Water diffusion coating

We first used isotope substitution in diffuse neutron scattering measurements to determine the distribution of water molecules and counterions (n-butylammonium ions) around the clay layers in the gel state, and obtained a unique picture of a dressed macroion in solution. We obtained a structure in which the naked clay plate of 10 A thickness was extended out to about 35 A by layers of water molecules and counterions. The dressed macroion has exactly two layers of water molecules coating the clay layers these layers are 6 A thick on both sides, extending the effective clay plate out to 22 A, before any counterions at all are found. This is in direct contradiction to the Stem layer picture, widely held in colloid science, that... 

Figure 24.14 Schematic representation of water diffusion through a coating with and without water-insensitive adhesion of the coating to the substrate.

KEYWORDS interfaces, impedance, dielectric spectroscopy, non-destructive testing, durability, diffusion, coatings, water, neutron reflectivity... 

This leaves PMMA and PC as the contenders. The disc design is asymmetric, with an impermeable aluminium coating on one side, so dimensional changes caused by water diffusing into the polymer make the disc bow. The water absorption of PMMA at saturation relative humidity is 2.1wt.%, compared with 0.4% for PC. The diffusion constants at 23 °C for water are 0.5 x 10 and 4.8 x 10 mm s , respectively. The CD surface warping must be less than 0.6°, for the laser spot to focus properly. This rules out a PMMA disc with one side sealed, because it would expand over a period of tens of days as water diffuses through the 1mm thick... 

Filifomi corrosion initiates at the defects of organic coatings and is accelerated by soluble sulfates, chlorides, and carbon dioxide, which enhance acidification at the corrosion site [111], The filament cell structure consists of an actively corroding site and an inactive tail saturated with corrosion products. As shown in Fig. 7.22, water diffuses under the coating into the delaminated area. 

FIGURE 18.7 Biocides are microencapsulated in silica microparticles and the particles incorporated into the coating. When water diffuses toward the metal surface to be protected, the biocide chemicals are released, providing protection for sustained periods of time. (Image courtesy of Ceramisphere, kindly reproduced from www.ceramisphere.com.)... 

The initial effect of water on the coating can increase its electrical resistance (Fig. 5.3d). This seems to be related to the adhesive postcure. The water diffuses very slowly through the coating, since the noticeable drop in electrical resistance begins to be observed after some months of submersion of the coating in water. 

Drug release from stearic acid-coated microspheres may occur by diffusion when microspheres come in contact with aqueous fluids in the G1 tract. This release may occur when water diffuses into the interior of the microsphere, and allows the drug to diffuse across the release coat of the microsphere to the exterior [82], In addition, stearic acid may act as an emulgent that regulates the rate of drug release from microspheres [83], After ingestion, the drug will disperse and dissolve upon contact with GI fluid, possibly by interactions between stearic acid and the suspension media [85],... 

TD Diffusion Coating. Carbides are coated on to iron and steel by dipping in a molten salt bath for 1-10 hours. The bath is mainly borax added to low cost carbide precursors. Coatings 5 to 15mm thick are deposited, and cooled in air or by quenching in oil or water to obtain optimum mechanical properties. (Toyota R D Laboratories, Japan. Engrs. Dig. 36, (7), 1975, p27). 

Marais, S., Metayer, M. et al. Surface modification by low-pressure glow discharge plasma of an unsaturated polyester resin effect on water diffusivity and permeability. Surface and Coatings Technology, 122 (1999), p. 247-259... 

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