微波烧结法制备含钪扩散阴极及其发射性能研究

采用溶胶凝胶结合氢还原法制备出Sc均匀掺杂的钨粉,随后采用微波烧结法成功制备出浸渍型含钪扩散阴极。对Sc掺杂钨粉特性、Sc掺杂钨海绵基体微观结构、阴极发射性能和阴极表面活性物质分布进行了分析,结果显示:Sc以Sc2O3的形态均匀分布于平均粒径1μm的钨粉中,海绵体骨架主要由大小均匀的亚微米级准球形颗粒构成,表面孔结构良好,孔分布均匀,平均孔径在0.46μm左右,Sc_2O_3均匀分布于基体之中。电子发射测试结果表明,该阴极950℃b时脉冲偏离点电流密度Jdiv为137.59 A/cm~2,发射斜率1.431。激活后的阴极表面Ba:Sc:O的原子比例为1.8:1:2.2,同时阴极表面存在大量的纳米粒子,对阴极发射有促进作用。     

粒度调控对钨阴极表面发射微区的影响

为了在微米尺度探究未分级钨粉、分级钨粉制备钨基体在阴极热电子发射性能上的差异,深入了解阴极表面微区电子发射过程和阴极发射机理,本文采用新型深紫外激光发射电子显微镜/热发射电子显微镜系统（DUV-PEEM/TEEM）对两种钨粉制备的阴极表面进行了光电子、热电子成像分析。结果显示,与未分级钨粉相比,分级钨粉制备钨基体的显微组织更加均匀,且闭孔率由1.44%降至0.47%;光电子+热电子联合成像精确得出两种阴极的发射均主要集中于孔隙及孔隙中的活性物质上;通过热电子图像对比及分析,分级钨粉制备阴极的热电子发射微区面积更大、分布更均匀;且在1050℃工作条件下,分级钨粉制备阴极的脉冲电流密度为30.79A/cm2,发射斜率为1.38;综合分析显示其具备更理想的本征热电子发射能力和发射均匀性,这对于了解阴极发射性能及改善热阴极制备工艺有一定的指导作用。     

钪系阴极基体的研究

采用氧化钪与钨机械混合、氧化钨与钪盐水溶液固液掺杂法制备了氧化钪-钨基体，采用扫描电镜及原位俄歇电子能谱方法研究了基体中钪的分布及阴极基体的抗离子轰击性能。结果表明，采用液固法制备的烧结体，氧化钪分布均匀，这样的结构有利于钪的扩散和补充，原位俄歇轰击实验结果表明，阴极基体具有良好的耐高温和耐离子轰击性。     

氧化钪混合钨基扩散型阴极表面结构的研究

采用XRD、SEM和AES等分析方法对氧化钪混合钨基及浸渍后的阴极微观结构及表面活性元素的行为进行研究.结果表明:基体内Sc_2O_3弥散均匀分布.在阴极激活过程中,Ba和Sc从内部向表面扩散,在阴极表面形成含Ba、Sc、O的表面活性层,其厚度为M型阴极活性层厚度的10倍以上.对自由钪的产生机制进行了探讨.     

Y2O3含量对Y-Gd-Hf-O直热式压制阴极发射性能的研究

为了提高Y-Gd-Hf-O压制式高温阴极的热发射性能,制备了Y2O3/HfO2摩尔比不同的S2O3掺杂Y-Gd-Hf-O直热式压制阴极。测试结果显示,当比值为5/2时,热发射能力最好,1500 ℃下发射电流为2.79 A/cm2。阴极支取直流发射电流密度1.0 A/cm2,在1500 ℃的工作温度下,已经稳定工作了1320 h,并在该温度下经过696 h的10 W连续电子轰击后,发射电流仍保持为初始值的86%,表现出良好的耐电子轰击能力。XPS结合深度刻蚀表明,发射活性层主要集中在距表面50 nm深度范围内。表层SEM、EDS分析表明,阴极经过激活、老炼,活性物质粒径变大,Y/Hf原子比低于初始值,且随着Y2O3含量的提高,阴极表层n型半导体Y2O3-x的含量相应地增加,对改善阴极表面的导电性、降低逸出功和提高阴极的热发射性能有促进作用     

复合稀土钼材料次级发射性能

利用溶胶-凝胶法制备稀土氧化物掺杂钼粉,随后利用放电等离子体烧结法将该粉末制备成稀土钼金属陶瓷材料,利用SEM、DTA、电子发射性能测试等方法对样品次级电子发射性能进行研究.结果表明:稀土氧化物均匀掺杂和组织的细化有利于材料发射性能提高,但不能降低其激活温度;经过高温氢气处理,样品的真空激活温度大幅降低,发射系数提高;稀土氧化物易吸收水分和气体的特性导致后续真空激活过程中阴极表层钼氧化,而高温氢气处理消除了样品中多余的水分和气体,保持了样品中金属与氧化物的相间分布状态,这是样品在活化前后发射性能发生变化的主要原因.     

Y2O3-Gd2O3-HfO2掺杂W基直热式阴极热发射及耐电子轰击特性研究

为了提高大功率磁控管阴极的耐电子轰击性能,首次采用Y2O3-Gd2O3-HfO2(Y-Gd-Hf-O)掺杂金属W粉制备大功率磁控管用直热式阴极。对不同质量百分比(wt%)Y-Gd-Hf-O掺杂W基直热式阴极的热发射及耐电子轰击特性进行了研究。实验结果显示,50 wt% Y-Gd-Hf-O掺杂W基直热式阴极具有较大的热发射能力,1500 ℃工作温度下即可提供1.0 A/cm2的拐点发射电流密度。10 wt% Y-Gd-Hf-O掺杂W基直热式阴极具有较好的耐电子轰击性能,经过14 W/cm2电子连续轰击200 h后,热发射电流密度仅下降0.1 A/cm2。最后,对Y-Gd-Hf-O掺杂W基直热式阴极热发射及耐电子轰击机理进行了有益的探讨。     

低温烧结孔隙度可控多孔钨

多孔钨作高电流密度阴极是钨的重要应用之一,它的多孔骨架是储备式阴极至关重要的部分.骨架中要浸渍电子发射化合物,这种化合物每从表面发射一次以后应立即有新的材料通过开孔孔道喂入表面孔隙,这就要求孔隙度十分均匀.     

用离子束控制材料电子发射性能及应用

研究了用离子束技术控制材料表面电子发射性能的方法，报告这一技术在抑制行波管栅极电子发射、制备场发射平板显示器阴极及改善生物医学材料凝血性能等方面的应用及结果。     

Effect of Oxide Particle Size on Electron Emission and Vacuum Arc Characteristic of Mo-La2O3 Cathode

采用高能球磨及热压烧结工艺制备了Mo-4%（质量分数,下同）La2O3纳米复合的阴极材料,其中La2O3的颗粒尺寸小于100 nm;作为比较,商业W-4% ThO2阴极材料中的ThO2颗粒尺寸为1~2 μm。Mo-La2O3纳米阴极材料的平均真空起始电场强度为2.97×107 V/m,比商业W-ThO2阴极材料低62.7%。纳米复合的Mo-La2O3阴极材料具有优异的电子发射性能,其电子发射点的分布面积和密度明显大于商业W-ThO2阴极材料。氧化物的颗粒尺寸对于阴极材料的电子发射性能以及真空电弧特性有显著的影响。随着La2O3颗粒尺寸的减小,Mo-La2O3阴极材料的电子发射性能提高。当La2O3的颗粒尺寸减小到小于100 nm时,Mo-La2O3 阴极材料的电子发射面积和能力显著增加。纳米复合Mo-La2O3阴极材料电子发射性能的增强归因于在相界面上形成了高的内电场和空间电荷区。     

镀铂栅极抑制电子发射性能研究

利用离子束辅助沉积（IBAD）方法在Mo栅极表面上沉积Pt膜，采用试验二极管方法测量和比较阴极活性物质Ba，BaO蒸发到镀铂栅极和纯钼栅极表面上后的电子发射性能。采用XRD，EDX，XPS等测试手段对其栅极表面进行对比分析和表征。实验结果表明：镀铂栅极具有明显的抑制电子发射性能，并初步探讨了离子束辅助沉积Pt膜抑制栅电子发射的机理。     

Evaluation of frictional characteristic for Zinc-coated steel sheet

Draw bead simulator (DBS) tests were performed to investigate the friction behaviors of various zinc-coated steel sheets. The friction of the coated steel sheet was evaluated by the ratio of drawing force for the coated steel sheet, T_c, to that for the uncoated steel sheet, T_s. The drawing force ratio, T_c/T_s, was compared with the coefficient of friction measured from Nine’s DBS test. It is clear that the drawing force ratio can be used as a convenient parameter to evaluate the friction of a coated steel sheet compared to the coefficient of friction. Due to the simplicity of the test procedure, this evaluation method is a useful for assessing the stamping formability of the coated steel sheet with respect to the friction behavior and also to investigate the lubricity of the stamping lubricant.     

Modification of Parylene film-coated glass with TiO2 nanoparticles and its photocatalytic properties

A titania film was deposited on Parylene-coated glass by a one-step, ultrasound-assisted procedure. The TiO₂ nanoparticles formed during the sonochemical hydrolysis of Ti(i-OPr)₄ were thrown to the surface and strongly attached to the Parylene substrate. By using different solvents (water, ethanol or their mixture) and reagent concentrations, the thickness, uniformity and crystallinity of the deposited layer were regulated. PVP was used to stabilize the highly homogeneous distribution of TiO₂ nanocrystals on the Parylene surface. The morphology and structure of the coated films were characterized by physical and chemical methods such as: X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), Rutherford backscattering spectrometry (RBS), and optical spectroscopy. The photocatalytic activity of the titania-modified Parylene film in the photo discoloration of methylene blue was demonstrated. The experimental results revealed a correlation between the uniformity of the nanostructured anatase titania film and its photocatalytic properties.     

等离子体球化处理和放电等离子烧结制备钡钨阴极多孔钨基体

采用等离子体球化处理和放电等离子烧结(SPS)相结合的方法制备了钡钨阴极多孔钨基体。研究了等离子体球化处理工艺参数对钨粉的球化率和性能的影响规律,以及SPS制备的多孔钨基体的微观组织和相应钡钨阴极的发射性能。结果表明:当喂粉速率和载气流量分别为2.4 g/min和4.0 L/min时,可得到球化率大于98%,且表面光滑、球形度高的球形钨粉;经球化处理后,钨粉的松装密度和流动性显著提高。与原料钨粉相比,采用球形钨粉制备得到的多孔钨基体的孔隙结构和分布均得到显著改善,且开孔率由18.3%提高至19.7%;相应的钡钨阴极在1050℃下的饱和脉冲发射电流密度由8.7 A/cm~2提高至11.2 A/cm~2。     

Electrochemical synthesis of polypyrrole films over each of well-aligned carbon nanotubes

Polypyrrole (PPy) films were uniformly electropolymerized over each carbon nanotube of the well-aligned carbon nanotube arrays. For comparison, PPy films were also coated on flat metallic titanium (Ti) and platinum (Pt) substrates by the same technique. The synthesis and the redox performance of the PPy films were conducted by cyclic voltammetry (CV). The structural characterization including the thickness and uniformity of the PPy films was carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is observed that the coating of the PPy film over carbon nanotubes is much faster than that on flat Ti/Pt surface. Furthermore, the redox performance of the PPy-coated carbon nanotube electrodes over flat Ti/Pt electrodes was significantly improved due to the high accessible surface area of the carbon nanotubes in the aligned arrays, especially in large film formation charge (Q_film). It is very promising that the electrode developed in this study could be used as high performance electrode in rechargeable batteries.     

Spatially resolved Langmuir probe measurements of a magnetically enhanced hollow cathode arc plasma

Hollow cathode arc discharges are efficient plasma sources and are applied in substrate pretreatment or plasma-activated deposition processes. In order to generate large volume homogeneous plasmas to guarantee uniformity of plasma activation and coating properties, in the presented configuration a ring-shaped anode is positioned coaxially around the hollow cathode tube. A magnetic field is applied, which is axial within the cathode tube and spreads out in the deposition chamber. In order to characterize the hollow cathode plasma, spatially resolved Langmuir probe measurements have been carried out. The charge carrier density maximum on the cathode tube axis reaches values up to 10¹³ cm^? 3. With increasing distance from the plasma source, the plasma density decreases and shows a smoother lateral profile. Maxwellian electron energy distribution functions are observed with spatially homogeneous electron temperatures in the range 1–4 eV. Increasing the chamber pressure leads to higher plasma densities and lower electron temperatures. Reduction of the gas flow through the hollow cathode tube results in a strong rise of the plasma density over two orders of magnitude. The magnetic field supports the low gas flow mode and leads to higher plasma densities, too. The results of the Langmuir probe measurements are discussed by means of the active zone model and are further related to optical emission measurements performed in the vicinity of the hollow cathode orifice.     

第二相粒子大小对Mo-La2O3阴极电子发射性能的影响

利用溶胶-凝胶、氢气还原及热压工艺制备了纳米复合Mo-4La2O3（质量分数,%）阴极材料,其显微组织中La2O3粒径小于100 nm,而常规Mo-4La2O3阴极中La2O3粒径为200~300 nm。在真空击穿实验中发现La2O3粒径对于阴极电子发射性能有显著的影响,纳米复合阴极的电子发射能力远高于常规阴极的发射能力,其电子发射点遍布整个阴极表面,而常规阴极电子发射点只是集中在一小块区域。通过建立金属-半导体电子相互作用模型,计算并绘制了Mo及La2O3中电子隧穿几率随La2O3粒径变化的关系曲线,解释了纳米复合阴极电子发射能力强的原因。     

Novel model for film growth based on surface temperature developing during magnetron sputtering

New physical phenomenon consisting in development of the surface temperature T_surf, which being equal to the substrate temperature T_s at the beginning of deposition, steeply increases and becomes several times higher than T_s at the end of the process, is revealed by means of IR-camera and new calorimetric method during sputter deposition of metal films. The reason for the phenomenon is the formation of a liquid-like layer on the growth surface with extremely low (∼10⁹ times lower than for metals) thermal conductivity. Variation in the film structure along thickness correlates with the variation in T_surf. To explain these effects we developed a model according to which film grows by “gas → liquid → solid” rather than “gas → solid” mechanism which is realized provided that the film grows from energetic atoms.     

造粒炭黑质量分数对Cu-Fe摩擦材料性能的影响

采用干压擦筛造粒法制备了炭黑造粒颗粒,研究了炭黑造粒颗粒质量分数对Cu-Fe摩擦材料显微组织、力学性能、摩擦性能的影响。结果表明：炭黑造粒颗粒易被压制成条状形态,当炭黑造粒颗粒质量分数较低时,其与金属基体能形成完整的界面,而含量较高时界面易出现孔洞和裂纹;随着炭黑造粒颗粒质量分数的增加,摩擦材料的力学性能先增加后降低、摩擦系数和磨损量均先降低后增加。当炭黑造粒颗粒质量百分数为5%时,摩擦材料的力学性能最大,摩擦系数最低,磨损量最小,材料的综合性能最佳。     

Field emission enhancement of ZnO nanorod arrays with hafnium nitride coating

Vertically well-aligned single crystal ZnO nanorod arrays were synthesized and enhanced field electron emission was achieved with hafnium nitride (HfN_x) coating under proper sputtering condition. HfN_x films with various composition have been coated on ZnO nanorod arrays using a reactive direct current (DC) magnetron sputtering system. Morphology and crystal configuration of the ZnO nanorod arrays were investigated by scanning electron microscopy and X-ray diffraction. The field emission properties of the coated and uncoated ZnO nanorod arrays were characterized. The as-grown ZnO nanorod arrays showed a turn-on electric field of 6.60 V μm^− 1 at a current density of 10 μA cm^− 2 and an emission current density of 1 mA cm^− 2 under the field of 9.32 V μm^− 1. While the turn-on electric field of the coated ZnO nanorod arrays sharply decreased to 2.42 V μm^− 1, an emission current density of 1 mA cm^− 2 under the field of only 4.30 V μm^− 1 can be obtained. A method to accurately measure the work function of the coated films was demonstrated.