Oxidation of Hf2SnC and Nb2SnC in Air in the 400–600°C Temperature Range

The oxidation behavior in air of fully dense, predominantly (92+vol.%) single phase, samples of Nb₂SnC and Hf₂SnC was studied in the 400–600°C temperature range. The oxidation products in both cases were SnO, SnO₂ and either Nb₂O₅ or HfO₂. The oxidation is characterized by an initial incubation period, the duration of which decreased with increasing temperatures, followed by a period of near-linear oxidation kinetics. Oxidation at temperatures as low as 400°C for 72 hr resulted in the total disintegration of bulk samples, and their total conversion to oxides. Comparison with published results indicate that the oxidation kinetics of Hf₂SnC are poorer than those of Hf or HfC. Similarly, Nb₂SnC is more prone to oxidation than pure Nb metal.     

自蔓延高温合成Ti2SnC粉体及反应机理的研究

采用自蔓延高温合成技术制备了Ti_2SnC粉体材料,利用XRD、SEM、EDS、TEM及DTA等分析手段对其形貌结构进行表征,在室温条件下其晶格参数a和c分别为3.186和13.630。分析了Ti2SnC的形成机制。在Ti-Sn-C反应体系中,Sn在232℃时熔化为液态,随着温度的升高,钛包裹在碳的外面形成钛碳层,继续加热Ti和Sn反应生成Ti-Sn金属间化合物TixSny,如Ti_6Sn_5和Ti_5Sn_3,在800℃左右钛碳层形成了TiC,在1100℃左右TiC与TixSny发生反应生成类盘状的Ti_2SnC。     

Synthesis of Ti2SnC from Ti/Sn/TiC powder mixtures by pressureless sintering technique

Ti/Sn/TiC powder mixtures were first employed to synthesize Ti₂SnC powder by pressureless sintering in the temperature range of 950–1250 °C at vacuum atmosphere. Ti₂SnC began to form at 950 °C, its content increased with increasing temperature. High purity of Ti₂SnC was obtained by sintering the mixtures with deficient Sn and TiC at 1200 °C for 15 min. A reaction mechanism was proposed to explain the formation of Ti₂SnC. The Ti₂SnC powder was characterized by scan electron microscopy (SEM) and X-ray diffraction (XRD). Using the above mixtures and process, the Ti₂SnC ceramic powder can be obtained on a larger scale.     

Mn+1AXn三元层状陶瓷增强铜基复合材料的研究进展

回顾了颗粒增强铜基复合材料的发展和常用颗粒增强相;简介了新型三元层状陶瓷材料Mn 1AXn,并将其主要成员与常用铜基复合材料增强相进行比较;介绍了Mn 1AXn陶瓷与铜的复合材料目前的研究进展;展望了该类复合材料的发展和应用前景.     

Ti3SnC2电子结构的第一性原理研究

采用密度泛函数理论框架下的第一性原理研究了Ti3SnC2的电子结构,利用GGA-PW91基组对Ti3SnC2晶体结构进行了优化,并计算了Ti3SnC2的能带结构、总态密度和各原子的分态密度.对能带和总态密度的计算结果表明,Ti3SnC2在费米能级处电子态密度较高,材料表现出较强的金属性,同时材料的导电性为各向异性.Ti3SnC2各原子的分态密度图的计算结果表明,其导电性主要由Ti2的3d电子决定,Ti1的3d态电子、Sn的5p态电子和C的2p态电子也有少量贡献.决定材料电学性质的主要是Ti的3d、Sn的5p和C的2p态电子的p-d电子轨道杂化,而p-d电子轨道杂化成键则使材料具有比较稳定的结构.     

一种从硫化砷渣中回收砷的新方法

介绍了采用质量分数30％的双氧水氧化浸出-氯化亚锡还原法处理硫化砷渣以制备单质砷的方法.比较研究了双氧水用量、反应温度、反应时间在氧化浸出试验中对砷浸出率的影响及浓盐酸用量、SnCl2与As摩尔比在还原试验中对砷回收率的影响.结果表明：当固液比为1∶7（固体质量与双氧水体积比）,反应温度为75℃,反应时间为6h时,砷的浸出率达到99.70％;将滤液加热浓缩至As质量浓度约1 450 g/L后,常温下,当浓盐酸与浓缩液体积比为1∶1,SnCl2与As摩尔比为1.2∶1时,反应8h后,砷的回收率达到99.14％.最终产物于105℃烘箱中干燥6h,经检测其单质砷质量分数为98.26％.     

Ti_2SnC原位自生TiC_(0.5)增强Cu基复合材料的制备及压缩特性

本文以Ti_2SnC陶瓷为先驱体,利用其高温下与Cu的反应原位自生TiC_(0.5)颗粒增强Cu基复合材料并研究了其压缩特性。通过差热分析、X射线衍射和扫描电子显微镜等手段分析了Ti_2SnC与Cu的反应行为,并探讨了制备工艺对复合材料的物相组成、增强相形貌及材料特性的影响。结果表明,Ti_2SnC与Cu在900°C就开始发生反应,Ti_2SnC中的部分Sn原子逃逸扩散到Cu基体内,留下TiC_(0.5)作为增强相颗粒;随着温度的升高,反应程度加剧;当温度达到1150°C时,Ti_2SnC全部分解,形成亚微米TiC_(0.5)增强Cu(Sn)复合材料。TiC_(0.5)颗粒随保温时间增加而更加均匀地分布在基体内。对于初始Ti_2SnC体积含量为30%的TiC_(0.5)/Cu(Sn)复合材料,保温时间从0 h增加至2 h,其抗压强度和压缩变形率分别从1109 MPa±11 MPa和24.4%±0.6%增加到1260 MPa±22 MPa和28.9%±1.1%。     

Sn修饰SBA-15、MCM-41催化剂的制备及顺酐酯化性能

以SBA-15和MCM-41分子筛为载体,负载无水四氯化锡,制备了SnCl4-SBA-15和SnCl4-MCM-41催化剂,考察了不同锡与硅物质的量比对催化顺酐与正丁醇酯化反应的影响。结果表明,SnCl4-SBA-15表现出比SnCl4-MCM-41更高的催化性能,顺酐转化率为99.8%,副产物较少,马来酸二丁酯的产率最高可达91.3%。采用X射线衍射、N₂物理吸附、傅立叶红外光谱和紫外-可见漫反射技术对催化剂进行表征,结果显示, SnCl₄-SBA-15具有较高的比表面积,较大的孔容和孔径,更有利于催化反应的进行。     

三元层状陶瓷Ti2SnC的研究进展

MAX相化合物由于兼具陶瓷和金属的综合性能而引起了广大研究者的关注,Ti_2SnC与其他M2AX相化合物相比很少被研究。Ti_2SnC具有高的韧性及模量、高的损伤容限、良好的导热导电性能及抗热震和抗氧化性能等。这些优异的性能使其成为高温结构和功能应用的潜在材料。文章主要综述了三元层状陶瓷Ti_2SnC的晶体结构、理论研究、合成方法、性能的研究进展,分析了利用不同方法合成Ti_2SnC的机理,并展望了其应用前景。     

Nanowire-based three-dimensional hierarchical core/shell heterostructured electrodes for high performance proton exchange membrane fuel cells

In order to effectively utilize expensive Pt in fuel cell electrocatalyst and improve the durability of PEM fuel cells, new catalyst supports with three-dimensional (3D) open structure are highly desirable. Here, we report the fabrication of a 3D core/shell heterostructure consisting tin nanowire core and carbon nanotube shell (SnC) grown directly onto fuel cell backing (here carbon paper) as Pt catalyst support for PEM fuel cells. Compared with the conventional Pt/C membrane electrode assembly (MEA), SnC nanowire-based MEA shows significantly higher oxygen reaction performance and better CO tolerance as well as excellent stability in PEM fuel cells. The results demonstrate that the core/shell nanowire-based composites are very promising supports in making cost effective and electrocatalysts for fuel cell applications.