The Effect of Oxygen Contamination on the Amorphous Structure of Thermally Sprayed Coatings of Cu47Ti33Zr11Ni8Si1 (open access)

The Effect of Oxygen Contamination on the Amorphous Structure of Thermally Sprayed Coatings of Cu47Ti33Zr11Ni8Si1

this research has shown that it is possible to deposit coatings of gas atomized Cu{sub 47}Ti{sub 33}Zr{sub 11}Ni{sub 8}Si{sub 1} powders containing various levels of oxygen contamination using plasma arc spray methods. The structure of the coating was found to depend primarily on the spray environment, with an argon atmosphere producing the most amorphous samples for a given starting powder. The oxygen content of the coatings reflected the relative levels of the oxygen contamination in the starting powders. The analysis of the starting powders displayed oxygen contents ranging from 0.125-0.79 wt.%. It was shown that higher oxygen levels lead to more crystalline structure in the starting powders as determined by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). This trend was found to be true for both the starting powders and for the plasma sprayed coatings. Chemical composition for all starting powders was very close to the nominal alloy composition. Chemical changes in the coatings involved the loss of Cu in coatings where high levels of oxidation were found. Cavitation erosion testing of selected coatings showed a weak trend that coatings prepared by vacuum plasma spray (VPS) had lower damage rates, but there was no clear data to indicate which …
Date: May 27, 2002
Creator: Besser, Matthew Frank
Object Type: Thesis or Dissertation
System: The UNT Digital Library
EXPERIMENTAL STATUS OF K YIELDS PVV-. (open access)

EXPERIMENTAL STATUS OF K YIELDS PVV-.

The experimental program for the study of the rare kaon decays, K + {pi}{nu}{bar {nu}} is summarized. A review of recent results is provided along with a discussion of prospects for the future of this program. The primary focus of the world-wide kaon program is the two golden modes: K{sup +} {yields} {pi}{sup +}{nu}{bar {nu}} and K{sub L}{sup o} {yields} {pi}{sup o} {nu}{bar {nu}}. The first step in an ambitious program to precisely measure both branching ratios has been successfully completed with the observation of two K{sup +} {yields} {pi}{sup +}{nu}{bar {nu}} events by E787. The E949 experiment is poised to reach an order of magnitude further in sensitivity and to observe {approx}10 Standard Model events, and the CKM experiment should observe {approx}100 SM events by the end of this decade. Limits on the neutral analog K{sub L}{sup o} {yields} {pi}{sup o} {nu}{bar {nu}} have been set by KTeV and within the next couple of years will be pushed by E391a. Measurements of the branching ratio should be made within the next 10 years by KOPIO, with a goal of {approx}50 events, and at the JHF, with a goal of up to 1000 events.
Date: May 27, 2002
Creator: KETTELL,S.H.
Object Type: Article
System: The UNT Digital Library
Pathway and Surface Mechanism Studies of 1,3-butadiene Selective Oxidation Over Vanadium-Molybdenum-Oxygen Catalysts (open access)

Pathway and Surface Mechanism Studies of 1,3-butadiene Selective Oxidation Over Vanadium-Molybdenum-Oxygen Catalysts

The partial oxidation of 1,3-butadiene has been investigated over VMoO catalysts synthesized by sol-gel techniques. Surface areas were 9-14 m{sup 2}/g, and compositions were within the solid solution regime, i.e. below 15.0 mol % MoO{sub 3}/(MoO{sub 3} + V{sub 2}O{sub 5}). Laser Raman Spectroscopy and XRD data indicated that solid solutions were formed, and pre- and post-reaction XPS data indicated that catalyst surfaces contained some V{sup +4} and were further reduced in 1,3-butadiene oxidation. A reaction pathway for 1,3-butadiene partial oxidation to maleic anhydride was shown to involve intermediates such as 3,4-epoxy-1-butene, crotonaldehyde, furan, and 2-butene-1,4-dial. The addition of water to the reaction stream substantially increased catalyst activity and improved selectivity to crotonaldehyde and furan at specific reaction temperatures. At higher water addition concentrations, furan selectivity increased from 12% to over 25%. The catalytic effects of water addition were related to competitive adsorption with various V{sub 2}O{sub 5}-based surface sites, including the vanadyl V=O, corner sharing V-O-V and edge sharing V-O oxygen. Higher levels of water addition were proposed to impose acidic character by dissociative adsorption. In addition, a novel combinatorial synthesis technique for VMoO was used to investigate the phase transitions of V{sub 2}O{sub 5}, solid solutions of Mo …
Date: May 27, 2002
Creator: Schroeder, William David
Object Type: Thesis or Dissertation
System: The UNT Digital Library
High Throughput Sample Preparation and Analysis for DNA Sequencing, PCR and Combinatorial Screening of Catalysis Based on Capillary Array Technique (open access)

High Throughput Sample Preparation and Analysis for DNA Sequencing, PCR and Combinatorial Screening of Catalysis Based on Capillary Array Technique

Sample preparation has been one of the major bottlenecks for many high throughput analyses. The purpose of this research was to develop new sample preparation and integration approach for DNA sequencing, PCR based DNA analysis and combinatorial screening of homogeneous catalysis based on multiplexed capillary electrophoresis with laser induced fluorescence or imaging UV absorption detection. The author first introduced a method to integrate the front-end tasks to DNA capillary-array sequencers. protocols for directly sequencing the plasmids from a single bacterial colony in fused-silica capillaries were developed. After the colony was picked, lysis was accomplished in situ in the plastic sample tube using either a thermocycler or heating block. Upon heating, the plasmids were released while chromsomal DNA and membrane proteins were denatured and precipitated to the bottom of the tube. After adding enzyme and Sanger reagents, the resulting solution was aspirated into the reaction capillaries by a syringe pump, and cycle sequencing was initiated. No deleterious effect upon the reaction efficiency, the on-line purification system, or the capillary electrophoresis separation was observed, even though the crude lysate was used as the template. Multiplexed on-line DNA sequencing data from 8 parallel channels allowed base calling up to 620 bp with an …
Date: May 27, 2002
Creator: Zhang, Yonghua
Object Type: Thesis or Dissertation
System: The UNT Digital Library