Electrical properties of C/C and C/C–SiC ceramic fibre composites Shraddha Singh, V.K. Srivastava * Department of Mechanical Engineering, Indian Institute of Technology, BHU, Varanasi 221005, India Received 8 February 2010; received in revised form 27 May 2010; accepted 21 July 2010 Available online 21 August 2010 Abstract The electrical properties of carbon/carbon (C/C) and carbon/carbon–silicon carbide (C/C–SiC) ceramic composites were measured. The results show that the capacitance decreases rapidly with an increase in frequency and it becomes constant above a frequency of 500 kHz, whereas the dissipation factor increases with increasing frequency. C/C–SiC composites give higher value than C/C composites due to the presence of microcracks. # 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: Carbon ceramic composites; C/C; C/C–SiC; Electrical capacitance 1. Introduction Ceramic matrix composites (CMC) have many potential applications as high-temperature structural components, because of their high strength at elevated temperature, low density, superior toughness and wear resistance. Originally, demands in space and aeronautics technology played the decisive role in the development of ceramic matrix composites. High specific characteristics and extreme temperature resis- tance are important in selection criteria for materials used in jet engines and thermal protection systems of new spacecraft and rockets. Among CMC, carbon fibre reinforced silicon carbide composites (C/SiC) have been extensively investigated and received certain practical applications. Within the last few years, the properties and the manufacturing methods of ceramic matrix composite (CMC) materials have been improved, so that the industry in general can share the profits of this new class of materials. C/C–SiC composites exhibit improved mechanical and thermal performance characteristics such as low density, high strength-to-weight ratio and wear resistance. It has been found wide applications in the field of aerospace and aeronautics industry for rocket nozzles and re-entry thermal protection shields of space vehicles. Ceramic brake discs and heat insulating materials are used in automotive industry because of their low cost manufacturing methods [1,2]. Further, SiC-based ceramics are known to exhibit excellent oxidation characteristics related to the formation of a protective silica scale (passive regime), which slows down inward diffusion of oxygen. Significant research is going on for the development of porous materials. Some of the porous material includes; graphite/carbon foam, ceramic foam and porous conducting paper for electrodes of fuel cells, etc. However, Si–SiC porous ceramic is derived from C/C–SiC composites, which exhibit superior performances over the conventional porous materials [3]. Silicon infiltrates into the cracks arising from the pyrolysis of carbon fibre reinforced matrix composite and form layers of protective segments over the carbon fibres resulting in the retardation of oxidation in C/C–SiC composite, when subjected to the high-temperature environ- ments. The carbon fibres that run through the C/C–SiC laminate are not completely covered by the silicon carbide/free silicon in the longitudinal direction of the fibres [4,5]. The above- mentioned facts of the C/C–SiC ceramics are difficult to obtain (Table 1). Hence, a controlled oxidation of the C/C–SiC composite in an oxidizing atmosphere should result in the oxidation of the carbon fibres only leaving behind a network of channels, resulting from depletion of carbon throughout the entire composite, forming a highly porous structure [6–8]. Ceramic composites are potential materials in the field of electrical and optoelectrical applications. Among passive electronic components, capacitors are of much importance for integrated circuits, because a large number of capacitors are used in electronic systems for various functions, such as signal de-coupling, switching noise suppression, filtering, and tuning. www.elsevier.com/locate/ceramint Available online at www.sciencedirect.com Ceramics International 37 (2011) 93–98 * Corresponding author. Fax: +91 542 2368428. E-mail address: vk_sa@yahoo.co.in (V.K. Srivastava). 0272-8842/$36.00 # 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2010.08.026