Viscoelastic behaviors and drying kinetics of different aqueous gelcasting systems for large Nd: YAG laser ceramics rods. Issue 6 (16th February 2020) - Yao, Qing
Abstract: Large and nondeforming Nd: YAG ceramic prepared by wet forming is of great importance as gain medium to obtain high‐power solid‐state lasers. However, it is difficult to achieve high‐quality laser ceramics due to insufficiency of the in‐depth understanding of transformation mechanism of gels viscoelasticity and effective control means during drying process. In this work, the rheological behaviors, viscoelastic characteristics, and mechanical strengths in classical acrylamide (AM) and novel Isobam (PIBM) gelcastings were systematically compared to explore the suitable route for the large‐sized 2% Nd: YAG transparent ceramics with high aspect ratio (>10). AM system exhibited a higher complex viscosity (1.82 × 10 5 Pa s), a shorter gel time (92.9 seconds), and a higher flexural strength (about 24.46 MPa) than PIBM system, and especially its ability to quickly gel was beneficial to the homogeneity of green body. In addition, the order of drying rates of wet gels in four drying media was observed as follows: 55℃ hot air> ethanol> solid desiccant> PEG‐11000 and the moisture diffusion coefficients were calculated and simulated to offer the deep consideration of drying kinetics. The "ethanol + 55℃ hot air" was regarded as an effective composite drying method to eliminate defect and to achieve φ 8 mm × 160 mm Nd: YAG ceramic with the in‐line transmittance of 83% @1064 nm. Therefore, not only the cognition of gel process, but also the defects control strategy is proposed. More importantly, this work greatly promotes the application of wet forming and laser ceramics in high‐power lasers.