ASIAN JOURNAL OF CHEMISTRY ASIAN JOURNAL OF CHEMISTRY http://dx.doi.org/10.14233/ajchem.2014.17005 INTRODUCTION The actual corrosion of composite materials quite often begins with reaction of the reinforcement material and espe- cially with any interface material (called the interphase) used to coat the reinforcement for debonding. One property that exacerbates is a mismatch in thermal expansion coefficients between the reinforcement and matrix, leading to microcracks. These microcracks allow the ingress of corrosive gases (e.g., oxygen) 1 . Actually, a large amount of the literature on composites is concerned with an evaluation of the internal reactions that take place among the various reinforcement, interphase and matrix materials. The seawater corrosion of SiC/Al was found to be more resistant than graphite/Al by Aylor and Kain 2 . This was attributed to a lack of a galvanic driving force between the SiC and the aluminum matrix, although both composites exhibited similar mechanisms of corrosion, essentially pitting of the metal matrix around the reinforcement material. Budruk et al. 3 studied the corrosion behavior of pure magne- sium, Mg-Cu (0.3, 0.6 and 1 vol. %) and Mg-Mo (0.1, 0.3 and 0.6 vol. %) composites in 3.5 % NaCl solution by weight loss Thermodynamic and Kinetic Study for Corrosion of Al-Si-Cu/Y 2 O 3 Composites RANA AFIF MAJED ANAEE Department of Materials Engineering, University of Technology, Baghdad, Iraq Corresponding author: E-mail: dr.rana_afif@yahoo.com Received: 8 January 2014; Accepted: 20 February 2014; Published online: 5 July 2014; AJC-15499 This study involves the effect of yttria with three wt. % (1, 2 and 3 %) on the corrosion behavior of Al-Si-Cu alloy in 0.1 N NaOH solution by potentiostat at four different temperatures 303, 313, 323 and 333 K. Corrosion parameters for these composite materials were determined by Tafel extrapolation method such as corrosion potentials Ecorr, corrosion current densities icorr and Tafel slopes bc and ba. The results of electrochemical study indicates that Al-Si-Cu/1 % yttria gave the lowest corrosion rate due to behaviour of yttria as protective layer which cover the metallic surface and enhances the passive film of Al2O3, while 2 and 3 % yttria may be behave as sufficient cathode leading to increasing the corrosion of base alloy because of the inhomogenous structure of an metal matrix composite which must be considered in designing a corrosion protection system. Thermodynamic study was achieved to estimate thermodynamic quantities of corrosion process ΔG, ΔS and ΔH. The results show spontaneous the corrosion in 0.1 N NaOH through the negative values of Gibbs free energy for composites and the lowest spontaneous process was for Al-Si-Cu/1 % yttria, the change in entropy values were positive and the lowest value was for Al-Si- Cu/1 % yttria. Also the change in enthalpy values was positive referring to endothermic nature of corrosion process. Kinetic study was applied using Arrhenius equation to estimate activation energies and the highest activation energy was for Al-Si-Cu/1 % yttria, this means that this composite need most energy to surmount the energy barrier. The relationship existed between values of the activation energy (Ea) and logarithm of pre-exponential factor (log A) for different material suggesting the operation of a compensation effect in kinetics of corrosion. This suggests that, the corrosion reaction proceeds on surface sites, which were associated with different energies of activation. Keywords: Corrosion, Composite material, Thermodynamic quantities, Kinetic study. and polarization methods. The corrosion rate increased with increasing volume fraction of reinforcement in Mg-Cu and Mg-Mo composites. Jamaludin et al. 4 studied the influence of heat treatment on the corrosion behavior of two Al-Cu matrix composites (15 vol % Al2O3p and 20 vol % SiCw) in 3.5 % sodium chloride solution by gravimetric measurements. Nickel et al. 5 studied the effect of plastic deformation on the corrosion and wear behavior of composites based on an Al-Cu alloy. Al2O3 or SiC particles in two different fraction (5 or 15 vol. %) by poten- tiodynamic polarization in NaCl solution. Bobic et al. 6 studied the corrosion behavior of metal matrix composites metal matrix composites with aluminium alloy matrix and they reviewed of boron-, graphite-, silicon carbide-, alumina- and mica- reinforced aluminium metal matrix composites. The reinforcing phase influ- ences on metal matrix composites corrosion rate as well as on various corrosion forms (galvanic, pitting, stress corrosion cracking, corrosion fatique, tribocorrosion). El-Sayed et al. 7 fabricated a series of different aluminum-graphite composites (Al-Gr), namely pure Al, Al-1%Gr, Al-2%Gr and Al-3%Gr. The surface of these composites was investigated using optical microscopy to examine the distribution of exfoliated graphite within aluminum in 3.5 % NaCl solution using many techniques. Asian Journal of Chemistry; Vol. 26, No. 14 (2014), 4469-4474