Effect of graphene concentration on thermal properties of alumina–graphene composites formed using spark plasma sintering

The thermal conductivity of carbon nanotubes (CNTs) and graphene is extremely high; nevertheless, the addition of CNTs into alumina produced conflicting results on its thermophysical characteristics. In the present study, a small amount, 0.88–8.5 vol%, of graphene was mixed with alumina. The green compacts were prepared by tape casting and laminating techniques. The composites were subsequently densified with spark plasma sintering technique. The addition of graphene produces lower density and smaller grain size after sintering. Consequently, these microstructure characteristics result in lower thermal conductivity. After correcting the effect of porosity and grain size, the addition of a small amount of graphene enhances slightly the thermal conductivity of alumina. As the amount of graphene is higher than 8 vol%, the thermal conductivity of composite is close to that of pure fine-grained alumina.