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By Ramesh Malhotra, Hubert E. (Deceased) Risser

THE WORLD Coal, as a source of energy and as a source of coke for the smelting of iron ore, has contributed significantly to the development of every major industrial nation of the world A number of other materials-oil, natural gas, wood, waste materials, water, and, in some applications, nuclear materials -can be used satisfactorily for the generation of heat and energy, but no generally acceptable and economic substitute has been found to supplant coke in iron ore smelting in conventional blast furnaces. In the development of many nations, coal provided the initial source of energy for industrialization Although coal provided more than 60% of the world's energy each year between 1902 and 1929, oil and natural gas have surpassed it as a source of energy in more recent years (Ref. 38, pp. 439, 441). Despite the rapid rise in importance of other fuels, a considerable amount of the total energy consumed is still supplied by coal. In 1972, coal supplied 32.1 % of the total world energy (Ref. 49, pp. 2-3). To produce this energy, 2.4 billion metric tons of coal were consumed-a 16.0% increase over the amount consumed in 1962. A further worldwide increase in the amount of coal used to supply energy is projected. According to Dr. Karlheinz Bund (Ref. 37, p 145), by the year 2000 world coal consumption could amount to 5 billion mt. Coal Resources and Production The world's coal resources are estimated to be about 10,872 billion mt. Of this amount, 1,297 billion mt are classified as measured reserves (Ref. 50, p. 57). In Table 13.A.1 the estimates of measured reserves and total resources, recent production, and the ratio of measured reserves to production of major coal-producing countries are shown. About 90% of the world's total coal resources are estimated to be in the USSR, the United States, and China. The United States ranks second in the world in coal resources, but in measured reserves, it ranks first. Because of the difference in rate at which available coal resources are being exploited, the ratio of measured reserves to actual production varies widely among areas and countries. France and East Germany have the lowest reserve to production ratios, 49.5 and 60.1, respectively. In Mexico, where currently less than 5 million mtpy of coal are produced, the ratio is 1257 For all countries producing more than 200 million mtpy of coal (except East Germany), the ratio ranges from 350 to 670. For the United States, the ratio is 669.7. In Table 13.A.2, distribution of the world's coal resources by area is shown. More than 97% of the total resources lie in the northern hemisphere, with Asia, including European USSR, having 63.4%. Only 1.9% of the total coal resources are estimat-

Jan 1, 1976

By A. C. Fieldner, W. A. Selvig

Ash in coal has always becri regarded as an undesirable substance, as the heat content of a coal dccreases in direct proportion to its ash contcnt. It represents so much inert materid that has to be transported, handled when the coal is burned, and finally disposed of. W. R. Roberts, in an address bcfore the Engineers' Society of Western Pennsylvania, Pittsburgh, on Sept. 29, 1925, said that on an annual output of five hundred rnillion tons of coal, a reduction of 3 per cent. of ash means fifteen million tons of refusc and a decrcase of $30,000,000 in freight charges. Ash also often prevents effieient utilization of the coal through the formation of clinker causcd by the mcltirig of the ash constituents when subjected to heat. The mineral constituents of coal may be of such nature as to make the coal unsuited for speeifie uses as for instance, high-sulfur coal for making metallurgical coke. While the usual proximate analysis of coal gives the amount of ash, it gives no information as to the nature and coniposition of the ash nor of the minera1 constituents from which the ash is produced. For the efficient washing of coal to remove ash-forining constituents it is desirable to know the composition and distribution of the ash-fonning constituents. Obviously such information is also desirable for the most efficient utilization of coal. Nature and Composition of Coal Ash Coal ash may be defined as the inorganic residue remailning after cornplete ignitior of coal. It is dcrived from the mineral constituents of thc coal. The ash-forming constituents may be roughly classified as inherent impurities and extraneous impurities. The former are mixed intimately with the coal substance, and arc derived either from the original coal-forming material or from external sources such as sedimentation and preeipitation while the vegetal coal-forming plant remains accumulated. The latter are present in the coal bed as partings, bands or nodules of pyrite! slate, shale, calcit,e, bone, etc. These are formed either during the laying down of the coal bed, or subsequently. Flag-

Jan 1, 1927

By Elwood G. Haney, R. N. Parkins

Stress corrosion cracking of two heats of 18 pct Ni maraging steel in rod form immersed in an aqueous solution of 0.6N NaCl at pH 2.2 has been studied on un-notched specimens stressed in a hard tensilf machite. Austenitizing temperature in the range 1830 to 1400 F has been shown to have a marked influence on the propensity to crack, the loulest austenitizing- temperature producing the greatest resistance to failure. In the nzosl susceptible conditions, the cracks followed the original austenile grain boundaries; but when tlze steels zcere heal treated to inproze their resistance to stress corrosion, the cracks becatne appreciably less branched and slzouqed significant tendencies to become trans granular. Electron metallography of the steels indicated the presence of snzall particles, possibly of titanium carbide, along- the prior austenite grain boundaries and these particles u:ere more readily detectable in the structures that were most susceptible to cracking. Crack propagation rates, which appeared to be dependent upon applied stress and structure, were usually in tlze reg-ion of 0.5 mm per hr and may, therefore, be e.xplained on tlze basis of a purely electrochetnical ,nechanism. However, there is some ezliderzce from fractography that crack extension may be assisted by ttlechanical processes. Anodic stit)zulation reduced the tiwe to fracture, although cathodic currents of small magnitudes delayed cracking-; further increase in cathodic current resulted in a sharp drop i,n fracture litne, possibly due to the onset of hydrogen ewbrittlement. THE use of the high strength maraging steels, with their attractive fracture toughness characteristics, is restricted because of their susceptibility to stress corrosion cracking in chloride solutions. Although this limitation has resulted in investigations of the stress corrosion susceptibilities of these steels, there have been few systematic studies aimed at defining the various parameters that determine the level of susceptibility. It is the case that the usual tests have been performed with the object of defining some stress or time limit, on unnotched or precracked specimens, within which failure was not observed,' but while such results may be of some use in design considerations, they are necessarily concerned only with the steels as they currently exist and not with their improvement to render them more resistant to stress corrosion failure. This omission may be considered unfortunate because the indications are that stress corrosion in maraging steels shows dependence on structure in following an intergranular path, and since experience with other systems of intergranular stress corrosion crack- ing is that susceptibility may be varied by modifying heat treatments, a similar effect may be expected with maraging steels. It is sometimes from such observations that a fuller understanding of the mechanism of stress corrosion crack propagation begins to emerge, leading in time to the development of more resistant grades of material. The present work was undertaken to study only one aspect of the influence of heat treatment upon the cracking propensities of the 18 pct Ni maraging steel, namely the effect of austenitizing temperature, although certain ancillary measurements and experiments have been undertaken. EXPERIMENTAL TECHNIQUES Most of the measurements were made on a steel, A, having the analysis shown below, although a few results were obtained on a steel, B, having a slightly different composition. Both steels were supplied in the austenitized condition, A as 3/8-in-diam rod and B as 1/2-in.-diam rod. Cylindrical tensile test pieces were machined from the rods: the overal length was 2 1/2 in., the gage length 1 in. and the diameter 0.128 to 0.136 in. The stress corrosion tests were carried out with the specimens strained in tension in a hard beam testing machine, the necessary total strain being applied to the specimen over a period of about 30 sec, after which the moving crosshead was locked in position and the load allowed to relax as crack propagation proceeded; the load relaxation was recorded. The load was applied after the specimen had been brought into contact with the corrosive solution, the latter being contained in a polyethylene dish having a central hole through which the specimen passed, leakage being prevented by the application of a film of rubber cement. The specimen was in contact with the solution for over half of its gage length and the solution was exposed to the air during testing. The solution was prepared from distilled and deionized water to which NaCl was added, 0.6N, and the pH adjusted to 2.2 by HCl additions. The composition of the solution

Jan 1, 1969

The Manufacturer's Viewpoint A prominent manufacturer of mining 'machinery not long ago expressed himself as being confident that he was securing the best kind of publicity for his product through the advertising pages of the monthly Bulletin of the American Institute of Mining Engineers. Such an expression coming from such a man is highly gratifying; yet it is justifiable when the high quality of reader and subscriber is taken into consideration. In fact, the majority of those using our advertising pages feel the same. It is to be regretted, of course, that others catering to our field do not realize the means at their disposal for presenting the points of interest of their product to the mining man. The question has been asked, " Do your members read their Bulletin?" They not only read the editorial pages, but they "admit being up-to-date enough to peruse the advertising section to "see what is new." The next question the prospective advertiser asks is, " Will the Bulletin bring inquiries?" The answer to this question holds good for any publication having as subscribers those who have purchasing or recommending power-yes, if the article advertised is not a stock one, that has been before the public for any length of time. To secure inquiries on, say, a standard centrifugal pump or any other standard product, the features of which are well known, is a most difficult proposition. Yet, of course, some inquiries are secured, but mostly from those having use for the catalogue or trade literature for reference purposes. It is safe to say that the traceable returns from advertising in trade publications hardly, if at all, pay for the advertising. The real returns are intangible, and result from the constant publicity, and keeping ?everlastingly at it." Who can say what subconscious effect is taking place when an advertisement is "glanced at," to say nothing of the effect produced when the copy is attractive and interests the reader. Time after time it has been proved that sales have been secured as a result of an advertisement, yet no inquiry had been made directly traceable to advertising.

Jan 8, 1915

By Henry F. Adams, Guy H. Ruggles

IN this paper the authors aim to chronicle the experience and salient points brought out in changing flotation reagents at a concentrator which had probably been using a mininium amount of oil at a minimum cost per ton, to a more complicated system requiring a partial chemical control. The original oils were coal tar and pine oil. The new reagents are lime, xanthate and pine oil. It was found that there were no insurmountable difficulties and eventually the cost of the new reagents per ton of ore proved to be very little more than that of the old. LIME PLANT When the question of handling lime came up there were two propositions open: (1) to handle the lime dry; (2) to handle it wet in the form of an emulsion. Granting that a dry lime feeder would function properly, delivering lime uniformly, the chief objection was the dust that would be raised when these feeders were being charged or operated, as the only possible location was on a gallery beneath which men were working. With this objection the handling of lime as an emulsion seemed to be the better scheme. The lime plant which was first installed was for experimental work on one section. This was gradually changed and developed until it was of sufficient size to accommodate 20 sections. The various changes will not be discussed and the following description deals only with the fully developed plant. Crude as it is, and perhaps somewhat expensive to operate, the lime-handling plant has been quite successful. Much has been learned which will pave the way for a better installation in the future. Burnt lime is received loose in standard gage box cars. This is the product of the kilns and has had no screening or sorting. A grab sample is taken from each car as it is unloaded. An average of the analyses of samples from 44 cars gave the following: [ ]

Jan 1, 1928

By George B. Langford

ON THE QUESTION of postwar controls there are today three schools of though ; some advocate state control of everything the socialists ; second are those who advocate the removal of all governmental control over industry - the freedom of enterprise ideal ; and third are those who advocate a middle course - sufficient control to stabilize economic and industrial life, and to prevent violent fluctuations such as we saw in the interwar years. I advocate this third course. I firmly believe un free enterprise, but not in freedom of enterprise, or laissez faire, and there is a great and significant difference between these two.

Jan 1, 1944

By Charles Willis

THE time is no longer when a man can act as an independent unit; the appreciation of the interdependence of one man upon another has emphasized the importance of the social unit. Epidemics have made us recognize that even a man's health is not distinctly his own to control as he pleases. The physical examination of workmen previous to employment started with an effort to prevent the spread of tuberculosis, for tuberculosis may be .detected in its early stages and cured. But it was soon found that many other diseases were detected and the saving of lives made possible. The physical examination does not mean the elimination of the unfit-on that basis it would utterly fail- but rather the measuring of a man's physical fitness and placing the man where he can do the best for himself, his fellow worker, and the company. Industry as a whole cannot expect to live up to the standard of physical examination set for the army, nor should it expect to do so, for in all branches of industry there are types of work that do not require -the same amount of endurance as does army work, and the placing of men with physical limitations in the work for which they are' capable permits a higher average of physical fitness for the work requiring physical excellence.

Jan 7, 1919

By Albert Mendelsohn, Charles F. Jackson

The system of stoping described in this paper was first introduced at the Champion mine of the Copper Range Co., Painesdale, Mich., in 1929, and since that time has been developed to a high state of efficiency. The method was devised to overcome some of the objections to the system of horizontal cut-and-fill stoping formerly employed at this mine and has done so successfully. The objections to the old system became more pronounced as the depth of mining operations increased and a change became a matter of necessity. While the combination of conditions encountered at the Champion mine is rather unusual, it is believed that the sublevel system developed there could be employed advantageously at other mines, though certain modifications might be necessary. This paper describes the method and the results obtained through its use, and suggests modifications for making it applicable under quite different conditions from those at the Champion mine. Champion Lode The lode being mined at the Champion mine is the heavily brecciated top of what is known in the district as the Baltic lava flow. The brecciated portion of the lode varies from 6 to 50 ft. in width. Under this breccia is the thinner, tighter, amygdular portion of the lode; under the amygdular portion is the trap footwall. Native copper is found deposited in the rock fragments of the breccia, in the cementing material of the breccia, in the amygdules and in the trappy rock under the amygdular part of the lode. In some places masses of copper many tons in weight extend far into the footwall of the lode. The Baltic lode on Champion property is 8000 ft. long, very straight along the strike, and dips uniformly 70' to the west for 3000 ft. in depth, at which point the dip begins to flatten slightly. The width of the copper-bearing portion of the lode varies from 10 ft. to as much as 80 ft. in a few places; the average width now mined is 17 ft. The lode rock is hard—the standard one-man drilling machines used in the mine drill from 10 to 14 in. per minute when mass copper is not

Jan 1, 1932

By D. H. Desy, L. C. Fincher

The magnesium-rich end of the Mg-Ti phase diagram was investigated. The liquidus, solidus, and solvus boundaries to 1 pct Ti were established. All alloys were prepared by saturating molten magnesium with titanium in a consumable titanium crucible under inert gas maintained at 230 psig. The liquidus of the Mg- Ti system was determined by analysis of dip samples taken from 700° to 1300°C under equilibrium conditions in a pressurized inert atmosphere furnace and by analysis of small ingots rapidly poured and quenched from 1400° to 1500°C. The solubility of titanium in magnesium ranged from 0.018 wt pet Ti at 700°C (0.012 wt pet at 650°C by extrapolation) to 1.035 wt pet Ti at 1500°C. The solidus for compositions ranging from 0.03 to 1.00 wt pet Ti was determined to be 650° ± 1°C by thermal analysis. The titanium solid solubility values ranged from 0.08 wt pet at 350°C to 0.19 wt pet by extrapolation to 650°C. The freezing reaction is peritectic. No intermetallic compounds were found in the system; the phase in equilibrium with molten magnesium saturated with titanium was found to be titanium with magnesium in solid solution. Solid titanium will dissolve at least 1.32 wt pct Mg. PREVIOUS investigations of the Mg-Ti system have shown considerable disagreement on the solubility of titanium in liquid magnesium. Furthermore, the solid solubility of titanium in magnesium has not been well established. Liquidus curves for previous work and for the present investigation are shown in Fig. 1. Aust and Pidgeon1 used a dip-sampling method on molten magnesium held in equilibrium with solid titanium under a protective atmosphere to determine the solubility and found that it ranged from 0.0025 wt pet Ti at 651°C to 0.015 wt pet Ti at 850°C. Eisenreich2 introduced titanium into molten magnesium by means of TiCL4 adsorbed on BaCl2. Ingots were then cast at various temperatures. Making the assumption that only the titanium dissolved in magnesium at the time of casting was soluble in H2SO4, Eisenreich determined the solubility of titanium in molten magnesium to range from 0.003 wt pet at 655°C to 0.115 wt pet at 800°C. Eisenreich also determined the solid solubility of titanium in magnesium to be 0.015 wt pet at room temperature and 0.045 wt pet at 500°C. Since the solid solubility just below the freezing temperature for the bulk of the alloy was much larger than the liquid solubility just above the freezing temperature, Eisenreich concluded that the freezing reaction was peritectic. Obinata et al.3 equilibrated molten magnesium with titanium in hermetically sealed titanium containers which were then furnace-cooled. The titanium content of the magnesium was then determined and found to range from 0.170 wt pet at 700°C to 0.85 wt pet at 1200°C. No intermetallic compound was found in the system. The Armour Research Foundation4 determined two points on the solvus by electrical resistivity methods: 0.00057 wt pet at 200°C and 0.0008 wt pet at 300°C. At higher temperatures, data were meaningless with no trends observable. The authors of this report believed that the lack of significant data at the higher temperatures was due to variations in specimen geometry, although there was no positive evidence to verify this supposition. The present investigation was undertaken to clarify the uncertainty in both the liquidus and solvus of the magnesium-rich end of the Mg-Ti system. EQUIPMENT AND MATERIALS The equipment used in this investigation, with some modifications, was essentially that used by Crosby and Fowler5 in their determination of part of the Mg-Zr phase diagram. The equipment, as modified for this work, is shown in Fig. 2. It consists of a sealed furnace chamber which can be pressurized with inert gas so that melts can be made above the boiling point of magnesium at atmospheric pressure. Melts are made by induction heating in a titanium crucible which, after diffusion of sufficient magnesium into the walls of the crucible to saturate the titanium at the sampling temperature, comprises the solid phase in equilibrium with the molten magnesium. Dip samples may be taken with the sampling tube, or the entire furnace may be tilted so that ingots may be poured into a mold in the side chamber. The principal difference from the earlier apparatus is in the thermocouple, which in the present equipment is enclosed in a protection tube and immersed directly in the melt. The tips of both the thermocouple protection tube and the sampling tube, which dip into the melt, are made of high-purity titanium. The 4 1/2-in.-long titanium tip of the sampling tube is threaded into a steel tube, O in Fig. 2, which extends through the top of the furnace. To determine whether the temperature at the tip of

Jan 1, 1969

By R. Philip Hammond

Monazite has had a Cinderella-like history. Although nearly go per cent pure rare-earth compound (rare-earth phosphate) it was sought at first not for the rare earths but for the sake of a minor constituent—thorium. The thorium, essential for the Welsbach gaslight mantle, was present in only small quantities and the principal constituents, the rare earths, were largely discarded. Gradually, however, the rare earths have developed uses of their own and today have left the thorium far behind in value. Occurrence Monazite was first produced commercially about 1886, in North Carolina, where it was collected in small sluices by farmers who found it in stream beds on their land. The deposits were later exploited on a larger scale, but were mostly abandoned in a few years, when monazite from Brazil came upon the market in far larger quantities. Domestic production ceased entirely in 1906. The Brazilian source is still active, together with Indian, Dutch East Indies, and Australian deposits. Several other localities in the United States have yielded monazite, but none of these has produced commercially as yet. Monazite occurs originally in pegmatite~ and gneisses, through which, unfortunately, it is scattered in highly dispersed form. All commercially useful deposits consist of transported monazite sands liberated by erosion and concentrated by the action of water, which has sluiced away lighter materials and concentrated the heavy (D = 5.0 to 5.2) grains of monazite, together with ilmenite, zircon, garnet, and other dense minerals. The Carolina deposits were in stream beds; most of the other deposits mentioned are on or near the seashore, where the action of the waves has served to concentrate the monazite. In most cases today, the sands are worked to obtain the ilmenite and zircon, as well as monazite. The minerals are separated by means of sluices, dry tables, and magnetic separators, and each is finally obtained nearly pure. No crushing or grinding is necessary. The concentrates are shipped in fiber bags. Composition of Monazite As Table I illustrates, monazite is the anhydrous orthophosphate of the cerium Table i.—Typical Analysis of a Monazite Sand (India). Per Cent Thorium oxide............................. 8.1 Cerium oxide.............................. 30.6 Lanthanum oxide........................... 15. 7 Neodymium oxide.......................... 10.5 Praseodymium oxide........................ 2. 9 Samarium oxide............................ 1.0 Europium. gadolinium, and terbium oxides.... 0.7 Yttrium oxide.............................. 0.4 Dysprosium, holmium, erbium. thulium, ytterbium. and lutecium oxides................. 0. 1 Silicon oxide............t................... 2.4 Calcium, aluminum, and iron oxides.......... 1.0 Uranium oxide............................. 0.3 Phosphorus pentoxide....................... 26. 2 a The values given for the rare earths following samarium are approximate. being based upon analyses of concentrated fractions derived from monazite. The composition given represents Travancore monazite carefully freed from other minerals. goup of rare-earth elements. A small amount of yttrium and terbium group phosphate is also present.* All the rare-

Jan 1, 1948

By R. Philip Hammond

Monazite has had a Cinderella-like history. Although nearly go per cent pure rare-earth compound (rare-earth phosphate) it was sought at first not for the rare earths but for the sake of a minor constituent—thorium. The thorium, essential for the Welsbach gaslight mantle, was present in only small quantities and the principal constituents, the rare earths, were largely discarded. Gradually, however, the rare earths have developed uses of their own and today have left the thorium far behind in value. Occurrence Monazite was first produced commercially about 1886, in North Carolina, where it was collected in small sluices by farmers who found it in stream beds on their land. The deposits were later exploited on a larger scale, but were mostly abandoned in a few years, when monazite from Brazil came upon the market in far larger quantities. Domestic production ceased entirely in 1906. The Brazilian source is still active, together with Indian, Dutch East Indies, and Australian deposits. Several other localities in the United States have yielded monazite, but none of these has produced commercially as yet. Monazite occurs originally in pegmatite~ and gneisses, through which, unfortunately, it is scattered in highly dispersed form. All commercially useful deposits consist of transported monazite sands liberated by erosion and concentrated by the action of water, which has sluiced away lighter materials and concentrated the heavy (D = 5.0 to 5.2) grains of monazite, together with ilmenite, zircon, garnet, and other dense minerals. The Carolina deposits were in stream beds; most of the other deposits mentioned are on or near the seashore, where the action of the waves has served to concentrate the monazite. In most cases today, the sands are worked to obtain the ilmenite and zircon, as well as monazite. The minerals are separated by means of sluices, dry tables, and magnetic separators, and each is finally obtained nearly pure. No crushing or grinding is necessary. The concentrates are shipped in fiber bags. Composition of Monazite As Table I illustrates, monazite is the anhydrous orthophosphate of the cerium Table i.—Typical Analysis of a Monazite Sand (India). Per Cent Thorium oxide............................. 8.1 Cerium oxide.............................. 30.6 Lanthanum oxide........................... 15. 7 Neodymium oxide.......................... 10.5 Praseodymium oxide........................ 2. 9 Samarium oxide............................ 1.0 Europium. gadolinium, and terbium oxides.... 0.7 Yttrium oxide.............................. 0.4 Dysprosium, holmium, erbium. thulium, ytterbium. and lutecium oxides................. 0. 1 Silicon oxide............t................... 2.4 Calcium, aluminum, and iron oxides.......... 1.0 Uranium oxide............................. 0.3 Phosphorus pentoxide....................... 26. 2 a The values given for the rare earths following samarium are approximate. being based upon analyses of concentrated fractions derived from monazite. The composition given represents Travancore monazite carefully freed from other minerals. goup of rare-earth elements. A small amount of yttrium and terbium group phosphate is also present.* All the rare-

Jan 1, 1948

By R. L. McCarron, G. R. Belton

The diffusivities of oxygen and sulfur in liquid iron have heen determined hy a capillary technique in which the surface concentrations of the solutes were established by means of appropriate H2/H2 and H2S/H, gas mixtures. Total diffusate and concentration profile results are shown to be in good accord, yielding for- 1560 and Supporting results at 1660°C are also presented. The conditions necessary to avoid gas transport control in this type of experiment are discussed. IN spite of their importance in understanding the kinetics and mechanisms of refining reactions, the dif-fusivities of oxygen and sulfur in liquid iron are not well established. Accordingly, as a first step in studies of rates of solute absorption from the gas phase into liquid iron, new measurements of these diffusivities have been made and are presented in this paper. The only published results for the diffusion of sulfur in pure liquid iron are those of Kawai.' He used a diffusion couple technique in which two cylindrical specimens, one containing sulfur and the other with negligible sulfur concentration, were joined together and held in a refractory capillary. After an experiment, the sample was quenched and the concentration distribution of the solute determined. Kawai recognized that significant changes in solute distribution occurred during melting and freezing and he attempted to correct the concentration profiles for these effects to give a sulfur diffusivity of 4.6 x 10-6 sq cm per sec at 1560°C. The method of correction, however, was not rigorous and the uncertainty in this result cannot be easily assessed. Koslov et a1.2 have reported the diffusivity of oxygen in iron as 7.8 x 10"3 sq cm per sec at 1660°C. This value appears to be unreasonably high but, unfortunately, details of their experiments are not available. Shurygin and Kryuk have used the rotating disc method for a study of oxygen diffusion in liquid iron. In their experiments a silica disc was rotated in liquid iron containing oxygen, and the rate of formation of liquid iron silicate was determined by measuring the decrease in weight of the disc. On the assumption that the rate of dissolution was controlled by the diffusion of oxygen in the iron, the diffusion coefficient was computed to be 5.2 x sq cm per sec at 1550°C. However, the Levich equation, which was used to interpret the rate data, was originally de- rived for the case of mass transfer between a solid disc and a single-phase liquid. The hydrodynamic and diffusion boundary layers in the iron stirred by a disc, via coupling of the silicate melt, may be appreciably different from those predicted by Levich's equations. Recently, Novokhatskiy and Ershov, using an identical experimental method to that of Shurygin and Kryuk, obtained a diffusivity for oxygen in liquid iron of 1.22 x 104 sq cm per sec at 1550°C: no reasons were offered for the disagreement. Schwerdtfeger5 has also recently studied the diffusivity of oxygen in liquid iron. He reacted shallow melts of liquid iron, 0.5 to 1.0 cm deep and contained in high-purity alumina crucibles, with appropriate H20-HZ-He mixtures. The total sample was analyzed, without sectioning, to obtain the average concentration of diffusate. A value at 1610°C of D = 12(3) x 10-5 sq cm per sec was obtained from the results of twenty experiments.= Oxygen profile measurements, which were carried out in three additional experiments using long capillaries and the semiinfinite boundary conditions, indicated a diffusivity about half that computed from the shallow bath experiments. Possible sources of error in Schwerdtfeger's study will be discussed later in this paper. EXPERIMENTAL TECHNIQUE The essential arrangement of the diffusion cell is shown in Fig. 1. The liquid iron was contained in an alumina capillary, 3 to 4 mm diam and 3 to 9 cm long, which was supported by a hollow alumina pedestal and this whole assembly was held within a movable alumina reaction tube. This tube, which was about 7 mm in bore

Jan 1, 1970

By Jerry H. Service, F. L. Partlo

The following investigation was undertaken to develop a method for determining with reasonable accuracy the depth of overburdens of 100 ft. or less. Seismic methods seemed to offer good possibilities. The problem differed from that of the familiar salt-dome location in that the depth of overburden to be determined is much less than is encountered in oil prospecting. This means that a much shorter time interval must be measured with accuracy. Refraction methods seem at present to offer greater possibilities than reflection. The air sound persists for from 0.1 to 0.5 sec., because of echoes, and seismic reflections coming during this time are difficult to detect. A seismometer sensitive to vertical vibrations only offers possibilities and has been used here with some success. It is hoped that the application of this type of seismometer to reflection shooting in this region may be investigated still further. The apparatus used consisted of a carbon-button seismometer followed by a three-stage, transformer-coupled, vacuum-tube amplifier and a General Radio string oscillograph. Time marks are provided by a 1000-cycle, 600-r.p.m., synchronous motor provided with five spokes which intercept the light to the camera at 1/50 sec. intervals. This motor is driven by a two-stage vacuum-tube amplifier of 3 watt output, actuated by a tuning fork. The power supply for the seismometer amplifier is one 2-volt storage and one 45-volt B battery. The motor amplifier is powered by a 6-volt storage battery and 6 to 225-volt, 15-watt motor generator. The temperature-frequency characteristics of the tuning fork have been determined and for ordinary working temperatures the error in time that would be introduced is less than M millisecond for time intervals up to 100 milliseconds. The impact is produced by a sledge blow for surface distances less than 100 ft. and dynamite for greater distances. Two steel balls with wires attached form an electric circuit through a 1-ft. piece of railroad rail upon which they rest. When the rail is struck by the sledge the balls rebound, opening the circuit and indicating the time of impact by a break in the oscillograph record line as at A, Fig. 3. When dynamite

Jan 1, 1934

By L. M. Cathles, W. Joseph Schlitt

A mathematical model describing the leaching of low grade industrial waste dumps in developed and solved by finite difference techniques. The leaching behavior of model dumps of different sizes, permeabilities, and waste characteristics, under different operating conditions, is then investigated using the model. It is shown that leaching is fastest for dumps 50-100 feet (15-30m) high, that permeability is very important for the effective leaching of large dumps, that slow leach kinetics of the waste may not be detrimental, and that the leaching of large dumps may be facilitated if leach solutions are preferentially applied to the hot, near-edge portions of the dump.

Jan 1, 1980

By E. C. Tveter, L. A. Roe

The authors present a general outline of the theory and development of heavy-liquid application to mineral processing. Patent literature and processes are reviewed with special emphasis on liquid recovery systems which have been employed or proposed. Advantages and disadvantages of the process are discussed together with the recent developments which have revived interest in this old concentration method. The most important single factor in this resurgence of interest is concluded to be the narrowing gulf between chemical engineering and mineral dressing which has opened the field for new concepts of mineral plant design. A partial summary of patents on heavy liquid separations is included. In spite of the fact that heavy-liquid separation with organic liquids has been used in the laboratory for over 50 years, this process has never graduated to large scale commercial use for any extended period. However, a variation of this process, the sink-float or heavy-media separation process has found wide acceptance and is used to separate minerals from diamonds to gravel. Materials used to increase the specific gravity of the pulps used as heavy media include sand, clay, barite, magnetite, galena, hematite, atomized lead and ferrosilicon. Because of the greater ease of recovery, the magnetic materials, magnetite and ferrosilicon, are the preferred media today. In the U. S. alone, heavy-media iron ore plants with a capacity of over 10 million tons of concentrate per year are in existence. Heavy-media separation involving use of solid, inorganic particles suspended in water rapidly found a wide range of commercial use with the introduction of magnetic media. The minerals engineer is experienced in working with suspensions and quickly learned to develop and control such media at a cost compatible to the type of separation desired. The natural superiority of a heavy liquid with uniform chemical and physical properties has never been questioned since its first use in laboratory mineral separatory procedures. It offers the only method for gravity separation of fine particles of relatively close specific gravity. The most important early attempt to make heavy liquid separations commercial were made by the DuPont Co. which began experimental work on Virginia limonite in 1904. The appended "Partial Summary of Patents" compiled by W.L. O'Connell of The Dow Chemical Co. demonstrates the quantity and sequence of this work. Both inorganic and organic parting liquids were investigated and numerous patents were issued on the use and recovery of these liquids. The work culminated in the heavy liquid plant of the Weston Coal Co. at Shenandoah, Pa. Chemical engineering design of this plant was the responsibility of Francis I. and Hubert I. DuPont. Heavy-liquid separation of coal almost achieved commercial status at this plant which actually processed over 20,000 tons of coal. The liquids used were tetrabromethane, pentachloroethane and trichlo-roethylene, with liquid losses ranging from 8.9 to 12.4 oz per ton of cleaned coal. The reasons for failure of this plant are not clear but probably involved toxicity problems as well as other problems in chemical engineering. Excellent economics were reported. A more recent pilot plant was built in 1954-55 by Norris Goodwin for the Inerto Co. to treat hectorite clay. This plant employed carbon tetrachloride in jigs with liquid recovery by evaporation. Although good separation was achieved, incomplete removal of the CCl, from the clay prevented commercial operation. The only present operations known to the authors employing heavy liquids for gravity separations are limited to the use of calcium chloride in certain coal washers and bromochloromethane in a small batch operation (one ton solids per day) for the separation of beryllium metal particles from slag materials. This is not strictly a minerals beneficiation problem but it has demonstrated the feasibility of such separations. PROBLEMS Critics of early attempts to commercialize heavy-liquid separation of minerals summarize the draw-

Jan 1, 1963

By A. W. Allen

THE technological study of the treatment of gold and silver ores has been largely responsible for the phenomenal strides which have marked the progress in this branch of metallurgy during recent years. In no other application of science to industry is system more imperative at every stage; correct formulation of result is only second in importance to efficiency of operation. Progresss in method has been largely the result of individual initiative, aided by the work of technical journals and metallurgical societies. There still remains a field for profitable discussion, and it is my intention to deal with some inconsistencies of expression common to a number of writers on the subject; and also to draw attention to the false impressions created by a statement which may, possibly, be only unintentionally misleading. I also take the opportunity of tracing the source of both metallurgical and economic result; and to question the desirability of the methods usually employed in arriving at a final statement. In the first place, I wish to deal with the question of extraction. This term may mean anything or nothing, and it is often used to mislead. In a report of a mining engineer as to the result of operations subsequent to the remodeling of a treatment plant prominence was given to the statement that the extraction had amounted to 91 per cent. On examination it was found that only a small percentage of the so-called extraction was calculated on actual bullion return, a proportion being figured from the gold left in the zinc boxes, and not recovered. In addition to this, a proportion of the extraction was said to be due to gold in concentrate. As there was no concentrating apparatus on the property and as concentration did not form a part of the scheme of treatment the matter was investigated, with the result that the concentrate, of lower gold content that the original ore, was found to be the result of an inefficient pumping system which failed to provide for the whole of the battery product delivered to it. The balance was stacked and, although itself of no marketable value, the gold content was allowed to form a basis of extraction figures.

Jan 7, 1914

By William Metcalf

IT is the object of this paper to oppose unnecessary changes, and the introduction of new and confusing terms. From the earliest times of which we have any record on the subject, iron has been divided into general classes. Whether iron was first known in the form of wrought iron or of steel, is a matter of no importance; but at the time when cast iron first became a prominent article of commerce, wrought iron and steel were old products¬steel, at that time, being generally made from wrought iron by the process of cementation. As steel was then properly defined as iron containing more carbon than wrought iron, so cast iron was appropriately defined as iron containing more carbon than steel. Until the year 1776, when Huntsman first began the manufacture of a new kind of iron by melting wrought iron and steel in crucibles, the above definitions were all that could be desired. At first, probably, owing to imperfect appliances, only a highly carburized iron was melted in crucibles, and this led to its being called cast steel. If our ancestors had found a name for this material not involving the use of the word steel, we would have been saved the trouble of the present discussion. As the arts developed, new uses were found for steel, and the products of the crucible were varied, until at the present day it is quite common to find steel containing no more carbon than average wrought iron, and other steel containing nearly or quite as much carbon as some cast iron. All of these various products of the crucible have retained, or received, the name cast steel, usually abbreviated to the simple word steel, without causing any confusion among producers or consumers in regard to terms or their meaning. In 1855, twenty-one years ago, the Bessemer process was introduced ; this was followed in a few years by the Siemens-Martin process, and the products of both were at once, and have ever since been, called steel, from the fact that they were identical in chemical and physical properties with crucible cast steel. At the present time, then, we have three subdivisions of cast steel, viz.: Crucible cast steel, Bessemer cast steel, and Siemens-Martin,

Jan 1, 1877

By P. R. Sperry, P. A. Beck, J. Towers

Dahl and Pawlek1 found that electrolytic copper develops extremely coarse grains at 1000°C after about 90 pct reduction by rolling. This coarsening occurs only under conditions of penultimate grain size, deformation, and alloying which lead to the "cube" recrystallization texture.l,2,3,5 The peculiar angular shapes and straight grain boundaries of the coarse grains were noted by several investigator.1,4,5 On the other hand, coarsening in Fe-containing aluminum or in AI-Mn alloys8 does not depend on a "cube" (or any well developed) recrystallization texture. It is true that increasing deformation by rolling, and, therefore, an increasingly well developed re-crystallization texture, are associated with decreasing incubation periods of coarsening.6-7-8 Nevertheless, coarsening readily develops in aluminum even after only 30 pct reduction by rolling, where the recrystallization texture is very weak.6,8 Also, coarsening was observed by Jeffries9 many years ago in sintered thoriated tungsten, which presumably has no preferred orientation. In all these cases coarsening is associated with grain growth inhibition by a dispersed second phase.8,9 The annealing temperature has to be suficiently high to overcome the inhibition at a few locations. But if it is too high, growth starts at many points, and the resulting grain size becomes much smaller.9 Normally, the coarse grains are more or less equiaxed, and the boundaries have a typical ragged appearance.6.8 Cook and Macquarie4 demonstrated that, in addition to the texture-dependent coarsening previously found at 1000°C,l electrolytic tough pitch copper may also coarsen at 800°C after 50 pct reduction by cross rolling. The coarse grains formed under such conditions have rounded shapes and ragged boundaries, like those in aluminum. When the annealing temperature is higher, the tendency for their formation decreases. All these observations suggest that the coarsening at 800°C is associated with inhibition by a second phase. Actually, coarsening at 800°C after 50 pct reduction by cross rolling was observed only in tough pitch copper,4 which contains Cu2O particles. On the other hand, the texture-dependent 1000°C coarsening occurs in both tough pitch and oxygen-free copper;4 it does not appear to depend on the presence of a dispersed second phase. However, the interpretation of the 800°C coarsening in Cu after 50 pct rolling as an inhibition-dependent process, similar to the coarsening in A1-Mn alloys, is somewhat weakened by the fact that this coarsening was reported4 to occur only after cross rolling, and not after straight rolling. It was, therefore, decided to re-examine this question. A 1 in. diam electrolytic tough pitch copper rod, No. 2 hard drawn, was annealed for 20 min at 700°C, rolled to 0.5 in., annealed 10 min at 700°C, and straight rolled to 0.064 in. It was then given a penultimate anneal of 20 min at 500°C and it was cut into four sections, which were given final reductions by straight rolling as follows: A 30 pct reduction of area B 50 pct reduction of area C 70 pct reduction of area D 90 pct reduction of area Specimens cut from the four sections were finally annealed at 800°C in an oxidizing atmosphere. Strip A remained fine grained up to 10 hr, but the specimen annealed 12 hr consisted of only 2 large grains. Strip B had a few scattered large (1/2 to 3/4 mm) grains after 1 min, although the balance of the specimen consisted of fine grains of about 0.02 mm. After 5 min there were several 10 to 15 mm grains present, and after 1 hr strip B was completely coarsened. The coarse grains had the same characteristics (see Fig 1) as those obtained by Cook and Macquarie at 800°C after cross rolling. Strip C had several grains of 0.05 to 1 mm after 1 min, but it was still largely fine grained after 12 hr. After 48 hr it consisted entirely of grains of about 0.5 to 4 mm, with an extraordinarily large number of twin bands. Strip D remained com- pletely fine grained after 4 hr at 800°C. These results indicate that, in the deformation range of 30 to 70 pct reduction, the incubation period for coarsening as well as the rate of growth and the final size of the coarse grains decreases with increasing deformation. Similar

Jan 1, 1950

By Bruce W. Gonser, Robert J. Nekervis

EACH metal has a unique combination of properties that distinguishes it from other metal;. Su& a combination may account for applications that cannot be met very well by anything else. This is particularly true of tin, one of the earliest metals used by man. Table i shows the consumption of tin in the United States by usage for the years 1949 and 1950, which may be considered to be generally typical of current usage. The major applications-tinplate, solders, bronze, and babbitt-were well established a century ago. Applications for the metal and (probably later) of tin alloys started more than 5000 years ago. Fortunately for the ancients, tin is one of the metals whose oxide is easily reduced by carbon. Nature further simplified the refining problem by providing only one ore of commercial importance, cassiterite (SnO2). Tin is easily reduced from cassiterite. All that is necessary is high heat in the presence of carbon. It is quite possible that back in the dawn of history, tin was discovered when black alluvial sand was thrown on a fire, either to bank it or to put it out. SOURCES OF TIN All the important tin-producing centers are in the southern hemisphere, far away from the' industrial consuming centers. Fig 1 shows their location and 1950 production. Reserves are adequate, and the industry is able to produce considerably more tin than is

Jan 1, 1953

By C. S. Giggins, F. S. Pettit

The oxidation of Ni-Cr alloys in 0.1 atm of oxygen has been studied at temperatures between 800" and 1200°C. For alloys with 30 wt pct or more Cr, continuous layers of Cr2O3 are formed during oxidation. In the case of alloys with chromium concentrations between approximately 5 to 30 wt pct, external scales of Cr203 are formed over grain boundaries whereas internal precipitates of Cr2O3 and external layers of NiO are formed at other areas on the alloy surface. When such conditions are present on the alloy surface, chromium diffuses laterally from those areas covered with a continuous layer of Cr2O3 to areas where a Cr2O3 sub scale exists and it is possible for the sub-scale zone to become separated from the alloy by a continuous layer of Cr2O3. Whether such a state will be attained depends upon the initial grain size of the alloy and the oxidation time. When the concentration of chromium in the alloy is less than 5 pct, Cr2O3 is formed internally both at grain boundaries and within the interior of grains and the alloy is covered with an external layer of NiO. MECHANISMS which describe the growth of oxide scales on nickel-base superalloys are complex and the effects produced by the various elements in these alloys on the oxidation behavior of superalloys are not clearly understood. In order to determine the influence of the different elements on the oxidation behavior of superalloys, it is first necessary to examine the oxidation properties of binary nickel-base systems which contain the principal elements present in the superalloys and then progressively more complex systems until compositions typical of the superalloys are attained. Chromium is present in virtually all nickel-base superalloys and the purpose of the present studies was to examine the selective oxidation of chromium in Ni-Cr alloys. The oxidation characteristics of Ni-Cr alloys have been extensively studied1-" to date principally as a result of the high oxidation resistance exhibited by some of these alloys. Ni-20Cr* has long been known *All compositions are given as wcight percent unless specified otherwise. to be oxidation resistant and is commonly used as resistance heating elements for service temperatures up to 1100°C. This alloy cannot be used for extended periods of time at higher temperatures because of the apparent reaction of the external scale with oxygen to form gaseous CrO3. In spite of the considerable work cited above some important aspects of Ni-Cr oxidation still remain unresolved. Virtually all of the previous studies agree that small additions of chromium to nickel, e.g., <10 wt pct Cr, result in increased oxidation rates as compared to that of pure nickel, whereas larger additions, e.g., 20 to 30 wt pct Cr, form alloys with substantially lower oxidation rates. The controversial aspects of the oxidation mechanisms for these alloys that still remain unresolved are as follows: 1) A description of the oxidation mechanism for the low chromium alloys. 2) A description of the oxidation mechanism for the high chromium alloys, particularly with respect to the composition of the external scale which results in the lower oxidation rates. 3) The specific alloy compositions at which the oxidation mechanism changes from that obtained for low chromium contents to that of the high chromium alloys and the reason for this transition. EXPERIMENTAL The Ni-Cr alloys listed in Table I were prepared from high purity metals by nonconsumably arc melting and casting as buttons. These alloys were then given a preliminary annealing treatment in argon at 815°C for 100 hr to promote homogeneity. Each button was cut into 0.250 in. thick sections that were subsequently cold-rolled to 0.050 in. thicknesses and annealed in argon at 815°C for 48 hr to provide a twinned, equi-axed grain structure. The grain size for these alloys was not uniform and the limits, within which the average grain size lies, are given in Table I for the single-phase alloys. All the alloys were single phase with the exception of the Ni4OCr alloy in agreement with the Ni-Cr phase diagram.&apos;&apos; Rectangular specimens were cut from the sheet to provide surface areas of approximately 2.5 sq cm. Exact areas were determined with a micrometer after surface preparation was completed. All of the specimens except the Ni-40Cr alloy and pure chromium were polished through 600-grit Sic abrasive paper, ultrasonically agitated in ethylene trichloride, rinsed with ethyl alcohol, and electro-polished. The specimens were electropolished in a 10 vol pct H2SO4 (conc), 6 vol pct lactic acid, methyl alcohol solution at 70" to 80°C for 2 min at a current density of 0.8 to 1.2 amp per sq cm. This electro-polishing procedure did not produce acceptable surfaces on the Ni-40Cr alloy nor on pure chromium and the oxidation properties of these materials were obtained for specimens polished through 600-grit Sic

Jan 1, 1970