Novel Hydrothermal Electrodeposition Technology For Preparation Of Yttrium Silicates Coating On Carbon/Carbon Composites

Abstract

Carbon/carbon (C/C) composites exhibit excellent mechanical properties such as high strength-to-weight ratio and the retention of strength at high temperature. The most important factor which currently precludes the use of C/C composites at high temperature applications is their oxidation in an oxygen containing atmosphere [I]. The deposition of an oxidation resistant coating on the C/C surface is one of the reasonable choices to solve this problem. Yttrium silicates have been shown to possess the required properties for use in oxidation resistant coatings. These can be summarized as low Young's modulus ... low thermal expansion coefficient, low oxygen permeabIlity and good erosion resistance [2]. The preparation technology is considered to be extremely important to attainina .. . 0 an antIcIpatIve yttrium silicate coating. Yttrium silicates coatings have been prepared by plasma spray and slip dipping method [3-5]. These preparation processes, however, must be carried out at hi~h temperature which will result in bad bonding between the coating and carbon substrate. The purpose of this work is to design a novel low temperature preparation technology to deposit yttrium silicate coating on C/C composites. Electrodeposition technology has been used to produce various coatings because of its numerous advantages such as the low cost, high efficiency and simple operation and, in particular, homogeneous coating on substrates with complex structures can be easily achieved. Moreover, the special physical and chemical conditions provided by a hydrothermal environment could effecti vely accelerate the speed of mass transfer and reduce the crystallization point without subsequent high temperature heat treatment as in conventional technology. In other words. hydrothermal technology makes it possible to acquire highl; crystallized coatings at low temperature with fewer t1aws. Therefore, the combination of electrodeposition and hydrothermal technologies is a promising way to deposit ceramic coatings such as yttrium silicates on constructed substrates.