Full
DONG Xuanjiang (1996-), female, Master candidate. E-mail: 635999416@qq.com
Outline
This 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.
Glass 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.
The 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.
This 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.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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