Characteristics of airborne gold aggregates generated by various methods: mass mobility characteristics and surface area

Aggregates are a common particle type in the air - irregular particles built up by smaller primaries/monomers. One aim of the work is to present and test methods, experimental and theoretical, to characterize aggregates in the transition regime with regards to properties relevant for toxicological and nano-technological applications. Furthermore, we characterize and compare the properties of the gold-aggregates generated by three generators. The generators tested were a high temperature evaporation furnace (HT) and two spark discharge generators, one commercially available (SDGP) and a custom built (SDGC). The SDGC has been applied in several studies relevant for toxicology.

For the characterization both online instrumentation, such as differential mobility analyzer and aerosol particle mass analyzer coupled in series (DMA-APM) and differential mobility particle sizer (DMPS), and off-line transmission electron microscopy techniques were used. Except from size, number, mass, and morphology, the surface area is a property of special interest. Based on the experimental data, the total surface area content of the aerosols was estimated using four approaches and the results are compared and discussed.

In general, the aggregate properties of the SDGC differ from the commercial, SDGP, with most of its properties lying between the SDGP and the HT. The mass-mobility relationship show that the particles were aggregated and was well described by a power-law function down to the smallest size measured (15 nm), with exponents of 2.18-2.35. Even though similar exponents, the effective density of the aggregates differs between generators. The diameters of the primaries composing the aggregates were ~5-10 nm depending on method and weighting, held together by a bridge corresponding to 62-70 % of the primary particle diameter. The observed variation in effective density could partly be explained by the analyzed primary particle size.

The predicted total surface areas, calculated using the suggested approaches, vary within a factor of 2, and the relative difference in the estimated surface area varied between generators. This variation could partly be explained by the properties here assessed but again, not fully. We suggest that this is either due to a varying primary particle size over the aggregate distribution, or that the morphology of the three types of aggregates generated was different in a fashion the employed methods and theories did not encompass.

Purpose:

Characterization of mass-mobility aerosols of gold aggregates.

The .zip-file contains data in an excel file. The data is divided between two tabs, where the first one lists size of primary particles over several hundred observations and the second one presents the results of the testing of the different generators. For the latter, size of particle works as the independent variable whereas dependent variables are weight, shape factor as well as effective density. The .zip-file also includes a codebook with variable descriptions in English. Show less..