Search results for: Matthew J. O’Keefe

Items from 1 to 14 out of 14 results

article

Mechanism and sensitivity of Fe-C coated long period fiber grating sensors for steel corrosion monitoring of RC structures

Yizheng Chen, Fujian Tang, Yan Tang, Matthew J. O’Keefe, more

Corrosion Science > 2017 > 127 > C > 70-81

The mechanism and sensitivity of long period fiber gratings (LPFG) corrosion sensor, which is made by coating LPFG with an inner layer of silver and an outer layer of Fe-C, are investigated in this study. Two silver and three Fe-C thicknesses were considered. Results indicate that a linear relationship is present between the change in the resonant wavelength and the mass loss of the outer Fe-C layer...

article

Structure and corrosion behavior of sputter deposited cerium oxide based coatings with various thickness on Al 2024-T3 alloy substrates

Yuanyuan Liu, Jiamu Huang, James B. Claypool, Carlos E. Castano, more

Applied Surface Science > 2015 > 355 > C > 805-813

Cerium oxide based coatings from ∼100 to ∼1400nm in thickness were deposited onto Al 2024-T3 alloy substrates by magnetron sputtering of a 99.99% pure CeO₂ target. The crystallite size of CeO₂ coatings increased from 15nm to 46nm as the coating thickness increased from ∼100nm to ∼1400nm. The inhomogeneous lattice strain increased from 0.36% to 0.91% for the ∼100nm to ∼900nm thick coatings and slightly...

article

Cerium-based oxide coatings

Carlos E. Castano, Matthew J. O’Keefe, William G. Fahrenholtz

Current Opinion in Solid State and Materials Science > 2015 > 19 > 2 > 69-76

Cerium-based oxide compounds are known for their wide range of applications in catalysis, corrosion prevention, electrochemical cells, photocatalysis, UV absorbers, biomaterials, microelectronics, optical devices, thermal coatings, and glass abrasives. The technological applications of these materials are possible due to a combination of the electronic structure of Ce and the size effects at the nanoscale...

article

Photo-assisted reduction in nanostructured cerium-based coatings

Carlos E. Castano, Matthew J. O’Keefe, William G. Fahrenholtz

Scripta Materialia > 2013 > 69 > 6 > 489-492

Nanostructured cerium-based coatings on AZ31Mg alloy substrates exposed to sunlight under ambient conditions had an ∼30% increase in Ce(III) species compared to unexposed coatings as measured by X-ray photoelectron spectroscopy. A decrease in film cracks and shift in bandgap from 2.5eV to 2.7eV were also measured. Visible changes in color, from yellow to translucent, with exposure were also observed...

article

Capacitive Properties and Structure of RuO2-HfO2 Films Prepared by Thermal Decomposition Method

Xuehua Liu, Junqiu Zhu, Xin Wang, Junmei Sun, more

Physics Procedia > 2013 > 50 > Complete > 416-420

Binary RuO2-HfO2 films on Ti substrates were prepared by a thermal decomposition method. cyclic voltammetric and charge/discharge properties of the RuO2-HfO2 electrodes were characterized. It was determined that the incorporation of HfO2 into RuO ₂ greatly improved the capacitive properties of the material. The RuO ₂ -HfO ₂ electrodes showed excellent cyclic stability, with...

article

Dissolution of cerium from cerium-based conversion coatings on Al 7075-T6 in 0.1M NaCl solutions

Simon Joshi, Elizabeth A. Kulp, William G. Fahrenholtz, Matthew J. O’Keefe

Corrosion Science > 2012 > 60 > Complete > 290-295

Cerium-based conversion coatings (CeCCs) were immersed in 0.1M NaCl for ∼500h over a range of pH (2.0–5.7) to investigate the dissolution of cerium species. Dissolution was detected by UV–vis spectroscopy only in the pH 2 solution. Similar cerium concentrations were detected from the dissolution of as-deposited and phosphate post-treated CeCCs. Solubility diagrams for Ce(OH) ₃ , Ce(OH) ...

article

Effect of alkaline cleaning and activation on aluminum alloy 7075-T6

Simon Joshi, William G. Fahrenholtz, Matthew J. O’Keefe

Applied Surface Science > 2011 > 257 > 6 > 1859-1863

The effect of alkaline cleaning and activation on the composition and thickness of the oxide layer on aluminum alloy 7075-T6 was studied. E–pH diagrams were developed to predict the effect of alkaline cleaning and activation solutions on the stability of the oxide surface layers. The thickness of the native oxide layer was determined to be ∼30nm by Auger electron spectroscopy depth profiling analysis...

article

Multifunctional UV (MUV) curable corrosion coatings for aerospace applications

Matthew J. O’Keefe, William G. Fahrenholtz, Ben S. Curatolo

Metal Finishing > 2010 > 108 > 2 > 28-31

article

The effect of post-treatment time and temperature on cerium-based conversion coatings on Al 2024-T3

Daimon K Heller, William G. Fahrenholtz, Matthew J. O’Keefe

Corrosion Science > 2010 > 52 > 2 > 360-368

Corrosion performance, morphology, and electrochemical characteristics of cerium-based conversion coatings on Al 2024-T3 were examined as a function of phosphate post-treatment time and temperature. Corrosion resistance improved after post-treatment in 2.5 wt.% NH ₄ H ₂ PO ₄ for times up to 10min or temperatures up to 85°C. Electrochemical impedance spectroscopy and polarization...

article

Screening study of spray solution parameters for depositing cerium-based conversion coatings on Al alloy 2024-T3

Shujiang Geng, Pu Yu, Matthew J. O’Keefe, William G. Fahrenholtz, more

Journal of Applied Electrochemistry > 2010 > 40 > 3 > 551-559

Cerium-based conversion coatings were deposited on aluminum alloy 2024-T3 by a spray process using a solution containing cerium chloride, hydrogen peroxide, and gelatin. As deposited coatings were composed of hydrated cerium oxide and were post-treated in a phosphate solution to improve corrosion performance. Coating solution parameters, including the pH (1–2.5), cerium chloride concentration (0.025–0...

article

Characterization of ultra-fast deposited polycrystalline graphite by a CO2 laser-assisted combustion-flame method

Travis McKindra, Sandeep Patil, Matthew J. O’Keefe, Yaoxuan Han, more

Applied Surface Science > 2009 > 255 > 9 > 5025-5030

High deposition rate, 750μm/min, crystalline graphite was deposited on WC substrates by a CO ₂ laser-assisted combustion-flame method at laser powers between 300 and 800W. The structures, which were identified as pillars, were characterized by various methods. The pillars were cylindrical in shape and grew to a size of approximately 3mm in length and in a few minutes. The laser power did not...

article

Chemical and morphological analyses of zinc powders for alkaline batteries

Martin G. Perez, Matthew J. O’Keefe, Thomas O’Keefe, Douglas Ludlow

Journal of Applied Electrochemistry > 2007 > 37 > 2 > 225-231

Zinc powders containing Bi, In and either Mg or Al were analyzed to determine chemical and morphological differences. Morphology and chemistry may influence the reactivity of Zn powders in the basic environment found inside alkaline batteries. Increased reactivity leads to increased Zn corrosion, increased hydrogen gas evolution, and possibly leakage of the battery electrolyte. The surface chemistry...

article

Identification of phases in zinc alloy powders using electron backscatter diffraction

Martin G. Perez, Edward A. Kenik, Matthew J. O’Keefe, F. Scott Miller, more

Materials Science & Engineering A > 2006 > 424 > 1-2 > 239-250

Scanning electron microscopy and electron backscatter diffraction (EBSD) were used for the structural characterization of phases in Zn alloy powders. Commercial Zn alloy powders contained additions of <1000ppm of Bi, In, Al or Mg. Bismuth and In have extremely low solubility in Zn and form intermetallic Bi–In compounds which segregate to the Zn grain boundaries. The Bi–In phases were <0.3μm...

article

Effect of coating parameters on the microstructure of cerium oxide conversion coatings

Benedict Y. Johnson, Joe Edington, Matthew J. O’Keefe

Materials Science & Engineering A > 2003 > 361 > 1-2 > 225-231

The microstructure and morphology of cerium oxide conversion coatings prepared under different deposition conditions were characterized by transmission electron microscopy (TEM). The coatings were formed by a spontaneous reaction between a water-based solution containing CeCl ₃ and aluminum alloy 7075-T6 substrates. Microstructural characterization was performed to determine the crystallinity...

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