Nuclear track microfilters: gas separation ability and β-radiation stability

Abstract

Nuclear track microfilters were produced by irradiating the polyimide foil UPILEX with highly energetic heavy ions and subsequent etching with sodium hypochlorite solution. Pore diameters and shape were investigated by scanning electron microscopy and a replica technique where the pores were electrochemically filled with metal. The results show that it is possible to form straight cylindrical pores with diameters in the range of 100 nm . The flow rate of air through the microfilters was determined. It turned out to be a linear function of the pore diameter at this pore size. With increasing pressure, the flow rate increases. At a certain level, the increase becomes non-linear, almost exponential. It can be assumed that this is due to stress-induced deformation of the polymer with an increase in the pore diameter. With the model system carbon monoxide and carbon dioxide the microfilters were tested for their ability for gas separation. Gas chromatographic measurements show that carbon monoxide penetrates faster through the microfilter, rendering gas separation possible. Possible applications of such microfilters for separating gases include radiation environment such as fusion reactors. For testing the β-radiation stability, the microfilters were stored in tritium gas. The microfilters appeared to be radiation resistant. After the storage time, no changes in the microfilter properties were found.