Effects of oxygen on the Liquid Silicon Infiltration (LSI) process

The Liquid Silicon Infiltration (LSI) process has been in use for decades for the series production of components of various SiC materials as well as for environmental barrier coatings. However, high rejection rates and variations in quality still occur. One major cause of this are oxygen impurities in the furnace atmosphere during the infiltration. They can significantly disturb the siliconization process resulting in a discoloration of the component surfaces and an incomplete infiltration of the pore channels. Using different preforms, measuring methods and furnaces, the influence of oxygen on the LSI process was investigated systematically. It was demonstrated that the phenomenon is effective in general and also affects other processes such as sintering of non-oxide ceramics. The mechanisms that can disrupt or even prevent the infiltration and sintering processes have been identified. Methods for the continuous monitoring of the furnace atmosphere are compared. Measures are presented to reduce the oxygen concentration and subsequently quality degradation and rejection rates.