Effects of age condition on the distribution and integrity of inorganic fillers in dental resin composites

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Compósitos preparados a partir de resíduo industrial de couro com elastômeros termoplásticos obtidos através de blendas de polietileno de baixa densidade e borracha natural

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Corrosion behaviour of aluminium syntactic functionally graded composites

Syntactic Functionally Graded Metal Matrix Composites (SFGMMC) are a type of composites reinforced by microballoons exhibiting a graded reinforcement distribution. These materials constitute a promising new generation of lightweight structural materials for aerospace, marine and shielding/insulation applications. In this work, A356 alloy reinforced with silica-alumina microballoons (SiO2-Al2O3) was processed by casting techniques. The influence of the microballoon distribution gradient on the corrosion behaviour of the composite was investigated by potentiodynamic polarisation and Electrochemical Impedance Spectroscopy (EIS). Composite surfaces were analysed before and after testing by Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) to determine the influence of microstructural changes.

A graphical tool for the tomographic characterisation of microstructural features on metal matrix composites

Research on the micro-structural characterization of metal-matrix composites uses X-ray computed tomography to collect information about the interior features of the samples, in order to elucidate their exhibited properties. The tomographic raw data needs several steps of computational processing in order to eliminate noise and interference. Our experience with a program (Tritom) that handles these questions has shown that in some cases the processing steps take a very long time and that it is not easy for a Materials Science specialist to interact with Tritom in order to define the most adequate parameter values and the proper sequence of the available processing steps. For easing the use of Tritom, a system was built which addresses the aspects described before and that is based on the OpenDX visualization system. OpenDX visualization facilities constitute a great benefit to Tritom. The visual programming environment of OpenDX allows an easy definition of a sequence of processing steps thus fulfilling the requirement of an easy use by non-specialists on Computer Science. Also the possibility of incorporating external modules in a visual OpenDX program allows the researchers to tackle the aspect of reducing the long execution time of some processing steps. The longer processing steps of Tritom have been parallelized in two different types of hardware architectures (message-passing and shared-memory); the corresponding parallel programs can be easily incorporated in a sequence of processing steps defined in an OpenDX program. The benefits of our system are illustrated through an example where the tool is applied in the study of the sensitivity to crushing – and the implications thereof – of the reinforcements used in a functionally graded syntactic metallic foam.

Nanostructured TiO2-based composites for light absorption

Metal oxide nanocomposites were prepared by two different routes: polyol and sol-gel. Characterization by X ray diffraction showed that the first process produces directly a two-phase material, while the sol-gel powder never showed second phase below 600°C. Light spectroscopy of the treated powders indicated similarities for the processed materials. Although the overall material compositions are about the same, different structural characteristics are found for each processing. With the exception of Ti-Zn materials, all the double metal oxide powders showed higher absorbance than either TiO2 powder.

Tribocorrosion behaviour of hot pressed CoCrMo−Al2O3 composites for biomedical applications

Alumina/alumina wear couple can lower the wear rates and thus metallic ion releasing on load bearing metallic implant materials. However, the low fracture toughness of ceramics is still a major concern. Therefore, the present study aims to process and to triboelectrochemically characterise the 5 and 10 vol.-%Al2O3 reinforced CoCrMo matrix composites. Corrosion and tribocorrosion behaviour of the composites were investigated in 8 g L−1 NaCl solution at body temperature. Corroded and worn surfaces were investigated by a field emission gun scanning electron microscope equipped with energy dispersive X-ray spectroscopy. After tribocorrosion experiments, wear rates were calculated using a profilometer. Results suggest that Al2O3 particle addition decreased the tendency of CoCrMo alloy to corrosion under both static and tribocorrosion conditions. However, no significant influence on the corrosion and wear rates was observed in composites mainly due to increased porosity and insufficient matrix/reinforcement bonding.

Performance of different rubber tree clones against South American leaf blight (Microcyclus ulei)

This study was aimed to evaluate the behaviour of eighteen clones of Hevea brasiliensis (rubber) against South American leaf blight and tostudy progress of the disease. The experiment was conducted in Cachoeiro de Itapemirim-ES, where 18 clones were evaluated. The experi-mental design was a randomized block with four replicates; each experimental unit consisted of three plants. Evaluations were performed at15-day intervals on 30 leaflets per tree. Disease incidence was quantified and infection classified according to the stages of development andtype of damage. Leaf blight occurred during the entire experimental period; however, disease intensity varied with the resistance level of theclones and the time of year. Clones FX 3864, RRIM 725, RRIM 711, IAC 300 and IAN 873 exhibited the highest resistance to leaf blight.