Influence of carbon on the interfacial contact angle between alumina and liquid aluminum

The wetting of alumina by pure liquid aluminum was investigated over the temperature range 900-1300 °C by the sessile drop method under a dynamic vacuum of 10^-4-10^-5 Pa. When the substrate is carbon coated, the terminal contact angle is reduced to 40° at 1300°C for times longer than 4500 s. In the absence of carbon, the final angle is 82° for the same conditions. Reactive wetting is suggested by the observation of undercutting of the substrate and ridge formation at the leading edge of the liquid aluminum in all carbon-coated samples. Based on energy considerations, the following is among the thermodynamically favorable reactions: 4Al + 3C → Al₄C₃. Possible mechanisms for the observed carbon-enhanced wettability in the system are discussed.