Ceramics International 30 (2004) 2235–2239 Qualitative measurement of residual carbon in wet-chemically synthesized powders Emerson R. Camargo a,∗ , Elson Longo a , Edson R. Leite a , Masato Kakihana b a LIEC-Departamento de Qu´ ımica, UFSCar-Universidade Federal de Sã Carlos, Rod. Washington Luiz km 235, CP 676, São Carlos 13565-905, SP, Brazil b Materials and Structure Laboratory, Tokyo Institute of Technology, Nagatsuta 4259, Midore-ku, Yokohama 226-8503, Japan Received 9 September 2003; received in revised form 20 December 2003; accepted 9 February 2004 Available online 24 April 2004 Abstract Sodium niobate powders were prepared by the polymerizable complex (PC) method using a water-soluble Nb–malic acid complex and sodium carbonate. Niobium oxide pentahydrated was dissolved in hot oxalic acid (OA) solution, followed by the addition of NH 3 (30%) until pH 11, precipitating niobic-acid that was added into a solution of dl-malic acid (MA) at mole ratio of [MA]:[Nb] = 2:1. Na 2 CO 3 was added in the mole ratio [Na]:[Nb] = 1:1, and the solvent was eliminated at 70 ◦ C, forming a yellow gel without any segregation. The gel was calcined at 300 ◦ C for 3 h, and the (Na–Nb–MA) heated material was calcined in the range of temperatures from 400 to 900 ◦ C, from 5 min to 8 h. Pure NaNbO 3 (NN), free from amorphous carbon, which crystallized at temperatures higher than 450 ◦ C, was confirmed by a combined analysis using X-ray diffraction and UV–Raman spectroscopy. A correlation between the presence of residual carbon and the crystallite size, which was calculated using the Scherrer formula, was observed and qualitatively used to infer about this presence of residual carbon. © 2004 Elsevier Ltd and Techna S.r.l. All rights reserved. Keywords: A. Powders: chemical preparation; B. Grain size; B. X-ray methods; D. Niobates 1. Introduction In recent years, there has been a great deal of interest in preparation of multi-component oxide materials using wet-chemical routes. Potentially, these techniques allow a better mixing of the constituent elements and thus a better reactivity of the mixture to obtain pre-reaction products at lower temperatures [1,2]. One such technique is the so-called amorphous complex (AC) method [3–5], often called as the amorphous citrate method [5–7]. This technique is based on the synthesis of a solution of some soluble metal–organic complexes followed by the elimination of the solvent by means of evaporation, resulting in an amorphous gel that keeps the random distribution of cations from the starting solution. The organic fraction of this gel is removed by heat process between 300 and 600 ◦ C, resulting in a very fine, homogeneous and reactive crystalline oxide powder at tem- peratures lower than those used by the solid-state reaction ∗ Corresponding author. E-mail address: camargo@liec.ufscar.br (E.R. Camargo). method. Another widely used technique is the polymerizable complex (PC) method [8–12], originally known as the Pe- chini method [13]. This method slightly differs from the AC method by the presence of a polyalcoohol that allows a con- densation reaction between the soluble complexes, resulting in a rigid organic polymer that immobilizes the cations. Sim- ilarly to the AC method, the organic fraction is eliminated by heat process. Despite the fact that AC and PC methods have been widely and successfully applied in the synthesis of several niobates powders for different applications, such as di- electrics, ferroelectrics, catalysts, etc. [8–12,14–16] where the presence of residual carbon can be deleterious to the final designed application, there are few studies concerning the presence of this residual carbon in powders synthesized by these wet-chemical methods. Usually, the calcination temperature that is used to eliminate the carbon has been determined by a trial and error way. In this study, we demon- strated that there is a correlation between the presence of residual carbon and the crystallite size in ultra-fine NaNbO 3 (NN) powders synthesized by the AC method that can be 0272-8842/$30.00 © 2004 Elsevier Ltd and Techna S.r.l. All rights reserved. doi:10.1016/j.ceramint.2004.02.003