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Ultra High Temperature Ceramics (UHTCs) are the most promising candidates for high temperature applications in extreme environments, such as conditions experienced during re-entry of out space flying objects, for their known high melting points, good chemical and thermal stability and high thermal conductivity. To improve the densification and oxidation resistance of UHTCs, a second phase, such as silicon carbide, is usually added to monolithic UHTCs to form ceramic matrix composites. While UHTCs/composites have many unique advantages for high temperature applications, they are very difficult to densify due to their very strong covalent chemical bonds and very high melting point. Conventional methods for processing UHTCs usually use powders as starting materials. A major issue of the conventional methods is the poor mixing/processing of powders with different densities and sizes, especially for nano-sized powders. Thus more research needs to be focused on improving UHTCs' densification, microstructure and properties.This thesis studies the development of novel sol-gel techniques for preparation of starting materials and spark plasma sintering (SPS) for densification of UHTCs and composites. The thesis is organized into eight chapters. The First Chapter is an introduction to the thesis structure organization. The Second Chapter is the background of the research and literature review. Chapter Three is a description of the experimental procedures and characterization techniques. In the first result chapter, Chapter Four, silicon nitride ceramic and silicon nitride/titanium nitride composite were fabricated by hot pressing and spark plasma sintering (SPS) respectively to study the effect of the SPS DC current on the densification, microstructure and properties of conductive and non-conductive materials. A sol-gel based approach was investigated to improve the UHTC ceramics/composites with fine microstructures in Chapter Five. Although sol-gel techniques may not be suitable for making large bulk materials, they have unique advantages on modifying or improving the microstructures, properties and surfaces of materials through the solution chemistry approach. The sol-gel processing technique was used to synthesize TiC/SiC nanocomposites and followed by SPS sintering. Dense TiC/SiC composites were fabricated successfully to form a microstructure consisted of nano TiC and SiC grains. Work in Chapter Six used a sol-gel infiltration technique to fabricate dense TiC/SiC nanocomposites from porous TiC scaffolds. In Chapter Seven, zirconium diboride/silicon carbide composites of fine microstructures were successfully fabricated by sol-gel coating of ZrB2 powders and SPS sintering. Compared to conventional ceramic processing methods, the sol-gel based wet chemistry process has many unique advantages such as homogeneous mixing of starting materials, infiltration of porous green bodies with complex shapes, avoiding the formation of intermediate transit phase/liquid phase in sintering, restricting grain growth and assisting densification by reaction. Chapter Eight presents the conclusions of the thesis and provides some directions for future work.
A sol-gel route synthesized nanocrystalline hafnium carbide (HfC) and zirconium carbide (ZrC) for use in composite materials. The starting materials were zirconium and hafnium alkoxides and carbon was introduced by furfuryl alcohol. A block co-polymer surfactant homogenized the oxide and carbon components. Reduction to HfC and ZrC began at a low temperature of 1250°C and removal of the oxide phase was achieved at 1450°C. The carbide powder was nanocrystalline size less than 100nm. Production of HfC included a synthesis step that limited investigation of the sol-gel process. However, purchased alkoxides for zirconium allowed for detailed understanding of phase changes using X-ray Diffraction of the oxide and Raman Spectroscopy of carbon evolution. Morphology changes were observed using nitrogen gas sorption. Scanning and Transmission Electron Microscopy was used to image the carbide lattice, surface oxides and graphene-like carbons in the microstructure. While HfC synthesis demonstrated that shrinking core models apply, the ZrC results indicated that this type of nanoparticle carbothermal synthesis involved agglomeration and necking as a viable mode of mass transport in completing the carbothermal reduction. Understanding of this process allowed for the modest development of composites by sol-gel coating of powders. The sol-gel coating of ZrB2 was successfully applied to coat ZrC nanoparticles on the powder. Detailed refinement of carbon content in the sol-gel coating was necessary reduce the surface oxide intrinsic to the ZrB2 surface, while providing carbon for the sol-gel oxides. The sol-gel coating created a homogenous mix of ~200nm ZrC on the ZrB2 surface after heat-treatment at 1450°C. Densification of the ZrB2-5%ZrC powder was achieved by spark plasma sintering (SPS) at 1800°C, resulting in submicron sized ZrC particles at grain boundaries and triple points. The amount of carbon added to the sol-gel precursor dictated the porosity and thus some properties of the composites. Flexural strength of ~400MPa was obtained from the composites but no significant improvement of fracture toughness was observed. However, an improvement in hardness of about 20% was observed over monolithic ZrB2. The oxidation performance of the composites was improved by the addition of a sacrificial carbide phase. Sharp leading edge samples were oxidized at 3000°C and were compared to a traditional powder mixed composite. The finer and more homogenous distribution of ZrC caused gradual oxidation while maintaining leading edge stability. However, the powder mixed composite failed under the test. This illustrated the importance not only phase selection but also microstructural control. This indicated advantages in sol-gel processing of ceramic composites with improved densification, controlled grain size and improved properties.
With continued discoveries and innovations, the field of materials synthesis and processing remains as it has been for many decades, a vibrant and fertile area for research and development. It comes, therefore, as no surprise that every Pac Rim conference has had considerable emphasis on this topic with many symposia devoted to various aspects of this field. This Ceramic Transactions volume represents selected papers based on presentations in four symposia during the 8th Pacific Rim Conference on Ceramic and Glass Technology, held in Vancouver, British Columbia, May 31-June 5, 2009.
This valuable handbook has been compiled by internationally renowned researchers in the field. Each chapter is focused on a specific composite system or a class of composites, presenting a detailed description of processing, properties, and applications.
This book summarizes recent research and development in the field of nanostructured ceramics and their composites. It presents selected examples of ceramic materials with special electronic, catalytic and optical properties and exceptional mechanical characteristics. A special focus is on sol-gel based and organic-inorganic hybrid nanoceramic materials. The book highlights examples for preparation techniques including scale-up, properties of smart ceramic composites, and applications including e.g. waste water treatment, heavy metal removal, sensors, electronic devices and fuel cells. Recent challenges are addressed and potential solutions are suggested for these. This book hence addresses chemists, materials scientists, and engineers, working with nanoceramic materials and on their applications.
Provides the first comprehensive treatment of continuous and discontinuous ceramic fiber and whisker reinforced ceramic composites, written by 29 authorities in the field.
Provides coverage of all of the important aspects of carbon nanotube research, including synthesis, properties and potential applications.
This volume provides expert coverage of the state-of-the-art in sol-gel materials for functional applications in energy, environment and electronics. The use of sol-gel technology has become a hotbed for cutting edge developments in many fields due to the accessibility of advanced materials through low energy processes. The book offers a broad view of this growing research area from basic science through high-level applications with the potential for commercialization and industrial use. Taking an integrated approach, expert chapters present a wide range of topics, from photocatalysts, solar cells and optics, to thin films and materials for energy storage and conversion, demonstrating the combined use of chemistry, physics, materials science and engineering in the search for solutions to some of the most challenging problems of our time.
This book covers a wide range of conventional and non-conventional machining processes of various composite materials, including polymer and metallic-based composites, nanostructured composites and green/natural composites. It presents state-of-the-art academic work and industrial developments in material fabrication, machining, modelling and applications, together with current practices and requirements for producing high-quality composite components. There are also dedicated chapters on physical properties and fabrication techniques of different composite material groups. The book also has chapters on health and safety considerations when machining composite materials and recycling composite materials. The contributors present machining composite materials in terms of operating conditions; cutting tools; appropriate machines; and typical damage patterns following machining operations. This book serves as a useful reference for manufacturing engineers, production supervisors, tooling engineers, planning and application engineers, and machine tool designers. It can also benefit final-year undergraduate and postgraduate students, as it provides comprehensive information on the machining of composite materials to produce high-quality final components. The book chapters were authored by experienced academics and researchers from four continents and nine countries including Canada, China, Egypt, India, Malaysia, Portugal, Singapore, United Kingdom and the USA.
Ceramic nanocomposites have been found to have improved hardness, strength, toughness and creep resistance compared to conventional ceramic matrix composites. Ceramic nanocomposites reviews the structure and properties of these nanocomposites as well as manufacturing and applications.Part one looks at the properties of different ceramic nanocomposites, including thermal shock resistance, flame retardancy, magnetic and optical properties as well as failure mechanisms. Part two deals with the different types of ceramic nanocomposites, including the use of ceramic particles in metal matrix composites, carbon nanotube-reinforced glass-ceramic matrix composites, high temperature superconducting ceramic nanocomposites and ceramic particle nanofluids. Part three details the processing of nanocomposites, including the mechanochemical synthesis of metallic–ceramic composite powders, sintering of ultrafine and nanosized ceramic and metallic particles and the surface treatment of carbon nanotubes using plasma technology. Part four explores the applications of ceramic nanocomposites in such areas as energy production and the biomedical field.With its distinguished editors and international team of expert contributors, Ceramic nanocomposites is a technical guide for professionals requiring knowledge of ceramic nanocomposites, and will also offer a deeper understanding of the subject for researchers and engineers within any field dealing with these materials. Reviews the structure and properties of ceramic nanocomposites as well as their manufacturing and applications Examines properties of different ceramic nanocomposites, as well as failure mechanisms Details the processing of nanocomposites and explores the applications of ceramic nanocomposites in areas such as energy production and the biomedical field