a b s t r a c tGraphene platelets (GPLs) containing Al 2 O 3 nanocomposites, which exhibit anisotropic microstructure, have been prepared by spark plasma sintering (SPS), and effects of this anisotropy on mechanical, electrical and thermal properties of the nanocomposites have been investigated. 3 vol.% GPLs addition into monolithic Al 2 O 3 caused fracture toughness (K ıc ) to increase by 26.7% in the in-plane direction and to decrease by 17.2% in the through thickness direction. K ıc started to decrease in the in-plane direction and to increase in the through-thickness direction with further increase in the GPLs amount. The electrical conductivity of the nanocomposites exhibited a slight anisotropy with a lower resistivity in the in-plane direction. Oriented GPLs also led to a less resistive heat conduction path in the in-plane direction. ∼44% increase in the in-plane thermal conductivity was achieved at 600 • C with 15 vol.% GPLs addition into the monolithic Al 2 O 3 and this resulted in ∼52% increase in the k in-plane /k through-thickness ratio.

Three different graphite-based powders (expandable graphite and two different nano-graphite powders) were investigated as starting materials for an effective liquid phase exfoliation process in isopropyl alcohol (IPA). The prepared dispersions were analyzed and compared in terms of their graphene concentration, stability, number of graphene layers and quality, as well as the electrical conductivity of the prepared graphene-based materials. Good quality graphene dispersions (I D /I G < 0.3) with a relatively high concentration ($1.1 mg/ml) were prepared in IPA within 90 min sonication time by utilizing a high specific surface area ($175 m 2 /g) nano-graphite powder derived from natural graphite. Transmission electron microscope analyses of this sample revealed mostly folded and scrolled few layer graphene (FLG) sheets (<5 layers) entangled each other. The electrical conductivity of the thin film prepared from this dispersion was $15 and 86 S/m, before and after annealing, respectively. FLG prepared from expanded graphite, obtained by thermal treatment of expandable graphite, exhibited both much higher quality (I D / I G < 0.09) and electrical conductivity ($2104 and 19,200 S/m before and after annealing, respectively) when dispersed in IPA for 90 min. However, the graphene-based material concentration of the prepared dispersion was relatively low ($0.06 mg/ml).