Oxidation behavior of in-situ Al2O3/TiAl composites at 900℃ in static air

In-situ Al2O3/TiAl composites were successfully synthesized from the starting powders of Ti, Al, TiO2 and Nb2O5. The oxidation behavior of the composites at 900℃ in static air was investigated. The results indicate that the composite samples present a much lower oxidation mass gain. Under long-time intensive oxidation exposure, the formed oxide scale is multi-layer. The formation of the outer TiO2 layer is fine and dense, the internal Al2O3 scale has good adhesiveness with the outer TiO2 scale, and the TiO2+Al2O3 mixed layer forming the protective oxide scale is favorable for the improvement of oxidation resistance. It is believed that the incorporation of Al2O3 particulates into the metal matrix decreases the coefficient of thermal expansion of the substrate, and forms a local three-dimensional network structure that can hold the oxide scale. The formation of the oxide scale with fmer particle size, stronger adherence, less micro-defects and slower growth rate can contribute to the improvement of oxidation resistance. Nb element plays an important role in reducing the internal oxidation action of the materials, restraining the growth of TiO2 crystals andpromoting thc stable formation of the Al 2O3-riched layer,which is benfeicial to improve the oxidation properties.     

Wet friction performance of C/C-SiC composites prepared by new processing route

C/C-SiC composites with SiC island distribution were prepared via a new processing route. The fabrication process mainly included silicon infiltration by ultrasonic vibration, chemical vapor deposition (CVD), siliconizing, liquid phase impregnation and carbonization. The wear and friction properties were tested by an MM-1000 wet friction machine. The results show that SiC phases are mainly distributed between carbon fibers and pyrocarbons as well as among the pryocarbons. The dynamic friction coefficient of the composites decreases gradually from 0.126 to 0.088 with the increase of the surface pressure from 0.5 to 2.5 MPa at the same rotary speed. Furthermore, under the constant surface pressure, the dynamic friction coefficient increases from 0.114 to 0.126 with the increase of the rotary speed from 1 500 to 2 500 r/min. However, the coefficient decreases to 0.104 when the rotary speed exceeds 4 500 r/min. During the friction process, the friction coefficient of C/C-SiC composite is between 0.088 and 0.126, and the wear value is zero after 300 times brake testing. Foundation item: Project(2006CB600901) supported by the Major State Basic Research and Development Program of China; Project(0991015) supported by Guangxi Science Found, China; Project(200808MS083) supported by Guangxi Education Department Found     

Preparation and sintering of nano Fe coated Si3N4 composite powders

Fe/Si₃N₄ composite powder was synthesized by the heterogeneous precipitation-thermal reduction process, and then pressed into flakes under a pressure of 10 MPa. Flakes were sintered by pressureless and hot-pressing at 1 600 °C under 0.1 MPa N₂. The chemical composition, phases and microstructure of composite powder and sintered flakes were investigated by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the structure of composite powders is Si₃N₄ coated by nano Fe. The crystal phases of sintered flakes by pressureless are Fe(Si) compound, SiC and Si₃N₄. The crystal phases of the sintered samples by hot-pressing are Fe, Fe(Si) compound and Si₃N₄. It is found that crystal phases flakes obtained by pressureless and hot-pressing are very different. Foundation item: Project(50804016) supported by the National Natural Science Foundation of China     

活性炭的改性制备及其吸附脱硫性能

经不同质量分数的酸、处理时间、焙烧温度等条件对活性炭进行改性,利用静态法研究了改性活性炭对噻吩的吸附脱硫性能。通过BET表征,对三种活性炭吸附剂进行比表面积分析。实验结果表明：经质量分数为50％的HNO3,100℃,6h处理的活性炭的脱硫性能最优（约71．0％）,惰性气氛下高温焙烧活性炭的脱硫率比未处理活性炭的脱硫率普遍提高,增幅约20％。说明物理微观结构不是影响脱硫率变化的主要因素。     

块体非晶合金制备方法的研究进展

对大块非品合金的制备方法进行了总结和归纳,阐述了不同制备方法的基本原理,并对各种制备方法的优缺点进行了讨论.最后根据对不同制备方法的分析及探讨,对大块非晶合金制备方法的研究方向进行了展望.     

层状锰酸锂材料制备技术

<正>技术开发单位南京航空航天大学技术简介锂离子电池的正极材料一般采用钴酸锂材料,但由于钴资源缺乏,价格昂贵,特别是目前的钴价持续上涨,给锂离子电池生产企业带来了巨大的压力。另外,钴的稳定性差,容易分解产生气体放出     

金属玻璃及其复合材料制备技术

金属玻璃又称非晶态合金．既具有金属和玻璃的优点,又克服了它们各自的缺点。如金属易生锈、不耐腐蚀,玻璃不生锈、耐腐蚀,而金属玻璃就和玻璃一样不生锈、耐腐蚀;玻璃易碎,没有延展性,金属玻璃的延展性却高于钢．硬度超过高硬工具钢．     

Ti_3SiC_2陶瓷的制备、性能与应用

三元化合物Ti3SiC2兼具金属和陶瓷材料的一些优异特性,综合评述了其晶体结构、基本特性、合成与制备方法、性能以及应用,并提出了今后研究的方向.     

两性聚丙烯酰胺水分散体系的制备

以丙烯酰胺(AM)、甲基丙烯酰氧乙基三甲基氯化铵(DMC)以及丙烯酸(AA)为单体,聚甲基丙烯酰氧乙基三甲基氯化铵(PDMC)为分散稳定剂,2,2′-偶氮(2-脒基丙烷)二盐酸盐(V-50)为引发剂,在硫酸铵水溶液中成功制备了两性聚丙烯酰胺(am-PAM)。考察了分散稳定剂相对分子质量、反应介质pH值、反应温度以及搅拌速度对水分散体系的影响,并用红外光谱仪以及扫描电镜对产品结构进行表征。研究得到合成两性聚丙烯酰胺水分散体系的较佳工艺条件:PDMC的相对分子质量30×104～46×104,反应介质的pH5.0～6.5,反应温度55～65℃,搅拌速度75～125 r.min-1,所得体系相界面明显,颗粒呈球形。     

金属线材单晶化方法与设备

单晶制备技术是西安工业大学一个重要研究方向。1994年已在单晶金属线材的制备技术方面在国内率先展开研究。早期阶段开发出单晶连铸技术,理论上解决了固液界面形状位置的控制等关键性问题,近3年内获得国家自然科学基金、陕西省自然科学基金、国防“十五”项目等多项基金项目资助。