Surface buildup

The scrubbing or washing of wool and acrylic fibers causes the surface buildup of fiber balls on the fabric. These balls are also called knots, buttons, or pills and they are joined to the fabric by a few single fibers. Wool, of course has lower tensile and flexural strengths than acrylic fibers, so that the knots... 

Application of mold release agent always bears a risk of cycle time increase (application of mold release and mold cleaning), cost increase (time and cost of release agent), variable surface quality (differences in adhesion dependent on the quality of mold coverage by release agent), and surface buildup with related negative phenomena such as plateout and/or variable adhesion. The very notion of the... 

Fluctuating liquor level. This requires higher initial current density and more frequent repassivation cycles to form a tenacious passive layer. When immersed, the wet/dry zone of a tank exhibits a more positive potential than the remainder of tank, which may account for the higher corrosion rates there. However, it has been observed that the wet/dry zone does not get covered with surface buildup or deposits. The constantly immersed zone builds a thick surface deposit on these protected surfaces. 

The loss of antioxidants by migration was first observed in the 1960s for both elastomers [16,17] and polyethylene [ 18]. In a 1973 paper, Bair ]19] described a microscopy study of surface buildup of a hindered phenol antioxidant at a 0.08 percent level in a low-density polyethylene. Seventy percent of the antioxidant in antioxidant-polymer compounds was expelled in three days at 70 °C. He notes the danger of accelerated aging experiments, which do not account for this exudation. 

Ion implantation (qv) has a large (10 K/s) effective quench rate (64). This surface treatment technique allows a wide variety of atomic species to be introduced into the surface. Sputtering and evaporation methods are other very slow approaches to making amorphous films, atom by atom. The processes involve deposition of a vapor onto a cold substrate. The buildup rate (20 p.m/h) is also sensitive to deposition conditions, including the presence of impurity atoms which can faciUtate the formation of an amorphous stmcture. An approach used for metal—metalloid amorphous alloys is chemical deposition and electro deposition. 

Uses. Sound-absorbing materials are frequendy used to reduce reverberation, or the persistence of sound in a space after generation of the sound ceases to reduce focused reflections from concave surfaces to prevent echoes, or delayed sound reflections from distant surfaces and to prevent the buildup of sound by multiple reflections within rooms and other enclosures. Sound-absorbing materials also are used to reduce the transmission of noise from one location to another by multiple reflections from sound-reflecting surfaces. 

Since membrane fording could quickly render the system inefficient, very careful and thorough feedwater pretreatment similar to that described in the section on RO, is required. Some pretreatment needs, and operational problems of scaling are diminished in the electro dialysis reversal (EDR) process, in which the electric current flow direction is periodically (eg, 3—4 times/h) reversed, with simultaneous switching of the water-flow connections. This also reverses the salt concentration buildup at the membrane and electrode surfaces, and prevents concentrations that cause the precipitation of salts and scale deposition. A schematic and photograph of a typical ED plant ate shown in Eigure 16. 

Electrodialysis Reversal. Electro dialysis reversal processes operate on the same principles as ED however, EDR operation reverses system polarity (typically three to four times per hour). This reversal stops the buildup of concentrated solutions on the membrane and thereby reduces the accumulation of inorganic and organic deposition on the membrane surface. EDR systems are similar to ED systems, designed with adequate chamber area to collect both product water and brine. EDR produces water of the same purity as ED. 

Many of the by-products of microbial metaboHsm, including organic acids and hydrogen sulfide, are corrosive. These materials can concentrate in the biofilm, causing accelerated metal attack. Corrosion tends to be self-limiting due to the buildup of corrosion reaction products. However, microbes can absorb some of these materials in their metaboHsm, thereby removing them from the anodic or cathodic site. The removal of reaction products, termed depolari tion stimulates further corrosion. Figure 10 shows a typical result of microbial corrosion. The surface exhibits scattered areas of localized corrosion, unrelated to flow pattern. The corrosion appears to spread in a somewhat circular pattern from the site of initial colonization. 

---