The sessile drop method has been used to study the effects of temperature and atmosphere on the wettability of solid copper by liquid tin. The wetting tests have been carried out in both H2 and Ar atmospheres at temperature range 573-1023K. The wettability has been evaluated by measuring the angle of contact between solid copper and liquid tin. It has been found that contact angle does not change with time elapsing at temperature range 573-863K in both H2 and Ar atmospheres. Contact angle is time dependent at temperatures higher than 863K in H2 atmosphere. It has also been found that as the temperature rises, the contact angle decreases and shows its discontinuity in the temperature range 698-733K, and also that liquid tin wets solid copper in H2 atmosphere but not in Ar. The effect of atmosphere on the wettability of solid Cu by liquid Sn is discussed in relation to the values of the oxygen partial pressure which showed 10-23 and 1.013 Pa at 1273K in H2 and Ar atmospheres, respectively.

Abstract. The present study investigates the effect of the surface roughness of polymeric indoors floorings on the static friction of bare foot as well as foot wearing cotton and polymeric socks under dry, water, water + 5.0 vol. % soap, oil and water + 5.0 vol. % oil lubricated sliding conditions. Polymeric floor sheets of different roughness ranging from 0.05 and 11.0 µm were tested. The tested material is commonly used in entrance areas or corridors and in the sport halls. Cotton and polymeric socks as well as bare foot were frictionally tested. The results were compared to the friction caused by shoes as simulated by rubber test specimens of vee shape treads were prepared in the form of square sheets of 100 × 100 mm, 10.0 mm thickness. Experiments were carried out using a test rig designed and manufactured to measure the friction coefficient between the foot and the tested polymeric flooring materials.The experimental results showed that, at dry sliding, friction coefficient of rubber decreased with increasing surface roughness, while for bare foot and polymeric socks, friction coefficient decreased down to minimum then increased with increasing the surface roughness. Besides, friction coefficient decreased with increasing applied load. Minimum friction was observed at surface roughness ranging between 6-9 µm. In water lubricated sliding, friction coefficient of rubber increased up to maximum then decreased with increasing surface roughness. Maximum friction values were observed at surface roughness values ranging from 1.5 to 2.0 μm R a . Cotton socks showed the highest friction coefficient followed by rubber, bare foot then polymeric socks at 11 µm R a . Friction coefficient drastically decreased with increasing surface roughness at water and detergent lubricated sliding. For the tested flooring materials lubricated by oil, friction coefficient of rubber increased up to maximum values then decreased with increasing the surface roughness of the flooring 54materials. The maximum friction values were noticed at 4.0 µm R a . Bare foot displayed drastic reduction in friction coefficient, while cotton socks showed the highest values. When water was diluted by 5.0 wt. % oil, rubber smooth flooring surface displayed values of friction coefficient close to that observed for hydrodynamic lubrication where the two sliding surfaces are separated by the fluid film. As the roughness increased the fluid film was broken and friction increased. Cotton socks showed the highest friction compared to bare foot and polymeric socks.

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The sessile drop method was used to study the effects of surface finish, heat treatment and cold working on the wettability of solid Cu by liquid Sn. Wettability was evaluated by measuring the angle of contact between the solid and the liquid phases. It was found that electrolytic polishing is better for obtaining good wetting than mechanical polishing. It was . also indicated that annealing of solid Cu substracts could promote the wettability depending on the annealing period. Cold working was also found to have an influential effect on the wettability depending on the process and the degree of cold working. (Rolling promotes the wetting by decreasing the value of the contact angle of both mechanically and electrolytically polished Cu substrates, while pressing does not cause a significant effect on the contact angle of the mechanically polished samples but has an influential effect on the contact angle of the electrolytically polished samples). These results were discussed in relation to the crystal orientation and surface energy of the solid Cu substrates.

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