Fabrication of nitrogen-containing coatings in reed switches by pulsed ion-plasma treatment

Abstract

We focus on the detailed characterization of the coatings produced by pulsed ion-plasma treatment on contact surfaces of permalloy (iron-nickel) blades directly in nitrogen-filled reed switches. The measurements of electrical resistance, breakdown voltage and return factor of reed switches were carried out in situ prior to and after ion-plasma treatment, and the morphology and elemental (chemical) composition of the coatings were monitored ex situ by means of scanning electron microscopy and energy dispersive X-ray microanalysis. The main processes occurring on the contact surfaces in the course of ion-plasma treatment were discussed in the frame of anomalous glow and arc discharges theories by Mesyats. It was shown that ionplasma treatment allows fabrication of erosion- and corrosion-resistant nitrogenated iron-nickel coatings with the electrical resistance of 0.1 Ohm. In the optimal symmetrical mode with the processing time of ca. 7 min the nitrogen concentration in the coatings was estimated of 20 at %. Higher and lower nitrogen content and the presence of oxygen in the coatings showed negative influence on the electrical resistance, which determines the quality of reed switches. Prototype models of the reed switches with nitrogenated coatings successfully passed switchgear reliability tests and demonstrated the competitive capacity as regards the standard reed switches with electroplating coatings based on the noble metals.