Surface tension of Liquid Ti-V Alloys and their Interaction with Oxygen

Kurzfassung

Density and surface tension of electromagnetically levitated liquid Ti-V alloys are presented. Density is measured using a shadowgraph technique where the droplet is illuminated from one side by an expanded laser beam and the edge curve of the shadow picture is numerically integrated in order to obtain the volume of the sample. Surface tension is obtained by analyzing the spectra of the droplet oscillations. To this end, pictures of the sample are recorded with a digital camera at a framerate of 400 fps. Alloy samples are investigated with respect to temperature and composition. The entire compositional range is hereby covered, including the pure elements Ti and V. In all cases, density and surface tension obey linear laws with respect to temperature whereas the slopes are negative. The Ti-V alloys also exhibit ideal mixing behavior with respect to both, density and surface tension. In addition, Ti-O and V-O samples including controlled amounts of atomic oxygen ranging from 0.01 at. % up to 26 at. % are prepared by adding corresponding quantities of TiO2 to Ti and V2O5 to V. Part of these data have been measured during a parabolic flight campaign. While in these cases, it is still found that the surface tension decays linearly with temperature, its magnitude strongly depends on the amount of oxygen added. For constant temperature, and as function of bulk oxygen concentration, the surface tension curves exhibit the typical shapes of Belton-type isotherms. There is a plateau at low mole fractions x, corresponding to virtually clean surfaces, and a nearly linear decay of the surface tension with the log(x) when x exceeds a certain threshold. For both, Ti and V, this threshold is approximately 1.0 at. %, which is comparatively large and points towards a strong attractive interaction between the metal and oxygen. The data are discussed by thermodynamic models based on the Butler, Langmuir and Gibbs equations.