Raquel V. Vaz

Shear viscosity and nonlinear behavior of whole blood under large amplitude oscillatory shear

We investigated experimentally the rheological behavior of whole human blood subjected to large amplitude oscillatory shear under strain control to assess its nonlinear viscoelastic response. In these rheological tests, the shear stress response presented higher harmonic contributions, revealing the nonlinear behavior of human blood that is associated with changes in its internal microstructure. For the rheological conditions investigated, intra-cycle strain-stiffening and intra-cycle shear-thinning behavior of the human blood samples were observed and quantified based on the Lissajous-Bowditch plots. The results demonstrated that the dissipative nature of whole blood is more intense than its elastic component. We also assessed the effect of adding EDTA anticoagulant on the shear viscosity of whole blood subjected to steady shear flow. We found that the use of anticoagulant in appropriate concentrations did not influence the shear viscosity and that blood samples without anticoagulant preserved their rheological characteristics approximately for up to 8 minutes before coagulation became significant.

Performance of sub-micron diamond films coated on mould inserts for plastic injection moulding

In this article, results obtained from an investigation focusing on the application of diamond coatings on inserts for thermoplastic injection moulding applications are reported. The injection moulding industry can potentially benefit significantly from the use of diamond coatings on moulds typically employed in the injection moulding systems. Diamond films were coated on steel and onto silicon inserts and subsequently tested in real operating conditions. The moulded objects were analysed and the results were compared between bare steel and silicon inserts. The as-grown diamond coatings were characterised prior to and post the routine injection cycles using a number of techniques, such as Raman spectroscopy and SEM. Furthermore, the polymer finishing quality was assessed by optical microscopy for each material and coating used, and the results are presented and discussed in this article.

Carbon diffusion into steel during diamond chemical vapour deposition

In this study, we investigate the diffusion of carbon (C) and other elements into steel substrates (Impax Supreme?) during diamond chemical vapour deposition (CVD). The substrate temperature varied from 700 to 850?C by plasma power manipulations to enable the correlation of substrate temperature with diffusion length and depth of the above mentioned critical elements into steel during film growth conditions. Methane concentration is also a parameter which has been considered during the parametric analysis. The crystalline compounds formed during the diamond growth process were studied using XRD analysis. In addition, SIMS technique is used with depth profiling to monitor the diffusion of elements induced by the process. The results obtained enabled to improve traditional understanding about the mechanisms relating to diamond deposition on steel substrates using CVD processes.

Diffusion of critical elements in steel during thermal treatments in a diamond chemical vapour deposition atmosphere

In this study, it will be investigated the diffusion of critical elements, namely, carbon (C) and iron (Fe), into a steel substrate (Impax Supreme) during the diamond chemical vapour deposition (CVD) process. The substrate temperature was varied from 700 to 850°C by plasma power manipulations to enable the correlation of substrate temperature with diffusion length and depth of the above mentioned critical elements into steel during film growth conditions. Methane concentration is also a parameter which has been considered during the parametric analysis. The crystalline compounds formed during the diamond growth process are studied using XRD analysis. In addition, SIMS technique is used with depth profiling to monitor the diffusion of elements during the process. The results obtained enabled to improve traditional understanding about the mechanisms relating to diamond deposition on steel substrates using CVD processes.