A prototype design of a reactor for scalable functionalization of SWCNTs by the reaction of alkyl halides with Billups-Birch reduced SWCNTs is described. The Hauge apparatus is designed to allow for the safe handling of all the reagents and products under an inert atmosphere at controlled temperatures. The extent of reaction of Li/NH 3 solution with the SWCNTs is measured in-situ by solution conduction, while homogenous mixing is ensured by the use of a homogenizer, and thermocouple are placed at different heights within the reactor flask. Addition of an alkyl halide yield alkyl-functionalized SWCNTs, which may be isolated by solvent extraction leaving a solid sample that is readily purified by hydrocarbon extraction. As an example, reaction of SWCNT/Li/NH 3 with 1-iododecane yields dodecane-functionalized SWCNTs (C 12 -SWCNTs), which have been characterized by TG/DTA, XPS, and Raman spectroscopy. Sample extraction during the reaction allows for probing of the rate of the reaction in order to determine the end point of the reaction, which for C 12 -SWCNTs (at −78 • C) is 30 min.

The Billups-Birch Reduction chemistry has been shown to functionalize single-walled carbon nanotubes (SWCNTs) without damaging the sidewalls, but has challenges in scalability. Currently published work uses a large mole ratio of Li to carbon atoms in the SWCNT (Li:C) to account for lithium amide formation, however this increases the cost and hazard of the reaction. We report here the systematic understanding of the effect of various parameters on the extent of functionalization using resonant Raman spectroscopy. Addition of 1-iodododecane yielded alkyl-functionalized SWCNTs, which were isolated by solvent extraction and evaporation, and purified by a hydrocarbon wash. The presence of SWCNT growth catalyst residue (Fe) was shown to have a strong adverse effect on SWCNT functionalization. Chlorination-based SWCNT purification reduced the amount of residual Fe, and achieve a maximum I/I ratio using a Li:C ratio of 6:1 in a reaction time of 30 min. This result is consistent with published literature requiring 20-fold mole equivalents of Li per mole SWCNT with a reaction time of over 12 h. This new understanding of the factors influencing the functionalization chemistry will help cut down material and process costs, and also increase the selectivity of the reaction toward the desired product.

No abstract

Using an organic solvent-based formulation, flexible and homogeneous ZrB 2 tapes were cast for potential use as advanced aerospace exploration vehicles. Dispersant concentrations were optimized for attrition-milled ZrB 2 powder using gravitational sedimentation and viscosity measurements. Tape cast slurry formulations with varying amounts of binder (6-8 vol%), plasticizer (7-11 vol%), and solids loading (20-23 vol%) were used to optimize the casting slurry. An optimal slurry formulation was determined based on cast tape uniform particle distribution and flexibility without cracking. Thermal gravimetric analysis of the optimized tape was used to create a binder burnout schedule that did not alter the tape structure or particle distribution. Our organic solvent-based tape casting approach results in minimum oxygen contamination after colloidal processing and robust cast tapes with a thickness of 280 lm and green density of~41% theoretic density after binder burnout.