Showing papers by "Ángel Justo published in 2010"

Tailored synthesis of nanostructured WC/a-C coatings by dual magnetron sputtering

Abstract: Nanostructured coatings with variable contents of tungsten carbide (WC) and amorphous carbon (a-C) are prepared by controlling the sputtering power ratio using WC and graphite targets. XRD and TEM/ED analysis shows that increasing the C incorporation, the WC nanocrystalline phases evolve from γ-W 2 C to β-WC 1 − x . Further C enrichment leads to a nanocomposite structure of small WC 1 − x crystals dispersed in a-C matrix. The a-C at.% is estimated by XPS analysis and correlated with the observed tribo-mechanical properties. The hardness and friction properties vary from hard/high friction (36–40 GPa; μ = 0.6–0.8) to moderate-hard/low friction (16–20 GPa; μ ∼ 0.2) coatings depending on the film composition. The transition point is found for a-C content of 10 at.%. This correlates with a change from nanocrystalline WC to nanocomposite WC 1 − x /a-C coatings. The overall study will help to understand the previous literature data and will serve as guide for a tailored synthesis of these WC/a-C nanocomposites.

Determination of pigments and binders in pompeian wall paintings using synchrotron radiation – high-resolution x-ray powder diffraction and conventional spectroscopy – chromatography

Abstract: The employment of synchrotron techniques complemented by conventional laboratory systems has allowed us to deepen and improve our knowledge of Roman wall painting procedures. The palette identified in wall paintings from Pompeii and Herculaneum from the second century bc includes goethite, hematite, cinnabar, glauconite, Egyptian blue, and other components such as calcite and aragonite. Proof of the use of organic binders is provided by FTIR and PY–GC/MS. Therefore, the possibility of the use of ‘a secco’ techniques cannot be ruled out. Pigments in wall paintings are usually found in small percentages and conventional X-ray diffractometers do not detect them. Synchrotron radiation – high-resolution X-ray powder diffraction has allowed identification with only a few micrograms of sample.