One-step synthesis of a multi-functional anti-oxidation protective layer on the surface of carbon/carbon composites Ya-Cheng Lin a , Elizabeth M. Ruiz a , Richard G. Rateick Jr. b , Paul J. McGinn a , Alexander S. Mukasyan a, * a Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN 46556, USA b Honeywell Advanced Technology, 3520 Westmoor St., South Bend, IN 46637, USA ARTICLE INFO Article history: Received 19 May 2011 Accepted 5 September 2011 Available online 10 September 2011 ABSTRACT A multi-functional anti-oxidation (AO) protective coating is produced in one-step synthesis on the surface of the carbon/carbon (C/C) composite by a novel electrically induced liquid infiltration (EILI) method. The AO coating involves several protective layers which have dif- ferent anti-oxidation mechanisms. In this study phosphorus acid is applied as active-site poisoning agents to inhibit oxidations by forming stable glassy complex barriers that decrease oxygen diffusion. Simultaneously silicon carbide (SiC) or SiC/silica layers are formed on the surface of C/C composites that act as physical protection barriers for oxygen penetration. It is proved that under the optimum conditions the acid groups survive the high temperature EILI process. Oxidation tests reveal that formed coatings effectively protect C/C composite from oxidation: average percent of weight losses decrease from 30 to 1 wt.% and from 69 to 5 wt.% for the thermal (1150 K) and catalytic (920 K) oxidation tests, respectively. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Carbon/carbon (C/C) composites are noted for their low density and high strength-to-weight ratio, as well as having good mechanical properties at elevated temperatures. These characteristics make them appealing to the aerospace industry for applications such as rocket nozzles, noses and leading edges of reentry vehicles and gas turbine engine components [1]. The high temperature strength and wear resistance of C/C composites, in particular, make them attractive for use as aircraft brake disks, where tem- peratures are routinely around 1300 K under normal landing conditions but can be as high as 2300 K under critical conditions like rejected take-off [2,3]. However, the fact that C/C composite oxidizes at temperature as low as 600 K has required the development of protective anti-oxidation coat- ings for high temperature applications. To prevent oxidation and the consequential gasification, multiple-functional coating with different oxidation resistant mechanisms is the most effective solution. The anti-oxidation (AO) of C/C composites has been stud- ied in great detail in the past. Three main oxidation retarda- tion mechanisms are outlined: (i) by forming of a diffusion barrier, (ii) by, so-called, active-site poisoning and (iii) by cat- alytic inhibition. The most common protection method is to apply a coating that will inhibit oxygen diffusion towards the C/C component, as well as prevent the diffusion of carbon outward. For such barriers to work, two criteria should be met. First, the coating must have a strong bond with the car- bon substrate. Second, the coefficients of thermal expansion (CTE) of the composite and the coating must be as close as possible. The latter condition proves to be a difficult task due to the low CTE of C/C composites [3]. Mismatch of CTE can lead to cracks in the coating. Therefore, the main shortcoming of a diffusion barrier is often the occurrence of microcracks that allow oxygen diffusion [4]. 0008-6223/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2011.09.014 * Corresponding author: Fax: +1 574 631 8366. E-mail address: amoukasi@nd.edu (A.S. Mukasyan). CARBON 50 (2012) 557 – 565 Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon