Boron carbide (B₄C) is a non-oxide ceramic in the same class of nonmetallic hard materials as silicon carbide and diamond. The high hardness, high elastic modulus and low density of B₄C make it a nearly ideal material for personnel and vehicular armor. B₄C plates formed via hot-pressing are currently issued to U.S. soldiers and have exhibited excellent performance; however, hot-pressed articles contain inherent processing defects and are limited to simple geometries such as low-curvature plates. Recent advances in the pressureless sintering of B₄C have produced theoretically-dense and complex-shape articles that also exhibit superior ballistic performance. However, the cost of this material is currently high due to the powder shape, size, and size distribution that are required, which limits the economic feasibility of producing such a product. Additionally, the low fracture toughness of pure boron carbide may have resulted in historically lower transition velocities (the projectile velocity range at which armor begins to fail) than competing silicon carbide ceramics in high-velocity long-rod tungsten penetrator tests. Lower fracture toughness also limits multi-hit protection capability. Consequently, these requirements motivated research into methods for improving the densification and fracture toughness of inexpensive boron carbide composites that could result in the development of a superior armor material that would also be cost-competitive with other high-performance ceramics. The primary objective of this research was to study the effect of titanium and carbon additives on the sintering and mechanical properties of inexpensive B₄C powders. The boron carbide powder examined in this study was a submicron (0.6 μm median particle size) boron carbide powder produced by H.C. Starck GmbH via a jet milling process. A carbon source in the form ofphenolic resin, and titanium additives in the form of 32 nm and 0.9 μm TiO₂ powders were selected. Parametric studies of sintering behavior were performed via high-temperature dilatometry in order to measure the in-situ sample contraction and thereby measure the influence of the additives and their amounts on the overall densification rate. Additionally, broad composition and sintering/post-HIPing studies followed by characterization and mechanical testing elucidated the effects of these additives on sample densification, microstructure development, and mechanical properties such as Vickers hardness and microindentation fracture toughness. Based upon this research, a process has been developed for the sintering of boron carbide that yielded end products with high relative densities (i.e., 100%, or theoretical density), microstructures with a fine (∼2-3 μm) grain size, and high Vickers microindentation hardness values. In addition to possessing these improved physical properties, the costs of producing this material were substantially lower (by a factor of 5 or more) than recently patented work on the pressureless sintering and post-HIPing of phase-pure boron carbide powder. This recently patented work developed out of our laboratory utilized an optimized powder distribution and yielded samples with high relative densities and high hardness values. The current work employed the use of titanium and carbon additives in specific ratios to activate the sintering of boron carbide powder possessing an approximately mono-modal particle size distribution. Upon heating to high temperatures, these additives produced fine-scale TiO ₂ and graphite inclusions that served to hinder grain growth and substantially improve overall sintered and post-HIPed densities when added in sufficient concentrations. The fine boron carbide grain size manifested as a result of these second phase inclusions caused a substantial increase in hardness; the highest hardness specimen yielded a hardness value (2884.5 kg/mm²) approaching that of phase-pure and theoretically-dense boron carbide (2939 kg/mm²). Additionally, the same high-hardness composition exhibited a noticeably higher fracture toughness (3.04 MPa•m¹/²) compared to phase-pure boron carbide (2.42 MPa• m¹/²), representing a 25.6% improvement. A potential consequence of this study would be the development of a superior armor material that is sufficiently affordable, allowing it to be incorporated into the general soldier’s armor chassis.

Zirconium diboride (ZrB₂) is a ceramic material possessing ultra-high melting temperatures. As such, this compound could be useful in the construction of thermal protection systems for aerospace applications. This work addresses a primary shortcoming of this material, namely its propensity to destructively oxidize at high temperatures, as well as secondary issues concerning its heat transport properties.To characterize and improve oxidation properties, thermogravimetric studies were per- formed using a specially constructed experimental setup. ZrB₂-SiC two-phase ceramic composites were isothermally oxidized for ∼90 min in flowing air in the range 1500-1900°C. Specimens with 30 mol% SiC formed distinctive reaction product layers which were highly protective; 28 mol% SiC - 6 mol% TaB₂ performed similarly. At higher temperatures, specimens containing lower amounts of SiC were shown to be non-protective, whereas specimens containing greater amounts of SiC produced unstable oxide layers due to gas evolution. Oxide coating thicknesses calculated from weight loss data were consistent with those measured from SEM micrographs. In order to characterize one aspect of the materials' heat transport properties, the thermal diffusivities of ZrB₂-SiC composites were measured using the laser flash technique. These were converted to thermal conductivities using temperature dependent specific heat and density data; thermal conductivity decreased with increasing temperature over the range 25-2000°C. The composition with the highest SiC content showed the highest thermal conductivity at room temperature, but the lowest at temperatures in excess of ∼400°C, because of the greater temperature sensitivity of the thermal conductivity of the SiC phase, as compared to more electrically-conductive ZrB₂. Subsequent finite difference calculations were good predictors of multi-phase thermal conductvities for the compositions examined. The thermal conductivities of pure ZrB₂ as a function of temperature were back-calculated from the experimental results for the multi-phase materials, and literature thermal conductivities of the other two phases. This established a relatively constant thermal conductivity of 88-104 W/m·K over the evaluated temperature range. Further heat transport characterization was performed using pre-oxidized, directly resistively heated ZrB₂-30 mol% SiC ribbon specimens under the observation of a spectral radiometer. The ribbons were heated and held at specific temperatures over the range 1100- 1330°C in flowing Ar, and normal spectral emittance values were recorded over the 1-6 μm range with a resolution of 10 nm. The normal spectral emittance was shown to decrease with loss of the borosilicate layer over the course of the data collection time periods. This change was measured and compensated for to produce traces showing the emittance of the oxidized composition rising from ∼0.7 to ∼0.9 over the range of wavelengths measured.

The technological development and application of waste-to-resource strategy is significantly critical and crucial in both environmental and manufacturing industries, via which we do not only provide practical treatments to toxic waste materials but also translate them into usable products. It has been considered as a preferred method which should be applied in future wastewater treatment strategies. In this study, we investigated the process of incorporating cadmium oxide and nickel oxide into ceramic-based materials with the phases of CdAl4O7, and CdFe2O4. Such products are of less harmful effect to the natural environment and can also be of beneficial use with their good mechanical properties identified by nano-indentation. We proved the possibility and provided an opportunity to convert the waste from wastewater treatment process to a new material resource. XRD is preferred for characterizing solid mixtures to determine the relative abundances of crystalline phases during the reaction process. As a result, we can obtain the relative abundance information on the growth of the crystalline products, such as CdAl4O7, and CdFe2O4 according to the change of fabrication temperatures. In that case, the starting reaction temperature and the optimized temperature (at which the completed reaction could be achieved) could be revealed. In Cd-Al system, the starting temperature for CdAl4O7 formation is 900 °C, and the optimized formation temperature is around 1020 °C. On the other hand, for Cd-Fe system, such temperatures are of 700 °C and 850 °C correspondingly. In our research, it is shown that the ceramic-process is an effective strategy to stabilize the waste hazardous metals (cadmium and nickel) by materials such as aluminate, ferrite, and kaolin commonly used in ceramic industry. Through this method, the difficult-to-treat wasted metals would become reusable and applied in building and infrastructure projects. Products containing CdAl4O7, CdFe2O4 and NiAl2O4 have shown higher resistance to acidic leaching, comparing to CdO and NiO used as the starting materials to simulate the waste metal forms discharged from the industrial stream. Furthermore, similar measurements by alkaline attack on the sintered products (NiAl2O4 containing samples) were also studied. Besides the investigation to leaching behavior, the mechanical properties are also measured by nano-indentation in our work. The incorporation of metal waste into the fabrication of ceramic products is valuable due to the preferred stabilization mechanisms of crystal structures and the large volume of ceramic products needed by the construction industry. Furthermore, because the product safety and functionality should not be compromised, a fundamental understanding of the surface properties of metal containing phases should be further established, rather than relying solely on data from regulatory tests on bulk samples. Therefore, the results of this study demonstrate the superior mechanical properties of nickel spinel containing products, comparing to the cristobalite silica matrix, under severe acid attack. / published_or_final_version / Civil Engineering / Master / Master of Philosophy

This work addresses fundamental aspects of designing templates and curing conditions for the synthesis of mesoporous metal oxide thin films. The first section addresses selection of cationic-carbohydrate surfactant mixtures to synthesize templated silica thin films for selective adsorption of simple carbohydrates based on molecular imprinting. Nuclear magnetic resonance and fluorescence spectroscopy results suggest a novel structure for mixtures of alkyl glucopyranosides or xylopyranosides with cationic (trimethylammonium) surfactants. Despite thermodynamically favorable mixing, the carbohydrate headgroups in the mixed micelle adopt an inverted configuration with their headgroups in the micelle core, and therefore are inaccessible for molecular imprinting. This orientation occurs even when the alkyl tail length of the carbohydrate surfactant is greater than that of the cationic surfactant, but this limitation can be overcome by introducing a triazole linker to the carbohydrate surfactant. The next section addresses the effects of aging conditions on the structural and chemical evolution of surfactant templated silica thin films. The third section describes the synthesis of carbohydrate/cationic surfactant imprinted silica thin films with orthogonally oriented cylindrical pores by modifying the glass surface with a random copolymer. The last part of the dissertation addresses the effect of pore orientation on the transformation mechanism of block copolymer templated titania thin films during high temperature curing. Mesoporous titania thin films can be used for photochemical and solar cell applications, but doing so requires addressing the tradeoff between loss of mesostructural order and growth of crystallinity during thermal treatment. By using advanced x-ray scattering techniques it has been shown that the titania films with vertically oriented pores can better withstand the anisotropic stress that develops during thermal treatment compare to titania films with mixed pore orientation. For instance, films with parallel or mixed pores can only be heated at 400 °C for a brief time (~10 min) without loss of order, while orthogonally oriented films can be heated at 550 °C or greater for extended time periods (on the order of hours) without significant loss of long-range mesopore structure. Detailed kinetic modeling was applied to enable the comparison of activation energy for mesostructure loss in films as a function of pore orientation and thickness.

Health monitoring of aeronautic structures and human beings is becoming crucial because of the human safety issues. In this thesis integrated (IUTs) and flexible ultrasonic transducers (FUTs) have been developed using a sol-gel spray piezoelectric film fabrication technology. IUTs can be fabricated directly onto the structures with curved surfaces even on-site. FUTs were made using membrane substrates of thickness less than 75 mum. In-situ monitoring of AI airframe thickness was carried out and the thickness measurement accuracy was better than 36 mum and 41 mum for IUT and FUT, respectively. The thickness of the ice on top of the AI airframe was also measured. Two crucial piezoelectric constants d33 and d31 of the composite film were measured with laser interferometer and optical coherence tomography system, respectively. Pulse and breath of a human being were also monitored using flexible piezoelectric membrane sensors. In addition, bones in human body were observed using FUTs as well and their performance is comparable to that of commercial ultrasonic transducers.

High fuel utilization SOFCs could eliminate emissions from systems that include afterburners and potentially be suitable for carbon sequestration, while producing electricity more efficiently. Current fuel utilization operating points are typically chosen at approximately 85% for Ni-cermet anodes because higher fuel utilization frequently results in the formation of nickel oxide and reduces drastically the performance of the SOFC. In this work the feasibility of an in-plane graded anode architecture with a transition from a material with high catalytic activity to materials more stable under high fuel utilization conditions was evaluated through a steady-state SOFC finite element model. Thereafter, plasma spraying of solution precursor feedstock (SPPS) and suspension feedstock (SPS) was used to fabricate ceramic coatings that could potentially be used as SOFC anodes for high fuel utilization conditions. Microstructural, electrical and electrochemical properties of LST, LSBT and LSFCr coatings with additions of carbon black pore former were investigated.

High fuel utilization SOFCs could eliminate emissions from systems that include afterburners and potentially be suitable for carbon sequestration, while producing electricity more efficiently. Current fuel utilization operating points are typically chosen at approximately 85% for Ni-cermet anodes because higher fuel utilization frequently results in the formation of nickel oxide and reduces drastically the performance of the SOFC. In this work the feasibility of an in-plane graded anode architecture with a transition from a material with high catalytic activity to materials more stable under high fuel utilization conditions was evaluated through a steady-state SOFC finite element model. Thereafter, plasma spraying of solution precursor feedstock (SPPS) and suspension feedstock (SPS) was used to fabricate ceramic coatings that could potentially be used as SOFC anodes for high fuel utilization conditions. Microstructural, electrical and electrochemical properties of LST, LSBT and LSFCr coatings with additions of carbon black pore former were investigated.

No description available.

No description available.

Low temperature co-fired ceramic (LTCC) electronic packaging materials are applied for their electrical and mechanical properties, high reliability, chemical stability and ease of fabrication. Three dimensional features can also be prepared allowing integration of microfluidic channels and cavities inside LTCC modules. Mechanical, optical, electrical, microfluidic functions have been realized in single LTCC modules. For these reasons LTCC is attractive for biomedical microfluidics and Lab-on-a-Chip systems. However, commercial LTCC systems, optimized for microelectrics applications, have unknown cytocompatibility, and are not compatible with common surface functionalization chemistries. The first goal of this work is to develop biocompatible LTCC materials for biomedical applications. In the current work, two different biocompatible LTCC substrate materials are conceived, formulated and evaluated. Both materials are based from well-known and widely utilized biocompatible materials. The biocompatibilities of the developed LTCC materials for in-vitro applications are studied by cytotoxicity assays, including culturing endothelial cells (EC) both in LTCC leachate and directly on the LTCC substrates. The results demonstrate the developed LTCC materials are biocompatible for in-vitro biological applications involving EC. The second goal of this work is to develop functional capabilities in LTCC microfluidic systems suitable for in-vitro and biomedical applications. One proposed application is the evaluation of oxygen tension and oxidative stress in perfusion cell culture and bioreactors. A Clark-type oxygen sensor is successfully integrated with LTCC technique in this work. In the current work, a solid state proton conductive electrolyte is used to integrate an oxygen sensor into the LTCC. The measurement of oxygen concentration in Clark-type oxygen sensor is based on the electrochemical reaction between working electrode and counter electrode. Cyclic voltammetry and chronoamperometry are measured to determine the electrochemical properties of oxygen reduction in the LTCC based oxygen sensor. The reduction current showed a linear relationship with oxygen concentration. In addition, LTCC sensor exhibits rapid response and sensitivity in the physiological range 1─9 mg/L. The fabricated devices have the capabilities to regulate oxygen supply and determination of local dissolved oxygen concentration in the proposed applications including perfusion cell culture and biological assays.