HANDLING AND USES OF THE ALKALI METALS

Some Practical Aspects of Handling Lithium Metal

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H. C. MEYER, JR. Foote M i n e r a l C o . , 18 W e s t C h e l t e n A v e . , P h i l a d e l p h i a , P a .

Lithium metal, in general, is handled like other alkali metals. Differences in handling are due primarily to its higher melting p o i n t , g r e a t e r hardness, and reactivity with nitrogen. The metal, unlike sodium and potassium, does not ignite spontaneously on contact with water. Because of its higher melting point, liquid metal is handled at higher temperatures, which increases the hazard from burns. Low-carbon steel, or iron, is the most suitable construction material for use with lithium.

L l T H I U M metal, d u r i n g p r o d u c t i o n a n d subsequent p h y s i c a l processing, is s u b jected to a v a r i e t y of conditions. F o r t u n a t e l y , these conditions represent extremes not n o r m a l l y encountered b y a n y one user.

Production A t y p i c a l l i t h i u m cell consists of a graphite anode, a m i l d steel cathode, a n d a fused b a t h of l i t h i u m a n d potassium chlorides as the electrolyte, as s h o w n i n F i g u r e s 1 a n d 2.

Table I. Operating Conditions of Lithium Cell Salt temperature, ° C . Voltage C u r r e n t density, a m p . / s q . i n c h C u r r e n t efficiency, % R a w m a t e r i a l efficiency, % S p . g r . l i t h i u m metal, 400° C .

404 5.2 3.53 76 97 0.49

Figure 1. Lithium m e t a l cell 9

In HANDLING AND USES OF THE ALKALI METALS; Advances in Chemistry; American Chemical Society: Washington, DC, 1957.

A D V A N C E S IN


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Figure 2.

CHEMISTRY SERIES

Interior o f l i t h i u m m e t a l cell s h o w i n g g l o b u l e s of m e t a l

F i g u r e 3 gives the phase d i a g r a m for the l i t h i u m - p o t a s s i u m chloride b a t h (3). T h e n o r m a l operating temperature allows for some v a r i a t i o n f r o m the eutectic without freezing of the bath. Therefore, m a k e - u p l i t h i u m chloride need not be added to the bath continuously. In operation, the n e w l y f o r m e d l i t h i u m m e t a l wets the surface of the steel cathode, rises to the surface of the bath, a n d forms a pool of m o l t e n metal. F o r the cell materials given, there is little evidence of attack b y l i t h i u m metal, but there is attack b y the fused salt i n the splash area above the l i q u i d l e v e l . It is estimated that u n d e r n o r m a l operating conditions not more t h a n 5% of the l i t h i u m f o r m e d reacts i n the cell. P r o b a b l e reactions are (1) w i t h air d r a w n into the cell as the chlorine is d r a w n off (8), (2) w i t h moisture f r o m l i t h i u m c h l o r ide additions, (3) w i t h chlorine (4), a n d (4) w i t h carbon f r o m the anode (1). T h e metal i n the cell is n o r m a l l y coated w i t h these reaction products w h i c h gives it a mottled, r e d d i s h b r o w n , gray, black and white appearance (14). Analysis of this surface film indicates that l i t h i u m nitride, l i t h i u m carbonate, l i t h i u m h y d r o x i d e , and possibly l i t h i u m oxide are present i n v a r y i n g amounts. A n a l y t i c a l results are so scattered as to m a k e generalization difficult. T h e r e are indications, however, that the n i t r i d e is f o r m e d p r i m a r i l y f r o m d r y a i r ; the carbonate a n d h y d r o x i d e w h e n moisture is present (2). T h e l i q u i d l i t h i u m is d i p p e d f r o m the cell w i t h an i r o n dipper a n d cooled to about 3 0 0 ° C . T h i s permits a n y salt present to congeal. T h e metal is then cast ( F i g u r e 4) into i r o n molds coated w i t h an i n d u s t r i a l , white oil. O i l is also p o u r e d on the surface of the cooling m e t a l i n the m o l d . T h i s effectively limits f u r t h e r r e action w i t h the atmosphere. T h e cast metal is s i m i l a r i n appearance to a l u m i n u m . T h e t y p i c a l analyses g i v e n i n T a b l e II indicate that this m e t a l is not seriously contaminated b y the reactions metioned above.

Table II.

Typical Analyses of Lithium Metal

Na Κ Ν Cl Fe Al Si Ca L i (by difference)

%

0.09 0.01 0.005 0.01 0.001 0,001 0.001 0.0002 99.8

— — — — — — — —

0.15 0.10 0.02 0.2 0.01 0.01 0.01 0.0004


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M E Y E R — H A N D L I N G LITHIUM METAL


T h e cells are operated i n a m e t a l a n d concrete b u i l d i n g , not s p r i n k l e r - p r o t e c t ed a n d free of water or steam pipes. O p e r a t i n g personnel w e a r head shields, g o g gles, face masks, asbestos gloves, d u c k aprons, a n d loose-fitting coveralls. If m e t a l is s p i l l e d o n the s k i n , personnel are instructed to flood the area w i t h o i l , then r e port p r o m p t l y for m e d i c a l e x a m i n a t i o n . F i r e s i n the cells are most infrequent, g e n e r a l l y not self-sustaining. T h e y c a n be controlled b y c o v e r i n g w i t h the m o l t e n salt b a t h . W h e n m e t a l is s p i l l e d d u r i n g transfer to the molds, it occasionally starts to b u r n . T h i s u s u a l l y occurs o n l y d u r ing d a m p weather. ( T h e b u i l d i n g is not h u m i d i t y - c o n t r o l l e d . ) N o r m a l l y , these fires are p e r m i t t e d to b u r n themselves out. T h e y can, however, be controlled w i t h d r y z i r c o n i u m silicate, d r y g r a n u l a r graphite, or p r o p r i e t a r y products such as P y r e n e G l . C a r b o n dioxide extinguishers are not effective. Since l i t h i u m w i l l r e duce s o d i u m compounds, these should not be used (11). A l t h o u g h l i t h i u m chloride is effective w h e n d r y , it is so hygroscopic that its use is not r e c o m m e n d e d , for p r a c tical reasons.

A p a r t i c u l a r l y unpredictable type of to be catalyzed b y rust particles o n i r o n m e t a l a n d dross are left o n equipment. controllable b y the materials mentioned to users of m e t a l w h e r e these conditions

fire occurs i n the dross. These fires seem e q u i p m e n t a n d occur w h e n t h i n films of A l t h o u g h u s u a l l y of short d u r a t i o n , a n d above, they represent a potential h a z a r d m a y occur.

W h e n it is necessary to c l e a n equipment, m e l t i n g out, steaming w i t h d r y steam, a n d flooding w i t h water, or a c o m b i n a t i o n of these, are used. N o instances of fires r e s u l t i n g f r o m this procedure are k n o w n .

Packaging T h e official specifications for p a c k a g i n g l i t h i u m m e t a l are g i v e n b y the I n t e r state C o m m e r c e C o m m i s s i o n (6). T h e m e t a l is n o r m a l l y coated w i t h a n inert h y d r o c a r b o n such as Sonnenborn's B l a n d o l , a light, white m i n e r a l o i l ; Socony M o b i l ' s Industrial white o i l N o . 208A; or, if a heavier m a t e r i a l is desired, Sonneborn's Protopet 2 A . In these materials a n d even i n U . S . P . w h i t e m i n e r a l oil, some surface d i s c o l oration of the m e t a l w i l l occur unless the o i l is first cleaned b y p l a c i n g some s m a l l pieces of s o d i u m or l i t h i u m m e t a l i n the o i l for about 24 hours at r o o m t e m p e r a ture, p r i o r to use. Loss of m e t a l f r o m using untreated o i l is not c o m m e r c i a l l y significant.



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A D V A N C E S IN CHEMISTRY SERIES

Figure 4. C a s t i n g l i t h i u m m e t a l

It is important to have the container f u l l of l i t h i u m a n d o i l w i t h no free a i r space, as the l i t h i u m w i l l float i n the o i l a n d react w i t h the air, if present. U n c o a t ed l i t h i u m placed i n sealed light m e t a l cans w i l l often cause the c a n to collapse a r o u n d the metal. G l a s s containers are not r e c o m m e n d e d , because of possible breakage. is used, it should be p l a c e d i n a sealed m e t a l container.

If glass

F o r h a n d l i n g solid l i t h i u m , n o r m a l laboratory or c h e m i c a l operators' c l o t h i n g is r e c o m m e n d e d , i n c l u d i n g complete protection f o r hands, eyes, a n d arms. S p o n taneous ignition of the m e t a l or of the released h y d r o g e n does not n o r m a l l y occur on contact w i t h water. Because of this r e d u c e d h a z a r d , a n d the e x t r e m e l y i r r i t a t i n g n a t u r e of fine a i r - b o r n e particles of l i t h i u m oxide, flooding w i t h water is preferable to b u r n i n g f o r disposal of excess or scrap l i t h i u m . I n contact w i t h l i t h i u m , nitrogen a n d carbon d i o x i d e are not inert gases.

Uses F o r n o r m a l c o m m e r c i a l use, the m e t a l m a y be cleaned b y w a s h i n g w i t h k e r o sine or S t o d d a r d solvent. These, of course, r e m o v e o n l y the o i l . If the surface film must be r e m o v e d , this c a n be done m e c h a n i c a l l y w i t h a k n i f e or c h e m i c a l l y b y w a s h i n g w i t h a n h y d r o u s alcohol. A s a n e w surface film w i l l f o r m i n a f e w minutes i n a i r , this latter procedure is u s u a l l y necessary o n l y i f the m e t a l f r o m w h i c h the sample is cut has been o x i d i z e d o w i n g to i m p r o p e r storage. ALLOYS. T h e alloys that c a n be f o r m e d w i t h l i t h i u m are i n a sense a guide to suitable materials of construction for e q u i p m e n t to h a n d l e it. A l l o y s of l i t h i u m w i t h a l u m i n u m , c a d m i u m , copper, lead, m a g n e s i u m , manganese, n i c k e l , silver, s o d i u m , t i n , a n d zinc are reported (9, 10, 13, 14). C o m m e r c i a l use of these alloys has been l i m i t e d l a r g e l y to those of copper, m a g n e s i u m , a l u m i n u m , a n d silver. A s


M E Y E R — H A N D L I N G LITHIUM METAL

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the l i t h i u m is the m i n o r ingredient i n these alloys, it is n o r m a l l y added to the m o l t e n base metal. A t these temperatures (675° to 1100°C.) l i t h i u m w i l l react v i g o r o u s l y w i t h the a i r i f it is not m e c h a n i c a l l y s u b m e r g e d i n the base m e t a l . It w i l l also react w i t h such materials as o x y g e n , nitrogen, sulfur, phosphorus, a n d m a n y compounds of these elements that m a y be present i n the base metal.


L i t h i u m w i l l f o r m alloys w i t h some of these metals at temperatures o n l y slightly above its m e l t i n g point. I n r o u g h qualitative tests w i t h the l i t h i u m at 200° to 250 ° C . alloys containing 5 6 % zinc, 6 3 % copper, 28% a l u m i n u m , a n d 2 0 % tin were m a d e b y a d d i n g 60-mesh powders of these metals to the l i q u i d l i t h i u m . S o l u t i o n was r a p i d ; a l l melts were fluid i n the ranges e x a m i n e d . T h e t i n alloys were p y r o p h o r i c . T h e melts w e r e m a d e i n h e a v y o i l without a protective a t m o s phere. U n d e r these same conditions, alloys were not f o r m e d w i t h n i c k e l , m a n g a nese, t i t a n i u m , or z i r c o n i u m . T h e s e tests illustrate g r a p h i c a l l y the u n s u i t a b i l i t y of copper, brass, bronze, galvanized i r o n , a n d a l u m i n u m as materials to be used w i t h l i t h i u m at a n y t e m perature above its m e l t i n g point. T h e r e is appreciable attack o n most of the c o m m o n corrosion-resistant alloys c o n t a i n i n g n i c k e l at t e m p e r a t u r e s below 5 0 0 ° C . (12). In general, o n l y l o w - c a r b o n steel (5), n i o b i u m , t a n t a l u m , a n d m o l y b d e n u m are desirable materials of construction for m o l t e n l i t h i u m . M o l t e n l i t h i u m w i l l attack quartz, glass, a n d silicates i n general, a n d the l i t h i u m oxide often present i n m o l t e n l i t h i u m at h i g h temperatures is a n excellent flux for most oxides a n d silicates. I n some cases, it m a y be m o r e convenient to meter l i t h i u m to a reaction as a m e a s u r e d l e n g t h of r o d , w i r e , a n d r i b b o n . Because of the softness of the m e t a l , these operations are simple to p e r f o r m . I n laboratory tests a die c h a m b e r 3.75 inches i n diameter was fitted w i t h orifices r a n g i n g f r o m 0.125 to 0.5 i n c h i n d i a m eter. E x t r u s i o n s w e r e r u n at 32° a n d 100°C. Pressures r e q u i r e d to cause a flow of


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A D V A N C E S IN CHEMISTRY SERIES


at least 10 l i n e a l c m . p e r m i n u t e were determined as g i v e n i n F i g u r e 5. T h e die c h a m b e r used is s h o w n i n F i g u r e 6. A slug of l i t h i u m a p p r o x i m a t e l y fitting the die c h a m b e r was used. T h e freshly e x t r u d e d m e t a l was b r i g h t a n d s i l v e r y i n appearance. I n a i r , a d u l l , d a r k surface f o r m e d i n a f e w minutes. If protected w i t h o i l or p e t r o l e u m , the b r i g h t surface c a n be m a i n t a i n e d . DISPERSIONS. Successful p r e p a r a t i o n of a g r a i n e d l i t h i u m m e t a l or l i t h i u m " s a n d " is a h i g h l y e m p i r i c a l operation (7). F i g u r e 7 gives a schematic d i a g r a m of the equipment r e q u i r e d . In practice, the l i t h i u m m e t a l is heated to 200 ° C . u n d e r a light film of o i l . It is then p o u r e d into a preheated (140° to 150°C.) g r a i n i n g b o w l containing sufficient o i l to float the metal. A s the temperature of the m e t a l drops, it w i l l f o r m discrete m o l t e n particles w h i c h t h e n solidify. M a t e r i a l so f o r m e d was substantially 8 χ 18 mesh. B y h a v i n g the g r a i n i n g b o w l at a lower temperature, a finer product was f o r m e d . A d d i t i o n of seed m a t e r i a l such as p r e v i o u s l y g r a i n e d l i t h i u m , crystals of cryolite, or s o d i u m chloride d i d not seem to assist the formation of the grains. T h e p r o v e d u t i l i t y of s o d i u m dispersions has aroused interest i n the possible use of l i t h i u m dispersions. S u c h dispersions c a n be r e a d i l y p r e p a r e d . Tests have shown that a W a r i n g B l e n d o r w i t h suitable modification is satisfactory although others, such as the P r e m i e r Dispersator or the Cowles Dissolver, should prove at least as satisfactory. T h e W a r i n g unit used h a d a stainless steel c u p of 1000-ml. n o m i n a l capacity. T w o modifications were made. A resistance heater of 300-watt capacity was w r a p p e d a r o u n d the b o w l to melt the l i t h i u m . T h e bronze b e a r i n g a n d other c o p per containing parts of the dispersing m e c h a n i s m were r e p l a c e d w i t h m i l d steel. ( E x p e r i e n c e showed that these parts containing copper were subject to corrosion b y the m e l t e d l i t h i u m . ) T h e u n i t was operated at atmospheric pressure, using argon or h e l i u m as a protective atmosphere. A s the l i t h i u m must be melted, the m e d i a used were l i m i t e d to those w i t h b o i l i n g points not m u c h below 230 ° C , the m a x i m u m temperature used.

REVOLVING STEEL RAKE 1 STEEL ^BOWL

Figure 7. G r a i n i n g

Figure 6. E x t r u d i n g d i e a n d c h a m b e r

bowl

M e d i a actually tested i n c l u d e d light m i n e r a l o i l , U . S . P . , a n d eicosane, technical grade ( A t l a n t i c Refining C o . ) . L i t h i u m stéarate was used as a dispersion stabilizer. W i t h these m e d i a no dispersing agent seemed necessary. T y p i c a l batch formulations a r e : Grams L i t h i u m metal U . S . P . white o i l L i t h i u m stéarate

84 247 0.5

L i t h i u m metal Eicosane, tech. L i t h i u m stéarate

250 0.5

Ml. 159 294 173 321


MEYER—HANDLING LITHIUM METAL

15

T h e procedure used i n m a k i n g these dispersions w a s :


M e l t the l i t h i u m i n the m e d i u m containing the stabilizing agent i n the B l e n d o r c u p . W h e n melted, start B l e n d o r motor. Disperse for 10 to 45 minutes w i t h temperature at 210° to 2 3 0 ° C . C o o l w i t h B l e n d o r off. W h e n l i t h i u m m e t a l is melted, the film of reaction products o n its surface m a y h o l d the m e t a l i n its cut f o r m , even w h e n the center of the piece is melted. T h u s , care should be taken to prevent unnecessary heating. W i t h 10 minutes' dispersing time, the particles of l i t h i u m r a n g e d f r o m 15 to 50 m i c r o n s i n size. W i t h longer dispersing time the size seemed to stabilize at 10 to 20 microns. If, however, stirring is continued t h r o u g h the cooling period, a solid sponge of metal w i l l be f o r m e d w h i c h c a n be r e m o v e d f r o m the B l e n d o r i n one piece. W i t h o u t stabilizers, the l i t h i u m tended to settle out on standing overnight. W i t h the l i t h i u m stéarate stabilizer, the dispersions were still stable after 60 to 90 days' storage. T h e white m i n e r a l o i l dispersions were viscous liquids. T h e eicosane d i s p e r sions were interesting i n that below about 4 0 ° C . they were w a x y solids; above that point, t h i n liquids. T h e eicosane dispersions are p a r t i c u l a r l y convenient to use, because they c a n be cut a n d weighed i n this solid f o r m , yet are usable as l i q u i d dispersions w i t h o n l y moderate heating. STABILITY. T h e stability of the l i t h i u m i n these dispersions seems h i g h . Samples of both o i l - a n d eicosane-dispersed products showed only surface film d e c o m p o s i tion w h e n stored i n a i r at r o o m temperature for u p to 30 days. W h e n added to water there was a steady nonviolent e v o l u t i o n of h y d r o g e n . T h i n films of the dispersions exposed to a i r at r o o m temperature, reacted slowly over a p e r i o d of days. B a s e d o n a l i m i t e d observation, it seems safe to assume that l i t h i u m d i s persed i n the m e d i a g i v e n is no more hazardous to handle t h a n n o r m a l solid lithium.

Literature Cited (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)

Dafert, F . H., M i c k l a n z , R., Monatsh. 31, 981-96 (1910); 33, 63-9 (1911). D e a l , Β. E., Svec, H . J., J. Am. Chem. Soc. 75, 6173-5 (1953). E l c h a r d u s , E., Laffitte, P., Bull. soc. chim. France 51, 1572 (1932). F r a n k e n b u r g e r , W . , Z. Elektrochem. 32, 489-91 (1926). H e r o l d , Α . , M u l l e r , P . , A l b r e c h t , P . , Compt. rend. 235, 658-9 (1952). Interstate C o m m e r c e C o m m i s s i o n , Tariff N o . 9, p. 73. 206. J a c k s o n , J. H., U. S. Patent 2,651,835 (Sept. 15, 1953). K e l m a n , L. R., W i l k i n s o n , W . D . , Yaggee, F . L., A r g o n n e N a t l . L a b . Rept. A N L 4417 ( J u l y 1950) M a l o w a n , S. L., Metallborse 20, 873-4 (1930). M a s i n g , G . , T a m m a n n , G . , Z. anorg. Chem. 76, 183-99 (1912). Mote, M . W . , F r o s t , P . D . , " R e a c t o r H a n d b o o k , " V o l . 3, N o . 1, 169-72, A E C D 3647 (1955). Steiner, S., K n o l l s A t o m i c P o w e r L a b . L M S C -1 ( J u l y 1954). Weisse, E., B l u m e n t h a l , Α . , H a n e m a n n , H . , Zink Tech. Ber. 3, 1-13 (1948). Z i n t l , E., B r a u e r , G., Z. physik. Chem. 20B, 245-71 (1933).


HANDLING AND USES OF THE ALKALI METALS

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