Manufacture of Porous Frit Vents Using Space Holder Methodology for Radioisotopic Space Power Systems

Porous pure copper frits were produced by sintering via both pressureless and space holder methods. Frits function both as a gas pressure release path and radioisotopic fine filter for radioisotopic thermoelectric generators (RTG's) and radioisotopic heater units (RHU's). Highly precise and reproducible flow rates are a fundamental requirement in frit vent design, hence accurate characterisation of their morphological structure is crucial. A novel bulk sample characterisation algorithm "GAKTpore" is applied to scanning electron microscope (SEM) maps to study and quantify the effects of processing parameters on sample heterogeneity, pore dispersion, and pore morphology. The purpose of the investigation is to refine the process-property relationships and achieve manufacturable repeatable homogeneous morphological structures. In this study, copper was used as a surrogate for platinum alloys. All frits were tested via a purpose-built/in-house helium precision-flow rig in order to establish a link between permeability and surface morphology. Frits manufactured via the space holder route displayed great potential for the future development of the manufacture of frit vents for European RTG and RHU development programs.