bluuebunny/crossref_metadata_2025 huggingface dataset:
The Synthesis and Properties of Magnetic Nanoparticles
Authors: Drofenik Miha , Lisjak Darja , Makovec Darko
Published: March 2009

Magnetic nanoparticles are materials of great interest because of the remarkable fundamental properties exhibited by these materials as well as their technological potential in the area of biomedicine and other areas. The technologically useful properties of magnetic nanomaterials are not limited to their structural, chemical or mechanical behaviour, but also involve the phenomena that arise from their finite size and the surface effects that dominate the magnetic behaviour of individual nanoparticles. New techniques that have been developed recently have permitted researchers to produce larger quantities of nanomaterials and characterize them better. Here, some of the most promising procedures are reported, including techniques based on hydrothermal syntheses, sol-gel syntheses, co-precipitation syntheses, mechanochemical syntheses, sonochemical syntheses, spray pyrolysis and microemulsion-assisted syntheses.
The Influence of Acid Treatment on the Nanostructure and Textural Properties of Bentonite Clays
Authors: Vuković Z. , Milutinović-Nikolić A. , Krstić J. , Abu-Rabi A. , Novaković T. , Jovanović D.
Published: March 2009

The nanostructure and textural properties of acid-activated bentonite clays from the Bogovina coalmine were investigated. The acid activation was performed with HCl in the concentration range 1.5-7.5 M. The atomic force microscopy followed by image analysis was used in order to establish the influence of the acid treatment on the size of bentonite particles. Nitrogen adsorption-desorption isotherms at -196 °C were used to estimate the specific surface area, pore volume and pore size distribution. The acid treatment reduces the size of bentonite particles and increases the specific surface area and pore volume of the investigated bentonites. These effects are improved by increasing the acid concentration up to 4.5 M HCl. Further increase in acid concentration does not result in development of new porous structure.
Mathematical Modeling of Cell Distribution in Alginate Microbeads
Authors: Obradović B. , Bugarski B. , Todosijević Z. , Nedović V. , Bugarski D. , Vunjak-Novaković G.
Published: March 2009

Alginate is one of the mostly used hydrogels for cell entrapment aimed for applications in food industry, environmental engineering, pharmacy and biomedicine. One of the major parameters affecting cell viability and activity is cell distribution inside the immobilization matrix. In addition, changes in cell distribution over the cultivation time could indicate mass transfer limitations, favorable local environments or cell differentiation. In this study, immobilization and distribution of brewing yeast in alginate microbeads were investigated as a model system of colony forming cell growth. Cell distributions were attained by image analysis of histological cross sections of microbeads used in beer fermentation. A mathematical model based on cellular automata approach was developed for three-dimensional simulations of cell arrangement over the fermentation time.
Radioprotective Efficiency of Fullerenol in Irradiated Mice
Authors: Trajković S. , Dobrić S. , Djordjević A. , Dragojević-Simić V. , Milovanović Z.
Published: March 2009

In vitro studies have demonstrated that fullerenol, a polyhydroxylated derivative of fullerene (C60(OH)n n = 12-26), has a high antioxidative potential. Since any radiation injury is mainly a consequence of the action of free radical species, the aim of this study was to examine radioprotective efficiency of fullerenol in whole-body irradiated mice. The experiment was performed on male, adult, white mice, whole-body irradiated with Xrays doses of 6 to 8 Gy (X-ray energy of 8 MV). Fullerenol C60(OH)24 was given in doses of 10 and 100 mg/kg i.p. 30 minutes before irradiation. The experimental groups consisted of 25-30 animals each. The survival rate and body mass gain of irradiated animals were monitored for 30 days after irradiation. The mean lethal times (LT50) of irradiated mice and mean lethal dose of X-rays were calculated and compared. The results showed that fullerenol C60(OH)24, in a dose of 100 mg/kg i.p., prolonged LT50 of irradiated mice. This effect was especially pronounced in mice irradiated with 7 and 8 Gy of X-rays. It seems that radioprotective efficiency of fullerenol C60(OH)24 is more marked in mice irradiated by higher doses of X-rays.
Enthalpy of Formation of Cu2PbO2 and Revision of the Cu2O-PbO Phase Diagram
Authors: Čančarević M. , Zinkevich Matvei , Aldinger Fritz
Published: March 2009

The stoichiometric compound Cu2PbO2 has been synthesized by solid-state reaction from Cu2O and PbO in a sealed quartz ampoule. The optimum synthesis conditions are 910 K and 260 h. The enthalpy of formation of Cu2PbO2 has been measured with the use of high-temperature calorimeter. The enthalpy of reaction Cu2O + PbO = Cu2PbO2 is – 25.4 ± 1 kJ·mol-1 at temperature 968 ± 5 K. Standard enthalpy and Gibbs energy of formation of the Cu2PbO2 compound from elements and its entropy at 298.15 K are DfH° = – 413.086 kJ·mol-1, DfG° = – 353.165 kJ·mol-1 and S° = 135.165 J·mol-1·K-1. The eutectic reaction L → Cu2O + PbO was found to occur at 1017 ± 5 K. Using the thermodynamic database for Cu-Pb-O system the revised Cu2O-PbO phase diagram is proposed.
Solid State Phase Transformations under High Magnetic Fields in a Medium Carbon Steel
Authors: Zhang Yu Dong , Esling Claude , Zhao X. , Zuo Liang
Published: March 2009

High magnetic fields were applied to the austenite to proeutectoid transformation and tempering process in a 42CrMo steel. The thermodynamic and kinetic effects of the high magnetic field on the austenite decomposition show that it can obviously increase the amount of the product ferrite and accelerate the transformation by enhancing the Gibbs free energy difference between the parent and product phases. Moreover, the magnetic field can considerably lower the amount of low angle misorientations of ferrite in pearlite colonies and obviously increase the frequency of S3-29 coincidence boundaries, especially S3 boundaries, of the ferrite. But it has no obvious effect on crystallographic orientation distribution. When the field is applied to the high temperature tempering process, it can effectively prevent the directional growth of cementite along martensite plate boundaries and twin boundaries by increasing both the cementite/ferrite interfacial energy and the magnetostrictive strain energy. Finally, particle-like cementite is obtained. The magnetic field also obviously retards the formation and growth of the ‘distortion-free’ regions of the matrix.
Abnormal Grain Growth and Texture Development
Authors: Rollett Anthony D.
Published: March 2009

A theory for abnormal grain growth (AGG) in polycrystalline materials is revisited and extended in order to predict AGG in textured polycrystals. The motivation for the work is to improve our understanding of the origins of the Goss texture component, {110}<001>, during annealing of Fe-Si sheet. Since the AGG phenomenon in grain-oriented electrical steels is known to be dependent on the presence of a dispersion of fine second phase particles, the grain boundary
properties are treated as representative of the homogenized behavior of the material, and not necessarily the properties that would be measured directly. The predictions of AGG are presented in the form of maps in Euler space, showing which texture components are most likely to grow abnormally. For different models of grain boundary properties applied to a theoretically derived texture, different sets of texture components are predicted to grow; neither model, however, predicts growth of the Goss component.
Mechanisms of New Orientation Formation during Recrystallization of Old Deformed Aluminium Bicrystals
Authors: Paul Henryk , Driver Julian H. , Lens Arnaud
Published: March 2009

The crystallography of recrystallization nucleation has been investigated in channel-die deformed pure aluminium bicrystals with {100}<011>/{110}<001> and {100}<001>/{110}<001> orientations. The new grain orientations and misorientations were followed by systematic local orientation measurements using SEM and semi-automatic measurements in a TEM. In particular, orientation mapping combined with in-situ sample heating was used to investigate the formation and growth of new grains and their crystallographic orientation changes at very early stages of recrystallization. Grain boundary migration and ‘consumption’ of the as-deformed areas was always favoured along directions parallel to the traces of the {111} slip planes that had been most active during deformation. The orientations of the first formed nuclei were misoriented with respect to the orientations identified within the neighbouring deformed areas by α(<111>, <112>, or <100>)relations.
α→γ→α Transformation Texture Formation at Cold-Rolled Ultra Low Carbon Steel Surfaces
Authors: Yoshinaga Naoki , Kestens Leo , De Cooman Bruno C.
Published: March 2009

The influence of Mn on the surface texture formation through a®g®a transformation
was investigated. After the a®g®a transformation, a weak texture was formed at the surface of ultra low carbon cold-rolled sheet steel without Mn. In contrast, a sharp <100>//ND cube texture was observed in Mn alloyed ultra low carbon steel. In order to interpret the effect of Mn two alternative mechanisms were considered : (i) one assumption attributes the occurrence of the specific surface texture to the effect of outer-surface energy (ii) and according to an alternative hypothesis the release
of elastic work parallel to ND in the surface area is responsible for the observed <100>//ND surface texture.
Texture and Symmetry Relationships in Piezoelectric Materials
Authors: Key Thomas S. , Jones Jacob L. , Shelley William F. , Iverson Ben J. , Li Hsin Yu , Slamovich Elliott B. , King Alexander H. , Bowman Keith J.
Published: March 2009

The anisotropy that is inherent to piezoelectricity is directly tied to the symmetry of domains within the crystals of polycrystalline piezoelectrics. Alloy design for these oxide materials is often focused on influencing pinning of domain walls in polycrystals that have been subjected to high fields and elevated temperatures to introduce the ‘poled’ condition from which most piezoelectric devices operate. We have investigated a wide range of these oxides consisting of single phases or mixtures of phases that may be all or partially piezoelectric in character. Crystal symmetries investigated include tetragonal, orthorhombic, rhombohedral and monoclinic with some phase transitions evolving during high-temperature processing or during poling. Materials investigated include a range of bismuth titanates, lead titanates, lead zirconate titanates and sodium niobates. A variety of texture evaluation techniques, including area detector x-ray diffraction, synchrotron x-ray sources, and neutron sources have been utilized along with Rietveld diffraction modeling tools to enable a deeper understanding of domain textures, domain texture evolution and synergistic relations between crystallographic textures and domain textures. This paper documents an understanding of texture and anisotropy in these materials, and provides insight on approaches to optimize textures for high performance in these materials and demonstrates how these tools can be used to evaluate processing variations from production of these materials.
Allowance for Internal Microstresses and Texture in Evaluation of Residual Stresses in Cold-Drawn Steel Wires with Micromechanical Models
Authors: Zolotorevsky Nikolay Y. , Zisman A.A.
Published: March 2009

Under consideration is an allowance for internal grain-scaled stresses in the evaluation of residual macroscopic stress in highly textured polycrystals. The grain-scaled stresses have been evaluated with two micromechanical models: (a) a simplified model developed for a very strong <110> fiber texture and suggesting the corresponding peculiarity of slip pattern in constitutive crystals, and (b) a full-constraint model allowing for accommodation nature of the multi-slip pattern in these crystals. Both models satisfactorily predict the position and relative intensity of the nonlinearities of d{hkl}-sin2y curve. The former model, by treating magnitude of grain-scaled stresses as a fitting parameter, provides better correspondence to experimental data. The latter model, free of fitting parameters, overestimates the grain-scaled stresses, and, consequently, the oscillations of d{hkl}-sin2y curve.
Influence of the Cube-Texture and the Grain Growth on the Creep Behavior in Platinum-10%Rhodium Alloy
Authors: Ochiai Shouichi , Murakami Takeshi , Hashimoto Keizo , Ishii Nobuo , Hasegawa Koichi
Published: March 2009

In Pt-10mass%Rh alloys which were recrystallized using full annealing at or above 1273K after the cold rolling with the reduction ratio of both 90% and 98%, the formation of cube texture has already been found. When these primary recrystallized alloys are subjected to the further annealing at higher temperatures, the occurrence of the secondary recrystallization can be expected. In this study, the development of the cube texture and the process in the coarsening of crystal grains during the secondary recrystallization were investigated. In addition, the creep tests were carried out for the secondary recrystallized alloys and resultant creep properties were compared with those for the primary recrystallized alloys. It became clear that the cube texture which further developed during the secondary recrystallization in 98% rolled specimens exhibits the greater thermal stability than that in secondary recrystallized 90% rolled ones. During the secondary recrystallization, it was confirmed that the grains coarsened according to the law of tm, where t and m show time and a constant, respectively. The higher development of the cube texture and the coarsening of grains during the secondary recrystallization were found to have remarkable effects of improving the creep resistance.
Statistical Errors of Texture Entities Based on EBSD Orientation Measurements
Authors: van den Boogaart K.Gerald
Published: March 2009

The determination of an ODF, C-coefficients, property tensors and portions of texture components from EBSD orientation measurements is afflicted with statistical errors introduced by incomplete sampling of the grains. Since the measurements are highly spatially correlated and stochastically dependent, classical sampling theory does not apply. A general statistical method for error estimation in the presence of stochastically dependent observations has been developed and applied to the most important quantities of texture analysis. The method is based on the assumption of a finite range of dependence between different measurements and on the estimation of the covariance in the observed set of orientation. The methods allows the computation of standard measurement errors and confidence limits for the mentioned texture quantities. It can be used for an objective decision whether two textures are statistically equal or not, based on the comparison of estimated ODFs. Further we can decide statistically whether the ODF obeys certain types of symmetry (e.g. whether it is a girdle textures or whether it is symmetric about the shear plane observed in the field).
Lamellar Subdivision during Accumulative Roll Bonding of a Titanium Interstitial Free Steel
Authors: Reis Ana Carmen C. , Kestens Leo , Houbaert Yvan
Published: March 2009

Titanium alloyed interstitial free steel was processed by means of accumulative roll
bonding (ARB) in order to obtain an ultrafine grained structure. Ten consecutive rolling passes were applied at 480°C with a nominal reduction of 50% per pass and an intermediate annealing treatment of 5 min. at 500°C. A total true strain was obtained of evM = 8.0 which corresponds to an accumulated reduction of 99.9%. Orientation imaging microscopy was used to evaluate textures and microstructures. A pronounced lamellar structure was observed until the 5th pass with an incidence
of high angle grain boundaries predominantly parallel to the rolling direction. After the 6th pass (evM = 4.8) an increased fragmentation perpendicular to the rolling direction starts to develop in spite of the lamellar microstructure with an average spacing of approximately 1 µm. From the 7th pass onwards (evM ≥ 5.6) a random high angle grain boundary distribution develops which results in a more equi-axed ultrafine microstructure after the 9th pass (evM = 7.2) with an average grain width of 200 nm. As the rolling is carried out without lubrication, the surface areas display a slightly more fragmented structure than the midlayer sections and typical shear texture components are present in these surface zones (<110>//ND and <211>//ND fibre). Although the sheets are stacked upon each other after each subsequent pass, the shear strain microstructural and textural features are rapidly
decomposed in the midlayer in each subsequent rolling pass which is clearly revealed by the cross sectional orientation scan on the composite sample. Hence it cannot be concluded that the surface shear strain significantly contributes to the grain fragmentation in the bulk volume of the composite sample.
Texture Evolution during Cold Rolling of Low and High Carbon Steel. Measurement and Simulation
Authors: Walentek Artur , Hu Xiahua , Seefeldt Marc , van Houtte Paul
Published: March 2009

This paper presents simulations of the texture development during cold rolling of fully
pearlitic steel. In order to investigate the importance of including microstructural aspects into texture simulations the calculations were carried out with the FC Taylor Pearlite model which takes the lamellar microstructure into account and with the FC Taylor and LAMEL model which are dedicated for one phase materials. The results are compared with those for ULC steel. For both materials the LAMEL model results are in good agreement with experimental data, while for the pearlitic steel, the FC Taylor Pearlite model improves the predictions only slightly with respect to the FC Taylor model.
Characteristics of Recrystallization Texture Evolution in High Magnetic Field for Interstitial Free (IF) Steel Sheet
Authors: He Chang Shu , Zhang Yu Dong , Zhao X. , Zuo Liang , Esling Claude
Published: March 2009

High magnetic field is applied with the field direction parallel to the rolling direction during annealing of a cold rolled IF steel sheet. Results of X-ray ODF analysis show that, magnetic field annealing retards the normal recrystallization texture evolution for the IF steel sheet. It is worth noting that an abnormal increase of orientation intensity at {100}<110> is found after magnetic annealing for 25min at 650°C. When the magnetic field strength is increased from 10 Tesla to 14 Tesla, the a-fiber is further strengthened, especially the {100}<110> component. Combined with EBSD analysis results, it is considered that the magnetic field does not change the mechanism of recrystallization texture evolution for the IF steel sheet in the present case.
Uniformity of Grain Coarsening in Submicron Grained Al-Sc Alloy Containing Local Variations in Texture
Authors: Ferry Michael
Published: March 2009

The effect of fine particles on the uniformity of grain coarsening in a submicron grained Al-Sc alloy containing significant local variations in texture has been investigated using high resolution EBSD. The alloy was processed by severe plastic deformation and low temperature ageing to generate a fine-grained (0.8 µm diameter) microstructure containing either a dispersion of nanosized Al3Sc particles or a particle-free matrix. The initial processing generated a uniform grain size distribution, but the distribution of grain orientations was inhomogeneous with the microstructure containing colonies of grains consisting predominantly of either HAGBs or LAGBs with the latter possessing orientation gradients of up to 10 o/µm. Despite the marked differences in boundary character between these regions, the alloy undergoes slow and uniform grain coarsening during annealing at temperatures up to 500 oC with no marked change in the grain size distribution, boundary distribution and texture. A model of grain coarsening that takes into account the influence of fine particles on the kinetics of grain growth within an orientation gradient is outlined. The model predicts that a large volume fraction of fine particles (large f/r-value) tends to homogenize the overall rate of grain coarsening despite the presence of orientation gradients in the microstructure.
Dynamic Recrystallization during Compression of Mg-3%Al-1%Zn
Authors: Backx Petra , Kestens Leo
Published: March 2009

Magnesium is the lightest structural metal with a density of only 1.74 kg/dm3.
Furthermore the yield strength and fracture strain of cast magnesium alloys are as good as those of common grade aluminum alloys. Because of these favorable properties there is a lot of interest from the automotive industry to use magnesium and its alloys in order to produce lighter vehicles. Because of its hexagonal crystal structure magnesium displays a very high mechanical anisotropy and a poor formability. In order to address these problems the influence was studied of dynamic
recrystallization (DRX) on the microstructure and texture during compression of AZ31 samples (Mg-3%Al-1%Zn). Cylindrical samples were subjected to uniaxial compression tests at various temperatures and strain rates. The occurrence of DRX is revealed by optical micrographs that display bulging grain boundaries and the formation of newly formed grains. As DRX leads to grain refinement and grain refinement leads to an increased strength, DRX is an appropriate instrument to
improve the strength of this alloy. The texture evolution and the volume fraction of recrystallized grains during DRX are monitored by orientation microscopy. The orientation microscopy postprocessing software allows to calculate the textures of both original and recrystallized grains separately. It is shown that the recrystallized grains have a much more random texture than the original ones and that increasing the temperature and decreasing the strain rate have a positive effect on the randomization of the texture. Previous research has shown that a near random initial
texture produces a better formability (more than 40% failure strain at room temperature in a compression test) for this alloy [1]. This demonstrates that DRX can give rise to an improved ductility.
Microtexture Analysis of Friction Stir Welded Al 6061-T651 Plates
Authors: Kang Suk Hoon , Bang Woong Ho , Cho Jae Hyung , Han Heung Nam , Oh Kyu Hwan , Lee Chang Gil , Kim Sung Joon
Published: March 2009

Microstructural characteristics of friction-stir-welded Al 6061-T651 with varying rotating and advancing speed were examined by the electron backscattering diffraction (EBSD) installed in field emission-scanning electron microscopy (FE-SEM). It was found that FSW produced an equiaxed fine-grained microstructure in weld zone and the grain size in weld zone decreased up to about 4~6 µm with decreasing rotating speed. The primary textures developed in weld zone were {100}<001>, {110}<001> and {111}<110>. In thermo-mechanical affected zone, the change in grain size was not significant, however, large number of low angle grain boundaries were observed, which seems to be concerned with the formation of subgrains due to the development of dislocation cells.
The Development of an Innovative P/M Oil Control Ring from Concept to Production Line
Authors: Panelli Renato , Ferarrese André , Soave Reinaldo , Pegorer Ronaldo
Published: March 2009

The two major working characteristics of the oil control ring are: 1) to scrape the lubricant oil from the cylinder wall to the direction of the crankcase, and 2) to maintain a sufficient amount of lubricant oil to the compression rings above it in order to sustain a suitable lubricant film thickness between the rings and the cylinder. The oil control ring efficiency is the outcome of the combination of the following parameters: conformability, sort of the contact between the ring and the cylinder, contact pressure, and oil scraping dynamics. This work shows the development of an original oil control ring named Monoland, conceived by powder metallurgy design, having high conformability and optimized contact pressure that provides a superior oil scraping efficiency even with decreasing the friction losses. These qualities were achieved as an effect of an extensive product advance program established by Mahle Metal Leve Research and Development Center and Mahle Metal Leve Miba Sinterizados, which involved steps beginning from the product concept to the production streamline and passing through an extensive product validation program.
Consolidation of Compacted Zircaloy Chips via Vacuum Arc Melting - Analysis of the Electric Arc
Authors: Mucsi C.S. , de Faria Jr. Rubens Nunes , Galego E. , Rossi J.L.
Published: March 2009

The main objective of this work is to present the preliminary results on the analysis of the signals arising from the electrical arc, during the vacuum arc remelting of Zircaloy electrodes, aiming the automation of the fusion process. Zircaloy electrodes were made from compacted chips resultant of the machining of Zircaloy rods. The melts were performed in a prototype (vacuum arc remelting) VAR furnace under low pressure of argon and the arc was fed by a constant DC power source. Both filtered and unfiltered signals were recorded by means of a data acquisition system. The fast Fourier transforms FFT and autocorrelation integral were used as tools for data analysis. The result showed that the events occurring within the electric arc have a strong influence on the electric signals. The analysis allowed inferring that the VAR electric arc system has mainly a chaotic behaviour and sporadic periods of linear behaviour. The conclusion of this work is that a control system may be developed, based on the modelling of the non-linear behaviour of the arc, mainly chaotic. This may allow the achievement of an automatic control for the process and yield better quality products.
Simulation of Spouted Bed Using a Eulerian Multiphase Model
Authors: Duarte Claudio Roberto , Murata Valéria V. , Barrozo Marcos A.S.
Published: March 2009

Spouted bed systems have emerged as very efficient fluid-particle contactors and find many applications in the chemical and biochemical industry. Some important applications of spouted beds include coal combustion, biochemical reactions, drying of solids, drying of solutions and suspensions, granulation, blending, grinding, and particle coating. An extensive overview can be found in Mathur and Epstein[1]. The pattern of solid and gas flows in a spouted bed was numerically simulated using a CFD modeling technique. The Eulerian-Eulerian multifluid modeling approach was applied to predict gas-solid flow behavior. A commercially available, control-volume-based code FLUENT 6.1 was chosen to carry out the computer simulations. In order to reduce computational times and required system resources, the 2D axisymmetric segregated solver was chosen. The typical flow pattern of the spouted bed was obtained in the present calculation. The simulated velocity and voidage profiles presented a good agreement qualitative and quantitative with the experimental results obtained by He et al. [4].
A Study of the Rejects Recovery in a Column Flotation
Authors: Oliveira M.S. , Cioqueta D.R. , Sallum M. , Miro R. , Guimarães R.C. , Ataíde Carlos Henrique , Barrozo Marcos A.S.
Published: March 2009

Performing of the flotation process in columns started in the year 1981. Since then, this new flotation technique became usual in many countries, including Brazil, where nowadays flotation columns are installed in plants for iron and phosphate ore concentration. Sees the need of a rational use of the phosphate of Barreiro, Araxá (MG), whose medium useful life is esteemed in 30 years, Federal University of Uberlândia in partnership with Bunge Fertilizers looks for in this work to develop conditions for use of the rejects of the flotation process. A laboratory flotation column was operated in discontinuous mode in order to examine the mixture of two different types of collectors, ore conditioning time and reagents dosages. Contents between 22 and 29 % P2O5 were obtained and Apatite recovery varied in the range of 18 to 58 wt %. The results shows that the use of mixture of the synthetic reagent KE and the rice oil soap provided an increase considerable in the selectivity of the concentrate.
Chemical Synthesis by Pechini Method for Obtation of ZnO Varistors
Authors: Ribeiro P.C. , da Costa E.G. , Gama Lucianna , de Melo Costa Ana Cristina Figueiredo , Kiminami Ruth Herta Goldsmith Aliaga
Published: March 2009

The zinc oxide varistors are ceramic semiconductor devices doped with some metallic oxides such as: bismuth, nickel, manganese, cobalt, and others. The aim of this work is to characterize the varistors, obtained by the Pechini’s method, regarding their microstructure and electrical features. By using chemical synthesis, it has been produced ceramic powders. The powders have been compacted in the form of pellets and sintered at 1200°C/1h. The samples have been characterized by measurements of J x E, XRD and by SEM. The results show that the powders obtained through Pechini’s synthesis method and calcined at 700°C/1h have a particle size of less than 100 nm. The resulting microstructures show heterogeneous morphologies in a shape of pins and presence of inter and intragrain porosity. The electrically characterized results show that the produced varistors present a nonlinearity coefficient of 21 and breakdown voltage of 1590 V/cm.
Phase Amorphization during High-Energy Milling of Mixtures of Zirconia with Yttria or Ceria Powders
Authors: Muccillo R. , Franchi L. , Santos J.T. , Cosentino I.C. , Muccillo E.N.S.
Published: March 2009

Strontium ferrites powders were obtained by high energy milling process after calcinations of iron oxide and barium carbonate. Phase formations and crystallite size was determined using X-ray diffraction. Morphology, particle size and agglomeration stages were analyzed using scanning and transmission electron microscopy. Results show particles in the range of 14 to 40 nanometers, large agglomerates and crystalline phases formation.
Addition of Polyurethane to Portland Cement
Authors: Martinelli Antonio Eduardo , Melo D.M.A. , Lima F.M. , Bezerra Ulisses Targino , Marinho E.P. , Henrique D.M.
Published: March 2009

Portland cement is by far the most important binding material used in both civil construction and oil well cementing. However, especially in the latter application, its brittle nature impairs its ability to withstand dimensional changes due to thermal gradients (RT to approximately 200°C), typical of heavy-oil recovery operations. This often results in extensive cracking of the cement sheath and debonding of the cement-casing interface, which leads to loss of zonal isolation, gas migration and production of water and oil through the well annular. Portland-Polyurethane composites have been formulated and tested in an attempt to improve the deformation ability of the cement during thermal cycles without affecting the pumping behavior or high-temperature resistance of the material. Preliminary results confirmed that the addition of small contents of polyurethane considerably improved the plasticity of the cement in approximately 50% as well as decreased porosity and permeability. No significant changes were observed in the rheological behavior of the composite slurries with respect to plain Portland cement.
Synthesis, Rheological Behavior and Mechanical Characterization of Structural Fast-Setting Geopolymers
Authors: Martinelli Antonio Eduardo , Melo D.M.A. , Marinho E.P. , Batista T.W.J. , Araújo R.G.S. , Melo M.A.F.
Published: March 2009

Geopolymers are inorganic materials with ceramic characteristics that can be synthesized at room temperature from the setting of slurries. Their structure consists of aluminosilicate units that polymerize in alkaline environment. The setting rate and mechanical behavior of geopolymers strongly depends on the SiO2:Al2O3 molar ratio, polymeric precursor and polymerization cation. The present work reports the synthesis and characterization of 3.5:1 (SiO2:Al2O3) structural geopolymers prepared using either metakaolin (GPMK) or kaolin (GPK) as geopolymeric precursor in potassium hydroxide solution. GPMK depicted quick setting whereas GPK set only after 4 hours. The rheological characterization of the slurries revealed that plastic viscosity and yield point of GPK were 0.40 Pa.s and 14.2 Pa, respectively, whereas GPMK set instantly. The compressive strength of both geopolymers were measured after 24 hours and resulted in similar results, i.e., 4.6 MPa for GPMK and 4.4 MPa for GPK. The strength of both geopolymers was compatible to values typical of structural materials.
Synthesis and Thermal Characterization of Luminescent Powers of Terbium (III) with Mixed Ligands
Authors: da Silva Morais Crislene Rodrigues , Lopes Wilton Silva , Souza A.G. de , Santa-Cruz P.D.
Published: March 2009

This work deals with the synthesis and thermal decomposition of complexes of general formula: Ln(ß-dik)3L (where Ln=Tb+3, ß-dik=4,4,4-trifluoro-1-phenyl-1,3- butanedione(btfa) and L=1,10-fenantroline(phen) or 2,2-bipiridine(bipy). The powders were characterized by melting point, FTIR spectroscopy, UV-visible, elemental analysis, scanning differential calorimeter(DSC) and thermogravimetry(TG). The TG/DSC curves were obtained simultaneously in a system DSC-TGA, under nitrogen atmosphere. The experimental conditions were: 0.83 ml.s-1 carrier gas flow, 2.0±0.5 mg samples and 10°C.min-1 heating rate. The CHN elemental analysis of the Tb(btfa)3bipy and Tb(btfa)3phen complexes, are in good agreement with the expected values. The IR spectra evinced that the metal ion is coordinated to the ligands via C=O and C-N groups. The TG/DTG/DSC curves of the complexes show that they decompose before melting. The profiles of the thermal decomposition of the Tb(btfa)3phen and Tb(btfa)3bipy showed six and five decomposition stages, respectively. Our data suggests that the thermal stability of the complexes under investigation followed the order: Tb(btfa)3phen < Tb(btfa)3bipy.
Study of PSZ Sintered in Low Oxygen Partial Pressure
Authors: Reis Danieli A.P. , Almeida D.S. , Nono Maria do Carmo de Andrade , Silva Cosme Roberto Moreira , Neto Francisco Piorino
Published: March 2009

Thermomechanical and electrical properties of zirconia-based ceramics have led to a wide range of advanced and engineering ceramic applications like solid electrolyte in oxygen sensors, fuel cells and furnace elements and its low thermal conductivity has allowed its use for thermal barrier coatings for aerospace engine components. In this work, PSZ (partially stabilized zirconia) was studied to analyze the behavior during sintering in low oxygen partial pressure. Zirconia was partially stabilized with yttria 8 wt%. The sintering temperatures used were 1600, 1700, 1800 and 1900°C. The study of PSZ sintered in low oxygen partial pressure was done using Scanning Electron Microscope, X Ray Diffraction and density analysis. The values of samples density showed that the increasing in sintering temperature was favorable to the material densification. The monoclinic phase converted in tetragonal and cubic phases. The tetragonal phase maintains constant in all sintering temperatures, but the cubic phase increased at 1700 and 1800°C. The lattice parameters werecalculated and showed similar in all sintering temperature.
Synthesis and Characterization of Modified Clays as Sorbents of Toluene and Xylene
Authors: Vianna Marilda M.G. Ramos , Valenzuela-Díaz Francisco Rolando , Kozievitch Valquiria F.J. , Dweck Jo , Büchler Pedro M.
Published: March 2009

Benzene, toluene, ethylbenzene, and the xylenes (BTEX) are the major water-soluble constituents of gasoline that may contaminate soils and natural waters, which can be sorbed by organoclays. This study investigates the sorption of toluene and xylene by organoclays produced from Brazilian bentonite (SVC) and from Wyoming bentonite (SSA) with hexadecyltrimethylammonium (HDTMA), as well as by a commercial organoclay (SCo). The organoclays were characterized by X-Ray Diffraction, Differential Thermal Analysis, Thermogravimetry. Isothermal sorption were performed. The efficiencies of the organoclays on removing toluene increased in the order: SVC-HDTMA < SSA-HDTMA < SCo. The xylene sorption by SVC-HDTMA and SSA-HDTMA organoclays was about two times higher than by the SCo. These organoclays may be used as permeable reactive barriers or in ceramic filters for petroleum waste-water treatment systems.
Influence of Tin Oxide Addition in the Morphologic Characteristics of Zinc Oxide Powders Synthesized by Pechini's Method
Authors: Pereira G.J. , Gouvêa Douglas , Hiraoka S.M.
Published: March 2009

Zinc oxide is widely used in semiconductors fabrication, pigments and mainly in varistors. The electrical properties of ZnO based varistors are related to the grain boundary characteristics, and it can be modified using additives. In this work, zinc oxide based powders were prepared by chemical route derived from the Pechini’s method, and small amounts of tin ions were added to the system. The XRD measurements showed that the tin oxide not forming solid solution in the bulk, and it was observed that the increasing of tin concentration causes an increasing of the surface area at isothermal conditions of calcination. Once the isoelectric point was dislocated to more acid values, the hypothesis of segregation onto surface was considered.
Characterization of Granite Waste for Incorporation in Red Ceramic
Authors: Vieira Carlos Maurício Fontes , Monteiro Sérgio Neves
Published: March 2009

This work had as its objective the characterization of a granite powder waste from sawing operations with a view to its incorporation in red ceramic. The granite waste came from the municipal area of Santo Antônio de Pádua, State of Rio de Janeiro, Brazil. The characterization was performed in terms of chemical composition, particles size distribution, X-ray diffraction and thermal analysis (DTA/TG). The results indicate that the granite waste presents favorable characteristics for incorporation in red ceramic compositions due to its fine granulometry as well as a considerable fluxing potential related to its high amount of alkaline oxides.
Influence of Ti on Static Recrystallization in Near Net Shape Steels
Authors: Arribas M. , López Beatriz , Rodriguez-Ibabe J.M.
Published: March 2009

This study analyzes the recrystallization behaviour of Ti microalloyed low carbon steels processed by near net shape technology. Faster solidification rates associated with this technology allows for a finer precipitation of TiN particles that are very effective in controlling austenite grain growth during hot working. Furthermore, these small precipitates are shown to be able to retard ecrystallization compared to the kinetics of a plain carbon steel.
Recrystallisation Driving and Pinning Forces during Hot Rolling of a Low Nb-Microalloyed Steel
Authors: Gómez Manuel , Medina S.F.
Published: March 2009

The values of recrystallisation driving (FR) and pinning forces (FP) during the hot rolling of a low Nb-microalloyed steel were calculated using several expressions found in the literature. A comparative study of the hypothesis into the interaction between precipitates and migrating grain boundaries was carried out, and the methods for estimating volume fractions of precipitates and dislocation density were assessed. Though the criterion selected greatly influences the values obtained for both forces, FP grows faster than FR as the rolling temperature drops.
Continuous Casting of Microalloyed Steels. Influence of Composition and Operational Parameters in Billet Surface Cracking
Authors: Alvarez de Toledo G. , Arteaga A. , Laraudogoitia J.J.
Published: March 2009

Surface defects, mainly intergranular cracks (IGC), in as cast billet is the main concern for the production of microalloyed steels with the continuous casting process. A description is given of the IGC in the as cast billet surface and the main casting parameters influencing its formation. An analytical model of the influence of the microalloyed content in the formation of precipitates and the corresponding billet surface ductility at the temperature of billet straightening is presented. The model was validated with bibliographical ductility experimental values and was used to perform composition optimisation for continuous casting production. The analytical approach has been completed with a numerical precipitation model coupled with a continuous casting billet solidification model. The coupled program allows precipitate size distribution calculation in selected points of the cross billet section as a function of production parameters, steel composition and billet size. These precipitate distributions are important to detect ductility problems in billets and to optimise the operational parameters so as to avoid these problems.
Evidence of Strain-Induced Precipitation on a Nb- and N-Bearing Austenitic Stainless Steel Biomaterial
Authors: Giordani E.J. , Jorge Alberto Moreira , Balancin O.
Published: March 2009

Pilot-scale plate rolling experiments and laboratory thermomechanical processing experiments were carried out to understand the mechanism of microstructural banding in low-carbon microalloyed steels. The microstructural banding originates with large elongated austenite grains, which are present at the roughing stage of rolling. The large austenite grains develop when conditions favour abnormal grain growth during reheat and/or strain induced grain boundary migration (SIBM) in the first few rolling passes. Microstructural banding is eliminated by designing TMP schedules to avoid abnormal grain growth and SIBM.
Modeling of the Resistance to Hot Deformation and the Effects of Microalloying in High-Al Steels under Industrial Conditions
Authors: Siciliano Fulvio , Poliak Evgueni I.
Published: March 2009

The hot strip rolling of advanced microalloyed high strength steels still represents a new task to many mills due to the lack of data on the hot deformation resistance. With the aid of processing data from the Ispat-Inland hot strip mill, the “measured mean flow stresses” are calculated from the mill force using the Sims analysis and taking into account roll flattening, slip ratio and the redundant strain. A modification of the Misaka mean flow stress equation is proposed for C – Mn – Si – Al steels microalloyed with up to 0.02 % Nb. The effects of alloying and microalloying are then estimated. A new fitting parameter shows excellent agreement with the mean flow stress data from industrial processing of advanced high strength microalloyed steels. However, during the second half of the rolling schedule (lower temperature region), indications of austeniteto- ferrite transformation were found.
The Microstructure Evolution of Nb, Ti Complex Microalloyed Steel during the CSP Process
Authors: Wang Rui Zhen , Garcia C. Isaac , Hua Ming Jian , Zhang Hong Tao , DeArdo Anthony J.
Published: March 2009

The development of microstructure of Nb,Ti-bearing microalloyed steel during the CSP process was studied. Three samples were taken from the as-cast slab prior to tunnel furnace, intermediate bar after stand F2 and the hot band, respectively. In the as-cast slab, the average austenite grain size is 654 µm with a large size range from 150 to 2000 µm. In the intermediate bar after stand F2, the austenite grains are remarkably refined, but are heterogenous due to the incomplete recrystallization, which are in the size range of 23 to 116 µm. In the hot band is mainly non-polygonal ferrite. Microstructural heterogeneity exists in the hot band. It is attributed to the
heterogeneous austenite grain size in the intermediate bar and the less rolling reduction after stand F2. With regards to precipitation, cubic TiN and fine precipitates less than 20nm are commonly observed in the as-cast slab and the intermediate bar. Some complex (Ti,Nb)(C,N) precipitates with a slightly larger size also exist. In the hot band, most particles are complex (Ti,Nb)(C,N) precipitates, in a shape of irregular or cruciform. The fine precipitates which can strengthen the ferrite matrix are seldom seen. These results are in good agreement with the size distribution of the precipitates determined using small angle X-ray scattering method. The chemical phase analysis reveals that 45%Nb of the total and 43%Ti of the total are still in solution in ferrite of the hot band.
Austenite Grain Size of Thin Slab and Its Influence on Direct Hot Strip Rolling of Nb Microalloyed Steel
Authors: Zhang Hong Tao , Pang Ganyun , Wang Rui Zhen , Liu Chengbin
Published: March 2009

In the production with thin slab casting a serious problem of insufficient grain
refinement and microstructural inhomogeneity has been found. In this paper attention has been paid to the austenite grain size changes in thin slab of a high strength Nb microalloyed steel under as-cast conditions and after first rolling pass. For comparison, the conventional thick slab was also investigated. It was found that although as-cast thin slab shows a smaller average austenite grain size than that of as cast thick slab; the latter after reheating shows a much finer average austenite grain size. The first rolling pass at high temperature and with heavy reduction causes rapid recrystallization that contributes to austenite grain refinement.
The Kinetics of the Isothermal Bainite Formation in 1%C-1.5%Cr Steel
Authors: Luzginova N.V. , Zhao L. , Wauthier Aurelie , Sietsma Jilt
Published: March 2009

The kinetics of isothermal bainite formation at 483 K, 503 K and 533 K in a bearing SAE 52100 steel (1,01% C – 1,36% Cr – 0,32% Mn – 0,25% Si (wt.%)) is investigated theoretically and experimentally. It is found that the bainite formation becomes significantly slower with decreasing temperature. To interpret the results, a physical model with a concept of reconstructive approach proposed in the literature is applied. The model gives a reasonable agreement with experimental
results, although a certain deviation exists at the late stage of the transformation. This deviation is attributed to the diffusion coefficient used in the model without considering the effect of alloying elements, mainly chromium.
Mechanical Properties of Low-Temperature Bainite
Authors: García-Mateo Carlos , Caballero Francisca García , Bhadeshia Harshad K.D.H.
Published: March 2009

The mechanical properties of a bainitic microstructure with slender ferrite plates (20-65 nm in thickness) in a matrix of carbon-enriched retained austenite were characterized. The microstructure is generated by isothermal transformation at temperatures in the range 200-300°C. A yield strength as high as 1.5 GPa and an ultimate tensile strength between 1.77 to 2.2 GPa was achieved, depending on the transformation temperature. Furthermore, the high strength is frequently accompanied by ductility (£ 30%) and respectable levels of fracture toughness (< 45 MPa m0.5). This unusual combination of properties is attributed to the exceptionally fine scale of the carbidefree bainitic microstructure and the associated retained austenite.