Reactive wetting of liquid metals on ceramic substrates

This paper deals with a well known puzzling observation that sometimes the wetting is improved by a chemical reaction between a liquid and a solid substrate and sometimes just the opposite effect takes place. Here, contact angles of liquid Al on SiO2 and liquid Ti on Al2O3 have been measured. The surface and interface structures have been explored by scanning electron microscopy and energy dispersive X-ray spectrometry. According to the experimental observations, it turns out that the volume change of ceramic substrates during reaction plays a key role in the effect of chemical reaction on wetting. If the volume of ceramic substrate decreases after reaction, the wettability is not improved by the chemical reaction. This is the case of liquid Al wetting on SiO2. If the volume of ceramic substrate increases after reaction, the wettability is improved by the chemical reaction. This is the case of liquid Ti wetting on Al2O3. Besides our experimental observations, results from literature have been reviewed as well, which are in good agreement with the predictions based on the volume change criterion of ceramic substrate proposed in this paper.