Intergranular Films and Pore Surfaces in Synroc C: Structure, Composition, and Dissolution Characteristics

Abstract

High-resolution electron microscopy and scanning electron microscopy were used to determine the distribution of intergranular films, triple-point regions, and microvoids in synroc C. Diffraction contrast derived from interphase fdms, which were 1 to 3 nm thick, and from triple points showed them to be ill-defined crystallographically, and they may be described as glassy. Pores were usually several micrometers in extent and occurred principally in rutile-rich areas. The chemical composition of these structural features was obtained using analytical transmission electron microscopy, secondaryion mass spectrometry, X-ray photoelectron spectroscopy, and scanning Auger microscopy. Within intergranular films, elemental enhancement of cesium, sodium, potassium, and aluminum, and possibly silicon and molybdenum, was observed. Enhancement of cesium, sodium, phosphorus, aluminum, and silicon was found in triple-point regions. Fracture faces preferentially expose boundaries between grains, and ion exchange of specific elements (e.g., Cs, Na, Ca, and Al) from these surfaces proceeds rapidly at ambient temperatures. During the fabrication of synroc c , microvoids trap cesium vapor, and after cooling this condenses onto their surfaces. Recognition of the (simulated) waste species which segregate to intergranular films, triple points, and pores permitted the reinterpretation of published leach data for monolithic and crushed synroc C.

Mineralization of Radioactive Wastes by Fluidized Bed Steam Reforming (Fbsr): Comparisons to Vitreous Waste Forms, and Pertinent Durability Testing

“…This includes, but is not limited to, the following waste forms: SYNROC, Pu-ceramics, High Al-tailored ceramics, and supercalcines. [113,114,115,116,117,118,119] In particular, it has been determined that waste impurities tend to stabilize in the intergranular glassy phase and result in elemental losses which are an order of magnitude greater for some radioactive waste species. [118] Therefore, if radionuclides have preferentially partitioned to one phase or to the intergranular phase at elevated temperatures, these elements must be directly monitored during a durability test.…”

Evaluation of Synroc-C as a second-generation waste form

“…Another possibility is that the Cs released is from intergranular sites rather than from crystalline sites, so only residual Cs that is not structurally bound in crystals is dissolved. This type of mechanism has been suggested by Cooper et al (1986) on the basis of high-resolution electron microscope examination of Synroc-C.…”

Minerals, Ceramics and Glasses

“…Some examples of the use of these techniques applied to a fine-grained ceramic can be found in [36,37]. Comparison of results from each technique applied to the same material is often useful because the different analysis depths, i.e. "'"…”

“…The use of XPS and static SIMS in studies of fracture faces of ceramics can be particularly useful in these applications [37]. The use of XPS and static SIMS in studies of fracture faces of ceramics can be particularly useful in these applications [37].…”