Mechanical and electrical characterization of novel carbon nano fiber ultralow density foam

Abstract

Concomitant mechanical and electrical testing of carbon nanofiber foam samples, generated using the constrained formation of fibrous nanostructures process reveal the material to be a unique ultra-low-density foam with electrical properties appropriate for application as strain gauge. Samples of CFF, essentially a solid mat of intertwined nanofibers of pure carbon, were grown in a steel mold at ~550 Celsius (C) from a variety of catalysts exposed to fuel rich mixtures of ethylene and oxygen. Only those created from palladium (Pd) particle catalysts were found to produce macroscopic objects sufficiently robust for static and dynamic stress/strain tests. Transient and dynamic tests were used to fully characterize the mechanical properties of the novel foam. These tests clearly demonstrated that the material generated from Pd particles has viscoelastic behavior. The foam was subjected to compression cycles over diverse periods of time employing a die to maintain a fixed cross sectional area. The ultralow density material has a modulus of ~3.5 MPa, close to the one encountered in rubber-like substances. Given its carbonaceous nature, the new foam maintains its thermal stability up to 550 C in air. Simultaneous resistance/stress/strain measurements showed that there is a linear relationship between electrical resistance and strain that is remarkably consistent over many cycles. The novel ultralow density foam has many potential applications including sensing element of a strain gauge or energy absorber.