Improvement of intermediate-temperature oxidation resistance of Ti3AlC2 by pre-oxidation at high temperatures

Ti₃AlC₂ has good oxidation resistance at high temperatures owing to the formation of protective Al₂O₃ layer. However, as it is directly exposed to air at 500 °C and especially 600 °C, the scales formed on Ti₃AlC₂ exhibits poor protectivity because of the oxidation-induced microcracks, which limits the potential application of this technologically important material. In this work, the oxidation resistance of Ti₃AlC₂ at 500 °C and 600 °C was significantly improved by pre-oxidation at 1000–1300 °C for a short time of 2 h in air. The oxidation of the pre-oxidized Ti₃AlC₂ at 600 °C generally obeyed a parabolic rate law instead of the speed-up linear relation in the case without pre-oxidation. As revealed by X-ray diffraction, Raman spectroscopy results and SEM observations, the remarkable improvement of oxidation resistance after pre-oxidation was attributed to the protective layers formed on Ti₃AlC₂ during pre-oxidation, which inhibited the formation of anatase TiO₂ that resulted in the oxidation-induced microcracks. Moreover, this work confirmed that the mechanism proposed previously for the anomalous oxidation of Ti₃AlC₂ in air at 500–600 °C was correct.     

Ag/Al2O3 界面结构与O2分压关系的原子级热力学模拟

采用第一原理方法研究了Al终断（Al-terminated），O终断（O-terminated），Al2终断（Al2-terminated）的Ag／α-Al2O3界面．基于原子级热力学模拟，建立了Ag／Al2O3界面结构与O2分压关系．分别采用了参考Al化学势和参考O化学势作为环境变量的两种近似处理方法，发现它们预测的从Al终断向O终断转变的氧分压点相差约4个数量级．通过对界面热容的估算，判断出更准确的结果应在两个近似之间，而且用Al化学势作参照的结果应与实验结果更接近．Ag／Al2O3界面结构与O2分压的关系与文献报道的相应润湿性（wetting）实验具有同样的趋势．理论预测的结构转变点与实验结果的误差在合理的范围内．     

挤压铸造Al_2O_3／Al─Si合金复合材料的凝固组织与凝固模型

利用挤压铸造技术制备了Ａｌ２Ｏ３／Ａｌ─Ｓｉ合金复合材料，研究了这种复合材料的凝固组织．结果表明，氧化铝纤维可作为铝硅合金中硅相非自发形核的衬底，但是未观察到纤维对α相的细化作用；氧化铝纤维与浸渗压力影响了复合材料的凝固过程，复合材料具有不同于普通基体合金的最终凝固组织．基于实验结果和凝固理论，提出了Ａｌ２Ｏ３／Ａｌ─Ｓｉ合金复合材料的凝固模型．     

Characterization and Photoluminescence Properties of AluminaNanowires Elaborated by Arc-Plasma

Ultrafine powders containing alumina nanowires are synthesized by DC arc plasma from pure aluminium metal. Nanowires grow only when reactive gases are composed of nitrogen and less than ten percent of oxygen. Nanowires have the diameters ranging from 20 to 80 nm and lengths ranging from hundreds nanometers to tens of micrometers. A first assumption of the mechanism process is proposed, in which nanowires grow starting directly from the aluminium. Photoluminescence measurements show that the powders have three emission peaks around 435, 530 and 750 nm resulting from different kinds of defects such as oxygen vacancies, aluminium interstitial ions and surface defects.