The combination of methyl radicals: Photolysis of acetone at low pressures

VACUUM Classified A b s t r a c t s

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each o t h e r a solid precipitate w a s o b t a i n e d . A f t e r r e m o v a l of tile residual m o n o m e r b y freezing a n d v a c u u m s u b l i m a t i o n tile p r e c i p i t a t e w a s q u a l i t a t i v e l y f r a c t i o n a t e d into t h r e e c o m p o n e n t s : (a) Consisting e s s e n t i a l l y of poly acrylonitrile, (b) t h e block polymer, r e p r e s e n t i n g a b o u t one t h i r d of t h e t o t a l a n d c o n t a i n i n g 75 % acrylonitrile, (c) t h e u s u a l d e g r a d a t i o n p r o d u c t of poly m e t h y l v i n y l ketone. T h e e x p e r i m e n t s a p p e a r to confirm t h a t p h o t o l y s i s of poly m e t h y l v i n y l k e t o n e in t h e presence of acrylonitrile is i n s t i u m e n t a l in t h e s y n t h e t i c p r o d u c tion of t w o f u r t h e r p o l y m e r i c s p e c i e s - - p u r e poly acrylonitrile a n d a block p o l y m e r of b o t h materials. Sommaire : O n a t r o u v 6 que la p h o t o l y s e du ' p o l y m e t h y l v i n y l k e t o n e ' en presence d'acrylonitrile c o n d u i t ~ la p r o d u c t i o n de d e u x n o u v e a u x genres de polym6rique.

The Combination of Methyl Radicals: Photolysis of Acetone at Low P r e s s u r e s

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Canada. T h e m e c h a n i s m w h e r e b y m e t h y l radicals, p r i m a r i l y p r o d u c e d b y t h e d e c o m p o s i t i o n of a c e t o n e e x p o s e d to u l t r a - v i o l e t radiation, c o m b i n e to f o r m e t h a n e h a s b e e n i n v e s t i g a t e d before, d o w n to a c e t o n e p r e s s u r e s of 20 ram. Hg. T h e p r e s e n t i n v e s t i g a t i o n e x t e n d s this s t u d y d o w n to a p r e s s u r e level of 0.2 m m . Hg. T h e r e s u l t s o b t a i n e d c o n f i r m tile p r e v i o u s l y p o s t u l a t e d t h i r d b o d y r e q u i r e m e n t s for e t h a n e f o r m a t i o n , a c e t o n e itself a c t i n g as t h i r d b o d y . T h e e x p e r i m e n t a l reaction vessel was a q u a r t z cylinder 100 cm. long a n d 3.9 cm. in d i a m e t e r . H e a t i n s u l a t i o n was p r o v i d e d b y w r a p p i n g tile cylinder w i t h a l u m i n i u m foil a n d P y r e x t a p e a n d t h e u n i f o r m i t y of t h e t e m p e r a t u r e w i t h i n t h e cylinder was 32 1 ° over its whole l e n g t h a t 250°C. H e a t w a s supplied b y r e s i s t a n c e h e a t i n g . T b e r a d i a t i o n w a s o b t a i n e d f r o m a B . T . H . M E / D 250 W . d.c. q u a r t z w i n d o w l a m p w h i c h gives s t r o n g e m i s s i o n a t 3,130, %660, 3,906 a n d 4,047 A. To facilitate q u a n t u m yield m e a s u r e m e n t s t h e line 3,130 ~_ e m i t t e d b y t h e l a m p w a s isolated. L i g h t a b s o r p t i o n w a s m e a s u r e d b y m e a n s of a G L 935 photo-cell. N o r m a l l y 5 % c o n v e r s i o n of t h e a c e t o n e w a s r e g a r d e d as sufficient. All m a t e r i a l s u s e d in t h e reaction, i.e. r e a g e n t - g r a d e acetone, a c e t a l d e h y d e , benzene, perfluoromethylcyclohexane, p e r f l u o r o b u t a n e a n d c a r b o n dioxide, t h e latter few r e p r e s e n t i n g a d d e d gases, were purified b y distillation a n d o u t g a s s e d prior to use. Separa t i o n a n d a n a l y s i s of t h e r e a c t i o n p r o d u c t s w a s carried o u t b y k n o w n m e t h o d s a n d w a s checked w i t h t h e aid of a m a s s s p e c t r o m e t e r . E t h a n e w a s s e p a r a t e d o u t in a liquid n i t r o g e n t r a p (-210°C). R e s u l t s for v a r i o u s acetone p r e s s u r e s are g i v e n in g r a p h s . A d d i n g t h e gases m e n t i o n e d above increased t h e relative rate of e t h a n e formati(m. Sommaire : E t u d e du m d c a n i s m e de f o r m a t i o n d ' 6 t h a n e k p a r t i r de r a d i c a u x de m e t h y l p r o d u i t s p a r la p h o t o l y s e d ' a c d t o n e h basses pressions.

The Electron Microscopy of Photographic Grains.

Specimen Preparation Techniques and Applications

Abstract No. and References

Artide by J. E. Guillet & R. G. W. Norrish Nature x73 , 3.4.1954 625-627 183/1

Article bv R. E. Dodd & E. W. R. Steaeie Proe. Roy. Soe. 223A, May 1954 283-295 184/I

See A b s t r a c t N o . : l l l / I I

Evacuating Photographic Materials for Use in Electron Optical Apparatus

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See A b s t r a c t No. : l l 0 / I I

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An! reproved Replica Technique for Electron Microscopy of Paint Films United States. F o r t h e s t u d y of organic films, s u c h as films of soft p a i n t s , it is e s s e n t i a l to e m p l o y replica t e c h n i q u e s w h i c h exclude t h e risk of e x p o s i n g t h e film surface to h i g h t e m p e r a t u r e s . T h e a u t h o r s f o u n d t h a t t h e silver-silica replication t e c h n i q u e i n v o l v e s s u c h a risk a n d r e p o r t on a successful modification of t h a t t e c h n i q u e b y s u b s t i t u t i n g P V A (Elvanol, g r a d e 51-05) for silver for t h e n e g a t i v e replicas. Care h a s to be t a k e n t h a t tile n e g a t i v e is t h i n e n o u g h to o b t a i n a h i g h resolution a n d dissolves w i t h o u t i n j u r y to t h e silica. T h e P V A film is p r o d u c e d b y flooding t h e s p e c i m e n surface, d r a i n i n g off t h e excess a n d d r y i n g in a vertical position of t h e s p e c i m e n for 8 - 1 6 hours. L o n g e r d r y i n g periods result in brittleness. T h e P V A replica strips r e a d i l y f r o m p a i n t film applied to t i n p l a t e and, while f a s t e n e d to a m e t a l holder w i t h a d h e s i v e tape, is coated w i t h silica b y v a c u u m e v a p o r a t i o n . I t is desirable to prolong p u m p i n g at 10 -4 ram. H g u p to 16 h o u r s to e l i m i n a t e all t r a c e s of a b s o r b e d water. 0.8 rag. to 1.4 nag. of silica are e v a p o r a t e d , t h e t h i c k n e s s of t h e silica layer d e p e n d i n g on tile r o u g h n e s s of t h e surface. T h e finished c o m p o s i t e f i h n s are c u t into o n e - e i g h t h i n c h s q u a r e s a n d placed, silica-side up, in distilled water, w h e n t h e P V A dissolves a w a y quickly. T h e silica replicas are t h e n w a s h e d before t r a n s f e r to t h e s p e c i m e n grids. S h a d o w i n g of t h e replicas w i t h c h r o m i u m is r e c o m m e n d e d . T h e n e w m e t h o d h a s been used for t h e s t u d y of t h e u n d e r s i d e of e n a m e l films. 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 t e c h n i q n e s to gloss e n a m e l s a n d l a c q u e r s are g i v e n in illustrations. T h e n e w m e t h o d indicates p i g m e n t d i s t r i b u t i o n a n d related defects m o s t satisfactorily b u t finer details s u c h as molecular c o n f i g u r a t i o n a n d s m a l l d i s t o r t i o n s of t h e p a i n t vehicle are b e t t e r s h o w n b y silver-silica replicas. Sommaire : l)escription d ' u n e t e c h n i q u e de r6plique double, modifi66, p o u r r e m p l a c e r la t e c h n i q u e de rdplique a u silicate d ' a r g e n t d a n s la r6plique de surfaces molles de couche de p e i n t u r e .

186/I

Article by A. S. Powcll L. R. LeBras E. G. Bobalek, & W. Von Fischer J. Appl. Phys. 25, June 1954 757-760

The Electron Microscope with Particular Reference to Its Use in Biological Research. I See A b s t r a c t No. : 108/1I

181/i

Preservation of Foods with Ionising Radiations

i88/I

United Kingdom. A r e p o r t is g i v e n of a s h o r t s y m p o s i u m held a t C a m b r i d g e in F e b r u a r y 1954 on t h e a b o v e subject. T h e powerful sources of ionising r a d i a t i o n s t h a t h a v e r e c e n t l y b e c o m e available o p e n u p possibilities J u l y , 1954

Vacuum Vol I V No 3

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