Seawater immersion effects

L H Strait, M L Karasek and M F Amateau, Effects of seawater immersion on the impact resistance of glass fibre reinforced epoxy composites , / Compos Mater 1992 26(14) 2118-2133. 

Water Tests. In colorfastness to water, ISO 10S-E01, the test specimen is placed in contact with the chosen adjacent fabrics, immersed in water, and placed wet between glass plates and left for 4 h at 37°C. After drying, the effect on the test specimen and stain on adjacents are assessed. The test, colorfastness to seawater, ISO 10S-E02, is the same as EOl but uses 30 g/L anhydrous sodium chloride solution instead of water. To test for colorfastness to chlorinated seawater/swimming baths water, ISO 10S-E03, the specimen is immersed in sodium hypochlorite solution containing either 100, 50, or 20 mg of active chlorine per Hter at pH 7.5 for 1 h at 27°C, rinsed, dried, and assessed. 

This thin-film-composite membrane has been found to have appreciable resistance to degradation by chlorine in the feed-water. Figure 2 illustrates the effect of chlorine in tap water at different pH values. Chlorine (100 ppm) was added to the tap water in the form of sodium hypochlorite (two equivalents of hypochlorite ion per stated equivalent of chlorine). Membrane exposure to chlorine was by the so-called "static" method, in which membrane specimens were immersed in the aqueous media inside closed, dark glass jars for known periods. Specimens were then removed and tested in a reverse osmosis loop under seawater test conditions. At alkaline pH values, the FT-30 membrane showed effects of chlorine attack within four to five days. In acidic solutions (pH 1 and 5), chlorine attack was far slower. Only a one to two percent decline in salt rejection was noted, for example, after 20 days exposure to 100 ppm chlorine in water at pH 5. The FT-30 tests at pH 1 were necessarily terminated after the fourth day of exposure because the microporous polysul-fone substrate had itself become totally embrittled by chlorine attack. 

The action of macrocells in structures buried in the soil or immersed in water is different from that of structures exposed to the atmosphere two circumstances promote macrocell effects while another reduces them. First, concrete is wetter than in aerated structures and its resistivity is lower, particularly in structures immersed in seawater. This reduces the ohmic drop in the concrete and increases the size of the effective cathodic area in relation to the anodic one. Secondly, the soil or the seawater around the concrete is an electrolyte of low resistivity, and the macro-cell current can also flow outside the concrete. This further reduces the ohmic resistance between the anodic area and passive reinforcement. Thirdly, there is, however, a mitigating aspect. Oxygen can only diffuse with great difficulty through wet concrete and thus it hardly reaches the surface of the embedded steel. Depletion of oxygen at the surface of the rebar that is observed in this case makes initiation of corrosion very difficult, and, even when corrosion initiates, the driving voltage for the macrocell is very low. 

The protection of steel by aluminum coatings depends partly on the physical barrier effect to the coating itself (i.e., exclusion of the environment from the substrate) and partly on sacrificial action. The extent of the latter depends on the environment, the aluminum composition, and the area of steel exposed for example, in the presence of chloride ions, such as during immersion in seawater, aluminum would be fairly active, and the low-resistivity electrolyte would ensure satisfactory protection of the steel by sacrificial action. 

The nitric acid-cleaned silica, which was free from organic material as well as metal ions, was immersed in 4-10 mM solutions of selected metal salts at a series of pH values and washed, and the rate of dissolution was measured in a standard manner at pH 9.0. Metals with no effect at pH 2-9 were La, Mo. and Cr, and at pH 4-11 were Ca and Mg at pH 8, which is that of seawater. Al. Be, Fe. Ga, Gd. and Y all retarded dissolution. However. Al was unique in that when applied over the range from 5 to 9, it rendered the silica completely insoluble at pH 9. 

The basic laboratory calibration of a conductivity cell is obtained by immersing the cell with the CTD in tanks filled with seawater of different salinities. To avoid effects of thermal expansion of the cell on the calibration, all bath temperatures are kept the same to within 2 K. The basic calibration Cctd of the conductivity cell is referred to the conductivity of the baths and is valid for the overall bath temperature and at atmospheric pressure. 

Sirrruk A, Penumadu D, and Weitsman YJ (2010) Fatigue behavior of carbon fiber and vinyl ester sandwich facing material due to sea environment. In Ninth international conference on sandwich structures (ICSS-9). California Institute of technology, Pasadena, 14—16 June 2010 Sloan FE, Seymour RJ (1992) The effect of seawater exposure on mode I interlaminar fracture and crack growth in graphite/epoxy. J Compos Mater 26(18) 2655-2673 Smith LV, Weitsman YJ (1996) The immersed fatigue response of polymer composites. Int J Fract 82(1) 31 2... 

Tests in outdoor testing stations have shown that cladding provides an effective protection for many years, whether exposed to weathering or immersed in seawater [29]. The consumption of the cladding avoids corrosion of the underlying core (Figure B.5.5). 

Aluminium has no antifouling effect because its salts, including alumina (Al(OH)3), are not toxic for marine organisms. As a consequence, marine biological matter (algae and molluscs) will cover aluminium immersed in seawater very quickly if local conditions allow their growth. 

Figure 632 SAFT AMI 8,3.0 V, SOAhmagnesium-silverchloride seawater-activated batteries effect of repeated immersions in seawater (32g NaCI/l) on discharge performance at 20°C (Courtesy of SAFT)...

N. Le Bozec, M. L Her, C. Compere, P. Marcus, and D. Costa, Evidence for the effect of hydrogen peroxide produced by marine biofilms on the electrochemical behaviour evolution of stainless steel immersed in natural seawater. Proceedings of Eurocorr 2000, EFC, London, U.K., 2000. 

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