Edge-defined, film-fed growth process allows both tubular shapes and single crystallinity to be achieved. Beta alumina in single crystal form makes possible membranes with improved conductivities. Single crystal membranes also eliminate problems associated with electrical short circuiting of membrane due to possible sodium metal diffusion

Cocks, F. H.

Giner, J. D.

Stormont, R. W.

English

NASA Technical Reports Server

December 1973	 B73-10316 
• NASA TECH BRIEF 
Lewis Research Center
	 4V 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Single Crystal Tubes of Beta Alumina 
Single crystal tubes of sodium beta alumina have been 
produced for the first time. Prior art did not permit the 
growth of either tubular shapes or large single crystals of 
beta-alumina. However, a process called edge-defined, 
film-fed growth allows both tubular shapes and single 
crystallinity to be achieved. 
Sodium beta alumina is a solid state electrolyte 
membrane material suitable for use in high energy density 
batteries such as the sodium sulfur battery. The avail-
ability of beta alumina in single crystal form as opposed 
to plates of pressed and sintered powder would make 
possible membranes with improved conductivities. Such 
single crystal membranes would also eliminate problems 
associated with the electrical short circuiting of the 
membrane due to possible sodium metal diffusion along 
grain boundaries or through interconnected pores. One 
favorable geometry for such single crystals is tubular, with 
the high ionic conductivity direction of the membrane 
normal to the tube axis. Such properly oriented tubular 
single crystals of beta alumina may permit the construc-
tion of batteries with a longer lifetime, lower operating 
temperature and/or higher energy density. 
There . are, however, considerable difficulties associated 
with the crystal growth of sodium beta alumina. These 
difficulties are due principally to the fact that beta 
alumina appears to decompose peritectically (i.e., change 
composition in the solid-liquid-solid cycle), as well as to 
the high vapor pressure of sodium over beta alumina at its 
decomposition temperature. Single crystal tubes (5 mm 
(0.2 inch) O.D., 3 m (0.12 inch) I.D., 25-35 mm (1 . 1 .4 
inches) long) of sodium beta alumina have finally been 
fabricated by a process combining edge-defined, film-fed 
growth (EFG) and the use of excess Na 2 0 as a flux, 
together with up to 300 psi of an inert gas overpressure, 
to achieve the desired single crystallinity and chemical 
composition. 
Edge-defined, film-fed growth is a process by which a 
single crystal or dense polycrystal body can be formed 
having a shape controlled by the outside dimensions of a 
die, the growth actually taking place from an extremely 
thin film of liquid fed by capillary action from a crucible 
below. Since beta alumina appears to decompose pen-
tectically, it is necessary to grow this material from a melt 
containing an excess of Na 2
 0 in order to keep the growth 
temperature less than the peritectic decomposition tem-
perature. Furthermore, because of the high vapor pressure 
of sodium over such melts, it is necessary to use a high 
inert gas overpressure in order to suppress sodium loss 
during the crystal growth process. 
For the growth of tubular sodium beta alumina 
crystals, the following procedure is used: the crucible, 
EFG tube die, and charge are placed in a pressurized 
chamber capable of applying an overpressure of 300 psi of 
argon. When the crucible and charge are heated to 
produce melting, the liquid melt rises by capillary action 
to fill the feeding orifice in the die. A small heat sink or 
seed is then brought into contact with the melt at the top 
of this capillary feed slot. After adjustment of the melt 
temperature and seed withdrawal rate, the melt spreads 
across the top surface of the die, until further spreading is 
prevented by the 90 0 change in contact angle at the edges 
of the die. The growth of a tubular shape from a thin 
liquid meniscus is then established. The use of melt 
compositions enriched in Na2 0 enables this growth 
process to be carried out at temperatures below the 
decomposition temperature of sodium beta alumina. 
Notes: 
1. The edge-defined, film-fed growth process was de-
veloped by Tyco Laboratories, Inc., 16 Hickory Drive, 
Waltham, Massachusetts 02154. 
2. Further information is available in the following 
report: 
NASA CR . 121033 (N73-12810), Development of 
Single Crystal Membranes 
Copies may be obtained at cost from: 
Aerospace Research Applications Center 
Indiana University 
400 East Seventh Street 
Bloomington, Indiana 47401 
Telephone: 812-337-7833 
Reference: B73-10316
lr(ntr,,or1 
This document was prepared underthe sponsorship of the National 	 Government assumes any liability resulting from - the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19730000316 2020-03-17T06:58:32+00:00Z
3. Specific technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B73-10316 
Patent Status: 
NASA has decided not to apply for a patent. 
Source: R.W. Stormont, F.H. Cocks,

and J.D. Giner
Tyco Laboratories, Inc.

under contract to

Lewis Research Center
(LEW. 1 1844)
. 
. 
. 
B73-10316	 Category 04


Single crystal tubes of beta alumina

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