Congratulations to Victoria Christensen, PhD candidate, for having her recently-published paper in the Journal of the American Ceramic Society selected as EDITOR’S CHOICE.  The paper, entitled “Insights into internal oxidation of SiC/BN/SiC composites”, includes unprecedented SEM imaging of microstructural changes that occur in the vicinity of BN fiber coatings. 

The paper presents new observations of the physical manifestations of internal oxidation and volatilization in SiC/BN/SiC. BN is consumed in two stages: (i) through reaction with oxygen along interfaces with both the fiber and the matrix, producing concentric annular pockets of borosilicate glass and an intervening annulus of progressively-thinning porous BN; and (ii) subsequent volatilization, through reaction of boria with trace amounts of water vapor in the environment to form borohydroxide gases. The spatial extent to which these processes proceed is governed by a competition between outward diffusion of reaction gases through both matrix cracks and interface gaps produced by boria volatilization, and formation of oxides on the newly-exposed surfaces of fibers, matrix and coating.

Image: Longitudinal section of composite oxidized in flowing dry air at 1000°C for 12 h.