Abstract
The wetting of graphite by aluminium and Al–Si alloys was studied at 1273 K in a purified He-3 vol%H2 atmosphere with a Meniscograph to establish the usefulness of this method in metal/ceramics systems.
Wetting showed three characteristic phases with the change in adhesive tension (Fa). These are, (1) an initial phase with a decreasing Fa due to the dewetting of the specimen by the melt, (2) a quasi-equilibrium phase with constant Fa, and (3) a spreading phase with an increasing Fa produced by chemical reaction.
The wetting speed is the highest in the Al-20 mass%Si alloy system. It was confirmed with SEM and X-ray diffraction that Al4C3 is formed at the interface between graphite and the melt in alloys containing up to 10 mass%Si, whereas SiC is formed with a 20 mass%Si alloy melt. The transition from Al4C3 to SiC is caused by the activity of Si in the alloys.
The contact angle (θ) of the graphite/aluminium system, calculated from measured Fa, was smaller than that with the sessile drop method in the third phase. The difference between the Meniscograph and sessile drop methods must be associated with the condition of the liquid surface where aluminium vapor evaporates and decreases the partial pressure of oxygen in the atmosphere. The presence of an oxide film on the melt prevents the melt from evaporating and inhibits the spreading of Al on the graphite.
