Journal of Hazardous Materials 275 (2014) 1–9 Contents lists available at ScienceDirect Journal of Hazardous Materials j o ur nal ho me pa ge: www.elsevier.com/locate/jhazmat Minimum ignition temperature of nano and micro Ti powder clouds in the presence of inert nano TiO 2 powder Chunmiao Yuan a,∗ , Paul R. Amyotte b , Md Nur Hossain b , Chang Li a,c a Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines, Northeastern University, Shenyang 110819, China b Process Engineering & Applied Science, Dalhousie University, 1360 Barrington Street, Halifax, NS B3J 2X4, Canada c Department of Civil Engineering, Shenyang Jianzhu University, Shenyang 110168, China h i g h l i g h t s • MIT of micro Ti powder decreased sharply even with as little as 10% nano Ti powder. • MIT of micro Ti powder increased gradually with increased nano TiO 2 powder. • MIT of nano Ti powder was as low as 583 K even when mixed with 90% nano TiO 2 powder. • A MIT model was given for particle size estimation and inerting effect understanding. • Inert effect of TiO 2 on micro Ti was better than nano Ti subjected to hot surface. a r t i c l e i n f o Article history: Received 21 January 2014 Received in revised form 19 April 2014 Accepted 21 April 2014 Available online 28 April 2014 Keywords: Minimum ignition temperature Titanium powder Nanopowder Solid inertants Ignition sensitivity a b s t r a c t Minimum ignition temperature (MIT) of micro Ti powder increased gradually with increases in nano- sized TiO 2 employed as an inertant. Solid TiO 2 inertant significantly reduced ignition hazard of micro Ti powder in contact with hot surfaces. The MIT of nano Ti powder remained low (583 K), however, even with 90% TiO 2 . The MIT of micro Ti powder, when mixed with nano Ti powder at concentrations as low as 10%, decreased so dramatically that its application as a solid fuel may be possible. A simple MIT model was proposed for aggregate particle size estimation and better understanding of the inerting effect of nano TiO 2 on MIT. Estimated particle size was 1.46–1.51 m larger than that in the 20-L sphere due to poor dispersion in the BAM oven. Calculated MITs were lower than corresponding empirically determined values for micro Ti powder because nano-sized TiO 2 coated the micro Ti powder, thereby decreasing its reaction kinetics. In the case of nano Ti powder, nano-sized TiO 2 facilitated dispersion of nano Ti powder which resulted in a calculated MIT that was greater than the experimentally determined value. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Dust explosion is a common hazard encountered in the metal processing industry because most combustible metals can be as energetic and hazardous as organic fuels [1]. Explosibility param- eters are important considerations for dust explosion prevention and have been well documented for metallic particles in the micron range [2,3]. The unique physical and chemical properties of nano-sized metal powders cause increased explosion potential [4–7]. Parameters affecting explosibility for various nano-metal ∗ Corresponding author at: Institute of Safety Engineering, Northeastern Univer- sity, Box 265, Shenyang, Liaoning 110819, China. Tel.: +86 024 83681830; fax: +86 024 83681483. E-mail address: yuanchunmiao@mail.neu.edu.cn (C. Yuan). powders have been determined [8–11], and primarily include P max , (dP/dt) max , and minimum ignition energy (MIE) [4–11]. These results indicate that dust clouds from combustible nm- particle powders do not exhibit extreme explosion hazard (i.e., high Kst values) as expected, because of poor dispersibility and high coagulation, while showing experimental MIE values considerably lower than those of micro powders composed of equivalent mate- rials [12,13]. However, research on minimum ignition temperature (MIT) of dust clouds involving nano materials has been limited. MIT for pure nano titanium was much lower than that required to ignite micro titanium, and nano metal powder was readily combustible in contact with hot surfaces [4]. Similarly, nano-sized metal powders could be ignited by impact or friction heat when passing through the bend of a 20-L spherical apparatus [14]. Mixing an inert solid or a less flammable compound with a com- bustible dust is an application of the moderation principle [15,16]. http://dx.doi.org/10.1016/j.jhazmat.2014.04.047 0304-3894/© 2014 Elsevier B.V. All rights reserved.