<p dir="ltr">The next generation of advanced aerospace technologies will require strong materials able to withstand high temperatures in high stress environments. Ceramic matrix composites (CMCs) are becoming more popular solutions used to manufacture components for these challenging environments. CMCs take advantage of the high temperature capabilities and erosion resistance of ceramic materials combined with a fiber reinforcement matrix to enhance the strength beyond the capabilities of pure ceramics. Traditionally, CMCs are manufactured using a variety of methods including silicon infiltration, chemical vapor deposition, and polymer pyrolysis, but there are challenges with the available geometries, cost, and time associated with them. Additive manufacturing techniques have shown promise as methods to produce CMCs that can allow for a more tailored design of components and a reduced manufacturing time. However, it is challenging to construct parts with high fiber loadings that can retain their geometric accuracy and compare to more traditional methods of manufacturing CMCs. This research aims to develop and characterize photocurable CMC formulations and CMC inks with high fiber content that can be 3D printed. To do this, photocurable mixtures of preceramic polymer resins were synthesized and filled with pitch and polyacrylonitrile (PAN) based milled carbon fibers from 0-40 wt.%. Additional inks were mixed and tested without photocuring capabilities at solids loadings up to 65 wt.% to evaluate the printing capabilities of highly filled inks. Cure depth of photocurable inks, extrudability of each mixture, rheology of highly filled mixtures, and printing results were obtained. While photocuring CMC inks had a limit to its effectiveness at high solids loadings, a printable mixture with greater than 50 wt.% fiber reinforcements was shown to be viable. The results shown in this paper have significance for future work in additive manufacturing of fiber filled polymer inks and show promise to construct CMCs for aerospace applications.</p>

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 170-175). Also available via the Internet.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

No description available.

Les composites à matrice céramique (CMC) sont des matériaux constitués d’une matrice céramique renforcée par des fibres céramiques continues (généralement à base de SiC ou de C). Le travail de thèse présenté, réalisé en collaboration avec Snecma Propulsion solide et l’Agence De l’Environnement et de la Maîtrise de l’Energie, a pour objectif d’introduire des matériaux CMC au sein de pièces de moteurs d’avions civils, concurrençant ainsi les alliages métalliques actuellement utilisés. Pour ce faire, les matériaux CMC devront répondre aux exigences propres à l’aéronautique civil, à savoir qu’ils devront présenter une longue durée de vie en atmosphère oxydante dans une gamme de basse température (400-600°C) et avoir un coût compétitif. Dans ce contexte, des matériaux CMC constitués de fibres SiC de première génération, de coût moins élevé, sont étudiés, mais leur inconvénient majeur est leur plus grande sensibilité à l’oxydation. Des matrices auto-cicatrisantes multicouches à base de Si, B, et C ont été développées ces dernières années afin d’assurer une tenue à l’oxydation des fibres, mais elles ne sont pas opérantes dans la gamme de température imposée. Compte tenu d’études précédemment réalisées et des exigences requises pour l’application visée, l’objectif du travail présenté dans ce mémoire est de proposer des solutions pour améliorer la tenue à l’oxydation de renforts fibreux à base de fibres de SiC de première génération, dans la gamme de température 400-600°C, en évitant un surcoût de production trop important. / Continuous fiber-reinforced ceramic matrix composites (CFCCs) are an important class of materials for structural applications at elevated temperatures because of their improved flaw tolerance, large fracture resistance, improved toughness by crack deflection and crack bridging mechanism, low density and noncatastrophic mode of failure comparing with metallic materials. Fibers play a critical role in both the processing and performance of CFCCs. SiC-based fibers are considered leading candidate materials in the aerospace application, such as engine turbines. However, the major shortcoming of SiC-based fibers is their oxidative embrittlement and degradation, which is caused by the oxygen ingression from the micro cracks and interstitials in the composites, is the dominant life-limiting phenomenon of non-oxide composites. This study carried out with the financial supply of both Snecma Propulsion Solide and Agence De l’Environnement et de la Maîtrise de l’Energie has for objective to integrate SiC-based as reinforcement in CFCCs for civil aircraft engine application. In order to reach this objective, it is imperative to find a novel approach to diminish the oxygen ingression by developing protective fiber coatings.

This study proposed and evaluated a waste-to-resource strategy for beneficially using solid waste as ceramic raw materials. The sludge generated from waterworks and sewage treatment processes contains significant amounts of aluminum and iron, and the industrial sludge is enriched with high metal content. The hazardous metals in waste sludge may lead to metal bioaccumulation and cause adverse effects for ecosystem. This study aims to stabilize copper- and zinc-laden sludge in commonly available ceramic products, and to beneficially use waterworks and sewage sludge to incorporate waste metals. The study was first investigated by sintering simulated metal-laden sludge with Al-rich (γ-Al2O3, -Al2O3, kaolinite, mullite) and Fe-rich (Fe2O3) precursors. Secondly, the practicability of recycling Cu-bearing electroplating sludge as a part of ceramic raw materials was evaluated through thermal interaction with Al-rich precursors. Furthermore, the potential of using water and sewage treatment works sludge to stabilize metals were also examined. Sintering procedures were carried out within 650-1450 oC for 3 h, and phase transformations were studied using X-ray diffraction (XRD) with the quantification technique of Rietveld refinement analysis. The formation of CuAl2O4 spinel was initiated at 650 oC using γ-Al2O3, and the maximum copper transformation reached 80%. The copper incorporation into CuAl2O4 started at 850 oC and reached 95% in -Al2O3 system. The growth of CuAl2O4 was found at 750 oC using kaolinite, but at 900 oC in mullite system. The maximum copper transformation for both kaolinite and mullite reached ~80%. With CuAl2O4, decomposing, the formation of CuAlO2 predominated in alumina systems, but CuO and Cu2O were found in kaolinite and mullite systems. When using Fe2O3, the CuFe2O4 with tetragonal structure was observed at lower temperatures, and the cubic CuFe2O4 became predominant at 1000 oC. The formation of ZnAl2O4 spinel started at 750 oC in γ-Al2O3 system and at 950 oC in -Al2O3 system, respectively. The zinc transformation completed in both γ-Al2O3 and -Al2O3 systems at higher temperatures. The coexistence and competition between ZnAl2O4 and Zn2SiO4 were found using kaolinite and mullite. The increase of temperature to 1350 °C resulted in complete zinc transformation to ZnAl2O4 in mullite system. Through leaching tests, aluminates and ferrites were found to be superior to oxide and silicate phases in immobilizing hazardous metals. The leachates of aluminates and ferrites exhibited the behavior of incongruent dissolution, and the Zn2SiO4 leachate showed congruent dissolution. The CuAl2O4 spinel was observed when sintering Cu-laden electroplating sludge with aluminate precursors. The copper leachability decreased with CuAl2O4 developing and the lowest copper concentration in leachates was within the optimal temperature range for CuAl2O4 generation. Both copper and zinc were successfully incorporated into the spinel structure using waterworks sludge, and the cubic CuFe2O4 became the main component when using sewage sludge to stabilize copper. Overall, this study demonstrated a promising process to stabilize hazardous metals in waste materials, such as sludge, ash, and slag, through sintering with the inexpensive ceramic precursors. This may provide an avenue for economically reduce the environmental hazards of toxic metals by reliably blending them into the marketable ceramic products. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

No description available.

No description available.

No description available.

No description available.