Teflon coatings for ultra-high vacuum systems

Classified abstracts 603--608 41 Diffusion versus surface limitations in vapour-solvent growth of germanium. See abstract number 537. 41 Formation conditions, structure and electrical properties of Ge films deposited on single crystal substrates. See abstract number 574. 41 Evaporation techniques and properties of InSb films. See abstract number 575. 41 Recrystallization of cadmium sulphide films. See abstract number 576. 41 Vacuum deposited cadmium thin films. See abstract number 577. 41 Deposition parameters affecting epitaxial growth of single crystal films. See abstract number 578. 41 The generation of monoerystalline films of cadmium and mercury tellurides. See abstract number 582. 41 Influence of substrate temperature on the magnetic properties of thin permalloy films. See abstract number 583. 41 Volta potential studies of the ageing of gold surfaces. See abstract number 585. 41 Analysis of the ionization of caesium in tungsten capillaries. See abstract number 598. 41 603. Viseosity of metallic mercury (and its saturated vapour) over its entire liquid range, i.e. from its melting point (234.4°K) to its critical point (1733°K), and an estimate of its critical viscosity. (USA) The viscosities of both liquid metallic mercury and its saturated vapour have been determined experimentally up to about 900°K. Using Andrade's equation, correlating viscosity, temperature, and :specific volume, and from the known specific volumes of mercury up to the critical temperature, the viscosity of mercury and its saturated vapour are extrapolated to the critical point (1733°K). Advantage is also taken of the experimental straight-line relations for the mean viscosity, i,e. 1/2(true + rt,~atayap), vs temperature in the critical region. The critical viscosity of mercury is estimated t o equal 0.4~ cp. (Author) A V Grosse, JPhys Chern, 68, Nov 1964, 3419-3423. 41 : 47 604. Solvent vapour pressures in dilute solutions of gallium in cadmium. (USA) Cadmium solvent vapour pressures over solutions at 775°K and containing 0.008 to 0.25 mole fraction gallium obey the pressure relationship Pca a~ouea/Pcapure = 1 0.856Naa + 0.043N~a 2. The mathematical form of this relationship was deduced by analogy with Henry's law assuming that solutions are a random mixture of molecules or atoms which interact through short-range forces. The first coefficient, 0.856, was evaluated experimentally from precise and reproducible isopiestic balance measurements. It is presumed to measure the interaction of the gallium solute atoms upon neighbouring cadmium solvent atoms. The second coefficient, 0.943 as fitted to the isopiestic measurements of Predel, is included to describe the effect when solvent atoms have two solute neighbours. The data cannot be fitted to the usually accepted modified Raoult's law expression Pca auoyea/Pcapure = 1--N~a+bNaa 2. Also a vapour pressure estimate using the Duhem pressure relationship and Kleppa's calorimetric heats of solution of gallium in cadmium fails to predict the observed cadmium behaviour. (Author) G R B Elliott et al, J Phys Chem, 69, March 1965, 933-939. 41 605, High strength low alloy steels, (USA) Anon, Materials in Design Engineering, 61 (3), March 1965, 123-124.

and its chemical inertness should result in similar properties for chemisorption.]Thin layers of Teflon have been deposited in sections of an ultra-high vacuum system which were bakeable at 375 °C. The ultimate vacuum of 2 x 10 -~° torr was not reduced by the use of these films. Flash filament experiments using tungsten in the residual gases and in carbon monoxide illustrate the effectiveness of this technique. J H Singleton, 10 A VS Nat Vac Syrup, 1963, MacMillan, New

York, p 267.

44. Waxes, lubricants, cements, lacquers, paints, oils 44 Water adsorption on molybdenum disulphide containing surface contaminants. See abstract number 525.

46. Glass blowing, glass-to-metal and ceramic-to-metal sealing techniques 46 607. A 19 inch diameter bakeable metal ceramic seal. (USA) The hydride brazing process used for making a bakeable ceramicmetal assembly of 19 in. diameter and 42 in. long necessitated a re-examination of allowable thermal stresses, heating rate of the ceramic as well as a vacuum furnace for 1000°C and 700 litre volume. Mass spectrometer determinations were made of partial pressures above 350°C during brazing cycle, when the titanium exists in a highly reactive state. The troublesome outgassing of internal heat reflectors, needed to prevent excessive temperature gradients in the ceramic, was avoided through judicious use of auxiliary external heaters rather than using exceedingly high pumping speeds. K Kirchner, Trans 10 Ali'S Nat Vac Syrup, 1963, MacMillan, New York, p 170.

47. Outgassing data, vapour pressure data, gettering data, residual gases in vacuum systems, residual gas analysis 47 A study of the flash filament method. See abstract number 511. 47 Solvent vapour pressures in dilute solutions of gallium in cadmium. See abstract number 604. 47 Teflon coatings for ultra-high vaeuum systems. See abstract number 606.

49. Miscellaneous materials and techniques 49 608. Heat emittance properties of materials. (USA) G D Miller, Materials in Design Engineering, 61 (3), March 1965, 112-114.

V. Basic science and engineering 52. Physical chemistry 52 Oxidation of hydrocarbons adsorbed on oxide catalysts induced by cobalt-60 rays. See abstract number 534. 52 Texture of gaseous layers condensed on a eold substrate. See abstract number 542. 52 Methods of investigating the electro-physical parameters of semiconduetor epitaxial films. See abstract number 594.

43. Plastics and elastomers 43 : 47 606. Teflon coatings for ultra-high vacuum systems. (USA) It is frequently desirable to reduce the interaction of gas with the walls of a vacuum system. The surface coverage of teflon, by physical adsorption of gas has been shown to be relatively weak,

54. Biology, biochemistry, pharmaceutics, toxicology, organic chemistry 54 Lasers in medicine. See abstract No. 559. 331