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No description available.

Previous attempts to produce carbon nanotube (CNT) ceramic composites have resulted in poorly dispersed, unaligned and non-continuous CNTs in the composites with modest improvements in properties. The research presented in this thesis pertains to the production of dense aluminoborosilicate (ABS) glass matrix composites containing aligned and continuous multi- walled carbon nanotubes (MWCNT) of millimetre lengths. This was achieved by infiltrating CVD grown MWCNT preforms using a precursor sol and sintering which achieved 80 ± 2% dense composites. Focused ion beam milling together with image analysis showed that the composites contained 20 ± 2 vol.% MWCNTs, which are aligned and continuous within the glass matrix. Indentation studies showed greater damage tolerance in the composite compared to unreinforced ABS glass. Under compression, there is no significant change in the compressive strength between the composite and the unreinforced glass. The bend strength of microcantilever beams were 1.4 to 1.3 GPa for the composite and glass respectively. Elastic modulus of 84 GPa and fracture toughness (Kic of up to 2.4 MPa √m were obtained for the composite. The elastic modulus and fracture toughness results are an improvement of 30 % and 240 % over that of unreinforced ABS glass. Fracture surfaces showed apparent MWCNT pullout lengths of up to ~ 1 urn. Analysis indicates that crack bridging by intact MWCNTs provides the majority of the improvement in fracture toughness. Interlayer sliding of the MWCNTs and "sword in' sheath" failure mechanism of the MWCNTs prevented the maximum potential performance, with respect to elastic modulus and fracture toughness, from being achieved. Electrical conductivity in the alignment direction of the CNTs showed improvements by a factor of 106 compared to unreinforced ABS glass. Furthermore, improvement of a factor of ~ 10 in the thermal conductivity was obtained for the composite over that of ABS glass.

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Orientador: Estevão Tomomitsu Kimpara / Co-orientador: Marina Amaral / Banca: Eduardo Bresciani / Banca: Alberto Noriyuki Kojima / Banca: Júlio César Brigolini de Faria / Banca: Fabíola Pessôa Pereira Leite / Resumo: Este estudo avaliou o crescimento subcrítico de trincas de uma cerâmica à base de dissilicato de lítio, levando em consideração dois tipos de tratamento de superfície. Blocos de dissilicato de lítio parcialmente cristalizados, foram usinados até obter um cilindro com 12 mm de diâmetro. Após este processo, os cilindros foram cortados de forma a obter discos com espessura de 1,2 mm ± 0,2 mm, segundo norma ISO 6872/2008. Em seguida, 160 discos foram divididos em 2 grupos de estudo, de acordo com o tratamento de superfície: jateamento (Jateamento com partículas de 30 µm de alumina modificadas por sílica); e Ácido (Ácido Fluorídrico 5% por 20 segundos). As superfícies tratadas dos discos de todos os grupos receberam aplicação do agente de união silano, e foram submetidos ao tratamento térmico em um forno sob a temperatura de 100ºC durante 2 min. Todos os grupos receberam uma camada de cimento resinoso Panavia F. Vinte amostras de ambos os grupos foram submetidas ao ensaio mecânico de compressão, para a determinação da resistência à flexão biaxial, e vinte e cinco amostras de cada grupo foram submetidas ao ensaio de compressão para obtenção da resistência inerte. Trinta e cinco amostras de cada grupo foram submetidas ao teste de crescimento subcrítico de trinca. Este ensaio foi realizado em cinco taxas de tensão: 10-2, 10-1, 100, 101 e 102 MPa/s. Valores obtidos pelo ensaio mecânico de compressão: Jateamento (257,53 ± 21,22 MPa) e Ácido (279,44 ± 31,42 MPa). Valores obtidos pela resistência inerte: Jateamento (235,70 ± 28,63 MPa) e Ácido (343,30 ± 47,93 MPa). Os dados do coeficiente de crescimento subcrítico de trincas (n), parâmetro do CST (D), resistência característica (σc) e módulo de Weibull (m), com base no teste de crescimento lento de trincas foram: Jateamento (n=18 ± 1,7; D=205,38 ± 0,02; σc=246,72 / 236,86-256,99 MPa; m=10,46) e àcido (n=15.... / Abstract: This study evaluated the fatigue behavior of a lithium dissilicate ceramic regarding different surface treatments. Partially cristalized lithium dissilicate blocks (IPS e.max CAD) were shaped into cilynders (12 mm in diameter). Cylinders were sectioned into disc shaped specimens with 1.2 mm in thickness (± 0.2 mm), according to ISO 6872/2008. Half of the specimens were sandblasted with 30 µm silica particles (Rocatec soft system) and received a layer of silane + resin cement (Pavavia F). The other half of the specimens was etched with hydrofluoric acid (HF 5%, 20 s) and also received a layer of silane + resin cement (Pavavia F). Previously to resin cement application, the silane was heat treated at 100°C. The biaxial flexural strength was determined for each surface treatment (n=20), as the subcritical crack growth behavior at 5 stress levels: 10-2, 10-1, 100, 101 and 102 MPa/s. The fatigue limit will be determined with the stair case approach. Values obtained for the biaxial flexural strength teste were: Sandblasting (257.53 ± 21.22 MPa) and Acid (279.44 ± 31.42 MPa). values obtained by inert strength were: Sandblasting (235,70 ± 28,63 MPa) and Acid (343,30 ± 47,93 MPa). Slow crack growth behavior parameter (n), and CST (D), characteristic strength (σc) and Weibull modulus (m) were: sandblasting (n=18 ± 1.7; D=205.38 ± 0.02; σc=246.72 / 236.86-256.99 MPa; m=10.46) and Acid (n=15 ± 1.5; D=222.88 ± 0.02; σc=362.72 / 345.38-380.93 MPa; m=8.48). It can be concluded that the surface treatment with 5% hydrofluoric acid, lithium disilicate become more susceptible to subcritical crack growth than with the sandblasting aluminum oxide coated silica / Doutor

Huang Yong. / "May 2004." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

The Early-Middle Bronze Age in Cyprus (c. 2300-1650 BCE) is still poorly understood, in spite of Cyprus's strategic importance in the Mediterranean and the revolutionary cultural transformations that occurred at the end of this period. The west coast in particular, has remained a relatively blank spot on the map of the Eastern Mediterranean, where excavations have been entirely lacking until very recently. In the absence of excavated sites, a great deal of information regarding western Cypriot society from this period must be derived from pottery. This thesis aims to understand the nature of the ceramic material culture in the west through an analysis of the ceramics from the cemetery of Kissonerga-Ammoudhia, at present the largest corpus of western Cypriot funerary pottery from this period. The entire excavated assemblage is presented and a multidisciplinary approach to the ceramics is applied. A traditional typological study was conducted on the entire assemblage, and a microscopic petrographic analysis applied to a sample in order to identify the manufacturing techniques used by the potters. This corpus of information can be used to test the nature and validity of evidence for regional identity. Although there appears to be a broadly similar culture with the rest of the island, the ceramics from Ammoudhia nevertheless show significant differences to those from contemporary sites. This site contains a very large amount of Drab Polished ware; little known elsewhere, this poorly understood, but potentially vital type of pottery appears to be a western local tradition. Although originally dated to the late Middle Bronze Age, this thesis provides evidence for a considerably earlier date in western Cyprus. It also argues for this being a very long lived ware with particularly sophisticated manufacturing techniques, and is one of the technological precursors to Base Ring ware, the ubiquitous pottery vessels of the Late Bronze Age. This thesis places western Cyprus into an island-wide context, allowing for meaningful comparisons with contemporaneous sites and lays the foundations for a clearer understanding of the chronological and technological sequence, fitting into our understanding of the precursors to secondary state formation, in particular: funerary and ritual practices, trade and exchange and technological advances. This corpus from the Kissonerga Ammoudhia cemetery represents the first ever study of a large body of information from the Early-Middle Bronze Age of Western Cyprus. As such it can provide both the framework for further analyses, as well as the first glimpses of the unique culture of this area, and an understanding of how this region fits into the wider Bronze Age Mediterranean world.

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Commericially available BaTiO3 powder was die-pressed to discs, and sintered by a two-stage firing consisting of reducing in low oxygen partial pressures (pO2) and re-oxidizing in a higher pO2 to simulate the industrial process of manufacturing the multi-layer ceramic capacitors(MLCC). Both undoped and MgO-doped discs as well as commercial MLCC chips, provided by Ferro Electronic Material Systems, have been investigated for sintered microstructures using the scanning electron microscopy (SEM) and transmission electron microscopy (TEM), crystalline phases using the X-ray diffractometry (XRD), and dielectric properties using the frequency response analysis. A comparison between the microstructures is made in order to look for the microstructure origin of the macroscopic behaviour, e.g. dielectric properties.It is found that the crystalline phases have changed frompredominantly tetragonal to pseudo-cubic with MgO > 0.5 mol.%. Apart from grain growth being effectively suppressed in MgO-doped compositions, grains containing the characteristic ferroelectric domains in undoped samples have decreased significantly in number. The indication is that Mg2+ dissolving into the BaTiO3 lattice, substituting for the Ti4+ site reduces the c/a ratio. However, unlike what was reported before, no direct experimental evidence is found to support that grain growth inhibition is effected by Mg2+ segregation to grain boundaries.Dislocation loops are observed ubiquitously in all samples, although bothMgO doping and low pO2 have decisive effect on their density in sintered grains. In MLCC chips, the microstructure is characterised by core-shell grains representing the dissolution of solutes, and modulated grains representing the ordering of chemical defects, e.g. substitutional defects and oxygen vacancies forming defect clusters.Residual pores located intragranularly in the MLCC chips are also observed, and its origin discussed. The formation of such pores is attributed to vacancy condensation which is enhanced by the increased oxygen vacancies due to MgO doping, as an acceptor, and by low pO2 firing.

The period after A.D. 1100 in western Pennsylvania was a dynamic period in history occupied by diverse populations with rapidly changing social interactions. The Johnston site located in Indiana County represents one of the most important village sites during this period. Through a combination of ceramic analyses and radiocarbon dating previous hypotheses posited about this site are investigated. Archaeologists have relied on final twist direction of cordage impressions on shell-tempered and cord-marked ceramics to argue for population amalgamation between social groups from northwestern and southwestern Pennsylvania. In addition, ceramics recovered from the site have been used to define the date range for occupation at the site and for the Johnston phase of the late Middle Monongahela period. By combining radiocarbon dating and ceramic analyses these previous hypotheses are investigated. Specifically the usefulness of using cordage twist as a sole attribute to define social groups at the intrasite level is challenged. / Dr. Sarah Neusius Dr. Beverly Chiarulli Dr. Phillip Neusius