Critical comparison of ICP-OES, XRF and fluorine volatilization-FTIR spectrometry for the reliable determination of the silicon main constituent in ceramic materials

For the optimization of preparation processes for ceramic powders and compacts by pyrolysis of inorganic polymers, the intermediate and final products have to be monitored by in-situ analysis (in its original place) for main, subsidiary and trace components. In the determination of silicon in Si-N-C- based ceramic samples by ICP-OES after pressurized decomposition at temperatures between 220°–250°C too low concentrations of Si were found. Completely independent analytical procedures were applied to trace systematic errors, i.e. XRF after decomposition of the sample in a metaborate/boric acid melt and FTIR-spectrometry after reaction of the sample with fluorine. The low recoveries of Si were found to be due to losses, which amount up to 25% depending on the temperature and time applied for the pressurized decomposition. With the latter two procedures Si can be determined in the %-range with a relative standard deviation of 0.4% and 0.2%, respectively.