Efeito da Gália como aditivo de sinterização em eletrólitos cerâmicos à base de céria sintetizados pelo método de complexação de cátions

Fuel cells are considered one of the most promising ways of converting electrical energy due to its high yield and by using hydrogen (as fuel) which is considered one of the most important source of clean energy for the future. Rare earths doped ceria has been widely investigated as an alternative material for the electrolyte of solid oxide fuel cells (SOFCs) due to its high ionic conductivity at low operating temperatures compared with the traditional electrolytes based on stabilized zirconia. This work investigates the effect of gallium oxide (Gallia) as a sintering aid in Eu doped ceria ceramic electrolytes since this effect has already been investigated for Gd, Sm and Y doped ceria electrolytes. The desired goal with the use of a sintering aid is to reduce the sintering temperature aiming to produce dense ceramics. In this study we investigated the effects on densification, microstructure and ionic conduction caused by different molar fraction of the dopants europium (10, 15 and 20%) and gallium oxide (0.3, 0.6 and 0.9%) in samples sintered at 1300, 1350 and 1450 0 C. Samaria (10 and 20%) doped ceria samples sintered between 1350 and 1450 °C were used as reference. Samples were synthesized using the cation complexation method. The ceramics powders were characterized by XRF, XRD and SEM, while the sintered samples were investigated by its relative density, SEM and impedance spectroscopy. It was showed that gallia contents up to 0.6% act as excellent sintering aids in Eu doped ceria. Above this aid content, gallia addition does not promote significant increase in density of the ceramics. In Ga free samples the larger densification were accomplished with Eu 15% molar, effect expressed in the microstructure with higher grain growth although reduced and surrounded by many open pores. Relative densities greater than 95 % were obtained by sintering between 1300 and 1350 °C against the usual range 1500 - 1600 0 C. Samples containing 10% of Sm and 0.9% of Ga reached 96% of theoretical density by sintering at 1350 0 C for 3h, a gain compared to 97% achieved with 20% of Sm and 1% of Ga co-doped cerias sintered at 1450 0 C for 24 h as described in the literature. It is found that the addition of gallia in the Eu doped ceria has a positive effect on the grain conductivity and a negative one in the grain boundary conductivity resulting in a small decrease in the total conductivity which will not compromise its application as sintering aids in ceria based electrolytes. Typical total conductivity values at 600 and 700 °C, around 10 and 30 mS.cm -1 respectively were reached in this study. Samples with 15% of Eu and 0.9 % of Ga sintered at 1300 and 1350 °C showed relative densities greater than 96% and total conductivity (measured at 700 °C) between 20 and 33 mS.cm -1 . The simultaneous sintering of the electrolyte with the anode is one of the goals of research in materials for SOFCs. The results obtained in this study suggest that dense Eu and Ga co-doped ceria electrolytes with good ionic conductivity can be sintered simultaneously with the anode at temperatures below 1350 °C, the usual temperature for firing porous anode materials

Avaliação da incorporação combinada dos resíduos de cascalho de perfuração de poço de petróleo e de polimento do porcelanato em cerâmica vermelha

Among the industries, those that produce ceramic porcelain for use in construction industry and oil, during the exploration and production period, play an important role in the production of waste. Much research has been carried out both by academia and the productive sector, sometimes reintroducing them in the same production line that generated them, sometimes in areas unrelated to their generation, as in the production of concrete and mortar for the construction, for example, but each one in an isolated way. In this research, the aim is to study the combined incorporation of the waste drill cuttings of oil well and the residue of the polishing of porcelain, generated in the final stage of finishing of this product in a clay matrix, for the production of red pottery, specifically bricks, ceramic blocks and tiles. The clay comes from the municipality of São Gonçalo, RN, the drilling waste is from the Natal basin, in Rio Grande do Norte, and the residue of the polishing proceeds from a ceramic porcelain of the State of Paraíba. For this purpose, we used a mixture of a plastic clay with a non-plastic, in a ratio of 50% each, settling formulations with the addition of these two residues in this clay matrix. In the formulations, both residues were incorporated with a minimum percentage of 2.5% and maximum of 12.5%, varying from 2.5% each, in each formulation, which the sum of the waste be no more than 15%. It should be noted that the residue of the polishing of ceramic porcelain is a IIa class (not inert). The materials were characterized by XRF, XRD, TG, DTA, laser granulometry and the plasticity index. The technological properties of water absorption, apparent porosity, linear shrinkage of burning, flexural tensile strength and bulk density were evaluated after the sintering of the pieces to 850 °C, 950 °C and 1050 °C, with a burning time of 3 hr, 3 hr and 30 minutes, and 3 hr and 50 minutes, respectively, with a heating rate of 10 °C/minute, for all formulations and landing of 30 minutes. To better understand the influence of each residue and temperature on the evaluated properties, we used the factorial planning and its surfaces of response for the interpretation of the results. It was found that the temperature has no statistical significance at a 95% of reliability level in flexural tensile strength and that it decreases the water absorption and the porosity, but increases the shrinkage and the bulk density. The results showed the feasibility of the desired incorporation, but adjusting the temperature to each product and formulation, and that the temperatures of 850 °C and 950 °C were the one that responded to the largest number of formulations

Sinterização de matrizes cerâmicas à base de alumina reforçadas por carbetos a partir de precursores poliméricos

Ceramic composites produced with polymerics precursors have been studied for many years, due to the facility of obtaining a complex shape, at low temperature and reduces cost. The main objective of this work is to study the process of sintering of composites of ceramic base consisting of Al2O3 and silicates, reinforced for NbC, through the technique of processing AFCOP, as well as the influence of the addition of LZSA, ICZ and Al as materials infiltration in the physical and mechanical properties of the ceramic composite. Were produced ceramic matrix composites based SiCxOy e Al2O3 reinforced with NbC, by hidrosilylation reaction between D4Vi and D1107 mixtured with Al2O3 as inert filler, Nb and Al as reactive filler. The specimens produced were pyrolised at 1200, 1250 and 1400°C and infiltred with Al, ICZ and LZSA, respectively. Density, porosity, flexural mechanical strength and fracture surface by scanning electron microscopy were evaluated. The microstructure of the composites was investigated by X-ray diffraction to identify the presence of crystalline phases. The composites presented apparent porosity varying of 31 up to 49% and mechanical flexural strength of 14 up to 34 MPa. The infiltration process improviment of the densification and reduction of the porosity, as well as increased the values of mechanical flexural strength. The obtained phases had been identified as being Al3Nb, NbSi2, Nb5S3, Nb3Si and NbC. The samples that were submitted the infiltration process presented a layer next surface with reduced pores number in relation to the total volume

Ajuste estrutural e educação superior no Brasil: princípios negados

SILVA, Hiran Francisco Oliveira Lopes da. A juste estruturale educação superior no Brasil: princípios negados. 206 f., 2007. Tese (Doutorado em Educação) - Universidade Federal da Paraiba, João Pessoa, 2007.

Atuação do estado como empregador de última instância: uma proposta para eliminar o desemprego estrutural do Brasil

GOMES, Z. B. ; LOURENÇO, André Luís Cabral de . Atuação do estado como empregador de última instância: uma proposta para eliminar o desemprego estrutural do Brasil. In: Encontro Nacional de Economia Política,13., 2008, João Pessoa/PB. Anais... João Pessoa, 2008.

Desempenho internacional de empresas exportadoras: um modelo estrutural baseado em capacidades organizacionais e ambiente

The internationalization as an organizational phenomenon fundamentally strategic had as theoretical contributions some Schools that throughout the decades 60, 70, and 80 developed behavioral and economic approaches in order to explain the process. The behavioral approach deals with the perception of phenomenon as a gradual process from the perspective of the executives behavior (JOHANSON and VAHLNE, 1977; HALLÉN and WIEDERSHEIM - PAUL, 1979; CZINKOTA, 1985). This phenomenon in permanent theoretical and managerial evolution made an opportunity to build this investigation, whose goal is to analyse the impact comes from organizational capabilities and the external environment on the international performance of exporting firms. For both, were used as theoretical basis two types of analysis for the comprehension of international performance: Strategic Management - Industrial Organization and Resource-Based View and International Businesses - Current Economic and Behavioral. It was made a cross-sectional survey-based explanatory research, including 150 exporting companies with operations in the Northeast of Brazil. A conceptual model was made with eight constructs and eight research hypotheses, representative of the effects of external factors on international performance. The data were processed using the Exploratory Factor Analysis and Structural Equation Modeling. The structural equations model was reespecified and estimated through the use of the maximum-likelihood method up to achieve adequated values of indexes of adjustment. As the main theoretical contribution, were identified organizational and physical resources which shows the importance of the management skills development, of the learning capability and capability to establish strategic alliances abroad. That because the knowledge, as the operational point of view as in its strategic application, offers to organization conditions of market positioning which can create opportunities sustainable competitive advantages and which impact the performance of international companies

Cerâmica de Santo Antônio do Potengi: entre tradição e modernidade

In the Rio Grande do Norte, the craftsmanship is generating of economy, it involves a significant number of people and is diversified in its raw materials and particular type. As reference of the craft local, the ceramics supplied the primary necessities in the utilitarian domestic servants, acquired piety in the religious figures, were toy in infantile amusements and, finally, gained status of pure ornament. By its historical representation, the district of Santo Antônio do Potengi is considered the most important center of manufacture of craftpottery in the State. The work of the potters continues in that locality anchored between the familiar inheritance and the participation each more influential time of the public politics destined to the sector situation verified for visible alterations in the shape of the pottery from the decade of 1990 with the implantation of a cooperative destined to the collective production. We observe in this passage, that such actions in the measure where they objectify to structuralize conditions ideal to support the artisan making, do not benefit in significant way the social development them craftsmen. It is important not to lose of sight that exists some involved dimensions in this process and that these surpass the common interest for the object and the consequent economic connotation of its commercialization. They are knowledge that imply in the access to raw materials, in the peculiar of the formal aspects and productive methods, in the contextual relations organized to defend the survival of the activity

A concepção estrutural como expressão plástica: um olhar tectônico sobre arquitetura em madeira

This work regards to the structural conception as a formal element of design in wood architecture. On this approach, the group of projects studied is formed by some realized works of two important Brazilian architects: Severiano Porto and Marcos Acayaba. The time interval comprises the period from 1971 to 1997, which correspond respectively to the years of the creation of first and the last of the analyzed constructions. The research perspective concerns to the relationship between the parts, the whole and the building techniques adopted in each project. Moreover, the analysis focuses on the structure as the link among the different projectual ideas. Thus, the research method firstly includes a survey of specific bibliographies and documents which refer to the structural conception in wood architecture. Secondly,the buildings are analyzed according to the methods of architectural composition discussed through this work.

Desempenho térmico de coberturas: Um estudo comparativo entre as telhas de material reciclado, de fibra e betume, fibrocimento e cerâmica

This study aims to compare the thermal performance of tiles made from recycled material (waste packaging cardboard with aluminized film) with the tiles of fiber and bitumen, fiber cement and red ceramic with the aim of verifying the suitability of tile to be used in hot and humid climate of low latitude. The samples were selected according to the availability from Natal - RN market, as they are sold to the consumers. The methodology was based on studies that used experimental apparatus composed of thermal chambers heated by banks of incandescent bulbs, to analyze the thermal performance of materials. The tiles in the study were submitted to analysis of thermal performance, thermophysical properties and absorptance, using chambers of thermal performance, measuring the thermophysical properties and portable spectrometer, respectively. Comparative analysis of thermal performance between two samples of the recycled material with dimple sizes and different amounts of aluminum were made, in order to verify, if these characteristics had some interference on the thermal performance of them; the results showed no significant performance differences between the samples. The data obtained in chambers of thermal performance and confirmed by statistical analysis, showed, that the tile of recycled material have similar thermal performance to the tile of fiber cement. In addition to these tests was carried out the automatic monitoring of a building covered with tiles of recycled material, to verify its thermal performance in a real situation. The results showed that recycled shingles must be used with technical criteria similar to those used for fiber cement tiles, with regard to the heat gain into the building. Within these criteria should be taken into account local characteristics, especially in regions with hot and humid climate, and its use must be associated, according to the literature, to elements of thermal insulation and use of passive techniques such as vented attics, ceilings and right foot higher

A contribuição de técnicas modernas de reabilitação estrutural para autenticidade e integridade de edificações patrimoniais

This work discusses the study of the application of structural reinforcement and rehabilitation using modern techniques for interventions in repair works of historical buildings as well as the verification of the behavior of works that have already undergone different structural intervention techniques, with the objective of obtaining data to allow a comparative analysis of the advantages/disadvantages of techniques adapted in each case, regarding the interferences related the authenticity and integrity of the buildings belong to the constructed patrimony so as to obtain a basis for the theoretical foundation for choosing the best solution to be adopted in the case study which consists in an intervention of structural rehabilitation of the old historic building in the primary school "Augusto Severo"

Caracterização estrutural e avaliação das atividades farmacológicas da fucana B extraída da alga Dictyota menstrualis

Seaweeds are a major source of biologically active compounds . In the extracellular matrix of these organisms are sulfated polysaccharides that functions as structural components preventing it against dehydration. The fraction 0.9 (FucB) rich in sulfated fucans obtained from brown seaweed Dictyota menstrualis was chemical characterized and evaluated for pharmacological activity by testing anticoagulant activity, stimulatory action on the synthesis of an antithrombotic heparan sulfate, antioxidant activity and its effects in cell proliferation. The main components were FucB carbohydrates (49.80 ± 0.10 %) and sulfate (42.30 ± 0.015 %), with phenolic compounds ( 3.86 ± 0.016 %) and low protein contamination ( 0.58 ± 0.001 % ) . FucB showed polydisperse profile and analysis of signals in the infrared at 1262, 1074 and 930 cm -1 and 840 assigned to S = O bonds sulfate esters , CO bond presence of 3,6- anhydrogalactose , β -D- galactose non- sulfated sulfate and the axial position of fucose C4 , respectively. FucB exhibited moderate anticoagulant activity , the polysaccharides prolonged time (aPTT ) 200 ug ( > 90s ) partial thromboplastin FucB no effect on prothrombin time (PT), which corresponds to the extrinsic pathway of coagulation was observed. This stimulation promoted fraction of about 3.6 times the synthesis of heparan sulfate (HS) by endothelial cells of the rabbit aorta ( RAEC ) in culture compared with cells not treated with FucB . This has also been shown to compete for the binding site with heparin. The rich fraction sulfated fucans exhibited strong antioxidant activity assays on total antioxidant (109.7 and 89.5 % compared with BHT and ascorbic acid standards ) , reducing power ( 71 % compared to ascorbic acid ) and ferric chelation ( 71 , comparing with 5 % ascorbic acid). The fraction of algae showed cytostatic activity on the RAEC cells revealed that the increase of the synthesis of heparan sulfate is not related to proliferation. FucB showed antiproliferative action on cell lines modified as Hela and Hep G2 by MTT assay . These results suggest that FucB Dictyota menstrualis have anticoagulant , antithrombotic , antioxidant potential as well as a possible antitumor action, promoting the stimulation of the synthesis of antithrombotic HS by endothelial cells and is useful in the prevention of thrombosis, also due to its inhibitory action on species reactive oxygen ( ROS ) in some in vitro systems , being involved in promoting a hypercoagulable state

Extração, caracterização estrutural e atividades farmacológicas do olginato obtido da alga marrom Lobophora variegata (Lamouroux) Oliveira Filho, 1977

The alginic acid or alginates are acidic polysaccharides found in brown seaweed widely used in food, cosmetic, medical and pharmaceutical industry. This paper proposes the extraction, chemical characterization and verification of the pharmacological activities of brown seaweed variegata Lobophora . The alginate was extracted from the seaweed Lobophora variegata and part was sulphated for comparative purposes. The native extract showed 42% total sugar, 65% uronic acid, 0,36 % protein and 0% of sulfate, while the sulfate showed 39% , 60%, 0.36% and 27,92 % respectively. The presence of a sulfate group may be observed by the metachromasia with toluidine blue in electrophoresis system and characteristic vibration 1262,34 cm-1 in infrared spectroscopy connections assigned to S = O. We observed the formation of films and beads of native alginate, where more concentrated solution 6% resulted in a thicker and more consistent film. Native alginate showed proliferative activity at concentrations (25 and 50 mcg), (50 mg) and (100 mg) in 3T3 cell line in 24h, 48h and 72h, respectively , as the sulfated (100 mg) in 24 . Also showed antiproliferative or cytotoxic activity in HeLa cells of strain, (25 and 100 mg), (25 and 100 mg) and (25, 50 and 100 mg), to native, now for the sulfate concentrations (100 mg) in 24 (25, 50 and 100 mg) in 48 hours, and (50 and 100 mg ) 72h. For their antioxidant activity, the sulfated alginates have better total antioxidant activity reaching 29 % of the native activity while 7.5 % of activity . For the hydroxyl radical AS showed high inhibition ( between 77-83 % ) in concentrations, but the AN surpassed these numbers in the order of 78-92 % inhibition. The reducing power of AN and AS ranged between 39-82 % . In the method of ferric chelation NA reached 100 % chelating while the AS remained at a plateau oscillating 6.5%. However, in this study , we found alginates with promising pharmacological activities, to use in various industries as an antioxidant / anti-tumor compound

Estudo da moagem de alta energia e sinterização de pós compósitos W-Cu

The Tungsten/copper composites are commonly used for electrical and thermal objectives like heat sinks and lectrical conductors, propitiating an excellent thermal and electrical conductivity. These properties are dependents of the composition, crystallite size and production process. The high energy milling of the powder of W-Cu produces an dispersion high and homogenization levels with crystallite size of W very small in the ductile Cu phase. This work discusses the effect of the HEM in preparation of the W-25Cu composite powders. Three techniques of powder preparation were utilized: milling the dry with powder of thick Cu, milling the dry with powder of fine Cu and milling the wet with powder of thick Cu. The form, size and composition of the particles of the powders milled were observed by scanning electron microscopy (SEM). The X-ray diffraction (XRD) was used to analyse the phases, lattice parameters, size and microstrain of the crystallite. The analyse of the crystalline structure of the W-25Cu powders milled made by Rietveld Method suggests the partial solid solubility of the constituent elements of the Cu in lattice of the W. This analyse shows too that the HEM produces the reduction high on the crystallite size and the increase in the lattice strain of both phases, this is more intense in the phase W

Estudo da sinterização do aço inox 316L reforçado com 3% Carbeto de Tântalo - TaC

The present work shows a contribution to the studies of development and solid sinterization of a metallic matrix composite MMC that has as starter materials 316L stainless steel atomized with water, and two different Tantalum Carbide TaC powders, with averages crystallite sizes of 13.78 nm and 40.66 nm. Aiming the metallic matrix s density and hardness increase was added different nanometric sizes of TaC by dispersion. The 316L stainless steel is an alloy largely used because it s high resistance to corrosion property. Although, its application is limited by the low wear resistance, consequence of its low hardness. Besides this, it shows low sinterability and it cannot be hardened by thermal treatments traditional methods because of the austenitic structure, face centered cubic, stabilized mainly in nickel presence. Steel samples added with TaC 3% wt (each sample with different type of carbide), following a mechanical milling route using conventional mill for 24 hours. Each one of the resulted samples, as well as the pure steel sample, were compacted at 700 MPa, room temperature, without any addictive, uniaxial tension, using a 5 mm diameter cylindrical mold, and quantity calculated to obtain compacted final average height of 5 mm. Subsequently, were sintered in vacuum atmosphere, temperature of 1290ºC, heating rate of 20ºC/min, using different soaking times of 30 and 60 min and cooled at room temperature. The sintered samples were submitted to density and micro-hardness analysis. The TaC reforced samples showed higher density values and an expressive hardness increase. The complementary analysis in optical microscope, scanning electronic microscope and X ray diffractometer, showed that the TaC, processed form, contributed with the hardness increase, by densification, itself hardness and grains growth control at the metallic matrix, segregating itself to the grain boarders

Influência da gipsita no surgimento de eflorescência em telhas cerâmicas

The red ceramic industry is recognized as of major importance in Piauí State. The State capital, Teresina, is the greatest producer of this material ( production about 18 million peaces), which is used mainly for masonry sealing blocks. One of the most frequent problems in this kind of products is the efflorescence. This work has the main objective of studying the influence of gypsum addition on non-glazed tiles, by using the local industry production standards. The raw materials were characterized by FRX, DRX, TGA, DTA and AD. Extruded test specimens were made with the addition of 1, 3 and 5% of gypsum in the ceramic paste, burned at 850oC, 950oC and 1050oC and submitted to further technological tests and microestrutural analysis by the scanning electron microscope. In order to accelerate the aging of bodies of evidence, they were immersed in successive water baths and posterior drying. The reference ceramic paste showed tendency to efflorescence formation after drying and consolidated efflorescence after burning, but no affecting the technological results