Student Number : 0009815Y -
PhD thesis -
School of Physics -
Faculty of Science / Determining the properties of composites and how these relate to those of
the components and the microstructure is extremely useful as it enables the
understanding of existing materials and the design of new materials with a
variety of applications. However, the link between the ac conductivity data
and the microstructure and composition of the composite is not a simple
one. Simulations of binary composites are presented which show that from
relatively simple component properties arise complex composite properties.
Accurate identi¯cation of the components of composites, using characteristic
frequencies, is demonstrated for simulated and actual experimental data.
The Maxwell-Wagner and Brick Layer Models, which are often applied
beyond the range of their original derivation, are found to consistently ¯t
the data of yttria-stabilized zirconia ceramics measured at various tempera-
tures. The results from ¯tting single crystal and polycrystalline sample data
indicate that accurate modeling of the properties of the polycrystalline sam-
ples requires more theoretical work on the conduction mechanisms in single
crystals and the grains of the ceramics.
Data from a polyester-resin/silicon system is found to be best ¯tted us-
ing the Single Exponent Phenomenological Percolation Equation (SEPPE)
with experimentally measured component properties as input. The percola-
tion threshold obtained suggests a system where the insulator tends coat the
conductor. The results show that, with the actual component properties as
input, the SEPPE can be used to qualitatively and semi-quantitatively model
and ¯t composite ac conductivity data.
Analysis of the ac conductivity of liquid-phase-sintered silicon carbide ce-
ramics showed that for this system, the features often observed in the imped-
ance spectra are all due to a multi-component grain bondary/binder phase
and not the SiC grains. This multi-component grain boundary phase can be
¯tted accurately to the Brick Layer Model, indicating a microstructure where
an insulating component coats a more conducting component.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/1752 |
| Date | 16 November 2006 |
| Creators | Sauti, Godfrey |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 17522068 bytes, application/pdf, application/pdf |
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