Thesis (Ph. D.)--University of Pennsylvania.

Thesis (Ph. D.)--University of Pennsylvania.

Two HCP metals, titanium and zirconium, have been modelled using molecular dynamics and recently developed many-body potentials. These two metals have similar lattice parameters, c/a ratios, melting temperatures, elastic and dislocation properties and, more importantly, responses to radiation damage(Griffith 1988,1989 & 1991, Hood 1988 & 1993), but differ by nearly a factor of two in atomic mass, thereby allowing the direct investigation of the effect of mass on radiation damage in the HCP system. Using the MOLDY code, successfully modified for the HCP structure, these two models w re rigorously investigated with respect to their point defect properties, displacement threshold energy response, and cascade processes. A marked preference for interstitial sites within the basal plane was found, in accordance with previous static studies on HCP metals. The displacement threshold energy showed a complex dependence on orientation within the HCP structure, but at higher energies this effect was swamped by structural disruptions during cascade development. The effect of mass was exhibited as a proportional increase in the mean displacement threshold energy, which carries over into cascade generation. Cascade morphology was seen to undergo a transition at energies of -1 keV, associated with the onset of true cascade conditions. This transition was reflected most markedly in the relaxation time for the recombination phase beyond the cascade peak, and explanation is presented for the transition in terms of ballistic, energetic and temporal effects. The dissimilarities between the two models were found to be mainly attributable to the mass difference. The condition of the cascade core at the peak was seen to be close to that of a liquid, with some discrepancies which indicate a lack of true melting, and an absence of the vacancy clustering often associated with a molten cascade core. The approximation of liquid-like structure was supported by the isotropy of the cascade-induced atomic mixing, despite the preference for basal-plane movement in the solid state. In agreement with modelling of other metals, the defect production efficiency for true cascade conditions was well below the NRT estimate, and an empirical relationship between final Frenkel-pair numbers and PKA energy is presented. SIA clustering occurred to a similar extent in both models, and small clusters were highly mobile and confined to single <1120> rows in the basal planes. The implications of these findings for microstructural evolution are discussed, along with comparisons of the results with other systems.

No description available.

Current plastics are mostly derived from petrochemical sources, as it is a finite resource renewable replacements are sought after. Polymers derived from cyclic esters such as; lactide, valerolactone and caprolactone are of interest. An industrially viable method of producing stereocontrolled polylactide (PLA) from rac-lactide is desired. Previous work on poly(cyclic esters) is overviewed in chapter 1 with an emphasis upon PLA. Chapter 2 reports the coordination of Ti(OiPr)4 to homo/piperazine bridged bis(phenol) (salan) ligands. Under ambient conditions bimetallic structures were produced and a steric dependent equilibrium system is discussed. Forcing conditions resulted in monometallic homopiperazine salan complexes. Their application for the ring-opening-polymerisation (ROP) of rac-lactide is investigated. Homo/piperazine salan titanium catecholates were synthesised and their cytotoxicity investigated by collaborators. Chapter 3 details the synthesis of monometallic homopiperazine salan zirconium/hafnium isopropoxide complexes. Their utility for the ROP of rac-lactide in solution and solvent free systems are discussed. Bimetallic or tetrametallic solid state structures from attempts to coordinate Zr(IV)/Hf(IV) metals to piperazine salan ligands are also discussed. Chapter 4 discusses the complexation of AlMe3 with homopiperazine salan ligands. The resulting monometallic complexes were inactive for the ROP of lactide. Benzyl alcohol derivatives were synthesised and trialled for solvent free ROP of rac-lactide, δ-valerolactone, ε-caprolactone. Co-polymerisations were investigated and a tri-block polymer of poly(ε-caprolactone/δ-valerolactone/rac-lactide) was prepared. Chapter 5, trans-1,4-DACH salen ligands were synthesised and investigated as ligands with Al(III), Ti(IV), Zr(IV), and Zn(II) metal centres. Bimetallic Al(III) and Ti(IV) structures were characterised and trialled for the ROP of rac-lactide. Isotactic PLA was reported for aluminium complexes, dependent upon phenoxy substituents, and these polymerisations were shown to be immortal in nature. Chapter 6 details the synthesis of trans-1,2-DACH salalen ligands which were complexed to AlMe3, these initiators were investigated for the solution ROP of rac-lactide. The further synthesis of benzyloxy derivatives is also reported and they were utilised for solution and solvent free polymerisations of rac-lactide. The initiator’s behaviour is discussed with respect to varying amine and imine groups.

No description available.

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-04-12T21:33:19Z No. of bitstreams: 1 LEOPOLDO VIANA BATISTA NETO - DISSERTAÇÃO PPG-CEMat 2014..pdf: 2575700 bytes, checksum: a10f0685285492d2302637ed070d9631 (MD5) / Made available in DSpace on 2018-04-12T21:33:19Z (GMT). No. of bitstreams: 1 LEOPOLDO VIANA BATISTA NETO - DISSERTAÇÃO PPG-CEMat 2014..pdf: 2575700 bytes, checksum: a10f0685285492d2302637ed070d9631 (MD5) Previous issue date: 2014-08-28 / Filmes finos de Nitreto de titânio (TiN) e Nitreto de titânio-zircônio (TiZrN) foram depositados sobre substratos de aço inoxidável 316 usando o método de Sputtering RF para deposição dos filmes. O planejamento de experimentos (DOE) tem sido reconhecido como um método poderoso para otimizar um processo complexo na indústria. Os efeitos do presente estudo foram verificar a viabilidade e confiabilidade da aplicação do método DOE em processos de Sputtering RF, otimizar os parâmetros de processamento para o processo de deposição, identificando os parâmetros sensíveis que afetam a espessura da camada depositada (E.C.D) e a resistência à corrosão (Ecorr.). Para o método de Sputtering RF, dois parâmetros, a taxa e tempo de deposição foram escolhidos para serem os parâmetros do processo. Depois da deposição, a estrutura de camada depositada foi caracterizada por Difração de Raios X (DRX) e por Microscopia Eletrônica de Varredura (MEV). Após o ensaio de polarização, a corrosão foi realizada a fim de investigar a relação entre o início da corrosão e a espessura da camada depositada. A análise de variância (ANOVA) foi realizada para avaliar os parâmetros sensíveis e prever as condições ideais. Com base na análise estatística, os parâmetros mais sensíveis no processo de Sputtering RF foram tanto a taxa como o tempo de deposição do filme fino. As melhores condições de deposição foram a taxa de deposição máxima e tempo máximo. / Titanium nitride (TiN) and titanium-zirconium nitride (TiZrN) thin films were deposited on ASTM F 138 stainless steel substrates using de Sputtering RF methods. Design of experiment (DOE) has long been recognized as a powerful method to optimize a complex process in industry. The purposes of present study were to verify the feasibility and reliability of the application of DOE method on de Sputtering RF processes and optimize the processing parameters for the deposition process, in which the sensitive parameters that affected the film properties were also identified. For de Sputtering RF method, two parameters, deposition rate and time were chosen to be the operating parameters. After deposition, the thin film structure was characterized by X-ray diffraction (XRD), and high-resolution scanning electron microscopy (SEM). After the polarization test, the corrosion analysis was carried out in order to investigate the relationship between the corrosion initiation and the thickness of the deposited layer. The analysis of variance (ANOVA) was conducted to assess the sensitive parameters and predict the optimum conditions. Based on the statistical analysis, the most sensitive parameters in de Sputtering RF process were both the deposition rate and time. The optimum deposition conditions in each system were maximum deposition rate and time.

This Thesis describes the synthesis and characterisation of sulfonamide supported titanium, zirconium and aluminium complexes and their use as ring opening polymerisation catalysts for ε-caprolactone and rac-lactide. Chapter 1 introduces polyester use, development and characterisation in general. Metal catalysed ring opening polymerisation of cyclic esters is considered in a literature review of the field. Titanium, zirconium and aluminium complexes supported by polydentate sulfonamide ligands are also discussed. Chapter 2 describes the synthesis and characterisation of new sulfonamide supported titanium amide, isopropoxide and zirconium isopropoxide complexes. Their application as catalysts for the ring opening polymerisation of ε-caprolactone and rac-lactide is discussed and compared with known zirconium isopropoxide complexes supported by bis(phenolate) amine ligands. Chapter 3 describes the synthesis and characterisation of Cs symmetric titanium amide and alkoxide complexes supported by dianionic, tri- and tetradentate sulfonamide ligands. Zirconium alkyl and amide complexes supported by C3- symmetric trianionic ‘tren’ type ligands bearing three different sulfonamide groups are also presented. The application of these complexes for the ring opening polymerisation of ε-caprolactone and rac-lactide is described and compared with the complexes presented in Chapter 2. Chapter 4 provides an overview of the synthesis and characterisation of aluminium alkoxide and alkyl complexes supported by dianionic, tri- and tetradentate sulfonamide ligands. Solution state behaviour and solid state structures are presented and discussed. An assessment of these complexes for the ring opening polymerisation of rac-lactide is presented. Chapter 5 presents full experimental procedures and characterisation data for the new complexes reported. CD Appendix contains .cif files for all new crystallographically characterised complexes described, and additional polymerisation graphs.