Abstract
The erosion model of the surface coatings of reed switches considering different physicochemical processes occurring on the contact surfaces and inside the inter-electrode gap was proposed. According to that, the discrete electron avalanche (ecton) introduced in the explosive electron emission theory by Mesyats is considered as the main motive force responsible for the surface modification and mass transfer of materials in the course of breaking/shorting of the contacts. By means of SEM imaging and energy dispersive X-ray microanalysis of the contact surfaces after various numbers of switching cycles, the energy threshold of the ecton generation defining the erosion stability of the coatings was found to be proportional to the specific sublimation and ionization energies of coating materials. It has been shown that the total erosion of the coatings on the working surface of the contacts after the commutation test possess the resultant character; i.e., the specificities of erosion occurring after each commutation event are characteristic for the whole of the commutation test. In further development of our model, we suggested that a few monolayers of metals (or alloys) with low ionization potential deposited on the main coatings can improve the erosion stability of contacts.
Highlights
The surface erosion of magnetically operated hermetical contacts [1]occurring under the commutation of electrical current is similar in many respects to the processes taking place in the course of explosive electron emission, arc and spark discharges [2,3], electrical discharge machining and doping [4,5], surface modification by pulse discharges [6,7,8,9], and high-intensity ion, plasma, and laser irradiation of materials [10,11]
With low ionization potential deposited on the main coatings can improve the erosion stability of contacts
The results of the present study provide a detailed description and explanation of crater and disks formation, mass transfer, and materials redistribution on the contact surface of reed switches during the commutation of electrical circuits with an active load
Summary
The surface erosion of magnetically operated hermetical contacts (reed switches or RS) [1]occurring under the commutation of electrical current is similar in many respects to the processes taking place in the course of explosive electron emission, arc and spark discharges [2,3], electrical discharge machining and doping [4,5], surface modification by pulse discharges [6,7,8,9], and high-intensity ion, plasma, and laser irradiation of materials [10,11]. There are currently no generally recognized models explaining these processes, since they occur under non-equilibrium conditions, in limited volumes, and during short time intervals. It is known (e.g., [12,13] and references therein) that the erosion stability of materials depends on their thermophysical characteristics such as heat capacity and conductivity, melting point, etc. The criteria of erosion stability resting upon these characteristics (e.g., the Palatnik’s criterion [14]) cannot be considered as universal because they allow for the processes occurring. Mass transfer initiated by plasma, electron, and only in liquid vapor phases. Erosion in solid mass transfer initiated byofplasma, ion fluxes are and not considered in these criteria
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