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

• Hydrothermal carbonization of sucrose for depositing carbon coatings on titanium. • Graphene oxide assistance to form diamond-like carbon onto titanium surfaces. • Carbon structural control (platelets vs. spheres) by adding graphene oxide to hydrothermal sucrose. 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 °C and reaction times of 8, 16, and 24 h. At 16 h, the coatings had thicknesses of ∼4.0–65.0 µm, with a growth rate of ∼0.25–4.06 µm/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 °C indicated diamond-like phases with sp 3 fractions of ∼20–40 %. By annealing at T > 600 °C, the coatings continued to aromatize, but also had increases in sp 3 sites from desorption of volatile CO/CO 2 . In addition, X-ray photoelectron spectroscopy revealed surface species such as C-O, C=O, and COOR. Coating properties included adhesion strength of ∼2.5 ± 3.3 MPa, surface roughness (P q ) = 14.7 ± 9.2 µm, and interfacial contact resistance (ICR) > 10 4 mΩ cm 2 , except for the 1 % GO sample at ∼2.00 × 10 2 mΩ 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.