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By J. A. Fellows, Earnshaw Cook, Howard S. Avery

Heat-resistant alloys of the higher nickel and chromium ranges have been empirically developed through the practical experience of the past two decades to a position of significant industrial importance. Few quantitative metallurgical data have been published, however, that could be related directly to engineering specifications and design. Inadequate information led to the inauguration, in 1934, of a research directed toward a better understanding of the properties and performance of these steels at temperatures between 1400° and 2000°F. Investigation was concentrated upon the 26 per cent Cr:I2 per cent Ni type, which owes its extensive application to an excellent combination of economy, strength and surface stability at elevated temperatures. The requirements of the oil-refining industry have been prominent in influencing the scope and evolution of the program. Creep strength at the maximum allowable deformation ranges has been employed to evaluate the merits of these alloys. Permissible elongation rates vary from 1.0 per cent in one million hours for turbine blades to I .o per cent in ten thousand hours for tube supports and heating-furnace equipment. Throughout this paper, the limiting creep stress (L.C.S.) for a given temperature has been defined as the stress that will produce a uniform elongation rate (stage 11) of one per cent in ten thousand hours as extrapolated from rates per hour for tests of less than two thousand hours duration. Certain current specifications require a minimum L.C.S. of 1600 lb. per sq. in. at I800°F., of 3600 lb. per sq. in. at 1400°F., and include a tensile acceptance test at room temperature, after aging for 24 hr. at 1400°F., as a measure of embrittlement in service. An elongation of 4 per cent is considered satisfactory for general use, while a minimum of 9 per cent is prescribed on occasion. Many differences of opinion concerning the properties and performance of these alloys appear to result from their sensitivity to unappreciated variations of chemical analyses which, for example, may change their L.C.S. from 3500 to 350 lb. per sq. in. at 1800°F. Within broad chemical limits, it is possible to balance the six or more important elements present to attain desirable properties with a number of different combinations. One method for adjusting the composition has been described under the sponsorship of the Alloy Casting Institute,' in which, by maintaining a substantially austenitic* alloy, optimum creep strength and minimum tendency to embrittle after aging are expected. Unless, however, the limits are undesirably close, it has not been possible to ensure a moderate range of strength and of ductility by any chemical specification alone. There is a definite need

Jan 1, 1942

By G. Coetzer

"Prior to operating a non-recovery coke pilot plant oven, it was essential to ascertain coal cake stability during the loading of a 1 m3 (1 m × 1 m × 1 m) coal cake into the cold pilot-plant oven by a pusher mechanism. Previously established laboratory-scale compaction parameters, to obtain coal cakes with sufficient stability, were employed during the loading tests of the coal cakes. Two different coals were evaluated, namely Waterberg semi-soft coking coal (sscc) and Oaky North hard coking coal.It was demonstrated that lower applied compaction forces (14%) can be utilized during 1 m3 compaction, in comparison to laboratory-scale tests, to obtain similar wet cake densities, owing to differences in the effect of frictional forces. Wet cake densities for Waterberg sscc improved slightly (3%) to 1.13 t/m3 when utilizing 79 t/m2 applied force for a 1 m3 coal cake, in comparison to laboratory-scale tests. Similar results were obtained for Oaky North hard coking coal, with a 6% density increase to 1.27 t/m3 at a similar applied force. Porosities decreased by 13% and 32% for Waterberg sscc and Oaky North coal, respectively, when 1 m3 compaction was compared to laboratory-scale tests. An opportunity exists to further decrease the porosities of Waterberg sscc during compaction, whereas acceptable compaction parameters were achieved for Oaky North hard coking coal. Most major vertical cracks and the partial collapse of coal cakes were mitigated, and high-stability coal cakes were obtained that could be successfully loaded into the pilot-plant coke oven by a pusher mechanism.Factors contributing to the instability of the coal cake during loading into the oven, such as vertical cracks, are (i) the cubic geometry (1 m3) of the coal cake, (ii) friction exerted by the oven floor, and (iii) mechanical problems, such as a misalignment between the pusher machine feeder plate and the oven floor. IntroductionOperation of the stamp-charging horizontal 1 t electrically heated coke pilot-plant oven at Exxaro Resources requires coal cake stability during the loading of a 1 m3 compacted coal cake into the oven. In this case, a pusher plate is utilized to push the coal cake into the oven over the oven floor. This is in contrast to a ‘spoon’ or bottom plate feeding mechanism as found in industrial horizontal coke ovens. The pusher plate loading mechanism dictates that the coal cake should possess high stability and inherent strength owing to frictional forces exerted by the oven floor. In order to obtain a coal cake of acceptable stability for the 1 t coke oven, various compaction parameters need to be verified and established."

Apr 1, 2019

By Arne Landsberg

The Bureau of Mines has undertaken research to elucidate the chemistry involved in the efficient recovery and control of minor elements in base metal smelting operations. These elements should be effectively recovered not only because they have commercial value, but also because of their potential hazard to workers' health and the environment, if they are not controlled during processing. Cadmium, a minor metal in zinc ores, is the subject of this report. The roasting step of the complex zinc-smelting process was chosen for investigation because of the high potential for removing cadmium by volatilization during this primary stage. Commercial roaster feed materials were used to determine the sequence of reactions and the effect of these reactions on the volatilization of cadmium. Electron microprobe examination of both the commercial roaster product and oxidized sulfide solid solutions prepared in the laboratory showed that oxidized iron was of prime importance in preventing cadmium volatilization. The mechanism by which iron prevents cadmium volatilization is proposed, and a preheating technique is recommended for more effectively recovering cadmium prior to roasting.

Jan 1, 1981

By Jingzhong Kuang, Zheyu Huang, Chuanzhou Guo, Pengfei Liu

"In this paper, scheelite and scheelite coated with Pb2+ (SC) were synthesized by chemical precipitation with the help of ultrasonic. The role of the Pb2+ on scheelite was evaluated. Additionally, the dissolution behavior of minerals and the adsorption mechanism of collectors were investigated systematically via SEM, XRD, EDS. The results indicate that the ultrasonic cavitation can promote the formation of scheelite with large particle size and high crystallinity. Due to the exchange of WO4 2- and OH-, the dissolution of scheelite are not in a 1:1 equivalent amount by chemical formula and the concentration of WO4 2- is higher than that of Ca2+ in the solution because Pb2+ promotes the transfer of WO4 2- from scheelite surface into the solution. The dissolution of scheelite is an endothermic reaction and its enthalpy reaches the maximum value of 692.59J·mol-1 at pH=8~10. But the coating of Pb2+ changes the thermal effect of scheelite in the solution and the dissolution of SC is an exothermic reaction with the dissolution enthalpy of -262.30 J·mol-1. At pH=8~10, the adsorption capacity of sodium oleate and salicylhydroxamic acid on the surface of SC is higher than that of scheelite which delivers that Pb2+ contributes to the scheelite surface dissolution and enhances the adsorption of collectors on the mineral surface, thus achieving activation.INTRODUCTIONIn modern society, tungsten is a type of quite important rare metal and also a strategic resource. Because of its low vapor pressure, high melting point, good electrical and thermal conductivity properties, it is widely applied in high-temperature technology, lighting, machine and engine construction (Zhao,Z.W, 2013; Yan, W, 2017; Ilhan, S, 2013). Both scheelite and wolframite are the major tungsten deposits. With the depletion of easily-processed wolframite, scheelite has drawn a great deal of scientific and industrial attention. Scheelite can be recovered by flotation due to the metathesis of polarity and chargeability on minerals surface via adding regulators and collectors."

Jan 1, 2018

By Thomas E. Garnar

Zirconium and hafnium are curious elements because they are almost always found together in nature. Zirconium was discovered by Klaproth in 1789 and isolated 35 years later by Berzelius. Because hafnium's chemical properties are so close to those of zirconium, it was not discovered until 1923 when Coster and Von-Heresey detected it using x-ray spectrographic analysis. These elements occur most commonly in nature as the mineral zircon (ZrSiO4) and less commonly as the oxide baddeleyite (ZrO2). They also are found as a variety of other silicates. Zircon was identified as a component in alluvial and beach sands in 1895, but it was not produced in any quantity until 20 years later. Zircon is always a coproduct from TiO2 mining and processing. During World War I it was produced as a coproduct of beach sand mining for titanium minerals just south of Jacksonville Beach, FL, and was patented as a refractory. It was not until the 1930s when Zircon Rutile, Ltd. began mining at Byron Bay on the east coast of Australia that zircon was first used as a foundry sand. Later in the 1940s, NL Industries, Humphreys Gold Corp., and E. I. du Pont de Nemours & Co., Inc. began production of zircon sands from fossil beaches in northeast and northcentral Florida. Baddeleyite first became available as a commercial product in 1916, but never in the quantity of zircon. Zircon holds a unique position as an industrial mineral because it is used for both its physical and chemical properties as well as an ore of zirconium and hafnium metals. Australia is the major zircon producer followed by South Africa and the US. Zircon is also produced in India, Sierra Leone, Sri Lanka, Malaysia, China, Thailand, and Brazil. Undeveloped heavy mineral beach sand reserves containing zircon are known to occur in Egypt, Malawi, Senegal, and Tanzania. Locations are shown in Fig. 1. Mineralogy Zirconium and hafnium are always present together in naturally occurring compounds. Most commonly they form as the silicate sometimes containing iron, calcium, sodium, manganese, and other elements. Less commonly they are found as oxides in combination with titanium, thorium, calcium, and iron. Zircon is the most common form. It is extremely resistant to weathering, therefore, often it is present in ancient beach sands and placer deposits. Although resistant to alteration from external sources, it is vulnerable to internal alteration as the result of thorium and uranium substituting for zirconium either in the zircon lattice or in solid solution. Alteration to the metamict state takes place as radioactive emanations from these elements disorder the crystal lattice, accompanied by hydration, reduction in specific gravity, and changes in color. The mineralogy of zircon and baddeleyite and variation of physical and chemical properties are shown in Table 1. The effects of zircon's internal alteration and darkened color can be corrected by heating to 1000°C for 30 min or so. A certain time-temperature relationship makes it possible for decolorization and reordering of the crystal lattice to take place when heating at higher temperatures for shorter periods or at lower temperatures for longer periods. After heating, x-ray diffraction patterns are sharper, the grains may be harder, and except for particles of malacon, the grains will be white or colorless in the absence of grain surface coatings. The color change is only temporary and the particles slowly darken with time. Zircon fluoresces light yellow in shortwave ultraviolet light. If exposed to ultraviolet light for extended periods of time, white (calcined) zircon turns purple. With time the induced color begins to fade and eventually disappears (e.g., calcined Florida zircon exposed to ultraviolet light for 24 hr still retains faint, but discernible, purple color after six months).

Jan 1, 1983

By Richard T. Newcomb

Federal and utility industry research has largely ignored coal beneficiation techniques in the implementation of SOx control. This paper accepts the hypothesis that beneficiation cum scrubbing is the cheapest way for the vast majority of seams in the eastern coal provinces to comply with standards. Comparisons are based on point estimates of average beneficiation costs from a model of coal preparation (COBET) designed to simulate four levels of cleaning. The paper describes how economic theory can be applied to derive econometric supply functions from actual data on the geology of minable seams, washability and technical constraints. West Virginia is taken as an example of a producing region. Spatial supply functions are derived empirically from the engineering model simulations.

Jan 1, 1977

By F. Brost

In 1976, a decision was made to install a conveying system to transport ore 10.3 km (6.4 miles) from the new Eisenhower Partnership Mine to Twin Buttes. The system, supplied and installed by Cable Belt Limited, of England, represents a radical departure from conventional conveyor systems. The driving tension is applied through two endless wire ropes while the belt acts only as the carrying medium. Features of the system are a single 2240 kw (3000 hp) drive and a 60° angle bend. Construction was completed in two years. Full production was attained after several months' operation.

Jan 1, 1979

By Lori A. Simpson, Linda H. Liang

A high-rise building, consisting of two tower structures occupying the entire site, is in construction in San Francisco. The North Tower will consist of 12 and 35 stories above a one-level basement. The South Tower will consist of 9 and 22 stories over one partially below-grade level of common space; a portion of the South Tower will have a three-level basement. The towers will be supported on mat foundations bearing on native very dense sand in the footprint of the threelevel basement and on ground improved with soil-cement mixed (SCM) panels that extend through loose sand and marsh deposits into very dense sand. Shoring systems for the basement excavations include cantilevered and tiedback soldier-beam-and-lagging systems and SCM cutoff walls. Subsurface conditions include loose fill and Dune Sand and loose and soft marsh deposits overlying very dense sand of the Colma formation. Groundwater is approximately 15 to 22 feet deep; the three-level basement extends below groundwater. The site is on Market Street in San Francisco, with SF Municipal Railway (MUNI) and Bay Area Rapid Transit (BART) tunnels running below Market Street approximately 45 and 36 feet north of the site, respectively. Both tunnels are 16.5 feet in diameter. The top of MUNI and BART tunnels are 25 feet and 63.5 feet below street grade, respectively. BART has stringent requirements regarding construction adjacent to their facilities, including disallowing adding pressure to their tunnel, lowering groundwater by more than two feet, and vibrations from construction activities. Design of the shoring and the foundations within the BART zone of influence were subject to their design requirements. The project was also subject to a peer review, as required by the San Francisco Department of Building Inspection. We used FLAC to evaluate stresses at the BART and MUNI tunnels and on the SCM panels. This paper will present the mitigations needed to address seismic hazards and BART restrictions and to provide adequate foundation support for a tall building with high seismic loads.

Jan 1, 2017

By Lori A. Simpson

A high-rise building, consisting of two tower structures occupying the entire site, is in construction in San Francisco. The North Tower will consist of 12 and 35 stories above a one-level basement. The South Tower will consist of 9 and 22 stories over one partially below-grade level of common space; a portion of the South Tower will have a three-level basement. The towers will be supported on mat foundations bearing on native very dense sand in the footprint of the three-level basement and on ground improved with soil-cement mixed (SCM) panels that extend through loose sand and marsh deposits into very dense sand. Shoring systems for the basement excavations include cantilevered and tied-back soldier-beam-and-lagging systems and SCM cutoff walls. Subsurface conditions include loose fill and Dune Sand and loose and soft marsh deposits overlying very dense sand of the Colma formation. Groundwater is approximately 15 to 22 feet deep; the three-level basement extends below groundwater. The site is on Market Street in San Francisco, with SF Municipal Railway (MUNI) and Bay Area Rapid Transit (BART) tunnels running below Market Street approximately 45 and 36 feet north of the site, respectively. Both tunnels are 16.5 feet in diameter. The top of MUNI and BART tunnels are 25 feet and 63.5 feet below street grade, respectively. BART has stringent requirements regarding construction adjacent to their facilities, including disallowing adding pressure to their tunnel, lowering groundwater by more than two feet, and vibrations from construction activities. Design of the shoring and the foundations within the BART zone of influence were subject to their design requirements. The project was also subject to a peer review, as required by the San Francisco Department of Building Inspection. We used FLAC to evaluate stresses at the BART and MUNI tunnels and on the SCM panels. This paper will present the mitigations needed to address seismic hazards and BART restrictions and to provide adequate foundation support for a tall building with high seismic loads.

By Harry J. Cain

Introduction The property of Pioneer Gold Mines of B. C., Limited, is located in the Lillooet mining district of British Columbia, on Cadwallader creek, 54 miles distant by motor road from Shalalth, a station on the Pacific Great Eastern railway. Milling by the present Company was commenced in 1924, a small amalgamation plant, consisting of a crusher, Bryan mill, and plates being operated until 1928. Tailing from this plant was impounded and later treated in the 100-ton continuous counter-current decantation cyanide plant which was erected during 1927-28 and placed in operation during May of 1928. A second cyanide plant, employing continuous counter-current decantation, having a nominal capacity of 200 tons, has been erected during the past few months and was put into operation during September of the present year. The ultimate capacity of the combined units of the present mill has not been determined, but it is expected to be much in excess of the rated capacity. The Ore The ore, as received at the mill, consists chiefly of quartz carrying free gold, with small amounts of pyrite, arsenopyrite, and pyrrhotite in evidence, though probably amounting to less than one per cent of the total. Some gold is very closely associated with the sulphides. The country rock is a basic igneous rock, probably an augite diorite. Near the vein it is highly altered to sericite, which slimes readily on grinding, and does not settle very well. The quartz is of two types, clear and ribbon. In the latter, the ribbons, which are not much thicker than paper, consist of shattered sulphides. In crushing this ribbon quartz, breakage is often along the streaks, exposing these shattered faces to advantage in subsequent treatment. While gold is the metal for which the ore is mined, some silver is also present and is paid for by the mint. It is, however, unimportant from a commercial viewpoint. From the standpoint of crushing and grinding, the ore might be termed 'medium 'hard'.

Jan 1, 1932

By George S. Ansell, John B. Hudson, Stephen A. Koffler

The permeability of hydrogen through the a phase of palladium has been measured by a low pressure permeation technique under conditions such that bulk diffusion was the rate-controlling process. The observed permeability is described by the equation: J = 1.80 x 1O-3 P½exp(-3745)/RT) cc(stp)/sec/cm2/en over a range of hydrogen pressure, P, from 2.9 x 10-5 m Hg to 5.0 x 10-3 cm Hg, and over a temperature range, T, from 300" to 709°K. The fact that the permeability shows a square root dependence on pressure and a reciprocal dependence on thickness was taken as evidence that bulk diffusion, rather than surface reactions, was the rate-controlling process. The permeability data were used in conjunction with the solubility data of Salmon et al., to determine the diffusivity of hydrogen through palludium as: D = 4.94 x 10-3 exp(-5745/RT) cm2/sec There was no influence of sub structural defects observed over the temperature range employed. From the permeability data obtained, coupled with grain size measurements, it was concluded that the ratio of grain boundary diffusivity to bulk diffusivity was less than 105 over the range of temperature investigated. THE diffusive mass transport of hydrogen in the a phase of palladium has been studied previously by numerous investigators.' In spite of the large amount of attention this system has received, there is not good agreement between the results obtained in different investigations.' This is due in part to the fact that the mass transport was surface-limited during some of these studies, rather than being diffusion-controlled3-5 The reason for the disagreement in other cases is not clear. These studies made use of such techniques as rate of absorption from solutions6 and gases,' electrochemical potential,8 time lag,' and permeation10,11 to determine the mass transport behavior. Of these, the gas permeability technique is the only method which allows an easy test to determine if diffusion is the rate-controlling mechanism, thus eliminating the uncertainty regarding the limiting transport processes inherent in the other techniques. The two most recent permeability studies are those of Toda10 and Davis." Toda determined the permeability of hydrogen in the a phase of palladium over the temperature range from 170" to 290°C, and over the pressure range from 36 to 630 mm Hg utilizing a steady-state gas-permeability technique. Toda's result was: J = 1.41 x 10-3 P½ exp(-3220/RT) where J = specific permeability in cc(stp)/sec/cm2/cm, P½ = square root of the inlet pressure in (cm Hg)½, R = Universal gas constant, and T = temperature in deg Kelvin. Davis11 also employed a steady-state gas-permeability technique over the temperature range from 200" to 700°C and over the pressure range from 0.02 to 760 mm Hg. His result for the permeability of hydrogen in the a phase of palladium was: J = 3.15 x 10-3 P½ exp(-A440/RT) In the range of overlapping temperature for these two investigations, the values of the specific permeability calculated from the above two equations differ by a factor of about 1.8. In the present investigation, the permeation of hydrogen in the a phase of palladium was determined over a wide temperature range, 27" to 436oC, and over the pressure range from 2.9 x 10-5 to 5.0 x 10-3 cm Hg. This temperature range overlaps that of the previous investigations of Toda and Davis, but also covers the lower temperature range which has never before been investigated. The lower pressure range used here avoided the interaction between the dissolved hydrogen atoms observed at higher hydrogen concentrations.' MATERIALS The as-received palladium specimens were cold rolled from a casting and were supplied as 5.08 cm discs of 0.508 and 0.762 mm thickness. According to J. Bishop and Company specifications, the composition of the discs was 99.95 pct Pd, the balance being Cu, Ag, Au, and Ir. In order to obtain samples of varying grain size, the as-received discs were then heat treated. Sample 1 was treated for eight minutes in a nitrogen atmosphere at 810°C and then air-cooled. Sample D was heated first to 550°C in helium. The helium atmosphere was then immediately replaced by hydrogen and the temperature was slowly raised to 1220°C and held for 22 hr. The sample was then cooled to 550°C where the hydrogen was replaced by helium and the disc was further furnace-cooled to room temperature. Sample H was given the same heat treatment, only with hydrogen substituted for helium below 550°C. The reason that hydrogen was not used throughout the entire annealing cycle for samples D and H was to prevent the distortion encountered by low-temperature cycling in hydrogen observed by Darling." After these heat treatments were completed, the

Jan 1, 1970

By RICKARD HANSEN

With vehicles frequently found in mines and tires being a major fuel item, the risk of tire fires will be severe underground. This study presents an analysis of tire fires on mining vehicles to increase the knowledge of the risk and mitigating measures, which would improve the fire safety underground. Data from fire experiments and computational fluid dynamics (CFD) simulations were applied. It was found that the wheelhouse of a loader caused an increase in the flame tilt angle, decreasing the flame impingement and heat flux downstream. The flame temperature of a drilling rig tire was found to be higher than that of a loader tire, increasing the risk of igniting items. The construction of the wheelhouse/mudguard will contribute to a longer flame length by creating a fuel-rich environment. The CFD simulations predicted higher flame tilt angles for a drilling rig for higher flow velocities, indicating the influence of the wheelhouse/mudguard construction and tire geometry on the flame tilt angle. The construction of a loader resulted in flow behavior, where the short distance to the front mudguard/tire and the separation of flow directly downstream of the construction led to gases being steered past the front mudguard/tire. In a drilling rig case, the longer distance to the front mudguard/tire led to gases being directed toward the body of the vehicle after passing the area with flow separation.

By Frank D. Lamb, D. A. Woodard

"INTRODUCTION The iron-ore deposits near Cranberry, N. C., were worked as early as 1820, and records show that to date at least 1,500,000 tons of ore has been mined.. The early operators depended on selective mining and hand cobbing to yield a product containing 40 to 50 percent iron. Later, a magnetic concentrator was erected by the Cranberry Furnace Co. and was operated periodically until 1930. The magnetic cobbing method employed yielded satisfactory concentrates, but the plant was shut down because costs were too high. 4/Early in 1944, in connection with the sponge-iron program of the Bureau of Mines, North Carolina and Tennessee were surveyed for the purpose of finding a readily available source of high-grade iron ore for use in the experimental production of sponge iron at Salisbury, N. C., and samples from various sources were tested in the laboratory. The Cranberry ore proved to be best with respect to grade of magnetite concentrates produced, and it was decided that a pilot mill should be built on the Cranberry mine property and that the concentrate made there should be shipped to Salisbury for direct-reduction tests in a commercial brick kiln."

Dec 1, 1946

By B. C. Allen

Liquid surface tensions of copper and 18 Group IV-A to VIII transition metals (Ti, Zr, Hf, V, Cb, Ta, Mo, W, Re, Ru, Rh, Pd, Os, Ir, Pt, Fe, Ni. Co) have been measured by the static pendant-drop and dynamic drop-weight methods on the same rod sample. The drops were formed by electron-bombardment heating in high vacuum. Application of necessary corrections enabled determination of surface tensions to k2 pct and agreement between methods to * 1 to 4 pct for all the metals studied. Evidence is presented that the liquid surface was well screened by metal vapor, suggesting negligible adsorption of gaseous impurities and that the surface tensions measured are characteristic of the metals involved. Correlations between liquid surface tension and melting point, molar volume, heat of vaporization, and atomic number are presented and discussed. Temperature coefficients of surface tension were calculated using Eötvös' law. SURFACE tension and interface energies of metals are the result of incomplete atomic coordination resulting in a force perpendicular to the boundary, tending to minimize its area. These energies are important in many phases of metallurgy, including microstructure, sintering, joining, electronic emission, and lubrication, which in turn affect many physical and mechanical properties of metals. Liquid surface tension refers to the interface between the liquid and its own vapor or nonreactive atmosphere, and is considered a physical property of the liquid. Since equilibrium shapes can be readily obtained with liquids, the units of surface tension (force per length) and interface energy (energy per area) are interchangeable. Thermo-dynamically, the surface tension ?LV is given by the change in free energy F with surface area A at constant pressure P, temperature T, and composition N: for commercially important refractory metals, vanadium, columbium, tantalum,13,14 molybdenum,14 and tungsten,l5 and none for the rare platinum-group metals and rhenium. Measuring the surface tensions of transition metals is difficult because of their high reactivity and melting points. Of the many techniques available,16-18 the pendant-drop 19-21 and drop-weight methods17,22 are considered superior because they can be modified to eliminate persistent sources of contamination such as supports and capillaries necessary in the popular sessile drop, capillary rise, and maximum-bubble-pressure techniques. The necessary modification is to melt a drop on the tip of a vertical rod, which provides support through a solid of the same composition.13,15 The object of the work was to study the surface-tension behavior of copper and transition metals, having reasonably low vapor pressures. Liquid surface tension of each pure metal was systematically determined by using a combination of the static pendant-drop and dynamic drop-weight methods on the same rod. Liquid drops were formed by electron-bombardment heating in high vacuum. EXPERIMENTAL WORK As indicated in Table I, the metals studied were high purity and generally were obtained in rod form. The exceptions were titanium and zirconium, which were machined from crystal bars, and molybdenum (tot 11, osmium, and ruthenium, which were sintered and arc cast into rods. All the metals were ground or swaged to desired sizes between 1- and 7-mm diam, and centerless ground round and smooth to a finish better than 50 µ in., rms. Each rod was thoroughly cleaned with steel wool, degreased, acid etched, and dried. In a typical run, the rod was vertically clamped in a modified floating-zone electron-bombardment furnace designed after Calverley23 and Carlson.24 The specimen was outgassed and maintained positive at several kilovolts in a dynamic vacuum of 10-5 to 10-7 mm. The bottom end was enclosed by a tantalum pillbox and heated by electrons emitted from a hot concentric tungsten filament mounted on a movable bracket. The bombardment power was slowly raised until melting was observed. Power requirements ranged from 30 w for copper to 1300 w for 4-mm tungsten. The stabilized and out-gassed drop of near-maximum size was photographed at 4. 1X on panchromatic film at desired time inter-

Jan 1, 1963

By Oliver Bowles

DIMENSION stone is a convenient term applied to stone sold in blocks or slabs of specified shapes and usually of specified sizes, as contrasted with crushed, broken and pulverized stone, discussed in another chapter. Dimension stone includes cut stone, rough building stone, ashlar, rubble, paving blocks, curbing and flagging. Riprap-large, irregular blocks used for shore protection-is classed more properly with crushed and broken stone. COMPOSITION, VARIETIES AND PROPERTIES Stones used as blocks or slabs are of many kinds. The principal varieties are granite, sandstone, limestone and marble. Slate is covered in another chapter. Granite is a visibly granular crystalline rock consisting essentially of feldspar, quartz, and mica or hornblende. Limestone consists essentially of calcium carbonate, with which may be associated certain impurities such as clay, sand, or iron oxide. Dolomites and magnesium limestones used as dimension stone are classed with the high- calcium limestones, as they are used in the same way. Marble is a crystalline form of limestone. Sandstone consists essentially of silica in the form of sand grains cemented together into a coherent mass. Although rock occurrences are numerous and widespread, the ex- acting requirements of use condemn all but a small fraction of them for commercial use as dimension stone. No deposit that has closely spaced cracks, lines of weakness, or joints can be so used because sound blocks of moderate to large size are demanded. Uniform texture and grain size, constant and attractive color, and freedom from impurities that may cause stains or deterioration usually are required also. Hardness is a variable property. Granites are as hard as or harder than steel while limestones and marbles may be scratched easily with a knife. The hardness of a sandstone depends upon the degree of cementation of the grains. Workability depends to a considerable extent on hardness, but the degree of hardness has little influence on use except when stones are subjected to severe abrasion, as on steps or floors. "Texture" as applied to stone relates to the arrangement, uniformity, and size of the constituent grains.

Jan 1, 1949

Activity-composition-temperature relations for both gold and nickel have been determined for the solid and liquid states of the gold-nickel system by the application of the Margules equations. These relations are in satisfactory agreement with activity measurements of nickel in the solid state, the observed phase boundaries of the system between 700 and 1725°K, as well as being consistent with data on the enthalpy of mixing.

Jan 1, 1971

By G. Rajesh

Mathematical modeling of bioremediation has gained importance as it is used as an optimization tool for the remediation process involved in contaminated sites. The bioremediation of Cr(VI) has been studied taking into consideration the initial Cr(VI) concentration Cr(VI)ini, bacterial growth substrate concentration (S), maximum growth rate (µmax), yield coefficient (Y), half saturation constant (Ks), and inhibition constant (KI). As the enzymatic reaction is also affected by initial substrate concentration (Sini) and Ks, different ratios of (Ks/Sini) are analyzed. As the inhibition constant (KI) is not constant for all the enzyme reactions and it varies with Cr(VI)ini, the correlation between (KI) and Cr(VI)ini is developed. A set of differential equations pertaining to bioremediation of Cr(VI) has been solved using FORTRAN 90 program adopting the model developed. The results are verified with the experimental data from the literature and a good correlation has been obtained between the experimental data and the model predictions. Keywords: bioremediation, hexavalent chromium, mathematical model, inhibition kinetics

Sep 1, 2012

By Zhen Zhang, Jiang Diao, Xuan Liu, Tao Zhang, Bing Xie, Hong-Yi Li

Extracting vanadium from vanadium containing hot metal by LD process has been proven an effective solution for the utilization of vanadium-titanium magnetite ore, but the systematic analyses of vanadium extraction rate and mechanism by basic slag are seldom reported. In this study, mathematical model of vanadium transfer from metal to slag was formulated and the rates of vanadium extraction of hot metal with basic slag were investigated. The results indicated that the apparent vanadium extraction rate constant, kp, were in the range of 1.33~9.07×10-4g/(cm3·s). And the rate constant was increased with the increase of final slag basicity, reaction temperature and stirring gas flow. The apparent of mass transfer parameter decreases significantly from 0.13 cm3/ s to 0 cm3/ s in 20min, and the data changed as negative due to the decrease of slag oxidation and recovery of vanadium from slag to metal.

Jan 1, 2015

By Jerome Alexander

THE object of this paper is to show that many of the important phenomena of metals and alloys are due to the facts that, at some stage, metals and alloys, or some of their constituents, are in a colloidal state and that a portion of the metal or alloy tends to remain in this state. The so-called amorphous phase in pure metals is an isocolloid, consisting of colloidal groups of metal molecules that may be dispersed in still more finely subdivided metal; these colloidal particles are not truly amorphous, but may consist, in part, if not entirely, of ultramicroscopic crystals; as a result the expressions amorphous phase and amorphous theory might be replaced by the expressions colloidal phase and colloidal theory. Any substance is in the colloidal state when the constituent particles consist of molecular or atomic groups, whose size varies approximately from about 100µµ down to about 5µµ, that is from just below the limit of microscopic resolvability to the dimensions commonly ascribed to the larger molecules. Colloidality involves no assumption as to the shape, internal structure, or orientation of the colloidal particles; size alone is the critical factor. A colloidal system may therefore contain crystalline groups, or amorphous groups (non-crystalline, random or haphazard clusters), or a mixture of the two. All colloids consist of at least two phases, the subdivided substance, or dispersed phase, and the substance into which this is subdivided, the dispersion medium. It is not necessary that there be any chemical difference between the dispersed phase and the dispersion medium. As molecular forces are extremely powerful, their application may produce marked changes in the physical properties of metals. It is doubtful whether metal in the interior, especially of large masses, possesses the same properties as that on or near the surface, which alone is open to, inspection.

Jan 10, 1920

By Jerome Alexander

The object of this paper is to show that many of the important phenomena of metals and alloys are due to the facts that, at some stage, metals and alloys, or some of their constituents, are in a colloidal state and that a portion of the metal or alloy tends to remain in this state. The so-called amorphous phase in pure metals is an isocolloid, consisting of colloidal groups of metal molecules that may be dispersed in still more finely subdivided metal; these colloidal particles are not truly amorphous, but may consist, in part, if not entirely, of ultramicroscopic crystals; as a result the expressions amorphous phase and amorphous theory might he replaced by the expressions colloidal phase and colloidal theory. Any substance is in the colloidal state when the constituent particles consist of molecular or atomic groups, whose size varies approximately from about 100 down to about 5pp, that is from just below the limit of microscopic resolvability to the dimensions commonly ascribed to the larger molecules. Colloidality involves no assumption as to the shape, internal structure, or orientation of the colloidal particles; size alone is the critical factor. A colloidal system may therefore contain crystalline groups, or amorphous groups (non-crystalline, random or haphazard clusters), or a mixture of the two. All colloids consist of at least two phases, the subdivided substance, or dispersed phase, and the substance into which this is subdivided, the dispersion medium. It is not necessary that there be any chemical difference between the dispersed phase and the dispersion medium. As molecular forces are extremely powerful, their application may produce marked changes in the physical properties of metals. It is doubtful whether metal in the interior, especially of large masses, possesses the same properties as that on or near the surface, which alone is open to inspection.

Jan 1, 1921