Mossbauer Spectroscopic Study of Iron Redox in Silicate Glasses
EMSL Project ID
1014
Abstract
The objective of this study is to determine iron redox (Fe2+/Fe3+) in silicate based glasses prepared under reducing conditions. Recent reviews which have dealt with critical issues regarding the suitability of borosilicate glasses for nuclear waste disposal have identified liquid-liquid immiscibility and crystallization processes as having the potential to alter significantly storage behavior, especially chemical corrosion characteristics. Previous studies showed that multivalent cations such as Fe2+ and Fe3+ in silicate glass affect liquid-liquid immiscibility and crystallization. However, there is a lack of fundamental understanding how these multivalent cations affect glass chemistry resulting in either promoting or suppressing secondary phase formation depending on the redox ratio. In collaboration with the University of Arizona (UA), PNNL provides a technical support to one of their EMSP projects, "The Influence of Radiation and Multivalent Cation Additions on Phase Transformation Behavior in Sodium Borosilicate Glasses". To study the effect of iron redox on glass immiscibility and crystallization, PNNL is requested by UA, in FY 99, to prepare two glasses with different iron redox ratio and to determine the iron redox values using independent spectroscopic methods. The glass denoted AU-1 is composed of 35.7 mol%Na2O - 7.1 mol%Fe2O3 - 57.2 mol%SiO2 and the second one denoted AU-2 is composed of 18.5 mol%Na2O-0.5 mol%Fe2O3-81.0 mol%SiO2.
Iron redox ratios in the UA-1 and UA-2 glasses prepared under reducing conditions varied from 0.6 to 4.4 as determined using a calorimetric method. The technique for the sample preparation involves acid digestion of the powder samples in an ambient condition. It is possible that the iron redox may change during the acid digestion due to the oxidation of Fe2+ in the solution. Determination of reliable iron redox value is very important for this project. Therefore, it is desirable to use an alternative method for an independent check on the iron redox values in glass.
Mossbauer spectroscopy has been widely used to study Fe2+ and Fe3+ ions in silicate and other glass systems. The technique does not require dissolve solid glass in solution and hence the chemical environments of Fe2+ and Fe3+ in the glass are preserved. Therefore, we propose to perform a Mossbauer spectroscopic study determining the iron redox value in four reduced UA-1 and UA-2 glasses which have been measured for iron redox using the colorimetric method. The Mossbauer results from this study will be compared with the data obtained from the calorimetric measurements. A part of this work at PNNL will be combined with research data from the immissibility and crystallization study undertaken at the University of Arizona and published in journal articles.
Project Details
Project type
Exploratory Research
Start Date
1999-02-05
End Date
2000-02-05
Status
Closed
Released Data Link
Team
Principal Investigator
Related Publications
GL Smith, H Li, Kukkadapu RK, JV Crum, J Jeoung, W Poisl, and MC Weinberg. 2003. "Mossbauer and Optical Spectroscopic Study of Temperature and Redox Effects on Iron Local Environments in a Fe-Doped (0.5 mol% Fe2O3) 18Na(2)O-72SiO(2) Glass
." Journal of Non-crystalline Solids 317(3):301-318.