High current density results from a LaB/sub 6/ thermionic cathode electron gun

Nanocrystalline high-entropy hexaboride ceramics enable remarkable performance as thermionic emission cathodes

“…It was found that the emission current densities increased with increasing cathode temperature or applied voltage. In addition, it is worth noting that the maximum current density of the HEReB 6 -1 cathodes increased from 6.6 to 48.3 A/cm 2 when the cathode temperatures increased from 1,673 to 1,873 K, which was obviously higher than those of all the polycrystalline ReB 6 samples and almost higher than the ReB 6 single crystal [33] , [34] , [35] . In order to study the differences of emission current densities between the HEReB 6 -1 cathodes and the four individual ReB 6 cathodes at elevated temperatures, herein, we took their emission current densities at 1,873 K as an example.…”

A review on recent progress of thermionic cathode

“…Compound cathodes mainly include carbides and borides [13], and LaB 6 is the mostly representative compound cathode because of its high current density, high resistance to chemical poisoning, good metallic conductivity, low work function and low volatility [14]. The first work on the LaB 6 cathode with work function of 2.66 eV at 1127 °C was reported by Lafferty in 1951 [14], and until 1990, Herniter and Getty [15] achieved the beam current density of 30 A•cm -2 at 1744 °C. Later, Ebihara [16] measured a maximum current density of 20 A•cm -2 at 1600 °C with an effective work function (Ф) of 2.68 eV, and singlecrystal cathode was further developed with an increased current density up to 50 A•cm −2 at 1500 °C.…”

In situ(LaxGd1−x)B6cathode materials prepared by the spark plasma sintering technique

“…Furthermore, when the doping content is up to 1, its peak value increases to 36.20 A cm −2 at 1873 K. Thus, it can be concluded that with an increase of La doping contents, the emission current density should be improved. The above results can be compared with previous works: Yao et al [23] obtained an emission current density of 17.3 and 30.0 A cm −2 from LaB 6 single crystals at 1773 and 1823 K, respectively, under an applied voltage of 1 kV; Futamoto et al [2] have reported that the emission current density of LaB 6 single crystals prepared by the Al flux method is 8.5 A cm −2 at 1873 K under a high applied voltage; Goebel et al [24] obtained an emission current density of 20 A cm −2 from the polycrystalline LaB 6 cathode at 1970 K under a high applied voltage; Herniter and Getty [25] obtained an emission current density of 30 A cm −2 at 1870 K from the polycrystalline LaB 6 cathode under an applied voltage of 115 kV. The maximum emission current densities of the ternary hexaboride single crystals (La 0.97 Dy 0.03 )B 6 , (La 0.55 Pr 0.45 )B 6 , (La 0.58 Sm 0.42 )B 6 , (La 0.08 Sr 0.92 )B 6 , (La 0.98 Ba 0.02 )B 6 and (La 0.54 Ce 0.46 )B 6 prepared by the Al flux method [2] are smaller than 10 A cm −2 at 1973 K. The emission current density of LaB 6 obtained in this work is higher than the values mentioned above.…”