Search

This study presents the effect of stoichiometry and annealing condition on Ti–Cr AB2-type hydrogen storage alloys. Prior to annealing the majority phase of the as-cast alloys was the C14 Laves phase, with separate Ti and Cr phases. Annealing treatment (1273 K/14 d) led to a transition from C14 to C15 Laves phase structure. Both C14 (as-cast) and C15 (annealed) cell size increased with Ti content, up to a ratio (Cr/Ti) of 1.6, due to B-site Ti substitution in the lattice up to a limit. Pressure composition isotherm (PCI) measurements demonstrated alloys containing a greater Ti content had a better maximum hydrogen storage capacity (1.5 vs. 1.03 wt%) and lower plateau pressure (9.4 vs. 15.8 bar) at 253 K. Annealing resulted in a lower storage capacity (1.05 vs. 1.49 wt%), greater plateau pressure (ca. 30 bar) and flatter plateau slope (25 % reduction in plateau slope). Reduction in hydrogen storage capacity of annealed alloys could be due to diffusion of residual Cr in the alloy into the C15 Laves phase during the annealing process, thereby changing the local composition as confirmed through X-ray diffraction (XRD).

This article presents a comprehensive review of the current landscape and prospects of large-scale hydrogen storage technologies, with a focus on both onshore and offshore applications, and flexibility. Highlighting the evolving technological advancements, it explores storage and compression techniques, identifying potential research directions and avenues for innovation. Underwater hydrogen storage and hybrid metal hydride compressed gas tanks have been identified for offshore buffer storage, as well as exploration of using metal hydride slurries to transport hydrogen to/from offshore wind farms, coupled with low pressure, high flexibility electrolyser banks. Additionally, it explores the role of metal hydride hydrogen compressors and the integration of oxyfuel processes to enhance roundtrip efficiency. With insights into cost-effectiveness, environmental and technology considerations, and geographical factors, this review offers insights for policymakers, researchers, and industry stakeholders aiming to advance the deployment of large-scale hydrogen storage systems in the transition towards sustainable energy.

Processing of highly reflective and high thermally conductive materials (Cu, Ag, etc.) by laser powder bed fusion (LPBF) is of increasing interest to broaden the range of materials that can be additively manufactured. However, these alloys are challenged by high reflectivity resulting in unmelted particles and porosity. This is exacerbated for in-situ alloying techniques, where divergent optical properties of blended powders further narrow the stable processing window. One possible route to improved uniformity of initial melting is through coating powders with an optically absorptive layer. In-situ alloying of Ti-Ag was chosen as a model to assess this, given the potential of Ti-Ag as a novel antimicrobial biomedical alloy, facilitating an ideal model to assess this approach. High purity Ag powder was coated with Ti via physical vapour deposition. Barriers to reliable coating were investigated, with agglomeration of particles observed at a sputtering power of 100 W. In-situ laser micro calorimetry demonstrated a significant improvement in melting performance for coated Ag powder, with continuous tracks attained at 280 W vs. 320 W for uncoated powder, and absorptivity increasing from 27 % to 45 % at 320 W incident laser power. Subsequent in-situ alloying of the Ag powder when blended with commercially pure Ti powder demonstrated that improved absorptivity allowed for more uniform densification of the blended powder bed at lower energy density (0.7 ± 1.0 vs 7.1 ± 2.0 % porosity at 133 J.m-1). Ultimately, this offers a promising route to improved alloy development via LPBF, through application of a homogeneous, relevant coating.

This study describes the chemical conversion and heat treatment of Ti6Al4V microspheres (Ti6_MS), and the resulting effects on their electrocatalytic properties. The wet-chemical conversion (5.0 m NaOH, 60 °C, 24 h; Sample label: Ti6_TC) converts the top surface of the Ti6_MS powder into an ≈820 nm thick sodium titanate surface. Heat-treatment (Ti6_TC_HT) at 450 °C increases the stability of the surface, through partial titanate crystallization, while mitigating excess rutile formation. All samples are analyzed chemically (XPS, EDX, Raman, EELS), structurally (XRD and TEM), and morphologically (SEM, TEM), demonstrating the characteristic formation of sodium titanate dendritic structures, with minimal chemical, structural, and morphological differences due to the 450 °C heat-treatment. The effect of the preparation methodology on oxygen reduction reaction (ORR) electrocatalytic performance is also tested. The introduction of the sodium titanate layer changes the mechanism of the ORR, from a mixed 4 electron/2 electron pathway to a predominantly 2-electron pathway. By maintaining the microspherical nature of the material while also tuning the surface of the material toward different reaction mechanisms, a design strategy for new electrocatalyst materials is explored.

Improving the surface of medical implants by plasma spraying of a hydroxyapatite coating can be of critical importance to their longevity and the patient’s convalescence. However, residual stresses, cracking, undesired crystallisation and delamination of the coating compromise the implants lifetime. A promising alternative surface application is an alkali-chemical treatment to generate bioactive surfaces, such as sodium and calcium titanate and their derivatives. Such surfaces obviate the need for high temperatures and resulting micro-crack formation and potentially improve the bioactive and bone integration properties through their nanoporous structures. Also, metallic ions such as silver, gallium and copper can be substituted into the titanate structure with the potential to reduce or eliminate the infections. This review examines the formation and mechanisms of bioactive/antibacterial alkaline titanate surfaces, their successes and limitations, and explores the future development of implant interfaces via multifunctional titanate surfaces on Ti-based alloys and on alternative substrate materials.

Retaining a robust fibre-matrix interface in an aqueous environment has been an enduring challenge for fibre-reinforced biocomposites. This study addresses the issue by applying a polydopamine coating as a coupling agent to annealed and non-annealed phosphate-based glass fibres. The presence of the polydopamine coating was confirmed using X-ray photoelectron spectroscopy and Raman techniques. The thickness of the coating increased with treatment time, forming a bimodal structure, and showed good correlation with the percentage of surface nitrogen observed via XPS. A 6 h coating period was selected to balance fibre strength improvements against degradation caused by the aqueous coating solution. In-situ polymerised polycaprolactone composites were produced using the fibres, resulting in improved retention of strength and modulus when the fibres were both annealed and coated. This is the first example of long-term retention of wet strength properties for phosphate-based glass fibre composites, falling within the target range for bone healing (6–12 weeks).

A novel approach was developed to reduce the corrosion rate of magnesium (Mg) metal, utilising titanate coatings. Magnetron sputtering was used to deposit ca. 500 nm titanium (Ti) coatings onto pure Mg discs, followed by hydrothermal conversion and ion exchange reactions to produce sodium and calcium titanate coatings. SEM confirmed the characteristic nanoporous structure of sodium and calcium titanate, with thicknesses ranging from ca. 0.8 to 1.4 µm. XPS analysis confirmed the presence of Ti4+—O, Na—O, and Ca—O bonding, whilst Raman spectroscopy demonstrated characteristic vibrational modes (such as TiO6 octahedral vibrations) of the sodium and calcium titanate perovskite structure. Furthermore, corrosion studies through potentiodynamic polarisation measurements demonstrated the NB/NH CaTC samples to be superior in reducing Mg degradation, compared to other samples tested, through an increase in Ecorr from −1.49 to −1.33 V, and the reduction in corrosion current density, icorr, from 0.31 to 0.06 mA/cm2 for Mg and NB/NH CaTC samples, respectively. There was a clear trend noted for the NB/NH samples, which showed an increase in Ecorr to more positive values in the following order: Mg < Ti coated < NaTC < CaTC. These nanoporous titanate coatings have potential to be applied onto degradable plates for bone fracture fixation, or other orthopaedic applications.

In recent years, it has been found that small weight percent additions of silicon to HA can be used to enhance the initial response between bone tissue and HA. A large amount of research has been concerned with bulk materials, however, only recently has the attention moved to the use of these doped materials as coatings. This paper focusses on the development of a co-RF and pulsed DC magnetron sputtering methodology to produce a high percentage Si containing HA (SiHA) thin films (from1.8 to 13.4 wt. %; one of the highest recorded in the literature to date). As deposited thin films were found to be amorphous, but crystallised at different annealing temperatures employed, dependent on silicon content, which also lowered surface energy profiles destabilising the films. X-ray photoelectron spectroscopy (XPS) was used to explore the structure of silicon within the films which were found to be in a polymeric (SiO2; Q4) state. However, after annealing, the films transformed to a SiO44- Q0, state, indicating that silicon had substituted into the HA lattice at higher concentrations than previously reported. A loss of hydroxyl groups and the maintenance of a single-phase HA crystal structure further provided evidence for silicon substitution. Furthermore, a human osteoblast cell (HOB) model was used to explore the in vitro cellular response. The cells appeared to prefer the HA surfaces compared to SiHA surfaces, which was thought to be due to the higher solubility of SiHA surfaces inhibiting protein mediated cell attachment. The extent of this effect was found to be dependent on film crystallinity and silicon content.

Titanate structures have been of interest in many sectors, including healthcare, due to their ease of manufacture (low processing temperature and simplistic equipment), ion exchange potential to produce multifunctional (bioactive and antibacterial) surfaces, as well as their nanoporosity. However, their use has been limited to only Ti-containing materials due to the specific wet chemical methodology employed. The work presented in this thesis demonstrates one of the first studies to generate gallium-doped titanate structures as a multifunctional surface, specifically to assess their cytocompatibility and antibacterial potential for biomedical applications. Successive wet chemical (5 M NaOH; 60 oC; 24 h), ion exchange (4 mM Ga(NO3)3; 60 oC; 24 h), and heat treatment (700 oC; 1 h) stages were employed on Cp-Ti surfaces. Gallium was shown to be fully incorporated (ca. 9 at.%) into the nanoporous titanate structure, and completely replaced sodium (initial Na content ca. 3 at.%). The heat treatment stage crystallised the amorphous titanate layer, which increased the stability and reduced the maximum level of Ga3+ released (ca. 2.76 vs. 0.68 ppm for pre- and post-heat treated gallium titanate samples, respectively) into DMEM over 7 d. Finally, the heat-treated gallium titanate samples were shown to be cytocompatible, compared to the non-heat-treated samples, which demonstrated a significant (p < 0.0001) reduction compared to the TCP control. Unfortunately, neither gallium titanate samples exhibited robust antibacterial properties against S. aureus. The applicability of titanate structures was furthered in this thesis through the optimisation and characterisation of novel wet chemical (5 M NaOH; 60 oC; 24 h) titanate-converted Ti thin films deposited via DC magnetron sputtering. The films produced were deposited onto 316L SS to function as thin coatings for orthopaedic applications. This was in lieu of the ‘gold standard’ plasma sprayed hydroxyapatite (HA) coatings, due to

Titanate structures have been of interest in many sectors, including healthcare, due to their ease of manufacture (low processing temperature and simplistic equipment), ion exchange potential to produce multifunctional (bioactive and antibacterial) surfaces, as well as their nanoporosity. However, their use has been limited to only Ti-containing materials due to the specific wet chemical methodology employed. The work presented in this thesis demonstrates one of the first studies to generate gallium-doped titanate structures as a multifunctional surface, specifically to assess their cytocompatibility and antibacterial potential for biomedical applications. Successive wet chemical (5 M NaOH; 60 oC; 24 h), ion exchange (4 mM Ga(NO3)3; 60 oC; 24 h), and heat treatment (700 oC; 1 h) stages were employed on Cp-Ti surfaces. Gallium was shown to be fully incorporated (ca. 9 at.%) into the nanoporous titanate structure, and completely replaced sodium (initial Na content ca. 3 at.%). The heat treatment stage crystallised the amorphous titanate layer, which increased the stability and reduced the maximum level of Ga3+ released (ca. 2.76 vs. 0.68 ppm for pre- and post-heat treated gallium titanate samples, respectively) into DMEM over 7 d. Finally, the heat-treated gallium titanate samples were shown to be cytocompatible, compared to the non-heat-treated samples, which demonstrated a significant (p < 0.0001) reduction compared to the TCP control. Unfortunately, neither gallium titanate samples exhibited robust antibacterial properties against S. aureus. The applicability of titanate structures was furthered in this thesis through the optimisation and characterisation of novel wet chemical (5 M NaOH; 60 oC; 24 h) titanate-converted Ti thin films deposited via DC magnetron sputtering. The films produced were deposited onto 316L SS to function as thin coatings for orthopaedic applications. This was in lieu of the ‘gold standard’ plasma sprayed hydroxyapatite (HA) coatings, due to

Titanate structures have been of interest in many sectors, including healthcare, due to their ease of manufacture (low processing temperature and simplistic equipment), ion exchange potential to produce multifunctional (bioactive and antibacterial) surfaces, as well as their nanoporosity. However, their use has been limited to only Ti-containing materials due to the specific wet chemical methodology employed. The work presented in this thesis demonstrates one of the first studies to generate gallium-doped titanate structures as a multifunctional surface, specifically to assess their cytocompatibility and antibacterial potential for biomedical applications. Successive wet chemical (5 M NaOH; 60 oC; 24 h), ion exchange (4 mM Ga(NO3)3; 60 oC; 24 h), and heat treatment (700 oC; 1 h) stages were employed on Cp-Ti surfaces. Gallium was shown to be fully incorporated (ca. 9 at.%) into the nanoporous titanate structure, and completely replaced sodium (initial Na content ca. 3 at.%). The heat treatment stage crystallised the amorphous titanate layer, which increased the stability and reduced the maximum level of Ga3+ released (ca. 2.76 vs. 0.68 ppm for pre- and post-heat treated gallium titanate samples, respectively) into DMEM over 7 d. Finally, the heat-treated gallium titanate samples were shown to be cytocompatible, compared to the non-heat-treated samples, which demonstrated a significant (p < 0.0001) reduction compared to the TCP control. Unfortunately, neither gallium titanate samples exhibited robust antibacterial properties against S. aureus. The applicability of titanate structures was furthered in this thesis through the optimisation and characterisation of novel wet chemical (5 M NaOH; 60 oC; 24 h) titanate-converted Ti thin films deposited via DC magnetron sputtering. The films produced were deposited onto 316L SS to function as thin coatings for orthopaedic applications. This was in lieu of the ‘gold standard’ plasma sprayed hydroxyapatite (HA) coatings, due to