Submicronic-Scale Mechanochemical Characterization of Oxygen-Enriched Materials.

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.

Chemical Composition of Lithiated Nitrodonickelates Li3-xyNixN: Evidence of the Intermediate Valence of Nickel Ions from Ion Beam Analysis and Ab Initio Calculations.

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.

Li2.0Ni0.67N, a Promising Negative Electrode Material for Li-Ion Batteries with a Soft Structural Response.

The layered lithium nitridonickelate Li2.0(1)Ni0.67(2)N has been investigated as a negative electrode in the 0.02-1.25 V vs Li+/Li potential window. Its structural and electrochemical properties are reported. Operando XRD experiments upon three successive cycles clearly demonstrate a single-phase behavior in line with the discharge-charge profiles. The reversible breathing of the hexagonal structure, implying a supercell, is fully explained. The Ni2+/Ni+ redox couple is involved, and the electron transfer is combined with the reversible accommodation of Li+ ions in the cationic vacancies. The structural response is fully reversible and minimal, with a maximum volume variation of 2%. As a consequence, a high capacity of 200 mAh g-1 at C/10 is obtained with an excellent capacity retention, close to 100% even after 100 cycles, which makes Li2.0(1)Ni0.67(2)N a promising negative electrode material for Li-ion batteries.

High-resolution characterization of the diffusion of light chemical elements in metallic components by scanning microwave microscopy.

An original sub-surface, high spatial resolution tomographic technique based on scanning microwave microscopy (SMM) is used to visualize in-depth materials with different chemical compositions. A significant phase difference in SMM between aluminum and chromium buried patterns has been observed. Moreover this technique was used to characterize a solid solution of a light chemical element (oxygen) in a metal lattice (zirconium). The large solubility of the oxygen in zirconium leads to modifications of the properties of the solid solution that can be measured by the phase shift signal in the SMM technique. The signal obtained in cross-section of an oxidized Zr sample shows the excellent agreement between phase shift profiles measured at different depths. Such a profile can reveal the length of diffusion of the oxygen in zirconium under the surface. The comparison with the oxygen concentration measured by nuclear reaction analysis shows excellent agreement in terms of length of diffusion and spatial distribution of the oxygen. A rapid calibration shows a linear dependence between the phase shift and the oxygen concentration. The SMM method opens up new possibilities for indirect measurements of the oxygen concentration dissolved in the metal lattice.

Acute thrombosis of renal transplant artery: graft salvage by means of intra-arterial fibrinolysis.

BACKGROUND: Arterial thrombosis in a transplanted kidney is a serious complication that usually leads to graft loss. The purpose of our study was to evaluate intra-arterial fibrinolysis as a treatment of acute renal transplant artery thrombosis and to determine the maximum period of occlusion allowing a reasonable chance of graft salvage. METHODS AND RESULTS: Four patients underwent intra-arterial fibrinolysis for acute transplant artery thrombosis. Transplantations had been performed 29 days to 10 years before the fibrinolysis. Fibrinolysis was carried out by using recombitant tissue plasminogen activator (n=1) or urokinase (n=3). In one patient, anuric for 13 hr at admittance, fibrinolysis could not revascularize the graft artery. In a second patient, anuric for 48 hr at admittance, fibrinolysis did revascularize the graft artery, but dialysis could not be discontinued. In the two remaining patients, anuric for 19 and 20 hr at admittance, the graft artery was successfully revascularized and dialysis could be discontinued 1 week later. One of these two patients returned to dialysis 71 months later because of chronic rejection. Thirty-four months after the acute episode, the remaining patient had a patent artery and did not require dialysis. CONCLUSIONS: Fibrinolysis seems an efficient treatment that may save transplants after up to 24 hr of the arterial occlusion.