Carbon/carbon (C/C) composites exhibit excellent structural and thermomechanical properties [1]. However, their susceptibility to air oxidation at temperatures above 450 8C represents one of the major technological obstacles preventing wider commercialization of carbon/carbon technology. This has led to research on the improvement of the oxidation resistance of C/C composites. During our investigations on this aspect, we have found that sol–gel, technology which has attracted increasing interest in recent years, offers a feasible way of providing glass/ceramics based oxidation resistant coatings at low processing temperatures [2]. The scope of the investigation reported here was to improve the oxidation resistance of C/C composites by sol–gel derived zirconia–silica which fulfils the requirements for oxidation protection coatings of C/C composites. The silica–zirconia of different compositions was synthesized, characterized and applied to C/C composites to arrive at a suitable material that will enhance the oxidation resistance of C/C composites. Silica sol was prepared by hydrolytic polycondensation of TEOS in the molar composition of TEOS:H2O:CH3CN:HCl of 1:4:4:0.05. Binary oxides 20ZrO2 . 80SiO2 (20ZS), 40ZrO2 . 60SiO2 (40ZS) and 60ZrO2 . 40SiO2 (60ZS) were prepared by mixed hydrolytic polycondensation of TEOS and Zr-n-propoxide, which was carried out as described below after keeping the molar composition of Zr:PrOH:CH3COCH2COCH3 at 1:2:0.5 and that of TEOS:H2O:CH3CH:HCl at 1:4:4:0.05. TEOS (50 wt %) was prehydrolysed under vigorous stirring for 30 min containing full amount of water, acetonitrile and HCl. This prehydrolysed TEOS was then added drop to drop by the homogenous solution of TEOS (50%), zirconium-npropoxide, acetylacetone and propanol. The mixture was then stirred for 3 h at 30 8C. Coatings were applied by dip coating at a withdrawal speed of 2 cm miny1. The surface morphology was examined using scanning electron microscopy (SEM; Jeol 3SCF). X-ray diffraction (XRD; Siemens D-500; CuKα) was used to record the diffractograms. Dilatation behaviour and oxidation kinetics were investigated using TMA-40 and TG-50 modules, respectively, attached to a thermal analyser (Mettler TA3000) interfaced with TA72 software. Fig. 1 shows the X-ray diffractograms of materials heat treated at 600 and 1100 8C. The data reveals that the tetragonal phase of zirconia observed at 600 8C became prominent on further heat treatment to 1100 8C. A significant feature observed in this study is the appearance of diffraction peaks, related to zircon phase in the 60ZS material after heat treatment to 1100 8C. The results of a dilatometric study performed on the materials heat treated to 1100 8C in the temperature range 50–1000 8C are shown in Fig. 2. The data reflects the fact that binary oxides 20ZS and 40ZS showed three-step dilatometric behaviour, with steps observed at around 600 and 800 8C. In the case of the 60ZS material, a uniform dilatometric behaviour with a coefficient of thermal expansion (CTE) value of 4 ppm Ky1 was observed, which is quite comparable to that of C/C composites. Fig. 3 shows the dilatometric behaviour of the thin films of materials dried at up to 200 8C over a long period of time under ambient conditions. The data reflects that 20ZS and 40ZS materials showed a considerable amount of shrinkage up to 700 and 850 8C, respectively, and large shrinkage beyond