bluuebunny/crossref_metadata_2025 huggingface dataset:
Elaboration of Yttria-Stabilized Zirconia Films on Porous Substrates
Authors: Falcade Tiago , Tarragó Diego Pereira , Halmenschlager Cibele Melo , de Sousa Vânia Caldas , de Oliveira Claudia Trindade , Malfatti Célia Fraga
Published: October 2010

The development of solid oxide fuel cell has shown that the thin film concept for the electrode supported designs, based on the yttria-stabilized zirconia, is more promising than the research of new electrolyte materials. In this work, the spray pyrolysis process was investigated in order to obtain dense thin films of YSZ on porous ceramic substrates. High porosity LSM, a typical material of SOFC cathodes, was used as substrate. The precursor solution was obtained by zirconium and yttrium salts dissolved in a mixture of ethanol and propylene glycol, with volume ratio 1:1. The substrate was heated and maintained at a constant temperature (280°C, 340°C or 560°C). The as-obtained films were heat treated in a temperature of 700°C, aiming to obtain yttria-stabilized-zirconia films from the amorphous film. The morphology and microstructure of the films were characterized by scanning electron microscopy and X-ray diffraction.
Rheological Study of Yttrium Oxide Aqueous Suspensions
Authors: Santos S.C. , Setz L.F.G. , Yamagata Chieko , de Mello-Castanho Sonia Regina Homem
Published: October 2010

Yttria (Y2O3) has been used in many technological applications areas as luminescence material, high temperature and strength structural material, owing to its excellent optical and refractory characteristics. Applying conformation techniques using Y2O3 concentrated suspensions is adequated, if it is well controlled, so that assisting to obtain homogeneous ceramic bodies, reproductive and with complex geometry. Studies involving superficial behavior, stability conditions of suspensions and the behavior related to conformation give important information to control the processes in manufacturing ceramic components. In this work is presented a rheological study of Y2O3 aqueous suspensions, which concerns to solids and dispersant concentration and pH of media. Preparation of Y2O3 aqueous suspensions with solids concentration of 30vol% was possible, using 1wt% of ammonium polyacrylate (PAA) that was enough to gain the lowest viscosity of the suspensions.
Characterization of Clays Used in the Fabrication of Traditional Brazilian Ceramic Pans: Culture and Technique
Authors: Gadioli Monica Castoldi Borlini , de Aguiar Mariane Costalonga , Vieira Carlos Maurício Fontes , Monteiro Sérgio Neves
Published: October 2010

The fabrication process of clay pans in the state of Espírito Santo, southeast of Brazil, is a recognized part of the country’s popular culture. In Goiabeiras, a district of the state capital Vitória, the traditional production of these pans is the source of income for many families. The technique used in these ceramic pans is of indigenous origin, characterized by manual molding, outdoor burning and application of tannin dye. The clay pans are distributed to several Brazilian states and are nowadays conquering the external market. For producing these pans, two types of, yellow and gray, clays are used. The actual source of raw material comes from the deposit of the Mulembá valley, where a concern on the possibility of exhaustion exists. The objective of this study was then to characterize these two types of clays and so contribute to the continuity of traditional clay pan production by knowing the characteristics of the local clays in case of an eventual need for their replacement. Chemical analysis, X-ray diffraction, particle size distribution, plasticity and thermal analysis of the clays were performed. The results showed that the clays are high plasticity kaolinite with considerable amounts of SiO2 and Al2O3 as well as of alkaline oxides, earth alkaline oxides and Fe2O3.
Development of Ceramic Cutting Tools for Future Application on Dry Machining
Authors: Silva Olivério Moreira Macedo , Souza José Vitor C. , Nono Maria do Carmo de Andrade , Martins G.V. , Ribeiro M.V. , Machado João Paulo Barros
Published: October 2010

Advanced ceramic materials constitute a mature technology with a very broad base of current and potential applications and a growing list of material compositions. Within the advanced ceramics category, silicon nitride based ceramics are wear-resistant, corrosion- resistant and lightweight materials, and are superior to many materials with regard to stability in high-temperature environments. Because of this combination the silicon nitride ceramics have an especially high potential to resolve a wide number of machining problems in the industries. Presently the Si3N4 ceramic cutting tool inserts are developed using additives powders that are pressed and sintered in the form of a cutting tool insert at a temperature of 1850 oC using pressureless sintering. The microstructure of the material was observed and analyzed using XRD, SEM, and the mechanical response of this array microstructure was characterized for hardness Vickers and fracture toughness. The results show that Si3N4/20 wt.% (AlN and Y2O3) gives the best balance between hardness Vickers and fracture toughness. The Si3N4/15 wt.% (AlN and Y2O3) composition allows the production of a very fine-grained microstructure with low decreasing of the fracture toughness and increased hardness Vickers. These ceramic cutting tools present adequate characteristics for future application on dry machining.
Green Stoneware Containing Waste Metals
Authors: da Silva Antônio Carlos , Reinosa J.J. , Moya J.S. , Fernandez J.F. , de Mello-Castanho Sonia Regina Homem
Published: October 2010

Green stoneware tiles have been produced by the incorporation of galvanic waste to industrial compositions processed from kaolinitic clay, feldspar, quartz. Some compositions with recycled domestic glass are also prepared. The galvanic waste required a calcination step to eliminate the gas forming species prior its incorporation into industrial processes. The effective absorption of metal from the galvanic waste was attained through the formation of crystalline phases. The presence of chromite type particles in the porcelain matrix acts as “in situ” to form pigments. The crystallization process also produces a higher consume of metal cations in the surrounded area of the crystalline pigments. The followed procedure allowed to effectively immobilized up to 20 wt% metal waste in a porcelain stoneware that satisfy both the mechanical and the chemical standards required to massively commercialize such a product.
Diffusion Study of Alumina Gray Cast Iron Pair
Authors: Tonello Karolina Pereira Santos , Hernandes Vânia Trombini , Bressiani Ana Helena A. , Bressiani José Carlos
Published: October 2010

Specific properties of structural ceramics such as their mechanical and thermal stability permit their use in high-speed cutting processes that involve deep cuts and low wear rates. The process by which wear occurs in tribological contacts is complex and cannot be explained by one simple wear mechanism. The contribution of different mechanisms to the total wear of a component is related to the mechanical and chemical properties of both the materials and the contact interface. In this investigation, diffusion tests were carried out to determine the influence of chemical interactions between alumina composite and gray cast iron, without the interference of mechanical wear mechanisms. These tests were carried out at 1100°C using static couples. The tests did not generate a strong metal–ceramic interface, indicating that the alumina composites were chemically stable under the test conditions.
Crystalline Structure and Microstructural Characteristics of the Cathode/Electrolyte Solid Oxide Half-Cells
Authors: Chiba Rubens , Vargas Reinaldo Azevedo , Andreoli Marco , Santoro Thais Aranha Barros , Seo Emília Satoshi Miyamaru
Published: October 2010

The solid oxide fuel cell (SOFC) is an electrochemical device generating of electric energy, constituted of cathode, electrolyte and anode; that together they form a unity cell. The study of the solid oxide half-cells consisting of cathode and electrolyte it is very important, in way that is the responsible interface for the reduction reaction of the oxygen. These half-cells are ceramic materials constituted of strontium-doped lanthanum manganite (LSM) for the cathode and yttria-stabilized zirconia (YSZ) for the electrolyte. In this work, two solid oxide half-cells have been manufactured, one constituted of LSM cathode thin film on YSZ electrolyte substrate (LSM - YSZ half-cell), and another constituted of LSM cathode and LSM/YSZ composite cathode thin films on YSZ electrolyte substrate (LSM - LSM/YSZ - YSZ half cell). The cathode/electrolyte solid oxide half-cells were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results have been presented with good adherence between cathode and electrolyte and, LSM and YSZ phases were identified.
Incorporation of Civil Construction Rejects Materials in Structural Ceramic
Authors: Cosin Shirley , Kozievitch Valquiria F.J. , Rito J.E.D , Albanez N.E.K. , Cortés Guillermo R. Martín , Valenzuela-Díaz Francisco Rolando
Published: October 2010

Among the researches applied to the sustainable production of construction materials there are the incorporation of rejects from the civil construction to clayey masses to make bricks, tiles and other products of structural ceramics. Main objective of this paper is to show the results of these mixtures. Spherical samples had been conformed incorporating 1%, 5%, 10%, 20% and 30% of reject from the civil construction in mass. These samples had been evaluated on compressive strength after dried to 110°C and to color and compressive strength after burns to 950°C. The composition that presented better results had been conformed by extrusion in prismatic samples. Then, the dried to 110°C and burnt to 950°C samples had been evaluated on flexion strength and in linear retraction too. Industrial test was made having produced 1500 ceramic blocks that show similar or better properties of blocks without incorporation. It was measured the ceramic and leaching properties of the blocks. The mixture with 5% of rejects in the clayey mass show the better results in all tests.
Mechanical Properties of Nanostructured Zirconia
Authors: Silva C.P. , Santos C. , Silva Cosme Roberto Moreira
Published: October 2010

In this work itria stabilized ZrO2 based ceramics for dental applications has been sintered and characterized in terms of physical and mechanical properties. Nanostructured blocks were sintered at 1400 0C and microstrutured blocks sintered at 1600 0C. Both nanostructured and microstructured materials were characterized in terms of densification, crystalline phases, mechanical properties and microstructure. Fracture toughness and four point bending strength were evaluated and compared. For the nanostructured zirconia, the reduced grain size allowed the increase of its toughening capacity, generated from maximization of volumetric fraction of retained tetragonal zirconia particles. For this material higher bending flexural strength is related to induced nucleation of microcracks, increase of energy absorption during crack propagation and developed compressive surface stress. The fracture toughness obtained at nanostructured samples sintered at 1400 0C is approximately 20% higher when compared to microstrucutured samples. These results represent the toughening ability of nanostructured zirconia, originated from higher amount of retained tetragonal phase and grain boundary microcracks. The higher Weibull moduli in this case are indicative of material reliability improvement and these results are correlated to grain size and its influence at mechanical strength.
Fertilizer Drying in a Concurrent Rotary Dryer
Authors: Silvério Beatriz Cristina , Arruda E.B. , Murata Valéria V. , Façanha J.M.F. , Barrozo Marcos A.S.
Published: October 2010

Drying being one of the most energy-intensive operations is of great importance in the fertilizer industry. Rotary drums are often used for drying in fertilizer industry. This dryer consists basically of a cylindrical shell inclined at a small angle to the horizontal. Wet feed is introduced into the upper end of the dryer and the dried product withdrawn at the lower end. The inside of the shell is equipped with lifting flights. In the present work, the drying of granulated fertilizers (GTSP) using a concurrent rotary dryer was investigated experimentally. The fluid dynamics aspects and its influence on dryer performance were analyzed. The results obtained show that the concurrent dryer residence time and hold-up were lower than the ones of the counter-current dryer. The drying rate of the two dryer’s configurations was very similar, but the counter-current configuration removes a larger quantity of water from the particles of fertilizers.
Evaluation of the Behavior of Brazilian Bentonite Clays with Different Quantity of Quaternary Ammonium Salt
Authors: Barbosa Renata , Souza Dayanne Diniz , Araújo Edcleide Maria , Nóbrega Karine Castro , de Mélo Tomás Jefférson Alves
Published: October 2010

Paraíba is the main natural bentonite producing state of Brazil. Besides the advantage of abundance of bentonite clays, its transformation in organoclay is a simple method and there is only little study about the commercialization of Brazilian organoclays. In this work, Brazilian bentonite clay was organophilized with different quantity of a quaternary ammonium salt, such as 100, 125 and 150 wt.% in relation to Cationic Exchange Capacity (CEC) of the clay. The clays were characterized by X-ray Fluorescence (XRF), X-ray Diffraction (XRD), Thermogravimetry (TG) and Nuclear Magnetic Resonance (NMR). It was observed that with increasing amount of salt the degree of dispersion of the clay increased, leading in some cases to the delamination of the clay layers and its loss of thermal stability.
Evaluation of NiFe2O4 Spinel, Synthesized by Combustion Reaction, as a Catalyst for Selective CO Oxidation
Authors: Santos P.T.A. , Lira Hélio Lucena , Gama Lucianna , Argolo F. , Andrade Heloysa Martins Carvalho , de Melo Costa Ana Cristina Figueiredo
Published: October 2010

The selective reaction of CO oxidation (PROX) was named as the most attractive way to reduce the CO concentration, thereby purifying the hydrogen. The aim of this work is to make the structural and morphologic characterization of the NiFe2O4 spinel synthesized by combustion reaction, using glycine as fuel, and to evaluate as catalyst in the reaction of selective oxidation of carbon monoxide in the presence of hydrogen, oxygen and carbon monoxide. The powder was prepared by using a vitreous silica crucible on a hot plate at 480°C and according to stoichiometry established by theory of propellants and explosive. The powder was characterized by X-ray diffraction (XRD), FTIR, textural analyses, transmission electron microscopy (TEM) and catalytic measurements. The results from XRD show characteristic peaks of spinel phase without presence of secondary phases. The morphologic results show surface area of 3.1 m2/g and particle size calculated by TEM of 21.72 nm. The catalyst was active and selective for O2, reaching 100% of conversion.
Use of Brazilian Clay in Nylon 6 with Different Molecular Weight Nanocomposites
Authors: Araújo Edcleide Maria , da Paz Renê Anísio , de Mélo Tomás Jefférson Alves , Leite Amanda Melissa Damião , Barbosa Renata , Ito Edson Noriyuki
Published: October 2010

The effect of nylon 6 (Ny6) molecular weight on the development of polymer/layered silicates nanocomposites prepared by the melt intercalation technique was studied in this work. The nylon6/organoclay nanocomposites were prepared in the counter-rotational twin screw extruder. The results of torque rheometry showed that the presence of organoclay in the nylon 6 increased the torque. The results of X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed exfoliated and/or partially exfoliated structures.
Membranes from Nylon 6/Regional Bentonite Clay Nanocomposites
Authors: Leite Amanda Melissa Damião , Medeiros Keila Machado , Araújo Edcleide Maria , Maia Larissa Fernandes , Lira Hélio Lucena , da Paz Renê Anísio
Published: October 2010

In this work, it was produced hybrids organic/inorganic membranes of nylon6 and clay mineral constituted of silicate layers, from the interior of the Paraiba. The sodic clay was used in the untreated and treated (with quaternary ammonium salts) form (to become compatible with polymer). Commercial salts Genamin and Cetremide were used to prepare organoclay by cationic exchange reaction in aqueous phase. The nanocomposites were obtained by melt intercalation and from these nanocomposites it was synthesized the membranes for dissolution in predetermined amounts of formic acid and a precipitation in a non-solvent, also called immersion-precipitation technique to prepare thin films. Thus, on the basis of the results, it can be observed that the presence of the treated and untreated clay confer a significant alteration in the structure/morphology of the pores and the porosity of the membrane.
Hydrothermal Synthesis of Nanostructured Titania
Authors: Yoshito Walter Kenji , Ferreira Nildemar A.M. , Rumbao Ana Carolina S. Coutinho , Lazar Dolores Ribeiro Ricci , Ussui Valter
Published: October 2010

Titania ceramics have many applications due to its surface properties and, recently, its nanostructured compounds, prepared by hydrothermal treatments, have been described to improve these properties. In this work, commercial titanium dioxide was treated with 10% sodium hydroxide solution in a pressurized reactor at 150°C for 24 hours under vigorous stirring and then washed following two different procedures. The first one consisted of washing with water and ethanol and the second with water and hydrochloric acid solution (1%). Resulting powders were characterized by X-ray diffraction, N2 gas adsorption and field emission gun scanning and transmission electronic microscopy. Results showed that from an original starting material with mainly rutile phase, both anatase and H2Ti3O7 phase could be identified after the hydrothermal treatment. Surface area of powders presented a notable increase of one order of magnitude and micrographs showed a rearrangement on the microstructure of powders.
Nanocomposite Microcapsules from Powders of Polyhydroxybutyrate (PHB) and Smectite Clays
Authors: da Silva-Valenzuela Maria Graças , Wang Shu Hui , Wiebeck Helio , Valenzuela-Díaz Francisco Rolando
Published: October 2010

Drug delivery systems involving microcapsules provide an attractive way to improve the performance of many chemical and biological substances. These systems may be used for several industrial segments, especially medical, pharmaceuticals and cosmetics. PHB is a polyhydroxyalkanoate available in powder form, biocompatible, biodegradable and inert towards animal tissues. The obtained PHB/smectite clay nanocomposite improved the physical-chemical properties of PHB, including its biodegradability. In this work, we describe the preparation of microcapsules from two nanocomposites systems: a) PHB and Cloisite 20A organoclay (PHB1) and b) PHB and natural Brazilian green policationic clay (PHB2). When analyzed by XRD, the films and microcapsules did not show a d(001) peak, demonstrating an exfoliated structure for the nanocomposites. The films have shown by SEM an homogeneous distribution with the clay mineral particles spread homogeneously by the PHB film. The new microcapsules/nanocomposites showed an “hydrangea” morphology. The diameter of the microcapsules was variable between 0.5-15 µm.
Influence of the Sand Addition on the Processing, Properties and Microstructure of Red Ceramic
Authors: Vieira Carlos Maurício Fontes , Queiroz Luiz Fernando Teixeira , Monteiro Sérgio Neves
Published: October 2010

This work has as its objective to add sand, up to 25 wt.%, to a clayey ceramic body used for roofing tiles fabrication. Specimens were prepared by extrusion and fired at 850oC. The evaluated properties were: plasticity, water absorption and flexural rupture strength. The microstructure of the fired ceramic was evaluated by scanning electron microscopy. The results indicated that the sand improved the evaluated properties of the ceramic as well as its processing. The microstructure of the ceramic presented a minor amount of porosity as a function of the sand addition.
Two-Step Sintering of Samaria-Doped Ceria
Authors: Reis S.L. , Muccillo E.N.S.
Published: October 2010

Samaria-doped ceria is a candidate solid electrolyte for applications in intermediate-temperature solid oxide fuel cells. One of the main concerns related to this solid electrolyte is its low sinterability, even when prepared by chemical methods. In this work, an alternative method of sintering was used aiming obtaining high densification with negligible grain growth in the late stage of sintering. Commercial samaria-doped ceria powder was pressed into pellets and sintered following the two-step sintering process. The first (peak) temperature was varied from 1100 to 1500 °C and the dwell temperature between 1050 and 1400 °C with soaking time of 5 h. The sintered ceramics were characterized by several techniques to correlate the processing-property characteristics. Relatively high densification has been obtained. Electrical conductivity data obtained by impedance spectroscopy could account for the observed improved densification.
Activation Energy for the Sintering of Clay Based Ceramic Powder
Authors: Monteiro Sérgio Neves , Vieira Carlos Maurício Fontes
Published: October 2010

Clay based ceramic is one of the most used materials in the form of construction blocks, bricks and tiles. Sintering of clay powders is recommended to be carried out above 900°C to benefit from fluxing phase consolidation. However, solid state consolidation of clay bodies made with mixture of powders may occur bellow this temperature by surface diffusion within the nanopores of the layered silicate particles. The objective of this work was to characterize the activation energy for the sintering of plastic clay at temperatures bellow 900°C. Cylindrical samples of sintered kaolinitic clay powders were tested by diametrical compression at 500, 600, 700 and 800°C in the time interval from 5 minutes to 50 hours. The results showed that the value found for the activation energy could be related to the diffusion of the mineral species that compose the clay. Moreover, this activation value corroborates the efficiency of lower sintering temperature for practical fabrication of clay based ceramics.
Two-Steps Sintering of Alumina-Zirconia Ceramics
Authors: Manosso Milena K. , Pallone Elíria Maria Jesus Agnolon , Chinelatto Adilson Luiz , Chinelatto Adriana Scoton Antonio
Published: October 2010

Sintering in two-steps has been applied with success for densification of nanometric ceramic powders without grain growth. Another mechanism that alters the sintering process is the presence of rigid inclusions in the ceramic. In this work it was studied the effect of two-steps sintering and the presence of zirconia inclusions (5% in volume) in the microstructure of a commercial alumina. For this, the powders of alumina and zirconia were desaglomerated in a ball milling and uniaxially pressed at 80 MPa to form cylindrical compacts and isostatically cold pressed at 200 MPa. Temperatures of the steps were chosen starting from the curves of linear rate shrinkage in function of the temperature. The samples were characterized for apparent density, scanning electronic microscopic and mean grain size. The results showed that two-steps sintering and the zirconia inclusions were efficient to control the densification and grain size of alumina.
Efficiency Evaluation of ZrB2 Incorporation in the MgB2 Matrix Phase Using High-Energy Milling
Authors: Santos Felipe Antunes , Ramos Alfeu Saraiva , dos Santos Claudinei , Suzuki Paulo Atsushi , Rodrigues Júnior Durval
Published: October 2010

The present study suggests the use of high energy ball milling to mix (to dope) the phase MgB2 with the AlB2 crystalline structure compound, ZrB2, with the same C32 hexagonal structure than MgB2, in different concentrations, enabling the maintenance of the crystalline phase structures practically unaffected and the efficient mixture with the dopant. The high energy ball milling was performed with different ball-to-powder ratios. The analysis of the transformation and formation of phases was accomplished by X-ray diffractometry (XRD), using the Rietveld method, and scanning electron microscopy. As the high energy ball milling reduced the crystallinity of the milled compounds, also reducing the size of the particles, the XRD analysis were influenced, and they could be used as comparative and control method of the milling. Aiming the recovery of crystallinity, homogenization and final phase formation, heat treatments were performed, enabling that crystalline phases, changed during milling, could be obtained again in the final product.
Influence of the Sintering Conditions on the Mechanical Properties of Nanosized TZP Ceramics
Authors: Bondioli Marcelo José , Daguano Juliana K.M.Faria , Palmeira A.A. , dos Santos Claudinei , Strecker Kurt
Published: October 2010

Zirconia is a bioceramic material widely used for dental implants. In this work, the sinterability of nano-crystalline powders has been investigated by dilatometry in the temperature range of 1250 to 1400 0C with isothermal holding times of up to 8h. A slight increase in grain growth and an increasing linear shrinkage have been observed with increasing sintering temperatures. The sintered samples were submitted to Vickers' hardness and KIC tests and the results compared regarding the sintering conditions. It has been verified that satisfactory hardness and fractures toughness have been achieved after sintering above 1300 0C during 8h.
Influence of Heat Treatment on the Anelastic Properties of MgB2
Authors: da Silva Marcos Ribeiro , Grandini Carlos Roberto
Published: October 2010

The discovery of the superconductivity of MgB2 was of great importance, because this material is one of the few known binary compounds and has one of the highest critical temperatures (39° K). As MgB2 is a granular compound, it is fundamentally important to understand the mechanisms of the interaction of the defects and the crystalline lattice, in addition to the eventual processes involving the grain boundaries that compose the material. In this sense, the mechanical spectroscopy measurements constitute a powerful tool for this study, because through them we can obtain important information about phase transitions, the behavior of interstitial or substitutional elements, dislocations, grain boundaries, diffusion, instabilities, and other imperfections of the lattice. For this paper, the samples were prepared using the PIT method and were characterized by density, X-ray diffraction, scanning electron microscopy, electric resistivity, magnetization, and mechanical spectroscopy. The samples were measured in their as-cast condition and after an ultra-high-vacuum heat treatment. The results showed complex spectra, in which were identified relaxation processes due to dislocation movement, interaction among interstitial elements and dislocations, auto-diffusion, and movement of grain boundaries. Some of these processes disappeared with the heat treatment.
Effect of the Pressure and Temperature Cycling in the Sintering of Cubic Boron Nitride Composites under HPHT Conditions
Authors: Bobrovinitchii Guerold Sergueevitch , Skury Ana Lúcia Diegues , Monteiro Sérgio Neves
Published: October 2010

Owing to non-stable conditions generated during conventional HPHT sintering of cubic boron nitride (cBN) composites, it is not possible to predict both the yield and quality of the final product. Moreover, in the existing conventional technique, the particle size and amount of binding compounds that are associated with the composite may be responsible for defects and residual stress. In the present work, a novel technique of automatic cycling the pressure and the temperature was applied to the sintering of cBN composites bound with Ti2N and AI. This type of processing permitted to obtain a more uniform structure for the composites with ultra-fine layers of the binding compounds separating dispersed cBN grains. The technique improved the adhesion between the phases and contributed to decrease both the residual stresses and interfacial defects. As a consequence, the productivity related to machining of hard steels using inserts made of cycling HPHT processed cBN composites was increased by 170-180%.
A Method for an Improvement in the Quality of Diamond Composite Thermostable Material
Authors: Skury Ana Lúcia Diegues , Monteiro Sérgio Neves , Bobrovinitchii Guerold Sergueevitch , de Azevedo Marcia G.
Published: October 2010

It is still in focus the problem of obtaining high quality polycrystalline materials by means of sintering fine diamond powders. The most important task of this problem is the consolidation or improvement of the processed polycrystalline diamond. It is worldwide recognized that the plastic deformation of the diamond particles performs the most important role on the diamond powder consolidation. In some cases, the contact and shear tensions reconstruct the compact structure. In this work the sintering process used a mixture of micro and nanodiamonds. The sintering process was carried out in a toroidal high-pressure device. The effects of nanodiamond addition and sintering conditions on the microstructure and mechanical properties sintered diamond bodies were studied. The sintering parameters were pressure of 6.8 GPa and a temperature of 1850 K, and these conditions were maintained for 1 minute. Homogeneous sintered bodies were obtained, which have a Vickers' hardness over 40 GPa, and fracture toughness around 7.1 – 7.9 MPa.m1/2.
Effect of Nanodiamond Addition on the Mechanical Properties of Polycrystalline Metallic and Polymeric Composites
Authors: Bobrovinitchii Guerold Sergueevitch , Skury Ana Lúcia Diegues , Monteiro Sérgio Neves , Tardim Rômulo Crespo
Published: October 2010

One way to develop a new composite material or to improve its performance is to reinforce the matrix with a stronger dispersive phase. In principal, nanodiamonds can be used as reinforcement of composites owing to high surface energy, which allows an effective structure interaction with most utilized matrices. In this work, polycrystalline metallic–based composites and polymeric-based composites were investigated for the effect caused by addition of nanodiamonds. These composites were obtained at high compression pressures and combine with temperatures for certain short processing times. It was found that even small additions of nanodiamonds increase the wear resistance of the investigated composites.
Electrosintering Production of Novel Grade Diamond Composites
Authors: Bobrovinitchii Guerold Sergueevitch , Monteiro Sérgio Neves , Tardim Rômulo Crespo
Published: October 2010

This paper presents the results on the strength evaluation of sintered diamond-based composites with Co binder. The method of intensive electrosintering with a short heating pulse was applied by a high pressure of 0.5 GPa and a time of 2-40 s. Composites with different compositions and for different purposes, such as rock drilling and dressing tools, were investigated. The reactive cell was design with the purpose of preserving the diamond properties from the detrimental sintering temperature exposure. The results of this electrosintering technology permitted to obtain improved composites to be used in tools with higher indexes of performance and productivity.
Use of Eucalyptus Firewood Ash into Clayey Ceramic
Authors: Vieira Carlos Maurício Fontes , Gadioli Monica Castoldi Borlini , Monteiro Sérgio Neves
Published: October 2010

This work aims at evaluating the incorporation of eucalyptus firewood ash into clayey ceramic, through the physical and mechanical properties of the produced ceramics. Mixtures of kaolinitic clay from the municipal area of Campos of Goytacazes, in the state of Rio de Janeiro, Brazil, were prepared with additions of 0, 5, 10 and 20% in weight of ashes from eucalyptus firewood. Specimens were 20 MPa uniaxially press-molded and fired at 900°C. The evaluated firing properties were diametrical shrinkage, water absorption and mechanical strength by diametrical compression. The results showed that the incorporation of 10% wt. of firewood ash enhanced the properties of the clayey ceramic and since plasticity was optimised, water absorption decreased while the mechanical strength increased.
Porcelain: Convencional and Microwave Sintering
Authors: Gelfuso Maria Virginia , Chinelatto Adriana Scoton Antonio , Thomazini Daniel , Wendler Leonardo Pacheco , Costa Danilo Capistrano , Chinelatto Adilson Luiz
Published: October 2010

The porcelains are ceramics whose properties are strongly influenced by the microstructure developed after sintering. This microstructure can be changed, either by changing the composition as in the sintering conditions. New sintering methods, have allowed a greater control of the ceramics properties as a consequence of the final microstructure greater control. Microwave sintering is one of these techniques that have aroused a high interest in ceramics process because this method led to higher densification and the fine microstructure in much shorter time duration compared to conventional procedures. In this work it was studied the porcelain ceramics sintered under microwave and traditional heating conditions. Porcelains disks were prepared under a uniaxial pressure. One set of samples was sintered at in a conventional muffle furnace at range of 1250°C and 1300°C for 2 h. Another set of disks was sintered using a custom-made 2.45 GHz furnace at 1200°C temperature between 15 and 45 minutes. Density and microstructure information were obtained on microwave and convention processed samples by Archimedes principle and SEM (scanning electron microscope, JSM-5510 LV), respectively. Microwave sintering of porcelains promoted densification in much shorter time duration when compared to conventional method. The microstructure was strongly influenced by microwave heating, promoting an abnormal grain growth of the primary mullite.
Application of the Atomic Absorption Technical to Available the Concentration of Silver Ions Incorporated in Glass Matrix by Ionic Exchange Process
Authors: Mendes Elton , Silva K.F. , Teixeira A. , Silva Luciano , Paula M.M.S. , Angioletto Elídio , Riella Humberto Gracher , Fiori M.A.
Published: October 2010

Ion specimens can be incorporated in glasses or natural clays by ionic exchange process with different concentrations dependent of matrix´s type and of the ionic exchange parameters. In particular, the incorporation of silver ions presents high interest by its biocidal properties. A compound contending ion silver specimens presents bactericidal and fungicidal properties with effect proportional to ion concentration. This work presents results about application of the atomic absorption technical to determine the silver ion concentration incorporated in a glass matrix by ionic exchange process. The ionic exchange experiments were realized with different AgNO3 concentration and constant temperature. After ionic exchange process, the glass samples were submitted to characterization by Energy Dispersive X-Ray Spectroscopy and Atomic Absorption Techniques. The comparative results between different techniques showed that atomic absorption technical is adequate to determine ion silver concentration incorporated in the glass matrix after ionic exchange process.
Effect of pH and Fluoride on Behavior of Dental ZrO2 Ceramics in Artificial Saliva
Authors: Mukaeda L.E. , Robin A. , dos Santos Claudinei , Taguchi Simone P. , Machado João Paulo Barros , Borges L.A.
Published: October 2010

A considerable increase in the ceramic products demand occurred due to the evolution of dental restoration techniques and these materials must resist to the complex mouth environment. The pH of saliva can decrease significantly due to the ingestion of acidic foods and beverages and mainly due to reactions occurring during bacteria metabolism that lead to the formation of organic acids. Fluorides are also present in the mouth since fluorides are usually added in drinking water, mouth washes, tooth pastes and gels for the prevention of plaque and caries formation. The combination of low pH and presence of fluorides can lead to the formation of HF and HF2- which are detrimental to metallic and probably to ceramic devices. In this work, commercial blocks of ZrO2 ceramics (ProtMat Materiais Avançados® and Ivoclar®) were immersed in Fusayama artificial saliva of different pHs and fluoride concentrations. The properties of the as-produced ceramics (crystalline phases (XRD), microstructure (SEM), roughness (3D surface topography AFM) and mechanical resistance – Vickers hardness (Hv) and fracture toughness (KIC) were evaluated. Some of these properties were also determined after the immersion tests as well as the mass variation of the samples in order to evaluate the resistance of these ZrO2 ceramics to degradation under these conditions.
The Role of Particle Shape on the Sintering of Clay Based Ceramics
Authors: Monteiro Sérgio Neves , Vieira Carlos Maurício Fontes
Published: October 2010

The influence of the clay particle morphology on the structural consolidation process associated with high temperature sintering was studied. By computer modeling, the different degrees of packing related to the distinct shapes naturally assumed by the particle clays as well as the consolidation conditions, based on solid sate reactions and surface diffusion were simulated. The model was compared with experimental data of clays fired at several temperatures. This permitted to explain differences in the behavior of red ceramics that was sintered with clays presenting distinct particle shapes.
Unidirectional Infiltration Method to Produce Crown for Dental Prosthesis Application
Authors: Pontes F.H.D. , Taguchi Simone P. , Borges L.A. , Machado João Paulo Barros , Santos C.
Published: October 2010

Alumina ceramics have been used in dental prosthesis because it is inert, presents higher corrosion and shear resistance when compared to metals, excellent aesthetic, and mechanical resistance. In this work it was produced an infrastructure material for applications in dental crowns, obtained by glass infiltration in alumina preforms. Various oxides, among that, rare-earth oxide produced by Xenotime, were melted at 1450°C and heat treatment at 700°C to obtain the glass (RE-glass). The alumina was pre-sintered at 1100°C cut and machined to predetermine format (unidirectional indirect infiltration) and finally conducted to infiltration test. The alumina was characterized by porosity (Hg-porosity and density) and microstructure (SEM). The glass wettability in alumina was determined as function of temperature, and the contact angle presented a low value (<90º), showing that glass can be infiltrated spontaneously in alumina. The infiltration test was conducted at glass melting temperature, during 30, 60, 180, 360 minutes. After infiltration, the samples were cut in longitudinal section, ground and polished, and analyzed by XRD (crystalline phases), SEM (microstructure) and EDS (composition).The REglass presents higher infiltration height when compared to current processes (direct infiltration), and homogeneous microstructure, showing that it is a promising method used by prosthetics and dentists.
Use of Microwave Energy for Obtaining the Mullite
Authors: Brasileiro Maria Isabel , de Lima Santana Lisiane Navarro , Neves Gelmires Araújo , Menezes Romualdo Rodrigues , Lira Hélio Lucena , Gonçalves Wherllyson Patrício
Published: October 2010

The kaolin beneficiation industries produce waste that is rich in Al2O3 and SiO2, oxides that when sintered at high temperatures react to form mullite. Due to the rare occurrence of the mullite mineral in nature, the number of studies in order to obtain it has been growing in recent years due to its properties excellent. This study aims to examine the feasibility of the use of microwave energy as an alternative to synthesize mullite from kaolin residue, since the use of microwave energy in the synthesis of materials has gained importance for the speed and economy when compared to conventional methods. The compositions studied (residual kaolin + alumina) were established according to the stoichiometry of mullite. The samples were sintered in a microwave oven home changed, varying power and time. It was observed that with the increase of these variables the intensity of the peaks of the mullite phase increased.
Evaluation of the Cu Doping Effects in CeO2 Catalytic Supports Obtained by Combustion Reaction
Authors: Neiva Laédna Souto , Leal Elvia , de Melo Costa Ana Cristina Figueiredo , Mascarenhas Artur Jose S. , Andrade Heloysa Martins Carvalho , Gama Lucianna
Published: October 2010

This work has for aim to synthesize CeO2 catalytic supports doped with Cu2+ by combustion reaction method. Thus were obtained catalytic supports with the composition Ce1-xCuxO2 and the effect caused by doped element in the structure of the CeO2 was evaluated. The concentration value (x) of the Cu doped took over the values of 0.0; 0.3 and 0.5 mol. The catalytic supports developed were submitted to the structural characterization by X-ray diffraction, morphologic analysis by SEM and textural analysis by means of adsorption-dessorption of N2 by BET method. The results showed that the doped element (Cu) was not completely incorporated in the CeO2 structure and was evidenced that how much larger the quantity of Cu larger maid the disorder of the atomic structure of the obtained material. The analyzed supports present mesoporous nature structure.
Morphologic and Structural Characterization of the CoFe2O4 Synthesized by Combustion Reaction
Authors: Lima M.S. , Sousa Jean Pierre La Martini Lima , Vieira Débora A. , Lira Hélio Lucena , Sasaki J.M. , de Melo Costa Ana Cristina Figueiredo
Published: October 2010

CoFe2O4 powders were synthesized by combustion reaction using glycine as fuel, aiming obtaining nanosized and monophase powders. Thus, different conditions of external heating during the synthesis were investigated. The powders were prepared according to the propellants and explosives theory, using glycine as fuel in the stoichiometric proportion (Φe = 1). During the synthesis the flame temperature and time were measured. The resulting powders were characterized by X-rays diffraction and scanning electronic microscopy (SEM). The results show that the condition in which the synthesis was done it influences in the combustion flame temperature and time and contributes for the obtainment of powders with majority phase without secondary phases. Crystallite size varied of 33 to 50 nm. All powders presented morphology constituted by soft agglomerated formed by nanoparticles.
Ni-Zn Nanoferrites Synthesized by Microwave Energy: Influence of Exposure Time and Power
Authors: Vieira Débora A. , Diniz Verônica C.S. , Lira Hélio Lucena , Kiminami Ruth Herta Goldsmith Aliaga , Cornejo Daniel , de Melo Costa Ana Cristina Figueiredo
Published: October 2010

This paper describes the synthesis of Ni-Zn nanoferrites by combustion reaction using microwave energy as a heating source, and evaluates the performance of these materials as absorbers of electromagnetic energy at frequencies between 4 - 12 GHz. The influence of the synthesis conditions on the structure, morphology and absorption characteristics was investigated. The powders were characterized by DRX, BET, AGM and reflectivity measurements in the frequency bands of 8 to 12 GHz. The XRD results show the formation of Ni-Zn ferrite phase and Fe2O3 and Ni as secondary phases. The crystallite sizes ranged from 32 to 42 nm. The parameters of exposure time and power of the microwave oven changed the final characteristics of the resulting powders. The morphology of all the powders consisted of soft nanoparticle agglomerates. The best saturation magnetization and attenuation results were 70 emu/g and -4.1 dB in the frequency of 10 GHZ.
Evaluation of Glycine Excess over NiAl2O4 Catalysts Prepared by Combustion Reaction for Steam Methane Reforming
Authors: Leal Elvia , Neiva Laédna Souto , Sousa Jean Pierre La Martini Lima , Argolo Fábio , Andrade Heloysa Martins Carvalho , de Melo Costa Ana Cristina Figueiredo , Gama Lucianna
Published: October 2010

The aim of this work is to evaluate the catalytic activity of NiAl2O4 powders, prepared by combustion reaction with different glycine contents, for the steam reforming of methane. The NiAl2O4 powders were prepared according to the theory of propellants and explosives, using glycine reductant in stoichiometric ratio (Φe = 1) and in excess of 10% and 20% (Φe < 1). During the synthesis, parameters such as flame combustion temperature and time were measured. The samples were characterized by XRD, textural analysis by nitrogen adsorption (BET/BJH), TPR and evaluated as catalysts for the steam reforming of methane. The XRD results showed the presence of NiAl2O4 as major phase and traces of NiO and Ni in all the samples. The glycine content increase caused a decrease of crystallite size and an increase of surface area, from 29 to 39 m2/g. The TPR profiles showed reduction peaks of NiO species in weak interaction with the support, and reduction of nickel present in the NiAl2O4. It was observed that higher methane conversions were obtained in the presence of NiAl2O4 samples prepared using glycine excess. However, it was also observed a rapid deactivation of these catalysts due to high coke deposition onto the active surface phases.
Development of Polyamide 6/Ferrite Composites for Absorbers of Electromagnetic Radiation
Authors: Bezerra Daniella Cibele , de Gouveia Silva Taciana Regina , Araújo Edcleide Maria , da Paz Renê Anísio , de Melo Costa Ana Cristina Figueiredo
Published: October 2010

Composites consist of a mixture or combination of the two or more, micro or macro constituents that differ in shape and chemical composition and, in essence, are insoluble in one another. The polyamide is a polymer that presents dimensional stability, good resistance to impact without notch and excellent chemical resistance. Already the ferrites are absorbers of electromagnetic radiation and have versatility to be used as a composite of ferrites. The composite of polyamide6/ferrite was obtained by mixing 10 and 30wt.% of ferrite added to polyamide 6 in a Torque Rheometer Haake. The objective of this work was to develop of polyamide6/ferrite composites to be used as absorbers of electromagnetic radiation. The results were very promising and showed that occurs interaction between the ferrite and polyamide6.