Density, pretreatment techniques

The most common technique involves abrading the substrate surface with hard powders (preferably diamond), or ultrasonic treatment in a slurry of an abrasive powder (preferably diamond grit) in an organic liquid for a prolonged period. This type of pretreatment leads to embedding of the abrasive particulates into the surface as well as mechanical damage to the substrate, both of which are believed to enhance the nucleation density. The maximum nucleation enhancement is observed when diamond grit is used, and this has been attributed to implantation of diamond particles... 

Potentiodynamic polarization measurements are quite appropriate for determination of the pitting susceptibility of aluminum coatings, and/or the corrosion current density/ corrosion rate of coated steel products in general. ASTM G 102, Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements, describes the calculation of corrosion rates and other information from electrochemical measurements. Another example of the use of DC electrochemical methods to examine the corrosion performance of coated sheet materials is a study by D. A. Jones et al. [48]. The study used polarization resistance measurements to examine the mechanism of steel and coated sheet degradation under conditions of alternate immersion. Jones compared the polarization resistance of samples of low-carbon steel, unpainted galvanized, aluminum-coated, and Zn-Ni alloy coated steel during continuous immersion and alternate immersion. Alternate immersion cyclic exposure produced a thick oxide that led to significant underfilm attack. Jones found that phosphate pretreatment tends to increase the resistance of these materials to underfilm attack. This study is an excellent example of the way electrochemical measurements can be used as a complement to other techniques to elucidate mechanistic information. 

It was concluded first by Knorr and coworkers [1] that diffusion of molecular hydrogen is the rate-determining step of hydrogen evolution on smooth platinum and palladium electrodes pretreated anodically. The same conclusion holds for the anodic processes given by Eq. 1 and 2. The interpretation based on steady-state measurements [1] is valid at cathodic current densities — i < 1 mA/cm in strong acid electrolytes (0d.H+ 1)- The correctness of this interpretation has been substantiated by a number of independent techniques which allow the concentration Ch2 of H2 molecules adjacent to the surface to be determined ... 

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