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POLYMER-DERIVED SI-AL-C-N CERAMICS:OXIDATION, HOT-CORROSION, AND STRUCTURAL EVOLUTION
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
Processing and Characterization of Continuous Basalt Fiber Reinforced Ceramic Matrix Composites Using Polymer Derived Ceramics
Title
Processing and Characterization of Continuous Basalt Fiber Reinforced Ceramic Matrix Composites Using Polymer Derived Ceramics.
Creator
Cox, Sarah, Gou, Jihua, Kapat, Jayanta, Sohn, Yongho, University of Central Florida
Abstract / Description
The need for high performance vehicles in the aerospace industry requires materials which can withstand high loads and high temperatures. New developments in launch pads and infrastructure must also be made to handle this intense environment with lightweight, reusable, structural materials. By using more functional materials, better performance can be seen in the launch environment, and launch vehicle designs which have not been previously used can be considered. The development of high...
Show moreThe need for high performance vehicles in the aerospace industry requires materials which can withstand high loads and high temperatures. New developments in launch pads and infrastructure must also be made to handle this intense environment with lightweight, reusable, structural materials. By using more functional materials, better performance can be seen in the launch environment, and launch vehicle designs which have not been previously used can be considered. The development of high temperature structural composite materials has been very limited due to the high cost of the materials and the processing needed. Polymer matrix composites can be used for temperatures up to 260(&)deg;C. Ceramics can take much higher temperatures, but they are difficult to produce and form in bulk volumes. Polymer Derived Ceramics (PDCs) begin as a polymer matrix, allowing a shape to be formed and cured and then to be pyrolized in order to obtain a ceramic with the associated thermal and mechanical properties. The use of basalt in structural and high temperature applications has been under development for over 50 years, yet there has been little published research on the incorporation of basalt fibers as a reinforcement in the composites. In this study, continuous basalt fiber reinforced PDCs have been fabricated and tested for the applicability of this composite system as a high temperature structural composite material. The oxyacetylene torch testing and three point bend testing have been performed on test panels and the test results are presented.
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Date Issued
2014
Identifier
CFE0005320, ucf:50530
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005320
ELECTRONIC PROPERTIES AND MICROSTRUCTURES OF AMORPHOUS SICN CERAMICS DERIVED FROM POLYMER PRECURSORS
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
Electrical properties of polymer-derived silicoaluminum carboxide ceramics and their applications in micro-sensors
Title
Electrical properties of polymer-derived silicoaluminum carboxide ceramics and their applications in micro-sensors.
Creator
Cao, Yejie, An, Linan, Fang, Jiyu, Zhai, Lei, Chen, Quanfang, Orlovskaya, Nina, University of Central Florida
Abstract / Description
Polymer-derived ceramic (PDC) is a new kind of material which is directly synthesized by the thermal decomposition of polymer precursors. Due to their unique structure, which consists of the amorphous matrix phase and free-carbon phase, PDCs exhibit many distinguished properties even at high-temperature environment such as oxidation and creep resistance, amorphous semiconducting behavior as well as piezoresistive behavior. These outstanding properties make PDCs become promising candidates for...
Show morePolymer-derived ceramic (PDC) is a new kind of material which is directly synthesized by the thermal decomposition of polymer precursors. Due to their unique structure, which consists of the amorphous matrix phase and free-carbon phase, PDCs exhibit many distinguished properties even at high-temperature environment such as oxidation and creep resistance, amorphous semiconducting behavior as well as piezoresistive behavior. These outstanding properties make PDCs become promising candidates for various applications especially for high-temperature microsensors. However, most common used PDCs in the market now are SiC, SiCN and Si(M)CN ceramics, the high price and toxicity of their raw materials as well as strict operating requirements limit their applications. SiCO ceramics are appealing increasing attentions because they can cover these shortcomings of non-oxide ceramics, but their oxidation and corrosion resistance is so weak. In this dissertation, SiAlCO ceramics are chosen as main material. The addition of Al can improve the oxidation and corrosion resistance of SiCO ceramics. In this dissertation, the SiAlCO ceramics are synthesized by using silicone resin and aluminum tri-sec-butoxide (ATSB), then ceramic samples are obtained by pyrolyzing disk green bodies at 1000, 1100, 1200, 1300, 1400?C. Firstly, the composition, microstructure and structure evolution of SiAlCO ceramics are characterized via X-Ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Impedance spectroscopy (IS). The results indicate all ceramic samples pyrolyzed below 1400?C are amorphous and a sudden structure change point around 1100?C is observed due to the increase of degree of ordering. Si-C, Si-O, C-C/H, and C=C bonds are observed within the materials.Secondly, the room-temperature and temperature-dependent conductivity of the SiAlCO ceramics are studied. The optical absorption spectra are also measured. The conductivity increases by ~6 orders of magnitude when pyrolysis temperature increases from 1000 to 1400?C. A very high activation energy of 7.15eV is observed, and the redistribution of oxygen within the material is found to be responsible for it. Amorphous semiconductor behavior which follows the band-tail hopping (BTH) process is observed within this material. And the BTH process is resulted from unique electronic structures of the materials.Thirdly, SiAlCO ceramic exhibits extraordinary piezoresistive behavior with an extremely high gauge factor in range of 7000 ~16000, which is higher than that of any previously reported high-temperature materials. The coupling effect of pressure and temperature on the piezoresistive behavior is also studied. The piezoresistive stress coefficient increases with increasing temperature, which is contradictive to other reported materials. Such change of the piezoresistive stress coefficient is due to the change in the characteristic temperature, which is reversely related to the density of state within the band-tail level.In addition, SiAlCO also shows anomalous piezo-dielectricity with the positive pressure coefficient of the dielectric constant as high as 0.10-0.25 MPa-1, which is much higher than that of other high-temperature materials. The polarizability of the material also increases with increasing pressure. There behaviors are attributed to the unique cell-like structure of the materials.In the end, a pressure sensor is successfully developed. A supportive circuit is designed and the relationships among pressure, resistance and output voltage of the system are tested. The sensitivity of the sensor is calculated to be ?1 V=?15.125 Pa, indicating the SiAlCO ceramics are promising candidates for pressure sensor materials.
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Date Issued
2016
Identifier
CFE0006275, ucf:51052
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006275
Non-Oxide Porous Ceramics from Polymer Precursor
Title
Non-Oxide Porous Ceramics from Polymer Precursor.
Creator
Yang, Xueping, An, Linan, Fang, Jiyu, Zhai, Lei, Huo, Qun, Wu, Shintson, University of Central Florida
Abstract / Description
Non-oxide porous ceramics exhibit many unique and superior properties, such as better high-temperature stability, improved chemical inertness/corrosive resistance, as well as wide band-gap semiconducting behavior, which lead to numerous potential applications in catalysis, high temperature electronic and photonic devices, and micro-electromechanical systems. Currently, most mesoporous non-oxide ceramics (e.g. SiC) are formed by two-step templating methods, which are hard to adjust the pore...
Show moreNon-oxide porous ceramics exhibit many unique and superior properties, such as better high-temperature stability, improved chemical inertness/corrosive resistance, as well as wide band-gap semiconducting behavior, which lead to numerous potential applications in catalysis, high temperature electronic and photonic devices, and micro-electromechanical systems. Currently, most mesoporous non-oxide ceramics (e.g. SiC) are formed by two-step templating methods, which are hard to adjust the pore sizes, and require a harmful etching step or a high temperature treatment to remove the templates.In this dissertation, we report a novel technique for synthesizing hierarchically mesoporous non-oxide SiC ceramic from a block copolymer precursor. The copolymer precursors with vairing block length were synthesized by reversible addition fragmentation chain transfer polymerization. The block copolymers self-assemble into nano-scaled micelles with a core-shell structure in toluene. With different operation processes, hollow SiC nanospheres and bulk mesoporous SiC ceramics were synthesized after the subsequent pyrolysis of precorsur micelles. The resultant SiC ceramics have potential applications in catalysis, solar cells, separation, and puri?cation processes.The polymer synthesis and pyrolysis process will investigated by NMR, FTIR, GPC, TEM, and TGA/DSC. The morphology and structure of synthesised SiC hollow spheres and mesoporous ceramics were analyzed by SEM, TGA/DSC and BET/BJH analysis.Besides forming core shell micelles in selective solvent Toluene, we found that PVSZ-b-PS could also exhibit this property in the air water interface. By inducing the Langmuir-Blodgett deposition, a precursor monolayer with homogeously distributed povinylsilazane particles deposited on silicon wafer synthesized by spreading the diblock copolymer PVSZ-b-PS in the air water interface. After the pyrolysis process, orderly arranging SiC nano particles formed from the polymer precursor monolayer doped on the surface of silicon wafer, which shows great potential as an optoelectronic material. The deposition process and the relationship between compress pressure and monolayer morphology were studies, and the structure of monolayer and SiC dots were investigated by AFM, SEM.
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Date Issued
2014
Identifier
CFE0005564, ucf:50274
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005564
1, 2, and 3 Dimension Carbon/Silicon Carbon Nitride Ceramic Composites
Title
1, 2, and 3 Dimension Carbon/Silicon Carbon Nitride Ceramic Composites.
Creator
Calderon Flores, Jean, Zhai, Lei, Campiglia, Andres, Yestrebsky, Cherie, Zou, Shengli, Khondaker, Saiful, University of Central Florida
Abstract / Description
Polymer-derived ceramics (PDCs) are exceptional ultra-high temperature and stable multifunctional class of materials that can be synthesized from a polymer precursor through thermal decomposition. The presented research focuses on 1-D nanofibers, 2-D films and 3-D bulk, carbon-rich silicon carbon nitride (SiCN) ceramics. 1-D nanofibers were prepared via electrospinning for light weight, flame retardant and conductive applications. The commercially available CerasetTM VL20, a liquid...
Show morePolymer-derived ceramics (PDCs) are exceptional ultra-high temperature and stable multifunctional class of materials that can be synthesized from a polymer precursor through thermal decomposition. The presented research focuses on 1-D nanofibers, 2-D films and 3-D bulk, carbon-rich silicon carbon nitride (SiCN) ceramics. 1-D nanofibers were prepared via electrospinning for light weight, flame retardant and conductive applications. The commercially available CerasetTM VL20, a liquid cyclosilazane pre-ceramic precursor, was mixed with polyacrylonitrile (PAN) in order to make the cyclosilazane electrospinnable. Carbon-rich PDC nano?bers were fabricated by electrospinning various ratios of PAN/cyclosilazane solutions followed by pyrolysis. Surface morphology of the electro spun nanofibers characterized by SEM show PDC nano?bers with diameters ranging from 100-300 nm. Also, thermal stability towards oxidation showed a 10% mass loss at 623oC. 2-D carbon/SiCN films were produced by drop-casting a mixture of PAN/cyclosilazane onto a glass slide followed by pyrolysis of the film. Samples ranging from 10:1 to 1:10 PAN:cyclosilazane were made by dissolving the solutes into DMF to produce solutions ranging from 1% to 12% by weight. Green, heat-stabilized, and pyrolyzed 8% films were examined with FTIR to monitor the change in chemical structure at each step of the ceramization. SEM shows that high PAN samples produced films with ceramic embedded spheroid components in a carbon matrix, while high cyclosilazane samples produced carbon embedded spheroid.Finally, this research focuses on the challenge of making fully dense, 3-D bulk PDCs materials. Here we present a composite of SiCN with reduced graphene oxide (rGO) aerogels as a route for fully dense bulk PDCs. Incorporation of the rGO aerogel matrix into the SiCN has its pros and cons. While it lowers the strength of the composite, it allows for fabrication of large bulk samples and an increase in the electrical conductivity of the PDC. The morphology, mechanical, electrical properties and thermal conductivity of graphene-SiCN composite with varying rGO aerogel loading (0.3-2.4%) is presented. The high temperature stability, high electrical conductivity and low thermal conductivity of these composites make them excellent candidates for thermoelectric applications. Generally, carbon-rich SiCN composites with improved thermal and electrical properties are of great importance to the aerospace and electronics industries due to their expected harsh operating environments.
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Date Issued
2015
Identifier
CFE0005768, ucf:50095
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005768
SURFACTANT DRIVEN ASSEMBLY OF FREEZE-CASTED, POLYMER-DERIVED CERAMIC NANOPARTICLES ON GRAPEHENE OXIDE SHEETS FOR LITHIUM-ION BATTERY ANODES
Title
SURFACTANT DRIVEN ASSEMBLY OF FREEZE-CASTED, POLYMER-DERIVED CERAMIC NANOPARTICLES ON GRAPEHENE OXIDE SHEETS FOR LITHIUM-ION BATTERY ANODES.
Creator
Khater, Ali Zein, Tetard, Laurene, Zhai, Lei, University of Central Florida
Abstract / Description
Traditional Lithium-Ion Batteries (LIBs) are a reliable and cost-efficient choice for energy storage. LIBs offer high energy density and low self-discharge. Recent developments in electric-based technologies push for replacing historically used Lead-Acid batteries with LIBs. However, LIBs do not yet meet the demands of modern technology. Silicon and graphene oxide (GO) have been identified as promising replacements to improve anode materials. Graphene oxide has a unique sheet-like structure...
Show moreTraditional Lithium-Ion Batteries (LIBs) are a reliable and cost-efficient choice for energy storage. LIBs offer high energy density and low self-discharge. Recent developments in electric-based technologies push for replacing historically used Lead-Acid batteries with LIBs. However, LIBs do not yet meet the demands of modern technology. Silicon and graphene oxide (GO) have been identified as promising replacements to improve anode materials. Graphene oxide has a unique sheet-like structure that provides a mechanically stable, light weight material for LIB anodes. Due to its structure, reduced graphene oxide (rGO) is efficiently conductive and resistive to environmental changes. On the other hand, silicon-based anode materials offer the highest theoretical energy density and a high Li-ion loading capacity of various elements [20]. Silicon-based anodes that have previously been studied demonstrated extreme volumetric expansion over long cycles due to lithiation. Polysiloxane may be an interesting alternative as it is a Si-based material that can retain the high Li-ion loading capacity of Si while lacking the unattractive volumetric expansions of Si. Polymer derived ceramic-decorated graphene oxide anodes have been suggested to increase loading capacity, thermal resistance, power density, and mechanical stability of LIBs. Coupled with mechanically stable graphene oxide, polymer derived ceramic nanoparticle decorated graphene oxide anodes are studied to establish their efficiencies under operating conditions.
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Date Issued
2018
Identifier
CFH2000404, ucf:45765
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFH2000404
INTERFACIAL BEHAVIOR IN POLYMER DERIVED CERAMICS AND SALT WATER PURIFICATION VIA 2D MOS2
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
Development of Polymer Derived SiAlCN Ceramic and Its Applications for High-Temperature Sensors
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
Structure and Properties of Polymer-Derived SiBCN Ceramics
Title
Structure and Properties of Polymer-Derived SiBCN Ceramics.
Creator
Chen, Yaohan, An, Linan, Fang, Jiyu, Xu, Chengying, Zhai, Lei, Huo, Qun, Gong, Xun, University of Central Florida
Abstract / Description
Polymer-derived ceramics (PDCs) are a unique class of multifunctional materials synthesized by thermal decomposition of polymeric precursors. Due to their unique and excellent properties and flexible manufacturing capability, PDC is a promising technology to prepare ceramic fibers, coatings, composites and micro-sensors for high-temperature applications. However, the structure-property relationships of PDCs have not been well understood. The lack of such understandings drastically limited the...
Show morePolymer-derived ceramics (PDCs) are a unique class of multifunctional materials synthesized by thermal decomposition of polymeric precursors. Due to their unique and excellent properties and flexible manufacturing capability, PDC is a promising technology to prepare ceramic fibers, coatings, composites and micro-sensors for high-temperature applications. However, the structure-property relationships of PDCs have not been well understood. The lack of such understandings drastically limited the further developments and applications of the materials.In this dissertation, the structure and properties of amorphous polymer-derived silicon carbonitride (SiCN) and silicoboron carbonitride (SiBCN) have been studied. The SiCN was obtained using commercially available polysilazane as pre-ceramic precursor, and the SiBCN ceramics with varied Si-to-B ratio were obtained from polyborosilazanes, which were synthesized by the hydroboration and dehydrocoupling reaction of borane and polysilazane. The structural evolution of polymer-derived SiCN and SiBCN ceramics from polymer to ceramics was investigated by NMR, FTIR, Raman, EPR, TG/DTA, and XRD. The results show a phase-separation of amorphous matrix and a graphitization of (")free(") carbon phase, and suggest that the boron doping has a great influence on the structural evolution. The electric and dielectric properties of the SiCN and SiBCNs were studied by I-V curves, LCR Meter, and network analyzer. A new electronic conduction mechanism and structure model has been proposed to account for the relationships between the observed properties and microstructure of the materials. Furthermore, the SiBCN ceramics showed the improved dielectric properties at characterization temperature up to 1300 (&)#186;C, which allows the fabrication of ultrahigh-temperature wireless microsensors for extreme environments.
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Date Issued
2012
Identifier
CFE0004195, ucf:49014
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004195
THE FABRICATION OF POLYMER-DERIVED SICN/SIBCN CERAMIC NANOSTRUCTURES AND INVESTIGATION OF THEIR STRUCTURE-PROPERTY RELATIONSHIP
Title
THE FABRICATION OF POLYMER-DERIVED SICN/SIBCN CERAMIC NANOSTRUCTURES AND INVESTIGATION OF THEIR STRUCTURE-PROPERTY RELATIONSHIP.
Creator
Sarkar, Sourangsu, Zhai, Lei, University of Central Florida
Abstract / Description
Polymer-derived Ceramics (PDCs) represent a unique class of high-temperature stable materials synthesized directly by the thermal decomposition of polymers. This research first focuses on the fabrication of high temperature stable siliconcarbonitride (SiCN) fibers by electrospinning for ceramic matrix composite (CMC) applications. Ceraset™ VL20, a commercially available liquid...
Show morePolymer-derived Ceramics (PDCs) represent a unique class of high-temperature stable materials synthesized directly by the thermal decomposition of polymers. This research first focuses on the fabrication of high temperature stable siliconcarbonitride (SiCN) fibers by electrospinning for ceramic matrix composite (CMC) applications. Ceraset™ VL20, a commercially available liquid cyclosilazane, was functionalized with aluminum sec-butoxide in order to be electrospinnable. The surface morphology of the electrospun fibers was investigated using the fibers produced from solvents. The electrospun fibers produced from the chloroform/N,N-dimethylformamide solutions had hierarchical structures that led to superhydrophobic surfaces. A ÂÂÂÂ"dry skinÂÂÂÂ" model was proposed to explain the formation of micro/- and nanostructures. The second objective of the research is to align the multiwalled carbon nanotubes (MWCNTs) in PDC fibers. For this purpose, a non-invasive approach to disperse carbon nanotubes in polyaluminasilazane chloroform solutions was developed using a conjugated block copolymer synthesized by ATRP. The effect of the polymer and CNT concentration on the fiber structure and morphology was also examined. Detailed characterization using SEM and TEM was performed to demonstrate the orientation of CNTs inside the ceramic fibers. Additionally, the electrical properties of the ceramic fibers were investigated. Finally, the structural evolution of polymer-derived amorphous siliconborocarbonitride (SiBCN) ceramics with pyrolysis temperatures was studied by solid-state NMR, Raman and EPR spectroscopy. Results suggested the presence of three major components: (i) hexagonal boron nitride (h-BN), (ii) turbostratic boron nitride (t-BN), and (iii) BN2C groups in the final ceramic. The pyrolysis at higher temperature generated boron nitride (BN3) with a simultaneous decomposition of BN2C groups. A thermodynamic model was proposed to quantitatively explain the conversion of BN2C groups into BN3 and ÂÂÂÂ"freeÂÂÂÂ" carbon. Such structure evolution is believed to be the reason that the crystallization of Si4.0B1.0 ceramics starts at 1500 °C, whereas Si2.0B1.0 ceramics is stable upto 1600 °C.
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Date Issued
2010
Identifier
CFE0003446, ucf:48408
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0003446