A study of fumed silica particle deagglomeration associated with instrument sampling techniques and A comparison of NIOSH 7402 and the Tsai Diffusion Sampler for collecting and analyzing carbon nanotubes
Date
2018
Authors
Khattak, Jared, author
Tsai, Candace Su-Jung, advisor
Reynolds, Stephen, committee member
Jathar, Shantanu, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Accurate characterization of contaminant exposures is critical in ensuring worker safety. Worker exposures are commonly characterized by area monitoring and personal samples. This research includes two parts, which study real time instrument measurements and personal sampling methods for exposure assessment. Real time instruments (RTIs) are used to assess concentrations of airborne particles in manufacturing facilities. These instruments often contain a cyclone, and previous studies have shown that the cyclone may cause measurement variations by dispersing agglomerated particles. This mechanism is thought to increase particle concentrations and decrease particle size. To determine the cyclone effect in this study, three RTIs were evaluated; the scanning mobility particle sizer (SMPS), fast mobility particle sizer (FMPS), and the optical particle sizer (OPS). The SMPS and FMPS contain a cyclone, the OPS does not. Nanoparticles were generated and sampled through pouring and automatic stirring inside a glovebox enclosure. After particles were generated, the glovebox was thoroughly cleaned and measurements were taken in the glovebox. For both generation methods, the SMPS and FMPS recorded an average concentration of 1.2 x 103 particles/cm3 and 1.7 x 104 particles/cm3 more after runs where the cyclone was used than when the cyclone was not used. The OPS, which does not contain a cyclone, recorded minimal differences during the measurement period after the glovebox was cleaned when the cyclone was used and not used on the other instruments. This result indicated that the measured nanoparticle concentrations increased with cyclone use. The results of this study indicate that the cyclone does influence the concentrations recorded by RTIs, and should be cleaned to ensure accurate measurements. The personal sampling methods evaluated were the NIOSH 7402 method for collecting and analyzing Carbon Nanotubes (CNTs) and the Tsai Diffusion Sampler (TDS) method for sampling CNTs. To evaluate each sampling method, CNTs were generated in a small enclosure inside of a glovebox; CNTs were generated by manual stirring. RTIs also sampled during each experiment to provide an estimate of airborne CNT concentrations. Airborne concentrations were estimated using the particle counts from TEM grid samples prepared using both methods. The majority of CNT structures collected by the TDS were individual fibers and clusters smaller than one micron in diameter. The NIOSH 7402 sampler primarily collected larger agglomerates, with the majority of collected particles being larger than two microns in diameter. The average estimated airborne concentrations calculated from the TDS and 7402 method particle counting were 5,200 fibers/cm3 and 59 fibers/cm3 respectively. During the experiments the SMPS recorded an airborne concentration of 1,100 particles/cm3 and the OPS measured an airborne concentration of 33 particles/cm3. Because the concentrations measured by the RTIs significantly exceeded the estimated concentrations derived from the NIOSH 7402 method, it is recommended that the TDS sampler be used as the concentrations derived from this sampler would warrant a more conservative approach to worker safety.