| AVS 62nd International Symposium & Exhibition | |
| Thin Film | Tuesday Sessions |
| Session TF-TuA |
| Session: | ALD for Emerging Applications |
| Presenter: | Jesse Jur, North Carolina State University |
| Authors: | J.S. Jur, North Carolina State University K.L. Stano, North Carolina State University P.D. Bradford, North Carolina State University |
| Correspondent: | Click to Email |
Ultralow density materials (ρ ≤ 10 mg cm-3) have recently gained widespread attention, and have been realized in many forms including silica, and carbon-based aerogels, as well as engineered structures such as inorganic micro- and nanolattices. Porous metal oxides, particularly alumina, are desirable due to their semiconducting and dielectric properties as well as thermal, mechanical, and chemical stability. Historically, monolithic alumina aerogels have been fabricated using sol-gel processes. Although this and other self-assembly methods can produce very high surface area aerogels, they have a moderate low density (≥ 30 mg cm-3), and little to no control over pore size and structure. We present here a method by which aligned CNTFs are used as unique sacrificial templates for the formation of anisotropic, large-scale inorganic nanotube architectures that exhibit the combined characteristics of high surface area, ultralow density, and mechanical robustness. Using ALD, conformal coatings were deposited onto the CNTFs, followed by their removal via calcination in air to leave behind an interconnected network of thin-walled and aligned nanotubes of the ALD metal oxide. Analysis shows that the use of alumina ALD, one can achieve a density as low as 1.2 mg cm3, 16x lower than previously report alumina foams. Furthermore, both CNT/alumina hybrid foams and pure alumina nanotube foams exhibit unprecedented elastic recovery following 50% compression, and possess values for strength and Young’s moduli which exceed those of aerogels with similar densities. The scaling behavior of Young’s modulus to foam density for pure alumina foams exhibits a power-law dependence of n≈1.9, attributed to superb ligament connectivity. As a low thermal conductivity insulation, a foam of 1 cm thickness is demonstrated to reduce a flame temperature of 1000 ° C to 45 ° C after 5 min of direct flame contact.