A unique combination of acid treatment, aqueous colloidal processing, and spark-plasma sintering (SPS) has been used to fabricate high-density Al2O3 /single-wall carbon nanotube (SWNT) composites with well-distributed SWNTs and other carbon nanostructures ('nano-onions', diamond) at Al2O3 grain boundaries. This approach could be used to obtain well-controlled microstructures of ceramic/SWNT composites for tailored mechanical, electrical, and thermal properties. In addition, the colloidal approach for dispersing SWNTs presented here could be used for the controlled manipulation of SWNTs.

No abstract

Yttria tetragonal zirconia ceramic composites with 1, 2.5, 5 and 10 vol% nominal contents of graphene nanoplatelets (GNPs) were fabricated and characterized. First, the GNP dispersion in isopropanol was optimized to de-agglomerate the GNPs without damaging their structure. Then, submicrometric fully dense composites were obtained via spark plasma sintering (SPS) at 1250ºC with a 5 min holding time. The processing routine produced a nearly homogeneous GNP dispersion in the ceramic matrix, and the GNPs preferential orientation was perpendicular to the sintering compression axis. The Ceramic grain refinement due to the GNPs was also detected. The Vickers hardness measured on the plane perpendicular to the sintering compression axis (basal plane) was lower than on the cross sections. This anisotropy increased with the increasing GNP content, while the average hardness decreased. The electrical conductivity was also highly anisotropic, up to seven times higher for the basal planes. The electrical percolation threshold for these composites was estimated to be between 2.2 and 4.4 vol% of the GNP measured content.

No abstract

Phase-pure powders of stoichiometric BiFeO 3 have been prepared by mechanosynthesis. Ceramics sintered by either conventional heating in air or spark plasma sintering (SPS) followed by oxidative anneal in air are highly insulating with conductivity e.g. ~10-6 Scm -1 at 300 °C and activation energy 1.15(2) eV, which are comparable to those of a good-quality BiFeO 3 single crystal. By contrast, the as-prepared SPS sample without the post-sinter anneal shows higher conductivity e.g. -6 Scm -1 at 225 °C and lower activation energy 0.67(3) eV, indicating some reduction of the sample by the SPS process. The reason for the high conductivity observed in some ceramic samples reported in the literature appears to be unclear at present. ~10