Hench developed the first bioactive material, Bioglass®, based on a soda-lime phospho-silicate glass. Most materials, elicit a neutral response when implanted into the human body. Bioglass®, however, was seen to create a positive response by depositing the body’s natural bone substance, Hydroxyapatite on its surface. Although it is recognised that compositional modifications effect bioactivity, there is very little comprehension of the composition-structureproperty relationships that result in such bioactivity. The objective of this investigation, therefore, was to study such fundamental relationships with respect to two components often found in bioactive glass compositions – P2O5 and MgO. The first component studied was P2O5. The design of two series was undertaken – the first, a straight substitution of silicon for phosphorus, varying the network connectivity, NC, and the second, a charge compensating series, keeping the NC constant. 31P and 29Si MAS NMR of the two series provided evidence that the glasses were phase separated, with a predominantly Q2 silicate structure co-existing with phosphorus in a predominantly Q0 orthophosphate environment. Raman, FTIR, density measurements, differential thermal analysis and dilatometric analysis all further supported the existence of this structure. Dissolution studies in SBF highlighted the importance of phosphorus on bioactivity, with the glass dissolution rates of both series increasing with the addition of phosphorus. Instead of the dissolution of a glass depending solely on ion exchange reactions, as previously thought, it is proposed that dissolution depends upon the balance existing between the NC of the silicate phase and the existence of isolated orthophosphate rich domains. It is hypothesised that phosphorus in a phase separated structure is far more important than previously suspected, with its ability to preferentially dissolve into solution, dominating over the effect of NC on the resultant bioactivity of the glass and apatite formation. The second component investigated was magnesium oxide and its influence on the glass structure when substituted for calcium oxide. Two series of glasses were designed, the first series with a high sodium content and the second series with a low sodium content. In order to eliminate any influence due to silicate network disruption, all glasses were designed to have a constant NC of 2.04. All physical parameters were seen to be related strongly to the substitution of magnesium oxide, in both series. 31P, 29Si and 25Mg MAS-NMR of the high sodium magnesium glasses highlighted that magnesium, rather than acting to depolymerise the silicate network by acting as a network modifier, was acting partially as an intermediate oxide with a proportion entering the network as MgO4 tetrahedra. The decreasing Tg and Ts values and increasing thermal expansion coefficients, with increasing MgO substitution, supported this theory; with the significantly weaker bond strength of Mg-O, compared to Si-O, explaining the experimentally observed weakening of the network. The corresponding results for the low sodium magnesium glasses also pointed to magnesium acting as an intermediate oxide, however, with a smaller proportion entering the silicate network as MgO4 tetrahedra. It is suggested that magnesium acts as an intermediate oxide in highly disrupted glasses, with a more disrupted glass giving a higher proportion of MgO4. Dissolution studies in SBF settled the previously controversial subject of magnesium and bioactivity, with the addition of magnesium resulting in decreased glass dissolution rates and apatite formation in both series. This work has highlighted the importance of having a detailed understanding of the composition-structure-property relationships which exist in a bioactive glass. It is suggested that, from the contribution this work makes to this understanding, coupled with the knowledge gained from parallel studies, we are now at the point where a specific bioactive glass composition could be engineered, and tailored for a particular biomedical application.

Due to their remarkable properties and unique dimensions, carbon nanotubes (CNTs) are considered as an exciting nano-reinforcement in a variety of inorganic matrix composites. However, published data is unable to clearly define the role of CNTs on the properties of these composites, in particular, the mechanical properties including hardness, stiffness, strength and fracture toughness. This lack of knowledge is due in part to manufacturing issues, such as the dispersion of CNTs, densification of composites and microstructural changes during sintering. Moreover, interest in the electrical and thermal properties of inorganic matrix composites demands a comprehensive functional property evaluation. The still unexplored technological properties of these composites, such as thermal shock, ageing, friction and wear resistance, also deserve particular attention, in order to identify the extent of improvement that can be achieved due to CNTs. The microstructural characterisation including the nature of CNT distribution and their embedded morphology in brittle and amorphous matrices is still unclear, together with the nature of the CNT/matrix interface. Finally, the effect of different CNT aspect ratios on properties is yet to be investigated in order to choose the most suitable CNT sizes for desired composite performance. The present study is, therefore, aimed at developing a model composite system of uniformly dispersed CNTs of different sizes and loadings in a dense, brittle and amorphous matrix, and exploring the real effect of CNTs on physical, mechanical, functional and technological properties of these composites together with their microstructural and interfacial characterisation. Indigenously synthesised and functionalised multiwalled carbon nanotubes (MWCNTs) of four different aspect ratios (~31-65) were used as reinforcement, up to 10wt% (13.2vol%) loadings, while silica (SiO2) glass was chosen as an inorganic matrix. Heterocoagulation upon colloidal mixing provided composite powders with homogeneously dispersed MWCNTs while pressureless sintering produced dense (96-99%) composites. The randomly oriented MWCNTs in the glass matrix showed a mechanical MWCNT/glass interface due to the interlocking of MWCNTs with the matrix. The indentation fracture toughness was improved, by up to ~100%, but hardness and stiffness decreased by 21-38% and 20-37%, respectively. The electrical conductivity increased by >11 orders of magnitude but the thermal conductivity showed limited improvement, i.e. 41-48%. The effect of different MWCNT sizes on the mechanical properties, such as hardness, elastic modulus and indentation fracture toughness, could not be determined due to the decrease in the densities of the composites containing higher aspect ratio MWCNTs; however, the functional properties, such as electrical and thermal conductivity, increased in proportion to the MWCNT size. The presence of MWCNTs in the thermal shock resistant silica glass matrix did not produce thermal cracking after a single quench to 20oC from 1200oC or multiple quenches from 1000oC; however, devitrification of the glass was observed. During the thermal ageing of composites (up to 1000oC for up to 96h), no significant degradation was observed at lower temperatures (500oC) except limited surface MWCNT oxidation. However, at 750oC, considerable MWCNT oxidation was noticed, and at 1000oC, cristobalite was also formed producing surface cracking on cooling. The decarburisation depth due to MWCNT oxidation increased with time and temperature, and completely porous composites were obtained after oxidation of all of the embedded MWCNTs. The friction coefficient decreased with increase in MWCNT content, while the formation of a stable graphitic layer in composites containing 10wt% MWCNTs reversed the otherwise increasing wear rate. Finally, the established composite processing route was applied to a commercial borosilicate glass system containing up to 10wt% (17vol%) MWCNTs. The microstructure along with the resulting mechanical and functional properties ensured the applicability of the developed model system, which is believed to serve as a guide in future for preparation of other technically relevant inorganic matrix composites containing CNTs for improved properties.

This thesis primarily concerns development of a non-destructive inspection method for 3mol% Yttria-Stabilised Zirconia Polycrystal (3Y-TZP) ceramics used for dental applications and a scoping study on applying the technique to other ceramic materials applied in thermal barrier coatings and other fields. Zirconia ceramics are materials of great interest for various engineering applications, primarily due to their stiffness, hardness and wear resistance. These factors in combination with the complex manufacturing processes may reduce the material strength and durability due to induced cracking. Knowledge of the extent of this cracking must be obtained and often, if each part is unique as in biomedicine, the assessment must be carried out for every part non-destructively so the part can be subsequently used. Only a few techniques are known for inspection of Zirconia ceramics, however these techniques are not able to detect flaws in thick (above 500 μm) parts. The main limitation for optical inspection of 3Y-TZP is the highly scattering nature of the material due to its multicrystalline grain structure (grains size of 500 nm) which, particularly in the visible region, reduces imaging capabilities. However, a transmission window in the mid-infrared (between 3 and 8 μm) exists opening up the potential for inspection at these wavelengths. Mid-Infrared Transmission Imaging (MIR-TI) and Confocal Mid-Infrared Transmission Imaging (CMIR-TI) techniques were developed for inspection of 3Y-TZP parts which allow for detecting sub mm scale cracks. The measured imaging resolution for the MIR-TI is 42 ± 5 μm, whereas for the CMIR-TI it is below 38.5 ± 5 μm. The maximum sample thickness inspected with the MIR-TI and CMIR-TI is 6 mm and 3.5 mm respectively, considerably more than currently available inspection methods. The MIRTI technique provides fast inspection of the part due to the large field of view (11 by 7 mm), however the high cost and limited imaging resolution make this technique less attractive. The CMIR-TI technique on the other hand is more cost effective due to reduced cost of the infrared sensor and it provides an enhanced imaging capabilities. The promising results achieved with the MIR-TI and CMIR-TI techniques led to the development of reflection equivalents (Camera-MIRI and Confocal-MIRI) for ceramic coating measurements, however further in-depth experiments to determine and quantify the capabilities of both techniques are required.

Glass fibres are usually coated with a complex mixture of an adhesion promoter and film former in an emulsion. The former is usually a silane which enhances adhesion to the matrix while the latter protects the fibres from damage during handling and ma'nufacture. Chemical vapour deposition (CVD) which introduces a function alised coating'specific to the matrix has much potential as a gas phase environmentally friendly technique. One such technique is low power (cold) plasma polymerisation, which can deposit a conformal molecularly thin coating with expected functional chemistry. In this work, plasma polymerization was used to modify the interfacial adhesion between the fibres and epoxy resin, to improve the interfacial properties, provide a correlation between single filament and high volume fraction adhesion tests for composites, and ultimately demonstrate the value of plasma polymerization as a functional coating for fibre reinforcements. Specifically, uncoated E-glass fibre tows were continuously coated with acrylic acid / 1, 7octadiene or allylamine 11, 7-octadiene plasma copolymers in the plasma reactor to optimize the bond with matrix resin. The surface chemistry of the coated fibres was characterised using X-ray photoelectron spectroscopy (XPS) and trifluoroethanol derivatisation (TFE). The concentration of the functional group (COOH), which can react with epoxy groups in the matrix, in the deposit increased with the acrylic acid content in the monomer feed. The similarly reactive amine (NH2) group exhibited the same trend as allylamine concentration in the monomer feed. The results of single fibre tensile tests show that the plasma polymer coating did not affect the fibre tensile strength, but reduced the variability within the statistics of the data. The interlaminar shear properties of high glass fibre volume fraction (Vj) composite were measured and correlated with interfacial properties determined by the single fibre fragmentation test. The thickness of the plasma polymer coating was varied using the residence time in the reactor. It was shown that at a thickness < 5 nm the interfacial stress transfer at a fibrebreak, in a composite, was greatest. This was attributed to the formation of an interphase through diffusion of the matrix into the crosslink coating on the fibre surface.

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