Papers by Author: Maria Perraki

Abstract: The present work describes the synthesis of nitrogen doped multi-walled carbon nanotubes (CNx CNT). The chosen production method was the catalytic pyrolysis of a solid mixture containing [Ni(DMG)2] and melamine (C3H6N6), under an Αr atmosphere. A series of various experiments were performed, using different proportions of the reaction mixture, in order to optimize the production conditions of nitrogen doped carbon nanotubes. Finally, the produced materials were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), Raman spectroscopy as well as thermogravimetric analysis (TGA). The obtained data from all the above analyses, showed the formation of nitrogen doped carbon nanotubes of various diameters as well as nanofibers surrounded by byproducts such as aggregations of amorphous carbon and metallic catalyst, depending on the proportion of the reaction mixture.

Abstract: In the present work the geopolymerisation of blast furnace slag (GGBS) under varying conditions is being investigated. The experimental comprises the following parts: i) dissolution of slag in alkaline media and the investigation of the effect of the alkali ion (K or Na) on the dissolution of Al+3 and Si4+, ii) synthesis of slag based geopolymers and the investigation of the effect of the Si/Al ratio and the kind of alkaline ion on the development of the compressive strength and iii) characterization of geopolymers by means of XRD, FTIR and SEM/EDS measurements. As it is concluded, blast furnace slag geopolymers exhibit high compressive strength, with the maximum being 112.7±2 MPa. The Si/Al ratio of the starting material is found to affect strongly the development of the geopolymer compressive strength. The microstructure of slag–based geopolymers and the incorporation of Ca in the geopolymer matrix are also discussed.

Abstract: In the present work the geopolymerisation of metakaolin under varying conditions is investigated.The experimental part comprises the following parts: i) the synthesis of metakaolin based geopolymers and the investigation of the effect of the Si/Al ratio and the kind of alkali ion on the development of the compressive strength and ii) the characterization of the geopolymers by means of XRD, FTIR and SEM. As it is found the development of the compressive strength is strongly affected by the Si/Al ratio in the starting material and the kind of alkali metal, with the maximum being 70.1 MPa for a Si/Al ratio equal to 2.00. The Na- geopolymers show higher compressive strength compared to the NaK-geopolymers. Finally, low Si/Al ratios favour the formation of crystalline compounds (mainly zeolites), while Si/Al ratios higher than 1.5 lead to the formation of amorphous materials.