No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

High energy consumption is a crucial challenge in gas separation processes. With current energy intensive separation methods, there is a real need for more energy-efficient alternative technologies. Membrane technology demonstrates potential uses in industrial separation processes due to its potential energy efficiency, environmental friendliness, and small footprint. The continuous developments in material science contributed directly in enhancing the membrane performance through several engineering modifications such as thermal annealing, which presented visible improvements in gas permeation properties. The objective of this project was to investigate the thermal annealing of three fluorinated polymers (PAE1, PAE2, and TFMPD), aiming for favorable changes in gas permeation properties. In particular, each polymer was annealed for 3 h at various temperature values, targeting the intermediate stage, which is the zone where degradation started but a pure carbon structure stage was not formed yet. Overall, the thermal annealing study revealed that TFMPD had highest pure-gas separation performance among other polymers, in which the Robeson plots displayed that treated sample at 500 ºC surpassed the 2015 H2/CH4 upper bound, whereas the treated sample at 550 ºC surpassed 2019 upper bound of both CO2/CH4 and CO2/N2. Therefore, TFMPD can be a potential candidate polymer for membrane-based gas separation, especially for CO2 and H2 applications. This performance could be attributed to the internal structural changes in the polymer that occurred during thermal annealing. Hence, several characterization techniques were performed to detect these changes. For instance, it was realized that all polymers started crosslinking upon the thermal treatment at 350 ºC. Moreover, FTIR analysis indicated the release of several functional groups from treated polymers at high temperature values. Raman spectroscopy also confirmed that the observed substantial enhancement in gas permeation of annealed TFMPD at 550 ºC was due an early-stage carbon structure formation. Furthermore, several recommendations are proposed to continue the work in this project, which could lead to potential success of the thermally annealed polymers tested in this study in membrane-based gas separations applications.

<p> The work described in this thesis is devoted to the application of defect engineering in the development of silicon photonic devices. The thesis is divided into simulation and experimental portions, each focusing on a different form of defect engineered silicon: ion implantation induced amorphous silicon and solid-phase epitaxial regrowth suppressed polycrystalline silicon.</p> <p> The simulations are directed at silicon rib waveguide Raman laser applications. It is shown that a uniform, divacancy defect concentration will not enhance Raman gain. The excess optical loss and free carrier lifetime of rib waveguides with remote amorphous silicon volumes were simulated. Net gain was demonstrated depending on the geometry of the structure. For a waveguide structure with rib width, rib height and slab height of W = 1.5, H = 1.5 and h = 0.8 μm respectively, the optimal separation between the edge of the rib and the amorphous region is ~2.0 μm. Surface recombination velocity modification was shown to be an effective means to reduce free carrier lifetime.</p> <p> Experimental work was devoted to the characterization of a novel form of polycrystalline silicon created by amorphizing the entire silicon overlayer of a silicon-on-insulator wafer. Solid-phase epitaxial regrowth of the amorphous silicon is suppressed upon annealing due to the lack of a crystal seed and results in polycrystalline silicon. This material was characterized with ellipsometry, positron annihilation spectroscopy and x-ray diffraction. The material properties are shown to be heavily dependent on the annealing conditions. Ellipsometry showed that the refractive index at 1550 nm is comparable to crystalline silicon. Positron annihilation spectroscopy showed that the polycrystalline material exhibits a high concentration of vacancy-type defects while vertically regrown crystalline silicon does not. X-ray diffraction showed that the polycrystalline silicon is non-textured, strained in tension and is characterized by grain sizes less than 300 nm.</p> <p> Defect etching and optical measurements using a waveguide geometry were performed in order to characterize the lateral regrowth and the optical loss of the polycrystalline material. Lateral regrowth in the [011] direction was 1.53 and 0.96 μm for 10 minute anneals at 750 and 900 °C respectively, and at least 2.5 μm at 650 °C. Waveguide optical loss measurements with adjacent polycrystalline regions separated from the rib by at least 5.5 μm showed no separation dependence. The intrinsic optical loss of the polycrystalline material was estimated to be 1.05 and 1.57 dB/cm for TM and TE polarizations after a 900 °C anneal. Vertically regrown c-Si was shown to exhibit less than 3.0 dB/cm optical loss after annealing at 550 °C .</p> / Thesis / Master of Applied Science (MASc)

The automotive industry, has been innovating in the field of materials development in order to meet the demand for lower emissions, improved passenger safety and performance. Despite various attempts of introducing other lightweight materials (Al, Mg or polymers) in car manufacturing, steel has remained as the material of choice till date due to its excellent adaptability to systematic upgradation and optimization in its design and processing. One of the outcomes is the development of second generation high Mn TWin Induced Plasticity (TWIP) steels with excellent strength-ductility balance suitable for automotive applications. Cost effective high performance TWIP steel design is mostly based on its alloy design and advanced up and down stream processing methods (thermomechanical controlled processing (TMCP)) which can help achieve suitable microstructure to meet the property requirements. It has been observed that grain boundary migration (GBM) in austenite during high temperature TMCP stage dictates grain growth to control the final microstructure. This research work initially investigates the grain growth in Fe-30%Mn steel within a temperature regime of 1000-1200°C. Compared to conventional low Mn steel, austenite boundary mobility in Fe-30%Mn was found to be 1-2 orders of magnitude smaller. Atom probe tomography results showed no Mn segregation at austenite high angle grain boundaries (γ-HAGB) which rules out the effect of Mn solute drag on growth kinetics in Fe-30%Mn steels. Grain boundary character distribution (GBCD) study showed that the sample consists of two different population of grain boundaries. 50% of the grain boundaries are random HAGBs with high mobility. Remaining 50% are special in nature which introduce low mobility boundary/boundary segments in the global boundary network. The special boundaries are mostly in the form of Σ3 CSL boundaries or its variants like Σ9, Σ 27. These boundary/ boundary segments were introduced by the formation of annealing twins and their interactions with the random HAGBs. An attempt to investigate the effect of Mn on growth kinetics at 1200°C showed that Mn slows down growth kinetics up to 15 wt% predominantly by the formation of annealing twins. A qualitative study of the microstructures showed that as Mn concentration is increased from 1% to 15%, the annealing twin density increases resulting in Σ3 frequency to be 30%. The increased twinning frequency is attributed to the effect of Mn on lowering the stacking fault energy (SFE). Annealing twins, belonging to Σ3 CSL family, intersect the HAGBs resulting into twin induced boundary segments which possess very low mobility. In the light of this idea, slow grain growth in high Mn steel was attributed to the population of low mobility boundaries. The proposed ‘twin inhibited grain growth’ model clearly points to the low mobility boundary/boundary segments to be the rate controlling factor during grain growth in high Mn steels. The effect of carbon on grain growth in Fe-30%Mn steel showed that the presence of carbon makes the growth kinetics faster by a factor of 4 and 6 at 1200°C and 1100°C respectively. Although, atom probe tomography results indicated that in presence of carbon, Mn segregation takes place at γ-HAGBs in Fe-30%Mn steel, solute drag does not appear to play a role as it was seen that with increase in Mn content beyond 1%, the solute effect of Mn in slowing down HAGB migration becomes weak. Also, abovementioned higher mobility values are obtained from the growth kinetics of Fe-30Mn-0.5C. This once again highlights the fact that effect of Mn in slowing down grain growth is due to the low mobility of twin/twin related boundaries or boundary segments. Controlling grain growth has been commonly proposed to be accomplished through small addition (<0.1%) of microalloying elements (Nb, V and Ti) which can slow down GBM at high temperature by solute drag and at low temperature by precipitate pinning (Zener drag). This research work has also experimentally quantified the solute drag of Nb in a series of Fe- 30%Mn steels. Grain boundary mobility was estimated for various temperatures and niobium contents. An attempt was made to calculate the grain boundary mobility in presence of niobium using Cahn’s solute drag model. This calculated mobility, when used in the proposed ‘twin inhibited grain growth’ model, the predicted growth kinetics which showed very good fit with the experimentally obtained growth kinetics in case of Fe-30Mn-0.03Nb and Fe-30Mn-0.05Nb steels at 1100°C. The effect of Nb solute drag, thus captured using Cahn’s model, was shown to be slowing down only the HAGB migration in the microstructure, whilst the special boundary mobility was not affected by solute Nb. Another attempt was made through grain boundary engineering (GBE) to control grain growth in Fe-30Mn-0.5C steel. Using different TMCP schemes, GBCD was modified to produce maximum frequency of special boundary. Preliminary studies on grain growth of single step-grain boundary engineered samples did show a significant lowering of grain size compared to a no-GBE sample after grain growth. However, the effect of iterative GBE didn’t show any significant effect in controlling grain growth in spite of the fact that it increased Σ3 frequency to 64%. This probably indicates that the effect of GBE on grain growth by the formation of annealing twins/special low mobility boundaries is a complicated process which might involve twin/special boundary morphology, annihilation kinetics and formation of grain clusters in the microstructure other than the formation of immobile special triple junctions through the intersection of twins/special boundaries with the random HAGBs. / Thesis / Doctor of Philosophy (PhD)

No description available.