Selected Published Work
Alloy for resistance to polythionic acid stress corrosion cracking for hydroprocessing application
Study to determine the potential and properties of Type 347LN after exposure to temperatures that would sensitize normal austenitic stainless steels. Conclusion was that this alloy did not sensitize and thus would be resistant to polythionic acid stress corrosion cracking (PTA-SCC). Although the thesis of the paper was for this alloy to be used in hydroprocessing applications at temperatures above 450oC, it is applicable to processing conditions where PTA-SCC conditions might be present.
Unraveling the mystery: using microscopy in a metallurgical failure investigation
Root cause analysis of a fitting from a pilot plant. A combination of optical microscopy, metallography and scanning electron microscopy was employed. Failure was by a Cl stress corrosion cracking mechanism that was caused by poor design and assembly of the fitting and process line.
Analysis of a seized CANM plug and cage control valve in hydroprocessing service
Root cause analysis of a recycle gas heater control valve failure from a commercial hydroprocessing unit. The valve seized due to an accumulation of corrosion products that resulted from a very brief exposure to a high temperature hydrogen/hydrogen sulfide stream.
Liquid metal embrittlement of Alloy 800 hydrogen unit preheat tubes
Analysis of an unusual and unexpected failure mechanism. Chemical and metallographic analyses of the polished cross-section revealed the presence of Al, Si and Zn. Failure was attributed to liquid metal embrittlement by Zn with the source of the Zn being from a Cu/Zn catalyst.
Failure of UNS N10276 reactor in supercritical water service
Failure analysis identifying stress corrosion cracking of Alloy C276 in supercritical water pilot plant. The crack propagated by an intergranular propagation mechanism. Rapid intergranular corrosion was observed in the reactor at a point where the temperature of the water feed was in the high subcritical range.
Characterization of coke on a Pt-Re/γ-Al2O3 re-forming catalyst: experimental and theoretical study
Combination of Carbon K-edge NEXAFS, Raman spectroscopy, NMR, TPO, XPS and DFT calculation to characterize coke on Pt-Re reforming catalyst. With an increasing amount of coke on the catalyst the amount of hydrogenated carbon declines. DFT calculations and C-NEXAFS indicate that the carbon atoms are bound to the oxygen of a phenoxide-like species bound to the alumina.
Aberration-Corrected Transmission Electron Microscopy and in Situ XAFS Structural Characterization of Pt/γ-Al2O3 Nanoparticles
Concluded that flat two-dimensional morphology of sub-nanometer Pt crystallites were dispersed on catalyst support. The number of Pt atoms in these clusters was measured by aberration-corrected scanning transmission electron microscopy and it was found that there were about 15 atoms in a sub-nanometer cluster. The in-situ X-ray absorption fine structure analysis supported this finding.
Mechanistic Study of Pt-Re/γ-Al2O3 Catalyst Deactivation by Chemical Imaging of Carbonaceous Deposits using Advanced X-ray Detection in Scanning Transmission Electron Microscopy
Application of aberration-corrected scanning electron microscopy to characterize sub-nanometer metal clusters on a catalyst support and for first time chemically imaging showed location of these clusters. Chemical maps were also used to identify coke location on the catalyst. A two-step mechanism was concluded with coke initially streaming from the metal function.
Z-contrast imaging as a tool for atomic level analysis of bimetallic structures
Demonstration of application of aberration-corrected scanning transmission electron microscopy high angle annular dark-field intensity to differentiate Pt and Pd atoms in a sub-nanometer metal cluster was initiated. This work was further refined in subsequent publications and the results compared favorably to energy dispersive x-ray analysis. This technique also verified that the cluster morphology varied depending on the amount of each element present in the metal cluster.
From atoms to functional nanomaterials: Structural modifications as observed using aberration-corrected STEM
Use of aberration-corrected scanning transmission electron microscopy to develop next-generation catalysts is described. Two different catalysts are discussed, what can be learned from imaging them at the nano-scale, and how this can be translated into next-generation catalysts.