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

Abstract

In situ observation of sintering of ceramics is important to understand the sintering behavior, including the development of internal structures, and to fabricate ceramics with superior properties. However, there has been no studies thus far on high‐speed in situ observation of the internal structure of green and sintered bodies at high temperatures with micrometer‐scale resolution. Here, we applied swept‐source optical coherence tomography (OCT) to observe the evolution of the internal structure in Al2O3 green bodies during sintering. In situ OCT observations revealed that internal structure changes during sintering, such as the development of density distribution and growth of coarser pores. We could also obtain the sintering shrinkage ratio and relative density from the OCT images. The OCT observation of the internal structure during sintering of green bodies with added or stacked granules of different primary particle sizes confirmed that inhomogeneous regions developed as the densification progressed at high temperatures. These results indicate that in situ observation of the sintering behavior of ceramic green bodies using swept‐source OCT is a novel technique that facilitates real‐time observation of the evolution of the internal structure during sintering.

Novel <i>operando</i> observation technique based on combined optical coherence tomography–thermogravimetry for monitoring internal structural changes of drying ceramic slurries

“…In particular, three-dimensional observations, which have been performed to study the sintering behavior of ceramic green bodies, will be particularly useful. 17) In summary, using the combined OCT-TG system developed in this study, we succeeded in observing the internal structural evolution of a silica slurry during its drying. In the early stages of drying, the OCT signal intensity varied significantly owing to the Brownian motion of the silica particles in the slurry.…”

“…The slurry sheet was placed on the electronic balance and heated from the top using the infrared heater, and the drying slurry was observed continuously using the OCT camera set at the top. The ambient temperature was controlled at 50 °C, and the cross-section of the slurry sheet (width: 10 mm, height: 1.71 mm) was observed two-dimensionally with a B-scan (2D scan), which is obtained by laterally repeated A-scan (1D depth scan), 17) width of 3.68 ¯m/pixel every 1 s while heating, until there was no change in the weight of the slurry.…”