In order to increase understanding of the structure and bonding of aromatic molecules and their fragments on transition metal surfaces, a low-energy electron diffraction (LEED) study of benzene adsorption on Ir{100} has been carried out. Following benzene adsorption at 465 K, a c(2×4) LEED pattern is observed. Its formation is accompanied by the loss of two hydrogen atoms as H2, indicating that benzyne (C6H4) is formed. This is the first time an ordered overlayer of benzyne has been observed on a transition metal surface. It makes the structure accessible to LEED I–V analysis, providing the most reliable structural information for benzyne adsorbed on a transition metal surface to date. The benzyne species was found to be di-σ bonded to the bridge site with a 47° tilt angle to the surface normal.

The oxidation kinetics, and the structural evolution of the resulting surface scale, of cast transformationinduced plasticity (TRIP) steel (0.97 wt pct Al and 1.11 wt pct Si) has been investigated in the temperature range of 850 °C to 1250 °C under atmospheres with oxygen partial pressures close to 0.2 atm. Direct visualization using a high-temperature confocal scanning laser microscope (CSLM) showed that at 1050 °C and higher temperatures, a liquid oxide phase formed beneath the surface, penetrating and liquefying the scale that had formed initially. After a period of time, which was dependent on temperature, the liquid became fully crystallized. A microprobe analysis of the steel/scale interface indicated an Al 2 O 3 -SiO 2 -FeO n composition in the liquid oxide. This phase formed a network that penetrated the scale. The rest of the outer scale consisted primarily of Fe 2 O 3 , while Al-Si-rich oxides were observed close to the metal/scale interface. Thermogravimetric analysis indicated a parabolic growth rate below 1000 °C and a linear growth rate at 1000 °C. At higher temperatures, a parabolic rate dominated once again. The scale thickness appears to be limited by the time period during which the liquid oxide could contribute to rapid mass transfer, which resulted in the observed linear oxidation rate. As the upper temperature limit of the linear oxidation region is reached, the liquid oxide becomes enriched with FeO n , decreasing the stability of the liquid phase. This leads to crystallization of solid Fe oxides at the surface or the formation of appreciable amounts of Al-and Si-rich oxides at the interface. These processes block access of the liquid oxide to the steel.

No abstract

No abstract

No abstract