铌硼酸盐玻璃熔体的高温红外光谱

本文首次采用高温红外光谱及DSC—7差热分析技术研究了Nb₂O₅—B₂O₃—K₂O系统玻璃熔体结构,并建立了该系统玻璃和高温熔体结构模型。     

Ni基高温合金在LiCl-KCl熔盐中的腐蚀行为研究

熔盐电解精炼是乏燃料干法后处理的核心工艺单元,其反应容器需在高温、LiCl-KCl熔盐环境下长期服役,活泼合金元素Cr的选择性溶解使得钝化Cr₂O₃保护膜难以生成,结构材料面临严重的腐蚀问题,严重阻碍了干法后处理技术的工程化应用。Ni基高温合金在高温氯化物熔盐中的热力学性质稳定,是电解精炼反应容器潜在的候选材料,然而目前Mo、W等关键合金元素对Ni基高温合金在LiCl-KCl熔盐中的耐腐蚀性能影响暂不明确。采用浸泡腐蚀的方法,研究了Haynes 230、Inconel 625、GH 3535、Inconel 690和GH 4169五种Ni基高温合金在550 ℃、氩气气氛下LiCl-KCl熔盐中的腐蚀行为,采用X射线衍射、扫描电子显微镜及能谱分析对腐蚀产物的组成和形貌进行了分析。研究结果表明,五种Ni基高温合金在与LiCl-KCl熔盐相互作用的过程中均发生腐蚀失重,失重情况为Inconel 625＞GH 3535＞Haynes 230＞Inconel 690＞GH 4169。其中Inconel 625和GH 4169合金在基体近表层生成了富Mo氧化膜,导致外层(Cr,Fe)₂O₃与基体的热相容性变差,有明显的脱落趋势。相比高Cr含量的Inconel 690合金发生严重的电化学溶解,低Cr的GH 3535合金外层(Cr,Fe)₂O₃含量低,抗氧化能力也明显降低,使得氧向基体内部渗入。而Haynes 230合金外表面生成了富W的氧化物,有效地阻挡了Cl^-的侵蚀,在以上五种Ni基高温合金中具有最好的耐腐蚀性能。     

Testing procedure to obtain reliable potentiodynamic polarization curves on type 310S stainless steel in alkali carbonate melts

Potentiodynamic polarization measurements have been employed to evaluate the anodic behavior of a type 310S stainless steel in the eutectic Li/K molten carbonate. In general, the electrochemical tests yield useful information to predict the stability of the oxide films formed on the surface at the initial period of corrosion, although some precaution is required in the testing procedure as the reproducibility of results is seen to be adversely affected by the passage of large currents. Especially when the steel is in a passive state, erratic results are easily observed if the corrosion layer is being damaged by uncontrolled large currents. This is because the acid‐base properties of the melt are susceptible to deep changes by applied currents in the milli‐ampere range resulting in hysteresis phenomena in the polarization plot. Hysteresis is caused, on one hand, by acidic dissolution of the passive layer at high anodic currents and, on the other hand, by increased melt basicity due to oxide ion build‐up at high cathodic currents. An optimized testing procedure is therefore suggested that minimizes these effects by imposing a 2 mA/cm² threshold current during polarization measurements. Moreover, the conditions for the applicability of the linear polarization technique to estimate kinetic parameters have been discussed in relationship with the corrosion mechanisms analysed by impedance spectra. It is concluded that the presence of diffusional impedance terms and formation of surface resistive films in molten carbonates may result in not reliable polarization resistance values obtained with the linear polarization.     

Simulation study on molecular relaxation in ionomer melts

Relaxation behavior of ionomer molecule in melt state was investigated by Brownian simulation where motion of a bead-rod chain representing a linear ionomer molecule was calculated in two-dimension. Entanglement between the other molecules was assumed by a repulsive interaction between the chain and randomly located entanglement points. Effect of ion aggregates was also introduced by an attractive interaction between the chain and attractive sites randomly dispersed in the simulation box. Relaxation spectra of end-to-end motion and local bond orientation were obtained in equilibrium calculation for various chain lengths. The effect of the attractive site was discussed on the spectrum. It was found that on the end-to-end motion, the longer the chain was, the more discrepant the spectrum was, while on the bond orientation, the shorter it was, the more discrepant the spectrum was. On the basis of these results, a picture to describe the experimental phenomena was proposed.     

Equilibrium Distributions of Actinides and Fission Products in Pyrochemical Separation Systems, (II) LiCl-KCl/Cd System

Equilibrium distributions of actinides and fission products were determined in a LiCl-KCl/Cd system at 800–973 K. The redox potential of the system was controlled with the addition of reductant Li. Different distribution behaviors due to different group elements were observed. The group partitioning in this system was thus supported to be feasible. On reduction, however, the actinide and lanthanide elements were found to be less soluble in the Cd phase and to remain at the interface in the form of their solid intermetallics. A group partitioning process in which reductive extraction is combined with filtration was proposed on the basis of the present observations.     

Preparation of Al-Si-Ti Master Alloys by Electrolysis of Silica and Titania in Cryolite-Alumina Melts

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Oxidation–reduction processes in halide and oxohalide niobium containing melts. Part I: Interaction of fluoride–chloride and oxofluoride–chloride Nb(V) melts with niobium oxides

The interaction between the K2NbF7–KCl–NaCl melt widely used for niobium electrolysis and niobium oxides of higher (Nb2O5) and lower (NbO2 and NbO) oxidation states was studied by linear sweep voltammetry and analysis of the dissolution time dependences. Three monooxofluoride complexes, NbOF4–, NbOF2–5 and NbOF63–, may form at the mole ratio of Nb2O5:K2NbF7=1:3. No significant difference was found in the electrochemical behaviour of the complexes, but their discharge potentials become more negative with increasing number of fluorine anions in the complex. Due to the interaction of K2NbF7 with NbO2 and NbO, oxofluoride Nb(v) and fluoride Nb(iv) complexes form simultaneously in the KCl–NaCl melt. Thus, the content of the latter increase until the molar ratios in the melt become NbO2dissolv.:K2NbF7init.=1:2 and NbOdissolv.:K2NbF7init.=1:3 and decrease with further dissolution of oxides in the melt. Dissolution of lower niobium oxides in melts containing oxofluoride Nb(v) complexes was also studied.     

Kinetic Study of Amorphous Yttria-Alumina Fibers Using Differential Thermal Analysis

Differential thermal analysis (DTA) was used to study the crystallization phenomena in Y₂O₃-Al₂O₃ fibers formed via a melt extraction process. Such fibers are X-ray amorphous and optically transparent regardless of composition in the as-extracted state but can be crystallized to produce various equilibrium phases that depend on the original composition of the ceramic rods used in the extraction process. The activation energy values were calculated using Kissinger and Augis-Bennett equations by measuring the variation of the peak temperature in the differential thermal patterns with heating rate. X-ray diffractometry analysis was used to determine the phase formation in the fibers crystallized after the DTA scan.     

Properties of Nitrogen-Containing Yttria—Alumina—Silica Melts and Glasses

The viscosity and solubility of nitrogen in Y₂O₃–Al₂O₃–SiO₂ melts have been systematically examined. The effects of nitrogen content on viscosity for Y-Al-Si-O-N melts and on Vickers hardness of oxynitride glasses also have been examined. Although the viscosity of Y₂O₃–Al₂O₃–SiO₂ melts was decreased, the solubility of nitrogen into the melts was increased with increased Y₂O₃ content. These results indicated that the yttrium ion behaved as a network modifier. Therefore, the structural units for viscous flow became small, and the amount of nonbridging oxygen increased in the melts when the Y₂O₃ content increased. The viscosity of Y-Al-Si-O-N melts and Vickers hardness of oxynitride glasses remarkably increased with increased nitrogen content. These results suggested that the substitution of nitrogen for oxygen in the melts may have led to a high average coordination of nonmetal atoms and that the increased cross-linking produced a more rigid glass network.