The effect of surface coatings on the dustiness of a calcium carbonate nanopowder

Six calcium carbonate nanopowders that had been functionalized (coated) to enhance their use in a range of industrial applications were compared to the uncoated nanopowder (15–30-nm size range) from which they were made. The nanopowders were first characterized using the standard gravimetric rotating drum dustiness test (EN 15051 2006). All the functionalized powders showed a substantial increase in dustiness compared with the uncoated sample. The largest increase was some ×45, ×90 and ×331 higher for the inhalable, thoracic and respirable fractions, respectively, and would potentially give rise to much higher exposures to workers handling these powders. This article also investigated a range of additional measurement methods to extend the standard dustiness test to measure the particle size distribution and particle number concentrations. Several online instruments were compared in two sets of tests, as well as, offline transmission electron microscopy analysis. The results of these tests are discussed to assess the suitability and limitations of the measurement methods and to assess the best approach for extending the current gravimetric standard to include number concentration and size distribution measurements. It was concluded that questions remain over the performance characteristics of online charge detection instruments such as the FMPS and ELPI for dustiness testing, and such issues need to be resolved before a standardized test can be finalized.