Micro-Hollow Cathode Discharge Analysis of Lunar Regolith Simulants
Open Access
- Author:
- Mukherjee, Amrita
- Graduate Program:
- Energy and Mineral Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- April 13, 2012
- Committee Members:
- Randy Lee Vander Wal, Thesis Advisor/Co-Advisor
- Keywords:
- Micro-Hollow Cathode Discharge
Plasma
Lunar Regolith Simulants
Optical Emission Spectroscopy - Abstract:
- The main objective of this work was to develop and demonstrate a Micro-Hollow Cathode Discharge (MHCD) method for the compositional analysis of lunar regolith simulants. The MHCD technique thus developed was tested for the basic analytical figures of merit such as elemental detection and concentration, linearity and dynamic range and sensitivity to matrix effects. Analytical precision and accuracy, the two key factors, essential for analytical analysis were also evaluated. The data from the MHCD are presented in two formats. The first is in the form of scaling factors that include both instrumental response and proportionality of signal to element concentration within a particular mineral. This data is presented in the format of separate plots of scaling factors for each element, across the simulants. By this cross-simulant comparison, variations in element sensitivity, i.e. signal per unit concentration, is viewed across the range of simulants tested. This affords direct testing of potential matrix effects. Such effects may arise because of different crystallography or bonding of the elements of interest within the different mineral components of the simulants. If manifested, depending upon their magnitude, it may present limitations on accuracy of elemental concentrations or more broadly limit the ability to identify minerals based upon their elemental concentrations. The second method of comparing the datasets from the simulants was by element concentration, as varied by simulant identity. This comparison was aligned with standard analytical evaluation for signal linearity and dynamic range. In this study the limits for each metric were set by the range of simulants and their corresponding mineral contents. Apart from this fundamental analytical evaluation, a key reason for this evaluation was to illustrate the manner by which a sample of unknown mineral content would be compared to a database of known minerals for a particular experimental configuration of the MHCD-OES (Micro-Hollow Cathode Discharge Optical Emission Spectroscopy) technique. Though the MHCD signal is the dependent variable, signal from an unknown sample could be inverted through the calibration curve to determine an elemental concentration, for each element. The set of elemental concentrations so determined would then permit mineral identification. Normalization of spectra accounts for signal variation with sample mass and change in intensity with time for any particular sample charge. To be noted, both of such data comparisons include instrumental response factors that vary with wavelength, and hence element identity. Therein as a mineral identification tool, the database and analyses would be specific to the instrumental configuration at this stage of development.