AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Investigation of Carbon Nanotube Concentrations as Elemental Carbon
PATRICK O'SHAUGHNESSY, Ralph Altmaier, Craig Holder, University of Iowa
Abstract Number: 154 Working Group: Instrumentation and Methods
Abstract In this study, we compared the gravimetric mass of carbon black and two types of multi-walled carbon nanotubes (MWCNT): small-diameter (<8 nm) and large-diameter (50-80 nm) to the mass of elemental carbon (EC) quantified by NIOSH Method 5040. A novel laboratory-based system generated an MWCNT aerosol to collect mass on quartz fiber filters ranging from 1 to 30 μg. This system utilized LABVIEW software to control solenoid valves to shut off the sampling flow rate through cyclone samplers after a desired amount of aerosol mass was deposited on a filter. The system relied on real-time concentration readings from a photometer that, in combination with a known flow rate, allowed the mass collected over time to be calculated. Both quartz fiber and PVC filters were collected for assessment by Method 5040 and gravimetric analysis, respectively. Method 5040 was conducted by a certified lab using a temperature ramping scheme suggested by NIOSH. The gravimetric and EC results were compared, and a regression model was developed for each powder type. Additionally, the limit of detection (LOD) of the NIOSH Method 5040 for each powder type was determined. The regression models had significant slopes of 0.96, 0.62, and 0.70 for carbon black, small-diameter MWCNT, and large-diameter MWCNT, respectively. The LOD determination resulted in values of 8.8, 4.5, and 8.3 μg for carbon black, small-diameter MWCNT, large-diameter MWCNT, respectively. Assuming a sample flow rate of 4.2 L/min and an 8-hour sample duration, the concentration-based LOD of NIOSH Method 5040 was 4.4, 2.2, 4.1, and 15.8 μg/m3 for carbon black, small-diameter MWCNT, and large-diameter MWCNT, respectively. These findings indicate the analysis of EC is affected by the structure and elemental content of the CNTs in such a way as to under-report the EC associated with the carbon nanotubes.