TATIANE CRISTINA PORFÍRIO

TATIANE CRISTINA PORFÍRIO

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Electric field-assisted synthesis/sintering cerium oxide
2021 - PORFÍRIO, TATIANE C.; MUCCILLO, ELIANA N. dos S.; MUCCILLO, REGINALDO
Gadolinium oxide ceramic powders were mixed to cerium oxide ceramic powders, pressed to pellets, and sintered either at 1450ºC for 4 h or applying 200 V cm-1 electric field at 800ºC, 900ºC and 1000ºC. The structural phases and the microstructure of the sintered pellets were analyzed by X-ray diffraction and scanning electron microscopy, respectively. The formation of substitutional solid solution was followed by monitoring the increase of the electrical conductivity by impedance spectroscopy measurements and the X-ray diffraction patterns. The main results show that Joule heating due to the flow through the pellets of the electric current, which was produced by the application of the electric field, allows for promoting partial solid solution as well as partial sintering the ceria-gadolinia pellets. Moreover, grain growth that occurred in the high temperature sintered pellets was inhibited in the electric field-assisted synthesized/sintered pellets, being an alternative technique for producing cerium oxide-gadolinium oxide solid solutions.
Electric field-assisted synthesis/sintering cerium oxide
2021 - PORFIRIO, T.C; MUCCILLO, E.N.S.; MUCCILLO, R.
Gadolinium oxide ceramic powders were mixed to cerium oxide ceramic powders, pressed to pellets, and sintered either at 1450 °C or applying 200 V cm−1 electric field at 800 °C, 900 °C and 1000 °C. The structural phases and the microstructure of the sintered pellets were analyzed by X-ray diffraction and scanning electron microscopy, respectively. The formation of substitutional solid solution was followed by monitoring the increase of the electrical conductivity by impedance spectroscopy and X-ray diffraction. The main results show that Joule heating due to the flow through the pellets of the electric current, which was produced by the application of the electric field, allows for promoting partial solid solution as well as partial sintering the ceria-gadolinia pellets. Moreover, grain growth that occurred in the high temperature sintered pellets was inhibited in the electric field-assisted synthesized/sintered pellets, being an alternative technique for producing cerium oxide-gadolinium oxide solid solutions.
Samaria-doped ceria with impregnation of molten lithium/potassium carbonate for application as CO2 separation membranes
2018 - PORFIRIO, T.; MUCCILLO, E.N.; MARQUES, F.; MUCCILLO, R.
Composite membranes for carbon dioxide separation were obtained with vacuum infiltration of an eutectic mixture of potassium and lithium molten carbonates into a samaria-doped ceria (SDC) porous matrix at high temperature. Porous SDC were obtained by thermal removal of LiF sacrificial pore former. Scanning electron microscopy and scanning probe microscopy micrographs allowed for estimating pore volume and molten carbonate percolation through porous SDC. Impedance spectroscopy measurements at temperatures below and above the melting temperature of the carbonates show the contributions of oxide and carbonate ions to the total electrical conductivity of the ceramic membranes, which is dependent on the pore volume.
Thermal and electrical properties of CaCu3Ti4O12 synthesized by soft chemistry route
2018 - PORFIRIO, T.C.; MUCCILLO, E.N.S.
Calcium copper titanate powders were synthesized by a soft chemistry route, aiming to establish a cost-effective solution method to obtain sintered ceramics with giant electric permittivity (ε′) and low dissipation factor (tanδ). Powders and sintered pellets were characterized by several techniques. The thermal decomposition behavior of the porous foam evidences that a hydroxycitrate was formed below 200 °C. Single cubic perovskite-type phase was obtained after calcination of the precursor powder at 700 °C for 5 h. Negligible mass loss occurs above 400 °C. During heating the precursor material, CuO is the first crystallized phase. A giant ε′ and low tanδ are obtained after sintering. The extension of the thermal window of ε′ is wider than those of powders prepared by other methods.
Properties of porous samaria-doped ceria ceramics with lithium fluoride as sacrificial pore former
2016 - PORFIRIO, TATIANE C.; MUCCILLO, ELIANA N. dos S.; FRANÇA, YONE V.; MARQUES, FERNANDO M.B.; MUCCILLO, REGINALDO
Porous ceria: 10 mol% samaria (10SDC) ceramic solid electrolytes were prepared by solid state reaction with 0-50 vol.% lithium fluoride (LiF). Consolidation was done by heating to the melting point of LiF for 30 min to form a liquid phase, followed by elimination of LiF by capillarity after heating to 1500° C for 2 h, promoting intergranular porosity and 10SDC skeletal densification. Apparent density was evaluated by the Archimedes method, pore distribution by scanning electron microscopy and electrical properties by electrochemical impedance spectroscopy in the 5 Hz - 13 MHz frequency range and temperatures from 300 to 550° C. The main results show that porous ceramics with high skeletal density are obtained with sacrificial LiF. Moreover, the total electrical resistivity is directly related to the pore volume fraction. High temperature vacuum impregnation of lithium-potassium carbonate eutectic compositions onto the porous 10 SDC was carried out to consolidate composite SDC-molten carbonate ceramic membranes with tunable transport properties, for selective carbon dioxide separation. The enhancement of the total electrical conductivity was evaluated by electrochemical impedance spectroscopy. Percolation of the molten carbonate through the permeable porous membrane was ascertained by EDX analysis on both parallel surfaces of the membranes.
Effects of LiF addition on microstructure and dielectric properties of CaCu3Ti4O12 ceramics
2016 - PORFIRIO, T.C.; MUCCILLO, E.N.S.
The effects of small amounts of lithium fluoride sintering aid on the microstructure and dielectric properties of CaCu3Ti4O12 (CCTO) ceramics were investigated. CCTO polycrystalline ceramics with 0.5 and 1.0 mol% LiF, and without additive were prepared by solid state synthesis. Good densification (>90% of the theoretical density) was obtained for all prepared materials. Specimens without the sintering aid and sintered at 1090 °C exhibit secondary phases as an outcome of the decomposition reaction. The mean grain size is controlled by the amount of LiF in specimens containing the additive. Impedance spectroscopy measurements on CaCu3Ti4O12 ceramics evidence the electrically heterogeneous nature of this material consisting of semiconductor grains along with insulating grain boundaries. The activation energy for grain boundary conduction is lower for specimens prepared with the additive, and the electric permittivity reached 53,000 for 0.5 mol% LiF containing CCTO.
Estudo da densificação de eletrólitos sólidos à base de CEO2, preparados por técnicas químicas, utilizando a sinterização em duas etapas
2016 - PORFIRIO, TATIANE C.; TROMBINI, VANIA; MUCCILLO, ELIANA N. dos S.; ROCHA, RENATA A.
Eletrólitos sólidos são materiais nos quais ocorre a migração de íons, ou seja, apresentam uma condutividade parcial ou total devido aos deslocamentos iônicos e podem ser à base de ZrO2 ou CeO2, no caso de condutores de íons O2-. Para que um material atue como um bom eletrólito sólido, ele deve ter como características: alta condutividade iônica na temperatura de operação, homogeneidade da microestrutura; boa resistência ao choque térmico e alta densidade. O processo cerâmico ideal para a obtenção desses materiais deve permitir a síntese de pós cerâmicos com características definidas em relação à morfologia, tamanho e distribuição de tamanho de partículas e cristalinidade, e permitir a consolidação e densificação do material em temperaturas as mais baixas possíveis, com controle da microestrutura. Neste trabalho, a característica analisada será a densificação, utilizando o método de sinterização em duas etapas. O material previamente preparado foi caracterizado por difração de raios X para determinação da estrutura cristalina e por análise dilatométrica, para verificação da retração linear em função da temperatura. A partir das informações dessa análise, e também de dados da literatura para a sinterização em duas etapas do CeO2, foram determinadas as temperaturas e tempos para o tratamento térmico. Após a sinterização, as amostras foram caracterizadas pela densidade e por difração de raios X, para verificar a estabilidade da fase após o tratamento térmico. Os resultados mostraram as características dos pós em função do óxido utilizado como dopante e da técnica de síntese utilizada
Densificação e propriedades dielétricas do CaCusub(3)Tisub(4)Osub(12)
2016 - PORFIRIO, T.C.; MUCCILLO, E.N.S.
A tecnologia de capacitores cerâmicos compreende uma variedade de produtos baseados em materiais dielétricos destinados à armazenagem de energia elétrica, fazendo com que tais componentes sejam de grande importância na indústria eletrônica. Para tais aplicações, as principais propriedades que estes materiais devem possuir são elevada permissividade elétrica ε’ (acima de 103) e baixas perdas dielétricas, além de serem estáveis em um amplo intervalo de temperatura e frequência. Neste trabalho, pós de CCTO foram preparados pelo método de reação em estado sólido e, frações equivalentes a 0,5 e 1% em mol de LiF foram adicionados ao material sintetizado com o objetivo de diminuir a temperatura de sinterização dos compactos e assim, minimizar o desvio estequiométrico de cobre nas cerâmicas. Os resultados indicaram a possibilidade de obter materiais com densidade relativa acima de 91% da densidade teórica quando sinterizados em temperaturas abaixo daquelas usualmente empregadas. O tamanho e o formato dos grãos das amostras contendo aditivo são mais homogêneos do que aqueles observados nas amostras puras. Além disto, o LiF promoveu diminuição dos valores de perdas dielétricas sem que houvesse prejuízo nos valores de permissividade elétrica (valores acima de 30.000).
Synthesis of ceramic powders based on manganese, cobalt and nickel oxides
2006 - FRANCA, Y.V.; PORFIRIO, T.C.; MUCCILLO, E.N.S.; MUCCILLO, R.
Dielectric and microstructural properties of CaCusub(3)Tisub(4)Osub(12) synthesized by the coprecipitation technique
2014 - PORFIRIO, T.C.; MUCCILLO, E.N.S.