OS3-10
希⼟類珪酸塩ガラスの作製と相転移挙動の観察
Fabrication of rare earth silicate glasses and observationof phase transition behavior
⼤川采久 1, Nguyen Thanh Son2, ⻑⾕川拓哉 1, 中⼭忠親 3, ⽯川毅彦 4, 下⻄⾥奈 4, ⼩⼭千尋 4, 織⽥裕久
, Do Thi Mai Dung3, 殷澍 1, 5Ayahisa OKAWA1, Nguyen Thanh SON2, Takuya HASEGAWA1, Tadachika NAKAYAMA3, Chihiro
KOYAMA4, Hirohisa ODA4, Rina Shimonishi4, Takehiko ISHIKAWA4, Do Thi Mai Dung3 and Shu
YIN1,54

東北⼤学 多元物質科学研究所, Institute of Multidisciplinary Research for Advanced Material (IMRAM), TohokuUniversity1釧路⼯業⾼等専⾨学校 創造⼯学科, Department of Creative Engineering, National Institute of Technology, Kushiro
College2

⻑岡技術科学⼤学 極限エネルギー密度⼯学研究センター，Extreme Energy-Density Research Institute, Nagaoka
University of Technology

345

宇宙航空研究開発機構, Japan Aerospace Explanation Agency, Tsukuba
東北⼤学 材料科学⾼等研究所, Advanced Institute for Materials Research (WPI-AIMR), Tohoku University

1. Introduction
SiC fiber reinforced SiC matrix composites (SiCf/SiCm) demonstrate potential as the next generation ofgas turbine blades. However, SiC exhibits recession at high temperatures in an atmosphere with high watervapor. Therefore, an environmental barrier coating (EBC) is required. A general EBC system includes a Si bondcoat, which obstructs oxidation and enhances adhesion, and a top coat of rare earth (RE) silicates such as
RE2SiO5 and RE2Si2O7. Recently, high entropy RE silicates with five or more equivalent molar RE have garneredattention to improve the properties for EBC. The most promising structure is the polymorphism-free
β-RE2Si2O7 structure (with 6-coordination of RE less than 0.885 Å)1).
To prevent water vapor recession of SiC, the EBC must be dense. However, coatings fabricated bytypical thermal spraying processes are rapidly cooled and amorphized by the temperature difference with thesubstrate. Subsequent annealing crystallizes the coating, but eventually cracks and pores remain,compromising the effectiveness of the EBC. Although an irreversible phase transition from a metastable phase
to a stable phase with volume expansion during annealing is attractive to cause crack healing in coatings2), an
understanding of the thermal evolution of the coating microstructure and phases has not been established.
The analysis is complicated by the volatilization of SiO in thermal spraying, the local element segregation ofthe coatings3), and the multi-element composition of RE4). In addition, the thermophysical properties which
are important parameters in thermal spraying5), have not been reported for RE silicate. The purpose of thisstudy is to reveal the thermal evolution of microstructure and phases in RE silicate glasses without local
element segregation, thereby demonstrating crack healing, and to measure the thermophysical properties.
1 of 3

2.

Experimental Procedures
The RE elements Lu, Yb, Er, Y, and Ho were chosen to form β-RE2Si2O7. Henceforth, RE sites with equal

molar ratios of Lu, Yb, and Er will be denoted as 3RE, and when Ho and Y are included, it will be represented
as 5RE. RE nitrate (RE(NO3)3・nH2O) and sodium silicate (Na2SiO3・9H2O) were dissolved in 30 mL of distilledwater, respectively. The solutions were prepared to have stoichiometric ratios of RE:Si = 0.5 and 1.0. 2M HCl
was added to the Na2SiO3 solution, while diluted ammonia was added dropwise to the RE(NO3)3 solutions.
The two solvents were mixed, followed by sealing the mixed solution in a 100-mL autoclave with a 70% fillrate and holding at 220°C for 3 h. After washing by centrifugation, the obtained powder was exposed at 1600°C
for 10 h in air. The powder was irradiated with a CO2 laser using a gas-levitation furnace. The crystallographic
phases of the powders before irradiated with a CO2 laser were analyzed using X-ray diffraction. The CO2 laserirradiated samples were measured by Raman spectroscopy.
3.

Results and discussion
From the XRD patterns, the main phases of the synthesized RE2Si2O7 and RE2SiO5 powders wereidentified as β-RE2Si2O7and X2-RE2SiO5, respectively. The diffraction peaks are slightly shifted toward thelower diffraction angles as the average RE ionic radius becomes larger than that of Yb as the RE element
increases, causing lattice expansion. Figure 1 shows the photograph of CO2 laser irradiated samples. RE2SiO5
showed recalescence after melting and quenching. In addition, RE2SiO5 was non-transparent, which suggests
crystallization. Whereas RE2Si2O7, with a SiO2-rich composition, was transparent and vitrified, and pores wereobserved in the appearance of RE2Si2O7. The Raman spectrum of RE2SiO5, the increase in the RE elements
causes a marked broadening of the peak widths, indicating the presence of disordered atomic bonding. Inaddition, the Raman peaks corresponding to the Si-O bonds also become broader, which is attributed to thelattice distortion of the Si- and O- sublattices6). On the other hand, glassy RE2Si2O7 shows only broad bands,suggesting that it was amorphous, similar to the as-sprayed RE2Si2O77).
Figure 1. Photograph of the appearance of RE silicate after irradiation with a CO2 laser

References
1) Luo, Y., Sun, L., Wang, J., Du, T., Zhou, C., Zhang, J., Wang, J.: Phase formation capability andcompositional design of β-phase multiple rare-earth principal component disilicates. Nat. Commun., 14(2023) 1275, https://doi.org/10.1038/s41467-023-36947-62) Bakan, E., & Vaßen, R.: Crack healing mechanisms in atmospheric plasma sprayed Yb-silicate coatings
during post-process heat treatment, J Euro. Ceram. Soc., 43 (2023) 3684-3693,
https://doi.org/10.1016/j.jeurceramsoc.2023.02.0053) Vaßen, R., Bakan, E., Gatzen, C., Kim, S., Mack, D. E., Guillon, O.: Environmental barrier coatings madeby different thermal spray technologies, Coatings, 9 (2019) 784, https://doi.org/10.3390/coatings9120784
4) Peng, Y., Luo, Z., Wang, H., Du, T., Zhang, J., Sun, L., Wang, J.: Crystallization and phase evolution innovel (Gd1/6Tb1/6Dy1/6Tm1/6Yb1/6Lu1/6)2Si2O7 environmental barrier coating. Int. J. Appl. Ceram., 20(2023) 896, https://doi.org/10.1111/ijac.14210
5) Nasiri, M. M., Dolatabadi, A., & Moreau, C.: Modeling of liquid detachment and fragmentation during theimpact of plasma spray particles on a cold substrate, Int. J. Heat Mass Transf., 189 (2022) 122718,
https://doi.org/10.1016/j.ijheatmasstransfer.2022.122718
6) Liu, X., Zhang, P., Huang, M., Han, Y., Xu, N., Li, Y., Zhang, Z., Pan, W., Wan, C.: Effect of lattice distortion
2 of 37)

in high-entropy RE2Si2O7 and RE2SiO5 (RE= Ho, Er, Y, Yb, and Sc) on their thermal conductivity:
Experimental and molecular dynamic simulation study. J. Euro. Ceram. Soc., 43 (2023) 6407,
https://doi.org/10.1016/j.jeurceramsoc.2023.06.052
Garcia, E., Sotelo-Mazon, O., Poblano-Salas, C. A., Trapaga, G., & Sampath, S.: Characterization of
Yb2Si2O7–Yb2SiO5 composite environmental barrier coatings resultant from in situ plasma sprayprocessing. Ceram. Int., 46 (2020) 21328, https://doi.org/10.1016/j.ceramint.2020.05.228© 2023 by the authors. Submitted for possible open access publication under theterms and conditions of the Creative Commons Attribution (CC BY) license(http://creativecommons.org/li censes/by/4.0/).

3 of 3