CECILIA CHAVES GUEDES E SILVA

CECILIA CHAVES GUEDES E SILVA

(Fonte: Lattes)

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Possui graduação em Engenharia de Materiais pela Universidade Presbiteriana Mackenzie (1997), mestrado em Tecnologia Nuclear Aplicações pelo Instituto de Pesquisas Energéticas e Nucleares (2000) e doutorado em Tecnologia Nuclear Materiais pelo Instituto de Pesquisas Energéticas e Nucleares (2005). Atualmente é pesquisador do Instituto de Pesquisas Energéticas e Nucleares. Tem experiência na área de Engenharia de Materiais, atuando principalmente nos seguintes temas: materiais cerâmicos, biomateriais e materiais nucleares. (Texto extraído do Currículo Lattes em 08 out. 2021)

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Sintering of metallic diamond alloy powders
2023 - RESTIVO, THOMAZ A.G.; NONATO, RAPHAEL B.P.; FIGUEIRA, ROSSANA R.; FERREIRA, ODIRLEI A.; PADOVANI, CLAUDIO; ARANHA, NORBERTO; BALDO, DENICESAR; SILVA, CECILIA G. e; DURAZZO, MICHELANGELO
Metallic diamond (MD) is a new alloy class which hardness was found to surpass any current alloys at more than a twofold factor, up to 2500 HV (kgf mm−2). The alloy design employs simple metallurgical principles at the so-called Lattice Occupancy Project aided by Diamoy 1.0 software. The most important aspect of the alloy project considers the maximization of chromium equivalent values by selecting metallic elements for promoting body-centred cubic structures. Forming these alloys into parts is challenging, whereas powder metallurgy techniques appear as valid processing routes. The work studies the sintering behaviour of MD-4 and 5 alloy powders, being the hardest MD ones. High energy milled powder compacts were sintered in a dilatometer up to 1500 °C for 1 h under Ar-10%H2 atmosphere. Alloy MD-5 has shown intense shrinkage starting at 1150 °C, contrasting to marginal sintering of alloy MD-4. The latter has undergone transformations from 400 °C with strong expansion, which seems to block most of the sintering retraction at higher temperatures. Alloy powder MD-5 is a good candidate as a raw material for tool parts production by powder metallurgy, which can compete with cemented carbide hard tools.
Oxidation behavior of Si3N4-TiN composites at 1400 ºC
2023 - FERREIRA, T.S.; CARVALHO, F.M.S.; GUEDES-SILVA, C.C.
In this paper, the oxidation behavior of silicon nitride with different contents of TiN was evaluated at 1400 oC for 64 hours in air. The oxidized samples were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. Weight gain measurements have shown that the oxidation followed a multiple-law model with linear, parabolic, and logarithmic contributions. The samples presented high weight gain at the beginning of the process followed by the formation of an amorphous silica surface layer containing Y2Ti2O7 and rutile crystals. Cracks and holes were detected on the oxide layer. The oxidation resistance of the composites was strongly influenced by the initial content of TiN.
Mechanical properties and in vitro bioactivity of silicon nitride ceramics with SiO2, CaO, and MgO additions
2022 - SONA FILHO, CELSO R.; CARVALHO, FLAVIO M. de S.; GUEDES-SILVA, CECILIA C.
Silicon nitride ceramics with SiO2, CaO, and MgO as sintering aids were investigated in view of biomedical applications. In the current study, samples with four different compositions were pressureless sintered at 1750°C for 1 h under a nitrogen atmosphere. The samples were evaluated concerning densification, microstructure, mechanical properties, and in vitro bioactivity. Microstructures with elongated β-Si3N4 grains dispersed in an intergranular phase and with densities from 78.77 to 97.14% of the theoretical density were obtained. Higher contents of SiO2 resulted in the best densification and mechanical properties. Besides, replacements of CaO by MgO in the initial compositions affected Young's modulus and in vitro bioactivity. Considering the samples with relative density higher than 94.14%, those with lower values of Young's modulus had lower SiO2/MgO ratios. After immersion in SBF (Simulated Body Fluid), the samples with high porosity and/or partial replacements of CaO by MgO had their surfaces coated with a layer rich in calcium and phosphorus, morphologically similar to hydroxyapatite. Hence, producing silicon nitride ceramics with the potential to be used as orthopedic implants must consider ideal amounts of additives. In this article, the best combination of mechanical properties and mineralization capability was reached by the composition with low content of MgO, and high content of SiO2 and CaO.
Influence of silicon, strontium and aluminum oxides on silicon nitride ceramics for bone replacements
2020 - NASCIMENTO, SERGIO F. do; RODAS, ANDREA C.D.; CARVALHO, FLAVIO M. de S.; HIGA, OLGA Z.; SILVA, CECILIA C.G. e
Although silicon nitride ceramics have been shown very propitious to be used for bone replacements, some characteristics can be controlled to improve their osseointegrations process. One of them is the intergranular phase whose composition can be specified to stimulate mineralization and osteoblastic production. In this paper, the intergranular glassy phase was projected in order to contain silicon, strontium and aluminum oxides. Silicon nitride samples containing different contents of SiO2, SrO and Al2O3 were sintered at 1815oC for 1 hour and characterized by scanning electron microscopy and X-ray diffraction. Hardness and fracture toughness were determined by Vickers hardness test and compressive strength was evaluated using an universal material testing machine. The biological behavior was studied in regard to cytotoxicity and cell proliferation by means of in vitro experiments. The samples reached high densities (higher than 95 %TD), total α→β-Si3N4 transformation, fracture toughness higher than 6.5 MPa.m1/2, compressive strength up to 2500 MPa and Vickers hardness less than 9.8 GPa. All samples were non-cytotoxic and able to promote cell proliferation with great potential to be used as components for bone replacements. However, that sample with high content of strontium had the best results of cell proliferation, proving the importance of a careful choice of intergranular phase composition in silicon nitride ceramics.
Silicon nitride with titania, calcia and silica additives for orthopaedic applications
2020 - GUEDES-SILVA, CECILIA C.; RODAS, ANDREA C.D.; CARVALHO, FLAVIO M.S.; HIGA, OLGA Z.; FERREIRA, THIAGO S.
Titanium, silicon and calcium ions have demonstrated positive effects in bone healing. Therefore, this paper investigates the densification, mechanical properties and in vitro biological behaviour of TiO2, together with SiO2 and CaO, on silicon nitride ceramics to be used in clinical applications. The results revealed that the sintered samples reached high values of relative density and fracture toughness, non-cytotoxicity as well as good ability to promote cell proliferation and form a layer of carbonated hydroxyapatite on their surfaces, after immersion in simulated body fluid. The sample with the highest amount of TiO2 reached the highest value of relative density and the best results of cell proliferation and fracture toughness, indicating the great potential to be explored by in vivo experiments for later application as intervertebral devices.