Journal of Materials Processing Technology 178 (2006) 270–273 Novel synthesis of Al 2 O 3 nano-particles by flame spray pyrolysis A.I.Y. Tok ∗ , F.Y.C. Boey, X.L Zhao School of Materials Science & Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore Received 30 June 2004; received in revised form 15 November 2005; accepted 19 April 2006 Abstract This paper reports on a novel, inexpensive, flame spray pyrolysis method to synthesize agglomerate-free nano-sized Al 2 O 3 particles with a size range of 5–30 nm. The precursors and the resultant oxide powders were characterized by chemical analysis, X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) analysis and transmission electron microscopy (TEM). The novel flame spray pyrolysis method successfully synthesized nano-sized Al 2 O 3 of about 5–30 nm (-phase + -phase), and 80–100 nm (-phase, calcined) from AlCl 3 vapour. © 2006 Elsevier B.V. All rights reserved. Keywords: Al 2 O 3 ; Synthesis; Nano-particles; Calcination 1. Introduction Aluminium oxide (alumina, Al 2 O 3 ) is currently one of the most useful oxide ceramics, as it has been used in many fields of engineering such as coatings, heat-resistant materials, abrasive grains, cutting materials and advanced ceramics. This is because alumina is hard, highly resistant towards bases and acids, allows very high temperature applications and has excellent wear resis- tance [1–2]. Annual demand for alumina has been growing steadily. From an annual production of 38 million tonnes in 1995, its demand is expected to reach 667 million tonnes by the year 2005 [3–4]. Nanotechnology has become a key area in the development of science and engineering [5]. Nanotechnology basically involves the production or application of materials that have unit sizes of about 10–100 nm. Comparing micron-sized and nano-sized alu- mina particles, nano-alumina has many advantages. A smaller particle size would provide a much larger surface area for molec- ular collisions and therefore increase the rate of reaction, making it a better catalyst and reactant. Finer abrasive grains would enable finer polishing, and this would also give rise to new appli- cations areas like nano-machining and nano-probes. In terms of coatings, the use of nano-sized alumina particles would signifi- cantly increase the quality and reproducibility of these coatings [6]. ∗ Corresponding author. Tel.: +65 67 904 935; fax: +65 67 904 935. E-mail address: miytok@ntu.edu.sg (A.I.Y. Tok). There are several methods to synthesize nano-alumina [7–10], and these are categorized into physical and chemical methods. Physical methods include mechanical milling, laser ablation, flame spray and thermal decomposition in plasma. Chemical methods include sol–gel processing, solution combus- tion decomposition and vapour deposition. Most of the chemical methods have resulted in extremely low yield rates, and thus can- not be adapted to mass manufacturing. Physical methods like mechanical milling are not efficient as the size of the nano- particles cannot be easily controlled, and these methods are only limited to certain materials. Other methods such as laser ablation, vapour deposition and sol–gel are very costly as they require specialized equipment such as vacuum systems, high power lasers as well as expensive precursor chemicals. Finally, most systems are only possible for a specific range of materials. This papers reports on a novel flame spray pyrolysis method to produce nano-sized alumina particles using gas and aqueous precursors. This method has many advantages over the other methods as it is low-cost, easy to control particle size, simple processing, high production yield, and ease of conversion to mass manufacturing [11]. In this process, a high temperature flame is used to heat the feedstock material as well as spray it into a condensation chamber, where it will condense as nano-sized particles. 2. Experimental procedure 2.1. Precursor synthesis A commercial anhydrous AlCl 3 powder (purity 99.6%) from Mark, Germany was used as the starting material. Fig. 1 presents a schematic illustration of the 0924-0136/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2006.04.007