Graphene and Corrosion Protection
Since steel structures have existed, the prospect of corrosion has caused maintenance concern. According to the World Corrosion Organization, corrosion results in $2.5tr in damage to steel structures annually– roughly 3-4% of the yearly GDP of industrialized countries. There are numerous options to minimize both damage and related costs, such as galvanization with zinc, chromium, and other metals. Several of these metals are subject to intense pressure because of their REACH classification.
The most employed corrosion protection primers for extremely corrosive surroundings (characterized in ISO 12944-2018 as CX environment) are centered on zinc-rich epoxy formulations (zinc content over 80%), in certain instances altered with either with extremely sophisticated binder systems and/or additional corrosion safeguard pigments. For less corrosive environments, passive corrosion safeguarding pigments such as phosphates are usually adequate.
Zinc is categorized as extremely fish toxic and will be emitted as zinc oxide, which is also extremely fish toxic, in the last phase of the life cycle of a corrosion protection coating throughout a corrosive attack. This will result in environmental contamination near the steel construction. In 2012, the Chinese government released a mandate for lowering zinc in corrosion protection primers to increase environmental safeguarding when such systems are employed.
At the same time, Kirkland (Kirkland, N.T., Schiller, T., Medhekar.N.; Birbilis, N (2012). Exploring graphene as a corrosion protection”. Corrosion Science 56 (March 2012), 1 – 4) demonstrated that graphene might be a contender as a corrosion protection agent.
In 2016, Ramezanzadeh (Ramezanzadeh B, Niroumandrad S, Ahmadi A, et al. Enhancement of barrier and corrosion protection performance of an epoxy coating through wet transfer of amino functionalized graphene oxide, Corrosion Science, 2016, 103: 283-304) established a decrease in the decline of epoxy resins following the addition of 0.1 weight % of amino-functionalized graphene oxide. It is thought that graphene oxide may be able to react with hydroxyl ions, and chlorine ions are stopped from immersing into the coating.
Beginning in 2012, the studies prompted The Sixth Element to begin working on the Chinese government’s initiative to create a reduced zinc corrosion protection primer, blending zinc powders with graphene for enhanced performance.
Employing a specially-developed graphene type, known as SE1132, and large zinc powder particles (D50 above 10 µm), The Sixth Element could prove that a combination of 25 weight % zinc powder and one weight % of this graphene type, all established on dry film, leads to excellent corrosion protection performance in a 2k-epoxy primer. 3,000 hours could be accomplished in standard salt spray testing conditions (50 +/- 5 g of sodium chloride per liter of water at 35°C +/- 2°C, 50 µm dry film thickness)( see figure 1b). This finding is now safeguarded by a patent granted in China and the US (China patent No. CN201210108771.3, US Patent No. US9982142B2).
Explanation of the Success:
- Graphene has a substantial lateral size (in xy-direction, some µm each) with extremely low thickness in nano-meter scale (< 3 nm). This kind of particle creates a high pigment volume concentration applying the density of 2200 kg/m³. For the calculation, the volume of every particle must be calculated founded on the dimensions. Conventional formulas are unsuitable. The result of this high pigment volume concentration is that even with one weight %, many particles are present, substantially boosting the barrier properties of the coating system (see Figure 1 a).
- Because of its electrical conductivity, graphene also supports zinc in its cathodic safeguarding behavior by constructing a denser electrical network. This facilitates accelerated bleeding off of the corrosion current.
Figure 1. (a) Schematic of rGO dispersed in a coating layer, compared to spherical nanofillers or without coating; (b) Salt spray testing indicates the better anti-corrosive performance for SE1132-containing epoxy primer compared to conventional primer; (c) A rack in Nantong, China, applied with SE1132-enhanced anti-corrosive primer. Image Credit: The Sixth Element (Changzhou) Materials Technology Co.,Ltd.
Apart from SE1132, The Sixth Element has shown that the graphene types SE1133 and SE1233 may be employed as corrosion safeguarding additives in primer systems. Consumers in China and in Europe have effectively added primer formulations including graphene to the market (see figure 2).
Figure 2. Graphene powder products and graphene coatings products. Image Credit: The Sixth Element (Changzhou) Materials Technology Co.,Ltd.
In a global first, a graphene-based corrosion protection primer has been employed for coating the inner and outer wall of the steel erection of an off-shore wind energy plant in December 2014. Numerous paint assessments of the steel construction, performed in 2015 and 2019, validated the exceptional performance of the coating system containing the corrosion protection primer.
Figure 3. The graphene anti-corrosion coating system used in the wind turbine in 2014 to 2019. Image Credit: The Sixth Element (Changzhou) Materials Technology Co.,Ltd.
Particularly in China, more objects have been coated with graphene-based primers, which can be seen in Figures 4 and 5.
Figure 4. Graphene-based primer used in coastal radar base. Image Credit: The Sixth Element (Changzhou) Materials Technology Co.,Ltd.
Figure 5. Graphene-based primers used in railway ancohrage. Image Credit: The Sixth Element (Changzhou) Materials Technology Co.,Ltd.
In an additional initiative, The Sixth Element swapped to zinc particles of reduced size (D50 between 3 µm and 7 µm). In this instance, it was adequate to combine 0.6 – 0.8 weight-% of SE1132 with 25 weight-% to 28 weight % of zinc powder (all based on dry film) to obtain excellent outcomes in corrosion protection.
Research is ongoing to detail further the maximum capacity of graphene as a corrosion safeguarding agent in extremely challenging environments.
The Sixth Element (Changzhou) Materials Technology is at the forefront of manufacturing graphene and graphene products with a present manufacture amount of 400 t/a and an accessible facility of 1000 t/a since April 2020. The graphene types and graphene oxide from The Sixth Element are REACH registered. The Sixth Element possesses an ISO 9001-2015, an ISO 14001-2015 and an IATF 16949 certification
This information has been sourced, reviewed and adapted from materials provided by The Sixth Element (Changzhou) Materials Technology Co.,Ltd.
For more information on this source, please visit The Sixth Element (Changzhou) Materials Technology Co.,Ltd.