Preparation And Corrosion Properties Of The Coatings On 316L Surface

Supercritical water oxidation?SCWO?has been extensively used in the field of industrial wastewater and sludge treatment with supercritical water and oxygen as reaction medium and oxidant respectively.However,the corrosion of equipment has become a key factor restricting the industrialization of this technology.In this paper,the coating was prepared on the substrate surface by atmospheric plasma spraying?APS?to improve the corrosion resistance of the matrix.Firstly,the corrosion behavior of Al2O3/316L,TiO₂/316L was studied under the SCWO?500?,25MPa and 1000mg/L oxygen concentration?for 80h with a blank control group of 316L stainless steel.The corrosion resistance and corrosion failure mechanism of coating with better corrosion resistance were studied under different corrosion conditions?with oxygen concentration Omg/L,500mg/L and 1000 mg/L respectively,400?,450? and 500?respectively?based on the analyses of corrosion rate and morphology.The results show that Fe3O4 and NiO were developed on the surface of 316L stainless steel sample irregularly and loosely and the corrosion depth reaches 0.04mm.The surface of Al2O3/316L stainless steel is gully and the coating has fallen off in large area due to its weakness bonding strength.The surface of Ti02/316L stainless steel is relatively dense and the coating thickness has no obvious change due to the higher bonding strength.Compared with Al2O3/316L stainless steel samples,Ti02/316L stainless steel with lower corrosion rate has a better corrosion resistance.TiO₂/316L stainless steel presents crevice corrosion under different corrosion conditions.In SCW at 400 ?,25MPa with oxygen concentration of Omg/L and 500mg/L,the number of cracks and pores on the surface of TiO₂/316L stainless steel increases with the increase of oxygen concentration,and the thickness of the coating section has no obvious change.When the oxygen concentration is 1000mg/L,the surface of TiO₂/316L stainless steel cracked and the cross-sectional morphology of the coating emerges zigzag.And the remaining thickness of TiO₂ coating is about 0.08mm.The crack on the surface of TiO₂/316L stainless steel would broaden with the increase of temperature.Meanwhile,the NiO and NiFe2O4 are developed around the crack on the surface of TiO₂/316L,and the TiO₂ coating became thin with the increase of temperature.The corrosion has been aggravatted with the increase of corrosion temperature and oxygen concentration in the corrosive medium.