This research provides a comprehensive investigation in understanding the effect of the addition of graphene nano-platelets (GNP) on the mechanical, tribological and biological properties of glass/ceramic composites. We investigated two kinds of materials namely amorphous matrices like glasses (silica, bioglass) and polycrystalline matrices like ceramics (alumina). The idea was to understand the effect of GNP on these matrices as GNP was expected to behave differently in these composites. Bioglass (BG) was also chosen as a matrix material to prepare BG-GNP composites. GNP can improve the electrical conductivity of BG which can be used further for bone tissue engineering applications. The effect of GNP on both electrical conductivity and bio-activity of BG-GNP composites was investigated in detail. There were three main problems for fabricating these novel nano-composites: 1) Production of good quality graphene; 2) Homogeneous dispersion of graphene in a glass/ceramic matrix and; 3) Retention of the graphitic structure during high temperature processing. The first problem was solved by synthesising GNP using liquid phase exfoliation method instead of using a commercially available GNP. The prepared GNP were ~1 μm in length with a thickness of 3-4 layers confirmed using transmission electron microscopy. In order to solve the second problem various processing techniques were used including powder and colloidal processing routes along with different solvents. Processing parameters were optimised to fabricate glass/ceramic-GNP composite powders. Finally in order to avoid thermal degradation of the GNP during high temperature processing composites were sintered using spark plasma sintering (SPS) technique. Fully dense composites were obtained without damaging GNP during the sintering process also confirmed via Raman spectroscopy. Finally the prepared composites were characterised for mechanical, tribological and biological applications. Interestingly fracture toughness and wear resistance of the silica nano-composites increased with increasing concentration of GNP in the glass matrix. There was an improvement of ~45% in the fracture toughness and ~550% in the wear resistance of silica-GNP composites with the addition of 5 vol% GNP. GNP was found to be aligned in a direction perpendicular to the applied force in SPS. In contrast to amorphous materials fracture toughness and scratch resistance of alumina-GNP composites increased only for small loading of GNP and properties of the composites decreased after a critical concentration. There was an improvement of ~40% in the fracture toughness with the addition of only 0.5 vol% GNP in the alumina matrix while the scratch resistance of the composite increased by ~10% in the micro-ductile region. Electrical conductivity of the BG-GNP composite was increased by ~9 orders of magnitude compared to pure BG. In vitro bioactivity tests performed on BG-GNP composites confirmed that the addition of GNP to BG matrix also improved the bioactivity of the nano-composites confirmed using XRD analysis. Future work should focus on understanding electrical and thermal properties of these novel nano-composites.

Glass fibres are by far the most extensively used fibre reinforcement in thermosetting composites because of their excellent cost-performance ratio. However, glass fibres have some disadvantages such as non- renewability and problems with ultimate disposal at the end of a materials lifetime since they cannot be completely thermally incinerated. The possibility of replacing E-glass fibres with hemp fibres as reinforcement in sheet moulding compounds (SMC) is examined in this thesis. The composites are manufactured with existing SMC processing techniques and similar resin formulation as used in the commercial industry. An attempt is made to enhance/optimise the mechanical properties of hemp/polyester composites. For this the fibre-matrix interface is modified via chemical modifications with alkaline and silane treatments. Influence of hemp fibre volume fraction, calcium carbonate (CaCO3)filler content and fibre-matrix interface modification on the mechanical properties of hemp fibre-mat-reinforced sheet moulding compounds (H-SMC) is studied. The results of H-SMC composites are compared to E-glass fibre-reinforced sheet moulding compounds (G-SMC). In order to get a better insight in the importance of these different parameters for the optimisation of composite performance, the experimental results are compared with theoretical predictions made using modified micromechanical models such as Cox-Krenchel and Kelly- Tyson for random short-fibre-reinforced composites. These models are supplemented with parameters of composite porosity to improve the prediction of natural fibre composite tensile properties. The influence of impact damage on the residual exural strength of the H-SMC composites is investigated to improve the understanding of impact response of natural fibre reinforced composites. The result of penetration and absorbed energies during non-penetrating impact of H-SMC composites are investigated and compared to values for G-SMC. A simple mechanistic model has been developed for H-SMC composites and is used to get an insight into the impact behaviour of these composite as well as to provide a guideline to compare the experimental results with theoretically calculated data. The fracture toughness properties in terms of the critical-stress-intensity factor KIc, and critical strain energy release rate, GIc, of H-SMC and G-SMC composites are studied using the compact tension (CT) method. It was shown that fracture toughness of H-SMC composites is significantly lower than that of glass fibre reinforced composites (G- SMC). However, results show that with an optimum combination of fibre volume fraction, (CaCO3) filler and surface treatment of the hemp fibres can result in H-SMC composites that have fracture toughness properties that can be exploited for low to medium range engineering applications. It is recommended that to further improve the fracture toughness properties of these natural fibre reinforced composites more research needs to be devoted to the optimization of the fibre-matrix interface properties and ways of reducing porosity content in these composites. Finally, environmental impact of H-SMC composite with conventional G-SMC composite for automotive and non-automotive applications was compared. The composites were assumed to be made in a traditional SMC manufacturing method. Two different types of performance requirements; i.e. stiffness and strength were investigated for both the non-automotive and automotive parts. Two different disposal scenarios: landfill and incineration of the SMC product at the end of life was considered. The LCA results demonstrate that the environmental impact of H-SMC composites is lower than the reference G-SMC composites. G-SMC composites have a significantly higher environmental impact on climate change, acidification and fossil fuels than H-SMC composites. Where as H-SMC composites have a much higher impact on land use and ecotoxicity than G-SMC composites.

There are a number of “smart” coatings that can be applied to glass. These include self-cleaning coatings based on titanium dioxide, and low-E coatings based on fluorine-doped tin oxide. Products are often more desirable with colour options such as Pilkington Activ BlueTM. There are currently no alternatives to body tinting glass to achieve colour, which is a time-consuming and expensive procedure. The work in this project details a number of coloured coatings via the AACVD or combustion processing of metal nitrate/urea precursors.

Enamel damage and demineralisation are common complications associated with fixed orthodontic appliances. In particular, the clean-up of adhesive remnants after debonding is a recognised cause of enamel damage. Furthermore, fixed attachments offer retentive areas for accumulation of cariogenic bacteria leading to enamel demineralisation and formation of white spot lesions (WSLs). Bioactive glasses may be used to remove adhesives, preserving the integrity of the enamel surface, while also having the potential to induce enamel remineralisation, although their efficacy in both respects has received little attention. A systematic review evaluating the remineralisation potential of bioactive glasses was first undertaken. No prospective clinical studies were identified; however, a range of in vitro studies with heterogeneous designs were identified, largely providing encouraging results. A series of glasses was prepared with molar compositions similar to 45S5 (SylcTM; proprietary bioactive glass) but with constant fluoride, reduced silica and increased sodium and phosphate contents. These glasses were characterised in several tests and the most promising selected. This was designed with hardness lower than that of enamel and higher than orthodontic adhesives. Its effectiveness in terms of removal of composite- and glass ionomer- based orthodontic adhesives was evaluated against SylcTM and a tungsten carbide (TC) bur. This novel glass was subsequently used for remineralisation of artificially-induced orthodontic WSLs on extracted human teeth. The novel glass propelled via the air-abrasion system selectively removed adhesives without inducing tangible physical enamel damage compared to SylcTM and the conventional TC bur. It also remineralised WSLs with surface roughness and intensity of light backscattering similar to sound enamel. In addition, mineral deposits were detected on remineralised enamel surfaces; these acted as a protective layer on the enamel surface and improved its hardness. This layer was rich in calcium, phosphate, and fluoride; 19F MAS-NMR, confirmed the formation of fluorapatite. This is particularly beneficial since fluorapatite is more chemically stable than hydroxyapatite and has more resistance to acid attack. Hence, a promising bioactive glass has been developed.

Objectives: 1) To develop and investigate the bioactivities of a novel bioactive glass (BAG) composite designed as an orthodontic adhesive. 2) To investigate the preventive effect, and to test the bond strength of the adhesive. Methods: A novel, calcium and phosphate rich, and fluoride containing, bioactive glass (BAG) was prepared via the melt quench route and incorporated into an experimental resin to produce a light cured paste. The ratio of the resin to the powder was 20:80% respectively. The BAG powder was gradually replaced by a high fluoride and silica content glass (HSG) from 80%, to 60%, 50%, 40%, 25% and 0%. 90 disks (1.26mm thickness and 10mm diameter) were produced from each composition to be immersed in 3 solutions (demineralising artificial saliva pH=4 (AS4), remineralising artificial saliva pH=7 (AS7) and Tris buffer (TB) pH=7.3, 10 ml each. Measurements were taken at 10 time points (from 6 hours to 6 months) in 3 replicas in each solution. Ion release study was determined by ISE and ICP, and pH monitoring was conducted on the resulting solutions. Immersed disks were studied by FTIR, XRD, MAS-NMR and SEM for apatite formation. XMT were used to study the effects of this material on demineralisation/remineralisation in human enamel. Shear bond strength of the adhesive on bovine enamel were studied in different conditions using an Instron machine. Results: The pH increased with time for all the samples with BAG in all solutions and was linearly correlated to BAG loading. Ion release results revealed that the composite disks release up to 15ppm F-, 450ppm Ca2+ and 10ppm PO43- ions, and the release pattern is directly related to the immersion time, with the highest release found in AS4. FTIR spectra, XRD patterns and SEM images showed formation of apatite on all the BAG-resin disks, especially in AS4 and this increase with time. The MAS-NMR spectra indicated fluorapatite was also formed. The XMT studies showed that the novel material reduces demineralisation around the brackets by 80%. The shear bond strength of this novel material was comparable to that of Transbond XT. Conclusion: The novel BAG composites have significant long term releases of F-, Ca2+ and PO43- ions, especially in acidic conditions and form apatite (including FAP) in acidic and neutral solutions. This implies that the material has the potential as an orthodontic adhesive that can prevent white spot lesions around brackets.

Ever since Hench et al. first discovered bioactive glass in 1969, extensive interest was created because of the materials ability to chemically bond with living tissue. In this project the bioactivity of three different compositions of the bioactive glass Na2O-CaO-SiO2 have been studied. The compositions of the different glasses were A (25% Na2O, 25% CaO and 50% SiO2), B (22.5% Na2O, 22.5% CaO and 55% SiO2) and C (20% Na2O, 20% CaO and 60% SiO2). Their bioactivity was tested through biomimetic evaluation, in this case by soaking samples of each glass in simulated body fluid (SBF) and phosphate buffered saline (PBS). After soaking, the samples were analyzed with Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), Grazing Incidence X-ray Diffraction (GIXRD) and Fourier-Transform Infrared Spectroscopy (FTIR) to analyze if hydroxyapatite formed on the glass surfaces. Both the A and B glass showed bioactivity in SBF and PBS, while the C glass did not. Further work is necessary to determine which of the A and B glass has the highest apatite formability and the reason why the C glass were not bioactive.

Magister Scientiae Dentium - MSc(Dent) (Paediatric Dentistry) / The use of glass ionomer cement (GIC) restorative materials assists in the prevention of dental caries due to its long-term fluoride release. However, poor physical strength is one of the main drawbacks of GIC. A surface coating is recommended to improve the physical strength and is considered necessary during the overlapping stages of setting reactions of GIC restorative materials. The development of resin based coatings has improved the properties of the material but the effect on fluoride release needs investigation.

Thesis. 1977. Ph.D.--Massachusetts Institute of Technology. Dept. of Materials Science and Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / Ph.D.

Este trabalho consiste na caracterização óptica dos íons terras raras Er+3, Yb+3 e Gd+3 quando em vidros fluoroindatos. As técnicas utilizadas foram: absorção óptica, luminescência e tempo de vida. Foram realizadas medidas de upconversion em vidros dopados com os íons Er+3 e Yb+3 nas concentrações de 2% mol de ErF3 e concentrações de 0, 2 e 8% mol de Yb+3 com excitação em 0.8 e 0.98&#956m observando as transições 2H11/2 &#8594 4I15/2 4S3/2 &#8594 4I15/2 (verde) e 4F9/2 &#8594 4I15/2 (vermelho). Como resultado verificou-se que o Yb+3 aumenta a eficiência da emissão por upconversion no vermelho. Através de medidas espectroscópicas nos vidros fluoroindatos com Gd+3 não foi verificado tendência a cristalização destes vidros, mesmo para altas concentrações de Gd+3 Para o íon Gd+3em vidros fluoroindatos foram determinados os parâmetros de Judd-Ofelt, através dos quais determinamos as propriedades ópticas do íon e comparamos com os dados obtidos experimentalmente. Estes resultados se encontram em boa concordância / This work consists of the optical characterization of rare earth Er+3, Yb+3 and Gd+3 fluoroindate glasses by means of luminescence, optical absorption and lifetime techniques. Upconversion process were studied in Er+3, Yb+3 doped glasses (with the same ErF3 concentration and different Yb+3 concentrations) excited at 0.8 and 0.98&#956m. Transitions 2H11/2 &#8594 4I15/2 4S3/2 &#8594 4I15/2 (green) e 4F9/2 &#8594 4I15/2 (red) were detected. As a result, we conclude that the Yb+3 incorporation increases the emission efficiency of the red upconversion process. Spectroscopic measurements performed on Gd+3 fluoroindate glasses didn\'t point out crystallization tendency of the glasses, even for high Gd+3 concentrations. The Judd-Ofelt parameters of Gd+3 fluoroindate glasses were obtained, so that the optical properties of Gd+3 were determined. The results are in good agreement with the experiment

No presente trabalho, fizemos um estudo espectroscópico do vidro sódio aluminofosfato, cuja composição é (100-x) (NaPO3)3 - xAI(NaPO3)3visando utilizar a referida matriz como possível meio ativo para laser. Para isso, caracterizamos matrizes vítreas não dopadas e dopadas com o íon terra-rara Eu3+ e Nd3+. Nas matrizes não dopadas, procurou-se avaliar como algumas propriedades ópticas, como por exemplo, transmissão e alguns parâmetros estruturais (energia de fônon) se comportavam mediante a substituição sistemática do (NaPO3)3 pelo AI(PO3)3. O uso do Nd3+ como íon opticamente ativo nesta matriz vítrea, se deve ás suas excelentes características como elemento de prova. Para a caracterização destas amostras utilizamos diferentes técnicas, como por exemplo, excitação, luminescência sob excitação seletiva, absorção luminescência e tempo de vida. Os resultados obtidos, mostraram que com o aumento do alumínio a energia de fônon do vidro aumenta, o tempo de vida do nível 5D0 diminui e as bandas de emissão se alargam, o que indica que o alumínio causa uma desordem estrutural. O íon Nd3+, por ser um dos mais eficientes íons laseres, teve suas emissões avaliadas em função da composição, buscando uma matriz que otimizasse os parâmetros referentes à emissão laser. Devido a presença do grupo OH- na estrutura do vidro, o tempo de vida do nível laser 4F3/2 era menor que o calculado pela teoria de Judd¬-Ofelt, provocando então, uma baixa eficiência quântica de emissão (da ordem de 0.75). Então, a fim de evitar a presença dos referidos grupos, preparamos algumas amostras em atmosfera de nitrogênio (N2) dopadas com Nd3+, conseguindo assim, aumentar a eficiência quântica de emissão para 0.98 / In this work we have done a spectroscopic study on sodium aluminophosphate glasses of composition (NaPO3)- xAI(NaPO3)3 aiming to investigate the potential use of this glass host as laser active media when doped with Nd3+. Undoped samples were characterized to evaluate on what extent some optical properties, as transmission, and structural parameters (phonon energies), would be affected by systematic substitution of (NaPO3)3- AI(PO3)3. Since Eu3+ present excellent characteristics as a probe element, samples doped with this ion were characterized by excitation, luminescence with or without selective excitation, absorption and lifetime measurements. The results indicated that the phonon energy of the glass increases with increasing aluminum content, the lifetime of excited 5D0 state of Eu3+ decreases, and the emission bands are broadened. Such observations are evidences of an increase in structural disorder. Since Nd3+ is one of the most efficient laser ions, samples doped with it were also studied as a function of host compositional changes, aiming to optimize laser emission at 1.06 μm. Due to the presence of OH- groups in primarily prepared matrices, the experimental lifetime of laser level 4F3/2 was shorter than the one calculated by the Judd-Ofelt theory, resulting in a small quantum efficiency (≈0.75). To solve this inconvenience, Nd3+ doped samples were prepared under N2 atmosphere and that way, the quantum efficiency raised to a value of 0.97