Search Documents

By Norman E. Lehman

Pyrometasomalic mineralization occurs within meta-morphosed Paleozoic carbonates intruded by Laramide granodiorites. Two types of alteration developed shams in the district. The dominant type is post-magmatic which developed an early hydrous endoskarn phase, and intermediate anhydrous exoskarn phase, and a late hydrous phase affecting both sham types. A rare, second type is magmatic in age, lacks the hydrous phases, and developed a mineralogically-zoned endoskarn. Garnet exoskarns lacking associated plutonic rocks are stratigraphically controlled and contain an early anhydrous phase, an intermediate hydroxyl-bearing phase, and a late hydrous phase associated with base metal deposition.

Jan 1, 1981

By Edward F. Divers

Face ventilation is generally the most critical area in the coal mine ventilation system. Various studies have repeatedly shown that good ventilation is by far the most effective and least costly method of controlling dust and gas problems created during face operations. The Bureau of Mines has recently developed and assisted in the development of several new concepts in face ventilation systems, and in methods to accurately evaluate these systems underground. A new type of scrubber and ventilation system design built into the auger support frame of a continu- ous miner was developed. The objective was to improve face ventilation and reduce respirable dust concentrations. With this arrangement, one scrubber is mounted into each side of the boom. Laboratory and underground tests of various scrubber discharge arrangements showed good to excellent dust and methane control. Combined face ventilation systems, using both blowing and exhaust curtain, potentially offer dust and gas control and deeper cutting. Bureau tests at a mine using a combined face ventilation system and remote- control-operated continuous miners showed excellent dust and methane control. The advancement of line curtain systems beyond permanent supports without exposing workmen to roof fall hazards can be accomplished only with specially designed extendable devices. Numerous concepts for line curtain extension have been developed and tested. For the past several years, the Bureau has been testing various types of extensible face ventilation systems. These extensible systems can generally be classified as floor-, roof-, machine-, and rib-mounted systems. In the past 6 years, approximately 40 systems have been evaluated for feasibility. From these, several have been selected as practical or innovative and are presented herein. A technique developed by the Bureau to accurately and safely evaluate the effectiveness of face ventilation is also presented.

Jan 1, 1982

By Axel Sahlin

The day is long past when linen and cotton rags were the exclusive raw material of the paper-trade. Wood-fiber, chemically or mechanically prepared, straw, hemp and Esparto grass have largely supplied the demand, which the old materials did not suffice to fill. But even these newer fibers have been of late supplanted, to some extent, by mineral pulp. Weighting and filling materials have also been resorted to, partly to give body to the fabric, partly to increase its weight and reduce the cost per pound. China clay, sulphate of lime and soapstone have generally been employed as loading materials. Even though these materials lack fiber, their addition must by no means be viewed, as it too generally is, entirely as an adulteration. No doubt, to a certain extent, they weaken the paper ; but for ordinary grades the addition of these non-fibrous substances is a positive advantage, as they close the pores between the fibers and lend to the paper a great degree of opaqueness and a superior finish. Fibrous talc, as a form of pulp, has the same effect, without appreciably weakening the paper. When, therefore, some fifteen years ago, fibrous talc in large quantities, and of marvellous purity and whiteness, was discovered in the neighborhood of the town of Gouverneur, it was not long before the

Jan 1, 1893

By José Geraldo Vieira

Companhia Vale do Rio Doce (CVRD), founded in 1942, is located near the town of Itabira, Brazil. Its iron ore deposits include over 500 million metric tons (mt) of high-grade hematite and about 2 billion mt of itabirite (banded rock formed by thin alternate layers of hematite and silica). These deposits are part of the Iron Ore Quadrangle, of which the overall reserves have been estimated at more than 30 billion mt. The magnitude of the project meant difficult early years for the company, including large investments, extensive railroad rehabilitation, and construction of ore port and ore handling facilities. Companhia Vale do Rio Doce was organized as a stock company, and 91% of its shares are presently owned by the Brazilian government. Financing has been accomplished in part through loans from international monetary agencies foreign banks, and foreign industry, as well as Brazilian banks. The company markets mainly abroad. In 1967, it exported 10.6 long tons (It) of ore, principally to West Germany, Japan, Netherlands, Italy, France, United Kingdom, and the United States. The Rio Doce geographic region where CVRD operates is strategically located among the large population centers of Rio de Janeiro, Belo Horizonte, Salvador, and Vitoria (Fig. 1). It covers an area of approximately 81,000 sq km in the states of Minas Gerais and Espirito Santo, and its population in 1968 was about 3.5 million. This region presents excellent prospects for development, with factors favorable for forestry, agriculture, grazing, and exploration for minerals other than iron ore, Electric power (hydroelectric plants) is available, as well as two main systems of transportation: the Rio-Bahia highway and the Vitoria-Minas Railroad. Pioneer activities at Itabira started about 1720 as small gold mining centers. The town is about 80 km northwest of Belo Horizonte and

Jan 1, 1969

By T. A. Wright

THE SAMPLING of waste materials containing copper, lead and tin has taken on a new significance within recent years, and is of increasing importance, on account of the entry of some of the copper refineries into this field and the tendency towards consolidations among the smelters. In the past, such material was sold on the basis either of a rough or grab sample or of casual inspection of the lot. The two principal sources of this waste are the processes of fabrication and the scrapping of automobile, electrical, plumbing, railroad and other equipment. In both cases much material can be sorted, salvaged and sold by classification and grade to be melted "as is" or with the addition of new or virgin metal. The increasing care in classifying exercised in the large manufacturing plants tends to increase the proportion of this usable scrap; on the contrary, the increasing use of more complex and special non-ferrous alloys tends to make sorting and grading more difficult in turnings, borings, clippings, etc., and consequently is making sampling of more moment. In tin, lead, aluminum, and zinc furnace by-products such as ashes, drosses, skimmings, etc., the trade practice of evaluation has not varied much. For instance, tin drosses, battery lead, and aluminum skimmings are ordinarily sold on what is called' "metallic button" or "metallic recovery" or "metallic yield." Copper and lead waste, however, is being sold more and more on actual copper and lead contents based on sample and chemical analyses. This paper will be devoted chiefly to the sampling of materials suitable only for refining and recovery of one or more of the metals present. The methods described are often based on the fact that but one metal, such as copper, is to be paid for. The loss of volatile constituents in melting does not appreciably affect the final copper result, as the "after-melting" assay can be readily calculated to the "before-melting" basis, but if smelter efficiency continues to increase, so that in time zinc, for instance, may be recovered on a paying basis, the method of sampling dirty brass, for example, will have to be changed also.

Jan 1, 1928

By James Douglas

PROBABLY no well-informed engineer would ques¬tion the accuracy of the statement that the piece of equipment that comes nearest to being in universal use in modern hydrometallurgical and ore-dressing plants is the Dorr continuous thickener. The function of the device is to separate a thin mixture of liquid and solid particles into a thick pulp and a clear liquor. Another machine in wide use is the Dorr classifier, the purpose of which is to separate the coarse and fine particles in a pulp containing solids of various sizes. It is in recognition of the invention of these two devices and the vast amount of technical work in the successful application of them in the beneficiation of ores that the James Douglas Medal for 1930 has been awarded to John Van Nostrand Dorr. To gage the importance of the development of the thickener, particularly, it is only necessary to imagine the loss of time, capacity, and metallurgical efficiency that would result if all the Dorr tanks in the world were put out of operation for a day and replaced by the old methods of intermittent settling and decantation. Truly, the record is one of "distinguished achievement in non-ferrous metallurgy" that deservedly ranks the medalist with those who have preceded

Jan 1, 1930

By C. F. Quest

THE steel industry has a definite need in its tonnage mills for a formula relating expected tensile strength to the analysis of the steel. The McWilliam-Barnes1 and other less comprehensive formulas are used for this purpose, but these formulas were designed for an analysis range that does not include the medium manganese and silicon-bearing steels. This type of steel is being produced to meet the demand for tensile strength slightly higher than that of ordinary structural steel but not high enough to justify expensive alloy steels. The purpose of this paper is to present a somewhat more compre-hensive formula based on data accumulated over a number of years by the Inland Steel Co., and to discuss the method followed in obtaining a formula to fit the data. The resultant formula admittedly is still weak in some respects, but for the expanded analysis range appears to be an improvement over the other formulas. It is hoped that with the collec-tion of more data and possible collaboration with other mills studying this problem it will be possible to work out a more nearly perfect formula. Several publications have been issued on this subject. In some, the equation type of relation was evolved while others made a combina-tion of tables and an equation. The latter include work by Campbell2,3 and Webster.4,5 Campbell classified the steels as acid and basic and applied a different formula to each. For basic steels, he used the equation: Tensile strength = 41500 + 770C + 1000P + yMn [1] y was a variable depending on the carbon and manganese content of the steel and was listed in tables, Webster investigated acid Bessemer steel and developed the equation Tensile strength = 38000 + 800C + xP + yMn [2]

Jan 1, 1940

By AIME AIME

I would like to ask Bob Merrill whether he considers that horizontal concave curvature of a slope has any stabilizing effect, such as Jenike 1 suggested several years ago. The stabilizing effect is due to the restraint offered to radial movement by the curvature. We found in laboratory tests that if we constrained the rock with the same stresses as those measured in the pit then it would sustain a maximum stress about two or four times greater than when the same rock type was unconstrained. We are therefore definitely of the opinion that a constrained situation in a slope is favorable towards stability.

Jan 1, 1967

Discussion of Papers. Meetings of the Institute offer opportunity for social acquaintance and exchange of ideas, for the presentation of papers, and for discussions thereon ; also incidentally for viewing under especially favorable conditions mining operations and industrial establishments, and for hospitals-ties which demonstrate the brotherhood due to kindred interests. Placing sociability prominent is not to be assumed as relegating other features of meetings to subordinate positions; but during about 40 years of membership in the Institute, the value of acquaintances formed (often ripening into close friendship), and the interchange of data, have frequently demonstrated that the social feature of meetings is of great and lasting value to the membership. Of' a roll embracing 4,011 members, resident in all parts of our country, and scattered in various portions of the world, only a small fraction are able to attend meetings, even if the localities selected are alternately widely separated. Hence, the return which most -members receive for their annual assessment of dues is limited to the publications issued, and the credit of being recognized as a member of a great and worthy organization. Tile greater the value of tile contents of our publication, the fuller the return which goes to members. While the Institute disavows responsibility for views or statements made in papers which appear in its Transactions, the fact that these contributions, after passing proper censorship, are accepted by the Institute and spread before the world may properly be received by the writers as endorsements of their (the writers') ability to present a specific technical or industrial proposition worthy of being carefully read. But the mere presentation and publication of contributed papers falls short of fulfilling one important feature of our meetings. If the purpose is confined to having the writers' views, discoveries, theories, or methods published, this can be obtained through the technical or trade journals and magazines.

Jan 7, 1913

By Francis S. Kendorski

INTRODUCTION Nuclear waste has been generated since the time of the Curie's and continues to be generated worldwide at an ever-increasing rate as the world will (and should) rely more and more upon fission (and hopefully fusion) for power. Also, the needs for strategic weapons will also generate so-called defense wastes. The largest class of high level nuclear waste (HLW) is spent fuel, the tail end of the nuclear reactor fuel cycle. At present, spent fuel is stored at the reactors producing it or at a few accepting places for away-from-reactor storage. All such storage facilities, as presently constructed, will begin to run out of usable storage space during the next decade or so. Congress enacted and President Reagan signed into law in early 1983 the National Nuclear Waste Policy Act of 1982. This law provides for the permanent isolation of nuclear waste in deep geologic repositories. The Act sets 1998 as the date at which the first repository should be operational. This date is extremely ambitious, and the Department of Energy (DOE), which is charged with the responsibility of constructing and operating repositories, admits that this date will slip by at least a few years. The Act also provides for licensing of repositories by the Nuclear Regulatory Commission (NRC) in a fashion very similar to nuclear power generating reactors. This requirement imposes a very special rigor on the analyses, investigations, designs, construction, and operation of repositories so as to assure the protection of the public and the environment from radioactive contamination. In addition the states and affected Indian Tribes must be consulted, especially concerning siting, and, needless to say, no one wants a HLW repository in their back yard.

Jan 1, 1984

By C. F. Quest, T. S. Washburn

The steel industry has a definite need in its tonnage mills for a formula relating expected tensile strength to the analysis of the steel. The McWilliam-Barnes1 and other less comprehensive formulas are used for this purpose, but these formulas were designed for an analysis range that does not include the medium manganese and silicon-bearing steels. This type of steel is being produced to meet the demand for tensile strength slightly higher than that of ordinary structural steel but not high enough to justify expensive alloy steels. The purpose of this paper is to present a somewhat more comprehensive formula based on data accumulated over a number of years by the Inland Steel Co., and to discuss the method followed in obtaining a formula to fit the data. The resultant formula admittedly is still weak in some respects, but for the expanded analysis range appears to be an improvement over the other formulas. It is hoped that with the collection of more data and possible collaboration with other mills studying this problem it will be possible to work out a more nearly perfect formula. Several publications have been issued on this subject. In some, the equation type of relation was evolved while others made a combination of tables and an equation. The latter include work by Campbel12,3 and Webster.4,5 Campbell classified the steels as acid and basic and applied a different formula to each. For basic steels, he used the equation: Teosile etrength = 41500 + 770C + 1000P + yMn [1 y was a variable depending on the carbon and manganese content of the steel and was listed in tables. Webster investigated acid Bessemer steel and developed the equation: Tensile strength = 38000 + 800C + xTP+ yMn [2]

Jan 1, 1940

By C. F. Quest, T. S. Washburn

The steel industry has a definite need in its tonnage mills for a formula relating expected tensile strength to the analysis of the steel. The McWilliam-Barnes1 and other less comprehensive formulas are used for this purpose, but these formulas were designed for an analysis range that does not include the medium manganese and silicon-bearing steels. This type of steel is being produced to meet the demand for tensile strength slightly higher than that of ordinary structural steel but not high enough to justify expensive alloy steels. The purpose of this paper is to present a somewhat more comprehensive formula based on data accumulated over a number of years by the Inland Steel Co., and to discuss the method followed in obtaining a formula to fit the data. The resultant formula admittedly is still weak in some respects, but for the expanded analysis range appears to be an improvement over the other formulas. It is hoped that with the collection of more data and possible collaboration with other mills studying this problem it will be possible to work out a more nearly perfect formula. Several publications have been issued on this subject. In some, the equation type of relation was evolved while others made a combination of tables and an equation. The latter include work by Campbel12,3 and Webster.4,5 Campbell classified the steels as acid and basic and applied a different formula to each. For basic steels, he used the equation: Teosile etrength = 41500 + 770C + 1000P + yMn [1 y was a variable depending on the carbon and manganese content of the steel and was listed in tables. Webster investigated acid Bessemer steel and developed the equation: Tensile strength = 38000 + 800C + xTP+ yMn [2]

Jan 1, 1940

By W. L. Phillips

Stress-strain data are reported for sodium chloride, lithium fluoride, and magnesium oxide tested in compression at diffevent strain rates in the telrlperature range from 70° to 873°K. Quantitative equations are given for the stvain-rate dependence of the critical resolved shear stress and the initial rate of work havdening. The properties so determined are compared with results previously reported for metals. ALTHOUGH the effects of strain rate and temperature on the stress-strain characteristics of metals have been extensively investigated1,2 these effects have not been studied in detail in ionic crystals. In the only previous investigations on the effect of strain rate on the deformation of ionic crystals. Gilman and gohnston3 and Hulse and pask4 have shown that the yield stress of lithium fluoride and magnesium oxide at room temperature is proportional to the ninth or tenth root of the strain rate. CRYSTAL PREPARATION Lithium fluoride, sodium chloride. and magnesium oxide single crystals were purchased from the Har-shaw Chemical Co. The compression fixture and sample preparation have been described in detail previously.5 The detectable impurities in MgO were eight parts in 105 of Fe and six parts in 105 of Si; in LiF, six parts in 105 of Mg; and in NaC1, two parts in 105 of Fe and four parts in 10&apos; of Mg. The cleaved samples measured - 0.1 in. by 0.1 in. by 0.3 in. Prior to testing all samples were annealed at -0.8 of their melting point and cooled to room tempera- ture at 50 C per hr.&apos; Samples were strained at rates (<) of 0.1, 0.01, 0.002, and 0.0002 in. per in. per min. EXPERIMENTAL RESULTS Fig. 1 is a plot of the critical resolved shear stress a,. (extrapolation of slope of easy glide region to zero strain) of sodium chloride, lithium fluoride, and magnesium oxide tested at different strain rates as a function of temperature. In all crystals at all strain rates a, decreases with increasing temperature according to an equation of the type397 where uo is a stress constant, K is a constant, and T is the absolute temperature. The points in Fig. 1 are the average of six tests. It is evident that there is a break in the log 0,- temperature plots at a characteristic temperature T,. The constant K of Eq. [I] is dependent on strain rate, Fig. 2. The relationship

Jan 1, 1962

By Charles S. Barrett

Recrystallization textures—thc orientations of grains after recrys-tallization—have been studied extensively not only because of their metallurgical importance but also because of the information they yield regarding the atomic movements during reerystallization. Recrystallized grains must possess the same orientations as the submicroscopic nuclei from which they have grown, and thus they offer a direet road by which experimenters can penetrate the submicroscopic realm. Many perplexing results have come of these studies, but one of the most striking has been the apparent difference in behavior between single crystals and polyerystalline grains. For example, Burgers and Louwerse have shown1 that when single crystals of aluminum are deformed by compression and are reerystallized (at 600&apos; C.) the new grains appear with orientations that are different from the orientations of the deformed crystal in which they grew; but polycrystalline specimens, on the other hand, appear to have a [110] fiber texture both before and after reerystallization and thus to retain their texture during recrystallization. This apparent difference between the habits of single crystals and small grains is the subject of the first part of the present research and has been explained by findings reported herein. A similar situation appears to exist for aluminum when elongated or drawn into wires, for single crystals alter their orientation 2,3 and polycrystalline wires retain their texture"5*" upon recrystallization after elongation (at least with high-purity aluminum), and it is possible that the explanation found in this paper for compression can be extended to cover elongatioil and other types of deformation as well. The second part of this paper deals with the theory of reerystallization textures. In the most successful theory for aluminum reerystallized after compression,1 much weight is given to the orientation of highly stressed nuclei in the deformed material. Taylor&apos;s "local distortions" arc assumed to exist along the slip planes where displacement has occurred, consisting of fragments rotated in a specific way with reference to the slip plane and slip direction; namely, about an axis lying in the slip plane perpendicular to the slip direction.1,7,89

Jan 1, 1940

By Charles S. Barrett

Recrystallization textures—thc orientations of grains after recrys-tallization—have been studied extensively not only because of their metallurgical importance but also because of the information they yield regarding the atomic movements during reerystallization. Recrystallized grains must possess the same orientations as the submicroscopic nuclei from which they have grown, and thus they offer a direet road by which experimenters can penetrate the submicroscopic realm. Many perplexing results have come of these studies, but one of the most striking has been the apparent difference in behavior between single crystals and polyerystalline grains. For example, Burgers and Louwerse have shown1 that when single crystals of aluminum are deformed by compression and are reerystallized (at 600&apos; C.) the new grains appear with orientations that are different from the orientations of the deformed crystal in which they grew; but polycrystalline specimens, on the other hand, appear to have a [110] fiber texture both before and after reerystallization and thus to retain their texture during recrystallization. This apparent difference between the habits of single crystals and small grains is the subject of the first part of the present research and has been explained by findings reported herein. A similar situation appears to exist for aluminum when elongated or drawn into wires, for single crystals alter their orientation 2,3 and polycrystalline wires retain their texture"5*" upon recrystallization after elongation (at least with high-purity aluminum), and it is possible that the explanation found in this paper for compression can be extended to cover elongatioil and other types of deformation as well. The second part of this paper deals with the theory of reerystallization textures. In the most successful theory for aluminum reerystallized after compression,1 much weight is given to the orientation of highly stressed nuclei in the deformed material. Taylor&apos;s "local distortions" arc assumed to exist along the slip planes where displacement has occurred, consisting of fragments rotated in a specific way with reference to the slip plane and slip direction; namely, about an axis lying in the slip plane perpendicular to the slip direction.1,7,89

Jan 1, 1940

By Charles Barrett

RECRYSTALLIZATION textures-the orientations of grains after recrys-tallization-have been studied extensively not only because of their metallurgical importance but also because of the information they yield regarding the atomic movements during recrystallization. Recrystallized grains must possess the same orientations as the submicroscopic nuclei from which they have grown, and thus they offer a direct road by which experimenters can penetrate the submicroscopic realm. Many perplexing results have come of these studies, but one of the most striking has been the apparent difference in behavior between single crystals and polycrystalline grains. For example, Burgers and Louwerse have shown&apos; that when single crystals of aluminum are deformed by compression and are recrystallized (at 600° C.) the new grains appear with orientations that are different from the orientations of the deformed crystal in which they grew; but polycrystalline specimens, on the other hand, appear to have a [110] fiber texture both before and after recrystal-lization and thus to retain their texture during recrystallization. This apparent difference between the habits of single crystals and small grains is the subject of the first part of the present research and has been explained by findings reported herein. A similar situation appears to exist for aluminum when elongated or drawn into wires, for single crystals alter their orientation2,3 and polycrystalline wires retain their texture 4,1 6 upon recrystallization after elongation (at least with high-purity alumi-num), and it is possible that the explanation found in this paper for compression can be extended to cover elongation and other types of deformation as well. The second part of this paper deals with the theory of recrystallization textures. In the most successful theory for aluminum recrystallized after compression,1 much weight is given to the orientation of highly stressed nuclei in the deformed material. Taylor&apos;s "local distortions" are assumed to exist along the slip planes where displacement has occurred, consisting of fragments rotated in a specific way with reference to the slip plane and slip direction; namely, about an axis lying in the slip plane perpendicular to the slip direction. 1,7,8,9

Jan 1, 1940

By C. H. Stewart, R. A. Fagin

A two-dimensional, three-phasereservoir simulator was programmed for a large memory digital computer. It was designed to provide a practical solution to describing the complex physical relation between the natural forces and the physical properties of a heterogeneous reservoir when subjected to a specific set of conditions. A reservoir study is briefly described to illustrate application of the model. A full volumetric account of three phases (oil, gas and water) is performed simultaneously throughout an integration net representing the reservoir. Absence of one or two of the phases is treated as a special case of the more general situation. Expansion (or contraction) of all phases, including rock expansion, is performed so that the pressure calculation is the general unsteady-state case. To account for the large variations of subsurface elevation encountered in some reseruoirs, and to allow for segregation of the various phases, a gravity head term is included in the basic drive potential. Appropriate fluid and rock properties are used in polynominal surface form (functions of pressure and/or depth) or they can be entered as space variables at each position of the integration net. An unsteady-state water influx calculation, based on the method of van Everdingen and Hurst, l was connected to the boundary of the matrix to simulate aquifers of various sizes. In addition to reservoir calculations, three-phase fluid flow from the producing depth to the wellhead, including provisions for gas lift, was incorporated in the simulator. A workover routine was also built which can automatically switch to a different set of production relations when a gas-oil ratio or water fraction reaches a limit; or it can shut-in the well if prescribed. INTRODUCTION This paper describes a reservoir engineering mathematical simulator used to represent the complex interaction of natural forces and physical properties of a reservoir during natural depletion or with various injection schemes. The simulator, which was programmed for a large memory digital computer, is a two-dimensional calculation which handles three mobile fluid phases simultaneously (oil, gas and water). Basic requisites for the method are individual well production and pressure data, hydrocarbon fluid properties, geological data (producing depth and net sand), capillary pressure data, relative permeability data and permeability and porosity information. Matching the past performance of a combination drive reservoir often has yielded information concerning continuity and the validity of basic data. Detailed predictions of future performance can be made for continuation of current depletion methods (natural depletion) as well as for various types of recovery by gas or water injection. Combination injection cases and pattern studies can also be performed. Workover programs, gas lift and different types of artificial lift programs have been investigated using a technique similar to that described by Kern and Nicholson2 except that conditions of pressure and saturation at the block within which the well is located are used rather than average reservoir conditions. Drilling additional wells to optimize profit was explored, both as to number and location, by placing wells at different spots within the reservoir matrix. Special depletion processes can be examined, such as upstructure drainage and lateral (or strike) waterfloods in thin oil columns. In one case the mathematics of the simulator were modified to calculate the displacement in the vertical plane rather than in the horizontal plane. In this manner specific reservoir problems can be studied, such as coning of gas and/or water around production points, fingering along permeable stringers or, more generally, frontal advances in a heterogeneous section.

Jan 1, 1967

R. Schuhmann, Jr. (Purdue University)— Fulton and Chipman&apos;s results on rate of silica reduction from slags are analogous in many was to the results of Parlee, Seagle, and Schuhmann10 on rate of alumina reduction from alumina crucibles. Both investigations have given comparably low rates of reduction and slow approaches to equilibrium. Accordingly, we may hypothesize that the rate-determining step is the same in both kinds of experiments; that is, oxygen diffusion across the stagnant boundary layer on the liquid-metal side of the interface between the liquid metal and the oxide phase (slag or solid oxide). I suggest that silica reduction involves the following consecutive steps: I) At the slag-metal interface: SiO2(slag) Si+ 20 II) Transport of oxygen from slag-metal to gas-metal interface: a) diffusion across liquid-metal boundary layer at slag-metal interface. b) convection within the body of liquid metal. c) diffusion across boundary layer at metal-gas interface. 111) At the metal-gas interface: C +O- CO (gas) Iv) At the graphite-metal interface: C (graphite) -C At steelmaking temperatures it is reasonable to assume that equilibrium is attained in all three chemical reactions (I, 111, and IV) right at the respective interfaces. Convection within the stirred liquid metal (step IIb) is also rapid. Transport of Si and C should be orders of magnitude easier than transport of 0, because of the relatively high concentrations of Si and C. Accordingly, we might expect the overall reaction rate to be determined by boundary-layer diffusion of oxygen, either IIa or IIc. Fulton and Chipman&apos;s demonstration that bubbling CO through the system had no major effect on reaction rate indicates that IIc is not the slowest step. Therefore, it becomes logical to estimate the maximum rate for step IIa and to compare this theoretical estimate with Fulton and Chipman&apos;s experimental data. If oxygen diffusion across the liquid metal boundary layer at the slag metal interface (step IIa) is rate-determining, In this equation, dn sio, /dt is the rate of silica reduction in moles per sec,A is the area of slag-metal interface in sq cm, Do is the diffusivity of oxygen in sq cm per sec, 6, is the boundary layer thickness in cm, c,* is the oxygen concentration right at the slag-metal interface in moles per cubic cm, and co is the oxygen concentration in the body of the liquid metal, also in moles per cubic cm. Equilibrium data" on the silicon deoxidation reaction in liquid iron and steel at 1600°C indicate that the oxygen contents of the liquid metal in Fulton and Chipman&apos;s experiments at 1600°C probably fell in the range of 0.5 x10-3 x10-3wt pct. That is, the maximum conceivable value of co*-co for the system under consideration was on the order of 10"5 mole oxygen per cubic cm. On the basis of previously published data,1O,11 it is estimated that Do/0 will fall somewhere in the range from 10-3 to 10-1 cm per sec. The surface area A in Fulton and Chipman&apos;s experiments was approximately 20 sq cm, and the weight of metal involved was about 500 grams. Combination of all these figures with the above rate equation leads to an estimate that the rate of silica reduction should fall within the range from 0.002 to 0.2 wt pct Si per hr. This estimate is consistent with the experimental data. For example, Fulton and Chipman&apos;s Fig. 2 shows a change of about 0.3 pct Si in 10 hr, corresponding to an average rate of 0.03 pct per hr. According to the proposed hypothesis, increasing the temperature will increase the reaction rate ill two ways: 1) by increasing oxygen diffusivity and 2) by increasing the oxygen concentration (oxygen solubility) in the liquid metal. The combination of these two effects accounts for the high value of the observed activation energy. Summarizing, I propose that the rate of silica reduction, like that of the carbon-oxygen reaction, is diffusion controlled and that low oxygen concentration in the liquid metal is the major factor accounting for the very low observed rates of silica reduction. John Chipman (author&apos;s reply)—The authors thank Professor Schuhmann for his interesting contribution. His proposed explanation may well prove to be the correct one. There is clearly a need for much further experimental work on this problem, and further research is in progress.

Jan 1, 1961

By L. C. Graton

THE Federal taxes on incomes and excess profits are of course heavy. In 1917, the value of the mineral production of the United States was a little in excess of $5,000,000,000. The total of Federal taxes for that year, for the mineral producing companies, as computed by themselves, amounts, according to tentative compilations, to about $207,000,000, and the total for the comprehensive group of mineral and metal indus-tries to about $766,000,000, which figures represent respectively 9.5 per cent. and 35.1 per cent. of the total tax paid by all corporations. Be-cause of greater complexities in applying the revenue laws to mineral properties than to most other industries, opportunity is afforded for wide differences of view. The taxes indicated above, therefore, are not final

Jan 11, 1919

By D. Harker, M. J. Murphy

The mechanism by which age-hardening takes .place is still not completely understood. The principal theories range from the extreme of "precipitaiion-hardening" to that of "order-hardening," with many intermediate gradations. In the hope of obtaining new data on which to base a choice among the many theories, the authors have made electron micrographs of formvar replicas taken from metallic specimens at various stages of age-hardening. The results so obtained on an alloy of 2 per cent beryllium in copper and one of 20 per cent molybdenum in iron will be described in the following pages, as well as the technique used in preparing the replicas. Preparation of Formvae. Replicas of Metallic Specimens This section is concerned with the techniques that have roved successful in preparing formvar replicas for studying the microstructure of metals with the electron microscope. Because of its simplicity and accuracy, the formvar replica1 method developed in the General Electric Research Laboratory has been used exclusively, since it is much simpler than the silica replica method of Heidenreich and Peck2 and produces as good results. The formvar method to be described requires a technique acquired only by practice, and no foolproof set of rules can be given. it is a rapid method and a replica can be obtained in less than five minutes under favorable conditions. This does not mean that perfect replicas can be produced every five minutes, but rather that one can well afford to take several strippings* in order to produce a replica of high quality. The metallographic technique required for replica work—very fine polishing and etching with very dilute solutions—is described here. It can be said, in general, that almost any surface that has been carefully prepared for a photomicrograph at 1000 or more diameters can be used to obtain a replica for the electron microscope. Preparation of Metallographic Specimens The preparation of the metallographic specimens is somewhat more exacting than that usually given to samples to be used for inspection under the light microscope. After much experimentation, it was concluded that the best method consists in polishing the metal through to the coarse cloth, then etching and repolishing on final cloth until the layer of distorted metal is removed. After this procedure has been completed, a dilute etch—to approximately the depth necessary for a micrograph at 1000 diameters—usually produces a sur-

Jan 1, 1945