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No description available.

This project investigated the reactive formation of hafnium diboride (HfB2) in a variety of metallic environments, including blends with Bi, Cu, Ni, and Sb. HfB2 has garnered interest for a variety of applications due to its hardness, stability at elevated temperatures, as well as electrical and thermal conductivity. Experimental testing included differential scanning calorimetry (DSC) to reveal reaction initiation temperatures and enthalpies of reaction; and optical pyrometry to measure maximum reaction temperatures. Overall, DSC results indicated melting preceded reaction initiation; suggesting that the reaction initiation temperature for a certain blend occurred soon after melt formation, and could be broadly approximated by examination of binary phase diagrams. However, compositions containing bismuth ignited almost 200 ºC above the expected melting temperature. The maximum temperature measurement did not appear to correlate with reaction enthalpies as might be expected. This lack of correlation may be a result of an inability to capture the true maximum temperature due to the measurement frequency of the pyrometer, the disparity of heating rates between the two experimental methods, and/or to the influence of intermediate reactions on the temperature increase. / Master of Science

Hard and ultra-incompressible materials are of great interest due to their important applications in industry. A common route to design hard materials is combining transition metals with light and small covalent elements. Light elements such as carbon, oxygen, nitrogen and boron have been considered as good candidates. This study includes the synthesis of ReB2, OsB2 and another higher boride AlMgB14. Most of the techniques used for ReB2 synthesis reported 1:2.5 Re to B ratio because of the loss of the B during high temperature synthesis. However, as a result of B excess, the amorphous boron, located along the grain boundaries of polycrystalline ReB2, would degrade the ReB2 properties. Therefore, techniques which could allow synthesizing the stoichiometric ReB2 preferably at room temperature are in high demand. This thesis reported the synthesis of ReB2 powders using mechanochemical route by milling elemental crystalline Re and amorphous B powders in the SPEX 8000 high energy ball mill for 80 hours. The formation of boron and perrhenic acids are also reported after ReB2 powder was exposed to the moist air environment for a twelve months period of time. The synthesized ReB2 powder was characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, secondary ion mass spectrometry and Raman spectroscopy. OsB2 also shows its attractive properties. The hardness of orthorhombic OsB2 was reported to be 37 GPa, when the applied load is lowered to 0.245N. However, only one of the three predicted phases has been synthesized. In this study, the hexagonal OsB2 has been synthesized by the mechanochemical method. The lattice parameters of the Hex-OsB2 are iv α=β=90°, γ=120°; a=b=2.9047 Å, c=7.4500 Å. The synthesized OsB2 powder was annealed at 1050°C for 6 days, but no phase change was found. This shows that the Hex-OsB2 is very stable. Another promising hard material, AlMgB14, was also studied in this thesis. The AlMgB14 was synthesized at 1050 °C under normal pressure. Several different routes were tried and compared. It shows AlMgB14 cannot be synthesized merely by ball milling, which can bring the risk of oxidization. Magnesium metal is preferred to use as one of the raw materials.

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by Hon Wan Man = 鎂和硼化鎂複合材料的研究 / 韓韻文. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Hon Wan Man = Mei he peng hua mei fu he cai liao de yan jiu / Han Yunwen. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgements --- p.v / Table of contents --- p.vi / List of tables --- p.x / List of figures --- p.xi / Chapter Chapter 1 --- Introduction --- p.1-1 / Chapter 1.1. --- Background --- p.1-1 / Chapter 1.1.1. --- Conventional and unconventional superconducting materials --- p.1-1 / Chapter 1.1.2. --- Type I and type II superconductors --- p.1-2 / Chapter 1.1.3. --- Critical Temperature and Magnetic Properties (M-H Loops) --- p.1-4 / Chapter 1.2. --- Magnesium Diboride MgB2 --- p.1-6 / Chapter 1.2.1. --- Introduction --- p.1-6 / Chapter 1.2.2. --- Potential application and recent work of MgB2 --- p.1-6 / Chapter 1.2.2.1. --- Thin films --- p.1-7 / Chapter 1.2.2.2. --- Wires and tapes --- p.1-8 / Chapter 1.2.2.3. --- Powders and single crystal --- p.1-8 / Chapter 1.2.3. --- Factors affecting critical temperature in MgB2 --- p.1-9 / Chapter 1.2.3.1. --- Critical temperature versus lattice constants --- p.1-9 / Chapter 1.2.3.2. --- Critical temperature versus pressure --- p.1-9 / Chapter 1.3. --- Mg-based metal matrix composites (Mg-MMCs) --- p.1-10 / Chapter 1.4. --- Objectives and approaches --- p.1-11 / Chapter 1.5. --- Thesis layout --- p.1-12 / Chapter 1.6. --- References --- p.1-13 / Figures --- p.1-16 / Tables --- p.1-20 / Chapter Chapter 2 --- Methodology and instrumentation --- p.2-1 / Chapter 2.1. --- Introduction --- p.2-1 / Chapter 2.2. --- Experimental procedures --- p.2-1 / Chapter 2.3. --- Samples fabrication --- p.2-2 / Chapter 2.3.1. --- Powder metallurgy method (P/M) --- p.2-2 / Chapter 2.3.2. --- Argon atmosphere tube furnace heat treatment --- p.2-3 / Chapter 2.4. --- Characterization --- p.2-3 / Chapter 2.4.1. --- Differential thermal analyzer (DTA) --- p.2-3 / Chapter 2.4.2. --- X-ray powder diffractometry (XRD) --- p.2-4 / Chapter 2.4.3. --- Hot mounting and polishing --- p.2-4 / Chapter 2.4.4. --- Scanning electron microscopy (SEM) --- p.2-5 / Chapter 2.4.5. --- Transmission electron microscopy (TEM) --- p.2-5 / Chapter 2.4.6. --- Vibrating sample magnetometer (VSM) --- p.2-6 / Chapter 2.5. --- References --- p.2-8 / Figures --- p.2-9 / Chapter Chapter 3 --- Effects of sintering temperature on Mg-MgB2 composites --- p.3-1 / Chapter 3.1. --- Introduction --- p.3-1 / Chapter 3.2. --- Experimental results --- p.3-1 / Chapter 3.2.1. --- DTA and XRD analyses --- p.3-1 / Chapter 3.2.2. --- Microstructures --- p.3-2 / Chapter 3.2.2.1. --- Green sample --- p.3-2 / Chapter 3.2.2.2. --- Sample sintered at 550°C --- p.3-3 / Chapter 3.2.2.3. --- Sample sintered at 600°C --- p.3-4 / Chapter 3.2.2.4. --- Sample sintered at 700°C --- p.3-4 / Chapter 3.2.2.5. --- Hexagonal platelets --- p.3-5 / Chapter 3.2.3. --- Superconducting behaviors --- p.3-5 / Chapter 3.2.3.1. --- Critical temperature (Tc) comparison --- p.3-5 / Chapter 3.2.3.2. --- Magnetization loops (M-H loops) --- p.3-6 / Chapter 3.3. --- Discussions --- p.3-7 / Chapter 3.4. --- Conclusions --- p.3-9 / Chapter 3.5. --- References --- p.3-10 / Figures --- p.3-11 / Tables --- p.3-20 / Chapter Chapter 4 --- Effects of composition on Mg-MgB2 composites --- p.4-1 / Chapter 4.1. --- Introduction --- p.4-1 / Chapter 4.2. --- Experimental results --- p.4-1 / Chapter 4.2.1. --- XRD results --- p.4-1 / Chapter 4.2.2. --- Microstructures --- p.4-2 / Chapter 4.2.2.1 --- Mg-0 wt % B (Pure Mg) sintered at 650。C --- p.4-2 / Chapter 4.2.2.2 --- Mg-47 wt % B sintered at 650°C --- p.4-2 / Chapter 4.2.2.3 --- Amount of B in Mg sample --- p.4-3 / Chapter 4.2.2.3.1. --- Overview of Mg-5 to 40 wt % B --- p.4-3 / Chapter 4.2.2.3.2. --- MgB2 phase in different composition (Mg-5 to 47 wt %B) --- p.4-4 / Chapter 4.2.2.3.3. --- MgO phase in different composition (Mg-0 to 30 wt % B) --- p.4-4 / Chapter 4.2.3. --- VSM results (Critical temperature Tc comparison) --- p.4-5 / Chapter 4.3. --- Discussions --- p.4-6 / Chapter 4.4. --- Conclusions --- p.4-8 / Chapter 4.5. --- References --- p.4-10 / Figures --- p.4-11 / Table --- p.4-18 / Chapter Chapter 5 --- Growth Mechanisms --- p.5-1 / Chapter 5.1. --- Introduction --- p.5-1 / Chapter 5.2. --- Brief summary of SEM result --- p.5-1 / Chapter 5.3. --- Growth Mechanism of MgB2 --- p.5-2 / Chapter 5.4. --- Comparison of MgB2 grain size by XRD result --- p.5-7 / Chapter 5.5. --- Stoichiometric Ratio of MgB2 in different temperature --- p.5-7 / Chapter 5.6. --- Growth of the MgB2 platelets --- p.5-8 / Chapter 5.7. --- Conclusions --- p.5-10 / Chapter 5.8. --- References --- p.5-11 / Figures --- p.5-12 / Table --- p.5-15 / Chapter Chapter 6 --- Conclusions and Future Works --- p.6-1 / Chapter 6.1. --- Conclusions --- p.6-1 / Chapter 6.2. --- Future works --- p.6-2 / Chapter 6.3. --- References --- p.6-4

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No description available.

Thesis (M.Eng.). / Written for the Dept. of Mining and Materials Engineering. Title from title page of PDF (viewed 2009/06/17). Includes bibliographical references.

This dissertation discusses the synthesis, processing, and characterization of titanium carbide (TiC) and titanium diboride (TiB2) based materials for structural and electronic application. A series of TiB2 and TiC-TiB2 powders was prepared through a novel carbon coated precursors method. Reaction process, phase evolution, and microstructures were analyzed and characterized. The synthesized powders have the advantages of fine particle size (nano to submicron grade, 100nm to 800nm), high purity (low levels of contaminations such as free carbon and oxygen), loose agglomeration, and high surface area (~2.5 m2/g to 7.2 m2/g). Using the synthesized powders, three categories of composites were prepared: (1) TiB2-TiC-Ni composites with improved mechanical properties for structural applications; (2) TiB2-TiNiFeCrCoAl high-entropy alloy (HEA) composites with enhanced hardness and toughness for structural application; (3) TiC-Ti3Al based composites with good electrical and oxidation properties as the interconnect in solid oxide fuel cell. The author focuses on the sintering mechanism, microstructure and interface, reactions, and properties characterizations of above three types of composites. Correlations of processing-microstructures-properties are discussed and established based on scientific observation.