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By John W. Vanderwilt

The fluorescence of scheelite has been an important aid in recent years in the discovery and development of scheelite deposits. The use of fluorescence of synthetic compounds in industry, particularly in advertising, also has expanded greatly during the past decade. As a result, a number of new and convenient units for producing ultraviolet energy have become available, which have led to a greater application of fluorescence in the study of minerals. Studies have shown that the fluorescent color of a mineral may vary: (I) with the kind and quantity of trace elements, and (2) with the particular wave length of ultraviolet energy used. The wave length is dependent first on the type of generating equipment used, and finally on the filter employed to remove the visible light that may be present. A number of so-called ultraviolet lamps are listed and described, together with suitable filters known to be available. Scheelite fluoresces brilliantly with wave lengths of 2200 to about 3000Å., but not with longer wave lengths. The most convenient and efficient sources of ultraviolet for scheelite fluorescence are portable and laboratory units designed particularly for use with scheelite. So-called ultraviolet light globes of the photo-flood type emit wave lengths too long to cause scheelite to fluoresce. Attention is called to the minerals that fluoresce in a manner similar to scheelite, which necessitates a check test by means of characteristic physical properties. Chemical tests are the final authority both for identity and content of tungsten in scheelite ore. Introduction Recent development and extensive use of fluorescent lighting make it unnecessary to explain what fluorescence looks like. The fluorescent light tube is in reality a mercury vapor arc, which generates ultraviolet energy. Coating the inside walls of the tube is a substance, called a phosphor, that converts the ultraviolet rays to visible rays of light. In a like manner, certain minerals will transform ultraviolet energy to visible rays of various colors. The phenomenon of brilliant fluorescent colors cannot be satisfactorily described or reproduced photographically; a display must be seen to be appreciated. Only a few years ago fluorescence was regarded primarily as a source of entertainment, chiefly in spectacular displays of specimens in museums. The brilliant fluorescence of willemite, a zinc ore mineral, at Franklin, New Jersey, was utilized quite early in checking the efficiency of certain milling operations. Fluorescence has been used extensively in exploring for scheelite, as well as in mining this ore, during the past 10 years. The use of fluorescence in detecting scheelite, an important tungsten ore mineral, is well established, and much success has attended this new method; scheelite is a very inconspicuous white to gray mineral in ordinary light, but it

Jan 1, 1949

By John W. Vanderwilt

The fluorescence of scheelite has been an important aid in recent years in the discovery and development of scheelite deposits. The use of fluorescence of synthetic compounds in industry, particularly in advertising, also has expanded greatly during the past decade. As a result, a number of new and convenient units for producing ultraviolet energy have become available, which have led to a greater application of fluorescence in the study of minerals. Studies have shown that the fluorescent color of a mineral may vary: (I) with the kind and quantity of trace elements, and (2) with the particular wave length of ultraviolet energy used. The wave length is dependent first on the type of generating equipment used, and finally on the filter employed to remove the visible light that may be present. A number of so-called ultraviolet lamps are listed and described, together with suitable filters known to be available. Scheelite fluoresces brilliantly with wave lengths of 2200 to about 3000Å., but not with longer wave lengths. The most convenient and efficient sources of ultraviolet for scheelite fluorescence are portable and laboratory units designed particularly for use with scheelite. So-called ultraviolet light globes of the photo-flood type emit wave lengths too long to cause scheelite to fluoresce. Attention is called to the minerals that fluoresce in a manner similar to scheelite, which necessitates a check test by means of characteristic physical properties. Chemical tests are the final authority both for identity and content of tungsten in scheelite ore. Introduction Recent development and extensive use of fluorescent lighting make it unnecessary to explain what fluorescence looks like. The fluorescent light tube is in reality a mercury vapor arc, which generates ultraviolet energy. Coating the inside walls of the tube is a substance, called a phosphor, that converts the ultraviolet rays to visible rays of light. In a like manner, certain minerals will transform ultraviolet energy to visible rays of various colors. The phenomenon of brilliant fluorescent colors cannot be satisfactorily described or reproduced photographically; a display must be seen to be appreciated. Only a few years ago fluorescence was regarded primarily as a source of entertainment, chiefly in spectacular displays of specimens in museums. The brilliant fluorescence of willemite, a zinc ore mineral, at Franklin, New Jersey, was utilized quite early in checking the efficiency of certain milling operations. Fluorescence has been used extensively in exploring for scheelite, as well as in mining this ore, during the past 10 years. The use of fluorescence in detecting scheelite, an important tungsten ore mineral, is well established, and much success has attended this new method; scheelite is a very inconspicuous white to gray mineral in ordinary light, but it

Jan 1, 1949

By R. F. Mehl, G. V. Smith

THE decomposition of austenite in steels, because of its immense practical importance, has been subjected to extensive study in recent years from the point of view of the mechanism of the process.1-3 Although much information has been acquired, a number of questions, principally of theoretical interest, remain. One is that of the atomic-crystallographic mechanism by which each of the various reaction products forms. The isothermal reaction products of the eutectoid decomposition in plain carbon steels (to which this study is restricted) have conveniently been classified in three general groupings-pearlite, bainite, and martensite. Of these several products, pearlite and martensite have been studied extensively, but bainite has received only scant attention. As a result, the mechanism of the formation of pearlite and that of martensite are now fairly well understood while a great deal of uncertainty exists regarding bainite. PEARLITE Pearlite forms from austenite by the precipitation of alternate platelets of cementite and ferrite, which grow into the austenite matrix .2-5 The rate of reaction may be described in terms of a rate of nucleation and a rate of growth.2.3 Mehl and Smith6 have attempted to determine the lattice relationships existing between the ferrite in pearlite and the parent austenite. Using a pole-figure method of analysis, it was found that a limited number of ferrite orientations resulted from the decomposition of a single grain of austenite; it was not possible, however, to decide between two assumed ideal relationships, both of which appeared to account for the experimentally determined pole figure. It was definitely shown, however, that the relationship obtaining was quite different from that determined for the proeutectoid separation of ferrite.7 No attempt was made to determine the habit plane (matrix plane to which the precipitate lies parallel) of the pearlite lamellae. Belaiew8 earlier had stated that the number of directions assumed by the pearlite lamellae in a single grain of austenite was 12 (no details were given) and concluded wrongly, as Mehl and Smiths have pointed out, that the lamellae delineate the [210] planes of ferrite.* MARTENSITE It is known that martensite is a transitional constituent of body-centered tetrag-

Jan 1, 1942

By Edgar Stansfield

Introduction First, I should define more closely the vague term 'recent work' that appears in the title of this paper. Following the period of depression that was an aftermath of the first Great War, the Research Council of, Alberta carried on for ten years without a Council and without a financial yote by the Legislature. In November, 1942, a new Council was formed, under the chairmanship of the Hon. N. E. Tanner, Minister of Lands and Mines, and a vote was granted by the Legislature early in 1943. By 'recent work', I mean work during the present regime. The Council is now going full steam ahead, or would be if it could get suitable technical assistance and required apparatus and materials. Lack of these has so far made unnecessary my responsibility for seeing that we do not exceed our estimates. The Annual Meeting of the Research Council will be held in November (1945), and at that meeting the programme of work for next year will be discussed. The present time is therefore the correct time for any of you who may have ideas as to work which might profitably be undertaken by the Council, to submit these ideas for consideration. I propose to discuss my subject under several headings, and to give enough of these to show that the Council has wide interests.

Jan 1, 1946

By J. Rourke, F. S. Minshall, E. G. Zukas, C. M. Fowler, O&apos

The Hugoniot curves were determined for Fe-Si alloys containing up to 7 wt pct (13 at. pct) Si. The pressure of the transition increased as the silicon content of the alloy increased. Single crystals of 2.9 wt pct Si-Fe were also studied. The pressure of the transition was not dependent on crystallo-graphic orientation. All of the Neumann bands (mechanical twins) were attributable to (112) planes but not all of the {112} planes showed twin markings. A thorough study of the iron Hugoniot (the relationship between specific volume and pressure) under plane wave shock loading revealed a pressure transition at about 130 kbar shock pressure. The results of this investigation were reported by Bancroft, Peterson, and inshall1 in 1956. At the time of this discovery, it was felt that this was probably the a, to y transition normally found in iron and many of its alloys. Subsequently a number of iron alloy systems were surveyed in which the alloying element has a considerable effect on the normal a, to y transformation. The influence of carbon and nickel and/or chromium have already been reported.2,3 At the present time, there appears to be some doubt that this pressure transition is the usual a, to y transition In this study, Fe-Si alloys containing up to 7 wt pct (13 at. pct) Si were chosen for several reasons. To the present, the transition has been found only in iron-base alloys which were originally in the a, phase (bcc). Secondly, the y loop at atmospheric pressure extends to only about 2.5 wt pct Si. If the transition were a, to y, then one might expect a rather drastic pressure effect for alloys containing more than 2.5 wt pct Si. Finally, single crystals of Fe-Si alloys large enough for shock loading studies are readily available thereby making it quite easy to determine the effect of crystal orientation on the transition pressure and on the twinning behavior of the alloy. EXPERIMENTAL PROCEDURE Fe-Si alloys containing up to 7 wt pct Si were produced by normal vacuum casting procedures. Single crystals of Fe-2.9 wt pct Si were purchased from Monocrystals Co., Cleveland, Ohio. The orientations of these crystals were determined and samples cut so that the shock wave would be parallel (to within 1.5 deg) to either the (loo), (Ill), or (112) principal orientations. Three distinct experimental testing techniques were used. First, the pin technique, described elsewhere,4 was used to determine the transition pressure for the polycrystalline alloys as well as for the (111) and (112) orientations of the 2.9 wt pct Si single crystals. Secondly, the recovery studies, described in detail in an earlier paper,2 were used for determining the effect of alloy composition and crystal orientation on the plastic II compression-plastic I rarefaction interaction zone for several specific shock pressures. Finally, measurements of pressures above the two-wave threshold were made on the polycrystalline alloys so that more complete Hugoniot curves could be constructed for this alloy system. The optical techniques described by Rice et al.5 were used to measure the shock and free surface velocities of the samples from which the Hugoniot data were obtained. This method is applicable only in the single wave region, since velocities are obtained from the measured total transit times of the disturbances through measured sample thicknesses.

Jan 1, 1963

By David Kwietnewski

Roadheaders are gaining widespread acceptance in North America as a means for mechanical tunnel excavation. Until recently, almost all of the large-scale North American tunnel projects were excavated one of two ways ? the tried and true drill-and-blast method or with the use of tunnel boring machines (TBM), the hi-tech super-excavators. TBMs enjoyed fast-growing popularity worldwide as TBM manufacturers offered greater technology to meet the demand of the civil tunnel industry in the late 20th century. Recently, though, more tunnel projects, large and small, can thank the brute force of a roadheader for getting the job done.

Jan 1, 2011

By Ghassan Skybey

Australian coal mines uses state of the art technology in coal rib reinforcement. This paper highlights the development over the past 15 years in coal rib support technology, along with the advantages and disadvantages of each system. It also outlines the current trend in using coal rib reinforcement in speeding up the dowels installation to improve the current low drivage rate. An innovative cuttable dowel is discussed which improves the drivage rate. This new dowel is self anchoring it uses no resin anchor it has a 5 tonnes (5.51 tons) anchor capacity and can be fully installed in approximately 10 seconds.

Jan 1, 1995

By N. Plint, E. T. Pinkney

Copper segregation developments within the Anglo American Group are described with particular reference to the work of the TORCO Project Team. Some radical differences have been adopted in the mechan-ical approach as compared with methods used by previous workers. Most important among these are the following: (1) The heating unit is a fluidized-bed roaster. (2) A moving bed segregation chamber is used in which a packed bed of heated ore, to which reagents have been added, moves slowly downwards under gravity and is discharged at a controlled rate by means of a suitable valve mechanism. (3) The quantities of reagents used (sodium chloride and some form of carbon) are only a small fraction of those recommended by other investigators. (4) Retention times of only 2 min have been satisfactory for the complete segregation of many types of ore. Project TORCO is the code name given by Anglo American Corp. of South Africa, Ltd., to the investigation undertaken in Zambia to develop a plant capable of treating large tonnages of refractory copper-bearing ores by the segregation process. The process has now been under investigation for six years (1960-66) and during that period work has progressed from bench-scale laboratory tests through small-scale pilot-plant work to a 500-tpd commercial pilot unit. Test work has been carried out mainly on the ores of the Zambian Copperbelt and results have been encouraging. Recoveries on the order of 90% have been obtained on all Copperbelt ores tested with high concentrate grades. PRELIMINARY INVESTIGATION Laboratory scale segregation test work on Nchanga banded sandstone ore and oxidized ore from Kansan-shi was originally conducted by Professor Maurice Rey. SociCtC Miniere et Mktallurgique de Pefiarroya, in 1957. Both ores responded favorably to the process. In November, 1960, the consulting engineers of Anglo American Corp. of South Africa, Ltd., initiated preliminary investigations on the application of the segregation process to Copperbelt ores. In early laboratory work, samples were heated in a closed, externally heated tube furnace for one hour at temperatures ranging from 800 to 830°C. The free moisture content of the ore feed was 4% and reagent additions were 0.5% salt and 1.0% coal. Both salt and coal were pre-crushed to -48 mesh Tyler.* All samples except an ore from the Bancroft mine responded well to the process and recoveries of over 90% were obtained. The presence of dolomite was responsible for the relatively poor recoveries from the Bancroft ore, as tests on one of the other ores with additions of calcite or dolomite confirmed. Recoveries dropped from 94 to 45% Grades of all the rougher flotation concentrates produced were low at 10-15% copper. The laboratory investigation was then followed up on a pilot-plant scale. An attempt was made to carry out the segregation process in a coal-fired 5-ft-diam fluidized-bed roaster. The feed consisted of a banded sandstone from Nchanga to which 0.5% sodium chloride had been added. Reducing conditions were maintained in the roaster by the addition of coal in excess of that required for heating the feed. The excess coal and added salt constituted the segregation reagents and the temperature of the bed was held at approximately 750°C. Recoveries of copper and grades of concentrates were low. The reasons for lack of success were: (1) The reaction is a gaseous one and a fluidized-bed roaster is therefore unsuitable as a segregation unit. (2) Coal in excess of that required for heating was introduced into the fluidized bed and under these conditions some of the copper would be reduced in situ. The term "reduced in situ" is used here to describe any copper mineral reduced to the metallic state in its original site within the ore particles. If this copper is to be recovered by subsequent froth flotation it must first be liberated from the gangue by grinding or some other method which, in practice, is usually not feasible on ores of this type.

Jan 1, 1969

By Akihide Hosokawa

The void growth and coalescence in model materials involving a pre-existing three dimensional void array (i.e. multiple layers of a void array) was studied by X-ray computed tomography (XCT) coupled with in situ tensile deformation. To reduce the recording time, a new technique called fast tomography was employed. The model materials used in this paper were fabricated by the combination of an ultra-short pulsed laser machining system and a diffusion bonding technique, and two different types of arrays were prepared namely, FCC 1 and FCC 2 type array. This methodology allowed the authors to capture the entire process of growth and coalescence events of a void array embedded in the metal matrix. The failures in the both materials involved internal necking and shear localization. One of the highlights of this paper is that the plastic strain at the onset of void coalescence was measured for each model material. These values are in fact the adequate values to be compared with the coalescence strain predicted by existing void coalescence models such as the Brown and Embury model, the Thomason model and the Pardoen and Hutchinson model. The comparison suggested that the Brown and Embury model underestimated the coalescence in neither of the current model materials, while the Thomason model and the Pardoen and Hutchinson model showed a quite good agreement with the result for FCC 1 material. On the other hand the result from FCC 2 material agreed with none of the models probably due to the geometry of the void array that is not compatible with the existing models.

Jan 1, 2010

By William B. Plank

For the first time in four years the number of mineral engineering students in the 228 engineering colleges of the U. S. and Canada exceeds 10,000. According to figures just released by the American Society for Engineering Education, the current enrollment of all engineering students is 222,178. The total of 10,274 mineral engineering students, undergraduate and graduate, is a 4% pct increase over a year ago. Total engineering is 11 pct larger than last year, about the same as in 1949-50, and 24 pct above 1950-51.

Jan 4, 1955

By MARK H. LAMB

(Canal Zone Meeting, November, 1910.) THE recent growth of a sentiment among cyanide-plant designers against the use of gravity-stamps for the crushing preliminary to cyanidation may be said to date from the almost simultaneous perfection of the ribbed tube-mill liner and of the tall, air-agitation tank. The first step in the resulting change of practice was the universal adoption of the tube-mill for fine-grinding and the use of coarse screening oil the battery. This was the beginning of the surrender of supremacy by the gravity-stamp ; since merely the single fact that it was a more economical machine for crushing fine had retained it in favor as compared with ball-mills, rolls, or steam-stamps. The surrender, however, is not yet complete. It is the universal practice to use rolls where a relatively small tonnage is to be crushed coarse, as, for example, when coarse concentration is included in the plan of treatment. Power, attendance, repairs, and first-cost are smaller for the rolls, under such circumstances, than for stamps; and it is becoming daily more apparent that, with no concentration to provide for, the use of rolls and tube-mills, without the complication of trommels and elevators required by concentration, is rapidly gaining favor in the eyes of the leading designers. The next step was the use of the rapid-running Chilean mill between the gravity-stamps and the tube-mill, which again narrowed the field of operation of the gravity-stamp while radically widening its screen-aperture. Such a combination of stamps and Chilean mill offers advantages when fine concentration is necessary, since the reduction in the Chilean mill call be adjusted easily and governed by varying the screen-mesh. But even concentration is now looked at askance. One of the leaders of this metallurgy has abandoned the separation and

Jul 1, 1910

By Frank G. Norris

Slag control is adjustment of the composition of the slag, especially with respect to the FeO content. The theoretical method of slag control would be to charge a mixture of pig iron and scrap of given composition into the furnace, to melt always at the same carbon, and, after a uniform ore addition, to tap with a constant slag composition. Such conditions are not even approximated. Both scrap and pig iron are of variable, and, in many cases, unknown composition. The charge is oxidized to a variable extent during melting. The result is that the FeO content of the slag, and consequently of the metal at tap, varies over a wide range. In order to make a nearly uniform product, this variation must be compensated for in some way. One way is to adapt the ladle deoxidation to the requirements of the metal. The other is to control the slag. In a general sense slag control may be considered as a method of compensating for variations in the composition of the charge and in oxidation during melting. The method of slag control for low-carbon steel was developed by Dr. Herty at our Butler plant3. Use of this method enables the furnace operator to tap heats at a more nearly constant FeO content and, therefore, to use a more nearly uniform deoxidation practice. The desired FeO and the accompanying deoxidation will depend on the application of the product. This statement implies that 0.10 carbon steel finished with a 15 FeO slag may be essentially different from a 0.10 carbon steel finished with a 30 FeO slag. In making low-carbon steel, the desired carbon places a lower limit on the FeO content of the slag, because the slag must be sufficiently oxidizing for proper carbon elimination. With this degree of oxidation, the phosphorus specification is met without difficulty, and there is little danger of phosphorus reversion. Thus a limiting factor in high-carbon heats is of slight importance in low-carbon heats. For heats of 0.05 to 0.07 per cent carbon, the FeO content of the slag may be controlled at

Jan 1, 1935

By Frank G. Norris

Slag control is adjustment of the composition of the slag, especially with respect to the FeO content. The theoretical method of slag control would be to charge a mixture of pig iron and scrap of given composition into the furnace, to melt always at the same carbon, and, after a uniform ore addition, to tap with a constant slag composition. Such conditions are not even approximated. Both scrap and pig iron are of variable, and, in many cases, unknown composition. The charge is oxidized to a variable extent during melting. The result is that the FeO content of the slag, and consequently of the metal at tap, varies over a wide range. In order to make a nearly uniform product, this variation must be compensated for in some way. One way is to adapt the ladle deoxidation to the requirements of the metal. The other is to control the slag. In a general sense slag control may be considered as a method of compensating for variations in the composition of the charge and in oxidation during melting. The method of slag control for low-carbon steel was developed by Dr. Herty at our Butler plant3. Use of this method enables the furnace operator to tap heats at a more nearly constant FeO content and, therefore, to use a more nearly uniform deoxidation practice. The desired FeO and the accompanying deoxidation will depend on the application of the product. This statement implies that 0.10 carbon steel finished with a 15 FeO slag may be essentially different from a 0.10 carbon steel finished with a 30 FeO slag. In making low-carbon steel, the desired carbon places a lower limit on the FeO content of the slag, because the slag must be sufficiently oxidizing for proper carbon elimination. With this degree of oxidation, the phosphorus specification is met without difficulty, and there is little danger of phosphorus reversion. Thus a limiting factor in high-carbon heats is of slight importance in low-carbon heats. For heats of 0.05 to 0.07 per cent carbon, the FeO content of the slag may be controlled at

Jan 1, 1935

By Shiou-Chuan Sun

The froth flotation of coal, differing greatly from that of most minerals1-5, is not improved but rather impaired by temperatures higher than room temperature6-10 This phenomenon has long taunted us for an explanation. Gayle and Associates 8,9 reported the lack of relationship between their contact angle measurements and their flotation of American coals under various temperatures. Bailey and Whelan6 stated that the viscosity of flotation reagents, offering some clue for their flotation of British coals at low temperatures, could not be put forward as an explanation either in whole or in part for the effect of temperatures on coal-flotation. In this paper, a froth hypothesis is proposed to explain the flotation behavior of coals under various pulp temperatures. Test work involved the flotation of coals and the frothing of reagents.

Jan 1, 1966

This is an abstract from Environmental Service and Technology (Vol 32 No 20 1998) which will be o finterest to South African Mining and Metallurgical Scientists, involved in chromium mining and Metallurgical processing. Maybe the scourge of our dams and reservoirs?the water hyacinth can be put to good use! The novel technology of phytoremediation embraces plant accumulation processes for the cleanup of toxic heavy metals and organic chemicals. Several plant species have been identified that are excellent hyperaccumulators of a number of heavy metals, e.g., Brassica juncea (Indian mustard) and Thlaspe caerulescens (Alpine pennycress). Other speciesincluding Myriophyllum brasiliense(Parrot?s feather), Salixsp. (willow), and Popullussp. (poplar) have also demonstrated phytoremediating abilities.

Jan 1, 1999

By G. Jim Cardwell

The question "what constituents should be determined?" is one that defies a simple answer, because earth scientist being what you are, the rock and mineral analyst will eventually be called upon to determine about three quarters of the elements in the periodic table. The concentrations of these analyses will range from as low as 1 ppb to 100% of the material being analyzed. The most important thing to remember about a quantitative analytical result is that it can only be an estimate of the concentration of the analyte present. A measure of the reliability of that estimate is given by statistically derived statements of the precision and accuracy of the measurement. When evaluating your data an understanding of precision and accuracy are of paramount importance. Precision is the measure of agreement between replicate values while the accuracy of a determination is the concordance between it and the true value. There is no quarantee, however, that a precise answer is an accurate one. The numerical difference between the two values is the error. When evaluating your data, the repeats analyzed with your samples will identify the precision and control standards of U.S.G.S. or Canadian Certified Materials quality will identify the accuracy. The main problem is this data is routinely withheld from the report, or was it ever included in the analysis of your samples?

Jan 1, 1983

Never known as a conference to shy away from its share of off-color jokes, the Colorado Mineral Processing Division?s Annual Meeting returned to the Broadmoor Hotel in Colorado Springs, CO April 26-28 for its 62nd edition, this one held under the theme ?Does size matter (is bigger always better).? With the predictable jokes sprinkled in here and there, and a few unpredictable ones as well, the three-day conference featured a healthy mix of talks about some of the latest technical developments in the field of mineral processing, as well as insightful looks at some new operations in the western United States. This year, the Colorado MPD also launched the Wagner Equipment Student Scholarship program.

Jan 1, 2012

By W. P. Diamond

The Bureau of Mines has been involved in the drilling of vertical, horizontal, and directional coalbed gas drainage boreholes for mine safety since 1964. In that time, boreholes have been drilled in most of the major coal regions of the United States under a wide variety of geologic conditions. Many of the geologic conditions that occur in the coal measures are detrimental to gas drainage; others may be beneficial. Analytical techniques to determine the gas content of coal samples and evaluate regional trends of gas distribution have been developed. Drilling techniques that maximize the acquisition of coalbed gas data and geologic information have been determined. Although some of the geologic factors influencing the placement and potential success of coalbed gas drainage boreholes have been reported in papers on individual projects, a complete, systematic compilation has not previously been available. The objective of this paper is to pro- vide information on specific geologic factors that should be considered prior to, during, and after the drilling of coalbed gas drainage bore-holes. Many of the commonsense considerations that have been learned through many years of Bureau of Mines experience, but have generally not been reported formally, are included for those who may be considering coalbed gas drainage drilling for the first time, or who have not had the opportunity to encounter a substantial number of geologic situations.

Jan 1, 1982

By George Scott

MANY requests for information as to the possibility of washing coals to some predetermined percentage of ash or sulfur have suggested that the producers aim to satisfy some degree of purity set by the user of the fuel, rather than to attain the greatest economic benefit to all concerned. This paper is written to show that the highest economic purity of washed coal can be determined from washability studies of the raw coal, costs of mining and washing coal, and data on the effect of ash and sulfur on the value of the coal for the particular use for which it is intended.

Jan 1, 1929

By F. D. Rosi, C. A. Dube, B. H. Alexander

WHEN a deformed polpcrystalline metal is heated to a sufficiently high temperature, a recrystallized structure develops which consists of small, essentially stress-free grains. This transformation is referred to as primary recrystallization. Under certain conditions, on prolonged annealing of the specimens, a type of grain coarsening occurs in which a small number of grains commence to grow at various points by devouring the neighboring finegrained primary structure, which, in itself, exhibits a marked stability toward normal grain growth. This grain coarsening process has been referred to by Burgers' as "secondary recrystallization" or "exaggerated grain growth." Although much work has been done on recrystallization and growth processes, present knowledge of the factors which determine the occurrence and growth of secondary grains is inadequate for the advancement of a theory which accounts for the observed characteristics of this recrystallization phenomenon. In this respect, it would be important to make measurements of the velocity of growth of these large secondary grains. The early work of Feitnecht2 on aluminum showed that the size of secondary grains increased with temperature and time, suggesting that such measurements would be possible. More recently, Burgers1 found that the growth velocity of these grains in aluminum was constant over a large time interval, as is generally found for the growth velocity of primary grains in a uniformly deformed test piece.3-5 It is reasonable to expect that the determination of the activation energy of the secondary growth process might lead to a better understanding of the underlying atomic mechanism. This investigation, therefore, is one of a series primarily designed to measure the growth velocity of secondary grains at various temperatures for silver, copper, and aluminum. It is hoped that these studies along with those of orientation relationships, will establish a sound basis for theorizing as to the origin and nature of the secondary transformation. Experimental Procedure The metal used in the present investigation was high-purity silver (999.9 fine), which was supplied in the form of cold-rolled plates 0.250 in. thick. These plates were annealed at 500°C for 1 hr and then straight-rolled to a thickness of 0.04 in. in three reductions of approximately 45 pct, followed in each case by an anneal at 450°C for 1/2 hr. The 0.04 in. sheets were given a final reduction of approximately 50 pct, which resulted in a thickness of 0.02 in., thereby insuring two-dimensional crystal growth. Individual specimens of this material about 1x3 cm were used for all heat treatments, unless otherwise noted. The annealing was carried out under an atmosphere of argon in an Inconel tube furnace whose temperature was controlled to within -+2°C. Metallographic examination of the secondary transformation was accomplished by mechanically polishing the specimens on one side to approximately one half their thickness through 2/0 metallographic emery paper, and then electrolytically polishing in a solution of potassium ferrocyanide and sodium cyanide. With a current density of approximately 20 amp per sq dm, the time required to obtain a satisfactory surface varied from 3 to 5 min. Standard potassium bichromate was used to etch the electrolytically polished surfaces. A heavy etch with this solution produced a sharp contrast between the secondary grains and the fine-grained primary structure, darkening the latter while leaving the large secondary grains bright. All area measurements of the secondary crystals were made with a planimeter on enlarged tracings of the grains.

Jan 1, 1953