Browsing by Author "Rodrigues, P. C. R."
Now showing 1 - 3 of 3
Results Per Page
Sort Options
- Gibbs-Thomson effect as driving force for liquid film migration: Converting metallic into ceramic fibers through intrinsic oxidationPublication . Dias, Marta; Rosinski, M.; Rodrigues, P. C. R.; Correia, J.B.; Carvalho, Patricia AlmeidaABSTRACT: Liquid film migration is of great practical importance in materials engineering. The phenomenon has been shown to depend on thermal gradients and coherency strain, but no single driving mechanism seems capable of justifying the whole array of experimental observations. On the other hand, the inevitable capillarity effects are often disregarded due to the unknown 3-dimensional geometry of the system. Here, we present evidence of liquid film migration governed primarily by capillarity through a microstructural setup of cylindrical interfaces that allows clear interpretation and modeling. The experiments rely on the strong oxygen-gettering ability of tantalum fibers dispersed in a tungsten matrix and on field-enhanced diffusivity provided by pulse plasma compaction. Tantalum scavenges the residual oxygen present in the W powder and, as a result, oxide films grow around the fibers. These oxide tubes, in liquid state during sintering, migrate toward the fiber axis and eventually become oxide rods surrounded by metallic Ta. The process is driven by the Gibbs-Thomson effect that generates the required composition gradient across the liquid film. An analytical description of the film evolution is implemented by combining the incoming O flux with capillarity-driven migration. Possible contributions from other mechanisms are examined and the relevance of the Gibbs-Thomson effect to the general phenomenon of liquid film migration is established.
- O projecto EXCITEPublication . Caldeira, Rita; Gonçalves, M. A.; Guimarães, Fernanda; Rodrigues, P. C. R.; Walter, S.; Guedes, A.; ter Maat, G.ABSTRACT: The EXCITE (Electron and X-ray microscopy Community for structural and chemical Imaging Techniques for Earth materials) project, unites leading European facilities for electron and X-ray microscopy of earth materials. This project is mainly focused in providing access to existing high-end facilities in the field of earth and material sciences and, by this, enabling knowledge and experience exchanging of staff and potential users of the different key facilities (cutting-edge electron and X-ray microscopy) accessible for earth and material scientists as well as other potential users. LNEG and FCUL and FCUP provide access to their electron microprobe facilities. EXCITE is also committed to develop community-driven technological imaging advancements that will strengthen and extend the current implementation of state-of-the-art microscopy for earth-materials research.
- Transition metals responsible for striking colour variation in tourmalines : an EMP study of tourmalines from granites and quartz-tourmaline rocks associated to the Penamacor-Monsanto pluton (Eastern Central Portugal)Publication . Costa, Isabel Ribeiro da; Antunes, I. Margarida H. Ribeiro; Guimarães, Fernanda; Rodrigues, P. C. R.; Barriga, Fernando; Mourão, C.; Ramos, João Farinha; Hernandez, Récio