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Thermionic emission studies of activation sintered alloys.

Hameed, Sheikh Abdul. (1970) Thermionic emission studies of activation sintered alloys. Doctoral thesis, University of Surrey (United Kingdom)..

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The object of the present work was to investigate new alloy emitters using an activation sintering method for their preparation. It was also desired to study the effect of porosity on thermionic emission. Alloys of W-Pd, W-Ni, W-Co and W-Cu were chosen because Palladium and Nickel strongly promote sintering whereas Cobalt and Copper have a much lower activating powers, although they are otherwise closely related transition elements. The emitters were impregnated with optimum concentration of metal salts, reduced and sintered in hydrogen tube furnace. The technique results in an effectively monatomic emitting layer around each tungsten particle. The results show the reduction in work function of the emitters e.g. W-Pd ( 0.25 ev); W-Ni ( 0.20 ev); W-Co ( 0.40 ev) and W-Cu (0.30 ev). Presintered (porous) emitters have ten times more emission than fully sintered emitters, and their thermionic curves are heterogenous consisting of three steps in the saturation region. Porous emitters are characterized by a surface which consists of protuberances and cavities, and the heterogenous nature of emission is assumed to be associated with different depths of the cavities. Decay in saturation emission (with a rate coefficient of between 0.4- 0.55) has been observed in emitters which are sintering during emission; this phenomenon is not obtained in fully sintered materials and porous tungsten. A new correlation has been proposed to connect the work function of both elemental and duplex emitters with the number of electrons in the outershell of the component atoms. This correlation explains qualitatively the values of work function of most emitting surfaces. An attempt has also been made to quantitize the correlation by reference to the spectroscopically determined promotion energies of the s-p-d electronic states used in the hypothesis.

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors :
Hameed, Sheikh Abdul.
Date : 1970
Contributors :
Depositing User : EPrints Services
Date Deposited : 09 Nov 2017 12:16
Last Modified : 20 Jun 2018 11:14

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