No description available.

Titanium alloys find extensive use in the biomedical field, including applications in the form of a porous structure as a scaffold material for bone repair. Scaffold materials have demanding mechanical and biocompatibility requirements, which vary depending on the orthopaedic application. These requirements are determined by both the porous macrostructure of the foams and the strut wall microstructure. Therefore techniques are needed to characterise these structural features and relate them to the mechanical and physical properties. In this thesis new methods were developed to both manufacture titanium alloy foams and characterise them. Non- destructive X-ray micro-computed tomography (μCT) methods were employed to characterise the pore and interconnect size. The pore and interconnect size dominates the flow properties (permeability) of open-foam structures. Thus, μCT data was meshed and computational fluid dynamics analysis was performed to predict permeability. Direct finite element modelling, continuum micromechanics and analytical models of the foam were employed to characterise the elasto-plastic deformation behaviour. Pore anisotropy was quantified and related to the yield stress anisotropy, allowing identification of initial pore collapse. These results were validated against experimental measurements. Finally, the conventional production method of porous titanium is achieved through a costly multi-step powder metallurgical (PM) route. A new, potentially low cost, method was developed to produce porous titanium with properties similar or better than the existing titanium foam from a ceramic precursor via an electrochemical route. Two steps were involved: (1) preparing the ceramic precursor foam via a gel-casting route; and (2) reducing the oxide electrochemically via the FFC (Fray, Farthing and Chen) Cambridge process. The results of this preliminary study are very promising, with the foams produced via this method demonstrating mechanical and physical properties comparable to conventionally manufactured foams.

Designing tissue engineering scaffolds with the required mechanical properties and favourable microstructure to promote cell attachment, growth and new tissue formation is one of the key challenges in the tissue engineering field. An important class of scaffolds for bone tissue engineering is based on bioceramics and bioactive glasses. The primary disadvantage of these materials is their low fracture resistance under load and their high brittleness. These drawbacks are exacerbated by the fact that optimal scaffolds must be highly porous (>90% porosity). As a main focus of this thesis, a novel approach was investigated to enhance the structural integrity, fracture strength and toughness of partially sintered 45S5 Bioglass® based glass-ceramic scaffolds by polymer infiltration and to develop an understanding of the interaction of these two phases in the final composite structure. Commercially available synthetic poly(D,L-Lactic acid) (PDLLA) was incorporated as a coating onto the partially sintered Bioglass® based scaffolds by dipping technique. Two natural polymers synthesised from bacteria, which exhibit different properties to those of PDLLA, were also investigated: i.e. poly(3-hydroxybutryate) (P(3HB)) and poly(3- hydroxyoctanoate) (P(3HO)). The work of fracture of partially sintered 45S5 Bioglass® scaffolds was significantly improved by forming interpenetrating polymerbioceramic microstructures which mimic the composite structure of bone. It was demonstrated that coating with polymers such as PDLLA, P(3HB) and P(3HO) does not impede the bioactivity of the scaffolds but the extent of bioactivity, given by the kinetic of HA formation, was seen to depend on polymer type and on scaffold sintering conditions. Polymer coated 45S5 Bioglass® pellets sintered at the same condition as the scaffolds and immersed in SBF were investigated to better evaluate the bioactivity mechanism and interfacial properties of the materials. It was demonstrated that polymer coated 45S5 Bioglass® based glass-ceramic scaffolds can have higher bioactivity and improved fracture toughness when the basic scaffold structure is sintered at relative lower sintering temperatures leaving residual open porosity which can be efficiently infiltrated by the polymer. A bilayered scaffold structure was also designed and fabricated to develop for the first time a porous bioactive glass-ceramic scaffold coated with PDLLA nanofibers. Electrospinning was used to deposit a PDLLA fibrous layer on top of the bioactive glass scaffold. These scaffolds were developed for osteochondral tissue engineering applications. SBF studies showed that the extent of mineralisation of the PDLLA fibres depended on the fibrous mesh thickness. PDLLA fibres deposited for 2 hours did not mineralise when immersed for 7, 14 and 28 days in SBF making the structure suitable for osteochondral defect applications. Initial in vitro cell response studies showed that the bilayered scaffolds were non toxic and chondrocyte cells were able to proliferate on the PDLLA fibre layers, demonstrating the potential of the novel scaffolds for osteochondral tissue engineering.

Ordinary Portland cement (CEM-I) is widely used across the construction industry. It is the most commonly used cementitious binder for ground improvement applications such as deep dry soil mixing (DDSM) in the UK, due to its high strength performances. However, CEM-I production is one of the world’s most energy intensive and expensive industrial processes; contributing up to 7% of the world’s total CO2 emissions (McLellan et al., 2011). Hence, there is now significant pressure on the cement and construction industries to greatly reduce their CO2 emissions by developing “greener” alternatives to CEM-I, which are both more environmentally and financially sustainable in the long-term. Alkali activated industrial waste materials, known as geopolymers have been identified as potential alternatives to CEM-I. There are numerous advantages in recycling industrial waste materials such as ground granulated blast furnace slag (GGBS) and pulverised fly ash (PFA), including avoiding the need to transfer such materials to landfill, their abundant supply, negligible or zero production costs and for calcium-bearing wastes such as slags, their recently determined potential for carbon capture and storage (CCS). This thesis presents recent laboratory research which focussed on the potential for utilising alkali activated industrial waste materials as sustainable binders in DDSM to enhance the geotechnical properties of soft soils. The laboratory testing programme deployed geotechnical and mineralogical tests to determine the performance of the binders when incorporated into a soft alluvial soil, typically found in abundance across the UK. Comparisons with the strength and durability of untreated and stabilised soils have been made. The study indicates that from the by-products tested, soils stabilised with sodium hydroxide (NaOH) activated GGBS resulted in the greatest strength and durability improvements; with other materials tested showing smaller improvements. The addition of NaOH has been observed to allow pozzolanic reactions to occur, leading to improved mechanical properties; primarily strength, which increased with time. Abstract Secondary Minerals to Replace Cement in Stabilising an Alluvium ii The effectiveness of DDSM treatment in stabilising sections of high-speed railway lines with ground conditions dominated by soft and highly compressible soils, has previously been well demonstrated (Holm et al., 2002; Hughes and Glendinning, 2004). Traditionally, the monotonic strength properties of stabilised soils have been used to assess their suitability for stabilising railway embankments. However, the dynamic strength properties of such materials require investigation in order to provide better estimates of their field behaviour when subjected to complex loading conditions associated with high-speed railway embankments and high-frequency train traffic. Hence, this thesis combines monotonic and dynamic triaxial testing techniques to assess the suitability of the new GGBS-NaOH binder for stabilising high-speed railway embankments. After 28 days curing, the binder successfully demonstrated itself as an effective countermeasure against significant track displacements after the simulated passage of a typical InterCity 125 high-speed train. This thesis advocates that there is great potential for using GGBS-NaOH as a more environmentally and financially sustainable binder over CEM-I for DDSM projects in the UK, such as the proposed HS2 and HS3 rail links. However, further research and collaboration with the construction industry is still required before the new binder may be used on a commercial scale.

No description available.

Glass polyalkenoate cements (GPCs) are produced from a reaction between fluoroaluminosilicate glass powder with poly(acrylic acid) (PAA). These cements are widely used in dentistry as adhesive and tooth restorative materials. During the setting reaction, the Al(IV) changes its coordination number to Al(VI) and crosslink to PAA chains. In the present work, the structure of the glass and the setting reaction of GPCs were studied by 29Si, 31P, 19F and 27Al magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. The influences of alumina content as well as mixed cation such as Ca/Na and Ca/Sr on the glass structure were studied. The Q structure of the glass changed with the alumina content as the number of neighbouring Al in SiO4 network decreased. The decrease in alumina content also resulted in more disrupted glasses and a higher tendency to undergo amorphous separation and crystallization because there are more Ca cation available to form NBO and F-Ca(n). Furthermore, the influence of substituting sodium for calcium was investigated. The Q structure of the glass was not affected with the addition of Na. It was found that Na penetrates the phosphorus and fluorine environments and forms Na/Ca pyrophosphate and F-Ca(2)/Na(1) and Al-F-Na(n) species. The effect of Sr substituting for Ca was also studied. It was suggested that Sr may have a little influence on the glass structure due to their similarity in charge to size ratio. The Sr may slightly affect the phosphorus environment due to the difference in field strength of Ca and Sr. In this study, the setting reaction of GPCs was followed by 29Si, 31P, 19F and 27Al MAS-NMR spectroscopy. All GPCs continue to have a pyrophosphate environment of Q1 Al-O-PO3 3- regardless of the original glass composition. This suggests that the Al(IV) from the Al-O-P bonds are not released from the glass network, thus are not available to crosslink to PAA chains. Therefore, the phosphate content is important for controlling the working and the setting time of GPCs. The conversion of Al(IV) to Al(VI) was determined from the 27Al MAS-NMR data and the Al(VI):Al(IV) + Al(V) ratio was calculated in order to follow the setting reaction of the GPCs. The addition of fluorine in the GPCs was found to enhance the acid attack during the setting reaction. In contrast, it was suggested that Na delays the setting reaction by forming Na polysalts and hence, disrupting the crosslinking of Al3+ to PAA. Although the presence of Sr has little influence on the structure of the glass, the conversion of Al(IV) to Al(VI) is lower for Sr and mixed Ca/Sr cements than Ca cement. The difference is not yet fully understood, but it is suggested that it may be due to the larger size of Sr ions. A commercial GPC, Carbomer® containing fluoroapatite (FAP) designed to remineralise in the mouth was also studied. This study showed the involvement of the FAP component in the setting reaction and hence, the amount of FAP available for promoting the remineralisation process decreases. The Al(V) is present in all GPCs regardless of the setting time. In addition, the participation of Al(VI) from the glass in the setting reaction is not clear because both Al(VI) in the glass and in the cement matrix have very similar chemical shift. The present work suggests that there are two sites of Al(IV) after the setting reaction, which are attributed to the Al(IV) in the original glass and in the degraded layer of the glass. The reduction of Al-F-Na(n) and Al-F-Ca(n) species after the setting reaction and the unavailability of Al-O-P bonds for acid attack suggest that ion exchange between cations (Na and Sr) with protons from PAA may take place during the setting reaction. All GPCs show similar fluorine environments after setting. It was suggested that fluorine maybe bonded to Al in higher coordination states than four. Finally, there is a reconstruction of the silicate network during the setting reaction, as a result of the release of Al3+ and other ions from the glass network. It is assumed that the reconstruction of the silicate network depends on the release rate of the Al(IV). It is hoped that the improved structural understanding of the glass and the setting reaction of the GPCs obtained during this study will lead to the design of new GPCs for specific applications.

Incineration of waste is increasing in the UK as landfill resources diminish. Municipalwaste incineration produces waste residues; bottom ash, fly ash and air pollutioncontrol (APC) residues. The present research project focuses on APC residues, whichare a hazardous waste arising from cleaning of incineration flue gases. APC residuesmust be pre-treated before disposal at hazardous landfill or placed in permanentsecure storage. The aim of this research project was to produce novel glass-ceramicsfrom optimised combinations of waste materials to provide a stabilised, safe materialof value and to provide an alternative to disposal. Pre-treatment of the APC residuesby washing was necessary to remove soluble chloride phases. Electrostaticprecipitator (EP) dust and soda-lime glass cullet were combined with the washed APCresidues as sources of glass forming oxides and borate. An optimised boratecontainingsilicate glass was produced from the wastes, from which dense, sinteredglass-ceramics and bulk glass-ceramics were successfully fabricated. A powdersintering method was used to produce a dense sintered material from washed APCresidues, EP dust and glass cullet. It was determined that the use of commerciallyavailable sodium borate (Neobor?) could be used to replace the waste source ofborate to produce a sintered material of equal mechanical and physical properties. Themain crystalline phases of all heat treated materials were wollastonite and gehlenite. The resulting mechanical and physical properties of the glass-ceramics and sinteredmaterials indicated they would be acceptable as construction materials. The results ofthe research project indicate that thermal treatment is a convenient technology for thesafe utilisation of a problematic waste (APC residues from municipal wasteincineration) in new products of potential commercial interest.

Proton conducting ceramics based on acceptor doped perovskites are the subject of investigation as candidate electrolyte materials for Solid Oxide Electrolyser Cells (SOECs). Specifically, BaCe0.9Y0.1O3-[delta](BCY10) and BaZr0.9Y0.1O3-[delta](BZY10) were investigated. Samples with greater than 95% of the maximum theoretical density were successfully prepared using a BCY10 commercial powder. It was found that when small additions of ZnO were added to a BZY10 commercial powder, a density of greater than 95% of the theoretical maximum was achievable whereas without ZnO addition, the maximum achievable density was 85%. BCY10 was found to have a total conductivity approximately one order of magnitude greater than Zndoped BZY10 over the entire temperature range studied. Spray pyrolysis and sol-gel methods were used successfully to prepare single phase pure BZY10 powders. The sintering behaviours of the powders produced by spray pyrolysis were found to alter significantly with changes in powder processing parameters. BCY10 and Zn-doped BZY10 cells were tested in electrolysis and fuel cell modes and the effects of varying operating conditions on cell performances were studied. At 750oC, the Area Specific Resistances (ASR) of a BCY10 cell in electrolysis mode was found to be lower when the anode compartment was humidified to [approximately equal]83% than to[approximately equal]3%. Below this temperature, ASR values were greater when using increased humidity levels. It was concluded that a degree of oxide ion conduction may be beneficial to the operation of proton conducting electrolysers. Post-test, BCY10 cell cross-sections were imaged using scanning electron microscopy and analysed using Energy Dispersive X-ray (EDX) spectroscopy. Significant erosion of grain boundaries regions close the electrode-electrolyte interfaces was observed and EDX spectroscopy results suggested the formation of a secondary phase in these regions, possibly Y:CeO2. Had testing continued over an extended period of time it is probable that BCY10 cells would have undergone mechanical failure.

Cathodic electrodeposition (CELD) is achieved via hydrolysis of metal ions by electrogenerated base to form metal oxideihydroxide films on a cathodic substrate. Hydroxides and peroxides can then be converted to oxides by thermal treatment. In this study, Ti02 thin films (both rutile and anatase phases) and cobalt-doped anatase films were successfully produced through this method. These materials have presented applications in electronic and magnetic devices, such as piezo-ceramics as well as in catalysis. The CELD technology and the characterization of these thin films are described in detail in this thesis. The various parameters (deposition time, current density and annealing temperature etc.) that affect the characteristics ofTi02 films deposited on Pt and Ti substrates have been explored. Focus ion beam imaging (FIB) and scanning electron microscopy (SEM) analysis show that the thickness of the film increases as the deposition time increases. Applying current density greater than 30 mA'cm-2 results in the film having a porous structure, however, little difference between films was observed when the current density was 20 mA'cm-2 or less. XRD data gave an indication that the as-deposited films were amorphous; after annealing at elevated temperatures (400°C ~ 1000°C) anatase and rutile phases were formed successfully. Samples were thermally treated under three different atmospheres: air, argon and argon/hydrogen (10% hydrogen). Different characteristics were observed after annealing. SEM and atomic force microscopy (AFM) show that the particle size increased after annealing in argon and argon/hydrogen. Preferred orientation ofthe films annealed in different atmospheres was observed and further investigated using high temperature in-situ XRD. Ti1-xCOx02-o films were successfully prepared on Ti and Si substrates. When the annealing temperature was above 600°C a CoTi03 phase was detected in the film, whilst maintaining the anneal temperature below 600°C resulted in only anatase peaks ((101) and (200)) being observed. The films annealed at 400°C show room-temperature ferromagnetism as determined by vibrating sample magnetometry, and the magnetization per unit volume was of the right order of magnitude (0.2-0.6JlB/CO) for dilute ferromagnetic oxide thin films. X-ray absorption spectroscopy studies showed that the cobalt was present as Co2+ and the XRD data were consistent with cobalt substituted anatase lattice as the lattice parameter increased from 9.0080(2) to 9.4780 (3)

Sol-gel derived bioactive glasses with the 70S30C composition (70 mol% SiO2 and 30 mol% CaO) have high potential as materials for bone regeneration and devices for sustained drug delivery. They bond to bone and have a unique tailorable nanoporosity, which affects protein adsorption and cellular response. The first aim of this thesis is to fully characterise the evolution of the nanoporous structure of sol-gel derived bioactive glass for the first time, to fully understand its nanostructure evolution and control. Nanoparticles that were produced early in the sol-gel process, agglomerated into larger particles during gelation and during thermal stabilisation. Calcium was found to not enter the silica network until the material was heated to 400 °C. This has implications for the homogeneity of the calcium distribution in sol-gel derived bioactive glasses. Region separation was found within sol-gel derived bioactive glass monoliths produced by the standard procedure. The calcium concentration and nanoporosity were found to be higher near the edge of the monoliths. This is believed to be caused by calcium accumulation on the outer surface of the monoliths during the drying stage of the sol-gel process. The homogeneity of monoliths was successfully improved by using Teflon moulds. To provide further control of the nanostructure of 70S30C, a method for increasing the nanopore diameter from 12 nm to 30 nm was devised by adding specific amount of trimethylethoxysilane (TMES) during the sol-gel process. A series of amounts of TMES were added at different time points during the sol-gel process. Solid state nuclear magnetic resonance (NMR) and electron microscopy were used to explore the mechanisms behind the changes in nanostructure. Protein adsorption to sol-gel glass was investigated using in situ studies by monitoring the adsorption of fluorescent-labelled proteins onto various types of solgel derived bioactive glasses under confocal microscope with fibrinogen as model protein. Fibrinogen molecules were found to penetrate into inner nanopores of TheraGlass® (a commercial glass with 17 nm nanopores) whereas no penetration was found into sol-gel derived silica (with 3 nm nanopores). Protein interactions were further studied by conducting bioactivity tests with SBF supplemented with 10% serum. Apatite deposition was found inhibited by the interference of serum proteins.