Helium is purified when cooled in a low pressure environment until it becomes superfluid. The liquid helium is then filtered through iron oxide particles. Heating, cooling and filtering processes continue until the purified liquid helium is heated to a gas

Hildebrandt, A. F.

English

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Rod 
be Fitting 
Pressure Ves -. 
Helium Fill T 
Liquid Heliun 
.	
Cork 
Liquid Nitrog 
Dewar Conta
Accumulation Chamber
for Filtered Helium
ron Oxide 
Re r 
;intered Iron Plugs 
Infrared Light 
Heats Coil 
M arch-_064
NASA TECH BRIEF
Brief 63-10235 
-	
-i--
This NASA Tech Brief is issued by the Technology Utilization Division to acquaint industry 
with the technical content of an innovation derived from the NASA space program. 
Cryogenic Filter Method Produces Super-Pure Helium and Helium Isotopes 
ALTERNATE HEATING METHOD 
The problem: Purification of helium to produce 
super-pure helium gas for experimental use and to 
separate the various isotopes of helium. 
The solution: Cool helium to a temperature below 
2.19 degrees K in a low-pressure environment, so that 
part of the helium becomes super-fluid, then filter 
through a material with extremely fine pores. 
How it's done: Liquid helium is filtered, while in 
the lambda 11 state (super-fluid, a state of practically 
zero viscosity) through iron oxide particles such as
jewelers' rouge. Normal liquid helium cannot pass 
through this filter. The filtering equipment consists 
of an iron oxide filter with sintered iron plugs at each 
end. One end is connected by a tube to an accumula-
tion or storage chamber; the other end is connected to 
a liquid helium intake in a thick-walled vessel. A glass 
tube closes the filter (helium) intake. 
The equipment is lifted out of the thick-walled 
vessel, thoroughly cleaned to remove impurities, 
heated to 300 degrees C to drive out moisture, and 
Am	 (continued overleaf) 
MW
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States Govern-
ment. nor NASA, nor any person acting on behalf of NASA: A. Makes 
any warranty or representation, express or implied, with respect to the 
accuracy, completeness, or usefulness of the information contained in
this document, or that the use of any information, apparatus, method, 
or process disclosed in this document may not infringe privately-owned 
rights: or B. Assumes any liabilities with respect to the use of, or for 
damages resulting from the use of, any information, apparatus, method, 
or process disclosed in this document.
https://ntrs.nasa.gov/search.jsp?R=19630000028 2020-03-11T16:46:14+00:00Z
then lowered into the thick-walled vessel containing 
liquid helium in a Dewar system cooled by liquid ni-
trogen. 
Liquid helium is next brought to the lambda II state 
(the point at which super-fluid helium begins to form) 
by placing it in a low pressure environment (below 
30 mm). A breaker rod is depressed to break the glass 
tube. This allows the super-fluid, liquid helium to 
enter the filter, flow through the sintered iron plug 
and into the accumulation chamber. Since only super-
fluid helium can pass through the filter, all impurities 
are stopped. When the accumulation chamber is filled 
with pure liquid helium, the entire helium bath and 
equipment is heated above the lambda II point so that 
no super-fluid remains. Heating prevents helium from 
flowing backward since normal liquid helium cannot 
pass through the iron oxide. 
The process of filling the accumulation chamber 
can be speeded up by using an infrared light source. 
A coil with a heat-absorbing surface is connected be-
tween the filter and the accumulation chamber. An 
infrared source, placed outside the Dewar system, 
emits light, heats the coil, and causes the super-fluid 
liquid helium to become normal. When super-fluid 
liquid helium is in the coil, it diffuses out of the coil 
through the filter as well as from the filter into the coil. 
Heating causes liquid helium in the coil to become 
normal liquid helium, which is unable to flow out 
through the filter. The process of diffusion will
force liquid helium into the coil and from there into 
the accumulation chamber. The final step is to 
open the shut-off valve on the accumulation 
chamber and allow the purified liquid helium to heat 
up to a gas and to fill the pressure vessel. 
Notes: 
I. This process is also useful in separating isotopes 
of helium. Helium 3, which exists in minute 
amounts together with the most common isotope, 
helium 4, may be separated out. Although helium 
3 remains liquid at low temperatures and does 
not stick to iron oxide particles, it does not become 
super-fluid like helium 4. Therefore, helium 3 
experiences considerable resistance in passing 
through the minute pores of the filter and diffuses 
through the filter more slowly than helium 4. 
2. Use of this method is suggested for research lab-
oratories and chemical processing where ultra-high 
purity helium, or its isotopes, are required. 
Patent status: NASA encourages the immediate 
commercial use of this invention. It is owned by 
NASA, and a patent application has been filed. When 
patented, royalty-free non-exclusive licenses for its 
commercial use will be available. Inquiries concerning 
license rights should be made to NASA Headquarters, 
Washington, D.C. 20546.
Source: A. F. Hildebrandt 
Jet Propulsion Laboratory (J PL-374) 
Brief 63-10235


Cryogenic filter method produces super-pure helium and helium isotopes

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