Densification during hot-pressing of carbon nanotube–metal–magnesium aluminate spinel nanocomposites

Abstract

The densification by hot-pressing of ceramic-matrix composites containing a dispersion of carbon nanotubes (CNT), mostly single-walled, is studied for the first time. Fifteen different CNT-Co/Mo-MgAl 2 O 4 composite powders containing between 1.2 and 16.7 vol.% CNT were prepared by catalytic chemical vapour deposition. The in situ growth of CNT within the oxide powder made it possible to obtain a highly homogeneous distribution of CNT. Low contents of CNT (up to 5 vol.%) are beneficial for the first shrinkage step (up to 1100 • C), dominated by the rearrangement process, while higher contents are detrimental. At higher temperatures (1100-1300 • C), CNT clearly inhibit the shrinkage, and this detrimental effect regularly increases with the CNT content. Several explanations are proposed, in relation with the particular mechanical properties of CNT and their highly connected web-like distribution within the material.

Ceramic matrix composites containing carbon nanotubes

“…One of the first studies on synthesis of CNT/ceramic composites (published in two parts) was authored by Peigney and co-workers 39,40 [41][42][43][44][45][46][47][48] . These composite powders can then be hot pressed to form macroscopic composites.…”

Colloidal processing, hot pressing and characterisation of electroconductive MWCNT-alumina composites with compositions near the percolation threshold

“…11 Another explanation is given by Peigney et al who attribute the increased grain rearrangement to the fact that CNTs facilitate sliding at grain contacts and therefore to a lower friction coefficient between grains. 12 As a consequence the grain rearrangement densification mechanism will be increased. The second decrease in densification rate can be related to the formation of a rigid network of MWCNT providing a sintering constraint.…”

“…Other authors attribute the decrease in shrinkage in the longitudinal direction to a decrease in shear stresses in the longitudinal direction, redistributing the stresses in the transversal direction, and therefore inhibiting plastic flow. 12 Hot pressing of alumina-CNT nanocomposites has been studied by several authors. 14-16 It is not easy to compare the results of this study with those found in literature as…”

Hot pressed and spark plasma sintered zirconia/carbon nanofiber composites

“…4 In the last few years new ceramic/carbon nanotube composites have been developed and a number of authors have reported improved mechanical and functional properties in the case of ceramic/CNT composites compared to the monolithic material. [7][8][9][10][11] Three main problems have been recognized during these investigations; dispersion of the CNTs in the matrix, 12 densification of the composites and degradation of the CNTs. Conventional mixing of CNTs with the matrix powder requires long milling times which may damage the CNTs.…”