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Author: search.filters.author.Akbi, MohamedSubject: search.filters.subject.Work function

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    Work function measurements of contact materials for industrial use
    (IOP, 1998) Akbi, Mohamed; Lefort, André
    The nature of the contact material is important for the characteristics of electric arcs and particularly for the electronic emission. Work functions of new industrial materials made with silver alloys and silver oxide alloys are not known at present. An experimental set-up is described which allows work function measurements from room temperature up to 700 K. The Fowler method was used for the measurement of the work function by the photoelectric effect. As a first application of the experimental device, work functions of metals (Ag, Cu, Ni, Sn and Zn) were determined. Furthermore, the influence of industrial surface treatment such as the application of electric arcs and repeated mechanical shocks on the Ag contact work surface was studied by SEM to observe their effect on electron work function. Breaking arcs in air cause a remarkable increase in the work function of the silver contact material by progressive formation of silver oxides
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    Experimental determination of work function of silver alloys
    (1994) Lefort, Andre; Akbi, Mohamed; Parizet, Marie-Jose
    Models about arc roots need a good knowledge of physical constants characterizing contact material. With pure metal, all the constants are well known; but for alloys some are not known. In this paper we relate how we have measured work function of silver alloys. Measuring method used is the Fowler one where photoelectronic current produced by different ultraviolet radiations is measured in high vacuum. Experimental set-up have been tested for pure materials and then, have been applied to some silver alloys. Results about pure metals show an evolution of the work function with temperature; it decreases when temperature increases. Results about silver-nickel alloys show a large dependence of obtained results with the preparation of contact surface. For example, polishing and cleaning induce, because of atom migration, a large modification of the ratio of the two components on surface; this phenomenon induces a variation of work function comparatively with obtained values with prLtary product. By heating alloy contact in high vacuum we have observed large variations of work function, which result from material component vaporisation by sheets. Surface analyses by electron microscope produce proves of the phenomenon. An empirical relation is given to calculate work function of binary alloy when this constant is known for each alloy component
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    Effects of arcing in air on the microstructure, morphology and photoelectric work function of ag- Ni (60/40) Contact materials
    (World academy of science, engineering and technology, 2015) Akbi, Mohamed
    The present work aims to throw light on the effects of arcing in air on the surface state of contact pastilles made of silvernickel Ag-Ni (60/40). Also, the photoelectric emission from these electrical contacts has been investigated in the spectral range of 196- 256 nm. In order to study the effects of arcing on the EWF, the metallic samples were subjected to electrical arcs in air, at atmospheric pressure and room temperature, after that, they have been introduced into the vacuum chamber of an experimental UHV set-up for EWF measurements. Both Fowler method of isothermal curves and linearized Fowler plots were used for the measurement of the EWF by the photoelectric effect. It has been found that the EWF varies with the number of applied arcs. Thus, after 500 arcs in air, the observed EWF increasing is probably due to progressive inclusion of oxide on alloy surface. Microscopic examination is necessary to get better understandings on EWF of silver alloys, for both virgin and arced electrical contacts
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    On the temperature dependence of the photoelectric work function of contact materials
    (2014) Akbi, Mohamed
    The nature of the contact material plays a key role to determine the characteristics of the electric arcs and particularly those of the electronic emission. Mechanical and thermodynamic properties as well as electron emission of such complicated alloys present a lack of reliable and accurate experimental data. The purpose of this paper is to present the development of a method for measuring photoelectric work function of pure contact materials that are actually used in relays. Also reported in this manuscript are the results of experimental work whose purpose has been the buildup of a reliable photoelectric system and associated monochromatic ultra-violet radiations source, and the photoelectric measurement of the electron work functions (EWF) of contact materials. In order to study the influence of temperature on the EWF, a vacuum furnace was used for heating the metallic samples up to 700 K. The Fowler’s method of isothermal curves was used for the photoelectric measurement of the EWF. As a first test of the experimental UHV set-up, the EWF of the silver contact materials, namely pure polycrystalline metals (Ag, Cu, Ni, Sn and Zn) were investigated to study the influence of surface cathode temperature on the EWF. In the present study, the photoelectric measurements about silver contacts have shown a linear decrease of the EWF with increasing temperature, i.e. the temperature coefficient dt d􀁉 􀁄 􀀠 is constant and negative: 􀁄 􀀠 􀀐4.58􀂘10􀀐4eV / K in the experiment temperature range [300 K 􀀐 780 K]