| dc.description.abstract | Although there is a fast growth in the production and application of nanomaterials, very little research about the fire and explosion hazards associated with nanomaterials has been done. Dust explosion studies on micro-size materials show that combustible engineered nanomaterials may possess high risk for explosion because increased specific surface area of nanomaterials may improve the ignition sensitivity and explosion severity. This study focuses on combustion and explosion of carbon nanofibers (CNFs), considering its large-scale production, wide application, and various handling processes. This study characterizes the morphology of CNFs with scanning electron microscope, the particle size distributions with Spraytec and Beckman Coulter, and the thermal stability with thermogravimetric analysis. Explosibility tests are performed in a customized 36-L dust explosion vessel and a minimum ignition energy apparatus (MIKE 3). Combining the characterization tests, explosibility tests, and theoretical analysis, this study provides a good understanding about combustion and explosion risk of CNFs after different processes – milling duration, and annealing at 1500 °C or 3000 °C.
In general, this study concludes that the minimum ignition energy of CNFs is higher than 1 J, which indicates a low ignition sensitivity. Minimum explosible concentration of CNFs varies from 105 g·m^-3 to larger than 300 g·m^-3. The maximum overpressure is about 8 bar. CNF is classified as St-1 combustible dust with a deflagration index around 100 bar·m·s^ -1 .
It is also found that the smaller agglomerates caused by milling process not only reduces the minimum explosible concentration (MEC), but also increases the maximum pressure increase rate [dP/dt]max. Besides, the annealing process, either 1500 °C or 3000 °C, improves the graphite degree of CNFs and hence decreases the explosion severity with a lower [dP/dt]max. Additionally, the 3000 °C annealing process reduces the iron content within CNFs and hence increased MEC. It is because the pyrophoric Fe-NPs could be ignited remotely with a favorable penetration topology of CNF agglomerates and therefore promotes the heating of unburnt CNFs and facilitates the overall combustion and explosion process. This study also modifies an estimation method for maximum overpressure and proposes a heterogeneous model explaining the influential factors. | en |
