Silicon carbide whiskers: characterization and aerodynamic behaviors

Silicon carbide (SiC) whiskers are fiberlike materials with a wide range of industrial applications. Industrial hygiene samplings of the material are taken to monitor and control possible exposures to workers. This study characterizes an SiC whisker in detail, including its width-length distribution, aspect ratio, particle density, and aerodynamic size distribution. The SiC whiskers were aerosolized, and samples from a filter, cascade impactor, and aerosol centrifuge were taken. The diameter-length distribution of SiC fibers determined by electron microscopy from filter samples was found to follow the bivariate lognormal distribution. The aerodynamic size of a fiber aerosol depends not only on the particle dimension and density but also on the orientation of its axis with respect to flow. The results show that the aerodynamic size distribution obtained from the impactor was consistent with the predicted value, assuming the long axis of the fiber was parallel to the flow toward the collection substrate. On the other hand, the aerodynamic size in the aerosol centrifuge was consistent with results for a perpendicular orientation. A larger aerodynamic size (20-25%) was obtained in the case of impactor data as compared with centrifuge data. The respirable fraction estimated from the cascade impactor data was 65%, consistent with the estimate from bivariate analysis (67%) but smaller than the estimated fraction from the aerosol centrifuge (76%). The results show that the data obtained with the bivariate analysis of fiber dimensions had good correlation with the cascade impactor data, and this approach can be used to predict the aerodynamic size distribution and the size-selective fractions for fiber aerosols from filter samples.