he extent of BiInO₃ substitution in the perovskite system xBiInO(₃)-(1 - x)PbTiO₃ and the corresponding raise in the transition temperature were investigated using thermal analysis, dielectric measurements, x-ray diffraction, and electron microscopy. Maximum tetragonal perovskite distortion (c/a = 1.082) was obtained for x = 0.20, with a corresponding Curie temperature of 582°C. Phase-pure tetragonal perovskite was obtained for x less than or equal to 0.25. Compound formation after calcining mixed oxide powders resulted in agglomerated cube-shaped tetragonal perovskite particles, which could be fired to 94.7% of theoretical density (TD). Niobium-modified BIPT ceramics with PT contents of 80% and 85% were found to possess significantly lower dielectric loss at elevated temperatures, making it possible to polarize the materials. Piezoelectric properties were measured for a 1.5 mol% Nb -0.15BI-0.85PT composition with a transition temperature of 542°C; the longitudinal piezoelectric coefficient and coercive field were found to be 60 pC/N and 125 kV/cm, respectively. Compositions of xBiLaO₃-(1 − x)PbTiO₃ over the range 0 < x < 0.225 were calcined and sintered. Dielectric constant with temperature and differential scanning calorimetry measurements were in excellent agreement with respect to a Curie-like tetragonal to cubic transformations starting at 495°C for pure PbTiO₃, shifting to lower temperatures with increasing x. For compositions of x > 0.05, a second higher-temperature (∼600°C) endotherm, and matching dielectric anomaly, were consistently observed, for which there were no structural changes indicated by hot-stage x-ray diffraction. This transformation was interpreted to be similar to a Curie transformation in relaxor ferroelectrics in which localized segregation of B-site cations (below the resolution limit of x-ray diffraction) facilitated ferroelectric behavior.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (p. 153-161).

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 217-223). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 217-223). Also available on the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Peter F. Green. Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

O estudo do processo de fusão e solidificação da água contida dentro de materiais confinantes tem sido amplamente discutido em química, biologia, física, geologia, e com diversas aplicações tecnológicas, tais como aplicação na fabricação de etanol de segunda geração, ou etanol celulósico, separação de fases, fabricação de nanomateriais. Pesquisas mostraram que as temperaturas de transição da água nanoconfinada são muito sensíveis ao diâmetro do poro, mas que podem ser pouco afetadas pela natureza, hidrofóbica ou hidrofílica, da superfície do poro. Outra importante constatação em experimentos de fusão e congelamento em nanoporos é que nem toda água presente nos poros pode ser cristalizada até gelo. A existência de uma camada de água pré-fundida em nanoporos tem sido confirmada através de experimentos. Com o objetivo de entender mais profundamente como a temperatura de transição da água confinada depende da natureza da parede confinante e do tamanho do confinamento, propõe-se um modelo de nanoporos de celulose para o confinamento, onde varia-se o diâmetro e comprimento do nanoporo, além da natureza da parede do nanoporo. Nossos estudos, mostram que para sistemas hidrofóbicos, com formação de camada de água líquida na parede, as temperaturas de transição variam desde relativamente baixas, para menores valores de calor latente, até atingindo a temperatura de transição da água bulk, para calor latente mais alto. Enquanto que para sistemas hidrofílicos, para nenhum dos valores de calor latente trabalhados, e para nenhum tamanho do sistema, a temperatura de transição atinge o valor de bulk. / The study of the fusion process and water solidification inside confining materials has been widely discussed in Chemistry, Biology, Physics, and Geology, and has various technological applications as the usage and fabrication of second generation ethanol or cellulosic ethanol, phase separation, and nanomaterials fabrications. Researches have shown that nanoconfined water’s transition temperature are highly sensitive to the pore. Another interesting remark on freezing and fusion experiments on nanopores is that not all water present in pores can be crystallized into ice. The existence of a water layer pre-melted on nanopores has been confirmed through experiments. Aiming at understanding deeply how water’s transition temperature depends on the nature of the confining wall and size, a cellulose nanopore model is proposed to the confinement, where the nanopore diameter and length are varied, besides the nature of the wall of the nanopore. Our studies show that for hydrophobic systems, with the liquid water layer formation on the wall, the transition temperatures vary from relatively low latent heat to smaller values, even reaching the temperature transition on bulk water to higher latent heat. While for hydrophilic systems, for none of the latent heat used and no system size the transition temperature reaches bulk value.

Made available in DSpace on 2014-10-09T12:47:50Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:26Z (GMT). No. of bitstreams: 1 08511.pdf: 4385457 bytes, checksum: a0c4d3d31c582b2a850f8616fec84e9e (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-06-11T19:29:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-03-25Bitstream added on 2014-06-13T19:38:22Z : No. of bitstreams: 1 lombardo_cel_me_arafo.pdf: 3996119 bytes, checksum: c7eb8e08977bab50ee60b2bacfeaab4e (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Este estudo avaliou o efeito da irradiação por microondas e da armazenagem em água sobre as propriedades viscoelásticas de duas resinas para base de prótese (Lucitone 550- L e Vipi Wave- VW) e duas resinas para reembasamento imediato (Kooliner- K e Tokuyama Rebase Fast II- TR II). Oito corpos-de-prova (40 x 10 x 3,3 mm) de cada material foram avaliados por meio de análise térmica dinâmico-mecânica (DMTA) após: acabamento (controle 1), armazenagem em água por 7 dias (controle 2), um (MW1) e 7 ciclos de irradiação por microondas (MW7). Para cada corpo-de-prova, ciclos de DMTA foram realizados dentro de intervalos de temperatura diferentes. Os valores do módulo de armazenamento (E’) e de amortecimento mecânico (tan δ) a 37ºC foram obtidos no primeiro e último ciclos de DMTA. A partir do último ciclo, os valores de E’ na temperatura de transição vítrea (Tg) e o máximo de tan δ também foram obtidos. Os dados foram submetidos à análise de variância a dois critérios e ao teste de Student-Newman-Keuls (α=0,05). Além disso, mensurações de temperatura no interior de corpos-de-prova de cada material, durante a irradiação por microondas (650 W/ 3 min), foram realizadas por meio da utilização de sensor de fibra óptica. Seis corpos-de-prova de cada material foram avaliados. Durante a irradiação por microondas, todos os corpos-de-prova atingiram a temperatura de ebulição da água em aproximadamente 130 s. A partir do primeiro ciclo de DMTA, MW 1 e controle 2 aumentaram significantemente os valores de E’ e reduziram os valores de tan δ de K a 37ºC (P<0,05). No último ciclo de DMTA, o tan δ de K e TR II foi significantemente reduzido após MW1 (P<0,05). MW7 reduziu os valores de tan δ de K (P<0,05). Os valores de E’ de L e VW foram semelhantes entre si e superiores aqueles produzidos por K e TR II (P<0,05). Na Tg, K produziu o menor E’ e seu máximo... / This study evaluated the effect of microwave irradiation and water storage on the viscoelastic properties of two denture base resins (Lucitone 550-L and Vipi Wave-VW) and two reline resins (Kooliner-K and Tokuyama Rebase Fast II-TR II). Eight specimens (40x10x3.3mm) of each material were evaluated by dynamic mechanical thermal analysis (DMTA) after: processing, water storage for 7 days (WS), one (MW1) and 7 cycles of microwave irradiation (MW7). For each specimen, DMTA runs were carried out within different temperature intervals. Values of storage modulus (E’) and loss tangent (tan δ) at 37ºC were obtained from the first and last runs. From the last run, values of E’ at the glass transition temperature (Tg) and maximum tan δ were also recorded. Data were analyzed by 2-way ANOVA followed by Student-Newman-Keuls test (α=0.05). In addition, measurements of the inside temperature of each specimen during microwave irradiation (650W/3min) were conducted using a fiber optic temperature sensor. Six specimens of each material were evaluated. During microwave irradiation, all specimens reached the boiling temperature of water at approximately 130 s. From the first DMTA run, MW1 and WS significantly increased the E’ and decreased the tan δ of K at 37°C (P<0.05). From the last run, the tan δ of K and TR II was significantly decreased after MW1 (P<0.05). MW7 decreased the tan δ of K (P<0.05). The E’ of L and VW was similar and higher than K and TR II (P<0.05). At Tg, K produced the lowest E’ and its maximum tan δ was increased after MW1 (P<0.05). The Tg mean values were arranged as: L>VW>TR II>K (P<0.05). Microwave irradiation and WS did not detrimentally affect the viscoelastic properties of the denture base and reline resins evaluated.