Thermal barrier coatings (TBCs) are widely used for thermal protection of hot section components in turbines for propulsion and power generation. Applications of TBCs based on a clearer understanding of failure mechanisms can help increase the performance and life-cycle cost of advanced gas turbine engines. Development and refinement of robust nondestructive evaluation techniques can also enhance the reliability, availability and maintainability of hot section components in gas turbines engines. In this work, degradation of TBCs was non-destructively examined by photostimulated luminescence spectroscopy (PSLS) and electrochemical impedance spectroscopy (EIS) as a function of furnace thermal cycling carried out in air with 10-minute heat-up, 0.67, 9.6 and 49.6 - hour dwell duration at 1121°C (2050°F), and 10-minute forced-air quench. TBCs examined in this study consisted of either electron beam physical vapor deposited and air plasma sprayed yttria-stabilized zirconia (YSZ) on a variety of bond coat / superalloy substrates including bond coats of NiCoCrAlY and (Ni,Pt)Al, and superalloys of CMSX-4, Rene‟N5, Haynes 230 and MAR-M-509. Detailed microstructural characterization by scanning electron microscopy and energy dispersive spectroscopy was carried out to document the degradation and failure characteristics of TBC failure, and correlate results of PSLS and EIS. Mechanisms of microstructural damage initiation and progression varied as a function of TBC architecture and thermal cycling dwell time, and included undulation of the interface between the thermally grown oxide (TGO) and bond coats, internal oxidation of the bond coats, and formation of Ni/Co-rich TGO. These microstructural observations were correlated to the evolution in compressive residual stress in the TGO scale determined by PSLS shift. Correlations iv include stress-relief and corresponding luminescence shift towards stress-free luminescence (i.e. = 14402 cm-1 and  = 14432 cm-1 ) associated with subcritical cracking of the TGO scale and stress-relaxation associated with gradual shift in the luminescence towards stress-free luminescence (i.e.  = 14402 cm-1 and  =14432 cm-1 ) is related to the undulation of TGO/bondcoat interface (e.g., rumpling and ratcheting). Microstructural changes in TBCs such as YSZ sintering, TGO growth, and subcritical damages within the YSZ and TGO scale were also correlated to the changes in electrochemical resistance and capacitance of the YSZ and TGO, respectively. With thermal exposure the YSZ/TGO resistance and capacitance increased and decreased as result of sintering and TGO growth. With progressive thermal cycling damages in the TGO was related to the TGO capacitance showing a continuous increase and at failure TGO capacitance abruptly increased with the exposure of bondcoat. Further correlations among the microstructural development, PSLS and EIS are documented and discussed, particularly as a function of dwell time used during furnace thermal cycling test, with due respect for changes in failure characteristics and mechanisms for various types of TBCs

No description available.

The purpose of this investigation was to determine the products of the electrolysis of dimethyl lithium amide. / Master of Science

M. Tech. Metallurgical Engineering. / Investigate the dissolution behaviour of sphalerite minerals in sulphuric acid using ferric ions as oxidants. The specific objectives are to study the following: 1. the mineralogical characteristics of sphalerite ores ; 2. mineralogical effects on dissolution kinetics in sulphuric acid and 3. Effect of ferric ion concentration on the dissolution kinetics of sphalerite ores in sulphuric acid. Mineralogy is a critical area in mineral processing and has to be considered during process design stage, and during each processing stage. The type and concentration of oxidizing agent depend on the mineralogical composition of the ore. Many researchers investigations and test-works have been reported on leaching of sphalerite using both ferric sulphate and ferric chloride (Al-Harahsheh and Kingman, 2007; Rath et al., 1981). However, little or no studies have been reported on the combined oxidants.

published_or_final_version / Chemistry / Master / Master of Philosophy

The lifetime of the polymer membrane ion-selective electrode is, in general, short when compared to that of the glass pH electrode. It is the manner in which the elctroactive materials are entrapped in the ion-selective membranes which accounts for this lifetime difference. In the polymer membrane electrode a high molecular weight electroactive material is dissolved in the plasticized polymer membrane. Because it is hydrophobic, this material is much more compatible with the low dielectric membrane phase than with the aqueous analyte phase. It, of course, has some solubility in the aqueous phase and, in time, leaches from the membrane. In the glass pH electrode, the electroactive material is the SiOH group which is covalently attached to the insoluble glass membrane. Because it is attached, it cannot be leached from the membrane. The purpose of this study was to investigate the possibility of covalently attaching the electroactive material to the polymer membrane in polymer membrane electrodes. In this weay, it was hoped that electrodes with much longer lifetimes could be obtained. Cation selective electrodes based on sulfonated polystyrene were investigated first. Sulfonation was accomplished by dipping polystyrene membranes into chlorosulfonic acid. Electrodes of both the conventional (i.e., with internal reference) and coated-wire types were prepared. Neither gave satisfactory response. Cation selective electrodes based on the perfluorinated, sulfonic acid containing ion exchange polymer NAFION 120® were investigated next. This material produced well-behaved Cs⁺ electrodes but electrodes responsive to larger cations (e.g., tetrapropylammonium and dodecyltri-methylammonium) could not be obtained. This may be due to ion-pairing in the membrane phase between these larger cations and the polymer bound sulfonate groups. To help answer some of the questions encountered during these investigations of electrodes based on covalently attached sulfonate groups, polymer membrane electrodes based on dinonylnaphthalenesulfonic acid were prepared and investigated. These electrodes were found to have very great selectivity for high molecular weight organic cations relative to inorganic and smaller organic cations. This type of selectivity is analogous to that obtained in ion pair solvent extraction of cations with a high molecular weight anionic species. Since a number of species of clinical, biological and toxicological interest are, at physiological pH, high molecular weight organic cations, electrodes based on dinonylnaphthalenesulfonic acid show great promise for determination of such species. An electrode for the determination of the drug phencyclidine was prepared to demonstrate the potentialities of drug analysis with this type of electrode. A microcomputer-based potentiometric analysis system was used to collect and analyze the data in this study. This system was one of the first stand-alone microcomputer systems employing a high level computer language to be described. The IMSAI 8080 Microcomputer and the computer language CONVERS were used.

The objective of this thesis is to study the effect of process conditions on structure and electrochemical properties of polyacrylonitrile (PAN)/carbon nanotube (CNT) composite film based electrodes developed for electrochemical capacitors. The process parameters like activation temperature, CNT loading in the composite films are varied to determine optimum process conditions for physical (CO2) and chemical (KOH) activation methods. The PAN/CNT precursors are stabilized in air, carbonized in inert atmosphere (argon), and activated by physical (CO2) and chemical (KOH) methods. The physical activation process is carried out by heat treating the carbon precursors in CO2 atmosphere at activation temperatures. In the chemical activation process, stabilized carbon precursors are immersed in aqueous solutions of activating media (KOH), dried, and subsequently heat treated in an inert atmosphere at the activation temperature. The structure and morphology are probed using scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The specific capacitance, power and energy density of the activated electrodes are evaluated with aqueous electrolytes (KOH) as well as organic electrolyte (ionic liquid in acetonitrile) in Cell Test. The surface area and pore size distribution of the activated composite electrodes are evaluated using nitrogen absorption. Specific capacitance dependence on factors such as surface area and pore size distribution are studied. A maximum specific capacitance of 300 F/g in KOH electrolyte and maximum energy density of 22 wh/kg in ionic liquid has been achieved. BET surface areas in excess of 2500 m2/g with controlled pore sizes in 1 - 5 nm range has been attained in this work.

Thesis (Ph. D) -- University of Western Sydney, Nepean, 1999. / A thesis presented for the degree of Doctor of Philosophy, Centre for Electrochemical Research and Analytical Technology, University of Western Sydney, Nepean. Includes bibliographical references.

Thesis (Ph.D.)--Baylor University, 2007. / Includes bibliographical references (p. 199-203)

Thesis (M.S.)--Ohio University, August, 1995. / Title from PDF t.p.