Abstract:In this study, Ce 1x Sm x O 2x/2 ceramics were synthesized by sol-gel route and solid state sintering method. The phase structure was analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy. The morphologies of the synthesized powders and the corresponding bulk samples were observed using scanning electron microscopy (SEM). Their thermal diffusivities and thermal expansion coefficients were measured by the laser-flash method and the pushing-rod method, respectively. Results show that pure Ce 1x Sm x O 2x/2 powders with single fluorite structure are synthesized successfully, and their microstructures of the corresponding bulk samples are very dense. With the increase of Sm 2 O 3 content, their thermal expansion coefficients decrease due to the higher electro-negativity of Sm 3+ ions as compared with that of Ce 4+ ions. Their thermal conductivities at 1000 ℃ lie in the range of 1.62-2.02 W/(m·K) due to the phonon scattering caused by the substituted atoms and oxygen vacancies. The Ce 1x Sm x O 2x/2 ceramics can be used as ceramic candidates for novel thermal barrier coatings (TBCs).
An unprecedented base-promoted multi-component one-pot dearomatization of N-alkyl activated azaarenes was developed to construct complex and diverse bridged cyclic polycycles with multiple stereocenters in a highly regio- and diastereoselective manner.
An
unexpected cleavage of the C
sp3
–CF3 bond of CF3-hydrobenzoxazoles has been disclosed,
affording a range of 2-aryl benzoxazoles under metal-free and redox-neutral
conditions. This transformation has demonstrated broad substrate scope
and good compatibility of functional groups. 2-Aryl benzothiazole
and 2-aryl benzoimidazole could be smoothly assembled in the same
manner. On the basis of preliminary mechanistic studies, base initiated
and aromatization driven β-carbon elimination was considered
to be the key step for the formation of 2. This reaction
offers an alternative, facile, and sustainable route to access important
2-aryl benzoxazole motifs.
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