Properties of high density LaB₆cathode prepared by spark plasma solid phase sintering

Preparation and Characterization of Grain Size Controlled LaB 6 Polycrystalline Cathode Material

“…According to the previous study, [15] the emission current density of coarse powder sintered has just reached to 24.2 A/cm 2 with applied voltage 1000 V at 1903 K. This current density is much lower than that of LaB 6 sintered from nanopowder. Hence, the emission current density of nanopowder sintered LaB 6 increases 75% than the coarse one.…”

“…An example of the product nanometric grain size despite the agglomeration is shown in Fig. 3, which depicts the fracture surface of a sample sintered at 1000 ∘ C. According to our previous investigation, [15] the high density bulk LaB 6 polycrystalline were fabricated by SPS using LaB 6 commercial coarse powders with an average particle size of 10 µm. This method effectively reduced the sintering temperature and holding time compared with the conventional hot-pressing methods, [16] since the sintering mechanism of SPS is fundamentally different from conventional heating.…”

Excellent Thermionic-emission Performances of (Ce$lt;inf$gt;1-x$lt;/inf$gt;Gd$lt;inf$gt;x$lt;/inf$gt;)B$lt;inf$gt;6$lt;/inf$gt; with Ultra-low Work Functions

“…k=8.62×10-5 eV/K, 发射 常数 A 设定为理论值 19.1 A/(cm 2 •K 2 )[18] 。有效逸出 功 高纯氩保护气压为 0.4~0.6 MPa, 氩气流 速为 1.5~2.0 L/min。 二次区熔以制备的多晶棒为籽晶, 以一次区熔过的晶体为料棒, 晶体生长速度减小为 6~8 mm/h。 图 1 为 Ce 0.9 Gd 0.1 B 6 单晶体实物照片, 从图 中可以看出晶体粗细均匀, 表面光滑, 没有气体和杂 质溢出的痕迹, 表明晶体生长均匀。 晶体直径为 5 mm, 长度为 30 mm。 由此可见, 区熔法可以制备大尺寸的Ce 1-x Gd x B 6 (x=0~0.3)单晶体。 Ce 1-x Gd x B 6 的晶格常数逐渐减小, 晶格畸变程度 增大, 表明 Gd 原子的替代导致晶格的收缩。 单晶体的质量表征 图 3 (a)为360°Phi 扫描 X 射线单晶衍射仪对 Ce 0.95 Gd 0.05 B 6 晶体的快扫结果, 从图中可以看出, 衍射 斑点清晰、相互独立、没有发生劈裂现象, 且具有良好 轴对称性, 初步判定 Ce 0.95 Gd 0.05 B 6 晶体为单晶。 图 3 (b) 图 1 Ce 0.9 Gd 0.1 B 6 单晶的实物照片 Fig. 1 Photograph of Ce 0.9 Gd 0.1 B 6 single crystal 图 2 Ce 0.9 Gd 0.1 B 6 单晶的断口 SEM 照片 Fig.…”

Floating Zone Growth and Thermionic Emission Property of Single Crystal CeB 6

“…One of the reasons for that could be that the grain boundaries of polycrystalline materials obstruct electron transport, which leads to an increase of work function. The average effective work function at 1673 K, 1773 K and 1873 K can be calculated by the Richardson formula: [22] 𝜙 𝑒 = 𝑘𝑇 ln( 𝐴𝑇 2 𝑗0 ), where 𝑘 is the Boltzmann constant, 𝑘 = 8.62 × 10 −5 eV/K; 𝐴 is the emission constant, 𝐴 = 19.1 A/cm 2 •K 2 ; 𝑗 is the zero field current density at different temperatures, it is obtained by a "Schottky" plot of ln𝐽 versus 𝑉 1/2 . The calculation results show that the average effective work function of the single crystal is about 2.44 eV, which is less than the value of 2.6 eV for the polycrystalline one.…”