The sol-gel and hydrophobic properties of antifriction coatings for use in high-speed mini-turbogenerators

The state of the surface of organic-inorganic coatings derived by sol-gel technology on a steel surface and their effect on the reduction of the air friction losses of a mini-turbogenerator rotor were studied. Two hypotheses about the effect of the surface condition on the reduction of the air friction losses—by improving the surface smoothness and by creating a superhydrophobic surface—were suggested and tested. Smooth epoxy-titanate coatings including those doped with a fluorine-containing organosilicon polymer and superhydrophobic surfaces based on hydrolyzed methyltriethoxysilane with an aerosol additive were tested on a model mini-turbogenerator test setup. It was established that the smooth coatings reduce the total friction losses of the mini-turbogenertor by ∼5%, while the superhydrophobic coatings reduce them by ∼7%.