SUPFLU-1223; No. of Pages 9 J. of Supercritical Fluids xxx (2006) xxx–xxx Synthesis of nanoparticulate yttrium aluminum garnet in supercritical water–ethanol mixtures Albertina Caba˜ nas a,∗ , Jun Li b , Paul Blood b , Tadeusz Chudoba c , Witold Lojkowski c , Martyn Poliakoff d , Edward Lester b,∗∗ a Departamento de Qu´ ımica-F´ ısica I, Universidad Complutense de Madrid, E-28040 Madrid, Spain b School of Chemical, Environmental and Mining Engineering, University of Nottingham, Nottingham NG7 2RD, UK c Institute of High Pressure Physics (UNIPRESS), Warsaw PL-01142, Poland d School of Chemistry, University of Nottingham, Nottingham NG7 2RD, UK Received 25 May 2006; received in revised form 26 June 2006; accepted 30 June 2006 Abstract Single-phase YAG nanoparticles have been produced by the rapid hydrolysis and dehydration of Al 3+ and Y 3+ salts in EtOH–H 2 O mixtures using continuous supercritical water hydrothermal synthesis. The effects of the nature of the starting solution, the metal concentration, the EtOH content, the flow rate and the temperature on the particle size were studied. EtOH promotes crystallization and highly crystalline materials are obtained at relatively low temperatures. Furthermore the critical temperature of EtOH–H 2 O mixtures is lower than that of pure H 2 O, reducing the operating temperature. From the variables studied, the most important parameter seems to be the temperature and much smaller particles have been obtained when experiments are conducted under supercritical conditions (average 50 nm), in comparison to near critical or subcritical conditions (average 150 nm). The method is simple and clean and requires neither addition of a base to the system nor the use of very high reaction temperatures and potentially allows the continuous production of large quantities of material. © 2006 Elsevier B.V. All rights reserved. Keywords: Supercritical water; Yttrium aluminum garnet; Nanoparticles; Water–ethanol mixtures; Hydrothermal synthesis; Solvothermal synthesis 1. Introduction The synthesis of yttrium aluminum garnet (YAG or Y 3 Al 5 O 12 ) has received much attention on account of its use in structural and functional materials [1]. Because of its high creep- and oxidation-resistance at high temperature and low heat conductivity, YAG might also be suitable for high temper- ature structural components, e.g. inside gas turbines [2]. Single crystal YAG is the most creep-resistant oxide available and has been used for fiber reinforcement and in ceramic composite cut- ting tool material [3]. Polycrystalline YAG also has considerable potential as a refractory fiber material [4]. Among its functional properties, YAG possesses a high efficiency of energy transfer and is resistant to radiation damage, which therefore makes it ∗ Corresponding author at: Departamento de Qu´ ımica-F´ ısica I, Ciudad Uni- versitaria s/n, E-28040 Madrid, Spain. Tel.: +34 91 394 4200; fax: +34 91 394 4135. ∗∗ Corresponding author. E-mail addresses: a.cabanas@quim.ucm.es (A. Caba ˜ nas), Edward.Lester@Nottingham.ac.uk (E. Lester). ideal for laser lenses. The usable transmittance range of YAG extends from the UV to the mid-IR range, making it very useful for IR and laser windows, with a very low absorption coefficient [5]. Furthermore YAG displays a cubic crystal structure, which imparts optical isotropy (unlike sapphire). Doping YAG with dif- ferent trivalent ions changes the optical properties of the doped materials [6,7]. YAG has also been used in phosphors for scan- ners and contrast-enhanced display applications [8]. Whether manufacturing YAG for phosphor applications or ceramic fabri- cation, fine-sized particles with no agglomeration are desirable. YAG powder is conventionally prepared from the solid-state reaction of Y 2 O 3 and Al 2 O 3 at 1600–1800 ◦ C. However the pro- cess is very slow (10–20 h) because YAlO 3 (YAP) and Y 4 Al 2 O 7 (YAM) phases are formed as reaction intermediates and they only transform into single-phase YAG at high temperatures [6]. Finer particles can be prepared using wet chemical routes such as sol–gel [9], co-precipitation [10], combustion [11] and spray pyrolysis [12]. Sol–gel and co-precipitation techniques require additional high temperature heat treatment in order to produce single-phase crystalline materials. Furthermore aggregation of the products during the post-heating treatment is quite common. 0896-8446/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.supflu.2006.06.006 Please cite this article as: Albertina Caba ˜ nas et al., Synthesis of nanoparticulate yttrium aluminum garnet in supercritical water–ethanol mixtures, J. of Supercritical Fluids (2006), doi:10.1016/j.supflu.2006.06.006.