Fig. 5

SEM micrographs of typical fracture surfaces of the a non-immersed specimen, magnified views of b center and c outer parts in a, d specimen immersed in 0.2 % APF solution, magnified views of e center and f outer parts in d, g specimen aged for 24 h at room temperature in air after immersion, magnified views of h center and i outer parts in g, j specimen aged for 240 h at room temperature in air after immersion, and magnified views of k center and l outer parts in j