Characterisation of powders using\ud microwave cavity perturbation

Doctoral thesis English OPEN
Cuenca, Jerome A. (2015)
  • Subject: TK

The contribution in this thesis is a novel application of microwave cavity perturbation in\ud the characterisation of the fundamental properties of powders.\ud This thesis shows that microwave cavity perturbation is very good at characterising the\ud magnetite to maghemite phase change through dielectric and magnetic measurements.\ud This is very important in material science since conventional techniques, though powerful\ud and are able to verify the change, use complex methods. Quantifying di�erent forms of\ud magnetite and maghemite is important for magnetic drug delivery and EMI absorbers.\ud This thesis shows that microwave cavity perturbation can be used to measure the impurities\ud of nanodiamonds through simple dielectric measurements. This is important because\ud other methods again may involve complex systems, while microwave cavity perturbation\ud can provide a fast, sensitive �gure of merit. Nanodiamonds are used in drug delivery and\ud bio-labelling which requires accurate surface characterisation.\ud This thesis shows that microwave cavity perturbation can measure in-situ temperature dependent\ud and photocatalytic responses in materials such as titania using a novel correction\ud procedure. Microwave cavity perturbation has not been used with this correction procedure\ud before which simpli�es the system when monitoring systematic errors. This work is\ud important as it shows how simple microwave cavity perturbation systems can provide insight\ud to thermally activated processes and veri�cation of some photocatalytic mechanisms\ud in powders for use in pigmentation and light induced drug delivery.
  • References (169)
    169 references, page 1 of 17

    2 Theory: Microwave Cavity Perturbation 31 2.1 Principle of MCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.1.1 Simpli ed MCP Equation . . . . . . . . . . . . . . . . . . . . . . . . 33 2.1.2 Depolarising and Demagnetising MCP Equation . . . . . . . . . . . 34 2.1.3 Cavity Wave Equations . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.1.4 TM Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 2.1.5 TE Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.2 Resonator Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 2.2.1 Cavity (ZR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 2.2.2 Antennas and Cross Coupling (ZC(!) and j!Lkl) . . . . . . . . . . . 49 2.2.3 Impedance Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 2.2.4 Scattering Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 51 2.2.5 Resonance Asymmetry . . . . . . . . . . . . . . . . . . . . . . . . . . 53 2.3 Cavity Measurement Procedure . . . . . . . . . . . . . . . . . . . . . . . . . 58 2.3.1 Coupling Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 2.3.2 VNA to provide S-Parameters . . . . . . . . . . . . . . . . . . . . . . 58 2.3.3 Errors in measurement . . . . . . . . . . . . . . . . . . . . . . . . . . 60 2.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

    3 Methodology: Microwave Cavity Systems 63 3.1 Methods to measure microwave magnetism . . . . . . . . . . . . . . . . . . 64 3.2 A simpler approach: Multi-mode MCP . . . . . . . . . . . . . . . . . . . . . 65 3.3 Design of Cyl- and Cyl-" Systems . . . . . . . . . . . . . . . . . . . . . . . 66 3.3.1 Dielectric Measurement Modes . . . . . . . . . . . . . . . . . . . . . 67 3.3.2 Magnetic Measurement Modes . . . . . . . . . . . . . . . . . . . . . 68 3.3.3 Breaking Degeneracy for Magnetic Modes . . . . . . . . . . . . . . . 69 3.3.4 Calibration and Gnmp of Cyl- . . . . . . . . . . . . . . . . . . . . . 71 3.3.5 Calibration and Gnmp of Cyl-" . . . . . . . . . . . . . . . . . . . . . 72 3.3.6 Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 3.4 Experiment: Extraction of Magnetic Properties . . . . . . . . . . . . . . . . 75 3.4.1 Aims and Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 3.4.2 Measured Resonant Frequency and Quality Factor . . . . . . . . . . 75 3.4.3 Cavity Calibration for Permittivity and Permeability . . . . . . . . . 77 3.4.4 Samples and Procedure . . . . . . . . . . . . . . . . . . . . . . . . . 78 3.4.5 Permittivity Measurements . . . . . . . . . . . . . . . . . . . . . . . 79 3.4.6 Permeability Measurements . . . . . . . . . . . . . . . . . . . . . . . 82 3.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

    4 Methodology: Microwave Cavity for Temperature Dependent Properties 85 4.1 Measuring temperature dependent dielectric and magnetic properties . . . . 86 4.2 A Novel Approach: Using Nodal modes for Temperature Correction . . . . 87 4.3 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 4.3.1 Temperature Dependence of Frequency . . . . . . . . . . . . . . . . 88 4.3.2 Temperature Dependent Bandwidth . . . . . . . . . . . . . . . . . . 89 4.3.3 Nodal Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 4.3.4 Method for Applying Correction . . . . . . . . . . . . . . . . . . . . 92 4.4 Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 4.4.1 Aims and Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 4.4.2 Node Perturbation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 4.4.3 Ambient Temperature Drift . . . . . . . . . . . . . . . . . . . . . . . 95 4.4.4 Empty Temperature Ramp . . . . . . . . . . . . . . . . . . . . . . . 96 4.4.5 Sample Holder Ramps . . . . . . . . . . . . . . . . . . . . . . . . . . 99 4.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

    5 Study: Microwave Characterisation of the Fe3O4 to -Fe2O3 Transition 103 5.1 Synthesis and Characterisation of -Fe2O3 . . . . . . . . . . . . . . . . . . . 104 5.2 A Novel Approach: MCP to measure oxidation state . . . . . . . . . . . . . 105 5.3 Experiment: MCP measurements of annealed Fe3O4 . . . . . . . . . . . . . 108 5.3.1 Aims and Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 5.3.2 Samples and Procedure . . . . . . . . . . . . . . . . . . . . . . . . . 108 5.3.3 XRD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 5.3.4 XPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 5.3.5 VSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 5.3.6 MCP Permittivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 5.3.7 MCP Permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 5.4 Experiment: MCP Temperature Dependent Mechanisms of Fe3O4 . . . . . 123 5.4.1 Aims and Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 5.4.2 Samples and Procedure . . . . . . . . . . . . . . . . . . . . . . . . . 124 5.4.3 Temperature dependent MCP permittivity of Fe3O4 . . . . . . . . . 124 5.4.4 Temperature dependent permeability of Fe3O4 . . . . . . . . . . . . 127 5.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

    6 Study: Microwave Determination of Impurities in Nanodiamond 133 6.1 Characterisation of Nanodiamond Purity . . . . . . . . . . . . . . . . . . . . 134 6.2 A Novel approach: MCP to measure impurities . . . . . . . . . . . . . . . . 135 6.3 Experiment: Determination of impurities with MCP . . . . . . . . . . . . . 136 6.3.1 Aims and Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 6.3.2 Samples and Procedure . . . . . . . . . . . . . . . . . . . . . . . . . 136 6.3.3 Raman Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 6.3.4 XRD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 6.3.5 FESEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 6.3.6 MCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 6.4 Experiment: Frequency Dependence and Loss Mechanisms . . . . . . . . . . 145 6.4.1 Aims and Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 6.4.2 Analysis of MBCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 6.4.3 Samples and Procedure . . . . . . . . . . . . . . . . . . . . . . . . . 147 6.4.4 Broadband MCP and MBCP . . . . . . . . . . . . . . . . . . . . . . 149 6.4.5 Microwave Loss Mechanism . . . . . . . . . . . . . . . . . . . . . . . 151 6.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

    7 Study: Photo-reactivity of Titania Powders 155 7.1 Characterising photo-reactivity . . . . . . . . . . . . . . . . . . . . . . . . . 156 7.2 A Novel approach: Improved Nodal MCP Method . . . . . . . . . . . . . . 158 7.3 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 7.3.1 Photo-excitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 7.3.2 Carrier Lifetime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 7.4 Experiment: Photo-reactivity of Anatase and Rutile . . . . . . . . . . . . . 161 7.4.1 Aims and Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 7.4.2 Samples and procedure . . . . . . . . . . . . . . . . . . . . . . . . . 161 7.4.3 UV-VIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 7.4.4 MCP Photo-excitation . . . . . . . . . . . . . . . . . . . . . . . . . . 164 7.4.5 MCP - Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 7.4.6 Trapped charges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 7.4.7 Lifetime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 7.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

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