挤压浸渗金属基短纤维复合材料浸渗压的理论分析及应用

本文根据Laplace方程及流体力学的基本原理建立了挤压浸渗法制备金属基复合材料的浸渗压模型,应用该模型对ZA22/Al₂O₃复合材料的浸渗过程进行了理论分析.以此为指导制出了性能优良的ZA22/Al₂O₃复合材料.      

(Ni0.75Fe0.25-xMgO)/YSZ anode for direct methane solid-oxide fuel cells

(Ni_0.75Fe_0.25-xMgO)/YSZ samples—with a varying weight percentage x (0, 5%, 10%) of MgO with respect to Ni_0.75Fe_0.25—were prepared and studied as anodes for intermediate temperature solid oxide fuel cells (SOFCs) operated on humidified methane (3% H₂O). Among the cells with different anode compositions, it was found that the cell with the (Ni_0.75Fe_0.25-5%MgO)/YSZ anode showed the highest power density, giving 648 mW cm⁻² at 800 °C. The cells with MgO-doped anodes were able to operate stably for 20 h under a current density of 0.53 A cm⁻² at 700 °C without observed degradation, while the cells without MgO degraded rapidly. The mechanisms responsible for the superior performance and duration of the (Ni_0.75Fe_0.25-5%MgO)/YSZ anode were analyzed.     

Characterization and electrochemical performances of Ba2−xSrxFeO4+δ as a novel cathode material for intermediate-temperature solid oxide fuel cells

Novel cathode materials, Ba_2−xSr_xFeO_4+δ (x = 0.5, 0.6, 0.7, 0.8, 1.0), for intermediate-temperature solid oxide fuel cells on a samaria-doped ceria (SDC) electrolyte were prepared by the glycine–nitrate route and characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric (TG) analysis, electrochemical impedance spectroscopy and steady-state polarization measurement. SEM results showed that the electrode formed a good contact with the SDC electrolyte after sintering at 1000 °C for 2 h. The value of δ in Ba_1.0Sr_1.0FeO_4+δ materials was calculated from the TG results. The electrochemical impedance spectra revealed that Ba_2−xSr_xFeO_4+δ had a better electrochemical performance than that of Ln₂NiO₄ (Ln = La, Pr, Nd, Sm). In the Ba_2−xSr_xFeO_4+δ (x = 0.5, 0.6, 0.7, 0.8, 1.0) family, the composition Ba_1.0Sr_1.0FeO_4+δ exhibited the best electrochemical activity for oxygen reduction. The polarization resistance of Ba_1.0Sr_1.0FeO_4+δ on SDC electrolyte was 1.11 Ω cm² at 700 °C, which was less than half that reported for Ln₂NiO₄ at the same temperature.     

PARTICLE DISTRIBUTION IN CENTRIFUGAL ACCELERATING FIELDS

Based on continuum theory and moving law of particles, a model is presented to obtain gradient distribution of particles in centrifugal accelerating field, by which the particle distribution in gradient composite material can be predicted. The simulation shows with increases in rotating time, four regions gradually appear from the internal periphery to the external one, they are free region, transition region, steady region and surface reinforced region, and the latest three regions are defined as a rich region. Finally, the steady region disappears, and the rich region only includes transition region and surface reinforced region. The influences of centrifugal acceleration coefficient G, primary volume fraction 0, pouring temperature θP and density difference between the particle and the metal matrix on particles gradient distribution are studied in detail. The results of the theoretical analysis agree with experiment ones. Both of analysis and experiment results indicate that with the increase in G a