Structural evolution and synthesis mechanism of ytterbium disilicate powders prepared by cocurrent chemical coprecipitation method

Nannan Wu,Yalei Wang,Rutie Liu,Qingbo Wen,Huaifei Liu,Xiang Xiong

doi:10.1016/j.ceramint.2022.01.011

Abstract

Ytterbium disilicate powders were synthesized by cocurrent chemical coprecipitation method. The influence of Si/Yb molar ratio and calcination temperature on compositions and structures of Yb2Si2O7 products were investigated. The formation mechanism and thermal behavior of precursor as well as the phase evolution of Yb2Si2O7 were also discussed in depth. Results show that pure β-Yb2Si2O7 powders with nanoscale size can be obtained from the precursor with Si/Yb molar ratio of 1.1 after being calcined at temperatures above 1200 °C. The Yb2Si2O7 precursor is an amorphous polymer cross-linked with -[Si–O-Yb]- chain segments which are formed though Yb atoms embedding in the -[Si–O–Si]- network. After a continuous dehydroxylation and structural ordering, the amorphous precursor transformed into α-Yb2Si2O7 crystals by atomic rearrangement. Elevated calcination temperature can induce to the coordination structures and environment evolutions of structural units and then converted to stable (Si2O7) groups and (YbO6) polyhedrons, which results in the formation of β-Yb2Si2O7.

Highlights

SiC ceramic matrix composites (CMCs) have been regarded as new generation hot section materials applied in gas turbine engines due to their excellent high-temperature capability, which can provide critical support for leading the revolutionize development of advanced vehicle technologies
Correlation analysis confirmed that the synthesis temperatures of X1-Yb2SiO5, α-Yb2Si2O7 and β-Yb2Si2O7 are between 900 °C and 1000 °C
With the calcination temperature elevated to 1100 °C, significant compositional change of the Y1 − 1100 and Y2 − 1100 can be observed in the XRD patterns

Summary

Introduction

SiC ceramic matrix composites (CMCs) have been regarded as new generation hot section materials applied in gas turbine engines due to their excellent high-temperature capability, which can provide critical support for leading the revolutionize development of advanced vehicle technologies. SiC CMCs exhibit lower durability in high-velocity combustion resulting from the rapid surface recession in oxidizing and water vapor environment [1, 2]. Environmental barrier coatings (EBCs) emerged as the times require for protecting SiC CMCs substrate materials against corrosive media [3–7]. The Yb2Si2O7 materials exhibit excellent corrosion resistance of water vapor and CaO-MgO-Al2O3-SiO2 (CMAS). B.T. Richards et al [18] prepared a bi-layer Yb2Si2O7/Si EBC coating on SiC substrates through an optimal design of CTE matching, which exhibited excellent steam-cycling durability at 1316 °C in a flowing 90%H2O/10%O2 environment. After 40–50 thermal cycles between room temperature and 1350 °C, the Yb2Si2O7 layer still maintained better structural integrity resulting from their outstanding thermal shock resistance. Comprehensive analysis shows that Yb2Si2O7 materials exhibit great potential applying in EBCs system

Methods

Results

Conclusion