F. Mirambet

Crystal and magnetic structures of U2Ni2Sn investigated by neutron diffraction and 119Sn Mössbauer spectroscopy

Abstract The U 2 Ni 2 Sn stannide has been studied by means of neutron powder diffraction and Mossbauer spectroscopy. This compound crystallizes in the tetragonal P4/mbm space group in an ordered version of the U 3 Si 2 -type structure and orders antiferromagnetically below T N = 25(1) K. At T = 1.5 K the magnetic structure is collinear with uranium magnetic moment (1.05(5)μ B ) perpendicular to the tetragonal c -axis. 119 Sn Mossbauer spectroscopy at 4.2 K shows that tin atoms see a zero hyperfine field, in agreement with the proposed antiferromagnetic order.

Crystal structure of U2Pt2Sn: a new derivative of the tetragonal U3Si2-type structure

The crystal structure of the new ternary stannide U2Pt2Sn has been investigated by both X-ray powder diffraction and electron diffraction. It crystallizes in a tetragonal unit cell with a= 768.1(1) pm and c= 739.1(1) pm. This crystal structure is a new superstructure of the tetragonal U3Si2-type which appears on account of the existence of short Pt–Pt distances. The crystal structure of U2Pt2Sn is described taking into consideration those of UPt and UPt2Sn.

Influence of corrosion products nature on dechlorination treatment: case of wrought iron archaeological ingots stored 2 years in air before NaOH treatment

Abstract Three wrought iron ingots immersed during 2000 years at 12 m deep in Mediterranean Sea were stored after excavation for 2 years without specific protection in air. After that period, two of them were treated by immersion in a NaOH solution, while the third was used to describe the corrosion system resulting from the storage conditions. This characterisation was achieved by a combination of microanalytical techniques. It could be concluded that though ferrous hydroxychloride β-Fe2(OH)3Cl was the main Cl containing phase at the time of excavation, akaganeite [β-FeO1–x(OH)1+xClx] was the only one present in the rust layers after storage. In order to determine the influence of corrosion products nature on dechlorination treatment, the evolution of a corrosion system composed of both Cl containing phases β-FeOOH and β-Fe2(OH)3Cl has been followed during in situ NaOH experimental treatment. Specific behaviours of each phase to the dechlorination treatment have been revealed.

Evaluation of new non-toxic corrosion inhibitors for conservation of iron artefacts

Abstract The anticorrosion performances of new non-toxic inhibitors based on carboxylic acids extracted from vegetable oil have been evaluated for the protection of iron artefacts. Electrochemical measurements and natural aging tests have demonstrated the efficiency of those inhibitors in the context of temporary treatments. Surface analysis coupled with in situ X-ray absorption near edge structure experiments has revealed that their anticorrosion properties are correlated to the precipitation at the metal surface of a protective layer made of iron carboxylate.

Transport and magnetic properties of U2Ni2Sn and U2Co2Sn

Abstract We report resistivity (ρ), thermopower ( S ) and magnetic susceptibility (χ) measurements on ternary stannides U 2 Ni 2 Sn and U 2 Co 2 Sn. An indication of antiferromagnetic order is found in U 2 Ni 2 Sn with T N = 25 K, whereas U 2 Co 2 Sn exhibits a paramagnetic behaviour down to 4.2 K.

Magnetic and electrical properties of the UM2Sn stannides (M Co, Rh)

Abstract The new ternary stannides UCo 2 Sn and URh 2 Sn crystallize in an orthorhombic ordered superstructure of the cubic ‘Heusler’ phase. UCo 2 Sn is a Pauli paramagnet. The magnetic susceptibility of URh 2 Sn follows a Curie-Weiss law above 130 K and tends to saturate below 6 K. Its electrical resistivity decreases strongly below 50 K and varies as ρ ≅ aT 2 at low temperatures. These results suggest that URh 2 Sn is a spin-fluctuation system.

Magnetic ordering in the new ternary stannide U3Rh4Sn13

Abstract U3Rh4Sn13 melts noncongruently and crystallizes in the cubic Yb3Rh4Sn13-type structure with α 9.6416 A. Magnetic, electrical, specific heat measurements and a 119Sn Mossbauer spectroscopy study reveal that this stannide undergoes a magnetic transition near 17.5 K. At low temperature, U3Rh4Sn13 shows an enhanced electronic specific heat coefficient (γ0 = 0.225 J/K2Uatom) as observed in magnetically ordered heavy fermions compounds. In addition below the magnetic transition temperature a broadening of the two quadrupole splitting of the Mossbauer spectrum indicates clearly the presence of a hyperfine field at the Sn sites.U3Rh4Sn13 exhibits a magnetic ordering temperature that is much higher than those already observed for similar stannides containing rare earths.