镍基合金TLP扩散焊接头中二元共晶沉淀相Ni-M(B、Si、Zr和Hf)的性能

采用基于密度泛函理论的第一性原理平面波赝势计算方法,计算了Ni-M(B、Si、Zr和Hf)二元共晶沉淀相(Ni2B、Ni3B、Ni3B2、Ni23B6、Ni3Si、Ni5Zr和Ni5Hf)的相稳定性、弹性常数、硬度及相应的电子结构。相稳定性计算结果表明,二元共晶沉淀相结构稳定性变化趋势由高到低的顺序为Ni3Si、Ni5Zr、Ni2B、Ni5Hf、Ni3B、Ni3B2、Ni23B6,这意味着降熔元素Si形成的Ni3Si沉淀相稳定性强于降熔元素B、Zr和Hf形成的沉淀相。弹性力学计算表明,Ni3B2表现为很强的各向异性,Ni2B、Ni3B和Ni3Si表现出一定的各向异性,而Ni23B6、Ni5Zr和Ni5Hf则表现为较强的各向同性。二元共晶沉淀相B/G值均大于1.75,这意味着它们为延性相。硬度计算的由小到大的小趋势为Ni3B2、Ni3B、Ni23B6、Ni2B、Ni5Zr、Ni3Si、Ni5Hf,其与各相中Ni 3d与B 2p,Si 3p,Zr 4d和Hf 5d的原子轨道杂化强度密切相关。

Synthesis and upconversion luminescence of Lu_2O_3:Yb^(3+),Tm^(3+) nanocrystals

Lutetium oxide nanocrystals codoped with Tm3＋ and Yb3＋ were synthesized by the reverse-like co-precipitation method, using ammonium hydrogen carbonate as precipitant. Effects of the Tm3＋, Yb3＋ molar fractions and calcination temperature on the structural and upconversion luminescent properties of the Lu2O3 nanocrystals were investigated. The XRD results show that all the prepared nanocrystals can be readily indexed to pure cubic phase of Lu2O3 and indicate good crystallinity. The experimental results show that concentration quenching occurs when the mole fraction of Tm3＋ is above 0.2%. The optimal Tm3＋ and Yb3＋ doped molar fractions are 0.2% and 2%, respectively. The strong blue （490 nm） and the weak red （653 nm） emissions from the prepared nanocrystals were observed under 980 nm laser excitation, and attributed to the 1G4→3H6 and IG4→3F4 transitions of Tm3＋, respectively. Power-dependent study reveals that the 1G4 levels of Tm3＋ can be populated by three-step energy transfer process. The upconversion emission intensities of 490 nm and 653 nm increase gradually with the increase of calcination temperature. The enhancement of the upconversion luminescence is suggested to be the consequence of reducing number of OH- groups and the enlarged nanoerystal size.

EDTA快速法测定锌焙砂、锌焙尘中总Zn

本文介绍了锌冶炼使用的锌焙砂、锌焙尘原料样用酸分解,加入氯化钡,使铅生成难溶共晶沉淀,使锡、铝、钛络合沉淀,并使铁、锰生成MnFeF6式结晶沉淀,以抗坏血酸与硫氰酸盐联合掩蔽铜,在不需要分离的情况下,加入PH5.5缓冲溶液,以甲基百里酚蓝为指示剂,用EDTA标准溶液滴定Zn的总量。本方法具有简单、快速、准确等特点,方法的相对偏差(RSD=?)为0.159%~0.205%,加标回收率在99.52%~100.40%之间,适合作为锌焙砂中铁量测定的分析方法。

Effects of co-precipitation temperature on structure and properties of La and Y doped cerium zirconium mixed oxides

Due to the oxygen storage and release properties,cerium zirconium mixed oxides are recognized as the key material in automotive three-way catalysts.To reveal the effects of co-precipitation temperature on structure,physical and chemical properties of multi-doped cerium zirconium mixed oxides,a series of La and Y doped cerium zirconium mixed oxides(CZLYs)were synthesized via a co-precipitation method,and the physical and chemical properties of CZLYs were systemically characterized by XRD,N_(2) adsorption−desorption,TEM,XPS,oxygen storage capacity(OSC)and hydrogen temperature programmed reduction(H_(2)-TPR).The results show that co-precipitation temperature is an important parameter to influence the crystal size,oxygen storage capacity and thermal stability of CZLYs.When the co-precipitation temperature was 60℃,the best redox properties and thermal stability of CZLYs were obtained.After thermal treatment at 1100℃for 10 h,the specific surface area and oxygen storage capacity of the corresponding aged sample were 15.42 m^(2)/g and 497.7μmol/g,respectively.In addition,a mechanism was proposed to reveal the effects of co-precipitation temperature on the structure and properties of CZLYs.

Morphology and photoluminescence of BaMoO_4 micro-and nano-crystals synthesized by coprecipitation method

Barium molybdate（Ba Mo O4） micro- and nano-crystals were synthesized by the coprecipitation method. Utilizing the water as the solvent provides octahedron-like nanostructures. These nano-crystals were structurally characterized by X-ray diffraction, energy dispersive X-ray micro-analysis, Fourier transform infrared spectra. The size and shape were observed by scanning electron microscopy. The optical properties were studies by ultraviolet-visible diffuse reflectance spectroscopy and photoluminescence measurements at room temperature. The effects of temperature, solvent, surfactant and barium source were considered to obtain a controlled shape. It is found that the morphology, particle size and phase of the final products are extremely affected by these parameters.

Sintering temperature reflected cation distribution of Zn^(2+) substituted CoFe_2O_4

The most remarkable effect in spinel ferrites is the strong dependence of properties on the state of structural disorder and,in particular,on the cation distribution.The structural characterization of a Co-Zn ferrite nanoparticle sample was reported which prepared by wet chemical co-precipitation method.The samples were sintered at three different temperatures viz.650℃,850℃ and 1050℃ for 12 h.The structural details like:lattice constant and distribution of cations in the tetrahedral and octahedral interstitial voids have been deduced through X-ray diffraction (XRD) data analysis.Lattice constant was found to increase with the increase in Zn2+ ions and sintering temperature.Theoretical intensity ratios of (220),(400),(440) planes were considered,as these reflections are sensitive to cations on the A and B sites.Close agreement of the theoretical intensity ratio with the intensity ratio observed from XRD pattern supports the occupancy of Zn2+ ions and Co2+ ions on the octahedral and tetrahedral sites,respectively.

Adjusting Na doping via wet-chemical synthesis to enhance thermoelectric properties of polycrystalline SnS

Tin sulfide (SnS) has analogous structural features to tin selenide (SnSe), but contains more abundant resources as compared with SnSe. SnS has elicited attention as a potential eco-friendly therm oelectric (TE) material. However, the intrinsic carrier concentration of SnS is very low, thereby hindering the performance improvement of the material. This study proposes that the TE properties of polycrystalline Nadoped SnS (synthesized through an improved chemical coprecipitation) can be significantly enhanced. The maximum power factor (PF) of 362 μW m^-1K^-2 at 873 K was achieved, presenting a state-of-the-art value for the polycrystalline SnS. Considering the merits of the improved electrical properties and lower thermal conductivity of SnS, the highest ZT was up to 0.52 at 873 K even without intentional chemical doping. This study offers an effective approach for improving the PF to achieve high ZT in SnS. Hence, we expect that this new perspective can be extended to other dopants and broaden the scope of synthesis technology.