Search Documents

By Arthur M. Langer

Since the promulgation of the first Federal Asbestos Standard by the Occupational Safety and Health Administration in 1972, other federal agencies have modified the standard to better carry on their own unique missions. The instruments used to identify and measure asbestos, the sampling protocol, and the criteria used to define asbestos, have been modified to some degree. The Mine Safety and Health Administration regulates and controls asbestos dust in the mining and mineral commodity industries. However, crushed stone and processed ores contain mineral fragments that are frequently difficult to distinguish from asbestos. Mineral nomenclature, instruments for particle analysis, and sampling strategy must be accommodated to some degree to make asbestos control workable and meaningful. Precedent in other agencies has made consideration of these changes possible. Newly identified amphibole asbestos minerals have further complicated the agency?s regulatory charge. Changes in its Asbestos Standard are now being considered. Crushed taconite ore in the Eastern Mesabi highlights many of these issues. ©2008 Published by Elsevier Inc. Keywords: Amosite; Grunerite asbestos; Crocidolite; Riebeckite asbestos; Tremolite asbestos; Actinolite asbestos; Winchite asbestos; Richterite asbestos; Arfvedsonite asbestos; Fluor-edenite asbestos; Asbestos defects; Cleavage fragment; Mineral habit; Mesabi amphiboles

Jan 1, 2008

By A G. L Pratt

Inclined troughed belt conveyors are more frequently being selected from a range of alternatives, which include shafts and trucks for ore haulage in underground mass mining projects. Belt conveyor haulage systems are being operated with lifts exceeding those normally associated with truck haulage systems and approaching the limits of shaft haulage systems. A belt conveyor haulage system, in this context, incorporates subsystems for: crushing,tramp detection and removal, andhaulage. This paper presents details of recent inclined troughed belt conveyor systems for underground mining operations, and explores the application of inclined troughed belt conveyors for the increasing demands of future underground mass mining projects.

Jan 1, 2008

By Jesús E. Gómez

This work is a continuation of a paper presented in the 32nd DFI Annual Conference, Colorado 2007, titled ?Hollow Core Bar Micropiles - Design parameters interpreted from 260 load tests.? The first paper presented the results of the verification and proof tests performed for the retrofit of two bridges with hollow core bars that used 260 micropiles. It included an interpretation of the unit bond values in the different soils where micropiles were installed. Recently two additional bridges within the same geological environment were also retrofitted using 144 hollow core micropiles. This paper includes the interpretation of the additional data from the proof tests performed and refines recommended values for design of hollow core bar micropiles in soils similar to those encountered in these two projects. The authors believe that the data collected will significantly add to the relatively small existing database on micropile tests and may also be useful during implementation of the LRFD design methodology.

Jan 1, 2008

By B. Valentim

The methodology used to obtain fly ash subsamples of different sizes is generally based on wet or dry sieving methods. However, the worth of such methods is not certain if the methodology applied is not mentioned in the analytical procedure. After performing a fly ash mechanical dry sieving, the authors compared those results with the ones obtained by laser diffraction on the same samples and found unacceptable discrepancies. A preliminary study of a wet sieving analysis carried out on an economizer fly ash sample showed that this method was more effective than the dry sieving. The importance of standardizing the way samples are handled, pretreated and presented to the instrument of analysis are suggested and interlaboratory reproducibility trials are needed to create a common standard methodology to obtain large amounts of fly ash size fraction subsamples.

Jan 1, 2008

By M. Abzalov

"Control of analytical data quality is usually referred to in the mining industry as Quality Assurance and Quality Control (QAQC), and involves the monitoring of sample quality and quantification of analytical accuracy and precision. QAQC procedures normally involve using sample duplicates and specially prepared standards whose grade is known. Numerous case studies indicate that reliable control of sample precision is achieved by using approximately 5% to 10% of field duplicates and 3% to 5% of pulp duplicates. These duplicate samples should be prepared and analyzed in the primary laboratory.Bias in the analytical results can be identified by inclusion of 3% to 5% of the standard in each sample batch. Several different standards are used, with values spanning the practical range of grades in the actual samples. A blank (a sample in which the concentration of metal of interest is below detection limit) should also be included. Standard samples alone cannot identify biases introduced during sample preparation, and therefore approximately 5% of the duplicate samples (coarse rejects and pulp) should be processed and assayed at another, external, reputable laboratory.This paper discusses techniques used for estimation of errors in precision and accuracy, and overviews diagnostic tools. It is shown that one of the most commonly used methods, the Thompson-Howarth technique, produces consistently lower results than other methods. These results reflect the nature of this method, which relies on the assumption of a normally distributed error, and thus produces biased results when errors have a skewed distribution. This study concurs with the suggestion of Stanley and Lawie (2007: Exploration and Mining Geology, v. 16, p. 265-274) to use the average coefficient of variation (CVAVR(%)) as the universal measure of relative precision error in mine geology applications: Le contrôle de la qualité des données analytiques est habituellement désigné sous l’appellation d’Assurance et Contrôle de la Qualité (ACQ), elle implique le suivi de la qualité des échan¬tillons et la quantification de la reproductibilité et la précision analytiques. Les procédures des pro¬grammes d’ACQ impliquent habituellement l’usage de duplicata et de standards analytiques dont la teneur est connue. Plusieurs études de cas indiquent qu’une bonne fiabilité du contrôle de la précision des échantillons est atteinte par l’usage de 5% à 10% de doublons sur le terrain et de 3% à 5% de doublons de pulpe. Ces duplicata devraient être préparés et analysés au laboratoire principal.Un biais des résultats analytiques peut être identifié par l’inclusion de 3% à 5% d’échantillons standard dans chaque envoi d’échantillons. Plusieurs standards sont utilisés, avec des valeurs couvrant l’étendue des teneurs habituellement rencontrées dans des échantillons réels. Un blanc (un échantillon dans lequel la concentration d’un métal donné est sous la limite de détection) devrait aussi être inclus. L’emploi exclusif d’échantillons standards ne permet pas l’identification de biais résultant de la préparation des échantillons, de telle sorte qu’environ 5% des duplicata (rejets grossiers et pulpes) devrait être traités a un autre laboratoire indépendant et fiable.Cet article passe en revue les techniques utilisées pour évaluer l’erreur liée à la précision et a la reproductibilité, et effectue aussi un survol de divers outils diagnostiques. Il ressort de cet examen qu’une des techniques les plus fréquemment utilisées, la méthode Thompson-Howarth, fournit des estimés systémati¬quement inférieurs à ceux provenant des autres méthodes. Ces résultats sont un reflet de la nature de cette méthode, laquelle assume une distribution normale de l’erreur, biaisant ainsi les résultats lorsque l’erreur présente une distribution asymétrique. La présente étude recommande de privilégier l’usage du coefficient moyen de variation (CVAVR(%)) en tant que mesure universelle de la précision relative de l’erreu"

Jan 1, 2008

By M Schmid

German hard coal mining operations have decreased for more than 40 years. Current political decisions are leading to a discontinuation of subsidised black coal mining by the year 2018. This decision will, however, be reviewed once again in the year 2012. The enormous increases in productivity, which were achieved in previous years, have so far not led to an achievement of market requirements. Coal mining at depth of more than 1200 m in multiple seam environments is not yet competitive in global comparison. In 2008 the 24 faces left in eight mines produced about 20 million tonnes of usable steam coal. Management and the workforce will be reduced in parallel; from today until 2012 by more than half. The average age of personnel is increasing dramatically and nearly no new personnel are recruited. With this background in mind, increasing continuously coal mining productivity becomes more and more difficult. Above all, this goal was reached by mechanisation, then by increasing the mining machine power and then by enhanced machine control systems. The first attempts to automatically operate full face equipment from above ground were in the early 1980s. After successful automation of the face equipment, the emphasis is now on mine logistics. Autonomous monorail transport was introduced and tested in 2007. Since the development rate of machine improvements has its limits, the focus is on the full interaction of the total production system. Here information technology (IT) becomes important; the driver for more productivity. Actual developments aim for the complete and general homogeneous IT infrastructure both above ground as well as underground. The explosive environment needs high level investments in safe technology, eg access points for WLAN and fibre optics for underground use (ATEX certification). New technology availability also drives the enhancements of management and process control systems. Innovations in the mining industry often comprise technology advances through the adoption of well-known technologies. With virtual reality (VR) teaching and training systems advanced computational instruments, both in software and hardware development, were applied in the German coal mining industry for ten years. Widening lists of applications as well as the encouraging achievements show the economical benefits of investing in virtual reality technology both for teaching and training and for knowledge management. The paper discusses the actual technical achievements as well as in IT infrastructure utilisation and also in employment of virtual reality based systems. Special focus and deeper insight will be given to the fibre optics and WLAN hardware integration as well as software developments. The pocket personal computer (PC) is used to enhance underground material transport and data acquisition. The knowledge-based maintenance system (KBMS) integrates real-time virtual reality knowledge elements, such as repair process descriptions. It gives access to expert documentation by intelligent search algorithms and 3D representations of major mining machinery.

Jan 1, 2008

By Biserka Lucheva, Tzonio Tzonev

"A unique DC electric arc rotary furnace with capacity 150 kg has been designed and constructed for the recycling of low-quality scrap and aluminum dross. The main constructive feature of this furnace is that the axially positioned graphite electrodes (cathode and anode) are placed 100 mm away from the rotation axis of the furnace. A specific characteristic of the construction is the possibility one of the electrodes (the anode) apart from moving axially (parallel to the furnace axis) to move at 90° outside the working space. High recovery rate of metal aluminum from aluminum dross (92%) was realized in this furnace. This is the reason for construction of industrial DC electric arc furnace.IntroductionThe consumption of aluminum waste has been rising continuously on a world scale, which is a great stimulus for the development of the technology for aluminum recycling.To recover the aluminum in dross, the conventional recycling process uses salt rotary furnaces heated with a fuel or a gas burner. This treatment process produces a secondary dross containing alumina, salts, impurities and a small amount of aluminum. Molten aluminum is tapped from the furnace and the residue is then dumped from the furnace. It has been the practice to dispose the residue in a landfill. Improvement of this technology, known as the oxy-fuel process, uses a gas burner enriched with oxygen to increase the thermal efficiency [1]. Recent studies show that the most efficient aggregate for recycling of aluminum scrap has turned out to be the rotary tilting furnaces, heated by plasma or electric arc, for which the use of flux is not necessary [2,3].Accordingly, there is a substantial need in the industry for an improved process for recovering free aluminium. It is particularly desirable that such process be cost effective and ecologically safe."

Jan 1, 2008

This paper reviews the history of refractory materials, highlights the development of refractory technology over the years, draws attention to the technology behind these materials, and comments on future developments in this field. By walking the path with refractory materials, from their initial uses in BC times, to the composite materials that are used nowadays, and the nanotechnology developments that are currently taking place in this field, the reader will come to agree that refractory materials are indeed very ?cool?! Keywords: refractory materials; bricks; monolithic materials.

Jan 1, 2008

By Willard C. Lacy

A mining operation begins with prospecting and exploration-stages with long periods of investment and high risk of failure. However, success in exploration ultimately determines survival of the mining industry. Prospecting and exploration may discover evidence of a mineral occurrence and outline its size and character, but ore deposits that support mining are "made" through the collective efforts of project geologists, geophysicists, geochemists, metallurgists, engineers, chemists, lawyers, and even politicians (Joralemon, 1975). Some deposits may go through multiple cycles of rejection and recommendation, discovery and development, decline and abandonment, rediscovery and development, etc., as economic, technological, or political conditions change or geologic understanding is improved. Peters (1987, p. 233) graphically illustrates the normal life cycle of a mine and the position of exploration in the cycle (Fig. 4.0.1). During the past fifty years, mineral exploration has evolved from comparing evidence of mineralization of prospects with that of known deposits to a more quantitative science employing many facets of geochemistry, geophysics, multispectral sensing from space, computer data storage, analysis, modeling, and most importantly, a better understanding of ore genesis. This modem approach to exploration began in the late 1940s and continues to develop. Exploration efforts peaked in the 1960s with emphasis upon the search for porphyry copper deposits, Mississippi Valley lead-zinc deposits, and volcanogenic massive sulfide copper-lead-zinc deposits. It peaked again in the middle and late 1980s with emphasis upon micron-size disseminated gold and epithermal and stratiform precious metal deposits.

Jan 1, 2008

By P Jackson, J Rea, M D. Goodz

The Morning Star Gold Mine has operated over a 101-year period, producing gold from narrow quartz veins and sulfide stockworks hosted mainly within a dioritic-gabbroic dyke. The deposit has been developed over a vertical depth of 980 m with drilling extending the vertical depth to greater than 1200 m. Currently there is a total Inferred Resource of 4.6 million tonnes at a grade of 6 g/t for 910 000 ounces of contained gold resources, which comprises an underground project and a surface project. Significant variation exists between the grade of drill core intersections and that observed in face sampling and subsequent production reconciliation (250 - 650 per cent). Studies were carried out on ten major production reefs, where the grades of drill intercepts were compared with face samples collected during development and mining. The implications of this study have been used as justification to assign production or stope/development grades where applicable to resources that are direct extensions of the historical development headings. Grade assignment and its impact on sensitivity for gold resources are detailed and show a 40 per cent variation in the gold resource, depending upon whether a production or calculated stope grade is used in grade assignment for the major reef deposits. Recent diamond drilling has intersected approximately 40 new gold bearing quartz reefs and sulfide zones that contain all the key mineralogical and structural indicators, and traditional large variations in gold grades similar to the historical major production zones. The implications of grade factoring and grade assignment are the greatest challenges confronting the resource estimation team in defining grade for these new zones. Grade assignment is seen as a method of balancing known historical production observations with the irregular grade distribution inferred from drill core assay results. Ongoing mine development and bulk sampling works are planned to validate the grade assignment process. The first stage of this process is the trial mining of the newly discovered Maxwell Reef (MR). The stope drawpoints were completed in August 2008 and the MRS1 stope is scheduled for completion in September. The stope reconciliation results will be presented at the October 2008 conference.

Jan 1, 2008

By Miguel Barron

Recently, a new lance design for BOF steelmaking has been proposed in the literature. This lance, in addition to six peripheral inclined supersonic nozzles, contains a vertical centered nozzle whose oxygen flow is independent from the main oxygen supply. The above authors affirm that their lance maximizes the droplet generation without causing spitting. In this work, the performance of a lance with four peripheral nozzles and one vertical centered nozzle is numerically modeled by means of Computational Fluid Dynamics software. Transient two dimensional computer simulations were carried out considering two phases, namely molten steel and gaseous oxygen. Numerical results confirm that bath agitation and droplet generation are enhanced as a result of the vertical centered nozzle, however a proper performance of this lance, related to a conventional one, strongly depends on the Mach number of the oxygen jets and the lance height.

Jan 1, 2008

By Valcana Stoyanova

The distribution pattern, abundance variations and types of polymetallic nodules and associated megabenthic communities in area covers more than 60 000 km2 laid out in the eastern Clarion-Clipperton Zone (CCZ) is presented. Our observations are based on data from 158 boxcore stations collected during the cruise of the Interoceanmetal (IOM) in 2004 on board of RV Yuzhmorgeologiya. Although those polymetallic nodules for two decades been subject to prospecting and exploration studies carried out by IOM, the knowledge of megabenthic communities and their distribution pattern within nodule field was extremely limited. With purpose to evaluate the relationship between polymetallic nodules and associated benthic megafauna, an comparison analyze was carried out in respect to their composition, types, abundance across the studied area owing into account the local particular feature of bottom topography. It is suggested that the nodule-bearing seafloor supported more diverse fauna (higher number of morphotypes) than the nodule-free areas. Moreover, based on correlation between types of nodules and associated faunal morphotypes frequency the apparent relationship is considered. The most abundant megafaunal taxa (between 68 ? 92%) is essentially associated with the occurrence of the diagenetically growth nodules type (D-type and its D1-subtype); the role of the H and HD nodule-types was variable. In respect to the bottom topography, the highest diversity in the structure of megafaunal communities was recorded in the gently undulating plains and on the horst slopes, thus the highest nodule abundance occur on the topographic slopes.

Jan 1, 2008

To solve the mining safety and health needs of the future, access to, and sharing of, timely and relevant information will be crucial. The next generation of the Web will provide tools (RDF, OWL, SPARQL, etc) to define and link content for more effective discovery, integration, and reuse across applications and organisations. A recent Gartner Research Report (Finding and exploiting value in Semantic Web technologies on the web, May 2007) predicts these technologies will begin to coalesce in ten years. Implementing this Semantic Web requires structured web content described via metadata (information about information). If an industry or enterprise bases its metadata on a common vocabulary, it becomes possible to share and reuse information. The National Institute for Occupational Safety and HealthÆs (NIOSH) Mining web site provides access to more than 1500 NIOSH-developed publications, products, and topic pages on issues as diverse as ground control, respiratory diseases, and mine emergency management. As the site has grown, locating content has become increasingly difficult. To improve the searching process, a panel of internal experts representing all major research programs was established to develop a controlled vocabulary for indexing that content. The outcome is the NIOSH Mining Safety and Health Thesaurus, a faceted, hierarchical thesaurus containing hundreds of mining safety and health terms organised into 20 facets (eg diseases, injuries and disorders; hazardous events and exposures, equipment, engineering and administrative controls). One immediate goal of this project is to reduce the complexity of locating information on the NIOSH Mining web site by implementing metadata and faceted information retrieval techniques. Another goal is to stimulate discussion in the international mining community regarding developing metadata standards so the industry is ready to adopt future Semantic Web technologies to improve access to mining safety and health information.

Jan 1, 2008

By Jesus Gonzalez

Peirce-Smith converters (PSC) are long cylindrical chemical reactors where copper matte reacts with air. Traditionally, air is injected laterally through submerged tuyeres at different subsonic velocities. However, the accumulated experience in steelmaking, particularly in the basic oxygen furnace (BOF) process, shows that the gas bottom injection may improve the mixing efficiency of a liquid pool. The aim of bottom injection is to maximize the copper kinetic energy meanwhile avoiding excessive reactor splashing. When gas is injected from a single orifice at the bottom of a liquid pool, two main gas flow regimes can be identified, bubbling and jetting. In this work, a PSC with bottom air injection is studied by means of multiphase 3D CFD numerical simulations considering multiple air velocities. Special attention is paid to the bubbles and jet formation mechanism. The mixing efficiency is measured by calculating the turbulent kinetic energy of the copper matte.

Jan 1, 2008

By María Eugenia Castro, Silvia Galasso, Jorge Duca, Claudia Osuna, Ernesto Esparza

"We present a procedure for treatment of non-active solutions equivalent to the solutions obtained from dissolution of ionic exchange resins used in purification of a nuclear reactor primary cooling system containing Co, Ni, Cs and its isotropic varieties as main radioactivity source. Finally it is immobilized into a ferritic matrix by calcination which avoids its future leaching into environment.In order to achieve the objective of this treatment, a bivalent and a trivalent iron salt is added to the solution. Then, either a base or an acid is added, depending on the initial pH of the treated solution, with a Cs precipitating additive in order to reduce Co and Cs by precipitation, flocculation and adsorption. Controlling the amount of precipitating reactives it is possible to modify the activity/volume rate becoming a medium into a low radioactivity waste.The leaching test result applied over the ferritic sample is lower than the minimum limit established by law. Therefore, it can be kept safely in a interim storage."

Jan 1, 2008

By Scott G. Britton

Mine exploitation is a broad subject whose focus is the technical skills or efforts needed for the extraction of mineral from a known ore body. Mine exploitation can be considered the very core of the mining engineering discipline. It begins at the conclusion of the exploration and development stages of mining and ends when the ore body is exhausted and the mine (or mines)closes and is reclaimed. Section 8 on mine exploitation is comprised of seven chapters: (1) classification of mining methods, (2) mine surveying and mapping, 3) systems engineering, (4) computer methods, (5) labor relations and training, (6) management and administration, and (7) mine closure, sealing, and abandonment. Each chapter focuses its efforts towards providing detailed and useful information for the engineer on basic mine exploitation principles. The information can be applied to a broad range of mining problems without regard to mineral type or mining method.

Jan 1, 2008

The fluorspar deposits at Okorusu, Namibia are closely related to an alkaline igneous ring complex of late Cretaceous age (125¦7 Ma). The fluorite ores consist of relatively fine-grained purple replacement fluorite and subsequent coarser-grained purple and green vug-filling fluorite crystals. Homogenisation temperature measurements for 38 primary fluid inclusions shows that main stage purple to green fluorite crystals were deposited over a temperature range from 166¦C to 144¦C, and minor late yellow fluorite was deposited at lower temperatures from 132¦C to 128¦C. Homogenisation and freezing temperatures measured for 18 primary fluid inclusions shows that the fluorite-depositing fluids were less saline than Mississippi Valley-Type (MVT) ore fluids and overlap the lower temperature range of fluids that deposited epithermal ore deposits. Mining in three open pits (A, B and C) at Okorusu has gradually provided exposures which reveal that the fluorite orebodies have been emplaced primarily by the preferential replacement of carbonatites. Evidence for the replacement of carbonatite includes: replacement remnants of carbonatite within the fluorite ores; goethite pseudomorphs after the carbonatite minerals, pyroxene, pyrrhotite and magnetite, which are disseminated in the fluorite ores; andpartial replacement by fluorite of a large sill-like carbonatite body in the A pit. Electron microprobe analyses of minerals in unreplaced portions of the carbonatites show that their mineralogy consists of titaniferous magnetite, diopside pyroxene, apatite, biotite and calcite. Magnetite contains 6.97 per cent to 10.46 per cent TiO2, averages 8.44 per cent TiO2, and has an average V2O3 content of 0.35 per cent. At high magnifications under the scanning electron microscope (SEM), the magnetite shows abundant fine ulv÷spinel exsolution lamellae arranged in a cloth texture. Apatite contains moderately high fluorine contents that range from 3.21 to 5.0 per cent and average 4.2 per cent, and apatite crystals range in total rare earth oxides from 1.7 per cent to 2.61 per cent. Pyroxenes in the carbonatites are iron-rich diopside, and they contrast to pyroxenes in the fenites that are aegirine-augite. All of the microprobe analyses for mica crystals in the carbonatites give biotite compositions. Microscopic examination of fluorite concentrates from Okorusu provides mineralogical information important to the resolution of beneficiation problems. Fluorite ores that are related to carbonatites are typically accompanied by phosphorus benefication problems. The cause for the presence of phosphate in some of the Okorusu fluorite concentrates is a function of the presence of binary locked fluorite-apatite particles. The fluorite ores have also replaced marble locally in the A pit, especially along the A band in the B pit, and dominantly in the orebody proposed for the new C pit. Those ores are characterised by fine grain sizes, faint remnant bedding, lack of carbonatite mineral pseudomorphs and local presence of remnants of unreplaced marble. Concentrates derived from those fluorite ores are devoid of phosphorus, but commonly have elevated silica contents due the presence of free quartz. Carbonatite and marble were preferentially replaced by fluorite because the calcite was readily soluble in the presence of the fluorite-depositing fluids and the dissolution of calcite provided calcium for the formation of fluorite. 

Jan 1, 2008

By K Friese, H P÷llmann

Clinoptilolites, modified with sodium, produced a material which has been tested for the ability to remove Hg (II) from aqueous nitric acid. The amount of adsorption depends on contact time, acid concentration of aqueous solution and initial mercury concentration. The study of the kinetics of mercury uptake revealed that all sorbents exhibit a fast rate of sorption. The highest sorption capacities were observed for sodium forms, and were up to five times higher than for the unmodified zeolite. The maximum sorption capacity toward mercury is determined as 0.093 ¦g/g at an initial concentration of 10.0 ¦g/L for a clinoptilolite from Tsagaantsav deposit (Mongolia). The sorption of Hg (II) has an ion-exchange nature and consists of three stages, ie the adsorption on the surface of microcrystals, the inversion stage and the ion exchange in the interior of the microcrystal. Sorption capacity decreases with the increase of mercury concentration. The presence of other metal ions such as Cd (II), Cu (II), Ni (II) and Zn (II) increases Hg (II) uptake capacity. Finally, sorption for Hg (II) was investigated in batch systems to evaluate the short-term stability of the sorption properties.

Jan 1, 2008

Knowledge of the crystal chemistry of carbonate apatites is very important for the development of the concept of biomineralisation and the creation of a scientific base for new biocompatible materials for medical purposes. The present work is devoted to research results on various synthetic and biological carbonate apatites obtained at Saint Petersburg University over many years. All-important problems will be considered such as the location of CO32- ions in the apatite structure, the ionic substitutions in various biological apatites and the development of synthesis methods for their analogues. Syntheses of apatites were realised by precipitation methods and under hydrothermal conditions (from solid compounds and by calcite treatment). Biological samples used in this study were physiogenic and pathogenic apatites formed in the human organism, eg in teeth and in renal and salivary stones and dental calculi as well as apatites from fossils of different taxonomic families (brachiopods, conodonts, fishes, reptiles, mammal) with different geological ages and burial conditions. The study of the crystal chemistry of carbonate apatites has been carried out by powder (including high-temperature measurements) and single-crystal X-ray diffraction methods, IR-spectroscopy, thermal analysis and various chemical analytical techniques.

Jan 1, 2008

By Taegong Ryu

The thermal plasma process has been applied to the preparation of nanosized tungsten carbide (WC1-x). The reduction and carburization of the vaporized chloride by methane-hydrogen mixtures produced nanosized WC1-x powder, with a small amount of WC or W2C phase. The products were characterized using XRD, carbon analyzer, and TEM. The effects of plasma torch power, the flow rate of primary plasma gas (Ar) to generate plasma flame, and the addition of secondary plasma gas (H2) on the product composition were investigated. The tungsten carbide (WC1-x) powder had a particle size less than 30 nm. The powder was treated under hydrogen atmosphere to fully carburize the WC1-x, and W2C phases to WC as well as remove excess carbon in the product. Finally, WC powder with a grain size less than 40 nm was obtained.

Jan 1, 2008