Rare Earth Oxide Refractory Metal Salt Impregnated W Based Directly-Heated Cathode

doi:10.15541/jim20160008

Abstract

Abstract:

Cathode plays an important role in the magnetron. In order to enhance the emission current, reduce the operation temperature and prolong the lifetime of the pure W cathode applied in the magnetron, a new La₂O₃/Y₂O₃-Gd₂O₃-ZrO₂ impregnated W based directly-heated cathode was developed. The thermionic emission properties of the La₂O₃/Y₂O₃-Gd₂O₃-ZrO₂ impregnated cathode were measured. The results show that the La₂O₃-Gd₂O₃-ZrO₂impregnated cathode can provide more than 0.18 A /cm² current density for the space charge limitation (SCL) at 1600℃. Under the same thermionic emission level, the working temperature of the La₂O₃-Gd₂O₃-ZrO₂impregnated cathode is at least 300℃ lower than that of the pure W cathode. Lifetime of the La₂O₃-Gd₂O₃-ZrO₂ impregnated cathode reaches 2100 h at 1750℃ with dc load of 0.5 A/cm². The Y₂O₃-Gd₂O₃-ZrO₂ impregnated cathode can provide more than 0.6 and 3.4 A /cm² current density for SCL at 1400℃, 1700℃, respectively. Under the same thermionic emission level, the working temperature of the Y₂O₃-Gd₂O₃-ZrO₂ impregnated cathode is at least 400℃, lower than that of the La₂O₃-Gd₂O₃-ZrO₂ impregnated cathode. Lifetime of the Y₂O₃-Gd₂O₃-ZrO₂ impregnated cathode reaches 2600 h at 1600℃ with dc load of 1.5 A/cm². At last, the thermionic emission mechanisms of the two new impregnated cathodes are discussed reasonably.

Key words: directly-heated cathode, rare earth oxide, thermionic emission, lifetime, emission mechanism

CLC Number:

O462

QI Shi-Kai, WANG Xiao-Xia, LUO Ji-Run, HU Ming-Wei, LI Yun. Rare Earth Oxide Refractory Metal Salt Impregnated W Based Directly-Heated Cathode[J]. Journal of Inorganic Materials, 2016, 31(9): 987-991.

Figures/Tables 9

Fig. 1 I-V dc emission characteristics curves of La2O3-Gd2O3- ZrO2 impregnated cathode

Fig. 2 Thermionic electron emission density vs temperature of La2O3-Gd2O3-ZrO2 impregnated cathode and pure W cathode

Fig. 3 Lifetime curve of La2O3-Gd2O3-ZrO2 impregnated W based cathode

Fig. 4 I-V dc emission characteristics curves of Y2O3-Gd2O3- ZrO2 impregnated W based cathode

Fig. 5 Thermionic electron emission density versus temperature of La2O3/Y2O3-Gd2O3-ZrO2 impregnated cathode

Fig. 6 Lifetime curve of Y2O3-Gd2O3-ZrO2 impregnated W based cathode

Fig. 7 SEM image (a) and XRD pattern (b) of La2O3-Gd2O3- ZrO2 refractory metal salt

Fig. 8 SEM image (a) and XRD pattern (b) of Y2O3-Gd2O3- ZrO2 refractory metal salt

Table1 Element composition of the La2O3/Y2O3-Gd2O3-ZrO2

Elements	La₂O₃-Gd₂O₃-ZrO₂		Elements	Y₂O₃-Gd₂O₃-ZrO₂
Elements	at%	wt%	Elements	at%	wt%
La	13.95	38.35	Y	17.44	35.44
Gd	1.39	4.33	Gd	1.21	4.45
Zr	20.55	37.01	Zr	17.78	36.88
O	64.11	20.31	O	63.57	23.23
Total	100.00	100.00	Total	100.00	100.00

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