High surface area neodymium phosphate nano particles by modified aqueous sol–gel method Sasidharan Sankar a , Krishna Gopakumar Warrier a, *, Rajesh Komban b a Materials Division, National Institute for Interdisciplinary Science and Technology, Council of Scientific & Industrial Research, Thiruvananthapuram 695 019, Kerala, India b Institut fu ¨r Chemie, Anorganische Chemie 1, Universita ¨t Osnabru ¨ck, Barbarastraße 7, 49069 Osnabru ¨ck, Germany 1. Introduction Synthesis of rare earth phosphates has gained considerable attention over the years [1–4], since they have wide range of potential applications in the form of powders, coatings or dense sintered parts. Structural stability at higher temperatures above 1900 8C, high melting point [5] and non-reactivity with other oxides make these materials potential candidates for use at elevated temperatures. This class of phosphates has also been identified for use for encapsulating radioactive wastes for safe permanent disposal [6]. Rare earth phosphates are also well reported to have diverse applications in various fields like fluorescent coatings [7], bioimaging [8], and phosphors [9]. NdPO 4 particles are reported to have tribological applications due to layered structure. Furthermore, NdPO 4 has found considerable applications in laser physics [10], and as ceramic materials [11]. With Rare earth phosphates being found as promising catalysts/ hosts [12], NdPO 4 supported catalysts have also been reported for polymerization of styrene [13] with increased initiation efficiency and also in biosensing application [14]. NdPO 4 is certainly a very interesting material for its properties due to the reduced dimensionality and applications. The synthesis of NdPO 4 particles was reported by various techniques like direct chemical reaction [14], flux assisted [15], heating [16,17], hydrothermal [18,19], microwave assisted [20] and solid state reaction methods. The synthesis of NdPO 4 by much simpler methods such as sol–gel method has not been attempted in detail, as seen from the literature unlike lanthanum and cerium phosphates. Sol–gel process is well reported to be superior to many other preparation methods, since intimate mixing of components ensures homogeneity of the final product and applications from coatings to powders can be addressed with a single preparation scheme. Therefore an attempt has been made here to synthesize of NdPO 4 through sol–gel process starting from neodymium nitrate. Nanosize rod shaped NdPO 4 particles with high specific surface area are reported here and along the procedure for synthesis, a precipitation–peptization mechanism followed by electrostatic stabilization is being adopted. 2. Experimental 2.1. Synthesis Neodymium nitrate, 99.9% pure (M/s Indian Rare Earths Ltd., India) and orthophosphoric acid, 88% (SD Fine Chemicals, India) were used as precursor material for the preparation of neodymium phosphate particles. 0.05 M solution of Nd(NO 3 ) 3 6H 2 O was prepared in de-ionized water and was kept under stirring using a mechanical stirrer for 30 min. Orthophosphoric acid solution was Materials Research Bulletin 46 (2011) 2373–2377 A R T I C L E I N F O Article history: Received 13 April 2011 Received in revised form 27 June 2011 Accepted 24 August 2011 Available online 1 September 2011 Keywords: Ceramics Sol-gel chemistry X-ray diffraction Phase transactions Electron microscopy A B S T R A C T Synthesis of nano rod shaped neodymium phosphate (NdPO 4 ) particles with specific surface area as high as 107 m 2 g 1 and an average length of 50 nm with aspect ratio 5 was achieved using modified sol gel method. Crystallite size calculated from the X-ray diffraction data by applying Scherer equation was 5 nm for the precursor gel after calcination at 400 8C. NdPO 4 was first precipitated from neodymium nitrate solution using phosphoric acid followed by peptization using dilute nitric acid and further gelation in ammonia atmosphere. The calcined gel powders were further characterized by surface area (Brunauer–Emmet–Teller nitrogen adsorption analysis), Transmission electron microscopy, scanning electron microscopy, UV–vis and FT-IR analysis. Transmission electron microscopy confirms the formation of rod like morphology from the sol, gel and the calcined particles in nano size range. These particles could be compacted and sintered at as low as 1300 8C to a density of 98.5% (theoretical) with an average grain size of 1 mm. ß 2011 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +91 471 2515280; fax: +91 471 2515280. E-mail address: wwarrierkgk@yahoo.co.in (K.G. Warrier). 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.2011.08.050