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725. Electron beam melted tungsten
286
Classified Abstracts
including a specially-built hydrogen lamp which operates inside the microscope column thus avoiding the need for an optical system. The effects of surface films on the emission are considered, including favourable effects, and one interesting experiment described makes use of a deposited thin film in which the U.V. intensity is enhanced by allowing standing waves to be set up, as in the classical experiment of Wiener. Some examples are shown of electron micrographs obtained by photoemission, including one showing the magnetic domain structure on a cobalt crystal ; it is supposed that magnetic microfields are here responsible for A number of examples are illustrated of the contrast obtained. microscopes in which the specimen is made to emit by bombardment with high-voltage electrons, and there is some discussion of the scanning electron microscope which has received considerable attention in recent years. In this system, the primary electron beam is made, by a technique very similar to that used in a television camera, to scan the surface of the specimen. The secondary electrons emitted are picked up by an electron multiplier, and the resulting current made to modulate the brightness of a cathode-ray tube which is being scanned in synchronism with the main beam. Thus a television-type display is obtained. In the case of secondary emission induced by ion bombardment, attention is given to the effect of different types of ion on the image quality, and also of the angle of incidence of the ions. It is interesting to note that such a microscope can be used to study sputtering rates of the target/specimen. There are several plates showing micrographs of platinum, uranium, calcite and alumina, the study of insulators by secondary emission being feasible. The article concludes with a brief mention of the use of thermionic emission in these instruments. The specimens can be activated by depositing barium or caesium to reduce the work function. G. Mollenstedt and F. Lenz, Advances in E1ectronic.r and Electron Physics, 18 (1963), 231-328.
34.
High Altitude and Space Technology 34
721. Hypersonic, viscous, compressible flow in the shock layer of a rounded nose cone travelling in a moderately rarefied atmosphere. (France) M. M. Oberai, C. R. Acad. Sci. 257 (l), I July 1963, 41-43. (In French) 34 722. A new form pressure.
of the
dependence
of limiting
plasticity
34 723.
Electric propulsion.
(U.S.A.)
A paper discussing certain methods of propulsion appropriate to space vehicles. The electric arc system is purely thermal. Both a.c. and d.c. arcs in hydrogen are referred to, with the hot gas reaching an exhaust speed of 10 to 12 km/set. Ion propulsion makes use of electrostatic repulsion, with a scheme for injecting electrons into the ion stream as it leaves the exhaust, in order to neutralize the charges on the ions and so prevent their being drawn back into the vehicle. Caesium vapour ionized by contact with hot tungsten, and mercury vapour ionized by electron impact, are mentioned. The possibility of charging heavier particles such as dust or colloid particles is under investigation. Exhaust velocities of 30-300 km/set are reported. Plasma systems make use in various ways of the forces which combined electric and magnetic fields can exert upon charged particles. Some of the practical difficulties encountered in applying these methods of propulsion are discussed, and there is a list of projects for actual space flights now in preparation. Possible efficiencies of the order of over 50 per cent are expected. E. Stuhlinger,
36.
Electr. Engng.,
82, July 1963, 459-465.
Drying, Degassing and Concentration 36
724. Vacuum degassed steel for wires and rods. (Great Britain) Anon., Engineer, 217 (5647), 17 April 1964, 706.
37.
Metallurgy,
Inorganic Chemistry, Chemistry
Analytical
37 (U.S.A.) 725. Electron beam melted tungsten. M. F. Hawkes (digested from NASA Technical Note D-1707, May 1963), Metal Progress, 85 (4), April 1964, 186-188. 37 726. Vacuum annealing of copper wire. (Great Britain) Anon., Engineer, 217 (5635), 24 Jan. 1964,181-182.
on
(U.S.S.R.)
L. D. Livshits, Dokl. Akad. Nauk S.S.S.R., 86-90. (In Russian)
721-727
37 154 (I), 1 Jan. 1964,
(U.S.A.) 727. A method for growing rare-earth single crystals. H. E. Nigh, J. Appl.Phys.. 34 (ll), Nov. 1963, 3323-3325.
Classified Abstracts
including a specially-built hydrogen lamp which operates inside the microscope column thus avoiding the need for an optical system. The effects of surface films on the emission are considered, including favourable effects, and one interesting experiment described makes use of a deposited thin film in which the U.V. intensity is enhanced by allowing standing waves to be set up, as in the classical experiment of Wiener. Some examples are shown of electron micrographs obtained by photoemission, including one showing the magnetic domain structure on a cobalt crystal ; it is supposed that magnetic microfields are here responsible for A number of examples are illustrated of the contrast obtained. microscopes in which the specimen is made to emit by bombardment with high-voltage electrons, and there is some discussion of the scanning electron microscope which has received considerable attention in recent years. In this system, the primary electron beam is made, by a technique very similar to that used in a television camera, to scan the surface of the specimen. The secondary electrons emitted are picked up by an electron multiplier, and the resulting current made to modulate the brightness of a cathode-ray tube which is being scanned in synchronism with the main beam. Thus a television-type display is obtained. In the case of secondary emission induced by ion bombardment, attention is given to the effect of different types of ion on the image quality, and also of the angle of incidence of the ions. It is interesting to note that such a microscope can be used to study sputtering rates of the target/specimen. There are several plates showing micrographs of platinum, uranium, calcite and alumina, the study of insulators by secondary emission being feasible. The article concludes with a brief mention of the use of thermionic emission in these instruments. The specimens can be activated by depositing barium or caesium to reduce the work function. G. Mollenstedt and F. Lenz, Advances in E1ectronic.r and Electron Physics, 18 (1963), 231-328.
34.
High Altitude and Space Technology 34
721. Hypersonic, viscous, compressible flow in the shock layer of a rounded nose cone travelling in a moderately rarefied atmosphere. (France) M. M. Oberai, C. R. Acad. Sci. 257 (l), I July 1963, 41-43. (In French) 34 722. A new form pressure.
of the
dependence
of limiting
plasticity
34 723.
Electric propulsion.
(U.S.A.)
A paper discussing certain methods of propulsion appropriate to space vehicles. The electric arc system is purely thermal. Both a.c. and d.c. arcs in hydrogen are referred to, with the hot gas reaching an exhaust speed of 10 to 12 km/set. Ion propulsion makes use of electrostatic repulsion, with a scheme for injecting electrons into the ion stream as it leaves the exhaust, in order to neutralize the charges on the ions and so prevent their being drawn back into the vehicle. Caesium vapour ionized by contact with hot tungsten, and mercury vapour ionized by electron impact, are mentioned. The possibility of charging heavier particles such as dust or colloid particles is under investigation. Exhaust velocities of 30-300 km/set are reported. Plasma systems make use in various ways of the forces which combined electric and magnetic fields can exert upon charged particles. Some of the practical difficulties encountered in applying these methods of propulsion are discussed, and there is a list of projects for actual space flights now in preparation. Possible efficiencies of the order of over 50 per cent are expected. E. Stuhlinger,
36.
Electr. Engng.,
82, July 1963, 459-465.
Drying, Degassing and Concentration 36
724. Vacuum degassed steel for wires and rods. (Great Britain) Anon., Engineer, 217 (5647), 17 April 1964, 706.
37.
Metallurgy,
Inorganic Chemistry, Chemistry
Analytical
37 (U.S.A.) 725. Electron beam melted tungsten. M. F. Hawkes (digested from NASA Technical Note D-1707, May 1963), Metal Progress, 85 (4), April 1964, 186-188. 37 726. Vacuum annealing of copper wire. (Great Britain) Anon., Engineer, 217 (5635), 24 Jan. 1964,181-182.
on
(U.S.S.R.)
L. D. Livshits, Dokl. Akad. Nauk S.S.S.R., 86-90. (In Russian)
721-727
37 154 (I), 1 Jan. 1964,
(U.S.A.) 727. A method for growing rare-earth single crystals. H. E. Nigh, J. Appl.Phys.. 34 (ll), Nov. 1963, 3323-3325.