Vapor-phase synthesis of a solid precursor for a-alumina through a catalytic decomposition of aluminum triisopropoxide Tu Quang Nguyen a , Kyun Young Park a, *, Kyeong Youl Jung a , Sung Baek Cho b a Department of Chemical Engineering, Kongju National University, 275 Budae-dong, Cheonan, Chungnam 330-717, Republic of Korea b Korea Institute of Geoscience & Mineral Resources (KIGAM), 92 Gwahang-no, Yuseong-gu 305-350, Republic of Korea 1. Introduction a-Alumina is one of the most important oxides because of its high melting point, high wear resistance, high electrical insulation, good chemical, thermal, and mechanical stability [1]. The unique properties of a-alumina make it useful in a variety of applications including catalyst, polishing, electronic, and bioceramics [2,3]. Increasing attention has been paid to the development of nano- sized a-alumina particles. Park et al. [2] reported a preparation of 50 nm a-alumina by sol–gel processing of aluminum triisoprop- oxide (ATI). A solution method of producing 100 nm a-alumina particles using a seed crystal has been patented [4]. Recently, nanosized g-alumina particles were produced by neutralization of aluminum chloride solution with bases at ambient temperature [5,6] or by thermal decomposition of a mixture of sucrose and aluminum nitrate solution at 400 8C [7]. The calcination of the g- alumina particles derived from the thermal decomposition led to a-alumina particles, 44–55 nm in size. In contrast to these liquid- phase methods that involve a series of time consuming steps such as filtration, washing and drying, vapor-phase methods capable of producing dry nanoparticles in one step were reported by which trimethylaluminum (TMA), aluminum tri-sec-butoxide (ATBO), or anhydrous aluminum chloride vapor was oxidized, decomposed, or hydrolyzed [8–10]. ATI is less hazardous than TMA and higher in aluminum content than ATBO. ATI has been used for vapor-phase preparation of thin films [11,12]. To our knowledge, however, there is no report on the vapor-phase preparation of particles using ATI. The admission of ATI vapor into a flame would probably yield alumina nanoparticles similar in structure to the fumed alumina that has been commercially produced by flame hydrolysis of aluminum chloride vapor. The alumina particles produced from the flame process are known to be severely agglomerated due to the high temperature, and the phase of which is a mixture of g, d, and a. To obtain a- alumina particles based on any vapor-phase method, two stages may be required; in the first stage amorphous or transient alumina particles are produced and in the second stage these particles are calcined for hours to transform the phase into a. In the present study, solid particles that can be used as precursor for nano-sized a alumina were prepared by decomposition of ATI vapor at a temperature of about 200 8C. The use of such a low temperature is an advantage, compared with the high-temperature flame process. ATI, which is solid at ambient condition, was vaporized and decomposed with HCl as catalyst. The particles as- produced are not alumina but intermediates, AlO x Cl y (OH) z , which turned into a-alumina upon calcination. The conversion of ATI and the particle size and morphology of the alumina precursor were investigated under varying decomposition conditions. The calcina- tion condition for the transformation into a-alumina was studied. Materials Research Bulletin 46 (2011) 2199–2203 A R T I C L E I N F O Article history: Received 12 October 2010 Received in revised form 13 May 2011 Accepted 14 September 2011 Available online 21 September 2011 Keywords: A. Ceramics B. Chemical synthesis C. Thermogravimetric analysis C. X-ray diffraction A B S T R A C T A new solid precursor, hydrous aluminum oxide, for a-alumina nanoparticles was prepared by thermal decomposition of aluminum triisopropoxide (ATI) vapor in a 500 mL batch reactor at 170–250 8C with HCl as catalyst. The conversion of ATI increased with increasing temperature and catalyst content; it was nearly complete at 250 8C with the catalyst at 10 mol% of the ATI. The obtained precursor particles were amorphous, spherical and loosely agglomerated. The primary particle size is in the range 50–150 nm. The ignition loss of the precursor was 24%, considerably lower than 35% of Al(OH) 3 , the popular precursor for alumina particles. Upon calcination of the precursor at 1200 8C in the air with a heating rate of 10 8C/ min and a holding time of 2 h, the phase was completely transformed into a. The spherical particles composing the precursor turned worm-like by the calcination probably due to sintering between neighboring particles. The surface area equivalent diameter of the resulting a-alumina was 75 nm. ß 2011 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +82 41 521 9354; fax: +82 41 554 2640. E-mail address: kypark@kongju.ac.kr (K.Y. Park). Contents lists available at SciVerse ScienceDirect Materials Research Bulletin jo u rn al h om ep age: ww w.els evier.c o m/lo c ate/mat res b u 0025-5408/$ – see front matter ß 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.materresbull.2011.09.011