Chromate inhibition

Comparison of tensile lap shear strengths solvent-based chromate-inhibited primers versus nonchromate and low VOC primers [42]... 

Non-chromate and low-VOC containing primers are capable of excellent performance. Table 4 shows the results of a comparison of various environmentally acceptable primers with 250°F curing adhesive with the standard BR 127 solvent-based chromate inhibited primer [42]. 

Epoxy based primer systems remain the best suited for the corrosion protection of magnesium. Cathodic epoxy electrophoretic paints , chromate inhibited epoxy-polyamide primers and high temperature stoving epoxy sealers are used to provide protection up to 180°C. For higher temperature applications up to 300°C, epoxy silicone or polyimide based systems can be used. 

Very interesting behavior of incorporating anions can be observed when a multicomponent electrolyte is used for oxide formation. Here, anion antagonism or synergism can be observed, depending on the types of anions used. The antagonism of hydroxyl ions and acid anions has been observed in a number of cases. Konno et a/.181 have observed, in experiments on anodic alumina deterioration and hydration, that small amounts of phosphates and chromates inhibit oxide hydration by forming monolayer or two-layer films of adsorbed anions at the oxide surface. Abd-Rabbo et al.162 have observed preferential incorporation of phosphate anions from a mixture of phosphates and chromates. 

O-ring seals in a pump pumping chromate inhibited water at 196°C (385°F)... 

III. INHIBITION BY SOLUBLE CHROMATE A. Overview of Chromate Inhibition... 

Electrochemical techniques alone cannot reveal all the relevant aspects of chromate inhibition, and key characterization experiments involving surface analysis, solution analysis, or other techniques are required to help understand inhibition. For this reason, several useful nonelectrochemical techniques are also discussed. These techniques provide a means for examining the effects of inhibition under free corrosion conditions where electrochemical methods are not well suited for measuring corrosion rate. 

Overall, these results indicate that chromates inhibit corrosion by elevating the pitting potential on aluminum with respect to the corrosion potential, which decreases the probability for the formation of stable pits. In general a chromate chloride concentration ratio in excess of 0.1 is necessary to observe significant anodic inhibition. 

Anodic passivation of steel surfaces can be efficiently achieved by metal chromates. Chromates of Intermediate solubility (e.g., zinc chromate and strontium chromate) allow a compromise between mobility in the film and leaching from the film to be achieved. Chromates inhibit corrosion in aqueous systems by formation of a passivating oxide film. The effectiveness of chromate inhibitors in aqueous systems depends on the concentration of other ionic species in solution, for example, chloride. Synthetic resin composition can also significantly influence the effectiveness of chromate pigments. The effect appears to be related to the polarity of the resin (20) chromate pigments appear to be less effective in resins of low polarity. 

Comparison between the chromate inhibition test and a cytochemical method for the determination of glucose-6-phosphate dehydrogenase deficiency in erythroc5d es. 

Other forms of coating systems which contain corrosion inhibitors include in-situ phosphatising coatings such as those described by Neuder et al. [126] where functionalised aryl-phosphonic and arylphosphoric acids were added to an epoxy primer. The inhibitors were shown to deposit uniform metal-phosphate products on the substrate surface and provide a similar level of performance to chromate-inhibited control samples when tested over 3000 h in a neutral salt spray test. 

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