Hardness and flexural strength of single-walled carbon nanotube/alumina composites

Abstract

This work adds new experimental facts on room temperature hardness and flexural strength of alumina and composites with 1, 2, 5 and 10 vol.% single walled carbon nanotubes (SWNT) with similar grain size. Monolithic Al 2 O 3 and composites were spark plasma sintered (SPS) in identical conditions at 1300ºC, achieving high density, submicrometric grain size and a reasonably homogeneous distribution of SWNTs along grain boundaries for all compositions with residual agglomerates. Vickers hardness values comparable to monolithic alumina were obtained for composites with low (1 vol.%) SWNT content, though they decreased for higher concentrations, attributed to the fact that SWNT constitute a softer phase. Three point bending flexural strength also decreased with increasing SWNT content. Correlation between experimental results and microstructural analysis by electron microscopy indicate that although SWNT agglomerates have often been blamed for detrimental effects on the mechanical Manuscript Click here to download Manuscript: paper alumina para J Mat Sci -corregido (1).docx Click here to view linked References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2 properties of these composites, they are not the main cause for the reported decay in flexural strength.

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

“…The results of flexural strength of composite C4 of this study, s F ¼ 600 ± 50 MPa, are analogous to the flexural strength for 1 vol% SWNT/Al 2 O 3 (in the range 520e610 MPa) [33] (composite tested with the same experimental set up and same specimen dimensions). They are also comparable to the value s F ¼ 526 ± 84 obtained for 1.2 vol% DWNT/ 3YTZP [42].…”

“…This result can be explained with the same arguments used to analyze flexural strength results from Al 2 O 3 / SWNT composites [33]. In these alumina composites, with SWNT content ranging from 1 to 3 vol%, flexural strength decreased when SWNT increased.…”

“…Flexural strength was measured as the maximum stress before breakdown, s max , in 15 Â 2 Â 1 mm 3 bars, the surface under tension polished to 1 mm, using a prototype three point bending test arrangement described elsewhere [33], specially designed for the small specimens' size. Correlation with the maximum applied load, F, is given by:…”

“…In spite of the above mentioned efforts, still a small percentage of carbon nanotubes in ceramic/CNT composites remain in agglomerates, especially in the case of single walled carbon nanotubes [27,32] due to their high tendency to aggregate via Van der Waals forces and also due to thermodynamic considerations for the particular geometry of the SWNTs compared to the ceramic powder [25,27]. Although recent studies show that these agglomerates are not responsible for the degraded mechanical properties in alumina/SWNT composites [7,33], they are not desirable for several reasons. They introduce heterogeneities in the composites and most important, they decrease SWNT efficiency since when agglomeration occurs the real quantity of SWNT dispersed in the grain boundaries does not coincide with the nominal amount of SWNT introduced in the composite.…”

Mechanical and electrical properties of low SWNT content 3YTZP composites

“…To the best of our knowledge, absence of decrease or increase of hardness with increasing CNT content in ceramic matrix composites has only been reported for Al 2 O 3 with 1 vol% SWNT composites, 34 since most of the authors report a decrease of hardness, even for composites with low CNT content. 11, [14][15][16] The decreasing trend reported by previous authors for 3YTZP/CNT composites is shown in Figure 4(a).…”