INSTALLATION AND OPERATION OF AUTOSORB-l-C-8 FOR BET SURFACE AREA MEASUREMENT OF POROUS MATERIALS

PINSTECH-221

INSTALLATION AND OPERATION OF AUTOSORB-l-C-8

FOR BET SURFACE AREA MEASUREMENT

OF POROUS MATERIALS

Abdul Sattar Ali Khan

Chemistry Division

Directorate of Science

Pakistan Institute of Nuclear Science and Technology

P.O. Nilore, Islamabad, Pakistan.

Abstract

A u t o s o r b - l - C - 8 , m a n u f a c t u r e d by Q u a n t a c h r o m e I n s t r u m e n t s , U S A is a fully automated B E T s u r f a c e a r e a and porosity a n a l y z e r . In p r e s e n t report, t h e installation and operation of A u t o s o r b f o r e v a l u a t i o n of B r u n a u e r - E m m e t t - T e l l e r ( B E T ) s u r f a c e area by physisorption of n i t r o g e n on solid p o r o u s materials is d i s c u s s e d in s t e p w i s e m a n n e r . T h e A u t o s o r b h a s been s u c c e s s f u l l y installed arid it is w o r k i n g p r o p e r l y . T h e Q u a n t a c h r o m e I n s t r u m e n t s s u r f a c e area r e f e r e n c e material w a s a n a l y z e d a n d t h e o b s e r v e d B E T s u r f a c e area o f reference material w a s f o u n d to b e in close a g r e e m e n t with t h e reported v a l u e of 107 r r f / g . It m e a n s that A u t o s o r b can b e used satisfactorily for a c c u r a t e m e a s u r e m e n t of B E T s u r f a c e area of p o r o u s materials. T h e e v a l u a t i o n of B E T s u r f a c e area, a v e r a g e p o r e d i a m e t e r and total p o r e v o l u m e o f V u l c a n X C - 7 2 c a r b o n and A l u m i n a g r a n u l e s with and w i t h o u t c o b a l t c o a t i n g is also discussed. T h e present report m a y b e u s e f u l for q u i c k installation and operation of A u t o s o r b for evaluation o f B E T s u r f a c e a r e a by p h y s i s o r p t i o n of nitrogen on solid p o r o u s materials.

Table of Contents

S. U Description Page #

A b s t r a c t i T a b l e o f C o n t e n t s ii L i s t o f F i g u r e s 111 1. I n t r o d u c t i o n 1 2. I n s t a l l a t i o n o f A u t o s o r b s o f t w a r e 2 4. S h u t t i n g d o w n t h e A u t o s o r b 4 5. P r o c e d u r e f o r B E T s u r f a c e a r e a a n a l y s i s 4 5.1 D e g a s s i n g o f s a m p l e s 5 5.2 S a m p l e a n a l y s i s 7 5.3 M e t h o d o l o g y o f B E T s u r f a c e a r e a m e a s u r e m e n t 10 6. E v a l u a t i o n o f B E T s u r f a c e a r e a o f s e l e c t e d p o r o u s m a t e r i a l s 11 6.1. R e f e r e n c e m a t e r i a l 11 6.2. V u l c a n X C - 7 2 c a r b o n 12 6.3. A l u m i n a g r a n u l e s 12 7. C o m p a r i s o n o f o b s e r v e d a n d r e p o r t e d d a t a o f B E T s u r f a c e a r e a 12 8. E v a l u a t i o n o f total p o r e v o l u m e a n d a v e r a g e p o r e d i a m e t e r 13 9. C o n c l u s i o n s 18 10. R e f e r e n c e s 18 i i

List of Figures

Figure # Description Page #

F i g u r e 1. A u t o s o r b - l - C - 8 , Q u a n t a c h r o m e , U S A 1 F i g u r e 2. E n t e r i n g o f i n s t r u m e n t s e t t i n g s 2 F i g u r e 3. H e l i u m and a d s o r b a t e line c o n n e c t i n g p o r t s l o c a t e d on t h e r e a r s i d e of A u t o s o r b and f i l l i n g o f d e w a r f l a s k 3 F i g u r e 4. I n i t i a l i z a t i o n of A u t o s o r b m o n i t o r 4 F i g u r e 5. D e g a s s i n g o f s a m p l e 5 F i g u r e 6. O u t g a s s e r s e t t i n g s f o r p r e p a r a t i o n o f s a m p l e 6 F i g u r e 7. S a m p l e s t a t i o n w i t h f i t t i n g o f s a m p l e cell, P0 cell a n d t h e r m i s t o r 8 F i g u r e 8. P h y s i s o r p t i o n a n a l y s i s p a r a m e t e r s 8 F i g u r e 9. S e l e c t i o n o f a n a l y s i s p o i n t s 9 F i g u r e 10. E d i t i n g o f a n a l y s i s p o i n t s 9 F i g u r e 11. B E T p l o t o f 1/w ( P0/ P - 1 ) v e r s u s P0/ P f o r n i t r o g e n a d s o r p t i o n on r e f e r e n c e m a t e r i a l L o t N o . 3 0 0 5 14 F i g u r e 12. B E T p l o t o f 1/w ( P0/ P - l ) v e r s u s P0/ P f o r n i t r o g e n a d s o r p t i o n on V u l c a n X C - 7 2 c a r b o n 15 F i g u r e 13. B E T p l o t of 1/w ( P0/ P - l ) v e r s u s P0/ P f o r n i t r o g e n a d s o r p t i o n on A l u m i n a g r a n u l e s 16 F i g u r e 14. B E T p l o t o f 1/w ( P0/ P - l ) v e r s u s P0/ P f o r n i t r o g e n a d s o r p t i o n on c o b a l t c o a t e d A l u m i n a g r a n u l e s 17

1. Introduction

T h e B r u n a u e r - E m m e t t - T e l l e r ( B E T ) s u r f a c e area is the a r e a o f t h e p o r e s available for adsorption o f nitrogen gas in solid p o r o u s materials. T h e A u t o s o r b - l - C - 8 ( F i g u r e 1) m a n u f a c t u r e d by Q u a n t a c h r o m e I n s t r u m e n t s U S A is a fully a u t o m a t e d and user friendly instrument for B E T s u r f a c e area and p o r e size m e a s u r e m e n t s . D u r i n g o p e r a t i o n o n e can view the a c c u m u l a t e d data, t h e isotherm and all associated g r a p h s and analytical results. T h e installation o f A u t o s o r b s o f t w a r e is also simple and r e q u i r e s technical i n f o r m a t i o n such as entering t h e m o d e l / ID o f the i n s t r u m e n t etc. d u r i n g installation o f s o f t w a r e .

T h e v a r i o u s s t e p s of operation of A u t o s o r b f o r B E T s u r f a c e a r e a m e a s u r e m e n t are not discussed clearly in the o p e r a t i n g m a n u a l [1] and h e n c e it m a y be d i f f i c u l t for new operator to install and o p e r a t e t h e A u t o s o r b i n d e p e n d e n t l y . T h u s t h e aim o f this report is to discuss the installation and o p e r a t i o n o f A u t o s o r b f o r m e a s u r i n g t h e B E T s u r f a c e area of p o r o u s materials s o that it m a y b e c o m e m o r e c o n v e n i e n t f o r a n y n e w o p e r a t o r to h a n d l e the A u t o s o r b i n d e p e n d e n t l y for m e a s u r e m e n t of p h y s i s o r p t i o n B E T s u r f a c e area o f porous material by nitrogen a d s o r p t i o n .

2. Installation of A u t o s o r b software

B e f o r e i n s t a l l a t i o n o f A u t o s o r b s o f t w a r e , f i r s t l y p l u g t h e 2 5 - p i n m a l e e n d of the serial c a b l e into t h e 2 5 - p i n s o c k e t labeled " R S 2 3 2 " at t h e r e a r o f t h e A u t o s o r b a n d p l u g t h e 9-pin f e m a l e e n d o f t h e serial c a b l e into t h e serial p o r t o f t h e P C . N o w s w i t c h on t h e PC and run t h e s e t u p f i l e in t h e f o l d e r labeled d i s k 1.

T h e A u t o s o r b s o f t w a r e s e t u p p r o c e e d s u n d e r t h e f a m i l i a r I n s t a l l S h i e l d ® W i z a r d . A f t e r f i n i s h i n g t h e i n s t a l l a t i o n , t h e A u t o s o r b p r o g r a m is l a u n c h e d a n d a w i n d o w s h o w n in F i g u r e 2 is o p e n e d . S e l e c t c o m m u n i c a t i o n p o r t 1, A S I c h e m i s o r b , 1 m m H g t r a n s d u c e r , pirani g a u g e a n d e n t e r t h e serial n u m b e r o f A u t o s o r b . T h e s e r i a l n u m b e r o f A u t o s o r b - I - C - 8 is 1 1 5 0 6 0 1 2 7 0 1 w h i c h is l a b e l e d on t h e b a c k s i d e o f t h e A u t o s o r b b o d y . A f t e r e n t e r i n g all required s e t t i n g s , c l i c k O K t o c o m p l e t e t h e installation o f A u t o s o r b s o f t w a r e . Instrument Settings fodei [ f e n | - ' P o r t • Vacuum gauged; \ , yo> £ ; J iW'.'U'"-'" '.'.-"-J <' F i g u r e 2. E n t e r i n g o f i n s t r u m e n t s e t t i n g s .

3. Starting the Autosorb for BET surface area measurement

Starting of A u t o s o r b - l - C - 8 is described as f o l l o w :

1. C o n n e c t h e l i u m and a d s o r b a t e input lines f r o m the r e s p e c t i v e c y l i n d e r s to the s p e c i f i c ports p r o v i d e d at rear of the A u t o s o r b as s h o w n in F i g u r e 3.

2. Set the p r e s s u r e r e g u l a t o r to 10 psi on both h e l i u m and nitrogen c y l i n d e r s .

3. Insert s a m p l e cell or stainless steel pin into t h e s a m p l e station, P0 station, and each

d e g a s s i n g station.

4. Fill t h e d e w a r flask and cold trap d e w a r f l a s k with liquid nitrogen up to the required level.

(A) (B)

F i g u r e 3. H e l i u m and a d s o r b a t e line c o n n e c t i n g ports located on the rear side of

A u t o s o r b and filling of d e w a r flask.

5. Run A u t o s o r b p r o g r a m on P C prior to s w i t c h i n g on the m a i n p o w e r supply o f A u t o s o r b . T h e A u t o s o r b - l - C - 8 requires 2 2 0 v o l t s input p o w e r s u p p l y .

6. First turn on t h e t w o m a i n b r e a k e r s and t h e n e l e c t r o n i c b r e a k e r located on the b a c k s i d e o f t h e A u t o s o r b .

7. A s soon as t h e e l e c t r o n i c b r e a k e r is switch on, t h e A u t o s o r b s o f t w a r e is initialized and the p r o g r a m d i s p l a y s v a r i o u s m e s s a g e s in t h e A u t o s o r b m o n i t o r w i n d o w which are self e x p l a n a t o r y . D u r i n g this p r o c e s s , t h e s o f t w a r e also a s k s t h r e e questions. Enter " n " in each c a s e in t h e reply box and click < r e t u r n > as s h o w n in F i g u r e 4. 8. N o w the A u t o s o r b is ready to be used f o r s u r f a c e area m e a s u r e m e n t s .

Autosorb Monitor

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Shutting down the Autosorb

The following procedure should be adopted to shut down the Autosorb:

1. Insert sample cell or stainless steel pin into the sample station,

P

0

station, and each

degassing station.

2. Turn off the electronics breaker first and then both mains power breakers located on

the rear side of the instrument.

3. Disconnect the gas input lines from the instrument.

4. Close the gas regulator to avoid the leakage of gases.

5. Procedure for BET surface area analysis

BET surface area measurements of a porous material may require pretreatment at

certain elevated temperature to remove the adsorbed moistures. Degassing stations are used

for this purpose. There are two degassing station along with digital temperature controllers

and hence two samples can be degassed simultaneously at any desired temperature. The

procedure of degassing is as follow:

5.1 Degassing of samples

T h e d e g a s s i n g is required to r e m o v e the a d s o r b e d w a t e r m o l e c u l e s f r o m t h e s a m p l e . T h e d e g a s s i n g o f solid s a m p l e s is usually d o n e at 3 0 0 °C. D i f f e r e n t s a m p l e m a y require d i f f e r e n t t e m p e r a t u r e for c o m p l e t e r e m o v a l o f a d s o r b e d w a t e r m o l e c u l e s f r o m the s a m p l e . T h e d e g a s s i n g p r o c e d u r e is d e s c r i b e d step by step as f o l l o w :

1. T a k e a r e q u i r e a m o u n t o f s a m p l e in s a m p l e tube.

2. Fit the s a m p l e t u b e to o n e o f t h e d e g a s s i n g station (1 or 2) as s h o w n in F i g u r e 5. 3. Fit t h e required v a c u u m trap t u b e in t o the cold t r a p fitting and fill t h e cold trap

d e w a r f l a k w i t h liquid nitrogen up to the required level u s i n g p r o v i d e d leveler. Enter the cold trap t u b e into the D e w a r f l a s k and fit t h e D e w a r f l a k to the holder present on t h e f r o n t s u r f a c e o f A u t o s o r b .

4. Switch on t h e digital t e m p e r a t u r e controller present i m m e d i a t e l y b e l o w the respective d e g a s s i n g station. Set t h e required t e m p e r a t u r e f o r d e g a s s i n g of the s a m p l e . T h e t e m p e r a t u r e c o n t r o l l e r will r e m a i n o f f until t h e o u t g a s station is loaded. 5. Enter the s a m p l e t u b e into t h e h e a t i n g m a n t l e attached to t h e f r o n t side o f the

A u t o s o r b . C l a m p t h e h e a t i n g m a n t l e c a r e f u l l y with p r o v i d e d c l a m p (not to break the t u b e ) for h o l d i n g t h e s a m p l e t u b e inside t h e h e a t i n g m a n t l e d u r i n g o p e r a t i o n .

Vacuum trap

dewar flask _Heater

Figure 5. D e g a s s i n g o f s a m p l e

Autosorb Outgasser

F i g u r e 6. O u t g a s s e r settings for p r e p a r a t i o n of s a m p l e .

6. N o w in t h e o p e r a t i o n m e n u o f the A u t o s o r b p r o g r a m , click t h e o u t g a s s e r .

7. Select correct o u t g a s station (1 or 2) and t h e t y p e of b a c k fills gas ( H e l i u m or A d s o r b a t e ) and then click load as s h o w n in F i g u r e 6. In d o i n g so, the selected out gas station will be loaded and the L E D o f t h e r e s p e c t i v e station and the digital t e m p e r a t u r e c o n t r o l l e r will lit green w h i c h indicates t h e o u t g a s station has been loaded. T h e t e m p e r a t u r e of t h e h e a t i n g m a n t l e will rise and it c a n b e v i e w e d on the front panel d i s p l a y by c l i c k i n g t h e s p e c i f i c b u t t o n (1 or 2) f o r d e g a s s i n g station. 8. T h e s a m p l e is said to b e o u t g a s s e d if it p a s s a test o f p r e s s u r e rise limit of 50 micron

/ m i n w h i l e heated and 2 0 m i c r o n / m i n w h e n at r o o m t e m p e r a t u r e . It is r e c o m m e n d e d to test o n e station at a time.

9. A f t e r c o m p l e t i o n of o u t g a s s i n g , switch o f f the t e m p e r a t u r e c o n t r o l l e r to cool down the s a m p l e long b e f o r e c l i c k i n g on r e m o v e .

10. W h e n the t e m p e r a t u r e o f s a m p l e r e a c h e s to the room t e m p e r a t u r e then click on r e m o v e to s t o p t h e d e g a s s i n g process. T h e c o m p l e t i o n of r e m o v a l of d e g a s s i n g station can be c h e c k e d by c l i c k i n g the i n s t r u m e n t status u n d e r operation m e n u . A f t e r c o m p l e t i o n of r e m o v a l p r o c e s s , t h e g r e e n L E D s w i t c h e s o f f .

5.2 Sample analysis

1. U n s c r e w t h e fitting o f t h e s a m p l e t u b e f r o m t h e d e g a s s i n g station and fit t h e SS stud to the d e g a s s i n g station.

2. R e f i t t h e s a m p l e t u b e s to s a m p l e station w h i c h is clearly indicated in Figure 7. C o n n e c t the P0 t u b e to t h e PG station for m e a s u r e m e n t s o f s a t u r a t e d v a p o r pressure

of nitrogen.

3. Fit the t h e r m i s t o r for s e n s i n g t h e liquid nitrogen level b y t h e A u t o s o r b d u r i n g analysis.

4. In t h e a n a l y s i s m e n u , click p h y s i s o r p t i o n a n a l y s i s p a r a m e t e r s to o p e n the w i n d o w s as s h o w n in F i g u r e 8.

5. Enter a short s a m p l e ID and file ID u p to 8 c h a r a c t e r s . 6. Enter a brief s a m p l e d e s c r i p t i o n up to 50 c h a r a c t e r s . 7. E n t e r o p e r a t o r n a m e .

8. Select nitrogen as a d s o r b a t e .

9. Select f i n e e v a c u a t i o n and k e e p M a x i - d o s e on. 10. Select P0 station and e n a b l e t h e t e m p c o m p e n s a t i o n .

11. Select a p p r o p r i a t e s a m p l e tube f r o m t h e m e n u .

12. Enter u0 " in t h e o u t g a s t i m e and o u t g a s t e m p e r a t u r e selection areas b e c a u s e the

s a m p l e has m a n u a l l y been o u t g a s s e d prior to analysis.

13. N o w select a n a l y s i s points, t o l e r a n c e and e q u i l i b r i u m t i m e and click O K as s h o w n in F i g u r e 9. T h e 3 - t o l e r a n c e limit and 2 min e q u i l i b r i u m t i m e is c o m m o n l y used. 14. Select required a n a l y s i s points and t h e n click O K .

15. A f t e r selection of all a n a l y s i s p a r a m e t e r s , click Start.

16. T h e A u t o s o r b will begin the analysis and it will control all set p a r a m e t e r s a u t o m a t i c a l l y . A s soon as t h e fist analysis p o i n t is a c h i e v e d , t h e A u t o s o r b s o f t w a r e will create a plot o f v o l u m e of gas a d s o r b e d v e r s u s relative p r e s s u r e .

17. For v i e w i n g t h e results, right click on t h e graph and go to t h e edit r a w data tag. E n a b l e required p o i n t s for u s i n g t h e m in e v a l u a t i o n of B E T s u r f a c e area by j u s t c l i c k i n g on t h e point, s e l e c t i n g t h e switches and t h e n c l i c k i n g on the " S e t s e l e c t e d " and finally " O K " as s h o w n in Figure 10.

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S a m p l e tube

Figure 7. S a m p l e station with fitting of s a m p l e cell, P0 cell and thermistor.

Physisorption Analysis Parameters Sample ID

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Ssmpie Description

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3 point BET (0.1,0 2,0.3]

III

Five Point SET (0.10,0.15,0.20,0.25,0.30)

'• V Seven Pant BET (0.05,0.075,'0.10.0.15,0.20.0 25,0.30] [ Eleven Point BET (0.05 to 0.30 in 0.025 increments) j

Outgas Time. !OLO ' Hourt Outgas Temp. : [0.5 DoseWizard j }0 • •• I a-oCon'i; v Enable :

Cell type: I 12mm w/o rod jr

(pressure:0.10000000 ToLeianc8:3 Equilibration 2 F1ags:A W Pressure:0.20000000 Tolerance: 3 Equilibration 2 Flags:A M [Pressure: 0.30000000 Tolerance:3 Equilibration: 2 Flags: A M

M m M S W *

M i s

F i g u r e 9. Selection of a n a l y s i s points.

Edit Raw Data and Tag?

Pressure 0.0525 0.1008 0.1464 [0.2052 jO. 2473 . H i 0.3461 0.4019i 0.4519' 0.5000 0.5528 0.6023 0.6512 0.6965: • 25.265'- M 29.67Q M;, . ' 38'074- ., . 401458. • • • • • - S p S i * i i i t

m

50.184 ' 54.357 59.604

Cleat All Select All

m

_'M'ii

mmm.

Delete Selected Points

f r f j r | p 1

• r i r :• Slatisticd-Thickness I f •• i f ^ S l ^ i l i f si I Set Selected F i g u r e 10. Editing o f a n a l y s i s points. 9

5.3 Methodology of BET surface area measurement

T h e detail d i s c u s s i o n on d i f f e r e n t t h e o r i e s for e v a l u a t i o n o f s u r f a c e area of porous m a t e r i a l s is a v a i l a b l e in o p e r a t i n g m a n u a l o f A u t o s o r b [1]. S i n c e B E T m e t h o d is most w i d e l y used for s u r f a c e area m e a s u r e m e n t s , it is d i s c u s s e d here in detail for c o n v e n i e n c e . T h e B r u n a u e r - E m m e t t - T e l l e r ( B E T ) m e t h o d m a k e s u s e of the f o l l o w i n g equation for d e t e r m i n i n g t h e s u r f a c e area o f solid p o r o u s m a t e r i a l s :

P

(1)

w h e r e W is the w e i g h t o f gas a d s o r b e d per gram of s a m p l e at a relative pressure of P/Po and Wm is the w e i g h t of gas a d s o r b e d per g r a m of s a m p l e for c o m p l e t e m o n o l a y e r

c o v e r a g e o f a d s o r b e n t s u r f a c e . T h e term C is the B E T c o n s t a n t . T h e plot of 1/W(P0/P-1) vs.

P/P0 is linear in the P / P0 r a n g e o f 0.05 to 0.35 w h e n u s i n g nitrogen as the a d s o r b a t e . A

standard m u l t i p o i n t B E T m e t h o d of s u r f a c e area m e a s u r e m e n t r e q u i r e s a m i n i m u m of three points in the a p p r o p r i a t e relative p r e s s u r e range. T h e v a l u e o f Wm is required for s u r f a c e

area m e a s u r e m e n t . It m a y be e v a l u a t e d f r o m t h e s l o p e and intercept o f the B E T plot as follow: slope = s = — — - (2) W . C intercept = i = — — (3) W C Y V By c o m b i n i n g e q u a t i o n 2 and 3, o n e m a y get

W

m

= — (4)

S + I

If Ac s is t h e cross s e c t i o n a l area o f a d s o r b a t e m o l e c u l e s t h e n t h e s u r f a c e a r e a S per gram

S = •— ^ (5) M

w h e r e M is the m o l e c u l a r w e i g h t o f the a d s o r b a t e m o l e c u l e s and N is the A v a g a d r o ' s n u m b e r ( 6 . 0 2 3 xlO2"5 m o l e c u l e s / m o l e ) . For nitrogen as an a d s o r b a t e , t h e v a l u e o f M is

2 8 . 0 1 2 3 and Ac s is 16.2 A 2 at 77 K and h e n c e by s u b s t i t u t i n g the v a l u e of k n o w n

p a r a m e t e r s into Eq. 5 w e get:

S = 3 4 8 2 . 6 2 7 Wm( m2/ g ) (6)

T h u s it is p o s s i b l e to c a l c u l a t e t h e B E T s u r f a c e area of solid s a m p l e s by j u s t f i n d i n g the value of Wm f r o m t h e B E T plot.

6. Evaluation of BET surface area of selected porous materials

T h e B E T s u r f a c e area o f r e f e r e n c e material, V u l c a n X C - 7 2 c a r b o n and A l u m i n a granules with and w i t h o u t cobalt c o a t i n g w e r e e v a l u a t e d and d i s c u s s e d in f o l l o w i n g sections.

6.1. Reference material

T h e Q u a n t a c h r o m e s I n s t r u m e n t s s u r f a c e area r e f e r e n c e material (Cat. N o . 2 0 0 5 of 2 * •

Lot No. 3 0 0 5 ) h a v i n g B E T s u r f a c e area o f 107 m / g w a s used f o r v a l i d a t i o n of data. T h e accurately w e i g h t e d s a m p l e of r e f e r e n c e material w a s d e g a s s e d at 3 0 0 °C f o r o n e hour before m e a s u r i n g t h e B E T s u r f a c e area. T h e B E T a d s o r p t i o n d a t a o f r e f e r e n c e material is presented in T a b l e 1 and the plot of l / w ( P0/ P - l ) v e r s u s P / P0 is s h o w n in F i g u r e 11. T h e

•y

B E T s u r f a c e a r e a o f r e f e r e n c e material w a s f o u n d to b e 103.6 m / g w h i c h is in close a g r e e m e n t with t h e r e f e r e n c e v a l u e . It m e a n s that t h e n e w l y installed A u t o s o r b is w o r k i n g properly and o n e can e v a l u a t e the B E T s u r f a c e area of p o r o u s material a c c u r a t e l y .

6.2.

Vulcan XC-72 carbon

T h e B E T a d s o r p t i o n d a t a obtained d u r i n g nitrogen a d s o r p t i o n on V u l c a n X C - 7 2 is given in T a b l e 2 and t h e p l o t of l / w ( P0/ P - l ) v e r s u s P / P0 is s h o w n in F i g u r e 12. T h e

calculated v a l u e o f B E T s u r f a c e area o f V u l c a n X C - 7 2 c a r b o n is also in c l o s e a g r e e m e n t with the reported v a l u e o f 2 3 2 m2/ g [2].

6.3. Alumina granules

T h e B E T a d s o r p t i o n d a t a obtained d u r i n g n i t r o g e n a d s o r p t i o n on A l u m i n a granules is given in T a b l e 3 and t h e c o r r e s p o n d i n g plot of l / w ( P o / P - l ) v e r s u s P / P o is s h o w n in Figure 13. T h e B E T s u r f a c e area of A l u m i n a g r a n u l e s w a s f o u n d to b e 2 8 4 . 8 m2/ g w h i c h is

close to the reported v a l u e o f 2 8 4 m2/ g [3]. T h e B E T a d s o r p t i o n d a t a o f s a m e g r a n u l e s but

coated with c o b a l t is given in T a b l e 4 and the c o r r e s p o n d i n g p l o t o f l / w ( P0/ P - l ) versus

P/Po is s h o w n in F i g u r e 14. In this case the B E T s u r f a c e a r e a d e c r e a s e d significantly as c o m p a r e d with the fresh A l u m i n a g r a n u l e s w i t h o u t c o b a l t c o a t i n g . It is attributed to the blocking of p o r e s p r e s e n t in A l u m i n a granules. T h i s result also i n d i c a t e s that B E T s u r f a c e area is entirely d i f f e r e n t f r o m t h e usual g e o m e t r i c s u r f a c e a r e a o f solid s a m p l e s . T h e B E T s u r f a c e area d e p e n d s on t h e area o f p o r e s available for a d s o r p t i o n o f nitrogen gas.

7. Comparison of observed and reported data of BET surface area

T h e c o m p a r i s o n o f t h e o b s e r v e d v a l u e and reported v a l u e o f B E T s u r f a c e area of various materials is given in T a b l e 5. It is clear f r o m the data in T a b l e 5 that t h e observed B E T s u r f a c e area o f r e f e r e n c e material is in close a g r e e m e n t w i t h t h e reported value. M o r e o v e r , the o b s e r v e d B E T s u r f a c e area of V u l c a n X C - 7 2 c a r b o n and A l u m i n a g r a n u l e s are also in close a g r e e m e n t w i t h t h e reported v a l u e s . It m e a n s that t h e n e w l y installed A u t o s o r b - l - C - 8 is w o r k i n g p r o p e r l y a n d it can b e u s e d f o r a c c u r a t e m e a s u r e m e n t of B E T surface area o f solid p o r o u s materials.

8. Evaluation of total pore volume and average pore diameter

T h e total p o r e v o l u m e is derived f r o m the a m o u n t of v a p o r a d s o r b e d at a relative pressure close to unity by a s s u m i n g that the p o r e s are then filled with liquid a d s o r b a t e . T h e v o l u m e of nitrogen a d s o r b e d (Va d s) c a n be c o n v e r t e d to the v o l u m e of liquid nitrogen (Vl i q)

contained in the p o r e s by u s i n g t h e f o l l o w i n g r e l a t i o n s h i p :

V ,i q= n Vm (7)

W h e r e n is t h e n u m b e r of m o l e s of nitrogen a d s o r b e d at relative p r e s s u r e close to unity, and Vm is t h e m o l a r v o l u m e i.e. v o l u m e of o n e m o l e o f liquid nitrogen (34.7 c m3/ m o l ) .

Since

n = ^ = (8) M M

W h e r e M is t h e m o l e c u l a r w e i g h t of nitrogen gas, wa d is t h e w e i g h t o f nitrogen gas

adsorbed, d is t h e d e n s i t y of nitrogen gas (1.251x10" g/cm ) and Va d s is the v o l u m e of

nitrogen gas a d s o r b e d . Putting v a l u e o f n into Eq. 8 a f t e r s u b s t i t u t i n g the v a l u e s o f k n o w n p a r a m e t e r s w e get

Vh c l= 1 . 5 4 9 7 x l 0 -3Va d s (cnrVg) (9)

For cylindrical pores, t h e a v e r a g e d i a m e t e r (D) o f t h e p o r e s in " n m " m a y be calculated by using the f o l l o w i n g relation:

4Vlui x l O3 VH

D - C1 = 6 . 1 9 8 8 - ^ ( n m ) (10)

S S

Since t h e pores, w h i c h are not filled b e l o w a relative p r e s s u r e o f unity, would have negligible c o n t r i b u t i o n to t h e total p o r e v o l u m e . D u e to this r e a s o n , the total v o l u m e of nitrogen gas a d s o r b e d " Va d s" at relative p r e s s u r e close to unity is used to calculate the total

pore v o l u m e and a v e r a g e p o r e d i a m e t e r . T h e calculated v a l u e s o f total p o r e v o l u m e and average p o r e d i a m e t e r o f v a r i o u s m a t e r i a l s are p r e s e n t e d in T a b l e 6.

T a b l e 1: E v a l u a t i o n o f B E T s u r f a c e a r e a o f r e f e r e n c e m a t e r i a l C a t . N o . 2 0 0 5 o f Lot. N o . 3 0 0 5 . A n a l y s i s p a r a m e t e r s : W e i g h t o f s a m p l e t a k e n : 1.0351 g A d s o r b a t e : N i t r o g e n Bath T e m p . : 7 7 . 0 0 O u t g a s T e m p : 3 0 0 . 0 ° C O u t g a s T i m e : 1.0 h r s A n a l y s i s T i m e : 7 0 m i n P / P o t o l e r a n c e : 3 E q u i l i b r i u m . T i m e : 2 m i n

Multipoint data:

P / P o

Volume adsorbed

(cm

3

/g) STP

1 / ( W ( P0/ P - 1 ) ) 1 . 0 0 8 2 x 10"' 2 5 . 2 6 5 2 3 . 5 5 1 2 . 0 5 1 6 x 10"' 2 9 . 6 7 0 4 6 . 9 6 0 3 . 0 4 5 7 x 10'1 3 3 . 7 7 6 4 1 0 . 3 7 0 R e s u l t : B E T s u r f a c e A r e a = 1 0 3 . 6 m2/ g 0.00 0.10 0.20 0.30 0.40 Relative pressure "P/Po"

F i g u r e 11. B E T p l o t o f 1/w ( P0/ P - l ) v e r s u s P0/ P f o r n i t r o g e n a d s o r p t i o n on r e f e r e n c e

T a b l e 2: E v a l u a t i o n o f B E T s u r f a c e area o f V u l c a n X C - 7 2 c a r b o n . A n a l y s i s p a r a m e t e r s : W e i g h t o f s a m p l e t a k e n : 0.2 g A d s o r b a t e : N i t r o g e n Bath T e m p . : 7 7 . 0 0 O u t g a s T e m p : 3 0 0 . 0 °C Outgas T i m e : 1.0 hrs A n a l y s i s T i m e : 64 min P/Po t o l e r a n c e : 3 Equilibrium, T i m e : 2

Multipoint data:

P / P o

Volume adsorbed

(cm

3

/g) STP

1 / ( W ( P0/ P - 1 ) ) 9 . 9 7 6 7 x 10"2 5 9 . 6 3 6 0 1.487 2 . 0 4 4 1 x 10"1 6 7 . 4 4 0 5 3 , 0 4 8 3 . 0 5 0 8 x 10"1 7 4 . 4 4 3 0 4 . 7 1 8 Result: B E T s u r f a c e A r e a = 2 2 3 m2/ g

F i g u r e 12. B E T plot o f 1/w (Po/P-1) v e r s u s P0/ P for nitrogen a d s o r p t i o n on V u l c a n X C

-72 carbon.

T a b l e 3: E v a l u a t i o n o f B E T s u r f a c e a r e a o f A l u m i n a g r a n u l e s . A n a l y s i s p a r a m e t e r s : W e i g h t o f s a m p l e t a k e n : 0 . 2 6 2 6 g A d s o r b a t e : N i t r o g e n B a t h T e m p . : 7 7 . 0 0 O u t g a s T e m p : 3 0 0 . 0 ° C O u t g a s T i m e : 1.0 h r s A n a l y s i s T i m e : 7 0 m i n P / P o t o l e r a n c e : 3 E q u i l i b r i u m . T i m e : 2

Multipoint data:

P/Po

Volume adsorbed

(cm

3

/g) STP

i/(W(P

0

/P-i))

9 . 6 3 7 3 x 10'" 6 4 . 1 7 1 4 1 . 3 3 0 2 . 0 1 4 0 x 10'2 7 8 . 1 9 1 2 2 . 5 8 1 3 . 0 1 6 6 x 10"2 9 0 . 7 8 1 0 3 . 8 0 7 R e s u l t : B E T s u r f a c e A r e a - 2 8 4 . 8 m2/ g 0.00 0.10 0.20 0.30 0.40 Relative pressure "P/Po"

F i g u r e 13. B E T p l o t o f 1/w (Po/P-1) v e r s u s P0/ P f o r n i t r o g e n a d s o r p t i o n o n A l u m i n a

T a b l e 4: E v a l u a t i o n of B E T s u r f a c e a r e a of c o b a l t coated A l u m i n a g r a n u l e s . A n a l y s i s p a r a m e t e r s : Weight of s a m p l e t a k e n : 0 . 2 4 5 1 g A d s o r b a t e : N i t r o g e n Bath T e m p . : 7 7 . 0 0 O u t g a s T e m p : 3 0 0 . 0 °C Outgas T i m e : 1.0 hrs A n a l y s i s T i m e : 70 min P/Po t o l e r a n c e : 3 Equilibrium T i m e : 2

Multipoint data:

Volume adsorbed

(cm /g) STP

i / ( V V ( i V i L ) ) 1.0327 x 10"' 2 2 . 5 9 7 0 4 . 0 7 8 2 . 0 4 2 8 x 1 0 " ' 2 6 . 6 3 6 4 7.711 3 . 0 4 2 0 x 10'1 3 0 . 4 7 0 5 11.480 Result: B E T s u r f a c e A r e a = 94 m2/g 0.00 0.10 0.20 0.30 0.40

Relative pressure "P/Po"

Figure 14.

B E T plot o f 1/w ( P o / P- 1 ) v e r s u s P0/ P f o r nitrogen a d s o r p t i o n on cobalt

T a b l e 5. B E T s u r f a c e a r e a v a l u e s o f d i f f e r e n t materials.

BET surface area

Type of porous materials

^ Ref.

Observed Reported

value

value

Q u a n t a c h r o m e r e f e r e n c e m a t e r i a l _{103.6 107} V u l c a n X C - 7 2 c a r b o n _{2 2 3 2 3 2 [2]} A l u m i n a g r a n u l e s 2 8 4 . 8 2 8 4 [3] T a b l e 6. T h e d a t a o f a v e r a g e p o r e d i a m e t e r and total p o r e v o l u m e o f d i f f e r e n t p o r o u s materials.

Total pore

Average pore

Type of porous materials

volume

diameter

(cm

3

/g)

(nm)

Q u a n t a c h r o m e r e f e r e n c e aterial _{0 . 4 6 17.7} V u l c a n X C - 7 2 c a r b o n _{1.04 18.7} A l u m i n a g r a n u l e s 0 . 3 7 5.26 C o b a l t c o a t e d A l u m i n a g r a n u l e s 0 . 3 2 13.6

9. Conclusions

T h e installation/ o p e r a t i o n of A u t o s o r b and c a l c u l a t i o n s o f B E T s u r f a c e area, total pore v o l u m e and a v e r a g e p o r e d i a m e t e r of d i f f e r e n t p o r o u s material are clearly d e s c r i b e d in the present report for e n a b l i n g t h e n e w operator to o p e r a t e t h e A u t o s o r b i n d e p e n d e n t l y . T h e r e s e m b l a n c e of o b s e r v e d d a t a o f B E T s u r f a c e a r e a of r e f e r e n c e material with t h e reported data also indicates that the n e w l y installed A u t o s o r b is w o r k i n g p r o p e r l y and it can be used for accurate m e a s u r e m e n t of B E T s u r f a c e area o f p o r o u s m a t e r i a l s .

10. References

1. O p e r a t i n g m a n u a l Q u a n t a c h r o m e I n s t r u m e n t s A u t o s o r b - 1 A S I W i n Version 1.51 P / N 0 5 0 6 1 R e v B , 2 0 0 5 .

2. M. C a n n o , A. R. D. Santos, J.G. R. P o c o , M . Linardi, J o u r n a l o f P o w e r S o u r c e s 173 ( 2 0 0 7 ) 8 6 0 - 8 6 6 .