Faculty Publications

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Author: search.filters.author.Chavana, N.Subject: search.filters.subject.Alumina

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    An investigation of slurry erosion behaviour in plasma-sprayed carbon nanotube-reinforced fly ash/alumina coatings using experimental analysis and artificial neural computing for marine and offshore applications
    (Elsevier Ltd, 2024) Chavana, N.; Anil, A.; Jambagi, S.C.
    This study investigates carbon nanotube (CNT)-reinforced alumina fly ash (FA) coatings, namely AF (unreinforced), 1CAF (with 1 wt% CNT), and 2CAF (with 2 wt% CNT), on marine-grade steel. Microstructural analysis shows 1CAF coatings denser by ∼15.32% due to CNT reinforcement, while 2CAF coatings display ∼9.68% increased porosity from CNT agglomeration. Raman spectroscopy confirms CNT retention. 1CAF coatings exhibit ∼14.66% higher microhardness, ∼15.96% higher adhesion strength, and ∼15.66% improved fracture toughness compared to AF coatings, attributed to pore sealing through CNT reinforcement. Enhanced erosion resistance (∼14.59%) in 1CAF coatings was observed due to improved mechanical properties and CNTs mitigating crack propagation. Validation through an artificial neural network (ANN) modeling and regression analysis supports 1CAF coatings’ promise for harsh marine environments, offering enhanced durability. © 2024 Elsevier Ltd
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    An effective utilization of raw fly ash obtained from thermal power plants using thermal spray technique to improve corrosion resistance for marine applications
    (Elsevier Ltd, 2024) Chavana, N.; Jambagi, S.C.
    Marine-grade steel structures in offshore environments often corrode due to the aggressive environmental conditions. Many ceramic materials can cater to this demand. However, as per economic and ecological concerns, fly ash (FA), an industrial waste, can be another strong contender to control corrosion. Therefore, the present study developed composite coatings of fly ash with additives ((50-48) wt.% Al2O3; 0–2 wt% carbon nanotube (CNT)) onto marine-grade steel using a plasma spray technique to improve its corrosion resistance. The microstructure of 1 wt% CNT-reinforced alumina-FA (1CAF) coating was denser than 2 wt% CNT-reinforced alumina-FA (2CAF) coating due to the uniform dispersion of CNT and, thereby, uniform remelting of coating at localized sites. Consequently, the microhardness and adhesion strength of the 1CAF coating were improved by ∼14.66 % and ∼15.96 %, respectively. Further, Rietveld's analysis of coatings showed that quartz, being the primary phase for corrosion control, was 19.23 ± 0.87 %, 16.33 ± 1.04 % and 14.60 ± 1.87 % for alumina-FA (AF), 1CAF, and 2CAF, respectively. The electrochemical impedance spectroscopy and the salt spray corrosion tests showed that 1CAF coating corrosion resistance was improved by ∼11.2 % compared to AF coating, even with a lower quartz phase (∼15.08 %) due to the densification of coating. This densification was due to the remelting by CNT to seal pores in the coating. Furthermore, for the same reason, an increase in coating resistance and charge transfer resistance of 1CAF coating by ∼80.9 % and ∼19.93 %, respectively, were seen in the equivalent circuit analysis, showing great promise in controlling interfacial corrosion. Further post-treatments like plasma or laser treatments can seal the coatings further to improve corrosion resistance. Therefore, such coatings are expected to withstand harsh, corrosive environments and are well-suited for marine applications. © 2024 Elsevier B.V.
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    Numerical and Experimental Investigation of Thermal Barrier Effects of CNT-Reinforced Fly Ash/Alumina Coatings in Diesel Engine Pistons
    (American Chemical Society, 2025) Chavana, N.; Sarkar, B.; Jambagi, S.C.
    Fly ash (FA), an industrial byproduct from coal combustion, presents significant disposal challenges, especially in developing nations. Given its mineralogical properties, FA shows potential in thermal spray coatings. This study evaluates FA-based coatings for pistons to improve thermal management in internal combustion engines through numerical simulations, analyzing their effects on the temperature distribution, thermal stress, and combustion efficiency. FA coatings were also applied to marine-grade steel with additives (50 wt % Al2O3 and 0-2 wt % CNT) to assess high-temperature performance. Microstructural analysis revealed that 2 wt % CNT-reinforced (2CAF) coatings showed agglomeration, reducing microhardness by ?9.27% compared to 1 wt % CNT-reinforced (1CAF) coatings. The XRD analysis of 1CAF indicated ?56.51% transformation of corundum to ?-alumina, lowering thermal conductivity by ?15.40% compared to alumina/FA (AF) coatings, while 2CAF coatings showed increased conductivity due to CNT inhomogeneity. For piston applications, simulations showed an ?24.59% rise in maximum surface temperature, from 241.39 to 300.76 °C, and an ?62.06% reduction in heat flux, indicating enhanced durability and reduced cold-start emissions. Thermal cycling demonstrated that 1CAF coatings outlasted AF and 2CAF, suggesting FA-based TBCs as sustainable and economical options for enhanced engine performance and waste valorization. © 2025 American Chemical Society.