Liquid-liquid phase separation and phase diagrams of simulated Fernald waste glasses
- Catholic Univ. of America, Washington, DC (United States)
Previous study of crystallization behavior in heat-treated Fernald waste glasses has produced an extensive data base of crystal phases likely to appear in various composition ranges and their corresponding liquidus temperatures. In addition, we have frequently observed amorphous phase separation in these glasses and, occasionally, evidence of crystallization originating from such phase separation. These glasses contain more than 10 components. The composition ranges for the major components are: MgF{sub 2} 10-26 wt%; CaO 4-27 wt%; Al{sub 2}O{sub 3} 3-15 wt%; SiO{sub 2} 25-40 wt%. The morphology of the phase separation as observed in the Scanning Electron Microscope (SEM) is dark, spherical, globules dispersed in a continuous matrix. Globules are depleted in Mg, Ca and F, and enriched in Al and Si compared to the matrix. Phase separation occurs more frequently in melts relatively higher in Si and F. A more systematic study on a simplified and simulated seven component system (Al{sub 2}O{sub 3}, B{sub 2}O{sub 3}, CaO, Fe{sub 2}O{sub 3}, SiO{sub 2}, Na{sub 2}O and MgF{sub 2}) has been undertaken to determine the subliquidus miscibility gap and liquidus curve data. Glasses were formulated by varying the concentrations of MgF{sub 2}, CaO, Al{sub 2}O{sub 3}, and SiO{sub 2} within the ranges specified above at fixed levels of Fe{sub 2}O{sub 3}, B{sub 2}O{sub 3} and Na{sub 2}O. The miscibility gap and liquidus curve were obtained by heat-treating the glass samples at different temperatures and observing any phase separation and crystallization in the SEM and the Transmission Electron Microscope (TEM). We report the results of this study to enhance the understanding of the thermodynamic properties of multi-component silicate systems which are usually the basis of nuclear waste glasses.
- OSTI ID:
- 47893
- Report Number(s):
- CONF-931108--Vol.333
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
BOROSILICATE GLASS
FEED MATERIALS PRODUCTION CENTER
FLUORIDES
LOW-LEVEL RADIOACTIVE WASTES
PHASE DIAGRAMS
PHASE STUDIES
RADIOACTIVE WASTE MANAGEMENT
RADIOACTIVE WASTE PROCESSING
REMEDIAL ACTION
SCANNING ELECTRON MICROSCOPY
TRANSMISSION ELECTRON MICROSCOPY
VITRIFICATION