THOMAZ AUGUSTO GUISARD RESTIVO

THOMAZ AUGUSTO GUISARD RESTIVO

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Micrograded ceramic-metal composites
2019 - RESTIVO, THOMAZ A.G.; BECCARI, RAFAEL F.; PADILHA, WELLINGTON R.; DURAZZO, MICHELANGELO; TELLES, VICTOR B.; COLETI, JORGE; YAMAGATA, CHIEKO; SILVA, ANTONIO C. da; SUZUKI, EDUARDO; TENORIO, JORGE A.S.; MELLO-CASTANHO, SONIA R.H.
The article shows new designed cermets and processes concerning primary to applications as thermal insulation materials with low emissivity. A new projected microstructure was obtained where dense regions (micropellets) rest inside the main porous pellet. The feature resembles a frozen hypercube, therefore such architecture is called hyper-pellet/ cermet. The processing method to obtain the hyper-cermet is based on sequential tape castings and sintering techniques. Ni-zirconia lamellae were prepared by a special mechanochemical process followed by sintering, which remain inside the main pellets as a dense region. The whole pellet is turned to be porous by employing pore-forming additives. All the constituents and porosity shapes are aligned along the disc/ flake planes. Thermal conductivity is estimated for the materials up to 800 °C by a flash diffusivimeter. Ceramographic analyses show graded density regions with directional constituents and pores. Applications of such materials are foreseen as temperature insulation materials and thermal radiation shields.
Low-temperature densification of ceramics and cermets by the intermediary stage activated sintering method
2018 - RESTIVO, THOMAZ A.G.; DURAZZO, MICHELANGELO; MELLO-CASTANHO, SONIA R.H. de; MOREIRA, ANA C.; GRACIANO, SERGIO; TELLES, VICTOR B.; TENORIO, JORGE A.S.
The article explores new concepts in order to promote ceramic and cermet materials sintering at lower temperatures between 1200 and 1300 C. The principle of the new process method called intermediary stage activated sintering (ISAS) involves the preparation of the ceramic powder with dispersed doping agents, such as nanotubes and fibers, which shape the pore structure at pressed pellets with stable interconnected thin cylinders between the grains. This feature resembles and extends the condition found during the intermediary stage sintering, which enhances the ions diffusion rate along tubular pores to increase shrinkage. Carbon nanotubes (CNT) and nanofibers are homogenized into cubic zirconia and alumina in amounts ranging from 1 to 10 vol% at high-energy milling devices and ultrasound disruptor under ethanol media. Ni, Cu and Mo/MoO3 can be also added to provide tubular channel filling. Sintering of uniaxially pressed pellets is carried out in a dilatometer and tubular furnaces at 1200/1300 C under air, argon and controlled oxygen partial pressure atmospheres. TG/DTA/MS analyses of sample pellets reveal the oxidation and gas release temperature and duration. The results demonstrate the ISAS process concept is valid since it further increases the ceramic final density by 8% of the theoretical density at 1200 C, leading to close the porosity at 1300 C, compared to 1500–1600 C temperatures at conventional process. Short CNT and cellulose nanofiber were found to be the best additives in this sense.
TG/DTA-MS evaluation of methane cracking and coking on doped nickel-zirconia based cermets
2014 - RESTIVO, THOMAZ A.G.; MELLO CASTANHO, SONIA R.H.; TENORIO, JORGE A.
Cermet materials based on metallic nickel and cubic zirconia are the key material for applications on solid oxide fuel cells and high temperature water electrolysis. The main advantage is the possibility of direct feeding a hydrocarbon fuel, like methane, or even an alcohol as a source of hydrogen. The reforming reaction on the Ni catalyst surface can produce hydrogen continuously. However, the resulting catalyst poisoning by carbon deposition (coking) imparts their broad application. The work shows the evaluation of coking tolerance of some cermets prepared by mechanical alloying techniques and compares new additives specially chosen in order to avoid coking and increase the catalytic activity. Refractory metal additives besides copper were added to the basic cermet. While copper is a known doping agent that avoids coking, the refractory metals (Mo and W) have a twofold effect: promote sintering at lower temperatures and increase Cu activity due to their mutual immiscibility. Results of TG/DTA-MS analysis demonstrate both refractory metals have increased the coking tolerance as well as the catalytic activity during diluted methane cracking. Molybdenum and tungsten additives are promised regarding the improvement of these cermet materials for high temperature electrochemical devices.
Cinetica de sinterizacao do composito de NiO-YSZ obtido pela rota de coprecipitacao
2009 - YOSHITO, W.K.; RESTIVO, T.A.G.; USSUI, V.; LAZAR, D.R.R.; PASCHOAL, J.O.A.
Microstructure design by mechanical alloying
2009 - RESTIVO, THOMAZ A.G.; MELLO CASTANHO, SONIA R.H.
Aspects of the liquid cerium electrodeposition in molten halide media
1991 - RESTIVO, T.A.G.; PESSINE, E.J.
Desenvolvimento de um reator para eletrolise ignea de metais de terras raras
1992 - RESTIVO, T.A.; PESSINE, E.J.
Cinetica de sinterizacao dos pos de NiO-YSZ sintetizados pela tecnica de combustao
2010 - YOSHITO, W.K.; RESTIVO, T.A.G.; USSUI, V.; LAZAR, D.R.R.; PASCHOAL, J.O.A.
Sinterabilidade de pós de NiO-YSZ sintetizados pela técnica de combustão
2010 - YOSHITO, W.K.; RESTIVO, T.A.G.; USSUI, V.; LAZAR, D.R.R.; PASCHOAL, J.O.A.
Pós de NiO-YSZ, utilizados como anodo de células a combustível de óxido sólido, foram sintetizados por combustão a partir de soluções nítricas de zircônio, ítrio e níquel e uréia como combustível. Os pós foram caracterizados por difração de raios-X, microscopia eletrônica de varredura e de transmissão, adsorção gasosa (BET) e espalhamento de feixes de laser. O tamanho médio dos aglomerados, após a moagem, foi de 0,36 mm e o tamanho de partícula aproximadamente 10nm. O comportamento de sinterização dos pós prensados uniaxialmente foi estudado por dilatometria utilizando o método quasi-isotérmico e a equação empírica de MakipirttiMeng. A energia de ativação obtida entre 900 - 950ºC foi de 367,16 KJ.mol-1 e entre 1000 – 1100 ºC de 677,15 KJ.mol-1. O mecanismo dominante nesta faixa de temperatura é de difusão pelo contorno de grãos. Amostra sinterizada a 1400 ºC apresentou densidade relativa de 93% e distribuição homogênea das fases NiO e YSZ.
Caracterizacao metalografica de cerio metalico eletrodepositado em meio de sais fundidos
1994 - RESTIVO, T.A.G.; PESSINE, E.J.; SANTOS, N.A.; ARAUJO, E.G.