Corrosion resistance, epoxy formulation

In contrast, hydrolyzed silane compounds, presumably adsorbed as oligomeric films, confer corrosion resistance in both hydrating and Cl environments. These inhibitors can also couple with applied epoxy primer or adhesive formulations to further protect the metal against corrosion by strengthening the metal-epoxide bond. The organosilanes do not appear to affect the curing process, e.g., % crosslinking, of the polymeric epoxy systems. 

Durcon. A series of cast, plastic, epoxy formulations manufd by the Duriron Co for use in corrosion resistant equipment such as pumps, valves, fans and others Ref CondChemDiet (1961), p426... 

Epoxy-based primers are commonly used in the aerospace and automotive industries. These primers have good chemical resistance and provide corrosion resistance to aluminum and other common metals. Primer base resins, curing agents, and additives are much like adhesive or sealant formulations except for the addition of solvents or low-viscosity resins to provide a high degree of flow. 

These plastics used in RPs (Chapter 15) can withstand many of the world s most aggressive chemical environments. Different formulated epoxies permit meeting exceptional corrosion resistance, different performance such as the ability to withstand exothermic stresses that are built up during curing, used in different temperature ranges. 

Substituting a solid epoxy for the liquid epoxy as shown in Table III (Formulations 5 and 6), extends the pot life out to 6 hours at 60% volume solids. Both the solid and liquid epoxy based systems give excellent coatings with good corrosion resistance. 

Coating formulations and properties have been detailed in technical bulletins (31). The epoxy-polyamide system is popular because it provides an unusual degree of inherent corrosion resistance. This will be discussed in detail later. The system is unusually tolerant as compared to related systems, such as amine cured, since the ratio of components is not particularly critical. Tolerance is also demonstrated because it may be applied to wet surfaces and to surfaces with tightly bound rust. Indeed, formulations are available that may be applied under water to structures such as submarines and off-shore oil well riggings. Both the corrosion resistance and the tolerance relative to application on poorly prepared wet surfaces are believed to be functions of the surface activity of the polyamide resin. Related also to the surface activity are the unusually strong adhesive properties that the system demonstrates with a broad range of substrates. 

The dramatic corrosion resistance of epoxy-polyamide coatings is demonstrated by the data in a Government military specification, Mil-P-24441 (ships). This specification coating, at a relatively high solids of 61% by volume, is formulated entirely without... 

In addition to the above applications, this class of phenolic resins may be used with epoxy resins to form either solution or powder coatings for pipes, electrical parts, or metal items that require excellent corrosion resistance. A representative formulation is shown ... 

A second generation of phenolic dispersions, patented by J. S. Fry (33). involved the post dispersion of phenolic resins in a mixture of water and water-miscible solvents. To conform with air pollution regulations, the solvent was held to 20 volume %, or less, of the volatiles. A heat-reactive phenolic resin dispersion (34) and a phenolic-epoxy codispersion have become commercially available based on the above technology. Supplied at 40-45% solids, these products, which have a small particle size (0.75-1.0 ym), are better film formers than the earlier dispersions. Used alone or in blends with other waterborne materials, corrosion-resistant baking coatings may be formulated for coil coating primers, dip primers, spray primer-surfacers, and chemically resistant one-coat systems. Products of this type are also tackifiers for acrylic latexes, and such systems have been employed as contact, heat seal, and laminating adhesives for diverse substrates. 

At lesser rubber levels, heavy duty solventless coatings models based on dlethylenetrlamlne or fatty polyamide cures, showed elastomer-modification (10 phr rubber level) to advantage in Gardner impact, mandrel bend and corrosion-resistance testing (41). Impact testing (direct and reverse) gave 110 and 60 in-lbs, respectively for the rubber-modified fatty polyamide cured epoxy coating (14 days at R.T.), whereas a control formulation tested 10 in-lbs in each mode. 

The most widely used epoxy resins are reaction products of either bisphenol A or a novolac phenolic resin with epichlorhydrin. When used to manufacture corrosion-resistant structures for use in the chemical process industry, epoxy resins are generally hardened with either aromatic or cycloaliphatic amines. The hardeners for epoxy resins are, with few exceptions, added at levels varying from 20phr (parts per hundred resin) to lOOphr. This means that the hardener is actually quite a high proportion of the matrix resin and has quite a profound effect on the mechanical and corrosion properties of the cured resin. Thus the selection of the most suitable hardener is critical to the eventual success of the application. Epoxy resins have viscosities of several thousand mPas at room temperature, which makes it much more difficult to wet out glass fibre efficiently with them than with polyesters. Wet-out therefore involves heating the resin formulation to between 40°C and 60°C to reduce the viscosity to less than 1000 mPas. 

Chem. Descrip. Water-reducible epoxy ester in 2-butoxy ethanol Uses Epoxy for coatings, MIL-P-5 32 primers, topcoats for metal consumer goo, maintenance and dip coatings modifier for latex coatings to improve corrosion resist. can be formulated into VOC-compliant water-based primers/enamels... 

Epoxy resins can be formulated with a wide range of properties. These medium to high priced resins are noted for their adhesion. Epoxy linings provide excellent chemical and corrosion resistance. They exhibit good resistance to alkalies, nonoxidizing acids, and many solvents. Typically, epoxies are compatible with the following materials at 200°F/93°C unless otherwise noted ... 

The three main epoxy resins used in the formulation of corrosion resistant mortars are based on Bisphenol A, Bisphenol F, and epoxy phenol. The corrosion resistance as well as the physical and mechanical properties will be determined by the type of hardener used. 

At ambient temperatures epoxy formulations can be provided that will resist normal atmospheric corrosion. The general resistance is shown in Table 8.6 and the operating temperature ranges are given in Table 8.7. 

Phenolic thermoset resins are the oldest thermoset materials. They do not find as wide an application in the corrosion-resistant field as do the epoxies, vinyl esters, polyesters, and furans. As with other thermoset resins, they can be formulated to meet certain properties, but in general they do not have the range of corrosion resistance of the other thermosets. Table 8.6 shows their resistance to atmospheric corrosion and Table 8.7 gives their operating temperature range. 

A Starting formulation with epoxy incorporation to improve adhesion and corrosion resistance is given below ... 

Adhesives based on hydrolysis resistant chemistry (i.e., adhesives D and E) show a high retention of initial properties after exposure to an aggressive corrosion environment and the failure occurs cohesively within the adhesive. The cure reactions of these adhesives involve the formation of hydrolysis resistant carbon-nitrogen bonds in reactions involving the free N-H functionality of the Versamid or Genamid hardener with the oxirane functionality of the epoxy resin that is present in the adhesive formulation ... 

Water is sometimes used as a solvent for water-soluble resins. Certain epoxy adhesives are available as water-based emulsion or latex formulations. In the early 1970s, during the time of the petroleum crisis, water-based adhesives were thought of as a possible replacement for solvent-based adhesives systems. However, water-based adhesives never met the lofty expectations primarily because of the time and energy required to remove water from the bond line, the corrosion that the water causes in drying ovens, and the poor moisture resistance of cured water-based adhesives. 

Aluminum powder, in particular, is frequently employed at relatively high concentrations in high-temperature epoxy adhesive formulations. The filler provides improvement in both tensile strength and heat resistance, and it increases the thermal conductivity of the adhesive. Aluminum powder fillers also reduce undercut corrosion and, hence, improve adhesion and durability of epoxy adhesive between bare steel substrates. It is believed that this is accomplished by the aluminum filler providing a sacrificial electrochemical mechanism.27... 

Epoxies became popular for the first generation of electrically conductive adhesives introduced in the mid-to-late 1960s. The early adhesive formulations contained organic solvents, which often became trapped in the bondhne during cure and resulted in voids, especially under large chips and substrates. These early adhesives also contained large amounts of ionic impurities, notably chloride ions, which, in the case of nonconductive adhesives, resulted in reduced electrical resistivity, ion migration, and corrosion, especially in humid environments. Early epoxies were also... 

---