TrimethoxyboroxineâAn Extinguishing Agent for Metal Fires

Trimethoxyboroxine—An Extinguishing Agent for Metal Fires J. D. COMMERFORD, D. L. CHAMBERLAIN, JR., and J. W. SHEPHERD 1

Downloaded by UNIV ILLINOIS URBANA-CHAMPAIGN on October 12, 2016 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0023.ch013

Callery Chemical Company, Callery, Pa.

Metal fires present a serious problem to the producers a n d processers of such metals as magnesium, tita nium, a n d zirconium. Titanium a n d zirconium in the form of sponge, a n d all of these metals in the form of chips or turnings, will ignite easily a n d , when burn ing, their combustion will be supported even by nitro gen. Trimethoxyboroxine, a n organic ester of boric oxide, is a liquid having unique characteristics which are useful for extinguishing such metal fires. It has been used to extinguish magnesium chip fires, mag nesium casting fires, molten magnesium spill fires, titanium turning fires, titanium sponge fires, titanium powder fires, a n d zirconium sponge fires, a n d also to control small sodium a n d sodium-potassium alloy fires.

Trimethoxyboroxine is a colorless liquid p r e p a r e d b y t h e r e a c t i o n o f m e t h y l b o r a t e w i t h b o r i c o x i d e . I t was first r e p o r t e d (2) b y Schiff i n 1867 a n d w a s assigned t h e f o r m u l a B O ( O C H ) . M o r e recently i t has been d e s i g n a t e d B g C ^ O C H g ^ . Goubeau a n d K e l l e r (1) r e p o r t e d t h e p r e p a r a t i o n a n d c h a r a c t e r i z a t i o n o f s e v e r a l s u b s t i t u t e d boroxines, i n c l u d i n g t r i m e t h o x y b o r o x i n e , i n 1951. T h e y cite t h e molecular weight a n d t h e R a m a n s p e c t r a as e v i d e n c e f o r t h e c y c l i c s t r u c t u r e s h o w n b e l o w . 3

Ο CH 0—B^

^B—OCH

3

3

A A \

/

Β

I

OCH3 T h e p r o p o s e d c y c l i c s t r u c t u r e i s i s o e l e c t r o n i c w i t h benzene a n d b o r a z i n e . T h e o r g a n i c c h a r a c t e r i s t i c s of t h i s s u b s t a n c e a r e p a r t i c u l a r l y n o t i c e a b l e i n i t s miscibility w i t h m a n y organic liquids. A m o n g t h e compounds w i t h w h i c h i t i s m i s c i b l e a r e ( T a b l e I ) : p h t h a l a t e esters, h a l o g e n a t e d h y d r o c a r b o n s , a n d t r i e t h y l p h o s p h a t e , w h i c h m a y be of i n t e r e s t as c o m p o n e n t s of s p e c i a l t y e x t i n g u i s h i n g agents. 1

Present address, S t a n f o r d Research I n s t i t u t e , Menlo P a r k , C a l i f .

158

METAL-ORGANIC COMPOUNDS Advances in Chemistry; American Chemical Society: Washington, DC, 1959.

COMMERFORD, CHAMBERLAIN, AND SHEPHERD—TRIMETHOXYBOROXINE


Table I.

Solubility of Organic Liquids in Trimethoxyboroxine

Solute Benzene Toluene Xylene 2,3-Dimethylbutane n-Pentane Ligroin Dimethyl ether Isopropyl ether Methyl ethyl ketone Dimethylformamide Carbon disulfide Carbon tetrachloride Chlorobromomethane Triethyl phosphate 2-Ethylhexyl phthalate 1

Solubility, Grams/Ml. T M B

0.6 0.45

159 at 2 5 ° C .

Remarks

Separates on cooling Separates on cooling Separates on cooling

Solution warms on mixing Viscosity Viscosity Viscosity Viscosity

of 0.8 molal soin. = 44.6 cs. at 32°F.° of 0.9 molal soin. = 37.1 cs.at32°F. 36.5 cs. at 32°F. of 1.1 molal soin. of 0.1 molal soin. = 123 cs. at 32°F.

Viscosity of T M B at 32°F., 122.8 cs.

I n t h e p r e p a r a t i o n of t r i m e t h o x y b o r o x i n e f o r use as a m e t a l fire e x t i n g u i s h i n g agent, s o l d b y C a l l e r y u n d e r t h e t r a d e m a r k T B M , m o r e e m p h a s i s h a s been p l a c e d o n obtaining a composition of m a t t e r w i t h a certain density a n d viscosity rather t h a n a p u r e c h e m i c a l . T h i s i s because these p r o p e r t i e s h a v e effects o n n o z z l e s p r a y p a t t e r n s a n d t h e e m p t y i n g t i m e o f t h e e x t i n g u i s h e r . T r i m e t h o x y b o r o x i n e m a y be c o n s i d e r e d as a c o m p o n e n t o f t h e s y s t e m m e t h y l b o r a t e - b o r i c o x i d e . I n t h i s s y s t e m t h e d e n s i t y a p p e a r s t o change i n a r e g u l a r m a n n e r w i t h i n c r e a s i n g t o t a l b o r i c o x i d e c o n t e n t . T h e v i s c o s i t y o f t h i s s y s t e m increases r a p i d l y , h o w e v e r , once t h e m o l e r a t i o o f b o r i c o x i d e to m e t h y l b o r a t e exceeds 1. T h e s e r e l a t i o n s h i p s are s h o w n i n F i g u r e s 1 a n d 2. F i g u r e 2 i s a p l o t o f v i s c o s i t y vs. t e m p e r a t u r e o n a p o r t i o n o f A S T M V i s c o s i t y C h a r t E . T h e I .30


160

ADVANCES IN CHEMISTRY SERIES

50000 20000 10000 5000 >

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Figure 2.

Viscosity of compositions in the system boric oxide -methyl borate vs. temperature ASTM Viscosity Chart Ε

l a t t e r i s a m o d i f i e d s e m i l o g p a p e r w h i c h gives s t r a i g h t - l i n e p l o t s f o r t h e v i s c o s i t i e s o f p e t r o l e u m p r o d u c t s a n d o t h e r N e w t o n i a n fluids. I t c a n b e seen t h a t t r i m e t h o x y b o r o x i n e m a y b e c o n s i d e r e d a N e w t o n i a n fluid. T w o r e a c t i o n s o f t r i m e t h o x y b o r o x i n e o c c u r d u r i n g its use as a m e t a l fire e x t i n g u i s h i n g agent. U n d e r t h e influence o f heat, t r i m e t h o x y b o r o x i n e b r e a k s d o w n i n t o m e t h y l b o r a t e a n d b o r i c oxide as s h o w n i n E q u a t i o n 1. M o r e i m p o r t a n t , b o r i c oxide i s also t h e p r i n c i p a l p r o d u c t f r o m t h e c o m b u s t i o n of t r i m e t h o x y b o r o x i n e i n a i r as i s i n d i c a t e d i n E q u a t i o n 2. B 03(OCH3)3-^^ B(OCH ) + Β Λ 3

3

2B 03(OCH )3 + 9 0 3

3

2

-> 3 B 0 2

3

(1)

3

+ 9H 0 + 3C0 2

2

(2)

M e t a l fires a r e difficult t o e x t i n g u i s h because of t h e g r e a t r e a c t i v i t y o f t h e m a t e r i a l s a t t h e i r i g n i t i o n t e m p e r a t u r e s . A t these t e m p e r a t u r e s t h e y w i l l c o m b i n e w i t h m a n y m a t e r i a l s w h i c h a r e o r d i n a r i l y c o n s i d e r e d t o b e r e l a t i v e l y i n e r t , s u c h as n i t r o g e n . T h e r e f o r e , effective e x t i n g u i s h i n g of a m e t a l fire is o b t a i n e d o n l y b y c o m p l e t e exclusion of t h e atmosphere o r b y cooling t h e mass of t h e m e t a l below i t s i g n i t i o n t e m p e r a t u r e . T h e s e effects a r e u s u a l l y o b t a i n e d b y b l a n k e t i n g t h e fire w i t h a d r y i n e r t s o l i d m a t e r i a l t o exclude t h e a t m o s p h e r e o r b y a p p l y i n g a n o r g a n i c l i q u i d w h i c h has a h i g h heat of v a p o r i z a t i o n t o cool the m a s s b e l o w t h e i g n i t i o n t e m p e r a t u r e .


COMMERFORD, CHAMBERLAIN, AND SHEPHERD—TRIMETHOXYBOROXINE

161

T r i m e t h o x y b o r o x i n e , b e i n g a l i q u i d , possesses t h e a d v a n t a g e s o f t h e o r g a n i c l i q u i d e x t i n g u i s h i n g agents i n t h a t i t c a n b e a p p l i e d as a s t r e a m o r a s p r a y d e p e n d i n g u p o n the c o n d i t i o n s of t h e fire. T h e i n o r g a n i c c o m p o n e n t of t r i m e t h o x y b o r o x i n e , b o r i c o x i d e , w h i c h is regenerated b y e i t h e r t h e r m a l d e c o m p o s i t i o n o r c o m b u s t i o n , i s a v e r y effective e x t i n g u i s h i n g agent. A t t h e t e m p e r a t u r e o f t h e b u r n i n g m e t a l , b o r i c o x i d e m e l t s t o a flux w h i c h flows o v e r t h e h o t m e t a l a n d excludes t h e a t m o s p h e r e .


A s a r e s u l t o f these c h a r a c t e r i s t i c s m e t a l fire e x t i n g u i s h m e n t w i t h t r i m e t h o x y b o r o x i n e is f r e q u e n t l y m o r e r a p i d t h a n w i t h o t h e r e x t i n g u i s h i n g agents, less e x t i n g u i s h i n g agent i s r e q u i r e d , a n d f r e q u e n t l y m o r e u n b u r n e d m e t a l is r e c o v e r a b l e . In ad dition, t h e products of combustion ( E q u a t i o n 2) are v i r t u a l l y nontoxic. I n t h e case of c h i p o r sponge fires, b u r n i n g o c c u r s o v e r a c o n s i d e r a b l e a r e a a n d i n a d d i t i o n penetrates w i t h i n the mass. T r i m e t h o x y b o r o x i n e should be a p p l i e d over t h e e n t i r e a r e a i n a s t r e a m , i n c l u d i n g p a r t i c u l a r l y t h e h o t t e s t p o i n t s w h e r e t h e fire i s p r o g r e s s i n g i n w a r d . C a s t i n g fires a r e c h a r a c t e r i z e d b y i n t e n s e l y w h i t e spots o n t h e surface w h e r e b u r n i n g is o c c u r r i n g as w e l l as b y a g e n e r a l fire o v e r a n y p o o l s of molten metal that m a y have formed. A g a i n t r i m e t h o x y b o r o x i n e s h o u l d be d i r e c t e d t o w a r d s t h e h o t t e s t spots i n a s t r a i g h t s t r e a m . H o w e v e r , i f a l a r g e m o l t e n p o o l i s p r e s e n t , care s h o u l d b e exercised t o a v o i d d i s t u r b i n g t h e s u r f a c e . I n s u c h cases, m o s t efficient use of t r i m e t h o x y b o r o x i n e w i l l be o b t a i n e d i f i t i s a l l o w e d t o flow o v e r t h e m o l t e n fire o r i f i t is a p p l i e d as a s p r a y . T h e s e c o n d a r y fire f r o m t h e c o m b u s t i o n of t r i m e t h o x y b o r o x i n e i s c h a r a c t e r i z e d b y g r e e n i s h flames 2 t o 3 feet h i g h . T h e r e is also a c l o u d of w h i t e s m o k e . T h i s fire subsides q u i c k l y w h e n t h e a p p l i c a t i o n of t r i m e t h o x y b o r o x i n e i s s t o p p e d . One a p p l i c a t i o n o f t r i m e t h o x y b o r o x i n e is u s u a l l y sufficient t o e x t i n g u i s h t h e m e t a l fire. I f s m a l l areas o f b u r n i n g m a t e r i a l a r e m i s s e d , s h o r t b u r s t s o f t r i m e t h o x y b o r o x i n e w i l l q u e n c h t h e m r a p i d l y . I f t o o m u c h t r i m e t h o x y b o r o x i n e is used, a s m a l l s e c o n d a r y fire w i t h green flames 2 t o 3 inches h i g h w i l l c o n t i n u e t o b u r n f o r s e v e r a l m i n u t e s . A t t h i s p o i n t t h e v i g o r o u s fire m a y be c o n s i d e r e d o u t . H o w e v e r , t h e residue w i l l b e q u i t e h o t . T h e residue c a n b e left t o c o o l b y itself o r , i n c e r t a i n cases i f t h e r e i s t h e d a n g e r o f i g n i t i n g o t h e r flammable m a t e r i a l s , a s t r e a m of w a t e r c a n b e used t o c o o l the u n b u r n e d m e t a l .

Test Fires S e v e r a l m e t a l fires were i g n i t e d a n d e x t i n g u i s h e d w i t h t r i m e t h o x y b o r o x i n e . T h e t r i m e t h o x y b o r o x i n e w a s used i n s t a n d a r d w a t e r - t y p e e x t i n g u i s h e r s p r e s s u r i z e d w i t h d r y n i t r o g e n . T h e s e e x t i n g u i s h e r s h a v e s e v e r a l features w h i c h l i m i t t h e effective use of t r i m e t h o x y b o r o x i n e . A t p r e s e n t , o t h e r l a b o r a t o r i e s a r e w o r k i n g o n p r o g r a m s t o develop better equipment a n d techniques of a p p l i c a t i o n . T h e trimethoxyboroxine used i n these tests c o n f o r m e d t o t h e specifications s h o w n i n T a b l e I I .

Table II. Physical Properties of Trimethoxyboroxine Property Total % B 0 3 « 2

Specific gravity at 25°C. Viscosity at 25°C. Turbidity Pour point Refractive index, n & Flash point (COC) ° 6

2

Typical Product 59.7 1.216 13.0 cs. 100 -22°F. 1.3986 90°F.

° Theoretical for trimethoxyboroxine is 60.0% boric oxide. Turbidity determined as % transmission of white light. b

B r o k e n z i r c o n i u m sponge ( 2 0 - m e s h ) w a s used f o r o n e fire; 4 p o u n d s of sponge were a r r a n g e d i n a p y r a m i d a b o u t 9 inches i n d i a m e t e r a n d were i g n i t e d . T h e fire spread r a p i d l y over t h e surface. T r i m e t h o x y b o r o x i n e was a p p l i e d i n a straight


ADVANCES IN CHEMISTRY SERIES

162


s t r e a m f o r 10 seconds a n d c o m p l e t e l y e x t i n g u i s h e d t h e fire. L e s s t h a n 0.5 g a l l o n o f t r i m e t h o x y b o r o x i n e w a s used. A f t e r t h e residue cooled, i t w a s b r o k e n o p e n . Under t h e c r u s t o f b o r i c oxide t h e r e r e m a i n e d a l a r g e percentage o f u n b u r n e d z i r c o n i u m . T h e residue w a s e x t r e m e l y difficult t o r e i g n i t e . A p r o p a n e t o r c h h a d t o b e u s e d t o b u r n t h e b o r i c oxide f r o m t h e surface o f t h e z i r c o n i u m b e f o r e i g n i t i o n o c c u r r e d . A t i t a n i u m sponge fire w a s e x t i n g u i s h e d w i t h s i m i l a r r e s u l t s . A n o t h e r fire w a s s t a r t e d w i t h g r a n u l a r t i t a n i u m sponge a n d t h e n a b l o c k of sponge 8 x 8 x 8 inches w a s p l a c e d o n t o p . I t i g n i t e d r a p i d l y a n d t h e fire b u r n e d u p w a r d . A g a i n less t h a n 0.5 g a l l o n o f t r i m e t h o x y b o r o x i n e w a s sufficient t o e x t i n g u i s h t h e fire. O n e x a m i n a t i o n of t h e l a r g e piece o f sponge i t w a s f o u n d t h a t t h e i n w a r d p e n e t r a t i o n o f t h e fire w a s halted. T r i m e t h o x y b o r o x i n e w a s a p p l i e d as a s t r a i g h t s t r e a m t o a 1 7 - p o u n d m a g n e s i u m c h i p fire f o r 18 seconds. T h e fire w a s k n o c k e d d o w n e x c e p t f o r a f e w s m a l l spots o n one side. A s e c o n d s h o r t s p r a y i n g f o r 5 seconds c o m p l e t e l y e x t i n g u i s h e d t h e fire. T h e residue w a s a l l o w e d t o cool, t h e n i t w a s o p e n e d a n d e x a m i n e d . A b o u t 8 0 % of t h e m a g n e s i u m c h i p s were u n b u r n e d . T h e t r i m e t h o x y b o r o x i n e h a d s t o p p e d t h e i n w a r d p e n e t r a t i o n of t h e fire i n t o t h e p i l e . L e s s t h a n 0.5 g a l l o n of t r i m e t h o x y b o r o x i n e h a d been u s e d . A 16-pound magnesium casting was ignited w i t h 5 gallons of n a p h t h a . A f t e r 4 minutes t h e casting began t o melt a n d a m i n u t e later i g n i t i o n a t various spots was observed. A f t e r t h e fire h a d b u r n e d f o r 8 m o r e m i n u t e s , a s u b s t a n t i a l p o r t i o n o f t h e c a s t i n g h a d m e l t e d . T h e fire w a s b u r n i n g o v e r m o s t of t h e m o l t e n a r e a a n d o n t h e c a s t i n g . T r i m e t h o x y b o r o x i n e w a s a p p l i e d as a s t r a i g h t s t r e a m f o r 6 seconds. T h e n t h e s e c o n d a r y fire w a s a l l o w e d t o die d o w n a n d i n t e r m i t t e n t s p r a y s o f t r i m e t h o x y b o r o x i n e were d i r e c t e d a t v a r i o u s spots. T h e t o t a l e l a p s e d t i m e w a s 4 0 seconds. O n l y 3.5 p o u n d s o f t r i m e t h o x y b o r o x i n e were u s e d t o e x t i n g u i s h t h e fire c o m p l e t e l y . T r i m e t h o x y b o r o x i n e w a s a p p l i e d as a s p r a y o n a 1 2 - p o u n d s o d i u m fire s u c h as m i g h t o c c u r w i t h a s p i l l . T h e fire w a s e x t i n g u i s h e d . H o w e v e r , a f t e r 2 o r 3 m i n u t e s t h e b o r i c oxide c o a t i n g d i s s o l v e d p a r t i a l l y a n d s m a l l p a t c h e s o f t h e m e t a l surface r e i g n i t e d . T h e s e flare-ups were e x t i n g u i s h e d w i t h a s e c o n d s h o r t s p r a y i n g . A t o t a l of a b o u t 0.5 g a l l o n o f e x t i n g u i s h i n g agent w a s u s e d . W i t h fires of t h i s t y p e e x t r e m e care m u s t b e t a k e n n o t t o d i s t u r b t h e s u r f a c e of t h e m o l t e n m e t a l . I f t h e surface is a c c i d e n t a l l y b r o k e n , t h e l i q u i d m e t a l w i l l r e i g n i t e .

Literature Cited (1) Goubeau, J., Keller, H., Z. anorg. u. allgem. Chem. 267, 1-26 (1951). (2) Schiff, H., Liebigs Ann., Chem. Suppl. 5, 170 (1867). RECEIVED for review May 10, 1957. Accepted June 1, 1958.


TrimethoxyboroxineâAn Extinguishing Agent for Metal Fires

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