Aluminum oxide-lead interface

Electron tunneling spectroscopy applied in a different experimental configuration can yield the vibrational structure of adsorbates. For example, by adsorbing a monolayer of molecules at an aluminum oxide-lead interface, the vibrational spectrum of benzoic acid was obtained by plotting d V/dP, the second derivative of the applied voltage with respect to the tunnel current, versus the applied voltage V. The result is shown in Figure 5.19. The experiment was performed at 4.2 K. 

Stragier H, Cross JO, Rehr JJ, Sorensen LB, Bouldin CE, Woicik JC (1992) Diffraction anomalous fine structure A new X-ray structural technique. Phys Rev Lett 69 3064-3067 Strawn DG, Scheidegger AM, Sparks DL (1998) Kinetics and mechanisms of Pb(II) sorption and desorption at the aluminum oxide-water interface. Environ Sci Technol 32 2596-2601 Strawn DG, Sparks DL (1999) The use of XAFS to distinguish between inner- and outer-sphere lead adsorption complexes on montmorillonite. J Colloid Interface Sci 216 257-269 Strawn DG, Sparks DL (2000) Effects of soil organic matter on the kinetics and mechanisms of ( ) sorption and desorption in soil. Soil Sci Soc Am J 64 144-156 Stumm W (1992) Chemistry of the Sohd-Water Interface. John Wiley Sons, Inc, New York... 

Another technique that has proved useful in establishing chemical bonding of coupling agents at interfaces is inelastic electron tunneling spectroscopy (ITES). For example. Van Velzen [16] examined 3-(trimethoxysilyl)propanethiol by this technique. Approximately monolayer quantities of this silane were adsorbed on the barrier oxide of an aluminum-aluminum oxide-metal tunneling junction two metals were investigated, lead and silver. It was concluded that the silane is... 

It is necessary to exceed the critical anodic potential (23) bd for the electrochemical breakdown of passivation by pitting and consists of these factors (i) presence of halides at the interface (ii) induction time for the initiation of the breakdown process, leading to localized conditions that may increase the localized corrosion current density (iii) development of favorable conditions inside the pits for propagation when the local sites become immobile and localized at certain sites. Electrochemical breakdown of some metal oxides is possible in the case of copper, lead, and tin cathodically to metal while ferric oxide is reduced to the ferrous ion in aqueous solutions. Zinc and aluminum oxides are not cathodically reducible and in these cases hydrogen is reduced. The vigorous evolution of hydrogen assisted by electron conducting zinc oxide can accelerate the breakdown of passivity. 

Ni Sorption on Clay Minerals A Case Study. Initial research with Co/clay mineral systems demonstrated the formation of nucleation products using XAFS spectroscopy, but the stmcture was not strictly identified and was referred to as a Co hydroxide-like stmcture (11,12). Thus, the exact mechanism for surface precipitate formation remained unknown. Recent research in our laboratory and elsewhere suggests that during sorption of Ni and Co metal ions, dissolution of the clay mineral or aluminum oxide surface can lead to precipitation of mixed Ni/Al and Co/Al hydroxide phases at the mineral/water interface (14,16,17,67,71). This process could act as a significant sink for metals in soils. The following discussion focuses on some of the recent research of our group on the formation kinetics of mixed cation hydroxide phases, using a combination of macroscopic and molecular approaches (14-17). 

The often used FPL etdi of an aluminum-lithium alloy bonded with polysulfone leads to interfacial (at the metal oxide/polymer interface) failure (38) which is a surprisingly uncommon type of failure. The results leading to this assignment are shown as XPS C Is and O Is narrow scan spectra in Figure 15. This definitive assignment of failure mode is based on the fact that one failure surfece has an oi gen photopeak similar to the pretreated adherend before bonding and the other failure surfece has an 0 gen photopeak similar to the adhesive. 

Metals such as titanium, aluminum, nickel, and stainless steels have been pursued for bipolar plate applications [5,8,10-12], However, these research efforts met limited success because of the chemical instability of the metals in the fuel ceU environment, especially when in contact with the acidic electrolytic membrane. Corrosion of the metal bipolar plate leads to a release of cations, which can both lead to an increase in membrane resistance and poisoning of the electrode catalysts [12]. The oxide film formed on the surface of the self-passivating metals also results in high voltage losses across the plate/macro-diffuser interface [8,11]. 

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