Measuring gas pressure by counting single molecules

418

Classified Abstracts 1024--1036 33

34 : 23 : 43

Observation of carbon monoxide and oxygen on tantalum with the field-emission microscope. See Abstr. No. 970.

1030. Performance of silicon materials in thermal-vacuum environments. (U.S.A.)

33 On the observation of the dissociation of adsorbed CO on tantalum in a field-emission microscope. See Abxtr. No. 971.

Weight loss in vacuum as well as changes in physical and electrical properties after prolonged thermal-vacuum exposure are given for silicon rubber, encapsulating compounds as well as for resins and greases used in high-vacuum systems. Methods are discussed for processing each type to give best results under space environment.

33 A laboratory installation for melting and processing metal-ceramic materials by electron beam in vacuum. See Abstr. No. 1007. 33:22 1024. Measuring gas pressure by counting single molecules. (Great Britain) Study of the field emission from very fine metal points has shown fluctuations in the emission current at low gas pressures. Gas molecules near the point are ionized and consequently attracted Their return to the emitter disturbs the layer of adsorbed gas characteristic of fine points and this causes a change in the emission current. If the gas pressure is low enough, i.e. below 10--5 torr, the ionic impacts will be of the order of a few hundred a second or less and are easily counted. A pressure gauge using this principle suggests itself. L. Jacob, New Scientist, 23 (406), 27 Aug. 1964, 494-495.

34.

C. L. Whipple and E. G. Curtindale, Trans. 10 Nat. Vac. Syrup., New York, 1963, 63-68. 34:19 1031. Space simulation and its effects on materials. (U.S.A.) The author discusses the effect of ultra-violet radiation between 2000 and 4000~ and prolonged exposure to high vacuum on pigments, silicon rubber and other materials. C. R. Blair, Dielectrics in Space Symposium, (Pittsburgh, 1963), 21 pp.

36.

Drying, D e g a s s i n g and Concentration

1032. Freeze drying faces the future. (US.A.) R. V, Hughson, Chem. Engng., 71 (15), 20 July 1964, 155-160.

36

H i g h Altitude and S p a c e T e c h n o l o g y

34 1025. The space environment as a dielectric. (U.S.A.) The limitations of the vacuum environment when used as a dielectric are discussed. The effects of the solar corona as well as of micrometeoroid bombardment receive special attention. A. S. Denholm, Dielectrics in Space Symposium, Pittsburgh, 1963, 21 pp. 34 : 22

1026. Vacuum measurement techniques for space simulation chambers. (U.S.A.) Low pressure molecular kinetics may cause the gas flux incident on a test vehicle inside a space chamber to differ markedly from that striking the chamber wall. The author describes a method of measuring the flux distribution on the vehicle in order to define the effective vacuum as distinct from that measured by a gauge mounted in the wall of the chamber. A modified type of wall gauge is described which reduces this type of error. D. H. Holkeboer, Trans. 10 Nat. Vac. Syrup., 1963, New York, 292-296. 34 1027. Space friction evaluations of sintcred MoS; sleeve bearings.

37.

M e t a l l u r g y , Inorganic Chemistry, Analytical Chemistry 37

A laboratory installation for melting and processing metal-ceramic materials by electron gun in vacuum. See Abstr. No. 1007. 37 : 16

1033. Gas analysis with a molecular sieve.

(U.S.A.)

The method depends on a study of the desorption spectrum of sorbed gases as the solid adsorbent is gradually raised in temperature from 196°C to 300°C. Gas mixtures ranging from 1-10 -a torr. 1. can be separated with suitable molecular sieves. The ~tscending order in the temperature of desorbing is H2, A, 02, CH4, N2, CO, CO2, and HzO. Y. Murakami and H. Okamoto, Trans. 10 Nat. Vac. Syrup., New York, 1963, 93-96. 37

1034. Nickel and Nickel Alloys. (U.S.A.) Anon., Mat. Des. Engng., 60 (1), July 1964, 97-108.

(U.S.A,) Sleeve bearings for lightly loaded oscillatory shafts were constructed from sintered mixtures of MoS2 and silver and tested under vacuum conditions. Frictional torque was smaller than when operating in air ; there was no cold welding and no gross seizure occurred. J. C. Heindl and R. J. Belanger, Trans. 10 Nat. Vac. Symp., New York, 1963, 27-31, 34 : 57 1028. Vacuum fatigue tester. (U.S.A.) ]?he machine allows transmission of high bending moments into the vacuum chamber, under constant load conditions. B. Steverding, Rev. Sci. lnstrum., 35 (5), May 1964, 565-568. 34 : 30 1029. An ultra-high vacuum ultra-violet irradiation chamber with

controlled temperature.

(U.S.A.)

The chamber was designed for the valuation of space vehicle thermal control coatings. Ultra-violet irradiation is carried out with A as low as 1800A~ at pressures of the order of 10- 9 tort and sample temperatures ranging from --320 °F to 225 °F. G. R. Blair and P. M. Blair, Trans. 10 Nat. Vac. Syrup., New York, 1963, 69-71.

38.

Distillation, Organic Chemistry, Isotopic Gas Analysis 38 : 15

1035. Pressure drop measurement of a packed rectifying distillation column under reduced pressure. (Japan) The experiments described by the author cover the pressure drop acron polystyrol columns, 35 and 80 mm dia. and 1 m long when packed with either ¼ in. McMahon mesh or Raschig rings of various diameters. The absolute pressure in the system was varied between .1 and 400 torr, the pressure drop being measured at flow rates ranging from 10 to 800 kg/m2h. Results are presented in terms of Reynolds number and friction factor. I t appears that the vapour flow through the column is viscous provided the Reynolds number is below a certain limiting value. It. Nakawaga and R. Tsunoda, J, Vae. Japan, 7 (1), 1964, 23-27. (In Japanese)

39.

M i s c e l l a n e o u s Applications 39 : 20

1036, EIastomeric coatings. (U.S.A.) Anon., Mat. Des. Engng., 60 (2), Aug. 1964, 99-106.