To augment the thermionic emission capacity and prolong the lifetime of the cathode for medical accelerators,the rare-earth oxide La2O3 was employed to dope IVB group refractory metal oxides ZrO2 or HfO2 to fabricate the thermal electron emission active materials.After a series of processes such as ball milling,isostatic pressing,and high-temperature solid-state sintering,two remarkable active substances,namely La2Zr2O7 and La2Hf2O7,were successfully synthesized.Subsequently,these electron emission materials were utilized to prepare the rare-earth lanthanide ceramic cathodes.Finally,a comparative study was conducted on the thermal electron emission characteristics of the cathodes.The results showed that when the working temperature was 1600 ℃(brightness temperature)and the anode voltage was 300 V,the thermal emission current densities of La2Zr2O7 and La2Hf2O7 cathodes were 2.03 and 1.24 A/cm2,respectively.Conforming to Richardson's linear extrapolation,the absolute zero work functions of these two materials were determined to be 0.97 eV and 1.52 eV,accordingly.The results of the lifetime test showed that when the DC load was 0.5 A/cm2,the lifetime of the cathode exceeded 3100 and 7000 h,respectively.Furthermore,the surface microstructure,chemical structure of the active material,elemental composition,and contents of the cathodes were analyzed with SEM,XRD,EDS,and other equipments.The results indicate that the generation of oxygen vacancies is main reason for the improvement of the thermionic emission abilities of the rare-earth lanthanide ceramic cathodes.
关键词
医疗加速器/磁控管/阴极/稀土镧盐陶瓷/热发射/发射机理
Key words
medical accelerator/magnetron/cathode/rare-earth lanthanide ceramic/thermionic emission/emission mechanism
维普
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