Electron irradiation may be a useful method for treating inorganic cosmetic powders such as talc for undesirable microorganisms if it can be established that no loss of quality or efficacy results as a consequence of the technique. A commercial electron accelerator was used to prepare bulk samples by exposure to electron irradiation under different conditions. A morphological characterisation of the control talc was carried out using microscopy techniques and focused on the particle size, shape and surface features of individual particles. Asperity dimensions vs. Roughness values were compared. Assessment of the bulk properties of the powders as a function of absorbed dose showed no serious impact on the quality or efficacy of the powder for cosmetic applications. The particle size and the level of dust expelled during impact were maintained. Changes to the surface chemistry of the irradiated powders were apparent from an increase in pH and water retention with increasing dose. Improvements to the fragrance retention occurred for both irradiated powders tested. Importantly a satisfactory microorganism level was achieved with the lowest absorbed dose level tested i.e. 5 kGy. Analysis of the crystallography did not show the development of a new phase. Mechanical testing using a slip-peel tester found an increase in the stick-slip behaviour occurred for the powder exposed to the highest absorbed dose only. Atomic force microscopy (AFM) testing of the lift-off force showed an increase in adhesion with increasing dose. Surface roughness increased with dose, while no change in elastic properties was found using nanoindentation suggesting the differentiating factor is due to surface features. Microstructural analysis used the transmission electron microscope (TEM). Voids were observed, which decrease in size, yet increase in number with increasing voltage. Prior to void development a loss of crystalinity is seen using electron diffraction. Explorative data analysis using factor analysis and Independent Component Analysis was performed on the void development data to discover the controlling mechanisms. Two distinct normally distributed populations were identified, each driven by 2-3 critical mechanisms. The distinct behaviour differences of the mechanisms may be utilised for characterisation of more complex properties of crystal microstructures.
| Identifer | oai:union.ndltd.org:ADTP/242219 |
| Date | January 2007 |
| Creators | Hauptstein, Anneliese, Materials Science & Engineering, Faculty of Science, UNSW |
| Publisher | Awarded by:University of New South Wales. School of Materials Science and Engineering |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Anneliese Hauptstein, http://unsworks.unsw.edu.au/copyright |
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