Journal of Power Sources 195 (2010) 1463–1471 Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour Chemical vapor synthesis and characterization of aluminum nanopowder Jin Won Choi, Hong Yong Sohn ∗ , Young Joon Choi, Zhigang Zak Fang Department of Metallurgical Engineering, University of Utah, 135 South 1460 East, Room 412, Salt Lake City, UT 84112-0114, USA article info Article history: Received 23 July 2009 Received in revised form 1 September 2009 Accepted 2 September 2009 Available online 11 September 2009 Keywords: Hydrogen storage Chemical vapor synthesis Aluminum nanopowder Nanocrystalline materials abstract Aluminum is a component in many promising hydrogen storage materials such as aluminum hydride and complex aluminum hydrides. In this research, Al and TiAl 3 -containing Al nanopowders were prepared by a chemical vapor synthesis (CVS) process using Mg as the reducing agent. XRD and EDS results indicated that the produced powder was composed of Al or Al with TiAl 3 . The shape of the powder was spherical with the average size in the range of 10–50 nm measured by SEM, TEM, BET and ZetaPALS compared with the typically larger than 100 nm for commercially available fine Al powders. In addition, the effects of the operating conditions such as Ar flow rate, precursor feed rate and reaction temperature on the properties of the product powder were investigated. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Hydrogen is one of the most promising alternative energy car- riers [1,2]. Currently, the simplest and most common method of hydrogen storage uses thick-walled pressurized tanks. Other methods such as liquid hydrogen in a cryogenic tank, physisorp- tion of hydrogen, metal hydrides and complex hydrides, many of them containing aluminum, as well as the use of hydrocarbons have been studied [1–6]. Metal hydrides and complex hydrides offer a safe way to store hydrogen. However, the kinetics of dehydrogenation is too slow in a near-ambient temperature and the reactions are not readily reversible under reasonable condi- tions [3,6]. To overcome these barriers, nanoparticles and doping elements are considered. Recent studies have shown that the dehy- drogenation temperature can be lowered and the reversibility of hydrides such as sodium alanate can be increased by doping the compounds with Ti [7–9]. In addition, nanoscaled materials offer many advantages. The small size of these materials strongly enhances the kinetics of hydrogenation and dehydrogenation by increasing the reaction and diffusion rates. In other words, the reactivity per unit mass of nanostructured materials due to the large surface area is significantly higher and the diffusion path from surface to bulk is shorter than that of the larger sized materi- als. The synthesis techniques for nanosized materials include gas condensation, plasma processing, chemical vapor synthesis (CVS), sol–gel, rapid quenching, crystallization of amorphous solids and ∗ Corresponding author. Tel.: +1 801 581 5491; fax: +1 801 581 4937. E-mail address: h.y.sohn@utah.edu (H.Y. Sohn). mechanical milling/alloying [10,11]. Most methods require an extensive effort to control the size of the particles in the nanome- ter range to prevent agglomeration and oxidation due to the highly reactive nature of the particle surface. Chemical vapor synthesis is a method to prepare solid powders by vapor phase reactions. It was developed from the chemical vapor deposition technique to form particles instead of a film. CVS has considerable flexibility in producing nanomaterials by the use of a wide variety of precur- sors. The CVS process, which has been successfully developed at the University of Utah, involves reducing a vapor phase mixture of volatile precursors of the constituent metals by magnesium vapor or hydrogen, depending on the thermodynamics of the synthesis reactions. The key advantages of this process are the small size of produced particles, the ability to produce powders of many differ- ent compositions, the homogeneity of powder composition, and the ease of doping element addition in one-step synthesis. Sohn et al. [12–15] applied the basic concepts of the hydrogen reduction of metal chlorides to the CVS of intermetallic and metal alloy pow- ders. When hydrogen is used, these chemical vapor reactions can generally be written as follows: mMCl x (g) + nNCl y (g) + 0.5(mx + ny)H 2 = M m N n (s) + (mn + ny)HCl(g) (1) where M and N represent two different metals with x and y being the valences and M m N n being the intermetallic compound formed. Another key feature of chemical vapor synthesis is that it allows the formation of doped or multi-component nanoparticles through the use of multiple precursors. Sohn et al. [16] synthesized WC–Co com- posite powder by reducing WCl 6 and CoCl 2 precursors. Choi et al. [17] prepared Mg nanoparticles doped with Ti in a vapor phase reac- tion, which showed superior hydrogen storage properties. Ehrman 0378-7753/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2009.09.007