Liquid metals dissolved oxygen concentration

In lead alloys, the corrosion kinetics of austenitic steels is linear and the dissolution rate increases with temperature and seems independent of the dissolved oxygen concentration and the liquid metal or alloy velocity in a low fluid velocity range. Empirical correlations have been established to express the corrosion rate [26] ... 

Similar relationships can be written for the dissolution of hydrogen and oxygen. These relationships are expressions of Sievert s law which can be stated thus the solubility of a diatomic gas in a liquid metal is proportional to the square root of its partial pressure in the gas in equilibrium with the metal. The Sievert s law behaviour of nitrogen in niobium is illustrated in Figure 3.8. The law predicts that the amount of a gas dissolved in a metal can be reduced merely by reducing the partial pressure of that gas, as for example, by evacuation. In practice, however, degassing is not as simple as this. Usually, Sievert s law is obeyed in pure liquid metals only when the solute gas is present in very low concentrations. At higher concentrations deviations from the law occur. 

The same principles apply for oxygen in solutions as diverse as liquid metals or blood. Because the oxygen is dissolved, the voltage measured depends upon the activity of the oxygen in the solution. For low concentrations, the activity can be approximated to the concentration, hence ... 

The above distinction between non-reactive and reactive systems does not take into account the possible effect on reactivity and wettability of the furnace atmosphere. The concentration of dissolved oxygen in the liquid close to the S/L/V triple line will lie between two limits. The first of these is that for congruent dissolution of the oxide. This can be calculated using equations (6.8) by assuming that local equilibrium is established between the liquid metal and the oxide at the interface. This limit will be identified as Xq where the superscript I denotes its relevance to the interface. The second limit, Xq(Po2) at the liquid surface, is determined by equilibration with the furnace atmosphere in which the oxygen partial pressure is Pq2 (see Figure 6.3). Note that even if Xq and Xq can be calculated, it is impossible in practice to calculate the actual value of XQ at the... 

Solutions are usually classified according to their physical state, as solid, liquid, or gaseous. The physical state of a solution is determined by the solvent. Many alloys are solid solutions of one metal dissolved in another. For example, brass, which is used to make musical instruments and many other objects, is a solution of copper and zinc. Air is a gaseous solution containing nitrogen, oxygen, and other gases. Carbon dioxide (a gas), alcohol (a liquid), and salt (a solid) each dissolve in water (a liquid) to form liquid solutions. Water is the most common solvent in the laboratory and in many fields. Water solutions are known as aqueous solutions. Because they are so important, in this section we will concentrate on the properties of aqueous solutions. Some solutions and their compositions are illustrated in Table 1. 

Solutions include different combinations in which a solid, liquid, or gas acts as either solvent or solute. Usually the solvent is a liquid. For instance, sea water is an aqueous solution of many salts and some gases such as carbon dioxide and oxygen. Carbonated water is a saturated solution of carbon dioxide in water. Solutions are common in nature and are extremely important in all life processes, in all scientific areas, and in many industrial processes. The body fluids of all forms of life are solutions. Variations in concentrations of our bodily fluids, especially those of blood and urine, give physicians valuable clues about a person s health. Solutions in which the solvent is not a liquid are also common. Air is a solution of gases with variable composition. Dental fillings are solid amalgams, or solutions of liquid mercury dissolved in solid metals. Alloys are solid solutions of solids dissolved in a metal. 

The results of the present work may be applicable for diagnostics of oxygen sensors at more complicated applications, such as measurement of oxygen activity in liquid sodium, lithium, or lead-bismuth heat carriers for atomic power plants. Corrosion and mass transfer in nonisothermal lead-bismuth circuits with temperatures of a heat carrier of 300-500°C do usually occur at a concentration of dissolved O2 of 10 - 10 mass %. The proposed impedance method is developed for determining the level and the character of polarization at the electrolyte-electrode interface, which ensures a continuous oxide protection of materials against corrosion by means of zirconia sensors in all tanperature regimes of exploitation of liquid-metal circuits. 

The principle solutions ensuring high corrosion resistance of structural materials in heavy liquid metal coolant were found using oxygen dissolved in the coolant. It has been shown as a result of long-term studies that this corrosion resistance essentially depends on concentration of dissolved oxygen. 

This estimation is a very simplified one and does not take into accoimt a possible oxidation of iodide to elemental iodine in the sump water. At the very low iodine concentrations present and at the temperatures under consideration, thermal oxidation caused by dissolved oxygen proceeds rather slowly, as far as it is not catalyzed by UV light or by traces of metals. According to the calculations reported by Bums and Marsh (1986), a fraction of only about 10 of the original iodide is thermally oxidized in the ten days following the accident. Since the extent of iodide oxidation in the sump water is determined by the redox potential of the liquid... 

Several liquid redox processes have been developed for smaller-scale (ca. 0.25-20 t sulfur day ) applications, achieving 99.9-t- % recovery. For example, SuIFerox and ARI-LO-CAT use complexed Fe species to oxidize absorbed H2S in acidic solutions, and Stretford, Unisulf, and Sulfolin use vanadium (V) in slightly alkaline solutions as the oxidant for absorbed HS ions. Atmospheric oxygen is the ultimate oxidant in all such processes, as it reoxidizes the reduced form of the dissolved metal species, the concentrations of which are not so limited as that of dissolved oxygen ... 

As was said previously, in the case of lead or lead-bismuth, for low oxygen concentrations a dissolution process is observed. This dissolution process can be divided into three stages the dissolution reaction, the diffusion of the dissolved element in the diffusion boundary layer and the transport of this element in the liquid metal. Consequently the dissolution process is governed by three fluxes ... 

The kinetic constants of the Tedmon law are obtained by adjustment of experimental results. The external magnetite layer is assumed to dissolve in the liquid metal and that its dissolution is mass transfer-controlled. Its rate thus depends on the dissolved oxygen and dissolved iron concentrations, on the diffusion coefficient and the solubility of iron in the liquid metal or alloy. The code calculates the dissolved iron concentration on each point of the circuit and takes into account the influence of the fluid velocity on the dissolution of the magnetite layer. However, the erosion or the spallations of the oxide layer are not taken into account by the MATLIM code. 

The electrode is very robust and can be used to determine the pH of solutions in the pH range 4-12 with an accuracy of 0.2 pH unit it does not contaminate the liquid under test, and since it has a low resistance, it can be used with a simple potentiometer. The electrode cannot, however, be used in the presence of dissolved oxygen, oxidising agents, hydrogen sulphide and heavy metal ions, or in highly acid or alkaline solutions. The E/pH conversion curve depends on the nature and concentration of the substances in the solution under test. The electrode is very susceptible to change of temperature. 

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