Year of Publication

2019

Degree Name

Master of Science in Materials Science and Engineering (MSMSE)

Document Type

Master's Thesis

College

Engineering

Department

Chemical and Materials Engineering

First Advisor

Dr. John Balk

Abstract

Scandate cathode under various processing stages: scandia nano-powder, tungsten scandia mix powder, sintered and impregnated pellets, were characterized with techniques that included electron microscopy, EDS, XPS, and work function measurements. The size and shape uniformity of nano-scale scandia particles changed from round to square and polyhedron during heat treatment. Reduction in size and improvement in size uniformity as heat treating temperature increased were observed. When determining the highest Sc coverage, three assessment methods were used and with their combined results, it was concluded that set VII had the highest Sc at%. In the sintered pellets, it was observed with SEM that more initial scandia coverage in the mix powder sets corresponded to a larger number of scandia particles distributed over the tungsten surface. The structure of the cross section made on pellet surface was porous which was expected in any functional cathode. Kelvin probe measurements revealed that work function values of sintered pellets were similar and decreased by approximately 0.6 eV after the impregnation. A cross section on the impregnated pellet surface revealed that the pores that existed in sintered pellets were gone and filled with impregnated materials that emerged to the surface during impregnation.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2019.024

Funding Information

This work was financially supported via a Phase II STTR award “Reliable Manufacturing of Scandia-Doped Tungsten Powders for Thermionic Cathodes” (ID numbers N00253-17-C-0014), sponsored by the US Navy.

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