AgSnO2电接触材料熔桥行为的高速摄像研究

本研究以AgSnO₂电接触材料为研究对象,借助高速摄像技术并与电接触试验机组成电接触-高速摄像试验体系,观测电触头对在不同负载条件下熔桥行为的基本特征和规律,并进行定量测量研究,同时通过扫描电镜(SEM)和能谱分析(EDS)对熔桥行为后触头表面的微观结构和元素分布进行分析。结果表明,AgSnO₂触头熔桥演化行为可分为接触区域熔化、熔桥稳定存在和熔桥失稳及断开三个阶段,熔桥和电弧现象可以同时存在,并且存在一定的协同和竞争关系,AgSnO₂触头材料的熔桥尺寸为微米级(0.027-0.295 mm),熔桥直径随电流的增大而增大,熔桥长度随电流的增大而减小,熔桥演化行为过程中熔桥形状依次表现为墩粗型、圆柱型和哑铃型,熔桥行为会改变触头的表面形貌和元素分布。     

新型无银触头材料

采用粉末冶金技术研制了一种新型无银触头材料,该材料的综合性能,如密度、硬度、电阻率、灭弧特性及温度特性与银氧化物触头材料接近.当新型无银触头材料的相对密度与银氧化物触头材料的相对密度相同时,两者电阻率相当,而其硬度高于银氧化物触头材料的;温升和通断能力试验结果表明:所研制的无银触头在许多应用领域中,如在电力机车上可替代银氧化物触头材料.实验表明:该材料的相对密度大于98%,硬度(HB)大于950 MPa,电阻率小于2.78 μΩ·cm.     

C-MoS2-Fe2O3(Fe3O4)纳米润滑剂对无镀铜焊丝导电嘴磨损的影响

针对无镀铜实心焊丝在机器人自动焊接时导电嘴磨损问题,采用机械涂敷法在无镀铜实心焊丝表面制备了C-MoS₂-Fe₂O₃(Fe₃O₄)纳米复合润滑剂,研究了润滑剂配比对导电嘴磨损性能的影响. 结果表明,C-Fe₃O₄涂层的润滑性能优于C-Fe₂O₃涂层的润滑性能,随着涂层中纳米MoS₂含量的升高,导电嘴的抗磨性能增强. 纳米复合润滑剂在焊丝与导电嘴的摩擦界面发生摩擦化学反应形成了保护性的自修复膜,此膜主要由润滑性能优异的FeO,MoS₂,MoO₃组成,避免了焊丝与导电嘴内表面的直接接触,从而减少了导电嘴的磨损. 氧化磨损、磨粒磨损和电弧烧蚀是导电嘴磨损的主要机制.     

Elastic behavior of La0.67Ca0.33MnO3:ZrO2 composites

A series of Colossal Magneto Resistance materials, with compositional formula (1 − x) La_0.67Ca_0.33MnO₃ + xZrO₂ (where x = 0%, 10%, 20%, 40%, 60%, 80%) were prepared by sol–gel technique. When characterized structurally by X-ray diffraction they are found to have cubic structure. After measuring their bulk densities, the ultra sonic longitudinal (V_l) and shear velocities (V_s) were measured at room temperature using the pulse transmission technique. Using the ultrasonic data, the values of Young's and rigidity moduli along with Poisson's ratio and Debye temperatures have been calculated. As the materials are porous, zero porous elastic moduli have also been arrived at using a well-known model. The observed variation of elastic moduli with varying ZrO₂ concentration has been explained qualitatively.     

Investigation of reaction between LiNH2 and H2

The reactions for LiNH₂ under a H₂ and an Ar flow were investigated, respectively. The results showed that LiNH₂ can be converted into LiH and NH₃ by reacting with H₂ under a H₂ flow condition, whereas LiNH₂ is converted into Li₂NH and NH₃ by decomposition under an Ar flow. Moreover, the reaction between LiNH₂ and H₂ can be accelerated by mixing LiNH₂ with LiH as well as doping LiNH₂ with TiCl₃. The confirmation of reaction between LiNH₂ and H₂ is helpful for the deeper insight in the systems of Li–N–H and Li–Mg–N–H for hydrogen storage materials.     

Remarkable improvement of hydrogen sorption kinetics in magnesium catalyzed with Nb2O5

Kinetics of hydrogen absorption and desorption reactions was investigated on the MgH₂ composite doped with 1 mol% Nb₂O₅ as a catalyst by ballmilling. The composite after dehydrogenation at 200 °C absorbed gaseous hydrogen of 4.5 mass% even at room temperature under lower pressure than 1 MPa within 15 s and finally its capacity reached more than 5 mass%. On the other hand, the catalyzed MgH₂ after rehydrogenation desorbed 6 mass% hydrogen at 160 °C under purified He flow, which followed the first order reaction. From the Kissinger plot, the activation energy for hydrogen desorption was estimated to be 71 kJ/mol H₂, indicating the product was significantly activated due to the catalytic effect of Nb₂O₅.     

Competing interactions and dimensional crossover in (Er0.5Y0.5)2Cu2O5 studied by EPR

Copper spin dynamics in (Er_0.5Y_0.5)₂Cu₂O₅ solid solution has been investigated by electron paramagnetic resonance (EPR) technique. The temperature dependence of the EPR integrated intensity of the resonance line has showed a pronounced maximum at low temperatures and has vanished at the transition to the antiferromagnetic ordering at T_N = 11 K. The temperature at which the EPR integrated intensity reaches maximum was different for the heating and cooling runs. Study of the product of integrated intensity and temperature has allowed determination of the dominating interactions in a particular temperature range. A model used previously to describe the AFM modes in the antiferromagnetic state of Y₂Cu₂O₅ was applied to explain the observed changes in the EPR spectra. A dimensional crossover from 2D to 3D magnetic behaviour was observed at 55 K and interpreted in terms of the spin correlation length.     

表面修饰对AgSnO2触头材料组织性能的影响

研究了表面修饰对AgSnO2触头材料的组织和性能的影响。考察了分散剂聚乙二醇对纳米SnO2溶胶的表面修饰作用;分析了化学镀的工艺对纳米掺杂AgSnO2电触头材料性能的影响。结果表明：采用分散剂和化学镀对纳米SnO2表面进行修饰,减少了纳米SnO2的硬团聚,改善了Ag与SnO2之间的浸润性和相容性,使AgSnO2触头材料的电导率提高23％,抗拉强度提高66％,伸长率提高100％,解决了AgSnO2材料的机加工性能差的问题。     

Preparation of nanosized sodium-aluminum tungstate, NaAl(WO4)2

Investigations are carried out for preparing nanosized pure phase of NaAl(WO₄)₂ by means of solid state synthesis with mechanical activation, applying the sol-gel method (Pechini) and by co-precipitation. It is shown that it is not possible to obtain pure phase when the initial substances are in stoichiometric amounts due to the simultaneous formation of a number of accompanying tungstate phases. The reasons for their origin are discussed. A method is demonstrated for obtaining a pure phase of NaAl(WO₄)₂ by co-precipitation of aqueous Na₂WO₄ and Al(NO₃)₃ solutions with considerable excess of Na₂WO₄. It is proved that NaAl(WO₄)₂ with particle size 40-80 nm is obtained with final synthesis of the powders at temperature 600-650 °C and duration of thermal treatment of 1-2 h.     

Arc erosion behavior of a nanocomposite W-Cu electrical contact material

The erosion behavior of a nanocomposite W-Cu material under arc breakdown was investigated. The arc erosion rates of the material were determined, and the eroded surfaces and arc erosion mechanisms were studied by scanning electron microscopy. It is concluded that the nanocomposite W-Cu electrical contact material shows a characteristic of spreading arcs. The arc breakdown of a commercially used W-Cu alloy was limited in a few areas, and its average arc erosion rate is twice as large as that of the former. Furthermore, it is also proved that the arc extinction ability and arc stability of the nanocomposite W-Cu material are excellent, and melting is the major failure modality in the make-and-break operation of arcs.     

Sm0.5Sr0.5CoO3 cathode material from glycine-nitrate process: Formation, characterization, and application in LaGaO3-based solid oxide fuel cells

Cathode material Sm_0.5Sr_0.5CoO₃ (SSC) with perovskite structure for intermediate temperature solid oxide fuel cell was synthesized using glycine-nitrate process (GNP). The phase evolution and the properties of Sm_0.5Sr_0.5CoO₃ were investigated. The single cell performance was also tested using La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) as electrolyte and SSC as cathode. The results show that the formation of perovskite phase from synthesized precursor obtained by GNP begins at a calcining temperature of 600 °C. The single perovskite phase is formed completely after sintering at a temperature of 1000 °C. The phase formation temperature for SSC with complete single perovskite phase is from 1000 to 1100 °C. The SrSm₂O₄ phase appeared in the sample sintered at 1200 °C. It is also found that the sample sintered at 1200 °C has a higher conductivity. The electrical conductivity of sample is higher than 1000 S/cm at all temperature examined from 250 to 850 °C, and the highest conductivity reaches 2514 S/cm at 250 °C. The thermal expansion coefficient of sample SSC is 22.8 × 10⁻⁶ K⁻¹ from 30 to 1000 °C in air. The maximum output power density of LSGM electrolyte single cell attains 222 and 293 mW/cm² at 800 and 850 °C, respectively.     

Hydriding/dehydriding behavior of Mg2CoH5 produced by reactive mechanical milling

Complex Mg₂CoH₅ hydride was obtained by a combined procedure that included a milling stage of a 2Mg–Co mixture under argon followed by reactive mechanical alloying (RMA) under hydrogen, both at room temperature. During RMA, MgH₂ is produced at short milling times (10 h) and Mg₂CoH₅ (50 wt%) after 90 h. Improvement in the yield and the formation times could be associated with both refinement of microstructure and enhancement of intermixing of Mg–Co during pre-milling stage. DSC studies of Mg₂CoH₅ phase produced by RMA show that the starting decomposition temperature is about 205 °C.Absorption and desorption PCIs were determined under static (300 °C) and dynamic (230–330 °C) conditions. An important hysteresis and two plateaus were observed and correlated with formation/decomposition of Mg₂CoH₅ (high-pressure plateau) and Mg₆Co₂H₁₁ (low-pressure plateau) hydrides. For comparing hydrogen sorption kinetics, Mg₂CoH₅ (65 wt%) was also obtained by a sintering method at 410 °C and 6.0 MPa of hydrogen pressure. Absorption was very fast in the temperature range of 150–350 °C, independently of synthesis procedure. However, desorption curves showed a better behavior for RMA powders.MgCo was observed after decomposition of Mg₂CoH₅ under particular thermal treatments, while MgCo₂ phase was not detected. The results of this study reinforce the idea that kinetics factors related with atomic mobility play a key role in the formation of Mg–Co intermetallics.     

Mn3O4 doped with nano-NaBiO3: A high capacity cathode material for alkaline secondary batteries

In this paper we report a novel Mn₃O₄ electrode doped with nano-NaBiO₃. It is demonstrated that doping with nano-NaBiO₃ alters the electrochemical inertia of Mn₃O₄, converting it into a rechargeable secondary alkaline cathode material that exhibits highly efficient charge/discharge properties. While a pure Mn₃O₄ electrode can barely maintain a single charge and discharge cycle, the cycling capacity of the Mn₃O₄ electrode doped with nano-NaBiO₃ can reach and become stable at 372 mAh g⁻¹ under 60 mA g⁻¹. The doped cathode can also maintain a cycling capacity of 261 mAh g⁻¹ while holding a 95.3% reversible capacity after 60 cycles at a high rate of 500 mA g⁻¹. Moreover, the experimental results indicate that charging time for an alkaline battery using doped Mn₃O₄ cathode could possibly shorten to as little as 30 min.     

掺杂对WCu电触头材料电弧特性的影响

利用粉末冶金技术制备出分别掺杂0.3%B、2.0%Nb和1.5%Ce (质量分数)的WCu电触头材料,采用高速摄影技术和抗电弧烧蚀实验探讨不同掺杂元素对钨铜电触头材料电弧特性的影响.结果表明:真空击穿时,WCu电触头材料的电弧演化过程可以分为起弧、稳定燃烧和灭弧3个阶段;掺杂0.3%B、2.0%Nb和1.5%Ce的WCu电触头材料的电弧寿命比未掺杂的长,截流值小;等离子云体积大,颜色浅,在样品表面燃烧区域大,电弧分散,燃弧能量分散;电弧燃烧稳定,无放射状光芒.含有掺杂元素的WCu电触头材料的抗电弧烧蚀性能均得到明显改善;其中最明显的为WCu-B电触头材料,其抗烧蚀性能提高了近30%.     

Dielectric dispersion in Li2O–MoO3–B2O3 glass system doped with V2O5

Li₂O–MoO₃–B₂O₃ glasses containing different amounts of V₂O₅, ranging from 0 to 1.5 mol%, were prepared. The dielectric properties (viz., constant ′, loss tan δ, AC conductivity σ_ac over a wide range of frequency and temperature) have been studied as a function of the concentration of vanadium ions. The variation of AC conductivity with the concentration of V₂O₅ passes through a maximum at 0.8 mol% V₂O₅. In the high-temperature region, the AC conduction seems to be connected with the mixed conduction, viz., electronic and ionic conduction. The dielectric relaxation effects exhibited by these glasses have been analyzed quantitatively by pseudo Cole–Cole plot method and the spreading of relaxation times has been established. Further analysis of these results has been carried out with the aid of the data on ESR, IR and optical absorption spectra.     

Electrochemical performances of Ag–(Bi2O3)0.75(Y2O3)0.25 composite cathodes

The electrochemical performances of Ag–Y_0.25Bi_0.75O_1.5 (YSB) composite cathodes on Ce_0.8Sm_0.2O_1.9 (SDC) electrolytes have been investigated at intermediate temperature using AC impedance spectroscopy. The results indicated that the electrochemical performances of these composites are quite sensitive to the compositions and the microstructures of the cathode. The optimum YSB addition to Ag resulted in 10 times lower area specific resistance. The ASR of Ag-50 vol.% YSB was about 0.12 Ωcm² at 700 °C as compared to 3.9 Ωcm² for Ag cathodes. The observed high performance of Ag–YSB composite cathodes might be due to the high oxygen-ion conductivity of YSB and its high catalytic activity for oxygen reduction.     

Structure and electrochemical performance of FeF3/V2O5 composite cathode material for lithium-ion battery

Orthorhombic structure FeF₃ was synthesized by a liquid-phase method using FeCl₃, NaOH and HF solution as starting materials, and the FeF₃/V₂O₅ composites were prepared by milling the mixture of as-prepared FeF₃ and the conductive V₂O₅ powder. The properties of FeF₃/V₂O₅ composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge/discharge and cyclic voltammetry measurements. Results showed that the FeF₃/V₂O₅ composites can be used as cathode material for lithium-ion battery. Electrochemical measurements in a voltage range of 2.0–4.5 V reveal that the addition of conductive V₂O₅ improves significantly the electrochemical performance of FeF₃, and the FeF₃/V₂O₅ composite prepared by milling for 3 h exhibits high discharge capacity and good cycle performance, and its discharge capacity maintains about 209 mAh g⁻¹ at 0.1 C (23.7 mA g⁻¹) after 30 cycles.     

Improvement in hydrogen sorption properties of Mg by reactive mechanical grinding with Cr2O3, Al2O3 and CeO2

We tried to improve the hydrogen sorption properties of Mg by mechanical grinding under H₂ (reactive mechanical grinding) with oxides Cr₂O₃, Al₂O₃ and CeO₂. The hydriding rates of Mg are reportedly controlled by the diffusion of hydrogen through a growing Mg hydride layer. The added oxides can help pulverization of Mg during mechanical grinding. A part of Mg is transformed into MgH₂ during reactive mechanical grinding. The Mg+10wt.%Cr₂O₃ powder has the largest transformed fraction 0.215, followed in order by Mg+10wt.%CeO₂ and Mg+10wt.%Al₂O₃. The Mg+10wt.%Cr₂O₃ powder has the largest hydriding rates at the first and fifth hydriding cycle, followed in order by Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. Mg+10wt.%Cr₂O₃ absorbs 5.87wt.% H at 573 K, 11 bar H₂ during 60 min at the first cycle. The Mg+10wt.%Cr₂O₃ powder has the largest dehydriding rates at the first and fifth dehydriding cycle, followed by Mg+10wt.%CeO₂ and Mg+10wt.%Al₂O₃. It desorbs 4.44 wt.% H at 573 K, 0.5 bar H₂ during 60 min at the first cycle. All the samples absorb and desorb less hydrogen at the fifth cycle than at the first cycle. It is considered that this results from the agglomeration of the particles during hydriding–dehydriding cycling. The average particle sizes of the as-milled and cycled powders increase in the order of Mg+10wt.%Cr₂O₃, Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. The quantities of hydrogen absorbed or desorbed for 1 h for the first and fifth cycles decrease in the order of Mg+10wt.%Cr₂O₃, Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. The quantities of absorbed or desorbed hydrogen increase as the average particle sizes decrease. As the particle size decreases, the diffusion distance shortens. This leads to the larger hydriding and dehydriding rates. The Cr₂O₃ in the Mg+10wt.%Cr₂O₃ powder is reduced after hydriding–dehydriding cycling. The much larger chemical affinity of Mg than Cr for oxygen leads to a reduction of Cr₂O₃ after cycling.     

Tetragonal-cubic phase boundary in nanocrystalline ZrO2-Y2O3 solid solutions synthesized by gel-combustion

By means of synchrotron X-ray powder diffraction (SXPD) and Raman spectroscopy, we have detected, in a series of nanocrystalline and compositionally homogeneous ZrO₂-Y₂O₃ solid solutions, the presence at room temperature of three different phases depending on Y₂O₃ content, namely two tetragonal forms and the cubic phase. The studied materials, with average crystallite sizes within the range 7-10 nm, were synthesized by a nitrate-citrate gel-combustion process. The crystal structure of these phases was also investigated by SXPD. The results presented here indicate that the studied nanocrystalline ZrO₂-Y₂O₃ solid solutions exhibit the same phases reported in the literature for compositionally homogeneous materials containing larger (micro)crystals. The compositional boundaries between both tetragonal forms and between tetragonal and cubic phases were also determined.     

固相-水热法制备LiFePO4-Li3V2（PO4）3复合材料及其电化学性能（英文）

分别采用固相-水热法和球磨法制备磷酸亚铁锂-磷酸钒锂复合正极材料(LiFePO4-Li3V2(PO4)3)。电化学性能测试表明,LiFePO4-Li3V2(PO4)3复合正极材料的电化学性能远远高于 LiFePO4和 Li3V2(PO4)3单独作为正极材料的性能,并且以固相-水热法制备的复合材料性能优于以球磨法制得的复合材料。研究发现 LiFePO4-Li3V2(PO4)3复合材料有 4 个氧化还原峰,相当于 LiFePO4 和 Li3V2(PO4)3 氧化还原峰的叠加。采用固相-水热法制备的LiFePO4-Li3V2(PO4)3 复合材料形貌较为规则,且有新相物质产生,这是导致其电化学性能较好的原因。