Y-Al化合物对铝合金性能影响的价电子理论分析

Y是稀土铝合金中常用的添加元素,Y和Al可以形成五种不同的化合物,Y-Al化合物对稀土铝合金的性能有重要的影响.基于固体与分子经验电子理论(EET)和键距差方法(BLD),计算了五种Y-Al化合物的价电子结构和化学键键能,从价电子结构层次探讨了五种Y-Al化合物对稀土铝合金强度、塑性和高温稳定性的影响.计算结果表明,五种Y-Al化合物对铝合金的室温强度都有较好的增强作用;YAl3的塑性最好但稳定性极差;Y3Al2和Y2Al的脆性高,对铝合金的塑、韧性有严重的削弱;YAl2的强度和塑性居中,但稳定性最强,熔点高,对铝合金的室温强度、高温稳定性和高温强度都有显著的贡献.因此,在稀土铝合金的制备中,应促进YAl2相的生成.     

钨硅二元体系化合物稳定性、力学性能和电子结构的理论计算研究

钨硅二元体系化合物除了具有难熔金属硅化物共有的高熔点、高强度、强的抗氧化性和抗形变能力的同时,还表现出了许多其它卓越的性能特点,目前已得到广泛的应用。基于密度泛函理论对钨硅二元体系所形成化合物WSi_2和W_5Si_3的稳定性、力学性能和电子结构进行了研究。通过计算5种钨硅二元体系相结构的点阵常数、形成焓、弹性常数、体模量、剪切模量、拉伸模量、泊松比、各向异性因子以及维氏硬度等物理量得到其晶体结构和力学性能等信息。此外,通过对WSi_2和W_5Si_3的总体和局部态密度的计算得到钨硅二元体系化合物的成键机制。计算结果表明,在钨硅二元体系化合物的5种稳定相结构中,β-WSi_2表现出了最高的稳定性和力学性能。态密度的计算结果也进一步证实了这一点。同时,态密度的计算结果表明这5种稳定相结构的成键机制均是较强的共价键和一定程度金属键的混合。结果可对基于钨硅二元体系化合物的新材料的设计提供新线索和理论基础。     

二元金属类水滑石的合成及其作为前驱体对NOx的吸附性能研究

用共沉淀法合成了多种二元金属类水滑石化合物,对其进行了XRD、IR表征,并测试了焙烧产物对NOx的吸附性能.结果表明,合成的样品都具有典型的水滑石层状结构;二元金属类水滑石化合物MAl-HTlcs(M=Cu,Mg,Zn,Co,Ni)对NOx均具有良好的吸附性能,其中锌铝型类水滑石(摩尔比Zn/Al=3)对NOx的吸附速率及饱和吸附量最大,饱和吸附量为1851mg/g.     

商用超导材料技术概况

从最初的单金属、二元化合物到三元和多元化合物,超导材料以其广阔的应用前景和巨大的应用价值,受到了广泛的关注。超导现象最初由荷兰科学家昂内斯于1911年,在液氦中观察汞的电性能时发现。随后铌钛(NbTi)、铌三锡(Nb3Sn)等二元合金化合物相继被发现,超导合金材料开始进入实用化。由于超导合金具有低     

两种偶氮席夫碱类化合物的合成与变色性能研究

采用冰浴法合成了偶氮化合物,再与2-羟基1-萘醛进行缩合反应,得到未见文献报道的2种偶氮类席夫碱化合物A和B.并研究了光照和溶液pH值等条件对溶于二甲亚砜(DMSO)的化合物A和B紫外可见(UV-Vis)吸收光谱的影响.发现随着紫外光照时间的延长,2种化合物的小于400nm的峰强降低,而大于400nm的峰强增加.随着溶液pH值增大,其UV-Vis吸收光谱的最强的吸收峰都出现明显红移.研究表明2种偶氮席夫碱类化合物都具有可逆的光致变色性以及受pH值调控的光致变色行为.     

一种特定设计的富勒烯寡聚核苷酸对PCR的抑制作用

以HeLa细胞β-actin cDNA的聚合酶链式反应(PCR)分析为实验模型,比较研究了针对β -actin cDNA序列设计合成的一种富勒烯寡核苷酸(FONC)和4种其他不同侧链结构的富勒烯衍生物--三丙二酸富勒烯(TMA C60)、富勒醇(fullerol)、二加成亚甲基富勒烯二膦酸酯(BMPF)及单加成亚甲基富勒烯二膦酸(MMPAF)对PCR的作用,发现在实验条件下,这5种化合物均能抑制PCR,且存在浓度依赖性,但以FONC的活性最强,它们的活性比较结果是FONC>TMA C60>fullerol>MMPAF>BMPF.加入活性氧清除剂甘露醇、叠氮化钠和L-抗坏血酸-2-磷酸酯镁不能逆转fullerol却能逆转FONC的抑制作用.实验结果提示,这种特定设计的FONC对PCR具有较强的抑制活性,其作用机理不同于其他富勒烯衍生物 .实验结果为进一步研究FONC的潜在应用提供了依据.     

钙钛矿结构的有机-无机杂化功能材料:(p-CphAH)2PbCl4

利用溶液降温的方法从盐酸溶液中生长出一种新的有机-无机层状钙钛矿结构的单晶(p-CphAH)2PbC14(p-CphAH为对氯苯铵离子).借助于元素分析值、核磁谱、X射线衍射方法、紫外及荧光光谱,系统研究化合物的结构和光学性能.标题化合物晶体为浅黄色长棱柱体,单斜晶系,C2/m空间群;a=2.2149(5)nm,b=0.7737(3)nm,c=1.7083(5)nm,β=104.784(5)°,V=2.8310(2)nm3.     

高温超导体研究新发现-MgB2

今年一月,日本科学家Nagawatsu等人发现了二硼化镁超导体,引起国内外的普遍关注.这是一种机关报的简单二元金属间化合物超导体(每个晶胞只有三个原子),超志转达变温度Tc高达39K,几乎是Nb3Ge(a15型金属间化合物超志体中Tc最高,23.2K)和YP2B2C(金属间硼碳化合)的两倍.     

基于丙二腈的含能化合物的合成研究进展

丙二腈是一种重要的有机合成原料。介绍了丙二腈分子中亚甲基和氰基的反应特性。利用氰基的反应活性可以构建氮杂环母体骨架,可进一步赋予能量,设计并合成多种性能优异的含能化合物。丙二腈作为原料可以合成3, 4-二(3’-硝基呋咱-4’-基)氧化呋咱(DNTF)和1, 1’-二羟基-5, 5’-联四唑二羟胺盐(HATO)等新型含能材料。系统综述了构建呋咱、四唑、异呋咱、偶氮桥联、醚桥联等含氮含能化合物的合成方法。同时,重点介绍了典型含能化合物的爆轰性能等物理化学性能。对基于丙二腈的含能化合物的合成思路和方法进行总结并提出建议,为未来设计、合成具有自主知识产权且性能优异的新型含能材料提供参考。     

Mg65Cu25Y10合金的电化学贮氢能力

传统镁合金因在腐蚀反应过程中吸氢而性能下降.从另一方面考虑,Mg-TM(TM=Ni,Cu)合金由于形成金属间化合物,具有贮氢能力而引人关注.Mg2Ni和Mg2Cu是其中2种重要的金属间化合物,Mg2Ni的理论贮氢能力为3.6%,而Mg2Cu仅为2.6%.通过添加有利于氢化物形成的元素,如Y,Ce,La,改变Mg-Cu系合金的成分,可以增强其贮氢能力.另外,发现镁和它的具有细晶组织的二元化合物,例如,具有纳米晶或非晶结构的二元化合物,在较低温度下吸氢率提高了.     

Crystalline and quasicrystalline phases in AlCuFe and AlCuFeCr alloys

Different chemical compositions of the AlCuFe and the AlCuFeCr systems have been studied. The liquid melts have been cast in different mould types where the rate of cooling can be varied. The experimental results showed that for slow solidification rates and in the case of the ternary alloys, binary compounds can only be obtained. However, for higher cooling velocities, binary, ternary and quasicrystalline compounds were obtained. In the quaternary case, higher cooling velocities produce an amorphization tendency in the obtained alloy. But for slow rates of cooling, binary, ternary and quasicrystalline compounds were obtained. High rates of cooling in the ternary alloys produce a microstructure with a high density of star-shaped dendrites. Some of these dendritic formations display apparent ten-fold rotational symmetry. This revised version was published online in November 2006 with corrections to the Cover Date.     

Formation of functional coatings based on interstitial compounds on titanium under the conditions of thermodiffusion saturation

We analyze the contemporary approaches to the formation of functional protective coatings based of binary and ternary compounds on the surfaces of titanium alloys by the method of thermodiffusion saturation. Generalizing the accumulated results, we show that, in order to improve the operating characteristics of the surface, the basic direction in the engineering of titanium surface should be shifted from the formation of binary compounds (oxides, nitrides, and carbides) to the formation of ternary compounds (carboxides, carbonitrides, and oxynitrides). The experimental results demonstrating the advantages of coatings based on ternary compounds are presented. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 3, pp. 17–26, May–June, 2006.     

Dislocation core structure in the B2 phase of Nb-40%Ti-15%Al

Dislocation cores in the B2 phase of Nb rich alloys in the Nb-Ti-Al system were simulated using the embedded atom method. The alloy composition examined is Nb-15Al-40Ti. The site occupancies, elastic constants and average relaxed APB energies in these ternary B2 intermetallics were determined previously and compare favorably to the experimental values. We simulated 1/2111 and 100 dislocations in various orientations of the dislocation line. The results were compared with the dislocation core structures that are typical of other B2 compounds. Although the values of the APB's that characterize this ternary alloy are relatively low, the 100 dislocations were not found to split spontaneously during the simulation into two 1/2111 partials. The structures observed for these dislocations are basically similar to those found in other B2 binary compounds. The main difference is that the core structures in the ternary compound tend to loose the well defined preference for certain crystallographic pines that is typical of binary B2 compounds.     

Characterization of mechanical properties in the Ir---Nb---Zr intermetallic system

The mechanical properties of very high melting intermetallic compounds are examined in the Ir---Nb---Zr system. The Ir---Nb---Zr system contains two related high temperature L1₂ intermetallic compounds, Ir₃Nb and Ir₃Zr, with similar lattice parameters and melting points of 2450 and 2280°C respectively. Microhardness and compression tests show that the Ir₃Nb possesses twice the strength of the Ir₃Zr despite their marked similarities in electronic structure and cohesive properties. Furthermore, preliminary studies of a ternary L1₂ compound of composition Ir_0.71Nb_0.21Zr_0.08 show that it has a high temperature strength greater than that of either of the binary systems. Total energy electronic structure calculations confirm the similarity in the cohesive properties of the binary compounds, and point to differences in the density of states at the Fermi level as a possible reason for their dissimilar mechanical behavior.     

Tribological properties of carbonitride coatings formed on titanium by thermodiffusion carbonitriding

We have studied the tribological properties of VT14 titanium alloy with carbonitride coatings formed by the contact and noncontact method and binary (oxide and nitride) coatings. In the case of the contact method, specimens are saturated in a graphite backfill, and in the case of the noncontact method, specimens are located above it. We have investigated the wear resistance of a “titanium disk–bronze block” friction pair in AMH-10 hydraulic fluid under a load to 3 MPa on a friction path to 15 km. It has been established that coatings based on ternary interstitial compounds (titanium carbonitrides) provide a higher wear resistance than that of coatings based on binary interstitial compounds (titanium nitrides and oxides).     

Prediction of Magnetic Susceptibilities in Diamagnetic Binary Fluid Mixtures

A model is proposed to predict magnetic susceptibilities in diamagnetic binary fluid mixtures. The model predictions are compared to experimental information for nine binary systems including polar and non-polar compounds. The predictions are also compared to the results obtained from the traditional Boyer-Donzelot equation. For all systems analyzed, the model predicted magnetic susceptibilities closer to the experimental values than those predicted from the Boyer-Donzelot equation. The deviations from the experimental values decrease when the binary system exhibits a positive excess magnetic susceptibility.     

Surface tension and density measurement of liquid Si–Cu binary alloys

Surface segregation is very important for understanding the surface tension of binary systems. In case of a regular solution, the surface segregation is calculated using the Butler model. However, in the case of a complex system, like those forming intermetallic compounds, it is difficult to express the surface segregation. In order to discuss surface segregation in systems forming intermetallic compounds, we measured the density and surface tension of a Si–Cu binary system. We found the effect of clusters in both density and surface tension experimental data. The composition dependence of surface tension was expressed by a modified ideal solution model.     

The effect of pulsed magnetic fields on the real structure of indium arsenide crystals

Experiments on InAs crystals demonstrate that exposure to pulsed magnetic fields can increase the phase homogeneity and structural perfection of the binary phases of A^IIIB^V semiconductor compounds.     

θ Correction to the Analytical Expressions for Calculating Activities from Phase Diagrams Involving Intermediate Compounds

A set of correct expressions for calculating activities and activity coefficients from binary phase diagramsinvolving intermediate compounds are presented in this paper by the introduction of a correct parameter θ.The application of these expressions to system Mg-Sn shows that they are quite feasible.     

Effect of the type of chemical bonding on surface autosegregation processes

Experimental studies of thermally stimulated surface autosegregation (TSAS) processes on single crystals of binary and ternary (oxide) compounds and analysis of our and others’ results are used to assess the effect of the type of chemical bonding on surface segregation processes in chemical compounds. Parameters are proposed that relate the segregation tendency to characteristics of segregation processes. The surface segregation tendency is shown to become less pronounced with increasing bond ionicity.