Mechanical and electrical properties of low SWNT content 3YTZP composites

Abstract

Fully dense 3 mol% Y 2 O 3 -ZrO 2 (3YTZP) composites with low single wall carbon nanotube content (0.5, 1 and 1.5 vol% SWNT) were prepared by colloidal processing and Spark Plasma Sintering. SWNT were distributed at ceramic grain boundaries and also into agglomerates. Characterization of SWNT agglomerates indicated that increase in SWNT vol% does not imply an increase in agglomeration. SWNT agglomerate density was related to the evolution of hardness and fracture toughness with SWNT vol%. Electrical properties of the composites were characterized in a wide temperature range, and percolation threshold was estimated. A model allowing separation of the individual SWNT bundles contribution to resistance from the resistance due to junctions between bundles was proposed for composites with a percolating SWNT network. Keywords

Enhanced carbon nanotube dispersion in 3YTZP/SWNTs composites and its effect on room temperature mechanical and electrical properties

“…Interfacial bonding between 3YTZP ceramic grains and SWNT is not very strong [7], so when SWNTs are mostly located in GBs and more homogeneously distributed, more interconnected, their influence is larger, resulting in a reduced hardness value. Therefore, improving SWNT dispersion decreases hardness because it increases SWNT content in GBs, in an analogous way to the decrease in hardness reported as a consequence of increasing nominal SWNT content in 3YTZP/SWNT composites [7,43]. A larger area of GBs covered by SWNT also facilitates grain boundary sliding at high temperatures, which has been proved by creep tests [36].…”

“…Raman spectra of the SWNT used in this study showed a not negligible D band (I D /I G~0 .30) which obviously increases I D /I G ratio of the corresponding composites. Smaller I D /I G ratios were obtained from composites prepared with similar methods but different SWNTs in previous works [7,43]. Raman spectra from composites C2, C4 and C5, prepared using high energy ultrasonic probe to improve dispersion present systematically a smaller I D /I G ratio than composites C1 and C3 processed with lower energy ultrasonic agitation (see values in Table 3), which indicates that the energy and working time of the ultrasonic probe was reasonable and did not damage the SWNT crystallographic integrity.…”

“…We have already obtained that enhancing SWNT dispersion and minimizing agglomeration results in an increased percentage of SWNT in the GBs. It is clear that with small SWNT contents such as used in this study (1 vol%), near the percolation threshold [35,43], a small increase of the SWNTs present in GBs will result in percolating carbon nanotube networks which will make possible electrical conductivity. Thus, measuring electrical conductivity in these materials gives us a very clear and reliable method to asses SWNT distribution in GBs.…”

“…On the other hand, the processing techniques used for improving SWNT dispersion have proved to be effective in enhancing electrical conductivity of the composites and in decreasing the percolation threshold of the 3YTZP/SWNT composites below 1 vol%, previously estimated between 1 and 1.5 vol% for composites sintered by a similar processing routine but without high energy ultrasonic probe [35,43]. …”

“…Therefore, low content SWNT/ 3YTZP composites (up to 2.5 vol% SWNT) seem more interesting than high SWNT content for structural applications which require good mechanical properties, since they show mechanical properties similar or even superior to the ceramic matrix and they conduct electricity, the percolation limit reported between 0.4 and 1.5 vol% SWNT [43].…”