Different Evolutions of the Microstructure,Texture, and Mechanical Performance During Tension and Compression of 316L Stainless Steel

Metallurgical and Materials Transactions A - The tensile and compressive behaviors of 316L stainless steel at room temperature were compared. The differences between the stress–strain...     

The base‐catalyzed,low‐temperature interesterification mechanism revisited

For the base‐catalyzed interesterification reaction carried out at low (<100 °C) temperatures, a number of mechanisms have been proposed in the literature. As these mechanisms are not in accordance with experimental observations, a novel mechanism will be proposed instead. This novel mechanism assumes that the reaction of a base (such as sodium methanolate) with the oil will eventually lead to the abstraction of an α‐hydrogen from a fatty acid moiety and that the enolate anion thus formed acts as the catalytic intermediate. This enolate can re‐abstract a proton from the hydroxyl group of a partial glyceride, whereupon the resulting alcoholate attacks the carbonyl group. This leads to a new ester and a glycerolate anion that then regenerates a new enolate anion. If the enolate anion reacts with methanol, this will lead to the formation of a fatty acid methyl ester and a glycerolate anion that again regenerates an enolate anion. Reaction with water leads to catalyst inactivation by converting the enolate anion to an unreactive fatty acid moiety (free fatty acid or soap) and a partial glyceride. Thermal inactivation of the enolate intermediate is assumed to be through the formation of catalytically inactive β‐keto esters. The accelerating role of acetone is explained by assuming this compound to act as a highly mobile hydrogen transfer agent that facilitates the reaction between the glycerolate anion and the α‐hydrogen atoms in fatty acid moieties. The above assumptions are independently supported by the observation that the addition of acetone‐d₆ to an interesterifying reaction mixture leads to the almost quantitative incorporation of deuterium into the α‐position of fatty acid moieties. Theoretical calculations on the enolate–alcohol system at PM3 level are also in agreement with the enolate mechanism.     

The oxidation of tantalum-based thin films

Using different techniques (Auger electron spectroscopy, Rutherford back-scattering spectrometry, transmission electron microscopy and electrical measurements) a region of tantalum nitride layer composition was found where the increase in resistance (during thermal oxidation) is caused only by the decrease in thickness of the metallic part of the film. By means of the very sensitive method of the resistance measurements these compositions were shown to be suitable for the study of the thermal oxidation kinetics in the temperature range 266–464°C and in the oxidized thickness x range from the “air oxide” to 80 nm.Empirical $\text{d}\text{x}\text{d}\text{t}\text{=}\text{f}\text{(x)}$ functions determined at different temperatures were compared with the well-known oxidation rate laws of the literature. The shape of these empirical functions was described by the use of the $\text{d}\text{x}\text{d}\text{t}\text{=A}\text{sinh}\text{(}\text{B}\text{x}\text{)}$ rate law.     

Cross-sectional composition investigations of sputtered tantalum nitride thin films by secondary ion mass spectrometry

Secondary ion mass spectrometry (SIMS) provides the possibility for cross-sectional composition investigations of thin films. It is a very useful tool for the analysis of changes occurring under technological processes such as oxidation under heat treatment or anodization conditions. In the case of sputtered tantalum nitride films the results of SIMS analyses show that the really conductive part of the film is the middle section and that is bordered on both sides by insulator-like layers. These results confirm the conclusions of our earlier investigations. The SIMS spectra also show that during oxidation the concentration of the tantalum nitride in the outer layer decreases.