Cyclic high temperature corrosion studies of carbon nanotubes-Cr₂O₃ composite coatings on boiler steel at 900^°C in molten salt environment

Abstract

Purpose Molten sulphate-vanadate induced hot corrosion is the main reason of failure of boiler tubes used at high temperatures in thermal power plants. The hot corrosion can be encountered by applying thermal spray coatings on the alloy steels. In this perspective, this paper aims to attempt to investigate the effect of carbon nanotubes reinforcement on Cr2O3 composite coatings on hot corrosion behaviour of ASTM-SA213-T22 steel in a corrosive environment of Na2SO4 – 60%V2O5 at 900°C for 50 cycles. Design/methodology/approach The coatings have been deposited with high velocity oxy fuel process. The samples were exposed to hot corrosion in a Silicon tube furnace at 900°C for 50 cycles. The kinetics of corrosion behaviour were analysed by the weight gain measurements after each cycle. Corrosion products were analysed with X-ray diffraction, scanning electron microscopy, energy dispersive and cross-sectional analysis techniques. Findings During investigations, the carbon nanotubes (CNT) reinforced Cr2O3 composite coatings on T22 steel were found to provide better corrosion resistance in the molten salt environment at 900°C. The coatings showed lower weight gain along with formation of protective oxide scales during the experiment. Improvement in protection against hot corrosion was observed with increase in CNT content in the coating matrix. Research limitations/implications The addition of CNT has resulted in reduction in porosity by filling the voids in chromium oxide coating, with interlocking of particle and has blocked the penetration of corroding species to enhance the corrosion resistance of the composite coatings. The corrosion rate was found to be decreasing with increase in CNT content in coating matrix. Originality/value It must be mentioned here that high temperature corrosion behaviour of thermally sprayed CNT-Cr2O3 composite coatings has never been studied, and it is not available in the literature. Hence, present investigation can provide valuable information for application of CNT-reinforced coatings in high temperature fuel combustion environments.

Hot corrosion behaviour of different Cr3C2–NiCr coatings on boiler tube steel at elevated temperature

“…The high corrosion is shown in macrograph of the uncoated substrate and weight change continuously with the very first cycle and went increasing after every cycle. Kamal et al (2017) had suggested that Na 2 SO 4 on reacts with V 2 O 5 form NaVO 3 , (Goyal et al, 2018a(Goyal et al, , 2018b(Goyal et al, , 2018c(Goyal et al, , 2019cRani et al, 2017;Zhou et al, 2017). In case of 20 per cent Cr 3 C 2 -80 per cent (NiCr) coating, the macrograph shows better surface of the substrate.…”

Effect of Y2O3 mass fraction on electrochemical corrosion performances of laser cladded CrNi coatings in 3.5% NaCl solution

“…The process of generating Cr 2 O 3 protective film was similar to that of CrNi-5%Y 2 O 3 coating. The embedded Y 2 O 3 particles filled the existing gaps and cracks (Goyal et al, 2018a(Goyal et al, , 2018b, and the continuous Cr 2 O 3 film was formed on the coating to prevent corrosive ions from contacting the substrate. Meanwhile, the Y 2 O 3 improved the compactness of the Cr 2 O 3 film, which hindered the diffusion of Clto the coating.…”

“…Figure 6(d) shows the electrochemical corrosion process of CrNi-15%Y 2 O 3 coating. The addition of Y 2 O 3 provided more nucleation positions, which promoted the grain boundary coarsening to enhance the stability of the Cr 2 O 3 protective film (Goyal et al, 2018a(Goyal et al, , 2018b. In this case, the Cr 2 O 3 film reduced the contact area between the coating and corrosive medium and prevented the coating from being corroded, which led to the corrosion cracks were gradually reduced.…”

Time effect of graphene coating in between metallic layers of Copper-Nickel on corrosion behavior for carbon steel in saline water

“…So the advanced coatings improve in properties in their morphological, electrical, thermal, and mechanical characteristics [2], [3], Gr is applied as a corrosion inhibitor for metals. where a monolayer and multilayer graphene-coated onto metal surfaces have excellent barriers to oxygen diffusion, that renders the underlying metal inert from environmental oxidation [4]- [8].So, graphenebased anti-corrosion coatings are used to improving surface properties of a substrate [9], [10]. Gr consists of carbon atoms that are strongly bonded to form a hexagonal network, graphene has been generating sustained interest for many fields [11], [12].Cuplating is used with both Ni and Cr plates and is considered to be the most preferable coating surface due to its ability to be spreader in a uniform layer and ductile with no pores with the advantage of polishing capability if several layers are used [13].Niplating can be used as a protecting agent against corrosion that can in the abrasion applications, resisting agent against the corrosion also as smoothing substance for other materials [13], [14].Multilayer chromium, nickel, and copper on the carbon steel, lead to copper and nickel are initially anodic versus chromium and become cathode versus carbon iron, when the electrolyte reaches the inner layer, galvanic corrosion take place [15].Resistance of a metal to electrochemical degradation was increasing by a coating of Cu with Gr.…”