Mössbauer spectroscopy was used to study the microstructures in a synthetic analogue of an Apollo 15 green glass. Different quench rates are found to yield glass structures that are markedly different with respect to iron atom site occupation and charge. Faster quenching rates yield a less dense structure that can accommodate more iron in four-fold sites. In the denser glasses (more slowly cooled) the iron tends to favor higher coordination. The short distances between six- and four-fold sites in the structure (on the order angstroms) provide that the iron will come to its "equilibrium" partitioning value in the structure that is formed on quenching. This structure is representative of the melt at the specific glass transition temperature for the quenching rate experienced. Samples quenched into air exhibit metastable valence state changes. This ionization process occurs during the longer cooling time and may be driven by the structural densification within the melt as cooling takes place. Such structural changes are correlated with the structure of lunar green glass sample # 15426, and possible genetic interpretations are considered.
ASJC Scopus subject areas
- Ceramics and Composites
- Electronic, Optical and Magnetic Materials