The oxygen potential of the systems Fe+FeCr2O4+Cr2O3 and Fe+FeV2O4+V2O3 in the temperature range 750–1600°C

From electromotive force (emf) measurements using solid oxide galvanic cells incorporating ZrO₂-CaO and ThO₂?YO_1.5 electrolytes, the chemical potentials of oxygen over the systems Fe+FeCr₂O₄+Cr₂O₃ and Fe+FeV₂O₄+V₂O₃ were calculated. The values may be represented by the equations: $$\begin{gathered} 2Fe\left( {s,1} \right) + O_2 \left( g \right) + 2Cr_2 O_3 \left( s \right) \to 2FeCr_2 O_4 \left( s \right) \hfill \\ \Delta \mu _{O_2 } = - 151,400 + 34.7T\left( { \pm 300} \right) cal \hfill \\ = - 633,400 + 145.5T\left( { \pm 1250} \right) J \left( {750 to 1536^\circ C} \right) \hfill \\ \Delta \mu _{O_2 } = - 158,000 + 38.4T\left( { \pm 300} \right) cal \hfill \\ = - 661,000 + 160.5T\left( { \pm 1250} \right) J \left( {1536 to 1700^\circ C} \right) \hfill \\ 2Fe\left( {s,1} \right) + O_2 \left( g \right) + 2V_2 O_3 \left( s \right) \to 2FeV_2 O_4 \left( s \right) \hfill \\ \Delta \mu _{O_2 } = - 138,000 + 29.8T\left( { \pm 300} \right) cal \hfill \\ = - 577,500 + 124.7T\left( { \pm 1250} \right) J \left( {750 to 1536^\circ C} \right) \hfill \\ \Delta \mu _{O_2 } = - 144,600 + 33.45T\left( { \pm 300} \right) cal \hfill \\ = - 605,100 + 140.0T\left( { \pm 1250} \right) J \left( {1536 to 1700^\circ C} \right) \hfill \\ \end{gathered} $$ . At the oxygen potentials corresponding to Fe+FeCr₂O₄+Cr₂O₃ equilibria, the electronic contribution to the conductivity of ZrO₂?CaO electrolyte was found to affect the measured emf. Application of a small 60 cycle A.C. voltage with an amplitude of 50 mv across the cell terminals reduced the time required to attain equilibrium at temperatures between 750 to 950°C by approximately a factor of two. The second law entropy of iron chromite obtained in this study is in good agreement with that calculated from thermal data. The entropies of formation of these spinel phases from the component oxides can be correlated to cation distribution and crystal field theory.     

Transformation of α-Fe2O3 to Fe3O4 Realized by Mechanochemical Reaction of α-Fe2O3 and SrCO3

A transformation from ??-Fe₂O₃ with rhombohedral structure to Fe₃O₄ with spinel face-centered cubic (fcc) structure was realized by ball milling the mixture of SrCO₃ and ??-Fe₂O₃ powders with molar ratio of 1:3 under ambient air in the current work, but it was not observed by ball milling the ??-Fe₂O₃ powders. The transformation is due to a mechanochemical reaction between SrCO₃ and ??-Fe₂O₃ in the milling process, and the ??-Fe₂O₃ catalyzes the decomposition of SrCO₃, while the decomposition promotes the transformation of ??-Fe₂O₃ to Fe₃O₄. X-ray diffraction, X-ray photoelectron spectrometry, and magnetic measurements indicate that the transformation finishes completely upon milling of 120?hours, and the mixture milled for 120?hours consists of Fe₃O₄ and a Sr element. However, Sr does not incorporate into the Fe₃O₄ but exists in grain boundary of the Fe₃O₄ in a form of a Sr-O bond. It is found that the product obtained by ball milling the mixture is different from that prepared by sintering the mixture at atmospheric pressure, which product is SrFeO_2.97 with cubic structure. The mechanism of the transformation and origin of difference in products obtained in the ball milling and sintering processes are also discussed in the current work.     

Determination of gibbs energy of formation of cuspidine (3CaO · 2SiO<Subscript>2</Subscript> · CaF<Subscript>2</Subscript>) from the electromotive force method using CaF<Subscript>2</Subscript> as the solid electrolyte

The standard Gibbs energy change for the following reaction has been directly determined by electromotive force (EMF) measurement using CaF₂ as the solid electrolyte in the temperature range from 1313 to 1329 K.

Synthesis, Structure and Ionic Conductivity of La2／3-x Li3x MoO4

AlargenumberofM0 .5A0 .5M′O4 (M :rareearthion ,Bi3+,Fe3+,Cr3+,etc .A :alkaliion ,Cu+,Ag+,etc .M′ :Mo ,W )withtetragonalscheelite typestructurehavegoodcatalyticproperties .Aslumines centsubstrates ,theyhaveexcellentsensitizationtolu minescenceofrareearthion .Manyresearchesontheirstructure ,catalytic ,magneticandluminescentproper tieshavebeenmadesince 196 0s[1～ 10 ] .Thegeneralformulaforcompoundswiththetetragonalscheelite typestructureisAM′O4 wherethecationM′istetrahe drallycoordinat…     

The Synthesis of the Fe3O4 Nanoparticles and the Analysis of the Current–Voltage Measurements on Au/Fe3O4/p-Si Schottky Contacts in a Wide Temperature Range

The iron oxide (Fe₃O₄) magnetic nanoparticles were synthesized via the organic solution phase method and used for the fabrication of the Au/Fe₃O₄/p-Si rectifying device. The variation in electrical characteristics of the Au/Fe₃O₄/p-Si Schottky contacts was investigated as a function of temperature using current–voltage (I–V) measurements in the temperature range of 40 K to 370 K (?233 °C to 97 °C). The I–V characteristics of the contacts indicated extremely strong temperature dependence. The double distribution of barrier heights was found in the Fe₃O₄/p-Si Schottky diodes from the I–V-T measurements. The Schottky barrier height (Φ_b) increases with the increasing temperature, while the ideality factor n decreases. The nonlinearity in the activation energy plot was observed, which is attributed to barrier inhomogeneities by assuming a Gaussian distribution of barrier heights at the Fe₃O₄/p-Si interface. The Richardson constant measured from the temperature-dependent I–V characteristics is 2.99 A/K² cm², which is lower than the ideal value.     

Migration and Reaction Mechanism of Barium in BaSO4–CaCO3–Fe2O3 System during Sintering

With the increasingly strict requirements of blast furnaces on the sinter quality, analyzing the phase transition process and reaction mechanism of special elements in the sintering process plays an important role in understanding the sintering process and improving the sinter quality. Herein, the decomposition process of barite during sintering and the influence mechanism on the bonding phase of calcium ferrite are studied by laboratory experiments and thermodynamic calculations. The results show that calcium ferrite and ferric oxide can promote the decomposition of barite and reduce the decomposition temperature in the sintering process. The generated barium enters the calcium ferrite phase and affects the strength and melting point of calcium ferrite. With the increase of barium content, the strength of calcium ferrite sample increases from 1.62 to 2.00 kPa, and the initial melting temperature of calcium ferrite sample stays at 1473 K. However, with the further increase of barium, the sample strength and melting temperature both show a worsening trend. Finally, based on the research results, some suggestions for sintering production are put forward, and the optimal barite content is determined. Results help to better understand the reaction process and action mechanism of barium in the sintering process.     

Copper solubility in FeO−Fe2O3−SiO2−Al2O3 slag and distribution equilibria of Pb,Bi, Sb and As between slag and metallic copper

The solubility of copper in silica-unsaturated fayalite slags containing an average of about 8 pct Al₂O₃ was measured by equilibrating the slag with metallic copper at 1200 and 1300°C under CO?CO₂ atmospheres with oxygen potentials in the rangep _{O 2}=10^?6 to 10^?11 at. The copper solubility, which was found to be dependent upon the oxygen potential, was expressed in terms of the Fe/SiO₂ ratio, temperature and activity of CuO_0.5. The distribution of Pb, Bi, Sb and As between copper and slag was measured concurrently by doping the metallic copper. The distribution coefficient was defined by (mole fractionX in metal)/(mole fractionX in slag) assuming the FeO?FeO_1.5?SiO₂?AlO_1.5?CuO_0.5 system slag. The distribution coefficient for lead was found to be a function of the oxygen potential, and a PbO activity in the slag of 0.07±0.01 was measured over the range of 1200 to 1300°C. Dissolution of Bi, Sb and As in the slag was found to be independent of the oxygen potential suggesting atomic rather than oxidic dissolution. The observed distribution coefficient for Bi and Sb was 30. The observed distribution coefficient for As was 300, but this is subject to error up to one order of magnitude due to analytical uncertainty of slag. The data are useful in analyzing minor element behavior in copper smelting processes.     

Experimental Verification of the Thermodynamics of Critical Aspects of the Carbothermic Reduction of Alumina. Part II: Thermogravimetric Study of the Reaction of Al2O3–C Mixtures and the Al2O3–Al4C3 Phase Diagram

The thermodynamics of several aspects of the carbothermic reduction of alumina have been examined. In Part I, the results of measuring the evolved CO from the reaction between Al₂O₃ and C mixtures were used to determine the temperature and carbon contents for carbide formation at alumina saturation and at carbide saturation in the Al₂O₃–Al₄C₃ system. In this part of the paper, results are presented for a thermogravimetric study of the reactions of Al₂O₃ with carbon, as well as those for the determination of the Al₂O₃ liquidus line and the Al₂O₃–Al₄O₄C eutectic in the Al₂O₃–Al₄C₃ phase diagram. The critical temperature for Al₂O₃ and C to react, producing gas at 1 atm., was in agreement with that predicted from thermodynamics and measured in Part I of this paper. However, the Al₂O₃ liquidus appeared to be steeper and the eutectic temperature lower than the predicted phase diagram.     

Physico-Chemical Investigation of Component Interactions of the Si ― Al ― O ― N ― Ti System in the Region Si3N4 ― AlN ― Al2O3 ― SiO2 ― TiN ― TiO2. Part 1. Subsystems Si3N4 ― Al2O3, Si3N4 ― TiN,and Al2O3 ― TiN

Using the methods of differential thermal and x-ray diffraction analysis an investigation was made of component reactions in the Si Al O N Ti system, particularly between the compounds Si ₃N₄ Al₂O₃, Si₃N₄ TiN, and Al₂O TiN under conditions approximating those used in the hot pressing of composites. It was established that in the reaction of Si₃N₄ with Al₂O₃, -sialon, SiO₂, AlN, and the intermediate reaction products (mullite and X-phase) are formed. In the reaction of Si₃N₄ with TiN, as a result of the decomposition of Si₃N₄ at 1650-1900°C titanium disilicide is produced, which forms eutectics with free silicon and residual TiN at 1320 and 1280°C, respectively. The reaction of Al₂O₃ with TiN similarly leads to the formation of a eutectic between Al₂O₃ and spinel at 1850°C. The presence of eutectic liquids in the specimens after sintering promotes densification of the material, and improves certain of its mechanical properties.     

Preparation and Electrorheological Performance of SiO2 Particle Materials Adsorbed with YF3, Y2（CO3）3, Y2（C2O4）3 or YPO4

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Cyclic-oxidation behaviours of the powder-metallurgy TiAl–4Nb–3Mn and TiAl–2Nb–2Mo beta-gamma alloys

For this study, cyclic-oxidation tests for the powder-metallurgy TiAl–4Nb–3Mn and TiAl–2Nb–2Mo alloys were carried out in air between room temperature and 900°C, and the oxidation behaviours under cyclic oxidation were compared with those under isothermal oxidation. The morphologies and structures of the oxides are identical to those from isothermal oxidation, except for the Mn-oxide formation on the top surface in the case of the TiAl–4Nb–3Mn alloy. The growth rate of the oxides in the TiAl–2Nb–2Mo alloy is slower and more stable than that of the oxides in the TiAl–4Nb–3Mn alloy, and severe internal oxidation is also evident in the latter alloy; however, the weight gain showed a sudden drop in the TiAl–2Nb–2Mo alloy that is mainly due to the enhanced formation of titanium nitrides at the interface.     

Physicochemical Investigation of the Reaction of Components of the Si — Al — O — N — Ti System in the Si3N4 — Al2O3 — AlN — SiO2 — TiN — TiO2 Region. Part 2. Subsystems Si3N4 — AlN,TiN — AlN,Al2O3 — AlN

The reaction of components of the Si — Al — O — N — Ti system in its elements Si ₃N₄ — AlN, TiN — AlN, and Al ₂O ₃ — AlN was investigated by differential thermal and x-ray diffraction analysis. It was established that upon hot pressing mixtures of Si₃N ₄ and AlN (up to 1950°C) free silicon is formed by the decomposition of Si ₃N₄, which reacts with oxygen present as an impurity to form SiO. When TiN reacts with AlN a phase with the spinel structure (Al₂₃O ₂₇N ₅), which can form only in the presence of excess oxygen, appears in addition to the initial components. Spinel is also produced by the reaction of Al ₂O₃ with AlN. In this case a eutectic between Al ₂₃O₂₇N₅ and Al₂O₃ is observed.     

Viscosities of ternary systems Y（NO_3）_3＋La（NO_3）_3＋H_2O,La（NO_3）_3＋Ce（NO_3）_3＋H_2O,La（NO_3）_3＋Nd（NO_3）_3＋H_2O and their binary subsystems at different temperatures

Viscosities were measured for the ternary systems Y(NO3)3+La(NO3)3+H2O, La(NO3)3+Ce(NO3)3+H2O, and La(NO3)3+Nd(NO3)3+ H2O and their binary subsystems Y(NO3)3+H2O, La(NO3)3+H2O, Ce(NO3)3+H2O, and Nd(NO3)3+H2O at 293.15, 298.15 and 308.15 K. The results were used to test the applicability of simple equations for the viscosity of the mixed solutions. The predictions agreed well with measured values, implying that the viscosities of the examined electrolyte solutions could be related to those of their constituent binary solutions using these simple equations.     

Further characterization of the aluminum peroxide oxide,AlO2, formed by interfacial reaction between Pt and α-Al2O3

A new metastable aluminum peroxide oxide, AlO₂, was recently shown to form by an interfacial reaction in the presence of a kinetic constraint during diffusion-bonding of Pt and α-Al₂O₃. Further studies of the properties, bonding, formation kinetics and chemistry of AlO₂ are described and the current state of knowledge of the kinetics of its formation is summarized. Raman spectroscopy on AlO₂ gave several peaks in the frequency range characteristic of peroxide ions, providing the strongest evidence yet for their presence. Electron microprobe analysis detected only Al and O, with any other elements, if present, being below the detectability limit of the wavelength dispersive technique. Rutherford backscattering spectroscopy at the carbon resonance energy could detect no carbon within the AlO₂. Studies of the effect of temperature on the formation of AlO₂ show that it forms after heating for 24 h in the temperature range of 1200 to 1400°C, but not at or below 1100°C. Heating in air at 1200°C causes AlO₂ to first transform to a cubic form of Al₂O₃ before finally reverting to α-Al₂O₃. The dielectric constant of AlO₂ is 22.7, approximately twice that of α-Al₂O₃ parallel to the c direction, and the hardness of 8.4 GPa is approximately one-half that of α-Al₂O₃.     

Preparation and Luminescence Properties of the New Long Phosphorescent Phosphors Ba1-x Cax Al2O4 ： Eu^2＋ , Dy^3＋

New long phosphorescent phosphors Ba1-x CaxAl2O4:Eu^2 , Dy^3 with tunable color emission were prepared and studied. The emission spectra show that the tuning range of the color emission of the phosphors is between 498 and 440 nm, which is dependent on x, under the excitation of UV. The wavelength of the afterglow increases with the increasing of x until x equals 0.6. The XRD patterns show that the single phase limit in the phosphors is below x value of 0.4.The Thermolumineseence spectra were measured to investigate the traps created by the doping of Dy^3 .     

Production of the Al–B Master Alloy by Aluminothermal Reduction of KBF4 and B2O3 in a Medium of the Molten Salt Flux

Russian Journal of Non-Ferrous Metals - The process of obtaining the Al–B master alloy by the aluminothermal reduction of KBF4 and B2O3 using fluoride fluxes KF–AlF3 and...