| Popis: |
The effects of added oxygen gas on analytical glow discharges (GD) -, significant changes in electrical characteristics, and emission line intensities of both analyte and carrier gas (usually Ar) - have been shown experimentally and predicted by computer models. However, past experimental studies were either limited to one or two spectral lines for each element, or used oxygen concentrations far higher than those likely in analytical work. These changes can seriously affect both the stability of the glow discharge and the analytical results. Contamination by oxygen traces can be curtailed by using high purity carrier gas, modern vacuum techniques and a “clean” instrument. However, the complexity of discharge processes is far greater when oxygen traces are present in the sample either as constituent such as Fe2O3, Ti2O3 and Al2O3 or within an alloy. Investigations were carried out in three separate locations - at Imperial College London (IC), The Swiss Federal Laboratories for Materials Science & Technology EMPA, Thun, Switzerland and The Leibniz-Institut für Festkörper- und Werkstoffforschung IFW, Dresden, Germany. Optical spectra generated in pure argon, Ar/O2 and Ar/H2 plasmas have been recorded using the IC high resolution vacuum UV Fourier transform spectrometer allowing for the first time a detailed study of the effects of added oxygen on observed intensities of emission lines from a large number of energy levels; these spectra have been compared, again for the first time, with spectra from a calamine sample (hot rolled alloy steel with oxide layer) in a pure argon plasma. A Specturma GDA650 instrument was used to record time-resolved spectrochemical information during the analysis of calamine. Glow discharge time of flight mass spectrometry (GD-TOFMS) experiments were carried out at EMPA with iron, titanium, copper, gold and iron oxide samples. Changes in emission intensities and ion signals of both analyte and carrier gas with addition of O2 are reported and discussed and compared to the cases of H2 & N2 additions. |
