No abstract

Non-catalytic oxidation kinetics of diesel engine soot and more than a dozen commercial carbon black samples was investigated using non-isothermal and isothermal thermogravimetric analysis (TGA) experiments. The effect of various operating parameters, such as oxygen flow rate, initial sample mass, oxygen partial pressure, crucible type, and ramp rate, on the oxidation rate was investigated. Three types of TGA experiments (non-isothermal single-ramp rate, non-isothermal multiple-ramp rates, and isothermal) were conducted and analyzed to extract the kinetic parameters for oxidation. Activation energies for oxidation of carbon black samples ranged from 125 to 257 kJ/mol, whereas that for soot oxidation was ∼155 kJ/mol. Furthermore, oxidation rate trends were explained on the basis of structural characteristics, such as scanning electron microscopy (SEM)-based average particle size and Brunauer–Emmett–Teller (BET) surface area. In general, a low particle size and high surface area were associated with a higher oxidation rate and vice versa. A thorough understanding of the non-catalytic oxidation kinetics developed in this work along with the correlation of the oxidation rate with the structural parameters may assist in efficient oxidation of diesel engine soot during the regeneration of diesel particulate filters.

A silica-filled polydimethylsiloxane (PDMS) composite M9787 was investigated for potential outgassing in a vacuum/dry environment with the temperature programmed desorption/reaction method. The outgassing kinetics of 463 K vacuum heat-treated samples, vacuum heat-treated samples which were subsequently re-exposed to moisture, and untreated samples were extracted using the isoconversional and constrained iterative regression methods in a complementary fashion. Density functional theory (DFT) calculations of water interactions with a silica surface were also performed to provide insight into the structural motifs leading to the obtained kinetic parameters. Kinetic analysis/model revealed that no outgassing occurs from the vacuum heat-treated samples in subsequent vacuum/dry environment applications at room temperature (∼300 K). The main effect of re-exposure of the vacuum heat-treated samples to a glove box condition (∼30 ppm by volume of H2O) for even a couple of days was the formation, on the silica surface fillers, of ∼60 ppm by weight of physisorbed and loosely bonded moisture, which subsequently outgasses at room temperature in a vacuum/dry environment in a time span of 10 yr. However, without any vacuum heat treatment and even after 1 h of vacuum pump down, about 300 ppm by weight of H2O would be released from the PDMS in the next few hours. Thereafter the outgassing rate slows down substantially. The presented methodology of using the isoconversional kinetic analysis results and some appropriate nature of the reaction as the constraints for more accurate iterative regression analysis/deconvolution of complex kinetic spectra, and of checking the so-obtained results with first principle calculations such as DFT can serve as a template for treating other complex physical/chemical processes as well.