Stability of the D8m-Ti5Sn2Ga compound. Experimental determinations and first principle calculations

International audienceIn this paper we discuss the formation of the ternary compound Ti5Sn2Ga (tau) with the D8(m) structure. Phase equilibria with participation of the tau-phase were studied experimentally, and partial solidus projection and isothermal section at 1300 degrees C were plotted. At the solidus temperatures the ternary compound is in equilibria with two continuous solid solutions: (1) between Ti2Sn and Ti2Ga (named Ti-2(Sn, Ga)) and (2) between Ti5Sn3 and Ti5Ga4 (named Ti-5(Sn, Ga)(3-4)). At 1300 degrees C Ti2Sn and Ti2Ga do not form continuous solid solution, and the ternary compound participates in equilibria with Ti-5(Sn, Ga)(3-4), and Ti2Sn, Ti2Ga and Ti3Sn based phases. The formation energy of the D8(m)-Ti5Sn2Ga compound is calculated by using electronic density-functional theory (DFT) using pseudopotentials constructed by the projector augmented waves (PAW) method in the generalized gradient (GGA) approximation for the exchange and correlation energy. The calculated lattice parameters are in good agreement with the experimental values. According to the experiments and the ab initio calculations, the D8(m)-Ti5Sn2Ga compound is stable and possesses a domain of off-stoichiometry

Evidence of an ordered ternary phase in the section Ni–Ti5Sn3 of the ternary Ti–Ni–Sn: Crystal structure and phase stability

International audienc

Microporous composite SiO2-TiO2 spheres prepared via the peroxo route: Lead(II) removal in aqueous media

Composite microporous SiO2-TiO2 spheres and micro/mesoporous TiO2 spheres were prepared via the template-free two-step synthetic route using aqueous peroxotitanate solution and tetraethyl orthosilicate (TEOS) as precursors. Both the composite SiO2-TiO2 and pure TiO2 spheres prepared by the solvent-exchange method were initially non-porous, but the applied reflux treatment in water-ethanol suspension successfully transformed them into microporous materials with high apparent surface areas approaching 500 m2·g− 1 and the micropore volume of 0.17 cm3·g− 1, while maintaining the same morphology. The prepared composites retained high values of pore volume and specific surface area up to 400 °C of thermal treatment temperature. The crystallization of TiO2 into the anatase phase in the mixed oxide occurred only at 700 °C, that process was also accompanied by the significant reduction of pore volume, as well as apparent surface area values. The prepared materials were tested as adsorbents for the lead(II) removal; they demonstrated high adsorption capacities, reaching 340 mg(Pb2 +)·g− 1. Moreover, the mixed silica-titania oxide was found to be more efficient adsorbent at low pH values.South Ural State University is grateful for financial support of the Ministry of Education and Science of the Russian Federation (grant No 16.2674.2014/K). University of Oviedo gratefully acknowledges financial support from the Spanish MINECO (MAT2013-40950-R and MAT2016-78155-C2-1-R). Igor Krivtsov thanks for the support the Russian Foundation for Basic Research 16-29-10757-ofi.Peer reviewe

Microporous composite SiO2-TiO2 spheres prepared via the peroxo route: Lead(II) removal in aqueous media

Composite microporous SiO2-TiO2 spheres and micro/mesoporous TiO2 spheres were prepared via the template-free two-step synthetic route using aqueous peroxotitanate solution and tetraethyl orthosilicate (TEOS) as precursors. Both the composite SiO2-TiO2 and pure TiO2 spheres prepared by the solvent-exchange method were initially non-porous, but the applied reflux treatment in water-ethanol suspension successfully transformed them into microporous materials with high apparent surface areas approaching 500 m2·g− 1 and the micropore volume of 0.17 cm3·g− 1, while maintaining the same morphology. The prepared composites retained high values of pore volume and specific surface area up to 400 °C of thermal treatment temperature. The crystallization of TiO2 into the anatase phase in the mixed oxide occurred only at 700 °C, that process was also accompanied by the significant reduction of pore volume, as well as apparent surface area values. The prepared materials were tested as adsorbents for the lead(II) removal; they demonstrated high adsorption capacities, reaching 340 mg(Pb2 +)·g− 1. Moreover, the mixed silica-titania oxide was found to be more efficient adsorbent at low pH values