Celio A. Costa

Effect of notch-root radius on the fracture toughness of composite Si3N4 ceramics

In-situ silicon nitride and a whisker-reinforced silicon nitride-silicon nitride composite, densified via gas pressure sintering and hot pressing, respectively, were evaluated using the single-edge V-notched beam (SEVNB) fracture toughness technique. The mean value ofKIC for each material was 5.7 and 7.9 MPa·m1/2, respectively, and the toughness was influenced by the presence of the elongated Si3N4 grains in the microstructure. The notch radius was observed to have the same effect as a sharp crack when notch-root radius was smaller than 10 µm, which was considered to be a realKIC for these materials.

Fracture toughness of Si3N4 processed by gas pressure sintering and hot pressing

This present work evaluates the influence of microstructure on the fracture toughness of two types of silicon nitride. The two microstructural types of silicon nitride were processed using the gas pressure sintering (GPS) and hot pressing (HP) pathways. The fracture toughness was measured using the Single Edge V-Notch Beam (SEVNB) and Chevron Notch Beam (CNB) methods. The results from both methods for the two forms were in close agreement (with a maximum variation of 5.8%); the KIc of the material processed by HP was 35% higher than that of GPS and the grain length had a direct influence on the fracture toughness.

Data on tensile tests and NMR measurements of poly(vinilidene fluoride) before and after stress relaxation

Poly(vinilidene fluoride) was characterized before and after stress relaxation by tensile tests and time-domain nuclear magnetic resonance (TD-NMR). Tensile tests were performed to provide mechanical properties, focused on the data of elastic modulus for this matter. The TD-NMR technique was used to calculate the fraction of crystalline, constrained amorphous and free amorphous phase, and the transversal relaxation time of each of these phases.

Evaluation of Aged PVDF by Instrumented Indentation Technique

Instrumented indentation (IIT) is proposed as an alternative mechanical evaluation technique to identify ageing of semicrystalline thermoplastic polymers such as PVDF. This technique does not require special geometries such as standard tensile experiments and allows following changes in mechanical properties as deeper penetration depth are imposed. Therefore, it is able to detect differences in mechanical properties along the thickness of the material. For PVDF aged in crude oil, it was found that for shallow indentations the viscoelasticity effects are minimized. For deeper indentations it was possible to observe a loss of rigidity with aging time. The technique also allows to determine yield behavior.Copyright

Effect of Supercritical CO2on PVDF

The pre-salt fields have a high content of carbon dioxide (CO2) that can be in the supercritical state due to reservoir conditions of temperature and pressure. This high concentration of carbon dioxide has a direct impact on the strategies used in the exploration and exploitation of the reservoir, including the selection of materials and equipment used in the wells. Risers are parts of flexible lines made up of several layers and are very important equipment in offshore operations. Flexible lines are widely used in various operations to extract and transport fluids in the wells, as well as one of the solutions to the challenges of the pre-salt. Poly (vinylidene fluoride) (PVDF) is a polymer used in the manufacture of the sealing layer of the risers. In this paper, PVDF samples were exposed to supercritical CO2 and analyzed for volume, density and mechanical properties and compared to unexposed PVDF.Copyright

Synthesis of Powders Nanometer Al2O3 Method by Sol-Gel

This study aimed to produce nanometric powders of alumina by sol-gel route. Six samples were produced by varying the amount of water for dilution of aluminum nitrate and the calcination temperature. The final products were evaluated by thermogravimetric analysis, scanning electron microscopy, X-ray diffraction and particle size. It could be noticed that, beyond the time of gelation and calcination temperature, the addition of water also influenced the average size of the clusters.

Processing and Characterization of Al2O3-YAG Composite

Oxide ceramics show better oxidation resistance at high temperatures than other ceramics; however they are more susceptible to plastic deformation at elevated temperatures [. If their high temperature mechanical properties could be improved, they would be expected to open a wide range of applications as structural material [2, 3]. Several studies have revealed [4, 5] the potential use of YAG oxides as reinforcing component oxide in a ceramic matrix. Both YAG and Al2O3 have similar thermal expansion coefficient and they are chemically stable because of their low O2 vapor pressure. In addition, there is no solid state phase transition as the temperature rises, but the eutectic reaction at 1826°C with Al2O3 molar concentration of 81.5% and 18.5% for Y2O3 which enable a fusion processing, turning the Al2O3-YAG composites very attractive. This eutectic reaction is possible in the restrictive composition from 18.5 to 20.5 mol% Y2O3 [6].

Efeito da zircônia na sinterização de SiC com adições de Al2O3 e Y2O3

The liquid phase sintering of silicon carbide (SiC) with additions of Al2O3 , Y2O3 and ZrO2 was studied. The high energy milling process resulted in the secondary additivation of the powder, being ZrO2 the major phase. The final microstructures showed a strong influence of the crystalline phases on the average size of the particles, as well as on the ZrO2 content. The secondary additivation of ZrO2 and the consequent formation of the ZrC phase showed a beneficial effect on densification. The sintering obtained by ultrafine powders with milling times of 4 and 6 h and with ZrO2 contents of 12% and 16%, respectively presented values of apparent densities higher than 95%.

Moagem de pós de carbeto de silício em moinho planetário

Po de alfa carbeto de silicio (a-SiC) foi cominuido em moinho planetario durante os periodos de tempo de ½, 2, 4 e 6 h. A velocidade de rotacao foi de 300 rpm, o meio de moagem foi alcool isopropilico e os corpos moedores foram esferas de zirconia estabilizada com ceria. Os pos cominuidos foram caracterizados quanto ao tamanho e distribuicao de tamanho de particula, a composicao quimica, as fases cristalinas e a morfologia. Observou-se uma grande reducao no tamanho de particulas, que passaram de micrometricas para submicrometricas e ate nanometricas, alteracao da distribuicao das mesmas de bimodal para unimodal, e a geracao de aditivacao secundaria causada pelo meio de moagem.