Biomimetic route to hybrid nano-Composite scaffold for tissue engineering

Hydroxyapatite-poly(vinyl) alcohol-protein composites have been prepared by a biomimetic route at ambient conditions, aged for a fortnight at 30±2°C and given a shape in the form of blocks by thermal cycling. The structural characterizations reveal a good control over the morphology mainly the size and shape of the particles. Initial mechanical studies are very encouraging. Three biocompatibility tests, i.e., hemocompatibility, cell adhesion, and toxicity have been done from Shree Chitra Tirunal, Trivandrum and the results qualify their standards. Samples are being sent for more biocompatibility tests. Optimization of the blocks in terms of hydroxyapatite and polymer composition w.r.t the applications and its affect on the mechanical strength have been initiated. Rapid prototyping and a β-tricalcium – hydroxyapatite combination in composites are in the offing

High Temperature Specific Heat Capacity Measurement of Ni2+XMn1-XGa

The investigation of Ni2MnGa ferromagnetic shape memory alloys relies on accurate and complete phase diagrams for the various phase transitions these materials exhibit. However, very little work has been performed to investigate the high temperature order/disorder phase transitions. This project tries to fill some of the gap in the phase diagram through a systemic composition based investigation of Ni2-XMn1+XGa (X=-0.2, 0.0, 0.2, 0.8 and 1.0) using high temperature specific heat measurements. The work has produced a phase diagram in the composition range measured and demonstrated that the order/disorder transition temperatures and Curie temperatures follow the predicted trend as seen in similar studies of different alloy compositions. This work has also characterised the melt temperature of the five compositions measured. As part of the investigation of the high temperature phase transitions, a ‘High Temperature Adiabatic Calorimeter” was developed, which was commissioned using four reference samples (copper, Stainless steel, graphite and molybdenum). The developed system used a linearly drifting baseline to improve the speed, accuracy and stability of the system. This modification to the standard adiabatic calorimeter measurement scheme required extensive development of the analysis techniques and development of new approaches (e.g. heating phase analysis and finite element modelling analysis). The system was demonstrated to operate well between room temperature and 1350 K, producing accurate specific heat data that compared well with the standard data for the commissioning samples. Due to time constraints this system was not used for the Ni2MnGa investigation

Studies on the Impact Initiation and Kinetics of Condensed Phase Reactives with Application to the Shock Induced Reaction Synthesis of Cubic Boron Nitride

Shock induced reaction synthesis is a complex, scientifically rich field with the potentially to produce novel materials with unique properties. This work seeks to understand the processes governing shock induced reaction synthesis. Particular emphasis is placed on the reaction kinetics of condensed phase reactives under various mechanical and thermal heating rates. This understanding was then applied to the synthesis of cubic boron nitride through shock induced reaction synthesis. Mechanical initiation of reactions in powder systems involve complex interactions that can yield unexpected results. Two materials that exhibit similar thermal responses can behave very differently under the same loading conditions due to differences in their mechanical properties. Reactive composite powders with small characteristic dimensions can exhibit short ignition delays and reduced thermal ignition thresholds; however, a full understanding of the response of these powders to rapid mechanical loading is still unclear. This work seeks to clarify the role of mechanical properties in impact induced ignition by considering the response of nanolaminate (NL) powders and high energy ball milled (HEBM) Ni-Al powders subjected to impact loading. The powders were placed into a windowed enclosure and mechanically loaded using a light gas gun, which allowed the resulting reactions to be observed using high-speed imaging. Even though the thermal ignition temperatures for the two powders are within 30 °C of each other, it was observed that the NL powders reacted on the microsecond timescale, immediately following the compaction wave for a short distance before decoupling from the compaction front. In contrast, the HEBM powders reacted after a several millisecond delay and clearly propagated as a deflagration front. Microindentation showed that the HEBM powders are much more ductile than those of NL. This suggests that the primary difference between the behavior of these materials on impact results from the ability and degree of the material to fracture, illustrating that the mechanical properties of a reactive material can have a dramatic effect on ignition during impact loading. By using the jump equations to understand compaction events, it is easy to think about the compaction wave as a discontinuity, with no structure. In practice this is not the case. Both shock waves and compaction events have been observed to have a structure with a finite thickness. Studies of the propagation of shocks through monolithic solids have shown that the strain rate, which is directly related to the shock width, scales with the pressure rise to the fourth power. Studies of dynamic compaction of porous materials have shown that this relationship is closer to linear. This work seeks to study the effect that increasing the crush strength of the compact has on the width of the compaction wave. Ball milling is used to produce strain hardened powders that are then pressed to form a porous compact. Plate impact experiments are performed to evaluate the equation of state and measure the shock width of both milled and unmilled powders. The results show that a Mie-Gruneisen equation of state accurately predicts the response of all materials tested; however, the compaction width is found to change with milling condition. For all materials tested, the compaction width is found to decrease with increase pressure rise; however, the unmilled material is found to have a longer rise time compared to the ball milled material. This results in a reduction in apparent viscosity with increased crush strength. It is suggested that stress waves percolating ahead of the compaction front (since the velocity of the compaction wave is below the acoustic velocity of the parent material) and their interaction defines the compaction width. In a weaker material, a weaker stress is required to begin compaction, resulting in a broader front compared to a stronger material and an increased viscosity. Despite their widespread use, the reaction pathways of thermite (reduction-oxidation) reactions are relatively unknown. Multilayer thin films produced through magnetron sputtering provide a highly controlled geometry and direct contact between reactives, making them an ideal platform to study atomic-scale processes underlying thermite reactions. This work utilizes the multilayer thin film geometry to study the combustion and reaction pathway of equimolar Al-NiO. The low heating rate kinetics and product phase growth are studied through hot-stage X-ray diffraction and differential scanning calorimetry. The results indicate significant product formation beginning as low as 180°C, and results in the formation of nickel aluminum intermetallic phases. Hot-plate ignition experiments show that ignition occurs in the solid state for fine bilayer thicknesses, with a transition to melt dependent reaction for multilayers with larger bilayer thicknesses. Laser ignition and self-propagating reactions are observed to exhibit a similar length scale dependence in reaction behavior. The activation energy determined from the hot-plate ignition experiments was found to be less than that for the laser ignition experiments, indicating a heating rate dependent response. This work culminates with the direct synthesis of cubic boron nitride through shock loading of 3B+TiN composite particles. It was found that reduction of the diffusion distance through high energy ball milling before loading was critical for success, with unmilled powders showing no evidence of reaction after recovery. The results show the possibility of rapid reaction occurring in a condensed phase system at microsecond timescales. As a results, optimization of this process may provide a route for the fabrication and discovery of other advanced compounds

Nature’s Optics and Our Understanding of Light

Optical phenomena visible to everyone abundantly illustrate important ideas in science and mathematics. The phenomena considered include rainbows, sparkling reflections on water, green flashes, earthlight on the moon, glories, daylight, crystals, and the squint moon. The concepts include refraction, wave interference, numerical experiments, asymptotics, Regge poles, polarisation singularities, conical intersections, and visual illusions

The Plaston Concept

This open access book presents the novel concept of plaston, which accounts for the high ductility or large plastic deformation of emerging high-performance structural materials, including bulk nanostructured metals, hetero-nanostructured materials, metallic glasses, intermetallics, and ceramics. The book describes simulation results of the collective atomic motion associated with plaston, by computational tools such as first-principle methods with predictive performance and large-scale atom-dynamics calculations. Multi-scale analyses with state-of-the art analytical tools nano/micro pillar deformation and nano-indentation experiments are also described. Finally, through collaborative efforts of experimental and computational work, examples of rational design and development of new structural materials are given, based on accurate understanding of deformation and fracture phenomena. This publication provides a valuable contribution to the field of structural materials research

Antenna near-field wave studies in magnetized plasmas as part of the optimization of auxiliary heating in fusion devicesAntenna near-field wave studies in magnetized plasmas as part of the optimization of auxiliary heating in fusion devices

C

Doctor of Philosophy

dissertationAl 5xxx alloys are widely used in marine and offshore structures for their excellent balance of weight, strength, ductility, weldability, and corrosion resistance. However, they can become sensitized when exposed to elevated temperature for a long time, which is caused by the precipitation of intergranular β phase. β phase is anodic to Al matrix and can be selectively dissolved by corrosive solutions, such as sea water, and cause intergranular corrosion and stress corrosion cracking. In the present study, Al 5xxx alloys (Al 5083, Al 5456, Al 5050, Al 5052, and Al 5154) were aged at constant temperatures (40, 50, 60, 70℃) and cyclic temperatures (40-45, 30-70, 50-70℃) for as long as 57.5 months. The microstructure was investigated using electron backscatter diffraction (EBSD), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS), atom probe tomography (APT), and small angle neutron scattering (SANS). Experimental results reveal that a phase transformation process from GP zones to β’/β phases occurs for precipitates formed in both Al 5083 H131 and H116 aged at 70℃. The size of intergranular and intragranular β phase increase with aging time. In addition, a model based on local equilibrium of chemical potential and multiclass precipitates number evolution was adopted to predict the multiphase precipitation process in the Al-Mg binary system. The overall trend of precipitate radius and number density predicted by the model match well with experimental results. Moreover, the particle size distribution (PSD) of different Mg-rich precipitates demonstrates their different stages of precipitation. A classical nucleation-growth-coarsening theory for the description of intergranular precipitation is formulated, which adopts a collector plate mechanism, an equivalent average Mg concentration at the grain boundary, and a new coarsening expression. Three coarsening mechanisms, the modified LSW (Lifschitz-Slyozov-Wagner), the Kirchner mechanism, and a combination of these two mechanisms, are compared. Modeling results reveal that the Kirchner mechanism will break down when continuity ( ) is close to 1. According to the new model, the coarsening mechanism still accounts for a small fraction (only 10%) in the final growth rate after aging at 70℃ for 40 months, which is confirmed by the precipitate size distribution data. Thickness and continuity results predicted by the new model agree well with experimental results obtained from scanning transmission electron microscopy (STEM) images of Al 5083 H131 alloys aged at 70℃ for different times. In addition, the new model is also applied to a high-temperature 180℃ situation, where precipitate coarsening is observed. ASTM G-67 Nitric Acid Mass Loss Test (NAMLT) results of Al 5050 H32, 5052 H32, 5154 H32, 5083 H116, 5083 H131, and 5456 H116 alloys were obtained to evaluate the Degree of Sensitization (DoS). A linear relationship between continuity and mass loss was adopted to predict the mass loss of Al 5083 H116 and H131 aged at constant and cyclical temperature, and the modeling results agree well with experimental mass loss data