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By P. Tsang

The stability of longwall chain pillars depends not only on the mechanical properties of coal and surrounding rocks, but also geological and mining conditions. In order to evaluate the effects of each, variable, the orthogonal experiment design was employed in this study for significance analysis. The study concluded that the stability of longwall chain pillars is mainly controlled by the ratio of pillar stress to pillar strength, the ratio of Young's moduluds of the roof to coal and floor to coal, entry width, pillar width and the internal friction angle of coal. Additionally, horizontal stress, panel width and mining height also play a significant role.

Jan 1, 1994

By Salam Moubarak, Thomas Camus

"INTRODUCTION Since the introduction, several decades ago, of the first concepts of tunnel boring machines (TBMs), the unremitting increase of mechanized and automated tasks and the reduction of manual tasks carried out by human operators have gone hand in hand with the continuous improvement of these machines. In the present state of TBMs, the replacement of worn cutting tools is a critical, tedious, and dangerous manual operation especially for earth pressure balanced (EPB) and slurry TBMs. For such pressurized TBMs, hyperbaric interventions are used. They consist in replacing the pressurized soil/mud inside the chamber with compressed air that balances the face pressure. The operators can then ""dive"" into the chamber; however, because the human body cannot naturally undergo pressure changes, they have to follow strict procedures that have been developed for subsea divers, based on decompression stops. Indeed such interventions are actually quite often performed by professional deep-sea divers. The pressurized TBMS are consequently equipped with a manlock that allows for the required compression and decompression cycles. Hyperbaric interventions increase risk to the operators and require long decompression procedures that increase the TBM idle time and reduce its efficiency. At higher pressures, over 3.5 bar (ITA Report No 10, 2011), specific equipment and special gas mixes and/or saturation techniques are recommended (Lamont, 2012). Such procedures are even more expensive and time consuming although the duration of work in the pressurized area can be very limited for health and safety reasons. Contractors are therefore increasingly interested in automating these operations to reduce the risks to human workers and improve the TBMs performance. Moreover, the demand for new, ambitious and challenging tunneling projects (very deep, high pressure boring) is ever increasing, but the supply of suitable TBMs is limited and the risk from working in the hyperbaric environments becomes increasingly unacceptable. Impact of hyperbaric interventions The UK Health & Safety Executive has analyzed the consequences of working in intermediate pressure compressed air. The retrospective study of decompression illness (DCI) indicated that at certain pressures its incidence was around 2% of all exposures. More worryingly it showed that over 20% of the exposures commonly undertaken by shift workers in tunneling (those over 1 bar pressure for 4 hours or more) resulted in DCI. It was concluded that on some contracts up to 50% of shift production workers experienced DCI at some time during the contract, a situation which was considered to be wholly unacceptable (Lamont, 2006)."

Jan 1, 2016

By Frank E. Chase

Preventing pillar squeezes, massive pillar collapses, and bumps is critical to the safe and efficient recovery of coal during room-and-pillar retreat mining. To help prevent these problems, the U.S. Bureau of Mines (USBM) has developed the Analysis of Retreat Mining Pillar Stability (ARMPS) computer program. ARMPS calculates stability factors (SF) based on estimates of the loads applied to and the load-bearing capacities of, pillars during retreat mining operations. The program can model the significant features of most retreat mining layouts, including angled crosscuts, varied spacings between entries, barrier pillars between the active section and old (side) gobs, and slab cuts in the barriers on retreat. It also features a pillar strength formula that considers the greater strength of rectangular pillars. The program may be used to evaluate bleeder designs as well as active workings. A data base of 110 pillar retreat mining case histories has been collected across the United States to verify the program. It was found that satisfactory conditions were very rare when the ARMPS SF was less than 0.75. Conversely, very few unsatisfactory designs were found where the ARMPS SF was greater than 1. 5.

Jan 1, 1995

By T. J. Durbin

At some surface and underground mines, control of ground-water inflow involves significant costs. These costs include the capital costs for installing a dewatering system, power and other costs to operate and maintain the system, and costs to treat and dispose of the water that is collected. To minimize these costs, design of a dewatering system utilizing wells has been formulated in terms of a nonlinear operations research problem using quadratic programming. Using this formulation, the locations, depths, pumping rates, and pumping schedules of wells are selected so as to minimize the total costs of the dewatering system.

Jan 1, 1993

By Kevin Andrews, SETAREH GHAYCHI AFROUZ

Ground control analysis and groundwater inflow assessments for underground coal mines require in-depth field investigations including, but not limited to, geological and geotechnical core logging, downhole geophysical logging, laboratory rock strength testing, and packer (Lugeon) testing. Field and laboratory data collection are time consuming and expensive, and an initial understanding of the expected trends among various geotechnical and hydrogeological parameters can assist with the planning and optimization of geotechnical characterization studies and grouting plans. In this study, a comprehensive database is analyzed, comprised of important rock mass characteristics (hydraulic conductivity, rock quality designation (RQD), and lithology) for coal-bearing rocks in the Central Appalachian Basin. Statistical analysis of the data is completed to establish an enhanced understanding of geotechnical and hydrogeological conditions expected to be encountered as underground coal mining passes near and beneath streams and rivers. The results of the study provide valuable reference material for the coal mining industry for completion of shaft installations, mine stream crossings, environmental assessments, and grouting and mine dewatering designs.

Jul 1, 2023

By Jeroen van Eldert, Daniel Johansson, Henrik Ittner, Håkan Schunnesson

"Numerous aspects of underground construction, from structural stability to construction costs, depended on the tunnel quality, including blast damage and the Excavation Damage Zone. Accurately quantifying the extent and severity of damaged rock is a problem. Recent technical developments in the field of Measurement While Drilling (MWD), including software for on-board logging and on-site analysis, have shown potential for rock-mass characterization. Ground Penetrating Radar (GPR) and P-wave velocity measurement have also improved and show similar potential. This paper explores the use of MWD, GPR and P-wave velocity measurements and uses them in techniques for excavation damage characterization and prediction. The paper is based on data collected from a small underground waste-collection site in central Stockholm, Sweden. The data is correlated against rock-mass characteristics and their responses are evaluated. Results indicate potential for excavation damage characterization for all tested techniques, which could minimize blasting damage and improve the over-all tunnel quality. 1 INTRODUCTION During underground excavation the rock mass is influenced in many ways. The Excavation Damage Zone (EDZ) is a result of these influences. The EDZ can be defined by an irreversible change in rock mass properties, for example increased permeability. EDZ is influenced by the excavation method, the rock mass properties and the in-situ stresses in the area of the tunneling. Since the 1990s research has been done on the EDZ by Emsley et al. (1997), Christiansson et al. (2005), Olsson et al. (2009), Ouchterlony et al. (2009), Ittner et al. (2014), and Siren et al. (2015). Based on past literature the EDZ have in this paper been separated in the following subzones: 1. Failure Zone or over-break is the area outside the planned tunnel profile, including the Look-Out and hole deviation. This zone consists of fracture networks (both natural and blasting-induced), that caused rock fall-outs. The extent of the over-break can be determined by volumetric scanning and photogrammetry and the half cast factor can be used as a damage indicator. 2. The Damaged Zone is split into three parts and but the quantity and depth of damage is difficult to measure. Although it can be visualized by sawing of rock slices in the tunnel wall (Olsson et al. 2009), diamond coring (DC) or P-wave velocity reduction (Jern 2001): a. Inner Damage Zone (Crush Zone): It is located directly around the drill hole, and is caused by the shock-wave energy of the detonation. The micro fractures in the Crush Zone produce a white-wash (rock dust) in the half cast. b. Transition Zone: This zone consists of micro fractures that connect and form macro fractures, both radially and parallel to the tunnel wall. The macro fractures are caused by the gas expansion during the detonation of the explosive; it increases the pressure in the (micro) fractures and creates the macro fractures. Seismic reflection, rock slicing and core drilling can be used for the examination. c. Progressing Zone: In this zone the existing radial fractures propagate due to the increase gas pressure inside these macro fractures. Examination methods are seismic reflection, rock slicing and core drilling. In addition, the Peak Particle Velocity (vibrations) could be used to estimate the depth (Tesarik et al. 2011)."

Jan 1, 2016

By Faruk Oksuz, Dave Schiemann, Matt Trotter, Mike Padilla, Miguel Sanchez, Carmen Scalise

"Chicago’s Tunnel and Reservoir Plan (TARP) is a nearly $4.0 billion and over 30 years long program and arguably the largest and longest combined sewer tunnel and reservoir system in the world. Recently, a massive tunnel construction is underway for connection of the McCook Reservoir to the existing TARP tunnel system. Once completed in two stages in 2017 and 2019, the reservoir will hold 38 billion-liters (10 billion-gallons) of combined sewer overflows (CSO) and flood waters from the city of Chicago and over 20 communities in Cook County, Illinois. McCook Main Tunnel will connect Chicago TARP’s Mainstream Tunnel to the McCook Reservoir. Connecting two 10-meter (33-ft) diameter tunnels at 92 meters (300 feet) underground has not been a simple task for the McCook Tunnel Project participants, the project owner U.S. Army Corps of Engineers (USACE), local sponsor Metropolitan Water Reclamation District (MWRD) of Greater Chicago, designer Black & Veatch, and the contractor, Kiewit Infrastructure Company (Kiewit). Yet alone excavating and lining massive size tunnels, the team is also challenged with live tunnel conditions in TARP Mainstream Tunnel that carries CSO and flood flows from city of Chicago which runs full during rain events and must remain in service at all times. The project is a noteworthy feat for engineering and construction with the upcoming installation of world’s largest underground wheel gates for flow control within the tunnel. In this paper, we describe one of its kind elements of this major tunnel system along with key design and construction considerations, specifically for the live tunnel connection which is a rare occurrence in the tunneling industry. INTRODUCTION The McCook Main Tunnel system consists of a 10 m (33 ft) finished diameter and 490 m (1,600 ft) long hard rock tunnel constructed from a 27.5 m (90 ft) diameter and 92 m (300 ft) deep main gate and tunnel construction access shaft. The gate shaft houses six high head 4.4 m by 9 m (14.5 ft by 29.5 ft) wheel gates to be installed in the bifurcated and steel lined section of the tunnel. The tunnel also includes portal and energy dissipation structures as it daylights into the reservoir."

Jan 1, 2016

By A. T. Yu

Technology and economies of scale have, in the past decade, brought about the emergence of giant vessels. Meanwhile, to answer the need for rapid dispatch, as a means of combating the proportionately far greater demurrage charges, shiploading and unloading speeds have soared (Ref. 1, 2, 3). As the loading and unloading rates have dramatically increased, so has the cloud of dust grown in unbearable proportions. It not only has threatened to be a real menace to machinery and men, but in certain instances has also seriously jeopardized fish and marine life (Ref. 4). In an era when ecology is king, dust in shiploading and unloading can no longer be shrugged off as a mere public nuisance, and its control is now duly recognized as of grave concern to all. Even if public outcry were not a problem, from the operator's own parochial point of view, dust can adversely affect productivity and the well-being of the operating personnel. Without adequate control, it can also result in costly equipment maintenance, particularly when the dust is micronic in size, and abrasive. The Hierarchy of Control Techniques Given the great fortune of not yet having to deal with gas and odors, in the jargon of pollution control, our problem is confined to having to control "particulates" only. To deal with "particulates", the myriad of dust control techniques can be utterly confusing to those who are not entirely well versed in the methodology. Our analysis of what is available to date results in the following hierarchy of logical preferences: 1. Prevention 2. Removal 3. Suppression 4. Containment 5. Dilution Since it deals with the root cause, prevention always outranks the cure. Once the dust is generated, removal nips it in the bud. Only when dust removal is

Jan 1, 1972

By Clarence A. Johnson

The discovery of the Prudhoe Bay field temporarily reduced interest in the development of coal conversion processes, but interest is being re¬newed by the current energy crisis. According to M.A. Wright, Chairman of the Board of Humble Oil and Refining Company(l), the reserve in the Prudhoe Bay bield has been confirmed to be about 10 billion barrels. At first glance this appears to be an extremely large reserve which will eliminate supply problems for the United States for some time. This feeling of security is lost when one realizes that by 1980 the world will consume the reserves of a Prudhoe Bay or a Libya, or Venezuela in less than a year, based on the recent predictions of U.S. and world reserves made by Eastman-Dillon, Union Securities Company(2). Recent forecasts of U.S. demand and source of supply made by Kenneth E. Hill of Eastman-Dillon are shown in Figure 1. This forecast shows a decline in domestic supplies (excluding Alaska) after 1973, with the total domestic supply leveling off in 1975 at about 13 million barrels per day. Since the predicted demand increases from about 14 million barrels per day in 1970 to about 20 million barrels per day in 1980, about 35% of domestic consumption must come from imports or non-conventional sources by 1980. More imminent is the shortage of low sulfur fuel oil which has been created by the new, tough air pollution regulations that are basically legis¬lating eastern coals out of the market. As an alternate to importing large quantities of low sulfur fuel oil or importing and desulfurizing regular fuel oil, one of two domestic solutions is possible: stack gas clean-up or solids fuel pretreatment. Stack gas clean-up may be the cheapest approach for old installations, but fuel pretreatment has real advantages for new installations. Coal pretreatment at the mine could eliminate all solids fuel handling

Jan 1, 1972

By J. G. Nalven

On July 1, 1999, most domestic metal mines will have to report releases of toxic chemicals into the environment for the first time as required by SARA Title 313. Some of these reportable releases will appear huge in relation to reports by other industries. The reasons for the potentially large reportable releases, special considerations for mining operations, and strategies for dealing with the reports are described. Data composited from experience with several mining companies is presented in the context of a typical gold mine.

Jan 1, 1999

By L. Giraldo, S. Cotten

"INTRODUCTION The vision for a “Mine Escape Vehicle” (MEV) is to provide capabilities to better enable underground travel to allow miners to escape to safety in the event of a major mine emergency such as a fire or explosion. Enhanced transportation and survival capability such as a MEV may have minimized or eliminated the loss of life associated with several of the mine disasters that occurred in 2006, which together resulted in the deaths of 19 miners. Although the most desirable response in an emergency is for the miners exit the mine, if escape proved to be impossible, the miners could use the vehicle to proceed to an underground point of refuge to await rescue. Under a NIOSH contract issued in April 2008, Raytheon developed a conceptual vehicle design including (1) the capacity to provide life support functions for a number of miners, (2) operate in a reduced oxygen atmosphere with little or no visibility, and (3) travel at speeds faster than miners could walk out of the mine. The proposed MEV concept envisioned modification of a personnel carrier (a.k.a. a “mantrip”) that would be used every day during normal mine operations, not a specialized vehicle reserved only for or dedicated solely to escape. The MEV concept also included escape aids that are detachable from the vehicle in the event that the vehicle must be abandoned on the way out of the mine and the dismounted miners had to proceed on foot. To advance MEV development, NIOSH awarded a second contract in 2010 to Raytheon to build, test, and evaluate the performance of a proof-of-concept MEV that culminated in a 7-month performance evaluation of vehicle in an Eastern Kentucky coal mine (Figure 1). User feedback and lessons learned from the proof-of-concept vehicle evaluation provided support for the general MEV approach, guidance related to the practicality of MEV capabilities, and indication of specific technology shortcomings for this application."

Jan 1, 2015

By Erik S. Bernard

"INTRODUCTION Conventional steel bar reinforcement is used in many tunnel linings to provide high flexural and tensile load resistance. These Reinforced Concrete (RC) tunnel linings may suffer flexural cracking during service or, in the case of precast concrete segments, during production, handling, or installation. Cracks can lead to corrosion of steel reinforcement, so limits are placed on maximum acceptable crack widths to reduce the likelihood of corrosion during the intended design life (AFTES, 2013; MC2010, 2012). However, the relatively light level of reinforcement used in many applications can result in quite wide in-service crack widths, so either additional steel bar reinforcement is required to limit maximum crack widths, or fibers can be included to control crack widths. Numerous investigations have been undertaken into the efficacy of including steel fibers to reduce crack widths in conventionally reinforced members (Stang and Aarre, 1992; Abrishami and Mitchell, 1997; Bischoff, 2003; Dupont and Vandevalle, 2003; and Jansson et al, 2010), but steel fibers suffer the problem that they are at least as sensitive to corrosion at cracks as steel bars and therefore have similarly tight limits placed on acceptable crack widths (AFTES, 2013). An alternative means of maintaining narrow crack limits in RC members has therefore been sought. The current investigation was instigated following an observation that theories promoted as an explanation for the ability of steel fibers to reduce crack widths in reinforced concrete flexural members (Deluce et al, 2014) do not depend on the material composition of the fibers used but instead depend primarily on the tensile stress generated by the fibers across cracks. Since it is known that macro-synthetic fibers are capable of equaling the post-crack tensile capacity of steel fibers, it has been hypothesized that macro-synthetic fibers are also capable of reducing crack widths in reinforced concrete flexural members but with the added advantage that macro-synthetic fibers are completely immune to the effects of corrosion. Use of macro-synthetic fibers to reduce maximum crack widths in reinforced concrete flexural members subject to aggressive environmental exposure is more rational than use of steel fibers because steel fibers are very sensitive to the corrosive effects of environmental exposure at cracks. The current investigation was therefore undertaken to explore the potential use of macro-synthetic fibers to reduce maximum crack widths in reinforced concrete members subject to flexure. Barchip BC54 fibers were selected as they are one of the most widely used and competitive high performance macro-synthetic fibers currently available."

Jan 1, 2016

By V. A. Scovazzo

The analytical pillar design procedure employing the Wilson equation is based on the site-specific material strength of the floor, pillar, and roof rock. Stable pillars so designed will sometimes be larger than those designed using empirical methods thus providing more stability or at other times smaller than empirically designed pillars thus conserving natural resources. Presented here is a detailed procedure for the analytical design of soft rock pillars using the Wilson Equation. An example of this procedure is presented that uses data from a mine in the Owl Seam in Southern Appalachia. These Owl Seam pillars are now in use and are performing as expected. Also addressed is an assessment of the Dr. Scovazzo?s analytically designed pillars based on pillar performance data gathered by Dr. Mark in the Southern Appalachian Coal Field.

Jan 1, 2010

By F. Segobia, M. Portal, F. Ysla, A. Mujica, L. Goicochea

The “Building Our Future” project is a collaborative initiative between the UNC SME Student Chapter and the Water and Earth Museum (MAT) of Asociación Los Andes Cajamarca (ALAC), both corporate entities of Newmont Yanacocha. Its mission is to promote responsible and sustainable mining among new generations while fostering a culture of equality and respect. This comprehensive educational program integrates sustainable development goals and includes workshops led professionals and external experts who share their personal stories to inspire students from rural and urban educational institutions to follow their dreams. Additionally, for this year 2024, the project development and implemented an interactive mobile application that educates users about the use of minerals in everyday life through four levels: Minerals in the Home, Minerals in Medicine, Minerals in Transportation, and Minerals in Agriculture. This multi-faceted approach seeks to raise awareness about the importance of mining in Peru’s economic, environmental, and social development, ultimately fostering a new generation of informed and engaged citizens who understand the vital role of mining in a sustainable future.

Feb 1, 2025

By T. L. Heisler

The Cigar Lake project, located in northern Saskatchewan (Figure 1), is one of the world?s largest high grade uranium deposits, with reserves of 150 million kilograms of uranium in a deposit averaging 430 metres below the surface. The Cigar Lake project is being developed by Cigar Lake Mining Corporation (CLMC) which is owned by Cameco Corporation (48.75%), Cogema Canada (36.375%). Idemitsu Uranium Exploration Canada Ltd. (12.875%) and Korea Electric Power (2%). Mining the Cigar Lake orebody is presenting a very real challenge due to the high grade and the ground conditions in and around the orebody. Presently, an underground test of various mining methods is underway.

Jan 1, 1992

By D. M. Ziebarth

"During the mid to late 1960’s, the underground potash industry in Saskatchewan was born. For the next four decades the industry operated at a steady pace supporting a large part of the world demand; until 2008 when the potash market heightened. Operators were motivated to capitalize on this increased demand, new mines were proposed while existing mines were planning upgrades. Potash Corporation of Saskatchewan (PCS) was one of the major producers planning upgrades to their production facilities quickly, including modifying the existing headframe and shaft at the PCS Cory Site to accommodate a new 1500 tonne per hour hoisting plant. Upon completion of the project, the innovative operations group continuously reviewed methods to increase production and reduce operating costs, allowing PCS to continue being competitive on the world market. This paper will describe the design challenges encountered during the development of the infrastructure around an operating facility whilst minimizing down time, schedule, capital and construction costs. This paper will also explore the strategy to increase capacity of the newly commissioned hoisting plant. BACKGROUND Potash production is a major Saskatchewan industry, and has played a significant role in the economy for over 40 years. Production commenced in 1962 when water problems were overcome at the International Minerals and Chemical (IMC) mine near Esterhazy, Saskatchewan. A surge of development by other companies resulted in twelve companies opening ten mines by 1970. In 1975 Potash Corporation of Saskatchewan was created by the government of Saskatchewan and shortly thereafter purchased several mines in Saskatchewan, including the Cory Mine (Cory), near Saskatoon. Cory has been in operation since 1968 and is located 12 km (7.5 mi) west of Saskatoon in central Saskatchewan. The mine is located in the center of the world’s largest potash deposit, 1,000 m (3300 feet) below surface. PCS has embarked on sizable capital expansions of more than CDN $7 billion. The Cory CDN $1.6 billion expansion was expected to raise operational capability of the site to 2.7 million tonnes per year, an increase of 1.9 million tonnes per year (MTPY). To achieve 2.7 MTPY of finished product and considering the 22.6% average production recovery1, 12 MTPY of ore must be hoisted to surface for processing. To deliver this rate required upgrading of the hoisting plant to 1500 tonne per hour (TPH). To accomplish this ambitious challenge, creative thinking, careful planning and a cohesive team was needed to work together to ensure the schedule, budget and most importantly the work was completed safely"

Jan 1, 2017

By B. C. Litzinger

Minerações Brasileiras Reunidas S.A. - MBR is a brazilian iron ore mining company geared for the export market. It is controlled by Companhia Auxiliar de Empresas de Minerações - CAEMI through its subsidiary Empreendimentos Brasi leiros de Minerações - EBM which holds 51% in MBR and is formed by CAEMI, the six major japanese steelmills and five japanese trading companies, Universe Tankships, Inc., and Indústria e Comércio de Minérios S.A. - ICOMI. The remaining 49% of MBR's capital are held by St. John del Rey Mining Company, a subsidiary of The Hanna Mining Company. MBR iron ore reserves exceed 1.5 billion tons of high grade ore distributed in 36 deposits located in the so-called IRON QUADRANGLE in the State of Minas Gerais. The Aguas Claras Mine is the largest presently known and highest grade deposit owned by MBR. Other mines such as Pico, Mutuca and Jangada are in operation at a combined rate of production of about 2 to 2. 5 million tons per year. The project consists of mine, railroad and marine terminal (slide). The Aguas Claras deposit, which is located about six kilometers southeast of Belo Horizonte the Capital of Minas Gerais, was selected for initial development. The Sistema Regional Centro of the Rede Ferroviária Federal, through its 6th Division known as the "Central " is responsible for the transportation of MBR ore, and provided the necessary railway construction to connect Mine and Terminal. The Terminal is located on Guaiba Island near the entrance to Sepetiba Bay, at about 120 kilometers west of Rio de Janeiro.

Jan 1, 1974

By Joseph Clare

It’s not the 1960s anymore. Upgrading wastewater pipelines in the current era demands the latest trenchless technology to minimize impacts. King County Wastewater Treatment Division in Seattle, Washington is designing a nearly mile long Direct Pipe® influent sewer combined with microtunneling to replace a 1960s era trunk sewer constructed along and within Coal Creek and its natural area. Trenchless installation using Direct Pipe® and microtunneling was chosen due to reduce impacts to residential neighborhoods, natural creek environments, and the constraints of topography

Jun 13, 2021

By K. S. Venkataraman

The physical properties of clay-water systems depend on the complicated system of forces between the clay particles themselves, and between the clay particles and the ions in the liquid phase. The kind and distribution of ions in, on, and between the clay particles and the size and the shape of the particles are the basic factors determining the macroscopic behavior of clay-water systems. Understanding the system requires a knowledge of the nature of the clay particles, their size, structure, composition, and surface properties, and of the manner in which they interact with ions [and molecules] in the surrounding liquid [or other medium]. The validity of Professor Brindley's words (Brindley, 1958), written three decades ago in the context of making pottery, whitewares, and electrical porcelains, transcends time, and the basic message is perhaps all the more important in the considerably expanded use of ceramics for structural, thermal, tribological, electronic, and other applications. Silicon carbide, silicon nitride, and sialons have been studied in the last two decades for high- temperature structural and tribological applications, particularly for using in internal combustion engines. Titanates, zirconates and niobates of barium, strontium and lead, have high dielectric constants, and are extensively used in the formulations for making capacitors. Hexagonal ferrites (molecular formula MO.6Fe2O3) are in use for making permanent magnets for fabricating miniature motors, and for assembling loud speakers, particle accelerators etc. Cubic ferrites such as magnesium-zinc ferrite and nickel-zinc ferrite are used as transformer cores, and for other high-frequency applications. In this context, Richerson's recent book (Richerson, 1984) on the general scope of traditional and technical ceramics is a good starting point for an overview of contemporary ceramics technology. Glasses are a whole class of amorphous materials used widely as sintering aids, and for making glass-bonded ceramics and glass-ceramic composites. Composites are yet another burgeoning field where two or more particulate components are used for improving the performance of ceramics. For all these applications, the inorganic starting materials are almost always submicron and near-micron powders. Understanding the powders' physicochemical properties, and their surface chemical interactions with the surrounding liquid/gaseous medium is-necessary for making reliable ceramic parts at competitive prices. Even though ceramics science and engineering has attained its separate identity in universities and the industry, ceramists themselves would concede that ceramics science is a cross-disciplinary field, having incorporated and assimilated within itself many principles from several apparently disjointed disciplines. Principles of material science, graduate-level physics and chemistry, polymer science, surface and colloid chemistry, transport phenomena, particle technology, unit operations commonly used in chemical engineering and mineral processing, and statistics and applied mathematics are integral part of any ceramics curriculum in universities. Added to this is the fact that all bench-scale successes in making ceramic parts are to be scaled-up for larger throughput operations. Understanding and applying process engineering principles of comminution, classification, drying, calcination, etc. then becomes essential. CERAMIC FORMING: Despite the diversity of the materials and processes, conceptually, the steps involved in making ceramic parts have remained the same over several decades: The different components for making the pan (usually one or more powders plus other forming and sintering additives) are proportioned and mixed thoroughly, and the well-mixed formulations are consolidated into desirable shapes known as "green bodies." Usually binders such as wax, clay, organic polymers and surfactants, whether dispersed or dissolved in a suitable liquid are used during mixing the batch for giving strength for the green bodies. In the dried green state, the inorganic powders typically occupy only 55 to 60% of the bulk volume of the body, depending on the particle size distributions of the powders and the forming history, with mostly inter- particle voids accounting for the rest of the void volume. SINTERING: The formed bodies are then fired in high- temperatures kilns/furnaces during which the parts are exposed to a predetermined temperature profile, and "soaked" for a certain duration at the final high temperatures, typically between 1200 K and 1900 K, and then cooled to room temperature. The gaseous atmosphere in the furnace is controlled (oxidizing, reducing, or inert) when necessary. During the initial stages of firing, volatile liquids evaporate, and during the intermediate temperatures between 400 and 600 K, the the organic polymeric additives pyrolize and oxidize into water vapor, CO, C02, and other gases. At still high temperature, the glasses, when present, soften, and simultaneously, the ceramic particles rearrange into a network of grains with definite grain boundaries so as to reduce the total interfacial free

Jan 1, 1990

By T. P. Meloy

Riffles on a shaking table have a major effect on particle separation. This effect is modeled in a spreadsheet.

Jan 1, 1993