Cryogenic Power Transmission Technology-- Cryogenic ...
85
Cryogenic Power Transmission Technology-- 1 Cryogenic Dielectrics Quarterly Report July 1, 1975-September 30,1975
Transcript of Cryogenic Power Transmission Technology-- Cryogenic ...
Cryogenic Power Transmission Technology-- 1 Cryogenic Dielectrics
Quarterly Report July 1, 1975-September 30,1975
DISCLAIMER
This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
DISCLAIMER
Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.
National Technical Information Service U.S. Department of Commerce
5285 Port Royal Road, Springfield, Virginia 22161 Price: Printed Copy $5.00; Microfiche $2.25
This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the Energy Research and Development Administration, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights. -
Contract No. W-7405-eng-26
Activity No. HA 01-01-00-0 *
CRYOGENIC POWER TRANSMISSION TECHNOLOGY -
CRYOGENIC DIELECTRICS
Quarterly Report
July 1, 1975 - September 30, 1.975
Cryoelectrics Section Engineering Sciences Group Thermonuclear Division
APRIL 1976 - -- ~
NOTICE
. . : .
. . - -- - - - - - . --
NOTICE This document contains information of a preliminary nature and was prepared primarily for internal use at the Oak Ridge National Laboratory. It is subject to revision or correction and therefore does not represent a final report.
OAK RIDGE NATIONAL LABORATORY Oak Ridge, Tennessee 37830
operated by UNION CARBIDE CORPORATION
for the ENERGY RESEARCH AND DEVELOPMENT ADMINISTRATION
~ISTRIBUTION OF. THIS DOCUIL1EN.T IS .'NLIMI.TEQ YI
T H I S P A G E
W A S INTENTIONALLY
LEFT BLANK
iii
TABLE OF CONTENTS
ABSTRACT . . . . . . . . . . . . . . . . . . . . . I . CRYOGENIC DIELECTRICS
APPENDIX A . . . . . . . . . . . . . . APPENDIX B . . . . . . . . . . . . . . APPENDIX C . . . . . . . . . . . . . . REFERENCES . . . . . . . . . . . . . . FIGURE CAPTIONS . . . . . . . . . . . I1 . DISPERSION HARDENING OF ALUMINUM
APPENDIX D . . . . . . . . . . . . . . REFERENCES . . . . . . . . . . . . . . . FIGURE CAPTIONS . . . . . . . . . . .
THIS PAGE
WAS INTENTIONALLY
LEFT BLANK
Abs t r ac t
During t h e r e p o r t i n g per iod eever ing J u l y 1 t o September 30, 1975, d i e l e c t r i c s t r e n g t h measurements were c a r r i e d o u t i n l i q u i d helium under both a c and d c f i e l d cond i t i ons , u s ing point-to-plane e l e c t r o d e geometry. The e f f e c t of contaminat ion on t h e d i e l e c t r i c s t r e n g t h of l i q u i d helium w a s a s se s sed by d e l i b e r a t e l y in t roduc ing dry n i t r o g e n and atmospheric a i r i n t o t h e helium dewar. No change i n d i e l e c t r i c s t r e n g t h of any s t a t i s t i c a l s i g n i f i c a n c e was observed as a r e s u l t of contamination.
I n o r d e r t o c o r r e l a t e t h e r e s u l t s ob ta ined us ing point-to-plane e l e c t r o d e s wi th those obta ined under uniform f i e l d cond i t i ons , t h e e l e c t r i c a l f i e l d enhancement f a c t o r w i th point-to-plane geometry was es t imated through t h e use of a computer program.
D i e l e c t r i c s t r e n g t h and p a r t i a l d i scha rge measurements were a l s o taken on a two-layer po lyo le f in sample i n p re s su r i zed hel ium environ- ment, u s ing an epoxy p re s su re v e s s e l immersed i n l i q u i d helium. Because of imperfec t ions i n t h e sample, t h e p a r t i a l d i scharge d a t a showed poor r e p r o d u c i b i l i t y . However, t h e breakdown r e s u l t s a r e encouraging i n t h a t c l ean breakdowns cou1.d be obta ined i n t h e range of 20 kV without f l a sh - over t o ad j acen t conductors.
E l e c t r o s t a t i c f i e l d c a l c u l a t i o n s p e r t a i n i n g t o s u r f a c e f l a shove r s tud ie s , were c a r r i e d out . The e l e c t r i c a l f i e l d s along t h e s u r f a c e of t h e i n s u l a t o r were compared wi th those e x i s t i n g i n t h e gap and t h e t r i p l e j unc t ion under d i f f e r e n t geometr ies .
The in t e rmed ia t e v o l t a g e c r y o s t a t I V 1 opera ted throughout t h e q u a r t e r wi th no f a i l u r e s . IV2 and IV3 aga in developed l e a k s upon cool ing t o l i q u i d n i t r o g e n temperature. A h e a t exchanger f o r IV3, f o r ope ra t ion under s u p e r c r i t i c a l helium environment, i s be ing f a b r i c a t e d .
The e l e c t r i c a l and vacuum s e r v i c e s w e r e completed t o t h e high- vo l t age c r y o s t a t t e s t s t and , and t h e room-temperature i n s u l a t o r s t a c k and o u t e r dewar tank were s u c c e s s f u l l y evacuated. The l i f t mechanism f o r t h e dewar tanks was assembled and t e s t e d s u c c e s s f u l l y . The f l a t G-10 f i b e r g l a s s cryogenic i n s u l a t i n g d i s c was a t t a c h e d t o i t s mounting f l ange and i s now be ing leak- tes ted .
The high-vol tage t ransformer r e p a i r work was completed a t t h e K-25 motor shop, and t h e t ransformer was r e i n s t a l l e d a t t h e t e s t a r e a . A Doble t e s t on t h e t ransformer revea led an unacceptably h igh power f a c t o r , presumably due t o mois ture abso rp t ion i n t h e primary i n s u l a t i o n dur ing long exposure t o t h e atmosphere. The mois ture is be ing removed and t h e power f a c t o r improved by e l e c t r i c a l l y h e a t i n g t h e t ransformer and simul- taneously f i l t e r i n g t h e o i l .
A 250 kV, 600 J impulse gene ra to r , c o n s i s t i n g of 10 s t a g e s , has been purchased from Universa l Vo l t ron ic s . This u n i t i s now be ing proof-. t e s t e d p r i o r t o f i n a l acceptance. The u n i t i s capable of provid ing bo th l i g h t n i n g and swi tch ing surges .
Aluminum-gold alloys in various solution-heat-treated, quenched and aged conditions continue to be characterized as to RRR, microhardness and electron transmission microscopy. All aluminum composites thus far tested have failed to meet the high standards of RRR required.
Other activities include presentation of a paper at the Cryogenic Engineering Conference in Kingston, Ontario; participation in the Annual Information Meeting of the ORNL Thermonuclear Division; a visit to the USSR by H. M. Long under the Technical Exchange in Superconducting Power Transmission; and collaboration with the superconducting cable program at BNL and LASL. . --
I. CRYOGENIC DIELECTRICS
In t roduc t ion : A i m s and Goals
The major o b j e c t i v e of t h e C r y o e l e c t r i c P r o j e c t i s t o o b t a i n t e s t
d a t a on t h e d i e l e c t r i c behavior of s o l i d , l i q u i d , and gaseous m a t e r i a l s
a t cryogenic temperatures . These d a t a w i l l be used i n t h e des ign of
cryogenic superconducting power t ransmiss ion l i n e s (SPTL). An SPTL
des ign can be broken down i n t o f o u r major systems: conductor , e l e c t r i -
c a l i n s u l a t i o n , coo lan t , and thermal i n s u l a t i o n . Each of t h e s e must
meet c e r t a i n des ign s p e c i f i c a t i o n s t o ensure proper cab le ope ra t ion , a s
w e l l a s wi ths tand t h e r i g o r s of f i e l d i n s t a l l a t i o n , thermal cyc l ing , and
e l e c t r i c a l t r a n s i e n t s produced by network f a u l t s , switch ope ra t ion , and
l i g h t n i n g surges . I n o rde r t o a s s e s s t h e performance of cryogenic
d i e l e c t r i c s under such cond i t i ons , we a r e ca r ry ing out breakdown s t r e n g t h
t e s t s wi th dc , a c , and impulse v o l t a g e s on cryogenic l i q u i d s , and on
m u l t i l a y e r samples of t h i n p l a s t i c t apes . ' F l a s h o v e r v o l t a g e s w i l l a l s o
be measured on s o l i d i n s u l a t o r s and wrapped t ape s t r e s s cones immersed
i n cryogenic l i q u i d s . Attempts w i l l b e made t o l e a r n t h e e f f e c t of
mechanical s t r e s s e s , r e s u l t i n g from f i e l d i n s t a l l a t i o n and cooldown, on
t h e e l e c t r i c a l performance of t h e i n s u l a t i o n . P a r t i a l d i scha rge (e lec-
t r i c a l a r c i n g i n sma l l f laws i n t h e i n s u l a t i o n , causing long-term
d e t e r i o r a t i o n b u t n o t l ead ing immediately t o complete e l e c t r i c a l . break-
down) w i l l b e monitored a s a func t ion of t h e thermodynamic cond i t i ons
and previous e l e c t r i c a l and thermal h i s t o r y . A l l of t h e s e experiments
w i l l b e c a r r i e d ou t under t h e f u l l ranges of temperature and p re s su re of
i n t e r e s t f o r p r a c t i c a l SPTL des igns ; t h a t is , from about 4.2 - 10 K and
1 - 10 atm.
A. A c t i v i t y During Quarter
1. Experimental Equipment
a ) High-Voltage Cryos ta t :
The mechanical l ayou t was completed f o r t h e e l e c t r i c a l w i r ing
of t h e t e s t s t a n d f o r t h e high-vol tage c r y o s t a t . The e l e c t r i c a l w i r ing
t o t h e c o n t r o l pane l and t h e necessary pneumatic and water l i n e s were
I n s t a l l e d . The r e f r i g e r a t i o n system £ o r the. d i f f u s i o n pump b a f f l e wac
a l s o completed. A 25 cm Var ian l i qu id -n i t rogen b a f f l e has been ordered
which w i l l improve t h e e f f i c i e n c y of t h e vacuum system. Operat ion of
t h e v a l v e s and pumps from t h e c e n t r a l c o n t r o l pane l was found t o be
s a t i s f a c t o r y .
One l a y e r of a luminized mylar was wrapped on t h e i n n e r c r y o s t a t
t ank and t h e copper l i q u i d n i t r o g e n s h i e l d was ins ta l . l ed over i t . I n
t h e n e x t q u a r t e r t h e copper s h i e l d w i l l b e wrapped wi th supe r - in su la t ion
and t h e o u t e r vacuum tank w i l l be s l i p p e d over t h e complete arrangement.
The p rev ious ly designed c r y o s t a t l i f t i n g system was i n s t a l l e d
du r ing t h i s q u a r t e r . The l i f t system, c o n s i s t i n g of f o u r long screw
j a c k s , enables one t o r a i s e o r lower t h e c r y o s t a t tanks a s one assembly
over t h e lower end of t h e h igh v o l t a g e bushing. Af t e r several ~ . a r e f l l l
ad jus tmen t s , t h e system opera ted very w e l l . The l i f t mechanism can be
see11 in Flg. 1, which shows t h e p r e s e n t s t a t u s of t h e c r y o s t a t .
The 0.9-m diameter f l a t f i b e r g l a s s head (Fig. 2 ) f o r c l o s u r e of
t h e bottom of t h e vacuum bushing was welded t o i t s frame, b u t s e v e r a l
s m a l l l e a k s have y e t t o be s e a l e d be fo re t h e head can be f a s t ened t o t h e
bushing. Negot ia t ions have cont inued wi th . the ITE Imper ia l Corporat ion
and wi th Westinghouse on t h e purchse of a commercial con ica l epoxy
i n s u l a t o r . P r i c e quo ta t ions and d e t a i l e d engineer ing drawings have been
rece ived from t h e s e companies and a r e be ing reviewed. I n a d d i t i o n ,
des ign c a l c u l a t i o n s and drawings f o r a custom-made c o n i c a l head a r e
be ing prepared f o r submission t o s e v e r a l manufacturers .
b) In te rmedia te Voltage Cryos t a t s :
A l l t h e experiments dur ing t h i s q u a r t e r were conducted us ing
I V 1 . The c r y o s t a t IV2, which was f i t t e d wi th a Mycalex i n s u l a t o r a t t h e
co ld end, leaked on cooldown. The l e a k developed f i r s t a t t h e l e a d O-
r i n g s e a l , and f o r subsequent cooldowns a t t h e epoxy j o i n t . Repeated
a t tempts t o r e p a i r t h e l e a k r e s u l t e d i n a c rack on t h e Mycalex d i s c . A
f i be rg l a s s - r e in fo rced G-10 epoxy d i s c was t h e r e f o r e made t o r e p l a c e t h e
Mycalex. The c r y o s t a t , wi th t h i s new d i s c , i s now w a i t i n g t o b e leak-
t e s t e d . The in te rmedia te -vol tage c r y o s t a t IV3 was assembled and connected
t o i t s pumping system. A l e a k developed i n t h e b r a s s f l a n g e epoxied
onto t h e Mycalex i n s u l a t o r . Brass p l a t e t h i c k enough t o machine t h i s
f l a n g e i n a s i n g l e p i ece was n o t a v a i l a b l e , and s o t h e f l a n g e was turned
from two th inne r p l a t e s which were so lde red toge the r . The l e a k was
t r a c e d t o t h i s j o i n t , and was prnhahly caused by t h e s t r e s s e s developed
i n b o l t i n g t h e f l a n g e t o i t s mate on t h e ground tube. I t was s e a l e d by
re -so lder ing t h e j o i n t , and was s u c c e s s f u l l y evacuated a t room tempera-
t u r e . However, a second l e a k developed on cooldown of t h e c r y o s t a t , a t
t h e low temperature end of t h e bushing. This l e a k i s now be ing i n v e s t i -
ga ted . I n t h e meantime, t h e h e a t exchanger f o r r e f r i g e r a t i n g t h e helium
around t h e e l e c t r o d e s i s be ing f a b r i c a t e d . This system, shown i n Fig. 3 ,
w i l l a l low ope ra t ion of t h e c r y o s t a t w i t h s u p e r c r i t i c a l helium.
c) Repai r of Transformer B of 700 kV a c Tes t Se t :
The oi l - impregnated k r a f t paper c y l i n d e r t h a t f i t s between t h e
pr imary and secondary windings of Transformer B w a s descr ibed i n t h e
las t q u a r t e r l y r e p o r t . Ea r ly i n t h i s q u a r t e r t h e c y l i n d e r was i n s t a l l e d
over t h e primary winding, and t h e secondary winding was then c a r e f u l l y
mounted over both of them. The assembly is shown i n Fig. 4. The core
l a m i n a t i v ~ i s and b o l t s w e r e t h e n i n s t a l l e d , and t h e complete assembly wuc
f i r m l y b raced wi th a wooden frame ( a s shown i n Fig. 5 ) , s o t h a t t h e
windings would n o t s h i f t p o s i t i o n when be ing r o t a t e d 90' t o an u p r i g h t
p o s i t i o n .
The windings were then i n s t a l l e d i n t h e t ransformer tank , and t h e
r e p a i r e d t r ans fo rmer was moved from t h e Oak Ridge Gaseous Di f fus ion
P l a n t t o t h e Y-12 p l a n t , where i t w a s pos i t i oned i n t h e h igh v o l t a g e
area. A r eco rd ing acce lerometer was mounted on t h e t ransformer t o
measure any impacts occu r r ing dur ing t r a n s p o r t . No impacts were recorded.
A s t a n d a r d Doble test w a s perfn-ed on t h e t ransformer as souu as
i t w a s i n p lace . The primary and secondary windings t e s t e d s a t i s f a c t o r i l y
with a t u r n s r a t i o of 70;1; evidently t h e problem wi th t h c ahartel l LULU
i n t h e secondary h a s been co r rec t ed . However, t h e t e s t i n d i c a t e d a
power f a c t o r of 33% f o r t h e i n s u l a t i o n from primary t o ground. This
r e s u l t compares unfavorably with Transformer A , which shows a power
f a c t o r of 0.5%. A s imple Megger t e s t of primary winding r e s i s t a n c e t o
ground a l s o showed only 30 MS1 f o r Transformer B , a s a g a i n s t 7000 MS1 f o r
Trailsf o,mrr A.
Since t h e t ransformer o i l t e s t e d t o a s u i t a b l e l e v e l , we hypothesized
t h a t mo i s tu re had s e t t l e d i n t h e t ransformer windings, which had been
exposed t o a i r f o r s e v e r a l m o n t h s , wh i l e t h e t ransformer w a s be ing
r epa i r ed . This theory was r e in fo rced by d i scuss ions wi th Hipot ronics
s e r v i c e r e p r e s e n t a t i v e s . We decided t o d r i v e t h e mois ture ou t by hea t ing
t h e windings d i r e c t l y . Accordingly, t h e secondary winding was sho r t -
c i r c u i t e d and t h e primary was energized ($70 A primary, $1 A secondary,
Q600 w a t t s ) . Meanwhile t h e o i l was cont inuously f i l t e r e d . Thermal
cyc l ing seemed t o be t h e optimum method f o r removing t h e moisture. By
t h e end of t h e q u a r t e r t h e power f a c t o r was 4%, and t h e p r i m a r y - t e
ground r e s i s t a n c e as measured by t h e Megger was on t h e o r d e r of 250 ML?.
The heat ing-cool ing cyc le and f i l t e r i n g w i l l cont inue i n t o t h e next
q u a r t e r i n t h e hope of f u r t h e r improving t h e s i t u a t i o n . The power
f a c t o r should be a s low a s p o s s i b l e i n o rde r t o minimize i n s u l a t i o n
l o s s e s , s i n c e such l o s s e s could reduce t h e l i f e t i m e of t h e i n s u l a t i o n .
d) Impulse Generator:
I n t h e l a s t q u a r t e r i t was r epo r t ed t h a t we ordered a 250 kV,
.600 J impulse gene ra to r , c o n s i s t i n g of 10 s t a g e s , from Universa l Vo l t ron ic s .
Ear ly during t h i s q u a r t e r t h e u n i t was . ready f o r acceptance t e s t s , and
S. W + Schwenterly v i s i t e d t h e p l a n t a t M t . Kisco, New York on J u l y 17 t o
wi tness t h e t e s t s . During t e s t i n g i t was found t h a t whi le most s p e c i f i -
c a t i o n s were met, t h e f r o n t of t h e l i g h t n i n g wave had unacceptable
l e v e l s of o s c i l l a t i o n . his problem was subsequent ly so lved a t t h e
p l a n t by inco rpora t ing a r e s i s t i v e v o l t a g e d i v i d e r i n p a r a l l e l wi th t h e
o r i g i n a l c a p a c i t i v e d i v i d e r , and on August 19 Sc l~wenter ly v i s i t e d t h e
p l a n t aga in t n i n s u r e t h a t t h e genera tor opera ted s a t i s f a c t o r i l y . The
impulse genera tor a r r i v e d a t t h e l abo ra to ry by t h e end of August and
f i n a l acceptance t e s t s resumed a l~ l los t immediately. During t h e course of
t h i s t e s t i n g , t h e f i r i n g c i r c u i t f o r t h e t r i g a t i o n gap f a i l e d . Attempts
t o r e c t i f y t h e problem i n t e r n a l l y d i d n o t succeed, and a f a c t o r y repre-
s e n t a t i v e i s scheduled t o v i s i t t h e l a b o r a t o r y i n t h e f i r s t week of next
q u a r t e r . The problem appears t n be minor, p r i u ~ a r i l y e l e c t r o n i c , and
except f o r t h i s t h e g e n e r a t o r seems t o be ope ra t ing s a t i s f a c t o r i l y .
D i e l e c t r i c s t r e n g t h measurements under impulse cond i t i ons a r e scheduled
t o s ~ a r t e a r l y du r ing t h e n e x t q u a r t e r .
During the q u a r r e r an ac rcaistanct! b r fdge empioying phase-
s e n s i t i v e lock-in d e t e c t i o n was designed and cons t ruc t ed f o r r e s i s t a n c e
thelmometry. A schemat ic of t h e c i r c u i t appears i n Fig. 6. The three-
t e r m i n a l method of connec t ing t h e thermometer i s used t o ba lance out
l e a d r e s i s t a n c e s . The a c technique avoids e r r o r s from thermal emf's and
n o i s e pickup.
A Burr-Rrown t r u e rms-to-dc conver tor h a s been purchased and w i l l
bc w i r e d Lnrn t h e v o l t a g e d i v l d e r i n s t rumen ta t ion t o a l low monitor ing of
a c v o l t a g e s wi th a dc c h a r t r eco rde r .
A high-speed Tekt ronix camera, which m a t e s w i t h our 7904 nsril_. lo-
scope , has been purchased t o a l low s i m p l i f i e d r eco rd ing of impulse d a t a
and f a s t p red ischarge phenomena.
On July 30 w e llad a demonstrat ion of t h e Guildl.Jne high vo l t age
c u r r e n t comparator b r i d g e by R. Brodkin and R. O'Donnell of Gu i ld l ine
Ins t ruments , and W . Wightman of BCS Ins t ruments . Although we were
impressed wi th t h e s e u s i r i v i t y and e a s e of ope ra t ion of t h i s ins t rument ,
w e d i d n o t f e e l t h a t i t s p r i c e of approximately $15,000 was a j u s t i f i a b l e
expend i tu re under c u r r e n t program o b j e c t i v e s .
2 . Col labora t ion wi th Other Labora to r i e s
Our p r e s e n t commitment wi th Brookhaven Na t iona l Laboratory i s t o
o b t a i n d i e l e c t r i c s t r e n g t h and p a r t i a l d i scha rge d a t a on polymeric
i n s u l a t i n g f i l m s i n helium environment. The f i r s t phase of t h e program
cons i s t ed of conducting measurements on s i n g l e s h e e t s of i n s u l a t o r s i n
slowly b o i l i n g l i q u i d helium. It was a l s o hoped t h a t d a t a could be
taken a t p re s su re s up t o 3 a t m , b u t s o f a r t h e problems wi th t h e I V 3
c r y o s t a t have prevented t h i s . Aside from t h e p re s su r i zed tests, we have
obta ined d a t a on a l l t h e f i lms from BNL which were o r i g i n a l l y s e l e c t e d .
The second phase of t h e program involves t e s t s on modified v e r s i o n s
nf t h e f i lms i n t h e o r i g i n a l s e l e c t i o n p l u s any new f i l m s rece ived . We
a r e s t i l l i n t h i s phase and have been t e s t i n g samples a s they a r e rece ived
from BNL.
The d a t a were t r ansmi t t ed t o BNL over a s e r i e s of te lephone c a l l s ,
and on September 1 7 , S. W. Schwenterly and M. M. Menon v i s i t e d Brookhaven
t o d i s c u s s t h c r e s u l t s . Brookhaven expressed c r i t i c a l need f o r e n t e r i n g
t h e t h i r d phase of t h e program, involv ing measurements i n s u p e r c r i t i c a l
helium envi ro~lue l i t us ing m u l t i l a y e r t a p e s w i t h and wi thout b u t t gaps.
Pre l iminary t e s t s have been made on a p ro to type p re s su r i zed m u l t i l a y e r
sample, a s d i scussed i n Sec t ion B.2. The problems a r e s t e a d i l y be ing
overcome, and we a r e q u i t e hopefu l t h a t we w i l l b e a b l e t o begin an
i n t e n s i v e program of t e s t s i n p re s su r i zed helium dur ing t h e next q u a r t e r .
We have cont inuing con tac t w i th t h e Los Alamos dc SPTL program. On
J u l y 29, D r . P. Chowdhuri from LASL v i s i t e d u s t o d i scuss t h e i r d i e l ec -
t r i c needs. A t t h a t t ime t h e r e were some u n c e r t a i n t i e s regard ing t h e
choice of t h e type of d i e l e c t r i c , b u t by t h e end of t h e q u a r t e r
D r . Chowdhuri c a l l e d sugges t ing some p o s s i b l e candida te m a t e r i a l s . On
September 17, S. W. Schwenterly and M. M. Menon met D r . Chowdhuri a t BNL
and had f u r t h e r d i s c u s s i o n s on t h e s u b j e c t . Los Alamos has now abandoned
t h e i r o r i g i n a l i d e a of u s i n g a room-temperature d i e l e c t r i c , and has
chosen i n s t e a d a cryogenic d i e l e c t r i c . It now appears t h a t t he d i e l e c t r i c
work f o r t h e Los Alamos Program w i l l b e very s i m i l a r t o t h a t f o r t h e
BNL Program, al though the m a t r r i a l s nccd n o t Le t h e same i n v i ~ w of t h e
l c o o s t r i n g e l l l requirement on d i e l e c t r i c l o s s e s f o r a d c superconducting
cab le . Our exper ience w i t h f i l m d i e l e c t r i c s under a c f i e l d cond i t i ons
should t h u s a c c e l e r a t e p rog res s w i th d c measurements. The p re sen t
unders tanding i s t h a t LASL w i l l a c q u i r e candida te t a p e m a t e r i a l s and
w i l l send them t o u s f o r d i e l e c t r i c s t r e n g t h and p a r t i a l d i scharge
measurements. M. M. Menon i s scheduled t o v i s i t t h e LASL Cable P r o j e c t
on October 7 t o a t t e n d t h e i r annual review.
On J u l y 15, M. M. Menon v i s i t e d NRS-Gaithercburg t o aLtend t h e
review meeting on t h e i r d i e l e c t r i c program. A t t h a t t i m e , two samples
of f i b e r g l a s s - r e i n f o r c e d epoxy (G-10) were l e f t w i t h t h e NBS group f o r
l o s s a n g l e measurements a t low temperature and h igh fioldo. The dissl-
p a r i o n tacLur uf G-10 was one a r e a of concern t o u s , because we use it
i n a l l o u r c r y o s t a t s . They have now provided u s w i t h t h e d a t a (600 u
r a d i a n a t 31 kV/cm and 4.2 K), which w e f e e l i s w e l l w i th in accep tab le
l i m i t s . The t o t a l power d i s s i p a t e d i s given by
P = CV2 w t a n 6,
where C i s t h e capac i t ance of t h e s t r u c t u r e conta in ing t h e i n s u l a t i o n , w
i s t h e frequency, and t a n 6 i s t h e d i s s i p a t i o n f a c t o r . We e s t i m a t e t h e
capac i t ance of t h e p o r t i o n of t h e c r y o s t a t con ta in ing t h e G-10 d i s c t o
b e 5 pF a t 30 kV and 60 Hz. The power d i s s i p a t e d i s then
2 -6 < P = ( 5 pF) (30 kV) (2n) (60 sec-l) ( 6 6 0 ~ 1 0 ) = 1 mW,
w e l l below t h e conduction h e a t l e a k of a few t e n t h s of a w a t t .
High-voltage impulse t e s t s on d i e l e c t r i c subassemblies and on com-
p l e t e d cab le s e c t i o n s w i l l r e q u i r e an impulse gene ra to r w i th much g r e a t e r
dimensions and energy than t h e UVC u n i t . BNL and LASL have a l s o reques ted
l a r g e impulse gene ra to r s , and t h e ques t ion of economical p rov i s ion of
high-voltage impulse c a p a b i l i t y t o a l l t h r e e programs has been d iscussed - cons iderably dur ing t h e p re sen t q u a r t e r . I f only a s i n g l e gene ra to r can
be bought, i t must be app ropr i a t e t o a l l t h e programs. We have been
reviewing t h e requirements of BNL and LASL a s d iscussed i n t h e meeting
a t BNL on September 17 , w i th t h e o b j e c t of developing c r i t e r i a f o r
choosing t h e most f e a s i b l e and economical a l t e r n a t i v e .
3. E l e c t r o s t a t i c F i e l d Ca lcu la t ions
a ) Flashover on c y l i n d r i c a l d i e l e c t r i c su r f aces :
Measurements of t h e s u r f a c e f l a shove r f i e l d of t h e d i e l e c t r i c
a r e d e s i r a b l e , wi thout t h e i n f l u e n c e of v a r i o u s charging processes which
normally occur a t the j o i n t s b e t w ~ ~ . n t h e e l e c t r o d e s and t h e d i e l e c t r i c .
This w i l l a l low a b s o l u t e r a t h e r t han r e l a t i v e assessment of t h e degrada-
t i o n in t roduced by v a r i o u s j o i n t des igns . For t h e s e measurements, w e
have considered t h e use of a p a i r of t o r o i d a l e l e c t r o d e s around (but n o t
touching) a c y l i n d r i c a l d i e l e c t r i c specimen wi th t h e hope t h a t s u r f a c e
f i e l d s on t h e d i e l e c t r i c w i l l b e h igh enough t o produce s u r f a c e f l a shove r
i n l i q u i d helium wi thout con tac t between t h e t o r o i d s and d i e l e c t r i c ;
M r . P. OIConnor, an Oak Ridge Associated U n i v e r s i t i e s summer s t u d e n t , has
used a computer program provided by our consu l t an t , D r . W. F. Westendorp,
t o c a l c u l a t e t h e e l e c t r i c f i e l d s produced by a p a i r of t o r o i d s a t ground
and h igh v o l t a g e which surround a c y l i n d e r of d i e l e c t r i c . He found t h a t
t h e maximum f i e l d i n t h e hel ium between t h e t o r o i d s can be g r e a t enough
t o g i v e breakdown i n t h e hel ium be fo re s u r f a c e f l a shove r occurs . O'Connor
i n v e s t i g a t e d t h e e f f e c t of modifying t h e t o r o i d s i n t o t h i c k d i s c s w i t h
h o l e s through t h e i r c e n t e r s . The r e s u l t s show t h a t t h i s imprnves the
r a t i o of s u r f a c e f i e l d t o t h ~ f i e l d bc tweei~ the d i s r s . With a r e l a l i v e
d i o L e c t r i c pcru leabi l i ty of 4 , t h e s u r f a c e f i e l d was about 90% of t h e
uniform f i e l d between t h e d i s c s . However, t h e l o c a l f i e l d s a t t h e
rounded edges of t h e h o l e s were s t i l l about twice a s high as t h c s u r f a c e
f i e l d s , s o t h a t p a r t i a l d i scha rge i n t h e helium is s t i l l l i k e l y t o
precede f l a shove r . It may be t h a t p o t t i n g additional. epoxy around t h e s e
i n n e r edges w i l l s o l v e t h i s problem, a l though f u r t h e r c a l c u l a t i o n s w i l l
t hen b e necessary to d c t c m i n t : Lhe e f f e c t of t h e a d d i t i o n a l epoxy on t h e
s u r f a c e f i e l d s . M r . O'Connor's r e p o r t i s given i n Appendix B.
1) Enhancement f a c t o r s f o r point-plane e l e c t r o d e s :
Another computer program has been completed by Westendorp t o
c a l c u l a t e t h e e l e c t r i c f i e l d aL t h e sphe r i ca l t i p of a can-i.cal p o i n t
w i L h arbitrary cone a n g l e and d i s t a n c e from a grounded plane. The
c a l c u f a t i o n s have been a p p l i e d i n t h e a n a l y s i s of our point-plane helium
breakdown d a t a , d i scussed is Sec t ion 33.1, t o dotermiae the maximum
s u r f a c e e l e c t r i c f i e l d on t h e p o i n t t i p a t breakdown. A t e c h n i c a l memo-
randum (ORNL-TM-5137) h a s been w r i t t e n by Westendorp on t h i s work,
and t h e f i r s t page i s reproduced i n Appendix C , a long wi th p l o t s of
enhancement f a c t o r s v s gap f o r v a r i o u s t i p r a d i i .
4. Other A c t i v i t i e s
During t h e per iod of J u l y 21-25, H. M. Long and M. M. Menon made a
t r i p t o Kingston, Ontar io t o p a r t i c i p a t e i n t h e Cryogenic Engineering
Conference. They presented a paper e n t i t l e d " D i e l e c t r i c S t r eng th of
Liquid Helium Under S t rongly Inhomogeneous F i e l d Conditions". This
paper has s i n c e been accepted f o r p u b l i c a t i o n i n t h e forthcoming i s s u e
of Advances i n Cryogenics.
The Annual Information Meeting of t h e Thermonuclear D iv i s ion took
p l ace on August 27-28. S c i e n t i s t s and engineers from many l a b o r a t o r i e s
and u n i v e r s i t i e s a t t ended t h e meeting. A p o s t e r s e s s i o n on t h e Cryo-
e l e c t r i c Program was presented .
During t h e per iod of September 6-October 5 , 1975, H. M. Long made
a t r i p t o Moscow, Ya l t a , Alushta and Leningrad, t o p a r t i c i p a t e i n t h e
US-USSR s c i e n t i f i c and t e c h n i c a l exchange i n t h e f i e l d of supercon-
duc t ing power t ransmission. During h i s t r i p he presented a paper ,
" D i e l e c t r i c Strength. of Liquid Helium Impregnated P l a s t i c Tapes," a t t h e
symposium organized by t h e Krzhizhanovsky I n s t i t u t e a s p a r t of t h e US-
USSR exchange and an i n v i t e d paper a t t h c f i r s t Soviet Conference on
Technica l Appl ica t ions of Superconduct ivi ty . He a l s o v i s i t e d s e v e r a l
l a b o r a t o r i e s engaged i n app l i ed superconduct iv i ty r e sea rch . An a b s t r a c t
regard ing h i s a c t i v i t i e s i s inc luded i n Appendix A.
B. Experimental Work
1. Dielectric Strength Measurements in Liquid Helium with Point-Plane
Electrodes
During the beginning of the quarter, the breakdown strength measure-
ments using point-to-plane geometry were extended to include alternating
field conditions. The stainless steel electrodes were the oame as Ll~uae
used i.n previously reported work.' They consisted of n conical i ~ n i n t
wirh an 18" half-angle and a 10-cm diameter plane with rounded edges.
Bcfsre conducting the measurements, the electrodes were polished to
remove prior breakdown damage. Photomicrographs (Fig. ll), taken after
the experiments were concluded, showed that the point tip was roughly
spherical or elliptical, with an average radius of about 230 pm. A
similar measurement, made at the conclusion of the earlier tests, showed
an average tip radius 01 166 ym. Since no systematic drift of the
breakdown voltages was noted during either seL uf experiments, it will
be assumed that melting of the point tip, as breakdowns were accumu-
lated, was negligible.
Preliminary measurements with ac voltage on the freshly polished
electrodes did not agree with the dc results reported earlier. We
therefore undertook a series of measurements with both dc and ac voltages
to determine whether the discrep~ncy aLosc solely from the tip-radius
change or from some additional factor such as contamination. These
measurements also allowed direct comparison of peak ac and dc breakdown
voltages under identical conditions. The new dc measurements were
consistently higher than those reported earlier. This was particularly
the case when the point electrode was negative. Here the new breakdown
vo l t ages were up t o twice t h e e a r l i e r ones. Day-to-day v a r i a t i o n s i n
barometr ic p re s su re were much t o o sma l l t o account f o r t h i s change.
I n o rde r t o s e e whether contaminat ion was t h e cause f o r t h e d iscrep-
ancy i n t h e measured breakdown va lues , measurements were made i n l i q u i d
helium which had been d e l i b e r a t e l y contaminated wi th dry n i t r o g e n o r
atmospheric a i r . For comparison, f u r t h e r measurements were a l s o taken
i n t h e " t e c h n i c a l l y pure" l i q u i d a s withdrawn from t h e s t o r a g e dewar.
The r e s u l t s of our i n v e s t i g a t i o n s a r e summarized i n Tables I through V I ,
and g raph ica l ly i l l u s t r a t e d i n F igs . 7 through 9 . All a c v o l t a g e s i n
t h e t a b l e s a r e r m s un le s s o therwise noted. The dashed l i n e s i n Fig. 7
i n d i c a t e t h e d c r e s u l t s r epo r t ed c a r l i e r . A s i n our e a r l i e r measure-
ments, t h e p o l a r i t y e f f e c t was q u i t e no t i ceab le . For t h e t e c h n i c a l l y
pure l i q u i d , t h e breakdown s t r e n g t h w i t h nega t ive p o i n t e l e c t r o d e was
always s i g n i f i c a n t l y sma l l e r than t h a t w i th p o s i t i v e po in t . With a l t e r -
n a t i n g f i e l d , t h e peak va lue of breakdown f i e l d i n gene ra l ag rees wi th
dc va lues taken wi th t h e p o i n t e l e c t r o d e negat ive .
The s c a t t e r i n t h e r e s u l t s was cha rac t e r i zed by a s t anda rd dev ia t ion
of about 20% f o r both p o l a r i t i e s ; This ag rees wi th t h e p o s i t i v e po in t
measurements r epo r t ed e a r l i e r . However, t h e e a r l i e r nega t ive p o i n t
measuremerlts e x h i b i t e d a s t anda rd d e v i a t i o n of on ly 10%. Fur the r con-
s i d e r a t i o n w i l l b e g iven t n t h i s p o i n t l a t e r .
The p o i n t was v i s ~ ~ a l l y observed dur ing t h e measurements wi th a h igh
q u a l i t y 20-power t e l e scope and a system of m i r r o r s . No evidence of pre-
breakdown l i g h t emission o r l i q u i d motion could b e seen. However, t h e
breakdown itself produced a r eg ion of d i f f u s e b o i l i n g a l l around t h e
p o i n t . This p e r s i s t e d f o r n e a r l y 1 s e c . Whether t h i s b o i l i n g r e s u l t e d
from d i r e c t t r a n s f e r of energy from t h e a r c t o t h e surrounding helium o r
from h e a t i n g of t h e p o i n t by t h e a r c was n o t c l e a r .
I n o rde r t o i n t r o d u c e n i t r o g e n o r a i r i n t o t h e l i q u i d helium, t h e
fo l lowing procedure was adopted. The helium dewar was evacuated a t
l i q u i d n i t r o g e n temperatllre w i th a r o t a r y LlurnF, thcn p c r ~ L l a l l y t i l l e d
with ~ ~ i t r o g e n o r ail: 11nti-1 t h e dcwar ~ e g l s r 0 r e d a vacuum nf about 165 mm
of mercury, and f i n a l l y brought t o atmospheric prcosure - by i n r rndus ing
d r y hel ium gas. L iquid hel ium was then t r a n s f e r r e d i n t o t h e dewar. The
contaminat ion i n t h e l i -quid could be s e e n a s a f i n e m i s t covering t h e
e l e c t r o d e s . Breakdown measurements were c a r r i e d ou t i n t h e l i q u i d
hel ium contaminated i n t h i s way, and t h e r e s u l t s a r e l i s t e d i n Tables I V
through VI and g r a p h i c a l l y r ep re sen ted i n Fig. 8. A comparison wi th
measurements made i n t e c h n i c a l l y pure l i q u i d helium (Fig. 7) shows t h a t
t h e change i n breakdown s t r e n g t h i s of no s t a L 1 s t i t a l s i g n i f i c a n c e .
F ig . 9 , which r e p r e s e n t s t h e average va lues , shows a s l i g h t i n c r e a s e i n
breakdown s t r e n g t h w i t h contamination. Th i s could ve ry w e l l be due,
however, t o t he r e l a t i v e l y s m a l l number of observa t ions (20), coupled
w i t h t h e f a c t t h a t breakdown v a l ~ l ~ s e x h i b i t e d a large s c a t t e r . Moreover,
s i m i l a r changes could b e observed even i n normal l i q u i d hel ium when
meacurements were r epea t ed on d i f f e r e n t days ( see f o r example, Tables I
and 11) . The on ly o t h e r l i k e l y exp lana t ion f o r t h e diocrepancy between t h e
e a r l i e r d c d a t a and t h e v a l u e s taken i n t h e p r e s e n t q u a r t e r i s t h e
change i n r ad ius of t h e p o i n t i t s e l f . I n o r d e r t o e v a l u a t e t h i s e f f e c t ,
w e asked ou r c o n s u l t a n t , D r . Westendorp of General E l e c t r i c Research
Table I. Breakdown Data i n Technica l ly Pure Liquid Helium (Poin t Negative)
- d 'B min 'B max 'B 0 ITB No. of Date
(mm> (kv ) (kV ) (kv) (2) Readings
Table 11. Breakdown Data i n Technica l ly Pure Liquid Helium (Poin t P o s i t i v e )
- d
'B min 'B max 'B o1VB No. of Date
(mm> (kv ) (kv) (kv ) (2 > Readings
Table 111. I3reakdom Data i n Technica l ly Pure Liquid H e l i u m a c F i e l d Condit ions
- 'B min 'B max 'B Peak VB o/VB No. of Date
(-> ( k.V ) (kv) (kv) (kV) (Z) Readings
Table I V . Breakdown Data i n Liquid Helium Contaminated by Nitrogen (Poin t Negative)
- d min
v s max ITB No. of Date
(-1 (kv > (kV (kv ) (% > Readings
Table V . Breakdown Data i n Liquid Helium Contaminated by A i r (Point Pos i t ive )
'B min 'B ' max No. of
(mm> (kv ) (kv) (kv ) (%> Readings
Date
Table V I . Breakdown Data i n Liquid Helium Contaminated by A i r (Point Negative)
'B min 'B max No. of Date
( I d (kv) (kv) (kv ) (% > Readings
Labora to r i e s , t o c a l c u l a t e t h e f i e l d enhancement f a c t o r v s gap f o r our
p o i n t contour . H i s c a l c u l a t i o n s a r e summarized i n Appendix C , and
f u r t h e r d e t a i l s are publ i shed i n ORNL-TM-5137. The s u r f a c e breakdown
f i e l d (E ) a t t h e p o i n t f o r a g iven gap i s fuund by mul t ip ly ing t h e h , s
enhancement f a c t o r f by t h e average breakdown f i e l d :
where d i s t h e e l e c t r o d e gap.
F ig . 10 compares t h e mean s u r f a c e breakdown f i -e lds f o r the rarljer
i6 b yu~ p o i n t t o t h o s e found l a t e r w i th t h e 230 pm p o i n t . With p o s i t i v e
p o i n t , t h e two sets of d a t a sets a r e i n s u b s t a n t i a l agreement. However,
t h e s u r f a c e breakdown f i e l d s f o r t h e nega t ive 166 urn p o i n t a r e s t i l l
almost 50% lower than t h o s e wi th t h e n e g a t i v e 230 pm p o i n t . The p o s i t i v e
and n e g a t i v e breakdown f i e l d s with sphere-plane e l e c t r o d e s ( s o l i d and
dashed l i r i e s i n t h e f i g u r e ) a r e somewhat lower. The h ighe r s u r f a c e
breakdown f i e l d s f o r point-plane e l e c t s o d e ~ a r e probably a r e s u l t of tlie
small a r e a of t h e t i p , coupled wi th i n h i b i t i o n of a rc propagat ion by t h e
r a p i d f a l l of t h e p o t e n t i a l g r a d i e n t w i th i n c r e a s i n g d i s t a n c e from t h e
p o i n t . Space c'harge may a l s o p lay a r o l e , and w i l l be discuosed 1at;er.
I n view of t h e good agreement between, t h e s u r f a c e breakdown f i e l d s
c a l c u l a t e d f o r t h e two p o s i t i v e p o i n t s , i t seems q u i t e p l a u s i b l e t h a t
most of t h e d iscrepancy i n brcakdowll v o l t a g e s was due t o t h e change i n
t h e t i p r a d i u s of t h e p o i n t dur ing r epo l i sh ing . However, t h e incons is -
tency of t h e nega t ive p o i n t va lues i s s t i l l a mystery. It m a y be t h a t
one o r two m i c r o a s p e r i t i e s on t h e t i p of t h e 166 pm p o i n t ( s ee F ig . 11)
could have reduced t h e breakdown f i e l d f o r t h e nega t ive po in t . Such
m i c r o a s p e r i t i e s might a l s o have caused t h e anomalously low s c a t t e r noted
f o r t h e nega t ive 166 um p o i n t da t a . Measurements by ~ e w i s ' w i th poin t -
p lane e l e c t r o d e s i n hexane have shown t h a t when t h e p o i n t i s p o s i t i v e ,
t h e breakdown v o l t a g e depends s t r o n g l y on t h e p o i n t m a t e r i a l and condi-
t i o n , b u t wi th nega t ive p o i n t , breakdown i s determined only by t h e
o v e r a l l p o i n t geometry and by t h e l i q u i d . A s i m i l a r d i f f e r e n c e i n t h e
e l e c t r o d e s u r f a c e e f f e c t s f o r p o s i t i v e and nega t ive p o i n t may e x i s t i n
l i q u i d helium (but w i th t h e p o l a r i t i e s r eve r sed ) . The e f f e c t s of contami-
n a t i o n by pump o i l vapor3 a l s o cannot be d iscounted . We p l an t o r e t u r n
t o t h e s e experiments a t a l a t e r s t a g e when w e can a f f o r d t o do s o wi thout
causing de lays i n t h e r e s t of our commitments.
The marked p o l a r i t y e f f e c t observed i n t h e s e experiments m e r i t s
f u r t h e r d i scuss ion . This e f f e c t i s gene ra l ly expla ined i n terms of
space charge d i s t o r t i o n of t h e f i e l d nea r t h e p o i n t . I n most conven-
t i o n a l gaseous and l i q u i d d i e l e c t r i c s , t h e p o s i t i v e i o n s a r e more massive
and hence much s lower than t h e e l e c t r o n s , u n l e s s e l e c t r o n at tachment
processes a r e poss ib l e . Avalanches i n t h e h ighe r f i e l d r eg ion nea r t h e
po in t r e s u l t i n a net p o s i t i v c space charge, s i n c e t h e e l e c t r o n s a r e
r a p i d l y swept t o t h e anode. This space charge s h i e l d s t h e nega t ive
p o i n t from t h e anode and- t ends t o prevent breakdown, w i th t h e r e s u l t
that t h e nega t ive p o i n t breakdown v o l t a g e s a r e u s u a l l y h ighe r than those
wi th p o s i t i v e p o i n t . I n l i q u i d helium, however, a survey of t h e l i t e r a -
t u r e on i o n m o b i l i t i e s 4 shows t h a t t h e p o s i t i v e i o n s a r e much f a s t e r
than e l e c t r o n s , because t h e e l e c t r o n s form l a r g e bubble complexes i n t h e
l i q u i d . Thus, space charge nea r t h e p o i n t should be nega t ive , and t h e
p o s i t i v e p o i n t breakdown v o l t a g e s should be h i g h e s t , i n agreement wi th
experiment .
Breakdown S t r e n g t h and P.D. Measurements of Polymeric Films
I n o r d e r t o v e r i f y some of t h e r e s u l t s of i n t r h s i c d i e l e c t r i c
s t r e n g t h measurements on polymeric f i l m s r epor t ed i n t h e last q u a r t e r ,
w e cont inued our work w i t h p l a s t i c s completely encapsula ted by epoxy.
During t h e cou r se of t h i s work w e found t h a t t h e p re s su re t hae can be
a p p l i e d on t h e f i l m by p r e s s i n g t h e s p h e r i c a l e l e c t r o d e s i s c r i t i c a l .
Even a s l i g h t f i n g e r p r e s s u r e on t h e e l e c t r o d e s causes den t s i n t h e
f i l m . For example, w i t h t h e Van Leer Valeron polye thylene f i l m , dropping
a b a l l weighing 3 .7 gm on to t h e f i l m from a h e i g h t of about 3 cm pro-
duced a v i s i b l e den t . Even i f t h e weight i s p laced g e n t l y , one e l e c t r o d e
can suppor t a s t a t i c l o a d of no more than 200 grns without producing a
v i s i b l e d e n t on t h e f i lm . These meaeurcmenfs indicated t h a t extreme
c a r e must b e exe rc i sed du r ing t h e epoxy encapsula t ion . W e prcpared dl1
encapsu la t ed Van Leer Valeron sample f o r experiments by employing s p r i n g s
which e x e r t s l i g h t p r e s s u r e on t h e e l e c t r o d e s , and by c a s t i n g t h e epoxy
under vacuum t o p reven t a i r bubbleo . IIowever , breakdown s t r e n g t h measure-
mento w i t h t h i s sample showed unusual ly h igh va lues , va ry ing i n a wide
range , which suggested t h a t epoxy had in t ruded i n t o t h e i n t e r e l e c t r o d e
space . An x-ray photograph of t h e f i lm. shown t n Fig. 12, coirfl~rncd
t h i s .
During t h e la t te r h a l f of t h e q u a r t e r w e decided t o t r y a new i d e a
wherein the epoxy encapsu la t ion i s a l s o used as a s m a l l p r e s s u r e v e s s e l .
A specimen assembly i n c o r p o r a t i n g t h i s i d e a i s shown i n F ig . 13. Two
l a y e r s of Cryovac D-330 W p o l y o l e f i n , w i th t h i cknesses of 38 ym each,
were used a s t h e sample. The p r e s s u r i z i n g tube terminated between t h e
two f i lms . The f i l m s were provided wi th a 3 .3 cm h o l e a t t h e c e n t e r , s o
t h a t t h e epoxy p r e s s u r e v e s s e l was mechanical ly supported a t t h a t p o i n t ,
prevent ing bulg ing under p re s su re . I n o r d e r t o provide adequate mechani-
c a l s t r e s s r e l i e f a t t h e sha rp ends of t h e f i l m , two o-r ings were used
a t t h e sample edges a s shown i n t h e f i g u r e . E ight p a i r s of s t a i n l e s s
s t e e l b a l l s , 0.9525 cm i n diameter , equa l ly spaced along t h e circum-
f e rence of a 6.35 cm diameter c i r c l e , se rved a s t h e e l e c t r o d e s . The
epoxy was c a s t under vacuum, wi th t h e mold i n t h e v e r t i c a l p o s i t i o n , and
t h e e l e c t r o d e s were he ld i n p l ace wi th t h e h e l p of screws a t t a c h e d t o
t h e t e f l o n mold. The th i ckness of t h e i n s u l a t i o n between each p a i r of
e l e c t r o d e s was c a l c u l a t e d by measuring t h e th i ckness between t h e two
e x t r e m i t i e s of t h e b a l l s and s u b t r a c t i n g from i t twice t h e diameter of
t h e b a l l s . Unfortunately, a f t e r t h e e n t i r e assembly was c a s t , such
measurements showed v a r i a b l e i n s u l a t i o n th i ckness , sugges t ing t h a t epoxy
had in t ruded i n t o t h e i n t e r e l e c t r o d e reg ion , i n s p i t e of a l l t h e precau-
t i o n s t h a t were taken.
Although t h e specimen assembly proved t o be inadequate t o conduct
meaningful measurements, we decided t o u se i t t o ga in some exper ience
wi th our new p r e s s u r i z i n g system and a l s o t o check our p a r t i a l d i scharge
d e t e c t o r i n i t s balanced mode. The p r e s s u r i z i n g system enabled us t o
l e t pre-cooled ( 7 7 K ) helium gas i n t o t h e space between t h e f i l m s . A
Jennings v a r i a b l e vacuum c a p a c i t o r r a t e d 15 kV r m s was used a s t h e
ba lanc ing arm f o r t h e d i s c h a r g e . d e t e c t o r . P.D. measurements were con-
ducted a t v a r i o u s p re s su res up t o 30 ps ig . However, t h e r e s u l t s of t h e
measurements, i n view of t h e v a r i a b l e n a t u r e of t h e i n s u l a t i o n , d id no t
. July 29:
J U ~ ~ 30:
August 1:
A~lp~ist 13:
Scptembel- 10:
Septcmber 24:
allow us to fo~mulate any definite conclusions. We did, however, gain
experience in pressurizing helium and conducting careful P.D. measure-
ments under these conditions. We have also learned that epoxy casting
with the films and electrode in place is not practical.. We are cur-
rently considering ways and means of overcoming the problems. We are
also fabricating a cooling coil for our intermediate-voltage cryostat
(IV 3), so that t h e helium dewar can be pressurized to keep the helium
temperature within admi s s i ,b l e limits.
C. Vicito~s
The following people vistted us during the quarter:
July 9: W. F. Westendorp, consultant, Schenectady,
New York
P. Chowdhuri, LASL
W. Wightman, BCS Tnstrumento
R. Brodkin, Guildline Instruments
R. J. O'Donnell, Guildline Instruments
P. Komarek, Kernforschungszentrum, Karlsruhe,
W. Germany
P. DubOfs, C.G.E. Laboratory, Marcoussis,
France
H. Heumann, AEG-Telefunken, Rheydt, W.
W. Germany
G. M. L. Sommerman, consultant, Pittsburgh,
Pennsylvania
D . Future P lans
During t h e coming q u a r t e r , e f f o r t s w i l l b e made t o improve our
methods f o r d i e l e c t r i c t e s t i n g of polymer f i l m s . A new sample ho lde r
w i l l b e cons t ruc ted which w i l l a l low i n j e c t i o n of p re s su r i zed helium
between t h e f i l m l a y e r s and w i l l n o t r e q u i r e t ed ious c a s t i n g of epoxy
each t ime t h e sample i s changed. Pre l iminary dc measurements w i l l be
conducted, and a new program of dc breakdown experiments w i l l be planned
i n c o l l a b o r a t i o n w i t h members of t h e LASL SPTL p r o j e c t . The new 250 kV
Universa l Vo l t ron ic s impulse gene ra to r w i l l b e used f o r l i g h t n i n g and
swi tch ing surge breakdown tests on polymer f i l m s .
I f t ime permi ts , f u r t h e r work w i l l b e done wi th 'breakdown in l i q u i d
helium, t o c l e a r up some of the i n c o n s i s t e n c i e s found i n e a r l i e r measure-
ments. Capab i l i t y f o r measurements i n p re s su r i zed l i q u i d and vapor w i l l
be developed i n p a r a l l e l wi th t h a t f o r polymer f i l m s .
I n s t a l l a t i o n of t h e r e p a i r e d 350 kVac t ransformer w i l l be completed,
and t e s t i n g of t h i s t ransformer w i l l be carried ou t .
Assembly of t h e high-vol tage c r y o s t a t w i l l cont inue , and we w i l l
soon be ready t o perform t h e f i r s t cooldown t e s t s on t h e l a r g e 1 - m
helium dewar .
APPENDIX A
Report of Foreign Trave l t o Moscow, Y a l t a , Alushta and
Leningrad, USSR, September 6, - October 5, 1975
H. M. Long
Abst rac t
The purpose of t h i s t r i p was t o p a r t i c i p a t e i n t h e US-USSR Scien-
t i f i c and Technical Exchange i n t h e f i e l d of superconduct ing power
t ransmiss ion a s p a r t of t h e o v e r a l l exchange i n Energy Research and
Development, t o p r e s e n t a paper a t t h e F i r s t USSR Applied Supercon-
d u c t i v i t y Conference, and t o v i s i t s e v e r a l l a b o r a t o r i e s engaged i n
app l i ed superconduct iv i ty r e sea rch and development.
A working p l a n covering t h e US-USSR coopera t ion i n superconducting
power t ransmiss ion f o r t h e per iod of 1976-1978 was developed i n a s e r i e s
of meetings a t t h e Krzhizhanovsky Power Engineering I n s t i t u t e i n Moscow
and embodied i n a p ro toco l s igned by t h e l e a d e r s of t h e two s i d e s .
The Applied Superconduct ivi ty Conference h e l d a t Camp Eureka,
Alushta , Crimea, revea led a broad program of superconduct iv i ty research
and development i n t h e Sov ie t Union. subsequent t o u r s of i a b o r a t o r i e s
i n Leningrad and Moscow provided f i r s t -hand conf i rmat ion t h a t t h e pro-
grams a r e w e l l s t a f f e d and adequate ly funded.
Tl~e T-7 superconduct ing tokamak at t h e Kurchatov I n s t i t u t e of
Atomic Energy Rcscsrch appears t n he on schedule. The f i r s t s i x c o i l s
of fo r ty -e igh t were mounted and ready f o r test wh i l e th i r ty- two o t h e r
c o i l s were completed and ready t o be i n s t a l l e d i n t h e i r c o i l ca ses .
Completion ?is expected i n e a r l y 1976.
APPENDIX B
E l e c t r o s t a t i c F i e l d Ca lcu la t ions f o r Surface Flashover S tud ie s
Summary of Work Done June-August 1975
Paul O'Connor, ORAU
A computer program by W. F. Westendorp f o r c a l c u l a t i n g e l e c t r i c
f i e l d s a t a d i e l e c t r i c s u r f a c e i n connect ion wi th s u r f a c e f l a shove r
experiments h a s been descr ibed i n a prev ious r e p o r t . E s s e n t i a l l y , t h e
method involves s u b s t i t u t i n g f i n i t e charge elements f o r conductors and
po la r i zed d i e l e c t r i c s , then gene ra t ing and so lv ing a system of l i n e a r
equat ions express ing t h e boundary cond i t i ons on a s u i t a b l e number of
f i e l d p o i n t s . The unknowns i n t h e equat ions a r e t h e magnitudes of t h e
r e p r e s e n t a t i v e charges; once t h e s e a r e known, t h e p o t e n t i a l a t any p o i n t
may be e a s i l y determined.
The o r i g i n a l f l a shove r measurement geometry cons i s t ed of a s o l i d
d i e l e c t r i c c y l i n d e r threaded through two t o r o i d a l e l e c t r o d e s i n such a
way t h a t t h e r e was no con tac t between t h e me ta l and d i e l e c t r i c . This
arrangement was chosen t o e l i m i n a t e t h e complicat ing i n f l u e n c e of junc-
t i o n e f f e c t s on t h e experimental measurements. The problem wi th t h i s
geometry was t h a t t h e e l e c t r i c f i e l d a long t h e s u r f a c e of t h e d i e l e c t r i c
was always sma l l e r than t h e f i e l d i n t h e r eg ion where the two t o r o i d a l
e l e c t r o d e s approach each o t h e r most c l o s e l y . This could l ead t o break-
down i n t h e l i q u i d helium medium between t h e e l e c t r o d e s be fo re t h e
f l a shove r v o l t a g e was reached. The computer code was modified t o calcu-
l a t e t h e p o t e n t i a l g r a d i e n t i n t h i s r eg ion a s w e l l as on t h e d i e l e c t r i c
s u r f a c e , t o derermine L l ~ e amount: by which they d i f f e r e d . These ca lcu la-
t i o n s showed t h a t t h e e l e c t r i c f i e l d between t h e e l e c t r o d e s was g r e a t e r
than t h a t a long t h e d i e l e c t r i c s u r f a c e by a f a c t o r of 2.3 o r more,
depending on t h e p a r t i c u l a r geometry under cons ide ra t ion (Fig. B-1).
A modif ied e l e c t r o d e conf igu ra t ion was then i n v e s t i g a t e d i n an
a t t empt t o minimize t h e d i f f e r e n c e between t h e f i e l d a t t h e d i e l e c t r i c
s u r f a c e and t h a t n e a r t h e e l e c t r o d e s . The t o r o i d a l e l e c t r o d e s were
r ep l aced by f l a t c i r c u l a r d i sk6 wi th c e n t r a l h o l c s through w l ~ i d l t h e
d i e l e c t r i c rod passed, and a v a r i a b l e gap between t h e d i e l e c t r i c and
conductor . Th i s r e s u l t e d i n a f a i r l y uniform f i e l d i n t h e e n t i r e reg ion
between t h e p l a t e s . It was found t h a t t h e maximum f i e l d on t h e cy l inde r
s u r f a c e i n t h i s c o n f i g u r a t i o n w a s more than 90% of t h e f i e l d s t r e n g t h i n
t h e l i q u i d helium between t h e e l e c t r o d e s (Fig. B-2).
However, t h e u s e of f l a t e l e c t r o d e s l e a d s t o s t r o n g f i e l d s near
t h e i r i n n e r edges, which could cause p a r t i a l d i scharge i n t h e helium a t
r e l a t i v e l y low a p p l i e d v o l t a g e s . Another program mnd i f i ca t ion wao made
t o s tudy t h e s e edge e f f e c t s and t o enable t h e e q u i p o t e n t i a l l i n e s t o be
p l o t t e d . It w a s found t h a t t h e 100% e q u i p o t e n t i a l l i n e followed a
n e a r l y c i r c u l a r a r c a t t h e i n n e r edge of t h e high-vol tage e l e c t r o d e
wi thout 6he u s e of a d d i t i o n a l f i e l d p o i n t s and charges , t hus s imu la t ing
a t h i c k d i s k w i t h a rounded i n n e r edge. The th i ckness of t h e d i s k , and
hence t h e r a d i u s of cu rva tu re of t h e edge, could be vn r i cd hy the usu uf
o t h e r i n p u t parameters . The r e s u l t s of t h e s e c a l c u l a t i o n s showed t h a t
t h e f i e l d a t t h e e l e c t r o d e edge was indeed s t r o n g e r than t h a t on t h e
d i e l e c t r i c , by a f a c t o r which depended on t h e r a d i u s of t h e e l e c t r o d e
edge. Using t h e geometry which gave t h e most uniform o v e r a l l f i e l d s
( c y l i n d e r r a d i u s 0.3, p l a t e width 1 .0 , e l e c t r o d e spac ing 0.5, d i e l e c t r i c -
e l e c t r o d e gap 0.1) and ' a d i e l e c t r i c cons tan t of 4, t h e e l e c t r o d e th ick-
ness and edge r a d i u s were va r i ed . The b e s t r a t i o of f i e l d s t r e n g t h on
c y l i n d e r l f i e l d a t e l e c t r o d e edge w a s 0.46, w i t h i n t h e l i m i t s necessary
t o i n s u r e t h e accuracy of t h e program. This occurred f o r a t h i c k p l a t e
wi th a l a r g e r r a d i u s of curva ture , A t y p i c a l s e t of e q u i p o t e n t i a l l i n e s
f o r t h i s geometry i s shown i n Fig. B-3.
APPENDIX C
The Enhancement Fac tor of t h e E l e c t r i c F i e l d
i n t h e Point-Plane Conf igura t ion
To f a c i l i t a t e t h e i n t e r p r e t a t i o n of our point-plane breakdown d a t a ,
a computer program was w r i t t e n by our consu l t an t , W. F. Westendorp, t o
c a l c u l a t e t h e e l e c t r i c f i e l d enhancement f a c t o r i n a point-plane geome-
t r y . The d e t a i l s of t h e c a l c u l a t i o n , i nc lud ing a l i s t i n g of t h e program
i n BASIC, have been publ ished i n ORNL-TM-5137. The f i e l d was c a l c u l a t e d
by s imu la t ing t h e conductors wi th s u i t a b l e l i n e , p o i n t , and r i n g charges ,
applying t h e r equ i r ed boundary cond i t i ons , and summing t h e i n d i v i d u a l
c o n t r i b u t i o n s of t h e charges t o t h e p o t e n t i a l a t a given po in t . I f t h e
average f i e l d i? i s def ined as t h e r a t i o of t h e v o l t a g e t o t h e e l e c t r o d e
gap, t hen t h e maximum s u r f a c e f i e l d a t t h e p o i n t i s h ighe r by a f a c t o r f ,
t h e enhancement f a c t o r . Table C-I and Fig. C - 1 g i v e va lues of t h e
enhancement f a c t o r f o r a p o i n t w i th 18' ha l f -angle and t i p r a d i i of 166 ym
and 230 ym. These va lues were used t o c a l c u l a t e t h e s u r f a c e breakdown
f i e l d s i n Sec t ion B . 1 . Because t h e enhancement f a c t o r should depend
only on geometry and no t a b s o l u t e dimensions, two p o i n t s wi th t h e same
ha l f -angle should show t h e same enhancement f a c t o r a t equa l r a t i o s of
gap t o t i p r a d i u s g / r . For t h e 230 pm p o i n t , g / r = 4.35 a t g = 1.0 mm
and f = 20.0. For t h e 166 pm p o i n t , g/r = 4.22 a t g = 0.7 mm and f =
19.4. More exac t agreement may b e obta ined by i n t e r p o l a t i n g becween t h e
va lues i n the t a b l e .
Table C-I
Enhancement F a c t o r vs Gap f o r 18' Point-Plane Elec t rodes
Trip Radiuo 166 pm
' h i p Radius 230 pm
REFERENCES
1. Cryogenic Power Transmission Technology-Cryogenic D i e l e c t r i c s ,
~ u a r t e r l ~ Report , October 1 - December 31, 1974, ORNL-TM-4900
(June 1975).
. 2 . T. J. Lewis, Proc. I.E.E. - 100, P t . IIa, 141 (1953).
3. J. Gerhold, Cryogenics - 12, 370 (1972).
4. Cryogenic Power Transmission Technology-Cryogenic D i e l e c t r i c s ,
Semiannual Report , ORNL-TM-4187 (March 1973) .
FIGURE CAPTIONS
1. High v o l t a g e c r y o s t a t and t e s t s t and .
2. F l a t G-10 f i b e r g l a s s head f o r h igh v o l t a g e c r p o s t a t .
3. Cooling c o i l f o r in te rmedia te -vol tage c r y o s t a t I V 3. A: copper
cool ing c o i l s ; B: suppor t s t r u c t u r e f o r cool ing c o i l s ; C : copper
convect ion s h i e l d ; D: h e a t e r w i re s ; E: window i n dewar.
4. Transformer B of 700 kV test s e t , p r i o r t o reassembly of i r o n core.
5. Completed Transformer B i n wooden suppor t frame, ready t o be s e t
up r igh t .
6 . Schematic of a c r e s i s t a n c e b r i d g e f o r thermometry.
7 . Point-plane breakdown v o l t a g e s i n t e c h n i c a l l y pure l i q u i d helium
wi th 18O, 230 um po in t . Dashed l i n e s show e a r l i e r d a t a w i th s i m i l a r
166 ym po in t .
8. Point-plane breakdown v o l t a g e s i n air-contaminated l i q u i d helium.
9. Comparison of breakdown vo l t ages wi th point-plane e l e c t r o d e s i n
t e c h n i c a l l y pure and a i r contaminated l i q u i d helium. Curve 1 - r m s
ac, pure l i q u i d helium; Curves 2 and 3 - dc, p o i n t nega t ive , pure
helium and air-eontaminated helium r e s p e c t i v e l y ; Curves 4 and 5 -
dc, po in t p o s i t i v e , pure and air-contaminated helium r e s p e c t i v e l y .
10 . Calcu la ted maximum s u r f a c e breakdown f i e l d s w i t h point-plane e lec-
t r o d e s i n pure l i q u i d helium.
11. Pho todc rographs of 166 pm and 230 u m p o i n t s .
12. X-ray of to ta l ly-encapsula ted film sample.
13 . Cross-sect ion of pro to type p re s su r i zed encapsulated f i l m sample.
B-la Surface f l a shove r geometry - t o r o i d s on d i e l e c t r i c c y l i n d e r .
B-lb P o t e n t i a l v s d i s t a n c e - t o r o i d s i n d i e l e c t r i c c y l i n d e r .
B - 2 . Potential vs distance - modified toroids on dielectric cylinder.
B - 3 . Equipotentials between modified toroids.
C-1. Plot of enhancement factor vs gap for various point radii.
Fig. 2
ORNL- DWG 76-! 510
Fig. 3
Fig. 5
ORNL- DWG 76- 4828
Hz VAC
STANCOR P-6134 (410 V PRIMARY, 6.3 V C.T. SECONDARY)
F i g . 6
RESISTANCE BOX
1 LOCK- IN
AMPLIFIER
THERMOMETERS
4
ORNL-CWG 76- 1513R
I I I 1 vB MA, (POINT+)
vs MAX (POINT-)
0 /
I I I I I *
0 2 4 6 8 ! 0 12
GAP SEPARATION (mm)
F i g . 7
ORNL-DWG 76-1511 80
4 6 8 10 12 GAP SEPARATION (mm)
- 'B MAX ( POINT +)
v~ MAX ( POINT - )
AVERAGE
VB MIN (POINT +) -
V~ MIN (POINT - )
-
I
Fig. 8
1
80 DRNL-DWG 76-1512
4 6 8
G A P SEPARATION ( m m )
Fig. 9
NEGATIVE POINT
ORNL-DWG 76-1829 I 1
0 0 -
O * POSITIVE POINT 1 6 6 - p m RADIUS -.
2 3 0 - p m RADIUS - A 0.
- 0
0 -
0 ---- SPHERE-PLANE - 0 0 0 -
O O .
0 I 2 3 4 5 6 7 8 9 10
GAP (mm)
Fig. 10
Ci
AL
-
- -
A - A
-
B -
- A A A A
I I
I
0 . h I I
INCHES 0 . h
iy v y v , l M ~ m ~ a I1
I , , 12m 14Ud t-
0.04 l NCH ES .05
F i g . 11
ORNL- DWG 76- 1509
0 1 2 3 4 5 I I I I I 1 I I I I I
crn
4 9
ORNL DWG. 75-2550
C H A R G E RING )(BOUNDARY PT. Fig. B-la
ORNL-DWG 76-1508 100
- A POTENTIAL AL.ONG SURFACE
POTENTIAL BETWEEN PLATES -
- -
- -
- -
- -
-
-
I - I
I -
y- MIDPLANE
I
DISTANCE FROM GROUND P L A N E
Fig. R-2
ORNL-DWG 76-1506
0.1 uni t M
Fig. B-3
ORNL- DWG 76- 1830
0 0.2 0.4 0.6 0.8 1 .O 1.2 G A P (cm)
Fig . C-1
11. DISPERSION HARDENING OF ALUMINUM
A . R e s u l t s
We a r e cont inuing t o c h a r a c t e r i z e t h e RRR and microhardness of
so lu t ion -hea t - t r ea t&, quenched and aged a l l o y s of u l t r a -h igh p u r i t y
aluminum con ta in ing 0.07, 0.12, and 0.26 w t % gold. A number of t h i n
f o i l specimens of t h e s e a l l o y s i n v a r i o u s hea t - t r ea t ed cond i t i ons have
been examined by t ransmiss ion e l e c t r o n microscopy. I n i t i a l l y we exper-
ienced some d i f f i c u l t y i n prepar ing contaminat ion-free f o i l s . Now,
however, techniques have been worked o u t t h a t w i l l p rovide us w i t h
reasonable f o i l s from which we can o b t a i n q u a n t i t a t i v e information
regard ing p r e c i p i t a t e morphology, shape, s i z e , i n t e r f a c i a l cha rac t e r -
i s t i c s and number d e n s i t y . We in t end t o c o r r e l a t e t h i s in format ion wi th
t h e RRR and microhardness proper ty measurements.
Based on the work a l r e a d y performed, we i n t u i t i v e l y f e l t t h a t a
h igher RRR might be achievable i n a n aged a l l o y con ta in ing 0.16 w t %
gold. To t e s t t h i s i n t u i t i o n we prepared a n a l l o y of t h a t composition
i n t h e same manner a s t h e o the r a l l o y s ( s e e e a r l i e r q u a r t e r l y r e p o r t s i n
t h i s s e r i e s ) . This m a t e r i a l has now been f a b r i c a t e d i n t o specimen s tock
and measurements w i l l commence s h o r t l y .
Mechanical s t r eng then ing of aluminum by means of long f i b e r s embedded
wi th in a ma t r ix of aluminum has been suggested a s a p o t e n t i a l l y a t t r a c -
t i v e a l t e r n a t i v e t o s t r eng then ing by p r e c i p i t a t i o n hardening. Our previous
work has shown t h a t commercially suppl ied composites do n o t meet t h e
high s t anda rds of RRR r equ i r ed . We f e l t t h a t t h e impuri ty of t h e
aluminum ma t r ix m a t e r i a l was by and l a r g e r e s p o n s i b l e f o r t h e l a c k of
h igh conduc t iv i ty i n t h e s e composites. . During t h e l a s t q u a r t e r of FY-75,
a program was conducted by Y-12 Metallurgical Development to produce
specimens of filament-reinforced high-purity aluminum. Zone-refined
aluminum was cast around a low-volume fraction of high-strength fila-
ments in an effort to increase strength without significantly altering
the superior electrical conduction characteristics of the matrix. The
pressure-vacuum liquid infiltration technique, which was developed in
1 earlier Y-12 work, was utilized to produce test specimens. The details
of the processing techniques and some of the characteristics of the
resulting composite specimens are described in the Appendix. The RRR
of each of these composite specimens was determined, along with that of
two zone-refined aluminum dummy specimens which had been prepared in the
same way and with the same equipment as the composites but with no
fibers. The results are presented in Table I.
Table P. P.acidua1 Rcaistance Ratio 01 Alu~ul~~ulu Composites Prepared by Y-12 Development
Reinforced Matrix Fiber Material Material RRR
A1 (zone refined)
Second try
None 13.1
None
B-BN
3 vol % G vol X
3 vol % 100 to 200 6 vol % 120 to 140 9 vol % 140
W+3% Re
2 vol 5 3 vol % 6 vol. %
These f i n d i n g s sugges t t h a t t he aluminum w a s be ing contaminated
during t h e mel t ing and c a s t i n g procedure, as t h e RRR was reduced from
13,000 ( s t a r t i n g m a t e r i a l ) t o 13.1. X-ray f luo rescence a n a l y s i s r evea l ed
t h e contaminants t o be tantalum and/or tungs ten . E f f o r t s t o improve
t h e technique served t o r a i s e RRR t o 500 - 700. It would seem, however,
t h a t a d d i t i o n a l , and perhaps major, design improvements a r e needed
be fo re t h e l i q u i d - i n f i l t r a t i o n c a s t i n g technique could produce e l e c t r i -
c a l l y s u i t a b l e aluminum composites. On t h e o t h e r hand, t h e composites,
with t h e except ion of t h e ones wi th tungs ten a l l o y f i b e r s , were s i g n i -
f i c a n t l y b e t t e r than t h e commercially suppl ied ones t e s t e d e a r l i e r .
This s t r e s s e s t h e importance of t h e i n i t i a l p u r i t y of t h e aluminum
matr ix m a t e r i a l and t h e need t o minimize contamination from t h e sur -
roundings dur ing p repa ra t ion of t h e composite.
APPENDIX D
Aluminum Matr ix Composites
John G. Banker
Ma te r i a l s
Zone-refined aluminum was provided f o r t he experimental samples by
ORNL. Reinforcement m a t e r i a l s which were r e a d i l y a v a i l a b l e from e a r l i e r
composite programs were: ' (1 ) boron f i l amen t s w i th a BN s u r f a c e c o a t ,
produced by Avco Corporat ion, of 0.145 mm d iameter , c o n s i s t i n g of a
0.013 mm tungs ten core surrounded by boron CVD depos i ted t o 0.142 mm
d iameter , a l l of which i s surrounded by a t h i n BN l a y e r produced by
chemical r e a c t i o n wi th anunonia; (2) s i l i c o n ca rb ide f i l amen t s of
0.142 mm diameter w i th a 0.013 mm tungs ten core , CVD produced by Avco;
and (3 ) tungsten-3 rhenium wire of 0.127 mm diameter , from General
E l e c t r i c .
Equipment
A res i s tance-hea ted vacuum furnace wi th t i l t - p o u r c a p a b i l i t i e s was
u t i l i z e d f o r t h e s e experiments. A second h e a t i n g element was added t o
t h e furnace t o provide t h e necessary mold hea t ing . The equipment i s
schemat ica l ly descr ibed i n F ig . 1. The mel t ing c r u c i b l e was made of
uncoated, ATJ-grade g raph i t e .
The mold des ign is shown i n Fig. 2. The mold was a l s o made from
ATJ g r a p h i t e and was n o t coated w i t h a r e l e a s e agent . A s shown, t h e
mold c a v i t y w a s 5 mm diameter by 60 mm long.
Process ing
The f i l amen t s were cu t i n t o 75 nun long segments and t h e proper
number were counted f o r each composite, depending upon t h e volume f r a c t i o n
d e s i r e d . The ends of each f i lament bundle were then po t t ed i n a s l u g
of Sauere isen Cement ( b a s i c a l l y S i02) 12 mm long by 4.5 mm diameter .
The p o t t i n g w a s r e q u i r e d t o hold t h e f i l amen t i n p l ace dur ing t h e sub-
sequent c a s t i n g ope ra t ion . (Due t o r e l a t i v e l y poor w e t t a b i l i t y , t h e
s u r f a c e t e n s i o n on molten meta l t ends t o f o r c e loose f i l amen t s t o g e t h e r
i n t o a t i g h t bundle.) A f t e r a l lowing the Sauere isen t o harden, t h e
f i l a m e n t bundle was loaded i n t o t h e specimen mold.
'l'he d e s i r e d weight of aluminum was c u t from t h e i n g o t s , c leaned i n
a s o l u t i o n of 70% H3P04, 25% H2S04, and 5% HN03 a t 60-80°C f o r 10 min,
and washed i n d i s t i l l e d water . The charge was loaded i n t o t h e c r u c i b l e
and t h e fu rnace chamber was evacuated t o l e s s than 1 .0 Pa.
The meta l w a s hea t ed t o 850°C whi l e t h e mold was hea ted t o 600°C.
A f t e r a 15-min soak , t h e molten aluminum was poured i n t o t h e mold. The
fu rnace chamber was immediately r e tu rned t o atmospheric p re s su re , pro-
v i d i n g a f o r c e f o r d r i v i n g t h e molten charge i n t o t h e evacuated mold
and i n t o t h e i n t e r - f i l a m e n t c a v i t i e s . ,
R e s u l t s
Table.11 lists t h e f i l amen t type and volume f r a c t i o n combinations
produced. F igs . 3a, b and c a r e x-ray p o s i t i v e s showing the gene ra l
soundness and f i l a m e n t d i s t r i b u t i o n i n s e v e r a l of t h e specimens. F ig . 4
shows a t y p i c a l f i l a m e n t matrix d i s t r i b u t i o n i n 8 3-vol X boron f i l amen t
composite. Table 111 shows t h e rule-of-mixtures s t r e n g t h es t imated f o r
the composite specimens2 when i t i s assumed t h a t no f i lament s t r e n g t h
deg rada t ion occurs and t h a t t he y i e l d s t r e n g t h of t h e mat r ix i s 3.45 MPa.
The f i l a m e n t s t r e n g t h s a r e 585 MF'a f o r t h e tungs ten rhenium, 3 . 1 GPa
f o r S i c , and 3.8 GPa f o r BN coated boron.
TABLE 11. Composite Specimen Summary
Filament Type
Volume Fraction Quantity Filament Produced
Silicon Carbide
BN Boron
None
TABLE 111. Rule-of-Mixtures Composite Tensile Strength
Filament Loading ROM Strength (MPa)
3% Sic 96
6X S i c 189
9X Sic 282
3% NB Boron 117
6% BN Boron 224
3% W-Re 2 1
6% W-Re 3 8
Real s t r e n g t h v a l u e s of 2 H 0 % of t h e ROM s t r e n g t h s a r e a n t i c i p a t e d
due t o bundle f a i l u r e c h a r a c t e r i s t i c s , f i l amen t s t r e n g t h degrada t ion ,
and uneven f i l a m e n t d i s t r i b u t i o n .
Chemical a n a l y s e s w e r e conducted t o determine i f ma t r ix p u r i t y was
maintained. P o t e n t i a l sources of contaminat ion were t h e g r a p h i t e
c r u c i b l e s , fu rnace hardware (such as oxide from tantalum b a f f l e s and
Lu~lgsten e lements ) , and reactinn. with th~? r e i n f o r o i n g f i l amen t s . Tl~e
p o t e n t i a l f o r contaminat ion from each of t h e s e sources could be reduced
s i g n i f i c a n t l y i f a p roces s ing system were designed s p e c i f i c a l l y f o r
producing t h e s e m a t e r i a l s .
F u t u r e Work
A product ion system f o r producing long l eng ths of r e in fo rced rod
o r t ube would r e q u i r e a cont inuous c a s t i n g ope ra t ion , i n p l a c e of t h e
b a t c h c a s t i n g system used i n t h i s e f f o r t . From exper ience wi th cont in-
uous c a s t i n g appa ra tus f o r producing six-fi3,ament magnesium/boron t ape ,
i t i s a n t i c i p a t e d t h a t f i l amen t alignment would be e a s i e r and s t r e n g t h
deg rada t ion lower, compared wi th t h e ba tch c a s t i n g process . Development
of a s u i t a b l e c h i l l - t y p e d i e i s a n t i c i p a t e d t o b e t h e major problem i n
developing a low f i l amen t - f r ac t ion cont inuous casting apparati is , 4-11
cont inuous ly c a s t composites d i scussed i n a v a i l a b l e l i t e r a t u r e have ran-
t a i n e d a h igh filamenr: f r a c t i o n , e l imina t ing t h e need f o r a s o l i d i f i c a t i o n
d i e . Fig. 5 s chemat i ca l ly d e p i c t s a p o t e n t i a l continuous c a s t i n g
appa ra tus .
- REFERENCES
1. J. G. Banker, "Metal Matrix Composite Fabrication by Liquid
1nf iltration," SAMPE Quarterly, Vol. - 39 (January 1974) . 2. S. W. Tsai et al., Effect of Constituent Material Properties on
the Strength of Fiber-Reinforced Composite Materials, AFML-TR-66-190,
p . 14 ( ~ u ~ u s t 1966) .
THIS PAGE
WAS INTENTIONALLY
LEFT BLANK
FIGURE CAPTIONS
1. Furnace arrangement for static pressure-vacuum casting.
2. Casting mold showing location of filaments.
3. (a)(b)(c) Radiographs of several composite specimens taken at
120' intervals to show filament distribution. The tab at the left
of each specimen indicates filament type and volume percent loading.
The large-diameter tungsten filaments are obvious. The small-
diameter cores of the boron and Sic filaments can be discerned
upon close observation.
4 . Typical filament distributian in an aluminum-3 wt % boron composite.
5. Schematic of composite continuous casting apparatus.
ORNL-DWG 75-48420
VACUUM
CHARGE METAL
VACUUM CHAMBER
Fig. 1
ORNL- DWG 75- 4 8119
,5-mm -DIAM HOLE
MOLD MATERIAL : ATJ GRAPHITE
DIMENSIONS ARE I N MILLIMETERS
F i g . 2
EE 'SId
-1 1,1.1 L., . L
0
p4
01 5%9DIS
/----
/0 L
./\,\
0/ C /0 L-
915% E0 C..
:IN 8
0#
EEEL91-A
89
ORNL-DWG 75-18118
INERT GhS
MCLTEN METAL
ILL MOLD EXIT
LPREHEAT FURNACE LCRUCJBLE
LcoLLIMAmR
Fig. 5
I n t e r n a l D i s t r i b u t i o n
S. E. B e a l l J. Blevins (ERDA-ORO) L. G. Christophorou Document Reference Sec t ion , Y-12 W. F. Gauster G. G. Kel ley R. H. Kernohan C . C . Koch Laboratory Records Laboratory Records RC D i r e c t o r , RTSD, ERDA, OR0 CR L ib ra ry R. S. L iv ings ton H. M. Long M. M. Menon F. L. M i l l e r 0. B. Morgan ORNL Pa ten t Of f i ce S. W. Schwenterly S. T. Sekula Thermonuclear Div is ion Library R. A. Vandermeer A. Zuclcer
Ex te rna l D i s t r i b u t i o n 1
48. G . Bogner, Siemens AG Research Labora to r i e s , 852 Erlangen, Germany
49. J. M. Bonnevil lc , Hydro-Quebec I n s t i t u t e of Research Technical Engineering and Thermodynamics Laboratory, P.O. Box 1000, Varennes, Quebec, Canada J o l 2 PO
50. R. Boom, Un ive r s i t y of Wisconsin, 513 Engineering Research Bui ld ing , 1500 Johnson Drivc, Madison, W I 53706
51.-54. D r . Alvin C l o r f e i n e , D iv i s ion of E l e c t r i c Energy Systems, U.S. Energy Research and Development Adminis t ra t ion , 20 Massachuset ts Avenue N.W. , Mail S t a t i o n G-234, Washing- ton , DC 20545
55. C . M. Cooke, Massachuset ts I n s t i t u t e of Technology, High Voltage Research Laboratory, Building N-10, Cambridge MA U21.39
56. E. D . Eich, Power Technologies, Inc . , Box 284, Milwood, NY 10546
57.-83. ERDA TIC, P.O. Box 62, Oak Ridge, TN 37830 84.-87. E. B. Forsy th , Brookhaven Nat iona l Laboratory, Upton, L . I . ,
NY 11973 88. E. 0 . F o r s t e r , Esso Research and Engineering Co., P.O. Box 45,
Linden, N J 07036 89. M. Fukasawa, H i t a c h i Cable, Ltd. Research Laboratory, The 1st
Department 5-1, Hitaka-cho, Hi tachi -sh i , Ibaraki-ken, Japan
E. Gamin, Stanford Linear Accelerator Center, Stanford University, P. 0. Box 4349, Stanford, CA 94305
Dr. Roy W. Gould, Department of Applied Physics, California Institute of Technology, Pasadena, CA 91109
Dr. Harold Grad, Courant Institute, New York University, 251 Mercer Street, New York, NY 19012
P. Graneau, Underground Power Corp., 205 Holdenwood Road, Concord, MA 01742
David Hartmann, Bonneville Power Authority, P.O. Box 3621, Portland, OR 97208
R. L. Hirsch, ERDA, Division of Controll~d Therrnonuclcar Research, Washington, DC 20545
C. H. Hoogerhyde, Public Service Cas and Electric Co. of New Jersey, 8n Park Place, Mcwark, NJ 07101
M. Jeffries, General Electric Co., P.O. Box 43, Bldg. 37, R a o n ~ 3G5, Schenectady, NY 12301
M. Jones, National Bureau of Standards, Institute for Basic Standards, Cryogenic Division, 275.00, Buulder, CO 80302
W. F. Keller, Los Alamos Scientific Lahoratory, University of California, P.O. Box 1663, Los Alamos, NM 86544
C. N. King, Stanford University, Department of Applied Physics, Stanford, CA 94305
P. Komarek, Kernforschungszentrum Karlsruhe, Institut fur Experimentelle Kernphysik IIT, D75 Karlsruhe, Postfacl~ 3640, Germany
S. Linke, Cornell University, School of Electrical Engineering, 204 Phillips Hall, fthaca, NY 14850
B. Maddox, Central Electricity Research Laboratories, Electrical Engineering Division, Kelvin Avenue, Leatherhearl , Surroy , England
R. Meyerhoff, Union Carbide Corp., Technical Center Linde Research Laboratories, Tarrytown, NY 10591
M. Muleahy, Department of Research and Environmental Affairs, Boston Edison Co., 800 Boylston Street, Boston, MA 02199
J. Nichol, Arthur B. Little Company, Inc. 20 Acorn Park, Cambridge, MA 07140
Oskars Petersons, National Bureau of Standards, High Voltage Meat;ur.ement bectlon, Bldg, 22C, Room B-344, Washington, DC 20234
Dr. T. Prael~duser, Raether Str. 4, 4147 Aesch. B1, Switzerland Mario hbinowitr , Elecbr lr! Powcr Iksearcl~ Insrirute, 3412
Hillview Avenue, Palo Alto, CA 94304 E. H. Reynolds, British Insulated Callenders Cables, Ltd.,
38 Wood Lane, London W12 7DX, England Dr. David J. Rose, Department of Nuclear Engineering, Massa-
chusetts InsLILute of Technology, Cambridge, MA 02139 C. H. Rosner, Intermagnetics General Corp., Charles Industrial
Park, New Karner Road, Guilderland, NY 12084 Dr. George M. L. Sommerman, 2402 Collins Road, Pittsburgh
PA 15235 Z. J. J. Stekly, Magnetic Corporation of America, 179 Bear Hill Road, Waltham, MA 02154
115. D. K. Stevens, DPR-ERDA, Washington DC 20545 116. C. E. Taylor, L-382, Lawrence Livermore Laboratory, P.O.
Box 808, Livermore, CA 94550 117. Dr. B. M. Weedy, Electrical Engineering Dept., The University
Southampton, United Kingdom 118. Dr. W. F. Westendorp, 17 Front Street, Schenectady, NY 12305 119. Dr. R. Wimmershoff, AEG-Telefunken Kabelwerke Ag, Muelheim,
W. Germany 120. J. Wong, Supercon, Inc., 9 Erie Drive, Natick, MA 01760 121. Dr. Herbert H. Woodson, Chairman, Department of Electrical
Engineering, The University of Texas at Austin, Austin, TX 78712
122. A. Zanona, Commonwealth Edison Company, Technical Center, 1319 South First Avenue, Maywood, IL 60153
a US. GOVERNMENT PRINTING OFFICE: 1976-74&189/310
