Journal of the European Ceramic Society 27 (2007) 3545–3550 Surface characterisation and modification of submicron and nanosized silicon carbide powders S. Novak a,∗ , J. Kovaˇ c b , G. Draˇ zi´ c a , J.M.F. Ferreira c , S. Quaresma c a Department for Nanostructured Materials, Joˇ zef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia b Department for Surface Engineering and Optoelectronics, Joˇ zef Stefan Institute, Ljubljana, Slovenia c Department of Ceramic and Glass Engineering, CICECO, University of Aveiro, Aveiro, Portugal Received 1 November 2006; received in revised form 31 January 2007; accepted 10 February 2007 Available online 29 March 2007 Abstract The surface characteristics of two grades of silicon carbide powders were analyzed and modified with the aim to control and tailor their behaviour in colloidal suspensions. The as-received submicron and nanosized SiC particles were both found to be covered with a thin oxygen-containing layer, composed mostly of SiO 2 and SiC x O y ; however, their electrokinetic behaviours in aqueous suspensions were observed to be different. We coated the powders with a thin layer of aluminium oxy-hydroxide, which was found to modify their electrokinetic behaviours in aqueous suspensions. The composition and structure of the aluminium-containing layer were characterized by X-ray photoelectron spectroscopy (XPS) and TEM analyses. This coating may subsequently serve as a homogeneously distributed source of a low amount of sintering additive in manufacturing the SiC-based material for fusion application. © 2007 Elsevier Ltd. All rights reserved. Keywords: Powders-chemical preparation; Suspensions; SiC; Coating; Nuclear applications 1. Introduction The properties of silicon-carbide-based materials depend to a large extent on the composition and properties of the SiC starting powders, in particular on the chemical composition of their surfaces. In colloidal processing the preparation of a well- dispersed and highly loaded slurry of fine powder is one of the key steps towards producing high-performance ceramics. When nanosized powder is used, the role of the powder surface becomes even more important, due to the large specific surface area and increased reactivity with chemical species from the environment. In the case of silicon carbide for fusion application, where a strict control of composition is needed in order to assure acceptable behaviour of material at extreme conditions, powder surface oxidation is one of the common sources of problems dur- ing processing. Furthermore, limited amount of homogeneously distributed sintering additive is required in production of fusion- relevant SiC-ceramics, and morever, the content of the elements ∗ Corresponding author. Tel.: +386 1 477 3271; fax: +386 1 477 3221. E-mail address: sasa.novak@ijs.si (S. Novak). effecting the activation after irradiation with neutrons must be strictly limited. 1 One of the possible methods to meet these requirements is application of the additives as thin layers on ceramic particles. The main motivation of the present work was to control the surface properties of fine SiC-powders in order to enable their effective processing in suspensions, and at the same time to enable better sintering with the aid of a homogeneously distributed sintering additive. To achieve this, we coated the as-received commercial submicron and nanosized SiC powders with a thin layer of aluminium hydroxide, that should act as a sintering aid. Literature survey shows, that for the coating of non- oxide powders, e.g., SiC and Si 3 N 4 , various processes have been used, mostly employing Al-nitrate and Al-secondary butoxide as precursors to form Al-hydroxide coatings. 2–5 The proposed procedures result either in formation of a thin layer or in adhe- sion of fine “coating” particles at the matrix particles. Although several papers discuss the coating procedures and behaviour of the coated powders (mostly submicron), no report on compre- hensive study of the applied coating layer was found. In our work, attempts were undertaken to confirm the production of continuous coating layer at the SiC particles and to establish its composition. For this purpose we used two complementary 0955-2219/$ – see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2007.02.199