Transmittance enhancement of spark plasma sintered CaF2 ceramics by preheating commercial powder

• Published in: Journal of the European Ceramic Society Vol. 41; no. 8; pp. 4609 - 4617
• Main Authors: Wang, Ping, Huang, Zhifeng, Morita, Koji, Li, Qizhong, Yang, Meijun, Zhang, Song, Goto, Takashi, Tu, Rong
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-07-2021
• Subjects: CaF2 transparent ceramics; Carbon contamination; Preheating; Specific surface area; Transmittance; Specific surface area; Carbon contamination; CaF2 transparent ceramics; Preheating; Transmittance
• ISSN: 0955-2219; 1873-619X
• DOI: 10.1016/j.jeurceramsoc.2021.03.014

•The highest transmittance of CaF2 ceramic using commercial powder was prepared by SPS up to now.•Source and interdiffusion of carbon contamination were investigated.•The relationship between large grain size and transmittance was firstly reported in CaF2 transparent ceramics.•Discoloration disappear due to the microstructure change of powders caused by preheating treatment.
Spark plasma sintering (SPS) is a convenient approach for preparing transparent CaF2 ceramics. However, carbon contamination is a key issue that should be addressed to achieve high transparency. In this study, a commercially available CaF2 powder was preheated under vacuum before performing SPS to mitigate carbon contamination. During the preheating of the CaF2 powder, impurities adsorbed on the particle surface, such as H2O, CO2, and O2, are desorbed. Moreover, the interdiffusion of carbon contaminants is suppressed due to the pre-sintering of the raw powder. The in-line transmittance of the CaF2 ceramic prepared from the preheated powder increased to 85 % at the wavelength of 1100 nm, which is 38 % higher than that of the ceramic prepared without preheating. In addition, the in-line transmittance increased with increasing grain size of the ceramic, possibly because of the decrease in the number of scattering sources with the reduction in the grain boundary fraction.