A Study on La_2O_3-Y_2O_3-Mo Secondary Emission Material

Thephenomena ,mechanismandtheapplicationofsecondaryemissionofmanykindsofmaterialshavebeenstudiedsincethesecondaryemissionphenomenawasdiscoveredbyCompellin 1899.Withthedevel opmentofelectronictechnologythephenomenaofsec ondaryemissionhavebeenincreasinglyappliedinmanyfields[1,2 ] ,especiallyinhighpowermagnetrontube .Nowadays ,thecathodesofhighpowermag netrontubeusedinthefieldsofbroadcast,correspon denceandnationaldefensearemainlyBa Wcath odes[3] andsomeTh Wcathodes .However ,Ba Wcathodeishard…     

Thermionic properties of Mo-La203 cathode wires

The recent advances in Mo-La203 thermionie cathode materials were presented. It is shown that Mo-La2O3 catlxxie has better ductility, radioactive pollution-free, excellent thermionic electron-emission properties and lower operating temperature compared with W-ThO2 cathode. At operating temperature 1350- 1400℃, the average saturation current of the Mo-La2O3 cathode is 118 mA, the corresponding average current density is 367 mA/crn2, and the average emission efficiency is 11.8 mA/W. The lifetime of diode is more than 2 000 h when the stable emission current is 80 mA.Moreover, the lifetime of practical 6T51-type triode is more than 1000 h. These advances show that the Mo-La2Ch cathode electron tube is closer to industrv application.     

氧化钨直接碳化SPS原位合成致密WC块体材料

用放电等离子烧结技术将WO3和炭黑的混合粉原位合成为致密的WC块体.研究了合成工艺和配碳量对块体的物相、致密度和显微组织的影响,结果表明:在860℃～1060℃温度范围内,炭能快速地将WO3还原成W,同时发生碳化反应,温度继续升高发生烧结.含碳量低时,块体中有杂相W或W2C,含碳量合适时,块体的物相为纯WC,致密度达到WC的理论密度,晶粒在500nm左右.     

显微成像系统分辨率问题讨论（特邀）

空间分辨率是光学显微成像系统的核心指标,根据光学衍射理论,成像系统的空间分辨率由照明光波长与显微物镜的数值孔径共同决定。而在实际成像过程中,根据不同判据得出的显微成像系统分辨率略有差异,需要根据光源的相干性和被观测目标的结构等特征选择合适的判据来准确计算成像系统分辨率。通过理论分析和数值模拟,给出了不同情况下成像分辨率的计算方法,并对比了在相干光源和非相干光源照明下,对双缝目标和双点目标成像时成像分辨率的差异。     

多晶Ag基带上YBCO超导膜的TFA-MOD制备法

探讨了三氟乙酸盐受热分解(TFA-MOD)方法在多晶织构Ag基片上制备YBCO膜的工艺参数与薄膜的成分和取向、表面形貌及超导电性之间的关系。通过优化工艺参数，在1cm Ag{110}(110)基带上制备了成分单一、纯c-轴取向及较好面内取向的YBCO膜，Tc=90K，,Jc=15000A／cm^2。     

氧化钨/碳SPS原位合成WC硬质合金的XPS研究

以WO3＋14.5%C（质量分数,下同）的混合粉作为原始粉末,采用放电等离子烧结（SPS）在不同温度下烧结保温3 min,直接一步合成致密WC硬质合金.借助于X射线光电子能谱（XPS）分析了合成样品的元素价态变化,探讨了SPS原位合成的过程和机理.结果表明：随着烧结温度的升高,样品中的W元素的价态逐步由氧化态的W＋6,W^＋5,W^＋4过渡到单质W^0＋和碳化物态的W^＋2;而样品中的碳元素价态却逐步由单质碳转变为化合碳,氧化物态的晶格氧强度逐渐降低,以碳氧键存在吸附的氧强度逐渐增强.XPS分析结果表明,在SPS原位合成中,WO3首先被碳还原,并经历了一系列中间钨氧化物状态后得到金属钨,然后金属钨进一步发生碳化反应最终形成WC.     

离心SHS陶瓷衬管铁过渡层的研究

对离心ＳＨＳ（Ｓｅｌｆ－ｐｒｏｐａｔａｔｉｎｇＨｉｇｈ－ｔｅｍｐｅｒａｔｕｒｅ　Ｓｙｎｔｈｅｓｉｓ自蔓延高温合成）陶瓷衬管的铁过渡层组织结构及性能研究发现，铁过渡层与陶瓷层为“抛锚”结合，过渡层与基体层为冶金结合。对铁过渡层进行ＳＥＭ、ＴＥＭ及ＤＥＡＸ分析发现，Ｆｅ层中残存有未分离的陶瓷粒子，具有较高的位错密度及发达的亚晶组织，且发现了少量的索氏体和屈氏体组织，认为这是由于钢基体中的碳渗透到铁层中引起的。这些都是造成铁过渡层硬度较高甚至超过钢基体的原因。     

钨的应用及对振兴我国钨业的几点建议

一、引言钨具有比重高、熔点高、硬度高、强度高、蒸气压低、电阻率低、热膨胀系数小和电子发射性能好等特点。此外,钨耐酸、碱和液态金属的腐蚀。因此,钨在国民经济和     

Fabrication of YBCO films on Ag substrate by TFA-MOD method

Biaxial aligned YBCO films have been successfully deposited on Ag { 110 } (110) textured polycrystalline substrates by metal-organic decomposition (MOD) method using Trifluoroacetate Salt (TFA). The influence of firing temperature and Ag surface defects on phase purity and texture, surface morphology of YBCO films was studied. Holding temperature at 900℃ for 30 rain benefits to improve orientation and connectivity of YBCO films. The surface of YBCO films deposited on unpolished Ag substrate has many holes and stripes, which are parallel to the rolling stripe on Ag substrates. To eliminate the rolling stripe on the Ag surface, Ag substrates were polished prior to films deposition. The film grown on polished Ag substrates has a smooth surface and good connectivity of grains without parallel stripes. The YBCO films have an onset of transition around 90K and critical current densities of 15000 A/cm^2.     

超细镍粉在电磁防护功能材料中的应用

利用化学还原方法获取超细镍粉，将其制备成电磁防护涂料，分别测试30－1000MHz频段范围的屏蔽效能和2－18GHz频段范围的吸波性能。结果显示：在测试范围内，含量为80％的超细镍粉涂料屏蔽性能为－20~-30dB之间，含量为85％的超细镍粉涂料吸波性能为0~-9dB之间。将200目镍粉与超细镍粉以4:1的比例混合制成含量为75％的涂料，测试结果表明：在10kHz-1GHz范围内，屏蔽效能可提高到－30~-40dB之间。扫描电镜分析结果显示：混合镍粉在涂料中的分散性较好，粒度较大的镍粉能起到一定的填充作用，而超细粉又形成了一定的链状结构，增加了导电通路，可以使屏蔽效能增加。