INTERNAL FRICTION OF COAL AND OF OTHER NATURAL MACROMOLECULAR SOLIDS

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INTERNAL FRICTION OF COAL AND OF OTHER NATURAL MACROMOLECULAR SOLIDS

M. Weller, C. Wert

To cite this version:

M. Weller, C. Wert. INTERNAL FRICTION OF COAL AND OF OTHER NATURAL MACROMOLECULAR SOLIDS. Journal de Physique Colloques, 1983, 44 (C9), pp.C9-191-C9-196.

�10.1051/jphyscol:1983924�. �jpa-00223370�

JOURNAL DE PHYSIQUE

Colloque C9, suppliment au n012, Tome 44, d6cernbt-e 1983 page C9-191

INTERNAL FRICTION OF COAL AND OF OTHER NATURAL MACROMOLECULAR SOLIDS

M. Weller and C.A. wertr

Max-Planck-lnstitut far MetaZZforschung, I n s t i t u t far Werkstoffwissenschaften, S t u t t g a r t , F.R.G.

' M a t e r i a ~ s Research Laboratory and Department of MetaZZurgy and Mining Engineering, U n i v e r s i t y of I Z Z i n o i s a t Urbana-Champaign, U.S.A.

Rgsurn6

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^{On a} t r o u v g que l e f r o t t e m e n t i n t 6 r i e u r d e charbon e s t

-

g e n e r a l e m e n t c h a r a c t e r i s t i q u e pour l e s s o l i d e s polymsres n a t u r e l s . Des p i c s de f r o t t e m e n t i n t g r i e u r a n a l o g u e s d ceux mise e n e v i d e n c e dans l e charbon a p p a r a i s e n t d a n s l e b o i s , l ' a m b r e et l e s c h i s t e b i t u m i n e u x , e n p l u s d ceux q u i d & j S s o u v e n t o n t &t& o b s e r v g s dans l e s polymsres s y n t h 6 t i q u e s . Des e x p g r i e n c e s d 6 t a i l l G e s s u r

p l u s i e u r s p r o p r i & t & s d e s p i c s d b a s s e s t e m p e r a t u r e s o n t c o n d u i t 5 d e s modsles q u i d e v i e n n e n t d e p l u s e n p l u s c e r t a i n e s .

A b s t r a c t

-

The i n t e r n a l f r i c t i o n o f c o a l h a s been found t o b e a g e n e r a l c h a r a c t e r i s t i c o f n a t u r a l p o l y m e r i c s o l i d s . Damping peaks s i m i l a r t o t h o s e s e e n i n c o a l a r e found i n wood, amber and o i l s h a l e , i n a d d i t i o n t o t h o s e r e p o r t e d many t i m e s i n s y n t h e t i c polymers. D e t a i l e d measurements of many o f t h e p r o p e r t i e s o f t h e low t e m p e r a t u r e peaks have l e d t o d e t a i l e d models which a r e g r a d u a l l y becoming more c e r t a i n .

I. I n t e r n a l F r i c t i o n o f Coal.- I n t e r n a l f r i c t i o n peaks i n c o a l , f i r s t r e p o r t e d by u s two y e a r s ago / I / , have been found t o b e a g e n e r a l f e a - t u r e o f many c o a l s . We f i r s t r e p o r t e d measurements on a bituminous coal.

( i n t h e f o l l o w i n g d e s i g n a t e d as bituminous 1 ) . These measurements a r e reproduced i n F i g u r e 1 . The i n t e r n a l f r i c t i o n peaks d e s i g n a t e d a s Y ,

/3

and a a r e t r u e r e l a x a t i o n peaks s i n c e t h e modulus ( f 2 ) shows t h e c h a r a c t e r i s t i c d r o p t h r o u g h t h e a r e a o f t h e r e l a x a t i o n (upper l i n e i n F i g . 1 ) . We have c o n t i n u e d t h e s e e x p e r i m e n t s on a g r e a t many c o a l s / 2 / . Some t y p i c a l examples are shown i n F i g . 2 , c u r v e s a , b , c and d . We used an i n v e r t e d t o r s i o n pendulum w i t h a m e a s u r i n g f r e q u e n c y o f a b o u t 1 H z . Curve a i s from F i g . 1 f o r bituminous c o a l 1 o f approximate 82% c a r b o n c o n c e n t r a t i o n (on a d r y , a s h - f r e e b a s i s + ) ) . Curve b shows t h e i n t e r n a l f r i c t i o n ( I F ) f o r bituminous 2 w i t h lower c a r b o n c o n t e n t ( 7 7 % ) , c u r v e c i s f o r bituminous 3 w i t h 85%C. Curve d shows t h e I F f o r a n a n t h r a - c i t e o f c a r b o n c o n c e n t r a t i o n 93%. From t h e s e f o u r measurements, t h e f o l l o w i n g s t a t e m e n t s can be made:

f ) Coal s c i e n t i s t s commonly s p e c i f y t h e carbon, oxygen and hydrogen c o n c e n t r a t i o n of t h e macromolecular s o l i d i n s e v e r a l ways. For example, t h e carbon c o n c e n t r a t i o n of bituminous 1 on an "as-received" b a s i s was72.31carbon. S i n c e c o a l s commonly c o n t a i n a g r e a t d e a l of m i n e r a l m a t t e r , t h e carbon c o n c e n t r a t i o n can a l s o be expressed i n terms of t h e d r y , a s h - f r e e b a s i s ( d . a . f ) , an a n a l y s i s o b t a i n e d by burning t h e c o a l a t low temperature and c a r e f u l l y collecting a l l o f t h e a s h which remains a f t e r combustion.

This carbon c o n c e n t r a t i o n f o r bituminous 1 was 81.78 carbon. Sometimes t h e carbon con- c e n t r a t i o n i s expressed i n terms of t h e mineral-matter-free b a s i s , which i s determined by t r e a t i n g t h e m i n e r a l m a t t e r i n a s l i g h t l y d i f f e r e n t way t h a n producing an a s h from it. Commonly, t h e a s h - f r e e b a s i s and t h e m i n e r a l - m a t t e r - f r e e b a s i s a r e w i t h i n a p e r c e n t o f each o t h e r . The a s - r e c e i v e d c o n c e n t r a t i o n may be many p e r c e n t d i f f e r e n t from t h e s e two.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983924

C9-192 JOURNAL DE PHYSIQUE

1. ) Three damping peaks e x i s t i n c o a l , t h e cx

,

and )"peaks.

2 . ) The p o s i t i o n o f t h e s e peaks i n t e m p e r a t u r e f o r a c o n s t a n t frequen- cy i s a b o u t t h e same f o r a l l c o a l s , T h i s i m p l i e s t h a t t h e r e l a x i n g u n i t s a r e s i m i l a r among c o a l s o f g r e a t l y d i f f e r e n t r a n k .

3 . ) The h e i g h t o f t h e r e l a x a t i o n s v a r i e s remarkably w i t h c o m p o s i t i o n . T h i s i m p l i e s t h a t t h e number o f r e l a x i n g u n i t s o f a g i v e n k i n d respon- s i b l e f o r t h e v a r i o u s peaks v a r i e s remarkably among t h e c o a l s .

4.) Measurements on s i x more c o a l s , n o t shown i n t h i s p a p e r , a l s o f i t t h e s e c o n c l u s i o n s . These d a t a w i l l b e p u b l i s h e d e l s e w h e r e .

IL.Measurements on o t h e r Polymers.- Measurements o f many s y n t h e t i c polymers show i n t e r n a l f r i c t i o n peaks remarkably s i m i l a r t o t h o s e of F i g u r e s 1 and 2. We r e p o r t e d on t h e measurement f o r nylon i n a n e a r - l i e r p a p e r / 2 / . I t showed damping p e a k s s i m i l a r i n p o s i t i o n t o t h e

=,

@ a n d y p e a k s i n c o a l . Examination o f a g r e a t many p a p e r s i n t h e polymers l i t e r a t u r e ( s e e e . g . / 3 / ) shows d a t a v e r y s i m i l a r t o t h o s e we o b t a i n e d f o r n y l o n . Again, two o r t h r e e peaks a r e commonly s e e n and t h o s e peaks which a p p e a r a r e always found i n a p p r o x i m a t e l y t h e same l o c a t i o n s a s f o r t h e t h r e e p e a k s f o r c o a l .

Wood i s a n a t u r a l p o l y m e r i c s o l i d . I t c o n s i s t s of f i b r i l s of c e l l u l o s e and h e m i c e l l u l o s e a r r a n g e d i n c r o s s - l a p p e d l a y e r s d i a g o n a l l y a b o u t t h e c e l l w a l l . The c e l l u l o s e f i b r i l s a r e cemented t o g e t h e r by l i g n i n , a h i g h l y complex macromolecusar m a t e r i a l . We e a r l i e r found / 4 / t h a t wood had two r e l a x a t i o n p e a k s , t h e @-peak and t h e % - p e a k , which we f i r s t saw i n some oak and beech. We have c o n t i n u e d t h o s e measurements w i t h a l o n g s e r i e s on spruce-wood c u t from v e n e e r s h e e t s u c h a s would b e used i n t h e manufacture o f plywood. We u s e d t h i n s t r i p s c u t l o n g i t u d i - n a l l y w i t h t h e g r a i n . A measurement on t h e o r i g i n a l s p r u c e wood (which c o n t a i n s 2 9 . 3 % l i g n i n , t h e r e s t b e i n g c e l l u l o s e and h e m i c e l l u l o s e ) i s shown i n F i g . 3. One s e e s t h e w - p e a k n e a r 400 K and t h e f l - p e a k n e a r 200 K. F o r wood t h e y - p e a k i s a b s e n t . T h i s a b s e n c e i s c r i t i c a l i n o u r m o d e l l i n g o f t h e r e l a x a t i o n s i n t h e n a t u r a l m o l e c u l a r s o l i d s s i n c e c e l l u l o s e and h e m i c e l l u l o s e c o n t a i n r i n g s o f carbon and oxygen a l o n g w i t h s i d e u n i t s CH20H and OH w i t h no i n t e r v e n i n g m e t h y l c h a i n s -CH2-CH2-CH2-. We have made a g r e a t many measurements on p a r t i a l l y d e l i g n i f i e d wood t o assess t h e r e l a t i v e r o l e o f t h e c e l l u l o s i c m a t e r i a l and l i g n i n ; t h o s e measurements w i l l b e i n c l u d e d i n a n o t h e r m a n u s c r i p t / 5 / . The i m p o r t a n t f a c t o r i s t h a t t h e fi-peak and t h e K-peak a r e p r e s e n t i n a l l t h e woods we have examined and t h e y - p e a k i s a b s e n t . The n a t u r a l hydrocarbon, amber, a l s o shows damping p e a k s . We have mea- s u r e d t h r e e ambers, t h e famous B a l t i c S e a amber, which i s d e r i v e d from a p i n e r e s i n , a n amber from t h e Dominican r e p u b l i c which i s d e r i v e d from a d e c i d u o u s t r e e s a p , and a r e s i n from Venezuela. Some o f t h e s e measurements have been r e p o r t e d e a r l i e r /4/; w e show t h e I F f o r a B a l t i c amber i n F i g . 4 . One a g a i n s e e s t h e o - p e a k t o be p r e s e n t , a s m a l l y-peak and no K-peak. P e r h a p s a n = - p e a k would b e p r e s e n t i f we c o u l d make c a r e f u l enough measurements, b u t t h e ambers a r e s o s o f t t h a t t h e e l a s t i c modulus d r o p s n e a r l y t o 0 above 400 K . Thus, we have been u n a b l e t o t r a c e o u t theoC-peak f o r t h e ambers. However, one s h o u l d n o t e a g a i n t h a t t h e /j- and )?-peaks o c c u r a t t h e same tempera- t u r e a s i s t r u e a s o f t h o s e i n o t h e r macromolecular s o l i d s .

F i n a l l y , we have made measurements on two samples o f o i l s h a l e . One was a Colorado o i l s h a l e from t h e famous Green R i v e r f o r m a t i o n

-

^{t h i s}

s h a l e c o n t a i n s a b o u t 20 g a l l o n s o f kerogen p e r t o n o f s h a l e . The measurement f o r t h a t s h a l e was r e p o r t e d e a r l i e r / 4 / . We have a l s o measured on o i l s h a l e o f German o r i g i n ; t h a t measurement i s shown i n F i g . 5. T h i s specimen came from t h e famous o i l s h a l e d e p o s i t s i n Holzmaden e a s t o f S t u t t g a r t n e a r t h e Hauff Museum. Again one s e e s t h e same damping p e a k s a s b e f o r e . They a r e somewhat s m a l l e r s i n c e t h e volume o f macromolecular m a t e r i a l p e r u n i t volume o f s o l i d i s r e l a t i v e - l y s m a l l

-

most o f t h e s h a l e i s i n d e e d r o c k . M i n e r a l o g i s t s have f o u n d ,

in fact, that the kerogen in shale is mainly a cementing film which lies in the interstices of a jumble of small minerals (mainly oxides, sulfides, phosphates and carbonates). The stress is apparently trans- mitted elastically through these rocks to the hydrocarbon material

lying interstitially between the microscopic mineral grains and the relaxation occurs within the kerogen itself. Damping peaks similar to those we show in Fig. 5 are to be expected from these minerals.

Summarizing: The relaxations we have demonstrated to exist in all of these natural hydrocarbons, as well as those known to exist in the synthetic polymers, are extremely similar in their locations. Thus, the molecular motions responsible for these relaxations must, indeed, be similar through this whole class of materials. This does not mean that the relaxing entities are identical among the solids, but they are of the same class.

1II.Dielectric Relaxation.- Polymeric materials are commonly insulators.

However, they are not usually perfect dielectric media and often show large dielectric loss. In fact, many of them show loss peaks charac- teristic of reorientation of specific dipole units. Thus, it was natural for us to attempt to determine the loss characteristics of other natural macromolecular solids. We have seen loss peaks in the ambers, in wood and in some of the coals. This measurement is diffi- cult to make because the capacitance of a typical wafer is so small that lead-problems can interfere with the measurement. However, by using specimens with guarded electrodes (from silver paint) and a special sample holder this problem can be fairly well eliminated / 6 / . Fig. 6 shows a measurement of the dielectric loss angle made at three frequencies on a typical coal, bituminous 2 (77%C d.a.f.) correspon- ding IF-curve b from Fig. 2. This coal was chosen because it had, as can be seen from Fig. 2, a large /%peak in mechanical relaxation. A similar measurement was made for bituminous 3 (85% d.a.f.). Data for these two specimens are plotted in Fig. 7 in an Arrhenius plot. One sees that the relaxation has an activation energy of about 0.45 eV and a value of

To

of about 1 .3x10-13s.

Two things are important:

1 . ) The mechanical &peak has its dielectric analogue. This means that

the relaxing entity is polar.

2.) No indication of the dielectric analogue of the mechanicalr-peak is seen. This is also true for other coals and for amber on which we have made similar types of measurements. Thus, the entity responsible for the mechanical Y-peak has no electrical polar-momentum.

IV. Kinetics of the Y-Relaxation.- The kinetics of they-peak for bituminous 1 has been measured over a wide range of frequencies. Some measurements were made by the torsion pendulum method and some were made using mechanical after effect. The data all fit together in a nice Arrhenius plot as seen in Fig. 8. The value of H is seen to be about 0.18eV and

To

has the value 1.1~10-8s. This large value implies that this is a cooperative motion among many atoms.

V. Models.- The chief goal of this paper was to establish more defini- tive models for these relaxations. We draw the following conclusions from the observations reported herein and from others to which we have alluded.

1 . ) A series of relaxations is seen in the natural macromolecular

solids which have great similarity. In general, three relaxations are observed. Anoc-peak occurs somewhat above room temperature. This peak is similar to many peaks seen in synthetic polymers. The peak has usually been ascribed to the sliding motion in amorphous polymers of large segments. It usually occurs in the vicinity of the glass transi- tion temperature Tg.

C9-194 J O U R N A L D E PHYSIQUE

I n polymers which a r e p a r t i a l l y c r y s t a l l i n e , twooC-peaks a r e o f t e n s e e n , one a s s ~ c i a t e d w i t h t h e c r y s t a l l i n e u n i t s and t h e o t h e r w i t h t h e amorphous f r a c t i o n of t h e s o l i d . I n c o a l and kerogen we u s u a l l y saw b u t o n e a - p e a k , implying t h a t t h e m a t e r i a l was amorphous. I n some o f t h e wood specimens we saw twooc-peaks, i m p l y i n g t h a t some c r y s t a l l i n e c h a r a c t e r of t h e c e l l u l o s e m a t e r i a l e x i s t s i n wood.

2 . ) AB-peak e x i s t s i n a l l m a t e r i a l s we have examined w i t h i n t e r n a l f r i c t i o n . I t i s a l s o found t o be e l e c t r i c a l l y p o l a r s i n c e a d i e l e c t r i c l o s s - p e a k i s found i n a l l m a t e r i a l s (amber, c o a l and wood) which we have measured. F u r t h e r m o r e , t h e v a l u e o f Z f o r t h e r e l a x a t i o n i s v e r y s m a l l , n e a r a t o m i c f r e q u e n c i e s . Thus, t h e g e l a x i n g e n t i t y must b e s m a l l , p e r h a p s it i s r e o r i e n t a t i o n o f t h e hydrogen atom i n t h e OH u n i t which i s a t t a c h e d t o more r i g i d segments o f t h e macromolecular s o l i d . I t c o u l d be l a r g e r u n i t s , i n f a c t , a f l - p e a k has been s e e n f o r s i d e u n i t s h e a v i e r t h a n OH / 7 / .However, it c o u l d n o t b e t h e c o o p e r a t i v e motion o f a l a r g e number o f atoms, e l s e t h e v a l u e o f would t h e n b e much l a r g e r .

3.) T h e y - p e a k i n c o a l , amber and k e r o g e n must have a d i f f e r e n t o r i g i n . I t does n o t have a r e l a x i n g e n t i t y which i s p o l a r , s i n c e we have n o t s e e n a d i e l e c t r i c analogue o f t h e mechanical r e l a x a t i o n . We w i l l look f u r t h e r i n some c o a l s t o v e r i f y t h i s p o i n t f u r t h e r , b u t i t seems s a f e t o draw t h i s c o n c l u s i o n from measurements we have made up t o now.

F u r t h e r m o r e , t h e v a l u e o f To i s v e r y l a r g e r e l a t i v e t o a t o m i c p e r i o d s o f v i b r a t i o n , hence i t seems l i k e l y t h a t it i s c a u s e d by t h e coopera- t i v e motion o f l a r g e u n i t s . T h i s f i t s w i t h t h e model o f t h e t w i s t i n g o r bending o f l i n e a r segments of c h a i n s such as t h e methylene c h a i n - C H 2 - C H ~ - C H Z . . . I n t h e n a t u r a l hydrocarbons t h e s e c o u l d be t h e l i n e a r u n i t s which c o n n e c t t h e a r o m a t i c c l u s t e r s known t o make up t h e c o a l s t r u c t u r e .

We a r e i n t h e m i d s t o f a l o n g e r s t u d y t o work o u t t h e dependence o f t h e h e i g h t o f t h e r - p e a k on t h e c a r b o n c o n c e n t r a t i o n o f t h e c o a l s we have examined ( i n t h e language o f t h e c o a l s c i e n t i s t s , t h e r a n k o f t h e c o a l ) . T h a t measurement i s n o t q u i t e complete s i n c e i t demands c a r e f u l e x a m i n a t i o n o f a dozen c o a l s t o e s t a b l i s h enough p o i n t s on t h e c u r v e t o show c l e a r l y t h e b e h a v i o u r . We have made enough measurements, though, t o suppose t h a t t h e c o a l s w i t h carbon c o n c e n t r a t i o n around 82% have a maximum v a l u e o f t h e y - r e l a x a t i o n s t r e n g t h and t h a t it f a l l s o f f on b o t h s i d e s o f t h a t v a l u e . We a r e b o t h t r y i n g t o f i l l i n a s u f f i c i e n t number o f p b i n t s on t h a t c u r v e t o show t h a t i t i s t r u e and t o d e v e l o p a p h y s i c a l model o f why i t s h o u l d b e s o .

Acknowledgments.- C . Wert acknowledges t h e s u p p o r t of t h e D i v i s i o n o f M a t e r i a l s S c i e n c e s , Department o f Energy, under c o n t r a c t number DE-AC02-76ER1198. He a l s o acknowledges s u p p o r t o f t h e Humboldt S t i f - t u n g , Bonn, f o r a n extended s t a y i n West Germany, d u r i n g which a p a r t o f t h i s work was c a r r i e d o u t . We a l s o acknowledge t h e i n t e r e s t and s u p p o r t o f D r . J . D i e h l . The c a r e f u l and p a t i e n t work o f M i s s Hamm, M r . Henke, M i s s Lakemeyer and M r . Rahn i n S t u t t g a r t i s g r a t e f u l l y acknowledged. One o f t h e specimens o f c o a l , d a t a shown i n F i g s . 2c and 7 was k i n d l y s u p p l i e d by t h e Penn S t a t e C o a l Bank; we a r e g r a t e f u l f o r t h e g i f t o f t h i s c o a l .

R e f e r e n c e s

/ I / C . A . Wert and M. W e l l e r , J. de Physique

g,

S u p p l . no. 1 0 ,

42,

581 (1981)

.

/2/ C.A. Wert and M. W e l l e r , J.Appl.Phys. 53, 6505 ( 1 9 8 2 ) .

/ 3 / N.G. Mc Crurn, B.E. Read and G . ~ i l l i a m z A n e l a s t i c and D i e l e c t r i c E f f e c t s i n S o l i d s J . Wiley, New York, 1967.

/ 4 / C.A. Wert, M. W e l l e r , R e p o r t Univ. I l l . and MPI-Metallforschung MPI/82/W1, 1982.

/5/ C.A. Wert, M. Weller and D. Cauffield, to be publ. in Wood Sci.

/6/ M. Weller, C.A. Wert, to be publ..

/7/ J. Heijboer, Ann.New York Acad.Sci.

2 ,

105 ( 1 9 7 6 ) .

Fig. I : IF and modulus ( fL) for coal bituminous 1

.

10 x l d P

8 Tan 8

Temperature

- 1.0

6 - -

I S

4 - ^{0 LO 80 120} 1M) 200 2LO 280 320 350 LOO LLO L80K

- 05 Temmture

2 -

Fig.3: IF for spruce with 29% lignin

I I 0

-

o 12s 240 360 K (two subsequent heating curves)

.

Temperature

Bituminous I -

*. -. _"

Carbon daf 81.8%

-

-

-

-;

^/

8 .lo-?

2 7- 6

kec2 5 1.5 Tan:_

11 x10-~

10 9

7 Ton6

Fig.2: IF spectrum for different coals. a: bituminous 1 (82%C), b: bituminous 2 (77%C), c: bituminous 3 (85%C), d: anthracite (93%C)

1 1 ' , 1 1 ' 1 1 , ' 1 1 1 ' 1 1 1 1 1 ' I '

Spruce- 293% 1qnm -

n

- - IS1 tun ^{r. I1}

-- 2nd wn ~GI* hatvlg to 3 7 5 ~ 6smi ; '\.j ;;-

I I

- I -

I I

1 -

I I

f _3- -

6 -

Y

5

-

0 LO 80 120 160 200 2L0 280 320 360 LOO LLO L8OK

~ 1 ~ 1 ~ 1 1 1 ~ 1 ~ 1 ' 1 ~ 1 ' 1 ' 1 ' 1 1 '

- I\

I

-

a

8 -

-

-

I \ ,

I L'

-

I I ¹

I 1

-

1 -

I

C9-196 JOURNAL DE PHYSIQUE

240 3 6 0 K

'

Tempnature

8.

%I0*

6 - Tma.

4

Fig.4: I F spectrum of B a l t i c amber.

Boftic Amber--elm Bemrtein klor F r C g s l H t

Blturninous 2

.05 run 2

1

internal friction Internal

A Bituminous 2 triotiin

PSOC 2 9 6 dielettrlc reloralion

F i g . 5 : I F spectrum of o i l s h a l e ( G l s c h i e f e r ) from Holzmaden.

Fig.6: D i e l e c t r i c l o s s f o r c o a l bituminous 2 .

Temperature

I I I

1000 '5O 125 ^{iOO K}

bdO I

Pig.7: Arrhenius p l o t f o r t h e f l - p e a k i n two c o a l s .

F i g . 8: Arrhenius p l o t f o r t h e Y-peak i n c o a l bituminous 1 .