Vacuum distillation of liquid metals: Part II. Photographic study
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INTRODUCTION
V A C U U M distillation of liquid metals has attracted extensive theoretical and quantitative experimental study. However, there has not been a photographic examination of the process aimed at illustrating the phenomena which have previously been modeled and measured. This paper presents photographs of vacuum distillation experiments and discusses their relevance to the theory and industrial application. The photographs portray (i) melt surface behavior, (ii) gas flow patterns and chamber pressure effects, and (iii) vapor condensation characteristics. In particular, the gas flow patterns provide strong support for the vacuum distillation model, Part I. Other photographs illustrate problem areas for industrialization such as surface films and condensate collection.
I1.
EXPERIMENTAL
The vacuum distillation apparatus and experiments have been described in Part I in which kinetics of copper and tin elimination from melted steel scrap were measured. Photographs were taken through two windows in the chamber wall, one of which viewed the melt surface and the other which was in the chamber door and viewed the space above the liquid metal bath. Both still frame and cine films were exposed.
III.
Fig. 1 --Portion of the melt surface and crucible wall showing the surface to be covered with a thin film of alumina. Jagged fissures in the film can also be seen. Magnification 0.76 times, Pch = 10 pa, T = 1950 K.
B. Gas Flow Patterns and Chamber Pressure Effects
Evaporating metal vapors jet rapidly away from the liquid metal surface when chamber pressure is less than melt vapor pressure. At the edges of the flow, the vapors cool by heat transfer to the surroundings, and in these cooled regions the
RESULTS
A. Melt and Melt Surface Behavior
The liquid steel surface was always covered with a thin film of alumina (from aluminum killing) for a brief period following meltdown of the steel charge. Photographs of the melt surface completely covered with the film and partially covered as the film was dissipating are presented in Figures 1 and 2, respectively. The small amount of film which eventually remained on the melt surface accumulated at the melt perimeter due to melt surface curvature (Figure 3). This figure also shows the condition of the melt surface during a typical experiment. R. HARRIS is with the Department of Metallurgical Engineering, McGill University, Montreal, Quebec, Canada H3A 2A7. W. G. DAVENPORT, formerly with McGill University, is now with the Department of Mines and Metallurgy, University of Arizona, Tucson, AZ 85721. Manuscript submitted March 26, 1982.
METALLURGICAL TRANSACTIONS B
Fig. 2--Melt surface and crucible wall showing the surface partially clear of film. Accretions can be seen on the crucible wall from previous evaporation. Magnification 0.28 times, Pch = 10 pa, T = 1950 K.
ISSN 0360-2141/82/1211-0589500.75/0 9 1982 AMERICAN SOCIETY FOR METALS AND THE METALLURGICAL SOCIETY OF AIME
VOLUME 13B, DECEMBER 1982--589
Fig. 3 - - M e l t surface, free of film except for a small amoun
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