Abstract
In this work a double contribution to the characterization of molten In and In-Sn alloys considered as main components of an important class of lead free solder materials is shown: the study of the influence of oxygen on the capillary phenomena and the XRD investigation of the structure of liquid in a range of temperatures around that of liquidus. The surface tension behaviour of In-Sn binary alloys at different compositions, in terms of effective oxygen pressure, were compared with the data of pure In and the theoretical predictions, revealing that the lower oxidizability of indium was shown to control indium-tin alloys with a tin content up to about 80 at% , due to the presence of the most volatile oxide In2O. From the XRD spectra the radial distribution functions (RDF) have been determined for each alloys. Experiments of High Temperature X-ray diffraction (HT-XRD) showed that atomic clustering forms in the melt immediately before the appearing of the first solid. The structure of clusters is correlated to that of solid.
Highlights
The In-Sn based alloys are principally used as lead free brazing materials [1,2] due to unique combination of their properties as well as a good alloying tendency with copper, widely used as substrate in electronic industry [3]
A double contribution to the characterization of molten In and In-Sn alloys is here presented: - Dynamic Surface Tension (DST) measurements addressed to validate the theoretical approach able to explain the mechanisms that keep the surface of molten metallic system oxygen-free despite the thermodynamic driving force
The theory [10,11] indicated that the reaction of the alloy to oxidation tends to be similar to that of the less-oxidizable component thanks to the contribution of the volatile oxide which should prevent the surface oxidation even if the corresponding metal is present in low percentages. - High Temperature X-ray diffraction (HT-XRD) permits the direct monitoring of phase transformations [15,16,17,18] and present experiments have been addressed to investigate possible structural changes occurring in the
Summary
The In-Sn based alloys are principally used as lead free brazing materials [1,2] due to unique combination of their properties as well as a good alloying tendency with copper, widely used as substrate in electronic industry [3]. A double contribution to the characterization of molten In and In-Sn alloys is here presented: - Dynamic Surface Tension (DST) measurements addressed to validate the theoretical approach able to explain the mechanisms that keep the surface of molten metallic system oxygen-free despite the thermodynamic driving force. These mechanisms involve, in particular, the evaporation of metal oxides from the metal interface and make it possible to define the effective oxygen partial pressure consistent with the saturation of a steady liquid phase [9]. The results were examined by focusing the attention on atomic clustering in the liquid phase correlated to the solid crystalline structure
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