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Continuous vacuum hot-pressing
Classified abstracts 3512-3523 system. We observed a typical dissociation efficiency of 0.63 from the hydrogen discharge and of 0.73 from a mixture of hydrogen and argon. After coating with concentrated ortho-phosphoric acid. a hydrogen dissociation efficiency as high as 0.82 could be observed. The fraction of dissociated oxygen molecules was measured to be 0.33. (Germany) A Ding et al, Rev Scient Instrum, 48 (8), 1977, 1002-1004. 34
3512. Production of neutral atoms by pulsed laser heating. (USA) Sodium and thallium surfaces were heated in vacuum by a short intense pulse from a CO, TEA laser. The time-dependent emission of neutral atoms following the laser pulse was measured in the density atoms/cm3 by monitoring the absorption from a range IO”-lo** beam of resonance light. The temperature of the metal surface and the depth of heating after the laser pulse were obtained using a theoretical model. The results show that at the end of the laser pulse the temperature of the surface is close to the boiling point for the metal independent of laser energy in the range lo”-lo9 W/cm2. The surface temoeratures were 593 and 934 K for sodium and thallium, respectively: The depth of heating is greater than can be explained by heat conduction alone. It is suggested that during the laser pulse the metal is heated by a shock wave. The results also point out the limitations of pulsed laser vaporization in the production of neutral atoms from refractory materials. AT Prengel et al, J Appl Phys, 48 (8), 1977,3551-3556. 34
3513. An electron gun witb outlet of large-section current in the atmosphere. (USSR) Design and results of experimental investigations of an electron thermionic gun generating a current with a 1 m side square cross section are described. At an accelerating voltage of 130 kV the current density is 10m4 A/cm2 at nonuniformity less than 20% behind a window of aluminium foil with thickness of 18 and 30 pm in the atmosphere. The working pressure in the gun vessel is 2 x 10T5 torr. VI Federov and L P Shanturbr, Prib Tekh Eksper, No 1,1976,153-l 55 (in Russian). 35. PROCESSING
OF MATERIALS 35
Some effects of heat treatment and electron irradiation on the cathodolumbrescence spectra of Cub&. (USA) The cathodoluminescence spectra of sulphur-saturated and sulphurdeficient CuIn!& has been studied at 40 and 80 K over the photon energy range 0.47 I hv I 2.0 eV. The spectrum of sulphur-saturated specimens exhibits four distinct bands with maxima at approximately 1.55, 1.20, 0,80 and 0.60 eV. The spectrum of sulphur-deficient samples consists of a band with a main peak at 4.60 eV and secondary maxima at 4.58 and -0.55 eV. When sulphur-saturated samples are heated in vacuum, the spectrum changes gradually from the sulphur-saturated form to the sulphur-deficient form. High-energy (10 MeV) electron irradiation on a sulphur-saturated sample results in a reduction of intensity of the dominant 1.55 eV band and a growth of a broad band with a maximum around 0.80 eV. S D Miffleman et al, J ApplPhys, 48 (9), 1977,3878-3882. 3514.
35
3515. Continuous vacuum hot-pressing. (GB) A study has been made of the conditions for vacuum hot-pressing of a mixture of magnesium oxide plus 2 w/o lithium fluoride for the production of transparent ceramics. The results have been used in formulating a design criteria for a continuous vacuum hot-press for the production of rods of transparent material. Single pellet hotpressing results have shown that although transparent magnesia can be produced over a wide range of temperatures and pressures, the optimum conditions are lOOO”C, 1000 psi held for 10 min under high vacuum. When these conditions are applied to ‘continuous’ production, the resultant rod is translucent with regions of transparency. The design of the continuous hot-press has successfully incorporated the use of silicon nitride as a die and die-set material. D J G Coates et al, Vacuum, 27 (9), 1977,531-535. 35
3516. On the nature of dislocation loops in As-implanted and postannealed Si wafers. (USA) Si wafers were implanted with As ions to a concentration of lOi atoms/cm’ and subsequently annealed in the temperature range 600-1000°C in an atmosphere of a low partial pressure of Ar. The surface density of the resulting interstitial dislocation loops was 158
measured. The comparison with electrical measurement data suggests that the extra planes in the loops do not consist, at least in their majority, of As atoms. (Greece) P Pavlidl et al, J Appl Phys, 48 (8), 1977,3612-3613. 35
3517. High-temperature conductivity of undoped and copper-doped selenide. (Germany) The electrical conductivity of undoped and Cu-doped CdSe crystals is measured in an evacuated two-zone quartz ampoule over the temperature range 600 to 1000°C as a function of partial cadmium and selenium vapour pressures. The results are interpreted in terms of a distribution of Cu on the substitutional and interstitial states. J Varvas and T Nirk, Phys Status Solidi (a), 33 (l), 1976, 75-84. 35
High-temperature chamber for investigation of structure of alloys by the Mossbauer effect. (USSR) A universal vacuum high-temperature chamber for investigation of alloys by the Mossbauer effect at both absorption and scattering is described. Oil-free pumping of the chamber provides a residual gas pressure of 5 x lo-’ torr at specimen temperature of 1500°C. N A Tomashevskiy, Prib Tekh Eksper, No 1, 1976, 207-208 (in Russian). 3518.
35
3519. Vacuum-melting determination of nitrogen in metals by fast neutron activation with radiochemical 13N isotope separation. (USSR) The samples of refractory metals are activated by 14 MeV neutrons at a fluence of 5 x 10”. The produced radioactive isotope ‘sN is a positron source with a halftime of 10 min. The samples after neutron irradiation are introduced through an airlock into a vacuum furnace and melted in a graphite crucible. The released gases are pumped into the measuring cell in which the activity of 13N is determined. The sensitivity of the method is 3 x lo-“ per cent weight. 0 V Zavyalov et al, ZavodLab, 42 (l), 1976, 32-34 (in Russian). 35
Thermodynamics of As2S3 evaporation. (USSR) Mass spectra of As& evaporation products are investigated at 600 K and electron acceleration voltage 75 eV. Thermodynamic calculations of the process of As2S3 evaporation are presented. It is shown that sublimation of As2S3 is determined by the equilibrium between solid As2S3 and gaseous AS.& and S2. A S Pashinkln et al, Neorg Mater, 12 (5), 1976, 814-817 (in Russian). 3520.
35
3521. Preparation and physico-chemical characteristics of crystals of PbTe-SnTe solid solutions at their growth by the directed crystallization method. (USSR) Growth of crystals of PbTe-SnTe solid solutions has been carried out in sealed ampoules evacuated to 1 x 10e4 torr and placed in a vertical furnace with temperature gradient. The distribution of concentrations of components along ingots and microhardness are measured. R Kh Akchurin et al, Neorg Mater, 12 (5), 1976, 838-842 (in Russian). 35
Relation between electron work function and some physical properties of silicides of transition metals of IV group. (USSR) Electron work function, electric resistivity, thermal emf, thermal expansion and microhardness of disilicides of IV group metals and of various silicide phases of titanium are investigated. The electron work function was measured using the contact potential difference and thermionic emission methods. Investigation of temperature dependences of resistivity and thermal emf have shown that the examined silicides possess metal-like character. The value of work function depends on the concentration of silicon and metal in silicide and it correlates with such characteristics of bond strength as the coefficient of thermal expansion and microhardness. G V Samsonov et al, Neorg Mater, 12 (5). 1976, 850-853 (in Russian). 3522.
36. VACUUM STUDIES
INSTRUMENTATION
FOR SURFACE 36
Investigation of surface diffusion by means of a locally resolving vibrating capacity method. (Germany) A locally resolving vibrating capacitor method for measuring contact potential changes has been developed and was applied to the 3523.
3512. Production of neutral atoms by pulsed laser heating. (USA) Sodium and thallium surfaces were heated in vacuum by a short intense pulse from a CO, TEA laser. The time-dependent emission of neutral atoms following the laser pulse was measured in the density atoms/cm3 by monitoring the absorption from a range IO”-lo** beam of resonance light. The temperature of the metal surface and the depth of heating after the laser pulse were obtained using a theoretical model. The results show that at the end of the laser pulse the temperature of the surface is close to the boiling point for the metal independent of laser energy in the range lo”-lo9 W/cm2. The surface temoeratures were 593 and 934 K for sodium and thallium, respectively: The depth of heating is greater than can be explained by heat conduction alone. It is suggested that during the laser pulse the metal is heated by a shock wave. The results also point out the limitations of pulsed laser vaporization in the production of neutral atoms from refractory materials. AT Prengel et al, J Appl Phys, 48 (8), 1977,3551-3556. 34
3513. An electron gun witb outlet of large-section current in the atmosphere. (USSR) Design and results of experimental investigations of an electron thermionic gun generating a current with a 1 m side square cross section are described. At an accelerating voltage of 130 kV the current density is 10m4 A/cm2 at nonuniformity less than 20% behind a window of aluminium foil with thickness of 18 and 30 pm in the atmosphere. The working pressure in the gun vessel is 2 x 10T5 torr. VI Federov and L P Shanturbr, Prib Tekh Eksper, No 1,1976,153-l 55 (in Russian). 35. PROCESSING
OF MATERIALS 35
Some effects of heat treatment and electron irradiation on the cathodolumbrescence spectra of Cub&. (USA) The cathodoluminescence spectra of sulphur-saturated and sulphurdeficient CuIn!& has been studied at 40 and 80 K over the photon energy range 0.47 I hv I 2.0 eV. The spectrum of sulphur-saturated specimens exhibits four distinct bands with maxima at approximately 1.55, 1.20, 0,80 and 0.60 eV. The spectrum of sulphur-deficient samples consists of a band with a main peak at 4.60 eV and secondary maxima at 4.58 and -0.55 eV. When sulphur-saturated samples are heated in vacuum, the spectrum changes gradually from the sulphur-saturated form to the sulphur-deficient form. High-energy (10 MeV) electron irradiation on a sulphur-saturated sample results in a reduction of intensity of the dominant 1.55 eV band and a growth of a broad band with a maximum around 0.80 eV. S D Miffleman et al, J ApplPhys, 48 (9), 1977,3878-3882. 3514.
35
3515. Continuous vacuum hot-pressing. (GB) A study has been made of the conditions for vacuum hot-pressing of a mixture of magnesium oxide plus 2 w/o lithium fluoride for the production of transparent ceramics. The results have been used in formulating a design criteria for a continuous vacuum hot-press for the production of rods of transparent material. Single pellet hotpressing results have shown that although transparent magnesia can be produced over a wide range of temperatures and pressures, the optimum conditions are lOOO”C, 1000 psi held for 10 min under high vacuum. When these conditions are applied to ‘continuous’ production, the resultant rod is translucent with regions of transparency. The design of the continuous hot-press has successfully incorporated the use of silicon nitride as a die and die-set material. D J G Coates et al, Vacuum, 27 (9), 1977,531-535. 35
3516. On the nature of dislocation loops in As-implanted and postannealed Si wafers. (USA) Si wafers were implanted with As ions to a concentration of lOi atoms/cm’ and subsequently annealed in the temperature range 600-1000°C in an atmosphere of a low partial pressure of Ar. The surface density of the resulting interstitial dislocation loops was 158
measured. The comparison with electrical measurement data suggests that the extra planes in the loops do not consist, at least in their majority, of As atoms. (Greece) P Pavlidl et al, J Appl Phys, 48 (8), 1977,3612-3613. 35
3517. High-temperature conductivity of undoped and copper-doped selenide. (Germany) The electrical conductivity of undoped and Cu-doped CdSe crystals is measured in an evacuated two-zone quartz ampoule over the temperature range 600 to 1000°C as a function of partial cadmium and selenium vapour pressures. The results are interpreted in terms of a distribution of Cu on the substitutional and interstitial states. J Varvas and T Nirk, Phys Status Solidi (a), 33 (l), 1976, 75-84. 35
High-temperature chamber for investigation of structure of alloys by the Mossbauer effect. (USSR) A universal vacuum high-temperature chamber for investigation of alloys by the Mossbauer effect at both absorption and scattering is described. Oil-free pumping of the chamber provides a residual gas pressure of 5 x lo-’ torr at specimen temperature of 1500°C. N A Tomashevskiy, Prib Tekh Eksper, No 1, 1976, 207-208 (in Russian). 3518.
35
3519. Vacuum-melting determination of nitrogen in metals by fast neutron activation with radiochemical 13N isotope separation. (USSR) The samples of refractory metals are activated by 14 MeV neutrons at a fluence of 5 x 10”. The produced radioactive isotope ‘sN is a positron source with a halftime of 10 min. The samples after neutron irradiation are introduced through an airlock into a vacuum furnace and melted in a graphite crucible. The released gases are pumped into the measuring cell in which the activity of 13N is determined. The sensitivity of the method is 3 x lo-“ per cent weight. 0 V Zavyalov et al, ZavodLab, 42 (l), 1976, 32-34 (in Russian). 35
Thermodynamics of As2S3 evaporation. (USSR) Mass spectra of As& evaporation products are investigated at 600 K and electron acceleration voltage 75 eV. Thermodynamic calculations of the process of As2S3 evaporation are presented. It is shown that sublimation of As2S3 is determined by the equilibrium between solid As2S3 and gaseous AS.& and S2. A S Pashinkln et al, Neorg Mater, 12 (5), 1976, 814-817 (in Russian). 3520.
35
3521. Preparation and physico-chemical characteristics of crystals of PbTe-SnTe solid solutions at their growth by the directed crystallization method. (USSR) Growth of crystals of PbTe-SnTe solid solutions has been carried out in sealed ampoules evacuated to 1 x 10e4 torr and placed in a vertical furnace with temperature gradient. The distribution of concentrations of components along ingots and microhardness are measured. R Kh Akchurin et al, Neorg Mater, 12 (5), 1976, 838-842 (in Russian). 35
Relation between electron work function and some physical properties of silicides of transition metals of IV group. (USSR) Electron work function, electric resistivity, thermal emf, thermal expansion and microhardness of disilicides of IV group metals and of various silicide phases of titanium are investigated. The electron work function was measured using the contact potential difference and thermionic emission methods. Investigation of temperature dependences of resistivity and thermal emf have shown that the examined silicides possess metal-like character. The value of work function depends on the concentration of silicon and metal in silicide and it correlates with such characteristics of bond strength as the coefficient of thermal expansion and microhardness. G V Samsonov et al, Neorg Mater, 12 (5). 1976, 850-853 (in Russian). 3522.
36. VACUUM STUDIES
INSTRUMENTATION
FOR SURFACE 36
Investigation of surface diffusion by means of a locally resolving vibrating capacity method. (Germany) A locally resolving vibrating capacitor method for measuring contact potential changes has been developed and was applied to the 3523.