Search Documents

In several of the States of Australia, mining on private property has been seriously hampered by the fact that large areas of land have been alienated from the Crown before the discovery of gold or other minerals. In Western Australia this difficultyhas only occurred to a small extent, and has largely been overcome by an act entituled "An Act to Permit Mining on Private Property, No. XXIX., 'October, 28th, 1898." Under this act, the holder of a miner's right can apply for a gold mining lease on private land; such applicant may treat privately with the owner of such land as to the amount of compensation to be paid for surface ,damage, or the case may be brought before the Warden who will assess the damages. Private land used as a garden, orchard, or vineyard is exempt from lease, unless the applicant has authority from the owner, or such lease is limited to a greater depth than 100 feet from the lowest part of the surface.No lease shall be granted of any mines under any private land in any municipality unless either the applicant has authority from the owner, or such lease is limited to a greater depth than two hundred feet from the lowest part of the surface.The same regulation applies to leases of private land on which any hospital, asylum, or public building is situated or under or within one hundred and fifty yards laterally of any...

Jan 1, 1901

By Spooner H. W

The paper describes the search for mineral deposits in an area of 4,500 sq. miles of south-west Tasmania. The area is one of difficult access and the problem of speedy movement and maintenance of field parties was solved by the use of helicopters. The programme has followed a systematic pattern of the aerial photography of the exploration area with the preparation of photQmosaics and topographical base sheets from these mosaics. Geological maps were initially prepared by photogeological interpretation and making use where possible of pre-existing information. The maps produced were later checked by ground traverses. Geophysical maps were obtained by the use of airborne magnetic, electromagnetic and radiometric methods. Geophysical and geological anomalies were checked on the ground by a campaign using ground geophysical equipment in the former case and geological and geochemical work in both instances. Audio Frequency Magnetic and Induced Polarization techniques were used in an area which was covered by several hundred feet of Tertiary sediments.The campaign has reached the stage of the drilling of specific targets.INTRODUCTIONThis paper describes the activities of Lyell-E.Z. Explorations (L.E.E.), an organization which was formed in 1956 by the Mt. Lyell Mining and Railway Co. Ltd. and the Electrolytic Zinc Co. of Australasia Ltd. to explore for mineral deposits in an area of approximately 4,500 sq. miles in southwest and southern Tasmania. To provide the necessary personnel and equipment for this project the exploration resources of both Companies were pooled and augmented and a headquarters was established in Queenstown. The work was directed by a Committee of four made up of officials from both Companies; a review of this structure has recently been presented by Hall (1959).

Jan 1, 1960

By P. J. Rowsell, M. D. Waller

Paper presented at a meeting on: Artificial intelligence in the minerals sector, held in Nottingham, UK, 20 April 1993. The applications of artificial intelligence systems in the upstream petroleum industry are reviewed. Particular emphasis is placed on current and potential applications in drilling engineering. Several recent advances in drilling technology have led to a large increase in the quality and volume of data available. This combined with the escalating cost, particularly of off-shore operations, is testing the traditional reliance on the skill and judgement of rig operators. AI systems offer enormous scope in enhancing and aiding the performance of these operations

Apr 1, 1994

By J. Bennetts

As part of its mission to develop technology that will help increase the supply of critical and strategic minerals from domestic resources, the Bureau of Mines has investigated methods for beneficiating platinum-group metal ores from the Stillwater complex, Montana. This report presents the result of a bench-scale study employing froth flotation to recover a sulfide concentrate containing platinum-palladium values from a mineralized gabbro. Best results were obtained with a flotation scheme utilizing a mercaptobenzothiazone collector and sulfuric acid. Rougher concentrates containing approximately 11 oz Pt-Pd/ton and 90 pct of the metal values in the ore were obtained. Subsequently, cleaner concentrates containing approximately 26 oz Pt-Pd/ton and between 80 to 85 pct of the Pt-Pd values in the ore were prepared.

Jan 1, 1980

By S. J. Parry, D. M. Evans, D. L. Buchanan

The reef is a PGE-enriched sulphidic zone, stratigraphically associated with and overlapping the C1d chromitite layer, that was formed by magmatic processes at the 1e-1d subunit boundary. Two distinct patterns of PGE enrichment are related to the presence or absence of Cr2O3 oversaturation during sulphide liquation that occurred during a complex sequence of changes at this boundary

Apr 1, 1996

Contents.SummaryIntroductionSituation, climate, topographyHistorySize of depositsPrevious investigationsGeological History of AreaMap compilationHistorical summaryNature and Significance of Granitic RocksSynchronous granitesMain subsequent granitesSignificance of types of bathylithsGeological StructureNorth-south anticlineCross-foldingFormation of channelwaysHydrothermal Depth-Zoning at CobarAssociation of Ores with PorphyryOrigin of replacement porphyriesTransgressive porphyriesSummary of ore-porphyry relationshipsSource of the Copper and GoldProspecting Targets, Cobar-NymageeGeneral ApplicationBroken HillThe Bendigo FieldKalgoorlie-Coolgardie, Western AustraliaConclusions

Jan 1, 1950

By S. Kelebek, J. A. Finch, Zhenghe Xu, S. R. (Ram) Rao

To improve SO2 emission compliance, pyrrhotite from Sudbury copper-nickel ores is being depressed with DETA. To understand the mechanism of depression, the role of complexing in controlling metal-ion activation of pyrrhotite was investigated. DETA was found to remove Cu and Ni ions but leave hydrophilic ferric species on the pyrrhotite surface. The metal:DETA ratio appeared to be 1:2. Cu was more readily removed than Ni, but the combination of DETA with sulphur dioxide was equally effective for both metal ions. Certain combinations of DETA, Ni ions, xanthate and dithionite (S2O4) or dithionate (S2O6), as representative derivatives of SO2 in water, produced hydrophilic precipitates. These may enhance pyrrhotite depression

Jun 19, 1905

By P. H. Carr, G. G. Marino, K. A. Patel

Extensions to a correctional institution at Wabash Valley, Indiana, required development over abandoned coal-mine workings, at 90 m depth, where subsidence was possible at surface. Backfilling of the flooded mine in critical areas was determined to be the most cost-effective method of limiting the risk of damage to the buildings. Containment grout was first placed in selected entries and cross-cuts of each mine area; the remaining volume was then filled with a readily flowing infill grout. Where a high proportion of an area was taken up by rubble, calcium lignosulphonate was used as a retarder and plasticiser to increase penetration. Grout movement was monitored from adjacent boreholes with an electrical resistivity probe during grouting, while after the work was finished core samples were obtained from verification holes drilled in the backfilled areas

Jun 19, 1905

By Edward W. Parsons

The transverse force developed by expansion-shell rock-bolt anchors on the wall of a drill hole as the bolt is tensioned was measured by the Bureau of Mines using a device specially designed and fabricated for attachment to a universal testing machine. Load cells equipped with electrical-resistance strain gages provided the data from which the transverse force, in pounds, was calculated. Seven different expansion-shell anchors were tested, and the ratio of transverse force to bolt-tension load was found to range between 0.98 and 1.94 to 1.0. The drag load appeared to be the major cause of the transverse-force variation, but the relative effects of individual factors that affected the ratio between the transverse force and the bolt tension were not determined.

Jan 1, 1968

By M. M. Wong

Beryllium possesses attractive properties for use in the nuclear and space fields. Since fused-salt electrorefining can be employed to produce this metal in high-purity form from low-grade or scrap metals, the Bureau of Mines investigated electrorefining of beryllium in electrolytes composed of a LiC1-KC1 eutectic mixture plus varying amounts of BeC12. Results showed a 99- percent or better reduction of oxygen and magnesium and a substantial reduction of other minor metallic impurities. Extremely pure beryllium metal was produced. Operating variables, including BeCl2 concentration in the bath (3.5 to 16.5 mole-percent), temperature of operation (450° to 550° C.), and cathode current density (45 to 770 a,/sq, ft.), were studied; their effects on the deposition of metal, working condition of the bath, and purity of the refined metal are discussed. The safety precautions used in handling beryllium in the laboratory are also described.

Jan 1, 1962

By S. H. Lorain

Mechanized dirt-moving equipment has greatly increased the scope of prospect trenching by lowering the costs and increasing the speed of such work. Where the soil covering was more than 3 or 4 feet deep, operators were quickly discouraged and abandoned surface exploration in favor of shaft sinking, drifting, or diamond drilling; wildcat trenching was seldom undertaken, even where the soil covering was thin. Although power shovels, trench diggers, and draglines are useful under special conditions, caterpillar-mounted angledozers will usually do the same type of work and have a far wider range of adaptability. They are therefore incomparably the most generally useful equipment for the purpose. Since 199 the Bureau of Mines has been engaged in a widespread search for minerals useful to the war program; this work required a great deal of pioneer exploration in areas where known outcrops were marginal or subcommercial by pre-war standards. Engineers in charge of field operations were quick to perceive the applicability of mechanized trenching on a fairly large scale, particularly in the Northwestern States, where completely exposed vein-outcrops are rare. Probably no other organization to date has done a comparable amount of angledozer prospect trenching under such a wide range of conditions. The following comments and accompanying cost tables are based on work performed chiefly in Idaho, under a variety of physical and climatic conditions. The most important applications of the angledozer for such work may be described under three heads:

Jan 1, 1944

Properties of coal which are significant in relation to preparation for carbonization and conversion are reviewed, and existing coal preparation technology which has been used for production of cleaned coal of suitable ash content and petrographic composition for carbonisation, pyrolysis, hydrogenation and similar processes is described. Possibilities for application of this technology to some Australian coal seams is examined briefly. It is concluded that further survey work is required related to the optimization of selective crushing and concentrating operations, with the aim of maximizing production of quality products for carbonisation, etc mainly from Australian seams with only moderate coking characteristics.

Jan 1, 1980

By Gary J. Cwick

Mineral resources of the Rice Valley Wilderness Study Area (WSA), in the Mojave Desert of southeastern California, were investigated by the U.S. Bureau of Mines and U.S. Geological Survey during 1980. The study consisted of an examination of mines, prospects, and mineralized areas by the Bureau: of Mines and geological, geochemical, and geophysical investigations by the Geological Survey. Little indicated potential for the presence of mineral resources exists in the valley floor segment of the study area. The Big Maria Mountains section of the study area has some potential for mineral resource development. Decorative building stone from both bedded quartzite deposits and weathered limestone surface rubble (driftwood stone) has been produced from the Big Maria Mountains segment of the study area. Total production is unrecorded but probably small. A 700,000 ton (640,000 t) quartzite resource was inferred and 4,500 tons (4,100 t) of driftwood stone within the study area was estimated. A relatively pure limestone deposit inside the study area contains an inferred resource of 14 million tons (13 million t). One prospect suggests a potential for the presence of manganese resources although none were estimated. The likelihood of discovering oil, gas, coal, uranium or geothermal energy is low; potential sources are not known to exist.

Jan 1, 1982

By J. E. Hove

The high temperature physical properties of graphite are reviewed and interpreted in the light of present day knowledge of the mechanisms affecting these properties. The thermal and mechanical behaviors only are discussed and, whenever possible, comparisons are made with other refractory materials. Possible further studies are indicated, including some carbide work. AS long as the term high temperature implied only temperatures up to about 1000°C, the materials problems which arose could usually be handled by fairly conventional metal alloy types, such as the Co-Cr-Ni superalloys, for which there exists a great deal of technology. Perhaps this temperature can still be considered an upper limit for normal applications, but it is certainly true that the number of abnormal applications is increasing rapidly. The advent, in recent years, of ram-jet and rocket missiles and of high power nuclear reactor heat sources has raised a host of questions concerning the basic problem of what material to use in the temperature range up to 2000°C and higher. While there are, of course, many metals, in the second and third transition series, which melt at considerably higher temperatures than this, these metals are, at present, pretty well excluded from practical use by other considerations, such as re-crystallization, chemical activity, or excessive plastic deformation. The behavior of metals, from the standpoint of dislocation theory, is just beginning to be understood and thus there is some hope for the future development of very high temperature metals, but the immediate problems would most logically appear to have solutions involving the nonmetals, such as the refractory ceramics and graphite. For this reason, there is presently a great deal of engineering and experimental research being performed on the latter materials, much of this research being exploratory in the sense of gathering new property data. The situation, so far as graphite is concerned, is somewhat more fortunate than with the other refractory solids in the sense that a great deal is already known about its basic properties. This stems both from the fact that the carbon-carbon bond has been of interest to chemists for a long time (and graphite can be considered as a very large aromatic molecule, if desired) and the fact that its properties, both as a function of temperature and of radiation damage, are of critical importance to nuclear reactor designers. It is still true, of course, that such fundamental questions as why graphite remains solid to such a high temperature and why it has such a high thermal conductivity cannot entirely be answered at the present time. It is, nonetheless, meaningful and instructive to consider such problems in the light of existing knowledge. This is what the present paper will attempt to do. Before going on, it may be appropriate to classify graphite and justify its discussion before readers primarily interested in metals. Graphite is comparatively unique among materials in that there is always a property or group of properties which precludes calling it either a metal, a semiconductor, or a ceramic. It has the high electrical and thermal conductivities of a metal, but the artificial, poly-crystalline types show a negative thermal coefficient of electrical resistivity, generally characteristic of semiconductors. On the other hand, semiconductors, by definition, show an ever increasing resistivity as the temperature is lowered, whereas graphite approaches a finite, and, indeed, a rather low resistivity in the region of 10°K and, furthermore, a good single crystal of graphite has a positive temperature coefficient, as for a metal.' On still another hand, its porosity and brittleness at lower temperatures would put graphite in the ceramic class although, unlike most ceramics, it is readily machinable and has a high resistance to thermal shock. All things considered, it is probably more nearly appropriate to call graphite a metal than anything else. Although certainly outstanding in some ways, graphite has its peculiarities and, especially if the reader is unfamiliar with the data, it is probably valuable to review some representative property variations at high temperature. This review is meant to be mainly illustrative and no attempt has been made to be exhaustive. Review of High Temperature Properties At ordinary pressures, graphite does not melt, but sublimes directly into the gaseous phase at about 3700°C. Although the phase equilibrium diagram is still in some doubt, graphite will melt, at a slightly higher temperature, at pressures in excess of about 100 atm. The chief difficulty of using graphite in an oxidizing atmosphere is that the reaction rate becomes quite high at fairly low temperatures. If a threshold oxidation temperature2 is defined as the temperature at which graphite loses 1 pet of its weight in 24 hr, the value in air is 450°, the value in steam is 700°, and the value in carbon dioxide is 900°C. Efforts are presently being made to raise this threshold temperature either by impregnation with a retardant of some type (sodium tung-state and phosphoric acid, for example) or by a suitable metal or oxide coating. It is probably fair to say that, to date, these attempts have not shown any outstanding success in all respects. Most commercial graphites are fabricated by impregnating a carbon flour (say of coke or lampblack particles) with some type of hydrocarbon

Jan 1, 1959

By C. Feng, W. E. Krul

A study was made of the development of texture and the anisotropy in plastic flow of Ti-8Al-1Mo-1V alloy. Based on Pole figure determinations, the shifting of texture induced by rolling at approximately 400°C was found to be due primarily to slip rotation for the major Portion of the material. Grain boundary shear is believed to be an important factor. The anisotropy of the textured alloy was examined in terms of the variations of yield stress under tension and the ratio of bi -axial strain increments µp, in the temperature range 25" to 290°C. The results were related to Hill&apos;s theory on plastic anisotropy. The Schmid factors of (1100)[1120], (1101)[1120/, and (1101)[1120] slip systems were analyzed and found to be compatible with the observed anisotropy. Cross-slip between these planes was proposed as a possible deformation mode. In a number of published articles, considerable interest has been directed to the possible achievement of texture hardening in hcp metals. Following Backofen, Hosford, and Burke,&apos; this phenomenon was related to the yield criteria of the material and was expressed in terms of the biaxial strain ratio, r = d?w/d?l. The higher the value of r, the greater is the expected potential for texture hardening under certain loading conditions. For a given material, r varies with direction. Such variation can be traced to the anisotropy in plastic flow and can be explained within the framework of the various modes of deformation. Hatch2 found that a high r value coincides with a texture whereby the (0001) pole is closely aligned with the surface normal for sheet materials, Based on the analysis of the slip on the {1010}, {1011}, and (0001) planes, Lee and Backofen3 and Avery, Hosford, and Backofen4 concluded that the resistance to thinning is reduced by the operation of the (0001) <1120> slip system; with this reasoning they were able to explain the low r values (i.e., r « 1) observed in magnesium alloy sheets in the rolling direction and in commercially pure titanium in the transverse direction. The general equation, dealing with plastic flow in a polycrystalline aggregate has been used to correlate the plastic anisotropy and texture. In this expression, T and s are shear and normal stresses, and dri and d? are shear and normal strain increments, respectively. Assuming that five slip systems are operative within each grain and applying the principle of maximum work,5,6 one can determine the m value among the available systems. On this basis, Hosford7 and Chin, Nesbitt, and Williams&apos; were able to correlate m with yield stress under plane-strain compression, and Svensson9 was able to predict the variation of yield stress in textured aluminum. These workers made their analyses from materials in which slip operation is known to be associated with plastic flow. Questions remain regarding the derivation of Hill&apos;s theory on plastic anisotropy,10,11 since it was formulated on von Mises&apos; yield criterion.&apos;&apos; Its ability to deal with other forms of deformation has been in doubt.13 Others have discussed the validity of Hill&apos;s quadratic equation relating strain and yield stress.14&apos;15 For hcp titanium, deformation by various modes of slip and twinning operations has been reported.16-20 If all possible modes of deformation operate and contribute substantially to the plastic flow, it is difficult to imagine how the quadratic expression can suitably describe the anisotropic plastic flow of titanium alloys. Backofen and Hosford15 considered that Hill&apos;s is a macroscopic theory and implied that the major mode of deformation by slip mechanism will adequately describe anisotropy of the material. In the present investigation, slip operation will be shown to play the major role in the development of sheet texture induced by rolling of a commercial titanium alloy. Although twinning and other modes of deformation may also operate, their operation is believed to be secondary. The anisotropic properties of the sheet, which can be expressed in terms of directional variation of r, µp = -d?w/d?l and the yield stress will be shown to be governed primarily by slip operation. MATERIALS AND EXPERIMENTAL TECHNIQUES The titanium alloy chosen for the present investigation had a nominal composition of 8 wt pct Al, 1 wt pct Mo, 1 wt pct V, and 0.1 wt pct interstitial impurities. Sheets varying between 0.1 and 0.15 in. thickness were used. The alloy was received in a condition which was prepared by rolling at 900°C and annealing at 700°C. Subsequently, the sheets were subjected to further reduction in thickness by rolling at 400°C. A total reduction in thickness of 65 to 70 pct was obtained by a series of quick passes in a rolling mill with intermediate reheating. Further reduction in thickness was not possible due to cracking developed at the edges of the sheets. X-ray measurements were conducted in a Siemens and a Norelco unit to determine the texture of the sheets. Reflection techniques were used exclusively with CuK, radiation and a nickel filter. The loss of X-ray intensity due to geometric defocusing was calibrated with a technique described previously." The (0001), (1010), and (1071) pole figures were plotted from 0 to 80 deg, and to present the texture elements quantitatively, inverse pole figures were constructed following the technique described by Jetter, McHargue, and Williams.22 Tensile experiments were carried out at 25", 175",

Jan 1, 1970

By W. M. Yim

Experimental results are presented which indicate that transverse striations in horizontal zone-leveled Bi-Sb alloy crystals are due to irregular growth rate resulting from thermal fluctuations in the melt (Iring gowth. Thc thermal fluctutations arose from two different sources. The first type was brought about by periodic fluctuations in the furnace temperature. The second type can be attributed to turbulent therrrol conlcclion in the trzelt near the solid-liquid inteyace. Tile arrzplitlcde ond fvequency of the tetiperaticre fluctlrations vesultity from llle lhevnal con1,ecrrell. The striation spacings in Lhe crystals covvelale well with the periodicity 0.f the tempevature flueluatiors. Altliough the strialiors represenl corrlpositiozul inhoiHogeneity oh a rzicroscule, less than f.z cil. be1 S6 in Best&apos;s as deterrirzed by electron-pro be chalq&apos;sis, the slriations roerre fbund to ILUL&apos; no rrleusuanble effect on electical vesistirity rwr on weak field macgnetoresistance of. the Bi-Sb a1lu.y in the ternpevutue ),unge 4.Polo 300°K. DURING the course of an investigation on the horizontal growth of semimetals,&apos; it was found that crystals of Bi-Sb alloys contained many closely spaced parallel arrays of striations. These striations occurred perpendicular to the growth direction and parallel to the solid-liquid interface. We shall refer to them as transverse striations, or just striations&apos;&apos;, to distinguish them from lineage substructures or longitudinal striations which form parallel to the growth direction and have been known to be associated with cellular structures.&apos; Similar transverse striations have been reported previously to occur in other materials prepared by horizontal growth: metals,4 semiconductors,5 as well as their alls. - Various methods of crystal preparation have apparently little effect on the occurrence of the transverse striations. They form whether the crystals were grown by the vertical Czochralski technique, withe1&apos; or without&apos;3- rotation, or by the horizontal zoning methd.- Thus, the transverse striations are not limited to any one class of materials, nor to any particular method of preparation. It is likely, therefore, that all of the observed transverse striations may have some common cause. Previously, workers agreed that periodic changes in the growth rate bring about the striations. However, no agreement exists as to the origin of the growth-rate fluctuations. Some attributed the discontinuous growth to a purely external cause, such as fluctuations in the furnace temperature, jerky motions in the crystal pulling mechanism, or a nonsymmetrical temperature distribution in the melt (in the case of crystals grown by the Czochralski technique with rtation). Others looked for the cause in some fundamental property of the growth process itself. For instance, a certain degree of supercooling is required to initiate growth from the melt. But, with further growth, the degree of supercooling decreases because of the liberation of the heat of solidification at the solid-liquid interface. Thus, crystal growth would be brought to a halt until sufficient supercooling is resotred and the cycle begins again.3&apos;11 According to this model, periodic fluctuations in the melt temperature should exist at the solid-liquid interface. Since the periodic fluctuations in growth rate would result in changes in the segregation coefficient of solute atoms, crystals containing the transverse striations may, in some cases, show a periodic impurity fluctuation along the length, resulting in a degradation of electrical properties. The resistivity striations in doped germanium&apos;9-10 or lnsbB are well-known examples of this microsegregation. The present work was undertaken to explain the exact origin of the transverse striations, and to assess the extent of their effect on chemical homogeneity as well as on electrical properties of Bi-Sb alloy crystals. Results from our previous study of the crystal growth of Bi-Sb alloys1 indicated that the transverse striations may arise from the temperature fluctuations in the melt during growth. This paper will show that the melt temperature fluctuations are indeed responsible for the occurrence of the transverse striations. I) EXPERIMENTAL Although the transverse striations have been observed in all slow-grown Bi-Sb alloys across the entire compositional range, we selected a composition, Big3Sbs, for the present study in view of the extensive data available on the crystal growth of this alloy from a previous study.&apos; High-purity bismuth and antimony, both a 6-nine grade by the manufacturer&apos;s emission spectrographic analysis, were used throughout. Independent mass-spectrographic analysis showed, however, that the starting materials were more nearly a 5-nine grade. each containing metallic impurities of approximately 10 ppm atomic. In zone-leveled Big5Sb5 alloys, the total metallic-impurity content was slightly lower, about 7 ppm atomic, indicating that some degree of purification was achieved during the growth. None of the electrically active impurities, such as tin and lead (acceptors) and tellurium and selenium (donors), were present in significant quantity in undoped Bi95Sb5. Typical analysis of the undoped Bi95Sb5 alloy is shown in Table I. Nonmetallic impurities, such as carbon and oxygen, were detected, sometimes as much as 100 ppm, in both the starting materials and the zone-leveled alloys: but the data were only qualitative. Temperature fluctuations in the melt were monitored over 1 or more days by means of a 5-mil chromel-

Jan 1, 1967

By David J. Mack, Dennis R. O’Boyle

The mechanical properties of three polycrystalline intermediale Phases that have the y bvass structure were measured in compression between 400° and 900°K. At the lower testing temperatures— termed Region I— no plaslic deformalion occurred prior to brittle fracture. A1 higher temperatuves— lermed Region III—the three phases deformted plaslically for all strain rules from 1.5 to 36.0 x 10-4 sec-1. The homologous temperature for the inilialion of plaslic flow increased in the same order as tile atomic size difference between atoms in each plmse (0.50Tmp for y AgZn, 0.62Tmp for y CuZn, and 0.76 Tmp for y CuCd). The increased flow resistance oj. y CuCd above 0.50Tmp is explaitzed in terms of the more random arrangement of copper and cadmiwn atoms on the laltice sites of&apos; the y bvass slrilctlire. Plaslic deformation of the three intevmiediate phases in the smooth plaslic flow region appears to be controlled by oacancy-induced dislocation climb. RESULTS are reported in this paper on the mechanical properties of three binary intermediate phases having the complex cubic y brass structure (D82, 143m) containing fifty-two atoms in the unit cell. The structure of the prototype y brass phase, y CuZn, was first analyzed by Bradley and Thewlis&apos; based on the X-ray work of Westgren and Phragmen.2 The y brass structure can be visualized as an arrangement of twenty-seven body centered cubes (3 by 3 by 3) into a unit cell containing fifty-four atoms. From this cell the center atom and the four corner atoms are removed and the remaining fifty-two atoms are slightly displaced, resulting in the y brass structure. Approximately thirty-five binary intermediate phases that have an electron to atom ratio of 21:13 have been reported to form the y brass structure. The three y brass intermediate phases selected for this study are formed from elements in groups IB and IIB of the first and second long period. Each compound exists over a composition range that includes the stoi-chiometric composition A5BB (Cu5Zn8, Ag5Zn8, Cu5Cd8). y CuZn (a0 = 9.944A) has solubility limits extending from 57 to 67 at. pct Zn at 500°C apd melts peritecti-cally at 834°C; y AgZn (a0 = 9.326A) has a solubility range from 58 to 63 at. pct Za and melts peritectically at 661°C. y CuCd (a, = 9.596A) melts congruently at 563°C and has a maximum range of solubility extending from 58 to 64 at. pct Cd. In order to minimize coring and microporosity during solidification, the composi- tion of the compounds that form peritectically (y CuZn and y AgZn) was chosen so that the temperature difference between the liquidus and the solidus is only a few degrees centigrade. In selecting y brass compounds for this study, phases were avoided that contained a transition element or that had an electron to atom ratio greater than 1.70. Hume-Rothery et a1.3 has observed that, when the electron to atom ratio of y brass intermediate phases exceeds 1.70, atoms begin to drop out of the unit cell to maintain a constant electron to unit cell ratio. EXPERIMENTAL PROCEDURE Each of the three intermediate phases was prepared from elements having a purity >99.999 pct. Only trace quantities of impurities (<0.0001 pct) were detected by spectrographic analysis of the four elements. A master alloy of each compound weighing approximately 130 g was prepared by melting the elements in evacuated sealed quartz tubes heated in an electric furnace. Specimens having the desired diameter for the mechanical property measurements were obtained by remelting the master alloy in a Vycor tube under argon and drawing specimens from the melt into 4-mm-diam quartz tubes. To obtain a smooth surface on specimens drawn from the melt, the inside of the quartz tube was coated with a thin layer of graphite formed by thermally decompositing acetone. All specimens were imbedded in sealing wax and cut to the proper length with a diamond-impregnated cut-off wheel. The individual specimens (4 mm diam by 8 mm long) were then sealed in evacuated Pyrex tubes and homogenized at 500°C for 72 hr. Chemical composition, variations over the length of the rod (10 cm long) were generally less than 0.2 pct and the analyzed composition differed from the desired composition by less than 0.5 pct.4 Metallographic evaluation of the specimens after homogenization showed no evidence of a second phase in any of the compounds. The average grain size of the specimens after homogenization was 1 to 2 mm. All mechanical property measurements were carried out in an argon atmosphere using a compression apparatus described previously.5 Prior to applying the load to the specimen, the test apparatus was evacuated, back-filled with argon, and heated to the test temperature for 20 min to establish thermal equilibrium. EXPERIMENTAL RESULTS Mechanical properties measured as a function of temperature and strain rate for each of the three y brass phases were similar. From room temperature to the ductile-to-brittle transition temperature, only elastic deformation was observed prior to fracture.

Jan 1, 1968

By John W. Burd

A system is described for the simultaneous deposition of epitaxial layers on as many as eight substrates. A high degree of uniformity of both physical and electrical characteristics is achieved in the films. Variation of film thicknesses is consistently less than ±10pct within a wafer and from wafer to wafer within a run with the variation typically on the order of 55 pct. Composition variation of GaAs1-x PX layers within a wafer and from wafer to wafer within a run is consistently less than 51 pct. Electrical evaluation of the films by several techniques indicates excellent doping uniformity within a wafer and from wafer to wafer within a run. Mobilities for lightly doped GaAs films at 300°K are consistently >6000 cm2 v-1 sec-1 and mobilities > 7000 cm2 v- 1 sec-1 are regularly attainable. Techniques for the preparation of material with carrier concentrations from 1 x 1015cm-3 to 1 x 1019 cm-3 n-type and 5 x 1016 to 5 x 1018 cm-3 p-type are discussed. METHODS for the preparation of 111-V compounds by vapor phase reactions have been extensively reported in the literature.1-6 Almost all of the apparatus described for these various methods are suitable for processing one or at the most a very limited number of wafers simultaneously. With the recent rapid advances in the use of vapor grown GaAs for microwave oscillators and GaAs1-xPx as visible light emitters the requirements for these materials are steadily increasing. In order to satisfy these requirements it is necessary to move from a laboratory scale apparatus to one which is capable of processing a large number of wafers simultaneously. Desirable features would be a high degree of uniformity among the wafers and good reproducibility from run to run. The apparatus to be described fulfills these requirements very well. DISCUSSION The various methods reported in the literature can be classified under three headings: 1) closed tube, 2) open tube, and 3) the close-spaced method. Of these three the open-tube method is the most amenable for scale-up to a manufacturing process. It is the most versatile and the various operating conditions can be more precisely controlled than with the other two methods. A number of chemical reactions may be used to achieve vapor-phase growth of 111-V compounds. Sev-era1 of the more generally used reactions are shown in Fig. 1. All of these reactions have the following points in common: 1) generation of a volatile group III(Ga) species by the reaction of the transport agent (halide or HC1) with either Ga or GaAs, 2) introduction of the Group V(As and/or PI component, 3) a method of adding dopant, if desired, and 4) a region in which deposition from the vapor will occur and form as a single crystal epitaxial film on the substrates. The laboratory scale reactors permit the hot re-actant gases to flow into the relatively cooler deposition zone and pass successively over the several substrates which are arrayed along the long axis of the tube parallel to the gas flow. With this arrangement the composition of the reactant stream is continually changing as solid material is deposited on each successive substrate. As a result of this changing gas composition the reaction driving force also changes from substrate to substrate and the degree of uniformity of layer thickness, doping level, and so forth, is poor. This effect can be partially overcome by imposing a controlled temperature gradient along the deposition region to compensate for change in gas composition. However, even when this is done variations in layer thickness on the order of 30 to 40 pct are common and as high as 50 pct are frequently experienced between adjacent wafers in the tube. To expand this arrangement to a large number of wafers would only increase the nonuniformity from the first to last wafer in the line. From the above discussion the two undesirable features of changing gas composition and temperature gradient become evident. A reactor system which eliminates or minimizes these undesirable features is one in which the apparatus is mounted vertically as shown schematically in Fig. 2. The vertical mounting permits the disposition of a number of substrates on a suitable support so that all wafers are at the same vertical height in the furnace and hence at essentially the same temperature. By using only a single row of wafers the reactant gas mixture passes over only one substrate in its path through the reactor. Thus the two undesirable features of changing gas composition and temperature gradient are minimized. An additional design feature which further minimizes temperature variations is rotation of the substrate holder. Rotation serves to integrate any radial temperature gradient existing around the resistance heated furnace. A photograph of a reactor assembly at the completion of a run is shown in Fig. 3. MATERIAL PREPARATION Apparatus. Although any of the several chemical systems shown in Fig. 1 are adaptable for use in this apparatus the one generally used is System 2, the hydride synthesis system. This system has been de-

Jan 1, 1970

By E. T. Turkdogan, M. T. Hepworth, R. P. Smith

The permeability of oxygen in 0 iron in the tempera-ture range 700" to 900 C and in 6 iron at 1450°C was determined by the rate of internal oxidation of iron, containing -0.1 pct Al. The solubility of oxygen in zone-refined iron was determined by equilibration with hydrogen-water vapor gas mixtures at 1450" and 1510°C; oxygen solubilities , for iron in equi1ibriu.rn with molten oxide, are found to be 66 and 83 ppm for these two temperatures, respectively. The diffusivity of oxygen in iron at 14500C3 as calculated from the permeability and solubility data, is (4.1 * 0.6) x 10 "B sq cm per sec. OXYGEN is one of the most common impurities present in iron or steel, mainly in the form of oxide inclusions. In the study of many metallurgical problems concerning solid iron, it is often desirable to know with a reasonable accuracy the solubility and diffusivity of oxygen over a wide temperature range. The solubility of oxygen in solid iron has been the subject of numerous studies yielding highly discordant results as seen for example from the literature surveys made by Meijering &apos; and Schenck et a1.&apos; As shown by Kitchener et aL3 and by Sifferlen, the high oxygen solubilities reported by many investigators are the result of oxidizable impurities which are often present in iron. In addition, there have been experimental problems associated with icaccuracy of oxygen analysis of iron containing less than 100 ppm 0. A number of studies have been made on the permeability of oxygen in a and y iron using Fe-Si, Fe-Mn, and Fe-A1 alloys in the internal-oxidation experiments.1&apos;2&apos;5&apos;6 However, no direct measurements have been made of the diffusivity of oxygen in iron. In the present work two sets of experimental measurements were made: permeability and solubility studies at 1450" and 1510°C and permeability studies only in the range 700 to 900°C. In both sets of permeability measurements slab-shaped specimens containing small predetermined amounts of aluminum in solution were exposed at constant temperature to gas mixtures of hydrogen, water vapor, and argon for varying times. These specimens were quenched, sectioned, and examined for oxygen penetration by metallographic observation of aluminum oxide particles which formed. From these data, it is possible to calculate the ratio of the diffusivity of oxygen in iron, D, to the equilibrium constant K for the reaction Hz(g) * O (dissolved in iron) = H,O(g). EXPERIMENTAL Permeability Measurements at 1450°C. An ingot of vacuum-carbon deoxidized iron containing 0.086 pct A1 was prepared, using commercial "Type lO4A Plas-tiron"; after hot rolling, specimens were machined into slabs a by 2 by 2 in. The impurity contents were: S, P < 0.002 pct; C, Mn < 0.01 pct; each of all other Usual impurities < 0.004 pet. The amount of oxide inclusions in this material, determined by a bromine-methyl acetate extraction, corresponded to about 20 ppm 0 in the iron which agreed well with the results of vacuum-fusion analysis. Each specimen was annealed at 1450°C for 1 hr in purified hydrogen, polished to a smooth surface, and then introduced into a controlled oxidizing atmosphere in a recrystallized alumina tube at 1450°C. The constant temperature zone (*3"C) was about 3 in. in length. The gas composition was controlled by mixing argon with hydrogen (using calibrated constant-head flow meters) and passing the mixture through a column of a mixture of oxalic acid dihydrate and 10 pct anhydrous oxalic acid, to establish a required water-vapor content in the gas mixture. The temperature of the oxalic acid dihydrate column was controlled by a thermostat. The total gas flow was in the range 800 to 1000 cu cm per min. The exit gas from the reaction tube was passed through a weighing bottle containing a desiccant, to cross-check the degree of water-vapor saturation, which for all experiments was about 97 pct of those derived from the data of Baxter and Lansing.1 For a typical experiment, a specimen was introduced into the furnace in a stream of dry argon and hydrogen. The specimen was then rapidly raised by a Pt-Rh alloy wire into the hot zone and allowed to reach the reaction temperature, at which time the oxidizing gas mixture was introduced. The oxygen potentials employed were sufficient to oxidize aluminum but not to cause liquid iron oxide to form. After a specified time, the experiment was ended by dropping the specimen onto a water-cooled copper block at the bottom of the reaction tube. The depth of the internally oxidized zone, hereafter called the "case", was determined by sectioning the specimen at right angles to the long direction. The section was then examined under a microscope equipped with a micrometer stage. In general, the oxide particles were fairly uniform in size and distribution, forming a reasonably well-defined interface between the oxidized and unoxidized region. A typical cross section as observed at X30 is shown in Fig. 1. A thermal macroetch was used in one selected specimen to delineate the case. A cross section of a previously oxidized slab was polished and reheated at 1450°C in a hydrogen atmosphere for about 10 min. Upon quenching, the surface relief shown in Fig. 2 was produced; causes of this effect are unknown. Permeability Measurements Below 900°C. A slightly

Jan 1, 1967

By Jessica Elzea, Haydn Murray

The term bentonite was first proposed in 1898 by Knight, a year after he had named this clay taylorite, because taylorite had been previously used for another mineral. The name taylorite was after the Taylor ranch, the site of the first mine, near Rock River, WY, and the name bentonite is from the Benton Shale in which the clay was thought at that time to occur. The Benton Shale was, in turn, named after Fort Benton, MT, located more than 640 km miles north of Rock River. Early in the 20th century, several geologists recognized that bentonite, mainly in beds in Cretaceous and Tertiary rocks, originated from transported volcanic materials. This recognition led to definitions based on origin, the one most widely quoted and generally accepted by geologists is the following definition by Ross and Shannon (1926): "Bentonite is a rock composed essentially of a crystalline clay-like mineral formed by devitrification and the accompanying chemical alteration of a glassy igneous material, usually a tuff or volcanic ash; and it often contains variable proportions of accessory crystal grains that were originally phenocrysts in the volcanic glass. These are feldspar (commonly orthoclase and oligoclase), biotite, quartz, pyroxenes, zircon, and various other minerals typical of volcanic rocks. The characteristic clay-like mineral has a micaceous habit and facile cleavage, high birefringence and a texture inherited from volcanic tuff or ash, and it is usually the mineral montmorillonite, but less often beidellite." The difficulty in applying the foregoing definition to bentonite as an industrial mineral commodity is that it is based on origin and is restricted to an ash, tuff, or volcanic glass parent material. Therefore, deposits consisting of the clay minerals required by this definition, but having uncertain origin or parent materials, cannot properly be called bentonite. Furthermore, many deposits in the western United States and in other countries that have formed from rocks other than the types required by the definition are being mined and sold as bentonite. Perhaps the best definition of bentonite as an industrial mineral is one given by R.E. Grim in a plenary lecture at the International Clay Conference (AIPEA) at Madrid, Spain, June 27, 1972. According to this redefinition, which will be used in this chapter, bentonite is a clay consisting essentially of smectite minerals (montmorillonite group of some usages), regardless of origin or occurrence. This definition solves the problem of the difference between the geologic and industrial usages of the term and overcomes the difficulty in assigning a name to smectite clay that formed from igneous rock other than ash, tuff, or glass, or those of sedimentary or uncertain origin. However, bentonite, when used with this meaning is still a rock term (consisting of more than one mineral), and it will not be possible to distinguish it from fuller&apos;s earth in many instances. One way of classifying bentonite is based on its swelling capacities when wet or added to water. Bentonite having sodium (Na+) as either the dominant or as an abundant exchangeable ion typically has very high swelling capacities and forms gel-like masses when added to water. Bentonite in which exchangeable calcium (Ca++) is more abundant than other ions has much lower swelling capacities than sodium varieties. Some calcium types swell little more than common clay, and most crumble into granular masses in water. Intermediate calcium-sodium bentonites, the so called mixed types, tend to swell moderately and to form gels of lesser volumes than equal masses of the sodium type bentonite. Because of the general relationship of swelling and exchangeable ion characteristics bentonite is commonly divided into the high swelling or sodium, low swelling or calcium, and moderate swelling or intermediate types. The term sub-bentonite (Davis et a]., 1940) is used inconsistently in industry for the low or moderate swelling varieties. The authors believe the use of this term should be discouraged because of its implication of low quality or low value and the lack of a mineralogical or use basis for it. In the United States bentonite is also classified by geographic location and the uses for which it is sold. Inasmuch as most of the low swelling calcium type occurs in states bordering the Gulf of Mexico, this variety is commonly called Southern bentonite. The largest high swelling sodium bentonite deposits and the major producing districts are in Wyoming and adjacent states. Therefore, this bentonite is commonly called the Wyoming or Western type. Such terms as drilling mud bentonite, foundry bond bentonite, and taconite bond bentonite relating directly to use are applied in marketing. Other terms including high and low yield bentonite, high and low gel bentonite, and high and low strength bentonite are also used to distinguish different grades. The varied classifications notwithstanding, bentonite occurs in so many different varieties that some cannot logically be classified according to any of the foregoing groupings. One of these types is hectorite, which is a high swelling lithium-bearing variety of smectite occurring mainly in California and adjacent states. It is, therefore, not a Wyoming type, and it occurs even farther west than the so called western bentonites. Others are bentonites having magnesium (Mg++) or hydrogen (H+) as the most abundant or dominant exchangeable ion. These types are neither sodium nor calcium varieties, and apparently some are low swelling, whereas others have rather high swelling capacities. Still another type of bentonite, the so-called potassium type, K-bentonite, or metabentonite, occurs in Ordovician and other Pa-

Jan 1, 1994