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  Partner: UNT Libraries
 Department: Department of Materials Science and Engineering
 Decade: 2000-2009
 Year: 2003
 Collection: UNT Theses and Dissertations
Characterization of cure kinetics and physical properties of a high performance, glass fiber-reinforced epoxy prepreg and a novel fluorine-modified, amine-cured commercial epoxy.

Characterization of cure kinetics and physical properties of a high performance, glass fiber-reinforced epoxy prepreg and a novel fluorine-modified, amine-cured commercial epoxy.

Date: December 2003
Creator: Bilyeu, Bryan
Description: Kinetic equation parameters for the curing reaction of a commercial glass fiber reinforced high performance epoxy prepreg composed of the tetrafunctional epoxy tetraglycidyl 4,4-diaminodiphenyl methane (TGDDM), the tetrafunctional amine curing agent 4,4'-diaminodiphenylsulfone (DDS) and an ionic initiator/accelerator, are determined by various thermal analysis techniques and the results compared. The reaction is monitored by heat generated determined by differential scanning calorimetry (DSC) and by high speed DSC when the reaction rate is high. The changes in physical properties indicating increasing conversion are followed by shifts in glass transition temperature determined by DSC, temperature-modulated DSC (TMDSC), step scan DSC and high speed DSC, thermomechanical (TMA) and dynamic mechanical (DMA) analysis and thermally stimulated depolarization (TSD). Changes in viscosity, also indicative of degree of conversion, are monitored by DMA. Thermal stability as a function of degree of cure is monitored by thermogravimetric analysis (TGA). The parameters of the general kinetic equations, including activation energy and rate constant, are explained and used to compare results of various techniques. The utilities of the kinetic descriptions are demonstrated in the construction of a useful time-temperature-transformation (TTT) diagram and a continuous heating transformation (CHT) diagram for rapid determination of processing parameters in the processing of prepregs. Shrinkage ...
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Deposition and characterization of pentacene film.

Deposition and characterization of pentacene film.

Date: December 2003
Creator: Singh, Nidhi
Description: Many organic materials have been studied to be used as semiconductors, few of them being pentacene and polythiophene. Organic semiconductors have been investigated to make organic thin film transistors. Pentacene has been used in the active region of the transistors. Transistors fabricated with pentacene do not have very high mobility. But in some applications, high mobility is not needed. In such application other properties of organic transistors are used, such as, ease of production and flexibility. Organic thin film transistors (OTFT) can find use as low density storage devices, such as smart cards or I.D. tags, and displays. OTFT are compatible with polymeric substrates and hence can find use as flexible computer screens. This project aims at making 'smart clothes', the cheap way, with pentacene based OTFT. This problem in lieu of thesis describes a way to deposit pentacene films and characterize it. Pentacene films were deposited on substrates and characterized using x-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The substrate used was ~1500Å platinum on silicon wafer or bare silicon wafer. was used. A deposition system for vacuum deposition of pentacene was assembled. The XRD data for deposited pentacene films shows the presence of two phases, single ...
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Electrochemical synthesis of CeO2 and CeO2/montmorillonite nanocomposites.

Electrochemical synthesis of CeO2 and CeO2/montmorillonite nanocomposites.

Date: December 2003
Creator: Wang, Qi
Description: Nanocrystalline cerium oxide thin films on metal and semiconductor substrates have been fabricated with a novel electrodeposition approach - anodic oxidation. X-ray diffraction analysis indicated that as-produced cerium oxide films are characteristic face-centered cubic fluorite structure with 5 ~ 20 nm crystal sizes. X-ray photoelectron spectroscopy study probes the non-stoichiometry property of as-produced films. Raman spectroscopy and Scanning Electron Microscopy have been applied to analyze the films as well. Deposition mode, current density, reaction temperature and pH have also been investigated and the deposition condition has been optimized for preferred oriented film formation: galvanostatic deposition with current density of -0.06 mA/cm2, T > 50oC and 7 < pH < 10. Generally, potentiostatic deposition results in random structured cerium oxide films. Sintering of potentiostatic deposited cerium oxide films leads to crystal growth and reach nearly full density at 1100oC. It is demonstrated that in-air heating favors the 1:2 stoichiometry of CeO2. Nanocrystalline cerium oxide powders (4 ~ 10 nm) have been produced with anodic electrochemical synthesis. X-ray diffraction and Raman spectroscopy were employed to investigate lattice expansion phenomenon related to the nanoscale cerium oxide particles. The pH of reaction solution plays an important role in electrochemical synthesis of cerium oxide films ...
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