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By S. Y. Tan

As continual complementary metal?oxide?semiconductor (CMOS) scaling requirements, metal gate/high-k dielectric/Si gate stacks are expected to replace poly-Si/SiO2/Si gate stacks in the future CMOS sub-45 nm technology node. Hafnium based oxide is a promising candidate to replace SiO2 as a gate dielectric, due to its much higher dielectric constant (high-k) and stability. The key challenges of successfully adopting the high-k dielectric/Si gate stack into advanced CMOS technology mostly come from the interfacial properties. The origins of the electrical and physical characteristics of the dielectric oxide/bulk interface were studied in detail. The leakage current density-voltage (J-V) and capacitance-voltage (C-V) measurement techniques were employed to study the dielectric oxide/Si interface. The effects of the post-deposition annealing (PDA) treatment on the interface charges of dielectric oxides were studied. We found that the PDA can effectively reduce the trapping density and leakage current, and eliminate hysteresis in the C?V curves. Besides, the changes in chemical bonding features at HfO2/Si, HfSiO/Si and HfSiON/Si interfaces due to PDA treatment were evaluated by XPS measurements. The XPS analysis provides a better interpretation of the electrical outcomes. As a result, both HfSiO and HfSiON films have exhibited superior performance in terms of thermal stability and electrical characteristics.

Jan 1, 2010

By Sergio N. Monteiro

Jute fiber reinforced polymer composites are among the most investigated and applied natural composites. In this past decade the mechanical properties of these composites has been assessed for various types of test conditions. However, the reported results correspond mainly to short-cut jute fiber composites, which do not present the highest mechanical strength as compared to continuous fibers of the same kind. In order to complement these results, the present work evaluated the mechanical behavior, by means of flexural tests, of polyester matrix composites reinforced with continuous jute fibers. Bend tests were conducted in standard specimens with up to 40% of jute. Fracture analysis by SEM displayed the rupture mechanisms. The results showed an improvement in some flexural properties with incorporation of jute fiber. However, a low fiber/matrix interfacial stress was responsible for limitation in the values attained by some properties.

Jan 1, 2010

By T. T. Chen, J. E. Dutrizac

"Grooved cast Pb-Ag anodes are used by some zinc refineries to improve current efficiency. It was found that the manganese oxide scale formed on a grooved Pb-0.75% Ag anode consists mainly of MnO2, which occurs characteristically in rhythmically banded colloform structures and adheres to a layer of ""Pb02+PbS04"" that oxidized from the anode. The relatively homogeneous and nearly fracture-free morphology of the ""Pb02+PbS04"" layer suggests the relatively uniform corrosion of the anode. Deposition of the Mn oxide initially follows the contours of the anode surface, but the grooves eventually become filled with Mn oxide and gypsum. Hydrous Mn oxides and amorphous Mn oxides are believed to be also present in the manganese oxide scale. Tiny particles of PbS04 and SrS04, together with gypsum, other impurities and micro-pores, tend to concentrate in the grooves.IntroductionManganese is a common impurity in hydrometallurgical zinc processing circuits. The manganese originates from sphalerite (Zn,Fe,Mn)S and from the Mn02 added to the leaching circuit to oxidize ferrous ions [1]. Manganese in the sphalerite follows Zn through the roasting, leaching and purification processes, and is present as Mn(II) in the purified ZnS04 solution. The Mn in the added Mn02 is reduced to Mn(II) during the oxidation of the ferrous ions present in the leach solutions. In both cases, MnS04 is generated, and the MnS04 accumulates in the purified solution. In the cellhouse, Zn is plated at the cathodes to produce high quality metal. The Mn(II) is partly oxidized at the anode surface to Mn(IV), and the Mn(IV) precipitates as a scale on the surface of the anode and as a sludge on the bottom of the electrolysis cells. The presence of a thin layer of manganese oxide scale on the surface of the Pb-Ag anode can minimize the corrosion of lead and, accordingly, reduce the contamination of the electrodeposited zinc. However, a heavy manganese scale build-up can cause ""staining"" of the zinc deposits and reduced current efficiencies. Consequently, periodic anode cleaning to remove excess manganese oxide scale is carried out routinely in commercial operations."

Jan 1, 2011

By T. T. Chen

The manganese oxide scales, consisting mainly of MnO2, characteristically occur in banded colloform structures which adhere to porous layers of PbSO4 and PbO2 that oxidized from the rolled Pb-0.7% Ag anodes. Hydrous Mn oxides, Mn3O4 and amorphous Mn oxides are believed to be also present. Tiny particles of gypsum, PbSO4, SrSO4 and AgCl are entrapped in the colloform masses. The gypsum originated from the Zn electrolyte; strontium carbonate was added to the ZnSO4 solution to control Pb, and silver originated from the anodes. Some of the colloform bands contain minor amounts of Pb, implying a limited degree of dissolution of the Pb during electrolysis. Other colloform bands incorporate trace amounts of Zn. Colloform structures permeated with silica gel are presumably caused by the high silica content of the electrolyte.

Jan 1, 2009

By Sergio N. Monteiro

Fibers extracted from the ramie plant have been traditionally used in textile and are now being considered as polymeric composite reinforcement owing to their superior strength. Recently the mechanical behavior of ramie fiber reinforced polyester composites was investigated but no significant improvement was found. Therefore, the objective of this work was to carry out a similar investigation by changing the type of polymeric matrix. Specimens with up to 30% in volume of ramie fibers incorporated into epoxy were bend-tested until fracture. The results showed a moderate improvement with a tendency of decreasing stress for higher amounts of ramie fibers due to the weak interface developed with the epoxy matrix.

Jan 1, 2009

By P. N. Anyalebechi

"The as-cast microstructure of two commercial-size ingots of aluminum alloy 3004 produced by the electromagnetic casting process was quantitatively characterized. This involved the quantitative determination of through-thickness and across-width variations in dendrite cell size, grain size, macrosegregation of alloying elements, interparticle spacing, and the types, volume fractions, and sizes of the constituent or second phase particles. More than ninety-five percent of the constituent phases in the ingots consisted of the A16(Mn,Fe) phase; the desirable a-Al 12(Fe,Mn)3Si phase was not detected in any of the ingots by Guinier X-ray diffraction analyses or electron probe X-ray microanalyses. A significant microstructural heterogeneity through the thickness and across the width of both ingots was observed. For example, macrosegregation, and the sizes of the constituent phase particles, dendrite cells, and grains increased concomitantly from edge to mid-width and from surface to center of the ingots. There was a -20% depletion (negative macrosegregation) of Mg and a +54-87% enrichment (positive macrosegregation) of Ti in the center of the ingots. With the exception of grain size, there was no significant microstructural difference between the two ingots examined. The causes and practical implications of the observed microstructural heterogeneity in the ingots are discussed.IntroductionThe first step in the fabrication of majority of wrought products of aluminum and its alloys is the casting of large ingots or billets of simple shapes (round or rectangular). The sizes of the ingots vary from 10 mm to 450 mm diameter or 25 mm to 780 mm thick. The quality of the finished products is established at the ingot casting stage. This is because the microstructural characteristics, such as secondary dendrite cell size or arm spacing, amount of alloying elements retained in solid solution, macrosegregation, and the characteristics of second phases, produced during casting cannot be reversed by subsequent processing. Up until twenty-five years ago, the effect of as-cast microstructure of large ingots on the structure and behavior of thin sheets (0.34 mm thick) during drawing and ironing processes was incorrectly assumed to be minimal or nonexistent. This was based on the erroneous notion that the thermal treatments and large reduction (>99.94%) and strain that the ingot undergoes during production of the sheets completely destroys the original ingot structure and its inherent heterogeneity. However, the effects of ingot structure can, a priori, be deduced from the observed effects of constituent phase particle size, type and volume fraction on recrystallization, development of texture during annealing and deformation, and earing. In fact, careful examination of the behavior of products produced from different size ingots or castings have shown that the original microstructure of the ingot has a direct impact on the properties and performance of the end products."

Jan 1, 2011

By Vahid Rastegar

"Characterization of the microstructure and revealing dendrites in the microstructure and also measuring the dendrites arm spacing and the distribution of silicon were studied in various pieces of compacted graphite cast irons with 0.17, 0.185, 0.2, 0.22 and 0.24 percent of mischmetal. Black-white and color metallography (quantitative and qualitative) were carried out on the various steps of the cast samples. Distribution of silicon was studied quantitatively using spot analysis with scanning electron microscopy. Furthermore, effects of two variables (cooling rate and mischmetal percentage) on dendrites arm spacing were investigated.In order to color metallography, the samples were plunged into a boiling solution of 18% KOH, 9% NaOH and 9% picric acid in distilled water. It was inferred that the microstructure coloration varies according to the sequence: green-->red-->yellow-->blue-->dark brown->light brown as the silicon content decreases. After observing dendrites, dendrites arm spacing was measured. In this method, it seems to be possible to predict the mechanical properties of compacted graphite cast irons by knowing dendrites arm spacing and without any destructive testing. After studying the two variables, it was concluded that dendrites arm spacing decreases as the amount of mischmetal increases and it increases as the cooling rate increases.IntroductionIn general, detecting of primary austenite dendrites is not possible in cast irons due to their solidification system. Observing the dendrites in the room temperature is possible only in those gray cast irons that contain type D graphite. With collecting data of dendrites arm spacing (DAS) measurements, it could be possible to achieve the mechanical properties of cast irons without any destructive testing. In this research by applying a particular method, primary austenite dendrites and also distribution of silicon in the microstructure has been observed."

Jan 1, 2012

By Gervais Soucy, François Quesnel, Pierre Hovington, Wen Zhu, Karim Zaghib, Jocelyn Veilleux

The properties of lithium titanates anodes in Li-ion batteries are highly dependent on their secondary constituents. While their main phase is usually constituted of Li4Ti5O12, significant quantity of lithium titanates compounds of various stoichiometry are often present, due to either the processing, usage or aging of the material. These may go underreported, as many of these spectrums overlap or display low signal in X-ray diffraction (XRD). Samples of nanosized lithium titanates synthetized by inductive plasma were characterized by XRD and scanning electron microscopy (SEM), as they provide a regular yet typical crystallite size and shape including multiple phases. A Rietveld refinement was developed to extract the composition of these samples. Mass balance through further annealing and differential scanning calorimetry (DSC) enthalpy measurements from phase transformations were also used as identification and validation techniques.

Jan 1, 2015

By Shadia J. Ikhmayies

SnO2:F/CdS:In bilayers were produced by the spray pyrolysis technique on glass substrates. The structures were characterized by recording and investigating their transmittance curves, I-V plots, X-ray difractograms (XRD) and by observing their scanning electron microscope (SEM) images. From the I-V plots it was found that the SnO2:F forms an ohmic or quasi-ohmic contact with CdS:In. XRD patterns show the polycrystalline nature of the films and show that there is a small shift in the position of the (200) line of SnO2:F without the appearance of new peaks. The morphology of the structures are compared with those of SnO2:F alone and CdS:In alone on glass substrates.

Jan 1, 2009

By G. L. Peralta

Geothermal energy is an important source of power in more than 12 countries and is a potential source in 50 countries. However, the exploration and use of geothermal resources generate residues such as scale and sludge. The scale is from the steam distribution pipes while the sludge is from cooling ponds. These solids contain significant levels of elements which are of environmental importance notably, arsenic, sulfur, copper, zinc and lead that require safe treatment and disposal. The compositions, phases, textures, morphologies and size of scale and sludge particles have been studied by laser particle size analysis, light microscopy, scanning electron microscopy, X-ray microanalysis, and X-ray diffraction. In addition, their leachability was tested with protocol leaching procedures and sequential extractions. The detailed spatial relationships and speciation of the environmentally significant constituents have received particular emphasis. The information obtained is useful in understanding how the scale and sludge are formed, their leaching behavior if disposed of in a landfill and in developing appropriate treatment strategies.

Jan 1, 1994

By Justin Karl, Ali Gordon, James DeMarco, Yongho Sohn

"Aluminum metal-matrix composites are lightweight materials that have the potential to supplant steel in many applications. The current work helps to identify the parameters that confer maximal strength and ductility. Torsion tests were performed on the as-cast aluminum metal-matrix composite A359-SiCp-30% at a variety of temperatures and twist rates. Dependence of material properties on temperature and strain rate were identified from equivalent stress-strain curves constructed from the reduced data. Examination of the microstructure was performed on the as-cast material and on fracture surfaces. A temperature-and strain rate-dependent constitutive model was applied to simulation of the mechanical response of the torsion specimen. Trends in material properties corroborate and extend trends identified previously under tensile loading with regard to temperature and strain rate dependence. Shear properties of simulated specimens agree with properties obtained through experimentation.IntroductionAluminum metal-matrix composites (A1-MMCs) have become increasingly popu1ar in recent years. While unreinforced aluminum alloys have low densities and high ductilities, they are not suitable for many applications due to their lack of strength and stiffness. To provide added strength and stiffness while maintaining favorable densities, it has become common to reinforce aluminum alloys with silicon carbide in various forms, although usually the inclusions are in the form of whiskers or particles. The result is a composite material with superior specific strength and stiffness. While whisker-reinforced composites are expensive due to the necessity of processing by nonstandard techniques and have low transverse properties when rolled, particle reinforced Al-MMCs have transverse material property values almost as high as the longitudinal properties and are not as expensive to process as whisker-reinforced Al-MMCs [1]."

Jan 1, 2012

By Denise Cristina de O. Nascimento

Natural lignocellulosic fibers are increasingly being used as polymeric matrix composite reinforcement owing to economical and environmental advantages as renewable and biodegradable materials. Among these, the piassava fiber extracted from a palm tree native of South America stands as one of the most rigid with a potential to be used as composite reinforcement. Therefore, the present work investigates the notch toughness behavior, by Izod impact tests, of epoxy composites reinforced with up to 40 % in volume of continuous and aligned piassava fibers. It was found that the incorporation of piassava fibers results in significant increase in the impact energy of the composite. Scanning electron microscopy analysis showed that the nature of the piassava fiber interface with the epoxy matrix is the major responsible for the superior toughness of the composite.

Jan 1, 2009

By Ailton S. Ferreira, Rubén J. Sanchez Rodriguez, Sergio N. Monteiro, Felipe Perissé D. Lopes, Teresa E. Castillo

"Polyester composites reinforced with natural lignocellulosic fibers have, in recent times, been gaining attention in engineering areas as lighter and cheaper alternatives for traditional composites such as the ""fiberglass"". One of the strongest, the curaua fiber, is today being considered as reinforcement of composites for automobile interior parts. In fact, several research works are currently being dedicated to curaua fiber composites since physical and mechanical properties are required for practical uses. In this work, the thermal behavior of polyester composites reinforced with up to 30 % in volume of curaua fibers was investigated by differential scanning calorimetry, DSC. The results showed endothermic and exothermic events associated with water release and possible molecular chain amorphous transformation. Comparison with similar composites permitted to propose mechanism that explains this DSC thermal behavior.IntroductionThe modem composite materials, especially those reinforced with synthetic fibers such as glass and carbon, have been used since last century to attend the demands required by most technological fields, from home appliances to aerospace [1]. In fact, fiber composites offer significant advantages over monolitic materials, such as common metallic alloys, plastic and ceramics. One of the most important is the ratio between the ultimate stress and the density, known as the specific strength. For example, in common glass fiber polymer composites, the so called ""fiberglass'', the specific strength of around 400 MPa.cm3/g is higher than any conventional monolitic material. However, drawbacks exist. The energy required to fabricate ""fiberglass"" generates large emissions of C02, which are responsible for global warming. Moreover, ""fiberglass"" is not recyclable and cannot be incinerated [2]. As a result, most synthetic fiber composites end up in landfills or contribute to rivers and oceans pollution."

Jan 1, 2011

By Leonardo Mota, Felipe Perissé Duarte Lopes, Marcelo Gomes da Silva, Sergio Neves Monteiro, Helion Vargas

"Natural fibers, as a class of material, are attracting the interest of engineering sectors owing to specific advantages such as comparatively reduced cost and lower density as well as environmental benefits associated with renewability and biodegradability. For industrial applications, thermal properties, among others, are required. These are major requirements, especially in the case of an insulating natural fiber. In the present work, thermal properties of the curaua were investigated by photothermal techniques, i.e., the open photoacoustic cell and a method based upon the monitoring of the temperature evolution as a function of time. This investigation, in tum, permitted to evaluate two important thermal properties: the thermal diffusivity and the specific heat capacity of the curaua fibers. Indirectly, by means of simple mathematical relations, the thermal conductivity was also obtained. The results were compared with other materials and characterize the curaua fiber as an efficient insulator.IntroductionMaterials are gaining attention in recent years owing to their benefits for the environment as compared to synthetics. Being biodegradable, yearly renewable and recyclable, the natural planted-based are considered fully sustainable [1]. In particular, their life-cycle, from growing to industrial processing, absorbs as much C02 as it is emitted and makes them neutral with respect to greenhouse gases responsible for global warming [2]. Typical examples of these environmentfriendly materials are the lignocellulosic fibers that have been used in simple items such as ropes, baskets, textile, modest roofing, etc, since the beginning of our civilization [3]. In the past few decades, these natural fibers have been extensively investigated [ 4-1 O] as a possible reinforcement phase of polymer composites in substitution for synthetic fibers. In fact, engineering application of lignocellulosic composites are today in the market, especially in the automobile industry [11-13]. Out of the hundreds available natural fibers, only part of them exhibits superior properties to be qualified for composite reinforcement."

Jan 1, 2011

By Helvio P. G. Santafé Jr., Ruben J. S. Rodriguez, Sergio N. Monteiro, Teresa E. Castillo

"The coir fiber extracted from the husk of the coconut fruits are worldwide available in tropical regions as a low cost lignocellulosic by-product for many applications including composite filler in automobile parts. Possible uses above room temperature require information on the thermal behavior of these coir fiber composites. Therefore, the objective of this work was to perform thermogravimetric, TGA and DTG, analysis on polyester matrix composites incorporated with different volume fractions of coir fiber. In general, it was found that thermal degradation associated with weight loss occurred in three stages. Changes were also observed in the DTG peaks that could be attributed to the coir fiber participation through the decomposition of its lignocellulosic structure.IntroductionThe development of new materials has always been motivated by the need of improved properties. This was the case of modem composites with combination of properties that surpass those of conventional monolithic metallic alloys, ceramic or polymers, from which composites are made. A typical example is the synthetic fiber reinforced composite with specific strength i. e, ultimate stress divided by density, higher than any other monolithic material. Today, however, our global society is concerned with serious environmental problems and thus demanding that new materials be developed with distinct characteristics. They are known as environmentally correct and are expected to be sustainable, which corresponds to the condition of being biodegradable, renewable, recyclable and neutral with respect to C02 emission, considered the main responsible for global warning [1]. Synthetic fiber composites cannot meet these requirements. Consequently, new composite reinforced with cellulose-based natural fiber are being developed [2-8] and are already replacing the synthetic ones in several engineering fields including the automobile industry [9-11]. These composites have additional advantages owing to the lignocellulosic fiber benefits of being diversified, abundant, less expensive, lighter and of societal interest [8]. In some cases even technical advantages such as non-abrasive effect to processing equipments and more flexibility exist in comparison to synthetic fibers."

Jan 1, 2011

By T. T. Chen

Copper anodes generated from copper scrap are relatively rich in Sn, Zn and Fe. Because of the presence of oxygen, only trace amounts of Sn occur in solid solution in the copper crystals. Thus, Sn occurs mainly as SnO2, Cu-Sn-Ni oxide and Sn-Ni-Zn oxide in the copper anodes, and Zn and Fe occur mainly as minor constituents in the Sn-Ni-Zn oxide and Cu-Sn-Ni oxide. During electrorefining, these oxide species are liberated from the copper anodes and report directly to the anode slimes. The trace amounts of Sn present in solid solution in the copper crystals dissolve but reprecipitate as Sn arsenate or a Sb-As-Sn-O phase. Accordingly, high Sn contents in copper anodes do not lead to elevated Sn concentrations in the electrolyte.

Jan 1, 2010

By C. M. F. Vieira

This work has as its objective to characterize ceramic bodies for vitrified tiles elaborated with the mixture of nepheline-syenite flux and kaolinitic clay. Formulations were prepared with 0, 30 and 50 wt.% of nepheline-syenite incorporated in a kaolinitic clay. To determine the physical and mechanical properties such as dry bulk density, linear shrinkage, water absorption and flexural rupture strength, specimens were prepared by 30 MPa uniaxial pressure-molding and then fired in a laboratory furnace at 1150oC. The microstructure of the fired ceramics was evaluated by scanning electron microscopy. The results indicated that the nepheline-syenite improved the evaluated properties of the clay and attended the specifications of vitrified ceramic tiles.

Jan 1, 2010

By Jürgen Antrekowitsch, Thomas Griessacher

The recovery of valuable metals from residues like dusts and sludges is nowadays state of the art. Depending on the complex constitution, a recovery of different metals can – in the majority of cases – only be performed with considerable energy input in high temperature processes together with insufficient yields and newly generated residues. Often, the behavior of the dust or sludge in the process during melting or reduction is unknown. In this work, a detailed characterization of selected residues like steel mill filter dusts, cupola furnace dusts and leaching residues is done. The different steps of getting from solid particles into a homogenous liquid phase were investigated. Although high temperature processing leads to high reaction speeds, the complexity of residues keeps the system away from thermodynamic equilibrium. With this research program, some basics are generated to understand smelting and reduction and the gap between thermodynamical calculations and real behavior can be explained.

Jan 1, 2008

By Xuewei Lv, Maojun Zhou, Xiaobo Huang, Rende Zhang

"The characterization of the surface roughness of the mineral particles is of vital importance for the studies of the mineral processing. In this study, an evaluation of the roughness of the iron ore particles, with the measurements of size distribution and the measurements of specific surface area with the liquid nitrogen absorption, was developed. The main theory of this method is the fact that the roughness of the particle influences the specific surface area apparently. The specific surface area of the particles can be measured with the laser diffraction method and the liquid nitrogen absorption method. The influence of the surface roughness of the particle can be measured with the nitrogen absorption and cannot be measured with the laser diffraction. Therefore, the roughness can be got by comparing the specific surface area with two measurement methods.IntroductionThe characterization of the surface roughness of the mineral particles is of vital importance for the studies of the mineral processing. There are three main methods for measuring the size distribution of mineral particles: sieving, laser diffraction, and sedimentationl). Many techniques involve sedimentation such as the Horiba2, 3) and the Cyclo-sizer1). In the mineral industry, size distribution is usually determined by sieving because it can be carried out accurately for all particle sizes larger than 45 . The preferred method to obtain the size distribution of finer particles is laser diffractometry. The technique has several advantages: it produces measurements in a few minutes with considerably less labor compared with the cyclo-sizer and for a range of sizes considerably wider in comparison with the sedigraph4). The equivalent-sphere size distribution reported by laser diffractometry is valid for metallurgical calculations and can be routinely used in mineral processing plants. The surface area of the particles can be measured by the BET method of nitrogen adsorption, or it can be calculated from the size distribution. However, the latter calculation requires the size distribution to be accurately known across the whole size range, and assumptions have to be made about the shapes and surface roughness of the particles and presence or absence of pores (see below). The BET method is based on the physical adsorption of gas over the whole exposed surface area and measures the surface area stemming from the roughness and open pores on the surface of the particle5). The calculation of the surface area from the size distribution is usually based on the assumption that all the particles are smooth spheres, without considering the shape and/or roughness of the particles. Determining the surface roughness of the particle with these methods, is the objective of this study."

Jan 1, 2012

By C. J. Beyke

Slags and/or mattes from three secondary lead producers were studied as part of an effort to develop treatment methods for these lead-bearing residues. Each company used a somewhat different production process. Company A used a reverberatory furnace followed by a blast furnace. Company B used only a blast furnace. Company C used both a reverberatory and a blast furnace, and the scrap material was desulfurized with sodium carbonate prior to smelting. The slag matrix produced from sulfur-bearing scrap consisted mainly of iron-calcium silicates; the slag from desulfurized material was similar, but also contained sodium. In all the slags most lead was present in metallic form, often alloyed with tin, antimony, arsenic, and/or iron. Slag from Company B contained the most alloying elements, often as discrete subparticles within the lead droplets. Mattes were produced at Companies A and B; predominant phases were pyrrhotite and magnetite, while lead was present in metallic form and as galena.

Jan 1, 1995