Study On Preparation And Properties Of CNTs/Ceramic Composite Explosive Emission Cathode

The explosive emission cathodes can provide extremely high current density and current intensity,which is the core component of the electron beam source and determines the electron emission characteristics to a great extent.The carbon nanotubes?CNTs?has been considered as important cathode material for explosive emission cathodes because of its large aspect ratio and high enhancement factor.However,it also shows some key problems such as long delay time and insufficient stability.Based on the local field enhancement mechamisim,the“mixed cathode”and“interface cathode”were constructed by mixing carbon nano tube and diectric ceramics in this paper.The imapcts of diectric ceramics and the cathode structure on the electron emission characteristics were inverstigated.The mixed explosive cathodes of carbon nanotubes/Al₂O₃ ceramic and carbon nanotubes/BaTiO3 ceramic were prepared by a dry pressing methode.As the volume ratio of carbon nanotubes increases from 10vol%to 25vol%,the emission current densities of carbon nanotubes/BaTiO₃ mixed cathodes increases from 7.10 kA/cm² to17.04 kA/cm².In addition,the results show that the single emission characteristics of the carbon nanotubes/Al₂O₃ mixed cathode are similar to that of carbon nanotubes/BaTiO₃ cathode,but the repetitive frequency stability is better than that of the carbon nanotubes/BaTiO₃ cathode.After 1000 emission tests,no significant decrease of the current densitiy for the mixed cathode of carbon nanotubes/Al₂O₃ is observed,indicating its good long life characteristic;During the emission process,the ablation of carbon nanotubes is serious at the edge for mixed cathode,which is largely determines the emission life of the mixed cathodes.In this paper,the interface explosive cathodes with different carbon nanotubes amounts and different ceramic substrates were prepared by coating process.As the mass ratios of carbon nanotubes increased from 5wt%to 35wt%,the current densities of carbon nanotubes/BaTiO₃ cathode increased from 42.5 kA/cm² to 106.5 kA/cm² and then decreased to 89.6 kA/cm².In addition,the single emission characteristics of carbon nanotubes/BaTiO₃ at 10wt%are slightly better than the carbon nanotubes/Al₂O₃:the current density reaches 84.69kA/cm²,and the delay time is only 5ns,but the stability of the carbon nanotubes/Al2O3 cathode is better than that of the carbon nanotubes/BaTiO₃ cathode.The emission repeatability of interface cathode with multi-layer structure is better than the cathode with single-layer structure.When the emission frequencies increase from 5Hz to 20Hz,no obvious inflection point is found in the current waveform,which shows faster front edge and the smaller fluctuation.After1800 emission tests,no significant reduction on the cathode current happens,indicating its good emission life.The emission life of interface cathodes is mainly determined by the carbon nanotube ablation and film shedding.