Solubility and thermodynamic properties of Li2O in LiF-CaF2 melts

Solubility of Li₂O in LiF-CaF₂ melts was studied as a function of temperature, and it was found to increase from 10.6 wt pct at 1058 K to 14.8 wt pct at 1133 K. The liquidus temperature of 4LiF • CaF₂ + Li₂O (saturated) melt was determined to be 1004.5 ± 2.5 K. Activity of Li₂O in the melt was determined as a function of temperature using conventional and Temkin ap-proaches. The partial molar Gibbs energy, enthalpy, and entropy of formation were deduced at the given temperature and composition range studied. The results showed that the system ex-hibits a negative deviation from Temkin's ideality.     

Solubility of carbon in CaO-Al2O3 melts

Carbon distribution ratios between CaO-Al₂O₃ slags and Fe-0.0003 to 0.8 mass pct Al-0.2 to 5.6 mass pct C alloys were measured at 1873 K in an Al₂O₃, CaO, or graphite crucible. The carbon distribution ratios were dependent on the oxygen potential, determined by theAl/(Al₂O₃) equilibrium, not by theC/CO (P _co = 1 atm) equilibrium. The (mass pct C)/a _c ratios were proportional to the activity of Al in logarithmic form with a slope of 2/3, indicating that carbon in slag is dissolved as C^2? ion. Solubilities of carbon in CaO-Al₂O₃ slags were also measured at 1873 K under the CO-CO₂-Ar gas mixtures in an Al₂O₃ or graphite crucible. It was found that C^2? ion is present in the range of log $P_{O_2 } $ (atm) < ?15 and CO ₃ ^2? ion in the range of log $P_{O_2 } $ (atm) > ?7.     

Computer study of structure, thermodynamic, and electrical transport properties of Na3AlF6-Al2O3 and CaF2-Al2O3 melts

Structure, thermodynamic, and electrical transport properties of Na₃AlF₆-Al₂O₃ and CaF₂-Al₂O₃ melts were examined by molecular dynamics. Ionic models were constructed for Na₃AlF₆-Al₂O₃ and CaF₂-Al₂O₃ melts at 1283 and 2000 K, respectively. It was found that in the Na₃AlF₆-Al₂O₃ melts, stable aluminum-fluorine-oxygen groups are formed. Although bonds between F⁻ and Al³⁺ ions in the first coordination shell are weaker than between O²⁻ and Al³⁺ ions, very stable negatively charged AlF ₆ ³⁻ groups are formed at low oxygen concentrations in the Na₃AlF₆-Al₂O₃. This results in migration of aluminum to the anode in an external electric field. In the CaF₂-Al₂O₃ melts, positively charged aluminum-oxygen groups dominate. This results in migration of aluminum to the cathode at almost all Al₂O₃ concentrations. Therefore, in Na₃AlF₆-Al₂O₃ melts, the Al³⁺ ion as a component of the complex anion has a negative partial conductivity and the O²⁻ ion has positive partial conductivity; in CaF₂-Al₂O₃ melts, Al³⁺ has a positive transport number while O²⁻ has a negative transport number.     

Solubility of nitrogen and carbon in CaO-Al2O3 melts in the presence of graphite

CaO-Al₂O₃ slags were melted in graphite crucibles under N₂-CO-Ar gas mixtures at 1600°C. The contents of total nitrogen, cyanide and total carbon of the slags were determined by chemical analyses of quenched samples taken by suction from the melt. The nitrogen is present in the melt as nitride N^3- ion and cyanide CN^-1 ion, and carbon as cyanide and carbide C_2- ion. The equilibrium constants for the respective reactions were evaluated. It is found that the nitride capacity of the melt decreases whereas the cyanide and carbide capacities increase with increasing CaO/Al₂O₃ ratio.     

Solubility of nitrogen and carbon in CaO-Al2O3 melts in the presence of graphite

CaO-Al₂O₃ slags were melted in graphite crucibles under N₂–CO–Ar gas mixtures at 1600°C. The contents of total nitrogen, cyanide and total carbon of the slags were determined by chemical analyses of quenched samples taken by suction from the melt. The nitrogen is present in the melt as nitride N⁻³ ion and cyanide CN⁻¹ ion, and carbon as cyanide and carbide C ₂ ²⁻ ion. The equilibrium constants for the respective reactions were evaluated. It is found that the nitride capacity of the melt decreases whereas the cyanide and carbide capacities increase with increasing CaO/Al₂O₃ ratio.     

The thermodynamic properties of melts in the system MnO-SiO2

The activity of MnO in MnO-SiO₂ melts has been measured at 1400, 1500 and 1600 °C by means of the technique in which equilibrium is established between the melt, a gaseous atmosphere of fixed oxygen pressure and a Pt-Mn foil immersed in the melt. The variation of the activity of SiO₂ with composition and temperature and the integral free energies, and partial heats and entropies are derived. The activity of MnO and the free energy of formation of liquid Mn₂SiO₄ are well represented by Whiteway, Smith and Masson’s polymerization model of liquid silicates with Ink _1,1 = −5212/T + 1.011. Correlation of the results of the present study with previous measurements indicates that solubility of SiO₂ in MnO-SiO₂ melts is a significant function of oxygen pressure.     

LiF-YF3-Y2O3体系密度与表面张力的研究

LiF-YF3-Y2O3体系的密度和表面张力直接影响熔盐电解法制备钇合金的整个过程,在1 273~1 373 K使用阿基米德法和脱离法测定不同配比LiF-YF3、LiF-YF3-Y2O3的密度和表面张力。结果表明,随着熔盐温度的升高,LiF-YF3的密度和表面张力呈线性降低,同时,随着熔盐中YF3含量的升高,其密度和表面张力随之增大。对于LiF-YF3-Y2O3（0~5%）体系,随着Y2O3质量百分含量的增加,熔盐的密度和表面张力会先逐渐增大,当Y2O3含量超过2%后,熔盐的密度和表面张力逐渐下降。最后通过拟合获得合理的经验公式,确定熔盐密度和表面张力的变化规律。     

Thermodynamic modeling of the interaction of Y2O3 with Nb-Si-based melts

Thermodynamic modeling of the interaction of the yttrium ceramics with Nb-Si-based melts alloyed with Ti, Cr, Hf, and Al is performed. It is shown that the result of their chemical interaction is the formation of a solid solution of hafnium oxide (HfO₂), while other elements almost do not participate in the interaction. It is revealed in the course of modeling that the main interaction mechanism is the reduction of yttrium oxide upon its dissolution from ceramics into the metallic solution, in which the Y content depends on the temperature, composition, and amount of the metallic phase.     

The thermodynamic activity of MnO in melts containing SiO2, B2O3, and TiO2

The activity of MnO in the systems MnO-Ti₂ and MnO-B₂O₃, and in pseudobinary sections in the systems MnO-TiO₂-SiO₂, MnO-TiO₂-B₂O₃ and MnO-SiO₂-B₂O₃ have been measured at temperatures in the range of 1400 to 1550 °C by means of the technique in which equilibrium is established between the melt, a gaseous atmosphere of fixed oxygen pressure and a Pt-Mn foil immersed in the melt. The excess free energies of melts in the system MnO-TiO₂ at 1500 and 1550 °C are closely represented by the regular solution formalism withG _xs = −55280N _MnO ·N _{TiO 2} J, and the form of the variation ofa _MnO, within the narrow composition range amenable to study at 1400 °C in the system MnO-B₂O₃, is characteristic of a system of polyanions. The negative deviations ofa _MnO from a proposed model behavior, observed in melts in the systems MnO-SiO₂-TiO₂ and MnO-B₂O₃-TiO₂, are explained in terms of the influence of preferred ionic interactions between Ti₄₊ and O₂ and between Mn₂₊ and the O₋ groups on the polysilicate or polyborate anions. The activity of MnO is independent of composition in the system 2MnO · SiO₂−3MnO · B₂O₃ and the thermodynamics of mixing are calculated from application of polymer theory. The influence of B₂O₃ and TiO₂ on the activity of MnO in manganese silicates is discussed with reference to the proposed use of B₂O₃ and/or TiO₂ as substitutes for CaF₂ as the flux for steelmaking slags.     

Solubility and thermodynamic properties of oxygen in solid molybdenum

The solubility of oxygen in solid Mo, determined in the range 1400 to 1900°C by equilibrating rods of zone-refined Mo with mixtures of Mo and MoO₂ powders, can be expressed as ln Χ_O ^α(sat) (atom fraction) = 5.86 - 27,900/T Using the known value of the free energy of formation of MoO₂, the chemical potential of oxygen in the dilute solid solution is calculated to be μ^α _O1/2μ^o _O2 = ΔG ^α _O = -10,760 + (6.92 +R ln χ^μ _O)T ± 1000 cal/g-atom oxygen The heat of solution of oxygen in Solid Mo, ΔH_Oα = -10,760 ± 3000 cal/g-atom oxygen, and the excess entropy for the interstitial solid solution ΔS_Oα(xs, i) =- 9.10 ± 1.5 cal/degree, g-atom oxygen, assuming that the oxygen atoms reside in the octahedral interstices of bcc Mo.     

Electrical properties of phases in the ZrO2 - Y2O3 - La2O3 system

An investigation was made of the electrical properties of phases with the cubic fluorite, pyrochlor, and C-Y₂O₃ structures, and the tetragonal ZrO₂ structure (T-ZrO₂) in the ternary system ZrO₂ - Y₂O₃ - La₂O₃. For comparison, the electrical conductivity of a number of specimens with the fluorite structure in the binary system ZrO₂ - Y₂O₃ and with the pyrochlor structure in the ternary system HfO₂ - Y₂O₃ - La₂O₃ was also studied. The specimens were prepared from nanocrystalline powders synthesized by the hydrolysis of zirconium salts in an acid medium at high temperatures. Conductivity was measured over the range 300–950°C in air. It was shown that phases with the fluorite and T-ZrO₂ structures in the investigated systems possess the highest electrical conductivities. Translated from Poroshkovaya Metallurgiya, Nos. 3/4(412), pp. 40–46, March–April, 2000.     

A thermodynamic study of BaO-BaF2-Cr2O3 system fluxes used for dephosphorization of chromium-containing iron melts

Activities of Cr₂O₃ in BaO-BaF₂-Cr₂O₃ ternary fluxes are determined using a −Mo|Cr+Cr₂O₃‖ ZrO₂(MgO)‖{Cu-Cr}_alloy + (Cr₂O₃)_fluxes|Mo+ solid electrolyte cell in conditions of BaO-BaF₂-Cr₂O₃ system fluxes equilibrium with {Cu-Cr} alloy. Effects of Cr₂O₃ mole fraction, ratio, and temperature on activities of Cr₂O₃ are investigated. The results indicate that Cr₂O₃ activities increase with an increase of its mole fraction, decrease with an increase of ratio, and decrease with an increase of system temperature. It can be concluded from XRD and chemical analysis that the isothermal phase diagrams of BaO-BaF₂-Cr₂O₃ fluxes are composed of nine zones at 1523 K and four zones at 1673 K, respectively. Isoactivity diagrams of the ternary system are given here. Additionally, the factors affecting dephosphorization and chromium retention of the fluxes are also investigated.     

A thermodynamic study of PbO-GeO2 melts

Abstract

The thermodynamic properties of molten PbO-GeO₂ solutions have been determined by reversible electromotive-force measurements on oxygen concentration cells. The results are discussed with reference to the PbO-SiO₂ system. A polymeric anion model advanced by Masson and associates is reviewed and is tested against the measurements of activity, relative partial enthalpy and relative partial entropy of PbO from both systems.

Résumé

Les propriétés thermodynamiques des solutions PbO-GeO₂ à l'état liquide ont été déterminées par des mesures de force électromotrice d'une pile de concentration reversible à base d'oxygène. Ces résultats sont discutés par comparaison avec ceux obtenus pour le système PbO-SiO₂. En utilisant le modéle d'anion polymérique proposé par Masson et ses associés, nous avons comparé nos résultats de la mesure de l'activité, l'enthalpie relative partielle et l'entropie relative partielle de PbO dans les deux systèmes.     

氧化钪在冰晶石-氧化铝体系中的溶解性能研究

通过三因子一次正交回归实验设计，测定了在Na3AlF6-3%MgF2-3% CaF2体系中，Sc2O3溶解度随分子比、温度和Al2O3添加量变化的函数关系。研究表明，减少氧化铝添加量和升高温度均有利于Sc2O3在熔盐中的溶解，分子比对Sc2O3溶解度的影响主要体现在与Al2O3添加量的交互作用，通常情况下分子比对Sc2O3溶解度的影响不大。在现代点式下料电解槽的操作条件下，Sc2O3的溶解度可以达到3％-5％，完全能够满足电解铝钪合金的需要。     

Solubility of some transition metal oxides in cryolite-alumina melts: Part I. Solubility of FeO,FeAl2O4, NiO,and NiAl2O4

The solubilities of FeO, FeAl₂O₄, NiO, and NiAl₂O₄ were measured in cryolite-alumina melts at 1020 °C. FeO was found to be the stable solid phase at alumina concentrations below 5.0 wt pct, while FeAl₂O₄ was stable above that. The corresponding figure for the nickel system was 3.0 wt pct Al₂O₃. These values correspond to Gibbs energies of formation of the aluminates (from the constituent oxides) of −17.6 and −29 kJ/mol, respectively. In alumina-saturated melts in the range 980 to 1050 °C, the solubilities of both aluminates increased with increasing temperature, the apparent enthalpies of solution being 65 kJ/mol for FeAl₂O₄, and 249 kJ/mol for NiAl₂O₄. Investigation of the solubilities of the aluminates as a function of the NaF/AlF₃ ratio in alumina-saturated melts at 1020 °C showed maxima at a molar ratio of around 5. The results are discussed in terms of the species apparently existing in the solution, and are consistent with the solute species being fluorides, not oxyfluorides. The activity coefficients of FeF₂ (liquid) and NiF₂ (solid) in dilute solution in cryolite are found to be 0.22 and 1.2, respectively.     

Activities in NaF-AlF3 melts saturated with Al2O3

The electromotive force of the concentration cell has been determined at 1000°C for molar ratios NaF/AlF₃ on the right-hand side 4.0 to 0.46. On the assumption of unit transport number of Na+, relative activities of NaF and A1F₃ are derived. Absolute values at a molar ratio of 2.48 were established by measuring the sodium content of aluminum in equilibrium with the melt. At a molar ratio of 3, –NaF = 0.31 and^aAlF₃ = 0.00058. At molar ratios below 0.65, where the melts are saturated with AlF₃, the calculated value of^aAlF₃ is 0.81 instead of 1. Possible reasons for the discrepancy are discussed.     

掺杂不同质量分数Y_2O_3、MgO对Al_2O_3陶瓷显微结构及介电性能的影响

利用放电等离子烧结技术制备了不同质量分数Y_2O_3单独掺杂及不同质量分数Y_2O_3、MgO共同掺杂的Al_2O_3陶瓷,研究了烧结助剂掺杂质量分数对Al_2O_3陶瓷显微结构及介电性能的影响。结果表明,孔隙率是影响Al_2O_3陶瓷介电性能的主要因素;单独掺杂质量分数为0.25% Y_2O_3时,Al_2O_3陶瓷得到最优的介电性能,介电常数(ε_r)为9.5±0.2,介质损耗(tanδ)稳定在10~(-3)数量级以内;同时掺杂Y_2O_3和MgO能进一步改善其介电性能,当两者质量分数均为0.25%时,得到最优值,介电常数(ε_r)为10.3±0.2,介质损耗(tanδ)稳定在8×10~(-4)以下。     

高含量La_2O_3/Y_2O_3对钼合金微观组织与性能的影响

采用粉末冶金方法制备了不同质量分数La_2O_3/Y_2O_3复合稀土氧化物掺杂的钼合金,观察了钼合金物相构成、显微组织和断口形貌,测试了其力学性能。结果表明:掺杂La-2O_3/Y_2O_3钼合金的物相组成为La_2O_3、Y_2O_3和Mo;锻造态钼合金横截面的晶粒尺寸随La_2O_3/Y_2O_3含量增加而减小,锻造态钼合金纵截面的显微组织为明显的纤维状织构组织形态;锻造态Mo(La_2O_3)3.0(Y_2O_3)0.5钼合金的横截面断口为韧窝断裂和少量解理断裂,纵截面断口为沿晶脆性断裂;合金抗弯强度和弯曲角随La_2O_3/Y_2O_3含量的增加先增加后降低,Mo(La_2O_3)3.0(Y_2O_3)0.5钼合金抗弯强度达到1133 MPa,弯曲角达到38°。