The equilibrium observed during modified chemical vapor deposition (MCVD) of silica glasses doped with fluorine is investigated by chemical thermodynamics. The influence of the flow rate of Freon-12 and sulfur hexafluoride on the efficiency of the incorporation of fluorine into the condensed phase is analyzed. It is revealed that, at very low flow rates of fluorinating reactants, more than 50% of fluorine can be incorporated into the glass. The refractive index and the efficiency of the conversion of SiCl 4 into the fluorine-doped silica glass are studied as functions of the vapor-gas phase composition.

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A novel theoretical and experimental approach for lifetime modelling of MCrAlY coatings for stationary gas turbines has been undertaken using the Inverse Problem Solution (IPS) technique. With this technique feasible experimental data acquired after a defined experimental time t e are used as input values for the model parameters estimation. In the first stage of the approach a model, based on the oxidation and diffusion processes (Fick's first and second law) was assumed, which considers the Al concentration profile across the coating. The measured average Al concentration profiles in the two-phase g+b and g - regions of coating as well as base metal were used as input values for the model parameters estimation and calculational prediction of the long term diffusion and oxidation behavior of the coating was performed. The time, when the b-NiAl phase is completely consumed was assumed as the coating lifetime end. Exposure experiments were carried out with a NiCoCrAlY coating (200 micron thickness) with 8% Al in air at 900 °C and 950 °C, currently up to 10000 h. The oxide scale is growing continuously and no other oxides were observed. The average and b-NiAl phase concentration profiles of Al across the coating thickness were determined by electron microprobe and image analysis systems in the initial state after 700 and 10000 h of oxidation. The concentration profile measured after 700 h was used as input values for the model parameters estimation in order to calculate the Al and b-NiAl phase concentration profiles after 10000 h. The computational forecast for 10000 h at 950 °C and 900 °C are in good agreement with the measured data. The approach was applied for NiCoCrAlY (200 micron thickness) coating lifetime modelling at 950 °C and 900 °C as well as for different coating thicknesses at 950 °C

The compositions of fluorogermanosilicate glasses prepared by the modified chemical vapor deposition (MCVD) method are calculated in terms of equilibrium thermodynamics. The calculations are based on the assumption regarding the formation of a mixture of pure oxide particles. This assumption is confirmed by the IR transmission spectra of porous deposits.

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