Draft Genome Sequence of Frankia sp. Strain BCU110501, a Nitrogen-Fixing Actinobacterium Isolated from Nodules of Discaria trinevis

Frankia forms a nitrogen-fixing symbiosis with actinorhizal plants. We report a draft genome sequence for Frankia sp. strain BCU110501, a nitrogen-fixing actinobacterium isolated from nodules of Discaria trinevis grown in the Patagonia region of Argentina

Isothermal and cyclic oxidation behaviour of hot-pressed MSi2 compounds (with M = V, Ti, Cr)

International audienceThe oxidation resistance of MSi2 compounds with M = V, Ti, Cr was investigated from 450 to 950 degrees C in air under isothermal and cyclic conditions. Vanadium, chromium and titanium disilicide were not subjected to the pest phenomenon at 650 degrees C over 800 1-h cycles. The results demonstrated very low weight gains regardless of the testing conditions. Oxidation tests were also performed over long duration (1000 h) to identify the oxidation products. The MSi2 compounds were all subjected to the simultaneous oxidation of M and Si despite the formation of a protective silica scale. Increasing the duration of oxidation enhanced the protective properties of the silica scale. Therefore, short-term measurements (by thermogravimetry) did not allow an extrapolation of the MSi2 lifetime. The formation of molten V2O5 induced a higher oxidation rate of VSi2 and delayed the establishment of the protective silica scale compared with CrSi2 and TiSi2

The ability of silicide coating to delay the catastrophic oxidation of vanadium under severe conditions

International audienceV-4Cr-4Ti vanadium alloy is a potential cladding material for sodium-cooled fast-neutron reactors (SFRs). However, its affinity for oxygen and the subsequent embrittlement that oxygen induces causes a need for an oxygen diffusion barrier, which can be obtained by manufacturing a multi-layered silicide coating. The present work aims to evaluate the effects of thermal cycling (using a cyclic oxidation device) and tensile and compressive stresses (using the three-point flexure test) on the coated alloy system. Tests were performed in air up to 1100 degrees C, which is 200 degrees C higher than the accidental temperature for SFR applications. The results showed that the VSi2 coating was able to protect the vanadium substrate from oxidation for more than 400 1-h cycles between 1100 degrees C and room temperature. The severe bending applied to the coated alloy at 950 degrees C using a load of 75 MPa did not lead to specimen breakage. It can be suggested that the VSi2 coating has mechanical properties compatible with the V-4Cr-4Ti alloy for SFR applications

Thermodynamic modeling of the V-Cr-Si system

International audienceIn the present work, an assessment of the V-Cr-Si system was done. Mainly based on previously ternary experimental data on the isothermal section at 1200 C and on the liquid-solid equilibria, a thermodynamic modeling of the ternary system was performed within the CALPHAD approach using the Thermo-Calc and the Pandat software packages and taking into account data from existing assessment of binary sub-systems. Four intermediate phases were considered as stoichiometric compounds (Cr,V)(Si)y with substitution of Cr and Vat Si ratio constant: (Cr,V)Si, (Cr,V)5Si3, (Cr,V)liSi5 and (Cr,V)6Si5. Two others phases (Cr,V)Si2 and (Cr,V)3Si presenting a slight domain of homogeneity, were described as (Cr,Si,V)1(Cr,S02 and (Cr,Si,V)3(Cr,Si,V)1 respectively. The metallic liquid phase and the terminal solid solutions of chromium and vanadium were described by the disordered solutions model as (Cr,Si,V)1(Va)3. The silicon admitting any solubility, its description was limited to (Si). The resulting thermodynamic optimization led to a good agreement with experimental data