Dennis G. Swartzfager

Distribution of Pt and Re in PtRe:Al2O3 naphtha reforming catalysts

Abstract The benefit of Re in PtRe: Al 2 O 3 naphtha-reforming catalysts is clear, but its disposition and function are not. We report here results of surface analysis of ion-scattering spectroscopy and microanalysis by energy-dispersive X-ray spectroscopy in a scanning transmission electron microscope. On both reduced and reduced and sulfided commercial-type catalysts, we found that Re is not significantly associated with Pt, but rather is widely dispersed on the support surface. Sulfiding essentially covers the Re, but leaves most of the Pt exposed.

Strain effects in surface segregation—The Au/Ni system

Previous studies have reported segregation of the minority element to the surface at both ends of the gold–nickel phase diagram. These results, which contradict the predictions of bond‐breaking arguments, were attributed to strain effects arising from the large atomic size difference between gold and nickel. Such effects for this and other alloy systems have been calculated by an elastic continuum model which suffers from several limitations. A pair‐potential model is proposed here which overcomes these difficulties. Dilute alloys of gold and nickel were studied by ion‐scattering spectroscopy to test these predictions. The calculations predict and the measurements show that the surface of either gold‐rich or nickel‐rich alloys becomes enriched in gold.

In situ tem and iss studies of supported metal ‘SMSI’ catalysts

Supporting catalytic metals on reducible oxides may give rise to a special state termed ‘strong metal-support interaction’ (SMSI) after severe reduction. It is characterized by sharply reduced chemisorption, enhanced thermal sintering resistance and, in at least some instances, altered metal particle morphology. Proposed causes include electron donation from the support to the metal and encroachment of the support over the metal. We have sought evidence for its cause, applying ion beam surface analysis and in situ transmission electron microscopy (TEM) combined with electron energy loss spectroscopy (EELS) to Pt:TiO2. The support was prepared by hydrolyzing titanium isopropoxide; the Pt was applied by ion exchange from the tetramine hydroxide. Specimens were reduced from 473 K to 873 K in flowing, purified H2 and examined without intervening air exposure; some were also reduced in a special reaction cell on the TEM. Results of the ion beam surface analysis contradict the notion of support encroachment over the metal or metal migration into the support. However, in the SMSI state Pt becomes less ‘visible’. Both in situ and ex situ TEM showed no change of particle size or morphology accompanying SMSI. The EELS showed a decrease in the ratio of the titanium L3 edge to the L2 at the onset of SMSI. This result and the Pt ‘visibility’ change point to underlying electron structure changes, which presumedly are also responsible for the loss of chemisorption capacity. Further work is needed to elucidate just what these changes might be.

Characterization of Multilayered Automotive Paint Systems Including Depth Profiling and Interface Analysis

Design and development of today’s high performance, original equipment manufacturer (OEM) paints and coatings requires the ability to do surface and interface analysis, as well as depth profiling. Obtaining compositional information as a function of locus enables one to better understand the relationship of chemical functionality, component distribution, and network architecture to the product performance (i.e., chemical, physical, mechanical and appearance properties/durability). A multi-technique approach was found effective in providing the desired compositional information, combining infrared (IR), Raman, time-of-flight secondary ion mass spectrometry (ToF-SIMS), and tunneling electron microscopy (TEM) analyses. The complementary information resulting from these techniques gave a detailed view of coating system chemistry and morphology, including insights on service life prediction. This, in turn, offers feedback for optimizing system design with respect to material properties, environmental factors, material processing and application considerations.

Correlation of surface segregation with bulk diffusion for binary metal alloys

Abstract Previous treatments of surface segregation in metal alloys have all failed in some systems, due either to inadequacies in the theories or in the thermochemical data. A new model is proposed here using only alloy diffusion data. Predicted surface compositions agree quantitatively with ISS measurements and qualitatively AES results.

Glass-encapsulant interface characterization following temperature and humidity exposure

The ability to optimize and consistently control the properties of the polymer-glass interface in thin film PV laminates in an important aspect of module reliability. Using variable rate peel delamination methods developed to isolate the encapsulant/glass interface, ion migration and interfacial chemistry have been studied following temperature and humidity exposure. In this presentation we will review quantitative AFM (Atomic Force Microscopy) and XPS (X-ray Photoelectron Spectroscopy) analyses linking failure modes with interfacial chemistry.