Effect of thermal insulation on microstructural homogeneity and onset temperature of flash sintered materials

The present work aimed to reduce the microstructure heterogeneity inherent to flash sintering by using alumina blankets as a thermal insulator around ZnO cylindrical samples during the sintering process, under different electric field conditions. Thermal insulation significantly reduced the flash onset temperature and the grain size heterogeneity. For higher electric fields, a temperature reduction as high as 480 °C was observed, which also led to lower densification. These findings were discussed in terms of changes in the heat loss dynamics coupled with the adsorbed water retention, both promoted by the applied thermal insulation. A model to estimate the temperature at stage III of flash sintering was proposed. The final temperature reached with thermal insulation did not differ significantly from the ones without it. Thus, thermal insulation could represent an alternative route to flash sinter materials with lower furnace temperatures with energy savings up to 78 % and a more homogeneous microstructure.     

Electrochemical and microstructural characterization of cyclic redox behaviour of SOFC anodes

The oxidation of Ni to NiO in solid oxide fuel cell (SOFC) anode will result in large bulk volume change, which may change the interfaces of the two phases in the anode cermet and thus may cause significant performance degradation. The reduction and oxidation (redox) of the Ni/YSZ cermet were studied at 800 ℃. Anodic polarization measurements were performed before and after redox cycles. The anode current density at an overpotential of 100 mV kept decreasing during the whole redox treatment. It decreased from 19.11 to 7.95 mA·cm-2 after two redox cycles. Anode supported unit cell was assembled for cell's discharge measurements. Cell performance declined after each redox cycle. The maximum power density decreased from 126.28 to 40.32 mW·cm-2 . The microstructural changes after redox cycling were recorded using scanning electron microscopy (SEM). The results reveal that after re-oxidation, the Ni gets coarse and has a higher porosity; the nickel network structure turns to be desultory.     

高温预析出对Al-Zn-Mg-Cu铝合金显微组织、强度和应力腐蚀抗力的影响

通过改变固溶条件 ,对Al Zn Mg Cu高强铝合金采用先高温后低温的两步固溶处理 (高温预析出 )来改善晶内和晶界的析出状态 ,研究了高温预析出对Al Zn Mg Cu铝合金的金相组织、强度和应力腐蚀性能的影响。结果表明 ,4 6 5℃高温预析出在保持较高强度和塑性的同时 ,可以改善合金的抗应力腐蚀性能     

Self-organized porous TiO2 and ZrO2 produced by anodization

The present work investigates the electrochemical formation of self-organized high aspect ratio TiO₂ and ZrO₂ nanotube layers. The formation and growth of a self-organized porous layer can be achieved directly by anodization without any templates in fluoride containing electrolytes. The morphology of the porous layers is affected by the electrochemical conditions such as the electrolyte composition, the pH and the exact polarization treatment (such as the potential sweep rate from the open-circuit potential to the anodizing potential). For Ti, nanotube layers are formed with diameters varying from approx. 20 nm to 100 nm and lengths from approx. 0.25 μm to 2.5 μm depending on the electrolytes and pH. On the other hand, for Zr, tubes of 50 nm in diameter and up to approx. 17 μm in length can be grown—a key parameter in this case is the potential sweep rate. The large difference between Ti and Zr in the achievable thickness of nanotube layers indicates a difference in the growth mechanism which may be based on the different chemical dissolution rates of electrochemically formed oxides.     

液态铝合金表面张力快速检测新方法与装置

表面张力是液态合金的重要物性参数之一,铝合金表面张力与其变质处理效果及充型能力等质量参数密切相关,研究铸造铝合金表面张力快速检测方法及装置,对于开发铝合金熔炼质量炉前实时评价系统具有非常重要的实际意义.介绍了一种液态铝合金表面张力快速测试的新方法和新装置,新方法以固定时间内吹入被测液体的气泡个数以及气泡在生长过程中内部压差变化为信息参数,通过回归公式求解表面张力.基于该方法研制的表面张力新型测试装置由单片机测控单元、探头及其锁紧和升降机构、供气单元等部分构成.采用新装置可在5 s内测得铝合金表面张力,且具有较高的测试精度.     

Influence of Reinforcement Content and Matrix Composition on the Oxidation Resistance of Aluminum-Matrix Composites (A3xx.x/SiCp)

A study was made on the influence of the SiCp proportion and the matrix concentration of four composites (A360/SiC/10p, A360/SiC/20p, A380/SiC/10p, A380/SiC/20p) on their oxidation behavior. Gravimetric tests were used in a kinetics study of the corrosion process at different temperatures (350, 400, 450, and 500°C). The influence of corrosion on mechanical properties was evaluated by hardness measurements. The nature of corrosion products and the influence of the microstructure on the morphology and growth of the oxidation layer were analyzed by SEM and low-angle XRD. The extent of the damage due to oxidation for Al/SiCp composites increases with the SiCp concentration due to the increase of nucleation sites. One of these nucleation sites is in the interface region between the matrix and the particles. Oxidation was influenced more by the percentage of alloy elements in the matrix than by the proportion of SiCp reinforcement. The presence of Cu and Ni in the matrix favors the oxidation process through the formation of different intermetallic compounds.     

Corrosion resistance of austenitic stainless steel separator for molten carbonate fuel cell

STS310S and SC-STS310S (simultaneously co-deposited chromium and aluminum onto 310S austenitic stainless steel substrate by pack-cementation process) were used as separator materials on the cathode side of a molten carbonate fuel cell. With the STS310S, corrosion proceeded via three steps; a formation step of unstable corrosion product, a protection step against corrosion until breakaway, and an advance step of corrosion after breakaway. The final corrosion product was LiFeO₂ and the loss of mass was 6.5 mg/cm² after a corrosion test of 480 hr at 650°C. The SC-STS310S showed more effective corrosion resistance, however, than did common STS310S. There was especially no corrosion loss on the SC-STS310S after the 480 hr corrosion test. It is anticipated that it will be very useful as an alternative separator on the cathode side off the MCFC in the future.     

表面氧化层对TiMn1.25Cr0.25储氢合金活化性能的影响

通过TiMn1.25Cr0.25合金粉活化前在空气中暴露不同的时间,探讨了表面氧化层的形成对其活化性能的影响。活化测试结果表明：合金的活化难度随着合金在空气中暴露时间的延长而加大。俄歇电子能谱(AES)结果表明,在空气中暴露后的合金表面形成了一层大约6nm-10nm厚的表面氧化层,正是这层氧化层的形成加大了合金的活化难度。扫描电镜(SEM)结果表明合金的活化过程与合金的碎化有着密切的联系。     

Effect of theθ-α-Al2O3 transformation on the oxidation behavior ofβ-NiAl + Zr

Isothermal oxidation of NiAl + Zr has been performed over the temperature range of 800–1200°C and studied by TGA, XRD, and SEM. A discontinuous decrease in growth rate of two orders of magnitude was observed at 1000° C due to the formation of -Al₂O₃ from -Al₂O₃. This transformation also resulted in a dramatic change in the surface morphology of the scales, as a whisker topography was changed into a weblike network of oxide ridges and radial transformation cracks. It is believed that the ridges are evidence for a shortcircuit outward aluminum diffusion growth mechanism that has been documented in a number of¹⁸O tracer studies.     

Performance of positive and negative electrodes in amorphous manganese oxide supercapacitor

Using potassium permanganate and acetic manganese as the reactants, amorphous manganese oxide was prepared with mechanochemical method. XRD was used for microstructure characterization, while cyclic voltammetry and constant current charge-discharge were used for electrochemical performance testing. The positive electrode （PE） and negative electrode （NE） were investigated respectively in amorphous manganese oxide supercapacitor, aiming to find their different performances in charging-discharging. The results show that the crystalline structure is destroyed in both the PE and NE material during charge-discharge process. Thereinto, the NE suffers a bit more seriously. When cycling, the PE potential scope diminishes while the NE potential scope enlarges. The increased inner resistance makes the NE curves almost bended to be a right angle, but not the PE curves. The cell＇s equivalent series resistance （ESR） is more dependent on the NE, and the capacitance is mainly determined by the rapid descent of the NE potential range. The capacitances of the NE are highly rate-dependent, decreasing from 121.3 to 53.1 F/g, by 56.2%, over the range of 5-25 mV/s. However, the PE appears to be weakly dependent and its capacitance is only dropped by 22.1%.