Densification and Thermal Properties of Zirconium Diboride Based Ceramics PDF Download
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Author: Matthew Joseph Thompson
Publisher:
ISBN:
Category : Borides
Languages : en
Pages : 430
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Book Description
"The research presented in this dissertation focuses on the processing and thermomechanical properties of ZrB2 based ceramics. The overall goal was to improve the understanding of thermal and mechanical properties based on processing conditions and additives to ZrB2. To achieve this, the relationships between the thermal and mechanical properties were analyzed for ZrB2 ceramics that were densified by different methods, varying amounts of carbon, B4C, or TiB2 additions. Four main areas were investigated in this dissertation. The first showed that decreased processing times, regardless of densification method, improved mechanical strength to >500 MPa. This study also revealed that lower oxygen impurity contents led to less grain coarsening. The second study showed that higher heating rates narrowed the grain size distribution, which resulted in strengths above 600 MPa. However, the decreased processing times led to retention of ZrO2, which decreased the thermal conductivity. The third study revealed that carbon additions interacted with ZrO2 and WC impurities introduced during powder processing to form (Zr,W)C, which led to higher thermal conductivity than ZrB2 with no carbon added. The last area examined the effect of solid solution additions on the electron and phonon contributions to thermal conductivity. The formation of solid solutions decreased thermal conductivity to
Author: Matthew Joseph Thompson
Publisher:
ISBN:
Category : Borides
Languages : en
Pages : 430
Get Book Here
Book Description
"The research presented in this dissertation focuses on the processing and thermomechanical properties of ZrB2 based ceramics. The overall goal was to improve the understanding of thermal and mechanical properties based on processing conditions and additives to ZrB2. To achieve this, the relationships between the thermal and mechanical properties were analyzed for ZrB2 ceramics that were densified by different methods, varying amounts of carbon, B4C, or TiB2 additions. Four main areas were investigated in this dissertation. The first showed that decreased processing times, regardless of densification method, improved mechanical strength to >500 MPa. This study also revealed that lower oxygen impurity contents led to less grain coarsening. The second study showed that higher heating rates narrowed the grain size distribution, which resulted in strengths above 600 MPa. However, the decreased processing times led to retention of ZrO2, which decreased the thermal conductivity. The third study revealed that carbon additions interacted with ZrO2 and WC impurities introduced during powder processing to form (Zr,W)C, which led to higher thermal conductivity than ZrB2 with no carbon added. The last area examined the effect of solid solution additions on the electron and phonon contributions to thermal conductivity. The formation of solid solutions decreased thermal conductivity to
Author: Sumin Zhu
Publisher:
ISBN:
Category : Ceramic materials
Languages : en
Pages : 360
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Book Description
"The first part of this dissertation was aimed at studying the densification of ZrB2 ceramics by pressureless sintering techniques. Various processes have been applied to coat ZrB2 powders with polymer precursors, which were used to produce C after charring. After sintering at 1900°C, relative density increased of ~70% for uncoated ZrB2 to >99% for ZrB2 coated with at least 1.0 wt% C. Thermodynamic analysis suggested that C reacted with and removed oxide impurities (ZrO2 and B2O3) that were present on the ZrB2 particle surfaces, which promoted densification by minimizing grain coarsening"--Abstract, leaf iv.
Author: Jason Michael Lonergan
Publisher:
ISBN:
Category : Borides
Languages : en
Pages : 216
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Book Description
"This dissertation focuses on the thermophysical properties of high purity zirconium diboride ceramics. These ceramics have shown promise for potential applications such as leading edge materials for next generation hypersonic vehicles. The overall goal of this work was to improve the understanding of the thermal properties and maximize the thermal conductivity of ZrB2. Four main areas were investigated in this work. First, the sintering kinetics and the intrinsic thermal properties of reaction processed ZrB2 were studied and compared to ZrB2 produced by hot pressing commercial powders. The reaction process produced ceramics with higher thermal conductivity and enhanced densification. Next, Hf impurity concentrations were varied showing that decreasing Hf content increased thermal conductivity. Finally, isotope enrichments were performed showing that lighter isotopes increased lattice frequency and subsequently thermal conductivity. Fully enriched Zr10B2 had a thermal conductivity of 145 W/m·K which is the highest value for ZrB2 reported to date. Scattering models based on quantum mechanics were used with density functional theory to analyze the effects of impurities and isotopes on the electron and phonon density of states. Overall, this work adds insight into the fundamental mechanisms behind the thermophysical properties of ZrB2. Tailoring compositions to reduce Hf content and adjusting boron isotope concentration has led to improved thermal properties at all temperatures. The processing conditions, reported properties, and insights gained from models will help the realization of ZrB2 as a leading edge material for the next generation of hypersonic vehicles"--Abstract, page iv.
Author: Devon Lee McClane
Publisher:
ISBN:
Category : Borides
Languages : en
Pages : 113
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Book Description
"This research focuses on the thermal properties of zirconium diboride (ZrB2) based ceramics. The overall goal was to improve the understanding of how different transition metal (TM) additives influence thermal transport in ZrB2. To achieve this, ZrB2 with 0.5 wt% carbon, and 3 mol% of individual transition metal borides, was densified by hot-press sintering. The transition metals that were investigated were: Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, and Re. The room temperature thermal diffusivities of the compositions ranged from 0.331 cm2/s for nominally pure ZrB2 to 0.105 cm2/s for (Zr, Cr)B2 and converged around 0.155cm2/s at higher temperatures for all compositions. Thermal conductivities were calculated from the diffusivities, using temperature-dependent values for density and heat capacity. The electron contribution to thermal conductivity was calculated from measured electrical resistivity according to the Wiedemann-Franz law. The phonon contribution to thermal conductivity was calculated by subtracting the electron contribution from the total thermal conductivity. Rietveld refinement of x-ray diffraction data was used to determine the lattice parameters of the compositions. The decrease in thermal conductivity for individual additives correlated directly to the metallic radius of the additive. Additional strain appeared to exist for additives when the stable TM boride for that metal had different crystal symmetries than ZrB2. This research provided insight into how additives and impurities affect thermal transport in ZrB2. The research potentially offers a basis for future modeling of thermal conductivity in ultra-high temperature ceramics based on the correlation between metallic radius and the decrease in thermal conductivity."--Abstract, page iv.
Author: William G. Fahrenholtz
Publisher: John Wiley & Sons
ISBN: 111892441X
Category : Technology & Engineering
Languages : en
Pages : 601
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Book Description
The first comprehensive book to focus on ultra-high temperature ceramic materials in more than 20 years Ultra-High Temperature Ceramics are a family of compounds that display an unusual combination of properties, including extremely high melting temperatures (>3000°C), high hardness, and good chemical stability and strength at high temperatures. Typical UHTC materials are the carbides, nitrides, and borides of transition metals, but the Group IV compounds (Ti, Zr, Hf) plus TaC are generally considered to be the main focus of research due to the superior melting temperatures and stable high-melting temperature oxide that forms in situ. Rather than focusing on the latest scientific results, Ultra-High Temperature Ceramics: Materials for Extreme Environment Applications broadly and critically combines the historical aspects and the state-of-the-art on the processing, densification, properties, and performance of boride and carbide ceramics. In reviewing the historic studies and recent progress in the field, Ultra-High Temperature Ceramics: Materials for Extreme Environment Applications provides: Original reviews of research conducted in the 1960s and 70s Content on electronic structure, synthesis, powder processing, densification, property measurement, and characterization of boride and carbide ceramics. Emphasis on materials for hypersonic aerospace applications such as wing leading edges and propulsion components for vehicles traveling faster than Mach 5 Information on materials used in the extreme environments associated with high speed cutting tools and nuclear power generation Contributions are based on presentations by leading research groups at the conference "Ultra-High Temperature Ceramics: Materials for Extreme Environment Applications II" held May 13-19, 2012 in Hernstein, Austria. Bringing together disparate researchers from academia, government, and industry in a singular forum, the meeting cultivated didactic discussions and efforts between bench researchers, designers and engineers in assaying results in a broader context and moving the technology forward toward near- and long-term use. This book is useful for furnace manufacturers, aerospace manufacturers that may be pursuing hypersonic technology, researchers studying any aspect of boride and carbide ceramics, and practitioners of high-temperature structural ceramics.
Author: Dipankar Ghosh
Publisher: Elsevier Inc. Chapters
ISBN: 0128057165
Category : Technology & Engineering
Languages : en
Pages : 75
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Book Description
Author: Gregory John Kenneth Harrington
Publisher:
ISBN:
Category : Ceramic materials
Languages : en
Pages : 238
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Book Description
"The research presented in this dissertation is focused on the thermal conductivity (k) of ZrB2 ceramics. The goal was to develop a better understanding of how various solid solutions and second phases affect the thermal and electrical transport in ZrB2, with a focus on the effect of C, W, and ZrC. The first study showed C additions improved densification and it was proposed that the reduction of boria was the impetus for this result. Boron carbide was formed by the reaction of excess C with reduced B and its formation was mitigated by the addition of ZrH2. This allowed the ZrB2-C binary system to be evaluated for study two. Study two showed the k of ZrB2 is reduced by C in solid solution and as a second phase due to the decrease in the electron contribution to thermal conductivity. Conductivities of 99 (25°C) and 76 W/m·K (2000°C) were obtained for the most pure ZrB2 (0.026 wt% C in solution and 0.2 vol% zirconia) produced in this study, which are the highest reported values for ZrB2 processed using commercial powders since 1980. The third study evaluated the electrical resistivity of ZrB2 up to 1860°C using the van der Pauw technique. Separate linear regimes were observed below and above 950°C, whereas, previous studies assumed a linear relation. Finally the effect of ZrC on the (Zr,W)B2 solid solution was evaluated in study four. The formation of (Zr,W)C initially increased k, but further ZrC additions decreased k. In the end, this research provides both: (1) usable information for the design of future ultra-high temperature ceramic systems; and (2) fundamental research that lays the groundwork for future studies aimed at understanding thermal transport in diboride based materials"--Abstract, page iv.
Author: Eric William Neuman
Publisher:
ISBN:
Category : Borides
Languages : en
Pages : 259
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Book Description
"Research presented in this dissertation focused on the mechanical behavior of ZrB2 based ceramic at elevated temperatures. Flexure strength, fracture toughness, and elastic modulus were measured at temperatures up to 2300°C for three compositions: monolithic ZrB2 (Z); ZrB2 - 30 vol% SiC - 2 vol% B4C (ZS); and ZrB2 - 10 vol% ZrC (ZC). In argon, Z, ZS, and ZC had strengths of 210 (at 2300°C), 260 (at 2200°C), and 295 MPa (at 2300°C), the highest temperatures tested for each composition. Fractography was used extensively to characterize the strength limiting flaws as a function of temperature. Strength of ZS in argon was controlled by the SiC cluster size up to 1800°C, and the formation of B-O-C-N phases that bridged SiC clusters above 2000°C. For ZC, surface flaws introduced during specimen preparation were the source of critical flaws in the material up to 1400°C, sub-critical crack growth of surface flaws between 1600 and 2000°C, and microvoid coalescence above 2000°C. It was also shown that thermal annealing at either 1400, 1500, or 1600°C improves the strength and modulus of ZS at temperatures between 800°C and 1600°C. Heat treatment at 1400°C for 10 hours produced the largest improvement in strength, 430 MPa at 1600°C versus 380 MPa for the as processed material. As a whole, the research pointed to several key microstructural features currently limiting the mechanical properties at the highest temperatures. In particular, removal of unfavorable secondary phases, and improved control over microstructure, should be promising methods to improve the elevated temperature properties of ZrB2 ceramics."--Abstract, page iv.
Author: Bikramjit Basu
Publisher: John Wiley & Sons
ISBN: 9781118037294
Category : Technology & Engineering
Languages : en
Pages : 504
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Book Description
This book covers the area of advanced ceramic composites broadly, providing important introductory chapters to fundamentals, processing, and applications of advanced ceramic composites. Within each section, specific topics covered highlight the state of the art research within one of the above sections. The organization of the book is designed to provide easy understanding by students as well as professionals interested in advanced ceramic composites. The various sections discuss fundamentals of nature and characteristics of ceramics, processing of ceramics, processing and properties of toughened ceramics, high temperature ceramics, nanoceramics and nanoceramic composites, and bioceramics and biocomposites.
Author: A. O. Surendranathan
Publisher: CRC Press
ISBN: 1482220458
Category : Technology & Engineering
Languages : en
Pages : 525
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Book Description
This book covers the fundamental aspects of ceramics and refractories. All refractories are ceramics, but all ceramics are not refractories. The book classifies and describes these materials, and examines their availability in nature. It examines the availability of these materials in nature, how they are extracted from nature, and how some of these materials are synthesized, and explains their structure-property correlation. It also addresses how they are designed for various applications and more.
