Sea water, composition

WA water quality labs by atomic absorption and autoanalyzer techniques. Charge balance calculations Indicated that all dissolved species of significance were analyzed. Comparison of filtered and unflltered aliquots suggested that un-lonlzed species were not present In appreciable quantities. Sampling and analysis uncertainties were determined by the operation of two co-located samplers for 16 weeks. The calcium and sulfate data were corrected for the Influence of sea salt to aid In the separation of the factors. This correction was calculated from bulk sea water composition and the chloride concentration In rainwater (11). Non seasalt sulfate and calcium are termed "excess" and flagged by a ... 

Holland (15) notes that the major part of the oceanic sediments may well be detrital. Garrels (5) has recently estimated that to account for the stabilization of sea water composition since the birth of the ocean, only about 7% of the sediments need to have reacted. 

Sea-water compositions may have alternated between incursions of volcanically influenced plumes, reduced and sulphide bearing, with episodes of more oxidized sulphate bearing ambient water from shallower levels. In this setting, sulphate and nitrate in relatively oxidized upper-level incoming sea water, periodically strongly influenced by the chemistry of vent plumes, is reacted against more reduced chemical species from within the mud, and from deeper-level water. 

The chemical exergy is calculated with respect to the sea water composition as follows ... 

Differences in the ingredients. Both laboratories used artificial sea water. Ingle et al. used the formula of Kester et al. (1967) (minus borate), while Berner used Turekian s compilation of sea water composition and included all species with concentrations greater than fluoride (hence borate was included). 

Generai description. Galvanic corrosion refers to the preferential corrosion of the more reactive member of a two-metal pair when the metals are in electrical contact in the presence of a conductive fluid (see Chap. 16, Galvanic Corrosion ). The corrosion potential difference, the magnitude of which depends on the metal-pair combination and the nature of the fluid, drives a corrosion reaction that simultaneously causes the less-noble pair member to corrode and the more-noble pair member to become even more noble. The galvanic series for various metals in sea water is shown in Chap. 16, Table 16.1. Galvanic potentials may vary with temperature, time, flow velocity, and composition of the fluid. 

Substances such as brass, wood, sea water, and detergent formulations are mixtures of chemicals. Two samples of brass may differ in composition, colour and density. Different pieces of wood of the same species may differ in hardness and colour. One sample of sea water may contain more salt and different proportions of trace compounds than another. Detergent formulations differ... 

Type 316-This has a composition of 17/12/2.5 chromium/nickel/molyb-denum. The addition of molybdenum greatly improves the resistance to reducing conditions such as dilute sulfuric acid solutions and solutions containing halides (such as brine and sea water). 

Ocean sea water is roughly equivalent in strength to a 3 j % w/v solution of sodium chloride, but it has a much more complex composition, embodying a number of major constituents, and traces at least of almost all naturally occurring elements. For convenience, however, the concentration of salts in any sample of sea water is expressed in terms of the chloride content, either as chlorinity or as salinity. Both these units are again subject to arbitrary definition and do not conform simply to the chemical composition. 

Constancy of composition The validity of these arbitrary conversions depends on the constancy of the ratios of the various dissolved salts. It is a remarkable and important fact that, except where there is gross dilution or contamination, the relative proportions of the major constituents of sea water are practically constant all over the world. 

Table 2.14 gives the composition of sea water of 19 parts per thousand chlorinity. 

It is generally agreed that steel composition within the range practical for ship plate has little influence on the corrosion rate in sea water... 

All ordinary ferrous structural materials, mild steels, low-alloy steels and wrought irons corrode at virtually the same rate when totally immersed in natural waters. Wrought iron may be slightly more resistant than mild steel in a test in sea-water at Gosport, Scottish wrought-iron specimens lost about 15% less weight after 12 months immersion than specimens of ordinary mild steel. As shown in Table 3.5, the process of manufacture and the composition of mild steel do not affect its corrosion rate appreciably . 

Corrosion problems that arise are frequently discussed under the headings (a) sea-water, and (b) fresh waters, but there is, in fact, no sharp dividing line, since some harbour, estuarine and brackish well waters are mixtures of sea-water and fresh water and are often variable in composition. In the past, corrosion problems were serious, particularly in sea-water service, but resistant alloys have been developed and although trouble still occasionally arises this is more frequently due to poor design or operation rather than to lack of materials suitable for the application. 

Figure 4.17 illustrates the corrosion occurring on high-purity AZ31 and ZW3 in contact with steel bolts. Tested alone in sea-water, the corrosion rate of the former is much the lower. It is evident from the illustration, however, that the governing factor in galvanic corrosion is the type of electrolyte present rather than the composition of the alloy. 

Variations in solution composition throughout a test should be monitored and, if appropriate, corrected. Variations may occur as a result of reactions of one or more of the constituents of the solution with the test specimen, the atmosphere or the test vessel. Thus, it is important that the composition of the testing solution is what it is supposed to be. Carefully made-up solutions of pure chemicals may not act in the same way as nominally similar solutions encountered in practice, which may, and usually do, contain other compounds or impurities that may have major effects on corrosion. This applies particularly to artificial sea-water, which is usually less corrosive than natural sea-water. This subject is discussed in detail in a Special Technical Publication of ASTM, and tests with natural, transported and artificial sea-water have been described . Suspected impurities may be added to the pure solutions in appropriate concentrations or, better still, the testing solutions may be taken directly from plant processes whenever this is practical. 

Small variations in solution composition may also affect the value of any critical velocity. In laboratory tests using recirculating artificial sea-water the presence of dissolved copper from copper alloy test-pieces has been shown to affect the value of the critical velocity for such materials . 

Table II summarizes analytical data for dissolved inorganic matter in a number of natural water sources (J3, 9, J 9, 20, 21). Because of the interaction of rainwater with soil and surface minerals, waters in lakes, rivers and shallow wells (<50m) are quite different and vary considerably from one location to another. Nevertheless, the table gives a useful picture of how the composition of natural water changes in the sequence rain ->- surface water deep bedrock water in a granitic environment. Changes with depth may be considerable as illustrated by the Stripa mine studies (22) and other recent surveys (23). Typical changes are an increase in pH and decrease in total carbonate (coupled), a decrease in 02 and Eh (coupled), and an increase in dissolved inorganic constituents. The total salt concentration can vary by a factor of 10-100 with depth in the same borehole as a consequence of the presence of strata with relict sea water. Pockets with such water seem to be common in Scandinavian granite at >100 m depth.

Redfield, A. C. (1934). On the proportions of organic derivatives in sea water and their relation to the composition of plankton. In "James Johnstone... 

Holland, H. D. (1974). Marine evaporites and the composition of sea water during the Phanerozoic. In "Studies in Paleo-oceanography (W. W. Hay, ed.), pp. 187-192. Society of Economic Paleontologists and Mineralogists, Tulsa, Oklahoma, Special Publication 20. 

The failure to identify the necessary authigenic silicate phases in sufficient quantities in marine sediments has led oceanographers to consider different approaches. The current models for seawater composition emphasize the dominant role played by the balance between the various inputs and outputs from the ocean. Mass balance calculations have become more important than solubility relationships in explaining oceanic chemistry. The difference between the equilibrium and mass balance points of view is not just a matter of mathematical and chemical formalism. In the equilibrium case, one would expect a very constant composition of the ocean and its sediments over geological time. In the other case, historical variations in the rates of input and removal should be reflected by changes in ocean composition and may be preserved in the sedimentary record. Models that emphasize the role of kinetic and material balance considerations are called kinetic models of seawater. This reasoning was pulled together by Broecker (1971) in a paper called "A kinetic model for the chemical composition of sea water."... 

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