单晶六硼化镧的制备及主要应用

六硼化镧（LaB6）是一种理想的阴极材料。介绍了LaB6单晶的制备方法及晶体结构特征，讨论了LaB6晶体在摘要热阴极和场发射阵列阴极方面的性能及应用情况。     

LaB6热阴极陶瓷材料的研究进展

简要介绍了目前LaB6材料的研究现状及其用途，综述了国内外LaB6陶瓷粉末、多晶体、单晶体的制备工艺，并展望了LaB6材料的发展前景。     

LaB6薄膜的制备工艺研究

分别用电子束蒸发和电泳的方法在不同的衬底上制备出了LaB6薄膜,用扫描电镜（SEM）对样品表面形貌进行了分析,同时利用x射线衍射（XRD）分析了成膜参数衬底温度以及退火处理对LaB6薄膜结晶性能的影响。结果表明,所得样品为LaB6多晶薄膜,合适的衬底温度和退火处理能够提高LaB6薄膜的结晶质量。并对两种成膜方式进行了比较。     

Field ion microscopic observations of LaB6 on tungsten

The importance of field ion microscopy as a unique surface microscopic technique has been pointed out with particular reference to the lanthanum hexaboride (LaB₆)-deposited refractory metal cathodes. In the core, field ion microscopic observations of LaB₆ deposited tungsten are described. The observations are discussed in relation to the field electron emission microscopy of LaB₆/W system. The paper ends with a few comments on the scope of further study of this or a similar system using the field ion microscopy and the atom probe field ion microscope.     

Synthesis of LaB6- and NbB2-Based Eutectic Structures via Carboborothermic Reduction of a Hydroxide Mixture

Inorganic Materials - A powder mixture of eutectic composition in the LaB6–NbB2 system has been prepared by carboborothermic reduction of a La(OH)3 + NbO0.5–2(OH)4–1 hydroxide...     

LaB6单晶体制备方法的特点和进展

综述了LaB6单晶体的国内外研究现状及进展.分别对铝熔剂法、气相沉积法、熔盐电解法、区域熔化法等几种主要的LaB6单晶体制备方法的特点进行了简要的总结和分析.在4种主要的制备方法中,区域熔化法生产效率高,适于制备大尺寸LaB6单晶阴极,且制备的LaB6单晶体纯度高、质量高.     

A new route for the synthesis of submicron-sized LaB6

Submicron crystalline LaB₆ has been successfully synthesized by a solid-state reaction of La₂O₃ with NaBH₄ at 1200 °C. The effects of reaction temperature on the crystal structure, grain size and morphology were investigated by X-ray diffraction, scanning electron microscope and transmission electron microscope. It is found that when the reaction temperature is in the range of 1000–1100 °C, there are ultrafine nanoparticles and nanocrystals that coexist. When the reaction temperature elevated to 1200 °C, the grain morphology transformed from ultrafine nanoparticle to submicron crystals completely. High resolution transmission electron microscope images fully confirm the formation of LaB₆ cubic structure.     

LaB6功能陶瓷材料的研究现状

综述了目前办内外ＬａＢ６功能陶瓷材料的研究概况及应用,综合了制备ＬａＢ粉末,多晶、单晶的各种工艺。     

Point-contact spectroscopy of the electron-phonon interaction in single-crystal LaB6

Point-contact spectra of single-crystal LaB₆ are obtained, yielding the energy positions of all the phonon modes up to 160 meV. A relatively strong anisotropy of the spectra is observed. It is related to the anisotropy of the phonon system. The point-contact electron-phonon interaction function and the point-contact electron-phonon interaction parameter are compared with published calculated data and a qualitative agreement is found. From the measured spectra the temperature dependence of the LaB₆ electrical resistivity and heat capacity are calculated.     

高纯多晶LaB6纳米块体阴极材料的制备及表征

采用放电等离子烧结技术, 以氢直流电弧法制备的La-LaH₂纳米粉末为原料, 制备了高纯LaB₆多晶纳米块体热阴极材料. 系统研究了LaH₂的脱氢反应、SPS合成LaB₆的烧结反应式, 并用XRD、SEM、TEM和AFM对LaB₆烧结块体的相与结构进行了表征. 实验结果表明, LaH2在796.4℃时发生脱氢反应; SPS制备得到了单相LaB₆纳米多晶块体, 纯度达到99.867%, 相对密度达到99.2%, 和其他烧结方法相比, 样品显微硬度及抗弯强度等性能显著提高. 晶体为大小均匀, 形态规则完整的等轴晶, 50MPa, 烧结温度1250～1350℃范围内平均晶粒尺寸为120nm, 随烧结温度的升高, 晶粒尺寸逐渐增大.     

Study of mechanical properties of LaB6 single crystal by nanoindentation

The nanoindentation has been used to study a specificity of the elastoplastic transition in a lanthanum hexaboride single crystal during the localization of the deformation in a submicron region both with a low (cleavage) and high (mechanical polishing) dislocation density in a sample. An abrupt elastoplastic pop-in due to a homogeneous nucleation of dislocations in the contact region in shear stresses close to the theoretical shear strength of LaB₆ in value has been observed in testing the single crystal cleavage on the (001) plane. On mechanical polishing the elastoplastic pop-in during the indentation has been smoothed because of the motion and multiplication of dislocations already existing in the contact region. An increase of the hardness by 5 GPa in an imprint depth of 120 nm has been caused by the deformation hardening of the sample surface.     

LaB6 and TiB2 electrodes for the alkali metal thermoelectric converter

LaB₆ and TiB₂ electrodes for the alkali metal thermoelectric converter (AMTEC) were prepared from the respective powders by a screen-printing method and their electrode properties were investigated. Optimum values were obtained for particle size, thickness and porosity of electrode. When the vacuum level of the low-temperature side of the AMTEC increased above 10 Pa, the power density decreased remarkably. These results can be interpreted as different electrode processes in the AMTEC: (1) a charge transfer process, (2) surface diffusion on the electrode, (3) desorption from electrode particles, and (4) vapour-phase diffusion in the electrode pore. The maximum power density was 0.54 W cm^–2 (LaB₆) and 0.24 W cm^–2 (TiB₂ at 800 °C.     

Synthesis and structure of BN coatings on SiC nanofibers

The Gibbs potential has been calculated as a function of temperature for a number of BN synthesis reactions. Detailed studies of BN chemical vapor deposition on SiC nanofibers were used to develop a technique for BN coating production from nontoxic precursors. The optimal synthesis temperature was 1300°C. Transmission electron microscopy characterization of the BN/SiC nanocables thus produced showed that the coatings were 10–20 nm thick and had a hexagonal structure.     

Crystallographic characterization and indentation mechanical properties of LaB6-ZrB2 directionally solidified eutectics

LaB₆-ZrB₂ eutectics were directionally solidified by a zone melting process. The microstructure and crystallography were characterized by X-ray diffraction, optical microscopy and transmission electron microscopy. The anisotropies of hardness and indentation fracture toughness were assessed by making measurements along different crystallographic directions on both transverse and longitudinal sections. While the hardness did not vary appreciably between the two orientations, the fracture toughness was observed to be highly anisotropic. Toughening behavior was observed on longitudinal sections with crack deflection and bridging mechanisms apparent. Cracks were difficult to initiate on transverse sections along directions perpendicular to the growth direction, but for 20 N loads an indentation fracture toughness of 11 MPa could be measured.     

BN/EG纳米流体的制备及稳定性研究

通过两步法制备了氮化硼/乙二醇(BN/EG)纳米流体,研究了超声振荡时间、pH值、分散剂种类及添加量3种因素对其稳定性的影响。结果表明超声分散时间太长或太短都不利于流体的稳定性,实验中取30min最好;酸或碱的加入都会使BN/EG纳米流体稳定性急剧恶化;适量分散剂PVP的加入能够明显改善BN/EG纳米流体的稳定性。     

热解炭(PyC)/BN复合粉的制备及其吸波性能

以尿素、硼酸和热解炭(PyC)粉为原料, 利用化学转化法, 在1750℃、N₂气氛下反应6 h, 制备了PyC/BN复合粉。采用XRD、XPS、SEM、DTA/TGA对PyC/BN复合粉的物相组成、化学成分、表面形貌及抗氧化性能进行了表征, 并用矢量网络分析仪测试了PyC/BN复合粉在2~18 GHz频段内的吸波性能。结果表明: 生成的h-BN颗粒在PyC粉表面形成包裹层, 其尺寸为几十至几百纳米。相比于PyC粉, PyC/BN复合粉的抗氧化性能明显提高, 在1200℃时其质量仍剩余50%以上, 而PyC粉在940℃时已被氧化完全。同时, 由于波阻抗增大, 电子位移极化、界面极化、多重散射和λ / 4干涉相消作用, 使得PyC/BN复合粉在相同厚度下(d=2 mm), 其反射率峰值达到-27.2 dB, 反射率小于-10 dB的频宽为2.6 GHz; 且随着厚度的增加, 其反射率峰值均小于-10 dB, 并出现多重吸收峰。PyC/BN复合粉可作为理想的轻质、耐高温、强吸收的吸波剂应用于微波领域。     

聚硼氮烷先驱体制备氮化硼陶瓷纤维的研究

以ＢＣｌ３和ＨＮ（ＳｉＭｅ３）２为原料，合成了具有可纺性的聚硼氮烷先驱体，并以此先驱体为原料在单孔纺丝装置上熔融纺制成先驱体丝，将先驱体丝在ＢＣｌ３，ＮＨ３气氛下进行不熔化处理，使得聚硼氮烷由线型结构向平面网状和体型转变，最后在Ｎ气气氛下热处理至１６００℃，获得了ｈ－ＢＮ陶瓷纤维。