title: High-temperature stability and saturation magnetization of superparamagnetic nickel nanoparticles in microporous polysilazane-derived ceramics and their gas permeation properties.
abstract: Superparamagnetic Ni nanoparticles with diameters of about 3 nm are formed in situ at room temperature in a polysilazane matrix, forming Ni/polysilazane nanocomposite, in the reaction between a polysilazane and trans-bis(aceto-kO)bis(2-aminoethanol-k(2)N,O)nickel(II). The thermolysis of the Ni/polysilazane nanocomposite at 700 °C in an argon atmosphere results in a microporous superparamagnetic Ni/silicon oxycarbonitride (Ni/SiCNO) ceramic nanocomposite. The growth of Ni nanoparticles in Ni/SiCNO ceramic nanocomposite is totally suppressed even after thermolysis at 700 °C, as confirmed by HRTEM and SQUID characterizations. The analysis of saturation magnetization of Ni nanoparticles in Ni/polysilazane and Ni/SiCNO nanocomposites indicates that the saturation magnetization of Ni nanoparticles is higher than expected values and infers that the surfaces of Ni nanoparticles are not oxidized. The microporous superparamagnetic Ni/SiCNO nanocomposite is shaped as a free-standing monolith and foam. In addition, Ni/SiCNO membranes are fabricated by the dip-coating of a tubular alumina substrate in a dispersion of Ni/polysilazane in THF followed by a thermolysis at 700 °C under an argon atmosphere. The gas separation performance of Ni/SiCNO membranes at 25 and 300 °C is assessed by the single gas permeance (pressure rise technique) using He, H2, CO2, N2, CH4, n-propene, n-propane, n-butene, n-butane, and SF6 as probe molecules. After hydrothermal treatment, the higher increase in the hydrogen permeance compared to the permeance of other gases as a function of temperature indicates that the hydrogen affinity of Ni nanoparticles influences the transport of hydrogen in the Ni/SiCNO membrane and Ni nanoparticles stabilize the structure against hydrothermal corrosion.
authors.affiliation: Fachbereich Material-und Geowissenschaften, Technische Universität Darmstadt , Jovanka Bontschits Strasse 2, D-64287 Darmstadt, Germany.
authors.forename: Mahdi
authors.initials: M
authors.lastname: Seifollahi Bazarjani
authors.forename: Mathis M
authors.initials: MM
authors.lastname: Müller
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Kleebe
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Jüttke
authors.forename: Ingolf
authors.initials: I
authors.lastname: Voigt
authors.forename: Mehrdad
authors.initials: M
authors.lastname: Baghaie Yazdi
authors.forename: Lambert
authors.initials: L
authors.lastname: Alff
authors.forename: Ralf
authors.initials: R
authors.lastname: Riedel
authors.forename: Aleksander
authors.initials: A
authors.lastname: Gurlo