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216. Coefficients of evaporation and condensation
342
Abstracts 2 0 9 - - 2 [ 9
13.
16 : 17
Vacuum Applications 13 : 39 : 42
209. Methods of Cleaning Glass by Vapour Degreasing and Ultrasonically Agitated Solvents. United Kingdom. T h e p r o d u c t i o n of clean glass surfaces for v a c u u m e v a p o r a t i o n p u r p o s e s has been studied, u s i n g a n u m b e r o f different chemical cleaning techniques. T h e principal cleaning m e t h o d s investigated were v a p o u r degreasing, u s i n g a range of solvents, a n d high- a n d low-frequency ultrasonic agitation o f an isopropyl alcohol bath. T h e cleanliness of glass surfaces after t r e a t m e n t was assessed f r o m their coefficient of friction, welting properties a n d a d h e r e n c e to v a c u u m deposited coatings. In t e r m s o f these properties v a p o u r degrcasing in pure isopropyl alcohol p r o d u c e d the cleanest surface. However, low-frequency u l t r a s o n i c agitation was the m o s t effective m e t h o d o f r e m o v i n g gross surface c o n t a m i n a t i o n . T h e cleaning o f intricately s h a p e d c o m p o n e n t s is briefly discussed and it is s h o w n t h a t the gas pressure a b o v e the cleaning m e d i u m m u s t be initially reduced to allow t h e solvent to enter cavities a n d t h u s provide m a x i m u m irradiation of the surface. U l t r a s o n i c cleaning was f o u n d to be m o s t effective when operated at low frequency 25 kc/s with an u n d e g a s s e d fluid u n d e r a t m o s p h e r i c presstlre. T. Punter, Brit. J. Appl. Phys., 10, 332-336, July 1959.
14.
216. Coefficients of Evaporation and Condensation. United States. A m o d e l is developed for crystal g r o w t h a n d e v a p o r a t i o n which invokes the Kossct concept of a crystal surface being c o m p o s e d of low index Facets, of low binding energy for a d s o r b e d a t o m s , s e p a r a t e d by ledges o f higher binding energy. T h e t r e a t m e n t indicates that surface diffusion kinetics are i m p o r t a n t in m o s t instances of crystal g r o w t h and ewlporation. Prior kinetic treatments, such as those inwHving limitations of crystal growth because of e n t r o p y effects ur dilTusion in the v a p o r phase, are modified to include surface diffusion effects. Values for e v a p o r a t i o n a n d c o n d e n s a t i o n coefficient predicted by the kinetic t r e a t m e n t are c o m p a r e d with experimentally d e t e r m i n e d values. (Author) J. P. Hirth a n d G. M. Pound, .I. Phy~. ('hem., 64, 619-626, M a y 1960. 16
217. Diffusion of Hydrogen in Thorium. United States. T h e diffusivity of h y d r o g e n in t h o r i u m was m e a s u r e d f r o m 300 to 900 <. Over this t e m p e r a t u r e rangc, D 2.92 . 10 .a exp ( - 9 7 5 0 / R T ) . T h e diffusivity increased with c o n c e n t r a t i o n above 600 ° but did not vary significantly with purity, grain size or cold working. T w o difffcrcnt m e t h o d s of d e t e r m i n i n g diffusion c o n s t a n t s were used a n d gave similar values. ~A uthorl D. T. Peterson a n d D. G. Westlake, J. Phy.~. (Twin., 64, 649-651. M a y 1960.
Kinetic Theory of Gases
210. Torsion Balance Measurements with Molecular Beams. United Kingdom. A torsion balance is described for rneasuring the m o n l e n t u n l carried by the molecules in a m o l e c u l a r b e a m with an intensity of a b o u t 10 ~-~m o l / s or more. T h e b e a m s t r u c k a vane s u s p e n d e d on a p l a t i n u m fibre 3t~ in diameter. T h e balance could be u s e d at elevated t e m p e r a t u r e s . At r o o m t e m p e r a t u r e , m e a s u r e m e n t s of the balance deflexion were m a d e to 1 part in 500, tinder f a v o u r a b l e conditions. An investigation was m a d e of the intensity of a m o l e c u l a r b e a m o f c a r b o n dioxide f o r m e d by a fairly simple m o l e c u l a r - b e a m generator, which is described. D e v i a t i o n s of gas flow f r o m m o l e c u l a r flow a n d a t t e n u a t i o n o f the b e a m by scattering were i m p o r t a n t factors. D. W. Bassett a n d A. J. B. R o b e r t s o n , Brit. J. Appl. Phys., 10, 534-538, Dec. 1959.
16.
G a s e s and S o l i d s 16
211. The Chemisorption of Gases on Chromia Surfaces at Low Temperatures. D. S. M a c l v e r a n d H. H. Tobin, J. Phys. Chem., 64, 451-457, April 1960. 16
212. Physical Adsorption on Chemisorbed Films. N o t e by D. S. M a c l v e r a n d H. H. Tobin, J. Phys. Chem., 64, 683-686, M a y 1960.
16 213. The Diffusion of Hydrocarbons in Polyisobutylene. Note by G. Blyholder a n d S. Prager, J. Phys. Chem., 64, 702-703, M a y 1960. t6
214. Successive Differential Absorptions of Vapors by Glassy Polymers. A k i r a K i s h i m o t o , H i r o s h i Fujita, H i s a s h i Odani, M i c h i o K u r a t a a n d M i k i o T a m u r a , J. Phys. Chem., 64, 594-598, M a y 1960.
16 215. The Theory of Diffusion Controlled Absorption Kinetics with Accompanying Evaporation. R. S. H a n s e n , J. Phys. Chem., 64, 637-641, M a y 1960.
16:52
218. The Oxidation of Evaporated Barium Films (Getters). Note by S. J. G r e g g a n d W. B. Jepson, Brit. ,I. Appl. Plow.. 9, 417-418, Oct. 1958. 16 : 33 : 47
219. Properties of Getters in Electronic Tubes. United States. In the first part of the paper flash gctters are discussed, w h o s e active part is a thin metal film obtained by e v a p o r a t i o n f r o m a getter assembly. T h e properties of the getter a s s e m b l y which are c o m p a r e d for different getters are subdivided i n t o : pre-flashing propertics (resistance to air a n d moisture, a n d f r e e d o m f r o m particles), flashing properties (flashing t e m p e r a t u r e a n d time, yield of tictive metal, dircctiomll vaporization a n d gas content) a n d post-flashing properties (freedom f r o m particles a n d - - f o r s o m e special types of g e t t e r s - freedom from m a g n e t i s m ) . As for the properties of the getter film, two o f these, a d h e r e n c e a n d volatility, do not concern a d s o r p t i o n . T h e a d s o r p t i o n properties as such are d e t e r m i n e d by gettering rate a n d getter capacity. M e t h o d s of m e a s u r i n g the a d s o r p t i o n properties at very low pressures are discussed, a n d values o f initial getter rates a n d of capacities arc given for different getter materials a n d gases. As for the capacity of the getter, it is a s s u m e d t h a t this h a s reached its final value when the rate has fallen to a figure which is equal to thc a d s o r p t i o n rate of the c a t h o d e in the tube. T h e capacity d e p e n d s on t e m p e r a t u r e in two a s p e c t s : it increases with o p e r a t i n g temperature, but it is reduced by intermediately heating the getter film a b o v e the o p e r a t i n g t e m p e r a t u r e . A discussion of desorption s h o w s that n o n e of the c o m m o n gases can be desorbcd f r o m b a r i u m getter films at m o d e r a t e t e m p e r a t u r e s . The p r e p a r a t i o n a n d activation of bulk getters, which are gellers m a d e f r o m powder, sheet or wire, is discussed in the second part. a n d rate a n d capacity values for such getters are given. The capacity values s h o w a s t r o n g increase with t e m p e r a t u r e owing to which the bulk getters become superior to flash getters of equal area at t e m p e r a t u r e s above a b o u t 500°C. As for desorption, only h y d r o g e n so far, has been f o u n d desorbable at temperatures up to 9 0 0 ' C . lAuthorl J. S. W a g e n e r , Proe. 4th National Conf. on Tube Techniques, p. I. New Y o r k University Press, N e w Y o r k 1959.
Abstracts 2 0 9 - - 2 [ 9
13.
16 : 17
Vacuum Applications 13 : 39 : 42
209. Methods of Cleaning Glass by Vapour Degreasing and Ultrasonically Agitated Solvents. United Kingdom. T h e p r o d u c t i o n of clean glass surfaces for v a c u u m e v a p o r a t i o n p u r p o s e s has been studied, u s i n g a n u m b e r o f different chemical cleaning techniques. T h e principal cleaning m e t h o d s investigated were v a p o u r degreasing, u s i n g a range of solvents, a n d high- a n d low-frequency ultrasonic agitation o f an isopropyl alcohol bath. T h e cleanliness of glass surfaces after t r e a t m e n t was assessed f r o m their coefficient of friction, welting properties a n d a d h e r e n c e to v a c u u m deposited coatings. In t e r m s o f these properties v a p o u r degrcasing in pure isopropyl alcohol p r o d u c e d the cleanest surface. However, low-frequency u l t r a s o n i c agitation was the m o s t effective m e t h o d o f r e m o v i n g gross surface c o n t a m i n a t i o n . T h e cleaning o f intricately s h a p e d c o m p o n e n t s is briefly discussed and it is s h o w n t h a t the gas pressure a b o v e the cleaning m e d i u m m u s t be initially reduced to allow t h e solvent to enter cavities a n d t h u s provide m a x i m u m irradiation of the surface. U l t r a s o n i c cleaning was f o u n d to be m o s t effective when operated at low frequency 25 kc/s with an u n d e g a s s e d fluid u n d e r a t m o s p h e r i c presstlre. T. Punter, Brit. J. Appl. Phys., 10, 332-336, July 1959.
14.
216. Coefficients of Evaporation and Condensation. United States. A m o d e l is developed for crystal g r o w t h a n d e v a p o r a t i o n which invokes the Kossct concept of a crystal surface being c o m p o s e d of low index Facets, of low binding energy for a d s o r b e d a t o m s , s e p a r a t e d by ledges o f higher binding energy. T h e t r e a t m e n t indicates that surface diffusion kinetics are i m p o r t a n t in m o s t instances of crystal g r o w t h and ewlporation. Prior kinetic treatments, such as those inwHving limitations of crystal growth because of e n t r o p y effects ur dilTusion in the v a p o r phase, are modified to include surface diffusion effects. Values for e v a p o r a t i o n a n d c o n d e n s a t i o n coefficient predicted by the kinetic t r e a t m e n t are c o m p a r e d with experimentally d e t e r m i n e d values. (Author) J. P. Hirth a n d G. M. Pound, .I. Phy~. ('hem., 64, 619-626, M a y 1960. 16
217. Diffusion of Hydrogen in Thorium. United States. T h e diffusivity of h y d r o g e n in t h o r i u m was m e a s u r e d f r o m 300 to 900 <. Over this t e m p e r a t u r e rangc, D 2.92 . 10 .a exp ( - 9 7 5 0 / R T ) . T h e diffusivity increased with c o n c e n t r a t i o n above 600 ° but did not vary significantly with purity, grain size or cold working. T w o difffcrcnt m e t h o d s of d e t e r m i n i n g diffusion c o n s t a n t s were used a n d gave similar values. ~A uthorl D. T. Peterson a n d D. G. Westlake, J. Phy.~. (Twin., 64, 649-651. M a y 1960.
Kinetic Theory of Gases
210. Torsion Balance Measurements with Molecular Beams. United Kingdom. A torsion balance is described for rneasuring the m o n l e n t u n l carried by the molecules in a m o l e c u l a r b e a m with an intensity of a b o u t 10 ~-~m o l / s or more. T h e b e a m s t r u c k a vane s u s p e n d e d on a p l a t i n u m fibre 3t~ in diameter. T h e balance could be u s e d at elevated t e m p e r a t u r e s . At r o o m t e m p e r a t u r e , m e a s u r e m e n t s of the balance deflexion were m a d e to 1 part in 500, tinder f a v o u r a b l e conditions. An investigation was m a d e of the intensity of a m o l e c u l a r b e a m o f c a r b o n dioxide f o r m e d by a fairly simple m o l e c u l a r - b e a m generator, which is described. D e v i a t i o n s of gas flow f r o m m o l e c u l a r flow a n d a t t e n u a t i o n o f the b e a m by scattering were i m p o r t a n t factors. D. W. Bassett a n d A. J. B. R o b e r t s o n , Brit. J. Appl. Phys., 10, 534-538, Dec. 1959.
16.
G a s e s and S o l i d s 16
211. The Chemisorption of Gases on Chromia Surfaces at Low Temperatures. D. S. M a c l v e r a n d H. H. Tobin, J. Phys. Chem., 64, 451-457, April 1960. 16
212. Physical Adsorption on Chemisorbed Films. N o t e by D. S. M a c l v e r a n d H. H. Tobin, J. Phys. Chem., 64, 683-686, M a y 1960.
16 213. The Diffusion of Hydrocarbons in Polyisobutylene. Note by G. Blyholder a n d S. Prager, J. Phys. Chem., 64, 702-703, M a y 1960. t6
214. Successive Differential Absorptions of Vapors by Glassy Polymers. A k i r a K i s h i m o t o , H i r o s h i Fujita, H i s a s h i Odani, M i c h i o K u r a t a a n d M i k i o T a m u r a , J. Phys. Chem., 64, 594-598, M a y 1960.
16 215. The Theory of Diffusion Controlled Absorption Kinetics with Accompanying Evaporation. R. S. H a n s e n , J. Phys. Chem., 64, 637-641, M a y 1960.
16:52
218. The Oxidation of Evaporated Barium Films (Getters). Note by S. J. G r e g g a n d W. B. Jepson, Brit. ,I. Appl. Plow.. 9, 417-418, Oct. 1958. 16 : 33 : 47
219. Properties of Getters in Electronic Tubes. United States. In the first part of the paper flash gctters are discussed, w h o s e active part is a thin metal film obtained by e v a p o r a t i o n f r o m a getter assembly. T h e properties of the getter a s s e m b l y which are c o m p a r e d for different getters are subdivided i n t o : pre-flashing propertics (resistance to air a n d moisture, a n d f r e e d o m f r o m particles), flashing properties (flashing t e m p e r a t u r e a n d time, yield of tictive metal, dircctiomll vaporization a n d gas content) a n d post-flashing properties (freedom f r o m particles a n d - - f o r s o m e special types of g e t t e r s - freedom from m a g n e t i s m ) . As for the properties of the getter film, two o f these, a d h e r e n c e a n d volatility, do not concern a d s o r p t i o n . T h e a d s o r p t i o n properties as such are d e t e r m i n e d by gettering rate a n d getter capacity. M e t h o d s of m e a s u r i n g the a d s o r p t i o n properties at very low pressures are discussed, a n d values o f initial getter rates a n d of capacities arc given for different getter materials a n d gases. As for the capacity of the getter, it is a s s u m e d t h a t this h a s reached its final value when the rate has fallen to a figure which is equal to thc a d s o r p t i o n rate of the c a t h o d e in the tube. T h e capacity d e p e n d s on t e m p e r a t u r e in two a s p e c t s : it increases with o p e r a t i n g temperature, but it is reduced by intermediately heating the getter film a b o v e the o p e r a t i n g t e m p e r a t u r e . A discussion of desorption s h o w s that n o n e of the c o m m o n gases can be desorbcd f r o m b a r i u m getter films at m o d e r a t e t e m p e r a t u r e s . The p r e p a r a t i o n a n d activation of bulk getters, which are gellers m a d e f r o m powder, sheet or wire, is discussed in the second part. a n d rate a n d capacity values for such getters are given. The capacity values s h o w a s t r o n g increase with t e m p e r a t u r e owing to which the bulk getters become superior to flash getters of equal area at t e m p e r a t u r e s above a b o u t 500°C. As for desorption, only h y d r o g e n so far, has been f o u n d desorbable at temperatures up to 9 0 0 ' C . lAuthorl J. S. W a g e n e r , Proe. 4th National Conf. on Tube Techniques, p. I. New Y o r k University Press, N e w Y o r k 1959.