Modification of tribology and high-temperature behavior of Ti-48Al-2Cr-2Nb intermetallic alloy by laser cladding

In order to improve the tribology and high-temperature oxidation properties of the Ti-48Al-2Cr-2Nb intermetallic alloy simultaneously, mixed NiCr-Cr₃C₂ precursor powders had been investigated for laser cladding treatment to modify wear and high-temperature oxidation resistance of the material. The alloy samples were pre-placed with NiCr-80, 50 and 20%Cr₃C₂ (wt.%), respectively, and laser treated at the same parameters, i.e., laser output power 2.8 kW, beam scanning speed 2.0 mm/s, beam dimension 1 mm × 18 mm. The treated samples underwent tests of microhardness, wear and high-temperature oxidation. The results showed that laser cladding with different constitution of mixed precursor NiCr-Cr₃C₂ powders improved surface hardness in all cases. Laser cladding with NiCr-50%Cr₃C₂ resulted in the best modification of tribology and high-temperature oxidation behavior. X-ray diffraction (XRD), optical microscope (OM), scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS) analyses indicated that the formation of reinforced Cr₇C₃, TiC and both continuous and dense Al₂O₃, Cr₂O₃ oxide scales were supposed to be responsible for the modification of the relevant properties. As a result, the present work had laid beneficial surface engineering foundation for TiAl alloy applied as future light weight and high-temperature structural candidate materials.     

FRACTAL ANALYSIS OF CATALYST NiO/α-Al_2O_3

We found that the Freundlich formula H=kC~(ln)can be used todescribe the isothermal adsorption curve of support α-Al_2O_3 with fractalstructures in nickel nitrate solutions.where n is relative to the surface fractaldimension D of α-Al_2O_3.     

双臂型方酰胺多齿配体的合成(三)

1,3-取代方酰胺内鎓盐分子中,二氧环丁烯结构单元上的氧相与富电,应有较好的配位能力。Maneke和Gauger虽然注意到这一点,但有关研究仍不多。为有效利用二氧环丁烯上氧的配位性,在其邻近的空间合理地配置齿形结构的配位链,以协调和加强分子的配位功能,改善配     

Theoretical studies of the spin Hamiltonian parameters and the local structures for the tetragonal Cu centers in the LKB glasses

The spin Hamiltonian parameters (g factors g_∥, g_⊥ and the hyperfine structure constants A_∥, A_⊥) for the Cu²⁺ centers in the lithium potassium borate (LKB) glasses xLi₂O·(30 − x)·K₂O·70B₂O₃ (0 ≤ x ≤ 25) were theoretically studied using the high-order perturbation formulas of these parameters for a 3d⁹ ion in a tetragonally elongated octahedron. The [CuO₆]¹⁰⁻ clusters in the LKB glasses are found to suffer the relative elongations of about 3% along the tetragonal axis due to the Jahn-Teller effect. The concentration dependences of the g factors are illustrated by the approximately linear decrease of the cubic field parameter Dq as well as the increases of the covalency factor N and the relative elongation ratio ρ due to the slight expansion of the cell volume or bond lengths with increasing the Li₂O concentration x. Meanwhile, the slow non-linear increases of the hyperfine structure constants are described as the rough exponential increase of the core polarization constant κ with x due to the increase of the tetragonality of the systems. The theoretical spin Hamiltonian parameters and their concentration dependences show good agreement with the experimental data. To evaluate validity and applicability of the present theoretical model and formulas, the EPR results of the Cu²⁺ centers in similar lithium sodium borate (LNB) xLi₂O·(30 − x)·Na₂O·70B₂O₃ (5 ≤ x ≤ 25 mol%) glasses are also analyzed and compared with those in the LKB systems using the uniform model and formulas.     

Investigations of the local structures and spin Hamiltonian parameters for the trigonal Rh and Ir centers in rhombohedral BaTiO3

The local structures and spin Hamiltonian parameters (g factors and the hyperfine structure constants) of the Rh⁴⁺(4d⁵) and Ir⁴⁺(5d⁵) centers in rhombohedral BaTiO₃ are theoretically investigated from the formulas of these parameters for a nd⁵ (n = 4 and 5) ion with low spin (S = 1/2) in a trigonally distorted octahedron. From the calculations, the impurity ions are found not to occupy exactly the host Ti⁴⁺ site in BaTiO₃ but to suffer a slight inward shift (0.13 Å) towards the center of the oxygen octahedron along the C₃ axis, yielding much smaller trigonal distortion as compared with that of the host Ti⁴⁺ site. The theoretical spin Hamiltonian parameters based on the above impurity axial shifts are in good agreement with the observed values.     

取代苄基瞵酸脂与取代苯甲醛反应的动力学研究

本文报导几种中等活性的瞵酸脂与各种取代苯甲醛反应的动力学研究, 并考查了中等活性的瞵酸脂组分及中等活性的醛组分上不同取代对反应速度的影响。     

螺[1-溴-4-(1R,2S,5R)-l-孟氧基-5-氧杂-6-氧代双环[3.1.0]己烷-2,2'-(3'-α-膦酸二乙酯基-(S)-苯甲氧基-4'-l-(1R,2S,5R)-孟氧基丁内酯)]的晶体结构

报道了标题化合物合成和晶体结构。X-射线结构分析表明,该化合物的分子式为C39H58BrO10P,Mr = 797.74,晶体属于单斜晶系,空间群为P21,晶胞参数a = 12.858(3), b = 25.130(5), c = 14.125(3) ? = 105.15(3), V = 4405(2) ?, Z = 4, Dc = 1.203 g/cm3, ?= 1.019 mm-1, F(000) = 1688,R = 0.0726, wR = 0.1201,共收集到9691个独立衍射点,其中可观测点5638个(I≥2s(I))。每个分子中有6个环,13个手性中心,2个五员环呈信封式构象,并分别与三员环组合成[2.4]螺环和[3.1.0]桥环化合物,4个新生成的手性中心的绝对构型为C(6)(S), C(7)(S), C(3)(R), C(2)(R),新引入的磷酸酯官能团C(9)为S构型。     

LiMgPO_4:Tm,Tb的热释光和光释光陷阱参数

采用高温固相法合成了LiMgPO_4:Tm,Tb粉末样品,测定了热释光陷阱参数激发能E和频率因子s.用脉冲退火和多次退火方法研究了其光释光陷阱参数E和s,并与用多速法得到的热释光的结果进行了比较.对不同β射线剂量照射的样品发光曲线的研究表明,300°C高温峰属于一级动力学发光峰.通过对热释光和光释光陷阱的相关性研究表明,经200°C预热的热释光信号(对应于300°C高温峰)和光释光信号很有可能来自于同一深度的陷阱.     

碳杂金属镍微球的制备及对葡萄糖的电催化氧化性能

以葡萄糖酸钠与硝酸镍为起始原料,通过水热合成法,制备了碳杂Ni(OH)2复合微球(C-Ni(OH)2),Ni2+的沉淀剂OH-是由葡萄糖酸钠水解提供的;以制得的C-Ni(OH)2微球为前驱体,在N2气氛围中下焙烧8 h,制得了碳杂金属镍(C-Ni)微球,通过场发射扫描电子显微镜(FE-SEM)、X射线衍射(XRD)、X射线能谱(EDS)和N2气吸附脱附实验等测试技术对其进行了分析,结果表明,C-Ni微球具有较大的比表面积和孔容,分别为276 m2/g和0.248 cm3/g;对葡萄糖氧化有良好的电催化作用。     

载体对甲烷在镍催化剂上分解反应的影响

开发洁净廉价的燃料替代石油已成为各国竞相研究的热点。从环境友好的观点出发 ,Ｈ2 气是一种理想的洁净燃料 ,其燃烧产物只有Ｈ2 Ｏ ,对环境无任何污染 ,Ｈ2 气将成为未来人类主要的能源。因此 ,近年来各国竞相开发大规模廉价的制氢和储氢技术。目前 ,碳及碳氢化合物制合成气法[1 ,2 ] 以其成本低和技术成熟已成为当前大规模制氢最常用的方法 ,包括碳氢化合物的水蒸气重整、ＣＯ2 重整、催化部分氧化法和自热重整[1～ 4] 。近年来又兴起了甲烷催化分解制氢[5,6] 。以上各方法均包含甲烷在镍催化剂上的分解过程[7,8] 。Ｒｏｓｔｒｕｐ Ｎｉ…