The results of investigation on the oxidation behavior of orthorhombic Ti 2 AlNb alloy are presented. Oxidation was carried out in static air atmosphere at two temperatures: 700 and 800°C. The investigation of the material structure of the specimen and chemical composition of oxidation products was performed. It was determined that the alloy shows a sufficient high-temperature corrosion resistance only at 700°C.

No abstract

No abstract

No abstract

The synthesis and structural properties of new mono‐ and bis‐macrocyclic cyclidene complexes of copper(II) andnickel(II) are presented. The compounds with aliphatic ligands are flexible enough to stabilize metal centers in the three oxidation states +1, +2, and +3. All the electron‐transfer processes in the 16‐membered mono‐ and binuclear macrocyclic complexes of copper(II) and nickel(II) were fast and reversible. Two polymorphic forms of the 16‐membered mononuclear complex of nickel(II) were isolated in the solid state and characterized. The 16‐membered macrocyclic complexes show both U‐ and Z‐shape conformations. The deviation of the macrocyclic ligand from planarity affects the electrochemical properties of the complexes and leads to stabilization of different oxidation states of the Cu and Ni metal centers. Substitution of the exocyclic nitrogen atoms with a second alkyl group increases the deviation from planarity and induces rotation of the functional groups at the meso position relative to the macrocyclic ring. In the bis‐macrocyclic complexes, the electron‐donating properties are improved and the formal potential of the metal(II)/metal(III) system is less positive with increasing linker length between the macrocyclic units. The acceptor properties of the metal(II) complexes are weaker, the formal potential of the metal(II)/metal(I) couple being shifted to more negative values.

This study presents the test results of Ti-46Al-7Nb-0.7Cr-0.1Si-0.2Ni alloy isothermal oxidation with regard to a coating of SiO 2 deposited by the sol-gel method. The oxidation test was carried out in air at 900°C. The SiO 2 coating is not an effective and stable diffusive barrier, which would considerably improve oxidation resistance of Ti-46Al-7Nb-0.7Cr-0.1Si-0.2Ni alloy.

No abstract

Multicenter (bi-, tri-, and tetranuclear) tetraazamacrocyclic complexes were self-assembled from Ni and Cu tetraazamacrocyclic mononuclear units and α,ω-diamines as building blocks. The structures of all compounds studied were proved by spectroscopic methods (ESI MS and NMR spectroscopy). Electrochemical experiments revealed reversible one-electron electrode processes at each of the Ni(2+) and Cu(2+) centers with formation of metal cations in oxidation state +3. Long linkers allow bi- and trinuclear complexes with noninteracting metal centers to be obtained. In the case of the short linkers (e.g. ethylenediamine) higher, trinuclear species are formed as major product. The structures of the bis- and tris-macrocyclic systems were confirmed by single-crystal X-ray diffraction. The tris-macrocyclic systems form cations in the shape of triangles partially filled with counterions and solvent molecules. The cations form positively charged layers, which interact in the crystal lattice with the neighboring negatively charged layers of anions. In solution, the trinuclear complexes exhibit strong host-guest interactions with 9,10-dimethyltriptycene due to complementarity of shape and size of this guest molecule. The association constants were determined by NMR spectroscopy and voltammetry, and very good agreement was obtained. The structural flexibility of the tetranuclear complex with long linkers allows for attractive interactions between the metal-complexing macrocycles that result in folding of the molecule. On the contrary, no folding is possible in the case of short linkers consisting of two CH(2) groups.