A TEM-based method as an alternative to the BET method for measuring off-line the specific surface area of nanoaerosols S. Bau a, ⁎, O. Witschger a , F. Gensdarmes b , O. Rastoix c , D. Thomas d a Institut National de Recherche et de Sécurité, INRS, Laboratoire de Métrologie des Aérosols, Rue du Morvan CS 60027, 54519 Vandoeuvre Cedex, France b Institut de Radioprotection et de Sûreté Nucléaire, IRSN, Laboratoire de Physique et de Métrologie des Aérosols, BP 68, 91192 Gif-sur-Yvette Cedex, France c Institut National de Recherche et de Sécurité, INRS, Laboratoire d'Analyses Inorganiques et de Caractérisation des Aérosols, Rue du Morvan CS 60027, 54519 Vandoeuvre Cedex, France d Laboratoire des Sciences du Génie Chimique, LSGC/CNRS, Nancy Université, BP 2041, 54001 Nancy Cedex, France abstract article info Article history: Received 25 May 2009 Received in revised form 21 October 2009 Accepted 20 February 2010 Available online 26 February 2010 Keywords: Nanostructured powder Airborne nanostructured particle Specific surface area BET analysis TEM analysis Overlap coefficient Primary particle size distribution At the present time, no stabilised method exists allowing an estimation of the specific surface area for airborne nanostructured particles (nanoaerosols). Recent toxicological studies have, however, revealed biological effects linked to the surface area of these particles. Only the BET method, which can determine the specific mass surface area of a powder, constitutes a reference both in toxicology and in the materials domain. However, this technique is not applicable to nanostructured aerosols given the mass quantities of particles required (between approximately some mg to hundreds of mg taking into account the limit of quantification of existing BET instruments). To characterise the specific surface area of airborne nanostructured particles, a method based on analysing transmission electron microscopy (TEM) images is proposed. This has recourse in particular to previous work carried out in the area of nanoparticles originating from combustion (soot), and takes into account structural parameters of nanostructured particles including the number distribution of primary particles, their overlap coefficient and the fractal dimension of agglomerates and aggregates. The approach proposed in this work was applied to five commercially-available nanostructured powders of differing natures (SiO 2 , ZrO 2 , Al 2 O 3 , Fe 2 O 3 and Fe 3 O 4 ). This first involved their prior analysis by the BET method and then being placed in suspension in aerosol form using a vortex-type shaker system. The procedure to calculate the specific surface area using image analysis was then applied to the sampled aerosols and compared to the BET measurements. The experimental results obtained on the five nanostructured powders cover a range of specific surface areas from 20 to 200 m 2 /g, the primary particles having mean diameters varying from 7 to 47 nm. Close agreement was observed between the two approaches which, taking into account measurement uncertainties, are statistically equivalent at significance level α = 0.05. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Nanomaterials are defined as materials having constitutive elements with external dimension in the nanoscale (i.e. between approximately 1 and 100 nm), and which are designed with specific properties in mind [1–3]. Indeed, the physical, chemical and/or biological properties of traditional materials can evolve as a function of the size of the constitutive elements until they become very different from those that can be observed for the solid material [4]. Hansen et al. [5] established a classification of nanomaterials. Their work has resulted in a division of nanomaterials into three categories: (1) volume nanostructured materials such as nanoporous materials, the ceramic zeolites used in the field of catalysis, etc., (2) surface nanostructured materials including surface coatings applied to glass with self-cleaning properties, etc., and (3) materials made up of nanostructured particles, for example colloidal suspen- sions, nanostructured powders, nanocomposites and nanostructured aerosols. In addition, the specific properties of nanomaterials are partly linked to their high surface area to volume ratio. Thus, the specific surface area constitutes a dominant characteristic of nanostructured particles. Nanostructured particles, which can come from nanomaterials in divided form, have also been classified in the work of Maynard and Aitken [6]. It should be emphasised that the primary elements can then be found in individual form or grouped in agglomerates or aggregates (dimension can then extend to some hundreds of nanometers). A number of research projects have shown health effects related to nanostructured particles [7–11]. As a result, the prevention issues are high regarding nanostructured particles for health and safety at work Powder Technology 200 (2010) 190–201 ⁎ Corresponding author. Tel.: +33 383509890; fax: + 33 383508711. E-mail address: sebastien.bau@inrs.fr (S. Bau). 0032-5910/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2010.02.023 Contents lists available at ScienceDirect Powder Technology journal homepage: www.elsevier.com/locate/powtec