Iodine-containing aluminum-based fuels for inactivation of bioaerosols Y. Aly a , S. Zhang a , M. Schoenitz a , V.K. Hoffmann a , E.L. Dreizin a,⇑ , M. Yermakov b , R. Indugula b , S.A. Grinshpun b a New Jersey Institute of Technology, Newark, NJ, United States b University of Cincinnati, Cincinnati, OH, United States article info Article history: Received 2 April 2013 Received in revised form 12 July 2013 Accepted 13 July 2013 Available online 8 August 2013 Keywords: Metal combustion Reactive materials Bio-agent Inactivation abstract Inactivation of aerosolized biologically viable Bacillus atrophaeus endospores (stimulant of the B. anthracis bio-agent) in combustion products of air-acetylene flames seeded with different aluminum-based pow- ders was investigated. A flow of bioaerosol was introduced into the environment above the flame. The mixing of the combustion products with bioaerosol particles occurred when the combustion tempera- tures were cooled off to approximately 170–260 °C (the cross-sectional weighted average temperature). The flame was seeded with pure Al powder as well as with composite AlI 2 and AlBI 2 powders prepared by mechanical milling. The iodine content was close to 20 and 15 wt.% for AlI 2 and AlBI 2 powders, respectively. The burn rate was highest for particles of pure Al and lowest for particles of AlBI 2 . It was also observed that in the flame, particles of AlBI 2 had the lowest temperature compared to other materials. Despite a lower iodine concentration, the combustion products from the flame seeded with AlBI 2 exhibited the highest levels of inactivation of the aerosolized spores. The flame products of AlI 2 have also shown an effective inactivation. The inactivation levels observed for the unseeded flame and flame containing pure Al, were much lower and similar to each other; these inactivation levels were con- sistent with relatively weak thermal stress experienced by the bioaerosol at the relatively low tempera- tures of the exhaust gas. The highest level of inactivation observed for the combustion products of AlBI 2 composite powder is attributed to its lower burn rate and respectively more homogeneous mixing of the iodine-containing products with the exhaust gases. Ó 2013 The Combustion Institute. Published by Elsevier Inc. All rights reserved. 1. Introduction Recent interest in halogen-containing reactive materials [1–10] has been galvanized by their potential applications for mitigating the spread of hazardous, active biological microorganisms that could be aerosolized as a result of explosion. Halogens are well- known for their biocidal properties, and their presence in the com- bustion products of an explosive charge is expected to significantly reduce the concentration of viable microorganisms, escaping from the high-temperature blast zone. Different methods of incorporat- ing halogens in reactive materials have been considered. Prepara- tion of halogenated oxidizers is one of the recently explored approaches [9]. New forms of iodine oxides have lately been syn- thesized and characterized [6,7]. In most cases, however, such oxi- dizers readily react with atmospheric moisture and may be difficult to handle. In addition, using such oxidizers as a compo- nent of an explosive would require modifying the entire formula- tion, typically designed to be fuel rich in order to exploit the energy of combustion with the ambient oxygen. In a different ap- proach, reactive compositions including halogen-containing ther- mites are being explored [3–5,8–10]. In this case, the halogen- containing oxides, such as I 2 O 5 are combined with metal powders; various nano-scale mixtures or composites are often prepared for rapid reaction. Such materials can be extremely reactive, generat- ing pressure and iodine vapors upon initiation. These compositions are typically very easy to ignite, so that their handling and storage might present additional challenges. The approach explored in this research effort involves incorpo- rating halogens into metal fuel additives included in the metallized explosives [1,2,11,12]. In particular, aluminum-based materials are addressed because of the widespread use of aluminum powders in energetic formulations [13–15]. In this approach, the halogen- modified metal powders have characteristics similar to those of regular metal powders, including high density and energy density, making them attractive ingredients in explosive compositions. The powders prepared to date contained as much as 20% of iodine, which is released during the powder combustion and substantially improves the biocidal effect of the metal combustion products on aerosolized microorganisms [1]. In previous work, AlI 2 composite materials were prepared and characterized. Their effectiveness was tested against aerosolized Bacillus atrophaeus (BG) endospores 0010-2180/$ - see front matter Ó 2013 The Combustion Institute. Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.combustflame.2013.07.017 ⇑ Corresponding author. Fax: +1 973 596 8436. E-mail address: dreizin@njit.edu (E.L. Dreizin). Combustion and Flame 161 (2014) 303–310 Contents lists available at ScienceDirect Combustion and Flame journal homepage: www.elsevier.com/locate/combustflame