Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Dispersing nanodiamond (nD) particles in metallic matrices can be achieved by ball milling resulting in metal-diamond composite powders. The matrices have been selected considering the whole range of carbon affinity: copper that shows extremely reduced affinity towards carbon phases, potentially compromising the composite interfaces, and nickel and tungsten that are mild and strong carbide formers, respectively, displaying thus intermediate and strong carbon affinities. For the latter matrices, dispersing carbon phases represent a challenge due to carbide conversion.

The materials produced are designated as Cu-10nD, Ni-10nD and W-20nD (where 10 and 20 indicate the atomic fraction of nD). Close monitoring of the milling conditions enabled to homogeneously disperse the carbon phases and obtain nanostructured matrices (Figures 1 (a-c)), as well as to minimize milling media contamination and carbide formation, especially in the case of the W-based composite. Apparent interfacial bonding could be inferred the from transmission electron microscopy (TEM) images.

The metallic matrices have been subsequently dissolved to allow for a detailed analysis of nanodiamond. Electron diffraction demonstrated that its crystalline structure was preserved during milling (Figure 2). Microhardness measurements revealed remarkable strength enhancements of the nanostructured composites over that of pure metals of comparable grain sizes (Table 1). The strengthening mechanisms that justify the hardness increments in Cu-10nD and Ni-10nD include second-phase reinforcement (due to the potential load bearing ability of diamond), as well as Orowan and solid solution strengthening. The hardening effect observed in the W-20nD composite over that of pure milled tungsten is probably related to the nanodiamond reinforcement, nevertheless the influence of a fine dispersion of carbides cannot be ruled out.

This work has been performed under the Contract of Association between EURATOM and Instituto Superior Tecnico. Financial support was also received from the Fundação para a Ciência Tecnologia (FCT) grants with references PTDC/CTM/100163/2008, Pest-OE/SADG/LA0010/2011 and PEST-OE/CTM-UI0084/2011.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Tungsten (W) was select for an extensive use in nuclear fusion devices due to its low neutron activation, high melting point and sputtering threshold as well as low hydrogen inventory. Nevertheless, W is brittle at low and moderate temperatures, which results in abnormal thermal stress, component fracture and extra erosion under reactor operation due to inherent thermal cycling events. An attractive way to solve these problems involves the addition of other refractory metals in the W matrix and tantalum (Ta) is a natural candidate. It has a high ductility, toughness and radiation resistance relative to those of W and transmutes to W by high-energy neutron irradiation. Recently, IST proposed the production of W-Ta composite by mechanical synthesis.

The composite should reveal the individual properties of the pristine phases as long as the interdiffusion between the components is significantly avoided during the consolidation/sintering route of the final material. Sintering operations at temperatures higher than 1300ºC lead to significant improvements in the final densification and thermal conductivity of the composites, which is crucial for fusion applications. However, W and Ta interdiffusion can be relevant above 1300ºC, mainly due to diffusion of W into Ta, and the aim of the present work is to control the mechanism.

W-Taf composites presenting 10 and 20 at.% of Ta where produced by alloying W powders and Ta fibres with a planetary ball milling route (MA) and by consolidating the mixture with spark plasma sintering (SPS) in the 1300-1600ºC temperature range. The final densifications remain fairly constant in both composites after sintering at different temperatures (83 to 87%) and the elemental interdiffusion remained low at 1300ºC. Nevertheless, the diffusivity of W in Ta became significant at 1600ºC, leading to the formation of a solid solution zone with a stoichiometry close to W16Ta84. The mechanism was followed by scanning electron and energy-dispersive X-ray spectroscopies (SEM/EDS; Figures 1 and 2, Table 1). Fabrication routes yielding high densifications and low interdiffusion are currently under investigation.

The work has been supported by the Contract of Association between Euratom and IST and by the Fund. Ciência e a Tecnologia contracts PTDC/CTM/100163/2008, Pest-OE/SADG/LA0010/2011 and PEST-OE/CTM-UI0084/2011.

The high melting point, high sputtering threshold and low tritium inventory rendered W as a potentially suitable material in fusion devices. The major problem associated with presently available tungsten grades as structural materials is its brittleness at lower temperatures. This is further worsened by irradiation embrittlement. A strategy for ductility improvement is producing a composite, with the brittle W matrix being reinforced by short fibres of tantalum. As Ta is more ductile than W it can therefore divert or stop cracks propagating in the W matrix. In the present research Ta short fibres and powder were used as reinforcement component for W by alloying Ta short fibres or powder in a W powder matrix. The composites were subsequently irradiated with deuterium to assess the retention of this hydrogenic species in the materials.

The irradiated composites, with Ta contents of 10 or 20 at%, were produced from pure elemental powders (W-Ta powder composites), and pure W powder and Ta fibre (W-Ta fibre composites) with 100 μm in diameter by low energy ball milling in argon atmosphere. These materials were consolidated via spark plasma sintering (SPS) in the temperature 1200 to 1600 ºC range. Pure W and Ta plates (controls) and W-Ta composites were irradiated with He+ ions (optional pre-implantation step) and D+ ion beams at room temperature with fluences in the 1020-1021 at/m2 range. Blistering and deuterium retention in W and Ta plates and in W-Ta composites were studied with scanning electron microscopy (SEM), X-ray diffraction and thermal desorption analysis. The deuterium concentration was evaluated trough nuclear reaction analysis (NRA) using 0.75 to 2.1 MeV 3He+ beam and the D(3He,p)α reaction.

The investigations showed that deuterium irradiation induced microstructural modifications producing blistering in Ta plates as well as in W-Ta composites (Figure 1). These effects increased substantially in the Ta and W-Ta materials with the He pre-implantation step, while blisters have not been observed in the W plates either for D+ or He+ plus D+ implantation. Higher deuterium retention was observed by thermal desorption for the composites than for the W plates. Moreover the present study revealed that D+ trapping in the composites is dependent on the microstructure with higher retention observed for fibers than for powder.

This work has been performed under the Contract of Association between EURATOM and Instituto Superior Tecnico. Financial support was also received from the Fundação para a Ciência Tecnologia (FCT) grants with references PTDC/CTM/100163/2008, Pest-OE/SADG/LA0010/2011 and PEST-OE/CTM-UI0084/2011. The authors wish to acknowledge Jorge Rocha the implantation in W-Ta samples.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Due to its good thermal and electrical conductivity, improved plastic properties and excellent corrosion and oxidation resistance, copper is being widely used worldwide. Nevertheless, for some particular application, it is still desirable to improve copper strength, wear and fatigue resistance properties. These characteristics can be enhanced by suitable modification of materials microstructure by using solid state processing techniques, such as Friction Stir Processing (FSP). This technique makes use of non-consumable rotating tools to induce heat and severe plastic deformation in the materials to be processed. The complex thermo-mechanical phenomena developed inside the stirred volume, promotes strong microstructural modifications, which cautiously controlled, enables deeply transforming the microstructure of the materials being processed. In fact, FSP thermo-mechanisms leads to significant grain refinement, which drove the use of this technique towards producing ultrafine grained structural metallic materials from aluminium and other ductile metallic alloys. Due to the high macro and microstructural heterogeneity resulting from FSP methodologies, as well as the extremely refined structure resulting from it, the microstructural characterization of processed materials is an especially difficult task, which requires skilled researchers as well as important microscopy and microanalysis resources.

In present work, 1 mm thick plates of phosphorus deoxidised copper (Cu-DHP), temper class R 240, were friction stir processed using the conical and scrolled shoulder tools, shown in Figure 1, and varying processing parameters, namely, two different tool rotation rates (ω = 400 and 1000 rpm) and a constant traverse speed (v) of 250 mm/min. The specimens for analysis were removed transverse to the processing direction, and prepared for both optical and TEM analysis. The optical micrograph images were obtained from polished specimens, etched with FeCl3 and Hid reagents. Samples for TEM were polished mechanically from both sides down to a thickness of about 0.15 mm and then electropolished using a double jet thinner. A dilute solution of orthophosphoric acid (2:1) at room temperature under 10V tension was used. TEM analysis was carried out at 100 kV.

A strong influence of the processing conditions on the microstructural refinement was observed, being found that the tool geometry, which has a close relation with the plastic deformation and dynamic recrystallization kinetics, inside the stirred volume, is determinant in FSP results. In Figures 2.a and b are shown, respectively, optical and TEM images of the non-processed material, showing a coarse grain structure with mean grain size of 18 sm. Most of the grains display families of parallel slip lines, as shown in the TEM image of Figure 2.b. In the same way, microstructural analysis of the processed samples revealed the formation of more or less refined grain structures, according to the processing conditions in use. In Figures 3 and 4 are shown pictures of processed samples, obtained using the conical and scrolled shoulder tools under hot (ω = 1000 rpm) and cold (ω = 400 rpm) processing conditions. For the samples processed with the conical tool and hot processing conditions (Figure 3.a), the average grain size (8 m) was clearly coarser than that of the sample processed at 400 rpm (Figure 3.b), for which the average grain size registered was 1 m. For the samples processed with the scrolled tool (Figure 4) no important differences in grain size were obtained when changing the tool rotation rate. A significant decrease in grain size, up to 500 nm, was registered for these samples. By comparing the results it is possible to conclude that, under similar processing conditions, the scrolled tool induced higher grain refinement than the conical tool, which is related with the stronger plastic deformation achievable with this geometry.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Rare-earth intermetallic compounds with high Fe concentrations and adopting the ThMn12–type and Th2Zn17-type structures have attracted considerable attention in the field of permanent magnets. A large number of experimental studies has been done on these compounds, which are usually measured on alloys structurally characterized only by powder X-ray diffraction (XRD). However, the materials are often multiphasic and their quenched or annealed microstructures evidence homogenization ranges, second phases (resulting from segregation) and on-going phase transformations that may not be easily detectable by XRD. Additional microstructural studies on these systems are therefore required.

Among the Fe-based systems, the ThMn12–type and Th2Zn17–type structures usually require stabilization by a third element, such as Ti. In the present work Nd:11Fe:Ti has been prepared by melting Nd, Fe and Ti in an arc furnace followed by subsequent splat-quenching and/or annealing treatments. The resulting materials have been characterized by XRD, scanning and transmission electron microscopy coupled with energy dispersive spectroscopy.

The results have shown that the presence of α-Fe(Ti) could not be avoided during the solidification of the Nd:11Fe:Ti alloy. Furthermore, the microstructure morphologies and elemental analyses showed that at moderate cooling rates a secondary crystallization phase of Th2Zn17–type appeared in the Nd:11Fe:Ti alloy as result of a peritectic reaction. This lower temperature phase was however not detected in the splat-quenched material, where the high cooling rate route suppressed its crystallization. Nevertheless during a subsequent heat-treatment at 800 ºC the following decomposition took place: NdFe11Ti → Nd2(Fe,Ti)17 + α-Fe(Ti) + Fe2Ti. This reaction had already been proposed by Jang and Stadelmaier, who suggested that the NdFe11Ti compound is unstable at temperatures below 1000 °C. The current study shows that this transformation results in the fine lamellar intergrowth of the Th2Zn17-type phase in ThMn12-type grains, displaying random distribution of planar defects (Figure 1). The reciprocal space of the combined parent and intergrown phases has been mapped through a series of 3-D microdiffraction experiments (Figure 2). This allowed to establish that the preferred orientation relation between the two phases is (020)1:12//(003)2:17 and [100]1:12//[110]2:17, with the invariant plane sitting at 1:12//(333)2:17 planes.

The work was supported by the Portuguese Science Foundation through the CTM/48617/2002, PEst-OE/CTM-UI0084/2011 and CFMC-PEst-OE/FIS/UI0261/2011 grants.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Polymer nanocomposites are a recent class of materials that have drawn considerable attention in recent years, due to the significant improvements in several properties. Even though a lot of research has been performed on the preparation of these materials, the homogeneous dispersion of nanoparticles in polymeric matrices, especially in non-polar, is still a difficult task. Thus, frequently nanocomposites exhibited worst properties than conventional polymers that limit their effective application. One way to improve nanoparticles dispersion is by using an in situ sol-gel method, which is based on a reaction between a precursor, containing the inorganic particle, and a polymer followed by hydrolysis-condensation reaction. Therefore, the present work aims to use microscopy techniques to investigate the dispersion of nanoparticles containing aluminium in PP and EVA matrices, prepared by a sol-gel process in the melt.

Polypropylene modified with maleic anhydride (PP-g-MA, Polybond 3200) supplied by Crompton and ethylene-vinyl acetate (EVA) with 12 wt.% (EVA12, Escorene Ultra UL 00112) and 27 wt.% (EVA27, Escorene Ultra UL 00328) of vinyl acetate supplied by Exxon Mobil, were used as organic matrices to prepared the nanocomposites. The precursor, aluminium isopropoxide (Al(Pr-i-O)3), used as received in powder state, was supplied by Sigma Aldrich. Nanocomposites with the same composition were prepared by melt mixing in an internal mixer under constant processing conditions, as previously describe by Oliveira. The hybrid nanocomposite (HN) synthesized with PP-g-MA was called HN-Pr, with EVA12 was HNEVA12 and the one synthesized with EVA27 was HNEVA27.

Samples characterized by SEM were fractured at low temperature and gold coated. Samples analysed by TEM were sectioned by cryo-ultramicrotomy using a diamond knife at -60 ºC and -140 ºC under liquid nitrogen for EVAs and PP-g-MA nanocomposites, respectively. X-ray microanalysis mapping was performed in 300 μm2, in the same place where SEM analysis was made, with an energy dispersive X-ray Spectrometer (EDS) from Link eXL II from Oxford Instruments attached to the SEM.

SEM micrographs presented in Figure 1a, b and c show that while HN-Pr has a homogeneous and rough surface, HNEVA12 and HNEVA27 have homogeneous and smoother surfaces. The presence of nanoparticles agglomerations can not be observed in the micrographs, which indicates a good dispersion and interaction between organic and inorganic components. Therefore, in order to investigate nanoparticles dispersion TEM analysis were performed and the results presented in Figure 2 evidence different degrees of nanoparticles dispersion in polymeric matrices and distinct sizes. The best dispersion was achieved in HN-Pr followed by HNEVA27. The average particle size is 200, 130 and 120 nm for HN-Pr, HNEVA12 and HNEVA27, respectively. The differences in particles dimension can be explained by the extension of the chemical reaction, which in agreement with other techniques, it was higher for EVA27. EDS analysis results presented in Figure 3 render 2.84, 5.07 and 3.49 % of aluminium content in the analysed area of HN-Pr, HNEVA12 and HNEVA27, respectively.

In this study, it was observed that reaction extension has a great influence on size and dispersion of the generated nanoparticles. According to SEM and TEM results, the smallest nanoparticles were achieved in EVA27. Moreover, for the three nanocomposites prepared well dispersed nanoparticles were obtained. The EDS spectrum confirmed the presence of aluminium in nanocomposites structure.

This work showed that microscopic technics are very powerful on the characterization of new polymer matrix nanocomposites.

The authors are grateful to the Portuguese Foundation of Science and Technology (FCT) Project SFRH / BD / 39085 / 2007 for the financial support.

There is a wide range of surface analysis techniques which are, generally, complementary. Nuclear and non-nuclear techniques have been available. Nuclear techniques, which are non-destructive, provide for analysis over a few microns close to the surface of the sample, giving absolute values of concentrations of isotopes and elements. They have been applied in areas such as scientific, technologic, industry, arts and medicine, using MeV ion beams. Nuclear reactions permit tracing of isotopes with high sensitivities. We use ion-ion nuclear reactions, elastic scattering and the energy analysis method where, at a chosen energy of the incident ion beam, an energy spectrum is recorded of ions from nuclear events, coming from several depths in the target. Such spectra are computationally predicted, giving target composition and concentration profile information. A computer program has been developed in this context, mainly for flat targets. The non-flat target situation arises as an extension. Successful applications of the method are given using the 18O(p,α0)15N reaction and elastic scattering of (4He)+ ions. SEM and TEM are used as useful complementary techniques.

Two types of samples were prepared containing thick and thin oxides, respectively. The first sample (S1) was obtained by high temperature oxidation of austenitic steel in C 18O2 gas. Weight gain measurements had given a 4.2 μm thick oxide. SEM has shown a reasonably flat oxide (Figure 1 (a)). The second sample (S2, also labelled Al/Al2O3) was obtained by anodization of high purity aluminium at 100V in an aqueous solution of ammonium citrate. An oxide thickness of 0.1370 μm was expected. TEM has given an oxide film thickness of 0.1340 μm (Figure 1 (b)). The 18O(p,α0)15N reaction at Ep=1.78 MeV and 165º was used to analyse sample S1. Figure 2 (a) shows a good computed fit to data. A 18O step concentration profile was found, corresponding to a thick 18O oxide with thickness X1=4.4 μm. Sample S2 was analysed by elastic scattering of α particles at Eα=2.0 MeV and 165º. Figure 2 (b) shows a good computed fit to data. A thin oxide film thickness of X1=0.1350 μm was found, close to the TEM value. The fit also shows a ratio of atomic densities of O and Al slightly above 1.5. The combined use of nuclear techniques, SEM and TEM microscopy has proved to be very important for surface analysis of materials. The reported results would be difficult to obtain by other techniques.

Supports from University of Beira Interior and FCT (Fundação para a Ciência e a Tecnologia)/PEst-OE/FIS/UI0524/2011 (Projecto Estratégico-UI524-2011-2012) are acknowledged.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Rare-earth intermetallic compounds adopting the tetragonal ThMn12–type structure and containing high Fe concentrations have attracted considerable attention in the field of permanent magnets. Among them, the Y-Fe-Mo series has been extensively investigated, especially by X-ray diffraction (XRD), but the microstructural characterization was very limited.

In the present work, Y:11Fe:Mo has been prepared by melting Y, Fe and Mo in an arc furnace followed by splat-quenching and/or annealing treatments. The structure, chemistry and magnetic domain configurations of the resulting polycrystalline aggregates have been investigated by XRD, scanning and transmission electron microscopies (SEM and TEM, respectively), energy dispersive X-ray spectroscopy (EDS) and Lorentz microscopy.

A special emphasis was given to Lorentz microscopy, where contrast is based on the Lorentz deflection imposed on electrons by the passage through a magnetic specimen. The magnetic domains have been imaged by the intermediate lens in Fresnel mode, with the objective lens switched off. In these conditions the intermediate lens is defocused so that out-of-focus images of the specimen are formed: the magnetic domain walls are imaged as alternate bright (convergent) and dark (divergent) lines. For the overfocused image, bright lines occur at the position of domain walls for which the magnetisation on either side is deflecting the electrons towards the wall, whereas dark lines are observed at the walls for which the magnetisation on either side is deflecting the electrons away from the wall. The opposite contrast is observed at the underfocused image.

The results have shown that the tetragonal YFe11-xMoy phase is predominant, with a cellular dendritic morphology (Figure 1), but a considerable presence of -Fe(Mo) could be inferred, forming a coarse intercellular eutectic mixture. Significant Fe segregation occurred during annealing. However, this composition variation corresponded to an extremely limited evolution of the lattice parameters, the Rietveld analysis pointing to Fe vacancies at the 8i sites on the annealed material. XRD and EDS results indicate that the fraction of point defects in the ThMn12-type structure adapts to the processing route and that the stable configuration depends on the temperature. The current study also showed that grain boundaries are usually associated with domain walls and that YFe11Mo grains present internal domain walls forming stripe/maze patterns characteristic of high anisotropy materials (Figure 2), while residual -Fe(Mo) grains exhibit vortex configurations (see arrows in Figures 2 (a-c)).

The work was supported by the Portuguese Science Foundation through the CTM/48617/2002 and PEst-OE/CTM-UI0084/2011 grants.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

ION JELLY® patented technology is based on the cross-linking of Ionic Liquids (ILs) with Gelatin that results in a viscous gel that can be molded into a film or a block, and solidifies by cooling below 35 ºC . The outcome of this combination is a transparent, light and flexible conductive polymer that adapts perfectly to a great variety of surfaces. Some of the key properties of ION JELLY® are: high stability up to 180ºC, large electrochemical window and bio-compatibility. Taking in consideration the attractive attributes of ILs, that provide a stable and friendly environment for the enzymes, where they retain their catalytic activity, combined with the morphologic advantage of gelatin, we have decided to study this new protein-ionic-based material regarding water content, swelling behaviour, and structural morphology by scanning electron microscopy (SEM).

The properties of [emim][EtSO4] and [bmim][N(CN)2] ION JELLY® films were compared with those of solely gelatin. Thin films were prepared with different amounts of water or phosphate buffer and left to maturate in a controlled atmosphere for 4 days. Swelling was carried out in water at 4ºC and films were lyophilized afterwards. SEM images of ION JELLY® and gelatin films were obtained prior and after these steps.

ION JELLY® films were rubbery while gelatin films were glassy. Water-made ION JELLY® had completely smooth surfaces, just like gelatin, but buffer-made ION JELLY® exhibited salt crystals on the surface, as well as some superficial pores (Figure 1). Free water content in [emim][EtSO4] ION JELLY® was found to be greater than [bmim][N(CN)2] ION JELLY® and gelatin.

The swelling ratio of both types of ION JELLY® was close to 100%, while gelatin swelled 8 times more. The swollen lyophilized gelatin films formed a heterogeneous and highly porous network (Figure 2), while ION JELLY® films were more homogeneous with a lower degree of porosity (Figure 3).

These results showed that ION JELLY® is a polymer with a more tightly bound structure than gelatin. This material allows water to penetrate, but possesses a higher rigidity that prevents too much mobility of the polymeric chains. Considering that it’s a biocompatible polymer, lyophilized swollen ION JELLY® could have potential applications as a scaffold for biological material.

Financial support received from the Portuguese Science and Technology foundation (Fundação para a Ciência e Tecnologia) under the grants SFRH/BD/77568/2011, PTDC/EBB-BIO/114288/2009, PTDC/EBB-BI/099237/2008 and SFRH/BPD/41175/2007 and Projecto Estratégico IBB: PEst – OE/EQB/LA0023/2011

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

A gold solidus of Valentinian I, Emperor of Rome (A.D. 364-375) shown in Figure 1, and belonging to a private collection, was subjected to material and stylistic analysis, in order to ascertain about its authenticity. Due to the rarity of such a coin, only non-destructive analytical techniques were used, namely Scanning Electron Microscopy (SEM), Particle Induced X-ray Emission (PIXE), electrical resistivity and optical microscopy.

Examination by SEM revealed that, in common with coins minted by this emperor, the solidus was die-struck as evidenced by the surface flow lines indicating metal movement under the dies (Figure 2). Wear traces presented an unorganized pattern. The coin was also examined for signs of stress-corrosion cracking but no evidence of this were found. The coin also shows traces of what appear to be soil residues; small quantities of these residues can also be seen in porosities in the coin face (arrow in Figure 3).

Analysis by PIXE showed that the coin was made from an alloy of gold (97.9%), silver (2.0%) and copper (0.1%) (Figure 4). The high gold content is likely to be overestimated due to surface depletion of the silver and particularly the copper, which is caused by slight dissolution of these more reactive metals in the burial environment. Nevertheless, this effect is usually small and in agreement with other solidus from Valentiniano I. Also, the high gold content may lie behind the lack of stress-corrosion cracking.

The presence of platinum group element (PGE) inclusions is, in some cases, indicative of alluvial gold provenience. Both, optical microscopy and PIXE, were used to detect them but it was not possible to identify their presence. Typically, the concentration of these elements is in the order of ppm, although for this specific period different values have been reported. Considering the experimental conditions used (2 MeV accelerated proton beam and a 50 μm Mylar foil in front of the X-ray detector) the limit of detection of the PIXE technique is close to the expected trace concentration. More energetic proton beam (>3MeV) or the use of specific filter for the X-ray signal in the low energy region, i.e. Zinc foil 75 μm thick, are the future experiments to be carried out in order to detect the presence of such characteristics PGE elements.

In order to understand the presumable surface gold enrichment, electrical conductivity measurements were used. The values obtained (1.50-1.56)x1017 S/m show a lower conductivity as compared with the reference value for a 97% Au, 3% Ag alloy (3.54x1017 S/m), indicating that indeed the coin bulk has a lower gold content.

As for the stylistic analysis, there is no sound agreement about the coin authenticity, but the tendency is to consider it a good one. The compositional and structural characterization of cultural heritage artefacts usually limit the number of available techniques to those considered as non-destructive and non-invasive, such the one presented in this work. This restriction also constricts and difficult the desired straight conclusions but, on the other hand, increase the multidisciplinary of the work, applying techniques usually dedicated to the material science characterization to cultural heritage.

V. Corregidor acknowledges the funding support from the FCT-Ciência program. Financial support was also received through the PEST-OE/CTM-UI0084/2011 and PEST-OE/FIS/UI0275/2011 grants.