WTC2005-64353 ACTIVATION OF SIC SURFACES FOR VAPOR PHASE LUBRICATION BY CHEMICAL VAPOR DEPOSITION OF FE

ABSTRACT Vapor phase lubrication (VPL) has been proposed as a method for lubricating high temperature engines. During VPL, lubricants are delivered through the vapor phase to high temperature engine parts and react on their surfaces to deposit a thin, solid, lubricating film. Although ceramics such as SiC are desirable materials for high temperature applications, their surfaces are unreactive for the decomposition of TCP and thus not amenable to vapor phase lubrication. As a means of activating the SiC surface for TCP decomposition we have used chemical vapor deposition of Fe from Fe(CO) 5 . Modification of the SiC surface with adsorbed Fe accelerates subsequent decomposition of TCP and deposition of P and C onto the surface. In the temperature range 500 -800 K, m-TCP decomposes more readily on Fe-coated SiC surfaces than on SiC surfaces. The C and P deposition rates depend on the thickness of the Fe film and are further enhanced by oxidation of the Fe. This work provides a proof-of-concept demonstration of the feasibility of using vapor phase lubrication for ceramics

Adsorption-induced auto-amplification of enantiomeric excess on an achiral surface

1132Nsciescopu

Enantioselective separation on naturally chiral metal surfaces: DL-aspartic acid on Cu(3,1,17)R&S surfaces

1135Nsciescopu

Enantiospecific Adsorption and Decomposition of D- and L-Asp Mixtures on Cu(643)R&S

The study of molecular chirality is essential to understanding the fundamentals of enantiospecific chemical interactions that are ubiquitous in the biochemistry of life on Earth. At a molecular level, there is insufficient understanding of chiral recognition and enantiomer–enantiomer interaction (aggregation) of chiral molecules adsorbed on surfaces. Here, using enantiospecific isotopic labelling and surface sensitive techniques, we show that when the two enantiomers of chiral aspartic acid (Asp) are adsorbed on the naturally chiral Cu(643)R&S surfaces, they decompose enantiospecifically depending on the chirality of the surface. The non-linear kinetics of the surface decomposition mechanism amplifies the difference between the decomposition rate constants of the two adsorbed enantiomers resulting in highly enantiospecific decomposition rates. Further, we also demonstrate that Asp enantiomers aggregate homochirally on several chiral and achiral surfaces, amplifying the enantiomeric excess on the surface with respect to that in the gas phase, |ees |>|eeg. Our results show that it is possible to discern the enantiospecific behavior of a complex adsorbate such as Asp and shed light on molecular level enantiospecific interactions on surfaces. The enantiospecific isotope labelling methods discussed in this paper allow probing of both the qualitative features of the Asp decomposition mechanism on Cu(643)R&S and quantitative aspects of the adsorption equilibria of enantiomer mixtures

Enantiospecific adsorption of amino acids on naturally chiral Cu{3,1,17}R&S surfaces

Gas-phase equilibrium adsorption of D- and L-serine (Ser) mixtures and D- and L-phenylalanine (Phe) mixtures has been studied on the naturally chiral Cu{3,1,17}(R&S) surfaces. C-13 labeling of the L enantiomers (*L-Ser and *L-Phe) has enabled mass spectrometric enantiodiscrimination of the species desorbing from the surface following equilibrium adsorption. On the Cu{3,1,17}(R&S) surfaces, both equilibrium adsorption and the thermal decomposition kinetics of the D and *L enantiomers exhibit diastereomerism. Following exposure of the surfaces to D/*L mixtures, the relative equilibrium coverages of the two enantiomers are equal to their relative partial pressures in the gas phase, theta(D)/theta*(L) = P-D/P*(L). This implies that adsorption is not measurably enantiospecific. The decomposition kinetics of Ser are enantiospecific whereas those of Phe are not. Comparison of these results with those for aspartic acid, alanine, and lysine suggests that enantiospecific adsorption on the naturally chiral Cu surfaces occurs for those amino acids that have side chains with functional groups that allow strong interactions with the surface. There is no apparent correlation between amino acids that exhibit enantiospecific adsorption and those that exhibit enantiospecific decomposition kinetics.1112Nsciescopu

Competing forces in chiral surface chemistry: enantiospecificity versus enantiomer aggregation

The enantiospecific adsorption of enantiomer mixtures on surfaces is dictated by two competing forces: the enantiospecificity of adsorption energetics and the propensity of enantiomers to aggregate into homochiral (conglomerate) or heterochiral (racemate) clusters. These phenomena have been studied by measuring the surface enantiomeric excess, ee(s), of chiral amino acid mixtures adsorbed on Cu single-crystal surfaces and in equilibrium with gas-phase mixtures of varying enantiomeric excess, ee(g). Alanine adsorption on Cu{3,1,17}(R&S) surfaces is non- enantiospecific, ee(s) = ee(g), because alanine enantiomers do not interact with either the surface or with one another enantiospecifically. Aspartic acid adsorbs enantiospecifically on the Cu{3,1,17}(R&S) surfaces; ee(s) not equal ee(g), even during exposure to a racemic mixture in the gas phase, ee(g) = 0. Exposure of the achiral Cu{111}} surface to nonracemic aspartic acid, ee(g) not equal 0, results in local amplification of enantiomeric excess on the surface, vertical bar ee(s)vertical bar > vertical bar ee(g)vertical bar, as a result of homochiral aggregation. Finally, despite the fact that the Cu{653}(R&s) surfaces are chiral, the adsorption of aspartic acid mixtures yields vertical bar ee(s)vertical bar > vertical bar ee(g)vertical bar, indicating that homochiral aggregation dominates enantiospecific adsorbate-surface interactions. All of these types of behavior are captured by a Langmuir-like adsorption isotherm that includes competition between enantiospecific adsorption and both homochiral (conglomerate) and heterochiral (racemate) aggregation of chiral adsorbates.113Nsciescopu

WTC2005-64353 ACTIVATION OF SIC SURFACES FOR VAPOR PHASE LUBRICATION BY CHEMICAL VAPOR DEPOSITION OF FE

ABSTRACT Vapor phase lubrication (VPL) has been proposed as a method for lubricating high temperature engines. During VPL, lubricants are delivered through the vapor phase to high temperature engine parts and react on their surfaces to deposit a thin, solid, lubricating film. Although ceramics such as SiC are desirable materials for high temperature applications, their surfaces are unreactive for the decomposition of TCP and thus not amenable to vapor phase lubrication. As a means of activating the SiC surface for TCP decomposition we have used chemical vapor deposition of Fe from Fe(CO) 5 . Modification of the SiC surface with adsorbed Fe accelerates subsequent decomposition of TCP and deposition of P and C onto the surface. In the temperature range 500 -800 K, m-TCP decomposes more readily on Fe-coated SiC surfaces than on SiC surfaces. The C and P deposition rates depend on the thickness of the Fe film and are further enhanced by oxidation of the Fe. This work provides a proof-of-concept demonstration of the feasibility of using vapor phase lubrication for ceramics