Coatings are layers of specific materials applied over any bulk material to achieve specific properties the bulk material cannot achieve. Functional coatings can serve the purpose of protecting the bulk material against corrosion, mechanical abrasion, environmental damage, fouling, microorganisms and more. In this article, AZoNano explores how graphene-based coatings and ceramic-based coatings compare.
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Graphene vs Ceramic Coatings: An Introduction to Graphene and Ceramics
Graphene, an allotrope of carbon, has a layered structure of carbon rings formed in a hexagonal lattice structure. This arrangement of carbon in two-dimension gives properties such as high thermal conductivity, electrical conductivity, mechanical strength and many other properties that could contribute to versatile applications.
Other properties of graphene are thermal stability, chemical stability, low-cost processability, environment friendliness and highly flexible graphene layers, showcasing graphene’s suitability for coating applications.
Ceramics are a big family of materials that have been utilized in several applications for many decades. Ceramics are hard, brittle, and environmentally friendly. Ceramic materials are also known for having a long life span.
Their thermal and electrical resistant properties, along with the chemically stable nature of the ceramic materials, make them suitable for a wide range of applications.
Graphene vs Ceramic Coatings: Reinforcing Ceramic Coatings with Graphene
Ceramic coatings are hard coatings primarily used for harsh environments. However, the low toughness property of ceramic coatings limits the applications of these coatings, as reported in a review article published in Surface and Coating Technology.
The toughness of ceramic coatings has been reportedly enhanced through methods involving grain size refinement, grain boundary reinforcement, solid-state solution and precipitation method, ion bombardment and multilayering.
Other methods include the introduction of toughening agents involving metal phases and carbon allotrope additive, phase transformation and optimizing coating morphologies.
Interestingly, graphene-reinforced ceramics have attracted the interest of the scientific community.
A study conducted by Da et al. reports on the tribological behaviors of graphene-reinforced ceramic coatings. They investigated the tribological behavior of the coating at three different temperatures of room temperature, 200 °C and 500 °C. The study exhibits enhancement in the fracture toughness and hardness of the coating with the incorporation of graphene in the ceramic material.
Graphene vs Ceramic Coating: Synthesis Methods
Ceramic coatings are reported to be developed through various methods, including gas flame spray, vacuum deposition and arc discharge plasma. These methods involve deposition at higher temperatures that require the high-temperature processability of the bulk materials.
For graphene-based coatings, structural and chemical modifications of the graphene are responsible for tuning the surface properties of the coatings, as reported by Nine et al. This approach involves the functionalization of the graphene basal planes and edges with the carbonyl and hydroxyl groups.
Graphene coatings are reported to be developed in two approaches: dry and wet processing. The processing includes chemical vapor deposition, electrophoretic deposition, rapid thermal annealing, organic molecules pyrolysis deposition, spray coating, spin coating, and plasma spray coating.
Graphene vs Ceramic Coating: Applications
Ceramic coatings are widely used for corrosion and wear-resistant coatings for steel bulk materials. Researchers have been studying ceramic-based coatings for corrosion prevention to increase the life span of the materials.
Ceramic coatings as high-temperature thermal barrier coatings have received interest due to their high thermal stability, high melting point, low thermal conductivity and high-temperature phase stability.
Yttrium-stabilized zirconia is one of the most explored ceramic topcoat layers for thermal barrier coatings, with applications in heat engines and aircraft turbine blades, as reported by Stover et al.
Bioactive, bio-inert and resorbable categories of ceramic coatings have also received research interest. Bio-glasses and calcium phosphate are the most studied ceramic materials that are bioresorbable, as reported by Nilawar et al.
Graphene coatings have also been explored as corrosion-resistant coatings. The two-dimensional structure of graphene, impermeable to most gases, liquids and reactants, prevents them from reaching the bulk material and thus acts as a barrier to corrosion. The article by Nine et al., describes the various applications of graphene coatings.
Graphene composite coatings have reported applications as fire/flame retardant materials, as graphene can withstand high temperatures without any change in its mechanical properties.
Tribological applications of graphene coatings have been explored by the scientific community. As graphene is reported to be the thinnest, lightest and strongest material, graphene coatings exhibit high mechanical robustness when in single-layered form.
Anti-fouling properties of graphene coatings have been developed to have self-cleaning surfaces, anti-sticking coating, water-repellent coatings and many more. These have applications in wastewater treatment, marine structures, desalination systems and vehicles.
Graphene vs Ceramic Coatings: Commercial Landscape
The commercial landscape of ceramic coatings is much more developed compared to that of graphene-based coatings.
A survey report by Future Market Insights reported that the compound annual growth rate of the ceramic coating market will expand by 7.6% from 2022 to 2023. As per the survey, ceramic coatings are reported as the best coating compared to any other alternatives.
Graphene coating or graphene-ceramic composite coatings that have reported enhanced qualities could be further developed by developing the coating techniques and material synthesis. For now, ceramic coatings hold dominance over the commercial coating market, but as the global graphene market continues to evolve, the rise of graphene-based coatings may be on the horizon.
References and Further Reading
Wang, Y.X. and Zhang, S., (2014). Toward hard yet tough ceramic coatings. Surface and Coatings Technology, 258, pp. 1-16. doi.org/10.1016/j.surfcoat.2014.07.007.
Da, B., Rongli, X., Yongxin, G., Yaxuan, L., Aradhyula, T.V., Yongwu, Z. and Yongguang, W., (2020). Tribological behavior of graphene reinforced chemically bonded ceramic coatings. Ceramics International, 46(4), pp. 4526-4531. doi.org/10.1016/j.ceramint.2019.10.180.
Nine, M.J., Cole, M.A., Tran, D.N. and Losic, D., (2015). Graphene: a multipurpose material for protective coatings. Journal of Materials Chemistry A, 3(24), pp. 12580-12602. doi.org/10.1039/C5TA01010A.
Stöver, D. and Funke, C., (1999). Directions of the development of thermal barrier coatings in energy applications. Journal of Materials Processing Technology, 92, pp. 195-202. doi.org/10.1016/S0924-0136(99)00244-7.
Nilawar, S., Uddin, M. and Chatterjee, K., (2021). Surface engineering of biodegradable implants: Emerging trends in bioactive ceramic coatings and mechanical treatments. Materials Advances, 2(24), pp. 7820-7841. doi.org/10.1039/D1MA00733E.