Two calcium-cobalt silicates were synthesized in which cobalt occupies different structural positions. The crystal phases belong to two main structural silicate types. In the Co-åkermanite structure (Ca 2 CoSi 2 O 7 ), cobalt cations take tetrahedral coordination toward oxygen atoms. In the Co-pyroxene structure of CaCoSi2O6, cobalt displays octahedral coordination. Ca2CoSi2O7 was prepared by solid-phase synthesis and CaCoSi2O6 was prepared by sol-gel method. The synthesis of the phases was confirmed by XRD, FTIR, and EPR data. On the basis of the XPS analysis, it can be concluded that Co 2+ cations exist in the studied silicates. Thus, it is possible to study the catalytic activity of two silicate phases containing Co 2+ cations in different coordinations: tetrahedral and octahedral. It was found that cobalt silicates with crystal structures corresponding to pyroxene and åkermanite possess catalytic activity in the reactions of complete oxidation of CO and toluene. Co-pyroxene exhibits higher catalytic activity than Co-åkermanite, but the higher cobalt content on the surface of Co-pyroxene should also be taken into account. Then, it turns out that catalytically active complexes with Со 2+ ions in tetrahedral coordination are more efficient than those with such ions in octahedral coordination when equal concentrations of cobalt were used on the surface of the catalysts.Résumé : On a réalisé la synthèse de deux silicates de calcium et de cobalt dans lesquels l'atome de cobalt occupe des positions diverses dans la structure. Les phases cristallines appartiennent à deux types principaux de structures de silicate. Dans la structure åkermanite du Ca2CoSi2O7, les cations du cobalt occupent des positions de coordination tétraédrique par rapport aux atomes d'oxygène. Le Ca2CoSi2O7 a été préparé par une synthèse en phase solide alors que le CaCoSi2O6 a été obtenu par méthode sol-gel. Les synthèses des phases ont été confirmées par des données de diffraction des rayons-X (DRX), d'infrarouge à transformée de Fourier (IR-TF) et résonance paramagnétique électronique (RPE). Sur la base d'analyse de données de spectroscopie photoélectronique des rayons-X (SPX), il est possible de conclure que, dans les silicates étudiés, il existe des cations Co 2+ . Il est donc possible d'étudier l'activité catalytique des deux phases de silicate contenant des cations Co 2+ dans des environnements de coordination différents : tétraédrique et octaédrique. On a trouvé que les silicates de cobalt avec une structure cristalline correspondant à celle du pyroxène et de l'åkermanite présentent une activité catalytique dans les réactions d'oxydation complète du CO et du toluène. Le Co-pyroxène possède une activité catalytique plus élevée que celle de la Co-åkermanite; toutefois, on doit tenir compte du fait que la teneur en cobalt est plus élevée sur la surface du Co-pyroxène. Il en découle alors que, pour des concentrations identiques de cobalt à la surface des catalyseurs, les complexes catalytiquement actifs comportant des ions Co 2+ en coordinatio...

LaCoO3 powders are studied because they exhibit interesting electrical, magnetic and catalytic properties. In this paper, new synthesized La2O3-CoO-SiO2 powders with different quantity of silica were prepared via solgel method in aqua media, starting from metal nitrates with different chelating agents. The relation between the reaction in solution, crystallization pathway and morphology were discussed. In LaCoO3-SiO2 powders, depending on the content of SiO2 and the treatment temperature (700-1100?C), different crystalline phases (LaCoO3, Co2 SiO4 and La9.31 (SiO4 )6 O2) were observed with the crystallite sizes ranging from 50 to 100 nm. It was proved that chemical composition and nature of used additives has influence on the phase formation and structure of obtained nanomaterials.

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Glass ceramics from the CaO–P2O5–SiO2 system were synthesized. They were characterized by XRD, SEM and EDX methods. It was found that they contain two crystalline [Whitlockite, Ca3 (PO4)2 and Hydroxylapatite, Ca5 (PO4)3 (OH)] and one residual amorphous phase. The ceramics are composed of porous aggregates of fine particles with predominant macro- and mesopores in it. The ceramics were used as a functional filler in natural rubber based composites, as the filling is in the range of 5–50 phr. The influence of the chemical nature and structure of the ceramics and the degree of filling on the vulcanization characteristics, physicomechanical parameters, dielectric and dynamic properties, the coefficient of thermal conductivity and the volume resistivity, including external pressure or bending on the specimens were investigated. An influence of the filler and the degree of filling on all studied properties was found. All tested composites have dielectric parameters (ε′, real part of complex permittivity; ε′′, imaginary part of complex permittivity; σ, conductivity; tanδɛ, tangent from dielectric loss angle) suitable for use as substrates and insulating layers of flexible antennas. Particularly impressive are composites containing 30 and 50 phr fillers, which have the lowest tangent from dielectric loss angle values.

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