Optical diagnostics of metals in high temperature environments.

Abstract

The thesis presents results for the detection of metal species in high temperature environments using optical techniques. Three optical techniques, namely laser Polarisation Spectroscopy (PS), Atomic Emission Spectroscopy (AES) and Laser-Induced Breakdown Spectroscopy (LIBS) have been employed. Each technique possesses some unique characteristics to achieve the aims of this work. The PS technique has been employed to detect atomic sodium (Na) in the seeded flames and plume of burning solid-fuel particles and to investigate atomic iron (Fe) in the welding fume plume. A mathematical equation has been developed to describe the lineshape of the target metal using PS technique in the high temperature environments, as follows: [figure omitted] The capability of PS technique employed for the quantitative measurement has been assessed. Due to the nonlinear measurement, the quantitative measurement using PS is not applicable in this work. In particular, the atomic Na released from burning solid-fuel particles. However, the qualitative analysis of atomic Na and Fe has been demonstrated. The time-resolved records of atomic Na released from the burning solid-fuel particles and the Stark shift of atomic Fe in the welding fume have been observed. The AES technique has been used to record the temporal atomic Na and K released from burning solid-fuel particles. The qualitative analysis of the simultaneous release of atomic Na and K using AES has been demonstrated. However, the quantitative analysis is not applicable in the present experimental arrangement. The temporal records of atomic Na and K were associated with the instantaneous shrinkage of burning solid-fuel particles. This implies that the release of atomic Na and K is related to the burning particle size. It was observed that the peak release of atomic Na and K released from the burning solid-fuel particles occurred at the end of char phase simultaneously. The quantitative measurement of atomic Na and K released from burning solid-fuel particles using LIBS has been achieved. The time-resolved histories of atomic Na and K released from burning solid-fuel particles are consistent with those measured using PS and AES. Unlike conventional quantitative measurement using LIBS, a particular absorption, termed as signal trapping to the calibration process, caused by the atomic Na or K in the outer seeded flames has been indentified. The overall comparison among three optical techniques summarizes the advantages and disadvantages of the metal detection in high temperature environments. The PS technique is capable of being applied to detect metal species in strong background environments. The AES possesses the capability of multi-element detection in flames with the characteristics of low cost, good sensitivity and simple experimental arrangement. However, the quantitative analysis of target metal species is not eligible for both techniques. The LIBS technique demonstrates the quantitative analysis with an appropriate calibration curve.