75 Crystalline Calcium Polyphosphate Fibers E. J. G R I F F I T H
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Monsanto Company, St. Louis, M O 63166
Asbestos
Two molecular types of silicates are referred to as asbestos. Chrysotile is a magnesium silicate built upon a layered structure of silicate rings and Mg(0H) . The layered structure causes the sheets to roll into cylinders approximately 200Å in diameter. Amphibole asbestos may contain a variety of cations but is built upon a double chain silicate structure. The chrysotile asbestos is always found as an asbestiform crystal while the amphiboles may be either acicular or asbestiform. The diseases attributed to asbestos are a result of the fiber morphology and stability of the fibers rather than any specific chemical reactions between the asbestos and a host organism. It is probable that any refractory substance of similar morphology should stimulate similar diseases. Ingleman and Malgren (1) first demonstrated that long chain polyphosphates were enzymatically degraded by Aspergillius Niger in a manner similar to the enzymatic hydrolytic degradation of adenosine triphosphate in energy transfers of biological systems. Phosphatase chemistry has been the subject of numerous research efforts and the concepts are well established. The utility of asbestos is a result of a number of extraordi nary properties exhibited by the minerals. They are nonflammable, temperature resistant fibers composed of fibrals about 200Å in diameter, exhibit tensile strengths up to 1·10 psi, and moduli as great as 25·10 psi. The fibers are particularly resistant to attack by biological organisms and corrosive environments. 2
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Phosphate F i b e r s The c h e m i s t r i e s o f p h o s p h a t e s a n d s i l i c a t e s a r e s i m i l a r , b u t the morphology o f t h e c r y s t a l s o f t h e s p a r i n g l y s o l u b l e phosphates a r e u n s u i t e d f o r f i b e r a p p l i c a t i o n s . Amorphous p h o s p h a t e g l a s s e s c a n b e e a s i l y s p u n i n t o f i b e r s i n a p r o c e s s s i m i l a r t o t h e manu facture offiberglass. U n f o r t u n a t e l y , amorphous p h o s p h a t e s l a c k b o t h s t r e n g t h and h y d r o l y t i c s t a b i l i t y . 0097-6156/81/0171-0361$05.00/0 © 1981 American Chemical Society
Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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C a l c i u m p o l y p h o s p h a t e s o f a metaphosphate c o m p o s i t i o n [ C a ( P 0 ) 2 ] h a v e p r o p e r t i e s and m o l e c u l a r s t r u c t u r e s w h i c h s h o u l d y i e l d a s u b s t a n c e w h i c h i s r e f r a c t o r y i n most e n v i r o n m e n t s b u t i s r a p i d l y d e g r a d e d i n s y s t e m s c o n t a i n i n g a c t i v e enzymes. None o f t h e known s y s t e m s o f c a l c i u m p h o s p h a t e s y i e l d f i b r o u s c r y s t a l s , a l t h o u g h v e r y s h o r t a c i c u l a r c r y s t a l s have been grown.(2) When c a l c i u m p o l y p h o s p h a t e s a r e grown f r o m a s o d i u m o r p o t a s sium u l t r a p h o s p h a t e m e l t , a f i b r o u s c r y s t a l w i t h d i a m e t e r s as low a s 3μ and l e n g t h s as l o n g as 3cm w e r e g r o w n . The u l t r a p h o s p h a t e m a t r i x s e r v e s two f u n c t i o n s : 1) i t i s a g r o w i n g medium w h i c h a l l o w s t h e g r o w t h o f l o n g , v e r y s l e n d e r c r y s t a l s ; and 2) i t c o n t r o l s t h e r e l e a s e o f CaO t o t h e c r y s t a l l i z i n g p o l y p h o s p h a t e a n i o n s p e r m i t t i n g t h e p o l y p h o s p h a t e c h a i n s t o grow t o v e r y h i g h m o l e c u l a r weights. When c r y s t a l l i z a t i o n i s c o m p l e t e d t h e f i b r o u s p h o s p h a t e c a n be e x t r a c t e d f r o m t h e u l t r a p h o s p h a t e m a t r i x by l e a c h i n g t h e s y s t e m w i t h hot water.
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The w a l l s f o r t h r e e o f t h e s i d e s o f t h e t h r e e - d i m e n s i o n a l t r i a n g u l a r phase d i a g r a m have been p u b l i s h e d , b u t the i n t e r n a l d e t a i l s o f t h e d i a g r a m a r e b u t p o o r l y u n d e r s t o o d . I t can be s t a t e d t h a t f i b r o u s c a l c i u m p o l y p h o s p h a t e s c a n be g r o w n t h r o u g h o u t t h e u l t r a p h o s p h a t e d i a g r a m d o m i n a t e d by [ C a ( P 0 ) ] c r y s t a l s . An a p p r o x i m a t e p h a s e d i a g r a m i s shown i n F i g u r e 1. 3
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Property of Fibers The c a l c i u m p o l y p h o s p h a t e f i b e r s a r e v e r y v e r y s l o w l y d i s s o l v e d i n w a t e r . E v e n i n b o i l i n g 0.1N HC1 t h e f i b e r s a r e r e s i s t a n t t o d e g r a d a t i o n , b u t t h e f i b e r s a r e n o t as r e s i s t a n t t o b o i l i n g 0.1N NaOH s o l u t i o n s . See F i g u r e 2. The f i b e r s a r e h i g h l y c r y s t a l l i n e and s i n g l e c r y s t a l t e n s i l e s t r e n g t h measurements r a n g e f r o m 2 · 1 0 p s i t o 1·10 p s i , while the modulus o f e l a s t i c i t y ranges from 10·10 p s i to 26·10 p s i . These v a l u e s are comparable to the p u b l i s h e d v a l u e s f o r c h r y s o t i l e asbestos. C h r y s o t i l e a s b e s t o s i s decomposed a t t e m p e r a t u r e s b e l o w 500°C. C a l c i u m p o l y p h o s p h a t e f i b e r s do n o t m e l t a t t e m p e r a t u r e s b e l o w 970°C, b u t t h e β-phase p h o s p h a t e i s c o n v e r t e d t o α-phase p h o s p h a t e a t 940°C. 6
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Animal Studies A l l a n i m a l s t u d i e s made w i t h c a l c i u m p h o s p h a t e f i b e r s h a v e shown t h a t t h e f i b e r s a r e d e g r a d e d by t h e enzymes i n l i v i n g s y s tems . To d a t e , t h e p h o s p h a t e s h a v e been t e s t e d as i m p l a n t s i n t h e p l e u r a l o r p e r i t o n e a l c a v i t i e s of r a t s . As was t o be e x p e c t e d
Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
GRIFFITH
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Polyphosphate
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Fibers
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p o 2
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Figure L A schematic phase diagram for CaO- Na 0- P 0 system based on published diagrams. [Published diagrams: Na 0-P 0^, CaO-P 0 , (4); and Na 0-CaO-P 0 , (5).] 2
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Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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75.
GRIFFITH
Crystalline
Calcium
Polyphosphate
Fibers
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w i t h i m p l a n t s o f p h o s p h a t e s , t h e f i b e r s and t h e i r d e g r a d a t i o n p r o d u c t s a r e n u t r i e n t s f o r a l l b i o l o g i c a l s y s t e m s and no a d v e r s e r e s u l t s have been o b t a i n e d .
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Conclusion I t i s concluded that calcium polyphosphate f i b e r s a r e v i a b l e c a n d i d a t e s a s s a f e r e p l a c e m e n t s f o r a s b e s t o s i n many o f i t s a p p l i c a t i o n s , p a r t i c u l a r l y i n t h o s e a p p l i c a t i o n s where human e x p o s u r e i s considered hazardous. Literature Cited
1.
Ingelman, B.; Malgren, H. Acta. Chem. Scand. 1947, 1, 422; 1948, 2, 365; 3, 157. 2. Abe, Y. Nature 1979, 282, 55. 3. Morey, G. N. and Ingerson, E. Am. J. Sci., 1944, 242, 4 4 H i l l , M. L., Foust, G. T., and Reynolds, D. S. Am. J. Sci. 1944, 242, 547. 5. Gremier, J. C., Martin, C., and Durif, A. Bull. Soc. Fr. Mineral. Cristallogr. 1970, 93, 52. R E C E I V E D June 30,
1981.
Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
