Search Documents

By Bertrand L. Johnson

Barite, the natural sulfate of barium (BaSO4), is the most important barium mineral. Normally it is white (opaque to translucent), but impurities sometimes render it yellow, gray, blue, brown, red, or black. Brown or red stains are commonly caused by iron oxide. Barite is unusually heavy (specific gravity, about 4.5); in fact, it is one of the heaviest of the nonmetallic minerals. It is brittle and fractures unevenly. The hardness of barite ranges from 2.5 to 3 but is usually about 3. It can be scratched by a copper coin. Pure barite contains 65.7 percent BaO and A.3 percent S03. Much of the crude barite ore mined, however, contains impurities; thus it has a lower content of barite and consequently less barium oxide. Commercial analyses show its total BaSO4 content. Barium also occurs in nature as the mineral witherite (BaCO3), which, however, is not common in the United States, and commercial deposits have been found only in California. Witherite is a yellowish-white, light-gray, or Kite mineral with a specific gravity of about 3, a hardness of 3 to 4, and an uneven to subconchoidal fracture.

Jan 1, 1941

By R. Farrar

Protective canopies for conventional electric face equipment, including shuttle cars, operating in low coal (less than 48 inches) were designed, fabricated, installed and evaluated on in-mine machines engaged in regular coal mining operations. This work was performed under contract to the U.S. Bureau of Mines, Pittsburgh Mining and Safety Research Center. The canopies will support a vertical load of 18,000 pounds and provide protection against both roof falls and contact with the mine rib. Canopy configurations were established based on human engineering studies, full scale canopy mockups, and in-mine observation and consultation with mine and equipment manufacturing personnel. Overall height of each canopy is hydraulically adjustable between a minimum of 32 inches and a maximum of 40 inches. Canopy tops are open framework, welded structures, covered with expanded metal mesh. Structural members are 1 3/4-inch or 2-inch square tubing of AISI 413ON and ASTM A500 material, respectively. The canopy tops are typically supported by an understructure and upright post arrangement that is either integrated into the current operator platform or attached to the machine frame. The four upright corner posts house the hydraulic actuators. Canopy tops are elevated horizontally. Canopies are welded or bolted to the existing machines. Installation is accomplished with a minimal amount of interface modifications. No major machine design changes are required. Canopies were trial installed and load tested at the manufacturer's facility prior to installation on the in-mine machines. Canopies were installed on a Joy 14BU10 Loader, 16RB-3AH Cutter, and two 21SC Shuttle Cars, and a Galis 300 Roof Drill and 460-S Face Drill. Canopy installations were evaluated in the Jewell Ridge Coal Company No. 12 and Big Creek Tiller Mines. Operational time accumulated on the installations during evaluation ranged from 1 week to 14 weeks of two-shift operation. All five canopy designs, manufacture, and test were successfully accomplished. The five canopies met all safety requirements. Three of the five canopies were deemed to be completely successful from an operator's point of view. That is, mine management as well as the machine operator found that the canopies did not impede the operation of the machines to function with the same efficiency as before the installation of the canopies. The loader canopy, in fact, appeared to have provided a mole efficient operation of the loader by providing added safety to the operator from rib contact thus allowing him to concentrate more fully on the loading function. Operational problems were encountered with the shuttle car and the roof drill. The shuttle car canopy obstructed visibility to an objectionable amount and the roof drill canopy impeded maneuverability of the machine, more than doubling the roof bolting time.

Jan 1, 2012

By J. J. Forbes

The original organic act establishing the Federal Bureau of Mines in 1910 and the amended act of 1913 indicated that promotion of the health and safety of mine workers was to be ore of the chief functions4/ of the Bureau. Many of the field and laboratory studies pursued by the Bureau are designed to improve conditions under dish minors must work. As the Bureau has no legal authority to enforce safety rules, it must rely upon cooperation of employer, employees, State mining or other departments, and labor organizations for success in promulgating its finding and making recommendations. The staff of the Safety Division, which is essentially a service organization of the Bureau, is composed of 28 safety instructors, 29 engineers, 18 clersk, and 7 others engaged in promotion of an educational program in an effort to improve conditions in the mining industry. The work is directed from 14 safety stations in the United States and 1 in Alaska. The work of the personnel, of the mine safety car that operates in. the anthracite region of Pennsylvania was supervised and directed by the district engineer in charge of the Wilkes-Barre (Pa.) Safety Station.

Jan 1, 1940

By S. James Campbell

Ladies and Gentlemen: Never in the history of our mining industry has the emphasis on public relations been accelerated as much as it has in the last few years. Knowing of your keen interest in this subject I consider it a great privilege that your program committee has asked me here to discuss the crushed stone segment of our industry approach to this important part of our daily business lives. As you are aware, crushed stone operations are present in almost every segment of the country wherever aggregates for construction projects are required. The tonnage of crushed stone produced is second only to sand and gravel - another source of aggregates - and this together with sand and gravel amounts to over half of the tonnage of all mined products in the United States. What is unique about this industry that will be of interest to all of you in analyzing how they have approached Public Relations? The fact that it is so wide-spread is of course obvious, but perhaps a more significant nature of this segment of the mining industry that has brought it more in the limelight of public interest and on a larger scale is the location of a large part of the quarries quite close into the urban area and population centers where you have the greatest demand for aggregate products.

Jan 1, 1969

By K. E. Waters, J. E. Nesset, F. Rosenblum, R. Langlois, J. A. Finch

"Some sulphide mineral mixtures when exposed to air and a warm and humid environment can exhibit a self-generating temperature rise, referred to as self-heating or spontaneous heating. The observed self-heating derives from the oxidation reactions of the active sulphides. In previous publications by the authors, it was proposed that the self-heating of sulphides proceed in three distinct stages; namely, Stage A, Stage B and Stage C. In Stage A (<100OC) the sulphides, in the presence of moisture are oxidized, generating heat through a series of sequential reactions and forming elemental sulphur as one of the products. In Stage B (>100OC) the elemental sulphur produced in Stage A is further oxidized to generate additional heat and SO2. Stage C (>~380OC), sometimes referred to as thermal runaway or roasting, is not addressed in this paper. This communication focuses on the type and role of elemental sulphur found in Stages A and B, and the sequence of reactions that is occurring in Stage A. The sequence is divided into two phases, the first based on galvanic interaction between the sulphide minerals that generates an acidic environment but little heat, and the second involving the production of H2S which rapidly oxidizes to produce heat and elemental sulphur. To date, data suggest that the primary oxidation product formed in Stage A is the stable orthorhombic a-S8 form of elemental sulphur. Above 96OC the a-S8 transforms to a monoclinic ß-S8 structure which is less stable and will readily oxidize to generate heat and SO2. Above 159OC a proportion of the ß-S8 sulphur will transition to a polymeric Sµ form of sulphur which can readily volatilize. INTRODUCTION Some particulate and granular materials, when exposed to appropriate atmospheric and physical conditions, can exhibit a self-induced temperature rise resulting from accumulated heat due to internal exothermic oxidation reactions. This phenomenon is commonly referred to as self-heating or spontaneous heating. Under favorable physical and environmental conditions, these reactions can elevate the temperature of a given material from ambient to the point of auto-ignition. Self-heating behaviour should not be equated to pyrophoric behaviour which describes a group of materials (e.g. certain finely powdered metals) that will ignite spontaneously in air below 55OC. There are numerous materials such as coals, hay, forestry wood products, food products to name a few that can exhibit self-heating behaviour. This publication continues the focus of the authors on the self-heating of sulphide mineral mixtures. Many of the metals of commercial use found in nature are in the form of these sulphides which must be mined, crushed, ground and concentrated prior to smelting or hydrometallurgical processing in order to produce primary metal. The issues of sulphide self-heating therefore pertain to the mining and processing of metals."

Jan 1, 2018

By G. R. Hopkins

According to reports received by the Bureau of Mines, Department of Commerce, as of January 1, 1929 there were 413 completed refineries in the United States, with a total daily crude-oil capacity of 3,509,540 barrels. In addition, 14 refineries, with a potential capacity of 99,000 barrels, were being constructed. Of the completed refineries, 341, with a capacity of 3,325,890 barrels, or 95 per cent of the total capacity, were in operation; and 72, with a capacity of 183,650 barrels, or 5 per cent of the total, were shut down. The improved condition of the refining industry in 1928 was indicated in several ways; namely, in an increase in the total capacity of the completed plants, in the opening up of a few plants which were shut down during 1927, in a decrease in the number of plants dismantled, and in an increase in the number of plants under construction. The majority of the refiners have followed a steady expansion program commensurate in most cases with the increase in demand for petroleum products. Obsolete equipment has been dismantled and modern equipment has been installed, with the net result that the total capacity of the completed refineries in the United States has shown a steady increase since January 1, 1918, the date of the first Bureau of Mines survey. Between January 1, 1928, and January 1, 1929, the number of completed plants fell from 423 to 413, but their total capacity increase 259,160 barrels, or 8 per cent. This compares with an increase in runs to stills of domestic and foreign crude petroleum of 10 per cent, and of domestic crude alone of 7 per cent.

Jan 1, 1929

By Catherine T. Ziten

Introduction ?Environmental assessments required for permitting ?Focus on ammonia produced through mine construction & blasting ?Water quality guidelines: federal, provincial, IGO ?Reported values are typically estimates from other projects ?Predictive modelling of ammonia aimed to assist planning

May 1, 2009

By George A. Roberts, Arthur H. Grobe

H. H. Hausner (Sylvania Electric Products Inc., Bayside, N. Y.)—I tested the 18-8 stainless steel powder described by Grobe and Roberts and the results were excellent. The powder was compacted and sintered in purified hydrogen to a very low density (approximately 20 pct and more porosity). Where the other powders show very little ductility when sintered to such a low density, the described stainless steel was surprisingly high in ductility. I would appreciate it if the authors could give us some data on a similar powder but without silicon and also data on 430 stainless steel powder. H. S. Kalish (Sylvania Electric Products lnc., Bay-side, N. Y.)—I should like to verify the excellent results obtained by Grobe and Roberts with their pre-alloyed stainless steel powder. It seems to me, however, that their data are conservative and that even better densities and higher tensile strength can be obtained with these powders by the selection of proper particle size fractions. The accompanying data were obtained by sintering compacts pressed from the powder made by Vanadium-Alloys Steel Co. to 0.8 in. in diam about % in. high in a cylindrical double action die without the use of lubricant. The compacts were sintered for 1 hr at 2370°F in hydrogen purified by passing it through a Deoxo unit (palladium catalyst) and a Lectrodryer. Even the density obtained using the as-received (—100 mesh) compacted at 40 tsi was quite high as was the hardness. This indicates that by increasing the sintering temperature slightly above 2350°F the coining and subsequent secondary sintering operation can be avoided. With the — 325 mesh fraction, however, very much higher density can be obtained and a high hardness. I have no tensile data to present, but I feel that it is not too optimistic to expect. that unusually high tensile strengths and good ductility can be obtained in this sintered material on the basis of the density and hardness data. The sintered stainless steel made by the above-described methods came out of the furnace very bright and clean. The purified hydrogen atmosphere is important in sintering stainless steel to reduce the oxide present in the powder. The result of such a sintering is good densification and good ductility of the sintered product. G. A. Roberts (authors&apos; reply)—We are greatly indebted to Messrs. Hausner and Kalish for their discussions of our paper. Their encouraging remarks are greatly appreciated and their confirmatory data will do much to add to the value of the paper. At the present time it is impossible to provide complete data on a similar stainless steel powder without silicon, but we do know that, in general, the properties are slightly inferior. Data on such a powder and on other stainless steel types are to be published in the near future.

Jan 1, 1952

By C. Richard Tinsley

INTRODUCTION The economic analysis (Chapter 3), the engineering studies (Chapter 10), the credit structure (and the consequential funding sources) - Chapter 11, and the overall feasibility structure for any venture are all directed to determining one major decision element: How much and how certain is the reward for taking these risks? Risk assessment is a surprisingly weak area of analysis and is usually addressed in a checklist fashion. It is much preferable to deal within a risk system so that the inevitable tradeoffs among risks are correctly made. DEFINITION The first step toward risk definition must be to ascertain all of the risks to which a project or a company is exposed; otherwise one will remain ignorant of the possibility of a financially crippling loss until it occurs. (Carter and Crockford, 1974). However, simply stating what "risk" is can lead to debate. For example, risk could be (adapted from Vaughan, 1982): -the chance of a loss - uncertainty of loss -possibility of loss - uncertainty -dispersion of actual from expected results - probability of an outcome different from the one expected - possibility of an occurrence of an undesirable contingency -a condition in which a possibility of a loss exists. For the minerals industry financier, the last definition is probably the most appropriate. However, from a mineral company&apos;s point of view the definition might well include the possibility of not achieving the expected financial return. RISK CLASSIFICATION Risk identification will be readily agreed as the all-important first step. There are five major "branches" of risk classification. These are: -Statistical -Modellers -Checklist -Project Financing -Insurance The Statistical set discovered probability theory and any risk discussion soon deteriorates into a mathematical jungle (Megill, 1977; Hartman, 1976; Reutlinger, 1970; and Pouliquen, 1970).Their use of terminology tells its own story: coin toss (binomial distribution), gamblers&apos; ruin, delphi (oracle) techniques, monte-carlo simulations, random walks, etcetera. These techniques inadequately represent the judgements necessary in an increasingly complicated and interrelated world. The risk Modellers have turned to the computer to handle these inter-relationships but soon find barriers because of "simultaneity". Certainly the computer has its uses to conduct various analyses (marketed as "sensitivity" analyses) but very often one finds that this involves changing one or two variables at a time, all other things being equal. Unfortunately, in a modern and complex world all other things do not remain equal. The statisticians will, no doubt, jump to their own defence by citing this

Jan 1, 1985

By J. S. Hansen

To advance technology that can conserve critical materials, the Bureau of Mines investigated a cast-on hard-surfacing that wear resistance and confines alloy additions to wear-prone surfaces. Wear-resistant material in form is on a polystyrene , the is embedded in a mold of unbonded s and the wear-resistant material is transferred to a cas surface at the time of For low-stress abrasion, derived from high-carbon ferro-chrome had higher wear resistance than did commercially available weld-hard. The microstructure of the was typi-white iron carbides. Free carbon added to the ferrochrome powder produced more M7C3 carbides than did material contained in surfacings made from ferrochrome alone, and improved the wear resistance. Several white iron powders with greatly reduced chromium contents also white iron contain-M7C3 carbides. One derived from white iron powder had wear resistance to that of weld-deposited hard facings. Among the parameters investigated, surfacing thickness was found to have a or influence on diffusion of elements out of the , microstructure, and wear resistance. The results of field tests on bucket-wheel excavator teeth and plowshares with cast-on hard surfacing are given.

Jan 1, 1985

By Heinrich Ries

I. INTRODUCTION. THE facts is presented in this paper, based chiefly on recon¬naissance made, during the summer of 1903, by myself and my assistant, Mr. R.. C. Brooks, cover practically all that portion of Texas lying east of the 99th meridian. The work was undertaken for the University of Texas Mineral Survey, and was to have been extended over the entire State, but the sudden termination of the survey prevented even the official publication of the results already obtained. Most of the mineral resources of Texas were fully treated by the First Geological Survey, but the clay-industry was tit that time little developed, so that only a few scattered notes concerning it are to be found in the Survey reports. The extensive exploitation of the clay-deposits, however, has emphasized their commercial importance, and has also made accessible many facts of exceptional interest concerning their geologic conditions. The erection of new plants for the utilization of clay-products is usually preceded by more or less prospecting, which, by reason of the scarcity of outcrops, and the geologic and topographic conditions of eastern and southeastern Texas, is often slow and difficult work. This is especially true in the Tertiary and Pleistocene areas, where the structural conditions much resemble those of the Atlantic coastal plain, the deposits being mostly lenticular in form, and surrounded by beds of sand. II. GENERAL GEOLOGY OF THE CLAY-DEPOSITS. The accompanying sketch-map, Fig. 1, shows the location of nearly all the deposits examined, their relation to the geology of the State, and the type of clay found in each. The geology is based on the published work of Hill, Cummins, Tail, Adams, Hayes and Kennedy, but the boundaries have unfortunately not been determined over the entire region covered by the map, and, in many areas, are only approximate. It will be seen that the clay-deposits range from Carboniferous to Pleistocene in age, the older deposits being found in the northwestern part of the area, while those of Cretaceous and Tertiary age lie to the east, southeast and south. The Pleistocene clays are found in part in a belt along the coast, and in part along many of the larger rivers, where they often underlie extensive terraces.

Sep 1, 1906

By P. N. Anyalebechi

A comparative study of the mechanical properties of automotive steering knuckles produced by three different shape-casting related processes has been conducted. It involved the characterization of the tensile and fatigue properties of aluminum alloy A356 knuckles produced by the vacuum/pressure riserless casting (VRC/PRC), pressure counter pressure casting (PCPC), and the hybrid Cobapress (a casting-forging) processes, in accordance with the appropriate ASTM standards. Surprisingly, the knuckles produced by the hybrid Cobapress process exhibited the lowest strength. For example, the average 0.2% yield strength of the Cobapress knuckles was 31 MPa and 40 MPa less than that of the VRC/PRC and PCPC knuckles, respectively. However, between stresses of 150-200 MPa, the fatigue lives of the VRC/PRC, PCPC, and Cobapress knuckles were comparable. But above 200 MPa, the Cobapress knuckles exhibited the lowest fatigue life. The observed differences in the mechanical properties are attributed to the inherently different microstructures of the different knuckles.

Jan 1, 2009

By S. D. Dladla, S. Ramsamy

The majority of the tailings dam operations in South Africa will be required to comply with the new Global Industry Standard on Tailings Management (GISTM) within the next one to three years, depending on the dam classification and the requirements of the respective investors and insurers. With up to 72 auditable requirements, the implementation of the Standard needs careful planning and prioritization. This paper focuses on the practical steps to GISTM compliance for tailings facilities in operation in South Africa. The discussions are based on current practices, South African regulations, and industry standards requirements. The possible changes in dam classifications and the associated requirements are presented.

Jun 2, 2022

By John B. Ivey

This is a geologic study of the U.S. Bureau of Mines Oil Shale Tract in the Piceance Creek Basin of Rio Blanco County, Colorado for the preparation of a set of detailed surface geologic maps, measurement and identification of joint attitudes and frequencies, and the classification and mapping of the soils of the area.

Jan 1, 1978

By P Tzeferis

An exploratory laboratory work was carried out on microbial leaching of poor non-sulphide nickel ores, not amenable to conventional mineral processing operations. The results have shown that domestic low-grade lateritic ores of limonitic or haematitic type are amenable to bioleaching by fungal strains of Aspergillus sp and Penicillium sp. Maximum nickel and cobalt recoveries achieved were 60 per cent and 50 per cent respectively. Losses of soluble nickel in the fungal biomass were found in the range 3 - 11 per cent. Chemical analysis of the leach liquors showed the presence of significant amounts of citric, oxalic and other organic acids, indicating the role which certain metabolic products of fungal activity may play in the process. Possibilities for future investigations are discussed.

Jan 1, 1997

By S. Y. Tshipeng, A. T. Kaniki

"RÉSUMÉ La lixiviation acide d’un minerai oxydé cupro-cobaltifère en milieu non réducteur et en milieu réducteur en utilisant le Fe2+ et le métabisulfite de sodium (SMBS) a été étudiée et les résultats ont été comparés. Les tests de lixiviation ont été effectués à température ambiante, dans une pulpe à 30 % solide, avec une vitesse d’agitation de 600 tr/min, un potentiel redox de 350 mV pour les tests en milieu réducteur, et un pH de 1,8. Les tests de lixiviation avec usage du SMBS comme réducteur ont donné la meilleure cinétique de lixiviation du cuivre. Pour le cobalt, c’est l’usage du Fe2+ qui a donné la meilleure cinétique de lixiviation. L’augmentation de la dose du fer dans la solution au-delà de 5 g/L a influencé négativement les rendements de lixiviation du cuivre et du cobalt. ABSTRACT Acid leaching of a copper-cobaltiferous oxide ore in a non-reducing environment and in a reducing environment using Fe2+ and sodium metabisulfite (SMBS) was studied and the results compa¬red. The leaching tests were performed at room temperature, in a 30% solids pulp, with a shaking speed of 600 rpm, a redox potential of 350 mV for the tests performed in the reducing environment, and a pH of 1.8. The leaching tests using the SMBS as a reducing agent produced the best copper leaching kinetics. As for cobalt, the best leaching kinetics was achieved using Fe2+. An increase in the amount of iron in the solution above 5 g/L negatively influenced copper and cobalt leaching yields. INTRODUCTION La République Démocratique du Congo (RDC) est un pays reconnu dans le monde pour son sous-sol qui regorge d’énormes quantités de cuivre et de cobalt (USGS, 2014; Palisade Research, 2016). La technique qui semble être la plus recommandée pour extraire à la fois le cuivre et le cobalt des minerais oxydés cupro-cobaltifères est la lixivia-tion acide en milieu réducteur. Cette technique est appliquée par la majorité des sociétés minières qui exploitent ces minerais dans l’ex-province du Katanga en RDC, à savoir: Tenke Fungurume Mining, Mutanda Mining, Kamoto Cop¬per Company, Sicomines, Gécamines, Boss Mining, Chemaf, Ruashi Mining et Somika. L’usage d’un agent réducteur est indispensable pour l’obtention d’un bon rendement de lixiviation du cobalt. En effet, plusieurs chercheurs s’accordent sur le fait que le cobalt trivalent de l’hétérogénite (CoO·2Co2O3·6H2O) est insoluble à l’action de l’acide seul; il ne devient soluble qu’après réduction en cobalt bivalent (Mwema, Mpoyo, & Kafumbila, 2002; Mulaba-Bafubiandi, Ndalamo, & Mamba, 2007; Ferron, 2008; Seo, Choi, Kim, & Tran, 2013; Stuurnam, Ndlovu, & Sibanda, 2014)."

Jan 1, 2018

By G. S. Beaumont

This report presents a programme of work to demonstrate the use of a surface-based centralised computer control system for the remote monitoring and control of underground conveyors in a US coal mine. The system selected for demonstration was the &apos;Dynalink&apos; Micro MINOS system which is manufactured by Hawker Siddeley Dynamics Engineering Limited. The site selected was Barnes S Tucker Lancashire No. 20 Mine located near Carrolltown, Cambria County, Pennsylvania. The system concept, operating and application software was designed and developed by the. British National Coal Board. The report describes the selection of the site, specification of the system requirements, commissioning, operation and evaluation of the system under typical US mine operating conditions. Experience with the system, based primarily on the system reliability and performance of conveyor control, was favourable. Mine management personnel felt that the system had successfully achieved its objectives and were keen to expand monitoring and control to other activities.

Jan 1, 1986

By Basil B. Zavoico

The production of all Russian fields incressed from approsimatctly 74,000,000 bbl. during 1926-27, to approximately 83,000,000 bbl. during 1927-28. Of this amount Baku was responsible for 54,.500,000 bbl., Grozny for 25,800,000 bbl., and Emba for 1,200,000 bbl. Accordingly, the proportional importance of the Grozny oil field has been considerably increased, the present production being twice that of 1913. The most notable factor of production during 1927-28 was the importance of gushers; 40.8 per cent. of the total was thus obtained. In the Baku fields 26 per cent. of the total, and in Grozny 74.2 percent&apos;. of the total were produced by naturally flowing wells. This may be explained by the reduction in authorizations for drilling by the central authorities, and, accordingly, the local trusts increased the production to the planned figures at the expense of the proved prolific reserves. In Baku region, the Surnkany oil field produced 36.1 per cent. of the total Baku production, or an equivalent of 53,800 bbl. per clay, the largest percentage coining from the fifth horizon. Nest year&apos;s plans call for continual development of that horizon as well as of the sixteenth horizon in the Bibi-Eibat field, which was opened lately. In the Grozny fields the New Area (Bellik) WAS responsible for 79.4 per cent. of the total production. The authorized plan for 1928-29 production calls for 92,200,000 bid., and a reasonably accurate estimate for 1932--33 production is placed at. 156,000,000 bbl., with Baku contributing 101,800,000 bbl., Grozny 44,100,000 bbl., Emba 6,200,000 bbl., Kuban 2,100,000 bbl., Saghalien Island 1,400,000 bbl., and Russian Turkestan 400,000 bbl. In connection with recent discoverices in the Baku area these figures art. quite conservative. The average production per well per day in the Baku oil fields was 49.2 bbl., in Grozny 175 bbl.; in detail, Surakany oil field averaged 250 bbl., and the New Area in Grozny 514 bbl. per day. New completions in all Baku fields averaged 264 bbl. per day, and in Grozny 970 bbl. pel. day. These figures show a considerable progress in the technical developnlent of all fields, compared even with the prerevolution figures, since all the mprovements are noted in the fields that arc over 30 years old.

Jan 1, 1929

By Nicholas J. Grant

It is the purpose of this paper to examine a number of the recent developments in powder metallurgy, being most concerned with those which are yet to prove themselves rather than those which have achieved commercial maturity. Such developments include the production of very much coarser and very much finer powders, down to the near-micron size range. Also considered are activated sintering, direct powder rolling and extrusion (both hot and cold), brazing and welding, hydrides of reactive metals, oxide dispersion strengthened alloys and theoretical evaluations. Introduction T HERE surely can&apos;t be very much argument with the fact that powder metallurgy has made large advances on many fronts during the past ten or more years (1). These advances have taken place in raw materials, in processing, in product development and in a better understanding of many of the phenomena which occur in the various steps involved in powder metallurgy. It should be clear, in view of such growth, that it will not be possible to highlight all of the new developments in the present paper. Many of these developments,

Jan 1, 1965

By S. L. Weber, D. E. Banks

"Silicosis was first reported by the ancient Greeks and is apparently as old as human history. The prevalence of this illness peaked in the last half of the 19th century and the early part of this century, when mechanized industry was developing and the relationship between dust exposure and disease was less well understood. Yet, even today in devel-oped countries, sporadic outbreaks of silicosis occur when workers are consistently exposed to silica particles of respir-able size (0.5 to 5.0 µm in diameter) at levels exceeding those recognized to be safe.Silicon dioxide or silica. is the earth's most abundant mineral. Silica is considered to be either free (i.e.. unbound to other minerals) or combined. Minerals with high amounts of free silica include quartz (including granite) flint. Chert, opal, chalcedony, and diatomite. Combined forms of silica are called silicates and include, among others, asbestos talc and kaolin.In the crystalline form, silica exists as quartz, cristobalite, and tridymite (Fig. 28). Of these quartz is ubiquitous in the environment and occurs as sand and as a part of many rocks. Cristobalite and tridymite occur naturally in lava and can be formed by the heating of quartz or amorphous silica. Cristo-balite is more tibrogenic than quartz. Amorphous silica is noncrystalline and, therefore, is relatively nontoxic and does not cause silicosis. It occurs as diatomite (skeletons of pre-historic marine organisms) or as vitreous silica (glass), the result of carefully melting and then quickly cooling free crystalline silica. Heating diatomite with or without alkali (a process known as calcining), forms cristobalite and adds the respiratory toxicity of free crystalline silica.There are many opportunities for occupational exposure to respirable crystalline free silica. Some of the commonly en-countered occupations in which the risk of silicosis exists are reported in Table 20.Silicosis. the pulmonary disease caused by the inhalation of silica particles of respirable size, is most commonly cate-gorized by findings on the chest radiograph. The most typical presentations simple silicosis and progressive massive fibrosis appear different radiologically but are grouped under the category of classic silicosis because they are a part of the radiographic spectrum of this illness. Radiographically, simple silicosis appears as small (less than 10 mm in diameter), rounded opacities, typically predominant in the upper lung zones. Progressive massive fibrosis is the result of the coalescence of these small nodular opacities and appears as larger opacities (more than 10 mm in diameter), again typicallydistributed in the upper lung zones."

Dec 1, 1995