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.
