Abstract
The addition of graphene-based nanostructures (GBNs) can improve the inherent fragility of ceramics and provide them with improved electrical and thermal conductivities. However, both the starting material (ceramic matrix and GBNs) and the processing/sintering approach are crucial for the final composite microstructure and properties. This work focuses on the influence of the content and dimensions of the GBN filler (10 and 20 vol%; 3 and ~150 layers), the powder-processing conditions (dry versus wet), and the homogenization method (ultrasound sonication versus high-energy planetary ball milling) on GBN/tetragonal zirconia (3YTZP) composites. The microstructure and electrical properties of the spark plasma sintered (SPS) composites were quantified and analyzed. The highest microstructural homogeneity with an isotropic microstructure was achieved by composites prepared with thicker GBNs milled in dry conditions. A high content (20 vol%) of few-layered graphene as a filler maximizes the electrical conductivity of the composites, although it hinders their densification.
Highlights
Graphene-based nanostructures (GBNs) have recently come into scientific focus as a second phase in order to overcome the inherent fragility of ceramics
Concerning the starting materials, different advanced ceramics have been used as matrices, such as Si3 N4 [1], which has the highest fracture toughness reported for 1.5 vol% graphene-based nanostructures (GBNs) filler content [2], SiC [3,4], hydroxyapatite [5], alumina [6,7], and, more recently, zirconia [8,9]
The results indicate that the increase in GBN content from 10 to 20 vol% inhibits densification of the composites when the thickness of the GBN is very small
Summary
Graphene-based nanostructures (GBNs) have recently come into scientific focus as a second phase in order to overcome the inherent fragility of ceramics. The microstructure and performance of the composites are highly dependent on (i) the starting materials (ceramic used as a matrix and the quality, dimensions, and content of the GBN), and (ii) the processing approach and sintering conditions used. These features must be taken into account in order to obtain specific properties. For more than 10 layers, the GBN electronic structure is the same as for Ceramics 2018, 1, 153–164; doi:10.3390/ceramics1010014 www.mdpi.com/journal/ceramics
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