return scrap from the casting operation by means of a Wellman Seaver Morgan Co. 7,000 lb capacity charging machine. The charge crane has a 20 ft boom and fork peel provided with an air ram to push material off the peel. The machine travels on overhead tracks and can be moved in any direction. The boom can be raised and lowered and swung through an arc of 180". With well stacked units of 6,000 lb, an experienced operator can put the first charge into the furnace in 40 min. After charging, the steel framed silica brick charge door is put in place and sealed with clay. After melting and skimming off the slag, the copper is blown until an oxygen content of 0.40 pct is reached. The metal is then heated to 2180°F, covered with coke, and poled. Poling is continued until a 3 in. diam test billet, 8 in. long, shows a flat set. The oxygen content is usually 0.030 pct at this time. At the end of poling, a temperature of 2160" to 2180°F is desired. In the side of the furnace opposite the charging door is the taphole slot, extending 36 in. upward from the bottom of the furnace. It is 4½ in. wide at the outside face and widens to 9 in. at the inside face of the furnace. It is filled with a wet mixture of sand, fireclay, and crushed coal. Flow of metal

Jan 1, 1957

For many years it has been known that large bodies of iron ore existed in Iron and Washington counties in Utah. The ore is chiefly hematite-both hard and soft-though some magnetite is found. No definite and complete estimate of the iron ore reserves of the state have been made. The U. S. Geological Survey estimated that 40,000,000 tons of ore were disclosed by development work averaging only 35 feet below the surface of the ore. The ore is found along an area about one and a half miles wide by twenty miles long, and for the most part on the eastern and southern slopes or foothills of Three Peaks. Granite Mountain and Iron Mountain. Later estimates by others have gone as high as ore in sight 164,000,000 tons, probable ore 300,000,000 tons and possible ore 1,000,000,000 tons. Whether this last estimate is too great or not there is sufficient iron ore in Utah to justify the starting of an iron industry. Two companies are now mining iron ore in Utah, the Columbia Steel Corporation and the Utah Iron Corporation. The mine of the Columbia Steel Corporation is at Iron Springs a few miles west of Cedar City. About 650 tons, of ore a day is being shipped to the blast furnace at Ironton. The ore is mined by the glory hole method. After being drilled it is blasted to the bottom of the several glory holes and is dropped through chutes into cars on the ore haulage level below. It is then hauled by electric locomotives to the crushing plant, where it is crushed to blast furnace size before going to storage bins. Some of the softer ore is brought to the chutes by Fresno scrapers.

Jan 1, 1925

By J. H. Scaff, H. C. Theurer, E. E. Schumacher

The microwave region of the radio spectrum was effectively utilized in radar designs during the recent war and it has become of increasing interest in the field of communications. Work in this field has led to an important use for silicon—that of the point contact rectifiers†1 in the frequency converter of microwave (radar or radio) receivers—and has stimulated considerable interest in the electrical properties and preparation of silicon and its alloys. Silicon is an electronic semiconductor. Its conductivity at room temperature results principally from the presence of certain impurities. While for metals an increase in impurity content increases the resistivity, for semiconductors such as silicon the opposite occurs and, in general, the addition of impurities lowers the resistivity. Silicon materials may be classified into one of two groups depending upon the manner in which the impurities contribute to electrical properties. These have been termed for convenience p-type or n-type. P-type silicon develops a very large positive thermal emf against metals, has a Hall coefficient of positive sign and a low resistance direction in point contact rectification with the silicon positive with respect to the point. N-type silicon, on the other hand, develops a negative thermal emf against metals, has a Hall coefficient of negative sign and a low resistance direction in rectification with the silicon negative with respect to the point. Impurities which produce n-type silicon are called donors inasmuch as these elements contribute to electrical conductivity by donating electrons to an unfilled energy band in the silicon. On the other hand, elements which produce p-type silicon are known as acceptors as these impurities contribute to the electrical conductivity by accepting electrons from a filled energy band permitting what is known as conductivity by "holes" in which the sign of the carriers appears to be positive. A general treatment of the mechanism of conduction in semiconductors from the viewpoint of modern band theory has been given recently by Pearson,2 by Becker, Green and Pearson,3 and by Torrey and Whitmer.4 In this investigation boron and aluminum have been found to be acceptors, and phosphorus, arsenic, and antimony to be donors in silicon. Data on the effect of boron and phosphorus on the electrical properties, when present singly and in combination, have been acquired. These data are discussed in the present paper. Raw Materials Used and Methods for Adding Seeond Constituents Silicon from two sources was used in this work and these will be referred to as A and B respectively. Silicon A is a material of high purity supplied by the Electro Metallurgical Co. It is prepared by chemical purification of "commercial" silicon obtained from the arc furnace reduction of SiO2. It contains 99.8 pct silicon, minimum, with small amounts of calcium, iron, aluminum, boron, and phosphorus as the principal impurities. This material was extensively employed in these studies as well as in the commercial preparation of rectifier materials. Silicon B is a material of high purity from the du-Pont Co. It is prepared by a pyrolytic reduction of Sicl4 and is free of analytically detectable amounts of boron and phosphorus. Its use permitted study of the effect of boron and phosphorus individually on the properties. This material contains, however, spec-troscopic traees of a number of metals, some of which affect electrical and rectification properties. Typical analyses for the two grades of silicon are given in Table 1. To make controlled additions of boron to the charge it was necessary to employ a low boron content master alloy since the quantity of boron to be added was usually only a few thousandths of one percent. The alloy containing nominally one percent boron was prepared by melting chemically pure boron with silicon A using the melting techniques for 320 g silicon

Jan 1, 1950

By W. V. Green

The creep-rupture behavior of commercial powder-metallurgy tungsten rod is reported for temperatures of 2250°, 2500°, 2700°, and 2800°C, stresses up to 7000 psi, and times up to 4 hr. The temperature dependence and the stress dependence of creep rates are evaluated. Rupture time is fitted to the Larson-Miller parameter and compared to lower-temperature and higher stress results reported by pugh.4 THE tensile strength of single-crystal wire1 and of polycrystalline wire2 have been measured by Goucher. More recently Bechtold3 and pugh4 have studied the mechanical properties of tungsten rod between room temperature and 1200°C. Since tungsten has the highest melting point of all metals, it should retain useful strength to very high temperatures, and should find many applications in missiles, rockets, and so forth. Therefore, the mechanical usefulness of polycrystalline tungsten rod was investigated in the 2250" to 2800°C temperature range by short-time creep-rupture tests. MATERIALS TESTED Creep specimens were machined from 1/2-in. round commercial tungsten rod which was manufactured from powder by cold pressing, sintering, and hot swaging. Purity reported by the vendor was 99.95 pct W. Spectrochemical analyses showed "traces" (less than 0.01 pct) of silicon, iron, and titanium, and "faint traces" (less than 0.001 pct) of calcium and manganese. Carbon content was 30 ppm and nitrogen content was 70 to 110 ppm. No oxygen analysis was obtained. Room-temperature stress-strain tests on the as-received tungsten gave badly scattered results. Threaded end specimens broke at the threads. When these specimens were retested using shoulder grips, the specimens broke at the shoulders. No fractures occurred in the gage lengths. The fracture stresses were: 127,000; 137,000; and 154,000 psi for three specimens which fractured at the shoulders. The microstructure of the as-received tungsten rod is shown in Fig. 1. SPECIMENS USED Fig. 2 shows the two types of creep specimens tested. The threaded-end type specimen, which was used in most tests, had a 3/4-in. gage length and 1/4-in. gage diam. The cone-end specimen, which was used primarily to investigate the effects of a smaller gage diameter and the practicability of the modified grips and specimen, had a 3/4-in. gage length and a 1/8-in. gage diam. In both cases, the gage length terminated at 0.005-in. high shoulders which served as fiducial marks for optical strain measurements. Surface finish on the gage length was 16 µ-in. rms. Creep rates and rupture times were not significantly different for the two types of specimens and were not affected by electropolishing the specimens before testing. TESTING PROCEDURE The constant-load creep-testing machine used has been described by Smith, Olson, and Brown.5 In it the specimen is held vertically by grips of similar material and on the axis of a cylindrical tungsten or tantalum heater-tube. The specimen is loaded by means of the specimen grips, a pull rod (which is sealed to the chamber lid by a vacuum-tight bellows), a mechanical lever system, and hanging dead weights. Both specimen and grips are heated by radiation from the heater-tube, which is heated by its own electrical resistance. An optical system views the incandescent specimen through slits in the radiation shielding and heater-tube. The optical system projects an enlarged image of the specimen gage length on a ground-glass screen. Periodic gage-length measurements are made on this image with two cathetometers. Thorium oxide coatings on the specimen threads or conical end surfaces completely prevented diffusion-welding of specimens to grips, and were used

Jan 1, 1960