Dissertations / Theses on the topic 'Bismuth silicate'

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.
Includes bibliographical references (leaves 206-213).
Photorefractivity is the modulation of index of refraction due to nonuniform illumination, and numerous applications have been demonstrated utilizing this nonlinear optical property. However, commercial production is seriously impeded by the inability to produce bulk material with the homogeneity of opto-electronic properties that is required for device applications. Bismuth Silicate, Bi12SiO20, (BSO) is a photorefractive material with outstanding properties including a fast response time and high sensitivity is studied. Its photorefractivity is due to a native defect whose exact nature and origin have not been unambiguously determined. Motivation for current research arose from unexplained optical variations observed in BSO that implicate convective interference as playing a role in native defect formation. Microgravity growth experiments are proposed in order to establish a controlled, convection-free environment to study the origin and nature of the critical native defect. This work aims at resolving critical aspects of performing quantitative microgravity growth experiments that include the interaction of BSO melts with its confinement material; development and characterization of a vertical Bridgman-Stockbarger growth system with a quantifiable, reproducible, and controllable thermal environment; and Bridgman-Stockbarger growth experiments. A comparative analysis of crystals was done in order to establish the relationship between variations in opto-electronic properties as a function of changes in growth conditions. Wetting experiments revealed the sessile drop method to be inappropriate for the BSO-platinum system due to grain boundary pinning. No fundamental difference between the wetting behavior in a terrestrial and a low gravity environment was observed.
(cont.) Results from the comparative analysis indicate a lower defect concentration in Bridgman-Stockbarger material as compared to Czochralski material. The ambient atmosphere during processing and high temperature annealing was found affect material response, including removal of the photochromic response and decrease of carrier lifetime. The lack of the critical defect in hydrothermal BSO, and its existence in all melt grown material indicates that the melt plays a fundamental role in its formation. Clustering in the melt is implicated in the literature from nonlinear melt properties. It is therefore hypothesized that these clusters in the melt act as precursors for native defect formation and subject to gravitationally induced convection. The support of the National Aeronautics and Space Administration is gratefully acknowledged.
by Michaela E.K. Wiegel.
Ph.D.

Les verres de silice dopés par le Bismuth sont très prometteurs en raison de leurs applications potentielles en termes de lasers à fibres et d’amplificateurs optiques large bande destinés aux télécommunications optiques. Toutefois, la nature des centres optiquement actifs dans de tels verres demeure un sujet d’intenses débats. Les méthodes spectroscopiques magnéto-optiques sont des outils puissants pour l’étude des centres paramagnétiques au sein de la matière condensée. Dans ce travail de thèse, les techniques de dichroïsme circulaire magnétique, de polarisation circulaire magnétique de l'émission et de résonance magnétique détectée optiquement ont été mises en œuvre pour étudier les verres dopés par le Bismuth. En association avec les méthodes spectroscopiques conventionnelles, nous avons montré la coexistence d’au moins deux types de centres optiquement actifs dans des verres de silice dopés par le Bismuth sans autres co-dopants et de trois types dans un verre aluminosilicate dopé par la Bismuth. L’analyse des données expérimentales a révélé que tous les centres proviennent de systèmes ayant un nombre pair d’électrons (ou de trous). Deux centres ont été identifiés aux ions Bi+ et aux défauts du réseau vitreux qui interagissent via des processus de transfert d’énergie. Le troisième centre est attribué aux clusters d’ions Bismuth et a été observé seulement dans des verres aluminosilicates fortement dopés. Pour la première fois, nous avons montré expérimentalement que l’effet laser dans le proche infrarouge est due à une transition interdite à partir du premier état excité d’un défaut du réseau vitreux
Bismuth-doped silica glasses are interesting due to the promising applications in fiber lasers and amplifiers for the communication purposes. Unfortunately, the nature of the optical active centre(s) in such glasses is still a subject of intense debuts.Magneto-optical methods of spectroscopy are very powerful tools for the investigation of paramagnetic centres in condensed matters. In this thesis, the magnetic circular dichroism, magnetic circular polarization of luminescence and optically detected magnetic resonance techniques were implemented to investigate Bi-doped silica glasses. Together with the methods of the conventional optical spectroscopy, we demonstrate the coexistence of at least two types of optical centres in a Bi-doped silica glass without other co-dopants and three types in a Bi-doped aluminosilicate glass. The analysis of experimental data revealed that all centres originate from systems with an even number of electrons (or holes). Two centres were identified as Bi+ ion and some defect in the glass network that interact via the energy transfer processes. The third centre is assigned to the clusters of Bi ions and it was observed only in the highly doped aluminosilicate sample. For the first time, we showed experimentally that the lasing related near-infrared luminescence is caused by a forbidden transition from the first excited state of the defect centre

Ce travail porte sur l'influence de nanoinclusions de silice sur les propriétés de transport du bismuth. Une technique de métallurgie de poudre est employée pour la production de poudres nanocomposites Bi-Si02. Des poudres Bi-y % vol. Si02 (0 [inférieur ou égal à] y [inférieur ou égal à] 15) sont élaborées par coévaporation de bismuth et de silice dans un four à arc. Une étude de la microstructure des poudres nanocomposites indique que les grains de bismuth sont systématiquement enrobés d'une couche de silice de quelques nanomètres d'épaisseur. Un mécanisme de formation des poudres à partir de bismuth, d'oxydes de bismuth et de silicium est proposé. Dans les matériaux massifs, la taille de grains est plus faible pour les nanocomposites que pour le bismuth car la silice empêche la diffusion lors du frittage. La résistivité électrique, le pouvoir thermoélectrique et la conductivité thermique de bismuth polycristallin et de nanocomposites sont mesurées entre 65 K et 300 K. La résistivité électrique est gouvernée par une compétition entre la concentration des porteurs et leur mobilité qui résulte soit en un comportement métallique, soit en un comportement semi-conducteur. La concentration de porteurs ainsi que la mobilité sont extraites à partir de mesures de 5 à 300 K du coefficient de Hall et de la magnétorésistance pour des champs allant de 0 à 7 T. Un comportement extrinsèque du bismuth et des nanocomposites est mis en évidence à basse température (T < 50 K). Il est expliqué par la présence d'états d'énergie additionnels dus aux joints de grains. Le pouvoir thermoélectrique des nanocomposites est plus élevé que celui du bismuth, l'explication se trouvant dans la présence de barrières de potentiel induites par la microstructure. La conductivité thermique des nanocomposites est fortement réduite par rapport à celle du bismuth, et elle est insensible à la fraction volumique de silice en raison d'un effet prédominant de la taille de grain sur la diffusion des phonons.

Le bismuth présente des propriétés thermoélectriques modérées sous forme massive. La réduction de sa dimensionnalité (les nanofils de Bi) permet d’améliorer sa propriété thermoélectrique, c’est-à-dire l’amélioration du coefficient de Seebeck S, la diminution de la résistivité électrique et de la conductivité thermique. Ces nanofils permettraient une utilisation pour la réfrigération Peltier. Les silices micro- et méso-poreuses possèdent des canaux qui permet de confiner les atomes de Bi et donc d’y intercaler des fils de Bi de diamètre de l’ordre nanométrique. Le Bi fusionné à haute pression a été compressé sous haute pression afin de l’insérer dans ces pores. La haute pression et la haute température sont obtenues par la cellule à enclume de diamant et la presse gros volume nommée CONAC28. La dynamique des réseaux et la stabilité des différentes phases de Bi ont été tout d’abord étudiées. Les résultats expérimentaux sont cohérents avec ceux calculé et le spectre de Bi III a été observé pour la première fois. Les échantillons composites Bi/silice micro- ou meso-poreuse élaborés ont été caractérisés par DRX, Raman, MEB, TEM, et DNP. Certaines techniques de caractérisation étaient efficaces pour confirmer l’intercalation du Bi dans les pores. Dans le cas de Bi/MFI, les chaines de Bi ont été observées avec le MET et présentent un diamètre de 6Å. Le nombre moyen de Bi par maille (14 Bi) a été déterminé par l’affinement Rietveld en utilisant le modèle calculé (24 Bi/maille). Des calculs DFT ont été réalisés pour les nanocomposites Bi/MFI afin de prévoir ses propriétés physiques. Ceux-ci montrent les composites avec 14 Bi/ maille présenterais une énergie de bande interdite entre 0,4eV et 1,69eV. Dans le cas de Bi/nanotubes de silice, seule la MET a permis la mise en évidence des nanotubes remplis avec Bi de diamètre de 4nm élaboré en CED ou des bâtonnets de Bi de diamètre autour de 10nm élaboré dans la CONAC28. En plus, les nanotubes dans le composite Bi/nanotube se sont cristallisés en quartz. Les mesures physiques ont été ensuite réalisées pour déterminer si les propriétés thermoélectriques sont améliorées. Avec la méthode de Van der Pauw, on a observé l’augmentation de la résistivité électrique des composites (10 fois et 3,3 fois élevés que celle de Bi massif). Par contre, le coefficient de Seebeck mesurée avec la méthode de pointe chaud présente un même ordre de grandeur pour Bi massif et les composites. Par conséquent, les mesures sur les nanofils de Bi isolés seront nécessaires
Bulk bismuth has moderate thermoelectric properties. The reduction of its dimensionality (for example Bi nanowires) can improve its thermoelectric properties, in other words, this reduction can improve the Seebeck coefficient, and decrease the electrical resistivity and thermal conductivity. These nanowires could be used for Peltier refrigeration. Micro- and mesoporous silica? have channels that allow to confine Bi atoms and thus to create nano-sized Bi wires inside. Molten Bi at high pressure was compressed under high pressure in order to insert it into the pores. High pressure and high temperature are generated by a diamond anvil cell (DAC) and a CONAC28 large volume press. The lattice dynamics and the stability of the different phases of Bi were first studied. The experimental results are consistent with those calculated and the Raman spectrum of Bi III was observed for the first time. The Bi/silica micro- and meso-porous composite samples were characterized by XRD, Raman, SEM, TEM, and NPD. Some characterization techniques were suitable to confirm the synthesis. In the case of Bi/MFI, Bi chains of 6Å were observed with TEM. The average number of Bi atoms per cell (14 Bi) was determined by the Rietveld refinement using the calculated model (24 Bi/cell). DFT calculations have been performed for Bi/MFI nanocomposites to predict their physical properties. They show that the composites with 14 Bi would have a gap energy between 0.4eV and 1.69eV. In the case of Bi/nanotubes, only TEM could be used to characterize the nanotubes filled with 4nm diameter Bi nanowires prepared in the DAC or Bi rods of diameter around 10nm produced in CONAC28. In addition, the nanotubes in the Bi/nanotube composite transformed into crystalline quartz. Physical measurements were also performed in order to check if the thermoelectric properties are improved. Using the Van der Pauw method, an increase of electrical resistivity was observed (10 times and 3.3 times higher than in bulk Bi). However, the Seebeck coefficient measured has the same order of magnitude for both bulk Bi and the composites. Therefore, the measurements of isolated Bi nanowires will be necessary

A detailed study of fabrication and characterisation of bismuth (Bi) doped silica optical fibre has been investigated. Three different fibre fabrication techniques were applied to study the possible influence on Bi-luminescence: modified chemical vapour deposition (MCVD) and the solution doping technique, MCVD chemicalin- crucible deposition technique and the powder-in-tube (PIT) technique. Spectroscopic absorption and Bi luminescence and fluorescence decay properties under different pumping wavelengths and with different host glass compositions are presented and provide important information for device applications. The influence of unsaturable loss on laser performance is investigated. The feasibility of direct laser diode pumping of Bi-doped fibre lasers at the wavelengths of 915 and 975 nm was examined by measuring excited state absorption in Bi-doped silicate fibres for the wavelength range of 900 -1300 nm. Enhancement in spectroscopic properties of Bi-doped fibre, by H2-loading, has been examined. Bi-doped fibre laser operating in the wavelength region of 1160-1179 nm has been demonstrated. The fibre laser performance at 1179 nm was investigated incorporating different cooling arrangements. The operation of Bi-doped fibre amplifier at 1179 nm, in both low and high input signal regime, was also examined. An all-fibre, narrow-linewidth, high power Yb-doped silica fibre laser at 1179 nm has been demonstrated. Furthermore, theoretical work confirms that the proposed laser architecture can be easily scaled to higher power

Ce travail est consacré à l’étude du frittage de matériaux céramiques et métalliques en vue de leur co-frittage pour l’élaboration d’un composant magnétique mis en forme par un procédé d’impression jet d’encre. L’étude et la compréhension du frittage du matériau isolant (à base de silice) avec ou sans additifs de type TiO2, Bi2O3, ZnO se sont appuyées sur l’identification in situ par MEBE et DRX des transformations de phases et des mécanismes de densification intervenant au cours du traitement thermique. Il a été notamment montré que ces additifs pouvaient jouer le rôle soit de modificateur soit de formateur du réseau de la silice vitreuse et conduire ainsi à de fortes variations de la température de cristallisation et de densification. Les cinétiques de densification et l’amplitude des retraits des matériaux isolant, conducteur et magnétique étant très différentes, plusieurs voies d’amélioration ont été préconisées en vue de leur cofrittage : dopage du matériau conducteur, température de calcination du matériau magnétique. . . . Ces choix ont permis, à terme, la réalisation de composants bimatériaux mis en forme par impression jet d’encre aux designs proches de celui du composant final
This work deals with the study of the sintering of ceramic and metallic materials to allow their co-sintering for the development of a magnetic component shaped by ink-jet printing. The study and understanding of the sintering of the dielectric material (composed of silica) with or without additives such as TiO2, Bi2O3, ZnO relied on the in situ characterizations by ESEM and XRD of the phase transformations, the mechanisms of densification occurring during the heat treatment. It has been shown that these additives could act either as former or modifier of the vitreous silica network and lead to large variations in the crystallization température and densification. The densification kinetics and shrinkage amplitude of the dielectric, conductive and magnetic materials are very different, several improvement possibilities were advocated for their co-sintering: doping of the conductive material, calcination température of the magnetic material. . . . These solutions allowed the élaboration of bimaterial components shaped by ink-jet printing with designs close to the one of the final component

L'etude de la reactivite du pentachlorure de molybdene en phase gazeuse a 30c sur des oxydes de vanadium, de niobium ou de bismuth supportes sur silice se situe dans le cadre plus general de la preparation de catalyseurs a base d'oxydes mixtes supportes sur silice. Une interaction preferentielle entre le molybdene et l'oxyde supporte plutot qu'avec la silice, a ete observee. Une phase mixte se forme avec l'oxyde de vanadium (oxychlorure de vanadium et de molybdene) et avec l'oxyde de bismuth (molybdate de bismuth) alors qu'avec l'oxyde de niobium, seule une interaction de surface est presente. Ces interactions s'accompagnent du transfert de l'electron du molybdene (au degre d'oxydation +5) vers le vanadium (+5) et de l'absence de transfert mais avec delocalisation de l'electron du molybdene sur le niobium (+5), en accord avec les reactions d'oxydo-reduction deduites des inegalites des potentiels redox standards des couples en solution. En revanche, la formation du molybdate de bismuth (+3) suppose l'oxydation du molybdene au degre d'oxydation (+5) en (+6), ce qui est en desaccord avec la reaction d'oxydo-reduction deduite de l'inegalite des potentiels redox des couples (bi3+/bi et mo#6#+/mo#5#+). Le protocole de preparation (impregnation puis greffage, impregnation en deux etapes, coimpregnation) des catalyseurs a base d'oxydes de vanadium et de molybdene a une influence sur la nature des especes de la phase supportee sur la silice et sur la proportion d'ions vanadium et molybdene de surface. Cette proportion a pu etre correlee a celle des differents centres acido-basiques caracterises par la reaction test d'oxydation menagee du methanol. Les catalyseurs a base d'oxydes simples ou mixtes (v, mo, v-mo, bi-mo, ca-mo) supportes sur silice presentent pour cette reaction un comportement inhabituel caracterise par des oscillations temporelles de l'activite catalytique

Ce travail de thèse porte sur l'étude de nouveaux matériaux vitreux, dopés par des ions bismuth ou des nanoparticules d’or, à destination de l’optique guidée. L’efficacité optique dans l’infrarouge des composants réalisés avec des verres dopés bismuth sont limitées par la méconnaissance du centre émetteur. Nous étudions ici les propriétés de luminescence d’un système plus simple : la silice pure. L’évolution des propriétés spectroscopiques, avec la température, d’une fibre optique micro-structurée à cœur de silice dopée bismuth est étudiée. Nous en déduisons les énergies de vibration du centre émetteur. L’influence de l’atmosphère de fabrication de préformes sur leurs propriétés spectroscopiques a ensuite été établie. Un procédé de fabrication de préformes par déposition chimique en phase vapeur (MCVD) est utilisé pour synthétiser des préformes sous atmosphères contrôlées. Les propriétés optiques de ces préformes et fibres optiques conventionnelles sont présentées. Ces résultats corroborent la présence dans la silice d’un centre émetteur dans l’infrarouge lié à une entité réduite du bismuth. Nous étudions alors les propriétés optiques linéaires et non-linéaires de verres massifs et de fibres optiques dopés par des nanoparticules d’or. Leur résonance plasmonique de surface est mise à profit pour fabriquer un verre dont le coefficient non-linéaire est supérieur à celui de la silice. Des monolithes de silice Sol-Gel dopée et densifiée à des températures basses sont utilisés pour la réalisation de fibres optiques micro-structurées. Nous observons un comportement d’absorbant saturable pour le verre massif alors que la fibre optique présente un comportement de limitation optique
This thesis concerns the properties of two chemical elements which are bismuth ion and gold nanoparticles, for silica doped optical fiber. Efficiency device set up with bismuth doped silica fibers are limited by the misunderstanding of the infrared luminescent center. To this aim, we decided to use the stack and draw process to realize a microstructured optical fiber with a silica core doped only with bismuth. Evolution of spectroscopic properties of the optical fiber versus temperature is reported. We employed a model to deduce vibrational energies of the luminescent center. In a second time, we studied influence of the manufacturing atmosphere of Bismuth doped optical preforms on their spectroscopic properties. A chemical vapor deposition is use with more or less atmosphere during collapse step. Spectroscopic properties of bismuth doped silica preform are presented and discussed. All these results seem to confirm the presence in bismuth doped silica glass of a low valence state or a reduce species of the bismuth element. The second study concerns the linear and nonlinear properties of gold nanoparticles doped bulk glasses and optical fibers. In this work, we propose to start from monolithic silica xerogel with controlled porosity. It is then possible to obtain gold nanoparticles-doped glasses that can be used for the realization of micro-structured fibers using the Stack and Draw technique. Linear and nonlinear properties of bulk glass and optical fibers are studied. We will also present the properties the bulk glass that behaves like a saturable absorber and the optical fiber which presents optical limitation

碩士
國立臺灣大學
化學工程學研究所
88
Manufacture of Non-linear optical(NLO) single crystal is the fundamental technology of optical process unit. NLO single crystal can apply to optical information processing, calculation and image stockpile. It come to important recently. We made up bismuth silicate(BSO) crystal by Floating-Zone method. BSO can apply to real-time optical information processing, optical computing, incoherent-to-coherent optical image conversion, real-time interferometry, image amplification and phase conjugation because of it’s sensitive properties. It also can apply to optical electric sensor or optical magnetic field sensor. We attempted to make up the most suitable feeding rod for floating-zone crystal growth by using different sintering method. We also discussed the cause which influence the stability of melting zone. And then we solved the unstable of melting zone. Beside we discussed the influence of crystal quality by using different crystal growth rate, crystal diameter, seed and temperature.

碩士
國立臺中教育大學
科學教育與應用學系碩士班
104
In this study, a series of the bismuth silicate and bismuth silicate composite graphitic carbon nitride (g-C3N4) are prepared using autoclave hydrothermal methods. The novel heterojunctions of BixSiOy/g-C3N4 is fabricated by the hydrothermal method for the first time, in which g-C3N4 is synthesized by calcinations at 540℃ in muffle furnace. Bismuth silicate is prepared by Bi(NO3)3 and Na2SiO3, dissolved in an 1M HNO3 aqueous solution and adjusted the pH value, and then the aqueous solution is transferred into a 15 mL Teflon-lined autoclave and is heated to 150 oC for 8 hours. Finally, the BixSiOy and g-C3N4 are mixed in different ratio in a autoclave and is heated to 150oC for 4 hours. The products are characterized by XRD, SEM-EDS, FE-TEM, HR-XPS, PL, DR-UV, BET, FT-IR, and EPR. inorder to discuss the photocatalytic efficiency of bismuth silicate and bismuth silicate composite g-C3N4. Photocatalytic efficiency of the catalyst is use of photocatalytic degrading of organic pollutants - crystal violet (CV) by measuring crystal violet (CV) concentration.

碩士
國立臺中教育大學
科學教育與應用學系碩士在職專班
105
In this study, bismuth silicate and bismuth silicate composite graphene oxide (GO) and composite graphitic carbon nitride (g-C3N4) are prepared using autoclave hydrothermal methods. The novel heterojunctions of Bi12SiO20/GO and Bi12SiO20/g-C3N4 are fabricated by the hydrothermal method for the first time. Bismuth silicate is prepared by Bi(NO3)3 and Na2SiO3, dissolved in an 3M NaOH aqueous solution and adjusted the pH value . The aqueous solution is then transferred into a 15 mL Teflon-lined autoclave and heated to 100oC for 4 hours. Bi12SiO20/GO or Bi12SiO20/g-C3N4 is mixed in different weight ratio independently in a autoclave and heated to 100 oC for 4hours. The products are characterized by XRD, SEM-EDS, FE-TEM, HR-XPS, PL, DR-UV, BET, FT-IR, and EPR. To discuss bismuth silicate and bismuth silicate composite with graphene oxide and graphitic carbon nitride for photocatalytic efficiency, photocatalytic efficiency of the catalyst is used for the photocatalytic degradation of organic pollutants - crystal violet (CV) and 2-hydroxybenzoic acid . The measurement of crystal violet (CV) concentration, that the reaction rate constant k of Bi12SiO20 / 20wt%-GO and 5wt%-Bi12SiO20/g-C3N4 is 0.050h-1 and 0.078 h-1, respectively. This study shows that the ratio of Bi12SiO20：GO and Bi12SiO20： g-C3N4 strongly affect composite morphology, light response and photocatalytic activity.

碩士
國立臺灣大學
化學工程學研究所
90
Nonlinear optical (NLO) crystals are important components in optoelectronic devices, and their growth is also a critical technology in the industry. Particularly, with the fast development of the optical information processing, computing, and storage, the need of photorefractive materials increases dramatically. Extensive research has been focused in this field. However, the quality of the crystals is often a bottleneck in its applications. By traditional Czochralski method, it is difficult to get good diameter control during growth. And with segregation effect, it can not grow single crystal with compositional uniformity. Therefore, we attempt to develop a non-traditional crystal growth technique, the so-called Zone-Leveling Czochralski (ZLCz) method. The ZLCz growth technique is a combination of the zone-melting (or leveling) and the Czochralski methods having the advantages of both methods. With the developed set up we have grown the important photorefractive single crystals, such as Bismuth Silicate (BSO). In this research project, we discuss the mechanism of diameter control and established the stable crystal growth condition. Nevertheless, bubble inclusion problem is always found in the process. By using an inner crucible, we are able to solve this problem.

博士
中山醫學大學
口腔科學研究所
101
White-colored mineral trioxide aggregate (WMTA) has been widely used in dental root canal filling treatment. However, there are several drawbacks of WMTA, including the discoloration potential, presence of toxic elements, difficult handling, and long setting time. The purpose of this study was to develop the new calcium silicate endodontic material as an alternative material for the endodontic applications. The effects of different pH (pH 7.4 and 4.0) of simulated body fluid (SBF), and Bismuth Oxide (Bi2O3) on the physicochemical properties of the dicalcium silicate cement were investigated. The morphology, weight loss, porosity, diametral tensile strength, in addition to pH changes in the cement-immersed solutions were evaluated. The physicochemical properties and osteogenicity of calcium silicate cements containing Bi2O3 in varying ratio were also examined. The size of precipitated apatite spherulites on the cement surfaces after soaking in the pH 7.4 solution for 1 day was greater than that in the pH 4.0 solution. Solution pH did not significantly affect (P > 0.05) the diametral tensile strength of cements. After soaking in SBF for 30 days, the sample was associated with a weight loss of 0.8% in the pH 4.0 solution; whereas in the pH 7.4 solution showed a weight increase of 0.2%. A greater porosity of the cement soaked in a pH 4.0 was found compared with that in the pH 7.4 solution. The setting time increased significantly (P < 0.05) with increasing ratio of Bi2O3. The pH value and diametral tensile strength of the cements were slightly affected by introducing Bi2O3. The solubility of the three radiopaque cements ranged between 0.8% and 1.1%, which was significantly (P < 0.05) lower than that of MTA (1.4%). 20 wt% Bi2O3 led to a lower cell proliferation, differentiation and calcium deposits of MG63 on the cement compared with the other cements. It is concluded that the addition of 10 wt% Bi2O3 to calcium silicate cement showed well setting time, radiopacity and osteogenic activity may has a potential for being used a endodotic retro-filling material as an alternative to WMTA.

Trabalho final do 5º ano com vista à atribuição do grau de mestre no âmbito do ciclo de estudos de Mestrado Integrado em Medicina Dentária apresentado à Faculdade de Medicina da Universidade de Coimbra.
Objective: The purpose of this study was to investigate and compare chromatic alterations of an inorganic silicate-based cement, also known as white mineral trioxide aggregate (WMTA), submitted to different environmental conditions using the CIE L*a*b* system evaluated by two different methods. Methods: Twenty-four samples of WMTA (ProRoot® MTA, Dentsply Tulsa Dental, Johnson City, TN) were randomly distributed in four groups (n=4). In group 1 the samples did not undergo any additional treatment (negative control group). In group 2 WMTA samples were light irradiated for 60 seconds using a LED poliwave curing unit. In group 3 and 4 WMTA samples were coated with a layer of glycerine and adhesive, respectively and light irradiated for 60 seconds. A commercial spectrophotometer (VITA Easyshade® Advance 4.0, VidentTM, California, USA) and calibrated photographic digital analysis were used to determine colour coordinates from the CIE L*a*b* system of each sample after three different time points: 30 minutes, 48 hours and 7 days. In order to understand the chemical alterations associated to colour variations of the material x-ray diffraction analysis was also conducted. Data was analysed using statistical software IBM® SPSS® Statistics, version 20. Results: Consistency between the two colour measuring methods was not observed. Significant colour variation was observed for group 3. X-ray diffraction analysis showed no differences between compounds. Conclusion: WMTA showed significant dark discolouration after irradiation with an LED poliwave curing unit in an oxygen-free environment promoted by glycerine although after 48 hours discolouration had faded. The same light irradiation protocol associated to an oxygen-free conditions achieved by an adhesive resin layer did not induce significant discolouration at the end of the experiment protocol.

碩士
國立中正大學
化學工程研究所
103
This research are devoted to make Bismuth-Telluride-based alloy thin film thermoelectric generators fabricated by a electroplating method, the three-dimensional Bismuth-telluride-based alloy thin film prepared by potentiostatic electrodeposition technique onto three-dimensional polystyrene templates which were formed on stainless steel substrates via blade coating method, hot pressing-annealing method and pure annealing method was further treated. The thermoelectric generators assembly, cannot use directly on to the stainless steel, it must have great electrical insulating properties and low thermal conductivity of the material as a substrate. In this study, using an epoxy resin and silicone resin transfer thermoelectric films, and to explore the transfer success rate and thermoelectric properties after the transfer. The output power can also be affected by thermoelectric properties and structure design of the thermoelectric generators. This study produced three kinds of film thermoelectric generators with different substrates and post-treatment method, and the compare its performance. When the epoxy resin as a substrate, the open-circuit voltage of 2.58/5.13mV, short-circuit current of 75/25μA and estimated maximum output power of 48/32nW are obtained from 1 pair/2 pairs of legs connected by Ni electrodes and a temperature difference of ∆T=11K；When the silicone resin as a substrate, the open-circuit voltage of 1.98/3.90mV, short-circuit current of 70/24μA and estimated maximum output power of 35/23nW are obtained from 1 pair/2 pairs of legs connected by Ni electrodes and a temperature difference of ∆T=8K. The results found of different substrates film thermoelectric generator, in the same heat source, epoxy resin can cause a great temperature difference of ∆T=11K, the lower silicon resin of ∆T=8K, presumably due to the thermal conductivity of the silicon resin is preferably, likely to cause heat loss. In different designs, the same sectional area of the thermoelectric thin film, a single pair of p-n of the structural design of the series has a high short-circuit current value and the maximum output power value, and the two pairs of p-n to the series have a high open-circuit voltage value.