No abstract

Calcium silicates are the main components in cement clinkers. Alite, the nesosilicate or island silicate Ca 3 SiO 5 , also named C 3 S in cement chemistry notation, represents the main phase in Portland cement clinkers. Due to the metastability of Alite at room temperature, quenching from high temperatures is mandatory for phase preservation and impurities are important structure directing factors. Those two aspects result in a plethora of published polymorphs. Many Alite polymorphs described in the literature are characterized by various degrees of disorder within the SiÀ O substructure which is a direct consequence of afore mentioned features (i. e. quenching and presence of impurities). Here we report on the CaCl 2 -flux mediated synthesis and structural characterization of an aP162 Alite featuring a fully-ordered [SiO 4 ] tetrahedron substructure. The orientation of the [SiO 4 ] tetrahedron substructure is discussed based on the Nishi and Takéuchi nomenclature and is equivalent to the Golovastikov model reported in 1975. Rietveld analyses of a synthetic clinker and three commercial CEM I clinker substantiate that the aP162 model can successfully be applied for clinker phase analysis. Besides the structural characterization, quantum chemical band structure calculations based on Density Functional Theory methods illustrate the expected electrically isolating character of Ca 3 SiO 5 .

Durch Reaktionen zwischen Festkörper und Gasphase lassen sich Phosphorverbindungen kinetisch kontrolliert herstellen. Deren Strukturen reichen von molekular über Schichten bis zu Spiralen. Daraus resultieren interessante physikalische Eigenschaften: Sie sind Supraleiter oder lassen sich um 180 ° biegen.