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  Partner: UNT Libraries
 Department: Department of Materials Science
 Degree Level: Master's
 Collection: UNT Theses and Dissertations
Cure kinetics and processing parameters of neat and reinforced high performance epoxy resins : evaluation of techniques

Cure kinetics and processing parameters of neat and reinforced high performance epoxy resins : evaluation of techniques

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Date: December 1999
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). The changes in physical properties indicating increasing conversion are followed by shifts in glass transition temperature determined by DSC and temperature-modulated DSC (TMDSC), 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 for rapid determination of processing parameters in the processing of prepregs. Copyright is held by the author, unless otherwise noted. All rights reserved. Files: Thesis.pdf Special Conditions
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Hypotheses for Scratch Behavior of Polymer Systems that Recover

Hypotheses for Scratch Behavior of Polymer Systems that Recover

Date: May 2002
Creator: Bujard, Bernard
Description: Scratch recovery is a desirable property of many polymer systems. The reason why some materials have demonstrated excellent scratch recovery while others do not has been a mystery. Explaining the scratch resistance based upon the hardness of a material or its crosslink density is incorrect. In this thesis, novel polymers were tested in an attempt to discover materials that show excellent scratch recovery - one of the most important parameters in determining the wear of a material. Several hypotheses were developed in an attempt to give an accurate picture of how the chemical structure of a polymer affects its scratch recovery. The results show that high scratch recovery is a complex phenomenon not solely dependent upon the presence of electronegative atoms such as fluorine.
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Preparation and Characterization of a Treated Montmorillonite Clay and Epoxy Nanocomposite

Preparation and Characterization of a Treated Montmorillonite Clay and Epoxy Nanocomposite

Date: December 2000
Creator: Butzloff, Peter Robert
Description: Montmorillonite reinforced polymers are a new development in the area of nanocomposite materials. Since reinforcement of epoxy is important to the development of high strength adhesives and composite matrices, the introduction of montmorillonite to epoxy is of interest. Compositional effects on epoxy reactivity, on molecular relaxation, and on mechanical properties were investigated. Change in reactivity was determined by Differential Scanning Calorimetry. Tensile properties at room temperature indicated improved modulus and retention of strength of the epoxy matrix but a decreased elongation to failure. Depression of dry nanocomposite glass transition was observed for nanocomposites beyond 5% by weight montmorillonite. Samples that were saturated with water showed lower moduli due to the epoxy matrix. The greatest moisture absorption rate was found at 7%, the least at 3%.
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The effects of color concentrate in polyolefins.

The effects of color concentrate in polyolefins.

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Date: December 2001
Creator: Flora, Paul
Description: Throughout history consumer products were generally manufactured from wood and metal. They either had to hold their natural color or become subject to painting. When plastics entered the industry, it was recognized for its ease of shaping, re-usability, physical properties and its low cost. One of plastics' greatest benefits is its ability to hold a given color from within allowing it to avoid use of paint. This paper will give a brief overview on the effects of pigments when incorporated in a polyolefin. It will provide a classification of the main types of pigments and how each effect the properties of the product through: crystallization, weatherability, opacity, coloristic values and of course viscosity.
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Stability of Field Emitter Arrays to Oxygen Exposures

Stability of Field Emitter Arrays to Oxygen Exposures

Date: December 2002
Creator: Godbole, Soumitra Kumar
Description: The purpose of these experiments was to determine the degradation mechanisms of molybdenum based field emitter arrays to oxygen exposures and to improve the overall reliability. In addition, we also evaluated the emission current stability of gold-coated field emitter arrays to oxygen exposures. oxygen at 1x10-6 torr was introduced into the chamber through a leak valve for different lengths of time and duty cycles. To ensure identical oxygen exposure and experimental measurement conditions, tips on half the area of the FEA were fully coated with gold and the other half were left uncoated. The emission current from the gold coated half was found to degrade much less than that from the uncoated half, in the presence of oxygen. Also in the absence of oxygen, the emission current recovery for the gold-coated side was much quicker than that for the uncoated side.
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Mineral-filled polypropylene: Improvement of scratch resistance

Mineral-filled polypropylene: Improvement of scratch resistance

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Date: December 2001
Creator: Khatib, Jamal F.
Description: A potential alternative to acrylonitrile-butadiene-styrene (ABS) and polycarbonate+ABS (PC+ABS), pigmented mineral-filled polypropylene (PP) finds an opening in automotive interior components such as instrument panels, knee bolsters, consoles, etc. Because of the lack of surface aesthetics, pigmented mineral-filled PP is experiencing a limitation to its acceptance in many applications. This study focuses on exploring various mineral fillers and additives in polypropylene to provide a material with enhanced scratch resistance. Several physical properties including Rockwell and Shore D hardness are investigated, and it is determined that Filler W improves scratch resistance. It is also determined that Filler T-filled-PP has poor scratch resistance even with the addition of a lubricant.
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Materials properties of ruthenium and ruthenium oxides thin films for advanced electronic applications.

Materials properties of ruthenium and ruthenium oxides thin films for advanced electronic applications.

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Date: May 2006
Creator: Lim, ChangDuk
Description: Ruthenium and ruthenium dioxide thin films have shown great promise in various applications, such as thick film resistors, buffer layers for yttrium barium copper oxide (YBCO) superconducting thin films, and as electrodes in ferroelectric memories. Other potential applications in Si based complementary metal oxide semiconductor (CMOS) devices are currently being studied. The search for alternative metal-based gate electrodes as a replacement of poly-Si gates has intensified during the last few years. Metal gates are required to maintain scaling and performance of future CMOS devices. Ru based materials have many desirable properties and are good gate electrode candidates for future metal-oxide-semiconductor (MOS) device applications. Moreover, Ru and RuO2 are promising candidates as diffusion barriers for copper interconnects. In this thesis, the thermal stability and interfacial diffusion and reaction of both Ru and RuO2 thin films on HfO2 gate dielectrics were investigated using Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). An overview of Ru and RuO2/HfO2 interface integrity issues will be presented. In addition, the effects of C ion modification of RuO2 thin films on the physico-chemical and electrical properties are evaluated.
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Thermal, Electrical, and Structural Analysis of Graphite Foam

Thermal, Electrical, and Structural Analysis of Graphite Foam

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Date: August 2001
Creator: Morgan, Dwayne Russell
Description: A graphite foam was developed at Oak Ridge National Laboratory (ORNL) by Dr. James Klett and license was granted to POCO Graphite, Inc. to manufacture and market the product as PocoFoam™. Unlike many processes currently used to manufacture carbon foams, this process yields a highly graphitic structure and overcomes many limitations, such as oxidation stabilization, that are routinely encountered in the development of carbon foam materials. The structure, thermal properties, electrical resistivity, isotropy, and density uniformity of PocoFoam™ were evaluated. These properties and characteristics of PocoFoam™ are compared with natural and synthetic graphite in order to show that, albeit similar, it is unique. Thermal diffusivity and thermal conductivity were derived from Fourier's energy equation. It was determined that PocoFoam™ has the equivalent thermal conductivity of metals routinely used as heat sinks and that thermal diffusivity is as much as four times greater than pure copper and pure aluminum. SEM and XRD results indicate that PocoFoam™ has a high degree of crystalline alignment and near theoretical d spacing that is more typical of natural flake graphite than synthetic graphite. PocoFoam™ is anisotropic, indicating an isotropy factor of 0.5, and may yield higher thermal conductivity at cryogenic temperatures than is observed in ...
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Mechanical Properties of Polymer Modified Mortar

Mechanical Properties of Polymer Modified Mortar

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Date: August 2002
Creator: Palos, Artemio
Description: The mechanical properties of the polymer-modified mortar are markedly improved over conventional cement mortar. We utilized recycled ABS in powder form and a polymer latex emulsion, polymer percentage ranges from 0 to 25 percent by polymer/cement ratio were investigated. The mechanical properties investigated were compression strength and adhesion strength. Compression strength effects did not have an impact on adhesion strength. Adhesion strength was calculated with pullout testing apparatus designed by the author. Results indicate that recycled ABS had a lower adhesive strength than the acrylic latex emulsion and the base mortar, but did increase in adhesive strength when mixed with maleic-anhydride. The adhesive strength was investigated for a Fiber Reinforced Polymer (FRP) made of an "E" glass fiber that is a continuous strand roving oriented and pre-tensioned longitudinally in an isopthalic polyester matrix material. The FRP rebar was compared to standard steel rebars, and found that the standard steel corrugated rebar had a higher adhesive strength, due to mechanical interlocking. This was clarified by measurements using a smooth steel rebar. Characterization of the polymer-modified mortar was conducted by pore analysis and scanning electron microscopy. Scanning Electron Microscopy was implemented to view the polymer particles, the cement fibrils formed by the ...
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Polyamide-imide and Montmorillonite Nanocomposites

Polyamide-imide and Montmorillonite Nanocomposites

Date: August 2001
Creator: Ranade, Ajit
Description: Solvent suspensions of a high performance polymer, Polyamide-imide (PAI) are widely used in magnetic wire coatings. Here we investigate the effect that the introduction of montmorillonite (MMT) has on PAI. MMT was introduced into an uncured PAI suspension; the sample was then cured by step-wise heat treatment. Polarized optical microscopy was used to choose the best suitable MMT for PAI matrix and to study the distribution of MMT in PAI matrix. Concentration dependent dispersion effect was studied by x-ray diffraction (XRD) and was confirmed by Transmission electron microscopy (TEM). Differential scanning Calorimetry (DSC) and Thermogravimetric analysis (TGA) was used to study impact of MMT on glass transition temperature (Tg) and degradation properties of PAI respectively. Micro-hardness testing of PAI nanocomposites was also performed. A concentration dependent state of dispersion was obtained. The glass transition (Tg), degradation and mechanical properties were found to correlate to the state of dispersion.
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