Search Documents

By B. Stas, L. Siska, L. Dlouhy, A. Skrabis

The basic research program of the Scientific Coal Research Institute at Ostrava - Radvanice into the problem of geophysics has been influenced by the specific nature of present urgent geo- physical problems in mines and directed to attain higher grade of effectiveness, safety, and overall economy in mining activity. The research has been divided into two basic trends: Seismoaccoustic research deals with questions pertaining to safety in mining especially when work is in coal seams under "heavy roofs", i-e., thick beds of sandstone prone to rock bumps and characterized by caving. Methods have been developed with the definite aim to determine the time and space prognosis of critical states of tension in the rock mass when stability is disturbed as a result of mining activity. Seismic research is directed towards the determination of detailed structural and tectonic elements of the internal geological formation of the Carboniferous rocks, the establishment of continuity or tectonic faulting of coal seams, and the evaluation of magnitude, shape, and time changes in the rock mass surrounding the mine workings. The measurements have been applied either from the surface or in the underground workings according to the specific nature of individual problems. Satisfactory results have been obtained in some branches of this research, other branches being still in the stage of development. Remarkable results have been achieved in the development of seismoaccoustic methods designed to establish the time prognosis of dangerous dynamic phenomena accompanying the process of strata deterioration above the worked longwall face. One of the most

Jan 1, 1971

"Human accidents are caused by production accidents, generally ones (such as derailment of cars, falling rock, etc.) that have occurred numerous times before an employee was actually involved. Prevention of human accidents is, one of the essentials in cutting operation costs, and advocates of safety are studying economics to assist them in their work of preventing accidents.Workman's compensation insurance or compensation for human accidents is a true operating cost, and is the only purely tangible measure available which gives a measurement of the cost of accidents even though, as will be pointed out later, it represents but a portion of the total cost of human accidents.In using premiums paid for compensation insurance as a measure of the cost of accidents, it must be kept in mind that most insurance laws, as pointed out in a former paper (Serial 2590 of the Bureau of Mines) provide a waiting period before compensation for the lost-time wages starts, with the compensation limited to definite percentages of the wages. The waiting period and limited compensation combined tend to limit the amount paid to an injured workman who, if he receives 1/3 of the lost-time wage, will probably have been reimbursed as high as the average injured workman.The total or complete economic cost of human accidents, must include, in addition to compensation paid for lost time, and the portion of the lost-time wage suffered by the workman for which he is not compensated, the additional cost to the company through-(a) temporary decreased production by the breaking down of the morale, etc., (b) the breaking in of a new employee which is admittedly expensive,(c) the increased liability of human and production accidents caused to or by the new employee.Another charge against accidents, which is not included in the compensation payment, is the economic loss through the killing of as workman who has no dependents. Few of the States' laws require any compensation except burial expenses to be paid for fatalities to persons having no dependents. It is estimated by the United States Bureau of Labor Statistics that the economic loss through a fatality is 6000 shifts. If each fatality was compensated for this amount of time and at half-time wages, using an average wage of $5.00 per shift, the compensation for fatality based on the economic loss would be $15,000. but the average actual compensation paid for each fatality is about $3,000."

Jul 1, 1924

By H. C. Chang, N. J. Grant

REEP studies and measurements in most in-V> stances are based on a relatively gross gage length. Even in some recent theoretical studies on the mechanism of creep, changes were followed by means of X-rays and metallography without regard for the behavior of the individual grains and grain boundaries.'" Analytical studies of creep have frequently indicated that more than one competing process is operative and that the ultimate creep performance depends on the effects of temperature, time, and strain rate as well as grain size.'-" he grains and grain boundaries are known to respond differently to these variables but the extent of the response is still little known, especially in poly-crystalline materials where the relative orientations of grains and grain boundaries are important. This paper reports some experimental observations of the behavior of the grain boundaries and their effect on the deformation in the grains. High purity aluminum was used to avoid complications of aging reactions, second phase, inclusions, etc. Experimental Procedure A small vertical nichrome wound furnace was built to permit direct loading on the test specimen. This furnace is capable of operating up to about 1300°F with reasonable temperature distribution. A ground rectangular quartz window, 1.25x0.5 in., is imbedded in the external stainless steel tube to permit observations of the creep process with a microscope. An argon atmosphere ,was provided to prevent oxidation. The quartz window caused a temperature gradient between the back and front surfaces of the specimen of 15" at 700°F. The temperature gradient could be cut down to 3°F along the length of the specimen by adjusting shunts across the furnace windings. An ordinary metallurgical microscope with a working distance of 14 mm was rebuilt so that it could be moved in three mutual perpendicular directions. Visual examination could be made with either a 30X eyepiece or a 15X filar eyepiece. Using an objective of focal length 24.3 mm and a numerical aperture 0.20 a total magnification of 120X or 240X could be obtained. High purity aluminum rated at 99.995 pct was supplied by the Aluminum Co. of America as % in. then the gage portion was further machined to 3/16 in. diam. The ends were Y4 in. diam and threaded to fit available specimen holders. Two opposite flat surfaces of the gage portion were obtained by milling, giving final dimensions of the gage portion of 3/4x3/16x3/32 in. Machined specimens were first electropolished in Jacquet's solution.' Reference marks were produced by pressing a thin sewing needle into the surface of the specimen. The specimen was then annealed at 900°F for 24 hr and at 1150°F for 12 hr. Typical macrostructures of specimens treated in this manner are shown in Fig. 1. The range of the grain size was 1 to 5.5 mm (see Fig. l), but most of the grains were of 2.5 mm and went through the whole thickness of the specimen. The specimen was re-electropolished and etched electrolytically to reveal the grain boundaries. In order to reveal the orientation difference of the grains, etch pits were produced on the surface of the grains by etching in a mixture of hydrochloric and nitric acids (HC1, 45 pct; HNO,, 10 pct; H,O, 45 , by volume). The specimens were very carefully put into the holders and furnace; yet even with this care, fine slip lines were developed on the specimen surface.

Jan 1, 1953

By J. H. M. Thomeer

A method is presented that provides a mathematical description of capillary pressure curves and, probably, of differences in pore geometry of samples. The technique is based on the observation that the location and shape of a capillary pressure curve reflect characteristics of the pore structure of the sample. INTRODUCTION It has been noted1-5 that the observed differences in shape and location of capillary pressure curves reflect some basic properties regarding the pore geometry of the samples. For example, according to basic concepts of capillarity, the following statements can be made regarding the location and shape of a capillary pressure curve.* The location of the curve with respect to the (Vb)pc and PC axes is a measure of the interconnected pore volume and of the cross-sectional area of the pore first entered by mercury, respectively. The shape of the curve depends on the interconnection of the pores and the sorting of the pore sizes. It has been the object of this study to use this information as a starting point in an attempt to find a unique mathematical description of the PC — (Vv)p, relations of different samples. It may be expected that parameters in such a relation can then be used to describe differences in pore geometry of these samples. For a practical description of the PC — (Vb)p, relation, however, it appears desirable to describe each curve (i.e., each sample) by a limited number of parameters so that the curves taken from all samples form a family, each member of which is uniquely determined by one single combination of values of all parameters.

By Jos. R. Guiteras

This paper has been written to describe briefly the mining and milling of gold and silver ores in the Black Canyon and neighboring mining districts in Yavapai County, Ariz. The description of present operations is the result of a 10-day visit to the region by the writer in March 1936. Acknowledgments The author is indebted to earlier writers on the geology and mining in this regions and to the mine managers and their staffs, whose courteous cooperation has made possible the assembling' of material for this paper. Individual acknowledgments are made in the text.

Jan 1, 1936

By William Gleason

"Caterpillar is the largest manufacturer of mining equipment in the world. In hundreds of surface mines around the globe, Caterpillar’s flagship 793 haul trucks can be found moving material for copper, coal, gold, iron ore and other mines. Likewise, its iconic yellow bulldozers are at mine sites the world over — the company recently announced the sale of its 40,000th large dozer. And since its acquisition of Bucyrus in 2011, Caterpillar has positioned itself to become a worldwide leader in the underground mining sector as well.But don’t think that the company is resting on its reputation. As evidence of its commitment to the global mining sector, as well as its confidence in the future of mining, Caterpillar invited mining trade press, including Mining Engineering, to its Tinaja Hills Training Center near Tucson, AZ in November to introduce the latest editions to its mining portfolio. The two-day event focused mostly on the newest electric drive haul trucks, the Cat 796 AC, which will operate in the 326-t (360-st) class, and the 798 AC in the 360 t (400 st) weight class.Caterpillar representatives also spoke about new offerings in the underground space as well as the newest version of the D11 large dozer.“It has been 10 years since we launched the F Series,” Jean Savage, Caterpillar’s vice president, surface mining and technology said. “Since then, we have been on a journey to serve our mining customers and we wanted to have trucks in every application. Today, we are launching two new trucks that will allow us to fill out our portfolio.”While Caterpillar previously offered the broadest range of off-highway haul trucks to the mining industry, it was noticeably absent from the 326-t (360- st) and 360-t (400-st) weight classes."

Dec 1, 2018

By Kung-Lee Wang

FOLLOWING the rapid recovery of previous years, the U.S. economy continued the upward trend and moved forward moderately and sporadically during the first half of 1962. There was a slow-down in the recovery rate, which was especially notable in the third quarter. The economy recovered in the fourth quarter, and by the end of 1962 the gross national product amounted to $555 billion, a new high, 7 percent above that of 1961. Production, employment, personal income, and corporate profits all achieved new peaks, but unemployment continued high and the prospects for improvement remained poor. The economy again failed to us~ its full potential; 1962 was a good year, but not good enough. During 1962, all industrial production climbed from the low in January to a high in late summer which lasted through the fall, and declined slightly at yearend. Mining production followed this pattern closely and most sectors were approaching record highs. Most minerals gained in value and volume of production. The steel-associated minerals group was the only exception, and it sustained a small net loss. The nonfuel minerals industry opened the year at a high level, maintained this high level until late summer, with the peak in May, and drifted downward toward the end of the year. The gains recorded by nonferrous metal mining partly offset the loss of ferrous metal mining, resulting in a small gain for metal mining as a whole. The upsurge of construction material minerals output was primarily responsible for the substantial increase in production of nonmetals other

Jan 1, 1963

By B. L. Averbach, M. Cohen, C. H. Shih

The isothermal formation of martensite is studied in Fe-Ni-Mn and Fe-Mn-C alloys under conditions where the athermal transformation is completely avoided, there being no martensite present at the beginning of the isothermal reaction. The initial rate of martensite formation is extremely low under these conditions, but it increases greatly as soon as some martensite is formed. It appears that true initial characteristics of the isothermal reaction can be studied only in samples wherein the formation of martensite on cooling is completely eliminated. THE phenomenon of isothermal martensite formation is well established1 -" but the observations have been made in the presence of varying quantities of athermal martensite. Complete avoidance of athermal martensite and the formation of martensite under pure isothermal conditions have been reported by Kurdjumov and Maksimova2 in an Fe-Ni-Mn alloy (23 pct Ni, 3.4 pct Mn, and the balance Fe) and have been confirmed by recent experiments of Cech and Hollomon in a similar alloy. In each case, the isothermal transformation rate was a maximum at the beginning of the transformation and decreased as the reaction proceeded. These initial transformation rates were used by Fisher7 for the confirmation of calculated nucleation rates based on classical nucleation theory extended to include the effect of elastic strain energy. Cech and Hollomon have admitted, however, that up to 3 pct martensite formed on cooling in their samples and thus was present at the initiation of their isothermal runs. In this paper, experiments on similar alloys are described, except that care was taken to remove the incidental martensite developed at the surface prior to the isothermal reaction. It is shown here that the reaction rate at the beginning of the strictly isothermal reaction is very low. As soon as some detectable amount of martensite is produced, the transformation rate increases rapidly but ultimately decreases as the reaction proceeds. When martensite is allowed to form isothermally in the presence of about 2 pct of prior martensite, the apparent initial reaction rate is a maximum and corresponds to the observations of Kurdjumov and Maksimova and Cech and Hollomon. It is evident that the cooperative nature of the martensitic reaction results in a significant stimulating or autocatalytic effect on the isothermal reaction rate. Experimental Procedure The chemical compositions of the alloys used in this investigation are listed in Table I. The Fe-Ni-Mn alloys A and B were melted in an induction furnace, cast into ingots 2 in. diam by 4 in. long, and forged into % in. diam rods. The manganese steel (alloy C) was melted in an arc furnace and cast into ceramic molds 1/4 in. diam by 5 in. long. The rods were sealed in evacuated Vycor tubes and homogenized at 1175" to 1200°C for 50 hr. The long homogenization resulted in some manganese loss from the surface, producing a thin layer of transformed material. This surface layer was removed by grinding and the specimens were then swaged to 0.050 in. diam wire. Measurements of electrical resistance were made with a Kelvin double bridge to follow the course of the martensitic transformation. A small permanent magnet was also useful in scanning an entire specimen for small localized quantities of martensite. This test is almost as sensitive as the electrical resistance method in detecting the presence of martensite (which is ferromagnetic in these alloys) and it was especially useful in deciding whether a specimen was completely free of martensite. The wire specimens (0.050 in. diam by 2.5 in. long) were sealed in evacuated tubes and austenitized for 5 min at 1150°C. The specimens were quenched into water and, unless otherwise stated, stress-relieved for 1 hr at 650 °C in order to induce greater uniformity in the subsequent martensitic transformation. As dem-

Jan 1, 1956

By K. V. S. Sastry, V. P. Mehrotra

A laboratory investigation was carried out to study the influence of asphalt, bentonite, and corn starch binders on the pelletization kinetics of coal fines and on the quality of the resulting pellets. Pellet quality was evaluated in term of the compression strength, impact resistance (drop test), abrasion resistance, and resistance to severe weather conditions. The amount of binder addition did not significantly influence the pellet growth kinetics. However, the pellet quality varied markedly depending upon the type and the amount of binder wed. Experimental results are explained on the basis of the mechanism of interaction between the coal particles and the binders. Of the three binders tested, corn starch proved to be the best in all respects but for the resistance to water penetration. Finally, a combination of corn starch (imparting strength) and asphalt emulsion (imparting resistance to water penetration) was found to yield the best quality coal pellets.

Jan 1, 1983

By James F. Allan

"The Kipawa yttrium-zirconium prospect is located about 150 km south of Noranda, Quebec. Yttrium-zirconium mineralization occurs in an elongate, regionally metamorphosed and deformed peralkaline complex in the Grenville terrain. The mineralized zone, as defined by =.0.10% Y2O3, is 1300 m long and 10 m to 30 m wide. Zirconium content typically ranges from 0.50 to 1.20% ZrO2, The mineralized zone strikes northwest and dips 20 degrees to 35 degrees to the southwest. It occurs at the structural base of the peralkaline complex in syenite gneiss and calc-silicate rocks and is conformable with both the footwall contact of the complex, and the layering and gneissosity in the enclosing rocks. Minerals of economic interest are eudialyte (sodium-zirconium silicate), mosandrite (sodium-titanium silicate), britholite (calcium-silica phosphate), and a few other uncommon zirconium and titanium silicate minerals.The highest and most continuous yttrium grades occur in the upper part of the syenite gneiss unit in areas containing eudialyte, mosandrite and minor britholite. Yttrium also occurs in britholite in calc-silicate rocks and in mosandrite in syenitic rocks in the lower part of the syenite gneiss unit. Both the yttrium-bearing minerals and yttrium grades are erratic in the lower part of the unit. Zirconium is generally more uniformly distributed than yttrium. A peralkaline granite gneiss phase of the complex intrudes the syenite gneiss and possibly truncates it, and the mineralization, near the southern boundary of the mineralized zone.The mineralized zone is coincident with a radiometric anomaly and discontinuous yttrium and zirconium soil anomalies.More drilling and metallurgical studies will be required to determine the economic viability of the yttrium and zirconium mineralization at Kipawa."

Jan 1, 1992

By J. N. Roberts, K. V. Gow

In a recent review of the field of plastic deforrnation of metal single crystals, Maddin and chenl indicated the need for systematic investigations of the crystallography of the slip process with special attention to: a) The effect of the orientation of a crystal on the appearance of slip lines, b) The effect of high temperatures on the slip systems of aluminum, c) The effect of strain rate on the crystallography of slip. The present paper deals with the effect of temperature and strain rate on the mechanism of deformation of aluminum single crystals similarly oriented for single and duplex slip. The work of several investigators has shown that in aluminum at high temperatures other slip systems in addition to the predicted {I l l) <101> may operate. The most generally reported additional systems

Jan 1, 1959

By James F. Allan

"The Kipawa yttrium-zirconium prospect is located about 150 km south of Noranda, Quebec. Yttrium-zirconium mineralization occurs in an elongate, regionally metamorphosed and deformed peralkaline complex in the Grenville terrain. The mineralized zone, as defined by =.0.10% Y2O3, is 1300 m long and 10 m to 30 m wide. Zirconium content typically ranges from 0.50 to 1.20% ZrO2, The mineralized zone strikes northwest and dips 20 degrees to 35 degrees to the southwest. It occurs at the structural base of the peralkaline complex in syenite gneiss and calc-silicate rocks and is conformable with both the footwall contact of the complex, and the layering and gneissosity in the enclosing rocks. Minerals of economic interest are eudialyte (sodium-zirconium silicate), mosandrite (sodium-titanium silicate), britholite (calcium-silica phosphate), and a few other uncommon zirconium and titanium silicate minerals.The highest and most continuous yttrium grades occur in the upper part of the syenite gneiss unit in areas containing eudialyte, mosandrite and minor britholite. Yttrium also occurs in britholite in calc-silicate rocks and in mosandrite in syenitic rocks in the lower part of the syenite gneiss unit. Both the yttrium-bearing minerals and yttrium grades are erratic in the lower part of the unit. Zirconium is generally more uniformly distributed than yttrium. A peralkaline granite gneiss phase of the complex intrudes the syenite gneiss and possibly truncates it, and the mineralization, near the southern boundary of the mineralized zone.The mineralized zone is coincident with a radiometric anomaly and discontinuous yttrium and zirconium soil anomalies.More drilling and metallurgical studies will be required to determine the economic viability of the yttrium and zirconium mineralization at Kipawa."

Jan 1, 1992

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&apos; 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&apos; 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", &apos; 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 P. A. Beck, W. D. Manly

In a recent note Sully and Head1 showed that the Cr-Fe sigma phase is isomorplious with the Cr-Co gamma phase, and that the lattice constants are also nearly identical. In a preliminary investigation of the ternary Cr-Co-Fe system at 800°C at this laboratory the above findings were confirmed, and it was found by microscopic techniques, using various etching reagents, that the two binary phases form an urinterrupted series of solid solutions with each other. These solid solutions occupy a straight narrow band which cuts across the 800°C isothermal section of the ternary system, connecting the two binary phases. A detailed investigation of the Cr-Co-Ni ternary system at 1200°C disclosed that here, too, the Cr-Co gamma phase extends deep into the ternary system in the form of a long narrow lip. The fact that this sigma type lattice is sustained even when well over half of the Co atoms in it are replaced by Ni atoms, with relatively little change in the Cr content, clearly indicates that Ni itself has a certain tendency to form the sigma phase with chromium. This tendency is hidden in the binary Cr-Ni alloys, where the sigma phase is not known to occur, but it becomes operative in the presence of a suficient amount of Co. The interpretation of these facts in terms of electron concentrations is rendered difficult by the uncertainty of our present knowledge of the valency electron structure of the transition elements in their alloys. However, Sully and Heal&apos;s results and the present work suggest that intermetallic phases with signla type lattice may occur more frequently in these little investigated alloys than heretofore suspected. In particular, it is expected that a similar phase may exist in the V-Co and perhaps in the V-Ni system, in analogy to the known sigma type phase in the V-Fe system, and that all these sigma type phases may form extensive solid solutions with one another.

Jan 1, 1950

By John Chapman, J. C. Vaughan

Although a considerable amount of practical importance attaches to systems involving gases and molten metals, little is known regarding the effects of alloy elements upon the solubility of gases in liquid iron. The solubilities of hydrogen1 and nitrogen2,3 in pure liquid iron arc known and it has been shown that small amounts of silicon and aluminum3 exert only a small effect upon the solubility of nitrogen but greatly increase its rate of solution. This paper presents the results of a study of the solubility of nitrogen, at pressures approximately one atmosphere, in molten iron containing up to 15.8 per cent silicon. EXPEBIMENTAL METHOD There are two general methods by which the solubility of a gas in a molten metal may be determined. In the first, which Sievertsl employed, the gas is measured from a burette into the enclosure containing the metal and the amount absorbed is found by subtracting from the total volume that of the dead space in the container. The second method, which was used successfully for pure liquid iron, is to expose the molten metal to the gas until absorption ceases, then to solidify and analyze the metal. In either method the stirring produced by inductive heating prevents the development of a stagnant layer at the metal surface and ensures actual attainment of equilibrium. Obviously the second method is accurate only when the saturated metal is capable of solidifying without gas evolution. Since the rate of solution of nitrogen in iron is increased by the presence of silicon, it was to be expected that the rate of evolution would be correspondingly increased and for this reason the first method was selected. A sketch of the furnace is shown in Fig. 1. A small high-frequency coil having 17 turns fitted closely around a fused silica tube, 2 in. in diameter, in which was placed, on a bed of 60-mesh alumina sand, an

Jan 1, 1940

By N. Jaffe, J. E. Dorn

The effect of stress on the creep rate of high-purity poly crystalline aluminum in the intermediate temperature range was investigated by conducting creep tests at a series of different stresses and by decreasing the stress abruptly during the course of primary and secondary creep. Three series of decreases in stress tests were conducted: the stress was decreased in primary and secondary regions of creep at 347.5°K and the stress was decrensed in primary creep at 327°K. The results demonstrate the effects of structure and temperature on the stress dependence of the creep rate. The trends in the creep rate after a drop in stress are complicated and show that recovery takes place. The experimental results were compared with Friedel&apos;s theory for cross-slip, the experimentally determined energy for a constriction being in good agreement with the theoretical estimate proposed by Stroh. PREVIOUS investigations have shown that the ap-- parent activation energy for creep of polycrystalline aluminum, over the range from about 250° to 380°K, is approximately 27,400 cal per mole,&apos; a value that is to a first approximation insensitive to the applied stress, the creep rate, and the creep strain. Several facts strongly support the thesis that creep, in this temperature range, is controlled by the rate-determining mechanism of cross-slip: 1) Recovery of the cold-worked state can take place by a number of mechanisms prominent among which is climb and cross-slip. Astrom2 reported rapid recovery of cold-worked polycrystalline aluminum at 340° to 370°K giving an activation energy of 28,000 cal per mole and additional recovery at the higher temperatures of 455° to 478°K giving an activation energy of 36,000 cal per mole. Whereas the latter process was clearly identified with the climb mechanism, the former process. which has an activation energy in good agreement for that of creep in the same temperature range, is most likely due to recovery by thermally-activated cross-slip. 2) Single crystals of aluminum exhibit sharp slip-

Jan 1, 1962

By J. C. Vaughan, John Chapman

Although a considerable amount of practical importance attaches to systems involving gases and molten metals, little is known regarding the effects of alloy elements upon the solubility of gases in liquid iron. The solubilities of hydrogen1 and nitrogen2,3 in pure liquid iron arc known and it has been shown that small amounts of silicon and aluminum3 exert only a small effect upon the solubility of nitrogen but greatly increase its rate of solution. This paper presents the results of a study of the solubility of nitrogen, at pressures approximately one atmosphere, in molten iron containing up to 15.8 per cent silicon. EXPEBIMENTAL METHOD There are two general methods by which the solubility of a gas in a molten metal may be determined. In the first, which Sievertsl employed, the gas is measured from a burette into the enclosure containing the metal and the amount absorbed is found by subtracting from the total volume that of the dead space in the container. The second method, which was used successfully for pure liquid iron, is to expose the molten metal to the gas until absorption ceases, then to solidify and analyze the metal. In either method the stirring produced by inductive heating prevents the development of a stagnant layer at the metal surface and ensures actual attainment of equilibrium. Obviously the second method is accurate only when the saturated metal is capable of solidifying without gas evolution. Since the rate of solution of nitrogen in iron is increased by the presence of silicon, it was to be expected that the rate of evolution would be correspondingly increased and for this reason the first method was selected. A sketch of the furnace is shown in Fig. 1. A small high-frequency coil having 17 turns fitted closely around a fused silica tube, 2 in. in diameter, in which was placed, on a bed of 60-mesh alumina sand, an

Jan 1, 1940

By Frank L. Hess

In 1876 cassiterite was identified in the placer gold from the northern Black Hills, and such a mixture could have come only from Nigger Hill or one of the streams draining the hill, because in no other part of the northern hills have cassiterite and gold been found together. Nigger Hill is in western Lawrence County, South Dakota, and on it is the little camp of Tinton. The Wyoming line runs along the west side of the hill and crosses the ridge which is the hill&apos;s continuation about miles north-northwest of Tinton.

Jan 1, 1938

By R. V. Ramani, S. Shankar

"The phenomenon of re-entrainment is seen in environments such as sand dune formation, soil erosion, fugitive dust emission and the spread of radionuclides from accidents involving nuclear weapons. A thorough review of existing literature reveals that work on re-entrainment of dust in mine atmospheres is scant. The present study was undertaken as a part of ongoing research at the Generic Mineral Technology Center on Respirable Dust at the Pennsylvania State University on the development of methods to predict ambient dust concentrations in mine atmospheres (Ramani, 1983). The contribution of re-entrainment to the spatial and temporal concentration of dust in mine airways is being studied. The research has included wind tunnel and in-mine studies.A set of seven experiments was performed under controlled conditions in the US Bureau of Mines' Lake Lynn Laboratory mine. Two types of source coal dust, anthracite and bituminous, were subjected to various airflow rates and were subjected to walking by two different individuals. Six sets of instruments were used along the test section for sampling airborne particles. The average air velocity just above the coal dust bed varied between 2.1 to 3.2 m/sec.Due to re-entrainment as a result of the airflow conditions, the average respirable dust concentration in the center of the mine airway increased to 0.09 mg!m3 (standard deviation= 0.03 mg/m3)from an initial value of 0.02 mg/m3. The concentration of all (total) airborne dust increased to 0.17 mg/m3 (standard deviation = 0.10 mg/m3) from an initial value of 0. 02 mg/m3. The action of people walking, however, caused higher amounts of re-entrainment. The average concentration of respirable and total dust at the center of the mine airway increased to values of 0. 28 mg/m3 (standard deviation of 0.12 mg/m3) and 1.53 mg/m3 (standard deviation of 1.0 mg/m3), from initial values of 0.03 and 0.05 mg/m3, respectively. Jr was observed that the dust concentrations were much higher near the floor, immediately at the end of the coal-dust bed.Depending on the level of activity and the amount of dust deposited in the mine airways, re-entrainment may become an important source of airborne dust in areas away from the point of actual mining."

Dec 1, 1996

By J. B. Austin, R. L. Rickett

Measurements of the rate of decomposition of austenite at constant temperature are commonly represented by plotting the percentage transformed on linear coordinates against time on either a linear or a logarithmic scale, a method that yields a curve that in shape resembles an integral sign (Fig. 1). A graph of this kind is not always convenient because extrapolation to the beginning or end of the transformation, or even intebrpolation, may be uncertain unless there are a large number of observations, which seldom happens; furthermore, the degree of consistency of a set of measurements is difficult to judge from such a curve. It is desirable therefore to find some mode of plotting, or even better to find a standard variety of graph paper, that gives a straight line instead of the integral shape. The straight line has many advantages; the number of readings required to fix the position of the curve is greatly reduced, interpolatiorr is easy and rapid, extrapolation can be carried out with greater confidence and, finally, the consistency of the measurements is readily estimated from the scatter of the points. The last advantage is particularly valuable when the data are obtained by direct microscopic examination alone, because they are influenced by the skill of the observer in estimating the relative size of areas, possibly also by undetected inhomogeneity of the specimen. A search for ways of representing the observations as a straight line yielded two methods which are described in this paper. The paper also includes an account of some interesting relations brought to light in applying these methods to the available experimental data. Usually the best way to derive such a method of plotting is to base it on established principles of chemistry and physics, as has been done, for example, for the temperature variation of the equilibrium constant of a chemical reaction. But so little is known of the mechanism of the decomposition of austenite, and so little is available in the way of well established background for changes of this kind, that it is simpler to rely upon purely empirical means. The general plan therefore is to study existing data with a view to finding some function of the direct observations that will

Jan 1, 1939