The adsorption of some organic vapours by Wool and Nylon

The adsorption of some organic vapours by Wool and Nylon

VACUUM Classified A b s t r a c t s IV Special Subsidiary Subjects -- 4° -- GASES AND VAPOURS -- IV Abstract No. and References 4° Adsorpti...

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VACUUM Classified A b s t r a c t s

IV

Special Subsidiary Subjects --

4° --

GASES

AND

VAPOURS

--

IV

Abstract No. and References



Adsorption of Gases on a Silicon Surface United States. The adsorption of argon, nitrogen, carbon dioxide, carbon monoxide, hydrogen, o x y g e n and w a t e r v a p o u r on a silicon surface has been examined using a mass spectrometer and a flash filament technique. Measurements were made at 300°K (room temperature) and at gas pressures between 10 -~ and 10 "4 mm. Hg. The decomposition of carbon dioxide and w a t e r v a p o u r at various t e m p e r a t u r e s has also been studied. A filament was cut f r o m a silicon crystal, etched and m o u n t e d in a glass tube. This tube could be evacuated t h r o u g h the ionisation c h a m b e r of a m a s s spectrometer from which the inlet leak h a d been removed. M o l y b d e n u m leads were soldered to the ends of the filament to carry the heating current, and t e m p e r a t u r e s within the range of visible radiation were determined w i t h an optical pyrometer. The silicon filament was first outgassed for several days in the best v a c u u m attainable in the s y s t e m (about 10 -8 mm.). Adsorption of argon, nitrogen, hydrogen, carbon monoxide, carbon dioxide and w a t e r was tested as follows: The filament was flashed several times to 1,200 ° in vacuo and the gas was t h e n introduced into the t u b e while the filament was cold. After v a r y i n g time intervals, and with the gas still flowing, the filament was flashed. D u r i n g the r u n the spectrometer was focussed on the m a s s of an ion f r a g m e n t of the gas, and the gas desorbed was m e a s u r e d on the recording oscillograph. At the same time, as a check, the change in pressure in the t u b e was read on an ion gauge. To test the reversibility of the isotherm, the gas could be p u m p e d o u t before flashing the filament. I n the pressure range 10-~-10 -4 m m . H g the change in pressure on flashing was between 10 -s and 10 -s m m . Hg. I n cases where reaction occurred, as in the decomposition of w a t e r and carbon dioxide, the spectrometer was focussed on an ion f r a g m e n t of one of the reaction p r o d u c t s w i t h the gas flowing t h r o u g h the s y s t e m and the filament cold. T h e silicon was t h e n heated in steps of 100 or 50 ° and a continuous record was obtained of the partial pressure of the decomposition product. Adsorbed oxygen c a n n o t be determined b y flashing the filament since it comes off as silicon oxide which is not sufficiently volatile to reach the ionisation chamber. I n this case the silicon was flashed in a high v a c u u m and allowed to cool. Oxygen was a d m i t t e d and pressure-time curve was plotted. At the end of the r u n the s y s t e m was evacuated with the filament remaining cold. Oxygen was t h e n re-admitted and a second pressuretime curve was plotted. The first curve shows adsorption and the second does not. If steps are t a k e n to p r e v e n t adsorption on the glass a p p a r a t u s , a comparison of the two curves provides a m e a s u r e of the adsorption of o x y g e n on silicon. The experiments indicate t h a t at 300°K and at pressures below 10 -4 ram. Hg, argon, nitrogen and carbon monoxide are not adsorbed: H y d r o g e n and carbon monoxide are adsorbed w i t h o u t reaction. W h e n carbon dioxide was passed over the filament, heated above 800 °, decomposition occurred to carbon monoxide and, presumably, an oxide'of silicon. I n the case of oxygen almost every oxygen molecule striking the filament was adsorbed until the first oxide layer was formed. The 'sticking probability' t h e n decreased as f u r t h e r oxide layers were built up. A monolayer of oxygen was adsorbed on silicon at pressures near 10 -s m m . The h e a t of adsorption of oxygen on silicon was calculated to be 173 kcal./mole. W h e n the filament was flashed after the adsorption of w a t e r vapour, m o s t of the gas desorbed was hydrogen, twice as m u c h h y d r o g e n being desorbed as after t h e a d s o r p t i o n of molecular hydrogen.

1/IV

Paper by J. T. Law & E. E. Francois J. Phys. Chem.

6o, March 1956 353-358

Study of the Absorption in K m W a v e s of GasesAdsorbed by Silica Gel or Titanium Oxide See A b s t r a c t No.: 77/II

2/IV

MultilayerAdsorption e n P l a n e Surfaces by Capacity Measurements I. Adsorption on Glass at High Relative Pressures See A b s t r a c t N o . : 78/I1

3/IV

The Adsorption of Some Organic Vapours by Wool and Nylon United K i n g d o m . The literature gives some information a b o u t the penetration of nylon and wool b y non-solvents in the liquid phase, b u t less a b o u t the m e c h a n i s m of absorption in the v a p o u r phase, and this chiefly concerns w a t e r vapour. W o r k has now been done on the adsorption of organic vapours. A McBain and B a k r spring balance w a s used. The reagents were enclosed in a sealed glass capsule in a t u b e (liquid reservoirs) and could be released b y d r o p p i n g a steel ballbearing. The v a p o u r reservoir was connected to a Barr and Stroud 2-stage, high v a c u u m , lens coating unit. The balance spring was made of P y r e x glass, annealed for 8 h o u r s at 200°C. The a p p a r a t u s was evacuated to a pressure of 10 -4 ram. Hg. F o r low t e m p e r a t u r e experiments, it was enclosed in an air t h e r m o s t a t . For high t e m p e r a t u r e s , the adsorption t u b e was immersed in a thermostatically-controlled paraffin oil b a t h with the reagent reservoir outside so t h a t it could be heated independently to a higher t e m p e r a t u r e t h a n the b a t h to accelerate v a p o u r production. The b a t h w a s of copper, w i t h a P y r e x glass w i n d o w for observing the spring; oil was circulated t h r o u g h a copper coil. Preliminary adsorption tests on nylon and wool were conducted with hydroxylic compound: acetic acid, ethanol, ethylene glycol, methanol, phenol, n-propanol and water, and with various non-hydroxylic compounds. The former showed concentrations of adsorbate of >1600, >550, 380, >1450, >1150, >510, and >1750 m-mol./Kg, respectively, whereas the latter showed nil-260, only aniline and dioxan s h o w i n g a n y appreciable adsorption. D a t a for adsorption-desorption rates are given. I n a comparison of ethanol, m e t h a n o l and water, the rates of b o t h adsorption and desorption of nylon increased in the order of decreasing molecular size: ethanol < m e t h a n o l < water. The whole of the adsorbed m e t h a n o l could be desorbed. The isotherms for the three v a p o u r s d e m o n s t r a t e t h a t m e t h a n o l and w a t e r

4]IV

October, 1956

Vac uum Vol. VI

295

VACUUM Classified A b s t r a c t s

Abstract No. and References

IV --

Special

Subsidiary

Subjects

~

IV

Contd.

Article by H. R. Chipalkatti, V. B. Chipalkatti & C. H. Giles J. Soc. Dyers & Colourists 7 I, Nov. 1955 652-660

5/iv

are a b s o r b e d b y n y l o n to the s a m e e x t e n t , b u t wool a d s o r b s less m e t h a n o l t h a n water. B o t h n y l o n a n d wool a d s o r b e t h a n o l less r e a d i l y t h a n m e t h a n o l , i s o t h e r m s for m e t h a n o l v a p o u r a n d w a t e r v a p o u r on n y l o n are a l m o s t i d e n t i c a l . The m a x i m u m a m o u n t a d s o r b e d is I m o l e / k g , for bot h. C urve s for a d s o r p t i o n r a t e s of m e t h a n o l v a p o u r on wool are shown. ,At s a t u r a t i o n v.p., a d s o r p t i o n rises to 8 mol e s / kg., e q u i v a l e n t to 6 5 % of t h e t o t a l a m o u n t of p o l a r g r o u p s in wool, i.e., p e p t i d e , h y d r o x y l , a n d a m i n o a n d free acidic g r o u p s in t h e side-chains. If t h e whole of t h i s a d s o r b a t e is p r e s e n t as a m o n o l a y e r in a m o r p h o u s p a r t s of t h e fibre, 23% of t h e fibre m u s t be inaccessible to t h e m e t h a n o l molecule. To t e s t t h e possible effect of t r a c e s of m o i s t u r e on t h e a d s o r p t i o n of h y d r o p h i l i c v a p o u r s , t h e r a t e of a d s o r p t i o n on wool of i n t e n s i v e l y dri e d gl a c i a l acetic acid w a s c o m p a r e d w i t h t h a t of t h e n o r m a l l y dried acid a n d found to be m u c h lower, a d s o r p t i o n on d r y wool of h y d r o g e n c hl ori de gas w a s b a r e l y m e a s u r a b l e . R a t e c u r v e s of p h e n o l v a p o u r on wool a t 25% 60 ° 70 ° a n d 80°C a n d on n y l o n a t 25°C are shown. On n y l o n t h e r e w a s a s l i g h t d i s c o n t i n u i t y in t h e c u r v e s a t 25 ° a t 0.94 m o l e / k g . On t h e a s s u m p t i o n t h a t p h e n o l mols. are a t t a c h e d to each a m i d e g r o u p t h i s is e q u i v a l e n t t o 5,3% of t h e t o t a l n u m b e r in t h e fibre. A c c e s s i b i l i t y of t h e a m o r p h o u s regions is therefore lower t h a n w i t h m e t h a n o l b u t t h e h i g h affinity of p h e n o l ensures r a p i d p e n e t r a t i o n of t h e c r y s t a l l i n e regions. N e i t h e r n y l o n nor wool suffers d a m a g e a t t e m p e r a t u r e s up to 150 ° for as long as 8 ho u r s a t a p r e s s u r e of 10 -4 ram. Hg. A d s o r p t i o n e x p e r i m e n t s could t he re fore be c o n d u c t e d w i t h alizarin, benzoic acid, a n d ~ - n a p h t h o l a t t e m p e r a t u r e s up to 140°C. A s t r i k i n g i nc re a s e in a d s o r p t i o n c a p a c i t y of b o t h n y l o n a n d wool in successive cycles of a d s o r p t i o n a n d d e s o r p t i o n w a s revealed. I t m a y be a t t r i b u t e d t o a p r o g r e s s i v e b r e a k d o w n of t h e c r y s t a l s t r u c t u r e of t h e fibres b y d i s r u p t i o n of i n t e r n a l h y d r o g e n b o n d s anti t h e i r r e p l a c e m e n t b y n ew a t t a c h m e n t s to tile b u l k y molecules of t h e a b s o r b a t e . The energies of a c t i v a t i o n of v a p o u r s c a l c u l a t e d from t h e i n i t i a l slopes of the r a t e c u r v e s are t a b u l a t e d .

Semiconductivity and Catalysts in the N i c ke l O xi de System See A b s t r a c t No.: 156/I

6/IV

The Surface Areas of Evaporated Metal F i l m s See A b s t r a c t No.: 55/II1

7/IV

Article by P. F. Glaseock Atomlcs 6, Dee. 1955 363-369 8/IV Article by A. Finkelstein & 3'[. Lesimple J. N,uclear Energy 2, Dec. 1955 101-109 9/IV Article by C. V. Robinson N ucleonic,~ x3, Nov. 1955 90-91

296

Gas Counting Techniques in Biochemistry II. United K i n g d o m . The d e t e r m i n a t i o n of t r i t i u m is discussed in s a m p l e s t)repared from b i o c h e m i c a l s p e c i m e n s as d e s c r i b e d in P a r t I of t h e article. The t r i t i u m c a n be d e t e r m i n e d as w a t e r v a p o u r or an h y d r o g e n , b u t in e i t h e r case t h e c o u n t e r s b e c o m e c o n t a m i n a t e d t o a n i n c o n v e n i e n t e x t e n t a n d t h e a u t h o r prefers to p r e p a r e a n organic v a p o u r or gas from t h e specimen. Thi s c a n be r e a d i l y m a n i p u l a t e d w i t h t h e a i d of l i q u i d a i r t r a p s - - a n o t h e r d i s a d v a n t a g e of h y d r o g e n is t h a t i t c a n n o t . The gas r e c o m m e n d e d b y t h e a u t h o r is b u t a n e , p r e p a r e d from t h e r a d i o a c t i v e w a t e r b y t r e a t m e n t w i t h a G r i g n a r d r e a g e n t . The r e a c t i o n t u b e s used hol d a b o u t 13 ml. a n d are c o n n e c t e d to t h e a p p a r a t u s b y a cone j o i n t a n d a v a c u u m s t o p c o c k - - s i l i c o n e v a c u u m grease is used. Six t u b e s are p r e p a r e d a t a t i m e : 1.5 ml. of a 2N s o l u t i o n of n - b u t y l m a g n e s i u m b r o m i d e in d r y e t h e r is p i p e t t e d i n t o each a n d t h e e t h e r t h e n r e m o v e d on t h e r o u g h v a c u u m line b y d i s t i l l i n g - o v e r i n t o a t r a p cooled b y l i q u i d air. R e m a i n i n g t r a c e s of e t h e r are r e m o v e d b y b a k i n g t h e t u b e s on t h e h i g h v a c u u m line a t 120°C for 1 hr. a n d t h e labelled w a t e r is t h e n s u b l i m e d i n t o a r e a c t i o n t u b e - - a b o u t 10 mg. c a n be h a n d l e d . The t u b e is t h e n a g a i n h e a t e d to 120°C for 1 hr. a f t e r w h i c h t h e s t o p c o c k is o p e n e d a n d t he b u t a n e d r i v e n off t o c onde n s e in a t u b e a d j a c e n t to t h e c o u n t e r ; a n y u n r e a c t e d w a t e r is i n t e r c e p t e d b y a U - t u b e chilled b y solid CO 2. T h e b u t a n e is d i v i d e d i n t o t w o or more s a m p l e s in s e p a r a t e t u b e s i s o l a t e d b y s t o p c o c k s a n d e a c h t h e n a d m i t t e d t o t h e s t a i n l e s s steel c o u n t e r a t a pressure of 12.5 cm. Hg. The c o u n t e r t h e n w o r k s a t a b o u t 2.4 kV. The specific a c t i v i t i e s of t h e s a m p l e s s h o u l d agree to w i t h i n 1.5%. Some e x a m p l e s of t h e a p p l i c a t i o n of t h e g a s - c o u n t i n g t e c h n i q u e in b i o c h e m i s t r y are briefly discussed; The c h e a p n e s s of us i ng t r i t i u m t o l a be l a f a t t y acid (e.g.) r a t h e r t h a n a c a r b o n isotope, is e m p h a s i s e d . T r i t i u m is r e a d i l y o b t a i n a b l e w i t h a h i g h specific a c t i v i t y . A f u r t h e r a d v a n t a g e of t h e t e c h n i q u e s described is t h a t s e v e r a l e x p e r i m e n t s can be m a d e a t once, b y u s i n g s e ve ra l isotopes; for e x a m p l e , t r i t i u m , C ~3 and C ~4 can be used t o label different p a r t s of a mol e c ul e a n d t h e n a s s a y e d i n d e p e n d e n t l y .

The Determination of T r i t i u m in Tritiated Water France. A s i m p l e d e t e r m i n a t i o n of t r i t i u m in t r i t i a t e d w a t e r h a s been de ve l ope d, u s i n g t he r e a c t i o n of t r i t i a t e d w a t e r on c a l c i u m carbide, a n d c o u n t i n g t h e a c e t y l e n e forme d in a c a l i b r a t e d i o n i s a t i o n c h a m b e r . No m e m o r y effects h a v e been o b s e r v e d ; a s l i g h t isot opi c s e p a r a t i o n w a s d e t e c t e d a n d e s t i m a t e d . (Authors)

Improved Methane Proportional Counting Method for Tritium Assay United States. An i m p r o v e d form of t r i t i u m a s s a y b y m e a n s of a m e t a l i n c l u d i n g m e t h a n e g e n e r a t i o n a n d prop o r t i o n a l c o u n t i n g r e p o r t e d p r e v i o u s l y is described. I n t h e ne w v e r s i o n a m e t a l s y s t e m c a n be used. The m e t h o d i n c l u d e s r e a c t i o n of a l a b e l l e d a q u e o u s s a m p l e w i t h a m e t h y l G r i g n a r d r e a g e n t to g e n e r a t e l a b e l l e d m e t h a n e , p u r i f i c a t i o n , t r a n s f e r of t h e gas i n t o a c o u n t i n g c h a m b e r a n d o p e r a t i o n of t he c h a m b e r as a p r o p o r t i o n a l co unter. A 0.2 ml. s a m p l e is r e q u i r e d a n d 8 ml. of I N C H a M g I d i s s o l v e d in b u t y l ether. The efficiency of t h e m e t h o d is 11%. D e t a i l s of t h e e q u i p m e n t a n d o p e r a t i o n a l p r o c e d u r e are given.

Vacuum Vol. V I

October, 1956