@article{DONG2025, 
author = {Xuanjiang DONG and Debo YANG and Zhu CUI and Dongyu WANG and Yunjie JIAO and Zhanyuan DU and Kun ZHAO and Yongchang ZHU},
title = {Effect of Mixed Alkali on Structure and Properties of R2O–CaO–Al2O3–SiO2 Glass},
year = {2025},
journal = {Journal of the Chinese Ceramic Society},
volume = {53},
number = {12},
pages = {3770-3778},
keywords = {calcium aluminosilicate glass, mixed alkali effect, raman spectroscopy, infrared spectroscopy, high temperature resistivity},
url = {https://www.sciopen.com/article/10.14062/j.issn.0454-5648.20250310},
doi = {10.14062/j.issn.0454-5648.20250310},
abstract = {IntroductionThis study was to investigate the influence of mixed alkali effect on the structure and properties of a R2O–CaO–Al2O3–SiO2 glass system, to provide theoretical support and practical guidance for optimizing the formulation of high–level radioactive liquid waste (HLW) glass vitrification technology. The safe disposal of HLW is a critical aspect for the sustainable development of the nuclear industry. The Joule-heated melter vitrification as an internationally engineered and implemented method could immobilize radioactive waste via melting HLW with base glass frit in an electric furnace to form a stable vitrified product for long-term containment.MethodsGlass samples with varying Z-values (i.e., Z = n(Na2O)/(n(Na2O) + n(Li2O)) were prepared by a high-temperature melting method. Their structure and properties were systematically analyzed by infrared spectroscopy, Raman spectroscopy, and high-temperature resistivity analysis.Results and discussionThe structural characterization revealed that the silicate tetrahedral units Q2 and Q3 are the primary structural units influencing glass properties. The structure exhibits regular changes as Z-value increases. At Z=0.2, the proportions of Q3 and Q4 reach the maximum values, while Q1 and Q2 reach the minimum values. At Z=0.6, Q1, Q3, and Q4 proportions reach the maximum values, while Q2 reaches the minimum value, indicating the most compact glass structure and the most significant mixed-alkali effect.The results of performance tests demonstrate that the physical and thermal properties both are governed due to the mixed–alkali effect The density and thermal expansion coefficient both increase with increasing Z-value. The density reaches the maximum value as Z=0.6, while the thermal expansion coefficient has the minimum value. The glass transition temperature (Tg) initially decreases and then increases, reaching its minimum as Z=0.2. The high-temperature viscosity has the maximum value as Z=0.4 and the minimum value as Z=0.6.For the electrical properties in single-alkali systems, the resistivity at the melting temperature (T2) decreases in an order of K2O > Na2O > Li2O, while it at the forming temperature (T4) decreases in an order of K2O > Li2O > Na2O. In the mixed-alkali system, the resistivity reaches the maximum value at Z of 0.6–0.8, being correlated to the "blocking effect" of alkali ions. The activation energy for electrical conduction changes nonlinearly with Z-value. In single-alkali systems, it increases in the order of Na2O < Li2O < K2O.ConclusionsThis study clarified the mixed-alkali effect on the R2O–CaO–Al2O3–SiO2 glasses, particularly highlighting the low viscosity as Z = 0.6 and the high resistivity characteristics as Z = 0.6–0.8. These findings could provide a clear guidance for glass formulation design.}
}