Precipitation in original Duralumin A-U4G versus modern 2017A alloy

Precipitation in Duralumin, a historic quaternary alloy of the type: Al–Cu–Mg–Si, was never fully studied nor observed by current electron microscopy techniques. This article presents the full characterization and comparison of two alloys: a Duralumin (A-U4G) from the 1950s collected on a vintage aircraft and its modern equivalent: a 2017A alloy. The as-received and peak-aging states were analysed with DSC, SAXS and TEM advanced techniques. It is shown that old Duralumin and modern 2017A present a similar nanoprecipitation in the as-received state and behave similarly upon artificial aging. As opposed to what has been reported in the past, three types of precipitates participating in hardening were found upon aging: θ’-Al2Cu, Q’(Q)-AlCuMgSi and Ω-Al2Cu

Acute aquatic toxicity to zebrafish and bioaccumulation in marine mussels of antimony tin oxide nanoparticles

Antimony tin oxide (Sb2O5/SnO2) is effective in the absorption of infrared radiation for applications, such as skylights. As a nanoparticle (NP), it can be incorporated into films or sheets providing infrared radiation attenuation while allowing for a transparent final product. The acute toxicity exerted by commercial Sb2O5/SnO2 (ATO) NPs was studied in adults and embryos of zebrafish (Danio rerio). Our results suggest that these NPs do not induce an acute toxicity in zebrafish, either adults or embryos. However, some sub-lethal parameters were altered: heart rate and spontaneous movements. Finally, the possible bioaccumulation of these NPs in the aquacultured marine mussel Mytilus sp. was studied. A quantitative analysis was performed using single particle inductively coupled plasma mass spectrometry (sp-ICP-MS). The results indicated that, despite being scarce (2.31 × 106 ± 9.05 × 105 NPs/g), there is some accumulation of the ATO NPs in the mussel. In conclusion, commercial ATO NPs seem to be quite innocuous to aquatic organisms; however, the fact that some of the developmental parameters in zebrafish embryos are altered should be considered for further investigation. More in-depth analysis of these NPs transformations in the digestive tract of humans is needed to assess whether their accumulation in mussels presents an actual risk to humans.Fundação para a Ciência e Tecnologia | Ref. 2020.04021.CEECIN

Transmission Kikuchi Diffraction, a powerful imaging technique for nanoscale structural characterisation of cultural heritage materials

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Chemical phase segregation during the crystallization of Ge-rich GeSbTe alloys

International audienceGe-rich Ge–Sb–Te alloys are materials with potential for new non-volatile memories named Phase Change Memories offering an extended range of possible applications. However, the origin of their superior properties, notably their much higher transition temperature and increased thermal stability, is unknown. Using a variety of transmission electron microscopy based techniques, we have investigated the changes that affect the structure and composition of such alloys during thermal annealing. We show that, although Ge-rich Ge–Sb–Te materials can be grown as amorphous layers of homogeneous compositions, the primary effect of annealing is to activate phase separation between stable Ge and Ge–Sb–Te phases. This phase separation starts at 380 °C while the material is still amorphous and leads to the nucleation of the first Ge nanocrystals. Increasing the annealing temperature to 400 and then to 450 °C allows the crystalline Ge phase to grow by driving the Ge excess out of the matrix, which, finally, leads to the formation of large (30–50 nm) crystals with the face-centered-cubic Ge–Sb–Te structure. After annealing at 500 °C for 30 minutes, the layer fully crystallizes and consists of a population of large (50–100 nm) face-centered-cubic Ge–Sb–Te crystals with a stoichiometry close to 225 buried in a matrix composed of small Ge nanocrystals. This study evidences that the superior properties of Ge-rich alloys do not result from the intrinsic properties of some Ge-rich crystalline phases but from kinetic factors. The formation of a two phase Ge/Ge–Sb–Te material involves long range diffusion of atomic species, first and foremost, Ge

Impact of β-phase in TiAl alloys on mechanical properties after high temperature air exposure

International audienceIn this paper, the influence of high temperature air exposure on the tensile properties at room temperature and on the fatigue strength at high temperature of two TiAl alloys, is studied. The alloys, Ti-48Al-2Cr-2Nb (Ti-48-2-2), and Ti-44Al-4Nb-1Mo-0.1B (TNM-B1), both exhibit near-gamma microstructures, but the TNM-B1 alloy contains significant amounts of beta phase. Air exposure at high temperature (650-700°C, 500 h) induces significant loss of ductility, and decrease of fatigue strength at high temperature, in the case of the beta-containing TNM-B1 alloy, but not for the gamma-Ti-48-2-2 alloy. This indicates a potential influence of the presence of beta phase for embrittleme nt. Because embrittlement is believed to be the consequence of microstructure modifications in the sub-surface, first attempts have been performed to investigate these local phenomena. For this purpose, SEM, FIB, STEM-EDX and ACOM techniques have been employed. Destablilization of beta and, to a lesser extent, of gamma into alpha2, has been observed in the sub-surface of the TNM-B1 alloy. We interpret this as a consequence of oxygen diffusion during the high temperature air exposure, which would promote formation of alpha2 phase in which oxygen solubility is high, at the expenses of the beta and gamma phases of lower oxygen solubility

Synthesis of (B- and/or N-) substituted carbon nanoforms

cited By 0; Conference of 11th IEEE Nanotechnology Materials and Devices Conference, NMDC 2016 ; Conference Date: 9 October 2016 Through 12 October 2016; Conference Code:125383International audienceHeterogeneous single wall carbon nanotubes and graphene were synthesized using the electric arc method. The arc conditions were monitored to study the correlation between the operating parameters and the obtained products. Substitution with boron and/or nitrogen was confirmed through spectroscopic chemical analyses. It was found that, as soon as N is present in suitable amount, the formation of BN islands within the graphene lattice prevails over other atom arrangements

Synthesis of (B-C-N) Nanomaterials by Arc Discharge Using Heterogeneous Anodes

cited By 2International audienceIn spite of the current prevalence of the CVD-based processes, the electric arc remains an interesting process for the synthesis of carbon nanoforms, thanks to its versatility, robustness and easiness. It also allows performing in-situ substitution of carbon atoms by hetero-elements in the graphene lattice. Our work aims to establish a correlation between the plasma properties, type and chemical composition (and the substitution rate) of the obtained single-wall carbon nanotubes. The plasma was characterized by optical emission spectroscopy and the products were analyzed by high resolution transmission electron microscopy and core level Electron Energy-Loss Spectroscopy (EELS). Results show that a high boron content leads to a plasma temperature decrease and hinders the formation of nanotubes. This effect can be compensated by increasing the arc current and/or yttrium content. The optimal conditions for the synthesis of boron- and/or nitrogen-substituted nanotubes correspond to a high axial plasma temperature associated to a strong radial gradient. EELS analysis confirmed that the boron incorporates into the graphenic lattice

A new linear transfer theory and characterization method for image detectors. Part II: Experiment

International audienceA novel generalized linear transfer theory describing the signal and noise transfer in image detectors has been developed in Part I (Niermann, this issue, [1]) of this paper. Similar to the existing notion of a point spread function (PSF) describing the transfer of the first statistical moment (the average), a noise spread function (NSF) was introduced to characterize the spatially resolved transfer of noise (central second moment, covariance). Following the theoretic results developed in Part I (Niermann, this issue, [1]), a new experimental method based on single spot illumination has been developed and applied to measure 2D point and 4D noise spread functions of CCD cameras used in TEM. A dedicated oversampling method has been used to suppress aliasing in the measured quantities. We analyze the 4D noise spread with respect to electronic and photonic noise contributions

Natural aging on Al-Cu-Mg structural hardening alloys - Investigation of two historical duralumins for aeronautics

International audienceThis article presents the metallurgic study of sixty years old structural hardening Al-Cu-Mg alloys recovered from a double-deck aircraft Breguet 765. This study aims to characterize and understand the evolution of alloys over very long periods thanks to an approach coupling materials characterization and archives researches. The focus is made on two ancient age hardening Al-Cu alloys: A-U4G and A-U4G1, whose compositions are close to the international designations 2017A and 2024 respectively. Multi-scale structural investigation was carry out and mechanical properties were extracted. It is shown that despite natural aging during long periods, these alloys exhibit mechanical properties (yield strength, ultimate tensile strength and rupture strain) close to the expected original specifications

Probing the impact of energetic argon ions on the structural properties of ZnO:Al/TiO2 heterostructures

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