| Abstract |
The present thesis aims fundamentally to the study of chemical reactions of silicon monoxide SiO and elemental silicon Si with water and ethanol molecules in the gas phase. Especially, the chemical mechanism of the reactions that leads to the formation of solid deposited products containing the typical silicon groups SiO, SiH, SiC and SiOH, was studied These reactions had not been studied before, although they are very important for the synthesis of novel silicic materials, in chemistry and new material technology in general and possess various industrial applications. SiO and Si fragments are extracted through evaporation, when a pulsed CO2 laser beam is directed towards the surface of solid amorphous SiO and Si targets, respectively. The reactions of the extracted SiO and Si particles with H2O and CH3CH2OH molecules took place in a static reactor in presence of water and ethanol vapors in various concentrations. The products of the reactions deposit onto a NaCl substrate horizontally situated 1 cm away from the irradiated target. The final solid deposits were characterized using FT-IR spectroscopy and the volatile products were characterized using mass spectrometry. The solid products mainly contain the typical bands SiO, SiH, SiOH, CH and SiOSi. Finally, the optimum experimental conditions for the production of solid deposits were defined, by modulating the laser output, the number of the laser pulses and the pressure of the ambient gas. The mechanism of the under estimation reactions in the gas phase that leads in the formation of the final products was defined. Specifically for the SiO reactions, the extracted from the laser ablated solid SiO target, SiO monomers, react with the ambient gas molecules through insertion reactions, forming in general highly reactive and vibrationally excited products (intermediate complexes), silanones mostly. Laser ablation may also causes in very small amounts the formation of clusters such as (SiO)n, SixOy, Sin. Additionally, silanones either undergo dimerization and form cyclo-dimers that finally deposit, or react with water and ethanol molecules and form various final products. Similarly for the Si reactions, the extracted from the laser ablated solid Si target, Si atoms, react with the ambient gas molecules through insertion reactions and form highly reactive and vibrationally excited products (intermediate complexes), mostly silanones. Finally, silanones either undergo dimerization and form cyclo-dimers that deposit or, react with water and ethanol molecules and form various final products.
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Μελέτη αντιδράσεων πυριτίου (Si) και μονοξειδίου του πυριτίου (SiO) με νερό (H2O) και αιθανόλη (CH3CH2OH) στην αέρια φάση
