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Wunsiedel, Germany

SchUtz M.R.,University of Bayreuth | Sattler K.,University of Bayreuth | Deeken S.,DRONCO AG | Klein O.,DRONCO AG | And 5 more authors.
Journal of Applied Polymer Science | Year: 2010

Silsesquioxanes are formed in situ during mixing and curing of a phenolic resin and a molecular silane precursor (3-(triethoxysilyl)-1-propaneamine) yielding a nanocomposite. As indicated by a higher onset temperature, a higher characteristic decomposition temperature, and a lower maximum heat flow, the thermal stability of the nanocomposite is significantly improved over the pristine resin. Moreover, the bending strength and the strain at break could also be enhanced by 36% and 51%, respectively. The nanocomposite was characterized by 29Si solid- state NMR, STEM/EDS, TGA, DSC, and three point bending tests. The STEM/EDS measurements showed a homogenous distribution of silsesquioxanes in the phenolic resin. © 2010 Wiley Periodicals, Inc.

Adasch V.,DRONCO AG | Schroeder M.,Albert Ludwigs University of Freiburg | Kotzott D.,Albert Ludwigs University of Freiburg | Ludwig T.,Albert Ludwigs University of Freiburg | And 2 more authors.
Journal of the American Chemical Society | Year: 2010

Single crystals of a new magnesium boride carbide MgxB 50C8 (x = 2.4-4) were synthesized from the elements in a metallic melt using tantalum ampules. Crystals were characterized by single crystal X-ray diffraction and electron microprobe analysis. The variation of the Mg content results from different reaction conditions. The composition Mg ∼3B50C8 is by far the most favored. It fulfills the electron counting rules of Wade and Longuet-Higgins and thus explains the light-green to yellow transparent color. The structure of Mg ∼3B50C8 (C2/m, Z = 1, a = 8.9384(12) Å, b = 5.6514(9) Å, c = 9.6021(13) Å, β = 105.86(1)°) consists of B12 icosahedra. The icosahedra are interconnected by four exohedral B-B bonds to layers. The layers are connected to a three-dimensional covalent network by C2 and CBC units and further exohedral B-B bonds. The Mg sites are partially occupied. Different site occupation factors cause the various compositions and colors (Mg 2.4B50C8, brown; Mg4B 50C8, black). The vibrational spectra show the modes of B12 icosahedra and C2 and CBC units as well. Measurements of the microhardness according to Vickers and Knoop revealed remarkably high values of HV = 3286 (32.0 GPa) and HK = 3165 (31.5 GPa), which exceed the values of B4C. Optical spectra reveal a band gap of 2.7 eV for Mg∼3B50C8, in agreement to the observed color. This justifies an ionic description, and the formula can be written as (Mg2+)3(B12 2-) 4(CBC+)2(C2)2. © 2010 American Chemical Society.

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