金属火灾熔痕的显微组织及物相成分的实验研究

利用X-射线衍射(XRD)和3D图像处理软件(Image-pro)研究了四种不同火灾类型金属熔痕的显微组织、平均晶粒度、物相组成及其分布规律。结果表明：金属火灾熔痕主要由立方晶系的Cu₂O和胞、枝状的Cu组成。在四种不同的起火方式下,金属熔痕的显微组织和成分有显著的差别：(1)一次短路的火灾熔痕平均晶粒度为3～5 μm,其Cu₂O含量最低;过载熔痕的平均晶粒度与一次短路的类似,但其Cu₂O含量为30%左右;(2)二次短路熔痕中含有一定数量直径较大的微观空洞,平均晶粒度约为30 μm;其Cu和Cu₂O衍射峰出现展宽和辟裂,烧蚀程度最深;(3)火灾熔痕中粗大的Cu₂O等轴晶衍射峰强度最大,且显微组织中几乎没有微观空洞存在。     

The effects of oxygen vacancies on the electrical properties of W,Ti doped CaBi2Nb2O9 piezoceramics

Different type doped CaBi₂Nb₂O₉ (CBN) ceramics were prepared by a conventional solid state sintering method. The number of oxygen vacancies were decreased or increased by the introduction of W⁶⁺ and Ti⁴⁺ doping in CBN ceramics. The influence of W⁶⁺, Ti⁴⁺ and W⁶⁺/Ti⁴⁺ dopants on the microstructures and electrical properties of CBN-based ceramics was investigated. The voids and spherical morphology in the SEM image of W, Ti co-doped ceramics indicate that W, Ti co-doping could change the microstructure of CBN-based ceramics. Impedance analysis results show that the electrical properties of CBN-based ceramics have a close relationship with the number of oxygen vacancies. W doping and W, Ti co-doping decrease the oxygen vacancies, as a result, the resistance and piezoelectric properties were increased and the frequency dispersion of dielectric properties were restrained.     

不同耐热型春玉米品种对高温的光谱特征响应

运用两种光谱仪（SPAD-502叶绿素仪与Sunscan植物冠层分析仪）分析了华北平原不同耐热型春玉米品种的光合性能对灌浆期高温的光谱学特征响应。田间试验于2011年—2012年在河北省吴桥县进行。品种选用天玉198、兴玉998与天润606,设置2个播种期（4月15日与4月25日）,于灌浆期测定3个光谱特征值,即叶绿素相对含量（SPAD）、叶面积指数（leaf area index, LAI）与光合有效辐射（photosynthetically active radiation, PAR）。结果表明,播种期4月15日与4月25日相比,春玉米灌浆期≥33 ℃日最高气温的天数与日均温分别增加了3.5 d和0.8 ℃,而日照时数、降雨量、气温日较差及生育期长短均相似; 天玉198与兴玉998、天润606相比,耐热指数（stress tolerance indices, STI）分别高2.9%,11.0%; 根据STI由大到小的顺序,将天玉198、兴玉998与天润606分别定为耐热型、较耐热型与不耐热型品种; 播种期4月15日,天玉198比兴玉998、天润606的产量分别高4.1%,13.7%,SPAD分别高12.5%,19.6%,LAI分别高5.3%,5.6%,PAR分别高4.0%,14.0%; 播种期4月25日,产量分别高1.3%,2.8%; SPAD分别高3.5%,6.0%,LAI分别高1.7%,4.1%,PAR分别高-4.4%,0.9%; 三个品种在高温胁迫环境下产量差异显著,耐热型品种具有显著的产量、SPAD与LAI优势（p＜0.05）。播种期4月15日相对于4月25日,天玉198、兴玉998、天润606的产量分别降低了3.2%,5.9%,12.6%; SPAD分别降低了8.6%,12.4%,15.7%; LAI分别降低了11.7%,17.6%,19.8%; PAR分别降低了3.4%,11.3%,14.5%; STI与SPAD的降幅（r=-0.883,p＜0.05）、LAI的降幅（r=-0.853,p＜0.05）均呈显著负相关,与PAR的降幅（r=-0.923,p＜0.01）呈极显著负相关; SPAD的降幅与PAR的降幅（r=0.872,p＜0.05）呈显著正相关; LAI的降幅与PAR的降幅（r=0.943,p＜0.05）呈极显著正相关。综上所述,耐热型春玉米品种在灌浆期受高温胁迫时,能够在个体层面保持相对较高的叶绿素含量,在群体层面保持相对较高的叶面积,进而保持了较高的光能截获与利用,削弱了高温对光合的抑制程度,缩小了产量降幅,实现了高产与稳产; 品种的耐热性可以通过其光谱特征（SPAD,LAI和PAR）对高温的响应作为鉴定与评价的主要指标之一,为利用光谱特征研究玉米耐热性提供了依据。     

Crystallization and grain growth characteristics of yttria-stabilized zirconia thin films grown by pulsed laser deposition

Knowledge about the crystallization and grain growth characteristics of metal oxide thin films is essential for effective microstructural engineering by thermal post-annealing and the integration to Si-based miniaturized electroceramic devices. Finite size and interface effects may cause fundamentally different behavior compared to three dimensional macroscopic systems. This work presents a comprehensive investigation of the crystallization kinetics and microstructural evolution upon thermal post-annealing of amorphous 200 nm and 1.2 μm thin films of 8 mol% yttria-stabilized zirconia grown by pulsed laser deposition (PLD) using ex- and in-situ X-ray diffraction, Raman spectroscopy, and electron microscopy techniques. The layers exhibit a remarkably low crystallization temperature of 200-250 °C while exposure to energetic electrons induces the formation of randomly dispersed ~ 20 nm sized crystallites already at ambient temperature. The isothermal amorphous to crystalline phase transformation kinetics can be described quantitatively by the Johnson-Mehl-Avrami-Kolmogorov model. They reveal characteristics of a three dimensional growth under cation bulk diffusion control with heterogeneous nucleation that changes from continuous to instantaneous initial seeding at temperatures above 300 °C. Large (> 100 nm) equiaxed grains are formed rapidly without a stabilization of transient nanocrystals during the thermally induced phase transformation. A stagnation of normal grain growth resulting in a logarithmic normal size distribution is observed once the average grain dimensions approach the film thickness. The results on the crystallization and grain growth of the PLD-grown YSZ films are evaluated with regards to the fabrication of YSZ solid electrolyte membranes for Si-supported micro solid oxide fuel cells and gas sensors.     

Maxwell–Wagner polarization in grain boundary segregated NiCuZn ferrite

The present work investigates the polarization response in polycrystalline Ni_0.9−yCu_yZn_0.1Fe_1.98O_4−δ (y = 0, 0.1, 0.2, 0.3, 0.4, 0.5) ferrite synthesized by solid–state reaction method. X-ray diffraction analysis confirmed cubic spinel phase formation in the calcined samples. Sintered samples contain a continuous network of CuO-rich segregation along the grain boundaries for y ≥ 0.2. Dielectric spectra showed a relaxation peak for y ≥ 0.2 in the frequency range of 1 kHz–1 MHz. This relaxation has been explained based on Maxwell–Wagner polarization considering two-layer model in connection with two heterogeneous dielectric media.     

A novel approach to accelerate the reaction between Ti and Al

Pure Ti foils and SiCp/Al composite foils were employed to investigate the parabolic growth kinetics of TiAl₃ at 660 °C. Compared with pure Al foils, the introduction of SiC particles significantly refined TiAl₃ grain size by the solid solution of silicon. Corresponding refinement mechanisms were concluded from the perspective of the nucleation of TiAl₃. Micromechanics analysis shows that the fine TiAl₃ grains own a small viscous resistance, and subsequently an improvement in the reaction rate could be achieved. This meaningful law also applies extensively to Ni/Al and Fe/Al systems.     

A theory for grain boundaries with strain-gradient plasticity

In this work, the effect of the material microstructural interface between two materials (i.e., grain boundary in polycrystalls) is adopted into a thermodynamic-based higher order strain gradient plasticity framework. The developed grain boundary flow rule accounts for the energy storage at the grain boundary due to the dislocation pile up as well as energy dissipation caused by the dislocation transfer through the grain boundary. The theory is developed based on the decomposition of the thermodynamic conjugate forces into energetic and dissipative counterparts which provides the constitutive equations to have both energetic and dissipative gradient length scales for the grain and grain boundary. The numerical solution for the proposed framework is also presented here within the finite element context. The material parameters of the gradient framework are also calibrated using an extensive set of micro-scale experimental measurements of thin metal films over a wide range of size and temperature of the samples.     

粮食中磺酰脲类除草剂的UPLC/MS/MS测定方法

建立了多类粮食作物中15种磺酰脲类除草剂的超高效液相色谱-串联质谱联用仪(UPLC/MS/MS)多离子监测(MRM)的多残留检测方法。样品经乙腈提取,乙腈饱和的正己烷液-液分配,石墨化碳氨基小柱净化,采用UPLC-MS/MS(ESI+)测定。方法中各种磺酰脲类除草剂在5～200μg/L浓度范围内线性良好,相关系数在0.9995～0.9999。在5～100μg/kg范围内,平均加标回收率在71.6%～115.3%之间,相对标准偏差不大于15%。各种药物的定量限(S/N≥10)均可达到5μg/kg。该方法可同时满足大豆、大米、玉米等多种粮食中磺酰脲类除草剂的检测需求。     

Microstructure of sintered ND-Fe-Ga-B magnets with Mo and MoS2 addition

The effect of Mo and MoS₂ additions on the magnetic and microstructure properties has been investigated in Nd-Fe-Ga-B sintered magnets. Coercivity can be increased by both the additions, but the MoS₂ addition provides the larger increase per Mo atom for up to 0.6 at.% Mo. Microstructure investigation reveals a new amorphous intergranular Ga rich phase. This phase forms a thin layer in the grain boundaries and leads to a wetting behavior of the grain boundary phase, therefore increasing the coercivity. Molybdenum addition in the form of MoS₂ is found to modify the Nd₂Fe₁₄B phase, rather than form new minority phases, and the coercivity enhancement of the magnet is due to the increased anisotropy field of the hard magnetic phase.     

Thermal stability of grain boundaries in nanocrystalline Zn studied by positron lifetime spectroscopy

Nanocrystalline Zn prepared by compacting nanoparticles with mean grain size about 55 nm at 15 MPa has been studied by positron lifetime spectroscopy. For the bulk Zn sample, the vacancy defect is annealed out at about 350 °C, but for the nanocrystalline Zn sample, the vacancy cluster in grain boundaries is quite difficult to be annealed out even at very high temperature (410 °C). In the grain boundaries of nanocrystalline Zn, the small free volume defect (not larger than divacancy) is dominant according to the high relative intensity for the short positron lifetime (τ₁). The oxide (ZnO) inside the grain boundaries has been found having an effect to hinder the decrease of average positron lifetime (τ_av), which probably indicates that the oxide stabilizes the microstructure of the grain boundaries. This stabilization is very important for the nanocrystalline materials using as radiation resistant materials.