Deposition of diamond-like carbon onto titanium by hydrothermal carbonization: Controlling structure from graphene oxide assisted growth

Carbon coatings were deposited onto titanium coupons by hydrothermal carbonization of sucrose and graphene oxide (GO) solutions. The ratio of GO-to-sucrose was varied, increasing GO concentration by weight (wt.) from 0:1 (sucrose) to 1:1000, 1:300, and 1:100. Deposition included temperature (T) = 180 degrees C and reaction times of 8, 16, and 24 h. At 16 h, the coatings had thicknesses of similar to 4.0-65.0 mu m, with a growth rate of similar to 0.25-4.06 mu m/h. By adding 0.1-1 % wt. GO, the coatings' morphologies transitioned from micro-spheres into micro-platelets. However, transmission electron diffraction did not suggest crystallinity in either structure. Raman collected from T = 180-1000 degrees C indicated diamond-like phases with sp(3) fractions of similar to 20-40 %. By annealing at T > 600 degrees C, the coatings continued to aromatize, but also had increases in sp(3) sites from desorption of volatile CO/CO2. In addition, X-ray photoelectron spectroscopy revealed surface species such as C-O, C=O, and COOR. Coating properties included adhesion strength of similar to 2.5 +/- 3.3 MPa, surface roughness (P-q) = 14.7 +/- 9.2 mu m, and interfacial contact resistance (ICR) > 10(4) m Omega<middle dot>cm(2), except for the 1 % GO sample at similar to 2.00 x 10(2) m Omega<middle dot>cm(2). Possible mechanisms for the formation of spherical vs. platelet structures are provided, such as the creation of spheres by polymerization of 5-(hydroxymethyl)-2-furaldehyde (5-HMF) and platelet formation from preferential growth of 5-HMF using GO molecules as templates.