DEVELOPMENT OF OXIDATION RESISTANCE COATINGS BY SOL-GEL PROCESS

Abstract

Hot corrosion and Oxidation are serious problems in internal combustion engines, power generation equipment, marine, industrial, and land-base gas turbines, industrial waste incinerators, paper and pulp and other industries. The reason behind this is the usage of wide range of fuels coupled with increased operating temperatures, which leads to the degradation. The present results reveal the interest of sol—gel coating technique to improve Boiler steel high temperature oxidation resistance .A zircornium sol—gel coating appears to enhance the oxidation resistance during cyclic oxidation test. In present experiment high temperature oxidation(in air) and hot corrosion (in Na2SO4+60%wt. V205 salt medium) of Boiler Steel Al grade and Superco 605 superalloy have been performed at 900°C under cyclic conditions. The two different materials are taken for the better comparison of results developed by Sol-Gel processing. The mass gain measurements were performed after each cycle to establish the kinetics of oxidation using thermo gravimetric technique. X-ray diffraction (XRD), Field emission scanning electron microscopy/energy dispersive spectroscopic analysis (FESEM/EDAX) and X-ray mapping techniques were used to analyze the oxidation products. Cross- section technique is used for the confirmation of the thickness of the oxide layers produced by cyclic oxidation. Sixty five years ago Geffcken and Bergen prepared single oxide coatings by the sol-gel process and Schroeder developed a thin film physics. The first products appeared on the market in 1953 and large scale production in 1959 with automotive rear-view mirrors; later anti-reflection coatings and sun shielding windows were introduced using Ti02 and Si02. Dislich and Hinz elaborated the chemical basis for the preparation of multicomponent oxides, glasses, glass ceramics and crystalline substances in 1969 and published their results in 1971. So from 1971 on it was known that any type of multicomponent oxide can be synthesized using the alkoxides of the different elements by the sol-gel process. iii The applications for sol gel-derived products are numerous like. Protective and decorative coatings and electro-optic components can be applied to glass. Macroscopic optical elements and active optical components as well as large area hot mirrors, cold mirrors= lenses and beam splitters all with optimal geometry can be made quickly and at low cost via the sol-gel route. With the viscosity of a sol adjusted into a proper range, both optical and refractory ceramic fibers can be drawn which are used for fiber optic sensors and thermal insulation, respectively but if the viscosity is so balanced that it may be used as Thick coating on the substrates, this is the main challenge. iv