THE DEVELOPMENT OF SUPERCONDUCTING MATERIALS I N CHINA

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THE DEVELOPMENT OF SUPERCONDUCTING MATERIALS I N CHINA

S. Han

To cite this version:

S. Han. THE DEVELOPMENT OF SUPERCONDUCTING MATERIALS I N CHINA. Journal de

Physique Colloques, 1984, 45 (C1), pp.C1-373-C1-378. �10.1051/jphyscol:1984175�. �jpa-00223731�

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Colloque C l , supplément au n° 1, Tome 45, janvier 1984 page Cl-373

THE DEVELOPMENT OF SUPERCONDUCTING MATERIALS IN CHINA

S. Han

Electrical Engineering Institute, Accidentia Sinica, Beijing, China Résumé :

La nécessité de développer les aimants supraconducteurs suscite un grand intérêt dans de nombreux laboratoires chinois pour la recherche et la production des matériaux supraconducteurs. Cet article rend compte du développement des matériaux supraconducteurs en Chine au cours des dix dernières années et de la situa- tion présente, principalement dans le domaine des matériaux d'utilisation pratique tels que Nb-Ti, Nb3Sn, V3Sn et quelques autres composés. Un effort important a été consacré à l'amélio- ration de Je et Hcj. Finalement, les perspectives de développe- ment de ces matériaux en vue des applications aux aimants supraconducteurs seront brièvement exposées.

Abstract :

According to the requirement of the development of superconducting magnets, the research and production of superconducting materials are much interested in many laboratories in China.

This article will review the development of superconducting materials in the past ten years in China, and the present situations, mainly in the field of practical materials, Such as NbTi, Nb3Sn, V3Ga and some other compounds. Much effort has been put on the improvements of Jc and Hc2 . Finally,

from the point of view of the development of superconducting magnets in China, the general out look for the future of the superconducting materals will be briefly presented as well.

INTRODUCTION

During the last decade, owing to the development of applied superconductivity a wide scope of research and development work of superconducting materials has been under- taken in many laboratories in China, such as:

General Research Institute for Nonferrous Metals, (Beijing); Baoji Research Institute .of Nonferrous Metals; Changsha Research Institute of Mining and Metallurgy; Shanghai Research Institute of NQnferrous Metal under the Ministry of Metallurgical Industry, and Physical Institute; Shanghai metallurgical Institute; Shen-Yang Metal Institute under Academia Sinica, etc. From physical properties, practical materials to the emerging materials, many of the different aspect of superconducting materials has been carried out. This article will give a brief review emphasis will be put on the practical superconducting materials, NbTi, Nb3Sn and V3Ga.

The NbTi conductors are widely used in fabricating of different types of magnets. Much efforts has been put on the development of multifilament composite conductors and improving the critical current density Jc of the conductors. A series of different kinds NbTi wire and conductors are developed, and can be dilivered in amount of tons in a not so long period.

The research and development work of Nb, Sn materials are much interested in some labor- atoties now. The technique of fabricating Nb3Sn tayes by chemical vapor deposition

(CVD) method, and by the surface diffusion process was investigated several years aga, and now the technique of fabricating multifilament Nb3Sn are actlvly carrying on in some laboratories.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984175

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Cl-374 JOURNAL

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PHYSIQUE

R e c e n t l y , t h e h i g h f i e l d m a t e r i a l s a n d l a r g e s c a l e c o n d u c t o r s r e s e a r c h work c o n c e r n i n g t o c o o l i n g method s u c h a s f o r c e d f l o w a n d s u p e r f l u i d He ( 1 . 8 k ) a r e i n t e r e s t e d i n some l a b o r a t o r i e s , a n d t h e e m e r g i n g m a t e r i a l s works a r e a l s o u n d e r t a k e n . T h i s a r t i c l e w i l l g i v e a b r i e f d e s c r i p t i o n a b o u t t h e v a r i o u s a s p e c t s o f t h e d e v e l o p m e n t o f s u p e r c o n d u c t - i n g m a t e r i a l s i n C h i n a .

NbTi CONDUCTOR

( 1 ) S i n c e e a r l y s e v e n t i e s a n d t h e s u b s e q u e n t y e a r s , many l a b o r a t o r i e s h a v e p a i d much a t t e n t i o n t o d e v e l o p m e n t o f NbTi m u l t i f i l a m e n t a r y c o n d u c t o r s , up t o now t h e f o l l o w i n g d i f f e r e n t k i n d s o f c o n d u c t o r s a r e d e v e l o p e d a n d u s e d i n f a b r i c a t i n g d i f f e r e n t m a g n e t s .

*

T y p i c a l r o u n d - wires:

The r o u n d wires w i t h t h e d i a m e t e r o f 6 0 . 2 , 80.3, 4 0 . 4 , d 0 . 5 , d 0 . 7 5 a r e w i d e l y u s e d i n t h e small and s m a l l medium s i z e m a g n e t s , o r a s t h e e l e m e n t s t r a n d w i r e f o r t h e c a b l e s . G e n e r a l l y t h e r a t i o o f Cu t o NbTi a r e 1-2, a n d t h e f i l a m e n t d i a m e t e r a r e 8-301111.

F o r e x a m p l e , a s t a n d a r d p e r f o r m a n c e o f d 0 . 5 w i r e i s l i s t e d a s f o l l o w s :

MF-Nb-50Ti w i r e , d 0 . 5 , Cu/NbTi r a t i o 1 . 2 , f i l a m e n t number 1 6 3 , f i l a m e n t d i a m e t e r 26fim, t w i s t p i t c h 1 5 m m . S h o r t s a m p l e a t 4.2k, t h e c r i t i c a l c u r r e n t was t a k e n t h a t p r o d u c e s a v o l t a g e o f 1 pv/cm.

T a b l e 1 P e r f o r m a n c e o f a t y p i c a l r o u n d w i r e

From t h e a b o v e list i t was f o u n d t h a t t h e c r i t i c a l c u r r e n t d e n s i t y J c d e c r e a s e d a b r u p - t l y . We h a v e t e s t e d t h e MF-Nb-46.5Ti w i r e , i t s J c a r e b e t t e r i n t h e h i g h f i e l d r e g i o n .

R e c t a n g u l a r c r o s s s e c t i o n c o n d u c t o r

I n o r d e r t o i n v e s t i g a t e t h e medium s i z e s u p e r c o n d u c t i n g m a g n e t s w i t h a d i a b a t i c s t a b i l - i z a t i o n mode, two k i n d s o f l o w e r Cu/NbTi r a t i o r e c t a n g u l a r c r o s s - s e c t i o n c o n d u c t o r s w e r e d e v e l o p e d , The c r o s s - s e c t i o n a r e 2.09X1.54rnm2 ( 1 ) a n d 3.28X1.81mm2 ( 2 ) r e s p - e c t i v e l y . The p e r f o r m a n c e o f t h e c o n d u c t o r - 1 is shown i n f o l l o w i n g :

C o n d u c t o r s i z e 2 . 0 9 ~ 1 . 54=3.21gmm: Cu/S.C r a t i o = 2 , Number o f f i l a m e n t 5 0 4 , f i l a m e n t d i a m e t e r 501m, t w i s t p i t c h 35mm.

T a b l e 2 C r i t i c a l c u r r e n t o f c o n d u c t o r

The c o n d u c t o r - 2 h a s a c r o s s - s e c t i o n o f 3 . 2 8 ~ 1 . 8 1 m m ~ , Cu/SC r a t i o 2 , number o f f i l a m e n t 500, f i l a m e n t d i a m e t e r 60-701111, t w i s t p i t c h 50mm. The c r i t i c a l c u r r e n t d e n s t y J c a t 4 . 2 , 5T c a n r e a c h t h e same l e v e l as t h e c o n d u c t o r - 1 , i s a b o u t 1 . 6 ~ 1 0 ~ A / c m ~

.

* NbTi c o m p o s i t e c o n d u c t o r w i t h h i g h Cu/S.C r a t i o

F o r a l a r g e magnet p r o j e c t w i t h t h e c r y o g e n i c s t a b i l i z a t i o n mode a NbTi c o m p o s i t e c o n d u c t o r was d e s i g n e d a n d f a b r i c a t e d . The main p a r a m e t e r s o f t h e c o n d u c t o r a r e as f o l l o w s :

C o n d u c t o r s i z e 3.67mm2

,

f i l a m e n t d i a m e t e r 7 0 ~ m , number o f f i l a m e n t s 4 3 2 , t w i s t p i t c h 6omm, Cu/S.C 10,

The c o n d u c t o r was t e s t e d i n t h e f i e l d from 5T up t o 10T, The r e s u l t s a r e a s t h e f o l l p w s :

T a b l e 3 P e r f o r m a n c e o f t h e h i g h Cu/S.C r a t i o n c o n d u c t o r

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*

P u l s e d magnet c o n d u c t o r

Some s u p e r c o n d u c t i n g m a g n e t s o p e r a t i n g u n d e r t h e c o n d i t i o n o f p u l s e d f i e l d o r t h e o s s i l a t i n g f i e l d s u p e r i m p o s e d o n a D.C f i e l d , i t r e q u i r e s t h e c o n d u c t o r s w i t h l o w e r A.C l o s s o r h i g h s p e e d e x c i t i n g r a t e . They a r e u s e d a s t h e m a g n e t s o f h i g h e n e r g y a c c - e l e r a t o r , t h e p u l s e d e n e r g y s t o r a g e a n d t h e f i e l d magnet o f s u p e r c o n d c u t i n g g e n e r a t o r , e t c .

A c c o r d i n g t o t h e s e r e q u i r e m e n t s s e v e r a l k i n d s o f p u l s e d magnet c o n d u c t o r s w e r e deve- l o p e d , t h e b r a i d a n d t h e f l a t c a b l e s w i t h Cu a n d CuNi-Cu m a t r i x , The p e r f o r m a n c e o f t h e s e c o m p o s i t e c o n d u c t o r s a r e l i s t e d a s t h e f o l l o w i n g t a b l e .

T a b l e 4 P e r f o r m a n c e of p u l s e d c o n d u c t o r s

c a b l e c a b l e c a b l e

b r a i d ( 1 1 s t r a n d ) ( 2 3 s t r a n d ) ( 2 3 s t r a n d ) M a t e r i a l

Type o f c o n d u c t o r S t r a n d d i a m e t e r Number o f s t r a n d F i l a m e n t d i a m e t e r , pm Number o f f i l a m e n t

p e r s t r a n d F i l a m e n t t w i s t e d

p i t c h , cm

T r a n s p o s a t i o n p i t c h o f s t r a n d s , cm

F i l l i n g m a t t e r Cu, CuNi/NbTi

S p a c e f a c t o r o f c o n d u c t o r C u r r e n t c a p a c i t y ( 5 T ) A C r i t i c a l c u r r e n t d e s i t y

. J c ( l ~ ~ ~ / c m ) ( 5 T )

NbTi b r a i d

Indium 1:l 0.457

NbTi-CuNi f l a t c a b l e ? (4.3X1.35mm )

0 . 7 5 11 1 2 1 3 6 9

NbTi-CuNi f l a t c a b l e ( 9 . 3 ~ 1 . 2 6 ~ ~ ' ) 0 . 7 5

2 3 6 5 9 9 5

NbTi-Cu f l a t c a b l e

A s e r i e s o f s o l e n o i d and d i p o l e s were wound a n d t e s t e d w i t h t h e a b o v e c o n d u c t o r s . I t shows t h e CulQi~Cu m a t r i x f l a t c a b l e h a s r e a c h e d a good p e r f o r m a n c e .

* Hollow s u p e r c o n d u c t o r

I n o r d e r t o i n v e s t i g a t e t h e m a g n e t s w i t h s u p e r c r i t i c a l He c o o l i n g mode, t h e s i m p l e h o l l o w c o n d u c t o r was f a b r i c a t e d . The main s p e c i f i c a t i o n a r e a s t h e f o l l o w i n g : T a b l e 5 Main s p e c i f i c a t i o n o f t h e h o l l o w c o n d u c t o r

c o n d u c t o r c o n d u c t o r p a s s a g e w i r e d i a . f i l a m e n t Cu/SC J c ~ b ~ i ( 5 T t

t y p e 8ize(mm2 ) size(mmz ) (mm) d i a ( p m ) r a t i o 4 . 2 k ) l ~ ~ ~ / c m '

c o m p o s i t e 3.25X3.8 1.8X1.2 0.3 18-30 10-2O:l 1 . 5

c o n d u c t o r

b u n d l e 8.3X8.3 0 . 7 5 0 1 O : l 1 . 5

c o n d u c t o r 5.8X5.8 3 0 1 O : l 1 . 5

( 2 ) Some a p p l i c a t i o n e x a m p l e s o f t h e C h i n e s e NbTi C o n d u c t o r s

The d e v e l o p m e n t o f s u p e r c o n d u c t i n g c o n d u c t o r s p r o m o t e t h e s u p e r c o n d u c t i n g m a g n e t s . H e r e a r e some e x a m p l e s o f t h e m a g n e t s which h a s u s e d t h e C h i n e s e s u p e r c o n d u c t o r s f o r t h e d e s i g n , t e s t a n d f a b r i c a t i o n s .

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Cl-376 JOURNAL DE PHYSIQUE

T a b l e 6 Some e x a m p l e s o f t h e a p p l i c a t i o n o f C h i n e s e NbTi c o n d u c t o r s

t y p e o f magnets main p a r a m e t e r s o f magnet c o n d u c t o r s

l a b o r a t o r y m a g n e t s 1) b o r e 4 0 - 1 0 0 ~ " B=6-8T 6 0 . 2 , 6 0 . 4 , 6 0 . 7 5 MF-NbTi 2 ) b o r e 300"" B=5T round w i r e ; C r o s s - s e c t i o n 3 ) o u t e r f i e l d o f t h e 3mm2 r e c t a n g u l a r NbTi

h y b r i d e magnet c o u n d e r o r a n d d i f f e r e n t c r o s s - s e c t i o n o f t h e r e c t a n g u l a r c o n d u c t o r S c i e n t i f i c i n s t r u m e n t magnet: i n e r d i a , 160mm 60.42 MF-NbTi r o u n d w i r e 1 ) magnet f o r l a r g e f o r m a t 8=1.5T homogenity o f

e l e c t r o - c a m e r a f i e l d 5 ~ 1 0 - "

2 ) Mossbauer s p e c t r o s c o p y Bore 56"'"' 60.6 MF-NBTI r o u n d w i r e h i g h t 1 9 9 . 5 ~ ~

3 ) G y r o t r o n magnet (wave l e n g t h 4"")

NMR i m a g i n g

M a g n e t i c s e p e r a t i o n D-Shaped c o i l

0.C D i p o l e ( f o r t h e MHD t e s t )

S o l e n d o i d

S u p e r c o n d u c t i n g g e n e r a t o r C r y o g e n i c s t a b l e magnet

P u l s e magnet 1 ) D i p o l e - 1

3 ) S a l e n o i d

B=7.3T

a p e r t u r e 140mm c e n t r a l f i e l d 3T, o f f i e l d 2x10-3 Bore 1000mm B=0.5-1.5T d l f f e r e n t t y p e s D-3, 442""x670mm B0=5T

Bore 215mm B=4T

~ = 7 9 0 ~ ~ 1 ) Bore 400"'"'

B=5.25T 2 ) Bore 600mm

60.42 MF-NbTi r o u n d wire hornogeni t y

M F J ~ T i r o u n d w i r e 6 0 . 5 MF4b T i round w i r e c r o s s - s e c t i o n 3, 6mm2 r e c t a n g u l a r s o l i d c o n d u c t o r c r o s s - s e c t i o n 6mm2

r e c t a n g u l a r s o l i d c o n d u c t o r m m2 c r o s s - s e c t i o n 3 , 6

r e c t a n g u h r s o l i d c o n d u c t o r s B=4.l7T

8 0 0 KVA c r o s s - s e c t i o n 1.2X2.8 ^mm2

2T s o l e n d o i d Bore 350mm

r e c t a n g u l a r s o l i d c o n d u c t o r . h i g h Cu/S.C r a t i o n ( 1 0 : l ) 3.6X7"'" c o m p o s i t e c o n d u c t o r B=4T

a p e r t u r e 1 0 0 rnm B r a i d . 29 s t r a n d s . d 0 . 3 l e n g t h 700mm

c e n t r a l f i e l d 4.6T a p e r t u r e 150""

l e n g t h 700mm c e n t r a l f i e l d 4.1T 1 ) Bore 1 2 0 m m

B=5.6T

Ic=1910A,ramp r a t e 5.6'l'/4.2 s e c 2 ) Bore 156""

B=6T Ic=5000A i n e r d i a . 63.8Cm o u t e r d i a . 1 1 7 ' ~ 1=176'

1 2 5 f i l a m e n t (19um) 5 . 9 ~ 0 . 9 ~ " '

11 s t r a n d f l a t c a b l e Cu-CuNi m a t r i x f i l a m e n t d i a . 12pm 11 s t r a n d f l a t c a b l e a s a b o v e

2 3 s t r a n d f l a t c a b l e Cu-CuNi-matrix F i l a m e n t d l a . 6pm

~ = 2 ~ 1 0 m m ' ( S u p e r c o n Cu/S.C=15 c o n d u c t o r ) B0=5.T

M i r r o r confinement a p p a r a t u s 2 s o l e n o i d , s e p a r a t e d a t 7 ~ 0 . 2 5 / 0 . 3 7 ~ ~ ~ b ~ i c a b l e 506"'"' d i s t a n c e , c e n t r a l

f i e l d 2.5T s o l e n o i d o p e r a t i n g f i e l d 4.1T

( 3 ) Some p r o b l e m s o f NbTi c o n d u c t o r s

A l t h o u g h t h e NbTi c o n d u c t o r s h a v e b e e n u s e d i n f a b r i c a t i n g d i f f e r e n t m a g n e t s , t h e e f f - o r t s o f r e s e a r c h a n d d e v e l o p m e n t o f NbTi s u p e r c o n d u c t i n g m a t e r i a l s a r e s t i l l a i m e d a t e n s u r i n g t h e p r o d u c t i o n q u a l i t y , a n d e n h a n c i n g t h e c r i t i c a l c u r r e n t d e n s i t y o f t h e

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The work of enhancing Jc was conducted through improving the melting method for NbTi alloy, and the heat treatment and cold work process, No less than three times of heat treatment at 250-400°C for 1-lOhr and 60-95% cold work between the two heat treatmente are found to be one of a good process for obtaining high Jc in NbTi composite.

In order to make NbTi 50/Cu superconducting composite for obtaining high current density, cold work and heat treatment must be regulated and coordinated appropriately. It has been shown that after suitable heat treatment and cold work for the optimum NbTi 50/Cu multifilamentary composite, the highest critical current density has reached 3.9-4.14~10~~/cm~ for the short sample. The value of Jc (4.2k, 5T) for commercial available NbTi50/Cu composite has reached 2.5-3.0~10~~/cm~

.

Besides, the influence of different extrusion heating programs after assembling a billet on the performance of conductor has been studied. Now the hydrostatic extrusion was proposed as a type of metal forming to be used.

In order to increase the Hc2 of NbTi conductor, introducing other element, such as NbTiTa, are interested in some laboratories recently. It seems to be another good way to get high field magnet with the superfluid He cooling method.

Nb, Sn AND V, Ga

(1) Nb,Sn is a very important superconducting material for the high field magnets. From the beginning of seventies some laboratories have been carried out this work in China.

The focus of the research and development works are aimed on the technique of fabricating Nb3Sn tapes and multifilamentary Nb,Sn wires. Two methods of fabricating the Nb,Sn tapes, the chemical vapor deposition (CVD) method, and the surface-diffusion process were developed.The technoque of multifilamentary Nb3Sn, by means of the "bronze process", "in situ" method and some other method are carried out in some laboratories several years ago.

* High tape rate CVD process Nb? Sn tape

In order to increare the tape rate during vapor deposition and the performance of Nb,Sn tapes, some growth characteristics of Nb,Sn layer in continuos CVD process has been studied. According to the result of the correlation between critical current density Jc and microstructure of Nb,Sn as well as the dynamics of crystal grain growth, a new VCD technique of fabricating high quality Nb3Sn tapes with fast speed was developed, By use of the high rate and multilayer deposition process to produce commercial

~b,Sn tape, the tape rate increased to 80-100m/hr (max. 160m/hr), the length of single tape is longer than 1000m. The Jc for short sample (2.5mm in width) is about 1.2~106 A/cm2, The Ic and Jc of the conductor as a whole is listed as following for the commercial tapes.

Table 7 Performance of Nb,Sn tape short sample

CVD width thickness current capacity (4.2K)

Nb, Sn tape (mm) (pm)

5T 10T

Ic ( A ) Jco(conduct- Ic (A) Jco (conductor)

or 104~/cd l ~ ~ ~ / c m ~

A 2.6 140 380 10.4 130 3.6

B 2.6 160 480 11.5 200 4.8

* Diffusion process Nb, Sn tape

A modified diffusion method for Nb,Sn tape at 650-800°C with a tin-riched Cu-Sn coat- ing was developed in Ningxia Institute.

Gong tapes with thickness of 35-50pm and width of 2.5 or 5 mm are made of pure Nb or Nb-1%Zr alloy by the melting-rolling or powder-metallugical method. Pancakes of the tape coated with Cu-Sn layer are heat-treated at 650-800°C for 12-40 hours in vacuum to ensure the formation of uniform Nb,Sn layers.

The short sample critical current for the tapes 2.5 mm width at 4.2k and 5T has a Jc of 6~105A/cm~ in the Nb, Sn layer.

* Multifilament Nb, Sn

In early seventies, the technique of fabricating multifilament Nb3Sn wire by "bronze

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process" has been carried out in Baoji Institute of Non-ferrous Metals. Subsequently, some other laboratories are interested in that field too.

Much efforts has been put on the studies of the effects of heat treatment on the Nb3Sn layer thickness, critical current density and other properties of the conductors. For example, to find the level of the MF-Nb,Sn wire by "bronze process", a d0.52mm multifilament Nb3Sn wire consists of 3145 filament (4@m in dia.) embedded in a 12wt% tin bronze. The ratio of bronze to Niobium is 2.8:l. The Niobium and bronze occupy 71.4%

of the cross section of wire. In the conductor Cu with Ta diffusion barries are used for stabilization.

The overall critical current density J C O ~ of MF-Nb, Sn wire heat-treated at 700°C, 168hr is showing in the following:

Table 8 Performance of MF-Nb3 Sn wire

In addition, a kind of MF-Nb,Sn cable by bronze process, reaction before winding is made by Changsha Institute, and it is preparing to wind a He gas-cooling magnet.

Multifilament powder metallurgy process Cu-Nb,Sn wires

A multifilament powder metallurgy process of Cu-Nb3Sn is developed recently. In such conductors a certain number of cores are inserted into the copper matrix. The structure of each core is similar to that of the In-Situ Cu-Nb3Sn conductors, The only difference is that, the Nb content of each core is 57wt% before reaction heat treatment of Nb3 Sn.

The result of this method indicates that this conductor has a good current capactity Jc of l.l~105A/cm* at 4.2k, 11T.

Multifilament powder metallurgy process (high Nb content) is a new way to niake CU-Nb3Sn conductor with discontinous fibres which have high current capacity. It still needs further improving of the properties of the conductor.

Besides, In order to improve the fabricating process of MF-Nb3Sn wire, the rich-Tin Nb tube method has been initiated recently. The preliminary investigation results has shown that this method has some advantages in simplifying the fabricating process and reach a good properties of the MF-Nb3Sn wire also.

( 2 ) V3Ga

The technology and properties of multifilament V3Ga composite wire have been studied by bronze method sfnce the middle of seventies, The critical current density Jc of V3Ga at high field is listed as follows: MF-V3Ga wire, %0.69mm, filament number 1100, filamen diameter 7pm, short sample at 4.2k.

Table 9 Parameters of V, Ga wire

B (T) 8 10 12 15 18.7

( 3 ) Before concluding my presentation of theprmtical superconducting materials, I'd

like to mention that some laboratories in China are interesting on the emerging materials, such a Nb,Ge films, which has been prepared by mears of electron beam co-evaporat- ion apparatus, or D - C , magnetron sputtering. Meanwhile the CVD method is also utilized to prepare the Nb3Ge tapes, Besides, the Nb3A1 and other new materials are also finding the possibility as a further useful supercondcuting materials.

CONCLUSION

Me have made some progress in the development of practical superconducting materials in the past decade, B~rt most of the application in superconducting magnets are still in the laboratory testing stage. It is necerrary to emphasize that more attention is putting on the research and development works of magnets and its application. For the practical superconducting materials, to increase the crictical current density Jc of NbTi conduct- or, and to develop the large scale composite conductor with high stability and low A.C LOSS are still necessary, meanwhile, the high field practical superconducting materials, especially the high quality ME-Nb3Sn conductors are all the important factors for the further development of the practical superconducting materiats in China.

ACKNOWLEDGEMENTS

The author wish to express the gratitude to my colleagues G.S.Yuan (General Reseasch Institute of Nonferrous Metals), J.R.Fang (Chang-sha Research Institute of Mining and Metallurgy), L.Zhou, (Baoji Research Institute of Nonferrous Metals) who have helped to provide materials and valuable discusion to the preparation of this article.