Produção de monoglicéridos através de catalisadores de argila

As reações de esterificação do glicerol com ésteres de ácidos gordos, na presença de catalisador originam monoglicéridos que possuem inúmeras aplicações em diversas indústrias e são emulsionantes e antibacterianos. Para a produção dos monoglicéridos, nomeadamente a monolaurina, recorreu-se à utilização de catalisadores heterogéneos de características básicas, após modificação de uma bentonita recolhida na Serra de Dentro (SD), Ilha do Porto Santo e de uma argila comercial, a K10. Estas argilas foram modificadas recorrendo a uma solução de hidróxido de lítio, e posteriormente calcinadas a diferentes temperaturas, 350, 450, 550 e 650ºC. Todas as argilas foram posteriormente caracterizadas recorrendo à difração de raios X, aos indicadores de Hammett, à titulação potenciométrica e à espectroscopia de infravermelho que confirmaram o carácter básico dos materiais produzidos. Os produtos de reação foram analisados e quantificados por cromatografia gasosa. A caracterização dos catalisadores demonstra que temperaturas de calcinação superiores a 450ºC provocam uma diminuição da força da base devido à excessiva perda de água resultante da calcinação. A produção de monolaurina é maior quando ocorre a reação do glicerol com o laurato de metilo na presença de argilas baseadas na SD, em particular o material calcinado a 450ºC como catalisador (rendimento em monolaurina de 43%). Não se detetaram outros produtos reacionais, mas a sua formação não é de excluir. Para a minimização da produção potencial de subprodutos, testou-se, também, uma reação de acetalização do glicerol com acetona originando o composto solketal. Os resultados desta reação, apesar de indiciarem uma elevada seletividade para o produto pretendido, não foram elucidativos em termos de ordenamento dos catalisadores em termos de atividade catalítica. Posteriormente fez-se uma tentativa de reação do solketal com o laurato de metilo na presença de catalisador heterogéneo básico de argila, não se tendo observado atividade catalítica.

Caracterização de revestimentos de edifícios antigos

Como é de conhecimento geral as argamassas de revestimento antigas diferem das argamassas atuais, tanto na sua produção, como nos seus constituintes e até na sua resistência e durabilidade. O presente trabalho surge com o principal intuito de dissertar sobre a caraterização de algumas argamassas de revestimento e de enchimento antigas na Região Autónoma da Madeira. Desta forma foram realizados vários ensaios como a difração de raios X, a análise termogravimétrica, a determinação da percentagem do resíduo insolúvel com ataque àcido e a análise granulométrica, podendo assim ficar-se com uma ideia dos seus minerais, a quantidade de carbonato de cálcio utilizada, a quantidade de material insolúvel no ácido clorídrico e a granulometria (tamanho/dimensões) das areias. A escolha das amostras baseou-se nos critérios de maior longevidade dos edifícios, a não reabilitação destes e a possibilidade da realização do estudo dessas habitações (i.e. acessibilidade física e legal). Quanto aos ensaios efetuados, a opção de os ter utilizado prende-se com as técnicas disponíveis no Laboratório Regional de Engenharia Civil (LREC).

Durabilidade do betão: caracterização de amostras de betão recolhidas ao longo de dois túneis da Região Autónoma da Madeira

Na realização deste trabalho pretendeu-se caracterizar amostras de betão recolhidas ao longo de dois túneis da Região Autónomo da Madeira com o objetivo de traçar um perfil de composição e relacionar com a durabilidade. Para tal foram recolhidas amostras em dois túneis, o Túnel da Cruz Vermelha e o Túnel da Encumeada. De modo a caracterizar o betão foram realizados ensaios de carbonatação, determinação do teor de cloretos em profundidade em laboratório, termogravimétrica, análise macroestrutural e de difração raios X. Realizou-se uma previsão de quando é que as armaduras poderão deixar de estar passivadas devido a carbonatação (período de iniciação) e quando é que os túneis deverão ser alvos de reparações devido a corrosão (período de propagação). Tentou-se verificar a influência da carbonatação em altura no Túnel da Cruz Vermelha. Demonstrou-se que a fissuração é uma zona de fácil acesso para as substâncias agressivas penetrarem para o interior do betão, nomeadamente o dióxido de carbono relacionado com a carbonatação. Demonstrou-se também que é possível determinar a profundidade carbonatação através da difração de raios X. Verificou-se que o método (difração de Raio X) usado para determinar a composição do betão de ambos os túneis é viável. Constatou-se que praticamente todas as carotes apresentam pontos com valores de cloretos superiores aos permitidos pela norma atualmente em vigor (NP EN 206-1: 2007). Uma das possíveis razões para esses valores é o facto de na RAM, a areia utilizada no fabrico do betão ser de origem marítima. Em termos da profundidade de carbonatação verificou-se que praticamente em todas as amostras, o valor determinado ainda não tinha alcançado as armaduras e deste modo encontravam-se passivadas, com exceção a carote nº10 (Túnel Encumeada) em que a carbonatação já tinha ultrapassado o valor do recobrimento e a armadura já apresentava sinais de corrosão.

Synthesis and characterization of lanthanum- and yttrium-doped Fe2O3 pigments

MELO, D. M. A. et al. Synthesis and charactezarion of lanthanum and yttrium doped Fe2O3 pigments. Cerâmica, São Paulo, v. 53, p. 79-82, 2007.

Infiltração de sal de alumínio em fibras de sisal para obtenção de fibras de alumina

ANDRADE JR., T. E. et al. Infiltração de sal de alumínio em fibras de sisal para obtenção de fibras de alumina. Cerâmica, v.51, n.317, p.37-41.ISSN 0366-6913. Disponível em:. Acesso em: 06 out. 2010.

Estudo da síntese e sinterização de pós compósitos do sistema Ta-Cu

Ta-Cu bulk composites combine high mechanical resistance of the Ta with high electrical and thermal conductivity of the Cu. These are important characteristics to electrical contacts, microwave absorber and heat skinks. However, the low wettability of Ta under Cu liquid and insolubility mutual these elements come hard sintering this composite. High-energy milling (HEM) produces composite powders with high homogeneity and refines the grain size. This work focus to study Ta-20wt%Cu composite powders prepared by mechanical mixture and HEM with two different conditions of milling in a planetary ball mill and then their sintering using hydrogen plasma furnace and a resistive vacuum furnace. After milling, the powders were pressed in a steel dye at a pressure of 200 MPa. The cylindrical samples pressed were sintered by resistive vacuum furnace at 10-4torr with a sintering temperature at 1100ºC / 60 minutes and with heat rate at 10ºC/min and were sintered by plasma furnace with sintering temperatures at 550, 660 and 800ºC without isotherm under hydrogen atmosphere with heat rate at 80ºC/min. The characterizations of the powders produced were analyzed by scanning electron microscopy (SEM), x-ray diffraction (XRD) and laser granulometry. After the sintering the samples were analyzed by SEM, XRD and density and mass loss tests. The results had shown that to high intense milling condition produced composite particles with shorter milling time and amorphization of both phases after 50 hours of milling. The composite particles can produce denser structure than mixed powders, if heated above the Cu melting point. After the Cu to arrive in the melting point, liquid copper leaves the composite particles and fills the pores

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

Efeito do tratamento térmico do titânio sobre a proliferação de células pré-osteoblásticas

Titanium is a biomaterial widely employed in biomedical applications (implants, prostheses, valves, stents). Several heat treatments are usually used in order to obtain physical properties required to different applications. This work studied the influence of the heat treatment on microstructure of commercial pure titanium, and their consequences in growth and proliferation of MC3T3-E1 cells. Discs of titanium were treated in different temperatures, and characterized by optical microscopy, image analysis, wettabillity, roughness, hardness and X-ray diffraction. After the heat treatment, significant modifications in these properties were observed. Pattern images of titanium, before and after the cell culture, were compared by overlapping to analyze the influence of microstructure in microstructure and preferences guidance cells. However, in general, titanium discs that showed a higher residual strength also presented an increase of cells numbers on surface

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

Obtenção e caracterização de nanopartículas de argilominerais

Natural nanoclays are of great interest particularly for the production of polymer-based nanocomposites. In this work, kaolinite clays from two natural deposits in the State of the Rio Grande do Norte and Paraiba were purified with thermal treatment and chemical treatments, and characterized. Front to the gotten data, had been proposals methodologies for elimination or reduction of coarse particle texts, oxide of iron and organic substance. These methodologies had consisted of the combination of operations with thermal treatments, carried through in electric oven, and acid chemical attacks with and hydrogen peroxide. The Analyzers Thermogravimetric was used to examine the thermal stability of the nanoclays. The analysis indicated weight losses at temperatures under 110 ºC and over the temperature range of 350 to 550 ºC. Based on the thermal analysis data, the samples were submitted to a thermal treatment at 500 °C, for 8 h, to remove organic components. The X-ray diffraction patterns indicated that thermal treatment under 500 °C affect the basic structure of kaolinite. The BET surface area measurements ranged from 32 to 38 m2/g for clay samples with thermal treatment and from 36 to 53 m2/g for chemically treated samples. Thus, although the thermal treatment increased the surface area, through the removal of organic components, the effect was not significant and chemical treatment is more efficient, not affect the basic structure of kaolinite, to improve particle dispersion. SEM analysis confirms that the clay is agglomerated forming micron-size particles

Síntese, caracterização e estudo da regeneração do silicoaluminofosfato-11 (SAPO-11)

heterogeneous catalyst such as a silicoaluminophosphate, molecular sieve with AEL (Aluminophosphate eleven) structure such as SAPO-11, was synthesized through the hydrothermal method starting from silica, pseudoboehmite, orthophosphoric acid (85%) and water, in the presence of a di-isopropylamine organic template. For the preparation of SAPO-11 in a dry basis it was used as reactants: DIPA; H3PO4; SiO4; Pseudoboehmite and distilled water. The crystallization process occurred when the reactive hydrogel was charged into a vessel and autoclaved at 200ºC for a period of 72 hours under autogeneous pressure. The obtained material was washed, dried and calcined to remove the molecular sieves of DIPA. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (FT-IR), nitrogen adsorption (BET) and thermal analysis (TG/DTG). The acidic properties were determined using adsorption of nbutylamine followed by programmed thermodessorption. This method revealed that SAPO-11 shows an acidity that ranges from weak to moderate. However, a small quantity of strong acid sites could be detected there. The deactivation of the catalysts was conducted by artificial coking followed by the cracking of the n-hexane in a fixed bed with a continuous flow micro-reactor coupled on line to a gas chromatograph. The main products obtained were: ethane, propane, isobutene, n-butane, n-pentane and isopentane. The Vyazovkin (model-free) kinetics method was used to determine the regeneration and removal of the coke

Síntese e caracterização de NiO-CGO para anodo e eletrólitos sólidos e base de Céria para SOFC

The direct use of natural gas makes the Solid Oxide Fuel Cell (SOFC) potentially more competitive with the current energy conversions technologies. The Intermediate Temperature SOFC (IT-SOFC) offer several advantages over the High Temperature SOFC (HT-SOFC), which includes better thermal compatibility among components, fast start with lower energy consumption, manufacture and operation cost reduction. The CeO2 based materials are alternatives to the Yttria Stabilized Zirconia (YSZ) to application in SOFC, as they have higher ionic conductivity and less ohmic losses comparing to YSZ, and they can operate at lower temperatures (500-800°C). Ceria has been doped with a variety of cations, although, the Gd3+ has the ionic radius closest to the ideal one to form solid solution. These electrolytes based in ceria require special electrodes with a higher performance and chemical and termomechanical compatibility. In this work compounds of gadolinia-doped ceria, Ce1-xGdxO2-δ (x = 0,1; 0,2 and 0,3), used as electrolytes, were synthesized by polymeric precursors method, Pechini, as well as the composite material NiO - Ce0,9Gd0,1O1,95, used as anode, also attained by oxide mixture method, mixturing the powders of the both phases calcinated already. The materials were characterized by X ray diffraction, dilatometry and scanning electronic microscopy. The refinement of the diffraction data indicated that all the Ce1-xGdxO2-δ powders were crystallized in a unique cubic phase with fluorite structure, and the composite synthesized by Pechini method produced smaller crystallite size in comparison with the same material attained by oxide mixture method. All the produced powders had nanometric characteristics. The composite produced by Pechini method has microstructural characteristics that can increase the triple phase boundaries (TPB) in the anode, improving the cell efficiency, as well as reducing the mass transport mechanism effect that provokes anode degradation

Estudo da zircônia reforçado com alumina

Ceramics materials have good properties including chemical stability, high hardness and wear resistance. Moreover, due to its fragility, can suffer failure under relatively low levels of tension. Actually zirconia is the material of choice in metal free dental prostheses used in dentistry due its inertia in physiological environment, good bending strength, hardness and fracture toughness. The alumina and mixed tungsten and titanium carbides additions, acting as reinforcement elements in the zirconia matrix, have as their main objective the improvement of mechanical properties of this material. In this work, samples of zirconia, zirconia with 30% wt of alumina and zirconia with 30% wt mixed carbides were analyzed. The samples were sintered by uniaxial hot pressing on 30 MPa pressure, for 1 hour in an argon atmosphere. They were physically characterized by porosity and density measurements, and mechanically by 3-points bending strength and Vickers microhardness. The X-ray diffraction was used for the phase identifications and microstructure was examined by scanning electron microscopy (SEM). The addition of mixed carbides as reinforcement elements in zirconia matrix provides improvements in all properties analyzed in this work. The alumina addition has dropped the zirconia strength, although it caused improvement in other properties

Caracterização termo-mecânica de interconectores metálicos recobertos com filmes de LaCrO3

The cells unitaria of the solid oxide fuel cell are separated by means of interconnects, which serve as electrical contact between the cells. Lanthanum Chromite (LaCrO3) has been the most common material used as interconnect in solid oxide fuel cells. Reducing the operating temperature around 800 º C of cells to solid oxide fuel make possibilite the use of metallic interconnects as an alternative to ceramic LaCrO3. Metallic interconnects have advantages over ceramic interconnects such as high thermal conductivity, electricity, good ductility, low cost, good physical and mechanical properties. In this work evaluate the thermo-mechanical properties of the metallic substrate and coated metallic substrate with the ceramic LaCrO3 film via spray-pyrolysis, in order to demonstrate the feasibility of using this material as a component of a fuel cell solid oxide. The materials were characterized by X-ray diffraction, oxidation behavior, mechanical strength, optical microscopy (OM) and scanning electron microscopy (SEM). The X-ray diffraction proved the formation phase of the LaCrO3 on the metallic substrate and the identification of the phases formed after the oxidative test and mechanical strength at high temperature. The oxidation behavior showed the increased oxidation resistance of the coated metallic substrate. It was noted that the mechanical resistance to bending of the coated metallic substrate only increases at room temperature. The optical microscopy (OM) has provided an assessment of both the metallic substrate and the LaCrO3 film deposited on the metal substrate that, in comparison with the micrographs obtained from SEM. The SEM one proved the formation of Cr2O3 layer on the metallic substrate and stability of LaCrO3 film after oxidative test, it can also observe the displacement of the ceramic LaCrO3 film after of mechanical testing and mapping of the main elements as chromium, manganese, oxygen, lanthanum in samples after the thermo-mechanical tests.

Síntese, caracterização e cinética da decomposição térmica dos materiais cerâmicos PrMO3 (M = Ni ou Co)

In this work have been studied the preparation, characterization and kinetic study of decomposition of the polymerizing agent used in the synthesis under non-isothermal condition ceramics PrMO3 of general formula (M = Co and Ni). These materials were obtained starting from the respective metal nitrates, as a cations source, and making use of gelatin as polymerizing agent. The powders were calcined at temperatures of 500°C, 700°C and 900°C and characterized by X-ray Diffraction (XRD), Thermogravimetric Analysis (TG / DTG/ DTA), Infrared Spectroscopy (FTIR), Temperature Programmed Reduction (TPR) and Scanning Electron Microscopy (SEM). The perovskite phase was detected in all the X-rays patterns. In the infrared spectroscopy observed the oxide formation as the calcination temperature increases with the appearance of the band metal - oxygen. The images of SEM revealed uniform distribution for the PrCoO3 and particles agglomerated as consequence of particle size for PrNiO3. From the data of thermal analysis, the kinetics of decomposition of organic matter was employed using the kinetics methods called Model Free Kinetics and Flynn and Wall, in the heating ratios 10, 20 and 30° C.min-1 between room temperature and 700°C. Finally, been obtained the values of activation energy for the region of greatest decomposition of organic matter in samples that were determined by the degree of conversion (α)