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The outgassing properties of mica with particular reference to the life performance of thermionic valves
Classified Abstracts 600-608
45.
Soldering, Welding, Brazing, Solders 45
600. Brazing comes of age. ’ R. L. Peaslee, Mech. Engng, 84 (6), June 1962, 36-41. 45 601. Vacuum brazing of stainless steel in beryllium. United States. A new technique of brazing stainless steel to beryllium results in vacuum-tight joints twice as strong as those previously obtained. Pre-treatment of the component surfaces, as well as the brazing operation itself, is done in a furnace (Author) capable of maintaining a vacuum of 0.1 micron. E. M. Whitson, Metal Progr., 82 (l), July 1962, 93-95.
47.
Outgassing Data, Vapour Pressure Data, Gettering Data
47 602. Kinetics of CS desorption from tungsten. M. D. Scheer and J. Fine, J. Chem. Phys., 37 (I), 1 July 1962, 107-113. 47 603. Vapor pressure of gallium, stability of gallium suboxide vapor, and equilibria of some reactions producing gallium suboxide vapor. United Stares. Vapour pressures of gallitim in the literature are too high because Ga,O(v) formed in the reaction of gallium with the quartz effusion cells used for the measurements. Gallium was found to be less reactive with alumina than with quartz. Measurements in an alumina effusion cell gave vapour pressures for gallium that obey the expression, log P (atm) = -14,900/T -0.515 log T + 7.34. Values for nHfzss(Gazocv)) of -17.4 f 0.7 and -19.7 5 0.7 kcal/mole were found for the reaction of gallium with quartz and magnesium oxide, respectively. The latter value was employed to calculate the equilibria in forming Ga,O(v) from the following pairs of reactants : gallium-gallia, graphite-gallia, tin-gallia, gallium-alumina, and gallium-water vapour. The vapour pressures of silver and tin were determined and compared with literature values to check the constants of the system. (Authors) C. N. Cochrane and L. M. Foster, Feb. 1962, 144.
281
electrodes in a thermionic valve, has been found to be the largest potential source of gas in a valve. Total gas quantities of about 5000 ml. torr g-l have been measured. Most of this gas is evolved at temperatures about 750°C when the mica decomposes and exfoliates. By the use of clamps the exfoliation can be avoided and the mica outgassed completely. Using such outgassed mica spacers in thermionic valves it is found that there is no improvement in performance when compared with valves using mica that has not been de-gassed-even though a small part of the mica is in contact with the cathode core operating at 730°C. It is deduced that the gas evolution from the standard processed mica spacers during normal running of the valve must be negligibly small. However, the presence of mica does limit the degree of processing that valves can be subjected to on the pump though the worst effects of outgassing can be avoided by careful mechanical design. (Author) R. W. Lawson,
Vacuum, 12 (3), May/June
1962, 145-152. 47 : 22 : 33
A low-cost recording ionization vacuum gauge. See Abstr. No. 553. 47 : 13 : 22 : 49 Properties of an omegatron tube employing a lanthanum boride filament. See Abstr. No. 548.
49.
Miscellaneous
Materials
and Techniques 49
605. Determination of the weight of material sealed into a phial under vacuum. P. P. Rutherford, Chem. & Zndustr., (36), 8 Sept. 1962, 1614. 49 606. Effect of adsorbed phases on the electrical conductivity of synthetic crystalline zeolites. D. N. Stamires, J. Chem. Phys., 36 (12), 15 June 1962, 3174-3181. 607. Solubility of helium in liquid hydrogen. L. 0. RoeKg, J. Chem. Phys., 37 (1), 1 July 1962, 114-l 19.
J. Electrochem. Sot., 109,
49 608. Joining refractory metals by thermochemical means. Anon., Metal Progr., 82 (1), July 1962, 10.
47 : 16 604. The outgassing properties of mica with particular reference to the life performance of thermionic valves. Great Britain. Muscovite (ruby) mica, used to locate the various
49:13:22:47 Properties filament.
of an omegatron tube employing a lanthanum See Abstr. No. 548.
boride
45.
Soldering, Welding, Brazing, Solders 45
600. Brazing comes of age. ’ R. L. Peaslee, Mech. Engng, 84 (6), June 1962, 36-41. 45 601. Vacuum brazing of stainless steel in beryllium. United States. A new technique of brazing stainless steel to beryllium results in vacuum-tight joints twice as strong as those previously obtained. Pre-treatment of the component surfaces, as well as the brazing operation itself, is done in a furnace (Author) capable of maintaining a vacuum of 0.1 micron. E. M. Whitson, Metal Progr., 82 (l), July 1962, 93-95.
47.
Outgassing Data, Vapour Pressure Data, Gettering Data
47 602. Kinetics of CS desorption from tungsten. M. D. Scheer and J. Fine, J. Chem. Phys., 37 (I), 1 July 1962, 107-113. 47 603. Vapor pressure of gallium, stability of gallium suboxide vapor, and equilibria of some reactions producing gallium suboxide vapor. United Stares. Vapour pressures of gallitim in the literature are too high because Ga,O(v) formed in the reaction of gallium with the quartz effusion cells used for the measurements. Gallium was found to be less reactive with alumina than with quartz. Measurements in an alumina effusion cell gave vapour pressures for gallium that obey the expression, log P (atm) = -14,900/T -0.515 log T + 7.34. Values for nHfzss(Gazocv)) of -17.4 f 0.7 and -19.7 5 0.7 kcal/mole were found for the reaction of gallium with quartz and magnesium oxide, respectively. The latter value was employed to calculate the equilibria in forming Ga,O(v) from the following pairs of reactants : gallium-gallia, graphite-gallia, tin-gallia, gallium-alumina, and gallium-water vapour. The vapour pressures of silver and tin were determined and compared with literature values to check the constants of the system. (Authors) C. N. Cochrane and L. M. Foster, Feb. 1962, 144.
281
electrodes in a thermionic valve, has been found to be the largest potential source of gas in a valve. Total gas quantities of about 5000 ml. torr g-l have been measured. Most of this gas is evolved at temperatures about 750°C when the mica decomposes and exfoliates. By the use of clamps the exfoliation can be avoided and the mica outgassed completely. Using such outgassed mica spacers in thermionic valves it is found that there is no improvement in performance when compared with valves using mica that has not been de-gassed-even though a small part of the mica is in contact with the cathode core operating at 730°C. It is deduced that the gas evolution from the standard processed mica spacers during normal running of the valve must be negligibly small. However, the presence of mica does limit the degree of processing that valves can be subjected to on the pump though the worst effects of outgassing can be avoided by careful mechanical design. (Author) R. W. Lawson,
Vacuum, 12 (3), May/June
1962, 145-152. 47 : 22 : 33
A low-cost recording ionization vacuum gauge. See Abstr. No. 553. 47 : 13 : 22 : 49 Properties of an omegatron tube employing a lanthanum boride filament. See Abstr. No. 548.
49.
Miscellaneous
Materials
and Techniques 49
605. Determination of the weight of material sealed into a phial under vacuum. P. P. Rutherford, Chem. & Zndustr., (36), 8 Sept. 1962, 1614. 49 606. Effect of adsorbed phases on the electrical conductivity of synthetic crystalline zeolites. D. N. Stamires, J. Chem. Phys., 36 (12), 15 June 1962, 3174-3181. 607. Solubility of helium in liquid hydrogen. L. 0. RoeKg, J. Chem. Phys., 37 (1), 1 July 1962, 114-l 19.
J. Electrochem. Sot., 109,
49 608. Joining refractory metals by thermochemical means. Anon., Metal Progr., 82 (1), July 1962, 10.
47 : 16 604. The outgassing properties of mica with particular reference to the life performance of thermionic valves. Great Britain. Muscovite (ruby) mica, used to locate the various
49:13:22:47 Properties filament.
of an omegatron tube employing a lanthanum See Abstr. No. 548.
boride