The Effect of Relative Humidity on the Corrosion-resisting Property of Fluorocarbon Coating

The effect of relative humidity on the corrosion-resisting property of fluorocarbon coating was investigated by water vapor transmission technique and electrochemical impedance spectroscopy technique. Measuremerits were carried out on samples, which were tested in an accelerated corrosion environment for the same time （300, 500, 800 and 1000 h ）. The experimental results were obtained as follows： （i） The water absorption, coating resistance and corrosion rate of metal under the coating changed with relative humidity and aging time, the results obtained by EIS are good consistent with those by water vapor transmission technique ; （ ii ） when the subject investigated presented two time constant, the goodness of fit by EEC R （ C （ R （ CR ） ） ） was inferior to that by EEC R（ C（ R（QR） ） ）, but the error of parameters acquired from the former was smaller, by which we could analyze the experiment result quantitatively. With the appearance of diffusion layer on the metal, the difference of metal capacitance was aggravated, the error of parameters acquired from EEC R（ C（ R（ C（RW） ） ） ）was bigger than that from EEC R（ C（ R（ Q（ RW） ） ） ） .

Thin Films for Coating Nanomaterials

For nano-structured solids （those with one or more dimensions in the 1-100 nm range）, attempts of surface modification can pose significant and new challenges. In traditional materials, the surface coating could be several hundreds nanometers in thickness, or even microns and millimeters. In a nano-structured material, such as particle or nanofibers, the coating thickness has to be substantially smaller than the bulk dimensions （100 nm or less）, yet be durable and effective. In this paper, some aspects of effective nanometer scale coatings have been discussed. These films have been deposited by a non-line of sight （plasma） techniques; and therefore, they are capable of modifying nanofibers, near net shape cellular foams, and other high porosity materials. Two types of coatings will be focused upon： （a） those that make the surface inert and （b） those designed to enhance surface reactivity and bonding. The former has been achieved by forming 1-2 nm layer of --CF2- （and/or CF3） groups on the surface, and the latter by creating a nano- layer of SiO2-type compound. Nucleation and growth studies of the plasma-generated film indicate that they start forming as 2-3 nm high islands that grow laterally, and eventually completely cover the surface with 2-3 nm film. Contact angle measurements indicate that these nano-coatings are fully functional even before they have achieved complete coverage of 2-3 nm. They should therefore be applicable to nano-structural solids. This is corroborated by application of these films on vapor grown nanofibers of carbon, and on graphitic foams. Coated and uncoated materials are infiltrated with epoxy matrix to form composites and their microstructure, as well as mechanical behaviors are compared. The results show that the nano-oxide coating can significantly enhance bond formation between carbon and organic phases, thereby enhancing wettability, dispersion, and composite behavior. The fluorocarbon coating, as expected, reduces bond formation, and therefore, effective as an inert layer to passivate nanomaterials.