Prof.  Guoqin  Cao
Zhengzhou University,  China

Title: Zr-Si based coating materials: Opportunities and challenges

Abstract:

Silicide materials, especially zirconium silicide, have good thermal matching characteristics and chemical compatibility with zirconium alloy, as well as structural stability and oxidation resistance at high temperature. In recent years, based on the far-source plasma sputtering system, the research group has done detailed research on the application of zirconium-silicon based coatings through the design of composition and structure. The specific research contents are as follows: 1) The structure of Zr/Si multilayer films was designed, and the competitive formation and multilevel protection effect of amorphous passivation films at Zr-Si-O (ZSO) interface were confirmed. In the multilayer system, the phase selection of amorphous ZSO was a scale-dependent process determined by the competitive consumption of Zr layers by silicification and oxidation. 2) Based on the characterization of XPS and EELS, the oxygen-induced chemical bond reassignment (OBR) process and the formation mechanism of amorphous Zr-Si-O layer in the initial normal working condition of Zr-Si coating were established for the first time. At the initial stage of oxidation, the surface unoxidized silicon tends to further combine with Zr, resulting in enhanced hybridization between Zr and Si, which was conducive to the formation of amorphous oxide layer. The chemical bond is strengthened and the silicon-rich transition layer was formed by the OBR process. The stability of the amorphous oxides (Zr/Si atomic ratio, 2:1) was maintained. The subsequent bonding relaxation of amorphous ZSO was the key structural basis for water stability. 3) Further, amorphous Zr-Si-O coatings with different Zr/Si atomic ratios were prepared by sputtering method. The adsorption energy of hydroxide on silicon atoms was increased by the change of amorphous bonding structure (-Si-O-Si - → -Zr-O-Si -), and the reaction dissolution of silicon was inhibited in high temperature and high pressure water. On this basis, the bonding mixing enthalpy and the compact arrangement rules of amorphous atoms were combined, and the composition basis of the structural stability of amorphous ZSO coating in the service process was explored (two interfacial stability: Zr/ZSO, ZSO/H2O). Ensuring the content of silicon was high enough was the basis of oxygen resistance, and the contribution of zirconium was reflected in inhibiting the reaction between silicon and high temperature water.
Key words: Silicon solution; bonding state; phase selection; high entropy silicide; high entropy oxide

Biography:

Silicide materials, especially zirconium silicide, have good thermal matching characteristics and chemical compatibility with zirconium alloy, as well as structural stability and oxidation resistance at high temperature. In recent years, based on the far-source plasma sputtering system, the research group has done detailed research on the application of zirconium-silicon based coatings through the design of composition and structure. The specific research contents are as follows: 1) The structure of Zr/Si multilayer films was designed, and the competitive formation and multilevel protection effect of amorphous passivation films at Zr-Si-O (ZSO) interface were confirmed. In the multilayer system, the phase selection of amorphous ZSO was a scale-dependent process determined by the competitive consumption of Zr layers by silicification and oxidation. 2) Based on the characterization of XPS and EELS, the oxygen-induced chemical bond reassignment (OBR) process and the formation mechanism of amorphous Zr-Si-O layer in the initial normal working condition of Zr-Si coating were established for the first time. At the initial stage of oxidation, the surface unoxidized silicon tends to further combine with Zr, resulting in enhanced hybridization between Zr and Si, which was conducive to the formation of amorphous oxide layer. The chemical bond is strengthened and the silicon-rich transition layer was formed by the OBR process. The stability of the amorphous oxides (Zr/Si atomic ratio, 2:1) was maintained. The subsequent bonding relaxation of amorphous ZSO was the key structural basis for water stability. 3) Further, amorphous Zr-Si-O coatings with different Zr/Si atomic ratios were prepared by sputtering method. The adsorption energy of hydroxide on silicon atoms was increased by the change of amorphous bonding structure (-Si-O-Si - → -Zr-O-Si -), and the reaction dissolution of silicon was inhibited in high temperature and high pressure water. On this basis, the bonding mixing enthalpy and the compact arrangement rules of amorphous atoms were combined, and the composition basis of the structural stability of amorphous ZSO coating in the service process was explored (two interfacial stability: Zr/ZSO, ZSO/H2O). Ensuring the content of silicon was high enough was the basis of oxygen resistance, and the contribution of zirconium was reflected in inhibiting the reaction between silicon and high temperature water. Key words: Silicon solution; bonding state; phase selection; high entropy silicide; high entropy oxide