A study to evaluate wear and corrosion inhibition, and the mode of molecular bonding of a fluorinated schiff base compound (imine compounds), a condensation reaction product of 4-fluorobenzaldehyde and 4,4'-benzidine, onto AISI 1010 steel surface was undertaken to develop a new lubricant additive for greases. Physical vapor adsorption and chemisorption techniques were used for the deposition of schiff base on the metal surface. The schiff base was found to adhere best with the physical adsorption technique. It involved heating of freshly cleaned specimens suspended over schiff base in an all-glass covered container placed in a vacuum oven maintained at 420° F for approximately 70 hours. Potentiodynamic polarization measurements, made in a 0.1 % sodium chloride solution, showed a drastic shift of the anodic polarization curves to lower current densities for the steel specimens coated with schiff base. The calculated corrosion inhibition efficiency was >90 percent for the compound under both deposition techniques. The four-ball wear test showed a 34-40 % reduction in scar size when used as an additive to a MIL-G-24139 grease.
Specular reflectance Fourier transform infrared (FTIR) spectra recorded for the specimens coated by physical vapor adsorption method suggested that the schiff base was physically (planar/flat film deposition) adsorbed on the metal surface. This may be attributed to the presence of empty d-orbitals in iron which forms an easier coordinate bond with the non-bonding electron pair of the N-atom in the schiff base. This was further supported by the absence of an infrared band near 1624 cm−1 for the non-cyclic -C=N-bond which may be attributed to reduced conjugation and increased pi-electron density distribution over the whole schiff base molecule, and thus giving rigidity to the resulting non-cyclic single =C-N= bond. However, more experimental efforts will be required to further elucidate the structural bonding of schiff base with the steel surface.
