Important Uses for Element Oxygen?


1. what's our current understanding of the fundamental reason that oxygen is essential for life?

What type of oxygen? Atomic? Molecular? What type of life? All life? Aerobic organisms? Humans only?

2. Development of an oxide-dispersion-strengthened steel by introducing oxygen carrier compound into the melt aided by a general thermodynamic model

The thermodynamic model described in Thermodynamic model section has been employed to make certain predictions and a rather general model for the FeNiMn-Y-TiO system behavior such as identities and stability of phases at equilibrium condition. We minimized the total free energy of the system under the constraints of experimental composition of the alloy, i.e. Fe 80.82, Ni 9.66, Mn 7.22, Y 1.02, and Ti 1.28 (at.%). In this regard, the Gibbs energy of Y O , TiO , FSS, Y TiO , Y Ti O oxides as well as FeNiMn-Y-Ti liquid phase has been calculated to reach the equilibrium state of the system. In Fig. S5, the calculated Gibbs energy of the liquid phase is compared with the results of Thermo-Calc software, for instance. There is a good agreement between the results of current modeling and those of the software. The predicted stable phases of the FeNiMn-Y-TiO alloy at 1873 K against different oxygen partial pressures are shown in Fig. 6a,b. In Fig. 6a, the equilibrium solubility of Y and Ti in the liquid phase is demonstrated as a function of oxygen pressure. Figure 6b shows the phase percentage of the stable Y-Ti oxides in various oxygen pressures. Based on these thermodynamic calculations, TiO , Y Ti O , FSS (fluorite-type solid solution), and Y O are the four probable stable Y-Ti oxides depending on the oxygen pressure of the system at 1873 K. All the mentioned oxide phases are stable up to the room temperature except for the FSS phase which decomposes into Y O and Y TiO by a eutectoid reaction at 1673 K35,37. Therefore, hereafter, the FSS phase has been ignored from thermodynamic modeling results in order to simplify the representation of the stable phases at room temperature. Figure 6c,d show the thermodynamic equilibrium phase separated state of FeNiMn-Y-TiO system considering the above assumption. Generally, a reduction of oxygen pressure will result in a reduction of stable oxide compounds in the system. Simultaneously, there will be an increase in Y and Ti dissolution and there will also be more Y and Ti in the melted FeNiMn phase. In fact, these thermodynamic modeling results indicate that in the high oxygen pressure condition, TiO and Y Ti O are more stable oxides as expected from TiO -Y O pseudo-binary phase diagram under 1 atm37. By decreasing the oxygen pressure, TiO starts to decompose into O and dissolved Ti (TiO Ti O ); consequently, the concentration of Ti in the liquid phase increases slightly. After complete dissolution of TiO in the liquid phase, Y Ti O becomes the only stable oxide within limited range of oxygen pressure. At much lower oxygen partial pressures, Y Ti O oxide also decomposes into Ti, Y TiO , and O (Y Ti O Ti Y TiO O ). After the complete consumption of Y Ti O , Y TiO is the only stable oxide within the small range of oxygen pressure. In the next step, as a result of further decrease in the oxygen pressure, Y TiO starts to dissolve and concurrently Y O starts to form (Y TiO Ti Y O O ). By the end of this reaction, all the Ti content of the system is completely dissolved in the liquid phase and Y O remains as the only stable oxide. By the continuation of the decline of oxygen pressure, Y O can also decompose into O and dissolved Y (Y O 2Y O ). Therefore, as shown in Fig. 6c, the amount of the dissolved Y in the liquid phase rises significantly. Finally, after complete decomposition of Y O , all the Y-Ti oxides disappear completely and the total amount of Y and Ti content is in the form of dissolved element in the FeNiMn liquid phase. Due to the fact that solubility of oxygen for the FeNiMn-Y-Ti system in the liquid phase is negligible (less than 10 ppm for this work conditions according to the Sieverts' law calculation), we have ignored it in the current modeling. Moreover, inasmuch as the Y and Ti elements exhibit higher affinity for oxygen compared with other elements of the system, it can be assumed that all the oxygen in the solidified alloy is in the form of Y-Ti oxides only. This assumption is in agreement with the previous results which have reported the formation of Y O until complete consumption of the oxygen content in the yttrium-bearing alloys40,45. Therefore, the oxygen content of the solidified alloy could be calculated by considering the phase percentage of all Y-Ti oxides. This value has been also shown as a function of oxygen partial pressure by solid black lines in Fig. 6a,c. In Fig. 7a, the change in the oxides phase fraction of the FeNiMn-Y-TiO system is plotted as a function of the oxygen content. The highlighted regions in Figs 6c,d and 7a demonstrate the stability region of Y O and Y TiO oxides which were observed experimentally in this alloy. Based on the Fe-10Ni-7Mn-1.6Y-1.8TiO (wt.%) alloy composition, there is about 2.49 at.% oxygen in the alloy as a result of TiO oxygen carrier addition. Moreover, the former study performed on the FeNiMn-0.8Y alloy with similar processing conditions has revealed that only 0.116 at.% oxygen has entered the system from different sources such as raw material impurities or vacuum leakage during melting process40. Thus, all oxygen content in the current alloy should be around 2.61 at.% which is in reasonable agreement with the modeling results that indicate the maximum range of Y O and Y TiO region to be 2.63 at.% oxygen (Fig. 7a). Figure 7b demonstrates oxygen alloy content curves of the FeNiMn-Y-TiO system at different temperatures. These curves show all the formation, stability, and decomposition steps of Y-Ti oxides. Therefore, this figure can be considered as a comprehensive representative of the system stability at different processing conditions. Surprisingly, it can be seen from the figure that changes in temperature and pressure of the system do not lead to a considerable change in the final phase constituents of the system. Instead, the equilibrium state of the system is mainly determined by the input value of oxygen in the form of TiO oxygen carrier. According to the figure, by changing the temperature, oxygen alloy content curves only shift slightly in the direction of horizontal axis. These displacements in the curves occurred within a very small range of the equilibrium oxygen pressure (between 1018 to 1032 atm). From the practical viewpoint, this negligible change of the equilibrium oxygen pressure is insensitive in this system. Thus, based on the thermodynamic results, it can be concluded that the formation of various complex Y-Ti oxides in the FeNiMn-Y-TiO system is independent of the experimental conditions such as melting temperature or vacuum furnace quality. This unique feature can propose the oxygen carrier method as a feasible method for manufacturing a new generation of ODS alloys. The calculated map of the equilibrium phases of the FeNiMn-Y-TiO system at different temperatures and oxygen partial pressures is shown in Fig. 8. The nine different regions can be recognized in the map. These regions can be divided into two different categories of stable and reaction regions. In stable regions, the amounts of the formed oxides as well as the liquid phase composition remain almost constant during oxygen pressure changes. But in reaction regions, the formation and decomposition of different Y-Ti oxides can occur simultaneously and as a result of this, the amount of dissolved Y or Ti can change in the liquid phase based on their consumption in the Y-Ti oxides. The map shows that with a decline in the oxygen pressure, five different stable regions containing various Y-Ti oxide phases, i.e. I: TiO Y Ti O ; III: Y Ti O ; V: Y TiO ; VII: Y O ; and IX: without oxide appear sequentially. The four reaction regions occurring among these stable regions are also indicated in Fig. 8. In the reaction region of VI, Y TiO decomposes into Y O , O , and dissolved Ti with a decline in the oxygen pressure. Thus, Y TiO , Y O , and the liquid phase which contains Fe, Ni, Mn, and Ti elements, are the stable phases in this region. The stable oxides of this region are consistent with the experimental results which show that Y TiO and Y O are the stable phases of the solidified FeNiMn-Y-TiO alloy. In the current system, regions IV, VI, and VIII are more important due to considerable variation of the oxygen alloy content occurred in these regions. It means that within a wide range of system oxygen content, as shown in Fig. 7a, the equilibrium state of the system is placed in these three regions. Thus, on the basis of current thermodynamic modeling, the stable phase constituents of each of these three regions can be easily achieved by controlling the oxygen content of the alloy as a result of oxygen carrier adjustment. The importance of the described thermodynamic modeling as a numerical technique for the design of the new ODS alloys is apparent for the metallurgists. The developed model drawn upon available thermodynamic data can be easily employed to design new systems with different final phase constituents of Y-Ti oxides using oxygen carrier concept. Whether the oxygen carrier technique will have a beneficial effect on the high temperature properties of the alloys during creep deformation and how to adapt this concept to more complex commercial usable alloys will have to be shown in the future.

3. Dose oxygen dissolves in water?

sure O2 dissolves in water..not to a great extent but around 8 mg/liter ( 8ppm). The colder the water the more O2 dissolves up to the maximum of 8-9 mg/liter.This is why it is important in a limited water environ ( like a tank ) that the water be aerated to replace the O2 that is being taken out of the water by the fish respiring.

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