室温下压致铁钴镍合金的bcc→hcp相变

 本文采用高压X光衍射方法在金刚石对顶压砧中在位地（in situ）研究了Fe₆₈Co₂₄Ni₈（wt%）合金在室温下的压致bcc→hcp结构相变和直到40.5 GPa的等温压缩行为。实验结果表明该合金在常压下为bcc结构，晶格常数a₀=(0.287 0±0.000 1) nm，体积V₀=(7.119±0.007) cm³/mol，密度ρ₀=(7.981±0.008) g/cm³；在20.9 GPa附近出现bcc→hcp结构相变，两相共存压力区约10 GPa，在此区域内有晶面间距d(002)_hcp=d(110)_bcc，且原子平面(002)_hcp//(110)_bcc，hcp相比bcc相体积减小(0.33±0.02) cm³/mol；高压相hcp结构的晶格参数比值c/a=1.608±0.004；相变后原子配位数的增加使得hcp相(002)平面内及(002)平面间的最近邻原子间距比bcc相最近邻原子间距分别增大约1.6%和0.5%；用Murnaghan状态方程对实验数据进行最小二乘法拟合，得到bcc相B₀=(130±13) GPa，B₀'=12.6±0.5；hcp相V₀=(6.62±0.04) cm³/mol，B₀=(243±21) GPa，B₀'=6.8±0.3；对于该合金的bcc→fcp相变时的结构转变机制做了详细的讨论。     

Mössbauer effect study of the decagonal quasicrystal Al65Co15Cu20

The ⁵⁷Fe Mössbauer effect study at 5.0 K and in an external magnetic field of 9.0 T on a high-quality stable decagonal quasicrystal Al₆₅Co₁₅Cu_19.9Fe_0.1 is presented. It is shown that the iron atoms are located in two distinct classes of sites. The values of the principal component of the electric field gradient tensor and the asymmetry parameter at these sites are, respectively, ?1.90(10)?×?10²¹ V/m², 0.97(15) and ?3.95(12)?×?10²¹ V/m², 0.00(17).     

微脉冲电子枪的初步实验研究

给出了微脉冲电子枪的模拟计算及其初步实验结果. 该电子枪采用铜铝镁合金作为冷阴极材料, 在以磁控管作为微波功率源的出束实验中得到了100mA/cm²的电流密度.实验结果与次级电子倍增解析计算和SEEG程序的模拟计算结果基本符合, 初步验证了微脉冲电子枪的基本原理, 为今后实验中得到更大的电流密度打下了基础.     

3004铝合金“反常”锯齿屈服现象的研究

在应变速率为5.56×10^-5s^-1—5.56×10^-3s^-1的范围内，在不同温度下(从223K至773K)，对3004铝合金进行系列拉伸试验，探索其锯齿屈服规律；通过激活能的计算、内耗研究、微观组织观察和能谱分析，探讨锯齿屈服的机理与物理本质.结果表明，3004铝合金在形变过程中会出现动态应变时效现象；发现了一种“反常”的锯齿屈服现象：在出现锯齿屈服的温区内，存在锯齿屈服临界应变量转变温度T_t， 关键词： 动态应变时效 锯齿屈服 铝合金 内耗     

STM/AFM studies of the evolution of morphology of electroplated Ni/W alloys

The surface morphology evolution of Ni/W alloys was studied, as a function of the alloy composition. Using the modified plating baths developed in our laboratory recently, electroplated Ni/W alloys with different W content, in the range of 7–67 atom percent (a/o), can be obtained. This was found to lead to different structures, ranging from polycrystalline fcc-Ni type structure to amorphous, followed by orthorhombic with increasing W content in the alloy. Powder XRD was studied to determine the crystal structures. Ex situ STM, AFM and SEM were used to study in detail the surface morphologies of the different alloys, and their evolution with increasing W content.

The important findings are that a mixture of two crystalline forms can give rise to an amorphous structure. Hillocks that are usually a characteristic of epitaxial growth can also exist in the amorphous alloys. Oriented scratches caused by stress can also be formed.

Up to 20 a/o of W is deposited in the alloys in crystalline form, with the fcc-Ni type structure. Between 20 and about 40 a/o an amorphous structure is observed, and above that an orthorhombic crystal structure is seen, which is characteristic of the NiW binary alloy. Careful choice of the composition of the plating bath allowed us to deposit an alloy containing 67 a/o W, which corresponds to the composition NiW₂.     

High-throughput concept for tailoring switchable mirrors

The optical properties, the switching kinetics and the lifetime of hydrogen switchable mirrors based on Mg-Ni alloys are determined with particular regard to the composition of the optically active metal-hydride layer in combination with the thickness of the catalytic capping layer. For this, a high-throughput experiment is introduced. The switching kinetics and the reversibility of switchable mirrors are strongly thickness dependent, though the details hinge on the fine structure of the clustered capping layer. Therefore, the kinetics is correlated with the surface structures of Pd on Mg_yNi_1−y as investigated by scanning tunneling microscopy. The results are explained by the so-called strong metal-support interaction (SMSI) state, characterized by a complete encapsulation of the capping layer clusters by oxidized species originating from the support. The SMSI-effect is less important with increasing Pd-layer thickness, and is suppressed by a good wetting of the Pd-clusters on the optically active film. This explains the critical thickness for the catalyzed hydrogen uptake observed in many switchable mirror systems. Moreover, the degradation of the kinetics during cycling is found to depend on the Pd-layer thickness and on the gas environment. Only films, covered with at least 15 nm Pd, show small degradation caused by the SMSI-effect. The SMSI-effect is partly reversible: after changing the gas environment from hydrogen to oxygen, the oxide on the Pd-clusters can be partly removed.     

Alloy formation in mechanically activated mixtures

The physical mixtures of hydroxocarbonates of Cu and Ni with aluminium were activated using a laboratory planetary mill. The chemical reactions and alloy formations as the effects of grinding were followed by the phase analysis of solid products based on the thermogravimetry and X-ray diffractometry. Experimental evidence indicates that the nature of reactions and products of mechanical activation was dependent on the amount of aluminium and time of grinding. This revised version was published online in July 2006 with corrections to the Cover Date.     

Chain length effect on dynamical structure of poly (vinyl pyrrolidone)-polar solvent mixtures in dilute solution of dioxane studied by microwave dielectric relaxation measurement

Dielectric relaxation study of the binary mixtures of poly(vinyl pyrrolidone) (PVP) (Mw=24000, 40000 and 360000 g mol⁻¹) with ethyl alcohol (EA) and poly(ethylene glycol)s (PEGs) (Mw=200 and 400 g mol⁻¹) in dilute solutions of dioxane were carried out at 10.1 GHz and 35°C. The relaxation time of PVP-EA mixtures was interpreted by the consideration of a wait-and-switch model in the local structure of self-associated ethyl alcohol molecules and also the PVP chain length as a geometric constraint for the reorientational motion of ethyl alcohol molecules. The formation of complexes and effect of PVP chain length on the molecular dynamics, chain flexibility and stretching of PEG molecules in PVP-PEG mixtures were explored from the comparative values of dielectric relaxation time. Further, relaxation time values in dioxane and benzene solvent confirm the viscosity independent molecular dynamics in PVP-EA mixtures but the values vary significantly with the non-polar solvent environment.     

一维应变压缩下TC4钛合金绝热剪切研究

 利用内径为57 mm的压缩气炮，在撞击速度为0.2~1.2 km/s（相应的靶中压力为3~15 GPa）范围内进行对称碰撞实验，以研究TC4（Ti-Al6-V4）钛合金在一维应变冲击压缩条件下的绝热剪切现象。对回收得到的受冲击样品，在扫描电镜（SEM）下进行细观金相分析。结果指出，一维应变冲击压缩条件下，TC4钛合金中绝热剪切带产生的对称碰撞速度阈值为500 m/s（相当于样品中的压力为5.87 GPa）；主剪切带与冲击方向约为45°角，带上有圆形和椭圆形两种孔洞且随碰撞速度的增大而增多和长大，这是典型的韧性损伤特征。随碰撞速度增大，产生与主剪切带成15°角的支剪切带。这些与理论预言相符。X射线能谱分析结果指出，剪切带内材料发生了(α+β)→β相的转变，是典型的相变带。剪切带的温度估算与实验提供的信息吻合。