Nanocrystalline powders of Ce 0.5 Zr 0.5 O 2 were synthesized and characterized for the application as a catalyst support and oxygen storage medium in automotive catalysis. Detailed pair-distribution function analysis of the neutron diffraction data revealed an unusual structure of the nanocrystallites, consisting of domains of Ce 0.4 Zr 0.6 O 2 composition of ∼25-30 Å in size in a matrix of Ce 0.7 Zr 0.3 O 2 . The domains cannot be detected by conventional diffraction analysis because the crystallographic structure and orientation of the atomic planes are the same for all ceria-and zirconia-enriched regions within the crystallite, which therefore gives rise to Bragg scattering as a whole. The oxygen storage capacity did not show a correlation with either crystallite size or surface area of the samples. We suggest that the smaller size of zirconia-enriched domains associated with larger interfacial area between ceria-and zirconia-enriched regions is responsible for the increase in oxygen storage capacity.

A simple model is presented for the elastic behavior of a powder compact that has undergone small amounts of sintering. The analysis shows that the elastic constants are sensitive to small changes in the interparticle contact areas. The elastic constants are also shown to be dependent on factors relating to the structure of the powder compact, such as the particle coordination number. It is concluded that such elastic constant measurements are a valuable tool in studying adhesion within compacts, the mechanisms involved in the initial stages of sintering and the characterization of powders.

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Black carbon (BC) mass and solid particle number emissions were obtained from two pairs of gasoline direct injection (GDI) vehicles and port fuel injection (PFI) vehicles over the U.S. Federal Test Procedure 75 (FTP-75) and US06 Supplemental Federal Test Procedure (US06) drive cycles on gasoline and 10% by volume blended ethanol (E10). BC solid particles were emitted mostly during cold-start from all GDI and PFI vehicles. The reduction in ambient temperature had significant impacts on BC mass and solid particle number emissions, but larger impacts were observed on the PFI vehicles than the GDI vehicles. Over the FTP-75 phase 1 (cold-start) drive cycle, the BC mass emissions from the two GDI vehicles at 0 °F (-18 °C) varied from 57 to 143 mg/mi, which was higher than the emissions at 72 °F (22 °C; 12-29 mg/mi) by a factor of 5. For the two PFI vehicles, the BC mass emissions over the FTP-75 phase 1 drive cycle at 0 °F varied from 111 to 162 mg/mi, higher by a factor of 44-72 when compared to the BC emissions of 2-4 mg/mi at 72 °F. The use of a gasoline particulate filter (GPF) reduced BC emissions from the selected GDI vehicle by 73-88% at various ambient temperatures over the FTP-75 phase 1 drive cycle. The ambient temperature had less of an impact on particle emissions for a warmed-up engine. Over the US06 drive cycle, the GPF reduced BC mass emissions from the GDI vehicle by 59-80% at various temperatures. E10 had limited impact on BC emissions from the selected GDI and PFI vehicles during hot-starts. E10 was found to reduce BC emissions from the GDI vehicle by 15% at standard temperature and by 75% at 19 °F (-7 °C).