Carbon black and fumed alumina exhibiting high interface-derived mechanical energy dissipation

High interface-derived dissipation has been discovered by instrumented indentation in carbon black and fumed alumina. Both materials comprise nanoparticle aggregates that interlock mechanically upon compaction without a binder. The high dissipation is attributed to the high deformability and the abundance of interfaces. Compared to carbon black, similarly 600-kPa compacted 100-mN maximum-load tested fumed alumina gives lower dissipation (2.1 vs. 4.1 μJ, both values being higher than the highest previously reported value for any material, 0.175 μJ for dental enamel), lower maximum displacement (72 vs. 134 μm), higher fraction of displacement that is permanent (0.74 vs. 0.59), higher modulus (41 vs. 7 MPa), higher fractional dissipation (0.80 vs. 0.70), and lower solid content (12 vs. 18 vol.%). These differences are attributed to the greater compressibility of carbon black. The relative movement of the particles of carbon black or the graphite layers of exfoliated graphite becomes less reversible as the degree of compaction increases. Microwave-exfoliated graphite (5.25-MPa compacted, 37 vol.% solid) gives lower dissipation (1.0 μJ) and higher modulus than carbon black or fumed alumina. Furnace-exfoliated graphite (5.25-MPa compacted, 43 vol.% solid) gives even less dissipation than microwave-exfoliated graphite, due to its greater compressibility and consequent greater deformation reversibility.