Specimen thermionic emitters were electropolished and electroetched to study the effect of surface preparations on improving thermionic emission. The best technique found was to electropolish the annealed rhenium surface and then electroetch it. The effect of electroetching was to remove other crystal planes faster than basal planes

Van ~someren, L.

English

NASA Technical Reports Server

November 1966	 Brief 66-10493 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U. S. space 
program and to encourage their commercial application. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Study Shows Effect of Surface Preparations on Improving 
Thermionic Emission 
Specimen thermionic emitters were electropolished 
and electroetched as part of a program to study the 
effect of surface preparations on improving thermionic 
emission. 
It was known that the best thermionic emission 
is achieved from the (110) plane of tungsten, and that 
these planes have the highest atomic density. It was 
also known that the highest atomic density in the 
rhenium lattice was found on the basal planes. There-
fore, techniques were investigated which would 
maximize the amount of basal plane on the surface of 
a polycrystalline rhenium emitter. The best technique 
found was to electropolish the annealed rhenium sur-
face and then electroetch it. Both operations were 
performed in an electrolyte consisting of: 
175 ml Butanol 
175 ml Methanol 
175 ml Perchloric Acid (density 1.54) 
50 ml Ethylene Glycol Monobutyl Ether 
Electropolishing was carried out at about 30 volts, 
and electroetching at about 5 volts, with the specimen 
as anode. The effect of electroetching was to remove 
other crystal planes faster than basal planes, and
thus maximize the amount of basal plane on the 
specimen surface. 
The electroetching resulted in roughening of the 
electropolished surface; however, the increase in 
thermionic emission was greater than could plausibly 
be accounted for in terms of the increased area of the 
emitter surface. 
Note: 
Inquiries concerning this innovation may be di-
rected to:
Technology Utilization Officer 
Jet Propulsion Laboratory 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: t66-10493 
Patent status: 
No patent action is contemplated by NASA. 
Source: Lawrence van Someren 
of Thermo Electro Engineering Corp. 
under contract to 
Jet Propulsion Laboratory 
(JPL-SC- 140) 
Category 01 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
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Study shows effect of surface preparations on improving thermionic emission

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