Scaling the Stiffness, Strength, and Toughness of Ceramic‐Coated Nanotube Foams into the Structural Regime

Abstract

Natural materials such as bone and tooth achieve precisely tuned mechanical and interfacial properties by varying the concentration and orientation of their nanoscale constituents. However, the realization of such control in engineered foams is limited by manufacturing‐driven tradeoffs among the size, order, and dispersion uniformity of the building blocks. It is demonstrated how to manufacture nanocomposite foams with precisely controllable mechanical properties via aligned carbon nanotube (CNT) growth followed by atomic layer deposition (ALD). By starting with a low density CNT forest and varying the ALD coating thickness, we realize predictable ≈1000‐fold control of Young's modulus (14 MPa to 20 GPa, where E ∼ ρ 2.8), ultimate compressive strength (0.8 MPa to 0.16 GPa), and energy absorption (0.4 to 400 J cm–3). Owing to the continuous, long CNTs within the ceramic nanocomposite, the compressive strength and toughness of the new material are 10‐fold greater than commercially available aluminum foam over the same density range. Moreover, the compressive stiffness and strength equal that of compact bone at 10% lower density. Along with emerging technologies for scalable patterning and roll‐to‐roll manufacturing and lamination of CNT films, coated CNT foams may be especially suited to multifunctional applications such as catalysis, filtration, and thermal protection.

Tuning the mechanical properties of vertical graphene sheets through atomic layer deposition

“…In all of the samples, the strain recovery increased with an increase in the applied load, but was typically smaller in coated VG sheets than in pristine VG sheets. This is in contrast to previously reported measurements of CNTs, where graphene petals as well as ALD alumina coating enhanced the strain recovery [2,3]. The opposite behavior observed here can be attributed to the differences between an array of CNTs and VG sheets.…”

“…Over the full range of loads, the ALD coated samples clearly have a higher stiffness than the bare samples and a trend of increasing stiffness with increasing alumina thickness is also observed. The enhancement in stiffness and modulus may be explained by stronger interlocking and coupling of VG sheets due to the alumina coating as well as an increase in the bending stiffness of individual VG sheets due to the coating, similar to what has been observed for CNTs [2].…”

Electrically Conductive Hierarchical Carbon Nanotube Networks with Tunable Mechanical Response

“…For CNT forests, the onset of the nearly horizontal plateau region is initiated by coordinated CNT buckling. As previously observed, the stiffness of an alumina-coated CNT forest increases due to the increased bending stiffness of constituent CNTs and increased rigidity of CNT–CNT bonds. , For the relatively large diameter parent CNT forests tested here, the increased stiffness due to alumina coating was approximately 100% relative to uncoated CNT forests. After secondary growth of CNTs, small diameter CNTs provide mechanical reinforcement by filling the interstitial regions between adjacent large diameter parent CNTs.…”

Bottom-Up Synthesis and Mechanical Behavior of Refractory Coatings Made of Carbon Nanotube-Hafnium Diboride Composites

“…For cellular materials, it is generally found that the modulus and strength scale with the density following a power law in the form ∼ρ n , where n ranges from 1 to 3 . It is known that n ≥ 2 for bending dominated foams. , We find that the density-modulus scaling of HfB 2 -CNTs is characterized by n = 3.37, which agrees with previous work on SiC- and Al 2 O 3 -coated CNTs. , Notably, a lower exponent can be advantageous when the objective is the construction of ultralight foam, such as stretch-dominated trusses, without sacrificing the mechanical behavior. In this case, the objective is to use conformal coating to fill a low-density material, such as VA-CNT.…”