Journal of the European Ceramic Society 26 (2006) 3881–3886 Wetting behaviour of Y 2 O 3 /AlN additive on SiC ceramics R.M. Balestra ∗ , S. Ribeiro, S.P. Taguchi, F.V. Motta,C. Bormio-Nunes Department of Materials Engineering (DEMAR), Faculty of Chemical Engineering of Lorena (FAENQUIL), Polo Urbo Industrial, Gleba AI6, CP 116, 12600-970 Lorena, SP, Brazil Received 2 May 2005; received in revised form 27 November 2005; accepted 16 December 2005 Available online 20 February 2006 Abstract The wetting of SiC plate by Y 2 O 3 /AlN additive was analysed using the sessile drop method. The wetting behaviour was observed by image capture system using a CCD camera during the heating, in argon atmosphere. The contact angle was measured as a function of temperature and time. After the wetting test the SiC plus additive samples were cut in order to observe the thickness plate cross section. The additive area and the interface between SiC and additive were analysed using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The wetting of SiC by Y 2 O 3 /AlN is influenced by the presence of a solid phase in some of the additive drops that depends mainly on the additive composition and consequently on the temperature. The measured contact angles were below 7 ◦ , reaching 0 ◦ for Y 2 O 3 /AlN additive tested at the eutectic composition, indicating a very good wettability of Y 2 O 3 /AlN on the SiC. © 2006 Elsevier Ltd. All rights reserved. Keywords: Wettability; Interfaces; SiC; Y 2 O 3 ; AlN 1. Introduction It is well known that the bonds between silicon and carbon atoms in SiC (silicon carbide) are very strong, as a consequence, SiC has a low self-diffusion coefficient. This property limits the production of high density SiC ceramics by solid phase sinter- ing. In order to get a high density ceramic, some metallic oxides (additives) can be added to SiC. The objective is to form a liq- uid phase during the sintering. The liquid phase sintering (LPS) results in a material with an homogeneous microstructure and therefore suitable to achieve good mechanical properties such as a high toughness. 1–6 The important variable of the LPS process to obtain SiC ceramic is the wetting of the solid phase (SiC) by the liquid phase (additive). The wetting behaviour is measured through the contact angle (θ) between the solid SiC and the liquid drop formed by the additive. The solid–liquid systems may be of two types, i.e. non-reactive and reactive. In non-reactive systems, the contact angle θ is expressed as a function of the surface energies solid–liquid (γ SL ), liquid–vapour (γ LV ), solid–vapour (γ SV ), as well as the adhesion work (W a ). The mutual dependence of sur- face energies, adhesion work and contact angle is described by ∗ Corresponding author. Tel.: +55 012 3159 9954; fax: +55 012 3153 3006. E-mail address: roselibalestra@yahoo.com.br (R.M. Balestra). Young and Yong-Dupr´ e equations, 7–16 that are given by Eqs. (1) and (2): γ SV = γ SL + γ LV cos θ (1) W a = γ LV (1 + cos θ) (2) When a reaction occurs at the interface, the free energy change per unit area per unit time also enhances wetting. In this case, the Young equation should be corrected for this driv- ing force. 7,10 The smallest contact angle in reactive system is given by Eq. (3), cos θ min = cos θ 0 - γ r γ LV - G r γ LV (3) where θ 0 is the contact angle of the liquid on the substrate in the absence of any reaction, G r is the Gibbs free energy of the chemical reaction, γ r is the change in the interfacial energies brought about by the chemical reaction. One possible source of reaction is related to the oxygen partial pressure in the furnace. The reaction of oxygen with the substrate of SiC can form a thin film of SiO 2 . However, at temperatures higher than 1475 K, in vacuum, the SiO 2 film evaporates accord- ing to the reaction of Eq. (4). 10 2〈SiO 2 〉 s +〈SiC〉 s → 3(SiO) g ↑+(CO) g ↑ (4) 0955-2219/$ – see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2005.12.022