Development of the capillary flow porometry technique for the characterization of gasoline particulate filter walls

Abstract

The capillary flow porometry (CFP) technique was studied and implemented for the characterization of porous ceramic materials used in gasoline particulate filters (GPFs). To implement and apply the technique to these materials the impacts of CFP experimental parameters were studied. Measurement results using a ceramic wall-flow filter sample were used to determine operation parameters needed to perform accurate CFP measurements. The results demonstrated that higher molecular weight silicone oil fluids (AK 5 and AK 10) have sufficiently low volatility to avoid issues with evaporation of the wetting liquid during testing that was seen with conventional fluorocarbon-based porometry liquids and a low molecular weight (high volatility) silicone fluid (AK 0.65). To use the high molecular weight silicone fluids for dry curves obtained after wet-curve measurements, baking samples in an oven for 2 h at 550 °C was required to completely dry the sample. It was also found that replicate wet and dry tests did not impact filter microstructure, allowing repeated tests to be performed on the same sample. Appropriate pressure ramps rates when using the AK 5 and AK 10 wetting fluids were determined to be less than 2.52 kPa/min. Using the CFP parameters determined, the technique was applied to study the characteristics of 10 different ceramic filter wall samples composed of cordierite and aluminum titanate. The sample CFP results showed that pore throat sizes fell within a range from ∼15 to 42 μm for the samples tested. A linear relationship between the mean flow diameter from CFP and the median pore diameter from mercury intrusion porosimetry (MIP) with an R2 value of 0.97 and a slope of 0.68 ± 0.04 μm/μm was found, potentially indicating that it might be possible to substitute CFP data taken using non-toxic fluids for MIP results in some instances.