Study the Corrosion and Corrosion Protection of Brass Sculpture by Atmospheric Pollutants in Winter Season

Abstract

Brass is an important metalloid which is used in construction of sculptures. It is noticed that sculpture of brass is corroding due to interaction of pollutants. The pollutants develop chemical and electrochemical reaction on the surface of base material. Their concentrations of corrosive pollutants are increased in winter season. The air quality becomes very poor in winter season. Inside sculpture different forms of corrosion are observed like galvanic, pitting, stress, crevice etc. The major components of pollutants are oxides of carbon, oxides of nitrogen, oxides of sulphur, ammonia, ozone and particulates. Among these pollutants oxides of sulphur and ammonia are major corroder of brass. Ammonia is observed moist air to form ammonium hydroxide. It produces chemical reaction with brass metal and form complex compounds like [Zn(NH4)4](OH)2, [Zn(NH4)4]SO4, [Zn(NH4)]CO3, [Cu(NH4)4](OH)2, [Cu(NH4)4]SO4, [Cu(NH4)]CO3 etc. Oxides of sulphur react with moist air to exhibit sulphurous and sulphuric acids. They interact with brass to develop corrosion cell zinc metal and it is oxidized into Zn2+ ions and these ions are active to humidity and carbon dioxide to yield Zn(OH)2.ZnCO3.2H2O. Copper is converted into Cu2+ and it reacts with moist air and carbon dioxide to produce Cu(OH)2.Cu(CO3)2 and these complex compound detached on the surface of brass metal by rain water. These pollutants change their physical, chemical and mechanical properties and they also tarnish their facial appearance. Brass’ sculpture is affected by uniform corrosion. This type of corrosion can be control by nanocoating and electrospray techniques. For this work (6Z)-5,8-dihydrazono5,8-dibenzo[a,c][8]annulene and TiO2 are used as nanocoating and electrospray materials. The corrosion rate of material was determined by gravimetric and potentiostat technique. The nanocoating and electrospray compounds are formed a composite layer on surface of base metal. The formation of composite layer is analyzed by thermal parameters like activation energy, heat of adsorption, free energy, enthalpy and entropy. These thermal parameters were calculated by Arrhenius, Langmuir isotherm and transition state equations. Thermal parameters results are depicted that both materials are adhered with sculpture through chemical bonding. The surface coverage area and coating efficiency indicates that nanocoating and electrospray are produced a protective barrier in ammonia and sulphur dioxide atmosphere.