Oxygen tensioactivity on liquid-metal drops.

The influence of oxygen on the surface tension of liquid metals is a topic of undoubted interest as the formation of oxide films, or even oxygen contamination of the metal interface, represents the main source of error in determining the surface tension. The evaluation of gas-atmosphere mass exchanges under stationary conditions allows the evaluation of an effective oxygen pressure at which the oxidation of metal becomes evident. This effective oxygen pressure can be considered as a property of the system and, according to experimental evidence, can be many orders of magnitude greater than the equilibrium pressure. The measurement of the surface tension is a good way of studying interface properties, their temporal change and their connections to transport and reaction rates. This paper represents a review of a work undertaken with the aim of understanding oxygen mass transport at the liquid metal surface in relation to the study of capillary phenomena at high temperature.

Secondary ion mass spectrometry in the characterisation of boron-based ceramics.

A secondary ion mass spectrometry (SIMS) study of Zr- and Ti-based borides is reported: ZrB2 ceramic samples (with and without nickel addition) and a TiB2-Ni-B4C/Cu joint were investigated. For Zr-based samples, SIMS measurements show evidence for induced effects by the presence of nickel with regard to oxygen and hydrogen absorption and zirconia formation. In the case of the TiB2-Ni-B4C/Cu joint, the ceramic-metal interface region was analysed and the extent of Cu diffusion into the ceramic material was established. SIMS results were in agreement with previously obtained SEM-EDS data.

Adsorption Kinetics of Alkylphosphine Oxides at Water/Hexane Interface

A theoretical model is presented to describe the adsorption of surfactant molecules at the water/oil interface for the case when transport across the interface must be considered due to the solubility of the surfactant in both liquid phases (aqueous solution drop in an oil phase). The theory is based on a diffusion-controlled adsorption model and a numerical difference scheme is used to solve the problem for closed finite systems. By simulating adsorption-desorption processes, the influence of the geometrical and thermodynamic parameters on the dynamic adsorption behavior is studied. In particular, the effects of the volume ratio, surfactant concentration, diffusion coefficients, and distribution coefficient on the process are analyzed. The model allows quantitative interpretation of the experimental data obtained for an alkyldimethylphosphine oxide at the water/hexane interface. The interfacial tension signals, presenting a minimum under some conditions, are fitted by the theoretical curves.