Fabrication of transparent ceramics by millimeter‐wave sintering

Abstract

The distinctive features of the millimeter‐wave sintering which make a method appealing for fabrication of optical ceramics are discussed. Among them are the absence of high temperature resistive heaters and the problem of their service life, favorable for elimination of porosity the inverse temperature distribution inherent in the volumetric microwave heating, highly uniform distribution of the millimeter‐wave energy in applicators allowing for the sintering of large‐size articles. This paper reports the results of the research on fabrication of optically transparent ceramics of compositions Nd:Y2O3, Yb:YAG, and Yb:(LaY)2O3 using a gyrotron‐based set‐up operating at frequency of 24 GHz. The green bodies of different compositions were compacted from powders produced by different methods: Nd:Y2O3 from the powder synthesized by laser evaporation of the target, Yb:YAG from a mixture of commercial powders, Yb:(LaY)2O3 from powder fabricated by self‐propagating high‐temperature synthesis. Laser oscillation was obtained from the sintered samples of all compositions. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Transparent Ceramics at 50: Progress Made and Further Prospects

“…were able to obtain significant (albeit not high) transparency for alumina, spinel and γ‐AlON by MW sintering at high temperature without subsequent HIP; High‐frequency MW sintering has yielded the best results with Bykov et al. producing transparent disks of Nd:Y 2 O 3 , Yb:YAG ( T ~78% for t = 0.5 mm), and Yb:(LaY) 2 O 3 using a gyrotron‐powered machine working at 24 GHz . While impressive, the results are not yet (for thicker parts) at a level allowing the use of such parts in laser applications.…”

Flash Microwave Sintering of Transparent Yb:(LaY)2O3 Ceramics

“…The common practice of laser ceramics fabrication involves sintering in resistive ovens at a temperature of about 1750°C for up to 20 h, usually in high vacuum or in hydrogen atmosphere . Recently, following the conventional long‐term sintering procedure (heating at a rate of 2°C…6°C/min up to 1770°C with a hold for 10 h), 5 at.% Yb:(La 0.1 Y 0.9 ) 2 O 3 ceramic samples with the optical properties that enable lasing were sintered using the 24 GHz microwave power . In this study, the same materials are microwave sintered in the flash sintering mode.…”

“….6°C/min up to 1770°C with a hold for 10 h), 5 at.% Yb:(La 0.1 Y 0.9 ) 2 O 3 ceramic samples with the optical properties that enable lasing were sintered using the 24 GHz microwave power. 18 In this study, the same materials are microwave sintered in the flash sintering mode. The factors that are responsible for the flash microwave sintering effect are discussed, along with its similarity and dissimilarity with the flash sintering under an applied voltage.…”

Y2O3-doped Al2O3 transparent ceramics prepared by low temperature microwave sintering

“…Y 2 O 3 is commonly used as grain-growth inhibitor in alumina ceramic for obtaining small grain size, which is an important prerequisite for producing transparent ceramic [1] . Microwave process offers several advantages, such as more rapid and uniform heating, shorter processing time, finer microstructure, enhanced densification and improved materials properties [2] .…”