Dissolved oxygen content

DISSOLVED-OXYGEN CONTENT-CC PER LITER Figure 4-460. Corrosion in sodium chloride solution containing dissolved oxygen. (From Ref. [197].)... 

The conductivity of the environment low conductivity hinders the ionic current flow hence distilled water is less corrosive than a solution of sodium chloride with the same pH and dissolved oxygen content. 

The dissolved oxygen content of surface oceanic water is mainly determined by its biological history it always tends, by solution from the air, towards... 

Hydrazine is conventionally added in an amount equivalent to at least KX) of the dissolved oxygen content. In principle, additions should be made after thermal deaeration to economise on reagent usage, but in practice in some cases more thorough scavenging is found to result if hydrazine is added before the deaerator. This may reflect the kinetic aspects of the reaction with oxygen. 

It is often difficult to conduct laboratory tests in which both the environmental and stressing conditions approximate to those encountered in service. This applies particularly to the corrosive conditions, since it is necessary to find a means of applying cyclic stresses that will also permit maintenance around the stressed areas of a corrosive environment in which the factors that influence the initiation and growth of corrosion fatigue cracks may be controlled. Among these factors are electrolyte species and concentration, temperature, pressure, pH, flow rate, dissolved oxygen content and potential (free corrosion potential or applied). 

Discussion. One of the most useful titrations involving iodine is that originally developed by Winkler18 to determine the amount of oxygen in samples of water. The dissolved oxygen content is not only important with respect to the species of aquatic life which can survive in the water, but is also a measure of its ability to oxidise organic impurities in the water (see also Section 10.103). Despite the advent of the oxygen-selective electrode (Section 16.36) direct titrations on water samples are still used extensively.19... 

Calculate the dissolved oxygen content and express it as mg L 1 1 mL of Mj80 thiosulphate = 1 mg dissolved oxygen. 

The predicted pH is 8.34, a value lying within but toward the alkaline end of the range 7.8 to 8.5 observed in seawater (Fig. 6.1). The dissolved oxygen content predicted by the calculation is 215 qrnol kg-1, or 6.6 mg kg-1. This value compares well with values measured near the ocean surface (Fig. 6.2). 

Geochemists (e.g., Thorstenson et al., 1979 Thorstenson, 1984) have long recognized that at low temperature many redox reactions are unlikely to achieve equilibrium, and that the meaning of Eh measurements is problematic. Lindberg and Runnells (1984) demonstrated the generality of the problem. They compiled from the watstore database more than 600 water analyses that provided at least two measures of oxidation state. The measures included Eh, dissolved oxygen content, concentrations of dissolved sulfate and sulfide, ferric and ferrous iron, nitrate and ammonia, and so on. 

As an example of modeling a fluid in redox disequilibrium, we use an analysis, slightly simplified from Nordstrom et al. (1992), of a groundwater sampled near the Morro do Ferro ore district in Brazil (Table 7.2). There are three measures of oxidation state in the analysis the Eh value determined by platinum electrode, the dissolved oxygen content, and the distribution of iron between ferrous and ferric species. 

Here, we set oxidation state in the model using the dissolved oxygen content and calculate the distribution of species assuming redox equilibrium. 

The ratio of ferrous to ferric species represents a redox state considerably less oxidizing than suggested by the dissolved oxygen content. The measured Eh falls between these values. Because the values vary over a range of more than 500 mV, this water clearly is not in redox equilibrium assuming that it is gives an incorrect distribution of iron species. 

The dissolved oxygen content of a solution can be determined by measuring the diffusion current that results at a selected voltage. The Clark electrode was developed for this purpose and various modifications have subsequently been introduced. It consists basically of a platinum electrode separated from the sample by a membrane which is permeable to oxygen, e.g. Teflon or polyethylene. A reference electrode of silver/silver chloride in potassium chloride is used to complete the system (Figure 4.21). When a voltage that is sufficient to give the... 

Two bioassays are employed to evaluate the effect of samples on terrestrial life forms. For gas samples, the plant stress ethylene test is presently recommended. This test is based on the well-known plant response to environmental stress release of elevated levels of ethylene (under normal conditions plants produce low levels of ethylene). The test is designed to expose plants to various levels of gaseous effluents under controlled conditions. The ethylene released during a set time period is then measured by gas chromatography to determine toxicity of the effluent. For liquid and solid samples, a soil microcosm test is employed. The sample is introduced on the surface of a 5 cm diameter by 5 cm deep plug of soil obtained from a representative ecosystem. Evolution of carbon dioxide, transport of calcium, and dissolved oxygen content of the leachate are the primary quantifying parameters. 

An elecrochemical device for detecting dissolved oxygen content. The well known Clark electrode consists of a platinum wire tip surrounded by a thin film of electrolyte solution that is shrouded by a plastic membrane. The membrane is permeable to oxygen, but impermeable to... 

In conventional aluminum-deoxidized steels, the extra-low dissolved oxygen content maintains the sulfur in solution in the liquid stoel until the end of the solidification process. Since sulfur exhibits virtually no solubility in the solid steel — less than 0,001% in the bcc structure — a > iS-Fe eutectic suddenly precipitates at the as cast grain boundaries, the so called "Type II" structure described by Sims ( ). This weakens the as cast structure and also results in elongated MnS inclusions in the hot rolled steel plates, coils, sheets, bars, wires etc, as shown in Figure 5,... 

Svetlichny, L.S., Yuneva, T.V., Shulman, G.E. and Houseman, J.A. (1994). Utilisation of protein in the energy metabolism of the cladoceran Moine micrura at varying dissolved oxygen contents (In Russian). Doklady Akademii Nauk SSSR 337, 428-430. 

Table 3.4 lists the parameters in the order by which they would usually stabilize. Temperature and pH are usually the first ones to stabilize because they are not very sensitive to the influx of fresh water. That is why they are not as good stabilization indicators as the other parameters. Their measurements, however, are important for data interpretation and should always be made during groundwater sampling. Dissolved oxygen content and turbidity, which is the measure of the particulate matter content in water, are typically the last ones to stabilize. 

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