High Volume Production of Conductivity-Enhanced CNTs for Advanced Obscuration

The proliferation of remote sensing technology, particularly in the IR regime, necessitates advanced and adaptable countermeasures for every component on the battlefield. Recently, metallic carbon nanotubes (mCNTs) with a particular length and diameter distribution have been shown to be excellent absorbers of infrared radiation (IR) through plasmon interaction. However, currently available mCNTs are too expensive to be used in battlefield IR obscuration applications. In Phase I American Boronite Corporation produced record quantities (>25g) of CNTs with predominantly metallic chirality. The diameter distribution centered at 1.6 nm, well within the Phase I objective, while the CNTs as grown were extremely long (>100 µm) and nearly defect free. For most electromagnetic and structural applications, long CNTs are extremely desirable. For tunable IR absorption, however, we need to have metallic short CNTs (<100 nm) with a length distribution we can control. We explored a variety of post-processes based on wet chemistry and kinetic techniques, all of which render our CNT sheet into a fine CNT powder with significantly shorter length distribution. We also explored a variety of analysis techniques to measure the individual CNT dimensions and IR absorption capability. A unique Raman spectroscopy technique made available by our Los Alamos National Laboratory (LANL) collaborators provided broadband Raman spectroscopy across the entire visible spectrum and showed that the most intense radial breathing modes (RBMs) associate with metallic chiralities, supporting the characteristic metallicity of the CNTs. Atomic force microscopy (AFM) rapidly determined a maximum average CNT length after post-processing. We explored a variety of Infrared (IR) spectroscopy techniques from a liquid transmission cell with CNTs suspended in deuterated water. We also measured their solid-state diffuse reflectance. In Phase II we will upgrade our existing carbon reactors to expand our production capacity of the newly established metallic CNT architecture (injector designs, fuel/gas chemistries and temperature profiles) with the goal of delivering 5 kg of mCNTs by the end of the program.