Effect Of Oxygen Potential Research Articles

Study on reaction of 15-15Ti with fission products under various oxygen potential

ABSTRACT The effect of oxygen potential on the Fuel-Cladding Chemical Interaction (FCCI) of 15-15Ti cladding material was studied in this paper. In the test, the materials have been exposed to simulated fission products at 600◦C for 120 h under the oxygen potential in equilibrium with Mo/MoO2 and Cr/Cr2O3.The general corroded depth was roughly 30 µm. Furthermore, the results also show that corroded depth on the cladding surface increase with the increase of oxygen potential. No intergranular attacks were observed, which might be caused by the absence of the high-temperature gradient. A single layer of CrTe is assumed to be formed under low oxygen potential, whereas cesium and oxygen may play an important role under high oxygen potential. Moreover, FCCI may impose a great threat to the integrity of China designed 15-15Ti material.

Thermodynamics of boron removal in slag refining of Fe-Si alloy

Two metallurgical purification techniques, namely solvent refining and slag treatment, were combined to remove boron from silicon. Silicon was alloyed with iron and the alloy was subjected to slag treatment by a ternary of CaO-SiO2-Al2O3 at 1600 °C (1873 K). Effects of oxygen potential and basicity of slag on boron removal were investigated through changing the SiO2/Al2O3 and CaO/SiO2 ratios, respectively. Results indicate that these two parameters have major effects on partition ratio of boron. A critical oxygen potential value, which yields the highest partition ratio of boron, was calculated as approximately 9 × 10−18 atm. Partition ratio of boron was normalized with oxygen potential at each slag composition in order to isolate the effect of basicity. Borate capacity values were calculated for different slags and it was shown that this parameter is only a function of temperature and slag composition. The kinetics of boron removal was quantified and the total mass transfer coefficient of boron was calculated as 7.48 × 10−6 cm/s.

Effect of oxygen potential on Co solubility limit in La–Co co-substituted magnetoplumbite-type strontium ferrite

La–Co co-substituted magnetoplumbite-type (M-type) strontium ferrite is typically used as a base material for high-performance hard ferrite magnets. Generally, the unquenched orbital moment of Co2+, substituted for Fe3+, is thought to enhance magnetic anisotropy and then coercivity. La3+ is substituted for Sr2+ to compensate for the charge unbalance associated with Co2+ substitution. Even if the synthesis starts with equal amounts of Co and La, the Co contents of the resulting samples are generally lower than the La contents because of the partial reduction of Fe3+ to Fe2+. We studied how the oxygen potential suppresses the formation of Fe2+ and expands the Co solubility range in this system. Polycrystalline samples, synthesized under oxygen partial pressures of 0.2, 1.0, and 387 atm, were characterized by powder X-ray diffraction, wavelength-dispersive X-ray analysis, and magnetization measurements. We reveal that the application of higher oxygen pressure dramatically expands the Co solubility range, resulting in the enhancement in magnetic anisotropy. We successfully synthesized Sr-free LaFe11CoO19 with high magnetic anisotropy using the hot isostatic pressure (HIP) technique.

Chemical potential of oxygen in (U, Pu) mixed oxide with Pu/(U+Pu) = 0.46

Chemical potential of oxygen in (U,Pu) mixed oxide with Pu/(U + Pu) = 0.46 was measured for the first time using H2/H2O gas equilibration combined with solid electrolyte EMF technique at 1073, 1273 and 1473 K covering an oxygen potential range of −525 to −325 kJ mol−1. The effect of oxygen potential on the oxygen to metal ratio was determined. Increase in oxygen potential increases the O/M. In this study the minimum O/M obtained was 1.985 below which reduction was not possible. Partial molar enthalpy ΔH¯O2 and entropy ΔS¯O2 of oxygen were calculated from the oxygen potential data. The values of −752.36 kJ mol−1 and 0.25 kJ mol−1 were obtained for ΔH¯O2 and ΔS¯O2 respectively.

Reactive sintering of U0.85Am0.15O2−x blanket fuels in various oxygen potentials

The effect of oxygen potential on the sintering behaviour of U1−yAmyO2−x (y=0.15) has been studied. Sintering tests were performed in an Ar–4% H2 atmosphere with various partial pressures of oxygen. It has been shown that the density is significantly affected by the sintering atmosphere. A density higher than 93±0.5% has been achieved at −390kJmol−1. Pore morphology varies from an open to a closed type as the oxygen potential increases.

A Study in the Thermodynamic Behavior of Nickel in the MgO‐SiO2‐FeO Slag System

AbstractThe dissolution behavior of nickel in the MgO‐SiO2‐FeO slag system was investigated by using the thermodynamic equilibrium technique. Nickel distribution ratio between molten MgO‐SiO2‐FeO slag and molten Fe‐Ni alloy at 1773 K and 1873 K was measured to understand the dissolution mechanism of nickel into the slags. In particular, the effect of oxygen potential and basicity on the distribution of nickel was investigated. Nickel distribution between slag and Fe‐Ni alloy increased with higher oxygen potential showing a slope of 1/2. For basic slag systems near the olivine saturated composition, the nickel distribution ratio increased with higher basicity and for acidic slag systems near the cristobalite saturated composition, the nickel distribution ratio decreased with higher basicity. Thus, the nickel dissolution into the MgO‐SiO2‐FeO slag system showed two independent mechanisms similar to that found in the CaO‐SiO2‐CaF2 system. The contour of the iso distribution ratio was represented in the MgO‐SiO2‐FeO ternary phase diagram. From the results, an optimum slag composition was determined to be near the olivine saturated with approximately $X_{MgO} /X_{SiO_{2} } $ of 0.8 at 1773 K and 1.0 at 1873 K.

Effect of Oxygen Potential on Crack Growth in Alloys for Advanced Energy Systems

The effect of oxygen partial pressure on crack growth rates in Alloy 617 has been studied using both static and fatigue loadings at 650°C over the oxygen partial pressure range 10−19−10−3 atm. Tests were conducted at either the constant stress intensity factor K for static conditions or the constant ΔK in fatigue. Oxygen concentration was measured on both the inlet and outlet of the test retort as well as in situ with a probe located directly at the specimen surface. For fatigue loading the crack path was observed to be transgranular but crystallographic with a decreasing growth rate as the oxygen concentration decreased. However, for static loading the crack path shifted to intergranular at the same Kmax (fatigue) and exhibited what appears to be an increasing crack growth rate with decreasing oxygen concentration.

Effect of oxygen potential on the sintering behavior of MgO-based heterogeneous fuels containing (Pu, Am)O 2−x

The effect of oxygen potential on the sintering behavior of MgO-based heterogeneous fuels containing (Pu, Am)O 2− x was experimentally investigated. Sintering tests in various atmospheres, i.e. air, moisturized 4%H 2–Ar, and 4%H 2–Ar atmosphere, were carried out. The sintering behavior was found to be significantly affected by the oxygen potential in the sintering atmosphere. The sintered density decreased with decreasing oxygen potential. The (Pu, Am)O 2− x phase sintered in a reductive atmosphere had hypostoichiometry. The aggregates of the (Pu, Am)O 2− x phase sintered in the reductive atmosphere grew, in comparison with those in the oxidizing one. The sintering mechanism was discussed in terms of the difference in sintering behavior of (Pu, Am)O 2− x and MgO.

S0305-3-4 SOFC構成セラミックスの機械的特性に及ぼす酸素ポテンシャルの影響に関する研究(SOFC構成材料の信頼性(3))

S0305-3-4 SOFC構成セラミックスの機械的特性に及ぼす酸素ポテンシャルの影響に関する研究(SOFC構成材料の信頼性(3))

Applications of thermodynamic modeling in copper converting operations

Abstract A thermodynamic model of the copper P-S converter has been developed to predict the behavior of magnetite in the converter slag, amounts of slag and matte, compositions of slag and matte, volume of the bath, bath temperature, slag blow endpoint determination and SEMTECH OPC signals. The predictions of bath temperature, slag and matte compositions, and magnetite content in the slag have been validated by industrial data. The effects of fluxing strategy, returns and skim charges, oxygen enrichment, and temperature on the magnetite formation in the slag have been predicted and discussed. The effect of oxygen potential, SiO2/Fe in slag, detection of slag blow endpoint, and temperature on slag viscosity, liquidus temperature of converter slag and skimming operation has been modeled and discussed as well. Some applications to industrial operations have been presented.

Copper Matte Penetration Resistance of Basic Refractories

Penetration resistance is viewed as the first property that must be evaluated for the selection of new refractories, because it is known that melt penetration can promote or enhance the main wear mechanisms in copper converters, namely, dissolution, erosion, and spalling. In this work, a penetration test was designed to control the oxygen potential over typical laboratory prepared converter melts by injecting a mixture of inert gas and oxygen according to thermodynamic calculations. The effects of oxygen potential and matte grade on burned magnesite chrome brick and spinel direct bonded brick were studied using operating conditions typical of copper converters, and their relative performance was evaluated using high-grade and low-grade matte at oxygen potentials of 10-7 and 10-6 atm. Under these conditions, it was determined that spinel direct bonded brick outperformed the magnesite-chrome brick.

還元途上における酸化鉄の凝集に及ぼす酸素ポテンシャルの影響

還元途上における酸化鉄の凝集に及ぼす酸素ポテンシャルの影響

Liquidus Surface of “Lime Ferrite” Slags at Intermediate Oxygen Potentials

‘‘Lime ferrite’’ slag with limited silica content has proven to be a valuable choice in the modern processes of copper smelting and converting due to several advantages that this slag offers compared to classical silicate slags. Nevertheless the liquidus surface of this slag has been experimentally measured only at low oxygen potentials such as in equilibrium with iron or near it and in air. Although most of the smelting and converting processes that use this slag occur at intermediate oxygen potentials, the liquidus surface of this slag is not known at these conditions and the effect of oxygen potential and silica has not been correctly understood. This has brought some confusion in literature as well as in the industrial practice. In this work the liquidus surface of the calcium ferrite slags has been quantified by the means of a new thermophysicochemical model and a new type of liquidus surface diagrams which are very convenient for any industrial process that uses calcium ferrite slags. These diagrams can be easily used to select the lowest liquidus temperature of calcium ferrite slags at a minimum cost and can help design several fluxing strategies in copper smelting and converting processes. The effect of the oxygen potential and silica is also quantified and important industrially related conclusions are drawn.

Thermodynamic behavior of nickel in CaO-SiO2-FetO slag

The distribution ratio of nickel between Ag-Ni alloy and CaO-SiO2-FetO slag at high temperatures was measured to clarify the dissolution mechanism of nickel in this melt. Also, the nickel oxide capacity was suggested and was compared to phosphate and sulfide capacities. The dissolution mechanism of nickel into the CaO-SiO2-FetO slags could be described by the following equation from the effect of oxygen potential and slag basicity on nickel dissolution behavior: $$Ni(1) + \frac{1}{2}O_2 (g) + O^{2 - } (slag) = NiO_2^{2 - } (slag)$$ The nickel oxide capacity increases with increasing CaO/SiO2 ratio at a fixed FetO content. When the ratio of XCaO to \(X_{SiO_2 } \) (C/S) is about 1.1 to 1.3, log \(C_{NiO_2^{2 - } } \) increases with increasing FetO content up to about 35 mol pct, followed by a nearly constant value of \(C_{NiO_2^{2 - } } \cong 10^3 \). In the composition of C/S=0.5 to 0.7, log \(C_{NiO_2^{2 - } } \) exhibits a maximum value at about 50 mol pct FetO. From the iso-\(C_{NiO_2^{2 - } } \) trends in ternary phase diagram, nickel oxide capacity dominantly depends on FetO content in slags; it exhibits a maximum value of \(C_{NiO_2^{2 - } } \cong 10^3 \) at \(X_{Fe_t O} \cong 0.5\). The relationship between nickel oxide capacity and phosphate (sulfide) capacities exhibit linear correlations, as expected from theoretical equations.

Effects of oxygen potential on tritium release from Li 2O

Effects of oxygen potential on tritium recovery from Li 2 O were quantitatively studied by in-situ tritium release experiments named TTTEx at the University of Tokyo using sweep gases of He + H 2 and He + H 2 +H 2 O. The oxygen potential in the experimental system was calculated from the chemical composition of the sweep gas. It was found to be influenced by the oxygen concentration at the surface of samples which was strongly affected by the method of pre-treatment. The tritium release rate was found to be affected both by the oxygen potential and by the swamping effect with H 2 and/or H 2 O in the sweep gas. Chemical form of the recovered tritium also had a strong relationship with the oxygen potential in the sweep gases.

Effects of oxygen potential on tritium release from Li2O

Effects of oxygen potential on tritium release from Li2O

The behavior of iron-sulfur species in fluidized-bed gasification on coal

The behavior of iron-sulfur species derived from pyrite, especially that present in the coal feed as particles of free pyrite, is of concern in the operation of fluidized-bed coal gasifiers. Work conducted at the Institute of Gas Technology (IGT) has shown that the decomposition of pyrite in a U-GAS® pilot plant has yielded a liquid phase that spreads on the surface of ash particles. Formation of a liquid phase in decomposition of pyrite in an inert atmosphere has also been observed in connection with the investigation of boiler deposits. To aid in understanding the behavior of iron-sulfur species, we have prepared an Fe S phase diagram at temperatures relevant to coal gasification and with equilibrium sulfur potentials exhibited, for the most part, as hydrogen sulfide to hydrogen mole ratios; in a fluidized-bed gasifier, the latter can easily be obtained from the composition of the reactor product gas, which closely approximates that in the back-mixed fluidized bed. To show, in addition, the effect of oxygen potential in the bed, we have also prepared phase stability diagrams at 100°F intervals from 1500 to 2000°F (816 to 1093°C). According to the Fe S diagram, formation of an iron-sulfur liquid in the gasifier or in an inert atmosphere cannot be explained on the basis of equilibrium considerations. Instead, a kinetic explanation, based on increased concentration of iron in the exterior regions of the decomposing pyrite particle, as sulfur is removed from the surface, is much more plausible. Phase stability diagrams indicate that a liquid composed of iron, sulfur, and oxygen could be formed in steam-oxygen gasification of high-sulfur coal at temperatures above 1850°F (1010°C). However, no evidence of its formation was found by optical petrography in the examination of solids from the U-GAS pilot plant in which steam-to-hydrogen mole ratios ranged up to about 2, but formation of a submicroscopic liquid layer on iron sulfide particles could have been responsible for deposition of these particles in the hot cyclone of the U-GAS pilot plant. Its formation in steam-air gasification, where the steam-to-hydrogen mole ratio typically is about 0.6, is less likely.

The effect of oxygen potential on phosphorus in the CaO-Al2O3 system

The effect of oxygen potential on phosphorus in the CaO-Al2O3 system

Mechanical Properties and Erosion Behaviour of Nickel Aluminides

Microstructure and mechanical properties of electro slag cast and twin-roll cast nickel aluminides were studied in both cold-rolled and annealed conditions. The poor mechanical properties of the cold rolled and annealed specimens from the twin-roll cast group have been attributed to the presence of casting defects and the lack of sufficient deformation to destroy the as-cast microstructure. The erosion resistance of three nickel aluminides was studied in the laboratory and compared with that of stainless steel 304 and alloy 800H. The effects of oxygen potential, erosion temperature and impingement angle were investigated. It was found that erosion resistance of the alloys was similar to that of 304 stainless steel but slightly better than that of alloy 800H. Raising the erosion temperature from 25°C to 600°C or replacing N2 by air as carrier gas for erodant had no significant effect on wear rate. However, the rate was significantly reduced by changing the impingement angle from 30 to 90°.

Mechanical Properties and Erosion Behaviour of Nickel Aluminides

Microstructure and mechanical properties of electro slag cast and twin-roll cast nickel aluminides were studied in both cold-rolled and annealed conditions. The poor mechanical properties of the cold rolled and annealed specimens from the twin-roll cast group have been attributed to the presence of casting defects and the lack of sufficient deformation to destroy the as-cast microstructure. The erosion resistance of three nickel aluminides was studied in the laboratory and compared with that of stainless steel 304 and alloy 800H. The effects of oxygen potential, erosion temperature and impingement angle were investigated. It was found that erosion resistance of the alloys was similar to that of 304 stainless steel but slightly better than that of alloy 800H. Raising the erosion temperature from 25°C to 600°C or replacing N2 by air as carrier gas for erodant had no significant effect on wear rate. However, the rate was significantly reduced by changing the impingement angle from 30 to 90°.