Time-Temperature Transformation Phase Diagrams for Developing Advanced Glass Ceramic Nuclear Waste-forms

该项目的目的是了解英国废玻璃中陶瓷相的成核和生长，以开发整体玻璃陶瓷（GC）废物形式，以固定临界裂变产物（FP），否则这些产物会从玻璃基质中相分离出来。硼硅酸盐玻璃（BSG）已用于固定高放射性废物，虽然大多数FP可容纳在玻璃基质中，但一些FP如Mo、镧系元素和贵金属在BSG中的溶解度有限，因此它们发生相分离/结晶。陶瓷氧化物可以在其稳定的晶体结构中包含这些FP，并且更耐浸出和辐射损伤。因此，需要设计玻璃陶瓷（GC），其在熔融温度下为单相硼硅酸盐玻璃，同时经历液相分离，然后在缓慢冷却时大块结晶成目标相。因此，即使正确的化学计量应确保形成所需的晶相，但改变冷却速率也会影响玻璃基质中晶相的形成。因此，有必要发展一个基本的了解导致从熔体到GC wasteform作为功能的冷却速率和composition.Work的相变将涉及了解热化学因素吸引不同的陶瓷相结晶内的CaZn BSG矩阵和研究各种冷却速率的影响，以模仿那些发生在真实的大规模的玻璃wasteform制造过程。将使用衍射技术、电子显微镜和化学分析工具来表征陶瓷的微观结构和结构相。还将进行原位XRD和DSC，以密切监测结晶的开始。将对项目最后阶段的样品进行浸出（腐蚀）和耐辐射性能测试，并与目前使用的CaZn BSG进行比较。

The purpose of this project is to understand nucleation and growth of ceramic phases in UK's waste glasses in order to develop monolith glass-ceramic (GC) wasteforms to immobilize critical fission products (FP) that otherwise phase segregate out of the glass matrix. Borosilicate glasses (BSG) have been used for immobilizing high-level waste and while most FP's can be accommodated in the glass matrix, some FPs like Mo, lanthanides, and noble metals have limited solubility in BSG and hence they phase separate/crystallize. Ceramic oxides can incorporate these FPs in their stable crystal structure, and are more resistant to leaching and radiation damage.Thus there is a need to design glass ceramics (GC) that are single-phase borosilicate glass at melting temperatures while undergoing a liquid-phase separation, followed by bulk crystallization into targeted phases upon slow cooling. Thus, even though correct stoichiometry should ensure formation of the desired crystalline phases, varying cooling rates can affect the formation of crystalline phase in the glass matrix. Hence there is a need to develop a fundamental understanding of the phase-transformations leading from melt to GC wasteform as function of cooling rate and composition.Work will involve understanding thermo-chemical factors attracting the crystallization of different ceramic phases inside a CaZn BSG matrix and studying the effects of various cooling rates to mimic those occurring in real large-scale glass wasteform fabrication processes. The microstructure and structural phase of the ceramics will be characterized using diffraction techniques, electron microscopy and chemical analysis tools. In-situ XRD and DSC will also be performed to closely monitor the onset of crystallization. The samples in the final phase of the project will be tested for their leaching (corrosion) and radiation tolerant properties compared against the presently used CaZn BSG.