Search Documents

By M. Radwan

This research reports on the synthesis of advanced silicon-based structural ceramics from mixtures composed of natural sand (Sinai white sand), reclaimed silicon and graphite by the nitriding combustion synthesis method. With pulverized sand (? 40 m), we found that the nitriding combustion can be realized at self-sustaining mode in the SiO2?Si?C system under 3 MPa nitrogen pressure. Depending on the composition of the starting mixtures, single-phase silicon oxynitride (Si2N2O) powder as well as new Si3N4?Si2N2O and Si2N2O?SiC composite powders with controllable chemical compositions were successfully developed. The measured thermograms of various combusted mixtures and the thermodynamic characteristics of possible exothermic reactions in this system were discussed to explain the nitriding combustion behaviour and mechanism. Near-full dense Si2N2O were fabricated from synthesized Si2N2O powder with 5 wt % oxide additive by the spark plasma sintering (SPS) method at 1600 °C. The dense Si2N2O samples had good mechanical properties (18.7 GPa Vickers hardness, 3.3 MPa m1/2 fracture toughness and 363 MPa strength) and excellent chemical and oxidation resistance. The synthesized composite powders were also densified to high densities (> 90 % of theoretical values) by SPS technique. The results obtained in this study can be seen as a new route to prepare important silicon-based structural ceramic powders with various compositions/properties from cheap starting materials which makes them potential for wide range of applications.

Jan 1, 2006

By M. E. Ramos Rada

Mexicana de Cobre, which is part of Grupo Mexico, carried out studies for the construction of a copper refinery in the La Caridad Metallurgical Complex located in Nacozari, in the state of Sonora, Mexico. After the studies were concluded, the decision was made to construct a 180,000 t/y refinery using the state of the art permanent cathode Kidd Process. The basic engineering was developed by Fluor Daniel and the detail engineering and the construction were carried out in record time by the Mexican company Bufete Industrial. During the construction phase, Grupo Mexico decided to expand the refinery, and actions were taken to increase its capacity by an additional 120,000 t/y; the final result was a refinery capable of producing 300,000 tonnes of grade A cathode per year. Construction began in January 1996, and the operation of the first stage began on July 1, 1997. The operation of the second stage commenced on January 7, 1998. The capacity of the first stage was reached in November, 1997 and the total capacity of the refinery was achieved in May, 1998. This presentation describes the process and equipment installed in the refinery, the steps leading to the start-up, the operation and the results obtained during the first two years, the handling of anodes with high impurity contents, and the problems confronted and the way they have been solved. It also includes personnel productivity, the control parameters and the most relevant data on the operation of the process.

Jan 1, 1999

By Shichao Zhao, Ke Xie, Qijie Zhai, Wenbin Xia, Yuanyi Guo, Changjiang Song

"This paper investigated the structure evolution and phase formation ofFe-(11,13,15wt.%)Mn alloy under near-rapid solidification conditions. It is found that the area ratio of equiaxed zone in the Fe-13Mn alloy is the largest. And the primary dendrite arm spacing of Fe-(11,13,15wt.%)Mn alloy increased clearly with increasing distance from the surface. The volume percentage of HCP phase increased with increasing manganese content in the range from 11 pct to 15pct.IntroductionThe developing trend of automobile is the energy conservation, enviromnent protection, light weight, and high security. So the material would be required to the higher strength, higher plasticity and more likely to processing of automotive steel. Fe-Mn based alloys is considered as a potential material to the third generation automobile steel for its high damping performance [1], good mechanical properties [2-3], and high young's modulus [4]. And it is important that metastable HCP phases of Fe-Mn based alloys, which attracts technological interest for theoretical and experimental research [5-6].Metastable materials have been extensively used in the area of iron steels. Among various fabrication methods for high performance materials, rapid solidification is one of most popular ways to produce advanced materials by obtaining metastable phases. The solidification of metals in metastable phases provides access to an extended range of materials properties with novel properties [7]. Thus, in this work, Fe-Mn alloy metastable materials prepared by near rapid solidification is studied."

Jan 1, 2013

By T. V. Jayaraman, Kranti Kumar, Paul Praveen J., Dibakar Das, A. R. James

"Lead free piezoelectric ceramics with high piezoelectric coefficients are in great demand for sensor and actuator applications. Synthesis and characterization study of one such lead free system, barium zirconate titanate - barium calcium titanate [xBZT-(1-x)BCT] (x = 0.5), via solgel method have been carried out. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the formation of single phase BZT-BCT nanoparticles (<50 nm). The as-synthesized powders were calcined at 1000°C and the powders were pressed into cylindrical pellets. Solid-state sintering of the green pellets at 1550°C for 2 hrs resulted in single phase perovskite structure. Hysteresis loops were obtained which indicates the ferroelectric nature ofBZT-BCT. The bulk ceramic samples with the highest sintered density (~93%) were subjected to electrical poling and the piezoelectric properties ( d33, kp, & i:,) were measured. The structure and piezoelectric properties were investigated and correlated for the given composition of the BZT-BCT system.IntroductionPiezoelectric ceramics are widely used in various sensors and actuators and most of the piezoelectric ceramics, which are presently used, are lead based, which contains at least 60% lead (Pb) by weight. The critical disadvantage of these lead based piezoelectric ceramics is their hazardous effect related to the toxicity of lead, which poses a serious environmental concern starting from their processing to the disposal stage[l]. It is well known that a material to be a good piezoelectric it requires a morphotropic phase boundary (MPB) i.e. the composition induced phase transition between any two ferroelectric phases."

Jan 1, 2013

Steel Ladle in Bhilai Steel Plant, SAIL, India, passes through VAD & LF-RH route and this exposes refractory lining to a severe operating conditions. Ladles are lined with in-house manufactured MgO-C refractories. Lining life used to be 35 heats, out of which 18-20 heats were through VAD/LF-RH, hence, ladle availability had become a constraint. Laboratory studies were carried-out to optimize granulometry and composition. Granulometry was developed by adopting Andearssen packing model. A suitable plasiticiser was identified to eliminate inconsistency caused due to variation in resin quality and weather condition. It reduced variation in green bulk density from 6 to 1.3%. Abrasion and slag erosion studies were conducted, which shows that with increase of carbon, abrasion resistance decreases and corrosion resistance improves. Based on these studies, graphite in slag zone was increased from 10 to 12.5% and in metal zone it was reduced to 7.5%. Different process parameters of brick making were optimized to make MgO-C bricks of maximum bulk density with reduced coke porosity. Modified bricks have bulk density of 2.99-3.02 g/cc and coke porosity of 9.5-10.5%. Further, shape of the bricks were changed from side arch to mini keys and thickness was increased from 80 to 100 mm. Mini key bricks are pressed from sides, thus eliminating variation in thickness which is critical dimension for dry joints. These modifications improved average lining life of steel ladles to 64 heats, which includes 37-40 secondary heats. Maximum life obtained is 87 heats.

Jan 1, 2006

By K. Pagalthivarthi, P. V. Desai

"During solidification of alloys, many inter-related physical processes, such as melt convection, mass diffusion, heat transport, macrosegregation and melt-undercooling occur. Several research workers have studied one or more of these effects separately. To answer important questions on solidification behavior, an overall approach interrelating the processes is necessaryAs a first step toward accomplishing the overall modeling, the freezing of a binary liquid metal is examined. The various stages during freezing of the alloy are critically described to build a continuum model for the entire process. Diffusive mixture theory is used to write the conservation equations for the liquid and the mushy zones. The concept of local thermodynamic equilibrium in the presence of curvature effects is used to restrict the number of degrees of freedom within the mushy zone. Constitutive equations relating flux quantities and affinities, the governing differential equations and boundary conditions are discussed briefly for the freezing process.IntroductionA solidification study encompasses such facets as solifidication time, microstructure, macrosegregation of the solute, shrinkage effects and soundness of the casting. Influence of one or more of the coupled heat and mass transfer phenomena such as local solute redistribution, thermosolutal convection, melt undercooling at dendrite tips and heat dissipation to the ambient have all been previously examined [1-3J. Several studies have examined the individual facets of alloy solidification as isolated processses. In fact, the transport processes occur simultaneously and a comprehensive model should include their inter-relationships. In particular, some of the existing studies of the mushy zone [4-6J do not emphasize thermodynamic completeness. This work represents an attempt to develop a thermodynamically consistent model of the entire solidification process on physical grounds."

Jan 1, 1986

By S. G. Kumar, R. G. Reddy

"Niobium aluminides offer the advantage of higher high temperature capability compared to other intermetallic aluminides due to the refractory nature of niobium. However, the reaction sequence in Nb-Al system is sluggish and currently there is a great interest in the processing aspects of these materials. In the present study, a systematic investigation was undertaken to compare the effect of different powder metallurgy processing routes on the phase relations and microstructure of 66Nb-22AH2Ti (in atom percent) alloy. The three different process routes adopted were: (i) cold pressing followed by reaction sintering; (ii) cold pressing and hot pressing followed by sintering; and (iii) arc melting, hydride-dehydride process to make the alloy powder followed by cold pressing and then sintering. The samples are analyzed by XRD, Optical Microscopy, SEM-EDS and EPMA. The analysis showed that alloy pellets made from pre-alloyed powders i.e., arc melting followed by hydride-dehydride process, gave good densification and more Nb3Al formation.1. IntroductionTo improve the performance standards of turbine engines, materials scientists are challenged to develop materials that have· high thrust-to-weight ratio with high specific strength, high specific modulus and good environmental properties at elevated temperatures. The conventional high temperature materials like nickel based superalloys are high in density and hence many of the high temperature materials scientists have focussed their attention on intermetallic aluminides like Fe-AI, Nb-AI, Ni-AI and Ti-AI in recent years. The phase relations and properties of alloys based on Fe-AI, Ni-AI and Ti-AI are fairly well known whereas little is known about the alloys based on niobium aluminides."

Jan 1, 1996

By Peter K. Liaw, Niann-i Yu, Wei Zhao

"For a plain-weave Nicalon ™ fiber fabric-reinforced silicon carbide (SiC) ceramic composite, little attentation has been paid to the effect of fabric stacking sequence on its mechanical behavior. In this paper, fiber-fabric stacking sequence effects on the elastic stress distributions, ceramic matrix-cracking stress, effective elastic moduli, and flexural strengths of laminated flexural test bars are quantified. A quantification model is established based on the combination of classical laminated plate theories and a fiber undulation model developed by Chou et al. A FORTRAN program is compiled to implement the modeling, which can be run in a SUN work station. The mechanical performance of a continuous fiber-reinforced ceramic-matrix composite (CFCC) with a [0/30/60] lay-up was analyzed and predicted. The variation in the fiber-fabric stacking sequence can vary the elastic stress distributions along the thickness direction of specimens, magnitude of ceramic matrix-cracking stress, effective elastic moduli of the laminate, and crack initiation sites as well as fracture modes. Moreover, all these factors contribute to scatter in flexural strengths of the CFCC.I. IntroductionWith enhanced fracture toughness and the ability of non-catastrophic (graceful) failure behavior, CFCCs are currently under evaluation for high-temperature structural applications in heat exchangers, combustors, hot-gas filters, boilers components, first walls and high-heat flux surfaces gas turbines, space vehicles and nuclear reactors.[1-8] Extensive applications of CFCCs by industry are still hampered by an insufficient understanding of the mechanical behavior, and sometimes, the lack of a well-developed and widely accepted design philosophy, in addition to the high-production costs."

Jan 1, 1998

By Richard H. De Voto

The McDonald Gold Project and two satellite gold deposits near Lincoln, Montana, contain at least 9.9 million ounces of gold and 30 million ounces of silver. The McDonald gold deposit alone contains 7.2 million ounces of gold reserves that can be open-pit mined and processed by cyanide heap leaching at a projected cash operating cost of $190 per ounce. The deposit is predominantly oxidized with no chance of acid production, and can be mined, operated, and reclaimed with minimal permanent environmental disturbance other than the creation of an open pit filled with a fresh-water lake which would support trout. The Seven-Up Pete Joint Venture, the owner of the McDonald Gold Project, commenced permitting of an open-pit, heap-leach operation in November 1994. In 1998, Montana citizens passed an anti-cyanide, open-pit mining initiative, 1-137, which banned any new open-pit gold mine which uses cyanide processing, The Venture has conducted extensive studies, including metallurgical testing of the treatability of McDonald ores with alternative lixiviants, and has determined that all other mining and metallurgical treatment systems are vastly uneconomical in the recovery of gold and silver from the McDonald deposit. Therefore, the Venture&apos;s proposed open-pit mining and cyanide heap-leach processing is the only technology that can be applied economically to the McDonald deposit. Further, the analyses convincingly demonstrate that the proposed open-pit, cyanide heap leaching technology results in maximum resource conservation of this valuable and unique deposit and poses far less risk to human health and the environment than any of the alternative technologies.

Jan 1, 1998

By Fashina Olugbenga Emmanuel, Ghazali Akeem, Adegbola Adekunle Amos, Omotoyinbo Joseph Ajibade, Olaniran Oladayo

"Modern engineering materials are required to be light weight and corrosion resistant, coupled with high strength and hardness. In this work, Al formed the parent metal and alloyed with 2.03% of Copper by sand casting process. The cast product 2024 was warm worked at various temperatures ranging from 300 to 5600c at 5%, 10%, 15% and 20% deformation respectively and aged accordingly. The results showed that the mechanical properties vis-à-vis hardness, tensile improved with increasing % deformation at a higher temperature. This was due to the progressive close-up of the voids emanated from casting by increasing deformation which is evident from the micrographs. MATLAB was also adopted to generate a model capable of determining the trend of flow of stress at operating temperatures. This was of immense value due to an increasing impact at higher percentage deformation with temperatures. Hence, Al -alloys will find applications in land vehicles, ships, trains, and aircraft, at elevated temperature.INTRODUCTIONThe problem of safe vehicle design with maximum impact energy absorption is a significant subject in structural crash worthiness design [1]. All engineering designs are expected to ensure the safety of users' life. This informed several studies meant to probe the causes of component failures in equipment, vehicles, and aerospace design and decide on appropriate solutions through materials selection techniques. A common example is in the design of crankcases and heads, piston, and cylinder blocks. As with engine blocks, cylinder heads can be made of Cast Iron or Aluminium Alloy. A head made of Aluminium alloy is lighter in weight than if it were made of Cast iron [2]."

Jan 1, 2013

By Fiseha Tesfaye, Pekka Taskinen

"A thermodynamic study of the equilibrium phase assemblage AgBi3S5-Bi2S3-S was made by an EMF-technique, using the RbAg4l5 solid electrolyte. The ternary phase was synthesized from the pure Ag2S and Bi2S3 in an evacuated silica ampoule and grinded into powder and mixed with appropriate compositions of B12S3 and S, in a series of experiments, for pressing in to pellets. The pellets were assembled to form the galvanic cells Pt (-) | Ag ] RbAg4ls | AgBi3S5+ Bi2S3 + S + (C) I Pt (+). The EMF-measurements were made in the temperature range 299 - 460 K.In this paper, thermodynamic functions of the ternary phase AgBi3S5 (pavonite) have been determined. The agreement between the obtained results and the literature values were established.IntroductionThe complex group of ore minerals constitutes from trace amounts to a major proportions of sulfosalts. Although the sulfosalts rarely form massive ore bodies, they are commonly associated with rich sulfide ore minerals for the base and precious metals and widely distributed in a metal poor sulfide minerals [1]. For instance, Ag-bearing sulfosalts are encountered in ore minerals for the production of the base metals and are common sources of silver. Nevertheless, thermodynamic properties of the sulfosalts are poorly known.Reliable thermochemical data are essential for quantitative modeling of the chemical behavior of the sulfosalts in equilibrium with sulfides, which in turn would promote the optimization of complex minerals treatment and extractive metallurgy of the valuable metals."

Jan 1, 2012

By Alex Meystel, Diran Apelian

"In this paper, an outline is given for a theory of intelligent control (IC) of manufacturing processes (MP) based upon what all of them have in common: all MP's can be represented as distributed networks of sequential/parallel elementary ""lumped"" models; all elementary models are organized by definite input-output conditions, and by the set of constraints; all elementary models incorporate not only well defined physical knowledge, but also assumed physical knowledge, expert knowledge, expected knowledge to be obtained during the process from sensors, etc. This creates a hierarchy of elementary controllers coordinated by local coordinators of different levels up to a global coordinator. The latter verifies the adequacy of MP by using a holistic image of the process: depictogram. The structure of knowledge based controller is introduced, and the analytical/linguistic tools of control are presented. The concept entails a number of perspectives which are discussed in the conclusions.1. IntroductionIt is becoming increasingly clear to those of us in Engineering and Technology oriented fields that the so called ""service industries"" do not create wealth. Moreover, it is now accepted that manufacturing is the key to the creation of wealth from a socio-economic point of view. This appreciation of the importance of manufacturing is reflected by the transformations we are seeing in our factories, as well as the changes in both curricula and research activities of our universities. Though we find these changes to be in the right direction, there is yet much more to be done to advance the frontiers of manufacturing and materials processing as we approach the third rnillenium."

Jan 1, 1988

By Geir Wedde, Anders Sorhuus

"Vast quantities of energy are released as heat to the environment from industrial operations. Many countries target waste heat recovery to mitigate CO2 emission. Exhaust gases from industries such as primary aluminium smelting, carry a substantial portion of the waste heat generated. For a cost efficient capture of more valuable heat (higher exergy), heat exchangers should operate on the exhaust gases upstream of the gas treatment plants. Heat exchange surface would be exposed to dust laden gases with risk of fouling. Heat exchangers of innovated design and operation have overcome the potential of excessive fouling rates. Heat exchangers of the ""shell and tube"" design have been demonstrated for exhaust gases from ferroalloy as well as primary aluminium smelters. In addition to the heat recovery, gas cooling results in smaller gas treatment plants with lower costs and reduced emission. The aluminium experience is exampled in the paper.IntroductionIndustrial usage of energy continues to grow as a result of increasing volumes of production, a trend that is likely to continue in the coming decades as living standards keep rising globally. World energy consumption (Figure la) is to grow 49 % by 2035 (ref. 2010) as reported by EIA [1]. The industrial sector consumes somewhat more than 50% of the total world energy consumption predominantly the energy increased demand comes from non-OECD countries in Asia. The industrial consumption by production of metals iron and steel accounts for 14 % and for non-ferrous metals 3 % mostly for aluminium production (Figure lb). Aluminium production will be discussed in this paper as an example of an industry with large quantities of waste heat to recover"

Jan 1, 2012

By Ray Y. Lin, Sunil G. Warrier

"Low cost processing of metal matrix composites is an essential requirement for this class of materials to be acceptable in commercial application. In an effort to reduce the cost of processing of metal matrix composites, an infrared pressureless liquid infiltration technique has been developed. The salient features of infrared infiltration are that it is rapid, simple and a low cost process. The rapid processing capability causes very little oxide formation on the alloy resulting in both improved wetting and flow characteristics and reduced oxygen contamination in the composite. Thus, vacuum is normally not required. Using infrared inflltration, aluminum and titanium matrix composites have been prepared under an ambient argon atmosphere. Reinforcements in these composites include carbon fibers, silicon carbide Nicalon fibers and Textron's SCS fibers. Microstructural and mechanical test results indicate that completely consolidated composites with good fiber distribution, limited interfacial reaction and high mechanical properties can be manufactured by this process. IntroductionAluminum and titanium matrix composites reinforced with ceramic reinforcements are strong candidates for numerous applications in the aerospace and automotive industries. Aluminum matrix composites are commonly fabricated by either solid state vacuum hot pressing, liquid state pressure infiltration or squeeze casting [1]. Although liquid state pressure infiltration and squeeze casting has significant advantages over solid state processes, the requirement for pressure makes these composites uneconomical for large scale industrial application. Titanium matrix composites are primarily fabricated by solid state diffusion bonding [2]. Pressureless liquid infiltration can significantly reduce the cost of fabrication in both the composite systems. However, during pressureless infiltration processes, several complications concerning the wetting characteristics and chemical compatibility arise."

Jan 1, 1994

By Aline Maria dos Santos Teixeira, Francisco Manoel dos Santos Garrido, Joao Alves Sampaio, Marta Eloisa Medeiros

"Rocks for crops is a natural practice for soils fertilization which consists on adding rocks to the soil while water decomposes the rock, through chemical weathering, and gradually releases nutrients to the soil solution. This practice can be considered an alternative to the low production of potassium fertilizers in Brazil. In this context, the phonolite rock was characterized in order to evaluate its application as an alternative source of nutrients to the Brazilian agriculture. The phonolite studied is an igneous, volcanic rock with alkaline character that is chemically composed of a high grade of potassium due to the presence of feldspar minerals. In order to quantify the minerals present in the sample, characterization was carried out using several techniques such as X-ray diffraction, X-ray fluorescence and scanning electron microscopy.IntroductionBrazilian soils are generally acidic and nutrient poor due to the tropical climate in which high temperatures and intense rainfall favor a rapid decomposition of the rocks that from the soil. And as agriculture is one of the main bases of the country's economy, large amounts of fertilizer are used to make the soil productive.Although Brazil has large reserves of potassium, the demand for potash fertilizer is higher than the national supply, which makes the country dependent on fertilizer imports, especially in the form of potassium chloride. Thus, we must look for economic alternatives to traditional fertilizer [1].Stonemeal is a natural practice for soil fertilization that consists in adding basic or ultrabasic rocks to the soil so that water, through chemical weathering, decomposes the rock while it gradually releases nutrients."

Jan 1, 2011

By Tanm Engin, Ali Riza Tarakcilar, Derya Dispinar

"Nowadays, the casting industry is developing parallel with the information technologies (IT). Particularly the casting simulation software is being frequently used in foundry floors for casting quality control and optimisation. In this study, the filling and solidification analysis of a rolling roll manufactured by spherical graphite cast iron were carried out by Vulcan casting simulation software. The appropriate defect relieving suggestions were presented by anticipation of defects that may form during the casting process.IntroductionThe optimisation of a casting process has long been the most focused area in manufacturing plants. Many of the work involve not only the process itself but the cost as well. When it comes to the process, it is important to be able to control the defects that may form during casting.The casting process begins with the melting of a charge; followed by pouring into the mould cavity. One of the most important factors is the difference in the liquid/solid density which may lead to porosity. On the other hand, turbulence during filling is another significant factor in casting operations [1].During solidification, due to the density difference between liquid and solid, porosity might form which leads to crack-like defects. There are several other factors that may determine the quality of a casting such as segregation, inclusions, grain size and etc. However, porosity is one of the first parameters that can be easily determine and controlled by the help of simulation software. Simulation is a cost-effective tool in the optimization of process parameters and castings can be visually observed. Time loss and economic expenses could be minimized [2]."

Jan 1, 2012

By Dai Xi

In the present work, the viscosities of molten FenO-MgO-SiO2 and FenO-MgO-CaO-SiO2 semi-synthetic slags for nickel flash smelting were measured in the temperature range from 1473 to 1723K by a rotational viscometer. The ratio of Fe to Si02 was fixed at 1.2, calcium and magnesium oxide contents varied in the range from 2 to 8 mass% and 9 to 12 mass%, respectively. The results showed that silicate anions became smaller by increasing CaO content, which results in a decrease of the viscosity of the slag. In the case of MgO addition the viscosity behavior was complicated. At MgO content below II mass%, the viscosity increased with the increase of MgO at all temperatures tested. However, when the MgO content was above II mass%, the viscosity decreased slightly for FenO-MgO-CaO-SiO2 system. At higher MgO contents, low-viscosity slags can be obtained by adding CaO. At a given composition, .the viscosity decreased with increasing temperature. The higher the temperature, the more MgO can be added before saturation. The effect of Fe3O4 on the viscosity was quite significant. The viscosity of slag increased by 300mPa-s at 1573K when Fe3O4 content varied from 3 to 9 mass%. The viscosity values are presented as the functions of temperature and composition. A comparison between FenO-MgO-SiO2 and FenO-MgO-CaO-SiO2 systems is given in this study.

Jan 1, 2003

By Esperidiana A. B. Moura, Mariana N. Sartori, Vijaya K. Rangari, Angel Visentim Ortiz, Francisco R. V. Diaz, Rene R. Oliveira

"This work presents the preparation and characterization of a nanocomposite based on Poly(butylene terephthalate) PBT and Brazilian smectitic clay (bentonite chocolate clay). Before being incorporated as clay nanoparticles in PBT resin, the clay was organically modified by the addition of a quaternary salt and sodium carbonate. PBT/Clay nanocomposite (96.3:3.70 wt %) was obtained by using a twin-screw extruder machine. After extrusion process, the nanocomposite was characterized by tensile, flexural and impact tests, SEM, Vicat, HDT, DSC, TGA and XRD tests. The results showed that the properties of the nanocomposite obtained were superior to those of neat PBT. Concerning the temperature of thermal distortion (HDT) an expressive gain of around 45 % was presented to PBT/Clay nanocomposite compared to PBT evidencing the interaction of nanofiller with the polymeric matrix.IntroductionPolymer-clay nanocomposites, also called as polymer layered silicates nanocomposites have attracted much attention from both industry and academia over the past decade because they frequently exhibit unexpected properties. In contrast to the traditional fillers, nanofillers, in particular, nanoclay, is found to be effective. The addition of a small amount (< 5 wt.%) can show significant improvement in mechanical, thermal and barrier properties, flammability resistance, and electrical/electronic properties of the final polymer nanocomposite without requiring special processing techniques. Also, as with other nano-size particles, the overall crystallization rate and the glass transition temperature are also affected. It is generally believed that the improvement of properties of nanoclay composites is directly related to the complete exfoliation of silicate layers in the polymer matrix. However, a processing technique that produces complete exfoliation is still a technical challenge [1,2]."

Jan 1, 2012

By L. Klinger, T. Werber, LA Levin, A Katsman

"The process of catastrophic carburization known as ""metal dusting"", whereby a solid metallic material is converted into fine particles in a carburizing atmosphere, was analyzed. It was shown that this conversion is the result of plastic deformation and subsequent fracture accompanying diffusional phase formation in the near-surface layer. The process is controlled by internal stresses arising during phase transformation. Competition between stress generation and relaxation may result in the attaining the ultimate strength in the near-surface layer and its fracture. Such a mechanism of metal disintegration may occur in a certain temperature interval depending on the kinetic and geometrical parameters of the system - the diffusivities of the alloy's components, the ratio between specific volumes of the new and the old phases, and the ultimate plastic strain. The temperature interval for disintegration of carbon steel, the rate of disintegration, and the period of the disintegration cycle, were evaluated and compared with experimental data. IntroductionCatastrophic carburization, known as ""metal dusting"", consists in conversion of a solid metallic material into fine particles. The process occurs in a carburizing atmosphere at elevated temperatures. The corrosion product, usually named ""coke"", consists of metallic particles dispersed in a loose carbon matrix. Under industrial conditions metal dusting takes place, for example, in a gas mixture of CO and H2 or in hydrocarbon environments. Steels, nickel- and cobalt alloys are susceptible to this kind of wastage in the temperature range 400-800°.A mechanism of metal dusting in steels was proposed by Hochman [1] and later developed by Grabke and coworkers [2-5]. According to the proposed model, the process consists of the following reaction steps:"

Jan 1, 1996

By Keizo Uematsu, Satoshi Tanaka, Nozomu Uchida, Yutaka Saito

"Effect of moisture content must be fully understood for controlling the granule compaction of ceramics. It changes the mechanical behavior of spray-dried granules applied for compaction process, and governs the structure and properties of .ceramics. To understand the time-dependent change in processing, the kinetics was examined for change of moisture content for granules placed in a die and the pressed compacts also. The results were explained in terms of apparent moisture diffusion coefficients. They varied non-linearly with the PVA content in the granules. The results were explained through the non-uniform PVA distribution in the granules.IntroductionMoisture must be controlled in compaction process to produce the green compacts having uniform structure. It affects glass transition temperature of binder and thus the deformation behavior of powder granules under an applied stress. Several studies [1-7] have clarified the effect of moisture content on the compaction behavior of granules and the structure of resultant compacts for both die pressing and cold isostatic pressing (CIP) of pre-formed compacts. In these studies, the moisture contents in the system were equilibrated with the humidity in the atmosphere before compaction. In practice, however, the moisture content in the system may vary with time if the relative humidity of surrounding atmosphere is different from what the granules were equilibrated previously. This is very likely case in real production processes. However, the kinetics of moisture change in the granules as well as in the pre-formed powder compacts have not been well studied. For controlling the microstructure in a system, it is necessary to fully understand the kinetics of moisture change and its relevance to packing structure of powders."

Jan 1, 2000