Graphene Coatings for the Corrosion Protection of Base Metals

Tortuosity but Not Percolation: Design of Exfoliated Graphite Nanocomposite Coatings for Extended Corrosion Protection of Aluminum Alloys

“…The stochastic inclusion of m -phenylenediamine units within polyamic acid inhibits crystallization and thus yields an amorphous, pliant, and formable polymer matrix. The excellent dispersion of UFG within polyamic acid has been extensively characterized in our previous work ,, and is facilitated by the in situ synthesis of the polymer around the exfoliated graphite platelets; ππ interactions of the basal planes of the exfoliated graphite framework with the conjugated anhydride result in the growing polymer framework encasing the filler UFG nanoplatelets. UFG/polyamic acid formulations have been prepared with 5, 10, and 17 wt % UFG loadings, which as delineated in Figure correspond to two different regimes ( vide infra ): the 5 wt % UFG/PEI sample corresponds to well-dispersed UFG below the percolation threshold, where physical isolation of UFG flakes is maintained and the coatings provide tortuous and extended pathways for diffusion of corrodant species through the polymeric network, whereas the 10 and 17 wt % UFG/PEI samples correspond to stabilization of continuous percolative, conductive networks across the polymer matrix.…”

“…Graphene has received significant attention as a means of designing more sustainable coatings for corrosion inhibition. The efficacy and mechanism of corrosion inhibition provided by graphene remain somewhat controversial; the debate derives in part from the diversity of materials delineated as graphene coatings (ranging from monolayer graphene grown by chemical vapor deposition and transferred onto metal substrates to exfoliated graphene, graphene oxide dispersed within polymeric matrices and cast as nanocomposite coatings, electroplated graphene/metal thin films, and tubular graphene derived by Nguyen and co-workers through thermal annealing) − and the differences in their mode of interfacial interaction with the surfaces sought to be protected. , Notably, given challenges inherent to the industrial production of pinhole-free monolayer graphene, much of the literature has focused on related materials that are much more readily accessible. While the electronic structure and thus transport properties of such materials are strongly dependent on the layer thickness, the barrier protection derived from ion-impervious 2D sheets is anticipated to be largely preserved even for functionalized derivatives and thicker platelets that are not monolayer graphene.…”

Sustainable Coatings on Metallic Alloys as a Nowadays Challenge

“…Magnesium-based nanocomposite coatings have been developed, but, due to the high reactivity of Mg particles, the safe preparation of a surface-passivated Mg surface is difficult, especially in some environments [159]. The graphene nanocomposite coating with sub-30 µm thickness is a successful alternative when it is dispersed in a matrix such as a polyetherimide matrix, showing very good corrosion inhibition of Al 7075 substrates, even when exposed to saline environments for a long time [160].…”

Tortuosity but not Percolation: Design of Graphene Nanocomposite Coatings for the Extended Corrosion Protection of Aluminum Alloys

“…The efficacy and mechanism of corrosion inhibition provided by graphene remains somewhat controversial; the debate derives in part from the diversity of materials delineated as graphene coatings (ranging from monolayer graphene grown by chemical vapor deposition and transferred onto metal substrates to exfoliated graphene and graphene oxide dispersed within polymeric matrices and cast as nanocomposite coatings and electroplated graphene/metal thin films) 14,15 and the differences in their mode of interfacial interaction with the surfaces sought to be protected. 11,16 The tendency for galvanic corrosion to occur between two coupled materials is most frequently predicted using the galvanic series measured in sea water. While the value of the electrode potential of graphene, or for that matter, graphite, varies as a function of the surface chemistry, the reported value of +0.150 V (pure graphite versus SCE) 17 is substantially higher as compared to pure aluminum (-0.76 V versus SCE; corrosion potential of Al 7075-T6 is -0.765 V versus SCE); 18 consequently, galvanic corrosion of the latter is possible upon direct coupling.…”

“…The stochastic inclusion of m-phenylenediamine units within polyamic acid inhibits crystallization and thus yields a nonregular, amorphous, pliant, and formable polymer matrix. The excellent dispersion of graphene within polyamic acid has been extensively characterized in our previous work,11,16,34 and is facilitated by the in situ synthesis of the polymer around the graphene platelets; π-π interactions of the basal planes of the graphene framework with the conjugated anhydride result in the growing polymer framework encasing the filler UFG nanoplatelets. UFG/polyamic acid formulations have been prepared with 5, 10, and 17 wt.% UFG loadings, which as delineated inFigure 2correspond to two different regimes (vide infra): the 5 wt.% sample corresponds to well-dispersed UFG below the percolation threshold, whereas the 10 and 17 wt.% samples correspond to stabilization of continuous percolative networks across the polymer matrix.…”