High temperature resistant slurry based coating for steel

The current technologies for high temperature protective coating based on composite systems, such as complex oxides, silicide, aluminides, carbides and nitrides etc. are meant for high temperature service alloys,which are not easily removable from meal surface In the present investigation, studies were made to provide a barrier type of protective coating over steel surface. the coating consisted of metallic aluminum powder, asbestos powder, cobalt oxide, kaoline, Al2O4 TiO2 and ZrO2 and the binders. The binders, such as aluminium phosphate, sodium silicate, ethyl silicate, modified sodium silicate and Ivory-400 were used. It was aimed to produce a slurry based coating which would be strippable as desired in subsequent processing. The coating particulates were added in varying amount varying from 1-10 % by weight of the binder. Mild steel sample of 50 mm x 2 mm were used for the test. The coating was applied over the steel samples and dried for 24 hours in open air before the test. The coated and un-coated steel samples were exposed at temperature of 500-800 degrees C for 2-4 hours. After the over of desired period of exposure, the samples were taken out, allowed to cool in air and pickled in inhibited acid for 5-10 minutes for the removal of the scale. The loss in weight per unit surface was expressed as oxidation/scaling loss. The amount of protection given by the coating was calculated as usual. The modified silicate binder is found to be superior to both sodium silicate and ethyl silicate because it has greater spreadability and better compatibility with respect to sodium silicate. Aluminium phosphate does not provide good adherence to the substrate. Ivory-400 available in the market is also superior because of its greater spreadability, stability and adhesion as compared to the Aluminium phosphate. The data are discussed in detail