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Title: PRODUCTION OF BULK CERAMIC SHAPES FROM POLYMER DERIVED CERAMICS.
Creator: Hill, Arnold Hill, An, Linan, University of Central Florida
Abstract / Description: A method has been developed to produce bulk ceramic components from a class of ceramics known as polymer derived ceramics. In the past polymer derived ceramics have been limited to thin film applications or in the fabrication of MEMS devices. The reason being that when the polymer is into a ceramic, large quantities of gas are generated which produce internal pressure that fractures the ceramic components. The method developed here solves that issue by casting into the polymer a 3 dimensional...
Show moreA method has been developed to produce bulk ceramic components from a class of ceramics known as polymer derived ceramics. In the past polymer derived ceramics have been limited to thin film applications or in the fabrication of MEMS devices. The reason being that when the polymer is into a ceramic, large quantities of gas are generated which produce internal pressure that fractures the ceramic components. The method developed here solves that issue by casting into the polymer a 3 dimensional network of polymer fibers in the form of a foam which, during pyrolysis, burns out and leaves a network of open channels that allows decomposition gases to escape thus preventing pressure from building up. The inclusion of the polymer foam allows for the formation of strong plastic like green bodies which can be machined into any shape. The green bodies are then pyrolized into ceramic components. This process allows for the simple and inexpensive fabrication of complex ceramic components that have the potential to replace current components that are made with traditional methods.
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Date Issued: 2008
Identifier: CFE0002037, ucf:47605
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002037

Title: REDISTRIBUTION OF MANGANESE ION IMPLANTED IN SILICON.
Creator: Shunmugavelu, Arun, An, Linan, University of Central Florida
Abstract / Description: Ion implantation and the subsequent redistribution of manganese atoms in Czochralski Silicon (Cz-Si) and Floating Zone Silicon (Fz-Si) due to thermal annealing between 300 C and 1000 C is studied using Secondary Ion Mass Spectroscopy. The samples ion implanted at 340 C showed multiple peak formation above 900 C. This was not observed for the samples ion implanted at room temperature. Cz-Si and Fz-Si showed similar redistribution profiles.
Date Issued: 2007
Identifier: CFE0001909, ucf:47477
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001909

Title: POLYMER-DERIVED CERAMICS: ELECTRONIC PROPERTIES AND APPLICATION.
Creator: xu, weixing, An, Linan, University of Central Florida
Abstract / Description: In this work, we studied the electronic behavior of polymer-derived ceramics (PDCs) and applied them for the synthesis of carbon nanotube reinforced ceramic nanocomposites and ceramic MEMS (Micro-Electro-Mechanical Systems) structures. Polymer-derived SiCN ceramics were synthesized by pyrolysis of a liquid polyureasilazane with dicumyl peroxide as thermal initiator. The structural evolution during pyrolysis and post-annealing was studied using FTIR, solid state NMR and Raman. The results...
Show moreIn this work, we studied the electronic behavior of polymer-derived ceramics (PDCs) and applied them for the synthesis of carbon nanotube reinforced ceramic nanocomposites and ceramic MEMS (Micro-Electro-Mechanical Systems) structures. Polymer-derived SiCN ceramics were synthesized by pyrolysis of a liquid polyureasilazane with dicumyl peroxide as thermal initiator. The structural evolution during pyrolysis and post-annealing was studied using FTIR, solid state NMR and Raman. The results revealed that the resultant ceramics consisted of SiCxNx-4 as major building units. These units were connected with each other through C-C/C=C bonds or by shearing N/C. The amount of sp2 free carbon strongly depends on composition and processing condition. Electron paramagnetic resonance (EPR) was used to investigate electronic structure of PDCs; the results revealed that the materials contain unpaired electron centers associated with carbons. Electronic behavior of the SiCN ceramics was studied by measuring their I-V curves, temperature dependence of d.c.-conductivities and impendence. The results revealed that the SiCN ceramics exhibited typical amorphous semiconductor behavior, and their conductivity varied in a large range. The results also revealed that the materials contain more than one phase, which have the different electronic behavior. We explored possibility of using polymer-derived ceramics to make ceramic MEMS for harsh environmental applications with a lithography technique. The cure depth of the polymer precursor was measured as a function of UV intensity and exposure time. The experimental data was compared with the available theoretical model. A few typical SiCN parts were fabricated by lithography technique. We also prepared carbon nanotube reinforced ceramic nanocomposites by using PDC processing. The microstructures of the composites were characterized using SEM and TEM; the mechanical properties were studied characterized using nanoindentation. The significant improvement in mechanical properties was observed for the nanocomposites.
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Date Issued: 2006
Identifier: CFE0001228, ucf:46885
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001228

Title: POLYMER-DERIVED SI-AL-C-N CERAMICS:OXIDATION, HOT-CORROSION, AND STRUCTURAL EVOLUTION.
Creator: Wang, Yiguang, An, Linan, University of Central Florida
Abstract / Description: Polymer-derived ceramics are a new class of materials synthesized by thermal decomposition of polymer precursors. Previous studies have shown that the materials exhibit excellent thermo-mechanical properties and can be stable at temperatures up to 2000oC. Furthermore, the novel polymer-to-ceramics process enables the manipulation of the ceramic structures at the atomic/nano level by designing the chemistry of polymer precursors and controlling the pyrolysis conditions, thereby, the properties...
Show morePolymer-derived ceramics are a new class of materials synthesized by thermal decomposition of polymer precursors. Previous studies have shown that the materials exhibit excellent thermo-mechanical properties and can be stable at temperatures up to 2000oC. Furthermore, the novel polymer-to-ceramics process enables the manipulation of the ceramic structures at the atomic/nano level by designing the chemistry of polymer precursors and controlling the pyrolysis conditions, thereby, the properties of ceramics. In this dissertation, oxidation/hot-corrosion behavior and the structural evolution of Si-Al-C-N ceramics have been studied. The structural evolution and crystallization behavior of the SiCN and SiAlCN ceramics are investigated using FT-IR, XRD, and NMR. The results revealed that aluminum could greatly affect the structural evolution and crystallization behavior of polymer-derived ceramics, resulting to better stability. The oxidation kinetics of the SiCN and SiAlCN ceramics in air is determined by directly measuring the thickness of the oxide scale with SEM as a function of oxidation time. The results revealed that while the oxidation of the SiCN ceramics follows parabolic kinetics in all of the ranges of testing temperatures, oxidation of the SiAlCN ceramics is complicated: their oxidation rates are similar to that of SiCN ceramics at the earlier stage, but they decrease to very low levels after a certain time. The oxidation rate of the SiAlCN ceramics is more than an order of magnitude lower than any other silicon based ceramics previously reported. The transportation behavior of oxygen through the oxide scales is studied by 18O diffusion. The results indicate that oxidation is controlled by molecular oxygen diffusing through the oxides for both SiCN and SiAlCN ceramics; however, the oxygen diffusion rate in the oxides on SiAlCN ceramics is remarkably retarded. The structures of the oxides are characterized by XRD and NMR. A structural model is advanced to account for the aluminum effect on the oxygen diffusion in the oxide. The oxidation and hot-corrosion kinetics of the SiCN and SiAlCN ceramics in water vapor are determined by measuring their weight changes as a function of annealing time. The kinetic constants, kp and kl, are obtained by fitting the weight-change data with a paralinear model. The results reveal that the SiAlCN ceramics have a much better corrosion resistance than the SiCN and CVD SiC/Si3N4. After annealing at 1400oC for 300 hours, the SiAlCN-20 still retains more than 70% of its original strength, while the SiCN only retains about 20% of its original strength. The improvement in oxidation/hot-corrosion resistance of the SiAlCN ceramics is attributed to the low activity of the SiO2 in the Al2O3-containing silica. In summary, I have developed a new class of high-temperature materials, Si-Al-C-N ceramics. It is demonstrated that these new materials have excellent oxidation and corrosion resistance and thermal stability. Together with their easy processability, the materials will find many high temperature applications such as environmental barrier coatings, ceramic matrix composites, and MEMS for harsh environments.
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Date Issued: 2006
Identifier: CFE0001017, ucf:46810
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001017

Title: SYNTHESIS AND CHARACTERIZATION OF POLYMER-DERIVED POROUS SICN CERAMICS.
Creator: wei, yun, An, Linan, University of Central Florida
Abstract / Description: The synthesis and characterization of porous SiCN ceramics produced by the method of polymer-derived ceramics were studied in this work. The polymer-to-ceramic conversion technique is a novel revolution in the methods for fabricating porous materials with controlled morphologies and tailored properties. The porous SiCN ceramics can be successfully prepared from thermal decomposition of polymeric precursors (polysilazane) and the pore former (polyvinyl alcohol (PVA)). The fabrication...
Show moreThe synthesis and characterization of porous SiCN ceramics produced by the method of polymer-derived ceramics were studied in this work. The polymer-to-ceramic conversion technique is a novel revolution in the methods for fabricating porous materials with controlled morphologies and tailored properties. The porous SiCN ceramics can be successfully prepared from thermal decomposition of polymeric precursors (polysilazane) and the pore former (polyvinyl alcohol (PVA)). The fabrication procedures involved the mixing of the pre-ceramic precursor with appropriate concentration of the PVA, curing, pyrolysis and subsequent PVA removal, leaving pores in the ceramic matrix. The material obtained revealed a homogeneous amorphous microstructure consisting of Si, C and N elements. The effects of the concentration and the particle size of PVA on the bulk density, open porosity, line shrinkage, microstructure, pore size, permeability, mechanical behavior, oxidation behavior and thermal stability were examined in this thesis. An increase in both concentration and particle size of PVA contribute to a decrease in the bulk density and an increase in the open porosity and line shrinkage. The morphology development, in particular, was investigated by scanning electron microscopy (SEM). The properties in terms of the pore size and permeability were measured by the water expulsion method. The mechanical behavior of the porous SiCN ceramic was characterized by the three- point bending strength test, thermal shock strength test and hertzian indentation strength test. The flexural strength and hertzian indentation strength of these porous ceramics at room temperature decrease with an increase in porosity. However, the flexural strength after thermal shock was significantly improved by increasing the temperature change. The oxidation behavior and thermal stability of porous SiAlCN ceramics were also explored by the mass change versus oxidation time and temperature. The phase evolution at different temperatures was also investigated by XRD analysis.
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Date Issued: 2008
Identifier: CFE0002359, ucf:47792
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002359

Title: ELECTRONIC PROPERTIES AND MICROSTRUCTURES OF AMORPHOUS SICN CERAMICS DERIVED FROM POLYMER PRECURSORS.
Creator: JIANG, TAO, An, Linan, University of Central Florida
Abstract / Description: Polymer-derived ceramics (PDCs) are a new class of high-temperature materials synthesized by thermal decomposition of polymeric precursors. These materials possess many unique features as compared with conventional ceramics synthesized by powder metallurgy based processing. For example, PDCs are neither amorphous nor crystalline. Instead, they possess nano-domain structures. Due to the direct chemical-to-ceramic processing, PDCs can be used for making components and devices with complex...
Show morePolymer-derived ceramics (PDCs) are a new class of high-temperature materials synthesized by thermal decomposition of polymeric precursors. These materials possess many unique features as compared with conventional ceramics synthesized by powder metallurgy based processing. For example, PDCs are neither amorphous nor crystalline. Instead, they possess nano-domain structures. Due to the direct chemical-to-ceramic processing, PDCs can be used for making components and devices with complex shapes. Thus, understanding the properties and structures of these materials are of both fundamental and practical interest. In this work, the structures and electronic behavior of polymer-derived amorphous silicon carbonitrides (SiCNs) were investigated. The materials were synthesized by pyrolysis of a commercially available liquid precursor. Ceramic materials with varied structures/properties were successfully synthesized by modifying the precursor and using different pyrolysis temperatures. The structures of the obtained materials were studied using XRD, solid state NMR, EPR, FTIR and Raman Spectroscope. The electronic behavior of the materials was investigated by measuring I-V curves, Hall effects, temperature dependent conductivity. The experiments were also performed to measure UV-Visible absorption and dielectric properties of the materials. This work leads to the following significant progresses: (i) developed quantitative technique for measuring free carbon concentration; (ii) achieved better understanding of the electronic conduction mechanisms and measured electronic structures of the materials for the first time; and (iii) demonstrated that these materials possess unusual dielectric behavior and provide qualitative explanations.
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Date Issued: 2009
Identifier: CFE0002702, ucf:48174
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002702

Title: Fatigue Lifetime Approximation based on Quantitative Microstructural Analysis for Air Plasma Sprayed Thermal Barrier Coatings.
Creator: Bargraser, Carmen, Sohn, Yongho, An, Linan, Heinrich, Helge, University of Central Florida
Abstract / Description: The durability of thermal barrier coatings (TBCs) affects the life of the hot section engine components on which they are applied. Fatigue is the general failure mechanism for such components and is responsible for most unexpected failures; therefore it is desirable to develop lifetime approximation models to ensure reliability and durability.In this study, we first examined the microstructural degradation of air plasma sprayed ZrO2-8wt.%Y2O3 TBCs with a low-pressure plasma sprayed CoNiCrAlY...
Show moreThe durability of thermal barrier coatings (TBCs) affects the life of the hot section engine components on which they are applied. Fatigue is the general failure mechanism for such components and is responsible for most unexpected failures; therefore it is desirable to develop lifetime approximation models to ensure reliability and durability.In this study, we first examined the microstructural degradation of air plasma sprayed ZrO2-8wt.%Y2O3 TBCs with a low-pressure plasma sprayed CoNiCrAlY bond coat on an IN 738LC superalloy substrate. The durability of TBCs were assessed through furnace thermal cyclic tests carried out in air at 1100(&)deg;C with a 1-, 10-, and 50-hour dwell period, preceded by a 10-minute heat-up and followed by a 10-minute forced-air-quench. Failure mechanisms of the TBCs were thoroughly investigated through materials characterization techniques including: X-Ray Diffraction, Scanning Electron Microscopy, and Energy Dispersive X-Ray Spectroscopy.Quantitative microstructural analyses were then carried out to document the growth of the thermally grown oxide (TGO) scale, the depletion of the Al-rich ?-NiAl phase in the bond coat, and the population and growth of micro-cracks near the YSZ/bond coat interface. Trends in the TGO growth and the ?-phase depletion in the bond coat followed those of diffusion-controlled processes(-)parabolic growth of the TGO and exponential depletion of the ?-phase. Formation and propagation of cracks within the YSZ resulted in complete spallation of the YSZ topcoat from the bond-coated superalloy substrate.Evolution in these microstructural features was correlated to the lifetime of TBCs, which showed cracking within the YSZ to be the cause of failure; thus a lifetime approximation model was developed, via modification of Paris Law, based on the experimental data. The model predicted the TBC lifetime within 10% of the experimental lifetime.
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Date Issued: 2011
Identifier: CFE0004087, ucf:49145
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004087

Title: Imaging long-range orientational order in monolayers of amphiphilic molecules with scanning probe force microscope and liquid crystal optical amplification.
Creator: Liang, Wenlang, Fang, Jiyu, Deng, Weiwei, An, Linan, Huo, Qun, University of Central Florida
Abstract / Description: Monolayers of amphiphilic molecules at interface provide a unique system for understanding the thermodynamic and rheological properties of quasi two-dimensional systems. They are also an excellent model accessible for studying cell membranes. The feature of long-range organization of molecular tilt azimuth in monolayers at the air/water interface is one of the most interesting findings over the past two decades, which leads to the formation rich and defined textures. By observing the changes...
Show moreMonolayers of amphiphilic molecules at interface provide a unique system for understanding the thermodynamic and rheological properties of quasi two-dimensional systems. They are also an excellent model accessible for studying cell membranes. The feature of long-range organization of molecular tilt azimuth in monolayers at the air/water interface is one of the most interesting findings over the past two decades, which leads to the formation rich and defined textures. By observing the changes in these textures, the transitions between tilted monolayer phases can be detected. We study the boojum and stripe textures formed in the liquid-condensed phase of pentadecanoic acid (PDA) monolayers at the air/water interface and find that they can be preserved after being transferred to glass substrates at low dipping speeds at a temperature lower than the room temperature. Frictional force microscopy confirms the long-range tilt order in the transferred boojums and stripes of PDA, implying the interaction of the PDA molecules with the glass surface does not change the tilt order. Polymerized stripe textures of pentacosadiynoic acid (PCA) monolayers can also be transferred onto solid substrates. Atomic force microscopy shows that the PCA stripe textures represent the regular variations of molecular packing densities in PCA monolayers. Furthermore, we find that the molecular orientation and packing density changes in monolayers can induce the local order of nematic liquid crystals. Due to the long-range orientation correlation of nematic liquid crystals, the boojum and stripe textures in monolayers can be observed by an optical microscope after liquid crystal optical amplification.
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Date Issued: 2011
Identifier: CFE0004498, ucf:49294
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004498

Title: Generation and printing of strictly monodisperse droplets.
Creator: Duan, Hongxu, Deng, Weiwei, An, Linan, Cho, Hyoung, University of Central Florida
Abstract / Description: Highly monodisperse droplets are attracting great attention both in many research areas, such as aerosol science, combustion, and Nano-manufacturing. This thesis invents a novel aerosol generator: (")Periodic Electro Hydro-dynamic Chopper(") termed as (")PEHD chopper("), and develops a new method to directly print micro-patterns with monodisperse droplets. The principle of the PEHD chopper is to use the fringe electric field of a capacitor to introduce controlled perturbation on a liquid jet...
Show moreHighly monodisperse droplets are attracting great attention both in many research areas, such as aerosol science, combustion, and Nano-manufacturing. This thesis invents a novel aerosol generator: (")Periodic Electro Hydro-dynamic Chopper(") termed as (")PEHD chopper("), and develops a new method to directly print micro-patterns with monodisperse droplets. The principle of the PEHD chopper is to use the fringe electric field of a capacitor to introduce controlled perturbation on a liquid jet.We first derived the governing equations for a circular inviscid liquid jet under transverse electric fields. The electric fields were obtained through numerical simulation. Then we used a high speed camera (up to one million frames per second) to visualize the jet break-up as well as the droplets' size and shape.The experiments show that the PEHD chopper can effectively (")chop(") a neutral micro-jet and generate highly monodisperse micro-droplets, which diameter range from 100 (&)#181;m to 500 (&)#181;m. To reduce the droplet size, PEHD chopper with a butterfly design is applied on a typical single electrospray. In this configuration, the jet swings at long wavelengths (?(>)?R), where ?R is the Rayleigh wave length, but breaks up into highly monodisperse droplets near 2?R and ?R without satellite droplets. The butterfly configuration combined with electrified jet expands the diameter range into 20 (&)#181;m to 100 (&)#181;m.Finally, we demonstrate the electrospray printing of Polymer Derived Ceramics (PDC) for sensor applications in harsh environment. A modified single ES with an additional driving electric field is used to directly print PDC precursor without mask, we achieved 1D feature as narrow as 35 (&)#181;m and a micro pentagram pattern. Moreover, after pyrolysis of PDC at 1100 (&)deg;C in nitrogen, amorphous alloys of silicon, carbon and nitrogen (SiCN) are obtained. The samples exhibit excellent good integrity and adhesion to the substrate.
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Date Issued: 2013
Identifier: CFE0005094, ucf:50720
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005094

Title: Carbon nanotube (CNT) metallic composite with focus on processing and the resultant properties.
Creator: Billah, Md Muktadir, Chen, Quanfang, Bai, Yuanli, An, Linan, Orlovskaya, Nina, University of Central Florida
Abstract / Description: Metal-carbon nanotubes (CNTs) composites are the promising advanced materials that are being developed to take the advantage of the exceptional properties of CNTs. Because of the intrinsically strong in-plane atomic SP2 bonding CNTs offer high young's modulus (1.0(-)1.8 TPa), high tensile strength (30(-)200 GPa) and high elongation at break (10(-)30%). The thermal conductivity of individual single-walled carbon nanotube (SWCNT) and multi-walled carbon nanotube (MWCNT) are about 6000 W/m-K and...
Show moreMetal-carbon nanotubes (CNTs) composites are the promising advanced materials that are being developed to take the advantage of the exceptional properties of CNTs. Because of the intrinsically strong in-plane atomic SP2 bonding CNTs offer high young's modulus (1.0(-)1.8 TPa), high tensile strength (30(-)200 GPa) and high elongation at break (10(-)30%). The thermal conductivity of individual single-walled carbon nanotube (SWCNT) and multi-walled carbon nanotube (MWCNT) are about 6000 W/m-K and 3000 W/m-K, respectively. Therefore it is expected that by incorporation of CNTs in metal matrices multi-functional composites can be used ideally as thermal interface materials, light-weight high-strength structural materials, electric components, optical devices, electromagnetic absorption materials etc. However, so far results are far from satisfied for CNT composites, mainly due to the fact that there are two main key issues remained without good solutions for CNT composites: the poor uniformity in CNT dispersion and the weak interfacial bonding between CNTs and the matrices. In this study, MWCNTs were functionalized and coated with metals like Cu and Ni by electroless deposition methods prior to their application. Metal coatings result in strong interfacial bonding at CNT-metal interfaces and uniform dispersion. During metal coating processes CNTs are physically separated in electrolyte and after coating they get physically retain the separation by the coated metal layer that they are not allowed to aggregate to form bundles. Moreover, after metal coating, the resultant density of Ni-coated MWCNTs is close to that of molten metal matrix. This prevent separation of CNTs due to buoyancy effects and results in uniform dispersion. Metal coating on CNTs surfaces also allows to form strong interfacial bonding with the metal matrices.SnBi alloy has been identified as novel lead-free thermal interface material (TIM) for electronics packaging. However the thermal conductivity and the mechanical strength of pure SnBi alloy are not sufficient to withstand harsh environment imposed by powder electronics. Therefor how to increase the thermal conductivity and the mechanical strength of SnBi solders becomes important. In this study, MWCNTs have been added into SnBi alloy to form SnBi/CNT composite solders by different material processing methods. First, in sandwich method Cu-coated CNTs were added to the 70Sn-30Bi alloy and mixed mechanically. UTS was increased by 47.6% for 3 wt. % Cu/CNTs addition. Second. Ni-coated CNTs were added by sonication assisted melting method in fabricating 70Sn-30Bi solder. For 3 wt. % Ni-coated MWCNTs, equivalent to 0.6 wt. % pure MWCNTs, UTS and YS were increased by 88.8 % and 112.3% respectively. In addition the thermal conductivity was also increased by more than 70%. Ni-coated CNTs were also added to pure Al by powder metallurgy method. For 7 wt. % Ni/CNTs having diameter 30-50 nm, UTS and YS were increased by 92.7% and 101.6% respectively. For CNTs having diameter 8-15 nm, UTS and YS were increased by 108.9% and 128.2% respectively for 7 wt. % addition. All these results are first time obtained that are much greater than published data on CNT/metal composites. Results discussion and mechanism in reinforcement were also presented.
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Date Issued: 2017
Identifier: CFE0006567, ucf:51320
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006567

Title: High Temperature Materials Characterization and Sensor Application.
Creator: Ren, Xinhua, Gong, Xun, Wahid, Parveen, Wu, Xinzhang, An, Linan, University of Central Florida
Abstract / Description: This dissertation presents new solutions for turbine engines in need of wireless temperature sensors at temperatures up to 1300oC. Two important goals have been achieved in this dissertation. First, a novel method for precisely characterizing the dielectric properties of high temperature ceramic materials at high temperatures is presented for microwave frequencies. This technique is based on a high-quality (Q)-factor dielectrically-loaded cavity resonator, which allows for accurate...
Show moreThis dissertation presents new solutions for turbine engines in need of wireless temperature sensors at temperatures up to 1300oC. Two important goals have been achieved in this dissertation. First, a novel method for precisely characterizing the dielectric properties of high temperature ceramic materials at high temperatures is presented for microwave frequencies. This technique is based on a high-quality (Q)-factor dielectrically-loaded cavity resonator, which allows for accurate characterization of both dielectric constant and loss tangent of the material. The dielectric properties of Silicon Carbonitride (SiCN) and Silicoboron Carbonitride (SiBCN) ceramics, developed at UCF Advanced Materials Processing and Analysis Center (AMPC) are characterized from 25 to 1300oC. It is observed that the dielectric constant and loss tangent of SiCN and SiBCN materials increase monotonously with temperature. This temperature dependency provides the valuable basis for development of wireless passive temperature sensors for high-temperature applications. Second, wireless temperature sensors are designed based on the aforementioned high-temperature ceramic materials. The dielectric constant of high-temperature ceramics increases monotonically with temperature and as a result changes the resonant frequency of the resonator. Therefore, the temperature can be extracted by measuring the change of the resonant frequency of the resonator. In order for the resonator to operate wirelessly, antennas need to be included in the design. Three different types of sensors, corresponding to different antenna configurations, are designed and the prototypes are fabricated and tested. All of the sensors successfully perform at temperatures over 1000oC. These wireless passive sensor designs will significantly benefit turbine engines in need of sensors operating at harsh environments.
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Date Issued: 2012
Identifier: CFE0004791, ucf:49727
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004791

Title: Interdiffusion Study of Mg-AA6061 System.
Creator: Fu, Mian, Sohn, Yongho, Coffey, Kevin, An, Linan, University of Central Florida
Abstract / Description: Magnesium (Mg) is a light-weight metal that has extraordinary physical and chemical properties for many potential applications in automobile, military, and electronics. Aluminum alloys, because of its light-weight, high strength and corrosion resistance have a wide range of commercial applications. Given these two, sometime competing, alloy systems, there are now many applications where the metallurgical compatibility of Mg- and Al-alloys are required for engineering applications. One such...
Show moreMagnesium (Mg) is a light-weight metal that has extraordinary physical and chemical properties for many potential applications in automobile, military, and electronics. Aluminum alloys, because of its light-weight, high strength and corrosion resistance have a wide range of commercial applications. Given these two, sometime competing, alloy systems, there are now many applications where the metallurgical compatibility of Mg- and Al-alloys are required for engineering applications. One such case is the development of diffusion barrier for U-Mo metallic fuel in Al-alloy cladding, where Mg, with its complete immiscibility with U and Mo is being considered as the diffusion barrier. While negligible diffusional interaction between Mg and U-Mo alloys have been reported, diffusional interaction between the Mg and Al-alloy cladding has not been investigated. In this study, solid-to-solid diffusion couples were assembled using discs of pure Mg (99.999 %) and AA6061 Al-alloy. After preparation, Mg was diffusion bonded to AA6061 in sealed quartz capsule at 300(&)deg;, 350(&)deg;, and 400(&)deg;C for 720, 360, and 240 hours, respectively. Scanning electron microscopy was used to inspect the interdiffusion zone, while phase identification was performed using X-ray energy dispersive spectroscopy. One specific phase that exists in the binary Mg-Al system, labeled (")epsilon(") was observed and characterized by transmission electron microscopy. From the preceding data, the growth rates as well as interdiffusion coefficients of the intermetallic phases were extracted and compared to previous investigations using pure Mg and Al.
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Date Issued: 2013
Identifier: CFE0005333, ucf:50521
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005333

Title: Characterization of Waste-To-Energy (WTE) Bottom and Fly Ashes in Cementitious Materials.
Creator: An, Jin Woo, Nam, Boo Hyun, Yun, Hae-Bum, Chopra, Manoj, An, Linan, University of Central Florida
Abstract / Description: Waste-to-Energy (WTE) ashes (or called as municipal solid waste incineration ashes) have been recycled in the areas of road bed, asphalt paving, and concrete products in many European and Asian countries. In those countries, recycling programs (including required physical properties and environmental criteria) of ash residue management have been developed so as to encourage and enforce the reuse for WTE ashes instead of landfill disposal. However, the U.S. has shown a lack of consistent and...
Show moreWaste-to-Energy (WTE) ashes (or called as municipal solid waste incineration ashes) have been recycled in the areas of road bed, asphalt paving, and concrete products in many European and Asian countries. In those countries, recycling programs (including required physical properties and environmental criteria) of ash residue management have been developed so as to encourage and enforce the reuse for WTE ashes instead of landfill disposal. However, the U.S. has shown a lack of consistent and effective management plans as well as environmental regulations for the use of WTE ashes. Many previous studies demonstrated the potential beneficial use of WTE ash as an engineering material with minimum environmental impacts. Due to persistent uncertainty of engineering properties and inconsistency in the Federal and State regulations in the U.S., the recycling of WTE ash has been hindered, and they are mostly disposed of in landfills. The goal of this study is to identify beneficial use of WTE ashes as construction materials; thus, the recycling program of WTE ashes will become more active in the U.S. One of potential applications for the WTE ashes can be cement-based materials because the ashes contain good chemical components such as calcium and silicon. Moreover, toxics (heavy metals) can be bound or encapsulated in cement matrix; thus, the leaching potential can be reduced. The specific objectives are: (1) to understand the current practice of the reuse of WTE ashes as construction materials, (2) to physically and chemically characterize WTE bottom and fly ashes, (3) to investigate the effects of WTE bottom and fly ashes in cementitious materials (e.g. cement paste and concrete) as replacement of either cement of fine aggregate with emphasis on cement hydration, and (4) to investigate the environmental impacts of WTE bottom ash on leaching when used in cement-based materials. Fundamental properties of MSWI bottom ash and fly ash were studied by conducting physical, microstructural, and chemical tests. Petrographic examinations, such as scanning electron microscopy (SEM), energy dispersive x-ray (EDX), and x-ray diffraction (XRD) were performed in order to identify chemical composition of the ash and to determine their contents. To evaluate the main side effect of ash when used in concrete, the creation of a network of bubbles due to the presence of aluminum, ashes and aluminum powder were submerged in high pH solution, and the evolution of hydrogen gas was measured. Efforts were made to investigate the influence of WTE ashes on engineering properties of cement paste and concrete specimens when part of Portland cement and fine aggregate are replaced with ground and sieved WTE ashes. Cement paste and concrete cylinders were cast with various amounts of mineral and fine aggregate additions, respectively, and their strength and durability were investigated. Subsequently, optimum mix proportioning of the WTE ashes was investigated when they are used in cement paste and concrete specimens. In addition, the leaching characteristics of major alkaline and trace elements from concrete containing varied amounts (10%-50%) of BA were investigated by Synthetic Precipitation Leaching Procedure (SPLP) batch testing.
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Date Issued: 2015
Identifier: CFE0006251, ucf:51070
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006251

$A modeling framework of brittle and ductile fractures coexistence in composites$

Title: A modeling framework of brittle and ductile fractures coexistence in composites.
Creator: Qiao, Yangyang, Bai, Yuanli, Gou, Jihua, Kassab, Alain, Gordon, Ali, An, Linan, University of Central Florida
Abstract / Description: In order to reduce the weight of automobiles and aircrafts, lightweight materials, such as aluminum alloy, advanced high strength steel, composite materials, are widely used to replace the traditional materials like mild steel. Composite materials are complicated in material mechanical properties and less investigated compared to metallic materials. Engineering composites can be categorized into polymer matrix composites (PMCs), metal matrix composites (MMCs) and ceramic matrix composites ...
Show moreIn order to reduce the weight of automobiles and aircrafts, lightweight materials, such as aluminum alloy, advanced high strength steel, composite materials, are widely used to replace the traditional materials like mild steel. Composite materials are complicated in material mechanical properties and less investigated compared to metallic materials. Engineering composites can be categorized into polymer matrix composites (PMCs), metal matrix composites (MMCs) and ceramic matrix composites (CMCs) according to their matrix materials.A set of mechanical experiments ranging from micro scale (single fiber composite and thin film composite) to macro scale (PMCs and MMCs) were conducted to fully understand the material behavior of composite materials. Loading conditions investigated includes uniaxial tension, three-point bending, uniaxial compression, simple shear, tension combined with shear, and compression combined with shear.For single fiber composite and thin-film composite, details of each composition are modelled. For the PMCs and MMCs which have plenty of reinforcements like fibers and particles, the details of the composition of structures cannot be modelled due to the current limitations of computing power. A mechanics framework of composite materials including elasticity, plasticity, failure initiation and post failure softening is proposed and applied to two types of composite materials.Uniaxial tension loading is applied to several single fiber composites and thin film composites. A surprising phenomenon, controllable and sequential fragmentation of the brittle fiber to produce uniformly sized rods along meters of polymer cladding, rather than the expected random or chaotic fragmentation, is observed with a necking propagation process. A combination of necking propagation model, fiber cracking model and interfacial model are proposed and applied to the finite element simulations. Good predictions of necking propagation and uniform fragmentation phenomenon are achieved. This modeling method of the micro-scale phenomenon reveals the physics inside composites in micro scale and helps the understanding of the process of nano fragmentation.Unidirectional carbon fiber composites were tested under multi-axial loading conditions including tensile/compression/shear loadings along and perpendicular to the fiber direction. Compression dominated tests showed a brittle fracture mode like local kicking/buckling, while tension dominated tests showed a fracture mode like delamination and fiber breakage. Simple shear tests with displacement control showed matrix material hardening and softening before total failure. The proposed modeling framework is successfully applied to the PMCs. A new parameter ? was introduced to represent different loading conditions of PMCs. Numerical simulations using finite element method well duplicated the anisotropic elasticity and plasticity of this material. Failure features like delamination was simulated using cohesive surface feature. It is also applied to carbon fiber composite laminates to further validate the proposed model.A round of experimental study on high volume fraction of metallic matrix nano composites was conducted, including uniaxial tension, uniaxial compression, and three-point bending. The example materials were two magnesium matrix composites reinforced with 10 and 15% vol. SiC particles (50nm size). Brittle fracture mode was exhibited under uniaxial tension and three-point bending, while shear dominated ductile fracture mode (up to 12% fracture strain) was observed under uniaxial compression. Transferring the Modified Mohr Coulomb (MMC) ductile fracture model to the stress based MMC model (sMMC), the proposed modeling framework is applied to this material. This model has been demonstrated to be capable of predicting the coexistence of brittle and ductile fracture modes under different loading conditions for MMCs. Numerical simulations using finite element method well duplicated the material strength, fracture initiation sites and crack propagation modes of the Mg/SiC nano composites with a good accuracy.
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Date Issued: 2018
Identifier: CFE0007078, ucf:51977
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007078

Title: INTERFACIAL BEHAVIOR IN POLYMER DERIVED CERAMICS AND SALT WATER PURIFICATION VIA 2D MOS2.
Creator: Li, Hao, An, Linan, Jung, YeonWoong, Zhai, Lei, Feng, Xiaofeng, Yu, Xiaoming, University of Central Florida
Abstract / Description: In the present dissertation, the behavior of the internal potential barrier in a polymer-derived amorphous SiAlCN ceramic was studied by measuring its complex impedance spectra at various dc bias as well as different testing and annealing temperatures. The complex impedancespectra of the polymer-derived a-SiAlCN were measured under various dc bias voltages in a temperature range between 50 and 150?(&)deg;C, as well as different annealing temperatures (1100-1400 (&)deg;C). All spectra,...
Show moreIn the present dissertation, the behavior of the internal potential barrier in a polymer-derived amorphous SiAlCN ceramic was studied by measuring its complex impedance spectra at various dc bias as well as different testing and annealing temperatures. The complex impedancespectra of the polymer-derived a-SiAlCN were measured under various dc bias voltages in a temperature range between 50 and 150?(&)deg;C, as well as different annealing temperatures (1100-1400 (&)deg;C). All spectra, regardless of temperature and bias, consist of two semi-circular arcs,corresponding to the free-carbon phase and the interface, respectively. The impedance of the free-carbon phase is independent of the bias, while that of the interface decreased significantly with increasing dc bias. It is shown that the change of the interfacial capacitance with the bias can be explained using the double Schottky barrier model. The charge-carrier concentration and potential barrier height were estimated by comparing the experimental data and the model.The results revealed that increasing testing temperature led to an increased charge-carrier concentration and a reduced barrier height, both following Arrhenius dependence, whereas the increase in annealing temperature resulted in increased charge-carrier concentration and barrier height. The phenomena were explained in terms of the unique bi-phasic microstructures of the material. The research findings reveal valuable microstructural information of temperaturedependent properties of polymer derived ceramics, and should contribute towards more precise understanding and control of the electrical as well as dielectric properties of polymer derivedceramics. Furthermore, the desalination performances and underlying mechanisms of two-dimensional CVD-grown MoS2 layers membranes have been experimentally assessed. Based on a successful large-area few-layer 2D materials growth, transfer and integration method, the 2D MoS2 layers membranes showed preserved chemical and microstructural integrity after integration. The few-layer 2D MoS2 layers demonstrated superior desalination capability towards various types of seawater salt solutions approaching theoretically-predicted values. Such performances are attributed to the dimensional and geometrical effect, as well as the electrostatic interaction of the inherently-present CVD-induced atomic vacancies for governingboth water permeation and ionic sieving at the solution/2D-layer interfaces.
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Date Issued: 2019
Identifier: CFE0007830, ucf:52813
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007830

Title: Diffusion and reaction in selected uranium alloy system.
Creator: Huang, Ke, Sohn, Yongho, An, Linan, Xu, Chengying, Coffey, Kevin, Heinrich, Helge, University of Central Florida
Abstract / Description: U-Mo metallic fuels with Al alloys as the matrix/cladding are being developed as low enriched uranium fuels under the Reduced Enrichment for Research and Test Reactor (RERTR) program. Significant interactions have been observed to occur between the U-Mo fuel and the Al alloy during fuel processing and irradiation. U-Zr metallic fuels with stainless steel claddings have been developed for the generation IV sodium fast reactor (SFR). The fuel cladding chemical interaction (FCCI) induced by the...
Show moreU-Mo metallic fuels with Al alloys as the matrix/cladding are being developed as low enriched uranium fuels under the Reduced Enrichment for Research and Test Reactor (RERTR) program. Significant interactions have been observed to occur between the U-Mo fuel and the Al alloy during fuel processing and irradiation. U-Zr metallic fuels with stainless steel claddings have been developed for the generation IV sodium fast reactor (SFR). The fuel cladding chemical interaction (FCCI) induced by the interdiffusion of components was also observed. These interactions induce deleterious effects on the fuel system, such as thinning of the cladding layer, formation of phases with undesirable properties, and thermal cracking due to thermal expansion mismatches and changes in molar volume. The interaction between the fuel and the cladding involves multi-component interdiffusion. To determine the ternary interdiffusion coefficients using a single diffusion couple, a new method based on regression via the matrix transformation approach is proposed in this study. This new method is clear in physical meaning and simple in mathematical calculation. The reliability and accuracy of this method have been evaluated through application to three case studies: a basic asymptotic concentration profile, a concentration profile with extrema and a smoothed concentration profile with noise. Generally, this new method works well in all three cases.In order to investigate the interdiffusion behavior in U-Mo alloys, U vs. Mo diffusion couples were assembled and annealed in the temperature range of 650 to 1000(&)deg;C. The interdiffusion microstructures and concentration profiles were examined via scanning electron microscopy (SEM) and electron probe microanalysis (EPMA), respectively. Interdiffusion coefficients and activation energies were calculated as functions of temperature and Mo composition. The intrinsic diffusion coefficients of U and Mo at the marker composition were also determined. The activity of U and the thermodynamic factor of the U-Mo alloy have been calculated using the ideal solution, the regular solution, and the subregular solution models based on the molar excess Gibbs free energy of the U-Mo alloy. The calculated intrinsic diffusivities of U and Mo along with the thermodynamic factor of the U-Mo alloy were employed to estimate the atomic mobilities and the vacancy wind effects of U and Mo according to Manning's description.To explore potential diffusion barrier materials for reducing the fuel cladding chemical interaction between the U-Mo fuel and the Al alloy matrix/cladding, the interdiffusion behavior between U-Mo alloys and Mo, Zr, Nb and Mg were systematically studied. U-10wt.%Mo vs. Mo, Zr and Nb diffusion couples were annealed in the temperature range from 600 to 1000(&)deg;C. A diffusion couple between U-7wt.%Mo and Mg was annealed at 550(&)deg;C for 96 hours. SEM and transmission electron microscopy (TEM) were applied to characterize the microstructure of the interdiffusion zone. X-ray energy dispersive spectroscopy (XEDS) and EPMA were utilized to examine the concentration redistribution and the phase constituents. For the U-Mo vs. Mo diffusion couples, the interdiffusion coefficients at high Mo concentrations ranging from 22 to 32 at.%Mo were determined for the first time. In the U-Mo vs. Zr diffusion couples, the Mo2Zr phase was found at the interface. The diffusion paths were estimated and investigated according to the Mo-U-Zr ternary phase diagram. Thermal cracks and pure U precipitates were found within the diffusion zone in the U-Mo vs. Nb system. The growth rate of the interdiffusion zone was found to be lower by about 103 times for Zr, 105 times for Mo and 106 times for Nb compared to those observed in the U-10wt.%Mo vs. Al or Al-Si systems. For the diffusion couple of U-Mo vs. Mg, the U-Mo was bonded very well to the Mg and there was negligible diffusion observed even after 96 hours annealing at 550(&)deg;C.For a more fundamental understanding of the complex diffusion behavior between U-Zr fuels and their stainless steel claddings, U vs. Fe, Fe-15wt.%Cr and Fe-15wt.%Cr-15wt.%Ni diffusion couples were examined to investigate the interdiffusion behaviors between U and Fe and the effects of the alloying elements Cr and Ni. The diffusion couples were annealed in the temperature range from 580 to 700(&)deg;C for various times. Two intermetallic phases, U6Fe and UFe2, developed in all of the diffusion couples with the U6Fe layer growing faster than the UFe2 layer. For the diffusion couples of U vs. Fe, extrinsic growth constants, intrinsic growth constants, integrated interdiffusion coefficients and activation energies in each phase were calculated. The results suggest that U6Fe impeded the growth of UFe2, and the boundary condition change caused by the allotropic transformation of U played a role in the growth of the U6Fe and UFe2 layers. The reasons why U6Fe grew much faster than UFe2 are also discussed. The additions of Cr and Ni into Fe affected the growth rates of U6Fe and UFe2. The solubility of Cr and Ni in U6Fe and UFe2 were determined, and it was found that Cr diffused into U more slowly than Fe or Ni.
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Date Issued: 2012
Identifier: CFE0004548, ucf:49238
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004548

Title: Experimental study and modeling of mechanical micro-machining of particle reinforced heterogeneous materials.
Creator: Liu, Jian, Xu, Chengying, An, Linan, Gordon, Ali, Bai, Yuanli, Gong, Xun, University of Central Florida
Abstract / Description: This study focuses on developing explicit analytical and numerical process models for mechanical micro-machining of heterogeneous materials. These models are used to select suitable process parameters for preparing and micro-machining of these advanced materials. The material system studied in this research is Magnesium Metal Matrix Composites (Mg-MMCs) reinforced with nano-sized and micro-sized silicon carbide (SiC) particles.This research is motivated by increasing demands of miniaturized...
Show moreThis study focuses on developing explicit analytical and numerical process models for mechanical micro-machining of heterogeneous materials. These models are used to select suitable process parameters for preparing and micro-machining of these advanced materials. The material system studied in this research is Magnesium Metal Matrix Composites (Mg-MMCs) reinforced with nano-sized and micro-sized silicon carbide (SiC) particles.This research is motivated by increasing demands of miniaturized components with high mechanical performance in various industries. Mg-MMCs become one of the best candidates due to its light weight, high strength, and high creep/wear resistance. However, the improved strength and abrasive nature of the reinforcements bring great challenges for the subsequent micro-machining process.Systematic experimental investigations on the machinability of Mg-MMCs reinforced with SiC nano-particles have been conducted. The nanocomposites containing 5 Vol.%, 10 Vol.% and 15 Vol.% reinforcements, as well as pure magnesium, are studied by using the Design of Experiment (DOE) method. Cutting forces, surface morphology and surface roughness are characterized to understand the machinability of the four materials. Based on response surface methodology (RSM) design, experimental models and related contour plots have been developed to build a connection between different materials properties and cutting parameters. Those models can be used to predict the cutting force, the surface roughness, and then optimize the machining process.An analytical cutting force model has been developed to predict cutting forces of Mg-MMCs reinforced with nano-sized SiC particles in the micro-milling process. This model is different from previous ones by encompassing the behaviors of reinforcement nanoparticles in three cutting scenarios, i.e., shearing, ploughing and elastic recovery. By using the enhanced yield strength in the cutting force model, three major strengthening factors are incorporated, including load-bearing effect, enhanced dislocation density strengthening effect and Orowan strengthening effect. In this way, the particle size and volume fraction, as significant factors affecting the cutting forces, are explicitly considered. In order to validate the model, various cutting conditions using different size end mills (100 (&)#181;m and 1 mm dia.) have been conducted on Mg-MMCs with volume fraction from 0 (pure magnesium) to 15 Vol.%. The simulated cutting forces show a good agreement with the experimental data. The proposed model can predict the major force amplitude variations and force profile changes as functions of the nanoparticles' volume fraction. Next, a systematic evaluation of six ductile fracture models has been conducted to identify the most suitable fracture criterion for micro-scale cutting simulations. The evaluated fracture models include constant fracture strain, Johnson-Cook, Johnson-Cook coupling criterion, Wilkins, modified Cockcroft-Latham, and Bao-Wierzbicki fracture criterion. By means of a user material subroutine (VUMAT), these fracture models are implemented into a Finite Element (FE) orthogonal cutting model in ABAQUS/Explicit platform. The local parameters (stress, strain, fracture factor, velocity fields) and global variables (chip morphology, cutting forces, temperature, shear angle, and machined surface integrity) are evaluated. Results indicate that by coupling with the damage evolution, the capability of Johnson-Cook and Bao-Wierzbicki can be further extended to predict accurate chip morphology. Bao-Wierzbiki-based coupling model provides the best simulation results in this study. The micro-cutting performance of MMCs materials has also been studied by using FE modeling method. A 2-D FE micro-cutting model has been constructed. Firstly, homogenized material properties are employed to evaluate the effect of particles' volume fraction. Secondly, micro-structures of the two-phase material are modeled in FE cutting models. The effects of the existing micro-sized and nano-sized ceramic particles on micro-cutting performance are carefully evaluated in two case studies. Results show that by using the homogenized material properties based on Johnson-Cook plasticity and fracture model with damage evolution, the micro-cutting performance of nano-reinforced Mg-MMCs can be predicted. Crack generation for SiC particle reinforced MMCs is different from their homogeneous counterparts; the effect of micro-sized particles is different from the one of nano-sized particles.In summary, through this research, a better understanding of the unique cutting mechanism for particle reinforced heterogeneous materials has been obtained. The effect of reinforcements on micro-cutting performance is obtained, which will help material engineers tailor suitable material properties for special mechanical design, associated manufacturing method and application needs. Moreover, the proposed analytical and numerical models provide a guideline to optimize process parameters for preparing and micro-machining of heterogeneous MMCs materials. This will eventually facilitate the automation of MMCs' machining process and realize high-efficiency, high-quality, and low-cost manufacturing of composite materials.
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Date Issued: 2012
Identifier: CFE0004570, ucf:49196
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004570

Title: Development of Polymer Derived SiAlCN Ceramic and Its Applications for High-Temperature Sensors.
Creator: Shao, Gang, An, Linan, Fang, Jiyu, Xu, Chengying, Chow, Lee, Deng, Weiwei, University of Central Florida
Abstract / Description: Polymer-derived ceramic (PDC) is the name for a class of materials synthesized by thermal decomposition of polymeric precursors which excellent thermomechanical properties, such as high thermal stability, high oxidation/corrosion resistance and high temperature multifunctionalities. Direct polymer-to-ceramic processing routes of PDCs allow easier fabrication into various components/devices with complex shapes/structures. Due to these unique properties, PDCs are considered as promising...
Show morePolymer-derived ceramic (PDC) is the name for a class of materials synthesized by thermal decomposition of polymeric precursors which excellent thermomechanical properties, such as high thermal stability, high oxidation/corrosion resistance and high temperature multifunctionalities. Direct polymer-to-ceramic processing routes of PDCs allow easier fabrication into various components/devices with complex shapes/structures. Due to these unique properties, PDCs are considered as promising candidates for making high-temperature sensors for harsh environment applications, including high temperatures, high stress, corrosive species and/or radiation. The SiAlCN ceramics were synthesized using the liquid precursor of polysilazane (HTT1800) and aluminum-sec-tri-butoxide (ASB) as starting materials and dicumyl peroxide (DP) as thermal initiator. The as-received SiAlCN ceramics have very good thermal-mechanical properties and no detectable weight loss and large scale crystallization. Solid-state NMR indicates that SiAlCN ceramics have the SiN4, SiO4, SiCN3, and AlN5/AlN6 units. Raman spectra reveals that SiAlCN ceramics contain (")free carbon(") phase with two specific Raman peaks of (")D(") band and (")G(") band at 1350 cm-1 and 1600 cm-1, respectively. The (")free carbon(") becomes more and more ordered with increasing the pyrolysis temperature. EPR results show that the defects in SiAlCN ceramics are carbon-related with a g-factor of 2.0016(&)#177;0.0006. Meanwhile, the defect concentration decreases with increasing sintered temperature, which is consistent with the results obtained from Raman spectra.Electric and dielectric properties of SiAlCN ceramics were characterized. The D.C. conductivity of SiAlCN ceramics increases with increasing sintered temperature and the activation energy is about 5.1 eV which higher than that of SiCN ceramics due to the presence of oxygen. The temperature dependent conductivity indicates that the conducting mechanism is a semiconducting band-gap model and follows the Arrhenius equation with two different sections of activation energy of 0.57 eVand 0.23 eV, respectively. The temperature dependent conductivity makes SiAlCN ceramics suit able for high temperature sensor applications. The dielectric properties were carried out by the Agilent 4298A LRC meter. The results reveal an increase in both dielectric constant and loss with increasing temperature (both pyrolysis and tested). Dielectric loss is dominated by the increasing of conductivity of SiAlCN ceramics at high sintered temperatures.SiAlCN ceramic sensors were fabricated by using the micro-machining method. High temperature wire bonding issues were solved by the integrity embedded method (IEM). It's found that the micro-machining method is a promising and cost-effective way to fabricate PDC high temperature sensors. Moreover IEM is a good method to solve the high temperature wire bonding problems with clear bonding interface between the SiAlCN sensor head and Pt wires. The Wheatstone bridge circuit is well designed by considering the resistance relationship between the matching resistor and the SiAlCN sensor resistor. It was found that the maximum sensitivity can be achieved when the resistance of matching resistor is equal to that of the SiAlCN sensor. The as-received SiAlCN ceramic sensor was tested up to 600 degree C with the relative output voltage changing from -3.932 V to 1.153 V. The results indicate that the relationship between output voltage and test temperature is nonlinear. The tested sensor output voltage agrees well with the simulated results. The durability test was carried out at 510 degree C for more than two hours. It was found that the output voltage remained constant for the first 30 min and then decreased gradually afterward by 0.02, 0.04 and 0.07 V for 1, 1.5 and 2 hours.
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Date Issued: 2013
Identifier: CFE0004937, ucf:49602
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004937

Title: High Volume Fraction Mg-based Nanocomposites: Processing, Microstructure and Mechanical Behavior.
Creator: Liu, Jinling, An, Linan, Suryanarayana, Challapalli, Fang, Jiyu, Bai, Yuanli, Lin, Kuo-Chi, University of Central Florida
Abstract / Description: Mg-based metal matrix nanocomposites (MMNCs) with mechanical properties, superior to those of coarse-grained composites, are promising structural materials for applications in the automotive and aerospace industries. The research in this area was primarily focused earlier on either micro-scaled reinforcements or nano-scaled reinforcements with very low volume fractions. MMNCs with high volume fractions have not been explored yet. In this research, we study the processing, microstructures and...
Show moreMg-based metal matrix nanocomposites (MMNCs) with mechanical properties, superior to those of coarse-grained composites, are promising structural materials for applications in the automotive and aerospace industries. The research in this area was primarily focused earlier on either micro-scaled reinforcements or nano-scaled reinforcements with very low volume fractions. MMNCs with high volume fractions have not been explored yet. In this research, we study the processing, microstructures and properties of MMNCs containing ceramic nanoparticles up to 30 vol.%.We first investigated the mechanical alloying of Al2O3 nanoparticles and pure Mg under high-energy ball milling conditions. The phase evolution and their distribution were evaluated as a function of milling time. Then, the thermal stability of the formed nanocomposites was investigated by annealing it at high temperatures. It indicated that an exchange reaction had occurred to a large extent between Mg and Al2O3 resulting in the formation of Al and MgO phases. Additionally, the reaction between Al and un-reacted Mg led to the formation of Mg-Al intermetallics.Due to the reaction between Mg and Al2O3 during the milling and annealing process, we attempted to synthesize Mg/SiC nanocomposites. The mixed powders containing 0, 5, 10 and 15 vol.% SiC were produced by high energy ball milling and then the powders were consolidated via spark plasma sintering. The phase constitutions and microstructures of the Mg/SiC nanocomposites were characterized. SiC nanoparticles (average particle size ~14 nm) appear to be homogeneously dispersed within the matrix, and the average inter-particle spacings of all the Mg/SiC nanocomposites were smaller than 50 nm. Microscopic methods, even at high magnifications did not reveal any significant porosity in the as-processed MMNCs.Mechanical characterization of the Mg/SiC nanocomposites was conducted using the microindentation test. Besides the microhardness test, different intermediate pause times and loading rates were used to evaluate the stiffness and loading rate sensitivity of our samples. The abnormal microhardness and loading rate sensitivity were showed for the Mg-15 vol.% SiC samples. At the same time, the monotonic increase of stiffness with volume fraction was exhibited in the Mg/SiC nanocomposites.Finally, we investigated the quasi-static and dynamic response of Mg/SiC nanocomposites and microcomposites, and discussed the underlying mechanisms. Strain softening was noticed in the milled Mg sample under quasi-static compression. Similarly, the strengthening effect leveling off was also observed in the Mg-15 vol.% SiC samples under either quasi-static or high-strain rate uniaxial compression conditions. No significant plastic deformation was observed in the Mg/SiC nanocomposites. The estimated strain rate sensitivity of all the Mg/SiC nanocomposites in this work was around 0.03, which is much smaller than 0.3 and 0.6, observed for 100 nm and 45 nm grain size pure Mg individually. In particular, the existing models fail in predicting the inverse volume fraction effect, and other mechanisms are yet to be explored. The presence of SiC nanoparticles may play an important role that leads to this difference.
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Date Issued: 2013
Identifier: CFE0004879, ucf:49672
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004879

Title: Rhenium, osmium and iridium diborides by mechanochemistry: Synthesis, structure, thermal stability and mechanical properties.
Creator: Xie, Zhilin, Orlovskaya, Nina, Blair, Richard, Gou, Jihua, Raghavan, Seetha, An, Linan, University of Central Florida
Abstract / Description: Borides are implemented in a range of industrial applications due to their unique mechanical, electrical, thermal and catalytic properties. In particular, transition metal diborides are of special interest. In the recent years, borides of rhenium (Re), osmium (Os) and iridium (Ir) have been studied as for their ultra-hardness and superior stiffness. In this dissertation, a mechanochemical method is introduced to produce rhenium diboride (ReB2) powder, a novel hexagonal osmium diboride (h-OsB2...
Show moreBorides are implemented in a range of industrial applications due to their unique mechanical, electrical, thermal and catalytic properties. In particular, transition metal diborides are of special interest. In the recent years, borides of rhenium (Re), osmium (Os) and iridium (Ir) have been studied as for their ultra-hardness and superior stiffness. In this dissertation, a mechanochemical method is introduced to produce rhenium diboride (ReB2) powder, a novel hexagonal osmium diboride (h-OsB2), and iridium boride powders. Densification by Spark Plasma Sintering (SPS), thermal stability and mechanical properties of h-OsB2 were also studied. ReB2 was recently reported to exhibit high hardness and low compressibility, which both are strong functions of its stoichiometry, namely Re to B ratio. 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. ReB2 powder was synthesized at low temperature 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 month period of time.Hexagonal osmium diboride (h-OsB2), a theoretically predicted high-pressure phase, has been synthesized for the first time by a mechanochemical method, i.e., high energy ball milling. X-ray diffraction (XRD) indicated the formation of h-OsB2 after 2.5 hours of milling, and the reaction reaches equilibrium after 18 hours of milling. The lattice parameters of the h-OsB2 are a=2.916(&)#197; and c=7.376 (&)#197;, with a P63/mmc space group. Transmission electron microscopy confirmed the appearance of the h-OsB2 phase. The thermal stability of h-OsB2 powder was studied by heating under argon up to 876 (&)deg;C and cooling in vacuo down to -225 (&)deg;C. The oxidation mechanism of h-OsB2 has also been proposed. The hexagonal phase partially converted to the orthorhombic phase (20 wt.%) after spark plasma sintering of h-OsB2 at 1500(&)deg;C and 50MPa for 5 minutes. Hardness and Young's modulus of the h-OsB2 were measured to be 31 (&)#177; 9 GPa and 574 (&)#177; 112 GPa, respectively by nanoindentation method.Prior to this research a number of compounds have been prepared in Ir-B system with lower than 2 boron stoichiometry, and no IrB2 phases have been synthesized experimentally. In this dissertation, three new iridium boride phases, ReB2-type IrB2, AlB2-type IrB2 and IrB have been synthesized with a similar mechanochemical method. The formation of these three phases has been confirmed by both X-ray diffraction (XRD) and transmission electron microscope (TEM) after 30 hours of ball milling and 48 hours of annealing. The IrB2 phases have hexagonal crystal structures and the new IrB phase has an orthorhombic crystal structure. The segregation of iridium from iridium borides' lattices has also been studied by high resolution TEM.
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Date Issued: 2014
Identifier: CFE0005911, ucf:50832
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005911

Diffusion (2)	+ -
Polymer Derived Ceramics (2)	+ -
Polymer derived ceramics (2)	+ -
robust control (2)	+ -
sensor (2)	+ -

5CB (1)	+ -
8CB (1)	+ -
AFM (1)	+ -
Alloy (1)	+ -
Bile acids (1)	+ -
Carbon Nanotube (1)	+ -
Cavity resonator (1)	+ -
Cementitious Materials (1)	+ -
Ceramic Thin Film (1)	+ -
Ceramics (1)	+ -
Coexistence of Brittle and Ductile Fractures (1)	+ -
Composite (1)	+ -
Composites Modeling Framework (1)	+ -
Corrosion (1)	+ -
Crystallography (1)	+ -
Derived (1)	+ -
Diblock Copolymer (1)	+ -
Diffusion Barrier Materials (1)	+ -
EPR (1)	+ -
Electronic properties (1)	+ -
Finite Element Analysis (1)	+ -
Generation (1)	+ -
Hierarchical Mesopores (1)	+ -
High temperature sensor (1)	+ -
Hollow Nanospheres (1)	+ -

An, Linan (30)	+ -
University of Central Florida (30)	+ -
Fang, Jiyu (8)	+ -
Xu, Chengying (6)	+ -
Bai, Yuanli (5)	+ -

Orlovskaya, Nina (5)	+ -
Sohn, Yongho (5)	+ -
Zhai, Lei (5)	+ -
Chen, Quanfang (4)	+ -
Coffey, Kevin (4)	+ -
Gong, Xun (4)	+ -
Deng, Weiwei (3)	+ -
Heinrich, Helge (3)	+ -
Huo, Qun (3)	+ -
Lin, Kuo-Chi (3)	+ -
Gordon, Ali (2)	+ -
Gou, Jihua (2)	+ -
Raghavan, Seetha (2)	+ -
Wahid, Parveen (2)	+ -
Wu, Shintson (2)	+ -
An, Jin Woo (1)	+ -
Bargraser, Carmen (1)	+ -
Billah, Md Muktadir (1)	+ -
Blair, Richard (1)	+ -
Cao, Yejie (1)	+ -
Chen, Yan (1)	+ -
Chen, Yaohan (1)	+ -
Cheng, Haitao (1)	+ -
Cho, Hyoung (1)	+ -
Cho, Hyoung Jin (1)	+ -

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