THE INITIATION OF SPONTANEOUS INFILTRATION OF ALLOYS INTO CARBON PREFORMS IN AIR

It was found in a previous work that the AI-Si alloy could spontaneous ly infiltrate into carbon preforms in air. In this study, the initiati on stage of the infiltration process was investigated in detail throug h two different infiltration experiments. In one experiment, carbon pr eforms were fully dipped into an alloy bath that was exposed to air, a nd in the other experiment a carbon preform was only partially dipped into an alloy bath that was protected with a flowing Ar or N-2 gas. Ex perimental results have suggested that the initiation of infiltration is controlled by the pressure of oxidizing gases such as O-2 or CO at the infiltration front and is not affected by the presence or absence of N-2 gas. The critical pressure of oxidizing gases is estimated to b e on the order of 10(-4) atm for systems investigated in our experimen ts. An effective way to reduce the O-2 or CO pressure is to flush a pr eform with nonoxidizing gases during or before infiltration, or to use an active metal to reduce the O-2 pressure and thus the corresponding CO pressure.