RESUMO
Nano metal oxides are common combustion catalysts for enhancing the burning rate of solid propellants. Cr2O3 nanoparticles (NPs) are efficient combustion catalysts for the pyrolysis of energetic components. In this study, Cr2O3 NPs were synthesized via a modified sol-gel method and further used for studying the thermal decomposition of nitrocellulose (NC). Differential scanning calorimetry (DSC) and thermogravimetry-Fourier-transform infrared spectroscopy (TG-FTIR) analyses indicate that the Cr2O3 NPs can be safely used with NC and the mechanism of the reaction between Cr2O3/NC and pure NC follows the Avrami-Erofeev equation: f(α) = 3(1 - α)[-ln(1 - α)]1/3/2. The peak temperature and activation energy (E a) for the thermal decomposition of Cr2O3/NC are lower than those of pure NC. NO2 was detected at a lower temperature after NC was mixed with Cr2O3 NPs; this indicated the catalytically accelerated bond cleavage of NC by Cr2O3 NPs.
RESUMO
Single grain zircon U-Pb geochronology has demonstrated great potentials in extracting tectonic and atmospheric circulation signal carried by aeolian, fluvial, and fluviolacustrine sediments. A routine in this sort of studies is analyzing 100-150 grains and then compares zircon U-Pb age spectra between the measured sample and the potential sources. Here we compared the zircon U-Pb age results of the late Miocene-Pliocene Red Clay sequence of two neighboring sites from the Chinese Loess Plateau where similar provenance signal is expected. Although the results from the 5.5 Ma sediment support this prediction, the results from the 3 Ma sediment at these two sites differ from each other significantly. These results emphasize the importance of increasing analysis number per sample and combining the zircon U-Pb geochronology with other provenance tools in order to get reliable provenance information.
RESUMO
Well-distributed eolian red clay in a wide area of northern China is believed to imply the onset of an ancient East Asian monsoon system since Late Miocene. Two continuous red clay sequences spanning the time interval 7-2.6 Ma and 11-2.6 Ma in the Chinese Loess Plateau was investigated to determine the magnetic orientation and grain alignment in the primary fabric of eolian sediments. The north-westerly orientation of the AMS of the eolian red clay sequences parallels the material transportation direction, which differs from the model that suggests that airborne dust from overlying loess-paleosol sequences were transported by the East Asian winter monsoon and fixed by the East Asian summer monsoon. Our results further reveal that present-day climate and air circulation patterns differ from those of the pre-Quaternary, and may provide evidence of a prevailing wind during deposition of the red clay.
