- Email: [email protected]
373. The Betograph, an improved apparatus for the determination of the specific surface area of powders and porous substances
154
Classified Abstracts 369--375
13.
Vacuum Applications 13
369. Vacuum packed sliced Wiltshire bacon. Great Britain. Expeliments were carried out on some 500 packs of bacon in which the flavour of the bacon, cooked after storage for various periods at different temperatures, was assessed. The bacteriology of the raw samples was studied and analyses of the nitrate, nitrite and salt content were made. Some tentative conclusions were drawn. The n o r m a l Wiltshire cure, followed by smoking, appears often to give bacon suitable for v a c u u m packing. Storage life was however found to be variable and unpredictable. D.A.P. A. G. Kitchell, FoodProeess.
16.
& Paekag., 32 (376), Jan. 1963, 3-9.
G a s e s and S o l i d s
16:52 370. On the mechanism of thermal decomposition of nitrous oxide at a platinum filament. India. L a n g m u i r and Hinshelwood have formulated a theory of birnolecular surface reaction which assumes that reaction can only take place between moleculets, adsorbed side by side. Whilst this m a y be true in the majority of cases, certain experiments suggest that an activated complex may be formed by the interaction of an adsorbed molecule or a t o m with an a t o m or molecule in the gas phase or the Van der Waal's layer. The author attempts to show that the heterogeneous decomposition of N 2 0 (50 to 290 torr, 32°C) at a platinum filament (970°C) is of this kind. In this connexion he investigated the Joshi effect in a mixture of (1) N~O2 and N 2 0 ; (2) 2N2 + 02 ; and in pure 02. The Joshi effect in the thermal decomposition products (mixture (1)) [pN~O 35 torr, 31°C] was m u c h larger than that obtained under electrical decomposition (mixture (2)) [pNzO 62 torr, 30°C] whilst the effect with pure 02 was very small. The a u t h o r concludes that during the thermal decomposition of N20, some labile electronegative radical is formed on the surface of the catalyst by the interaction of chemisorbed atomic oxygen with nitrogen in the gas phase. The gradual coverage of the catalyst surface could be seen f r o m the increase in the magnitude of the Joshi effect with progress of the reaction and the attainment of a constant value towards the final stages "~,V. J. S.
N. R. Murty, Die Naturwissenschaften, 447-448.
49 (19), Oct. 1962,
16 : 40 : 47 371. Hydrogen sorption by barium films in the pressure range 10 -3 to 10 -4 torr. Germany. The sorption of hydrogen by barium getters at r o o m temperature in the pressure range 10 -3 to 10 -4 torr has been studied. The capillary method was used. The time dependence over a period of hours is expressed by the equation 1/~/t, as expected for a diffusion p h e n o m e n o n . The effects of pressure and barium film thickness on the getter efficiency are discussed. The initial sorption velocity and the sorption capacity were found to agree with published results. (in German) (Authors) G. R a u s c h e r and G. Standt, Vakuum-Technik, 11 (1), Feb. 1962, 17-20. 16 372. Physical adsorption at low pressures and coverages. Germany'. Physical adsorption isotherms have been measured for argon, krypton and xenon at pure zirconium surfaces (powder and evaporated metal film) at 77 ° and 90°K. Equilibrium pressures have been determined down to 10 -1° torr, and the saturation pressure ratio P/P0 covers, e.g. for argon, the range 1 × 10 -12 to nearly 1. The coverage densities extend f r o m 10 -6 to more t h a n two m o n o m o l e c u l a r layers. The results of the m e a s u r e m e n t s can be expressed by isotherms of the Freund-
lich type. The method of m e a s u r e m e n t employed is well suited to the determination of the surface area of evaporated metal films in high v a c u u m devices, if xenon is used as adsorbate. (in German) (Author, modified) N. Hansen, Vakuum-Technik, 11 (3), April 1962, 70-77. 16:29 373. The Betograph, an improved apparatus for the determination of the specific surface area of powders and porous substances. Germany. The standard method for the determination of the specific surface of porous substance depends on a knowledge o f the adsorption isotherm of an inert or noble gas on the substance in question. The method, known as the BET method after the names of its originators in 1938 (Brunaver, E m m e t t and Teller), is lengthy since its isotherm has to be determined point by point. Moreover qualified staff is required to obtain the necessary accuracy. The apparatus described by the author is based on a proposal of Schlosser. It is fully automatic and the adsorption isotherm is recorded continuously by means o f two m e m b r a n e m a n o m e t e r s with range 0-50 torr for the absolute pressure and 0-10 torr for the pressure difference. The apparatus can cope with specific surface values ranging from 0.1 m2/g to 2000m2/g, the average time for a full determination being 20rain for normal substances. This time can be utilized to prepare further sample for test, spare receptacles being available for this purpose, w.J.s. H. J. Bultermann, Le Vide, 17 (99), M a y / J u n e 1962, 201-207.
16 : 22 374. In0uence of sorption on pressure measurements carried out in ultra-high vacuum. Germany. The acceptance test of turbomolecular v a c u u m p u m p s concern the volume of air aspirated (m3/h) and the final pressure reached. The a u t h o r describes the methods adopted by his firm, the volume aspirated is measured in the usual m a n n e r by noting the pressure difference across a calibrated throttle by means of two Bayard-Alpert gauges, care being taken that the aspirated gas is dry. The time required to reach the final pressure is reduced if the p u m p is heated. This however should only be attempted after a pressure of the order of 10 -7 torr has been reached in order to ensure that no important leaks exist. It is also necessary to have had sufficient running time to remove all oily contaminations f r o m the intake side of the p u m p before heat is applied so as to obviate danger of carbon deposits due to cracking. A normal test run requires approximately 50 h subdivided as follows : (1) After 1 h run a pressure of 2 × l0 7 t o r t is reached (no leaks) ; (2) the p u m p is warmed to 120°C after a further 45 h, the pressure has dropped to 5 >~. 10 -9 torr and heat is cut o f f ; (3) the p u m p is allowed to cool to r o o m temperature after a further 5 h, the final pressure of 6 × 10 -1° torr is reached. The residual gas consists mainly of H2 and H~O. There was no trace of hydrocarbons, w . J . s . W. Pupp, Le Vide, 17 (99), M a y / J u n e 1962, 227-230.
16 Production, general properties and gas absorption of oxide films produced by electron evaporation. See Abstr. No. 441.
17.
Thermodynamics
Large hydrogen condensation pumps for ultra-high vacuum. Abstr. No. 395. 18.
17 See
Gaseous Electronics 18:56
375. Ionized gas microwave amplifier. Anon., Brit. Commun. & Electron., 9, Oct. 1962, 768.
Classified Abstracts 369--375
13.
Vacuum Applications 13
369. Vacuum packed sliced Wiltshire bacon. Great Britain. Expeliments were carried out on some 500 packs of bacon in which the flavour of the bacon, cooked after storage for various periods at different temperatures, was assessed. The bacteriology of the raw samples was studied and analyses of the nitrate, nitrite and salt content were made. Some tentative conclusions were drawn. The n o r m a l Wiltshire cure, followed by smoking, appears often to give bacon suitable for v a c u u m packing. Storage life was however found to be variable and unpredictable. D.A.P. A. G. Kitchell, FoodProeess.
16.
& Paekag., 32 (376), Jan. 1963, 3-9.
G a s e s and S o l i d s
16:52 370. On the mechanism of thermal decomposition of nitrous oxide at a platinum filament. India. L a n g m u i r and Hinshelwood have formulated a theory of birnolecular surface reaction which assumes that reaction can only take place between moleculets, adsorbed side by side. Whilst this m a y be true in the majority of cases, certain experiments suggest that an activated complex may be formed by the interaction of an adsorbed molecule or a t o m with an a t o m or molecule in the gas phase or the Van der Waal's layer. The author attempts to show that the heterogeneous decomposition of N 2 0 (50 to 290 torr, 32°C) at a platinum filament (970°C) is of this kind. In this connexion he investigated the Joshi effect in a mixture of (1) N~O2 and N 2 0 ; (2) 2N2 + 02 ; and in pure 02. The Joshi effect in the thermal decomposition products (mixture (1)) [pN~O 35 torr, 31°C] was m u c h larger than that obtained under electrical decomposition (mixture (2)) [pNzO 62 torr, 30°C] whilst the effect with pure 02 was very small. The a u t h o r concludes that during the thermal decomposition of N20, some labile electronegative radical is formed on the surface of the catalyst by the interaction of chemisorbed atomic oxygen with nitrogen in the gas phase. The gradual coverage of the catalyst surface could be seen f r o m the increase in the magnitude of the Joshi effect with progress of the reaction and the attainment of a constant value towards the final stages "~,V. J. S.
N. R. Murty, Die Naturwissenschaften, 447-448.
49 (19), Oct. 1962,
16 : 40 : 47 371. Hydrogen sorption by barium films in the pressure range 10 -3 to 10 -4 torr. Germany. The sorption of hydrogen by barium getters at r o o m temperature in the pressure range 10 -3 to 10 -4 torr has been studied. The capillary method was used. The time dependence over a period of hours is expressed by the equation 1/~/t, as expected for a diffusion p h e n o m e n o n . The effects of pressure and barium film thickness on the getter efficiency are discussed. The initial sorption velocity and the sorption capacity were found to agree with published results. (in German) (Authors) G. R a u s c h e r and G. Standt, Vakuum-Technik, 11 (1), Feb. 1962, 17-20. 16 372. Physical adsorption at low pressures and coverages. Germany'. Physical adsorption isotherms have been measured for argon, krypton and xenon at pure zirconium surfaces (powder and evaporated metal film) at 77 ° and 90°K. Equilibrium pressures have been determined down to 10 -1° torr, and the saturation pressure ratio P/P0 covers, e.g. for argon, the range 1 × 10 -12 to nearly 1. The coverage densities extend f r o m 10 -6 to more t h a n two m o n o m o l e c u l a r layers. The results of the m e a s u r e m e n t s can be expressed by isotherms of the Freund-
lich type. The method of m e a s u r e m e n t employed is well suited to the determination of the surface area of evaporated metal films in high v a c u u m devices, if xenon is used as adsorbate. (in German) (Author, modified) N. Hansen, Vakuum-Technik, 11 (3), April 1962, 70-77. 16:29 373. The Betograph, an improved apparatus for the determination of the specific surface area of powders and porous substances. Germany. The standard method for the determination of the specific surface of porous substance depends on a knowledge o f the adsorption isotherm of an inert or noble gas on the substance in question. The method, known as the BET method after the names of its originators in 1938 (Brunaver, E m m e t t and Teller), is lengthy since its isotherm has to be determined point by point. Moreover qualified staff is required to obtain the necessary accuracy. The apparatus described by the author is based on a proposal of Schlosser. It is fully automatic and the adsorption isotherm is recorded continuously by means o f two m e m b r a n e m a n o m e t e r s with range 0-50 torr for the absolute pressure and 0-10 torr for the pressure difference. The apparatus can cope with specific surface values ranging from 0.1 m2/g to 2000m2/g, the average time for a full determination being 20rain for normal substances. This time can be utilized to prepare further sample for test, spare receptacles being available for this purpose, w.J.s. H. J. Bultermann, Le Vide, 17 (99), M a y / J u n e 1962, 201-207.
16 : 22 374. In0uence of sorption on pressure measurements carried out in ultra-high vacuum. Germany. The acceptance test of turbomolecular v a c u u m p u m p s concern the volume of air aspirated (m3/h) and the final pressure reached. The a u t h o r describes the methods adopted by his firm, the volume aspirated is measured in the usual m a n n e r by noting the pressure difference across a calibrated throttle by means of two Bayard-Alpert gauges, care being taken that the aspirated gas is dry. The time required to reach the final pressure is reduced if the p u m p is heated. This however should only be attempted after a pressure of the order of 10 -7 torr has been reached in order to ensure that no important leaks exist. It is also necessary to have had sufficient running time to remove all oily contaminations f r o m the intake side of the p u m p before heat is applied so as to obviate danger of carbon deposits due to cracking. A normal test run requires approximately 50 h subdivided as follows : (1) After 1 h run a pressure of 2 × l0 7 t o r t is reached (no leaks) ; (2) the p u m p is warmed to 120°C after a further 45 h, the pressure has dropped to 5 >~. 10 -9 torr and heat is cut o f f ; (3) the p u m p is allowed to cool to r o o m temperature after a further 5 h, the final pressure of 6 × 10 -1° torr is reached. The residual gas consists mainly of H2 and H~O. There was no trace of hydrocarbons, w . J . s . W. Pupp, Le Vide, 17 (99), M a y / J u n e 1962, 227-230.
16 Production, general properties and gas absorption of oxide films produced by electron evaporation. See Abstr. No. 441.
17.
Thermodynamics
Large hydrogen condensation pumps for ultra-high vacuum. Abstr. No. 395. 18.
17 See
Gaseous Electronics 18:56
375. Ionized gas microwave amplifier. Anon., Brit. Commun. & Electron., 9, Oct. 1962, 768.