AN IMPROVED SOL-GEL PROCESS FOR THE NANO-STRUCTURED CORROSION RESISTANT ALUMINA COATINGS

摘要

Present investigation is an improved sol-gel process for the nano - structured alumina coatings. The time consumed in the synthesis of alumina sol in the present process is significantly reduced to around 5 to 6 hrs as compared to existing sol-gel process of synthesis of alumina sol. In the present process a complete hydrolysis of aluminium iso-propoxide is obtained within 5-6 hrs and completion of process is followed by peptization by addition of dil nitric acid. A complete conversion of white suspension into bluish white colloid alumina (boehmite) sol is visually confirmed resulting in a very simple and less time consuming process of synthesis. The synthesized sol is of appropriate viscosity and remained stable for several days. The sol is used for the development of corrosion and oxidation resistant nano structured alumina coatings on various steel substrates. The coatings are found to possess alumina particles (~ 8 nm in size) arranged in a regular pattern. The nano structured alumina coatings is found to improve the corrosion resistance substantially of mild steel, 9Cr-lMo ferritic steel and 304L stainless steel in 3.5% NaCl and chloride containing acidic environments. The coatings are proved to be efficient in protecting 9Cr-lMo ferritic steel in highly oxidative air and air/salt environments at elevated temperatures. Present invention related to improved sol gel process for alumina coating development can be used for the enhancement of the service life of iron and nickel based steel in aqueous and high temperature oxidative environments.