Coating epoxy layer

Eor IR-ERAS (external reflection absorption spectroscopy), steel substrates (1mm thick) are cut to 25x25 mm size. Spin-coating of EPl (directly after mixing, 10000 rpm, 10 s) produces thick ca. 5 pm layers on these substrates. Eor DSC, 7 mm steel disks (0.7 mm thick) are cut and spin-coating provides epoxy layers (ca. 10 pm) on the disks. All samples are first cured at RT for 48 h and subsequently post-cured at Tc=40°C for 24 h (PC40). 

Figure 16.4 Electrochemical corrosion cell used for testing the ennobling effect of a conducting polymer. The mild steel sample (1) is coated by a thin epoxy layer and is in contact with a 0.1 M UCIO4 solution (aerated or deaerated) through a small hole. Polymethylthiophene (PMT) is deposited on a Pt electrode (2) a saturated calomel electrode (3) and a Pt counter-electrode (4) are used with either (1) or (2) as the working electrode. Electrodes (1) and (2) are galvanically connected and can be disconnected from the electrical circuit for specific measurements. (Reprinted with permission from Electrochimica Acta, Corrosion protection by ultrathin films of conducting polymers by U. Rammelt, P.T. Nguyen and W. Plieth, 48, 9, 1257-1262. Copyright (2003) Elsevier Ltd)...

The direct and indirect effects of fillers oti the photostability of polymer compositions are well known. With the recent interest in nanopowdered fillers reports of their effectiveness as photostabilizers is beginning to be reported in the literature. For instance ZnO and Ti02 nanoparticles (primary particle size 25-70 nm) were studied in acrylic coatings. A layer that carried at least 5 weight percent of the nanoparticles was needed to shield the underlying layers from UV exposure and hence degradation [162]. Nanoscale titania was also evaluated as a stabilizer in epoxy coatings [163]. 

The intermediate layer ensures a powerful bond between the epoxy primer and the external coating. This intermediate, adhesive layer consists of a thin (200-300 xm) coating of specially formulated PP copolymer with polar groups grafted onto the polymer backbone. These polar groups establish bonds with the epoxy layer while the affinity to PP creates a strong bond with the outer layer. 

Cholewinski etal.[73] prepared a robust superhydrophobic bilayer coating containing PDMS-functionalized silica particles on top and an epoxy bonding layer at the base. It was fabricated with a facile dip-coating process that embedded micro-scale PDMS-functionalized silica particles with nano-scale roughness into an epoxy layer spin-coated onto a substrate. The APCAs of the coatings remained stable after four tape tests but no CAH values were reported. 

Chalking also occurs to some extent with several other types of polymers. It does not directly affect corrosion protection but is a concern because it eventually results in a thinner coating. The problem is easily overcome with epoxies, however, by covering the epoxy layer with a coating that contains a UV-resistant binder. Polyurethanes are frequently used for this purpose because they are similar in chemical stfucture to epoxies but are not susceptible to UV breakdown. 

Binder resins for coatings Epoxy crosslinker for photographic subbing layers Epoxy hardener for dry transfer colorations of metallic surfaces Thermosensitive copying paper resins... 

Chen, C., Khobaib, M., and Curliss, D. (2003) Epoxy layered-sihcate nanocomposites. Progress in Organic Coatings, 47, 376-383. 

The coating is applied to protect the steel from corrosion due to the acid or alkaline condition of the soil surrounding the pipe in service. Usually, the process requires three layers. First, an epoxy powder is applied to achieve adhesion to the pretreated metal and therefore resistance to cathodic disbondment. Second, a tie layer of polyolefin copolymer is applied and third a thick layer of polyethylene is cascaded, which in effect protects the epoxy from physical damage. 

In a study of dental silicate cements, Kent, Fletcher Wilson (1970) used electron probe analysis to study the fully set material. Their method of sample preparation varied slightly from the general one described above, in that they embedded their set cement in epoxy resin, polished the surface to flatness, and then coated it with a 2-nm carbon layer to provide electrical conductivity. They analysed the various areas of the cement for calcium, silicon, aluminium and phosphorus, and found that the cement comprised a matrix containing phosphorus, aluminium and calcium, but not silicon. The aluminosilicate glass was assumed to develop into a gel which was relatively depleted in calcium. 

Procedure. Core floods were carried out in horizontally mounted Berea sandstone cores of length 61 cm and diameter 5 cm. Porosity varied from 18 to 25% and brine permeability from 100 to 800 Jim2. The cores were coated with a thin layer of epoxy and cast in stainless steel core holders using molten Cerrobend alloy (melting point 70°C). The ends of the cores were machined flush with the core holder and flanges were bolted on. Pore volume was determined by vacuum followed by imbibition of brine. Absolute permeability and porosity were determined. The cores were initially saturated with brine (2% NaCl). An oil flood was then started at a rate of lOm/day until an irreducible water saturation (26-38%) was established. 

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