German scientists unveil their discovery of the lightest material in the world, with a record-breaking density almost five times lower than that of the previous title holder.
Step aside aerogel. Move over metallic microlattices. There’s a new material in town - It’s jet-black, it’s conductive and its low density makes it the lightest material in the world. It’s called Aerographite.
The work, published jointly by the University of Kiel and the Technical University of Hamburg, appears in the July issue of Advanced Materials [Mecklenburg et al. Advanced Materials, 24,3486–3490, 2012. DOI: 10.1002/adma.201200491].
0.01% of the material consists of a network of interlinked, thin-walled carbon microtubes; the rest is air, resulting in a density of 0.18 mg/cm3. The carbon tubes are not made from layers of graphene like carbon nanotubes, but are more similar to vitreous carbon. It’s the 15 nm thick, self-supporting, porous walls of the carbon tubes that class Aerographite as a carbon nanomaterial.
Aerographite as almost five times lighter than the nickel microlattice that previously held the title, and is 5000 times less dense than water. 1 kg of the material would occupy a volume roughly equivalent to that of a Mini Copper.
The material is produced using a specifically-developed CVD-process. Zinc oxide (ZnO) tetrapod nanocrystals are used as sacrificial templates on which to grow the Aerographite network. CVD is used to coat the ZnO crystals with carbon. Injected hydrogen gas is then used to reduce the template crystals, causing them to collapse and leaving the carbon network intact. Prof. Rainer Adelung of Kiel University described the process; “Think of the Aerographite as an ivy-web, which winds itself around a tree (the ZnO). Then take away the tree”.
Aside from its low density, it is the other properties of Aerographite that make it so interesting. Despite the fact that it is 99.99% air, it is completely optically opaque. It is also superhydrophobic – a feat only achieved by aerogels after post-production chemical treatment.
Aerographite is electrically conductive, and the author shows that electrodes made from the material and used in a double-layer capacitor show a power capacity of 1.25 Wh/kg.
It is structurally resilient; many lightweight materials can withstand compression, but Aerographite also displays an ultimate tensile strength of 160 kPa (when its density is 8.5 mg / cm3). Its low Poisson ratio also means that it shows complete shape recovery after compression by 95%.
As with any new material, many potential applications of Aerographite have been suggested, but the most promising include lightweight batteries and water purification.