Improving the high-temperature oxidation resistance of titanium alloys in air is a prerequisite for extending their use in turbojet engines. A better understanding of the role of atmospheric nitrogen is required for this purpose. Here, we studied the insertion kinetics of nitrogen in titanium at 650 °C in air up to 100h. Moreover, the nitrogen mass gain, and its ratio over the total mass gain, were quantified as a function of the oxidation duration by using Nuclear Reaction Analysis. It was found that nitrogen inserts into titanium with a parabolic kinetics and a rate constant about 1500 times smaller than oxygen.

The addition of Si is known to improve the oxidation resistance of pure titanium and titanium alloys. However, most past studies concern the influence of relatively large Si contents (0.35–8 wt

Conventional techniques that measure the concentration of light elements in metallic materials lack high-resolution performance due to their intrinsic limitation of sensitivity. In that context, scanning microwave microscopy has the potential to significantly enhance the quantification of element distribution due to its ability to perform a tomographic investigation of the sample. Scanning microwave microscopy associates the local electromagnetic measurement and the nanoscale resolution of an atomic force microscope. This technique allows the simultaneous characterization of oxygen concentration as well as local mechanical properties by microwave phase shift and amplitude signal, respectively. The technique was calibrated by comparison with nuclear reaction analysis and nanoindentation measurement. We demonstrated the reliability of the scanning microwave technique by studying thin oxygen-enriched layers on a Ti-6Al-4V alloy. This innovative approach opens novel possibilities for the indirect quantification of light chemical element diffusion in metallic materials. This technique is applicable to the control and optimization of industrial processes.

Surface laser treatment (SLT) using nanosecond IR lasers has been shown to improve the tribological behaviour of titanium. Here, we studied the fretting wear of SLT-functionalized pure titanium in a mixture of reactive gases O2 (20 vol.%) + N2 (80 vol.%). The contact geometry was a ball on a plane and the ball was made of bearing steel. The very small amplitude of relative displacement between reciprocating parts in fretting wear makes the evacuation of wear particles difficult. Moreover, the oxidation mechanism of the debris depends on the accessibility of the surrounding atmosphere to the tribological contact. This work focused in the analysis of debris generation and oxidation mechanisms, and sought to differentiate the role of oxygen forming part of the ambient O2 + N2 gas mixture from oxygen present in the surface layer of the SL-treated titanium. Before the fretting test, the surface of the commercially pure titanium plates was treated with a laser under a mixture of O2 + N2 gases with oxygen enriched in the 18O isotope. Then, the fretting tests were performed in regular air containing natural oxygen. Micro-Raman spectroscopy and ion beam analysis (IBA) techniques were used to analyse the TiO2 surface layers and fretting scars. Iron oxide particles were identified by Raman spectroscopy and IBA as the third body in the tribological contact. The spatial distribution of 18O, Ti, 16O and Fe in the fretting scars was studied by IBA. The analysis showed that the areas containing high concentrations of Fe displayed also high concentrations of 16O, but smaller concentrations of 18O and Ti. Therefore, it was concluded that tribological contact allows the oxidation of iron debris by its reaction with ambient air.

Lamellar lithiated nitridonickelates have been investigated from both experimental and theoretical points of view in a wide range of compositions. In this study, we show that the nickel ion in lamellar lithiated nitridonickelates adopts an intermediate valence close to +1.5. This solid solution can therefore be written Li3-1.5xNixN with 0 ≤ x ≤ 0.68. Attempts to introduce more nickel into these phases systematically lead to the presence of the endmember of the solid solution, Li1.97Ni0.68N, with metallic nickel as an impurity. The LiNiN phase has never been observed, and first-principles calculations suggested that all the structural configurations tested were mechanically unstable.

Isotopic labelling was used to track the diffusion of nitrogen during the oxidation of Titanium in air at 700 degrees C. Alternate exposure in 15N2-labelled air and regular air was used. The nitrogen is mainly located at the oxide/ metal interface and forms essentially a nitride phase close to Ti2N. Each nitrogen isotope was quantified by Nuclear Reaction Analysis. Nitrogen quantity doubles between 5 and 20 h, which represents 16% respectively 12.5%, of the total mass gains. The nitrogen is partially renewed by both inward and outward diffusion during the oxidation. A model for nitrides migration is proposed.

Nitrogen is known to play a role in the oxidation of titanium and titanium alloys in air. This paper shows the strong correlation between the high temperature oxidation kinetics of eight near-alpha titanium alloys, in the class of Ti6242S, exposed for 3000 h in air at 650 degrees C. Nuclear reaction analysis (NRA) was used to quantify and locate the nitrogen inside the material. An excellent linear correlation between the total mass gain measured by gravimetry and the nitrogen mass gain measured by NRA is revealed: less the alloys oxidize, more the nitrogen in involved in the oxidation process.

The LiCl-KCl molten salts method has been used in order to intercalate strontium into graphite. Combination of XRay Diffraction (XRD) experiments and ion beam analyses attests the obtaining of a monophasic sample. Its chemical composition corresponds to the Li0.2K0.6Sr0.4C6 formula, revealing the synthesis of a quaternary Graphite Intercalation Compound (GIC), in agreement with the high repeat distance of 640 pm determined from its 00l XRD and with the 1D electronic density profile. The very high-quality data obtained by hk0 diffraction and rotating crystal method lead to a 2D organization of the intercalated sheet described by a large hexagonal unit cell containing 78 carbon atoms. Such quaternary phase including simultaneously alkali and alkaline-earth metals is unique and can only be prepared from molten salts method, opening new perspectives concerning graphite-based two-dimensional materials.

In this paper, we present the three first stages currently known Ba-based Graphite Intercalation Compounds (GIC). They are synthesized using the LiCl-KCl molten salts method, which is especially efficient in order to help the intercalation of barium into the 2D graphitic galleries. According to the chosen reaction conditions, it is possible to obtain either the BaC6 binary compound or one of the two quaternary phases whose intercalated sheets contain simultaneously lithium, potassium and barium. By combining X-ray diffraction measurements and ion beam analyses for these compounds, their chemical formula is well established: Li0.2K0.6Ba0.35C6 for the & alpha;-phase, Li0.2K0.75Ba0.6C6 for the & beta; one and BaC6 for the binary.The intercalated sheets of this last compound are single-layered. Its repeat distance reaches 529 pm and its 2D unit cell is hexagonal and commensurate with the graphene one with a parameter of 430.6 pm However, & alpha;- and & beta;-phases are much more complex. For & alpha;- compound, the intercalated sheets are three-layered with an interplanar distance of 650 pm, while for & beta;-phase, they are six-layered and the interplanar distance reaches 950 pm Both 2D unit cells are hexagonal, with a planar lattice parameter a of 1074 pm and 1280 pm respectively.Finally, a model of reaction mechanism is proposed, which breaks down the intercalation process into several steps: intercalation of lithium (LiC6), then replacement by barium (BaC6), next, formation of the & beta;-phase, and ultimately its elimination to the benefit of the & alpha; one. Thus, this latter appears as the most stable GIC in this LiClKCl molten medium.

We investigate the oxidation of TiZrNbHfTa high entropy alloy between 550 degrees C and 650 degrees C as a surface hardening method. Coarse-grained specimens with grain boundaries perpendicular to the surface exhibit catastrophic oxidation, while ultrafine-grained, cold-rolled specimens show a continuous mass gain and the formation of an adherent, mu m-sized, vitreous oxide layer. Underneath, TiZrNbHfTa decomposes into a bcc- and an hcp-phase, while selective internal oxidation of hafnium and zirconium occurs upon oxygen inward diffusion. Oxygen concentration- and microhardness-depth profiles confirm an increase in oxygen concentration and hardness at the surface, raising the initial hardness by four times to 1522 +/- 64 HV0.5.

The synthesis of a novel first stage GIC containing simultaneously lithium, potassium and barium through a solid–liquid reaction by molten salts method is described. Such a route has been largely developed in our laboratory for intercalation of metals into graphite. The interplanar distance of this quaternary compound reaches 950 pm and exhibits poly-layered intercalated sheets defined by X-ray measurements. The Li 0.2 K 0.75 Ba 0.6 C 6 chemical formula of the compound is determined by ion beam analysis and this GIC is remarkably homogeneous. This GIC is the first poly-layered one containing barium.

Boron/carbon/nitrogen (B/C/N) materials and boron/carbon (B/C) materials having graphite-like layered structures were synthesized by using a chemical vapor deposition (CVD) method. Calcium (Ca) was intercalated into the B/C materials by the reaction of Ca vapor with the host B/C film to form an intercalation compound with a second stage structure as a main product. Ca was also co-intercalated with lithium (Li) into the B/C/N materials by using a liquid-alloy method to form an intercalation compound. These are the first examples of syntheses of Ca and Ca-Li intercalated B/C and B/C/N materials. A nuclear microprobe analysis (NMA) indicated the compositions of the original host B/C/N and B/C materials to be BC2.6N0.55 and BC6.4, and the Ca-Li intercalated compound to be Ca0.67Li0.42(BC3.3N0.50) and suggested the homogeneity of these materials and the compound. We also found that the NMA is one of the most accurate methods for determining the compositions of air and water sensitive intercalation compounds as well as complex systems like B/C/N and B/C materials.

We report the role of ultrasonic shot-peening (SP) and laser-shock peening (LSP) on the insertion of atmospheric nitrogen during high temperature oxidation of pure titanium and the improvement of its oxidation resistance. Ion Beam analysis showed that for short oxidation durations, a layer of Ti2N is formed at the oxide-metal interface. However, only the LSP treatment leads to the formation of a long-term stable nitrogen-rich layer which acts as a barrier for the diffusion of oxygen. This explains the efficiency of the LSP treatment to reduce the oxidation of Ti and prevent embrittlement.

To protect copper artefacts of the cultural heritage from atmospheric degradation protective treatment must be applied. Two types of protective treatments: microcrystalline wax (Cosmollo?d wax) and decanoate solution (HC10) were tested. Two aspects were considered: the penetration of the treatments in the corrosion layers, and its durability. Equivalent efficiencies for both treatments were demonstrated. The penetration of the treatments seems to depend essentially on its application mode. Re-corrosion experiments of treated samples under immersion in D2O demonstrate that the efficiency and the durability with time or after water leaching depend on the penetration of the treatments in the corrosion layers.

The synthesis route in molten salts allows the bulk intercalation into graphite of elements hardly intercalated by themselves. XRD and ion beam analyses show for instance the possible synthesis of SrC6.

Zr-C thin films are grown on single-crystalline MgO(001) substrates via ultra-high vacuum dc magnetron sputtering of Zr target in 10 mTorr Ar-C2H4 gas mixtures with ethylene partial pressures (pC(2)H(4)) between 2 x 10(-7) Torr and 2 x 10(-4) Torr at substrate temperature T-s = 923 K and using pC(2)H(4) = 2 x 10(-6) Torr at 723 K <= T-s <= 1123 K. The as-deposited layer microstructure and composition are determined using X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. We find that the layers sputter-deposited at T-s = 923 K using the lowest pC(2)H(4) = 2 x 10(-7) Torr are polycrystalline, close-packed hexagonal structured Zr:C solid solutions. At higher pC(2)H(4) = 2 x 10(-6) Torr and 2 x 10(-5) Torr, we obtain films composed of free-carbon (C) and NaCl-structured ZrCx, x = 1. The amount of C increases 104% with ten-fold increase in pC(2)H(4) from 2 x 10(-6) Torr to 2 x10(-5) Torr. At the highest pC(2)H(4) = 2 x10(-4) Torr, the layers are Xray amorphous with similar to 49 at.% C. Films grown at 723 K <= T-s <= 1123 K using constant pC(2)H(4) = 2 x 10(-6) Torr exhibit qualitatively similar microstructures, irrespective of Ts, composed of dense columnar ZrCx grains surrounded by C and corrugated surfaces. Our results suggest that the compositional and microstructural evolution of Zr-C films during reactive sputter-deposition of Zr is highly sensitive to ethylene partial pressure, with as little as 0.02% of the total pressure sufficient at T-s >= 723 K to obtain ZrCx films.

The intercalation of gold into graphite has been achieved thanks to a solid-liquid method using potassium metal-based molten alloys. Numerous syntheses have been performed varying the reactive alloy composition, the reaction temperature and the reaction time. The optimization of these parameters allowed to synthesize three novel ternary graphite intercalation compounds (GIC) containing poly-layered intercalated sheets, called alpha, beta and gamma. Thanks to a specific X-Ray diffraction study, the c-axis stacking sequence of the three compounds was determined. The α-GIC, which is a metastable compound, contains mixed potassium and gold two-layered intercalated sheets. The β-GIC and γ-GIC contain very thick well ordered three-layered and five-layered sheets respectively. The very high repeat distances of the latter compounds are clearly explained by the amount of intercalated metals, precisely determined using nuclear microprobe analyses.

We present the successful intercalation of europium into graphite by using an original method based on LiCl-KCl molten salts mixture. After solubilization of europium in the liquid chlorides mixture at 450 degrees C, reactivity toward graphite is investigated. We evidence the formation of the first stage EuC6 Graphite Intercalation Compound (GIC) with a repeat distance Ic = 487 pm. Using 00l X-ray diffraction and ion beam analysis, we show that europium is intercalated into the bulk with remarkable degree of homogeneity. This is also confirmed by magnetic measurements that clearly put in evidence the antiferromagnetic transition at about T-N = 40 K. Below such temperature the characteristic step-like behavior of metamagnetic transitions was found by isothermal magnetization measurements, that is generally visible only in highly pure samples. (C) 2018 Elsevier Ltd. All rights reserved.

A ternary graphite-potassium-gold compound K1.3Au1.5C4 was synthesized by immersing a pyrographite platelet in various potassium metal-based molten alloys. Numerous reaction parameters were investigated (duration, temperature, composition of the alloy) in order to determine the stability conditions of the ternary compound. Using complementary X-ray diffraction and ion beam analysis experiments, the optimal conditions of preparation of this compound have been pointed out. The composition and homogeneity were evidenced by ion beam analysis and X-ray diffraction allowed to determine its repeat distance (1311 pm) and its c-axis stacking sequence (K-Au-Au-Au-K). The 2D unit cell observed thanks to Transmission Electron Microscopy (TEM) is square with a = 1192 pm, no-commensurate with that of graphite. (C) 2018 Elsevier Ltd. All rights reserved.