Observation of Internal Structure of Ceramics and Slurry by Optical Coherence Tomography

Abstract

Optical coherence tomography (OCT) is an observation technique utilizing optical interferometry. Images of the internal structure of opaque materials can be obtained dynamically and three-dimensionally in a few seconds. In this work, the internal structures of ceramic sintered body and slurry was observed by OCT. In the case of Al 2 O 3 ceramics, an artificially induced spherical defect having smaller than 50 µm in diameter which lies 700 μm below the top surface was observed successfully. Furthermore, it was observed that the internal structure of Al 2 O 3 slurry was drastically changed during drying, followed by formation of a crack in the dried green body.

Prediction of strength based on defect analysis in Al₂O₃ ceramics via non-destructive and three-dimensional observation using optical coherence tomography

“…Finally, a three-dimensional image (termed C-scan) is also obtained by two-dimensional scanning of the light nondestructively. 18) The depth at which information can be obtained with A-scan is determined by the refractive index of the material and the laser's ability. When Al 2 O 3 is observed with commercially available OCT, the typical coherence length, namely observable depth, is 2.3 mm.…”

“…It is also reported that spherical artificial pores with dimensions of 50¯m at a depth of 700¯m were observed from the surface in Al 2 O 3 . 18) The prediction of strength based on defect analysis in ceramics using OCT is not performed to date. However, OCT is a useful tool to observe defects in ceramics because OCT can obtain high-speed, high-resolution, non-destructive, and threedimensional observations.…”

In situ observation of evolution of internal structure of alumina during sintering by swept‐source OCT

“…In the infrared transmission image, bright spots with sizes of several tens of micrometers were also observed. According to our previous reports, the bright pairs in the OCT images originate from the reflections at the upper and lower surfaces of the pore 23,24 . Although SEM observations of the same positions are not available in this study, it is suggested that there are large pores in the Al 2 O 3 ceramics that grew during sintering.…”

“…We have been employing optical coherence tomography (OCT) to observe the internal structure of ceramics 23,24 . OCT is a nondestructive observation method based on optical interferometry 25–27 .…”

“…We have been employing optical coherence tomography (OCT) to observe the internal structure of ceramics. 23,24 OCT is a nondestructive observation method based on optical interferometry. [25][26][27] Moreover, a relatively new OCT system, swept-source OCT, was initially applied to a commercially available apparatus for imaging the choroid and sclera at the back of the retina in 2012.…”