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41. Metals and alloys
Classified abstracts
472-480
stability following 5000-h exposure to temperatures of 1540 and 1700°C. At the highest temneratures investigated (1540 and 1700°C) the tensile strengths of the two basic materials were essentially equal. At lower temperatures, chloride tungsten possessed lower yield strength but higher ultimate strength than fluoride tungsten while the behaviour of the duplex material was generally intermediate. Apparent anomalies in high-temperature elongation behaviour are explained on the basis of grain boundary cavity formation and recrystallization. The grain size of fluoride tungsten changed only slightly following 5000-h treatment at 1700°C. In contrast, chloride tungsten possessed both poor resistance to grain growth and an accompanying relatively high ductile-brittle transition temperature. W A Bryant, J Vat Sci Technol, 11(4), 1974,695-699. 472. Oxidation (USA)
of Nb as studied by the uv-photoemission
37 technique.
The initial stages in the oxidation of Nb have been studied by the uv-photoemission technique for photon energies below 12 eV. Changes of structure in the electron distribution curves for different oxygen exposures and temperatures are correlated with formation of different types of Nb oxides. Electronic structure changes due to formation of at least three different oxides or mixtures of oxide have been observed. NbO, and the NbO oxides seem to form first as a thin protective layer. The pentoxide, NbzOs, is obtained after heavy oxidation. Practical implications of the formation of NbO in the interface between NbZOI and Nb metal are discussed. I Lhuiau and W E Spicer, J Appl Phys, 45 (9), 1974,372&3725. 37 473. Evaporative segregation in 80% Ni-20% Cr and 60% Fe-40 % Ni alloys (USA) An analytical approach is outlined to calculate the evaporative segregation behaviour in metallic alloys. The theoretical predictions are based on a ‘normal’ evaporation model and have been examined for Fe-Ni and Ni-Cr alloys. A fairly good agreement has been found between the predicted values and the experimental results found in the literature. K P Gupta et al, J Vat Sci Technol, 11 (5), 1974,896-898. 37 474. Effect of annealing on the surface composition of stainless steel 410. (USA) Atom-probe analysis shows the depletion of chromium from the surface of stainless steel 410 tips subjected to heating in vacuum. Times necessary for depletion are lower by a factor of lo4 than those found by Park er al in which planar surfaces were analysed by the X-ray appearance potential technique. This is explained on the basis of the great sensitivity of depletion rate upon the surface-to-volume ratio. The atom-probe specimens have a surface-to-volume ratio similar to catalytic powders, and thus the results of preferential evaporation may be more realistic for the study of powder catalysts which are subject to annealing. The present work also cautions atom-probe experimenters in drawing conclusions from the abundance of atomic species after an alloy tip has been annealed in vacuum. S V Krishnaswamy et al, J Vat Sci Technol, 11 (5), 1974, 899-902. 37 475. Vacuum sealed filtration apparatus. (GB) The two portions of the filter unit are held together and clamp the filter by the action of the same partial vacuum that is used for the filtration. The vacuum acts on an annular piston, outside the radius of the filter area, and is formed by the two portions of the filter unit. (Australia) B D Scott and H R Jitts, Lab Practice, 23 (8), 1974, 43 1. 39, MISCELLANEOUS
APPLICATIONS
39 476. On the IO-year static vacuum integrity of vacuum foil insulation for an implantable artificial heart. (USA) Vacuum multifoil insulation systems are being developed for an implantable artificial heart. These insulation systems are thermally efficient and physically compact, being able to limit heat losses to less than 0.024 W/cm’ with an 832°C temperature gradient across a 0.5cm insulation thickness. The maintenance of a 10-3-torr static vacuum for 10 year is critical to the success of the implantable artificial heart. The determination of the maximum allowable pressure for 140
satisfactory vacuum foil insulation performance is reported. Also, the outgassing characteristics of several Ti and NblZr insulation packages were evaluated after 300 h of thermal testing and about 3600 h after final fabrication. The only gas found in the system was hydrogen, and possible sources of hydrogen are considered. Finally, outgassing characteristics of specific vacuum foil insulation material such as electroplated Ni, as well as procedures used to eliminate gas loads from this material are reported. R C S&berg, J Vat Sci Technol, 11 (4), 1974, 806-812. 39 477. Ion etching of thin windows in silicon. (USA)
Ion etching is used to fabricate thin windows, 5-10 p thick and N l-cm diam, in silicon wafers. The method involves a simple variation of a widely used ion source, and provides etch rates of -20 r/h over the l-cm diam area. The surface of the window is flat and smooth, having a mirror-like finish. The edge of the window is sharp and is defined by the directionality of the ion beam. In this experimental arrangement, the material to be etched acts as a cathode; therefore the method is applicable to all electrically conductive materials. E G Spencer et al, J Vat Sri Technol, 11 (5), 1974, 863-864.
IV. Materials and techniques vacuum technology
used in
40. GASES AND VAPOURS 40 478. Low-energy electron impact study of acetone. (USA) The electronic energy states of acetone vapour were studied with a low-energy, high resolution, electron impact spectrometer with a molecular beam target. Similar spectra were taken with a second electron spectrometer having a static gas target. Both spectrometers consisted of a monochromator and an analyser section. The back pressure in the settling chamber is held at about 25-100 torr producing 1 or 2 x 1Om6 torr in the main chamber. The newer electron spectrometer is described in some detail. The spectra from both spectrometers are essentially identical. W M St John et al, J Chem Phys, 61 (3), 1974, 763-767.
41. METALS
AND ALLOYS
4t 479. Friction and wear of plasma-sprayed NiO based coatings. (USA) The friction and wear characteristics of plasma-sprayed NiO-CaF, coatings on Income1 601 substrates were studied at 760°C and load of 5.17 x 10“ N/m*. The rubbing surface was a lithia alumina silicate ceramic matrix simulating a rotating heat exchanger for use in automotive gas turbines. Average friction coefficients varied from 0.28 to 0.58 with coating wear rates of 0.2 x 2.1 x 10m3 cm/100 h. Optimum wear performance was achieved for the prespray composition 92/S weight % NiO/CaF,. G D Moore and J E Ritter, J Vat Sci Technol, 11 (4), 1974, 754758.
47. OUTGASSING DATA, VAPOUR PRESSURE DATA, GETTERING DATA, RESIDUAL GASES IN VACUUM SYSTEMS, RESIDUAL GAS ANALYSIS 47 480. A study on the maximum tolerable pressure in a residual gas analyser. (USA) The tolerable pressure in a magnetic sector-type mass spectrometer with respect to an undisturbed linear relation between the ion current measured at the collector and the pressure in the mass spectrometer has been studied. The different factors contributing to a disturbance of this relation and their corresponding different values for the tolerable pressure will he discussed. It is shown that by an increase of the pressure above 10d4 torr (m 10-2Pa) the positive space charge and scattering at the residual gas are predominant factors causing a deterioration of the performance of the instrument. The mass dependence of these two factors is discussed by comparing theoretical and experimental results. (Netherlands) H W Werner and A J Linssen, J Vat Sci Technol, 11(4), 1974,843-847.
472-480
stability following 5000-h exposure to temperatures of 1540 and 1700°C. At the highest temneratures investigated (1540 and 1700°C) the tensile strengths of the two basic materials were essentially equal. At lower temperatures, chloride tungsten possessed lower yield strength but higher ultimate strength than fluoride tungsten while the behaviour of the duplex material was generally intermediate. Apparent anomalies in high-temperature elongation behaviour are explained on the basis of grain boundary cavity formation and recrystallization. The grain size of fluoride tungsten changed only slightly following 5000-h treatment at 1700°C. In contrast, chloride tungsten possessed both poor resistance to grain growth and an accompanying relatively high ductile-brittle transition temperature. W A Bryant, J Vat Sci Technol, 11(4), 1974,695-699. 472. Oxidation (USA)
of Nb as studied by the uv-photoemission
37 technique.
The initial stages in the oxidation of Nb have been studied by the uv-photoemission technique for photon energies below 12 eV. Changes of structure in the electron distribution curves for different oxygen exposures and temperatures are correlated with formation of different types of Nb oxides. Electronic structure changes due to formation of at least three different oxides or mixtures of oxide have been observed. NbO, and the NbO oxides seem to form first as a thin protective layer. The pentoxide, NbzOs, is obtained after heavy oxidation. Practical implications of the formation of NbO in the interface between NbZOI and Nb metal are discussed. I Lhuiau and W E Spicer, J Appl Phys, 45 (9), 1974,372&3725. 37 473. Evaporative segregation in 80% Ni-20% Cr and 60% Fe-40 % Ni alloys (USA) An analytical approach is outlined to calculate the evaporative segregation behaviour in metallic alloys. The theoretical predictions are based on a ‘normal’ evaporation model and have been examined for Fe-Ni and Ni-Cr alloys. A fairly good agreement has been found between the predicted values and the experimental results found in the literature. K P Gupta et al, J Vat Sci Technol, 11 (5), 1974,896-898. 37 474. Effect of annealing on the surface composition of stainless steel 410. (USA) Atom-probe analysis shows the depletion of chromium from the surface of stainless steel 410 tips subjected to heating in vacuum. Times necessary for depletion are lower by a factor of lo4 than those found by Park er al in which planar surfaces were analysed by the X-ray appearance potential technique. This is explained on the basis of the great sensitivity of depletion rate upon the surface-to-volume ratio. The atom-probe specimens have a surface-to-volume ratio similar to catalytic powders, and thus the results of preferential evaporation may be more realistic for the study of powder catalysts which are subject to annealing. The present work also cautions atom-probe experimenters in drawing conclusions from the abundance of atomic species after an alloy tip has been annealed in vacuum. S V Krishnaswamy et al, J Vat Sci Technol, 11 (5), 1974, 899-902. 37 475. Vacuum sealed filtration apparatus. (GB) The two portions of the filter unit are held together and clamp the filter by the action of the same partial vacuum that is used for the filtration. The vacuum acts on an annular piston, outside the radius of the filter area, and is formed by the two portions of the filter unit. (Australia) B D Scott and H R Jitts, Lab Practice, 23 (8), 1974, 43 1. 39, MISCELLANEOUS
APPLICATIONS
39 476. On the IO-year static vacuum integrity of vacuum foil insulation for an implantable artificial heart. (USA) Vacuum multifoil insulation systems are being developed for an implantable artificial heart. These insulation systems are thermally efficient and physically compact, being able to limit heat losses to less than 0.024 W/cm’ with an 832°C temperature gradient across a 0.5cm insulation thickness. The maintenance of a 10-3-torr static vacuum for 10 year is critical to the success of the implantable artificial heart. The determination of the maximum allowable pressure for 140
satisfactory vacuum foil insulation performance is reported. Also, the outgassing characteristics of several Ti and NblZr insulation packages were evaluated after 300 h of thermal testing and about 3600 h after final fabrication. The only gas found in the system was hydrogen, and possible sources of hydrogen are considered. Finally, outgassing characteristics of specific vacuum foil insulation material such as electroplated Ni, as well as procedures used to eliminate gas loads from this material are reported. R C S&berg, J Vat Sci Technol, 11 (4), 1974, 806-812. 39 477. Ion etching of thin windows in silicon. (USA)
Ion etching is used to fabricate thin windows, 5-10 p thick and N l-cm diam, in silicon wafers. The method involves a simple variation of a widely used ion source, and provides etch rates of -20 r/h over the l-cm diam area. The surface of the window is flat and smooth, having a mirror-like finish. The edge of the window is sharp and is defined by the directionality of the ion beam. In this experimental arrangement, the material to be etched acts as a cathode; therefore the method is applicable to all electrically conductive materials. E G Spencer et al, J Vat Sri Technol, 11 (5), 1974, 863-864.
IV. Materials and techniques vacuum technology
used in
40. GASES AND VAPOURS 40 478. Low-energy electron impact study of acetone. (USA) The electronic energy states of acetone vapour were studied with a low-energy, high resolution, electron impact spectrometer with a molecular beam target. Similar spectra were taken with a second electron spectrometer having a static gas target. Both spectrometers consisted of a monochromator and an analyser section. The back pressure in the settling chamber is held at about 25-100 torr producing 1 or 2 x 1Om6 torr in the main chamber. The newer electron spectrometer is described in some detail. The spectra from both spectrometers are essentially identical. W M St John et al, J Chem Phys, 61 (3), 1974, 763-767.
41. METALS
AND ALLOYS
4t 479. Friction and wear of plasma-sprayed NiO based coatings. (USA) The friction and wear characteristics of plasma-sprayed NiO-CaF, coatings on Income1 601 substrates were studied at 760°C and load of 5.17 x 10“ N/m*. The rubbing surface was a lithia alumina silicate ceramic matrix simulating a rotating heat exchanger for use in automotive gas turbines. Average friction coefficients varied from 0.28 to 0.58 with coating wear rates of 0.2 x 2.1 x 10m3 cm/100 h. Optimum wear performance was achieved for the prespray composition 92/S weight % NiO/CaF,. G D Moore and J E Ritter, J Vat Sci Technol, 11 (4), 1974, 754758.
47. OUTGASSING DATA, VAPOUR PRESSURE DATA, GETTERING DATA, RESIDUAL GASES IN VACUUM SYSTEMS, RESIDUAL GAS ANALYSIS 47 480. A study on the maximum tolerable pressure in a residual gas analyser. (USA) The tolerable pressure in a magnetic sector-type mass spectrometer with respect to an undisturbed linear relation between the ion current measured at the collector and the pressure in the mass spectrometer has been studied. The different factors contributing to a disturbance of this relation and their corresponding different values for the tolerable pressure will he discussed. It is shown that by an increase of the pressure above 10d4 torr (m 10-2Pa) the positive space charge and scattering at the residual gas are predominant factors causing a deterioration of the performance of the instrument. The mass dependence of these two factors is discussed by comparing theoretical and experimental results. (Netherlands) H W Werner and A J Linssen, J Vat Sci Technol, 11(4), 1974,843-847.