Emission Properties of Cathode Materials Based on LaNi$_5$–CNT Composites

I. M. Sydorchenko$^{1}$, N. A. Shevchenko$^{1}$, Ye. A. Tsapko$^{1}$, I. Ye. Galstan$^{1}$, H. Yu. Mykhaylova$^{1}$, E. G. Len$^{1,2}$

$^{1}$G. V. Kurdyumov Institute for Metal Physics, NAS of Ukraine, 36 Academician Vernadsky Blvd., UA-03142 Kyiv, Ukraine
$^{2}$Kyiv Academic University, N.A.S. and M.E.S. of Ukraine, 36 Academician Vernadsky Blvd., UA-03142 Kyiv, Ukraine

The emission of electrons under the action of laser and/or concentrated solar radiation from cathode materials based on carbon nanotubes (CNTs), LaNi$_5$, CNT+LaNi$_5$, CNT+LaNi$_5$+Cs, CNT forest on a Ni substrate, as well as the effect of aging processes on the emission properties of the corresponding samples is investigated. As found, for a cathode made of carbon nanotubes, when an anode from Mo is used, the emission current at a temperature of about 240°C increases by an order of magnitude in comparison with a cathode from LaNi$_5$ and reaches 13 mA; The maximum emission current from the cathode with LaNi$_5$ rises rapidly at temperatures above 450°C when an additional voltage is applied, and at its value of 90 V the current reaches 9 mA. As found, the addition of the LaNi$_5$ intermetallic compound to CNTs increases the emission threshold for the composite by almost 10 times, and the maximum emission current density doubles (from 3 to 6 A/cm$^{2}$). Such an increase in emission characteristics is caused by an increase in the concentration of electrons due to their transfer to nanotubes from metal particles, which indicates a significantly higher electrical conductivity of the LaNi$_5$+CNT composite when the CNT content is <30 wt. %. Highest values of the emission current density (13.6 A/cm$^{2}$) are observed for the CNT+LaNi$_5$+Cs sample at a relatively low laser pulse energy (0.1 J). This material also showed the best results in experiment with the sun. The study of aging processes revealed a significant deterioration in the emission characteristics of all samples, except for the CNT+LaNi$_5$+Cs nanocomposite and CNT on a Ni substrate. The slow time change of the of CNT+LaNi$_5$+Cs emission properties is caused by the diffusion of Cs from the bulk of the sample onto its surface and the reduction of LaNi$_5$ oxide. The emission properties of the CNT forest on the Ni substrate under the action of laser irradiation are enhanced—the direct emission current increase by about a factor of 4 due to the improvement with time in the adhesion between the CNTs and the substrate.

Key words: thermionic converters, concentrated solar radiation, laser-assisted emission, composite metal–carbon nanotubes, aging.

URL: https://mfint.imp.kiev.ua/en/abstract/v43/i12/1707.html

DOI: https://doi.org/10.15407/mfint.43.12.1707

PACS: 68.37.Hk, 78.45.+h, 79.60.Jv, 79.70.+q, 81.05.U-, 85.30.Tv

Citation: I. M. Sydorchenko, N. A. Shevchenko, Ye. A. Tsapko, I. Ye. Galstan, H. Yu. Mykhaylova, and E. G. Len, Emission Properties of Cathode Materials Based on LaNi$_5$–CNT Composites, Metallofiz. Noveishie Tekhnol., 43, No. 12: 1707—1718 (2021) (in Ukrainian)

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