Due to its low vapor pressure, gallium, when substituted for mercury in a liquid slip ring system, transmits substantial amounts of electrical current to rotating components in an ultrahigh vacuum. It features low electrical loss, little or no wear, and long maintenance-free life

Przybyszewski, J. S.

English

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fl erical 
Cylindrical 
Specimen 
May 1969	 Brief 69-10138 
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NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Liquid Gallium Rotary Electric Contact 
To Alternating Current 
Output Of Milliohmmeter 
One of the most formidable problems encountered 
in an ultrahigh vacuum (10 - 1 l torr) environment is the 
transmission of substantial amounts of electrical cur-
rent to rotating components. The basis for the problem 
lies in the selection of a slip ring having little or no 
wear, a very long maintenance-free life and low elec-
trical loss. Under ordinary atmospheric conditions, 
the liquid mercury slip ring fulfills all of these require-
ments, but due to the prohibitively high vapor pressure 
of mercury, this simple, reliable slip ring system cannot 
be used in ultrahigh vacuum. 
Gallium, which has a very low vapor pressure, was 
substituted for mercury in a liquid slip ring system 
with excellent results under ultrahigh vacuum con-
ditions. The gallium rotary electrical contact consists 
of a copper ring mounted on a rotating shaft that is
immersed in a copper cup containing gallium. (See 
figure.)Some mild abrasion of the copper surface, 
while it is in contact with the liquid gallium, is neces-
sary for the gallium to wet the copper surface. The 
gallium is initially liquified by a small electric heater 
mounted on the gallium cup and will remain liquified 
because of the heating effect of the electrical current 
flowing through the slip ring, so that the heater can 
then be shut off. 
This type of slip ring has operated in a vacuum of 
lO 11 torr, periodically carrying currents of 25 amperes 
dc, for a period of two years with no maintenance. A 
moderate amount of outgassing occurs during the 
initial period of contact rotation and as the contact 
temperature increases, bakeout of the vacuum system 
in which this type of rotary slip ring is used must be 
I 	 n(ic1tid oscricti 
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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limited to 250° F because of gallium corrosion prob-
lems with copper which have been encountered at 
higher temperatures. Routine bakeouts of 250° F have 
been used with this type of slip ring for two years with 
no apparent degradation of the slip ring components. 
Notes: 
1. Documentation is available from: 
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Price $3.00 
Reference: TSP69-10138
Technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B69-10138 
Patent status: 
No patent action is contemplated by NASA. 
Source: John S. Przybyszewski 
(LEW- 10828)
. 
S 
Brief 69-10138
	 Category 03


Liquid gallium rotary electric contract

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