高周波誘導真空溶解におけるCu-Ag合金からの銀の蒸発速度
1973 年 37 巻 9 号 p. 958-963
詳細
1973 年 37 巻 9 号 p. 958-963
In order to determine the rates of evaporation of silver from liquid Cu-Ag alloys under vacuum, copper, silver and Cu-Ag alloys are melted in vacuum at temperatures from 1100 to 1400°C by use of a high-frequency induction furnace. The rates of evaporation of copper at 1200 and 1300°C are much higher than those in previous studies, some of which are considered to show the maximum rate of its evaporation. This can be explained by the idea that the temperature of the surface of the liquid copper is higher than that in the bulk. The rates of evaporation of silver from liquid Cu-Ag alloys follow first-order kinetics and the rate constants at the measuring temperatures of 1200, 1280 and 1400°C range from 2.2×10−3 to 5.2×10−3 cm·sec−1. Most observed values of the evaporation coefficient defined by Olette on the basis of the Hertz-Langmuir-Knudsen equation are in the range of 23 to 55. The calculated ratios of the concentration of silver at the surface of the liquid alloy to that in the bulk (Cs⁄Cb) at 1200 and 1280°C are greater than unity in disagreement with the experimental results.
This disagreement can be explained by the idea that the temperature of the surface of the liquid alloy is higher than that in the bulk as in the case of pure liquid copper. The surface temperatures calculated on the basis of an equation explaining the relation between the observed and calculated evaporation coefficients in iron alloys are 1340, 1350∼1380 and 1400°C at the measuring temperatures of 1200, 1280 and 1400°C, respectively. It is considered that the observed rate constants and evaporation coefficients show their values at these surface temperatures. Evaporation coefficients calculated at the surface temperatures are 60 to 70, being generally greater than the observed ones. Values of Cs⁄Cb at the surface temperatures, which were calculated from the values of evaporation coefficients on the basis of the above equation, are 0.5 to 0.7. This shows that the rates of evaporation of silver are mixed controlled.
