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851. A study of the adhesion and cohesion of metals in high vacuum
Classified abstracts 843-852 particular approach to the attainment of clean surfaces and surfaces with a controlled concentration of surface adsorbate is discussed. The results of the first year effort on this program are summarized. H Saltsburg and J N Smith, Rep GA-7108; AFOSR-66-1360; AD635153, Apr 1966 (General Dynamics Corp, San Diego, Calif). 33 843. Injection of intense large diameter ion-beams onto low-density gases. (USA) Experimental tests of a method of injection of large diameter, intense positive ions into low density gases are described. 20 keV, 15 mA beams are projected through a supersonic annular gas nozzle which furnished a large aperture, while providing differential pumping to allow up to 30 millitorr pressure in the collision chamber. D H Martin et al, J Appl Phys, 37, 1966, 4317-4319. 33 844. The influence of adsorbed gas on photon production by low-energy electron bombardment. (Great Britain). A study is made of the production of photons when a gold target is bombarded by electrons of energy 200 cV or less. Photon detection is accomplished by means of electron ejection from a neighbouring molybdenum surface. Better reproducibility of results than reported hitherto is attributed to the use of modern vacuum techniques and the minimization of charged particle flux from target to detector. Significant and reproducible differences in structure may be interpreted as characteristic of O2 and H2 adsorption on the target surface. F A Baker, Brit J Appl Phys, 17 1966, 1559-1567. 33 845. A vacuum, hot stage, straining microscope designed for deformation and environmental studies up to 1000°C. (Great Britain) A vacuum, hot stage, straining microscope is described, which was developed for studying surface changes in macrostructure of nuclear fuel element canning materials during relaxation, or creep deformation under oxidizing and non-oxidizing conditions. Specimens can be observed at magnifications up to × 500, pressures down to 10 -8 tort and temperatures and loads up to 1000~C and 2 tons respectively. B J R Hndgson et al, J Sci lnstrum, 45, 1966, 843-844. 34. HIGH ALTITUDE AND SPACE TECHNOLOGY 34 : 27 Using radiokrypton for detection of leaks in space vehicles. See abstract number 793. 34 846. Experimental investigation of ultrahigh vacuum adhesion as related to the lunar surface. (USA) Adhesion force was measured as a function of load force, crystalline orientation, surface roughness and type of forepump used. Two types of adhesional behavior were found for the air-formed surfaces. The first appeared only under load, increasing rapidly with increasing load; was of relatively large magnitude; and was present only at ultrahigh vacuum. Extensive surface damage and material transfer also were noted. This behavior is cau~d by the action of the normal silicate atomic bonding forces. The second type was present at zero load, showed little load dependence, was of relatively low magnitude, persisted in dry nitrogen, and did not produce surface damage or material transfer. This behavior is most probably caused by the action of the dispersion forces. It was found that silicate adhesion can be the major factor in determining the behavior of lunar materials and that its precise role is critically dependent upon the nature of the contacting surfaces. J A R y a n , Rep NASA-CR-76430; DAC-59288, Jun 1966 (Douglas
Aircraft Co, Santa Monica, Cal(f). 36. DRYING, DEGASSING AND CONCENTRATION 36 847. Control of vacuum drying of tanned leathers. (France) The vacuum drying of Cr-tanned calfskin was investigated. A pressure of 400 g/cm ~- on the leather was necessary throughout the drying period. It was necessary to dry the leather to 25-30 per cent moisture content, stake it for a time and then complete the vacuum drying to 15 per cent moisture content. P Bocciardo, Rev Tech lnd Cuir, 58, 1966, 250 (in French) 36 848. Apparatus for rapid degassing of liquids. (USA) The liquid contained in the bottom of an evacuated chamber is circulated and discharged as a fine spray into the space above the
liquid. The dissolved gases flash off and the liquid droplets rejoin the body of the liquid. R Battino and F D Davis, Anal Chem, 38, 1966, 1627-1629. 37. METALLURGY, INORGANIC CHEMISTRY, ANALYTICAL CHEMISTRY 37:31 Use of vacuum-melted metals in electrical vacuum apparatus. See abstract number 831. 37 : 33 Work function of metals in inert gases. See abstract number 837. 37 849. The design and development of a dynamic brush wear measurement apparatus. (USA) An apparatus that permits the continual measurement of electrical brush wear in high vacuum is described. As the sensing element a linear voltage differential transformer is used and its output is displayed on a potentiometric recorder. Resolution may be obtained from 0.0001 inch to 0.025 inch total wear, thus permitting wear-rate measurements from 10-7 in/hr to 1 in/hr to be made. Calibration curves are shown, and the results from several tests are plotted and analyzed. Accuracy is shown to be better than 0.5 per cent. J C Horton and J E Owens, Rep NASA-TM-X-53425, April 1966
(NASA, Marshall Space Flight Center, Huntsville, Alabama). 37 850. An experimental and theoretical investigation of the thermal contact resistance. (USA) For predicting thermal contact resistance in a vacuum environment a restrictive analysis based on a model of macroscopic elastic contact between mating members was conducted. Three resistances in series were considered: the macroscopic constriction resistance, the microscopic constriction resistance and the film resistance. Preliminary calculations showed that the macroscopic resistance was of major importance. The model has three dimensionless parameters for correlating data: the Blot modulus, the elastic conformity modulus, and the interstitial conductance. It was concluded that the model indicates the effect of the many parameters, and provides a means of designing high or low resistance interfaces; it also indicates if accurate predictions are possible. A M Clausing, Rep NASA-CR-76807, ME-TN-242-3, July 1966
(Illinois Univ, Urbana, Engineering Equipment Station). 37 851. A study of the adhesion and cohesion of metals in high vacuum. (USA) The contact surfaces were cleaned prior to loading by argon or xenon ion bombardment or by wire brush abrasion. The applied loads exceeded the nominal yield stress. Although the ion bombardment produced substantial changes in the surface electron work function as determined by the retarded field diode technique, the resultant adhesion values were generally negligible. Smooth, flat surfaces of copper showed greater bonding than roughened surfaces. Using the abrasion method, the adhesion of both soluble and insoluble metal pairs was studied. The results showed that lattice solid solubility was less important than surface cleanliness and ductility, in governing the extent of interfacial welding. Under optimum conditions, bond efficiencies up to 90 per cent were obtained for extremely ductile metals. M J Hordon and J R Roshrlng, Rep NAS.4-CR-76S28, 1966 (National
Research Corp, Cambridge, Massachusetts, Research Div).
Norton Exploratory
39 852. Apparatus for measurement of friction and adhesion at ultrahigh vacuum. (USA) An apparatus is described which has been used to measure both friction and adhesion over a wide temperature range ( - 168 to 538°C") in ultrahigh vacuum (down to 5 x 10 ~0 tort). By using sealed reentrant tubes, a number of major gas sources such as electrical wiring and insulation, thermocouples, heaters and strain gauges are eliminated from inside the vacuum chamber. The specimen normal load is introduced through a gimbals mounted, bellows-sealed arm projecting into the vacuum chamber. For friction experiments, the gimbal ring is oscillated by an external motor and crank, thus causing reciprocating sliding of a pin type specimen while in contact with a fiat specimen. The variations of friction and adhesion with temperature were measured in the apparatus confirming its effectiveness as a basic instrument. R D Brown and R A Burton, Rev Sci lnstrum, 37, 1966, 1699-1701.
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Aircraft Co, Santa Monica, Cal(f). 36. DRYING, DEGASSING AND CONCENTRATION 36 847. Control of vacuum drying of tanned leathers. (France) The vacuum drying of Cr-tanned calfskin was investigated. A pressure of 400 g/cm ~- on the leather was necessary throughout the drying period. It was necessary to dry the leather to 25-30 per cent moisture content, stake it for a time and then complete the vacuum drying to 15 per cent moisture content. P Bocciardo, Rev Tech lnd Cuir, 58, 1966, 250 (in French) 36 848. Apparatus for rapid degassing of liquids. (USA) The liquid contained in the bottom of an evacuated chamber is circulated and discharged as a fine spray into the space above the
liquid. The dissolved gases flash off and the liquid droplets rejoin the body of the liquid. R Battino and F D Davis, Anal Chem, 38, 1966, 1627-1629. 37. METALLURGY, INORGANIC CHEMISTRY, ANALYTICAL CHEMISTRY 37:31 Use of vacuum-melted metals in electrical vacuum apparatus. See abstract number 831. 37 : 33 Work function of metals in inert gases. See abstract number 837. 37 849. The design and development of a dynamic brush wear measurement apparatus. (USA) An apparatus that permits the continual measurement of electrical brush wear in high vacuum is described. As the sensing element a linear voltage differential transformer is used and its output is displayed on a potentiometric recorder. Resolution may be obtained from 0.0001 inch to 0.025 inch total wear, thus permitting wear-rate measurements from 10-7 in/hr to 1 in/hr to be made. Calibration curves are shown, and the results from several tests are plotted and analyzed. Accuracy is shown to be better than 0.5 per cent. J C Horton and J E Owens, Rep NASA-TM-X-53425, April 1966
(NASA, Marshall Space Flight Center, Huntsville, Alabama). 37 850. An experimental and theoretical investigation of the thermal contact resistance. (USA) For predicting thermal contact resistance in a vacuum environment a restrictive analysis based on a model of macroscopic elastic contact between mating members was conducted. Three resistances in series were considered: the macroscopic constriction resistance, the microscopic constriction resistance and the film resistance. Preliminary calculations showed that the macroscopic resistance was of major importance. The model has three dimensionless parameters for correlating data: the Blot modulus, the elastic conformity modulus, and the interstitial conductance. It was concluded that the model indicates the effect of the many parameters, and provides a means of designing high or low resistance interfaces; it also indicates if accurate predictions are possible. A M Clausing, Rep NASA-CR-76807, ME-TN-242-3, July 1966
(Illinois Univ, Urbana, Engineering Equipment Station). 37 851. A study of the adhesion and cohesion of metals in high vacuum. (USA) The contact surfaces were cleaned prior to loading by argon or xenon ion bombardment or by wire brush abrasion. The applied loads exceeded the nominal yield stress. Although the ion bombardment produced substantial changes in the surface electron work function as determined by the retarded field diode technique, the resultant adhesion values were generally negligible. Smooth, flat surfaces of copper showed greater bonding than roughened surfaces. Using the abrasion method, the adhesion of both soluble and insoluble metal pairs was studied. The results showed that lattice solid solubility was less important than surface cleanliness and ductility, in governing the extent of interfacial welding. Under optimum conditions, bond efficiencies up to 90 per cent were obtained for extremely ductile metals. M J Hordon and J R Roshrlng, Rep NAS.4-CR-76S28, 1966 (National
Research Corp, Cambridge, Massachusetts, Research Div).
Norton Exploratory
39 852. Apparatus for measurement of friction and adhesion at ultrahigh vacuum. (USA) An apparatus is described which has been used to measure both friction and adhesion over a wide temperature range ( - 168 to 538°C") in ultrahigh vacuum (down to 5 x 10 ~0 tort). By using sealed reentrant tubes, a number of major gas sources such as electrical wiring and insulation, thermocouples, heaters and strain gauges are eliminated from inside the vacuum chamber. The specimen normal load is introduced through a gimbals mounted, bellows-sealed arm projecting into the vacuum chamber. For friction experiments, the gimbal ring is oscillated by an external motor and crank, thus causing reciprocating sliding of a pin type specimen while in contact with a fiat specimen. The variations of friction and adhesion with temperature were measured in the apparatus confirming its effectiveness as a basic instrument. R D Brown and R A Burton, Rev Sci lnstrum, 37, 1966, 1699-1701.
255