Oxygen sea water

Tantalum has a high resistance to general outdoor atmospheres. Tantalum and the Ta-lOW alloy are virtually immune to sea water at ambient conditions and tantalum is only tarnished in oxygenated sea water at 26°C. 

In the test for oxygen binding, 02-electrode measurements were made by diluting samples of oxygenated sea water with equal-sized volumes of either deaerated sea water or deaerated vanadocyte suspensions. If vanadocytes could bind 02, the concentration of dissolved 02 should be lower in the sample diluted with vanadocytes, than in the one diluted by deaerated sea water. However, no difference in the post-dilution sea water oxygen concentration was found between the two the results fell on the calibration curve. This finding has now been extended to tunicate blood cells rich in iron, rather than vanadium64. ... 

Thermodynamic calculations show that chromate is the expected form in oxygenated sea water, while the insoluble Cr(III) species would predominate in very low-oxygen (so called suboxic ) or anoxic waters. However, it is important to note that thermodynamic calculations only predict elemental spe-ciation at equilibrium (when the rates of formation and destruction are balanced), but they do not consider the rates of conversion themselves. For example, Cr(III) should not exist in oxygenated sea water, but its rate of oxidation to Cr(VI) is slow (days to months), meaning that Cr(III) can persist in oxic water ( kinetic stabilization ). In the eastern North Pacific Ocean, Cr(VI) displays a surface concentration of 3 nmol 1 (Figure 2A), but then decreases rapidly to a minimum of 1.7 nmol 1 at 300 m depth and increases below this to levels of 4-5 nmol in the deeper waters. While chromate appears to display a mixture of scavenged and nutrient-like behavior, the Cr(VI) minimum occurs at the same depth as the widespread suboxic zone in the eastern Pacific. 

The presence of dissolved solids in water further reduces the solubility of oxygen. Sea water contains roughly 10 000 mg dm NaCl. At 25°C, this reduces the solubility of oxygen from 8.4 to 7.6mgdm. Typically, fish growth is inhibited below about 6 mg dm of dissolved oxygen. 

Storage of oxygenated sea water in contact with brass sampling bottles causes... 

Hydroxylamine has a limited stability in oxygenated sea water at pH 8 and may not be sufficiently stable to coexist with oxygen even at the very low oxygen concentrations found in some areas of the Pacific ocean. However, under anaerobic conditions in the sea and in lakes, hydroxylamine is stable and may be present. 

In a similar vein, mean seawater temperatures can be estimated from the ratio of 0 to 0 in limestone. The latter rock is composed of calcium carbonate, laid down from shells of countless small sea creatures as they die and fall to the bottom of the ocean. The ratio of the oxygen isotopes locked up as carbon dioxide varies with the temperature of sea water. Any organisms building shells will fix the ratio in the calcium carbonate of their shells. As the limestone deposits form, the layers represent a chronological description of the mean sea temperature. To assess mean sea temperatures from thousands or millions of years ago, it is necessary only to measure accurately the ratio and use a precalibrated graph that relates temperatures to isotope ratios in sea water. 

The solubility of oxygen in water with a salt content up to 1 mol L is only dependent on the temperature. The oxygen concentrations in equilibrium with air amount to (in mg L- ) 0°C, 14 10°C, 11 20°C, 9 and 30°C, 7. The depth of water has no effect in the case of ships. In Hamburg harbor in summer, 7.3 mg L are measured in depths up to 7 m. The value can be much lower in polluted harbors and even fall to zero [8]. In the open sea, constant values are found at depths of up to 20 m. With increasing depth, the Oj content in oceans with low flow rates decreases [12] but hardly changes at all with depth in the North Sea [13]. 

Pitting Environments. In ordinary sea water the dissolved oxygen in the water is sufficient to maintain passivity, whereas beneath a barnacle or other adhering substance, metal becomes active since the rate of oxygen replenishment is too slow to maintain passivity, activation and pitting result. 

In sea-water, the increase of pH adjacent to the surface of cathodes brought about by the reduction of oxygen leads to the deposition of films of calcium carbonate and magnesium hydroxide . Such film deposition often results in a gradual decrease in the rate of galvanic corrosion of the more negative members of couples immersed in sea-water. 

Dissolved oxygen is a very important factor in the corrosion of metals immersed in sea water. Because of its biological significance, a vast amount... 

Sea water of normal salinity, in equilibrium with the atmosphere, has the following oxygen contents (compare Table 2.14) ... 

The open-circuit potential of most metals in sea water is not a constant and varies with the oxygen content, water velocity, temperature and metallurgical and surface condition of the metal. 

The general indication of the results in this table is that the corrosion rates of non-ferrous metals increase with depth in spite of lower temperatures and lower oxygen concentrations than at the surface. It was noted in the paper by Kirk that the results at depth were typical of the variation of performance of these materials experienced on numerous occasions in surface sea water. A notable exception was for aluminium alloys of the 5000 (Al-Mg) and 6000 (Al-Mg-Si) series which had good resistance to corrosion... 

A surgical implant is constantly bathed in extracellular tissue fluid. Basically water, this fluid contains electrolytes, complex compounds, oxygen and carbon dioxide. Electrolytes present in the largest amounts are sodium (Na ) and chloride (Cl ) ions. Most of the fluids existing in the body (such as blood, plasma and lymph) have a chloride content (and pH) somewhat similar to that of sea water (about 5 to 20g/l and pH about 8) . 

At sufficiently high rates of flow in natural waters enough oxygen may reach the surface to cause partial passivity, in which case the corrosion rate may decrease. In sea-water, owing to the high concentration of chloride ions, the corrosion rate increases with velocity. In one series of tests, corrosion under static conditions was 0-125mm/y, 0-50mm/y at 5 ft/s and 0-83 mm/y at 15 ft/s. 

Nickel-iron alloys fully immersed in sea-water may suffer localised corrosion which can be severe under conditions where oxygen is constantly renewed at the surface and the formation of protective corrosion products is hindered, e.g. in fully-aerated flowing sea-water. In quieter, less oxygenated conditions, average corrosion rates of Fe-36Ni are low and well below those for mild steel, as exemplified in the data given in Table 3.33 . However the resistance to localised attack is not improved to the same extent. 

The corrosivity of a natural water depends on the concentration and type of impurity dissolved in it and especially on its oxygen content. Waters of similar oxygen content have generally similar corrosivities, e.g. well-aerated quiescent sea-water corrodes cast iron at ratesof 0 05-0-1 mm/y while most well-aerated quiescent fresh waters corrode iron at O Ol-O-1 mm/y. 

Palladium is considerably less resistant to anodic corrosion than platinum, though it may be used for evolution of oxygen from alkaline solutions. It is attacked rapidly when used as an anode in sea-water, and dissolves quantitatively in acid chloride solutions. 

Paints used for protecting the bottoms of ships encounter conditions not met by structural steelwork. The corrosion of steel immersed in sea-water with an ample supply of dissolved oxygen proceeds by an electrochemical mechanism whereby excess hydroxyl ions are formed at the cathodic areas. Consequently, paints for use on steel immersed in sea-water (pH 8-0-8-2) must resist alkaline conditions, i.e. media such as linseed oil which are readily saponified must not be used. In addition, the paint films should have a high electrical resistance to impede the flow of corrosion currents between the metal and the water. Paints used on structural steelwork ashore do not meet these requirements. It should be particularly noted that the well-known structural steel priming paint, i.e. red lead in linseed oil, is not suitable for use on ships bottoms. Conventional protective paints are based on phenolic media, pitches and bitumens, but in recent years high performance paints based on the newer types of non-saponifiable resins such as epoxies. 

Oxygen, dissolved in sea-water in equilibrium with a normal . atmosphiere 76C mm) of iair saiurated with water vapour... 

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