From optical fibers to window panes, silicate glass is widely used because of its excellent optical properties and durability. However, it can be weakened by water-induced corrosion. This is problematic for applications of silicate glass, including optical, environmental, pharmaceutical, and industrial uses where the glass comes in contact with water. Recent experiments now show that coating glass with a single layer of graphene can be an effective way to prevent this corrosion from occurring. 

Reported in ACS Nano, the work was led by Bin Wang, Ben Cunning, and Rodney S. Ruoff from the Center for Multidimensional Carbon Materials of the Institute for Basic Science, which is located at the Ulsan National Institute of Science and Technology (UNIST) in the Republic of Korea, and carried out in collaboration with UNIST scientists.
 
Common silicate glass is composed of silicon dioxide, sodium oxide, calcium oxide, and other additives. The corrosion is caused by hydrogen ions diffusing from the water into the glass and exchanging places with sodium ions diffusing out from the glass. This ion exchange increases the pH of the water and therefore the rate of corrosion, leading to surface roughness and making the glass easier to fracture. The rate of corrosion also depends on the temperature and humidity of the environment and the composition of the glass, among other factors.

To better protect glass devices, scientists are investigating ways to block this diffusion ion exchange while maintaining transparency. In previous work, a group led by Ruoff observed that graphene protects copper and copper nickel alloy foils from oxidation in air. Different groups have demonstrated graphene’s excellent barrier properties in other contexts. 

These results suggest that graphene could inhibit the diffusion and exchange that causes water-induced corrosion in glass, says Ruoff. “We also realized that apart from being moderately chemically inert and impermeable, some of the other materials properties of graphene would be well suited for this application, including high optical transparency since it is so thin, and that it is electrically conductive,” he says. 

To put this to the test, the team used single-layer graphene films grown by chemical vapor deposition and transferred them onto glass plates, one film per side. They also created bilayer samples by transferring two single-layer films onto each side of glass plates. The samples were immersed in deionized water for up to 120 days at 60°C, as was a control group of bare plates. The team monitored surface changes at regular intervals and performed fracture tests.

Plates coated with graphene were much more stable than the control group. The bare plates had significantly more surface roughness as indicated by atomic force microscope measurements and their average fracture strength decreased by about 10% as a result of 120 days of immersion. In contrast, the surface and strength of the graphene-coated plates were essentially unchanged. 

Follow-up experiments indicate that hydrogen ions likely penetrated the graphene and reached the glass through defects, but at a slower rate than in bare glass. This, in addition to measurements of the sodium ion concentrations at different depths in the glass, suggest that the graphene coating works primarily by inhibiting the exchange of hydrogen ions with sodium ions. 

The team is working to eliminate defects in the coating and Ruoff looks forward with optimism.  “Researchers are discovering new ways to grow higher quality films, and over much larger areas, and to transfer it to other substrates more efficiently. Glass coatings are just one of the numerous potential applications that could be commercially realized when high-quality graphene production and transfer matures and becomes affordable,” he says.

Carlo Pantano, a materials scientist at The Pennsylvania State University with expertise in glass corrosion, agrees. “I think this offers a great opportunity for industry to take advantage of breakthroughs in 2D [two-dimensional] materials; in this case, not only for corrosion protection but also for hydrophobicity,” Pantano says. “The challenge lies in the development of efficient processes to coat large sheets of glass as well as to remove the coating for some downstream applications.” 

Read the abstract in ACS Nano.