Crystal plane evolution of grain oriented alumina ceramics with high transparency

Hot‐pressing platelet alumina to transparency

“…The best platelet alumina sample in this study (P‐1800‐0‐10‐7) has an in‐line transmission of 65.3% at 645 nm. At the time of publication, and to the best knowledge of the authors, this is the fourth highest in‐line transmission reported for transparent alumina . It is noteworthy that this platelet alumina sample was hot‐pressed at lower pressures (10 MPa) when compared to equiaxed‐alumina samples from HIP or SPS at higher pressures (>200 MPa) .…”

“…However, alumina is birefringent due to its anisotropic rhombohedral crystal structure, causing light scattering at the grain boundaries and limiting transparency . It has been shown that light scattering from birefringence can be minimized by aligning alumina powders along the same crystallographic direction with a high magnetic field prior to densification . While this alignment method is effective, it may be limited in terms of scalability as the high magnetic fields required (>12 T) can only be obtained in small volumes.…”

“…Relative densities greater than 99.95% are required to achieve transparency in polycrystalline ceramics . There are several different sintering methods used to process alumina to such densities, including pressureless sintering . hot‐isostatic pressing (HIP), spark plasma sintering (SPS), and hot pressing .…”

“…Heuer et al claimed that by applying the pressure at the maximum temperature, substantial primary recrystallization occurs in the powder compact, which assists in densification. However, they used an equiaxed‐morphology alumina powder in their studies, as have all other studies aiming to produce transparent alumina . To the extent of the author's knowledge, there have been no reported attempts to hot‐press platelet‐morphology alumina powder to transparency.…”

Effects of heating rate on the microstructure and mechanical properties of rapid vacuum sintered translucent alumina

“…Rapid vacuum sintering has rapid heating and cooling rates at the sintering temperature below 1700 1C, meanwhile it can achieve considerably high density within very short sintering time (in ten minutes). Thus compared with the above mentioned sintering methods rapid vacuum sintering manifests distinct advantages in preparing ultrafine materials [12][13][14]. As a result of its lower sintering temperature and shorter sintering time, the grain size and size distribution of its products can be controlled.…”