| One of the limitations in the use of ceramics in critial applications is
due to the presence of microcracks, which may arise from differential
thermal expansion and phase changes, among others. Acoustic emission
signals occur when there are abrupt microdeformations in a
material and thus offer a convenient means of non-destructive detection
of microcracking. Examples of a study of acoustic emission
from microcracking due to anisotropic thermal expansion in low
thermal expansion single phase ceramics such as niobia and sodium
zirconium phosphate ceramics and due to phase changes in zirconia
and superconducting YBa.Cu30 7_x ceramics are ptesented, together
with the case of lead titanate ceramics, which exhibits both a phase
change (paraelectric to ferroelectric) and an anisotropic thermal
expansion. The role of grain size on the extent of microcracking is
illustrated in the case of niobia ceramics. Some indirect evidence of
healing of microcracks on heating niobia and lead titanate ceramics
is presented from the acoustic emission results. |
