Substrate corrosion

Although the above experiments involved exposure to the environment of unbonded surfaees, the same proeess oeeurs for buried interfaces within an adhesive bond. This was first demonstrated by using electrochemical impedance spectroscopy (EIS) on an adhesive-covered FPL aluminum adherend immersed in hot water for several months [46]. EIS, which is commonly used to study paint degradation and substrate corrosion [47,48], showed absorption of moisture by the epoxy adhesive and subsequent hydration of the underlying aluminum oxide after 100 days (Fig. 10). After 175 days, aluminum hydroxide had erupted through the adhesive. 

Palladium Advantages have been claimed for new baths (e.g. using chelated complexes ). Antler summarised the use of palladium as coatings, inlays and weldments in electronic connectors . Crosby noted that palladium deposits are of two kinds (1) soft but continuous or (2) hard but porous or cracked. To resist wear and substrate corrosion on contacts, he proposed the application of type 1 (from a bath with tetranitropalladium(ii) anion) over type 2 (from solution containing tetramminepalladium(ii) cation) . 

This is the one example in which metal is not the substrate. Corrosion takes on a new meaning the coating here is required to protect the substrate from direct attack by corrosive substances, from water to more powerful household or industrial chemicals, such as grease, alcohols and bleach. We are concerned with the industrial application of thin protective layers to paper (e.g. labels), card (e.g. playing cards) and many wooden articles, including industrially finished doors, window frames and, particularly, furniture. 

Table I shows that the corrosion rate in the Standard pH i(.5 paint was larger than that in the Non-Standard (zinc phosphate free) paint at pH 6, with all rates decreasing with time. The rates decreased with further increase of paint pH to 8. The increased tendency of flash rusting with increase of pH from 6 to 8 was, therefore, associated with lower substrate corrosion currents. Comparison between Non-Standard and Standard paint adjusted to pH 6 with NHj showed little difference in corrosion rates implying that pH was more influential than the presence of zinc phosphate at this pH. Adjustment of the Non-Standard paint with HjSO to an equivalent pH 4.5 of the Standard paint showed good agreement between corrosion rates. This result also indicated pH to be more influential than the presence or absence of zinc phosphate with regard to corrosion currents. The absence of flash rusting at pH 4.5 is therefore associated with higher corrosion currents.

The corrosion potentials show a general trend of increasing values with decreasing substrate corrosion, with the exception of the polyester and the novolac epoxy cured with an aromatic/cycloali-phatic amine. 

Weight change data were obtained for only four of the seven coatings, and those data showed no correlation with the extent of steel substrate corrosion. The polyester showed a weight loss, rather than a weight gain, probably due to an attack and dissolution of the epoxy by the acid. 

Chemical Surface Modification. In considering the interface, one must contemplate not only the possibility of moisture disrupting the bond but also the possibility of corrosion of the substrate. Corrosion can quickly deteriorate the bond by providing a weak boundary layer before the adhesive or sealant is applied. Corrosion can also occur after the joint is made and, thereby, affect its durability. Mechanical abrasion or solvent cleaning can provide adhesive joints that are strong in the dry condition. However, this is not always the case when joints are exposed to water or water vapor. Resistance to water is much improved if metal surfaces can be treated with a protective coating before being bonded. 

Coating-substrate decohesion and formation of a condensed electrolyte at the interface Substrate corrosion... 

Thermal insulation effects by limiting the substrate and membrane temperature to prevent thermal damage and (3) Reduce permeation of corrosive fluid to the substrate, thus minimizing its corrosion rate. CRM linings, such as acid brick and monolithic cements, also prevent "wash", which is the removal of the membrane or substrate corrosion products by the circulating medium. Even when the fluid eventually reaches the membrane or substrate surface, the amount is relatively small, thus limiting chemical attack, and any corrosion products are trapped beneath the masonry shield. 

If the environment slowly attacks either the substrate or the membrane, the interposition of a brick lining between the contained liquid and the substrate or membrane will reduce to a tiny trickle the amount of chemical that reaches the membrane or substrate. Corrosion products, if any, are trapped behind the brick and cannot be washed away to uncover further material to be corroded, so that the corrosion slows down and may eventually stop. Example In a dished bottom, cylindrical steel tank containing a mixture of acid and oil, the steel was lined originally with sheet natural rubber. The rubber lining swells as the oil enters it, but the brickwork holds it in place until the rubber has swollen into all the pores of the brickwork and blocked them preventing any more of the contained liquid from passing behind the brick. 

The design of any SFE system will be a function of the application, and the details will vary depending on the size and the mode of the process (batch or continuous), the nature of the extracted material and the substrate (corrosive, toxic, and benign), and the fluid employed. The only guaranteed commonality with all such systems is the necessity to ensure safe operation. Proper safety precautions must be observed in the handling and maintenance of the required high-pressure equipment the consequences of a failure can be severe. 

Chem. Descrip. Aliphatic polyamine adduct (80%) in water Uses Hardener for solid epoxy resin disps. or emulsified liq. resins for use in water-reducible coatings on metallic substrates, corrosion-protection primers (in combination with Beckopox EH 386w)... 

Uses Adhesion promoter for baked alkyds, polyesters, acrylics, and lacquers onto metal substrates corrosion-inhibiting pretreatment or base coating for galvanized steel and aluminum suitable for food-contact coatings... 

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